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October 11

Have people really fused with their own sofas?

It always sounded like an urban legend to me, but it has been reported (a couple of times, that I can recall over the years) in the mainstream media that people have actually sat on their sofas for so long that their flesh had actually grown into and fused with the fabric. Now, it wouldn't be the first time that some random piece of bullshit that circulated on the internet was picked up and reported as news in one of the less reliable newspapers - but seriously, is there even any way that this could even work in reality?

If you were literally never moving from your sofa for 'x' number of years (that always seems to be a common element in these stories) and therefore inevitably pissing and shitting all over yourself where you were, then surely you'd die of an infection or get eaten by bugs long before you could actually grow into your seat - and your home would become so much of a biohazard that the local authorities wouldn't stand for it? --Kurt Shaped Box (talk) 01:12, 11 October 2013 (UTC)

I think more realistically that someone with an open sore, such as a bedsore, could have the clot/discharge stuck to the fabric in a way that made it painful or perhaps even damaging to move him without considering the issue. Wnt (talk) 02:45, 11 October 2013 (UTC)

Googling "skin fused to couch dies" gets you a lot of hits, although some seem to be recycled stories. Google news gets no hits. This detailed story was published in the Mail. Obviously the skin is not going to grow blood vessels into the couch. But a several year old callous would be pretty thick and not easy to remove in place. We're not really in a place to question the sources. μηδείς (talk) 02:56, 11 October 2013 (UTC)

Common mistake: callous is an adjective. What we need here is the noun callus. -- Jack of Oz ^{[pleasantries]} 12:46, 11 October 2013 (UTC)

I knew something looked off. μηδείς (talk) 16:36, 11 October 2013 (UTC)

Always trust your gut. What you have left of it, anyway.  :) -- Jack of Oz ^{[pleasantries]} 18:30, 11 October 2013 (UTC)

I happened upon Nip/Tuck while channel surfing one night, and saw an episode about a woman who was so impossibly, grossly, disgustingly, insanely obese that she had lost the ability to move and had totally merged with her sofa, where she had remained for some years. Still mentally alert and talking volubly. Still eating (she had a helper) and eliminating waste products (the helper didn't go there). The smell was apparently indescribable. The plastic surgeon's job was to somehow separate her from the sofa. After they achieved this, the house had to be demolished. How true to actual real life this dramatisation was, I cannot say, but I really hope it was uber-exaggerated. -- Jack of Oz ^{[pleasantries]} 03:13, 11 October 2013 (UTC)

The adjective you are looking for is "extremely" obese. Compulsive overeating is a common psychological condition, so common that most of suffer from it in a mild form. Please don't blame the victim. There but for the grace of God... Itsmejudith (talk) 20:50, 11 October 2013 (UTC)

OK, I accept that. I know about weight issues and eating disorders, having lived with both of them for a very long time, and I have experienced many cruel barbs from others, so I would never blame the victims and I certainly wasn't doing so above. It's just that, saying "extremely obese" would in no way have given you an impression of how monstrously enormous this person was. Obviously it was all, or mostly, artificially added to her real body, because I don't believe any human could possibly be that big. Think of Mr Creosote from Monty Python's The Meaning of Life and you're getting towards the ballpark. -- Jack of Oz ^{[pleasantries]} 05:05, 12 October 2013 (UTC)

Thanks for your thoughtful response. It seems that the main thing to be angry about is that the lady had so little support until it was too late. Also, perhaps, that the TV show was sensationalising in pursuit of ratings rather than bringing a complex topic to public attention. From what you've said, "extreme" is the precise word in this case, i.e. it was at the far end of what is physically possible. Itsmejudith (talk) 22:42, 13 October 2013 (UTC)

Well, so long as we're citing fiction, here's the pièce de résistance of all skin fusing. μηδείς (talk) 03:33, 11 October 2013 (UTC)

This Tetsuo also has fusion problems. Akira's way better though. Effovex (talk) 04:18, 11 October 2013 (UTC)

• It happens. The Associated Press/Yahoo News (normally reliable sources) has an article here about a woman from Missouri who had fused to her vinyl recliner. Here is a similar story from a TV station in Florida about a woman fused to her couch after 6 years. --Jayron32 12:11, 11 October 2013 (UTC)

Why do light rays bend while passing from one medium to another (during refraction)?

Why do light rays bend while passing from one medium to another (during refraction)? Scientist456 (talk) 04:04, 11 October 2013 (UTC)

See Refraction#Explanation. Bubba73 ^{You talkin' to me?} 05:00, 11 October 2013 (UTC)

This article does not explain the bending of light deeply. Scientist456 (talk) 06:16, 11 October 2013 (UTC)

Per Lagrangian mechanics and Hamiltonian mechanics, the path taken by a particle is such that the action (the difference between the particle's kinetic energy and its potential energy, integrated over the path) is stationary (which usually means it's a minimum), i.e. the first-order variation of the action is zero. In layman's terms, you could say the path taken is the most efficient one. The analogy my professor used is this: imagine you're on the beach, and someone is drowning. To get to them, you have to run across the beach for some distance (easy) and swim some distance (harder by a factor n). The extreme paths are one where you minimise the swimming part but have to run a lot, and the one where you minimise the running but have to swim a lot further. As it turns out, the quickest way to get to the drowning person is the path where $\sin \theta _{1}=n\sin \theta _{2}$ -- i.e., it is given by Snell's law. If you recall that the refractive index n is the factor by which light in a medium travels slower than c, that means light bends simply because it's the quickest path. See also: Hamiltonian optics. --Link ^(t•c•m) 09:18, 11 October 2013 (UTC)

diffrent matiryals transfer light in diffrent speed , ray of light moves forwerd and backwerd many time in time and stabilize on the fastest way , that way the light bend . thanks Water Nosfim — Preceding unsigned comment added by 81.218.91.170 (talk) 12:08, 11 October 2013 (UTC)

The thing is , To get to know the fastest way, you have to return from it with knowledge of its speed, ie to return from her back in time , Water Nosfim — Preceding unsigned comment added by 81.218.91.170 (talk) 12:56, 11 October 2013 (UTC)

I don't pretend to understand it, but try the last paragraph of this: http://www.sparknotes.com/physics/optics/light/section3.rhtml — PhilHibbs | talk 15:03, 11 October 2013 (UTC)

Metal used in hard disk drive chassis?

What kind of metal alloy is used in a hard disk drive chassis? any sources? Electron9 (talk) 04:10, 11 October 2013 (UTC)

I'm almost certain it is just aluminum. But I'm not having luck finding a good source. 203.110.235.8 (talk) 05:39, 11 October 2013 (UTC)

I can't see why aluminium would be used. All the HDD's I have examined have a diecast chassis. Diecasting is (at high production volumes) cheap, and produces a strong accurate product with a vety good finish. The HDD's I have examined have the typical light grey finish of diecasting in alloys that are mainly zinc. Not that it is common for lay men to mistake zinc diecastings for aluminium. 121.221.33.239 (talk) 11:12, 11 October 2013 (UTC)

I recently had to destroy a hard drive of a computer I was discarding, to prevent data theft, and finally chose to drill through it to destroy the memory platter since it could not be easily smashed with a hammer or hatchet. The metal case seemed far harder than aluminum or zinc. Odd little fasteners were used to assemble it which I did not have in my set of screwdrivers and bits. I don't see why it would need to be armored since it is normally inside the computer case. Steel would provide some protection against external magnetism which might affect the stored data. Edison (talk) 14:47, 11 October 2013 (UTC)

What is the material in the top lid ..? Electron9 (talk) 21:49, 11 October 2013 (UTC)

Looking at an old Seagate HDD before me, it is (speaking as an engineer) a Magnesium alloy. Can't give any ref other than this. [1] The molding, tolerances, stiffness, economics, etc., can only be matched this alloy (unless you go to very exotic materials -in which case it would appear very different from the thing before me). --Aspro (talk) 21:55, 11 October 2013 (UTC)

It is amazing how much alloying can change a metal's properties. Pure aluminium is soft and ductile, whereas when alloyed with a little copper, becomes tough and rigid. One should not assume what the dominant metal component material is from the apparent properties. I can imagine that rigidity and low cost would be the primary criteria for a HDD chassis. Magnetic shielding is unlikely to be a consideration, since stray magnetic fields will be too weak to have a significant effect on modern magnetic recording media. — Quondum 20:07, 12 October 2013 (UTC)

Being die cast does not exclude aluminum as a possible candidate. Here is one website (blocked link, google ehow "What Are Computer Hard Disk Drives Made Of?") which supports my original answer. The housing is very rigid and is usually made of thick aluminum. Vespine (talk) 00:45, 14 October 2013 (UTC)

Duralumin is not used in diecasting, (re Quondum's link). Note that adding copper to aluminium does NOT make duralumin. While copper is the next largest fraction after aluminium, it is the other elements added (principally manganeses) that make it duralumin. If other elements are not added in significant fractions, or other elements are added, it becomes aluminium bronze with a nice gold colour and completely different mechanical properties, or nordic gold, used for coining, for instance.

However, you are certainly correct in saying the alloyed elements can make a big difference in properties, which is why zinc alloys used in diecasting are not soft like pure zinc. 121.221.33.239 (talk) 00:56, 14 October 2013 (UTC)

What kind of spider is this?

I saw this at Hayes & Harlington Station in west London.

https://dl.dropboxusercontent.com/u/8129635/Photo%2016-08-2013%2016%2019%2053.jpg

— PhilHibbs | talk 14:52, 11 October 2013 (UTC)

The distinctive markings on the back suggest that it's a Steatoda nobilis or False Widow spider. They have become more common in the UK kn recent years, and have been the subject of some alarming, but possibly overstated or hoaxy, stories - see e.g. this one (warning: alarming image) which came up on my Facebook feed today. 16:39, 11 October 2013 (UTC)

Some more from the reliable folks at the BBC, which I saw a few days ago on the telly: False widow spider sightings in the UK on the rise. Alansplodge (talk) 18:38, 11 October 2013 (UTC)

Happens in the US too; just today the paper had an article about a man who had vanished and was declared dead 30 years ago, but showed up alive (and not a zombie) recently, much to the surprise of his remarried widow. Gzuckier (talk) 04:07, 13 October 2013 (UTC)

Looks more like a Steatoda grossa to me. — PhilHibbs | talk 14:41, 5 November 2013 (UTC)

Say WHAT? Nostril specific sniffing test for Alzheimers

Can someone cast suitable aspersions on the credibility of this? [2] [3] (original report: [4]) I know nothing is impossible in biology, but......... this really puts that to the test! (I don't have access to the journal, never heard of it, and it's from the University of Florida... still...) Wnt (talk) 16:22, 11 October 2013 (UTC)

There's nothing about it that strikes me as outright impossible, but it's a small-scale pilot study with loose methodology, and those sorts of things often don't hold up when done on a larger scale with more careful methodology. In short, good enough to justify a more thorough investigation; not good enough to take seriously as a diagnostic tool yet. (I don't have access to the journal either; I'm judging by the abstract.) Looie496 (talk) 16:43, 11 October 2013 (UTC)

I do have access, and a quick scan of the paper doesn't reveal anything strikingly bad about it. They're just measuring olfactory discrimination type responses, as they say in the paper, it is known that the olfactory cortex is an early victim of AD (loss of smell is well described). So not too shocked there. Whether it will translate into a clinically relevant test, time will tell. As far as the journal goes, I'd never heard of it either, and I work as a neuroscience researcher, and have published in the Journal of Neuroscience amongst others. It seems to be a genuine journal though, if not a very impressive one, with only an impact factor of 2.4. EDIT: Forgot to address the nostril specific effect, yes that's a bit odd, but possibly one hemisphere is affected earlier in the disease process than the other? Not sure. Fgf10 (talk) 17:12, 11 October 2013 (UTC)

(ec) Not crazy at all. (Argument from incredulity isn't generally a helpful analysis technique.)

There's a lot of literature out there that report microsmia(diminished sense of smell) and anosmia (loss of sense of smell) as symptoms associated often associated with Alzheimer's disease. AD patients often have trouble sensing and identifying particular odors, even at very early stages and while having very mild cognitive impairments. For an overview, try Rahayel et al. (2012) "The effect of Alzheimer's disease and Parkinson's disease on olfaction: a meta-analysis" Behav. Brain Res. 231(1):60-74. It is also known that there tends to be left-right asymmetry in the loss of gray matter in Alzheimer's patients (the refs are in the paper), so it's not unreasonable to hypothesize there might be an associated asymmetry in sense of smell.

Thanks for pointing this out - I should have thought to look at the reference list. [5] looks useful. Wnt (talk) 17:49, 11 October 2013 (UTC)

As Looie496 says, it's a single small study at a single clinic. There are the usual concerns and caveats about the robustness and reproducibility of such studies in general, but I didn't see any obvious red flags, and it suggests an area for further research. TenOfAllTrades(talk) 17:13, 11 October 2013 (UTC)

Ethics in scientific research

Why is that in the 19th century and early 20th century people could do whatever they wanted in science without any limitations of ethical standards? I learned that cars were invented prior to mandating that you can't drink and drive at the same time! In science, you hear stories about unethical well-known experiments that were carried out, like that experiment where Clark Hull trained Ernest Hilgard to blink in anticipation of a slap to the face. Fortunately, the slaps did not dissuade Hilgard from going on further into research. 164.107.102.72 (talk) 16:37, 11 October 2013 (UTC)

This actually seems more like a Humanities question - you should get better answers there. I can't think of a good scientific source that could explain it, though obviously we can reference developments like the Nuremberg Code without a deep understanding of the cause and effect involved. But at a time where slaves could be whipped with impunity, or later on, where "free" blacks and the poor were routinely exploited under Jim Crow, I can hardly imagine a code of ethics would be more than rudimentary, except within isolated subcultures. Wnt (talk) 16:41, 11 October 2013 (UTC)

It's certainly true that ethical standards have become stronger over time, but it's not true that people were ever able to do whatever they wanted with no limitations. For example, in the 19th century and earlier, people who studied human anatomy often had to obtain material by illegal means, and were subject to very severe penalties if they were caught. Looie496 (talk) 16:49, 11 October 2013 (UTC)

The ethical values have evolved over time. Also, we now have a more formal system of approving research proposals, testing whether ethical guidelines are satisfied is a standard part here. But you can't blame previous generations for not having our ethical norms, as they are subjective to some degree. E.g. the limit on your blood alcohol level for diving is rather arbitrary, and there is no limit on many other prescription drugs that will also affect driving abilities. Another example is that we have rules of pollution, but air pollution isn't taken very serious. Euthanasia is illegal in many countries because of opposition from religious organizations. That's arguably a severe human rights violation of those terminally ill people who are now deprived of making the choice to end their lives. In the grander scheme of things, the way we treat the environment is so bad that if ET were to arrive here on Earth he would probably decide to exterminate the entire human race.

So, my point is basically that most people will tend to support whatever the ethical values of the society he lives in are, and will view the ethical values of other societies as being "wrong". Count Iblis (talk) 16:55, 11 October 2013 (UTC)

Um... I think Clark and Ernest are both white. And none of you have mentioned ethics in animal research. 164.107.102.72 (talk) 17:09, 11 October 2013 (UTC)

• Ethics in specific fields tend to evolve over time and only after the field itself develops. The rules of the road in driving such as highway passing rules didn't develop until after driving was around for a while. Horse whispering and other non-coercive methods of "breaking" horses have only developed in the last century, while horses have been ridden since 4000 BC. The notion that infants didn't really feel or suffer from pain ended only in our lifetimes. Educated Romans often had very admirable ethical codes, such as Stoicism, but there is a reason people of the countryside were called villains and pagans. Progress isn't unidirectional--the British Empire ended slavery and high-seas piracy, both of which have made striking comebacks. Historically speaking, animal research is a very recent phenomenon. See also Steven Pinker's The Better Angels of Our Nature. μηδείς (talk) 00:25, 12 October 2013 (UTC)

Medeis, I think you better read slavery as the British Empire did not end it. Saudi Arabia didn't abolish slavery until 1962 and they still had about 300,000 slaves in 1963. I doubt too that the BE was able to eradicate piracy. CambridgeBayWeather (talk) 05:16, 12 October 2013 (UTC)

I am aware of such continued local slavery and piracy, but didn't think it necessary to mention there were pockets of such barbarity. μηδείς (talk) 05:50, 12 October 2013 (UTC)

• In the UK the Anatomy Act 1832 was passed to prevent the illegal trade in corpses mentioned above and the Cruelty to Animals Act 1876 set strict limitations on scientific experiments on animals calculated to cause pain. The Cruelty to Animals Act had developed from earlier Acts put in place to protect animals. See also: History of animal testing#Early debate. Richerman (talk) 23:20, 12 October 2013 (UTC)

• The claim that people "could do whatever they wanted" is simply false. The legal system has always regulated what people can do vis-a-vis each other, that is, for as long as it has existed. Before there were laws, there were other means, such as, if someone slapped someone on the face, they could slap them back. Ethics committees and similar review bodies did not invent the idea of social control. From the pdf found by googling "clark hull ernest hilgard slap", see here, there is nothing suggesting how hard the slap in the face was, so any claims about the ethical standards are open to debate. The history of the modern ethics process begins with Karen Ann Quinlan, and is something of a response to specific circumstances. You may like to look into the history a little further. IBE (talk) 03:39, 13 October 2013 (UTC)

There are many possible answers to your question, but I'll give three:

1. Professional science has only existed since the mid-19th century, and modern medicine is later still. It takes a while for consensus to form. Even today, there is no consensus among the scientific community about the morality of stem cell or animal research.

2. There were early regulations, but they weren't as extensive or protective as today's. Richerman gave two good examples.

2. Isaac Newton said "If I have seen further, it is by standing on the shoulders of giants." He was talking of science, but the same is true of morality. You have all of mankind's knowledge at your fingertips, searchable with a speed unimaginable even 50 years ago. The world has gathered 150 years of experience in professional science, experimented with every conceivable form of moral code, seen horrors like the Holocaust or Unit 731, and done away with war or even borders on an entire continent. Looking back at someone from 1800 and asking how he could be so immoral is like berating Ptolemy for not landing a rover on Mars. For all you know, future generations might look upon today's slaughterhouses and animal research labs in the same way we look upon the Holocaust. --Bowlhover (talk) 06:13, 13 October 2013 (UTC)

Digital clock speeding up.

Hi.

I've had this clock for about twenty years. It's a Cosmo Time, model #E517A. In the last two days, it's been counting fast (about 22 seconds per "minute"). Any ideas what's going on here? InedibleHulk (talk) 17:15, 11 October 2013 (UTC)

See if the clock has a 50/60 Hz mains frequency switch that your cat has bumped to the wrong position. Other random possibilities: it's running on battery instead mains (uses wonky internal crystal instead of mains frequency), dirt or moisture got inside it, broken electronics, your utility company has switched to remotely readable electric meters and the clock is confused by their control signals. 88.112.41.6 (talk) 17:37, 11 October 2013 (UTC)

That last one seems possible. I'll have to look into it. Maybe the dirt thing, too (I'm a heavy smoker, but have been the whole time). Thanks for the tips. InedibleHulk (talk) 17:56, 11 October 2013 (UTC)

Check for the Hz switch though, or 110/220 volt switch. Because if you live in 50 Hz world and your clock is configured to 60 Hz, that's *exactly* 22 seconds per minute overclocked. 88.112.41.6 (talk) 18:10, 11 October 2013 (UTC)

I don't see a switch, and think I live in 60Hz land (Ontario). But I'll look harder (at my clock and recent Hydro news). When I unplugged the clock, I noticed the 12:00 flashed much faster than normal. In 15 minutes, it's already 4 minutes ahead. Just another reason to hate smart meters, I guess. InedibleHulk (talk) 18:19, 11 October 2013 (UTC)

Back of the clock says "AC/CA 120V 60 Hz 5W". InedibleHulk (talk) 18:21, 11 October 2013 (UTC)

Not necesarrily a smart meter issue. Google suggests that it has a 9V battery backup, which means everything probably runs off DC internally. I would guess something has failed in the oscillator circuit that it uses to keep time. Running it off battery would let you know if the problem is in the clock or in the incoming power. Katie R (talk) 18:47, 11 October 2013 (UTC)

Perhaps. If I find a 9-volt battery, I'll test that. Ten minutes off right now. InedibleHulk (talk) 18:50, 11 October 2013 (UTC)

Can't find a battery. But my "minute" was 45 seconds, at last check. Seems to be gradually speeding up, so I'd guess the 22-second connection to 50/60 was coincidence. My smart meter is consistently turning to a row of 8s every two seconds (for whatever that's worth). From what I've learned today of quartz timekeeping and the eastern power grid, I'm leaning toward blaming Hydro. I can't think of anything that would have damaged the crystal (before I checked for a switch, the clock hadn't moved for months).

I think I have enough of a start to try and solve this on my own now. Thanks, folks. I won't trouble the Science Desk with the question of whether to freeze or starve for time-of-use pricing this winter, which becomes the bigger issue, the more I Google. InedibleHulk (talk) 19:57, 11 October 2013 (UTC)

Amazingly, that kind of horrid inaccuracy is just what I expect from a Chinese digital clock running off the battery. But, clocks are cheap, so I'd just pitch it out and replace it. StuRat (talk) 00:56, 12 October 2013 (UTC)

Honestly, I firmly believe that any clock with a cord is a monument to stupidity that ranks right up there with the Pyramids of Egypt. The point of a clock is to be reliable; the nature of electricity not to be; and that's not even getting into the issue of a clock using so much power that its "emergency battery backup" that can keep it going for four hours contains sufficient energy to launch it halfway into space. I have an old digital alarm clock, no cord, that dates back to somewhere in the late 1980s, which I remember getting a single new 1.5V battery for perhaps twice, with a loud alarm and an easily readable display (though not illuminated). And I don't understand how things like yours are allowed to exist. Wnt (talk) 03:13, 12 October 2013 (UTC)

OK, I'll bite. Why are the Pyramids of Egypt "a monument to stupidity"? -- Jack of Oz ^{[pleasantries]} 04:53, 12 October 2013 (UTC)

Well, they were designed to protect the dead pharaoh and all his treasures, but were mostly robbed in short order. Later pharaohs realized that a pyramid is just like a giant "Rob me !" sign, and hid their tombs, instead. And, I suppose that wasting all those resources which could be better spent on roads, etc., could be viewed as stupidity, depending on your POV. StuRat (talk) 10:59, 12 October 2013 (UTC)

Pyramids and electric clocks and the Great Wall of China and eight-track tape players and that sort of thing all qualify as things that "seemed like a good idea at the time." ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:14, 12 October 2013 (UTC)

Meh. I live an unstructured life, so the time of day is mostly just a curiosity. And this clock answered that curiousity for decades. It's still somewhat aesthetically pleasing (compared to a pyramid), and I have other clocks, if I need to know. If a battery or cleaning can fix it, it's still a great clock. InedibleHulk (talk) 18:45, 12 October 2013 (UTC)

You sound like the guy in an old Cheech and Chong bit, where someone's trying to sell Chong a watch, and he says, "I'm not into time, man." ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:54, 12 October 2013 (UTC)

Makes sense. I also look like Chong. InedibleHulk (talk) 18:48, 13 October 2013 (UTC)

So Stu, I wonder why we don't just call them the Pharoahs' Tombs. -- Jack of Oz ^{[pleasantries]} 16:48, 13 October 2013 (UTC)

One possible cause of a digital clock losing its accuracy, from my experience: A couple of customers in the same neighborhood reported that after the power was off and restored, their digital thermostats ran fast. Investigation showed that a component in the clock (capacitor?) synchronized it to the mains frequency, and the spike from the interruption (lightning related) had burned out the coupling component, allowing them to run on their own frequency, which happened to be fast. Alternatively a spike or age related failure could have damaged or changed a component in the oscillator circuit of your clock, if it does not synchronize the the mains. Edison (talk) 19:32, 12 October 2013 (UTC)

The last outage was lightning-related (and almost fried me), but at least a month ago. Maybe it caused some damage, which gradually got worse. I can't see screws on the clock, so putting off opening it lest it doesn't fit back. But I'll definitely look for burns when I do.

If failing after twenty years of satisfactory performance, you might consider replacing your watch with a radio-controlled watch. Whether your life is unstructured or not, it's nice to know that your watch is correct to the nearest second. You'll know if you actually need to run to catch the bus. Less stress. If you have the luxury of arriving late whenever you please for work or any other appointment, well good for you! Otherwise, the Casio ones (Waveceptor) are not very expensive. They function well in my experience, although I've had to manually adjust the time zone when traveling sometimes, if my hotel room has been in a city center, surrounded by tall buildings. --NorwegianBlue ^talk¨

It's an alarm clock with the problem. My watch is fine, though I rarely wear it. I mainly see buses, meetings, planes and hotels in movies. Not quite Cletus the Slack-Jawed Yokel, but closer to that end of the spectrum. InedibleHulk (talk) 18:48, 13 October 2013 (UTC)

I'm with you there. If you are constantly late for things, you don't need a better watch/alarm clock, you need to restructure your life so people stop expecting you to be places at specific times. :-) StuRat (talk) 21:52, 13 October 2013 (UTC)

As someone with a reliable watch that used to catch the bus into work, while the watch ma be acurate to the nearest second, the busses rarely are! MChesterMC (talk) 10:17, 14 October 2013 (UTC)

Photonic molecules

Can someone give a really dunce-level (and above all, long) explanation of photonic molecules? (Some of the results might be used to edit the article)

In particular:

• Why is there such a thing as a Rydberg blockade? What conditions prevent adjacent molecules from having the same excited state? What is the range of the effect, and what particle mediates it? Does it apply only to electrons, or would it also affect nuclear isomers? Can it be used for some kind of imaging akin to X-ray crystallography that maps the positions of pairs of excitable atoms? Etc. You don't have to answer some of these unless you really want :)

• How does a photon excite an atom while passing through it?

• What exactly is dispersive coupling?

• The photons exit the cloud as "normal photons (often entangled in pairs)". Does this mean that they are not photonic molecules at that point, but subject only to normal quantum entanglement?

• Does the photon "appearing to have mass" relate directly to the refractive index? Where does this mass come from? Does this work the same way as the Higgs boson gives mass to other particles? Does photon "mass" fold spacetime (ever so slightly) like Higg-derived mass?

Admitting utter confusion... Wnt (talk) 17:26, 11 October 2013 (UTC)

I suspect that you'll find few people who are less confused about this than you are. It takes specialized knowledge to be able to answer pretty much any of these questions. One could start to make guesses on some of these. What I say here should be treated as pure speculation; perhaps it will serve to trigger some responses and corrections from others.

• I'm skipping your first bullet.
• A Rydberg atom has an electron that is exited to nearly the point of ionization, where the energy levels are very close to each other. It seems likely that a low-energy photon will be able to easily excite it further during a normal photon absorption process, because of the availability of states with energy levels close to the level necessary. If the atom is in a suitably prepared superposition of Rydberg states, it seems reasonable that the incident photon would encode its quantum state (momentum, energy, polarization) on the excited electron, and that this could manifest as preferential emission of a photon with similar characteristics after some delay.
• Dispersive coupling probably relies on an interaction between dispersion and non-linearity in a medium. An example might be in Soliton (optics), where the effect occurs at high intensities and keeps a photon pulse very closely confined – either laterally or longitudinally. One might imagine a similar effect here, except that the number of photons is very small.
• I interpreted the photons to be normal photons upon exit, entangled as you suggest. It would only be within the medium that they could interact and form "molecules".
• A quantum field "appearing to have mass" would normally relate to how it propagates as wave. In the simplest case, this would lead to a propagation velocity that slows to zero as its energy drops to some critical value, its "rest mass". This occurs in superconductors, where photons below the critical energy only propagate into a superconductor as virtual particles: they "appear to have mass" inside the superconductor, which could be interpreted to lead to the Meissner effect. This would perhaps also be seen as a reducing refractive index (starting at ∞) at energies above the critical photon energy. The case here is likely to be more complicated.

So, now I'll wait for others to shoot all this down... — Quondum 19:39, 12 October 2013 (UTC)

October 12

Eat stuff or convert light into energy

Is there a living being that can or could do both? Did some species lose the ability to do photosynthesis and started eating things? OsmanRF34 (talk) 02:42, 12 October 2013 (UTC)

Euglenozoa ancestrally have the ability to do both (autotrophic and heterotrophic) but kinetoplastids have lost the ability, including some very serious human etiologic agents. Wnt (talk) 03:08, 12 October 2013 (UTC)

Carnivorous plants do both. --Jayron32 03:16, 12 October 2013 (UTC)

There's also a certain Mediterranean wasp that can both eat stuff and do photosynthesis -- I forgot its name, though. 24.23.196.85 (talk) 20:16, 12 October 2013 (UTC)

The Oriental hornet has been featured in some articles for this. — Quondum 01:07, 13 October 2013 (UTC)

(edit conflict) There are many examples of living things that do both. Photosynthesis#Evolution might be a good place to start. Giant clams and upside-down jellyfish are a few examples. Saprophytic plants (no article?) such as some species of Triuridaceae are examples of species that have lost the ability to photosynthesize.--Wikimedes (talk) 20:19, 12 October 2013 (UTC)

File:Elysia chlorotica (1).jpg

Elysia chlorotica larva

There is Elysia chlorotica, a sea slug (gastropod) and other members of its genus. And I believe there are symbiotic flatworms as well, but I couldn't find a name or get an article. μηδείς (talk) 00:24, 13 October 2013 (UTC)

Here's a bit on photosynthetic flatworms [6]. Apparently they are considered to be salt water aquarium pests.--Wikimedes (talk) 02:08, 13 October 2013 (UTC)

Yeah, I saw that link. They don't give or link to a scientific name, and the pictures in the gallery look like different species. μηδείς (talk) 16:34, 13 October 2013 (UTC)

But, species that eat stuff and transform light into energy, just use the eaten stuff as nutrient, or as a source of energy too? And why would any species lose the ability to use light? Where is the advantage of having to hunt other living beings? OsmanRF34 (talk) 22:31, 13 October 2013 (UTC)

There will be no general rule about whether nutrients or energy are the primary benefit derived. Some species will use energy obtained from eaten stuff (e.g. the Oriental hornet), some probably not (such as the Venus flytrap, which probably primarily derives nitrogen-containing nutrients from the digested insects, which tend to be insufficiently supplied by the soils that it grows in). As a general rule, though, when a species occupies an ecological niche in which it gains no benefit from an adaptation, this adaptation will eventually disappear. A fish species that lives in lightless caves eventually loses its eyes after many generations; species that live where light or other necessary factors for using the energy in light is lacking will lose the ability to use the light in time. Even if a reliable alternative is present which makes an adaptation valueless, the adaptation will be lost. — Quondum 23:56, 13 October 2013 (UTC)

Einstein disproof of Friedmann's expanding universe calculations?

When Friedmann showed that the equation of General Relativity meant that the universe must be either expanding or contracting, did Einstein at first propose a proof that Friedmann was wrong (and later retract the proof)? Bubba73 ^{You talkin' to me?} 05:09, 12 October 2013 (UTC)

That would be Einstein's non-zero Cosmological constant which he later described as his "greatest blunder". SpinningSpark 21:31, 12 October 2013 (UTC)

That is what the statement sounds like to me, but it said that he had a proof "later retracted" that Friedmann was wrong about asserting that the original GR says that the universe must be either expanding or contracting - and that part I don't know about. Bubba73 ^{You talkin' to me?} 21:39, 12 October 2013 (UTC)

Searching Google Books, I found a reference to this in "The Inflationary Universe" by Alan Guth, p.45: [7]. -- BenRG (talk) 05:28, 13 October 2013 (UTC)

Google won't allow access to that page of the book for me, but here is part of Einstein's retraction I got with a differnt search for anyone else having the same problem;

My objection rested however — as Mr. Krutkoff in person and a letter from Mr. Friedmann convinced me — on a calculational error. I am convinced that Mr. Friedmann's results are both correct and clarifying. They show that in addition to the static solutions to the field equations there are time varying solutions with a spatially symmetric structure.

Guth also says "In spite of this comment, Einstein still believed that the Friedmann solutions were of no relevance, as he remained confident that the universe is static". A belief he held until Hubble's momentous discovery. SpinningSpark 09:44, 13 October 2013 (UTC)

What roads (non-mwy) in the UK have jct numbers?

I know the A55, the A14, and the A12.Is that all?Or is there more?I don't know. Pls if someone would give those in Ireland then help welcome. — Preceding unsigned comment added by Puntaalpo (talk • contribs) 09:29, 12 October 2013 (UTC)

This is more of a Misc Desk Q than Science. StuRat (talk) 10:54, 12 October 2013 (UTC)

It doesn't belong here, but I will note the A1 in England does (there is also an A1 in Northern Ireland and I can't speak for that one). --TammyMoet (talk) 12:59, 12 October 2013 (UTC)

You can download a pdf map from this Highways Agency page which seems to have the answers to your question. It is very detailed and takes a while to download and load. SpinningSpark 22:38, 12 October 2013 (UTC)

mwy = motorway and jct = junction? --NorwegianBlue ^talk 17:28, 13 October 2013 (UTC)

That was my understanding when I answered. Fairly unambiguous I think. SpinningSpark 19:35, 13 October 2013 (UTC)

Peterborough is a hotbed of junction numbers[8][9] and, as you would expect, WP regards the matter as encyclopedic – Road transport in Peterborough#Numbered Junctions. Thincat (talk) 20:14, 13 October 2013 (UTC)

October 13

Floor tile material

I'm trying to determine the material some floor tiles are made of. At first, I thought they were vinyl, but after examining a few broken pieces, I now think it's something else. The tile pieces seem too heavy (dense) to be vinyl. They also feel cool to the touch, suggesting a higher thermal conductivity than familiar plastics. The tiles are about 1/8 inch thick (~ 3.2 mm). When I looked at the side of a broken piece, I noticed a rough texture that you're expect from broken earthenware. I also noticed a few sparkling (reflective) particles. What material could that be? Any educated guesses? --173.49.18.190 (talk) 03:06, 13 October 2013 (UTC)

Ceramic, just like you thought. Was that a bathroom tile? 24.23.196.85 (talk) 06:10, 13 October 2013 (UTC)

Ceramic is a possibility that I considered, but one thing I didn't mention was that the tiles seem at least somewhat flexible, as they seem to conform to and reveal the unevenness of the concrete floor below it. The location is not a bathroom. The tiles don't have any features that suggest they are designed for bathrooms. --173.49.18.190 (talk) 13:07, 13 October 2013 (UTC)

If it's from an older house, especially pre-1950's, it could be linoleum. Linoleum was made by mixing all manner of mineral powders, wood flour, etc, in a mixture of pine resin and linseed oil as a binder. The pine resin and linseed oil cured to a hard plastic, and the back side was often given a rough surface. Linoleum is extremely durable and you still sometimes find it. The fillers used, which probably account for >95% of the mass, do provide a higher thermal conductivity and considerably more thermal inertia that modern plastics. 121.221.33.239 (talk) 07:49, 13 October 2013 (UTC)

They could well be linoleum but a word of warning. Many vinyl floor tiles made between 1920 and 1990 contain asbestos and you should get professional advice before disturbing them see: here. Richerman (talk) 09:19, 13 October 2013 (UTC)

I don't know the vintage of the tiles, but they don't seem to have been laid during the period you mentioned (I think they're newer.) Do tiles that contain asbestos have markings or other telltale signs identifying them as such? --173.49.18.190 (talk) 13:07, 13 October 2013 (UTC)

No. In my country there are laboratories that will examine a sample and for a small fee tell you if there is asbestos. I guess there will be similar labs in other Western counries. 121.221.33.239 (talk) 15:08, 13 October 2013 (UTC)

No - if you look at the website I mentioned above it says "Vinyl flooring and wallpaper that contain asbestos cannot be recognized on sight" but it does tell you how to deal with them. However, it's not for me to say whether you should follow that advice or not - you must decide that for yourself. Richerman (talk) 19:21, 13 October 2013 (UTC)

It sounds like vinyl composition tile (VCT), which is a mixture of clays and other minerals in a vinyl resin binder. It's the ubiquitous 12" x 12" tile material seen in schools, large grocery and discount stores (Walmart uses square miles of the stuff), and institutional buildings all over North America. It replaced the more-durable vinyl asbestos tile (VAT), which used asbestos fibers as part of the composition, in the 1970s. It's not always obvious which is which, though VAT isn't especially dangerous unless it's been abraded or pulverized. Usually (but not always) VAT is more brittle than VCT, which will bend a little before breaking, and tends to come in 8" x 8" or 9" x 9" configurations as well as 12" x 12". There is no specific marking for asbestos tiles, since at the time they were being made and installed, asbestos was considered a good thing and was incorporated into a wide range of building products. Here's one manufacturer [10]. Acroterion (talk) 19:05, 14 October 2013 (UTC)

Vegetable identification

Hi guys. What is the vegetable behind the Apple? Thanks. Ben-Natan (talk) 05:39, 13 October 2013 (UTC)

It looks like a gourd. Plasmic Physics (talk) 06:26, 13 October 2013 (UTC)

Some variety of Cucurbita pepo, perhaps a yellow crookneck squash. μηδείς (talk) 20:32, 13 October 2013 (UTC)

Solution book of University Physics with modern Physics 13th edition

While solving problems of Sears and Zemansky's University Physics (by Hugh D. Young and Roger A. Freedman) 13th edition, I face two problems. First, answers of only odd-numbered problems (not the even-numbered problems) are given in the end of book. Whenever I solve even-numbered problems, I am not able to check whether my answers are right or wrong. Second, some problems are really very tough. Also, neither my teachers nor my friends use that book, and they often make excuses whenever I ask my unsolved problems to them. Therefore, I need a link to a website or any solution book. Thanks for helping me. Scientist456 (talk) 07:49, 13 October 2013 (UTC)

You need this booklet with answers to even numbered questions which should have come with the book. You can buy second hand copies from Amazon Marketplace (sorry, I can't post a link, the site seems to be on the blacklist) but most of them do not specify which edition they are for and I don't know how different the questions are between editions. SpinningSpark 10:41, 13 October 2013 (UTC)

What is a prepalate?

The prepalate is at 6.

I am contributing to the article on Kitab al-'Ayn, the first dictionary for the Arabic language. The author arranged the letters according to the source of pronounciation instead of alphabetically.
"Oh, that's a question for the language section of the reference desk."
No, ominous voice. I don't need to know about linguistics, I just need to know what a prepalate is. Is that another word for the hard or soft palate, for example? MezzoMezzo (talk) 10:33, 13 October 2013 (UTC)

This diagram comes from our article Places of articulation. The prepalate is at 6, between the very back of the alveolar ridge and the hard palate. The hard palate is at 7 and the soft palate further back still, at 8. It's a small area and often seems to be subsumed into the areas surrounding it for linguistics purposes. A Google search reveals that oral surgeons do often refer to it as a discrete area in the context of describing the extent of cleft palate. - Karenjc (talk) 12:10, 13 October 2013 (UTC)

What is the scientific explanation for this !

on link http://www.youtube.com/watch?v=jxOyST6gM_A — Preceding unsigned comment added by 37.237.196.193 (talk) 11:03, 13 October 2013 (UTC)

Very amatuerish camera trickery, eg stop motion shooting/editing. For arms shown projecting thru solid objects, chromakeying is the proffessional way to fake it, but this video is sufficiently rough and blurry that they could simply have made a hole in a sheet of fibreboard or similar. 121.221.33.239 (talk) 12:53, 13 October 2013 (UTC)

This is not amateurish camera trickery. The video quality isn't as good as one might expect under the circumstances, but the person involved is Criss Angel, a famous magician, and the video is apparently a (somewhat low quality) copy of an episode of his TV show Criss Angel Mindfreak, which presumably was broadcast with a much higher video quality. Criss Angel is easily rich enough to afford a high-quality custom built trick gate. Red Act (talk) 03:28, 14 October 2013 (UTC)

Your search keywords are "revealed" and "exposed". There are hundreds of videos trying to explain these magics tricks. Cacycle (talk) 17:47, 14 October 2013 (UTC)

A very rich dude acting as a boofhead and using professional staff and equipment to do work with a very amatuerish look then. 121.215.39.252 (talk) 23:51, 14 October 2013 (UTC)

Well, yeah, that's kind of his shtick. His genre is guerrilla magic, so it fits the style he's aiming for to look like an unpolished amateur "average joe" that you might happen to see walking down the street on an average day, except that he's doing something astonishing. I think the idea is that the "magic" is supposed to seem more amazing if it takes place under ordinary circumstances involving an ordinary guy, instead of taking place on a stage under the auspices of a guy in a fancy outfit, under circumstances that are clearly highly controlled. Red Act (talk) 01:28, 15 October 2013 (UTC)

Is there any picture of the mixed flow compressor in the pratt and whitney pw 600f?

hey guys do you know if any picture of the mixed flow compressor in the Pratt and whitney pw 600f exists? cause pratt and whitney mentioned this themselves and the wikipedia artickle says it but there is only one patent picture buzt it downt shows rhe mixed flow compressor..Saludacymbals (talk) 17:12, 13 October 2013 (UTC)

You've seen our Pratt & Whitney Canada PW600 article I take it? SpinningSpark 21:33, 13 October 2013 (UTC)

yes i saw the article but there is only the picture of the fan and not the compressor. so is there any picture of it?

amazing spider web bridge line (which type of spider?

http://www.youtube.com/watch?v=zubftSpCg2E in this video you can see an amazingly thick bridgeline of a spider web but there is a photo in the description of this type of spider. dguys do you know wich type it is? maybe darvins bark? Saludacymbals (talk) 18:36, 13 October 2013 (UTC)

Male and female variation, height and puberty

It is often said that men are taller than women; however, some women are taller than some men.

It is often said that girls begin puberty somewhat earlier than boys; is it also true then that some boys begin puberty earlier than some girls?--Whatdeanerwastalkingabout (talk) 23:57, 13 October 2013 (UTC)

While the logical link you are suggesting is fallacious, the answer is yes, some boys begin puberty at an earlier age than some girls. Puberty onset depends on a variety of factors, including sex, genes, nutrition and social circumstances. So boys with favorable factors for early puberty will experience it earlier than girls with unfavorable such factors. Effovex (talk) 01:56, 14 October 2013 (UTC)

It is often said that women are more fallacious than men. But some men are more fallacious than women. μηδείς (talk) 02:18, 14 October 2013 (UTC)

The trouble with women is that they all make sweeping generalisations :) Richerman (talk) 09:09, 14 October 2013 (UTC)

• People say men are cunning linguists. However, some women are more cunning linguists then men. — Crisco 1492 (talk) 09:15, 14 October 2013 (UTC)

Hmmm... I was going to say something about women being more fellatious but thought better of it. Richerman (talk) 09:24, 14 October 2013 (UTC)

What in the world did you think I was punning about? μηδείς (talk) 18:56, 14 October 2013 (UTC)

You could always try phallacious. -- Jack of Oz ^{[pleasantries]} 11:06, 14 October 2013 (UTC)

Note being one to engage in such puns and frivolity, let me try to give a straight answer. Things such as you describe generally follow a bell-shaped curve. I'm limited to what I can draw here, using ASCII text, but here's a rough idea of what it looks like:

  ^       _
  |      / \
N |     /   \
  |    / MEN \
  +------------>
       Height
  

That graph shows the number of men at each height. Note that there are more men of average height than very short or very tall men. If we did the same graph for women, we would find a similar pattern. although the average would be less than for the men:

  ^    _
  |   / \
N |  /   \
  | /WOMEN\
  +---------->
    Height

If we then graph both together, we get lots of overlap:

  ^    _  _
  |   / \/ \
N |  /  /\  \
  | /W /  \ M\
  +------------>
      Height

So, this shows that the average woman is shorter than the average man, but there are some women taller than some men. It's also likely that the tallest man will be taller than the tallest woman, and the shortest woman will be shorter than the shortest man, although not always, as the bell-shaped curve tends to become more variable at the ends. Now, you will sometimes find a pair of bell-shaped curves which don't overlap, like the weight of adult mice versus the weight of adult cats:

  ^    _        _
  |   / \      / \
N |  /   \    /   \
  | /Mice \  /Cats \
  +------------------->
         Weight

In that case, we could say that all adults cats are heavier than all adult mice. StuRat (talk) 13:05, 14 October 2013 (UTC)

Any two bell-shaped curves overlap by definition, a normal distribution does not have upper or lower limits. It's just that the overlap in some cases is negligible, so the chances of finding a cat smaller than a mouse are very small (assuming that their sizes really follow the bell-curve). - Lindert (talk) 14:06, 14 October 2013 (UTC)

Which of course brings us to the point of contention that most readily occurred to me, because they aren't necessarily likely to follow a bell curve at all. Stu's initial framing premise that "things such as the [the OP describes] generally follow a bell-shaped curve" is not necessarily at all true. It would depend greatly on the feature being considered (with considerable variation even amongst the obvious and superficial phenotypical features). Snow (talk) 22:06, 14 October 2013 (UTC)

Hippety Hopper. DMacks (talk) 14:10, 14 October 2013 (UTC)

Well no, it may not always be the best model, but I think he did a good job of showing how overlapping distributions lead to plenty of cases that happen differently than the average case. And because of the Central limit theorem, bell curves pop up all over the place in nature. In the case of height or start of puberty, it makes sense to expect a roughly bell-shaped curve, even though it obviously won't go off to infinity like an ideal one, and may have other deviations explainable by the properties of the things being measured. Katie R (talk) 14:46, 15 October 2013 (UTC)

Yes, it's not possible to have an infinite height or a zero/negative height. For puberty, I suppose it's possible for somebody to have some medical condition which causes them to live their entire life without hitting puberty. Puberty could also begin at, or even before, birth, due to some medical condition, but obviously can't start before conception. I have no idea whether such medical conditions actually exist, but they are theoretically possible. StuRat (talk) 17:48, 15 October 2013 (UTC)

October 14

Do fruit flies spontaneously generate?

I have seen and raised the maggots of Drosophila melanogaster in genetics lab in college. But although I have had briefly self-sustaining colonies of whatever teensy fruit fly is endemic to the NE US come into the house with fresh produce, why have I never seen one of their babies? (And please don't post pictures.) Thanks μηδείς (talk) 02:15, 14 October 2013 (UTC)

For the same reason you never see a baby pigeon - you're not looking in the right place! Richerman (talk) 09:19, 14 October 2013 (UTC)

Perhaps the best place to look is where fruit or their skins have been allowed to acidify, as might be suggested by the first answer in this link. While they may fly inside to lay their eggs on fresh fruit, they might be developing into maggots and then flies outside in the discarded compost and garbage. — Quondum 15:52, 14 October 2013 (UTC)

History of Animals, although it is not the latest scientific research on the matter, supports the theory of spontaneous generation. Thincat (talk) 09:59, 14 October 2013 (UTC)

Aristotle may have been a great philosopher, but as a scientist he was a bust. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:38, 15 October 2013 (UTC)

A great white marble bust. Plasmic Physics (talk) 02:42, 15 October 2013 (UTC)

As a serious note, Aristotle's science was excellent. He tried to induce principles based on observation. The problem with his science is that for the next millennium and a half people repeated his conclusions as dogma without using his method or testing his results. μηδείς (talk) 23:06, 15 October 2013 (UTC)

Fruit flies, humans and everything else we have here did in fact spontaneously generate from a cloud of Helium and Hydrogen gas. Count Iblis (talk) 02:57, 15 October 2013 (UTC)

'Everything' requires more than hydrogen and helium, what about the other elements? Plasmic Physics (talk) 03:18, 15 October 2013 (UTC)

The other elements can be spontaneously generated from hydrogen. Count Iblis (talk) 14:07, 15 October 2013 (UTC)

Spectral radiance/Planck's law

The article on spectral radiance, which I was linked to from the Planck's law article, defines spectral radiance as "the quantity of radiation that passes through or is emitted from a surface and falls within a given solid angle in a specified direction".

The Planck's law article states that the spectral radiance of a black-body, $B(\nu ,T)$, is given by

$B(\nu ,T)={\frac {2h\nu ^{3}}{c^{2}(e^{\frac {h\nu }{kT}}-1)}}.$

I'm trying to relate this law to the definition of spectral radiance above. I'm guessing the surface referenced to in the definition refers to the surface of the black-body, correct? But what solid angle are we talking about? Solid angles are defined with respect to a point (ie the origin of a coordinate system), but no such point is identified in the Planck's law article.

The reason I'm asking this question is that I'm confused about the derivation of the Stefan-Boltzmann law from Planck's law. I would have thought that, to use the notation from the article,

$j^{\star }=4\pi \int _{0}^{\infty }B(\nu ,T)d\nu$,

where the factor of 4π comes from the fact that there are 4π steradians in a sphere. But apparently,

$j^{\star }=\pi \int _{0}^{\infty }B(\nu ,T)d\nu$,

and I don't really understand why.

Finally, is the radiation emitted by a black-body at a particular point on its surface travelling perpendicular to the surface at that point? — Preceding unsigned comment added by 74.15.138.165 (talk) 02:36, 14 October 2013 (UTC)

A black body radiates in all directions from any part of its surface. A black body also absorbs radiation coming from any direction inpinging on any part of its surface. The law of reciprocity applies, and you can easily verify that all directions apply by looking at a hot enough black body surface from any angle. It does not appear dark at any off-normal angle. 121.215.39.252 (talk) 04:35, 14 October 2013 (UTC)

You can derive the Stefan-Boltzmann law from Planck's law as follows. Consider a box filled with thermal radiation in thermal equilibrium. This is described by Planck's law it is isotropic. The energy density as a function of frequency is some function u(nu) (so u(nu) dnu is the amount of energy per unit volume in the frequency interval between nu and n + dnu ). Then because the photons move at speed of c and are isotropic, the flux of photons with frequencies between nu and nu + dnu coming from a small solid angle dOmega is c u(nu)dnu dOmega/(4 pi). Now imagine a small black sphere of radius r inside this isotropic photon gas.

How much radiation will this sphere absorb per unit time? We don't need to calculate any integrals to find out, if we look at photons coming from any particular direction, then the intercepted flux by the sphere is the same as what a disk perpendicular to that direction of radius r would absorb. So, the sphere absorbs an energy per unit time of pi r^2 c u(nu)dnu dOmega/(4 pi) from the incident photons coming from photons from any solid angle range dOmega. Sice both the radiation and the sphere is isotropic, this doesn't depend on Omega, so we can integrate over all solid angles by multiplying by 4 pi. The total flux through the sphere from the photons from any direction is thus pi r^2 c u(nu)dnu = A/4 c u(nu)dnu where A is the surface area of the sphere. Since a black object at temperature T will emit as much radiation per unit time and frequency as it would absorb when placed inside a photon gas of temperature T, this means that a sphere will emit thermal radiation per unit frequency and unit area of c u(nu)dnu/4. This is then also valid for a black object of any arbitrary shape, because each emitted photon comes from some point on the surface and how much radiation each surface element emits per unit time, doesn't depend on the orientation of the other surface elements, as the emission process is a local process. Count Iblis (talk) 14:58, 14 October 2013 (UTC)

Another way to think about it: A piece of hot surface emits only into a half-space, so maybe the factor should be 2 π instead of 4 π. But if it really would be 2 &pi then it would have to emit the same energy into every direction of that half-space, and so if you start with a hot glowing sheet of some material being perpendicular to your line of sight, and then you tilt it, you should still receive the same amount of light from the surface, despite the fact that the surface's image on your retina is now smaller. I.e. the glowing sheet should actually look brighter if you tilt it. This obviously isn't true; the correction factor is equal to the cosine of the angle. Thus, we need an integral not only over the frequencies, but also over the angles:

$j^{\star }=\int _{\Omega }cos(\theta )\int _{0}^{\infty }B(\nu ,T)d\nu d\Omega$

Written out in full:

$j^{\star }=\int _{0}^{\frac {\pi }{2}}\int _{0}^{2\pi }cos(\theta )\int _{0}^{\infty }B(\nu ,T)d\nu sin(\theta )d\phi d\theta$

Thanks, I understand now. 74.15.138.165 (talk) 17:26, 15 October 2013 (UTC)

Icek (talk) 09:17, 15 October 2013 (UTC)

Are neutron star collision energies as large as supernova energies?

I've read that the nature of the energy emitted is mainly in gamma rays, and that unusual magnetic fields are created, so it's somewhat different than a supernova, but is the "pow" comparable in energy?76.218.104.120 (talk) 04:18, 14 October 2013 (UTC)

Well, a supernova certainly gives off more energy at once, when it explodes, but it's quite possible that the total energy given off from a neutron star, or even a normal star, over it's life, might be more. StuRat (talk) 12:41, 14 October 2013 (UTC)

I imagine that the OP was referring to the energy emitted at the time of a collision between two neutron stars, as might happen when they spiral into each other. This is one of the speculative sources of gamma-ray bursts. — Quondum 18:00, 14 October 2013 (UTC)

Cytomegalovirus and HIV

This letter to Nature, dated 1990, suggests a relationship between cytomegalovirus (CMV) and Human Immunodeficiency Virus (HIV) infection where CMV increases susceptibility to HIV infection. I can't, for lack of google-fu, find any more recent discussion of this relationship between these two viruses. I don't really expect an answer to the question, but I'm looking for instruction that my google-fu might become stronger and am expecting that the masters at the reference desk will know how to find such things. Specifically, it'd be nice to have an actual paper that discusses this link, rather than just a letter. 71.231.186.92 (talk) 04:39, 14 October 2013 (UTC)

Have you searched Google Scholar, http://scholar.google.com/schhp?hl=en, rather than plain old Google? μηδείς (talk) 04:56, 14 October 2013 (UTC)

Yeah, a couple of ways. 71.231.186.92 (talk) 05:24, 14 October 2013 (UTC)

I have read the same, that there is a strong relation. Electron9 (talk) 07:30, 14 October 2013 (UTC)

Three things - firstly, you might not be aware that a "letter" in Nature is an actual, proper, peer-reviewed academic paper in it's own right, for presumably historical reasons Nature calls it's shorter papers "letters" and it's longer papers "articles". The difference is explained in more detail here [11]. Secondly you might want to have a look through these results [12], which are (most of) the papers which cite your paper (I got to this be searching for the title of your paper in google scholar and clicking the "Cited by" link below it). Google scholar doesn't have quite as good coverage as the proprietary databases that also do this, but those are really expensive. I find this search approach is normally the best for looking for more recent discussion on the topic of a paper. Finally you should keep in mind that the paper claims to have found a link between CMV and HIV infection in human fibroblasts, grown in vitro. This may or may not be in any way reflective of the situation in vivo. You should also bear in mind that fibroblasts are not the primary site of infection in HIV, although they can become infected. As far as I can tell from my quick read of the abstract this paper suggests one of the mechanisms by which this can occur, and would probably have no bearing on the primary site of infection which is the CD4 T cell (it would not affect these cells in the same way as the virus utilises the CD4 receptor to gain entry to these cells, rather than an Fc receptor, which is what is induced by the CMV in the McKeating et al. system). Equisetum (talk | contributions) 12:31, 15 October 2013 (UTC)

Is light from light-emitting diode emitted with same phase?

Does light from light-emitting diodes have the same phase ..? Electron9 (talk) 07:29, 14 October 2013 (UTC)

No, a normal LED is an incoherent source. SpinningSpark 07:34, 14 October 2013 (UTC)

Not with a normal LED, but a laser diode is a closely related device which does produce coherent light. Red Act (talk) 15:24, 14 October 2013 (UTC)

What is the opposite of Wikipedia's List of mental disorders?

Is there a list of things that are unique to a healthy, able, sane mind? What is the study of ideal brains called? — Preceding unsigned comment added by 174.65.23.49 (talk) 11:42, 14 October 2013 (UTC)

Mental health and positive psychology study that sort of thing. Unique though, hmm, what is unique to a healthy animal? it can't be six legs like an insect or a trunk like an elephant. Dmcq (talk) 13:29, 14 October 2013 (UTC)

Yes, I would have said "things that are common to a ...", instead of "unique". One example might be having all parts of the brain be operational, such as can be shown on a blood-glucose utilization scan. However, some people have been amazingly functional with even large portions of their brains disabled or absent. StuRat (talk) 13:42, 14 October 2013 (UTC)

Thank you. — Preceding unsigned comment added by 174.65.23.49 (talk) 16:13, 14 October 2013 (UTC)

My brother-in-law wrote a book about that and titled it Optimal Human Being. It seems to get the idea across. Looie496 (talk) 20:23, 14 October 2013 (UTC)

Can axon tracts travel *around* the internal capsule?

Can axon tracts travel *around* the internal capsule, or must all the axon tracts travel *through* the internal capsule thereby making the internal capsule a gateway canal-like thing between the cortices and rest of the body? I am having trouble visualizing the bigness of the internal capsule in 3D in my head, based on 2D myelin-stain representations. (Hey, it isn't easy, particularly if this brain sliced in coronally at one or a few locations!) 164.107.102.151 (talk) 17:59, 14 October 2013 (UTC)

If you are asking whether there are any direct pathways between the cerebral cortex and spinal cord that don't travel through the internal capsule, the answer as far as I know is no. But there are a number of indirect pathways that go by completely different routes. Our internal capsule article ought to be helpful to you for visualizing it. Looie496 (talk) 20:17, 14 October 2013 (UTC)

October 15

Overview of chemistry - book?

Can you recommend me a book that is an overview of chemistry? An overview as in it would have a short description of numerous sub-fields and some of their main results and references. --81.175.225.92 (talk) 00:22, 15 October 2013 (UTC)

Any high school or introductory college text will probably suffice. The Central Science by Brown, LeMay, and Bursten, or General Chemistry by Kotz and Purcell are two that I have used before. --Jayron32 00:54, 15 October 2013 (UTC)

Jayron, do you mean Chemistry and Chemical Reactivity by Kotz & Purcell, or General Chemistry by Kotz, Treichel, & Weaver? 121.215.39.252 (talk) 03:25, 15 October 2013 (UTC)

Both, actually. I've use the two of them, and was trying to recall by memory, and conflated the two. --Jayron32 10:45, 15 October 2013 (UTC)

ray of light theory of eyes

one of our articles says " The first theory, the emission theory, was supported by such thinkers as Euclid and Ptolemy, who believed that sight worked by the eye emitting rays of light."

Let's try to understand how the Greeks could have thought so. Why don't people see in a dark room? (cave etc)? Why does a 'source' of light need to be seen in this case, if eyes cast their own light? Most perplexingly - if eyes cast their own light, why can't we see the 'eyes' of other people glowing in the dark, for example? Could you explain a little the very loose kind of thinking that made this almost kind of make sense in a childlike way? 212.96.61.236 (talk) 00:30, 15 October 2013 (UTC)

Well, cat's eyes and some other animals reflect light, and that could be mistaken for emitting light. Perhaps they just thought human eyes emitted "invisible light" (what we might call infrared or ultraviolet), which changed to visible light under the right conditions. StuRat (talk) 00:49, 15 October 2013 (UTC)

But we clearly don't see in the dark... moreover, put someone in a darkish place and then put a whole chorus full of people in front of it, their eyes all shining into it: that person can't see any better. so....? I mean it just seems so unworkable... 212.96.61.236 (talk) 01:11, 15 October 2013 (UTC)

I see in the dark, and furthermore my eyes are sensitive to near IR (down to 800 nm) and near UV (up to 320 nm) -- the IR looks a dark reddish-brown, and the UV looks gray. 24.23.196.85 (talk) 05:04, 15 October 2013 (UTC)

That seems extremely unlikely, unless you are a bird, and even then you wouldn't be able to see IR. The visible spectrum is 390 to 700nm, no reference I've seen shows the outliers being anywhere close to 320-800. That's much further outside the realms of believable than human biology would permit. I would find some sources of true IR and UV light to really test yourself in a double-blind manner (you can start with the LED at the end of a remote control, with someone who isn't you pressing a button in such a way that you can't tell if they're pressing it). If real, go present your self to the Guinness record-keepers. — Sam 63.138.152.139 (talk) 14:24, 15 October 2013 (UTC)

People (like my mother) who had cataract surgery before the latest generation of implantable lenses became available are able to see a little way into the ultra-violet. The idea that you could see into the infra-red or in total darkness is ridiculous. If User:24.23.196.85 truly has these super-powers then (s)he should go find a reputable laboratory where these capabilities may be investigated. (...or WP:NOR...either way). SteveBaker (talk) 15:16, 15 October 2013 (UTC)

Of course it's not possible to fully reconcile reality with the emission idea, which we know to be wrong. People have speculated on the reasons why this idea was so popular -- and there is even discussion on the question of why many people continue to believe it today. That comes down to thinking of ways that the emission theory has intuitive appeal. StuRat mentioned one reason (shiny eyes of animals). Another possibility is the subjective experience of heat or palpable pressure when someone is watching you; this matches the social understanding that a person who's staring at you is doing something to you, rather than you to them. As for the question about the loss of sight in darkness, that was explained either by some interaction of the sunlight with your eye's light, or by the idea that the eye doesn't create the light, but gathers it in and then sends it out again at whatever you're looking at. Here is a discussion of some of the past arguments for the emission idea: [13]. And a paper [14] and short article [15] discussing the question from the point of view of science education. --Amble (talk) 02:15, 15 October 2013 (UTC)

Are you looking for a source, or chat partners to tell you you are right? We can't tell you how correct you are, but we can recommend you read visual perception, emission theory, and intromission theory. μηδείς (talk) 02:19, 15 October 2013 (UTC)

I am offering some answers that have been given to the original question, and was slow in adding the sources from which I drew the information. --Amble (talk) 02:45, 15 October 2013 (UTC)

I am not the boss here, feel comfortable adding what you think appropriate. μηδείς (talk) 02:48, 15 October 2013 (UTC)

Superman's eyes emit light. But he's a strange visitor from another planet, where apparently things work differently. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:33, 15 October 2013 (UTC)

Resolved

binder related to textile.

Hi, I want to know that which chemical can decrease the strength or stickiness or can make it completely useless to work.. but I want to know a chemical name, addition of water do decreases its strength but I after a lot of research I havnt got any chemical which can help me out in decreasing the strength of binder.. Pleas help me out. — Preceding unsigned comment added by 182.180.45.104 (talk) 09:44, 15 October 2013 (UTC)

Can you be more specific? There are many different kinds of binder and many different kinds of textile. Water is a chemical, and it can be used to dilute many binders, as can many solvents.--Shantavira|^{feed me} 11:54, 15 October 2013 (UTC)

I have a hard time following your Q, but if you're trying to dissolve something, then most things which can be dissolved are water-soluble, oil-soluble, or alcohol-soluble. So, one of those will probably work. Peppermint oil, for example, can dissolve lots of adhesives. If none of those work, then a strong acid or a strong base might work. StuRat (talk) 17:38, 15 October 2013 (UTC)

i am using binder nameing UD BINDER of BASF for textile printing. i have discusses it with many chemist but non of them helped me out.. i had used a lot of acids to decreases its strength but non of them work out even though i had used strong base also but not succeeded but when I add strong base in the paste which is use in printing after 2 days it's make it like rubber but i want some thing like when i add that powder based chemical in that printing paste it become useless.. its strange but i want to make the printing paste totally unworkable and it happens only when binder losses its strength.. so I want powder based chemical which make binder totally use less..

It might help if you explained what you are trying to achieve. Why do you want to make the binder useless? Wouldn't that be the same as just not using a binder? SpinningSpark 22:25, 15 October 2013 (UTC)

I think the OP must have got some printing paste on his/her clothes, and is trying to find some chemical that will remove it. What I don't know is why he/she is using strong acids and bases, despite the danger of ruining the clothes in question altogether. 24.23.196.85 (talk) 23:27, 15 October 2013 (UTC)

Thermal radiation

I have read the articles on Thermal radiation and Black-body radiation, and I am still struggling to understand the actual mechanism that causes radiation to be emitted from energetic atoms. The explanation in Thermal radiation just says:

These atoms and molecules are composed of charged particles, i.e., protons and electrons, and kinetic interactions among matter particles result in charge-acceleration and dipole-oscillation. This results in the electrodynamic generation of coupled electric and magnetic fields, resulting in the emission of photons, radiating energy away from the body through its surface boundary

I have two conflicting models in my head, from forgotten Physics classes. One or both may be completely incorrect. They are

• If you take a dipole magnet and vibrate it, you will produce an EM wave. If you were able to vibrate it really really really fast, the frequency of that EM wave would be that of visible light, so it would emit visible light. In a warm body, each atom is like a tiny dipole magnet that vibrates, producing EM waves.
• In a warm body atoms are colliding with each other, occasionally causing electrons to jump energy levels. When they return, they may emit photons. Thermal radiation is caused by these emitted photons.

Is either explanation close to correct? — Sam 63.138.152.139 (talk) 14:08, 15 October 2013 (UTC)

The second statement is basically the quantum mechanical version of the first, but then specialized to electrons. The first picture is a classical picture of vibrating charges, but then if you describe this more precisely using quantum mechanics, each such vibrating charge is an (approximate) harmonic potential and there are then energy levels here too. So, it also emits radiation due to the system falling back to a lower energy level.

The relevant processes are spontaneous emission when making a transition to a lower energy level, excitation when absorbing a photon, and stimulated emission. Count Iblis (talk) 14:19, 15 October 2013 (UTC)

Hmmm, you say the second statement is a QM version of the first, but there seems to be a very critical difference: in my "vibrating magnet" explanation I can make my magnet produce *any* frequency by vibrating it faster or slower. In my QM explanation, my iron magnet could only produce those few precise frequencies defined by the energy differences in the electron shells of iron atoms (the "quantum" of quantum mechanics), right? — Sam 63.138.152.139 (talk) 14:35, 15 October 2013 (UTC)

If you look more precisely at e.g. the rotation of molecules mentioned by Gandalf below, then there are energy levels there too, but they are so densely packed that it looks like a continuum. Also, you have to take into account the interactions between the different molecules, an N particle system will have energy levels that for large N will be extremely densely packed. So, physically you putting a magnet in your hand and letting it vibrate at seemingly an arbitrary chosen frequency, or an atom emitting a photon are not distinct physical processes. The former involves many more particles and has a far larger number of degrees of freedom, so the emitted photons can have many more possible frequencies. But it is ultimateley the same quantum theory that explains everything (classical mechanics is only an approximation to quantum mechanics; unlike classical mechanics, quantum mechanics is always valid). Count Iblis (talk) 15:23, 15 October 2013 (UTC)

Both explanations are (more or less) correct, depending on the wavelength of the radiation. Infrared radiation and microwave radiation are caused by vibrations and rotations of molecules. Shorter wavelengths, such as visible light and ultraviolet radiation, are caused by transitions of electrons between energy levels within atoms/molecules. There is a table at Electromagnetic spectrum#Rationale. Gandalf61 (talk) 14:36, 15 October 2013 (UTC)

Wow. Thank you for that table -- my jaw just dropped. I had simply no idea that the continuum of the EM spectrum was caused by separate distinct processes, rather than a continuum of one process (like vibrating atom faster and faster). Thanks! — Sam 63.138.152.139 (talk) 14:41, 15 October 2013 (UTC)

Follow-up question, after seeing the table that Gandalf61 linked to. (please excuse me: my brain is trying to crush together two mental models that have always happily lived in separate bins and now need to be entangled together):

For the "vibrating dipole" model, my physics teacher always likened it to a whip: if your bar magnet is sitting on a table, there is a magnetic field line coming straight out of the North pole. Move the magnet and that field line shifts, but the displacement moves away from the magnet like a wave down a whip, traveling at the speed of light. Vibrate it back and forth and you get an EM sine wave. This was my model for thermal radiation, and a key point of this is that the wave has an amplitude in *physical space*, and that amplitude is the displacement of the magnet (or atomic dipole). That is, in magical-theoretical-world, if you put out metal filings and viewed the magnetic field lines like kids do in school, and your filings were absolutely weightless and frictionless etc etc., wiggling the magnet side to side would produce a sine wave of filings that you could even photograph (ignoring the speed of light).

In the QM model, an electron drops to an lower energy level and the energy is lost to a photon that is emitted with a specific frequency based on its energy. But this "frequency" has always seemed to me to be almost metaphorical -- the photon is a packet of energy with an associated wavelength, but it's not like a sine wave wiggling through space with an actual physical amplitude.

Now I find that both models are kind-of correct for different frequencies. Are both photons of exactly the same "kind"? Is the vibrating magnet actually producing a sine wave with an amplitude in physical space? How about the photon emitted by the electron? The two explanations seem so different, yet it seems they both produce the exact same thing. — Sam 63.138.152.139 (talk) 15:06, 15 October 2013 (UTC)

You need to note a couple of things. Firstly, merely vibrating a magnet DOES NOT produce electromagnetic radiation. If you mechanically rotate a bar magnet, you will get a rotating magnetic field, that is all, no matter how fast or slow you rotate or move it. To get EM radiation, you must have both a varying magnetic field AND a similarly varying electric field in the proper phase relationship. This is easily demonstrated as it is easy to produce very intense varying magnetic fields by passing large varying currents through a wire coil. However, by other means you can produce radio waves that embody significant energy yet the magnetic filed component may be quite small compared to that produced by a current in a coil.

Secondly, yes a warm body DOES radiate EM radiation (with a continuous spectrum albiet peaked at a given frequency). However, this does not require, and mostly does not involve, collisions between atoms or molecules (or collisions between any sort of particle. Collisions cannot occur in a solid or in a pure crystal. But all non-trasparent substances radiate. For instance, carbon, a solid, is a near perfect black body radiator at all temperatures in which it can exist as a solid, including up to the sublimation point, ~3900K, at which it will glow yellowish-white.

Collisions are relevant when considering gasses. Collisions transfer energy from one molecule to another, by the impact changing the translational and rotational velocity of the molecules concerned. Atoms and molecules must distribute their energy between translation, rotation, and electron orbital configuration. Only the spontaeous changes in orbital configuration contribute to black body radiation. The division of energy between translation & rotation, and electron orbitals, is governed by the emission laws.

[Special:Contributions/121.215.39.252|121.215.39.252]] (talk) 15:12, 15 October 2013 (UTC)

If you vibrate a magnet you will have a time dependent magnetic field and hence an electric field. Count Iblis (talk) 15:26, 15 October 2013 (UTC)

So, please Count Iblis, explain then why a radio transmitter needs an antenna, and does not radiate significant energy from its tank coil. After all, considerable energy goes into the tank coil, every half cycle of the carrier frequency, far more (typically 10 to several hundred times) than what leaves the antenna into space. That energy does not leave the coil by going off as EM radiation, it gets passed back and forth to and from that tank capacitor. And as I alluded to ealier, the magnetic component of the EM leaving the antenna my be considerably weaker than the magnetic field near the tank coil. Do not be confused by the fact that any time-varying magnetic field will induce a voltage in nearby conductors, and the electric field thereby created may result in some EM radiation as a secondary effect.

Lastly, consider this: A sinusoidaly varying current in an ideal coil absorbs no energy (as does a sinusoidal current in a capacitor) as the current is 90 degrees out of phase with the voltage. However, EM radiation contains/carries energy, lost to space, which is why an antenna presents an electrical resistance at its terminals (practical antennas may display reactance as well, but resiatnce is always present). Since an ideal coil, which of course does produce a sinusoidal magnetic field, absorbs no energy, there can be no EM radiation. Vibrating a magnet, and any other rythmic mechnical thing you can do to a magnet is not essentially diffrent to driving a periodic current through a coil. In vibrating a mass, you exchange kinetic energy between the mass and the driving device, twice each cycle. In vibrating a magnet in free space, some of the energy gets stored twice each cycle in the magnetic field but it always returns to the driving device, also twice each cycle.121.215.39.252 (talk) 15:45, 15 October 2013 (UTC)

Let's stick to one well defined example, let's consider the vibrating magnet modeled as an exact dipole magnet and work out this example from first principles in full detail. Here you can't a priori assume that a freely vibrating magnet will execute an exact harmonic motion and will therefore not radiate any energy, as you would then assume what you want to prove. An outline of this is is as follows. What you need to do is solve the Maxwell equations (taking e.g. the case of a frced harmonic motion of the magnet) which leads to an expression for the electromagnetic fields which are given in terms of the retarded potential, so the magnet at position r' and time t contributes to the field at position r at time t + |r-r'|/c, this time lag is going to lead to an 1/r contribution to the asymptotic behavior of the fields. If you ignore this time lag, then there is no 1/r behavior. Then the energy flux is proportional to the square of the fields which behaves as 1/r^2, therefore energy will leak away to infinity (the energy flux through a sphere of radius r is the proportional to r^2*1/r^2 = 1, so this stays finite in the r to infinity limit).

Another way to approach this, which is however not so practical for calculations, is to consider the problem of the self-force in electromagentism. If you consider the freely oscillating magnet, then it will oscillate according to a damped harmonic oscilator. But where does the damping force come from? This is, of course due to the emitted radiation, but the source of that is the magnet itself. How to properly deal with this was only solved recently. Count Iblis (talk) 17:56, 15 October 2013 (UTC)

Count Iblis, you cannot just ignore a logical argument and go off somewhere else in gibber-land. You need to show why my discussion above is wrong - and you haven't done that, because I have merely recited facts well known to graduates in electrical and electronic engineering world-wide. There is no difference between a magnetic field established by a current carrying coil (or a straight conductor for that matter) and a magnetic field established by a simple dipole magnet. In free space, an ideal coil or conductor absorbs no energy, and no EM radiation occurs. (In practice, of course, while we can have superconductors, we cannot have completely free space. There is always other (imperfect) conductors somewhere with closed loops. Current will be induced in the closed loops, setting up their own varying magnetic fields, which will do the same to the originating coil. By Lenz's Law (for which the proof is the impossible existence of perpetual motion machines) the induced voltage in the originating coil will always be in a direction/phase that will oppose the originating current, thus synthesising an electrical resistance.) I discussed sinusoidal exitation above to simplify it for the OP, however my argument does apply to any varying exitation, as any engineer will know (think in s-plane). 120.145.145.144 (talk) 00:41, 16 October 2013 (UTC)

Surgical Caps and Shoe Covers

Hello. How do you visually distinguish between surgical caps and shoe covers? They look very similar. Thanks in advance. --Mayfare (talk) 16:13, 15 October 2013 (UTC)

Er, well, I'm not sure how to answer this. If you were physically presented with them, the difference would be obvious. If you're looking at a photo, it's hard to come up with solid criteria, because shoe covers are often crumpled and folded in a way that makes their shape hard to recognize. Basically hair covers are round, about a foot in diameter, and relatively thin; shoe covers are foot-shaped with the opening on one end, and pretty robustly constructed. Looie496 (talk) 16:44, 15 October 2013 (UTC)

It may depend on which part of the world you are living in (you don't give your county of origin) but I would say that visually 'shoe covers' are just large enough to encapsulate the foot and 'caps' are larger enough to cover the head, hair (and Tin foil hats for those quacks that feel they need ware need them). --Aspro (talk) 16:52, 15 October 2013 (UTC)

Head covers and shoe covers are generic medical supplies, used in vast quantities (along with gloves, masks, and gowns), and I think they're probably the same shape all over the world. In the veterinary facilities where I've worked, the most obvious difference was that the shoe covers were bright blue and the head covers were white. Looie496 (talk) 17:04, 15 October 2013 (UTC)

If you do a Google Image search for both items you will see there are big differences between the two. The shape to begin with, round for the head and narrow for shoes.Shoe CoverSurgical CapHope this helps! Mike (talk) 16:57, 15 October 2013 (UTC)

Domestic waste solder

I have a handful of bits of solder, mostly crap sucked up with my desoldering tool and bits that ran off during tinning my soldering iron. I live in Edinburgh, Scotland. Should I make an effort to dispose of this in a special way or is that just for commercial enterprises producing large quantities of waste? --2.97.26.56 (talk) 20:12, 15 October 2013 (UTC)

Around here, (in California, in the United States), you would get in touch with your local county's Household Hazardous Waste program and determine the best way to dispose of those types of materials. If you're actually in Edinburgh, here's the website for your city government waste service. Nimur (talk) 20:39, 15 October 2013 (UTC)

It's WEEE, something that ideally you wouldn't put in the landfill waste stream. They do accept WEEE at Edinburgh's community recycling centres (it goes in the "small electrical"). But obviously a wee freezer bag full of WEEE (ahem) isn't worth driving out to e.g. Sighthill. Personally I keep a ziploc freezer bags of the little nasty stuff that they don't collect at the kerb (batteries, CF bulbs, WEEE, paint, etc.) and take it to the recycling place only when I'm taking something large. -- Finlay McWalterჷTalk 20:40, 15 October 2013 (UTC)

Okay, thanks. I'll hold onto it until my next visit to the recycling centre. 2.97.26.56 (talk) 21:22, 15 October 2013 (UTC)

By the way, you should no longer be using lead containing solder unless it is for maintenance of equipment that predates the ROHS directive. SpinningSpark 22:17, 15 October 2013 (UTC)

While it may come in scope of local regulations, I would not be concerned about a mere handfull. You need to keep things in perspective and understand the partly political motivation for the European Lead-Free Directive. Lead is ubiquitous in the environment. Those that frame laws and regulations seem not to understand how and why. Lead was used in all manner of things, including paint. That contributes to lead dust everywhere. Another source is the used of lead sheathing in power and telephone cables for about 80 years, until satisfactory plastic sheaths were developed in the 1970's. I was involved in the installation and testing of lead sheathed cables in the 1960's and 1970's. The sheath was about 3 mm thick and the cable pressurised with air, so as to enable detection of sheath damage and keep out moisture. Those cable still in use have become porous, consantly leading air. In many cases the lead has become paper-thin. Where has the lead gone? Leached into the soil generally of course - where it can be further distributed whenever someone disturbs the soil for building construction or whatever. Authorities became concerned about the lead levels in the blood of childen 30 or so years ago. They thought that lead in gasoline was the problem, so various countries around the World banned lead in gasoline. That improved things a bit in the USA because of their high population densities, considerable use of private cars, and low use of diesel engines in trucks. But Australia and Europe, which have always used diesel engines in any sort of truck, didn't see much change in blood levels. So Europe decided to ban the use of lead altogether - at least that will mean lead levels don't get any worse, and help countries like Australia where some of the environmental contamination comes from dust released in the mining, processing, and transport of lead.

In any case, the lead in solder is pretty much trapped with the tin and rendered harmless. There has never been much concern about electronics technicians and electronics factory staff being affected by lead from solder - though it has always been standard to caution workers to wash hands before eating.

120.145.145.144 (talk) 01:07, 16 October 2013 (UTC)

Human mortality question

Based on known age-specific mortality rates, what is the expected time between successive deaths of the world's oldest inhabitant?→31.54.112.70 (talk) 22:42, 15 October 2013 (UTC)

A little over one year. You don't have to estimate it, since we know the true answer: World's oldest person#Chronological list of the verified oldest living person since 1955. Someguy1221 (talk) 22:48, 15 October 2013 (UTC)