Wikipedia:Reference desk/Archives/Science/2012 July 1

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July 1

PC to PC communication using laser torch

what will be the transmitting and receiving circuit diagrams for 'pc to pc data transfer using laser torch?' — Preceding unsigned comment added by Rosemail9876 (talk • contribs) 06:02, 1 July 2012 (UTC)

Here are circuit diagrams for a voice communicator that in principle could be modified to carry low-speed data. Another way to transfer data between PCs is physically as a writeable CD or DVD, which also involve lasers. DriveByWire (talk) 00:32, 2 July 2012 (UTC)

And there are free space laser communication systems to connect computer networks together. They are superceded by wireless ethernet mostly. But may have the advantage of a lack of signal spillover. The cuircuit could be similar to a fibreoptic transceiver, but with a much higher power laser, and to get the best you would have to cope with frequency shifts and temporary drop outs (when birds flew through the path) Graeme Bartlett (talk) 03:03, 2 July 2012 (UTC)

You may be interested in RONJA.--Srleffler (talk) 01:28, 3 July 2012 (UTC)

For electricity (and in general): wireless energy transfer. ~AH1 ^(discuss!) 18:25, 3 July 2012 (UTC)

wiggly line in molecule diagram

Ya got yer benzene ring with –CH2-CH-NH2 ... and what's that wiggly thing? —Tamfang (talk) 06:09, 1 July 2012 (UTC)

It indicates that the bond is not in the plane of the page (or monitor screen) i.e. it projects either towards you or away from you, but it doesn't indicate which way specifically, so it's probably a mixture of the two isomers. 112.215.36.172 (talk) 07:31, 1 July 2012 (UTC)

Actually, these would not constitute two isomers. Whether it's going into or coming out of the page makes no difference to the structure, as the single bonds may rotate freely. 112.215.36.172 (talk) 07:53, 1 July 2012 (UTC)

They can rotate, but they can't swap positions. The carbon attached to the squiggly methyl group is bound to three distinct species, so the molecule is almost necessarily chiral. See also Amphetamine#Chemical_properties. Someguy1221 (talk) 08:13, 1 July 2012 (UTC)

Yeah, you're right. It's definitely chiral. 101.170.42.168 (talk) 18:09, 1 July 2012 (UTC)

The "Skeletal formula" article has lots of details about the various conventions used in these types of diagrams. The specific structure the OP mentions is even the exact one used to illustrate the wavy-line meaning for stereochemistry:) DMacks (talk) 15:44, 2 July 2012 (UTC)

question about foreskin retraction

Hi,I find a photograph series of foreskin retraction ,which is http://commons.wikimedia.org/wiki/File:A_Foreskin_Retraction_Series.JPG I want to ask if the process of the foreskin retraction is automatic in the above picture when the penis expands to erection ,or foreskin pulled back after the glans by the hands? Thanks!!! Pdh2441 (talk) 08:23, 1 July 2012 (UTC)pdh2441(talk), June 26,2012

I don't think "retraction" is the right description, as the penis lengthens and extends beyond the foreskin during an erection. StuRat (talk) 08:57, 1 July 2012 (UTC)

From our article: "There is considerable variation in the degree to which the foreskin retracts during erection; in some adults the foreskin remains covering the glans until retracted by sexual activity." For the specific picture you linked to, I haven't a clue. Probably no one will be able to answer that question, short of tracking the subject down and asking him. Evanh2008 ^{(talk|contribs)} 09:04, 1 July 2012 (UTC)

I could be wrong, but it looks to me like the erection level of the penis hasn't significantly changed in most of the photo implying it was retracted manually. Nil Einne (talk) 17:52, 2 July 2012 (UTC)

Note that foreskins aren't unique to humans, and many other animals would lack the ability to retract the foreskin manually, therefore it must be accomplished automatically. StuRat (talk) 09:09, 1 July 2012 (UTC)

....or not at all.--Shantavira|^{feed me} 14:33, 1 July 2012 (UTC)

Or as the above ref suggests incidentally by sexual activity. Nil Einne (talk) 17:52, 2 July 2012 (UTC)

Does the Abyssinian Highland Zebu exist?

I came across the article Abyssinian Highland Zebu and went to expand it a little but I failed to find much on it. The only two places I have found it referenced is http://dad.fao.org/cgi-bin/EfabisWeb.cgi?sid=-1%2Creportsreport8a_50001170 which is the reference for the article, and http://www.ajol.info/index.php/ajb/art%20icle/viewFile/58020/46385 which is a research paper. I checked out the other two names given on the reference site, but none of those gave results for it either. — Preceding unsigned comment added by Manofgun (talk • contribs) 13:21, 1 July 2012 (UTC)

From what I gather, the Abyssinian Highland Zebu is also known as the Ethiopian Highland Zebu or the Abyssinian Shorthorned Zebu. The International Livestock Research Institute has a page on this breed (or group of breeds): [1]. - Lindert (talk) 14:51, 1 July 2012 (UTC)

So if the Abyssinian highland zebu is basically the abyssinian shorthorned zebu, should the highland zebu page be deleted? Manofgun (talk) 23:22, 1 July 2012 (UTC)

probablity of ejection in the photoelectric effect

I wanted to ask that if an electron absorbs a photon of energy 'e' which is greater than the work function, will the electron surely be ejected? Or is there some probability that the energy will just be re emitted?

P.S.- Our teacher at high school said there was no surety of ejection in the photoelectric effect, but i am not so sure on this one.

I would reformulate the problem this way. The work function on average has a certain value for a sample of material; but the magnitude of the work function for any individual electron follows a distribution. So, you can statistically encounter some electrons who would not be ejected by the same energy photon, and conceivably you could trace that to a defect or nonuniformity in the material's lattice structure.

On a completely different tack, raman scattering is the complex interaction of a photon with a material; it is rarely covered in high school physics classes because it's such a strange (and weak) effect, but it is real. It will often be explained as a "non-linear optics" phenomenon. If you treat the photoelectric effect as a special case of Raman scattering, you normally have an elastic collision, but occasionally have an inelastic scattering, yielding a photon with an unexpected wavelength, and an electron with an unexpected energy. The formal mathematics of this process are described in our article. Nimur (talk) 15:57, 1 July 2012 (UTC)

Not to be confused with ramen scattering, which is when I try to break up my ramen noodles before putting them in the pot, and pieces go flying across the kitchen. :-) StuRat (talk) 17:25, 1 July 2012 (UTC)

Getting rather off topic here, but this is why i smash them up while they're still in the bag. :-) 209.131.76.183 (talk) 14:56, 5 July 2012 (UTC)

about universe

is there any power that runs the whole universe.if it is there then what is it — Preceding unsigned comment added by Ram manohar 01 (talk • contribs) 16:26, 1 July 2012 (UTC)

The power that runs the universe is pizza. Looie496 (talk) 16:34, 1 July 2012 (UTC)

Please try to at least let someone give a helpful answer to a question before you start making inane comments. --Tango (talk) 18:16, 1 July 2012 (UTC)

The energy released by the Big Bang, I suppose. This created atoms which have enough nuclear potential energy to power stars, once ignited, and generated enough gravitational potential energy to ignite the stars, too. It also created some heat/background radiation, but, being rather evenly distributed, that's not much of a power source. StuRat (talk) 17:17, 1 July 2012 (UTC)

What do you mean by "power that runs the whole universe"? If you mean a higher power (ie. some kind of god or gods or spiritual force or whatever), then that's not within the realms of science and we can't help you on this desk. If you "power" as in energy, then the energy that runs the universe is just energy. If you mean some kind of underlying explanation for why things happen the way they do, then that's that physics is all about - trying to come up with that explanation. --Tango (talk) 18:16, 1 July 2012 (UTC)

If you're asking what powers the expansion of the universe, that's dark energy. I suppose dark energy per unit time would be dark power, but I don't think anyone ever uses that term in that sense. 101.170.42.168 (talk) 18:32, 1 July 2012 (UTC)

Dark energy causes the expansion to accelerate. Most of the existing rate of expansion is just momentum imparted by the big bang, though (at least, I think it is most, it's definitely a large proportion). --Tango (talk) 19:19, 1 July 2012 (UTC)

Ok, our article Metric expansion of space says it is roughly half and half. --Tango (talk) 19:21, 1 July 2012 (UTC)

Actually, all of it is currently powered by dark energy. Momentum is just that, and continues in the absence of any power being supplied. Power is the rate of energy being supplied, and momentum makes no contribution to that. 101.170.42.157 (talk) 19:24, 1 July 2012 (UTC)

Ok, then, half the expansion is unpowered. --Tango (talk) 19:35, 1 July 2012 (UTC)

That's the spirit. 101.170.42.157 (talk) 19:39, 1 July 2012 (UTC)

It makes no sense to talk about "dark power"--that's a fundamental misunderstanding of the nature of dark energy. According to the best evidence available, dark energy is distributed uniformly across the universe with an energy density that does not change with time. Its effect on the universe's evolution depends solely on the value of this density. This energy, if that's what it really is, cannot be transferred or transported like energy through a heat pump; thus, "dark power" is a meaningless term. --140.180.5.169 (talk) —Preceding undated comment added 02:08, 2 July 2012 (UTC)

No Drinking on Dialysis

Hello. Why are patients on dialysis not permitted to drink? I understand why they feel thirsty when the unit extracts the blood for cleaning. But what can go wrong if they just have a sip? Thanks in advance. --Mayfare (talk) 16:47, 1 July 2012 (UTC)

We cannot give medical advice. Please consult a quilified medical practitioner. Roger (talk) 16:51, 1 July 2012 (UTC)

Medical advice is telling them what they should do to improve their health, not explaining medical clinic rules. StuRat (talk) 17:12, 1 July 2012 (UTC)

I don't believe there is a universal ban on drinking fluids while on hemodialysis. However, some clinics might want to ban eating and drinking, as it interferes with their ability to measure how much weight was taken off the patient by the dialysis, which is an important metric in determining how the patient's treatment is going. They could, of course, weigh anything the patient consumes and figure that into the calculation, but that would mean extra work for them. A secondary consideration is that drinks can be spilled, possibly damaging valuable medical equipment. (Of course, patients in hospital rooms consume fluids, but here the assumption is that a patient can go a few hours without a drink.) When my Dad was on dialysis, we found that some clinics/nurses were absolute Nazis about the rules, while others strived to accommodate the patients. StuRat (talk) 17:12, 1 July 2012 (UTC)

A successful dialysis was not seen until well after WW2. Was one of the "absolute Nazi" clinicians Dr. Josef Mengele? DriveByWire (talk) 00:14, 2 July 2012 (UTC)

Not only can spillage damage machines but, if what you say is correct in the OP's case, spillage would throw off the measurements of weight loss. It would be difficult and likely impossible to measure what a person spilled versus what they drank. Dismas|^(talk) 19:14, 1 July 2012 (UTC)

But if you have kidney failure, you can't drink much anyway, so why would you want to drink while on dialysis? Count Iblis (talk) 19:27, 1 July 2012 (UTC)

Sure they can drink, as long as the dialysis removes the water. Also, those with high output renal failure need dialysis to remove the waste, but can still pee out the water on their own. In any case, during dialysis, as the water is removed from their body, they naturally become thirsty, especially if the clinic overdoes it and dehydrates them. StuRat (talk) 21:00, 1 July 2012 (UTC)

I understand that many (most?) hemodialysis patients are placed on very strict fluid control regimes. This paper, for instance, states:

Advice on the restriction of fluid intake is a cornerstone of management of patients with kidney failure. Doctors ‘prescribe’ fluid restrictions on ward rounds for patients with acute renal failure. Nurses on the dialysis unit, backed up by dieticians and psychologists, exhort patients to drink less, telling those with large inter‐dialytic weight gains that they are putting themselves at risk of heart failure and death.

though it goes on to argue that sodium control is more effective, "Look after the salt intake, and the water will look after itself." A web search suggests that the standard fluid intake limit is about 1 liter per day. I recall how surprised I was when I first heard this. A dialysis nurse I knew was complaining about about a patient, saying "Mr. X lived it up this weekend, drinking as much as he wanted to, but he sure paid for it today." I assumed she meant that he was drinking alcohol until she clarified that it was water. -- ToE 23:09, 1 July 2012 (UTC)

Most likely, they don't want patients to eat or drink in case something goes wrong that requires emergency surgery. Surgeons don't want to perform operations if you've had anything to eat or drink in the last 8 hours, due to chances of you vomiting while under anesthesia (and subsequently choking to death on it). — The Hand That Feeds You:^Bite 17:25, 2 July 2012 (UTC)

Hemodialysis isn't likely to make surgery necessary. The most common immediate issues it causes are low blood pressure, dehydration, and problems from inappropriate medications/quantities administered intravenously during the session, none of which are addressed by surgery. An infection could require surgery (lancing the infected area and draining it), but an infection wouldn't set in until well after the session ended. StuRat (talk) 18:27, 2 July 2012 (UTC)

Another concern with food and drink is that they can introduce bacteria into the area they want to keep sterile. StuRat (talk) 18:27, 2 July 2012 (UTC)

What level of weight loss causes stretch marks?

Well title is pretty self explanatory, what's the rate of kilos lost I should limit myself in order to avoid blemishes?Bastard Soap (talk) 18:45, 1 July 2012 (UTC)

This question sounds like a request for medical advice. 101.170.42.166 (talk) 19:09, 1 July 2012 (UTC)

But then this may be too expensive for most people. Count Iblis (talk) 19:22, 1 July 2012 (UTC)

This is strongly dependent on age. Younger people have more elastic skin than older people, so they can lose weight more rapidly without getting stretch marks. But even with age taken into account, skin elasticity is still pretty variable. Lots of women do fancy things in order to maintain it; I have no opinion about whether any of them are effective. Looie496 (talk) 19:01, 1 July 2012 (UTC)

I'm a bit confused. Rapid weight gain causes stretch marks, while rapid weight loss can cause sagging skin. StuRat (talk) 21:02, 1 July 2012 (UTC)

That's what I thought, but our article mentions both weight gain and weight loss as causes. --Tango (talk) 22:16, 1 July 2012 (UTC)

Perhaps the unsupported sagging skin stretches under it's own weight, causing stretch marks. StuRat (talk) 02:18, 2 July 2012 (UTC)

I think weight gain causes the stretch marks while weight loss makes the stretch marks visible. As for what you should do, that does come down to medical advice, it would depend on too many personal factors, such as your skin type, your current weight, your weight history, etc... The best you could get here are personal opinions and anecdotes which might not apply to your situation and could just as likely make your case worse instead of better. Vespine (talk) 22:43, 1 July 2012 (UTC)

Some ranges would be nice,for example most 20 year olds can lose easily 1kg per week,30year olds 1kg per two weeks. Some numbers and statistics to get an idea. I'm not aiming for an extreeme weight loss mind you,I'm probably safe, just want to make sure and possibly warn people who are dieting too harshly. You're a bit too loose on the medical question thing, every question concerning biology is a medical question. You should only refrain from providing information which can be dangerous. You can only stop me from getting stretch marks here you cannot cause harm as I won't change my program unless I find it will cause stretch marksBastard Soap (talk) 23:16, 1 July 2012 (UTC)

It's not just about giving "dangerous" information, it's about accurate information. If you're just asking about general opinions on weight loss and stretch marks, that information is easily available a mere google search away. Vespine (talk) 00:23, 2 July 2012 (UTC)

I'm looking for numbers to get a general idea. If there is no accurate information, information with a known level on inaccuracy is the second best thing.And no, I'm not here for opinions, I'm here for the science on this, however little of it there might be. Science really seems to drop the ball on fitness stuff. Bastard Soap (talk) 04:50, 2 July 2012 (UTC)

I doubt there would be a study, as it would be unethical to have people lose weight at variable rates, to see which ones suffer ill effects. (Noting that losing weight quickly enough to cause stretch marks may well cause other medical problems, too.) StuRat (talk) 18:21, 2 July 2012 (UTC)

An animal study wouldn't be too unethical. So we know nothing concrete about it? I'd expect some ammount of knowledge to have arisen from trial and error aloneBastard Soap (talk) 20:26, 2 July 2012 (UTC)

I'm not sure if an animal study would be much use, as animal skin is quite a bit different (thickness, hair cover, etc.) and many other animals are designed to rapidly gain and lose weight, like those which hibernate. StuRat (talk) 20:29, 2 July 2012 (UTC)

So, what you get, instead, is people self-reporting the conditions under which they got stretch marks, which doesn't qualify as "scientific research", but is still better than nothing. StuRat (talk) 20:31, 2 July 2012 (UTC)

possibly warn people who are dieting too harshly for that purpose sagging skin is more graphic example. I recently saw a documentary on woman in her late thirties who got it after she rapidly lost weight after having gastric bypass. I think they said she was doing over 10kg a week. Not sure why losing wight would cause strech marks, furthermore there seem to be other causes for them to appear, but there are ways to prevent them, especialy if you are dieting and thus know you are going to lose wight and should do something to prevent side effects ~~Xil (talk) 00:37, 6 July 2012 (UTC)

Solar electrolysis

Can a solar panel be used to perform electrolysis, splitting water into hydrogen and oxygen? 64.229.5.242 (talk) 23:03, 1 July 2012 (UTC)

Directly, or indirectly? Plasmic Physics (talk) 23:15, 1 July 2012 (UTC)

Apparently yes, either way, according to my chemistry textbook. (The ones used for direct water splitting may not be the ordinary silicon-with-trace-amounts-of-phosphorus-and-boron kind, though...) Whoop whoop pull up ^{Bitching Betty | Averted crashes} 23:52, 1 July 2012 (UTC)

Yes. A solar panel or any other source of DC (direct current) can electrolyse water provided it overcomes the water cell potential nominally 1.23 V. Electrolysis of water (see article) works much faster when a water-soluble electrolyte e.g. NaCl (salt) is added to raise the conductivity of the water. DriveByWire (talk) 23:49, 1 July 2012 (UTC)

But that would cause the production of sodium hydroxide and chlorine gas instead of oxygen gas, although it would produce hydrogen gas either way. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 23:52, 1 July 2012 (UTC)

Photoelectrolysis. Zing! ~AH1 ^(discuss!) 18:04, 3 July 2012 (UTC)

I have a photovoltaic array that produces 3 amps at 13 volts in full sun. How many liters of hydrogen at normal room temperature and normal atmospheric pressure would it be able to liberate per hour? Using carbon electrodes, which is a better choice to make the water conductive without undesirable deposits on the electrodes or undesirable adulterants in the hydrogen and oxygen, sulfuric acid or hydrochloric acid? Edison (talk) 14:50, 4 July 2012 (UTC)