Wikipedia:Reference desk/Archives/Science/2013 December 5

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December 5

AGRIS vs AGROVOC thesaurus

In the context accessing Agricultural library resources.Both AGRIS and the AGROVOC thesaurus are used, yet they are not "compatible". A comment from an expert or person involved is welcome. --Connection (talk) 09:21, 5 December 2013 (UTC)

This page is for asking specific questions. If you are having no luck on the AGRIS talk page, I suggest you take this to Wikipedia:WikiProject Agriculture. You may need to wait some time for a response.--Shantavira|^{feed me} 13:44, 5 December 2013 (UTC)

Why whenever I seek cooperation I find people harrassing me!? I need this to develop my own Library database, the purpose is how to integrate both. My mistake I took it first to the AGRIS talk page!--Connection (talk) 07:28, 6 December 2013 (UTC)

Maybe I completely misunderstand the problem, but as far as I can see, AGRIS uses a (hierarchical) category system, see the list here. It has a number of main categories, one of which is "Natural Resources (P)". In that category there are subcategories like "Nature conservation and land resources (P01)", "Soil erosion, conservation and reclamation (P36)".. (see here, choose Classification scheme= AGRIS/.. category=natural resources P )

Every article would be put in one (or more?) of these categories. (not sure if more than one is allowed).

AGROVOC is a thesaurus, containing relevant (agriculture related) terms, together with relationships between the terms, like "related", "narrower", "broader" term; RT, NT, BT; which is basically also a hierarchical structure, BT at higher level, NT at lower, RT at same level. For example "Natural resources" has as BT "Resources", as RTs "resource management", "Resource conservation", "Wilderness areas", "production possibilities", "Biological production" ... as NTs "Nonrenewable resources", "agricultural resources", "marine resources", "energy resources" ...

There are about 130 categories in AGRIS, but tens of thousands of AGROVOC terms.

A category "Seed production (F03)" tells you very little about the content, in contrast to a list of agrovoc terms: wild plants, microsatellites, Helianthus, plant genetics, Interspecific hybridization, phenotypes, Plant breeding, Meiosis.

Some examples of articles from the same category, irrigation, which is the subject category F Plant production > F06 Irrigation.

• This article has as Agrovoc terms: greenhouses, irrigation schemes, pot plants, growing media, experimentation, indigenous knowledge, research
• This one has: Machinery industry, Russian Federation, Pipes, Trickle irrigation, Sweet peppers, Irrigation, Water conservation costs, Farm equipment
• Another: Calcareous soils. Flax, Irrigation frequencies, Micronutrients application, Flax fiber yield.

While some categories in AGRIS have identical names as AGROVOC terms, they have nothing to do with each other, and you should not look for compatibility or similarity in structure between the two. There is a short, fixed list of categories, and an almost endless list of possible index terms, to which new terms are added every day. Ssscienccce (talk) 21:13, 7 December 2013 (UTC)

Surface gravitation of "kissing" spheres?

Suppose two earth-sized spheres were just touching eachother (ignore for a moment the fact that they would be compelled to merge). What would the surface gravitation be like? That is, if you were to walk around between them, what would it be like on different points on their surfaces? I imagine the gravity at the point that they touch would be almost zero, wouldn't it (and if they had atmospheres the gasses would most likely be stripped away and drift off from this point)? Any ideas? -70.112.97.77 (talk) 15:43, 5 December 2013 (UTC)

You can calculate the gravitational potential using Gauss's law for gravity. This is actually a very easy calculation, because you have assumed fixed, rigid, non-moving spheres; so each sphere can be trivially treated as a point-mass. Nimur (talk) 16:42, 5 December 2013 (UTC)

Are you also assuming the spheres are not orbiting about their barycenter? If they are, the tidal acceleration of the distal faces will be huge, flinging much of the mass into space, regardless of a gravity somewhat under two gees. μηδείς (talk) 17:48, 5 December 2013 (UTC)

Please see Roche lobe. For a pair of non-rigid planets or stars, a configuration in which each one fills out its respective Roche lobe is, in principle, stable. They will both be tear-shaped, touching at the pointed ends. You may also want to see Rocheworld and Last Exile for works of fiction that explore this theme. --Dr Dima (talk) 19:27, 5 December 2013 (UTC)

Supposing they're made out of scrith, equal mass and radius, and touching, it is as Nimur says just the gravity toward two point masses. If you are off a little bit (dy) from the merge point, then the inward force is going to be 2g sin (dy/(r+dy)) (r/r+dy)^2. For this small dy, sin (dy/(r+dy)) ~= dy/(r+dy), so this is 2g dy r^2 /(r + dy)^3. So if your planets are 6000 km diameter and you stray 10 km, the gravity pulling you back to the center is 1/300 normal gravity. At that point, there will be a sqrt(6000^2 + 10^2 = 36000100) = 6000.00833 -> minus 6000 and * 2 = 16.6 meter gap between the two planets. Your gravity to the center of one planet will be off by the square of the distance, i.e. 36000100/36000000 or 2.78 x 10^-6, which is doubled because you're that much further from the other, or about 1/400000 normal gravity. So regardless of the surface you stood on you'd still feel you were being drawn more or less straight "down" to the kissing point rather than at any angle toward the nearer planet. Unless I fouled up, which is not unlikely on this one! (note, however, that mascons coulod really throw everything off; see that article for how much unrequited gravity one might apply) Wnt (talk) 20:21, 5 December 2013 (UTC)

If they are made out of scrith, you'll be dead before you ever see the kzin that kills you. μηδείς (talk) 20:39, 5 December 2013 (UTC)

So .. if J get it right, .. one could, near the center, hop between the two halves of that double planet .. floating, always sure to land somewhere near the center region again? --217.84.69.206 (talk) 20:01, 6 December 2013 (UTC)

The planets wouldn't quite be touching if you could stand at the center, but if I suppose they had, say, the 16.6 meter gap I mentioned, then gravity toward either would be about 1/400000 of normal gravity as described above. So you'd have a really hard time noticing that you weren't completely weightless. I should also note that the "centrifugal force" that normally reduces gravity would enhance it in this case (because away from the center of a mutually rotating system is toward the surface) but it would be reduced by an equivalent amount as the gravity because you're so close to the center point. Wnt (talk) 05:54, 7 December 2013 (UTC)

Interesting. Thanks for the answers everyone! -70.112.97.77 (talk) 03:20, 6 December 2013 (UTC)

The atmosphere would not float off at that point, instead it would be the place of maximum pressure. The point is like the center of the Earth. If that was hollow there would be no gravity, but there still is pressure from all around. Graeme Bartlett (talk) 20:13, 6 December 2013 (UTC)

Oh my, there's a challenger math problem for the audience! To calculate the air pressure you need to figure out the volume of the space between the touching planets, how much air (assuming normal Earth atmospheres to start) there is to fill it, what the weight of the column of air is (remember, it's weightless at the bottom!). Yikes. I don't even have a sense of whether the pressure would be less or more than 1 atm, given these contrary factors. This should definitely be worth the extra credit points in the AP Calculus class, I guarantee it. :) Wnt (talk) 05:58, 7 December 2013 (UTC)

Fiddling about with some bad Python just now (no guarantees!) I came up with the figure that you'd need at least 17 planets worth of air to have normal atmospheric pressure at the center, with the atmosphere extending outward 771 km! What's weird (tell me if I messed up) is to think that the "column of air" is a wedge; an entire equator-full of air rests upon a single tiny crevice at the center. (While many things are doubtless wrong with this simulation, at least it gave the same result with 1 meter and 2 meter step sizes)

import math
radius = 6371000 # using average radius; we're ignoring rotation anyway though...
heightstep = 2 # meter
totalmass = 5e18 #kilograms of air in the atmosphere
density = 28.8 / 22.4 # grams per liter at STP = kilograms per cubic meter
# density = density * 1000 # grams per cubic meter rather than cubic decimeter
# density = density / 1000 # kilograms , not grams
g = 9.806665 # newtons = kg m / s ^ 2 per kg
atm = 101325 # newtons per meter squared

def slice(pressure, height):
    # height is perpendicular to the line linking the two planets, outward from the center
    # cleavage is parallel to the line linking the two planets
    # circumference is AROUND the line linking the two planets
    circumference = height * 2 * math.pi
    cleavage = (radius*radius + height*height)**0.5 - radius
    rgrav = g * (radius/(radius + cleavage))**2 # gravity toward one planet's center
    cgrav = 2 * rgrav * math.sin(height/radius) # gravity toward common center
    slicevolume = circumference * cleavage * heightstep
    slicepressure = cgrav * heightstep * (pressure/atm) * density
    slicemass = slicevolume * pressure * density
    # print (circumference, cleavage, slicevolume, slicemass)
    sliceweight = cgrav * slicemass
    # slicepressure = cgrav * slicemass / (circumference * cleavage) # force per unit area
    nextpressure = pressure - slicepressure # counting down...
    pass
    return nextpressure, slicemass

pressure = atm
masscount = 0
height = 0
while (pressure > 1):
    height = height + heightstep
    pressure, massinc = slice(pressure, height)
    masscount += massinc
    if (height % 1000 == 0):
        print (pressure, massinc, masscount, height)

Wnt (talk) 14:07, 7 December 2013 (UTC)

Masochistic pigeons

I passed two pigeons in a fountain, sitting in cold tap water, on a cold-looking "full-contact stone" (unlike say large-grained concrete or something, which is probably not a "full-contact stone" for pigeons), on a sunless day, in 55F weather, and not drinking. Why would they do that? 12.196.0.56 (talk) 16:35, 5 December 2013 (UTC)

For the two pigeons in question. They do not experience having their feet in cold water, the same way as a I and you would (assuming your a Homo sapien too) . As always... Wikipedia has an article about the why: Rete_mirabile#Birds--Aspro (talk) 16:56, 5 December 2013 (UTC)

If I understand correctly, birds in general are not cold-sensitive in their feet or talons, as if the process "fools" their brains into thinking the temperature is just fine? ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:07, 5 December 2013 (UTC)

Define "just fine". The birds do not sense the cold as uncomfortable, full stop. Birds also also unable to feel the pain of capsaicin. It doesn't mean the birds are being fooled. There's no "fooling" going on, which would imply that whatever is different-from-human is suboptimal. Birds don't feel cold the way humans feel cold, but there's no "fooling" and there's no "fine". WHat is normal for birds is not normal for humans, and visa versa, without placing normative value on either birdness or humanness. --Jayron32 17:13, 5 December 2013 (UTC)

OK, I think I get it now. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:53, 5 December 2013 (UTC)

Here is a bit more on why birds feet don't freeze. [1] Of course Tom Lehrer and his girlfeind also found another way alleviating any and all, of the pigeons sufferings[2]. ♬Two pigeons in the fountain, which one will the strychnine bless?♪--Aspro (talk) 17:47, 5 December 2013 (UTC)

Don't forget it takes two masochistic pigeons to tango. :) Wnt (talk) 20:03, 5 December 2013 (UTC)

But they were sitting, not standing, and about the entire the bottom of the birds were in the water. 12.196.0.56 (talk) 19:02, 5 December 2013 (UTC)

Maybe they like cold temperatures, the way that some people do. 24.23.196.85 (talk) 02:47, 6 December 2013 (UTC)

Did you observe them before that ? Maybe they were just engaged in some athletic flying, overheated, and are now using the cold water to cool off.

Another theory, perhaps they have some type of parasite (do they get fleas ?), and the cold water stops them from biting. StuRat (talk) 08:56, 6 December 2013 (UTC)

Could they just have been bathing? I'm not sure about pigeons, but I've seen gulls happily splashing around in water when it can't be much above freezing out. Also, birds tend to run hot. In the region of 40-44 degrees C, if I remember correctly. I'm not sure how that would affect a bird's perception of the cold. It may even be literally impossible to know for certain how a bird perceives anything. --Kurt Shaped Box (talk) 15:23, 6 December 2013 (UTC)

• Where would anybody get the impression that 55 degrees is cold weather? The pigeons don't have bare underparts unless they have a brood patch. μηδείς (talk) 21:41, 6 December 2013 (UTC)

• • Cool enough that a 40 degree bath seems like overkill. 12.196.0.56 (talk) 07:39, 8 December 2013 (UTC)

Best skin color etc.

What combination of human race-like traits would be best adapted to New York City? It wouldn't be Finnish or dark African for example, evolution would select against that without sunscreen and Vitamin D in milk. I suspect the people Henry Hudson met would be close but given the migration history maybe they didn't reach equilibrium yet? I can still see some "Mongoloidism" in Amazonians and Polynesians and Mongolia is like 40 degrees below zero. Heck, even some of India's women have a trace of Chineseism. No racist, Indian women are goddesses to me. Of course hunter-gatherers and postindustrials have different degrees of sunlight and weather exposure and typical clothing coverage, and the heat island effect has caused 5 to 10 degrees of unglobal warming. Even the paradaisical wilderness with a few small farms found by Europeans is artificial. The Native Americans burned or cut meadowless forest into their own image. (for hunting) 12.196.0.56 (talk) 18:43, 5 December 2013 (UTC)

A very difficult question indeed. I would be tempted to pull out a painting of the Manhattan tribe and be done; but we know that their ancestors travelled very widely indeed - Africa, Asia, Europe, Siberia, Alaska. What you would want to evolve optimally is a reaction norm - a set of responses to different environments, anywhere a New Yorker might want to travel (but where might that be, and where would he evolve to want to?). Tanning in some conditions and not others. Wearing clothing, perhaps, according to the ever changing climate, from Ice Age to heat island to runaway manmade greenhouse, though the latter tends to defeat adaptation. How do you evolve to constant migration, changing fashion, changing environment? The clear thing is that we haven't yet - there isn't time - but perhaps some photogray mechanism awaits in the future. But to choose a single color? It is an impossible calculation. What evolution does when it encounters the impossible is to try a lot of different options, with genetic variation, keeping genes around so that it is always ready. There's no predicting nor accounting for what happens in the end, it just does, I guess. Wnt (talk) 19:58, 5 December 2013 (UTC)

• "Chineseism"? It's a stretch even to pretend there's a question here. The Lenape Indians inhabited the area before the Europeans came. Eskimos are darker than Poles, and New York City is at the same latitude as Istanbul. There's no way to answer this. μηδείς (talk) 20:36, 5 December 2013 (UTC)

• Just because you don't have the answer doesn't meant that there isn't one. I'd find an ethnic group at the same latitude (N or S of the equator), and same elevation, which has been isolated for a very long time, and that should be the "ideal shade". However, note that modern inventions like sunblock and vitamin pills alter the calculations considerably, so you'd need to assume those were not available. StuRat (talk) 08:51, 6 December 2013 (UTC)

You've quite missed the point. Cultural habits like clothing and diet override any attempt at a simple equation of lattitude and color. I assume you understand that Eskimo live far to the north of the Polish, for example, yet are far darker than them on average. This is not a question about a spherical cow. And I would still like to know wtf "chineseism" is. μηδείς (talk) 18:38, 6 December 2013 (UTC)

Well, some Indian women's lips remind me of my first girlfriend (Chinese) and their hair is thicker and can grow longer than Europeans, right? 12.196.0.56 (talk) 08:25, 8 December 2013 (UTC)

Snow and ice reflect UV light. Inuit snow goggles were worn to protect against snow blindness. But those wouldn't protect the skin, so... Ssscienccce (talk) 01:56, 7 December 2013 (UTC)

My understanding is that the Eskimo are thought to have remained dark because they get plenty of Vitamin D from their diet. Lack of that vitamin is supposed to be what drives the selection pressure towards lighter skin. --Trovatore (talk) 07:02, 7 December 2013 (UTC)

Yes, that's correct, Trovatore. μηδείς (talk) 17:31, 7 December 2013 (UTC)

That's also an option, maybe a more likely one, I'm not even sure if there would have been enough time to get their current skin color if they first had evolved white skin. Selection pressure due to Vit D deficiency could be significant, due to excessive UV not so much, at least not in the arctic where people cover most of their skin. Unless eye color and risk of cataract is significant, not exactly my area of expertise... Ssscienccce (talk) 10:00, 7 December 2013 (UTC)

Can I point out our article Human skin color to you? Skin color is rapidly selected for, the differences between Europeans and Chinese have happened within the last 50 thousand years. Dmcq (talk) 09:17, 6 December 2013 (UTC)

The first answer above says "What evolution does when it encounters the impossible is to try a lot of different options, with genetic variation, keeping genes around so that it is always ready." This is ascribing a purpose to evolution which is something it doesn't have. Random genetic mutations are produced all the time - whatever the situation. Some are beneficial and some are a hindrance. The beneficial ones tend to propagate and the non-beneficial ones tend to die out. Evolution is totally without purpose and works by natural selection. Richerman (talk) 15:01, 6 December 2013 (UTC)

That's a metaphorical way of expressing it, basically anthropomorphizing the process of evolution. Evolution can be characterized as "how God works". ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:34, 8 December 2013 (UTC)

2011 Tōhoku earthquake and tsunami.

How much damage/casualties from the quake? --78.156.109.166 (talk) 19:53, 5 December 2013 (UTC)

You can look this up at 2011 Tōhoku earthquake and tsunami.--Shantavira|^{feed me} 20:01, 5 December 2013 (UTC)

I mean from the quake alone, not the tsunami. --78.156.109.166 (talk) 15:29, 6 December 2013 (UTC)

In the article: "Of the total confirmed victims, 14,308 drowned, 667 were crushed to death or died from internal injuries, and 145 perished from burns." If we assume that no one drowned from the quake itself (i.e. before the tsunami) than the upper limit would be about 900 deaths from the quake. However, it is likely that some of the crush injuries and fires were also triggered by tsunami effects, so the true total for the quake alone is probably smaller. Dragons flight (talk) 21:36, 6 December 2013 (UTC)