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IIT JAM

SHOULD I TRY TO IIT JAM PHYSICS IF MY NUMERICAL PHYSICS IS NOT VERY GOOD BUT THEORITICAL IS BEST??101.62.252.146 (talk) 07:28, 28 May 2015 (UTC)[reply]

Do you mean this sort of thing http://www.iitg.ac.in/jam2015/pdfs/PH_QP.pdf - if so i'm afraid it is almost entirely numerical (and easy) Greglocock (talk) 08:28, 28 May 2015 (UTC)[reply]

May 28

Notes on B.Sc.Agriculture

I hope this is the right place to ask. I couldn't find or how to find any relevant sites for B.Sc.Ag notes, sites for free downloading text books regarding the subject. Anyone knows such sites. Please share. There are also whole list of agricultural college, I wanted to know if any provides recorded video lectures, notes or just anything about B.Sc.agriculture study materials. Also, people talk about mit opencourseware and other, how help myself from it... Please help... :)

Thanks,

Learnerktm 08:25, 28 May 2015 (UTC)[reply]

You can try here. It does say "The portal is accessible to all Faculty, Teachers, Students and any one interested in the field of Agriculture and Allied Sciences" although I have no idea what you can access for free. The home page for all their courses is here. The MIT open courses website is here but I can't find an agriculture course - not every university will run an Agriculture course and it doesn't look like the do one. There are lists of free online Agriculture courses here and here. Richerman (talk) 08:54, 28 May 2015 (UTC)[reply]

Starling bill colour

According to common starling, a starling's bill changes colour during the year. What mechanism achieves this? Does the bill "grow" and the colour spread from the base to the tip? Or is the colour infused into a static bill somehow? -- SGBailey (talk) 08:26, 28 May 2015 (UTC)[reply]

This paper relates the yellow colour in the breeding season specifically to the hormone androgen, although without a mechanism. Mikenorton (talk) 12:25, 28 May 2015 (UTC)[reply]

Interesting. Thanks. -- SGBailey (talk) 12:32, 28 May 2015 (UTC)[reply]

Thanks, I was wondering exactly the same thing myself. μηδείς (talk) 01:29, 29 May 2015 (UTC)[reply]

Is amino acid folding unweightedly random?

This is going to be a bit of a strange question, due to nearly complete ignorance of the writer in this area. I ask to settle a dispute with a friend.

Presupposing an environment where all amino acids were present and without external guidance by a cell, etc. does every protein that could form from the acids have an equal chance of occurring? To phrase it simply: do amino acids have a "preference" for certain configurations over others?

Can the probability of a protein's formation without biological or other guidance be calculated by 26^{acid iterations} or some other simple fashion? Mr.Magik-Pants (talk) 19:08, 28 May 2015 (UTC)[reply]

I did a simple web search for "random polypeptide" "inclusion bodies" and instantly summoned up [1], which says what I would think: "Proteins can fold in reasonable times (typically from 10E-2 to 10E3 seconds) because they do not search blindly through this enormous phase space [of all possible secondary structure and tertiary structure]. Guided by locally favorable energetics, they first form secondary structures, and then assemble in a more or less straightforward way to a final configuration. In contrast, random polypeptide chains often have multiply degenerate ground states with radically different configurations [i.e. they can fold more than one way]. Even ones that have a unique free-energy minimum tend to fold slowly, becoming trapped for long times in metastable structures far from the ground state. Naturally occurring proteins are probably a special subset of all possible sequences of amino acids: those that fold swiftly and consistently to a single lowest-energy state." (it goes on to explain that proteins that don't fold correctly tend to get caught up in inclusion bodies) Wnt (talk) 19:56, 28 May 2015 (UTC)[reply]

This is what I would think, too. Thanks a bunch. Mr.Magik-Pants (talk) 21:16, 28 May 2015 (UTC)[reply]

Based on the wording of the question (which contradicts itself several times), I don't think you clearly understand the distinction between the amino acid sequence of a protein, and the way it folds in 3D. They are quite different things. The confusion makes it hard for me to understand what you are asking. When you ask, "does every protein that could form from the acids have an equal chance of occurring", are you asking about every amino acid sequence or every 3D folding structure? Looie496 (talk) 20:43, 28 May 2015 (UTC)[reply]

~~Sorry for being so confused. I think I'm talking about possible sequences, but it makes sense that not every sequence could fold, which is the answer I think I was driving for if that makes sense~~.Mr.Magik-Pants (talk) 20:53, 28 May 2015 (UTC)[reply]

Alrighty, I'm going to try to clarify my question. With a random chain of let's just say the 26 core? main? most common? amino acids, is it more likely that the chain will fold into a natural protein or more likely the the chain will not fold or not fold into a natural protein? Mr.Magik-Pants (talk) 21:35, 28 May 2015 (UTC)[reply]

I don't know where you get the number 26 from, there are 20-23 basic amino acids. Anyway, a random chain will definitely fold in some way, but the chance that it will resemble a natural protein is extremely small. Note also that while folding occurs naturally because it is energetically favorable, there are also special proteins called chaperones which help other proteins fold into the proper shape. - Lindert (talk) 22:15, 28 May 2015 (UTC)[reply]

Actually, most random protein sequences likely don't have any sort of defined folded structure. They're either intrinsically disordered proteins or they're arbitrarily sticky and will agglomerate into amorphous blobs. Then there's a whole class of amyloid proteins which have semi-regular structure, but not in any sort of "well folded" fashion. Well folded proteins are a small subset of total protein sequences. -- 160.129.138.186 (talk) 23:53, 28 May 2015 (UTC)[reply]

The number 26 is merely a product of misrecollection. I guess I was close though. Mr.Magik-Pants (talk) 23:12, 28 May 2015 (UTC)[reply]

The OP may be interested in reading Protein structure prediction which is basically the entire field of study which covers all of his questions. WP:WHAAOE. --Jayron 32 23:45, 28 May 2015 (UTC)[reply]

May 29

Why would the North Pole be full of oil (alledgedly)? Was is not always a cold place where life couldn't thrive?

Why would the North Pole be full of oil (alledgedly)? Was is not always a cold place where life couldn't thrive?--82.159.164.102 (talk) 17:29, 29 May 2015 (UTC)[reply]

The North Pole is not full of oil. The oil is in Northern Alaska, places like Barrow, Alaska and the Arctic National Wildlife Refuge and places like that. Still, assuming you mean the oil in Northern Alaska, remember that plate tectonics is a thing. No patch of the Earth's crust has been where it is now forever, it all moves and drifts around quite a bit; there are also dramatic changes in climate; at times in the past there have been temperate conditions near the poles and no ice caps, for just one example during the period of the Paleocene–Eocene Thermal Maximum. Petroleum#Formation also makes clear, most of it comes from zooplankton and algae, i.e. tiny critters living in the sea. Most oil reserves are under the locations of former seas. So, the notion that oil currently exists in the frigid, low-life areas of earth doesn't mean that those parts of earth were always frigid, and didn't used to support a lot of life, especially of the kind that forms oil. Indeed the existence of the oil is one of the ways that we know what the earth USED to look like. --Jayron 32 17:39, 29 May 2015 (UTC)[reply]

Much of Alaska's oil is outside of ANWR. You might find these keywords helpful in your search: the North Slope and the Prudhoe Bay Oil Field (among many others). The State of Alaska has a great website full of resources, North Slope Regional Geology (there is even a full-length book for interested readers) and the US Geological Survey's Energy Resources program has a website, Alaska Regional Studies with a lot of accessible information on the geology and geological history of Alaska as it applies to energy resource exploration.

Although these regions are quite northerly, and many of the famous oilfields of Alaska are above the Arctic Circle, they are still quite distant from the geographic north pole: the Earth is quite large. Furthermore, Alaska is quite green: more of Alaska is green than you might expect, and very little of the state actually experiences permafrost. When I visited Fairbanks in the summer, I found the climate to be very similar to that in Northern California; when I visited Kodiak in the winter (in Southern Alaska, although out at sea and quite cold), I found the winter storm weather to be milder than certain winters I experienced in Upstate New York. Life thrives in Alaska; wildlife and vegetation is nearly everywhere - mostly because there are very few people to ravage it.

Nimur (talk) 18:11, 29 May 2015 (UTC)[reply]

I'm not sure if there has been much oil exploration at the actual North Pole. There wouldn't be much point in a company searching for oil there, as the constantly moving ice pack on top would make for difficult drilling, either exploratory drilling or for production purposes. Global warming may soon melt the ice in summer, but having wells you could only tap in summer would still be problematic. Perhaps some system could be devised to send the oil via pipelines to the nearest land, but that sounds like an enormously expensive proposition. A continuous attack by ice breakers might also be able to keep the ice pack from destroying a drilling platform, but again that would be prohibitively expensive. StuRat (talk) 18:39, 29 May 2015 (UTC)[reply]

(I'm just speculating, but so are you...) I think it is conceivable to imagine having manned or automated submersibles fuel from a site well beneath the ice at any time of year. The ballisting issues would be a bitch, especially if you're not allowed to exchange the oil tanks with seawater + air for environmental reasons, but I imagine they'd think of something. Wnt (talk) 20:24, 29 May 2015 (UTC)[reply]

The arctic is a very productive ecosystem during the summer. See insolation - the region does receive less than other places on Earth, but not by a huge factor, and not relative to places you think of as having oil. Also, bear in mind that living organisms have no actual purpose in becoming part of hydrocarbon deposits. You can have a peat bog in one spot and a barren hillside close by, both receiving the same amount of sun and rain, but one is just better recycled than the other. In the case of the Arctic, plankton are well evolved to survive freezing; nonetheless the yearly cycle might cause some loss to the sea floor (however, I have absolutely no idea if that is really a factor). Last but not least, remember that in geological time all the features of the Earth's crust have moved due to plate tectonics. Wnt (talk) 20:22, 29 May 2015 (UTC)[reply]

Ocean drilling is done on the continental shelves, not normally in deep oceanic basins. Deep ocean basins are area where new crust has been created by sea-floor spread, as along the Mid-Atlantic Ridge. Most oil deposits are from land plants that were sequestered on land during the Carboniferous, and which a now usually buried at some depth under continental surface. The North Sea beds, for example are flooded continental shelves, not deep-sea crust. μηδείς (talk) 05:02, 30 May 2015 (UTC)[reply]

@Medeis: By "North Pole", people mean the Lomonosov Ridge, which various countries are trying to connive to make into their national waters. According to our article the ridge comes up to within 400 meters of the surface. I suppose what comes next is for somebody to dump 400 meters of debris on top of some part of it and fortify a military base there to help argue their claim... Wnt (talk) 11:17, 30 May 2015 (UTC)[reply]

Yes, you're pointing out an example of the principle I was discussing. As the Lomonosov Ridge actually is part of a bit of unusual submerged continental crust, it may indeed have oil deposits. μηδείς (talk) 19:19, 30 May 2015 (UTC)[reply]

Windmill without blades

I saw a news report at http://www.theengineer.co.uk/energy/news/spanish-firm-proposes-bladeless-wind-turbine/1020399.article

Some questions:

1) Is this actually going to be substantially quieter than bladed windmills (including at 'subsonic' frequencies) or not?

2) Will this actually avoid harming birds?

3) Will this provide power under as wide a range of conditions as a bladed windmill?

4) Why does it actually have to move back and forth, rather than just experiencing the force of the wind in place?

Wnt (talk) 20:14, 29 May 2015 (UTC)[reply]

I think the real problem is that the device will have a hard time generating a megawatt (as claimed). Hooke's law tells us:

Energy = 1/2 k x²

...for displacement x and spring constant k.

If we assume the wind can repeatedly move the device to displacement x, then we can calculate an energy extraction rate per unit of time, and deduce a maximum possible power (assuming perfect mechanical and electrical transduction). Obviously, a real thermodynamic system will have conversion loss.

The spring equation also tells us how fast the device will naturally oscillate, as a function of its mass.

You can crunch these numbers yourself, if you don't already have an intuition that this is implausible... and I think you will find that it is unreasonable to assume we can extract a million watts from oscillation unless the device is swinging great distances at high speeds. If it does these things, what material will it be built from? The developers claim fiberglass...

(I should emphasize that these back-of-the-envelope calculations are not hard physical limits: strictly speaking, a rod forced to oscillate by the wind could theoretically extract any amount of energy on each swing. These calculations do, however, provide context for the energy scales that are characteristic to this setup).

You can read about the physics of wind turbines. There is a reason that wind turbines like to use very large, very long blades: the power extraction and the efficiency increase dramatically as the blades are built at larger length scales.

If you aren't intuitively familiar with dynamic analysis of oscillating beams, also read about elastic beam equations. This is a standard problem in engineering dynamics or advanced mathematics. You can find thousands of worked examples online; here's an introductory lecture note from San Jose State University on Applications of Second Order ODEs. Once you work this math out (and repeat about a million times), you'll have a good quantitative intuition about energy and power in these scenarios.

Nimur (talk) 23:08, 29 May 2015 (UTC)[reply]

I numbered your Q's above so I could reply to each:

1) Vibrations in the ground might be more of a problem than audible sound. People and animals living nearby might not like that.

2) It shouldn't harm birds unless they fly into it or try to nest nearby. I'd paint them a bright color (not sky blue) to make them less likely to fly into it.

3) It might work better in low winds that a traditional windmill, since there's no friction to overcome to get it going.

4) You can't generate electricity in this device without some motion. Compare with a bicycle pump. Can you get it to work just by pushing on it harder and harder, without ever reversing direction ? StuRat (talk) 02:47, 30 May 2015 (UTC)[reply]

The physics of this does confuse me. I understand that mechanical work requires that the work be done over a distance that the object is moved; otherwise you could do work just sitting on the couch! Also that if you're going to reduce the energy of the wind by slowing it down (relative to your rest frame) you also have to take some momentum and put it somewhere. Even so, well... there are ridiculously inefficient mechanisms by which some energy clearly can be extracted. If the wind happens to be blowing at atmospheric reentry speeds, we know the tower would glow cherry red and could power steam boilers inside it. If the tower is made of aqueous gel, separated by a barrier, the higher pressure of O2 means that there would be more oxygen molecules on one side than the other, and you could use that to power a symporter to create a proton gradient and generate electricity (in some absolutely miniscule amount). I feel as if there is precedent, then, for somehow evading the need for the seemingly required motion, and so then the question is whether there's an actual limit to how clever a method someone potentially could devise. Wnt (talk) 13:43, 30 May 2015 (UTC)[reply]

Isn't one of the missing premises above that the arms will oscillate sideways in an oblique wind as the Tacoma Narrows Bridge did in the famous video? The wind won't be pushing the arm forward, then pulling it back. It will be setting up a harmonic oscillation. Also, birds can see in ultraviolet, so markings in ultraviolet on a neutral blue-grey should be feasible. Also, birds don't usually fly into swaying trees or the towers of windmills. It's the hazard of swiftly rotating bladetips with which they have no familiarity, not tall things that sway. μηδείς (talk) 04:55, 30 May 2015 (UTC)[reply]

Birds do fly into windows, so stationary objects can be a problem, if they can't see them. The UV reflective paint is a good idea, but there might not be much UV to reflect at dawn and dusk, and there's also the concern of low flying prop planes etc., so they still should be painted bright colors, for those reasons. StuRat (talk) 15:11, 30 May 2015 (UTC)[reply]

That's just an easily solvable engineering question, not a point of actual disagreement between us. And while birds do fly into windows fatally (I have discussed it here before from experience), how many documented deaths are there from birds flying into trees?

I do not believe that windmills harm birds. At least, not in any meaningful way. A bat could hit its head against anything, even in a familiar environment. However, bats reproduce like rats, and so this is not a problem. Birds are definitely quite intelligent and have a better perception of their environment as us. --Llaanngg (talk) 13:14, 30 May 2015 (UTC)[reply]

It's estimated that a few 100,000 birds a year are killed by wind turbines. Were they more common, the death toll could be much higher. Perhaps the solution is to use housecats as biofuel. μηδείς (talk) 19:09, 30 May 2015 (UTC)[reply]

Good reference... excellent suggestion. :) Wnt (talk) 19:16, 30 May 2015 (UTC)[reply]

(edit conflict) Estimates tend to be between 5 and 20 birds per turbine per year, or several hundred thousand bird deaths per year in the US. Whether or not this is significant is a matter of perspective. Cats are estimated to kill more than a billion birds in the US per year. On the other hand, cats probably don't kill many adult bald eagles or golden eagles or other large endangered species, which has been a problem at a number of wind farms, e.g. [2]. Dragons flight (talk) 19:11, 30 May 2015 (UTC)[reply]

Mitigating dengue fever in US flooded areas with mosquito bits

I was looking at [3] and have questions about [4], in particular how often do BtI mosquito treatments need to be applied? Months or years and how many between applications? 2001:558:1418:31:ED6B:3F1F:8C10:4F0E (talk) 20:19, 29 May 2015 (UTC)[reply]

May 30

animals and humans

I just watched this https://www.youtube.com/watch?v=-NDAd-wn_9M and was shocked at how picky female animals can be on looks. Why is it that for humans male cares mostly about looks but for animals its opposite? I mean when there are gender differences male animals are always better looking, for human it's opposite (best females look better than best males). — Preceding unsigned comment added by Money is tight (talk • contribs) 10:15, 30 May 2015 (UTC)[reply]

One difference is that for most species the male is merely a "sperm donor", so all the female cares about is that he is healthy, which can be judged by looks. In humans, on the other hand, males were historically important to the survival of the children, due to the resources they bring (wealth) and their position in the social hierarchy (power). So, wealth and power may be more important than looks alone, to human females. Of course, having a wealthy and powerful husband (which probably means old) and getting impregnated by young, handsome, and therefore presumably healthy, males is the best of both worlds, provided they don't get caught. StuRat (talk) 11:12, 30 May 2015 (UTC)[reply]

Best of both worlds? For immediate gratification, maybe, but not biologically. If the sexy poolboy is a dunce whose poverty ridden alcoholic family all die at 50 due to a genetic condition, getting impregnated by him would not at all be ideal. It's also entirely possible that the powerful old rich man was a looker when young, has fathered some quite successful children, and will live to 100. μηδείς (talk) 19:03, 30 May 2015 (UTC)[reply]

Young sperm carry fewer mutations, and so are more desirable in that sense. And every pool boy comes from a line that has won out in countless generations of natural selection to reach the present day. While it is possible to assess whether there is something seriously wrong with an organism, the examination only goes so far - and the instinctive examination of basic physical vigor is more likely to target the genes of most interest biologically; natural selection doesn't care if your kid is a drunk or an astronaut, only how many kids he has. (Cue Idiocracy - and ponder why that premise hasn't come true in any previous generation) Wnt (talk) 19:23, 30 May 2015 (UTC)[reply]

Yes, that's true, but most congenital mutations are linked to the age of the mother's eggs. Sperm with serious mutations will often lead to spontaneous abortion or failure to conceive, and male fertility does decline over time. But sperm are produced anew, while eggs have been eggs since before the mother's birth, so they have had a lot more time to acquire lethal mutations. Should the woman find she can't conceive the couple could always discuss using a close male relative of his as a sperm donor. If the object is just to have a baby, not a rich and powerful 60 year-old's baby, then of course the woman could resort to the pool boy. There's no accounting for logic. μηδείς (talk) 21:40, 30 May 2015 (UTC)[reply]

I went to look this up, and actually see there's been some development of the idea [5] - apparently sperm that undergo mutations can actually have a positive selection driving their abundance in the testis. Achondroplasia, for example. Which means I'm no longer so sure about the rate of overall spontaneous mutation in sperm with age, when such positively selected traits are excluded. In any case, older women characteristically have overall issues with large chunks of chromosome in older eggs (nondisjunction) rather than point mutation per se. (not accounting for trinucleotide repeats...) Wnt (talk) 01:49, 31 May 2015 (UTC)[reply]

Thanks, Wnt, that's interesting, it would explain the relatively high spontaneous rate of achondroplasia compared to other expressed genetic mutations. I posted a chart showing a huge jump in the rates for Trisomy 21 with mothers older than 35. I am unaware of any similar issue for males at that age, but obviously sperm quality is not going to increase with age. μηδείς (talk) 02:44, 31 May 2015 (UTC)[reply]

Sexual dimorphism may not answer all of your questions, but it would be a good start. I don't think "better looking" is a very useful phrase here; in this photo of Mandarin ducks the male is flamboyant but the female is quite pretty in my opinion. Who's better looking is a matter of personal taste, something like art appreciation. ―Mandruss ☎ 11:21, 30 May 2015 (UTC)[reply]

Another article the OP should read (rather than StuRat's "I don't have to provide references because everything I say is stuff I already know" kind of answer) is sexual selection. It's a fairly comprehensive article, and also covers humans, there are further links in that article you can follow to articles about how the concept plays out in humans in even more detail. --Jayron 32 19:06, 30 May 2015 (UTC)[reply]

Do milk-cows need to give birth to calves to produce milk?

Do milk-cows need to give birth to calves to produce milk? Or, is it possible to trick the cow's organism through hormones into believing that a calf was born, and milk has to be produced?--Llaanngg (talk) 13:17, 30 May 2015 (UTC)[reply]

[6] says they do need to have had a calf to produce milk. BbBrock (talk) 13:38, 30 May 2015 (UTC)[reply]

Yes, under normal conditions the cows would need to have had a calf. The question whether it's still theoretically possible to make them produce milk with a hormone treatment does not get addressed by this claim. --Llaanngg (talk) 16:16, 30 May 2015 (UTC)[reply]

See induced lactation. μηδείς (talk) 18:55, 30 May 2015 (UTC)[reply]

Physiological reasons for vegetarianism and veganism

Is there a good source suggesting non-ethical, possibly genetic reasons for vegetarianism and veganism (excluding meat allergies)? I only found that androstenone in pork may cause aversion, but nothing more than that. My sister had been an avid meat eater during childhood and early teens, but turned largely vegan for non-religious reasons citing unpleasant smell. I'm, however, omnivorous and start to feel myself uncomfortable after abstaining from meat for 2-3 days. I suspect metabolic differences between two sexes and higher energy requirements for males, but not entirely sure. Brandmeister^talk 21:32, 30 May 2015 (UTC)[reply]

I was thinking perhaps a problem with digesting creatine might be relevant, but due to creatine's central metabolic role, such a disorder might simply be lethal during early development. In any case, I was unable to fid anything on line about where one should avoid creatine. μηδείς (talk) 01:13, 31 May 2015 (UTC)[reply]

Meat is usually harder to digest than vegetable matter, with the usual exception for unusual allergies, and for a lot of people fish and to a much lesser extent poultry is an exception. Most of the added stress is on the immune system and artery plaques. If you absolutely must have dairy, insisting on grass fed is a good idea, but whether it's cost effective is anyone's guess. I hope the plan to seed the North Atlantic with iron continues to strengthen Pacific salmon stocks. 75.148.42.9 (talk) 01:17, 31 May 2015 (UTC)[reply]

As for you only being able to go off meat for 2-3 days, that probably means you haven't completely compensated for the missing nutrients. You'll need a new source of protein, like beans and nuts (or dairy, eggs, and fish if you are less strict). You'll also need to ensure you get enough iron, vitamin B12, etc. StuRat (talk) 01:53, 31 May 2015 (UTC)[reply]

B6 and cal-mag-D-sunlight are next on (and comprise the remainder of the?) vegan checklists. 63.225.115.25 (talk) 02:25, 31 May 2015 (UTC)[reply]

May 31

How many times has sex evolved?

How many times has sex evolved? For example, did it evolve independently in plants and in animals? Please use simple language as I am not a biologist. I suppose the answer will depend on what sex is, and the various stages of its development? 82.31.133.165 (talk) 08:14, 31 May 2015 (UTC)[reply]