Wikipedia:Reference desk/Archives/Science/2014 October 15

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October 15

water hands arthritis now

hello

i have recently been alerted to a claim by a fellow piano teacher that washing your hands immediately after playing piano or writing or typing reports or playing parappa the rapper or any other strenuous sort of activity with your hands may eventually result in arthritic symptoms because water erodes rock or something like that

although the rock water weathering thing part i doubt holds any credence is there any scientific basis for these claims? she said she heard it from dr oz some time ago and given his track record and the track records of other talking heads so to speak i would like to know if these claims are true or not thank ~Helicopter Llama~ 00:35, 15 October 2014 (UTC)

Wikipedia has an article titled Arthritis which lists different kinds of arthritis. Nowhere does it (or any articles on the specific types of arthritis) list cleaning your hands as a potential cause, even in relation to piano or video game playing. --Jayron32 01:57, 15 October 2014 (UTC)

Water does erode rock over time, but what the heck that has to do with erosion of the joints is beyond me, assuming you actually have flesh covering those joints, and thus the water doesn't drip directly on them. However, Dr Oz does often follow up otherwise sound advice with some such silliness as "If water can do this to the Grand Canyon, imagine what it could do to your joints". The only way I can picture hand-washing actually affecting the joints is if the water is hot or cold, and that warms or cools the finger joints. Of course, if that was the problem, simply changing the temperature of the water would be the obvious solution. StuRat (talk) 02:01, 15 October 2014 (UTC)

Bone is a living matrix with a calcite substrate. It doesn't "erode" except for osteoporosis which is hormonally and nutritionally mediated, see calcium and Vitamin D/ Otherwise, see your general practitioner who will professionally advise you whether this bee ess is bee ess. μηδείς (talk)

Umm, "bone erosions" is the medical term for the bone destruction that occurs in rheumatoid arthritis, see for example Schett G, et al, Bone erosion in rheumatoid arthritis: mechanisms, diagnosis and treatment. Nat Rev Rheumatol. 2012656-64. PMID 23007741. --109.189.65.217 (talk) 19:16, 16 October 2014 (UTC)

That piano teacher sounds like he heard an old wives' tale in the distant past and somehow stuck with it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:06, 15 October 2014 (UTC)

The explanation given is certainly nonsense - but that doesn't mean that it's necessarily bad advice. I could imagine that washing your hands cools down the muscles - and perhaps that has a deletrious effect? After all, we use hot and cold treatments to help muscle pain and stiffness and to control inflammation. SteveBaker (talk) 14:32, 15 October 2014 (UTC)

So he might be right for the wrong reason? If so, the next step would be to see what doctors (other than Oz) recommend for easing arthritic pain: hot vs. cold. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:37, 15 October 2014 (UTC)

To be clear, I'm not saying that this is good advice - I'm merely pointing out that it might be. For sure, erosion of rock by water has absolutely nothing to do with it...but that doesn't mean that the advice doesn't work. It might (for other reasons) be good advice or it might be completely terrible advice. SteveBaker (talk) 05:05, 16 October 2014 (UTC)

I like to point out that Dr. Oz has had the distinction of "winning" two Pigasus_Awards, for his general quackery and "refusal to face reality". See also the description here [1]. This does not mean the man is incapable of making true statements, but to me it means that most things he says should be treated with a healthy dose of skepticism. SemanticMantis (talk) 16:35, 15 October 2014 (UTC)

My family and its obvious genetic traces are legion. But really, I completely fail to see what the problem with "refusal to face reality" is. I checked with my 387 cousins and they're all as mystified as I am. -- Jack of Oz ^{[pleasantries]} 08:59, 16 October 2014 (UTC)

The thin layer of fat in your skin ought to keep any water on your joints from eroding them. If your joints were vulnerable to water damage because "water erodes rock," then you'd better stock up on scissors... because everyone knows "rock breaks scissors." Of course, you could protect yourself from water-mediated joint damage by covering your joints with paper strips when you wash your hands, because "paper covers rock" (someone stop me... ) loupgarous (talk) 16:28, 17 October 2014 (UTC)

Why do the nuts usually end up on the top of the muesli?

Shaking and stirring the container only mixes the muesli evenly for a while, the nuts seem to be able to "float" to the top. Roger (Dodger67) (talk) 11:38, 15 October 2014 (UTC)

That's a classic question. Please see Granular convection.--Shantavira|^{feed me} 12:08, 15 October 2014 (UTC)

.. aka the Muesli effect (same article). AndrewWTaylor (talk) 12:19, 15 October 2014 (UTC)

LOL @ Muesli effect. You may want to read about Rheology, the "science of the flow of matter" to understand how solid matter can to some degree also "float" aka behave like fluid matter. --Kharon (talk) 12:45, 15 October 2014 (UTC)

Thanks. It's really called the muesli effect.... :)

The nuts will normally be well mixed to start with because the dispenser will have settled into a steady state, shaking and stirring unmixes them. You might also like to look the pictures of circular mounds of stones at frost heavingDmcq (talk) 14:42, 15 October 2014 (UTC)

One interesting counter example is Raisin Bran cereal. They noticed that shipping tended to unsort the mix, and raisins fell to the bottom. So now they add raisins after the box is ~50% full of pure flakes, so that the raisins tend to spread out evenly during shipping. Can't find an online ref, this is described in the book "Why Do Clocks Run Clockwise, and Other Imponderables", by David Feldman. SemanticMantis (talk) 16:30, 15 October 2014 (UTC)

That's clever, thanks for that. Dmcq (talk) 19:37, 15 October 2014 (UTC)

...AKA Brazil nut effect. See here [2] for a nice video demonstration, and links to some relevance for asteroids such as 25143_Itokawa. SemanticMantis (talk) 16:25, 15 October 2014 (UTC)

structural columns

Is the column in this picture supporting any load from the ceiling or building structure. I don't think it is. It looks like its taking no load. The only possible load on it is axial compression just from it being attached to the sides in my opinion. I don't think it's taking any load from the ceiling. Am I correct? http://m.english-heritage.org.uk/about/news/kenwood-house-restored/

The columns at the right hand end in the first photo on that page?

They might just be decorative - but that long pink and white beam might need to be supported in the middle, in which case, they'd be structural. Although the beam isn't under vertical load from structure above it, it does have some weight of it's own - so it's remotely possible that it's really a relatively thin beam that's coated with a bunch of heavy plaster-work decoration. If the beam sagged down a bit, maybe it would bend enough to crack the plaster-work decoration.

I'd guess that the columns are purely decorative though. The beam across them might also be decorative - but if not, it's probably in tension, preventing the walls from moving outwards under the forces from the domed ceiling behind it.

SteveBaker (talk) 14:28, 15 October 2014 (UTC)

I agree with Steve that the beam, if anything, is in tension and if it needed supporting for weight, it most likely would need it from the ceiling so everything is in tension and the weight is transferred to the walls. But the other clues that it's decorative seem to be replication of Greek/Roman Golden rectangle proportions (on edit, our Golden ratio has more. In addition after reading the article on the picture, the original architect Robert Adam returned architecture at the time to the more classical Golden ratio era and developed the Adam style). If the height and width ratio of all the different rectangles created in that room aren't identical, I'd be very surprised (architect should be fired). The height to the beam relative to the width of the room, the height of the columns relative to the space between them, the H/W ratio of windows, bookshelves, etc, are all the same though some are horizontal, some are vertical. Using the proportions in art and architecture are very prevalent and our article sadly lacks more than just the mathematical formulation. Years of watching Donald Duck in Mathmagic Land did not go to waste (though I still can't play billiards). Watch it as it never gets old and will show lots of examples. --DHeyward (talk) 15:24, 15 October 2014 (UTC)

[Reusing ground current]

This question was misfiled at the top of the page, so I've moved it down. Wnt (talk) 13:56, 15 October 2014 (UTC)

After use of electricity unused current returns back through neutral wire which

Is not used later,can we reuse that returned electricity of neutral wire again???

Poster was Diwas pandey

Electricity is made up of electrons in a conductor, which move much like water flowing down a hill. But instead of the height above ground, it is the voltage that matters. When electrons return to ground, they are like water that has flowed down the hill. To get energy out of them, you would have to let it flow even further down (to a positively charged electrode) or pump it back up again (with a battery, for example).

It is possible to shock yourself on a ground wire if you disconnect it from the breaker box. This is because a ground wire is not a ground wire if it isn't grounded. You can connect any number of devices one ground wire to the next (in series) - however, the voltage each receives is reduced, which in many cases means they won't work. That is like taking a fast-flowing stream and giving it a long slow way to go downhill instead - it becomes more sluggish. Wnt (talk) 14:03, 15 October 2014 (UTC)

Ideally ground current is zero. There's no reuse as the net flux of current is zero (except for things that charge up). In the U.S. there are single phase 120V/240V and three phase 120/208V systems (there's others but these provide 120V for common outlets). Ideally, the load is balanced across the 240V or 208V terminals which has the effect of reducing current in the neutral wire preferably to zero. The neutral wire only carries the net difference. This is important for a number of reasons including IR drop (which raises neutral voltage above ground) and ground loops. Balancing loads also allows reduced neutral wire sizing and shared neutrals. By code, the neutral wire is only bonded to ground at the service entrance. --DHeyward (talk) 14:59, 15 October 2014 (UTC)

ebola in animals

Can ebola infect a cat? if it can, would the cat show symptoms? By the way i am not asking for advice and i don't have any immediate concern about my health or any cats, but it does alarm me to see ebola in America.

According to the CDC [3], there is presently no evidence that dogs or cats exposed to Ebola will either become sick or spread the virus. No sick pets have been documented in West Africa or anywhere else. Previous work has indicated that dogs can be affected by Ebola [4] if they have close contact with infected people or animals (e.g. eating corpses), but that the dogs do not seem to develop any apparent symptoms. At present, it is assumed that in the absence of symptoms dogs are unlikely to spread the disease. So dogs and cats are not at high risk as far as we know. However, it may be worth noting that pigs will catch the disease, become symptomatic, and spread it highly effectively [5]. Dragons flight (talk) 15:32, 15 October 2014 (UTC)

There was a case recently with a dog which was indeed euthanized to prevent spread of Ebola; here is a story about how animal rights people collected a third of a million signatures to save the dog. (Gee, I wonder if anyone tried a petition to save the 20,000 Liberians...) Apparently the isolation scheme of leaving the dog with 33 pounds of dog food and a bathtub of water wasn't thought to be good enough. (Feeling glad I'm not a landlord) Wnt (talk) 19:50, 15 October 2014 (UTC)

Yes, Spain destroyed a dog without even attempting to test whether it had Ebola. On the other hand, Dallas has isolated the dog belonging to the sick nurse there and taken steps to provide for its long-term care, with no plans to euthanize it. Dragons flight (talk) 21:25, 15 October 2014 (UTC)

Are they going to simply let it leave isolation once testing shows no signs of Ebola or will they continue to keep it in isolation (perhaps with further testing) until sufficient number of days have passed that they no longer consider it a risk? Nil Einne (talk) 12:23, 16 October 2014 (UTC)

Some searching found [6] which says the dog will be kept in isolation for 21 days and they may not even bother to test it depending on what health authorities suggest and that decomination procedures will be used to dispose of faeces or other material from the dog found in the house. I presume, but it isn't clearly stated, that similar rules will be applied to the dog one isolation. That source also includes pictures of how the dog was taken from the house although the level of caution may be more to do with the house in general that just the dog.

Anyway it seems that the Spanish authorities and Dallas authorities views on this matter aren't actually that different as both seem to consider that the risk from the dog, however low, requires careful management and that testing won't be sufficient to allay concerns. They seem to primarily differ in their views on whether resources should be spent on caring for the dog, and perhaps also on whether it's an acceptable risk to expend that effort (although I'm not so sure on this one, it may be simply the first). It's possible differing views on the rights of the owners (which for better or worse is largely how the human-animal relationship is treated in law) also come in to play [7]. Despite well meaning comments like, [8] it's clearly more complicated than simply differing views on the worth of animal life since both allow the widespread raising and killing of animals for food.

Nil Einne (talk) 13:20, 16 October 2014 (UTC)

Woman having a penis

I understand that a man can have a vagina if he remove or had his penis cut due to cultural or other reasons. But, how does a woman get a penis or is it a man with a penis get a breast transplant or implant? If a man does get a breast implant and doesn't remove his penis and dates a man or marries one, would that make them gay? I am confused on how to understand this transsexual and transgender issue.

See Sex reassignment therapy. Ruslik_Zero 19:25, 15 October 2014 (UTC)

Phalloplasty and Metoidioplasty speak to the surgical processes you inquire about in your first question; in common parlance, these are called "female-to-male" sexual-reassignment surgeries, and a person undergoing these procedures (typically in conjunction with a form of hormone replacement therapy) is known as a trans man, just a person "transitioning" to a female identity is known as a trans woman. A transgendered woman (born male) may choose to undergo hormone therapy alone, they may keep the genitalia they were born with but undergo surgery for breast implants or to create other feminine secondary sexual features, or they may have full sexual reassignment surgery, but in most cases they are likely to identify as female and are said to suffer from gender dysphoria, the condition of perceiving the sex of one's body as differing from the gender that feels natural to them. As to the sexual orientation of two genetic males engaged in an intimate relationship, one of whom identifies as female but has not undergone full sexual reassignment, that's largely a matter of perspective, and opinions vary widely both from those within such relationships and without. Generally, and increasingly, it is considered most tolerant to let those inside such relationships to decide for themselves what the combination of gender identities and physical sexes involved mean about their sexual orientations. It's understandable that some people unfamiliar with these concepts can be confused by the many overlapping and not-always consistent terminology, but the key to understanding the many different perspectives on the matter is to first understand the distinction between sex and gender and to not get too hung-up on nomenclature, whenever the situation allows you to avoid it. Snow talk 08:07, 16 October 2014 (UTC)

Smoke detector placement and orientation

Smoke detectors are commonly mounted on the ceiling, facing downward. But do they actually have to be?

Wouldn't smoke detectors work fine as long as they're facing toward the open air, away from the surface they're against? For example, wouldn't a smoke detector work just as well against the wall, facing sideways away from the wall, or on the floor, facing upwards?

If placed on a bookshelf, does it matter whether the smoke detector is placed on a high shelf or a low shelf, as long as it has open air access?

—SeekingAnswers (reply) 19:53, 15 October 2014 (UTC)

This guide from the National_Fire_Protection_Association says that wall mounting is OK, but they should be within 12" of the ceiling [9]. The reason is fairly simple: smoke rises. Consider a case where there is a small fire on the floor in a corner, and the smoke detector is in the opposite corner. It will trigger sooner if placed near the ceiling, compared to being placed near the floor. SemanticMantis (talk) 20:57, 15 October 2014 (UTC)

And from this instruction sheet for a smoke detector "Smoke, heat and other combustion products rise to the ceiling and spread horizontally. Mounting the detector on the ceiling in the centre of the room places it closest to all points in the room." In a fire a few minutes warning can be the difference between survival and death - go with the manufacturer's recommendations for their product. Richerman (talk) 21:03, 15 October 2014 (UTC)

Near doors in bedrooms is best. ceiling elevation changes are also places where smoke detectors should be placed. In residences, smoke detectors are not really necessary in the center of rooms as fires rarely can develop from any place. Rather, they are placed between points of ignition and people and along their escape routes. Hallways, bedrooms, etc, are where most smoke detectors are placed. usually within 3 feet of a door and within 12 inches of the ceiling. Commercial buildings have them distributed throughout mostly as early warning for Fire Department. --DHeyward (talk) 01:02, 16 October 2014 (UTC)

Why is Germany's power-to-gas so far ahead of the English-speaking world's?

Please compare http://de.wikipedia.org/wiki/Power-to-Gas with http://en.wikipedia.org/wiki/Power_to_gas

Why is the former so much more well-developed? 76.88.167.15 (talk) 21:16, 15 October 2014 (UTC)

Because Germany is technology world leader in many sections of that field. Like for example Type 212 submarines. Also german automotive and mechanical engineering industry is huge and thus takes a big share in the worldwide struggle to transite traffic and industry away from Petrochemistry. --Kharon (talk) 21:36, 15 October 2014 (UTC)

The OP might be asking about the relative development of the two articles in those two language editions of Wikipedia, rather than the relative development of the actual technology in the two countries. Since Wikipedia is edited by its readers, the amount of development of specific articles generally depends on the popularity of that particular language edition, as well as how important some particular topic is within the culture of societies that use that language, but is also subject to randomness based on a few editors being particularly interested in some topic. Because the English Wikipedia has the most viewers and readers, it also has the most editors, so in general, English Wikipedia articles are better developed than corresponding articles in other language editions, such as the German Wikipedia, but in this case, it appears that a few German editors care greatly about the topic and so have developed the article more. —SeekingAnswers (reply) 22:37, 15 October 2014 (UTC)

You are free to copy material between the different language editions of Wikipedia, however you must acknowlege in the edit summary that is was copied from de: If you do not speak German well, you can use machine translation to assist, but you must tidy the resultant English into grammatically correct prose. CS Miller (talk) 15:33, 16 October 2014 (UTC)

I suspect that it has to do with the reunification of East and West Germany. Many of the East German power plants would have been heavily polluting and poorly maintained, and also perhaps incompatible with West German standards, necessitating scrapping those plants and starting fresh. This is a very expensive process, but does provide the opportunity to incorporate the newest technologies. In most of the English speaking world, the situation was not as dire as East Germany, so the temptation was not to scrap outdated plants, but just keep them going with minor upgrades. However, when all the new German plants near the end of their life cycles, they will be in the same situation, where minor upgrades can keep them limping along, at less cost than total replacements. StuRat (talk) 16:00, 16 October 2014 (UTC)

How to convert an arbitrary monochromatic light (its wavelenght) to a displayable trichromatic light (that is an sRGB screen)?

Is there some linear interpolations formulaes which approximate this conversion (as exact conversion is not possible) while complying with the en:Wikipedia:No original research? ... — Preceding unsigned comment added by 77.199.96.124 (talk) 22:41, 15 October 2014 (UTC)

If you read the sRGB article, or any other resource on this topic, you will notice: the outer curved boundary is the monochromatic locus. That means that a wavelength can directly map to the XY colorspace. The formula for this curve is specified by any of several standards; for example, the CIE 1931 standard specifies tristimulus parameters. Then you can use the standard transform to the RGB color space of your choice, i.e. sRGB.

So: if you had pure monochromatic light, you would first compute its corresponding X,Y value by multiplying by the standard tristimulus functions. If you want to over-mathematicalize things, this computation is a weighted integral in which you are premultiplying the stimulus standard function with a dirac delta at the monochromatic light wavelength. In other words, three values are obtained by evaluating the three standard stimulus functions at that wavelength. Next you would multiply that 1x3 matrix by one of the standard 3x3 color space conversion matrices to obtain an "R/G/B" triplet.

Here is some reference code, RGB VALUES FOR VISIBLE WAVELENGTHS by Dan Bruton of Texas A&M / Austin State University Observatory. This code is written in the FORTRAN language, and was the standard model for the MATLAB MuPAD toolbox implementation of RGB::fromWaveLength. His model does not incorporate standard tristimulus functions to approximate human perception; in other words, it is a radiometric, rather than photometric, model.

In actual practice, there's a lot more guess-work and standards-fudging than you might expect! Nimur (talk) 02:35, 16 October 2014 (UTC)

The steps are:

1. Convert from the wavelength to XYZ using color matching functions (as found here, for example) and then to linear sRGB using the matrix multiplication from sRGB#Specification of the transformation.
2. Somehow convert those RGB coordinates into RGB coordinates in the range [0.0, 1.0].
3. Convert that to (nonlinear) sRGB using the formula from the sRGB article.

Steps 1 and 3 are easy. Step 2 is hard because there's no right way to do it. At least one of the three RGB coordinates you get from step 1 will be negative. You can fix that by adding white, i.e. by adding an equal amount to all three coordinates. If you add the minimum amount of white (so that the smallest coordinate is 0.0), then normalize so that the largest coordinate is 1.0, the result will be fine for individual hues, but it will make a weird-looking spectrum with artificial lines and brightness gradients because the amount of white and the normalization factor vary wildly. If you want to display the whole spectrum, you will probably want to add a fixed amount of white across the whole range, and scale by a fixed amount, but this will lead to boringly desaturated colors.

the function that Nimur linked looks very inaccurate and I wouldn't use it if you care about getting the hues right. There's no such thing as a "radiometric" conversion to sRGB. -- BenRG (talk) 17:02, 16 October 2014 (UTC)

Well, BenRG, perhaps you disagree with the utility of that equation; but there does exist such an equation, and it is used by one of the most prominent vendors of image processing software, a package that is used by many researchers across the globe... this specific equation has been published in peer-reviewed journals with applications ranging from color image processing for video compression to hyperspectral imaging research; it has been recognized by the IEEE and the SPIE; it has been adopted by commercial vendors and open-source software...

Presumably, though, you are able to determine that "there's no such thing," and that its accuracy is insufficient for any purpose, so I guess I'll defer to your extensive expertise in the field.

Nimur (talk) 18:37, 16 October 2014 (UTC)

You can look at Bruton's code and at the definition of sRGB and see that the code is wrong. The mathematics isn't very difficult. Most obviously, it puts the RGB primaries (#F00, #0F0, #00F) at 645nm, 510nm, and 440nm, while the correct locations (for sRGB primaries and D65 white point) are roughly 610nm, 550nm, and 465nm, so the hues are actually very far off. The code doesn't claim to be based on sRGB, and in fact predates sRGB (which was published in late 1996), but I don't see how it could be accurate with any red-green-blue primaries. 510nm is more teal than green, and 440nm is violet.

I do see evidence that this function is very widely used, to the point that it's hard to find spectral images that show the correct hues, but this one seems to. This chromaticity diagram is also accurate. (Many other chromaticity diagrams on Commons and the web are incorrectly green at the top, such as this one, but they're otherwise pretty accurate.)

You wrote "His model does not incorporate standard tristimulus functions to approximate human perception; in other words, it is a radiometric, rather than photometric, model." That doesn't make sense, and I think you made it up. That was what I was trying to say, more politely, when I said that there's no such thing as a "radiometric" conversion to sRGB. -- BenRG (talk) 21:25, 16 October 2014 (UTC)

Why not simply use Yxz and let the device apply whatever transforms it needs to display the data containing the brightnesses and chromaticities? Count Iblis (talk) 20:10, 16 October 2014 (UTC)

Old school is to use a rotating color-wheel with area or yime of each color tuned to the sensors sensitivity. Thre lenses, each with a filter did the same thing. --DHeyward (talk) 08:22, 19 October 2014 (UTC)