Wikipedia:Reference desk/Archives/Science/2010 December 23

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December 23

ASB THE POLYMATH- opc question

What is the chemical composition of OPC drum coating solution i.e. CTL liquid? what can I use to coat OPC drums at home? —Preceding unsigned comment added by 117.242.112.81 (talk) 09:28, 23 December 2010 (UTC)

It would help if you could explain what those abbreviations mean. StuRat (talk) 15:52, 23 December 2010 (UTC)

OPC seems to mean Organic PhotoConductor and CLP should be Charge Transport Layer. --Cookatoo.ergo.ZooM (talk) 21:09, 24 December 2010 (UTC)

I expect the OP is asking about how to make a Xerox copier. Cuddlyable3 (talk) 15:54, 25 December 2010 (UTC)

Two questions about lightning

1. Several years ago, I was in my apartment sitting in front of my computer. To my left was my stereo and to my right was my electric guitar and amp. Everything was plugged in. There was a sort of thunderstorm outside, nothing too heavy, but suddenly, there was a massive explosion of sound, but I never saw any light. As I sat there, time seemed to slow down, and in an extremely slow fashion, my entire body felt like it was expanding. I later described it to people as if every cell in my body had become a balloon and was being filled with a bit of air. I didn't move, either because I couldn't or because I wouldn't, and I honestly thought I was going to explode. But there was absolutely no pain. Just that uncomfortable feeling that lasted a few moments, and then my body "deflated" just as slowly. By the time I realized the situation was over, my computer was shut off. Everything was dead, and only the electric guitar still worked (half of the amp was destroyed, but it still worked on one insert). I've looked at the articles on positive lightning and lightning EMPs, and I've since done some research on Google, but I haven't been able to find any human recounts of physically witnessing an EMP. So my question is, was what I went through a lightning EMP of sorts? What was it doing to my body?
2. Back in the early 90s, I was backpacking through the US southwest during a storm. On the horizon, a strange bolt of lightning appeared. I cannot find an image of what it looked like (I've looked online for years), but imagine a straight bolt of lightning from sky to ground, but every few yards (massive estimation), the bolt expanded into a huge ball. There were three or four balls of light, like Christmas lights on a string, or popcorn on a necklace, within this bolt (or on this bolt), thus: ---O---O---O---O---. I keep running into ball lightning, but this wasn't a single ball of light moving around strangely. This was merely a bolt with a few glowing globs built in. The bolt acted like any bolt would: it appeared quickly, then faded quickly.

Any ideas on what it could be? Thanks for any help on this! Reflectionsinglass (talk) 09:28, 23 December 2010 (UTC)

Something like this: Transcranial magnetic stimulation may be related to what happened to you. This is interesting too: Ball lightning#Transcranial magnetic stimulation (and a nice synchrony with your next question). Regarding #2 the first thought that came to mind was birds :( - the bolt may have traveled from bird to bird before hitting the ground, and each bird burst into flame (I hope they died quickly :( Was the storm very sudden? I assume birds normally take cover during a storm. Another idea: Cosmic rays are hypothesized to stimulate lightning[1] strikes, maybe it was a meteor? It's possible that could do it too (but I've never actually heard or read anything to suggest that, so it's speculation only). Ariel. (talk) 09:47, 23 December 2010 (UTC)

For #2, perhaps it was Bead Lightning? Or perhaps it was more an optical effect, due to over-saturation of your retina? -- JSBillings 14:13, 23 December 2010 (UTC)

For 1), I wonder if it wasn't so much the effects of an EMP on your physiology that you experienced as it was a startle response that you experienced when you heard the massive explosion of sound. Was that thunder, or did it come from your amp and speakers before they blew? WikiDao ☯ (talk) 20:02, 23 December 2010 (UTC)

Simpler causes than EMP for the subjective effects the OP reports might be tentatively confirmed or eliminated by taking an EEG test. In the hospital procedure, strobe light may be used to stimulate a possible abnormal (epilepsiform) response. Cuddlyable3 (talk) 15:51, 25 December 2010 (UTC)

Light

Does light can be used disturb the moving particle be any metal or nonmetal (car, fish, ball,etc) because of its dual character in nature (as particle cum wave)? Please provide me is it possible? isn't it. (or) How it can be possible? (else) Any other suggestions regarding it. Kanniyappan (talk) 10:52, 23 December 2010 (UTC)

Light can move an object because light has momentum like anything else. But it's not because of the dual character of light. Just like if you throw grains of sand at something you can move it, you can do the same with light - but light does not weigh very much, so it barely moves the object. But light does move single atoms quite well, since atoms weigh so little. How well do you read English? I can link to some articles about this, the main ones would be solar sail and Radiation pressure, the others would be Momentum of photon and laser tweezer, but those are harder to read. Maybe this version is easier? simple:Radiation pressure. Ariel. (talk) 11:07, 23 December 2010 (UTC)

One clarification, a photon has no rest mass, so it's not like sand in that way. It does, however, have the equivalent to mass due to it's speed (the speed of light, of course). This is a result of relativity, which is difficult to explain (perhaps someone else will try). And, of course, both waves and particles can do work, so either model of light can explain why it can move objects. StuRat (talk) 15:47, 23 December 2010 (UTC)

(ec) In fact, light weighs exactly zero - its mass is exactly zero. A photon can have momentum, because in the relativistic treatment, momentum is not exactly equal to (mass × velocity) as it is in Newtonian mechanics. In fact, we have an article/section on relativistic momentum which explains this well. In mathematical terms, relativistic momentum is defined by a Lorentz transform; in "laymans' terms", you can simply understand that even a massless particle (such as light) can carry momentum and cause another massive particle to "move" after a collision. The simplest worked example is called Compton scattering, in which incident light hits matter and exchanges momentum and energy with an electron. The equations that define Compton Scattering are explained in our article; depending on the energy of the incident light, it can cause total ionization of an electron. More sophisticated light/matter interactions are described in detail by other processes; the photoelectric effect is one of the more practical uses of light impinging on matter. Nimur (talk) 15:53, 23 December 2010 (UTC)

You said: "in "laymans' terms", you can simply understand that even a massless particle (such as light) can carry momentum and cause another massive particle to "move" after a collision". That doesn't seem intuitively obvious, to me. In fact, I would assume the opposite, based on lighter objects causing proportionally less movement. StuRat (talk) 21:22, 23 December 2010 (UTC)

I make no assertions that any of that is intuitive or obvious - but it is correct and is the way that light interacts with matter in this universe. If you want to get an intuitive feel for relativistic light/matter interaction, all I can suggest is to spend a lot of time working with experimental setups that exhibit this momentum property of photons, and after you see the experimental results turn up the same way a whole lot, they will seem perfectly "normal" and intuitive to you. Or, if you are not the type who wants to independently verify such things, you can accept this fact on faith and trust myself and the many physics textbooks that attest to its veracity. Nimur (talk) 21:46, 23 December 2010 (UTC)

I'm not doubting that it's true. After all, I said as much in my first post. I'm just saying it's not intuitive. StuRat (talk) 00:06, 24 December 2010 (UTC)

BTW there is a reason I did not mention the massless nature of light, and that's because while it obviously has zero rest mass, while it's traveling it does have mass, inertia, momentum and everything else a massy particle has. And except for its refusal to change speed it acts exactly like something with mass. And even the zero rest mass thing is just another way of saying that when it doesn't exist it doesn't have mass. Remember that when light stops the mass doesn't disappear (zero rest-mass) the mass gets deposited onto whatever stopped the photon and the photon is converted into something else. Pretty much the only implication of zero rest-mass is that it travels exclusively at the speed of light, and the implications of that are beyond the scope of the original question. Ariel. (talk) 22:18, 23 December 2010 (UTC)

Thermoelectric

Can u please give me the emf induced and current flowed when thermoelectric couples of zinc and copper wires kept with 5°C of change in junction temperatures between hotter and colder junction kept at a distance of one meter? Please give also any other thermocouples gives more emf or current for the same standards mention above.Kanniyappan (talk) 11:04, 23 December 2010 (UTC)

The Seebeck coefficient of a metal isn't quite constant, but in the 0-100°C range, it's about 3.4μV/K for zinc, and about -1.8μV/K for copper.[2] So from the second equation in the article section Thermoelectric effect#Seebeck effect, a zinc/copper thermocouple with a temperature difference of 5°C will produce an EMF of about 26μV (with no load).

The current produced would depend on the load, as per Ohm's law. For very low-resistance loads, the non-zero resistance of the wires would need to be taken into account, and for that, you'd need to specify the cross-sectional area of the wires used, so that the resistance of the wires can be computed from the resistivity of zinc (59.0nΩm) and copper (16.78nΩm).

For materials that exhibit the thermoelectric effect more strongly, see Thermoelectric materials. Red Act (talk) 17:54, 24 December 2010 (UTC)

Dragon's breath

It's been very cold here in Blighty lately and this has had me wondering. Is there a specific temperature at which dragon's breath appears? (when you can see your breath when you exhale on a cold day). --TrogWoolley (talk) 14:28, 23 December 2010 (UTC)

The short answer is 'it depends'.

The longer answer is, it depends on the current relative humidity, ambient temperature, and local wind. The air that you exhale is going to be fairly close in temperature to your core body temperature (it just came straight from your lungs, after all) and at close to 100% relative humidity at that temperature. What that means is that the dew point for that air – the temperature at which the exhaled air is supersaturated with moisture and capable of precipitating out liquid water droplets as fog or dew – is just a few degrees below your body temperature. So, if that's true, why is it that you don't see a cloud of fog all the time?

First, when air saturated with moisture is chilled, droplets don't form instantaneously; the process takes some time to occur, and often relies on the presence of nucleation sites (little bits of dust and whatnot) in the air to kick the process off. Nucleation and droplet formation are faster when the temperature is further below the dew point and the air is more supersaturated, so visible fog formation is more likely in chillier air.

Second, fog is forestalled if the supersaturated air is diluted rapidly to a non-saturated state. If there is rapid, turbulent airflow (blustery wind!) in front of your face, then the exhaled supersaturated air is mixed quickly with very unsaturated ambient air and no droplets form. Finally, the effectiveness of this dilution is going to depend on how much water there is the air around you. If the ambient air is nearly saturated with water, then you need to mix a much greater volume of it with your breath to dilute the resulting blend down to an unsaturated state — if the ambient relative humidity is high, you'll be able to see your breath much more readily than under conditions of low humidity. (Under low-humidity conditions, any droplets that do form will also evaporate and disappear much more rapidly.) TenOfAllTrades(talk) 15:30, 23 December 2010 (UTC)

Good answer. One other thing I would add is that lighting conditions matter. The ideal lighting condition would be darkness with a sunbeam right on your breath, so that the lighted water droplets stand out against the darkness. On the other hand, if the sunbeam is in your eyes, and not on your breath, you may not see your breath. StuRat (talk) 15:42, 23 December 2010 (UTC)

I wondered the same thing and actually tried to work it out myself. To give a "rough" answer, where I live in Melbourne Australia, under the conditions that were present when i conducted my experiments, I found the temperature to be around 11 or 12 degrees (EDIT: Celsius) when I could begin to see my exhaled breath. I however have no idea how much that could vary depending on the other conditions mentioned above, such as humidity. Vespine (talk) 01:12, 24 December 2010 (UTC)

Resolved

- thanks guys! --TrogWoolley (talk) 11:15, 24 December 2010 (UTC)

is flow of holes called current flow?

flow of electrons is called as the current flow, but whereas the holes are also moving from the p region to the n region. Then why can't we say that the flow of holes is called as the current flow? —Preceding unsigned comment added by 117.197.186.12 (talk) 17:41, 23 December 2010 (UTC)

Hole flow and electron flow are just two ways to look at the same thing. If a hole flows one way, it means that an electron went the opposite way. Some people find it easier to think in terms of hole flow. Some find it easier to think in terms of electron flow. -- kainaw™ 17:46, 23 December 2010 (UTC)

Perhaps see conventional current (which redirects to the conventions section of current but seems to say it nicely). RJFJR (talk) 18:04, 23 December 2010 (UTC)

Climate change and biodiversity

People keep on warning about the "devastating" effects global warming could have on biodiversity, yet the geological past and present of our planet points to the contrary. We should take into account three main things:

• In periods such as the Eocene, global temperatures were much higher than today, just like biodiversity. Biodiversity has been declining ever since the world started to cool in the Miocene. Therefore, warmer climates are more conducive to a high biodiversity.
• Biodiversity hotspots in all the world are concentrated in warm areas, whereas polar areas are much poorer. It's better to lose a small percentage of species to global warming than a large percentage to global cooling.
• It is naive to believe that, if we don't alter the climate, it will stay the same forever. If the climate doesn't warm up, we're headed straight for a new glacial period which really won't do much good to biodiversity.

Why do people continue to consider climate change bad? Are there any factors I haven't thought of (not counting hippyish, kumbayah-irrational arguments). --79.89.248.148 (talk) 19:08, 23 December 2010 (UTC)

I think the problem are the speed of change. I think fast climate change in any direction is one cause for mass extinction events. Diverse ecosystems move very slowly and many will be extinct be cause of the climate change. It is possible that the biodiversity would be greater after some millions of year with higher temperature but most predictions relating to AGW take a shorter time scale of millennias or less. Of course will the climate continue to change what ever we do but the AGW are faster than most natural changes. --Gr8xoz (talk) 19:41, 23 December 2010 (UTC)

In addition to the speed of the change, it's a matter of changing the climate to something we aren't used to, or prepared for. Sure, many plants and animals will thrive, but our coastal cities will all be flooded by rising sea level, and Europe will lose the Gulf Stream and become as cold as it really should be, at that latitude. Much more severe hurricanes will make living near the US Gulf or Atlantic coasts a bad idea, and tornadoes will do the same for the Central Plains states of the US (and soon Canada). So, if we all are willing to move north and inland, then we can survive. But considering the portion of humanity that lives in warm areas or near the sea, that's a tall order. Also, some species, like polar bears and certain penguins, may become extinct, because the climate to which they have evolved will no longer exist. StuRat (talk) 20:29, 23 December 2010 (UTC)

I encounter conceptual problems with Biodiversity#definitions and Biodiversity#Human_benefits. Are we trying to save and promote the diversity of the megafauna (i.e. pandas, which are largely decorative), the microfauna (which we depend on), or the humans? These lead to different notions of "diversity" - for instance, does "diversity" include the diversity of diseases hostile to humans and injurious to our food supply? Do we score the pandas higher than worms because they're bigger, or lower than worms because they're useless (not even doing much good for their own ecosystem), or equal because they're a species? Is preserving an animal in a zoo, or a seed in a seedbank, a valid way of preserving biodiversity, or does the biodiversity have to be active in an ecosystem, and if so, for what reason? So you end up with political and philosophical questions about what sort of world is a good world, and how we view ourselves. Are we concerned about biodiversity because a lack of genetic variation might spoil our plans to turn the world into a massive farm, or because it might spoil our plans to turn the world into a massive garden, or just because we like genes for their own sake? Like Gr8xoz says, are we worrying about the next thousands of years, or the next billions of years? Different agendas produce different definitions of "harmful". 213.122.23.52 (talk) 07:52, 24 December 2010 (UTC)

Why exactly do you say 'we'? What use are you to me? I'm more interested in pandas than I am in you. Dmcq (talk) 10:24, 25 December 2010 (UTC)

drug

are there any stimulant drugs that are not also vasoconstrictors — Preceding unsigned comment added by Kj650 (talk • contribs) 19:43, 23 December 2010 (UTC)

Modafinil, and most of the racetams. Vasoconstriction is a peripheral side-effect of adrenergic drugs, therefore the more readily the drug crosses the blood-brain barrier, the less likely it is to cause vasoconstriction. There are also drugs which act independently of the adrenergic system, such as dopamine reuptake inhibitors, dopamine agonists, certain nicotinic agonists, histamine agonists (or H3 receptor inverse agonists/antagonists) and drugs which stimulate orexin receptors/release. --Mark PEA (talk) 20:12, 23 December 2010 (UTC)

isint cocaine a dopamine reuptake inhibitor and a vasoconstrictor — Preceding unsigned comment added by Kj650 (talk • contribs) 21:03, 23 December 2010 (UTC)

Yes but it's also a noradrenaline reuptake inhibitor, which is probably responsible for this effect. (It also inhibits serotonin reuptake, and these drugs are normally referred to as triple reuptake inhibitors). --Mark PEA (talk) 18:16, 24 December 2010 (UTC)

Beer pong

In beer pong, if the ping pong is spinning along the sides of the cup, blowing will cause the pong to rise out of the cup. Why? And if I take a glass half-way filled with juice and turn it over, with a piece of cardboard covering the top, the liquid won't fall...what's the reason for this? Thanks. 65.92.7.244 (talk) 23:49, 23 December 2010 (UTC)

I think first is bernoulli effect. See the experiments here: [3]. The second is because the piece of cardboard would have to move downward, decreasing the pressure in the glass, and that causes the higher pressure under the cardboard to push it back up. StuRat (talk) 00:05, 24 December 2010 (UTC)

Place a sheet of paper or a playing card on a flat smooth table and blow lightly along the table - you can make the paper float. It's the same principle and it's called Bernoulli's principle and is quite similar to the venturi effect. Ariel. (talk) 00:38, 24 December 2010 (UTC)

I'm still having trouble seeing it. Bernoulli says that the pressure created by fast moving fluid is less than that of slow moving fluid. But where is the fluid traveling faster? If the ball goes up, then it should travel faster above the ball, but why would it? 65.92.7.244 (talk) 02:06, 24 December 2010 (UTC)

Because when you are blowing above the ball, the air is now moving faster above the ball, so the pressure drops above the ball. --Jayron32 03:22, 24 December 2010 (UTC)

But isn't it also moving faster under the ball? And if not, why does blowing air underneath a ping pong ball keep it up? 65.92.7.244 (talk) 04:31, 24 December 2010 (UTC)

You are confusing two slightly different things. Air moving directly at the ball will move it; air is matter, and matter in motion has momentum, and it can transfer that momentum to the ball. Hence, blowing directly under the ball will cause it to move up. However, blowing past the ball, as in not directly at the center of the ball, but such that the air moves past the ball, will cause the pressure to drop. There is an INCREASE of pressure in the direction of airflow, that is in front of the puff of air, and an equivalent DECREASE of pressure perpendicular to the air flow. The trick is to blow NEXT to the ball (i.e. very close to it) but not AT it, so that the air moves past the ball, but not at it. --Jayron32 04:36, 24 December 2010 (UTC)

What!? air pressure, bernoulli's principal!? Try this: take a cup and hold it a couple inches from your mouth, now blow in it. What do you feel? Your own breath blowing back in your face! The air has no where to go but out. if you are still confused put some salt in the cup and do it again. Why didn't the salt stay in the cup?????? —Preceding unsigned comment added by 165.212.189.187 (talk) 14:56, 24 December 2010 (UTC)