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July 8

On Growth and Form

I've heard a lot of good things about 'On Growth and Form', but the book is also nearly 100 years old. Is it still the best text on its topic, or has it been superseded by something more modern? 65.92.7.168 (talk) 00:55, 8 July 2012 (UTC)

It's a standard text like Helmholtz' On the Sensation of Tone which, due to its quality, remains a basic introductory text in its field, and hasn't been supeseded for what it covers, which is the basic geometry of bilogical form. I saw it on the shelves for undergraduate bio courses in the Ivy League schools in the 1990's. For a reader with general interests it's worth getting from the library and thumbing through, not spending money on with the expectation that you need to master it. Of course, developments in embryology and genetics since take the field from the level of what with D'Arcy Thompson is basically an art to one of the most complicated of sciences. The Shape of Life: Genes, Development, and the Evolution of Animal Form was a cutting edge popular work when it was published in 1996, dealing with the comparative genetic regulation of development such as the HOX genes. It's hardly up to date now, but it's still highly recommended. μηδείς (talk) 01:48, 8 July 2012 (UTC)

'On Growth And Form' is a truly marvellous book, IMO. But it is certainly not up-to-date. It was not up-to-date fifty years ago.

In 1961, Cambridge University Press published an Abridged Edition edited by John Tyler Bonner. The introduction to that edition is well worth reading for an understanding of the remarkable nature of D'Arcy Thompson's book. Wanderer57 (talk) 02:23, 9 July 2012 (UTC)

Electrides of elements with Z>173

Untriseptium and unsepttrium both state that unsepttrium is the heaviest possible neutral element.

But couldn't the elements beyond unsepttrium theoretically exist in a quasi-neutral state as their own electrides, such as unseptquadium(I) electride, [Usq⁺][e^-], unseptquadium(II) electride, [Usq²⁺][e^-]₂, and unseptpentium(II) electride, [Usp²⁺][e^-]₂, with the minimum oxidation state of the element in the electride being Z - 173? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:31, 8 July 2012 (UTC)

I won't pretend to know all the physics, but it seems to me that if heavier elements can not hold their own electrons in orbitals, there would be no reason that they could form an electride either. -RunningOnBrains^(talk) 03:07, 8 July 2012 (UTC)

*waits for explanation* Whoop whoop pull up ^{Bitching Betty | Averted crashes} 03:20, 8 July 2012 (UTC)

Well, the binding force for ionic bonds is the electromagnetic force, the same force that keeps electrons in their orbitals, so if an electron can not be bound in an orbital I don't see why it could be bound in a bond. Like I alluded to before though, I am certainly not an expert in nuclear (or quantum) physics.

The problem for the highly charged nucleus is not losing an electron from the outer shell, but that the field around the nucleus is so strong that the vacuum is split into positron and electrons with the resultant destruction of the innermost electron. Alternately I suppose you can think of the potential energy of the inner electron has become so negative it exceeds the rest mass of the electron. It would be like matter falling into a black-hole and crossing the event horizon. see Extended periodic table#End of the periodic table which needs an expert to improve it (not me). However sodium can spontaneously form an electride when it is put under pressure, where you can get black sodium, red sodium and transparent sodium, all electrides. It sounds a good topic for Whoop to write up. This phenomenon could do with more investigation and perhaps more elements can form electrides by themselves. Graeme Bartlett (talk) 07:19, 8 July 2012 (UTC)

Brain dead pregnant woman

What was the name of the pregnant woman who according to this webpage was declared brain dead at 24 weeks gestation but was kept on life support for another 9 weeks to allow the delivery of the baby? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 06:14, 8 July 2012 (UTC)

Christine Bolden?[1] Not sure it's the same person, but hard to say. That webpage is not a great source of physiologically accurate assumptions in the questions it asks. 71.212.249.178 (talk) 06:45, 8 July 2012 (UTC)

No, the woman in the article I mentioned did not give birth to twins, was kept on life support for twice as long, and was way back in 1988. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 06:58, 8 July 2012 (UTC)

Not answering the question; hatted. Wnt (talk) 20:49, 8 July 2012 (UTC)
The following discussion has been closed. Please do not modify it.
We should list all articles about these incidents that we can find so that maybe we can find out which one that webpage was referring to. (There should already be a list of those somewhere on Wikipedia though...) Whoop whoop pull up Bitching Betty | Averted crashes 07:07, 8 July 2012 (UTC) List of women who were declared brain dead while 24 weeks pregnant and were kept on artificial life support for nine more weeks in order to allow for delivery? Evanh2008 (talk|contribs) 07:16, 8 July 2012 (UTC) WILL YOU PLEASE NOT MAKE FUN OF THIS QUESTION?!?!?!?!?!?!?!?! Whoop whoop pull up Bitching Betty | Averted crashes 07:47, 8 July 2012 (UTC) Why not? Didn't you ask it for time-wasting fun, like most of your questions? Wickwack120.145.35.180 (talk) 12:33, 8 July 2012 (UTC)

I suspect you will not find the name online as all other references seem to derived from a single medical ethics paper (you can see the abstract here) and details of this nature tend to be kept confidential. But if your interests runs deep enough, you can try contacting the article's authors who may have already received consent to share said information Snow (talk) 07:06, 8 July 2012 (UTC)

• The case study is reported in PMID 3392814, available online in full here. The woman is not named, though. Looie496 (talk) 15:59, 8 July 2012 (UTC)

Patients are rarely named in the medical literature. Exceptions are people long gone (>100 years). OsmanRF34 (talk) 19:29, 8 July 2012 (UTC)

about wireless electricity transmission

is it possible to transmit electricity in a long distance? I am working in this project.It will be really beneficial. please give me some suggestions. — Preceding unsigned comment added by 1.38.16.23 (talk) 07:39, 8 July 2012 (UTC)

Yes, you can convert it to methane which can be transmitted in a pipeline. 71.212.249.178 (talk) 07:50, 8 July 2012 (UTC)

You could just transmit the electricity through the pipeline, so long as it's a good conductor and you insulate it properly. — DanielLC 20:26, 9 July 2012 (UTC)

Depending on the distances involved, a synthetic methane pipeline can be more efficient, thanks to improvements in water electrolysis over the past decade. 71.212.249.178 (talk) 01:46, 10 July 2012 (UTC)

Yes, electricity can be transmitted without wires. See Microwave transmission#Microwave power transmission and Wireless energy transfer for details. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 07:51, 8 July 2012 (UTC)

There are four ways (and only 4 ways) to transmit electrical power from one place to another, without recourse to doing non electrical things like produce gas and pipe the gas:- 1) by wires (conduction), 2) by capacitive coupling, 3) by induction, and 4) by radio progagation. Sorry to dissapoint, but misguided but often mentioned efforts by Tesla, and wacky proposals for enormous satelite-to-earth systems notwithstanding, only conduction of wires is any good in practice, and it works really well. Electricity grids traverse netire continents. Capacitive coupling and induction come under the heading of "wireless energy transfer" and is inherently good for short distances only (distance <= diameter of devices). Capacitive coupling has had no significant commercial use as far as I know, but inductive transmission's main applications are swipe cards and RFID identification, and powering implanted medical devices from powered sources worn in clothing. Radio progation requires a transmit antenna, a recive antenna, and a space between the two, and as such is governed by the path loss equation, well known to radio engineers. The physics of the path loss equation is such that while radio waves can be detected at truly enormous distances (of galactic scale), radio propagation is really only practical for transmission of information, and not power. Typical path loss values are of the order of 10's of watts to kilowatts transmitted, and microwatts to picowatts received. If this is for a school project, I suggest you look up the 4 methods, get some undertanding why the physics means only transmission by wires is used in practice, then look at the various refinements of wire transmission, viz: High voltage AC, Extra High Voltage DC, and 3-phase transmission. Transmision of power by light is in some ways more promissing, as lenses and lasers offer much better directivity (ie are better focused into a beam) than do practical radio antennae, but even light transmission is also governed by the path loss equation, and will only be used for specail or niche applications. Keit124.178.37.91 (talk) 10:53, 8 July 2012 (UTC)

Transmission by wire is expressly disallowed by the OP. 84.209.89.214 (talk) 18:34, 8 July 2012 (UTC)

There was a cute project in Popular Electronics (i think) in the 60s, which was a crystal radio with a one transistor amplifier which was powered by the output from another crystal radio tuned to a strong local station. Gzuckier (talk) 05:26, 9 July 2012 (UTC)

That cute principle is covered here, with a reference to Radio-Electronics, 1966. DriveByWire (talk) 14:58, 9 July 2012 (UTC)

Practical transmission by light is used either for communication in optical fibers or in free space for switching tv channels. It is not useful for power transmission. Roger (talk) 14:15, 8 July 2012 (UTC)

Light is not currently used for power transmission (except is a few novel demonstrations, eg powering toy helicopters), but has much greater potential than does radio frequencies, for the reasons given above - this may be more appropriate to what the OP was looking for. Not only is much better beam focussing realisable in practice, but very high power lasers are practical. So in that sense, yes, it IS useful. Keit121.221.215.121 (talk) 14:50, 8 July 2012 (UTC)

Toy helicopters are only controlled, not powered, by light - they have LiPoly batteries on board. The controller works the same way as a tv remote. Roger (talk) 15:10, 8 July 2012 (UTC)

That was my first thought too, but then I remembered that this article in New Scientist covered a small helicopter in which power was beamed to it using a laser. Brammers (talk/c) 16:44, 8 July 2012 (UTC)

Not sure exactly what 'Keit' 121.221.215.121 was referring to there, but Microwaves have been used to power a helicopter, over a short distance and rather in-efficiently "In this experiment, the microwave energy itself was transferred with an efficiency of 51% over a distance of twenty-five feet, and then converted with an efficiency of 50% into DC power of 100 watts which was used to drive an electrical motor. ... A few months after this demonstration in microwave power transfer, personnel of the Raytheon Company conducted experiments with an electrically powered helicopter having rotor blade diameters of four and six feet. These helicopters exhibited an excess lifting capability sufficient to carry a lightweight receiving antenna and a close-spaced thermionic diode rectifier." Ref. "Experimental Airborne Microwave Supported Platform" (PDF). (4.1 Mb) (page 2). Not particularly practical. - 220 of ^Borg 16:53, 8 July 2012 (UTC)

The LaserMotive page may be of interest re. lasers for power transmission.--220 of ^Borg 18:07, 8 July 2012 (UTC)

The sun transfers energy over very long distances and we are able to transform that into electricity using solar cells so yes, wireless long distance transfer of electricity is possible. There are other methods as mentioned above.— Preceding unsigned comment added by ScienceApe (talk • contribs) 15:04, 8 July 2012

Unfortunately, conversion of light to electricity is highly inefficient, with additional inefficiencies added by conversion of the electricity into light at the source and losses during transmission. StuRat (talk) 17:33, 8 July 2012 (UTC)

By the standards of electrical transmission by wires, yes. However, CO2 lasers are available in large powers (~100 kW and more) with a conversion efficiency of up to 20%. Laser diodes are available in powers up to the kW range and somewhat better efficiency. Recoversion at the recived end can be done with photovoltaic cells, which typically have efficiencies of 25%. Laser beams can be highly focused - ending up with a spot only meters in diameter on the moon has been demostrated. Therefore, over significant distance, and end-to-end efficiency of around 10% is possible. That's pretty disgusting compared compared to typical electricity grid routes, but still usuable. Keit60.230.203.147 (talk) 01:44, 9 July 2012 (UTC)

Isn't 20% of 25% already down to 5%, with a further reduction due to absorption or scattering in the air ? Also, unless you happen to have a straight line of sight where you can safely fire hi-powered lasers, you may need to use relay stations, such as a satellite. With just one relay, we are talking less than 5% of less than 5%, or less than 0.25% efficiency, unless you can reflect the laser and reduce the losses in that way. StuRat (talk) 03:59, 9 July 2012 (UTC)

Yes. But my point was that transmission by laser is pretty disgusting efficiency-wise (though heaps better than using radio wavelengths), and you've just reinforced that. I was a bit sloppy in typing - I left out the efficiency possible with laser diodes, reportedly up to 40%. However, I intentionally left out scattering, as the OP is clearly after hypotheticals, and you can reduce the loss due to scattering by optimum choice of wavelength, and reduce it to any desired level by sufficient beamwidth. And in space, scattering should be very low. Keit121.221.86.50 (talk) 11:50, 9 July 2012 (UTC)

OK, using your optimistic 10%, we are down to 1% with a single relay. Unless, as mentioned, the laser can be reflected with more than 10% efficiency. Do you know if this is the case ? StuRat (talk) 17:41, 9 July 2012 (UTC)

Ordinary mirrors are almost 100% efficient, but would require very precise positioning, orders of magnitude better than current earth satellite standards. Doesn't seem at all insurmountable though, except for one critical thing: Precise postioning/aiming of satellites is done by periodic firing of small rocket motors (eg hydrazine jets). Current satellites have a limitted service life due to running out of positiong motor fuel, so if aiming needs to be more accurate, I expect fuel consumption to be prohibitive. Keit124.178.139.176 (talk) 02:07, 10 July 2012 (UTC)

Instead of moving the entire satellite, how about if they just move the mirror, and a counter-weight on the opposite side ? The power to move the mirror and counterweight could be from solar panels (or maybe a small portion of the laser energy). I expect they would eventually need to move the entire satellite, but much less often with this system. StuRat (talk) 04:42, 10 July 2012 (UTC)

Obviously it's more inefficient, but it's wireless. Some things obviously can't have wires. I always imagined that airplanes could be fed electricity via satellites (with solar panels) in orbit to increase their flight time. Such a design could theoretically keep an airplane flying indefinitely. Certainly would have some technological hurdles to overcome though. ScienceApe (talk) 11:51, 10 July 2012 (UTC)

(edit conflict)The OP was specifically asking about electricity transmission, but allowing 'energy' transmission this will pass. ;-) Certainly it is possible to transmit energy (electrical or other) using electro-magnetic radiation over long distances. Somewhat impractical for point-to-point use on a planetary surface though, which is what I think they are getting at. You need a fusion generator the size of a Star to begin with. - 220 of ^Borg 18:07, 8 July 2012 (UTC)

Flow of current by Electric arc is also possible. Air breaks down at about 30 kV/cm so the achievable distance may not be very long, but once established the arc behaves almost as a short circuit through which large power can be transmitted without wire. 84.209.89.214 (talk) 18:34, 8 July 2012 (UTC)

Actually, it's no good. To transmit power from one point to another distance point, you need a return circuit/conductor. So you need two arcs, not just one. Since, for transmission over a distance, the two arcs must have a length vastly greater than their specing, it won't work. An arc seeks out the shortest path, so you'll just get an arc between to two terminals of the transmitter. In any case, an arc is NOT a short circuit - in welding, for example, the voltage drop is of the order of 20V over a few millimeters, and the power lost in the arc is the source of welding heat. Keit60.230.203.147 (talk) 01:51, 9 July 2012 (UTC)

Two arcs are needed, yes (or one with a ground return when the distance is on Earth). The arcs must be spaced by more than double their length, yes (though once struck that requirement is reduced). I said "almost", not quite, a short circuit. Electric arcs have a peculiar negative resistance: the voltage drop goes down as the current increases. I agree electric arcs are much better suited to welding, heating and detonation than wireless transmission of electricity but I think the possibility should be included in your list if it is to be exhaustive. 84.209.89.214 (talk) 02:50, 9 July 2012 (UTC)

Still not quite right. While you can certainly lengthen an arc once it has struck, the two arcs wil be drawn towards each other by magnetic forces (the proximity effect). Or, if an earth return is used (whic I should have thought of), the one arc will be similarly be drawn towards the earth. In any case a requirenet to start with transmitter electrodes further apart than the transmitting distance hardly qualifies as distance transmission - you might as well lay the transmitter "antenna" on its side and be done with it. So, no, it doesn't warant being in the list. Keit60.230.203.147 (talk) 03:18, 9 July 2012 (UTC)

Electric arcs are extremely hot, so the ionized current path rises into an "arch," the word Humphrey Davy used to describe it circa 1811, which he later shortened to "arc." I have seen a lot of electric arcs, and I have never seen one "drawn towards the earth." I agree that if the phase and neutral, or the three phases, were close to each other, they would arc across rather than arcing to the remote "load" unless there were nonconductive barriers between phases, such as the ceramic parts used in utility air-break circuit breakers. Magnetic coils can also be used to steer an arc, as is done in circuit breakers, and as was done in high power arc radio transmitters such as the Poulsen system. A vapor other than air can be used instead of air, as was done in arc transmitter voice radio in the early 20th century. Edison (talk) 19:54, 11 July 2012 (UTC)

If you are going to provide magnetic steering coils along the route, you might as well just make them straight end-to-end wires carrying the electricity. If you are going to have a special gas (and no gas will give anything like a useful advantage over air in this application, you are going to need tubes to contain it in. Might as well use the tubes as conductors. Keit124.182.147.203 (talk) 01:43, 12 July 2012 (UTC)

In this picture current is flowing across the wireless gap between the rail and the pickup shoe and supplying uninterrupted power to the inductive load of the motor. "Distance" is a relative, not absolute, concept. DriveByWire (talk) 15:28, 9 July 2012 (UTC)

Well, yes, but clearly not within the context of the OP's request for "long distance" transmission. Keit124.178.139.176 (talk) 02:00, 10 July 2012 (UTC)

High voltage transformers and overhead lines commonly use electrically- or hand-operated three phase disconnects. They are high above the ground and have a large spacing between phases. Many are non-loadbreak devices, intended to interrupt only capacitive charging current. Typically when they are opening, a piece of metal on the moving part contacts a metal hook and the (small) current then flows from this "whip" to the stationary hook, until it snaps loose, breaking the current. I once saw one accidentally interrupt an unknown number of amps of load current, while in a parallel connection with another networked line. When the whip snapped free, current continued to flow across the gap on all three phases, without a phase to ground or phase to phase fault occurring. The three arcs were bright (blue green as I recall) and loud, and eventually the current stopped flowing when the gap got large enough as the operator cranked the disconnect open. For a few seconds, megawatts of 3 phase 138kv power were flowing "wirelessly" through the arcs. Certainly it would not be a recommended way of supplying current, since it was likely to arc to ground or across phases, and since the high temperature arc was burning away copper from the conductive parts of the switch. An electric arc furnace melts down scrap metal via a 3 phase arc, using perhaps 4kv. Similarly arc welding carries much lower voltage high current electricity to the metal parts being welded. Folks opposed to overhead high voltage transmission lines used to demonstrate that the field below the 345 or 765 kv AC lines is strong enough at ground level to light a fluorescent tube. Near high voltage DC transmission lines, a metal roof has to be grounded to avoid giving someone a nasty shock when they touch it. In an AC transmission switchyard, a few feet of wire quite a distance from the bus can pick up enough stray voltage to make a visible arc. Near a conductor carrying a hundred amps or more, a permanent magnet might vibrate in your pocket like a buzzer from the stray magnetic field. I have heard a crystal radio a mile or more from a radio station drive a loudspeaker to a nice listening volume with no battery powered circuitry. Edison (talk) 19:34, 11 July 2012 (UTC)

Keith Henson is interested in laser transmission of power. That can be more efficient than other wireless and pipelineless methods, but it's still a huge loss and practical applications don't exist yet because of the huge losses, unless you count laser cutting and heating directly. 70.91.171.54 (talk) 22:14, 8 July 2012 (UTC)

Since he just signs his name "Keit", how do you know his full name ? StuRat (talk) 04:08, 9 July 2012 (UTC)

It ain't me - I'm not the slightest bit interested in laser trasmission of power, and my real name is nothing like Keith anything. But as an Engineer, I understand the implications of the well known (to Engineers) path loss equation. I assumed that Keith Henson is some joker known in the poster's locality. Keit120.145.142.105 (talk) 09:26, 9 July 2012 (UTC)

Keith Henson, wikilinked above too. 71.212.249.178 (talk) 01:51, 10 July 2012 (UTC)

OK, just coincidentally similar names. StuRat (talk) 04:37, 10 July 2012 (UTC)

With only 4 letters to go on, how do you know they are similar? Keit120.145.23.26 (talk) 14:49, 10 July 2012 (UTC)

Within the context of one question, having two different names mentioned that happen to start with the same 4 letters seems unlikely. This reminds me of my bank, which, to protect my security, only gives out the last 4 digits of my account numbers when they give me a balance statement. The bad news is, I'm the unlucky 1/10,000th person who happens to have two accounts that end in the same 4 digits. StuRat (talk) 20:28, 10 July 2012 (UTC)

You must be not the unlucky 1/10,000, but something like the unlucky 1/100,000,000th person, as at least one of the last 4 digits is usually a hash digit, hashed from all other digits (same idea as your income tax ID), including the other 3 included, but not the BSB digits. http://en.wikipedia.org/wiki/Hash_function This lets bank clerks detect immediately a typing error, without consulting records. Without hash digits, a percentage of payments would be continually going to the wrong accounts every time somebody made a single typo. Wickwack120.145.199.129 (talk) 07:06, 11 July 2012 (UTC)

Another means of wireless electric transmission exists which is by ground current. It is very inefficient and Keit may not welcome it in the list. Nevertheless, if one drives two rods a distance apart into the ground and applies a voltage between them, not all the resulting earth current flows in a straight line between them. A receiving pair of rods can collect a fraction of the transmitted voltage at a considerable distance, if they are aligned optimally. I once had fun "energising" a large field with music from an ordinary amplifier with the loudspeaker output terminals connected to earth rods a couple of meters apart. The music could be heard anywhere in the field on sensitive headphones connected to a pair of nails pushed appropriately into the ground. DriveByWire (talk) 15:31, 9 July 2012 (UTC)

Many who became interested in electronics, including me, have also had fun doing this. It has been used communication in underground mines. It is actually a form of conductive transmission, which I already included in my list of 4 forms. Ground cuurent transmision is weofully inefficient and good for information transfer, not power transmission. Keit124.178.139.176 (talk) 02:00, 10 July 2012 (UTC)

Perhaps you are already familiar with the early wireless telephone experiments of Nathan Stubblefield, who used inductive transmission as well as conduction through the ground and through water 1892-1908. Edison (talk) 20:11, 11 July 2012 (UTC)

Yet another way is via a truckload of charged capacitors. Some electric vehicles may already have these on board. See supercapacitor. Graeme Bartlett (talk) 22:05, 9 July 2012 (UTC)

Or you could set up a conveyor belt of rechargeable batteries! Good imaginative call, but a pipe carrying gas (see 2nd post) would be a lot simpler, cheaper, and durable. You can also transmitt power via belts or chains. In case someone thinks chain drives are only short distance, I point out that before electricity, some large cities powered their trams by the cable and grip system (http://en.wikipedia.org/wiki/Cable_car_(railway)) - the steam power house pulled cables installed down a slot in the road - each tram clamped a "grip" onto a cable, and released it to stop. Still in use in San Fanscisco when I visited. But is this within scope for the OP?? It has nothing to do with electricity. Keit124.178.139.176 (talk) 02:00, 10 July 2012 (UTC)

• Tesla's proposals to transmit power wirelessly seem to have been dismissed above rather quickly. His work seems to have quite a following in some circles, and more discussion might be appropriate. Edison (talk) 02:26, 10 July 2012 (UTC)

Quite a following in recent fashionable circles not involving qualified engineers! There's plenty here for the OP to chew on, and I see little value in going into why Tesla, who made important contributions to the electrical art, nevertheless promoted something that was completely daft, known to be daft at the time, and known to be daft ever since - such discussion would inherently go off-topic or off on a tangent. However, if you are curious, there is no reason why you can't post a question of your own, such as "Why did Tesla's ideas for wireless power transmission come to nothing?", or "Why did Tesla's financial backing for Wardencliffe fail?" or some such. You might trigger some discussion, but be sure to read the Wikipedia articles on Telsla & Wardencliffe first. Note that Tesla's demonstrations of power transmission without wires involved methods 2 & 3 listed in my first post above and were therefore only very short distance. Keit120.145.175.84 (talk) 04:02, 10 July 2012 (UTC)

Its funny you keep saying Tesla, concepts were daft, considering there was also a "Daft Electric Light Company" in 1892, headed by Mr Leo Daft It's funny reading old court transcripts about the "Daft electric railway. " There are some engineers and physicists today, not just unqalified engineers as you assert, who see some merit in some of Tesla's notions about wireless power transmission. The use of lasers to remotely propel space probes has also had a lot of coverage from seemingly well qualified space travel designers. See [2]. See Beam-powered propulsion. Who cares if the efficiency is 1% or .01%, when the thing is out in space and there is obviously no way to run a cable from the generating station to it? Carrying the fuel off the ground at liftoff of a conventional rocket into space is also very inefficient. Edison (talk) 19:46, 11 July 2012 (UTC)

I entirely agree with your comments ("Who cares....) about laser transmission - that's why I mentioned it in my first post. However, Tesla's ideas are another matter. Can you cite or name a suitably qualified professional Engineer that sees merit in it? Physicists are another matter. The role of a physicist is that of a scientist - explain part of how something might work. He need only focus on one thing. The role of an engineer is much more rigorous - make something work. That means an Engineer must consider everything related. Scientists are optimists; Engineers are skeptics. Keit124.182.27.45 (talk) 03:20, 12 July 2012 (UTC)

However, Tesla's ideas failed largely because electricity generation is expensive, so you can't just give it away for free (as metering would be impossible under such a system) and allow huge portions of it to be wasted. If, at some point in the future, we find a way to produce electricity dirt cheap, in a centralized location (let's say by nuclear fusion), then that equation might change. StuRat (talk) 04:49, 10 July 2012 (UTC)

Yes, we are going off topic, as I expected, but while Stu's revenue reason is often quoted, its not the full story. When profesional radio broadcasting started in Australia (1920's), idiot politicians passed laws to create the "sealed set scheme". Under this system, when you purchased your radio set, it was tuned to the chosen station and sealed. You paid a fee to that radio station, which was government owned. Naturally such a dumb scheme imediately failed - you can't stop people from tuning to whoever they want. However, it was replaced by a scheme where every radio owner was compelled to pay a licence fee just for owning a radio, whether they tuned into the govt station or not, or even whether or not they turned the thing on. That was a simple practical scheme that worked, and stayed in place until the 1960's, when the widespread sale of small transistor radios made it impossible to police - license fees were then abandoned. The moral is that just because something is technically difficult to administer, it doesn't mean it cannot be solved by laws and treaties, though the dumbness of politicians does not make it straightforward. The real problem with Tesla's power transmission scheme is that almost all the transmitted power would have simply dissappeared into "thin air". That's no doubt why, when Tesla's backers backed away, he couldn't find replacement financiers. No doubt if he had been able to show it worked, his next step would be to sell it to govts, either directly or thru a licencing system. Of course, radio being what it is, an even better scheme is possible and became universal - commercial sponsorship. Keit121.221.86.127 (talk) 06:20, 10 July 2012 (UTC)

In Germany, they still do the licensing thing with radio and television. 203.27.72.5 (talk) 07:18, 10 July 2012 (UTC)

Last time I heard, they still do in Britain as well - but the British always were a strange lot, with almost all doing what they are told, just because they were told, and a steady number with radios and TV's not declared. So their Govt had a fleet of "detector vans" that drove round detecting the magnetic field from the TV Cathode Ray Tube scanning coils. Must have been a bit of a blow now that CRT's have been replaced by the various flat-screen technologies (eg LED) that don't have scanning coils. At one time they were detecting back-radiation from the tuners in both radios and TV's, but that became no good with the change from tubes to transistors (in the 1970's for TV's). Keit121.221.79.37 (talk) 10:10, 10 July 2012 (UTC)

But, when they detected a radio or TV in use in a home, then what ? Did the license restrict use to a particular house ? If not, they would have no way of knowing if the device being used in the house was a registered one or not. Or did merely using one constitute adequate cause for them to pound on the door and demand to see a license for the device ? StuRat (talk) 20:35, 10 July 2012 (UTC)

In Australia, it was the responsibility of the house owner or lessor to have a licence to cover for any reciever on the premises (regardless of who owned it), and any reciever installed in a vehicle kept that that address. Hotels were required to have a licence if any guest had a radio or TV with them. According to an article in the journal Wireless World some years ago, the detector crews drove slowly down the street. As they went past each house, and picked up the magnetic scanning field or tuner back radiation (TV users who don't pay the fee tended to use rabbit ears & not an external antenna), they checked against a list of address who did have licences, When they found an unlicenced address emitting a scanning field, they checked the building plan, which they obtained from local government. By elementary direction finding, field strength measurement, and frequency measurement of tuner back radiation if detected, they then could knock on the door, and say something like "You have an unlicenced TV set in the 2nd bedroom switched on and tuned to Channel 4". That, and the sight of the detector van with its direction finding antennae pointing at the 2nd bedroom, was usually sufficient to scare the resident into admitting guilt. If they didn't admit guilt and told the detection officers to nick off, a search warrant, which must be granted by a justice of the peace, as for any police search of a private home, was required. Keit124.178.136.133 (talk) 01:53, 11 July 2012 (UTC)

Wouldn't that give them time to remove the TV or radio from the premises ? StuRat (talk) 18:22, 11 July 2012 (UTC)

Yes. Keit124.182.147.203 (talk) 01:14, 12 July 2012 (UTC)

In Germany the license pertains to the household. Over there they were enforcing it by just coming and checking your house if you don't have a license to make sure you're not watching TV (or listening to the radio) without a permit. In future they're just going to force people to pay for the license irrespective of whether or not they have a radio or TV which also alleviates your concern about the "TV registration office" being a target for invading armies. 203.27.72.5 (talk) 21:31, 10 July 2012 (UTC)

So not having a TV or radio license was sufficient cause for them to search your house ? Apparently the denazification program didn't work. I have no objection to charging everyone a tax, regardless of use, as that's basically what the US does, with taxpayer subsidies to PBS, NPR, etc., although it's not broken down as such on our tax forms. And, realistically, just about everyone uses a radio and/or TV. StuRat (talk) 22:19, 10 July 2012 (UTC)

StuRat, this is Germany we're talking about. They denazified by making thoughts and opinions criminal. Without irony. 203.27.72.5 (talk) 00:02, 11 July 2012 (UTC)

As per usual, wikipedia has an article on this topic. 203.27.72.5 (talk) 20:21, 10 July 2012 (UTC)

However, the article has some serious errors. For instance it includes under Detection a lot of nonsense about the British authorities refusing to disclose the detection technology and claims it has not been demostrated that detection is possible! The technology has been fully disclosed in both prefessional journals and in commercial elecronics magazines, such as Wireless World / Electronics World. Keit124.178.136.133 (talk) 01:53, 11 July 2012 (UTC)

Well, go on Keit. Be bold. 203.27.72.5 (talk) 03:52, 11 July 2012 (UTC)

You would think that Europeans would have learned their lesson, that invading armies can go to the records office, and then confiscate all the radios. This is also true of guns, but, of course, there are more serious consequences to having millions of unregistered guns than either TVs and radios. StuRat (talk) 20:44, 10 July 2012 (UTC)

Don't worry about it. When the Japanese invaded South East Asia during World War 2, they didn't waste time with record offices. They just broadcast a demand that all citizens hand over their radios on pain of severe punishment. Keit124.178.136.133 (talk) 02:00, 11 July 2012 (UTC)

Sure they can, but presumably members of the resistance would keep their radios anyway, unless the Japanese knew just where to look for them. StuRat (talk) 18:16, 11 July 2012 (UTC)

Absolutely! Not only that, resistance fighters and prisoners of war built their own radios, using parts stolen from the Japs. Keit124.182.147.203 (talk) 01:29, 12 July 2012 (UTC)

In South East Asia in the 1940, there wouldn't have been too many locals with electricity, let alone radios. And the European colonialists didn't have to do anything rebellious like hold on to radios to cop a bit of punishment off the Japs. It would have been pretty obvious where to look for people that have underground radios. Hint: they're the same places that you target for pilaging most everything else of value. 203.27.72.5 (talk) 21:11, 11 July 2012 (UTC)

Electricity has little to do with it. In 1940, most rural areas of Australia didn't have mains electricity either, except in town centres. The chicken farming area I grew up in, only 30km from a capital city, did not get electricity until about 1970. But we allways all had radios since broadcasting stated (1920's) - battery powered radios in the house, and car radios in our cars. In fact battery powered radios pre-date mains electricity radios. Keit124.182.147.203 (talk) 01:29, 12 July 2012 (UTC)

Wow, I didn't know compact batteries had been around for so long. But still, surely they would have been quite expensive for south east asian rice farmers. And how many other uses were there for batteries back then? Looking at the houses that have recently purchased batteries would narrow the list a fair bit. 203.27.72.5 (talk) 21:06, 12 July 2012 (UTC)

Seriously, StuRat. Are you purposly steering the conversation on ever increasingly tangential lines just to prove Keit's prediction correct? 203.27.72.5 (talk) 21:26, 10 July 2012 (UTC)

How to change the way the jet stream flows

The jet stream is flowing South of Britain causing bad weather, disrupting Wimbledon and it will likely cause problems for the London Olympics. So, how would one go about pushing the jet stream North? Count Iblis (talk) 15:32, 8 July 2012 (UTC)

At this point in the history of science and technology, and for the next couple of hundred years at least, the only method that has the faintest chance of success is prayer. Dominus Vobisdu (talk) 15:49, 8 July 2012 (UTC)

The only plausible way is by reducing global warming. And that isn't a joke answer: the details are very complex, but in a general way global warming should increase the meander in the jet stream, causing it to make more frequent southward excursions. Looie496 (talk) 15:52, 8 July 2012 (UTC)

This is highly speculative, and I'd like to see if there's any evidence of it. One of the consequences of increasing greenhouse gasses is that the equator-to-pole temperature gradient will decrease (this part is not up for debate, it's simple physics), leading to a weaker jet stream on average, and (here's the speculation on my part) a less meridionally amplified (fewer north-south meanders) Rossby wave pattern. So if my educated guessing is correct, global warming would lead to sunnier summertime weather for the British Isles. This is of course ignoring a huge amount of uncertainty in ENSO and other large-scale patterns. -RunningOnBrains^(talk) 18:48, 8 July 2012 (UTC)

Why would the temperature gradient decrease ? More of a greenhouse effect should make it much hotter where more sunlight hits, near the equator, but not much hotter where no sunlight hits at all, as at the poles on winter. To me, this means a greater temperature gradient from equator to pole, at least in winter. StuRat (talk) 04:27, 9 July 2012 (UTC)

From the article on Venus (which has a runaway greenhouse effect); "The surface of Venus is effectively isothermal; it retains a constant temperature not only between day and night but between the equator and the poles." Compare that to other celestial bodies that have a smaller or absent greenhouse effect e.g. Mercury which has 140K of mean temperature variation from 0°N, 0°W to 85°N, 0°W and it's obvious what effect the greenhouse effect has on pole to equator temperature variation. Those quotes have refs in the articles too. 203.27.72.5 (talk) 21:57, 9 July 2012 (UTC)

I don't think you can assume that just because the overall trend from no atmosphere to thick atmosphere is more even temperatures that this automatically means this trend doesn't reverse itself at any step along the way. Considering the complexity of the interactions involved, I'd be surprised if it was that simple. For comparison, if you noted that the chance a person who is 100 will die that year is higher than the chance that a person who is 0 will die that year, and just assumed that the chance a person will die at each year in-between must therefore steadily increase, then you would be wrong. StuRat (talk) 22:10, 9 July 2012 (UTC)

I didn't make that assumption. You did in your comment above (though with the opposite understanding of the effect). 203.27.72.5 (talk) 22:21, 9 July 2012 (UTC)

I don't know what you're trying to say. BTW, are you RunningOnBrains ? StuRat (talk) 22:33, 9 July 2012 (UTC)

No, I'm not RunningOnBrains. This is what was trying to point out:

RunningOnBrains: From an analysis using simple physics, a stronger greenhouse effect leads to less pole to equator temperature variation.

StuRat: Here is a simple physical mechanism which predicts the opposite.

203.27.72.5: Since we're doing a first order, simplistic analysis, here is a simple model that is consistent with RunningOnBrains' prediction.

StuRat: Your simplistic model is invalid because it's too simple. This is a complex process and needs complex analysis. *says nothing about validity of own simplistic mechanism*
203.27.72.5 (talk) 23:16, 9 July 2012 (UTC)

But my model is less simplistic, as it at least deals with climate examples here on Earth, eliminating variables like tidal locking and variable distance from the Sun, that don't apply to Earth. StuRat (talk) 23:25, 9 July 2012 (UTC)

Here's NASA's take on the matter. 203.27.72.5 (talk) 23:56, 9 July 2012 (UTC)

And to eliminate the variables like tidal locking and variable distance from the Sun, we could use an Earth based model by comparing the Cretaceous with the present. The Cretaceous had "a very gentle temperature gradient from the equator to the poles", 6 times preindustrial CO₂ levels and an average surface temperature 4°C higher. 203.27.72.5 (talk) 00:01, 10 July 2012 (UTC)

OK, that NASA link certainly seems more relevant than the climates of other planets, but I notice they use "could" versus "will" whenever they say anything about the equator-to-pole temperature variance being more gradual, so it sounds like they aren't exactly sure. Then there's those graphs showing the effects of greater temperature variance, which seem at odds with the text. (I realize that the graphs may be temperature variance at one location, versus from the pole to the equator, but, at least now, temperature variation at any point is caused by polar air masses versus equatorial air masses moving into an area, so it is related.) StuRat (talk) 04:29, 10 July 2012 (UTC)

Yeah, I don't get that graph either. It seems to disagree with the notion that the atmosphere would be closer to isothermal overall. 203.27.72.5 (talk) 04:57, 10 July 2012 (UTC)

Whoa, totally missed this branch of the thread, sorry I never responded. That NASA graph has nothing to do with north-south temperature gradients, it's describing the local variation in temperatures, and it's an if graph; each panel shows the effects of one possible scenario. The body of the article does say, however, "Global warming could affect storm formation by decreasing the temperature difference between the poles and the equator".

Here's the simple physics I alluded to (I use the term "simple" liberally): if you trap outgoing longwave radiation (which is what greenhouse gasses do), you are essentially decreasing the rate of cooling of the planet. However, this cooling is actually most efficient in the warmest areas; i.e. the tropics, and less efficient at the poles. This is because the intensity of outgoing radiation is proportional to the temperature to the 4th power (the Stefan–Boltzmann law), so the rate of cooling will increase less at the poles. Note that when I say "rate of cooling" I mean the power of the outgoing black-body radiation, not an actual decrease in temperature. I hope I've explained this clearly, one of my (much smarter) friends was explaining this to me last week and probably put it much better than I can.

As an additional contributing factor, decreasing sea ice from increasing temperatures will decrease albedo in polar regions, which will increase solar heating there, but this is really a less important secondary effect if my educated speculation is correct. I should also point out that so far the greatest warming has been in arctic regions, so recent history supports this notion.-RunningOnBrains^(talk) 05:52, 10 July 2012 (UTC)

Regarding the graphs, even if they are only one possible scenario, their inclusion, and the exclusion of any showing a decrease in temperature variation, seems to show that whoever included the charts think that this is the more likely scenario. The author of the text, on the other hand, went the other way, but seemed rather noncommital about it.

And what about my argument, that greenhouse gases will trap more solar radiation at the equator, where there's more to be trapped, than at the poles, where, at least in winter, there no solar radiation to trap at all ? Perhaps, combining your theory and mine, we will get less temperature variation in summer, but more in winter. StuRat (talk) 06:08, 10 July 2012 (UTC)

This might be the deepest indent I've ever gotten to :)

About the graphs, I think you're confusing variance with gradient. Those graphs say nothing about the pole-to-equator gradient.

And about the GHG-trapping, you're thinking about it too simplistically. You're using the (usually effective) analogy of greenhouse gasses somehow "trapping" solar radiation, which really isn't true; the explanation I gave above is the actual physics behind it. However, now that I've sat down and done some of the math, I am beginning to doubt myself; it's way to late, I'll try to get a better explanation to you tomorrow. -RunningOnBrains^(talk) 07:33, 10 July 2012 (UTC)

You must have missed my earlier comment, so I'll repeat it here: "(I realize that the graphs may be temperature variance at one location, versus from the pole to the equator, but, at least now, temperature variation at any point is caused by polar air masses versus equatorial air masses moving into an area, so it is related.)". StuRat (talk) 20:39, 10 July 2012 (UTC)

The greenhouse effect should dampen out both spacial and temporal temperature variation. You can see this even if you are thinking of solar radiation as being trapped in. It's because the rate of energy being dissipated from the Earth's surface by thermal radiation is effectively slowed, so there is more time for convection and conduction to play a role in determining the surface temperature. Direct solar illumination plays less of a role and mixing of warm and cold gases comes to dominate. If you do take the more accurate approach of realising that GHGs absorb and reemit IR, then you will also see the effect of that radiation going in all directions, and thereby spreading heat to other latitudes and longitudes rather than directly into space or at the surface of the Earth. 203.27.72.5 (talk) 07:49, 10 July 2012 (UTC)

And the best way to prevent weather from interfering with British sport events is to move those events to someplace else with better weather. Wimbledon, in particular, frequently had poor weather, long before global warming became a concern. StuRat (talk) 17:28, 8 July 2012 (UTC)

There is no way to change weather patterns reliably. Rossby waves (the waves in the jet stream flow) are dynamically chaotic, meaning that a small perturbation now will result in large changes in future behavior. That's why weather prediction is essentially useless after 7 days; you driving to work tomorrow could cause a perturbation that would result in a difference of 1000 km of the position of the jet stream two weeks from now. -RunningOnBrains^(talk) 18:39, 8 July 2012 (UTC)

I say we kill all the butterflies, as they are the cause of all this chaos. :-) StuRat (talk) 20:17, 8 July 2012 (UTC)

Tricky. Nice Land Rover ice cream van, though. . . dave souza, talk 20:30, 8 July 2012 (UTC)

Question: If small changes affect the pattern, doesn't that mean that with enough computing power, a humanly achievable input could affect which way it goes? I'm thinking that setting a forest on fire should be about the most we can do; for finer control but much less effect I'd think that a wind farm could be switched to generate power or spin freely on perhaps a second-to-second scale? Wnt (talk) 20:54, 8 July 2012 (UTC)

Setting off thousands of nukes would be the most we could do, but this may not be advisable. :-) Also, theoretically the causes of chaos ultimately reduce down to quantum effects, which are, by definition, random and uncontrollable. StuRat (talk) 21:23, 8 July 2012 (UTC)

To Wnt, no, and you have fallen prey to the same false assumptions that researchers had in the 1950s and 60s. Back then, weather control was a hot ticket, and was beginning to seem feasible with improvements in computer modeling. Famously, Edward Lorenz, a meteorologist and the founder of the field of chaos, discovered that atmospheric flow contained unstable points, where a small perturbations could lead to huge differences in a short period of time. However, when he attempted to show his results to other scientists, and they told him "Oh, you're talking about weather control". But they failed to see (as you do now) that every point in the flow has this instability; any perturbation that you make is insignificant compared to the (literally) trillions of small perturbations that are below the resolution of computer models, and can only be quantified (in a very rough way) by ensemble forecasting. When we say "a butterfly flapping its wings can lead to a hurricane a month later", this is equally true of every butterfly, every person, indeed, everything that can not be represented in the computer model.-RunningOnBrains^(talk) 00:17, 9 July 2012 (UTC)

But if you know absolutely everything about the system's original state, you can predict exactly what will happen. Which includes predicting exactly what will happen after you make just such perturbation. Which means you can figure out exactly how you should perturb the system to, say, move the jet stream north over Scandinavia. For every set of exact initial conditions and one exact time frame, there is only one possible outcome. A mathematical equation always has exactly the same solution; for example, 1 plus 2 always equals 3, and the positive square root of 144 is always 12. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:11, 9 July 2012 (UTC)

You're still thinking in terms of classical Newtonian mechanics, where every action has an identifiable cause. In quantum mechanics, this is no longer true, things are truly random. A common example is radioactive decay. While, on the average, it's rather predictable, when we get down to an individual atom we can't predict when it will decay. And things as small as individual atoms eventually affect weather patterns. So, you ultimately can't predict or control the weather with exact precision, but can only do the same type of bulk averaging that gives us the half-lives for atomic decay. StuRat (talk) 03:55, 9 July 2012 (UTC)

It's not even necessary to introduce quantum mechanics; this is a classical mechanics problem with no known solution (see Navier–Stokes existence and smoothness; it's actually one of the last unsolved problems in Newtonian mechanics) -RunningOnBrains^(talk) 15:57, 9 July 2012 (UTC)

Also, by the time you finish running a computer model, the initial conditions have already changed in unpredictable ways. Do you propose that it will ever be feasible to include every molecule of the planet in a computer model; and even if we could (which we won't), how would we manage to get information about the location and momentum of everything? Even if you somehow had perfect weather stations with no observation error (impossible) for every cubic meter of the atmosphere (also impossible) taking measurements every second, you could not predict the weather even one month in the future (from the book "Chaos: Making a New Science", which I highly recommend as one of the best lay-person science books I've ever read). Plus, the equations of motion are nonlinear equations, meaning that they can not be solved exactly by computers, as they require iterative solutions which introduce floating-point errors.

Impossible is not a word I use often (I majored in physics, after all), but perfect weather prediction is impossible. -RunningOnBrains^(talk) 15:55, 9 July 2012 (UTC)

I think some heuristic tricks might be important. For example, just looking at jet stream time lapse, it seems like it comes in very steadily toward the Pacific coast of the U.S., then oscillates wildly as it hits the mountains. So I'd think you could have more impact if you target that spot. I'd think that, over time, you could come up with a sort of "finite state machine" like model for which way the jet stream is going to go if it's going this way at a certain time, and evaluate what circumstances tend to make it shift. And the key instances when you actually want to change the weather aren't when this is too unpredictable, but when it's too predictable - when it always goes the same way and no rain falls in Texas for half a year. I'm not going to say it's possible, but ... I don't know of any theory that says you can't lever a semi rig out of mud pit with a toothpick if you're really, really, really clever about it. ;) Wnt (talk) 16:16, 9 July 2012 (UTC)

Unnoticed effects would eventually cause problems, but as long as we're willing to keep modifying things, we can keep it on the right track. We just have to make sure that the effects we control are at least as large as the ones we don't know about or lack the computing power to predict. I'm not sure how much this is, but I'd bet it's at least in the nuke range. It could very well take more than all we have. Given that "eventually" is a week from now, we'd have to use them that often. — DanielLC 20:21, 9 July 2012 (UTC)

It's true that we could control the weather by your suggested means instead of trying the "small nudge" method which is doomed to fail due to chaos, but then we must compete with the energy scales of atmospheric motions, which are as of now (and the foreseeable future) completely impractical. For instance, a rough approximation of the energy involved in a single hurricane is approximately 200 times the entire world power output. We'd be better off using that energy to moving Wimbledon indoors :) -RunningOnBrains^(talk) 21:05, 9 July 2012 (UTC)

Man...if we had that much energy, we could move Wimbledon so indoors...203.27.72.5 (talk) 22:06, 9 July 2012 (UTC)

Major local forest fires are hard to arrange on a regular basis. The Himalayas and the Rockies play a huge role in the path of the northern jet streams. I suggest building a mountain range or blasting a path through an existing one. Of course valium is probably a much cheaper and effective way to deal with climate change anxiety. μηδείς (talk) 21:05, 8 July 2012 (UTC)

Ah, yes, I've seen this one proposed before. Now where'd I leave the family atomics? :) Hmmm... seriously, though, the part about building a mountain range is interesting. If you lay a series of cables with streamers across a wide mountain pass, can you disrupt laminar flow of the air to create a turbulence that would dissipate a significant portion of the wind's force against the cables or the walls? If you control several such passes in such a way, can you thus change the overall vector of the surface air flow emerging from the far side of the range? Wnt (talk) 21:32, 9 July 2012 (UTC)

Funny I didn't even think of dune, which I have read 5 times. μηδείς (talk) 05:08, 10 July 2012 (UTC)

Ha, I' see I've kicked off a big discussion here :) . What about this variant of Wnt's and μηδείς' suggestion. A huge balloon connected to the ground by cables could be put into the jet stream... Count Iblis (talk) 02:03, 10 July 2012 (UTC)

That's an awful lot of mass to create a very little resistance, given you'd run into a power law relation between the cross section of the balloon and its mass. It would also want to flutter, and would probably end up failing catastrophically. Also, of what use would it be except when the wind were trying to blow through its path? μηδείς (talk) 05:08, 10 July 2012 (UTC)

(edit conflict)

Well, the jet stream doesn't pass near the ground; it's typically from 300-200 hPa, which is around 7-10km altitude. It doesn't pass through mountain passes; it barely grazes the tops of some peaks (and that's just in the Himalayas) Also it is (order of magnitude) 100 km across and 1 km deep (it's actually around 3-5 km deep usually, and its width varies quite a bit). You'd need a helluva lot of balloons to make a significant impact, and the string would have to be incredibly long and incredibly strong, a combination which is not yet technically possible (I'm thinking the realm of carbon nanotubes).

And even with all this you could not predict the impact precisely. I'm going to sound like a broken record or a politician, but Rossby waves are chaotic! I feel like most of you aren't understanding the full weight of this statement. It is no exaggeration to say that the difference in one degree of temperature in one small area can have drastic impacts even in short- to medium-range forecasts. Just look at the image accompanying our article on ensemble forecasting. All those models were given the exact same data; the only differences are in model resolution and the parameterization of small-scale processes. And even at 3 days out, there is a spread of several hundred kilometers in the predicted position of Hurricane Rita. And this was one of the better predictions; just take a look at these model predictions for the recent Tropical Storm Debby (2012). Hilariously uncertain.

I realize that hurricanes are a different phenomenon from what we're discussing, but just look at the current GFS ensemble precipitation forecast for 5 days from now. Each of those panels is the same model, the same data, just with small perturbations introduced to the initial conditions (every ensemble member is a realistic representation of the atmosphere, i.e. consistent with the millions of bits of observational data fed into the model) . I apologize that the image isn't very big, but you can clearly pick out storms that are in different positions, different intensity, or just plain aren't in some of the ensemble member forecasts.

Chaos is impossible to control, we can only hope to understand it enough to suit our own needs. Close-to-perfect 1-day forecasts are certainly feasible, and good forecasts out to 14 days could be in our future (but only in certain flow regimes; some are more unstable than others!), but anything beyond that is asking too much.-RunningOnBrains^(talk) 05:31, 10 July 2012 (UTC)

How (in terms of physical motions and mechanics) does a slug foot walk?

In terms of physical motions and mechanics, how do slugs move about? I note 'succeeding waves of muscular contraction which move down the undersurface of the foot' (http://wiki.answers.com/Q/How_do_snails_move_around) - but how does this work, physically? How do 'succeeding waves of contraction' make the slug move forward? My four-year-old wants to know. (I would love to show him a video of a slug moving its foot upon glass, if this could help us to understand, but I see no such thing.)82.31.133.165 (talk) 19:47, 8 July 2012 (UTC)

Do you know how an inchworm moves ? It's like that, only the "arch" distance above the surface is tiny (and filled with slime), so it's not easy to see. Also, an inchworm actually picks up one end at a time, while a snail or slug just slides it along the surface on slime. Your 4-year old can probably do it too, by putting him in a sleeping bag and having him sit on his butt and feet, and scoot along by pulling his feet close to him, then pushing them away. As he will note, this method of movement is rather slow. But slow can be good for a snail or slug, if it makes them too slow to trigger the motion sensitive vision in predators. StuRat (talk) 20:05, 8 July 2012 (UTC)

This video [3] clearly shows the waves of muscle contraction. I found it by searching "slug locomotion" on youtube. Related is peristalsis, which is basically the same thing, but in a tube. Our article has some nice diagrams that might help explain. SemanticMantis (talk) 20:31, 8 July 2012 (UTC)

LOL, I love the note bellow the video: "Attention: disgust risk!" Notice that the author of the video also includes a description that might be perfect for the OP to use to describe the mechanism to his son: "Their muscles move under their bulky body relatively steadily forward - similar to the chain drive of a big tank!" Snow (talk) 22:08, 8 July 2012 (UTC)

If your son enjoys slug motion he will love that of snakes, which have several different types. Unfortunately our article is rather limited on the topic, but it lists the main types for your further research. See Snake#Locomotion and http://www.youtube.com/watch?v=5CchyctRFrQ. μηδείς (talk) 20:59, 8 July 2012 (UTC)

When was this ice age?

Someone in commons has an issue with a category. I don't speak pre-history though. If someone would like to pop over and help it should be apreciated. I hope science is the correct section here. If not we can close here and open in another desk. http://commons.wikimedia.org/wiki/Category_talk:Ice_age_410k-380k_BP --Canoe1967 (talk) 20:22, 8 July 2012 (UTC)

An interglacial is a warmer period like the present when ice age glaciers have retreated. I have no personal knowledge of whether the period of 410kya to 380kya was an interglacial or not, but the image at the article I linked to seems to imply it was. μηδείς (talk) 20:45, 8 July 2012 (UTC)

July 9

EQUATION HELP;;;

pro e can plot curvs with equations we give. I am in urgent need of the following equation.Any mathematician kindly help me..:

i need equation for a twisted pair wire(2 wires only wound in form of a helix along a circle.Such as a two

TWISTED CABLE PICTURE

The figure below shows a twisted cable .i need equation for such a twisted curve made along a helix. as such a twisted wire in form of a telephone cable.RIGHT!!

TELEPHONE CABLE

Sameerdubey.sbp (talk) —Preceding undated comment added 03:26, 9 July 2012 (UTC)

Your 2nd link doesn't work for me. If you simply want a 2D model, use a positive and negative sine wave for the two wires. For example:

Y = sin(X)/10

Y = -sin(X)/10

I divided by 10 to flatten them out a bit, you can change this if you want them flattened more or less. Let us know if you need to plot a 3D helix, and/or add thickness to the wires, or if you need to simulate 3D by having the wire in front alternate each time they cross. (However, beware that each of these changes make the implementation more complex.) StuRat (talk) 03:37, 9 July 2012 (UTC)

Thanx a lot for quick reply.However i want a 3d model.and the wires would not overlap,they are twisted actually as shown in the figure.I think this would become simpler if i think in terms of cylindrical coordinate. i forgot to mention that the helix must form a closed circle.

i am giving a link for twisted wire once again. telephoner cable

once again stating my whole proble. 1.a twisted wire(2 strands only) 2.in form of helix(like telephone cable) 3.helix must form a closed curve

actually i am trying to make 3d model for a circular core wound with twisted wire.ok plz help 203.197.246.3 (talk) —Preceding undated comment added 06:37, 9 July 2012 (UTC)

Do you want something like this: [4], but modeled in 3D ? Also, you didn't say whether you need to represent wire thicknesses, or just show the center-lines. If you do want to show the thickness, do you want a surfaced model or a solid model ? StuRat (talk) 06:51, 9 July 2012 (UTC)

If you just want the center-lines, it's just (cos kt, sin kt, t) and (-cos kt, -sin kt, t), where k is a constant proportional to how twisted you want it. If you want thickness, you could approximate it with (cos ku + r cos v, sin ku + r cos v, u) where r is the minor radius if it's not very twisted, or with (cos ku (1 + r sin v), sin ku (1 + r sin v), u + r cos v) if it is. If you want something more accurate, I'd have to think about it more, so I'd rather not until I know that's what you actually want. You could toy with that last r to make it look better. — DanielLC 20:11, 9 July 2012 (UTC)

Silicone dioxide in vitamins for hair

I have read sbout silicone dioxide in food as additives what about hair vitamins? I am researching a product sold on the internet under a company called Hair Essentials for Women. This product is being marketed to women for thinning hair or want stronger thicker hair> My concern is how safe is it in capsule form? Does it really affect the linning of our stomach? — Preceding unsigned comment added by 174.112.156.3 (talk) 04:02, 9 July 2012 (UTC)

I've never heard of silicone dioxide, are you sure you have that right ? Silicon dioxide, on the other hand, is basically sand, so I wouldn't expect it to be particularly helpful or harmful (unless inhaled). AFAIK, it's just filler, often added to dilute super sweet artificial sweeteners to get them closer to the net sweetness of sugar. StuRat (talk) 04:17, 9 July 2012 (UTC)

It is an additive used as said as a filler and to prevent powders from clumping. The danger from ground glass is mechanical. It has to be above a certain size to pose a threat of irritation. The grade used in food (like taco seasoning powder) and drugs is non-problematic. μηδείς (talk) 04:23, 9 July 2012 (UTC)

Agreed, unless it's inhaled. I also would think it would tend to grind down the teeth over the years, since it's very hard, but the capsules should avoid this (on the plus side, it might help to remove dental plaque and dental calculus when not in capsules). I also wonder if it qualifies as non-nutritive dietary fiber. StuRat (talk) 04:29, 9 July 2012 (UTC)

Yes, when I worked as a prep-cook I used to make the chili, and the ground glass would form a nice white cloud no matter how I tried to pour it. See Silicon_dioxide#Health_effects. Baking soda and salt, or even table sugar is much better if you need an abrasive to brush your teeth. No, it is definitely not fiber, fiber is absorptive. You want to keep your intake to a minimum: the poison is in the dose. μηδείς (talk) 04:49, 9 July 2012 (UTC)

I had a similar problem with cinnamon forming a cloud, but figured out a solution. I pour it directly into liquid (like applesauce), which limits the cloud size. Then, before I turn the container back upright, I put the lid on. This prevents the second cloud that comes out when the cinnamon falls back down to the bottom of the container. I try to do all this quickly, while holding my breath, and then evacuate the area, to avoid breathing any cinnamon clouds that were produced. (Anyone who has ever inhaled a cloud of cinnamon powder will appreciate why I take such precautions.) StuRat (talk) 00:29, 10 July 2012 (UTC)

Why can't the extra dimensions of M-theory be temporal?

M-theory requires 7 hidden dimensions, so why must these be spatial rather than temporal dimensions? Hcobb (talk) 12:25, 9 July 2012 (UTC)

I don't know much about this, but the importance of 9+1 dimensions in string theory is related to a special property of Spin(9,1) (see [5] at the end of the page). That property isn't shared by Spin(8,2), Spin(7,3), etc., though it is shared by Spin(8) and, I think, Spin(10,2) and so on. M-theory adds one spatial dimension to that. Don't ask me why. -- BenRG (talk) 17:41, 9 July 2012 (UTC)

environmental science

what are the different types of biomes? — Preceding unsigned comment added by Scmcforpeace83 (talk • contribs) 12:46, 9 July 2012 (UTC)

That seems like something that could be answered by reading our article entitled "biome". DMacks (talk) 12:49, 9 July 2012 (UTC)

Newton's atoms in my body

Now there's a wide spread saying that your body contains atoms that were once in [put a famous person here]'s body. Now that seems nice, and the reason they offer for this is that atoms circulate in nature and since the number of atoms in human body is huge, there are at least some atoms in our body that belong to somebody. Well, first of all, I agree that elements circulate in nature, but how long does it take for them to do so? given that some of the people they exemplify are pretty recent in history, I'm skeptical about this claim, I mean I'm sure that atoms in my body were there in the body of some prehistoric animals for sure, but individuals in recent history?! and given all the plants and animals (including people) that have ever existed, aren't there at least some individuals that didn't make it to my body? It seems a bit unlikely to me. does the "shuffling" of atoms through history happen this fast and this radically?--Irrational number (talk) 13:24, 9 July 2012 (UTC)

Water circulates much faster than solids, and air even faster than that. It is certainly plausible that most of the air you breathe contains atoms that have been around the world in relatively short timeframes. I'm not so sure how well the claim holds up in the end though. Even though we have ridiculously huge numbers of atoms in us, there are a lot more atoms in the environment that aren't currently part of any human. Just because you have something like 10^25 (for example - i made the number up) more atoms than the number of people that ever existed doesn't necessarily make it likely that at least one has come from each person. 209.131.76.183 (talk) 14:20, 9 July 2012 (UTC)

(ec)Molecules in air move as fast as the wind, recent examples of which are radioactive fallout from the Chernobyl disaster in Ukraine arriving 36 hours later in Finland and the rapidly changing area of Air travel disruption after the 2010 Eyjafjallajökull eruption. You don't have to be on this planet very long to have a high probability of sharing gas with him and her. DriveByWire (talk) 14:40, 9 July 2012 (UTC)

We did the math for this in high school. The result is pretty convincing, although we assumed for simplicity that once in the air a molecule stays in the air, and that people don't rebreathe the same molecules, and came up with an estimate of 1,000 atoms per breath having been breathed by Jesus as well. Even correcting for air molecules leaving the atmosphere and people not breathing unique molecules in every breath the number should remain well over 100. The math desk might work out a formula for you. μηδείς (talk) 17:04, 9 July 2012 (UTC)

Saying that one specific person's atoms are likely in your body is VERY different from saying that the atoms of every individual who's ever lived is in your body. Suppose that, for a random person, you're 99.999% likely to have one of his atoms. That means that for 1 million random individuals, there's only a 1 in 22,000 chance (0.99999^1000000) that you'd have an atom from every single person. --140.180.5.169 (talk) 17:32, 9 July 2012 (UTC)

Yes, but the likelihood is much, much, much, much, much much higher than 99.999%, which is merely 1/100,000. How many atoms are there in a mole, how many moles does someone breathe a day, and how many days do they live? The number that gives is incredible. Divide it by the number of liters in the atmosphere and you get molecules per liter. A helpful visualization to comprehend the numbers is to imagine a raindrop magnified to the size of the earth. The water atoms would be the size of basketballs. That's just one drop of water. μηδείς (talk) 17:40, 9 July 2012 (UTC)

I'll point out, as I do every time this topic comes up, that atoms and molecules are indistinguishable quantum particles and hence it's quite meaningless to ask whether a particular atom now is the same as a particular atom from a long time ago. It probably does make sense to talk about what fraction of yourself was formerly Newton, but it doesn't make sense to compute a probability that you have at least one former Newton atom, because all atoms are a mixture of former Newton and non-former-Newton. -- BenRG (talk) 17:56, 9 July 2012 (UTC)

You realize, of course, that your interpretation of that article ("all atoms are a mixture of former Newton and non-former-Newton") is entirely wrong. Atoms may swap outer electrons, but the electrons themselves and the nuclei of the atoms maintain their integrity excepting radioactive decay. μηδείς (talk) 18:27, 9 July 2012 (UTC)

It's not an interpretation of that article, but a true statement about quantum mechanics. If the article really says otherwise then it should be fixed. The reason that particles lose their identity when in close proximity is that every interaction has contributions from Feynman diagrams in which the particles switch places and other diagrams in which they don't. -- BenRG (talk) 19:06, 9 July 2012 (UTC)

The central point of that article is that electrons, protons, and neutrons are indistinguishable from each other because they don't have smaller identifying features. Any electron is as good as another. But under normal circumstances, nuclei simply do not flow into one another. That's Heraclitus or Deepak Chopra, not Richard Feynmann. μηδείς (talk) 19:22, 9 July 2012 (UTC)

If that's the point of the article, it's misleading. That's why we can't tell them apart, not why we know they're the same. We know they're the same because quantum states with the particles switched interfere, which only happens if they're the same state. For example, if the amplitude of state A is 0.1 and the amplitude of state B is 0.1, the probability of getting A is 0.1^2 = 0.01, and the same for B. The probability of A or B is 0.02. If the two states are the same except with two identical bosons switched, the probability of getting either state is 0.04. If they're not the same state, that's a 0.01 chance of getting A, a 0.01 chance of getting B, and a 0.02 chance of ... what exactly?

You could claim that the universe is just symmetric in such a way that any two particles have the same/opposite amplitude when switched. If you accept the Many Worlds interpretation, this would mean that you share the atoms of an equally likely alternate universe Newton. If you accept the Copenhagen interpretation, it means that any time two identical particles get entangled, they have a 50% chance of switching. Quantum entanglement has been found on relatively large scales, which would seem to imply that any action on a smaller scale would cause entanglement. The quarks in nearby atoms are constantly interacting via., among other things, their electric charges. Every time the waveform collapses, the quarks could end up in any of the nuclei. — DanielLC 19:51, 9 July 2012 (UTC)

It seems that the original poster has asked a specific question, and gotten some very ambiguous answers shrouded in debate about the appropriateness of various methodologies. ..."How long does it take" ... for a molecule to move from place to place... this is predominantly dictated by the mean free path and the drift velocity; for molecules in common substances, an answer can be determined, subject to realistic parameters. The extent to which the calculations of those parameters will require quantum-mechanics, as opposed to being suitably-well approximated by classical statistics, will depend on the type of molecule. So, for example, a very large organic carbon compound will probably behave fairly well like a classical particle (albeit one with a strange shape, moment of rotational inertia, and so forth); while an individual oxygen or hydrogen atom will probably behave in a way that is much better described using the ugly statistical formulations that quantum physics requires to accurately make predictions. For lack of a better model, and given that the OP hasn't precluded the use of a spherical cow model, it seems fair to assume that every molecule on the planet (including those inside living organic tissues) could be considered as a member particle of a gigantic Maxwellian gas, whose temperature is approximately the average surface temperature of our planet; so simply calculate the average molecular speed, and you've got an approximation for the rate of particle circulation. You can use the diffusion equation to estimate the mean distance traveled by any individual particle. Once you've got that model working, you can add in as much additional complexity as you like to correct for all of the terrible, invalid assumptions that are clearly due to such a simplistic model. If you're interested in classical statistical physics, I always recommend the red book of Statistical Physics and Thermodynamics. If you're interested in quantum mechanical statistics, there exists a plethora of very bad texts to choose from. Nimur (talk) 21:48, 9 July 2012 (UTC)

"We are star dust."

"Yes, but we're also made of dino poo." :-) StuRat (talk) 18:56, 9 July 2012 (UTC)

So we're both golden ... and brown? Clarityfiend (talk) 20:50, 9 July 2012 (UTC)

...and we've got to get our dino poo back to the garden. StuRat (talk) 21:00, 9 July 2012 (UTC)

Back to the quantum physics, can we please get a ref on how often atmospheric nuclei in different molecules at room temperature (or even the temperature of lava) can be expected actually to intermingle? In atoms per year? As for the mean free path, it is something like 10cm, travelling at 1,000kmph, at room temperature, but that is hardly relevant on the timescale since newton. Weather mixes the atmosphere pretty well on that sort of time scale. μηδείς (talk) 22:14, 9 July 2012 (UTC)

If you're using quantum physics, the answer is that they're already the same nuclei. You could mess around with the question enough to get something that looks like the sort of answer you'd expect (so long as the particles don't get too close together), but the question itself is fundamentally flawed.

If you insist on messing with it to get the sort of answer you're looking for, the atoms in your body and the atmosphere intermingle every time you eat and breathe. When you digest food, the carbon in it gets stored in fat. When you exercise, the carbon in your fat gets exhaled in CO2. The CO2 gets absorbed by plants, and gets eaten by someone else. I'm not sure exactly how long it takes to get spread around in the air, but the bottleneck is probably the time between plants getting picked and eaten. — DanielLC 05:09, 10 July 2012 (UTC)

My thinking as well; even ignoring the rather crucial issue of unique persistent identity we could still spend days just proposing metabolic, climatological, geological, and ecological factors that need to be taken into account, to say nothing of resolving them with any precision. That being said, the OP is clearly looking for a ballpark estimate -- that is, is it more likely than not? And my (half-)impressionistic take on it is that he has reason to be skeptical - the likelihood of possessing an atom from any one particular historical figure (again, assuming we ignore the indescernability principle), especially a recent figure, is probably small - if not exactly astronomically small. That's a rather unempirical answer, I know and I hope to see the math take root here for something more concrete, but I'd be surprised if even rough estimates suggest it to be likely. If we're going to try though, might I suggest A subpage? since the discussion is likely to get quite involved? Unless someone knows a reason not to create a subpage on the RefDesk. I can always copy our work over to subpage in my user space later if we aren't finished by the time this thread is archived. Snow (talk) 12:11, 10 July 2012 (UTC)

Medeis, I just want to mention that the identity question I'm talking about comes from whole nuclei swapping places, not from any process involving the constituent nucleons. The amplitude for some kind of mix-and-match rearrangement of two nuclei is vanishingly small because of the energy barrier, but there's no energy barrier to this nucleus going over there and that nucleus coming over here. They just go around each other, they don't pass through each other or teleport. Nevertheless they follow Bose-Einstein or Fermi-Dirac statistics in these processes. If they merely had the same properties (but weren't "indistinguishable" in the quantum sense) they would follow classical statistics and it would be possible to figure out which was which after an arbitrary amount of time. -- BenRG (talk) 16:30, 10 July 2012 (UTC)

So now that atoms are maintaining their identity? Before it was "all atoms are a mixture of former Newton and non-former-Newton". You have yet to make a coherent claim and provide a ref for it. μηδείς (talk) 16:39, 10 July 2012 (UTC)

Medeis, with due respect, I think you need to stop attacking BenRG's words (because, more often than not, he tends to be exactly correct); and instead, you should reacquaint yourself with exactly which quantities are known to be quantized. Those quanta describe physical parameters that are defined as "indistinguishable" according to the indistinguishability principle - because they have no other properties. Nimur (talk) 18:05, 10 July 2012 (UTC)

I never claimed that atoms of the same isotope are distinguishable based on their properties. Frankly, if BenRG wants to come here and imply how tired he is of having to correct people all the time the responsibility certainly does lie with him to make a coherent and consistent statements and to back his facts with refs. To say theoretically that two identical atoms may switch places with each other with and unspecified frequency in no way indicates that it is meaningless to say that one is breathing atomic nuclei which someone else breathed. It's an absurd claim based on a new agey wagey pseudo-grasp of science. I don't intend to comment on this any more, since it might imply I think the matter is open to argument. But I will be impressed when I see numbers and refs. μηδείς (talk) 22:52, 10 July 2012 (UTC)

I hate people like Chopra who say "quantum mechanics!" to justify whatever crap they believe in. And I don't like to call quantum mechanics weird or unintuitive because I think that's a cop out. But there is a reason that many physicists describe it that way. What I'm describing, whether it sounds strange or not, is an essential and basic feature of quantum mechanics. I don't understand what you think quantum mechanics is, if you don't think it's this. The only reference that makes sense is any introductory quantum mechanics textbook, or maybe QED (book). In QED there are Feynman diagrams like the ones I was talking about in figures 59 and 60 (pages 93 and 94) in my copy. Please don't come back and say that those diagrams don't prove anything. I'm not saying that the diagrams by themselves prove anything. I'm just trying to point you to a relevant part of the book, in case you don't want to read the whole thing.

I'm sorry I sounded testy in my first post. I was kind of testy at the time, but that's no one's fault but mine. -- BenRG (talk) 05:14, 11 July 2012 (UTC)

The reference desk has had a similar question more than once but I couldn't find it in the archives. Here is a similar off wiki discussion: [6]. Rmhermen (talk) 15:42, 10 July 2012 (UTC)

The fact that atoms are identical in QM is actually a trivial issue here (the state is a sum over permutations of the labels you assign to the atoms). What you need to do is formulate the problem in terms of a well defined correlation function. Count Iblis (talk) 17:47, 11 July 2012 (UTC)

environmental science

describe chaparral. give and describe the three types of chaparral. differentiate those three

S.C.M.C."WARFARE" (talk) 13:28, 9 July 2012 (UTC)S.C.M.C."WARFARE"

We have an article on chaparral. Read it. Then do your own homework. AndyTheGrump (talk) 13:31, 9 July 2012 (UTC)

the white whale

A friend recently visited Cook Inlet, Alaska where she saw the locally endangered Beluga. Why, she asks, is it still legal to use their eggs for caviar if they are endangered? μηδείς (talk) 17:13, 9 July 2012 (UTC)

Whales are eutherian mammals, and thus do not lay eggs. Beluga caviar is the eggs of the beluga (sturgeon), which lives in the Caspian Sea, and not in Alaska. AlexTiefling (talk) 17:16, 9 July 2012 (UTC)

According to beluga (sturgeon), this fish is "critically endangered", so I suppose the question still makes sense... -- Ed (Edgar181) 17:27, 9 July 2012 (UTC)

In terms of a worldwide ban, the article also suggests the obvious answer is correct, i.e international politics. Unfortunately (IMO) it is generally difficult to get action to protect some endangered species when a fair number of countries, particularly influental ones are against the idea. However the OP's comments are unclear. As far as I know they live in the US and their friend was obviously visiting a part of the US. According to our article and supported by [7], importing Beluga caviar has been illegal in the US since 2005 and illegal to trade in interstate commerce. It's still legal to trade intrastate it if it was imported before the ban, but it seems likely any beluga caviar that remains legally imported in the US must now be very rare and therefore very expensive whatever the state (although there is probably some variance). If the OP or their friend is aware of a source of Beluga caviar in the US that isn't so I suggest they contact the appropriate authority (FWS?) as it's likely it's illegally imported. BTW, the earlier source which despite some later statements only mentions specific bans on Beluga caviar from the Caspian and Black Sea may lead one to believe it's possible to get it from the Adriatic Sea which our article mentions as a possible habitat. But this apparently incredibly outdated source (it doesn't mention the 2005 US bans nor does it mention the 2006 CITES ban although it does support the idea international politics are making a ban difficult) [8] suggests they haven't been seen there since 1980. Nil Einne (talk) 19:00, 9 July 2012 (UTC)

What I wonder about is whether the sturgeon will be fished to extinction, or whether the fishing will stop once the price gets too expensive for the consumers to justify. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:15, 10 July 2012 (UTC)

It seems to be a veblen good, so maybe not. StuRat (talk) 16:47, 10 July 2012 (UTC)

The reason the beluga whale and the beluga sturgeon share the same word in their name is that both derive from the Russian word белуха (belukha), meaning "white". Ghmyrtle (talk) 09:40, 10 July 2012 (UTC)

Beluga caviar is not white. μηδείς (talk) 22:43, 10 July 2012 (UTC)

No, the but the fish is white(ish). 203.27.72.5 (talk) 23:16, 10 July 2012 (UTC)

Terrell rotation matrix

How do you find the matrix for Terrell rotation? I understand that Terrell rotation isn't quite linear, but I just want the first approximation. — DanielLC 19:58, 9 July 2012 (UTC)

Just apply the Lorentz transform to the nearest- and farthest- points on the object, or to any vertices you like; and fit a rotation to the transformed vertices. (If you only use two vertices, that is very straightforward). This is covered in Tipler's introductory relativity chapters, if I recall correctly; and does not require very advanced mathematics. Nimur (talk) 21:31, 9 July 2012 (UTC)

No. You'd have to calculate when and where the points crossed your past time cone. Since it's nonlinear, it would only work in the limit. Of course, the answer itself will only work in the limit for the same reason, so that's not that big a problem. You'd need four points to do it since it's not really a rotation (three if you're only doing it in two dimensions, which I am). Finally, I need an equation for it. I was hoping someone, somewhere already calculated it out. — DanielLC 04:47, 10 July 2012 (UTC)

The easiest way to understand the appearance of a "moving" object is by working in a frame where the object is at rest. Then it's just an ordinary linear perspective projection modified by aberration. I'm not sure how to write down a formula for this—I think it's easier to just understand the geometry of the situation, so you can solve any particular problem of this kind, than to memorize a complicated general formula. -- BenRG (talk) 06:00, 10 July 2012 (UTC)

I don't want to memorize it. I want to program it. — DanielLC 07:21, 10 July 2012 (UTC)

Well, what I said still applies—the appropriate formula will depend on what sort of program you want to write. If you want to visually simulate relativistic motion through a static scene, you can do that as follows: do an ordinary nonrelativistic 3D rendering of the scene onto a cube map with the camera at the player's instantaneous location, then, for each point in your final image, take a ray in that direction, modify it by the aberration formula (using the player's velocity relative to the scene), intersect it with the cube map, optionally apply some kind of color and brightness transformation, and you're done. This is the same basic approach as Fisheye Quake except that you're using the aberration formula instead of a fisheye projection. On any graphics card with programmable pixel shaders you should be able to do this in real time for an arbitrarily moving (and accelerating) player.

The relativistic aberration page only tells me how to mess with the angle. Not the distance. Come to think of it, do I do the distance the light was sent from, or would it mess with parallax and end up being closer/further than it appears? — DanielLC 20:17, 10 July 2012 (UTC)

There's no distance in aberration. It acts on rays of light, not points in spacetime. I assume you're asking because you need a value for the z buffer. If so, the easiest way is probably to pick a reference frame (such as the rest frame of the environment) and use the distance (=time) in that frame. See below. -- BenRG (talk) 02:55, 11 July 2012 (UTC)

If you're thinking more along the lines of a text-based program that solves a parametrized word problem, tell me what the word problem is and I'll come up with a formula. -- BenRG (talk) 07:53, 10 July 2012 (UTC)

My program is a relativistic shoot-em-up. It can find where it's supposed to draw a bullet or enemy, but I want to know how to warp the image properly. In principle, I could just have it check where to draw every vertex, and then attach lines from there, but this seems like a waste of processing power. — DanielLC 20:17, 10 July 2012 (UTC)

I approve of this project. :-) When I first saw Fisheye Quake I thought about doing a relativistic Quake, but never actually got around to it.

I recommend that you render each independently moving object in the way I suggested above: first render to a cube map, then apply aberration (and perhaps other effects) with a pixel shader. Here's some detail about how to do that.

• You need to keep track of a coordinate frame for each rigid object in the game (landscape, player, opponent, bullets) and a fixed background frame in which you express the dynamical position of everything. You need to know how to transform between all of these. The transformations will vary with time. All this is standard in 3D graphics, but there are two differences here. First, these are spacetime coordinate systems (x, y, z, t), and the transformations between them are Poincaré transformations (Lorentz transformations, rotations, and translations). Second, because light has a finite speed, you need to keep a historical record of coordinate transformations for each object instead of just the "current" transformation. This is complicated, but I'll assume you know how to do it. The rest is pretty easy. :-)
• To render a frame, do the following for each object other than the player:

• Find the point of intersection of the player's past light cone with the object's worldline. You mentioned that you already know how to do this. From now on when I talk about object coordinates I mean the object's historical coordinate frame at that point on its worldline.
• Transform the player's spacetime position into object coordinates.
• Render six views of the object into six square offscreen RGBZ buffers, with a 90° field of view, with the camera located at the spatial part of the transformed player position and facing in the ±x, ±y, ±z directions. This is standard 3D stuff, except that doing the lighting correctly is tricky. I'm going to ignore lighting for now.
• For each pixel on the screen:

• Find the pixel's location in player coordinates. I assume you know how to find the x, y, z coordinates. The t coordinate needs to be −sqrt(x²+y²+z²), so that the line from the player (origin) through the pixel location is a past light ray.
• Transform the player location and the pixel location into object coordinates. Find the intersection of the (spatial part of the) ray through the two of them with the cube map.
• Optionally alter the RGB value from the cube map. I'm going to ignore this for now.
• Find the point on the ray with t = Z, where Z is the Z value from the cube map (I'm treating the Z values as negative integers with 0 being the camera's location). Note that this point lies on the surface of the object. Transform the point into player coordinates (or background coordinates, or any other coordinate system you like, as long as it's the same for every object in this frame). Take the transformed t coordinate as your new Z value.
• Write the transformed RGB value and transformed Z value to the output buffer.

That's it. Note that I didn't use the aberration formula anywhere in this. All transformations are Lorentz (Poincaré) transformations. I think this makes things simpler (and faster).

If you just want the rotation, not the aberration, as you originally requested, then you can bypass the cube map and write directly to the output buffer. However I don't think it's any easier to do it this way, and it may not even be much faster (on a modern GPU). If you really want to do it, I'll work out some steps.

If you're interested in proper lighting, redshift, etc., I'll try to figure out some way of doing that. It's not easy, and may make the game hard to play.

Note that to really be relativistically correct you need to deal with the twin effect somehow. If player Alice is standing still and player Bob is circling around her, you need to freeze Bob's game occasionally to allow Alice to "catch up". It's not hard to do this correctly, but it might detract from the fun of the game. Alternatively you could slow Bob's game down, but that feels wrong to me, since it gives the wrong impression about Bob's subjective perception of time. -- BenRG (talk) 02:55, 11 July 2012 (UTC)

That's alright, Bob won't find that the handicap worries him too much. Girls are terrible at first-person shooters. 203.27.72.5 (talk) 05:35, 11 July 2012 (UTC)

A shoot 'em up is 2D, and generally single player. I am considering making a multiplayer option, mostly just because I figured out how. Shoot 'em ups commonly have a button to slow time down. I could make it so that you can slow time down until you reach your opponent's past time cone, and if you reach their future time cone, it just turns on automatically. This system would also neatly avoid network lag problems.

I suppose I probably have more than enough computing power to check each vertex individually. It's just that transforming the sprites seems simpler and more elegant. Also, that way I won't have to deal with tachyons having parts that you can't see, and other parts that you can see twice. I could limit it to slower-than-light particles only, which would get me out of all the necessary stuff to make tachyons dodgeable, not to mention the time travel paradoxes, but that would just feel like a missed moment of awesome. Especially because of the paradoxes.

I can't imagine leaving out the lighting effects. Imagine all the cool stuff you could do with them. Give a bullet a transparent infrared skull on a violet background, and it will look like a red skull when it's flying towards you, and then turn blue once you dodge it. Paint flowers on an enemy, and you can see those ultraviolet patterns on them when they fly away. Anyway, I've largely figured out how to do it. I'll just have the brightness of each color component be the brightness of the color times the visibility of that frequency at that color receptor. — DanielLC 05:35, 11 July 2012 (UTC)

In a 2D shooter the camera is effectively at infinity, which makes it of limited use to the player if you take the speed of light limit seriously. If you ignore that problem, then moving objects are simply Lorentz contracted. There's no Terrell rotation in this situation (though the Lorentz contraction can lead to an effective rotation: a line with slope 1, horizontally contracted by a factor of 2, is a line with slope 2). There's also no aberration. The redshift factor is the gamma factor of the moving object (independent of direction). There's never a blueshift. This would probably be kind of boring.

The best I can come up with for this type of game is to have the camera hovering a relatively short distance above the game field, tracking the player (perhaps simultaneously with respect to the lab frame), and filming the field with a wide-angle lens. If the game objects are 3D meshes (even though the action is 2D) then the method I described above will still work, and it will handle everything including Terrell rotation, but with a large number of independent moving objects it may be too slow. I can work out how to optimize it if this is indeed what you want to do. Lighting is still complicated.

The difficulty with Doppler shift is that there's no way to do it correctly in the RGB color model. An object colored #000000 might glow in the infrared, in which case it turns red when blueshifted, or it might not. If the shifts are small then you can probably fake it convincingly. You may also want to think about the brightening/dimming associated with aberration (I don't know if it has a name, but it's related to the headlight effect). -- BenRG (talk) 18:07, 11 July 2012 (UTC)

I suppose what I'm doing would best be described as taking the point of view from the ship, and then, without correcting for optical abberations, working out what it would look like from above. Think of it like those things they show radar images on that show how far away stuff is and in what direction as if it was a picture taken from above, even thought it was taken from right there. Also, I am not planning on using an RGB color model. I'm planning on using a (frequency, intensity) model.

A radar-like screen can show whatever it wants. Realistically it would show whatever would allow the pilot to shoot things most effectively. It certainly wouldn't show Doppler shift, for example, since that wouldn't be helpful at all. There is no "relativistically correct" thing for it to show, unless you literally want it to use its sensors to figure out what the scene would look like from above, in which case the correct thing to show is what the scene actually looks like from above. Relativity can tell you what you'll see, but it can't tell you what your point of view looks like from someone else's point of view. That doesn't make any sense. -- BenRG (talk) 21:50, 11 July 2012 (UTC)

Is [9] and Rotation matrix too simplistic? DriveByWire (talk) 15:38, 11 July 2012 (UTC)

I'm not sure what to say about the external page. It makes things much more difficult than they need to be by doing everything in the rest frame of the camera, instead of the rest frame of the object. I'm not sure how a Lorentz contraction could be visible in this two-dimensional world, where the image in the camera is just a line. The line in the camera does get shorter when the object is moving, because of the headlight effect. The interesting observation that Penrose and others made circa 1960 is that a moving sphere always has a circular outline, not (as you might expect) an oval, but you need all three spatial dimensions for that effect. Regarding the rotation matrix, the easiest way to understand the Terrell rotation is as a real rotation related to the camera's spatial location in the rest frame of the object, so a rotation matrix will work when drawing the object just as in ordinary 3D graphics. But the camera image (not the object itself) is also altered by aberration. If the object has a large angular size at the camera's location then aberration will distort straight lines into curved lines, but if the object is small then aberration will stretch or shrink the image but not distort it much. -- BenRG (talk) 18:07, 11 July 2012 (UTC)

It is false. The contraction part of Terrell rotation does not counter out Lorentz contraction, and doesn't even necessarily apply in the same direction. If an object is moving towards you, it will look longer than it really is. If it's moving away, it will look much shorter. If you want to know what it really ends up looking like, I suggest checking out Light Speed!. — DanielLC 18:41, 11 July 2012 (UTC)

Note that the description of optical aberration at http://lightspeed.sourceforge.net/about.html is wrong, which may be the reason for some of your confusion. I think that their images are probably relativistically correct, they just have the terminology wrong (and they're doing it the hard way). -- BenRG (talk) 22:31, 11 July 2012 (UTC)

Higgs boson

Is it possible to block Higgs bosons or manipulate the Higgs field in some way to reduce another particle's mass? --146.7.96.200 (talk) 21:07, 9 July 2012 (UTC)

Not at this time, nor for the conceivable future, save via the intervention of Clarkeian "magic". — Lomn 21:12, 9 July 2012 (UTC)

Is it theoretically possible? --146.7.96.200 (talk) 21:56, 9 July 2012 (UTC)

Not in any meaningful sense under present theory (see above need to invoke "magic"). — Lomn 23:00, 9 July 2012 (UTC)

From my limited understanding, it is roughly as theoreticaly possible as a perpetual motion machine. It would need to violate laws which we hold as some of the most certain laws we have. Vespine (talk) 01:20, 10 July 2012 (UTC)

Yes, and in the early universe the Higgs field was different, it was zero on average, causing the mass of particles to be zero. When the universe cooled, the Higgs field settled down at its minimum energy, which is not at zero field strength, causing particles to gain mass. Count Iblis (talk) 01:28, 10 July 2012 (UTC)

Hold on a second. If you heat a system above the electroweak unification temperature, you can no longer describe the Higgs interaction as "giving mass to the particles", but that doesn't mean it just disappears. Unless I'm seriously confused, what you get at high temperatures is a complicated interacting soup that in no way resembles a bunch of free massless particles. Technically they are massless, but technically they're massless at low temperature too.

Also—as you no doubt know but the original poster probably doesn't know—almost all of the mass of ordinary baryonic matter (the stuff we're made of) comes from the strong force binding the protons and neutrons, not from the Higgs field. Even if you could dial the Higgs field down to zero (which you can't) it would hardly make any difference in the mass of any ordinary object. It would make enough of a difference that cellular chemistry would no longer work and everybody would die, but not much of a difference numerically. -- BenRG (talk) 05:45, 10 July 2012 (UTC)

• So, do we have an article that explains which particles have mass independent of Higgs, and which would be massless with a zero (high energy) Higgs field present?
• Also, as I (don't) understand it, the Higgs is a scalar field, so the field level can only be lower or higher than it is now. If I have a majik laser pointer that shoots a big beam of very fast-moving Higgs particles, will the field in the area it lights up (before they decay) be lower or higher? Wnt (talk) 15:53, 10 July 2012 (UTC)

All of the elementary particles in the standard model, except the Higgs itself, get an effective mass through the Higgs interaction. In composite particles the binding energy and the kinetic energy of the particles also count as mass. So basically it's the elementary particles that are massless.

The Higgs boson is a wave in the Higgs field, so it alternates between higher and lower than normal. -- BenRG (talk) 04:41, 11 July 2012 (UTC)

And note that you don't need to use the Higgs field to change the mass of particles. What makes the Higgs field special is that it achieves its minimum energy state when the field strength isn't zero. This then causes particles to gain a mass in the vacuum. Then if you want to use some field to make the mass of a particle different from what it is in vacuum, you can use any field that couples to that particle. E.g. the mass of an electron in a very strong electromagnetic field is slightly different from its vacuum value. The shift of the squared mass of an electron in the beam of a laser is given by:

${\frac {\Delta m^{2}}{m^{2}}}=2\alpha \lambda _{e}\lambda \rho$

where $\alpha$ is the fine structure constant, $\lambda _{e}$ the electron Compton wavelength, $\lambda$ the wavelength of the laser beam and $\rho$ the density of photons in the laser beam. Count Iblis (talk) 01:42, 10 July 2012 (UTC)

Habitatable zone at the tip of RGB

About the tip of RGB in 7.59 billion years I was wondering where will earth-like habitable zone be located (Jupiter and Sautrn's system, or more likely Pluto)? General calcualations, yes I know Jupiter and Saturn's orbit will be further out roughly 1.7 times further out (roughly 8.8 AU and 17 AU) but the thing is the luminosity greatly increases by 3000 times. The mathematic calculations yahoo answers figure out is 3000/5.2x1.7 for Europa, and 3000/9.5x1.7 for Titan to figure out the surface condition for Europa and Titan. Is this possible at the tip of RGB, Europa can end up colder than earthlike temperature today of only -40F? I was wondering what is the coldest temperature estimate Europa may be in 7.59 billion in the future. I don't know what other calculations will work according to the tip of RGB, the star's temperature is alot cooler, if that matter.69.226.40.110 (talk) 21:09, 9 July 2012 (UTC)

I did a quick search and found this mentioned in Terraforming of Europa, alas, not with good sources that I noticed... I see [10] this talks about it reaching Mars, but it says nothing of Jupiter... of course, the huge caveat with all this is that the planetary orbits are likely to shift as the sun expands, and if so... well, just about anything can happen. Wnt (talk) 21:21, 9 July 2012 (UTC)

If humans (or our descendents) are still around in 7.59 billion years to worry about it, I suspect technology will have advanced to a level where we could just move the Earth wherever we wanted to. Although, by then, only a small portion of humanity may live on Earth (those who like to do things in the quaint, old-fashioned way). StuRat (talk) 21:30, 9 July 2012 (UTC)

For information, RGB refers to the Red Giant Branch phase of a sun's evolution. That is predicted for our Sun in about 5 billion years. DriveByWire (talk) 21:48, 9 July 2012 (UTC)

Am I not clear at the first place? I mean when sun peak the luminosity and size at the end of the giant stage at 3000 times the luminosity and when sun reaches the maximum radius of 1.0 or 1.2, could Europa at that time when sun being 3000 times brighter stay at the temperature below -40F? I don't know how to calculate that way. --69.226.40.110 (talk) 22:31, 9 July 2012 (UTC)

It wasn't clear to me what the B meant, although I knew you were talking about a red giant. StuRat (talk) 23:39, 9 July 2012 (UTC)

I meant when the sun's giant reaches its maximum size and luminosity could Europa just heat up only up to -40F where Mars surface temperature is today?--69.226.40.110 (talk) 23:46, 9 July 2012 (UTC)

Pluto will never be a habitable planet. μηδείς (talk) 02:44, 10 July 2012 (UTC)

As we've explained to you a dozen times before, nobody knows the answers to these questions. You are quoting numbers that are just the best guesses of a particular paper. There are numerous papers, all with different answers, because we're talking about what will happen in billions of years time and there is far too much uncertainty to draw any firm conclusions. Asking essentially the same question again and again is not going to change the answer. --Tango (talk) 14:59, 10 July 2012 (UTC)

What do you mean by dozen times before? How can you know it was the same person asking? — Preceding unsigned comment added by Plusanother (talk • contribs) 21:56, 10 July 2012 (UTC)

The same writing style and, essentially, the same question. It is obviously the same person. --Tango (talk) 02:13, 11 July 2012 (UTC)

To be a lot less rigorous, the habitable zone article points out that this is approximately a simple inverse-square relationship - so to make Jupiter, at 5 AU, inhabitable, you need a Sun 25 times as bright. But looking for more on this, I happened across [11], which suggests that the Sun will get less than 20 times brighter by 12.1 Gyr, at which point it starts pulsing and losing mass catastrophically and they abandoned attempts to model the results. Those authors favored a 200K water-ammonia life possibility on Titan for a few hundred million years. Of course, even 0.01 Gyr is a very long time if you happen to be a good gardener with an extensive assortment of seeds, so I wouldn't rule out the notion of some balmy paradise Jupiter moon existing for some brief span near the end. Wnt (talk) 15:45, 10 July 2012 (UTC)

Product of animal menstruation?

Recently I got into a discussion with a radical vegan and she, besides calling me cruel, inhumane, close minded, and so on, also said that I was set on eating products of animal menstruation. Although I did not understand when she said it, I believe she meant eggs. So, first does it make sense? was it really eggs? Is that normal within the vegan community to talk like that about eggs? Second, according to menstruation, it only refers to certain mammals, does any serious person talk about some form of avian menstruation? Third, is there any non-animal menstruation? OsmanRF34 (talk) 22:20, 9 July 2012 (UTC)

You can't reason with radicals, doesn't really matter what the topic is. You are right that birds don't technically menstruate, but one PART of menstruation: the expulsion of an unfertilized ovum is technically what laying an egg is, so it's not really a massive stretch IMHO to call a chicken egg a "chicken's period". But so what? My fav breakfast is chicken periods with slices of pig's arse, yum! It's an Appeal to emotion, we associate menstruation with "disgust", I personally don't know why, I think it has religious roots really, but I think in fact, there's nothing disgusting about it. In fact, mayube you could ask the vegan what she finds so disgusting about menstruation? Vespine (talk) 22:46, 9 July 2012 (UTC)

Slight technicality there Vespine, it is not pig's arse, but pig's chest. Pigs arse is still good though!! Caesar's Daddy (talk) 07:30, 10 July 2012 (UTC)

Many vegetarians are fine with milk and eggs, as no animal has to die to get those. As for your third Q, if you are asking if there are animals that don't menstruate, then yes, there are. For example, cats don't, but dogs do.

A retort you could make, if she likes honey, is to tell her that it's bee spit. Or, if she likes fruit, tell her she is eating plant ovaries. StuRat (talk) 22:53, 9 July 2012 (UTC)

Bee vomit, actually. Delicious! Ratbone58.164.228.40 (talk) 02:25, 10 July 2012 (UTC)

She was a vegan: so no animal products (which come from animal slavery, with or without killing). Veganism is all about animal rights in a very radical way.

The third point is about the redundancy: why animal menstruation? Is there something that could be called vegetable menstruation somewhere? OsmanRF34 (talk) 23:25, 9 July 2012 (UTC)

As far as "animal slavery", that's a fair characterization of factory farming, but how does she feel about "happy" free-range chickens ? StuRat (talk) 23:38, 9 July 2012 (UTC)

I don't believe vegans share your definition of slavery = factory farming and I don't believe I'll talk again with her about such topics, so my understanding might be limited. Anyway, as far as I could understand, no captivity of animals is acceptable to her: no milk, no eggs. It's not only the killing. It's the slavery. And she has the equivalent of normal people's opinion on slavery but applied to animals. Mainstream citizens do not accept slavery, even if the master treats the slaves well. So, she doesn't accept animal slavery. OsmanRF34 (talk) 00:10, 10 July 2012 (UTC)

If somebody wanted to provide me with food, housing, and medical care, and, in return, only asked something from me which I couldn't use anyway, like, say, my urine, I'd sign right up ! StuRat (talk) 19:19, 10 July 2012 (UTC)

THAT wouldn't be slavery, since someone asked you for something. That's trading. Just imagine the opposite case, if you get imprisoned, get lots of food to make you fat, health care only if it were economically viable, otherwise they let you die, and at the end they would eat your fat ass. — Preceding unsigned comment added by Plusanother (talk • contribs) 22:38, 10 July 2012 (UTC)

You seem to be talking about factory farming, but I was talking about free-range chickens raised for their eggs, which aren't imprisoned, but are free to come and go as they please. They also aren't fed so much that they get fat, since they aren't for eating, but for laying eggs. And comparing the health care they get with the lack of any in a wild bird, it seems like a good deal. StuRat (talk) 23:55, 10 July 2012 (UTC)

I would say she's talking out of her arse (if you'll pardon the expression), birds don't menstruate. I think you will find the Menstruation (mammal) article more informative. If you meet her again, tell her she's flogging a dead horse (sorry!). As for non-animal menstruation, it's the shedding of the uterine lining so, by definition, it's only possible in animals. Richerman (talk) 23:32, 9 July 2012 (UTC)

She means animal as opposed to human. I agree with Vespine's and StuRat's points. My last girlfriend that was a vegetarian would eat eggs and milk, just "nothing with eyes". And she would point out to people that she wore leather because there was no suitable substitute, but would prefer something else if it were available. Much more reasonable than telling people they were eating chicken abortions. μηδείς (talk) 23:48, 9 July 2012 (UTC)

The funny thing is, the factors that drove the evolution of brains big enough to allow us to worry about these ethical dilemmas are thought by some to include the consumption of fish and shellfish and that we later learned to cook meat. Richerman (talk) 00:01, 10 July 2012 (UTC)

Just out of curiosity, what use of leather can't be substituted with something else? Wnt (talk) 00:23, 10 July 2012 (UTC)

I suppose elegant shoes, specially men's ones, have to be of good quality leather. OsmanRF34 (talk) 00:30, 10 July 2012 (UTC)

Quality hiking shoes were her main concern. She moved to Colorado from the east coast due to her love of winter sports. μηδείς (talk) 00:47, 10 July 2012 (UTC)

What about substituting hiking for canasta? 203.27.72.5 (talk) 01:25, 10 July 2012 (UTC)

What in bloody hell would she need leather shoes to play canasta for?

Umm.....if she played canasta instead of hiking, she wouldn't need the shoes, and the cows wouldn't have to die for her hobby. 203.27.72.5 (talk) 03:04, 10 July 2012 (UTC)

The cattle are dying anyway. And the poor canasta plants? Who's thinking about their well-being? μηδείς (talk) 03:41, 10 July 2012 (UTC)

Just got to say to those claiming veganism is extemely radical, you need to check out Jainism, they won't even kill plants or bacteria. Unique Ubiquitous (talk) 01:36, 10 July 2012 (UTC)

They certainly will kill bacteria and various other microorganisms simply by having a functional immune system. 203.27.72.5 (talk) 02:04, 10 July 2012 (UTC)

I assume their religion only requires them to attempt to minimize the deaths they cause, not eliminate them entirely. I'd also assume they put more value on large animals than bacteria. StuRat (talk) 02:44, 10 July 2012 (UTC)

The immune system kills invaders, not the native flora, whose cell numbers outnumber those of your body by ten to one. μηδείς (talk) 02:49, 10 July 2012 (UTC)

Are you absolutely sure that the immune system never, ever kills any of the native flora in the body? I'm pretty sure some opportunistic infections are due to native flora that are normally kept in check by the immune system. 203.27.72.5 (talk) 03:16, 10 July 2012 (UTC)

Ah, yes. Candida albicans is a good example. 203.27.72.5 (talk) 03:19, 10 July 2012 (UTC)

It's biology, not math. Of course there are exceptions. Such organisms are like clonal colonies, in any case, not groups of unique zygotic individuals. The body does not usually kill them off entirely. I am not a Jain, but I would assume the relevant point is that you are not voluntarily going out of your way to kill bacteria which inhabit your body without invitation in the first place.

Well, my point is that regardless of what Jains might say or think or believe, they will kill a variety of things no matter what they do. 203.27.72.5 (talk) 03:44, 10 July 2012 (UTC)

Your italics sound just like my niece. You understand the difference between killing a leaf and killing an entire unique individual plant? Almost all infections are by clones, identical cells, like the leaves of plants rather than individual zygotes. μηδείς (talk) 03:53, 10 July 2012 (UTC)

I note with no little amusement how the supposedly radical vegan manages to justify using leather. It reminds me of something Mark Twain said, in the voice of Huck Finn talking about his aunt, who was always condemning smoking and drinking. "She took snuff, but that was alright, cause she done it herself." ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:12, 10 July 2012 (UTC)

I think you have confused Osman's radical vegan with Medeis' vegetarian ex. AlexTiefling (talk) 09:40, 10 July 2012 (UTC)

I was actually thinking of someone I know who's a "devout" vegan who also smokes cigarettes. Go figure. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:58, 10 July 2012 (UTC)

What's the problem with that? Cigarettes are not animal products.

For most vegans, their health is at least part of the reason for their dietary choices, which makes such an unhealthy choice as smoking surprising. StuRat (talk) 17:16, 10 July 2012 (UTC)

OK, but there are also enough vegans who are vegans due to ethical reasons. It's not necessarily a contradiction. — Preceding unsigned comment added by 188.76.173.109 (talk) 18:13, 10 July 2012 (UTC)

Most vegans I know smoke all sorts of things that aren't good for their health, and I really don't finding it suprising at all. According to Hippie; "Hippies rejected established institutions, criticized middle class values, opposed nuclear weapons and the Vietnam War, embraced aspects of Eastern philosophy, championed sexual liberation, were often vegetarian and eco-friendly, promoted the use of psychedelic drugs which they believed expanded one's consciousness, and created intentional communities or communes." 203.27.72.5 (talk) 20:12, 10 July 2012 (UTC)

It's ironic that their ethics toward others apparently does not extend toward themselves. I wonder, though, if they got their wish and all "enslaved" domestic chickens were turned loose, how long would it be before canines and raptors had pretty well wiped them off the face of the earth? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:03, 10 July 2012 (UTC)

Actually, feral chickens do quite well for themselves, although they are not caged layers. μηδείς (talk) 23:43, 10 July 2012 (UTC)

And frankly it's a poor argument for all of the excesses of the meat industry to claim that you really are just concerned with what would happen to all the poor animals if you weren't keeping them in small pens and slaughtering them. It's just not very likely that that's what's keeping you up at night. (I'm not a vegan, but I don't pretend that factory farming is anything ethical.) --Mr.98 (talk) 00:28, 11 July 2012 (UTC)

There's no question that the extreme factory farming that you're alluding to is cruelty to animals. It's a fact of life that every living thing eats and eventually gets eaten. It's good to treat domestic animals as humanely as possible or practical, up to and including the method of slaughtering. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:58, 11 July 2012 (UTC)

We're definitely out of our league here. If someone wants to ask how it is that humans can think that we can enforce an ethical code on behalf of animals that the animals themselves have never followed toward one another and never will follow, better ask the folks at the Humanities desk... Wnt (talk) 21:32, 11 July 2012 (UTC)

July 10

What is an extended structure?

What is the precise meaning of an "extended structure" in chemistry?

I want to understand "the design and construction of extended structures"[12] in the context of adsorbents. Also "extended solids" seems to be a synonym (used in the title of a paper listed there).

From Googling, it seems to be often used in the context of large complex molecules such as DNA and melanin.

Thanks! --Chriswaterguy talk 00:47, 10 July 2012 (UTC)

Okay, no takers yet...

As far as I can work out (guess, really) it's where a material doesn't have molecules in the usual sense, but a more or less consistent, repeating structure. But that sounds like a crystal: "A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly, repeating pattern extending in all three spatial dimensions." That article states that there are crystals with covalent bonds, so it's not that either.

Is it a synonym for crystal, but emphasizing the importance of the structural details? With research into adsorbents, the structure is critically important; with rock salt, the internal structure isn't of so much interest for most people dealing with it. (I suspect there's more to it than this, though.) --Chriswaterguy talk 06:58, 11 July 2012 (UTC)

As far as I can see from the use of the term here and here, it refers to the structure above the unit cell level i.e. how the unit cells stack together. It looks like it would be important when there are more than one unit cell type present, since the way unit cells stack together is generally pretty obvious. From my understanding of what a unit cell is, if there are supposedly different unit cells alternating throughout the structure, then the unit cell has been incorrectly identified, and should incorporate both of the other "unit cells" into one which does simply repeat without interuption. It also seems to have a special meaning in biochemistry. 203.27.72.5 (talk) 07:27, 11 July 2012 (UTC)

Actually, look at the section "Description of crystal structures" here. It basically says that understanding the unit cells as I said above is occasionally insufficient to describe the structure, so then they talk about extended solid-state structures that have multiple unit cell types. 203.27.72.5 (talk) 07:38, 11 July 2012 (UTC)

In the context of surfaces (which I think is what you're looking at since you mention absorbents) it might mean the structure at the surface according to this paper. I suppose in that sense it's the structure "extended all the way to the edge". Here's yet another paper that defines the term in a completely different way - using it to refer to the structure incorporating charge density. From this FAQ I think it just means any rendition of the structure that shows more than one unit cell, even if they are identical and repeating. So, in summary, it means a lot of things to a lot of people even just within the field of chemistry. 203.27.72.5 (talk) 08:07, 11 July 2012 (UTC)

How do ants detect rain long before it arrives?

Topic says it all. ScienceApe (talk) 02:10, 10 July 2012 (UTC)

They can't. No wait, they can. Or can they? 203.27.72.5 (talk) 02:21, 10 July 2012 (UTC)

Phase IV: http://www.youtube.com/watch?v=gcjBIkS-QC4 . μηδείς (talk) 02:34, 10 July 2012 (UTC)

The simplest way, I imagine, would be to detect falling barometric pressure, like a barometer does, to predict bad weather. (This could be done with an air sac exposed to the atmosphere, which would shrink when pressure rises, and grow when it falls. I wonder if they have anything like that.) StuRat (talk) 02:39, 10 July 2012 (UTC)

Who says they can? What would you expect them to do? The black ants on my lawn can't. On the few fine days we've had this summer in the UK they build little towers of fine soil among blades of grass in which they place their pupae only for these to be washed out by a sudden shower. I know it's OR but no less reliable than some of the sites cited above. Caesar's Daddy (talk) 07:27, 10 July 2012 (UTC)

It's true that Lasius niger in the UK don't move their colonies before heavy rain but here in Thailand where the rainy season can be a serious problem for ants, it's commonplace to see entire colonies of what I assume are Paratrechina longicornis with multiple queens emigrate hours before heavy rain, often into your house, or at least off the ground. They neatly arrange the larvae and pupae into piles on higher ground or hold onto them all until the rains have finished. Then they leave. Sean.hoyland - talk 10:05, 10 July 2012 (UTC)

Fascinating, I've never heard of such a behaviour in an ant species that is not generally nomadic by nature. As to the sensory mechanism they use to perceive these oncoming events, I agree it is likely to be barometric in nature, but would not discount some form of hydrometeor perception (specifically, a level of precipitation which is noticeable to the ant well in advance of the rain that we perceive) or even temperature. I do not think an exposed air sac is likely as it is not consistent with any precursor organ or physiological structure I am familiar with in ants and many animals are believed to have barometric perception without the need for such an external feature. It's worth noting that barometric pressure would be an inconsistent mechanism for most species of ant to detect rain on the horizon since most drops in pressure do not herald rain, but in a region like Thailand the correspondence is higher than on average, meaning the mechanism would be more dependable for species living in such a context. Add in the amount of rain involved and it makes sense why these particular ants might have the capability where most others lack it. Snow (talk) 13:00, 10 July 2012 (UTC)

The sac wouldn't need to be external, just have access to external air, say via a pore. Could be like the human ear, with a membrane covering a hole. StuRat (talk) 17:10, 10 July 2012 (UTC)

How can air conditioning units be measured in BTUs?

It makes no sense to me. That's a bit like measuring a car's engine in miles. BTU is a unit of energy. Surely when one decides on an air conditioning unit / heat pump one chooses one with a certain power rating, like watts or BTU per hour or something like that. How does BTU hold any meaning? I can state that a one watt air conditioning unit can produce 100,000 BTU (provided you run it for about 30,000 hours - about three and a half years). 41.164.7.242 (talk) 07:33, 10 July 2012 (UTC) Eon

British thermal unit indicates that "BTU" in that context is used as shorthand for "BTU per hour". ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:07, 10 July 2012 (UTC)

And a car's lifetime, including its engine, is typically measured in miles, at least in the United States. In the same way, aircraft engines are measured in hours of running time. Miles or hours determine the maintenance and replacement intervals. ~Amatulić (talk) 22:58, 10 July 2012 (UTC)

HIV transmission by insect

Are there any proven cases of HIV being transmitted by mosquito bite? Or by any other insect bite? I'm wondering if I'm being told duff information. -- 84.12.35.122 (talk) 08:23, 10 July 2012 (UTC)

Our article suggests that HIV cannot in theory be transmitted by a mosquito bite, because mosquitoes inject only saliva into their victims, not regurgitated blood, and HIV is not present in the insect's saliva. It suggests one potential transmission route: if a mosquito containing HIV-infected blood were to be swatted against someone's skin, the infected blood could enter the victim's body via a scratch or open wound, but it cites no known examples. Wikipedia is not itself a reliable source, but the article does cite sources. The results of a Google search on the question appear to agree that there have been no reliably documented cases of HIV infection via mosquito bite. - Karenjc 08:50, 10 July 2012 (UTC).

On any other insect bite it looks less certain to me. Bubonic plague seems to transmit with regurgitated blood from flea into host for example. Simultaneous infection with Bubonic plague (to cause the regurg) and HIV looks technically plausible? --BozMo talk 10:55, 10 July 2012 (UTC)

Unlikely, given the prevalence of fleas and not a single documented case of this happening. Mind you diseases which display such a pathology/epidemiology tend to be those which have evolved for a long time to exploit exactly that route of transfer. Bear in mind also that HIV does not survive for long outside of the human body, even when it's not being attack by the immune system of another host creature. Also note that flea bites do not usually re-introduce blood when they feed multiple times -- Y. pestis has a particular mechanism for causing the flea to regurgitate the blood during a second feeding, a mechanism HIV does not share. Snow (talk) 13:17, 10 July 2012 (UTC)

How can you document such a thing? There are probably many HIV infected people who cannot spot the origin of their infection and most of us are mostly not aware when we were beaten up by a mosquito, and even, I dare to say, some people die of AIDS without realizing it what is killed them. — Preceding unsigned comment added by Plusanother (talk • contribs) 22:01, 10 July 2012 (UTC)

Well, I wouldn't exactly say that it's outright impossible, just that such a case has never been empirically documented (or even suggested as likely in serious medical literature that I know of, though the potential of the mechanism has been explored nonethless), and that it seem unlikely given what we know about the disease's pathology and the physiology of the two host organisms. Keep in mind that HIV research is a prolific field; if this was happening it's almost certain we'd know about it (and any researcher who proved the existence of the mechanism would be propelled to life-long acclaim). Snow (talk) 00:37, 11 July 2012 (UTC)

I strongly doubt it's documentable, because given the social aspects of HIV transmission modes, there are doubtless many people who will strongly deny the usual routes of infection, but who didn't get it by mosquito. The only way we could find out would be to play with a captive population and HIV-fed mosquitoes, and I doubt we've done that even at Diego Garcia, though you never know any more. Wnt (talk) 21:28, 11 July 2012 (UTC)

Hmm, mosquito bites can transmit other viral diseases, such as dengue fever and malaria, so I'm wondering why it's so implausible that HIV can't possibly be present in mosquito saliva. ~Amatulić (talk) 23:04, 10 July 2012 (UTC)

Dengue fever and malaria are caused by protozoans which actively move into the saliva. μηδείς (talk) 23:42, 10 July 2012 (UTC)

Wrong about dengue, which is viral, was thinking of Chagas' disease. μηδείς (talk) 00:43, 11 July 2012 (UTC)

There are two layers to answering that question. First there's the proximal explanation of the mechanisms (as referenced above). But to address the issue more broadly and in terms of pragmatics, there's the explanation that the virus already has a perfectly suitable (and, unfortunately, highly efficient) mechanism for propagating itself. While technically not a living organism (depending on your definition), a virus does have a kind of evolutionary course, and each has adapted to operate in highly specific context. The balance the HIV virus has struck does not (at present) allow it to survive outside the human body for long, nor to exploit routes of infection which do not involve human-to-human contact. Developing such traits would likely require significant trade-offs for the disease which, given it's current virulence and tenaciousness, are not necessarily beneficial to it. Snow (talk) 00:48, 11 July 2012 (UTC)

So why is it so easily transmitted through sharing used needles and blood transfusions? 203.27.72.5 (talk) 00:55, 11 July 2012 (UTC)

Those are very intimate routes of transmission protected from exposure to oxygen which rips apart the viral coat of HIV almost immediately. Mosquito saliva also has anti-coagulants and digestive enzymes which destroy the virus. μηδείς (talk) 01:06, 11 July 2012 (UTC)

If HIV is destroyed on contact with oxygen, shouldn't it be destroyed in vivo as your blood passes through the lungs? 203.27.72.5 (talk) 01:22, 11 July 2012 (UTC)

Well, individual virions are constantly being destroyed by the regular metabolic processes of the body (as well as by the immune system, even in the case of AIDS), but their numbers are such that they can weather these storms, sometimes even laying relatively "dormant" in certain tissues (nervous tissue is particularly susceptible to certain viruses, for example) and then re-amassing themselves as the opportunity presents itself. Snow (talk) 01:34, 11 July 2012 (UTC)

And the transmission of infected blood of one individual into the bloodstream of another tends to be more immediate and consist of markedly larger amounts. On top of all of this, mosquitos rarely need more blood than they can consume in a single feeding; in most cases they use it to drive egg fertilization and engage in such feeding only as necessary (though some more aggressive species do use it as a more consistent means of sustenance). Snow (talk) 01:29, 11 July 2012 (UTC)

Large amounts of the virus are actually destroyed in vivo, but the blood is a buffered, supportive environment (ignoring the immune response) and keep in mind that oxygen in the blood is largely bound by hemoglobin. Also, as I said elsewhere, biology is not math, and there are exceptions. It is entirely possible HIV may have been transmitted by insect bite, just unlikely and impossible to prove after the fact. Would anyone like to volunteer as a test subject? μηδείς (talk) 01:36, 11 July 2012 (UTC)

Is it so unlikely that it's not worth doing an experiment with simian immunodeficiency virus , a couple of chimps and several hundred mosquitos? There's also this link for anyone who's interested. 203.27.72.5 (talk) 02:14, 11 July 2012 (UTC)

There is an infinite difference of scale between the yes-or-no possibility and the almost-zero likelihood of something happening. You pay me enough, I will indeed get a mosquito to infect a chimp with SIV. But if the prospect of dying of AIDS from a bugbite actually frightens you you might as well go on benzodiazepines to prevent yourself from dying of a meteor strike. μηδείς (talk) 02:33, 11 July 2012 (UTC)

Nah, the word of the CDC is good enough for me. I was just interested in the whys and hows of it all. 203.27.72.5 (talk) 04:43, 11 July 2012 (UTC)

There is no obvious reason why it would be absolutely impossible for someone to get a bit of HIV infected blood from a mosquito or tick into a scratch and catch the disease. Mosquitoes and ticks obviously have large dollops of blood in them, which could include various pathogens. The CDC says that one unit of HIV might get transmitted in 10 million mosquito bites. It isn't clear whether the "1 unit" is enough to cause an infection, but how many millions of mosquito bites take place each year? Maybe a billion in the US, if each person gets bit 3 times. But few of the mosquitoes would have had a previous partial meal on an infected person. Insect-born pathogens were shown to be the cause of numerous diseases of people and animals, but typically in models where the pathogen survives and fluorishes in the mosquito, unlike HIV. West Nile is transmitted by skeeters who have previously bitten an infected animal, and I would be much more concerned about getting West Nile from a mosquito bite. There might be a reason for governmental authorities to poo-pooh any possibility of HIV infected blood getting carried to infect a victim who gets bitten by the insect, or who swats a blood-filled insect and it enters the bite or some other scratch, since if the small possibility were shown to exist, people might demand that HIV infected persons have to dwell far away from uninfected persons. Combine a small likelihood of insect transmission, and the societal harm from restricting HIV infected persons to something like leper colonies on a remote island, and you could get unwarranted denials."Trust me, I'm from the Government and I'm here to help you" just does not resonate with credibility for many people. Edison (talk) 20:30, 11 July 2012 (UTC)

For extremely good reason. The Government, being run by big business, does not help anyone other than its own constituent bourgeoisie. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 21:15, 11 July 2012 (UTC)

While they might not be always 100% truthful, they are here to help. Edison even pointed out that the only reason for downplaying the truth is to strike a balance between the "likelihood of insect transmission, and the societal harm from restricting HIV infected persons to something like leper colonies on a remote island". If the CDC says it's not worth worrying about, I'm not going to worry about it. But for interests sake I wanted to know just how unlikely it was. 203.27.72.5 (talk) 22:03, 11 July 2012 (UTC)

There probably is a risk of insect being a vector transmission path. The problem is how to scientifically document a transmission mechanism with low probability, long (10y) incubation time, and where the victim may not even beaware of the insect bite in question, nor would any experiment be ethical. As for the truth factor in authorities, just consider that they have other priorities than yourself! Take rather a look at the mechanism involved rather than any "we know better" from authorities. Kitchen knifes and salads is another path. Heard of any restaurants with guaranteed HIV free staff lately? So: does the blood sucked up by the mosquito present an infection risk (for HIV)?, can it be pushed into a person be smacking it? can viruses migrate from the blood into the saliva? Any data where the number of viable viral particles is measured would be interesting. And can't be THAT hard to establish. Then probabilities can be calculated. Electron9 (talk) 00:25, 12 July 2012 (UTC)

Well, it's not as if the issuehasn't been studied. (Those are just a few amongst scores that treat the issue that I found in a cursory search). You're quite right that incubation periods often muddle the issue some for any disease, but that doesn't researchers can't determine a given vector as impossible for a given virus based solely on what they do know about the pathophysiology involved. Or even on strong epidemiological evidence; one of those examples I included in this post points out that if mosquito were capable of transmitting the disease then you wouldn't see as striking a trend on the age-range of new infections -- barring infections by transfusion and mother-to-child, almost all new cases excluded the very young and the very old, for obvious reasons, but if mosquitos were transmitting the disease, their dispersed selection of targets would not allow this to be the case. Now, this might not be satisfying to those who might argue that it could still have happened just a handful of times, but puttign together statistical evidence (bearing in mind the massive numbers involved) and a number of different findings as regards the pathology of the disease and the physiology of the carriers, it's about as certain as anything gets in medical science. As to the disease being transmitted by someone prepping a salad, that's obviously unrealistic and if there are indeed kitchens that go out of their way to not hire personnel with HIV, and then are foolish enough to advertise the fact, you can probably expect to see some discrimination lawsuits on the matter in the near future (and the plaintiffs will almost certainly win too, if we're talking about any country in the English speaking west here). Even if you meant that the HIV-infected individual cut themselves then I still don't see it happening. First off, consuming anything less than ounces of infected blood is probably not likely to cause infection (unless you had a large open cut in the mouth or somewhere else in the upper digestive tract). Second, its unlikely a salad with any amount of blood on it is going out to a customer and three -- don't eat your salad if it comes with blood on it! Snow (talk) 09:28, 12 July 2012 (UTC)

What about a HIV positive teppanyaki chef? 101.173.170.146 (talk) 10:47, 12 July 2012 (UTC)

Hah! Well, if your teppanyaki chef is stabbing himself, you're taking your life into your own hands being so close to him regardless. Snow (talk) 12:11, 12 July 2012 (UTC)

Actually, those references you cite have a case of mumble. "Extremely low or nonexistent", "extremely unlikely", aren't actually answers as to whether one case has ever occurred. They're practical answers for everyday living; still, if you run into someone who claims to have experienced an Immaculate Infection, they deserve to be given the benefit of the doubt. Because it's biology, and you never really know. Speaking of which, if a chef serves up his own testicles, [13] even if properly cooked, what are the odds that a piece of viral RNA or integrated DNA can become transfected into a vulnerable epithelial cell. Hmmm.... (but then again, he wasn't in one of the risk groups! Wnt (talk) 13:26, 12 July 2012 (UTC)

Evolution of the four fundamental forces

I seem to recall there was a section in my physics book that gave a timeline of when the four forces evolved. Which came first, and when, etc. Is there any article here that gives a timeline? ScienceApe (talk) 11:44, 10 July 2012 (UTC)

Chronology_of_the_universe#Very_early_universe ? --BozMo talk 12:10, 10 July 2012 (UTC)

The "orthodox" sequence is that gravity separated first, followed by the strong force, and finally the weak force separated from the electromagnetic force when the Higgs mechanism gave rest mass to W and Z bosons but not to photons - see this timeline. But as of now only the final one of these three phase transitions is understood in any detail - different sources give different answers about the timing and mechanism of the first two, with varying amounts of speculation. And if you add supersymmetry breaking to the mix, that complicates the picture even more. Gandalf61 (talk) 12:15, 10 July 2012 (UTC)

Infant eye glasses

I know that with toddlers who can at least talk, they do vision tests with symbols of things like boats and houses, but I've seen infants barely able to crawl with glasses. How can doctors ascertain the visual acuity of someone who can't tell you what they're seeing because they haven't acquired any language higher than "bbbbb whaa whaa abababa"? 20.137.18.53 (talk) 12:16, 10 July 2012 (UTC)

The glasses could be used to correct a squint: NHS link. Brammers (talk/c) 12:51, 10 July 2012 (UTC)

It is possible to measure the roundness of the eyeball using modern equipment. This will indicate astigmatism, which can bee corrected using glasses. --TammyMoet (talk) 13:53, 10 July 2012 (UTC)

There is an instrument called a “Retinoscope” which we use to shine a light into the toddler’s eye from a distance of about 17 inches. We can interpret the reflection that comes back from the back of the toddlers retina into the pupil area. As we move the instrument from side to side, the reflected light we are watching will move either in the same direction as our instrument or in the opposite direction. This tells us whether we are dealing with nearsightedness or farsightedness. The speed of motion of the reflected light is an indication of how much prescription power will be required. In a seasoned practitioner’s hands we are able to very precisely determine how much and what power is required without asking the toddler a single question. We do the same with adults who can’t communicate or are illiterate or can’t speak the same language, as in third world countries where in some instances on field trips no communication is possible at all. It’s pretty neat. Dr. Dhavid Cooper DriveByWire (talk) 14:18, 10 July 2012 (UTC)

The illiterate part doesn't make sense. At the eye doctor, they never actually ask me to read the letters, in any case, they just ask which is clearer. Now, when I get a driver's license, then I have to read the letters, because there they want proof that I can see clearly, but even there, they could substitute symbols like houses and dogs and ice cream cones. As far as people who don't speak the language, all they need to communicate is "better" or "worse", which could be a thumbs up and thumbs down. StuRat (talk) 16:55, 10 July 2012 (UTC)

Going back over 20 years when I was an adult literacy tutor, I taught a young man who wore bottle-end glasses but who still couldn't see you unless he stood right up close to you. He was more or less unable to read, and over about 18 months we worked on that. One day he walked in to class with new glasses, which were much thinner, and he didn't stand right next to me. What had happened was that he'd finally been able to read the letters and texts the optician had been giving him during his eye test, and the prescription was exactly what he'd needed - for the first time ever. --TammyMoet (talk) 19:01, 10 July 2012 (UTC)

If his eye doctor had simply asked when it looked clearer, rather than ask him to read the letters, the whole problem could have been avoided. It seems that some eye doctors need to be retrained. I suspect that, to avoid embarrassment, the student had faked being able to read, and, once he guessed the letters correctly, continued to say them that way, even as they got blurrier with stronger lenses. The eye doctor should also switch the letters used at each increment, if asking people to read them, to avoid such deception. StuRat (talk) 19:10, 10 July 2012 (UTC)

Tammy has pulled your leg, Stu. Quite apart from the fact that anybody with even half a brain would sooner or later, and most likely very much sooner, discover for himself whether the prescribed specs were right (if like me, you need a different prescription for reading than for distance, you probably do what I do - if I am reading and want to look at a clock some distance away, I just hold my reading specs a couple of cm forward off my nose - that changes the effective power by about 2 diopters and matches my distance prescription), the optometrist would have had to be a complete moron. Usually they check by homing in on the correct prescription from different directions. If you give wrong answers (as naughty children sometimes do) they soon detect it. Whenever I have had my eyes checked, the optometrist has first used a retinoscope to quickly get a rough idea, then uses the big-E chart to fine-tune.

I must correct some misconceptions however. It is not sufficient for the optometrist to ask "which is clearer?" The preception of what is clearer can differ from that which is best read. The patient may have the impression that the letters on the chart are their clearest, yet a small change in lens power of cylinder axis may improve his accuracy in reading the letters, particularly if he is getting specs for the first time. Usually what they do is ask "Which is better - first or second? (changes setting, pauses, changes setting back again) second or first?". then as it gets pretty good, they change to asking "Please read the 2nd last line." or similar. Then they distract you, change setting again, - and what do you know, one of those fine print letters seems to have changed!

Also, just because someone you know suddenly rocks up with lenses noticeably thicker or thinner, it DOES NOT necessarily mean they have radically changed prescription. It could be that he/she has changed to lense material of different refractive index. Spectacle shops these days tend to push the newer high-index lenses for cosmetic reasons, but the high-index materials have poorer colour dispertion. Wickwack60.230.208.161 (talk) 02:37, 11 July 2012 (UTC)

When you talk about "eye doctors", are they optometrists or opthamologists? 203.27.72.5 (talk) 22:10, 10 July 2012 (UTC)

Presumably an optometrist, if his only vision issue was that he needed glasses. StuRat (talk) 02:15, 11 July 2012 (UTC)

Infants are resolute about throwing off eyeglasses that do not help their vision. DriveByWire (talk) 14:20, 10 July 2012 (UTC)

I'm betting an infant would also throw off a pair of glasses frames with no lenses at all just because the plastic is touching their temples. 20.137.18.53 (talk) 17:57, 10 July 2012 (UTC)

You can just compare their reactions without needing them to speak. If they ignore a toy, they probably can't see it clearly enough to realise it is something interesting. So you change the lenses until they show interest in the toy, at which point you know they can see it. --Tango (talk) 15:03, 10 July 2012 (UTC)

What's the street value of testogel?

Testogel, which I will not link as it is merely a redirect, is a form of testosterone that comes as sachets of gel, the idea being that someone with low testosterone can apply it to themselves. It is prescription medication meant either for hypogonadism or for FtM transexuals.

However it could also be used by body builders as it is an anabolic steroid. What is the street value of a pack of 30 x 50mg sachets of it? Egg Centric 13:37, 10 July 2012 (UTC)

Where are you? Is the purchase you ask about illegal? DriveByWire (talk) 14:26, 10 July 2012 (UTC)

I'm not interested in making any purchase - or indeed making any sale. I am legally prescribed testogel and being on the isle of man it costs me £3.65 a month (as any prescribed drug does). I was just interested in what the street value of it is as I enjoy boasting about that sort of thing in pubs (I am also prescribed another drug that has a much higher street value, incidentally, but that is irrelevant to this question). Egg Centric 17:38, 10 July 2012 (UTC)

You can order steroids legally via US webshops. Count Iblis (talk) 15:29, 10 July 2012 (UTC)

It's a bit hard to accurately assign a street value, even for a given location. A crack head that wants it might not be able to pay much of anything, or might offer a stolen stereo, whereas the token party-girl rich lawyer's daughter might pay a few quid, not realising that it can be so easily obtained legally. Oh, and purely out of interest, is yours prescribed for hypogonadism or FtM transexualism? 203.27.72.5 (talk) 22:02, 10 July 2012 (UTC)

It's just me or do other people also find it funny that the OP is on the Isle of Man? Plusanother (talk) 00:04, 11 July 2012 (UTC)

Surely 84,000 dooinneyyn(?) all have to be somewhere. That's not including Moddey Dhoo who can chase a greater number of cats than available tails. DriveByWire (talk) 15:13, 11 July 2012 (UTC)

Mick Jagger (a popular singer m'lud) has called for all drugs to be legalised on the Isle of Man. It seems that Narcotics Anonymous meetings are held at St. Joseph's Catholic Church, Douglas, Isle of Man. DriveByWire (talk) 22:29, 10 July 2012 (UTC)

Domestic wiring

I formatted this as a new question. DriveByWire (talk) 14:24, 10 July 2012 (UTC)

Which wire is used in domestic wiring? — Preceding unsigned comment added by Nikhilbdvg (talk • contribs) 14:17, 10 July 2012 (UTC)

Depends on the load and the local electrical code. In the U.S. most common is 3-wire 14 gauge for 15 amp circuits. You also see 12 gauge for 20 amp circuits for heavier loads (large appliances, a/c, etc.) Rmhermen (talk) 14:34, 10 July 2012 (UTC)

There are various kinds of domestic wiring. Suggest you read the article.--Shantavira|^{feed me} 15:40, 10 July 2012 (UTC)

'Non-metallic-dry' or NMD is the common wire used for woodframe in Canada. Most only count the insulated conductors though so 14/2 NMD would be 14 guage, (15 amp), black, white and bare ground. 14/3 has a red. Don't use heat trace cable though. I heard about a guy that stole a bunch of wire from work and wondered why is walls got warm and none of his stuff worked very well.--Canoe1967 (talk) 18:29, 10 July 2012 (UTC)

Why wasn't there fusion in the early evolution of the universe?

The strong nuclear force existed only a few fractions of a second after the Big Bang, and only a few fractions of a second later protons formed. So what was stopping the universe from undergoing fusion at around this time since presumably the required heat and pressure was present? 148.168.40.4 (talk) 16:01, 10 July 2012 (UTC)

According to the article, most helium-4 in the universe is thought to trace back to fusion "shortly after the Big Bang". See Big Bang nucleosynthesis. From 3 to 20 minutes after the Big Bang, protons and neutrons were stable, but fusion was still possible. Wnt (talk) 16:11, 10 July 2012 (UTC)

Too much heat and pressure was present. It's basically the same reason why million-degree-Celsius steam does not condense into ice. Looie496 (talk) 16:13, 10 July 2012 (UTC)

Wnt is right. There was fusion during the Big Bang nucleosynthesis. 203.27.72.5 (talk) 21:57, 10 July 2012 (UTC)

Yes, but, as Wnt said, not until around the 3 minute mark. The OP was asking about fractions of a second after time zero. The answer is that it was simply too hot for fusion then -- if anything fused together for an instant, something would slam into it and break it apart an instant later. Looie496 (talk) 22:58, 10 July 2012 (UTC)

It's an interesting question, and I don't really know enough to answer. But my understanding from the article is that first the quark-gluon plasma cooled down, but even then proton-antiproton pairs were being produced spontaneously at 10^-6 second, maybe later. So you don't have the situation where a cooling quark-gluon plasma would spit out intact iron nuclei because they're the most stable degradation product; they'd get hit instantly by antiparticles (indeed, almost always would contain antiparticles...) and be blown apart. At the latest point, right before the pairs stop being produced, there should only have been enough energy to make single nucleons, not alpha and anti-alpha pairs and such. After that, Looie's answer applies. I assume three minutes is when there was too little energy left to knock helium atoms apart, and twenty was when there was too little left to knock them together. (For comparison, consider how high temperatures favor production of nitrogen oxides, and lower but not too low temperatures resolve them to nitrogen and oxygen in a catalytic converter) Wnt (talk) 13:17, 12 July 2012 (UTC)

Electromotive force in an unclosed circuit

Even if an electric circuit is unclosed, the source of voltage continues to work — and the energy that would move the charges in the circuit, had the circuit been closed, is still there.

What resists the emf in an unclosed circuit? Intuitively, the gap in the circuit can be viewed as a resistor with infinite resistance that would imply infinite energy loss, had the current not been zero. But Ohm's and Joule's laws are abstractions. What's their physical sense at the ends of the gap, in terms of individial charge carriers (e.g. electrons)?

And what happens in the circuit, in the immediate vicinity of the gap, in the first moments after it is closed (e.g. by connecting wires or flipping a switch), enabling the flow of current? How do the charges flow and how does the information that the circuit was closed propagate from the gap to the circuit as a whole? - Sikon (talk) 16:53, 10 July 2012 (UTC)

Close circuit: electrons bounce back. Open circuit: electrons stop bouncing back. 188.76.173.109 (talk) 18:16, 10 July 2012 (UTC)

The free electrons have nowhere to go, so stay in the wire, until connected to another wire, then they flow into it. The charge in the wire (modeled by the percentage of free electrons) is equal to that of the source, say the battery terminal, so all flow stops. StuRat (talk) 18:25, 10 July 2012 (UTC)

At the level of the electrons, its best to analyse the situation using electric potentials and the "lines of force" along the gradient of the potential. The electric potential at a point is a measure of the energy at that point due to electrons and protons around it attracting and repelling any charge placed there. In a conductor like a metal, if no current is flowing, the potential all over its surface is the same; the electrons which are free to move jostle around so that no point is more crowded than another.

When a switch is open, the two metal contacts are at slightly different potentials - one is more crowded with electrons than the other. However, the electrons are bound to the surface of the metal (because of the metal nuclei) and it takes some energy for them to escape -either as free electrons or by jumping onto the air molecules and forming ions. If the voltage (electron overcrowding/shortage) is low enough, no electrons can escape from one surface to another. If the voltage is sufficiently high some of them will break out of their bonds and move between the metal and the air molecules. These air ions will zoom away from the metal surface, gaining speed as they are repelled and smash into more air molecules as they go to the other metal surface. In short order you will have a white hot stream of ions and electrons tearing across the gap. This is a spark.

As soon as the gap is closed, electrons from the more crowded side flow into the less crowded metal. (The electric field from these new electrons travels to all corners of the universe at the speed of light. But this field of course dies of as 1/distance-squared with the constant of decay depending on dielectric shielding by things in the way.) These electrons push the electrons around them, who in turn push the electrons around them and so on, letting the electrons at the far end of the wire flow out. In most wires, the electrons are packed so tightly and can move so rapidly that the effect is instantaneous. The time taken for the bunched-electron wave of information to travel down a line can be significant if you turn the switch on and off fast enough- for example in radio transmission.Staticd (talk) 19:01, 10 July 2012 (UTC)

We answered a similar question about Surface charges on an open circuit recently. DriveByWire (talk) 21:45, 10 July 2012 (UTC)

What causes a material to reflect light and why does light travel slower through matter than vacuum?

• What causes some materials to reflect light (metals for example)?
• What causes different materials to have different refractive index (i.e. light waves travel at different speed through it)?

85.230.137.182 (talk) 18:46, 10 July 2012 (UTC)

The article Refractive index gives a microscopic explanation of the slowing of light. DriveByWire (talk) 21:52, 10 July 2012 (UTC)

Light speed is around 186,000 miles per second in a vaccuum, or some such. I wonder, what is the slowest speed that light has ever been measured - and whether it's possible to slow it down even more. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:59, 10 July 2012 (UTC)

See slow light. 203.27.72.5 (talk) 23:07, 10 July 2012 (UTC)

That's a different kind of slowness than the refractive-index aspect. DMacks (talk) 03:09, 11 July 2012 (UTC)

Not being a scientist, I didn't totally follow the article, but it basically answered my question. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:50, 11 July 2012 (UTC)

There is a touching story about a scientist who invented a slow glass through which light takes over a year to pass. He tested panes of the glass in his house and afterwards spent many days in the garden, occasionally looking up and waving. The explanation is that his wife had died the previous year. DriveByWire (talk) 14:33, 11 July 2012 (UTC)

That sounds like Light of Other Days by Bob Shaw. Gandalf61 (talk) 14:49, 11 July 2012 (UTC)

The reflection in a metal is basically because it conducts electricity. The electromagnetic wave in the light causes electric current to run on the surface of the metal. An electric field cannot exist parallel to the metal surface, and yet the light wave would normally have one. The net result of this is another light wave that bounces off in just the right direction for a reflection with the phase altered to cancel out that electric field. Graeme Bartlett (talk) 08:26, 11 July 2012 (UTC)

That sounds utterly wrong to me. I'm pretty sure that EMR does not induce a current in metal that it is incident on. This would also imply that all conductive materials are reflective, which they aren't. And what's so special about the visible spectrum in all of this anyway? Why should x-rays not induce a current in metals and reflect throught that mechanism if visible light does? 101.173.85.81 (talk) 09:26, 11 July 2012 (UTC)

Certainly currents are induced (in a perfect conductor, they are only surface currents); see also penetration depth. The visible spectrum is special because at higher frequencies the electric currents induced fail to precisely match the phase of the incident radiation, so absorption results instead; see also plasma frequency. --Tardis (talk) 13:20, 11 July 2012 (UTC)

Specular reflection#Explanation and Fresnel equations. DriveByWire (talk) 14:40, 11 July 2012 (UTC)

See the article on Plasmons--78.150.236.161 (talk) 19:52, 11 July 2012 (UTC)

Mysterious behavior of high-speed projectiles

Is it possible that a bullet (gun-shot) fired from a high-velocity rifle (say M-16 etc.) instead of entering the human head, orbit around it, breaking it's move-in-a-straight line rule and enter the skull from back side (opposite side , not available to gunner ) i.e. changing it's course of movement. If yes, then what laws of physics make it possible ? 124.253.91.183 (talk) —Preceding undated comment added 21:27, 10 July 2012 (UTC)

Unless the gun is actually firing very small, maneuverable rockets, no. What made you ask the question? Someguy1221 (talk) 21:32, 10 July 2012 (UTC)

I know it sounds idiotically strange ! I am asking this question because it has happened... — Preceding unsigned comment added by 124.253.91.183 (talk) 21:38, 10 July 2012 (UTC)

If so then you have already answered your own question "Is it possible....[?]". The article Orbit equation gives the physical laws that govern a gravitational orbit. I think it impossible to satisfy them with practical values for the bullet mass, head mass and bullet tangential velocity. The value of Escape velocity would surely be exceeded. Might the incident have actually been an accident with a Boomerang? DriveByWire (talk) 22:11, 10 July 2012 (UTC)

The 5.56 NATO round fired by AR-15 family rifles was known as the tumbler during the Vietnam war due its strange terminal ballistics. After striking flesh the bullet would move in counter-intuitive directions leading to exit wounds where you wouldn't expect them. A vet once told me a story about seeing a dead VC with a single entry wound near his navel, and a single exit wound near his collar bone. 203.27.72.5 (talk) 21:53, 10 July 2012 (UTC)

Intriguing. Do you happen to have a source or remember if they determined the compositional elements of the rounds that caused this uncommon ballistic profile? I'd be very interested in studying the issue since our current article on the round does not make mention of it (though it does note an unusually high degree of fragmentation for the round's mass and profile). Was the issue prevalent with regard to the M-16 or particular firing modes? Snow (talk) 00:18, 11 July 2012 (UTC)

No reliable sources, but here is a forum thread that basically confirms the same story my vet friend told me. As the posters note, having the centre of mass towards the rear increasing the chance of tumbling on contact with a medium denser than air. 7.62x39 are even worse. They often start to tumble end over end without impact with anything. You know this is happening when your bullet holes look like this. 203.27.72.5 (talk) 00:46, 11 July 2012 (UTC)

Thanks for the link (and actually there does seem to be some decent literature linked to there). And yeah, that explanation seems consistent with the yaw and accuracy issues that are noted on our 5.56 NATO article. I wonder how much the tumbling itself contributes to the fracturing or if they are better characterized as both the result of the round's center of mass. I'll peruse the literature and see if I can't find a way to note this behaviour as a brief mention in the relevant articles. Thanks again! Snow (talk) 01:03, 11 July 2012 (UTC)

I suspect that you are merely confusing the entrance and exit wounds. While, typically, the entrance wound is smaller than the exit would, that's not always the case. StuRat (talk) 22:08, 10 July 2012 (UTC)

That sounds like an element of a conspiracy theory, namely one related to the JFK assassination. Plusanother (talk) 22:07, 10 July 2012 (UTC)

A bullet found on Connally's hospital gurney, and two bullet fragments found in the presidential limousine, were ballistically matched to a 6.5 × 52 mm Italian Carcano M91/38 bolt-action rifle found on the 6th floor of the Texas Book Depository. The M16 fires a different 5.56×45mm cartridge, and there were not many M16's around on November 22, 1963. Obviously the existence of an M16 bullet that can fly backwards in space and time, and leave no trace, is exactly the kind of secret that a conspiracy of the CIA, the KGB, the American Mafia, the Israeli government, FBI director J. Edgar Hoover, sitting Vice President Lyndon B. Johnson, Cuban President Fidel Castro, anti-Castro Cuban exile groups and the Federal Reserve won't reveal. DriveByWire (talk) 22:46, 10 July 2012 (UTC)

You forgot the Rothschild and Rockefeller families and the Bilderberg Group. They are into this too, pushing the ropes from behind the scene. Plusanother (talk) 23:09, 10 July 2012 (UTC)

I've talked about gunshot wounds with a lawyer at some length, some time ago, and one point he emphasized rather emphatically is that bullets can behave extremely unusually once inside the human body. It's not weird physics, it's the fact that ammunition does not always have sufficient force to break out of the body at all points, and will hit various hard and soft things inside the body, and can do weird things like follow bones (get shot in the arm, exit wound out the leg, was one example the lawyer had seen). No weird physics there — just chaotic movement and complex systems. So, just a priori, I wouldn't rule it out, though it doesn't seem especially likely. But given enough gunshot wounds... --Mr.98 (talk) 00:23, 11 July 2012 (UTC)

There's also a simple ricochet, where the bullet could bounce off an object behind the target, say a tree, and hit the target from the rear. This could be the entire bullet, or just a fragment, if it shatters when hitting the first object (more likely if it first hit a rock). StuRat (talk) 00:29, 11 July 2012 (UTC)

Mystery solved? In all seriousness, OP, this behaviour is inconsistent with the basic physical principals we'd expect to be at work here - as noted by others above, the gravitational influence of the mass of the head upon the bullet would be miniscule compared to its forward velocity of the round -- nor could atmospheric resistance account for such a radical arc in said trajectory. Snow (talk) 01:16, 11 July 2012 (UTC)

Weirder yet was the soldier that got shot though his privates during the civil war. The musketball carried on and hit a female civilian in the abdomen and she got pregnant from it. I think they got married after the war when they figured out what happened.--Canoe1967 (talk) 15:50, 11 July 2012 (UTC)

Never happened. Someguy1221 (talk) 16:02, 11 July 2012 (UTC)

It did happen, it was Dilbert, a robot, a cow, and some aliens, though. μηδείς (talk) 16:34, 11 July 2012 (UTC)

But wasn't Dilbert getting shot at from the rear anyway? [14]--Aspro (talk) 23:03, 11 July 2012 (UTC)

I saw a murder trial in which someone killed a man with two shots to the head from a 32 caliber pistol. One round entered under the scalp on the side of the head, and tunneled around from the side of the head to the back of the skull, where it lodged in the neck muscles, but unlike the OPs incident, it did not proceed to break through the skull in the back, but at least it ended up in the right spot to do so if it still had sufficient velocity and tumbled the right way. Edison (talk) 20:18, 11 July 2012 (UTC)

July 11

Dangerous Good Classification

I've been asked to determine the amount of soluble lead in a mixture of minerals in order to work out its Dangerous Goods Classification. The method is predefined and straight forward, but I'm trying to work out for my own interest how the results of this test enable us to classify the mixture. I'm told that if the concentration of soluble Pb exceeds 5% of the dry mass, then the material is a Class 6.1: Poison. But that class is actually defined as having an oral toxicity of equal to or less than 200mg/Kg in an animal. So I don't see how the 5% number is anything more than an arbitrary cut off. Does anyone have any idea how this works, or better yet actual experience with classifying class 6 dangerous goods? 203.27.72.5 (talk) 04:39, 11 July 2012 (UTC)

Well, the higher the percentage of lead, the less you'd need to consume to be poisoned. Presumably more toxic substances would be considered poisonous in lower percentages, so the total amount you would need to consume to be poisoned is the same in both cases. I'm not sure why they chose 5%, though. They must have some idea in mind of how much a person (a toddler, a person with pica, etc.) might reasonably consume. StuRat (talk) 05:47, 11 July 2012 (UTC)

It's not lead as such though. It's soluble lead. Total lead doesn't even come into it (and it's well over 50% for many of these materials). Is there a known LD50 of "soluble lead" of around 10mg/kg? 203.27.72.5 (talk) 05:55, 11 July 2012 (UTC)

Looking at a variety of material safety data sheets, it does seem that the LD50 for aqueous lead is ~10mg/kg in rodents. The precise number varies wildly depending on precisely how the lead has been solubilized. The most lethal forms of lead appear to be those bound to organic compounds. Acute LD50s are missing from MSDSs for simple lead salts, although they include doses that cause illness over time, which is actually quite low. Someguy1221 (talk) 07:41, 11 July 2012 (UTC)

Can you tell me what compounds you're refering to so I can look up the MSDSs? This is most definitely an inorganic lead species, most likely a mixture of PbS, PbSO4 and maybe some oxides. 101.173.85.81 (talk) 09:22, 11 July 2012 (UTC)

Heavy metals accumulate in tissue, so you can't use LD50 here. "CDC considers a blood lead level of 10 μg/dL to be a level of concern for children. EPA limits lead in drinking water to 15 μg per liter."[15] This is not medical advice. You should consult a trained professional toxicologist for your question. 71.212.249.178 (talk) 17:03, 11 July 2012 (UTC)

Actually telling the poster how to categorize a good for shipping isn't medical advice, it's legal advice - still, unfortunately, beyond our purview. However, it sounds like the OP is asking for an explanation of the reasoning behind this rule, not help in figuring out and applying it. My assumption is that the 5% figure is by weight, and so the rule tells you how much soluble lead there is in a given weight shipped. If what's being considered is how much lead will leach into the soil around a crash scene if firefighters hose down the burning package, then I suppose that's sort of reasonable if you're considering the fire as being of some set size in terms of mass. If it's the damage done if the stuff pours out of a hole in the package and a kid skateboarding around the company's loading dock face-plants into a pile of it ... less so, but anything more realistic might be too bureaucratically challenging for all involved. Wnt (talk) 18:25, 11 July 2012 (UTC)

To clarify, I'm not the one working out the dangerous goods classification. I'm just providing data to someone, who is passing that data to someone who is working it out. As Wnt said, I'm just interested in how they got the 5% figure from the actual definition. The LD50 is prescibed in the definitions, so if you want to argue that it's not important and we should look at chronic toxicity, take it up with the United Nations Economic and Social Council. It looks like Someguy hit on it above, but I'm still waiting for him to let me know what compounds he looked at the MSDSs for. You don't need to assume that the 5% figure is by weight, I gave that in the statement of the question "5% of the dry mass". And leaching into soils, etc. sounds more like criteria for Class 9: Environmentally hazardous material (although the wikipedia article on that is a bit vague). I don't think specific, plausible scenarios come into it really. It's "just how toxic is it?", not "how likely is it that some one will eat it?". 203.27.72.5 (talk) 20:36, 11 July 2012 (UTC)

Bell / clapper

I have a long case grandfather clock which chimes in a rather tinny way. How can I improve its voice? Kittybrewster ☎ 11:02, 11 July 2012 (UTC)

Such clocks need regular cleaning and lubrication, but there are fragile parts and delicate adjustments so don't just attack it with oil or WD40. You could cause a lot of damage if you're not careful. Having said that, before calling a professional I would visually inspect the mechanism to ensure it is clean and that the hammer(s) and gong(s) (it's unlikely to be a bell and a clapper) are moving smoothly and not fouling anything. The hammer should only touch the gong momentarily, not come to rest on it. If there is a pad on the hammer it might need replacing.--Shantavira|^{feed me} 11:44, 11 July 2012 (UTC)

On this page you can hear grandfather clock chimes and identify your own, probably the Westminster chimes. Here is a video that shows the chiming mechanism of an (unspecified) grandfather clock receiving attention. If yours is like this, check that the tubular bells hang freely. Other videos on the linked YouTube page give insights into other types of clocks. DriveByWire (talk) 14:16, 11 July 2012 (UTC)

You may also have spiderwebs, dust bunnies, or even a crack in one of the noise making parts.--Canoe1967 (talk) 15:42, 11 July 2012 (UTC)

Can you identify what's wrong with the sound ? Different sounds may indicate different problems:

1) Short decay: If the sound quickly stops, this could be a sign that it just needs cleaning, as all that dust may dampen the sound. Or, perhaps the gong is attached to something which absorbs the sound too quickly, like wood. This could be the result of a poor repair job.

2) If you are hearing multiple strikes instead of one, then either the hammer is hitting more than once or the gong is hitting something else.

3) Out of tune: Likely because the mass of the gong is off. Again, this could be due to a poor repair job, say if they attached it with a different fastener than the original.

4) Buzzing: Could indicate a crack in the gong, in which case it would need to be replaced (they could try repairing it, but it will probably never sound quite right). StuRat (talk) 17:58, 11 July 2012 (UTC)

Ant evolution question

First and foremost I want to make it clear that I accept evolution as a fact. Just have a specific question about it.

I heard that ants evolved from wasps and that certain traits such as stingers which they inhereted from wasps do show up in certain species of ants. So if this is true, it stands to reason that the genes that code for those stingers should be homologous to the genes that code for the stingers on wasps. My question is, are they in fact homologous? My other question is, are ant wings also coded by homologous genes that code for wasp wings? 148.168.40.4 (talk) 14:52, 11 July 2012 (UTC)

Our article Ant says "Ants evolved from a lineage within the vespoid wasps.", so what you heard is apparently true. I don't know the answers to your questions for sure, but I would take it that pretty well all insect wings are homologous, and I would think the stings are too. But you need to be careful about your terminology. When you say "are ant wings also coded by homologous genes", this is a misleading simplification: a structure as complicated as a wing will be coded by a huge number of genes, many of which will also control other things quite unrelated to wings. I'm sure there are particular genes without which wings will not form at all, but that does not mean that those particular genes 'code for wings'. --ColinFine (talk) 16:12, 11 July 2012 (UTC)

The only way the genes wouldn't be homologous would be if the structures were lost entirely and then reevolved from scratch. Even then, if they still existed, the same genes might be used over again to form the new structures. In this case the animals are so closely related and the structures so conserved there is no question of their not being homologous. μηδείς (talk) 16:27, 11 July 2012 (UTC)

Nesting for clarity, not replying to Colin, heh

I don't know if there have been any attempts at mapping ant or wasp genomes and comparing them (AFAIK, only fruit flies have been studied that extensively), but yes they are. We don't need to examine their genes to know that they are homologous every time (since we're not even that savvy yet at identifying specific genes). Most of the times comparative morphology and developmental morphogenesis is more than enough. See our articles for Body plan, Hox genes, and Evolutionary developmental biology. In the same way that human and chimpanzee hands are obviously homologous, so are ant and wasp (and other Hymenoptera) wings and stingers (and legs, and eyes, and jaws, etc.).

Note that despite popular misconception, ant "stings" are from the abdomen, not from bites. And these stings can range from being delivered by piercing or being sprayed directly at an opponent. Nevertheless, both ant and wasp stings come from the same structure also present in other insects, albeit highly modified - the ovipositor. And they still function as such in some species.

Wings are a special case as they can evolve to be suppressed partially or wholly during development by genetic or environmental "switches". A phenomenon known as polymorphism (as in human sexual dimorphism). In most ants polymorphism is exhibited by "castes" where sterile female workers and soldiers are all wingless while the fertile queen and males are winged (at least temporarily). In wasps, some extreme examples are in the family Mutillidae, better known as velvet "ants", whose females are wingless and resemble ants while the males remain winged. Same thing with the chalcid wasps, whose males may sometimes even be neotenic, retaining wingless worm-like forms with the sole purpose of mating with females before the females leave the hosts.

Rest assured, like Colin said above, all wings of all insects (not just ants and wasps) are homologous, even in cases where the wings may be reduced to only one pair (with the hindwing having evolved into knob-like balancing structures known as halteres in Diptera, or the forewings being modified into protective armored coverings known as elytra in Coleoptera) or absent altogether. See also Insect wing (particularly the section on its evolution and morphogenesis).

Lastly, all ants today evolved from a single ancestor, but you must understand that like how humans did not evolve from chimps, ants as well did not evolve directly from modern wasps. Instead they both share a common wasp-like ancestor. The ancestors of ants, wasps, and bees diverged from each other at around 160 million years ago. Ancestors of eusocial ants and wasps in turn diverged from each other at around 140 to 110 million years ago. The oldest known ant fossil is the Cretaceous Sphecomyrma freyi preserved in amber from ~80 million years ago. Like its name suggests, it was more like a "wasp-ant" in that though it was indisputably an ant (possessing the metapleural gland unique to ants) it also exhibited characteristics which are undeniably from wasp-like ancestors (which includes a retractable sting, among others).-- OBSIDIAN†SOUL 16:27, 11 July 2012 (UTC)

List of sequenced animal genomes#Protostomia - Several insects have had their genomes sequenced, including several ants and wasps. Unique Ubiquitous (talk) 16:34, 11 July 2012 (UTC)

There's a certain amount of philosophy involved in homology, and so peculiar details emerge. For example, Diptera and Strepsiptera both have a pair of wings, they both probably have the vast majority of the controlling genes in common... problem is, one has forewings and the other has hindwings, with the others greatly reduced. So if you look into the genetics you'll find Ultrabithorax has different effects on these wings, even though at first glance it looked like a homologous network. Evolution does that a lot, and not always in ways you can see - it can duplicate a gene, use two copies for a while, then one lineage gets one copy and the other gets the other and you're left scratching your head trying to figure out why the genes diverged from one another so much sooner than the animals you're studying. Wnt (talk) 18:15, 11 July 2012 (UTC)

Regarding 'ant "stings" are from the abdomen, not from bites', I suppose it can be a bit of both e.g. Oecophylla majors haven't retained a functional sting but they do bite and spray the bite with acid from the end of their abdomen. It looks like this after a few seconds. Sean.hoyland - talk 18:53, 11 July 2012 (UTC)

The fantastic "helmets" of treehoppers are actually a third "wing" pair

I meant that the bite itself is not the one delivering the venom, as most people seem to have the misconception that the venom glands are located at the ant's mandibles like in snake fangs.

The bite-and-spray behavior is actually the norm in formic acid-spraying ants (formicines) when dealing with larger animals. While in others, like some myrmicines (e.g. fire ants and bulldog ants) and the primitive ponerines (e.g. trap-jaw ants), they only bite (if at all) to gain a foothold, while injecting the venom (not spraying, though the organs responsible are both derived from ovipositors) with functional stingers. The venom of the latter two subfamilies are also more similar to venom used by wasps, and are often extremely painful and in some cases medically significant.

Also, in addition to Wnt, there's also an ancestral third wing pair attached to the first segment of the thorax, which has since been lost in most modern insect body plans. It reappeared among treehoppers as their "helmets" (see picture). Insects, like most higher animals (including humans) are derived from repetitive body segments that later became modified and/or fused as they evolved to become more specialized (traces of that is evident in our embryonic stages). Ancestral insects therefore actually had one pair of "wing" appendages for each body segment (though they were not wings then, of course). They were eventually suppressed by Hox genes (like the previously mentioned Ultrabithorax) for all body segments except two, which eventually became used for flight. Except for treehoppers, apparently, which somehow broke the mold. And given that a third pair was more or less superfluous when it reappeared, evolution got creative with it instead. :P -- OBSIDIAN†SOUL 22:22, 11 July 2012 (UTC)

Air Conditioning

Regarding energy usage to cool a home, are the following two situations equivalent?

• 1 Outdoor temperature = 80º and indoor thermostat & temperature = 72º
• 2 Outdoor temperature = 81º and indoor thermostat & temperature = 73º hydnjo (talk) 15:09, 11 July 2012 (UTC)

No, but many methodologies will consider them "approximately" equal. We have an article on degree days, which links to many related concepts. Nimur (talk) 15:29, 11 July 2012 (UTC)

Both situations have an 8º differential so if they are not equivalent then which will require more energy to maintain? hydnjo (talk) 17:15, 11 July 2012 (UTC)

I suspect that the lower temperatures will require ever so slightly more energy, considering that to go from 8 degrees above absolute zero down to absolute zero would require an infinite amount of energy. StuRat (talk) 17:46, 11 July 2012 (UTC)

True. See Carnot engine for the formula, which is indeed based on a ratio of temperatures in kelvins. That formula describes how much energy you can extract by reversing the process, which for a perfect air conditioner is theoretically equivalent. A specific, real air conditioner, with real coolant with a real boiling point, will act differently from that, however, and I can't tell you how. Wnt (talk) 18:01, 11 July 2012 (UTC)

In general, engines work at higher efficiency in a lower ambient temperature, so the air conditioner working in 81 degree weather is slightly less efficient. The inside temperature change gives the target amount of energy which has to be spent, which simply requires it run a certain amount of time, and is not relevant to the efficiency of the engine sitting in the unchanging heat outside the window. Strictly speaking, the heat capacity of air does change by a very small amount, so the amount of energy needed to be expended will differ as the cooler air has a higher heat capacity. This is no where near the difference you run into at the heat of condensation of the boundary conditions of solidification or absolute zero. There is no way to calculate which is greater, the better efficiency or the greater work at the lower temperature, without the specifics. But my gut feeling is the difference in efficiency will be higher, given most air conditioners are inefficient, and it will take more input energy to cool from the higher temperature. μηδείς (talk) 20:08, 11 July 2012 (UTC)

• Think the answer here lays in the laws of Thermodynamics. As one learns when at school: it is easier to add heat to something that is already hot than to something that is cold – thus the revers is true also. So, as the temperatures drops (regardless of ∆t remaining constant) the efficiency must drop. Ergo, case 1... “Outdoor temperature = 80º and indoor thermostat & temperature = 72º” will require more energy to maintain the same temperature differential (∆t) than case two. --Aspro (talk) 22:35, 11 July 2012 (UTC)

I think, Aspro, you might be thinking about the heat of fusion of ice, which much requires more energy to melt a solid liter of ice entirely to water at a constant 32 degrees than to raise a liter one degree from 32 degrees to 33. There is no law that says it is easier to heat hot things than cold ones. That being said, according to Thermal efficiency air conditioners aren't strictly rated by efficiency, since they are not heat engines. μηδείς ([{User talk:Medeis|talk]]) 01:50, 12 July 2012 (UTC)

Case 1 (80/72) is essentially the more efficient for refrigerative airconditioning. This is partly because of the charecteristics of compressors and refrigerant fluids, and partly because the saturation moisture contaent of air is less at lower temperatures - saturation conditions exist at the evaporator, thus less work is done removing moisture at lower temperatures. Manaufacturers of compressors provide curves of efficiency vs evaporator and vs condensor temperatures in their application datasheets - these always show greater efficiency at lower temperatures. However, in practice you can get some anomallies as the compressor is normally cycled on and off by the thermostat. Each time the compressor is started, it works inefficiently for a while until refrigerant conditions are stabilised. Ratbone58.167.247.229 (talk) 02:05, 12 July 2012 (UTC)

Neutralize soap?

What's the most effective way to neutralize liquid soap that has been spilled inside a rucksack (unwashable) ..? Electron9 (talk) 18:44, 11 July 2012 (UTC)

Does 'unwashable' mean it can't get wet or can't handle the punishment of a machine? If it can handle warm water you could just soak it until the soap dissolves and dilutes. The warmer the water the faster it will work. You could try dry cleaning but that may be a cost issue. If there is perfume in the soap that may last longer but should go away by September when school starts.--Canoe1967 (talk) 18:57, 11 July 2012 (UTC)

It means it should not be put in a machine because the water protection may suffer. And the protection may have chemical components that I don't want in the machine. So I thought about something chemically better than plain hot water. Electron9 (talk) 20:33, 11 July 2012 (UTC)

In that case, you can go ahead and machine wash it, then spray it with water-proofing agent after it dries. (You should be able to buy that at a shoe store.) StuRat (talk) 20:36, 11 July 2012 (UTC)

Does unwashable mean unsoakable and unrinsible? 71.212.249.178 (talk) 19:07, 11 July 2012 (UTC)

I'd first physically remove as much as possible, with a sponge. Then soak it, say in the tub. You may need to drain the water and replace it several times, until you stop seeing suds. Tumble dry on low heat. (If you literally have a rucksack that falls apart if it gets wet, on the other hand, then throw it out and get a better one.) StuRat (talk) 19:11, 11 July 2012 (UTC)

If it has leather parts you may wish to treat those with leather water-proofing, etc. first. Can you get a manual for your pack or a similar one that says how to treat the leather?

The number one best chemical to neutralize soap is water. Think about it. What other kind of substance could you imagine that isn't it self going to be a pain (or require water) to remove? Vespine (talk) 22:51, 11 July 2012 (UTC)

To answer your hypothetical, an oil-based substance may be appropriate, especially if the rucksack is leather. Special leather oils are good for leather, and any greasy substance in sufficient quantity will neutralize a soap. I don't recommend blindly attempting this solution in the example at hand, though. BigNate37_(T) 22:54, 11 July 2012 (UTC)

Make sense as soap decomposes flesh which protect itself with.. oil. The question is then what amount and type of oil. The rucksack is made with textile. Electron9 (talk) 04:05, 12 July 2012 (UTC)

If it's textile, then just use water. Otherwise you'll need soapy water to get the oil off it anyway. 203.27.72.5 (talk) 04:11, 12 July 2012 (UTC)

Why are commercial aircraft round?

Couldn't all the Boeings and Airbuses be less like a cylinder and more flat? It seems to me that lots of space gets lot due to this cylindrical form. OsmanRF34 (talk) 22:15, 11 July 2012 (UTC)

A round cross-section is the strongest shape, anything ovular would require stronger materials to achieve the same structural integrity. This may be the reason they are round: to minimize structural mass. Granted, I am not an aerospace engineer, nor close to it. BigNate37_(T) 22:28, 11 July 2012 (UTC)

It's not just structural integrity, but also the ability to stand the overpressure of maintaining close to one atmosphere at a height where ambient air pressure is only ~20% of normal. --Stephan Schulz (talk) 22:32, 11 July 2012 (UTC)

How is the ability to tolerate overpressure any different to structural integrity? 203.27.72.5 (talk) 22:39, 11 July 2012 (UTC)

Is that why combat aircraft pilots are often seen to be using a breathing apparatus? I.e., to allow the cockpit to have less of a pressure differential without affecting the pilot, because they are too small to be perfectly round? BigNate37_(T) 22:36, 11 July 2012 (UTC)

Note that they are not perfectly round and are slightly oval in shape. The Embraer E-170 for example is 3.35m high and 3.01 meters wide. 203.27.72.5 (talk) 22:38, 11 July 2012 (UTC)

Wide-body aircraft like the Boeing 747 and Airbus A380 are far from round. 203.27.72.5 (talk) 22:49, 11 July 2012 (UTC)

Cross-section comparison of Airbus A380 and Boeing 747-400

— Preceding unsigned comment added by 203.27.72.5 (talk) 22:51, 11 July 2012 (UTC)

They're shaped like beer cans for the same reason. Hcobb (talk) 22:41, 11 July 2012 (UTC)

I'd question two premises. One, I highly doubt much space is wasted at all in a modern jet liner. There's an incredible amount of stuff that gets packed into that cylinder. Two, it's not really "space" that is the issue anyway, it's more about weight. Anything that "looks" like wasted space is probably required for access. Don't forget that just about every single component in the plane must be able to be inspected and replaced if required at some stage, so packing everything as tight as possible to save "space" doesn't sound like a great idea for more then one reason. Vespine (talk) 22:47, 11 July 2012 (UTC)

Just to second what Vespine said, those "wasted" spaces are filled with things like ballasts and fuel tanks that can take just about any shape you like. The space in a modern airliner is used with efficiency you're not likely to see anywhere else, unless you happen to be flying a bit higher. 203.27.72.5 (talk) 23:01, 11 July 2012 (UTC)

Actually, to slightly contradict part of what Vespine said, space is a major issue in addition to weight. Drag is (generally speaking) inversly proportional to density, so unused "wasted" space (if it actually existed) would lower the average density of the aircraft and increase drag. This is obviously all from an initial design of the aircraft perspective. I'm not suggesting that existing aircraft could fill in those gaps with extra passengers' luggage to reduce drag :). 203.27.72.5 (talk) 23:22, 11 July 2012 (UTC)

I didn't say aircraft are cylindrical, just like a cylinder. Another point: there is less wasted space because commercial aircraft combine cargo (not related to the passengers flying in it) with passengers as best as it gets. But if it were more flat in the y-axis, you could reduce the cargo space and put more people into it. The resulting aircraft would look more like a big wing (and you could have shorter wings). It's clear to me that there are lots of calculations and reasons for the shape that aircraft have, but I'd be happy with a couple of hints. OsmanRF34 (talk) 23:30, 11 July 2012 (UTC)

Something else to consider is the comfort factor in each seat. In the Airbus 380 diagram above, it looks like tall outside passengers on the upper deck will have their necks bent by the fuselage wall. Passenger comfort alone would dictate a rounded square cross section be used, but anyone who has ever been on an airplane can attest that passenger comfort is obviously only a minor concern. StuRat (talk) 23:53, 11 July 2012 (UTC)

Well maybe not anyone. To quote one airline passenger, "If you travel as much as we do you appreciate the improvements in aircraft design of less noise and more comfort – provided you don't travel in something called economy class, which sounds ghastly." 203.27.72.5 (talk) 00:49, 12 July 2012 (UTC)

Size of Earth's orbit last 2000 years

Has the size of the Earth's orbit around the Sun changed significantly in the last 2000 years, as this article says? Bubba73 ^{You talkin' to me?} 22:58, 11 July 2012 (UTC)

See Earth's orbit. But here's the spoiler: no it hasn't. 203.27.72.5 (talk) 23:02, 11 July 2012 (UTC)

Thanks. I thought that it hadn't changed that much in 2000 years, but I don't see anything in that article addressing it. Bubba73 ^{You talkin' to me?} 23:26, 11 July 2012 (UTC)

The paper that is described by that Daily Mail article is freely available here. The Daily Mail article is misleadingly worded. Even though the Earth's orbit has not changed significantly, the precession of the Earth's axis combined with the elliptical shape of its orbit has caused a small change in the distance from the Sun during June-July-August, and that's the change that the authors invoke to account for their data. Looie496 (talk) 23:26, 11 July 2012 (UTC)

(See our article on Milankovitch cycles for more information.) Looie496 (talk) 23:35, 11 July 2012 (UTC)

Airliner cabin air

Does the air in an airliner cabin recirculate, or is there some mechanism to exchange it with outside air without losing the cabin pressure? 203.27.72.5 (talk) 23:14, 11 July 2012 (UTC)

Humans exhale carbon dioxide (and depending on the in-flight meals... other gases too). This has to be got rid of so stale air gets bleed off. Therefore, air can not be recirculated. The banning of smoking also meant that the amount new air added to the cabin could be reduced -thus saving the costs of pressurizing greater amounts of air to keep the interior atmosphere agreeable. To save more costs, they also reduced (in the last decade), the cabin pressure – but to the detriment of passengers suffering from emphysema and other medical conditions that low air pressure can aggravate. To counter the possible resulting in-flight emergencies from this new practice, some air-lines are now carrying portable automatic heart defibrillators on board -as if to say – we endeavour to take great care of our customers as always. I don't know what is better – a twenty cents cheaper ticket or free electric shocks.Also, On some air-line carriers you might also notice a very odd smell wafting over you. [16]--Aspro (talk) 23:42, 11 July 2012 (UTC)

Ah, are you sure about the trend in cabin pressure? The sources I've looked at seem to suggest the opposite. (See, for example, cabin pressurization.) The new Boeing 787 and Airbus A380 have effective cabin altitudes of 6000 ft and 5000 ft, respectively, significantly lower than the 7000-8000 ft seen on older aircraft. I suspect that you may be the victim of similar misconceptions about the quality of cabin air today versus a decade or two ago. The amount of air supplied per passenger hasn't changed much over the last forty years; if anything, the banning of smoking aboard aircraft has made the air cleaner for everyone: [17]. TenOfAllTrades(talk) 00:18, 12 July 2012 (UTC)

So, is it that some of it recirculates and some is bled off and replaced? And how does the mechanism work that replaces it? It must be some sort of compressor I take it. Does it work a bit like a ramjet or is it just a normal air compressor? 203.27.72.5 (talk) 00:35, 12 July 2012 (UTC)

The turbine engines that drive modern airplanes are giant air compressors. Air is bled from the compressor stage of the engine and cooled in a heat exchanger; and then it is fed into the cabin, both to keep it pressurized and to replace air that is vented from the cabin in the interests of eliminating carbon dioxide, moisture and odours. Some older airplanes, such as the Vickers Viscount, obtained their air for ventilation and pressurization from blowers - mechanical compressors attached to the engine. Dolphin (t) 00:45, 12 July 2012 (UTC)

Thanks. 203.27.72.5 (talk) 00:58, 12 July 2012 (UTC)

Resolved

July 12

derivation of the kintetic theory equation

Hello.

My question is related to the derivation of the equation pv=1/3nMwC^2. Most of the derivations I have seen assume that the average time between colisions, t, is 2l/Vx when l is the length of the cube. When assuming this, you actually assume that each molecule travel from one wall to the other wall at constant velocity without any clashes with other molecules. this is an unlikely assumption, yet those derivations do succeed. my quastion is - why? and where can i find more rigorous and accurate derivation?

I am sorry for my poor english...

Thanks in advance, 94.159.137.4 (talk) —Preceding undated comment added 06:54, 12 July 2012 (UTC)

Isn't the assumption really that the collisions with other particles are elastic? If it does elastically collide with any other particle, it transfers momentum which that particle then in turn transfers to the wall after exactly the same amount of time has expired. This results in the same net effect for the wall, so the predicted pressure is exactly the same. 203.27.72.5 (talk) 07:41, 12 July 2012 (UTC)

I thought about this interpretation, but I don't think it's true. It would be true only when moving particle collides with a static particle. Think about collision between two particles with same mass and opposite X-component velocity - They both would be stopped. 94.159.137.4 (talk) —Preceding undated comment added 09:20, 12 July 2012 (UTC)

If they stopped, the kinetic energy would be destroyed; so they can't stop as long as energy is conserved. Imagine two billiard balls colliding head on. They don't stop, they bounce back in opposite directions. 101.173.170.146 (talk) 09:34, 12 July 2012 (UTC)

Yes, you are right, my fault. Yet I would be happy to see a rigorous derivation. 94.159.137.4 (talk) —Preceding undated comment added 09:51, 12 July 2012 (UTC)

On matters of mathematical rigour, I'm the last one that should be commenting, but is the derivation at Kinetic_theory#Pressure_and_kinetic_energy adequate? 101.173.170.146 (talk) 10:56, 12 July 2012 (UTC)

No, because of reasons I wrote above. You can see this thread in physicsforums.com, which explains the problem clearly (especially on "loom91"'s notes), yet no complete answer was given. 94.159.137.4 (talk) 11:32, 12 July 2012 (UTC)

A more accurate derivation can be found in the book: "Fundamentals of Statistical and Thermal Physics", by F. Reif, secion 7.13 page 278 and further. It starts with the heuristic derivation, followed by an exact calculation. Note that in the heuristic derivation the formula you get contains the square of the average speed, while in the exact calculation, you get the correct expression containing the average of the squared velocity. Count Iblis (talk) 17:33, 12 July 2012 (UTC)

Oughterlony immunodiffusion

My question concerns the interpretation of Oughterlony immunodiffusion which I think it, the content in Wikipedia, can make people misunderstand some good points. For example Ag A contains two epitopes so called X and Y while Ag B contains epitope Z, if both Ags react with the mixed Ab which contains anti-X, anti-Y and anti-Z, the result should come out without any relationship (of identity, partial identity or non identity). Is that right? I think this technique was created before immunologist really understand about antigenic determinants. It originally is for study the relationship of each class of antibody. The content in the web can make people understand that the two Ags which are not relate to one another still give a result of non-identity. — Preceding unsigned comment added by 110.164.187.222 (talk) 12:05, 12 July 2012 (UTC)

You never posted an exact title as requested at Wikipedia:New contributors' help page/questions#Interpretation of Oughterlony's technique. Is this about Ouchterlony double immunodiffusion? I'm not qualified to discuss the topic. PrimeHunter (talk) 12:10, 12 July 2012 (UTC)

As explained at Precipitin, the antigen must be multivalent - if there's just one epitope per antigen, then it will react with an antibody, but it won't form a large gel-like complex; you'll have two dead-end epitopes stuck to one monomer antibody (four to IgE, ten to IgM - see antibody. I think F(ab')2 fragments are OK, but don't try to use Fab fragments. ;) ). Antibodies and antigens will ignore those that are not matches, so if you have two unrelated multivalent antigens, each should find its own favorite antibodies and form complexes with them somewhere or other, but ignore the other antibodies. That means that you could have multiple white lines, or even white lines crossing one another. Mix in a little bit of the right fluorescent antibody (or apply it to the gel afterward) and you could mark which is which in pretty colors if you want. Wnt (talk) 13:38, 12 July 2012 (UTC)

looking for a chart

from organogenesis

hi! i'm a biology student, taking a course in comparative anatomy. i am looking for a chart [or something similar], which will: show the origin of the organs [what came from the mesoderm, ectoderm, etc.], and maybe even more- like what originated in the neural crest.

thanks! — Preceding unsigned comment added by 212.76.110.252 (talk) 16:10, 12 July 2012 (UTC)

You should read the relevant articles. Also check out embryogenesis and organogenesis, whic is a stub, but which has the picture I posted. You'll probably do better with a google image search. μηδείς (talk) 16:41, 12 July 2012 (UTC)

do you have any idea which key words i should use? i am looking for something with more details- like the somits.

thanks again... — Preceding unsigned comment added by 212.76.110.252 (talk) 16:48, 12 July 2012 (UTC)

Well, to begin with, see somites... but admittedly, that's not the image you want yet... Wnt (talk) 18:07, 12 July 2012 (UTC)

You should really just fool around with searches like "organ mesoderm", etc., at google images. You will immediately get hundreds of choices to browse through, rather than one at a time from us. μηδείς (talk) 18:56, 12 July 2012 (UTC)

Lasers

Wavelengths of the visual spectrum

Is the blue-violet laser stronger than the green one ? ( We are talking about pointers )124.253.89.189 (talk) 16:52, 12 July 2012 (UTC)

According to laserpointersafety.com, a violet pointer is more dangerous than a blue one, which is in turn much more of a hazard than a green one. Clarityfiend (talk) 17:11, 12 July 2012 (UTC)

What about this one. Is it exactly blue or violet ? Last time this very vendor fooled me into buying a three AAA battery laser (green) which he claimed is powerful enough to light up a matchstick ( It doesn't, though it does produce a slight sensation of heat on skin ) — Preceding unsigned comment added by 124.253.89.189 (talk) 17:51, 12 July 2012 (UTC)

On the colour spectrum, the higher-frequency colours have higher energy. Lower wavelengths means higher frequencies means higher energy. This is also why red is less harmful to your night vision than green. — Preceding unsigned comment added by BigNate37 (talk • contribs)

This isn't strictly true; red light does not affect your night vision as much because rod cells (responsible for low-light vision) are less responsive to higher wavelengths; the chart in that article shows they are most sensitive to blue-to-green wavelengths. -RunningOnBrains^(talk) 19:52, 12 July 2012 (UTC)

Timeline for noticeable adverse effects from 100% recirculated commercial airline cabin air

The post above ("Airliner cabin air") got me thinking (I don't know why, but I had just assumed that airline cabin air was recirculated, at least to a large extent, which I now realize is pretty daft).

Let's take for the sake of this example a modern Boeing 767-300 outfitted with a 2-class cabin, and a full passenger capacity of 269 people. Assuming that there is NO exchange of air, and that the 100% of the air is continually recirculated, how long would it take for enough oxygen to be depleted such that some passengers will begin to experience adverse effects from the lack of oxygen? How long would it take for the majority of the passengers to lose consciousness or even die due to the lack of oxygen? --Zerozal (talk) 17:06, 12 July 2012 (UTC)

As for how long before it becomes uncomfortable, that's just a few minutes. Between lower oxygen, higher carbon dioxide and other gases, high humidity, and high temperature, it's hard to know just what makes it "stale", though. The various factors can also affect each other, like high temp and humidity causing people to emit more body odor, making the air quality quickly worsen. StuRat (talk) 17:27, 12 July 2012 (UTC)

Talking of cabin pressure in aircraft and it's effect upon humans, is it possible to get rid of hijackers by suddenly lowering the pressure ? It will cause all humans in cabin to lose consciousness (without causing any permanent damage upon them). Later all can be revived easily by bringing pressure to normal. But by that time hijackers would be nicely bound and gagged, and their toys taken away...124.253.89.189 (talk) 18:09, 12 July 2012 (UTC)

It doesn't make much sense to me. Whatever people have to deal with the terrorist, would need a mask and oxygen tank. And the terrorists could also have a mask and oxygen tank (smuggled into the plane in the same way they smuggled the weapons). Besides that, cockpit doors are reinforced nowadays, and pilots are trained not to cave in. Any terrorist without a bomb won't cause much harm. 79.148.233.179 (talk) 18:20, 12 July 2012 (UTC)

Middle Eastern climate

Why is the Middle East so hot and dry even in areas that aren't in a rain shadow? --146.7.96.200 (talk) 18:38, 12 July 2012 (UTC)

Much of North Africa and the Middle East was once covered in forests. These were killed in Neolithic times by slash-and-burn farmers, and the soils were destroyed by overfarming and overgrazing by goats. See Deforestation#Prehistory. See also Cedars of Lebanon for a tree which was once quite widespread in the Middle East. With the soils destroyed, little local surface water remained to support a local rain cycle. The eastern US, for example, is very far from the Gulf of Mexico and the Pacific where its weather often originates. But there is enough retained local surface water that evaporation that occurs in Pennsylvania can fall as rain in New Jersey. Iraq is not going to get much rain that originates as evaporation in Jordan. μηδείς (talk) 18:52, 12 July 2012 (UTC)

This effect is also reinforced by the fact that the Middle East is in the Horse latitudes, where large-scale atmospheric subsidence (sinking of air) caused by the Hadley circulation suppresses large-scale rainfall. It's a major reason why much of Australia is desert as well.-RunningOnBrains^(talk) 19:58, 12 July 2012 (UTC)

why are IAU constellations biased towards the West?

Why do they not include any Asian, Arabic, African or Native American constellations? The Arabs advanced astronomy while Europe lingered in the Dark Ages, yet none of their culture is credited in modern astronomy. The [{Chinese constellations]] are extensive, more so than the Greek ones. Why are modern astronomers so racist? 76.104.28.221 (talk) 20:00, 12 July 2012 (UTC)