Wikipedia:Reference desk/Archives/Science/2008 April 22

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April 22

different times

can you please tell what the abbreviations A.M.and P.M. stand for as in desiginating morning and night in telling time.I think P.M. stands for prime meridian but not sure.....Thank-You —Preceding unsigned comment added by 75.170.141.107 (talk) 01:41, 22 April 2008 (UTC)

ante meridiem and post meridiem See our article "12-hour clock". --Milkbreath (talk) 01:48, 22 April 2008 (UTC)

Additionally, the prime meridian is the line of longitude that passes through Greenwich (i.e. 0 degrees East/West). Angus Lepper^{(T, C, D)} 21:49, 22 April 2008 (UTC)

electrical phenomenon

I'm looking for a reference which might describe an electrical phenomenon I've just witnessed.

I made a plastic cylinder about an inch wide and about four inches in diameter and wrapped it with about 40 turns of enameled wire and encapsulated it with glue. I hooked up this coil up in place of my stereo speakers and played a tone. Although there is no speaker diaphragm and no magnets I can hear the tone coming from the coil. How is this possible? 71.100.160.42 (talk) 05:57, 22 April 2008 (UTC)

The skeptic in me says that it isn't happening. How exactly is it hooked up to your speakers? Sure the sound is not coming from the speakerS? What kind of plastic? PVC?--Shniken1 (talk) 06:06, 22 April 2008 (UTC)

If the wire isn't 100% glued down in every place, then the wire will move in response to the changing magnetic field in the coil and you'll definitely hear that. You might also take a steel food can, cut out one end, and then hold the other end near your energized coil; that should produce quite a bit more sound than the wire alone. Yo might also want to read about magnetostriction although I don't think copper wire itself is susceptible to that. But it is a big factor in why steel cores in electromagnets make noise.

Atlant (talk) 11:53, 22 April 2008 (UTC)

Please be careful. It sounds like you only have about 10 feet of wire in your coil, which will look to the amplifier like a dead short. This extremely low impedance coil will draw excess current from the amplifier output and could destroy it. To simulate the coil of the speaker you would need many turns of fine wire in a series of layers to get up to 4 ohms (or 8 ohms) depending on the amplifier specifications. Otherwise an audio transformer could be used to step up the coil impedance to a value the amplifier could handle. That said, the windings of the coil could attract and repel each other, allowing some tone to be heard. The first telephones used a steel needle (like a skewer) suspended on a sound board inside a coil to reproduce sound. A coil alone, without something ferromagnetic, would be far less efficient at producing sound. Edison (talk) 14:09, 22 April 2008 (UTC)

Yes, thanks for the warning. What components would be effected? Would the damage caused by low speaker output resistance resulting in a virtual short circuit cause the MOSFET to be destroyed or only degraded? I have an AM/FM radio tuner, tape and auxiliary amplifier I found at a thrift store that requires an extreme balance knob offset in order for output to be equalized. Also would an 8 ohm audio transformer hooked to the speaker output solve the problem? 71.100.160.42 (talk) 20:27, 22 April 2008 (UTC)

Your point is well taken, but remember that we're talking about reactive impedance, not DC resistance. And most solid-state amps are pretty good at protecting themselves from short circuits anyway, especially when you're only driving them at moderate "volumes". If it's a real concern, our poster can always put a small fixed resistance (say, two ohms) in series with his test coil.

Atlant (talk) 17:41, 22 April 2008 (UTC)

If the coil had an impedance of say .2 ohms and you put a protective 2 ohm resistor in series, then the coil would only get about 1/11 of the power and would drop way down in audibility. Seems like a losing proposition. Calculate the resistance of your winding from a wire table, or the reactance from complicated formulas to combine with resistance to get impedance. Then the turns ratio or impedance ratio of the transformer would have to be such as to somewhat match the coil impedance. Perhaps an old transformer from a public address speaker designed for the "70 volt" system would work, or an output speaker from an old vacuum tube audio device. Or you could build am amplifier designed to drive a low impedance load. The impedance of a speaker winding is mostly resistance, isn't it? Someone might try measuring the resistance of a speaker coil labelled 8 ohms. And I don't know that all transistor amps are self protected against shorts, although I know some amps have fuses or breakers. Edison (talk) 22:41, 23 April 2008 (UTC)

I don't know this for certain, but I believe that most of the "impedance" seen in a speaker winding is, in fact, the counter EMF that is generated as the voice coil moves through the magnetic field. I'm pretty sure if you stuck a speaker on an impedance bridge, you'd get a much different results when the voice coil is free to move as compared to what you'd get if the voice coil is mechanically restrained from moving.

Atlant (talk) 12:44, 24 April 2008 (UTC)

Magnetism

Hi, Can anyone tell me what actually causes magnetism?? How does a magnet know that a thing near it, is made of iron, nickel, etc.....I mean, why should it attract only ferromagnetic substances? And why do certain substances have strong magnetic properties while others don't ? What's so special about them?? I've read in my physics textbook that if a magnet is divided it forms two new magnets and so on. So, at the smallest level, will an atom act as a magnet? If it does, why doesn't every other atom act as a magnet, ie. , why can't another substance, like calcium or magnesium be magnetic? And also, how does it act from a distance? (I have similar doubts about most other forces like gravity. I've heard of gauge bosons but I can't imagine how if some particles go back or forth it can pull or repel an object.........) 116.68.71.178 (talk) 06:27, 22 April 2008 (UTC) The 15-yr old

• No-one can tell you what "causes" magnetism, we can just say it exists and describe its effects.
• A magnet doesn't "know" anything, it just emanates a magnetic field.
• A magnetic field does not only attract ferromagnetic substances, it exerts a force on any ferromagnetic, paramagnetic and diamagnetic materials and also on moving electric charges.
• Strong magnetic properties result in materials where the conditions are right, see Ferromagnetism#Physical_origin, which also describes how a single atom acts as a magnet.
• As to how it acts from a distance, the best I can do there is: because the electromagnetic force acts at a distance. You can have your doubts about forces acting at a distance, but then don't turn on the radio or jump off buildings ;)

Hope that helps a bit, others can add more. Franamax (talk) 08:06, 22 April 2008 (UTC)

Thanks a lot. This cleared up most of my doubts. And I certainly won't jump off a building to see the working of forces at a distance! 116.68.70.17 (talk) 12:26, 22 April 2008 (UTC) I asked the question

Note that gravity might not work the same way as the other forces—this is still an unresolved issue in physics. It might "just" be a deformation in spacetime, and the apparent force might "just" be matter going along a path of least resistance in spacetime.

As for "on the smallest level, will an atom act as a magnet?"—it depends on the atom, but magnetism is basically related to the fact that electrons and protons have different charges, and that under certain configurations the collective charges line up and produce a field (which is why not everything appears magnetized to us). On the smallest level (or something approximating it) a lone electron acts like a magnet.

I too find gauge bosons hard to visualize—clearly thinking of them as little billiard balls that fly out of things is wrong, though it is what comes to mind. Instead just think of them as "the things that cause the fields". The fields are easy enough to visualize abstractly, even if they don't conjure up much by means of a mechanical analogy. --Captain Ref Desk (talk) 13:18, 22 April 2008 (UTC)

116.68, keep in mind here that you will never get an answer to "exactly why does this happen". Gauge bosons, photons, electrons, whatever - don't get confused by the talk about particles and waves, there are no such things, as CRD says, there are no such little billiard-balls flying about. Our imperfect human minds need analogies we can understand, like "particles" and "waves", because those are things we can see in our physical lives. These ideas help us make predictions about what will happen in our world, but don't embrace the idea that there is really some little thing flying around that says "gauge boson" on the side. See also Tao and The Tao of Physics. Franamax (talk) 00:49, 23 April 2008 (UTC)

Thanks. That helped, and also opened up another question in my mind.......... How do we (in the sense,humans) know about so many things like bosons, waves,etc. etc. and other so, so minute things? Can't the way we see it be wrong?? I've read in a book that Immanuel Kant (I believe it's him, but not sure) classified everything into two - "nuomena" that's the absolute truth that can't be known , and "phenomena" - truth as we see and experience it. So, everything we perceive could be different from reality, and what we understand could be just within the limitations of our brains senses..........I don't know much but it was just a question that popped up. 116.68.70.86 (talk) 12:25, 23 April 2008 (UTC) The 15- year old who asked the question.

Well, you're not going to find the ultimate answer to that question here - it's been plaguing people since we noticed we were conscious beings. If you find that question interesting, you'll like philosophy (as you seem to have discovered?). Anyhow, in terms of entities that science has "discovered" like photons, electrons, etc, it is fairly pointless to argue about whether or not they really exist. From a scientific point of view, positing the existence of photons or elections with specific properties allows us to simply explain or predict phenomena that we observe. It's kind of a closed system - we observe something, we come up with the simplest possible explanation, and test to see if that explanation can always explain the phenomenon, and make sure that explanation doesn't contradict any other explanations. So...is it real? It doesn't matter, because it works. --Bmk (talk) 04:52, 25 April 2008 (UTC)

That's a good point! So, I needn't bother, if all things I see, exist in reality, I just need to mind my own bussiness, in a sense. Thanks. 116.68.70.51 (talk) 10:34, 25 April 2008 (UTC)A 15 year old

Maclean vs Maclear (OCR typos)

OK, OCR typos aren't really a science question, but could someone look at this webpage (cached version) from the Royal Society, and check that I'm not making things up here. That page lists a "Thomas Maclean" as one of the Royal Medal winners for 1869. I spent a while searching for this guy on Wikipedia and the internet, before realising that this seems to be a typo for Thomas Maclear. A few other scattered webpages refer to him as "Thomas Maclean" (for example, this book from the 1880s), but most (for example, here) say Thomas Maclear and never mention any alternative spelling. Is this likely to be a mistake that spread at some point, or could there be another reason? I've corrected Royal Medal (and left a note on the talk page), but is it worth pointing out that the Royal Society website seems to have the wrong name? Or is it just possible that all the other sources are wrong and that Maclear is the mistake?? Carcharoth (talk) 06:41, 22 April 2008 (UTC)

Searching the RS archives for Thomas Maclean finds nothing, whereas search for Thomas Maclear finds him listed as a fellow. I'd say the RS has it wrong on the first page you link, but right elsewhere, and Maclear is likely the right name. Franamax (talk) 07:01, 22 April 2008 (UTC)

And the London Gazette of 1860 awards the knighthood to Maclear. Looks like a typo on the list of medal winners. Franamax (talk) 07:19, 22 April 2008 (UTC)

Should have thought of that! Thanks. The fellows archive page lists his Royal Medal, just to confirm it. Carcharoth (talk) 07:33, 22 April 2008 (UTC)

I hit "Contact Us" on the RS website and let them know. We'll have to share the honours I'm sure they'll confer for pointing it out. Hope it's a fruit basket! Franamax (talk) 07:37, 22 April 2008 (UTC)

What about the book from the 1880s...? Carcharoth (talk) 07:51, 22 April 2008 (UTC)

According to the site, the transcriptions were made by John and Jerry Grover, and according to the contents page for Peek's Account, it was transcribed from hand-written text, so it is fairly certainly in error. Not an OCR error, a "what the heck does this say" error of the old kind :) Franamax (talk) 08:33, 22 April 2008 (UTC)

Hedge that, they might mean his "hand" as in a sockpuppet, I'd still say it's a transcription error though. Franamax (talk) 08:40, 22 April 2008 (UTC)

"Buffer" for speech?

It seems to me that the brain has a sort of "buffer" for speech, analogous to a computer's buffer for keystrokes.

I have noticed, for example, that sometimes if I am not completely paying attention when a person is talking, that this "buffer" will catch a few seconds of their speech and hold it, but my brain will not parse the speech into meaning until I have turned my attention to it.

I do not know if this buffer is for sound in general or if it is just for speech.

What is this buffer called? —Preceding unsigned comment added by 71.139.143.2 (talk) 08:03, 22 April 2008 (UTC)

The brain has a sensory memory and it is used for any kind of information not just speech. If you hear a bell ringing without paying too much attention you can retrieve the number of rings within seconds. Mr.K. (talk) 09:39, 22 April 2008 (UTC)

Occasionally, find that I occasionally need to "replay" a string of phonemes in my head and run a sort of PRML algorithm based on the likely context of the phonemes before I can figure out what's being said. (See also Maximum likelihood.) This occurs when the phonemes could match "phrase A" just as easily as they could match "Phrase B". That's when I notice this sort of short-term auditory memory.

Atlant (talk) 12:07, 22 April 2008 (UTC)

Steven Pinker's The Language Instinct discusses blowing your buffer with sentences that require you to keep things on a stack until the last word:

That many teachers are being laid off in a shortsighted attempt to balance this year's budget at the same time that the governor's cronies and bureaucratic hacks are lining their pockets is appalling.

--Sean 12:37, 22 April 2008 (UTC)

This has been called "echoic memory." A stream of speech or other sound seems to flow through memory and fade away, but if there is a retrieval cue, we can retrieve several seconds of it. An example is if one is reding the paper at the breakfast table and the significant other is chatting away, or daydreaming in class while a teacher lectures away, the reader or daydreamer can often retrieve enough of the unattended speech to give a response that makes it appear they were paying attention. The Wikipedia article does not cover some earlier experiments in the area which dealt with a stream of unattended speech. Edison (talk) 14:01, 22 April 2008 (UTC)

The interesting thing is that you can file "false" memories. Your brain (and you) will be convinced that the thing that it remembers was what actually happened. This fact has recently shed a lot of doubt on the validity of eyewitness accounts. --Lisa4edit (talk) 07:36, 23 April 2008 (UTC)

Since eyewitness accounts differ anyway, wouldn't that have counted against their validity before this fact was applied? Julia Rossi (talk) 09:03, 23 April 2008 (UTC)

chomsky's theory involves a more serious buffer, which not only holds the content of the speech until the end but after that it is worked on to generate the "deep meaning" so that you can understand the difference between "man eating sharks" and "man eating sardines", for a trivial example; or convert "the dog bit the man" and "the man was bitten by the dog" etc. to identical final products. Gzuckier (talk) 19:09, 23 April 2008 (UTC)

While watching a typist take dictation a few years ago, I noticed lthat she only started typing a few seconds AFTER the dictating began. Although people said that typists did not care about or understand what was being read to them, I realised that the typist could not type effectively without getting the gist of what was meant, and only then typing the words. I think all typists (I am a pretty fast touch typist mystelf and have often typed from dictation) need to understand what is intended. This can be clearly seen if they are asked to type a list of unrelated words. It is rare for a typist, even one who “doesn’t care” about the significance of what is intended to make mistakes with homonyms, for example writing “the HEART ran through the forest”, when HART is intended. Moreover, all typists are irritated when the dictater does not offer the prose in naturally logical bite size pieces, and stops half way through phrases and so on. In like manner, I believe everyone listening to speech partially disengages mentally from the stream, and then “catches up” after a couple of seconds. The art of being able to easily comprehend long and complex passages of speech or text is much atrophied in contemporary society. Hava a look at writing, either novelistic or argumentative from the 1800s, People were expected to read sentences that were longer than most paragraphs are now, and with the subject separated from its associated verb by many lines of text, including phrases nested within other phrases. Myles325a (talk) 07:14, 24 April 2008 (UTC)

What are the "doors" or entryways on a ship/boat called?

Specifically, the entryways from one section to another. Not the cabin doors. BrokenSphere^{Msg me} 16:47, 22 April 2008 (UTC)

Hatch. Hatchway. Companionway. Watertight bulkheads? Other terms?

Atlant (talk) 17:33, 22 April 2008 (UTC)

The entryway through which the person in the photo is using to go through. She's climbing over a bulkhead but what's the oval doorway called? --BrokenSphere^{Msg me} 17:43, 22 April 2008 (UTC)

The oval hole? An oval hole at most, I'm afraid. The best alternative is going to be the specific type of door, bulkhead and similar. 81.93.102.185 (talk) 18:56, 22 April 2008 (UTC)

If there's a watertight door that can be used to shut off the area then I guess a watertight door, if said door is normally kept open to facilitate passage? BrokenSphere^{Msg me} 20:15, 22 April 2008 (UTC)

How would the hole be called a "door?" Edison (talk) 20:24, 22 April 2008 (UTC)

If there is a watertight door (unseen here perhaps, I can't recall) that can be shut to cut off sections of a vessel to halt flooding. This pic is of a submarine, after all. However my question is for all maritime vessels. "Door" doesn't seem very nautical to me, however for cabins or quarters I guess those can have "doors" for privacy, right? BrokenSphere^{Msg me} 20:29, 22 April 2008 (UTC)

Speaking for the US Navy, they are called "Watertight Doors" and a google search for that term gives lots of pictures. The example you show has been modified/mangled to no longer work. You can tell it used to be a WTD because the "coaming" (the wide lip all around the oval) is a good 3/4" thick, and 5 or 6" wide , and there is still one dog-wedge visible on the lower left. When new and in use, there were at least 4, and probably 6 or 8 of these evenly spaced around the coaming. The door would have been on the other side of the frame, with "dogs" (latches) that ran up these wedges, forcing a rubber gasket on the edge of the door up against the coaming. In it's current condition, it's only purpose is to injure people, so it is normally referred to as a "knee-knocker". -SandyJax (talk) 20:33, 22 April 2008 (UTC)

A company which sells watertight doors (with dogs) for ships calls it [1]an "opening" (more specifically "clear opening." Some patents refer to the "door frame" which this seems to be. The entire assembly could be called a watertight door, but if one said "I walked through the watertight door" others might snicker. Still, in the testimony in the hearing about the [[Titanic] sinking, crewmen said they "went through watertight doors."[2] referring to the complete door and frame. Edison (talk) 20:46, 22 April 2008 (UTC)

Elephant relative

I'm trying to remember the name of a small furry animal which somewhat resembles a guinea pig, but, oddly enough, is most closey related to elaphants. If anyone knows its scientific and common name I would greatly appreciate it. BeefJeaunt (talk) 18:08, 22 April 2008 (UTC)

Never mind, found it: Hyrax. BeefJeaunt (talk) 18:15, 22 April 2008 (UTC)

Heat from Lights

Good day, I'm considering retrofitting the lighting system in my warehouse from Metal Halides to a T5 lighting sytem. I'm concerned that the reduced amount of heat generated by my lighting system(450 watts to 234 watts) will have an advverse effect on my heating bill during the winter months. Please tell me what effect such a retrofit would have on my heating bill, if any? Total number of fixtures = 200

thanks, Vinsanity3 —Preceding unsigned comment added by Vinsanity3 (talk • contribs) 18:54, 22 April 2008 (UTC)

Without doing any math or knowing your geographic location, heating fuel, local costs, etc. a good rule of thumb might be that you will have to pay as much for heating as you will save on electricity, for those months when you would need to have a 20KW electric heater running continuously to heat the building. Franamax (talk) 19:06, 22 April 2008 (UTC)

You absolutely cannot expect volunteers here to replace the need for licensed professionals in advising you on important engineering decisions such as this. That said, if the lights produce less heat, then all other things being held constant, that heat would have to be produced by the heating plant. If the spaceheating is by electricity, then there would be less of a difference than if the heating plant burned fossil fuel. Then consider the cost per unit of heat from the electricity versus the fuel used by the space heating system. If you needed a larger furnace, but the cost per unit of heat from the furnace was less than the cost of the heat from the present electric lights, someone needs to do some economic calculations and cost projections for you to make an intelligent choice. In a residence, with gas heat, one might actually consider putting the incandescent light bulbs back in in the winter to augment the heat from the furnace which is marginally undersized, but putting the compact fluorescents in in the summer to reduce the air conditioning load. Edison (talk) 20:22, 22 April 2008 (UTC)

It depends on what method of heating you're using.

• If you're using electric heat, your bill will be about the same: electric lights and electric heaters are equally efficient at heating.
• If you're using any other form of heating, your bill will probably be lower: in almost every part of the world, electric heat is the most expensive way of heating a building.

--Carnildo (talk) 21:40, 22 April 2008 (UTC)

The practical upshot is that incandescent bulbs put out very little ambient heat. Even then, let's just pick a random number: let's say running all the lightbulbs in an entire house increases the ambient temperature by 3 degrees during a day. That means in winter, you have a "free" 3 degrees of heat your furnace does not have to put out. However, in summer, that's an extra 3 degree penalty your cooling system has to compensate for! So, overall, it's not saving you anything. By switching to low-powered bulbs, you're objectively saving money on your electric bill, so I'd say the decision is simple there. -- Kesh (talk) 00:28, 23 April 2008 (UTC)

Sorry Kesh, disregarding the fact that the discussion is about halide bulbs, not incandescent, any electrical device puts out almost exactly what it says on the label - is it's a 40W bulb, you get 40 watts of heat. 8W of that is light, which is converted to heat when it meets its surroundings, 32W is indeed converted into sensible heat. Incandescent bulbs are in fact very efficient devices for producing ambient heat. Electrical devices are generally 100% efficient at producing heat, that's what they do (see thermodynamics). And by the numbers already supplied, we're talking about 20 kilowatts of heat, which is actually not bad, think 20 hairdryers.

You are somewhat correct in your argument about summer vs winter, but the OP is asking about a warehouse, which generally doesn't use any cooling in summer, usually you open the big doors at either end so the outside air can go through. The OP is trying to make an economic decision here - as Edison says, the question should be evaluated by a licensed professional who can best determine where the cost-savings are and how long they will take to be realized. We don't even know whether the OP lives in the desert or the Arctic, how well the building is insulated, we know nothing! Franamax (talk) 01:10, 23 April 2008 (UTC)

incandescent bulbs put out very little ambient heat Where do you get that idea kesh? Approximately 90% of the power consumed by an incandescent light bulb is emitted as heat, rather than as visible light. —Preceding unsigned comment added by 79.76.212.84 (talk) 00:54, 23 April 2008 (UTC)

And.... the visible light is absorbed, and becomes... heat. damn efficient heaters, light bulbs. i got a tiny nightlight bulb stuck to the wall beneath my thermostat, attached to a timer, which serves to crank the heat up and down for my daily routine, and you need only a tiny bulb not very close to the stat. and of course, everybody who raises chickens in a box in their kitchen knows you have to stick a small light bulb in there to keep them warm; if you used like 100 watts they'd end up kentucky fried before their time. odd but related note: the local Sears Hardware has normal looking light bulbs, labeled and sold as replacements specifically for easybake ovens. Gzuckier (talk) 19:17, 23 April 2008 (UTC)

Incandescent light bulbs produce an amazing amount of heat. Various numbers are bandied about for the efficiency/efficacy of incandescent lights, but perhaps 95% of the energy they consume produces heat rather than visible light. That is still a vast economic improvement over candles, kerosene lamps, or gas lights which were their predecessors. Right now compact fluorescent lights are the light bulb of choice, but in a very few years they should be displaced by LED lamps, which are thus far low in output and too expensive. Edison (talk) 05:47, 23 April 2008 (UTC)

Two points, Kesh: one is that summer and winter need not be of the same length or severity for the OP, and the other is that cooling is actually easier than heating here. See SEER: standard modern air conditioning systems need only one third to one fourth the amount of energy to run as they remove from the building. So, supposing (reasonably) that gas heat is used that costs half as much as electric heat, and neglecting the issues of heat distribution called out below (because fans are cheap), we have that in the winter the electricity to run the lights is half repaid by the reduced gas usage, and in the summer no more than a third again the power of the lights is required to evacuate their heat. Of course, none of this really matters; the only way that reducing the power of a lighting system could possibly hurt would be if the normal heating system were somehow less efficient (in money) than the electric heat provided by the lamps, in which case I would suggest replacing that heater with a box of light bulbs! Practically speaking, the retrofit would not be useful in a cold climate (where the heater was effectively always running) where the heater costs nearly as much as electric heat, because not enough energy will be saved to recoup the cost of the new lights. --Tardis (talk) 17:28, 23 April 2008 (UTC)

Reply to all: Yes, lightbulbs put out a lot of heat for their size. However, the amount of heat put off by a bulb is insignificant if you're looking at the overall household temperature. Now, I'll admit that I did overlook the fact the OP is talking about a warehouse. In that case, insulation is likely a bigger factor than the light bulbs when it comes to temperature, but large incandescents may have an effect in a building of that type. Still, I don't see it as enough to offset the long-term costs of changing to lower-powered bulbs. -- Kesh (talk) 20:47, 23 April 2008 (UTC)

I assume that your lights are mounted on/near the ceiling of your warehouse. Since warm air rises (see convection) the simple mathematical heat output of the lamps will not come close to the actual usable heat. Warehouses are not known for well insulated ceilings/roofs. My guess would be that a sizable portion of the heat from your light gets "lost". Your heating system on the other hand is designed to deliver heat where it's needed. --Lisa4edit (talk) 07:56, 23 April 2008 (UTC)

Very true, one of the first things I thought of. However, this is an industrial situation and that's where the pros come in to help with solutions - for instance, an 80,000 sq ft warehouse I'm familiar with was fitted with a ceiling-to-floor recirc duct (8-foot square) with a large squirrel-cage fan to effectively recirculate the air to floor level with two-year payback. An adjacent 180,000 sq ft mfg plant was fitted with a recirc duct and motorized ceiling vents for summer heat release. This was Southern Ontario (-20C to +30C) and not applicable to all climates. Point here is that we are really not in a position to give good answers about a building with 200 lights in it, but the OP might be able to get answers for free if they just ask the vendor the right questions. Franamax (talk) 10:42, 23 April 2008 (UTC)

Keep in mind that it will probably save money during the summer months, so if you install during spring then you will get the greatest cost benefit. As for heating, I imagine that waste heat from lights is probably a less energy efficient heating method than an actual heating system, so you will probably save some money during winter as well. Hope that helps! -- HiEv 10:41, 23 April 2008 (UTC)

of course, in winter the lights are on a lot more than they are in summer; when the AC is laboring away at noon, i haven't got the lights on; at 5 pm in the winter they go on, but in the summer not for a few hours more. on a related note, some folks point out that moving daylight savings time earlier as we do now may save electricity on lighting, but in the southern states it also means that folks come home when it's warmer and start up the AC an hour more every day. Gzuckier (talk) 19:17, 23 April 2008 (UTC)

Breathing question, again

When I hold my breath, and exhale a bit, I feel relieved, and as if I can hold my breath for longer. Have I somehow cheated? 81.93.102.185 (talk) 19:20, 22 April 2008 (UTC)

I don't know if you have cheated; what rules are you playing by? :-)

The human respiratory system detects the concentration of carbon dioxide in the lungs. Excess carbon dioxide results in a reflex to breathe. Note that this is contrary to what might be expected: your lungs can't measure the amount of oxygen in them; they measure the carbon dioxide. Getting rid of a bit of that CO2-laden air in your lungs tricks your central nervous system into thinking you don't need to breathe just yet. Weregerbil (talk) 19:49, 22 April 2008 (UTC)

Well, but you don't lower the concentration of CO2 in your lungs by breathing out; you do lower the absolute amount, but it's harder to explain how the breathing reflex would be triggered by the absolute amount. So there still seems to be something to be explained. My guess would be that something in the feedback mechanism says "oh, OK, he's complying, alarm bells can go silent now", and only a short time later notices that, no, the CO2 concentration is even higher than before. But it's just a guess. --Trovatore (talk) 20:04, 22 April 2008 (UTC)

Quite the interesting and logical take on it, Trovatore. That satisfies me, though I'm sure someone qualified out their bum will come by. :) 81.93.102.185 (talk) 20:06, 22 April 2008 (UTC)

I'll note here that it's also my understanding that breathing is controlled by CO2 concentration in the blood, not the lungs. Franamax (talk) 20:15, 22 April 2008 (UTC)

Good point. Another possible explanation that occurs to me is that perhaps when you exhale, you lower the pressure in your lungs (do you? not sure) and therefore the partial pressure of CO2. That could potentially lower the blood concentration of CO2. --Trovatore (talk) 20:19, 22 April 2008 (UTC)

It certainly feels like you lower the pressure. However, whether that lowers the pp(CO2) is not a given, wouldn't you need to look at the graphs of pp(CO2) vs. pp(N2) at constant temperature with varying pressure? Franamax (talk) 20:25, 22 April 2008 (UTC)

Exhaling is achieved through raising the pressure in your lungs. When you lower the pressure in your lungs, air flows in. Skittle (talk) 21:53, 22 April 2008 (UTC)

Well, but when you're holding your breath, you're blocking the airways so the air can't escape. When you exhale, you unblock them. As the air begins to flow, the pressure should diminish. --Trovatore (talk) 21:58, 22 April 2008 (UTC)

Qualitatively, when your lungs are most inflated, your body tissues are most distorted from their normal shape, so one might conclude that the pressure (return to normal shape) is at a maximum. Also if you fill your lungs and relax, you find that a lot of air exits quickly, which indicates a higher differential pressure. I'm thinking that the "feel-better" response to letting a little air out may just reflect a reduced sense of overall discomfort to the combination of increased need-to-breathe and overfilling-of-lungs. Whether there is an effect on actual blood CO2 concentration, I think depends on the various pp(X) graphs of gaseous and dissolved carbon dioxide and nitrogen. We need a chemical engineer/physiologist to weigh in here! Franamax (talk) 23:03, 22 April 2008 (UTC)

Nope, I'm sticking with the air in your lungs being at atmospheric pressure when air is neither entering or leaving. I can experiment with 'sealing' and 'unsealing' my throat, and when my lungs are full no air flows unless I force it out. If you have your lungs full 'to bursting', it may feel uncomfortable because you're stretching your body, but the air isn't at higher pressure than atmospheric until you start breathing out. Unless you 'seal' your throat and then deliberately try to breath out, but that wasn't what we were talking about. Breathing out relies on raising the pressure of the air in your lungs; if it didn't, air would not flow out. The 'tricking your brain for a moment' explanation seems more sensible. Skittle (talk) 12:06, 24 April 2008 (UTC)

I don't have a definitive answer either, but I will offer that this phenomenon has nothing to do with the partial pressure of CO₂ in the lungs (so-called alveolar PCO₂). Rather, ventilation has to do with arterial PCO₂, and to a lesser extent arterial PO₂ and pH.

My guess is that the phenomenon is related to the reflex that controls the depth of breathing. In human infants, this is regulated in large part by the Hering-Breuer reflex. Distension of the lung's air sacs activates stretch receptors that signal the brain to stop inspiring. I don't know of the equivalent reflex in adult humans, but I would assume it at least partly mediates the phenomenon you describe. --David Iberri (talk) 22:42, 24 April 2008 (UTC)

Right about global warming?

Is this right about global warming - the equations are wrong because of the boundary conditions, etc? Bubba73 (talk), 19:56, 22 April 2008 (UTC)

There's a few different answers here: the equations may indeed need correction, but that doesn't necessarily mean "global warming is wrong". Science is always in flux, there are many people looking at this subject, and if that scientist is correct, his ideas will soon enough be incorporated into the various models which simulate the warming process. It's turned out that it's not so simple as just changing the terms of an equation, the Earth system is much more complex, there is indeed controversy at the moment about warming at higher altitudes. However, keep in mind that 95% (at least) of the science does point to a warming trend. I'm somewhat disturbed at seeing this published on a blog, and there is a statement in there that '"runaway" greenhouse warming hasn't happened in the Earth's past', which I'm not sure is a true statement. Anyone else have a comment here? Franamax (talk) 20:38, 22 April 2008 (UTC)

Can't comment on the maths but Daily Tech isn't reknown for their analytic genious or fact checking. They come close to The Inquirer when it comes to tech news, and this isn't tech news. Also note the views of Stephen E. Schwartz who's work was mentioned in the blog Nil Einne (talk) 20:49, 22 April 2008 (UTC)

I at least understand what he is saying about differential equations and boundary conditions, but I haven't been able to find anyone that is an expert on the physics that agrees with him. Bubba73 (talk), 22:23, 22 April 2008 (UTC)

I did a quick search found a couple of comments indicating that a number of Miskolczi assumptions are flawed or baseless. Search for "Miskolczi" here or here (mainly comment #174) and that might help. There seems to be a lack of interest in debunking it since it only managed to get published in a minor (Hungarian) journal. I've also seen comments by others that Daily Tech is more interested in exciting sounding stories than accurate or reliable reporting. -- HiEv 10:27, 23 April 2008 (UTC)

Thank you for that information. Bubba73 (talk), 16:49, 23 April 2008 (UTC)

the math is pretty involved, alright, and i haven't seen it explained with the right and/or wrong boundary conditions filled in at any level I could follow, to prove or disprove it. on the other hand, from what i've seen in the past from "global warming debunkers", if i can't follow the math, you can rest assured that they sure can't, so these folks tossing the paper around as though they had some clue, are clearly just parroting what they've heard from folks just as ignorant. so, until I see it thusly explicated, i at least will have to suspend judgement on a mathematical proof or not; however, based on the sociological evidence of the "data" and logic presented by these guys in the past, specifically including Daily tech, it's not going to turn out to be a hill of beans. see also "the climate isn't really warming", "the sun is warming the climate", "it stopped warming in 1998", "mars is warming", "carbon dioxide isn't the most important greenhouse gas", "carbon dioxide is a requirement for life", "what about water vapor?", "what about china and india?", "you can't prove that carbon dioxide absorbs infrared outside the lab", "models can demonstrate anything you want them to", "Models can't demonstrate the current climate", "it's volcanoes", "it's cosmic rays", etc. etc. etc. etc. Gzuckier (talk) 19:31, 23 April 2008 (UTC)

I keep wondering about that Global Warming debate. Just because mathematicians could not solve Zeno's paradox (and some are still debating if that has been achieved) hasn't stopped people from moving from A to B and actually arriving. Just because we don't know all the answers to Global Warming doesn't mean it's not happening. --Lisa4edit (talk) 08:35, 23 April 2008 (UTC)

Actually, Zeno's paradox has been solved, and the solution is that an infinite sum can have a finite value (as e.g. the sum 1/2+1/4+1/8+1/16+1/32..., which converges to 1). Hence the time that the turtle can keep Achilles at bay also is finite, albeit decomposed into infinitely many time spans. --Stephan Schulz (talk) 09:00, 23 April 2008 (UTC)

SS, can you send me the computer printout that proves the solution by printing 1 at the end? Take your time, save paper and just send me the remainder when you give up :)

Lisa, you're right, uncertainties will never disappear (except that you will die sometime, but even then, how will you know for sure?) You have to act on probabilities in an uncertain world. We will never know for sure about global warming, we'd have to run the same planet through 20 or 30 different 100-year cycles to be sure. That's why the climatologists are so busy running simulations. because we only have one shot at the real thing. What we have to do is to make sure that our particular real-life experiment works out so that our kids and grand-kids can look back and say "you did good" :) Franamax (talk) 10:23, 23 April 2008 (UTC)

Ummm...you don't prove non-trivial things by computer addition, but by logical argument. In this case, the simplest argument is geometric. Take a line segment that is one unit long. Mark off a spot at 1/2. Then mark off one at 3/4, then one at 7/8, at 15/16, and so on. It is obvious that you can continue this process forever without ever reaching 1. The newly marked of segments are your new summands. The total marked length is your sum. There are many other proofs for the convergence of this series...I'll teach them at EUR 160/hour ;-). --Stephan Schulz (talk) 17:03, 23 April 2008 (UTC)

?? x=1/2+1/4+1/8+1/16+1/32... x+1=1+1/2+1/4+1/8+1/16+1/32..... 2x=1+1/2+1/4+1/8+1/16+1/32... therefore, x+1=2x. hopefully, you can take it from there. hats off to my high school math teacher. Gzuckier (talk) 18:24, 23 April 2008 (UTC)

Nice one. But you are destroying my market ;-) --Stephan Schulz (talk) 19:26, 23 April 2008 (UTC)

it's cause the euro is up and the dollar is down. Gzuckier (talk) 19:32, 23 April 2008 (UTC)

I blame this thread for getting me sucked into the black hole that is the Zeno's Paradox article and its talk page. When I started reading the pages and pages about trying to apply quantum mechanics to macroscopic objects my head just about exploded. You owe me a new head.Mad031683 (talk) 21:37, 23 April 2008 (UTC)

Bush will be out of office in January, I think. You can have his. The outside is somewhat used, but the inside is like new ;-). --Stephan Schulz (talk) 07:32, 24 April 2008 (UTC)

Will solar energy kill the Earth?

Sunlight:

• Absorbed:
  • Absorbed by earth → becomes heat.
  • Absorbed by plants:
    • Used immediately by humans → becomes heat.
    • Stored as fixed caron.
  • Converted into human usable energy → becomes heat.
• Reflected into space.

Let's say you are the Good King of Blah Blah Land, a cloudless tropical nation populated by honest-working and Earth-loving people. Your beautiful country is powered by a highly efficient and clean combined cycle natural gas power plant (60% efficiency). The aged power plant is very good but you really want to do the Earth a favor, so you replace it with a solar farm.

Your country has a desert covered with white quartz sand (50% reflectance, simplified figure). Your UFO-based national advisor provides you with several square kilometers of solar panels (10% reflected, 80% becomes heat, 10% becomes elctricity) shipped from Altair IV. Highly-paid union workers installed the panels in the desert in record time without any labor dispute and job injury.

Let's say your citizens need 1 unit of energy per day (they sleep all night and work all day). Your gas plant needs to consume 1.6 unit of energy to output 1 unit of energy. 0.6 unit of energy is released as waste heat. The unused desert absorbs 5 units of energy as heat.

Now to provide as much energy, your solar farm dissipates 8 units of waste heat ... At least you emit no CO₂.

Will your good intention make the world an even hotter place? -- Toytoy (talk) 20:08, 22 April 2008 (UTC)

The total flux of solar radiation hitting the Earth and re-radiating into space absolutely dwarfs the amount of energy involved in electricity usage. The debate is not about heat-balance per se, it is about releasing long-stored carbon quickly into the atmosphere in the form of gases which enhance the greenhouse effect, i.e. as carbon dioxide. Using solar panels doesn't change the amount of heat input into the Earth system by the Sun, although it may change the wavelength of the energy re-radiated into space. Currently, it looks like reducing CO2 emissions is a good thing, so I'd say the king is doing good. Franamax (talk) 20:22, 22 April 2008 (UTC)

On second thought, burning fossile fuels only heats up the Earth one-time. The released CO₂ makes the Earth more capable of absorbing solar energy ALL THE TIME. -- Toytoy (talk) 01:40, 23 April 2008 (UTC)

If the solar cells were on a giant dessert not a giant desert than it would get melted and people would not be happy.--Shniken1 (talk) 06:37, 23 April 2008 (UTC)

If you're only converting 10% into power and 80% ends up waste heat then you're doing it wrong. The heat should be used for power. Take a look at the Solar thermal energy for a design more suited to the situation you describe. At high enough temperatures you can get over 60% thermal efficiencies, which would match or beat your natural gas plant, but without the pollution or need for fossil fuels, plus it would reduce the desert's reflectance. So, it looks like solar energy saves the Earth in that situation. -- HiEv 09:41, 23 April 2008 (UTC)

Decent introductory treatment of quantum mechanics?

I've got a decent informed-and-interested-layman's understanding of quantum mechanics, coupled with a bit of ability and high school physics. Is there any reasonable (preferably free, online; lucid hard-copy textbooks are appreciated, though) treatment of the subject that would be both accessible to me but which would also provide sufficient of a formal introduction (maths doesn't overly scare me) that I could begin to make a little more sense of a lot of the information I'm finding. I've tried reading our articles on the subjects, but suffer the same problem I did trying to do the same with maths – not knowing where to start and a logical progression from there, I end up looking at one topic and having about a dozen more tabs open trying to understand other keywords in that topic. Cheers. Angus Lepper^{(T, C, D)} 22:12, 22 April 2008 (UTC)

This is a continual problem with technical articles in Wikipedia. They are not accessible in that complex concepts are already assumed to be understood by the reader, or at best links are provided, but those links require following more links to understand, ad infinitum. I believe the cure is to have people who don't specialize in that field write, at very least, the intro for each article, so it won't remain knee-deep in techno-babble. If you feel up to it after learning the basics, please feel free to fix our articles on those topics. StuRat (talk) 22:31, 22 April 2008 (UTC)

The Feynman Lectures on Physics. Buy it, read it. Franamax (talk) 22:43, 22 April 2008 (UTC)

On that point, I agree with StuRat that technical articles tend to stay that way not because people don't try to make them clearer to readers, but maybe because the techs that write them don't trust accessible language so the problem persists. My experience, anyway. : / Julia Rossi (talk) 23:12, 23 April 2008 (UTC)

The problem is that accessible language is imprecise. When you get into complicated systems, it's important to keep the language precise so as to avoid confusion. That does, unfortunately, make it difficult for those not already knowledgeable in the field to pick up on the topic right away. -- Kesh (talk) 22:18, 24 April 2008 (UTC)

If the precise language is causing confusion, I suggest it be left for later sections where an in-depth discussion is warranted. A simplified intro should be always be included up front. For example, an "atom" can be described in the intro as "a clump of protons and neutrons in the nucleus, orbited by electrons in shells". In later sections the concepts of S, P, D and F orbitals and probability envelopes can be introduced. StuRat (talk) 01:26, 25 April 2008 (UTC)

You suggest it, I suggest it, many people suggest it, but it just doesn't stick because it hurts those used to precise language :) 79.66.99.37 (talk) 18:02, 25 April 2008 (UTC)

You could try to search for quantum mechanics lecture notes - they are sometimes online, like this one or this one. Icek (talk) 18:09, 25 April 2008 (UTC)

have you come across this article yet? SEems like a good place to get a broad udnerstanding on a variety of topics. Introduction to quantum mechanics --Shaggorama (talk) 08:13, 28 April 2008 (UTC)

Nitrogen

here is some stuff about nitrogen that i couldn't find and would like to know.

Atomic mass

1. of protons
2. of neutrons

Cost for sertan amount what family it belongs to —Preceding unsigned comment added by 76.14.124.175 (talk) 22:55, 22 April 2008 (UTC)

Atomic mass: 14.0067

Protons; 7

Neutrons; 7

See Nitrogen

Zrs 12 (talk) 23:03, 22 April 2008 (UTC)

Warning, Zrs has given some data but this may be the average, there are various stable and unstable isotopes which each have their own properties. Franamax (talk) 23:08, 22 April 2008 (UTC)

Oh yeah, my bad. The data I have given is for Nitrogen 14. There are other isotopes as well, however. See Nitrogen 15 for one example of another nitrogen isotope. Zrs 12 (talk) 23:11, 22 April 2008 (UTC)

How is carbon dioxide dissolved into water in pop?

When I was in chemistry today, my teacher said that carbonated water in pop is an excellent example of a gas dissolved in a liquid. However, I realized that since carbon dioxide is a nonpolar molecule, it can't possibl[y] dissolve in water, which is a superpolar molecule since it has hydrogen bonds. So then...how does carbon dioxide dissolve in water???--Dem393 (talk) 23:28, 22 April 2008 (UTC)

I'm sure there's more to the story than this, but my understanding is that the polarity means it doesn't dissolve particularly well, but it still dissolves. The pressure helps keep it in. Friday (talk) 23:32, 22 April 2008 (UTC)

A couple of things...firstly, solubility is not a matter of soluble vs. insoluble. It's actually a continuum of degrees of solubility. It is based on the chance at any given moment that two solute particles will stick to eachother when they pass one another, and the chance at any given moment that two solute particles stuck together will dissociate into the surrounding medium. When the first case is extremely more likely than the second, we call the substance insoluble, and when the second case is extremely more likely, we call the substance soluble. And so it actually completely untrue that something "can't possibl[y] dissolve in water." If it is unfavorable to dissolve, it will simply dissolve less. That said, carbon dioxide has a solubility in water of 1.45 g/L, over twenty times less soluble than table salt, but it does dissolve. And further, the polarity of the molecule is not all there is to it. The C=O bonds are themselves polar. So while there are no permanent dipole-dipole interactions taking place, the oxygens still have a limited ability to accept hydrogen bonds. We can see this even better in acetone; acetone is completely miscible with water, while its base hydrocarbon (propane) is quite insoluble (0.1g/L).

And to comment on the "pressure" comment above, yes, that does matter quite a bit. In the case of soda, the solute is basically a region of carbon dioxide gas above the uncarbonated soda. The solvent is the soda beneath. Increasing the pressure increases the chance that a molecule of CO2 will drop into the solution, increasing its solubility. And similarly, once you open the soda bottle and release that pressure, it will slowly decarbonate. Someguy1221 (talk) 23:45, 22 April 2008 (UTC)

Er, acetone might not have been the best example, as it's polar. But a similar argument holds for trans 1,2-dichloroethylene and ethylene (6.3g/L [3] vs. 35 mg/L). Someguy1221 (talk) 00:29, 23 April 2008 (UTC)

Thank you for that info. It really cleared up some confusion! I have another question: is the solubility of CO2 aided by its synthesis with water, as shown in this article?--Dem393 (talk) 00:15, 23 April 2008 (UTC)

It aids the solubility, yes, but most dissolved CO2 remains as is, most of the time (see Carbonic acid). Someguy1221 (talk) 00:29, 23 April 2008 (UTC)

CO2 itself is very insoluble in water, much less then 1.45g/L. But when that small amount does dissolve it is turned into carbonate and carbonic acid which are both much more soluble. Le Chatelier's principle tells use that this will cause more CO2 to be dissolved until an equillibrium between atmospheric CO2, dissolved CO2, dissolved CO32- and HCO3- is set up. Without these transformations CO2 would be much more insoluble in water than it is.

On a side note these reactions cause the water to become more acidic, this is seen in the worlds oceans as atmospheric CO2 concentrations increase. Also temperature greatly affects this equilibrium, as oceans get warmer less CO2 can be dissolved, so more ends up in the atmosphere, and the planet gets warmer and less CO2 can dissolve etc until we all die...--Shniken1 (talk) 00:27, 23 April 2008 (UTC)

I have another question, but first, could you please clarify what CO32 is? Ok, now here's my question: in chemistry class, I also learned the solubility guidelines. One of the guidelines say, "Most carbonates...are insoluble, except those of sodium, potassium, and ammonium." Carbonic acid is a carbonate, and the hydrogen ion isn't listed as an exception. Therefore, does that mean that carbonic acid isn't soluble in water? How would carbonation work then?--Dem393 (talk) 01:26, 23 April 2008 (UTC)

the 2- was an indication of a net charge. Carbonic acid is soluble in water as it dissociates - C02 + H20 ---> H2C03 ---> H+ + HC03- Wisdom89 _{(T / ^C)} 01:29, 23 April 2008 (UTC)

An interesting historical note: See Joseph Priestley's notes from 1772 on carbonating water [4]. He is regarded as the inventor of soda pop. "If water be only in contact with fixed air (carbon dioxide) it will begin to imbibe it, but the mixture is greatly accelerated by agitation.." He noted that stale beer could be carbonated and revived. Edison (talk) 05:39, 23 April 2008 (UTC)

Hmmm...I was sure that Priestley got knighted..no mention of it in the article...--Shniken1 (talk) 12:01, 23 April 2008 (UTC)

Thank you all for your help.--Dem393 (talk) 00:59, 24 April 2008 (UTC)

Coming to a head

A quick question about abscesses as they occur in skin and superficial tissue. Often times when an abscess occurs it is at first several millimeters deep in the skin, and later on (whether from the natural progression or therapeutic intervention), the abscess "comes to a head", appearing, at least in part, closer to the surface. My question is this: what exactly is occurring during this process? Is the part which comes to the surface simply a fistulous tract, does the entire abscess itself move closer to the surface, or does the tissue between the abscess and the epidermis atrophy? Tuckerekcut (talk) 23:46, 22 April 2008 (UTC)

Seems rather like magma in a volcanoe working its way to the surface, with the volcanic eruption being akin to squeezing the zit or lancing the abcess. Edison (talk) 05:27, 23 April 2008 (UTC)

i always assumed that part of this was the continuous growth of new epidermis pushing out the old epidermis, which would result in the evolutionary advantage of making it that much harder for infections to penetrate. vs the serious infections that happen when they penetrate into the lower strata. Gzuckier (talk) 18:26, 23 April 2008 (UTC)