Content deleted Content added

Inline

Revision as of 11:50, 26 August 2013

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

Shortcut

WP:RD/S

Want a faster answer?

Main page: Help searching Wikipedia

How can I get my question answered?

Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
Post your question to only one section, providing a short header that gives the topic of your question.
Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
Don't post personal contact information – it will be removed. Any answers will be provided here.
Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
Note:
- We don't answer (and may remove) questions that require medical diagnosis or legal advice.
- We don't answer requests for opinions, predictions or debate.
- We don't do your homework for you, though we'll help you past the stuck point.
- We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

August 22

if Mars still have more greenhouse effect like Earth

Before I didn't think planetary atmosphere and compositions are important in determining habitable zone but my college professor told me planetary atmosphere and composition are important to determine where the habitable zone will be, so if Mars have more greenhouse effect and atmosphere pressure roughly same that of Earth will it be much warmer than it is now? If it will be warmer than what will the average planetary temperature be? 23 F? If Titan didn't have any greenhouse effect will Titan be even colder?--69.233.252.198 (talk) 02:14, 22 August 2013 (UTC)[reply]

To determine the final temperature you'd have to know exactly how much greenhouse effect there will be. Venus is an example of a runaway greenhouse effect. The gas giants also have a pronounced greenhouse effect, although there they may be heated more by internal sources (radioactive materials, tidal forces, etc.). StuRat (talk) 09:12, 22 August 2013 (UTC)[reply]

The OP's question about Mars reminds me of what Carl Sagan had to say about the possibility of terraforming Mars and Venus. For Mars, you have to create greenhouse effects somehow. For Venus, it's the opposite - you have to introduce something that will somehow consume greenhouse gases. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:20, 23 August 2013 (UTC)[reply]

The immediately obvious solution would be to funnel enough of the gas from Venus to Mars.... 86.141.186.4 (talk) 12:53, 23 August 2013 (UTC)[reply]

Sure, a flexible, stretchable conduit of some kind, hundreds of millions of miles long. That shouldn't be too difficult to engineer. Kind of like a gigantic siphoning hose. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:34, 23 August 2013 (UTC)[reply]

Wormhole X-Treme! --Stephan Schulz (talk) 14:39, 23 August 2013 (UTC)[reply]

Heh, he's got a point. There are a lot of things that aren't too difficult to engineer, it's just the building part that gets you. :) But at least in fantasy you could use an elaborate system of momentum exchange tethers to exchange small packets of mass between Mars and Venus with relatively small energy investment total. Wnt (talk) 18:49, 23 August 2013 (UTC)[reply]

Do how old scientific articles matter the accuracy of informations?

Thistold me the article I linked were published in 1993 [1] and 1997 (Once and Future of the Sun) and is not a recent document. Do how old the scientific paper is published matters how accurate the information gets. Then why didn't the previous editors repost what their works in 1993 when the newer informations came up? I didn't thought the published dates matters that much. Or these authors are not require to repost information when new informations come up. Do these authors change their mind when the newer evidence comes up? I thought if they have changed their mind they suppose to repost their works they done in their earlier studies.--69.233.252.198 (talk) 02:38, 22 August 2013 (UTC)[reply]

Yes how the information is published does matter to how accurate the information is or at least how much you can trust it. If it's published in a refereed journal it means that someone else, who also works in the same field, has read it and not found errors within it. While if it's just put up on the web without being refereed it may well be correct but the information hasn't been independently scrutinised. As for the age of a paper, for a start computers are a lot more powerful now so you can enter more information. So with the same data you can get more accurate answers. Also the structure of the Standard Model of the Sun has changed quite a bit since 1992 with the lunch of SOHO. For new information a new paper would be written, submitted, reviewed and published. The old paper would be untouched after publication (there is only one publication run).Dja1979 (talk) 03:08, 22 August 2013 (UTC)[reply]

This is a largely subjective matter. It depends on the field of science or mathematics you're talking about. For example, Lord Kelvin's paper entitled "On the Age of the Sun's Heat engages in discussion on whether something made of coal could possibly be producing that much heat! Yet papers written by the exact same guy about the laws of thermodynamics in the exact same year remain as entirely valid and useful references, even today. Some fields just move faster than others!

As Dja1979 points out - recent spacecraft missions are still revolutionizing our knowledge of the sun - and papers from just a decade ago are unlikely to be of much use. Scientists working in a particular field tend to have a good knowledge of how far back they can reasonably refer without picking up on outdated information.

SteveBaker (talk) 13:53, 22 August 2013 (UTC)[reply]

It depends on the study done and the assumptions made. Sometimes a paper from a century ago can be a true pleasure to read, and as relevant today as the day it was written. There are even rare cases in which an ancient publication is found which was more knowledgeable than modern sources on a point (see Ge Hong regarding artemisinin) Wnt (talk) 14:38, 22 August 2013 (UTC)[reply]

Absolutely. It's not so much a matter of age, but a matter of what, if anything, has changed the scientific community's understanding since then. Math is not a science (in my view), but the results of math papers from e.g. 1900s are just as true now as they were then. Even in science, many old papers can be valid and useful for decades. If the OP is interested in specific examples in a given field, we could try to provide suitable refs. Of course, many old papers are outdated, because their findings have either overturned or improved (especially in younger subfields of e.g. computer science or genetics). This is generally held to be a good thing: it is how our understanding progresses, and is built in to the prevailing philosophy of science, specifically, Karl Popper's principle of falsifiability. (My WP:OR is that most currently practicing scientists are implicitly proponents of the Popperian view, even if they don't know it by that name, or don't think about philosophy of science much.) SemanticMantis (talk) 16:32, 22 August 2013 (UTC)[reply]

I'm not sure this issue got adequately dealt with in the responses above: scientists certainly do change their minds as new evidence comes up. This is central to science; without it, there is no science. Once a paper is published, though, it is not subsequently modified. Partly, this is because of the long history of paper publishing, where it is not so easy to 'repost' something that has been published. More importantly, it makes referencing clear: when one refers to a paper from 1993, one doesn't have to worry that the text might have changed by the time your readers go look it up. Instead of modifying the already-published paper, scientists publish new papers. An expert in the field would know what papers are still worthwhile and which are outdated. For the nonspecialist, it is best to rely on secondary sources such as books, which review and summarize material and put it in context. This is one of the reasons why Wikipedia prefers secondary sources to primary ones for referencing. --50.196.55.165 (talk) 00:11, 27 August 2013 (UTC)[reply]

How do I identify a new type of earthworm?

having been around for many years, raised on a farm, dug worms for fishing, and gardened forever, I have discovered a completely different kind of worm this past week. I live in northern Ohio and came accross an area which has a very strong and firm eartworm population of 3 to 4 inch red colored worms that go crazy when uncovered. They twist and turn rapidly, they are very hard to hold on to, and they move very fast. Their bodies are very firm almost like a snake and they flop all over the place. Diameter is large. They are really strong and not at all like the thousands of giant earthworms that I have encountered before. They can extend themselves like a regular earthworm but their ends are very pointed. Can someone tell me if this is an unusual worm and what it might be? — Preceding unsigned comment added by 184.59.176.230 (talk) 17:22, 22 August 2013 (UTC)[reply]

Any photos you can offer? I can't help you either way, but someone else might be able to if you have one. Mingmingla (talk) 18:15, 22 August 2013 (UTC)[reply]

Just a guess, maybe a red wiggler? As their name suggests, they are feisty, and if I recall correctly, they are rather firm. They prefer compost to ordinary dirt. Was anything else different about this patch of dirt? Also check for the characteristic putrid smell that red wigglers release when agitated. SemanticMantis (talk) 19:18, 22 August 2013 (UTC)[reply]

Getting a tattoo while tanned or burnt

My friend is plannning on getting a tattoo after a holiday in Spain. He likes to ta his skin and thinks getting a tattoo the week after will pose no problems. My logic is that this is a bad idea and could probably scar him if he gets sunburnt. Not to mention the chance of blistering and a longer healing time. Does anyone know anything on this matter? Thanks ツ Jenova 20 ^(email) 18:16, 22 August 2013 (UTC)[reply]

Some would argue that this is a borderline medical advice request. I don't know anything about tattoos, and Googling produces conflicting advice from various sources. Bearing in mind the medical disclaimer we usually wheel out in such cases, I would suggest you persuade your friend to consult the tattoo artist he is intending to use, in advance of his holiday. A reputable professional will be happy to advise him. - Ka renjc 22:57, 22 August 2013 (UTC)[reply]

Borderline maybe but it's a hypothetical. I was always told when i got sunburnt that you shouldn't scratch it. Someone getting a tattoo over sunburn and making the area bleed seems like it would at the least scar or cause issues with healing. I'm not looking for medical advice, i'm asking a hypothetical question and interested if anyone knows. Thanks ツ Jenova 20 ^(email) 08:10, 23 August 2013 (UTC)[reply]

Your friend is thinking of getting a tattoo and you're asking if it's likely to cause a scar if his skin is sunburnt - in what sense is that a hypothetical question? Richerman (talk) 08:37, 23 August 2013 (UTC)[reply]

I suppose i didn't word that well. I'm not asking if he should get it done, i'm just asking if there are any issues or studies on sunburn and scarring, healing, etc, when the skin is scratched or damaged further while healing. I think there would be but the Sunburn article doesn't really mention skin damage other than cancer. It's hypothetical in the sense that i've made assumptions for a made up scenario. If we can't do that then every health question here should be tagged in this way as medical advice. In that way most health questions and topics on cancer or common ailments should be banned from here as medical advice. See the point I am making? Thanks ツ Jenova 20 ^(email) 08:59, 23 August 2013 (UTC)[reply]

But you didn't ask about sunburn and skin damage in a general sense, you gave what sounded like a question about a very specific situation. You even include a time frame and a vacation place.Phoenixia1177 (talk) 09:56, 23 August 2013 (UTC)[reply]

Indeed. A hypothetical question would be "if someone with a recent suntan got a tattoo, could this cause any problems ?". Jenova20 (talk · contribs) gave too many specific details for their question to be treated as hypothetical. This question definitley looks like a request for Medical advice, and Karenjc (talk · contribs) has given the only response that we can in that situation. Gandalf61 (talk) 10:11, 23 August 2013 (UTC)[reply]

Never mind. Not that important ツ Jenova 20 ^(email) 10:18, 23 August 2013 (UTC)[reply]

It's well established that the hepatitis-armed scribble artists who do these things are not part of the medical profession, so factors affecting the quality of their work are not medical advice. I imagine that even the slightest bit of actual sunburn would make their practice particularly unpleasant. But the aesthetic and practical issues are harder to judge. The practitioners deal with all shades and toughnesses of skin, usually, but if the thing is meant to be seen while tanned, would it help to do it while tanned? If not would it be improperly shaded for the lighter skin? I'm afraid my aesthetics is just don't: there must be 10,000 ugly marks for every one that isn't immediately unappealing. That's not an answer of course but it illustrates how hard an answer is. Wnt (talk) 18:44, 23 August 2013 (UTC)[reply]

I have a Toad in my house but I can't find him!!!

Okay, so I'd just finished mowing the backyard, when I saw an Eastern American toad on my porch. Now, a lot of cold blooded things like to come up on my porch to get sun, lizards, toads, frogs, and insect you can imagine...so I usually just say hi and ignore them. Except...THIS ONE HOPPED IN THE HOUSE!!! I tried to catch it and put it back out but he got into the office. I searched everything, my boxes of cables, the papers on my desk, my cat's stomach, basically turned the whole place upside down...but I can't find him!!! I just know the poor little fellow will die of starvation or dehydration if I don't find him soon, is there anything I can do to lure him out? --Free Wales Now! what did I screw up? 18:38, 22 August 2013 (UTC)[reply]

Maybe make a toad home (google images here [2]), put in a moist sponge and hope it attracts the toad? I'd place one near where he was last seen, and another in the basement, if you have one. BTW, many toads, especially large ones, don't need much water on a daily basis, and only return to water to breed. So dehydration is not a big risk in the next few days, especially if you have a basement, which would also probably have toad food... SemanticMantis (talk) 19:13, 22 August 2013 (UTC)[reply]

It should be easier to hear and see him at night, since they're nocturnal. Might even try the same door it came in through. Like Mantis says, there's likely no immediate danger. Toads are generally much less susceptible to drying out than frogs, and cold-blooded animals don't starve so quickly. Cats generally hate the taste of toads, so I wouldn't look too hard into stomachs. A bit of damp grass may be tempting, if it's still there by tonight. InedibleHulk (talk) 19:34, 22 August 2013 (UTC)[reply]

They're pretty good at hiding. When I was a kid, one time my brother and sister and I were keeping a toad as a pet, in a cardboard box, and it escaped. For a couple of days we saw no evidence of it. But then in the middle of the night my dad got up to pee, went into the bathroom, turned on the light, looked into the toilet -- and there was the toad staring up at him. He made us get rid of it. Looie496 (talk) 22:04, 22 August 2013 (UTC)[reply]

Great story :) I hope the OP updates us if he finds it. SemanticMantis (talk) 01:40, 23 August 2013 (UTC)[reply]

In light of the above anecdote, might putting a pan of water someplace on the floor attract the toad? ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:31, 23 August 2013 (UTC)[reply]

The cat might not eat it, but may very well kill it nonetheless. You might want to lock the cat into a room far from where the toad was last seen, with water and a litter box, until you find the toad. Of course, if the toad squeezes under the door and sits in the cat's water bowl, I'd say his life expectancy will be substantially reduced. :-) StuRat (talk) 02:02, 25 August 2013 (UTC)[reply]

Let nature take its course. After all, your porch (and hovel) is not its natural habitat. Therefore, take comfort that local population pressure was probably high enough to drove him or it, to venturer into you humble abode to look for pastures a new. If your concerned about these little amphibians – then just think. If you spend -just a few hours- making your back-yard more amphibian friendly, then the demise of 'your' singular house bound ' toad will be made up handsomely by the increase in the local population. Maybe, in a few months time, your wife, whilst doing her spring cleaning ( if she still does these old fashioned household activities), may find a little mummified body of this toad in some back cupboard. Place it (the corpse) in a little glass jar to show your grand-children as a lead into explaining why these little amphibians mean so much... ecological-wise. Then show them how you have reformed your back-yard to become amphibian friendly. By then, these toads may have become so numerous that one can no longer step out onto to said porch without one of Kermit's relatives going 'crunch' under one's feet. As Stalin said: One death is a tragedy but millions of deaths are just statistics.--Aspro (talk) 15:20, 25 August 2013 (UTC)[reply]

Explanation for the acronym SWE

The phrase "SWE Stereo" appears on my television screen to reveal the audio utilized by a local TV station in their broadcast. The TV station is SLCCTV (Salt Lake Community College TV, channel 86-1701) located in SLC, UT. Directly below SWE Stereo is the resolution value "480i SD" (standard definition}. Thank you, Thomas J Tippett Tjtippett (talk) 19:10, 22 August 2013 (UTC)[reply]

Just a guess, but might it have something to do with Secondary Audio Programming? If you have an SAP button on your remote or set, try pressing it and see if you get Swedish. InedibleHulk (talk) 19:49, 22 August 2013 (UTC)[reply]

Another guess is it has something to do with this satellite terminal the station might use. Do you know if the station has any connection to the ABC 4 station? ABC is said to use this system. InedibleHulk (talk) 20:07, 22 August 2013 (UTC)[reply]

Effects of music while working & studying on performance

I listen to music several hours a day while studying (I'm a math student) and I wonder how much it affects my performances. Does the type of music (rhythmical/calm/powerful/..., vocal music or not, etc.) and genre (I hear mostly classical music and film soundtracks) matter? Thank you. 23:07, 22 August 2013 (UTC) — Preceding unsigned comment added by 84.109.248.221 (talk)

Mozart effect might be relevant. Googling "effect of background music" gave a few promising-looking links, including this (MS Word doc) on 'The effects of background music on learning, performance and behaviour' and this on 'The effect of background music and background noise on the task performance of introverts and extraverts'. AndrewWTaylor (talk) 08:35, 23 August 2013 (UTC)[reply]

I'm a high school teacher who moves around a bit between different schools. Just started in a new school for a four week stint. As usual, many students have asked if they could listen to music while they worked, insisting that they work better that way. (Some didn't ask, and DID listen. They won't any more.) Andrew - that study could be very useful. Might just print out that abstract for sharing with students. HiLo48 (talk) 09:28, 23 August 2013 (UTC)[reply]

It's a commons highschool science-fair project...comparing different styles of music (better students remember to analyze both style itself and alignment with subject's preference separately), different types of tasks, etc. It's rare that their background "research" consists of more than the popularized version of the Mozart effect--even if they cite the original study they obviously didn't read it--or any of the later publications strongly refuting the popular form. Sigh. DMacks (talk) 09:34, 23 August 2013 (UTC)[reply]

Temperature ranges of gas giant moons

When my teacher keeps telling me planetary composition, albedo, and atmosphere gases are also important to determine planet's and moon's surface temperature, I keep thinking these factors are not important. But Does the airless moon of gas giants have temperature ranges small or the global temperature of Jupiter, Saturn, Uranus' moon have wide temperature fluctuation between day and night. Enceladus (moon) Say the minimum surface temperature is 32 K and the maximum surface temperature is 145 K. I checked Europa (moon) it said the minimum surface temperature is 50 K and maximum surface temperature is about 125 K. --69.233.252.198 (talk) 23:12, 22 August 2013 (UTC)[reply]

You keep thinking the atmosphere is not important and keep being wrong. It's very important. To give you an idea, Earth's average surface temperature would be about 60 degrees Fahrenheit lower if the Earth didn't have an atmosphere. That's a significant change. Dauto (talk) 23:47, 22 August 2013 (UTC)[reply]

One other critical factor is tidal heating. Moons close in to gas giant planets can have rather large tidal heating, compared with solar heating. StuRat (talk) 01:57, 25 August 2013 (UTC)[reply]

August 23

the shape of heart

What is the geometric shape of the heart? Can I say that the heart is a truncated cone? (I do not think it is a truncated cone that is not really like that) — Preceding unsigned comment added by 46.210.149.99 (talk) 00:18, 23 August 2013 (UTC)[reply]

Asked and Answered on the Maths Desk

The following discussion has been closed. Please do not modify it.

For what purpose? In what context? μηδείς (talk) 00:28, 23 August 2013 (UTC)[reply]

Let's presume the context is the human heart. Why does the purpose matter? Perhaps it's so that the IP can make a Heart-Shaped Box. --Demiurge1000 (talk) 02:06, 23 August 2013 (UTC)[reply]

Kind of like a softball that's been hit a few too many times. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:12, 23 August 2013 (UTC)[reply]

Is softball played much in Israel? CambridgeBayWeather (talk) 04:55, 23 August 2013 (UTC)[reply]

Nah, they play strictly hardball. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:01, 23 August 2013 (UTC)[reply]

Breathing

If I inhale a mixture of gases called air which is 78.09% nitrogen, 20.95% oxygen, 1 % water vapour, 0.93% argon, 0.039% carbon dioxide, what mixture of gases do I exhale? Th4n3r (talk) 10:48, 23 August 2013 (UTC)[reply]

Amongst other things, it'll depend on your species, how long you held the breath, and the various physical conditions of your body. 86.141.186.4 (talk) 12:49, 23 August 2013 (UTC)[reply]

I think we can expect that the vast majority of those posting questions here are homo sapiens, and I might even go out on a limb and suggest that they are homo sapiens sapiens. StuRat (talk) 01:54, 25 August 2013 (UTC) [reply]

It depends on a great number of factors. Googling "rest oxygen consumption" returns a number of sites that give the oxygen consumption of adults as around 5% of what's available. It's converted to an equal volume of carbon dioxide. On this basis, the exhaled air will be 78.1 % nitrogen, 19.9% oxygen, 1.09% carbon dioxide, 1% water vapour, and 0.93% argon. Note that what you breaqth out is little changed from what you breath in, which is why mouth to mouth rescusitation works. Anything that increases metabolic rate will increase the conversion of oxygen to carbon dioxide - digesting a meal, physical exercise, thinking hard. Reacting to enviromental conditions will also increase it - for example shivering when cold. If you increase your body rate by either eating to much and getting fat, or building up muscle mass by exercise, your metabolic load increases but your lung volume capacity does not. (If you are quite obese, you lung capacity may be reduced, making you breath harder even at rest) Hence an increase in body weight will increase the percentage conversion of oxygen to carbon dioxide. Note that 1% water vapour in air represents 100% relative humidity at temperatures lower than 16 C, but only 20% rel humidity at 40 C. At the higher temperatures within the human comfort range, the body looses small amounts of water vapour to expired air. 1.122.214.154 (talk) 13:07, 23 August 2013 (UTC)[reply]

Don't forget that the water content will also increase; there's a lot of wet surface area inside the lungs. (The number above corresponds to only about 45% humidity at 20°C.) TenOfAllTrades(talk) 13:35, 23 August 2013 (UTC)[reply]

As is evident, especially in the winter, or when exhaling onto a glass surface. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:29, 23 August 2013 (UTC)[reply]

Alternative classification of Carnivora

Since not all Carnivora are in fact obligate carnivores and some are omnivores, is there some better and common (possibly unique) feature among them? Perhaps some taxonomists have proposed something on that? Brandmeister^talk 10:58, 23 August 2013 (UTC)[reply]

I would venture to suggest: their descent and relatedness. Linnean taxonomy used to be based on an ad-hoc mixture of visually obvious physical similarities, which taken in aggregate gave clues to organisms' actual relatedness (and were sometimes ambiguous or misleading), but nowadays it uses the much more rigorous methods of Cladistics, and can be corroborated by direct genetic comparisons. Characteristics that specific groups might have largely or uniquely in common are handy aide-memoires, but not ultimately definitive, because Evolution (if you'll excuse the trope). {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 12:53, 23 August 2013 (UTC)[reply]

Yes, ultimately ancestry is the real basis of classification. Often there are physical features that are highly characteristic, but they may not be obvious -- for example the layout of the teeth is often one of the most informative things. So is the bone structure of the foot. I don't know enough about this group to say anything specific, though. Looie496 (talk) 14:59, 23 August 2013 (UTC)[reply]

Yes, not all Carnivorans are obligate carnivores -- so what? As Carnivora indicates, the extant Carnivorans form a monophyletic group, which is about as good as it gets for modern cladistics/systematics. I'm not sure what feature they would all share, because the pinnipeds are a rather different from the rest. Perhaps there is some shared skeletal feature, but it would be pretty opaque to a non-specialist. As .195 says above, what they share is common descent. Conceivably, we could change the name to "Foofles", while keeping all members the same, but that would cause its own headaches. The way the International_Code_of_Zoological_Nomenclature works, names should follow the Principle of priority, unless there is some other good reason to change them (e.g. splitting an old paraphyletic group into two or more new monophyletic ones). Finally, beware the etymological fallacy! Hope that helps, SemanticMantis (talk) 15:03, 23 August 2013 (UTC)[reply]

That is, in my opinion, naming that order because of dietary habits is problematic (and, possibly, in other cases too): several non-carnivorans also prey and eat meat as their staple food, thus also being eligible for the name Carnivora. Just found a source, which says in particular: "carnivorans never develop shearing dentition beyond the original P4/mi carnassial pair, and this combination of shearing and grinding dentition has served Carnivora well". Perhaps the International Commission on Zoological Nomenclature will someday reconsider :) Brandmeister^talk 17:51, 23 August 2013 (UTC)[reply]

I understand your objection to Carnivora, but it is actually very common for things to work out this way. It's just what happens when we prefer original names, but also want to use modern tools to make clades as large and inclusive as they can correctly be made. Does it bother you that not all hemiptera have "half-wings"? Or that not all Orthoptera have "straight wings"? It's a terrible system, but it's the best we've got :) SemanticMantis (talk) 18:15, 23 August 2013 (UTC)[reply]

See etymological fallacy. Come back if you have some questions about the relevance of that article to this problem. --Jayron32 14:56, 24 August 2013 (UTC)[reply]

Enemy locked onto heat signature; release flares

In the game Battlefield 3, one mission requires the player to occupy the gunner position in some sort of fighter aircraft. When the enemy locks onto the heat signature, a system of the aircraft occupied by the player warns the player and warns further when a missile is fired. The player is expected to release flares to thwart the enemy missile. How does the system recognise that the enemy aircraft has locked onto the heat signature? --89.241.229.123 (talk) 14:14, 23 August 2013 (UTC)[reply]

By what method does the attacker "lock on"? If it's via radio waves, those waves could be detected by the target vehicle's systems. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:28, 23 August 2013 (UTC)[reply]

Is the question about how the video game software operates this feature, or how its real-world counterpart works? Video games tend to use "omniscient software" that is aware of enemy moves, which simplifies the design and allows the creators to provide the desired user-experience.

In real life, a heat-seeking missile is not easy to detect. Because infrared missiles uses passive homing, they don't broadcast any type of strong signal. So the defending aircraft must use its own active RADAR to detect an unidentified object in the area; its onboard computer must calculate a trajectory and identify it as a potential missile; and then by deduction, it can be assumed to be a heat-seeker if it satisfies certain characteristics (size, velocity, RADAR signature - or lack thereof). This is an estimation problem that is prone to error and misidentification. Electronic warfare aircraft may escort fighter-aircraft in combat; these special airplanes carry more and better RADARs and computers (and other instruments) to help reduce error. Modern air doctrine emphasizes "Coordinated Command and Control" - enabling multiple airplanes, as well as ground and satellite facilities, to share combat information in real time, to help reduce errors in identification of unknown targets. Nimur (talk) 14:43, 23 August 2013 (UTC)[reply]

Here's a link to a Missile Launch Detector that Lockheed Martin makes [3]. It's a bit hard to tell, but it seems to work by detecting the IR flash of missile launch and then tracking the hot exhaust during flight. This discusses, briefly, the large dust and smoke plume from a Surface-to-air missile. Neither of these detection methods will work with a passive IR guided missile until the missile launches.Tobyc75 (talk) 18:18, 23 August 2013 (UTC)[reply]

Is there any condition in which two vectors can be divided?

Is there any condition in which two vectors can be divided? Concepts of Physics (talk) 14:52, 23 August 2013 (UTC)[reply]

This is not a common terminology for any commonplace operation in engineering or physics. You can define many mathematical operators that have qualitative similarities to division and accept vectors as inputs. But most people who use those operations prefer to use a different, more precise term, like computing an inverse or left-multiplication by the adjoint matrix. Nimur (talk) 14:57, 23 August 2013 (UTC)[reply]

This was discussed at length a month ago. Red Act (talk) 15:04, 23 August 2013 (UTC)[reply]

This page shows division of two vectors. Is this method correct? Concepts of Physics (talk) 15:28, 23 August 2013 (UTC)[reply]

That is a correct example for R (programming language) where the term "vector" is understood to be a one-dimensional array and where division is done element by element. This is a different use of "vector" than Vector (mathematics and physics). -- 200.7.90.57 (talk) 15:52, 23 August 2013 (UTC)[reply]

Division is the inverse of multiplication, so before answering that question you must chose some kind of multiplication to invert. The most common multiplication methods for vector dot product and cross product cannot be inverted. Dauto (talk) 18:20, 23 August 2013 (UTC)[reply]

If you want a fancy name for the operation described by 200.7.90.57, try Hadamard product. --Wrongfilter (talk) 21:05, 23 August 2013 (UTC)[reply]

Gap spanners on the International Space Station

What are the "gap spanners" that I read about astronauts installing on the International Space Station? The best I can find is that they are "used by spacewalkers to get from one module to another", but I can't find any details. Are they cables? Are they rods? What are they made out of? How are they attached? Are there any good photos of them online? -- 200.7.90.57 (talk) 15:30, 23 August 2013 (UTC)[reply]

Astronaut Jerry L. Ross, who flew on STS-88, explains gap spanners in this crew interview, available from spaceflight.nasa.gov:

“

Because the Unity node is so large in diameter we couldn't mount all the hardware on the outside of its structure that we wanted to, while it was still in the payload bay of the orbiter, and the launch environment that exists there. So, Jim and I will be installing a series of additional handrails, or handholds, on the outside of the station which we'll need for tasks, either on our flight or future ones. We'll also be putting some additional foot restraint sockets on the outside of the structure that we can plug our foot restraints into to do tasks on this EVA as well as others. We have a thing called a gap spanner, which is really nothing more than a long piece of strap that we're going to attach between a couple of handholds and cinch tight. That is a way of bridging a gap that was too long between handholds to provide a continuous translation path for crewmembers to operate on the station.

”

So, it seems like a gap spanner is a pretty mundane piece of cloth... until you realize that it's a festering breeding ground for orbital space-fungus! Here's a very high resolution photo from the same page of a ground technician swabbing the fungus off a gap spanner. Nothing is mundane or routine in manned space flight! Nimur (talk) 14:24, 24 August 2013 (UTC)[reply]

Thank you, Nimur. You're my hero! -- 200.7.90.57 (talk) 15:39, 24 August 2013 (UTC)[reply]

the haert rate in different bodies sizes

What is the reason that the big body is with low heart rate and a small body is with high heart rate? In example: addult from 10 years and above has heart rate of 60-100 per minute while an infant (until 90 days) has heart rate of 80-205 per minute! The same things are in animals. In example: the elphent has 25 HR per minut while the mouse has about 500 heart rate per minuts! So, in short: Why does as much as the body smaller the heart has high heart rate? 95.35.239.134 (talk) 16:36, 23 August 2013 (UTC)[reply]

It's partially related to one's activities. Many small animals are much more active than big ones, as such they require higher physical performance (particularly, better oxygen supply) which in turn requires high heart rate. Mice in particular are constantly vigilant to avoid predators, requiring higher physical performance and as such high heart rate. Brandmeister^talk 18:08, 23 August 2013 (UTC)[reply]

All right on mice you can say that they are active, but what do you say about babies compared to children? Children more active and yet they have only 60-100 beats per minute compared to babies who sleep most of the day and have between 85 -205 beats per minute.95.35.239.134 (talk) 19:56, 23 August 2013 (UTC)[reply]

My guess is that the size of the heart is also important, as a bigger heart can of course pump more blood than a smaller one if both were pumping at a similar speed. Since blood flow is limited by the elasticity of the blood vessels, I'm guessing a big heart pumping very quickly could create too much pressure and rupture the veins, especially if the diameter of the various types of veins does not increase proportionally to the size of the heart. I'm unable to confirm my guesses with reliable sources at the moment, however. Effovex (talk) 20:11, 23 August 2013 (UTC)[reply]

The typical operating speed (and presumably the most efficient speed) of mechanical devices, such as pumps, motors, and engines, trends to be inversely proportional to their size. Perhaps someone here with a mechanical engineering background can speak to this point. -- 200.7.90.57 (talk) 20:37, 23 August 2013 (UTC)[reply]

Indeed, though the reasons are somewhat different. The heart pumps by successive contractions. That means that at every beat it accelerates a small quantity of blood, which then gets decelerated in the blood vessels. The kinetic energy imparted to the blood depends on the ex-chamber spurt time, and the stroke/spurt distance. In a small animal the stroke distance (which is proportional to the length and to the width of the heart) is less, so to impart the same kinetic energy per unit volume of blood, and thus get the same blood velocity, the time per beat must be shortened. In animals of all sizes, the required blood velocity is much the same, as it is set by capilary wall thickness, gas and nutrient diffusion range, and tissue requirements. 1.122.171.86 (talk) 00:36, 24 August 2013 (UTC)[reply]

survive in a space station without air renewal

Suppose you are in the International Space Station, with destroyed air renewal systems and no other sources of oxygen.

You have plenty of food and water (but you cannot use it to produce oxygen). At the beginning the air is fresh.

How long can you survive there? Months? --Blacknight87 (talk) 17:27, 23 August 2013 (UTC)[reply]

Several days, certainly not reaching one month, I think (around one week at best) until the buildup of carbon dioxide reaches critical point. To extend the survival period it's possible to isolate every room by sealing hatch or whatever and once the CO2 level in one room reaches uncomfortable point, move to another. But still there should be some emergency backup system out there. Brandmeister^talk

There are Oxygen candles in the ISS. CO2 is usually deadly at about 10%. A human produces about 1 kg of CO2 a day. The molar mass of CO2 is 44 g, so 1 kg is about 23 moles or about 500 l of CO2 under normal condition. The ISS has a pressurized volume of 837 m³. So 10% concentration should be reached in 160 (person-)days. That is a lot longer than I would have expected. --Stephan Schulz (talk) 18:33, 23 August 2013 (UTC)[reply]

But is it enough oxygen for 160 days? --Zhitelew (talk) 18:57, 23 August 2013 (UTC)[reply]

Since one molecule of O2 makes one molecule of CO2, and both gasses have more-or-less (for small values of less!) the same volume under normal conditions, yes. Unless I made a stupid mistake ;-). --Stephan Schulz (talk) 19:40, 23 August 2013 (UTC)[reply]

I suspect that that 10% figure is rather too high. NIOSH (CDC) puts the IDLH level at 4% [4], noting that it produces symptoms of intoxication within 30 minutes at 5%, and unconsciousness after a few minutes at 7%. A study on submariners reported that extended exposure to 3% CO2 produced only mild symptoms, provided sufficient oxygen was provided. Using a more realistic 4% threshold, the lone astronaut on the ISS is good for perhaps 60 days—assuming that there are no other chemical or biochemical processes on board that produce additional carbon dioxide..... TenOfAllTrades(talk) 23:22, 23 August 2013 (UTC)[reply]

To look at it from another direction, the Lunar Excursion Module (LEM) on the ill-fated Apollo 13 mission had an internal volume of 6.7 cubic meters...less than 1% of the internal volume of the ISS. The oxygen and CO2 removal provided in the LEM was intended to be enough for 72 man/hours (2 men, one and a half days) - and had to suffice for 288 man/hours (three men, four days) to get the crew safely home. Notably, they didn't run even close to being short of oxygen - but when the CO2 removal system was rapidly overwhelmed, they ran to the brink of CO2 poisoning until the famous "square peg into a round hole" fix was developed. But you can see that even with only 1% of the volume, it took a considerable amount of time for the extra astronaut to overwhelm the LEM's filters to the point of danger. With over 100 times as much volume, that would take 100 times a long. This suggests that (a) Oxygen deprivation would not be an issue - CO2 would be the major problem and (b) that User:Stephan Schulz's calculations are probably about right. SteveBaker (talk) 21:16, 23 August 2013 (UTC)[reply]

Part of the reason why the CO2 level rose so 'slowly' in the LM was that the scrubber unit wasn't fully exhausted. As the scrubber gets to the end of its lifetime, the particles of lithium hydroxide in the canister acquire a coating of lithium carbonate, making them much less efficient absorbers of CO2 (as the gas has to diffuse through the inert carbonate to get to the active hydroxide). While the scrubber canister would normally be replaced at that point, if one is willing to tolerate an elevated partial pressure of CO2 in the cabin then one can run the canister much closer to exhaustion—let those little particles marinate in more concentrated CO2, consuming the lithium hydroxide more completely and absorbing more CO2 before their retirement.

In the case of the LM, its original canisters had a design capacity for efficient scrubbing of 60 man-hours, but could remain in service for twice that time at a cost of higher ambient CO2 levels if absolutely necessary. (On Apollo 13, they ran for 107 man-hours before the CM units could be connected.) In addition, there was a spare unit good for another 40 man-hours of normal use (80 man-hours in an emergency) if the square-peg-round-hole fix took longer than anticipated. [5] If the scrubbers were completely gone, using the 1 kg per day per person round figure Stephan employed above, the lunar module would have been out of luck in less than half a day. TenOfAllTrades(talk) 23:11, 23 August 2013 (UTC)[reply]

Thanks! That's great information. But I think the conclusion is the same - it's not running out of oxygen that's the problem. It's build-up of CO2. If CO2 could be perfectly removed, how long would it be before the astronauts have too little oxygen? My gut feel is that it's MUCH longer. SteveBaker (talk) 15:55, 24 August 2013 (UTC)[reply]

Do they have suicide pills on board so they don't have to suffocate to death? How long /would/ they last if the zombie apocalypse suddenly happened or something? Is it CO2 poisoning or is there something else needed from the ground that must happen before the air runs out? 108.27.81.195 (talk) 00:56, 24 August 2013 (UTC)[reply]

Under normal conditions, they keep a Soyuz capsule docked on the station that can be used as an emergency return vehicle if necessary. Assuming conditions on the Earth's surface are survivable there is a good chance that the crew would attempt to return to Earth before they ran out of air. However, I'm not entirely sure how easy or difficult it would be to manage a reentry if ground control had been destroyed. Dragons flight (talk) 04:23, 24 August 2013 (UTC)[reply]

They don't really need suicide pills - CO2 is commonly used for animal euthanasia, and of course they have a perfect "high altitude chamber" close at hand. Wnt (talk) 07:03, 25 August 2013 (UTC)[reply]

Also, until 2007, cosmonauts were issued with the TP-82 pistol - according to our article, they're still issued with "a regular semi-automatic pistol" - so they probably have at least one gun up there as well. Tevildo (talk) 17:35, 25 August 2013 (UTC)[reply]

Femininity facial analysis?

The Bradley/Chelsea Manning story has me wondering: with all the fancy facial recognition software, and research into reactions people have toward averaged faces, is there a program available that can analyze "femininity" in a face, either from a 2D picture or in person/3D? To me Manning's face always seemed a little bit female, and I was wondering if that is quantifiable. If so, does it actually predict some increase in odds of being transgendered or gay? Wnt (talk) 18:59, 23 August 2013 (UTC)[reply]

Here's a good list of refs, 101 of them about determining/sex gender of human faces via computer vision algorithms [6] (search is articles related to a seemingly influential paper on the topic [7]). There seems to have been a boom in the 1990-2006 range, but it's still being researched at a steady pace. It looks like even 10 year old routines can discriminate about as well as humans (~90% accuracy, hair removed or hidden), using things like support vector machines. Two articles jumped out as highly relevant to your question: "What's the difference between men and women? Evidence from facial measurement" [8], and "Boosting Sex Identification Performance" [9]. Some of these papers might have code online as supplementary material, or allow a (sufficiently savvy) reader to implement the algorithm. I didn't look for "off the shelf" software. SemanticMantis (talk) 21:01, 23 August 2013 (UTC)[reply]

Well, how does one DEFINE femininity? Seems to me like this is a highly subjective thing to evaluate. 24.23.196.85 (talk) 01:07, 24 August 2013 (UTC)[reply]

How about with science, like SemanticMantis demonstrated with references and logic, and a surprisng lack of caps. Shadowjams (talk) 06:05, 24 August 2013 (UTC)[reply]

Yes, defining femininity is problematic. Note also that the papers are mostly about determining sex, not gender. In this case "female-ness" might be a better word than femininity, when discussion how computer algorithms score faces. SemanticMantis (talk) 14:24, 24 August 2013 (UTC)[reply]

How about those physical traits that estrogen gives. For testosterone that would be square face, baldness, beard etc. Electron9 (talk) 17:29, 26 August 2013 (UTC)[reply]

And note that feminine men are only a subset of gay men ("twinks"). There are others who are ultra-butch ("bears"), and everything in-between. StuRat (talk) 01:46, 25 August 2013 (UTC)[reply]

I should thank SemanticMantis for some good sources ... though I haven't managed to access several of them in full as of yet. Do you know whether these 90% or so accurate algorithms misidentify the same people as being of the wrong sex, or is it different for each one? It didn't look like anyone was actually trying to identify "quantitative" variations in sex though. Wnt (talk) 07:00, 25 August 2013 (UTC)[reply]

Wnt, I think that quantitative "scoring" does happen inside the algorithms, but no idea on if one face fools all the algorithms, or each is tricked by different faces. I suppose there should be some "Standard face set", but not sure how many of those papers use it.

For the support vector machine approach, some finite list of quantified attributes is used to represent each face as a vector. The goal of the machine is to make the best hyperplane to separate the data so that females are on the "right", and males on the "left". In this case, the hyperplane would describe the the most androgynous faces. So you could at least come up with an "androgyny score", based on distance to the separating hyperplane, and then large distances would be either "very male" or "very female", depending on which side of the hyperplane the face is on. Anyway, if you want a specific paper, drop me a line on my talk page or email, I can probably send you pdf. SemanticMantis (talk) 18:13, 26 August 2013 (UTC)[reply]

Geology/Pleistocene/CLIMAP

During the 1970's, CLIMAP was created to draw a map of the world at the time of the glacial maximum, 13Kya, (or is it earlier?). Where can I find that map and where can I find maps of North America between then and now. I have a particular interest in Lake Bonneville and Lake Agassiz.Bobgustafson1 (talk) 19:19, 23 August 2013 (UTC)[reply]

You might start with out article on CLIMAP: Climate: Long range Investigation, Mapping, and Prediction. It contains a reference to "CLIMAP (1981). Seasonal reconstructions of the Earth’s surface at the last glacial maximum in Map Series, Technical Report MC-36. Boulder, Colorado: Geological Society of America.", which probably provides many more details, though you'd probably need a good research library to find that book. However, it would be a mistake to think of CLIMAP as aiming to "draw a map". Rather it was a collection of related research projects to document conditions as they existed on Earth about ~18 kya. There would be many maps, some regional, some global, each reflecting or summarizing different parts of the investigation. In addition, other results of the related studies are probably scattered through various academic journals from that time period. Since you asked, reading about Lake Agassiz and Lake Bonneville might also be useful. My impression though is that our understanding of Lake Agassiz and its changes through time have improved greatly since the 70s, so you might want to look at more recent reviews. Dragons flight (talk) 20:14, 23 August 2013 (UTC)[reply]

Adults

Do mle adults have XY chromosomes and female adult humans have XX chromosomes? If so, is it possible to change theses chromosomes? Pass a Method talk 22:07, 23 August 2013 (UTC)[reply]

See biological sex, gender, sex chromosomes, XY sex-determination system, aneuploidy, sex differences in humans. The short answer to the first question is "mostly". The short answer to the second is "no". 86.163.2.116 (talk) 22:17, 23 August 2013 (UTC)[reply]

Yes, mostly; no. See also, incomplete penetration. μηδείς (talk) 04:54, 24 August 2013 (UTC)[reply]

See also, hmmm, androgen insensitivity, testicular feminization, freemartin, intersex, Klinefelter syndrome Turner syndrome, XYY syndrome. Note that there is research underway to extend X inactivation to chromosome 21 so as to offer treatment to people with Down syndrome, for example, but this is still far off (no obvious research path to a successful, safe whole-body gene therapy of every cell to do it). But it wouldn't be much to modify that to a goal of changing the sex chromosomes. That said, wrong-sex gonads and other tissues in someone of the other sex hormonally can be cancer risks, so even if you make the change without incident the goal itself might have additional dangers. Wnt (talk) 19:42, 24 August 2013 (UTC)[reply]

August 24

World's biggest skyscraper

What's the world's biggest skyscraper by basically, uh, how big it is, that is the volume enclosed by the outside walls? I wonder how Shanghai Tower stacks up. 108.27.81.195 (talk) 00:45, 24 August 2013 (UTC)[reply]

See List of tallest buildings. Dismas|^(talk) 00:54, 24 August 2013 (UTC)[reply]

I think 108 IP is asking about the biggest building by VOLUME, not height. But I have no idea where to get this info -- can someone help? 24.23.196.85 (talk) 01:06, 24 August 2013 (UTC)[reply]

See List of largest buildings in the world, which answers that very question. WHAAOE. --Jayron32 01:07, 24 August 2013 (UTC)[reply]

Bah! I was close. Was getting called away to something else while replying, so I didn't get a chance to double check. Dismas|^(talk) 01:11, 24 August 2013 (UTC)[reply]

The Boeing building is by far the largest building by volume, but it's not much of a skyscraper. The two lists linked here would need to intersect. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:52, 24 August 2013 (UTC)[reply]

I believe there's a Wikipedia tool for that (in fact, I used it not too long ago to look for movies set in London during certain time periods -- you just enter "Films set in London" and, say, "Films set during the 1940s", or in your case, "Largest buildings" and "Tallest buildings") -- does anyone remember what's this tool called? 24.23.196.85 (talk) 04:08, 24 August 2013 (UTC)[reply]

Are you perhaps thinking of WP:CATSCAN? Dismas|^(talk) 04:10, 24 August 2013 (UTC)[reply]

Yep, that's the one! Thanks! 24.23.196.85 (talk) 04:14, 24 August 2013 (UTC)[reply]

Strongest known tornado outside of the United States; A question about the Fujita scale

I searched for this both online and in Wikipedia articles, but I could not find the answer. Basically, what is the strongest known or recorded tornado (in terms of intensity) outside of the United States? As a side question (although related), are either the Fujita scale or the Enhanced Fujita scale outside of the United States and Canada? Narutolovehinata5 ^tccsdnew 03:54, 24 August 2013 (UTC)[reply]

The article List of F5 and EF5 tornadoes has seven entries from Europe - see also List of European tornadoes and tornado outbreaks, List of Asian tornadoes and tornado outbreaks and List of Southern Hemisphere tornadoes and tornado outbreaks, although those articles generally don't have the intensities listed. The Enhanced Fujita scale is based on damage to typical American structures ("Manufactured Home – Double Wide", "Large, Isolated Retail Building [K-Mart, Wal-Mart]"), so I don't believe it's used outside the USA and Canada - our article doesn't say otherwise. Tevildo (talk) 11:53, 24 August 2013 (UTC)[reply]

According to this website, there were two strongest tornadoes in Europe, both T10-T11 on TORRO scale (one struck France on 19 August 1845 and the other one Italy on 24 July 1930). In terms of deaths the strongest one seems to be Daulatpur–Saturia tornado. Brandmeister^talk 13:57, 24 August 2013 (UTC)[reply]

Astigmatisms and autostereograms

I'm looking for solid references (preferably ones that pass WP:MEDRS) discussing astigmatisms and autostereograms, but so far all I've found are forums and similarly unreliable sites at which people chat about the subject. Basically looking for something explaining the effects (or lack thereof) of astigmatisms on astigmatics' ability to "do" autostereograms, but something talking about other aspects of the process of "doing" autostereograms for astigmatics would be helpful. A little context, in case that help — I've been trying fruitlessly to teach an astigmatic acquaintance how to "do" autostereograms, and I'd like to know if the literature suggests that it's impossible/harder/no different/whatever. Nyttend (talk) 12:38, 24 August 2013 (UTC)[reply]

Firstly - there are two very different uses of the term "astigmatism" - one form (which I have in one eye) is when the lens of one or both eyes is not spherical so the focal distance is different vertically and horizontally and things are perpetually blurry in one direction or the other. This is easily corrected with glasses or contact lenses - and even uncorrected, it does not prevent one from seeing autostereograms (I see them just fine).

The other use of the term is for people who's eyes don't move correctly to line up on the object being concentrated on. They may be cross-eyed or have a lazy eye. Those people cannot see autostereograms because they rely on correct positioning of the two eyes to produce a 3D image.

So we're only talking about the SECOND kind of astigmatism. But it's even more confusing than that.

The problem is that MANY people are born with slightly crossed eyes or a "lazy eye" (Astigmatism-of-the-second-kind). In almost every case, this fixes itself within a month or so of birth - and all is well. But for about 5% of people, it takes three or more months to "fix itself" and once the obvious problem goes away, it seems like the person can see just fine

However, what happens (without medical intervention) is that the circuitry in the brain that learns how to fuse two separate images into a single three-dimensional representation doesn't develop properly in those people because this part of the brain forms in the first few months after birth. This problem has only been properly recognized in the last 20 years or so - and it's only properly diagnosed and treated (eg with eye patches) in a few places in the world. This afflicts about 5% of the population (although that number is dropping as the problem is recognized).

If you're one of the 5% then both of your eyes work fine, you can have 20/20 vision and your eyes can track targets perfectly - but your depth perception is not as good as it should be - and things like 3D movies and virtual reality headsets don't seem any better than 2D movies and 2D computer graphics. These people are easily recognized because they say things like "I don't see what the big deal is with 3D movies - they don't look any different!" But the problem with autostereograms is worse because the "image" is only present as a 3D displacement - so for people in the 5%, they stand NO CHANCE of understanding them.

There have been some successes in treating this condition - it seems that brain plasticity is sufficient that the problem can be treated with special exercises (at least in some cases). People who have had the treatment are AMAZED at how much different the world looks afterwards.

SteveBaker (talk) 15:48, 24 August 2013 (UTC)[reply]

The "second kind" you describe is strabismus; I haven't heard it called astigmatism. While it is clear that strabismus would interfere with stereograms, I think it is conceivable that astigmatism would also prove something of a hindrance, because any distortions imposed by the lens would appear to go in different directions for the two images to be fused, making them more difficult to align. Wnt (talk) 16:37, 24 August 2013 (UTC)[reply]

Not trying to sound unappreciative, Steve, but I'm specifically looking for solid sources, e.g. something in an ophthalmology or optometry journal discussing the subject. Nyttend (talk) 17:03, 24 August 2013 (UTC)[reply]

Yeah - I understood that (I don't have such things) - but I did want to clarify that a mindless search for "astigmatism" would produce confusing results. Also, even people who's eyes do all the right things may fail at understanding autostereogram because of the brain development thing. It would be necessary to be sure that an astigmatic (type I) was failing to understand an autostereogram because of the astigmatism rather than because of happening to be one of the 5%. SteveBaker (talk) 22:58, 24 August 2013 (UTC)[reply]

What scientific problems have been proven impossible to determine?

--121.7.36.13 (talk) 13:12, 24 August 2013 (UTC)[reply]

None (by definition). Dauto (talk) 13:52, 24 August 2013 (UTC)[reply]

Science does not deal in absolutes like proofs. We can prove scientific facts only ever with respect to a given theory, and support for a scientific theory is always tentative in principle (although what a scientist considers "tentative" is often more certain than what we consider "facts" in everyday life). There are a number of problems in math (including theoretical computer science, mathematical logic, and similar disciplines) that are proven to be impossible to answer in general. Examples include the Halting problem, the Post correspondence problem, and the Entscheidungsproblem. --Stephan Schulz (talk) 13:56, 24 August 2013 (UTC)[reply]

Even proving you can't for instance solve the halting problem doesn't mean there can't be an oracle machine that always gives the correct answer. It is very highly improbable though! Dmcq (talk) 14:33, 24 August 2013 (UTC)[reply]

There are many concepts which seem, at first glance, to be simple to the uninitiated which are, not merely difficult to prove, but actually proven to be impossible to determine. Many of the concepts surrounding "quantum" fields are governed by the Uncertainty principle, for example, which doesn't merely state that somethings are outside our current technological grasp of determining, but that they are physically impossible to determine, for example certain pairs of properties, such as momentum and position, are impossible to know simultaneously for any sufficiently small particle. --Jayron32 14:54, 24 August 2013 (UTC)[reply]

No - the proof relating to the halting problem doesn't say that you can't solve it - only that a Turing Engine can't solve it. I could disagree though that the halting problem "has proven impossible to determine" though - we've looked at it - and we are 100% sure that you cannot write a computer program that looks at another computer program and tells you whether that program will halt or not. This isn't some kind of mysterious unsolved problem - it's that we have total and complete certainty that some particular determination cannot be made. It's like the laws of thermodynamics say that you can't make a perpetual motion machine - or that the uncertainty principle says that you can't simultaneously know the position and momentum of an electron - or that godels' theorem shows that there exist some class of mathematical theorems that can never be proved or disproved.

I think we should help the OP to refine the question a bit. There are many areas of doubt to consider:

Some things we know for 100% certainty cannot ever exist: A Perpetual motion machine or a computer program that can tell whether other computer programs will eventually halt or not, an engine that'll propel a spacecraft at the speed of light...that kind of thing. It's not just that we haven't discovered a way to make these things - it's that we know for 100% sure that they are impossible.
Some things we know for 100% certainty we cannot ever measure: The nature of light from a star that lies outside of the observable universe, the exact position and momentum of an electron. These are fundamentally unknowable things.
Some things we definitely don't know - but might one day know: What is dark matter? What caused the first living thing to appear on earth? More research is needed - but we can probably work out the answer somehow.
Some things are reasonably well known but not with sufficient accuracy: Are there planets orbiting other stars that are habitable by humans? (Almost certainly - but maybe not.) How much temperature rise will we experience if we continue to dump CO2 into the atmosphere at present rates? (Definitely too much...but we don't know exactly how much too much.)
Some things that we expect to be true but cannot yet prove: Can every even integer greater than 2 be expressed as the sum of two primes? (We're pretty sure that the answer is "Yes" - but we can't yet prove it.)
Some things that we thought were probably true for the longest time - but were finally disproved: Euler's sum of powers conjecture, for example.
Some things that nearly everyone thought were false for the longest time - but were finally proven true: Continental drift, for example.
Some things that we thought were true - but are only approximately true - or are only true in special cases: Newton's laws of motion, for example.
Some things are "unfalsifiable" - we can never prove them false, but they might one day turn out to be proven true: The existence of God, The "simulation hypothesis", for example.
Some pairs of ideas that both seem to be "proven" true - but are contradictory in nature so either we're missing something, or one or both of them must actually be slightly incorrect: Gravity and Quantum Theory, for example. Gravitational theory works great at large scales and Quantum theory works great at small scales - but when the two intersect (eg at the boundary of a black hole), they predict different outcomes - so we know there is a problem somewhere.
Some things that many non-scientists THINK scientists have trouble with - but which are actually well understood: How come a bee can fly with wings that seem to be too small? (Wingtip vortices are exploited by bees in a way that was not obvious to one writer - and everyone took that as "Scientists say that bees can't fly - look how stupid scientists are!")

I'm sure there are other categories of doubt and error that I haven't thought of...but to find concrete examples, our OP needs to be much more specific. SteveBaker (talk) 15:28, 24 August 2013 (UTC)[reply]

Good list, but you are confusing the two most distinct classes. The Halting problem is proven to be impossible to solve for a Turing machine (or, indeed, any kind of algorithmic machine - the diagonal proof does not really depend much on the specifics of the machine). A perpetuum mobile, on the other hand, is impossible under the laws of thermodynamics. But the laws of thermodynamic are just very well-supported assumptions. There is nothing logically impossible about them changing tomorrow (just assume that reality is a giant computer simulation, and tomorrow they put in a new patch). But there is no patch to reality that makes a the Halting problem for general Turing machines solvable. Of course, the Halting problem for real computes is trivially solvable (in theory), since they only have a finite number of states. --Stephan Schulz (talk) 16:26, 24 August 2013 (UTC)[reply]

Thermodynamics is a bit of a tricky case - see Constantin Carathéodory, who formulated a derivation of the second law based entirely on mathematics (and the concept of "heat", which may reconnect it to the physical world - I'm not a good enough mathematician to comment). It's on a lot firmer ground than special relativity, at least. Tevildo (talk) 16:39, 24 August 2013 (UTC)[reply]

(ec) A good answer, as always, but I'm not sure about all of the "100%" examples. I would say that we should distinguish between mathematical propositions (such as the halting problem), which can be conclusively proved, and scientific propositions (such as the inability for a spacecraft to reach c). The contradiction of such a statement will be inconsistent with our current understanding of the universe, but it's not _impossible_, in the way that a solution to the halting problem or a proof that 2 + 2 = 5 would be. (Incidentally, the non-observability of light from a star outside the observable universe is an analytic truth that doesn't even require mathematics to demonstrate - the fact that the observable universe is finite is a tentative scientific proposition that could (theoretically) be false). Tevildo (talk) 16:35, 24 August 2013 (UTC)[reply]

Why do the women have less blood than men?

←I've seen once (I don't remember where) a math formula of calculation for a blood quantity in the person. So, according to the formula, when you ask how much blood this person has, if he is a man you give 0.75 mili liter for every one kg of his body, and if she is a woman you give 0.65 for every kg of his body, and if it's baby you give 0.85 for every kg of his body. So, first of all, I would like to know if is it true. and second, according to this formula we can understand that the woman has less blood than man. In example, when a man is 60 kg, he has 4.5 liter of blood (60 times 075), when a woman is 60 kg she has 3.9 liter of blood, it's happen when both of them is in the same weight! It's about 13.5 percent less compared to a man. So, to sum up I have two questions, but the one depends in the another one: 1. is the formula true? (and if it's true, what is his origin). 2. why the women have less blood thatn men. 95.35.88.167 (talk) 18:18, 24 August 2013 (UTC)[reply]

Your units are wrong - those should be deciliters (dL) per kg, or you need to shift your decimal over a couple of places - but the values are approximately correct. The difference between men and women is primarily down to different body fat percentage. Adipose tissue (fat) contains less blood per kilogram of total weight than muscle or most organ tissues. The average amount of circulating blood per kilogram of body weight is lower in obese individuals (fat makes up more of their total body weight) and higher among young people. Infants can go higher than 100 mL of blood per kilogram: [10]. All these numbers are approximate, and will vary from person to person and study to study. This paper shows the distributions of values for typical children and adults at various stages of development. Note that figure 1B plots blood volume per kg of body weight, whereas figure 1A plots volume per kg of lean body mass—the values become statistically indistinguishable in adult males and females when you eliminate the contribution of body fat. TenOfAllTrades(talk) 20:39, 24 August 2013 (UTC)[reply]

metal mixture

I want to mixture of 50%copper+ 15%silver+12%cadmium+23%zinc but its breaking when I want make its its 37guage stripe. Why? You have any solution or metal which helpful to make its soft?? — Preceding unsigned comment added by 59.161.69.236 (talk) 19:57, 24 August 2013 (UTC)[reply]

A few points

The properties of a metal alloy may be very sensitive to the particular process used to make them.
even small amounts of impurities may have large effects.
how are you attempting to make the stripe? Hot or cold? Cutting or stretching? details do matter.

Dauto (talk) 21:21, 24 August 2013 (UTC)[reply]

Are you using Sheet metal#gauge measurement here - 37 gauge = 0.17 mm ??

Why waste good silver mixing it with cadmium and zinc? Cadmium in particular has sort of a mixed reputation. I suppose it's better than lead, but... well, anyway, our article on solder does mention "Sn-3.5Ag-0.74Cu-0.21Zn" (reading down I see there are several of these, but all 95% tin) Also "KappRad" Sn40Zn27Cd33. It looks like the solder recipes are meant to be near eutectic points for low melting temperature, which may not matter.

Point is: where did you get this recipe? If you're reinventing metallurgy on your own you'll have many disappointments. (I do wonder if you might find tin, due to its ductility, a component preferable to cadmium? Or maybe bismuth? But I am so not qualified to say any such thing!) Wnt (talk) 23:13, 24 August 2013 (UTC)[reply]

There are some alloys fairly close to the OP's mixture at List of brazing alloys, but everything we list has a larger Ag/Cu ratio. Tevildo (talk) 23:35, 24 August 2013 (UTC)[reply]

Yea, copper is quite ductile, and silver is fairly ductile, too. I'd suspect the problem is the cadmium and/or zinc, making it too brittle. Try lowering the ratio of one or both of those. If you need to keep that ratio, you will have to treat it more gently, like only work it a small amount, then reheat it and let it cool, to relieve the stress, before working it again. StuRat (talk) 01:36, 25 August 2013 (UTC)[reply]

A mineral that heats on contact

Is this really a special mineral with such characteristics, or just a normal hot rock? If it's the former, what's it called? Thanks, 84.109.248.221 (talk) 23:06, 24 August 2013 (UTC)[reply]

Looks like a typical internet fake to me. If the rock had been buried in the ground and emitted heat sufficient to char paper for thousands, perhaps millions of years until it was dug up - what would be the power source for such a thing? To my eyes, it looks like a lump of coke or even a barbeque briquette that someone heated up and then used to take the photos. We only have his word that it was hot when dug out of the ground. Yeah - maybe it could just maybe be radioactivity - but the amount of radiation it would take to make that much heat would probably have killed the guy who took the photos by now. SteveBaker (talk) 03:34, 25 August 2013 (UTC)[reply]

It's definitely not radioactive, it'd be quite lethal if so; most likely, it's a hoax. However, on the chance that it isn't: the outcomes look more like a chemical reaction (the glove doesn't look burned, but stained.) It could be a bunch of Iodine prills, or crystals, stuck together some way. While such a find would be exceedingly unlikely for any legit (or natural) reason- iodine can be used to manufacture meth, someone may have stumbled on a stash of it. At any rate, like I said, that's all quite unlikely, it's probably a scam.Phoenixia1177 (talk) 05:45, 25 August 2013 (UTC)[reply]

I also thought it looked like it could be iodine, both due to the black discoloration of paper and the brown discoloration of the glove. The "metallic" appearance isn't really that far off from iodine either. However, I assume the "rock" results from some industrial source, not meth manufacture. (the second is more newsworthy, but not really that big a chunk of the overall use of the element!) Wnt (talk) 08:05, 26 August 2013 (UTC)[reply]

August 25

Fear and adrenaline

I read an article ( http://www.scientificamerican.com/article.cfm?id=scared-to-death-heart-attack) which claimed that fear can cause high levels of adrenaline which can lead to arrhythmia and eventually cardiac arrest, even in healthy people. But surely, this is very rare in people who don't have underlying health conditions. Even intense exercise, a popular activity performed by many, releases adrenaline and raises heart rate, and this is seen as beneficial to overall health. So how can fear be any different? I would argue that fear may also be beneficial, many people enjoy controlled fear such as roller coasters, which have the same effect and claim that this actually reduces stress. Clover345 (talk) 00:36, 25 August 2013 (UTC)[reply]

It normally only becomes a problem with long-term fear. Brief episodes of fear rarely cause heart attacks, despite it being a TV trope where the murderer scares somebody with a heart condition in order to kill them. StuRat (talk) 01:30, 25 August 2013 (UTC)[reply]

What is long term? Even people who have anxiety over an upcoming event whether its an exam or a speech they have to give to a large audience, rarely die from cardiac arrests. People who are uncomfortable with public speaking may for example be anxious and therefore have elevated heart rates for up to weeks before the event. Clover345 (talk) 10:41, 25 August 2013 (UTC)[reply]

Those roller coasters all have rules prohibiting people with heart problems - who also have to get clearance from their doctors to exercise. Martial54 (talk) 02:59, 25 August 2013 (UTC)[reply]

Nobody has to get clearance from doctors to exercise. Doctors can give "orders" to their patients, but there is no law requiring the patients to obey those orders. Looie496 (talk) 05:49, 25 August 2013 (UTC)[reply]

The legal authority of doctors over their patients has nothing to do with the effects of high heart rate on heart attacks which is the question asked. Rmhermen (talk) 13:30, 25 August 2013 (UTC)[reply]

You can be scared to death, but this isn't something I would be seriously concerned about. The purpose of the study was, probably, less "here's a way you can die" and more "let's see if this trope can actually happen". At any rate, if you're interested in the phenomena, some articles (related) you may have interest in are Parasympathetic rebound, Baskerville effect, and Takotsubo cardiomyopathy; and, less directly related, Fear, Panic attack, Acute stress reaction, Fight-or-flight response. The latter links are related only in so far as they involve stress responses due to fear/anxiety.Phoenixia1177 (talk) 03:53, 25 August 2013 (UTC)[reply]

For Op: stress increases your risk for heart disease, you may want to consider [11] for the general idea. The links I've given above discuss more acute cases of stress response. It is unlikely that a single given event will cause heart <Insert Fatal X> to happen, thus while the anxiety over public speaking may not cause you to just keel over on the spot, if you have to do it repeatedly and it is a stressor, it can cause you to be more at risk for heart related issues.Phoenixia1177 (talk) 10:54, 25 August 2013 (UTC)[reply]

Not too bright...

I just bought a floor lamp with 5 light bulb sockets. Each says "To reduce the risk of fire, do not exceed use of a 60 watt incandescent or 13 watt CFL bulb". Now, a 13 watt CFL puts out the same amount of light as a 60 watt incandescent bulb. However, I don't see why I couldn't use 23 watt CFL bulbs, which are equivalent in lumens to 100 watt incandescent bulbs. As I understand it, there are three ways a high wattage bulb could cause a fire:

1) The electricity in the wires leading to the bulb could cause the wire to overheat. This should strictly be proportional to the wattage, shouldn't it ? That is, a 23 watt bulb should always create less heating of the wires than a 60 watt. Am I wrong here, and does the power factor play a role in heating ?

2) The bulb itself gets hot, and this is a result of inefficiency in conversion of electricity to light. However, the CFL is far more efficient, so I'd expect a 23 watt CFL to only convert some 5 watts to heat, while an incandescent 60 watt bulb converts something like 45 watts to heat.

3) A CFL does also have a ballast, and heat is produced there, too. Is heat here somehow worse than up in the bulb ? Maybe it can't dissipate as easily ?

So, is there any logic to the 13 watt CFL restriction, given that a 60 watt incandescent is acceptable ? StuRat (talk) 02:17, 25 August 2013 (UTC)[reply]

According to EnergyStar [12], you can use any bulb that is 60 watts, incandescent or cfl. These sites come to the same conclusion [13], [14]; but, they'r not as authoritative (though, it appears to be a common question.) As far as I can tell, the reason for the recommendation is that it should produce roughly the same amount of light; rather than prevent fire. (Just to point it out, since it is about fire risk, some people online say that there is a risk, but I haven't seen any clear explanation of why, nor have I seen this from any authoritative site.)Phoenixia1177 (talk) 03:10, 25 August 2013 (UTC)[reply]

Incandescent lamps convert about 5% of the electricity into light - and all the rest has to be waste. So 57 watts of waste. A CFL is about 5 times more efficient - about 25% of the energy turns into light. That's why a 13 watt CFL produces roughly the same amount of light as a 60 watt incandescent. But the CFL generates only about 10 watts of waste. Naively then, the 13 watt CFL ought to produce about five times less heat than the 60 watt incandescent...and I'd guess that heat is what matters in your floor lamp.

My best guess is that the people who printed that label had read that a 13 watt CFL is equivalent to a 60 watt incandescent - and mindlessly reasoned that they know that their appliance overheats with a more-than 60 watt bulb - and therefore it must also overheat with an "equivalent" CFL.

I think the label is wildly wrong! You ought to be able to use CFL's up to about 76 watts (which produce six times as much light - but only the same amount of waste heat as a 60 watt incandescent).

I suppose it's remotely possible that the inefficiencies in CFL's manifest themselves more dangerously than incandescents (eg producing more UV light or something) - and it's possible that the shape of the CFL blocks airflow and traps heat to a greater extent than an incandescent.

But the remarkable coincidence of the numbers they chose strongly suggest that the lamp manufacturers are idiots. SteveBaker (talk) 03:25, 25 August 2013 (UTC)[reply]

Yes, that was my guess, which explains the dual meaning of the title I chose. I just wanted to check with you guys to see if I was missing something. StuRat (talk) 03:37, 25 August 2013 (UTC)[reply]

Is the lamp certified by Underwriters Laboratories? μηδείς (talk) 17:31, 25 August 2013 (UTC)[reply]

Quick point. The risk of fire might come from the quality of the wiring in the fixture, rather than the accumulated heat output. So using a CFL of 76 watts would exceed the 60 watt rating of the wiring (a watt of electricity is a watt of electricity, regardless of if it's being converted to light or heat), even if it didn't exceed the 60-watt lightbulb heat equivalent. -- 205.175.124.72 (talk) 20:23, 25 August 2013 (UTC)[reply]

The wiring is almost certainly safe up to several hundred watts. It's actually amps that matter, and wiring that can carry less than an amp is rarely used for mains electricity. Dbfirs 06:49, 26 August 2013 (UTC)[reply]

If the OP is from a 120 V country, his 5 60 W bulbs will draw a total of 2.5 A. -- 200.7.90.57 (talk) 11:43, 26 August 2013 (UTC)[reply]

Yes - but we're really talking about why they'd put a 13 watt limit on the CFL - it makes no sense since even a 60 watt CFL would produce less heat (and need the same wire thicknesses) compared to the 60 watt incandescent. The 76 watt number comes about from heat considerations alone - so technically, you're right and a 60 watt CFL ought to be the highest power you could be 100% sure would be safe. That said - it's pretty safe to assume that the wiring will have enough of a safety factor to support 76 watts without problems. SteveBaker (talk) 22:26, 25 August 2013 (UTC)[reply]

Perhaps it's just a bit of an "idiot proof" measure? If someone put in a 100W equivalent CFL bulb, the next person to swap it might assume that 100W is safe for the fixture, since they got used to the high light output. Vespine (talk) 23:16, 25 August 2013 (UTC)[reply]

engineering

Good time, I am a ICSE student and i am interested in science. I wanted to know the fields in engineering. As in what what subjects are there, what types of engineering are there, if I like any 1 field in engineering then what to do for it. please help me in this matter. you would be very much thankful. 115.242.18.161 (talk) 03:34, 25 August 2013 (UTC)₵[reply]

See list of engineering branches, to start. StuRat (talk) 03:39, 25 August 2013 (UTC)[reply]

physics

what would happen to a seed if we planted them in a rotating wheel and provided them with all its needs. The question is how will that plant grow as we know that the roots grow towards the gravity and the shoot part of the plant grows towards the light in what manner will it grow in the rotating wheel??? — Preceding unsigned comment added by 115.242.66.252 (talk) 06:23, 25 August 2013 (UTC)[reply]

Excellent question. The spirit of science is all about inquiry. Try it and find out. Let us know your results. Dolphin (t) 07:15, 25 August 2013 (UTC)[reply]

Gravitropism is studied using clinostats as you suggest, and in space stations. In addition to gravity, plants use light (phototropism), water (hydrotropism), and touch (thigmotropism) to orient themselves.

In the absence of gravity, plant roots tend to seek out water and nutrients, and shy away from light. Leaves grow to maximize light collection. Many plants will grow just fine and look like they normally would. I don't know what something like a tree would do though. 88.112.41.6 (talk) 07:39, 25 August 2013 (UTC)[reply]

What size wheel and how fast? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:12, 26 August 2013 (UTC)[reply]

Stanford Torus / Elysium orbital habitat

Hullo. Having just seen the movie Elysium, I've been looking at some details of the Stanford Torus. The movie features an orbital habitat similar to a Stanford Torus, but it didn't appear to be rotating very fast, and had an open "top" on the actual habitat section!! Could someone please answer a couple of questions for me?

Your "Stanford Torus" article says that to get about 1G in the habitat ring, a structure 1.8km diameter needs to rotate at 1 rpm.

1. If the diameter was bigger would it need to rotate faster or slower to get the same G force?
2. If you are in a habitat that has 1 g at your feet level, but zero G at 900 meters above your head, how would the gravity gradient on your body affect you?
3. Would it actually be possible to have an open top on the habitat ring the way the movie does?

Thanks in advance 122.108.189.192 (talk) 07:55, 25 August 2013 (UTC)[reply]

You can read more about artificial gravity created by spinning here, or do the math yourself over here. Spoiler; larger diameters means you'll have to spin slower to maintain gravity. WegianWarrior (talk) 08:45, 25 August 2013 (UTC)[reply]

A difference of two parts in 900 in gravity from head to foot would not really be noticeable. An open top means that air will constantly be lost, but the rate of loss might not be a serious problem if there is a constant renewal (as on Earth). According to Atmosphere of Earth, the tropopause is about 12 kilometres up, and there are gases beyond that, so a mere 900m seems inadequate to retain a proper atmosphere. Perhaps someone can calculate the loss rate? Dbfirs 16:45, 25 August 2013 (UTC)[reply]

The Stanford torus is a mile in diameter, which is less than the scale height of gasses in the Earth's atmosphere (as Denver residents will attest). Therefore, it could not exist uncovered. I don't know if the movie uses a true Ringworld (or at least one around the Earth); if it does, and if it uses very, very high walls, it might work. Or maybe they have force fields? Actually just architectural invisibility might suffice, unless you see ships going through the 'empty' space at will - it shouldn't be that hard to make a metamaterial which is transparent with no refractive effect on light, when present as a nearly perfectly flat architectural element. Wnt (talk) 08:13, 26 August 2013 (UTC)[reply]

the heart realy in the size of the fist?

I saw in once forums someone that ask a doctor (cardiologist) if the heart in the size of the fist, and he answered that it's not exactly and it's not scientific to say such. So, my question is how is 'scientific' size of the heart? 176.13.1.78 (talk) 12:34, 25 August 2013 (UTC)[reply]

Our own article on heart also suggests that it is roughly fist-sized, but that is just a comparison to give lay people a rough idea of how large it is; there's no reason to think it's a particularly accurate measurement. You could very easily have an enlarged heart, but small hands, or vice versa. If an internal organ needs to be measured for size, you'd have to do some kind of medical imaging, such as a CT scan. Matt Deres (talk) 13:01, 25 August 2013 (UTC)[reply]

I looked briefly before and found that normal hearts were about 300 g, hypertensive hearts over 400. [15] The actual proportion with body mass wasn't given in that source. The density shouldn't be much more than 1 so that should be 300-400 ml. But I got bored and didn't look up the volume of a fist - if one of us happens to have a beaker handy we should push our hand in and see how much water is displaced. Wnt (talk) 08:16, 26 August 2013 (UTC)[reply]

Hairs and nails

Why do our hairs and nails keep on growing even when they consist of dead cells? Concepts of Physics (talk) 14:24, 25 August 2013 (UTC)[reply]

Because the root isn't dead. See Human hair growth and Nail (anatomy)#Growth. AndyTheGrump (talk) 14:27, 25 August 2013 (UTC)[reply]

Underwater train

Are there any trains/monorails that go underwater? ScienceApe (talk) 16:12, 25 August 2013 (UTC)[reply]

Do you mean without a tunnel? Dbfirs 16:20, 25 August 2013 (UTC)[reply]

Yes, without a tunnel. ScienceApe (talk) 18:00, 25 August 2013 (UTC)[reply]

The Brighton and Rottingdean Seashore Electric Railway had underwater tracks, with the cars supported on suitably ornate ironwork. I don't think there were any railways where the cars themsevles ran underwater - there would be insufficient force (due to the buoyancy of the air in the cars) to keep them on the track. Tevildo (talk) 16:29, 25 August 2013 (UTC)[reply]

Only if you filled the things with air. — Preceding unsigned comment added by 109.144.132.49 (talk) 19:27, 25 August 2013 (UTC)[reply]

True, of course, but the only sensible use for such a train would be for entertainment (as in the Brighton example), so it would need to carry passengers who could see out of it. It wouldn't be commercially viable to move goods by underwater railway rather than by boat. Tevildo (talk) 19:34, 25 August 2013 (UTC)[reply]

Fair point. The only thing I can suggest then is the rails that ships are dragged in and out of the water on at some shipyards. — Preceding unsigned comment added by 109.144.146.36 (talk) 19:40, 25 August 2013 (UTC)[reply]

There used to be a ride at Disney World based on 20,000 Leagues Under the Sea, where a mockup of the Nautilus ran around a submerged route on rails. Rojomoke (talk) 23:22, 25 August 2013 (UTC)[reply]

We have an article - 20,000 Leagues Under the Sea: Submarine Voyage. Not really an underwater train though: "The attraction vehicles were not actual submarines, but instead boats in which the guests sat below water level". 23:45, 25 August 2013 (UTC)

I remember going on that actually when I was a kid. Brings back memories. ScienceApe (talk) 04:33, 26 August 2013 (UTC)[reply]

Conceptually they could be useful for mining manganese nodules and methane clathrate and such, but in practice, the ready mobility and relocatability of shipping must vastly outweigh any leverage that could be obtained taking cars of ore up obliquely to the beach. Wnt (talk) 08:20, 26 August 2013 (UTC)[reply]

August 26

Which source is more trustworthy on masturbation?

The following two websites seem to contradict each other.

Source: http://www.babymed.com/getting-pregnant/male-masturbation-fertility-sperm-count

The first source suggests that masturbation decreases a man's fertility, because it advises that a man should conserve the ejaculations for intercourse in order to maintain a higher sperm count.

Source: http://www.mayoclinic.com/health/male-masturbation/AN01189

The second source suggests that masturbation has no effect on a man's fertility or sperm count.The two sources contradict each other, because masturbation can't affect and not affect the fertility at the same time. It has got to be one or the other, not both. Though, it may also be both but under different conditions. Sneazy (talk) 04:08, 26 August 2013 (UTC)[reply]

I don't think there is a contradiction. I believe the 1st source would be referring to immediate sperm count, where as the 2nd is referring to long term sperm count "in general". For example, someone who masturbates 5 times a week will not have a sperm count higer or lower then someone who doesn't masturbate at all. However, if you masturbate the day of your sperm count test then your sperm count will obviously be lower then someone who hasn't ejaculated at all in the last few days. In fact, I recently had some personal experience in precisely this regard and can tell you that the recommnedation is to not ejaculate at least three days before your sperm count test as this will provide an "optimal sample" for testing. So, I guess what it is saying is that it's possible that masturbating right before you have sex or even up to a day before could affect your fertility, but NOT that masturbating in general will affect your sperm count. Vespine (talk) 05:47, 26 August 2013 (UTC)[reply]

If it's not obvious, I'll add that sperm is produced in the testes at a rate far slower then most young males can expel it. It's is held in reserve in the epididymis until it is "required", but if it is ejaculated more then once every day or two you will be firing less then a full magazine, simply because you have not given enough time for the reserves to refill. In fact, the 1st source is less accurate because it is not masturbation that lowers the sperm count, it's the ejaculation, so even if you had intercourse with your mistress before having intercourse with your wife, your sperm count would be just as low on the 2nd occasion as if you masturbated. Vespine (talk) 05:58, 26 August 2013 (UTC)[reply]

Boric acid

What is the pK_a1 for the deprotonation of boric acid? Yes, I know what I'm asking - I'm aware of the dominant hydrolysis reaction taking place under aqueous conditions. Plasmic Physics (talk) 07:53, 26 August 2013 (UTC)[reply]

What is the equilibrium constant for:

B(OH)₃ (s) + H₂O (l)

{\ce {<<=>}}

[B(OH)₃H₂O] (aq) ? Plasmic Physics (talk) 08:01, 26 August 2013 (UTC)[reply]

Line on globe

On an old (ca 1915) globe, there is a great circle marked with a double line. It crosses the equator at 18°W and at 162°E, at an angle corresponding to the Earth's axial tilt, and is tangent to the tropics at 72°E (in India) and at 108°W (in the South Pacific). What might be the purpose of this line? 85.226.204.42 (talk) 08:53, 26 August 2013 (UTC)[reply]

Teflates

Does anyone know exactly why teflates (with OTeF⁻
₅) are such great oxidizing agents (They even oxidize Kr and Xe!)? Double sharp (talk) 11:16, 26 August 2013 (UTC)[reply]

Extensively drug-resistant bacteria

It seems that there's more and more news about bacterial diseases that are resistant to (almost) all available antibiotics. Are we doomed? Will there always be new antibiotics waiting to be discovered that can treat bacterial diseases, no matter how much the bacteria evolve? It seems that the odds are stacked against humans in this fight, because to be useful any new antibiotics not only need to kill bacteria, they also need to be safe for humans. Will we run out of safe compounds to try? --173.49.10.42 (talk) 11:50, 26 August 2013 (UTC)[reply]

@@ Line 287: / Line 287: @@
 Does anyone know exactly ''why'' teflates (with {{chem|OTeF|5|-}}) are such great oxidizing agents (They even oxidize Kr and Xe!)? [[User:Double sharp|Double sharp]] ([[User talk:Double sharp|talk]]) 11:16, 26 August 2013 (UTC)
+== Extensively drug-resistant bacteria ==
+It seems that there's more and more news about bacterial diseases that are resistant to (almost) all available antibiotics. Are we doomed? Will there always be new antibiotics waiting to be discovered that can treat bacterial diseases, no matter how much the bacteria evolve? It seems that the odds are stacked against humans in this fight, because to be useful any new antibiotics not only need to kill bacteria, they also need to be safe for humans. Will we run out of safe compounds to try? --[[Special:Contributions/173.49.10.42|173.49.10.42]] ([[User talk:173.49.10.42|talk]]) 11:50, 26 August 2013 (UTC)