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March 16

Jet streams

My geography textbook says- "The movement of the westerly jest stream to the north of the Himalayas and the presence of the tropical easterly jet stream over the Indian peninsula during summer affects the monsoons." How? --Yashowardhani (talk) 05:55, 16 March 2013 (UTC)

Read Jet stream, for starters. In general, the jet streams affect weather because they aren't stationary, they shift around and help direct varying weather patterns. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:04, 16 March 2013 (UTC)

I still don't get it. — Preceding unsigned comment added by Yashowardhani (talk • contribs) 06:18, 16 March 2013 (UTC)

I'm more familiar with hurricanes, but presumably the same applies to monsoons. Jet streams serve somewhat like gutter guards in bowling, to corral the big storms between them. A powerful enough hurricane can "win" a fight with a jet stream, though. StuRat (talk) 06:03, 16 March 2013 (UTC)

The Nose Knows?

As a cynophile with a serious interest in criminology, I've read more than a little about cadaver dogs. My understanding is that they are specially trained to detect and respond to extremely minute quantities of cadaverine and/or putrescine. Of cadaverine in particular, I have read that it is nearly impossible to clean up every trace of it from something that has had contact with it, and that it is naturally present in semen and urine (in small quantities, but sufficient to contribute to the way they smell *to humans*). If these two facts are true, wouldn't every bathroom in the world and quite a few bedrooms smell at least as pungent as a well-scrubbed crime scene to one of the canine elite? Perhaps more significantly, I've read that cadaver dogs are trained to respond only to the smell of HUMAN decomposition, but cadaverine and putrescine are chemical compounds with fixed molecular structures, found in all decaying animal tissue. There's no such thing as distinctly "human" cadaverine, so how is the dog able to distinguish a place where a human body lay from a place where there was a dead rat, even after the passage of months or years? I don't doubt the reliability of cadaver dogs; I know they've only been proven wrong in about one percent of cases. I just wonder how it is exactly that they're able to do this, because the way I've read about it seems a little simplistic. — Preceding unsigned comment added by 172.3.129.135 (talk) 05:56, 16 March 2013 (UTC)

I suspect they use the cadaverine and/or putrescine to find the site, then, once close enough, they can detect the other, more subtle chemical odors which distinguish human decomp from other types. I would suspect that chimps would smell the closest to humans, so I wonder if a dead chimp can fool them. StuRat (talk) 06:07, 16 March 2013 (UTC)

They can distinguish a complex array of molecules, analogous to a signature. Some of the chemicals communicate "dead", while others communicate "human". ~:74.60.29.141 (talk):~ —Preceding undated comment added 07:13, 16 March 2013 (UTC)

Double-fuselage aircraft

I think an article about double-fuselage aircraft would be useful, although I have no knowledge of the field. Historical instances could be described along with the recent double-fuselage Airbus patent. Your thoughts? I was searching for this but found that the topic is not covered in Wikipedia.--Anixx1 (talk) 10:17, 16 March 2013 (UTC)

It's interesting we have no such article. But we do have Category:Twin fuselage aircraft for your reading pleasure. Someguy1221 (talk) 10:26, 16 March 2013 (UTC)

Radioactive sound

close request for medical advice
The following discussion has been closed. Please do not modify it.
Hi, I am from Japan, and I used to live in Fukushima Prefecture and moved south to Miyazaki Prefecture out of fears for radiation. I live with my mother and before moving I was wearing a mask and had a thing to detect radiation which I don't know how it's in English and before moving it made lots of sounds, loud sounds meaning that there was huge radiation. My question is whether that radiation stayed with me and If I run any health risk. — Preceding unsigned comment added by Hyerotaku (talk • contribs) 12:41, 16 March 2013 (UTC) Presumably the radiation detector was a Geiger counter of some kind. --Mr.98 (talk) 14:02, 16 March 2013 (UTC) This question is a request for medical advice. Only a medical doctor can determine if you are having health problems due to radiation exposure. Nimur (talk) 15:37, 16 March 2013 (UTC) The map in Fukushima Daiichi nuclear disaster and accompanying map should give a sense of the level of exposure, and Radiation-induced cancer gives some notion of the probability, though the article isn't very good. Wnt (talk) 16:36, 16 March 2013 (UTC)

If you can read and write Japanese, you can ask at the Japanese reference desk: ja:Wikipedia:調べもの案内.

—Wavelength (talk) 16:51, 16 March 2013 (UTC)

different sexual responses in women

This is kinda intimate question, but I mean it seriously and not as any kind of joke let alone being smutty or anything. But my boyfriend is interested in psychology, and knows some stuff about Freud, as do I. We both thought that his early material on how clitoral responses to sex are immature forms. But when my boyfriend began fondling me after we became a couple, some really interesting things happened. When it was foreplay and he was feeling my vagina with his fingers, I would become very wet after a while, which is normal of course, and then we would have sex.

But we had another kind of fantasy, which did not really have sex as its end result. You see, we are both very turned on by spanking fantasies. When he fondles me as he tells me how I am going to be turned over his knee and punished, I hardly get wet at all, even though it really makes me hot. On the other hand, my clitoris engorges with blood, and becomes like a stiff little ball, a bit like a penis. They are very different responses, and both of us can feel and attest that this is really happening, but we don't have any idea as to what is going on. It's like TWO different sexual responses based on different fantasies. We haven't asked anybody about it because it is so intimate, but we thought that here in Wikipedia, under the cover of anonymity, there might be some experts who could throw some light on this. Once again, this is real and I hope that no one thinks it is just a dirty joke. It's not. It's our own bodies and feelings, and we are just wondering as to what is going on. Sallysays (talk) 15:11, 16 March 2013 (UTC)

You're not going to get a great deal of 'help' here because many people will regard this as medical advice which we are not allowed to offer. What I would say in a general way is that what you are experiencing is, just as you surmise, different responses from different scenarios. This is widespread among the population and as long as you enjoy what you are doing and are not harming or affronting anyone else enjoy it. Sometimes with sex it is not always helpful to try and analyze everything that is going on. Freud knew little about physical (and probably emotional) sex but he had some theories about how guilty or otherwise some people feel about sex. Don't get hung up on the theory, just enjoy the practical. Caesar's Daddy (talk) 15:52, 16 March 2013 (UTC)

If this is a medical question, then so is a question about how best to roast a duck. :) Unfortunately, I have no idea how to answer it. I strongly suspect that erectile response, though commonly portrayed as all-or-nothing, must be somehow distributed throughout the body, a sort of general sensation/response that is only more prominent in certain familiar places. For example, nipples can become erect - sometimes - and I would suggest that so can the nose, in extreme cases in the form of honeymoon rhinitis. It seems like lots of other parts of the body can become arousable under some circumstances - the feet for example - and I recall reading of a paralyzed person transferring much of his former penile response to his thumb somehow. I personally think that each of these parts is potentially arousable independently of any other. Wnt (talk) 16:16, 16 March 2013 (UTC)

A doctor may have a 'hard' time with this question as I suspect it's not something covered in medical school! Sounds like something for the realm of a sexologist who I'm sure you can find online and anonymously. Sandman30s (talk) 08:10, 17 March 2013 (UTC)

There's nothing particularly surprising in the disparity between your differing responses, really. One scenario involves direct stimulation of the genital region and is more likely to involve parasympathetic nervous pathways which could stimulate lubrication more readily than purely mental/emotional triggers, regardless of overall level of arousal - we are talking about two different types of physical stimuli here, afterall, and it's not surprising that your body would react differently to them, , even though both would borrow upon many of the same physiological mechanisms. Remember also that not every nervous response involves information being passed directly back and forth between the brain (or even the CNS) and the stimulated region of the body; many are partially or completely locally reflexive and some of the former are processes involved in sexual response. In any event, consider that autonomic responses of this nature, including lubrication, sometimes occur during rape, compounding the emotional trauma of victims already struggling with a misplaced sense of shame, and we can make some safe assumptions about how much they enjoyed the stimulation. But even putting those extreme situations aside and looking at arousal in healthy interactions, it's clear that arousal is not one big spectrum of response (zero to a hundred), but a rather a complex composite of interconnected physiological and mental factors (more "a little paprika, a little thyme", and never exactly the same recipe). In fact, you hit upon this a bit in your own question when you noted that sex was not the end result of your fantasy; the fact of the matter is that humans are very lousy at distinguishing between various types of physical arousal (consider for example, the now well-replicated experiment in which men who were asked to meet a female grad student in a dangerous environment later rated her as more attractive than those who met her in a more neutral location; their acute stress response became mingled with their sexual appraisal) let alone distinguishing between different types of specifically sexual arousal. So, yes, not only is it possible to have two very different types of sexual response depending upon stimuli and context, it's a near certainty that you will have many different forms in your life but will be (hopefully blissfully) unaware of the subtleties between them. Snow (talk) 10:45, 17 March 2013 (UTC)

Of course the responses will be different, just as the stimuli are different. In the first instance, your boyfriend was directly stimulating the Bartholin's glands which produce the lubricating fluid. In the second instance, this direct stimulation is absent and, as Snow says, you were getting physically aroused by something different. Don't worry about it, get a copy of The Joy of Sex, and enjoy yourselves! --TammyMoet (talk) 18:21, 18 March 2013 (UTC)

Headphone socket problem

I've got a 3.5mm headphone plug going into (as one might expect) a 3.5mm headphone jack on my hi-fi - but I'm only getting the sound through the left channel. However, I can get stereo again if I only push the plug 3/4 of the way in.

There's nothing wrong with the headphones - I've tried them on a couple of other pieces of equipment and they work fine.

Any suggestions as to how I might be able fix this at home without opening up the stereo (or taking it to someone to fix it for me)? Or is it just the case that the socket needs replacing? I've had this sort of thing happen before on crappy equipment that I was never really bothered about fixing, but this is my main stereo now... --Kurt Shaped Box (talk) 15:22, 16 March 2013 (UTC)

Have you also tried other headphones on the stereo? μηδείς (talk) 16:23, 16 March 2013 (UTC)

Yes. Also with an extension cable. Same thing. --Kurt Shaped Box (talk) 18:26, 16 March 2013 (UTC)

The obvious work-around is to jam something into the jack to prevent the plug from going further than 3/4 in. Perhaps tiny balls of aluminum foil ? Be sure to add them slowly, and test after each one, so you don't go past the desired point. StuRat (talk) 16:30, 16 March 2013 (UTC)

When you push the jack in partway are you sure you're really getting stereo sound? Or are you just getting the one working channel in both speakers?

It would be weird it you actually got true stereo with an improperly plugged plug, but getting one channel from both speakers is what normally happens in that situation.

(bearing in mind that this is the final reply I wrote after I went back to check this out) Interestingly, it seems to have started working again now - but I'm aware that electronic equipment rarely fixes itself and it was definitely exhibiting the symptoms I described a few hours ago. Any thoughts... --Kurt Shaped Box (talk) 18:26, 16 March 2013 (UTC)

I suspect that your hifi is either broken or misconfigured (Is the balance knob cranked all the way over?) APL (talk) 17:07, 16 March 2013 (UTC)

The balance is fine - that was the first thing that I thought was wrong. --Kurt Shaped Box (talk) 18:26, 16 March 2013 (UTC)

My guess is that the hifi jack is either broken, or it isn't made for stereo sound. (They used to have mono headphones at one point, if I remember correctly.) If this is the case, then you only have 2 contacts in the jack, and 3 contacts on the headphones. Perhaps pushing it in 3/4 of the way makes it so the one contact in the jack touches both contacts on the plug. ~Adjwilley (talk) 18:20, 16 March 2013 (UTC)

It's definitely a stereo jack, FWIW. --Kurt Shaped Box (talk) 18:26, 16 March 2013 (UTC)

I'd say you have an intermittent open circuit somewhere between the amplifier and the headphone, most likely in the plug or the jack. FWIW 24.23.196.85 (talk) 05:37, 17 March 2013 (UTC)

I have some headphones which include a microphone. The microphone is just a little bulge in one of the wires from the earphone. Because of this, the little plug has one more ring on it than a plain stereo headphone, and if I push it all the way in, I only hear one channel. 99.140.253.109 (talk) 20:31, 16 March 2013 (UTC)

This is a common problem with wear and corrosion in the jack socket. If you are able to take your hi-fi apart (having unplugged it first, of course) to gain access to the socket, just gently clean the spring contacts with emery paper and very gently bend them in slightly towards the centre, but not too far or your headphone plug will not go in. If you plug in your headphones with the hi-fi opened up, then you will be able to see where there is a bad contact. Dbfirs 09:00, 17 March 2013 (UTC)

Alternatively, the contacts may be aligned properly but the slot itself malformed, such that the plug is skewed or leveraged at an inappropriate angle, forcing only one contact. I once had a device with a hard plastic o-ring on the outer surface of the socket of the jack, which was meant to grip the plug at its thickest point and hold it in place such that it made firm connection with the contacts inside. When the o-ring cracked, it released tension on the plug, allowing the weight of the cord to skew the angle of the plug such that only the one contact was made and it produced exactly the type of issue the OP is describing as a result. 108.248.176.172 (talk) 14:04, 17 March 2013 (UTC)

One thing I've seen on more than one piece of equipment is cracks in the solder joint between the jack and the circuit board, where there is typically not a great physical connection. The joint is typically subject to a lot of stress due to the cord leaning on the lever arm of the piece of the plug which protrudes, and one or more of the contacts breaks or gets loose and intermittent. Gzuckier (talk) 01:32, 18 March 2013 (UTC)

Runny nose / stuffy nose

When people get sick, they often experience either a runny nose or a stuffy nose. While we have article on both, neither seems to address the issue I am wondering about. When we get a runny nose or a stuffy nose in association with an illness is that because A) the illness / infection is directly causing problems with the nose, or B) the body is intentionally adjusting mucous production in an attempt to fight the illness / infection (i.e. its a natural response to infection)? I would assume that changes in nasal mucous composition might offer some protective benefit against certain nasal infections / irritants, so it seems plausible that it might be part of the body's natural response. However, I haven't seen anything that provides a detailed explanation of how and why people develop runny / stuffy noses. Dragons flight (talk) 16:56, 16 March 2013 (UTC)

It's actually both. Mucus production is a physiological response to agents that infect cells in the mucous membranes. Its function is to flush the agent out of the membranes. For viruses, for example, they infect cells, replicate massively, and then burst the cells and diffuse away to infect other cells. Flushing the membranes reduces the density of virus there. Looie496 (talk) 17:45, 16 March 2013 (UTC)

(ec) I believe it is an immune response designed to wash bacteria and viruses out of the nasal cavities. It might seem like this immune response is too late, but, once you are infected, that leaves you even more open to reinfection or additional infections, so keeping out additional microorganisms is important. Unfortunately, this is also a method to spread the disease to others, and some of the diseases may specifically trigger our immune response, in order to achieve this goal. StuRat (talk) 17:47, 16 March 2013 (UTC)

Hmmm, according to [1] it looks like the people getting placebo medications after laboratory infection with rhinovirus type 39 had the lower virus titer, but the difference wasn't significant. They had substantially fewer symptoms, however. Of course, this doesn't measure many things, including longer term effects, secondary infections, or antibody titer years later... I'm still not going to call the response worthless without more data than this. But it should be clear enough that if the virus is doing it "intentionally", it's doing it to spread, not to replicate. Wnt (talk) 18:10, 16 March 2013 (UTC)

Thinking back to AP biology (ugh, over a decade ago), a lot of the stuffy runny nose problems are actually caused by the immune system's response. That's why you still get stuffy when you have allergic reactions (i.e. when the immune system mistakes something harmless like pollen for a virus.) Unfortunately I don't remember any of the names of the cells that do the fighting (other than antibodies). ~Adjwilley (talk) 18:24, 16 March 2013 (UTC)

Histamine#Effects on nasal mucous membrane has a little bit, as does mast cell. --Jayron32 03:13, 17 March 2013 (UTC)

Thick rotor blades

Could the rotor of a helicopter be thicker, more resembling of aircraft wings? OsmanRF34 (talk) 19:53, 16 March 2013 (UTC)

Just over a week ago, I wrote a response to a similar question, comparing wings and rotors.

“ ...the thing to remember is that helicopter blades, fan blades, propeller blades, and fixed wings are all just airfoils. ...A helicopter rotor is different from (fixed-wing) airfoils; it is designed to provide lift and remain stable while the helicopter is operating in its normal flight envelope. ”

For good measure, here's The Helicopter Flying Handbook from the FAA, with all you need to know to start learning to fly helicopters. Nimur (talk) 20:21, 16 March 2013 (UTC)

And here's an easily-digestible quick read from NASA's technical archive, Desgn and Analytical Study of a Rotor Airfoil, and it's sibling-report, ...for an Advanced Rotor Airfoil (both produced for NASA out of Lockheed from 1980). As I summarized previously, and as both these reports clearly state, the primary design objectives (item number one, in fact) are limited by practical concerns like weight, manufacturability, and safety/reliability/durability. Table III in the first report lists dozens of airfoils tested and analyzed (including several NACA airfoils with various cambre). It even has a cartoon "design decisions flow-chart" on Page 64, indicating a few conditions that would encourage engineers to choose a thicker or thinner airfoil - with particular emphasis on the relationship between thickness and the drag divergence parameter. Nimur (talk) 20:46, 16 March 2013 (UTC)

See Sikorsky S-72 ScienceApe (talk) 22:13, 16 March 2013 (UTC)

Helicopter rotors and aircraft wings already resemble each other - but the chosen airfoils differ because the speed and AoA differs. It is also considered beneficial for a rotor blade to have a symmetrical airfoil, since it reduces the movement of the centre of pressure, whereas for fixed wing aircraft an asymmetrical airfoil is often preferred since it can provide more lift for less dreag. As a sidenote, the thickness of an airfoil is usually expressed as a percentage of the chord. Thus a wing for a passenger jet can be said to be just as thick as the rotorblade for a helicopter - but since the chord of the jet is longer, the measured thickness of the wing is several inches - or even feet - more. WegianWarrior (talk) 08:30, 17 March 2013 (UTC)

Aircraft wings are hollow! Rotor blades are usual not because they not only have to take up with much more than typical wing-forces (like vibration from switching airspeeds) but also with significant centrifugal force. So every extension of blade surface will get you a heavy extra weight for the hole rotor construction likely outweighing most or all gain in lift. --Kharon (talk) 12:09, 17 March 2013 (UTC)

One big problem is that when the helicopter is pitching or rolling, the swash plate is tilted and each rotor blade will change pitch twice in each revolution of the rotors. If the blades were wider, the rotational inertia about their long axis would be higher and it would be harder to get them to change pitch like that. This would, in turn, result in the helicopter being harder to control. This is enough of a problem in fixed wing aircraft so we (mostly) have ailerons, flaps and elevators rather than altering the pitch of the entire wing. Getting controls and actuators to do that inside a helicopter rotor would be really tough! Also, if the rotors are heavier, then the tendency of the body of the craft to rotate in the opposite direction of the rotors would be far greater - and since that force is controlled by the tail rotor, you'd need that to be MUCH bigger too. SteveBaker (talk) 19:28, 19 March 2013 (UTC)

Line of sight to the sun

Let's say you're naked in outerspace, and for some reason you don't die (just for the purposes of this question). If you have a direct line of sight to the sun (without anything else in the way), how hot will the side of your body facing the sun be compared to the side that isn't? ScienceApe (talk) 23:54, 16 March 2013 (UTC)

The answer depends on how far from the sun you are. Spectral_flux_density might be interesting. SemanticMantis (talk) 00:04, 17 March 2013 (UTC)

This third question from the last may be helpful. --PlanetEditor (talk) 01:20, 17 March 2013 (UTC)

After reading the NASA link above, I'd say that you would be pretty hot overall (over 100 C), but that there wouldn't be a huge temperature difference between the two sides of your body. I say this because I believe the rate of heat flowing from one side of your body to the other would be fairly large, especially if you're alive and your circulatory system is still going. But then you'd dehydrate pretty fast, being above the boiling point of water and in a vacuum. As a side note, I hope you're wearing sun screen, especially if you plan on performing this experiment naked. ~Adjwilley (talk) 01:32, 17 March 2013 (UTC)

What sunscreen is going to do when his body temperature is above 100 C? --PlanetEditor (talk) 02:05, 17 March 2013 (UTC)

If you were as far away as the Earth and rotating wouldn't you be about the same average temperature as the Earth? μηδείς (talk) 02:44, 17 March 2013 (UTC)

Approximately, yes; although some models also account for albedo or use a "gray-body" instead of black-body Stefan-Boltzmann law. This question is a typical homework problem in an astronomy class; apply your favorite variation of the equation for planetary surface temperature, accounting for as many non-idealities as necessary. Unlike planets and cows, a person might not be well-modeled as a sphere... If the question really is asking about the difference in temperature between illuminated and dark sides of an object, we must stop approximating the object as a sphere, and apply Fourier's law with an appropriate choice for heat capacity and thermal conductivity. Nimur (talk) 02:48, 17 March 2013 (UTC)

A bit hotter, since you don't have clouds to reflect some of the sunlight before it hits you. Sunlight can still reflect directly off you, but that's similar to it reflecting off the surface of the Earth. StuRat (talk) 02:50, 17 March 2013 (UTC)

Great thanks, that's exactly what I was looking for. I recall there being a huge disparity between something in the shade vs. in direct sunlight in space. That leads to my second question, why is it that night time (the side of the planet not facing the sun) doesn't freeze to those cold temperatures? Obviously nighttime is colder but if it's summer time, or near the equator, you can have a very very hot night, but that part of the planet is in the shade. Is it because of the retention of heat in the atmosphere? ScienceApe (talk) 08:09, 17 March 2013 (UTC)

Clouds in the atmosphere help to retain heat, so rapid cooling and frost is more likely with a clear sky, but the main effect preventing frost in summer is the thermal retention of the earth and oceans. Dbfirs 08:52, 17 March 2013 (UTC)

Agreed. Places without bodies of water or clouds (that is, deserts) do have temperatures drop dramatically at night. StuRat (talk) 08:56, 17 March 2013 (UTC)

Larry Niven's first story "The Coldest Place" (spoiler alert) Gzuckier (talk) 01:45, 18 March 2013 (UTC)

Your skin color might make a rather noticeable difference in how hot you get. Of course, once we turn into jerky, we'll probably all have similar coloration. StuRat (talk) 02:50, 17 March 2013 (UTC)

Here, Ice on the Moon... one of the greatest unresolved questions about lunar geology is exactly what thermal capacity and conductivity does the lunar substrata have? Though Apollo brought back lots and lots of surface material for study, we have never been able to directly study the geological properties of the subsurface. NASA's academic research consortium called this among the highest-priority unresolved scientific facts about the moon. Why does it matter? Because we're looking for icy permafrost in permanently shadowed areas of the moon, hoping these areas are cold enough to keep ice frozen - but that assumes that the thermal input comes from the sun - and we know that there is some thermal flux through the substrata. (Even shady regions will get some solar energy input that flows through the ground!) So, if we want to estimate how much ice there can possibly be, we need better thermal models for heat flow in the subsurface. In other words, how cold are the shadowed areas of the lunar polar regions? Are they cold enough for ice? To some extent, the LCROSS water vapor plume provided some new information. As we look for more water ice in more places around the solar system, we need all the information we can get to complete the picture - particularly when it comes to setting bounds on possible temperatures. Moral of the story: learn Fourier's law early, learn it well, apply it frequently; simulate your coffee thermal performance every morning,... because you never know when NASA will need to call you up to exercise those skills. Nimur (talk) 03:08, 17 March 2013 (UTC)

March 17

Holograms

I have read quite a bit on holography inc. bought books and here at Wikipedia but I cant find answers to these questions?

Here are my questions:

1. In addition to being required to interfere with the object beam, is the reference beams inclusion in the production stage simply a way of weaving a light source for viewing, into the production stage. It is a clever way of allowing a light source to illuminate the hologram for viewing without introducing new data which would destroy any hope of seeing the image? The reference beam being the purest form of light (monochromatic, coherent, collimated and with plane wavefronts) means it is the most reliably reproducible light source for viewing at a later date and venue?

2. Would the object beams' wavefronts expose the emulsion if the lasers' output was doubled (equalling the intensity of the peaks recorded with both an object and reference beam)?

3. I understand the speckles on the hologram are what have been recorded of the scene, so what are the swirling patterns we see in the emulsion?

Thanks in advance. — Preceding unsigned comment added by Eagle eyes 000 (talk • contribs) 14:32, 17 March 2013 (UTC)

The objective in holography is to recreate a three-dimensional light-field. The hologram itself is exposed on a single plane - which is a two-dimensional sample of the light-field from the original scene. To recreate a three-dimensional field, some additional light must be present. This is why a reference beam is used. The fact that we require monochromatic light, or laser light, is a practical limitation of the way we capture holograms in visible light. If we take the deep-dive into theoretical realms - or even if we consider acoustic tomography or holography, which operate on the same principle of reconstructing a full wavefield, we can see that the monochromatic reference beam is not a strict requirement, as long as we have the ability to reconstruct the reference with accurate phase. That process is possible - and easy - for, say, an ultrasonic scanner, but not easy for a visible light source, so we use a laser as a suitable source.

When you see wavy lines, you are seeing moire patterns. The actual "image" on the hologram's emulsion is a projection of the unfocused wavefield onto a plane. That projection is expected to have lots of periodicity for normal scenes, so it is expected to see moire patterns for the same reason they appear in other materials with similar patterns. Nimur (talk) 16:06, 17 March 2013 (UTC)

Moiré pattern   ←[correct link -74.60.29.141 (talk) 16:46, 17 March 2013 (UTC)]

Redirect created. Nil Einne (talk) 20:50, 17 March 2013 (UTC)

Usually redirects aren't created for article titles pluralized by appending letters—instead you write [[moire pattern]]s. But it doesn't matter since redirects are cheap. -- BenRG (talk) 02:13, 18 March 2013 (UTC)

While putting the pluralisation outside the wikilink may arguably be the preferred option in writing articles, this doesn't mean redirects from plurals shouldn't be created. In fact for frequent cases they should be because there is no expectation that wikilinks in the other way should be mass corrected particularly in comments, even Category:Redirects from plurals notes this ('do not replace these redirected links with a simpler link unless the page is updated for another reason'). There are also other advantages with the redirects existing, like in searching. While our search engine would generally end up suggesting the singular article as an option, a redirect will mean people automatically go to the article. Another advantage is external sites making linking errors will still find a target. In fact, Wikipedia:Naming conventions (plurals) notes this, 'Creating a redirect in cases like crayons is advisable as well, since third-party websites started adding automatic links to Wikipedia from their topics, and many of them follow the opposite convention, i.e., pluralization'. So from my experience redirects from plurals are very, very commonly created e.g. cats, humans, bananas, computers (all just random examples I didn't even both to test). Nil Einne (talk) 06:39, 18 March 2013 (UTC)

What do you mean by "To recreate a three-dimensional field, some additional light must be present"? -- BenRG (talk) 02:13, 18 March 2013 (UTC)

I was of course describing the reference illuminator, using somewhat coarse terminology.

When viewed, a hologram is not a static image. It is a light field, and it can be viewed from many different angles. It is a reconstruction of the original light field at all points in 3 dimensions, albeit it is an imperfect reconstruction, due to the limits of sampling and projection.

The exposed plane (the emulsion) is itself not three-dimensional. It is a 2-dimensional sample of the light-field at the plane of the exposure. To reconstruct the full light-field at all points, a source of illumination must be provided. Conventionally, that source is the "reference beam," a monochromatic source of the same type originally used to perform the exposure. The illumination scatters off the holographic emulsion, and the resulting light-field is a close approximation to the light-field of the original scene. This is how we can view the "scene" in three dimensions. The viewing-angles that are reconstructed - rather, the set of viewpoints where the reconstructed field is similar to the original field - are limited by the sampling aperture.

If we were modeling the wavefield, instead of synthesizing it in the real world, we could completely eliminate the reference illuminator. We could replace it with the "exploding reflector model" to cause the wavefield to "start emitting" with the sampling-plane as a boundary condition. In the real world, passive materials like photographic emulsions do not spontaneously "start emitting" wavefields - we must illuminate them. This numerical technique is used extensively in computed tomography to synthesize 3D imagery in a computer model, but we have no material that can synthesize such a wavefield, subject to the exposure-emulsion as a boundary condition, at optical frequencies, in the real world. Here is a reference on synthesizing an (acoustic) wavefield without re-injecting the source illuminator: the Exploding Reflectors model. BenRG, you may appreciate this approach, because it considers every possible wave interference interaction - including ordinary propagation in free space - as just a special case of Born scattering. I have seen this numerical technique (the "holography trick") applied to seismic imaging; positron tomography for medical imaging; ground-penetrating radar; imaging radar; and of course, wavefield optics modeling for computer-graphics. If you're incredibly interested, I can dig up papers for each one of these applications; but suffice to say, the wave physics and the math are all the same, even if the wave type is very different. Nimur (talk) 03:48, 18 March 2013 (UTC)

What you're calling the reference illuminator seems to be what the article calls the reconstruction beam. The original question was about the reference beam that's used when creating the hologram.

In lower-frequency cases you don't need the reference or reconstruction beams, even in real-world applications, because you can record and reproduce the waveform directly. At visible-light frequencies that's impossible (as far as I know) and the interference-pattern trick is a way around that. Even so, the emulsion doesn't record complete information about the light field in a plane (it only records the amplitude of the interference pattern) and the reproduced light field is not the same as the original, despite what a lot of presentations (including our article) seem to imply. This thesis seems to have a good mathematical treatment in sections 2 and 3.1. -- BenRG (talk) 17:21, 19 March 2013 (UTC)

I'm not sure if I understand your questions. Are you asking if the reference beam is really necessary? The answer to that is yes. There's no such thing as a film that records the phase of light; all film records only the intensity. The way you fake recording the phase is by combining the light reflected off the object with a reference beam from the same laser. If the reference beam has intensity A² and the object beam has intensity B² at a particular point on the film, then the combined intensity of the two is (by the law of cosines) A² + B² + 2 A B cos φ, where φ is the relative phase of the two beams at that point. (The absolute phase of both beams varies with time, but the relative phase doesn't, as long as the light is monochromatic and the scene isn't changing.) The reference beam intensity is constant across the whole film, and you can treat the object beam intensity as roughly constant also, so roughly speaking the intensity captured on the film depends only on φ. -- BenRG (talk) 02:13, 18 March 2013 (UTC)

Would methane hydrate extraction spill significant amounts of methane into the atmosphere?

Methane hydrates have recently been in the news as possibly a main fuel source of the future. However, environmentalist friends of mine are very negative about this development, mainly because they believe that the process would spill too much methane into the atmosphere. Is this likely to be true? B^e——C_ritical 17:17, 17 March 2013 (UTC)

Not sure, but note that, even if none spills and you get 100% combustion, you'd still produce carbon dioxide, which is also a greenhouse gas. StuRat (talk) 17:32, 17 March 2013 (UTC)

Methane would produce much less carbon dioxide as a fuel than other hydrocarbon sources. It's not carbon neutral unless carbon dioxide sequestration is used as part of the extraction process, but it give off much less CO2. Because it creates much less atmospheric CO2, the only question is whether methane emissions are a significant danger. B^e——C_ritical 17:40, 17 March 2013 (UTC)

Not more so than for "conventional" gas drilling (the techniques used in clathrate recovery are similar to those already widely practiced in conventional gas drilling and in enhanced oil recovery), and less so than for fracking of shale gas deposits. 24.23.196.85 (talk) 00:11, 18 March 2013 (UTC)

So the calculation would at least have to:

• Make some assumption of how much methane would be released during extraction.
• Take into consideration the amount of time that methane exists in the atmosphere (8-12 years?)
• Take into consideration the amount of CO2 which would not be released as a result of using methane instead of other soruces.

The guesses require knowledge of, for example, how much natural gas is lost from fracking in the ocean. And other knowledge. B^e——C_ritical 17:57, 17 March 2013 (UTC)

At the ocean bottom depths it may also be possible to form Carbon dioxide clathrate at pressures between 12 and 44 bars. (120 and 440 meters deep). So there could be a way to store this CO₂. Graeme Bartlett (talk) 10:35, 18 March 2013 (UTC)

Russian M4 Parka

Are there any wiki articles about Russian military clothing? I'm particularly interested in their winter clothing like the Russian M4 Parka--Tommythehook (talk) 17:24, 17 March 2013 (UTC)

I don't think we have much. However, you could start from, let's say, Afghanka, and see what you can find... By the way, it would be easier to answer if you gave a little more details: are you interested in military clothing of Russian Federation only? Or would Gymnasterka of Russian Empire and USSR count too? --Martynas Patasius (talk) 17:50, 17 March 2013 (UTC)

Or the Telogreika of World War 2 vintage? 24.23.196.85 (talk) 00:02, 18 March 2013 (UTC)

The god particle

From CBS news today "The Higgs boson is often called 'the God particle' because it's said to be what caused the 'Big Bang' that created our universe many years ago." That isn't the reason it is called that, is it? Bubba73 ^{You talkin' to me?} 17:50, 17 March 2013 (UTC)

No, that isn't the reason, see this NPR interview ([2], several other good links within) with Dick Teresi, who is reported to have coined the term. He discusses it at length, but the title of the piece is

“ The Man Who Coined 'The God Particle' Explains: It Was A Joke! ”

That's pretty clear to me. SemanticMantis (talk) 18:01, 17 March 2013 (UTC)

Thank you,

Resolved

. Bubba73 ^{You talkin' to me?} 18:17, 17 March 2013 (UTC)

I don't know... The Higgs Boson sure does look like the FSM... More evidence here. --Guy Macon (talk)

That's a picture of the long-lived products of one or more collisions in one of the LHC detectors. They all look like that. Even if that one is a Higgs candidate, the Higgs isn't visible in it, since (a) its lifetime is too short and (b) the same decays can happen without the Higgs, so the existence of the Higgs is inferred from an increase in the rate, not from any particular event. -- BenRG (talk) 21:49, 17 March 2013 (UTC)

According to the book itself, the name was invented by Lederman, not Teresi, and he originally called it "the goddamn particle" because it's been so hard to find. However it was Teresi who decided to use it in the title of the book, thus ensuring that idiot journalists would repeat it forever after. -- BenRG (talk) 21:49, 17 March 2013 (UTC)

I guess the thing you should always remember is that the Higgs boson is a proposed, and experimentally-testable incarnation of the Higgs mechanism. And, the Higgs mechanism is just a really really high-resolution explanation of mass. We already know that mass exists, and we already know that mass interacts gravitationally. The Higgs mechanism only arises because we want to be very precise when we say "mass," and when we say "exist," and so forth. By using incredibly high energy, we set up the scale lengths and scale time intervals in such a way that we can probe the interaction that causes gravitation.

This is much the same way that - prior to the discovery of the electon - we knew that there was electric charge in an atom. By carefully setting up experiments, we were able to clarify how electric charge is distributed in the atom. We were able to localize the position of that charge to a point particle, albeit subject to certain constraints on this localization. And, perhaps most importantly, we were able to use this knowledge to more thoroughly predict the way that charge interacts wih matter by correctly describing the role of the electron in atomic interactions: what we today call electrochemistry. From the macroscopic point of view, nothing changed because of this discovery: scientists had known for millenia that charge exists, and that atomic interactions are somehow mediated by electric charge carriers - but by completing the picture at a higher resolution, we improved our understanding and very probably expedited the experimental discovery of many new material properties, chemical reactions, semiconductivity, nuclear physics, and so on. So, discovering the Higgs boson probably won't cause the ground to fissure open; but these investigations help physicists make better predictions and design new experiments to further our understanding of fundamental interactions.

All these questions come down to a very existentialist question: why isn't the universe simple? If the universe were simple, we'd all be one giant isotropic homogeneous soup of uniform goop. There would be no electric charge; no mass; nothing that interacted with anything else; nothing would ever change; the universe would have always existed and would exist into perpetuity, without ever deviating from itsmsteady-state equilibrium; and yet we instead observe a universe full of different types of particles, with different charges and masses, that interact to form nucleons and atoms and molecules and sentient mammals. If we can only figure out the mechanism that caused that very first fundamental symmetry breaking, then all the electric charge and nuclear forces and ribosomes and koalas all follow from first principles, given enough time to evolve, and the universe makes a lot more sense. This is why theistic philosophers like to equate symmetry-breaking with what is effectively a dialect of Creationism. Actual physicists tend to be predictive and descriptive, rather than epistemological, so physicists don't usually care for that equation. Nimur (talk) 21:43, 17 March 2013 (UTC)

isn't your definition of simple subjective and or presumptuous? I mean relative to the cosmos? Maybe it is simple and we just dont know it yet.68.36.148.100 (talk) 01:10, 19 March 2013 (UTC)

Fair point; substitute the term "simple" with the term "symmetric," as that is the term that physicists actually use. Particle physicists have the tendency to assume symmetry is the "natural" state over a particular variable, until they discover otherwise, by experimentally showing a specific type of symmetry-breaking. Nimur (talk) 02:13, 19 March 2013 (UTC)

I don't think the Higgs interaction can be called "the interaction that causes gravitation". For one thing gravity is its own interaction, but also the Higgs mechanism is only responsible for ~1% of the mass of ordinary matter (see Proton#Quarks and the mass of the proton). It's true that nothing like the world as we know it would exist without the Higgs interaction, but the same can be said for many other parts of the standard model. -- BenRG (talk) 17:50, 19 March 2013 (UTC)

Charge Selectivity of Glomerular Barrier in Nephritis

Hello. Why can anionic proteins pass through the glomerular barrier more easily than neutral particles if both are not repelled by the basement membrane? A link to a journal article would be appreciated. Thanks a lot in advance. --Mayfare (talk) 22:00, 17 March 2013 (UTC)

A quick search for "Charge Selectivity of Glomerular Barrier in Nephritis" on Google Scholar:[3] yields "About 2,710 results".

This one looks promising:  The glomerular filtration barrier function: new concepts

~Good luck on your exam!  ;)  ~:74.60.29.141 (talk) 04:51, 18 March 2013 (UTC):~

March 18

Positive charge on flying insects?

I was just reading the article in New Scientist 2 march called "Electric plant auras guide foraging bees", and it states "As bees fly through the air, they-like all insects- acquire a positive charge". I can't find any references that discuss this further, is it a well known fact? and what causes it to happen? — Preceding unsigned comment added by 122.108.189.192 (talk) 07:04, 18 March 2013 (UTC)

This link would suggest that it's true for bees and the cause is given as "frictional electricity" as they fly, and here's another on the subject. Mikenorton (talk) 08:08, 18 March 2013 (UTC)

Thanks Mike, that last link is fascinating.122.108.189.192 (talk) 07:35, 19 March 2013 (UTC)

interstellar Bomb

Even if this is not trolling there is nothing going to be solved by this. CambridgeBayWeather (talk) 06:40, 19 March 2013 (UTC)
The following discussion has been closed. Please do not modify it.
Hello, I want to know, if it is possible to send an atomic Bomb (or any other Device that destroys more than 1 km²) so that it reaches a Star within a distance of about 100 Lightyears not later than in the mid 42th Century in operational conditions. Additionaly the exact orbit properties of the target are unknown, so it is necessary for the Device to determine the exact course within this star system while on flight. Please take this question seriosly, there is more on stake than you can imagine. (excuse my bad english, it's not my usual language.)--AlaneOrenProst (talk) 08:08, 18 March 2013 (UTC) The technology needed for interstellar travel is not available. And the energy needed for interstellar travel cannot be obtained from Earth. So keep your fantasy in the pages of science fiction books. --PlanetEditor (talk) 08:50, 18 March 2013 (UTC) just because the necessary technology isn't available now, did not mean it is impossible. The article you linkend already gives some possible ways to acomplish what is necessary.--AlaneOrenProst (talk) 08:58, 18 March 2013 (UTC) PS: and, no, this is not a science fiction book. This is reality.--AlaneOrenProst (talk) 08:59, 18 March 2013 (UTC) Well I think it is just about possible, at the moment there's no good reason to spend the enormous amounts that would be involved on such an undertaking, but I'd guess in another hundred years it might actually become practical to think about sending off a fast interstellar ship. By the way you don't need a bomb, just don't slow it and aything going at that speed will destroy a wide area. As far a I know there are no current threats from bug eyed aliens that need to be countered so I don't see the point of the 'this is reality' business. Dmcq (talk) 09:24, 18 March 2013 (UTC) currently there is no problem, but if we do not act now, the Prophecy will fullfil, and the terrible Event I want to avert will happen. --AlaneOrenProst (talk) 09:30, 18 March 2013 (UTC) PS: more exactly spoken: the Event will happen with a probality between 37,5% and 62,5%, acording to the prophecy.--AlaneOrenProst (talk) 09:33, 18 March 2013 (UTC) Sure, there doesn't seem to be any scientific limitations on such an idea. Any technology required is not impossible, as noted, it's just not something that humanity currently capable of doing. Plasmic Physics (talk) 09:27, 18 March 2013 (UTC) then we have to hurry to get the technology to be capable.--AlaneOrenProst (talk) 09:38, 18 March 2013 (UTC) Why the rush? Plasmic Physics (talk) 09:40, 18 March 2013 (UTC) Well Plamsa Physics, could you explain where would you get the energy required for interstellar travel? --PlanetEditor (talk) 09:42, 18 March 2013 (UTC) @Plasmic Physics: because of the Blackbird-Molotow-Reich-Effect. As more we wait, as harder it gets to escape the prophecy.--AlaneOrenProst (talk) 09:44, 18 March 2013 (UTC) Oh the BMRE! I don't see the urgency. Isn't that not for at least a couple millennia? We have plenty of time. Especially since in 3127 we can harness time dilation technology and postpone that event almost indefinitely or at least until 1234567. No worrys. Lets revisit this in a coupe hundred years just in case. Or just tomorrow when you come down.68.36.148.100 (talk) 03:27, 19 March 2013 (UTC) If you - or anyone else - can figure out a way to send a probe to a star 100LY distance then I think that guidance should be a simple matter to sort out... You wouldn't need a nuclear warhead btw - just keep accelerating the whole way and impact the probe into the target. Refer to kinetic bombardment, impact depth and relativistic kill vehicle for more information relating to the power of kinetic energy. If you could manage an acceleration of just 0.0001G - that is just shy of one mm/s^2 - then the probe would arrive in just under 2000 years with enough speed to punch a sizable hole in a planet. WegianWarrior (talk) 09:46, 18 March 2013 (UTC) well, that sounds like something we can work with. But a sizable punch is not needed. I do not want to kill a whole world, the "1 km²" is more or less all the damage needed.--AlaneOrenProst (talk) 09:51, 18 March 2013 (UTC) To everyone providing their opinion, the energy required for interstellar travel is not available on Earth. This makes interstellar travel impossible. --PlanetEditor (talk) 09:48, 18 March 2013 (UTC) For now. Someguy1221 (talk) 09:57, 18 March 2013 (UTC) It most certainly is available on earth as nuclear fuel. Plus they're not trying to send people. I think I'd much prefer a cleaner way than Project Orion though, ion drive has lots of room for improvement and also in the future it should be possible to assemble stuff automatically on say the moon instead so pollution might not be such a worry. Dmcq (talk) 10:46, 18 March 2013 (UTC) Yeah, sending a tiny Voyager-like probe to the interstellar space may be possible. It will take more than 80,000 years to reach the nearest star Proxima Centauri. Nearly 3000 human generations. So manned interstellar travel is impossible. --PlanetEditor (talk) 10:52, 18 March 2013 (UTC) The qualifier for that statement in the article is a bit ambiguous, it doesn't say how long a reasonable time lasts. Plasmic Physics (talk) 10:57, 18 March 2013 (UTC) Actually, sending "a tiny Voyager-like probe to the interstellar space" is certainly possible, because we have already done that (you might quibble if the Voyagers have reached "interstellar space", but there is no reasonable doubt that they will reach it). And I see no hard physical reason why it should not be possible to send e.g. an 0.01c mission out to other stars. If it's economically and politically feasible is another question, but scientifically and technically it shouldn't be that hard. See Project Orion (nuclear propulsion). --Stephan Schulz (talk) 13:31, 18 March 2013 (UTC) If we're not worried about 100g type acceleration or stopping at the far end it should be possible to do considerably better than 0.01c.. Dmcq (talk) 16:07, 18 March 2013 (UTC) Yeah, what the previous guy said... it isn't named Voyager Interstellar Mission for nothing. If you think about it, once you have attained escape velocity, which we could even manage with a manned capsule, decades ago, you are on an interstellar trip, as long as you have plotted your course so as not to get trapped in the gravity well of another solar system body. If Voyager could do it with flybys through the ecliptic, it shouldn't be very hard if you aim out of the ecliptic. The only additional requirement for your plan is getting there on time, and as everybody knows, in space without drag you can just add acceleration until you get to the speed you need. I'm too lazy to do the math right now, but aside from standard rocket engines, you have the choice of not very advanced technological stuff like nuclear powered ion-drive thrusters, because over a couple of millenia even a tiny fraction of a G of constant acceleration tends to add up. And then there are always the way-out-there drive concepts, like solar sails, possibly with a boost from terrestrial-based lasers, interstellar ramjets, etc. which could be developed into operation in part of the 2000 years you have to spare. Certainly, there is no guarantee that any of these will get you there on time and functional, but there is no hard and fast reason that makes it impossible. And, you could certainly try all of the above, in the hopes that at least one will succeed. You're probably more at risk of failure regarding the control and guidance systems being functional after 2000 years to aim the thing, as you require. Also note that in addition to the plain old impact at that speed being destructive enough to eliminate the need for an explosive payload, as previously mentioned, in fact if you get up to a high enough velocity and you have enough control to steer the thing, all you have to do is flip it over 180 degrees just before you get there as though you were trying to slow down, and the relativistic blue shift of the energy of your engine will do some really serious damage to whatever you're moving towards. Gzuckier (talk) 16:26, 18 March 2013 (UTC) ok, that sound's like something basical. Who schould I contact to make this real?--AlaneOrenProst (talk) 17:01, 18 March 2013 (UTC) If you really want to go up to 100 lightyears in only 2100 years, then at constant acceleration you'd need to reach nearly 0.1c. You could do it with as little as 0.05c if you mostly front-load your acceleration. A mere 100 kg of projectile going 0.05 c would require no less than 10 petajoules (1×1016 J) of energy to achieve this (and likely a great deal more due to inefficiencies). Setting aside the fact that a rocket that small could never store that much energy, the amount of energy is "only" about the equivalent of a 3 megaton nuclear bomb, which means it is on the range scale of things humans have achieved. If instead of 10 petajoules, we imagine the inefficient (or larger) rocket actually requires 10 exajoules (1×1019 J) then that's still only about 20% of global annual electricity production. Finding a way to channel that much energy into a rocket would be extremely challenging, but given one or a few centuries to figure it out and a united global effort to accomplish it, then I don't see any reason it shouldn't be possible in principle. I certainly wouldn't expect to see such an effort in my lifetime though. Dragons flight (talk) 16:42, 18 March 2013 (UTC) it should better happen within the next few years. The Blackbird-Molotow-Reich-Effect is already dragging hefty.--AlaneOrenProst (talk) 17:01, 18 March 2013 (UTC) Okay, I'll bite. What is this Blackbird-Molotow-Reich-Effect ? Just a pointer to a source or web page will do (maybe one that doesn't use block capitals or flashing neon fonts). Gandalf61 (talk) 17:16, 18 March 2013 (UTC) the Blackbird-Molotow-Reich-Effect basicly means, that, on the long run, to change anything in history via timetravel (and the only way I can imagine the Prophecy can be here is that it was send back in time) is impossible. The changes you can acomplish will ever follow a a*t^k*e^-n*t²) formula, so on short you have an exponentionally efect, but on the long run in converges against 0. This efect was discoverd by prof. phy. Molotow, one of the small pack of refuges who made it to the TMSC Hope, and who discoverd the timegate and how it works, dr. hist. Reich, another refuge and as historical advisor member of the time travel commando and cmdr. Kathrin Blackbird, second in command of the TMSC Hope and leader of the time Travel commando, which tried to avert the foundation of the Cygnian empire throgh travveling from 31th Century to 21th Century earth. --AlaneOrenProst (talk) 17:32, 18 March 2013 (UTC) I can imagine another way this alleged prophecy could "be here": Someone made it up. Created the idea in their imagination. It happens, you know. ←Baseball Bugs What's up, Doc? carrots→ 03:46, 19 March 2013 (UTC) Fine, there is nothing wrong imaging a fantasy future. But from a scientific point of view, let me clarify some points. Predictions sometimes ignore reality and science. For example, A. C. Clarke predicted that dinosaurs will be cloned by 2023, but his prediction was not based on science. There are multiple obstacles to manned interstellar travel which cannot be averted unless you alter biological and physical laws. 1. Microgravity: Humans can stay in microgravity in the ISS for months, but a lifelong stay in microgravity defies human biology. 2. A lifelong stay outside the protection of Earth's magnetic field and exposure to cosmic rays will be disastrous. 3. If humans plan to make a trip to another star, they will need resources (oxygen, food reserve for decades to centuries), health care, repair and maintenance crew. Any possible damage to the starship need to be repaired, necessitating the burden of a repair crew and machinery on board. All these are just impractical and can exist only on Star Trek. 4. At 0.01c, even a tiny atom can do incalculable damage to the spacecraft. Chances of collision with a Small Solar System Body is very high when you are traveling at 0.01c in a gigantic starship through the Oort cloud. 5. Humans can survive short-duration stay in space. But lifelong space journey needs a self-sufficient ecosystem to produce human needs. And an ecosystem can't exist beyond the habitable zone. So far, humans have been able to visit space with active support from Earth, and with the protection of Earth's magnetic field. Self-sufficiency in space without any contact with Earth is impossible. It is economically infeasible, biologically impossible. --PlanetEditor (talk) 17:03, 18 March 2013 (UTC) PS, I think we have been trolled. --PlanetEditor (talk) 17:03, 18 March 2013 (UTC) Well, you might be right about that one, but most of the rest is, quite simply, wrong. Microgravity would not be a problem - on the size of an interstellar space ship, you can use centrifugal force as an adequate replacement for gravity. Cosmic rays are a problem, but not an unsurmountable one. For one, we already know how to generate magnetic fields quite well. And the damage done by an atom at 0.01 c is very much calculable - an H atom (the most frequent kind by far) will have about 6.6e-15 J (i.e. not very much). For WIM, the most common kind if interstellar medium, there are about 0.01 ions per cubic centimeter. Going 3000 km/s, the total energy deposited per second per square meter is about 2.2 J, i.e. measurable, but not a problem (for comparison, at 20 degrees centigrade, black body radiation of that square meter is about 400 W). And chances of collision with any solar system body is actually quite low (and, for a given distance, independent of speed). If there were that much stuff out there, we wouldn't see the stars). --Stephan Schulz (talk) 19:37, 18 March 2013 (UTC) you seem to ignore the fact, nobody here is speaking about manned interstellar flight except you. And, no, I'm not a troll, I try to avert a catastrophy. --AlaneOrenProst (talk) 17:09, 18 March 2013 (UTC) My proposal would be to send a microscopic self-replicating machine to either a solar system that's nearby to the destination or to some planet of that same solar system. The machine will then grow all by itself using solar energy into a nuclear bomb factory and missile factories within a year. It would take only a small amount of energy to send such a factory to the desired destination at a speed close to c. Count Iblis (talk) 17:22, 18 March 2013 (UTC) Ok, I've got to ask - what is this catastrophe you're trying to avert? Richerman (talk) 17:41, 18 March 2013 (UTC) the multiverse-War, from 4169 onwards, cost 210 billion human lives (217 Billion gross) and ended a milenia long period of peace and prosperity. --AlaneOrenProst (talk) 17:44, 18 March 2013 (UTC) Why worry about something 2,000 years in the future, when there's so much stuff to worry about in the here and now? ←Baseball Bugs What's up, Doc? carrots→ 03:48, 19 March 2013 (UTC) WP:DENY. μηδείς (talk) 17:46, 18 March 2013 (UTC) Putting aside the dull issue of the questioner's motivation, how about the interesting part: is it impossible to power an interstellar manned mission with all the Earth's energy? According to Apollo 13 you can go to the Moon and back in 143 hours - so 72 hours (3 days) to send 43,000 kg including 3 men for something like 380,000 km (10^5). By comparison, Alpha Centauri is 4.36 ly = about 41200000000000 km (10^13). That leaves us with 10^8 times the distance to go. The article doesn't say how long we have, so let's take the OP's figure of 2000 years = 240000 the time to do it in. So the interstellar mission has to have an average speed that is about 400 times faster than that of the space probe, which does indeed suggest the need for 160000 times the fuel (to speed up that much faster and burn that much longer). If I suppose that the giant first stage of a Saturn V was mostly to escape the Earth's pull, and count therefore only something like 600,000 kg of fuel used to get to the Moon, that gets me about 1 trillion kilograms of fuel. Compared to 88 million barrels of oil used daily = roughly 12 billion kilograms? that should be what, 80 days worth, times some factor for the extra energy in rocket fuel. Hmmm. Now let's just go for raw kinetic energy. We want 43,000 kg travelling at an average 4.12E16 m/6.3E10 s = 6.5E5 m/s. That gives kinetic energy (4.3E4 kg) (6.5E5 m/s) (6.5E5 m/s) = 1.82 E16 kg m^2/s^2 = 18 petajoules. Load up 18 Tsar Bombas and you're set. (Well, 19, let's not forget the one to spread the message of civilization to the stars!) Compare to what joule says, 9.4 E 19 joules used in the U.S. per year. Either way, we have this huge advantage that we've considered 1/25 the OP's distance - so should pay 625 times more, or 136 years of oil production (if we had it) to go to his destination in his time frame - or we should get to Alpha Centauri in, oh, I dunno, article doesn't say, but let's say 80 years, which happens to be 1/25 of 2000... ditto. That sallot of energy. But it's still 18*625 Tsar Bombas = 11250 of them. Our article says there are 17,000 nuclear weapons in the world ... what a splendid use for them! Pity it would be impossible to get them all on a 50,000 kg mission, though I wonder how many factors shy it need really be. Wnt (talk) 22:25, 18 March 2013 (UTC) Wnt, feed the birds, not the trolls! 24.23.196.85 (talk) 00:14, 19 March 2013 (UTC)

suicide by hanging

whether there is any kind of noise from the mouth of a person who hanged herself or himself. 120.59.132.210 (talk) 08:33, 18 March 2013 (UTC) Saurabh pandey,— Preceding unsigned comment added by 120.59.132.210 (talk) 08:28, 18 March 2013 (UTC)

How often does it happen with someone else observing? I would think not very often. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:06, 18 March 2013 (UTC)

Public hangings were once a popular spectacle, so there were plenty of observers. If the hanging is done properly, death is instantaneous and the airway is swiftly closed, so not much chance of a noise from the mouth. But if a suicide is botched and the victim slowly dies of strangulation, they might well make some noise during the process.--Shantavira|^{feed me} 12:30, 18 March 2013 (UTC)

Some one who commits suicide by hanging is unlikely to use a long drop, so they will die by slow strangulation. There might be some noise from the mouth, but as there would be very little airflow through the constricted throat probably not very much. AndrewWTaylor (talk) 12:42, 18 March 2013 (UTC)

For more info on noise made by strangulation victims, see Strangers on a Train. 24.23.196.85 (talk) 00:00, 19 March 2013 (UTC)

Heat flow

If you have two bodies of different temperatures next to each other, what is the rate of heat flow between them? Is it just proportional to the difference between the temperatures? Is there an exact relationship?

150.203.115.98 (talk) 11:02, 18 March 2013 (UTC)

What you are looking for is Newton's law of cooling, which says that "the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings". Note that this is an empirical law, not a theoretical derivation or definition - however, it is useful because it is approximately true in a wide range of circumstances. Gandalf61 (talk) 12:09, 18 March 2013 (UTC)

Its dependent on materials and conditions because heat flows different already in single bodies of different materials. Its all exactly described in Thermodynamics. --Kharon (talk) 15:15, 18 March 2013 (UTC)

If the bodies are in contact (with good thermal conductivity at the contact area), and there is not much heat lost or gained to the surroundings, then Thermal conduction is the main factor in heat flow between them, and this is usually proportional to temperature difference in good conductors. ( I say "usually" because someone will point out exceptions, though I can't think of any.) If the bodies are not in contact, and the main transfer of heat is by Thermal radiation, then this is proportional to the fourth power of absolute temperature, making the rate of heat transfer more complicated because there is radiative transfer with the surroundings. Dbfirs 16:33, 18 March 2013 (UTC)

I would be remiss, after my elaborate rant above on Fourier's law, if I didn't point out an exception! The infamous Peltier effect, wherein electrical energy is expended to make the heat flow in the wrong direction (against the thermal gradient), is a great exception. Though, if you want to get really really into technicalities, heat is still flowing from hot to cold; but because the material is subject to an electric field and unique material properties, the electron gas has a different temperature than the substrate. All the necessary mathematics work out, anyway; per my standard reference, oh, probably Chapter 4 of Bittencourt for physics of dealing with multiple temperatures in an ionized plasma (though I don't specifically recall any discussion about solid-state "electron gas" plasmas in Bittencourt's textbook). Nimur (talk) 17:15, 18 March 2013 (UTC)

Thanks, I knew there would be an exception! Dbfirs 17:54, 18 March 2013 (UTC)

Drug Interaction

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

--Jayron32 18:54, 18 March 2013 (UTC)

A few questions regarding atomic energy levels (1&2) and orbitals (1)

I'm currently working on a paper dealing with aspects of Franck-Hertz experiment, and encountered some puzzling descriptions and symbols in an article published in the past, as follows:

1. The article includes a simplified energy level scheme of mercury. This scheme includes also a 7th & 8th levels, despite the fact that the outermost level in Hg is n=6. Any reason or explanation to this 'odd' diagram ?

2. It's claimed in this article that when a triplet appears it means that the electronic configuration consists of 2 electrons in 6s6p orbitals "giving a total P state where the spins are coupled to a total spin with quantum number S=1". How this 6s6p configuration came to be so ? what's the meaning of the quoted phrase ? - I'm familiar with spin physics, but the quoted phrase is seemingly unclear. It'll great to elaborate on these.

3. d orbital is distributed equally in space: x, y & z axes. However, as it's shown in various textbooks, and Wikipedia isn't excluded, there is a kind of a spatial preference: x & y are populated first, and the 'leftovers' go to z. What's the reason for this spatial asymmetry ? BentzyCo (talk) 14:01, 18 March 2013 (UTC)

Try these answers on for size

1. Energy levels exist regardless of whether there are electrons that fill them. Remember that energy levels are merely geometric descriptions of the solutions to the Schrödinger equation, and you can arbitrarily feed any set of quantum numbers into said equation to get the data for any energy level or orbital you wish, those orbitals "exist" in the sense that an electron given enough energy will "promote" to that energy level, even if it isn't the ground state for that atom. There are an infinite number of energy levels, but we generally stop describing them when it isn't useful to use them. For the purposes of the Bohr model (which only strictly works on a "one electron atom", but qualitiatively the principles behind it still hold for all atoms) one will still need to know what the energies of the n=7 and n=8 energy levels are for an atom, because energy imparted to electrons will still cause electrons to jump from the ground state to those higher states, and when they relax back down to the ground state from those higher energy levels, you can use the emissions data to calculate what energy those levels were at.
2. Triplet state describes the situation. For a two-electron system, if the electrons are in separate orbitals, they exist in a triplet state: Four total spin states, with two degenerate with each other: basically they would be up-up, up-down, down-up, and down-down, with the middle two being degenerate. If the two particular electrons are in the same orbital, their spins MUST be opposed (per the Pauli exclusion principle, so the only possibilities are the degenerate up-down and down-up states; since these are identical in energy this is called the singlet state. What your sentence sounds like is that there is some state of mercury (not familiar enough to know if this is the ground state or an excited state) which has a 6s¹6p¹ configuration, which gives rise to the triplet (the expected 6s² state would be a singlet state).
3. All the d orbitals are distributed evenly in space, in the sense that all 5 d orbitals, if overlaid and added together, will make a perfect sphere (this is strictly true of all orbitals of the same n and ℓ values). For any geometry higher than ℓ = 1, the complete set of orbitals will not be geometrically identical. As you note, there's one d orbital whose shape does not match the other four; likewise for f orbitals, there will be four of one shape, two of another, and a single of yet a different shape. I'm not completely familiar with how or why this works out that way, or what this means for the "order" that d orbitals fill in; however as far as I know it is completely arbitrary as all 5 d orbitals should be identical in energy. But at this point someone else will need to answer more authoritatively, as I can't quite find the answer in any of my searches, and I've either not known (or more likely forgotten) this little bit of chemistry. --Jayron32 17:38, 18 March 2013 (UTC)

Re #2, the triplet state is three total spin states, not four. The fourth is the singlet state. $\left|\uparrow \downarrow \right\rangle -\left|\downarrow \uparrow \right\rangle$ is the singlet state (ignoring normalization). It has that value regardless of the spin axis you choose, even though the choice of axis determines the meaning of the up and down arrows. $\left|\uparrow \downarrow \right\rangle +\left|\downarrow \uparrow \right\rangle$ is one component of the triplet state (note + instead of −). If you rotate the spin axis you will not get that, but rather some combination (superposition) of it with $\left|\uparrow \uparrow \right\rangle$ and $\left|\downarrow \downarrow \right\rangle$, which are the other components of the triplet (in one basis, anyway).

Re #3, the orbitals that you see in pictures are just a somewhat arbitrary basis set. As an analogy, try to find an orthogonal basis for the plane x+y+z=0. One possibility is (1, −1, 0) and (1, 1, −2): they both satisfy x+y+z=0 and their dot product is zero. They don't seem very symmetric, though, compared to the plane itself which is symmetric under arbitrary permutations of the x, y, z coordinates (not to mention the much larger group of continuous rotations). That's okay, because no particular vector (except (0, 0, 0)) has that symmetry; it's just the whole collection of vectors that's symmetric, and (1, −1, 0) and (1, 1, −2) is a perfectly good basis for that collection of vectors. Likewise, with the orbitals, the pictures you often see in books are just basis vectors for a space of solutions. The sum of those basis orbitals is still not rotationally symmetric, just like (1, −1, 0) + (1, 1, −2) = (2, 0, −2) is not rotationally symmetric. It's the space of orbitals spanned by the basis orbitals that's symmetric. To put it another way, if you rotate an orbital in this space, you always get another orbital that can be expressed as a sum of orbitals from the same (small, finite) basis set. -- BenRG (talk) 18:27, 18 March 2013 (UTC)

Dr Anna L

Hello, I had recently saw on Facebook, under the page Abandoned Asylums, a mansion that was owned by a Dr. Anna L. The pictures are amazing and the contents of this mansion is very dated ie: glass medicine bottles and the containers organs are preserved in etc. It is said that he was killed in a car crash about 20+ years ago. It also states that his family didn't care about the inheritance, this is also odd. There is something most intriguing about this person and would like to know more but I cannot find much except a video footage on youtube under Mansion of Dr Anna L. I don't think he is English but I'm not sure where he is from either. Is it possible that you could find out more about this person? Thanks Michelle Gecas 24.102.51.143 (talk) 14:39, 18 March 2013 (UTC)

Googling shows that the mansion is in Europe, probably the Netherlands, but it's hard to find search terms that give anything more than that. Looie496 (talk) 16:48, 18 March 2013 (UTC)

As far as I can see, all text in the Youtube video and the pictures is in German, so it is probably in Germany, Austria or the German-speaking parts of Switzerland, Belgium or Luxembourg. - Lindert (talk) 17:05, 18 March 2013 (UTC)

A little further research shows that it's in a spa town in the vicinity of Berlin, but the exact location is a secret passed around by word of mouth, no doubt because the place has already been looted to some degree. Looie496 (talk) 17:44, 18 March 2013 (UTC)

Amount of dissolved salts in a solution

I want to find out the amount of salts and other elements like nitrates, sulphates, chlorides, ammonium, phosphorous, potassium, magnesium, sodium etc in a solution. I guess that I should resort to titration but I am not sure which standard solutions and indicators to use, to find out the concentration of different elements and salts. Is there a web site (or a book) which gives the detailed procedures for finding out the concentration of these? My requirement is very much similar to Water chemistry analysis but that page doesn't give much info. I could pay some labs to do these tests for me but I want to do it at home, as I am likely to repeat the tests many times - WikiCheng | Talk 17:01, 18 March 2013 (UTC)

Could you please give a complete list of the substances you're testing for? 24.23.196.85 (talk) 00:19, 19 March 2013 (UTC)

A manual from a university lab course on quantitative analysis might be a good start.--Wikimedes (talk) 00:49, 19 March 2013 (UTC)

For 24.23.196.85: Here is the list of substances - Nitrates, Ammonium, Phosphorous, Potassium, Magnesium, Sulphates, Chlorides, Sodium, Iron, Boric acid, Zinc, Copper and Manganese. I am basically testing a nutrient solution for plants - WikiCheng | Talk 16:50, 19 March 2013 (UTC)

This is a big, big list! Do you have (or can you afford) any kind of spectrometry equipment? Because this is the easiest and most convenient way to test for all of these substances -- you just put your solution in the cuivette (or sampling flask), select the wavelength you want, put the sample into the instrument and measure the absorbance (or emittance). If not, then the analysis becomes much harder, because you'll have to take thirteen separate samples and analyze each of them for just one substance. In the case of phosphorus, magnesium, chloride, iron, zinc, copper and manganese, you can perform a gravimetric analysis: chloride with silver nitrate (note this will interfere with your nitrate determination); copper with H2S under acidic conditions (IN A FUME HOOD WHILE WEARING A GAS MASK!!!); iron and manganese together by adding alkali to pH of 8 (this WILL skew at least one of the other analyses); zinc with a sulfide salt under alkaline conditions; phosphorus and sulfate together by adding a calcium salt at pH of 8 or above; and magnesium by EDTA titration after precipitating ALL of the transition metals (iron, zinc, copper and manganese). As for the other substances: you can test for ammonium by adding alkali, absorbing the ammonia gas in boric acid, and back-titrating the boric acid solution with sodium carbonate; for phosphate by adding ammonium heptamolybdate and stannous chloride, followed by colorimetric or spectrophotometric analysis; for sulfate by adding barium chloride; and for nitrate by adding concentrated sulfuric acid, absorbing the gas in alkaline solution, and back-titrating with acid. As for potassium, sodium and boric acid -- sorry, you can ONLY analyze for them using spectrometric methods. (You realize how cumbersome this is if you don't have any spectrometric equipment?) 24.23.196.85 (talk) 02:56, 20 March 2013 (UTC)

Dollar bills and a reflecting telescope.

I was trying the other night to recall an anecdote about someone who placed a surprising amount of dollar bills on a large reflecting telescope to show ??how occluding part of the mirror does not affect the image. Maybe I have the reason back to front, but does anyone recall this story and hopefully provide a link. Richard Avery (talk) 19:21, 18 March 2013 (UTC)

It's certainly true that you can place things in front of the primary mirror of a Newtonian telescope and not block out parts of the image (although it does "affect" the image by making it dimmer). The mere existence of the secondary mirror (which blocks out parts of the primary) proves that. I'd be very surprised if anyone would be allowed to place dollar bills directly onto the mirror of a large telescope, simply because of the risk of scratching it or leaving some kind of undesirable contaminant behind. But what you describe would certainly work...I just don't see where the anecdote came from. SteveBaker (talk) 16:50, 19 March 2013 (UTC)

Indeed I'd expect that the damage done by touching the mirror would cost more to repair than the dollar notes used to entirely cover the mirror. If one used $100 bills for the experiment it might cover the costs but singles won't. Repolishing and coating large telescope mirrors costs significantly more than US$0.0624009 per square inch. (If you're wondering where that number comes from: current US banknotes all measure 2.61 by 6.14 inches) Roger (talk) 19:43, 19 March 2013 (UTC)

OK, thanks for taking the trouble guys. Richard Avery (talk) 22:50, 19 March 2013 (UTC)

Neutron instability - magnetic field effect

Are there some data (from measurements) concerning the effect of magnetic field to the mean lifetime of a neutron?--5.15.215.42 (talk) 21:37, 18 March 2013 (UTC)

Data on the number of books published annually in the world, 1950 and 2012

I have heard that data exists to identify the massive growth in books publihed in the last 50 to 60 years. I have found some UNESCO references to Scientific Publications but I was looking more broadly than just this. Is there any data I can readily access? — Preceding unsigned comment added by 124.187.78.18 (talk) 22:43, 18 March 2013 (UTC)

Some data are in the article "Books published per country per year".

—Wavelength (talk) 23:00, 18 March 2013 (UTC)

Can the energy needed for interstellar travel be obtained from Earth?

A message for those in the "Interstellar Bomb" section above who claim that "the energy needed for interstellar travel cannot be obtained from Earth":

This is a classic example of misquoting Wikipedia. It is instructive to examine how a good article was twisted into pseudoscience:

The original question asked about the feasibility of sending a few pounds (say, a nuclear artillery shell) on a one-way trip of 100 light-years with a flight time of roughly 2000 years. But of course the false claim isn't just that that trip is impossible, but rather that no trip is possible.

The Wikipedia page that supposedly supports this claim is at Interstellar travel#Required energy. To get the bogus claim, you have to:

• Change "trip" to "round trip"
• Change "arriving" to "decelerating on arrival".
• Change "a few pounds" to "big enough to support a crew."
• Change "no time limit" to "a few decades".
• Change "available energy" to "actual energy historically produced"

This may be a new record for misusing a Wikipedia page.

Not only is interstellar travel possible, but it has already been done, at least as far as starting the trip goes. It left in 1972. We will have to wait for a while before it reaches another star, but it will do so. --Guy Macon (talk) 23:51, 18 March 2013 (UTC)

"If deceleration on arrival is desired and cannot be achieved by any means other than the engines of the ship"

Uh, isn't the ship headed into a stellar wind at a considerable clip? Doesn't that count as a nifty power source for planetary encounters? Hcobb (talk) 23:59, 18 March 2013 (UTC)

Yes, stellar wind and a big sail can give you a considerable amount of braking. There is a limit, though; come in too fast and the sail won't have enough time to bring you to a stop before you blow past the star or hit something. --Guy Macon (talk) 05:50, 19 March 2013 (UTC)

If you converted the whole mass of the Starship Enterprise into energy (E=mc² etc) it would not go far anytime soon. Look at the math. Bit like saying that Neanderthal cavemen could achieve oceanic voyages by tossing a log into the sea, which washes up (eventually) on some distant shore. [4]--Aspro (talk) 00:02, 19 March 2013 (UTC)

Actually, it's like saying that no land-based species on earth could achieve oceanic voyages, while ignoring the fact that coconuts do it all the time. --Guy Macon (talk) 05:50, 19 March 2013 (UTC)

It is the oceanic current that pull off these feats with the coconuts. The coconuts are just joy-riders of this natural phenomena. Likewise, Voyager was just thrown into a gravitational 'current' whereby its rotational velocity was converted, so as to give it in excess of sun's escape velocity. Modern Homo- sapiens knew just where to throw this metal log in to the near shores of the great cosmos. It was the orbital velocity of earth that gave Voyager the initial oomff. The only difference is that Homo- sapiens could throw their robotic coconuts where as the coconuts palms could only drop.--Aspro (talk) 16:15, 19 March 2013 (UTC)

Sounds interesting. What's the Starship Enterprise's total displacement? 24.23.196.85 (talk) 00:29, 19 March 2013 (UTC)

You probably wont get an answer to that, because it is water bound vessels that 'displace' water at 1gram/cc, whilst space craft displace.. well - just space at ≈ 0 grams/cc.--Aspro (talk) 15:40, 19 March 2013 (UTC)

All right, then, the maximum gross weight (with full bunkers and magazines, that is)! I figured, if it's a ship, it must have a displacement... 24.23.196.85 (talk) 01:58, 20 March 2013 (UTC)

And what's the question? I just saw statements and no question, not even an implied one. Dmcq (talk) 00:52, 19 March 2013 (UTC)

The (slightly ungrammatical) question is in the section header. I don't have a horse in this race (or a good answer), but I can see why the OP is asking for further references/clarification, even if he is sounding a bit pointy. SemanticMantis (talk) 01:02, 19 March 2013 (UTC)

So completely misrepresenting what a Wikipedia article says isn't disrupting Wikipedia to make a point but talking about the misrepresentation is disrupting Wikipedia to make a point? You learn something every day... --Guy Macon (talk) 05:50, 19 March 2013 (UTC)

Oops! Left in an extra word. Fixed now. (Note to self: next time, smoke crack after editing Wikipedia...) The question is, "Can the energy needed for interstellar travel be obtained from Earth?". It was raised in the the "Interstellar Bomb" question, and I thought it best to discuss it outside of the material about time travel commandos trying to avert the foundation of the Cygnian empire through traveling from 31th Century to 21th Century earth. --Guy Macon (talk) 02:43, 19 March 2013 (UTC)

Here are some sources:

• [5]
• [6]
• [7] see the energy section --PlanetEditor (talk) 03:10, 19 March 2013 (UTC)

...which nicely shows that humans reaching the stars is unfeasible using today's technology or any projected future technology. Robots are another story. We have already launched several with enough velocity to escape the solar system and reach the stars -- but it will take a very, very long time to get there. --Guy Macon (talk) 05:50, 19 March 2013 (UTC)

I don't have an issue with Robots doing the trip in our place. As long as they are clever enough to build a civilisation upon arrival. --Lgriot (talk) 09:45, 19 March 2013 (UTC)

Where will they build civilization? --PlanetEditor (talk) 10:03, 19 March 2013 (UTC)

Alpha Centauri, of course. As everybody knows, Alpha Centauri is just version two of Civilization, but also with robots....and xenofungus. Those were dark times. Nimur (talk) 12:27, 19 March 2013 (UTC)

Ghandi when asked what he thought of Western civilization 'That would be a good idea'. ;-) You'd want to send robots first anyway to make certain the place was prepared and a good place to go to, I think you'd be talking about hundreds of years at the very least before humans followed or were seeded or whatever. Dmcq (talk) 12:32, 19 March 2013 (UTC)

Human survival needs Earth's magnetic field, average world temperature, pressure, proper distance from a star like sun, Earth's atmosphere with the exact composition, Earth's surface gravity and escape velocity, biosphere. Even humans would not have survived in the condition Earth was 100 mya. Now where will you get all these? Have a look at Rare Earth hypothesis. Humans can at most be able to set up a moon base or Mars base which will be occupied by rotating crew as the case with the ISS. And they will extract material resources from Mars, Moon, or near-Earth asteroids. --PlanetEditor (talk) 12:54, 19 March 2013 (UTC)

Why would Humans not be able to survive on Earth 100 mya? Also, why would atmospheric exact composition, Surface gravity and (escape velocity??) be needed? Dauto (talk) 14:45, 19 March 2013 (UTC)

Hmm, your question is proof that people love to imagine without caring for science. But I made a mistake. I should have said 150 mya, not 100 mya. Because upto the Late Jurassic (that lasted 150 mya), atmospheric CO2 levels were 4-5 times the current levels. Human respiratory system is not designed to breathe is an environment like this. High atmospheric CO2 means low atmospheric O2, so you inhale less oxygen each time you breathe, than what is necessary for your survival. The respiratory system of the genus Homo sapiens is designed to function in the atmospheric composition that you see today, or that Y-chromosomal Adam saw 237,000 years ago.

Human body is biologically designed to function in the gravity of Earth, i.e. 9.81 m/s2. On a long timescale of multiple decades, humans body will not function if the gravity differs too much from the value 9.81 m/s2. Earth's escape velocity plays crucial role in maintaining its atmosphere, and the composition of its atmosphere.. This in turn maintains the proper atmospheric pressure and temperature needed for human survival and the survival of plants (and edible plants). Without this escape velocity, you will not find the atmospheric composition, temperature, and pressure that you need to survive, you will not find the food (the nutrients) that you need to eat for proper nutrition. --PlanetEditor (talk) 15:41, 19 March 2013 (UTC)

You keep saying the weirdest things with absolute conviction. CO2 is a a critical, but miniscule part the the atmosphere. Over long periods of time, CO2 and O2 are only very weakly correlated. In particular, a CO2 concentration that is 5 times higher will have significant effect on our climate, but is below noticeable level for humans. Concentrations up to 0.5% (5000 ppm) are tolerated for work place conditions, and there usually is no harmful effect on humans even for permanent concentrations up to 3000 ppm. Atmospheric oxygen has likely varied from ~20% to ~25% during the Late Jurassic, which only lasted around 20 million years. Humans are very capable of living and operating at that level of oxygen. I'm not aware about any long-term studies of humans in different gravities - we know that humans work reasonably well at around 10m/s² (although knees and hips and discs tend to fail after "multiple decades" ;-), and we know that long-term microgravity has bad effects on humans. But that's about it - there are no experiments with 0.7g, or 1.1g. --Stephan Schulz (talk) 16:17, 19 March 2013 (UTC)

Oops, I made a grandiose mistake regarding CO2. Thanks for correcting me. --PlanetEditor (talk) 16:42, 19 March 2013 (UTC)

We may not have done many experiments at 0.7 to 1.1g - but we know that average adult humans who starve themselves until they weigh less than 100lbs function perfectly well - and even if someone who weighs 150lbs stuffs themselves with pizza and donuts until they are up at 300lbs, we know that they are still able to lead mostly reasonable lives. Sure, there are health issues at those extremes - but not enough to prevent us visiting, exploring and even colonizing a planet with 0.7 or 1.1g's. The effects of too much or too little weight on bones and organs is extremely well studied. I agree that it's uncertain whether we could live under much more or much less gravity - but if there is a problem, it's got to be something very subtle - not just joint and bone problems. SteveBaker (talk) 16:39, 19 March 2013 (UTC)

When we consider interstellar travel, we ignore the fact that humans are not immune to technological innovation. We'll soon have the technology to make artificial brains, which will radically alter the calculations about interstellar travel. Just like we today send files via email instead of having to physically travel by plane carrying a computer containing the file, in the future we'll travel from one galaxy to another by uploading ourselves to distant machines via radio communications. The more civilizations there are, the easier this way of travel is. If we are alone in our galaxy, then we would have to send some machines via conventional space travel to build up the necessary infrastructure first.

Presumably, members of advanced civilizations already travel this way through the universe, so we could try to download E.T. and make him answer all the Ref Desk questions! Count Iblis (talk) 15:43, 19 March 2013 (UTC)

"in the future we'll travel from one galaxy to another by uploading ourselves to distant machines via radio communications". Why take so much trouble? Genetically modify humans so that they can travel faster than light, and can live in space, immune to cosmic radiation. Genetically modified Homo sapiens extremophiles. Develop anti-aging science so that humans will eventually become immortal. They will not even need a planet to live in. The GM humans will hover in the vacuum of the space. The easiest way to colonize the Universe. --PlanetEditor (talk) 15:59, 19 March 2013 (UTC)

What makes you think it's possible to do those things by "genetic modification"? No amount of genetics will get you moving faster than light - that's a physical impossibility...it may be impossible to genetically modify the body to survive for years in space too. Even immortality has limits due to mental problems of being confined for thousands of years in a small spacecraft...you might have to become something non-human (or at least not recognisably or usefully human) in order to survive the trip. Living off-planet could well be virtually impossible due to the lack of material resources. Why try to modify humans to be something so radically different rather than just starting off with something that works from scratch (ie computers and solar panels). We know how to do the latter - but the former is very likely to be impossible. Your ideas simply don't survive what we know of actual science. SteveBaker (talk) 16:23, 19 March 2013 (UTC)

I thought Count Iblis is joking, so I replied with another joke. Anyway here is an interesting piece. --PlanetEditor (talk) 16:42, 19 March 2013 (UTC)

Kinetic energy is what's required here and that's just a function of mass and velocity. Hence, the critical questions are:

• MASS: What has to do the travelling? A tiny solar-powered computer is a lot easier to ship over there than a bunch of living humans with full life-support systems and food, air and water for the entire journey.
• VELOCITY: How much time can it take? Trying to get to the nearest star in a decade or two is vastly harder than if you're allowed to take a 1,000 year trip.

Those two issues each add many orders of magnitude to the energy calculations...issues of whether you need to decelerate or have a return-trip possibility are likely to be factors of two or four - irrelevant by comparison to my two previous questions. Worse still, the two questions are inextricably linked. Taking humans along with all of their support 'stuff' results in a need to get there fast enough for them to live long enough to survive the trip - so the mass you need to take along is gigantically more and the speed also has to be crazily high.

IMHO, the most likely way for "humanity" to reach other stars is to have us either develop artificial intelligence that's as good as our own - or to figure out a way to scan our brains and run our minds on an artificial (software) neural network. In either case, the thing that we really need to be out there (an intelligent brain) is just software. The spacecraft can be tiny...in principle the size of a grain of rice or so. If the "occupant" (be it AI or neural net) is just immortal software, then the passage of time for the trip is largely irrelevant. Hence, with this restriction, you can allow long trip times (of the order of millenia) and low mass (of the order of grams) - which makes it all seem quite possible...and as others have pointed out, we've already sent a couple of spacecraft of more than adequate size at comparable speeds. There are other variants of this - ship a small self-reproducing nanotechnological robot and some human DNA, or maybe a handful of frozen, fertilized ova. Have the robot make humans from local materials on arrival.

The bottom line is the same - it's much easier to ship ourselves as data than as atoms. SteveBaker (talk) 16:23, 19 March 2013 (UTC)

The short answer to the OP's question is that there is certainly enough energy available here on Earth. In addition to our robotic spacecraft which have been sent on long journeys, passenger ships could be accelerated to near light speed with simply the equivalent of a significant fraction of their rest mass energy, but the energy needed for deceleration, although it could come from earth, will likely be sourced from their destination planets. Furthermore, with evermore powerful mass drivers being built it may even happen! I enjoyed reading the few skeptical references given above, but I should explain how, with some resourceful robots and a few big guns, such travel should be possible, because mass drivers may very well become the real workhorses of interstellar commerce. To put some actual numbers on this idea, first consider that there was an acceleration record (see here) for a mass driver of 5km/s in 1cm length, which is 1.25*10^9 meters per second squared (since v=a*t and d=v*t/2, thus a=v^2/2*d=5000^2/2*.01=1.25*10^9) or a thousand times quicker than most firearms (per[8]) or 127 million g (about sixty to two hundred times greater acceleration than ultracentrifuges!)! To reach a significant fraction of the speed of light, a mass driver capable of such accelerations would need to be a "mere" 36,000 kilometers long ((3*10^8)^2/2*1.25*10^9). Thus, should such long-barrel guns be built by our star-hopping robots, and these guns are busily propelling various robotic payloads as well as robotic fuel tankers to and from our neighboring stars at near light speeds, then the fuel and reaction mass needed to supply the passenger ships' engines can be efficiently accelerated/decelerated by these guns. In other words, these large ships' insatiable propellant/fuel requirements would be obtained via frequent periodic inflight refueling by an extensive fleet of robotic tankers during their acceleration/deceleration periods that occur within a light year of each ship's departure and destination points. Overall fuel and propellant requirements to produce one g-force on the ships, although large, would therefore be manageable even with today's rocket propulsion systems. And even these current systems would likely become antiquated as even more powerful and efficient mass drivers are built! Again, I do not know for sure if large-scale mass drivers can actually become anywhere near powerful enough (there are "practical engineering constraints" according to the mass driver article!), but hopefully with a long and prosperous future ahead of us, I'm thinking that interstellar travel could be possible (and meeting up with a few of our distant neighbors' bug-eyed beauties too perhaps...). -Modocc (talk) 01:19, 20 March 2013 (UTC)

March 19

Why will tidal interaction destroy planet's orbits

is Tidal interaction Roche limit? Base on what I've learnt latter scientist believe Earth will be swallowed up because of tidal interaction but I don't know how it works. Yahoo answers said it is because the way sun rotates like if the day is longer than its year it can be tidally interact. Do sun currently have orbital period, sun is a star I wonder if it even orbits. Is Sun and Earth currently interact right now? I hear Moon eventually will get eaten up by Earth [9] before if it even gets toast by sun but I am not sure how it works. Mercury and Venus don't have an moon is it because it is too close to sun or is it possible it may once have moon and got eaten up by the planets. Do being too close to sun have anything to do if planets have a moon or not?--69.233.254.87 (talk) 00:53, 19 March 2013 (UTC)

I don't know about the rest of your question, but the Moon will definitely not be "eaten" by the Earth. In fact, it is actually moving away from Earth at a rate, if I remember correctly, of 5 cm per annum. Being able to retain a moon does not depend on how close to the Sun the planet is. Plasmic Physics (talk) 01:18, 19 March 2013 (UTC)

I am trying to figure out why will Earth get swallowed up by sun due to tidal interaction. Is it because of sun's rotation? Is Earth and Sun currently tidally interacted?--69.233.254.87 (talk) 01:34, 19 March 2013 (UTC)

Presumably because tidal heating saps the kinetic energy of an orbiting body. However, orbital dynamics are quite complicated, so I'm not going to fathom a guess as to if or when the Earth will be eaten (even ignoring the whole Sun-ballooning-up in 5 billion years). Someguy1221 (talk) 02:48, 19 March 2013 (UTC)

So tidal interaction comes in different definitions. Is there different types of tidal interactions. I just learnt there is two factors why earth will get eaten up by sun. 1.Weaker solar gases increase frictions 2. Tidal decay (I don't know what is that all about)--69.233.254.87 (talk) 05:04, 19 March 2013 (UTC)

The assumption is wrong. The Earth will not be eaten by the Sun because of tidal interactions. If it will be eaten, it will be due the the Sun growing enormously when it leaves the main sequence and turns into a red giant. Tidal interaction between the Earth and the Sun will push the Earth further out a bit. In general, when bodies are not totally rigid, there will be some transfer of rotational energy between orbiting and rotating bodies. Basically, the gravity differential between the near and the far side of the Sun will result in tidal bulges on the sun. Since the sun rotates faster than the Earth orbits it, the Earth-facing bulge will tend to lead the rotation, and hence will exert a force that speeds Earth along in its orbit (a less accurate but more concrete model is that Earth is trying to hold the bulges in place, while the Sun "slips" under them with non-zero "friction"). The effect is fairly small, however. The Roche limit is another effect - it is the boundary where the difference in gravity between the near and far side of the orbiting body is as great as the gravity that holds it together. In that case, a large body will simply disintegrate, because its own gravity can't keep it together. --Stephan Schulz (talk) 07:46, 19 March 2013 (UTC)

Wait a bit I am confused about Since the sun rotates faster than the Earth orbits it, the Earth-facing bulge will tend to lead the rotation. I heard is the sun will slow down its rotation [10], and Earth gravity will create a large tidal bulge. I don't know what is tidal bulge about. I am not sure what you mean by Earth facing bulge. Is solar wind that much important factor, or solar wind is negligible. I thought solar wind just make planets orbit to move outward. P.S. Actually when the sun reaches its maximum size is 7.6 billion years not 5 billion years.--69.233.254.87 (talk) 20:14, 19 March 2013 (UTC)

Currently, the Sun rotates approximately once in 30 days (it's a bit more complicated, because the Sun is not a solid body, and different parts rotate at different speeds). The Earth orbits the Sun once every 365.25 days. Now the Earth exerts gravitational attraction on the Sun. But gravity drops with the square of the distance. Thus, the Earth pulls hardest on the part of the Sun that is closest to it, less hard on the middle, and least on the part that is on the opposite side of the Sun. As a result, the near side bulges out towards the Earth, and the far side bulges away from it (because it's pulled less hard than the rest). Check this image - it's of the Earth-Moon system, but the same applies to the Sun-Earth system. Now if the Earth were always overhead the same spot on the Sun, that's all that happens. But the Sun rotates faster, and so it drags the bulge along with it. So the direction of gravity of the sun with respect to the Earth is no longer in the center of the Sun, but a bit offset in the direction of the rotation. This, in term, pulls the Earth along its path, and transfers rotational momentum from the Sun to the Sun-Earth system. So the Sun rotates a little bit slower, and the Earth moves away a little bit farther to compensate. If this continues forever, eventually the rotation of the Sun and the orbit of the Earth would synchronise. But the Sun will die before that happens. --Stephan Schulz (talk) 21:12, 19 March 2013 (UTC)

You are confusing me right now. The research said when sun becomes a giant it will slow down its rotation quickly. now sun rotates every 30 days, in 7.6 billion years it will only rotate once every 10,000 years which creates a large tidal bulge on sun's surface when sun almost stops rotating.--69.233.254.87 (talk) 23:06, 19 March 2013 (UTC)

If Mercury had a substantial atmosphere

If Mercury had a atmosphere like Earth will the planets temperature been alot cooler? When I was younger I would think Mercury is hot because it is close to sun. Is the reason mercury gets 850 F at daytime because there is no atmosphere to protect the extreme temperatures. If Mercury had an atmosphere like Earth how will its surface temperature be like? Daytime temperatures will be alot cooler like equator stay under 500 F, and the poles stay around 200 F? Will nighttime get be much milder with an atmosphere? --69.233.254.87 (talk) 00:59, 19 March 2013 (UTC)

It depends on what's in that atmosphere. Venus, similar to the earth in size, has an atmosphere, but much of it is acidic gas, and is extremely hot; as Carl Sagan once said, "A thoroughly nasty place." ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:04, 19 March 2013 (UTC)

There are more qualified people to answer this question than I, but in my limited understanding, the distance to the sun matters a lot, atmosphere or no. As Baseball Bugs said, the atmosphere's composition does matter, and one reason Venus is so hot is because it has a lot of CO2 in the atmosphere so it suffers from a pretty dramatic greenhouse effect. Also, I think the atmosphere would insulate against the huge day/night temperature swings. But the non-satisfying answer is that it depends on the atmosphere composition. I'll be interested to see what others have to say. ~Adjwilley (talk) 01:39, 19 March 2013 (UTC)

I mean if Mercury had a clear atmosphere like Earth does.-Earthlike atmosphere.--69.233.254.87 (talk) 01:35, 19 March 2013 (UTC)

My gut says the temperature would be more stable, but slightly warmer on average. That's just a guess. (I'm basing this partly on the fact that the moon is the same distance from the sun as the earth, but has a colder temperature on average, with much greater swings...+123C to -153C, I think.) ~Adjwilley (talk) 01:41, 19 March 2013 (UTC)

• A key factor here is that Mercury rotates very slowly, and the dark side becomes extremely cold -- our article says around 100K. That isn't cold enough to liquefy nitrogen, but it's easily cold enough to liquefy carbon dioxide. So you would get some heat transfer from the day side to the night side, but working out the parameters would be quite difficult and would depend on the composition of the atmosphere. Looie496 (talk) 01:58, 19 March 2013 (UTC)

It would be difficult for Mercury to maintain an earth-like atmosphere for long anyway. Oxygen reacts with almost everything - and it's only there because we have plant life - without that, the oxygen would probably react with iron in the crust and vanish from the atmosphere. Water vapor is only here because we have liquid oceans - and those can't be on Mercury unless the temperature is low enough so they won't boil and high enough that they won't freeze. CO2 (as someone already pointed out) would freeze solid on the dark side - so there would be no greenhouse effect from that. Mars and the martian atmosphere might be a better model for what Mercury could reasonably have. Also, Mercury is a very tiny planet - much smaller than Earth, Mars or Venus - and only about a third bigger than our moon...it doesn't have enough gravity to hold a dense atmosphere for very long. SteveBaker (talk) 15:34, 19 March 2013 (UTC)

V-22 Osprey

Is there a civilian version of the V-22 Osprey in any stage of development? 24.23.196.85 (talk) 01:10, 19 March 2013 (UTC)

Well, the AgustaWestland AW609 already exists, so... yes? Evanh2008 ^{(talk|contribs)} 05:11, 19 March 2013 (UTC)

Well, technically this would be a civilian version of the XV-15 rather than the V-22, but this is close enough for my purposes. Really, I was just thinking whether it would be plausible for Mackinac Lines (a fictional charter freight/air-taxi company that I made up for my book series dealing with air rescue) to acquire a couple of those.  :-) 24.23.196.85 (talk) 06:25, 19 March 2013 (UTC)

It's technically possible - but if the V-22 is anything to go by, those machines are likely to be horrifically costly to maintain to a reasonable degree of safety. It seems really unlikely that a civilian operation such as you describe would want such a thing rather than some combination of conventional helicopters and fixed wing aircraft. The AW609 is mostly selling to specific search-and-rescue organizations and things like coastal patrol. It would be great in an air rescue role - but I just doubt whether a freight/air-taxi company would buy such a thing. SteveBaker (talk) 15:23, 19 March 2013 (UTC)

The AW609 is still only a prototype and several years from being certified, so it's not actually selling to anyone yet. Roger (talk) 19:54, 19 March 2013 (UTC)

It could come in handy on their Arctic Division (specifically, for ferrying heavy and highly lucrative mining equipment to remote outposts in the tundra), but they'll have to wait for it to be certified. Maybe in some of the later novels, when (and if) it actually goes into series production. 24.23.196.85 (talk) 01:55, 20 March 2013 (UTC)

Fever

Is increased temperature a byproduct of the immune system working overtime or a reaction to infection that helps the immune system eliminate it?68.36.148.100 (talk) 03:17, 19 March 2013 (UTC)

See Fever#Pathophysiology which discusses the various internal and external things that can cause a fever. --Jayron32 03:24, 19 March 2013 (UTC)

Ok, I mean a fever from the flu. Not from hyperthermia. 68.36.148.100 (talk) 03:37, 19 March 2013 (UTC)

In this case, yes. 24.23.196.85 (talk) 04:47, 19 March 2013 (UTC)

... and "yes" to both cause and effect, or perhaps sometimes one and sometimes the other. Experts don't fully agree on this. Dbfirs 09:14, 19 March 2013 (UTC)

Could one of you clarify your answer? Both examples I gave are effects of getting an infection so I don't understand your" cause and effect" reference. Are you saying experts don't know if increased body temperature aides the immune system in fighting infection?68.36.148.100 (talk) 10:54, 19 March 2013 (UTC)

Fever is an immune reaction to certain infections, a particularly effective on in some cases. We have articles on everything you asked about... as everyone above referenced. You say a "byproduct" but that's the kind of anthropromorphic thinking that predominates a lot of low level science education ("the electron wants to go to the other atom")... it's an awful way to think about these things. Shadowjams (talk) 13:15, 19 March 2013 (UTC)

So as the immune system fights infection, it produces excess heat. The excess heat makes life harder for some kinds of infectious agents. Asking whether the excess heat is a "deliberate" thing or an "accidental" thing is to miss the point. If we believed in "intelligent design" then we might say that the "designer" deliberately wanted the excess heat to fight infection and so made it that way...but we don't (or at least, shouldn't!) believe that - so we have to ask whether the immune system merely evolved with an inefficient biochemical engine that produces a lot of waste heat - or whether it's actively evolved a mechanism that produces that much heat despite the existence of a more efficient, suitable and available biochemical pathway that would be just as effective. That's a tough question to answer - which (I suspect) is why (as User:Dbfirs claims) experts don't agree. Evolution is great at "repurposing" body parts and chemical pathways to do things that they had not previously intended. So it's perfectly possible that we've evolved to optimize the (initially incidental) heat output either to make fighting infection less energy-wasteful or more heat-producing...but evolution is quite capable of adjusting the balance between the two goals dynamically depending on the changing threats facing our bodies over the millenia. It's possible (perhaps even likely) that we're in a delicate perpetual balance between the two reasons you describe...the amount of heat we produce being tweaked from one generation to the next to produce the maximum heat-death in the bugs that ail us for the minimum drain on our bodies' energy supply. SteveBaker (talk) 15:06, 19 March 2013 (UTC)

I like the tone and don't entirely disagree, but I'm puzzled by parts of SB's answer. Inflammatory cytokines like IL-1, IL-6, and TNF alpha - which play important roles separate from what follows - stimulate production of Prostaglandin E2, which in turn stimulates the hypothalamus to raise body temperature by a variety of mechanisms. While the inflammatory cytokines are intrinsic to the immune response, the heat generated does not represent "excess heat" that is a byproduct of an inefficient biochemical pathway such as lymphocyte-mediated killing of virus-infected cells; rather, temperature is raised in a separate pathway (and I think Phil Mackowkiak would say that it has played an important role, in the past at least, in helping us fight infections). -- Scray (talk) 15:42, 19 March 2013 (UTC)

Just a reminder of a previous discussion on fever in cold-blooded animals [11]. Mikenorton (talk) 19:07, 19 March 2013 (UTC)

Bomb shelters

What kinds of structures (other than the Paris Metro) were used as bomb shelters in occupied France during World War 2? Thanks in advance! 24.23.196.85 (talk) 06:32, 19 March 2013 (UTC)

Well, any type of underground structure, such as a wine cellar, would offer some protection. Mines or caves are safer, but getting large numbers of people into them quickly would be problematic, as they might be far from population centers, with limited openings. StuRat (talk) 16:48, 19 March 2013 (UTC)

Air-raid_shelter#In_World_War_II. --PlanetEditor (talk) 18:57, 19 March 2013 (UTC)

There is a lot of information about the subject relating to Britain, but I can't find anything very specific for France. - Anybody?   ~:74.60.29.141 (talk) 20:36, 19 March 2013 (UTC):~

The folks over at the Humanities Desk are the real experts in historical research, try asking them. Roger (talk) 20:58, 19 March 2013 (UTC)

Force field implementation

How does Dreiding FF compare with Merck Molecular FF (94) for small molecules? Plasmic Physics (talk) 06:37, 19 March 2013 (UTC)

Do you expect that there will be a better answer than the source already listed in our article? DREIDING and MM94 are both published. The papers that introduced each one outlined the features, and compared to extant models. Nimur (talk) 14:00, 19 March 2013 (UTC)

Hydrogen Peroxide

Hydrogen Peroxide decomposes into water and oxygen in the following reaction:

2 H₂O₂ → 2 H₂O + O₂

Silver is a catalyst for this reaction. Does that mean silver decomposes into ionic silver (in other words: "silver ions") and the silver ions react to produce Ag_s? Cf: Wikipedia:Reference desk/Archives/Science/2013 March 14#Ozone Silver TarnishCurb Chain (talk) 10:49, 19 March 2013 (UTC)

I'm not familiar with this particular use of metallic silver, although, I'm aware that metal ions act in this way. If metallic silver is a catalyst here, then it would not neccessarily be ionised in the reaction. Plasmic Physics (talk) 11:32, 19 March 2013 (UTC)

Hydrogen peroxide may simply coordinate to the silver surface as part of the reaction. Plasmic Physics (talk) 11:33, 19 March 2013 (UTC)

I'm pretty sure that Plasmic is correct on the second part: The word catalyst means "participates in a chemical reaction, but is not consumed by it". If metallic silver were converted to silver (I) ions, then it wouldn't be a catalyst, it would be a reactant. The silver should act as a heterogeneous catalyst in this case. There's also no need to oxidize the silver, as the decomposition of hydrogen peroxide is a Disproportionation reaction; the hydrogen peroxide (the oxygen specifically) is both the oxidant AND the reductant. Once you balance the reaction, there's no left over electrons so no other elements should change oxidation state. --Jayron32 13:15, 19 March 2013 (UTC)

I agree. A catalyst, by definition, is not consumed in the reaction. (theoretically) ~Adjwilley (talk) 21:56, 19 March 2013 (UTC)

Curb intends to suggest that silver is reversibly oxidised in the reaction, as in: Ag ↔ Ag⁺ e^-. In this case, silver still acts as a catalyst. The question is: is this the key route of catalysis? Plasmic Physics (talk) 23:14, 19 March 2013 (UTC)

Not likely. If the silver ionized, it would dissolve into the solution. If it just acts as a surface catalyst, it wouldn't. I'm inclined to think that it does that. --Jayron32 02:25, 20 March 2013 (UTC)

Yes, it would dissolve into the solution, but the reduced silver would just precipitate out again. So, the metallic silver is just transfered to the bottom of the reaction vessel. Where the metallic silver ends up, is irrelevent, as long as the final amount of silver is equal to the initial amount of silver. Plasmic Physics (talk) 02:44, 20 March 2013 (UTC)

Instead of the bottom of the vessel, lets not forget the possibility of the formation of a colloid. Plasmic Physics (talk) 02:46, 20 March 2013 (UTC)

if hair would grou at the expansion rate of cancer cell

The human hair is made of cells, and created by cells. What would be the rate of hair growth, if the hair was expand as a cancer cell. How many cm of hair would have been growing in a day? — Preceding unsigned comment added by 77.125.128.88 (talk) 19:30, 19 March 2013 (UTC)

One important factor is that the hair itself is dead, so doesn't grow at all. The hair follicle, in the skin, is what extrudes the hair. So, you can't get an effect of hair cells spawning more hair cells, which spawn more, exponentially. I'd think the growth rate on men's facial hair would be close to the maximum rate, as there doesn't seem to be any reason for our bodies to possess the ability to grow hair faster than they do. What you could get is extremely thick hairs. StuRat (talk) 19:36, 19 March 2013 (UTC)

What is the Palacozoic?

I've come across a reference to a geological period called the "Palacozoic", but this term does not appear to exist anywhere on Wikipedia (which is really surprising). Let me make it clear the word is not Paleozoic or Palaeozoic (different spelling), which Wiki and Google want to redirect me to, it's "Palacozoic", no mistake. When you search Google with that specific word (rather then just similar words) it does turn up quite a lot of Geology papers using the term (see here), which is why it's even more surprising that it appears to be unknown on Wiki. So if there's any geologists out there, can you explain what the Palacozoic is and why it is not referenced anywhere on Wikipedia? --Hibernian (talk) 20:34, 19 March 2013 (UTC)

A brief check suggests to me that it might be an archaic term (books from the 19th C., etc.) — But it would be nice to find an explanation someplace on WP. ~:74.60.29.141 (talk) 20:41, 19 March 2013 (UTC):~

I'm convinced, especially after looking over the Google search results, that it is in fact an error for "Palaeozoic". Virtually all the cites are either from foreign authors or from Google Books, which uses OCR for transcription. Looie496 (talk) 20:49, 19 March 2013 (UTC)

I agree, it is just a typo, "e" and "c" can easily be confused, even more so if OCR is involved. Roger (talk) 21:03, 19 March 2013 (UTC)

I'm finding some recent (1980s-90s) publications from the Netherlands / Greenland; wonder if it could be related to re/translating "æ" ~ Perhaps this is a question for the Language desk (?) ~:74.60.29.141 (talk) 21:08, 19 March 2013 (UTC):~

We may be omitting the possibility this is the geological period of Pollack jokes. μηδείς (talk) 21:13, 19 March 2013 (UTC)

I originally saw the word written on this map of the geology of Ireland: [12], you can clearly see there that is says "Palacozoic" (comes from this website: Irish Base Metal Exploration). But I did another search for similar images and it turned up this map [13], that's a nearly identical map except now the name is changed to "Palaeozoic" (from this site: Conroy Gold and Natural Resources). So I can only conclude that is must just be a spelling mistake. Though if it's a fairly common mistake maybe Wikipedia should have Palacozoic as a redirect to Paleozoic. --Hibernian (talk) 02:31, 20 March 2013 (UTC)

New glasses every two years?

Do the eyes of an adult really get worse within 2 years? I doubt that any change in any organ can be noticed in such a short period. Is that a hoax spread by the glasses industry to sell more glasses? OsmanRF34 (talk) 21:00, 19 March 2013 (UTC)

Two years is enough time to observe a significant change in eye prescription. However, that does not mean that all people with prescription eyewear will undergo such a change, or that someone who had that much change over the prior two years will have that much over the next two as well. Note also that different people have different expectations about how good their eyesight should be. For example, I determine my need for evaluation based on how well I can read highway signage. If I drove for a living, I'd probably be pickier about how good my distance vision needs to be, and so I'd get a new prescription more frequently. — Lomn 21:24, 19 March 2013 (UTC)

It's not just about the eyes, it's about the state of the glasses themselves. I've had my current pair about 3 years (picking out new ones next week), and they are in a terrible state, battered and scratched and falling apart - and I only wear them in the evenings after removing my contacts. As it turns out my prescription had changed (by -0.25), but I was planning on getting a new pair anyway. Imagine an item of clothing that you wore all everyday, I would be amazed if it lasted two years--Jac16888 ^Talk 21:31, 19 March 2013 (UTC)

Effect of Acetone on ABS

It's fairly common knowledge that Acetone will melt ABS plastic. In my experience it turns it into a honey like goo, and the goo hardens again when the acetone evaporates. My question is: what effect does this have on the material properties of the plastic? Does the plastic return to its original state and strength, or will it crystallize with different material properties? Is it different than melting and then cooling the plastic with regular old heat? I've asked Google but haven't found much. ~Adjwilley (talk) 21:52, 19 March 2013 (UTC)

I'm not sure, but I think it should return to its original strength upon evaporation of acetone. FWiW 24.23.196.85 (talk) 03:04, 20 March 2013 (UTC)

3D Printing your own UAV - how far are 3D printers from this capability?

You see, any civilian interested in ending the regime of the last Stalinist bastion on Earth may obtain a 3-D printer that can put together parts of a UAV cargo/surveillance drone.

The cargo bay would drop supplies, many also 3D-printed themselves, intended to help dissidents rebel against the government and end the 60+ years of brutal madness:

• Guns prepackaged with suppressors, ammunition, and instructions to shoot a lone soldier, hide the body, and take the uniform and their armaments, as there wouldn't be enough ammo for purposes beyond this.

• Extra silencers for AK-47s and other firearms known to be carried by their goose-stepping henchmen, in order to suppress the weapons the dissidents pick up off of their oppressors.

• Bibles/other religious texts (from the religiously-inclined.)

• Parts for larger 3D printers

• Entire 3D printers, operated by solar, wind, or manual power (foot pedal or hand crank) as electricity is scarce otherwise, instructions for assembly / use thereof

• MREs

• Packs of seeds to grow food.

But the hardest part may be to print your own UAV. Obtaining one otherwise is even harder as there isn't much of a market to buy one, and 3D-printing a UAV may be cheaper anyway.

1. Solar panels for the top of the wings - would power the craft indefinitely. What hurdles would need to be crossed in order to start 3D-printing solar panels?
2. Weight and strength matters, to carry as much cargo as needed, and especially to withstand wind. What materials would be light and strong, and fairly 3D-printable?
3. Besides gasoline, which may not be most ideal to fuel UAVs, what easily obtainable "backup fuel" can be used for when not enough solar energy is present?
4. How printable is the engine for said backup fuel?
5. How much of a detriment would it be to install said backup engine?
6. Can a mini wind turbine be added somewhere so that a good wind can keep the plane powered in order to supplement (and sometimes take over) the solar energy?
7. Will DefCAD.com provide blueprints for stealth, civilian-operated UAVs so that no "Average Joe" would need to design one themselves?
8. What is the closest civilian-accessible American territory to that most contentious rogue nation on Earth? How easy is it to get there with a 3D printer?
9. Are there satellite frequencies accessible to civilians that one could use to operate the UAV?
10. If no such frequency is accessible, how else can civilians operate UAVs from hundreds, even thousands of miles away?
11. How easily 3D-printable are countermeasures against radar- and heat-seeking missiles?
12. How are all the needed raw materials obtained for the 3D printer in the first place, and how easily-obtainable are they?
13. How much might a good 3D printer cost by 2015, extrapolating for trends in 3D printer costs?
14. How much $ in raw materials would it take to print a fully-working recon/cargo UAV, in current prices?
15. How many other such cargo UAVs and cargo-drops could it take to help break the Stalinist government's iron-fisted hold on its people?
16. What are the cities and regions known to be least loyal to their regime?

When 3D printing becomes more accessible to civilians anywhere, they can certainly change the world and overthrow the most oppressive regimes. Of course though, that particular regime is going to need outside help. Thanks. --70.179.161.230 (talk) 22:18, 19 March 2013 (UTC)

Answer is very far. So no, don't get your hopes up again about going to work for the FSA as a UAV pilot (or if you resurrected your plans to work for the South Korean military them too). Nil Einne (talk) 22:39, 19 March 2013 (UTC)

Do 3D printers print electronic components?

Is that a peer-to-peer guerrilla plan?

do you have some millions to do that? Otherwise you won't gather the mass of bibles, guns, and whatever, to make a difference.OsmanRF34 (talk) 23:26, 19 March 2013 (UTC)

3D printers are not replicators. As I understand it, they currently use one material to make the end product. That's not going to get you a functioning UAV (or anything else), just a big blob in the shape of one. An expensive decoy, but not much else. Clarityfiend (talk) 00:30, 20 March 2013 (UTC)

However, there are Gun parts made on 3D printer (BBC) (which may have inspired this query?). ~:74.60.29.141 (talk) 00:42, 20 March 2013 (UTC):~

Wow. Where to start... First off, most 3D printers are either really expensive to purchase and operate, or only print plastic. Get a fancy one, and you can print 2 kinds of plastic at the same time. Also, the build volume for said printers is going to be much smaller than a UAV. Printing anything over 6 inches tall is often a problem. You may, however, be able to print pieces for a UAV: body, wings, flaps, etc. You won't be able to print the engine (the plastic would melt if you tried burning any fuel; same problem with guns), you wouldn't be able to print the electronics (metal problem again, plus you can't print computer chips), or the servos to control the flaps, etc. Also, 3D printed objects (using the extrusion process) are structurally weak, because they basically a big pile of plastic spaghetti, and whatever you print is likely to sheer in half if stressed.

That said... you can construct a drone for relatively cheap with some work and money. Check out diydrones.com for information on how to do that with an arduino microcontroller that can actually autopilot the plane (using built in GPS, compass, gyros, acceleration sensors, altitude sensors, etc.) and perform real missions. I'll bet you could design and 3D print some of the parts you'd need for a small airplane, though probably not big enough to drop a significant amount of supplies. And it'd put you out a couple thousand dollars. ~Adjwilley (talk) 00:59, 20 March 2013 (UTC)

What if, you use a coloidal nanometal ink, and use a laser to vapourise the continuous medium and sinter the nanometal into bulk material? Why has no one thought of that? It seems so simple. Plasmic Physics (talk) 02:31, 20 March 2013 (UTC)

Probably someone other than you has, or some near equivalent. However, for metal products, Numerically Controlled Machines (computer controlled machine tools) are well established, and have been in use for decades, and are now in such common use than even hobbyists/model makers are using them. They have always been accurate, work well with common steels and non-ferous alloys, and are cost effective - none of which would apply to your idea. Plus your idea would suffer from the same limittation as 3D printing has in plastic: it would necessitate removal of support elements, and also could not do cavities. If a sintered product is acceptable (for most mechanical products it is not suitable, but it does have its' niche) then conventional powder metalurgy using molds can be used. Wickwack 120.145.34.201 (talk) 02:46, 20 March 2013 (UTC)

I'm not sure what you mean by cavities, but I must stress that this modified process sinters as it prints, not afterward; also note that nanometal sinters more densely and at lower temperatures than micrometal. What about this idea then: using dual constructive interfering UV lasers in a CVD process, so that only where the beams intersect is metal deposited? Plasmic Physics (talk) 03:09, 20 March 2013 (UTC)

It would have the same geometric limitations as using scanning lasers to selectively solidify a liquid polymer - an early form of 3D printing. These can furnish a cavity that has a constant cross section projected in from a surface, or a cavity with sides sloped outwards, but not a cavity of arbitary axis with inwards sloped sides or a cavity of non-constant cross section, as the material solidified early can block the beam(s). Your idea has indeed been thought of before - see the wikipedia article Selective Laser Sintering. 3D printers based on the guided laying down of a plastic feed-wire are now getting quite common, even though they are only good for small plastic parts whre the application is verey non critical, and for "test feeling"/"hold in your hand" checking before committing to conventional manufacturing. I'd never seen nor heard of SLS until I decided to check Wikipedia just now. There's a place for everything. For instance, metal parts that are essentially a shaft having several diameters and a thread or two, copying capstan lathes, which work under hydralic control guided by a plate prototype are in my experince still the fastest way in small quantities - technology of the 1920's. Wickwack 121.215.31.187 (talk) 03:42, 20 March 2013 (UTC)

March 20

Two CFL bulbs on same line

I have two CFL bulbs on a single line split to two sockets. Sometimes both will light up. Usually, only one lights up. Both work fine. If I remove one, the other always works. I've had the ground checked. It is good. I've had the wiring checked. It is correct. Checking load while lights are on shows nothing unusual. So, after three electricians checked it, all three said that sometimes you can't put two CFL bulbs on the same line. Seriously? I've been searching and searching and I can't find a single webpage that discuses this kind of thing. Does anyone have information about what could cause this problem? — Preceding unsigned comment added by 71.204.230.66 (talk) 01:23, 20 March 2013 (UTC)

Here ya go: http://www.thecircuitdetective.com/

99.250.103.117 (talk) 03:56, 20 March 2013 (UTC)

Panstarrs help for tonight?

I've been trying all month to see this comet, and either weather has been bad or I just don't know where to look. I'm at 40° latitude, the sky is clear, it's 8 pm and it's finally getting dark. A forum on cloudy nights said this comet sets about 8:50, and I think they're reporting from Grand Junction.

I can see the moon and Jupiter. Any ideas where to go from there? I don't think there's a panstarrs plug-in for Stellarium (I'm on a mac anyway) and the lack of solid helpful advice in the news is pretty sparse.Reflectionsinglass (talk) 02:01, 20 March 2013 (UTC)

oh, Grand Junction is in Colorado, latitude-wise beneath me. If i have the moon, Jupiter, and the Pleiades all in a line, is Panstarrs anywhere near there? Reflectionsinglass (talk) 02:09, 20 March 2013 (UTC)

Try this site: [14]. Shadowjams (talk) 02:33, 20 March 2013 (UTC)

Oh my god thank you, Wikipedia should send you a check. Well the comet is behind a stupid mountain directly to the west and has been behind that stupid mountain for hours probably. I'll probably never get to see it. This is turning out to be a week of disappointments. Reflectionsinglass (talk) 02:39, 20 March 2013 (UTC)

Get one of those handy Marvin the Martian Illudium Q-36 Explosive Space Modulators – and get rid of that annoying mountain!  —74.60.29.141 (talk) 03:08, 20 March 2013 (UTC)