Wikipedia:Reference desk/Archives/Science/2016 April 27

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April 27

What is the most time which recorded about human being without sleeping?

I use an application of neuroscience quiz. One of the question is about the time that recorded about human being who went some days without sleeping. The options were 6 days, 7 days and 11 days, while the correct answer was 11 days. I would like to get a source for this thing (11 days). 93.126.95.68 (talk) 01:53, 27 April 2016 (UTC)

The source is very likely this: Randy_Gardner_(record_holder). Also noteworthy is that this is, apparently, for a healthy individual; people with severe disorders such as Fatal Familial Insomnia are probably excluded, as are people in a Persistent Vegetative State or coma (indeed coma is not sleep). --Dr Dima (talk) 02:14, 27 April 2016 (UTC)

Why do transmission substations gets overheated during black outs?

I would like to know why the transmission substations gets overheated as said in this lecture(Slide 5) when blackout occurs in step 4 since the demand of current can't be meted.Could anyone help me.JUSTIN JOHNS (talk) 10:39, 27 April 2016 (UTC)

Substations are carefully tuned so that their input equals their output; they don't have infinite storage capacity. If something happens downstream so that the output of the station cannot be accepted -- let's just say a power line breaks -- the substation is suddenly taking in more power than it can transmit, and that power has to go someplace, and that someplace is heat. So now this substation must shut down or it will melt. Which means the substations that were sending to this substation don't have anywhere to send their excess electricity. So they shut down too...cascading blackouts... --jpgordon^{::==( o )} 14:50, 27 April 2016 (UTC)

For that answer please see "not even wrong". A substation is a transformer and stores nothing whatsoever. 91.155.193.199 (talk) 16:17, 27 April 2016 (UTC)

No capacitors? Really? --jpgordon^{::==( o )} 16:37, 27 April 2016 (UTC)

Really. A capacitor can store a mere pittance of energy. In power distribution, capacitors are used for power factor correction, not to store even one second's worth of anything. Capacitors don't store no AC. 91.155.193.199 (talk) 16:48, 27 April 2016 (UTC)

OK, so why don't _you_ answer the question, rather than just snarking at details? --jpgordon^{::==( o )} 17:24, 27 April 2016 (UTC)

Did a while ago. Not that that is a prerequisite for pointing out a wrong answer. 91.155.193.199 (talk) 17:32, 27 April 2016 (UTC)

@Jpgordon: That almost makes sense... but it doesn't. Because if the substation "shuts down", where does all that incoming power go? Why can't it just shut down partly, send some of the power wherever the power would go if it shut down, and just take some to pass downstream? I'm sure there's a good engineering reason but it has to be more complicated than what you're saying. Wnt (talk) 15:18, 27 April 2016 (UTC)

That Powerpoint slide is not the clearest thing I have seen. My guess is that there is an area that is served by both local and remote power generation. When remote generation fails, local generation is overwhelmed and shuts down as well. Should see the original sources that were used to generate that Powerpoint slide to tell for real. 91.155.193.199 (talk) 16:48, 27 April 2016 (UTC)

Yes, that's a reasonable guess, but local generation is not mentioned in the PP slide. What the slide tells us is that the transmission stations were overloaded. That's because one transmission station feeds power into the area from one source, so if three sources (the slide tells us) were down, the remaining transmission stations (we don't know how many) each had to transmit more power (from where, we don't know, but there must have been at least one source still live) into the area to keep it live. Therefore some of the remaining stations overheated and shut down. The transmission stations in turn feed transformer stations. With some transmission stations out of action, that left fewer transformer stations than normal trying to supply the same area, so those stations in turn overheated and shut down. Note the distinction between transmission stations, which are switches, and transformer stations, which change the voltage.--Heron (talk) 17:46, 27 April 2016 (UTC)

Good point, and part of the complete answer to the OP's question, "Why do transmission substations gets overheated during black outs?" (sic).

The full answer is that transmission station switches are rated to carry so much electrical power or wattage of electricity, and no more. They're set up so that a transformer feeds them, and distributes some of the power passing through it (not stored in any way, a transformer's just a way of using electromagnetic induction to change the alternating current passing through it from one voltage to another without storing any power - though some power is dissipated through Joule heating of the windings of the transformer as the current increases and the voltage drops in the secondary windings of the transformer) to several switches which distribute power down through power transmission lines, ultimately to where the electricity is used.

When one of those switches fails or ceases to have power passing through it (as when one of more transformers downline from it fails and no longer draws current), it sometimes happens that more current flows through the other switches (for one of several possible reasons), which increases the wattage through those switches above their design limits (the voltage being about the same, but the current dramatically increased), so that Joule heating through the current-carrying parts of the remaining live switches increases accordingly beyond the temperature the switches were designed to work under, and they overheat.

This also works at the level of entire transmission stations - when one entire transmission station fails (no matter how), electrical power load can be shifted to other stations, and they can sometimes be subjected to current demand above their design limits, so that switches can get overheated and fail. That's one of the possible ways cascading power failures happen. loupgarous (talk) 18:33, 27 April 2016 (UTC)

@Jpgordon Oh really? The substations shown in the slide are transformers and the initial failures are upstream. Transformers have no power storage capacity (beyond one AC cycle) and have no problem with zero output load. There is no "excess electricity" involved, only cascading blackouts when substations shut down rather than supply excessive power demands. AllBestFaith (talk) 18:58, 27 April 2016 (UTC)

Yay! I was wrong about something. "The quickest way to get a correct answer on the Internet is to provide an incorrect one." --jpgordon^{::==( o )} 19:02, 27 April 2016 (UTC)

Aye, that would be Cunningham's law [1]. Your original answer did make sense to me, and I would have probably believed it if that was the only response, so this is an interesting thread. Of course it's totally fine to accidentally illustrate Cunningham now and then, but IMO we should all make it a point to not participate too heavily on either side (e.g. pointing out errors only [2], posting under the influence of the Dunning–Kruger_effect etc.). I'll also note that though I see several wikilinks above, none of them seem to refute your answer on their own. So even with your acknowledgement of incorrectness, we're still kind of trusting in the authority of strangers who know how to talk a good talk. And that's not to say I distrust the further refinements, just to point out how hard at can be to support a specific answer with a specific reference :) SemanticMantis (talk) 20:00, 27 April 2016 (UTC)

No need to link out to meta; Cunningham's law is blue:) DMacks (talk) 02:24, 28 April 2016 (UTC)

Ah ne'er so dire a Thirst of Glory boast,

Nor in the Critick let the Man be lost!

Good-Nature and Good-Sense must ever join;

To err is Humane; to Forgive, Divine.

-An Essay on Criticism, Part II , 1711, Alexander Pope (my bolding).

Wikipedia has an article about load shedding in electric transmission systems that cannot meet peak demands. I trust that providing a relevant reference does not strike jpgordon as another snark. AllBestFaith (talk) 15:34, 28 April 2016 (UTC)

Yeah all answer points out one single thing and that's 'the overload of current through these transmission stations was the cause of it's overheating'.I couldn't get how the grid can't meet the 'demand' as given in step 4 and 5 of the lecture(Slide 5).Does the author mean to say about the user's demand or about the current demand?

Can we stop this overheating by refusing the current to flow through these stations if a power failure occurs in one source?JUSTIN JOHNS (talk) 09:01, 28 April 2016 (UTC)

Yes, if a sufficient number of end users have smart switches that allow the distribution company to switch off the less essential consumption at times of overload, then the transformer could be kept at a safe temperature. The current flow is determined almost entirely by the end users, since the regulations in most countries do not allow the voltage to drop below a certain level. A transformer cannot "refuse" current. It's impedance on the input side is determined by the current flowing out to end users. Dbfirs 13:19, 28 April 2016 (UTC)

The important thing being the current flow through both the transformers and transmission switches. Joule heating causes current through a conductor to increase as the square of the current passing through it, so that the transformers and switches both tend to overheat when they're carrying more current than they're designed to carry (the voltage being relatively constant assuming no issues at the generating stations and high-tension distribution network). Heat in reactive loads such as transformers and resistive loads such as switches increases as the square of the current passing through them, which is why when one leg of a power distribution network fails, the other legs which parallel it immediately get hotter (if load is shifted through them from parts of the network which had been served by the failed leg). Overheating of the remaining legs can cause cascading power failures. loupgarous (talk) 18:57, 28 April 2016 (UTC)

In addition to switches which heat up when they carry high current, actual conductors heat up, sag and fail. Transmission lines also have other devices in series which can heat up and fail, such as current transformers which are connected to monitoring equipment and to protective relays, and wavetraps, which isolate radio frequency control signals passing along the transmission lines. They may have series reactances (inductors) to limit fault current if a transmission line shorts to ground .Some transmission substations have transformers which step up or step down the power from one transmission voltage to another, such as 765kv, 345kv and 138kv. Some transmission substations have 138kv phase shifting transformers which can carry 300 megavoltamperes, and can force the power to flow in the desired direction, within limits. Utilities run contingency studies to see which of these circuit elements become the limiting factor for various situations, such as the simultaneous outage of two transmission lines, or a line and a generating station. They upgrade as necessary to ensure a robust and reliable system. When more things are out of service than these design contingencies allow for then immediate load shedding is required to prevent widespread prolonged outages and equipment damage. If he operator hesitates to drop load because of political considerations,or the operator does not have access to actual system conditions such as breaker openings and overloads, or if non-technically sophisticated higher-ups forbid load shedding, then widespread blackouts may result. Edison (talk) 03:06, 29 April 2016 (UTC)

Can playing too much on the keyboard induce bodily injuries?

Is it possible to play for several hours or the whole day hours without sore arms and hands and fingers? 140.254.77.204 (talk) 14:46, 27 April 2016 (UTC)

(It's not clear whether you mean playing music on an organ/piano or video games on a PC/laptop.) I suffer from "mouse finger". That is, the pointer finger on my dominant hand gets sore at the tip, both from typing and using the mouse. I wouldn't call that an "injury", however. I try using other fingers to click on the mouse and type, to minimize the pain. StuRat (talk) 15:34, 27 April 2016 (UTC)

Like most things, you have to learn how to do it. An experienced pianist will have an exercise regime designed to strengthen hands, arms and shoulders, and the length of time he/she can play will have been built up gradually so that the body becomes accustomed to it. 81.132.106.10 (talk) 15:44, 27 April 2016 (UTC)

You may be interested in reading about repetitive strain injury, and perhaps carpal tunnel syndrome, which is associated with repetitive wrist movement. SemanticMantis (talk) 16:13, 27 April 2016 (UTC)

See the warning labels on some keyboards and not moving the whole body is covered by evolution with a reduced amount of food, only. See such diseases those number increases with the body weight. --Hans Haase (有问题吗) 19:54, 27 April 2016 (UTC)

People could try the simplest solutions first. In the days of manual typewriters, sectaries typed all day, every day. Cutting down and gluten and dairy containing foods often helped enormously. Maybe this why so many took to eating crispbreadlike Ryvita instead of ordinary bread – not to keep down their weight (most were skinny-as-rakes already) but they felt better as it contains very little gluten. Also, this may be why they had such beautiful figures, as people who are sensitive to gluten tend to put on weight and become pair-shaped. This maybe 'OR' on my part and based on straw-poll observations yet others appear to agree. [3], [4] What both of these articles fail to mention however, is that our modern diet is deficient in Omega III oils. Snake Oil (derived from the Chinese Water Snakes) is rich in these, which was why it was useful in treating joint pains. The charlatans that sold 'patented' medicine duly tried to ridicule it to increase their own sales. Yet joint pain is often associated with too little Omega III in the diet. Also, keeping the keyboard tilted reduces the amount of flex required in the hands.--Aspro (talk) 21:08, 27 April 2016 (UTC)

...You're joking, right? WP:MEDRSes please. Ian.thomson (talk) 06:58, 28 April 2016 (UTC)

Computer keyboards might be more likely associated with the carpal tunnel syndrome. Piano players more with their fingers. A keystroke on a piano drives the whole hammer. Problems in result are known for the old famous composers and pianists who played the piano all day. --Hans Haase (有问题吗) 06:51, 28 April 2016 (UTC)

Any piano player who uses only or even predominantly their fingers should give up and start again. The whole hand, the wrists, the forearms, the upper arms, the shoulders, the back, the buttocks, the legs and the feet are all involved. Not to mention the brain, the eyes and the ears. -- Jack of Oz ^{[pleasantries]} 23:34, 28 April 2016 (UTC)

Top bottom wing(s) of a plane

1. The F22-Raptor has the wings v-shaped, why are they not straight? -- Apostle (talk) 20:16, 27 April 2016 (UTC)

See Delta wing. Basically, it's because straight wings wouldn't work properly at the speed of the F22 (or any other modern fighter). Tevildo (talk) 20:21, 27 April 2016 (UTC)

When you have to pitch up the Nose in an small aircraft, like when starting or landing, the body will work like a Windshield for a straight up Wing far behind. There is much more airflow at the sides and thus such V-Wings are more effective. Ofcourse these positions makes it more complicated to steer as you dont get a simple yaw windforce but these planes are flown with computersupport today so they can be handled easy nomatter such complicated aerodynamics. B.t.w. the Boeing F/A-18E/F Super Hornet and Lockheed F-117 Nighthawk have these V-Wings too. --Kharon (talk) 01:26, 28 April 2016 (UTC)

Okay, thanks peeps -- Apostle (talk) 07:33, 28 April 2016 (UTC)

Before there was fly by wire, one solution to the problems of delta wings at slow speed was variable geometry or swing wing configuration, invented developed by Barnes Wallace and used in the General Dynamics F-111 Aardvark, Panavia Tornado and Grumman F-14 Tomcat. Alansplodge (talk) 12:04, 28 April 2016 (UTC)

Okay, noted. -- Apostle (talk) 18:09, 29 April 2016 (UTC)

Absence of Nipple development - Medical term?

(Nedical disclaimer noted.)

I noted the following from an IP contributor https://en.wikipedia.org/w/index.php?title=Henry_Morgan&diff=next&oldid=717460941, but I am wondering if nipple absence is an actual medical condition, albiet exceptionally rare? Sfan00 IMG (talk) 21:08, 27 April 2016 (UTC)

It is - see Athelia (disease). Tevildo (talk) 21:10, 27 April 2016 (UTC)

Now to determine if it was known in the 17/18th century :) Sfan00 IMG (talk) 21:29, 27 April 2016 (UTC)