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November 28

Sleep and lifespan

A friend of mine said he wants to "experience a longer life", so he's going to cut out an hour of sleep from now on. I thought this was pretty bizarre logic. It got me thinking though, if you were to cut out an hour of sleep from now on, would that shorten your lifespan? Would the extra hours you stayed awake equal the additional hours you would have been alive for? ScienceApe (talk) 02:34, 28 November 2010 (UTC)

Sleep deprivation can lead to immune system and other health problems. However, if your friend is cutting from say 8 to 7 hours of sleep a day as an adult, this could potentially increase lifespan. Simply not sleeping, and yet still expecting one to live much longer is not possible. ~AH1^(TCU) 03:18, 28 November 2010 (UTC)

You may be interested in scheduled napping to achieve more time awake. — DanielLC 05:41, 28 November 2010 (UTC)

I believe there have been studies in mice which show that limiting sleep has a positive effect on lifespan. Here is one article I found, i'm not sure how reputable the source is, Link. Calorie restriction has also been found to increase lifespan in mice but it's thought to not have a huge effect in humans, but there is an effect Link. But you have to ask yourself, if you're going to go through life tired and hungry, is it worth the few additional years at the end of your life? Vespine (talk) 23:13, 28 November 2010 (UTC)

And, of course, it bears stating that what applies to mice doesn't necessarily apply to humans: we are fairly different, particularly in this case. After all, sleeping and dreaming clearly has some important effects on our brains, and our brains are very different to mouse brains. And a lot of popularly-reported studies on how much sleep people need seem to give an average, which is reported as a universal optimum, when of course there is a lot of individual variation. I suspect this is more a problem of the reporting than the studies. Caveas. 86.161.109.130 (talk) 00:50, 29 November 2010 (UTC)

Looking for name of strange wart-like cutaneous growth on human foot with tentacles

Resolved

 – Reflectionsinglass (talk) 13:08, 1 December 2010 (UTC)

Hi. First off, a few notes, I am NOT looking for medical diagnosis or opinion ... except that "diagnosis" might be a sliding rule here. I do not have this problem, no one I know has this problem, and I am not going to lie and say this is for a "book I'm writing". I have been looking every few months for this gross thing, and I can't find it, so I'm turning to this as my last resort. I'm merely curious what it is.

20+ years ago, I caught something on my foot, possibly from a public swimming area (I swam a lot). I went to the doctor and had it treated and it's never returned. But in my adult years, I have been curious as to what exactly it was, since I no longer have medical records of this thing. So please: I hope someone can tell me what it was.

It is not a plantar wart. But it was like a very large wart on the heel of the foot, and it had thick, white tentacular cilia growing from the center. It was really gross, I admit. To cure the thing, I had to pluck the tentacles every night and then apply a strong liquid.

One could ask why on earth I would want to remember such a thing, but I'm simply curious. Again, if I had this problem in real life, at the moment, I would immediately go to the doctor's. I just want to know what it was that I had. Anyway, if this question still breaks some rules, feel free to remove it. Thank you, Reflectionsinglass (talk) 09:25, 28 November 2010 (UTC)

Have you been through our slightly gruesome article List of cutaneous conditions? 87.81.230.195 (talk) 10:16, 28 November 2010 (UTC)

I have! But not thoroughly; it's such a long list, and it's one of the pages I'd been perusing. If it's listed there, it would take me quite a while to find it. I just took another gander, but no luck. Lots of other interesting things that prove to me I was not born to be a doctor :) Reflectionsinglass (talk) 10:53, 28 November 2010 (UTC)

To discount a parasitic infestation: What geographical location were you in when you first noticed it and for the few weeks before? Was blood or other liquid observable when tentacles were removed. Was it painful or just uncomfortable during the day and during tentacle removal. Did you think of the medical tincture applied as being 'strong' because it had a pungent acidic smell, or of alcohol or did it smart, etc.? Were the tentacles smooth all round or did they have texture? Did they end as a point or flattish or bluntly. Where they elastic or not when pulled ( i.e. did they become longer and thinner before coming out). --Aspro (talk) 11:37, 28 November 2010 (UTC)

Hi Aspro. At the time, I was in Connecticut, though I don't recall what season (in case that would be helpful). No blood, no other liquid that I recall. It was not painful, though I do remember some of the tentacles would hurt (if I tugged on them) and I'd leave them alone, but evidently I used tweezers to pull out the ones that didn't hurt. They were smooth; they were the color of cooked white rice and about the same size, with pointy ends, and yes, slightly elastic. I don't know what my mom did with them afterwards, probably just threw them away. I recall the smell of the medicine well: it was not acidic, it was more "mechanical" smelling, like a thick alcohol, definitely pungent. Reflectionsinglass (talk) 04:16, 29 November 2010 (UTC)

The "tentacles" could be hyphae, suggesting something like Phaeohyphomycosis. DuncanHill (talk) 14:39, 28 November 2010 (UTC)

Whoa! No, definitely not that, this wasn't any serious skin lesion like that. Just a bump on the foot with white things coming out of it that had to be plucked and medicated. Went away and I haven't had a problem since. I won't discount "hyphae" in general, but definitely not the ...mycosis. Reflectionsinglass (talk) 04:16, 29 November 2010 (UTC)

If there is a scientific answer to this, it would be a diagnosis that might still be relevant to the OP's health. To arrive at that diagnosis, we would need a back-and-forth exchange of information about symptoms, signs, other conditions. It seems clear to me that this is a request for medical advice, and I suggest that this should end here. -- Scray (talk) 17:03, 28 November 2010 (UTC)

Hi Scray. The people here, including you, know best when to stop. There were no symptoms, signs, or other conditions except what I mentioned above... this would be in the vein of asking, "What was it that I had that was black, hairy, and all over my tongue?" and the answer would be black hairy tongue syndrome (or whatever lol). Not looking for any medical advice, I'm not asking, how it should be treated. In fact, whatever it is that I had was obviously treatable, it was treated quickly, and I've never had a problem since! I honestly think I've given all the info I can, this was a very long time ago. I just thought maybe someone here would have a quick and definite answer, and it didn't hurt to ask. Anyway, one last go, if anyone has any ideas? Reflectionsinglass (talk) 04:16, 29 November 2010 (UTC)

The original poster wrote: "I went to the doctor and had it treated". If that doctor's still around, I'd suggest writing to them to ask what the thing was. You never know, they might still have records. --Anonymous, 03:22 UTC, November 29, 2010.

I doubt it; it's been over 20 years. And tbh, this is just a matter of curiosity. I really won't be hunting this information down. It was just such a curious thing that I caught. Anyways, thanks for everyone's help so far! Again if the matter is over-the-line, feel free to close discussion. I'll check back again soon. Reflectionsinglass (talk) 04:16, 29 November 2010 (UTC)

Thanks for the extra information Reflectionsinglass. Without venturing as far as giving a diagnoses, I think I can explain what happens in these cases. This sort of infestation is most frequently found in the tropics and sub-tropics and rather more rarely in temperate zones but they do happen. A fly will choose a human as its host on which to lay its eggs -especially if one has fallen asleep whilst fishing. A very effective and simple way of dealing with this event is to force the lava out by restricting their air supply with an oily or greasy substance. If this also contains a little turpentine or something similar, that will help keep the wound sterile as well as persuade them to loosen their grip. The little blighters can then be removed with tweezers as they appear. Second-line treatment - Occlusion/suffocation approaches. The fact that it was painless and there were lots of them and shaped like grains of rice are helpful pointers, but there are apparently more flies that can infest humans than I at first thought when you posted you query so I am not going to even hazard a guess. Also, I doubt after all these years if your memory will remember enough details to reliably identify the exact species but there is an identification aid linked to on this sight. Identification key to species of myiasis-causing fly larvae. After many years have past, the brain can size on details which were never really present at the time, so personal I would not bother to search further and from a clinical point of view it is unimportant, so even the treating physician may not know (or need to know) the specie in order to deal with it effectively.--Aspro (talk) 12:37, 30 November 2010 (UTC)

Oh man, that is so gross! I looked at pictures of myiasis and that's just nasty. But that is definitely a tad closer to what I was looking for. I honestly believe that the tendrils were pieces of flesh, rice-sized in girth, but rather longer in length, not larvae, but it was so long ago, who knows. Your suggestion, however, is extremely helpful because of the various types of response to the species. Thanks so much for your help! I'm actually kind of grossed out now, to be honest (lol) and I think I'll wait a few more years to continue my hunt, or maybe I'll just be happy with forgetting the whole thing! Thanks again,Reflectionsinglass (talk) 13:08, 1 December 2010 (UTC)

I'm reminded of the very strange condition suffered by Dede, the Indonesian "tree man". [1] [2] —Steve Summit (talk) 12:44, 30 November 2010 (UTC)

It's been a while since I read about him. I had to specifically Google for his post-treatment appearance and it's definitely better... but not. The poor guy. Reflectionsinglass (talk) 13:08, 1 December 2010 (UTC)

Why shopuldn't you fill a hot water bottle from the domestic hot water supply?

I brought a hot water bottle that says in the instructions"Do not fill using water from a domestic hot water system as this can considerably shorten the life of the hot water bottle". Since it also warns against using boiling water the alternative is to part-heat a kettle. How is partly heating water in a kettle different from heating it in a domestic hot water system? The only difference I can think of is that the water from the hot water tap may have been kept warm for some time, but I can't see how this would make a difference. -- Q Chris (talk) 12:17, 28 November 2010 (UTC)

My loose guess is that it might have to do with impurities in the water — see, e.g. water softening. --Mr.98 (talk) 14:47, 28 November 2010 (UTC)

It's a wonder chemicalinterest has not answered this yet, is he asleep still :) It's the copper that's the problem with rubber. Case studies hot water bottle premature failure Obviously our article on hot water bottles requires this addition by a thermophilic editor who does not like to wake up in a wet bed.--Aspro (talk) 15:07, 28 November 2010 (UTC)

The original poster cited a British URL for the bottle. Many houses in Britain have water systems where only one (I hear) cold-water tap is fed directly from the mains, the hot-water system and other taps being fed from the tank. I can't find a Wikipedia article directly about this, but Water heating#Gravity system addresses it. Anyway, with such a system the hot water is in it longer and has more time to collect impurities. But I can't say if that actually is what they have in mind. --Anonymous, 03:33 UTC, November 29, 2010.

Yes, this is often the case in UK homes. The cold water comes straight from the mains, but if you turn on the hot tap, the water will come from a storage tank, commonly found in the roofspace/attic (although the water which comes out of the tap may be cold for some time depending on the vagaries of the heating system). This is why we were always told not to drink water from the hot tap, as it will be standing water, and tanks often have no lids. You can frequently tell the difference because the water pressure will be higher on the cold tap than the hot one. This page (a forum) contains some anecdotal information. See this from a national DIY chain which explains several kinds of residental water supply systems in UK homes. --Kateshortforbob _talk 14:44, 29 November 2010 (UTC)

Bose-Einstein condensate of light

Many years ago I imagined an idea in a fantasy game, in which people would lay out spheres of "one-way mirror" in the sun until the light would "crystallize" into "flasheesh", a basic magical reagent better known for its recreational abuse by magic users who would shimmer and eventually spontaneously combust from their addiction. It seemed to me just about the most absurd thing I could come up with. Until that is today, when I read someone had done something about like this, and that the Bose-Einstein condensate of photons was being considered as a viable commercial process for solar cells and lasers!^[3]

The above story in Nature News is written to be very accessible, but even so it leaves me with a host of unanswered questions. Why can only a certain number of photons enter the cavity before thermal equilibrium is no longer possible? Where do the photons go, and are they "bound" to the dye molecules? Can you physically shove such a condensate of photons to change their wavelength? When they talk about a "super-photon", are they merely waxing poetic?

As you can tell, I haven't accessed the paper, but this looks like a big story, and I hope that the people who understand it will make a new article to explain it on Wikipedia. Is it time to call the DEA? ;) Wnt (talk) 13:56, 28 November 2010 (UTC)

The photons are trapped in a resonant optical cavity (basically imagine a box with mirrors on all sides, though this box is microscopic and two dimensional). Quantum mechanics selects for wavelengths that are integer fractions of the dimensions of the box. For example, if you had a 1 m box, then you could have 1 m waves, and 1/2 m waves, and 1/3 m waves, etc. The actual box selects for light in the visible spectrum. So that's one selection constraint. The other constraint is that the temperature of the gas should be in thermal equilibrium with the box. (The dye they used is basically there to promote the creation of thermal equilibrium quickly enough that photons can't escape from the box or be absorbed on the walls before equilibrium is achieved.) The energy per photon increases as the wavelength decreases. The result is that certain photon states are forbidden. For example, even a single photon in a high enough state would require more energy than the entire collection of photons at thermal equilibrium is supposed to have. Similarly, the resonant nature of the box forbids very low energy photons from being formed because they would require wavelengths much longer than the box. As you push more and more photons into the box they will try to reach equilibrium, but because certain energy states are forbidden you end up with an excess being forced into the lowest available state. It is this non-thermal excess in the ground state that characterizes the Bose-Einstein condensate.

As for what the result is like, the resulting ground state population is basically a laser. You get a coherent population of photons at a particular wavelength. The trick here is that the wavelength is determined by the physical properties of the box and not the atomic properties of the substances involved. This means you could tune the wavelength by adjusting the size of the box, which could have a variety of practical applications and allow for lasers at wavelengths which we don't have an effective means of generating now. It is also interesting that this system essentially transforms arbitrary light of sufficient intensity into a laser beam (with some unknown efficiency). That could have a variety of applications with respect to solar cells and other processes that require light concentration. Dragons flight (talk) 21:29, 28 November 2010 (UTC)

By "super-photon" they presumably mean many photons in the same quantum state. Lasers do that too, so "super-photons" have been around for a while. This looks like an interesting experiment, but popular science magazines have a habit of reporting everything as though it's going to change the world. Chances are this won't. -- BenRG (talk) 02:41, 29 November 2010 (UTC)

I think I follow what you mean by "lowest available state", but just to check: Photons are bosons not subject to the Pauli exclusion principle, and a Bose-Einstein condensate involves particles all in exactly the same state. So I assume that the lowest available state is simply the longest wavelength that can bounce back and forth between the walls of the cavity. This also means that despite my initial perplexed reception, the photons aren't really "stopped" somehow, but simply bouncing back and forth between two closely spaced mirrors.

But what I don't understand is how the behavior of one photon differs from many. I'd think that even a single photon with a wavelength not matching the walls of the box would somehow be forced to end up having some wavelength that fits, which might be the lowest available state. Again, as bosons, I don't see how the photons can affect one another. Unless the box somehow cools the photons - and if so where does the energy go?

This keeps raising all kinds of questions in my mind:

• It makes me wonder what happens in an ordinary dye laser if the wavelength of the dye slightly disagrees with the spacing of the mirrors. Can you see the emission peak broken up into a set of integral wavelength multiples of the mirror spacing?

• Can photons trapped in a box be switched between spin states? I think it could have spin 1, 0, or -1 hbar per photon, though I'm not sure if that adds up to much. Can you use a box like that as some kind of "photon gyroscope"?

• Can you close off such a box and keep photons trapped inside for any length of time? How good can a mirror be when it is very small?

• Can you use a device like this to capture ambient light and convert it into a single frequency best suited for driving a chemical reaction or other electrochemical process? (I suppose that's also what the solar cells are about) Do the antenna complexes of plants know this physics?

Wnt (talk) 17:00, 29 November 2010 (UTC)

A very clear explanation by dragons flight there. As for interacting photons, recall how a laser work. In some you have maybe one photon knocking an atom to a higher energy state, then a second photon comes along pushing it to an even higher state, then it decays sending out a third photon. So even though photons do not interact, they are causally connected. The two first photons "caused" the third one. I imagine that the photons "interact" through such middle-men in this setup.

To answear your bullet points: Photon gyroscopes already exist. Photons have spin +1 and this won't change that far as I can see. Nor can this collection of photons apparently be trapped any longer than other photons, but the light may "last longer" if there's a delay in re-emitting photons from the dye. As for converting ambient light into a singel frequency, that also exists today in many ways, such as fluorescence chemicals used as whiteners in detergents. So this might be one of many ways to achieve that.EverGreg (talk) 13:31, 30 November 2010 (UTC)

Water not freezing below the bridge

I was walking around in park (the temperature was 0 C or below) and noticed that the water below the bridge and in nearby area for some reason did not freeze (and the birds were swimming there). Why is that? —Preceding unsigned comment added by 89.77.158.172 (talk) 14:31, 28 November 2010 (UTC)

Currents. Kittybrewster ☎ 15:01, 28 November 2010 (UTC)

The bridge may provide shelter from the cold (e.g wind chill factor) and it may also be emitting heat absorbed over the summer / from usage which does just enough to prevent the water there freezing. ny156uk (talk) 15:11, 28 November 2010 (UTC)

The simpler explanation is that the open water has been able to radiate its heat into space but under and around the bridge it has been reflected back. This is why ice can form over-night under a clear desert sky, even though the upper air temperature is above freezing.--Aspro (talk) 15:43, 28 November 2010 (UTC)

Has it been snowing or frosting where you are in Poland recently? If so, it seems likely that they would have been out there laying down salt on the bridge, which is then running off or blowing off the bridge onto the ice below, melting it. Especially if the bridge is a road bridge and not a footbridge, and has a lot of traffic over it. WikiDao ☯ (talk) 19:32, 28 November 2010 (UTC)

As this is a common phenomena under structures which have not seen gritted, I take that explanation with a pinch of salt ;-) No one has mentioned yet, that the air temperature reported is only around the freezing point. Therefore, I was expecting someone to also say, that perhaps the water has not had time to stratify (remember science lessons at school about the density of water and what parts of a lake are the first to freeze and which parts are the last). The water may be a lot deeper around the bridge which would be the reason why that spot will be the last to ice. Here is a link Understanding Pond Stratification. We need the OP to come back with some more observations.--Aspro (talk) 21:04, 28 November 2010 (UTC)

Beneath what other structures does this commonly occur? WikiDao ☯ (talk) 21:22, 28 November 2010 (UTC)

Roofed over boat moorings on pleasure lakes is one example. Common in the Victorian period before people could stay in all night and watch I love Lucy. --Aspro (talk) 21:40, 28 November 2010 (UTC)

An alternate explanation is that they have installed some sort of heaters around the bridge to stop the water from freezing. Having ice directly freezing against the bridge supports could have a detrimental effect on the life of the bridge. They may be deliberately stopping the water from freezing... --Jayron32 21:02, 28 November 2010 (UTC)

That's certainly an alternative explanation, but not a likely one unless "they" have a very cheap source of energy. Slightly more likely is that there is some form of warm water discharge near to the bridge. Dbfirs 21:55, 2 December 2010 (UTC)

Is a common feature of these cases that water is moving near some fixed object (pier, etc.) and/or something is moving in the water (birds paddling around, etc.)? I've often heard folklore (yeah yeah /) that turbulence makes water freeze more slowly, so water lapping at a piling would freeze after a still pond or a smooth gently-flowing stream. Sea ice#Formation of sea ice suggests this isn't a complete crock either. DMacks (talk) 22:07, 28 November 2010 (UTC)

Folk can be right too. Turbulence warms water and Mechanical equivalent of heat is your citation. Cuddlyable3 (talk) 22:47, 28 November 2010 (UTC)

Growing bacteria, beef bullion

I'm trying to grow bacteria with unflavored gelatin in petri dishes. I've heard to add beef bullion to the boiling water, then let it dissolve. Beef bullion is high in sodium, and sodium was used as a preservative in meats. Would sodium inhibit the growth of bacteria? Also, how would you identify the bacteria that grows, and what surfaces would bear the most bacteria? Albacore (talk) 17:00, 28 November 2010 (UTC)

Different bacteria require different Growth mediums. Once you know what you what to grow, you can choose a suitable source to provide the nutrients. Some of these bacteria can be very dangerous in such large quantities that end up in culture dishes -so beware. --Aspro (talk) 17:09, 28 November 2010 (UTC)

I'm really concerned, now that I've thought about it, that you are going to try doing this in the house – don't! Here are two links you might find useful: Safety Guidelines & MICRO-ORGANISMS FOR EDUCATION. The salts (sodium) in the beef bullion doesn't matter. After all, its best diluted down to half the strength normally used for making stock. At that level the salts will have little inhibitive effect. --Aspro (talk) 18:37, 28 November 2010 (UTC)

Geologic Time Scale

Found in the discussion of geologic time is a Geologic Time Scale. Where can a full size copy of this document be acquired?

Rolf Olson Salem, OR —Preceding unsigned comment added by 24.22.3.126 (talk) 18:44, 28 November 2010 (UTC)

Other than Geologic time scale, what exactly are you looking for? BTW: End the Holocene now, ask me how. Hcobb (talk) 18:54, 28 November 2010 (UTC)

How? WikiDao ☯ (talk) 19:38, 28 November 2010 (UTC)

Oh! Don't you read all of Wikipedia from A to Z? You don't need to do nothing, as it finishes in two years time.--Aspro (talk) 21:15, 28 November 2010 (UTC)

There are several diagrams on the discussion page. Do you mean this one:[4]. If so you can use the right-hand download tool. --Aspro (talk) 19:02, 28 November 2010 (UTC)

Your options for obtaining a large size print of a digital image are a) Tiled printing or "rasterbating" using an ordinary A4 PC printer, or b) use a printing company that is equipped to produce large placards. If you just need to present a large image, e.g. for a classroom lecture, consider using a Video projector instead of a paper document. Cuddlyable3 (talk) 09:03, 29 November 2010 (UTC)

For most of the pics, you first click on it, then click on "Full resolution" underneath to get the full image. If you mean the small Graphical timelines wiki table, a screen shot should work there. If you mean the much larger Table of geologic time, then the best I can do is to break it into 3 screen shots and prints those, since it's not a pic but rather a large wiki table. I have a max screen resolution of 1920×1200, but someone with a higher res might be able to print it all on one sheet, although the writing would then be tiny. Would you like us to provide you with it as 3 pics, so that you can print it, or do you know how to do that ? StuRat (talk) 15:02, 29 November 2010 (UTC)

Skinny vs baggy jeans in freezing weather

Being a student up here in Oswego, I know a lot about walking around all day in freezing wind/death snow. But this question has been seemingly unanswerable by my friends and I. What would be, according to science (if it is science that applies here), warmer, skinny jeans or loose, normal fitting jeans? Skinny jeans are closer to the skin, and seem to not let any of the cold air in, but because they are so close to the skin, the cold air gets closer to the skin, too. Looser jeans seem to have more room for the cold air to circulate around your skin. I've clearly tried to think about this for a long time! The jeans are both made of the same fabric, so that shouldn't be an issue. ?EVAUNIT^{神になった人間} 19:00, 28 November 2010 (UTC)

Yes, you need some trapped air. A pair of these underneath would also make all the difference. After all, if they're good enough for Clint Eastwood, they should be good enough for you. --Aspro (talk) 19:09, 28 November 2010 (UTC)

Looser will be better on the basis of allowing sweat to escape, and on the same note will allow hairs to stand out more. Also, what heat is emitted by your legs will travel more freely up the wider pants, creating a chimney-effect (if rather negligible). The baggier jeans will also be made of more fabric. In addition to this, any consideration of moisture favours baggier jeans: Skintights that grow wet will immediately cool down parts of your legs, while baggier jeans can keep this moisture at a range. 88.90.16.188 (talk) 19:11, 28 November 2010 (UTC)

Not answering the question, but there exist flannel lined jeans, such as these jeans from L.L.Bean (not spamming for them, but that's where I got my pair). They are quite comfortable in colder weather, though if they do get wet, they take forever to dry. Back on topic, tighter jeans may restrict circulation in extreme cases, which would be undesirable in colder whether. Buddy431 (talk) 19:34, 28 November 2010 (UTC)

Definitely looser. The amount or air that comes in because the opening is larger is nothing compared to the insulation the air gap gives you. Ariel. (talk) 20:55, 28 November 2010 (UTC)

Best to wear baggy jeans with layers underneath, such as jogging trousers, long underwear, leggings, or all three. Insulation is provided by trapped air, so loose layers are best. 92.15.14.132 (talk) 22:49, 28 November 2010 (UTC)

Old-style jodhpur pants may be best. They were baggy at the top (to allow air circulation inside) but narrow at the ankle (to prevent cold air from getting in). They were actually designed for horse riding, not for keeping you warm, but this would be a nice side effect, if made of the proper fabric (which would wick moisture away, such as cotton). We don't have a good pic of the old-style version in our article, so here's one from somewhere else: [5]. StuRat (talk) 14:45, 29 November 2010 (UTC)

Jeans are utterly unsuitable for cold weather. Get something in a nice woollen-worsted instead. DuncanHill (talk) 14:53, 29 November 2010 (UTC)

Looser jeans with a relatively tight bottom will do the best, I think the style is called "boot cut". Tight jeans just get the cold air closer to your leg. From my OR though, don't worry about your jeans, concentrate on covering your head (toque), neck (scarf), hands (gloves) and feet (socks'n'boots) as that is where the most heat loss (head & neck) and discomfort (hands & feet) occurs. Spend the big bucks on those accessories and they will last for decades. Franamax (talk) 21:56, 29 November 2010 (UTC)

One thing to bear in mind is that denim is a poor insulator, fabric-wise, as it is quite loosely woven and has a high wind chill factor. ([6], [7]). --Kateshortforbob _talk 09:55, 30 November 2010 (UTC)

It depends on what you compare it with. Thin synthetic materials, as in dress pants, can be even worse, and let's not forget bare legs. I was always shocked to see cheerleaders wearing skirts to the bus shop in mid-winter in Michigan. I suppose popularity has it's cost. StuRat (talk) 23:36, 1 December 2010 (UTC)

Sleep, tiredness, exercise

1) Why does taking a lot of exercise in the day make you sleep well that night? 2) Why does not getting enough sleep make you feel tired? You havnt been exercising all night, so why should you feel tired? 3) Why is the tiredness you get from not sleeping enough the same as the tiredness you get from exercising a lot? Do they have any differences? Thanks 92.15.14.132 (talk) 23:10, 28 November 2010 (UTC)

Have you looked at the articles about Fatigue (medical), Physical exercise and Sleep? Cuddlyable3 (talk) 08:52, 29 November 2010 (UTC)

I have now thanks, but they don't answer the questions. 92.24.176.72 (talk) 13:39, 29 November 2010 (UTC)

1) Exercise causes "damage" to the body, which must be repaired by additional sleep. I put damage in quotes, because it's not the usual permanent damage you might think of, but rather easily repaired damage. For example, micro-cracks occur in the bones, which are then filled in with more bone, strengthening them even more than before. Muscle cells are also repaired and expanded.

2) Even without exercise, some damage occurs (especially in the brain and eyes) and sleep is needed to repair that. So, if you don't get enough, your body tells you more is needed, by having you feel tired.

3) I'd expect the tiredness from exercise to be more in the muscles, tendons, and bones, such as aches, and regular tiredness to be more in the brain and eyes, in the forms of mental slowness and eye strain. StuRat (talk) 14:31, 29 November 2010 (UTC)

Circular logic

I had to do an experiment designed to show the "equivalence of mechanical work/energy and heat". This was done by heating a piece of copper with friction. The amount of work was calculated, and change in temperature of the copper was predicted using the heat capacity of copper. This was compared to the actual change in temperature of the copper.

But if the heat capacity of copper is determined experimentally by how much energy it takes to raise a mixed mass of copper one degree, then isn't the whole experiment circular? 70.52.44.192 (talk) 23:16, 28 November 2010 (UTC)

But the heat capacity of copper could be determined using chemical energy, like gas. Vespine (talk) 00:23, 29 November 2010 (UTC)

Or by Resistive heating, where the amount of energy put in can be measured quite accurately by maintaining a certain (known) current over a certain (known) voltage drop for a certain (known) amount of time. Buddy431 (talk) 01:50, 29 November 2010 (UTC)

...and thus you don't need to know the heat capacity of the piece of copper, merely the electric energy V*I*T that causes the same temperature rise as the frictional work. Cuddlyable3 (talk) 08:46, 29 November 2010 (UTC)

November 29

How well does heterodyne frequency downshifting preserve phase?

When an optical heterodyne is used to shift a terahertz signal to a lower frequency, how accurately is the original phase information preserved in a form which would be useful for interferometry? I'm particularly interested in 9-10 micron infrared; presumably that would use a CO₂ laser heterodyne -- but to which frequencies makes that range most useful for accurate interferometry, and how accurate does it turn out to be, in quantitative terms? I've read the Heterodyne and Laser Doppler vibrometer articles, [8], section III on p. 1253-4 of [9] and [10] and can't determine how well this works. Ginger Conspiracy (talk) 04:19, 29 November 2010 (UTC)

The phase will be critically dependent on the phase stability of the heterodyne. This can be measured nu the phase noise, measuring the spectrum of the supposedly stable oscillator. The idea will be to get a frequency offset you are interested in and make sure that the level of spurious signal is sufficiently below that of the carrier. However if you use the same oscillator signal to mix down with two or more points of a coherent signal, and then take the difference you will cancel out most of the noise introduced by an unstable oscillator. A 10 micron infrared is well beyond what I would term a terahertz signal. The quality that you would need is a narrowband enough heterodyne that when its spectrum is superimposed (convolved) on the desired downconverted signal you get no undesirable effects. Graeme Bartlett (talk) 08:08, 29 November 2010 (UTC)

Thanks very much. Phase noise is exactly what I was looking for. It's always a great pleasure to see such seemingly esoteric articles with such great content and external links. Ginger Conspiracy (talk) 03:35, 30 November 2010 (UTC)

Modified corn starch

When the ingredients listed for a food product include "modified corn starch", does that mean starch that was taken from corn and then modified, or starch that came from modified corn? NeonMerlin 06:00, 29 November 2010 (UTC)

The former. The starch is modified. The corn may (or may not) be modified, but that is irrespective of the name. See Modified starch. --Jayron32 06:04, 29 November 2010 (UTC)

LED Xmas light string efficiency

Thinking of buying some, and have a few Qs:

1) How does their efficiency compare with the following:

a) Incandescent Xmas light strings.

b) Regular incandescent lights.

c) Regular LED lights.

d) Regular CFL lights.

Efficiency being defined, of course, as lumens of light produced per watt of power used, but feel free to use other units, if you prefer. What I'm getting at with efficiency is knowing whether my electric bill will go up or down if I largely light the house with those strings instead of with regular lamps and overhead lights.

2) Also, how long should a string of LED lights last ? And when one light fails, will the rest continue ? Is there some point at which too many lights have failed, where the whole string will go out ?

3) As for safety, I assume that they use less energy and produce less heat than incandescent Xmas lights, so this should reduce the risk of fire, right ? StuRat (talk) 14:20, 29 November 2010 (UTC)

You are comparing mono-chromatic light to white light. The theoretical max for white light is 251 lm/W, but for a single color it's 683 lm/W (it varies a bit depending on the color). This is not just theoretical - it makes a huge difference in practice too. Since you need colored lights, LED is by far, no question about it, the most efficient. Incandescent, besides being inefficient, and hot, also looses a ton more efficiency by using a filter to make it colored. CFL can be made in a single color, but in practice it's not.

Re-reading what you wrote, are you trying to use them for general lighting? If so then CFL is best. See Luminous efficacy for chart. LED has a lot of vocal support, but it's not as efficient as CFL, and the color quality is worse too.

LEDs last about 20,000 hours, but they don't burn out, they just get dimmer. LEDs are probably wired in series. An LED needs about 5 volts, so you have about 24 of them in series for 120 volt service. I'm not sure of the failure mode of an LED (i.e. does it fail open or closed). But normally they don't fail anyway, unlike incandescents.

I'm not sure there is a lot of risk of fire from incandescents anyway (I mean you could, but in normal use it's not a problem) so that's not really a comparison. But less heat does mean a lower A/C bill. Ariel. (talk) 21:01, 29 November 2010 (UTC)

I'm not so sure about some of your claims.

For example the colour quality claim. For generic 5mm or similar LEDs sure. But high CRI (90+) LEDs do exist (see [11] for example). These tend to exist in warm white too although that's (IMHO) strong evidence that's a cultural thing so not really relevant. I don't know how these compare to state of the art CFLs but most people aren't using those (i.e. they seem satisfied with the lower quality) so it seems fair to point out you can get something which will probably be good enough if you really want. Of course CRI probably isn't perfect anyway [12] although that's somewhat of a field beyond me.

I don't know about the claim of LEDs not failing either. The 20k lifetimes are great in theory. But from what I've read many LEDs lights aren't living up to their purported lifes. In particular one problem is given the common high variance in Vf if these are matched into parallel arrays without proper regulation, some LEDs tend to be overdriven, these eventually fail and then the others are then overdriven so the how thing quickly fails. [13] [14] [15] I've also read of very quick and rather dramatic dimming of cheap Chinese white LEDs (mostly the 5mm etc kind) even with rather low non over-driven currents. LEDs have a big problem in they really don't like heat, it reduces the efficiency, changes the colour and drastically shortens the lifespan, so incandescent bulb replacements are still problematic. (Enclosed fixtures are usually a case of just don't get, except perhaps when it's purposely designed for LEDs.)

In terms of luminous efficacy, while CFLs probably still win here I don't think they will stay much longer, our article currently has 93 [16] which is over a year old. This compares to a best of 120 for CFLs from our article. But LEDs are advancing at a far faster rate AFAIK (compare the Cree XM-L LED launched recently with the XP-G launched last year for example [17], while these are raw LEDs the bulbs are clearly going to trend). Of course if you want high CRI or warmer whites you're worse off and I'm not sure how LEDs luminious efficacy compare with CFLs when at that level.

Price wise LEDs still have a way to go, particular since as I mentioned they may not last as long as sometimes claimed.

Nil Einne (talk) 22:05, 29 November 2010 (UTC)

What you wrote doesn't really dispute my claims. I have never understood why people keep saying LEDs have better color, CFLs and LEDs make colors by the exact same method! LED's have no advantage here. They make UV and phosphors change the color. CFLs do exactly the same thing. The difference is that CFLs generate a deeper UV, which helps a lot. I simply check the packages and displays in stores, and it's no contest - CFLs are far better. That post you linked says essentially "LEDs are not doing so well in color accuracy, so lets redefine color accuracy so LEDs do better".

On top of that color accuracy and efficiency are enemies of each other, so it doesn't help to compare a high efficiency 70cri led. Notice the Toshiba bulb: 93 lm/W is at 70 cri. If you want 90 cri it's only 69 lw/W which is much worse than a CFL for that CRI. The 160 lm/W is only at very very low power levels, and no mention is made of CRI. I don't agree that LEDs are advancing faster. They are advancing fast in total lumens, but in efficiency it's at a much slower pace (and remember low cri doesn't count). Maybe one day LEDs will be better, and I'm glad there are people funding the research by buying poorly performing LEDs, but I'm not going to (OK, actually I did buy an LED for a bedside lamp for kids, since it's unbreakable :). Ariel. (talk) 23:29, 29 November 2010 (UTC)

Long semi OT reply to IMHO questionable claims Nil Einne (talk) 18:32, 30 November 2010 (UTC)

Who said they have better colour? I didn't. Nor did StuRat. You however did claim they have worse colour, which I stick by my claim is questionable. For starters there are high CRI LEDs. Are these worse then the best CFLs? I don't know. You definitely haven't presented any real evidence that there are. Your anecdotal evidence is somewhat irrelevant since 1) People have different preferences 2) You haven't indicated how you compared, did you use colour swatches? Was any semblence of a blind test done 3) We have no idea what sort of LEDs were being compared, were high CRI LEDs even involved? Nor is it clear what CFLs are being compared. Now it may be that there aren't any real high CRI replacement bulbs, LED bulbs are still somewhat of a niche product as I've indicated. And as I've said, AFAIK the evidence suggests most people don't care that much about CRI so it's hardly surprising that of what does exist, manufacturers are concentrating on what's good enough for the majority rather then what a minority at the current time may want. That bit about people not caring that much is of course an important point. I admit I don't have clear evidence here but as I already said, most CFLs aren't that high CRI. In NZ the CRI isn't usually even advertised or specified from what I've seen. High CRI CFLs do exist but they tend to be niche products AFAIK. Now as I said, I don't have clear evidence like sales figures so I could easily be wrong, but I don't think I am. Given this, the claim that LEDs have worse colour is even more misleading since from most peoples POV you can get better CRI LEDs then what they're currently using in CFLs. This doesn't mean LEDs have better colour, I never said they do, it just means it's misleading to say CFLs have better coloru as you have done repeatedly. As for the CRI definition thing, well I said it's somewhat beyond my expertise. However I freely admit I trust actual published research, much more then I do claims by random wikipedians backuped by nothing so I'll trust the research suggesting CRI, something developed in the 30s and 60s may not be perfect. Even more so when the only apparent response said wikipedian has is that "LEDs are not doing so well in color accuracy, so lets redefine color accuracy so LEDs do better" yet some of this research was from 1995 and attempts were made to reform CRI itself in 1991-1999. Blue LEDs had started to gain interest by 1995 so I guess it's possible that people in 1995 were trying to fix the standard to give LEDs a leg up again CFLs but I admit wacky conspiracy theories have never been my thing. (This is not to say I'm denying such things tend to be very political our article itself says "The committee was dissolved in 1999, releasing (CIE 1999), but no firm recommendations, partly due to disagreements between researchers and manufacturers"). Ironically from what I've read one complaint possibly about CRI or at least luminous efficacy is that it underemphasises the blues which makes me wonder about your UV claim. I'm also a bit confused about the relevance of your anecdotal evidence anyway, surely all that matters if you think CRI is perfect is the CRI and colour temperature (and luminous efficacy), why worry about how they look? If you get equivalent CRI and colour temperature to what you prefer CFL and LEDs then these are the same and just compare the efficacy. Unless you are acknowledging that CRI isn't perfect. Note I already said you lose efficiency if you want increased CRI (or lower colour temperature) so I'm not really sure why you're repeating what I said. You've claimed a lower CRI LED is much worse then a low CRI CFL but provided no evidence. But rather then waiting for some, let me try to find something. For starters your claim is misleading anyway since the 69 lumens per watt is warm white not cool white which the 70 CRI is so it isn't just the higher CRI but the higher colour temperature. The 69 lumens per wat BTW is also 80 CRI not 90 CRI. But looking for highish CRI CFL, I was directed to (well the main site) [18] where we see EnergyMiser warm white 600 lumens 80 CRI with 55 lumens/w (ooops!). But moving on perhaps that's not totally fair since there's also a 68 lumens per watt 820 820 lumens warm white 80 CRI and a Phillips 700 lumens warm white 82 CRI 64 lumens per watt and uh lets ignore the TCP. The Toshiba doesn't specify what they mean by warm white so I'm presuming of course they mean 2700K like the others but I'm not that sure (I did find some claims the Toshiba was 2700K but none from Japan). While the CFLs here don't actually come out better I'm not suggesting these have the highest efficacy so I'll concede as I did in my first post CFLs probably still win. Particularly since, I've seen (a while before this this post) some evidence the Toshiba figures may be somewhat inflated (although I've read that's not uncommon with CFLs either) and I've also read that the Toshiba's in Japan have shit power factor and other issues because of lax standards in Japan and meeting the stricter standards in the EU and US lowers efficiency (I'm presuming the CFLs meet the stricter standards since that's a US site) [19]. (Another problem is of course heat as I've already emphasised, your LED bulb may be 600 lumens when you first turn it on, I wonder if it will still be that 8 hours later in a low airflow room and a somewhat enclosed space.) However as you may have guessed, I am awaiting support for your claim 'which is much worse than a CFL for that CRI'. You're right that low currents LEDs have greatest efficiency at low currents, this was perhaps not something I made clear enough in my original post. I'm ignoring your irrelevant claim that low CRI doesn't count since as I've already said while your welcome to your POV, there's no evidence it's held by the majority of people. The XM-L is still not really widely available so it's difficult to get good comparisons but from what I've seen 10% efficiency gain isn't unresonable. 10% may not seem like much to you but I'm sure quite a lot of industries will be happy with a 10% efficiency gain a year. I'm not aware CFLs are advancing at anything close to this rate. P.S. One of my earlier comparisons was a fluourescent light not a CFL which perhaps wasn't the fairest but since these are commercial available bulbs (as opposed to raw LEDs) I'm still willing to let it stand. I would note our luminous efficacy article suggests 46–75 for CFLs. P.P.S. The website I used above showed CFLs all had an advertised CRI of 80 or higher (although I was directed there when looking for highish CRI). My impression had been that many CFLs have a CRI of about 70-75. However I appear to be mistaken on this, for example I found [20] which shows all CRIs tested there (Australian) were 80+ and it is in fact the ANZ standard. I also find [21] which suggests ~80 is the norm. In that case, and given a CRI of ~70 seems the norm for cheap or generic LEDs I'll concede the average LED is worse then the average CFL. However it still doesn't change the fact you can get LED light bulbs better then the average CFL and in fact approaching the best CFLs e.g. [22]. (Efficacy wise that's 54 lumens/watt so not that great although I still don't know what the CRI for high 90+ CFLs are. Note that the Australian study I linked to found the luminous efficacy was around 60-80 lumens/watt for the 80.4-87.7 CRIs in that study so I'm still not seeing much evidence for these far better efficacy of CFLs that was alleged. These are real world independent tests however from my brief read thorough I think they found most manufacturers live up to their claims so I'm not sure if the LEDs are going to be much worse. Perhaps this is a matter of semantics, I don't consider 20-30% far better, particular considering the rate of advance of LEDs but perhaps you do. ) Nil Einne (talk) 18:32, 30 November 2010 (UTC) Maybe high CRI, high efficiency LEDs exist, but they are certainly not commonly available - I always check the lamp displays, and all the LEDs on display are very blue. And many of the LEDs don't even list lumens, which I find quite shady. Additionally the CFLs will say "warm/cool white", etc. The LEDs don't, they leave you to guess. I think you are arguing about LEDs that exist, and I am arguing only about those that I can find in a hardware store. Right now, if you go to buy a bulb in a store, CFLs beat LEDs, but I'm willing to accept that it's possible to buy great LEDs online. Ariel. (talk) 19:28, 30 November 2010 (UTC) Ok thanks for the clarification. I suspect however it depends where you live, I belief for StuRat this is the US so perhaps your comments are somewhat appropriate for him. But it wouldn't surprise me if the Toshiba linked above was available in some Japanese hardware stores. In NZ I don't think I've even seen a mass market retail store selling LED bulbs, nor in Malaysia (although haven't looked that well there, it's not something that interests me) so if you want LED bulbs buying from specialised stores is probably your only choice. Some of the bulbs, e.g. the Cree LR6 aren't really intended for the mass home market anyway given heat, cost and perhaps weight issues. Note in case this wasn't clear enough I wasn't trying to suggest LEDs are better at the moment, just that in terms of CRI, CCT and efficacy I don't think they are really that far from CFLs. Realisticly, the number of people interested in buying $100+ light is small (particularly given the care needed, the small number of advantages and the fact 5-10 years from now people will be laughing at the old prices) hence as I mentioned they still have a long way to go on price. Nil Einne (talk) 20:12, 30 November 2010 (UTC) (EC) Semi answering my own question I find [23] with a 13W CFL with CRI 93+, 780 lumens, 5500K CCT. That's 60 lumens/W in other words the Cree LR6 linked above doesn't seem that bad in comparison particularly noting it was launched in 2007 or 2008 from what I read (not sure whether it's undergone improvements since then). Nil Einne (talk) 20:12, 30 November 2010 (UTC)

Thanks for the answers so far. I had strings of LED Xmas lights in mind for two purposes:

A) Night lights. Should be more efficient than the incandescent night lights I use now. These are just so I can find the light switch without smashing my toe on the coffee table, etc. I do have one CFL night light, and I will probably keep that one.

B) Area lighting. I don't like having a single bright spot in the room, which either an overhead light or table lamp produces. Strings of Xmas lights would give a more even lighting.

As for the color, I'm flexible there. If I wanted white, overall, couldn't I combine different colored LED lights to get that ? StuRat (talk) 05:24, 30 November 2010 (UTC)

For evenly lighting a room, you might consider up-lighting. We have a room that was previously lit by small lights all 'round the walls, and now we have a bright free-standing lamp that directs its light in a cone facing the ceiling. It's maybe 4 or 5 feet lower than the ceiling. The light reflects off the white ceiling and evenly lights the whole room very satisfactorily. It's very impressive if you haven't tried it before. 86.161.109.130 (talk) 11:11, 30 November 2010 (UTC)

I can't offer that much advice since it's not something I've explored that much (I'm more interested in the flashlight arena). You may find some advice here [24] although be warned I've sometimes found the culture there fairly elitist and pro-American/anti-Chinese. However I've also seen a lot of fairly complex discussions about lighthing including custom solutions. (I'm not sure whether that's really what you're going for since it's likely to be rather expensive.)

My guess is using the white locations and right lens, reflectors etc will produce a far better result then a lot of small Christmas lights.

You can get RGB LED lights like this [25] but they tend to be orientated to having different colours rather then mixing the right white light for your purposes (although you may be able to do that, I don't really know). They also tend to be expensive, low powered and I expect not that efficient. I'm not particularly sure they give great CRIs either whatever you do. I suspect just having different colour lights won't work very well unless you are going for a disco/nightclub effect.

Nil Einne (talk) 18:50, 30 November 2010 (UTC)

Hmmm, "the white location" ? :-) StuRat (talk) 22:40, 30 November 2010 (UTC)

Computer modelling of Artificial consciousness

"Computer modelling shows that even consciousness can be generated with very small neural circuits....only a few thousand could be enough to generate consciousness." from http://www.sciencedaily.com/releases/2009/11/091117124009.htm

What computer modelling is this? I've tried searching. Thanks 92.24.176.72 (talk) 14:32, 29 November 2010 (UTC)

It's probably an artificial neural network. I've taken the liberty of cross-linking this to The computing ref desk. CS Miller (talk) 16:15, 29 November 2010 (UTC)

That popular article was based on this scientific paper. Discussion of artificial neural networks in that paper starts on page 7. The popular article is apparently being sloppy and exaggerative when it refers to the kind of cognitive tasks performed by artificial neural networks as discussed in the paper as being "consciousness". The paper itself does not use the word "consciousness". Red Act (talk) 16:25, 29 November 2010 (UTC)

Which is funny because "consciousness" is precisely the wrong way to describe what is going on. It's not surprisingly that you can make a small neural network count; counting is computationally easy. When humans count, they don't have a special counting neural network that they can invoke. If you tell someone to count by threes, or to stop counting and start again later, writing their number down so they don't forget it, they'll be able to seamlessly make the appropriate changes to their mental algorithm. So humans are able to reflectively modify their own cognition. Consciousness, normally defined as awareness of self, is the hard part. Executing little algorithms is easy, regardless of the substrate (neural networks, the symbol-manipulation of intelligent brains, or assembly language). Writing them is hard. A bee brain may be capable of counting, but I really doubt they can decide to count, or figure out how to count. Paul (Stansifer) 16:55, 29 November 2010 (UTC)

The problem of course is that we don't have a good operational definition to test for consciousness. This problem is discussed in our testing section of the Consciousness article. Nimur (talk) 19:00, 29 November 2010 (UTC)

Role of salt in ethanol precipitation of DNA

I don't understand the role of the salt. Does it cause the phosphate groups in the DNA to dissociate, giving up a proton? Or else if the the phosphate groups are already in the deprotonated form, why is the salt needed? Gidip (talk) 18:18, 29 November 2010 (UTC)

I was told it was because you needed a counter ion for the phosphate groups. In solution at neutral pH, the protons are already dissociated from the phosphate groups. Because of electrostatic repulsion, you can't force just the charged DNA into the solid phase - you need to counter the charge with a positive ion. The salt solution provides enough counter ions for the DNA to come out of solution as a neutral salt. (Note that DNA behaves the same as any other ionic species in this regards.) -- 140.142.20.229 (talk) 18:36, 29 November 2010 (UTC)

Well heck, we've got an ethanol precipitation article. DMacks (talk) 20:33, 29 November 2010 (UTC)

The net charge in the system has to be zero. Therefore, for every negatively charged dissociated phosphate group there is a proton. Then what's the salt for? Gidip (talk) 08:10, 30 November 2010 (UTC)

If they have a high propensity to dissociate (i.e., acidic), you would have to lower the pH to make that happen effectively. But you're right, if the solvent becomes non-dipolar enough, they would be more likely to stick. But they would stick as a covalent OH (not just ion-paired). Neutral covalent compounds are generally soluble in organic solvents, so you haven't accomplished the precipitation: the goal is to make the DNA insoluble, not just into some net neutral complex. So instead, seems like the goal is to promote formation of ionic salts of the phosphate. DMacks (talk) 09:16, 30 November 2010 (UTC)

Red bleach stains

Using laundry bleach, I occasionally splash some on my clothes, and get a stain. Typically the stain is lighter than the fabric, but I've recently encountered some odd exceptions:

1) A black pair of jeans had bright red dots where it was splashed. I guessed that the black color was, in fact, made up of multiple colored dyes, and that the red component was more bleach resistant than the others.

2) A white knit shirt, with a collar made of a different material, had the white collar turn pink (a pale rust color, to be more specific), while the rest of the shirt was unaffected. I can't use the previous explanation here. The rust color makes me think that there was actually some iron in the collar, which then oxidized when exposed to bleach. Is there any white dye which contains iron ? StuRat (talk) 20:55, 29 November 2010 (UTC)

I think your explanation for 1) is correct. As for 2), was the collar uniformly pink, or in a characteristic `splash' shape? If the former, I propose color was released from other fabrics, and preferentially bound with the collar. My understanding is that white cloth is not generally made these days by dying with white dye, but by bleaching off-white source material. SemanticMantis (talk) 23:04, 29 November 2010 (UTC)

2) It's the splash shape, any ideas ? The shirt might be very old, I inherited it. Also, the red showed up immediately when the bleach hit it. StuRat (talk) 05:07, 30 November 2010 (UTC)

Fusion and fusion

what I don't understand is were this energy comes from. Here's what I mean. The reaction of deuterium and tritium goes like this:
²H + ³H → ⁴He + ¹n + energy
Were does this energy come from? You are left with less mass than you did before, but you still have three neutrons and two protons, just like before, yet they are lighter. I don't see how you can get "light particles"; a proton is always a proton, with three quarks, right? --T H F S W (T · C · E) 21:42, 29 November 2010 (UTC)

I believe the answer is in the Binding energy. Vespine (talk) 21:57, 29 November 2010 (UTC)

Then why is there mass loss? Does the binding energy hover around the particles like dark matter around a galaxy? --T H F S W (T · C · E) 22:11, 29 November 2010 (UTC)

The loss of mass and release of energy are the same. I think this is ultimately the same reason a compressed spring has more mass than a spring at rest, i.e. E=MC^2. SemanticMantis (talk) 22:57, 29 November 2010 (UTC)

Exactly. If you need a particle to imagine being converted into energy, the mesons mediate the binding energy of the nuclear force, but they are very short lived, virtual particles, so it may make more sense to just think of conservation of energy. Ginger Conspiracy (talk) 23:14, 29 November 2010 (UTC)

I suspect the difficulty in visualizing this is because the popular image of "energy" is as a little lightning bolt, i.e., electrical energy. "Energy" is a far more diffuse and diverse concept though. Personally I think our way of visualizing nuclear reactions is harmed by our persistent representation of the energy released as a little lightning bolt, when it is really released as kinetic energy in the speed of the constituent parts. In any event, thinking of energy as a "thing" that hovers around (or zaps out) is going to mislead you every time. --Mr.98 (talk) 00:19, 30 November 2010 (UTC)

To answer the question, the energy in this case is almost certainly released as heat energy; the fact that the alpha particles are moving after being released means they have energy. The speed at which they move will be ultimately related to the amount of energy released by the reaction. Heat energy is just the energy of molecular motion. --Jayron32 04:14, 30 November 2010 (UTC)

The nuclear binding energy is actually negative, but that's not important; what's important is that the binding energy per nucleon is different for different elements (and isotopes). If you plot it as a function of nucleon count, you get a bowl-shaped curve with the lowest point at Iron-56, as shown here (upside down). Thus, you can liberate energy by putting small atoms together or by splitting big ones apart. -- BenRG (talk) 08:34, 30 November 2010 (UTC)

is this true?

http://i.imgur.com/GBGAY.gif
can you really build it like that or is it just an animation? 82.234.207.120 (talk) 21:43, 29 November 2010 (UTC)

Kentucky Do-Nothing. Plans are here. Here's the Facebook page. Buddy431 (talk) 21:49, 29 November 2010 (UTC)

Thanks! Now I finally have a name for those things. I had one when I was a kid but never knew the name. Dismas|^(talk) 07:12, 30 November 2010 (UTC)

Also known as a "Do-Nothing Machine" or "Bullshit Grinder", or more formally, as a "Trammel of Archimedes". When used to draw ellipses, they may be known as an ellipsograph. Buddy431 (talk) 20:11, 30 November 2010 (UTC)

I see that when the angle of the rod changes uniformly, there is simple harmonic motion in both axes. Is there a simple way to regulate the motion of the device so that it traces out an elliptic orbit around one focus according to Kepler's first law? (Despite some material at orbit equation, eccentric anomaly, true anomaly, etc., I should say that deriving this from scratch doesn't look easy...) Wnt (talk) 11:16, 30 November 2010 (UTC)

What exactly do you want it to do? You can easily change the size and shape of the ellipse it produces. See this demo. Buddy431 (talk) 20:14, 30 November 2010 (UTC)

Too many birds on a power line

Yesterday, I looked outside and saw that the power line to our house was completely filled with ravens. This wire is about 100' long, and was sagging quite a bit from the weight of the birds. I've lived here 17 years, and have never seen that many birds on one power line before. I have two questions: 1) what would cause that many ravens to congregate on my power line, and 2) is it possible for the birds to actually break the wire? Shuttlebug (talk) 21:44, 29 November 2010 (UTC)

The wires are strong enough for a person to hang from them, so I doubt birds could hurt it. Ravens like to group. I've frequently noticed large flocks right before storms. Ariel. (talk) 22:06, 29 November 2010 (UTC)

Probably planning a murder. HalfShadow 22:07, 29 November 2010 (UTC)

groan. DMacks (talk) 22:10, 29 November 2010 (UTC)

(edit conflict)Question1: I suspect that it was either 1) a group of young birds or 2) a group of males looking for females.

Question2: No. Metals, such as those cables are made of can be stretched and bent a long way before snapping. I have seen trees fallen on power lines and the lines have been almost touching the ground (of course, the poles were bent too). Are you sure that the birds were making it sag? Power lines always droop a bit. --T H F S W (T · C · E) 22:09, 29 November 2010 (UTC)

To answer question 2) Engineers who design these things are not complete idiots. Birds are known to congregate on power lines, and I am certain that the strength of the line is designed to take this into account. --Jayron32 04:11, 30 November 2010 (UTC)

I believe there was a documentary produced about ten years ago that studied this problem in depth. Wikipedia has an article about it if you're intererested. —Bkell (talk) 12:52, 30 November 2010 (UTC)

Ha, ha, Bkell, very nice connection.

Seriously, overhead power lines are constructed to some pretty amazing engineering standards. I don't know if bird loads are ever specifically accounted for, but in areas where it freezes, the standard is that the line must be able to support the weight of an ice coating up to five times the wire's diameter. In areas subject to extreme ice storms -- such as Quebec -- the standard is raised to ten times. (And yet, they are still occasionally pulled down due to stupendous quantities of encased ice. [26])

One of the most amazing demonstrations of the "hoisting capacity" of an overhead power line occurred in Seattle in April, 1998, when a small private airplane got tangled in one and dangled from it for a couple of hours [27] [28] before some very intrepid firefighters effected a one-of-a-kind rescue. [29] —Steve Summit (talk) 13:20, 30 November 2010 (UTC)

I think I need a small vacation/But it don't look like rain/And if it snows that stretch down south/will never stand the strain. --Trovatore (talk) 03:49, 1 December 2010 (UTC)

Not all power lines are the same. The one which supported the plane was 50 feet off the ground and supplied a steel mill and 2500 customers. It was likely a transmission or subtransmission high voltage line, and had little in common with the line carrying power to ones house from the transformer, or in many cases carrying power to the local transformer. The high lines may be steel reinforced, while the line in the alley or along the highway in front of your house may be far weaker. A 4kv or 12kv feeder might be relatively small copper wire. The service going from the transformer to a house might be rather small as well. Even so, it is hard to envision bird loading sufficient to break wire that stands up to wind and ice. Edison (talk) 17:20, 30 November 2010 (UTC)

Fluorescent light flashing after being switched off

The energy-saving fluorescent light in my kitchen has just behaved rather strangely. Just now I switched it off, after which it flashed at intervals of approximately 1 second, for a total time of about a minute. Right at the end of this just one of the three "loops" was flashing. What could cause this? Thanks, DuncanHill (talk) 22:15, 29 November 2010 (UTC)

The modern Compact fluorescent lamp have voltage control circuitry (the old ones chokes) so that they can run between 230 -ish volts and about 256 -ish volts. Once the power is off, it might just be the capacitors discharging. The reserved charge is dissipated each time the arc is achieved. After a few flickers the capacitors are completely discharges. Also, maybe you lighting loops are wired in the 'live' configuration. Nothing wrong with this (according to the UK regs) but important that you make sure the power's off before allowing you pinkies any where near the copper.--Aspro (talk) 22:42, 29 November 2010 (UTC)

Oh! And is your kitchen very cold. Dry air and low temperatures allow florescent tubes to exhibit behaviours not seen at higher temperatures. --Aspro (talk) 22:45, 29 November 2010 (UTC)

Has been very cold lately, and I think there's cold air coming into the flat above. DuncanHill (talk) 23:09, 29 November 2010 (UTC)

I asked this question just the other day! Zunaid 13:36, 30 November 2010 (UTC)

Antonov AN225- Personal experience and photographs available

Hi there,I flew on the AN 225 from Manchester in 2006, and have a little knowledge and plenty of photographs of it should they be of interest? —Preceding unsigned comment added by Filler9 (talk • contribs) 23:13, 29 November 2010 (UTC)

Please consider licensing your images and uploading them to Wikimedia Commons. Read Wikipedia:Uploading images and be sure you understand the implications of licensing your images; then use the uploading form to put them up. Also check out our article, and feel free to edit it to add content; but be sure you understand our verifiability policy and do not contribute original research. Nimur (talk) 23:21, 29 November 2010 (UTC)

(ec) Please consider improving the Antonov An-225 article and/or uploading your photos to the commons:Antonov An-225 Wikimedia Commons category. Ginger Conspiracy (talk) 23:22, 29 November 2010 (UTC)

November 30

Position of maximum depression on classical guitar top.

At present I am in the process of writing an article on the construction of the classical guitar, and am proposing a different method of reinforcing the top-plate. The method consists of a set of bars, radiating from a position in front of the bridge, which is where maximum deflection occurs, due to the action of the strings when plucked. Where that position is, can be calculated, I believe, with a formula to do with Modulus of Elasticity, when the following is known: The type of wood and thickness of the top-plate. The total tensile and torsional force applied to the bridge, from the strings. The edge pressure from the bridge. This little information is gained from the mechanical drafting certificate course I did more than 40 years ago, hence the sketchy description. —Preceding unsigned comment added by 58.175.87.33 (talk) 04:27, 30 November 2010 (UTC)

And your question is . . . ? 87.81.230.195 (talk) 14:25, 30 November 2010 (UTC)

We do have articles on Classical guitar and Classical guitar_making -- are they helpful? --- Medical geneticist (talk) 21:41, 30 November 2010 (UTC)

How accurate do you want the results? There is no shortage of finite element analysis applied to guitar body: Modal analysis of an acoustic guitar by finite element came up in a web search; and you can find even more scholarly, technical, and accurate modeling with a little effort. Obviously, the specific node point of maximum vibration amplitude is going to depend on the guitar body shape, materials, and how accurately your mathematical model matches physical reality. Nimur (talk) 21:49, 30 November 2010 (UTC)

Relativity questions

Expand long text

The Phenomenon of Far Event Dilation For a given event eA happened at time tA and location A, an observer at location O uses a camcorder with timer to record event eA, then the recorded event time ta will always behind tA, this is the phenomenon of Far Event Dilation. This is prepared for "Distance Relativity", please comment. 1. The Equation of Far Event Dilation The recorded event time ta can be calculated by ta=tA+(AO/c’) ---(1), c’ is the speed of light in the environment. 2. The Equation of Event Period If the event ends at location B and time tB, then the recorded time period can be calculated by (tb-ta)=(tB-tA)+((BO-AO)/c’) ---(2). 2-1. When BO=AO, that means, if A and B are located on the same sphere with center O, then, the recorded event period is always the same as the actual time period. 2-2. When BO>AO, that means, the event ends at a point farther away, then the recorded event period is larger than the actual event period. The event looks happening slower in the video. 2-3. When BO<AO, that means, the event ends at a point closer to O, then the recorded event period is smaller than the actual event period. The event looks happening quicker in the video.Jh17710 (talk) 06:27, 30 November 2010 (UTC) Distance Relativity Now, let us study the Far Event Dilation in one dimension space. We assume the event points A or B and the location O of the observer are always on the same line. We also focus on cases that either the event moves or the observer moves at constant velocity v. Then we will have two sets of time equations and one set of velocity equations. This is the main subject, please comment. 3. When observer moves, then |BO-AO|=v(tb-ta) 3-1. When BO>AO, (tb-ta)=(c’/(c’-v))(tB-tA) ---(3) 3-2. When BO<AO, (tb-ta)=(c’/(c’+v))(tB-tA) ---(4) 4. When event moves, then |BO-AO|=v(tB-tA) 4-1. When BO>AO, (tb-ta)=((c’+v)/c’)(tB-tA) ---(5) 4-2. When BO<AO, (tb-ta)=((c’-v)/c’)(tB-tA) ---(6) 5. Let the event be the motion of an object from A to B under the constant velocity of v and let the speed of that object be calculated as V by the observer, then: 5-1. When BO>AO, V=(c’/(c’+v))v ---(7), particularly when v=c’, we have V=c’/2. 5-2. When BO<AO, V=(c’/(c’-v))v ---(8), when v=c’, we find out V is infinitely fast. For example, if a base ball flies to me at the speed of c’ and when it passes the sign of 30 feet, that particular picture will take about 100 nanoseconds to reach my eyes, but, at around 99 nanoseconds, that base ball already hits my nose so that the speed of that base ball is unlimited fast to me. Actually, all photons run into our eyes at infinite fast speed.Jh17710 (talk) 06:27, 30 November 2010 (UTC) The Phenomenon of Far Ball Contraction We can calculate the distance of a ball by the equation based on the phenomenon of Far Ball Contraction, which is “A ball looks smaller when it is farther away.” This is just to show the fact that we cannot see the dimension representing far and near, we calculate that dimension. 6. Far Ball Contraction Formula If we hold a ruler 1 foot away from our eyes and measure a ball of radius r feet at distance of L feet away from our eyes to get radius of R feet, then, when the ball moves to another distance of L’ feet, the measured radius R’ feet will be R’=(RL)/L’ ---(9). We should keep both of L and L’ larger than (1+2r) feet to make the measuring job practical. 7. When the Ball is Replaced by a Brick If we replace the far ball by a Brick and look at the length and height side of that brick, then, we don’t know how wide that brick is. That means, we judge the distance of an object by the image of the length and height of the object that is perpendicular to our sight line, and normally, we have no way to tell how wide or how deep that object is.Jh17710 (talk) 06:27, 30 November 2010 (UTC)

Response

Jh17710: People who patrol the reference desk aren't going to answer homework questions for you; also we generally need questions to answer. It looks above like you have copied large swaths of text from some physics text somewhere. Is there a question anywhere in all of this? --Jayron32 06:48, 30 November 2010 (UTC)

Thanks for allow this section to stay. Yes, some question is big like the idea of "infinite speed".Jh17710 (talk) 05:30, 1 December 2010 (UTC)

There is no infinite speed. Speed is always relative between frames of reference. The practical limit to speed is the speed of light, which is very finite. The problem comes not in objects moving relative to each other; but in accelerating an object from "rest" (as defined in its own reference frame) to the speed of light. To do so would require infinite energy, which is impossible. --Jayron32 05:48, 1 December 2010 (UTC)

Let us look at your comment one by one. I believe that there is no actual infinite speed in real world too. Yes, speed can be relative speed to a reference frame or even, visual speed like if a ball flies at speed of c/2, then, how a camcorder records that ball moving forward and backwards at distance marks of 300 feet, 600 feet, and 900 feet? We will find out the forward speed is c and the backward speed is c/3. The actual speed may not excess c, but, we are unable to prove it yet. The main reason that we are unable to accelerate an object to the speed c should be the limitation of the speed of force. If the speed of force is c, then, a force will not push or pull an object to a speed higher than c, that is reasonable. Isn't it? If a visual speed can excess c we can enjoy the feeling of the speed of light or ultralight when technology advances to certain level.Jh17710 (talk) 04:34, 2 December 2010 (UTC)

... (earlier reply) ... and the point that the text seems to be trying to make appears false to me. For both ball and brick, we infer both distance and depth from past experience, and if we have doubt about our guess, we use parallax to check. The idea of "infinite speed" is also wrong. Have you read our article on Special relativity? Dbfirs 07:41, 30 November 2010 (UTC)

I will read it again. However, what do you think about the recorded event time period may be smaller than the actual event time period when event started and moved closer to the observer? I can derive it in detail.Jh17710 (talk) 05:30, 1 December 2010 (UTC)

I should also note that you're getting close to where fair use may give way to copyright violation, unless you're actually going to discuss bits and pieces of all that stuff in detail. Wnt (talk) 10:44, 30 November 2010 (UTC)

This is my idea. I posted it once early 2008.Jh17710 (talk) 05:30, 1 December 2010 (UTC)

Yes, there is the well-known Doppler effect where both the recorded time period and the frequency are changed by relative motion (as in an approaching emergency vehicle), but the equations are not the same for light as they are for sound (see Relativistic Doppler effect). Dbfirs 08:35, 2 December 2010 (UTC)

is it possible to blow up a planet like in Star Wars?

Lets say there were a really big gun or energy beam aimed at a planet the size of Earth? Could it actually cause the Earth to blow up, or would it just cause earthquakes and cause the rock to melt and things like this? I am not talking about an impact event, this is like something worse than that, like the Death Star, pretty much. But would the laws of phsics allow a planet to EXPLODE? is it even posible? —Preceding unsigned comment added by The Fat Man Who Never Came Back (talk • contribs) 03:42, November 30, 2010

Sure, it's possible in some sense, but not like in Star Wars. All in all, you should realize this planet is basically a lump of metal several thousand miles in diameter, stuff that likes to congregate (gravity) and will not easily be scattered into a gazillion pieces. The energy required to actually blow it up as you describe would be an immense amount.--Rallette (talk) 09:00, 30 November 2010 (UTC)

Someone worked out details on what you'll need to do it here. Have fun! --Sean 14:22, 30 November 2010 (UTC)

Also, the Earth is largely magma already, but supplying enough energy to destroy it would surely melt the rest of it, so it would look more like blowing a raindrop apart than a solid object. Sci-fi shows never seem to get this right. StuRat (talk) 23:50, 30 November 2010 (UTC)

Incidentally, the amount of energy required to vaporize a mass of iron the size of earth is around 3.7x10^31 Joules. That is equal to 9,232 trillion 1 megaton nuclear warheads, or 85 billion years of current human energy consumption. Googlemeister (talk) 16:51, 2 December 2010 (UTC)

What would happen if scientists blew up the moon?

What would be the consequences here on Earth if we blew up the moon? I imagine there would be all sorts of environmental disasters, but would there be any benefits?--The Fat Man Who Never Came Back (talk) 08:44, 30 November 2010 (UTC)

Some of this was discussed at Wikipedia:Reference_desk/Archives/Science/2006_November 7#Blowing up the moon and Wikipedia:Reference_desk/Archives/Science/2007 May 6#Earth's Spin. Wnt (talk) 10:47, 30 November 2010 (UTC)

This is one advantage. Paul (Stansifer) 14:41, 30 November 2010 (UTC)

This is another. ;) --Link ^(t•c•m) 19:47, 30 November 2010 (UTC)

You attribute some pretty impressive powers to these 'scientists'. In any event, the answer depends on what you mean by 'blew up'. If you just fracture it without giving any of the chunks lunar escape velocity, then they'll pretty much settle back into a new Moon. (The surface features won't be the same, obviously, but if the whole system stays gravitationally bound then you'll eventually get a Moon-sized approximately-spherical lump back.) If you manage to compress enough of it into a wee tiny black hole (bigger than CERN LHC-sized, so it won't evaporate immediately) it will eventually all collapse into a stable Moon-massed black hole (see Roger MacBride Allen's The Ring of Charon). In either case, not a whole lot happens on Earth. The former case generates an impressive light show, and the latter case makes it a bit darker at night, but tides won't be appreciably affected and the Earth will carry on essentially unchanged.

If you redistribute the mass of the Moon (as by pulverizing it into a ring in lunar orbit), or remove the Moon and all its mass entirely by some yet to be discovered magical phenomenon (or by virtue of it actually being a camouflaged alien spaceship, see David Weber's Mutineers' Moon) then you have serious effects on Earth. Getting rid of tides (well, most tides — there will still be miniscule tides from the Sun's attraction) will screw over a lot of coastal life. Depending on how quickly you remove or re-adjust the Moon's position, you might also get some serious earthquakes going on, as rapidly removing the Moon's pull on Earth may have the effect of 'twanging' crust.

If you use some unimaginably violent explosion to 'blow up' the Moon in what might be the most conventional picture of such an event, you're very likely to have some Texas-size chunks hit the Earth. When that happens, we have a massive winter, and most life on Earth dies. What benefits did you have in mind? TenOfAllTrades(talk) 14:45, 30 November 2010 (UTC)

Here's a fun article on the subject : The Straight Dope:I plan to destroy the moon. What effect would this have on the earth?

APL (talk) 15:37, 30 November 2010 (UTC)

Related question: does humanity at present time have the capacity to blow the Moon to smithereens? Bus stop (talk) 15:45, 30 November 2010 (UTC)

Certainly not. --Sean 18:51, 30 November 2010 (UTC)

All this and yet nobody mentions the late Alexander Abian. --Anonymous, 23:24 UTC, November 30, 2010.

Can we blow up comets?

A few years ago, we tried and failed to blow up a comet. We shot a missile at it, and it caused an explosion and released a dust cloud, but unfortunately the comet was not destroyed. In the future, if we shoot more powerful projectiles at comets, is it possible to destroy them altogether? What would happen to the galaxy if we eliminated all comets and meteors and asteroids?--The Fat Man Who Never Came Back (talk) 08:48, 30 November 2010 (UTC)

I think you've read the article wrong if you think the Deep Impact space mission was an attempt to destroy a comet. Nil Einne (talk) 10:53, 30 November 2010 (UTC)

If you blow it up, you just seperate a mass into smaller bits of mass. Each of the bits are still comets, just smaller. So nothing would "happen to the galaxy", except it would have smaller comets. --Lgriot (talk) 12:15, 30 November 2010 (UTC)

As has been hinted at above you should read the galaxy article to adjust your mental image of the scale of things.

It sounds like you may have meant solar system instead of 'galaxy'. If so, have a read of the Oort cloud article to get an idea of what sized job ridding the solar system of all comets would be. Blakk and ekka 12:33, 30 November 2010 (UTC)

All the comets in the Solar System make up the mass of about 5 Earths, and less than 1% of the mass of the Solar System as a whole. There's nothing you can do to a comet to have much effect on the Solar System, much less the galaxy. --Sean 14:25, 30 November 2010 (UTC)

First, Deep Impact was not attempting to blow up a comet any more then someone who crashes their car into the side of a mountain is trying to blow up the mountain. Second, the results of destroying a comet would have only the very smallest of effects on the solar system (and even then, only if you used something like antimatter to remove the mass entirely). It is unlikely that such changes would be detectable. On a local scale, if you exploded a comet that transected the earth's orbit, you might have some nice meteor showers in the future, but impacts to the planetary orbits would be essentially unaffected. Googlemeister (talk) 16:41, 2 December 2010 (UTC)

Which organelles contain DNA?

I always thought it was just the nucleus & either mitochondria (in animals) or chloroplasts (in plants). However, I found a passage in Lewis Thomas's "The Lives of a Cell" where he intimates that this property is shared by other organelles too:

Mitochondria are stable and responsible lodgers, and I choose to trust them. But what of the other little animals, similarly established in my cells, sorting and balancing me, clustering me together? My centrioles, basal bodies, and probably a good many other more obscure tiny beings at work inside my cells, each with its own special genome, are as foreign, and as essential, as aphids in anthills.

Is this an inaccuracy? The book was written in 1974. Thanks. AGradman / how the subject page

at 12:19, 30 November 2010 (UTC)

None of these sub-cellular bodies have their own genome. It sounds like Thomas may be putting forward a variation of Endosymbiotic theory. Blakk and ekka 12:49, 30 November 2010 (UTC)

I'm not sure if it was just a poor choice of words or genuine confusion but do note nearly all eukaryotes have mitochondrion, including plants. Nil Einne (talk) 13:53, 30 November 2010 (UTC)

In the case of centrioles, it may have been based on outdated research. From centrosome:

Research in 2006 indicated that centrosomes from Surf clam eggs contain RNA sequences. The sequences identified were found in "few to no" other places in the cell, and do not appear in existing genome databases. One identified RNA sequence contains a putative RNA polymerase, leading to the hypothesis of an RNA based genome within the centrosome. However, subsequent research has shown that centrosome do not contain their own DNA-based genomes. While it was confirmed that RNA molecules associate with centrosomes, the sequences have still been found within the nucleus. Furthermore, centrosomes can form de novo after having been removed (e.g. by laser irradiation) from normal cells.

--Sean 14:29, 30 November 2010 (UTC)

velocity of sound

why does the velocity of sound in water decrease after reaching a maximum velocity at a certain temperature —Preceding unsigned comment added by 41.221.209.6 (talk) 13:46, 30 November 2010 (UTC)

The effect I'm familiar with is that as a function of depth, the sound speed increases after reaching a minimum at a certain depth (which turns out to be temperature-related). Our Speed of sound article shows the effect but doesn't explain it well and explains it briefly. There's a better fuller discussion at DOSITS. In a nutshell: the speed of sound in seawater is proportional to temperature, to pressure, and to depth. Temperature decreases as depth increases, which is why the sound speed initially decreases as you descend below the surface. But then, of course, pressure begins to increase, and so the sound speed goes back up as you go really deep. —Steve Summit (talk) 14:12, 30 November 2010 (UTC), tweaked 14:48, 30 November 2010 (UTC), again 23:58, 30 November 2010 (UTC)

Speed of sound is related to density. Water is densest at 34F, so sound will travel through water fastest at that temperature. Pressure has a minor impact on the speed of sound in seawater, but it is a smaller impact then temperature. Googlemeister (talk) 16:36, 2 December 2010 (UTC)

Daytime flash dreams

Sometimes I tend to experience ultra-short (for about 0,5 sec) unconscious flash dreams while not sleeping, just resting. They look like normal night dreams, but appear even when my eyes are open. Most recently for example I saw a nice red motorcycle with bald biker. Is there a name for such phenomenon? —Preceding unsigned comment added by 89.77.158.172 (talk) 17:01, 30 November 2010 (UTC)

Well, this is not really a medical question and is quite common, so see daytime parahypnagogia--Aspro (talk) 17:09, 30 November 2010 (UTC)

Margarine and oils without saturated fat

Are there any brands or kinds of margarines and oils with little saturated fat? Even the "Light" margarine I have in front of me is over 9% saturated fat. Thanks 92.28.247.40 (talk) 17:26, 30 November 2010 (UTC)

Shortenings like margarine and crisco are just vegetable oil that's been "partially hydrogenated". Saturation is one of the main reasons these things are solid at room temperature. The unsaturated fat is lowers the melting temperature to make vegetable oil a liquid). The lowest saturated-fat content I see on that article's table is canola oil at 7%, and all the solid ones are somewhat higher. DMacks (talk) 17:34, 30 November 2010 (UTC)

In general the more saturated the oil the lower the melting point. So unsaturated oils are liquid at room temperature. However the length of the molecule (called the chain length) also plays a role, the shorter the chain the lower the melting point. As far as health goes just looking at saturated vs unsaturated is not enough, there is plenty of evidence that certain chain lengths are much unhealthier. In general longer chains are less healthy. So you can have an unsaturated, long chain oil that is less healthy that a short chain, but saturated oil. This is the main reason people switched to saturated palm oils, they might be saturated, but their oil has few bad health effects, and some believe actually improve health! In general it's best to eat oils that are commonly found in food. The reason is that the health effects of the oil are directly related to how well the body can "burn" the oil (lipid) for fuel. To burn the lipid requires enzymes, and the body has more enzymes for some types than for others. Another thing, Essential fatty acids (EFA) are the best type of lipid to eat, but they are all liquid and polyunsaturated. A manufacturer has a choice - they can make the margarine with some saturated fat, and a little unsaturated, or they can make it with polyunsaturated and more saturated (the high and low melting points cancel each other out). Which is better? You are getting more saturated fat, but also more EFAs, or less saturated fat, but no EFAs. My feeling is that the version with saturated, but also polyunsaturated is better, but the exact answer on the proper balance requires lots of studies that as far as I know have not been done. A final point is that I think it's better to eat a margarine with a variety of fat types in it, vs. one that is just one kind of lipid - even if you have to eat some saturated fat in the process. Whew, this post was longer than I expected, I hope it helps you. Ariel. (talk) 19:17, 30 November 2010 (UTC)

I cannot see the answer to my question in there, but thanks for trying. 92.28.247.40 (talk) 20:07, 30 November 2010 (UTC)

Basically what he's? saying is 1) It's rather unlikely there are any margarines without saturated oils. 2) If your concerned about health, just avoiding all saturated fats likely isn't the way to go (technically you didn't ask about this but given your question I don't think it was an unresonable response). Note that considering no 2 even if someone could make an oil without saturated fats, it's not likely they would. According to [30] one of the lowest saturated fat oils is enova brand but um [31]... In any case it sounds like weird stuff [32] P.S. It's also possible Ariel missed your point about oils at first since you referred to the saturated fat content in margarine rather then oils. I did. Nil Einne (talk) 20:30, 30 November 2010 (UTC)

One point is that the people who first made margarine wanted it to resemble butter, but it was a white liquid, not a yellow solid, so they added coloring and saturated fats (or the even worse trans-fats). Now that we know how unhealthy it is to solidify the margarine (which pretty much also will solidify in your veins), perhaps we should re-evaluate our need for it to be solid. You can get a squirt bottle of liquid margarine, and that sounds fine to me. You can probably butter your toast even quicker that way. StuRat (talk) 00:20, 1 December 2010 (UTC)

I think it's important to bear in mind two things. First is that triglycerides and other lipids are a heterogeneous collection of compounds, with many individual variations of molecular structure, any and all of which may be significant. Each lipid chain of the triglyceride has a varying length and a variable pattern of double bonds. Things like omega-3 fatty acids, omega-6 fatty acids, conjugated linoleic acid, arachidonic acid, eicosapentanoic acid and so on all have their own special purposes and effects. They are not merely "fuel", but form the cell membrane, modify proteins, and are used to make potent signalling molecules like prostaglandins, ceramide, sphingolipids .... it's a whole branch of biochemistry.

The other thing to bear in mind is that partially hydrogenated vegetable oil is not a natural fat, but a crude chemical mock-up of an animal fat in which the precise chemical components have been randomized. It's well known that trans fats have little place in normal biology, but there could be other random alterations.

What I would draw from this is that one should be very conservative regarding lipid sources, choosing sources with a long history of use like olive oil over those which someone has just started pressing out of a new plant, or worse, which have been created chemically. Wnt (talk) 11:04, 1 December 2010 (UTC)

It comes from a plant in either case, whether a biologic plant or a chemical plant. :-) StuRat (talk) 23:21, 1 December 2010 (UTC)

Bioluminescence

hi, Today I saw (in a video) a creature which made a Bioluminescence. It looked like fireworks. the liquid which he spitted (it was a marine animmal) had glown for 3 seconds,and then turn-off. and then, like a lightning it glew powerfully. does anyone know what that sea animmal's name? 84.228.119.63 (talk) —Preceding undated comment added 17:51, 30 November 2010 (UTC).

Well. There is this one, and as ever, Wikipedia has an article on it:Heterocarpus--Aspro (talk) 19:41, 30 November 2010 (UTC)

We also have Bioluminescence of course which lists a bunch of animals Nil Einne (talk) 21:32, 30 November 2010 (UTC)

The article on Heterocarpus however, features a shrimp which spits streams of blue luminous secretions and thus directly address the OP's question, which Bioluminescence does not. Otherwise, I would have provided that link. Which I did not, because it didn't. Yet, Heterocarpus links to any way -if you had read it!--Aspro (talk) 23:31, 30 November 2010 (UTC)

Apologies I misread the OPs question as being about which when splited grew for 3 seconds which I thought could easily apply to many animals showing bioluminescence. However I still believe the link was helpful as it teaches the OP that we also have an article on general concepts such as this, which list animals which show the concept so they may be more aware they can look themselves in the future (although unfortunately in this case the bioluminescence article doesn't seem to list Heterocarpus either directly or indirectly). While it's true (and expected) the article links to the concept, it may not occur to the OP to click on it.

Also, while it seems most likely your answer is what the OP is referring to, and this is not a field I know much about, I wonder if it's really the only possible correct answer as your second response seems to imply. As I understand the Vampyroteuthis infernalis article (which is linked from bioluminescence) they release a 'bioluminescent mucus containing innumerable orbs of blue light' (our article actually refers to fireworks although that may be a common description for bioluminescence). This may not be really liquid, although it's not clear how precise that term was meant (did the OP actually see the liquid, did they just see it in water and it looked like liquid?). (There may also be debate about whether spit is accurate for what the vampire squid does although again it seems possible the OP is using the term loosely.) Even less likely but perhaps still worth mentioning, our article says Antarctic krill spits out biolumiscent phytoplankton. If it is possible the OP is referring to something else, it seems to me there's even more merit to the general link

Nil Einne (talk)

P.S. [33] claims there's also planktonic protozoans that spit bioluminescent 'stuff' but unfortunately I've been unable to find what they're referring to from quite a few searches. Planktonic protozoans sounds unlikely to be thought of as marine animals, but who knows I guess. Nil Einne (talk) 12:55, 1 December 2010 (UTC)

P.P.S. From what I can tell, we don't have any real videos of Vampyroteuthis infernalis releasing their bioluminescent liquid (some simulations are all I could find), perhaps not surprising given the depth they live in, so it seems unlikely this is what the OP saw. (Planet Earth did have video of it using its photophores.) Nil Einne (talk) 12:55, 1 December 2010 (UTC)

Aggression, dementia, disinhibition

1) Some elderly people seem to be habitually hostile - are there any other things apart from dementia that cause this aggression in some elderly? 2) Does having dementia make people disinhibited? Thanks 92.28.247.40 (talk) 18:00, 30 November 2010 (UTC)

When any disease or injury effects the normal functioning of the pre-frontal cortex and especially when executive functions with in them are effected, it can result in more aggressive behaviour and/or dis-inhibition than would normally expected. Dementia does not always lead to more aggression but is more common than not. --Aspro (talk) 18:21, 30 November 2010 (UTC)

Ok, so aggression is a common result of dementia, but does being aggressive and elderly suggest dementia? Thanks. 92.28.247.40 (talk) 22:18, 30 November 2010 (UTC)

On its own - no. In combination with other things - maybe. Try the alzheimers-research.org.uk website for some more information. --Tagishsimon (talk) 22:22, 30 November 2010 (UTC)

Wouldn't hurt to check for it, but some old people can just be mean ol' bastards. HalfShadow 22:25, 30 November 2010 (UTC)

I seem to recall reading an article on social inhibitions, which claimed they were maximised in teenagers/young adults, and gradually decreased after that. This would suggest that elderly people in general are going to be less inhibited than other adults, regardless of whether they have dementia. Does anyone know more about this, or know where to find a referenced discussion? 86.161.108.241 (talk) 14:10, 1 December 2010 (UTC)

Being elderly and aggressive may suggest the effects of jading and nothing more. I wouldn't suggest that Grumpy Old Men have to have a medical reason for being that way when conditioning explains it quite well.
⋙–Berean–Hunter—► ((⊕)) 17:22, 2 December 2010 (UTC)

Why must some truffles be found and not grown?

This MSNBC article says that Piedmont white truffles cost around US$3,000 per pound because of low supply, and also claims "this is one food that can’t be formulated in a lab or grown in a greenhouse." Why? By now there must have been attempts to farm these truffles in order to try to cash in on this. What were the results? Comet Tuttle (talk) 19:02, 30 November 2010 (UTC)

That is a misleading statement. Truffle farms are, essentially, tree farms. It takes about 30 years to grow the trees (and the truffles). So, that statement could be true of any large tree. For example, you could claim that Christmas Trees are the one decoration that can't be formulated in a lab or grown in a greenhouse. What you actually mean is that the tree is big. You need a lot of room. So, for a lot of trees, you'd need an enormous greenhouse. Obviously, you'd use a field instead - which is what truffle farms use, large fields. -- kainaw™ 19:09, 30 November 2010 (UTC)

(after e/c)

Truffles grow on the roots of Oak trees. Perhaps they simply mean that truffles need vast orchards to cultivate, even though the truffles themselves are rather small? (Literally, adult oak trees are unlikely to grow in either a lab or all but the largest greenhouses.) APL (talk) 19:11, 30 November 2010 (UTC)

I see; thank you. I had jumped to the conclusion that finding truffles was a hunter/gatherer task and a crapshoot, rather than an organized and planned farming process. Comet Tuttle (talk) 19:26, 30 November 2010 (UTC)

Note that unsurprisingly our article has a section on cultivation Truffle (fungus)#Cultivation Nil Einne (talk) 20:34, 30 November 2010 (UTC)

The section is disappointingly sparse regarding information on which type of truffle is/has been cultivated. My understanding is that while black truffles are amenable to directed cultivation, white truffles are more recalcitrant. It isn't simply a matter of "plant tree->gather truffles". Not every tree of a host species will produce truffles, even if it's in a truffle producing area. We don't yet know exactly what the truffle is looking for in growing conditions. That's why it's said that (certain) truffles can't be cultivated. You can plant a bunch of host trees to increase the chance of getting truffles, but there's no guarantee that when they mature you'll be producing any significant amount of truffles from them. -- 140.142.20.229 (talk) 02:06, 1 December 2010 (UTC)

And it's not just getting them to grow on a tree's roots, but getting them to fruit and catching them when they do so. --Sean 16:02, 1 December 2010 (UTC)

December 1

NGC identification in Veil Nebula

The Veil Nebula in Cygnus comprises several NGC/IC items: 6960 (the Witch's Broom), 6992/6995/IC1340 (Eastern Veil), 6974 (faint patch near north boundary) -- and the one I'm asking about: NGC 6979. This is frequently associated with Pickering's Triangle (see, e.g. Astronomy magazine, or indeed Google search for Pickering+triangle+"NGC+6979"), but the coords usually given for 6979 (and displayed in Uranometria) appear to be closer to 6974 -- and Pickering's Triangle was reputedly discovered only photographically, in the early 1900s. So the question is: is NGC 6979 really Pickering's Triangle, and is there a clear, definitive reference for the identity? -- Elphion (talk) 01:43, 1 December 2010 (UTC)

I should add, our own article on the Veil Nebula -- the one I've been working on -- is not yet "definitive" :-) -- Elphion (talk) 01:46, 1 December 2010 (UTC)

I think I've found a reasonable definitive source: the NGC/IC Project (under NGC 1979) makes it clear that although Herschel's original position was none too precise, it referred not to Pickering's Triangle but to another knot of nebulosity. -- Elphion (talk) 21:33, 1 December 2010 (UTC)

Plastic-mirror

Can someone please tell if there's a material bendable and reflects (something like a plastic-mirror). If so, could you leave the name and the link in wikipedia (if exists).

Thank You. PD: sorry for my english, not my first language. —Preceding unsigned comment added by 190.218.125.158 (talk) 02:21, 1 December 2010 (UTC)

You can get stainless steel mirror sheets down to fractions of a millimeter that would be quite bendable. Something like this. Vespine (talk) 02:34, 1 December 2010 (UTC)

Also, aluminized mylar (we'll see if that comes up blue). --Trovatore (talk) 02:49, 1 December 2010 (UTC)

See also deformable mirror. --Mr.98 (talk) 03:21, 1 December 2010 (UTC)

Thank you, learned a lot. Is there anything solid that reflects exactly like a mirror? —Preceding unsigned comment added by 190.218.125.158 (talk) 04:14, 1 December 2010 (UTC)

I don't quite understand; if it's solid, and reflects like a mirror, then it is a mirror, right ? StuRat (talk) 05:25, 1 December 2010 (UTC)

The 3 mm stainless steel mirror sheets in the link above would be quite stiff, if that's what you mean by "solid". Or the 0.8 mm mirror sheets would be more bendable, but still much stiffer than aluminized mylar. Or were you looking for something like a curved mirror, which is bent but very stiff? Red Act (talk) 05:45, 1 December 2010 (UTC)

haha sorry :P . What i meant was something like silly putty —Preceding unsigned comment added by 190.218.125.158 (talk) 09:15, 1 December 2010 (UTC)

I don't think anything like putty could ever work as a mirror, because you need a even surface to make a recognizable reflection. A random blob would reflect light in all directions, and not make a clear image. StuRat (talk) 23:17, 1 December 2010 (UTC)

Silly Putty is actually a viscoelastic fluid, a type of non-Newtonian fluid, rather than being a (Hookean) solid. Specular fluids certainly exist; liquid mercury comes to mind, or even water at a grazing angle. And Silly Putty itself exhibits some specular reflection, in addition to diffuse reflection. But I'm having no luck trying to find a viscoelastic fluid that's highly specular in the visible spectrum. Red Act (talk) 00:50, 2 December 2010 (UTC)

What does the OP want to use it for? If they want to cast a mirrored shape, then an epoxy (or other casting resin) which contains a metal filler, can be rubbed with wire wool and buffed up to a mirror like shine. Resins and putties are available with a choice of several different fillers. Alternatively, coat the object with conductive paint, dry, then electroplate with chrome, etc. --Aspro (talk) 16:55, 2 December 2010 (UTC)

Laser distance meters

Are there any laser distance meters that are more-or-less equivalent to a Leica Disto (particularly in the sense of "having a range of at least 70 m"), but, rather than being hand-held units, come in the form of (essentially) a circuit board with a laser attached to it? That is to say, I'm looking for something programmable, intended for remote use, and long-range. --superioridad ^(discusión) 02:59, 1 December 2010 (UTC)

What does the OP want to use it for? Are you thinking of something along these lines. Laser scanner--Aspro (talk) 17:02, 2 December 2010 (UTC)

Global Warming and Ice Age

In The Day After Tomorrow, global warming caused an Ice Age. Could this really possibly happen in real life? —Preceding unsigned comment added by 202.168.107.2 (talk) 03:11, 1 December 2010 (UTC)

Global warming is a misnomer; the preferred term is "climate change", since what happens as a result of increased greenhouse gases is more nuanced than simply "the earth gets hotter". What is much more likely to happen is actually greater swings in climatic changes rather than simply a gradual increase in temperatures; one could envision decades or centuries that were markedly hotter OR colder than the current "normal" temperatures. The problem faced with anthropogenic climate change is not that it is predicted to make everything uniformly warmer; if it were that simple then it would be easier to design a fix; the earth is not merely going to get warmer on a regimented schedule. What is predicted to happen is an increasing unpredictability in climate; so there is no way to prepare for rapid and large changes. One of the problems with popular media when dealing with these problems is that there is a misinterpretation of these predictions. What most mainstream scientists who work in the area agree on is "We know climate is going to change in unpredictable ways", which gets misinterpreted as "We can't predict how climate will change" which gets further assumed to mean "We can't predict anything". You may also want to check out Snowball Earth for a past event with similar implication. --Jayron32 03:55, 1 December 2010 (UTC)

The movie is based on a genuine possibility but is vastly exaggerated. The climate of Europe is much warmer than it ought to be given its latitude, mainly because the Gulf Stream carries large amounts of heat there from the tropics. The Gulf Stream is ultimately driven by the sinking of cold salty water in the Arctic and North Atlantic, as part of the thermohaline circulation. There is a significant possibility that global warming, by eliminating Arctic ice, could cause the sinking of cold water to stop, thereby stopping the Gulf Stream and greatly chilling the climate of Europe. Such an interruption is thought to have happened during a cold period called the Younger Dryas, over 10,000 years ago, as a result of a sudden massive influx of fresh water into the North Atlantic. Even if it did happen, though, there is no way it could be anywhere near as rapid and dramatic as shown in the movie (as I've heard; I haven't seen it). Furthermore, the main effects would be on Europe, with lesser effects on North America. Looie496 (talk) 04:05, 1 December 2010 (UTC)

For comparison, the abrupt climate change at the beginning of the Younger Dryas took place over the course of several years, as opposed to drastic climate change occurring over the course of several days in the movie. Red Act (talk) 06:23, 1 December 2010 (UTC)

If you're in Britain at the moment, it feels like it's happening right now. Ghmyrtle (talk) 07:43, 1 December 2010 (UTC)

Wow snow in winter. Who would have guessed? Googlemeister (talk) 16:27, 2 December 2010 (UTC)

Snow in late autumn in southern England: actually surprising. 86.161.108.241 (talk) 17:14, 2 December 2010 (UTC)

You mean this southern England? Googlemeister (talk) 19:43, 2 December 2010 (UTC)

• 
  The Frozen Thames, Unknown 1677.
• 
  Thames Frost Fair, Thomas Wyke 1683.
• 
  Frost Fair of 1814, Luke Clennell 1814.

Yes, but a bit before my time old chap ;-) [34] Alansplodge (talk) 23:46, 2 December 2010 (UTC)

Cats and chocolate

Is it true that cats can die if they eat chocolate? Or is it just a myth? The Utahraptor^Talk/_Contribs 03:52, 1 December 2010 (UTC)

Absoltely, 100% true. See Theobromine poisoning. You can get poisoned by chocolate too; its just that YOU have to eat a lot more than the cat. Whereas you, based on weight, would probably have to eat several pounds of chocolate to get sick, cats can have nasty effects from a single Hershey bar. Cats and dogs also metabolize chocolate differently, so on a per-pound basis chocolate is also much more poisonous to them than to us. --Jayron32 03:57, 1 December 2010 (UTC)

I think a single pound of chocolate would make you pretty sick. Might not be from the theobromine. Just the same, the danger to cats and dogs is sometimes overstated a bit, I think. If you look up the LD50's by weight, they're not what you would call casual exposure.

If I recall correctly, cats are a bit more sensitive than dogs, but tend not to be interested in chocolate, because they don't have taste receptors for sweet. I imagine they'd have to be really hungry. Dogs occasionally do get poisoned, but if the numbers in the article the last time I looked at it are accurate, they do have to eat quite a lot. --Trovatore (talk) 04:12, 1 December 2010 (UTC)

It's probably better, however, to avoid feeding chocolate to pets. The toxicity level for theobromine is going to vary widely from pet to pet, given especially that a Chihuahua would get much sicker than a great dane eating the same chocolate bar. It's one of those things where, year, maybe your dog or cat would be fine, but it's not worth the risk. Just because someone can sprint accross a busy freeway and not get hit doesn't mean it isn't contraindicated to do so. Likewise, just because it may be possible to feed your pet chocolate and, by dumb luck, not end up with any ill effects doesn't mean its a good idea to do so. --Jayron32 05:52, 1 December 2010 (UTC)

Oh, I wasn't even considering the possibility of actively feeding them chocolate. Why would you do that?

I just mean that if you happen to drop the lemon creme from your box of See's and your German Shepard gets to it before you do, it's probably not worth bothering the emergency line at the vet. --Trovatore (talk) 09:58, 1 December 2010 (UTC)

That little black strap that depends from the backs of cars and scrapes along the road?

I'm seeing fewer of them these days (I'm in Australia) - but can anyone tell me what they're meant to be for, and what they're called?

Thanks Adambrowne666 (talk) 04:57, 1 December 2010 (UTC)

If they are at the sides, they could be curb feelers. I suspect that backup cameras are replacing them as the high-end option to let you know how you are doing backing up.

However, those really aren't meant to drag on the road. I can't think of anything that is, although theoretically they could use such a device to measure road friction and change shift points, etc., depending on how slippery the road is. I've not actually heard of this being done, though. One obvious problem would be that anything dragging on the road like that would quickly wear out. This could be handled by replacing the wearable portion, which just might be a cheap piece of plastic, but it would still be annoying to have to do this so often. Perhaps a system like a weed wacker could be used to automatically deploy the plastic string to the proper length from a large roll. The current traction-control system I am aware of detects slippage in the wheels and adjusts accordingly, but being able to prevent such slippage with proactive measures is certainly preferable to adjusting for it after it has happened. StuRat (talk) 05:10, 1 December 2010 (UTC)

Aren't they antistatic ground straps or something like that ? Not sure whether there is an article about them. Sean.hoyland - talk 05:16, 1 December 2010 (UTC)

List of auto parts has a link to ground strap but it redirects to a more general coverage of the topic. Sean.hoyland - talk 05:21, 1 December 2010 (UTC)

Cool idea StuRat, but no, those things are grounding (earthing) straps, to avoid static shock. [35][36][37] I personally have never gotten a shock from a car (at least not that I can remember), but it's possible that in dry, slightly dusty areas it could be a bigger problem. The last link I posted seems to indicate people are buying them as snake oil. They are obviously much more important in vehicles that are carrying lots of flammables, like gas trucks. Ariel. (talk) 06:56, 1 December 2010 (UTC)

Yes, the rubber in the neumatics isolates the car from the ground. I occasionally get static shocks when entering a car.

These straps have a very small side issue, they can make you the target of rays. When you are isolated, the charges in the ground won't reach you during a storm. But the strap connects you to the ground, and the charges in the ground can climb up your car and attract a ray, the same way as trees and housetops. --Enric Naval (talk) 07:52, 1 December 2010 (UTC)

I think you mean "lightning", not "rays" (or is this a national variant I'm unfamiliar with? "Lightning ray" seems to strike a chord...but given the many Manta rays and X-rays and gamma rays and orbital laser platform microwave rays, all of which can target you, it's probably better to be specific). I also think you are wrong. What keeps you safe in a car during a thunderstorm is not the isolation of the cars body from the ground (if it's raining, the water will conduct electricity, anyways), but the fact that the car is a Faraday's cage, and will conduct the electric charge from a lightning bolt into the ground on the outside of the vehicle. --Stephan Schulz (talk) 08:21, 1 December 2010 (UTC)

Yeah, I meant lightning, it's just my bad English. Yes, the vehicle will protect you... but make sure you don't touch any metal surface. Especially, don't touch the metal surface at two different places, since part of the current might decide to travel through your body instead of travelling through the metal. The car is not a perfect faraday cage since it's not a closed metal surface (there are openings in the cage, and part of the current could travel through the inside surface of the car chassis, depending on the shape and position of the holes).

I repeat that having a ground strap increases the chance of your car being hit by lighting. But I recognize that I don't know much the risk is increased. Maybe it's just increased by a tiny amount. I understand that car tires and not 100% rubber, they have conducting materials in their composition that make them resistors rather than insulators. A lighting has so much voltage that the little ground strap might not make much of a difference. Unfortunately, I can't find any definitive source on this topic. --Enric Naval (talk) 18:43, 1 December 2010 (UTC)

I don't think this is true. Lighting has enough potential that it can travel through several miles of air - the tiny bit of rubber in your tires makes no difference to it whatsoever. Adding a grounding strap doesn't change anything. Ariel. (talk) 20:08, 1 December 2010 (UTC)

Regardless of how far it has gone, most of it will still take the path of least resistance, or lightning rods would be useless. StuRat (talk) 23:14, 1 December 2010 (UTC)

They are frequently marketed, not as anti-shock devices, but as anti-motion-sickness devices. The science behind this seems a little fuzzy to me, but the idea is that the small build up of static electricity that naturally occurs in a car contributes to the sense of motion sickness in sensitive people. By releasing this static to the ground, people who are sensitive to motion sickness are supposed to feel more comfortable. While the ones for cars look like strips of plastic or cloth, larger vehicles sometimes use chains. My wife and daughter get terribly motion sick, so we tried them. There seemed to be a benefit, but it could well be chalked up to expectations of it working than anything "real". Matt Deres (talk) 14:52, 1 December 2010 (UTC)

Yes, I've seen them marketed as anti car-sickness devices. I think they work on the Tinkerbell principle. They certainly don't prevent static shocks when entering or alighting from cars in my experience. DuncanHill (talk) 15:29, 1 December 2010 (UTC)

Re: static buildup: In many years of driving, I only had one car which produced a big static buildup. It was a little compact car, and I learned to touch metal on the car as I stepped onto the ground to discharge it; otherwise if I touched it later there would be an easily felt spark. This also presented an explosion hazard when fueling it, if a spark had occurred. I expect the tires were of a composition which was less conductive than typically, and had not yet gained a coating of dirt. A piece of conductive plastic, perhaps carbon fiber filled, would easily drain off such static charge, or perhaps an anti-static conductive sprays could be applied to the tires to conduct from the metal wheel to the ground. The parallel combination of the conductive path of the four tires might not be as good an insulator as some people assume, since the rubber quickly gets covered with conductive grime, especially when damp, as in a typical lightning storm. Edison (talk) 17:03, 1 December 2010 (UTC)

Thanks heaps everyone - but what are they called? Adambrowne666 (talk) 22:16, 2 December 2010 (UTC) -- actually, from googling, it looks like they're just called antistatic straps - bit disappointing - more a description than a name...

bladder-caused sleep interruption

I just spent 90 minutes, equally divided between Wikipedia and a Medical Advice Encyclopedia, trying to determine HOW LONG IT TAKES for water to become urine stored in the bladder!

NO ANSWER FROM EITHER!

The information is simple and would be extremely useful to many of us who use your service to AVOID getting lost in the thickets of hyper-information (the disease many information providers suffer from) and hypochondria.

How long before hs (hour of sleep) should an otherwise healthy adult or child avoid ingesting liquids as a simple preventative to avoid an over-full bladder demanding attention!

This is extremely useful consumer advice, and SHOULD be simply and easily found in ANY discussion of physiology, bladdders, urine, or piss (pre-13th Century use). —Preceding unsigned comment added by 63.193.182.226 (talk) 08:24, 1 December 2010 (UTC)

Like so many simple questions this one does not have a simple answer that covers all eventualities. I have no source to point you at but my experience indicates that it can be somewhere between 30 and 45 minutes for ingested liquid to be excreted as urine in 'normal' circumstances. however there are a number of other factors that will affect this timing or the need to void urine. The age of the individual is a significant factor in determining the need for nocturnal voiding. More older people tend to have a reduced bladder capacity which is stimulated by smaller amounts of urine. A lot of food we eat contains water and this is likely to be extracted, processed and excreted over a longer time than my experience of 30 - 45 minutes. The activity of the kidneys is regulated to some degree by the individual's circadian rhythm which may reduce urine production during the night but start again at around dawn (or so). This widespread problem is not easily remedied and may be something that individuals have to accept as a consequence of ageing. And please, no-one come back to me on ageism - 'cos I am one of the aged! Richard Avery (talk) 08:51, 1 December 2010 (UTC)

63.193 you seem angry that the web is not up to your expectations. We are really sorry about that. I assure we will try to improve the web in order to avoid that you get angry again. --Lgriot (talk) 10:04, 1 December 2010 (UTC)

The IP may be referring to last night's episode of QI XL in the UK, in which it was claimed that if they needed to get up early, American Indians would drink a lot of water before they went to sleep, so that they would have to get up early to urinate.--Shantavira|^{feed me} 10:07, 1 December 2010 (UTC)

Beer is much more efficient than water for that - but then, you can't get a good pint in America, or a good cup of tea either, so I suppose it's fair enough to make do with water. DuncanHill (talk) 15:32, 1 December 2010 (UTC)

This is also handed down as Vietnam War lore: the person who was to take over the watch duties while a patrol was sacked out would drink a lot of water when he went to sleep, so he would wake up a couple of hours later. Also, anecdotally, parents of little bedwetters have been known to restrict the childrens' intake of fluids an hour before bedtime. Also anecdotally, an ageing male's bladder inevitably needs emptying in the middle of an 8 hour sleep period, even if there are no fluids in the hour before bedtime. Ageing females seem to do better on that count. Edison (talk) 16:53, 1 December 2010 (UTC)

Old men tend to have enlarged prostates, which limits bladder capacity. Also, drooling, sweating and respiration are other ways the body loses water at night, with the last two varying with temperature and humidity. StuRat (talk) 23:30, 1 December 2010 (UTC)

Part of the difficulty with this question is that water does not go straight from the stomach to the bladder. water is absorbed into the blood stream from the intestines (at a rate governed in part by the body's need for water - it's an osmotic action). once in the bloodstream it is governed by other hormonal and chemical regulatory processes. once it passes through the kidneys and begins accumulating in the bladder, awareness of it will vary from person to person. remember that the body is mostly water - unless you drink a lot of water you are not significantly changing the quantity of water in the system, and so the body will not feel any great haste to expel it. --Ludwigs2 16:37, 1 December 2010 (UTC)

The Reference Desks usually have a turnaround of several hours up to several days. Adjusting your expectations accordingly will reduce your frustration. --Sean 18:06, 1 December 2010 (UTC)

I think the 90 minutes on Wikipedia and the MAE was before coming to the reference desk. Red Act (talk) 20:30, 1 December 2010 (UTC)

There is such a thing as a Medical Advice Encyclopedia? It's the antimatter to the Wikipedia Reference Desk! Kill it with fire! Comet Tuttle (talk) 21:55, 1 December 2010 (UTC)

white poop

In an early episode of Life on Mars, Sam Tyler (shifted from 2006 to 1973) remarks, "White dog shit – that takes me back." Me too; I don't remember seeing it since 1965 (when I moved from Chicago to Pasadena). What changed? —Tamfang (talk) 09:47, 1 December 2010 (UTC)

No idea if it's the same reason but the dog poop in my yard turns white after it dries out. I noticed the difference once we switched our dogs over to a raw chicken diet. So, maybe commercial dog food became more prevalent around 1965? Dismas|^(talk) 10:01, 1 December 2010 (UTC)

(e/c) Dog food contains much less bone meal than it used to. That used to get excreted as calcium carbonate. There are multiple discussion posts all over the place about this, such as here. Ghmyrtle (talk) 10:02, 1 December 2010 (UTC)

I'm sure this has been asked on the RefDesks before - but I haven't been able to find the thread. Anyone else remember it? DuncanHill (talk) 15:38, 1 December 2010 (UTC)

I've only seen a lot of white poop after a snow has cleared. I assume it's either something being leached out or something to do with the poop being preserved longer than usual. At any rate, perhaps the Chicago->Pasadena move would account for the change in frequency? Ask your friends back home to take a white shit census! --Sean 16:08, 1 December 2010 (UTC)

My understanding is it's due to the reduction in tripe in dog diets.--DeKay01 (talk) 20:44, 1 December 2010 (UTC)

In The London Labour and the London Poor (a factual description of the poorest people in London in the 1840s), the lowliest occupation belongs to an old lady who is a "Dog Dung Collector" or "pure finder". She made her meagre living by picking up white dog droppings and selling them to the tanneries, who used them to treat leather somehow. She'd be out of a job now! Alansplodge (talk) 23:39, 2 December 2010 (UTC)

Bismuth reaction with acid

Does bismuth or its oxide react with any acid? Chemicalinterest (talk) 14:36, 1 December 2010 (UTC)

Yes. See the "Reactions with acids" section of this page. Red Act (talk)

I added the data from the page to the bismuth article. --Chemicalinterest (talk) 19:05, 1 December 2010 (UTC)

Drinking seawater

In the most typical case, it would kill you. But does that hold true for any ocean? The salinity of the oceans vary, so if it kills you in the dead sea, it doesn't mean that it also kills you in the Antarctic. Quest09 (talk) 17:38, 1 December 2010 (UTC)

We have an article about this. Drinking small amounts of seawater is not harmful, drinking large amounts can be. Exactly how much is "bad" will depend on the composition of the seawater and the person doing the drinking (including their hydration status, environment, level of exertion, any chronic health conditions, medications, etc). So, the direct answer to your question is almost certainly that any ocean's water can be harmful. A precise answer to the follow-on questions (how much of each would be) depends on many factors. -- Scray (talk) 18:06, 1 December 2010 (UTC)

The most interesting thing about that article is the revelation that simply eating fish will probably supply all or most of the water you need. Along with the apparent fact that consuming small amounts of seawater along with fish is minimally damaging. That's assuming the water itself is germ-free, which would be another story. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:25, 2 December 2010 (UTC)

(EC)Our Southern Ocean article, unhelpfully, does not provide information on its salinity. Ocean tells us that "Average oceanic salinity is around 35 parts per thousand (ppt) (3.5%), and nearly all seawater has a salinity in the range of 30 to 38 ppt" and elsewhere reminds us that there are localised variations, especially at river mouths and, presumably, ice melts. I think we can take it as a general rule that salinity will tend to be 3% or greater, and thus consumption is ill advised. --Tagishsimon (talk) 18:09, 1 December 2010 (UTC)

More than ill advised, I'll say it is lethal in any situation - Dead Sea or Southern Ocean. Drinking water has a upper limit of 1,000 ppt salinity. Much less than the less salty ocean. Mr.K. (talk) 18:17, 1 December 2010 (UTC)

Err, isn't 1,000 ppt salinity pure salt? Matt Deres (talk) 18:24, 1 December 2010 (UTC)

• Sorry, I meant 1,000 ppm instead of the typical 35,000 ppm that you normally find in seawater. Mr.K. (talk) 18:40, 1 December 2010 (UTC)

Depending on your definition of "Ocean". If you include the Dead Sea (which is unusual ;-), you should also include the Baltic Sea. The Baltic surface water is 4-5 times less salty than the average ocean water, and the northernmost reaches of the Gulf of Bothnia are basically fresh. --Stephan Schulz (talk) 18:34, 1 December 2010 (UTC)

This information shows it is all the more remarkable that one group of mammals, the marine mammals, live in or on the sea, have no access to fresh water and yet they survive and have done for millions of years. Does Wikipedia have some information about how these remarkable creatures satisfy their need for fresh water in an environment that consists entirely of salt water? Dolphin (t) 11:44, 2 December 2010 (UTC)

• You should know that better than us, Dolphin.Mr.K. (talk) 16:14, 2 December 2010 (UTC)

I was going to suggest salt glands, but it would appear from the article that marine mammals don't have these (there's no mention of them, anyway). Maybe evolution has made their kidney much more tolerant of salt than ours? --Kurt Shaped Box (talk) 11:59, 2 December 2010 (UTC)

The problem with drinking seawater is not that it will damage our kidneys. Your kidneys won't be able to excrete it and the concentration of sodium chloride in your blood will increase to a dangerous level. Sea mammals, on the other side, have kidneys adapted to their environment. See: "In making the change from terrestrial to aquatic living, cetaceans needed a way to accommodate for the higher salinity of their environment. Unlike human kidneys, which are just two singular renules (or balls), dolphins have two kidneys with multiple renules. These renules all function as separate kidneys which help filter out the higher amount of salt content they must deal with in their daily environment." From [38].Mr.K. (talk) 16:12, 2 December 2010 (UTC)

Our article on Sea Otters makes mention of the creatures large kidneys for the purpose of removing excess salt. Googlemeister (talk) 16:22, 2 December 2010 (UTC)

Not sure if the articles on marine mammals mention this or not, but marine mammals generally don't drink (to the point where frequent drinking is recognized as a symptom of illnesses including kidney damage.) They get their water from eating - fish, cephalopods, other mammals, rather than from drinking salt water directly. They still likely take in some amount of seawater just by being there. 173.11.110.109 (talk) 00:55, 3 December 2010 (UTC)

NASA astrobiology news

What astrobiology news from NASA await us tomorrow? --Mortense (talk) 19:02, 1 December 2010 (UTC)

We shall see tomorrow. Before that the reference desk is unlikely to provide you with solid information. For Internet denizens' speculation, you might enjoy a Slashdot discussion on the subject. 88.112.56.9 (talk) 19:06, 1 December 2010 (UTC)

Slashdot'ters are notoriously ignorant about astronomy subjects. --Mortense (talk) 19:16, 1 December 2010 (UTC)

How about the official-sounding MEDIA ADVISORY : M10-167 that was posted on NASA's homepage, announcing "NASA will hold a news conference at 2 p.m. EST on Thursday, Dec. 2, to discuss an astrobiology finding that will impact the search for evidence of extraterrestrial life." As has been pointed out, we will know tomorrow after they hold their conference. Nimur (talk) 19:21, 1 December 2010 (UTC)

Oddly, I'm pretty sure I do in fact know the answer, since my girlfriend accompanied Felisa Wolfe-Simon on her most recent trip to Mono Lake. Without giving anything much away, you can get an idea about the topic area by looking up Dr. Wolfe-Simon's prior work. Dragons flight (talk) 19:21, 1 December 2010 (UTC)

Feel free to give at least a little away. Where would these arsenic based life forms most likely be found outside earth? Beach drifter (talk) 20:12, 1 December 2010 (UTC)

I don't think that they'll have located anywhere in particular that it's more likely to find life. Nobody at present is really sure just how likely abiogenisis is and there's a school of thought that maintains that it's extremely unlikely. If they really have found a new organism that they can place right at the root of the phylogenetic tree it'll mean that life may have started twice, independently, here on Earth. That would make one of the inputs to the Drake equation slightly less of a guess. Blakk and ekka 22:15, 1 December 2010 (UTC)

It could be anything on a scale from interesting extremophile to second Abiogenesis. I saw Paul Davies talking about this a couple of times earlier this year and, if it's as promising as he seemed to think it was, it'll be very interesting indeed. 86.26.8.192 (talk) 21:58, 1 December 2010 (UTC)(edit Blakk and ekka 22:01, 1 December 2010 (UTC))

The news shall be: We have found such-and-such a chemical at such-and-such a location up in the outer space area above us in the sky. Comet Tuttle (talk) 21:54, 1 December 2010 (UTC)

Funny. I was asked to look at that astrobiology news and if we should aim for certain organometalics for the MOMA instrument on Exomars. The arsenic life forms (producing C-As bonds) I find them in the ocean, for example lobsters, the acumulate arsenobetaine in large quantities. The other group is mold they get ride of arsenic by converting it to trimethyarsin and then they let it go with the wind. So even here arsenic is a notable part of biochemistry.--Stone (talk) 22:14, 1 December 2010 (UTC)

Today some speculations came up that a arsenic based DNA was found. This would be one of the big stories every biologist would like to be involved.--Stone (talk) 16:54, 2 December 2010 (UTC)

Heres the News release. It is indeed a bacteria that can incorperate arsenic instead of phosphorus in itself. Unfortunately, it does not indicate a second abiogenisis; the bacteria in question, GFAJ-1, has merely evolved to tolerate and use arsenic (that's still pretty damn cool, though). Buddy431 (talk) 20:02, 2 December 2010 (UTC)

Synapse structure

What structurally maintains the proper synaptic cleft of the presynaptic and postsynaptic neurons of a synapse? If I simply lay two threads floating head to head in a liquid, unless there's something holding them in place, they're pretty much guaranteed to drift apart as soon as I move the system. 20.137.18.50 (talk) 19:13, 1 December 2010 (UTC)

There are cell adhesion molecules such as neuroligin that bind pre-synaptic and post-synaptic membranes; see Synaptogenesis#Signalling. Also, the entire synaptic cleft is encapsulated by glial cells; see Synaptogenesis#Central Nervous System Synapse Formation. Red Act (talk) 20:24, 1 December 2010 (UTC)

(ec)The article you linked gives a little info. "Both the presynaptic and postsynaptic sites contain extensive arrays of molecular machinery that link the two membranes together". The article specifically about chemical synapses (the usual kind discussed in schools, with chemical neurotransmitters, etc.) does not have any more info about this detail--would be great if someone could find it. The article about electrical synapses talks about the connexon channels and the diagrams suggest an interaction between the E1 and E2 domains of the connexin proteins. That last article has a section detailing what's currently known about how they link together. DMacks (talk) 20:28, 1 December 2010 (UTC)

Thanks Red Act! Could you add some notes to the synapse article about it? It's definitely important to the structure itself, not just the biological formation of them. DMacks (talk) 20:29, 1 December 2010 (UTC)

The chemical synapse article would be the place to add the information -- the synapse article is basically a disambig page, because the two types of synapses are so different structurally and functionally. Unfortunately this is an aspect of neuroscience I know very little about. Looie496 (talk) 21:00, 1 December 2010 (UTC)

There is a diagrammatic representation here on page 127. The chapter also goes into more detail.--Aspro (talk) 21:14, 1 December 2010 (UTC)

Christmas lights

My outdoor lights I have just hung says clearly not to connect more than three strands together or it will exceed their rating. Of course I have eight connected end to end on one side of the house and four on the other. Surely I am not the only one to go well over the limit stated on the box? Is it most likely the light stands would fail first or the outlet? Each plug on the strands has a fuse on it so would these go out first? Anyone have any solutions for wiring these lights without running extension cords from all over the place? Thanks. Beach drifter (talk) 20:07, 1 December 2010 (UTC)

If the lights are connected in parallel, then the expected failure mode is for a fuse or circuit breaker to blow. The secondary failure mode is for something somewhere to get very hot, so be careful. Looie496 (talk) 20:55, 1 December 2010 (UTC)

(ec)We would need more info, specifically the wire size, and the power consumed (watts) from each strand. Worst case scenario is a fire by overheating the wires that make up the strands. Hopefully the fuse would blow first, but it's not guaranteed. Can you link to the product if you don't know the specs? You can buy LED lights - they use a LOT less power. Ariel. (talk) 20:57, 1 December 2010 (UTC)

The product is rated at 61.2 watts/.51 amps, connected end to end for a maximum of 210 watts/1.75 amps. Beach drifter (talk) 21:01, 1 December 2010 (UTC)

If each plug is fused is the a UK 3 pin plug 240v. If so you'll likely have a 2 amp fuse and that is because the lights have 2 amp wire (why waist money on a heavier gauge just for little dinky lights). No, not a good idea. Hope you are also using a isolation transformer or an earth leakage trip to guard against finding electrocuted reindeer in the garden.--Aspro (talk) 21:29, 1 December 2010 (UTC)

Good point about the deer, we get them in the yard more frequently in the winter. Beach drifter (talk) 21:36, 1 December 2010 (UTC)

I don't really understand what you mean. 61.2 watts each, maximum of 4 does not equal 210 watts. Or do you mean each one is 210 watts? (So x 4 = 840 watts.) Also, what size are the wires? Ariel. (talk) 22:40, 1 December 2010 (UTC)

There are several different ways to answer this.

1. Good engineering practice -- which is sought for, and generally achieved, in the design of electric power systems and appliances -- is to design things so that they are inherently safe, not to depend on the user to keep them safe. As you suggest, you're certainly not the first person to have imagined that you can "probably get away with" stringing together eight strands of lights when the directions say there's a max of three.
2. With that said, though, Christmas lights were once a distinct exception to the above. A strand of incandescent lights consumes a significant amount of power. If they're strung in series (which is the common arrangement if you're, say, encircling your house), the total current drawn by all strands must pass through the plug and wires of the strand that's closest to the outlet. If you connect together arbitrarily many strands, sooner or later you can almost certainly get to the point where you've exceeded the current-carrying capacity of the wires of the first strand, but not exceeded the rating of the fuse or circuit breaker protecting the outlet you've got the whole mess plugged into.
3. With that said, though, the "Christmas light loophole" has, as near as I can tell, been closed. There are little fuses in the plugs, now, and these presumably protect the plugs and wiring from having too many series-connected strands tacked on downstream.
4. With that said, though, it's arguably good engineering practice to adopt a "belt and suspenders" approach, to try to be safe on your own, letting the protective devices like fuses and circuit breakers serve as a backup, rather than depending on them. So if the instructions say "no more than three", and if you really want to Follow The Rules, it would certainly be a Good Idea to connect no more than three. (But with that said, though, the no-more-than-three recommendation is sure to include a safety factor, whether or not it's enforced by a fuse. [But what's the safety factor? And is it a good idea to make use of it?])
5. With all of that said, though, the real question is, for multiple strands of Christmas lights constructed with wire of a certain gauge, all connected in series, plugged in to an outlet protected by a fuse or circuit breaker with a certain rating, how likely are you to actually start a fire? Let's say the wire is 18 gauge, and the circuit is protected at 20 amps. That 20 amp circuit is wired (if to code) using 12 gauge wire, which has twice the diameter and therefore four times the current-carrying capacity of 18 gauge. In other words, you can run 20 amps through 12 gauge wire all day long without it getting anything like too hot. By that token, you shouldn't run more than 5 amps through the 18 gauge wire. If you string together enough light strands to draw (say) 19 amps, you wouldn't blow the 20 amp circuit, but the 18 gauge wire would certainly get warm, if not hot. The question, then, is, would a nearly 4x overload cause the wire to heat up so much that the insulation would melt off or catch fire? And the answer is... I don't know. But these are definitely the kinds of numbers we're talking about, in that I can't imagine a string of Christmas lights wired with anything smaller than 18 gauge wire, and the outlet you plug it/them into is never (in the U.S., anyway) going to be fused at more than 20 amps. —Steve Summit (talk) 03:07, 2 December 2010 (UTC)

Dinosaur Combs and Wattles

Given than birds are descendants of dinosaurs, have there been anything found in the fossil record that tell us whether dinosaurs also had structures such as combs or wattles like their chicken or turkey descendants? Jeanpetr (talk) 20:50, 1 December 2010 (UTC)

Fossils only form under some very rare and special conditions. For flesh to fossilize it takes even rarer and more special conditions. While there have been billions of fossils found I believe there are only a tiny fraction have anything that can be recognized as flesh. However there are at least some scientists who believe dinosaurs may have had soft skin folds similar to combs and wattles. Vespine (talk) 21:50, 1 December 2010 (UTC)

Is this for reals?

http://www.youtube.com/watch?v=6QasA6NQXXQ&feature=related

Hoax? —Preceding unsigned comment added by 114.173.217.17 (talk) 21:04, 1 December 2010 (UTC)

No Hoax. Our Snakebite article even mentions this: A snake's detached head can immediately act by reflex and potentially bite. The induced bite can be just as severe as that of a live snake. Dead snakes are also incapable of regulating the venom they inject, so a bite from a dead snake can often contain large amounts of venom. I've heard that rattlesnakes are particularly notorious for this, there's several news stories to back this up. Vespine (talk) 02:50, 2 December 2010 (UTC)

About how long would it take for that reflex capability to dissipate? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:27, 2 December 2010 (UTC)

Circuits with LEDs

I'd like to play around with LEDs, and I'd like to understand a bit what I'm doing. In school, and at home, I did loads of circuits with little incandescent bulbs, and I know the basics of circuits with batteries, resistors, incandescent bulbs. I can calculate the voltages/currents/resistance of components in idealised parallel and series circuits. But we never did anything with diodes, apart from look at a graph of how voltage varied with current to get an idea of them being oneway (and make a circuitboard in Design and Technology without any explanation of the theory or how it worked, which wound me up). I have an idea that, apart from needed to hook them up with positive and negative the right way round, you have to be careful about the voltage across them, so you need to add a resistor of a particular value to get the right voltage.

Could someone recommend some easily-available write-up of relevant theory, ideally from a practical angle, to ease me into this area? If I get the voltage on an LED too high, will it blow up, fail early, or just not work? 86.161.108.241 (talk) 22:56, 1 December 2010 (UTC)

I have failed LEDs in all of the above methods. Connecting a LED directly to a 9v battery is a quick and easy way to blow them up. There are loads of tutorials online, just google LED totorial; here's a couple. Just because it's a chance to blow my own trumpet, here's my LED project I spent about 18 months on. Vespine (talk) 23:33, 1 December 2010 (UTC)

If LEDs are so sensitive to votages then why are they used in Opto-isolators? Hcobb (talk) 23:48, 1 December 2010 (UTC)

- because it is preferable to blow up a cheap LED than the expensive chips that it isolates from inappropriate voltages. Dbfirs 07:56, 2 December 2010 (UTC)

Thanks Vespine: it's hard to identify a good tutorial when you're new to something. I'd thought I'd need to carry out really careful iterative calculations with logs, based on what I was seeing in our articles, but that looks fairly easy. And your project fills me with confidence in your ability to judge the tutorial! Wow, that's cool. Looks like I'm buying components and solder tomorrow! 86.161.108.241 (talk) 23:54, 1 December 2010 (UTC)

(ec) I can direct you to some of the theory, though it might be a little short on the "practical angle" aspect. The electrical properties of semiconductors can be explained using band theory (note that semiconductors are crystals). (It may or may not be useful to read up a little on Maxwell-Boltzmann statistics, on how and why it breaks down when applied to fermions, and, subsequently, on Fermi statistics.) Once you understand semiconductors, you can move on to diodes, and then to LEDs. --superioridad ^(discusión) 00:00, 2 December 2010 (UTC)

My tip is just dive straight in, you'll learn heaps by just trying things out, you can get LEDs by the hundreds literally for a few dollars off ebay. Find a DC power pack and learn how to make a simple power supply using a 7805, or a variable one if you are adventurous (LM317). I'd also recommend a breadboard, it makes things a lot easier. The components you need are peanuts from places like futurlec.com , I don't usually shill but that place is really cheap and I've bought lots of stuff from them without any problems. Even if you visit a local shop it shouldn't be too expensive to get started. Vespine (talk) 00:10, 2 December 2010 (UTC)

Also might be worth mentioning, don't be tempted to start learning on the high power LEDs like CREE or Luxoen, they're a considerably different kettle of fish. Just start with a bunch of the cheapest LEDs you can find. Vespine (talk) 00:13, 2 December 2010 (UTC)

(edit conflict) We have a practical article: LED circuit. Basically: if you overdrive an LED, you'll cook it (when I did this, it just glowed quite brightly and rapidly dimmed into nothingness). You can overdrive it in either direction: backwards, it's a little sturdier, but also useless.

The math: P=IV, of which IV₀ is light (V₀ is approximately the minimum voltage to get light) and the rest heat, so $P_{h}=I(V-V_{0})$ is the heat your LED has to dissipate. When V increases beyond V₀, both of those factors increase rapidly (I increases exponentially in standard diode models). So the heating rate of your diode is very sensitive to voltage; there's a tiny range of voltages between "doesn't light" and "cooks". Hitting that target is really hard with just a voltage source (battery), so don't be tempted to say "Hey, these are 3V LED, says so on the box, so let me just put three in series on a 9V battery.". The basic trick is to add a resistor in series; then the voltage across the LED can't get high, because then the current would be large, but then the voltage drop across the resistor would exceed that of the source. See the graphical analysis: even if you move the bottom-right point (which represents the battery voltage) around, the intersection doesn't move much.

The article depicts this and shows how to calculate the appropriate resistance (always round up, of course, with real resistors). You can safely stack LEDs (even of different colors) in series with one resistor: you'll just be constrained by the lowest current rating, of course. It's not usually recommended to connect LEDs in parallel: it works, but tends to generate uneven lighting and shorter lifetimes. --Tardis (talk) 00:14, 2 December 2010 (UTC)

December 2

Scientific Child Rearing

Humans have been raising children since basically the dawn of time, so presumably we do an okay job of it on average. On the other hand, if you talk to ten different people, you are likely to get ten different opinions about how to deal with kids. Some people believe in being very strict, physical (e.g. spanking), or distant. Others will try to coddle their children and protect them from everything. Some parents assign lots of chores to their kids, and other parents do all the cleaning and work themselves. Some parents want to know everything about their kids lives and others leave them alone.

I could go on, but you get the idea. My question is this: Is there any objective evidence that certain parenting styles are more effective than others at ensuring that children grow up to be happy and successful adults? For example, do the kids of strict parents earn more over their lifetime? Do the kids of gentler parents have fewer (or more) psychological problems in adulthood?

I'm looking for references to scientific studies and other factual conclusions, rather than just personal opinion. Dragons flight (talk) 00:24, 2 December 2010 (UTC)

I think the problem is that I doubt you could even satisfactorily define happy and successful. Vespine (talk) 02:18, 2 December 2010 (UTC)

There are lots and lots and lots of studies of this sort. I don't know what the larger synthetic conclusions are, but surely there are some by this point, even if they are contested (and they certainly will be). --Mr.98 (talk) 02:50, 2 December 2010 (UTC)

Actually, that's pretty good, it gave me the idea to put meta analysis and meta analytic into the search field after "parenting style" and that comes up with some pretty interesting sounding results. don't have the time to go through any now, but i've bookmarked it. Vespine (talk) 02:59, 2 December 2010 (UTC)

A couple thoughts:

1) Different kids likely require different parenting styles. For example, some would benefit from permissive parents who let them do as they please, while other kids would get into serious trouble with such parents. Identifying which type of kids you have an adjusting your parenting style (sometimes for each sibling), may therefore be necessary.

2) Parents tend to think they did a good job if their kids turn out like them. So, parents who value education will think they did a good job if they end up with educated children, while parents who value athletics will think they did a good job if they end up with athletic kids. StuRat (talk) 21:50, 2 December 2010 (UTC)

The Marshmallow Trick

By many accounts, marshmallows, inserted anally, act as a laxative. What causes this effect? -mattbuck (Talk) 00:53, 2 December 2010 (UTC)

That's not how I learned to make smores. :-) StuRat (talk) 00:10, 3 December 2010 (UTC)

There are herbal laxatives (to be taken orally), such as "Easy Mover", that contain marshmallow (Althaea officinalis) extract. I don't know whether the marshmallow extract is the active ingredient, nor how it works, though our laxative article provides plenty of plant-based examples. Searching Pubmed did not provide any helpful leads, and I could not easily find reliable sources for the use of marshmallow rectally. -- Scray (talk) 01:36, 2 December 2010 (UTC)

But the modern marshmallow confection no longer actually uses the marshmallow plant (althaea officinalis) as an ingredient. Red Act (talk) 01:49, 2 December 2010 (UTC)

Indeed, I was adding that as an edit when I encountered an edit conflict ;-) -- Scray (talk) 01:56, 2 December 2010 (UTC)

Chemistry Laboratory technique

I'm looking for the name of a chemistry laboratory technique in which you "scratch" at the walls of a beaker to form a polymer. —Preceding unsigned comment added by David255 (talk • contribs) 00:57, 2 December 2010 (UTC)

Assuming you're forming a crystalline solid, and not a covalent polymer, I've always called the technique "scratching"! You basically form new nucleation sites on the inside surface of the beaker. Trituration (beating it into a solid) is similar in thermodynamic terms, but you usually work with much less liquid than for scratching. Physchim62 (talk) 01:58, 2 December 2010 (UTC)

Trituration is the term. Thanks! —Preceding unsigned comment added by David255 (talk • contribs) 02:33, 2 December 2010 (UTC)

Question from ANI

I don't know why ANI is trying to figure it out:[39], but someone there would like to know if Birds are Dinosaurs? 108.121.139.247 (talk) 01:30, 2 December 2010 (UTC)

That's me. See below. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:47, 2 December 2010 (UTC)

Birds = Dinosaurs?

OK, I would like to hear some expert opinions on this. According to one of the articles, birds are "an extant clade of dinosaurs". I understand birds are considered to be descended from dinosaurs, but is that the same thing as saying "birds are dinosaurs"? I don't think so, and have said as much at List of common misconceptions, but I'm no expert in this area. Thanks for any help you can provide. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:47, 2 December 2010 (UTC)

See here Origin of birds and Origin of birds#Features linking birds and dinosaurs. Heiro 01:51, 2 December 2010 (UTC)

Our Dinosaur article says: Consequently, in modern classification systems, birds are considered a type of dinosaur — the only group of which that survives until the present day. I rather randomly examined the October 3 edit from the history and verified the sentence (as ungrammatical as it looks) has been in the article at least since then, so it isn't a recent addition to confound the discussion mentioned at AN/I. Comet Tuttle (talk) 01:52, 2 December 2010 (UTC)

The Dinosaur intro goes on to talk about dinosaurs in the present tense, because of birds; but then later says: From the point of view of cladistics, birds are dinosaurs, but in ordinary speech the word "dinosaur" does not include birds. Additionally, referring to dinosaurs that are not birds as "non-avian dinosaurs" is cumbersome. For clarity, this article will use "dinosaur" as a synonym for "non-avian dinosaur". The term "non-avian dinosaur" will be used for emphasis as needed. Comet Tuttle (talk) 01:55, 2 December 2010 (UTC)

The origin of birds article begins by saying "The origin of birds is a contentious and central topic within evolutionary biology." It goes on to say that "most" scientists, etc., etc., which in my opinion is sufficient to keep the flat-out contention that "birds are dinosaurs" out of the misconceptions article. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:58, 2 December 2010 (UTC)

(edit conflict) If one defines "dinosaurs" as members of superorder dinosauria (in class reptilia) and "birds" as members of class aves, then "birds" are not "dinosaurs". Note that this is a taxonomic argument (i.e. based on how we have historically assigned words), which is different from a cladistic argument. A clade includes all of an organism's descendents, even if they aren't in the same taxanomic groups. The evidence is quite good that birds are in the dinosaur clade, even though they aren't in the superorder dinosauria. Personally, I would agree that "birds are not dinosaurs", even though "birds are descended from dinosaurs". In other words, I think the linguistic / taxanomic arguments are more relevant in this case. Dragons flight (talk) 02:01, 2 December 2010 (UTC)

Similarly, humans are not fish, bacteria, or rodents, even though humans are almost certainly descended from all of these. Dragons flight (talk) 02:15, 2 December 2010 (UTC)

I hate to nit-pick, but that's not exactly correct. Humans, fish, bacteria, and rodents all share a VERY distant common ancestor that was neither human, fish, bacteria, or rodent but had descendents that evolved into those four very different groups of organisms. Evolution is confusing enough to people without muddying the waters like that... --- Medical geneticist (talk) 14:35, 2 December 2010 (UTC)

I hate to nit-pick your nit-pick, but didn't our ancestry spend quite a bit of time as fish, most famously as Tiktaalik or other sarcopterygii? --Sean 19:38, 2 December 2010 (UTC)

Precisely. Here's the issue: The misconceptions list states to contrary to popular misconception (e.g. in The Flintstones, B.C., Alley Oop, etc.) humans and dinosaurs did not co-exist. The editor called TheThomas added the statement that birds are dinosaurs, which contradicts the alleged misconception. The question is how to resolve it. Seems to me the real "misconception" is that humans interacted with "classic" dinosaur species depicted in those cartoons, e.g. brontosaurus, t-rex, etc. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:22, 2 December 2010 (UTC)

If you're just worried about the practical problem, how about saying "In fact, most dinosaurs died around 65 million years ago after the Chicxulub event, whereas the earliest Homo genus (humans) evolved between 2.3 and 2.4 million years ago. A few dinosaurs survived the Chicxulub event, and we call their descendents birds." Physchim62 (talk) 02:35, 2 December 2010 (UTC)

It isn't really correct to say that a taxonomic argument is different from a cladistics argument. Different biological taxonomy systems exist; see Biological classification. Linnaean taxonomy has been around for close to 300 years, and is easily still the most widely used system, but the more modern cladistics is also a branch of taxonomy; see Phylogenetic taxonomy. According to Linnaean taxonomy, birds are not dinosaurs, since aves and reptilia are different classes. According to cladistics, birds are dinosaurs, because aves is a subclade of dinosauria (see the "Scientific classification" panel of Avialae). Neither one is "correct" or "incorrect"; they're just different systems, each with their own advantages and disadvantages; see Cladistics#Summary of advantages of phylogenetic nomenclature and Cladistics#Summary of criticisms of phylogenetic nomenclature. Red Act (talk) 03:46, 2 December 2010 (UTC)

Red Act has the most important thing to remember here: These are all human-created classification systems. Hypothetically, we could trace the ancestry of all life back to the first self-replicating molecule, and then move forward from there, creating a branching tree of life which includes every individual living thing to ever live; including me, my neighbors cat, and one of the little bacteria in my colon. How we classify those trillions and trillions of individual living things, how we group them, is ultimately done for our own convenience, and isn't indicative of anything more than that. We're pretty sure that, if you take that robin in my front yard, and go backwards through its parents and back and back and back, you eventually get to a dinosaur of some kind. Whether that means that the birds are dinosaurs or they are descendend from dinosaurs is a minor, and mostly moot issue. We use whatever definition is most convenient or useful. --Jayron32 04:05, 2 December 2010 (UTC)

(edit conflict with Dragons flight) I will second this. This question is not a science question, but rather a question of linguistics. There are two different (main) ways to classify organisms. Under one of them, birds are a part of the group that also includes dinosaurs. Under another, they do not. A Cladist would say, without any irony, that there is no such thing as a "reptile". There are Sauropsids, which include almost all of what are considered reptiles under the Linnaean system (including dinosaurs, but excluding a few, mostly extinct, "mammal like reptiles"), and also include birds. Up a level, there are Amniotes, including all creatures considered to be reptiles, as well as mammals and birds. Questions like this really highlight a flaw in the traditional Linnaean taxonomy: it's easy enough to define when creatures have evolved sufficiently to form a new group, but at what point does a creature cease to be a member of a group? Why don't we consider birds to be reptiles? Is it the feathers, the wings? Birds still have many of the traits we assign to reptiles: an Amniotic egg, and scales. To be fair, even mammals are still an awful lot like reptiles. We've lost our scales, and we regulate our own body temperature, but we've still got the important amniotic egg, as well as the older backbone and 4 legs. Buddy431 (talk) 04:28, 2 December 2010 (UTC)

Of course, at that level of precision, it's no longer a "tree" of life, strictly speaking. It's a directed acyclic graph. Now that I think about it, the usual (if not as precise as it might first appear) definition of species, in terms of being able to interbreed in such a way that the descendants breed true, may be specifically designed to allow the use of trees rather than DAGs whenever you look at the species level or coarser. --Trovatore (talk) 04:12, 2 December 2010 (UTC)

I would tend to quibble that "cladistics" is mostly an organizing principle and not really a taxonomy, since cladistics is about specifying relationships and is only rarely used to specify new names for things beyond "the clade of X". You could even accept cladistics as a starting point and define multiple different types of taxonomies on top of the relationship tree it generates. All quibbles aside though, I understand your point. That said, I don't think even strident cladists would want to embrace a system where all descendants of X were given the same name as X. It isn't conducive to either common or scientific communication to have a nomeclature system that allows for humans to also be called rats, fish, and bacteria. For the same reason, I would tend to think that saying "birds are dinosaurs" actually makes communication more opaque rather than less, and should be disfavored. That's my opinion anyway. Dragons flight (talk) 04:18, 2 December 2010 (UTC)

Birds are more closely related to dinosaurs then anything else alive today, including crocodiles; the "next" most closely related species. A rough analogy might be that birds and dinosaurs are to crocodiles like what humans and chimps are to mice. There are very few major morphological differences between dinosaurs and birds, funnily enough a long tail is one of them, which is also a difference between humans and chimps. Vespine (talk) 04:51, 2 December 2010 (UTC)

What humans do you know that have long tails? Cuz I've never met one... Do you have a long tail? Weird. --Jayron32 04:59, 2 December 2010 (UTC)

You know, all those chimps with tails. *face palm*... i was thinking monkeys when i wrote that.... I work in I.T., forgive me... lol. Vespine (talk) 05:21, 2 December 2010 (UTC)

clade n.[40] A group of animals or other organisms derived from a common ancestor species. The clade Dinosauria includes all dinosaurs as well as birds, which are descended from the dinosaurs. I think the linguistic argument that has arisen would be avoided if the definition were rephrased: clade n. A grouping of animals... Cuddlyable3 (talk) 10:34, 2 December 2010 (UTC) updated

Birds are dinosaurs in the same way that humans are monkeys. Wnt (talk) 11:41, 2 December 2010 (UTC)

No, birds are dinosaurs in the same sense that humans are primates. Matt Deres (talk) 14:52, 2 December 2010 (UTC)

The issue seems to center on how broadly the term "dinosaur" is used or perceived. It looks like we've got a misconception within a misconception. The average citizen has been told over and over that "dinosaurs went extinct 65 million years ago." That statement appears to be an oversimplification of the situation. When people think of "dinosaurs", and of the fantasy of early hominids interacting with them, they think of T-rex and Brontosaurus and like that; not birds. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:04, 2 December 2010 (UTC)

The word "dinosaur" was coined to describe ancient very large animals discovered as fossils. Birds are not "terrible lizards" - they are birds. The later use of the word "dinosaur" by scientists does not alter the fact that the word is in practice used, by most people most of the time, in a sense very close to that originally intended. Ghmyrtle (talk) 15:14, 2 December 2010 (UTC)

Good point. So perhaps the root issue of the misconception-within-the-misconception is a dichotomy between what the public thinks of as dinosaurs vs. what the scientists think of as dinosaurs. That opens another can of worms. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:20, 2 December 2010 (UTC)

And to further muddy the waters, according to Mammal our own mammalian ancestors were indeed around during the dinosaur age. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:23, 2 December 2010 (UTC)

Perhaps, but homo sapiens weren't. Birds were actually around during the late cretaceous as well (though theories exist they evolved twice etc.), so if birds aren't dinosaurs then all the dinosaurs did go extinct at KT. Chipmunkdavis (talk) 16:34, 2 December 2010 (UTC)

Trying to factor in what the average citizen thinks is a little pointless. The average citizen thinks that pterosaurs were dinosaurs. The average citizen thinks that ichthyosaurs were dinosaurs. The average citizen thinks a lot of things that are outdated, inaccurate, unbalanced, or just plain crazy. Matt Deres (talk) 17:23, 2 December 2010 (UTC)

But ... Until recently* the word "dinosaur" had no scientific definition! It was a word entirely for average citizens. Until recently, some sources would include pterosaurs and/or ichthyosaurs and others wouldn't and neither view was more "correct" than the other. Sure, most sources agreed that anything from Saurischia or Ornithischia could be called a dinosaur, but other stuff from that time period would also be included in many definitions. It didn't help that Saurischia and Ornithischia were not thought (at the time) to be closely related, so the whole thing was considered to be too arbitrary and contrived for formal use.

Even definitions that discounted pterosaurs or ichthyosaurs often wouldn't do so in a satisfying way, resorting to even more arbitrary qualifiers like "ground based" or "non-flying".

Later when it was realized that Saurishcia and Ornithischia were closely related they were able to come up with an actual scientific definition of "dinosaur" that included most of the animals everyone "knew" were dinosaurs.

So, don't criticize too harshly people still using the informal, layman's definition of the term. The layman's version came long before the scientific version.

* The 90s still count as "recently", right?

APL (talk) 17:58, 2 December 2010 (UTC)

I hope so. :( Keep in mind this has to do with "common misconceptions". Obviously, paleontologists are going to know the details of the current theories. The general public is not necessarily so well informed. The goal here is to try to come up with a better way to deal with the "misconception" that humans and dinosaurs interacted. A major part of that is defining just what a "dinosaur" actually is. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:02, 2 December 2010 (UTC)

Draft

It's much warmer inside my house than outside. So, I expected that opening the windows would cause the air inside to blow out, because the warm air inside should be at a higher pressure. But instead, I get a draft coming from the outside. What gives? 74.15.138.27 (talk) 05:57, 2 December 2010 (UTC)

If you heat air in a fixed volume the pressure goes up, but that doesn't mean that warmer air is inherently at a higher pressure. The difference in pressure inside and out isn't going to be related to the temperature difference. Instead it's going to depend on what the weather is doing outside (for example if the wind is blowing toward your window). 24.98.193.82 (talk) 06:04, 2 December 2010 (UTC)

To expand on 24.98's answer a bit; since your house is not perfectly airtight, it is likely at the same pressure as the outside, though at a different temperature. If you want to cool your house efficiently by opening the windows, your best bet is to open two windows on opposite sides of the room; this will allow for the air to move through your house; such that the cooler air can enter and the warmer air can escape. Placing an electric fan in the window will speed the process. --Jayron32 06:08, 2 December 2010 (UTC)

If you don't want a through-house draft, then opening a window at the top and bottom of the room is fairly effective at setting up internal-external convection currents. This is how sash windows work, see the bottom of that article. CS Miller (talk) 06:51, 2 December 2010 (UTC)

The reason you get a draft is the Chimney effect. The warm air inside the house is lighter than the cold air. So if you open a window at the bottom, you let cold air enter the house, and the warm air rises and exits through openings at the top (attics are usually ventilated). Ariel. (talk) 08:10, 2 December 2010 (UTC)

The draught flowing into the OP's house must be counteracted by an equal draught flowing out otherwise the house would explode. The two air flows may simply be through the lower and upper parts repectively of the window opening. Cuddlyable3 (talk) 10:06, 2 December 2010 (UTC)

Thanks. 74.15.138.27 (talk) 15:45, 2 December 2010 (UTC)

Evolution of the wavefunction

If you knew the current wavefunctions in a system, is it possible to determine the future wavefunctions? The time evolution of the wavefunction is deterministic in an isolated system BUT that does not account for wavefunction collapse - Is wavefunction collapse deterministic or stochastic, and does that mean that it is possible or not to determine the future wavefunctions with certainty? 220.253.217.130 (talk) 10:52, 2 December 2010 (UTC)

Many scientists would claim that there is no such thing as wavefunction collapse, since any "measurement" (i.e. interaction) can itself be described by deterministic wave function evolution. See many worlds interpretation . Obviousely, any measurement of an isolated system is an interaction with the outside world and thus, the system is no longer isolated. 157.193.175.207 (talk) 12:25, 2 December 2010 (UTC)

The outcome of a measurement is not deterministic, and this is pretty much true across the various QM interpretations except for hidden variable theories. When you make a measurement, the probability of which value the wavefunction will collapse to is determined by the value of the wavefunction, but the outcome is still stochastic. In terms of quantum decoherence, you become entangled in the state of what you're observing (which happens in a deterministic way) so that your wavefunction is a combination of all the different possible outcomes of the measurement. However, only one of those "you"s is the "you" that you experience, and you can't tell which one that's going to be, so in that sense it's still not deterministic. In other words, how the possible worlds will branch out is determined, but not which branch you'll seem to take. Rckrone (talk) 14:41, 2 December 2010 (UTC)

Can you safely drink rusty water?

Na, I'm not planning on doing it. This comes from a discussion I was having with someone yesterday about Irn Bru. He asserted that Irn Bru was originally just water that had sat in a vat with an iron girder in the bottom for a few weeks, sugared, carbonated and bottled (which is, I believe is a commonly held, albeit incorrect belief). Drinking rusty water (basically a suspension of iron(III) oxide, right?) as a regular beverage would make you rather sick, wouldn't it? --Kurt Shaped Box (talk) 12:12, 2 December 2010 (UTC)

Why would it make you sick? Iron poisoning is possible I guess, but iron oxide does not absorb very well in the body. Ariel. (talk) 12:16, 2 December 2010 (UTC)

Well water is known for being relatively highly mineralized, often with an "iron" taste, but I don't know that it's much of an issue. The issue with any water source is the possible presence of dangerous bacteria. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:17, 2 December 2010 (UTC)

Rust itself is pretty harmless, I believe, but may be associated with other contaminants that are not. There are many possible issues other than bacteria: arsenic, lead, PCBs, etc, etc. Looie496 (talk) 18:17, 2 December 2010 (UTC)

Objective scientific evidence for PMS?

What verified scientific evidence is there that pre-menstrual tension actually exists objectively? I ask because firstly, I get all the symptoms listed here http://www.womenshealth.gov/faq/premenstrual-syndrome.cfm#c except the second one, but I'm a man. Secondly, isnt expression of irritability because the behavioural standards expected of women in office etc situations are more lax that those expected of men - men get just as irritated but have to bottle it up? Thanks 92.24.186.163 (talk) 17:39, 2 December 2010 (UTC)

You feel intense bloating, pain, cramping, and resultant irritation on a regularly monthly pattern, as a man? You really ought to see your doctor about that, if so. --Mr.98 (talk) 00:24, 3 December 2010 (UTC)

Intelligent prey

Pigs are far more intelligent than dogs and cats, but to eat them is acceptable, whereas dog and cat meat is contraband in many places. What is the most intelligent animal that is regularly eaten, either by humans or by other animals? By "regularly" I mean that being eaten, or almost being eaten, is a part of its daily routine. LANTZY^TALK 19:49, 2 December 2010 (UTC)

Pigs are not an acceptable source of meat in many places: see Kosher and Islamic dietary laws. On the flip side of the coin, dogs, and to a lesser extent cats, are an acceptable source of meat in some areas: see Dog meat and Cat meat. What you consider an acceptable and unacceptable diet is not universally held. Buddy431 (talk) 19:58, 2 December 2010 (UTC)

That's true, but I don't think Jews and Muslims object to pig-eating on ethical grounds. They regard pigs as unclean, not as sentient pink friends. LANTZY^TALK 20:11, 2 December 2010 (UTC)

Probably whale. Looie496 (talk) 20:01, 2 December 2010 (UTC)

Monkey is eaten in many parts of the world. See this oddly-titled National Geographic article, New Monkey Species Discovered, Then Eaten. (Notably, this article has an addendum that addresses the cultural and ethical issues about meat, bushmeat, and defining which animals are "acceptable" to eat). I will point out that there is no authoritative "ranking" of intelligence amongst the animal world - classifying a food-animal as "intelligent" or not depends entirely on various definitions of intelligence. Nimur (talk) 20:02, 2 December 2010 (UTC)

An intelligent prey? A pig that wants to be eaten --Aspro (talk) 20:07, 2 December 2010 (UTC)

Of the most commonly-eaten animals (cattle, lambs, pigs, etc.), pigs are surely the most intelligent. In the less-commonly-but-not-too-uncommonly-eaten category, I'd say octopus. WikiDao ☯ (talk) 20:13, 2 December 2010 (UTC)

That National Geographic blog post from 2010 is eerily similar to this Onion article from 2005. -- BenRG (talk) 23:01, 2 December 2010 (UTC)

It has nothing to do with intelligence, but rather with friendliness to humans. No animals are intelligent enough for intelligence to make any difference, but the emotional relationship to humans does matter. Ariel. (talk) 21:15, 2 December 2010 (UTC)

Make any difference to whom? I know people who definitely wouldn't eat animals they thought were as intelligence as pigs or even cuttlefish. --Mr.98 (talk) 00:33, 3 December 2010 (UTC)

There's many other cultural factors besides intelligence. Muslims don't eat non-marine carnivores. I believe other people avoid carnivores based on the idea that they accumulate toxins because they are higher on the food chain. Also, dogs, cats, and horses have a companion status much more than other animals, which my explain why most cultures don't regularly consume them. Similarity to us is another big factor culturally. Intelligent non mammals dont get the same status for the purpose of eating them and experimenting on them as mammals, even if they are more intelligent than many mammals. Apes, monkies, and other simians also get a higher level of that respect in most cultures simply based on their perceived similarity to us. Roberto75780 (talk) 00:57, 3 December 2010 (UTC)

Split down the middle

Often people have survived the loss of a large portion of their brain, and there is also a procedure whereby the corpus callosum is severed, separating the two hemispheres. So what if a person's brain were completely split, all the way down to the spine, but left otherwise intact? Would the brain become, in effect, two brains? (Obviously, assuming a form of neurosurgery far beyond what we have today.) Without any means of interface, how could the hemispheres not diverge and become two distinct individuals sharing a skull? To continue the mad science, suppose we carry on down the spine, splitting the organism into two pieces, Mr. Right and Mr. Left. (Never mind the heartless Mr. Right - we'd have a cloned implant on ice.) Is it theoretically possible, given the general symmetry of chordates, to split one lengthwise into two living, functioning halves? Or is our symmetry specious and superficial? LANTZY^TALK 20:07, 2 December 2010 (UTC)

I'm not sure where you're going with wanting to split even the spinal column, but you can do just fine (as an "individual" person) with only half a brain (with of course some impairment – though some people have been born with only one hemisphere, and they do much better than the surgical patients). And of course you may also find our Split-brain article of interest. WikiDao ☯ (talk) 20:35, 2 December 2010 (UTC)

Such a person would be completely, or almost completely, paralyzed. The great majority of the motor outputs from the brain control the opposite side of the body, and the crossings (decussations) occur inside the brain, in the midbrain and brainstem. Looie496 (talk) 20:37, 2 December 2010 (UTC)

Our article Hemispherectomy touches on Looie496's statement. Comet Tuttle (talk) 21:01, 2 December 2010 (UTC)

So, as one would expect, bisecting the lower brain is quite a different matter than splitting the cerebrum. It looks like it will have to remain just a beautiful dream... Of course, theoretically, the decussations could be untangled and rewired. What if we try something a little less ambitious, and just cut down through the brain to where the decussations begin? LANTZY^TALK 21:04, 2 December 2010 (UTC)

decussation n. A crossing or intersection of lines etc. so as to form an X-shape. Cuddlyable3 (talk) 22:50, 2 December 2010 (UTC)

Forces in space

My friend told me that if you push against something in space, you will move away much more than you would on Earth. If this is true, is it something to do with Newton's Third Law? Or Momentum? I'd like this information to use it in something I'm working on. Thanks a lot! --Editor510 ^{drop us a line, mate} 21:44, 2 December 2010 (UTC)

I think I've sussed it, but I'm looking for confirmation, here. Is it that in space, you and another object would be exactly the same weight, thus making the Third Law kick in on a much larger scale than it does in gravity equivalent to 1 Earth?--Editor510 ^{drop us a line, mate} 21:55, 2 December 2010 (UTC)

No, it's not weight (not directly). The difference is whether you can brace against the earth, and transfer the reaction force there. If you can brace, you can move something without moving yourself (relative to the earth). In space, the third law still applies, but you have nowhere to put the momentum, so it must be you that goes flying. --Tardis (talk) 21:59, 2 December 2010 (UTC)

Oh, I get it. So you absorb all the momentum the Earth would usually absorb? That makes sense! Thank you!--Editor510 ^{drop us a line, mate} 22:02, 2 December 2010 (UTC)

Resolved

Editor510 you still need to get the terms right. You and another object usually have different masses which never change. On Earth the masses are experienced as weights. In outer space there is no weight. If you and the object are both standing on a perfectly slippery ice rink, then Newton's 3rd Law operates similarly to being in space. If you push the object, both you and the object start moving apart. Cuddlyable3 (talk) 22:42, 2 December 2010 (UTC)

December 3

Drinking from a lake

Whenever I watch survival shows on Discovery Channel, the hosts always say the water from lakes and creeks needs to be boiled before I drink it. So why don't animals drinking from the same water source get sick? Hemoroid Agastordoff (talk) 00:10, 3 December 2010 (UTC)

Animal immune systems will develop a resistance to the microbes they commonly encounter in their local water. In mammals, that resistance can also be partially passed to young animals by breastfeeding, which helps protect the young. In many cases, the human immune system would also develop a tolerance after prolonged exposure, but the first few times you tried the local water there is a chance you could get very sick. Water-borne pests are still a significant cause of death in some parts of the world. Altogether it is generally safer for humans to boil water they find outdoors. Dragons flight (talk) 00:17, 3 December 2010 (UTC)

Better than ice bottles

I heard from a friend that using antifreeze bottles rather than ice bottles can greatly increase the cooling effect in a picnic cooler. The basic idea is that by keeping the water liquid down to -18 °C, you will keep its heat capacity high, because water has about double the heat capacity of ice. This effectively doubles the power of the bottles(until it they reach 0 °C anyway).

My question is, does water with antifreeze in it have the same or similar heat capacity as plain water? How much antifreeze does it take to keep water liquid down to about -18 °C anyway? I think automotive antifreeze is good enough to -40 °C, so it can be diluted if antifreeze doesnt have as much heat capacity as water.

Oh by the way, for those who really like to get technical, I know the densities are all different so lets just assume we are dealing with volumetric heat capacity. I'm gonna use a four 2L Coke bottles in a big cooler and weight savings are insignificant. Roberto75780 (talk) 00:50, 3 December 2010 (UTC)

I don't this makes sense. The heat of fusion of water means that when ice melts it absorbs heat equivalent to what you'd need to raise its temperature by over 70°C. If you start with chilled liquid you lose that benefit. --Anonymous, 01:03 UTC, December 3, 2010.