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September 2

Non-fatal viruses

Are there any viruses that are not potentially fatal to humans first-hand? One that I can think of is HIV (which can allow other diseases to cause death), but are there others? Thanks. 64.229.153.184 (talk) 00:17, 2 September 2012 (UTC)

There are millions of viruses which don't use humans as vectors at all, i.e. the Tobacco mosaic virus doesn't even infect animals. Bacteriophages are a class of viruses that infect bacteria. --Jayron32 00:28, 2 September 2012 (UTC)

In before this gets removed as a request for medical advice. What Jayron said, basically. I'm not even sure that a significant portion of the viruses in existence are potentially fatal to humans. That would seem to be rather oddly genus-specific, and I think most viruses tend to use a rather small number of animal vectors. As I understand it, the principle of natural selection would also make killing the majority of your hosts something of a genetic/evolutionary dead end, wouldn't it? Evanh2008 ^{(talk|contribs)} 00:34, 2 September 2012 (UTC)

It's not intended to be for medical advice, just out of curiosity. 64.229.153.184 (talk) 00:52, 2 September 2012 (UTC)

Yes, it is not evolutionarily stable for a virus to kill most of its hosts (or at least to kill them too quickly). Among viruses that infect humans (which I think is what the question is intended to focus on), I believe there are many that are rarely lethal (I do not have a handy reference, a little help here?). As for references, the OP may be interested in Virulence#Evolution, and optimal virulence. Both of these articles describe the factors that promote and inhibit lethality in pathogens. Lastly, this is a perfectly legitimate (and interesting) question. It is in no way a request for medical advice, see User:Kainaw/Kainaw's_criterion SemanticMantis (talk) 01:52, 2 September 2012 (UTC)

Are you asking for viruses that simply can't kill humans, viruses that infect humans but don't kill, or viruses that make humans more likely to die but can't kill on their own? Someguy1221 (talk) 01:46, 2 September 2012 (UTC)

Infect but don't kill, sorry for not being clearer. 64.229.153.184 (talk) 01:55, 2 September 2012 (UTC)

A couple of examples: GB virus C and Transfusion transmitted virus. -- Scray (talk) 02:08, 2 September 2012 (UTC)

We all get influenza from time to time. Only in rare cases do flue viruses kill. Various forms of the herpes virus either produces no symptoms, just a rash when the human is under stress, or just a mild rash. Wickwack124.182.34.199 (talk) 02:14, 2 September 2012 (UTC)

That does not answer the original question. -- Scray (talk) 03:23, 2 September 2012 (UTC)

It depends on what the OP meant by "first hand" I suppose. Then he clarified it by saying "infect but don't kill". One could ask "is there any food known that doesn't kill?" Strickly speaking, it is possible I could choke on a piece of apple, therefore apple can kill. I know a fried who is alergic to nuts. She inadvertently ate a nut in a cake at a party once, and had to have an emergency traecheotomy. So, do we say apples and nuts are lethal? That would not be of any value. My friend's root problem is not nuts, it's a genetic mishap. Similarly, flu viruses should not be considered lethal, though in rare cases they will if there is some other factor. I doubt that significant numbers of folk die from even the worst of the herpes types. This quite different to ebola virus, which will kill you regardless of other factors. So, yes, the OP's question has been answered. — Preceding unsigned comment added by 124.182.13.142 (talk) 04:30, 2 September 2012 (UTC)

Most viruses kill some, usually small portion of people who get them, such as chicken pox. Flu kills 5-50,000 a year in the US, not all that rare. http://www.cdc.gov/flu/about/disease/us_flu-related_deaths.htm Chicken pox around 100. Any infection can kill if you have a weakened immune system or a particularly virulent mutant. See Viral disease for a start at their variety. 02:37, 2 September 2012 (UTC)

No, that is incorrect. As I noted above, GB virus C and Transfusion transmitted virus are non-virulent. There are zero reports that they've killed. -- Scray (talk) 03:22, 2 September 2012 (UTC)

Are you telling me, Scray, that you are unfamiliar with the meaning of the word "most"? μηδείς (talk) 15:49, 2 September 2012 (UTC)

I should have been more specific in stating my disagreement: I was referring to your statement that "any infection can kill..." - because the viruses I cited are highly prevalent, many episodes of infection in immune-compromised hosts have been studied, and no deaths have been observed (citations in the respective articles, which I've already linked). I'll also point out that the original question was about viruses that are "not potentially fatal" - hence your answer overall was not responsive to the initial query (which implicitly acknowledged that most viruses can be lethal). -- Scray (talk) 21:51, 2 September 2012 (UTC)

Okay, that makes quite a bit more sense. It is true, however, that any infection that potentially causes an immune response can kill, although "infections" that fly under the radar, and neither evoke a response nor incapacitate their hosts obviously won't. But I am not sure that they would then be called infections. I was taking Tammy's response below as a great example. Warts don't usually kill. But papilloma virus infections of the lungs in AIDS patients do kill, and the virus does induce various cancers. (Oh, a point which I see on further reading you have explicitly mentioned, minus rectal cancer.) μηδείς (talk) 22:34, 2 September 2012 (UTC)

Warts are transmitted by a virus. --TammyMoet (talk) 08:33, 2 September 2012 (UTC)

True, but with respect to the original question, the viruses that cause warts can be lethal (e.g. PMID 10197157, PMID 21242344) to people with reduced immunity. More importantly, HPVs causes cancers of the cervix and the head and neck - also relevant: PMID 19646562. -- Scray (talk) 22:03, 2 September 2012 (UTC)

Adeno-associated virus "is not currently known to cause disease and consequently the virus causes a very mild immune response." Not sure our immune response really is a consequence of our knowledge, but that's what the article says. Consider also the article Viral vector, although this is a bit cheaty since those viruses have typically been engineered to be harmless.  Card Zero  (talk) 14:53, 2 September 2012 (UTC)

Some 95% of the adult population is infected with Epstein-Barr Virus yet it is rarely fatal unless it leads to for example Burkitt's lymphoma or HIV-associated lymphomas. Wolfgangus (talk) 22:22, 2 September 2012 (UTC)

what is a linear dielecric material

explain. --150.203.114.14 (talk) 04:23, 2 September 2012 (UTC)

Well, linear, in this sense, means an output variable varies proportionately with an input variable, therefore, if the input doubles, so does the output (although it could be slightly more complicated if the line on the graph is offset from the origin). However, I'm not sure what the input and output variables are, in the case of a dielectric. StuRat (talk) 05:32, 2 September 2012 (UTC)

A dielectric is a material that can maintain charge seperation; that is if I apply an external charge to it, the charges in the material shift around; applied negative charge will push negatives away, leaving positive in its place. What makes something a dielectric is, if the external charge is removed, the charge seperation stays for a time. Ever rub a balloon on your hair and stick it to the wall? That's the dielectric effect. I'm not exactly sure what property is linear, but my guess is that one could have a dielectric whose charge response is linear with respect to the input charge; double the input charge creates double the charge storage on the dielectric. --Jayron32 05:56, 2 September 2012 (UTC)

Jayron has given a physicist's answer. Here's a perhaps more useful and complete engineer's answer:-

What makes a dielectric a dielectric is that it displays a dielectric constant, normally termed permitivity. Permitivity ε in a linear dielectric is given in farads per meter by D/E where E is the applied electric potential across the dielectric, volts per meter, and D is the resulting electric field (flux), ie charge , Columbs per square meter. This is analogous to ferromagnetic materials, which have a permeability, in henries per meter, μ = B/H. Just as real magnetic materials are non-linear, that is permeability varies with the strength of the applied field, and also displays hysteresis, a real dielectric's permitivity varies with the applied volts per meter, and displays hysteresis - that is, you get a different permitivity at any given voltage when increasing it, to what you get when passing thru that same voltage while decreasing it.

A perfect vacuum has a permitivity of 10⁷/(4 π c²) F/m where c is the vacuum speed of light. All real substances have a permitivity above the vacuum value.

Just as a linear magnetic material allows the construction of an inductance having no electrical energy loss, a linear dielectric allows the construction of a capacitor with zero electric energy loss. It being a real (imperfect) world, you can't have either. However in practical electrical calculations, you can generally get a useful result with minimum effort by assuming they are linear, and then if necessary applying simple corrections to allow for the energy loss.

Keit60.230.231.168 (talk) 08:34, 2 September 2012 (UTC)

How to know that a drug is safe?

I know that clinical trials test new drugs in rats or other animals and then in people, who are paid for that. But, Independent of the model, human or animal, you are using, you'll be always extrapolating the results and taking risk, won't you? So, how could we know whether a drug is safe for pregnant women or children? OsmanRF34 (talk) 13:37, 2 September 2012 (UTC)

Actually, until you test it and wait for a couple of years or so, you can't know with total certainty if a new drug is safe for you. There can always be side effects that haven't been noticed during the trials. Here in Sweden, we have children suffering from narcolepsy after a vaccination against the swine flu that was supposed to be safe. Lova Falk talk 14:31, 2 September 2012 (UTC)

Furthermore, clinical trials seldom are longer than at the most half a year. Some meds are taken daily for years and years, and long-term effects are assessed while patients take the meds. For instance SSRI. They were tested for a relatively short time, put on the market, and now we can see if they are safe also for long term use. Lova Falk talk 14:35, 2 September 2012 (UTC)

• This is really just a specific case of the problem of induction, which applies to all scientific research. Looie496 (talk) 17:04, 2 September 2012 (UTC)

In many cases we don't know whether a drug is 'safe' (whatever that means) for pregnant women, many drugs ([1] has some numbers) are untested in pregnant woman and the information sheet that comes with the drug warns of that. As mentioned in the earlier source, the Food and Drug Administration Amendments Act of 2007 has a number of amendments that relate to drug testing in children contionuing and extending from earlier legislation, [2] mentions only about 20% of drugs approved by the FDA were labelled for pediatric use before they began a pediatric program (from that source I think that was in 1997). Nil Einne (talk) 17:45, 2 September 2012 (UTC)

I can add to that that a lot of research is done on men, because you know, women have their changing hormones and periods and that could confuse results, and then we just happily generalize the results to women, not bothering about possible differences. Also, a lot of the times, no trials are done with children. Yet they do get the meds. Lova Falk talk 18:31, 2 September 2012 (UTC)

As the sources I linked to and text of my reply hinted at, if no trials were done on children then usually the drugs won't be approved for use pediatric use and therefore any such usage is off label in the US and I think many other countries with decent regulatory regimes (see e.g. [3] for NZ and Australia). Nil Einne (talk) 19:31, 2 September 2012 (UTC)

Apart from acne and being fat, most indications for these recently approved drugs would justify the risk I think. Ssscienccce (talk) 08:12, 3 September 2012 (UTC)

• Actually there's a bigger problem than this - you don't know if drugs have synergistic toxicity. For example, the melamine contamination of products was such a problem because safety tests of melamine by itself suggested it was practically safe. But combine it with a related compound, and it forms huge flakes by noncovalent associations vaguely reminiscent of the base pairing of DNA. These flakes clog up the kidney tubules and kill pets or people. No drug ever placed on the market has ever been scientifically tested in combination with every other drug, chemical, and natural bioactive substance with which a user ingest, and so none of them are truly known to be absolutely safe. Wnt (talk) 02:27, 5 September 2012 (UTC)

Sunrise progression

I took a series of sunrise pictures from an east-facing beach in Florida last spring, including this closeup of the sun just as it rose above the horizon. My question is this: what causes the wedge-shaped base between the sun's disk and the horizon? It's definitely not a camera artifact. Juliancolton (talk) 15:02, 2 September 2012 (UTC)

It's a mirage, more specifically a mirage of an astronomical object caused by the bending of light. -- MacAddct1984 ^{(talk • contribs)} 16:55, 2 September 2012 (UTC)

Notice as well how the sun is not round. That bending of the light is caused by refraction due to the atmospheric inhomogeneity. Dauto (talk) 21:06, 2 September 2012 (UTC)

More specifically an inferior mirage, and quite pretty. μηδείς (talk) 21:07, 2 September 2012 (UTC)

"Pocket" flashlight that recharged from sun-light or room-light amout of photons?

automatically light-recharged flashlight, that lesser the natural need to replace a battery or that could even cancel it. just like solar calculators work. does anything like it or near it even exists? thanks. 109.64.151.131 (talk) 21:26, 2 September 2012 (UTC)

Sure. Google "Solar flashlight" You can buy one for under US$ 20.00 Dauto (talk) 22:36, 2 September 2012 (UTC)

Link? How long is the charge? μηδείς (talk) 23:48, 2 September 2012 (UTC)

Well, there are those night light things you put on the sides of your front walk, but they aren't very impressive. After absorbing sunlight all day on that tiny solar panel, they give a weak light for a few hours, at best. To get a bright light that lasts all night, you would need a huge solar panel. There are inefficiencies at every step that make this the case. When they are all considered together, you might be lucky to get 1% of the light that hits the solar panel back in light from the flashlight. StuRat (talk) 03:27, 3 September 2012 (UTC)

There are flashlights that use a capacitor and solenoid/magnet to charge. All you have to do is shake them for a minute or two and they will light up for a few minutes. NightStar Rechargeable Flashlight is one example 83.70.170.48 (talk) 10:36, 6 September 2012 (UTC)

What sort of skin diseases are there that look like melanomas?

I know there are cancers and other diseases of skin vascularization that are red-brown and have irregular outlines, but haven't been able to find anything on line by looking at our article for melanoma or for diseases that look like melanoma. I am aware of the various sarcomas. Are there any other suggestions? Thanks. μηδείς (talk) 23:47, 2 September 2012 (UTC)

I'm sure you'll spend many happy minutes looking at this. --TammyMoet (talk) 07:51, 3 September 2012 (UTC)

OH, my. Thanks. μηδείς (talk) 19:47, 3 September 2012 (UTC)

Resolved

September 3

For how long has Schroedinger's Cat been rotting?

So, I have set up the cat experiment with enough air, food and water to keep the cat alive for 10 days. Only then do I open the box. Given that he has neither been alive nor dead for 10 days, he certainly cannot have been rotting for 10 days. Indeed, he should still be warm, whether alive or dead. If he has rotted, who observed him ten days ago to kill him? I don't want arguments in response to this question, I want previously published considerations of it. Thanks for the help. μηδείς (talk) 00:10, 3 September 2012 (UTC)

The premise of the question is wrong. It's not that he's been neither alive nor dead, he's been both at once (supposedly). 86.177.105.185 (talk) 00:53, 3 September 2012 (UTC)

Yes, so he has been rotting or not for ten days? Or just since the box was opened? Maybe just rotting for five as a compromise? A published source which discusses this dilemma would be appreciated. μηδείς (talk) 00:57, 3 September 2012 (UTC)

The physical processes of rotting (if it occurs) will introduce all kinds of interference with the supposed superposition of dead/non-dead states, vaguely akin to opening the box. I appreciate that you want published sources, so please excuse my unsupported replies. 86.177.105.185 (talk) 01:07, 3 September 2012 (UTC)

Isn't the whole point of the cat thing that at the macro scale it IS a paradox? It doesn't make logical sense. So trying to infer other logical conclusions from it is kind of pointless. Vespine (talk) 01:39, 3 September 2012 (UTC)

It makes conceptual sense for the cat to be alive and dead at the same time if you believe that interpretation; however, in reality the cat is a big and vastly complicated thing, and once you start taking into account physical process and interactions such as rotting, breathing, eating, etc., the original concept of the thought experiment becomes overwhelmed with other factors not originally relevant. 86.177.105.185 (talk) 01:54, 3 September 2012 (UTC)

Inasmuch as the scenario makes sense at all, he has been rotting (or not) for ten days. More specifically, over a ten day period, |alive> + |dead> evolves to |alive for ten days> + |dead for ten days>. A quick search of the arXiv and Google Scholar failed to turn up any discussions of this, though. -- BenRG (talk) 01:42, 3 September 2012 (UTC)

I believe you're thinking about the cat too literally. It is a metaphor, and if you were to try it with an actual cat, you're not going to observe any particularly strange quantum effects. The problem with your question comes about with the addition of an additional variable (the rotting process) that really has no analogous feature in quantum physics, but the cat isn't a great analogy to begin with. (If the cat is alive, he damn well knows it, whether anyone on the outside of the box does or not.) If you were to forget about all the various problems inherent with the paradox and the question, though, I believe BenRG's answer is correct. Evanh2008 ^{(talk|contribs)} 02:12, 3 September 2012 (UTC)

My personal interpretation is the same as BenRG's, and is expanded as follows: The problem is that the thought experiment is indeed usually portrayed as literally true, yet a cat's being dead is not just a yes-or-no thing--death as variously defined is a moment that has a temporal location. If a cat is dead, it means it has been dead for a finite time. That raises the question of how long he's been dead before the door was opened to check. If he's rotten, it implies he did die, not when the door was opened, but when the atom did indeed decay ten days ago, before anyone measured it. If he has only just died when the door opens, then not observing an atom's decay would delay the cat's death by ten days. But we all know unobserved atoms decay regardless of whether they are observed. (And we can even add that the atom has to decay within a certain time frame as a condition.) One could, as BenRG seems to be doing, posit that opening the door now reaches back into time and kills the cat ten days ago. That's what I would guess is the orthodox position. But none of these answers quite seems to fit with what is supposed to be going on. I cannot imagine that this situation was never suggested before, so I am quite interested in knowing what the literature suggests. I cannot believe that physicists don't know the difference between a freshly dead and ten-day dead cat. 02:26, 3 September 2012 (UTC)

Before you open it, the contents of the (perfectly isolated) box is a mini-many deadly cat worlds. Count Iblis (talk) 02:59, 3 September 2012 (UTC)

Unless I have missed it, that article doesn't seem to answer the "when did the cat actually die?" question. Are we supposed to assume it didn't actually die at any specific time, and hence hasn't rotted? Or that it did die, if it died, ten days before anyone opened the box? This seems like such an obvious question to a biologist that I cannot believe ther is no mention of this question in the literature. μηδείς (talk) 03:13, 3 September 2012 (UTC)

The only way the "paradox" is in any way useful or logical is if you have a perfect box- that is, there is no way to tell if the cat is "rotten" since any information cannot escape the box. Asking about rotten cats implies you have not understood what the thought experiment is supposed to demonstrate. 70.162.10.166 (talk) 03:44, 3 September 2012 (UTC)

While I have reservations about the seriousness of this question, no one else does, so I might as well through in my 2 cents. The problem with your above remark is that the cat is not a single particle, it is a whole bunch of them, this muddies up the whole affair, so let's try to simplify. Replace the cat with what we will call chemical X and instead of poison we have chemical Y. X and Y combine molecule for molecule to make a molecule of Z, for all X and Y to disappear and us to be left with just Z, it will take 10 days. Then, we can measure the amount of Z in the box to determine the length of time since the radioactive substance went off. So, what is the state inside the box before we look? In this case, the state is a super position of each possible count of Z molecules, the coefficients of which evolve in time so that higher numbers of Z are more likely at later times. The reason this question seems difficult is because "how long was the cat dead" is an entirely different question than "did the cat die", it's an entirely different Hilbert Space, looking at one in terms of the other confuses the issue and stretches the analogy past what it is meant to do. Phoenixia1177 (talk) 04:06, 3 September 2012 (UTC)

It died, if it did die, ten days before you opened the box. The whole situation is exactly the same as if you had a classical probabilistic distribution. If there's a 50% chance that the cat just died, ten days from now there will be a 50% chance that it died ten days ago. There is no interaction between the possible living cat and the possible dead cat. They are distinct possibilities that evolve independently. That's why in quantum mechanics if you start with |X> + |Y> and evolve it forward ten days, you always get |X after ten days> + |Y after ten days>. It's a manifestation of the probabilistic nature of the theory. Quantum mechanics is only different from classical probability if you later observe interference effects by doing something like a double-slit experiment. But that's not something you can do with cats, or any macroscopic system at room temperature. It's strictly more difficult than bringing the cat back to life.

You probably won't find a discussion of this in the literature because the part about the time evolution of |alive> + |dead> is too obvious to bear mentioning, and the rest is just cocktail-party philosophy. -- BenRG (talk) 04:12, 3 September 2012 (UTC)

I'm going to have to respectfully disagree with you. You're answer assumes we're talking about some event that happened, or didn't, but we aren't. If the poison goes off on day one, then in ten days the cat is ten days dead, if it goes off on day two then the cat is nine days dead, etc. A two day dead cat and a one day dead cat are not the same. That's the whole confusion, we aren't talking about if the poison went off, but when the poison went off (never being a possibility) For that reason, the cat must be a superposition of states from perfectly fine to ten days rotten and all in between. Really, we could dispense with the cat and just ask about the decay of the sample, which is a quantum problem, the cat serves no real purpose. [Also, as you point out, there is certainly know publication that would analyze this]Phoenixia1177 (talk) 06:40, 3 September 2012 (UTC)

I did assume that the poison is released (or not) at the beginning, which is what I think Medeis wanted. I also assumed that the cat wouldn't conk out for unrelated reasons later. If you want more realism you have to face the fact that these states make no sense anyway since you can't perfectly isolate a cat from its environment. -- BenRG (talk) 18:40, 3 September 2012 (UTC)

This is what you get when science nerds become famous. Talk about cats in boxes. Making other nerds think that's what science is, writing papers about quantum bomb detectors; "we can test a bomb without really testing it!" Why don't you show us with real bombs. Quantum eraser experiment, Delayed choice quantum eraser, Walborn et al. quantum eraser.. when I count the minimum number of detectors , polarizers, interferometers etc needed to perform these, I think a computer could simulate every conceivable thought experiment in a day. Maybe then they'd stop playing in their quantum sandbox and go do serious work. Like bridging the gap between their claim that "we have demonstrated in our experiment an interaction-free measurement with a figure of merit up to 1/2 i.e., half our measurements could be interaction-free", and the 2% detection rate, the dark counts, the convenient equalizing of detection rates by adjusting detector overbiases for "the purpose of this proof of principle" i.e., the actual results. There are complete libraries filled with new age mysticism, telekinesis, free energy and other crackpot ideas using quantum physics as support for their delusions. All these esoteric QM interpretations, just put them next to Aristotle's four causes, Heraclitus' "all things flow", the astrology of Tycho brahe and the philosopher's stone. </end of rant> Ssscienccce (talk) 15:09, 3 September 2012 (UTC)

Superposition does not come just like that, it came from the many worlds interpretation, and that came from back in time.

and If a particle falling apart,it should report the same world from the many worlds, and his time and his place is corelated to one world that you stabiliz on it . thanks water nosfim --81.218.91.170 (talk) 15:54, 3 September 2012 (UTC)

Look, Schrödinger's cat is stupid. Even Schrödinger thought so. It's famous because of the dead cat, not because of any merit as a thought experiment (much less a real experiment). The other experiments you mention are different. They're useful as illustrations of uniquely quantum effects, and they're experiments you can actually do and that could conceivably give results incompatible with quantum mechanics. Almost no one expects them to, since the quantum rules are too well tested at this point, but they're still better than Schrödinger's cat. -- BenRG (talk) 18:40, 3 September 2012 (UTC)

i got the honor to see "Cats" resurrected . Thanks water nosfim--81.218.91.170 (talk) 20:14, 3 September 2012 (UTC)

The bottom-line, regardless of Schrödinger's cat's merit or treatment, this definitive or indefinite cat has been discussed and elaborated on. I came across it plenty of times during the years I browsed the NCSU library stacks, but I found nothing regarding it of much consequence. Still, its entirely possible something similar to the OP's version can be found somewhere in that heap, along with the mostly incorrect QM interpretations that are nearly unfalsifiable. In recent years, the two most revealing experiments that I am aware of are the walking droplets [4] along with the successful measurement of individual particle paths and their stochastic interference pattern: described here and published here. The liquid analog entails some interesting particle-wave-like interactions, and although a similar medium, the aether, was once sought (and a form of it persists as a string-filled spacetime "mattress"), a medium is unessential. Modocc (talk) 20:32, 3 September 2012 (UTC)

Ok, maybe it's not the experiments themselves, but rather the way the are presented, either by the authors or by the media who report them. Take the article Quantum eraser experiment:

Because pairs of photons are entangled, giving one a diagonal polarization (rotating its plane of vibration 45 degrees) will cause a complementary polarization of its entangled pair member. So from this point on, the photons heading down toward the double slits will meet the two circular polarizers after having been rotated. And when photons enter either circular polarizer "half way off" from their original orientation, the result will be that on each sub-path half will be given one kind of circular polarization and half will receive the other polarization. The end result is that half the photons emerging from each circular polarizer will be "clockwise" and half will be "counter-clockwise." It will then be impossible to look at the polarization of a photon and know by which path it has come.

This seems a highly unlikely interpretation of the experiment. The Walborn paper itself isn't exactly an example of clarity, with ambiguous terms like "measuring the polarisation of the photon" or "destroying the information". The included data of coincidence counts and the detection time gives an indication of what is happening: there are large differences in total coincidence counts, the different setups "filter out" photons based on their polarization. But reading the article, one would assume that all photon pairs are detected and they change their behaviour in some magical way. Ssscienccce (talk) 15:14, 4 September 2012 (UTC)

Thing is, macroscopic objects behave classically because of a non-classical "weird" quantum effect, i.e. entanglement. The degrees of freedom of a macroscopic object get entangled with the environment, and that makes the object behave in an effectively classical way. So, if I detect purely classical behavior when looking at a macroscopic object, that is as much evidence for quantum mechanics as is doing some interference experiment using photons or measuring a violation of Bell's inequality. There is no alternative theory available that can explain classical behavior at the macro level, classical mechanics has already been falsified. Paradoxically, it would actually take an observation of a quantum effect on the macro scale where quantum theory predicts it shouldn't occur to falsify quantum mechanics.

Also, when one performs an interference experiment, this is also a probe of the validity of quantum mechanics for macroscopic systems. Take e.g. some interference experiment involving mirrors. Clearly, if the state of the mirrors would be affected by the photons bouncing off the mirrors, the interference pattern would be weakened, it would vanish if you could unambiguously tell which way the photon went using the state of the mirrors. So, you can intepret the fact that an interference pattern appears on the screen as experimental evidence that the momentum space wavefunction that describes the center of mass motion of the mirrors is a lot wider than the change in the photon momentum (in case you do the experiment with floating mirrors). Count Iblis (talk) 23:37, 3 September 2012 (UTC)

First the big world has same symmetry in time, then if easier for you, do first revelation of knowledge, and act in compliance . thanks water nosfim --81.218.91.170 (talk) 05:10, 4 September 2012 (UTC)

BenRG seems to have gotten the question right the way I meant it and Phoenix and IP70 are confusing an issue. The original condition is whether or not single radioactive atom with a 50% probability over a set initial "test" period decays, releasing a single photon. That photon is not entangled with anything. If it is detected druing the initial test period, a flask of poison is broken killing the cat.

Now, supposedly the cat is neither dead nor alive until you open the chamber to look. But what if you wait ten days to open the chamber? Would the cat have spent ten days rotting? If he was neither dead nor alive, did he rot over that period? If he rotted, was he not dead and rotting from the beginning regardless of our observation? Or did the rotting happen in some sort of instantaneous backwards time travel once the door was opened because of our observation? To push the absurdity, if he didn't rot, is this a way of preserving meat? The question is, how can the cat be in a state of superposition and rotting at the same time for ten days?

The instantaneous "he's dead and he's not dead until we observe him" description is plausible because we don't have to deal with the fact that dead cats rot over time. This development through time seems like an obvious objection to the theory that one has to wait for observation for the wave function to collapse. That is what surprises me, that no critic has asked what happens to the cat while it is in the state of superposition over time.

Surely I am not the first to raise this question? μηδείς (talk) 02:15, 7 September 2012 (UTC)

The cat is not "neither dead nor alive", it is both dead and alive (supposedly), until it is observed to be one or the other when the box is opened. If the superposition of dead/alive states could be maintained over ten days, then the cat would evolve as a superposition of "rotting cat" and "alive cat", and when the box was opened one or the other would be revealed. If the rotting cat was revealed then you would see a state that had been rotting for ten days. However, this is all impossible (even more so than the original thought experiment) because living and rotting cats are big and complicated objects, and the processes/interactions that they undergo will destroy the basis of the experiment. 86.146.104.131 (talk) 03:29, 7 September 2012 (UTC)

Sorry to the person above, I had the page up for a while before I clicked edit, I never saw your edit till I posted mine.Phoenixia1177 (talk) 03:39, 7 September 2012 (UTC)

Sorry for the initial confusion, I was assuming, since you mentioned time, that you were allowing the decay to happen at a later time if it didn't already occur. In the case you are discussing, the previous given answer that the cat will be in a superposition of the states |10 ten days rotted> and |10 days in box, but not poisoned> is the correct one. Ultimately, the various branches of the superposition all move forward in time. All introductory books on QM handle the question of how states evolve in time, some of these are approachable by someone with a little linear algebra experience and some calculus/basic physics courses (I'm not sure your background) Unfortunately, I'm not at home, so I don't have any recommendations at the moment. You can also look at our article on the Schrödinger Picture and the Schrödinger Equation and Hamiltonian(Quantum Mechanics), although I don't think any of them are overly helpful. You might also consider doing a google search of "Time Evolution in Quantum Mechanics", I'm sure some of the results should be of use.

As to the question of just how the cat ends up in either definite state, that is much thornier and I don't think it has a universal answer. However, it may help to look at things from a different perspective, namely that what we call definite states are the atypical. For an analogy, if you assume that the Earth is at the center of the solar system, you can still work out laws that predict the motion of the stars in the skies, however, these laws will not be elegant nor will they be intuitive. Similarly, looking at definite states as some special entitled things as opposed to just another superposition makes quantum mechanics seem far more mysterious. [Note: obviously there is a good reason to think about how definite states get entered and all that, I'm not advocating ignoring that, just looking at things from a different angle when useful.] Phoenixia1177 (talk) 03:38, 7 September 2012 (UTC)

I suspected the "both states keep evolving for ten days" answer would be given, since the "catmeat stasis" answer seems, to my intuition, to violate too many other laws. One of my undergrad majors was Bio, but I tested out of calculus, having gotten a 5 on AP Calculus in high school, so the furthest I went in math was series and summations, (and I mastered Springer Verlag's Chaos and Fractals when it came out) if that matters. What I really want at this point is some sort of source, preferably popular, Penrose is at my level, that discusses this specific issue, especially from a not unskeptical viewpoint. μηδείς (talk) 04:27, 7 September 2012 (UTC)

Objection to IP86. What does the fact that the cat is complex matter to the experiment? The decaying atom's photon is the simple causal agent. If that were a problem (and I am not saying it's not) wouldn't its complexity invalidate the original experiment without the 10 day delay as well? μηδείς (talk) 04:31, 7 September 2012 (UTC)

The complexity of the cat would matter if you were doing this as a real experiment, but we aren't and it doesn't. On to other matters, I, unfortunately, don't know much of the nontechnical literature on quantum stuff, so I doubt I'll be much help with that. Question: do you require a source to specifically talk about the cat or will anything on time evolution of super positioned states do? I ask because there is a book, I have the title at home, that should be readable (some math is required, though) that will discuss the concepts, but no cat- it is a philosophy meets QM book, it's interesting independent of any of this too, so that's a plus. If interested, I can get you the title.Phoenixia1177 (talk) 13:07, 7 September 2012 (UTC)

No, the cat was not important, the development over time is the issue. I will benefit from a book with clear prose that might use equations to illustrate. If the discussion is solely put forth in terms of math I'll probably get lost. But do give me the title and I'll look for it. μηδείς (talk) 16:29, 7 September 2012 (UTC)

For example, the equation at the top of the next thread below is above my pay grade. I know it has something to do with the (double?) integral of some sort of vector product. But I garner from the prose that the surface integral has to be zero presumably because otherwise you'd have a net polar magnetic "charge", in effect a magnetic monopole. μηδείς (talk) 16:37, 7 September 2012 (UTC)

The book I was thinking of is The Structure and Interpretation of Quantum Mechanics by R. I. G. Hughes, if you're feeling a little more mathematically inclined, you might try the first 7 or 8 chapters of Quantum Processes Systems, and Information by Benjamin Schumacher and Michael Westmoreland from Cambridge University Press.Phoenixia1177 (talk) 01:14, 8 September 2012 (UTC)

Is D necessarily zero?

Suppose you have a sphere. Suppose $\int \int {\vec {D}}\cdot d{\vec {A}}=0$. Is D necessarily zero? Or, is there some symmetry condition that forces D=0? --130.56.91.41 (talk) 02:47, 3 September 2012 (UTC)

D is a vector field and dA is the area element, right? Then if the vector field points along the surface of the sphere at every point, the integral will be zero even though D is not zero anywhere. In fact, Maxwell's equations of electromagnetism say that the surface integral of the magnetic field is ALWAYS zero, across any surface, even though magnetic fields themselves are clearly not zero everywhere. --128.112.70.89 (talk) 03:51, 3 September 2012 (UTC)

If D points tangentially to the sphere at every point then it will have to be zero somewhere by the hairy ball theorem. But that's not really important here. Staecker (talk) 16:40, 3 September 2012 (UTC)

Several conditions related to this mathematical formulation are explained in our article on Green's theorem, Stoke's theorem, and the divergence theorem, and the articles linked from there. The math is very widely used, especially in the study of electromagnetic fields. Nimur (talk) 15:03, 3 September 2012 (UTC)

D is Electric displacement field--130.56.84.156 (talk) 04:39, 3 September 2012 (UTC)

Minimal food requirements

Suppose we want to send a small human, perhaps 10cm shorter and quite a bit lighter than the average woman, to Mars. It'll be a short 545-day trip, and the only requirement is that the astronaut is alive at the end. Being emaciated, insane, and suffering from osteoporosis are all OK, because no matter how cruel the conditions, there won't be a shortage of people (even small women) willing to go. What's the absolute minimum amount of food, in weight and volume, the astronaut would require? Does being in space change the food requirements from what they would be on Earth? --128.112.70.89 (talk) 03:48, 3 September 2012 (UTC)

Not sure about earth, but the minimum average calories a person needs to maintain their current health is about 1,800, per Food energy, but that is quite activity dependent. --Jayron32 03:55, 3 September 2012 (UTC)

But that's for an average person, not for a small woman or really small man. Also, an Earth-dweller needs to walk around, think, pump blood, drive, and eat, all under Earth gravity. I'm thinking that the astronaut could be confined to a small space or chained to prevent any physical activity. That would be a serious animal cruelty if done to any animal on Earth, but as I said, there's be no shortage of people willing to endure that to go to Mars. Finally, how much mass and volume does 1 calorie translate to, given the most compact possible storage? --128.112.70.89 (talk) 04:04, 3 September 2012 (UTC)

If you don't care about the health of the individual and just want to send them so you could say you did it, why not send an animal instead ? StuRat (talk) 04:26, 3 September 2012 (UTC)

I think the story you've made up as the premise is a bit too silly. Of course no sane person would want to endure 545 days of near starvation to get to Mars. What happens AFTER the 545 days? They stop eating all together? Obviously one of the 1st requirements for any planetary mission would be to provide enough food to keep a person healthy. I think saying it'll be someone who is "small" or "woman" won't play a significant enough part, I think far more important qualifications would be "smart" and "sane". Look at sailors in the days of discovery, they surely endured harsh conditions, probably surviving on minimal rations, but even wealth and fame weren't enough incentive to willingly starve yourself as part of the plan. CErtain people in the army also probably know quite a lot about "minimums" required to keep people alive and healthy. Besides, if you're taking thousands of kilos of fuel and cargo and spending billions on R+D, it's hard to not justufy a few extra kilos of food, especially if you dehydrate it and use recycled water, then maybe you could recycle food too by growing some of your own? It seems absurd that anyone going on that sort of mission would be expected to starve as part of the "price". As for calorie density, lard, butter and nuts are about as high density as you get. Not sure how long you could eat just those three before the mere sight or smell of them will make you vomit. Vespine (talk) 04:37, 3 September 2012 (UTC)

I agree that nobody is going to send people on a suicide mission to Mars. However, the idea of sending people of small stature and low basal metabolic rate is a good one, as long as they aren't so small as to suffer health problems as a result. It's not just their mass and the mass of the food to consider, it then requires more fuel to accelerate that mass, and more fuel to accelerate the mass of that additional fuel, etc. So, if we compare two people, one whose mass and the mass of the food they eat, water they drink, and air they consume is half of the other, then the mass of the ship could be half as much as well. It's all proportional (with some non-proportional effects in the case of launching through thick atmospheres, like the Earth, but hopefully a space launch or Moon launch would be used to go to Mars). StuRat (talk) 19:59, 4 September 2012 (UTC)

Taking 1400 kcal per day, high energy food of 5kcal per gram, you'd need 152kg for 545 days. Don't know if 5 kcal per gram is a good guess, proteines and carbohydrates are 4 per gram, fats 9. Ssscienccce (talk) 15:23, 3 September 2012 (UTC)

Yea, that's about right for calorie-dense foods. Cashews, for example, have about 5.5 kcal per gram: [5], while macadamia nuts are a bit over 7: [6]. StuRat (talk) 20:07, 4 September 2012 (UTC)

@Stu: Because the public doesn't regard animal spaceflight to be as important as human spaceflight. Tell me, who was the first animal in space? How many times have you heard that milestone celebrated? How about the first human?

@Vespine: 545 days is the time for a round-trip, including 30 days of staying on Mars. A one-way trip takes 6 to 8 months unless you're willing to use a lot of fuel. The comparison with sailors is flawed because sailors needed to be competent at controlling their ship, while computers can land spacecraft on Mars just fine. Also, I never said that the astronaut had to be a starving wreck at the end, just that it's not a problem (so a safety margin is not required). --128.112.70.18 (talk) 15:15, 3 September 2012 (UTC)

Laika the space dog although the U.S. sent fruit flies suborbital much earlier. See animals in space. Rmhermen (talk) 22:45, 3 September 2012 (UTC)

Yes, I knew it was Laika, and also knew Yuri Gagarin was the first person in space. StuRat (talk) 19:52, 4 September 2012 (UTC)

Everyone of an age with good memory knows it was Laika. What is your point? If "Ozymandias the Maine Coon housecat" or "Maximilian the wire-haired dachsund" were sent on a one-way trip to Mars, do you imagine that no one would remember her or his name 50 years after? 98.220.239.210 (talk) 05:46, 5 September 2012 (UTC)

Yes, exceptionally old people know it was Laika, even though the first animals in space were technically fruit flies. 14 year olds like me, on the other hand, tend to know a lot about Gagarin and nothing about Laika, simply because it's not as memorable or significant an achievement. I'd also like to point out that the Apollo program was about landing a man on the moon--not flies, dogs, or cats, but a man. There's no reason that a new cold war, perhaps between China and the US, wouldn't be about landing a man on Mars.

Back to the question: as I (the OP) said, it's downright unethical to confine an animal to a tiny space and starve it for 500 days. That's not a problem with humans because a human can consent, and because humans already treat each other much more cruelly. Case in point: we euthanize animals suffering from terminal illness, but Christians have a problem with euthanizing humans in the same situation. --128.112.70.118 (talk) 02:36, 7 September 2012 (UTC)

Bauxite

What is "soundiferancic" in http://en.wikipedia.org/wiki/Bauxite?

It's under "Processing"

"Bauxite rocks are typically classified according to their intended commercial application: metallurgical, abrasive, cement, chemical, and refractory, cosmetic, electric, soundiferancic."

Thanks — Preceding unsigned comment added by 66.177.68.235 (talk) 04:26, 3 September 2012 (UTC)

I think it is a longstanding typographical error or something like that. A quick google search: [7] shows that the word exists only in the Wikipedia article on Bauxite and websites that directly copied the Wikipedia article. I'm not sure what it is trying to say, but I think you'd be safe removing the word entirely. It looks like gibberish. --Jayron32 04:36, 3 September 2012 (UTC)

It was part of a particularly nasty little vandalism edit by an anonymous editor in June (see [8]) that apparently nobody ever caught. It's a good thing that editor added the clearly nonsense word "soundiferancic," because the other things changed in that edit were not so obvious. I've reverted those changes. —Bkell (talk) 04:51, 3 September 2012 (UTC)

Good catch! --Jayron32 05:02, 3 September 2012 (UTC)

anatomy

is anatomy include in life science subject? i am a student of msc.(med.) anatomy .can i get some information about scope of anatomy? and can i give gate examination? — Preceding unsigned comment added by 117.224.24.237 (talk) 13:06, 3 September 2012 (UTC)

Anatomy can be classed as a life science according to our list. Does our article Anatomy help with your second question? If by "can I give gate examination" you're asking whether you can sit the Graduate Aptitude Test in Engineering, or use the results of that test for some purpose, you will need to discuss this with the university, college or examining board concerned. - Karenjc 14:35, 3 September 2012 (UTC)

Extinction

How often do they record that a species has gone extinct? Is there a place where they announce it every time when a species is recorded to have gone extinct? --Theurgist (talk) 15:24, 3 September 2012 (UTC)

This tool may not be precisely what you had in mind (and I hope others will make better suggestions), but you can search by many variables. For example, under "Assessment" you can choose "EX" (extinct) and one or more years (e.g. 2012) - that combination lists 138 new entries for extinct species in 2012. If they have a web service, you could conceivably automate the search and detect new entries. Perhaps registered users can get notifications - I have not registered. -- Scray (talk) 16:21, 3 September 2012 (UTC)

Which of these species has gone extinct, and which has merely moved on through evolution?

The question will also depend on what you mean by extinction. Homo erectus is extinct, but we are descendants of theirs, so they did not all die without progeny that are still living. This PBS website suggests the average mammal species exists for one million years, with ten million as about the maximum: http://www.pbs.org/wgbh/evolution/library/03/2/l_032_04.html On that basis almost all species that have ever existed are extinct. μηδείς (talk) 19:38, 3 September 2012 (UTC)

No, I don't mean million-year-long evolution; I mean reports that critically endangered or extinct in the wild species have gone extinct due to the death of the last known organism. --Theurgist (talk) 05:31, 4 September 2012 (UTC)

Gone extinct? this seems an odd expression, maybe it is because I have gone old that I find it difficult to accept. (with thanks to Lynne Fotheringham). Either species go or they become extinct. Richard Avery (talk) 07:16, 4 September 2012 (UTC)

I think the nearest thing to an "official announcement" of extinction will be found in the IUCN Red List that Scray linked to above. Gandalf61 (talk) 08:56, 4 September 2012 (UTC)

Even then, how would we treat the "extinction" of Homo erectus? Erectus colonized Africa and Eurasia. See human evolution. A subpopulation in Africa evolved into Homo sapiens. As it spread out of Africa, prexisting populations of Erectus in Asia dwindled, and went extinct. (This is the out-of-Africa theory, which not all people accept, but it is an example of a mechanism no one doubts exists.) Eventually there were very small pockets of Homo erectus, rare, and distinct from modern humans. So, did they actually go extinct? Or were they replaced by their own offspring? There are on the order of some 27 or so species in the clade Hominina which makes up all human ancestors more recent than our common ancestor with the chimpanzees. Are 26 of those species extinct? Or are only the ones that didn't evolve into us extinct? When a lineage goes extinct, as in the pterosaurs, the ammonites, and the trilobites, then the lineage is extinct. But are the dinosaurs extinct? It is not a clearcut distinction, and rigourous definitions are necessary.μηδείς (talk) 17:32, 4 September 2012 (UTC)

Speciation is very difficult to define (it is based on whether different parts of a population can reproduce together, but that is rarely a simple yes/no thing) and we draw quite arbitrary lines between species. Once you have an arbitrary line, it is fairly easy to define extinction, but it does depend heavily on where you draw that line. --Tango (talk) 11:24, 5 September 2012 (UTC)

Darold Treffert speculative claims regading genetic memory

I refer to this article, the last 3 or 4 paragraphs. Anyone has any insight or comments? Such claims call for some sort of response. Zarnivop (talk) 17:57, 3 September 2012 (UTC)

I don't think you will find many scientists who take that idea seriously. The argument is similar to the one Plato gave in his dialog Meno, where Socrates asks a slave a series of questions that purport to reveal inborn knowledge. There is of course a large amount of information encoded in the genome, but not many people would say it is likely that it takes such an explicit form. Looie496 (talk) 19:02, 3 September 2012 (UTC)

Well, it's science. Such claims can be verified. I find it unrealistic as it is, go accept that some 2Gb are enough to code a human being. To go further and require the poor 2Gb to contain "genetic memory" turns unrealistic to plain miraculous. Zarnivop (talk) 19:16, 3 September 2012 (UTC)

Both answers above seem more skeptical than they need be. There is no reason to discard offhand the possibility that some of our abilities are innate. This is not a new idea. See Nature versus nurture. Dauto (talk) 00:57, 4 September 2012 (UTC)

I didn't mean to deny that some of our abilities are innate: if nothing else, our ability to learn must be innate, or we could never even get started. I meant to deny that the ability to play the piano or to do fancy mathematics are innate. Looie496 (talk) 03:07, 4 September 2012 (UTC)

There are 4 different things that might be called "genetic memory", in humans:

1) One is covered under Genetic memory (biology)#In animals, dealing with immunity to disease, but this type is not passed on to the next generation.

2) A second is instinct, which has been known about for a very long time. This could seem like passed down memories, in some cases, as in you possibly being terrified by snakes along with previous generations, but the reality is that this tendency was passed down to all the generations because those who lacked this trait died out from encounters with venomous serpents. The origin of such traits is just mutations, not memories, but such mutations are selected for and thus passed down preferentially.

3) Epigenetics is the third, where the genes are changed in one generation, and passed down to others, as a result of experiences in that first generation. I believe periods of starvation are one such experience which changes the epigenetic code.

4) However, actually being able to recall what happened to a previous generation seems to be pure fantasy. See genetic memory (psychology). StuRat (talk) 03:00, 4 September 2012 (UTC)

Treffert claims clearly relate to #4 in your list, hence the strong skepticism. Zarnivop (talk) 05:50, 4 September 2012 (UTC)

There's also the idea of Memory RNA, based on experiments with "trained" flatworms being ground-up and fed to other worms who apparently showed the same learned behaviour. The work was done by James V. McConnell, who became a target of the Unabomber. Stress related proteins seem a more plausible explanation for the findings.

Treffert mentions memory of the "rules" of maths and music. I have no problem accepting that these are in part genetically encoded, change the frequencies of the notes used in a piece of music to random values and it will sound awful, even to a baby, we perceive certain frequency ratios as pleasant and I doubt this is simply based on experience. As for maths, clearly our brains have the capacity to perform maths, and the rules of maths are not some arbitrary conventions that we can change at will, so it's not impossible that evolution has "favoured brain structures implementing these rules", so to speak. But I wouldn't call it memory, it is something we are born with. Ssscienccce (talk) 16:12, 4 September 2012 (UTC)

Yes, I'd call it instinct. Basic counting, addition, subtraction, and perhaps multiplication and division may be instinctive in humans, since counting the number of lobes on the leaves on a plant, knowing if everyone is present, dividing food up evenly, etc., were important survival skills. Higher math is not. StuRat (talk) 19:45, 4 September 2012 (UTC)

Assassin's Creed uses "genetic memory" as a cute plot device to explain video-game rules, but it's not science. Human DNA actually holds only 3 x 10⁹ base pairs of information - i.e. 6 gigabytes. For people who download videos off the Internet that's not really a lot of storage space! And there's a reason - all genetic memory, whatever it is, has to fit in one tiny little sperm and one relatively small egg (0.12 mm = 0.0000017 cc) - the adult brain (about 1200 cc) has 700,000,000 times more space to hold information. Wnt (talk) 23:47, 4 September 2012 (UTC)

Principle of relativity

The (special) principle of relativity says that the laws of physics take the same form in any two inertial reference frames.

Can this principle be (slightly) generalized to say that the laws of physics take the same form in any two reference frames (possibly non-inertial) provided they move relative to one another at a constant velocity?

My gut feeling says that it's true, but a) I can't find a way to justify it, and b) I know that two observers that move relative to one another at a constant velocity in one reference frame might be accelerating relative to one another in another reference frame. This gives me some doubts... 65.92.7.148 (talk) 22:15, 3 September 2012 (UTC)

You may find the topics of Lorentz covariance and Noether's theorem to be of interest. Also General relativity and the Equivalence principle. All of those topics deal with the laws of physics as they apply to different frames of reference. --Jayron32 22:19, 3 September 2012 (UTC)

The generalization is certainly true. Your statement (b) is not true. Any combination of linear transformations gives a net result that is a linear transformation. Looie496 (talk) 22:24, 3 September 2012 (UTC)

But linear transformations keep you in inertial reference frames. What if you go from an inertial frame to a non-inertial one? 65.92.7.148 (talk) 23:08, 3 September 2012 (UTC)

Yes, you are right, if non inertial frames are considered, than two objects might be accelerating with respect to each other (that is the second derivative with respect to time of the distance between them is not zero) in on frame, while not accelerating with respect to each other in another frame.Dauto (talk) 00:08, 4 September 2012 (UTC)

To answer the OP, yes the laws of physics take the same form in any frame (whether its inertial or not) within General Relativity. Dauto (talk) 00:08, 4 September 2012 (UTC)

What if we restrict ourselves to just special relativity? 65.92.7.148 (talk) 01:04, 4 September 2012 (UTC)

I'm not sure I understand the question, but consider the following analogy: you can do Euclidean geometry using Cartesian x, y coordinates, and write down various equations expressing that a particular shape is a square, or whatever. If you pick a different Cartesian coordinate system x', y', those equations will be the same, except with ' after each x or y. You can say "the laws of Euclidean geometry take the same form in any Cartesian coordinate system", which is another way of saying that Euclidean geometry isn't affected by rotation or translation (since the Cartesian coordinate systems are related by rotation and translation). On the other hand if you pick some other wonky coordinate system p, q (it could be bipolar coordinates or something), the equations will look different, but they will look the same as if you'd used a wonky coordinate system p', q' which is related to p, q by rotation and translation. This isn't a generalization, it's just a consequence of what we already knew: Euclidean geometry isn't affected by rotation or translation. But the formulas for p' and q' in terms of p and q aren't going to be the same as the formulas for x' and y' in terms of x and y, so in that sense the relationship between the coordinate systems isn't the same. -- BenRG (talk) 02:15, 4 September 2012 (UTC)

If two reference frames are moving at constant velocity with respect to each other, they must have the same acceleration at all times. That's because the integral of a2-a1 can only be constant if a2-a1 is 0. So your question is really "if frame A is accelerating at 5 m/s^2, and frame B is accelerating at 5 m/s^2, do the same laws of physics apply in both?" The answer is trivially "yes", because what's going to differentiate the two frames? --128.112.70.118 (talk) 02:49, 7 September 2012 (UTC)

September 4

Reference frame for Dark Energy

Does Dark Energy have a preferred reference frame or is the value constant at every velocity? If it is frame invariant, then how do two different observers at different velocities come up with the same predictions for how galaxy clusters will evolve over time? If it does have a reference frame, then what is this and how do we determine what it is and how fast we are moving relative to it? Hcobb (talk) 01:09, 4 September 2012 (UTC)

It's frame invariant. I don't really understand your second question. Galaxy clusters aren't frame invariant—they have a state of motion. -- BenRG (talk) 01:54, 4 September 2012 (UTC)

Let's do a little thought experiment. Take two massive objects and place them at rest with respect to each other and exactly the right distance from each other so that the gravitational acceleration towards each other is exactly the same as the expansion of the Universe between them due to Dark Energy. These two masses will with respect to a stationary observer remain at rest with respect to each other. Now take another observer who is moving into these objects with them lined up in front of him. Do to his high speed he will see that these objects have increased masses and a reduced distance between them. Therefore from his point of view the normal level of Dark Energy is no longer sufficient to balance out the gravitational attraction, and so these two objects MUST be accelerating towards each other. So you have two different observers applying the same laws of physics and getting radically different results. Hcobb (talk) 02:24, 4 September 2012 (UTC)

You can't just plug the "relativistic mass" into Newton's law of gravitation to find the force and the acceleration. Instead, you would have to include the full momentum and energy, and use the relativistic form of Newton's second law too. Do this, and you'll get the same result in all frames of reference. --Amble (talk) 15:27, 4 September 2012 (UTC)

Actually, the thought experiment is more problematic than that. A Newtonian picture of gravity gives the wrong answers when high speeds are involved, even with a fully sophisticated application of special relativity to Newtonian gravity. Indeed, one of the earliest confirmations of general relativity was Eddington's observation of star light deflected by the sun being incompatible with a combination of Newtonian gravity and special relativity. Pure Newtonian gravity says that light isn't deflected by gravity, because it has no mass. Special relativity as applied to Newtonian gravity says that light should be deflected (a photon's mass being given as per E=mc²), but it gives the wrong value for the amount of deflection by a factor of two. The moral of the story is that when high speeds are involved, you have to view gravity from a general relativistic viewpoint, not as a force that causes an acceleration. Red Act (talk) 06:42, 5 September 2012 (UTC)

Dental question: Toothbrush vs. Toothpaste

I have a question about brushing teeth. Viewed from a high level (obviously), what percentage of the benefit comes from the brushing, and what percentage comes from the toothpaste? Phrased differently, perhaps, could it be said that brushing one's teeth without toothpaste gives about 80% of the benefit of brushing with toothpaste? 50%? 20%? Thank you in advance! Stingray Xray (talk) 01:25, 4 September 2012 (UTC)

This is an awkward question as brushing and the paste each serve different functions. Assigning a percentage benefit to brushing and to the paste implies that if you omit one, you'll still get the remaining percentage benefit - it doesn't work that way. Its a bit like asking what fraction of the motional benefit of a car comes the engine & transmission, and from the car body.

The main function of brushing is to disloge food particles, and rub the paste on the teeth. Toothpaste has several incredients, each designed to serve different roles. The main ingredient is an abrasive, typically pumice powder. The abrasive serves to remove food & bacteria stains and keep down tartar (deposits of minerals and baterial films). Modern toothpastes usually include a chemical that tends to weaken tartar, and antibateria agents, both of which may provide a small additional benefit above what the abrasive does. The next significant tootpaste incredients are directed at giving a nice taste in the mouth. Toothpaste packaging and promotion often includes mention of other things like delivering flouride, (However the chemistry of flourine means that any such benefit is negligible or completely non-existent), and reducing bad breath (however, if you are healthy, eat normal food, and are reasonably good at cleaning your teeth, you won't have bad breath anyway.)

So, if you brush without paste, you'll remove the food particles. That's good, as it removes what feeds bacteria. But without the paste, your teeth will most likely become yellow with tartar. If you go to a dentist with yelow teeth, he'll most likely be a lot more agressive in treatment, as he'll have more to remove before he can spot any cracks ("leaking" as they call it) or decay. And when he finds something, he'll go for the maximum corrective treatment, drilling & filling to the max, because he'll be thinking here's a dumb patient whose teeth are going to rot - whereas if you present with nice clean white teeth, he might be more likely to say "we need to watch that tooth, but it's ok until your next checkup", or maybe just do a little tiny acrylic fill.

It is difficult to find info on this on the internet that isn't likley to be commerically biased, or just mumbo jumbo. This is a good as any: www.dentalgentlecare.com/toothpaste.htm.

Wickwack121.215.159.205 (talk) 02:19, 4 September 2012 (UTC)

Wickwack, I appreciate your enthusiasm for the subject, but this is a very poor answer by Reference Desk standards. (1) You have not included a single reference except for your sideswipe at the end, a link to a few paragraphs written by some individual, non-notable dentist. (2) Factual inaccuracy. Stating that the main function of brushing is dislodging food particles and rubbing the paste on the teeth is nonsense. The main function is to remove biofilms that accumulate on the teeth because of the normal mouth flora. This can be demonstrated in your own mouth quite simply. (a) Brush your teeth and go to bed. (b) Sleep, then wake up and run your tongue around your teeth, front and back. Feel the texture. (c) Brush your teeth with no toothpaste. (d) Run your tongue around your teeth again. Feel how they feel smooth and polished and clean? That's not food particles that have been dislodged, and it's not the rubbing of paste on your teeth; it is the mechanical rubbing off of the biofilm that your mouth bacteria generates continuously. (d) Your gratuitous blowing-off of the benefits of fluoride, despite our referenced articles like Fluoride therapy, shows you're one of those weird anti-fluoridation activists, which would be OK with me if you supplied references ... but you haven't. (e) Your cynical note about dentists "drilling & filling to the max" because of yellow teeth is again nonsense. (f) This is a little much to ask, but if you could apply some imagination, you might not blow off my percentages question quite as much ... not that this means much to be based on your obvious unfamiliarity with the subject. (One alternative phrasing could have been something like "If two patients with similar mouths and dental activity were to be compared, one brushing with toothpaste and one brushing without, what would the differences be in their dental health, and by how much?") Please do not post to the Reference Desk without references. One reason is that it gives readers followup material; another is to reduce errors, like the many errors in this sad post of yours. Stingray Xray (talk) 16:46, 4 September 2012 (UTC)

Stingray, if you actually read what I wrote, you'd notice that I strongly AGREE with flouridation of water, and only regard mechanical application of flouride to teeth as probably useless. You'd also see that I gave a range of topics that any reader can follow up for themselves. I fully agree with and support the need for references in Wiki articles, but this is Ref Desk. Here, orginal research and even personal opinions are fine, provided they are constructive. I note that personal opinions and anecdotes on Ref Desk are very common, from many contributors. Just because a Wikipedia artcles said something is so doesn't make it right, and doesn't make it the last word. It is Wikipedia policy, and a good one, that Wikipedia is of most value not because of the content per se, but because it gives readers topics and terminology to search on, and links to references. Finally, if you don't like answers, then don't post questions - otherwise after a while you won't get any answers. Wickwack121.215.159.205 (talk) 22:07, 4 September 2012 (UTC)

Fluoride benefits ?

As for the benefits of fluoride, I'm under the impression that the fluoride in toothpaste doesn't do you much good, while a fluoride treatment, on the other hand, seems quite beneficial in hardening the teeth and thus resisting cavities (this is where you hold "trays" on your teeth while the solution soaks into your teeth, similar to some whitening methods). This hardening might, however, make chipping more likely. Is this all true, and, if so, why ?

I know that fluoride in large quantities is poisonous, so that might explain the toothpaste part, if they put in too little to be effective in order to avoid toxicity (say if a toddler eats a tube of toothpaste). Perhaps they can risk more in a dentist's office, where the treatment is given, since you are under their supervision when that is used ? StuRat (talk) 02:50, 4 September 2012 (UTC)

I was under the impression that brushing without fluoride doesn't do much good, hmm, will need to look into it. The Toothpaste section doesn't really say either way. On a related note, municipal Fluoridation is certainly effective at reducing cavities in a population. Vespine (talk) 03:23, 4 September 2012 (UTC)

I'm not so sure. We seem to get plenty of cavities in areas which do this. Do they just add too little, again to avoid potential toxicity ? I also get the impression that the benefits of fluoride are not cumulative, so small doses which add up to one large dose do not give the same benefit as the one large dose. Any truth to this ? StuRat (talk) 03:36, 4 September 2012 (UTC)

This is now off topic, and it would take too much time to track down references. But here's my take on it, based on a combination of what I've read in newspapers and my own knowledge:-

1. Putting flouride in toothpaste is just a marketing thing, with no actual benefit. It's not so much about how much they can safely put in, it's about the chemistry of flourine

2. While dentists may promote it, its something they can charge extra for, and some may actually believe in it, flouride treatment in the dentist's charir is useless for the same chemistry reasons. My own dentist says it's a con.

3. Some countries add flouride to the public water supply, as is done where I am (Western Australia). The flourine from this does get into the teeth and confer a useful benefit, as the body has metabolic pathways that get around the chemistry.

It may be useful to go thru the history of flouride in water in W. Australia. In the 1950's and 1960's there was a huge Government campaign to get children to brush their teeth effectively, at least twice a day. Advertising was directed at parents, we were taught proper brushing at primary school, nurses checked us at school, the works! This was because, pre-World War 2, as in USA, Britain, and elsewhere, most folk had poor teeth hygiene, and also by middle age mostly had no teeth. The market for false teeth was huge. However, all those post-war children still got lots of cavities. An investigation was done, which showed that the amount of flouride present naturally in West Australian water was much lower than in most European countries. So, in about 1964, the State decided to add flouride to the water. Sure enough, the next generation of children had far fewer cavities.

It follows from this, that if your area is like ours and has naturally low levels of flouride, then there is a marked benefit in adding it to public water. However, if your area already has lots of naturally occuring flouride, there is no need to add more. I read somewhere that the amount added by certain USA states is about 1/3 or so what the West Aust Govt adds for this reason - these US states already have significant natural flouride, so they don't need to add so much.

Because tooth decay is casued by a certain type of bacteria, you can get the benefit of flouride without getting any flouride yourself! I grew up in a semi-rural area where the main comercial activities are chicken ranching, orcharding, and some mixed farming (goats, pigs, & whatnot). The folk that live in the town are on the public water supply which is flouridated. Sure enough, town children tooth decay rates dropped markedly when flouride in water started. However, almost every farm, chicken ranch, orchard, or whatever, had and still have their own water supply - they are not on the town supply. Decay rates dropped in farm-raised children as well! Not quite as much, but almost as much. Why? Partly because when at high school, they drank the school water (on the town supply). And partly because their town friends had low decay, leading to low bacteria load in their mouths. Somehow the bacteria get from child to child (otherwise there wouldn't be any tooth decay bacteria).

In W Australia, tooth decay rates have been rising alarmingly in the last 10 years or so, in spite of flouride in the water. It is thought to be due to children drinking a lot more sugar softdrinks than before, and a lot less water (the McDonalds & Kentucky Fried effect "Would you like a large Coke with that?"). It may also be that the bacteria have evolved in response to the high flouride, and we now have stronger bacteria.

If you make it to adulthood without cavities, mostly you'll be fine from then on (assuming you brush effectively etc), regardless of flouride levels. Flouride helps, but it's while you are growing that it really matters.

I mention all this because you hear/see a lot of rot on the pros & cons of flouride in water etc. Evidence may appear contary unless you understand all the factors. Incidentally I grew up on a chicken ranch with no flouride in the water and went to school in a non-flouride area. I'm in my 60's now and still have all my teeth. Wickwack121.215.159.205 (talk) 04:55, 4 September 2012 (UTC)

What is the "chemistry" which prevents fluoride from hardening teeth when applied topically, but allows it to work when ingested ? I would have thought the reverse, as fluoride in the blood would only harden the teeth right around the root, while, if applied topically, it can harden the outside, where it's needed the most. StuRat (talk) 17:35, 4 September 2012 (UTC)

Stu, when I was doing an Engineering degree at university decades ago, I did a couple of chemistry units, taught by a lecturer who was an expert on water quality in municipal water supplies, as well as a couple of other fields. We covered the chemistry of flourine, and I recall that the chemistry of flourine was against direct mechanical application, in fact we had an assignment question on it. There has also been some info in consumer choice magazines in the years since. However, not being a chemist I can't recite it all from memory. If you would like to know, please ask in a separate question. You may get some good responses from others, or you may not. I will attempt to track down the info we had at Uni. It's off topic, so I'm not going to spend time on it here on this question. You will be aware than the body utilises a number of trace elements and other nutrients where activation energies in the chemistry works against it, but the body has evolved a range of complex enzymes & metabolic pathways to enable such elements etc to be used at the cost of some calories. Wickwack121.215.159.205 (talk) 04:53, 5 September 2012 (UTC)

Again, you have not cited any references. This is the Reference Desk. Please cite references. Stingray Xray (talk) 16:49, 4 September 2012 (UTC)

You did not provide any usefull references in your rant above either. E.g., you cited a WP article on biofilms, but that has only one para on dental film (tartar/plaque) and it has nothing that supports your rant. Wickwack121.215.159.205 (talk) 04:39, 5 September 2012 (UTC)

Fluoride effects the demineralization of teeth caused by organic acids produced by bacteria. It doesn't do anything to the bacteria themselves.

Trends in tooth decay decline were seen in countries that introduced water fluoridation, in countries that didn't have water fluoridation and in countries that stopped adding fluoride to drinking water.

Fluoride toothpaste is considered the main reason for tooth decay declines in industrialised countries.

On a different note: eating (hard) cheese after a meal reduces tooth decay because it helps the remineralization process. Ssscienccce (talk) 17:09, 4 September 2012 (UTC)

You get a ceratin bacteria load in your mouth anyway. Brushing with paste helps keep the bacteria load down. However, if there is inadequate flouride in the food & drink you consume, you will get more tooth cavities. And the cavities will get larger before you or your dentist notices in your annual checkup, assuming you have annual checkups. Cavities provide a more ideal home for bacteria than does the tooth surface, and brushing is ineefective at removing bateia from cavities. Thus, low flouride DOES increase the bacteria load in you mouth, further increasing the decay problam and increasing the probability of you pasing the bacteria on to others.

Regarding trends, it may be that some countries continue to see a reduction in cavities. Because decay is caused by a specific bacteria type, there will be other factors. However, in Australia, it is well documented that decay is rising again, despite flouridation. This does not invalidate flouridation of public water supplies for the reasons I gave above (increased softdrink consumption, decreased tap water consumption, possible evolution of mouth bacteria) - in fact flouridation is thus more important now than it was before. Wickwack121.215.159.205 (talk) 04:39, 5 September 2012 (UTC)

Also, I suspect that most bottled water is non-fluoridated, except for when it just contains tap water, leading to increased decay. Is this true ? StuRat (talk) 17:35, 4 September 2012 (UTC)

I can't speak for Stu's USA, but here in Australia, bottled water is essentially two types: (1) Water sourced from the public water supply and claimed to be filtered by the bottling companies. This water will have the same flouride content as what comes out the tap. (2) expensive, premium brand / boutique "spring water" imported fron Italy and eslewhere. I don't know what the flouride levels would be, but the cost limits its consumption to special occaisons, restaurants, and the like, so it won't matter much anyway. Wickwack121.215.159.205 (talk) 04:39, 5 September 2012 (UTC)

Strontium also has some benefits for teeth. Count Iblis (talk) 22:31, 4 September 2012 (UTC)

• To go really far afield on a favorite side-track [sorry :)] I'm thinking that the ancestral terrain in which humanity evolved should, on average, have the optimum level of natural fluoride in the water, or else we would have evolved a different preference. There is some population genetic evidence to suggest that humanity radiated out from the general region of Namibia (though personally I'm a fan of the Okavango Delta and larger regions which might have been similar millions of years ago...). I should note that at least one town in Namibia, Otjiwarongo, is noted in the literature for people with minor fluorosis due to natural fluoride concentrations of twice the usual recommended level. [9] So I think that fluoride in water can indeed be viewed as a true supplement, not a sinister drug conspiracy, though of course the infrastructure might be usable ..... Wnt (talk) 02:08, 5 September 2012 (UTC)

Exactly. Your statement is in accordance with what they State Govt told us when they started flouridation of water. Our water happens to have very low natural flouride levels, so adding it was a benefit. Other countries which have naturally high flouride levels meeting or exceeding the body's needs don't need to add it. Wickwack121.215.159.205 (talk) 04:21, 5 September 2012 (UTC)

Are disabled and mentally-handicapped people self-aware?

And by self-aware, I generally mean able to pass the mirror test. Futurist110 (talk) 03:42, 4 September 2012 (UTC)

Just a wild guess, but I think Stephen Hawking would pass. Clarityfiend (talk) 05:00, 4 September 2012 (UTC)

What about people with Down syndrome or other severe mental impairments? Hawking's impairment is more physical--he is extremely intelligent mentally. Futurist110 (talk) 05:07, 4 September 2012 (UTC)

I think you might want to try being a little more specific than "disabled", as I am somewhat confident that most paraplegics, amputees, and hearing-impaired people would pass the mirror test just fine. That said, I believe the age threshold for humans to pass the mirror test is around a year old or so, so any mentally handicapped person with a "mental age" over 12 months should be able to pass it as well. This would include the majority of those with Down syndrome. Evanh2008 ^{(talk|contribs)} 05:11, 4 September 2012 (UTC)

That's a simplistic view of mental age, and even if you could measure mental age below 1 year, I'm not sure it'll tell you much about the mirror test. In Phantoms in the Brain, the author Ramachandran describes a hemispatial neglect patient who seemed like a perfectly intelligent elderly woman in every way. Since she was neglecting her left field of vision, the author put a mirror in front of her so that her left side would seem appear in her right field of vision, and wondered how she'd react. She reached into the mirror to grab an object she saw in the mirror, and proceeded to complain that she couldn't get it because the mirror was in the way! Even a chimp can figure out how a mirror works, yet here was a perfectly intelligent woman who somehow couldn't understand the difference between a physical object and its reflection. --99.227.95.108 (talk) 06:04, 4 September 2012 (UTC)

Also, I agree that the answer to the OP's question depends heavily on how mentally-handicapped you're talking about. If you have anencephaly, there's no way you're even conscious, let alone self-aware. On the other hand, I am mentally handicapped (I have Asperger's syndrome), but I'm pretty sure I'm self-aware... --99.227.95.108 (talk) 06:11, 4 September 2012 (UTC)

Have you ever met somebody with Down syndrome? They obviously are self-aware (unless they have other much more serious impairments). Staecker (talk) 16:27, 4 September 2012 (UTC)

Not in real life, No. Futurist110 (talk) 18:29, 4 September 2012 (UTC)

If you've actually never met anyone with Down syndrome, you must have led a very sheltered life. I suspect that it is much more likely that you have, but weren't aware of the fact. AndyTheGrump (talk) 18:40, 4 September 2012 (UTC)

I've seen such people in passing and exchanged a few words, but not interacted enough to answer such questions with confidence. And the degree of impairment appears to vary widely. —Tamfang (talk) 21:52, 4 September 2012 (UTC)

You may wish to read Oliver Sacks's "The Man who Mistook his Wife for a Hat" for some insight into the tricks our brains can play on us once damaged. --TammyMoet (talk) 10:03, 4 September 2012 (UTC)

I'll also link you to the story of an old neighbour of mine: Sharon Parker. --TammyMoet (talk) 10:06, 4 September 2012 (UTC)

Our OP may benefit from watching the Paralympic Games currently under way. These Games signal the return of intellectually disabled athletes to the Games after it was discovered at the 2002 Sydney Games that some of them were just a bit too smart. HiLo48 (talk) 05:58, 5 September 2012 (UTC)

Rigid pavement

In rigid pavement design we use a variable with a unit of length which we call "radius of relative stiffness".Why we call it radius?With which circle is it related? — Preceding unsigned comment added by 116.90.230.202 (talk) 09:33, 4 September 2012 (UTC)

Searching around, I discovered that one Dr H. M. Westergaard [10] [11] is responsible for the name of the variable, and that this is the same Westergaard who invented a thing called the Haigh–Westergaard stress space, along with somebody called B. T. Haigh [12]. Beyond that, I'm guessing. I notice that the "stress space" maps three different kinds of stress (I don't know what they are) to the three spatial axes (up-down, left-right, forward-backward), so this might explain why an apparently spatial idea (radius) is being used in a context where it doesn't seem to apply: the circle is probably, in some sense, a circle of stress. Not a circle in ordinary space.  Card Zero  (talk) 12:29, 4 September 2012 (UTC)

It's measure of the stiffness of the slab relative to the stiffness of the subgrade. A measure of how much a load on a small area of the slab is distributed over a larger area of the subgrade. For example, take a thin slab on a subgrade of solid granite rock; the rock won't deform at all, so the total weight of a load would be carried by the area directly under the load and the "radius of relative stiffness" would be zero. The other extreme would be a concrete slab on an air cushion where the force is evenly distributed over the total area, regardless of the size of the slab. Its called radius because a point load will be distributed evenly in all directions, ie two points at equal distance from the load will experience the same force. Ssscienccce (talk) 19:29, 4 September 2012 (UTC)

Machining

What is grinding wheel signature? — Preceding unsigned comment added by Syed raziuddin (talk • contribs) 15:22, 4 September 2012 (UTC)

The characteristic pattern left by a particular grinding wheel? If I were to hazard a guess, that would be what I would think. --Jayron32 16:20, 4 September 2012 (UTC)

Depending on the context, this could also mean it's vibration profile/acoustic signature (unfortunately, our article is limited in scope to the naval usage). That is, the specific sound it makes. Analyzing changes in the sound can detect problems, like an imbalance, before they are otherwise obvious. StuRat (talk) 19:33, 4 September 2012 (UTC)

Breaking down hardened building cement or concrete

I am an electrician based in South Africa and have a problem with building cement that has dried inside an electrical conduit. Is there perhaps an acid or some sort of solvent that will either breakdown or dissolve the cement? 41.13.60.104 (talk) 17:23, 4 September 2012 (UTC)

Yes. Specifically, if the concrete contains lime, a strong acid should eventually dissolve it. But it's hard to imagine something that wouldn't also do damage to electrical conduit, any wires in it, and, by leaking out, the rest of the structure. If the conduit is completely blocked off, you would also have the problem of delivering the acid. And, if you did manage to dissolve the lime component, you would still be left with conduit full of sand, gravel, and acid. I really don't think this approach will work. Unfortunately, I'd say you need to abandon all hope of using that electrical conduit. You can either remove it and replace it, or, if this is impossible at this point, then leave it in place, but don't use it (if you do use wires already inside it, they are likely to overheat, as the concrete will act as thermal insulation). Just add new conduit. If the wall is entirely filled with concrete, you will need to drill a path for the new conduit. Cement filled walls are a bad idea exactly because of the problem of changing wiring or plumbing after it sets. StuRat (talk) 19:29, 4 September 2012 (UTC)

Lets get things into context. You are an electrician. So, can I take it you where not the one pouring concrete into places it was not supposed to go? Therefore, you should inform your supervisor that who ever poured the concrete have neglected their 'due care' and therefore are obligated to come back with their high pressure jet (of about 2,000 psi) and blast it off. Concreting companies should have this equipment because concrete will get stuck to a lot of their equipment so they need this type of gear. As StuRat has stated, there are many acids that will also remove set concrete. However, should your supervisor be week-knead and too shy to make a fuss and be looking towards 'you' for an answerer, then there are acid based mixers that are formulated for this sort of problem. Get on the works phone (i.e., let them pay for the call) and talk to a reputable company's 'technical department'. The sort of formulations you should enquire about is something based on something like glycolic acid. See for example: [13] Refrain from using this stuff to clean antique marble fireplaces etc., - not wise. --Aspro (talk) 22:37, 4 September 2012 (UTC)

Only very patient bakers should attempt a week-knead. :-) StuRat (talk) 22:44, 4 September 2012 (UTC)

And the boy gets a cigar! ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:04, 5 September 2012 (UTC)

Without elaborating at all, I see you guys don't understand the challenges of the building "industry" in South Africa. Applying North American (or whichever) standards to (South) Africa is like trying to introduce advanced engineering to a pre-schooler. Best of luck, Mr. Electrician ;) Sandman30s (talk) 13:08, 5 September 2012 (UTC)

While there are parts of Africa which lack industry, the nation of South Africa is not among them. See Economy of South Africa. StuRat (talk) 21:27, 5 September 2012 (UTC)

self combustion

What's the difference between spontaneous combustion and pyrophoricity?--Jsjsjs1111 (talk) 17:29, 4 September 2012 (UTC)

There might be some overlap, but I'm under the impression that "spontaneous combustion" typically refers to things that slowly heat to combustion temperature, like oil and gasoline soaked rags in a pile, versus pyrophoricity referring to things which ignite immediately in air and/or water. StuRat (talk) 19:23, 4 September 2012 (UTC)

What´s happen if we put a reference system in a photon ?

I´m trying to understand some concepts of quantum physics and I was thinking about time and space contraction. I´ve understood from articles that when particles take speeds near light speed, for observers that are in other referencial system, as in Earth for example, we have time dilation, so for referential system in a photon it should be a time and space contraction. If some particles takes speed as v=0,999999c , the contraction factor it should be 707. If speed of particles are 0,999999999999 c so space contractios it should be around 707107. So, as close we get from light speed, higher it will be the contraction. So whats happens to photon ? If we think in a referential system linked to photon, whats happen with time and space contractions ? May I think that in a photon speed, the time intervals compared with earth time, are so small that it will not take time to go from a point to another and, based of this photon can occupy several places in a space in same time ? Please help to understand this situation! — Preceding unsigned comment added by Futurengineer (talk • contribs) 17:45, 4 September 2012 (UTC)

There are two common answers to this that I have heard:

• This is a meaningless question; photons don't really have meaningful reference frames.
• You could imagine the photon's reference frame (still not a real thing) as being one where both time and space were infinitely contracted (that is, time is stopped and space is nothing).

The former is probably correct but boring; the latter is interesting but probably wrong. Take your pick! At least until someone with more physics chops shows up. (You might also be interested in the idea of the one-electron universe.) --Mr.98 (talk) 18:10, 4 September 2012 (UTC)

Mr 98's answer pretty much hit the target. The photon's reference frame is not a valid reference frame because it gives a infinite Lorentz factor. Another way to see that problem is that in this pseudo-referential the photon would be at rest, but that contradicts the principle of invariant light speed, one of the postulates of special relativity. Also, there is no possible Lorentz transformation that would lead into such a pseudo-referential so it is not an element of Lorentz group. Dauto (talk) 00:31, 5 September 2012 (UTC)

Great minds think alike, Futurengineer. From Einstein's Autobiographical Notes, "...a paradox upon which I had already hit at the age of sixteen: If I pursue a beam of light with the velocity c (velocity of light in a vacuum), I should observe such a beam of light as an electromagnetic field at rest though spatially oscillating. There seems to be no such thing, however, neither on the basis of experience nor according to Maxwell's equations. From the very beginning it appeared to me intuitively clear that, judged from the standpoint of such an observer, everything would have to happen according to the same laws as for an observer who, relative to the earth, was at rest. For how should the first observer know or be able to determine, that he is in a state of fast uniform motion? One sees in this paradox the germ of the special relativity theory is already contained." See [14] and [15]John Z (talk) 14:08, 5 September 2012 (UTC)

] Thanks everybody, I´m just wandering how explain that light(photons) goes for several paths before we measure that. Also, the spin of one electron seems to be linked to other in such way that if we change spin of one, the other change in same instant. And also we know that there is no actual vacuum in space but a sea of bosons. So, how understand this? It seems that the universe from perspective from elementary particles like photons could be different. That is why I was try to open my mind for news perspectives. — Preceding unsigned comment added by 187.64.171.240 (talk) 17:35, 5 September 2012 (UTC)

Regarding the problem of the linking of spins of fundemental particles, see Quantum entanglement. One's persective on quantum entanglement, that is, whether it is a sort of "no DUH?" kinda unsurprising fact which is expected, or whether it is some weird, unexpected, and odd occurance (called "spooky action at a distance" by Einstein et. al.), depends on which particular Interpretations of quantum mechanics you ascribe to. --Jayron32 17:42, 5 September 2012 (UTC)

Calorie-equivalent exercise compared to wading in a pool.

I'd like to know a range of how many calories per distance (or time, but distance is better) would be burned by wading in a pool filled to should(er) depth, and what sorts of activities would burn close to the same number of calories for the same person. In otherwords, I want proportional numbers, not absolute numbers. I have looked but we don't seem to have anywhere near a list of calories burned by activity. Thanks. μηδείς (talk) 18:42, 4 September 2012 (UTC)

Let me shoulder the burden of asking if "should" should be "shoulder". :-) StuRat (talk) 19:20, 4 September 2012 (UTC)

Look, I don't type these things. My fingers do. μηδείς (talk) 19:22, 4 September 2012 (UTC)

It will depend entirely on water temperature. In tepid water, you might as well be lying in bed. In cold water, you can burn a significant number of calories. And of course the more you move around, the more calories you will burn. Looie496 (talk) 22:12, 4 September 2012 (UTC)

I disagree with "In tepid water, you might as well be lying in bed". Wading through shoulder-deep water at a high speed takes a considerable effort, owing to the much higher density of water than air. StuRat (talk) 23:19, 4 September 2012 (UTC)

Medeis didn't say anything about high speed. Looie496 (talk) 00:13, 5 September 2012 (UTC)

I didn't want an argument, but a ref to a website with a list of calories for each exercise type. Assume 80 degrees F, although I though the resistence would be what matters. I meant at the highest speed one could go, that's usual for calorie-burning exorcises. μηδείς (talk) 01:06, 5 September 2012 (UTC)

Maybe what you want is here? Mayo Clinic is an authoritative organisation and I'd have thought this would be reasonably accurate. --TammyMoet (talk) 14:16, 5 September 2012 (UTC)

Yes, that's excellent, exactly the sort of thing I was looking for, although it doesn't give info for wading. Subjectively I think the 10mph bicycling would be about the closest in effort. μηδείς (talk) 17:18, 5 September 2012 (UTC)

Our article Water aerobics could do with some more development! Graeme Bartlett (talk) 09:36, 6 September 2012 (UTC)

Does nioxin shampoo make hair grow?

Currently most of my hair is shoulder length and the on my hair is jaw-length out grown bangs. How many faster would nioxin shampoo make it grow? Neptunekh2 (talk) 19:34, 4 September 2012 (UTC)

Comment: The Nioxin article looks a good contender for AfD - spam.--Aspro (talk) 19:41, 4 September 2012 (UTC)

[removed stray template] μηδείς (talk) 01:10, 5 September 2012 (UTC)

I can still see the question ! And the professional is called a trichologist. An' still think the article should be AfD'd.--Aspro (talk) 22:43, 4 September 2012 (UTC)

I suspect Nioxin is notable enough for an article. The existing article does look like an advertisement, but that's cleanup, not deletion. --Trovatore (talk) 23:20, 4 September 2012 (UTC)

The answer to the question is no; even the manufacturers don't claim it will make hair grow. As for the article, it desperately needs reliable sources, and the squishing of the spam links.--Shantavira|^{feed me} 12:12, 5 September 2012 (UTC)

Mind downloading

Would it eventually be possible to download's one entire mind into a virtual world? One of my friends made this proposal as a possible future response to severe overpopulation caused by a cure to aging. Futurist110 (talk) 22:07, 4 September 2012 (UTC)

Please review WP:CRYSTAL, and ask yourself how you think any of us might answer your question. AlexTiefling (talk) 22:08, 4 September 2012 (UTC)

We actually have an article on Mind uploading. Beyond pointing you to that article, the best answer anyone can give you is, "Maybe?" No one can provide accurate predictions about future technologies when we don't even understand the science that it relies on. Someguy1221 (talk) 22:12, 4 September 2012 (UTC)

It'll be SOP if the excellent Iain Banks is a futurologist and not an SF writer in desperate need of a technology to make galactic exploration practical. Bandwidth and storage wise it doesn't seem ridiculous, but the whole brain scanning part is still in its, well not even infancy, more like we have some sort of vague idea how memory works. The other bit is philosophical, if I make an exact copy of my mind, and boot it, and kill the original, is the new one 'me', or just a copy? My gut feel is that copies will feel like they are me, initially, but killing 'me' to make a copy is still dying. Greglocock (talk) 03:06, 5 September 2012 (UTC)

That issue can be addressed by not booting up until you die naturally. If we can do a scan of your brain each night as you sleep, and update the copy accordingly, then you would lose, at most, one day's worth of memories when you die. If you suffer from dementia, though, we might want to go back to a "checkpoint" taken before the dementia started. StuRat (talk) 03:18, 5 September 2012 (UTC)

This is purely my own opinion unreferenced here, so I hope Medeis doesn't hop and delete the thread, but I would personally be more comfortable if you simply blurred the distinction between mind and machine. Upload your brain to a machine that is built into your brain, constantly updating, and "assisting" you. As your brain naturally decays with age, the machine takes over more and more functions, eventually becoming your entire mind. This way there is no single moment when you stop being you and start being a machine. Then again, we still can't explain the experience of consciousness, or even know if it has a true scientific basis, so all my method accomplishes is making me feel better. Someguy1221 (talk) 03:24, 5 September 2012 (UTC)

"Eventually"? Why do you think this hasn't been done already, that you aren't there already? Didn't you get the How2getouttahere pamphlet at the entrance? Me, I'm going Back to Reality (Red Dwarf).John Z (talk) 13:52, 5 September 2012 (UTC)

As an alternative to activating a "last good version" (whose definition is nontrivial!), I've thought of wiring all available backups together, thus: each neuron, instead of connecting to other neurons in its own "slice", connects to the corresponding neurons in both adjacent slices. Knowledge acquired during the declining stage can then propagate to, and be processed by, the healthier versions. A big problem remains: where to connect the i/o ? —Tamfang (talk) 06:15, 6 September 2012 (UTC)

You are your body. Your consciousness is a harmonic relationship between your body and its environment, like a hum in tuning fork induced by an outside vibration. The simple answer is no. Copy the hum of a tuning fork onto a tape and destroy the fork then you are simply dead and playing the tape is a simulation, however self-satisfied it is and however comforting to others. But Someguy has it right. You are your body. If you can slowly replace parts of your body, whether by generating new cells, or replacing them with machine parts, without disrupting the major continuity of your consciousness, then you can have your actual immortality, rather than making a realistic Tupac hologram of yourself. PS. If I am missing a good reason for hatting this thread, let me know, and I will get on it right away. μηδείς (talk) 18:46, 5 September 2012 (UTC)

See Ship of Theseus. StuRat (talk) 21:24, 5 September 2012 (UTC)

One definition of 'me' is my living body. Another reasonable definition is my behavior. The thing that bothers me most about death (other than the unpleasantness of the transition) is that with me gone no one will do the things I intend to do. A software copy of me will have the same tastes, and therefore will carry on my projects, whether or not it is me in your philosophy. — I still prefer incremental prosthesis, though. —Tamfang (talk) 06:15, 6 September 2012 (UTC)

The phrase "my behavior" amounts to begging the question. An entity is its attributes. That includes the sum of its properties, states, qualities, actions, relationships, etc. The word "my" in my behavior stands in for "the behavior of this body". It is only the behavior of that body if it is the behavior of that body. Unless you are looking at behavior as an alienable, rather than inalienable possession. As in, I paid that hooker to pole dance, so that's my behavior she is doing. Or, "Look, dear, the mime is doing such a great impression of your walk!" If that's the case, Elvis is alive today...in each one of his impersonators. μηδείς (talk) 07:34, 6 September 2012 (UTC)

Only if they are exact replicas, which they are not. StuRat (talk) 10:29, 6 September 2012 (UTC)

Yet another bug ID question

The other day, in my yard in North Carolina, I spotted a rather large bee or bee-like insect (may have been a wasp or hornet, but it looked more bee-like to my untrained eye). It was unusually large for such an insect, and the coloration struck me. The main color of the head and thorax was a rusty brownish-red color, almost exactly like iron rust, while the abdomen was bright yellow striped, like a honey bee or yellow jacket. It was, however, considerably larger than either of those, perhaps twice the size of a typical honey bee. Anyone have a good guess as to what that might have been? I tried to snap a picture, but my phone camera's kinda sketchy, and I didn't get anything as it would move away by the time I could get it in frame. Doing some digging, the closest I could find was Sphecius grandis, but it wasn't quite that big (I don't think) and that species isn't known in this area. Any ideas on something kinda like that one but found in North Carolina? --Jayron32 22:20, 4 September 2012 (UTC)

My usual ref-desk answer to "bee-like insect" questions has been "some sort of hoverfly". There are so many species of the critters, however, that pinning down the exact one may be difficult. Googling for "North Carolina" syrphid will lead you to a lot of photos of various species; perhaps you can find one that resembles your sighting. Deor (talk) 01:02, 5 September 2012 (UTC)

Can you not upload a picture, Jayron? μηδείς (talk) 01:18, 5 September 2012 (UTC)

As I explained, I would have liked to, but I couldn't get him to sit still long enough to get one in my crappy flip-phone camera. The shutter response time was so slow that by the time I got him in frame and pushed the button, he'd moved out of frame. --Jayron32 03:53, 5 September 2012 (UTC)

Doing some more research, I think it might be some species of Polistinae (paper wasp) that I hadn't seen before. We've got more species of wasp around here than you can shake a stick at; on any given day if I look I can find half a dozen or more different ones in my yard. Though I've never seen one like this before (the rust color was rather striking), and though I can't find the exact one in any pics I have found, given the number and variety of wasps out there, I am thinking more and more that this is one of those. --Jayron32 04:07, 5 September 2012 (UTC)

Can runners prevent knee pain by injecting motor oil in their knees?

You need to refresh the oil in your car, so why not do the same with our knees? Almost no runners who have been doing long distance running for more than a few year are completely pain free. Count Iblis (talk) 22:26, 4 September 2012 (UTC)

I very much doubt it. However, if you're contemplating doing something like that, talk to your doctor first. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:35, 4 September 2012 (UTC)

Motor oil is toxic. You are not even allowed to empty it down the drain because it is poisonous, it must be disposed of properly. The only thing you would gain by injecting yourself with it is an entry in the Darwin Awards. Try feeding your car by sticking a hamburger and chips into the petrol tank and then topping up with a large coffee with a few spoons of sugar. Your car wouldn't like it any more than you'd appreciate drinking a cup of petrol. Dmcq (talk) 22:47, 4 September 2012 (UTC)

I would argue that it could reduce knee pain, since you will soon be dead and thus unable to feel pain. StuRat (talk) 22:53, 4 September 2012 (UTC)

Silly question; See Synovial fluid. The omega fatty acids in the oil obtained from the Chinese Water Snake have been found of use in joint conditions based on generations of empirical experience. However, merchants of patten medicine have regarded this treatment as a competitious threat to their lively hood and so have successfully hood winked the public into regarding it as 'snake oil' ---- which of course it is. --Aspro (talk) 23:14, 4 September 2012 (UTC)

Whether people have been using something for a long time says nothing about its actual efficacy; it could still just be placebo. (The placebo effect is still an effect, mind you. It's not synonymous with saying something is totally made up.) Show me some controlled studies that show it is better than mineral oil or just water and then we can talk like informed people. :-) --Mr.98 (talk) 13:05, 5 September 2012 (UTC)

A lot of work has now been done on eicosapentaenoic acid matched against placebo, both topical and oral, and so its been known how snake oil works for the passed few decades. Having so many indications it would be better I think if you pick one out for yourself. This is not a chat-room. --Aspro (talk) 20:09, 5 September 2012 (UTC)

Just found what what claims to be the earliest analysis of snake oil. [16]. Hope this helps.--Aspro (talk) 20:18, 5 September 2012 (UTC)

Some good answers above. Note that as this is biology, we really don't know until someone injects his knees with motor oil, which means that hopefully this will remain an open question for a long time coming. I don't know how quickly a hydrophobic liquid would leach out of the synovial space, but I'm thinking that longer term effects of injecting a solvent (but not short term effects like asphyxiation) would be comparable to huffing the same amount as a volatilized gas, which for anything but the smallest injection would be substantial. I'm not sure if this is comparable to injuries from hydraulic fluid injection (which alas does happen with some frequency) - that can net a litigant $250,000 in damages. [17] Wnt (talk) 23:33, 4 September 2012 (UTC)

You now better than this, Iblis, and enough fun already. μηδείς (talk) 01:17, 5 September 2012 (UTC)

Well, as Ford Prefect never said, science is fun, so fun is science... :) Really though, it's a pretty straightforward thought experiment, and if we focused less on the toxicity and more on the mechanics someone might enlighten us greatly about how knees work. Wnt (talk) 02:13, 5 September 2012 (UTC)

It's a question, not a request for medical advice. So, what about other fluids that are not toxic? Count Iblis (talk) 01:38, 5 September 2012 (UTC)

Even water on the knee is not good. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:58, 5 September 2012 (UTC)

But then the body does use lubricants, so why can't we produce something that does work and inject that into the joints? Count Iblis (talk) 02:05, 5 September 2012 (UTC)

This is done - search for "synthetic joint fluid" and you'll find many doctors' sites. (Someone should start an article...) One is Synvisc (that redirects to hyaluronic acid, which is scarcely deserving of being called such). But glancing over the sites, apparently the stuff, while it might allow for reduced inflammation, still is mostly a weekly injection to delay harsher measures. Wnt (talk) 02:20, 5 September 2012 (UTC)

I've also heard of injecting chicken fat - again, a temporary measure. But that's a substance rather more likely to be compatible with an organism than refined petroleum would be. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:39, 5 September 2012 (UTC)

Well, any animal product adds the possibility of infection, as we would be vulnerable to many diseases normally wiped out by our digestive system when we eat them. While motor oil is toxic, perhaps some version of petroleum jelly could be used. This is, after all, designed to be applied to the skin, so is non-toxic. However, it might still create problems if injected. StuRat (talk) 02:51, 5 September 2012 (UTC)

I should clarify that this was some kind of "purified" substance that was administered under a doctor's care. And nobody should be injecting themselves with anything unless they're doing it under a doctor's care. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:02, 5 September 2012 (UTC)

Ultimately, while the quality of one's synovial fluid is strongly correlated with the health of the joint, the reduction in quality is merely a symptom. Various injections may reduce pain and inflammation, but it won't help the joint beyond that. As for motor oil itself, even if you ignore the fact that it's a terrible idea, it's also a terrible lubricant compared to synovial fluid, not even to mention they are used in different contexts. The coefficient of friction inside a human joint is on the order of 10 times smaller than what you find in lubricated machine parts (see here and here). I suspect this is why the stuff that doctors (quacks and otherwise) use as synthetic synovial fluid is either a synthetic compound or something derived from an animal. And indeed, there are plenty of sites advertising this type of procedure [18]. Someguy1221 (talk) 02:57, 5 September 2012 (UTC)

This article on Runner's Knee (Patellofemoral Pain) suggests a variety of causes, none of which is a lack of synovial fluid. BTW, I've been running (admittedly fairly moderately, but I've done two full and many half marathons) since the 1970s and don't have any knee problems at all, unlike a lot of soccer and rugby players that I know. Alansplodge (talk) 14:13, 5 September 2012 (UTC)

September 5

Beams

an example beam

Beam engines generally seem to have a particular shape of beam that is wide near the pivot and thinner at the 2 ends. They also seem to generally be made of a vertical plate with wider girders at the edges and centre. Is there a name for this type of beam? After a bit of searching around to me they seem to me to vary somewhere inbetween a lenticular shape and a rhombus / double King post shape. Are the types of beam used on beam engines optimal for the job? What are the principles for calculating the ideal beam shape? Why are the solid beams used rather than a truss only design? JMiall₰ 00:34, 5 September 2012 (UTC)

I suspect that the shape is to avoid a weakness where the beam is pierced for the axle. Originally, a straight wooden beam was used[19]. This page says; "...by the end of the 18th Century the elegant BOULTON & WATT engines with their cast‑iron beams..." and the accompanying illustration ("figure H") shows an engine with the rhomboidal shape that you describe. Cast iron is a rather brittle material, and would crack if not thick enough. Alansplodge (talk) 13:17, 5 September 2012 (UTC)

A Short History of the Steam Engine By Henry Winram Dickinson gives the introduction date of the iron beam as "about 1797" (p.87) but no information on the shape - I'll keep digging. Alansplodge (talk) 13:31, 5 September 2012 (UTC)

Eureka! Everything you ever wanted to know about the subject in A treatise on the steam engine: historical, practical, and descriptive, Volume 2, By John Farey, London 1827. "In modern engines, the great lever (ie the beam) is always made of cast iron, instead of wood. The depth of the lever in the middle is made equal to the diameter of the cylinder, of nearly so... the depth at each end of the lever is usually one-third of the depth in the middle...". Hopefully, you can read the rest yourself. I would imagine that if you were making one with modern steel, then a truss would be a better solution. Alansplodge (talk) 13:40, 5 September 2012 (UTC)

Hammersmith cast iron strapwork or 'open' beam

Beam engines lasted about 200 years. For the first half of this, they were wooden, and wooden usually implies parallel beams. Kingposts were certainly used. Old Bess is one of the oldest surviving examples and shows a wooden beam that might have had its kingposts added some years after construction, following a fire and damage to the original beam. For the second century of this use, the beams were usually cast iron. In a few cases, wrought iron strapwork was also used to construct the beam as a truss. In one well known survivor from Hammersmith, there's even a cast iron strapwork beam, following the pattern of the wrought iron type.

Don't underestimate Victorian engineers. For about 50 years in the mid-19th century, structural theory (see the works of, or a history of William Fairbairn (just not ours)) progressed to a point where it exceeded manufacturing industry's ability to keep up. Although machines might have looked crude and still been built from the same materials, their stresses were now carefully calculated and beam shapes were being optimised.

Most of the reason was for the increasing speeds of some beam engines as steam pressure increased (mostly the compounds, rather than the Cornish). The hardest loaded portion of a beam engine isn't the beam, it's the supports for the beam pivot. As engine speed increases, this becomes a problem. As well as stiffening the fixed frames supporting this pivot, it was also useful to lighten the beam and so reduce these dynamic forces.

There are a few good beam engine sources around, and the Google copy of Farey is certainly one. The first volume in particular, on the earlier engines - there's not much else available for that period with the same level of detail.

Mostly I'd suggest raising this at talk:beam engine. There's a lot of work still to do on engines of this period. Andy Dingley (talk) 14:36, 5 September 2012 (UTC)

Also see Walking beam engine for a narrow use of what was probably the ultimate metal "kingpost" beam. Andy Dingley (talk) 14:45, 5 September 2012 (UTC)

Thanks for the replies. The book looks interesting. I also found this (the bottom 'Beam Development' section) which gives a history of beam types. JMiall₰ 17:28, 5 September 2012 (UTC)

Some further comment on the Hammersmith beam, from T E Crowley's book. These cast iron openwork beams appeared in the 1830s, from the work of a William West (not a name I recognise) as a lightweight beam. They weren't popular and the only survivors are the Cruquius engine and the 1854 Hammersmith beam. In 1862, a beam of this type at Hartley colliery broke, blocking the only shaft and leading to the deaths of 204 miners (and 43 pit ponies). Cracked beams weren't that unusual, and the Hammersmith beam has the typical repair bridle added above it (1866), which may have been a safety response to Hartley, as there's no sign of the beam actually having broken. Andy Dingley (talk) 10:27, 6 September 2012 (UTC)

Steel plate beam

Another rarity is the "plate" beam, built from riveted plate. Not common (maybe cost, as it should have worked well) and there's a survivor at Clay Mills. Seems that the Clay Mills(1885) engine is late enough for this to be steel plate, rather than wrought iron. That would support the cost theory and explain the rarity. Only for the later beam engines, after steel had become cheap, was a riveted beam cheap enough relative to cast iron. Andy Dingley (talk) 10:31, 6 September 2012 (UTC)

Black hole accretion disk spectra from ISM

What is the expected accretion disk spectrum peak and luminosity for an ordinary black hole in typical interstellar medium density of about one atom per cubic meter? I've been looking all over the web, arxiv, and specialist publications and can't find this. 199.16.130.122 (talk) 00:44, 5 September 2012 (UTC)

Would there even be an accretion disk in that density? Accretion requires energy loss, and since the particles are too spread out to interact with each other, there would not be any friction to slow them down. Any other forces that I could think of would be negligible, unless of course the black hole had significant charge (ie. by synchrotron radiation) or rotation (ie. by frame dragging). SamuelRiv (talk) 00:01, 6 September 2012 (UTC)

Well I found http://arxiv.org/pdf/astro-ph/9712284.pdf which is plenty to get me started for now. Maybe a citation search on it or the papers it cites can find something more recent. 199.16.130.122 (talk) 00:08, 6 September 2012 (UTC)

hearing loss - age

I'm trying to find a graph that shows the hearing loss (in Hz) by age tnx in advance 217.132.255.144 (talk) 10:22, 5 September 2012 (UTC)

[20] This page contains such a graph. Note that hearing loss is measured in dB, not Hz. — Preceding unsigned comment added by 194.176.105.145 (talk) 11:41, 5 September 2012 (UTC) (added signature) 194.176.105.145 (talk) 11:45, 5 September 2012 (UTC)

It is actually lost both ways; that is you lose the ability to hear quiet sounds, but you can also lose the ability to hear certain freqencies, both at the upper and lower ends of the spectrum. Our articles are a bit scattered on the matter, but you can find some information on frequency dependent hearing loss at Audiogram and Hearing range. Oddly, we don't seem to have any good information at Wikipedia on Hearing range of humans, the current article on Hearing range just covers other animals. --Jayron32 15:42, 5 September 2012 (UTC)

I seriously doubt this graph. I hear dog whistles, and I'm 46. As much as I'd like t5o consider myself spec ial in this regard, it's highly unlikely. Zarnivop (talk) 16:48, 5 September 2012 (UTC)

Any individual case does not invalidate the graph. Please read the qualification: "In humans the audible range of frequencies is usually said to be 20 Hz (cycles per second) to 20 kHz (20,000 Hz), although there is considerable variation between individuals, especially at the high frequency end, where a gradual decline with age is considered normal." -- ♬ Jack of Oz ♬ ^{[your turn]} 21:12, 5 September 2012 (UTC)

Semimetallic bonding

What is semimetallic bonding? (It's mentioned in Interchalcogen.) Double sharp (talk) 12:44, 5 September 2012 (UTC)

See Semimetal which has an explanation and some diagrams that explain the difference between proper metallic bonding and semimetalic bonding, according to band theory, which is the easiest way to think of these sorts of delocalized bonding models. --Jayron32 15:37, 5 September 2012 (UTC)

Just talking “easy”… it’s like a bounding which acts like a metal bounding in some conditions and like a non-metal in others… see this Iskánder Vigoa Pérez 18:01, 5 September 2012 (UTC) — Preceding — Preceding unsigned comment added by Iskander HFC (talk • contribs)

Malaria in other species besides humans

What adaptations have taken place in other mammals to cope with malaria? Are there adaptations akin to that which leads to sickle cell anemia in humans? I include in my question domestic animals like cattle, and of course other primates. Thanks, Rich Peterson198.189.194.129 (talk) 16:44, 5 September 2012 (UTC)

The article Malaria doesn't have anything much except a throw-away sentence confirming that Plasmodium does infect lots of other kinds of animals. I did find Plasmodium#Subgenera which covers Plasmodium infections in a wide range of other animals, if you read that section and follow some of the footnotes, it may lead you in the right direction. --Jayron32 16:50, 5 September 2012 (UTC)

This Nature paper from 2009 looks at malaria resistance in baboons. I didn't spot any other work on non-human animals. Looie496 (talk) 17:44, 5 September 2012 (UTC)

unsigned comment added by Iskander HFC (talk • contribs)

This paper (a proofed draft, but referenced to its sources) cites research suggesting that a genetic mutation has taken place in orang-utans, gorillas, chimpanzees and crab-eating macaques that offers some protection against Plasmodium, but with an increased risk of thalassemia-type disease. Interestingly, it also refers to research suggesting that the speciation of the crab-eating macaque and the rhesus macaque may have been driven by adaptation in the face of malaria. - Karenjc 18:17, 5 September 2012 (UTC)

Star collision

How long do I have to wait for a star collision in the milky way? I know that the center is very different to the rest so I would not count the center few hundred light years. The collision of binary or multiple star systems I would also like to exclude in this estimation. Is it more like years or million years? --Stone (talk) 19:18, 5 September 2012 (UTC)

The first question is whether you want true star-impacts-star collision or merely a close pass with gravitational effects on the two solar systems. The former is comparatively rare, and per our article on stellar collisions, happens about once every 10000 years within our galaxy. However, that's averaging in the denser portions of the galaxy; for the sun (and similar stars), you're talking about a handful over the full lifespan of the galaxy. For the latter, things are much more common. Our article estimates that sun-like stars (in the sense of location within the galaxy) come within one light year of another star about once every 2 million years. Given the millions of such stars in the galaxy, that sort of occurrence should be quite common. — Lomn 20:23, 5 September 2012 (UTC)

Thanks! I was waiting for a true collision. So I will wait. A star rogue planet collision will have roughly a similar chance to happen. The number of rogue planets is less defined than that of stars. --Stone (talk) 20:48, 5 September 2012 (UTC)

Bear in mind that the overwhelming majority of space is just that: empty space. If the sun were the size of a 1/2 inch diameter marble, the closest neighboring star would be about 210 miles away.--Shantavira|^{feed me} 21:03, 5 September 2012 (UTC)

High voltage and CFLs

My aunt still had mostly incandescent bulbs in her house, and they seemed to burn out very quickly. I suspect she has higher than normal voltage in her home, and this causes the lights to burn more brightly, overheat, and fail. She also had two light sockets damaged from excess heat. I replaced the incandescent bulbs will compact fluorescent bulbs. Will those be better able to withstand higher than normal voltages, since they generate so much less heat ? StuRat (talk) 21:41, 5 September 2012 (UTC)

The voltage is determined by the local substation, so I doubt high voltage is the problem. There might be some kind of poor connection or interference that causes some variability - that could easily shorten the life of a bulb. --Tango (talk) 22:00, 5 September 2012 (UTC)

This is a rural area, and they have their own transformer out on the pole. StuRat (talk) 22:07, 5 September 2012 (UTC)

So measure the line voltage. This is best done with a recording voltmeter, a specialist instrument for just this task (sometimes the voltage spikes when the local steelworks changes shift at 3am). Talk to your electricity company.

CFLs are generally quite good at regulating voltage though, but they do have their own problem that they really don't like thermal overheating. Even hanging some high-power types (like Megaman) as a pendant (hot tubes below their sensitive electronics) will cause early failures when they're perfectly satisfactory used in a table light. Andy Dingley (talk) 22:19, 5 September 2012 (UTC)

I will bring a meter and measure the voltage the next time I visit, but that won't be until next year. Meanwhile, I told her she should tell the electricity company about the problem, and request that they test her electricity with a recording voltmeter. StuRat (talk) 22:48, 5 September 2012 (UTC)

The first thing I do (as I'm not in the habit of walking around with a multi-meter) is to look at the brand of the light bulbs. Whatever the voltage turns out to be – some brands of bulbs (incandesent or otherwise) have much shorter life spans. See: [21]--Aspro (talk) 00:23, 6 September 2012 (UTC)

Other factors that can cause overheating are faulty or worn connections or pins within the light fitting, and using a bulb rated at a higher wattage than the fitting is designed for. Many fittings are rated at 60w max.--Shantavira|^{feed me} 05:56, 6 September 2012 (UTC)

You cannot just get away with measuring the voltage at one point in time. Instead you have to measure it over a period of weeks to see how it varies. If people off the same circuits are running large electric motors, you may get surges when they vary their load. A few seconds of extreme voltage is much worse than a constanT over 10%. Graeme Bartlett (talk) 09:30, 6 September 2012 (UTC)

September 6

Glyphosate based Herbicide

Can anyone direct me to the kinds of Glyphosate currently marketed? and the difference between a Glyphosate SL and Glyphosate WDG? Thanks! — Preceding unsigned comment added by Warrenssy (talk • contribs) 01:54, 6 September 2012 (UTC)

Google tells me that SL is a aqueous solution of the stuff, and that WDG may be a solid or powder ammonium salt formulation. Our Glyphosate article talks about various salt formulations and other mixtures/additives and their advantages. DMacks (talk) 02:04, 6 September 2012 (UTC)

Precipitation from NaBr and CaCl2

How can I analytically determine if a precipitate (of NaCl) will occur when mixing NaBr 15% by weight and CaCl2 3%-15% by weight? — Preceding unsigned comment added by Sslam (talk • contribs) 05:32, 6 September 2012 (UTC)

NaBr 90.5 g/100 mL (20 °C)

CaCl2 74.5 g/100mL (20 °C)

CaBr2 143 g/100 ml (20°C)

NaCl 359 g L−1 35.9 g/100 ml

What I can see from the given numbers is that you have to go more to 30-40% solutions to see precipitation. --Stone (talk) 07:17, 6 September 2012 (UTC)

You would need to check the oxidation states and electronegativity to discover if the reaction would occur. You would then need to check solubility tables to see at what concentration a precipitate might form. Then you'd need to hope you don't end up in super saturated territory. 83.70.170.48 (talk) 10:34, 6 September 2012 (UTC)

The oxidation states and electronegativity are of no problem with this compounds. --Stone (talk) 10:43, 6 September 2012 (UTC)

Psychosocial development

Accprding to most articles on psychosocial development, there are significant developments in adolescence and young adulthood up to about the age of 25 but are there significant developments beyond this? Clover345 (talk) 08:45, 6 September 2012 (UTC)

Y-shaped moth

What species/genus/family includes those moths that have wings so thin and straight when folded up that they look like a Y? I googled Y moth, but it turns out that's just a moth with the letter Y as a mark on its wings. To find out, I looked at the pictures in every Lepidoptera family article on Wikipedia, and still didn't find such a moth. So what are these moths? Wiwaxia (talk) 09:25, 6 September 2012 (UTC)

Like this one? It it's a plume moth. Alansplodge (talk) 09:44, 6 September 2012 (UTC)

research paper authors and collaboration

A scientific publication of research paper has 1 to many authors from different universities/institutions. Does that always mean the research work published was done in collaboration or partnership among those authors? or Are the works done independently (without collaborating, without even knowing that someone else is doing other parts of same work) and spliced for a single paper publication? — Preceding unsigned comment added by 213.120.141.254 (talk) 09:42, 6 September 2012 (UTC)

I never heard of a forced splicing by a publisher. All the articles I know more than one author personally were written in collaboration. The amount of work from each individual might vary strongly. Even getting a very known person on the publication improving the canche of publication although that person was not really involved is also done. --Stone (talk) 10:50, 6 September 2012 (UTC)

thanks friend.

Taboos in other animals

I know that other animals don't have culture as sophisticated as humans, but do they also share the behavior called "having taboos?" Human examples of taboos include taboos on sex, bodily functions, nudity, etc. But do animals have any behaviors that seem to be the equivalent of our so-called taboos or is this behavior unique to humans? Narutolovehinata5 ^tccsdnew 10:44, 6 September 2012 (UTC)

Many species avoid incest, and in particular mother/son incest. Mating attempts by non-alpha males and sometimes females are often taboo. Among social predators there are sometimes specific rules about who eats a kill first, and violation of that rule can have severe consequences. Defecating in the den/lair may be a no-no, too. StuRat (talk) 10:51, 6 September 2012 (UTC)