::::If not in an extreme case (rainforest or taiga) you should just go downhill until you eventually reach a creek. Following it will lead you to inhabited area long before hunger could become an issue. --[[Special:Contributions/131.188.3.21|131.188.3.21]] ([[User talk:131.188.3.21|talk]]) 13:32, 26 April 2009 (UTC)
::::If not in an extreme case (rainforest or taiga) you should just go downhill until you eventually reach a creek. Following it will lead you to inhabited area long before hunger could become an issue. --[[Special:Contributions/131.188.3.21|131.188.3.21]] ([[User talk:131.188.3.21|talk]]) 13:32, 26 April 2009 (UTC)
:::::That works even in the [{Juliane Kƶpcke|rainforest]]. In a flat, boggy area it might be more difficult. [[Special:Contributions/76.97.245.5|76.97.245.5]] ([[User talk:76.97.245.5|talk]]) 01:26, 27 April 2009 (UTC)
:::::That works even in the [[Juliane Kƶpcke|rainforest]]. In a flat, boggy area it might be more difficult. [[Special:Contributions/76.97.245.5|76.97.245.5]] ([[User talk:76.97.245.5|talk]]) 01:26, 27 April 2009 (UTC)
== SALTWATER FISHES ==
== SALTWATER FISHES ==
Revision as of 16:08, 27 April 2009
Welcome to the science section of the Wikipedia reference desk.
The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
Given the context, I assume you mean the "standard" one most commonly found in proteins? You can look at our Proteinogenic amino acid table and check the melting-point of each. In the more general sense, our amino acid article talks about their structure, and in particular the idea of a zwitterionic form and its physical properties. Is there a "rule of thumb" regarding being an ionic structure and having either generally high or generally low melting point? DMacks (talk) 01:52, 20 April 2009 (UTC)[reply]
Well, they decompose before they melt. But any covalent molecule is going to become a gas at sufficiently low pressure, isn't it? Looie496 (talk) 02:43, 20 April 2009 (UTC)[reply]
True 'nuf. I guess I was thinking "solid at room temp" and ignoring what actual other state or physical change occurs when they the solid falls apart:) A real question is whether they really behave as "covalent molecules" (implying neutral, not covalent ions) or as ions. For example, Glycine is fairly low molecular weight, but it listed as a decomposition (rather than melting) temperature of 233Ā Ā°C: there are clearly important ionic interactions and intermolecular stabilization. DMacks (talk) 04:24, 20 April 2009 (UTC)[reply]
Could we say that in (terrestrial) biological contexts, amino acids are always solids and almost always dissolved in water? ike9898 (talk) 20:00, 20 April 2009 (UTC)[reply]
The Zwitterion form makes amino acids more behaving like NH3+ caboxylates. Like most acid and amine salts they have higher melting points as the amine and carboxylic acid they consist of. So most of the amino acids I know are solids. --Stone (talk) 20:52, 20 April 2009 (UTC)[reply]
Solubility is interesting. Standard guide is "ionic stuff is water-soluble", but our amino acid article in the "Zwitterion" section notes: "Zwitterions have minimal solubility at their isolectric point and amino acids are often isolated by precipitation from water after adjusting the pH to their isolectric point." DMacks (talk) 21:01, 20 April 2009 (UTC)[reply]
Are there any (real) animals that can spit/spray corrosive substances as a defence mechanism?
Question as topic. When I say 'corrosive', I mean 'literally corrosive' (as in substances of the type mentioned in the linked article), not your run-of-the-mill toxic/foul-smelling compounds. I'm pretty sure that I once read about a species of spray beetle that has two specialized glands, producing two chemicals which are harmless alone but which when mixed together and concentrated into a high-pressure jet at the point of exit, form an incredibly nasty, highly-caustic substance (though I might be wrong). Thanks. --Kurt Shaped Box (talk) 01:45, 20 April 2009 (UTC)[reply]
I'm guessing it depends what you mean by 'literally corrosive' and 'defence mechanism'. The formic acid a number of ants use for defense (and offense) is I presume somewhat corrosive as with most acids although I expect it may not be the only (or even primary) compound in some cases. Fire ants use an alkaloid venom Solenopsin which has "cytotoxic, hemolytic, necrotic" properties. I'm not sure what the pH is but I'm guessing it's high enough that the substance could be considered literally corrosive even if that isn't a key part of the stings action. It seems the same it's the same for bee stings [1][2] while wasp stings are usually alkali (not sure what they contain). But in both cases, the same as with fire ants it's not really the key mechanism of action of their stings. Formic acid is also used by a number of other insects it appears [3]. As far as I'm aware, in none of these cases are the substances mixed outside the body, they're just (I presume) stored in specialised glands. Finally another example snake venom usually has digestive enzymes, would you consider them corrosive? Nil Einne (talk) 12:53, 20 April 2009 (UTC)[reply]
Well, if you put it that way... Yeah, gulls and fulmars can also spray their vomit at will when threatened. I guess that I was thinking more along the lines of species with defence mechanisms that work *primarily* by inflicting corrosive chemical burns upon a potential predator. --Kurt Shaped Box (talk) 00:06, 21 April 2009 (UTC)#[reply]
Hi, I am doing a physics problem, I am given values of , and T for some gas (assumed ideal) (note: it is done by web interface, values change every time) and asked to find the total translational kinetic energy of the atoms. The answer works out to be every time, and I'm not sure where that extra factor of 1/8 is coming from, could someone please help me? --130.216.30.234 (talk) 08:23, 20 April 2009 (UTC)[reply]
Also: related question (the one immediately following) is I am told that the balloon in the first part of the question (the one with of gas at and T) has been filled from some container containing of the same gas at and T, and asked how many of those same balloons could be filled using all the gas. The correct answer is always , or . There's that 1/8 again!! I have no idea where it's coming from! --130.216.30.234 (talk) 08:46, 20 April 2009 (UTC)[reply]
It is the correct answer. Either the answer you've been given is wrong, or there's some relevant feature of the question you're not telling us. Can you give us the exact wording, or just a link to the problem? Algebraist10:32, 20 April 2009 (UTC)[reply]
Okay, I was seconds away from posting it here when I just realised that I'm an idiot. In the original question, you had to calculate the volume of the spherical container using diameter, and I was not halving it before calculating volume, which of course would add an extra to my answers. Problem solved. Thanks for your time, everybody! --130.216.30.234 (talk) 11:34, 20 April 2009 (UTC)[reply]
Azimuth sweep angle?
In the game Call of Duty 4, in one mission you control the guns on a AC-130 Spectre Gunship. A guy on the plane says a couple of times: "Recalibrate azimuth sweep angle, adjust elevation scan." What does it mean? And yes I'm the guy who asked the Coriolis effect and sniping question . Just a big fan of COD4. And thanks for your answers. āPreceding unsigned comment added by 116.71.54.217 (talk) 08:52, 20 April 2009 (UTC)[reply]
I first thought of posting this on the Language ref desk, then changed my mind. Isn't something grammatically wrong with this line from Speed of light:
"Francis Bacon argued that the speed of light was not necessarily infinite, since something can travel too fast to be perceived."Jay (talk) 10:43, 20 April 2009 (UTC)[reply]
The grammar is ok but the logic is questionable because the underlying hypothesis about "something" is not explicit. The OP could bring this up on the article discussion page to see what others think. Would the following sentence be better? "Francis Bacon argued that the speed of light was not necessarily infinite, since it could just be travelling too fast to be perceived."Cuddlyable3 (talk) 11:12, 20 April 2009 (UTC)[reply]
Yes, sorry about that. I should have said logically wrong instead of grammatically wrong. Cuddlyable3's version is making sense to me now. The meanings I had in mind were: "Francis Bacon argued that the speed of light was not necessarily infinite, since nothing can travel too fast to be perceived.", and "Francis Bacon argued that the speed of light was not necessarily infinite, since something cannot travel too fast to be perceived.", both meanings are opposite of the original line. Jay (talk) 11:29, 20 April 2009 (UTC)[reply]
I think it's vague about what is being perceived; I mean, light is definitely perceived so he can't be referring to that. I assume he's referring to the finite speed being perceived i.e it's really fast and we can't tell the difference between that and infinite speed. How about
"Francis Bacon argued that the speed of light was not necessarily infinite, since it could be travelling at a very large but finite speed which was beyond the scope of contemporary experimental accuracy."
I think you nailed it. Light is perceived as something instantaneous in all "normal" situations, but that is just an artifact of imperfect observation - and that was the point Bacon was making. --Stephan Schulz (talk) 11:49, 20 April 2009 (UTC)[reply]
It seems like the original quote implies that Bacon argued that it's possible to imagine a thing that travels imperceptibly fast but not infinitely fast, and that light might be one of those things. User:cuddlyable3's version could be less clear depending on what Bacon actually said. Cuddlyable3's version implies that he specifically theorized that light could travel very fast, but doesn't specify whether Bacon thought this was a special case or whether other items could also attain imperceptible speeds. I have no idea which is correct, but they don't mean exactly the same thing.
This guy at least included a direct quotation from (Francis) Bacon and a citation: "'Even in sight, whereof the action is most rapid, it appears that there are required certain moments of time for its accomplishment...things which by reason of the velocity of their motion cannot be seenāas when a ball is discharged from a musket' (Philosophical Works of Francis Bacon; J.M. Robertson, Ed.; London, 1905; p. 363)." The ellipsis is awkwardly placed, though, and I don't happen to have a copy of the Philosophical Works lying around in which to examine Bacon's full argument. Deor (talk) 17:01, 20 April 2009 (UTC)[reply]
I should have guessed that Google Books would have snapped this up. If one reads the whole chapter, one can say only that Bacon seems to be rather unclear whether he's discussing physics or physiology. Sometimes he seems to be maintaining that light has a finite speed; at other times, he seems to argue that it's our visual impressions that require time for their formation. And I admit to not being able to make much sense of his discussion of the idea that starlight takes time to reach us: he seems to say that he has discarded his initial suspicions that this is so, and now believes that our perception of stars is instantaneous. Deor (talk) 18:00, 20 April 2009 (UTC)[reply]
I don't think it's the light that's being not-perceived it's the speed of light. If you have a friend standing on a far distant hilltop with a mirror and you light a candle - the time it takes for the light from the candle to travel to the mirror and back again is too fast to perceive. Bacon argues that the time might not be zero - but merely so short that you can't perceive the delay...smart guy...he turned out to be correct! SteveBaker (talk) 16:58, 20 April 2009 (UTC)[reply]
Scooter electric motors
I know how electric motors work (I've had to build them by coiling wires by hand). I was discussing scooters the other day and I thought about coasting. A motor with high torque is hard to turn by hand if there is no power. So, assuming scooters use high torque motors to move a lot of weight with one small motor, are those scooters able to coast (free-spinning axle with no power applied to the motor)? If so, is there a special type of electric motor that allows for a free-spinning axle or is my memory of electric motors completely wrong? -- kainawā¢14:14, 20 April 2009 (UTC)[reply]
I would do it with a clutch - somewhat backwards than a slipper clutch. I was just wondering how it is done in real scooters (and I'd rather not hunt one down and take it apart). -- kainawā¢18:39, 20 April 2009 (UTC)[reply]
Unless there is some load on the engine, I don't see why it should be hard to turn. Where would the energy be going? Electric motors can be tough to start spinning, because the rotor settles in a low-energy state. But once you're out of the bottom of the potential well, you get back the energy if you slip into the next. It's hard to notice if you turn the axle by hand, but obvious if you install e.g. a flywheel. You can see a similar effect with hub generators in bicycles - if you do not attach a load, a free spinning wheel will go a long time. --Stephan Schulz (talk) 08:54, 21 April 2009 (UTC)[reply]
When you spin an electric motor, it acts like a generator - so if you have a load (like the battery of the scooter) connected to the motor - then it may be harder to turn. For coasting, all that should be necessary is to install a switch that disconnects one of the wires leading to the motor - and it should free-run without problems. SteveBaker (talk) 19:42, 21 April 2009 (UTC)[reply]
How is "coasting" on an electric scooter different from cruising at constant speed? Is the questioner referring to an electric bicycle, where the harder you pedal the faster the motor makes it go to supplement your efforts, or an electric motorcycle where the battery provides all the propulsion? Regenerative braking uses the motor like a generator to put energy back into the battery (way less than 100% efficiency) rather than slowing by friction in a brake which turns the energy into waste heat. I agree that an electric motor should turn freely unless the bearings are shot or a winding is connected to something to brake electrically. Edison (talk) 22:52, 21 April 2009 (UTC)[reply]
When 'coasting' (at least on level ground) your speed doesn't stay constant. It slowly decreases due to friction & drag. In order to cruise at constant speed, you have to supply energy to the motor. SteveBaker (talk) 01:42, 22 April 2009 (UTC)[reply]
If you live in flatland, there is little need for coasting. With hills, you use battery power by turning the accelerator to get up one side of the hill. Then, you coast down the other without any accelerator at all. Similar to a car - you press on the gas to go up a hill and take your foot off the gas to coast down the other side.
Steve mentioned something that caused my initial concern. An electric motor is also a generator. If you force the axle to spin, it creates electricity. Part of the energy is used to create the electricity. My understanding is that the electrical potential is there with or without a battery connected. As reference - try spinning a starter motor for a car by hand. It is very hard. So, if that was the motor for your scooter, when you let off the accelerator, the scooter would quickly come to halt. That is assuming that the motor is directly connected to the wheel with no clutch or slip gear of any kind. -- kainawā¢16:55, 22 April 2009 (UTC)[reply]
No, you're missing the point. It's only hard to turn a car starter if it's connected to something. If you unhook all of the wires, it spins quite easily (unless it's broken or something!). SteveBaker (talk) 19:52, 22 April 2009 (UTC)[reply]
Yes - that is exactly my question... I thought it was always hard to turn. Being easy to turn when disconnected means that it is possible (though may not be the case) that you could connect an electric motor directly to a wheel and when power is disconnected it will allow the vehicle to coast along. Perhaps a fancy circuit could be in place to recharge a battery while it coasts, as long as the load of the battery doesn't kill the ability to coast. That, however, is a completely different topic. I was only wondering about the motor's ability to allow for free spin. -- kainawā¢00:32, 23 April 2009 (UTC)[reply]
My wife has owned a number of electric scooters - they don't have a clutch and they are not able to coast. In fact, they don't have any brakes either - cutting the power to the motor is the only way to stop, as the motor works as a brake. They do have a lever at the back which disengages the motor to allow you to manoeuvre the scooter into a small space by pushing it, but this is not in a such position that it could be used whilst riding on the scooter as you would have no way of braking. I suppose some people with limited mobility may enjoy the adrenalin rush of careering down a hill at speed in an unbraked vehicle (the thought of it takes me back a few years!) but the majority probably wouldn'tĀ :) Richerman (talk) 12:09, 27 April 2009 (UTC)[reply]
disappearance of gills in higher vertebrates and evolution of lungs (comparison with embryonic tadpole -> frog transition)
The whole process of an evolutionary mechanism in which the gills could be lost while the lungs developed seems kind of complex, because IIRC the gills are not evolutionarily homologous (or embryonically homologous) to lungs. So how would this sort of thing come about? Especially with the development of the circulatory system, since this would suggest a sort of fantastical rewiring that seems amazing to me -- suddenly you have to rerout the systemic and gill circulations back to the heart (whereas the gill circulation used to flow into the systemic circulation)? Can someone just clarify the whole process with me? Thanks. John Riemann Soong (talk) 17:45, 20 April 2009 (UTC)[reply]
(uh, What are you asking for clarification on? The maturation of tadpoles? Or the evolution of lungs? My reply here assumes that you're asking about evolution.)
Lungs and swim bladders did indeed evolve in addition to gills, probably in response to an environment featuring frequent oxygen-depleted water (such as lungfish inhabit today) to enable the fish involved to literally swallow air and absorb additional oxygen. However, lungs did not develop from earlier swim bladders: either the two homologous structures evolved as near parallel alternatives in two separate lineages, or (so I have seen suggested) lungs evolved first and then in some lineages that no longer needed so much supplementary oxygen (having returned to deeper waters?) they became swim bladders, still sometimes with oxygen absorbing capabilities but primarily now employed for buoyancy control. I love how often evolution repurposes organs for new tasks. 87.81.230.195 (talk) 22:59, 20 April 2009 (UTC)[reply]
Heart formation in a tadpole is a pretty damn complicated process. As far as I remember, it starts with one chamber and ends with three. For details, you can see, for example, Mohun et.al. "The Morphology of Heart Development in Xenopus laevis", Developmental Biology 218, 74ā88 (2000). --Dr Dima (talk) 04:58, 21 April 2009 (UTC)[reply]
Now, regarding your original question, the appearance of lungs and disappearance of gills occurred naturally with the transition from aquatic to terrestrial lifestyle. Some transitional, semiaquatic, or mud-dwelling species possess both lungs and gills. Axolotl - neotenicsalamander - has both lungs and gills, for example. By the way, vertebrates are not "special" in this respect. Coconut crab, too, has both gills and lungs, although gills are largely useless in an adult. --Dr Dima (talk) 05:14, 21 April 2009 (UTC)[reply]
As an aside - Coconut crabs are VERY cool. They often grow to three feet across and there are reports of six-foot coconut crabs - which are the kinds of thing you'd expect to see in old sci-fi movies! Kids in the area where they live keep them as pets and they can live for 30 years! Check out the article. SteveBaker (talk) 19:39, 21 April 2009 (UTC)[reply]
Witnessing evolution
I'm very interested in evolution, and I basically want to ask whether it's possible for someone who is not a scientist (I'm a university student though) to see evolution take place, and if so what would be the best way? Keep in mind that my knowledge of biology is rather limited but you would probably want to growing something like bacteria (possibly in a chemostat?), flies or fungi? I've heard of a fly experiment where a fly was given a different diet and in some 8 generations it had evolved. --BiT (talk) 18:30, 20 April 2009 (UTC)[reply]
Well, there are certainly experiments you can do with bacterial cultures that allow you to see evolution happening before your very eyes - but without some practical knowledge of lab techniques, I think they'd be hard for you to perform. 8 generations sounds a little short for the fly experiment - and in order for any evolution to happen at all, you'd need a very large number of flies to ensure a sufficiently diverse gene-pool. There are computer simulations of evolution that work fairly well. Richard Dawkin's "biomorphs" for example (see Weasel program). Google for "biomorphs" and you'll find several online versions of the program - and a bunch more that you can download for free. SteveBaker (talk) 21:05, 20 April 2009 (UTC)[reply]
Not sure how you would get access to a lab strain of E. Coli, but I agree that it's probably the easiest/most visible experiment you could try (the wiki page for it is here), due to the small size of bacteria and the extremely quick rate of reproduction, as well as the relative ease of culturing and "harmlessness" of the E. Coli itself. There are some other bacteria listed at Model organism. 124.154.253.25 (talk) 02:35, 21 April 2009 (UTC)[reply]
Yes, you could...theoretically. But one round of that test doesn't demonstrate evolution at all. A skeptic would rightly say that while 'Roundup' only kills 99% of plants, it's perfectly possible that the 1% survive by pure luck for environmental rather than genetic reasons. You'd have to go on and collect seeds from the survivors of that crop - grow them into plants and spray THEM with roundup in order to demonstrate a significant statistical improvement in the survival of the second generation - and thereby get any idea whether the roundup-resistance is inheritable. In fact, since it's highly likely that some plants are indeed surviving for environmental rather than genetic reasons - you'd probably need to do this over many generations in order to show a really convincing effect where 100% of plants survive being sprayed. You really need to prove a substantial increase in the percentage of plants that survive AND that this trait is inherited - or else all you've done is shown that some plants survive Roundup rather than that they EVOLVED a natural resistance to the herbicide. You might also need a VAST number of plants in each generation. If only one plant in a million carries some random mutation for roundup-resistance then you'll need to grow several million plants in order to have enough of them survive to make a million seeds for the second generation of the trials. Since the plants might take a year to grow to maturity and produce seed - this experiment could easily require acres of land and dozens of years in order to produce results.
That's why we do these kinds of experiments with bacteria - where an experimenter can easily have a few million bacteria available - and they reproduce and mature over hours rather than years. That's not to say that the experiment wouldn't work - just that you'd need to dedicate a LOT of money and years of your life to doing it using plant seed. SteveBaker (talk) 13:46, 21 April 2009 (UTC)[reply]
You would also need to be careful where you got your seeds - if they all come from the same, or a small number of, plants then there might not be sufficient genetic variation for any of them to survive due to genetic reasons (if you want to rely on random mutations, you need far more generations and a far larger population). --Tango (talk) 14:23, 21 April 2009 (UTC)[reply]
I was reading this. It says that one bit of semiconductor memory contains about 60,000 electrons. It struck me that that's a finite number of qubits. A qubit can only be determined once, so a bit of memory can only be read a finite number of times. You can use classical error correction to copy the bit of memory a bunch of times, but that just uses up your number of reads. This makes me suspect:
Any particular piece of information available on the Internet "degrades" (becomes less well-defined) over time as it's read. The more the information is distributed (Wikileaks :D) the less sure we can be of the integrity of the original and its copies.
Eventually we'll run out of information! Fortunately we have people typing on their keyboards and people uploading porn to 4chan, adding bits to the system. It's like Shannon entropy: my Linux box uses the unpredictable movements of my mouse cursor to increase the complexity of the parameters to its pseudorandom number generator. No outside input is a very bad idea. Without input the information on the hard drives and semiconductor memories of the Internet would degrade until they pass the manufacturer-guaranteed tolerances of their restoring logic and then you start losing information.
These are first impressions; what do you think? Can you only read a book a finite number of times before the information degrades? If you've already memorized it, is it really a "read" of the qubits? Is the repeated operation of a half adder (or a calculator, or a router) "reading" procedural information that will eventually degrade? .froth. (talk) 20:29, 20 April 2009 (UTC)[reply]
You're atempting to apply qubit theorems, like the No cloning theorem to classical bits. That's not really correct. There is really no limit to the number of times you can copy a classical bit. Dauto (talk) 20:44, 20 April 2009 (UTC)[reply]
And it's certainly the case that as a practical matter some bits in some computers are read trillions of times a day for years on end without problems and most of the bits on (say) Wikipedia are read maybe a few times a day at most...so the practical answer is also that this certainly isn't a problem. SteveBaker (talk) 20:57, 20 April 2009 (UTC)[reply]
There's no classical limit but classical bits are an idealization, right? The real world works in qubits, does it not? I know I'm mixing levels, that's the whole question: what do the qubit theorems mean for classical information theory? .froth. (talk) 01:25, 21 April 2009 (UTC)[reply]
A classical bit is consistent with many different quantum states. Quantum decoherence isn't a problem and the act of reading the classical bit will not change the bit (eventhough the quantum state will be changed), and you can read the bit as many times as you want. The qubit theorems have very little to do with classical information thory. Dauto (talk) 03:00, 21 April 2009 (UTC)[reply]
A qubit can be read any number of times and it will always give you the same result (in theory). Reading destroys the quantum properties of the qubit, but it doesn't destroy its classical value (0 or 1). Cloning and copying are different things. Copying means that if you started with a probability p of having a 0 and a probability q (=1āp) of having a 1, then you end up with a probability p of having two zeros and a probability q of having two ones. Cloning means that you end up with a probability p2 of having two zeros, a probability q2 of having two ones, and a probability 2pq of having a zero and a one. Both classical bits and qubits can be copied; neither classical bits nor qubits can be cloned. If classical cloning were possible then you could just read a single random bit from /dev/random and clone it to get as many random bits as you needed. In reality, if you need n random bits then you need to read at least n bits from /dev/random. The /dev/random driver has the same problem: it can't invent random bits to give you, it has to get them from somewhere. So there is a limited supply of randomness, and I think this is what you were talking about in your initial post. The randomness supply can run dangerously low on a standalone machine without good sources to replenish it (like a Winchester hard drive or a keyboard in active use). -- BenRG (talk) 13:25, 21 April 2009 (UTC)[reply]
Thanks for then clarification on the difference between cloning and copying. It is a relief to see that two completely different operations such as the reproduction of a qubit (cloning) and the reproduction of a classical bit (copying) receive different names. Dauto (talk) 14:49, 21 April 2009 (UTC)[reply]
I think you've misunderstood what BenRG was saying - he specifically talked about both quantum and classical bits being both cloned and copied, not one term for one and one term for the other. --Tango (talk) 22:17, 21 April 2009 (UTC)[reply]
I hear you. I heard him too. I just don't think what he said about cloning a classical bit makes any sense. A classical bit is either definitaly 0 or it is definitaly 1. It cannot be either one or the other with probabilities p and q=1-p. A quantum bit, on the other hand, cannot be copyed unless it's read first. And once it's read, the wavefunction colapses and it becomes a classical bit anyways. Dauto (talk) 22:43, 21 April 2009 (UTC)[reply]
"the Shannon entropy is a measure of the average information content one is missing when one does not know the value of the random variable" Yes classical bits too can have probabilities. And thanks BenRG that helps a lot. Basically you can copy bits, you just can't create new bits. Interesting.. algorithms can't create new information no matter how much procedural information the steps of the algorithm contain.. right? Can't map 5 bits of input into 6 bits of output. Fits in nicely with information entropy only increasing or standing still. .froth. (talk) 23:35, 21 April 2009 (UTC)[reply]
The inability to create information is well-known in information-theory - and mostly pre-dates all of this quantum stuff. If you think about it, that's not surprising because you can use some algorithm to take some set of source data and transform it into more bits of output data - but you could then compress redundant information out of the output by replacing it with the input - using whatever your algorithm is to uncompress it again on demand. So the actual information content of the output is no larger than the input. This is why computers can't generate proper random numbers without relying on some external input. It's been argued that this is why computers can never become intelligent - but that misses the point that humans are equally unable to create new information...it just seems like we can. SteveBaker (talk) 01:37, 22 April 2009 (UTC)[reply]
April 21
Bacteria passed on at birth: what about cloning?
I guess this question is equally valid for many species probably to be cloned in the near future, but it most directly concerns the Spanish Ibex previously "cloned" into a goat, and the Woolly Mammoth. I'm aware that the human body is host to a great deal more bacteria than there are cells in our body, and without most of those we wouldn't be able to survive, we may not even be able to call ourselves "human". Now I assume a lot of these are transmitted through the atmosphere, or possibly what we consume, but I can only assume that a lot of the more essential bacteria are passed on through the mother in the early stages of growth. When human cloning is concerned I don't see a problem as long as there is a surrogate mother, but with the Ibex and the Mammoth supposedly best cloned into some sort of a goat and an elephant, doesn't that cause major problems? I'm assuming that cultured bacteria are very different between species, but is that too much of an assumption? Also, even if it is possible in the future to clone and nurture to size an animal without some sort of surrogate, will the fact that they don't have access to native bacteria cause problems? Thanks! 124.154.253.25 (talk) 01:54, 21 April 2009 (UTC)[reply]
I seriously doubt that's a problem. For one thing, I believe your assumption that bacteria pass from mother to baby while the baby is still a fetus is incorrect. Most bacteria probabily colonise the baby after s/he's born. Besides the bacteria are different from person to person and that doesn't cause a problem, so I don't see how that's a problem. Dauto (talk) 02:44, 21 April 2009 (UTC)[reply]
I see. I guess I was under the mistaken assumption that there were bacteria essential (to the human digestive system), but apparently that's not the case, and we can live in sterile environments. (Now that I think of it, actually... that's pretty obvious!) According to gut flora though, some bacteria probably do pass from the mother to the baby during birth, but they are all incidental, and they will colonise the baby within the next few years anyway. Alright, thanks for the quick answer! 124.154.253.25 (talk) 03:05, 21 April 2009 (UTC)[reply]
I think bacteria in the gut are essential to the human digestive system (if you take lots of antibiotics you can get horrible stomach cramps due to the bacteria being killed off), but newborn babies only digest milk and aren't capable of digesting anything else - perhaps bacteria aren't required for digesting milk. There is plenty of time for bacteria to colonise the baby before they start eating solid food. --Tango (talk) 13:04, 21 April 2009 (UTC)[reply]
Columbus's New World "nightingale"
Christopher Columbus thought he heard the song of a nightingale not long after he landed in the Americas, where there are no nightingales. What kind of bird might he have mistaken for one? 69.224.37.48 (talk) 02:05, 21 April 2009 (UTC)[reply]
Possibly Catharus sp., not sure. In fact, I am not even sure the story is true. The version I know is Columbus saying "the only thing missing is a nightingale song", meaning he's confident the land is close. The two stories are not necessarily contradictory, though. Sorry. I wish I could help more. All the best, --Dr Dima (talk) 04:45, 21 April 2009 (UTC)[reply]
Gut flora
My wife and I were having a conversation today about gut flora, so I decided to read the article here. One bit in particular confused me a bit and I'd appreciate an explanation if you could...
The article states:
Immediately after vaginal delivery, babies have bacterial strains in the upper gastrointestinal tract derived from the mothersā feces.
Since I don't have any kids, I'm a little unclear on how bacteria from the mother's feces could get into the baby. I thought that expectant mothers were given a laxative to flush the bowels so that they don't eliminate during the birth. I also thought that the vaginal area in general, including the anus, would be cleaned before delivery. So, could someone clear up my confusion? (I realize that birthing procedures are different around the world due to varying sanitary conditions and such but I'm guessing that the reference (which I can't read from where I am) for this sentence deals with babies born in modern hospitals.) Thanks, Dismas|(talk)05:31, 21 April 2009 (UTC)[reply]
And having just read up from my question, I didn't realize that we had another, though different, gut flora question here today. Dismas|(talk)05:33, 21 April 2009 (UTC)[reply]
It was in relation to our new puppy and his diarrhea. When you have as many animals as we do, you get into some interesting conversations. Ā :-P Dismas|(talk)08:42, 21 April 2009 (UTC)[reply]
I think that there will be some (probably very few) faecel bacteria in the birth canal. I remember hearing that children born by caesarean have a higher occurence of allergies which is possibly associated with the lack of bacteria during delivery. Smartse (talk) 12:49, 21 April 2009 (UTC)[reply]
Actually, there are three parts to this: the existance of the gut bacterias, the transferring into the baby and the cleaning away of them that you describe. Naturally, some gut bacteria is present on the skin of the mother. There are so many zillion bacteria, that getting every single one off after a normal visit to the toilet is impossible with just wiping. These are in or close enough to the birth canal to be transferred to the baby either directly when the face passes or inderectly via hands, towels etc. In "modern" hospitals you say, mothers are cleaned. As a matter of fact, with the knowledge that bacteria is indeed most often healthy in these circumstances, Swedish hospitals have stopped sterilizing the mother with alcohol ahead of delivery. If some feces are pressed out during delivery (laxative is optional), it is simply wiped off. For the same reason, the baby is not cleaned after delivery, but just wiped off to keep the natural fat, bacteria and mucus on the skin - and nipples should not be sterilized either. -Mummy āPreceding unsigned comment added by 195.67.112.146 (talk) 12:11, 22 April 2009 (UTC)[reply]
I think it is zero for Spur gear and it could be anything less than 90 degrees for helical gears, although for practical purposes it is never even close to 90 degrees. It is the angle which the helix of the gear makes with the plane perpendicular to the longitudinal axis of the gear. Correct me if I am wrong. - DSachan (talk) 19:04, 21 April 2009 (UTC)[reply]
A quick Google check says that these are German standards. You'd probably have to be lucky to find anybody here who knows about them. Looie496 (talk) 21:09, 21 April 2009 (UTC)[reply]
What factors impose the ~550 m limit on the length of a 1000BASE-SX link? Is it modal dispersion, attenuation? What is the influence of chromatic dispersion in this kind of transmission? What is the bandwidth of a 1000BASE-SX signal? What are the alternatives? I've already read the Gigabit Ethernet article. Thanks in advance for your answers. 93.108.139.109 (talk) 11:07, 21 April 2009 (UTC)[reply]
Normally the range is limited by modal dispersion in multimode fibre. The range can be down to as low as 300m. Different paths of light in the fibre results in a bit being smeared out in time, and running over following bits. You can get increased range by using OM3 fibre rather than OM2. Or you slow down to 100meg and get 2km range. If you go single mode, by using single mode laser GBICs and single mode fibre, you can get much longer range, 10 km at 1310nm or further at 1550nm wavelengths. Graeme Bartlett (talk) 21:21, 21 April 2009 (UTC)[reply]
The encoding uses 8b/10b encoding which expands data rate to 1250 Mbps. The Nyquist theorem says that the minum bandwidth is half this. Just imagine a 1 and a 0 in a square wave making up one cycle of a wave. So that is 625MHz bandwidth. In practice it is a square wave and there will be odd harmonics as well. Graeme Bartlett (talk) 03:24, 22 April 2009 (UTC)[reply]
Which makes it a bit more difficult to cram for my orgo final ... I'm trying to keep track on when you would have to use aqueous solvents and what polar aprotic solvents to use, especially when you're using hydrogen halide gases. Would methylene chloride be suitable here? But you're adding peroxide, which I imagine may want aqueous solution, or would methylene chloride be suitable for distributing the peroxide too?
You are using Wikipedia articles to cram for your final exam? Man, you are in real trouble. A suggested order of preference for cramming for a course is a) your own notes b) the notes of someone else in your class c) the notes of anyone who has ever taken the course d) your textbook e) someone else's textbook f) any textbook on the same subject g) online lecture notes on the same subject h) Wikipedia i) X-men comics. DJ Clayworth (talk) 14:22, 21 April 2009 (UTC)[reply]
Protic solvent talks about some reaction solvent effects. It would be great if someone added info about solvent effects to the major orgoI/II-level reaction pages themselves. But here's the key: if you actually know a reaction mechanism (and there are only really like a half-dozen of them in all of organic chemistry!), it's easy to figure out what types of solvents are good or bad and you don't have to memorize these last-minute details...it really is easier to learn along the way! I'm with DJC here...if you're cramming, getting a broader perspective, learning about related ideas, etc are totally not what you're looking for, You just need to get 70% (I assume) of the the bare minimum info required for this specific exam. You don't care about anything except what is exactly part of the course as taught, so anything other than "stuff that is part of the course" (textbooks, notes, etc.) is only going to have the info you do want scattered among stuff you don't, and might not have the minute details or some special case that your prof has chosen as important for your course. DMacks (talk) 15:02, 21 April 2009 (UTC)[reply]
DNA sequencing
Hi all I am having trouble trying to understand the process of DNA sequencing. I've read the article on DNA sequencing but I am still a little confused so I hope that someone can help explain a few things to me. I understand that at the beginning there is a single strand of DNA and a primer joins on. The primer tells DNA polymerase where to begin transcription. The growth of the chain which begins with the primer is halted due to a dideoxynucleotide being incorporated into the sequence. Thats about all I do understand. Is there just one strand of single stranded DNA or lots of little single strands at the start? How does using radioactive or fluorescent nucleotides result in being able to tell the sequence of bases? If someone could give a brief explain DNA sequencing or tell me about any websites which may be of use that would be great. Thanks. āPreceding unsigned comment added by 92.18.166.121 (talk) 15:06, 21 April 2009 (UTC)[reply]
There are numerous primers and single strands in the mix at the beginning of the reaction. It proceeds essentially like PCR. Due to the presence of the terminating nucleotide, every conceivable length of polynucleotide based on size will be produced in the reaction. Because there are different color fluorescence probes for each nucleotide, an analyzer can read the bands on a gel. Each band represents a different size length. The machine simply reads from smallest to largest using the colors for the nucleotide. Wisdom89(T / C)15:11, 21 April 2009 (UTC)[reply]
Imagine that you only want to know where all the Cs are. So you do the reaction with As, Cs, Ts and Gs, but you also add a bit of dideoxy Cs. Then you can separate the products on a really good gel. Then you see a band at size 5, 7, 11, and 23 nucleotides (for example). This tells you that your sequence is XXXXCXCXXXCXC.You could repeat in separate tubes, but the dyes are just a shortcut to do it all in 1 tube. Hope that helps. Hit me up on my talk page if you want any more help. Aaadddaaammm (talk) 19:17, 27 April 2009 (UTC)[reply]
Just a comment (slightly offhand), but Viruses aren't really considered alive..it's the whole obligate intracelluar parasite definition. That may be a reason why they do not exist in the fossil record. Wisdom89(T / C)15:55, 21 April 2009 (UTC)[reply]
Well, the reason they don't exist in the geological record is because they are too small to form recognizable fossils and their molecular components can't survive for geological times, even in the rare LagerstƤtte that preserve soft tissues. There are "genetic fossils" consisting of viral DNA that has been incorporated to the genomes of living organisms, but it's hard to see how that can be used to date viruses further back than 500 million years at the very most. Looie496 (talk) 16:13, 21 April 2009 (UTC)[reply]
Yup, excellent point - I was going to mention the small size, but my first instinct was "alive"? That seems to be the first thing people think of when viruses are mentioned.Ā : ) Wisdom89(T / C)16:21, 21 April 2009 (UTC)[reply]
And classification is based on things such as the nucleic acid composition/sero markers/envelope etc.. and actual morphology - the latter only being successful with the advent of electron microscopy me thinks, and the former with molecular genetics. Wisdom89(T / C)16:37, 21 April 2009 (UTC)[reply]
If the furthest back that viruses can be dated is 500M years, where does the assertion that they probably existed as long as living cells come from? 65.121.141.34 (talk) 18:23, 21 April 2009 (UTC)[reply]
There is no evidence of when the first viruses arrived, and only indirect evidence for viruses on any timescale that isn't virtually now. That said, viruses are so simple (evolutionarily speaking) that it seems logical to predict that they would have arisen not long after the evolution of the first cells. Dragons flight (talk) 18:58, 21 April 2009 (UTC)[reply]
For sure we're not likely to find direct evidence for them. To the degree that they inadvertently dump pieces of their DNA as 'junk' sequences into that of 'normal' lifeforms, we can look back and say things like "this exact sequence of base-pairs appears in horses, dogs, people, koala bears and elephants - so it must have been from a virus that was around before the common ancestor of all of these animals"...if (for example) we found the same "junk" viral snippet in all plants AND all animals AND all Fungi, Bacteria, etc - then we'd be in a position to strongly suspect that this virus was around at the very beginning of life. But that is rather indirect evidence. SteveBaker (talk) 19:26, 21 April 2009 (UTC)[reply]
Or alternately instead of a common ancestor, perhaps a virus infection has transferred the genes from one species to another. This would appear more likely if the gene was missing from most other organisms. This happens with bacteria transferring genes to unrelated bacteria. Graeme Bartlett (talk) 21:02, 21 April 2009 (UTC)[reply]
The best chance to trace back viruses would be by their pathogenesis. It is not uncommon to find signs of disease or trauma in the fossils. I am not aware of any fossils that exhibit clear effects of viral disease of any sort, but that certainly does not mean there aren't any. In any case, I am talking about plants and animals that actually leave fossils large enough to be studied for the signs of any pathology. Viruses probably evolved long before that. --Dr Dima (talk) 20:22, 21 April 2009 (UTC)[reply]
Your argument doesn't make sense. Not all DNA comes from viruses, so the DNA shared between those species could just have come from a common ancestor originally. If two species share a bit of DNA but another species known to be in the smallest clade containing the first two species, then that might be evidence that both species were infected by the same virus some time after all three species split. (It could also be explained by mutation in the 3rd species, of course, examining more species would be required to get a conclusive result.) --Tango (talk) 12:21, 22 April 2009 (UTC)[reply]
To me, the most compelling evidence is the tropism that different viruses have for certain organisms, suggesting a very long period of coexistence.
Mimivirus is a virus found in infect primitive unicellular organisms like amoeba
There are numerous examples of viruses that affect only animals (and sometimes very specific species)
One possible explanation for this finding is that viruses existed as early as the primitive cells that were the common ancestors of all major branches of the tree of life, and then evolved in parallel with a group of organisms, gradually becoming selective for the replicative machinery or cellular physiology of that specific group. An alternative explanation is that viruses popped into existence at some point when all the major taxonomic groups were established, and somehow then became specific for those distinct kingdoms and phyla. The first of these is the simplest explanation (which as scientists we tend to like the best) -- that viruses "have probably existed since living cells first evolved." The mimivirus article suggests that it may even predate cellular organisms. --- Medical geneticist (talk) 21:02, 21 April 2009 (UTC)[reply]
Are all viruses harmful? Because if they were, and viruses just popped into existence wouldn't they basically kill species too fast for them to develop an immunity to them? An immune system wouldn't even know what a virus was. So I think the spontaneous virus appearance could be discounted. 65.121.141.34 (talk) 13:24, 22 April 2009 (UTC)[reply]
Right, this is my point -- there's a balance between the ability of the virus to enter the cell, replicate itself, and destroy the host cell (what you might consider being "harmful") with the ability of the organism to detect and destroy the virus before too much damage is done -- and this balance has been achieved over millenia of evolutionary "warfare" between viruses and their hosts. Often the viruses are so specific for the cell surface molecules expressed in their natural host species that they are completely incapable of gaining entry into cells from another species. However, consider what happens when a virus is able to move from its normal host into a host from a different species, usually the new host doesn't cope very well with the infection because the immune system has never "seen" anything like it (examples include bird flu and other zoonotic diseases). I only proposed the "alternative explanation" of viruses "popping into existence" to show how poorly this would explain the observed situation of host tropism. --- Medical geneticist (talk) 13:40, 22 April 2009 (UTC)[reply]
Things like viruses and bacteria that make a living by making other lifeforms sick have to be very careful not to kill off their hosts too rapidly or else they'll be unable to spread. I saw a study a few years ago about how "new" diseases are often extremely lethal for the first year or so - but then gradually lose their potency. That's because the disease organism is evolving. The bacteria/virusses that kill their hosts within hours have a very tough time spreading because the host doesn't have time to get close to enough others of it's kind to pass on the illness before it drops dead. Those bacteria/virusses have a hard time passing on their genes once the host dies - so the less virulent amongst them that allow their host to continue to live and (importantly) get close to others of it's kind - will be the survivors. So I don't think you can assume that all of life would be annihilated on the very first occasion it encountered a disease virus...evolution doesn't work like that. SteveBaker (talk) 19:49, 22 April 2009 (UTC)[reply]
I don't think anyone made the assumption that "all of life would be annihilated on the very first occasion it encountered a disease virus". But when viruses jump from their normal host (in which they've evolved to balance their ability to propagate versus the damage to the host, as you very correctly point out) into a new species (i.e. US), we often see horrible, horrible diseases like SARS, West Nile encephalitis, hemorrhagic fever, or Ebola. NOTE, however, that even in these terrible illnesses only a fraction of the infected individuals actually die, it's just that the fraction of people that DO die is much higher than other viral illnesses to which our immune systems have evolved to cope with. --- Medical geneticist (talk) 14:27, 23 April 2009 (UTC)[reply]
It is a common misconception that viruses are either inherently pathogenic or cytopathic. Viruses with those properties have been studied intensely for obvious reasons, and historically it was hard to discover and study viruses so efforts were focused on the ones that caused disease (pathogenic) or easy to identify (killed/injured cells in culture = cytopathic). More recently, it's become clear that we're awash in viruses that cause no apparent disease. Notable examples include GB virus C and TTV. These viruses don't appear to kill the cells they infect, and don't harm the people whom they infect (to our knowledge). In the past, we'd never have known about them, but with PCR it appears that most of us harbor TTV, for example. So, virus does not intrinsically equal disease or cell death. It seems likely to me that most viruses don't cause any disease - they just propogate quietly. --Scray (talk) 04:59, 23 April 2009 (UTC)[reply]
This is an excellent point, and it is another great piece of evidence that viruses (not to mention bacterial commensals) have been co-evolving with their hosts for millenia. --- Medical geneticist (talk) 14:27, 23 April 2009 (UTC)[reply]
Surly we can say that the immune systems of life on the planet come from being atk by virus amongst other things now if we apply that to a Crocadile then it goes to say that they date back to the oldest animals living on the planet.....
10:02, 18 August 2010 (UTC)ChaufriChaufri (talk)Ā ::: I believe viruses didnt arise much way back. The climatic scenario would have been unbearable for viruses of the old times. For me viruses evovled in the present day scenario (reffering to present day land dwellers). Viruses are broken DNA/ pieces from dying cells, pieces of DNA/RNA that were responsible for multiplication (contained genes for multiplication), when exposed to external environment of that dying cell, somehow adapted to it, collected a protein capsid.... Became A ViRuS.
Thus those viruses could only duplicate themselves in their respective MOTHER CELL from where they originated......
i.e. Bacteriophafes only attack bacteria... etc etc Ā ;)
Increase in rolling resistance on a wet road?
This question has been bugging me for a while, and I'm unable to find any figures on the net about this. When a car travels along a wet road, the tyre acts as a "pump" to move water away from the contact patch of the tyre. This uses some of the kinetic energy of the car, although some presumably is recovered as the water flows back in to the space behind the tyre, pushing it a little. Also, presumably, the majority of this energy is used in the process of moving this water out of the way of the tyre, heating the water, atomizing it into a spray and producing the characteristic noise associated with cars on wet roads. Not to mention the "stickyness" of water causing extra friction.
Does anyone have any figures for how much energy this process takes? For example, what kind of economy penalty can I expect in an average car at a given speed?
Certainly it's very noticable how a car slows down faster if you put it into neutral on a wet road than on a dry one - and if you run through a deep puddle in a small car, you can really feel it slowing you down. So there is certainly an effect - and for water in maybe the quarter-inch-or-deeper range, it's gotta be pretty significant. As for quantifying it...I've never seen anything like that out there and a Google search on likely terms didn't turn up anythink of use. The figures for aircraft tyres may not be comparable. Aircraft tyres are optimised for going in a straight line and not imposing too much drag on takeoff - where car tyres have to cope with the much more tricky business of cornering. If you look at an aircraft tyre, you'll see it has a simple circumpherential tread pattern with none of the fancy zig-zag or diagonal grooves you see in the tread patterns of cars - and that suggests to me that pumping water out from under the tyre isn't so important to them. So I don't have a good numerical answer for you - beyond that it must be reasonably large because of the degree of deceleration you feel when you coast through even a half-inch-deep puddle and that you can't use the aircraft figures. SteveBaker (talk) 20:07, 21 April 2009 (UTC)[reply]
Another difference between cars and planes which may be relevant is that the wheels of a car are its means of propulsion, they aren't on a plane. (Which is why, as we all know by now, planes can takeoff on a treadmill running backwards at takeoff speed.) --Tango (talk) 23:34, 21 April 2009 (UTC)[reply]
Just one data point.. I've noticed a decrease in highway mileage, often significant, in rain. Say, down to 28mpg from a more normal 32. Friday(talk)20:09, 21 April 2009 (UTC)[reply]
Yes - although some of that would be increased drag due to the raindrops effectively increasing the density of the air...also, you're running your wipers and (hopefully) your headlights - although that won't make a lot of difference to your mpg numbers. SteveBaker (talk) 01:16, 22 April 2009 (UTC)[reply]
Tire treads have aggressive cross-cuts or grooves to provide a place for the surface water to go so that "the rubber meets the road" and provides traction. Does this cause the tire to do work by lifting water from the pavement and presumably throwing it out sideways to make room for the water in the next rotation? If so, then the tire is acting as a pump, and the car engion or the kinetic energy of the car is the source of the energy, causing the car to slow down or requiring greater fuel per distance driven. Edison (talk) 14:10, 22 April 2009 (UTC)[reply]
Yes - that's exactly the mechanism - but it's hard to estimate the magnitude of it in order to answer the OP's question. Knowing the depth of the water and the speed of the car and the width of the tyres - we can figure out the amount of water that's being "pumped" away by the tyres - but we don't know how much kinetic energy that water leaves with - so we can't really figure out how much energy the car loses in doing that. We certainly know it's bigger than zero...but beyond that??? SteveBaker (talk) 19:42, 22 April 2009 (UTC)[reply]
The Beauty of the Universe
I might have the wrong section, please direct me to the right area if I do.
I was looking at photos of the Universe, specifically of Saturn's moon and rings, and I was completely awe-struck by it. You know, a deep down feeling that something is incredibly beautiful. I was not alone. The website's commentators made many similar remarks. They too don't seem to be alone. In general, it seems like most people find "beauty" in outer space. Here's my question, and it deals with the anthropology side of evolution. If humans evolved beauty in response to let's say conditions that promoted life (ex. a lake provides water ... landscape of a lake looks beautiful), why is it that things beyond our world, things that can't provide any form of subsistence strike such a note inside of many humans? āPreceding unsigned comment added by 24.131.131.5 (talk) 20:52, 21 April 2009 (UTC)[reply]
Is it beauty you are perceiving or awe? You use the term "awe-struck", which is how I would describe myself when, for example, I first saw the moon through a telescope. I think there is a difference between awe and beauty. Beauty (in this context) is a purely visual thing, but I think in order to be awe-struck by celestial objects you need a certain amount of understanding of what they are. You have, however vague and imprecise, a sense of the size and distance of the thing you are looking at - I think that is an important factor. I'm not sure what the evoluntionary benefit of awe is, though, so I can't really answer your question, just ask a slightly different one! --Tango (talk) 21:56, 21 April 2009 (UTC)[reply]
The question is pertinent in matters closer to home, I think. When did a person first look at a range of snow-capped mountains and find it beautiful, rather than simply forbidding? What was up with that?
I once read an account of a troop of chimpanzees, working their way through a jungle. They emerged into a sudden clearing, and beheld a humongous waterfall with water cascading great distances over rocks. Very dangerous. They started shouting, and jumping, and looking at it, and reacting with... what was that? Is it somewhere on the continuum towards an aesthetic sense? Impossible to say, I'm sure. -GTBacchus(talk)22:02, 21 April 2009 (UTC)[reply]
I believe I came across something a while ago that said the Romans and Greeks normally regarded forests and nature generally as threatening rather than beautiful, and the modern thing in the West of seeing nature as beautiful started quite recently with Romanticism in the 18th century. Dmcq (talk) 22:40, 21 April 2009 (UTC)[reply]
You respect and fear the enemy's strength; fearing big dangers is obviously advantageous. It turns to beauty and awe when you fear and admire your alpha male or chief, and promote the most fearsome warriors to high position. Being fearsome becomes favored (aesthetically pleasing)... so huge objects convey might and you hold them in awe. 72.236.192.238 (talk) 23:18, 21 April 2009 (UTC)[reply]
astronaughts
Well, to rain on the parade a bit, there are vast numbers of things in space that are utterly boring. You don't generally see pictures of them. And even for the things you do see pictures of, the colors are often greatly enhanced. Looie496 (talk) 00:15, 22 April 2009 (UTC)[reply]
To me, there was no danger in viewing the object. I understand my own feelings of danger or vulnerability. I've seen photos of astronauts in space juxtaposed to the looming Earth. There a simple sense of vulnerability and empathy for that man consumed my thoughts. Rather, when I saw the picture of Saturn's moon, with its craters and pale white color, without any coaxing, I felt that it was beautiful and like I said I was awe-struck. The image was viewed upon a 17 inch monitor, consuming maybe 1/2 of the screen. I don't think I feared its size, nor felt in anyway that it resembled a human that I might fear.
I think it's mostly observer bias. If you are an astronomer - in any given year, maybe you'll take hundreds of thousands of photos that are basically white dots scattered at random on a black background - and a couple of gaseous nebulae with unusual dust formations, etc. Which ones get nice names like "The Horsehead nebula" and go on your web site...and which ones get some six digit serial number with the date on the end and are kept in your large collection of other similar pictures that nobody ever sees?
Also, they have a lot of control over the look of the things. Most scientific data is collected in regions of the electromagnetic spectrum that humans can't see - so the "photos" aren't really photos at all - they are the result of running a bunch of computer programs on a string of numbers. You can make the colors come out any way you want - you can enhance the 'pretty' bits and tone down the 'ugly' bits. While you probably won't do that for the purpose of extracting scientific information - when you are preparing an image to put on your web site or the cover of your next book - you're very likely to set the software up with some pretty pastel colors and tweak them until it does look beautiful. There is no "right" or "wrong" when it comes to using "false color" techniques. So what you are seeing isn't that all of space is somehow beautiful - you're seeing just the bits that someone who stares at these things all day long finds beautiful...tweaked to make them look even more beautiful. It's no surprise that the results are usually pleasing. SteveBaker (talk) 01:12, 22 April 2009 (UTC)[reply]
Erm. I'm 100% sure these weren't enhanced by the computer. I was looking at a picture of Saturn's moon. It might have been cropped for dramatic effect, but it still doesn't change the emotional response I observed. āPreceding unsigned comment added by 24.131.131.5 (talk) 01:34, 22 April 2009 (UTC)[reply]
I'd be VERY surprised if the image you're thinking of was taken in Red/Green/Blue light at normal intensities and displayed with nothing more than cropping - they simply don't put that kind of instrument onto deep space probes because RGB photographs simply don't contain much that's of scientific benefit. The image was probably taken in IR or UV or with a monochrome camera using some combination of polarizing filters or something. If you're "100% sure" - tell us (in detail) how come you're so sure - because I'm REALLY sure you're 100% wrong! SteveBaker (talk) 04:02, 22 April 2009 (UTC)[reply]
Care to tell us what image you're talking about? To me, most pictures of Saturn's moons look like relatively boring lumps of rock. Sometimes lumps of rocks with an equally boring gray line behind them. (Except the one that looks like the Deathstar.)
One things that moon and asteroid pictures usually do have going for them is that they typically have pretty dramatic lighting. I'm not sure if that makes them "beautiful", but it certainly makes them striking. APL (talk) 03:35, 22 April 2009 (UTC)[reply]
Oh, actually, there's a very dramatic image of Mimas (The deathstar look-alike) that's just as you described, right on the Mimas page. It is a great image. It's aspect ratio will make it a good background image for my tablet PC. However, be aware that this is not a natural color image. Instead of Red/Green/Blue, it was taken in IR/Green/UV. The colors had to be adjusted to look approximately correct. (Here's a similar image in true color.]) APL (talk) 03:51, 22 April 2009 (UTC)[reply]
Yeah - there is no way an image like that has not been processed in some way. As our caption says - it was photographed in IR, Green and UV light - not Red, Green, Blue - and the interpretation of those three frequencies into light that we can see is largely an artistic matter. SteveBaker (talk) 04:02, 22 April 2009 (UTC)[reply]
Cassini's "red, green and blue" filtersI've been curious for a while about how true NASA's true-color images really are, so I went and tracked down the actual spectral response curves for Cassini's filters. They're available here. The description of "Nature's Canvas" (which APL linked above) says that it's a true color image made using red, green and blue filters. The source images are [5][6] and [7], which were taken through the RED+CL2, CL1+GRN, and BL1+CL2 filter pairs respectively. (CL1 and CL2 are clear filters.) On the right is a plot of the camera's frequency response curve with those filter pairs in place. The horizontal scale is wavelength in nanometers. I'm not sure what the vertical units are but I think they're CCD electrons per incoming photon. The vertical scale is linear and the maximum is around 0.23.
One interesting thing about these filters is that, compared to the human eye, they have very little ability to distinguish monochromatic colors. For example, they can't tell the difference between blue and violetāthey both show up as a nonzero value in the BL1 channel and zero in the other two channels. There might be a little bit of variation in the brightness of the BL1 channel, but that doesn't help because there's no way to tell the difference between a change of wavelength and an actual change of brightness. There's also no frequency discrimination in the 500ā570 nm and 640ā730 nm ranges, and very little in the red-yellow range where the RED and GRN filters overlap. If the value in the BL1 channel is zero and the values in the GRN and RED channels are nonzero and roughly equal, the spectrum might have a single peak somewhere in the red-yellow range (which a human would perceive as red/orange/yellow) or it might have a peak in the infrared and another in the 500ā570 nm range (which a human would perceive as green or cyan). There's no way to be sure. So you can't, strictly speaking, produce a true-color image from these filters.
On the other hand, real-world spectra are pretty predictableāthey don't vary much across the visible range. If you can come up with a model with only three adjustable parameters that approximates the spectra you actually expect to find in the scene, then the values from the BL1, GRN, and RED channels together fix the parameters of the model, and from that you can work out sRGB coordinates. A simple example would be to model the spectrum (in units of photons/mĀ²/s/nm) as a quadratic function of the wavelength. I actually tried doing this and got
(where I've applied an overall normalization to the matrix so that the largest entry is 1). So in this simplistic model you can pretty much plonk the BL1 data into the blue channel, but the red and green channels are more complicated. There's also the fact that I don't know how the CCD electron counts are related to the pixel brightness in the raw JPG/TIFF images, and this calculation gives you linear sRGB values which need to be gamma corrected, and my model isn't very good, and I probably made a mistake in the calculation. But anyway this gives the general idea of what you have to do to compose the raw images into something that might (if you used the right model) resemble true color. Note that you can get better color accuracy by using more than three filters, even though there are only three output channels, because with more inputs you can fit more parameters. The only exceptions are if your model is perfect already or you have three filters that are independent linear combinations of the human cone responses (in which case the model is irrelevant). You could produce a true color image from IR/Green/UV channels by this technique if you had a good enough model. I have no idea whether the official NASA images are really produced this way, though. I get the impression they do a lot of retouching to get the colors right, though in that case I don't understand why they use three source imagesāif they know the right colors beforehand, couldn't they just colorize a single one?
Incidentally, if you look at the three source images you'll notice that Mimas moves significantly against the background rings, so there was a fair amount of non-color-related Photoshopping required here too. Even more so with the sources for "Mimas blues" ([8][9][10]). Not that there's anything wrong with that, it's just interesting. -- BenRG (talk) 00:48, 23 April 2009 (UTC)[reply]
One reason why we think some astronomical objects are pretty is symmetry. Saturn's rings are rather symmetrical, as are the arms of a spiral galaxy. A planet or moon in a pic that shows no detail looks pretty, too. When you get to a resolution that shows the pockmarked craters and such, they don't look quite so pretty any more. So, then, why do we have this preference for symmetryĀ ? Since many biological systems use symmetry, a symmetrical plant, animal, or person is more likely to be healthy, so a better choice to eat, own, and/or mate with. StuRat (talk) 15:40, 22 April 2009 (UTC)[reply]
how much biological output is produced (by either weight or volume) daily by all of the world's population combined?
I've tried not to be too direct, but you can skip this question if you are having dinner or something. My question is: how much biological output is produced daily by all the people of the world combined, per "type". Either by weight or by volume.
This is surprisingly hard to find, I tried googling both total, and average production for both types using several phrases but could not find any numbers at all. Any ideas? 94.27.218.161 (talk) 21:28, 21 April 2009 (UTC)[reply]
By "biological output", do you mean feces and urine? And by "world's population" do you mean human population? If so, according to urine: "In adult humans the average production is about 1 - 2 L per day." Since there are about 6.8 billion people in the world, that comes to a total of about 7-14 litres/kgs of urine per day (actually, it's probably a little less since children presumably produce less than adults). I can't seem to find the appropriate numbers for feces, though... --Tango (talk) 21:46, 21 April 2009 (UTC)[reply]
I think you missed a rather important "billion" in your answerĀ :) In terms of faeces a roundabout figure would be 500g/person/day which gives about 3.5 million tonnes per day... NICE! Smartse (talk) 21:16, 22 April 2009 (UTC)[reply]
The OP said "both types", so we're looking for just two types. Feces and urine seem to be the most obvious two. --Tango (talk) 21:52, 21 April 2009 (UTC)[reply]
Food statistics might be easier to find (and nicer to contemplate) than waste statistics. I would assume that the total mass excreted as feces is less than the total mass ingested as food. If you assume that my daily poo weighs... one half as much as my daily bread? You'd probably be accurate within an order of magnitude, and this kind of calculation isn't going to be much more precise than that anyway, right?
More direct information about volume of waste might be available by considering a city and how much waste is treated daily - something else you could probably look up. -GTBacchus(talk)21:54, 21 April 2009 (UTC)[reply]
The total excreted as feces and urine will be less than the total consumed as food and drink, I'm not sure you can simply separate the two, though. Feces is mostly water, whether that is water that comes from the food, or whatever that comes from drink is difficult to determine (or even define). The waste processed by a city will be mixed up with lots of other stuff (mostly water from the mains supply and rain), so I doubt you'll get useful figures from that. --Tango (talk) 22:14, 21 April 2009 (UTC)[reply]
What about handling the question as if it were asked like How much inorganic matter is turned into organic matter by the Earth's biosphere daily?āPreceding unsigned comment added by 131.188.3.20 (talk) 00:27, 23 April 2009 (UTC)[reply]
Obviously, everything that exists in this world consists of specific elements, thus giving us it's molecular, or empirical formula. Now if we look at anything along with it's molecular/empirical formula, that certain thing consists of a "geometrical chemical shape." So, if everything has it's own shape, everything can be cured with some form of conversive, contradicted, form of that matter, which is what we call medicine.
--
So, TO MY QUESTION, does cancer have a molecular, or empirical formula? and if so, can you lead me to a site with it's geometrical shape?
No. Cancer is made up of cells, just like any other living tissue. The difference between cancer cells and other cells is just that cancer cells reproduce out of control. The difficulty with curing cancer is that the cancer cells are very similar to the non-cancer cells and you have to come up with a way to kill the cancer without killing the patient, which is very hard to do. --Tango (talk) 22:11, 21 April 2009 (UTC)[reply]
You have a basic idea, which is correct, that every substance is composed of specific elements which form molecules. However, the point you appear to be missing is that cells are made up from billions and billions of these molecules. Cancer is a process which affects cells as a whole, and cannot be treated by a lock-and-key mechanism which you appear to be describing. Instead, cancer must be treated by either limiting damaged, uncontrollable cells replication, or by killing off those cells which are damaged. I recommend you read up on cell (biology) which should give you an insight to what cells are composed of. If you have further questions, feel free to come back. Regards, --āCyclonenim |Ā ChatĀ 22:44, 21 April 2009 (UTC)[reply]
Okay, but even if cancer is made up of cells, don't these cells contain specific elements? And just like other viruses or bacteria, can medicine not be produced to react with these compounds that would cause the inactive cells in cancer to "undo" their inactiveness, and make them re-active, or turn them into another type of matter that would be helpful and plentiful to the body? If we could find the molecular formula, could we not change these cells into matter that would nuture the body instead of destroying it? (i.e. Some type of protein, sugar, hormone, etc...I'm not definite on the subject, it is just interesting, so I'm only throwing out some creative ideas!)
The problem is that the cancer cells are made up of exactly the same elements as the non-cancer cells. The differences are really tiny - a couple of protein molecules in a slightly different place, that sort of thing. We can do all kinds of things to cells, but we need to find ways of doing them to just cancer cells, which is hard. We do have ways of combating cancer and are inventing new ways all the time, but it is a really difficult problem to solve so we haven't got any perfect solutions yet. --Tango (talk) 00:17, 22 April 2009 (UTC)[reply]
All biological tissue is made almost entirely from carbon, hydrogen, oxygen and nitrogen - with a few bits and pieces of other elements. But the amounts and ratios of those things are very similar between (say) a lung cancer cell and a healthy lung cell. In fact, they might have utterly identical amounts of those elements - the only difference being something very subtle about the arrangement of them...and even then, the mis-arrangement is just in the DNA and that's a microscopically tiny fraction of all of the chemicals in the cell - just a few misplaced atoms in just the wrong place is enough. Worse still - a healthy muscle cell is way different to a healthy lung cell - but a cancerous lung cell is much more similar to a healthy one than the muscle cell is. These difficulties probably explain why we have not yet evolved a way for our bodies to cure themselves of cancer just as we can cure ourselves of the common cold. Most of the treatments for Cancer depend on targetting the way they behave. So when they go nuts and start reproducing like crazy, they don't build things like the blood vessels they need to get nutrients...so there are tricks like treating the patient with drugs that slow the development of new blood vessels that'll starve out the cancer cells and hopefully reduce their numbers. Sadly, doing that also prevents new blood vessels that you actually NEED from forming - hence the treatment can make you even sicker than the cancer did. SteveBaker (talk) 00:54, 22 April 2009 (UTC)[reply]
As others pointed out, the difficulty lies on the fact that cancer cells are so similar to normal cells. They are descendant from normal cells after all. But there are subtle methabolic differences that can be used to attack them. The lock and key idea is actually a good one and our own body makes use of some of those sublte methabolic differences to find the cancer cells and kill them. But there are no magic silver bullets and sometimes things get off hand. Dauto (talk) 01:03, 22 April 2009 (UTC)[reply]
Is it not possible through research that we could identify these microscopic, subtle changes in the inactive, harmful cancer cells to reverse the process by means of injecting some sort of "medicine" into the general area of the cancer? Or, is this what all the research for cancer is searching for? Since the alterations in the DNA sequences are microscopic, does this mean that the "lock and key" idea would not work because it would be impossible to specifically locate infected, maladaptive atoms (molecules) inside of the DNA sequences?
Indeed cancer research is directed toward finding shared characteristics of cancers that might represent therapeutic targets. There is no single simple DNA sequence change that is shared by cancers, not even for a single type of cancer. Sometimes there are themes that are shared, like suppression or mutation of tumor suppressor genes like P53, or over-expression of a protooncogene like myc, but these are neither uniform nor easy targets - they are "normal" genes being expressed at the wrong level for a particular cell type. Extremely bright and highly motivated people, many of whom have friends or family affected by cancer, are heavily engaged in this work. --Scray (talk) 02:21, 22 April 2009 (UTC)[reply]
All cancer treatments are dependent on exploiting the effects on the cell that the changes in its DNA has on it. The entire concept of chemotherapy is to develop toxins that kill cancer cells faster than normal cells. The problem with what you want is that the immutable differences between cancer and normal tissue (the changes in the DNA code) cannot be targetted by any developed method. This paper describes a fascinating (and theoretical) way of doing it, but at the moment, we're stuck with toxins, radiation, and cutting it out. Someguy1221 (talk) 02:15, 22 April 2009 (UTC)[reply]
I would hope that, at some point in the future (decades perhaps), a cure for all cancers could be developed which would work like this:
1) Take a sample of cancer from the affected individual, and also a sample of the same tissue without cancer from that individual (the "control").
2) Run both samples (with thousands of cells in each sample) through a computer which will analyze the genetic code and find the difference in the cancerous cells.
3) Program a virus to search for those cells which contain the cancerous genetic code. When it finds them, it can repair them, kill them, or mark them in some way so other agents (the person's own immune system or chemotherapy drugs) can then kill them. It would also be a good idea to make this virus incapable of reproduction once introduced to the patient's body, so the rate at which it works could be controlled. The virus could also be programmed to self-destruct once it finds a cancerous cell and does it's thing. If this control isn't present, so much cancerous tissue could be killed all at once that this would cause a new problem, a mass of decomposing tissue too large for the patient's body to clean it up quickly.
If the cancer has metastasized (spread to other organs/systems), then it may be necessary to repeat this process for each organ/system. StuRat (talk) 15:23, 22 April 2009 (UTC)[reply]
Good idea StuRat. That's pretty much what my idea was, which I titled "the lock and key." If we could track the genetic variations inside of the DNA samples, then we could find the "key" that would fit into the "lock" that would then reverse the process of the cancer, either [like you said] killing it, healing it, and/or making it beneficial to the body.
Lock-and-key isn't really a new idea, it's used in regards to enzymes and their substrates too. This method for curing cancer, however, it a pretty futuristic idea since at the moment we do not have a way to repair individual cells. The idea that they could be killed, perhaps by nanorobots when they are developed, is an interesting one that may be possible in the very long term future. That said, I prefer the idea marking cells with chemical markers so that the immune system can destroy them. That sounds the most plausible in time scale terms, but it's still a long way off. Regards, --āCyclonenim |Ā ChatĀ 07:04, 23 April 2009 (UTC)[reply]
StuRat makes an interesting point, but the idea of programming a virus to detect "the cancerous genetic code" is a bit far-fetched. The approach that seems to have people excited right now is to try to detect a gene expression profile that can uniquely identify a cancer cell; or even better a cell surface protein that is only expressed on cancer cells, and use drugs that can either target a key pathway that's abnormal in cancer cells or take advantage of the cancer cell surface marker to kill cancer cells more directly (rather than using systemic cell poisons). See Gleevec and Herceptin for current approaches that are based on these ideas. --- Medical geneticist (talk) 14:35, 23 April 2009 (UTC)[reply]
Detecting the cancerous genetic code is a bit far fetched, but it's one that (for some cancers) the science might exist now to make feasible. Check my post somewhere above on a PNAS paper on doing just that. The idea is to create a lethal vector that is inactivated by non-mutated DNA. Although I believe the author of that paper himself once said he hoped it would be a reality by 100 years from now, so that gives you sense of what he's even sure of. Someguy1221 (talk) 08:02, 24 April 2009 (UTC)[reply]
The only problem with that approach is that it may miss dormant cancer cells which currently don't exhibit any expression of the cancer. StuRat (talk) 07:57, 24 April 2009 (UTC)[reply]
Nanorobots is a pretty crazy, futuristic idea that would be great, but as you said, it is very far off. I've never heard of Gleevec and Herceptin though, but that's pretty cool. I'm not sure how you would trace and mark inactive cancer cells though, how would you? Wouldn't the tracer have to be the "key" to the cancer "lock" to be able to find the inactive cell in the mutated DNA?
The virus that identifies a cancer cell could then produce a chemical marker that would migrate to the cell wall. This could then be detected by other agents and/or could grant them access to the cell interior. StuRat (talk) 07:54, 24 April 2009 (UTC)[reply]
The virus wouldn't necessarily have to produce a marker. There are plenty of extremely lethal protein toxins, like translational inhibitors, the virus could make on its own to kill the cells pretty effectively. Someguy1221 (talk) 08:02, 24 April 2009 (UTC)[reply]
Right, but how would a virus know WHICH CELL is the cancer cell compared to normal cells? This is what I was saying, wouldn't the virus cell almost be like the "key" to the cancerous "lock" cell?
A synthetic enhancer of gene expression could be developed that only activates when a specific mutated DNA sequence is present (or a synthetic inhibitor could be developed that only activates when the normal DNA sequence is present). This would cause the remaining viral genes (that make lethal proteins) only activate in the cancerous cells (or only deactivate in the normal cells). This would require a knowledge of the complete DNA sequence of a patient's cancer, as well as their normal DNA. Additionally, there's the problem that not all cancer cells in a given cancer are identical (that's how resistance arises to chemo), so ideally the "lock" would have to be one of the earliest mutations to occur in the cancerous cell line. That said, there's also the problem that any protein designed to activate on binding a particular DNA sequence will have some degree of response to very similar sequences. That makes large deletions of DNA the safest mutations to target. In the paper I linked to previously ([11]), they describe doing exactly that. The actual key to their idea is a theoretical pair of restriction enzymes that only activate when they bind the normal DNA sequence that was deleted from the cancer cells. This restriction enzyme then destroys the lethal gene that was introduced along the restriction enzymes. So, precisely what you wanted, except backwards. There's a virus floating around the body that will try to kill any cell it enters. It has a self-destruct mechanism with a lock on it (the restriction enyzmes). The key to activate the virus' self destruct mechanism is normal DNA that is absent from the cancer. So all the cancer cells die, and the normal cells never know they were visited. Someguy1221 (talk) 01:55, 25 April 2009 (UTC)[reply]
So, once a restriction enyzme cuts the DNA down the two backbones, what happens to it? If the DNA notices the cancer cells and "self destructs" them, what happens to them?
An example of how it could work would be that the virus carries a lethal gene that codes for a toxin that blocks all protein synthesis, eventually killing whatever cell it entered. The restriction enyzmes are the self destruct mechanism, and they can only be activated by detecting the normal DNA. Once the DNA is cut, it slowly dissolves into individual nucleotides from normal cellular processes. So the cells that have normal DNA cause the virus to destroy itself before enough toxin is produed to kill the normal cell. Someguy1221 (talk) 07:32, 26 April 2009 (UTC)[reply]
If the DNA splits into multiple nucleotides, do those eventually come back together to form a new strand of DNA?
If the world record holder in the long jump decided to jump from the top of a mountain, how far would he be both horizontally and vertically from the point at which he jumped at the moment he started to fall vertically? 90.216.163.234 (talk) 00:19, 27 April 2009 (UTC)[reply]
Hiding from thermographic camera view by covering oneself in thick mud from head to toe...
...malarkey or effective way? Yes, I'm a Predator fanboy.
That wouldn't actually work in Real Life, would it? Yep, I'm aware that the Predator's visual filter mask is alien technology and may not (in the story) *actually* be a thermographic camera, in the way that we think of one. --Kurt Shaped Box (talk) 23:17, 21 April 2009 (UTC)[reply]
You might be able to get it to work for a short amount of time, but if it worked over a long period it would kill you. The human body produces a significant amount of heat and if that heat isn't allowed to escape the body rapidly overheats. If the heat is escaping, then it is visible to a thermographic camera. A better option is heating the surroundings up to body temperature (uncomfortably hot, but not fatally so, at least if you keep the humidity low). I believe both these options were discussed in a Mission Impossible film, or similar (although they didn't use mud but a special foam suit) - for the reasons I've stated, they went with the heating up the room option. --Tango (talk) 23:28, 21 April 2009 (UTC)[reply]
(after edit conflict) Thinking about it, the movie is set in the jungles of Central America, so the ambient temperature is going to be pretty high anyway. Slap on some thick wet mud to bring down your own surface temperature and it might work for a time (as you say). The black ops guys in Predator 2 used insulated foil suits when attempting to capture the creature. IIRC, they were tethered by hose to some sort of central refrigeration unit. --Kurt Shaped Box (talk) 23:57, 21 April 2009 (UTC)[reply]
The Pierce Brosnan remake of the Thomas Crown Affair used exactly this method of increasing ambient air temperature to "blind" the thermal cameras in the art museum.Ā :-) 61.189.63.224 (talk) 23:51, 21 April 2009 (UTC)[reply]
Yeah - but that's fiction - so we may safely ignore it. OTOH - the Mythbusters tried a whole bunch of ways to get past thermal sensing alarms and found that a white bed-sheet held up in front of you was entirely effective (and a darned sight less messy!). Evidently, something that's highly reflective of IR energy allows your body heat to be reflected back away from the camera. SteveBaker (talk) 00:35, 22 April 2009 (UTC)[reply]
Even if it is effective, what about Schwarzenegger's eyes? He doesn't put mud over his eyes (for obvious reasons), but shouldn't the preditor been able to detect the heat coming from his eyes? A Quest For Knowledge (talk) 00:44, 22 April 2009 (UTC)[reply]
Insufficient resolution on his HUD perhaps? I don't recall him being stood particularly close to Arnold in that scene. A lot of the Predators' gear seems to have technical limitations (e.g. a cloaking device that provides less than perfect invisibility when moving and malfunctions when wet, or an auto-tracking plasma cannon that struggles to acquire an accurate lock on a moving target). Or maybe he was looking for and expecting a human-sized heat source? Not finding one and dismissing the notion that a human could be smart enough to figure out the limitations of his thermal imaging (the mud thing was a lucky accident anyway), maybe he just figured that Dutch had somehow given him the slip and run off before he got there? --Kurt Shaped Box (talk) 01:23, 22 April 2009 (UTC)[reply]
Military anti-thermal-detection suit
This Q inspired me to ask one I've had on my mind. Is there a suit that could be designed to fool a thermal detection camera, over long time periods (many hours)Ā ? I'm going to assume that heating up the environment to body temp isn't an option here, and neither is holding a sheet in front of yourself. Here's a couple of thoughts I had to overcome the build-up of heat problem:
1) Have the suit carry a coolant to fight the build-up of heat. This could be a very simple design, with inside pockets holding the coolant close to the body, and thermal insulation on the outside of the suit. No circulation system would be needed. When the solider returns to base, he could replace the warm coolant packs with cold ones. The trick would be a finding a light-weight coolant which has a high thermal capacity.
2) Have the suit heat some liquid, such as water, then inject it far enough underground to hide the thermal trace. A large downward pointing needle could be affixed to the calf of the soldier, which would periodically inject the hot water into the ground. This would only work on soft terrain. Alternatively, the soldier could dump warm water on the ground when he judges himself to be safe from thermal cameras. If a source of cold water is available (river or lake), then a tank of cooling water could be loaded up inside the suit and the warm water released into the river or lake periodically. Such a suit would require a circulation system, but it might be possible to install one-way valves such that normal body movements would circulate the fluid.
There are a few tricky bits to get around. How to cover the face and hands without limiting maneuverability or limiting vision comes to mind. Also, The suit could not limit hearing or be noisy to use (crinkly aluminum sheets for example). Weight of course could be an issue. The more coolant you can carry, the more weight, but the longer the suit can go before a recharge. I don't think the needle idea would work because it would probably get broken while moving around, or else it might make you trip. Maybe it could be retracted or something. It is really going to depend on what you are doing while wearing the suit. If you are just standing in 1 place, it should be fairly easy. If you are in a special ops unit of the military, then it would be a lot harder to design. 65.121.141.34 (talk) 15:19, 22 April 2009 (UTC)[reply]
You're want to make sure that you didn't show up as a mysterious cool spot. The Predator would figure that out pretty quickly. APL (talk) 15:59, 22 April 2009 (UTC)[reply]
For military use - it's a lot harder. To fool a sensor, you only have to fool the kinda crappy image processing system that's hooked up to a cheap camera and saying something like: "If you see heat above 80 degF covering more than 10% of your pixels - ring the alarm". To fool human eyes (albeit looking through an infra-red camera or night vision goggles) is vastly harder. Having cool-packs isn't enough - you'd have to spread the body heat out uniformly - but you're still blocking the heat from whatever is behind you. When you look through night vision goggles, you see all the details of the trees and the grass and the road and vehicles, etc - and a human-shaped blob of any temperature whatever will look like a guy in a suit trying not to be notice! It's the EXACT same problem as trying to be invisible in daylight - you can't just be black or grey or the exact same AVERAGE color/temperature as the rest of your environment - you actually have to be an exact match for your environment - as seen from the point of view of the observer. Having said that, there are people who are trying to figure out how to make invisibility 'cloaks' - and if they ever succeed, then whatever they do will probably work perfectly well for IR imaging too...and of course you could merely seek to 'break up the shape' using camoflage techniques (but in the IR domain) and have some improvement. But as far as I know, this isn't a serious issue for the military right now. Most of the people that 'modern' armies are fighting are using techniques from 50 years ago - and they don't typically have night vision so going to a lot of trouble to hide from night vision devices isn't a huge deal right now. SteveBaker (talk) 19:37, 22 April 2009 (UTC)[reply]
Well, you'd still expect the special ops soldiers to keep hidden behind trees, in ditches, etc. However, if they are glowing brightly in infrared, that won't be enough. But, using an IR-suppression suit, in combination with standard stealth techniques, they should be able to avoid detection. As for "the enemy" not having IR scopes, they are cheap enough now that the military should consider them to be available to the terrorists. StuRat (talk) 03:15, 23 April 2009 (UTC)[reply]
You could try something like a thermocouple, which would cool the body by using the heat difference between it and the outside world to generate electricity which could then by used to power your equipment, or just dissipated in some invisible way. Done correctly, this could give you a suit that allows you to control the temperature at different points on the outside allowing you to create an IR version of the standard camouflage pattern. You would probably want something that can be adjusted depending on the time of day, ambient temperature, terrain etc. (you might have some of the suit the temperature of the sky and some the temperature of the trees, for example). --Tango (talk) 19:48, 22 April 2009 (UTC)[reply]
You could restrict your operations to times when the ambient temperature is close to human body temperature. Another option would be to breed a race of reptillian soldiers who radiate very little heat when at rest. A much cheaper option would be to cover your whole body with some very absorbent clothing, and continually douse yourself with water at ambient temperature, to keep yourself sopping wet. The surface of the clothing should equilibrate to something close to the dew point temperature, and if everything around you was similarly wet, you might not stand out. If you were in a very dry environment, such that the dew point temperature was well below the ambient temperature, this might not work well because you might appear as being too cool. Incidentally, Russian snipers in WWII in winter would put snow in their mouths so they would not give away their positions by exhaling vapor clouds. You may remember seeing that in Enemy at the Gates. --Teratornis (talk) 23:46, 24 April 2009 (UTC)[reply]
Gaussian random motion occurs when the probability distribution of the displacement between now and any later time is Gaussian. It basically means completely random motion: if you take an object that in every time increment moves a random amount in a randomly chosen direction, as long as the time increments are short enough the motion closely approximates a Gaussian random motion. It is, for example, a useful model of the movement of molecules in a gas. Looie496 (talk) 04:08, 22 April 2009 (UTC)[reply]
How do dot diagrams with little crosses or x's in place of some of the dots work? I see this in some diagrams and I'm not entirely sure what it means. 98.165.40.158 (talk) 04:32, 22 April 2009 (UTC)[reply]
I am, yes. I can't find anything on that page, but I've seen where some of the dots are replaced with crosses. What does this mean? āPreceding unsigned comment added by 98.165.40.158 (talk) 04:56, 22 April 2009 (UTC)[reply]
Do you mean all of the dots are replaced by crosses/plus signs, or a mixture? If it's the former, that's just stylistic - if not, the only time I've seen + signs is in relation to the valence of an ion. Wisdom89(T / C)05:01, 22 April 2009 (UTC)[reply]
The dot-and-cross diagram is a variation on the Lewis diagram that shows the electrons shared within each covalent bond. Dots and crosses are used to distinguish electrons donated by one atom from those donated by the other atom in the bond - electrons in the outer shell of one atom are shown by crosses, electrons in the outer shell of the other atom are shown by dots. In a normal covalent there will be one electron from each atom, so this is represented by a dot and a cross. In a dative covalent bond both electrons come from the same atom, so this is represented by two dots (or two crosses). You can see some examples of dot-and-cross diagrams on this BBC Bitesize page. Gandalf61 (talk) 10:52, 22 April 2009 (UTC)[reply]
Bruce Lee martial arts glowing light energy field
Perhaps more pseudo-science than science, but the science page is where are the smart geeky people are, so...here is my question... There is a(n apocryphal) tale that Bruce Lee had attained such an advanced level in his Martial Arts practice that at certain times he emitted a (green) glowing aura / energy field around his body. Does anyone know what this field is purportedly called or has anyone heard this story? I already looked at Tummo. Merci d'avance, Saudade704:50, 22 April 2009 (UTC)[reply]
Oddly enough, people who believe in this call it an aura: see aura (paranormal). --Anonymous, 05:00 UTC, April 22, 2009.
Yes, but this is something else...people who believe in Auras believe that everyone has one. But this is a special field of glowing energy that only envelopes certain high-level martial arts practitioners when they are in the zone / at the top of their game / about to kick ass. Apparently Bruce Lee had it. I found the name on the Internet 10 years or so ago, (I feel like it was a Chinese-sounding word) but now everything I Google turns up yoga stuff. I feel like BL's field was said to be green. Thanks Saudade706:12, 22 April 2009 (UTC)[reply]
Well, there was a movie called The Last Dragon in which the main character was inspired by Bruce Lee to attain an ability called "The Glow" which is essentially what you're describing, but this is fiction of course, no one in their right mind would believe it was based on something Bruce Lee could actually do. Truthforitsownsake (talk) 12:35, 22 April 2009 (UTC)[reply]
There is an awful lot of bullshit pseudo-science relating to auras. However, no properly designed experiment has ever shown that they exist - and since a ton of laws of physics would have to be overturned if they really DID exist, we have to employ Occam's Razor and say that since extraordinary claims (which aura's are) require extraordinary evidence (and we have ZERO evidence) - then we should simply say that they are bullshit and move on. Which is what I'm going to do now. SteveBaker (talk) 19:25, 22 April 2009 (UTC)[reply]
Additionally, there's also an awful lot of bullshit pseudo-science relating to martial arts. I have, among other things, had a conversation with someone who seriously insisted that the Five Point Palm Exploding Heart Technique from Kill Bill -- with which you can make someone's heart explode by poking them five times in just the right spots -- was a real thing. Like a lot of superstition and many urban legends in general, the fact that there are no credible demonstrations of incredible abilities like this doesn't seem to slow the people who believe in this crap down at all. (I have been told, on different occasions, that it's a secret, because the great martial arts masters don't want the governments to find out about these powers, or that the government doesn't want people to learn about their tools of control, or that only a very few enlightened people attain this knowledge -- which presumably explains why every other semi-literate martial arts fanatic on the internet knows these things for a fact....) -- Captain Disdain (talk) 22:42, 23 April 2009 (UTC)[reply]
Hi everyone, Thanks for all your help. I guess I am going to run with BenRG's suggestion of Qi and Truthforitsownsake's reference for "The Glow"Ā ! I'm really sorry if the question made the skeptical community angry. Notice that I prefaced the whole question with the word "Pseudoscience" and used "apocryphal" and "purported" and "said to be" throughoutĀ ! I was clearly trying to mark it as specious. I think the skeptics on Wikipedia are a bit too reactionary sometimes - like that woman on "The Skeptics Guide to the Universe" who seems always to be in attack mode. I wonder if the question, "What's that (more cryptozoological that zoological) animal called that is a horse with a horn?" would have gotten an angry rant about people that believe in non-existent animals rather than just the word "Unicorn". Just because some things don't exist in the world as empirical, sensible, material, testable, verifiable things does not mean they do not exist as conventionally agreed upon abstract concepts and entities in the cultural field. Sometimes these abstract concepts are said to be objects in the realm of science - like auras and kryptonite and warp drives. Know your audience! Hell, I gave Stevebaker a barnstar once! Thanks again! Saudade718:08, 25 April 2009 (UTC)[reply]
Well, I wasn't really directly speaking to you; I was just making a general observation about the topic at hand. I should perhaps have added a disclaimer. -- Captain Disdain (talk) 21:01, 25 April 2009 (UTC)[reply]
POSTED THIS QUESTION ON THE MATHAMATICS PAGE AND WAS SUGGESTED I POST IT HERE
I would like to add if i may that i do not have a great understanding or math and mistakenly as was pointed out asked if there was an equation that fits the model...Equation is the wrong word please ignore that but i would like a good solid answer.
I was bored sitting in work and a colleauge said look up Schrƶdinger's cat.... While reading it...... it seemed as if the only way to explain Quantum mechanics is "the end product of any situation is allready predetermined"; applying this to the riddle, as far as i see it would explain the answer to the Schrƶdinger's cat experiment...the cat is either pre destined to be dead or alive this was pre determined right back to the big bang hence all future things are all ready predestined....(god knows what that makes to a time theory?) For example we know the Sun will burn out but it hasnt happened yet' its fule will be used up it will swell then cool ECT....this is all ready predetermined.So my question is if the universe surrounding us is all ready played out and the end states are known (but not by the human race) is there an equation that would fit this model? Ok i dont want you to look at this and think this guy is a nutter 'which i am sure you will' but it makes sense to me....we just need to be able to see the future is allĀ :) Adrian O'Brien āPreceding unsigned comment added by 214.13.113.138 (talk) 12:29, 21 April 2009 (UTC)
I'm not sure but I think there is. Even if there is, the equation has to be really complicated. Also, I recommend you on posting this question on the science reference desk instead. Superwj5 (talk) 13:18, 21 April 2009 (UTC)
It is nice that you are interested in this - I suggest you read the article Quantum mechanics. Especially, it is recommended that you read the "overview" section and the beginning of the introduction. Just read what you understand and ignore what you don't. The other thing I wish to comment upon is your belief that mathematics is described by "equations". This is false. Group theory does indeed apply in quantam mechanics as well as probability theory, and the deep purpose of either subject has nothing to do with equations. Just let me stress that mathematics is not equations. If you are referring to the uncertainty principle, then:
Also, I recommend that you read Introduction to quantum mechanics first as this is (apparently) more accessible. I do not wish to discourage you from asking questions but I just wish to stress the mathematics that applies to theoretical physics is much deeper than you think (for example the application of knot theory (a branch of mathematics) to string theory (a branch of physics)). --Point-set topologist (talk) 14:14, 21 April 2009 (UTC)
All equations including mistaken ones fit the OP's notion of predetermination. It made me post this. Cuddlyable3 (talk) 14:25, 21 April 2009 (UTC)
I was under the impression that it was classical mechanics that deals with a deterministic world, while quantum mechanics deals with a probabilistic one. What I mean to say is that if the position and momentum of every particle in the world were known at one instant, the state of the universe at any future instant is easily obtained by applying Hamilton's (or Lagrange's) equations. However in quantum mechanics it is intrinsically impossible to know the position and momentum of even one particle to arbitrary precision, let alone all of them. I would disagree with the OP's statement that the end result of any situation is predetermined, as we can only state the probability of obtaining any particular end. mislih 23:08, 21 April 2009 (UTC)āPreceding unsigned comment added by 214.13.113.138 (talk)
Please use the proper, above-outlined method to post things instead of adding on to other people's questions. Then there will be no conflict. Saudade706:12, 22 April 2009 (UTC)[reply]
Nope, there is no predetermination. See Bell's theorem and Bell test experiments. Unobserved measures truly don't exist yet. You see, the trick is to just dispell your classical notion that a particle must have a single unique position and velocity at any given time. In the real world, a particle simultaneously occupies many positions, with a probability of being found at any given one upon being observed (whatever "observed" means). Although, of course, the Schrodinger cat has any number of issues, which I'm sure further responders will nitpick. Someguy1221 (talk) 06:16, 22 April 2009 (UTC)[reply]
Ok Saudade7 this was my question from the maths portal i just pasted the same question on here so there is no conflict.
The part of your answer if i may i struggle with is, we may not know what the predetermined out come is, or be able to see it but this does not mean it doesnt have one...push a rock off the cliff it will hit the floor this is predetermined even if it hasnt hit the floor yet...If the rock is in many diffrent places at the same time we still know at that place it will hit the floor. there can be many variables i.e. somebody catches the rock ect... but that could be a predetermination somebody was always going to catch the rock if you see what i mean? Please excuse my lack of knowledge of science and math but i am trying to understand:)As i see it probability rather than predetermination seems to fit but the particle/rock/cat is allready doing what it was predestined to do we just dont no it.... āPreceding unsigned comment added by 214.13.113.138 (talk) 06:39, 22 April 2009 (UTC)[reply]
Your idea that everything is predetermined, was, indeed, believed by scientists hundreds of years. This comes from classical mechanics, or common sense, and nobody dared to question it. Then in the last hundred years or so, great reforms began to occur based on experiments and sheer brilliance, culminating in Quantum Mechanics. At the heart of Quantum Mechanics lies the uncertainty principle. According to this outrageous fact, we can NOT even measure things around us as we like. There is always an uncertainty in measurement, inherent in the system. This has nothing to do with the faults of our measuring apparatus. For example, it may be possible to measure the length of a block of wood with a scale say down to an error of 1 mm. If we have an even better scale( say a vernier caliper) we might be able to measure it more accurately, say to .01mm. In PRINCIPLE, it is possible to measure with as much accuracy as we want, though it may not be practical. But in the realm of Quanto, there are fundamental restrictions even in principle. What's more, you the the length of a block is say 1 meter, whether or not you measure it, ie it is deterministic - already determined. The whole idea of determinism is gone in Quanto. Before the act of measurement, everything is just in a confused superposed state. The act of measurement forces it to take a value, which is then approximately measured. This might need some rereading and might be outrageous at first sight, but that is the way nature behaves. So if we assume Quanto uncle to be right, then determinism is just chucked out the window.... Rkr1991 (talk) 07:34, 22 April 2009 (UTC) āPreceding unsigned comment added by Rkr1991 (talk ā¢ contribs) 07:30, 22 April 2009 (UTC)[reply]
I meant you should have begun the process of asking your question by clicking on the "ask a new question by clicking here" link at the top of the page, rather than coming down here to the bottom of the page, clicking on the edit, and adding your question. It is just a simple a courtesy to others, like myself, who might be posting in a situation with sketchy Internet connection (I was at a cafe and needed to pirate an intermittent open signal). I had to wait for a new signal to re-post because your post time conflicted with mine as a result of your method. So I was cranky. The math portal has nothing whatsoever to do with the conflict. Saudade7 07:53, 22 April
\2009 (UTC)
Ok thats great thanks for the answers makes a lot more sense now, ill come forward 100 years and try to catch upĀ :) just like to add some great minds on here brilliant to see. Keep it upĀ :) NP's Saud i was on my third coffeeĀ :)
It may be surprizing to some people to realize that quantum mechanics, despite the uncertaity principle, is actually just as deterministic as classical mechanics, except for the wave function collapse that happens when an observation is performed. This is somewhat contradictory and to this day there is still some debate about whether the colapse is a fundamental phenomenon or just an epiphenomenon of quantum decoherence. The latter is considered more self-consistent and leads to an entirely deterministic theory. Dauto (talk) 14:53, 22 April 2009 (UTC)[reply]
I am no expert in QM, but I do use it on a regular basis. I have attended seminars by people researching entanglement as related to quantum computing, and while I cannot recall the exact arguments used the idea was put forth that either locality or causality can be preserved but not both. Is this related to your comment Dauto? By this I mean can we formulate a quantum theory in which the results of experiments is predetermined by initial conditions if we are willing to sacrifice locality (and accept "spooky action at a distance")? mislih00:00, 24 April 2009 (UTC)[reply]
Spooky action at a distance is unavoidable in quantum mechanics. EPR paradox and Bell's theorem are good articles to read about that. But that action at a distance cannot be used to send information faster than the speed of light and causality is safegarded. All that is true independently of wheather the colapse of the wavefunction is considered to be deterministic or not. Dauto (talk) 04:53, 24 April 2009 (UTC)[reply]
Ok; Just so i am clear A>B>C... Taken we do not no the action of something in Quatum Mechanics of say some type of particle but to say its path is not a predetermined path i feel is wrong. we can only say at are present understanding we do not know what that predetermination is or if it has one, we can theorise an answer so it fits with our understanding or our calculations but in the end we just dont know. It very well might be the case that all things have a predetermined path/outcome. which just dont have that ability of understanding YET. for example the world was thought to be flat at one point mathamaticians and scientist's would have provided evidence at the time to prove that; the best answer is the one that says at are PRESENT understanding it appears that there is no predetermination however that could be in-correct...Chromagnum (talk) 13:17, 27 April 2009 (UTC)[reply]
April 22
GLOBAL WARMING
Ok; the idea of global warming is consistant with it being a natural process all we do as humans is speed up that process...
Has there been thought on the idea of creating a large volcanic eruption which would place large amounts of what ever into the atmosphere and thus help cool the earth...Simlar effect in Victorian times when global temp was reduced due to an eruption. The Year Without a Summer 1800 and something? To control this even would be extremly difficult of course but would it work? āPreceding unsigned comment added by 214.13.113.138 (talk) 08:41, 22 April 2009 (UTC)[reply]
Or maybe there could be a way to divert an asteroid (nuclear blasts?) so it falls into Earth, the impact of which will result in blocking out of the sun like it's frickin dinosaur extinction time. That might also achieve your goal.āPreceding unsigned comment added by 94.27.153.3 (talk) 10:00, 22 April 2009 (UTC)[reply]
I am afraid that your second method is just silly. Life on Earth would not exist without sunlight and furthermore, the impact of an asteroid on the Earth's surface would result in many deaths. --PST10:10, 22 April 2009 (UTC)[reply]
First, what do you mean by "natural process"? "Natural" like in "without human intervention"? We have caused this by releasing greenhouse gases into the atmosphere that disturbed the balance, and now the system is "readjusting", so the mean temperature will rise until a new equilibrium in energy received/energy lost is reached. It is true that in the past "natural" warmings occured (over thousands of years), but as far as we know nothing even roughly comparable to the situation today ever happened (warming the planet in centuries or even decades). We are to blame! Now coming to the question: What makes you think that we are able to trigger a volcanic eruption? I don't say it is impossible, but at least nothing like this has been tried before (for good reasons, I'd think), so it would at least be a really uncontrollable, dangerous experiment. But now to the main caveat: You are confusing climate change with the actual weather. Climate is something that happens on the scale of several years, but the cooling you mentioned mainly affected a single year and then quickly (in climate scales) disappeared. To the contrary, a much discussed theory is that vulcanic eruptions in the past could have triggered massive climate changes which added to or even caused mass extinctions, because many lifeforms could not adapt fast enough to the changing world. This is because vulcanos also emit greenhouse gases, and large vulcanos can put an awful lot of them into the atmosphere in a short time. So in summary: I think it would be a real bad idea to try something we don't understand (vulcanic eruptions) to cure something we don't understand (the climate). TheMaster17 (talk) 10:08, 22 April 2009 (UTC)[reply]
To the second question with the meteor: I hope this is irony, because the answer has to be nearly the same: we have no idea how to divert an asteroid, because of very many practical problems on the way. And even if we could, we would bring an incalculable element into an already incalculable situation. TheMaster17 (talk) 10:17, 22 April 2009 (UTC)[reply]
(Reply to both PST and TheMaster) I could be wrong, but it looks to me like those two anons are unrelated. I'm pretty sure 94 was trying to be sarcastic indicating that the first idea was likely to be very difficult to achieve and to have serious side effect and so was (almost?) as silly as the second idea which I guess he/she hoped the OP could more easily see as an idea which would never work. Nil Einne (talk) 13:52, 22 April 2009 (UTC)[reply]
Well, of course the Earth has warmed and cooled before, but the current process is, as far as we know, different in that a) it's primarily driven by greenhouse gases (instead of them acting as a feedback to amplify an otherwise triggered warming trend) and b) it's a lot faster that anything we have seen before. So calling it "a natural process" that we "only speed up" is a very arguable position. What cools the Earth after a large volcanic eruption are aerosols, mostly sulfur-aerosols in the atmosphere. We have indeed injected a large number of those via industrial processes, and they have masked the early warming trend. Warming only became very notable when Europe and the US installed scrubbers to reduce acid rain and other negative effects of sulfur emissions. There also have been some proposals to actively introduce aerosols to reduce the warming. However, there are serious technical challenges and ecological side effects - and, since it's a global problem, it will be very hard to find a politically acceptable solution. Just imagine Mexico emitting large aerosol clouds that rain out as acid rain over Yosemite National Park, or emissions in Germany causing respiratory diseases in Poland and the Czech Republic. A final problem is that CO2 accumulates over a long time, while aerosols have a short atmospheric lifetime. So to counteract the effect of inreasing CO2 concentration, one would need ever-increasing aerosol emissions. There is some discussion at Mitigation of global warming. --Stephan Schulz (talk) 10:23, 22 April 2009 (UTC)[reply]
I think your point b is pretty worthless. Saying that the temperature is changing faster then anything we have ever seen before completely ignores the fact that written human history runs for thousands of years, and thermometers that operate independent of air pressure have only been around for 400 years tops. And do we have documents showing a daily temperature record for hundereds or thousands of locations so that we have a basis of comparison? I would say we don't have anything like that until the 19th century. So saying we have never seen anything like this before does not mention that we had our eyes closed the other 23 hours of the day. 65.121.141.34 (talk) 13:06, 22 April 2009 (UTC)[reply]
We don't have human recorded measurements but we do have quite good estimates of previous temperatures from ice core samples for example. Take a look at temperature record for more detail. We may have closed our eyes for the other 23 hours, fortunately there were cameras recording the 23 hours while our eyes were closed which we can now review. Nil Einne (talk) 13:52, 22 April 2009 (UTC)[reply]
In fact, the icecore registers the temperature at the place where the evaporation happened, not the place where the snow fell. Since there is a lot og mixing between one and the other, The ice core turn out to be an excellent proxy for the past global average temperatures. Dauto (talk) 19:42, 22 April 2009 (UTC)[reply]
But temperature changes exist all over the planet, not just at one location. If anything, the temps at the poles vary more than on the rest of the planet, so any global temp changes would be well-preserved in ice cores. Thus, Antarctic ice cores are a good indication of the global temperature. Also, we can go back a few thousand years by looking at tree rings. Rapidly warming weather would favor some trees and hurt others, and the tree rings from those years would reflect that. StuRat (talk) 14:36, 22 April 2009 (UTC)[reply]
But things other then temperature can have a big impact on tree rings, like drought or flooding or fire. Is there a way to differentiate? 65.121.141.34 (talk) 15:11, 22 April 2009 (UTC)[reply]
Yes, but not perfectly. The general idea is that drought and flooding are local effects that last a small number of years. By looking at tree rings over wide geographic areas and over longer time periods you get plot a general trend. See Dendroclimatology. APL (talk) 15:56, 22 April 2009 (UTC)[reply]
Yes, it's only useful for relatively recent history. I've read articles about attempts to use it to go back farther than 1000 years, but never spectacularly far back. 2 or 3 thousand at the absolute most. Still just a drop in the bucket compared to geologic time periods. APL (talk) 20:21, 23 April 2009 (UTC)[reply]
from the temperature record article,
"However, coverage of these proxies (tree rings and ice cores) is sparse: even the best proxy records contain far fewer observations than the worst periods of the observational record. Also, problems exist in connecting the proxies (e.g. tree ring width) to the variable of interest (e.g. temperature)." I am not saying global warming does not exist, I am just saying that the evidence supplied is less conclusive then most people are lead to believe. 65.121.141.34 (talk) 16:15, 22 April 2009 (UTC)[reply]
I'm not sure what you are saying. Are you saying you don't believe global warming is happening or are you saying that because the record of the past is less accurate than the present there is a possibility that something like what is happening now might have happened before and therefore it cold be natural and not man made? By the way the PaleoceneāEocene Thermal Maximum only 55 million years ago looks like it had spikes of 3Ā°C increases in less than a thousand years so there is a possibility that it was as bad as is happening now so that would bolster the second point of view if that is what you are saying. Dmcq (talk) 16:42, 22 April 2009 (UTC)[reply]
I am saying that there are holes in the theory that are not addressed well and thus it is not the scientific fact it is often purported to be. 65.121.141.34 (talk) 16:51, 22 April 2009 (UTC)[reply]
There may be holes in the theory, but your atempts here fall in the naive category. Denial isn't a scientifically acceptable alternative. Dauto (talk) 19:45, 22 April 2009 (UTC)[reply]
Yes, indeed. Scientist are humans like anybody else and can be partial. But we are not talking about a handfull of scientists. We are talking about the whole world wide community of climatologists. What you are proposing is a conspiracy involving the vast majority of the climatologists of the world. Unless you have some strong evidence to suport that idea, I think I am going to file it as an irrational conspiracy theory. Besides, what is the motivation behind that conspiracy? There isn't more money to be made just by supporting global warming theory. Dauto (talk) 00:16, 24 April 2009 (UTC)[reply]
Just because coverage is more sparse doesn't mean that it is inadequate. The question is, would we detect the current rise from the ice core? If we would, then the fact that the record is more sparse is largely irrelevant. Our excellent modern observation is good because we can see more carefully what is going on, it doesn't mean it's necessary to detect massive global warming Nil Einne (talk) 03:50, 23 April 2009 (UTC)[reply]
These kinds of ideas are what is increasingly being called "Plan B" amongst climatologists. If it's truly too late to stop emitting CO2 - or if we can't get international agreement - or if the 'runaway' scenario has truly kicked in - is there anything we can do to make the planet cooler and thus circumvent the worst of the danger? Well, volcano's definitely aren't it because they are actually a major contributor of greenhouse gasses. While the smoke from the ash plume would reduce temperatures for days, weeks, months or even perhaps a year or two - the CO2 it emits will still be in the upper atmosphere in 10,000 years time. So that particular trick certainly won't work. But there are other possibilities. It's known that the contrails from the exhausts of high altitude airliners is reflecting heat away from the earth to a small degree (it was noted that after the 9/11 attacks when all North American aircraft were grounded - the temperature shot up a couple of degrees!). So maybe we could make some more big white clouds up there and block sunlight that way? The really big problem with all "Plan B" approaches is that we really don't understand the complicated inner-workings of the whole planet to know whether one of these "cunning plans" would actually do more harm than good. For example - if we reflect away sunlight to make the earth cooler, plants that use sunlight to perform photosynthesis would do less well - this might result in disasterous world-wide crop failures - and since plants consume CO2 and output oxygen during photosynthesis - we might easily make MORE CO2 than we do now! In fact, it's hard (or perhaps, impossible) to imagine any kind of "Plan B" that might not have disasterous consequences. Worse still, these things have to be world-wide events - we're modifying the atmosphere for the entire planet - and you really can't go around doing that kind of thing without (at least) the agreement of all of the major governments of the world. While we may ultimately have no choice but to attempt something that wreckless - it would have to be a last-ditch effort when we know for 100% sure that we're doomed if we don't do it. But there are LOTS of "Plan B" ideas out there...covering large areas of the ocean with white foam polystyrene beads to make it reflect sunlight away...launching massive sun-screens into earth orbit to block sunlight...there are MANY choices! SteveBaker (talk) 19:19, 22 April 2009 (UTC)[reply]
As for aerosols such as sulfur dioxide, a better alternative is to launch them up to the stratosphere, where it doesn't interact with our weather. As for warming/cooling being part of a natural cycle, yes there has been a period of warming since the Younger Dryas, but that warming is no longer a part of the trend seen today. As for rapid climate change in the past, some of those events may have been caused by methane clathrate collapses (which are starting to occur today), but now instead of 3C of warming in several centuries (under 1,000 years), it could be 3C in several decades (less than 100 years). ~AH1(TCU)23:05, 22 April 2009 (UTC)[reply]
An ocean fertilization project has just failed - the algae bloom produced was just eaten by animals, which released most of the Carbon back into the atmosphere via their metabolic processes. [15] --Stephan Schulz (talk) 14:52, 23 April 2009 (UTC)[reply]
And see Law of unintended consequences. Intentional geoengineering in an attempt to offset our unintentional geoengineering that results from burning gigatons of fossil fuels is pretty scary. One should carefully review the history of previous engineering disasters, then scale up the risk to a global level. Engineering disasters occur when smart people get together and only anticipate some of the relevant consequences of their actions. See also Superiority (short story) and Wonder weapons. Technology can do some wonderful things, but it doesn't always deliver exactly the desired wonderful thing on the desired schedule. Technology develops best when people approach it incrementally, learning from their mistakes as they go. Humans cannot even write error-free software on the first attempt (or even after years of debugging by teams of skilled professionals). We don't have access to a "test planet" where we can try various geoengineering schemes to see how they will work, and to verify our models. --Teratornis (talk) 23:31, 24 April 2009 (UTC)[reply]
Ok stupid idea or not..i wasnt actully suggesting doing it i asked a THEORETICAL question of WOULD IT WORK? IE planet gets colder glaciers reform gulf stream stays blah blah blah....sure why not blow up the world divert astaeroids...Guess i need to solve the problem and argue about who is to blame NOT what i wanted suppose we could stick with recycle your fairy liquid bottles rock on the scientists! āPreceding unsigned comment added by 214.13.113.138 (talk) 07:26, 26 April 2009 (UTC)[reply]
People have already discussed why it may not work and the potential catastrophic side effects which could easily be worse then what you're trying to solve. There's not much more to say. As has already been mentioned there are a lot more ideas which are at least aren't quite as extreme which are being studied although even these already have many many difficulties and potential failings. No one bothers to study ideas which are so insane and inpractical that they aren't worth considering so you're not going to get much better then what has already been said. Also, I don't know of anyone who is arguing over who is to blame, except the denialists. Most people are arguing over how best to resolve it concentrating on things that are actually potentially possible. Nil Einne (talk) 01:53, 29 April 2009 (UTC)[reply]
B cell activation
Hi everyone just I have a couple of quick questions - Would I be correct in saying that B cells don't have to be activated by a helper T cell before they can produce antibodies? If they don't need helper T cells to activate them how are they activated in the absence of helper T cells - does another type of cell activate them into producing antibodies/forming plasma cells etc. or can they can activate themselves? If they can activate themselves (I don't know if they can or not)then wouldn't that render the helper T cell uneccessary in this sense? (I realise helper T cells probably have other functions aside from activating B cells.) Sorry if my questions are badly worded and thanks in advance to all who help! āPreceding unsigned comment added by 92.21.237.143 (talk) 11:21, 22 April 2009 (UTC)[reply]
"Some textbooks state that electricity within wires flows at nearly (or even exactly) the speed of light,[1] which can give the impression that electrons themselves move almost instantly through a circuit. The electrons in a typical wire actually move at a drift velocity on the order of centimeters per hour[2] (much slower than a snail). The random thermal motions of the electrons are much faster than this, but still much slower than light, and with no tendency to occur in any particular direction. It is the electrical signal that travels almost at the speed of light. The information that a light switch has been turned on propagates to the bulb very quickly, but the charge carriers move slowly.[citation needed]"
Wow, misconceptions are everywhere, including the Speed of electricity article and most of the things on the web that discuss this. When somebody asks for the "speed of electricity", what they usually mean is something like "If I switch on a light, how quickly does the signal travel from switch to light", or "if I send a signal along a wire, how quickly does it reach the receiver". To answer these questions requires cable theory. The answer you get depends greatly on the conductivity, boundary impedance, and capacitance of the wire, but it is always far slower than the speed of light. This article, for example, calculates the speed of signal transmission for a telegraph cable across the Atlantic -- a very fast carrier -- and gets a result of about 2x106 m/sec, or about 1/10000 of the speed of light. In other words, very fast in human terms (two seconds to cross the Atlantic), but very slow compared to light. The wires in your home are typically hundreds or thousands of times slower. For computer equipment, conduction speeds along wires are often an important design factor. Looie496 (talk) 18:21, 22 April 2009 (UTC)[reply]
The calculation for transatlantic cables may have been accurate in the days of the telegraph, but is not even close when most telephone cables are considered. Up until the mid-70s, transatlantic telephony used either satellite or copper cable. Satellite experienced noticeable delay, and cable did not. We can therefore estimate that the round-trip time was less than 100ms. Therefore for the signal to cross the atlantic, we can estimate a time of 50ms maximum, which is a speed of about 1x108 m/s, or about 1/3 the speed of light. --Phil Holmes (talk) 09:12, 23 April 2009 (UTC)[reply]
In a physics lab, we would send pulses down 200' coax cables and measure velocities of 2/3 c. Of course the pulse got smeared some and there are other issues to consider, but Looie's assertion that most wiring would be many orders of magnitude less than c seems unlikely to me too. Dragons flight (talk) 09:36, 23 April 2009 (UTC)[reply]
The way to imagine this (crudely) is to imagine an almost frictionless 200' long garden hose and some half-inch ball-bearings. If you stretch out the hose on level ground and roll a ball-bearing down the length of it - it might take 30 seconds to pop out of the other end. But if you fill the hosepipe full of ball bearings from end to end then if you try to push one ball in at one end - then another one pops out of the other end almost instantaneously. So even though the individual balls move fairly slowly - the time between stuffing one in one end and a DIFFERENT ball popping out of the other is quite short. The hose is a wire, the balls are electrons. The electrons move incredibly slowly - like watching the minute hand move on an analog clock. But when you push an electron into one end of the wire - a different one pops out the other end with a delay that's about equal to the speed of light. SteveBaker (talk) 19:06, 22 April 2009 (UTC)[reply]
Neat! Thanks for answers. The one I understand the best is from SteveBaker. That one I grasp the best and it makes sense on how the "speed of electricity" happens. --LordGorval (talk) 21:15, 22 April 2009 (UTC)[reply]
wikipedia article on E.D.T.A.[ethylene diamine tetra acetic acid]
in the above article,Uses in Medicine,Last entry is Use in Thalassemia Major to remove excess iron.Pl.indicate the reference of source i.e journal etc.thanks āPreceding unsigned comment added by 117.198.195.147 (talk) 12:59, 22 April 2009 (UTC)[reply]
Well to be fair to the OP, if our article says something (and it does "This therapy is used to treat the complication of repeated blood transfusions, which used in cases of severe thalassaemia") then it should be referenced (which it isn't). However that should be dealt with on the article talk page (which I've copied it to), not here Nil Einne (talk) 13:42, 22 April 2009 (UTC)[reply]
Yes, I know all challenged claims require a citation and are subject to removal if none is provided - but I got the impression that the anon was also interested in the veracity of the statement apart from just the quality of Wikipedia. Wisdom89(T / C)14:53, 22 April 2009 (UTC)[reply]
How to insulate an old homeĀ ?
My current house was built in the 1920s (I know, that's not old by European standards). The windows have all been replaced with triple-pane insulated windows. Now the problem is the walls. They are cold all winter long and hot all summer long. I don't believe there's any insulation at all (other than the bricks and wood of which the house is constructed, which offer minimal insulation value). The obvious answer is blown-in insulation. However, the wiring in the walls is sub-par and gets warm now. If it was buried under layers of insulation it might get hot enough the cause a fire. So, is there any way to insulate the walls, short of ripping all the walls apart to replace the wiringĀ ? One thought we had was to disconnect the existing wiring, leave it in place, and install exterior mounted wiring to replace the wall wiring. This would then allow for blown-in wall insulation. Is this idea feasibleĀ ? Has anyone done thisĀ ? Any other ideasĀ ? StuRat (talk) 14:11, 22 April 2009 (UTC)[reply]
Those sound like some possibilities. Do you know how much of an insulation value (R-factor) the thermal wallpaper providesĀ ? StuRat (talk) 20:11, 22 April 2009 (UTC)[reply]
If your wiring is getting hot, you should definitely replace it. (5-10% of all deadly house fires in the U.S. involve electrical causes[17]) Wiring from that era probably has degraded insulation (mine certainly did) but more importantly as code standards and appliance usage have changed, the system may not be laid out to properly handle the much higher electrical loads we now use leading to overheating of the wires. Rmhermen (talk) 16:02, 22 April 2009 (UTC)[reply]
It should definitely be rewired to start with. The old wiring can usually be used to pull through the new wiring; it certainly won't mean ripping any walls apart, and your house will be a lot safer.--Shantavira|feed me15:59, 22 April 2009 (UTC)[reply]
My thoughts too exactly. The insulation on ancient wiring can quite easily crumble and cause a fire, never mind the possibility of shocks. Do it now before it does you in. Dmcq (talk) 16:07, 22 April 2009 (UTC)[reply]
When you do get to the insulation I think your idea of blow in is best to start with. The problem with having thin insulation trying to do the whole job is with any bits which have to stick through may tend to get condensation at times, but they can be good supplementing the main business. Dmcq (talk) 16:18, 22 April 2009 (UTC)[reply]
To do a good job of blowing in insulation, you will need to make holes in the plaster or wallboard anyway, and patch and paint as part of the job. Therefore, the incremental cost of putting the new wiring inside the walls rather than outside the walls is much lower: the incremental cost is mostly in the wall repair. Depending on where you live, you may want to make the walls thicker to hold more insulation. This involves removing the plaster or wallboard and adding studs another set of studs, which should be offset from the existing studs. Of course, with the walls open you are no longer restricted to blown insulation. -Arch dude (talk) 20:13, 22 April 2009 (UTC)[reply]
Everyone seems to think new wires can be pulled through the walls using the old wiring. I'm far more skeptical that thin, 90 year old wires with deteriorating insulation wouldn't just break. Also, the builders may well have attached the wiring to studs using staples. And the walls are made of wet plaster, so the thought of tearing them open is horrifying. What about my idea of leaving the old wiring in place, disconnecting it, and putting new surface mounted wiring in placeĀ ? Has anyone done thisĀ ? StuRat (talk) 20:08, 22 April 2009 (UTC)[reply]
In addition to the fragility, a 90 year old home with the original wires would likely have knob and tube wiring instead of free-floating Romex-style power cable. (Applicable words from the article "Currently the United States NEC forbids use of loose, blown-in, or expanding foam insulation over K&T wiring. This is because K&T is designed to let heat dissipate to the surrounding air.") -- 128.104.112.117 (talk) 22:29, 22 April 2009 (UTC)[reply]
There are ways of "snaking" wire through walls without pulling on the existing wire (which being metal should not have gotten any weaker - if it has it is an even greater fire hazard) Another problem with knob and tube (which was less common already by the 20s) is that some insurers refuse to write policies for houses that still use it. Rmhermen (talk) 00:49, 23 April 2009 (UTC)[reply]
My house is also of that period, but the previous owner did a major renovation. Where the original double brick walls are still in place, they are now lined with another layer of wall of standard frame construction, which allowed space for insulation and new wiring. All wiring and plumbing in the house was replaced. That's the sort of job you'd need to do things properly, but as you can imagine, it can be awfully expensive. I think you need to talk to a renovation contractor (or rather, several of them) to talk about what is possible and what it might cost. --Anonymous, 23:23:23 UTC, April 22, 2009.
Hi there, I've been revising Dynamics for a few days now and come across this question, and I'm not too sure where to go for the final part.
Two particles of masses m1 and m2 move under their mutual gravitational attraction. Show from ļ¬rst principles that the quantity is constant, where r is the position vector of one particle relative to the other and M = m1 +m2 .
The particles are released from rest a long way apart, and fall towards each other. Show that the position of their centre of gravity is ļ¬xed, and that when they are a distance r apart their relative speed is .
When the particles are a distance a apart, They are given equal and opposite impulses, each of magnitude I , and each perpendicular to the direction of motion. Show that subsequently , where Ļ is the angular speed of either particle relative to the centre of mass and Āµ is the reduced mass of the system.
Show further that the minimum separation, d, of the two particles in the subsequent
motion satisļ¬es .
That's all okay until I get to the minimum separation bit, at which point I get a bit confused - could anyone let me know how to go about finishing this part of the question please? Thanks!Ā :) Otherlobby17 (talk) 14:44, 22 April 2009 (UTC)[reply]
It is possible to rearrange the angular momentum as an Effective Radial Potential. This is a "pseudo"-potential energy field. When added to the gravitational potential, there is a minimum of potential energy (this is the optimal radius for stable circular orbit); and another point at even lower radius, where effective potential is equal to the gravitational potential at infinite radius (this is the minimum separation for the scenario you described). This derivation is detailed in Marion & Thornton's dynamics textbook. I will try to dig out my notes on the subject. Nimur (talk) 15:56, 22 April 2009 (UTC)[reply]
No need - here's Effective potential (which should probably be renamed to something less general, like "Effective potential due to angular momentum"). To find the minimum separation, just locate the point where initial energy equals the potential energy. The particle can go no further (so it is at the minimum radius) unless new energy is added from another source. Nimur (talk) 16:00, 22 April 2009 (UTC)[reply]
While the effective potential idea works, it is not the simplest way to solve that problem. Before the Impulses, the system had both energy and angular momentum equal to zero. The Impuses transfer energy and angular momentum given by the formulae:
and both are conserved thereafter.
At the point of minimun separation, the velocity has no radial component
, and
which gives us energy and anguloar momentum
Solving the system of equations we get from this it is easy to show that
Adverts for toilet cleaning products always boast about how they kill "99.99% of all germs" in the toilet (in the UK, at least). Now, correct me if I'm wrong, but people don't go around licking toilet bowls regularly, do they? Exactly what would be the problem with germs inside a toilet? Is this just more advertising BS designed to sell products to ignorant consumers, or do germs inside a toilet pose a genuine threat of which I'm ignorant? Vimescarrot (talk) 14:50, 22 April 2009 (UTC)[reply]
I am reminded of a study on household germ contamination I read. They found that the most contaminated places in most houses were the cloth or scrubber used to clean kitchen surfaces, and the chopping board; the latter having some particularly nasty germs. The head of the study was quoted as saying "In the average house if I was forced to lick either the toilet seat or the chopping board, I'd choose the toilet seat every time". DJ Clayworth (talk) 15:43, 22 April 2009 (UTC)[reply]
And I would answer that he obviously does not know what he is even doing with this study. Just because you find bacteria on a surface, does not mean that anybody will become sick from licking it. I, as a biologist with training in immunology, would rather stick with Vimescarrot's explanation: Nobody eats out of the toilet, but everybody prepares food on kitchen surfaces. To what germs will our body be more resistent? And the problem, in reality, is the other way round: By cleaning all those bacteria which normally live there, you pave the way for bacteria that normally cannot grow there (because the "normal bacteria" outcompete them) and which could be "real" pathogens (meaning they can really make you sick, because your body has no immunity for them). There are few surfaces, in a hospital for example, that really need to be sterile. Most other things are perfectly "healthy" in everyday live even when they are covered with germs, unless your immunesystem is severely compromised. TheMaster17 (talk) 16:02, 22 April 2009 (UTC)[reply]
So microwaving my dishcloths to kill the germs on them is a bad idea? What about the fact that my mother wipes bloodstained hands on a cloth meant for drying hands that have just been washed? =p Vimescarrot (talk) 17:44, 22 April 2009 (UTC)[reply]
The chopping board may be a special case. The expert may have been concerned about getting germs from raw poultry. I wonder how he'd feel about a dry counter top? (compared to a dry toilet seat) APL (talk) 17:46, 22 April 2009 (UTC)[reply]
The stuff inside the toilet bowl can contribute to foul smelling odors. Also, doesn't flushing release a small aerosol of bacteria in to the air above the toilet? I remember reading that somewhere, I'm sure someone will prove me wrong. Livewireo (talk) 18:05, 22 April 2009 (UTC)[reply]
The dishcloth one always gets me. Is that measured before you place it in hot water (to get it wet ready to wipe a side), just after and before using to clean or after cleaning? I guess my point is - the circumstances will matter as much to the number of bacteria as the place you are measuring. I would expect that the reason for most people to want rid of germs from toilet seats is that they A) sit on them with a part of their body they otherwise only wash daily (or potentially less) compared to touching something with your hands (which would be washed numerous times a day by most). Also toilets are a place where people go to get rid of their 'waste' so they associate them with being dirty/unhygienic as a result it'd make perfect sense for a marketing/branding dept to make a point about their product killing germs there. After all that it still matters whether the bacteria is harmful or not. Numbers alone are a bit of a con in comparison to the type of bacteria? ny156uk (talk) 19:11, 22 April 2009 (UTC)[reply]
It's true that in the UK these adverts make us feel like we are surrounded by monsters, and that we should get rid of them before it's too late. However, if they wanted to be honest, they'd say "kill 99.99% of germs (99.9999999% of those being harmless)". Laurent (talk) 19:28, 22 April 2009 (UTC)[reply]
There's no such thing as a harmless germ. A germ is defined as a microorganism that can cause disease. A harmless bacteria is not a germ. APL (talk) 20:12, 23 April 2009 (UTC)[reply]
Toilet bowls normally contain far more "germs" than toilet seats. And they can be harmful to you if someone else in your household has a communicable disease which you don't want to catch. They also look and smell bad when you get ugly growths on the sides of the bowl. It's true that you aren't likely to be exposed to those germs though, with exceptions for pets or small children which happily drink from and play in the toilet bowls. However, nothing fancy is needed to kill those germs, bleach will do the job, although you need to scrub the bowl to get the bleach on all the microbes. Bleach in a thick gel would be even better, as that can stick to the sides of the bowl long enough to kill whatever needs killing. Many toilet bowl cleaners are just that, bleach in a thick gel in a bottle with an angled neck for ease of delivery. Note, however, that bleach and other cleansers may be worse for the children and pets than the original germs were, so keep them out of the bathroom during cleaning. StuRat (talk) 19:45, 22 April 2009 (UTC)[reply]
Products that kill "99.99%" of germs are likely to leave behind ones that are now more resistant to the antibiotic spray, creating what are sometimes called "superbugs". Also, humans don't usually drink from a toilet bowl, but a pet dog might. Another thing, MythBusters confirmed that flushing the toilet brings a small number of the fecal germs up into the air, thus landing on other items such as your toothbrush (in very detectable amounts, even if placed in enclosed containers). ~AH1(TCU)22:48, 22 April 2009 (UTC)[reply]
Such products are not antibiotics and thus there is minimal risk of inducing the formation of resistant strains of anything - Disinfectants such as benzalkonium chloride generally do not produce tolerance. Wisdom89(T / C)22:56, 22 April 2009 (UTC)[reply]
I've noted much more guarded language from advertisers of these products of late - one I noticed a couple of evenings ago said "Kills up to 99% of known germs that may do you harm"...which is pretty much saying "It might kill some bacteria"! The word "germ" is carefully vague - is this bacteria? fungi? viruses? The advertiser's favorite get-out-clause "up to" is a good one. If there are some really virulent bugs, then 1% of them will plenty enough to harm you. Evidently it only kills "known" germs (known by whom?) - and it might only kill the ones that would do me harm...what about my pets or whatever? SteveBaker (talk) 00:08, 23 April 2009 (UTC)[reply]
Are you really serious about microwaving a dishcloth to kill bacteria? What makes you think that this will work? As far as I know, microwaves only really heat water, and most spores of bacteria are water poor, plus they have a small volume, are very damage resistant and repair capable. I would assume microwaving for a long time will reduce the number of viable bacteria, but kitchen microwaving is not capable of sterilizing something. My main argument stays the same: For 99.99999999...Ā % of time that life on earth existed, there were no artificial antibiotics and no really sterile surfaces. Even considering that we have changed the rules lately (moving around the globe faster and changing the patterns of germs that can infect us, by changing the environment we live in), I'm totally fine with my immunesystem coping with the "usual" suspects like bacteria dwelling in my home, the soil, the food, the water or whatever I encounter on a regular basis. I think cleaning your home from 99.99% of bacteria on a regular basis does more harm than good, because you disturb the established pattern of microorganisms and so create a situation where really nasty things can creep into your home, that in addition are new to your immunesystem. I'm not saying that you shouldn't clean your home, but trying to keep it near-sterile every week is really overdoing it, without a clear justification why those things you try to eradicate should not peacefully coexist with you. TheMaster17 (talk) 08:12, 23 April 2009 (UTC)[reply]
I would assume that the idea is to heat the water in a damp dishcloth to boiling point (or so) and to keep it there long enough to sterilise it. But I'd be pretty surprised if that actually worked. If you merely warm it up to a nice comfy body-heat, you may actually be encouraging the bacteria to multiply. I strongly agree that an overly sensitive person can do more harm than good. Continually killing only 99% of bacteria simply encourages the remaining 1% to evolve to the point where you can't kill them that way. Better to reserve that killing capability until you actually need it for something. Also, it's been well documented that children NEED exposure to a wide variety of bacteria in order to develop immune responses to them. Children who are born into families of "neat freaks" get sick far more often than those of people with a more relaxed attitude to cleanliness. So, keep things clean - yes. Pay a heck of a lot of attention to places where you prepare chicken and such - but otherwise, chill out. We are able to withstand most of what the bacteria can throw at us without even noticing that we're doing it - and when we do get sick, modern medicine is there to help. Of course different rules come into play if you're actually immuno-compromised in some way (eg with AIDS or something). SteveBaker (talk) 11:53, 23 April 2009 (UTC)[reply]
A news report (this isn't it but it makes reference to it) recently recommended 2 minutes of microwaving as a way to sterilise dishcloths. MyhtBuster actually confirmed that there is no discernible difference between a toothbrush stored near a toilet in the bathroom and one stored in a seperate room, so I'm not sure which episode you saw...Anyway, thanks for this info, guys.Ā :) Vimescarrot (talk) 18:05, 23 April 2009 (UTC)[reply]
I was surprised by that too, because I remembered reading often that microwaving was reported as being an insufficient treatment for reducing pathogens. (e.g. in reheating leftover hamburger.) This is the study you were referring to, I think [18] If you want something really germy forget toilets and cutting boards, women's handbags tested as being really icky on the outside. 76.97.245.5 (talk) 18:29, 24 April 2009 (UTC)[reply]
And then there are the handles on the doors of "restrooms" that are used by people who've had their hands up their arses or all over their family jewels (or whatever the equivalent term for the female variety is) and don't wash. Telephone mouthpieces too. -- JackofOz (talk) 20:59, 25 April 2009 (UTC)[reply]
No. White vinegar is distilled, and is basically pure, dilute acetic acid. White wine vinegar is vinegar made from white wine, and it retains some of the complex flavors associated with wine. IMO, white vinegar is not very useful for cooking due to its simple flavor (but can be useful for cleaning coffeemakers, etc.), while white wine vinegar is quite useful for sauces, vinaigrettes, etc. -- Coneslayer (talk) 17:05, 22 April 2009 (UTC)[reply]
White (distilled) vinegar can be used for cooking, but would be used in pickling or acidifying something (like the water used to cook poached eggs) when you don't want to add any additional flavors. I wouldn't use distilled vinegar in something like a vinaigrette or sauerbraten, where the flavor of the vinegar is a major component of the dish. -- 128.104.112.117 (talk) 22:23, 22 April 2009 (UTC)[reply]
I think I am probably just not trying the right search terms, but where can I learn more about the tendency of some birds to collect (e.g. steal) shiny things and other man made objects for use in their nests? I'd like to know more about which birds do this and what types of things they go after. Dragons flight (talk) 23:38, 22 April 2009 (UTC)[reply]
Magpies hoard food; that behavior is well documented. I know magpies are also said to steal and hoard shiny objects, but I'm not sure there is any rigorous scientific study of that. If they do that at all, I guess it must be an extension of the food hoarding behavior. Now the bowerbird that Steve mentioned is a different story altogether. In bowerbirds, collecting colorful objects is a part of a (pretty damn impressive) courtship ritual. --Dr Dima (talk) 05:14, 23 April 2009 (UTC)[reply]
@Phil I ran out of google patience for a scientific study on magpies stealing, [19]. But if you get a chance to look inside a nest you can usually see some "evidence". If you do have magpies nesting nearby you could also leave a small piece of chrome plated metal out. (OR: The biggest thing I've seen one make off with was a make up mirror. The one's I encountered didn't go for aluminum foil but would take paper chewing gum wrappers that were aluminum coated.) The members of the crow family (which include Magpies and Jackdaws) have been found to be quite bright and they do get bored and play. The Kremlin used to have trouble with some crows claw-scating down their dome and peeling the gold off the roof. 76.97.245.5 (talk) 18:02, 24 April 2009 (UTC)[reply]
April 23
NRPGĀ ?
NRPG. I'm uncertain as to what it means, and don't know where it is located in the CNS. Possibly called the Nucleus reticularis paragigantoceullaris, it definately excites the Raphe magnus and is involved in opiod modulation of pain transmission. Is that what its called and am I correct in assuming its next to the gigantocellular nucleus. Any help would be most appreciated, many thanks MedicRoo (talk) 01:15, 23 April 2009 (UTC)[reply]
Googling informs me that it's located in the ventrolateral part of the medulla oblongata, and that your speculations are correct. Looie496 (talk) 16:51, 23 April 2009 (UTC)[reply]
Light through optical centre
Imagine that a light ray passes towards the direction of the optical centre of a convex lens.
when the light ray strikes the lens from air, it is not normally incident. So, it must be bent towards the normal at that point. It means that it will not pass through the optical centre. Even if it does, as it emerges out of the lens, it is not normally incident on the glass-air boundary. So it will be shifted away from the normal. It means that the light ray will emerge parallel to the incident ray. But the wiki article says that it will not get deviated. Please Explain with diagrams--harish (talk) 01:28, 23 April 2009 (UTC)[reply]
You didn't say what article you're talking about, but in any case, the ray will only emerge parallel to the incident ray if the angles of bending are exactly opposite when it enters and leaves the glass, which will only happen if the glass surfaces are parallel on both sides. For a convex lens as shown in the figure, the two sides of the glass are not parallel. Looie496 (talk) 02:46, 23 April 2009 (UTC)[reply]
The two surfaces are papallel at the center of the lens which seems to be the point of the question, though that is not entirely clear to me. Dauto (talk) 04:22, 23 April 2009 (UTC)[reply]
The image is poorly drawn. The upper and lower rays are shown changing direction by refraction at both lens surfaces, as occurs with a lens of real thickness, while the purported central ray is unreal as the OP noticed. To be consistent with the thin lens approximation, the rays should change direction only at the center line of the lens (and in that case the central ray can arguably be drawn as it is). Cuddlyable3 (talk) 00:08, 24 April 2009 (UTC)[reply]
So, the total answer is that the ray will experience a little bit of deviation if it is not along the principal axis. Right?--harish (talk) 01:11, 24 April 2009 (UTC)[reply]
I heard of the news today that medical research has shown that the use of Bonjela and similar over-the-counter treatments contain salts which could cause liver and/or brain damage in children under the age of 16. I'm curious in knowing which chemicals in Bonjela cause these side effects, and why the risk of damage to adults doesn't exist. Is it due to a more developed blood-brain barrier or maybe a metabolic deficiency that disappears over the age of 16? I can't find much reason why the same salts wouldn't cause toxic effects in adults. Regards, --āCyclonenim |Ā ChatĀ 07:08, 23 April 2009 (UTC)[reply]
Bonjela contains similar ingredients to aspirin, whose use is strongly correlated with Reye's syndrome in small children. That article itself mentions that the cause really is unknown, and my quick search of google scholar shows that this is still a very active area of research with little concrete evidence on any reason for the link, although the link itself is very firmly established for at least injested pills. Someguy1221 (talk) 07:41, 23 April 2009 (UTC)[reply]
Bonjela is amazing. I found it far more effective in treating mouth sores than comparable U.S. products. I have bought it from a London chemist at astronomical shipping charges after the tube bought in Britain ran out. Are they reformulationg it somehow to correct the problem but maintain the effectiveness? Edison (talk) 19:09, 23 April 2009 (UTC)[reply]
There was some iodine-compound stuff my friend managed to bring back from Sweden I think, and it's insane, you apply it and ulcer never comes back. Shame it's banned for whatever reason in the UK. Bonjela is the next best thing for us over 16sĀ :) Regards, --āCyclonenim |Ā ChatĀ 14:04, 24 April 2009 (UTC)[reply]
Oh, and to answer your question, they've just made packaging more obvious that under 16s shouldn't be using it, just like aspirin. Bonjela Teething Gel doesn't contain the salicylates, and therefore can still be used on chilren from 2 months to 16 years. Regards, --āCyclonenim |Ā ChatĀ 14:05, 24 April 2009 (UTC)[reply]
What could a super-large telescope array see?
I understand that the resolution or amount of detail that can be seen by telescopes, both optical and radio wave, increases with their width. And that very wide telescopes can be simulated by joining up two or more widely-spaced telescopes in an array. I know such arrays have been formed of radio telescopes at least. I'm not sure if optical telescopes have been linked like this yet, or if that is something for future technology.
My question is, if you had a very long baseline for two or more telescopes, such as one telescope being on earth and another on the moon or even on Neptune or Pluto, would the amount of detail be enough to see planets orbiting stars, or even see some surface detail on those planets? And is there any theorectical limit to the length of the baseline? 89.242.82.4 (talk) 10:56, 23 April 2009 (UTC)[reply]
What becomes tricky on very large scales is the speed-of-light limitations in the communications path between telescopes. Also, no matter how far apart you put your telescopes, their light-gathering abilities don't get any better - so imaging very dim objects doesn't really improve. SteveBaker (talk) 11:42, 23 April 2009 (UTC)[reply]
(ec) The technique is a type of astronomical interferometry called aperture synthesis. It's been done for a long time in radio astronomy; Very Long Baseline Interferometry can link radio telescopes across the entire face of the Earth. High-precision atomic clocks allow radio astronomers to synchronize and combine radio signals from widely separated telescopes.
The problem is quite a bit more difficult at optical wavelengths. Because radio waves are typically a million times (or more) longer than visible and near-infrared light waves, the problem of 'lining up' the data from multiple radio telescopes is correspondingly much easier than it would be for a similar array of optical telescopes. (On the plus side, the much-shorter optical wavelengths mean that comparable resolution can be obtained with a much smaller baseline size.)
Nevertheless, a substantial number of optical interferometers now exist: List of astronomical interferometers at visible and infrared wavelengths. One of the largest is the CHARA array in California; its six telescopes are linked optically through a series of vacuum-filled pipes to generate a 330-meter (1100-foot) baseline. Together, they can resolve features down to 0.0005 arcseconds (0.5 milliarcseconds) ā in 2007 they generated images of the surface of the star Altair, 17 light years away.
The twin 10-meter Keck telescopes in Hawaii can be linked optically to generate a very sensitive nulling interferometer with an 85-meter baseline. In that configuration, they are aimed at a star and configured so that the light from that star is optically cancelled-out between the two telescopes. Off-center light ā as from an extrasolar planet ā doesn't get cancelled out. In principle, the planet should become visible once it's no longer drowned out by the glare of its star.
Off the top of my head, I don't think there's any upper limit imposed by physics on the size of an interferometer array. The real bounds are the limitations of engineering. For an optical interferometer to work, you need to know and maintain the relative positions of the components with a precision of less than one micron (smaller than the wavelength of the light you're collecting). It's painstaking but possible to do when you've got a group of telescopes all together on the same mountain; it's a nightmare to manage if you want to put the telescopes further apart. Proposals exist for space-based optical interferometers as well, though as far as I know none are currently under construction. TenOfAllTrades(talk) 12:10, 23 April 2009 (UTC)[reply]
I don't want to spoil your wonderful answer, Ten, but I have to say that "vacuum-filled" made me do a double-take. Deor (talk) 13:08, 23 April 2009 (UTC)[reply]
Ha! Yes, I winced a bit when I typed it, too. I figured the minor scientific blasphemy could be excused for the sake of clarity of meaning. (When I was drafting the post, my original response described the system as being linked by 'vacuum tubes' ā precisely correct, but horribly confusing to anyone who read the phrase as meaning the electronic device rather than simple empty pipes. I also toyed around with 'evacuated' tubes, but that leaves one shaking one's head at the obvious necessity to remove people from the light path.) TenOfAllTrades(talk) 19:47, 23 April 2009 (UTC)[reply]
I think too much is made of these kinds of "minor blasphemies". The meaning is perfectly clear in context and the phrase is entirely useful. Language is just language - it doesn't have to reflect precisely the deep-down scientific truth - so long as everyone is clear about what is meant by it. SteveBaker (talk) 03:34, 24 April 2009 (UTC)[reply]
The only limit imposed by physics on the size of those arrays that I am aware of is the coherence length of the radiation. This length is proportional to the square of the wavelength, so it becomes an increasingly harder problem to deal with as the wavelength beeing used becomes smaller. The coherence length is also inversely proportional to the bandwidth so it is possible to get arbitrarily large length simply by using arbitrarily narrow bandwidths. There is no free lunch though. An arbitrarily narrow bandwidth makes the source arbitrarily dim and hard to see. There's a trade off here that is taken into consideration when deciding how large to build an telescope array. Dauto (talk) 18:04, 23 April 2009 (UTC)[reply]
So if you did have an array consisting of optical telescopes on the earth and the moon, or at equivalent distances on satelites, and assuming the engineering problems were overcome, then would you be able to see any surface detail on planets orbitting stars? The baseline distance would be far greater than that of current arrays. Is there any formula that relates array width to resolution? 89.241.44.96 (talk) 10:10, 25 April 2009 (UTC)[reply]
Does it seem like perpetual black night? Or might it even be whiteness, or nothingness? The blind spot on the eye is more like nothingness or whiteness rather than blackness, with the brain seeming to fill in what is there from the surrounding image. See http://www.colorcube.com/illusions/blndspot.htm As there are various causes of blindness, so the subjective experience may differ. 89.242.82.4 (talk) 11:07, 23 April 2009 (UTC)[reply]
For people who have been utterly blind since conception, whole areas of the brain related to vision don't develop so I doubt there would be any sense of 'blackness' - just no vision sense at all. That's impossible for a sighted person to even imagine and discussing what that means with a blind-since-birth person results in no common terms of reference. They can't explain what it's like to not have a sense that they never had. Can you explain to a dolphin what it's like to have no echolocation sense? Or to a fish, how it feels to have no lateral-line electrical sense? I don't think so. People who have become blind after being sighted will doubtless have a different sense of what it's like. SteveBaker (talk) 11:40, 23 April 2009 (UTC)[reply]
I once heard someone saying (I am not blind) that a completely blind person can see just as much with their eyes as I can see with my knees. That makes it pretty clear for me... -M āPreceding unsigned comment added by 195.67.112.146 (talk) 12:21, 23 April 2009 (UTC)[reply]
There is a phenomenon in perception (I'm blanking on the name right now, but it's related to change blindness and inattentional blindness) where the mind subtracts out a constant stimulus. It still may be registering at the sensory nerves, but after a while it is no longer perceived consciously. You've probably experienced this yourself. If there's a humming fan, after awhile it no longer registers, but when it turns off you can "hear" the silence. Likewise with scents - after a short period in a strongly scented room, you no longer can smell anything "off", but leave and reenter and the smell hits you. I would imagine the same would happen with a blind person. Immediately after becoming totally blind they might register a strong white/strong black perception. But after a while with that constant stimulus, the brain would ignore the signals coming from the optic nerves completely, and they wouldn't "see" anything at all. -- 128.104.112.117 (talk) 14:38, 23 April 2009 (UTC)[reply]
I have a blind friend who experiences different colours depending on the circumstances he is in, particularly when talking to certain individuals. I generate a blue/green colour. Normally he is not aware of any colour because he is not 'looking' but concentrating with his other senses. Richard Avery (talk) 14:54, 23 April 2009 (UTC)[reply]
I'd bet that too - otherwise how could he know that this 'color' is blue and not pink? If you'd never seen blue or pink they be just arbitary labels. Assuming Nil Einne is right (and it seems very likely) then this is just a case of synaesthesia - which is a rather well-known phenomenon, even in sighted people. SteveBaker (talk) 20:05, 23 April 2009 (UTC)[reply]
I linked this article before, but you might find it interesting in this regard. [21] It illustrates that even when a blind person regains sight the brain is having trouble interpreting what it is "seeing". 76.97.245.5 (talk) 17:22, 24 April 2009 (UTC)[reply]
Why do people collect things / derive satisfaction from completing sets of objects?
I am well aware of hoarding, but I'm interested in the more mundane and widespread human compulsion to collect things. I know we're not the only animal to do this, but I'm having a hard time seeing the evolutionary value of such a finely honed desire to accumulate things.
I'm sure there are occasional cases where an impressive collection of _____ resulted in the acquisition of a mate, but I doubt that that was the conscious goal of the collection to begin with.
So... why do (most) humans feel a need and derive satisfaction from collecting things? What is it about a complete set that soothes the mind? Oftentimes these objects serve no use other than to occupy space (and please the collector...)
61.189.63.224 (talk) 13:00, 23 April 2009 (UTC)[reply]
Not all human desires/traits are linked (clear or otherwise) to an evolutionary reason. We could speculate that things that are collectable have their roots in effort/time/reward. It takes time and effort to get a complete set of something, so the satisfcation is the reward. If you receive a complete set instantly it wouldn't have your emotional journey attached to it. I'm not sure that everything needs to have an evoluntionnary reason for existence. 194.221.133.226 (talk) 13:52, 23 April 2009 (UTC)[reply]
Just a guess: In prehistoric times collecting nuts and berries (food) may, on occasions, have made a difference between survival or not. Equally, gathering bits of timber (fire) and heaps of rock fragments (defense / tools) may have given some hominids an advantage in survival. Collecting stamps, beer coasters or Van Goghs could be just a sublimation of this. --Cookatoo.ergo.ZooM (talk) 14:23, 23 April 2009 (UTC)[reply]
Is it possible that it's a learned behavior planted in our heads by society? How many times in your life have you heard the phrase "collect all six" (or whatever quantity)? Is the drive to collect a set universal in all cultures, or only in capitalistic societies? 168.9.120.8 (talk) 14:29, 23 April 2009 (UTC)[reply]
Also note that extreme cases of "collecting" are considered compulsive hoarding and are classified by many psychologists as a personality disorder. In extreme cases, it can be linked to a variety of more serious conditions such as addiction, delusion, and obsessive-compulsive personality disorder. Viewed from this perspective, "collecting" may be seen as a disorder, rather than an vestigial evolutionary habit - but of course it depends on the severity and how much it interferes with other activities. Nimur (talk) 15:42, 23 April 2009 (UTC)[reply]
There is obviously value in an evolved tendency to collect stuff like food or sticks for a fire - but as the OP points out - we may get highly obsessed with having one of every kind of postage stamp released by Tibet - yet have no interest in collecting 400 almost identical postage stamps from Tibet. That's a totally different behavior. We would have no evolutionary advantage to collecting one of every kind of berry from the bushes near our caves - yet that's what we do with postage stamps. My guess is that it has more to do with tool use. When going hunting - you need one knife, one axe, one spear, one bow, etc - it's important not to leave without your complete "set" of tools - and it does you no good to have six knives with you if you forgot your spear. But that's a really wild guess...I bet the real answer is REALLY interesting! SteveBaker (talk) 16:29, 23 April 2009 (UTC)[reply]
It could just be a self-fulfilling thing. We collect things that are valuable, complete sets are often deemed more valuable than the sum of their parts, so we collect complete sets. There doesn't need to be a reason for complete sets to be considered valuable, they are because they are. It's like fiat currency. It has no inherent value, but because everyone thinks it has value, it does have value. --Tango (talk) 16:48, 23 April 2009 (UTC)[reply]
This same compulsion may be the cause of some Wikipedia editors creating stub articles about every highway exit, or other things that can be linked by succession boxes. The same satisfaction may accrue as when someone pops yet another US state quarter into an album. Edison (talk) 19:04, 23 April 2009 (UTC)[reply]
I have over 300 toy MINI Coopers...but I don't think they're valuable (well, except maybe one or two of them). It's not a matter of value...there is some deep obsessive streak in many people. Why we have that is hard to say - but it's clearly not the hope of monetary reward. SteveBaker (talk) 20:05, 23 April 2009 (UTC)[reply]
Collecting things isn't a particularly human trait. Just a couple of non-food examples: Bowerbirds collect all sort of decorative material to attract mates. Magpie nests often feature collections of lost glasses, spoons and assorted shiny objects. (Oops already mentioned in a post a bit higher upĀ :-) Birds roosting on rocky ground steal pebbles they consider attractive from neighboring nests. Octopus vulgaris uses shells and other collected items to protect it's eggs. Hermit crab are well known for their skills in decorating their shells with all sort of debris and anemones. Domestic cats and dogs are sometimes found to have a hiding spot for socks, gloves, hair ties or shoelaces that they "collected". 76.97.245.5 (talk) 17:06, 24 April 2009 (UTC)[reply]
The O.P. wrote: "I doubt that that was the conscious goal of the collection to begin with." In fact most adaptive behaviors do not result from conscious goal-formation. For example, most of the time when one human feels sexually attracted to another human, the cause of attraction is rarely a consciously felt desire to create offspring. In many encounters, perhaps even most, one or both partners have a consciously felt desire to thwart procreation. Quite clearly, in the ancestral environment it was not necessary to consciously desire children - it was only necessary for people to desire sex, and then be willing to love and care for the products.
As I pointed out before though - simply collecting a large number of food items in order to survive the winter isn't the kind of behavior our OP is interested in. The question is about the tendency for people to want complete collections containing one (and typically, only one) of every representative of some kind of set. You would not want a thousand very similar empty coke cans on a shelf in your garage - but there are people who try to have one of every variation on the coke can from 1950 or whatever. Someone who had a thousand empty coke cans with no particular 'meaning' to them would be labelled kinda crazy. Someone who had a collection of every different can Coke ever made would be considered somewhat amazing - but not really crazy. That's clearly nothing like the same behavior. We can easily understand the evolutionary drive to acquire large amounts of 'stuff' - but where did the drive to collect just one of each different 'something' to make a set come from? It's hard to guess. SteveBaker (talk) 00:22, 25 April 2009 (UTC)[reply]
Also as I suspect some contributors can such as SB attest to, collecting 300 Tibetian stamps, wikipedia highway articles, US state quarters, beer coasters or toy Mini Coopers, doesn't generally help to attract mates. Nil Einne (talk) 20:08, 25 April 2009 (UTC)[reply]
I have a collection of about 2,500 LPs, many of which I still play frequently (partly because I have some rarities that have not yet made it to CD transfer, and partly because I prefer the sound of LPs, even on crappy equipment such as I have). My collection includes some LPs that I played once, and never again. It also includes some LPs that I never played at all. These include the start of the complete set of Haydn symphonies (he wrote over 100 of them). A complete set occupies about 50 LPs. I acquired about half of them, then the company that produced them went bust or something. Although I've never played any of them (well, maybe just a couple), I've always been deeply, profoundly dissatisfied at owning only half the set. I've often asked myself: since I'm not that interested in Haydn, why did I start collecting his symphonies to begin with? I still have no answer to that. All I know is that my life would be immeasurably richer if I owned a complete set of unplayed Haydn symphonies rather than half a set of unplayed Haydn symphonies. Go figure. -- JackofOz (talk) 20:52, 25 April 2009 (UTC)[reply]
You might like to try Brain food, section 3.10 seems to have a few words about dietary brain enhancers. Most foods purported to assist brain function are of dubious value, but there's no accounting for placebos. Richard Avery (talk) 14:49, 23 April 2009 (UTC)[reply]
Wodehouse in the Jeeves account (early 20th century) was reflecting a common belief. Fish had been considered "brain food" way back in the 19th century, and nutrition books in the 21st century still claim it is "brain food," with some dissent that it is not particularly a brain food. See Google book search:[22]. Edison (talk) 19:01, 23 April 2009 (UTC)[reply]
Sugar enhances brain function over the short term by enhancing arousal, if you don't eat too much. Over the long term, I'm not aware of any solid evidence for foods whose value for the brain is different from their value for the body in general. You'll find vast numbers of claims all over the place, but solid evidence is sorely lacking. Looie496 (talk) 16:44, 23 April 2009 (UTC)[reply]
Grace Slick of Jeffersen Airplane in the song "White Rabbit" urges us to "Feed your head". It is not clear with what, but the audience at Woodstock seemed to know what she meant. Peace. Cuddlyable3 (talk) 19:25, 23 April 2009 (UTC)[reply]
Whilst not conlusive, there is a lot of evidence in support of the theory too. See [23], [24], plus many more in support on PubMed. The topic is still under heavy debate, but most articles seem to confirm the effect of n-3 fatty acids on the brain. Regards, --āCyclonenim |Ā ChatĀ 23:36, 23 April 2009 (UTC)[reply]
Many infant formulas are fortified with DHA (Docosahexaenoic acid) as DHA is used in metabolic pathways in the production of phospholipids found in the brain. It is also of rather high concentration in natural mother's milk. Primary natural source of DHA? Fish oil. Jeeves may have been on to something. --Jayron32.talk.contribs00:45, 24 April 2009 (UTC)[reply]
In case you're not kidding, let me say that I only add my name after I add the resolved flag to show that it's my opinion, based on the original poster's comments, that this question is now fully resolved. If you were kidding, then sorry to be such a nuisance. StuRat (talk) 07:48, 24 April 2009 (UTC)[reply]
Minimum amount of fuel to circumnavigate the globe
If you were limited to travelling only by propulsive transport (ie no bikes, swimming, hangliding etc) what is the minimum amount of fuel that you would have to use? And presuming that different vehicles will use more/less efficient fuel etc, what's the least amount of CO2 you'd emit doing it? If anyone has any thoughts that'd be great. 86.8.176.85 (talk) 19:18, 23 April 2009 (UTC)[reply]
Well, assuming you aren't going to let us use yachts or sailing ships or hot air balloons of any kind - the Virgin Atlantic GlobalFlyer circumnavigated on about 10,000kg of JP4 jet fuel. That was a solo flight in one of the most efficient planes imaginable - so it's probably about the best you can do in a plane. Concorde needed about sixty times as much fuel (and consequently, six refuelling stops) to do the same thing. Doing the trip in a boat ought to be a lot more efficient...especially if you can cheat and use sails. SteveBaker (talk) 19:57, 23 April 2009 (UTC)[reply]
If you don't count the fuel you use in the 1st 10 minutes, a satellite really can go around thousands of times while using no fuel. Otherwise, I would say That a helium balloon would do pretty well. 65.121.141.34 (talk) 20:29, 23 April 2009 (UTC)[reply]
The trouble with a helium balloon is that you do actually need to consume helium and ballast on those long flights because you have to 'steer' by rising up and dropping down into the wind currents that happen to be going in the direction you want to go. Doing a round-the-world trip on helium alone would be really tough! There are various hybrids of helium balloons and solar-heated hot-air (a "rozier"), for example. A rozier was the first balloon to circumnavigate the world - but it needed a lot of propane still - certainly less than the GlobalFlyer thing...but I suspect our OP won't let us use balloons. I love the satellite idea though - that's great! SteveBaker (talk) 20:38, 23 April 2009 (UTC)[reply]
As always, this sort of thing comes down to clearly defining some ambiguous criteria. As noted above, how strict is "propulsive"? Sailpower seems rather obviously against the spirit of what you've requested, but consider these less-obvious problems:
GlobalFlyer flew west-to-east to benefit from the jet stream, a non-propulsive ~150 kph boost
Satellites, considering launch propulsion, launch from west-to-east to benefit from the Earth's rotational velocity, a non-propulsive ~1500 kph boost.
Ships of various forms often exploit ocean currents, non-propulsive ~5 kt boosts.
Additionally, why disallow bikes or swimming? Humans require fuel and a decent CO2 estimate could be made.
For some specifics, the S9G reactor used in Virginia-class submarines has a design lifetime of 33 years and an estimated reactor mass of 360 kg.[25] The USS Triton required two months to circumnavigate the globe (the first submerged circumnavigation). The Virginia would "use" 1.8 kg of reactor mass over that time frame, with effectively no CO2 emissions associated with propulsion. ā Lomn21:15, 23 April 2009 (UTC)[reply]
To be complete, I'd argue you also have to amortize some cost for the radioactive nuclear vessel and other stuff that, upon decommissioning, has to be trucked somewhere to be buried and monitored for the next 10,000 years. Tempshill (talk) 22:15, 23 April 2009 (UTC)[reply]
A Cessna 150 cruising at 198 km/h consuming 23 L/hr of Avgas should be able to fly a 36 787 559km circumnavigation consuming 4 273 302 L. I wonder whether the OP wants such an abstract calculation or practical information?
The good news is that thousands of Cessnas have been produced so they are readily available, not too difficult to fly and you have room for a passenger. The bad good news is that the standard aeroplane needs a LOT of refuelling stops, about every 600km. Arranging that on land would need international negotiations and almost certainly demand a longer route. Over the oceans....well, if you are in no rush you could beg "friendly" aircraft carrier captains to let you land and fill up. Cuddlyable3 (talk) 23:44, 23 April 2009 (UTC)[reply]
You might want to check your decimal point ā the circumference of the Earth is roughly 36 thousand kilometers, not 36 million. That would make a much more reasonable four thousand liters of fuel. Cheers! TenOfAllTrades(talk) 01:50, 24 April 2009 (UTC)[reply]
Eeek! I'm not sure I'd want to contemplate landing (or taking off for that matter) from an aircraft carrier in a Cessna 150! It's a seriously scarey business in something like and F18 that's designed for the job. The lack of an arrester cable hook would mean you'd either have to pull off some impressively short landings or smack into the crash netting each time. The relative fragility of the landing gear would demand really smooth seas when you did it - and I honestly wouldn't want to be in a Cessna that's hooked up to a modern deck catapult for the take-off run! If you have to stick to land-based routes, you'll be taking some considerable detours...but still, I think you could do it using marginally less gas than the Virgin Atlantic GlobalFlyer - so perhaps this is still the best solution so far in terms of fuel efficiency. SteveBaker (talk) 03:30, 24 April 2009 (UTC)[reply]
The stall speed of a Cessna 150 is only 42 knots, minimum ground roll for landing is 450', 1075' for takeoff. Remember, the carrier would be travelling at least 25 and as much as 35 knots into the wind. No problem, no arresting gear or catapult required, it would be loads of fun, though a pitching flight deck might make it a little more interesting.āeric05:36, 24 April 2009 (UTC)[reply]
I don't remember which one, but in one edition of Microsoft Flight Simulator, landing some manner of Cessna on an aircraft carrier was one of the built-in "adventures". Who knows how accurate it was modeled. I'm not sure you'd be able to find carriers that carried the right fuel, though. (Maybe for helicopters?) APL (talk) 13:38, 24 April 2009 (UTC)[reply]
Well, the largest carrier on the planet is probably the Nimitz - it's entire deck is 1100' long - so your 1075' minimum take-off run would require you start at one end of the deck and you'd 'unstick' about 30' from the end...well, 30' minus the length of the plane - maybe you'd have three feet to spare. Yikes! But recall that the flight deck of a carrier doesn't work like that. The landing and take-off areas are both much shorter than the total length of the deck because the thing is designed to have planes landing and taking off simultaneously. Also, not many carriers are the size of the Nimitz - most are more like 800 feet long - and then you're flat out of luck for your take-off run. Worse still - the minimum take-off run you're quoting for a Cessna assumes a near-minimum take-off weight...and since we're nowhere near the next airfield - you're definitely going to be needing a full fuel load! As for steaming into the wind at 25 to 35 knots...yeah - it can definitely do that - but the turbulance that causes at the front and back end of the deck would flip a little cessna around like a dry leaf in the fall! You're going to need very light winds and a very, very calm ocean and the biggest aircraft carrier in the world to stand a chance in hell of doing that! (Maybe if we put a huge conveyor belt onto the carrier deck and landed on that?)Ā ;-) SteveBaker (talk) 13:48, 24 April 2009 (UTC)[reply]
If your airplane needs 50 knots airflow over the wings to fly, which is very close to the requirements of our Cessna 150, a takeoff into a headwind of only 5 knots (which is 10 percent of the takeoff speed) will reduce the length of the takeoff run by approximately 19 percent over what would otherwise be required with no wind. A headwind of 25 knots (50 percent of the takeoff speed) will reduce the ground run by 75 percent. Eichenberger, J. A. (2003). Your Pilot's License. p. 183.
I've never been on the flight deck of a carrier, so can't speak to how much turbulence there would be.
Sorry, but typed in the distance for landing over a 50' obstacle rather than the short field takeoff distance, it's actually 735'[26]. As to takeoff weight, the distance quoted is for a 1600 lb. aircraft, 22.5 gal. fuel (max is 38 gal.), 340 lbs. for pilot and passengers and 76 lbs. for baggage. From the flight manual, 1600 lbs, sea level, 59Ā°, 20 knot headwind, ground roll: 305'. No worries.āeric16:47, 24 April 2009 (UTC)[reply]
According to [27] which links to [28] and says "Cessna O-1B Birddog in the colors of the South Vietnamese Air Force. This aircraft was landed onboard USS Midway during the fall of Saigon in 1975, by a pilot who had never before landed on an aircraft", this was the only case of a Cessna landing on a aircraft carrier. I don't know how that compares to a 150 Nil Einne (talk) 15:57, 25 April 2009 (UTC)[reply]
The original questioner mentioned bicycles. Since you can't circumnavigate on a bike, the questioner must be thinking about switching vehicles. You could arrange your trip so that the last leg of the trip was made on a small, fuel efficient scooter carried on your original vehicle. I'm not saying it would be a safe thing to do, but you could cover about sixty degrees of longitude by scootering across Africa sticking reasonably close to the equator.
But then again, if you're going to take it to that ridiculous level, you might as well go all the way and procure some sort of solar car.APL (talk) 02:24, 24 April 2009 (UTC)[reply]
And if you're not in a hurry - or under any cost limitations - then a solar boat would not be out of the question so you don't have to worry about putting the car on a boat in order to get it across the wetter bits of the planet. The point is that if you have no time or budget constraints, you could use a series of electric cars and boats with batteries charged from solar panels - lined up waiting at each port of call along the way. But truly, a yacht makes more sense...plenty of people have sailed around the world using nothing more than the wind and a technology that's been around for thousands of years - it's a very do-able thing. This is one of those questions where you have to keep excluding the obvious, practical answers in order to get the answer the OP wanted - and that just gets silly! The proper answer is: zero...unless you're in a hurry or trying to do it within a particular budget. SteveBaker (talk) 03:30, 24 April 2009 (UTC)[reply]
Wow, thanks for ll these great answers guys. In answer to your musings, I'd be fine with any vehicle as long as it is powered by more than human energy, although I guess I'm more interested in fuel-burning methods. I like the ideas of a nuclear submarine and a solar car, though. I'd be fine with vehicle changes, and I'm interested in both hard numbers answers and "well, if you put a flux capacitor on a jetpack, then..." sort of answers too. Thanks, again, you've all been great. 86.8.176.85 (talk) 03:25, 24 April 2009 (UTC)[reply]
LAMP is Lutheran Association of Missionaries and Pilots. They fly donated planes across the oceans for Christian mission work, including providing planes for medical flights in third world countries. I read of one such plane which was flown from California to Hawaii enroute to Asia. It was a single engine small plane with extra fuel tanks, making a near-suicidal long duration over-water flight. When it contacted Honolulu air control, it was give priority for landing over larger commercial craft. They routinely do what are, basically, Charles Lindbergh flights.Edison (talk) 05:36, 24 April 2009 (UTC)[reply]
If you are not in a hurry, you could sit where you are and wait for plate tectonics to take you at least part of the way around in a few hundred million years. Best to position yourself as far as possible from a subduction zone, however. A somewhat faster option, but also not guaranteed to work, and probably not something you could survive, would be to seal yourself into a Drifter (floating device) and release yourself into the ocean. I'm pretty sure that some of these devices have circumnavigated the globe. Neither option requires any fuel for propulsion, but if you wanted to survive a circumnavigation in a drifter, you would probably need to pack enough food to last for several years, along with enough clothing to handle whatever climate regions you drifted through. --Teratornis (talk) 22:56, 24 April 2009 (UTC)[reply]
Nobody, except at the very beginning, said anything about latitude. If you start far enough south, you can go around many times, using this for propulsion, without needing to refuel until after several times around the world. And there's even a place where they have the fuel that you'd need to go around the world that way! Nyttend (talk) 12:50, 26 April 2009 (UTC)[reply]
Among the vertebrates, as far as I know, cats (but not lions), fennecs, and some snakes have vertical slit pupil; and goats have horizontal slit pupil. Frogs and toads have a variety of pupil shapes. Most others have a round pupil. Of the invertebrates, cephalopods have some pretty interesting eyes. A slit pupil is associated with eyes that have multifocal optics [29]. In addition to the slit pupil, cats also have a non-circular high-resolution region of the retina (not a true fovea AFAIR). This region is shaped like a lance-head or a distorted diamond, elongated horizontally, perpendicular to the pupil slit orientation. --Dr Dima (talk) 01:08, 24 April 2009 (UTC)[reply]
current procedure terminology - has it changed over the years?
I am currently researching a cancer case for a deceased fire fighter from 1970. His family is adamant that he died due to colon cancer, the death certificate states diverticular disease.
With the CPT, is it possible that in 1970 diverticual disease was the term used to describe colon cancer? I had another file from the 70's that stated a person passed due to lymphosarcoma, this turned out to be what was later referred to as non-Hodgkin's lymphoma.
I have looked for a history of the terminalology with out success.
I'm just Googling, but the first result if you google "diverticular disease" "colon cancer" states that the two diseases can have very similar symptoms and can be mistaken for each other, for what it's worth. Tempshill (talk) 22:18, 23 April 2009 (UTC)[reply]
Diverticular disease, particularly diverticulitis complicated by intestinal perforation and peritonitis, could be quickly fatal. Colon cancer might be present in such a situation but might not be listed as the proximate cause of death (either because the person filling out the form was unaware, or just not thinking of it). Death certificates are notoriously unreliable in this way. --Scray (talk) 02:05, 24 April 2009 (UTC)[reply]
April 24
Blowing bubbles
Why do the children's toys that you dip into soapy water to blow bubbles with have all those vanes on them? How is this design better than just a plain plastic loop? Dismas|(talk)00:04, 24 April 2009 (UTC)[reply]
The vanes (those grooves along the edge is what I assume you are refering to) hold extra soap, which is fed into the bubble blowing area after you blow a bubble. With a plain plastic hoop, you'd only get one or two bubbles before having to reload; the vanes allow for more bubbles to be blown on a single dip. As a father of a three-year old, I have must first-hand knowledge in this field of study... --Jayron32.talk.contribs00:39, 24 April 2009 (UTC)[reply]
I couldn't find any information specifically about the function of the globose nucleus. From "Color Atlas of Neuroscience", Greenstein, p. 202: "The spinocerebellum exerts control over axial musculature through the efferent outputs from the vermian cortex and the fastigial nucleus. It controls limb movements through outputs to the globose and emboliform nuclei." Other texts provide similar information. Axl Ā¤ [Talk]08:40, 25 April 2009 (UTC)[reply]
Water consumption while dehydrated
From the dehydration article: "It is wise to slowly drink liquids when dehydrated." I've heard that advice all my life but never really understood why. Also, how come most poisonous product labels advise: "if ingested, do not induce vomiting." I figure vomiting would be a good idea and all if you just swallowed something poisonous? TravisAF (talk) 02:41, 24 April 2009 (UTC)[reply]
Once someone starts re-hydrating, the risk is in rapid fluid shifts (since the dehydration won't get any worse). So there's generally no rush to the re-hydration, but overdoing it can cause electrolyte imbalances. Regarding your second question, it's a bad idea to induce vomiting for caustic substances like drain cleaners, because they can cause significant damage on the way up - better to let a poison control center advise on how to treat. --Scray (talk) 03:05, 24 April 2009 (UTC)[reply]
Another concern about induced vomiting is the risk of aspiration of vomitus into the lungs. Some toxins will be absorbed much more rapidly from the lungs than they would from the stomach, other nasties ā like the caustics Scray mentions ā are apt to do much more severe damage to the delicate tissues of the lung (compared to the relatively tough lining of the stomach). Inflammation of the lungs or trachea (caused by even small amounts of aspirated vomitus) may close airways and make a bad situation much worse. TenOfAllTrades(talk) 03:30, 24 April 2009 (UTC)[reply]
For more on the electrolyte-imbalance thing, see water intoxication. It can kill. --Anonymous, 03:59 UTC, April 24, 2009.
Indeed, if you are drinking water, rather than specially designed re-hydration fluids, you could get into serious trouble. Anything more than very mild dehydration should be treated with proper salts, not plain water. (Rule of thumb: If you can drink the re-hydration stuff without it being so disgusting it makes you gag, then you need it.) --Tango (talk) 10:30, 24 April 2009 (UTC)[reply]
It might be worth pointing out that "dehydration" goes way beyond just being thirsty. I've frequently come back from a desert hike or bike ride and slugged down a half gallon of water or Gatorade without ill effect. You have to be gallons down before you get into really serious concerns about rehydrating in the right way. Looie496 (talk) 19:00, 24 April 2009 (UTC)[reply]
Indeed, half a gallon wouldn't generally be enough to cause a problem. I think not eating properly can increase the risk - it's all about the balance between water and salt, if you aren't getting enough salt in your diet (NB: the required amount of salt is very low - this is not an excuse to put loads of salt on your chips!), even a small amount of water could be too much. When you've been on these hikes, etc., you have probably been eating high energy food like chocolate - the milk chocolate wrapper I've just looked at says it has 200mg of sodium per 100g, the RDA (according to Wikipedia) being about 1500mg, this is a good example of how much salt there is in many of the foods we eat. --Tango (talk) 19:56, 24 April 2009 (UTC)[reply]
Lost in the woods
If i became lost in the woods, why would i not just eat grass and leaves until i found my way? It seems obvious to me to eat them if i was starving. EVAUNIT-66603:38, 24 April 2009 (UTC)[reply]
The question is why you can't survive on grass and any old leaves: after all, some animals are happy with that sort of diet (and there are some leaves we do eat, such as lettuce). The main difference is that humans can't digest cellulose, which tends to be a large constituent of various kinds of plant material. Also, some leaves may be toxic, as Scray points out. However, we do have a long list of plants with edible leaves, with some cautions at the top. --Anonymous, 04:04 UTC, April 24, 2009.
You won't be able to get much nutrition from grass as was explained above. Dehydration should be bigger concern anyways. Dauto (talk) 04:29, 24 April 2009 (UTC)[reply]
If you get lost in the woods, you may want to remember that an average adult should survive some hours without shelter, some days without water, and some weeks without food. (YMMV: weather and your starting physical condition will greatly affect these estimates. If you are in the snow or in the desert, adjust accordingly.) "OMG! I NEED TO EAT RIGHT NOW!!!" should not be your first concern, even when you start to feel a bit peckish. First worry about sleeping out of rain, wind, hot sunlight, and night frost. Later think about clean water. 88.114.222.252 (talk) 12:44, 24 April 2009 (UTC)[reply]
There we go again. What's up with that? That's the second time I see someone on these pages talking about people not being able to survive more than a few hours without shelter. That's only true on the most extreme conditions. I would worry first about water if I got lost in a forest. Dauto (talk) 17:44, 24 April 2009 (UTC)[reply]
What woods, when and where? As noted above the human digestive system is ill adapted to gain much nutrition from grass. However, most forests will provide nuts and berries which you could very well live on for a while. You'd have to know what grows where and when locally. Many plant buds and some flowers are also edible and contain more energy than leaves. The problem would also be that gathering all those would be taking time you might spend better on finding the next road or river. (Most flowing water ends up at/near human habitation downstream sooner or later.) 76.97.245.5 (talk) 15:55, 24 April 2009 (UTC)[reply]
If not in an extreme case (rainforest or taiga) you should just go downhill until you eventually reach a creek. Following it will lead you to inhabited area long before hunger could become an issue. --131.188.3.21 (talk) 13:32, 26 April 2009 (UTC)[reply]
To clarify, most fish can only survive in one environment or the other, but there are some, such as salmon, which can handle either fresh- or salt-water. StuRat (talk) 07:38, 24 April 2009 (UTC)[reply]
"exact" is a tough thing here...the earth isn't a billiard ballapparently, it is...see below! But the numbers from the Earth article that TravisAF quotes above are pretty reasonable. The standard for the shape of the earth that is most commonly used in exacting applications is called 'WGS-84' or World Geodetic System from the World Geophysical Survey of 1984. The values it gives are the best "mean sea level" description of the shape available - and I presume that the numbers above are from that definition. However, if you stretched a piece of string around the circumpherence of the planet then measured it - the answer would not be exactly that given above - and the result would vary depending on where you measured it - and probably on where the sun and moon were at the time because shape of the earth is affected by tides. It's probably also worth mentioning that the surface of the earth is like a fractal - so a precise measurement even at a particular moment in time and a particular direction over the planet is going to suffer from the Coastline paradox (see also: How Long Is the Coast of Britain? Statistical Self-Similarity and Fractional Dimension).
"The earth isn't a billiard ball". From the above figures the earth's circumference varies by only a few parts in a thousand. Are billiard balls that accurately spherical? And the bumps in the earth are less than one part in a thousand. Are billiard balls smoother than that? DJ Clayworth (talk) 15:09, 24 April 2009 (UTC)[reply]
From Earth: "Local topography deviates from this idealized spheroid, though on a global scale, these deviations are very small: Earth has a tolerance of about one part in about 584, or 0.17%, from the reference spheroid, which is less than the 0.22% tolerance allowed in billiard balls." Dragons flight (talk) 15:16, 24 April 2009 (UTC)[reply]
Wow! That's a cool observation. But - an 0.17% tolerance means that when we say the circumpherence is 40,041.47 km - we're overstating the precision by a couple of orders of magnitude! SteveBaker (talk) 19:39, 24 April 2009 (UTC)[reply]
Of course, the number is almost exactly 40,000 kilometers because that was the original definition of the kilometer; it was defined as 1/10000 the distance between the north pole and the equator along a meridian of longitude; which would be 1/4th of a circumference. But you all knew that... --Jayron32.talk.contribs21:27, 24 April 2009 (UTC)[reply]
This reminds me of a study that I think appeared in the Journal of Irreproducible Results, where the authors tried to determine whether Nebraska (or maybe it was Kansas?) was indeed "as flat as a pancake". The conclusion was that it was very much flatter than a pancake. If it were only as flat as a pancake, there would be miles-deep canyons all over the place. Or something like that. --Trovatore (talk) 21:32, 24 April 2009 (UTC)[reply]
The above discussion correctly notes that the Earth is smoother than a billiard ball, but it's not quite round enough. Discussion here. --Sean22:46, 24 April 2009 (UTC)[reply]
Yes - the poles are considerably squashed compared to the equator. The problem here is that we're presented with numbers that are accurate to 10 meters! Even with (proportionately) billiard-ball smoothness - that's way too much precision. Having just one mountain or valley along your chosen "circle" will throw off your measurement of the circumpherence by vastly more than 10 meters! That number can only be the result of a specification for the idealised shape of the earth - per WGS-84's ruling on the matter. SteveBaker (talk) 00:06, 25 April 2009 (UTC)[reply]
Smoothness and roundness are similar. The way I think about it is as a "power spectrum". Using a spherical harmonic breakdown (such as the set of WGS-84 coefficients), you can actually see how much "energy" is contained at each "frequency" (really, it's not energy, because it's a geometric description, but "frequency" is a moderately reasonable word - the spherical harmonics functions map well as spatial frequencies, albeit not sinusoidal frequency). And I'm sure you could find some way to represent mass-distribution as gravitational potential energy too, so "energy spectrum" is not really such a bad terminology after all). Anyway, the point is, Earth's deviation from perfect sphere is evident at the lower-order terms of the spherical harmonic decomposition, and its roughness is evident from the magnitudes of the higher-order terms. With sufficient number of terms, (impractical and unwieldy, but definitely possible), every topographic feature could also be described. The magnitudes of those coefficients would be REALLY small (in the same way that a band-limited radio-signal has zero spectral power at "infinitely high" frequencies). Nimur (talk) 14:47, 27 April 2009 (UTC)[reply]
Name
What's the name given to a situation when you hear something going on in a dream, then you wake up to hear it going on in the real world? 58.165.23.195 (talk) 07:14, 24 April 2009 (UTC)[reply]
You might be thinking of something paranormal, such as precognition or premonition. Or you might have fallen asleep with the television on.
Sounds more like he's asking about a real-world sound making it into a dream (very possible) and then waking up with the sound still there. Nothing paranormal about it.Ā :) -- Aeluwas (talk) 08:49, 24 April 2009 (UTC)[reply]
Forgive me if I missed it, but I think I skimmed all the relevant pages on Wikipedia and didn't see anything. I've been wondering lately how the earliest links were drawn between proteins and genes. Many genetic mutations were connected to visible phenotypes long before the central dogma was developed. Was the connection with a particular protein made for any of these mutations? How were the chemical functions of the earliest studied proteins identified? Thank you. Someguy1221 (talk) 07:44, 24 April 2009 (UTC)[reply]
The current theory from my biology book is that RNA was a molecule which dabbled in several roles of the cell. It did things which we think of proteins doing--regulating the rates of reactions, and they were involved in metabolic pathways and they even stored "blueprints" for other RNA molecules (because remember, RNA can be transcribed off of another RNA strand--that is how RNA viruses do their thing, theey call it "the RNA directed synthesis of new RNA".
Also don't over hype the difference between RNA and DNA. The difference is only an oxygen on the sugar backbone. All that "difference" does is help the molecule be more stable. DNA can last several years, RNA can last only about 45 minutes on its own, without being sequestered from common reagent molecules.
The difference between RNA and protein, is well, that RNA is an acid. Both molecules owe their properties to organic chemistry. Both RNA (in the rna world) and current proteins had the same exact functional groups. However, proteins generally were more effecient, could fold better, and were recycleable.
In a way, your question could be answered that evolution took place and RNA simply became excinct because it is a fierce job market inside the cell, and well, RNA's job got sent overseas and only a few vestigial pathways still utilize RNA as a reactant in reactions today. Some even in your own cells!JameKelly (talk) 08:49, 24 April 2009 (UTC)[reply]
That answer seems a bit off topic to me... I certainly could be wrong, but the way I read the question, the OP is interested in the first example of a gene (i.e. the DNA sequence) being causally related to the protein it codes for. I think the answer you are looking for is found in the biochemistry article, which discusses the discovery and characterization of proteins. The first instance of a gene being linked to the enzyme it produces (from Biochemistry): "In 1958, George Beadle and Edward Tatum received the Nobel Prize for work in fungi showing that one gene produces one enzyme" (for research performed in the 1940's). The History of biochemistry article, which should be a good resource, is focused more on the 1800's and is surprisingly sparse on the advances of the 20th century. --- Medical geneticist (talk) 11:11, 24 April 2009 (UTC)[reply]
In addition (since the OP is interested in mutations & phenotypes) -- Archibald Garrod is widely acclaimed as the first to postulate that an inherited disorder could be due to deficiency of a particular enzyme, as in the case of alkaptonuria. However, although he made the connection in the early 1900's, the actual enzymatic deficiency was first demonstrated in 1958 and the gene mutations weren't described until 1996! In terms of the discovery of genetic mutations that cause disease, it's hard to ascribe a "first" for many things since many discoveries are made in parallel. There is a nice timeline at the National Human Genome Research Institute (http://www.genome.gov/25019887) that shows the progress from Beadle & Tatum's "one gene one enzyme" theory in 1941, the discovery of the double helix structure in 1953, discovery of the genetic code in the 1960's, development of DNA sequencing in the 1970's, to the first human disease gene Huntingtin being mapped in 1983 and cloned in 1993. Genes that are defective in chronic granulomatous disease, Duchenne muscular dystrophy, and retinoblastoma were all mapped and characterized in the 1980s-1990's, with many more following after that and still continuing today. --- Medical geneticist (talk) 13:12, 24 April 2009 (UTC)[reply]
Differential Capacitive sensors
Well i want to be very frank. I am a first year undergraduate Electrical Engg student. For joining one of my professors for a summer time project, he gave me a paper something to do with "Switched Capacitor Dual Slope Capacitance to Digital Converter For Differential Capacitive sensors". Unfortunately, being just a first year, i haven't the faintest inkling what these terms mean, except the term capacitor! I have tried searching on Google and wiki, but the sites only give highly technical information way above my head. However, i am determined to understand this topic. So can someone please explain me what the above mentioned terms are, in a down to earth, layman manner, so that a person with just basic electrical knowledge would catch the pointĀ ? Or perhaps suggest a link which does so? I am dearly in need of helpĀ !!Rkr1991 (talk) 10:13, 24 April 2009 (UTC)[reply]
Well, I'm no expert - but we can try to break up that turgid title into manageable bites:
Switched capacitor -- OK so we're going to use a switch to choose one of two or more capacitors.
Dual slope -- So the graph of some function is going to have two straight-line slopes. Probably because the slope changes when you switch from one capacitor to the other.
Capacitance to Digital convertor -- sounds like an analog to digital convertor that measures capacitance instead of voltage.
Differential Capacitive sensor -- well, whenever something is 'differential' you're either measuring the rate at which something changes or the difference between two things - this 'convertor' is clearly a 'sensor'.
So I guess (and I'm no expert either!) that this is a project to build a gizmo that measures some aspect of the capacitance of something using a computer. How it's gonna work is by somehow switching capacitors on and off. I think I'd start by searching on "Capacitance to Digital convertor" to understand how capacitance is measured digitally.
I agree that this does sound a little tough for a first year project - but that's the point of doing things like this with experts in the field. So talk to your professor. He's there to teach you - and if you don't understand what the heck this thing is - it's because (I presume) he has not yet taught you about it. That's his fault, not yours. So make every effort to read as much as you can - then go to him and ask for an explanation and a break-down of the project into bite-sized pieces.
Hopefully others here will be able to explain this in more detail.
(ec) A dual-slope analog to digital converter (ADC) is a specific type of ADC commonly used in digital multimeters. It is described in our article integrating ADC which is an alternative name for it. It is more accurate than a single-slope ADC because it lets through a greater number of clock pulses but is slower to update as a result. The "switched capacitor" bit of the title is probably referring to changes of range, which are achieved sometimes by switching the value of the integrating capacitor and sometimes by switching the value of an offset voltage or current. The "for differential capacitive sensors" is probably referring to the type of input that is being measured. Many transducers (eg displacement detector) are essentially capacitors and the quantity being measured physically moves one of the plates causing the capacitance to change. The requirement of the measuring system is thus to measure the capacitance, either absolute, or the difference between the transducer and a reference capacitor (hence differential). Of course, some of that is guesswork; for a more specific answer you will need to provide a link to the paper you are reading, or at least some of the details (author, exact title, journal, date etc) and hope someone here has access to it. SpinningSpark13:17, 24 April 2009 (UTC)[reply]
Learning something new requires juggling some number of unfamiliar concepts in short term memory. With time and effort, you can push concepts into your long term memory - once you have done that, you have "learned." When learning is difficult, that means you are encountering too many unfamiliar concepts at once to fit into your short term memory. This happens readily because short term memory is very limited - most people can only manipulate between four and seven "chunks" of information that way. Short term memory seems to work like a FIFO queue - if the unfamiliar chunks keep coming, they push earlier chunks out, and you lose them. Your emotional brain responds by generating emotions of anxiety and frustration. Long term memory, in contrast, is seemingly unlimited. As long as your brain continues to work, you can apparently just keep pushing more knowledge into your long term memory. The problem is that chunks can only move from short term memory into long term memory at a slow rate. Because short term memory is very limited, and long term memories can be slow to form, humans hit on a trick, thousands of years ago, to augment memory: writing. When you are trying to learn something that overwhelms your short term memory, you should immediately start writing. For example, read the paper you are trying to understand, but don't worry about understanding it right away. Instead, do this:
Make a list of all the terms in the paper you don't understand yet.
For each term, try searching the Web and so on, and write whatever you find that might relate to it.
Keep coming back each day, re-read the paper, review your list of terms, and see if you notice anything you missed before.
Look up all the references that the paper cites, read them, and see if any of them shed further light on your list of terms.
Identify your conceptual sticking points. You will figure out some terms sooner than others. When you figure something out, move it to the bottom of your notes. Keep the unknown items at the top.
Look for clues about the interrelatedness of terms. Probably every jargon term in the paper relates to the other jargon terms in various ways. The paper is not just a stream of consciousness list of random terms. You want to understand not only what each term means in isolation, but why the author used them all together. Sometimes you can understand the relationship between two items before you fully understand the items. See: ontology.
Show your notes to some experts, and ask them to comment. They may suggest introductory references you can read, or they may point out errors in your thinking. For example, you might have listed a particular concept more than once, because maybe the paper refers to it by synonyms. In that case, your problem got simpler, because instead of two concepts to learn, you find you only have to learn one.
I couldn't find the exact link on the net, but here are its detailsĀ : Novel Switched-Capacitor Dual Slope Capacitance to Digital Converter for Differential Capacitive Sensors by, Boby George, Member, IEEE and V Jagadeesh Kumar, member, IEEE. I hope someone would be able to find the exact paper, and then explain what exactly is the problem being approached, and the principle used in this case. I would like to add that it is not my professor's fault for not teaching this. I, being free in the coming summer, approached him for doing some extra work, and he has offered to take me in his research team as an assistant, if i can tell him what i understood from this.(He is one of the authors of this paper.) Thanks in advance for all the help.Rkr1991 (talk) 06:33, 25 April 2009 (UTC)[reply]
I would also like to thank 2 particular users - SpinningSpark and SteveBaker, who have both helped me out on numerous questions. Thanks for your time guysĀ ! And thanks to Teratornis too...Rkr1991 (talk) 07:13, 25 April 2009 (UTC)[reply]
No, I can't find it either, but I did find this and wonder if the paper you have is a pre-print of the published paper with a different title. Sorry, I don't have a current subscription to IEEE Explore so cannot read it, and it doesn't have an abstract. You might want to take a look at this book though, which you can preview in google books. SpinningSpark12:38, 25 April 2009 (UTC)[reply]
Eggplant is in the nightshade family which contains toxic substances. Hair loss may be an effect of poisoning from ingesting unripe/inedible parts of the plant or an allergic reaction. As our article notes aubergines are high in nicotine, which can cause hair loss through constriction of blood flow to the follicles and accelerated cell aging. That is for prolonged exposure and high quantities, though. I doubt the average person would regularly eat 9 kgs of eggplants. That would signify a highly deficient diet that would cause many other health effects. High doses of caffeine can also cause hair loss, while low doses actually stimulate hair growth. This page [[30]] recommends eggplant leaves as a remedy for hair loss, but I'd rate that one under "people will try anything". 76.97.245.5 (talk) 15:14, 24 April 2009 (UTC)[reply]
"Female" DNA
Google doesn't lie ... so there is "male DNA" and "female DNA" (the question for "male Cellulose" and "female proteins" (the shapely ones) comes later...). Question: When "female DNA" is found at a crime scene, does that mean that no Y-chromosome genes were found in this sample or was there another test doneĀ ? (because X-Chromosomes are found in males and females). Does "The blood in the car showed female DNA" actually mean "in the blood we found no Y-chromosome genes but lots of other genes and human markers, so it must be the blood of a woman/female"Ā ? Thanks --83.141.221.231 (talk) 14:38, 24 April 2009 (UTC)[reply]
I don't know the answer but most likely the absence of Y specific markers would indicate "female". Of course if the woman had AIS then the test would be misleading. And any test that relies on the absence of a marker is prone to contamination from other sources. David D.(Talk)14:42, 24 April 2009 (UTC)[reply]
Another possible way to confirm a "female" sample would to look at a lot of polymorphic markers on the X chromosome. A male would have only one in every case (hemizygous for X) but a female would be heterozygous for many of the markers. David D.(Talk)14:48, 24 April 2009 (UTC)[reply]
What would you see in the latter case? Female: More bands than usual (male)? Could you conclude from the complexity of the pattern whether the blood was from 1, 2, more women? In the meantime, I found the (a) (SRY-F + SRY-R) and (b) (PABX-F + PABX-R) Primer-pair approach. A male should give 2 bands, a female one band, a mix (of blood) of 2 females should give 2 diff. (PABX-F + PABX-R) results. --83.141.221.231 (talk) 15:06, 24 April 2009 (UTC)[reply]
You could not detect such a difference with PCR. It could be done using antibody pulldown, probably directed at lysine methylation on histones. In males the X sequences would far less represented than in females. But to be pedantic, what if a male had Kleinfelter's Syndrome (XXY)? Such a male would have half his X sequences silenced. And besides, the sensitivity would be problematic at a forensic level. David D.(Talk)00:58, 26 April 2009 (UTC)[reply]
You're all overthinking this. "We found female DNA" = "We did a karyotype and the sex chromosomes were 'XX"". "We found male DNA" = "We did a karyotype and the sex chromosomes were "XY". Depending on the circumstances, it may not even be as complicated as that....e.g. we found male DNA in the sperm specimen. - Nunh-huh01:12, 26 April 2009 (UTC)[reply]
Looks like you can differentially label the X and Y, so don't need a full karyotype.[31] That would also solve rare genetic combinations and multiple contributors, since it seems to allow counting of the chromosomes in whole cells. In other ideas, there are non-genetic ways to identify the sex of a biological sample, so "high levels of PSA" would mean the sample's DNA is probably male (though surprising-to-me high rate of false-positive), whereas DNA from a sample that also has high levels of various pregnancy horomones is from a female. Going the other way, if the biological sample is sperm, I can guarantee it contains DNA from a male. DMacks (talk) 07:24, 26 April 2009 (UTC)[reply]
Canis lilliputia and canis brobdingnag
What happens when a female St. Bernard/Wolfhound/Great Dane is impregnated by a male Chihuahua/Yorkshire Terrier/Toy Poodle? And what happens in the reverse situation? I assume this never happens naturally but would have to be by insemination (please correct me if I'm wrong). I imagine a very smalle female dog would have more trouble than the reverse situation, but is such a pregnancy viable? Are there any examples of such dogs carrying to term? And for the reverse, I imagine this might either kill the tiny female or, as the pup grows too big, her body will reject through a miscarriage? Or does it work that a female can carry and the combination of genes still results in a very small dog despite the large male breed? I've always wondered about this.--70.19.69.27 (talk) 21:42, 24 April 2009 (UTC)[reply]
Thank you for that link Deor. Extremely unsatisfying answers based on sheer speculation but that may be because the answers are simply unknown.--70.19.69.27 (talk) 03:37, 25 April 2009 (UTC)[reply]
I'm gonna take a stab in the dark and guess that this has to do with sorbitol, a sweetener that's often used in chewing gum and the excessive consumption of which can cause extreme weight loss due to its laxative effect. How much counts as excessive is probably going to vary from person to person, but frankly, it's not that hard to tell when you've eaten too much of it, what with the diarrhea and all. -- Captain Disdain (talk) 01:51, 25 April 2009 (UTC)[reply]
With another stab in the dark, chewing gum provides pretty much no nutrients; therefore it isn't 'necessary'; therefore it is "excessive consumption". That's taking a very extreme view that "excessive" means anything more than is necessary for life. DJ Clayworth (talk) 14:16, 27 April 2009 (UTC)[reply]
In the true spirit of modern "psychobabble", it's only too much if it is negatively interfering with other areas of your lifestyle. This tautological statement doesn't convey a lot of information, but it's used to describe a lot of addiction-spectrum conditions without making normative claims, moral pronouncements, or legal advice. Nimur (talk) 14:52, 27 April 2009 (UTC)[reply]
Line spectrum question
Doubly ionized lithium Li2+ (Z = 3) and triply ionized beryllium Be3+ (Z = 4) each emit a line spectrum. For a certain series of lines in the lithium spectrum, the shortest wavelength is 365.1 nm. For the same series of lines in the beryllium spectrum, what is the shortest wavelength?
I'm not entirely sure, but since 365.1nm is in the visible light spectrum that means it's in the Balmer series? Therefore you have to use the equation, 1/wavelength=R(1/2^2-1/n^2), and then solve for n. But when I solve for n I get 55.79 which doesn't make sense since it should be an integer. Also when I solve for n, I'm not sure where to plug that in. I'm thinking I need the equation, 1/wavelength=1.097x10^7(Z^2)(1/nf^2-1/ni^2), but I'm not entirely sure. Also I don't know which n I solved for in the original equation. 69.69.75.22 (talk) 00:08, 25 April 2009 (UTC)[reply]
You used the equation for Hydrogen. The correct equation is 1/wavelength=R(Z^2/2^2-Z^2/n^2) for a balmer series line. See Rydberg formula. The Z=1 for hydrogen, which is where you went wrong. The more general equation is needed for all other elements. --Jayron32.talk.contribs00:38, 25 April 2009 (UTC)[reply]
Forget about ni and nf. get the Rydelberg equation for the Lithium and devide by the Rydelberg equation for the beryllium. The mistery factor cancels out. Dauto (talk) 03:21, 25 April 2009 (UTC)[reply]
I need clarification on this issue. I know for endothermic solution reactions, solubility increases with temperature. Conceptually this makes sense dH is positive therefore Energy in the form of higher temperature must be invested to make this reaction happen. Secondly, Le Chatelier's principle also supports this.
Now, for exothermic reactions, Le Chatelier's principle suggests that solubility decreases with temperature since "heat" is a product here so the system will shift to reduce heat/temperature. However from a thermodynamics standpoint (dG=dH - TdS) such a reaction will be very spontaneous since dH is negative and T increases therefore the "-TdS" term becomes more negative and the overall dG is negative. Intuitively, I am slightly leaning more towards the Thermodynamics implication thinking that this scenario might be a limitation in the scope of Le Chatelier's principle.
Please explain the apparent paradox assuming there's one. I understand physics without nearly as much effort as I have to spend on rectifying chemistry!
P.S. I will try to incorporate whatever feedback this question generates into the paragraph here since I imagine that is where the information is best suited, correct?
Le Chatelier's principle is correct. To use Gibbs free energy as you've done you must assume an isobaric and isothermic process. Since the reaction is exothermic, the only way the process can also be isothermic is if the excess heat is being absorbed by the surroundings. As heat leaves the system, the change in its entropy must be negative (dS<0) throughing a wrench in your reasoning. Dauto (talk) 04:08, 25 April 2009 (UTC)[reply]
Indeed, to explain a little more; the Gibbs equation is a state function; so all values are as measured at any instant in time. It's not dTdS, its TdS, which means that the entropy value is not dependent on changes of temperature; it is dependent on absolute temperature at any point. It has nothing to do with whether the solution is heating up or cooling down, only with what the temperature is at the point where you are measuring the values. --Jayron32.talk.contribs04:30, 25 April 2009 (UTC)[reply]
Thanks for the answers. I realized I was trying to derive one from the other, but I didn't realize what I was asking. I was so stuck thinking that I just didn't see something, but the straightforward answers I have received today were very helpful and rock solid; this enabled me to reevaluate what I was seeking to find, and in hindsight I was trying to derive one from the other, which I can't so I can rest easy now and move on to the next subject. Thank you again, JameKelly (talk) 12:11, 25 April 2009 (UTC)[reply]
will 1,3,5-trimethoxybenzene react with hydrochloric acid? (Or even base?!)
I suspect it reacts with sulfuric acid, if I have my unknown correct. I didn't manage to complete an HCl or NaHCO3 reactivity test in lab however ... would the H+ attach to the ether oxygens, whereupon there is some weird nucleophilic substitution and the alkyl groups fall off (probably with some nucleophile at the end to stabilise the leaving group) and resonance stabilisation stabilises the former ether oxygen...? Or what? Why else would sulfuric acid attack 1,3,5-trimethoxybenzene? Surely it's not a strong enough electrophile (well, perhaps without the presence of SO3) to attack benzene bonds? John Riemann Soong (talk) 05:57, 25 April 2009 (UTC)[reply]
You may get some chlorine-for-methoxy substitution, but probably not in high yields, and you may also get a mixture of mono-, di-, and tri- chloro products. A low enough pH will protonate the oxygen, which will make methanol as a decent leaving group. The chlorine is likely just a good enough nucleophile to substitute here. --Jayron32.talk.contribs17:19, 25 April 2009 (UTC)[reply]
Yup, protonation of an ether oxygen is pretty good bet. But then I'd think more ikely to hydrolyze (I assume your "sulfuric acid" is a few-molar aqueous solution?). the Me-O side of this ether than the O-Ar side. Once you're at an oxonium, SN2 nucleophilic attack on the methyl seems easier than first going to an even less stable structure like aryl carbocation (SN1...can't do SN2 on an sp2 center). DMacks (talk) 07:01, 26 April 2009 (UTC)[reply]
I'm trying to find out why it would react with sulfuric acid (the bottle / lab manual said "concentrated"), but not 5% HCl ... I guess it was just the acidity of the solution? John Riemann Soong (talk) 08:00, 26 April 2009 (UTC)[reply]
Doesn't your textbook/lab-manual tell you what sorts of functional groups give a positive test for each of your qualitative analysis methods? Is conc. sulfuric a test for ethers or for aromatics? Your text (if it's any good) or other class materials would explain why/how each one behaves under the various test conditions. What exactly makes this test "positive" (something dissolves, precipitates, changes color, releases a gas, catches fire, ...)? DMacks (talk) 06:31, 27 April 2009 (UTC)[reply]
If the remainder of the solution isn't very volatile, and you aren't concerned with keeping it sterile, you can just leave the solution exposed to the air until the water evaporates. This could be done, for example, to create sea salt from sea water. StuRat (talk) 20:43, 25 April 2009 (UTC)[reply]
The blast radius of a nuclear bomb is a few miles, so let's be generous and say that 100 square miles would be affected. The area of Antarctica is about 5,000,000 square miles. That's 50,000 bombs - more than the U.S. and Russia have combined. That's not taking into consideration the fact that the ice can be quite thick, so one bomb probably wouldn't melt all of it in its assigned sector. Clarityfiend (talk) 09:39, 25 April 2009 (UTC)[reply]
(After edit conflict; another big number) Well, a typical nuclear test can create a crater hundreds of metres across, but that is still very small compared to the size of a whole continent. So let's crunch some numbers. Antarctica article says area of Antartica is 14 million km2 and 98% of the continent is covered by ice with an average depth of 1.6 km. So that is about 22 million km3 of ice. That has a mass of about 22 x 1018 kg. For simplicity, let's assume this is all just on the point of melting (so we ignore the heat required to warn it up to 0oC). Water (data page) says latent heat of fusion of ice is about 6 kJ/mol. 1 mole of ice has a mass of about 18 grammes, so 22 x 1018 kg is about 1.2 x 1021 moles, which will require about 7.2 x 1024 J of heat to melt it. One megaton is 4.184 x 1015 J, so 7.2 x 1024 J is about 1.7 x 109 Mt. The most powerful hydrogen bomb ever tested had an energy yield of 50 Mt. So to melt all the ice covering Antarctica, you would need at least 35 million hydrogen bombs, even if all if the bombs' energy was released as heat energy and absorbed by the ice. Gandalf61 (talk) 09:47, 25 April 2009 (UTC)[reply]
Agreed. By an independent calculation based on very similar assumptions I got an estimate of 50 million bombs. You could probably achieve the same effect with much less energy by painting the ice black and letting the sun do the work. --Heron (talk) 11:44, 25 April 2009 (UTC)[reply]
The first few bombs might result in dark dust falling on the rest of the ice, so it might not be necessary to paint it all, just use a few nukes. --Tango (talk) 14:51, 25 April 2009 (UTC)[reply]
I don't see where the dark material would come from - you're mostly blowing up kilometers-thick ice - what's going to get chucked up into the air will be water-vapor. Even dark dust would get tossed into the upper atmosphere. That would tend to block the sun - making the continent colder - and reducing the amount of melting. That's been a notable effect of large volcanoes and such. It's hard to predict - so it's far from obvious which effect wins. SteveBaker (talk) 15:39, 25 April 2009 (UTC)[reply]
Drop the bomb on a bit with thinner ice so you expose the ground underneath. I seem to recall using bombs to spread dark dust over ice to make it melt being proposed in the context of terraforming Mars - perhaps it wouldn't work so well on Earth, with a thicker atmosphere to hold onto the dust. --Tango (talk) 16:22, 25 April 2009 (UTC)[reply]
Nuclear weapons are very powerful against human-sized targets. But not geographical-sized targets. You could easily make a large area uninhabitable for humans with exceptionally "dirty" hydrogen bombs. But melting, totally destroying it, no. No more than you could crack the planet in half with nukes. --98.217.14.211 (talk) 17:31, 25 April 2009 (UTC)[reply]
Nukes alone would not do it, but there might be another way. If we were to find a large asteroid (or more), we could use nuclear pulse propulsion on it, and direct it towards Antarctica. It wouldn't be very easy with our current technological level, but I think it can be done. 69.69.75.22 (talk) 17:50, 25 April 2009 (UTC)[reply]
Yes, that might work. Antarctica wouldn't be an easy target, though. Most asteroids are in the plane of the solar system so for them to hit Antarctica it would need to be a "glancing blow". There wouldn't be much margin for error (too much one way, you miss Antarctica and hit something else, too far the other way and you miss the Earth entirely) and it would have to travel through more atmosphere, so more of it would burn up before impact so you would need to start with a larger asteroid (which means more nukes, or whatever else you use, would be needed to propel it). --Tango (talk) 18:57, 25 April 2009 (UTC)[reply]
It would be easier if you pick an asteroid with more or less the right orbit to start with. You need an earth-crossing asteroid with a highly inclined orbit, preferably eccentric as well. 1866 Sisyphus fits the bill but might be a little too big - it would be the dinosaurs all over again. I recommend 2102 Tantalus as a candidate missile. SpinningSpark22:35, 25 April 2009 (UTC)[reply]
Exploding a nuke directly over Antarctica probably wouldn't melt the continent, but exploding a few in the most vulnerable areas to subglacial seepage (which would undermine parts of the ice shelf) might do the trick. For example, Pine Island Bay in West Antarctica, and the Totten and Cook glaciers/ice shelves in East Antarctica. ~AH1(TCU)01:33, 26 April 2009 (UTC)[reply]
What's more, Antarctica is a continent ā a ton of explosions would melt the ice cap at a particular location, but you couldn't melt the continent any easier than you could melt land anywhere else. Nyttend (talk) 12:42, 26 April 2009 (UTC)[reply]
That's a good point. We interpreted the question as "melt the ice cap that covers Antarctica", but that isn't actually what the OP asked. --Tango (talk) 21:23, 26 April 2009 (UTC)[reply]
There is something I really don't understand. The North American Plate includes both continental and oceanic crust. Therefore, I imagine that the younger oceanic crust, which comes from the Mid-Atlantic Ridge, subducts under the older continental cruster (otherwhise, I guess there wouldn't be any old continental crust). But there is no convergent boundary within the North American Plate! Where is my mistake? Where is going the oceanic crust? Enherdhrin (talk) 10:48, 25 April 2009 (UTC)[reply]
PSĀ : sorry for my english.
The oceanic crust in the Atlantic isn't subducting; it's just pushing North America farther westward as it's created at the Mid-Atlantic Ridge. The subduction is taking place on the other side of the continent, as the westward-moving continental crust overrides the Pacific Plate. Deor (talk) 13:15, 25 April 2009 (UTC)[reply]
The explanation above is correct. I'm curious about that statement: "I imagine that the younger oceanic crust, which comes from the Mid-Atlantic Ridge, subducts under the older continental cruster (otherwhise, I guess there wouldn't be any old continental crust)." I don't understand your logic. There is no subduction zone on the east side of the northamerican continental crust, And yet, the continental crust is much older than the oceanic crust right next to it. I don't understand why you would think that's a contradiction. I isn't. Dauto (talk) 14:01, 25 April 2009 (UTC)[reply]
New oceanic crust is always being created at the Mid-Atlantic ridge, so the North American Plate always gets bigger, but the land area stays the same. The crust near the ridge at a certain distance is always of a certain age, but the crust closer to the continental shelf gets older and older, as does the land itself (discounting any newer orogenies). The expansion of the plate does not present a contradiction because plates are always being subsided somewhere else. ~AH1(TCU)01:19, 26 April 2009 (UTC)[reply]
The North American Plate is growing; the "continental" portion of it stays about the same size, and the "oceanic" portion is being added to at the Mid Atlantic Ridge. This is not a problem, since other plates, especially the Pacific Plate, are actually shrinking as they are being subducted under several plates, including the North American Plate. Crust creation and subduction is a zero-sum game, but not per plate, only over the whole earth. The individual plates are shrinking and/or growing based on what is happening at the plate boundaries.--Jayron32.talk.contribs01:33, 26 April 2009 (UTC)[reply]
@DeorĀ : thanks for your reply. @DautoĀ : AH1 and Jayron32 have perfectly analysed my mistakeĀ : I falsely assumed that the size of the North American was fixed. Thanks to all of you for your explanations.Enherdhrin (talk) 11:30, 26 April 2009 (UTC)[reply]
Male/female ratio
Seeing as both the birth and death rates are higher in males than in females, which gender is more prevalent in the world: male or female? 58.165.23.195 (talk) 13:42, 25 April 2009 (UTC)[reply]
All your questions are answered at human sex ratio. In short, more boys are born than girls (105:100), possibly an evolutionary method to balance out the ratio, although sex-selective abortion and female infanticide heavily skew the numbers in some countries. But demonstrating precisely what you said, the male:female ratio gets considerably skewed the other way in older and older populations. In some countries, the ratio amongst people over 65 is 70:100 or worse. Someguy1221 (talk) 13:54, 25 April 2009 (UTC)[reply]
I recall reading once that males are more likely to die in the womb but the ratio at birth was as you say, something like 105:100. This surprised me at the time and no explaination was offered. I presume most likely there's something going on earlier then is being detected here, e.g. females less likely to be implanted, male sperm more successful in fertilising ova (which entails a whole lot of possibile reasons), more male sperm etc. Alternatively sex selective abortion is more widespread then people realise. The book was a rather old sociology book so there may be more info available now. Nil Einne (talk) 19:48, 25 April 2009 (UTC)[reply]
Social Science/Sociological Question: What is the difference between Modernity and the Enlightenment?
Modernity and the Enlightenment are majoratively written about as two seperate entities, although they share similar features and are sometimes interlinked as one and the same. Please can someone identify what the features are that distinguish between the two? āPreceding unsigned comment added by Sheepdisease (talk ā¢ contribs) 14:42, 25 April 2009 (UTC)[reply]
The Enlightenment is a period; Modernity is a state of mind. Enlightenment leads to Modernity. Such is a very crude way to think about it but it mostly works. Both terms are rather vague (esp. modernity, which basically stands for whatever one wants it to). --98.217.14.211 (talk) 17:36, 25 April 2009 (UTC)[reply]
Storage of medicines
I've seen it many times that on the packaging of medicine it says "store at room temperature." I wonder why they don't say "store at a temperature below X Ā°C/Ā°F" instead. I think most medicines are not harmed by low temperature. (I can't imagine all over-the-counter medicines are transported in heated trucks during the winter months. Short-term exposure to low temperature must be OK for most of them.) What are some mechanisms by which medicines will go bad when stored at low temperature? (I can think of one: some components of a mixture crystallize out and settle at the bottom of the container, thereby changing the composition of the mixture.) --173.49.78.81 (talk) 15:40, 25 April 2009 (UTC)[reply]
They may just say that to clarify that they don't need to be refrigerated. If there was a maximum temperature (that wasn't so high as to be unnecessary to warn against) that they could be stored at, I think it would say so. --Tango (talk) 16:51, 25 April 2009 (UTC)[reply]
Also, need to target the lowest common denominator of consumer, who doesn't know what the actual numerical temperature is. So "room temp", "cool, dry place", "refrigerate" are clear and are good enough descriptions for safe and enough storage to have the expiration date be reasonable. Also, no reason to confuse people into storing stuff in the fridge "just to be sure I don't exceed this temperature" (people don't know how close they need to be or how long and how much too hot is bad...what the hell is a "degree"?). Yes, I have a jaded view of the typical consumer:( Some (and many more, more recently) do actually also specify a maximum temperature. One problem with fridge isn't the low temp, but that the low temp leads to condensation, and water can lead to pills losing structural integrity and also major chemical changes for things that need to be stored "dry" as well (a good Slow News Day evening news topic is how bad it is to store medicines in the cabinet next to a steamy hot shower). DMacks (talk) 18:59, 25 April 2009 (UTC)[reply]
In the case of dry meds, generally the colder they are stored the longer they will last. In the case of liquid meds, it may be important to avoid freezing, so the colder you can store them, without risking freezing, the better. As to why the manufacturers don't include such info; it simply wouldn't increase their profits to do so. First, they'd have to spend lots of money to determine how long their med lasts at various temps. Then they would also lose money if people are able to use old meds which otherwise would have been tossed out and replaced with new meds. So, they do the bare minimum and give some relatively short period for which they know the meds will last at room temps, and call it good enough. StuRat (talk) 20:34, 25 April 2009 (UTC)[reply]
I guess the next question is: Why don't countries impose laws on drugs companies requiring them to include such information? Probably because the benefit would be minimal and it isn't worth annoying people with extra red-tape. --Tango (talk) 23:40, 25 April 2009 (UTC)[reply]
From my past experience working within the Pharmacological Industry (*see disclaimer below) - Governments (via Regulatory Bodies like the FDA (US), MHRA (UK) etc) do expend considerable resources on determining and specifying exactly what information drugs companies should and must include on/in their products' packaging and information leaflets. Similarly, every drugs company expends considerable resources on complying:
Because if they don't they face potentially onerous penalties (even if no harm results - I know of one company forced into closure because it failed to properly maintain documentation proving its compliance with manufacturing regulations);
Because they don't want to hurt profits by actually harming their customers;
And because, believe it or not, most Pharma Industry people are decent human beings with consciences who genuinely want to provide the best and safest medications they can.
This leads me to conclude that such basic information as storage instructions, that has been scrutinised and worked on by both Regulators and Manufacturers, is likely to be about as appropriate as it can be. (Assuming a legitimate source - counterfeiting drugs and their packaging is a major global industry.)
(*Disclaimer: I was employed by a contracting company to administer facilities maintenance at a drug manufacturing/packaging/distribution site, but no longer have any connection with, or have any reason to doctor spin for, "Big Pharma.") 87.81.230.195 (talk) 19:45, 26 April 2009 (UTC)[reply]
Expansion of the universe
Is it true that the universe is expanding at an increasing rate? Meaning it's expanding faster now than it did billions of years ago? Also this statement found on the article, Metric expansion of space confuses me. It says, "The metric expansion leads naturally to recession speeds which exceed the "speed of light" c". What does "recession speeds" mean? 69.69.75.22 (talk) 17:44, 25 April 2009 (UTC)[reply]
Yes, current observations support an accelerating expansion. Recession speed means the speed at which two objects are moving apart (usually with us as one of those objects). We observe distant galaxies which have redshifts corresponding to them moving away from us faster than the speed of light. For normal motion, that is impossible, but since it is the universe itself expanding, rather than just objects moving through space, that rule doesn't apply. --Tango (talk) 18:53, 25 April 2009 (UTC)[reply]
To clarify: Those galaxies were not receding from us faster than the speed of light when the light we now observe was emitted. And, as best as we currently can determine, the universe's expansion first slowed down, and then sped up again. So if you asked "billions of years ago", you have to be specific. Current thinking is that gravity pulls the universe together, but dark energy pushes it apart. When the universe was smaller, gravity was the dominant force, slowing the expansion down. However, the universe still grew past the threshold where dark energy overtook gravity as the most significant large-scale force. --Stephan Schulz (talk) 23:46, 25 April 2009 (UTC)[reply]
Actually most of them were receding faster than c when they emitted the light we now observe. Recession speeds have mostly been decreasing since the big bang, so if they're larger than c now they were even larger in the past when the light was emitted. (There has been a slight increase recently, but only slightāthe predicted exponential expansion is still in the future.) In the diagram on the right, the red line is light emitted by the yellow object (a distant quasar) and detected 12ā13 billion years later by the brown object (Earth). Cosmological time is measured vertically from the cone's apex to its base, and distance is measured circularly around the cone (as shown by the orange line). The "recession speed" is the change in that distance over time. It can increase faster than c = 300,000 km/sec, but there's no direct connection between that and the speed of light, which is a local limitation on the angle that these lines can be tilted from the vertical. It's kind of hard to see in this image (easier in the top-down view), but the distance between us and the light increased at first, which means that the distance between us and the quasar was increasing faster than c then (and still isāthe speed is around 2c now and was around 3c then). -- BenRG (talk) 12:48, 26 April 2009 (UTC)[reply]
Just by the way, any observations of increased redshift in objects that already have an enormously large redshift would not indicate an accelerating expansion, because those objects are seen as they were farther in the past to begin with. Therefore, the acceleration would have to have been determined by other sources. ~AH1(TCU)01:04, 26 April 2009 (UTC)[reply]
The expansion affects the light in transit, so redshifts do contain information about the expansion after the light was emitted. Specifically what the redshift tells you is a(now)/a(then), and what you want to know is a''(t). If you measured the redshift of the cosmic microwave background for a long time (i.e. keeping "then" fixed while varying "now"), then an acceleration in the redshift would be direct evidence for accelerating expansion happening now. But we haven't been doing astronomy nearly long enough for thatāthe predicted rate of acceleration is about 0.3% per billion years per billion years. A better technique is to look at many objects at different redshifts, which amounts to varying "then" while keeping "now" fixed. The first actual evidence for accelerating expansion came from redshift measurements of type Ia supernovas out to zā1, which is several billion years back, enough to see a (somewhat noisy) trend. -- BenRG (talk) 12:48, 26 April 2009 (UTC)[reply]
acid
I went to the store but they only had 5% vinegar for sale remainder is water. Does anyone know a simple way that I can concentrate the vinegar I get from to store to 25%? Wikivanda199 (talk) 18:27, 25 April 2009 (UTC)[reply]
Acetic acid (the key ingredient in vinegar) boils at a slightly higher temperature than water (118C) and the combination doesn't form an azeotrope, so distillation should work. Boil the vinegar and more water will evaporate than acetic acids so what you end up with should be a higher concentration of acetic acid than you started with. Keep boiling it until you reach the desired concentration. --Tango (talk) 18:50, 25 April 2009 (UTC)[reply]
Many chemical supply companies will sell "glacial" acetic acid, which is about as concentrated as you can get. You can order some of that and dilute it down to 25% also. --Jayron32.talk.contribs18:56, 25 April 2009 (UTC)[reply]
Check also gardening, cleaning-products, and photo-lab suppliers (not sure what concentration is sold for stop bath)--lots of strong (and reasonably priced) chemicals. Googling around, apparently there are some vinegars that are much higher acid concentration than normal. DMacks (talk) 19:15, 25 April 2009 (UTC)[reply]
I've never seen it elsewhere, but a local East Asian food shop sells 5x concentrated white vinegar. (Strangely, it's from Germany. I think it's called "Essig Essenz". There's a warning on the label in big, bold letters "DILUTE BEFORE USING".) You might be able to get it at a specialty shop, or order it online. -- 75.42.235.205 (talk) 19:49, 25 April 2009 (UTC)[reply]
"Essig-Essenz" is commonly available in German supermarkets. It's sold as a food item with other vinegars, but is used for both food and non-food applications, in particular cleaning of tiles, or anything that suffers from lime build-up and can stand acid. For consumption, it is very boring and without real flavor if diluted with water, but it can be diluted with other fluids, in particular wine, to make e.g. interesting salad dressings. --Stephan Schulz (talk) 08:41, 26 April 2009 (UTC)[reply]
Ebay.com has a number of suppliers under "acetic acid". You can also look under "vinegar", but there are so many things under that category you should limit the search to "everything else." (that would include food). āPreceding unsigned comment added by 98.21.107.30 (talk) 21:15, 25 April 2009 (UTC)[reply]
Well if you had 25% vinegar and wanted to get down to 5%, you would just add water. So what you want is to add negative water. What is negative water? Well, for one thing, it could be water owed. So maybe you could buy the appropriate amount of distilled water on your credit card or borrow it from a friend and so on with your slips. I haven't worked out all the specifics however mathematically I believe my reasoning is correct. Let us know the results. 79.122.60.88 (talk) 12:48, 26 April 2009 (UTC)[reply]
That sounds like something out of an adventure game. I remember one that had a packet of "Instant something-or-other" with the instructions "Just add nothing!", so you had to add the contents of an empty bottle to it. You idea is much the same, just taken to a greater extreme. --Tango (talk) 21:17, 26 April 2009 (UTC)[reply]
How about adding NaOH or KOH as you have acetic acid in your diluted vinegar, and then evaporate all the liquid...you'll have solid sodium (or potassium) acetate left. Add to it an equivalent amount of hydrochloric acid having (at least) the desired concentration of acetic acid you want. Now you've got acetic acid and salt at whatever concentration the acid was. Distill it if you don't want to have any salt present--don't have to worry about being careful to separate the acetic acid from the water (which is pretty hard unless you have a good still from what I hear). DMacks (talk) 21:46, 26 April 2009 (UTC)[reply]
April 26
radical addition of alkynes
There are two (pencil and paper) subsyntheses I would like to make (well the reason I'm adding halogens is that I'm trying to attach the products onto an aryl group later, but that's not the issue). Can I check that the following ideas are valid:
first synthesis
First synthesis: I know alkene reactivity > alkyne reactivity, but would it be possible to use acid-catalysed hydration of just the alkene bond? If I set the temperature low enough, it would be possible to get a major product where I just added to the alkene bond but not the alkyne bond, right?
In addition, how would I design the reaction so I can "stop" at the alkene stage, and not do a double-hydrobromination? (My textbook says you can stop it for normal Marvkovnikov addition, without commentary on radical addition, such that you don't form geminal halides, but I have no idea how you would detect the optimal formation of your alkene product such that you could stop the reaction on time.)
In addition, does the overall idea of radical (anti-Markovnikov) addition of Br to an alkyne bond work? Are radical stability effects magnified such that the formation of 2-bromo product is limited? I assume that the radical addition for alkenes is much faster than the carbocation formation step, hence why the radical effect dominates, but is a radical on an sp-carbon going to be more unstable than say a radical on a secondary sp2 carbon? John Riemann Soong (talk) 08:34, 26 April 2009 (UTC)[reply]
second synthesis
Second synthesis: Assuming the validity of radical addition to an alkyne, this second synthesis seems to imply I would get a cis-product as well as a trans-product. I only want the trans-product. Is it possible to design a reaction that favours the formation of trans-product? (The formation of diastereomers isn't important for my first synthesis.) John Riemann Soong (talk) 08:34, 26 April 2009 (UTC)[reply]
Enhancement by implants
More and more often I would find a third arm or an implanted wlan interface to my computer very useful. Being in a hurry very often, I would greatly appreciate a way to put on my socks while continue to operate the keyboard, just as an example. Or to make a phone call, talking silently via some future-style nerve-reading interface while listening to some slow talking time-sucker on the normal phone.
I know this is far from practice, at least for otherwise healthy people (and thus this is not asking for medical advice), but what is the state of art for such enhancements? (Well, I know I could buy a headset for a start ...) 93.132.137.0 (talk) 11:45, 26 April 2009 (UTC)[reply]
Well - perhaps not as far as you think. If you'd be prepared to use your real hands for putting on your socks on, there is a guy who has demonstrated typing by thought alone ([32]). See Brain-computer interface for example. At present, it's rather slow (eight characters per minute!) - but it's getting there. There are plans to sell a starwars-themed toy that lets you control the motion of a ball moving up and down a tube by thought alone: [33]. So it's certainly possible. SteveBaker (talk) 14:54, 26 April 2009 (UTC)[reply]
The thing that has real prospects is "add-ons" to replace things that are missing, such as an amputated limb. The big problem with wholly new things like a third arm is that you don't have any brain circuitry to manage them. There are some tricks that potentially could be used to reconfigure brain circuitry that has other functions, but none of them are likely to come into play very soon. Looie496 (talk) 16:47, 26 April 2009 (UTC)[reply]
The strange thing is that when I try to put on my socks while brushing my teeth and wanting to do even more in parallel (but not attempting for certainty of failure) I really feel like I could handle a third or forth arm. After all, I frequently pick up things with my feet. (Maybe I was a spider in some previous life.) As for the links from Steve Baker (thanks!), they made me realize I won't need any extra limbs implanted when there is/would be the possibility to steer some detached actuators instead --- a kind of real-science telekinesis. 93.132.137.0 (talk) 22:04, 26 April 2009 (UTC)[reply]
Earthrise on the Moon
Earthrise, today's featured picture at Commons
Today's featured picture at Commons has the following caption: "Taken by Apollo 8 crewmember Bill Anders on December 24, 1968, showing the Earth seemingly rising above the lunar surface. Note that this phenomenon is only visible from someone in orbit around the Moon. Because of the Moon's synchronous rotation about the Earth (i.e., the same side of the Moon is always facing the Earth), no Earthrise can be visible from the surface of the Moon." I can understand this very well. However, would you always see the exact same scene? Would Earth appear to be basically a circle in the sky that doesn't move? Or would it move somewhat because the Moon isn't always precise-to-the-millimetre facing the same way? Just curious...Nyttend (talk) 12:55, 26 April 2009 (UTC)[reply]
It would appear as the Moon does from Earth, just larger -- that is, it would exhibit phases as well as size changes due to orbital eccentricities and the libration that allows us to see more than half the Moon. ā Lomn12:59, 26 April 2009 (UTC)[reply]
From the perspective of someone standing on the surface of the moon, the earth would stay in more or less the exact same place in the sky, hour by hour, day by day, year by year (it would move a little because the moon 'librates' - see image at right) - but as the long lunar day progresses from dawn to dusk to night, the earth would go through phases - just as the moon appears to go through phases from earth. SteveBaker (talk) 14:45, 26 April 2009 (UTC)[reply]
I haven't seen anything written about this, but the Earth would almost certainly have to move slightly, because the Moon's orbit is slightly elliptical rather than circular, and in addition is perturbed by the Sun. Looie496 (talk) 16:37, 26 April 2009 (UTC)[reply]
Also of course you would see evolving cloud patterns on the surface and a complete rotation every ~25 hours. It would be a lot more dynamic than the view we have of the Moon. -- BenRG (talk) 18:46, 26 April 2009 (UTC)[reply]
Googling on "libration in longitude", I found a page at demonstrations.wolfram.com that says the extent of this libration is 6Ā°. Since the Earth's visual diameter as soon from the Moon is about 2Ā°, it follows that there are parts of the Moon -- ones that we see roughly edge-on from the Earth's surface -- where you could indeed see the Earth rise. It would never come very high above the horizon, and later it would turn around and set in practically the same place, the whole cycle taking about a month. --Anonymous, 21:25 UTC, April 26, 2009.
This "almost stationary" earth phenomenon was a critical element of Apollo's lunar surface S-band communications antennae, which where directional and set up to point to one spot in the sky (towards Earth). Nimur (talk) 15:09, 27 April 2009 (UTC)[reply]
A new article on an interesting supernova. I'm an astronomy amateur and would therefore appreciate review of the text by someone with a little more experience. Thanks, āAnonymous DissidentTalk13:32, 26 April 2009 (UTC)[reply]
One of the missing info would be, is it in the Milky Way, in what galaxy, what distance? How fast did it rise and dim, to what magnitude (visible for whom?). All that theoretic stuff that now is in the article would just be a chapter. --Ayacop (talk) 18:20, 26 April 2009 (UTC)[reply]
I'm fairly sure I know the answer to this - but I need some evidence. At my local car club, we restore a lot of rusty old wrecks. Getting rid of rust is obviously important - but what I want to know is whether rust spreads because the rusty metal traps water and salt better than smooth metal - or whether it's because the existing rust is acting chemically as some kind of catalyst for reaction. It's obvious that rust starts as a little spot and then grows - it's just a question of what that mechanism is. I'm pretty sure it's not a chemical effect - but there is a big argument about it that needs resolving.
I think iron rust spreads because it's flaky. It exposes the material below to further rusting. (This is from something that I read about why iron and steel rust but aluminum doesn't. Catalysis was not mentioned.) --173.49.78.81 (talk) 15:38, 26 April 2009 (UTC)[reply]
As I understand it (which may not be very far), rusting is an example of electrochemicalcorrosion and any initial defect in the protective paint layer forms an anode with a current formed through the water (which is why salt water is so destructive because of its high conductivity). This link has some further explanation [34] which you may find useful. BTW both chloride and sulphate commonly act as catalysts in rusting. Mikenorton (talk) 19:00, 26 April 2009 (UTC)[reply]
I agree - rust is electrochemical, so it will induce local static voltage in the electrically connected metal. Because the rust is a worse conductor than the "pure" iron (or steel/alloy), it has some resistivity and the voltage does not equalize; current flows; and this current encourages the further rusting. (Those electrons have to go somewhere - and they go to the oxidation reaction, encourage it, and move along to the next spot). You can weld on some extra metal like Zinc to preferentially absorb that current, but I've never heard of this being used on a land vehicle (I'm no auto-body expert though). Anyway, I think this is neither mechanical (flaking) nor catalytic because the existing rust is actively participating in the electrochemical reaction throughout the entire connected surface. Nimur (talk) 15:14, 27 April 2009 (UTC)[reply]
On high-speed tallow candles
The Dictionary of Misinformation(a trivia book dedicated to debunking common misconceptions), in a section about the claims that a botfly can fly at 800 mph, says that "a tallow candle will penetrate a board at such a velocity". Is this true? I recall the Mythbusters refuting a similar proposition about a straw penetrating through a tree trunk in a hurricane(about 300 mph wind speed), but 800 mph is more than twice that, so I'm not sure how to extrapolate from that to the presumably softer candle. 69.224.37.48 (talk) 18:38, 26 April 2009 (UTC)[reply]
The Botfly thing has been debunked over and over (Here, for example) - one good reason being that it would have to consume more than it's own weight in food every few minutes in order to be able to produce that much energy.
But I wouldn't be quite so quick to dismiss the idea of the candle going through a board at 800mph. It's not the hardness of the candle that matters so much as the mass. When any object hits any other object and is stopped - all of the kinetic energy that the moving object had has to go somewhere. A candle weighs...I dunno...0.1kg let's say. At 800mph - 350 ms-1 it's going about a third of the muzzle velocity of a 50cal bullet with about three times the mass. But kinetic energy is proporitional to the SQUARE of the velocity - so it's going to deliver only about a third of the 'punch' of a modern 50cal bullet. However, the target is a "board" - perhaps just a half inch of wood. I've seen karate people smash "boards" with their open hands. I think that an 800mph candle would go through a "board" like a knife through butter!
The Mythbusters did point out that a straw couldn't go through a tree trunk - but they did get them to penetrate a fair way into the trunk (a tree trunk is a lot thicker than a board) - and they found that a heavier projectile would do considerably more damage. A candle weighs maybe 50 times more than a straw, we're talking about it going almost three times faster - so perhaps 450 times more energy - and through a 1/2" board rather than an 8" tree...I think that's no problem at all!
It would probably be seriously deformed (unless you shaped it to be very aerodynamic), but it is very difficult to stop something that is moving that fast - unless it had to travel a long distance through the air, I'm pretty sure it would make it in some form or other and, as Steve says, all that really matters is the mass, what form that mass is in is pretty much irrelevant. --Tango (talk) 22:54, 26 April 2009 (UTC)[reply]
Besides - the original "thought experiment" didn't say there was air - we may therefore assume the whole thing happen in a vacuum. At any rate, it's pretty much specified that the candle hits the board at 800mph...who knows how? SteveBaker (talk) 02:49, 27 April 2009 (UTC)[reply]
The board is toast. Same as if the board moving 800 mph in vacuum hit a stationary candle. Same as if foam space shuttle insulation hit a carbon fiber wing surface at several hundred miles per hour. Edison (talk) 04:42, 27 April 2009 (UTC)[reply]
I'm confused - the tallow candle is propelled to high velocity by some external energy source? Is it possible that they are using the (archaic) usage of "candle" to mean "rocket"? (This seems unlikely since they call it a "tallow candle", but a modern hybrid fuel rocket can work on paraffin with pretty good combustion). Is the idea that at 800 mph, even something as soft as tallow can penetrate a solid object? I'm also thinking that the flame exit velocity of a regular candle could actually be close to 800 mph (transsonic at high temperatures) in a very local sense; but I don't see how this convective flow would penetrate a board at 800 mph (unless the board is not combusting but is acting as a rocket nozzle or venturi tube... in that case, the flame gases could easily exit at 800 mph if confined to a small hole. Nimur (talk) 15:28, 27 April 2009 (UTC)[reply]
Battery Disposal
I decided to so some spring cleaning this weekend and my project turned up a ton of alkaline batteries. I raed on my the website for my community waste disposal agency that batteries manufactuerd after 1996 don't have lead in them and can be disposed of safely with regular garbage. Thing is, I have no idea how old these batteries are: no dates! are there any indicators I can look for to indicate lead safety? Thanks --Shaggorama (talk) 20:38, 26 April 2009 (UTC)[reply]
I have no idea about procedures in MD, but in the EU every supermarket provides receptacles for spent batteries. They all (I believe) contain heavy metals which is bad for the ears, not to mention refuse dumpsĀ :) --Cookatoo.ergo.ZooM (talk) 22:19, 26 April 2009 (UTC)[reply]
Best is a matter of opinion. You must explain to use what you define as being "best" to get an answer there. As for most durable (and ignoring the astroturf answer), tall festuca is popular for high-traffic areas that require durable grass. There are many types, so it is usually possible to find a type that grows in most areas that have sunshine. -- kainawā¢23:25, 26 April 2009 (UTC)[reply]
Hi. This is from a question that didn't really get answered last time, but hopefullt this is answerable. Let's say you have a depression in the land, and water is starting to fill it. I want a general formula that calculates the amount of time needed for water to completely fill the depression. I know parameters such as the average and maximum depth of the area, the elevation at which the water is coming, the area of land filled, the length that the water initially needs to travel in order to meet the lowest point, whether the depression is dry or already has water in it, etc. Would I need any other information such as the salinity of the water, the temperature, the curvature of the Earth, the density of the rock, the air pressure in the depression, the wind direction and speed, etc? Does the formula, d = t2(a/2) (where d is distance, t is time, and a is acceleration (9.98 m/s)) be related to this formula? Thanks. ~AH1(TCU)22:39, 26 April 2009 (UTC)[reply]
Surely all the information you need is the volume to be filled and the rate at which the water is flowing in? Divide one by the other and you have your answer. --Tango (talk) 22:49, 26 April 2009 (UTC)[reply]
Perhaps, but I need to calculate the rate at which the water is filling in, from parameters such as the depth of the depression using a type of formula. So, how do I do this? ~AH1(TCU)22:53, 26 April 2009 (UTC)[reply]
If the water is falling in from above the depression, then Tango is entirely correct: flow rate and volume are the only necessary parameters. If you add in drainage, you may need to move up to a differential equation, but even then, salinity and all that should be irrelevant. ā Lomn01:14, 27 April 2009 (UTC)[reply]
The rate the water is filling it in is something you need to measure, you can't calculate it without far more information that it is reasonable to have (assuming you are talking about a real world situation, rather than some idealised one). You need to measure the cross sectional area of the river that is filling it in and how fast it is moving, multiply those together and you get the amount of water filling the depression per unit time. --Tango (talk) 12:17, 27 April 2009 (UTC)[reply]
If you want to know the depth of water as a function of time then you're going to need to learn some calculus. You need an equation describing the shape of the depression - then you're going to calculate the integral of that function - and this new function can then be evaluated to figure the rate of filling. SteveBaker (talk) 02:43, 27 April 2009 (UTC)[reply]
Don't ignore the flow of water through the soil into the aquifer. Newton-Raphson matrix methods might help in providing non-determinate solutions.Edison (talk) 04:39, 27 April 2009 (UTC)[reply]
Yes, if there is significant drainage then it gets more complicated. The drainage will depend on how filled it is already so you will, as Lomn says, need a differential equation. --Tango (talk) 12:17, 27 April 2009 (UTC)[reply]
The Earth's magnetic field is certainly strong enough to have a noticeable repulsion: all you have to do is point an opposing magnetic pole and you will be repelled. That's how a compass works: it's a lightweight magnet, and if you flip it around, you can notice it being repelled from the "wrong" way and attracted towards pointing North. Levitation is hard because most of us are on the "side" of the earth as considering it a bar magnet, so the field is relatively weak and is substantially parallel to the surface. At the poles, the field is stronger and pointed perpendicular to the surface. However, the field is still really weak (0.6 gauss according to the article) and a gauss is a pretty small field, so you'd need something pretty light to be able to levitate well. DMacks (talk) 07:28, 27 April 2009 (UTC)[reply]
As well as being quite weak, the Earth's magnetic field is approximately uniform over distances of the order of a few metres. The force that turns a compass needle is a torque, which is present even in a uniform magetic field, because the forces on the two poles of the compass needle are opposite in direction. However, to produce a net force on a magnetised object you need to have a non-uniform magnetic field, to make the forces on the two ends of the object also different in magnitude. The Earth's magnetic field is so close to uniform that the net force on any reasonably sized magnetised object will be minute.
You do get a net force on a current carrier moving through a uniform magnetic field. 0.6 gauss is 60 microteslas, so a wire that is perpendicular to this strength of field will experience a force of 6x10-5 N per metre per amp - so to get a measurable force you need either a very long wire and/or a very large current. However, stronger magnetic fields produce bigger effects - this NewScientist item says that a field of 17 teslas can levitate a frogĀ ! Gandalf61 (talk) 12:24, 27 April 2009 (UTC)[reply]
Very small and charged items like electrons and some light ions do get trapped by Earth's magnetic fields, and can be "repelled", "trapped", "resonated", and a variety of other interesting magnetic-field related motions. Take a look at the Van Allen radiation belt article. Those electrons and ions, under gravity, would get pulled into the lower ionosphere; under thermal motion, they would blow into space pretty fast; but they get trapped in the magnetic field and pulled into an "equilibrium" distance, complete with fun bouncing helical orbits that look nothing like your classic Newtonian gravitational elliptic orbits! Nimur (talk) 15:34, 27 April 2009 (UTC)[reply]
Steam Table & Value Calculation???
Hi,
Can you tell me What is a steam table?.How to calculate the value of enthalpy,using steam table for a given value of pressure and temperature?.Please reply if you are having any idea about this, plz share with me.... āPreceding unsigned comment added by Smenonp (talk ā¢ contribs) 12:04, 27 April 2009 (UTC)[reply]
Steam table redirects to the Water data page steam table. If you don't understand enthalpy, there is an article on that also. Basically the idea is that the enthalpy of vaporization is not constant - it actually depends on the temperature of the source water. To really understand this, you have to realize that while the "boiling point" of water is the phase transition point, in reality there is an equilibrium reaction between water and its vapor at any temperature. The steam table will tell you the values you need to calculate the parameters of that vaporization reaction. Nimur (talk) 15:38, 27 April 2009 (UTC)[reply]
Chameleons Changing Colors As Camouflage?
I have a question regarding our article on List of common misconceptions, specifically whether or not chameleons change their color to match their surroundings as a form of camouflage. Our article currently states:
"Chameleons do not change color to match their surroundings. They are naturally camouflaged and, although they can change their skin color into a variety of different colors, these changes are caused by temperature or interaction with predators or other Chameleons.[1]".
Another editor is disputing this here [35]. The video [36] he cites appears to be legit to my eyes, but maybe this is a video of an anole and not a chameleon.
well, the video is not a legitimate source. it could easily be photoshopped (and probably isādoesn't look natural at all). by contrast, the source against it comes from a major university. Wikipedia has long guidelines about what is a reliable source, about how "original research" is not allowed, etc. --98.217.14.211 (talk) 14:08, 27 April 2009 (UTC)[reply]
Hmm, but the chameleon article itself states, with two (possibly less credible, but still) citations:
"Recent research indicates that they do not only change their color for reasons of camouflage, but also use colour changes as a method of communication, including to make themselves more attractive to potential mates." -- Aeluwas (talk) 14:22, 27 April 2009 (UTC)[reply]
The issue here is having good citations and reading what they actually say. If it can be cited effectively, great. If not, then no. In those cases, citation #1 is about communication, not camouflage ("Overall, our results suggest that the evolution of the ability to exhibit striking changes in colour evolved as a strategy to facilitate social signalling and not, as popularly believed, camouflage."). Citation #2 specifically says it is not about camouflage ("Chameleons can produce a wide range of colors and patterns on their skin, but they do this primarily to express mood, not to blend in with different environments."). So I'd say that the distillation of these sources that claims they are camouflage PLUS expression rather than expression and NOT camouflage is incorrect (certainly not what the sources say). --98.217.14.211 (talk) 14:28, 27 April 2009 (UTC)[reply]
What's so special about swine flu?
There is something I don't quite understand about this current swine flu panic we are having right now. I'm not trying to be flippant, but I don't really get what the big deal is. Every year influenza kills hundreds of thousands of people, every year new varieties of flu start spreading. I don't get why this particular one is getting so much attention? Is it deadlier than all those other varieties? Is it much more contagious? Belisarius (talk) 14:59, 27 April 2009 (UTC)[reply]
This outbreak is getting attention because of the possibility that it could become a pandemic. See swine flu. The H1N1 strain of flu is a subtype of Influenza A that descended from the virus that caused the "Spanish" influenza pandemic of 1918-1919 that "infected one third of the world's population (or ā500 million persons at that time) and caused ā50 million deaths." Sounds pretty important to me. --- Medical geneticist (talk) 15:27, 27 April 2009 (UTC)[reply]
But, so, why? Why is this influenza so much more dangerous than the gazillion other types of influenza out there? You know, the diseases that hundreds of millions of people contract every year, the diseases that kill hundreds of thousands of people annually? Belisarius (talk) 15:51, 27 April 2009 (UTC)[reply]
Drooling
I have a problem of drooling while I sleep. Usually when I wake up, I find my pillow wet from my saliva. At any normal time my mouth has excess saliva. Is there a cure for this? What basically is the problem? Thanks. āPreceding unsigned comment added by 116.71.46.207 (talk) 15:02, 27 April 2009 (UTC)[reply]
Resolved
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