Wikipedia:Reference desk/Archives/Science/2009 January 14

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January 14

Synthesis study?

Alright, I'm a nineteen year old college student, and I'm looking forward to a career designing and marketing analog synthesizers/guitar pedals. At this point I'm assuming a major in electrical engineering will be enough to help me realize my goal, but are there other fields I ought to look into? Kenjibeast (talk) 01:21, 14 January 2009 (UTC)

I imagine you'd want to know something about acoustics, especially bioacoustics, to know something about what sounds mesh well and sound nice to the human ear/brain.-RunningOnBrains 02:00, 14 January 2009 (UTC)

Our article on Audio engineering contains LOTS of links to other articles on related fields. I would recommend you start there and follow where it takes you... --Jayron32.talk.contribs 04:19, 14 January 2009 (UTC)

LED lamps - how they change colors so smoothly?

So called mood lighting. Could not find anything in LED lamp article. You can check some videos here: 1, 2, 3. I mean they actually change light emmited by diodes? Or they simply use multiple different wavelength diodes and dim one while light up another? TestPilot^{talk to me!} 05:51, 14 January 2009 (UTC)

Your guess is absolutely correct. (Actually, since LEDs can't really be 'dimmed', they are flashed on and off very rapidly; your eye perceives them as dimmer or brighter depending on what fraction of the time that they spend turned on.) Combinations of red, blue, and green lamps give different colors. There are many, many, many hobbyist plans describing ways you can build your own, if you're handy with a soldering iron; here's the first one I hit with a Google search: [1]. TenOfAllTrades(talk) 06:08, 14 January 2009 (UTC)

Hmm... How come the mood lighting associated with LEDs then? Incandescent light bulb available in different colors, and all are perfectly dimmable. So such system could easily be realized with more conventional technology... Could it be that some LED mood system actually change color of diodes? PS. From my research, a lot of LED lamps could be dimmed by conventional dimmers. Dimming by rapid switch on/off just an another option. Example: Cree LED LR24 TestPilot^{talk to me!} 06:26, 14 January 2009 (UTC)

Dimmer switches normally work by switching off and on during part of the supply cycle anyway rather than changing the voltage. So they would work with LEDs but it could be done more efficiently. I didn't see any technical details of that Cree LED LR24 however my guess would be that it has extra electronics to regulate the supply and that it switches the LEDs at a higher frequency all through the cycle depending on the switching of the input supply. Dmcq (talk) 11:28, 14 January 2009 (UTC)

Colored incandescent lamps are not very accurately colored - a green light bulb (for example) basically has green-colored paint filtering out the red and blue light from the bulb. But the resulting light is at best somewhat impure - lots of red and blue get out anyway - and no matter what, this is an inefficient bulb because (roughly) two thirds of the light is being absorbed by the paint and turning into heat. That tends to overheat the bulb - so colored incandescents have to be very low wattage.

LED's are the exact opposite - they only produce one narrow frequency of light. To make white light, you have to have a red, a green and a blue LED there to fill in all of the frequencies. However, none of the light is wasted - so they are very efficient. But more importantly, the control over the colors they produce is very precise. When you turn off the red and blue LED's and turn the green one on - you get very pure green light...much much better than the 'muddy' colors you get with a green incandescent.

The control of the brightness is actually easier with incandescents because you can just alter the supply voltage - but that doesn't work with LED's - you have to turn the power on and off a few thousand times a second and alter the amount of 'on time' versus 'off time' to control the average brightness - and rely on persistance of vision to make it look like the LED is dimming. Fortunately, that works very well and you have precise, accurate, repeatable color production.

So, yes, you can kinda do it with three dimmer switches and three colored incandescents - but the result is less than impressive. With the LED's you can literally get any color you could imagine.

SteveBaker (talk) 14:52, 14 January 2009 (UTC)

Uh wait? I have something to say this. I thought LEDs could dim. I have an electronic class in high school and we sometimes do demonstration labs and we used an LED and a Potentiometer and the more resistance that was added the less light was emitted by the LED. Does the Voltage decrease actually cause it to dim or does the LED just shut on and off rapidly like you said? Eric's Trip (talk) 21:27, 20 January 2009 (UTC)

Duration of Venlafaxine withdrawal symptoms?

Greetings,

This is not a request for advice. It is merely a request for facts.

I am wondering what the average expected withdrawal time for 300 milligrams of Venlafaxine (Efexor) would be, dropping from full dose to nothing immediately (yes, I know it's a bad idea, so you don't need to remind me (I've already done it (~10 days ago) and am not going back - I'm just curious as to how long before I'm back to normal).

Thanks a lot, --Aseld ^talk 07:17, 14 January 2009 (UTC)

Aseld, if it's all about you and your body, then afaican make out, it is medical advice that only your doctor who knows what "normal" is, can help you with. Sorry. However we have the articles Venlaxafine and Efexor for your curiosity. Julia Rossi (talk) 07:47, 14 January 2009 (UTC)

That statistic is not reported in any of the academic studies that I can find. Like Julia says, there are so many factors involved that only a medical professional familiar with you would be able to give you anything resembling a meaningful answer. It doesn't answer your question, but this is an insightful New York Times article which may (or may not) resonate with you. [2] Rockpocket 09:00, 14 January 2009 (UTC)

Venlafaxine is probably more effective than other antidepressants. However it has a relatively short half-life (about five hours) that exacerbates withdrawal symptoms, which is why it should be tapered slowly when discontinuing treatment. Axl ¤ [Talk] 10:57, 14 January 2009 (UTC)

There's also a difference between the "wash-out" time (the time it takes for the body to metabolize and excrete the drug as indicated by the half-life -- see pharmacokinetics for more details) and the time it takes for the body to return to it's pre-drug state. Psychoactive medications often cause changes in gene expression in neurons and even some changes in activity in neural circuits (you can find some references on these topics using PubMed), but it is unclear to me how long it takes to revert those changes. --- Medical geneticist (talk) 14:55, 14 January 2009 (UTC)

number of mice in lab

How many mice are living at the moment in the Jackson Laboratory? --Ayacop (talk) 09:58, 14 January 2009 (UTC)

ghits give 3000 genetically-designed mice (no date) and in 2000 claims it distributed more than 1.7 million research mice to 12000 research (centres) – an article in the Scientist for subscribers (not me). If this is the sales number there must be many more at the lab. Julia Rossi (talk) 11:06, 14 January 2009 (UTC)

At any one time: ~750,000. [3] Rockpocket 16:52, 14 January 2009 (UTC)

Breathing out - controlling the temperature/heat

The above comical exchanges (something about a cold thing steaming) got me thinking. I can breathe out and make it 'colder' (by doing a kind of fuh/th sound style blow) and 'hotter' (by doing a kind of 'ahhh' sound style blow). I guess the answer is really simple, but what's causing this? My guess is that the 'ahh' breathe is coming from 'deeper' in my lungs and so has warmed 'more'... 194.221.133.226 (talk) 11:31, 14 January 2009 (UTC)

No, what's going on is that you're using Charles's Law, which says that a gas gets hotter when compressed and cooler when it expands. By adjusting the shape of your mouth, you can control whether the air you exhale expands as it leaves your body. Make the opening wide and it won't expand, so it retains its original heat; make the opening narrow and it will expand and therefore become cool. (Of course the narrow opening also compresses it slightly, but the expansion goes on after the air has left your mouth, more than offsetting that effect.) --Anonymous, 11:40 UTC, January 14, 2009.

I'm skeptical as to whether the pressure difference between the two techniques would be enough to make this difference in perceived temperature. I've always believed that this had more to do with evaporation (and "wind chill"); when you "ahh", the air is moving slowly, so you feel the heat. When you "ffff", you're making a tighter, faster air jet, so your skin is cooled more quickly. The moisture in your breath magnifies the difference, by providing moisture to evaporate and cool the skin. But hey, I could be wrong. jeffjon (talk) 13:50, 14 January 2009 (UTC)

I agree - I doubt the temperature of the breath is measurably different. The difference is that your skin creates a thin layer of near-body-heat air - when you blow on it hard enough - you set up air currents that soon displace that warm air out of the way and the cooler ambient air gets to your skin and it feels cold. That's why you feel cold when you stand next to a fan. In warm weather, you are also removing humid air that contains the evaporated sweat and replacing it with dry air that allows the sweat to evaporate more easily - thereby pulling heat out of the skin. However, if you live in a hot climate (which Texas is for much of the year) and the ambient temperature gets over 100 degrees (ie significantly HIGHER than body heat) - you can really tell which of those two effects is going on. When humid air that's above body heat blows against your skin, you feel HOTTER - it's like a blast of heat when you open the door on an oven! But when dry air (even if it's hotter) blows on you - then you do actually feel cooler because of the evaporation effect. Hence the saying "It's hot - but it's a DRY heat." SteveBaker (talk) 14:41, 14 January 2009 (UTC)

Hmm, interesting discussion. I don't think I made up the explanation I posted as the first response; I think I saw it in a book (but too long ago to be able to actually cite it). It's easy to confirm that the cone of air current when you blow gets significantly wider than the opening of your mouth, which seems to imply that there is expansion going on. But none of this means that it's the right answer: in particular, the pressure change has to be pretty modest, with the widening cone mostly due to other aerodynamic reasons. So, apologies to M. Charles, but I now agree that other factors must be more important. --Anonymous, 04:50 UTC, January 15, 2009.

To be completely clear - I'm not saying that your answer is WRONG - just that I don't think it's the majority factor here. Certainly the pressure changes must have an effect - the gas laws being LAWS and all! I just don't think it's the biggest thing going on here. SteveBaker (talk) 14:34, 15 January 2009 (UTC)

If I blow extremely slowly through a very narrow opening between my lips, but while building up a fair amount of pressure (so that I have to contract my breathing muscles quite hard), the air still feels cold on the back of my hand. If I "huff" as fast as I can with a wide open mouth the air still feels warm. Unless my subjective impressions about the velocity of the air stream hitting my hand are way out this would seem to imply that the velocity/evaporation based effect proposed by SteveBaker and jeffjon is not dominant in these "extreme" scenarios. I realise this is blatently original research, but i'm an experimentalist at heart and couldn't resist. Echinoidea (talk) 22:02, 19 January 2009 (UTC)

two sets of DNA in one person - episode of house.

I am NOT asking for a diagnosis. Just saw an episode of house where they reckon two (IVF) embryos grew into one kid and so the kid had tissue in parts of his body which had different DNA to most of the rest of him. House said it's called something cainurism or keinurism or something sounding like that, i only heard him say it, it wasn't written. I haven't been able to find anything using google so I'm obviously getting the spelling wrong, or they made it up, which I didn't think they did. Anyone know if the condition is real and what it is? Vespine (talk) 11:34, 14 January 2009 (UTC)

It's real. The word is chimerism. --Anonymous, 11:42 UTC, January 14, 2009.

A plot device also used in an episode of CSI. --—— Gadget850 (Ed) ^talk - 11:51, 14 January 2009 (UTC)

Aaaah! Of course, from Chimera_(mythology). Thanks for the prompt reply. The article says there have only been 40 reported cases of humans with the disorder, wow, that House, some luck, lol... Vespine (talk) 11:58, 14 January 2009 (UTC)

I wouldn't call it a disorder in the cases where it doesn't cause any trouble but I don't seem to be able to put my finger on what a difference from the norm like that should be called. Dmcq (talk) 13:47, 14 January 2009 (UTC)

Sorry should just read better, a condition is quite a good word.Dmcq (talk) 13:49, 14 January 2009 (UTC)

So does that mean that someone with this condition could potentially commit a crime and then get DNA tested, and pass the test, and get away with the crime??91.111.119.120 (talk) 14:37, 14 January 2009 (UTC)

Yes, if the two DNA samples came from areas of the body with different DNA. However, the two sets of DNA would show up as siblings, so any siblings to the culprit might briefly be suspects. After they pass their DNA test, though, the cops would look for another (non-existent) sibling. StuRat (talk) 15:11, 14 January 2009 (UTC)

Which is the plot device in the CSI episode "Bloodlines".[4] --—— Gadget850 (Ed) ^talk - 21:29, 14 January 2009 (UTC)

See Lydia Fairchild for details, also Tetragametic humans. Article Genetic Mosaics. There's also microchimerism, which is probably very common indeed. When a woman is pregnant some of her cells will cross into the foetus, some of these will persist for years, and may actually be incorporated into the foetus' body. Conversely some of the foetus' cells may cross over into the mother and remain in her body for decades. A woman who has had many pregnancies may have cells from many different people in her body, it may even be the case that later siblings may have cells from older siblings because these have crossed from the mother into the younger sibs during the later pregnancy. Alun (talk) 21:08, 15 January 2009 (UTC)

Poor performance of guerrillas

Sorry to bring up the current Gaza conflict, but I was wondering how it was possible to the Hamas to cause such low level of casualties. Note: I don't want to start a discussion about politics or ethics, just about the scientific/military aspects of the conflict. We are not in the era of Gatling guns against sharpened sticks, where a modern army could win a fight without any casualties. I know that the Israeli army is better trained and has better equipment, but still, the other side has Kalashnikovs and RPGs, which are by no means obsolete. Without decent anti-armor capabilities they would have no chance on open ground, but a city presents a lot of possibilities for guerrilla warfare, and they even had time to prepare traps, hideouts, ambushes, escape routes, etc. The example of the 1956 Hungarian revolution comes to mind: the soviets had modern equipment, while the revolutionaries had only some obsolete ww2 weapons and hand-made Molotov cocktails, and still managed to cause nearly 2000 casualties and could hold the city for two weeks before more soviet reinforcements came in and won by overwhelming numbers. And many of the fighters never fired a gun before, they were not raised in an environment of constant warfare like Palestine. So, what do you think, what is the cause of that difference? The one dead and two wounded in the first few days of fighting in Gaza city seems strange for an actual war, when such numbers of casualties are not uncommon even on a simple training, without militants firing on them with assault guns from windows. --131.188.3.20 (talk) 13:38, 14 January 2009 (UTC)

But that's not how guerrilla warfare works. The whole point is NOT to try to stand up to large, well-equipped professional armies - that's exactly what they want you to do! When the big guys push towards you, you hide your weapons and melt away into the civilian population. When the big offensive is over, you dig your weapons out of the cache you made in your back yard and go back to picking off odd people here and there and lobbing mortars and rockets at easy targets.

This is why the civilian casualties are so high - the Israeli troops can't tell who is an enemy combatant and who is an innocent bystander. (Or perhaps, more correctly, which buildings contain enemy combatants and which have only innocents...and (nastily) - which have both). Someone high in their command chain says "we had a rocket attack coming from this village - go there and take out the bad guys" - the grunts head out - arrive in the village and everyone there is hiding in their homes trying to look innocent...so what do they do? Blow up a few likely looking places - make some noise - report back "job done". You get 30 civilian casualties and 2 guerrillas. The consequences for civilians is horrifying - but that's the root problem here. When ordinary people allow guerrilla's to hide in their midst - they are signing up for exactly what's happening right now. This is a 'no win' situation for either side - it's a mess - it's horrible. But there is a message here for innocents in places like this: When you allow your government to do this kind of thing - expect to have your children maimed and killed in the future. That in no way condones what the Israeli army is doing - but I don't see any other way they could achieve what their politicians are ordering them to do.

SteveBaker (talk) 14:31, 14 January 2009 (UTC)

I think you may have misunderstood the OP, Steve. I believe he was wondering why so few Israelis have been killed? 13 dead seems incredibly low if you're firing RPG indiscriminately into Israeli towns. -- MacAddct1984 ^{(talk • contribs)} 15:47, 14 January 2009 (UTC)

V-2s didn't kill that many people, either. Unguided, unaimed rocketry has a lot of terror ability but very little practicality when it comes to causalities. You have to get very lucky for your bomb to hit someone alive. Looking out my window now, in the middle of the day, if someone fired a small rocket into my little Massachusetts neighborhood, there is about a 90% chance they wouldn't hit any living being, though they'd do property damage. If you increase the warhead payload of the rocket, you can increase the hit rate, but then you have to invest more in propellant and etc. An RPG has relatively low firepower in such a situation. --98.217.8.46 (talk) 16:45, 14 January 2009 (UTC)

Israel also has extensive early warning capability so civilians are often able to take shelter. Of course the fact that they're probably more likely to die in a traffic accident doesn't negate the very real fear such attacks tend to cause as 98 emphasised Nil Einne (talk) 18:29, 14 January 2009 (UTC)

Early warning? Against what? A mortar shell that will hit in a few seconds? We're not talking about ICBM's that need half an hour to travel to the destination at the other side of the planet. --131.188.3.21 (talk) 23:12, 14 January 2009 (UTC)

Against rockets of course. The sirens are discussed in nearly every news report on the conflict I've heard of on the news or read. Indeed many reports come from journalists who are there when the sirens sound. I'm surprised you've never heard of them before. E.g [5] [6] [7]. How much time these sirens usually give I don't know, this says a few seconds [8] but in this case it was about a minute [9]. I'm guessing it would depend on how far the rocket is trvaelling, what kind of rocket it is and when the alarm is raised. For example, if a militant fires a volley of rockets the first one may hit in seconds but given the time taking to reload etc, I would presume that e.g. by the time the 6th hits it would have been about a minute. Of course, even a few seconds would often be enough to take some form of cover which is likely to reduce the chance of injury and death if the rocket does hit close by. Of course ironically the sirens probably also have the effect of increasing the fear such attacks cause for most of the population. Nil Einne (talk) 08:17, 15 January 2009 (UTC)

Another big difference is training. While the Soviet army at the time of your example had no anti-insurgency training, but were trained for WW2 style wars, the Israeli Defense Forces are specifically trained, and have years of experience in, anti-insurgency tactics. This, along with the factor Steve listed (that Hamas would rather kill civilians, both Israeli and their own, than risk combat with soldiers), makes a huge difference. StuRat (talk) 15:02, 14 January 2009 (UTC)

So you think the initial successes of the rebels in my example were some kind of Pyhrric victory, glorious at the beginning but sooner or later doomed? From a game theory point of view, would it have been a "better choice" instead of building barricades and fighting, just letting in the soviets without a gunshot, and then resorting to terrorism later? --131.188.3.20 (talk) 23:25, 14 January 2009 (UTC)

No, terrorism wouldn't have worked against the Soviet Union, as they'd just wipe out entire towns, or nations, without any qualms, to get at the terrorists. Terrorism never works against an adversary with superior military might which is willing to resort to genocide to win. StuRat (talk) 04:26, 15 January 2009 (UTC)

Military training has changed a lot since the 1950s. The US and countries that it has trained and lent aid to—including Israel—use training methods that were developed, by and large, in the 1960s and 1970s, and emphasize the ability of every individual soldier to kill. That doesn't seem like much but when you compare the no-fire rates of previous wars (soldiers who actually did not fire their guns, or fire over the heads of the enemies, subconsciously) it makes a huge difference.

Training makes a huge difference, though Hollywood films would lead us to think otherwise. There's a great book on this: On Killing: The Psychological Cost of Learning to Kill in War and Society, by a military psychologist. Check it out. When forces of this sort of training come up against irregular or poorly trained forces, they end up killing them at very, very high rates (though this does not always translate into military victory, for a variety of complicated reasons). --98.217.8.46 (talk) 15:24, 14 January 2009 (UTC)

Guerrillas were able to inflict a high rate of causualties against US forces in Vietnam and against Soviet forces in Afghanistan. A Quest For Knowledge (talk) 16:54, 14 January 2009 (UTC)

Not in comparison to the rates of casualties they themselves suffered. In Vietnam the US killed Vietnamese at a ratio of about 20:1. (And I don't think the Soviets were doing the sort of training I mentioned, so I won't count them, though I'm fairly sure the ratios are about the same.) But again, war isn't just about attrition. --98.217.8.46 (talk) 18:28, 14 January 2009 (UTC)

I think a big point people are missing is that Israel's medical facilities are largely unaffected by this crisis, very few casualties and very few buildings have been hit in Israel itself. Therefore, they can treat their wounded much, much more effectively than the doctors in Gaza who are working on little to nothing right now, and therefore cannot save people as effectively. —Cyclonenim (talk · contribs · email) 19:17, 14 January 2009 (UTC)

Thanks for all the interesting answers. However, my question was not about the artillery strikes ongoing before the current attack, but the actual urban combat. --131.188.3.20 (talk) 21:05, 14 January 2009 (UTC)

See the book I cited earlier. Training matters a whole lot. Fighters trained using WWII-era drills will get decimated by those using modern Behaviorist techniques. --98.217.8.46 (talk) 00:54, 15 January 2009 (UTC)

There is an alternative possibility. (I'm not saying it's true, however, as I will explain, it fits very well with my model of how societies work.) Perhaps there is no rocket fire, etc, and Israel is just making it up. I'm not saying that the Israelis don't actually live in fear of rocket attacks, or that there aren't constant warnings. I'm just saying that if the rocket attacks are just made up by Israel, or blown vastly out of proportion, it would explain why you're not seeing casualties as a result. Why does this explanation fit with my model of how societies work? You need look no further than Amercan and Bush's second term: he was elected easily, by keeping the population in fear. This is one of the only tools used to keep a population amenable to military exigencies they would not otherwise support: keep them in fear. So, if Israeli's military has a very different conception of how the neighborhood should be run than Israeli's population, an effective means of exerting their will over that of Israel's population is by keeping the population in fear and a state of war. We've seen it over and over in America, both recently and long ago, so I don't see why it shouldn't apply to another democracy very much like our own, Israel. (Of course, I'm not saying that this is in fact the reason for such few casualties; I'm just saying it seems highly plausible for me). —Preceding unsigned comment added by 82.124.85.178 (talk) 23:02, 14 January 2009 (UTC)

The Israelis aren't reporting any higher rates of rockets than are being observed by the press, as far as I can tell. The #1 reason you wouldn't lie about such a thing, if you were a government, is because it's pretty easy to check and confirm. (And the main "fear" that Bush used in the second election had to do with gay marriage, not terrorists.) Even the Israeli accounts of the rocket attacks are quite low—the issue is that they kept up despite warnings that they should stop them, not that they are killing many people. (And if you're going to go down the "maybe it's all just made up" rabbit hole, why wouldn't they just inflate the casualties, too?) --98.217.8.46 (talk) 00:54, 15 January 2009 (UTC)

Another point, at least about the very beginning of the war, is that the Israelis have had time to study Gaza, identify targets, and plan strategies. In that way it is not a traditional guerrilla war. I'm sure Israel began the war by targeting the ammo dumps, rocket facilities, and other Hamas assets that they already knew about from years of surveillance. Modern militaries can be very effective when they know what they are going after, especially if you can just blow up a building with a bomb or a tank. Going after targets that they don't have good intelligence about will probably prove a more challenging endeavor. Assuming a significant fraction of Hamas' assets survived the initial assault, I would expect to see them begin to inflict more losses on the Israeli forces (though still not comparable to the losses being inflicted by Israel). Dragons flight (talk) 02:03, 15 January 2009 (UTC)

Another distinct possibility is that the majority of Gazans are not fighting back. Nimur (talk) 17:23, 15 January 2009 (UTC)

If this were the case, who are the Israelis firing upon? --131.188.3.21 (talk) 22:20, 15 January 2009 (UTC)

Presumably the few who are fighting back? Alun (talk) 22:31, 15 January 2009 (UTC)

Plus a few hundred civilians, of course. Algebraist 22:32, 15 January 2009 (UTC)

Geography of Quebec

What is the cause of the semicircular gap in Quebec on the border of Hudson Bay ? It sure looks like a giant meteor crater: [10]. StuRat (talk) 14:54, 14 January 2009 (UTC)

As linked from the bay's article: Nastapoka arc. --Tardis (talk) 15:35, 14 January 2009 (UTC)

That's just a stub, which, strangely, didn't have a map (until I added one), and didn't mention Quebec (until I added it to the map's caption). All it has to say about the geology is:

"The Nastapoka arc is a geological feature located on the southeastern shore of Hudson Bay, Canada. It is a near-perfectly circular arc, covering more than 160° of a 450 km diameter circle. Due to its shape, the arc has long been suspected as the remnant of an ancient impact crater, but no evidence has been found that conclusively supports or discounts this theory. Another common explanation for the arc's origin is glacial loading during an ice age."

The glacial loading link is broken. Do we have an article on that and how it could produce such a circular arc ? StuRat (talk) 18:30, 14 January 2009 (UTC)

I think Post-glacial rebound is the article you're looking for, but I'm not sure enough to add a redirect. --NorwegianBlue ^talk 22:27, 14 January 2009 (UTC)

Do you know of any way that post-glacial rebound could produce a circular arc ? StuRat (talk) 04:20, 15 January 2009 (UTC)

No. I found the article through a google search. Here's the relevant quote from the article:

Recently, the term post-glacial rebound is gradually replaced by the term glacial isostatic adjustment. This is in recognition that the response of the Earth to glacial loading and unloading is not just limited to the upward rebound movement, but involves downward land movement, horizontal crustal motion, changes in global sea levels, the Earth's gravity field, induce earthquakes and also changes in the rotational motion. --NorwegianBlue ^talk 08:38, 15 January 2009 (UTC)

Thanks. I think I might remove that reference: "Another common explanation for the arc's origin is glacial loading during an ice age", as there doesn't seem to be any reason why that would produce a circular arc. StuRat (talk) 20:07, 15 January 2009 (UTC)

M2 Browning machine gun accessory

What's the name of that optical device mounted on the M2 Browning machine gun as seen in the picture? IR would be red or not....?! --77.4.32.145 (talk) 17:03, 14 January 2009 (UTC)

AN/TVS-5 Crewed Night Sight.[11] The Ma Deuce also has a blank adapter on it, as does the M16 to his side. --—— Gadget850 (Ed) ^talk - 17:31, 14 January 2009 (UTC)

Cool, maybe someone could add that to the file and most of all in the article about the gun. It's not there.... --77.4.32.145 (talk) 17:39, 14 January 2009 (UTC)

I had to think hard to remember the night sight and the blank adapter. I added this to the image description on Commons. --—— Gadget850 (Ed) ^talk - 17:58, 14 January 2009 (UTC)

Shall we assume that the photographer who took this shot is no longer among the living ? :-) StuRat (talk) 22:26, 19 January 2009 (UTC)

Bandy Ball

How is a bandy ball made?96.53.149.117 (talk) 17:48, 14 January 2009 (UTC)

This image from our article suggests that it's first cut from a solid chunk of cork then covered with a 'knitted' covering and finally painted. Weird. The "knitted" bit is definitely the oddest step. Interestingly, it seems that Golf derives from BandyBall - and the dimples in the golf ball originated as the dimples in the 'knitting' on the Bandy ball. SteveBaker (talk) 18:10, 14 January 2009 (UTC)

Given that you diverge from all history I have ever seen on both golf and the golf ball, I'm asking for some sauce. Or are you making some joke I have missed? 79.66.46.92 (talk) 19:06, 14 January 2009 (UTC)

(ec) ^{[citation needed]}? My understanding is that golf balls were originally smooth (or had a few seams); dimples were only added after golfers began to notice that 'used' balls – with scuffs and scratches – actually flew farther than perfectly smooth balls. See, for example, [12]. The origins of golf, meanwhile, are somewhat murky. TenOfAllTrades(talk) 19:10, 14 January 2009 (UTC)

http://www.madehow.com/Volume-3/Golf-Ball.html ^{[citation supplied!]}

"The game of golf goes back as far as 80 B.C. when the Roman emperors played a game called paganica using a bent stick to drive a soft, feather-stuffed ball (or feathery). This ball was up to 7 in (17.5 cm) in diameter, much larger than the Scottish version. By the middle ages, the sport had evolved into a game called bandy ball, which still used wooden clubs and a smaller ball about 4 in (10 cm) in diameter. Over the next five centuries the game developed on several continents and eventually evolved into the popular Scottish game known as golfe." SteveBaker (talk) 22:10, 14 January 2009 (UTC)

Hmmm, but that bit doesn't fit with a) the history of golf and golf balls given in the rest of the same article b) the history of golf and golf balls given in our article c) the history of bandy ball given in our article. Nor does it mention anything about the dimpling having originated with the knitting, which is good as it would almost certainly be wrong. Unless that section is in fact saying that the game paganica developed into many games over the centuries, including bandy ball and eventually golf, in a much more branching than linear manner. 79.66.46.92 (talk) 10:07, 15 January 2009 (UTC)

I know the English text of the picture says "knitting". However it looks more like Macramé. 08:39, 15 January 2009 (UTC)76.97.245.5 (talk)

USP

I know USP means the United States Pharmacopeia, but what exactly does it mean when the term USP follows the name of a drug, as in "Lidocaine HCl Injection, USP 2%" or "Clarithromycin Tablets, USP"?—msh210℠ 19:35, 14 January 2009 (UTC)

It means that the drug meets the standard specified in the pharmacopoeia. Standards will include purity, and lack of contaminants, or the precise definition of the product (for example does a plant based product include roots stems or leaves). Graeme Bartlett (talk) 20:18, 14 January 2009 (UTC)

Thanks.—msh210℠ 18:44, 15 January 2009 (UTC)

Human perception of light versus sound

I was reading recently about how the colour humans perceive as magenta does not technically exist (i.e. possess a wavelength). Rather, it is a colour invented by the brain to make sense of mixing blue and red inputs--if the wavelengths were averaged, the resultant colour would be green, from memory. Thus, the mind takes the visible part of light from the infinite dimension and turns this snippet into a loop: red -> yellow -> green -> cyan -> blue -> magenta -> red etc.

As a result, we don't have a hierarchical understanding of what colour is--i.e. we can't say if blue is 'less' than green or 'higher' than red.

Humans also only perceive a snippet of the sound spectrum (between about 50 and 20000 Hz from memory). This we do not loop, and thus end up with a hierarchy--we intuitively know if one note/sound is higher or lower than another.

What's the advantage of these different approaches in each case?

Disclaimer: My biology/psychology understanding is infantile, and my physics is rusty. —Preceding unsigned comment added by 86.43.214.168 (talk) 21:57, 14 January 2009 (UTC)

The color loop is partially a result of the way human vision works (Trichromacy has some info). The pigment in the eye which responds most strongly to red light has a secondary peak in the violet area, so we perceive red as being "close" to violet. Another part of the reason for the color wheel is human invention: the connection between red and violet is made by combining these two pigments gradually, simulating a smooth transition. (Color wheel has good info on this).

The way we perceive colors is by the stimulation of four nerve signals to varying degrees:Three color cone cells and rod cells which detect brightness. This is in complete contrast to the way humans perceive sounds, which is by basically counting the number of vibrations per minute of our eardrum.-RunningOnBrains 00:00, 15 January 2009 (UTC)

Doesn't matter - if you take PURE blue light and PURE red light and mix them (such as you do on the computer monitor right in front of your nose) - you get magenta. Turn off the red - and you see only blue. The little amount of blue that the red receptor can pick up is much higher in frequency. So the OP is correct. Weirder (IMHO) are the two sorts of 'yellow' out there - the kind that's a mixture of red and green and the kind that has a frequency halfway between the red and green. They both look identical to us - but they are as "different" as magenta and green by any objective measurement! At any rate - the difference between sound and light is simply how they are detected. Your eyes have sensors that operate (essentially) at just three frequencies. Your ears have a bazillion little hairs that respond with great sensitivity to the entire audio spectrum - so you can easily tell the difference between the sound of a 'C' and a 'D' played together as a chord - and a C# which is between those two frequencies. The lack of that 'pitch ambiguity' means that we don't get fooled in the ways our eyes do. Having said that - read about the Shepard tone and listen to the audio snippet at the bottom of the article. SteveBaker (talk) 02:29, 15 January 2009 (UTC)

Well, yes and no. If you take PURE blue light and PURE red light and mix them (such as you do on the computer monitor right in front of your nose) - you get the closest approximation that a monitor can make to magenta, which computer guys tend to call magenta, even though it is a pale imitation of the lovely color used by printers. - Nunh-huh 13:46, 15 January 2009 (UTC)

Well - let's be really careful about that statement (I'm a computer graphics guy - and I live and die by the answers to this kind of matter!). Certainly the color gamut of some printing processes are larger than for a CRT - meaning that there are in general some colors that you can print that cannot be represented on a CRT. However, if you examine the standard CIE chromaticity diagram for print and for CRT's you'll see that there are huge regions where print can't go but a CRT can. This image shows the colors a CRT can display (inside the triangle) and the colors that you can reach with CMYK offset printing (inside the rounder 'blob'). You'll see that there are indeed (as you claim) shades of magenta that an offset printer can produce that a CRT can't touch...but there are other shades of magenta where the reverse is the case. In truth, it depends on the individual monitor because (as this image shows) two monitors made by different processes (eg LCD versus Plasma versus CRT versus OLED versus DLP) - or even two CRT's made by different manufacturers often have different gamuts. Doubtless there are issues about where you buy your ink from when doing offset printing if different manufacturers use different pigments. FYI: The entire document from which I took those images is here - and it's quite an informative read. See also: [13] and [14]. SteveBaker (talk) 14:24, 15 January 2009 (UTC)

Well, yes, as a computer guy, you're talking about "magentas", but I'm talking about "magenta". Magenta was discovered by Emmanuel Verguin in 1858 while researching aniline dyes. He initially called it "fuchsine"; in Britain it became known as "solferino" and then "magenta". "Magenta" is the color of a particular chemical substance, whose structure is known, and was tweaked to form other dye colors: aniline yellow, bleu de Lyon, bleu de Paris, Nicholson's blue, aldehyde green, and various shades of violet. But only the first substance is properly "magenta". Garfield, Simon (2000). Mauve: How One Man Invented a Color That Changed the World. New York: W.W. Norton & Co. pp. 78–9. ISBN 0-393-02005-3. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help) - Nunh-huh 17:01, 15 January 2009 (UTC)

It may not be relevant, but the frequency of visible light is around 500 terahertz, or about 25 billion times higher than the highest sounds we can hear. It seems to me that it's probably not practical to directly measure the frequency of light as we do with sound, so an alternative method is required. Seeing how much of the light is absorbed by each of 3 different pigments and working out what colour it is from there is nowhere near as precise as a direct measurement, but it is far easier. --Tango (talk) 01:15, 15 January 2009 (UTC)

Thank you both very much for the helpful, informative replies--you've quenched my curiosity for the day! --86.43.214.168 (talk) 01:42, 15 January 2009 (UTC)

Already? You need more curiosity! --Tango (talk) 01:56, 15 January 2009 (UTC)

Well, you guys piqued my curiosity! I've bookmarked those two articles so I can read them later when I have time. I do find it rather fascinating that human beings (of all the species on Earth) are aware of their own limitations. A Quest For Knowledge (talk) 13:39, 15 January 2009 (UTC)

I strongly disagree with that last sentence. My dog knows her limitations. She knows (for example) precisely how high she can jump - and will not attempt to jump into the tailgate of my car - when she's only too happy to jump into my wife's car - there is only about an inch difference in height but that's right on her physical limit. She'll be coiled up like she's about to jump - then you can see her mentally judging the height - then she gives up and just looks at me for help. You're probably going to claim that she simply doesn't like being in the back of my car - but that's not so: she enthusiastically runs up to the back of the car but only gives up when she realises (for the hundredth time!) that it's simply too high for a clean jump. If I open the passenger door and tip the seat forward - she happily clambers in. I think most animals know all too well what their limitations are. We humans constantly look for things that separate us from "the animals" (we speak, we have grammar, we use tools, we make tools, we have wars, we are self-aware, we have compassion, we are aware of our own limitations) - when in reality there are plenty of other animals that can and do perform all of those things. The gap is much narrower than people would care to imagine. SteveBaker (talk) 13:52, 15 January 2009 (UTC)

Well, for non-obvious things. It takes a lot of ingenuity to figure out this color issue. A Quest For Knowledge (talk) 19:04, 15 January 2009 (UTC)

Now you're married?? The plot dickens. —Preceding unsigned comment added by 82.124.85.178 (talk) 18:08, 15 January 2009 (UTC)

How so? SB's wife/marriage has been mentioned numerous times before and I myself mentioned it in my reply to your earlier message, written before your message. Are you going to claim he said he belonged to a bachelor's club now (again without evidence I guess)? Nil Einne (talk) 22:22, 15 January 2009 (UTC)

We Poles are a deep and mysterious people. ;-) SteveBaker (talk) 01:44, 16 January 2009 (UTC)

Something smells fishy...

This isn't to besmirch the noble and wonderful vagina--they're great and i love 'em.

BUT I have noticed that during menstruation times, there is a distinct "fishy" odor.

What common ingredients are there that cause this? Is it the acidity?192.136.22.6 (talk) 23:14, 14 January 2009 (UTC)

Trimethylamine is enriched in menstrual blood, giving it a distinct odor. Rockpocket 00:57, 15 January 2009 (UTC)

In other words, it smells like fish because it smells like fish. Really. --jpgordon^∇∆∇∆ 17:00, 17 January 2009 (UTC)

Speed of light

I heard that the speed of light in a diamond is faster than the speed of light. Is this true that it can go faster than c through some medium than a vacuum? 130.127.3.249 (talk) 23:46, 14 January 2009 (UTC)

No, unfortunately. If it did, all of modern science would have to be thrown away. It is possible (though I'm not sure) that light travels faster in a diamond than it does in air. Do you happen to know where you heard/read this?-RunningOnBrains 00:02, 15 January 2009 (UTC)

After reading a bit more, it turns out that the speed of light in a diamond is significantly less than that in air, around 0.5c. -RunningOnBrains 00:08, 15 January 2009 (UTC)

(ec) See Faster-than-light#FTL_phenomena. I don't think a diamond as a medium, by itself, would give you apparent FTL behavior, but some media give what appear to be FTL results—the light is detected before it has left and things like that. But you cannot transfer information faster than the speed of light in a vacuum, which is what most people actually mean (though they don't know it) when they talk about faster-than-light speeds. The physics of it is rather complicated and not very well spelled out in that article. --98.217.8.46 (talk) 00:07, 15 January 2009 (UTC)

(3 edit conflicts... popular question!) It's slower in a diamond, not faster. The refractive index of diamond is 2.419, which means the speed of light in diamond is less than half that in a vacuum. It is, however, possible for light in certain circumstances to travel faster than the speed of light in a vacuum, but it depends on your definition of the speed of a wave - you may wish to read about phase velocity, group velocity and signal velocity. It's the signal velocity that can never be faster than c, the phase velocity and (occasionally) the group velocity can be faster, but that doesn't allow information to travel faster. --Tango (talk) 00:08, 15 January 2009 (UTC)

Also, refractive index (indicating the speed of light in a material) depends on the color (wavelength) of the light. As everyone knows, thats why a prism produces a color spectrum, and it's why diamonds sparkle with different colors. It's also why color aberration occurs with uncorrected lenses. For the refractive index of various transparent materials for light at 589 nanometres wavelength, see "List of Refractive Indices" in Wikipedia – GlowWorm —Preceding unsigned comment added by 174.130.253.174 (talk) 01:01, 15 January 2009 (UTC)

Silicon has a refractive index of 4.01, which is much higher than for a diamond. So why don't silicon crystals sparkle with different colors the way diamonds do? – GlowWorm —Preceding unsigned comment added by 174.130.253.174 (talk) 01:17, 15 January 2009 (UTC)

It may highly refract what light does go through, but isn't it pretty opaque? How it's cut will also be significant - diamond only sparkles properly if it is cut at just the right angles. --Tango (talk)

You're right, Tango. The material must be cut at the proper angles to get colorful refraction. As for refractive index, I found the following graph for silicon, from the Ioffe Institute in Russia:

http://www.ioffe.ru/SVA/NSM/nk/Silicon/Gif/asi.gif

If I understand the graph correctly, the refractive index of silicon depends on the strength of the light. In strong light, it becomes much less. Absorption of light also increases greatly as light strength increases. So silicon would not make a good jewel. But I wonder if that is what is used in the welder's helmets that have a viewing window which darkens under the bright light of electric welding. GlowWorm —Preceding unsigned comment added by 174.130.253.174 (talk) 03:52, 15 January 2009 (UTC)

No, the graph shows the components n and k of the complex index of refraction as a function of photon energy. This graph has nothing to do with how strong the light is. As for how the auto-darkening helmet works, see here. Dr Dima (talk) 05:32, 15 January 2009 (UTC)

A lot of confusion stems from improper use of the group velocity and phase velocity for an electromagnetic wave. Both of these quantities are always less than or equal to c, regardless of the material. In nondispersive materials, v_g = v_p. In dispersive materials, this equality is not preserved. Some (sloppy) scientists compare these two quantities and call one of them the "speed of light in the material" - so it is possible that this sloppy terminology has caused confusion. They should properly refer to the individual velocities, and reserve the phrase "speed of light" for unambiguous situations. Nimur (talk) 17:38, 15 January 2009 (UTC)