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June 6

Ballpoint pen ink

I've noticed that the ink from many ballpoint pens-- as well as from cheap disposeable fountain pens-- has a reddish or coppery-brown sheen, regardless of the ink's color. However, this vanishes when the ink dries or sinks into the paper(although it remains visible on non-porous surfaces). What component of the ink causes this metallic appearance? 69.111.189.55 (talk) 02:12, 6 June 2008 (UTC)

Well, until a chemist comes by, I found a patent for the composition of ball point ink: "An oil-based ink composition for a ballpoint pen which comprises a colorant, a resin and a solvent [of an alcohol... blah blah)" doesn't tell us much, but Ink brings up iron oxide. So for my money, oil sheen and/or iron oxide something. Julia Rossi (talk) 09:22, 6 June 2008 (UTC)

Mmmh - might be formation of dye at the surface - ie the dye might be a surfactant - inks probably contain surfactants. Also when ink liquid evaporates some dye might come out of solution - a bit like the skin on a milk pudding or something.. When it dries all the different colours are 'in the same place' so you won't notice the effect. You knew that inks (black) are made from different colour dyes (red/green/blue etc) - not all but most.87.102.86.73 (talk) 20:10, 9 June 2008 (UTC)

Huge Problem

Up until just recently, I've had a huge problem. The temperature in my bedroom was 90 degrees Fahrenheit. (Only a slight exaggeration.) I finally broke down and got a window air conditioner, and while that solved the temperature problem, now I have another huge problem. Every five minutes (only a slight exaggeration), the AC, apparently, draws too much electricity. This causes my lights to dim, among other things. And now it's starting to effect other things. For example, it has caused my computer to turn off and restart right when I'm in the middle of things. Is there anything I can do (that won't get me electrocuted) to resolve this? Digger3000 (talk) 03:35, 6 June 2008 (UTC)

Ask an electrician for help to upgrade your power, or secondly add a small UPS to your computer, so that it can withstand the power sags. Graeme Bartlett (talk) 06:01, 6 June 2008 (UTC)

Household wiring is supposed to deliver a reasonably steady voltage even when a heavy load comes on. Your description makes me worry that some part of your wiring is actually defective and unable to pass the proper amount of current; or alternatively that your wiring is overloaded and the air conditioner should be blowing a fuse or tripping a circuit breaker, but it isn't because the wrong size fuse/breaker is in place. Either of those conditions could be a fire hazard. Obviously I'm not in a position to say if there is a real hazard, but I really think you need to get an electrician in and have this looked at. --Anonymous, 07:36 UTC, 2008-06-06.

Anonymous is right. You describe a dangerous situation. See "Overcurrent". --Milkbreath (talk) 10:31, 6 June 2008 (UTC)

From my limited knowledge, I believe air conditioners are usually installed by electricians because they draw more current than normal. They circumvent the normal wiring of the house, using stronger cables.59.100.206.238 (talk) 11:15, 6 June 2008 (UTC)

Not window air conditioners. Those are just big appliances with standard plugs. --98.217.8.46 (talk) 19:58, 9 June 2008 (UTC)

I figured you might suggest a UPS. But the thing is, I do have my computer plugged into a UPS. Even so, my computer has completely lost power a few times. Not every time the power sagged, but a few times. And even when the UPS does do its job, it beeps every time the power sagged. And as annoying as that is, it'll probably be even more annoying when my house is burning to the ground. Yeesh, I should probably get that checked out, soon. Do you think it would help at all if there were fewer things plugged in in my room? There's not really much I can unplug, but I could try it. Digger3000 (talk) 11:56, 6 June 2008 (UTC)

Yes, as a temporary measure before getting an electrician to check your wiring I would definitley do whatever I could to reduce the load. -- Q Chris (talk) 13:34, 6 June 2008 (UTC)

A qualified electrician could monitor the voltage at the air conditioner outlet and at the main panel to determine the quality of the incoming voltage and the voltage drop from the panel to the outlet. I do not recommend an amateur trying to measure/correct these possible electrical problems because electricity can kill you. Low voltage at the air conditioner outlet can cause the motor to draw more current to maintain its mechanical output to the airconditioner compressor. The additional current causes the voltage seen by the air conditioner to drop, in a vicious circle until the current is so high that a breaker trips or the air conditioner motor overheats and a thermal protective device in it cause it to trip offline to cool down. Then the cycle repeats. Blowing a fuse or tripping a circuit breaker at the house utility panel may occur. The causes may be multiple, and in combination: 1)A long run of small (#14) wire from the utility panel to the air conditioner outlet. (Helped by having an electrician run a #12 20 amp circuit from the panel to the outlet. Putting in a larger fuse would be idiotic, of course). 2)Use of an extension cord to run the AC (Try plugging it directly into an outlet) 3)The circuit may be loaded down with other loads, such as the computer you mentioned. (Remedy:Get the air conditioner on its own circuit). 4)The air conditioner might be defective, inefficient or too large. Try a different one of the same size if available. Try a high efficiency one with a higher energy efficiency rating, which should draw less current, or try a smaller air conditioner. 5)The service wires from the transformer to the house might be too small, resulting in too-low voltage when the building draws high current. This is a job for an electrician or the utility, depending on where you live. 6) There might be a loose neutral connection between the utility and the house or inside the house wiring. Symptoms might be some light getting brighter when the air conditioner circuit voltage drops. A job for an electrician and the utility. 7)The utility might be supplying low voltage, due to loose connections in the service wires, your transformer being too small, a heavily loaded circuit or to your being near the end of the circuit, or to a lack of capacitor banks, or to intentional voltage reductions (brown outs) or to poor voltage regulation at the substation or along the feeder. If this is diagnosed by actual measurements, complaints to the utility, or to your public officials if the utility won't correct their deficiency,might get corrective action. If you can report to the utility that an electrician has measures illegal low voltage for extended periods (over 1 minute) at the main panel with an accurate RMS volt meter, you could demand that the set a recording voltmeter at the meter, to confirm the finding, and that they then correct it. In many US locations 114 volts (5% below 120) is the minimum legal voltage at the electric meter. This allows the voltage to drop a bit in the house wiring and still be able to operate the air conditioner at the other end of the house. Edison (talk) 13:42, 6 June 2008 (UTC)

Here's your answer. But as a stop gap solution you might just try putting it at a colder setting to make it run longer. It's the compressor start-ups that draw the most current. Or let it cool the room first, then turn it off and cool yourself with a fan for a few hours. Fletcher (talk) 14:12, 6 June 2008 (UTC)

I agree with Edison that an easy short-term solution is to put the AC on a difference circuit. Even if your electricity was working correctly you'd be blowing fuses/tripping circuits with that arrangement as you describe it. You'll either need another circuit installed or need to run an extension cord to a difference one. --98.217.8.46 (talk) 19:58, 9 June 2008 (UTC)

Another Unknown Equation

In the spirit of the question above, what's the meaning of engie's "favourite" equation? --antilived^{T | C | G} 05:22, 6 June 2008 (UTC)

I don't know what it means, but it's not an equation (no equals sign). Algebraist 13:27, 6 June 2008 (UTC)

It is apparently an expression for the amount of light reflected from an object illuminated by several sources. It's used in ray tracing. [1] --Heron (talk) 20:18, 6 June 2008 (UTC)

Holographic projection...

i would like to know if there is a technology confirming to holographic projection such that the projection is not made on any solid or liquid medium as in the case of Musion's 'Eyeliner foil' —Preceding unsigned comment added by 61.17.218.119 (talk) 07:02, 6 June 2008 (UTC)

Yeast and brewing

Does anyone know how to balance this reaction? C12H22O11 = C2H5OH + CO2 All the reactions I can find use glucose. But when making beer, they don't use glucose, they use maltose. I can't work out how to balance it though.

Thanks, Wikiwikijimbob (talk) 12:23, 6 June 2008 (UTC)

Don't discount the possibility that you might need a water molecule on one side or the other - on a brief look it seems to balance similarly to glucose if you add a water molecule on the left hand side. Not sure, though, but it's worth checking. ~ mazca ^talk 13:03, 6 June 2008 (UTC)

I'm going to second and say that you're going to need a water molecule on the reactant side and also may have copied down the formula of the original carbohydrate wrong. Carbohydrates have a C:H:O ratio of 1:2:1. EagleFalconn (talk) 14:26, 6 June 2008 (UTC)

No, that's the correct formula of maltose. Algebraist 14:30, 6 June 2008 (UTC)

The C:H:O ratio of 1:2:1 is only true for monosaccharides, and only in its most narrow meaning (discounting e. g. deoxy sugars). Icek (talk) 18:10, 6 June 2008 (UTC)

Thanks, it's much appreciated. Wikiwikijimbob (talk) 19:27, 9 June 2008 (UTC)

effect of overly large stimulus

Assuming you have a way to bypass the senses, imagine you have a microphone, a mechanical tounge, an artificial nose and a camera attached directly to your brain. What would happen if you received 100000000dB,the full light u a supernova and any other overly large stimulus which would normally devastate your receptive organs? 193.188.46.64 (talk) 12:37, 6 June 2008 (UTC)

Your guess is as good as anyone elses, it is difficult to give definitive answers to such speculative questions. Jdrewitt (talk) 13:08, 6 June 2008 (UTC)

For any realistic artifical sensory apparatus, though, it will be devastated by such a stimulus, just as an unassisted human would be. Algebraist 13:23, 6 June 2008 (UTC)

And even if it wasn't, a proportional signal to your brain would probably involve sufficient current that brain damage would ensue. Not to mention the effects on the rest of your body of being close to a supernova or a 100,000,000db noise! ~ mazca ^talk 13:26, 6 June 2008 (UTC)

I think the question is assuming that the artificial sensory apparatus are robust enough to cope with the stimulus however large and it is purely asking how would the brain interpret the signal (not how the rest of the body will cope). It really depends on how the sensor communicates to the brain which is too speculative since such a technology does not exist. Jdrewitt (talk) 13:35, 6 June 2008 (UTC)

Does the OP realise that the dB scale is logarithmic, and a 10⁸dB noise would have energy immeasurably greater than that of the observable universe? Algebraist 13:47, 6 June 2008 (UTC)

(ec with algebraist)Just to put this in perspective, the entire output of the sun is around 638dBμ. Even the largest galaxies with 10¹² stars still output less than 1000dBμ. I doubt that the amount of power represented by 100,000,000dB could be generated in the entire universe. Exposed to that kind of output, you are going to have bigger worries than what your sensors are made of. Sensors, you, your brain, your planet and your galaxy are all going to be vapourised. SpinningSpark 13:50, 6 June 2008 (UTC)

I think the most serious problem is that it'll cause the gravitational collapse of the entire universe. Algebraist 14:04, 6 June 2008 (UTC)

To be charitable to the OP I think we should assume the energy is just larger than what a person would normally encounter (but not so large as to destroy the universe!), and that the subject's body is protected from it, so he experiences it only through the artificial sensors. Not being a neuroscientist I really can't say what would happen; however, it seems unlikely the brain can distinguish signals at levels that would kill the physical body. I would think there is an upper limit beyond which it makes no difference how strong it is; the brain will interpret it as extreme light, extreme noise, etc. The artificial sensors would have to progressively step-down the signal so as not to damage neurons. A brighter light would have to be stepped down further, resulting in no difference in perception. But i don't know what happens at that upper limit of stimulation -- would it provoke a fight-or-flight response, a panic attack, a seizure? Fletcher (talk) 14:56, 6 June 2008 (UTC)

They would be rather poorly designed sensors if they provided enough current to damage the brain, they would reach their maximum safe output levels and that would be it. You'd see nothing but white and hear probably nothing but a whoosing sound of all the matter traveling past or perhaps a banging noise from the shockwave, if the sensors were calibrated to normal human sight and hearing. If they were calibrated for optimum observation of a supernova, then you would see the supernova, the amount of energy that the sensors receive does not have to correlate to a larger amount of energy put into the brain. Brain-computer interface may be enlightening. -- Mad031683 (talk) 16:39, 6 June 2008 (UTC)

Higher intensity of sensory input causes higher frequency of neuron firing, but no change in the action potential. The frequency is limited by the time needed to restore the resting potential, at least a few milliseconds. Icek (talk) 18:04, 6 June 2008 (UTC)

While I don't think these directly answer the OPs question, they may be interested in visual prosthesis and neural prosthetics as they describe the current state of the art. SpinningSpark 16:58, 6 June 2008 (UTC)

I was indeed assuming that the sensors where robust enough, and I just typed in an insanely huge number to stress that no person could receive such a stimulus naturally. So assuming the electronic interface communicates using normal neurons the largest signal possible will be determined by the inactive time of neurons? I was mostly interested in how would the brain change to accomodate these stimulus. How does the brain change in response to normal stimulus? Bastard Soap (talk) 20:07, 7 June 2008 (UTC)

flowers

which part of the flower is the pollen & the egg cells produced? —Preceding unsigned comment added by 96.10.123.85 (talk) 14:17, 6 June 2008 (UTC)

Have you looked at flower and plant anatomy? Those might be good places to start. Friday (talk) 14:39, 6 June 2008 (UTC)

Hypothetical Suicide only

This question has been removed due to the possibly dangerous outcomes that could amount from any answers given. Not only could the answers be seen as morally fragile, but there may also be legal implications should anyone stumbling upon the page take action with what they've heard. For these reasons I have removed the question, should anyone disagree they can talk to me further on my talk page. My sincere apologies to the OP. Regards, CycloneNimrod ^talk?_contribs? 21:12, 6 June 2008 (UTC)

Diagnosticians

What do diagnosticians actually do and why are they necessary when there are plenty of doctors who are specialised in different fields of medicine? Thanks. Clover345 (talk) 17:48, 6 June 2008 (UTC)

There are consultants for every field indeed. But what if you don't know which consultant to refer a patient to? Many symptoms are vague: Malaise, lethargy, widespread pain.... A diagnostician specialises in signs and symptoms rather than any specific disease or organ system. In many ways general practitioners act as diagnosticians (especially in the UK and Ireland where you cannot see a consultant directly, only by GP referral). Fribbler (talk) 17:59, 6 June 2008 (UTC)

According to the entry on diagnostician, it's simply a generic term for someone who makes diagnoses, and that someone is most likely a doctor. ~Amatulić (talk) 18:02, 6 June 2008 (UTC)

Could an A&E consultant act as a diagnostician and are there diagnosticians other than GPs in the UK? Clover345 (talk) 18:11, 6 June 2008 (UTC)

An A+E doctor (any rank) is a good example of a diagnostician. As far as I know, here in Ireland (which usually means it's the same in the UK) there arn't any "diagnosticians" by title such as there are on House. Fribbler (talk) 18:19, 6 June 2008 (UTC)

Here in the U.S., "diagnostician" is a descriptive term, not a specialty.Scray (talk) 03:41, 7 June 2008 (UTC)

BACILLI MICROORGANISMS

1)HOW DOES IT LIVE?

2)WHERE DOES IT LIVE (ITS ENVIRONMENT)?

3)DOES IT THRIVE BEST ALONE OR WITH OTHER MEMBERS?

4)WHAT ASSISTS IN ITS EXISTANCE?

5)HOW DOES ONE BECOME INFECTED WITH IT?

6)(CHAIN INFECTION) HOW DO MICROORGANISMS CAUSE INFECTION AND HOW TO PREVENT ITS SPREAD?

Genisa (talk) 19:51, 6 June 2008 (UTC)

Mmmm. Tasty, tasty homework. Sorry, we won't answer these for you but we can point you in the direction. Unfortunately, I don't know enough about this topic. Regards, CycloneNimrod ^talk?_contribs? 20:11, 6 June 2008 (UTC)

No, we cannot really answer these for you. Besides, it'll be worth your while to do a little research. Allow me to point you in the direction of a great and very informative website. [2]. Wisdom89 _{(T / ^C)} 20:21, 6 June 2008 (UTC)

Largest molar mass

What known compound has the largest molar mass? 65.31.80.94 (talk) 20:49, 6 June 2008 (UTC)

Periodic table. Wisdom89 _{(T / ^C)} 20:50, 6 June 2008 (UTC)

He asked for a compound. That can't be determined solely from the periodic table, can it? Ζρς ι'β' ^¡hábleme! 21:04, 6 June 2008 (UTC)

Well excluding answers like macroscopic crystals and neutron stars, the answer is probably a protein. The largest one in the human body is Titin at nearly 3 million Dalton. Any advances? SpinningSpark 21:35, 6 June 2008 (UTC)

DNA. Dragons flight (talk) 22:18, 6 June 2008 (UTC)

Backelit or any other cross linked polymere or a piece of graphite a sio2 crystal ..... there are many possible canidates.--21:38, 6 June 2008 (UTC)

I think for the purposes of this challenge that we can exclude polymers, as crystals are also excluded and look for a compound with a well defined formula, and therefore molecular weight. Earlier here we were trying to identify the densest gas. Graeme Bartlett (talk) 22:54, 7 June 2008 (UTC)

Natural occurence of dry ice?

Does solid CO₂ occur naturally anywhere on Earth? At high pressures, for example? Or the at -89.2C (cf. sublimation point of CO₂ -78C), would CO₂ precipitate from the air?

Cheers!

Aaadddaaammm (talk) 22:08, 6 June 2008 (UTC)

I have heard that the small partial pressure of CO₂ means that only a tiny amount of Carbon Dioxide solidifies, even at extremely low temperatures, so any dry ice formed would be invisible. Can't remember where I heard/seen that, though. Fribbler (talk) 01:12, 7 June 2008 (UTC)

Probably not naturally, although there may occasionally be liquid carbon dioxide in Carbonatite volcanic eruptions which start from the mantle. After the sun dies however there should be carbon dioxide frost formed, if the earth survives. Graeme Bartlett (talk) 23:00, 7 June 2008 (UTC)

Even if the Earth survives, the atmosphere will probably be completely blown away, so there won't be any CO₂ to sublime. --Tango (talk) 10:42, 8 June 2008 (UTC)

This chart indicates a vapor pressure of about 0.02 bar = 2 kPa at 154 K. The atmospheric partial pressure is only about 38 Pa. So even at -119°C it wouldn't solidify, for the same reason that water doesn't condense as long as relative humidity is below 100%. Icek (talk) 21:22, 8 June 2008 (UTC)

June 7

Stones in trees in Yellowwood State Forest

Regarding the new Wikipedia article about Yellowwood State Forest, is it possible the stone simply sat down on saplings and waited for them to grow? --77.125.94.96 (talk) 01:17, 7 June 2008 (UTC)

That's impossible. If a large boulder was weighing down a sappling, there is no way it would have been able to not only grow, but be able to support the weight of the rock, especially if it was just starting to grow.--十八 01:43, 7 June 2008 (UTC)

In any case it seems to me that it's just as unlikely that the boulder walked over and sat on a sapling as it is that it climbed a fully grown tree by itself. SpinningSpark 00:59, 8 June 2008 (UTC)

Phobos (moon)

I have a book on Mars with me that says if Phobos survives the Roche limit and does not break up, the moon will blast a crater over 100km across on Mars. How is the crater's diameter calculated given the object's velocity and volume?--十八 01:45, 7 June 2008 (UTC)

Just to let you know, this smells a little bit like a homework question. But answering your question straightforwardly, I would imagine that the crater's diameter is calculated given the object's velocity and mass (not volume) based on the energy that would be delivered to the regolithic substrate, this latter mostly based on theory investigated by experiments conducted by curious physicists tossing projectiles into things that resemble the Martian regolith. --arkuat (talk) 09:21, 7 June 2008 (UTC)

The article Impact crater might help. SpinningSpark 10:12, 7 June 2008 (UTC)

[3] has some information, for Earth at least. --Fangz (talk) 11:20, 7 June 2008 (UTC)

Thanks, I found this site through the site you provided which works fine. Also, to answer Arkuat's speculation, it's not homework per say. I'm writing a research paper and I wanted to calculate which parameters would have to be taken into effect for the crater to be over 100 km in size, as stated in the book (as it just gave the figure, not the calculations, or even the parameters, involved).--十八 00:54, 8 June 2008 (UTC)

Sorry for my speculation, I ought to have edited it out before posting. arkuat (talk) 05:46, 8 June 2008 (UTC)

Hi. This simulator has impacts for other planets, but it's a bit oversimplicified, and uses Marvin Martian as its theme. Thanks. ~AH1^(TCU) 13:57, 7 June 2008 (UTC)

Threshing and winnowing?

In agriculture, what is the relationship between the activities of threshing and winnowing? What I mean is, are they:

• exclusive either-or activities, two different ways of accomplishing the same purpose (that is, if you thresh, you do not need to winnow, or if you winnow, you do not need to thresh) OR
• both required activities that do not accomplish the same purpose (and if this is the case, does threshing have to come before winnowing, or winnowing after threshing, or does the order not matter?)

—Lowellian (reply) 01:49, 7 June 2008 (UTC)

The latter (and the former). Threshing means bashing the grains to get the chaff (seed-coats, bran) off the grain (what later gets ground up into flour). Winnowing means throwing the resulting mixture (separated, but still mixed in a heap) into the wind or water, to make a bunch of chaff floating away on the wind or water, and a heap of grain sinking in the wind or water. I'm guessing the confusion arises from modern-tech agricultural combines that do both jobs with one vehicle. --arkuat (talk) 06:38, 7 June 2008 (UTC)

Hybrid car mileage

Why do hybrid cars get better gas mileage in city than highway tests, when no others do? NeonMerlin 02:20, 7 June 2008 (UTC)

On the highway, a major energy loss is to wind and road friction, losses not addressed by hybrid technology (and hybrid generate most of their electricity during braking, which doesn't happen much on the highway). In the city, energy loss is during braking and idling. Hybrids recovery energy during braking, and shut off the gas engine during idling. Perhaps others have more technical answers, but I think of it in terms of primary energy loss and how it can be recovered.Scray (talk) 03:20, 7 June 2008 (UTC)

Interesting answer. I had always assumed -- without giving the matter much thought, until now -- that it was simply that batteries can't make a car go 60 mph.

So, Scray and I are both interested in others' more technical answers! -- Danh, 70.59.116.253 (talk) 22:54, 7 June 2008 (UTC)

Scray basically is right, there is not much to add. Electric engines are highly efficient, but the energy ultimately has to come from the IC engine. If you need continuous high energy output, your IC engine will run either way. The primary advantage of the electric engine is in energy recovery during braking and idling. And yes, batteries can make a car go any reasonable speed - this just depends on the dimensions of the engine. The first few land speed records were all obtained with electric cars (although the fastest one was only 65 miles per hour). --Stephan Schulz (talk) 23:35, 7 June 2008 (UTC)

I was under the impression that a big part of the gain comes from using a smaller ICE. An ICE large enough to provide sufficient peak acceleration is inefficient when you're not accelerating; with a hybrid vehicle the electric motor provides extra acceleration and you can get away with a smaller ICE, which leads to better efficiency even on the highway. Someone else will have to say whether this makes sense, since I know nothing about cars, but Hybrid electric vehicle#Benefits seems to back it up. -- BenRG (talk) 23:47, 8 June 2008 (UTC)

ICEs have a certain RPM at which they are most efficient. In hybrids, since the ICE is only generating electricity, it always runs at the most efficient speed. Even when accelerating on the highway, the ICE is still operating at peak efficiency. --Theeldest (talk) 20:11, 13 June 2008 (UTC)

A possible method for superluminal travel

I thought that if there is a warp in space, the area doesn't change, but the warp is curved. So, if anybody could travel straight forward in a warped area without being pulled to the center of gravity, the distance will be cut and superluminal travel may become possible. Can you please tell me is this method possible? Please reply!!! —Preceding unsigned comment added by Superwj5 (talk • contribs) 08:02, 7 June 2008 (UTC)

• Have you read the article on dark energy and especially the section on negative pressure yet? If not, I'm afraid you'll have to rephrase your question in simpler terms. --arkuat (talk) 09:11, 7 June 2008 (UTC)

• You might find the article Alcubierre drive interesting (but highly controversial) and also most the scientific papers cited in that article have links to online preprints. Another of our articles that you could look at is wormholes. SpinningSpark 10:20, 7 June 2008 (UTC)

• Much as I would like to have FTL travel (preferably in my lifetime), Einstein tells us that any form of superluminal communication will break causality - i.e. you can get next weeks lottery numbers today. Given that choice, I vote for a proper sequence of cause and effect.... --Stephan Schulz (talk) 13:41, 7 June 2008 (UTC)

  As long as you have local causality, things should be ok, and space warping techniques usually don't involve travelling faster than light locally, just faster from the perspective of the rest of the universe. Just losing global causality means what people usually call "time travel", is it really so bad to have a universe which allows for time travel? --Tango (talk) 13:34, 7 June 2008 (UTC)

  Yes! Nature abhors a time paradox... --Stephan Schulz (talk) 13:30, 7 June 2008 (UTC)

  Time travel doesn't necessarily involve paradoxes. --Tango (talk) 16:43, 7 June 2008 (UTC)

What you describe sounds similar to a possible method of time travel I read about (superluminal travel and time travel are very closely related) involving cosmic strings. I believe there were two orbiting each other and as you went round them in a particularly way, you got back to where you started from before you left. I don't remember the details, but it sounds vaguely like your idea. If wouldn't work with regular matter, it needs to be a cosmic string. --Tango (talk) 13:34, 7 June 2008 (UTC)

Many of these methods are summarized at Time travel# Time travel to the past in physics. Clarityfiend (talk) 18:54, 7 June 2008 (UTC)

Reduce voltage drop through a diode

I'm making a solar-powered microcontroller device using 5 0.47V 100mA max solar panels in series, feeding through a 7660 to double the voltage to power my IC (Atmel ATTiny13V) and my RF transmitter. According to the datasheet, I need 2 diodes in series from the 7660's output. That's 1.4V drop already, which is way too high for my purpose. I've switched to Schottky diode but that's still over half a volt lost. What are some ways to further reduce this loss? I've looked at synchronous rectification but have no idea what parts are available for drop in replacements for my diodes; I've also thought of using a transistor with the base and collector connected together, will that work? --antilived^{T | C | G} 08:50, 7 June 2008 (UTC)

Why do you have to use that device in particular? There are heaps of dc-dc converters out there for all kinds of different voltages. You would be better off selecting a device for the voltage you want to deliver, see for instance [4], rather than jump through hoops getting this one to do what you want. The one you have picked seems to be specifically for generating a negative rail from a positive one and can also co-incidentally do voltage doubling. Basically, it is not the best chip for the job. A quick Google search or a look through an electronics component catalogue will get you lots more to choose from. SpinningSpark 11:00, 7 June 2008 (UTC)

Availability is one thing, that device being instantly available is a huge plus. The one that you've linked to is a regulator not a voltage converter and therefore unsuitable for my use. Inverting voltage and doubling voltage are based on pretty much the same principle anyway so it's not unusual to see both functionalities on the same chip. --antilived^{T | C | G} 11:54, 7 June 2008 (UTC)

Actually, I think you will find that that device I pointed you to is a switching device rather than a linear regulator, it is just made to be pin compatible with linear regualtors of the 78xx series. However, your complaint is justified because it is step-down rather than the step-up you need. Sorry, my bad. Try this one [5]. I know inverting and doubling can be done with the same device, but neither of those things is what you really need. Availability - you are in New Zealand right? Try here [6]. SpinningSpark 13:59, 7 June 2008 (UTC)

No that's still not suitable for my use. My input voltage (from the solar cells) is only 2.35V max, and will almost certainly be lower than that during most of the day. I only need 20mA at the most so a device that can supply 2.5A is quite an overkill for me. --antilived^{T | C | G} 23:06, 7 June 2008 (UTC)

I'm not sure if this is an intelligent answer, but have you considered biasing the voltage? I know it is a solar cell of some description to generate electricity, but to power an IC, maybe putting the voltage drop amount across the diodes is a solution? Adamd1008 (talk) 20:41, 10 June 2008 (UTC)

United States Of America

Q:When is the national blonde brownie day celebrated in the U.S —Preceding unsigned comment added by 117.194.193.239 (talk) 12:28, 7 June 2008 (UTC)

See here: Wikipedia:Reference desk/Miscellaneous#United States Of America - Copied over there as this is the science desk. Regards, CycloneNimrod ^talk?_contribs? 13:16, 7 June 2008 (UTC)

Cancer stage vs grade

Is there a difference between the terms grade and stage with respect to cancer classification? --Seans Potato Business 17:17, 7 June 2008 (UTC)

The stage refers to the invasive ability of the cancer. The grade refers to how similar the tumor is to the surrounding tissues. See Cancer#Classification. Regards, CycloneNimrod ^talk?_contribs? 17:48, 7 June 2008 (UTC)

I think some clarification might help: Stage is the degree to which the tumor has invaded, not its ability to invade (a very aggressive tumor, with high ability to invade, can be detected at an early stage, i.e. before it has actually done much invading). Grade is determined by comparison to benign (surrounding) tissue, but is actually the dissimilarity relative to normal tissue (high grade means very different from normal).Scray (talk) 20:08, 7 June 2008 (UTC)

Scray is correct. A common saying in pathology helps one keep the two straight: "grade the tumor, stage the patient". --David Iberri (talk) 00:00, 8 June 2008 (UTC)

Stopping earth quakes

We have articles on weather control and asteroid deflection, but are there any proposed methods on stopping earth quakes? Is it possible to do this? ScienceApe (talk) 17:33, 7 June 2008 (UTC)

It's really not feasible since we can't stop plates from colliding with each other. Regards, CycloneNimrod ^talk?_contribs? 17:49, 7 June 2008 (UTC)

We had a discussion of this last year. See Wikipedia:Reference desk/Archives/Science/2007 October 11#Controlling earthquakes by setting them off. Algebraist 18:59, 7 June 2008 (UTC)

Well, there's fiction about it: the novel A földrengések szigete by Fehér Klára. Also in fiction, the Little Prince regularly cleans his volcanos so they don't have violent eruptions. – b_jonas 09:52, 9 June 2008 (UTC)

I know of no proposals for stoppng earthquakes, short of waiting for the core of the planet to cool. However, stopping earthquake damage is straightforward: earthquakes do not kill, buildings do. —Preceding unsigned comment added by 67.131.66.162 (talk) 18:16, 9 June 2008 (UTC)

Indeed, we even have an article on that: earthquake engineering. – b_jonas 19:10, 10 June 2008 (UTC)

Phenylketonuria

I have todo a 15 page essay on Phenylketonuria, and i need alot of research from this site, do you know where i can find 15 PAGES of INFORMATION including, pictures, graphs and websites that my science class can visit

--Katiesorfleet (talk) 17:38, 7 June 2008 (UTC)katiesorfleet

Phenylketonuria is a good start. That's the only article we have on it, otherwise just use Google. Regards, CycloneNimrod ^talk?_contribs? 17:50, 7 June 2008 (UTC)

Specifically, look at the sources at the bottom of Phenylketonuria. Like any other encyclopedia, you should not be using Wikipedia as a research paper source; you should using to get a general overview of the subject. Paragon12321 (talk) 21:17, 7 June 2008 (UTC)

Why is LSD illegal?

? ScienceApe (talk) 19:07, 7 June 2008 (UTC)

Well, the risk of a bad trip comes to mind. For other reasons you might want to read about the effects in the LSD article. - Dammit (talk) 19:12, 7 June 2008 (UTC)

According to the DEA, because it has "a high potential for abuse and serve[s] no legitimate medical purpose" [7], Someguy1221 (talk) 19:14, 7 June 2008 (UTC)

So same as alcohol and tobacco right? ScienceApe (talk) 02:53, 8 June 2008 (UTC)

I agree on tobacco (no redeeming qualities) - if it came to market today it would never get approved (so I can only surmise it is vested interests including farm lobbies and addicts that sustain the business). Alcohol in moderation, however, appears to have some benefits like reducing heart disease. Scray (talk) 03:29, 8 June 2008 (UTC)

Meanwhile marijuana, which does have a legitimate medical use and less of a danger from abuse than alcohol, remains illegal. I'd agree it's all a matter of when it was introduced. Those drugs introduced early on were accepted while the latecomers are seen as dangerous: "Those damn kids with all their pot, it makes me so mad, now light my cigar and get me my whiskey !". StuRat (talk) 18:26, 8 June 2008 (UTC)

Marijuana's initial illegality had a lot more to do with keeping wood pulp prices up than it being considered dangerous. Matt Deres (talk) 02:02, 9 June 2008 (UTC)

(ec) Because legislators in whatever jurisdiction it is you're talking about have made it so. In many jurisdictions, this is required by the UN Convention on Psychotropic Substances (full text). The preamble to that treaty states that it was passed to safeguard public health. Presumably they were thinking of flashbacks and Hallucinogen persisting perception disorder. Algebraist 19:18, 7 June 2008 (UTC)

I wouldn't say tobacco has no redeeming qualities, since studies have shown that nicotine is good for the brain. Just that the risks tobacco introduces far outweighs the benefits. --Wirbelwindヴィルヴェルヴィント (talk) 02:56, 9 June 2008 (UTC)

Toothpaste toxicity (fluoride)

There's a warning label on every tube of fluoride toothpaste that states that the poison control center should be contacted in case more toothpaste is swallowed than is used for brushing. This is because fluoride, the active ingredient in most toothpaste designed for adults, is toxic and can cause acute sickness or death if taken in sufficient concentration. Of course, almost nothing is entirely safe (even drinking too much water too quickly can prove fatal), and warning labels are notoriously overcautious. We've all swallowed toothpaste now and then with no ill effects. How much toothpaste would have to be ingested in order to induce fatal fluoride toxicity in an average-sized (say, 170 lb.) adult? —Preceding unsigned comment added by 66.215.224.253 (talk) 19:51, 7 June 2008 (UTC)

Maybe you should read fluoride poisoning. Anyway, there's no warning label on my tube of fluoride toothpaste. --Heron (talk) 20:24, 7 June 2008 (UTC)

Looks as though the probable toxic dose is about 5 mg/kg (many sources). Given your example of a 77 kg (170 lb) adult, that would be about 385 g. Labels of toothpaste I see list fluoride ion content around 0.14% w/v (0.14 g/100 mL, or 1.4 g/L), so 385/1.4 = 275 L (35.75 gallons). That's a lot of toothpaste!Scray (talk) 20:32, 7 June 2008 (UTC)

So we're looking at the thirty to forty gallon range - wow. Thanks, Scray. I guess the warning label is decidedly overcautious after all. According to the toothpaste article, ingesting too much toothpaste can cause minor digestive upsets such as nausea and vomiting, so I suppose someone has ingested enough of it in the past to suffer some discomfort, but it isn't anything serious after all as the packaging would imply (and Huron, most brands do include such a warning label on the box the toothpaste comes in or on the tube itself, as the aforementioned article will confirm). Stupid warning labels. —Preceding unsigned comment added by 66.215.224.253 (talk) 20:57, 7 June 2008 (UTC)

Umm isn't it 385 mg, which is 0.385g? At that level it'd only take 275mL, or roughly 2 tubes of toothpaste to reach the toxic dosage. --antilived^{T | C | G} 23:33, 7 June 2008 (UTC)

Yes, I think you're right. However, our article says the lethal dose is about 70mg/kg, did Scray drop a 0? What are the many sources? Or does toxic dose differ from lethal dose? --Tango (talk) 01:08, 8 June 2008 (UTC)

My deep apologies - and thanks to 66.215.224.253 for catching my gross slip of the prefix (i.e. I jumped from mg to g). I should have said 385 mg (not g) of fluoride, which then equates to about 275 mL of toothpaste, or a little more than 2 "family size" toothpaste tubes as the toxic dose. The lethal dose, about 14 times that (5 vs 70 mg/kg) would be about 30 large tubes of toothpaste. So, spit don't swallow, and don't worry about the fluoride unless someone comes up with convincing evidence that lower doses are toxic.Scray (talk) 01:30, 8 June 2008 (UTC)

This is all, of course, assuming it would be a adult that ate the toothpaste, which seems highly unlikely. If it were a young toddler, the lethal dose would be much more feasible. Paragon12321 (talk) 04:24, 8 June 2008 (UTC)

Wouldn't it be just as unlikely for a toddler to swallow a propotional amount of toothpaste, say 3 large tubes, as for an adult to swallow 30 ? Also, wouldn't they get ill from things other than fluoride (like the artificial sweeteners) at lower quantities of toothpaste ? StuRat (talk) 18:18, 8 June 2008 (UTC)

Well, I checked the label and the box, and they do advise supervising children under 7 to "minimise swallowing". I took that to mean that adults can guzzle as much of the stuff as they want. Looks like I'll have to limit myself to 2 tubes a day in future. --Heron (talk) 17:40, 9 June 2008 (UTC)

Using that logic, if a yellow flashing traffic light means "proceed with caution", what does a green light mean ? "Proceed with reckless abandon ?" :-) StuRat (talk) 05:05, 11 June 2008 (UTC)

There are other dangers to eating toothpaste and excessive fluoride other than death. If you eat toothpaste as a child you will develop dental fluorosis, which, while not at all life-threatening, is pretty lousy, and requires a lot of expensive dental work to correct. (So says someone who has a full upper set of veneers thanks to extreme fluorosis—$500 a tooth, to be replaced every 10 years or so, and an unpleasant procedure). --98.217.8.46 (talk) 01:33, 10 June 2008 (UTC)

applied sciences

Why is it that a physicist can become an engineer but a biologist cannot become a doctor? —Preceding unsigned comment added by Clover345 (talk • contribs) 20:47, 7 June 2008 (UTC)

Biology is a very different job than medicine. There's a difference between knowing how a cell works and knowing what to do if something is wrong with it. Generally, no one dies if a biologist makes a mistake. Paragon12321 (talk) 21:15, 7 June 2008 (UTC)

There is a difference between theoretical knowledge and practical skills. A physicist knows the theory behind engineering, so can probably design a nice new bridge, say, but they couldn't pick up a welding torch and make it. Likewise, a (human) biologist knows all the theory about how the body works, but they can't just pick up a scalpel and start cutting bits out of it. Knowing the theory is a good start and would certainly help you in a related applied job, but there is more to learn before you can actually start doing it. --Tango (talk) 21:20, 7 June 2008 (UTC)

I agree with Tango, though I bet a lot of physicists would have some learning to do before they could design a bridge. But being trained in biology would still be a giant head start if you wanted to become a doctor. I went to a small college with no official premed program, so most aspiring doctors majored in biology. --Allen (talk) 21:25, 7 June 2008 (UTC)

A physicist would have to get more training in the laws of physics as they apply to the field of engineering or his particular field of engineering before he could be successful as an engineer, or at any rate, if he didn't know enough about the laws of physics as they applied to engineering, he couldn't become an engineer, period. Even if he impressed someone with his credentials, he wouldn't last long at the job. There's nothing to stop a biologist from becoming a doctor, if he goes on to study the principles of biology as they apply to the human body (arguably a greater narrowing than that from physics to engineering, requiring greater specialization; remember, biology is the study of all that is alive, from bacteria to plants to ecosystems, and the correlation between "knowing how it works" and "knowing how to fix it" is much less in biology than in physics). Furthermore, because doctors deal literally with matters of human life and death, it is required in most places that they go to medical school, get a license, etc. Anyone who wants to become a doctor has to meet those requirements, regardless of prior training. A biologist would doubtless have an easier time than someone from an non-life sciences background in some aspects of medical training, but it's still necessary to get training in the field in order to go into the field. Diagnosis, administration of medication, surgery, psychiatry, and bedside manner are aspects of the medical field with little or no parallel in the field of biology as a whole, and many of them are crucial for any doctor to know. In short, medicine is a very demanding specialty that requires much knowledge that biologists simply don't possess - unless they go on to study medicine. 66.215.224.253 (talk) 21:27, 7 June 2008 (UTC)Aletheia—Preceding unsigned comment added by 66.215.224.253 (talk) 21:27, 7 June 2008 (UTC)

Let's also not generalize all physics here. A theoretical physicist is going to have a lot less at hand knowledge than, say, a physicist who specializes in materials science, when it comes to going into engineering. String theory does not tell you much about how to build a bridge; even a fairly generalist physics education does not tell you much about the properties of materials, of specialized techniques, of technologies. --98.217.8.46 (talk) 19:10, 8 June 2008 (UTC)

One difference to consider is that biological organisms are so complex that you really can't predict things very well from first principles. You could have the complete genome of an organism and be utterly unable to predict how many eyes it's going to have or how to treat its diseases. Most human-made -- i.e. engineered -- things are simple enough that you can understand them from the ground up in a way that biologists and doctors might never be able to. --Sean 01:23, 9 June 2008 (UTC)

A physicist may well be able to figure out how to design a bridge, but no engineering firms hire physicists as bridge designers. ike9898 (talk) 20:30, 10 June 2008 (UTC)

Synesthesia

Is there a type of Synesthesia involving smells? —Preceding unsigned comment added by 71.32.207.35 (talk) 23:13, 7 June 2008 (UTC)

This article mentions sound-odour synaesthesia. But it says that it's rare. Fribbler (talk) 23:50, 7 June 2008 (UTC)

I think its rarity can be explained in the context of the cross-activation hypothesis for the Neural basis of synesthesia, as the olfactory cortex in humans is relatively well isolated from other sensory cortex areas. --Dr Dima (talk) 06:26, 8 June 2008 (UTC)

June 8

Suppose that we discovered a large-ish asteroid on a collision course with the earth...

How close would it have to get to us before we could accurately calculate where the point of impact would be? --Kurt Shaped Box (talk) 01:46, 8 June 2008 (UTC)

Don't shoot until you can see the whites of their eyes. Hmm.. perhaps the point at which any changes in its speed or direction are found to be due mostly to the Earth's gravitational pull. The acceleration would theoretically have to be constant, or at least known at all times.--Russoc4 (talk) 01:53, 8 June 2008 (UTC)

Modelling orbits is mostly about having a large number of observations over a long time. Think of it this way. If an object is moving at a typical orbital speed of ~20 km/s, then a 1 m/s variation in that speed would lead to a change in the expected location of 150,000 km over 5 years, which would be a very noticable range of variation. If you have a long enough period of observations, you can be very precise about future orbital positions. For example 99942 Apophis, which will make a close approach in 2036, has it's predicted distance to Earth at that time nailed down to 3381 +/- 8 km (1-sigma). Dragons flight (talk) 02:44, 8 June 2008 (UTC)

Hi. 1950 DA, for example, has a roughly 1-in-300 chance of colliding with Earth in the 2800's, and we've calculated that the Earth's Atlantic Ocean faces the asteroid on its near pass/possible collision date. We don't know its exact chances yet, but we have observed its rotation enough to know this. Hope this helps. Thanks. ~AH1^(TCU) 16:49, 8 June 2008 (UTC)

Looking into the past

moved from talk page

If when we look towards the center of the Universe, we are looking billions of years into the past how is it, the Earth traveled to the distance it is now from the center of the Universe before the light from billions of years ago?

Did the matter that made up the Earth and the rest of the planets materialize in place?

Or did we actually travel faster than the speed of light?

Please excuse grammar and spelling.—Preceding unsigned comment added by 97.89.59.10 (talk) 01:29, 8 June 2008 (UTC)

Well we're obviously not anymore if we can see it. Not sure how that happened though. Probably we were quite close to those stars a looong time ago and space has been expanding at nearly the speed of light or something, so the light has been sloooowly catching up to us. So by the time it finally finishes its 1-inch trip by overtaking us, it's already billions of years old. I don't know, sounds wrong? --.froth. (talk) 03:32, 8 June 2008 (UTC)

There is no centre of the universe. When we say the universe is expanding, we don't mean it's all moving out from a centre, it's more like blowing up a balloon. The 2D rubber surface (ignore the fact that it's contained in 3D space, just think about the rubber) doesn't have a centre, each bit is stretching as you blow it up. If you draw some dots on it before you start you'll see those dots get further and further apart, but they never actually move, it's just the rubber inbetween them gets bigger. When all the matter was created shortly after the big bang, it filled the whole universe and has been spreading out as the universe expands ever since. This means bits of matter can be very far apart without having to have actually moved at all. --Tango (talk) 10:35, 8 June 2008 (UTC)

<----> Ok, even if there is not a center of the Universe, Which I’m not sure is true.

In order to look back in time and space to the Big Bang,

Would we have had to travel faster than the light in order to arrive here first in order to see it?

Is it possible the matter that makes us up arrived here before the light that was emitted from the Big Bang arrived.

could that be possible unless we actually traveled faster than that light, right?

I mean according to the rules; matter can not travel faster than light, so the light that was emitted then would have been at this point in time/space way before we arrived at this point in time/space right?

Please help me understand the logic.

Again please excuse grammar and spelling

<------>

See inflation (cosmology). Yes, the universe grew faster than the speed of light for a microscopic fraction of a second during the Big Bang. As a result, we are only now seeing light from matter we were next to previously (though at that time, none of the current matter had yet condensed). It is also worth noting that the cosmic microwave background, i.e. the "light of the big bang" actually was created ~3 minutes after the "bang", so that light comes from after we were seperated. Also see: Timeline of the Big Bang. Dragons flight (talk) 21:10, 8 June 2008 (UTC)

It's not true that the universe expanded faster than light during the inflationary epoch. Depending on how you define "expanding faster than light", either the universe never expands faster than light or it always expands faster than light; there's no definition that singles out the inflationary epoch. -- BenRG (talk) 23:27, 8 June 2008 (UTC)

(ec) The ideas of expansion of space, seeing "old photons" that are only now arriving to us, etc. comes up fairly often on the Science Ref-Desk. Here's a recent discussion focussing on how things can be further away than conventional "object at speed-of-light" would suggest: Wikipedia:Reference desk/Archives/Science/2008 March 26#Faster than light/Big Bang question. Not a direct answer to your question (which I don't fully understand), but something that may clarify some general/related ideas. DMacks (talk) 21:18, 8 June 2008 (UTC)

Actually, the CMB was released about 400,000 years after the big bang. You were close. ;) --Tango (talk) 21:33, 8 June 2008 (UTC)

The photon epoch begins at 3 minutes, the last scattering event (and end of equilibrium) came a few hundred thousand years later, but I think arguing that point is splitting hairs about what you mean by light created by the big bang. Dragons flight (talk) 21:49, 8 June 2008 (UTC)

We can see light from the early universe because the universe is homogeneous. The primordial fireball that emitted the light filled the whole universe, and the light that it emitted also filled the universe, and it still does, there being nowhere else for it to go. Cosmic inflation is the currently favored explanation for the homogeneity, but there's too little evidence at this point to say whether it's correct. -- BenRG (talk) 23:27, 8 June 2008 (UTC)

This is weird, and maybe I'm reading things wrong, but I believe you're all answering a question that wasn't asked and possibly even explaining them wrong...the way I'm reading the OP's question is "Why can we see into the past by looking at light from far away objects?" The answer is: Because the speed of light is finite instead of infinite. An easier example to understand is sound and the echo effect. When you shout at a large cliff, there is a delay between when your voice is projected and when it comes back as an echo. That time delay is due to the finite speed of sound. In fact, if you knew the speed of sound and the distance to that cliff you could calculate how long it took for your voice to get there (or knowing time you could calculate distance). In the same way, because we can determine the distance to the star using astronomical observation techniques, and knowing the speed of light and the fact that it is constant in the universe, we can determine how long ago the star emitted that light. EagleFalconn (talk) 14:13, 9 June 2008 (UTC)

Lunar Module Ascent Stage

A rocket launch on Earth is a jarring event even for a spectator. The sound and the fury of getting even a modest payload to Earth orbit is simply awesome. The scales involved seem overwhelming.

Why is it that a Lunar Module's Ascent Stage taking off for lunar orbit ( youtube link[8]) seems like such a walk in the park? It's not hundreds of feet tall, just 12. It only weighs as much as 5-10 cars. No ground crew required, no days sitting on a launch pad prepping. No drama whatsoever. Shouldn't the theatrics be 1/6th as much as they are on Earth? Sappysap (talk) 02:51, 8 June 2008 (UTC)

Well, it was just a vehicle to get the astronauts up into orbit (a few hundred miles?), not all the way to the Moon, so they didn't need much life support equipment. It also didn't have to overcome our stronger gravity, plus there was no air resistance or weather to worry about. For all these reasons, it didn't have to be as humongous as the Saturn V. Besides, who says there wasn't a lot of prep work anyway? Clarityfiend (talk) 03:25, 8 June 2008 (UTC)

It's not strictly proportional because you also need more fuel to lift the additional fuel, and more fuel to lift that extra fuel, ad infinitum. So, the higher the force of gravity, the larger percentage of the rocket that must be fuel. A chemical fuel rocket would hit some limit where it could never even achieve orbit from a planet with gravity above a certain level. (I wonder what that point would be ?). StuRat (talk) 14:16, 8 June 2008 (UTC)

Let's do some math to illustrate my point. If we say some type of fuel has enough energy so 10 lbs of fuel can lift 100 lbs of cargo into lunar orbit from the Moon, we would then need 60 lbs of fuel to lift that cargo into Earth orbit from the Earth, before we take into account the fuel needed to lift the fuel. Now, the 10 lbs of fuel would require 1 lb of fuel to lift, and that 1 lb would require 0.1 lb of fuel, for a total fuel weight of 11.1111... The 60 lbs of fuel would require 36 lbs to lift and that would require 21.6 lbs, etc., for a total fuel weight of 150 lbs. Note that the ratio between 150 lbs of fuel and 11.1111... lbs is 13.5:1, far more than the 6:1 ratio of gravity. This effect gets even worse when using fuels with less energy to mass.

So, we have the following reasons so far:

1) This "compounding effect" of fuel weight.

2) Only going to orbit versus escape velocity.

3) Air resistance.

4) The much lighter payload. StuRat (talk) 14:34, 8 June 2008 (UTC)

Don't forget the other implications of having no air resistance on the Moon. The lander is not required to have an cylindral, aerodynamic shape, so it doesn't need to be supported prior to launch while on the platform. Tail fins and other stablization systems are also not needed. On Earth, a rocket's exterior must be at least strong enough to withstand the air pressing on it. I'm not sure whether the casing adds significant weight to the craft, but no such strong structure is required on the Moon. --Bowlhover (talk) 15:59, 8 June 2008 (UTC)

Energy to orbit (neglecting air resistance) in terms of the central mass, M, radius of the object, R, and altitude to orbit, h, is approximately proportional to $M{R+h \over Rh}$. The mass of the moon is 7×10²² kg, versus 6×10²⁴ kg for the Earth. The radius of the Earth is 6370 km, versus 1740 km for the moon. And lastly you need ~180 km altitude to clear the Earth's atmosphere, versus only 20 km for the moon (to clear the mountains, though Apollo actually used 100 km).

Equating terms, you can see that for a given orbiter mass in order to get to orbit the moon you need only 1% as much energy as you do to orbit the Earth, mostly due to the Moon's greatly reduced mass. Since energy is basically proportional to fuel, you can do with far less fuel on the moon than on the Earth. And that's before considering air resistance, booster weight, and everything else one needs at Earth that you don't need at the moon. Dragons flight (talk) 17:17, 8 June 2008 (UTC)

That doesn't seem right; you should get 0, not infinite, energy as $h\rightarrow 0$. Just comparing the gravitational potential energy at R and $R+h$ gives me ${\frac {Mh}{R(R+h)}}$, giving 1.8% as much for the Moon/20km as for the Earth; is that what you meant? --Tardis (talk) 17:10, 9 June 2008 (UTC)

help-- i need some support in my research

hello great brains!!! i am trying to prove reflection of electromagnetic waves from metallic surfaces using basic principle of physics.does any one knows that is the proof going to be unique or it has been already done.actually i am trying to provide a firm reason for reflection of electromagnetic waves,in opposition to hypothetical proof provided by hugens.kindly help me that to which university would entertain such proofs.such that it gets recognized.

Reveal.mystery (talk) 2nd year Mechancal Engineering student India. —Preceding unsigned comment added by Reveal.mystery (talk • contribs) 03:34, 8 June 2008 (UTC)

I'm sorry but I don't understand the question. What are the "basic principles of physics" you're starting from? Maxwell's equations? Quantum electrodynamics? String theory? In at least the first two cases it's already been done. Why do you want to do this? —Keenan Pepper 04:00, 8 June 2008 (UTC)

I think what Reveal.mystery really asks is, "why does Huygens–Fresnel principle hold for the electromagnetic waves, and what fundamental principles of modern physics does it follow from?". Well, as Keenan said, if Maxwell equations are basic enough then, yes, it follows from them almost trivially. Simply assume the incident perturbation in electromagnetic field to be a harmonic plane wave (see equation in article if unsure what it is), and solve either numerically or analytically, whichever you like best. Play with shapes of obstacles and their dielectric constant to get the feeling for how the waves interact with surfaces and edges; this is not always easy analytically, so I would recommend using MATLAB. Now, on the other hand, if you are asking where Maxwell equations are coming from, then things really become much more complicated. First and foremost, there is a chicken and egg relation between special relativity and classical electromagnetism. And I really suggest you look no further than that at least until you are well familiar with the latter two. Hope this helps. --Dr Dima (talk) 06:09, 8 June 2008 (UTC)

I have moved the following new question here as it appears to be a continuation of this question. SpinningSpark 12:47, 8 June 2008 (UTC)

many many thanks to active wikipedists for their support. let me explain what actually i tried for: considering the wave nature of em waves i considered the interaction of the magnetic component of the wave with the metallic surface.now further on by applying lenzs law i propose the generation of an opposite directioned current in the plate.the interaction of the orginal and the field generated by lenzs law finally proves my point.

please helpme so that i may further more proceed in this area.basically i require it to be recognized by some university professor or any journal.since the subject dosent pertains to my branch ,such recognition would help me in my resume for my gre(M tech) interview.

Reveal.mystery (talk) 2nd year,Mechanical Engineering student (email removed per Ref Desk guidelines) india —Preceding unsigned comment added by Reveal.mystery (talk • contribs) 12:38, 8 June 2008 (UTC)

See Heinrich Hertz. He did the experiment you describe in 1886 and showed that electromagnetic waves can be reflected. You could experiment with it using a small dipole transmitting antenna, receiving antenna, and a transmitter and receiver, with a means of measuring signal strength, perhaps by measuring the AVC voltage in the receiver. I have read of physics demonstrations using the RF output (often US channel 3) from a video cassette recorder, with a small dipole antenna, and the same channel input on a TV receiver connected to a similar antenna. See [9] , [10] , [11]. Edison (talk) 19:28, 9 June 2008 (UTC)

I had to this as homework early last decade. To solve the Maxwell's equation you have to put on a few extra constraints, such as no electric field parallel to the surface of the plate. Electric charge can only travel on the surface of the plate. Lens's Law is already included in the Maxwell's equations. Graeme Bartlett (talk) 21:34, 9 June 2008 (UTC)

IF IT IS ALREADY DONE BY HERTZ .LET US DISCUSS WHETHER I AM CORRECT OR NOT .(sorry for caps). Consider the interaction of an electromagnetic wave with a flat metal surface ABCD.consider the wave to be incident along MN and reflected along NO.point of reflection being N. • According to the figure given above we consider a plane wave front of a electromagnetic wave which could be easily represented by a right handed system of axes. the wave propagates along z axis hence the wave propagation vector points along positive x axis.let us assume when the electromagnetic wave strikes the metalsurface at N with magnetic component along Z axis and the electric component along y axis.the dotted rectangle shows a small part of the metal.which we have used to represent the eddy current generated by em eave and the opposing current due to lenz's law as shown in figure.i had studied about the phase change of an em wave by 90 degrees on reflection from a rigid surface .i suppose phase chancge to be as such represented in figure.any em expert wikipedist pay some attention on my research.

Reveal.mystery mech engg student india

(talk)

Cancer screening

Does cancer screening refer only to the search for extant disease, and not individuals at risk from disease but that don't actually have it or can the term be used to encompass both? From my brief search it seems that the term is used to cover the search for existing disease only (even if in the early stages) so the ability to predict development of disease may not be inferred from the term. ----Seans Potato Business 11:26, 8 June 2008 (UTC)

You screen only for actual conditions, not for predispositions. If, for example, one tests a population for a gene that predisposes to cancer (say BRCA1), you're screening for the gene, not for cancer. - Nunh-huh 11:52, 8 June 2008 (UTC)

I think you're being too strict about the usage of "screening". In the US, pregnant women are routinely given prenatal screening for certain conditions of the fetus (such as Down's syndrome and spina bifidia). The screening detects elevated risks associated with certain conditions but does not give definitive diagnoses. In fact, the article on triple screen says:

The test is for screening, not for diagnosis,[4] and does not have nearly the same predictive power of amniocentesis or chorionic villus sampling.

--71.162.233.218 (talk) 13:46, 8 June 2008 (UTC)

Not too strict at all, they are screening for conditions that actually exist - but with imperfect tests. Nearly all screening tests need followup tests for diagnosis, because by their very nature, screening tests will have false positives. - Nunh-huh 03:01, 9 June 2008 (UTC)

Weather forecast

I'm not happy with current forecasts. I'd also like:

1) The predicted time of the highs and lows, and better yet a graph of predicted temps throughout the day.

2) A humidity forecast in a form similar to that listed above.

3) A wind speed forecast similar to that listed above.

Does anybody know where I can get such data ? StuRat (talk) 12:36, 8 June 2008 (UTC)

It might help if you said where you are (ie which country). And also what you are currently looking at. SpinningSpark 13:28, 8 June 2008 (UTC)

I'm in the US (Detroit) and use an Internet site for ad-free weather: [[12]]. I also can get forecasts for the temps every 3 hours or so from digital TV station 4-2, but only for the current day. StuRat (talk) 13:49, 8 June 2008 (UTC)

Have you looked at the NOAA site for your area[13] ? I didn't check if it meets all your spec but its a lot more than what you have already. Here's the link to their front page in case I got your local area wrong [14]. SpinningSpark 14:34, 8 June 2008 (UTC)

That works. I found their "tabular forecast" is what I want: [15]. Thanks ! StuRat (talk) 14:45, 8 June 2008 (UTC)

Hi. I live in Canada, and I can find a way to get all three. Here, The Weather Network[16] gives us hourly forecasts. As for hourly humidity and wind forecasts, The Weather Network gives us that every quarter part of the day, but I can also get it at Cleardarksky, although the measurements are vague. Hope this helps. Thanks. ~AH1^(TCU) 16:53, 8 June 2008 (UTC)

Thanks for the answers so far. Does anyone know of a weather forecast given as a graph ? StuRat (talk) 12:48, 9 June 2008 (UTC)

You've already tried the hourly weather graph tab[17] on the NOAA site right? What is missing there that you need? SpinningSpark 19:37, 9 June 2008 (UTC)

No, I hadn't found the graphs, only the tables. That looks good, except that it's for Detroit, Illinois instead of Detroit, Michigan, and I'm not sure how to change the city. StuRat (talk) 03:15, 10 June 2008 (UTC)

Ok, I figured out how to change the city, but, geez, that site's a real bi*** to navigate, isn't it ? I expected to be able to just pick on "Detroit IL" and type in "Detroit MI", but it's never that simple, is it ? StuRat (talk) 03:49, 10 June 2008 (UTC)

doh - sorry for the crap geography on my part, not my country. The easiest way I found to navigate that site is to start at the top level of weather chart http://www.weather.gov/ then click on the map on the area you want then repeatedly do that through (I think) three levels till you come down to a city. Then click on the type of data you want, which in your case is hourly weather graph. Hope that helps. SpinningSpark 02:39, 12 June 2008 (UTC)

That seems to work. It sure doesn't seem very intuitive, though. I expected to select the type of forecast (hourly graph), and then type in the city and state. StuRat (talk) 04:46, 13 June 2008 (UTC)

Wing layout

Why do most planes have only two wings?

Why layouts with double or three wings on each aren't more common?

And what about having a set of short wings stapled - not broader as the plane - over each other until the plane gets enough drag to fly? GoingOnTracks (talk) 12:53, 8 June 2008 (UTC)

See Biplane#Advantages and drawbacks to biplane designs. Xn4 13:31, 8 June 2008 (UTC)

We don't seem to have anything explaining the unpopularity of tandem wing designs, though. Algebraist 13:32, 8 June 2008 (UTC)

The unpopularity of tandem wing might be explained by its increased stability, which surprisingly, is not always desirable. Certainly for fighter aircraft, maneuverability is king and stability and maneuverability are mutually exclusive. Also, if sufficient stability can be achieved by other means (high mounted wings, dihedral etc) why go to the expense of additional wings. Also some large commercial aircraft (eg Boeing 747) achieve distributed CL (the reason for tandem wings increased stability) by means of the lifting body effect. SpinningSpark 14:05, 8 June 2008 (UTC)

Just one more point, the designer of the aircraft (Rutan Quickie) in the picture in the tandem wing article says he designed it that way so that it resembled the Stars Wars X wing starfighter. Probably not a lot of call for that outside of the kit plane market. SpinningSpark 14:17, 8 June 2008 (UTC)

One big factor seems to be the speed of aircraft. More wings means more lift but also more drag, both of which also increase with speed. Early planes went quite slowly, so needed all the lift they could get, and drag wasn't much of an issue. Current planes are much faster, so getting sufficient lift is possible from fewer wings, while keeping drag low is also more of an issue. StuRat (talk) 14:09, 8 June 2008 (UTC)

Excessive numbers of wings were included in some very early plane designs like the Phillips Multiplane [18] but triplanes are gone now, biplanes rares. Some canards seem like second sets of wings (Beechcraft Starship). Rmhermen (talk) 18:12, 8 June 2008 (UTC)

StuRat has it right - it's to do with drag (and mass). A single main lifting wing is usually the most efficient design to achieve a given lift with minimal weight and drag. In addition, the calculations required to design a multi-wing plane are much more complex, since there is a lot of interaction going on between the various wings (see the canard article for some of the trade-offs of using canards), so it's easier to optimise a one-wing design. — QuantumEleven 15:29, 10 June 2008 (UTC)

How do astronauts commit suicide?

Do they have some sort of suicide pill? Or are they expected to "sink" with the "ship"? —Preceding unsigned comment added by 88.6.118.85 (talk) 17:30, 8 June 2008 (UTC)

We are not a crystal ball - no astronaut has committed suicide in space yet. In fact, only three people have died while in space, the crew of Soyuz 11 due to a malfunctioning vent. (See also space accidents and incidents) While on Earth they have access to any suicide technique the rest of us do. Rmhermen (talk) 17:57, 8 June 2008 (UTC)

I think the original poster was asking about a situation where astronauts were stranded with no hope of rescue—would they be provided with means to commit suicide in lieu of 'waiting it out'? Obviously it hasn't happened yet, but it doesn't mean that no one has planned for it.

To reply to the question, as far as I can discern there is no record of NASA astronauts carrying suicide pills, nor is it likely that Soviet astronauts carried them. (Links to Q&A with shuttle crew, reference to Jim Lovell's book on the Apollo 13 mission.) Several astronauts and commentators note that there's no need to carry suicide pills on a space mission—venting the air from the capsule will do the job quite nicely, and loss of consciousness will occur in about fifteen seconds. TenOfAllTrades(talk) 18:09, 8 June 2008 (UTC)

The first person to perform a spacewalk, Leonov aboard Voskhod 2, secretly carried a suicide pill in case he had been unable to enter the spacecraft and had to be cut loose. --Bowlhover (talk) 18:50, 8 June 2008 (UTC)

Nonsense! How would he take the pill, considering he had a bloody big helmet on?--ChokinBako (talk) 11:30, 10 June 2008 (UTC)

I'm similarly puzzled, but it seems that Wikipedia is far from being the only source of the information. --Bowlhover (talk) 23:34, 12 June 2008 (UTC)

But is venting the air painless? How quickly can it be done? I doubt there's a "vent the air" button on the control panel. Wouldn't that be equivalent to a self destruct button? What if your buddies don't want to die with you? I think the original poster may have gotten the idea of a suicide pill from the movie Contact based on the novel by Carl Sagan. In it, Jodie Foster's character is given a suicide pill before she goes into the machine to take her to make contact with aliens. She is told that the pill has been given out to astronauts ever since the space program began, but it was never made public. She was told that the pill can be useful if she's stuck somewhere with no way to get back home, or trapped. Faced with the possibility of a slow painful death, the pill would put her out of her misery quickly and painlessly. She was also told that the pill is for all the reasons that they "could not think of". ScienceApe (talk) 18:53, 8 June 2008 (UTC)

That's fiction of course (rather a long drawn out one as I recall). I'd be more interested to know just how Leonov intended to administer his pill during the speacewalk given that's he'd be wearing his spacesuit.--Shantavira|^{feed me} 19:15, 8 June 2008 (UTC)

Nope, not drawn out at all. It was a very good movie. ScienceApe (talk) 02:45, 9 June 2008 (UTC)

Couldn't you just like take off your space helmet outside and suffocate?-- —Preceding unsigned comment added by Crystal eyes17 (talk • contribs) 20:59, 8 June 2008 (UTC)

I don't know about the Russian space program, but NASA spacesuits are designed in a way that the wearer can't possibly reach all the latches necessary to remove the helmet, and the assistance of a second astronaut is simply required to get out of it. Dragons flight (talk) 21:04, 8 June 2008 (UTC)

And even if you could get it off, the pressure would kill you before you suffocate since your blood (and all other fluids) would literally boil in the zero pressure of space.--十八 08:27, 9 June 2008 (UTC)

Well boil yes, but not "completely and instantly boil away" and not "astronaut swells up and explodes like in the cartoons":) Actually, the injury/death mechanisms don't seem related to the fluid-boiling issue at all See Vacuum#Effects on humans and animals for more info. DMacks (talk) 08:39, 9 June 2008 (UTC)

There's zero pressure outside your body, but inside, where the fluids are, there is still pressure supplied by your body. Assuming you don't try and hold your breath, which could result in your lungs exploding, death is usually by suffocation and if very quick (about 15 seconds to lose conciousness) - the vacuum almost "sucks" the oxygen out of your blood. --Tango (talk) 14:54, 9 June 2008 (UTC)

I'm pretty sure I heard of one instance where NASA astronauts were accidently subjected to a vacuum during training. I believe they passed out within 15 seconds before realizing anything was amiss, and without lasting injury. Someone may correct me if I'm wrong. Paul Davidson (talk) 13:50, 10 June 2008 (UTC)

I think they knew something was amiss. If memory serves, they reported their last memory before losing conciousness was of the saliva on their tongue boiling. Otherwise, you're right, they repressurised the room pretty quickly and the subject regained conciousness once the pressure got back up to a reasonable level, with no ill effects. I'm sure the incident is described on Wikipedia somewhere, I'll try and find it. --Tango (talk) 13:58, 10 June 2008 (UTC)

Found it: Human adaptation to space#Unprotected effects. Once again, we find that Wikipedia has an article on everything! --Tango (talk) 14:03, 10 June 2008 (UTC)

Garbage into oil?

Was there an attempt to turn garbage or sewage into oil? ScienceApe (talk) 18:42, 8 June 2008 (UTC)

Discover magazine says yes. The company responsible is Changing World Technologies. Clarityfiend (talk) 19:42, 8 June 2008 (UTC)

Why isn't this done on a much larger scale? We have enormous landfills that can be turned into oil. ScienceApe (talk) 02:47, 9 June 2008 (UTC)

When I expanded the CWT article, I found that their particular method costs $80 to produce a barrel of diesel, so until recently, it wasn't very profitable. Besides, the stuff in landfills would almost certainly have to have metals and other inorganic material removed, further raising costs. Clarityfiend (talk) 02:52, 9 June 2008 (UTC)

I can't provide a reference, but I know that the one large-scale implementation of this process (discussed in our article on CWT) had significant problems, including being shut down temporarily for generating very strong odors. ike9898 (talk) 20:24, 10 June 2008 (UTC)

See List_of_solid_waste_treatment_technologies#Advanced_waste_treatment_technologies methods include pyrolysis Gasification#Waste_disposal Thermal depolymerization amongst others - food waste is popular, as is garbage. Sewage is a possibility but more likely to be treated by Sewage_treatment#Anaerobic_digestion (as it is very wet) making 'biogas' which can be made into oil. If you are still interested try Waste management and follow the links...87.102.86.73 (talk) 17:23, 9 June 2008 (UTC)

The worst case of food allergies and religious food laws

What are the worst known cases of food allergies combined with restrictive religious food laws? E.g., you are not allowed to eat certain foods, but you are allergic to most of the foods that you are allowed to eat. Furthermore, most of the non-allergic and legal foods are not available in the place that you live. -- Toytoy (talk) 19:03, 8 June 2008 (UTC)

Religious food laws rarely limit the diet that much. For example, kosher and halal (which are similar in scope) limit barely a fraction of the pantheon of foods we could eat. I can't imagine a situation where one would need to circumvent these laws in order to avoid eating foods to which we are allergic. Fribbler (talk) 23:00, 8 June 2008 (UTC)

There was a somewhat related case mentioned in the radio recently. Certain christian priests complained that they have to administer masses in towns far away from their home so it would be best if they could drive, but they also have to drink wine for celebratory purposes on the mass, which of course excludes driving. – b_jonas 09:36, 9 June 2008 (UTC)

It's possible to be allergic to alcohol. Both that and gluten intolerance can make Holy Communion difficult. I read (but have lost the link) that members of the congregation may take only one, but Catholic priests must take both the bread and wine. 81.174.226.229 (talk) 11:00, 9 June 2008 (UTC)

http://www.catholicceliacs.org/Bishops.html ? —Keenan Pepper 12:05, 10 June 2008 (UTC)

To be technical, there's no such thing as an alcohol allergy, in large part because the ethanol molecule is way too small to be recognized by the immune system. One can however, have an alcohol sensitivity, which something else entirely. I can't find a specific reference to this on Wikipedia, but Mayo Clinic does a pretty good job. – ClockworkSoul 14:33, 10 June 2008 (UTC)

Let me add on to my statement a bit: there seem be be a number of reliable sources that suggest alcohol allergies do exist but are very uncommon. I'm more than a little skeptical, but I should at least acknowledge them. – ClockworkSoul 14:39, 10 June 2008 (UTC)

If you haven't come across it already, you may be interested in this [19] which mentions several case studies Nil Einne (talk) 18:38, 10 June 2008 (UTC)

Actually wikipedia covers Alcohol flush reaction and Alcohol tolerance resonably okay, which appears to be what the Mayo Clinic link is referring to. I'm not sure about alcohol allergies however. BTW, people with the alcohol flush reaction are unlikely to be trouble by receiving communion since the amount consumed is so low, it's unlikely to cause any problems. Nil Einne (talk) 18:35, 10 June 2008 (UTC)

Actually I was referring to the way my Dad's cousin vomits if a sauce contains alcohol which hasn't been completely evaporated by cooking, which may not be a proper allergy but doesn't sound like a mere tolerance issue. 81.174.226.229 (talk) 09:16, 11 June 2008 (UTC)

Rubber

Does all rubber contain latex? —Preceding unsigned comment added by 76.125.70.46 (talk) 20:01, 8 June 2008 (UTC)

In the area of rubber, latex does not indicate the contents of the rubber. It indicates that the rubber has not been vulcanized. -- kainaw™ 20:38, 8 June 2008 (UTC)

Latex is a pretty slippery term; its meaning depends quite a bit on context. Our article includes a fuller description of the different meanings. People who have a latex allergy are sensitive to natural rubber; they're likely not bothered by latex paint (which contains acrylic polymers). Generally – but not always – so-called 'latex rubber' is not vulcanized.

Synthetic rubber can be manufactured using a variety of compounds, many of which bear little resemblance to the ingredients of natural latex. Finally, the pedants will point out that 'latex' describes an aqueous emulsion; 'rubber' is what you get after the latex dries. Confused yet? TenOfAllTrades(talk) 15:54, 9 June 2008 (UTC)

Strange hypnagogic sensations

Sometimes when I'm just falling asleep, I experience a strange sensation -- it feels like my body is being distorted, changing in size or becoming stretched and compressed. It's not painful, but sort of dizzying and disorienting. This often accompanies the usual sensation of floating or falling, and sometimes sleep paralysis occurs at the same time. Is this a documented phenomenon, and what could its psychological or physiological basis be? 69.111.189.55 (talk) 21:45, 8 June 2008 (UTC)

Well, from your subject heading I guess you know about Hypnagogia... the article doesn't describe your experience exactly, but it seems in keeping with the broad set of weird things that happen in that state. Other than that, I don't know. --Allen (talk) 01:24, 9 June 2008 (UTC)

Wow. I used to feel that way often when I was a child and teen. I had forgotten all about that until I read this. At the time it was a bit disconcerting and I didn't know if it was something physiological or if it was all in my mind. My memories of the experience really don't sound anything like what is described in the hypnagogia article. It was more like my sense of scale was all weird; like my body was flattening, or if I closed my eyes I could see/feel in the blackness a perfect line, and I could let myself fall partly into it in a sense. At others it was like my fingers were huge, and it was a wonder I could move them. It is a very hard thing to describe. I don't think I could have then, and obviously I'm not doing a very good job of it now.

I think such sensations usually did happen when I was going to sleep, but I can't tell you if that was the only time or not (it's possible it also happened at other times when I was at rest and had a chance to calmly observe my sensations--e.g. meditation). Maybe it has something to do with the growing process; I haven't felt that way in my adult years. Then again, my sleeping habits have changed significantly since then too.

Anyway, sorry for the non-answer. It was great to hear someone else express the same kind of sensations that puzzled me, and I hope my rambling might in some way help you too, even if it isn't anything close to an "answer". (Keep in mind I'm not giving advise; if this is something you are at all concerned about, consult a medical professional.) --Prestidigitator (talk) 04:37, 9 June 2008 (UTC)

The "huge fingers" sensation happens to me, too; I also lose track of what position my arms are in. Indeed, it's kind of a relief to know that I'm not the only person who has these weird half-dream experiences. 69.111.189.55 (talk) 02:23, 10 June 2008 (UTC)

I used to get it when I was a teenager too. That is when I started to get sleep paralysis, too. My hands would feel enormous but not heavy in any way, just really big. The sleep paralysis was a seperate thing, though, and I experienced it more and more as I got into and went through my 20s. Take a look at the article Kanashibari. --ChokinBako (talk) 11:26, 10 June 2008 (UTC)

June 9

Prevnar vaccine

Is prevnar equally effective in India?Does it make sense to give prevnar to an infant in india, as the cost here is quite something. —Preceding unsigned comment added by 203.112.84.138 (talk) 09:35, 9 June 2008 (UTC)

The concern here is whether Prevnar, a pneumococcal conjugate vaccine available since 2000 in the U.S., and recently (2006) introduced in India, (see here) is effective, since it was developed to protect against the seven serotypes of pneumococcus that are most prevalent in the U.S.

Prevnar protects against serotypes 4, 6, 9, 14, 18, 19, 23, which cause 80-90% of disease in young children in the U.S. In Europe, which has a significantly lower incidence of invasive pneumococcal disease than the U.S., these 7 serovars account for only about 70-80% of that disease. In India, the most common serotypes in children under 5 years were 6, 1, 19, 14, 4, 5, 45, 12, and 7, in that order. [20] So Prevnar would protect against 4 of the 5 most common Indian serotypes, but would not protect against 1 and 5, which are more common in developing countries, and together make up 29% of Indian isolates. Clearly, if the vaccine had been formulated primarily for Indian use, it would have included these serovars rather than 18 and 23; and equally clearly, the vaccine protects against serovars that cause significant amounts of disease in India. An article in Indian Pediatrics notes that 25% of all child deaths in India are from pneumonia, and estimates that 30-40% of these are from pneumococcal pneumonia, meaning that between 123,000 and 164,000 children under the age of 5 die each year in India of pneumococcal pneumonia. Vaccines with either ten or thirteen serotypes, including 1 and 5, are likely to be available in 2010. India meets the WHO’s criteria for countries where pneumococcal vaccination should be a priority for introduction. The risks and benefits in any particular case must be decided in consultation between physician and patient. Since the concern here seems to be financial risk: The cost in 2006 was Rs 3750 per dose plus taxes, and was not covered under the extended programme for immunisation in India. If it chose to, the Indian government could obtain the vaccine at a cost of between 15 and 30 cents (U.S.) per dose. [21]. The editorial cited asks the Indian Academy of Pediatrics to urge the government to develop a process and timeline for introducing pneumococcal vaccination.

- Nunh-huh 20:18, 9 June 2008 (UTC)

Hmm, the question is posed as asking whether administering a vaccine is advisable. Isn't that medical advice? With all due respect to the responder, shouldn't this post simply be removed? Franamax (talk) 06:35, 10 June 2008 (UTC)

A request for information is not a request for advice, even if one can imagine that that information may ultimately be used in making a medical decision. No advice has been asked for or offered. The main distinctions between the referenced section in our Prevnar article is that the answer here is a bit more detailed, accurate, up-to-date, world-centric, and referenced than it is there. It's hardly censorable. A medical advice request would have been: "Should I give my baby Prevnar?". That wasn't asked. What was asked is "Is Prevnar effective at preventing disease in Indian babies?" - Nunh-huh 07:16, 10 June 2008 (UTC)

I'm normally a medical advice czar, but would have to agree with Nunh-huh here. The response was clearly not medical advice and concentrated on things like the cost-benefit to India etc and didn't answer much on what on whether it's advisable for a person to vaccinate their baby, which would depend on many factors and clearly should not be answered on the RD for precisely that and other reasons Nil Einne (talk) 22:38, 11 June 2008 (UTC)

Tooth restoration

before one restores a tooth permanently with amalgam can one temporize with IRM till gingiva improves and better moisture control is achieved for tooth to be restored are there any guidelines for it.

Thanks tanya —Preceding unsigned comment added by Mtanya (talk • contribs) 14:16, 9 June 2008 (UTC)

Is this a homework question? If so, could I have your name so that I never visit a dentist who asks random Internet dweebs to do their homework for them? Thanks. --Sean 14:52, 9 June 2008 (UTC)

Harsh - everyone starts with no knowledge and acquires it through training/education. That they ask for information (perhaps due to laziness at homework, or out of genuine need of help) isn't an indicator of their future abilities in the dental field. Oh and re the Q - I have no idea at all, sorry. ny156uk (talk) 17:23, 9 June 2008 (UTC)

You may want to check out the wikipedia articles: Dental restoration, Temporary restoration or Dental restorative materials, specifically Indirect Restorative materials (which is what I presume you mean by IRM). Checking out the citations in these articles will surely point you in the right direction. Jdrewitt (talk) 20:48, 9 June 2008 (UTC)

In this day of eliminating mercury in the mouth, someone is still using amalgam?—Preceding unsigned comment added by Julia Rossi (talk • contribs) 07:35, June 10, 2008

Amalgam is used as standard in many places; in the UK, for example, most NHS fillings are amalgam (if anyone's lucky enough to have an NHS dentist). Amalgam has many advantages over the resin alternatives (which can be found by reading amalgam), for which reason many dentists still recommend it for some work. The main advantage of resin compounds is cosmetic; it is not as effective for restoration, as it fails much sooner, can leak, and eventually shrinks, leading to bacterial growth and continued decay; if they are not maintained and replaced regularly there is a greater risk of root canal problems. It is also less effective for restoring larger areas. In addition, it is more expensive (particularly at the clinics which tell you of the dangers of mercury amalgam and offer to replace all your fillings for you). As to the possible toxicity of mercury amalgam, the jury is still out. I've got some amalgam fillings. If I go mad because of them, I'll let you know.  :) Gwinva (talk) 03:52, 11 June 2008 (UTC)

Incidentally Amalgam (dentistry) needs work. In the controversy part, it says "The most recent source[citation needed] of controversy has been from a December 1990 episode of the CBS news program 60 Minutes". I added the fact tag but the problem is obvious. Other then the fact this is uncited, it seems dubious to me that the most recent source of controversy could be conclusively said to be a 1990 episode of 60 Minutes. Especially since it's unclear how much controversy this generated internationally and the same section also says "In recent years evidence of serious toxic effects, for instance 25 studies of 5821 patients reviewed in "Effects of Amalgam Removal on Health", by Mats Hanson, plus a later study by Wojcik, Godfrey, Christie, Haley (2006)". (One would think this 2006 study generated some controversy) Nil Einne (talk)

Mercury, and cosmetic dentists with an alleged mi$$ion. I guess it's the processing which is more dangerous given that the vapour is toxic, but maybe in its set state, not the same problem (as testified to by Gwinva's erudition : ). In the mercury article there's a more recent ref to controversy – activity re bans in Norway 2007-2008 and needs references. Julia Rossi (talk) 23:46, 11 June 2008 (UTC)

Psychological concept of your perception of others

I vaguely remember a psychological/philosophical concept from the anime Neon Genesis Evangelion, which was along the lines of your perception of other people - their personality, appearance, your understanding of their motives and such, essentially the version of that person which you hold in your mind, which stems from your memories and previous encounters with this person - could be considered, philosophically speaking, as valid a description of them as that person's actual existing self. Does this concept have its roots in any psychological theory? Thanks. --Sum0 (talk) 20:05, 9 June 2008 (UTC)

That sounds like philosophy, not psychology. I don't see any psychological about that. --Tango (talk) 21:38, 9 June 2008 (UTC)

It's not quite what you say but "projection" could come into it if it means your perceptions are actually subjective. Closer to it is the empathy phenomenon. Julia Rossi (talk) 07:31, 10 June 2008 (UTC)

Enzymes that remove pet urine odor

I understand that certain "enzymes" can break down pet urine in carpets. Something about the enzymes consuming the bacteria. Supposedly the urine smell occurs as bacteria consume the urine. Enzymes are said to kill and or neutralize this activity and reduce or eliminate odor. My question is what exactly are the names of these enzymes ? _____ase I want to know so I can be sure the product I purchase will actually do the job. Thank You, 70.118.255.25 (talk) 23:33, 9 June 2008 (UTC)

I don't think your theory is correct. There are very few bacteria in urine, as it is both sterile initially and somewhat antiseptic. The smell is simply ammonia. Any chemical which reacts with ammonia to break it down into odorless components would work to control the odor. Since ammonia isn't a protein, it doesn't require an enzyme to break it down. 67.38.24.177 (talk) 03:08, 10 June 2008 (UTC)

I don't have a specific answer for the OP, but I want to address a couple of misconceptions in the answer above. First, there's normally very little ammonia in urine; instead, nitrogen is excreted as urea. Thus, fresh urine has very little odor. Certain bacteria produce urease, which will "split" urea and can produce ammonia as a by-product. I suppose it is possible to inhibit the ureases. Second, as this suggests, enzymes act on many molecules other than proteins.Scray (talk) 03:29, 10 June 2008 (UTC)

OP is right as least inasmuch as there is a product that digests or absorbs or renders inaccessible the nitrogen in cat-pee that bacteria feed on. They had to spray a bunch of it when I moved in a year ago - and she was such a nice girl who never even owned a cat, too. I'll try to ask one of the maintenance people next couple of days, but by all accounts, such a theory and product does exist. Franamax (talk) 06:13, 10 June 2008 (UTC)

Googling "pet urine odor" shows lots of (lame) home-remedies and several commercial products using enzymes. We can't recommend a single product, and you will really never get any single name of some particular enzyme that is the "right" one. They are all commercial products, you need to read the descriptions and customer reviews on various websites and figure it out. Reading through the links, there are two or three that I would try. If I can find out the particular product used for my case, I'll post it here. Franamax (talk) 06:30, 10 June 2008 (UTC)

June 10

Feisty baby gull...

Has anyone else here ever seen a gull chick deliberately starting a fight with an adult bird - and winning? Today, I had the opportunity to observe a colony of nesting Black-headed gulls at close quarters in their natural habitat. I noticed that most of the gull pairs had built their nests on small salt marsh 'islands', meaning that space was at a premium. The gulls (being typical gulls) were of course bickering, squabbling and pecking each other constantly over minor territorial encroachments and airspace above the nest. What surprised me, however was to see one of the older chicks joining in.

This particular bird was about 2/3 adult size with partially-grown wing feathers, so he/she was probably about three weeks old, or so. Yes, this youngster was starting fights with any adult gull which came too close to his mother's nest. Not only was he starting fights, more astoundingly he was winning them too! While I was watching, he must've seen off about 15 intruders with his chest-puffed, charging pecks. He certainly wasn't staying on his side of the line either - more than once, he chased an adult gull all the way across the island and into the water with his heel-snapping, causing absolute pandemonium amongst the uninvolved sitting hens. I just can't understand why the adult birds were prepared to take that from a chick...

Oh yes, in answer to the question someone asked the other day - it seems that baby gulls of this species *can* and do swim. I saw birds that were no more than a couple of days old trying to swim away from their nests (much to the annoyance of the parent gulls, who would corral them back, scolding loudly). They seemed to be fully waterproofed too. --Kurt Shaped Box (talk) 01:59, 10 June 2008 (UTC)

That sounds like behavior typically associated with species that have ascribed social status. That is, the offspring of the "alpha pair" may have the right to push around others, even adults. Do gulls exhibit such a complex social pattern as this ? 67.38.24.177 (talk) 03:04, 10 June 2008 (UTC)

I don't think so but I can't say for certain. I'm not as familiar with this species as I am with some of the others. --Kurt Shaped Box (talk) 14:39, 10 June 2008 (UTC)

gravitational redshift

The Pound-Rebka experiment showed that gamma rays lost energy/frequency as they fell through the building, due to gravitational redshift. Only by moving the emitter downward relative to the receiver could the gamma rays be given enough (doppler) frequency to be absorbed. This diagram and relativity-common-sense would seem to support that "time" runs slower for things (like photons) undergoing acceleration.

But the gravitational redshift article (and general relativity) says that light originating from a stronger gravitational field will have longer wavelength when received by an observer in a weaker gravitational field. Redshift for deceleration now! Which is it? The former makes more sense to me.. like a pendulum, the left-right motion of the wave in the horizontal direction stays the same, but the wavefront moves faster due to acceleration from gravity. So a stationary observer sees "more wave" go by for each cycle.. a redshift. So which is it for falling light? Redshift or blueshift? .froth. (talk) 05:27, 10 June 2008 (UTC)

Blueshift. If you move deeper in a gravity well, then you gain energy. Since photons can't actually move faster, the way this is manifest is by their blueshifting to higher energy state. Dragons flight (talk) 05:36, 10 June 2008 (UTC)

Fans and heating/cooling

Two questions:

1. If I put my hand in front of a fan, I can feel lots of air getting blown out. But if I put my hand behind the fan, I can barely feel any air getting sucked into the fan. So where does the air getting blown out the front of the fan come from? It feels like there's way more air coming out then getting sucked in.
2. It's summertime, and for the moment, I'm in a house without an air conditioner. At night, when the temperature drops, the second floor rooms stay way hotter than the first floor rooms and way hotter (by 5 to 10 degrees Fahrenheit) than the outside environment. Presumably, what is happening is that all the hot air from the first floor is rising up to the second floor and then getting stuck in the second floor rooms without being able to go out. I've tried opening all the windows on the second floor, but the temperature seems to still refuses to drop by much up there, probably because there is close to no wind these past few days. I was thinking that I could improve air circulation by sticking fans in the windows. My question is, if I did so, which way should I stick the fans? Would it be more effective in cooling the rooms to have the fans blowing cooler air from outside into the hot rooms, or to have the fans blowing the hot air inside the rooms out the window?

—Lowellian (reply) 07:09, 10 June 2008 (UTC)

Fan pushes air which is in front of its blades. It does not suck from behind. Window fan, or as I call it Exhaust fan may solve your problem. manya (talk) 07:33, 10 June 2008 (UTC)

I'm sorry, manya, but your explanation isn't correct. Fans generally take air from one side of the blade disk and push it out the other side of the blade disk. With regard to the original question, if the fan were mounted in a duct, so that all of the air was constrained to travel within the duct, I think you'd find that air flow would feel the same on either the inlet or outlet sides of the fan. But room fans aren't mounted within a duct so the airflow isn't so constrained. I think the cause of the effect is two-fold: air flows into the fan blades from a variety of directions and a rather large "subtended angle". Because of the large subtended angle, the inflowing air can move at a pretty low velocity and yet move into the blades a large volume of air. On the outlet side, though, the moving air stream is probably more focused, so the same volume of air needs to now move at a higher velocity. A second-order effect is that the outlet air stream probably tends to drag surrounding air along with it, decreasing the stream's velocity but further increasing its volume (in the same fashion as a jet pump moves more water). This would probably be a lot easier to explain if the Reference Desk were equipped with a wind tunnel so you could see, via the smoke streams, the various flows of air. ;-)

With regard to exhaust fans, see whole-house fan.

Atlant (talk) 12:06, 10 June 2008 (UTC)

Good answer! --Anonymous, 00:01 UTC, June 11, 2008.

The best way to clear out the air in a room is to have one window fan blowing air out, and another one across the room blowing it in. I speak from broken-air-conditioner-in-102-degree-weather experience. --Sean 12:56, 10 June 2008 (UTC)

I'm with Atlant with his explanation. To explain it slightly differently, the air being blown out of the fan is focused to travel in a specific direction by the shape of the blades, therefore the moving air takes up a given volume (lets call it x for fun). On the 'input' side of the fan, there is no such restriction on where the air comes from. As the blades push the air directly in front of them out of the way into the volume x above, there is a (momentary, instantaneous, imaginary, useful for this exercise) vacuum that is created because there is no air present. To keep the air pressure in the volume constant, the atmosphere rushes in 'uniformly' and 'from all directions'. Because its coming in from all directions, it occupies a greater volume and (as Atlant said) the flow rate is lower because theres a greater volume flowing.

To address your second concern, Sean is correct. Having all fans blowing outward would be the least useful solution because (assuming theres no other source of air) all of the air would have to travel through the rest of the (substantially warmer) house before it could reach the second floor, which would minimize cooling capacity. If all the fans face in, you'll get lots of cool air in but the warm air in the house will still be present increasing the amount of air that needs to be cooled. But having an equal number pushing in and pulling out will bring an influx of cool air (what the first method lacks) and also remove warm air (what the second method lacks). If done correctly, it will also reduce the amount of electricity needed compared to the other two. EagleFalconn (talk) 13:28, 10 June 2008 (UTC)

You don't even need the fans - just opening one window at the front of the house and one at the back (and the internal doors inbetween) will create a significant flow of air through the house. The fans will increase the effect, especially if there is no natural wind, but they aren't essential for the basic principle. --Tango (talk) 15:25, 10 June 2008 (UTC)

Here's an article I wrote on home cooling with fans: [22]. It seems to answer most of your questions listed under part 2. In your case, I recommend blowing cool air in on the lower floor and out on the second floor. Note that this will cool the lower floor more quickly than the upper floor, though, as the hot air on the lower floor must first move to the upper floor before being exhausted. You might want to sleep on the lower floor if it remains too hot upstairs. The other option is to have fans blowing in and out on both floors.

Note that the inside temp often increases after sunset because the exterior walls, which have been absorbing sunlight and changing it into heat, begin to radiate this heat inside the house. The delay between when the sunlight is absorbed and the heat reaches the inside has to do with the thickness of the walls and their thermal conductivity. Something like a 6 hour delay is typical for the average brick house. Thus, if the hottest point outside is at 3 PM, the hottest point inside may not occur until 9 PM. Hosing down the brick wall periodically may also help to reduce the heat which they contain. Be sure to close any windows, first, though. StuRat (talk) 20:52, 10 June 2008 (UTC)

I'll throw a couple more tidbits into this dicsussion, as I too lived in a house with no central AC for 25 years.

• If you only have one fan, have it exhaust the hot air.
• If there's any breeze at all, use it -- don't try to exhause hot air into the wind!
• If you have a built-in fan in the bathroom (a "fart fan"), use it too -- it's closer to the ceiling than anything else.
• Having a fan blowing on you is pseudo-cooling; you're increasing the evaporative effect but doing nothing to cool the rest of the room.

And despite all that, sometimes you just have to sleep on the floor in the basement :-). --Danh, 67.40.166.141 (talk) 23:49, 10 June 2008 (UTC)

I have to disagree on using a single fan for exhaust. That will result in a slight negative pressure in the home which may cause air to backup down chimneys, may suck in bugs and dust when you open exterior doors, etc. Also, a room in which the fan blows inward will quickly cool, and the air circulation will make it feel even cooler than it is, so that's a good place to sleep. StuRat (talk) 04:59, 11 June 2008 (UTC)

StuRat, the "single exhaust fan" is the exact working concept behind the whole-house fan. The idea, of course, is that you don't just exhaust from the house, you also open "inlet" windows , usually concentrating on the room(s) that you're currently occupying. This (and the damper that you've installed on your chimney) prevents pulling soot, bats, etc. down the chimney or radon from below the basement floor. And because the exhaust fan is usually located remotely from you, you don't hear it very much. I've lived in two houses now that had whole-house exhaust fans and found them to be very useful. Their principle disadvantage is that because you're circulating exterior air through the house, you're alos bringing in pollens and other exterior pollutants.

With regard to bathroom exhaust fans, before anyone implements that strategy, be sure you know where the exhaust from you bathroom fan goes! Some just recirculate through an activated carbon filter and those will be worse-than-useless in helping to cool you. And some that are meant to exhaust to the outside aren't properly installed. My curent house was an example of this. All our various bathroom fans exhausted into wall spaces and the previous owner's use of these fans resulted in nothing but the creation of rot. Mis-exhausted fans won't help keep you cool either.

Atlant (talk) 11:54, 11 June 2008 (UTC)

I suppose I'm biased here because we have a defective chimney with no cap or damper (which led to a friendly visit from our neighborhood squirrel doing his Santa impersonation), and the whole house smells of smoke when I have more fans blowing out than in. However, even in a home without a fireplace or with one tightly sealed, there are still exhaust vents from the water heater, furnace, and dryer (unless they are electric), so creating negative pressure in the home could cause those to back up. If they are properly functioning and enough windows are open they likely won't back up but will only work somewhat less efficiently. Another risk is that negative pressure can pull air out of the wall spaces, which might have mold spores in them, while a positive pressure would push the air in the wall spaces outside. However, as blowing air in (with windows open where you want to exhaust air) will result in just as much air exchange as blowing air out, why take the chance if you have the choice ? StuRat (talk) 14:59, 11 June 2008 (UTC)

One further point. I live in a house with an unfinished attic above the second floor. The "ceiling" of the attic is simply the underside of the roof structure, and the "floor" is the structure supporting the second-floor ceiling. The important thing is that the attic space is not thermally part of the house, but is part of the outdoors; the attic "floor", not the "ceiling", is covered with insulation. If your house is like this, it may be helpful to increase the ventilation between the attic and the outdoors by adding vents; since the attic is heated during the day by sunlight on the roof, ventilation reduces heat buildup. It may also be desirable to increase the amount of insulation, both to reduce warming of the second floor by the attic in summer and to reduce heat loss through the attic in winter. --Anonymous, 00:01 UTC, June 11, 2008.

Physics -- Force, Mass and Acceleration

I've been asked this question by somebody who found it in a book (which didn't bother to provide the answer): We know that F=ma. If we consider a constant acceleration, and then plot a graph of the force required to give/achieve that acceleration against different masses taken, the graph assumes the form of a curve. Why is it so, knowing that the relation between force and mass is linear? 117.194.226.154 (talk) 08:11, 10 June 2008 (UTC)

I'd be interested in seeing a sample of that graph, or at least the specific axes used (and anything else non-obvious, like not being simple/unconstrained linear motion, etc). As described, F vs m for some constant a should indeed be linear as you say. DMacks (talk) 08:17, 10 June 2008 (UTC)

I think the only reason it would curve is if a is being factored into the graph, and is only held constant at intervals, but not during the entire length of the graph, or else if a was always the same value it would be linear as stated.--十八 10:06, 10 June 2008 (UTC)

Yeah, it should be a straight line, unless we're missing a key detail. Of course, a line is a type of curve by the strict mathematical definition, so perhaps that's what it means... a rather strange way to say it, though. --Tango (talk) 12:48, 10 June 2008 (UTC)

Yeah, assuming a vacuum with no other forces acting on the mass, it should definitely be a straight line. Certainly in many realistic situations you would get a curve, though, due to things like air resistance or friction on the surface it's travelling on - is that perhaps what the book was referring to? ~ mazca ^talk 12:53, 10 June 2008 (UTC)

I suppose it could have a slight curve to it, because the gravity of the mass of the object to be accelerated is also attracting the mass of the observer, thus reducing the acceleration of the object away from the observer (or increasing the acceleration toward the observer). However, this effect would be beyond what could be measured, unless you were dealing with a rather massive object. StuRat (talk) 20:21, 10 June 2008 (UTC)

The question wasn't about gravity, it was about an arbitrary force. --Tango (talk) 22:42, 10 June 2008 (UTC)

The point is that if you have any two objects with mass (one being the observer and the planet, ship, etc., where they are located) there will be some gravitational attraction, which will affect acceleration of one object relative to the other, and therefore the force you must apply to achieve any desired acceleration. This has such a minor effect for objects of any reasonable mass that it can safely be ignored, but the effect would become measurable for massive objects. StuRat (talk) 04:51, 11 June 2008 (UTC)

I'm sorry, but I don't have any sample of that graph. The book didn't provide any. It only said that force was plotted on the y-axis, and mass on the x-axis. But I've been assuming that the graph was somewhat like a rectangular hyperbola. 117.194.225.216 (talk) 06:43, 11 June 2008 (UTC)

Do you have any details of the book (Title, Author, ISBN number) so we can try and find it online? SpinningSpark 06:58, 11 June 2008 (UTC)

Gyroscope

Why angular momentum is in direction of rotating axis?Shouldn't it be in the direction of spin? —Preceding unsigned comment added by 220.240.81.247 (talk) 12:40, 10 June 2008 (UTC)

The direction of spin is different on different parts of the spinning body, and at different times. Consider the hour hand on a clock, for example. At 12, the hand is moving to the right, at 3 it's moving down, at 6 it's going to the right left at 9 it's going up. The direction of the axis is the only direction which is constant (that's basically what "axis" means), so it's the only one you can usefully use in the definition of angular momentum. --Tango (talk) 12:51, 10 June 2008 (UTC)

At 6 it's going to the left. Am I allowed to just change your comment to fix minor mistakes like that? — DanielLC 14:22, 10 June 2008 (UTC)

Thanks! I've fixed it. I wouldn't mind you just correcting it, but others might - it's easiest just to reply like you did. --Tango (talk) 15:21, 10 June 2008 (UTC)

Neptune

A diamond on Earth retains a certain shape and hardness(?). What would happen to a diamond if it was placed on the planet Neptune? Will it become harder or change in any way? --Vincebosma (talk) 15:45, 10 June 2008 (UTC)

Also, what would happen if a human spaceship attempted to land on Neptune? --Vincebosma (talk) 15:45, 10 June 2008 (UTC)

This sounds like it might be a homework question, so I won't give you a complete answer. I think the first thing you need to consider is what you actually mean by "placed on" and "land on" - Neptune is a gas giant, there is no land, at least not without going deep down into the thick atmosphere. The things you'll need to consider when determining what will happen to things on Neptune are pressure and gravity. Our article on Neptune will give you some data that should help with that. --Tango (talk) 15:52, 10 June 2008 (UTC)

I guess I'm flattered you thought this was a homework question, but I am a 35 year old man with no homework. Just a curious question. So considering Neptune has no land, the question about diamonds and human spaceships won't matter. I was trying to determine what would happen to things like diamonds and human spaceships on planets (with land) that are at least 20x larger than Earth pressure-wise and gravitational-wise. --Vincebosma (talk) 15:57, 10 June 2008 (UTC)

Planets that large are almost certain to be gas giants. They will have a solid core, but it's a long way down. There will be very high temperatures and pressures, which diamonds can probably survive intact, but spacecraft wouldn't. You might find Galileo (spacecraft) interesting - it sent a probe into the atmosphere of Jupiter, which was destroyed by the harsh conditions (after sending back lots of useful data) - the article gives some details. It is possible to have spacecraft in the upper atmosphere, though, see Floating city (science fiction) for (a little) more information. --Tango (talk) 16:32, 10 June 2008 (UTC)

What you need is a phase diagram for carbon. We don't seem to have one on Wikipedia, but Google should find you several. If you know the local temperature and pressure, you can determine whether your diamond will be stable. I note that diamond is a pretty stable allotrope of carbon at high pressures and moderately high temperatures (thousands of degrees). There has been speculation in the past that the core of Jupiter may be (mostly) a large diamond, formed by the heat and high pressure. There's also suggestion that Jupiter will have layers of other rather exotic materials as well, including metallic hydrogen. TenOfAllTrades(talk) 17:19, 10 June 2008 (UTC)

According to our Neptune article, the core is several thousands of degrees hot, so a diamond could burn (if oxygen was present) or melt (but the high pressure might prevent this). StuRat (talk) 20:15, 10 June 2008 (UTC)

Hi. Well, probably due to its low density compared to earth, Neptune only has about ~2% more gravity than earth at the cloudtops (I don't remember the exact figure). Also, it has been theorised that the pressure at the cores of Uranus and Neptune can put methane under enough heat and pressure so that it forms diamonds (the CH₄ is stripped of its hydrogen, which forms metalic liquid hydrogen, then the leftover carbon is compressed into diamonds). It might be better to land on a moon of Neptune with reasonable gravity such as Triton, but it's -225C there. Depending on which layer of Neptune you are in, you may have to face temperatures anywhere from -240C to +15000C, gravity anywhere from 0.5x Earth to 220x Earth, and gasses from hydrogen to methane to ammonia. There might also be electrical storms in the planet. Hope this helps. Thanks. ~AH1^(TCU) 21:11, 10 June 2008 (UTC)

That 220g figure sounds highly suspect to me, do you have a source for that ? StuRat (talk) 04:43, 11 June 2008 (UTC)

Physics

Are there any scalar quantities which are formed by a product of 2 vector quantities? Can anybody give some examples of such. —Preceding unsigned comment added by 124.43.211.252 (talk) 16:19, 10 June 2008 (UTC)

Yes. See Mechanical work#Force and displacement for one example. --Tango (talk) 16:34, 10 June 2008 (UTC)

(edit conflict) Yes, there are several. It's unlikely that anyone here will answer your homework question for you, however. I'll give you a hint—force is a vector quantity. I suggest you examine the basic physics formulae that you've been taught and look for scalar and vector terms. TenOfAllTrades(talk) 16:38, 10 June 2008 (UTC)

Have you read dot product? Graeme Bartlett (talk) 06:16, 11 June 2008 (UTC)

Do your own homework, kid! 117.194.226.115 (talk) 18:11, 11 June 2008 (UTC)

Intelligence enhancing drugs

Have there been any drugs that show a positive correlation between intelligence and their use? ScienceApe (talk) 16:41, 10 June 2008 (UTC)

Have you looked at Nootropic? Friday (talk) 16:42, 10 June 2008 (UTC)

Do any of these replies help?--droptone (talk) 11:59, 11 June 2008 (UTC)

Looking-glass protein

Assume we found an alternate form of life identical to something we know is edible(say, an apple), except that the structure of its proteins and other molecules was opposite in chirality to that of life as we know it. If we ate such "looking-glass" food, would it be poisonous, or just pass through the body inertly? Would it even be possible for mirror-imaged proteins and molecules to form complex life similar to ourselves and what we eat? —Preceding unsigned comment added by 207.233.86.164 (talk) 17:30, 10 June 2008 (UTC)

There is no real bias within chemistry and chemical reactions for specific chiralities. That is to say that enantiomers have the same chemical properties. If we were to come across an apple that had the opposite chirality (for example, all the sugars in it were the enantiomer of dextrose) its effects would be difficult to say arbitrarily. There are certain molecules that the body would simply allow to pass right through as its different chirality would make it neigh impossible for any proteins to sucessfully catalyze the digestion. On the other hand, there are also molecules for which the change in chirality would make them horribly horribly poisonous. See thalidomide. There is no reason for biology to be biased towards R molecules, and to my knowledge research is being done to determine why that bias arose. If I recall correctly, the current theory has something to do with the strong force, which seems a little off kilter to me but I'm not really qualified to judge. (EagleFalconn) 17:46, 10 June 2008 (UTC)

The main theory I know of is that the chirality of organic molecules is purely by chance - it just happens that the first life forms to be successful were of that chirality and every life form since has therefore also been. It's an interesting issue, and has many consequences for the fundamental ideas of evolution. To the best of my knowledge, there is no reason why life couldn't form with everything the exact mirror image of what we observe. Interaction between life forms of each type (for example, us eating a mirror-apple) would be unpredictable, as you say, but interactions between molecules of one type should be indistinguishable from interactions between molecules of the other type. --Tango (talk) 17:53, 10 June 2008 (UTC)

Right, my point in the above comment was to say that there is a theory that states that R may have been favorable due to a strong force interaction, which is to say that it wasn't entirely chance but there was something driving it (perhaps competitive reaction kinetics). Interestingly, it isn't necessarily true that just because an interaction works R,R that it will work S,S. As I say above, enantiomers have the same chemical properties, however diastereomers do NOT. So just because we know what an R sugar coupling with an R protein will do, we don't know if it'll do the same thing with the S sugar and the S protein. EagleFalconn (talk) 19:38, 10 June 2008 (UTC)

That sounds off...unless there's a third chiral thing involved (external entity or noticeably affected by low-level like asymmetric Force), enantiomers are completely structurally identical and perfect 3D mirror images, so why wouldn't one think R-substrate + R-enzyme would be identical and bind identically (except perfectly enantiomerically) to S-substrate + S-enzyme? If they don't, then enantiomers aren't really "perfect mirror images". DMacks (talk) 19:48, 10 June 2008 (UTC)

I agree. Except for the possibility of very small effects with the strong or weak nuclear forces, the laws of physics are invariant with respect to taking mirror images, so the S versions of things should interact with each other in the same way the R versions do. --Tango (talk) 20:08, 10 June 2008 (UTC)

Well, but we know that diastereomers have different chemical properties (R,R != S,R != R,S != S,S) so while individually the substrate and the protein would be chemically identical to their enantiomers, wouldn't (A) the diastereomeric compound they make have different chemical and physical properties depending on whether it is R,R or S,S? And therefore, (B) Wouldn't the metabolization therefore have different requirements that the remainder of our body, having only been mirror imaged as opposed to also having metabolic processes changed (temperature, activation energy provided, catalyst (since R,R,R would, again, have different properties than S,S,S etc), would be unequipped to meet? We might say that its a small change, but biology is very sensitive to small changes because of the complexity of the systems. I'm guess I'm not really following your disagreement, do you disagree with point A or B? Also, I agree that the strong force thing is weird, I'm just repeating something I found in my organic textbook (Loudon 4th edition) that I used in my optics class. EagleFalconn (talk) 13:51, 11 June 2008 (UTC)

As long as you take the mirror image of absolutely everything, it shouldn't make any difference (except the results will all be mirrored, of course). When we say they have different chemical properties we mean in relation to everything else staying the same, if everything else is mirrored with them, the properties should be identical. Symmetry under parity inversions is a pretty fundamental law of physics. Incidentally, I think it's the weak force, not the strong force, which violates it (at least, that's what it says in that article), and the weak force governs things like radioactive decay, chemistry (and therefore biochemistry) is governed by the electromagnetic force, which is symmetric. --Tango (talk) 14:08, 11 June 2008 (UTC)

I looked up a citation, Loudon 4th Edition page 277 and 278. First part addresses enantiomers forming diastereomers (the substrate binding to the enzyme/protein):

Enantiomers have different reactivities with chiral reagents because diastereomers have different free energies. Just as diastereomers differ in their other physical properies they also differ in free energies. In this case, the transition state for the reaction of one enantiomer is the diastereomer of the transition state for the reaction of the other. Because diastereomeric transition states have different energies, the reaction of one enantiomer occurs more rapidly than the reaction of the other (Note that we may not be able to predict which enantiomer will be more reactive)

— Marc Loudon, Organic Chemistry 4th Edition, page 277

Emphasis not mine, by the way. I believe that the above guarantees that R,R would have a different reaction rate than S,S. In addition:

Disatereomers in general have different reactivities toward any reagent, whether the reagent is chiral or achiral. The reason is that, in the reactions of diastereomers, both the starting materials and the transition states are diasteromeric, and disastereomers have different free energies. Consequently, their standard free energies of activation, and hence their reaction rates, must in principle differ...We may not be able to predict which alkene is more reactive or by how much, but we can be sure that the two alkenes will not be equally reactive.

— Marc Loudon, Organic Chemistry, 4th edition, Page 288

This part indicates that the substrate, once bound to the protein, will also have different energetics. Does this sound reasonable? EagleFalconn (talk) 14:42, 11 June 2008 (UTC)

(outdent). Those quotes are exactly what we're saying and is what you're misinterpretting: it's talking about each of two enantiomers of one compound reacting with the same (one constant) enantiomer of another. See where it says diastereomeric transistion states are different? That means it's an S+S vs S+R type of comparison, not S+S vs R+R (which would be enantiomeric). So it's talking about how a "normal" enzyme reacts with its natural-sugar substrate vs with the enantiomer of that sugar, not how the enantiomer of the enzyme reacts with the enantiomer of the sugar. Or how the (enantiomeric) product of the (enantiomeric enzyme + enantiomeric sugar) would react with the rest of biology in a "normal" (non-enantiomeric-world) system. Consider hands and gloves: left hand fits into left glove identically to how right hand fits into right glove. But left vs right hand fit differently into left glove. And (left hand in left glove) shakes hands with someone else's left hand identically to how a (right hand in right glove) shakes hands with someone else's right hand, but (left hand in left glove) shakes differently with someone else's left hand vs right hand. DMacks (talk) 16:06, 11 June 2008 (UTC)

Point conceeded, thanks. The point that I was missing was that S+S is the enantiomer of R+R. EagleFalconn (talk) 16:23, 11 June 2008 (UTC)

Regarding specifically proteins and amino acids, and the effect of eating an apples with opposite chirality proteins: I'm pretty sure that the D-isomers of amino acids have greatly reduced bioavailability. This comes up because some chemical treatments that foodstuff might be subjected to, such as strong alkali, tend to racemize amino acids. ike9898 (talk) 19:52, 10 June 2008 (UTC)

Increased Gravitational Pull on Earth

What exactly will happen if the gravitational pull on Earth increased ever so slightly? Such as, will I weigh heavier, will certain animal or plant species suffer and die off, etc. --Vincebosma (talk) 19:43, 10 June 2008 (UTC)

That depends on what you mean by "ever so slightly". The Earth's gravity already varies by very small amounts depending on where you are (by about 0.5% or so), and that clearly doesn't have any major effects. It needs to be taken into account for some satellites, I believe, so changing the strength of gravity by less than a percent would probably mess up GPS, but that's about it. Everything would weigh more, but not enough to cause any significant effects. If you increase gravity enough, though, things would start to be unable to support their own weight and would collapse. How much you would need to increase it by depends on what you want to collapse, I don't have any example figures for you, though. I expect it would increase air pressure, although it may in fact decrease it above a certain altitude (the scale height would decrease). I'm not sure what effects that might have, but it could well affect the climate. It would cause the moon to move closer, shortening the length of a lunar month and increasing tidal forces. There are probably all kinds of other effects I haven't thought of, as well. How significant each of them will be depends on how much you increase gravity. --Tango (talk) 20:05, 10 June 2008 (UTC)

How about as a reference, instead of weighing 200 lbs, due to the increase, I weigh 250 lbs.....--Vincebosma (talk) 20:09, 10 June 2008 (UTC)

Among other things, the moon's orbit will destabilize causing it to impact Earth. Everything else is pretty minor at that point. (Assumes 25% more gravity w/ no other physical changes) — Lomn 20:31, 10 June 2008 (UTC)

A 25% increase in gravity would cause the moon to impact the Earth? I'll have to find the back of an envelope, but that sounds unlikely... Do you have the numbers for that, or are you just guessing? --Tango (talk) 21:51, 10 June 2008 (UTC)

According to the back of my envelope, a 25% increase in Earth's gravity would cause the Moon's closest approach to each to be about 2/3 of what it is now, that's nowhere near enough to hit the atmosphere and impact Earth. (Note, there are very rough numbers - I'll try a more accurate calculation in a sec.) --Tango (talk) 22:02, 10 June 2008 (UTC)

(The more accurate calculation is proving more complicated that it's worth, the 2/3 figure should be pretty close, and it's far far outside the atmosphere, so there's plenty of margin for error. --Tango (talk) 22:11, 10 June 2008 (UTC))

You're right, my back of the envelope was way off. — Lomn 23:27, 10 June 2008 (UTC)

But would that closer approach allow the Moon to much more efficiently strip off the atmosphere? That could have a somewhat negative impact. (takes a deep breath) Franamax (talk) 16:44, 11 June 2008 (UTC)

Clarify that - the moon is not in the atmosphere per se, but it is now sweeping out a zone with a higher density of gas molecules (I mailed my envelope with the water bill, no idea how much higher). Wouldn't moving the swept zone closer to the breathable part of the atmosphere increase the outward diffusion? Or not? Franamax (talk) 16:53, 11 June 2008 (UTC)

According to exosphere, the atmosphere ends at about 10,000km above the surface of the Earth, although I'm not sure how that's defined, seems pretty arbitrary to me. That's 16,000km above the centre of the Earth. At 2/3 it's current distance, the Moon would be about 270,000km away. That's a whole order of magnitude bigger, I think we can safely ignore all atmospheric effects. --Tango (talk) 17:42, 11 June 2008 (UTC)

Jumping from big heights

I have recently seen the Bourne Ultimatum (great film by the way) and was a bit confused by the ending. Bourne supposedly jumps from a ten, I think, storey building into a river and survives. This doesn't strike me as terribly realistic and I'm sure I wouldn't be quite as successful if I tried it. Is this Hollywood bending the laws of reality for its own needs again or is there some military training that can prepare you for jumps like that? Is it actually be possible? Thanks. 92.0.243.212 (talk) 20:16, 10 June 2008 (UTC)

Outside Magazine says "The highest Olympic-level dive distance is ten meters (33 feet), with good reason. Beware of injury at around 15 to 20 feet and know what you're doing above 30 feet. Anything over 50 is pro territory." The Discovery Channel explains "Perhaps the biggest misconception about cliff diving is that the diver is cushioned by the water below—this could not be further from the truth. When leaping from a cliff that is over 70 feet high, a diver hits the water at over 46 mph, regardless of his or her body weight." (70 feet is 21 metres) I do not know the answer to the training part of the question. WikiJedits (talk) 20:51, 10 June 2008 (UTC)

At the very least, you would expect him to break his legs on impact (did he at least land feet first? Diving head first from that height would almost certainly kill you!). Other than landing feet first, so your legs take the impact, not your head, I can't see anything you could be trained to do that would help. There is an urban legend about throwing something ahead of you to break the surface of the water so it won't be so hard when you hit it, but as far as I know, that's complete nonsense. --Tango (talk) 21:50, 10 June 2008 (UTC)

Kinda funny you should say that as, if you haven't seen all the Bourne films, in the first one he falls what looks like at least 10m from the top of a stairwell but survives because he was good enough to push some else over first and land on them. But again, could just be Hollywood's attempt at the wow-factor. 92.0.243.212 (talk) 20:29, 11 June 2008 (UTC)

You could be trained to execute a parachutist's landing where you hit with feet, then thigh, hip, shoulder, to spread the energy out. Also, according to one of those "Worst-Case Scenario" books, you should clench your buttocks so that a jet of water doesn't tear a hole in your colon. --Sean 22:50, 10 June 2008 (UTC)

The Golden Gate Bridge at 750 feet (220 m) is a popular spot for suicidal jumpers. Despite the extreme height, relatively cold water (50-60 F / 10-15 C), and frequent strong currents, about 2% of jumpers nonetheless survive. So it is certainly possible. A person like Bourne in peak physical health who presumably knows how to enter the water in a controlled way might well have a decent shot of executing a 100 ft dive, though it certainly wouldn't be easy or a sure thing that he would survive. So I'd say it is certainly possible, though I wouldn't recommend it. Dragons flight (talk) 22:07, 10 June 2008 (UTC)

See La Quebrada Cliff Divers, which daily dive off 45m cliffs - this is more than most 10 storey buildings. I assume that they survive ;-). I have dived 10m. If you enter the water optimally (for me that is vertical, feet first, as I'm a craven coward rational person), there is very little impact stress. If you are more than a little off, you get quite a kick. I don't want to experience what happens if you enter the water uncontrolled... --Stephan Schulz (talk) 22:24, 10 June 2008 (UTC)

I'm not going to give this a try but by 'optimally' what do you mean? A pencil dive, feet first? Would your body be tense, to keep you in that pencil shape, or relaxed, so that you don't break your bones on impact? 92.0.243.212 (talk) 20:33, 11 June 2008 (UTC)

Interesting. Seems you can do it, if you know what you're doing. Shows what I know! --Tango (talk) 22:40, 10 June 2008 (UTC)

This is a bit off topic, but I seem to recall that the water in at least some diving events is aerated. Is this primarily to give the diver a visual reference, or is it intended to provide a degree of cushion on entry? -- Tcncv (talk) 01:14, 11 June 2008 (UTC)

I don't know if the aeration actually exists, but if it did it would lower the surface tension of the water and lessen the impact force. However, the same amount of work would still need to be done to stop you, and so you'd need a deeper pool to do it.EagleFalconn (talk) 13:55, 11 June 2008 (UTC)

I know they have a small spray hitting the surface to make it easier to see where it is (so you know when to stop somersaulting, or whatever). I don't think it has any affect on the landing, though. I'm not sure how significant surface tension is to the impact force, I think it's just the fact that liquids are incompressible that makes them seem so solid (the water can't compress like a crash mat, it has to move out of the way, and that takes time). --Tango (talk) 14:00, 11 June 2008 (UTC)

Cat spray / Territorial marking

This question relates to a "cat pee" question posted by another user above. I'm convinced that the stuff that cats "spray" when marking their territory isn't urine. From having to clean it up, I know that it is oily and extremely musky. I assumed it was some sort of gland secrection, but our articles on cat and territorial marking refer to this stuff as urine. Can anyone clarify whether or not it is urine? ike9898 (talk) 20:18, 10 June 2008 (UTC)

I believe it is urine, but does include certain gland secretions which give it the distinctive smell (well, distinctive to cats - just smelly to us!) --Tango (talk) 21:45, 10 June 2008 (UTC)

It is urine plus anal gland secretions. According to this paper the secretions contain volatile fatty acids (which might constitute the greasy feel), putrescine, cadaverine, and ammonia(which contributes to the unholy smell). The secretion-urine mix also contain lipids and dead cells.--Lenticel ^(talk) 22:48, 10 June 2008 (UTC)

. . .another cup of tea anybody?! Richard Avery (talk) 06:47, 11 June 2008 (UTC)

ball lightning?

Hi. This morning there was a big thunderstorm where I live (southern Ontario). A friend told me he heard ball lightning. He reported the following:

• Two seconds of hissing, then a loud thunderclap
• It sounded like a Roman Candle (firework)
• The lights went dim noticeably for about 10 minutes, occasionally flickering, then suddenly went back to full power
• He had read a book containing information about ball lightning before the thunderstorm
• Location: less than 500 m from where I was at the time, was indoors

The thunderstorm:

• Can be classified as severe, but no warning was issued
• Lightning every several seconds
• Rainfall rate showing up as dark-red on The Weather Network radar
• Was located near a cold front
• Occured before 8 am EDT, did not weaken overnight
• Was located near central-eastern USA the night before, preceded by a few severe and non-severe thunderstorms in S. Ontario the afternoon and night before
• Severe thunderstorms lasted roughly 15 mins, entire storm roughly 25 mins, rain roughly 30 mins

I noticed:

• Frequent and bright lightning, sometimes within 1 km
• Thunder loud enough to wake me up
• Strong winds and gusts, ~80 km/h
• No noticible disruptions in electricity
• Widespread puddling of rain
• Enough rain to cause a mess indoors if the window is open
• Wind carrying still-falling rain nearing the ground producing waves

So, is it plausible that ball lightning really occured, and are these conditions condusive to ball lightning formation, or are there other plausible explainations? Thanks. ~AH1^(TCU) 20:54, 10 June 2008 (UTC)

God how I miss living in Southern Ontario, in the countryside, and watching those biggg storms come through. Torrential rain, blasting wind, hail - we only get polie thunder where I am now, you're lucky! Franamax (talk) 16:59, 11 June 2008 (UTC)

Without having seen the actual ball lightning, I don't think there's a lot that can be said. We don't know enough about ball lightning to know what conditions are conducive to it; in fact, we barely know that it even exists. Sure, it's plausible. And I'm sure there are other plausible explanations. The only weird part of what your friend describes is the hissing sound. I'm thinking maybe it was a transformer exploding. I don't specifically remember hissing sounds before transformer explosions I've heard, but it sort of rings a bell. Plus that would explain the localized disruption in electrical service. --Allen (talk) 21:21, 10 June 2008 (UTC)

If he didn't see ball lightning, why assume it was ball lightning? Hissing could be electrical arcing followed by the bang of a high voltage fuse fuse opening to clear the fault. Ten minutes later a utility troubleman could have replaced the fuse or closed a normally open switch to restore power. Scientists are somewhat skeptical about ball lightning. I would expect it is some sort of plasma of heated and electrically charged gas. Edison (talk) 00:00, 11 June 2008 (UTC)

Heard but didn't see is somewhat unreliable. I concur that the hearing was likely from the hydro system. In a similar storm in a similar location, I heard a serious ka-boom accompanied by a very clear sizzling sound (which you could also describe as hissing), out towards the road. The next day I had to call in for $400 worth of repairs to the control unit of my Miele washing machine. Draw your own conclusions. Franamax (talk) 17:07, 11 June 2008 (UTC)

About mirrors, and short sightedness

So I'm short sighted. Let's take this scenario: I am looking into a mirror which is six feet away. There is an object behind me which is 60 feet away. Ordinarily, I'd not be able to focus on this object very well, but I'm seeing this object behind me in the mirror. So there are two questions:

1. Will I be able to focus on the object? Am I focusing six feet away, or seventy-two feet (distance to mirror + distance from mirror to object) away?
2. Why?

Apply this scenario to an SLR camera and you'll see why I'm asking. Thanks guys. :D Lewis Collard! (lol, internet) 21:25, 10 June 2008 (UTC)

No, I don't think you would. You're trying to focus seventy two feet away, because that's how far the light has to travel. You can focus on the mirror itself, if you want; then you'll see clearly the dust and lint on it, but not the distant objects it reflects. --Allen (talk) 21:31, 10 June 2008 (UTC)

Whoah. Lewis Collard! (lol, internet) 21:36, 10 June 2008 (UTC)

I agree, you need to focus 72 feet away. I'm not sure what an SLR camera has to do with it - a camera contains a lens which focuses the light, rather than a plane mirror which just reflects it. --Tango (talk) 21:42, 10 June 2008 (UTC)

And what if I took the lens off? (I'd do this right now, but it's dark here...) Lewis Collard! (lol, internet) 21:49, 10 June 2008 (UTC)

Well, actually there's more than one lens, so it would depend on which one you removed. Single-lens reflex camera has a nice diagram showing them all. --Tango (talk) 22:26, 10 June 2008 (UTC)

Let me try a slightly more helpful answer: If you remove all the lenses (which is probably what you mean), the light would not be focused and you would get just a small amount of random light hitting the film/sensor and you wouldn't get a proper image forming. --Tango (talk) 22:37, 10 June 2008 (UTC)

As someone who owns an SLR, I tried exactly that. The result when I looked through the viewfinder: a uniform light-colored field. The result of taking a picture: a uniform 15% grey image. --Carnildo (talk) 23:49, 10 June 2008 (UTC)

Sounds about right. What were you pointing it at, and with how much light? --Tango (talk) 00:11, 11 June 2008 (UTC)

My living room, lit by indirect sunlight. Not much color or brightness variation. --Carnildo (talk) 21:39, 11 June 2008 (UTC)

In an SLR camera, there's a translucent "focusing screen" between your eye and the mirror. This screen is similar to a piece of frosted glass. The lens forms an image on the focusing screen, which you can see. But since the focusing screen is translucent, not transparent, you can't just look through the viewfinder and see through the camera without a lens to form an image—just as you can't look through the frosted glass on your boss's office door. (As a side note, when a lens is mounted and you see an image in the viewfinder, your eye is focusing on the image that's formed on the focusing screen. But that's only a couple of centimeters from your eye, which is closer than you can usually focus. This is possible because the viewfinder has a little lens, similar to reading glasses, that make the focusing screen "look like" it's far enough away to focus on, typically about 1 meter. Some cameras have an adjustment to this apparent distance, to accommodate different people's vision. Look up "diopter adjustment" in your manual.) -- Coneslayer (talk) 18:12, 11 June 2008 (UTC)

Photosystems and Primary electron acceptors

Hello, in high school biology, my master teacher taught me that in photosynthesis, light photons hit the photosystems I and II and causes them to pass their electrons to the primary proton acceptor. The primary proton acceptor then passes them to plastiquinon to go to the cytochrome complex. My question is, where is the primary proton acceptor in relation to the PS? http://en.wikipedia.org/wiki/Image:Thylakoid_membrane.png according to this diagram, is the primary acceptor INSIDE/PART OF the PS? Applefungus (talk) 22:06, 10 June 2008 (UTC)

Toenails

Why do we still have toenails? Are they just left over from our evoloutinary ancestors? But in that case do chimpanzees need to toenails? (im not even sure if they do!) Or do they actually serve some purpose? Thankyou x —Preceding unsigned comment added by 217.44.210.227 (talk) 22:22, 10 June 2008 (UTC)

Why do we still have an appendix? ;) Just because they are no longer functional does not mean they will automatically be lost. That's not quite how evolution works. Regards, CycloneNimrod ^talk?_contribs? 22:25, 10 June 2008 (UTC)

People can actually die from ingrown toenails, which cause infection (my grandpa died that way, with diabetes, age, and nursing home neglect contibuting to it getting out of control). So, there may be some evolutionary pressure to lose them, if they no longer serve any purpose. StuRat (talk) 22:48, 10 June 2008 (UTC)

Perhaps, but remember that evolution isn't a conscious entity, it doesn't solve every problem a species has. Just because toenails can be a danger, this doesn't mean that a specific mutation is going to happen in which toenails don't grow and which will pass down to the next generation. Also there is a big debate about whether or not humans can still evolve in that way, considering how we now, for the most part, treat everyone equally regardless of disease. Increasing medical capabilities also make it less likely. Regards, CycloneNimrod ^talk?_contribs? 22:51, 10 June 2008 (UTC)

Objects slipping from your hands and objects protruding from the ground are two reasons why toenails serve some function. They might not be the most effective protections if you bang your foot against a root or rock but they did served a purpose in our savanna dwelling ancestor and still do for the barefoot aficionados of today. That they might be disappearing would be an interesting study subject. 200.127.59.151 (talk) 23:12, 10 June 2008 (UTC)

There's actually a new hypothesis out about the appendix. --Allen (talk) 00:52, 11 June 2008 (UTC)

That they are small or not is genetic. They actually do function to protect and add sensitivity to the tips[23]. Like fingernails, they protect the sensitive nerve endings on the tips of our toes and fingers. Rather than see them as clawing tools, see them as little shields. And you might like this from Nail Anatomy[24] (it's a download document) about function and purpose:

There is also an important role in offence and defence. Proprioception is gained from pressure of the pulp against the hard underside of the semi-rigid nail plate. The nail plates give form and shape to the pulp of the digit and, by attachment to the distal phalanx control and stabilise the pulp. On the foot, the toe nail is most importantly functional in its proprioceptive role, its defence of the digit and in control of the toe pulp.

Julia Rossi (talk) 00:55, 11 June 2008 (UTC)

And note that just because you can die from something doesn't make it much of an evolutionary pressure. As your very example points out, your grandfather's toenails had no effect on his ability to reproduce, only being a problem late in life and when complicated by other late-in-life illnesses. I doubt they are disappearing—they seem like a pretty basic part of primate anatomy, and without any pressure against them, they're not going to be going anywhere fast. --98.217.8.46 (talk) 00:56, 11 June 2008 (UTC)

Yes, but younger people can die from them, too, especially if they have diabetes and ignore the problem. I suffered from infected ingrown toenails myself. If I hadn't lanced to abcess and treated the area with hydrogen peroxide I might not be here now. (If you are eating while reading this, you can thank me for helping you with your diet.) :-) StuRat (talk) 04:39, 11 June 2008 (UTC)

As you leap up and run to correct your diet, you can thank toenails for giving information to the brain[25] through the pressure incurred that helps keep you upright in your flight and when walking gingerly back to your seat. StuRat this may be the document for you! Julia Rossi (talk) 05:44, 11 June 2008 (UTC)

That doc lists one of the uses of toenails as "assisting in oral maintenance" ... wouldn't that result in picking the seeds from this morning's preserves out of one's teeth only to replace them with toe jam ? :-) StuRat (talk) 06:30, 11 June 2008 (UTC)

Well if you have diabetes, I think you have more serious problems then toe nails. I would venture to guess the evolutionary pressure would be on something else, perhaps what causes diabetes in the first place not on your toe nails. As for the more general problem of ingrown nails, I don't think it would have been a big problem until recently since the biggest causes, are problem ill fitting shoes and poor nail maitence. I don't think shoes until say the past few thousands years were likely to be very tightly fitting and I doubt people cut their nails much at all Nil Einne (talk) 10:32, 11 June 2008 (UTC)

Actually, damage to the feet is one of the main risks for diabetics. I don't know the reasons, but I'm sure Wikipedia has an article on it (try diabetes!). Of course, that's one of the main risks for diabetics today, we've only recently learnt how to manage the condition, so diabetics even just 100 (or maybe even 50) years ago would probably have died long before their feet started having problems, and you can't get much evolution in 4 or 5 generations (except in exceptional circumstances is that tautologous?!). --Tango (talk) 13:25, 11 June 2008 (UTC)

The problem with diabetics and foot injuries is that they have restricted blood flow to their feet, which means that injuries do not heal, since the white blood cells needed to fight infection don't arrive. Thus, even a minor injury to the feet (like an ingrown toenail) can present a high risk to a diabetic. StuRat (talk) 14:31, 11 June 2008 (UTC)

Wierd Subconscious Dream

I have had this on my mind for a very long time. Sometimes, when Im in bed, I experience a sense that my room is a lot more spacious than it actually is, and I am really small compared to my surroundings. I can usually "feel" as if I was aware of all the walls, the format of my room. I am usually not very tired when this happens, and Im wide awake. Also, in conjunction with this, I get a feeling or subconscious image of a small circle rolling tensely on an extremely perfectly smooth surface. Usually, the surface suddenly breaks in this seemingly endless continuity of smoothness, and it starts to get extremely bumpy, and the ball doesnt roll smoothly. This gives me a very desperate and anxious feeling. This "image", however, is purely 1 dimensional, and it is usually in a grey color. When the surface the ball is rolling on becomes chaotically uneven and incontinuous, I get a really anxious, uneasy, desperate feeling. I am pretty sure all of this is subconscious, however it is not a dream, because none of this could happen in real life, like a dream. The image and consequent feeling I get is like a television screen, I mean thats what I see. I want all of you to know I dont suffer from any kind of mental disorder I know of, maybe just a bit of stress. If anyone can identify what this is and its name, it would be greatly appreciated. —Preceding unsigned comment added by 189.4.19.134 (talk) 22:42, 10 June 2008 (UTC)

Sounds like astral projection, if you're willing to believe in it. There's little scientific evidence (if any) for it, though. Regards, CycloneNimrod ^talk?_contribs? 22:49, 10 June 2008 (UTC)

Actually, now I think about it, it's probably more related to some form of lucid dreaming. These can be exceptionally strange and are more believable scientifically (although there is still very little research for it) Regards, CycloneNimrod ^talk?_contribs? 22:53, 10 June 2008 (UTC)

June 11

Does MOND have problems with Newton's third law of motion?

I read carefully the MOND article in Wikipedia, and it seems to me that it would be difficult to reconcile the idea with conservation of momentum, or at least that only some $\mu (x)$ functions would be consistent (and I cannot figure out which).

Consider an isolated star with a single planet like Pluto, small, distant, and in an elliptical orbit. As I understand MOND, the planet will always be in a gravitational field such that $\mu (x)$=1, while the star will be in a field that will be close to $\mu (x)$=1 when the planet is at perehelion, but far from $\mu (x)$=1 at aphelion. Thus at perehelion, the change in momentum of the star will balance that of the planet, but at aphelion, the momentum change in the star will be significantly greater.

This will cause the combined system to accelerate slowly but continually in the direction from the star to the planet at aphelion. This acceleration will continue until the system enters the gravitaional field of a galaxy.

I suppose MOND enthusiasts could even argue that this provides a new mechanism for the growth of galaxies, but the whole thing strikes me as counter-intuitive.

Have I understood this correctly? John Blackwell (talk) 01:42, 11 June 2008 (UTC)

According to Bekensteins paper, Millgrom's original formulation of MOND does indeed have a problem with conservation laws and some other problems as well. However, Bekenstein goes on to give a Lagrangian/Relativistic formulation that does not (he claims) have these problems. Follow the link in the references section of the article to read more. SpinningSpark 07:19, 11 June 2008 (UTC)

Thanks - I guess I'm back where I am with many things - the accurate theories are beyond my understanding (or perhaps I'm just too lazy to put in the work to understand them) - but I can't see past the flaws in the simplified descriptions. —Preceding unsigned comment added by Johnblackwell (talk • contribs) 01:21, 12 June 2008 (UTC)

Beavers

I'm trying to find out how long it takes a beaver to fell a tree like an Aspen. The photo with the article refers to cutting a 10 inch tree overnight. I would like to know if there is any more specific information on the time, assuming that 10" overnight would be 10" in 8 hrs? or 10 hrs? or 12 hrs? —Preceding unsigned comment added by 65.255.187.5 (talk) 02:03, 11 June 2008 (UTC)

I remember seeing a very good nature documentary film on beavers; I think it was by Rein Maran, an Estonian cinematographer, if my memory serves me well (it was some 20 years ago...). If you can find that documentary, you will have the answer to your question. If you find this film on the web, please give a link. All the best, --Dr Dima (talk) 06:08, 11 June 2008 (UTC)

A quick google search finds a cached article [26] saying 6" in 15 minutes. Scaling that to 10" is three times longer, although the more mature tree would also have more hard wood. Don't know if that helps... Franamax (talk) 15:18, 11 June 2008 (UTC)

I believe the time needed scales with the cube of diameter, not the square, so it would take about six times as long. In order to fell a tree, a beaver chews a wedge-shaped ring, not a cylindrical ring, so the amount of material removed increases as the cube of the diameter. Also, you need to take into account non-linear factors such as fatigue. --Carnildo (talk) 21:45, 11 June 2008 (UTC)

Yes, it is the cube. Just for fun, I tried working out the formula for the volume. for a 90° wedge, chewing 3/4 of the diameter, I get .344D³. I can do that geometrically right, I don't need an integral? My math is a little rusty :) Franamax (talk) 01:38, 12 June 2008 (UTC)

Phthalate

Though controversial, phthalates are still being used in a variety of household applications (shower curtains, adhesives, perfume), modern pop-culture electronics and medical applications such as catheters. Notable recent examples include Apple Inc.'s iPhone and iPod, and personal computers. The company has been criticized by environmental supporters claiming that tests on a commercially-purchased iPhone returned "toxic" levels of the chemical, prompting public declarations for change due to its associated hazards.

— ., http://en.wikipedia.org/wiki/Phthalate

Are iPod nanos included?21:49, 6 June 2008 (UTC)68.148.164.166 (talk)

Wow, ophthalmology (and its few derivatives) isn't the only english word with a "phth" in it? – b_jonas 10:17, 9 June 2008 (UTC)

What difference would it make? That is, what possible path is there by which a (hypothetically) phthalate-loaded iPod could poison you?

Atlant (talk) 12:20, 10 June 2008 (UTC)

I'm concerned about phthalate's estrogenic effects.68.148.164.166 (talk) 03:22, 11 June 2008 (UTC)

Unless you grind up your iPod and sniffed all the powder the amount of phthalate exposure from your iPod is negligible, and if you did sniff the powder your biggest concern wouldn't be phthalates either. --antilived^{T | C | G} 04:14, 11 June 2008 (UTC)

The problem are plastics which are in contact with fat rich food. The people who suffer most are the people needing dialysis, because for a long time the tubing and the memranes in the dialysis machine contained high amount of phtalates doi:10.1002/1097-0274(200101)39:1<100::AID-AJIM10>3.0.CO;2-Q, but for the rest a phthalate rich iphone has no chance to poison you, because the skin is not very permeable.--Stone (talk) 07:23, 11 June 2008 (UTC)

What if you alternately fiddled with your iPod and ate potato crisps/chips all day every day? From my observations some people do exactly that. Some phthalate would dissolve in the fat. You might have to worry more about the oestrogenic/estrogenic effects of the soy/soya oil the chips/crisps were fried in though. Itsmejudith (talk) 11:39, 11 June 2008 (UTC)

Phthalates are of most concern in the developmental stages, so don't let your baby play with your iPod... Franamax (talk) 17:22, 11 June 2008 (UTC)

custom parts

does any one know a site where i can order custom metal parts? like say i wanted all the parts of a car engine...but i wanted them one third the size,where could i get that for cheap? —Preceding unsigned comment added by 76.14.124.175 (talk) 07:06, 11 June 2008 (UTC)

Hmm, not really a science question, but it might help to get an answer if you said what country you were in. SpinningSpark 07:24, 11 June 2008 (UTC)

One magazine I receive includes ads from custom metal fabricators, who can mill or make castings based on electronic CAD (machine drawing) files you email them, with quick turnaround. But unfortunately you said "cheap," which it certainly will not be. Wait a few years and "fabbers" may become as common as computer printers and scanners, and you can create your own miniature car engine via Desktop manufacturing. Edison (talk) 20:51, 11 June 2008 (UTC)

Fabbers usually work with low-melting-point materials, and occasionally with sintered metal powders. Neither is very good for making a car engine, which requires high temperature resistance and decent mechanical strength. --Carnildo (talk) 21:48, 11 June 2008 (UTC)

Opening Boxes of Tablets

There are 2 ends to my boxes of tablets (hayfever, paracetemol, aspirin, whatever). If I open it at one end I can get straight to the tray of tablets. If I open it at the other I have paper folded over the tray which contains warnings/instructions. I never look which end i'm opening so sometimes it will be (if you have the front facing you) the left-side and sometimes the right. Why is it that a good 80% of the time I get the paper-end? I would expect it to be 50/50 (2 ends, 1 end is 'clear' the other isn't) but I virtually always open it what is (to me) the 'wrong' end. I've asked a few other people and they find the same thing.

My guess is that it is down to the additional weight from the folded-paper, but wondered if A) do other people experience this too? and B) Does anybody know 'why' this might be? 194.221.133.226 (talk) 08:19, 11 June 2008 (UTC)

Here's two explanations:

1. The way the box is designed. The manufacturer wants you to look at the warnings, if only to avoid a lawsuit. Therefore, they may design the box so that it subconsciously encourages you to open it at the end with the paper.
2. It really is more like 50-50, you just don't notice it. Have you been keeping a log somehow? If not, there's a good chance that the percentage of the time you open it on the paper end is lower than you think, but you only notice a "pattern" when you open it on that end.

Or maybe you're just psychic. =) « Aaron Rotenberg « Talk « 08:42, 11 June 2008 (UTC)

I've not kept a log so it could well be that my brain is finding a pattern - i'll start a log (yeah i'm that kind of person) and see. The idea of the design sounds interesting though, I used to read a great blog that was called 'architecture of control' or something (it looked for designs that pushed people to do stuff/had a second purpose that people might not realise was actively intended). —Preceding unsigned comment added by 194.221.133.226 (talk) 09:36, 11 June 2008 (UTC)

This is related to the phenomenon I've observed whereby if a microwave oven has a turntable, and you follow the advice I've given elsewehere and set the food "off-center" on the turntable, when the cooking cycle is done, the turntable always ceases rotation with the food located at the back of the microwave oven. Seriously, I'd also suggest that the weight of the package insert instructions may be cueing you to more-often hold the box one way rather than the other. But I have no explanation for the microwave oven phenomenon except that maybe the peculiarities of the timer and turntable drive motor lead to the turntable always turning n.5 rotations (for those cooking-time values that I routinely use).

Atlant (talk) 11:41, 11 June 2008 (UTC)

How are you orienting the package? Main label side up, text reading left-to-right? That would be your first clue to unconscious positioning. There is also the possibility of the observer preferentially registering adverse events. On an unrelated note, I recall reading about a study which showed the probability that if you dropped your toast, it would land upside-down. so weird things do sometimes happen. Franamax (talk) 17:39, 11 June 2008 (UTC)

Franamax - the toast thing is to do with the average height of work-surfaces/table-tops and only having enough time for it to rotate from butter-side-up to butter-side-down (or at least that's the explanation i've been given and it sounds plausible). ny156uk (talk) 17:47, 11 June 2008 (UTC)

Neutrino oscillation and conservation

Suppose I measure that an electron is an electron neutrino at a given time, and I also measure that it has a certain velocity (subject of course to uncertainty). Now assume that later I measure that it's oscillated into a tau neutrino, with a different velocity. How does this work with conservation of mass/energy and conservation of momentum? I mean, you can make the velocity uncertainty arbitrarily small in both cases, so I don't see how the observer effect could account for this. Veinor ^{(talk to me)} 08:57, 11 June 2008 (UTC)

There is an explanation at neutrino oscillation. As far as I understand it, the hypothesised neutrino mass eigenstates have different masses and so propogate at different velocities (because of conservation of momentum). The mass eigensates are, in turn, combinations of flavour eigenstates, and so the mix of flavour eigenstates varies along along the neutrino's path. Therefore the probability of observing a particular flavour eigenstate varies according to whereabouts along the neutrino's path you make your observation. Gandalf61 (talk) 09:24, 11 June 2008 (UTC)

To put this more directly, flavor and momentum form an uncertainty relation, so if you had made the uncertainty on momentum arbitrarily small then you'd have no way of determining what kind of neutrino it was and vice versa. Dragons flight (talk) 17:28, 11 June 2008 (UTC)

Blow job pregnancy

Can I get a girl pregnant if I cum in her mouth when having a blow job, cause it goes into her but does it just get digested or is there a risk it might find its way to her uterous? —Preceding unsigned comment added by Milkly man (talk • contribs) 09:25, 11 June 2008 (UTC)

No, there is no connection between the digestive system and the uterus. — QuantumEleven 09:34, 11 June 2008 (UTC)

However there is a risk of the transfer of STDs. There is also a (minor) risk of pregnancy if your semen goes near the vagina somehow. Probably the greatest risk for pregnancy is if you do somehting like kiss your girl after the act and then perform unprotected oral sex on her. All in all, unless you are in a committed relationship and both of you have been checked for STDs since you entered into that relationship, any form of unprotected sex is simply a bad idea. Nil Einne (talk) 10:20, 11 June 2008 (UTC)

Angela Ermakova got pregnt from Boris Becker after transfering semen from a blow job, so it is possible if somebody wants it to happen. [27]--Stone (talk) 12:24, 11 June 2008 (UTC)

So did JD's girlfriend in Scrubs. Quipquip (talk) 20:12, 11 June 2008 (UTC)

If memory serves, that wasn't a blow job, it was a poorly aimed premature ejaculation. --Tango (talk) 21:31, 11 June 2008 (UTC)

Indeed I probably should have said, unless you are in a committed relationship, have both been checked for STDs and are both ready to and have talked about how you will deal with an unexpected pregnancy Nil Einne (talk) 22:02, 11 June 2008 (UTC)

Hi. I'm not really qualified to answer this, but I think I once read somewhere (I forget where) that a girl in Lesotho who was unable to reproduce and gave a BJ, then her boyfriend got angry and stabbed her in the stomach thus allowing seminal fluid to seep into her uterus and she became pregnant. Thanks. ~AH1^(TCU) 23:34, 11 June 2008 (UTC)

That sounds unlikely. If the knife pierced the uterus, it would probably be unable to support a fetus. The semen may get in and fertilise an egg, but it wouldn't be able to go to term. I suppose the knife could have hit a fallopian tube, and the semen got in that way, and the uterus was left unharmed, but that still seems unlikely. Also, if she was unable to reproduce, the semen getting in via a knife wound is very unlikely to make any difference. She probably got pregnant the old fashioned way and then got stabbed, and the whole infertility thing was just incorrect and has made for an interesting, but erroneous, story. --Tango (talk) 23:55, 11 June 2008 (UTC)

Hypothetical Questions about Gravity and the Sun

Question 1: What exactly would happen if the sun moved 500 miles away from earth?

Question 2: What exactly would happen if the earth slowed its rotation speed by, say, 20 miles?

Please note that I am a 35 year old man and these are not homework questions. I would like to know exactly what I would experience when these phenomonas happen. --Vincebosma (talk) 13:03, 11 June 2008 (UTC)

You wouldn't notice a 500 mile change in the orbit of the Earth. The variation in distance caused by the orbit not being a perfect circle is about 5 million kilometres, so 800km would be insignificant. Question 2 doesn't make sense, do you mean 20 miles per hour? And by rotation speed do you mean the Earth rotating on its axis, or orbiting the Sun? --Tango (talk) 13:16, 11 June 2008 (UTC)

On its axis. And 20 mph. Also what would I experience if it slowed down say 200 mph? Forgive me for my serious lack of science knowledge. Just trying to answer questions my nephew is asking me. He's only 6. --Vincebosma (talk) 13:30, 11 June 2008 (UTC)

Assuming you mean the speed at the equator (which is the fastest - the poles don't move at all), the actual speed is about 1040 mph. Slowing that down would result in a longer day. 20mph is about 2%, so the day would be nearly half an hour longer, 200mph is 20%, corresponding a day nearly 5 hours longer. Lengthening the day would have all kinds of effects. Most would be fairly minor for just 30 mins longer, although some animals and plants may be confused. 5 hours would confuse pretty much everything. It could also affect the climate. One of the causes of prevailing winds is the Earth's rotation, so slowing that rotation could result in slower wind speeds. It would also result in a slight increase in gravity due to reduced centrifugal force (which acts to cancel out part of the gravitational force), but that would be negligible (it would just reduce the difference between the poles and the equator). --Tango (talk) 13:55, 11 June 2008 (UTC)

(After edit conflict) This is a good opportunity to introduce your nephew to orders of magnitude. The circumference of the Earth is roughly 25,000 miles. So a point on the equator travels a distance of 25,000 miles every 24 hours due to the Earth's rotation on its axis. This is a speed of about 1,000 mph - the speed of a supersonic jet. If you were flying in a supersonic jet which slowed down by 20mph, would you notice the difference ? If every hour was 61 minutes instead of 60 minutes, would you notice the difference ? The Earth is about 93 million miles from the Sun. Compared to this distance, 500 miles is about 5 parts in a million. A millionth of a mile is about 1/16 of an inch. If you had to walk a mile, and then someone increased the distance by 5/16 of an inch, would you notice the difference ? Gandalf61 (talk) 14:03, 11 June 2008 (UTC)

Thank you, and congratulations, for trying to answer his questions. Too many parents/uncles/aunts give the "Because God said so." or "Because it is, stop asking." To help you explain the answers by Tango and Gandalf, it may be helpful (and instructive, and get you two some valuable play time, and get you outside) to perform this exercise. Go outside with a basketball and a marble (or, if you're not that commited to scale, which isn't quite as important at his age a golf ball or ping pong ball will do). Have him put the basketball down where he wants the sun to be. Then, hand him the Earth ball (the smaller one) and tell him to put it where the Earth is. It should be 534 feet away, assuming the basketball is the size of the sun (Note that at this scale, the earth is 1/4 of an inch in radius). You may need to go about a block away...its not quite a backyard exercise. Now, to answer his question of what would happen if the Sun moved 500 miles. Have him move the basketball 1 inch, or have him roll the ball once around or whatever. (The actual amount of movement would be .03 inches, but thats not particularly visual for a 6 year old). Ask him if he thinks its made a big difference. EagleFalconn (talk) 14:21, 11 June 2008 (UTC)

As for question 1, the distance of the Earth from the Sun is determined by the orbital speed. If you moved them apart by 500 miles without increasing the orbital speed, this would result in the Earth "falling" back those 500 miles, in about 3 months, and then another 500 miles closer to the Sun, in the next 3 months, then it would turn around and go back out to the original point in the next 6 months. So, if you had started with a circular orbit, this would make it slightly elliptical. However, since the orbit of the Earth is already more elliptical than that, this would either increase or decrease the eccentricity of the orbit, depending on whether the 500 extra miles were added when the Earth was closest or farthest from the Sun. StuRat (talk) 14:44, 11 June 2008 (UTC)

To really screw with his head, explain the Milankovitch cycles which dictate that we're all gonna die even if the Earth stays in its current orbit. Ice age! EagleFalconn, thanks for your excellent outline of a practical, understandable demonstration. I'll be able to use that in another 4 years or so :) Franamax (talk) 14:51, 11 June 2008 (UTC)

Hi. Well, as for the sun moving 500 miles away, that depends on which way it moves. If it moves horizonal and along Earth's orbital plane, it would be 500 miles closer than normal 6 months later. If it moved verticly (north-south), it might not be exactly 500 miles as from the Earth. However, distance from the sun can affect the climate. For example, currently the Earth is closer to the sun in the southern hemisphere summer than in the northern hemisphere, so the southern hemisphere gets more summer sun intensity. I'm not sure, but if the opposite were true, as can happen with cycles lasting tens of thousands of years, the Sahara might green, for example, but things like Global warming may disrupt these cycles. However, if the centre of the Earth were only 500 miles from the sun, then part of the Earth would be in the sun, and if the surface of the Earth were that far, we'd be in the sun's atmosphere and be past its Roche limit, and fall into the sun. The speed of our orbit around the sun is determined by several factors, which I'm not too familiar with, but is most likely dictated by distance from the sun. However, if our orbit speeded up dramaticly for whatever reason, the Earth would fly away from the sun due to centrifugal force, then slow down because the sun's gravity there is weaker. If you need articles that are written in Simple English which might be easier to explain, you can check the languages box in the article to see if there is one. Thanks. ~AH1^(TCU) 23:30, 11 June 2008 (UTC)

Rancid meat

Why can't you eat rancid meat if it is cooked? Surely if it is cooked really, really well then the heat will kill any bacteria, viruses or other germs that would make you sick. Pob The Plumber (talk) 13:41, 11 June 2008 (UTC)

Cooking the meat may sterilise it. But some toxins that were produced by the putrifactive bacteria survive the cooking process. Escherichia coli produces one such heat stable toxin. So dont eat last years, raw,forgotten Christmas Turkey now, cooked or not :-) Fribbler (talk) 14:05, 11 June 2008 (UTC)

Got it! Thanks. Maybe my mother-in-law would like a turkey sandwich..... Pob The Plumber (talk) 14:43, 11 June 2008 (UTC)

Just to clarify, rancid and putrid are not the same thing. One is oxidative decomposition, which makes things smell bad (rancid butter, rancid tuna), the other is a bacterial process. Nevertheless, if it's meat and it smells bad, throw it away. Franamax (talk) 15:01, 11 June 2008 (UTC)

One of the reasons why various cuisines developed highly-flavored/highly-scented/piquant sauces, of course, is...

Atlant (talk) 17:22, 11 June 2008 (UTC)

Why didn't all English gourmets and hunters die in centuries past from eating "high game" as discussed by Dickens [28] or in this 1889 book [29] or this recent publication [30] "The pheasant was not as well hung as the staff had told us and lacked the real oomph of high game." Apparently some gourmets still seek a "well hung" pheasant. Note: I strongly discourage eating rotten meat. Edison (talk) 20:44, 11 June 2008 (UTC)

Oh yumm, hare soup and make sure every drop of blood goes in it! Many meats are hung, for instance beef carcasses for 2-3 weeks, to allow the existing enzymes to partially "digest" the meat and soften it. Bacteria will grow only on surfaces, so the toxin load would not be high, and washing or boiling would handle it anyway (contrast with contaminated ground beef). Plus you need the right unlucky combination of toxin-producing bacteria and conditions under which the bacteria will be producing the toxin. I'm thinking that not all, but quite a few gourmets of ages past actually did die from eating spoiled food, they probably called it dropsy or something back then, before they figured out what was causing it. Franamax (talk) 00:37, 12 June 2008 (UTC)

Some mycotoxins in particular are nasty stuff. While they don't tend to be much of a problem on meat (well other then by meat from animals feed contaminated grains), they are a problem on grains and also fruit. Aflatoxin is one good example. As with bacterial enterotoxins and endotoxins, cooking does not destroy them so if you come across fruit or grains that look like they are moldy, throw them out. Particularly for anything soft as often what you see is only a small percentage of what is there. Nil Einne (talk) 22:00, 11 June 2008 (UTC)

Why don't we have 4 seasons every 27 days?

Hello giant minds! The Earth's 23.5 degree inclination pushes points on its hemispheres a few thousand miles either closer/farther from the sun causing seasons throughout the year. Shouldn't the Earth's massive "wobble" as it holds the Moon spinning around it cause the same effect? Earth orbits every 27 days or so (just like the Moon) around the barycenter of the Earth-Moon system, located thousands of miles from Earth's apparent center. Why am I not expecting snowstorms followed by beach weather every few weeks? Sappysap (talk) 15:06, 11 June 2008 (UTC)

The seasons happen because of tilt - the angle of the sun's rays to the Earth - not the distance. Those few thousand miles are insignificant for seasonal purposes. — Lomn 15:21, 11 June 2008 (UTC)

The reason is multi-fold. To address a common misconception you mention: The distance between the sun and the earth has almost no effect on the seasons. Between summer and winter, the change in the distance is about 3.1 million miles. However, the northern hemisphere's winter occurs when the Earth is closest to the sun. See [[31]] for more.

The first is the angle of insolation, which is the angle at which the sun's rays, directly striking the Earth's surface, strike the earth. The greater the angle, the less energy is transferred to the surface of the earth and its atmosphere. That is why summer occurs when the hemisphere you occupy is tilted toward the sun.

However, the Earth does not 'wobble' as the Moon revolves around it. The direction of the gravitational force between the moon and the earth does cause a center of rotation between the two of them, but that does not change the angle of insolation. There is no angle of insolation change due to the barycenter, though there is a slight distance change. However, if 3.1 million miles isn't making a difference, this certainly won't. EagleFalconn (talk) 15:27, 11 June 2008 (UTC)

For effects that are significant over the period of a month, see tide. --Prestidigitator (talk) 16:17, 11 June 2008 (UTC)

Sweating

A little background: I went for a bike ride the other day, it was about 15 degrees out, so I wore a t-shirt and some shorts to keep cool. During the bike ride, as is normal for me, I started sweating. This isn't much of a problem, but then this guy pulls up next to me on his bike wearing jeans, a sweater and a vest, and he's not sweating a bit. This blew my mind, as we were doing the same work--riding down the same street for essentially the same ammount of time, he on a mountain bike and me on a road bike, so I was actually doing a little less. What gives? Why was I sweating like a pig, and he not even uncomfortable? 142.33.70.60 (talk) 16:22, 11 June 2008 (UTC)

Just because he wasn't sweating doesn't mean he was comfortable. Some people just don't sweat much, which can make them overheat more easily. Also, weight makes a huge diff, as extra fat both provides thermal insulation and extra mass to move, requiring the burning of more calories. Cardiovascular fitness also makes a diff, as some people will be seriously stressed by that level of exercise while others "won't even break a sweat". StuRat (talk) 16:39, 11 June 2008 (UTC)

Assuming you meant it was 15°C, or 59°F, that seems cool enough that most people wouldn't sweat noticeably during a relaxing bike ride. StuRat (talk) 16:44, 11 June 2008 (UTC)

Also, maybe he hadn't been riding for as long as you? It takes a while after you start exercising for the body to produce enough excess heat to trigger sweating. —Ilmari Karonen (talk) 16:54, 11 June 2008 (UTC)

Cameras in rough times

Why do cameras often temporarliy show just noise when subject to violent vibrations? Example at 0:35. —Bromskloss (talk) 17:59, 11 June 2008 (UTC)

Theres a slight difference here between digital and film cameras, but the explanation is essentially the same. On a digital camera, when you press the button a sensor is triggered which takes a time average of (essentially) what color light is hitting the sensor at that particular pixel. If the camera is shaking, the average is going to be over a range of colors, usually resulting in a gray or other odd color, what you might call noise. On a film camera, its the same effect except instead of a detector you've got chemicals on a piece of film. The chemicals, being exposed to several different colors of light, will report all of them, which we typically see as white. EagleFalconn 18:20, 11 June 2008 (UTC)

Like motion blur, you mean? I don't think that's it. What I'm talking about looks more like the camera is about to fail completely, like if a signal cable is not properly plugged in, but spuriously loses contact. Mabye that's it – the signal cable losing contact? —Bromskloss (talk) 18:42, 11 June 2008 (UTC)

The sort of noise you see there is caused by a bad connection being vibrated so it isn't always transmitting a signal. --Carnildo (talk) 22:02, 11 June 2008 (UTC)

How come radio waves aren't stopped by walls and such?

You gotta ask to learn! If, for instance, AM waves have a wavelength of 100m to 1km (from Radio frequency), how come they can pass through walls and such? The way I see it is obviously wrong, so I'd be thankful for a few pointers, although I think that I've looked through the main articles. -- Aeluwas (talk) 18:05, 11 June 2008 (UTC)

The quantum mechanical view on it would be that for (1) photon to interact with an atom, that atom/molecule/whatever needs to have a valid energy transition available to it at the same energy as the photon or (2) the possibility for a Stokes collision.

For case (1), if the energy levels in the atom do not correspond to the energy of the photon, no interaction is allowed because no electron is available for promotion to a higher energy level. This rarely (I'm prepared to say never) happens with radio waves because the photons are of such low energy (a quantity which is inversely related to wavelength) that there are no electronic transitions available. Nuclear energy state transitions do occur in those areas, however those transitions are very difficult to achieve by inputting electromagnetic radiation and is better done with a magnet, as in NMR.

Case (2) There is a probability that an electron will 'collide' with a photon and remit the photon at the same wavelength or a different one. See Stokes shift. This is a very difficult effect to observe with radio waves, more so than with other types of light. In general, these collisions are very improbable and any experimentation with them has to be done with a laser to generate sufficient intensity so as to be able to collect data. EagleFalconn (talk) 18:33, 11 June 2008 (UTC)

I'll give a very general, non-technical answer. Because the walls aren't dense enough. Now if the walls were made of thick lead, then they would stop the radio waves. If you are in the center of a large building with lots of walls, or underground they would stop the radio waves too. ScienceApe (talk) 18:59, 11 June 2008 (UTC)

None of the above. There are two ways, both correct, to think of radio waves: either as oscillating electromagnetic (EM) fields or as photons. At the long wavelengths that you are talking about, the photon view is not helpful, and it is better to think of EM fields. An EM field is partly electric and partly magnetic, hence its name. In order to stop an EM wave, you need either an electrical or a magnetic barrier, or both. An electrical barrier needs to be an electrical conductor, like a sheet of copper or aluminium. A magnetic barrier is harder to achieve, but a layer of soft iron would work as both an electric and a magnetic barrier for low-frequency waves. Walls are generally made of neither electrical conductors nor magnetic materials, so they don't stop radio waves at the frequencies you are talking about.

Higher-energy radio waves (shorter wavelengths, like microwaves) behave more like light and are stopped by walls, but that's another subject. --Heron (talk) 20:04, 11 June 2008 (UTC)

I don't believe that is entirely true. Or at least saying I'm wrong isn't true. Putting a sufficient amount of matter in between you and the radio waves will stop them. If you were surrounded by say a kilometer of ice on all sides, it would block any EM radiation from getting in. ScienceApe (talk) 20:49, 11 June 2008 (UTC)

It is true that the shorter the wavelength is, the more like visible light the radio wave will behave, since the only difference between visible light and radio waves is that radio waves have a longer wavelength. I'm not sure microwaves are completely blocked by walls, though - if memory serves, the frequencies used by Wi-Fi are in the microwave range, and they certainly can go through walls, although the signal is noticeably weakened. --Tango (talk) 22:36, 11 June 2008 (UTC)

Actually, the absorption scale for radio waves in ice is many tens of km. For example, radar reflections are used to measure the shape of the bedrock under the ice at Antarctica. Also, in line with Heron, the limiting factor is still conductive impurities (mainly sulfates and H+ ions) and not bulk matter per se. Dragons flight (talk) 22:30, 11 June 2008 (UTC)

More like 5 KM actually. Nope, it really is bulk matter. You can take any matter and if you surround yourself with enough of it, it will block EM radiation. Denser material is better at stopping EM radiation than less dense material. ScienceApe (talk) 23:34, 11 June 2008 (UTC)

Strictly speaking denser is better, but free electrons (e.g. metals and ions) have a much, much greater effect on absorption/scattering than density. Dragons flight (talk) 00:10, 12 June 2008 (UTC)

A thin layer of iron, steel. or even iron hardware cloth will interrupt most AM or FM radio broacdasts by acting as a Faraday cage. By thickness, ferrous metal provides far better radio shielding than brick, rock, or concrete. Edison (talk) 20:31, 11 June 2008 (UTC)

Um, doesn't the thin layer of this stuff have to be somewhat enclosed? You can't really have no charge on the inside if there is no "inside". --Wirbelwindヴィルヴェルヴィント (talk) 04:13, 12 June 2008 (UTC)

The Radius of the Earth

Is it possible to calculate the radius of the earth simply by measuring the time between two sunsets, one observed by lying down and the other observed by standing up just after the sun (apparently) goes down while we were lying down?? If so, how?? —Preceding unsigned comment added by 117.194.226.115 (talk) 18:18, 11 June 2008 (UTC)

Have you tried drawing a picture of the scenario? -- Coneslayer (talk) 18:33, 11 June 2008 (UTC)

Yes. For an observer standing on the surface of the earth, his line of vision in both cases are tangents to the earth's surface. The sun covers 360 degrees in 24 hours, so supposing the time interval between the two sunsets is x seconds, we can calculate the angle covered by the sun in that time. But does that really help? I'm completely lost as to what to do after this. —Preceding unsigned comment added by 117.194.226.115 (talk) 18:38, 11 June 2008 (UTC)

This webpage explains the experiment: http://astronomy.nmsu.edu/nicole/teaching/ASTR110/lectures/lecture10/slide05.html . The experiment can be performed either at sunrise or sunset. If you measure the height of the standing person, denoted h (cm), and the time between the sunsets, denoted ΔT (s), then the radius of the Earth, denoted R (cm), can be found by the equation:

$R=h\cdot {\frac {\cos(\triangle T/240)}{1-\cos(\triangle T/240)}}$.

Convert R to more sensible units of meters or kilometers by dividing your answer by 100 or 100,000 respectively. Jdrewitt (talk) 20:48, 11 June 2008 (UTC)

Keep in mind that you should do this only where you have a true horizon (like watching the sun set over the ocean). Mountains, trees, or other large and relatively close obstacles are going to mess up the experiement completely. --Prestidigitator (talk) 21:06, 11 June 2008 (UTC)

Also keep in mind that atmospheric diffraction distorts the apparent positions of the Sun and the horizon. I don't know if this will have a noticable effect on the experiment, but when dealing with things as small as the timing differences involved here, it's worth thinking about. --Carnildo (talk) 21:59, 11 June 2008 (UTC)

Hottest time period in Earth's history

What was it? I have heard it may have been the Middle Cretaceous or the early Eocene, (Paleocene–Eocene Thermal Maximum), but from climate graphs of the earth, it is hard to tell because many periods are warm and I can't seem to find an exact answer. Thanks 142.150.72.199 (talk) 18:23, 11 June 2008 (UTC)

Hi. Well, I'm not sure, but I think it may have been sometime around the Hadean eon in the Precambrian, when the earth just recently formed, the crust was not yet solid, and the Earth was experiencing the Great Bombardment. However, if you include the future, there may be periods hotter than some mentioned above. Hope this helps. Thanks. ~AH1^(TCU) 23:08, 11 June 2008 (UTC)

Planet orbit question and the formation of our solar system

Are all the planet in our solar system revolving around the sun in the same direction? Are they all rotating/spinning in the same direction? If not, how is this possible? During the formation of our solar system, shouldn't they be revolving and rotating in the same direction due to the conservation of angular momentum? ScienceApe (talk) 19:02, 11 June 2008 (UTC)

All of the planets revolve the sun in the same direction: from the north pole of the sun, counter-clockwise. All the planets except for Venus also rotate counter-clockwise (again looking from the sun's north pole). See solar system, Venus, and formation and evolution of the solar system for more details. Jkasd 19:28, 11 June 2008 (UTC)

With regards to angular momentum and the formation of the solar system, how or why is Venus spinning clockwise? ScienceApe (talk) 20:25, 11 June 2008 (UTC)

Nvm, it seems like an impact event caused it. ScienceApe (talk) 20:26, 11 June 2008 (UTC)

Also, Uranus's axis is inclined at 98 degrees. And also see retrograde and direct motion. Jkasd 19:40, 11 June 2008 (UTC)

Weight of human hair

How much does one's head hair weigh? More precisely, is there a formula that can be used to estimate the weight of head hair based on length(and accounting for differences in hairline, bald spots, and such)? 69.111.189.55 (talk) 22:20, 11 June 2008 (UTC)

Flammable cleaning products

(No, I'm not a vandal.) Hello. What are the most flammable cleaning (or otherwise) products that a janitor could use in his work? (No, I'm not a janitor either.) Thanks in advance, Kreachure (talk) 23:15, 11 June 2008 (UTC)

Toluene would rank right up there, or any other solvent the janitor might be using for some purpose. Most chemicals and commercial products have a safety data sheet, googling the name plus "msds" will usually get you some good data. Franamax (talk) 00:50, 12 June 2008 (UTC)

Toluene has a very low flash point, but alcohols such as ethanol or isopropanol have much lower autoignition temperatures. However, the most flammable, common solvent is probably diethyl ether. Not sure if this would be found in many janitor closets, though. --Russoc4 (talk) 03:28, 12 June 2008 (UTC)

June 12

Succession in Commmunities

What happens to the number of kinds of plants as the years pass? —Preceding unsigned comment added by 72.67.191.161 (talk) 03:13, 12 June 2008 (UTC)

automatic sphygmomanometer

How does the machine measure the diastolic reading ? In manual readings it is when the sound of the pulse dissipates.Thommo123 (talk) 03:36, 12 June 2008 (UTC) Paul

See Korotkoff sounds. If the machine pumps the cuff pressure up sufficiently high and then slowly releases it, the point will come when Korotkoff whooshing sounds are heard at the brachial artery, at the pressure when the systolic pressure is sufficient to force blood through the restriction caused by the cuff. The K sounds continue with each heartbeat as the pressure drops until the diastolic pressure is reached, at which point the K sounds stop. Blood pressure machines I have dealt with just record the sound from the microphone and the pressure, and sends these two pressures to the readout. A comparator or trigger circuit can monitor the microphone sounds to decide when the K sounds are being produced. Edison (talk) 04:00, 12 June 2008 (UTC)

Berembang tree

What is a berembang tree? I know it is in Malaysia. I also know that fireflies thrive on it and twinkle among the berembang trees like lights on Christmas trees. But that is all that i know. Any help......

TCGKennedy —Preceding unsigned comment added by TCGKennedy (talk • contribs) 04:00, 12 June 2008 (UTC)

Modeling a Body Moving in a Fluid

I am not a Physics expert so I can only say that this is a Fluid Dynamics question but I don't even know where to look for this specific equation or what is it called. Basically, we already know that the faster a car moves (in air of course), the lower its MPG becomes because it takes more energy. This is the same as if I filled a bathtub with water and tried to move my hand through it. If I move slowly, it is easy. The faster I try to move, the harder it becomes. So my question is, is there a page on wikipedia (or in one of the books) or even somewhere else online, which talks about the general form of this equation (preferably with the constants gives)? I just want to know what exactly happens to my MPG as I increase my speed on the highway. I can guess that it decreases exponentially but how rapidly. If I double my speed, how does my MPG change? Thanks!69.232.109.213 (talk) 04:45, 12 June 2008 (UTC)

Robotic spacecraft maintains air pressure?

Does Robotic spacecraft maintain air pressure inside? If yes, what are benefits of air inside? I can think of using circulating air to control temperature inside. If air escapes in space, will there be any problem? —Preceding unsigned comment added by Ranemanoj (talk • contribs) 04:42, 12 June 2008 (UTC)