Wikipedia:Reference desk/Archives/Science/2012 January 20

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January 20

odd rabbit behavior

Where I live on the Kenai Peninsula we have snowshoe hares running around. As is indicated on the article, they undergo population spikes every so often, and one has been ongoing here for the last two years. Something I have observed is that at this time of year they are quite often found on the edges of roads, and they have this annoying/.stupid habit of running out in front of moving cars in the dark. I have seen them sit on snow berms on the side of the road and wait until a car got close, so that it's lights were illuminating the area right in front of the hare, and then they run out. So my question is, why would they wait like that? It seems completely counter-intuitive that theirt instinct would tell tham to wait until a threat was close before running directly in front of it. — Preceding unsigned comment added by Beeblebrox (talk • contribs) 00:58, 20 January 2012 (UTC)

Our Spotlighting article (while a pretty crappy one) describes some of this behaviour, telling us that "...many animals (e.g. foxes and rabbits) often remain to continually stare at the light and do not appear to see the light as a threat as they normally would view a human". HiLo48 (talk) 02:03, 20 January 2012 (UTC)

Interesting question, and I don't think there's a definitive answer. A few possibilities to consider:

• Your observations may have some bias, i.e. you aren't as likely to notice if the rabbits run away from the road when the car approaches.
• Fight or flight type instincts don't have to be perfect to be beneficial on average. For example, if the rabbits bolt in a random direction when threatened, this still may save more lives on average, compared to doing nothing. So it's not that surprising that the behavior stays around, even when it sometimes ends up killing the rabbit.
• As for the timing: the classic natural predator of the hare is the lynx. Footage such as this [1] shows how the hare gets away by being better at cornering, not by being faster in a straight run. In this case, the hare is better off not bolting until the last second.
• In many modern environments, cars may well kill more hares than lynxes. This could be providing selective pressure, and perhaps future generations will be slightly better at avoiding cars.
• Lastly, peak population density puts all kinds of pressures on the critters, they are competing intensely for good forage sites, etc. This is bound to make them act a little funny. SemanticMantis (talk) 02:21, 20 January 2012 (UTC)

• The rabbits are probably thinking the car is a predator, and applying their evasion method for those predators. Since those predators aren't as fast as cars, the rabbits can dart across their path, get the predator to turn sharply and tumble over, and thus get away. Obviously, this doesn't work well with cars (although some idiot will occasionally crash their car swerving to avoid them). StuRat (talk) 04:05, 20 January 2012 (UTC)

There is a theory here in Australia that Kangaroos, Deer, Water Buffalo, etc run out in front of vehicles at night because they are trying to escape from a scary/confusing situation, so they run into the only areas they can see clearly in, ie the area lit up by your headlights! I've certainly found that if I turn my headlights off they don't run out in front of me. — Preceding unsigned comment added by 124.191.177.248 (talk) 08:01, 20 January 2012 (UTC)

And of course one more thing to add is that hares have been selected to avoid lynx for millions of years, by lynx killing those who didn't behave in a logical lynx avoidance pattern, whereas cars have only been around in any significant number for 60 years. Evolution doesn't work that fast! A new hare behaviour may occur at some point cause by selective pressure, but by the time it occurs, we may already be in the process of replacing cars with another transport mechanism, which may or may not kill hare in a different manner. --Lgriot (talk) 09:32, 20 January 2012 (UTC)

Arctic Hare do the same thing. Curious though. Do snowshoes sometimes sit very still if you are walking? The Arctic hare will often let you walk past them without moving. I assume they don't see you as a threat and/or figure you can't see them. CambridgeBayWeather (talk) 23:55, 20 January 2012 (UTC)

Sitting perfectly still is actually a great defense mechanism in this case. Von Restorff (talk) 00:01, 21 January 2012 (UTC)

The one near my house was using the shadow created by the power/phone/street light pole. Now that I think about it the sitting still is a defence against the Snowy Owl. I watched an owl trying to catch a hare one day and as long the hare kept still the owl would too. When the hare made a break for it the owl would attack. At one point the owl was sitting on a sign and the hare right below it. CambridgeBayWeather (talk) 01:25, 21 January 2012 (UTC)

A common hypothesis is that the moving shadows are perceived as a danger, and run from onto the road. Polypipe Wrangler (talk) 20:12, 21 January 2012 (UTC)

• They do sometimes just sit still if a human or a moose is approaching, in fact I saw one do just that while I was out snowshoeing today. If they see a dog, though they run. Interstingly, my neighbors cat actually killed one and dragged it into the house yesterday. Beeblebrox (talk) 01:57, 23 January 2012 (UTC)

I want your neighbor's cat's kittunz for my Army of Darkness™ -- Obsidi♠n Soul 02:09, 23 January 2012 (UTC)

Blood dye

A few nights ago, I had a dream in which it became fashionable to dye one's blood green. This gave the skin a greenish tinge. Trendy people carried around syringes of green food coloring which they administered to themselves like insulin shots. I awoke with many questions. In principle, would it do harm to inject food coloring into the blood? Or is it inert and harmless? How much would it take to dye all the blood in one's body? Would a pocket-sized syringe be sufficient? Assuming you're pale in complexion, would your outward appearance be dramatically greener? How green could the blood get? (In my dream it acquired a lurid, absinthe-like appearance.) How long before the effect wore off? LANTZY^TALK 04:01, 20 January 2012 (UTC)

Not sure if it's harmful or not when injected, so don't try it. You probably could change blood color dramatically, but green would be difficult, being the opposite of red. I suspect green coloring would make the blood closer to black. You could probably manage a color closer to red, like orange or purple, provided you could find a safe dye. And yes, changing your blood color would dramatically change your apparent skin color, if you are pale to begin with. StuRat (talk) 04:10, 20 January 2012 (UTC)

If you want to change your skin colouration, overenthusiastic consumption of carrots (or other carotene containing vegetables) can turn you distinctly orange. Not recommended though, as there can be side effects. As for other colours, gold salts are apparently quite effective in turning people shades of grey. Irreversably.... AndyTheGrump (talk) 04:21, 20 January 2012 (UTC)

Read Argyria if you want to be blue-ish gray. Can someone find a picture for Stan Jones (politician)? Why green blood, and not blue? Von Restorff (talk) 12:05, 20 January 2012 (UTC)

Insulin shots are administered under the skin into fatty tissue, not into veins or arteries. Edison (talk) 05:45, 20 January 2012 (UTC)

Eating beetroot turns your urine pink (well it does with me), so presumably the red colouring must be in your blood to get to your kidneys. I wonder if it makes the blood look redder? No side effects apart from bright red faeces! — Preceding unsigned comment added by 124.191.177.248 (talk) 08:06, 20 January 2012 (UTC)

If you want to change the colour of your faeces, I recommend several pints of Guinness for a noticeable darkening, or spinach for a greenish tint. Then again if such things matter to you, I'd recommend expounding your interests elsewhere... AndyTheGrump (talk) 08:19, 20 January 2012 (UTC)

Methemoglobinemia results in blue or brown blood, and can visibly affect people's appearance: see the section on "Carriers" (sadly it doesn't have photos, but there's one here if you scroll down past the X-Men character). --Colapeninsula (talk) 12:52, 20 January 2012 (UTC)

That photo is of Paul Karason. He used to look like this, but later he looked like this. His girlfriend didn't seem to mind. Von Restorff (talk) 13:01, 20 January 2012 (UTC)

He isn't that way because of his genes. He's that way because he has Argyria — he essentially overdosed on collodial silver because he believed quack stories about its antibacterial powers. Totally different causes — the blog is wrong to list him that way. That blog in general is not what I would call a reliable source. --Mr.98 (talk) 13:54, 20 January 2012 (UTC)

I would assume that Karasons' hair is very light because of his age (58 then) but I am wondering if the silver had any effect? - 220 of ^Borg 06:08, 22 January 2012 (UTC)

A guy a few years ago surprised surgeons by spurting dark green blood all over the operating table: have a look at the links in sulfhemoglobinemia. Brammers (talk/c) 13:59, 22 January 2012 (UTC)

Farming fish

Are there any fish that are bred and harvested specifically for consumption? My understanding is that fish are mostly just caught in the wild, and they are left to replenish their numbers on their own without external forces to ensure their numbers are high. Is this correct? ScienceApe (talk) 11:44, 20 January 2012 (UTC)

Some fish are bred and harvested specifically for consumption (e.g. salmon, trout, sea bass, carp, tilapia, and catfish). See fish farming. Today more than 40% of the fish consumed is farm raised. Von Restorff (talk) 11:46, 20 January 2012 (UTC)

Farmed fish is a very big industry, especially within salmon production. In fact, almost all salmon that is offered to consumers is farmed. See the article on Fish farming. DI (talk) 11:52, 20 January 2012 (UTC)

Huge industry - also including shrimp, sturgeon, and many other fish. Lovely exhibit at EPCOT if you ever get there. Alligators do count as seafood? Collect (talk) 13:16, 20 January 2012 (UTC)

In the United States, most fish markets have signs which say which ones are wild and farmed near the price markers. My recollection is that most of them I've seen are farmed. The proportions no doubt vary by country, but "aquaculture has been growing rapidly worldwide, and in 2009, farmed fish and shellfish surpassed wild-caught stocks as the major source of seafood worldwide." So I'd say your understanding of this is probably not correct. --Mr.98 (talk) 13:18, 20 January 2012 (UTC)

It should also be noted that many farmed fish are better in terms of environment and sustainability. The top wild-caught fishes, especially cod and tuna, are apex predators in their environment, and so have a very low "convertability", i.e. they need a lot of food and territory to survive. These large commercial fish are essentially the lions of the fish world, so are impractical to farm; they also take a long time to grow to economical size for catching, so they take some time to rebound from overfishing. The reason you don't raise lions for food is that lions eat grass eaters. So, you have to first farm a whole lot of grass eaters (like, say, cows and goats) and then feed the grass eaters to the lions. It is much more economical and sustainable to just eat the grass eaters yourself. It's the same with fish: the wild fish we catch and eat themselves eat the small-to-medium sized fish similar to what we now farm. Now, fish farms are not perfect, and some have their own environmental problems, but aquaculture is likely the best route we have for sustainable fish consumption. I've seen shows that make the case that tilapia is one of the best options, even better than salmon, in terms of sustainability. --Jayron32 17:07, 20 January 2012 (UTC)

But there is some tuna farming. See Tuna#Aquaculture. 75.41.110.200 (talk) 22:06, 20 January 2012 (UTC)

This is a very controversial issue for us Alaskans. Popular bumper stickers here include "Friends don't let friends eat farmed fish" and "farmed salmon dyed for your sins." (farmed salmon has to be dyed to make it look like normal salmon meat) Our wild-caught salmon is devalued because of competition from farmed salmon, mostly from Chile. That salmon is fed antibiotics, are kept in high-concentration pens witht theiir own wastes floating around, and as I mentioned have to be dyed so the meat looks like salmon. Our method is somewhat different, we have numerous fish hatcheries such as the one at Trail lakes. The hatcheries produce fry which are relleased onto the wild to live in the normal manner of salmon. When they begin "running" back to the streams were they were released they are fished by both commercial and sport fishermen. The "fishing hole" at the Homer Spit is a perfect example of how this works, there isn't even a stream, just a manmade lagoon that the salmon come into, believing they have made it home and will be spawning. Instead we eat them. However we do have some straight up mariculture up here, Kachemak Bay, which is not a native habitat for oysters, has been producing farmed oysters (in my opinion of excellent quality and flavor) for some years now, but that is obviously a very different operation than salmon farming since oysters don't move about as salmon and other finfish do. Beeblebrox (talk) 02:08, 23 January 2012 (UTC)

solar panel construction

How do I wire (solder) my solar cells together to build a solar panel??? Please do not direct me to the buy a plan site I got ripped off already so I am broke.... I have 300 6 by 6 inch crystaline or monocrystaline cells but I dont know how to put them in a panel and wire connect them correctly.......Thanks Joe Green in Beaumont Texas.... — Preceding unsigned comment added by 24.242.111.205 (talk) 13:14, 20 January 2012 (UTC)

If you type "build a solar panel" into the search box at the website www.google.com and select the first result, it is this website which has the plans to build a solar panel from 6-inch monocrystaline cells. Those plans calls for 36 cells per panel, so you should be able to construct several. --Jayron32 15:23, 20 January 2012 (UTC)

Do the solar cells already have wire leads? That makes things much simpler. I have rarely been successful soldering leads to the tinned area on a solar cell. Edison (talk) 16:11, 20 January 2012 (UTC)

What do you plan to power with the final unit? It will make a difference - whether you want to connect them in parallel or in series; whether you need load balance circuitry or active power control circuitry, and so forth. Nimur (talk) 19:53, 20 January 2012 (UTC)

drug test

does tramadol show up the same as hydrocodine/oxycodine in a drug test — Preceding unsigned comment added by 71.51.57.30 (talk) 15:54, 20 January 2012 (UTC)

We cannot tell you, we cannot give medical advice. Von Restorff (talk) 16:53, 20 January 2012 (UTC)

But we can refer you to our tramadol article, and in particular the Detection in biological fluids section, which may help. (Or it might not, but it can't hurt to read it.) Mitch Ames (talk) 02:49, 21 January 2012 (UTC)

I can't quite figure why this question is deemed to be seeking medical advice. The OP does not refer to him/herself, there is no mention of personal action, there is no reference to illness or pathological condition. It could be regarded as a perfectly simple haematological enquiry. Perhaps if the OP had put in some disclaimer that this was a scientific question and did not apply to any person specifically then it would have been OK? Richard Avery (talk) 08:38, 21 January 2012 (UTC)

Efficiency Test for Evolutionary Algorithms

I was working on evolutionary algorithms, particularly a variation of DE that we have developed. As with most updates, it gives better results but with higher computing time, so i want to find out how good it really is quantitatively, like with some measures. For example the likes of Amdahl's Law or those in the wiki page on Algorithmic Efficiency that deal with cases were one or more of the desired characteristics are getting better at the expense of others. Basically i need some kind of measure depending on the final error and the computing time. Any suggestions?--tathagata 19:11, 20 January 2012 (UTC) — Preceding unsigned comment added by Nonstop funstop (talk • contribs)

Polyneuropathy and GABA

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the talk page discussion (if a link has been provided). --Jayron32 20:47, 20 January 2012 (UTC)

Atomic explosion in your hands

You have 2 half-spheres of pure plutonium-239 in your hands. Each half-sphere has a sub-critical mass - 9 kg. You join the half-spheres. Now you have a sphere of pure plutonium-239 with a super-critical mass (18 kg, almost two critical masses).

Should it explode?

Can you create a scenario where bringing together subcritical fissile masses results in a small explosion?

--Zhitelew (talk) 21:18, 20 January 2012 (UTC)

No. Read the second paragraph for your answer. KägeTorä - (影虎) (TALK) 21:24, 20 January 2012 (UTC)

They have a mass just above critical (in this case nuclear reaction becomes subcritical again within a few seconds). How about a half-spheres with sub-critical masses (each)? --Zhitelew (talk) 21:34, 20 January 2012 (UTC)

No, they were subcritical. Read the 'Incidents' section of that article to see. KägeTorä - (影虎) (TALK) 21:38, 20 January 2012 (UTC)

I mean joining the half-spheres:) Something like Gun-type fission weapon (but with the low speed). Also, small explosion is ok, I don't require a full explosion of the mass --Zhitelew (talk) 21:47, 20 January 2012 (UTC)

At the *very* best, you'll get a fizzle. But really you'll just die of radiation sickness. You simply can't whack the spheres together fast enough to get a decent explosion. Not even Thin Man was fast enough, which is why they abandoned it. See Predetonation. --Sean 21:49, 20 January 2012 (UTC)

Well, the OP did specify pure Pu-239. It's possible you could use pure Pu-239 in a gun-type device and get a substantial yield. But pure Pu-239 is hard to manufacture. The plutonium they had during WWII was not pure; it had lots of Pu-240 in it, which is why they couldn't use it in the Thin Man. --Mr.98 (talk) 21:56, 20 January 2012 (UTC)

If it's just a critical mass, you probably see nothing, but the rate of reaction rate is increasing. Eventually the thing will heat up and melt. If it's supercritical, the bits may have a small explosion and separate. But not a full nuclear explosion. Your hands are not adequate for holding together an exploding core enough for the reaction to build to that level. The cores in nuclear weapons need to be held together for a small amount of time for the reaction to really propagate like they do in a nuclear weapon.

Even rather simple nuclear weapons need a little more "help" than what you're describing to get even kiloton ranges of explosives: confinement, a tamper, a neutron initiator, etc. What you're describing is essentially an unshielded fast-neutron reactor, not a bomb. --Mr.98 (talk) 21:56, 20 January 2012 (UTC)

Can it works with another fissile material (in theory)? With something like californium-252. According to Critical mass article, you need only 3kg of californium-252, and the sphere is pretty small, so neutrons don't need to fly long --Zhitelew (talk) 22:14, 20 January 2012 (UTC)

Define "work"? Can you create a scenario where bringing together subcritical fissile masses results in a small explosion? Then almost certainly yes. Even the force of a single stick of TNT could presumably kill the person handling it before the equally lethal radiation. Figuring out where the transition from major criticality accident to minor nuclear fizzle occurs is likely to be very difficult though. If you want a nuclear detonation that is actually impressive however, then you probably need substantially more than your hands to manipulate the pieces regardless of the material being used. Dragons flight (talk) 22:33, 20 January 2012 (UTC)

I think irregardless you'll need something more than your hands. It'll heat up and expand and separate. A little explosion if any. But I'm just basing this on an intuitive notion of it, not actual calculations. The reaction process in a bomb is an exponential process, and almost all of the energy released is in the last couple of fission generations. But there are explosively significant generations before that. If there isn't something holding them together when they go through the "just a dab of TNT" generation of energy release, it won't ever get to the "really impressive amounts of energy" stage. --Mr.98 (talk) 23:58, 20 January 2012 (UTC)

I remember seeing a film with a guy doing exactly doing that in front of a group of people. A blue flash and and a loud boom and most of the people died of radiation sickness and inhalation of plutonium although the both spheres looked nearly intact.--Stone (talk) 14:50, 21 January 2012 (UTC)

I suspect the film you have in mind was Fat Man and Little Boy, which features a fictionalization of the Louis Slotin/Harry Daghlian cases. --Mr.98 (talk) 14:56, 21 January 2012 (UTC)

Joe Don Baker's character does that in the TV series Edge of Darkness (with rods of Pu); I've not seen the film remake but the description there suggests that scene isn't recreated. -- Finlay McWalterჷTalk 15:00, 21 January 2012 (UTC)

Escape velocity of major star

Could there exist a star with about 10 × 10³² kg in mass, therefore having an escape velocity of about 300,000 km/s (more than the speed of light?) If it could exist, would that mean that light could not escape that star? And hypothetically, what would that star look like? 64.229.180.189 (talk) 22:05, 20 January 2012 (UTC)

A stellar mass Black hole is precisely such an object. {The poster formerly known as 87.81.230.195} 90.197.66.242 (talk) 22:08, 20 January 2012 (UTC)

Note, though, that escape velocity is not strictly a function of mass; rather, it's a function of mass and distance. It is entirely possible to have a mass far greater than 10³² kg that has a lower escape velocity (such as a galaxy); it's conceptually possible (though not experimentally determined) to have a mass far less that has that escape velocity (see primordial black hole). Instead skewing the distance, it is entirely possible to escape the gravitational pull of a black hole if you start at sufficient distance (see the supermassive black hole at the center of the Milky Way, which the solar system is in no danger of falling into) so long as you don't get near the event horizon. — Lomn 22:55, 20 January 2012 (UTC)

If you bring in galaxies, I think it's even more complicated than that — galaxies are not closely approximated by spheres, so the escape velocity depends on the direction you're trying to escape in. At least I think it does. Let's say you're near the edge of the galaxy, a little above its plane. If you try to escape going "up" (normal to the plane of the galaxy), then the far limb of the galaxy is not receding as fast as if you try to go "out", so you should need more speed to overcome it.

Of course your total energy is the same at the same speed, so let's say you go "up" at the speed that would let you escape going "out" — maybe you fall back in, follow some complicated orbit, and eventually escape going "out", even without further rocket boost. Whether that counts as "escape velocity" I'm not sure — depends on what you're trying to capture by the notion, I suppose. --Trovatore (talk) 23:02, 20 January 2012 (UTC)

You are mistaken. Escape velocity depends only on gravitational potential energy, and does not depend on direction. Provided the gravitational field you are escaping from isn't itself changing, and you avoid colliding with any obstacles in your way, then the energy required to escape doesn't depend at all on the path you take. However, it is true that some paths will require a longer travel time to get "out", but not more energy. As a more practical side comment, when talking about the gravitational field of extended body, it is often possible to exploit changes in the gravitational field caused by the relative motions of its constituent parts in order to extract energy (e.g. gravitational slingshot). So for a truly static field, the escape velocity is the same regardless of the path you take, but for the practical deep space traveler, you would often want to exploit changes in the field to get you were you want to go while avoiding having to fire rockets as much as possible. Dragons flight (talk) 23:35, 20 January 2012 (UTC)

But if you're dealing with speeds near c, which is specifically what the OP is asking about, then the Newtonian model of gravity works poorly, including the Newtonian concept of gravitational potential energy. And with general relativity, direction does matter, even in a static, spherically symmetrical situation. For example, the photons in a photon sphere around a nonrotating black hole don't escape from being near the black hole, even though the photon sphere is outside the event horizon (namely, the photon sphere is at 1.5 times the Schwarzschild radius). But photons that start at a photon sphere, but travel straight outward (or actually anywhere within an exit cone instead of on its boundary), do escape the black hole. Red Act (talk) 04:18, 21 January 2012 (UTC)

Two things. First, 10 × 10³² kg = 10³³ kg. Is that what you meant, or did you intend 10³² kg? That is either 500 or 50 solar masses. While 50 solar mass massive stars do exist (see List of most massive stars), 500 solar masses is probably above the upper limit for stars (see Star#Mass and Eddington limit). The most massive star know is R136a1 at 265 solar masses (birth mass of probably 320 solar masses) and radius 35 solar radii.

Next, you mentioned an escape velocity of 300,000 km/s = c (the speed of light). As explained above, the escape velocity is dependent on the distance from the massive object. A common quoted figure is the escape velocity at the surface of a planet or star. The surface escape velocity for the earth is 11.186 km/s, for the sun is 617.7 km/s, and for R136a1 is about 1700 km/s (2.75 times that of the sun).

Our article defines the Schwarzschild radius as "the distance from the center of an object such that, if all the mass of the object were compressed within that sphere, the escape speed from the surface would equal the speed of light." Derived from Einstein's field equations, the formula, $r_{\mathrm {s} }={\frac {2Gm}{c^{2}}},$ is exactly what you get by naively substituting v_e = c and solving for r in the escape velocity equation. I assume that you came up with your 10³³ kg or 10³² kg figure by solving for m with a given r. For m = 10³³ kg, r = 1,485 km; and for m = 10³² kg, r = 148.5 km. That mantissa looks suspiciously familiar; 1 astronomical unit is 149.60×10⁶ km. Is that just a coincidence, or were you trying to determine the mass of a star which would have a Schwarzschild radius of 1 AU, and accidentally applied the conversion between km and m backwards, inducing an error of (10³)²? If the latter, some supermassive black holes will meet your criteria, but you'll have to look beyond our galaxy, as Sagittarius A* doesn't quite fit the bill. -- ToE 01:48, 22 January 2012 (UTC)