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March 13

What is the reason that it's not recommended to put hot foods in the refrigerator?

Normally people don't put hot food in the refrigerator. Is there a basis for that? if there is, what is the reason for that? 93.126.116.89 (talk) 00:34, 13 March 2018 (UTC)[reply]

If the food's too hot and too big (i.e. it has too much thermal energy), it can warm up the contents of the refrigerator so rapidly that the cooling equipment can't keep up, so you'll end up warming the refrigerator's interior too much. Nyttend (talk) 00:40, 13 March 2018 (UTC)[reply]

Hot food will produce allot of water vapor that will condense and freeze at the cooling element, building up a growing ice coat around it which prevents the fridge to cool down the air effective. Its also a waste of energy because the hot food will cool down fast without investing additional electrical energy with the fridge. Additionally the whole concept of preservation with a refrigerator is to keep the temperature low enough to keep all microorganisms in a Hibernation state. Every time the food gets warm again the microorganisms start eating and reproducing, thereby cutting down the time of the food they are on to the state of spoiled. So its no imminent drama if you put some hot food into your fridge but its still wrong in many ways. --Kharon (talk) 05:23, 13 March 2018 (UTC)[reply]

Also the water vapor from the hot food will condense ON the hot food as well and make it soggy. 2601:646:8E01:7E0B:0:0:0:64DA (talk) 06:41, 13 March 2018 (UTC)[reply]

Also, if the hot food is in a type of container that will crack from thermal shock, you don't want that to happen. --69.159.62.113 (talk) 16:54, 13 March 2018 (UTC)[reply]

I used to keep pot of boiled milk in refrigerator. Did so every day for a week or two. The acrylic sheet on which I used to keep the pot gradually developed cracks due to sudden temperature difference. Now I let it cool down a bit but when it is still hot I put in refrigerator to cool it quickly to prevent growth of microbes. manya (talk) 07:45, 13 March 2018 (UTC)[reply]

The best way to cool an item like this is to immerse it in cold water for a while, rather than put it in the refrigerator, for the reasons listed above. --TammyMoet (talk) 13:05, 13 March 2018 (UTC)[reply]

The problem that the contents of the fridge will heat up if you put hot stuff into it, is a lot worse with modern fridges that are a lot more energy efficient compared to older ones. Old fridges with poor thermal insulation can more easily deal with hot food, because they are pumping out heat at a much faster rate anyway. To store freshly prepared food you should cool it asap using e.g. cold water as suggested above. I usually put the food cooled in this way in the freezing compartment of the fridge, not to freeze it but to cool it rapidly down to just above freezing point. Also, the freezing compartment is isolated from the rest of the fridge, and the fridge will start to work immediately if you put something in there, while if you put something in the fridge, it will only start to cool the contents if the temperature rises above a set point. The faster you cool the food to below 10 C the better, a rule of thumb is that every hour at room temperature takes away about one day of safe storage time at fridge temperatures. Count Iblis (talk) 18:35, 13 March 2018 (UTC)[reply]

I just stick it outside for a few minutes. At −37 °C (−35 °F) it don't take long. CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 23:03, 13 March 2018 (UTC)[reply]

Err. What do you do in those few short and very long summer days in Cambridge Bay when temperature it gets up into in to the 80's ? Do you just eat Eat MacDonald's hamburgers and French fry takeaways? Come on. You must have fridge, otherwise you beer will go off. Oh! That is providing you're allowed to drink beer up there :¬) --Aspro (talk) 16:27, 15 March 2018 (UTC)[reply]

I'm not sure the last time I saw 80 °F (27 °C). Couple of summers ago we were in Hay River, Northwest Territories and it was 25 °C (77 °F) and that was more than hot enough. For MacDonald's I would need to go to Yellowknife and the return fare is over $2,000 so not really worth it. Of course we can get take-out burgers and fries from any of the 5 restaurants in town. Beer is allowed here but again you have to get it from Yellowknife, so hard liquor gives you the best value. And every house has a fridge and most houses will have a chest freezer as well. CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 12:44, 16 March 2018 (UTC)[reply]

Cormorant identification

What species are these? They looked more like Phalacrocorax auritus than any other North American species I found, but these look green, not the black of this species. But maybe it's my colorblindness, making me imagine that I'm seeing a dark green when it's really black. Nyttend (talk) 00:35, 13 March 2018 (UTC)[reply]

I'm not good with cormorants, but these don't appear green to me. However, while I have perfect colour vision, I'm not sure we can trust this image's colours as it has clearly been altered to compensate for the low-light. Matt Deres (talk) 02:03, 13 March 2018 (UTC)[reply]

Well, I used flash, but it's just as it came from the camera; I don't have any photo-editing software aside from Windows Paint. Nyttend (talk) 02:27, 13 March 2018 (UTC)[reply]

Yes, but the camera itself has built-in imaging software that takes the picture from raw data to jpeg. - Nunh-huh 05:29, 13 March 2018 (UTC)[reply]

Ah, okay; I thought this meant that it had been photoshopped. Nyttend (talk) 12:11, 13 March 2018 (UTC)[reply]

That definitely looks like a Double-crested cormorant to me. Though in the image given in that linked article, there are clearly some green shades. Polyamorph (talk) 12:17, 13 March 2018 (UTC)[reply]

Sterilizing hamsters

Miniature hamsters I bought (here in China) used to breed. Now they do not. I buy new ones when they die of old age. I suspect the wholesaler gives them some drug just before selling them to stop them from breeding. Is this possible. Anna Frodesiak (talk) 13:07, 13 March 2018 (UTC)[reply]

The answer may be more simple. “Warning. The following may read like something that has just come out of the Twilight Zone.“ You know how the Monsanto company spend billions convincing us that the GM's are safe and they are, - aren’t they? Because Monsanto spend billions cherry picking scientific proof that shows no health issues. But what about the Glyphosate herbicides? I just had to google Hamsters, Glyphosate, and Infertility and loads of stuff comes up. American human fertility rates are plummeting ( there could be other reasons for this but this includes couples that are desperately trying to start a family). What are you feeding your hamster on? The cheap GM stuff from the pet store? Make your own mind up. Please report back on how you got them breeding again. --Aspro (talk) 14:56, 13 March 2018 (UTC)[reply]

@Aspro: I just had to google Hamsters, Glyphosate, and Infertility and loads of stuff comes up. If you googled "moon landing hoax" or "electrosensibility health scandal" or "homeopathy discredited by Big Pharma" or "Holocaust did not happen" or "how dowsing works" or anything of the kind you would also have seen loads of stuff come up. You inconsciously preselected what conclusion you expected, the query reflected that and the results obliged.

Now I know next to nothing about hamsters, fertility, and glyphosphate, and it may well be that you are correct. But you should really, really, really have put up sources rather than giving a rant with vague pointers (and prefacing it with a warning that is is a rant does not make it any less a rant).

For instance, here's a serious-looking source that says (see paragraph I.C) that GM crops in China are mostly limited to cotton and papaya (at least until 2010), i.e. not stuff hamsters eat. Presumably the OP's hamsters are fed on local (=Chinese) pet food. Tigraan^{Click here to contact me} 16:53, 13 March 2018 (UTC)[reply]

As this is the science desk, I need to point out that Aspro's rant above has no basis in peer-reviewed science. Read it at your own peril. Fgf10 (talk) 18:44, 13 March 2018 (UTC)[reply]

Perhaps they stopped selling you females? Greglocock (talk) 15:45, 13 March 2018 (UTC)[reply]

I have not heard of terminator technology being used on livestock, but I cannot formally rule it out. I know of less-than-reversible sorts of male contraception like cottonseed oil that affect humans ... no idea how it affects a miniature hamster. I also have no idea if the entire randy colony of hamsters has simply caught a bad case of chlamydia (apparently Chlamydia muridarum does infect hamsters, according to our article), nor whether that sterilizes hamsters. In biology anything is possible, but not much is likely. Wnt (talk) 23:31, 13 March 2018 (UTC)[reply]

Just to let you all know, we feed the hamsters grains we buy, like whole oats, and also vegetables and peanuts. No pet store food.

Also, this sterility is present in the last few groups of around 8 hamsters we bought. We just got a new group and they are still too young to breed. We shall see. Anna Frodesiak (talk) 01:07, 14 March 2018 (UTC)[reply]

Ooh, I just found Chemical castration. Could the wholesaler get a hold of some of these chemicals, like SpayVac? Anna Frodesiak (talk) 01:09, 14 March 2018 (UTC)[reply]

Chemical castration isn't really permanent, and it seems like an added expense is implausible. I mean, it seems more conceivable (or at least more amusing) to picture a hamster assembly line passing beneath automated robot assembly probes that implant intrauterine devices in all the females. (I suppose every once in a while they get a male by accident, or the maintenance technician's finger, with tragic results) Wnt (talk) 03:11, 14 March 2018 (UTC)[reply]

But suppose a wholesaler could give the hamsters something in their food just before sale that would stop them from having babies. Their sales would increase. Anna Frodesiak (talk) 12:10, 14 March 2018 (UTC)[reply]

I was going to say I never heard of any such thing and doubted it was possible, but naturally I just had to try a quick web search first... came across [1]. Here is the PubChem entry. Says it causes ovarian tumors in mice but not in rats, and "in mice, the ED50 for the reduction in small oocytes by 4-vinylcyclohexene was 2.7 mmol/kg, whereas, no detectable oocyte loss occurred in rats at the highest dose of 4-vinylcyclohexene (7.4 mmol/kg)." PubChem as a compilation isn't exceptionally reliable, but it copied that abstract from here. Another study says " 4-vinylcyclohexene diepoxide (VCD, 40 mg/kg), was used to induce premature ovarian failure (POF). Methylparaben (MP, 100 mg/kg), propylparaben (PP, 100 mg/kg), and butylparaben (BP, 100 mg/kg) dissolved in corn oil were treated in female 8-week-old Sprague-Dawley rat for 5 weeks." [2] It also has some effect on hamsters: "Siberian hamsters were treated with VCD (240mg/kg i.p. daily for 10 days) during short days, and outcomes were compared with reproductively active females that were maintained and treated in long days. Primordial follicle numbers were significantly reduced by VCD under both day lengths, and reproductive quiescence in short days did not appear to render the ovaries less susceptible to VCD-induced follicle depletion." [3] I don't know if it works on proles but given the widespread use as an industrial chemical I imagine the data should be available. Wnt (talk) 15:30, 14 March 2018 (UTC)[reply]

Holy moly, Wnt. I think that may be it. Anna Frodesiak (talk) 19:24, 18 March 2018 (UTC)[reply]

Thank you all for the very thoughtful answers! Anna Frodesiak (talk) 19:24, 18 March 2018 (UTC)[reply]

Discarded plastic bags everywhere while there is a shortage of fuel

I watched a documentary, and it showed people using discarded plastic bags as cooking fuel. The people were breathing fumes. Is there a cooker that can burn old plastic bags without harming people? Anna Frodesiak (talk) 13:10, 13 March 2018 (UTC)[reply]

Bags are, in general, polyethylene. As a fuel it's pretty clean. As a pure hydrocarbon it contains only carbon and hydrogen, so the exhaust products will be carbon dioxide and water vapour. At worst, if burned in restricted airflow, carbon monoxide.

PVC, also used to make thin films for packaging, is another matter. The chlorine content is a problem if you're going to burn it, as are the plasticizers. Andy Dingley (talk) 16:24, 13 March 2018 (UTC)[reply]

The fact that the completely burned products are safe does not make burning the substance itself safe. One of the byproducts of incomplete combustion of polyethylene is surely going to be ethylene oxide. For that, the CDC states, "Ethylene oxide gas may produce immediate local irritation of the skin, eyes, and upper respiratory tract. At high concentrations, it may cause an immediate or delayed accumulation of fluid in the lungs. Inhalation of ethylene oxide can produce CNS depression, and in extreme cases, respiratory distress and coma. In some persons, ethylene oxide exposure may result in allergic sensitization, and future exposure may cause hives or a life-threatening allergic reaction." Looie496 (talk) 16:56, 13 March 2018 (UTC)[reply]

Whilst ethylene oxide wouldn't be a good thing, you're not going to produce that (or at least, not release a significant quantity of it) for a typical polyethylene flame in an adequate air supply. Andy Dingley (talk) 17:34, 13 March 2018 (UTC)[reply]

Google for diesel from waste plastic and take also a look on The Ocean Cleanup project. There are some people from India and also in Saxony, Germany. Buying meat in a super market today, You get a plastic package made from several plastics and coatings of several other plastics to keep fresh and save material. Conventional plastic recycling on this fails caused by the several different plastic types in one piece of plastic. Later production should be a process like performed in an oil refinery. --Hans Haase (有问题吗) 18:13, 13 March 2018 (UTC)[reply]

Plasticizer chemicals have a potential to be very harmful since they are suspected to interfere with human hormones. However "fuel" can contain very harmful chemicals as well, especially in developing countries where unrefined Crude oil is often used, since these can contain for example Naturally occurring radioactive materials and other poisons. --Kharon (talk) 12:14, 14 March 2018 (UTC)[reply]

"adequate air supply" may be the sticking point here. Many cooking fires are extremely inefficient.

Stoves, even simple camping stoves, with proper air-flow can greatly improve the quality of life for people still relying on cooking stoves. At least, that's the premise of a number of businesses and charities that supply such stoves to third-world countries. BioLite#HomeStove is the first one that comes to mind, but there are a few of them. ApLundell (talk) 00:09, 16 March 2018 (UTC)[reply]

Hi ApLundell. So, can that run on old plastic bags? Anna Frodesiak (talk) 07:15, 16 March 2018 (UTC)[reply]

"Improved cooking stoves" have been a stalwart of the appropriate technology movement since the start. Victor Papanek, for one, has written about them. Andy Dingley (talk) 10:19, 16 March 2018 (UTC)[reply]

Almost certainly not. A nice stove like that one will probably burn them more completely than normal cook fires, but plastics are too complicated, and unpredictable for an ordinary stove to reliably burn them safely. There's probably some specially made bio-plastics that would be OK in a good stove, but they would be a small minority, and there'd be no reliable way to identify them. ApLundell (talk) 22:15, 19 March 2018 (UTC)[reply]

What I'm getting at is a stove that safely runs on plastic bags. It would stop people from getting sick from fumes, would provide fuel, and kids would be running around gathering old bags for mom, which would clean up the environment too. Is there such a stove?

Anna Frodesiak (talk) 07:15, 16 March 2018 (UTC)[reply]

No, there is not. Almost every kind of plastic will release toxic fumes when burned, to a greater or lesser extent. They will burn, but they will not be safe to burn. Bastun^{Ėġáḍβáś₮ŭŃ!} 09:23, 16 March 2018 (UTC)[reply]

There are a couple companies apparently talking about offering stoves intended to burn plastic. The one that seems farthest along is the Energant K2, which claims to be able to safely burn fuel that is up to 8% plastic. [4] Modern high-efficiency stoves can reduce smoke by ~95%, and the same high efficiency helps to more thoroughly burn the fuel and reduce the number of toxic products. This would obviously be an advantage if one is going to try burning plastic. Of course, it also matters what you burn. Burning polyethylene is already much less hazardous than burning PVC or fluorinated plastics. However, it seems like their product development has stalled since they discussed it more than 3 years ago but it is still not available for purchase as far as I can tell. Perhaps the idea of a safe stove burning (small amounts) of plastic was still more wishful thinking than reality. Dragons flight (talk) 11:11, 16 March 2018 (UTC)[reply]

I guess, You will find the information, You are looking for in Polyoxymethylene dimethyl ethers (OME), (in German Polyoxymethylendimethylether or Oxymethylendimethylether). --Hans Haase (有问题吗) 08:19, 17 March 2018 (UTC)[reply]

Bastun, never safe, understood. Dragons flight, only 8% max., and wishful thinking on the best stove yet, understood. Pity. Hans Haase, thank you dear, but I found nothing much there. Anna Frodesiak (talk) 19:36, 18 March 2018 (UTC)[reply]

Oh, well. Thank you all for taking the time. I guess Earth and its silly fools will all have to live with these trillions of plastic bags everywhere. (Oh, and I just saw someone buy a bundle of zippy bags in a larger zippy bag and the shopkeeper put them in a bag for the customer. I'm not kidding. I asked why, and he said because that bag had a handle. Sorry Earth. We're not that bright.) Anna Frodesiak (talk) 19:36, 18 March 2018 (UTC)[reply]

Look on the bright side. Plastic represents carbon that won't be entering our atmosphere any time soon.

Once the bag has been manufactured, and if reuse as a bag isn't an option, then it'd probably be better for the environment to just bury it somewhere rather than burn it and contribute to both global warming and local smog. ApLundell (talk) 22:07, 19 March 2018 (UTC)[reply]

I constructed a small tea light out of aluminium foil, using an asbestos fiber wick, and it appears to burn HDPE milk containers quite cleanly. ChemWarfare (talk) 11:26, 21 March 2018 (UTC)[reply]

Vitamin K

I switched to a multivitamin that does not have vitamin K like my old one, since I still want vitamin K I plan to get it from food. The vitamin k article lists vitamin k1 (mainly in certain vegetables) and k2 (mainly in meat and dairy), but my old vitamin just says vitamin k. Does it matter which one you take? I am also confused by how much you need, since my vitamin lists the amount you need in mcg but wiki lists it as IU, what is the conversion?--User777123 (talk) 18:58, 13 March 2018 (UTC)[reply]

In case you don't know, mcg is a terrible way of writing μg, the actual unit. That might help with your searches. Fgf10 (talk) 19:35, 13 March 2018 (UTC)[reply]

Actually, it is not a bad way, but you're right it won't do well in searches and is widely considered obsolete. I just tried out Google and got four different sets of results with µg (using the HTML version), μg, microgram, and mcg. But it could be worse ... in the old days people would use pre-Unicode word processors where µ is just an "m" in symbol font, and inevitably they would mess with their fonts at the last minute before submitting a draft, which means that any "mg" published in the 1990s is like as not to be micrograms. I suspect, but do not know, that the Venezuelan horses killed by selenium were victims of something similar involving their home pharmacy's special recipe. Wnt (talk) 21:57, 13 March 2018 (UTC)[reply]

Your body actually stores, and uses, vitamin K2 (unless you are really a vegetable). However, any K1 in your diet gets converted to K2 by the bacteria in your gut - so it makes no significant difference which one you take. Wymspen (talk) 23:28, 13 March 2018 (UTC)[reply]

I've seen claims vitamin K is not even something that needs to be supplemented in most people with ordinary diets, an attitude our article reports but not enthusiastically. There are many people on warfarin whom doctors believe need to have less vitamin K activity than their diet would naturally provide. On one hand, there is thrombosis, heart attacks and strokes, death; on the other side uncontrolled bleeding, shock, ischemia, hematomas, death. You pay your money and take your chances. Wnt (talk) 23:38, 13 March 2018 (UTC)[reply]

Trying to answer the OP's question, I don't see where Wikipedia lists Vitamin K recomendations in IU. There may not be an IU measurement for Vitamin K (each vitamin has it's own IU standard that is developed individually, it's... confusing) and Vitamin K and Reference Daily Intake and Dietary Reference Intake list recommended Vitamin K intakes in micrograms. I'm not sure where on Wikipedia the OP is seeing it listed in IUs. But if they are looking for Vitamin K recomendations, there's three sources that list it in micrograms. --Jayron 32 19:27, 14 March 2018 (UTC)[reply]

March 14

Elbow skin

Does the skin on human elbows have a special scientific name, and if so what is it? FreeKnowledgeCreator (talk) 02:28, 14 March 2018 (UTC)[reply]

There is no term for the skin. It is not wenis or wagina, as Google searching will tell you. 71.85.51.150 (talk) 09:57, 14 March 2018 (UTC)[reply]

If you refer to thickened skin areas these are generally called Callus or in this case simply "elbow callus". --Kharon (talk) 11:59, 14 March 2018 (UTC)[reply]

You can certainly develop a callus on your elbow - it's possible - but the loose flap of skin there has more to do with the natural loss of elastin and collagen in skin as it ages. As a major joint, the skin gets stretched at the elbow and, with age, it ceases to rebound as it used to. Regardless, I'm pretty sure this question has to do with the "wenis" or "weenis" hoax going around. Matt Deres (talk) 02:57, 15 March 2018 (UTC)[reply]

Uh, no, not really. I don't follow puerile hoaxes. It was just a question, and Kharon answered it in a satisfactory manner. FreeKnowledgeCreator (talk) 02:03, 17 March 2018 (UTC)[reply]

If you follow that line, you get a specific answer to the question, as was done by this IP editor:

See here:[5].

- 86.152.38.218 15:45, 15 March 2018

Lol, I never heard of that before, but there was a character named Wienis in Asimov's Foundation series that I read as a teenager. I remember sniggering over it. 173.228.123.121 (talk) 07:10, 19 March 2018 (UTC)[reply]

can any odor be smelled during rain?

If there is a decomposing carcass, can the stink be smelled during a heavy downpour? Thanks. — Preceding unsigned comment added by 49.207.190.13 (talk) 14:29, 14 March 2018 (UTC)[reply]

Yes of course. Even humans notice the "clean" smell in and after a thunderstorm, which is actually a rise of ozon particles in the air. As you may know many animals have superior Olfaction, some a million times more sensible than human senses. They can even smell unterwater! --Kharon (talk) 17:07, 14 March 2018 (UTC)[reply]

You probably mean ozone, not "ozon". The smell of ozone is more irritating than pleasant. As Matt Deres says below, the topic is more fully treated in our article about petrichor, a word that will be familiar to Dr Who fans. --Trovatore (talk) 22:09, 14 March 2018 (UTC)[reply]

And in case someone invokes the old trope about the smell of "ozone" at the seaside, that smell is actually rotting seaweed. {The poster formerly known as 87.81.230.195} 90.211.131.202 (talk) 21:37, 15 March 2018 (UTC)[reply]

Ozone Park must've been named by someone misinformed. Sagittarian Milky Way (talk) 20:52, 16 March 2018 (UTC)[reply]

Recent research indicates that it depends on the specific odor. A 2017 paper in Science titled Poor human olfaction is a 19th-century myth says "When an appropriate range of odors is tested, humans outperform laboratory rodents and dogs in detecting some odors while being less sensitive to other odors. Like other mammals, humans can distinguish among an incredible number of odors and can even follow outdoor scent trails." [6] [7] CodeTalker (talk) 19:14, 14 March 2018 (UTC)[reply]

See also petrichor for the general "smell of rain". Matt Deres (talk) 21:08, 14 March 2018 (UTC)[reply]

Why do my sunglasses make purple look white?

I got them at a Dollar Store that only charges a dollar for everything, so they're nothing special. Here is more about them. A sign at a college near where I live changes every few seconds, and if the words or background look white without the sunglasses, they look purple with them.— Vchimpanzee • talk • contributions • 16:24, 14 March 2018 (UTC)[reply]

You know, the for $1.5 pairs from the gas station make purple look like...purple. You get what you pay for I guess ;) —SerialNumber54129^{...speculates} 17:18, 14 March 2018 (UTC)[reply]

I would hypothesize that the sign that changes every few minutes uses something like a light emitting diode that emits in a fairly narrow range of frequencies to produce each of three colors (RGB). Purple is R + B, which are transmitted well by the sunglasses, but the narrow peak of green light might be at the same frequency as a dye in the sunglasses. Perhaps the maker of the sunglasses, sort of like the maker of the display but in reverse, assumes that if you block out R and G and B in roughly equal amounts, the effect is simply a darkening of what the user sees. But if there is a narrow-frequency source that happens to match a narrow-frequency absorption, then the output will be very different to the human eye than expected! Wnt (talk) 18:52, 14 March 2018 (UTC)[reply]

Wnt has nailed it. "Looks white" is no longer any guarantee that some light source is "white", just that it fools eyes into thinking it is. This was an issue for a long time with fluorescent tubes, but with ubiquitous LEDs it's now becoming very obvious. I'm fitting a paint booth into my workshop and I've just gone back to incandescent lights for it, as the other lighting makes it impossible to correctly [sic] judge paint colours. Andy Dingley (talk) 19:05, 14 March 2018 (UTC)[reply]

You could do it with graphene. [8] You could do anything with graphene if you could do anything with graphene... actually though, I thought there was a trick for converting laser light to "white" light using non-graphene foam, or something, which I'm afraid I've forgotten, and I wonder if there's some other comparable technology. Wnt (talk) 19:16, 14 March 2018 (UTC)[reply]

It's quite likely that we'll see graphene or other metamaterials replacing existing phosphors in future lighting technologies. Their ability to act as broad-band phosphors gives much more natural lighting, rather than the few narrow spectral lines of RGB LEDs in combination, which are increasingly making any general lighting into an Ishihara plate. Andy Dingley (talk) 20:46, 14 March 2018 (UTC)[reply]

I wouldn't say the spectra of decent high CRI white LEDs is 'few narrow spectral lines in combination' although it's true they still have peaks. But then again so does much of what people call natural light to some extent. [9] [10] [11] [12] [13]. (I've tried to find decent research articles to include although maybe they aren't always the best. I believe one of the problems is that while there is a lot of research, quite a lot of it is proprietary and not that well published.)

Of course Colour rendering index isn't perfect as we know [14] (also our article). Still by now, most real developers (I.E. not the cheap Chinese factories trying to tick some box) of high CRI LEDs have moved beyond simply having high CRIs, including ensuring high R9 values one of the common weakpoints and often also high Colour Quality Scale too. Probably other things too, if you're actually in the market for high colour reproduction white LEDs, I suggest you look in more detail. For example, I think TLCI is still generally a separate thing from high CRI if that's something that matters to you. But maybe you can find some which achieve both.

Anyway whatever personal opinions of high colour rendering white LEDs, 'a few narrow spectral lines' seems high questionable. I mean even the classic white LEDs which has clear spectral deficiencies isn't really that, it's still fairly continuous. (See the earlier sources or the later ones.) We aren't talking about ancient fluorescent lights here.

Well unless you count light outside the visible spectrum but the obvious question is why? Efficiency demands suggest to me it's unlikely there will be that much usage of LEDs with significant light outside the visible spectrum except for specialised purposes like grow lights (and these will probably often be intentionally different from natural light). I mean I don't know what 'visible light' is for cats and dogs but I can't help thinking that pet friendly LED lights is always going to be a small market. If you have specific reasons for wanting non visible light, then I guess most LEDs suck for your purposes, but that doesn't mean most people have these demands.

BTW in case these is some confusion, the classic white LED is often only a blue LED with a yellow phosphor generally, Cerium-doped Yttrium aluminium garnet, [15] [16]. No RGB is involved. Modern high CRI LEDs generally have a more complex phosphor mix but I don't know if it's accurate to call this mix RGB. Probably RYB if you include the original blue component of the LED since I think one of the common things is to add a red phosphor. Some of the even fancier ones possibly add more, but even then I think many still have the yellow, so maybe you'll have RYGB or something. (I'm sure someone can find a R-G phosphor B LED, but I'd like to see some evidence this is a common thing.) You can get RGB LEDs but these are a rarity used for specific applications (LEDs which let you change colours for purposes including colour changing signs like Wnt mentioned) as they cost more and have other disadvantages.

As for graphene or metamaterials, never say never. But I'm far from convinced it's definite. We are getting good at using what we have, so IMO there will need to either be a significant efficiency or performance improment other than pure spectral one, cost or ease of production advantage (which probably ultimately comes down to cost anyway). See for example these comments from a researcher [17]. Of course it's a promotional story from the university and I don't even know how well recognised the person is in the field, and even if they are reputable they're only one person.

But if we look more widely, while there is interest in different production techniques, including graphene [18] [19] [20], one of biggest areas of active research seems to be quantum dot LEDs for general illumination (and not just displays) [21] [22] [23] so AFAIK not what are generally called metamaterials (although Graphene quantum dot is one are of interest [24]). And you'd note in both cases while colour rendering is mentioned, what they concentrate on is efficiency and other such gains.

Actually this is also reflected in the research articles on high CRI white LEDs. One of the big issues is how to add red without adding too much infrared or losing efficiency or luminous efficacy for other reasons. Getting a consistent colour spectra is also desirable since Product binning adds cost etc especially if you end up with too many of the stuff you don't want. (Well there are also other things like lifespan, including consistent colour and CRI over that life, as well as uniformity of light, how temperature affects performance and life, etc. Different technologies may or may not help with these.)

Particularly with the concern of blue light and circadian rhythms, there is increasing interest in tunable CCT and adjusting blue light level, while maintaining a high CRI [25] [26] (also the earlier one on graphene quantum dot). But even if this does become widespread, however it is achieved, if anything this speaks against an excessively broad spectrum. You don't want one that's only a few lines sure, but you want full one largely only within the visible light range and where you can cut down the blue light when you desire.

Nil Einne (talk) 07:52, 15 March 2018 (UTC)C)[reply]

Reading Wnt's source, I guess one issue I didn't touch on is the blue peak. This is something which it's true is still not dealt with by phosphor converted blue LEDs. It's probably true there's no easy solution. Proposals have includes phosphor converted violet LEDs instead of blue [27], but this has concerns including whether violet is actually any better. The other alternative would be to abandon phosphor conversion. I'm not convinced replacing current phosphors with graphene or something else would work, you'd likely need to modify basic operating principles and stop simply converting blue light . For many purposes you could probably simply filter the peak but with an obvious loss of efficiency/luminous efficacy. The obvious question is how much of a concern the blue peak is. Even per my comment above about concerns of blue light and circadian rhythms, as shown in the above sources the blue peak for low CCT high CRI lights tends to be rather small since you don't need much light in the blue part of the spectrum anyway so want to convert most of it. If you want higher CCT lights the blue peak is a bigger issue especially since it means your spectrum tends to be rather limited in part of the blue spectrum, although these aren't very popular in a lot of the West particularly in domestic settings for various reasons anyway. Still use in offices etc means this is an area of active research hence the violet LED proposals etc. Nil Einne (talk) 08:18, 15 March 2018 (UTC)[reply]

This is a good reason to be careful with very cheap sunglasses. Often they just use coloured plastic or glass to block some wavelengths of visible light. This does nothing about ultraviolet, which is what can damage your eyes, and in fact - because the darker light makes your pupils open wider - they can increase your exposure to dangerous UV. If you can get a UV light source, I'd recommend testing these glasses to make sure they're safe. One easy way to do it is demonstrated here - just shine the UV light through the glasses onto a banknote, and see if the watermark appears. Smurrayinchester 08:37, 15 March 2018 (UTC)[reply]
"..if the words or background look white without the sunglasses, they look purple with them", this is the exact opposite of what the title is. If the sunglasses make white appear purple I would worry that they are providing no ultraviolet protection at all whilst blocking the middle of the visible spectrum which would be quite bad for you in sunshine as your pupils would be wider with them on. Dmcq (talk) 14:33, 18 March 2018 (UTC)[reply]

March 15

What weapon (or tool) is in this picture?

In the image in [28], what is this guy holding in his hand? If this is a gun, shouldn't he put it in a safer position? Like muzzle pointing down or up? --Doroletho (talk) 02:59, 15 March 2018 (UTC)[reply]

Knitting needles EvergreenFir (talk) 03:04, 15 March 2018 (UTC)[reply]

I assume you mean on his lap. Cause if you definitely meant in his hand, what Evergreen said :). It's a short-barreled assault rifle with a foregrip, flashlight, optics, bipod and stock attached. Not sure what model it is, but the strange thing about this gun to me is that there's no obvious place to put a magazine, especially with the bolt looking like it's right above the trigger. So then the obvious place for the magazine would be inside the pistol grip, which would suggest this is a pistol-calibre assault rifle. Looking at such guns online, it resembles an MPA30DMG. Hopefully, he has the safety on and/or the gun is unloaded, though for safety you should do both of those, and have the barrel pointed in a safe direction. Someguy1221 (talk) 06:01, 15 March 2018 (UTC)[reply]

My guess is that it's one of the IWI ACE family (also looks like an Israeli soldier to me). Alansplodge (talk) 08:54, 15 March 2018 (UTC)[reply]

But those don't have a bullpup configuration. After a quick check I would suggest he has something like the IWI Tavor X95. Rmvandijk (talk) 13:26, 15 March 2018 (UTC)[reply]

Agreed. Alansplodge (talk) 22:18, 15 March 2018 (UTC)[reply]

There are many potential ways to make this situation appear safer, but I do wonder what the cultural / professional expectation is here. If other members of his unit saw this photo, would they criticize him for not having the barrel pointed in a safer direction (e.g. towards the floor)? Or would they simply assume the weapon is unloaded and not worry about the way it is positioned? Such judgments are often shaped by both written guidelines and cultural expectations. Dragons flight (talk) 10:13, 15 March 2018 (UTC)[reply]

Its shurely a X95 in some configuration. Israeli forces are in a civil war for 30-40 years now? We can assume they know what they are doing when handling weapons. You can be harmed by a car as well and statistically it looks as if weapons are saver than cars, given everyone carries or drives them around in countries like Israel or the United States. The only point is, what some people in the United States keep missing, that not everyone is fit to drive a car or carry firearms. That is where the danger is. Not in laying your machinegun in your lap or driving your kids to school in your car, when you have learned how to handle that savely. --Kharon (talk) 14:03, 15 March 2018 (UTC)[reply]

Of course many Americans are born into places where it's so inconvenient to do anything without a car that getting a license and passing car inspection is made easy. Perhaps to partially compensate speed limits also tend to be slower than much of Europe (112.65kph might be the most common by population). Sagittarian Milky Way (talk) 02:45, 16 March 2018 (UTC)[reply]

There are speed limits everywhere in Europe aswell. Only the famous Autobahn 8D in Germany is an exception. Also everyone easily getting a license, to drive a car or own a firearm, may not be the main problem as long as there are enough checks to make sure the unfit loose theirs fast. --Kharon (talk) 05:41, 16 March 2018 (UTC)[reply]

SMW didn't say there were no speed limits. EU rather than Europe but [29] says

speed limit for motorways in EU Member States is mostly 120 or 130 km/h. Germany does not have a general speed limit for motorways, but a recommended speed of 130 km/h. The general speed limit for rural roads in EU Member States is mostly 80 or 90 km/h and for urban roads 50 km/h.

So if it's true motorway speed limits in the US are often only 112.65 km/h, this does seem lower than common in the EU. I'm not sure if their claim is accurate though as Speed limits in the United States by jurisdiction says

Speed limits in the United States vary depending on jurisdiction, with 75 to 80 mph (120 to 130 km/h) common in the Western United States and 65 to 75 mph (100 to 120 km/h) common in the Eastern United States.

Admittedly the map shows the most populous Western state by far is excluded from this 'common' thing so maybe the population bit makes it true. Nil Einne (talk) 07:10, 16 March 2018 (UTC)[reply]

There's an inverse correlation of population density with speed limit in the US.

A thing the Wikipedia map doesn't usually show is urban Interstates (translation: E-road/4+ lane Australian National Route)are often slower than rural and not all stretches of rural Interstate have the highest limit of its state (many suburban miles count as urban). If this is common in Europe too that wouldn't be a difference though of course. For a few years after the national speed limit ended 104.6/88.5kph rural/urban motorway was I believe much more common but advances in car tech had encouraged states to raise them (with some holdouts i.e. New York State). From 1974 to 1987 it was 88.5kph nationwide but that was only because the federal oil conservation law was stricter then (yet the raising it to 104.6 on rural motorways was vehemently opposed by the National Safety Council, Public Citizen, Mothers Against Drunk Driving and the Insurance Institute for Highway Safety) Sagittarian Milky Way (talk) 20:28, 16 March 2018 (UTC)[reply]

I think this has a lot more to do with lobbies like those you pointed out forming "high-speed" and "low-speed" camps and disabusing politicians of any courage to change the status quo than anything else. Personally, I have not noticed any correlation in national speed limits and general road quality in Europe, although a common factor among most places is that the enforcement is more lax than in the US. 93.136.119.107 (talk) 00:25, 17 March 2018 (UTC)[reply]

"On the best estimate, about an eighth of the whole [Autobahn] network of 13,000km (8,000 miles) has no speed limit and about a third has a permanent limit, with the bit between coming and going according to need". [30] Alansplodge (talk) 15:55, 16 March 2018 (UTC)[reply]

Threshhold value of stimulus for triggering ejaculation

How can the intensity of stimulus necessary for triggering ejaculation be expressed in some physical-physiological units and what is its threshhold intensity or numerical value?--82.137.15.144 (talk) 23:58, 15 March 2018 (UTC)[reply]

For some research on this topic, see here [31], here [32] and here [33]. SemanticMantis (talk) 01:46, 16 March 2018 (UTC)[reply]

Some things are better measured by qualitative research than by metrics. Klbrain (talk) 00:15, 18 March 2018 (UTC)[reply]

"When you can measure what you are speaking about, and express it in numbers, you know something about it." Lord Kelvin. Dmcq (talk) 09:26, 18 March 2018 (UTC)[reply]

March 16

How can a pedestrian bridge fail so quickly?

Tragic news from Florida. I know it'd be speculation at this point, but surely this is one of the surest things to design for? Imagine Reason (talk) 01:57, 16 March 2018 (UTC)[reply]

I've been warning people to avoid speculation at the article, but there are several possibilities. One of the supports could have shifted or been pushed out of alignment (one appears to be tilted, but that could be an effect rather than a cause). There could have been an undetected flaw in the reinforcing connections, or a post-tensioning cable could have failed. Post-tensioned structures are designed to withstand cable failures within reason, but a failure is a spectacular event that could have unforeseen results - they release a lot of energy. Failures like this usually are the result of a bad connection of some kind. The design appears to be a kind of cable-stayed structure, but the component that failed was apparently designed to support itself during construction without the stays. This newspaper article [34] contains a great deal of speculation, but it describes some of the common adjustments that are made to this kind of structure, such as camber adjustment. Construction is often the most hazardous time for a structure, as the redundant systems of a fully-completed design are not in place and the structure may be subject to unusual stresses. Acroterion (talk) 02:10, 16 March 2018 (UTC)[reply]

Your link doesn't work, you lost an l at the end [35]. I also came across this from the same paper which IMO is a little better as while it's speculates on possible reasons, it makes it clearer it is just speculation and doesn't really suggest anything is the cause of he collapse [36]. Nil Einne (talk) 05:31, 16 March 2018 (UTC)[reply]

Oops, sorry. Here's another article that's fairly measured in its coverage [37]. Our article on L'Ambiance Plaza collapse is worth a read, as it also involved the placement of prestressed concrete structure that was fabricated elsewhere - in that case the movement was vertical, not horizontal. At L'Ambiance it was apparently a problem with evenly distributed support that led to a failure at a connection point. We can expect reports from construction standards organizations in the long run for the FIU accident. Acroterion (talk) 12:22, 16 March 2018 (UTC)[reply]

According to this report, the cables were being tightened after a stress test. Akld guy (talk) 21:40, 16 March 2018 (UTC)[reply]

Courtesy link to thus unfamiliar: Florida International University pedestrian bridge collapse. Matt Deres (talk) 12:47, 18 March 2018 (UTC)[reply]

It sounds like people are surprised it failed so quickly. Bathtub curve suggests an early failure is likely, as is a late failure. RJFJR (talk) 16:26, 20 March 2018 (UTC)[reply]

sending probe on Sedna

In 2076, planetoid 90377 Sedna reaches perihelion. Why dont the humans try to land a probe on sedna? I mean, if it lands successfully; it will be a free journey for a very very long distance. All have to be done is to tell the probe to "stay still" and "do nothing" for a few centuries. Once sedna is far long, the probe cab be awaken. Then it can study the outer rim, and edge of solar system. It will take around 12,000 years for sedna to reach the perihelion again. During that time, the probe can go to sleep again. It doesnt need to return by itself. In 12,000 years humans might have gone extinct, or must have built faster space ships. One of such ship can pick-up the probe.

Are there any plans of a mission similar to this? If not, why? —usernamekiran(talk) 12:44, 16 March 2018 (UTC)[reply]

It's not that much of a "free journey". It takes considerable energy to match the velocity of such a body. If you can do that, then the probe could have simply put itself into such an orbit anyway. A rendezvous and sampling mission is interesting in itself, see Philae et al, but it doesn't really change the orbital dynamics of a mission. Andy Dingley (talk) 13:02, 16 March 2018 (UTC)[reply]

To amplify Andy's point, landing a probe does not provide a "free journey" at all. There is a way to get assistance from an orbiting body such as a planet or asteroid, but it doesn't involve a landing; you have to do a slingshot maneuver. If the probe was able to bounce off a hard object like an idealized rubber ball, then bouncing off the asteroid would give the same benefit that a slingshot maneuver does. (That's because in the asteroid's frame of reference the slingshotting probe is in a hyperbolic orbit.) --69.159.62.113 (talk) 20:15, 16 March 2018 (UTC)[reply]

My gut feeling is that for a slow trip to put a permanent memorial on Sedna with minimum fuel expenditure, it would be better for it to be moving away from the Sun. That's because our probe, when it eventually reaches the dwarf planet, will need to slow down and otherwise change velocity to match its orbit, and that is easier if it's moving away than if it is moving sideways or coming toward Earth. The idea is delta v. This would not be the case if you wanted as fast a trip as feasible with a lot of fuel to burn, in which case the distance is what matters most. Wnt (talk) 21:48, 16 March 2018 (UTC)[reply]

Voyager 1 crossed the Heliosphere of our sun on August 25, 2012. Voyager 2 is currently still in the Heliosheath, aiming to measure its thickness. So the "study the outer rim, and edge of solar system" is already under way and done.

The United States dont seem as dedicated to the Space Race anymore tho its participation in the joint venture James Webb Space Telescope, in preparation to be launched 2019, will probably deliver more new science than all of the historic "spaceprobes" together. Other states dont seem to have very big plans too. Maybe that changes, maybe someone is secretly planning to become/send the first martian (Mr. Musk?). Btw. planning for the second space telescope (James Webb) started in 1996, more than 20 years(!) ago, so its not like finding a target and starting a probe to it some month later. The process to get politics to decide about the money for it can easily take a decade alone. --Kharon (talk) 23:13, 16 March 2018 (UTC)[reply]

Aphelion versus perihelion at those distances actually doesn't have much of an effect on the minimum fuel cost of the mission. The vast bulk of the fuel is simply spent getting off of Earth, and then out of its orbit [38]. It would certainly be faster to go when Sedna is closer to the Sun, but still crazy expensive. Also, from an engineer/scientist/politician's perspective, it would be kind of silly to launch something now, intended to go into hibernation for 60 years (and we can't possibly test in advance if it can survive for that long), when instead would could spend money on something that would yield results now, and not even think about visiting Sedna until its much closer. Someguy1221 (talk) 01:43, 17 March 2018 (UTC)[reply]

I'm assuming that the OP is thinking about planning/preparing for this now rather than necessarily launching it now although I agree it's way too far advanced. That said, in addition to all the problems highlighted above there seems to be another big challenge. If putting something into hibernation for 60 years is tricky, and I agree it is, imagine trying to put it into hibernation for a few centuries! I'm not convinced our current tech is able to produce electronics that can survive that long, especially in outer space, even given some protection by the planetoid. Even the power source is likely to be tricky. The Radioisotope thermoelectric generator plans using Americium-241 would probably do although with RTGs being in hibernation is irrelevant to the power source (don't know about the other components); hence most plans don't propose that. And as you've indicated there's both producing things that can last that long, and being confident they will last that long. Nil Einne (talk) 04:03, 17 March 2018 (UTC)[reply]

In theory Sedna could contribute useful resources, such as water for propellant and ores for solar panels and mirrors. There is no way to rule out some kind of geothermal energy, even toasty warm spots, without a better look-see. But you'd better bring a very big nuclear plant with you if you need power to mine enough material to make enough mirror to concentrate sunlight at 80 AU out (1/1600 the sunlight!). It might be best to see some bots making fully equipped living space on the Moon and Mercury before we try that one. But yes, as a base, Sedna can be seen as providing free passage to a tremendous amount of raw materials for future space intrigues. Wnt (talk) 21:19, 17 March 2018 (UTC)[reply]

1/6400 the sunlight at 80 AU, ~1/875,000 at aphelion... 93.136.39.109 (talk) 02:46, 18 March 2018 (UTC)[reply]

To build on the basic point already expressed, but not fully explained: in space, objects do not have the same familiar drags on them that they do on earth. Your scenario suggests a hitch-hiker jumping aboard a passing train to get a free ride out to the Oort cloud. A satellite attempting to land on Sedna would have to match Sedna's speed (i.e. the hitch-hiker would have to run as fast as the train). However, unlike earth-bound hitch-hikers and trains, the satellite and Sedna do not have to worry about friction - they obey Newton's first law of motion in a very different environment than what we experience in everyday life. Once a satellite gets up to the same speed as Sedna, hitch-hiking gives you no benefit as that speed is easily maintained - the satellite will keep going that speed forever (until something else interferes with it). Matt Deres (talk) 13:00, 18 March 2018 (UTC)[reply]

Slightly related, if humanity ever want to leave the Milky Way then getting a ride with (probably not on) exiled stars [39] leaving the galaxy may be of help in a distant future – but only because there may be useful resources to stay alive for a really long time. Your spaceship still has to catch up with the speed of the star like with Sedna, so there is no "free ride" advantage. PrimeHunter (talk) 02:57, 20 March 2018 (UTC)[reply]

FWIW, there are Jupiter gravity assist windows for 2033 and 2046 launches to go to Sedna (mentioned at 90377 Sedna#Exploration, actually). But no space agency is currently considering launching a probe to go there. Double sharp (talk) 14:36, 20 March 2018 (UTC)[reply]

Would babies and toddlers need less nap time in the day if they sleep more hours at night?

If pre-school children all sleep enough hours during the night time, do they really need "nap time" during the day? SSS (talk) 23:48, 16 March 2018 (UTC)[reply]

There seems to be a link: " For example, one toddler may sleep 13 hours at night with only some daytime catnapping, while another gets 9 hours at night but takes a solid 2-hour nap each afternoon.". Count Iblis (talk) 02:36, 17 March 2018 (UTC)[reply]

Sleep Duration From Infancy to Adolescence: Reference Values and Generational Trends. Alansplodge (talk) 12:33, 17 March 2018 (UTC)[reply]

Since retiring, I've drifted back to being polyphasic. --Aspro (talk) 19:38, 17 March 2018 (UTC)[reply]

Be aware that the amount and duration of naps and sleep anyone should get is a contentious issue and - at the very least - varies with age. Quick example here. Parents of newborns are inundated with conflicting information, but it's usually formulated the opposite way of the OP. For example, the received wisdom when my child was a newborn (15 years ago) was that having naps improved night-time sleep habits; babies that missed their nap(s) would be too cranky to properly get to sleep at night. That was the theory, anyway. Matt Deres (talk) 16:10, 18 March 2018 (UTC)[reply]

March 17

Continuous, emission and absorption spectrums

Does anyone know where I can find find the continuous, emission and absorption images for the elements? I am creating a periodic table of the elements and really want to have these added. I found the visible spectrum images on wikimedia, which is fine, and am content on using them. I have looked and searched and found nothing really, except for hydrogen mostly. The kalzium program on Linux distros has the emission and absorption images, but they are small (and the program hasn't been updated for 12 or more years). 68.68.64.65 (talk)

You want images? Abductive (reasoning) 06:47, 18 March 2018 (UTC)[reply]
Are you only interested in simple atomic spectra? Even the helium and rubidium spectra have features in them due to diatomic molecules. In the ultraviolet there may also be a continuum due to ionization. In the microwave region there might be lines due to nuclear spin. Even so, don't expect them to be completely characterized for all different conditions, eg temperature, fluorescent, electric discharge. There are publications with big lists of numbers for frequency and line strength around. There are numerous publications on the topic. If you get something good, you can update User:Graeme Bartlett/spectrum of calcium and User:Graeme Bartlett/spectrum of magnesium! Graeme Bartlett (talk) 07:27, 18 March 2018 (UTC)[reply]

Yes, Abductive, the images. Here are the ones I have been using so far: https://en.wikipedia.org/wiki/Spectral_line 68.68.64.65 (talk) 03:14, 19 March 2018 (UTC) — Preceding unsigned comment added by 69.63.88.54 (talk) 22:30, 18 March 2018 (UTC)[reply]

They seem to be a high quality and complete set of emission spectra in the visible range. Other than that you also want absorption spectra, how do those compare to what you want (spectral range, spectral resolution, graphical size, etc.)? DMacks (talk) 03:29, 19 March 2018 (UTC)[reply]

DMacks, I am trying to follow the makers of kalzium (in a way). I just wanted to add the 3 mentioned spectrums (like they had the emission and absorption in kalzium). I am satisfied with what I have now, I just thought that having the 3 would make it look "better". But I never realized looking for visible spectra without lines, just emission lines and just absorption lines spectra would be so difficult. Very grateful for what I found on Wikipedia. I couldn't find them anywhere else. Thanks folks for all your replies and help. 68.68.64.65 (talk) 14:28, 19 March 2018 (UTC)[reply]

March 18

Does light knock at least some electrons off from any material?

When light hits a material (any material), can we assume that at least some electrons will be displaced? If we put the material in the dark and illuminate it unevenly, how could we analyze the surface to find spots where light hit? --Doroletho (talk) 14:05, 18 March 2018 (UTC)[reply]

First of all, not all light photons will have any effect. They need to be of a high enough energy to do so, which means a high enough frequency - see photoelectric effect and Einstein's first, and Nobel-winning, 1905 paper. (light travels at a constant speed, so its energy depends on its frequency, not like the speed and kinetic energy of a massive particle.)

Secondly, metals and conductors will allow electrons to move freely over their surface. So even if they were displaced, they'd rearrange almost immediately. If the material is a semiconductor though, the effect of the light can be to render that spot conductive. As an insulator, the pattern of electrical charge is fixed in place; first as an even distribution, then as the remainder which wasn't exposed to the light. This is the basis of xerographic photocopying. Andy Dingley (talk) 15:40, 18 March 2018 (UTC)[reply]

And what instrument is used to analyze the surface of an insulator or semiconductor? --Doroletho (talk) 16:15, 18 March 2018 (UTC)[reply]

That would depend a bit on the context, and how fine a spatial resolution you want.

Classically, the instrument was the electroscope, mostly the gold leaf electroscope. It's also possible to make an electroscope with a fine wire probe, which can be scanned across an area to 'read' the charge over it. Like most sensitive charge-reading instruments, the reading process is both destructive (it removes the charge that was there) and also needs resetting after each measurement where charge was found. An electronic electrometer is a more modern version of this, and more convenient.

To see the spatial distribution of the charge, xerography can be used. With a semiconductor-coated metal drum (selenium or a semiconductor doped organic polymer) place a constant charge over the whole surface. Then write on it with light (either laser spot or a reflection of the photocopying target), then dust with a fine pigment powder. Light makes the semiconductor conductive, dissipating the charge through the metal drum. The pigment is attracted to the remaining charge, but only in the unexposed areas. Pressing a sheet of paper over this transfers the pigment, giving an image of the remaining charge, and the pigment can be fixed in place by heat fusing it to the paper. Andy Dingley (talk) 17:26, 18 March 2018 (UTC)[reply]

Lots of equipment is used to study a material's surface - there's even a name for the entire field of study: surface physics!

Wikipedia has an article, Surface metrology. I have seen commercial equipment for these purposes, called by any of various generic names: "surface metrology station," "laser metrology machine," "profiling machine," "surface roughness meter," ... and so on. For example, you can purchase a "Panasonic Advanced Metrology System Solution" from your local ... place ... that sells semiconductor fabrication test-equipment. Just don't ask how much it costs. As the promotional literature reminds you, "...what does poor quality really cost?"

Other equipment that can be used to study material surface physics of course includes the conventional optical microscope; the electron microscope in all its forms; the atomic force microscope; the Raman spectrometer; the four point probe; and many other unique and specialized types of equipment. Nimur (talk) 17:59, 18 March 2018 (UTC)[reply]

Semi-important nitpick: light only always travels at the same speed in a vacuum. It travels more slowly through a medium, and this is what gives rise to things such as refraction. I'm noting this because it appears to me that "light always travels at the same speed" is a common misconception. More than once I've seen people introduced to things like Cherenkov radiation express confusion because they believe this. --47.146.60.177 (talk) 03:01, 20 March 2018 (UTC)[reply]

See Ionizing radiation for the cut-off for appreciable effects of photon energies on electrons, broadly speaking. Acroterion (talk) 18:02, 18 March 2018 (UTC)[reply]

Well, if you use that term, proceed with caution: while it is true that "ionizing radiation" knocks electrons out of their atomic orbit, even "non-ionizing" radiation can add energy to an electron: as Andy linked above, that is called the photoelectric effect. In some materials, like metals and semiconductors, an energized electron has greater electron mobility and may migrate, even if its "parent atom" is not "ionized." If we're not extremely careful with terminology, we can lead to great confusion: when mobile electrons flow in a crystal lattice, we do not usually say that the individual atoms are "ionized." In detailed study of solid-state crystal lattices, we often use the term electron gas or "free electrons" to describe sufficiently-mobile electrons that are not specifically associated with individual nuclei. Importantly: these electrons and their weakly-associated nuclei are not ionized: the total amount of energy is too low to separate the electrons completely. In specific: there is not enough energy to move the electrons to infinite distance from the material lattice. Broadly speaking, ionizing radiation provides exactly enough energy to move the electrons to an infinite distance from their atomic nuclei: this exact quantity of energy is called the ionization potential. Nimur (talk) 18:17, 18 March 2018 (UTC)[reply]

Agreed, that's why I qualified my answer. Since the question was about displacement, as opposed to raising an electron's energy level, it seems relevant if the OP isn't familiar with the concept. Acroterion (talk) 18:20, 18 March 2018 (UTC)[reply]

Yes, thank you for the clarification. The key distinction is "how far" the electron can be displaced. Nimur (talk) 18:24, 18 March 2018 (UTC)[reply]

Some substances have a very high ionization energy. For example helium and neon. These need vacuum ultraviolet to shift an electron. So normal light does nothing too them and they are transparent. Many other transparent materials will need electromagnetic radiation in the ultraviolet to knock off electrons. Graeme Bartlett (talk) 22:37, 18 March 2018 (UTC)[reply]

Note that we're operating in the realm of quantum mechanics, where particles have a nonzero probability of escaping from an energy well, even with no boost at all. A boost too small to kick the particle out of the energy well by itself will nevertheless increase this probability. So the basic answer is that when we're dealing with Avogadro's number of particles, pretty much any incident light, regardless of how low its energy is, will increase the number of escaping electrons to some degree. Looie496 (talk) 01:02, 20 March 2018 (UTC)[reply]

March 20

Cognitive bias for thinking everything a science field produces is positive?

Is there a term for folks in particular science fields who are so enmeshed in what they're doing that they develop a cognitive bias for being optimistic about everything contributed to the world from their field?

Take me, for example, as someone with a software engineering background, I frequently found myself thinking in terms of software being able to solve any problem. But as I've distanced myself from the field, it becomes clearer how unobjective I was in thinking like that.

Is Pro-innovation bias the best fit? I am asking a user of the Wikipedia rather than as an editor -- I don't intend to use any answer for editing purposes. Stevie is the man! ^{Talk • Work} 15:28, 20 March 2018 (UTC)[reply]

That is difficult because a priori its also a central nature of science to test and refute theories when they are wrong. There are early greek idealized philosophical theories about the reign of the wise, today collected in the term Noocracy and there is also Technocracy as a similar concept. Taylorism and Fordism are something similar too. These all imply the believe that pure science is the best of all ways to rule, judge and organize. However again, science includes questioning its ideas, altho it may take some time to conclude it was not good like Albert Einstein about his help to develop the nuclear bomb or Alfred Nobel inventing Dynamite. Science even recently "invented" Technology assessment as a new science! --Kharon (talk) 16:37, 20 March 2018 (UTC)[reply]

Thank you. That goes in the direction I intend, but I am trying to focus on a particular cognitive bias of the scientist (as an imperfect human being) in a specific field (which can be any specific field), whereas they become so idealized by their field that they in a sense become PR or evangelists for it. They ignore (or pretend to ignore) the negative ramifications of what their field produces, while seizing opportunities to trample on critics, no matter how well-founded the criticism. They make continual efforts to mold the minds of others toward their "positives only" view of their field. Maybe such scientists are indeed PR folks with a scientific background, but I don't want to assume they are PR. I wonder if there is a true cognitive bias here. Stevie is the man! ^{Talk • Work} 17:08, 20 March 2018 (UTC)[reply]

It also depends on what you mean by science. I would consider software engineering to be a branch of engineering. Engineers typically think they can solve the world's problems. And they can do it better than most other people too, but you might end up with something like China with them in charge. Or did you mean computer science? Scientists tend to be a bit more modest. Dmcq (talk) 18:28, 20 March 2018 (UTC)[reply]

I'd rather not say what specific field I'm thinking of, as I would like to avoid a debate about that field. But I will say that a field where science is applied fits into this model. So you could say I'm referring to a cognitive bias of a scientist or engineer. Stevie is the man! ^{Talk • Work} 18:50, 20 March 2018 (UTC)[reply]

Lots of biases could be used to describe this, but no one single phrase says it all. In-group_favoritism is relevant. As for the science/engineering thing Dmcq mentions, see[40], which specifically calls out Physicists as thinking they can do anything. On the other hand, I know plenty of Mechanical and Electrical engineers that don't think software is engineering. Anyway, I agree that many members of any group can get carried away overvaluing the contributions and abilities of that group. You can see it with computer folks, you see with with some academics. You can find fashion experts who will look you straight in the eye and say that fashion is all that matters. It's a little bit of in-group favoritism with sort of a group-level Dunning-Kruger effect. Which is not to say that everyone in these groups does it. I agree with Dmcq insofar as most of the very accomplished scientists I have met tend to be very cognizant of their field's limitations. As for the value of getting some distance from the field, that is also much discussed, though under many different terms (and in different fields). See e.g. Field_theory_(sociology), Standpoint_theory, Overview_effect, Cognitive_shift, this blog post [41] on the value of outsider's perspectives. SemanticMantis (talk) 18:46, 20 March 2018 (UTC)[reply]

There's scientism and technoutopianism. Sagittarian Milky Way (talk) 18:55, 20 March 2018 (UTC)[reply]

March 21

Big toe anatomy

I am looking for information of the anatomy of the big toe, but all the pictures and info I can find only show the big toe joint close to the foot, I am looking for info on the first big toe joint that bends close to the nail, what is it called? I am also wondering if this is an actual joint with cartilage or just bones.--User777123 (talk) 04:04, 21 March 2018 (UTC)[reply]

That joint has a synovial membrane. The end bone has a double concavity. The bone is called Pedal distal phalanx 1. The big toe has no middle phalanx. There are collateral ligaments on either side. It is connected to plantar ligament connected to articular capsule. Info from Cunningham's Text-Book of Anatomy, 9th ed, by James Couper Brash. A picture of the bone is here: http://www.eskeletons.org/boneviewer/nid/12537/region/feet/bone/pedal_distal_phalanx_1 . It connects to Extensor hallucis longus muscle. Graeme Bartlett (talk) 07:40, 21 March 2018 (UTC)[reply]

Weighing scale

Can anyone please point me to a weighing scale which can measure mass up to 1 kg (or, if not, then at least up to 500 g), with the highest possible precision (if possible, ±10 mg or better, but if not, then the best available) and with the greatest possible accuracy? I bought one which meets these specs (or so I thought) on eBay, but it turned out to be a piece of junk -- just today I tried to weigh a 2 L beaker full of water, and it showed the weight as 1410 kg (and that right after calibration!), and as far as smaller weights (like empty beakers, or even a 1 L beaker half full of alumina powder), it remains stubbornly stuck at 0.00 g! 2601:646:8E01:7E0B:0:0:0:9ED6 (talk) 06:36, 21 March 2018 (UTC)[reply]

It appears that 2kg broke your 1kg limit scale. Anyway you want accuracy to 1 part in 100,000. You will have to take into account air buoyancy, which will vary at your precision with temperature and pressure. So you will need to weigh in a vacuum or have extra compensation. I can see examples that should be a good enough quality here: https://www.instrumentchoice.com.au/instrument-choice/other-meters/digital-scales-1/precision-and-analytical-balances and another here: http://www.scaleshop.com.au/adam-nimbus-nbl-e/ . Some of the scales here https://www.austscientific.com.au/product/balances/ have compensation for pressure and temperature (but I did not see humidity) and also prevent electric fields that also affect measurements. But they mostly do not meet your requirements for maximum. Graeme Bartlett (talk) 08:10, 21 March 2018 (UTC)[reply]

Actually, all 3 of them are good, but far too expensive -- I guess I'll have to settle for using 2 scales, one for weighing small amounts of chemicals (up to, say, 100 g) with high precision, and another one for weighing large amounts (up to 1 kg, preferably higher) with rather lower precision. 2601:646:8E01:7E0B:0:0:0:9ED6 (talk) 08:52, 21 March 2018 (UTC)[reply]

I'm slightly confused, did you scale support up to 1kg or did it supposedly support a higher weight limit? If it was only up to 1 kg and you tried to weigh something heavier like a 2L beaker full of water, it's not completely surprising it would break perhaps permanently as Graeme Bartlett has said. With the cheap scales I've bought from AliExpress I've generally gotten away with a fair amount of abuse. But if I was buying a expensive high precision scale from a proper manufacturer, I wouldn't be testing the limits especially to such an extreme. You can only go so far until you actually damage the strain gauge or whatever is used or something else. (In any case, for something from eBay particularly if it's new and from an uncertain manufacturer, you should always consider the possibility it may be DOA. So test it properly when it first arrives and report it to the seller if it is so you can get a replacement.)

Anyway I have seen ultra high precision, supposedly 1 mg scales, supporting up to 1 kg and with an enclosed measuring surface on AliExpress e.g. www.aliexpress .com/item/1kg-0-001g-1mg-electromagnetic-scale-calibration-weights/32810440445.html. And high precision, supposedly 10 mg, scales supporting up to 1kg are very common both the cheap dime a dozen ones which don't even have an enclosed measuring surface (so you know that at a minimum, the accuracy is very questionable) e.g. www.aliexpress .com/item/1PC-Professional-Pocket-1KG-0-01G-Scale-Digital-Jewelry-Precision-Balance-Weighing-Scale-With-Backlight-Keyboard/32819638592.html and those that do e.g. www.aliexpress .com/item/New-APTP457B-Precision-Jewelry-gold-food-weighing-counting-kitchen-scale-1KG-x-0-01g-Laboratory-analytical/32622805989.html.

I'm not suggesting you get these if you actually need these for an important reason (I do actually use a 0.01g scale from AliExpress/eBay but only really for fun, e.g. cooking, in fact 0.1g would do I mostly want something more than 1g and it's a choice between 3kg or so 0.1g and 1kg or so and 0.01g). But these suggest to me you should be able to get one from a decent manufacturer. As GB has said, if you actually need that level of precision you'll need to consider carefully compensation measures.

Nil Einne (talk) 08:36, 21 March 2018 (UTC)[reply]

For the record, the scale I have is rated to measure weights up to 3 kg (in fact, the calibration weights are 2 kg in all) -- therefore, my weighing the beaker could not possibly have anything to do with the malfunction (and in any case, it was stuck at 0 for smaller weights even before I weighed the beaker). 2601:646:8E01:7E0B:0:0:0:9ED6 (talk) 08:42, 21 March 2018 (UTC)[reply]

Does it have a zero button to re-zero it with no mass on the platform? Graeme Bartlett (talk) 09:58, 21 March 2018 (UTC)[reply]

Your description sounds like it was DOA. Even the best brands have this, so I wouldn't conclude from a single instance that the scale model is no good. If it sold as a new & working scale, the seller should set this right especially if they are a commercial seller. Nil Einne (talk) 10:40, 21 March 2018 (UTC)[reply]

What is "DOA"? 92.8.216.101 (talk) 13:41, 21 March 2018 (UTC)[reply]

The first sense at DOA—that is, dead on arrival. In the context of manufactured products, it means that the item was critically defective as-delivered. TenOfAllTrades(talk) 15:24, 21 March 2018 (UTC)[reply]

Reflector telescope design

I'm looking for a reflector telescope design where the secondary mirror is offset out of the telescope tube. My motivation is (1) aperture control and (2) better bokeh. thanks! --Masatran — Preceding unsigned comment added by 117.251.229.98 (talk) 07:33, 21 March 2018 (UTC)[reply]

I think they're called off-axis reflectors. A curved spider in an on-axis reflector would get rid of the diffraction spikes at least (Maksutovs have a small secondary mirror but have a corrector plate that can't be 100.000% transparent). Sagittarian Milky Way (talk) 08:02, 21 March 2018 (UTC)[reply]

How long after last frost before lawns need mowing?

What temperature do lawns consider a frost? 32? 30? 28? 107.77.173.12 (talk) 17:56, 21 March 2018 (UTC)[reply]

The growth rate of the grass depends on too many factors to give a simple answer - temperatures, moisture levels, grass species, soil nutrient levels, sunlight levels. If it stays dull, and just above freezing, the grass will grow a lot more slowly than if the temperature shoots up very quickly and there is plenty of sunshine. Wymspen (talk) 18:18, 21 March 2018 (UTC)[reply]

Today, many people cut their grass too short. If you keep it no shorter than 2 inches (and I don't mean bowling greens but garden lawns). That too, will help prevent weeds colonizing (so avoid the need for lawn weed treatments). When in the spring, the grass grows to 3 inches, mow it on a day when there is no 'frost'. It is only when the ground is frozen that damage is done because grass grows from the base and any physical trauma will damage the leaf buds. --Aspro (talk) 19:11, 21 March 2018 (UTC)[reply]