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May 27

What is the difference between erection and priapism?

5.28.171.142 (talk) 01:24, 27 May 2015 (UTC)[reply]

Free will. --Jayron 32 01:29, 27 May 2015 (UTC)[reply]

We have an article on this. Please at least pretend to have searched for our articles on topic next time. Ian.thomson (talk) 01:33, 27 May 2015 (UTC)[reply]

Um, free will is a bad answer, since both arousal and orgasm do occur during rape, and people laugh even when they find being tickled torture. (This was in the news recently, but for some odd reason google was unhelpful.) μηδείς (talk) 02:18, 27 May 2015 (UTC)[reply]

Entirely true. I suppose the difference is that priapism is an erection that is not in response to any stimuli. Free will was a bad way to express that. --Jayron 32 02:35, 27 May 2015 (UTC)[reply]

No one will hold it against you, Jayron. :) μηδείς (talk) 03:00, 27 May 2015 (UTC)[reply]

Well, sometimes it's nice if someone would hold it against me. At least it would let me know they were interested... --Jayron 32 03:01, 27 May 2015 (UTC)[reply]

As I understand it (and having read the WP article) the initial cause is irrelevant, it's the failure to go away that's the problem. Alansplodge (talk) 18:19, 27 May 2015 (UTC)[reply]

people often accuse me of the same thing as well... --Jayron 32 18:28, 27 May 2015 (UTC)[reply]

What kind of frog?

I think this is a type of tree frog, but I'm not sure. Can someone give more information? Bubba73 ^{You talkin' to me?} 02:02, 27 May 2015 (UTC)[reply]

I don't know that we can tell enough from just this angle. Do you have any images from other angles? --Jayron 32 02:05, 27 May 2015 (UTC)[reply]

It is in Lower Coastal Plain (Georgia). I took this tonight through my window. Bubba73 ^{You talkin' to me?} 02:06, 27 May 2015 (UTC)[reply]

Yes, but did you take any additional pictures showing the dorsal side, which may have useful markings in identifying the possible species, or just this one? --Jayron 32 02:11, 27 May 2015 (UTC)[reply]

By the way, it's also probably not a tree frog, as I don't see any of the major classifications thereof which are endemic to North America. --Jayron 32 02:13, 27 May 2015 (UTC)[reply]

Did some research. Doing the best I could working this dichotomous key from the picture we have, the best hit I came up with is the American green tree frog, or Hyla cinerea, which is everywhere in the Southeastern U.S. I have several I see all the time in my yard in North Carolina. A secondary possibility is the closely related Pine Barrens tree frog, which is much rarer, and not usually found in Georgia. I also don't see any evidence of the lavender and yellow stripes down the side. It looks like the common American green tree frog if anything. --Jayron 32 02:18, 27 May 2015 (UTC)[reply]

Did some more searching at that same site. Another close match is the Squirrel tree frog. --Jayron 32 02:21, 27 May 2015 (UTC)[reply]

Bejeezus! Frog Porn at WP? I am going to contact Drudge! (Yes, a dorsal view wold be more helpsome.) μηδείς (talk) 02:13, 27 May 2015 (UTC)[reply]

I added a dorsal view, taken from outside with a flash. He is eating an insect or spider. They may be called green frogs around here. Bubba73 ^{You talkin' to me?} 02:24, 27 May 2015 (UTC)[reply]

Looks like either a squirrel tree frog or American green tree frog then. Unless we have a trained batrachologist who stops by, we may not be able to get more definitive than that. I'm not sure I could tell either of those two apart even from the pictures in our articles. --Jayron 32 02:28, 27 May 2015 (UTC)[reply]

It looks more like the photos of the Squirrel tree frog to me, but biology was my weakest science. Bubba73 ^{You talkin' to me?} 02:30, 27 May 2015 (UTC)[reply]

It looks fairly certain it belongs to the Hylidae based on the skull and limbs. but it is very reckless to assign it to a specific genus. We'd really need a specific location even to opine, and an expert to be sure. μηδείς (talk) 02:57, 27 May 2015 (UTC)[reply]

This one is in Glynn County, Georgia. And there are plenty more where that came from - you should hear it around here when it rains! If it can be narrowed down, I'll add it to the right article - there aren't very many photos of the underside. Bubba73 ^{You talkin' to me?} 03:31, 27 May 2015 (UTC)[reply]

Looking at this further, I am curious why the waist is so wide. The other hylid frogs seem all to have skinny waists. Perhaps it's gravid? I despair because despite my batrachiophilia I lack a reference book on the subject. μηδείς (talk) 19:04, 27 May 2015 (UTC)[reply]

It could be - I just added a photo showing two such frogs, and compare them. Bubba73 ^{You talkin' to me?} 19:19, 27 May 2015 (UTC)[reply]

Cool pics. I think the foot structure indicates tree frogs. But why is one frog coughing up a beetle? μηδείς (talk) 21:15, 27 May 2015 (UTC)[reply]

It is eating the ~~beetle~~ insect. The photos are not in chronological order. The one of two frogs was made before the one where you see only some limbs sticking out. Bubba73 ^{You talkin' to me?} 23:01, 27 May 2015 (UTC)[reply]

Heat equation on the ice rink

moved to the mathematics ref desk, here
The following discussion has been closed. Please do not modify it.
I am moving theis to the math desk where an answer is far more likely, μηδείς (talk) 02:22, 27 May 2015 (UTC)[reply]

Sending a low-loss message to the distant future

Imagine I leave a letter in a shielded box embedded in some barren rock deep in an intergalactic void. Assuming it's protected from a million more immediate hazards, over a long enough time period, quantum fluctuations will destroy the letter. Would it be possible for someone who finds the illegible remains of the letter to open a wormhole to view the letter as it was in the past? I know it believed to be impossible to send information back in time through a wormhole, but what about forward in time?--79.97.222.210 (talk) 02:27, 27 May 2015 (UTC)[reply]

Sure you can send it forward in time. Just put it on a space ship and accelerate it to a really fast speed, on an arcing course that brings it back to earth. The time it arrives at earth compared to it's age is a function of time dilation, which is dependent only on its speed relative to earth. The faster you send it out and back, the further into the future (relative to it's own age) you will send it. --Jayron 32 02:34, 27 May 2015 (UTC)[reply]

Which works if the senders intend their message for the future. But what if people from 5 million AD want to read letters sent between Mark Anthony and Cleopatra? Is the information irrecoverably lost due to quantum fluctuations? We don't live in a clockwork universe after all.--79.97.222.210 (talk) 04:47, 27 May 2015 (UTC)[reply]

The messages from Antony to Cleopatra (presumably you mean the actual parchments with the actual ink on them) are irrevocably lost due to good old chemical and biological decay and decomposition. There's no need to bring in an esoteric idea like "quantum fluctuations". The texts are lost now, adding another 5 million years to now doesn't make them less lost. --Jayron 32 11:05, 27 May 2015 (UTC)[reply]

Before the discovery of quantum mechanics (QM) we didn't know those letters were truly lost when they rotted. If we lived in a clockwork universe, like they believed we did before the discovery of QM, you could work out the position and velocity of every particle in the universe, and with a powerful enough computer could know its complete history and future. That the paper letters have rotted away would not be important because you could literally have a computer work out what they said before they rotted. We don't live in such a universe however. You can't measure the world so precisely due to the uncertainty principle of quantum mechanics. And the further in the past an event occurred the more uncertainty there is when measuring it. This is what I meant by quantum fluctuations.

I know about QM but I don't understand relativity, which is a theory that apparently may allow for wormholes. I have read that some smart physicists don't think it's possible to change the past with a wormhole. In the last paragraph I noted that the further into the past an event occurred, the more uncertainty there is when measuring it. Is it plausible to get around this by using a wormhole to measure things from the past, without changing them? And thanks a lot for all of your help.--79.97.222.210 (talk) 11:53, 27 May 2015 (UTC)[reply]

No, not unless the letter comes with a very large corpus of easily definable terms in more recent and known languages, or with a really good illustrated picture dictionary. We have plenty of things from the Etruscan language, and so forth, that are almost entirely inscrutable since they are not defined very easily nor repeated in other languages. See also the Sumerian language which we know largely (and almost only) because it was translated into the Akkadian language and the Harrapan civilization whose language remains entirely disunderstood. μηδείς (talk) 02:51, 27 May 2015 (UTC)[reply]

You have put two questions. The answer to the first is "No". I come to that answer by logic without any deep knowledge of wormholes. We are assuming you can create a wormhole. We are assuming information can pass through a wormhole. You say "I know it believed to be impossible to send information back in time through a wormhole" and we are accepting your statement as true. Then the answer is "no" because standing in the future, at the future end of the wormhole, you cannot manipulate the past end of the wormhole to locate the paper and read it. This is because, as you say, you cannot send information back to past so you cannot send information back to manipulate the past end of the worm hole. The second question is effectively "Can you send information forward in time through a wormhole?" I cannot answer that, however the whole tenor of your statements and questions appear to be trying to logic out the first question & perhaps my first answer covers it without need to answer the second question. Lanyon (talk) 10:18, 27 May 2015 (UTC)[reply]

I found myself reading John McCarthy's website this weekend (because I have been studying the Lisp programming language and its early history). Among his writings, he has some very well-developed ideas on ~~futurism~~ futurism. Here are a handful of excerpts:

...regarding a precise definition of the "unimaginably far" future
...regarding human control of the future
...regarding implications of biology and technology projected forward by 10ⁿ years, for suitable choice of n

If you contemplate this problem deeply, you will find that the message will probably degrade for other reasons, long before you hit limitations of physics imposed by thermodynamics or quantum mechanics. It is probably safe to say that this is true for any possible information-storage mechanism you can contrive for your message. How can you communicate high-level semantic messages to some unknown recipient, unless you can first produce a formalization of language that permits you to describe abstract ideas in a universal way? Phrased another way: suppose you serialize the message into binary and guarantee zero bit error rate by some technological means. The bits can be preserved perfectly - but has the message been preserved? Only if the recipient knows how to interpret these perfectly-reconstructed bits!

Nimur (talk) 13:06, 27 May 2015 (UTC)[reply]

I suppose the "semantic" problem is similar to that of Communication with extraterrestrial intelligence (though perhaps slightly easier, if we assume the recipients will be at least vaguely similar to ourselves). Attempts to communicate with unknown recipients include the Pioneer plaques and Voyager Golden Records. AndrewWTaylor (talk) 13:59, 27 May 2015 (UTC)[reply]

Here [1] is a short article about specifically communicating to far future human societies (~10k years), with respect to the Yucca_Mountain_nuclear_waste_repository and the Waste_Isolation_Pilot_Plant. We also have some related info at Long-time_nuclear_waste_warning_messages, and here's a description straight from the source at WIPP/DOE [2]. Spoiler - include lots of redundancy, have several different message levels, and cover the whole place with scary spikes. SemanticMantis (talk) 15:12, 27 May 2015 (UTC)[reply]

(just spouting...) It depends a lot on who you want to communicate with. If you're content to reach *someone* *somewhere*, well, you need merely make some sort of switchable filter (such as a metamaterial that can pass or block radio waves depending on switch setting), make it a few miles wide, unfurl it into space. You then program it to block or allow the pulses from a particular pulsar, and anyone who happens to be in line with it - exactly in line with it - even hundreds of billions of years from now can read your binary message. Wnt (talk) 20:03, 28 May 2015 (UTC)[reply]

Can we get free electricity from a phone jack?

Can we get free electricity from a phone jack? How do phone companies deal with this? Do they limit the amount of power that can be leeched? Do they monitor consumption, and cut the line if it's too high? Or, is it so little that it's not feasible? --Llaanngg (talk) 16:20, 27 May 2015 (UTC)[reply]

Plain old telephone service does supply power: it provides 48 volts to the wall. However, this is not an ideal voltage source. If you attempted to sink a large amount of current (i.e., if you tried to power a large load like a television or a computer), you would trip the circuit breaker. The maximum allowable current in the United States is defined by the FCC, as part of "Part 68" (47 C.F.R. §68 CONNECTION OF TERMINAL EQUIPMENT TO THE TELEPHONE NETWORK). You can find exact values for the maximum current if you're willing to dive deep into the regulations. "Unofficial" publications provide technical data for the analog telephone electronics enthusiast: for example, www.part68.org - the website of an industry consortium - hosts Technical Requirements for Connection of Terminal Equipment to the Telephone Network, which includes short circuit behavior. Obviously, you can draw power from the system, subject to certain design limitations: many (mostly historical) devices (other than telephones) do this. For example, there are teletype terminals and telexes, fax machines, telephone bell ringers, flashing lights, assistive devices for the hearing-impaired; and so on.

You are not really getting electricity for free unless you are receiving telephone service for free. You are either paying for telephone service, or you are usurping the generosity of somebody else who is paying for it and supplying it to you at no charge.

Nimur (talk) 17:58, 27 May 2015 (UTC)[reply]

POTS! God bless you, Nimur. μηδείς (talk) 18:55, 27 May 2015 (UTC)[reply]

"Free" as in "used for other than its intended purpose providing of power for telephone calls", I suppose. There are some web pages and videos that show you how (for example) to charge an iPhone from a telephone socket, but this kind of thing is probably at least a violation of the phone company's terms & conditions, and possibly even a criminal offence in some places. AndrewWTaylor (talk) 18:05, 27 May 2015 (UTC)[reply]

Well, your assertion that this power is intended for powering "telephone calls" is overly narrow. The power is provided with the intent to power "terminal equipment", which is defined (in 47 CFR 68.3), as: "Terminal equipment. As used in this part, communications equipment located on customer premises at the end of a communications link, used to permit the stations involved to accomplish the provision of telecommunications or information services.

Nimur (talk) 18:08, 27 May 2015 (UTC)[reply]

Doorbell? :) Wnt (talk) 17:36, 28 May 2015 (UTC)[reply]

That's what the Ringer equivalence number is for. It's printed on the bottom of every landline phone. If you exceed the maximum your phone won't ring. Ariel. (talk) 00:53, 28 May 2015 (UTC)[reply]

Whoa. InedibleHulk (talk) 01:32, May 28, 2015 (UTC)

There is no circuit breaker. A dead short will make the exchange feed you dial tone until the timeout elapses and the exchange puts the line on the wetlist (busy signal). Most exchanges will continue to give you -48 even after that. The line has hundreds of ohms resistance, including resistance in the line card or other exchange equipment, which will limit the current and droop the voltage. Thus, even when you disable your telephone line in this way, it still won't give as much power as a USB connection. Jim.henderson (talk) 18:43, 29 May 2015 (UTC)[reply]

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 [3], 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]

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]

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]

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]

Mitigating dengue fever in US flooded areas with mosquito bits

I was looking at [4] and have questions about [5], 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]

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]

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]

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