Wikipedia:Reference desk/Archives/Science/2012 December 30

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December 30

Morse code

Two questions in one: (1) How many chars/min can a skilled operator transmit in Morse code (assuming that he/she has already encrypted the message beforehand)? (2) On average, how long did it take for the Gestapo to locate a radio operator using direction finding? Thanks in advance! 24.23.196.85 (talk) 05:19, 30 December 2012 (UTC)

2) This will depend on whether they are smart enough to send the message from a moving vehicle, or at least restrict themselves to short messages, each broadcast from a new location. StuRat (talk) 05:38, 30 December 2012 (UTC)

(2) I meant how long can an operator "safely" transmit continuously from one location and not have the Gestapo kick in the front door. 24.23.196.85 (talk) 05:45, 30 December 2012 (UTC)

Question 1 is answered in the Morse Code article. Zoonoses (talk) 07:00, 30 December 2012 (UTC)

Depending on what you want this answered for, you may need to take into account some additional facts not covered in teh Wiki article:-

1. While good operators can send and recieve at 40 word per min or more, that is for a perfect link. In a shortwave or medium wave radio link, fading and noise may interfere with reception - the operators will then send as slow as required. With good narrow band recievers, slow enough morse can be copied accurately at signal stengths far below the noise level (hiss, static, machine noise etc) that would obliterate voice. That is the advantage of morse - you can almost always get through when nothing else will, and it nees only simple low tech equipment.

2. Military operators have always been trained in "short codes" - combinations of 3 or 4 letters coresponding to entries in a list of common messages often sent. For example in the NATO code used by navies in and after WW2, to transmit from a flagship the message "I am going to turn right onto magnetic course 290 degrees" could be transmitted as something like "XDEX90".

3. For WW2, German operators were trained to send and recieve in moving noisy environments using specially built rigs closely simulating the noise, vibration, and shock as would be experienced in aircraft and vehicles & tanks under way and under attack. Other forces probably had similar training.

In France, the Gestapo & regular German forces had a simple way of tracing a covert transmitter located in a town somewhere. Back then, a radio transmitter either needed big batteries (the size of a car batteries) or were powered from house current power mains. Usually, house current was the choice. Upon detecting a transmitter and getting a rough direction in seconds they would go to the substation and cut the power for just as long as it took to move the switch up and down - say a fraction of a second. If a matching break in transmission was detected, they knew they had the right area. If transmission continued, they would then race to a likely pole switch feeding a street and do the same. Repeat as required. In this way they could identify the correct street and sometines the correct block of flats within minutes. Then they would just block the street off and thoroughly search every dwelling.

Wickwack 58.167.246.100 (talk) 07:38, 30 December 2012 (UTC)

There was a 1960's spy movie where they did the power cutting to determine which apartment in a building the spy was transmitting from, but in WW2 they used direction finding rather than cutting the power to parts of a city to locate a spy. Any sensible spy would suspend transmitting when the power went off and back on. It would be very time consuming to drive around a city and climb poles to cut power for transmitter locating, and the message would likely be complete before you could achieve more than one such cut. Spy transmitters of WW2 were generally made to work off batteries, in any event. A WW2 US radio operator I know said she could operate at 40 WPM, She had no trouble transmitting encrypted as opposed to plaintext. That is what she was trained on. Edison (talk) 22:28, 30 December 2012 (UTC)

Hmmm, can't tell you the history but just thinking about this it might be worth reconsidering. The point is though that the spy has no way to know that the power is about to be cut, and if the spy depends on electricity, or perhaps even electric light, then once the power is off the transmission will stop. In theory you could have people shut off power to a different little part of a city every ten seconds and figure it out to some high level of precision. I suppose one appealing aspect of the scheme is that if the spy is transmitting by some kind of link or mechanism you can't detect, then you might track where the spy himself is located rather than coming up with the triangulated position of a walkie-talkie taped to a telephone or whatever. Wnt (talk) 00:28, 31 December 2012 (UTC)

Also, if the message is in code, then it's likely to be much slower to transmit than plaintext for a couple of reasons:

• Try using handwriting or typing to copy an English sentence - then try writing or typing a random string of letters or numbers of the same length. It's much harder. If I ask you to type "The cat sat on the mat" - 22 characters, you can do it in probably a couple of seconds. If I ask you to type "RKA VXL ZQG SFG OGH KS"...it'll take you much longer. You can read "The cat sat on the mat" almost instantly, hold it in your mind and just type it out as fast as your fingers can move. "RKA VXL ZQG SFG OGH KS" is probably something you can only read three or maybe six characters at a time.
• If you make a mistake typing English text ("The cat sqt on teh matt") - then the guy at the other end can still read it. But if you make a mistake with some kinds of code - then you're probably going to produce gibberish when it's decoded. So much more care is needed. The message may need to be sent more than once so that the decoders can be sure you didn't make any mistakes.

So this isn't so much about morse code proficiency as about the way the code is handled. Many codes were simple English sentences: "The aardvark sees the mountain" might mean "I need you to attack the weapons depot north of Berlin at the time we previously agreed two nights from now".

SteveBaker (talk) 17:50, 30 December 2012 (UTC)

I disagree with Edison on the effectiveness of the power cutting method. I think he has missed that it was used in conjunction with rapid direction finding. Back then covert transmitters were MF of HF. In a city of well developed suburb, sufficiently accurate direction finding on HF to be used on its' own is not possible. Now, in WW2, if you were a French peasant, and a truck full of German soldiers comes down the street at speed, you didn't hessitate, you got out the way.

Another aspect to consider is that back then electricity distribution was open wires on poles, not underground cable. In open wire distribution, the occaisonal short from wind blown debri or birds happens from time to time, so electricity companies use reclosers. Reclosers are a circuit breaker that trips on overload same as a normal circuit breaker, then waits a predetermined delay, then reconnects. If the overload is still there it trips out again. But often the overload has gone, saving the electicity company manual intervention. So folk get used to short breaks and think nothing of it. Aslo, there was a war on. Short breaks in power happens in war.

However, Edison is quite correct in saying operators have no difficulty is transmitting (or recieving) coded messages or random sequences of characters as compared to plain text. This is partly due to training, and partly due to the nature of morse code. When keying, you think letter by letter, not word by word, as 40 words per min (about one letter per second) is actually a slow process.

Lastly, when transmitting an encrypted message, you NEVER re-transmit just because the recieving end didn't recieve all the characters. You compromise the coding security if you do. It was the (actually quite rare) mistakes like that that enabled the British to read vast quantities of German military traffic. What you do is leave the recieving end to make the best of it, or if necessary, wait a bit and encrypt a different text that has the same ultimate effect.

Wickwack 60.230.218.203 (talk) 02:28, 31 December 2012 (UTC)

You and I know that you shouldn't retransmit (well, not for some classes of code) - but back in WWII, it's likely that only a few people in Bletchly Park knew that...evidently the entire German military was unaware of this particular decryption exploit! SteveBaker (talk) 04:34, 31 December 2012 (UTC)

Perhaps. But I have a copy of Alan Turing - The Enigma, by Andrew Hodges, and some textbooks on encryption. These all make it clear that:-

1. The Germans were properly trained, but never the less made mistakes.

2. On of the less common mistakes that they made was to re-tramsit messages, and that did occiasonally help Bletchly chaps.

3. Their navy had separate encription/coding schemes for habour comms, fleet operations, and weather reports. The British could sometimes pickup habour comms and decript the relatively simple code. Then, match it up with the same thing transmitted using Fleet Ops encryption. They also matched up decripted weather reports also repeated on Fleet Ops. Big, big mistake. Once the British cracked a weather report and matched it to a same length message on Fleet Ops that day, they had the day's key to all the other Fleet Ops messages.

4. A few German operators, if they were not busy with official messges, would send common nursery rhymes (of the Mary had a little lamb sort), both to practice and maintain speed, and to ensure the radio link was available at all times. Big mistake. Once Bletchly realised that was what they were doing, they looked in light traffic periods for messages matching the length of common German rhymes and concentrate on those to get the day's key.

5. German operators did have one aspect of faulty training. They would commonly send messages with polite preamble, as in: TO General Berkhead FROM Captain Nichtwhitt SUBJECT Seizure of Town. Heil Hitler Blah Blah Blah ... Blah. Bad mistake. Never use standard forms in encrypted radio messages in a war. And never never use salutations like "Heil Hitler" in lots of messages.

6. The biggest mistake of all is that the German top brass, when faced with too many coincidences (as in British depth charge equiped aircraft intercepting German submarines far too often, or British merchant convoys diverting just after an order to submarines to intercept them), assumed that the British could not be reading the encrypted radio messages becasue a) the enigma encryption method was unbreakable (it essentially was, if used correctly every time) and their operators were properly trained. So instead of looking at procedures, they wasted a lot of time looking for harbour spies. And they assumed that Bristish radar was a lot better than it was, and better than was and is technically possible.

So, don't rule out that British operators were trained and did know not to re-transmit messages. Wickwack 120.145.54.24 (talk) 05:20, 31 December 2012 (UTC)

A clarification on the issue of re-transmitting: I'm not aware of any attack where two transmissions of the same cyphertext gives an attacker more information than one transmission; all the attacks I'm aware of require transmission of two different encryptions of the same plaintext. --Carnildo (talk) 03:26, 1 January 2013 (UTC)

Correct. If two copies of the same encrypted text somehow gave an attacker some advantage, he could make duplicates for himself - with carbon paper, or a mimeograph machine, or a pencil. There seems to be an above-average amount of wooly thinking in this thread. Zoonoses (talk) 06:20, 2 January 2013 (UTC)

[un-indent] Thanks for the info, everyone! So, 40 words/min on average, huh? That means that the transmissions can be kept very short indeed -- the one radio message I have so far in my novel has only 26 words (including agent ID, security tag and so on, but excluding the commas, stops and the final "over"), so it would take Blanche only about 40 seconds to transmit. I don't think even the best DF team can home in on something this short. (Francois will get to transmit the next message, but I intend to keep it similarly short.)  :-) 24.23.196.85 (talk) 05:45, 31 December 2012 (UTC)

No sweat. Note that punctuation was not normally sent. The word "over" only occurs in 2nd rate TV shows and novels. The reciever knows you've stopped transmitting anyway. Wickwack 120.145.145.21 (talk) 10:48, 31 December 2012 (UTC)

Thanks, Wickwack for a really helpful discussion! Clarification requested (or correction of my top-of-the-head arithmetic): the above says the transmission rate was about "40 words per min (about one letter per second)". The latter means 60 letters per minute, which combined with 40 words per minute means 1.5 letters per word. What am I missing? Duoduoduo (talk) 16:15, 31 December 2012 (UTC)

You've caught out my shocking mental arithmetic due to multitasking, and erroneous use of "letter" where "word" should go. 40 WPM equates to 0.67 words per second or 1.5 seconds per word as you say. Taking the standard typist's approximation that 1 word is 5 characters, that's 0.30 seconds per character. However my comments that sending morse is a slow process that encourages working on a charater by character basis and not thinking in words like we do when reading still stands. Someting else that may or may not be relevant to you is that if the channel gave good clear reception, military forces sometimes used time compressed morse. This reduced the probability of inteception and direction finding. And for submarines, it reduced the time required fully surfaced - always a good thing - surface travel means enemy planes can spot you, and and the rolling and pitching in a heavy sea can make sailors sick. The sending operator recorded the message first and then sent it at high speed. At the recieving end the message was recorded again (eg on a wire recorder) and played back at slow speed to read it. Covert agents would not have used this method however. Electronic equeipment back then was very bulky and heavy, and best kept as simple as possible for relaibility. Wickwack 124.178.61.38 (talk) 16:47, 31 December 2012 (UTC)

I'm afraid that 40 wpm claim is a load of rubbish. Very few trained operators can copy 40 wpm, even under perfect conditions. Almost no one on Earth can send 40 wpm with a straight key, especially under trying, wartime conditions. Seek out your local ham radio operator for some practical instruction. Zoonoses (talk) 06:14, 4 January 2013 (UTC)

Lorcaserin and what else? - FDA approved Obesity medication

i'v heard that except Lorcaserin, there's gonna be another Med', what is it's name? thanks. — Preceding unsigned comment added by 109.65.115.101 (talk) 06:32, 30 December 2012 (UTC)

Orlistat. OsmanRF34 (talk) 16:40, 30 December 2012 (UTC)

No. Orlistat was taken out. it gotta be something else. 109.65.115.101 (talk) 06:13, 31 December 2012 (UTC)

Is it Qsymia Article located here. Livewireo (talk) 19:21, 2 January 2013 (UTC)

What kind of chemicals would be produced when a Polyethylene plastic bag is burnt? How?

Sometimes I can smell a bit odor, so I guess it is not burnt into just carbon dioxide and water.--Inspector (talk) 09:54, 30 December 2012 (UTC)

First the long polymer chains can be broken down into alkenes and alkanes. These may give the waxy smell. There may also be partial oxidation of these to an aldehyde or primary alcohol. Graeme Bartlett (talk) 11:58, 30 December 2012 (UTC)

Combustion#Reaction mechanism suggests it starts with a hydrogen atom being stripped off by oxygen. The radical part of the polymer is highly reactive and can then further react with O₂ to form a peroxyl radical, which in turn can steal another hydrogen atom to make another radical and a peroxide. Graeme Bartlett (talk) 12:14, 30 December 2012 (UTC)

Of course, if you're just burning plastic bags - there is a good chance that it's not polyethylene anyway - there are lots of other materials used in plastic bags these days. Plastic film lists Polypropylene, Polyester, Nylon and Vinyl - along with various bioplastics. There are also things like dyes, plasticisers, release agents and who-knows-what involved in the combustion processes here. SteveBaker (talk) 17:41, 30 December 2012 (UTC)

For what it's worth, PVC and polyurethane are particularly nasty -- the former releases hydrogen chloride during burning (and often some chlorine gas as well), while the latter releases such highly toxic gases as prussic acid and formaldehyde. NOT a good idea to EVER burn those two! 24.23.196.85 (talk) 05:49, 31 December 2012 (UTC)

Does infrasonic results resonance in human body?

My physics teacher, as well as many Chinese websites [1][2][3][4][5], says that infrasonic results resonance in human body, thus 'infrasonic weapon' can be made. But Chinese Wikipedia says infrasonic doesn't damage human tissues, and English Wikipedia says it just cauese pain in the ear drums. I can't find anything about 'infrasonic weapon' which work by making resonance to human body on English websites, can anyone provide any information about it, please?--維基小霸王 (talk) 12:24, 30 December 2012 (UTC)

There's something in the Vladimir Gavreau article, but the article seems to think that it may have been imaginary. 71.79.67.209 (talk) 13:05, 30 December 2012 (UTC)

It seems diffrent because the frech imaginary one doesn't kill people by resonance.--維基小霸王 (talk) 15:00, 30 December 2012 (UTC)

There is a real lack of good research on this topic. To give a fairly bad example, the only recent paper I found in NCBI for infrasound and nausea is a review at [6] that deprecates the idea, though the authors very reluctantly cite (Leventhall G, Pelmear P, Benton S. A Review of Published Research on Low Frequency Noise and its Effects. Department for Environment, Food and Rural Affairs, London, UK; 2003. Yuan H, Long H, Liu J, Qu L, Chen J, Mou X. Effects of infrasound on hippocampus-dependent learning and memory in rats and some underlying mechanisms. Environ Toxicol Pharm. 2009;28:243–247. doi: 10.1016/j.etap.2009.04.011. Leventhall G. Infrasound from wind turbines - fact, fiction or deception? Can Acoust. 2006;34:29–36.) that loud infrasound does cause symptoms similar to those reported by subjects.

As someone who simply hears "infra"sound, some of the unquestioned assumptions of these researchers are very annoying - for example, they point out that infrasound "is emitted from road vehicles, aircraft, industrial machinery, artillery and mining explosions, air movement machinery including wind turbines, compressors, and air-conditioning units," without recognizing that indeed each and every one of these things is also annoying for the same reasons (but most of the other sources are mobile or intermittent). They furthermore fail to appreciate that infrasound "from natural sources like meteors, volcanic eruptions and ocean waves... Indeed, many mammals communicate using infrasound" is the reason why infrasound can be disturbing - because it is a warning of movements of substantial amounts of mass. They fail to appreciate that natural infrasound from wind, made up of multiple frequencies and ever-changing, can have a soothing quality. They also fail to appreciate the chief annoyance of infrasound, which is that unlike high-pitched sound that will not penetrate a window, or low-pitched sound that won't penetrate a wall or a pillow, infrasound seems to penetrate absolutely everything (except water). Now, to give them some credit, windmills I've encountered actually do produce mostly sound in high-pitched frequencies, but if you had a house next to one all you'd hear indoors would be the infra part, however large or small that may be.

Most crucially, however, their paper illustrates the absurdity of some of the sound figures given, because it actually makes use of measurements in dBA, a scale which is based on the idea that infrasound is inaudible and therefore is not even considered in taking sound measurements! All other scales either do not "normalize" sound to exclude those frequencies, or do so to a lesser degree. Wnt (talk) 19:56, 30 December 2012 (UTC)

The type of resonance that could occur in this case would be an acoustic standing wave. This requires a structure that is some multiple of a quarter of a wavelength (see e.g. Acoustic_resonance#Resonance_of_a_tube_of_air). Since the speed of sound in the human body (mostly water) is about v = 1500 m/s (speed of sound#water) and infrasound has frequencies below f = 20 Hz the body would need to have a length of at least ${\frac {v}{4f}}\approx 20{\text{ m}}$ to resonate. At high enough powers anything will be dangerous, but for ultrasound it will not be due to resonance. Ulflund (talk) 20:15, 30 December 2012 (UTC)

Not correct. A mass suspended in an elastic medium will resonate if the frequency is equal to 1 / (2Π (m.c)²) where m is the mass and c is the elastic compliance. Consider a loudspeaker: Quality loudspeakers as made with cone resonances as low as 20 Hz even with a cone diameter of only a few hundred mm. Thus it is quite possible that internal organs in the body could resonate at low frequencies. Wickwack 60.230.218.203 (talk) 02:37, 31 December 2012 (UTC)

I don't know about resonance, but I do know that at high volume, a particular frequency range may cause lethal cavitation to occur in the body. Plasmic Physics (talk) 06:28, 31 December 2012 (UTC)

Lethal cavitation is a process where the compression and decompression within the body (soundwaves travelling through it), causes soft body tissue to liquefy. There is at least one recorded death from lethal cavitation, where a person experimented with infrasound, and unknowingly found the correct range and generated a sound at elevated volume for only 3 seconds. He was paralysed and killed within that time. He was found intact, albeit with liquid brain matter exuding from his ears, burst bladder, basically if it was not for his skin, he'd have to be taken away in a bucket. Plasmic Physics (talk) 06:47, 31 December 2012 (UTC)

, if you please --Jayron32 06:54, 31 December 2012 (UTC)

About that, I saw it on a documentary on the C.I. Network or Dicovery Network. I don't remember what it was called, perhaps "A strange way to die"/"Strange ways to die"? Apparently, there is this underground social group who exploit the wellknown euphoric effect of infrasound, this person was experimenting with generating specific soundtracks to harnass this effect, with intention to sell. He found that 7 Hz was a good frequency... Plasmic Physics (talk) 07:29, 31 December 2012 (UTC)

No, it definitely was "10 Bizarre ways to die." Plasmic Physics (talk) 08:02, 31 December 2012 (UTC)

Another contributing factor: he played the sound at ~160 dB. Loud enough for items to be thrown of shelves. Plasmic Physics (talk) 20:42, 31 December 2012 (UTC)

Assuming the story is true, I'm betting it was the volume rather than the frequency that did it. 160 dB involves pressure differences around 4 kPa, which makes for a rather solid full-body impact several times a second. --Carnildo (talk) 03:33, 1 January 2013 (UTC)

Humans encounter that volume often enough at audible frequencies without turning into instant soup. Plasmic Physics (talk) 05:26, 1 January 2013 (UTC)

Resonance is most effective (or dangerous, depending on your POV) on perfectly rigid bodies, with crystals being about as close as we can come. Softer materials, like people, tend to absorb any vibration before it can build up. So, while it still might be possible, it would require far more energy than the proverbial opera singer shattering a champagne glass with her voice. StuRat (talk) 08:22, 31 December 2012 (UTC)

Are you talking through your arse again StuRat? For an object to mechanically resonate, there must be a resonant frequency. For there to be a resonant frequency, there must be mass, and there must be elasticity. The degree of resonance in real objects is determined by "Q", which is the ratio of the elasticity to the degree of damping (frictional loss), and the intensity of the forcing sound or vibration. A perfectly rigid object cannot resonate. First year physics I believe. 121.221.79.244 (talk) 00:27, 2 January 2013 (UTC)

Well, in that perfectly rigid objects don't exist in the real world, I suppose how they behave is indeterminate (if they really were completely rigid, I imagine any sound at all would shatter them, as they would have no capacity to absorb, transfer, or reflect sound energy). However, highly rigid bodies resonate nicely, like crystals. StuRat (talk) 07:03, 2 January 2013 (UTC)

Despite the apparent implausibility of resonance, the cochlea nonetheless detects vibrations according to tonotopy, based primarily on the stiffness of the basilar membrane, which is much smaller than 20m - even, as our article explains, for sounds under 20 Hz. Wnt (talk) 15:38, 31 December 2012 (UTC)

The notion of it being "euphoric" seems absurd, but the search term digs out unreliable and reliable sources interesting for further examination: [7], our own article brown note, a BBC article [8], even a New Scientist article I didn't find on PubMed before [9] ... and I didn't explore more than the first page and a half.

• Anthor source, which come from Chinese National TV China Central Television. This is my rough translation from 0:17 to 1:30:

Infrasonic weapon is a weapon which transmits infrasound that frequency below 20 Hz. The acoustic wave resonant with human body, which make related organ or part of body changing shape, displacing, even fracture to make the man injured or even dead. The weapon is disguised, fast, long distance, making no pollution to the environment, and no damaging to facilities. Nonlethal weapons that every contry is making will become very important in future wars.

Expert: Nowadays, infrasonic weapon has already been used. Typical infrasonic weapon includes: infrasonic generator (most common one at present). In 1995, the US Army tested this kind of weapon in Serb soldiers in Bosnia And Herzegovina. Having been exploded for seconds, Serb soldiers were faint, vomit, and unconscious.

--維基小霸王 (talk) 15:23, 2 January 2013 (UTC)

I'm having some trouble wading through the sea of disinformation out there, but [10] seems to suggest that infrasound weapons are theoretically possible, were examined as of 1992, but (it says) were found unsatisfactory due to trouble reaching the volume needed. Skull resonance per se seems excluded by plausible-sounding claims that the skull resonates at much higher frequencies (Google says it's in here...), yet my personal experience is that particularly low-pitched, dizzying infrasound from about 1/2 hour exposure to a nearby Bobcat excavator on a few occasions causes my coronal suture to get sore, which never occurred from any other cause, so I am perversely reluctant to concede the point. Wnt (talk) 16:04, 2 January 2013 (UTC)

Properties of blood

From my understanding, blood is a shear thinning fluid. So it acts like a liquid when you apply shear to it, I.e. when flowing but when the flow rate is reduced it behaves like a solid and that this is the property of blood which helps with clotting and recovering from injuries. My question is how does this property interact with platelets etc to help with this process? Is it the fact that platelets work better in more viscous fluids? 176.27.208.210 (talk) 13:31, 30 December 2012 (UTC)

why do doctors tell women not to douche

Women have been douching for thousands of years, in fact before modern medicine, Women used to cure infections in that area with douching. Now they tell people not to douche because it may disrupt Flora, as an experiment I tried not washing my skin for a month and got numerous staph infections. There is Flora on our skin, so I don't think there theory Is correct. Although they claim the vagina is self-cleaning, They also claim the ear is self-cleaning, however it is only self-cleaning to an extent, and it should be cleaned at least periodically inside. For example, if a man were to ejaculate into the vagina without a condom in my opinion it should be douched out with plain water. This also used used to be recommended in the olden days, because the sperm (which is a living thing) that does not leak out will basically rot in there.--Mk651117 (talk) 13:35, 30 December 2012 (UTC)

The Reference desks are a forum for asking questions, not a forum for expressing your own personal opinions about things. Looie496 (talk) 14:26, 30 December 2012 (UTC)

(e/c)You've phrased your question in such a way that it appears you're asking for medical advice, which we cannot give. If you have questions about your own habits, you should consult your family doctor. I can point out that our article on douche leads to this Science News article which goes over many of the downsides associated with the practice. Your separate claim of getting multiple staph infections simply by not washing an area of your skin sounds frankly incredible. If true, you should definitely seek medical attention. Matt Deres (talk) 14:28, 30 December 2012 (UTC)

I'm not a female so I don't douche I'm not asking for medical advise. --Mk651117 (talk) 16:56, 30 December 2012 (UTC)

Well this is a reference desk, so here is a reference. Alansplodge (talk) 20:24, 30 December 2012 (UTC)

An interesting quote from that study "In a 1997 meeting of the Nonprescription Drug Advisory Committee of the Food and Drug Administration (149), Dr. Andrew Onderdonk presented data looking at women with abnormal vaginal ecology, such as women with culture-positive vaginal yeast infections (32). His group treated women with either sterile water, a vinegar and water douching solution, or a povidone-iodine solution. Twenty-four hours after treatment with the various douche solutions, the only women whose vaginal microflora returned to normal were the women who used the povidone-iodine douche. This suggested that, in women who have an abnormal vaginal ecology, perhaps due to a vaginal yeast infection, douching with povidone-iodine may be beneficial and may help to return the vaginal ecology back to normal values. "

It would appear that that study says that a vaginal yeast infection can be cured with a single application of an iodine-based douche. It seems to me like the drug companies are trying to discourage douching so they can sell expensive drugs to treat vaginal infections when douching is a cheap alternative option.--Mk651117 (talk) 20:59, 30 December 2012 (UTC)

Sorry, I have no reference aside from my experience as a married male, but "rotting sperm" is definitely not generally a problem for women who do not douche. The problem with your skin experiment is that for your whole life you HAVE disrupted the flora on your skin by washing with soap every single day. By not washing you are not immediately returning your skin to it's "natural" state all of a sudden. There are millions of people around the world who do not wash with soap every day and apart from probably being a bit smelly to our sensibilities, do not suffer from constant staph infections. Vespine (talk) 00:22, 31 December 2012 (UTC)

Just one more note, your opening premise is a logical falicy known as appeal to tradition. Vespine (talk) 00:25, 31 December 2012 (UTC)

Vespine If someone disrupts their flora on their skin by washing It with soap every day that would make them more likely to get staph infections and if they stopped washing with soap for a month It should make them less likely according to the logic doctors have regarding vaginal flora. If this person stopped washing for a month their flora should return to normal by then and and make them more resistant to staph infections if anything. The irony of this is that if you read about staph infections as well as things like folliculitis and cellulitis one of the causes is poor hygiene, which rules out the fact that flora plays much part in infections. --Jason677 (talk) 01:02, 31 December 2012 (UTC)

I don't follow your logic. Flora is a balance, besides, we're talking about internal and external which are probably quite different from each other. But in any case, if you wash your skin with soap, you are removing the bulk of the flora on your skin, so staph infections are not more likely, because the WHOLE balance is too low, when you stop washing, the "bad" bacteria have less "good" bacteria to fight and can end up winning, that's how you get an infection. The bacteria is always there, but the balance has been thrown out. You can't say a month is enough time for the balance to return, it may never return. A similar thing happens when you undergo heavy duty antibiotic treatment, such as chemo therapy, the balance in your gut is thrown out, initially ALL the bacteria are affected, but when they start to recolonise, some bacteria can grow back faster then others and that's what can cause issues. Fecal transplant can be used as a treatment by giving the patient back the colonies of bacteria they previously had to re-establish their previous balance. I'm also not sure about the logic in your last sentance, a lot of infections are caused by bacteria present in the flora, so im not sure how you can deduce that flora doesn't play much part in infections. Vespine (talk) 03:08, 31 December 2012 (UTC)

So according to that logic if woman douched every day then they would not get a infection, only if they stopped douching would it be a problem. That study you posted also said that vinegar douches do not kill the "good" flora in the vagina, only the "bad" flora, for whatever reason. --Jason677 (talk) 12:17, 31 December 2012 (UTC)

No, according to that logic, washing the unbroken skin on your arms can not be compared to washing the mucous membrane inside a vagina. Mucous membranes are specifically susceptable to infections if the mucous which normally protects it is disrupted, for example by washing it off. To be honest, I'm actually not sure what you're trying to argue. What point are you trying to make? It doesn't sound like you actually know what you're talking about, I'm certainly no expert either, so what's your point? Do you dispute why doctors recommend not douching? It seems like there is more then enough references and links in our article to present a pretty good argument. Vespine (talk) 02:37, 2 January 2013 (UTC)

Add indicator lamp to heater

I have a question about electrical circuits. I have an electrical heater at home, powered by mains electricity (220V AC), which I use when changing my baby's diapers so she doesn't get too cold. Many models have a feature where they automatically turn off after a certain period of time (eg 10 minutes), but my heater does not have this feature. I only turn it on to change diapers, but occasionally I forget to turn it off, which is annoying as it uses a fair amount of power.

I would therefore like to add some kind of indicator light/lamp to remind me that the heater is switched on. Is there anything you can suggest which would accomplish this? I thought about wiring a light in series with the heater, but I only have 220V lamps, which wouldn't work in series with another 220V device. Any tips would be appreciated! — QuantumEleven 15:03, 30 December 2012 (UTC)

If you need to ask a question this basic, you are obviously not qualified to work on mains voltage cicuits. Therfore I suggest you take a different tack, which is simpler anyway. Purchase an multi-output extension lead. Typicall units have 4 outlets on a small box about 40 x 150 x 30 mm dependiong on style and country. These incorporate a neon light that indicates the power is on. Plug the extension lead/board into the wall outlet and teh heater into the lead/board. Get into the habit of switching on/off at the wall, and then the light will warn you that you have the heater powwered up. Wickwack 124.182.143.91 (talk) 16:41, 30 December 2012 (UTC)

Neon light ? I've never seen one of those on a power strip. They typically have an LED light (often in the power switch): [11], although older ones might have an incandescent light. If you don't have a wall switch on your outlet, be sure to get a power strip with a power switch on it, then turn the heater on and off there (I use my foot, since it's on the floor). In addition to a switch and indicator light, some also act as a surge protector, but that's more for protecting delicate electronic equipment, so you could skip that feature here, to save some money. StuRat (talk) 21:31, 30 December 2012 (UTC)

LEDs in a power strip??? StuRat, do you have any idea of the nonsense you talk? The Belkin unit you linked to has a neon light in the switch. In most countries, a wall outlet without a switch would be illegal, as the ability to switch off an appliance broken or on fire is an important safety requirement. Keit 120.145.54.24 (talk) 02:44, 31 December 2012 (UTC)

The Belkin unit doesn't say whether it's an LED or neon light. StuRat (talk) 04:06, 1 January 2013 (UTC)

LED is correct. Not neon. I can only imagine the waste of energy. And wall sockets almost never have switches in the U.S. Where are they required? Rmhermen (talk) 03:34, 31 December 2012 (UTC)

? you guys must be young; i'm old enough that my stock of power strips, switches and GFCs with pilot lights, etc. antedate the wide availability of LEDs and rely on the once ubiquitous NE2 bulb, a handy item with a current draw of a few milliamps whose availability at every Radio Shack I miss, due to a lifelong habit of wiring them (with a current-limiting resistor) across the after-the-switch power leads of all appliances such as the OP's heater which did not come with an indicator. Of course, that parallels the general switch from things relying on 110 volts (in America) to ones that run on batteries.  :::Gzuckier (talk) 04:39, 31 December 2012 (UTC)

Don't worry, those NE-2's are still readily available, and will be for years to come. For things that run on AC without any internal conversion to DC, and a myriad of applications that use the special characteristics of a gas discharge, there's nothing better than a small neon tube - cheap, simple, and yes, more energy efficient than a LED. Not as long life as a LED though. Just about every electronics hobbyist shop and trade supplier has them. We had RadioShack/Tandy in Australia for a while. I don't miss them. They stocked a small weird combination of odd bits and pieces at inflated prices. Firms like Dick Smith, Altronics, etc left them for dead. Keit 120.145.54.24 (talk) 05:01, 31 December 2012 (UTC)

Keit, are you going to admit you were once again wrong by saying power strips never come with LED indicator lights ? And how about not accusing me of talking nonsense (when it's you who doesn't seem to know squat about electronics, at least outside of your home country). StuRat (talk) 06:10, 31 December 2012 (UTC)

StuRat, put a sock in it. Not only am I a fully qualified professional electrical/electronic engineer, I have over 50 years experience, mostly in design, senior, and consultancy roles, and while I am not familiar with the US National Electrical Code (as it applies only in the USA) I am fully familiar with practices in countries whose standards are based on European standards, which is most countries in the World, Japan and the USA excepted. And I do know darn well what's in power boards and the like, and its never LEDs for the reasons given by Gzuckier and myself. Stop trying to defend the indefensible. Think before you post, check your facts, and you won't be picked on by me or anyone else (they do squawk now and then don't they?), because you won't be posting such bulldust. Keit 121.215.132.62 (talk) 10:41, 31 December 2012 (UTC)

Keit, WTF is wrong with you ? A simple Google search for "power strip with LED indicator" gives millions of results: [12] (that's more than "power strip with neon indicator"). Then there's our own article on them: Power_strip#Indication. You are the one who pulls this crap out of you ass and passes it off as true. You apparently know nothing about electronics outside of your country, so are utterly incompetent to "correct" anybody else. StuRat (talk) 03:54, 1 January 2013 (UTC)

There's nothing in the Wiki article that establishes that LEDs are used, though there is a single sentence mentioning LEDs. It wouldn't be the first time that a Wiki article has it wrong.

Only a complete idiot would believe that just because googling "power+strip+with+led+indicator+light" returns "about 1,610,000 results" then that means 1,610,000 pages describing power strips with LED indicator lights. What it returns is pages with those words in them somewhere, not necessarily in that sequence. When I clicked on your google link, the 1st page listed was the Wikipedia article. The second page, an Answers.com contribution, has a discussion on ground fault indicators, and a refernce to power strips and a separate unrelated link to LEDs as indicators in general, not related to power strips. The 3rd page, a question and answer page, has LEDs clearly associated with power strips, and also clearly indicates the author of the questions and answers has confused neons for LEDs as he describes a common fault that occurs with NE-2 -style neons when they age and never occurs with LEDs. The 4th page is an illustration of a range of electric products, including power strips with no mention of LEDs in them, and another quite different product with a dimmable LED viewing light in it. The 5th page, MadeInChina.com, is a catalog of a range of products, including power strips (no LEDs) and LED strips for room lighting - quite a different thing.

Get the picture now StuRat? I hope you don't need a comment on all 1,620,000 pages. Perhaps you are like some non-technical folk who think that anything that glows, is small, and is electric must be a LED. Quite often they are not. You even get coloured plastic lenses on Asian electronic equipment that looks just like a typical red, orange, or green led, but behind it is an NE-2 -style neon or even an incandescent pea lamp (as in some Japanese hifi/stereo equipment). But you will make a much better contribution to Ref Desk if you think before you post, and check your facts, rather than abuse anyone who says you are wrong. I know from your old posts you are an intelligent chap - you can do better. Your posts in recent times are getting worse - is there a reason? Keit 121.215.48.51 (talk) 09:54, 1 January 2013 (UTC)

I can't tell which links you refer to by the order of the Google return, since Google seems to return a different list for different people (I get 1,730,000 Ghits, not 1,610,000). I will provide the actual links. Here's the 2nd link returned to me: [13] (the first being Wikipedia). That seems to be talking about actual LED indicator lights on power strips with surge protectors, and they seem to be qualified individuals, being an electrical supply company. A bit further down the page, I find this link, which is similarly a company selling power strips, which claims they have LED indicator lights: [14]. This next link talks about why some power strips have flickering indicator lights and others are solid. According to this site, it's the neon ones which tend to flicker, and the LED ones don't: [15]. I could go on, but you get the point, many web sites talk about LED lights in power strips/surge protectors. Yes, Google gives lots of false returns, but the relative number of returns for LED being more than neon tells us something, that more web sites talk about LED indicator lights on power strips than neon indicators. Given this level of evidence, it's not reasonable for you to continue to insist that power strips with LED indicator lights do not exist. Even though I had not personally seen a power strip with a neon indicator light, I'm perfectly willing to accept that they exist, based on the Google returns, and you should be reasonable enough to do the same. You need to get over this mode of insisting that anything you haven't personally seen or heard of can't possibly exist.StuRat (talk) 03:48, 2 January 2013 (UTC)

I have seen perhaps one outlet per room controlled by a switch by the door, and that outlet is typically used for a lamp. Controlling all outlets with switches would inevitably lead to having clocks switched off, etc. StuRat (talk) 03:40, 31 December 2012 (UTC)

In the UK, every modern outlet has an individual switch (it's about 50 years since unswitched outlets were common). The exception is clock outlets which are fused but unswitched. These are now rare because of cheaper battery clocks. Dbfirs 11:12, 31 December 2012 (UTC)

I see. Do you have a switch by every outlet, or just a giant switch bank by the door ? If so, I sure hope they are labelled. Something else to note is that most rooms in the US have an overhead light fixture, also controlled by a switch near the door(s), so there is no outlet associated with that switch. StuRat (talk) 18:17, 2 January 2013 (UTC)

Yes, every outlet has a switch incorporated in the outlet, not separate. A double outlet has two separate switches. Unswitched outlets have not been normally available for about forty years, though they can occasionally be found in older houses that have not been rewired. The reasoning is presumably that the switches on some appliances can become faulty, so the outlet switch is an extra safety feature. Also, the higher voltage (typically 240v here in the UK) means that there is more risk in plugging and unplugging when the plug is "live" (though two other plastic safety features have been added in the last 60 years). Lighting fixtures are switched exactly as in the USA. Dbfirs 19:15, 2 January 2013 (UTC)

Are your outlets higher than in the US ? Here they are like a foot off the floor, typically (except in the kitchen and bathrooms), which would mean a lot of bending to turn switches on and off down there. StuRat (talk) 23:42, 2 January 2013 (UTC)

Some are still at skirting-board level, but the modern standard in new houses is to place them about 4 feet high to give easy access for wheelchair users. Dbfirs 08:51, 3 January 2013 (UTC)

Since I have a bad back, and have difficulty bending down to plug and unplug things, that sounds great to me. Can you pick me up at the airport ? I'll be on the next flight. :-) StuRat (talk) 19:18, 3 January 2013 (UTC)

You'd better not rush to book your flight, Stu, because the electrics in my house are at least fifty years old and mainly follow the American (and older British) practice of outlets at low level. The only ones at a convenient height are those that I've added. A cheap and easy solution is to mount a short cheap extension onto the wall at a convenient height and plug it in to the low-level outlet. Dbfirs 09:56, 5 January 2013 (UTC)

My current house has multiple outlets per room controlled by wall switches, in lieu of ceiling light fixtures. And yes, it is incredibly annoying; I have mostly put those little covers over them that prevent me from absentmindedly switching them off. Gzuckier (talk) 04:39, 31 December 2012 (UTC)

Better still, get a timer. You see those ones that will turn lights on and off at specific times of day. If you set that machine to turn on and off for just one hour in every 24 hours (say, on at midnight, off at 1am) - then, when you need to use the heater, rotate the dial to "midnight" - until it just turns on - then if you forget, the heater will turn it off again, automatically one hour later. Of course if you don't use the heater then it'll turn on again 24 hours later...but if it's a changing table, it's unlikely that you won't use it at least that often! By all means use a extension cord with a neon indicator too...but this would be a good back-stop. Since heaters use a lot of current, make sure that both extension cord and timer can handle that amount. SteveBaker (talk) 17:29, 30 December 2012 (UTC)

There's a couple of countdown or boost timers which you set and timeout and they're fairly cheap, but in fact the 24 hour timers tend to be even cheaper and all you need do is set only the switch off time and not the switch on time and you've got a good adjustable countdown with them. Dmcq (talk) 19:19, 30 December 2012 (UTC)

You might have trouble finding an appliance timer rated for the wattage used by a space heater. In the US, they typically draw 1500 watts, and those small outlet timers can't handle that. StuRat (talk) 21:27, 30 December 2012 (UTC)

The OP said their voltage is 220 V. Appliance timers rated for either 8 A or 10 A are quite common in 220 V and 240 V countries - that corresponds to 1760 to 2200 W. Keit 120.145.54.24 (talk) 02:44, 31 December 2012 (UTC)

I used to have space heaters hooked up to timers. One timer that I have left over says it is rated to 1700W (125V, US configuration). I don't remember where I bought it, but it wasn't hard to find.--Wikimedes (talk) 12:36, 31 December 2012 (UTC)

The weird thing is, in the U.S. I never even heard of the idea of having switches on outlet plates as a safety measure (outside of ground fault outlets, that is). I never questioned the idea that the "switch" is to pull out the plug. What am I missing? Wnt (talk) 19:30, 31 December 2012 (UTC)

The plug and socket are not designed to be a switch, so you should not routinely switch off by pulling out the plug (or switch on by pushing the plug in. Appliances should always be switched off using the on/off switch provided on the appliance if provided, then switch off at the wall outlet (termed a General Purpose Outlet [GPO] in official standards.), then pull out the plug if putting the appliance away. Switches are designed to give a clean sudden break so that arcing is minimised. However, in an emergency (eg appliance on fire) I would be quite happy to pull out the plug if there's no other option.

Regarding the safety requirement to have a switch at every wall outlet, one must remember that American electrical safety standards are lower than European and other standards (the concept of third pin earthing is comparitively new to USA - the rest of us have had it >100 years). That is not a criticism of the USA because a) it's a lot harder to kill yourself with 110 V than it is with 220 V (albiet still quite possible), and b) the USA was the first country to implement widespread commercial electricity distribution. Doubling the voltage makes switch arcing and wear a lot worse too. Other countries came later and were able to benefit from experience while the USA was stuck with early standards. Once standards are set it is very expensive to change. We saw the same thing in reverse with analog television - Britain was first with 405 lines and AM sound in 1938 - a significant achivement back then, but not really adequate in sound quality nor picture detail. The USA was next, starting TV just after WW2 with 525 lines and FM sound - a significant improvement compared to the British system. Europe and Australia was next in the late 1950's with 625 lines and FM sound and a few minor technical improvements. Nobody would think that made Australian TV engineers smarter than American or British TV engineers - they just came later and drew on American experience. A strong case can be made for 220/230/240 V rather than 110/115 V, especially with countries with lower density towns, but that is another subject. Keit 124.178.141.171 (talk) 00:59, 1 January 2013 (UTC)

The problem with that explanation is that I can't imagine why we would possibly want to switch to a 220 volt standard, even if it were totally free and easy (and if not doing so, why we would want these extra switches). Why the heck would I want a 220V television cable, a 220V floor lamp, a 220V anything, except the appliances that are already 220V with 220V outlets in the U.S. right now (and I am skeptical those are worth the trouble). I've been to some places with 220V and a B&B with a frayed connection to the lamp or a 220V wire running, for some reason inexplicable to man, to the shower head, is a questionable enterprise to my way of thinking...

Actually, come to think of it, if I were starting a new standard I think it would be to run everything on about 5 volts DC, so computers and cell phones and such wouldn't need power supplies. I imagine LED light bulbs could work well with it. I don't know about rigging an electric oven ... but hey, gas is better anyway. :) Wnt (talk) 05:38, 1 January 2013 (UTC)

The pros and cons for various voltages have been discussed repreatedly on Ref Desk, including quite recently. The fact is, each type of appliance or load has its own best or ideal voltage. 5V could never be succesfull, as when voltage is lowered, current must increase to conpensate. A 1 kW heater on 5 V would draw 200 Amps - the cables, plugs, and switches for 200 A would be immense. 110/115 V was not a bad choice for USA as USA has a high population density, with most folk living on small plots of land or no land of their own at all, as in blocks of flats or high rise flats. That in turn makes for short intervals between transformers, so the cost of distribution at final voltage is not too high. In Australia, 240 V was a good choice becasue we have an overall population density only a tenth of that of the USA (and the contrast was even greater when standards were set). We mostly have lived on large land plots, so there is a large distance between transformers. So the cost of final voltage distribution is relatively high in Australia, and the cost falls increased voltage, because the current is less. Keit — Preceding unsigned comment added by 121.215.48.51 (talk) 09:06, 1 January 2013 (UTC)

Why do some carbon compounds burn and others not?

Why don't granite, diamonds, limestone CO2 burn? But, methane and other do? OsmanRF34 (talk) 16:30, 30 December 2012 (UTC)

A chemical will only burn if it is in an environment that allows an exothermic reaction to take place. Looie496 (talk) 16:37, 30 December 2012 (UTC)

And why is an ignited match an environment that allows an exothermic reaction to take place in the case of paper, but not in the case of granite? OsmanRF34 (talk) 16:50, 30 December 2012 (UTC)

It's down to how tightly the carbon is bonded to the other elements in the compound (and to itself). If you burn some methane (CH4 - carbon and hydrogen) in oxygen, you get CO2 and H2O - carbon dioxide and water. The oxygen in the CO2 and H2O is bound more tightly to the Carbon and Hydrogen than those the carbon and hydrogen were bonded to each other in the methane. Put in terms of energy - the amount of energy it took to pull the methane molecules apart was far less than the amount that was released when the carbon and hydrogen bonded with the oxygen - so that reaction happens very easily. The reverse reaction would require massive energy input - lots of energy to pull the carbon and hydrogen away from the oxygen and very little (if any) regained if the carbon and hydrogen could somehow be turned back into methane. SteveBaker (talk) 17:23, 30 December 2012 (UTC)

Your premise is wrong. Diamond#history talks explicitly about combustion of diamond. --ColinFine (talk) 17:30, 30 December 2012 (UTC)

In fact a demonstration of burning a diamond in oxygen was shown in the Royal Institution Christmas Lectures only the other day. You can see it at http://www.bbc.co.uk/programmes/b01pp6bq but you may only be able to watch it from a UK ip adress. Richerman (talk) 18:02, 30 December 2012 (UTC)

It requires a LOT of heat though - the energy input to break apart those strong lattice bonds in order that combustion can occur. You can't just wave a match over it and expect it to catch fire. SteveBaker (talk) 18:26, 30 December 2012 (UTC)

Yes, he used a blowtorch in the RI demonstration. Richerman (talk) 19:07, 30 December 2012 (UTC)

Sorry, I just watched it again to check. He used a hydrogen flame light it and then after a few seconds he removed the flame and the diamond kept glowing as the carbon carried on combining with the oxygen to form CO2. Richerman (talk) 19:25, 30 December 2012 (UTC)

To be clear, carbon dioxide (CO2) is the product of burning, so it doesn't itself burn (it's the most stable combination of carbon and oxygen). Limestone is made up of CO2 which has dissolved in water and reacted reversibly to form carbonic acid (H2O+CO2=H2CO3) and then given up a hydronium (proton) because of alkaline conditions to yield bicarbonate HCO3-, which interacts with calcium ion to produce limestone (CaCO3). Since limestone is made from CO2 interacting by further (non-burning) means that don't require energy in, it doesn't produce energy out by burning. Lastly granite doesn't contain any carbon that I'm aware of. Wnt (talk) 19:21, 30 December 2012 (UTC)

Carbon dioxide can burn (or at least can provide an environment for something to burn). Set light to magnesium ribbon in a CO₂ atmosphere and the magnesium will burn quite happily, stripping the O from the CO₂ and generating a lot of soot. By the way that's probably graphite rather than granite. Tonywalton ^Talk 00:26, 31 December 2012 (UTC)

The OP may be confusing granite with graphite. --NorwegianBlue ^talk 19:54, 30 December 2012 (UTC)

Ah, of course. And that's interesting because graphite is actually used as a refractory. Looking into this, there seems to be some sophistication involved - the graphite might be treated with phosphates, or it might be intended to oxidize before silicon carbide components ... I don't presently really understand the industrial uses. "Graphite does not burn or support combustion. If ground to sub-micron sizes, graphite may ignite spontaneously in air." [16] Hmmm.... Wnt (talk) 00:16, 31 December 2012 (UTC)

Strictly speaking graphite does not burn; no solid does. What happens is that the heat (either initial applied heat, or heat of combustion) causes the graphite (or other substance) to sublimate to gasseous carbon, which burns very readily. It takes a lot of heat to sublimate graphite, you it is difficult to get started. In complex substances, ege wood, coal, pyrolisation occurs - the local heat causes the wood, coal, etc to break down into gasseous components that burn, and solid components (the ash) that will not.

The fact that graphite will burn if the temperature is high enough to sublimate it is why graphite moderated nuclear reactors are inherently dangerous, and there have been some serious accidents in England and elsewhere. If the control rods get stuck, up she goes. Keit 120.145.54.24 (talk) 02:55, 31 December 2012 (UTC)

Actually, the reason why graphite-moderated reactors are dangerous is because of their positive void coefficient -- which essentially means that when the reactor temperature increases, the nuclear reaction self-accelerates, possibly leading to a dangerous runaway reaction, (although we Americans have operated just such a reactor at Hanford Site for decades without any serious trouble). 24.23.196.85 (talk) 06:01, 31 December 2012 (UTC)

That may be so, but it's more complicated than that. And I do mean the graphite can catch fire and has done so. Windscale UK 1957 is an example. A graphite moderated reactor at Windscale had an unexpected temperature increase with control rods fully inserted. The reason was not understood at the time, due to a defective design, and the technicans took the wrong action, ultimately trying to correct it with emergency forced air cooling thru the graphite channels. Locallised very high temperatures had set uranium on fire - that and the oxygen forced in set the graphite alight. The positive reaction coefficient was understood at the time and had little or nothing to nothing to do with it. It is thought that failure to fully aneal the graphite, as required regularly in graphite moderated reactors, was the initial cause. When graphite self-aneals, heat is liberated. Graphite moderated reactors are cheap and simple to construct, but are full of tricks in operation. Keit 121.215.132.62 (talk) 10:27, 31 December 2012 (UTC)

I do not deny the foregoing -- my point is that the biggest operating hazard in a graphite reactor is due to the positive void coefficient. 24.23.196.85 (talk) 04:19, 1 January 2013 (UTC)

Article on energy effects of direct sunlight?

Do we have an article that discusses the effect caused by direct sunlight on a surface? I'm looking for something to describe what's going on in this picture, where sunlight has melted all the snow off the roof except for the area that's shaded by one of the chimneys. Shade doesn't help enough, its parent Category:Shading is actually a graphics thing, and Insolation may be useful, but it appears to be on a global or continental scale instead of something small enough to be measured in feet or metres. Nyttend (talk) 18:01, 30 December 2012 (UTC)

How about Solar gain? Richerman (talk) 18:05, 30 December 2012 (UTC)

Thank you. I've added the photo to the article; is the caption accurate and relevant? "Solar gain is illustrated by the snow on the roof of this house: sunlight has melted all of the snow, except for the area that is shaded by the chimney to the right". Nyttend (talk) 18:18, 30 December 2012 (UTC)

Sounds about right to me but I'm no expert. Richerman (talk) 19:00, 30 December 2012 (UTC)