Wikipedia:Reference desk/Archives/Science/2010 July 1

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July 1

Homogeneous Continuous-time Markov chains - analytical expressions for the finite time transition probabilities?

This looks like a question much better suited to the Wikipedia:Reference desk/Mathematics. Dolphin (t) 00:15, 1 July 2010 (UTC)

I have transferred this question to the Mathematics Reference Desk. See HERE. Dolphin (t) 00:30, 1 July 2010 (UTC)

Iron

Does the body use iron(II) or iron(III)? --75.25.103.109 (talk) 00:18, 1 July 2010 (UTC)

Both.._oops Fe2+ probably = See Hemoglobin - especiallly Hemoglobin#Iron's_oxidation_state_in_oxyhemoglobin . Sf5xeplus (talk) 00:21, 1 July 2010 (UTC)

Both. Most iron containing proteins are (nominally) iron(II), but iron is transported around the body (by transferrin) and stored (by ferritin) as iron(III). Physchim62 (talk) 10:24, 1 July 2010 (UTC)

Expiration of medicine

What does it mean for medicine to expire? Assuming we are dealing with a pharmaceutical that doesn't become harmful as it ages, how much of the active ingredients can be lost before it is considered expired? —Preceding unsigned comment added by 173.49.77.61 (talk) 00:22, 1 July 2010 (UTC)

Usually drugs just become less effective as they get older. Some could become harmful though - don't risk it! --Tango (talk) 00:27, 1 July 2010 (UTC)

Why do they get less effective? --RampantHomo (talk) 01:14, 1 July 2010 (UTC)

Various reasons. Oxidation, decay due to exposure to light (that's why they are often in dark brown bottles), etc.. --Tango (talk) 02:23, 1 July 2010 (UTC)

How about a reference here at the Reference Desk? The first google hit on why does medicine expire yields this Medscape article, in which a medical doctor concludes that almost all drugs are fine to take after the expiration date, which he says is merely the last date at which the pharmaceutical company asserts the drug is still effective. On the other hand, he cites one example in which a guy may have damaged his kidneys by taking expired tetracycline. Comet Tuttle (talk) 03:01, 1 July 2010 (UTC)

As an example, I recall from my chemistry class that Hydrogen peroxide molecules (H₂0₂) will drop the extra Oxygen atom at somepoint, and as this happens to collectively more Hydrogen Peroxide molecules, the contents of the bottle become more and more water, and less and less hydrogen peroxide, thereby significantly reducing the effectiveness over time. Falconus^{p t c} 03:34, 1 July 2010 (UTC)

Hydrogen peroxide is a special case - it's very unstable. Most (pretty much all) medicines are far far more stable. Concentrated hydrogen peroxide is unstable enough to be used as rocket fuel. Ariel. (talk) 10:32, 1 July 2010 (UTC)

Important distinction: it's important that a rocket fuel is "high energy" (thermodynamically unstable) not that it rapidly/spontaneously decomposes (somewhat unrelated kinetic issue, which is sometimes even a negative quality to have). Lots of excellent rocket fuels are easy to handle and store until they are made to react with a large release of energy. Some fairly low-energy molecules are labile enough that they can change slightly under mild conditions, leading to loss of intended activity. DMacks (talk) 14:17, 1 July 2010 (UTC)

I should have said "unstable enough to be used as a monopropellant rocket fuel". Ariel. (talk) 14:52, 1 July 2010 (UTC)

If the drug is not harmful after it expires, it may even still work due to the placebo effect. ~AH1^(TCU) 18:06, 2 July 2010 (UTC)

Help identifying this flower

I would like to know the species of this flower so I can add the image to the correct article, but I haven't got a clue! The background info for this photo is:

• In the UK in Oxfordshire
• Taken in March
• Found in open cut grass

Thanks in advance - Zephyris _Talk 00:47, 1 July 2010 (UTC)

Is it not speedwell (Veronica (plant) of some variety)? It looks like the thing I've always called speedwell, and if I had to guess from the articles I'd say it was Veronica persica. But hopefully a botanist will help you with the more specific species. 86.164.57.20 (talk) 01:40, 1 July 2010 (UTC)

Looking it up in Complete British Wild Flowers by Paul Sterry, which has photos of many kinds of Speedwell, then it could be Veronica persica, polita, or agrestis. V. persica - reddish stems, "white on the lower lip of the corolla". Cannot see a reddish stem, but the other part matches. The photo shown in that Wikipedia article is perhaps the wrong species therefore. 92.28.244.45 (talk) 09:57, 1 July 2010 (UTC)

Thanks guys, thats brilliant. From those descriptions it must be V. polita, I will replace the image on that page with this one. - Zephyris _Talk 13:13, 1 July 2010 (UTC)

I thought I had typed V. persica above, not polita. Anyway I have now corrected it, and the desrciption corresponds to V. persica, and the V. polita article photo needs to be changed back. 92.28.247.183 (talk) 19:15, 2 July 2010 (UTC)

Neodymium magnets

Do the neodymium and iron in neodymium magnets (Nd₂Fe₁₄B) oxidize over time? --75.25.103.109 (talk) 01:02, 1 July 2010 (UTC)

Not sure but they are almost always coated (ie Ni plated)...

" Neo magnets or rare earth magnets have poor resistance to corrosion and should have a coating or plating applied" [1] . Not sure of the details.Sf5xeplus (talk) 01:31, 1 July 2010 (UTC)

"Sintered Nd2Fe14B tends to be vulnerable to corrosion. In particular, corrosion along grain boundaries may cause deterioration of a sintered magnet. This problem is addressed in many commercial products by providing a protective coating. Nickel plating or two layered copper nickel plating is used as a standard method, although plating with other metals or polymer and lacquer protective coatings are also in use" from Neodymium magnet .. link from that article http://www.journalamme.org/papers_vol20/1369S.pdf Sf5xeplus (talk) 01:33, 1 July 2010 (UTC)

From first hand experience: Yes they rust! I have several of those magnets ripped out of hard disks. The glue they use to fasten it to the holder is very very good so I torn of the nickel layer and now the magnet is not protected at that point. After several weeks this area get redish coloured and if you touch it you have rust on your fingers. The material is sintered and has a large surface area making it vulnerable for corrosion along the former grains.--Stone (talk) 05:05, 1 July 2010 (UTC)

Weight loss

I was watching a comedy/sitcom TV series and there is a woman who is a bit...*ahem*... "un-thin" but she is not at all overweight or fat. She came up with this insane regimen to lose weight, eg eating nothing but 1 salad and coffee 3 days of the week and eating normally the other 4 but running 3 miles and biking 10. This made me think: how would a person who is of a somewhat higher but not immediately health-threatening weight lose weight? Like what kind of everyday changes should they make. This is on a hypothetical level of course, not for medical advice, since I noticed every diet seems to be geared only to the REALLY overweight people.—Preceding unsigned comment added by 68.248.225.254 (talk) 01:57, 1 July 2010

There is one and only one way of losing weight and it applies to everyone, regardless of their starting weight: you consume fewer calories than you burn. That is it (well, you could get liposuction, I guess). You can do that by eating less, exercising more or a bit of both. The important thing is to make sure you still get enough nutrition despite reduced calories - you still need plenty of protein, fibre, vitamins and minerals and a little fat. If you are interested in losing weight yourself then a nutritionist will be able to work out a diet for you that will have all the nutrients you need while having a certain number of calories based on the amount of exercise you will be doing. We can't give specific dietary advice here - there are too many factors involved. --Tango (talk) 02:31, 1 July 2010 (UTC)

The real trick is finding a method to ensure you actually do eat less than you expend. The diet mentioned above might work for that for that or another person, it might not. I've been fat since high school and tried several diets and exercise regimes and found the following: Exercise 3 times a week works a little for me, and at least makes me feel better. Low calorie diets don't work for me (I can't handle being always hungry). Low fat diets don't work for me (I can easily get or stay fat on bread alone!). Low carbohydrate diets (specifically strictly following the Atkins diet) worked (120kg to 98kg over 3 months) for me on my third attempt - it took me that long to learn that the diet doesn't work if I cheat or if I don't eat often enough. But everyone is different.

Every day changes that I've seen help people: Exercising more - cycling or walking to work or school; not snacking; eating 5 times a day rather than 3; eating only and exactly 3 times a day; not eating high fat food; not eating high calorie food; not eating processed food; cutting out a particular food (crisps, chocolate, bread, etc). --Psud (talk) 08:53, 1 July 2010 (UTC)

The general view is that diets don't work lifestyle changes do. There seem to be three main areas, actual nutrition, exercise and the psychology of nutrition and exercise.

The main thrust of most of the work I've seen has been that the most enduring weight loss is slow, over several months.

As with Tangos comments, it's a question of eating a balanced, healthy, diet and adding in some exercise. The exercise needn't be formal, but increasing exertion in daily life on a regular basis.

One of the main concerns about the psychology is that published diets are seen as some kind of magic bullet, rather than a stimulus to actually change behaviours. Hence the type of club based weight loss system where there is both mutual support, and tacit peer pressure.

As with Psud there are little changes, smaller more regular meals, although some of those are little more than formalised snacks. Snacking on fruit, nuts etc rather than processed products etc.

ALR (talk) 09:47, 1 July 2010 (UTC)

Ah, yes, thank you for making that point - I forgot to. Your new diet needs to be something you can happily stick to for the rest of your life, or you will almost certainly put the weight back on again. --Tango (talk) 15:59, 1 July 2010 (UTC)

I've recently started to think about a simple rule for health and weight loss: never eat processed foods. Only eat food in the same form it was alive, apart from cutting, and avoid meat also. Following this rule you would avoid the salt, fats, and sugars that routinely tempt us to eat too much. Something I do is to eat a lot of vegetables, as this fills you up, and fruits also. 92.28.244.45 (talk) 10:10, 1 July 2010 (UTC)

While there is merit to the above, you need to be careful that you are still getting B vitamins and protein if you are going to cut out meat completely. While I agree that vegie diets are easier to reduce calories, you do need to be aware of the nutrition provided by meat and ensure that you are including it. Googlemeister (talk) 13:32, 1 July 2010 (UTC)

You are probably thinking of Vit B12, which is abundant in fish and eggs. People also greatly overestimate the amount and quality of protein that adults need (according to these pages), and excess protein is now thought to be bad for you. Sardines are extremely rich in Vitamin B12, more than anything else you would eat I think. I suggested avoiding meat because of the saturated fat it contains, particularly with modern farming methods. The B vitamin folic acid is mostly obtained from vegetables I believe, as well as other B vitamins, although I am not an expert on individual B vitamins. If you are eating a diverse diet, then eating some red meat is going to be more harmful than good for you. 92.28.247.183 (talk) 19:22, 2 July 2010 (UTC)

I agree with ALR that diets don't work. I've read that this is because the logic of "eating less than you burn" does not apply. As long as you're not on a diet that severly restricts calory intake (say eating less than 1500 Kcal per day), the body will regulate its metabolic rate such that the fat cells stay filled to some fixed level. This also means that if you do lose weight as a result of sticking to a diet of, say, 1500 Kcal, you will eventually return to approximately your old weight if you start to eat a normal amount of kcals again, even if that is still less than what you were used to eating.

What does seem to work is eating healthier, sleeping better and getting more exercise. It could be that if you do this, the body will decide to keep the fat cells filled at a lower level. Count Iblis (talk) 15:39, 1 July 2010 (UTC)

You make a good point. I forgot to say that you need to consume only slightly fewer calories than your burn - your intake should stay at this new level for the rest of your life. Rapid weight loss doesn't work, you will almost certainly put the weight back on again. Your weight is a key factor in determining how many calories you burn, so as you lose weight the calories you are burning will reduce until you reach a new equilibrium and then you'll stay at your new weight. If you reduce your calories to 1500kcal/day then you won't reach an equilibrium before you starve, which is why you'll end up increasing your intake again. For a typical lifestyle, most people need around 2000-2500kcal/day. If you are overweight, chances are you are consuming more than that (and burning more than that due to your weight - most overweight people aren't constantly gaining weight). You shouldn't try to reduce your intake to less than 2000-2500, you should reduce it to 2000-2500. --Tango (talk) 15:59, 1 July 2010 (UTC)

See somatotype and constitutional psychology. For some people it will be more difficult to "lose weight". ~AH1^(TCU) 18:03, 2 July 2010 (UTC)

I'd recommend a look at [The Fat Nutritionist http://www.fatnutritionist.com/], particularly the Articles & Evidence on the right hand side. I especially recommend this article. In brief, if you've never dieted, have access to enough food, and have a fairly normal relationship with food, the weight you are is pretty much the weight you're always going to be. You can convert more of that fat to muscle, you can get fitter, but you're not going to be able to lose weight without eating less than you need, which is a bad thing. And once you've done that (by going on a diet) and failed, you will end up fatter than you were when you started. Human body shape varies, human weight varies (it follows a normal distribution), and there is no problem with being overweight as long as you're not morbidly obese. 86.164.57.20 (talk) 19:13, 3 July 2010 (UTC)

"There is no problem with being overweight as long as you're not morbidly obese"? The scientific consensus is that being overweight is very harmful - take a look. —Preceding unsigned comment added by 174.131.45.82 (talk) 19:29, 3 July 2010 (UTC)

No, the social consensus is that being overweight is very harmful. Whereas the paper I cited actually looked at 11,326 Canadians and whether they died, and found that being 'overweight' according to BMI was actually associated with lower mortality. Being 'obese' was associated with the same mortality as being 'normal weight'. Being 'morbidly obese' was associated with the same increased risk as being 'underweight'. And the way to end up morbidly obese when you're overweight is to start dieting and wait 10 years. 86.164.57.20 (talk) 20:10, 3 July 2010 (UTC)

"And the way to end up morbidly obese when you're overweight is to start dieting and wait 10 years." It is true that when some people try to lose weight, they manage to lose some weight but later gain more than they lost. This is more likely to happen if someone tries a diet that is very restricted in food choices or very low in calories. However, someone who is overweight should still try to lose that extra weight that he is carrying. Being overweight increases the risk of health problems, and people who are overweight can become obese if they do not change the bad habits that have made them overweight. Dieting sensibly enables a person to lose weight safely and gradually, with a lower risk of gaining it back. What we want to avoid is yo-yo dieting.174.131.40.152 (talk) 20:50, 3 July 2010 (UTC)

To help answer the original question, someone should ask his or her doctor before trying to lose weight to ensure that losing weight is necessary and safe. Some people can be told that they look fat or are overweight by people they know when, in fact, their weight is within the healthy range.174.131.40.152 (talk) 21:32, 3 July 2010 (UTC)

Suntan

I was playing tennis but I was wearing sandals and did not think to put sunscreen on my feet. Now they have some weird tanned stripes where the holes elt sun in. How long does it take to get "un-tan"? Is there any way I can speed up the process of getting un-tan, whih I assume is my body metabolizing melanin? THNX 68.248.225.254 (talk) 01:57, 1 July 2010

It's going to depend on your exposure to sun and varies from person to person, but it can easily be weeks. It would be quicker to just tan the rest of your feet, but I wouldn't recommend that - intentionally exposing yourself to sunlight is generally not to be recommended. You could try a fake tan, of course. --Tango (talk) 02:38, 1 July 2010 (UTC)

"Intentionally exposing yourself to sunlight is generally not to be recommended." Not recommend by who? Vampires? I am going to go out on a limb here and say that moderate exposure to the sun is generally not a major health concern. And I will base that statement off of the 6,000,000,000 or so people on this planet who encounter sunlight on a regular basis without keeling over. Granted if you are going to overdo it that results in a slight increase in your chance of skin cancer, but that doesn't mean you should not go out during the day. In fact, if you are not exposed to sunlight, you can have vitamin D deficiencies, so telling people not to go out in the sun can be detrimental to their health. Googlemeister (talk) 13:27, 1 July 2010 (UTC)

I said "intentionally". That means going outside for the purpose of exposing yourself to sunlight. Going outside for other reasons and just happening to be exposed to sunlight is a different matter entirely - you have to weigh up the benefit from whatever you are doing with the harm from the sunlight, and as long as you don't overdo it it is often worth going outside. The amount of sunlight required to get enough vitamin D is minimal - in fact, with a decent diet, it can be none at all, at most it's about 10 minutes with only your face and arms uncovered on an overcast day at temperate latitudes (for someone with reasonably fair skin). --Tango (talk) 16:06, 1 July 2010 (UTC)

"about 10 minutes with only your face and arms uncovered on an overcast day at temperate latitudes (for someone with reasonably fair skin)" at a time of day and year when the sun is high enough. Why would 'intentionally' exposing yourself to sunlight be any more dangerous than 'accidental' exposure: the sun doesn't check your intentions. For many people, intentionally exposing themselves to sunlight (because they otherwise live indoors, or in dark areas, or work night shifts, or...) is a useful and beneficial activity. And they don't keel over dead from it. Much advice in the UK (over the last 10 or so years) about sun exposure has been based on Australian practice, and I think we can all see the flaw in applying that to a country like Britain. 86.164.57.20 (talk) 19:03, 3 July 2010 (UTC)

The cells in the epidermis (the outer layer of skin) don't "untan" - they just die and eventually slough off. That process takes 27 days after the cell is first formed. In effect, you grow an entire new skin every four weeks! So if an epidermis cell was 'tanned' right after it was formed then the tan might not completely fade for 27 days. I think that's the worst case - but in practice, I doubt the suns' rays are able to tan those deepest layers of skin, so probably only the outer layer of 'older' cells got tanned - and they'll be around for less than 27 days. SteveBaker (talk) 03:50, 1 July 2010 (UTC)

Wash your feet a lot - it helps get rid of the surface of the skin. 92.28.244.45 (talk) 10:16, 1 July 2010 (UTC)

wth? How do you tan that quick? John Riemann Soong (talk) 16:02, 1 July 2010 (UTC)

A few hours of strong sunlight is more than enough for someone with reasonably fair skin to tan. Remember, the OP wasn't necessarily tanned enough for someone to notice them as being significantly tanned, just enough for there to be a noticeable difference between neighbouring tanned and untanned areas of skin. --Tango (talk) 16:08, 1 July 2010 (UTC)

Consistently wearing sandals in the summer will give you a "sandal tan". I find it usually fades by the wintertime. ~AH1^(TCU) 18:01, 2 July 2010 (UTC)

However, wearing sandals while playing tennis could have much more serious consequences than a "sandal tan"... 67.170.215.166 (talk) 23:03, 4 July 2010 (UTC)

Reptiles + amphibians

I currently have a 29 gallon fishtank that I'd like to transform into a aquaterrarium. I'm looking to drop the water level to about a fourth (and maintain the 7 fish I have now), add some newts and then put in 2-3 thick branches and have anoles in there as well. I'm under the impression that newts possess special toxic slime that they exude upon attack that will protect them from the anoles. Would that be a plausible set up? DRosenbach ^{(Talk | Contribs)} 02:31, 1 July 2010 (UTC)

Well many have poisonous skin eg Rough-skinned newt (also Newt#Toxicity), I suppose this would be easier to answer if you told us the type of newt.

Even so it's not clear that the anole would attack the newt (relative sizes?), or indeed that it would be aware of a poison, or that the poison actually acts as a deterrent (eg bitter) rather than species attrition.

Additionally I would wonder if the anoles and newts would be compatible in terms of their ecosystem - eg dry/damp??

87.102.17.114 (talk) 11:47, 1 July 2010 (UTC)

I would say fire-bellied newts, but I may get another type -- unsure. DRosenbach ^{(Talk | Contribs)} 03:35, 2 July 2010 (UTC)

Surface tension

On the surface of a liquid, there aren't any molecules above the surface molecules, hence they experience an attractive force towards the interior of the liquid. But what causes the increases force tangential to the surface? 70.52.45.181 (talk) 05:34, 1 July 2010 (UTC) Further questions: I'm looking at the following link, http://www3.interscience.wiley.com:8100/legacy/college/cutnell/0471713988/ste/ste.pdf. When considering how to define surface tension, the article makes reference to a C-shaped apparatus. Why is γ = F/2l and not F/l? It says something about there being two surfaces, but I only see one. Second question: In example one, the article considers the surface tension as applying a force outwards. But I thought surface tension was only inwards. I can see why compressing the liquid will produce some outward force against the needle, but why would that equal γL? It seems like those are two different phenomena. Thanks a lot guys! 70.52.45.181 (talk) 06:36, 1 July 2010 (UTC)

ok First question - there isn't really an attractive force towards the centre of the liquid (yes I know the pdf says that).. The molecules on the surface are in equilibrium, so the net force is 0. Obviously if you try to pull a molecule from the surface of the liquid then there will be a force resisting that. maybe this seems pedantic

Following on, still answering the first question: are you familiar with the Energy=force x distance relationship (or Force=dE/dx) - I think it makes surface tension a lot easier to understand... if so you can assume that the molecules at the surface are at a higher energy (since they are surrounded by less molecules .. and molecules gain energy by interacting with those next to them) .. Then assume that this 'surface energy' is proportional to area ie E=kA .. (k is a constant for air/water interface) - if you can work with that then it is fairly easy to show the answer to the second question without "hand waving" - it also proves that water surfaces generally form the shape of lowest surface area (ie a water droplet is spherical).

if not a different explanation will be necessary - but it gets a bit fiddly explaning just with text

Your third question - is this about a needle in water? (ie Example 1) - again - if you consider the surface area you will see that the surface tension acts in such a way to minimise the surface area (in this case it means flat) - so if the needle pushes the water down, the surface tension will try push the water back up into flatness.

Alternatively (3rd question) - try drawing the 'force arrows' in the water surface around the needle (as in diagram b page 2) - you will see that some of the force arrows are pointing upwards (more that 180 degrees of force arrows) - giving a net upwards force.83.100.252.42 (talk) 11:24, 1 July 2010 (UTC)

Sorry, if you don't mind I would like things to be kept to forces and such...grasping something in terms of energy and surface area-minimization is fine, but my understanding of this thing from a force perspective leads me askew, and that's something I have trouble living with. Sorry! 65.92.5.151 (talk) 03:26, 2 July 2010 (UTC) (PS my IP seems to be changing; don't worry it's OP, not an imposter :) ). 65.92.5.151 (talk) 03:27, 2 July 2010 (UTC)

Plaiting and fluffiness

When my hair has been plaited for more than a couple of hours, untwisting the plait and brushing my hair makes it go very fluffy. It eventually "calms down" hours later but can be pretty wild directly after this sequence.

My hair is not normally fluffy and it doesn't "fluff" after brushing any other time.

It's very wavy in thick sections when it comes out of the plait and I'm guessing this has something to do with the subsequent fluffiness, but I'm missing the connection or reason. Does anyone know why plaiting produces the effect? I tried searching for an answer, but it seems plaiting is a common answer to fluffiness and I therefore get a lot of false positives, :) Maedin\^talk 06:57, 1 July 2010 (UTC)

Does a penis have other functions besides urination and copulation?

Does penis have any other functions besides urination and copulation? For example, helping maintain balance as a man ealks (nude), or being a primary way to get off access heat during a heat wave, or being a sensory organ regarding thr environment, like a nose, or - anything at all? 92.224.206.50 (talk) 07:21, 1 July 2010 (UTC)

Re "sensory organ": Two men were peeing off the end of a pier at night when one remarked, "Gee, the water is pretty cold." The other replied, "And deep, too." -- 60.49.38.251 (talk) 09:58, 1 July 2010 (UTC)

Yes, read this Small penis rule  Jon Ascton  (talk) 09:12, 5 July 2010 (UTC)

Writing one's name in the snow. Cuddlyable3 (talk) 10:36, 1 July 2010 (UTC)

Masturbation? Which is used by some as "stress reliever"? --Enric Naval (talk) 10:40, 1 July 2010 (UTC)

The penis provides the site for visible circumcision that is performed for ritualistic or religious purposes. Any usefulness for maintaining balance is disproven by the considerable numbers of women and men with tight trousers who do not fall over. Cuddlyable3 (talk) 10:43, 1 July 2010 (UTC)

As far as balance goes, if it's long enough, you can use it as a tripod. --Enric Naval (talk) 10:56, 1 July 2010 (UTC)

Its dysfunctions and complications can be useful indicators of health problems; hypertension, for example, or a hormonal imbalance. More indicative, of course, if the onset of said side effect is sudden and/or the age isn't elderly. Though clearly not its primary application, it's still a gauge that females don't necessarily have (or at least not as obviously). Maedin\^talk 12:33, 1 July 2010 (UTC)

It functions as a differential analyzer of the attributes "surprise" and "panic". Surprise is the first time it won't the second time and panic is the second time it won't the first time. Cuddlyable3 (talk) 13:13, 1 July 2010 (UTC)

It's also a good MacGuffin for troll-like questions. --Tagishsimon (talk) 09:45, 2 July 2010 (UTC)

Credibility of hypotheses

What is it about a particular scientific hypothesis that makes it likely to reflect reality, or unlikely to reflect reality?--220.253.100.166 (talk) 08:49, 1 July 2010 (UTC)

Experiment :) --Dr Dima (talk) 10:12, 1 July 2010 (UTC)

See the article Falsifiability. Cuddlyable3 (talk) 10:34, 1 July 2010 (UTC)

A hypothesis is just an idea - until it's tested in some way, we don't know whether it's true or false. However, some hypotheses are more likely to be true than others. For example: You might hypothesize that I'll type the letter "e" more than once in the next sentence. Sadly, that turns out to be wrong. It was a good hypothesis - but until it was tested, we didn't know whether it was true or false. In general, a hypothesis that requires a violation of the known laws of physics/chemistry/whatever is much lessmore likely to be false than one that doesn't. Overturning some piece of well-established science is much less likely than proving something that's already known to be possible. If you hypothesize that T.Rex was able to run at 20mph, that's not an impossible thing - and by measuring fossil bones and looking for T.Rex footprints - you might be able to prove it...but if you hypothesize that the jet of gasses from a pulsar shoot out at twice the speed of light - then we're very nearly certain that this is false - just from general physics principles. SteveBaker (talk) 19:09, 1 July 2010 (UTC)

Only an omniscient being could answer this question, since the rest of us have no sure knowledge of the underlying reality. The hypotheses are the only scientific guide we humans have to reality. Occam's razor is helpful in keeping things simple. William Avery (talk) 19:54, 1 July 2010 (UTC)

Career in nanotechnology?

[I'm asking this question on behalf of a friend] I'm almost done my undergraduate studies in physics and I have started, for the first time really, to consider my career options. I've always enjoyed physics, and I would absolutely love to continue doing research in it, but I have been cautioned about the dangers of entering a overly theoretical discipline of physics. But there are plenty of fields with "real-word applications" that are certainly very interesting. In particular, something like condensed matter physics or theoretical chemistry seem worthwhile to pursue. However, a few weeks ago an old teacher of mine suggested that I look into nanotech, nanoelectronics in particular. It seems fascinating, and the technology and lab equipment are very impressive. My sole caveat is this: will I lose the physics I enjoy if I go into this? I want to work with the equations and study the mechanics of things...will that be jeopordized in something like nanotech? Thanks. 70.52.45.181 (talk) 10:52, 1 July 2010 (UTC)

Nanoelectronics involves or can involve a lot of condensed matter physics, and some theoretical chemistry (of the right sort) is also applicable - so your friend can carry on as normal :)

83.100.252.42 (talk) 11:31, 1 July 2010 (UTC)

Nanotech is a wide range of different things - from the very practical stuff like improved water filtration for use in the third world - to the highly theoretical stuff like Molecular assemblers. See List of nanotechnology applications. These days, saying that you want to work in Nanotechnology is like saying you want to do Math...it's used all over the place in a vast range of industries. I think this means that you should be able to find a niche somewhere between the so-practical-it's-just-engineering to the so-unlikely-that-research-funding-is-unobtainable. Somewhere in that spectrum, you should be able to find a job that pays well and lets you do the science you love. In case you didn't already check it out, we have lots of articles on the subject, including Nanoelectronics itself - and also Molecular electronics, Molecular logic gate, Molecular wires, Nanocircuitry, Nanowires, Nanolithography. NEMS, Nanosensor, Nanoionics, Nanophotonics and Nanomechanics. SteveBaker (talk) 18:57, 1 July 2010 (UTC)

Thanks to both of you for the informative and detailed responses. 65.92.5.151 (talk) 03:23, 2 July 2010 (UTC)

Wasps

A wasp (either a yellowjacket or common wasp, I think) somehow got into my bed this morning, with predictably hilarious consequences. While I treated the stings with hydrocortisone cream, they were still extremely painful, even after the swelling had gone down. So, my question: Bees use apitoxin and wasps apparently use "a chemically different venom designed to paralyze prey, so it can be stored alive in the food chambers of their young". What is the mechanism which causes the prolonged pain in bee and wasp stings? Apitoxin says that bee venom contains proteins which cause inflammation, but that some of the components are anti-inflammatory agents. Why this apparent contradiction? --Kateshortforbob _talk 11:10, 1 July 2010 (UTC)

I'm no doctor but from the sound of the article, apitoxin is multi-faceted. Some ingredients are anti-inflammatory while others are inflammatory, but not all work at the same time or on the same tissue. I suspect this dichotomy is part of why it hurts so much, the venom does different things at different stages ensuring that the wound will continue to cause pain and elude the body's self defense mechanisms. --144.191.148.3 (talk) 18:52, 1 July 2010 (UTC)

A hydrophobic cup?

What if a drinking cup has its inner surface lined with a hydrophobic material and water is poured into it? 67.243.7.245 (talk) 12:34, 1 July 2010 (UTC)

You've never drunk out of a polystyrene cup? Physchim62 (talk) 12:41, 1 July 2010 (UTC)

Cup holds water then. This happens a lot - paper cups with water proof coatings for instance. Was there some particular detail you where interested in? Sf5xeplus (talk) 12:54, 1 July 2010 (UTC)

Paper cup describes all the hellish details in full measure.Sf5xeplus (talk) 12:55, 1 July 2010 (UTC)

But water remains in a PS cup. It's not completely hydrophobic then? 67.243.7.245 (talk) 20:53, 1 July 2010 (UTC)

It is completely hydrophobic. Hydrophobic materials do not counteract the force of gravity; they merely are not miscible with water. That's all hydrophobic means. It just means that the material does not dissolve in or mix with water. They do not repel each other with a force in the way that, say, two north poles of a magnet will. The simply don't mix. When oil (a hydrophobic substance) and water are shaken, the seperate, but not from any force more complex than gravity; the less dense oil floats to the top because it is less dense, and thus lighter per unit volume, than the water. They aren't "forced apart" by any force. Likewise, water placed in a hydrophobic cup will simply sit in the cup and not soak through it. If you made a cup of hydrophilic material, like say salt, the water would dissolve the cup, making it not very useful as a cup. --Jayron32 05:54, 2 July 2010 (UTC)

You will get a convex Meniscus. Conversely, in a hydrophilic cup the meniscus will be concave. Ariel. (talk) 14:50, 1 July 2010 (UTC)

the cup shivers uncontrollably and cowers away from the water, if you persist in pouring water onto it, it "shuts down", curling into the fetal position and crying silently. If it is a prolonged experience in which the cup cannot get away, it can be permanently deformed psychology, perhaps hardly speaking a word for the rest of its life (or until treated). medications can help, but "water therapy", the naive idea that you should fight fire with fire, and just immerse the cup completely until it overcomes its fear, has disastrous results and is totally discredited; don't even think about it. 92.230.234.237 (talk) 13:08, 1 July 2010 (UTC)(Nonsense shrunk. Cuddlyable3 (talk) 13:58, 3 July 2010 (UTC))

be VERY careful around hydrophobic cups, in case they bite you.... Physchim62 (talk) 16:15, 1 July 2010 (UTC)

Help identifying this fruit

Unknown fruit.

I took this picture of a fruit on a tree in the botanic gardens in Oxford in February and have absolutely no idea what it is! Can anyone help? The fruit itself was around 4-5 cm diameter. Unfortunately as it was in the botanic gardens I have no idea of where in the world it is native to and the tree itself was fairly nondescript; ~7-10 metres tall with a trunk diameter of around 40-50 cm. The time of the year also meant there were no leaves for reference although the fruit was happy to stay on the tree over the winter - it was absolutely covered in these fruits. - Zephyris _Talk 13:21, 1 July 2010 (UTC)

Umm... not to be glib but if you were at the Oxford Botanical Gardens then why did not you just ask a botanist? 76.199.154.122 (talk) 17:46, 1 July 2010 (UTC)

Well I took a picture of what I thought was the species label for the tree... Turned out to be the species label for the miniature daffodils under the tree! - Zephyris _Talk 19:30, 1 July 2010 (UTC)

Do you remember if the tree had thorns? If it did, this might be a Bael. Googlemeister (talk) 18:26, 1 July 2010 (UTC)

I don't think it did, see the additional image. - Zephyris _Talk 19:30, 1 July 2010 (UTC)

Here's the number: 01865 286 690 you can ask them what's the tree above the daffodils. 71.161.46.51 (talk) 21:03, 1 July 2010 (UTC)

You might also find their website useful. It includes an interactive map (which regrettably does not identify individual plants) and an e-mail address for queries. 87.81.230.195 (talk) 05:43, 2 July 2010 (UTC)

They haven't been much help have they? My money is on the Dove-Tree or Ghost-Tree, Davidia Involucrata[2]. "Fruit: 3x2.8cm, obovoid (ie egg-shaped with the big end at the opposite end to the stalk), much ribbed, deep green and slightly glossy, ripening dark purple. Pedicel (ie stalk) 10-14cm, much swollen at the fruit end." (A Field guide to the Trees of Britain & Northern Europe, Alan Mitchell, Collins 1974). The English names come from the spectacular large white oval bracts in late May. "Also regrettably known as the 'Handkerchief Tree'" says Mr Mitchell. Discovered in W. China in 1904; the remarkable story of it's introduction to Western science can be found here[3], pages 40-41. A photo of the Oxford Botanical Dove Tree in full foliage is here[4]. Alansplodge (talk) 18:48, 2 July 2010 (UTC)

The dove-tree looks very plausible! I think I would put my money on that... - Zephyris _Talk 22:20, 2 July 2010 (UTC)

Found another picture[5]; scroll down to page 14. Is this the one? Alansplodge (talk) 22:44, 2 July 2010 (UTC)

That is definately the one! Nice detective work, thanks! 95.147.73.134 (talk) 20:49, 3 July 2010 (UTC)

Could it be a variety of walnut? Walnut shells are hidden inside a covering that looks like a fruit when growing. 92.28.247.183 (talk) 20:03, 2 July 2010 (UTC)

I thought of that but walnut trees have big chunky twigs[6], the nuts have short stalks and no ribs. Alansplodge (talk) 22:39, 2 July 2010 (UTC)

Would the car explode?

If something happened and a car's intake valve didn't shut all the way (or the valve suddenly developed a serious fissure while the car was in use) and the compression stroke came back up and the spark plug went off, is there anything stopping the combustion flame from streaking back through the lines to the fuel tank and causing a catastrophe?20.137.18.50 (talk) 14:04, 1 July 2010 (UTC)

The fuel line is full of liquid fuel. You need air in order to support combustion, so it would be hard to propagate the flame back very far prior to where air is mixed with the fuel vapors. DMacks (talk) 14:09, 1 July 2010 (UTC)

A Carburetor if there is one, also makes a barrier since the fuel must go through a narrow nozzle.87.102.17.114 (talk) 14:26, 1 July 2010 (UTC)

If a valve gets stuck open, you don't get compression and the fuel doesn't ignite properly. Aside from the fact of there being no air in the fuel lines, there isn't likely to be any combustion either. What happens is that the car sputters along, sounding really rough and developing very little power, because it's only running on three cylinders (assuming it's a four cylinder car that is!). Gasoline really doesn't burn very easily unless it's under hot or under pressure and in vapor form mixed with air. SteveBaker (talk) 18:39, 1 July 2010 (UTC)

A backfire in the intake is not unheard of on poorly maintained cars for a variety of reasons (such as timing, like you mentioned), and while it can easily damage intake manifold parts like rubber seals or sensors it is not likely to cause the fuel lines to catch fire for the aforementioned reasons. --144.191.148.3 (talk) 18:42, 1 July 2010 (UTC)

Yep. Remember - the car is a four-stroke machine. On the first down-stroke, gas/air is sucked into the cylinder. On the up-stroke, it's compressed...only the valve isn't closed so this just pushes most of the gas/air mixture back out again. Then the spark goes off - but there's hardly any gas/air mixture to ignite - and it's not hot and under pressure like it should be - so it probably won't ignite. The lack of a fuel burn means that there is nothing to push the piston back down again - aside from the inertia of the car and flywheel...but it'll go back down - sucking in whatever fuel and air is left in the cylinder. Then the exhaust valve opens and the piston goes back up - pushing most of whatever was in there out to the exhaust. But not all of the exhaust gasses will go out - lots of them will be pushed back to the carb. SteveBaker (talk) 18:45, 1 July 2010 (UTC)

Some cars have a Two-stroke engine that typically has no intake valve. Cuddlyable3 (talk) 13:47, 3 July 2010 (UTC)

How much energy required to reach infinite speed?

I can't remember the equation for how much energy is required to reach a given speed. What is it again? And what do you get when you feed infinity through it? Presumably no answer, since reaching c takes infinite energy.--92.251.129.172 (talk) 15:04, 1 July 2010 (UTC)

E=1/2 mv² where E=kinetic energy, m = mass and v= velocity. So, yes, at v= infinity, E = infinity. This is the non-relativistic definition of energy and velocity, so I am sure there are adjustments to be made for speeds close to light speed, however these adjustments actually make it worse; you hit infinite energy at the speed of light (3.00 x 10⁸ meters per second). So, you cannot ever reach the speed of light. It's a pain in the ass for science fiction authors, but the speed of light is a hard limit. --Jayron32 15:13, 1 July 2010 (UTC)

I thought they usually invented some warp drive or hyperdrive that somehow let them past lightspeed?--92.251.129.172 (talk) 15:25, 1 July 2010 (UTC)

Such things are utterly impossible given the laws of physics as we know them. But science fiction is fiction (meaning "it ain't all true"!)...and they are free to invent anything they want in order to make the plot work...and hand-waving away the speed of light limit is something you pretty much have to start off doing if you want people to go to other stars. A few science fiction authors don't do that...but they are certainly in the minority. SteveBaker (talk) 18:27, 1 July 2010 (UTC)

Hence "invented".--92.251.158.103 (talk) 19:59, 1 July 2010 (UTC)

Yes. The one E.E. Doc Smith invented for Lensmen just got rid of the pesky m in the above equation, so you only have to overcome the resistance of the interstellar medium. Unfortunately, they answer still is infinite (and the original question is physically meaningless - you cannot go faster than the speed of light without violating causality, no matter what your trick is). --Stephan Schulz (talk) 15:29, 1 July 2010 (UTC)

Well, there's a hidden assumption there that your "trick" is frame-independent. It's imaginable that there is some as-yet-undiscovered physical process that is not frame-independent, and that defines a preferred frame of reference which we have not yet been able to detect. Then you might be able to use that process to send information at arbitrary speeds in that preferred frame, but unlike in the case of the tachyonic antitelephone, you might not be able to "close the loop" to send information back to where it started from (which would allow the grandfather paradox).

In this scenario (for which, certainly, I am not claiming there is any evidence at all; this is a thought experiment), there would still be some observer, in motion relative to the preferred frame, who could observe an effect occurring before its cause in his time coordinate. But so what? That's just a coordinate. As far as I can see, there is no danger of paradox unless you can create a causal loop.

Another possible way out is, keep frame invariance, but throw out isotropy — the magic FTL drive works only when you're headed towards cosmic right; the usual speed limit applies to cosmic left. --Trovatore (talk) 03:44, 2 July 2010 (UTC)

The relativistic formula for kinetic energy is:

$E_{k}={\frac {mc^{2}}{\sqrt {1-(v/c)^{2}}}}-mc^{2}$.

Formally, setting v to infinity gives you a negative kinetic energy of -mc² ! But this is meaningless, because E_k tends to infinity as v approaches c, so you can't go through the "light barrier". Gandalf61 (talk) 15:30, 1 July 2010 (UTC)

so we can create a perpetual motion machine! All we need to do is get something to infinite velocity, and it will generate tons of free energy! Or maybe we need to use negative energy to get something going that fast. Googlemeister (talk) 15:43, 1 July 2010 (UTC)

No - none of those things work. The answer isn't infinity - it's the square root of some negative quantity. If (v > c) then (v/c)² is greater than one - so 1-(v/c)² is negative. If you take the square root of a negative number on your pocket calculator, it probably says "E" or "Error". You get a complex number - and those can't exist as actual quantities in the physical world - whenever you find a complex number as the final answer to a calculation, you know you've screwed up somewhere. That's WHY this equation says you can't travel faster than light. If the answer was merely infinity, we could possibly imagine some kind of meaning to the answer...but a complex number means "your math is broken somewhere" - and the reason it's broken is because you put a disallowed number into the equation. SteveBaker (talk) 18:27, 1 July 2010 (UTC)

I understood the answer would be meaningless I was jsut curious about what it would be.--92.251.129.172 (talk) 18:41, 1 July 2010 (UTC)

As v approaches infinity, the imaginary part decreases without limit. Thus, the energy would be real if it's moving at infinite velocity. Of course, from any other point of reference, it's going at a finite, but faster than light, velocity, and it comes out imaginary, so it doesn't really help.

You can question why you would even want to move your rest mass. Arguably "you" are an algorithm that your brain is computing and that can be sent using photons from one machine to another machine at lightspeed. So, travel at lightspeed is possible. Count Iblis (talk) 15:47, 1 July 2010 (UTC)

Well what they mean is matter cannot move at lightspeed. Although you could claim that since we are moving away from a certain galaxy at 0.6 c, and that same galaxy is moving the other way at 0.6 c, we are moving apart faster than the speed of light. ALthough that still isn't going the speed of light.-92.251.129.172 (talk) 15:53, 1 July 2010 (UTC)

You could claim that, but you'd simply be wrong, because relativistic velocities (i.e. ones that are a substantial fraction of the speed of light) don't obey simple arithmetic where 0.6 + 0.6 = 1.2; they obey more complex arithmetic where the answer can never be greater than 1.0: this seems counter-intuitive to us because our everyday logic is based on everyday experience which never includes relativistic velocities, but it has been extensively proved by observations and experiments. 87.81.230.195 (talk) 18:09, 1 July 2010 (UTC)

As I understand it, though, there is a sense in which a galaxy beyond the event horizon can be said to be moving away from us faster than the speed of light. It gets tricky to state exactly what this means. That general sort of question belongs to general rather than special relativity, and the math is hairy, and there's no longer always as clear a choice of coordinate systems as you might expect. --Trovatore (talk) 01:41, 2 July 2010 (UTC)

I think you mean a galaxy outside of our light cone. The event horizon is something different entirely. --Jayron32 01:53, 2 July 2010 (UTC)

What I mean is outside the observable universe in a certain sense. I have never entirely gotten straight what is the accepted terminology on this, but our observable universe article appears to be talking about all objects that could potentially have been affected by an event in the past, by which we could also have been affected. I mean the time-reversed notion — all objects that could potentially influence a future event that we could also influence. The language at particle horizon suggests that event horizon is used in this sense. --Trovatore (talk) 01:57, 2 July 2010 (UTC)

There is a connection with light cones, but no, "outside our light cone" is not the point exactly. The point is that our forward-facing light cone, and the forward-facing light cone of the galaxy in question, have empty intersection. --Trovatore (talk) 01:59, 2 July 2010 (UTC)

They're not moving, or at least not that fast. It's just that the intervening space is expanding. — DanielLC 07:42, 2 July 2010 (UTC)

Well, I was careful to say "there is a sense" in which it's moving away from us faster than light. --Trovatore (talk) 07:49, 2 July 2010 (UTC)

question about new planet

Time is talking about a new planet that someone got a photo of that is 500ly away. This planet is described as orbiting it's star at 330 AU, and has a surface temp of 2700K. To me this sounds more like a red dwarf star then a planet. Could someone familiar with the methodolgy give me a rough idea of how they can differentiate between a large planet and a very small star in orbit around another star (like Proxima Centauri)? Googlemeister (talk) 15:41, 1 July 2010 (UTC)

Make life easy for us and give us a link to the article, please!

This other article (from National Geographic) has a bit more detail about the planet. Its mass has been calculated at roughly eight times the mass of Jupiter. That's certainly big, but it's not 'star' big. Our own article on stars discusses the minimum stellar mass, which is something like eighty times the mass of Jupiter. The boundary is governed by the minimum mass required to sustain stable nuclear fusion in the stellar core; the gravitational attraction holding the star together has to be high enough to balance the pressure generated by core hydrogen fusion. There is a gray area as you go to objects with masses lower than that, but bigger than gas giants: the brown dwarfs. The intro to that article discusses the definitions (and the challenges associated with assigning objects to one category or the other). In general, the boundary between large gas giants and small brown dwarfs is taken to be at around 13 Jupiter masses.

Finally, the high surface temperature of the planet in the story is a bit of an anomaly. It's not being heated (significantly) by internal fusion, nor is its heat drawn from the parent star. Instead, this is a very young planet (just a few million years), and its very high temperature comes from gravitational collapse. (The gravitational potential energy freed up as matter fell in to form the planet appears as heat.) The young Earth went through a similar period as it was forming billions of years ago, it took millions of years before the crust cooled and solidified. TenOfAllTrades(talk) 16:00, 1 July 2010 (UTC)

I do kind of have to agree, though, that this is not what I think of as a referent for the word planet. Really I think the IAU got the definition wrong in a number of ways — rather than distinguish between "planets" and "dwarf planets" on the basis of this fairly silly clearing the neighborhood concept, it would have been more revelatory to draw a line between the "real" planets (that is, the rocky planets), and the gas giants, which are just another sort of cat entirely. --Trovatore (talk) 02:09, 2 July 2010 (UTC)

Trovatore and his pet peeve. Dauto (talk) 04:07, 2 July 2010 (UTC)

Why don't we write to the IAU and tell them to replanetize Pluto? 67.170.215.166 (talk) 01:11, 4 July 2010 (UTC)

1RXS J160929.1-210524, btw. --Sean 16:20, 1 July 2010 (UTC)

Trench binocular

The german de:Scherenfernrohr has no interwikis - but I think this instrument is well known. See the picture on the right. Can you help? --Eingangskontrolle (talk) 16:56, 1 July 2010 (UTC)

If you are asking what the instrument is, it is a periscope.--Shantavira|^{feed me} 17:08, 1 July 2010 (UTC)

Periscope seems closest, or else binoculars. The first talks about use in trench warfare but does not mention the design that has separate periscope for each eye of the binocular. The second, in binoculars#Military, specifically mentions this design and application, but is only a small part of a larger and wider-ranging article mostly about binoculars not the key periscope idea. DMacks (talk) 17:11, 1 July 2010 (UTC)

...and it's not even mentioned in trench warfare. DMacks (talk) 17:17, 1 July 2010 (UTC)

There doesn't seem to be a specific article in the EN Wikipedia. They're mentioned in passing, as "trench binoculars", in the binoculars article. Searching Google, there doesn't seem to be a general English language term for them, beyond "trench binoculars" or "rabbit ear scope". -- Finlay McWalter • Talk 17:13, 1 July 2010 (UTC)

Can someone who can read German more fluently than I check if de:Scherenfernrohr and its cited ref seem notable enough to make a Trench binoculars article? Although File:British trench periscope Cape Helles 1915.jpg looks like a simple (monocular) design not binoculars...hard to see clearly, so maybe better to do trench periscope instead of specifically binocular. DMacks (talk) 17:15, 1 July 2010 (UTC)

The link is available in english http://home.arcor.de/thuernagel/sf14-e.htm same person has a whole set of articles on "military optics" (or 'tactical optics') III Taktische Optiken http://home.arcor.de/thuernagel/katalog.htm . There's a mixture of reliable info and some small amount personal reflection/speculation in their (which is all probably completely right) website.

Also known as "donkey ears" in the UK.

Maybe a redirect to a new extended section in periscope? or a complete new article on 'tactical optics'?

I can't see enough there as it is.. though the article would probably survive on it's own as a stub on the assumption that there is more info out there, and the obvious fact that such items are of social-historical significance.87.102.17.114 (talk) 18:03, 1 July 2010 (UTC)

It's my understanding that they're a bit more than just binoculars with a periscopic lightpath. I believe (but can't find a reliable source to adequately support, otherwise I'd have started on the article) that the rabbit-eared variety (like this) are intended for field artillery spotters. My understanding is that the two lenses independently targettable; the spotter picks his target and aligns both lenses on it - he can then read off the angle from a little gauge, look up the corresponding distance in a little trig table, and report that to the gunners. It's obviously not as accurate as a proper survey with two theodolites separated by a measured baseline, but it's going to be better (and quicker) than just guessing and having to walk trial shots up and down. -- Finlay McWalter • Talk 17:41, 1 July 2010 (UTC)

I think it's just for observers - the wide position gives better stereoscopic view (ie less foreshortening) (Is this correct?)

You're thinking it's a rangefinder - the person says Scherenfernrohre are the predecessors of the stereoscopical rangefinders - the same site has info on these - they can look very similar - but are more meaty - eg http://home.arcor.de/thuernagel/em61.htm .. they could use the thing as a rough rangefinder though,as the article says.87.102.17.114 (talk) 18:03, 1 July 2010 (UTC)

Some info with pictures through in english here http://www.paulstiger1.co.uk/WWII-Optics-Collection.htm and here http://www.fieldgear.org/optics.htm 87.102.17.114 (talk) 18:16, 1 July 2010 (UTC)

The internet eh http://www37.atwiki.jp/strike_witches/m/plugin/ref/?guid=on&serial=921&w=500 ... 87.102.17.114 (talk) 18:24, 1 July 2010 (UTC)

If anyone is interested in writing the article on these particular type of thing then de:Artillerietruppe_(Wehrmacht) is useful - it says that they were used by forward observers for artillery.

Also searching "scissors telescope" shows that they were also used attached to tanks (with reliable sources, not forums).87.102.17.114 (talk) 19:04, 1 July 2010 (UTC)

It's a http://en.wiktionary.org/wiki/telestereoscope too.87.102.17.114 (talk) 19:04, 1 July 2010 (UTC)

Do the positions of stars change much relative to each other?

Will Alpha Centauri always be "about" the same distance from Earth? Suppose one picked any two stars at opposite sides of the galaxy. Does their position change much relative to each other? —Preceding unsigned comment added by 92.251.129.172 (talk) 18:28, 1 July 2010 (UTC)

The Wikipedia articles for many stars, such as Alpha Centauri gives their proper motion in the infobox at the right. -- Finlay McWalter • Talk 18:32, 1 July 2010 (UTC)

So the sky will be very different in a million years time?--92.251.129.172 (talk) 18:34, 1 July 2010 (UTC)

Yes; this page has movies of the Big Dipper over 200,000 years, and it changes substantially in that time. -- Coneslayer (talk) 18:49, 1 July 2010 (UTC)

See radial velocity for a sense of how the distances of stars change over time. Stars have even swung very close to the solar system in the past, and will likely do so again in the future—see Gliese 710 (negative radial velocity) for example. ~AH1^(TCU) 17:42, 2 July 2010 (UTC)

Tori Vienneau

was the Tori Vienneau murder case a suicide  ?

http://www.youtube.com/watch?v=LM6bBVd0f7s —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 18:30, 1 July 2010 (UTC)

Why are you asking us here? We're scientists, not Columbo. 87.102.17.114 (talk) 18:35, 1 July 2010 (UTC)

law —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 21:08, 1 July 2010 (UTC)

World building.

I'm sure questions like this have been asked many many times here, but I think mine is a little different.

Let's say I'm making a fictional planet and I want to make it as scientifically realistic as possible. I think I can handle most of the biological and geological topics, but mostly what I wanted to know about was meteorological and climatological. Things like ocean currents, jet streams, air masses and weather patterns, etc. What would the reference desk suggest as guidelines for creating the weather patterns on a fictional planet?

Also, I think I can handle most of the geology, but what confuses me most is plate tectonics. I can grasp the basic concepts of rifting and subduction and so on, but I don't think I know enough to create a fictional tectonic system on a fictional planet. This is important because drawing the maps of my world requires being consistent with tectonics.

63.245.168.34 (talk) 19:42, 1 July 2010 (UTC)

Make it pretty similar to Earth and you should be fine. If you stray from that, then really it's anybody's guess. We've only studied one planet in any great detail, so we don't know what else is possible. --Tango (talk) 19:52, 1 July 2010 (UTC)

Are you sure about that? We know that weather patterns are defined by some pretty basic physical laws like the Coriolis Effect and so on, and we're familiar enough with these rules and how they effect the atmosphere and the oceans that we can predict the weather with reasonable certainty. Also, don't you think that making it too similar to Earth would be very unlikely? 63.245.168.34 (talk) 20:05, 1 July 2010 (UTC)

Not necessarily, perhaps scientifically, a planet can only be inhabitable if it is similar to earth. I mean how likely is it for life to develop on a planet with almost 0 tectonic activity? Of course if the book is not about humanss (or similar to human) colonizing a planet, but about a chlorine breathing insect race, then of course all bets are off. Googlemeister (talk) 20:57, 1 July 2010 (UTC)

There is a whole book on this, created just for you: World-Building: A writer's guide to constructing star systems and life-supporting planets. There are other books in the series with titles like Aliens and Alien Societies. (I haven't read World-Building but have read Aliens. The latter covers a lot of bases and made me consider aspects I hadn't thought about.) Comet Tuttle (talk) 21:16, 1 July 2010 (UTC)

This is actually very difficult to deal with in a comprehensive way -- just consider how much the Earth's climate has varied over the past billion years, mainly as a consequence of the continents moving around. It is widely believed, for example, that the Earth was in a snowball state from 800-600 million years ago, with the oceans frozen over nearly down to the equator, due to all of the continental landmass being concentrated near the equator. In short, you can get anything from rainforests at the poles to glaciers at sea level at the equator, just by shifting the land around. Looie496 (talk) 22:41, 1 July 2010 (UTC)

That's mostly what I'm curious about. How does the shape of the land affect the climate?

Also, as for the planet being inhabited or inhabitable, in the context of my fictional universe, it's a terraformed planet with a young, engineered biosphere. Only inhabited by species that were brought to it by humans. There are no aliens in my fiction.

63.245.168.34 (talk) 00:12, 2 July 2010 (UTC)

Land has profound effect on climate. Generally speaking, the direction of prevailing winds over landmasses determines things like where deserts and forests will appear. If prevailing winds have a long Fetch over water, then the land downwind tends to be much rainier than if the winds have a long fetch over land. Also, there are effects like rain shadow, which makes land upwind of a mountain range rainier than land downwind of the mountain range; which is why Seattle is much rainier than say Spokane. --Jayron32 01:06, 2 July 2010 (UTC)

Also, land tends to heat up (and cool down) far quicker than water: you're better off swimming in the Mediterranean in October than in April, even if the land temperatures are similar. Physchim62 (talk) 01:58, 2 July 2010 (UTC)

From observations on exoplanets, astronomers can deduce a thermal "cimate" map of some planets, as they are hotter in some areas and cooler in others. However land and ocean have not yet been confirmed on any exoplanets, not even Super-Earths, so the hypothetical planet should be like Earth in the sense that it has mountains and oceans. As for the effects of land patterns on the overall climate of regions, here is a question I posted here way back, when I was proposing a way to model the climate that is probably much less complicated than supercomputer simulations but do not involve mathematical formulae and calculations. As I never got an answer, I'm not sure how accurate my method is, but it should be a good general approximation of the climate of a planet given its land masses, but its functioning is reduced when less is known about the planet. Regular weather patterns can be inferred from the location of quasi-stationary highs and lows, but there will always be great variations. We know the general climate of Mars, yet we still don't have the ability to predict global dust storms that often occur on the Red Planet or what exactly triggers them. Also, if the climate changes on your planet, the effects of that change are likely going to be harder to predict than just the climate map in a static climate. ~AH1^(TCU) 17:24, 2 July 2010 (UTC)

Micro rockets

Suppose we want to send a miniscule payload from the surface of the Moon to the Space station. Then it seems to me that at least in theory, the rocket could be made very small. So, what is the minimum mass of a rocket that is able to let a payload of mass m (assume m < 1 microgram) escape from the Moon's gravity, as a function of m? Count Iblis (talk) 22:56, 1 July 2010 (UTC)

What kind of fuel do you plan to use? By mass, do you include everything involved or just the rocket (projectile) that goes up into the air? I ask because different fuels have different masses. Also, assisted blastoff reduces fuel required. Further, the length of thrust is important. Do you want an explosion or a controlled thrust? -- kainaw™ 23:11, 1 July 2010 (UTC)

For a payload that small, the payload is irrelevant. What matters is how light an engine you can make. The smallest rocket able to lift a payload of a microgram will be essentially the same size as one able to lift a payload of a few hundred grams. That said, I can't think of anything with a mass of less than a microgram that I would want to send from the Moon to a space station, certainly not on its own - just put it in with something else that is going. --Tango (talk) 23:15, 1 July 2010 (UTC)

I see, so it is not possible to make microscopic engines? Count Iblis (talk) 00:59, 2 July 2010 (UTC)

I wouldn't say it's impossible, but I don't know of anyone ever doing so. There just isn't any reason to try. --Tango (talk) 01:19, 2 July 2010 (UTC)

Just fire it from a rifle? (I don't know how the space station would catch the bullet!) Dbfirs 07:13, 2 July 2010 (UTC)

See Space gun. It's a lot harder to get things into space than people on here seem to realize. --Mr.98 (talk) 11:37, 2 July 2010 (UTC)

This question is about launching from the Moon into the Moon's orbit. Gravity is 5/6 that on Earth and orbital distance is about 1/4 that of Earth. So, there are two things making it much easier. Gravity is much less. Orbit is much closer. Further, there is almost no atmospheric drag. So, I do not see why shooting a small projectile into orbit would be a big deal. -- kainaw™ 12:24, 2 July 2010 (UTC)

I've read that there's a limit to how small you can make a rocket. Unfortunately, they didn't actually say what the limit was. That said, getting it off the moon is much less difficult then getting it off the Earth. — DanielLC 07:32, 2 July 2010 (UTC)

Bottle rockets are pretty small... Googlemeister (talk) 18:17, 2 July 2010 (UTC)

In The Andromeda Strain book and movie, they dealt with this briefly (much more so in the movie), where an extraterrestrial could live as this infectious microbe such that only one cell needs to be launched into space, then becoming a superorganism upon arrival and mass infection on a habitable planet. A suggestion was that there would be any number of evolutionary advantages for a cell-colonial intelligence to be successful, one of which was the ease of resources for going into space and colonizing. That's getting off-topic, but that's why I find this question interesting.

I think the best way to get into space for that, then, is to begin with high-altitude balloons filled with hydrogen (or rigid vacuum). An easy calculation: the density of air is 1kg/m^3, so a little over one cubic meter of balloon is required to lift 1kg of payload. For a single cell in a colonial organism (density about water, 1000kg/m^3), we can easily find out the kind of balloon we need, though considering that we could wrap our organism in a (10-micron)^3 natural foam bubble filled with hydrogen released naturally from alkali oxidation, it's easily imaginable that organisms would get up to the edge of space by such means without intelligence to help. Of course, the smart cell would the burn the hydrogen once reaching the edge of space for a friction-free ride wherever, though they still have to break escape velocity to travel outside their solar system.

At 1km up we orbit the Earth at about 8km/s, and we start hydrogen burning with specific impulse of about 1000s to try to reach escape velocity 11km/s. So for payload mass m, we need to burn about 0.4m in fuel hydrogen, which is a really good deal since we can get as much fuel as we want up there with these balloons. I feel I must be missing something. SamuelRiv (talk) 02:57, 4 July 2010 (UTC)

Why does the ocean appear so high?

I took this picture of the Atlantic Ocean from an elevated train.[7] Am I unfamiliar with nature or does the ocean appear elevated especially towards the horizon? 67.243.7.245 (talk) 23:31, 1 July 2010 (UTC)

We do not know how the camera was oriented. The technical term for this parameter is the elevation of the camera - the angle it makes with respect to the horizon - and not to be confused with its elevation above sea-level. Obviously, by angling a camera, you can make the horizon appear to be at any vertical position inside the image. In addition, there may be an optical illusion of distorted perspective if the train's window has a weird aspect ratio or orientation, or if the train was actually tilted when you photographed the scene. The train was high above the ground, (the other kind of elevation), then you may see a lot more land in the foreground than usual, contributing to the unusual perspective. Nimur (talk) 23:51, 1 July 2010 (UTC)

Well, that's all valid, but also it looks like the foreground may be sloping downward a bit, which is a frequent cause of illusions of this sort. Looie496 (talk) 01:22, 2 July 2010 (UTC)

Actually, we do know how the camera was oriented -- if you're looking toward a horizon where the sea seems to form a sharp boundary against the sky (rather than fading into haze), a line from you to that horizon must be horizontal. (Horizon. That's why we call it "horizontal".) But as Looie says, the foreground is sloping, so this may contribute to the shoreline looking lower than you expect. --Anonymous, 04:14 UTC, July 2, 2010.

I think the reason is rather perception (or the lack thereof) of depth (in the sense of distance). On the structured foreground one has a pretty good feel for how the distance increases as one looks from the bottom of the picture to the land-sea boundary. The unstructured sea does not offer any depth indicator (increasing haziness doesn't help on this fairly clear day) so one does not perceive any distance difference between the land-sea boundary and the horizon. That's why the sea appears like a vertical wall, the entire blue surface at the same distance. I hope I understood the question correctly. --Wrongfilter (talk) 15:25, 2 July 2010 (UTC)

I've noticed the same effect while standing in an airport close to sea level—the ocean in the distance appeared somewhat distant as well as a bit elevated. Other than perspective could some kind of mirage effect explain the phenomenon? ~AH1^(TCU) 17:10, 2 July 2010 (UTC)

Plane Crash

What happens actually when an airplane (say a Boeing 747) crashes. How and why do people die, by the intense heat produced or by kinetic energy ? Is death swift or slow and painful ?  Jon Ascton  (talk) 17:33, 1 September 2010 (UTC)