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July 13

Millipede legs; restriction on total number

Centipedes always have an odd number of pairs of legs, meaning that their number of legs is always divisible by 2 but not by 4. But is there any restriction on how many legs a millipede can have?? Georgia guy (talk) 00:49, 13 July 2018 (UTC)[reply]

This article,[1] among others, says millipedes have four legs per segment. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:18, 13 July 2018 (UTC)[reply]

Which means that millipedes could never have the same number of legs as centipedes. --Jayron 32 00:16, 14 July 2018 (UTC)[reply]

One Internet site talks about 394 as a common number of legs; another says that millipedes always have an even number of pairs (meaning a number that is divisible by 4.) These 2 sources clearly contradict each other. Georgia guy (talk) 00:22, 14 July 2018 (UTC)[reply]

Sometimes a source won't have a leg to stand on. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:33, 14 July 2018 (UTC)[reply]

Encyclopedia of the Animal World, Elsevier 1972, calls the segments "rings" and says that most rings have 2 pairs of legs, while the first few rings only have 1 pair of legs. So it looks like the number of millipede legs could be divisible by four or two, depending on whether the number of segments with 1 pair of legs is even or odd.--Wikimedes (talk) 16:46, 14 July 2018 (UTC)[reply]

Discounting "common species have between 34 and 400 legs" in our millipede article, I haven't found a specific example of a millipede with the number of legs divisible by 4. From the 2nd paragraph of Millipede#Body: "The second, third, and fourth body segments bear a single pair of legs each and are known as "haplosegments"", which would indicate that the number of legs is never divisible by four. This [2] site says there are "often 3" haplosegments.--Wikimedes (talk) 17:18, 14 July 2018 (UTC)[reply]

And again I know nothing about birds

So, saw these little guys while boating. Didn’t see any larger birds that looked like adults of the same species. This was right on the waterline of a small island in a freshwater lake in the Kenai National Wildlife Refuge. They certainly acted like chicks, making little “cheep cheep” noises, staying right on the apparent nesting site, making no attempt to fly or swim. Anyone know what they might be? Beeblebrox (talk) 02:30, 13 July 2018 (UTC)[reply]

I certainly know nothing about birds too, but they look a bit like greater sage-grouse chicks to me. Alex Shih (talk) 02:46, 13 July 2018 (UTC)[reply]

Here is a website for Alaskan birds. Of course it is a big state with lots of avians so it might take some searching. To my untrained eye this is a bit like your pic - especially if you allow for variation in coloring for young chicks. I could be way off though. MarnetteD|Talk 04:30, 13 July 2018 (UTC)[reply]

Rats I missed where it stated that the turnstone is a coastal bird. Good luck in tracking it down. MarnetteD|Talk 04:33, 13 July 2018 (UTC)[reply]

The beaks are too substantial for turnstones, they're probably some kind of young gulls, which are notoriously hard to identify. Acroterion (talk) 00:36, 14 July 2018 (UTC)[reply]

The fact that this is a freshwater lake may narrow the field. I’m beginning to think they are maybe Arctic Terns. Most images I can find show a orangish-yellow beak, but some of juveniles show a duller beak as these have. Beeblebrox (talk) 17:19, 15 July 2018 (UTC)[reply]

Vitamin B11

I can't find the chemical formula for Vitamin B11 (pteryl-hepta-glutamic acid). Can you help? 121.44.187.6 (talk) 03:57, 13 July 2018 (UTC)[reply]

There isn't one in this list B vitamins#List of B vitamins. Hopefully someone else can help. MarnetteD|Talk 04:22, 13 July 2018 (UTC)[reply]

A google search bring up this. MarnetteD|Talk 04:24, 13 July 2018 (UTC)[reply]

BTW, although it's one of the few to be unsourced I'm fairly sure our article is right. There's no longer such a thing as a recognised Vitamin B11 in humans. Any source which still calls pteryl-hepta-glutamic acid (or PHGA or chick growth factor) as a human vitamin B11, or which says there is such a thing as a human vitamin B11, is either outdated or unreliable. Or maybe both. If someone is trying to sell you something with vitamin B11 for human consumption, run away. Nil Einne (talk) 08:46, 13 July 2018 (UTC) 09:53, 13 July 2018 (UTC)[reply]

This is the original poster. I am well aware it has no value for humans. It happens that I am in a family of chicken ranchers. 121.44.187.228 (talk) 08:53, 13 July 2018 (UTC)[reply]

This one was a head-scratcher. The problem is that references to Vitamin B11 basically end in the 1950s as far as the scientific literature goes (though the papers that studied it continue to be cited later). Many of the papers on the subject are behind paywalls even my library can't get past, and those that I can read predate the chemical identification of the molecule. The first clue I had that something was wayyy off was seeing articles much much later that cited these B11 papers while discussing folic acid! Indeed, NCBI's pubchem lists "vitamin B11" as one of the 200+ synonyms for folic acid[3]. Unfortunately, it's specifically listed in vendor synonyms. Which means, at some ponit, somewhere, folic acid has been sold as B11. Which does not mean that scientists consider it the same. Anyway, what I conclude, but can't be 100% sure of, is that it was identified as an essential vitamin for chicks, and later found to be a known compound, and the name was never used again. Someguy1221 (talk) 10:32, 13 July 2018 (UTC)[reply]

I did discover that some naturopaths & homeopaths sell what they call "Vitamin B11" as folate. What they are actually selling could be anything - particularly homeopaths, homeopathy being essentially 100% quackery, and B11 being useless for humans as noted. Can any nice chemist tell me how to arrive at a formula for pteryl-hepta-glutamic acid? OP 121.44.185.44 (talk) 13:55, 13 July 2018 (UTC)[reply]

It does apear to be a folate derivative. Here's a ref (I don't have time to chase the cited refs right now): doi:10.1021/jo00837a600. DMacks (talk) 14:15, 13 July 2018 (UTC)[reply]

Here's another one. Ok, so part of the problem was that it's actually pteroylhepta-γ-L-glutamic acid. Also explains the history. When people started purifying folic acid and identifying its chemical structure around the 1940s, it was found that there were many forms, some of which only differed in the length of the glutamate chain (as a name of a chemical rather than a class of chemicals, "folic acid" only has one glutamate). It was further found that the length of the glutamate chain affected the molecules bioavailability in a species-specific manner. That's it. That's all, nothing else magical or special. Different organisms like to get their folate while it's attached to different things. Someguy1221 (talk) 00:09, 14 July 2018 (UTC)[reply]

The article you found gave me exactly what I needed. Many thanks for your help. OP 118.209.58.129 (talk) 13:49, 16 July 2018 (UTC)[reply]

July 14

Mass of earth over time

This article discussing a meteorite impact 3 Ga ago claims that "when this asteroid hit, Earth was only a third its current size". I've interpreted that as meaning that the earth was 1/3 of it's current mass at that time, which I find very, very hard to believe. An alternative interpretation is not occurring to me either. I've been trying to find something like a graph of the mass of earth over time, but I can't find such a thing. I imagine it's because the mass of the earth only substantially changed in the period up to and during the formation of the moon (4.5 Ga ago), and that since then changes to the earth's total mass have been negligible. The late heavy bombardment (4.1 to 3.8 Ga ago) consisted of around 22,000 objects large enough to leave craters at least 20km in diameter on earth. Even if we assume all 22,000 of them were the size of 5 Astraea (which would leave a crater far larger than only 20km in diameter) and no ejecta escapes the earth's gravity, the event only would have increased the earth's mass by around 1%. Since the LHB, I don't think there have been any major sources of additional mass, and the slow accretion of additional mass which is negligible anyway has been opposed by the gradual loss of hydrogen and helium. Is there any possibility that the claim in this article is correct? Also, does anyone know if a graph of the estimated mass of the earth over time, even if it just covers the accretion and moon formation stages exists anywhere? 2A0D:5600:3:9:201:200:0:10B3 (talk) 08:26, 14 July 2018 (UTC)[reply]

Yeah, that's nonsense. I suspect what someone intended to say was that at 3 Ga, the earth was 1/3 it's present age, but somehow that got miscommunicated as "size". Dragons flight (talk) 08:34, 14 July 2018 (UTC)[reply]

(EC) Several of the comments under the article say that this should read "a third its current age". That is numerically correct, and presumably also what the author intended to write. If Earth had indeed tripled in size by whatever process, there would be no way that any traces of this crater would be detectable now. --Wrongfilter (talk) 08:36, 14 July 2018 (UTC)[reply]

(ECx2) Yeah I was right about to post the same, after "lulwhat?" I did check the the original paper to make sure, and no, it doesn't make this statement anywhere. Someguy1221 (talk) 08:36, 14 July 2018 (UTC)[reply]

Pfft. This is clearly a clever set-up for a geologically based "Yo mama..." joke. Matt Deres (talk) 02:49, 15 July 2018 (UTC) [reply]

See, they just admitted expanding Earth is true! Wake up sheeple! --47.146.63.87 (talk) 07:52, 15 July 2018 (UTC)[reply]

Note that Earth gains mass from meteors and loses mass from gasses stripped by solar wind and by radioactive decay -- at nearly identical rates [4] (estimates vary). —2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 18:04, 15 July 2018 (UTC)[reply]

July 15

Photography - tracking fast moving subjects

In professional filmmaking, how are cameras stabilised when they are following a fast moving subject close up? For example of an actor is sprinting and the cameras is right next to them following, how is the camera stabilised? Assuming that it’s not possible to use a guide rail. Let’s say the actor is sprinting over many obstacles and turning a lot and the filming is done in a public area. — Preceding unsigned comment added by 90.206.71.55 (talk) 12:15, 15 July 2018 (UTC)[reply]

Wildlife photographer Roger N. Clark explains The key to fast autofocus and focus tracking is the use of phase detection focus. The link shows examples. DroneB (talk) 12:55, 15 July 2018 (UTC)[reply]

SteadiCam, and many similar products, provide smooth video of motion using mechanical stabilization and a trained operator. Nimur (talk) 14:43, 15 July 2018 (UTC)[reply]

Steadicam's introduction was apparently a really big deal. I came across this recently and there's a couple interesting historical pages from the current manufacturer.[5][6] The "art museum steps" scene from Rocky was inspired by a very similar shot in the original Steadicam demo reel. The full sized ones (made for Hollywood movie cameras) are huge and expensive but they now have some small handheld ones for smartphone/gopro sized cameras that are pretty affordable I do not need another gadget.... Interestingly only a very recent (phone sized) model has a gyroscope: I had expected they all did, but apparently the traditional one is just an elastic mount on some gimbals, completely inertial. 173.228.123.166 (talk) 16:54, 15 July 2018 (UTC)[reply]

Yeah, SteadiCam is kind of an important invention; it is one of those inventions which is so simple in execution and so significant in addressing a very real problem that there's a tendency to try to genericize the trademark. This is one reason why the SteadiCam people are so aggressive in protecting their intellectual property - particularly when it comes to the very sensitive wording associated with motion picture credits! Nimur (talk) 20:13, 17 July 2018 (UTC)[reply]

Also there is a Hollywood profession of focus puller, someone whose sole duty is to focus the lens while the shot is in progress. That is not so easy to do automatically. The focus puller has to understand exactly how stuff will be moving in the shot and what parts are supposed to be kept in focus, so that the focus movements are pre-planned/choreographed but done in real time as the shot proceeds. 173.228.123.166 (talk) 16:58, 15 July 2018 (UTC)[reply]

A little web research shows bigger gyroscope stabilizers are a thing. ken-lab.com apparently originated them in the 1950s. There are other brands and some DIY ones now[7] (even one using old hard disk drives as gyros![8]) but it all seems cumbersome and low tech. I tried some stabilized binoculars in a store once (they have little piezo actuators that wiggle the prisms in the binocular to compensate for wobble) and they worked amazingly well, and optical image stabilization in camera lenses is similar, so I guess this gyro stuff is for heavier gear, higher amplitude vibration etc. 173.228.123.166 (talk) 19:16, 15 July 2018 (UTC)[reply]

Differences between hydrogen and most elements

Why do isotopes of hydrogen make such a big difference?? If all carbon on earth were C14 instead of the standard C12, it wouldn't affect life very much. But if all hydrogen on earth were H2 instead of the more common H1, we would die. Why do isotopes of hydrogen affect the element's behavior more strongly than isotopes of other elements?? Georgia guy (talk) 18:29, 15 July 2018 (UTC)[reply]

What are the bases of your two premises? ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:43, 15 July 2018 (UTC)[reply]

Bugs, this is kind of a well-known fact, except that the choice of C14 is unfortunate. C14 is very radioactive, with a half-life of only 6K years or so. If all carbon on Earth were C14, we would die promptly from radiation poisoning. But from a chemical point of view, I think GG is correct (the choice of C13 instead of C14 would probably have made the question correct).

I think the answer is that the extra neutron just makes a lot more difference when there's only one nucleon to start with. For example deuterium has double the mass of ordinary hydrogen. That affects the energetics of chemical reactions. Someone who knows more about quantum chemistry can probably elaborate, but I think this is the main point. --Trovatore (talk) 18:53, 15 July 2018 (UTC)[reply]

I guess this is also to do with energetics of reactions, just not chemical ones...but since the mass will effect the average velocity of the particles in solution, it would also have an effect on rates of diffusion. 61.247.39.121 (talk) 23:09, 15 July 2018 (UTC)[reply]

That's the basis for the original separation of uranium isotopes during the Manhattan Project. --Khajidha (talk) 14:20, 17 July 2018 (UTC)[reply]

The Heavy water#Effect on biological systems says

The larger chemical isotope-effects seen between protium (light hydrogen) versus deuterium and tritium manifest because bond energies in chemistry are determined in quantum mechanics by equations in which the quantity of reduced mass of the nucleus and electrons appears. This quantity is altered in heavy-hydrogen compounds (of which deuterium oxide is the most common) more than for heavy-isotope substitution in other chemical elements.

BTW it also mentions the, I agree well known, problems organisms have with heavy water. It's perhaps worth remembering that while it's sometimes worth challenging a statement made in a question where you have good reason to be uncertain if it's true, it's not necessary to challenge every single statement made especially ones you know nothing about. If you just wish to know more about something said, it would be better to phrase it as a question. Nil Einne (talk) 19:55, 15 July 2018 (UTC)[reply]

Which is what I did. And Trovatore immediately shot down the first of the two premises. And thank you for providing a source for the second premise. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:14, 16 July 2018 (UTC)[reply]

No you did neither of what I said. Your response wasn't a polite question for more information but questioning a basic well known fact that frankly anyone who hangs out at the Science desk should already some inkling of. If you had just wanted more info on this basic fact, you should have wrote a polite question asking for it, rather than unnecessarily questioning such a basic fact. BTW, it sounds like you remain confused. Trovatore clarified that while the OP's specific example was flawed, but both of their basic premises were in fact correct. As now supported by the article I linked to. (Albeit which didn't seem to be directly sourced.) Nil Einne (talk) 08:18, 16 July 2018 (UTC)[reply]

"If all carbon on earth were C14 instead of the standard C12, it wouldn't affect life very much." Is that a true statement? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:59, 16 July 2018 (UTC)[reply]

No idea why you're asking something we've already established was incorrect. If you're understanding of this discussion is so limited, I strongly suggest you just stay away from the RD for good or at least as a responder. This isn't even a case of a limited English ability where we can allow reasonable latitude. Your English ability is clear up to the task, your ability to understand very simple discussions appears not to be. Nil Einne (talk) 10:52, 17 July 2018 (UTC)[reply]

For the benefit of nitpickers, I should clarify that this depends on the precise wording and how it's interpreted and there's a chance we don't know for sure the answer to the question. Assuming that the statement is interpreted to mean it's always been that way, then there's a reasonable chance life would be different. It's possible it would not have managed to evolve although I expect more likely it would have evolved to cope with C14. It seems likely this would mean significant differences. Even more so with organisms that live very long (thousands years or more for example). Of course a wider point is that the short half-life means a world with C14 is unlikely to be plausible, I don't see how your world could ever produce enough C14 to keep it the primary form of carbon, well unless we're thinking about tiny amounts. If it's simply a case that all the C12 was magically replaced with C14, it would seem likely as Trovatore said that life would not cope with this and most would die out. Mind you, I'm not sure that there's anything in heavy water (or the other molecules of life with hydrogen) that means most of life couldn't also work with heavy water. So if life evolved in a world where most hydrogen was predominantly deuterium, I suspect life would also have managed to make a go with it. (But this is just a guess, I know too little to have any confidence.) This is of course moot to the question, since as I already mentioned anyone with basic scientific understanding could interpret what was meant. As someone had wanted to nitpick these and any aspects, that seems reasonable (especially if the question has been answered). But I still see no benefit to anyone questioning a very basic and basically correct premise namely that life which has evolved to cope with hydrogen-1 cannot cope with deuterium, rather than either politely asking for an explanation for something a person may reasonably be unaware of, or just leaving the question be. Nil Einne (talk) 11:28, 17 July 2018 (UTC)[reply]

You're starting to catch on. Life could have evolved to tolerate C14 and/or deuterium. But it didn't. Not on earth, anyway. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:22, 17 July 2018 (UTC)[reply]

All C14 would be a lot of radiation. Low-energy betas, but still. I think there's a better chance life could have evolved to use deuterium than C14. --Trovatore (talk) 18:10, 17 July 2018 (UTC)[reply]

See kinetic isotope effect. Changing ¹²C to ¹³C only raises its mass by about 8.3%. Changing protium to deuterium raises its mass by about 100%. It is no surprise that the consequences are therefore much bigger. Double sharp (talk) 04:25, 18 July 2018 (UTC)[reply]

Rinsing out a vessel

You have a 1 litre vessel full of soapy water. You want to rinse it until 0% soap remains (or nearly 0%). Which is most efficient?

Pour out the soapy water. Fill it 10% full of clean water. Swish it around. Pour it out. Repeat until 0% soap remains.
Pour out the soapy water. Fill it 50% full of clean water. Swish it around. Pour it out. Repeat until 0% soap remains.
Pour out the soapy water. Fill it 90% full of clean water. Swish it around. Pour it out. Repeat until 0% soap remains.

Anna Frodesiak (talk) 20:44, 15 July 2018 (UTC)[reply]

Strictly OR, but when camping (with limited potable water), I use something most similar to 1 for washing dishes, etc. However, I too, would be interested in a "scientific" answer. 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 21:17, 15 July 2018 (UTC)[reply]

I think the answer is going to vary a lot depending on what sort of "efficiency" Anna has in mind, and a little bit on what "0%" means. Of course you're never going to get to literally zero percent by any practically feasible method. But if you have a threshold in mind, you can optimize the procedure for getting to that threshold based on things like the amount of time spent, the amount of water used, how difficult it is to "swish". I don't think we can really come up with a definitive answer here. --Trovatore (talk) 21:18, 15 July 2018 (UTC)[reply]

I assumed "efficient" meant least amount of water used (and "nearly 0%" meant undetectable for ordinary use). 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 21:36, 15 July 2018 (UTC)[reply]

I guess by efficient I mean time and effort. Anna Frodesiak (talk) 21:41, 15 July 2018 (UTC)[reply]

In that case, I'd go with 3 (more intuitive than scientific answer). 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 21:45, 15 July 2018 (UTC)[reply]

(ec) Too complicated for a once-and-for-all a priori solution, I think. We'd need to have a model that incorporated the rate at which the soap diffuses into the clean water, the characteristics of the pot as regards "swishing", et cetera. Probably best to just try it a few different ways and see what works for you. --Trovatore (talk) 21:48, 15 July 2018 (UTC)[reply]

If the contaminant is just soap, a few quick rinses with small amounts of water is easiest and saves water. Say dumping out the vessel's contents leaves 1 ml of solution in it by surface tension (probably too high a guess). If you started out with 1ml even of pure soap and treat the rinsing as pure mixing into a solution, 3 rinses of 100ml each would get to 1/100³ or 10^-6 concentration, same as 2 rinses of 1000ml each, but probably quicker. See homeopathic dilution if you want to get silly. 173.228.123.166 (talk) 23:43, 15 July 2018 (UTC)[reply]

That assumes that the soap mixes evenly with the water, in a reasonable time. It's not clear that that assumption is reasonable. In my experience, it tends to stick to the pot, at least some sorts of pot. --Trovatore (talk) 03:43, 16 July 2018 (UTC)[reply]

Can this be changed to a more pure example to come up with a maths or physics type answer? For example, 1% dye. Add water. Allow for mixing by osmosis, etc. Anna Frodesiak (talk) 04:15, 16 July 2018 (UTC)[reply]

Trovatore, yeah, soap dissolves more readily in hot water if that helps. Anna, let's say it takes a seconds to draw a liter of water from your faucet, so x liters (say x=0.1) takes ax seconds. Then you spend b seconds sloshing it around and dumping it out (this is presumed independent of x), and there's c liters (like 0.001 liters = 1ml) of solution left in the pot after you dump it. You started with 1% dye (let's say you dump it immediately so only c liters of 1% dye are left in the pot before you start rinsing), so after n rinses of x liters each, the amount of dye left will be 0.01⋅(c/x)ⁿ and the time spent will be n⋅(ax+b) seconds. Let's say you want to rinse til the dye concentration is 10^-6. If x=0.1 this takes 3 rinses and 0.3a+3b seconds, and if x=1 it takes 2 rinses and 2a+2b seconds. I guess it takes about 10 sec to get a liter of water from my kitchen sink, and maybe b=5 sec of sloshing. In that case, the 2x 1 liter rinse is 20+10=30 sec and the 3x 0.1 liter rinse is 3+15=18 sec.

I guess if the number of rinses turned out to be much higher (like if you wanted 10^-100 concentration, which is physically silly) or if you treat n as a continuous variable, you could frame this as an optimization problem where you solve for x to minimize the time spent. You'd draw a graph that would have some minimum, write out equations and find where the derivative is 0. But of course you probably would want more parameters in the model than just the water fill rate and slosh/dump time. Anyway this is the general approach to what I think you were asking. 173.228.123.166 (talk) 05:03, 16 July 2018 (UTC)[reply]

So, based on the above, is it better to use less water more times or more water fewer times? Anna Frodesiak (talk) 05:11, 16 July 2018 (UTC)[reply]

You still have an undefined goal of "better"/"efficient". Do you mean in terms of time? Number of actions (which may not be the same as "time" if you consider it takes longer to do something with a larger volume)? Total amount of water used? Is there no worry about evaporation or surface tension ("stickiness" of the soap to the surface)? Is the soap completely and quickly water-soluble (with no residue of relevance, and not difficult to rinse away)? If you are merely trying to get the lowest possible remainder, then there is no cost and a definite gain to using a larger amount of water in each rinse (though when a container becomes very full, it is harder to mix it evenly). And heck, may as well do it lots of times too (again, no cost). But if you are trying to conserve total water usage, then "many smaller batches" is generally more effective than "fewer larger batches" as long as each batch is large enough to mix well, not evaporate, and pour out easily (practical concerns of handling the material). DMacks (talk) 05:19, 16 July 2018 (UTC)[reply]

For clarity, the OP has already said "I guess by efficient I mean time and effort" which while maybe not completely clear, does seem to suggest water used isn't much of a concern in and of itself. BTW, I suspect there's also a reasonable chance it may depend on whether the container can be closed especially if we using an extreme like only talking about the amount of water used and not considering anything else. Nil Einne (talk) 08:22, 16 July 2018 (UTC)[reply]

Well, this is a standard math question in German schools (usually with only two fixed schemes given). Under the usual assumptions (spherical cows on a perfectly slippery surface in a vacuum, i.e. perfect mixture of rinsing water and soapy water, a fixed amount of liquid remaining in the vessel after each rinse, no evaporation or other funny effects, optimisation goal is minimal water usage) the solution in the limit is to do an infinite number of rinses with no water at all ;-). The less water you use for a given rinse, the higher the concentration of soap in the solution you pour out. So for a given amount of water you want it to go in in as small increments as possible. --Stephan Schulz (talk) 09:24, 16 July 2018 (UTC)[reply]

The reason why that works isn't mysterious, nor even mathematical. Suppose you have a vessel partly full of soapy water. Do you wash it out better by (a) mixing fresh water into the soap-water, or (b) throwing out as much of the soap-water as you can first? Clearly there can be no merit to contaminating the fresh water unnecessarily. Wnt (talk) 12:41, 16 July 2018 (UTC)[reply]

Anna re So, based on the above, is it better to use less water more times or more water fewer times?, if it's based purely on minimizing time, there will be an optimum. We had 30 seconds for 2 rinses with 1 liter, and 18 sec for 3 rinses with 0.1 liter. Let's consider 0.01 liter so with the same parameters you need 6 rinses. That would be 30.6 seconds, even worse than rinsing with 1 liter. If the number of rinses doesn't have to be an integer, then in this case the optimum would be about 0.129 liters for 2.84 rinses taking 17.88 seconds. That makes 0.1 liters very close to ideal. 173.228.123.166 (talk) 20:36, 16 July 2018 (UTC)[reply]

The OP posed the question with three techniques, each one starting with throwing out the soapy water. Thus each of the three starts with the pan in the same condition. She wants to end with zero soap in the pan, so each of the three ends with the pan in the same condition, whose degree of cleanliness is immaterial; it's the same state for each of the three techniques. She indicated that time and effort were her criteria. The three are fills of 10, 50, and 90 percent, swishing, and tipping out repetitively until zero soap is left. There are finite times involved: to fill to 90% will take nine times as long as for 10%. The effort of lifting will also be greater, but let us assume that this is not onerous and ignore it. The question then comes down to how much time is involved in filling versus how efficient the three different filling levels are, i.e. 10% will fill quicker from the tap but does it require more fills than 90% to achieve the same soap reduction? Kitchen experience tells me that 90% filling will dilute soap remnants much more than 10% will, but at the expense of taking longer to fill. Therefore I'd have to go with the mid-range figure of 50% as the best compromise of the OP's stated choices. There may be a more efficient filling of say, 25-30 percent, but the OP did not give that as an option. Akld guy (talk) 22:42, 16 July 2018 (UTC)[reply]

Thank you, everyone! I really, really appreciate the thoughtful answers. I am sorry I am so bad at asking questions. I guess that is part of being good at science: forming the experiment. Thank you again. I will try it all in the kitchen and see how it pans out, no pun intended. Anna Frodesiak (talk) 20:29, 17 July 2018 (UTC)[reply]

July 16

Fed wasabi peanuts to seagull

Yesterday, I threw a few of my wasabi coated peanuts to a seagull.

I was under the impression that birds couldn't taste spicy food, but obviously I was wrong in this case. The poor thing started shaking its head, running back and forth, scratching at its mouth and then vomited. Seems that wasabi does the same to gulls as it does to people who don't like it.

(didn't do it on purpose just to mess with it, I swear - it seemed okay afterwards and was eating the pieces of sandwich I threw out)

I've seen birds eating habaneros with no issues. I don't think it even affects them in the same way it does people. What's different about wasabi? — Preceding unsigned comment added by 91.207.175.200 (talk) 08:28, 16 July 2018 (UTC)[reply]

Have you never notices that the hit from chillis is completely different from that of wasabi (as for that matter, black pepper, Sichuan pepper and galic)? The 'heat' from chillis comes from Capsaicin. As mention in that article, it causes a burning sensation when it comes into contact with mucous membranes in mammals. The hit in wasabi, whether real wasabi or most of the stuff you get in the West (and I think even a lot in Japan), green coloured horseradish, comes primarily from Allyl isothiocyanate. (Also mustard and radish.) As mentioned in the wasabi article but not in the other articles, it primarily comes in the nasal passage in humans. And it isn't hydrophobic like capsaicin so is more easily removed with water where oils (including an emulsion like milk) is the best solution. While our article doesn't specifically mention the effect in birds, it does mention animals not mammals. And the places where it is present in plants as a defense mechanism against herbivores suggests the plant wouldn't want any animal who consumes it unaffected. (Although as our article on capsaicin sort of indicates, while it's advantageous to the plant that birds are unaffected by capsaicin, we can't be sure how much of a factor this was in its evolution.) Nil Einne (talk) 09:10, 16 July 2018 (UTC)[reply]

It may depend on the bird. Anecdotally, some parrots appear to enjoy eating wasabi (or at least things marketed as "wasabi"). Google for parrots and wasabi, and you can find examples of people giving them as treats to birds that apparently like them. I don't know if they are sensitive to the wasabi but eat it anyway, just like some people like spicy things, or if they just aren't sensitive to it. To give another anecdote from a different species, we were trying to train a young puppy to stop chewing on furniture, so we got a spray that is intended to taste/smell awful and deter them. We quickly found this particular spray was worthless because she would follow us around and lick it off anything we sprayed. I assume she was tasting something, but she clearly didn't perceive it as undesirable. Dragons flight (talk) 09:26, 16 July 2018 (UTC)[reply]

Some more research found [9] who found cloned chicken TRPA1 was activated by allyl isothiocyanate. Then again they also found it was activated by capsaicin. (There's some more research into how capsaicin affects chicken TRPA1 later which I didn't read in detail.) This is also looks interesting: I haven't looked at the paper [10], but the abstract suggests they found that one of the mechanism allyl isothiocyanate affects mammalian or at least mouse TRPV1 appears to be by binding to the capsaicin binding site and so this doesn't occur in chicken TRPV1. That said, this is fairly remote from the question. Maybe because my searches are too technical, I haven't found any source which actually mentions whether birds are known to show any response to allyl isothiocyanate. It's easily possible of course that the effect observed by the IP was not due to allyl isothiocyanate but due to something else. I'd also note it may depend on quantity, some of the sources I read make me wonder whether birds are really completely immune to capsaicin as commonly suggested or the effect is just a lot milder so you'd need a very strong dose for them to notice anything. Nil Einne (talk) 10:33, 16 July 2018 (UTC)[reply]

BTW on the evolutionary point I made above, I probably should also mention while there may be real evolutionary advantage for birds to be unaffected, there may also be little advantage for birds to be affected since I'm not sure if many are likely to eat the parts. Nil Einne (talk) 10:41, 16 July 2018 (UTC)[reply]

I suspect that the "parts" is really the key to understanding this. In chili peppers, the capsaicin concentrates in the fruit. This makes some evolutionary sense: mammals chew their food, especially plant-eaters, so seeds could well be crushed or damaged by them. It pays off for the plant to have mammals avoid them. On the other hand, birds tend to swallow stuff whole. So, peppers eaten by birds would be transported and deposited whole in the feces - exactly what the plant "wants". Quite an elegant solution. Wasabi, horse-radish, and radish are set up differently. In those cases, it is the stem/root with the concentrated toxins. Since it's almost never in the plant's favour to have this portion eaten or damaged, it makes sense that a more widely applicable material would be used. Matt Deres (talk) 16:29, 17 July 2018 (UTC)[reply]

The bird eats a whole chili pepper in one bite? Remind me not to cross that bird. Wnt (talk) 20:02, 18 July 2018 (UTC)[reply]

Molecular term symbols and electronic configurations

I think that I've made some progress in learning to interpret molecular term symbols, given available molecular orbitals. Taking dicarbon, and it's first eight electronic states, I've determined the electronic configurations to be as follows:

X: [He
₂] 2σ²
_g2σ²
_u1π⁴
_u
a/A: [He
₂] 2σ²
_g2σ²
_u1π³
_u3σ¹
_g
b/B: [He
₂] 2σ²
_g2σ²
_u1π²
_u3σ²
_g
c: [He
₂] 2σ²
_g2σ¹
_u1π⁴
_u3σ¹
_g
d/C: [He
₂] 2σ²
_g2σ¹
_u1π³
_u3σ²
_g

I'm fairly sure that I've correctly determined the first five configurations, but I'm uncertain about the last two. Should I opt for a configuration where the 2σ
_u is fully occupied and the 1π
_g is not left empty? It just seems odd to me to have the lower orbitals partially occupied while the HOMOs are full. However, the configuration that matches my suggestion requires additional unpaired electrons that looks like it would be unfavourable, for it to retain the same term symbol.

d/C: [He
₂] 2σ²
_g2σ²
_u1π²
_u3σ¹
_g1π¹
_g

For reference, the term symbols can be found at https://webbook.nist.gov/cgi/cbook.cgi?ID=C12070154&Units=SI&Mask=1000#Diatomic. Also, are my first five determinations actually correct? Plasmic Physics (talk) 12:37, 16 July 2018 (UTC)[reply]

I have no idea, but let's put some links on the table for context: term symbol, dicarbon, Swan band, Molecular_term_symbol#Alternative_empirical_notation. This old paper gives a subjective sense of the energies involved (page 10) - the difference between their two bonding states is enough to leave the lower state's bond vibrating from 1.1 to 1.7 Angstroms in length! ... Wnt (talk) 18:26, 16 July 2018 (UTC)[reply]

That should really be renamed 'Supplementary empirical notation', as it is used in conjunction with term symbols, not in place of. Plasmic Physics (talk) 22:36, 16 July 2018 (UTC)[reply]

Note that a and A are not the same. the lower case sequence is in the triplet state, with two electron spins the same, whereas the capital sequence have the singlet state, spins opposite. Graeme Bartlett (talk) 03:48, 17 July 2018 (UTC)[reply]

I know. It's just that they are both representable by the same electronic configuration short-hand where spin is not accounted for. Plasmic Physics (talk) 06:15, 17 July 2018 (UTC)[reply]

I have a stupid question ... but I can't help it. I thought the first superscripted number was the spin multiplicity, which I thought was the singlet/triplet thing. So why does the NIST table have an entry for d ¹Σ_u⁺ when all the other lowercase entries have a 3 at the beginning, which I take to mean that they are triplets unlike the X ¹Σ_g⁺ ground state? Wnt (talk) 20:19, 17 July 2018 (UTC)[reply]

I'm reasonably sure that it's a typographical mistake for exactly that reason, and because there is already a d state listed with lower energy. Plasmic Physics (talk) 04:21, 18 July 2018 (UTC)[reply]

Well, that helps me, at least. ;) And that means the D <--> X in a column to the right is consistent with all the others, in defining a transition from this state to another (in this case ground). I should also note the B state you mention seems to be missing, though I'd think there has to be one, since it's empirical!

Again, just to put down some links and get this straight in my mind (it won't be new to the original poster) the u and g are nicely illustrated at [11], which makes it apparent for example that p_u is bonding and p_g is antibonding, unlike with s and d. (I could still use a better notion of what "inversion" means; flipping the picture upside down would work the other way if the p orbitals were rotated 90 degrees; maybe these are viewed from within a nodal plane) [after I RTFA: inversion is through a point, i.e. x,y,z to -x,-y,-z. gerade (even) = no change in sign]. s, p, d, f come from the atomic orbitals joined, and thus indicate the number of lobes (or homogenous for s=0) around the interatomic axis. The numbers before s/p/d are principal quantum number and indicate total energy for the MO and hence I would presume the number of concentric shells going in and out toward the axis, less angular momentum. (that's not shown in the link above; I assume their example atomic orbitals are 1s, 2p, 3d to avoid that kind of node) When combined to molecular orbitals, these appear to get levels that start at 1 (1 shell, no concentric nodes), so the 1π in [12] is produced from two 2p orbitals, as is the 3σ. The same two molecular orbitals appear at [13] labelled as π_2p and σ_2p, with numbers based on what they were formed from. In either case the sigma is lower energy than the pi in oxygen and up, due to attraction to more protons; it is a sigma because the p orbitals point at each other and thus remain symmetrical around the axis. Anyway, we can use the diagram from the illinoisstate reference above to visualize where we are putting these electrons (not quite per the Aufbau principle). The NIST gives thermal energy for each energy level, albeit in cm^-1, which might need to be multiplied by hc (in some convenient unit) per E = hc/λ for conversions, but so far I haven't managed to see how to confirm your chart by the energy levels, which will be influenced by pairing for example. Wnt (talk) 19:57, 18 July 2018 (UTC)[reply]

I'll put the configuration in chart form to show my dtermination. Maybe it would make more sense to you:

Plasmic Physics (talk) 20:44, 18 July 2018 (UTC)[reply]

	X ¹Σ⁺ _g	a ³Π_u	A ¹Π_u	b ³Σ⁻ _g	B ¹Σ⁻ _g	c ³Σ⁺ _u	d ³Π_g	C ¹Π_g	d ³Π_g	C ¹Π_g
ΔE (cm^-1)	0	716.2	8391.00	6434.2	unlisted!	13312	20022.50	34261.3	20022.50	34261.3
1π_g* = π_2p*									(+ )	( -)
3σ_g = σ_2p		(+ )	( -)	(+-)	(+-)	(+ )	(+-)	(+-)	(+ )	(+ )
1π_u = π_2p	(+-) (+-)	(+-) (+ )	(+-) (+ )	(+ ) (+ )	(+ ) ( -)	(+-) (+-)	(+-) (+ )	(+-) ( -)	(+ ) ( -)	(+ ) ( -)
2σ_u* = σ_2s*	(+-)	(+-)	(+-)	(+-)	(+-)	(+ )	(+ )	(+ )	(+-)	(+-)
2σ_g = σ_2s	(+-)	(+-)	(+-)	(+-)	(+-)	(+-)	(+-)	(+-)	(+-)	(+-)

I stole your table above and messed with it a little so I can add to it more easily -- hope that's OK, you can revert if I screwed it up. ;) (I'm afraid if we start multiple copies they will get the Hook.) Wnt (talk) 22:30, 18 July 2018 (UTC)[reply]

I don't mind. Actually, I think it better this way, I just made an adjustment to the labelling of the highest MO, and moved the anti-bonding asterisks to the labels. Plasmic Physics (talk) 22:34, 18 July 2018 (UTC)[reply]

Yeah, my foulup ... you ec'd me before I could fix. ;) I've added some energies though ~~the labels above them are confusing me a bit.~~ oh, never mind, there were two options for C and d from the beginning. Wnt (talk) 23:27, 18 July 2018 (UTC)[reply]

Ow. There are a bazillion sites with those MO diagrams showing "energy" as an axis ... trying to find one that puts numbers on that ruler is a whole other thing. But in searching I stumbled across [14] which gives the wavefunction of the ¹Σ_g⁺ state of C₂ as ... well, I don't know the math markup well enough to write it, check page 30. There are four terms with expansion coefficients depending on the radius... somehow this has to do with why a singlet state is most stable, see their explanation. I think I am in my familiar haunts, "not even wrong" territory, all over again. Wnt (talk) 23:39, 18 July 2018 (UTC)[reply]

OK, so now that it's neatly diplayed, what do your recon - which configuration for d and C should be more stable from a theoretical point of view? I'm not asking about c right now because I can't come up with a more reasonable alternative. Plasmic Physics (talk) 03:26, 19 July 2018 (UTC)[reply]

Well, putting the labels on top, the issue I think you mentioned initially is that the first two don't seem right in terms of spin. AFAIK if two electrons have opposite spins, then any angle you measure them from they should cancel out; but if they have the same spin, you can look from the "equator" and get zero, or look from the "pole" and see two half-spins adding up to 1. (to the degree that this mystical landscape exists) Your second choice is consistent with that, as are all the others. However, these may be just one possible term contributing to these energy levels... that last source I gave certainly should make good reading. I should note that it actually plots very different energies for a "1¹Σ_g⁺" and a "2¹Σ_g⁺" on page 29 ("complete-active-space (CAS) SCF calculations", for reference) ... is the latter from 3s orbitals? I don't recall this nomenclature. Their Figure 17 on Page 31 shows the ¹Π_u and ³Σ_g at equal stability (that's "orbital energy in hartrees", likely a useful search term) at a radius of 2.2 Bohr - sigma is more stable further out and pi closer, as you'd expect since a straight-on overlap of orbitals should reach further. Tug the molecule to 2.5 bohr and a ³Π_u is the lowest energy state; take it to 3.5 and b ³Σ_g^- becomes the lowest. (Incidentally, I don't know the basic issue if you can spin a molecule in vacuum like a planet and rely on conservation of angular momentum to make these actually be ground states by "centrifugal force", or if molecules necessarily are able to drop the angular momentum together with energy of rotation photon by photon until they are at rest) Wnt (talk) 12:01, 19 July 2018 (UTC)[reply]

I just fixed it up a bit. I could have sworn that I had the spins for the first d/C set around the right way. I also filled in the B term symbol. I'm reasonably certain that each state has only one term symbol, since a state is defined precisely by the electron configuration. Your reasoning sounds solid and all, but how does it apply to which d ³Π_g and C ¹Π_g configuration (state) is most stable? Plasmic Physics (talk) 13:06, 19 July 2018 (UTC)[reply]

There's a tutorial here; the TMP Chem channel there seems like it may contain more useful content, though I have yet to find an index. It doesn't cover C2, but illustrates that even a single partially filled molecular orbital can end up leading to all manner of term symbols! Wnt (talk) 21:57, 19 July 2018 (UTC)[reply]

I see what you intend, but that not what I'm trying to figure out. In the example for B₂ in the tutorial, it is demonstrated that there are multiple ways of partially occupying degenerate pi orbitals, corresponding to unique states shown by their term symbols. However, I'm trying to work backwards - I already have the term symbol, and I want to figure out the most likely configuration of the electrons that would genenerate said symbol. I'm essentially trying to solve problem seven of the text book chapter that you linked to earlier. Plasmic Physics (talk) 06:56, 20 July 2018 (UTC)[reply]

Planting with a machine gun

I had a crazy image in mind of a Vietnam-era helicopter planting crops by machine gun and, to my surprise, actually found real web references: seeds in bullets wanted (from the final halcyon days of Obama), for home defense or something (with a YouTube video that, like every video worth watching that used to be on YouTube, has been censored) even tree planting (though not actually fired at range. But all these are written as if they're the only ones who ever thought of it - I don't know any general terms to use, or principles that apply. I would suspect, for example, that plowing may be hard to do without, and seeds planted this way might never compete for enough nutrients to be agriculturally relevant; yet I've read at times claims that plowing is actually avoidable - I'm no farmer to know. Is it possible to embed seeds in biodegradable bullets and plant a reasonably successful crop from the air? Wnt (talk) 17:46, 16 July 2018 (UTC)[reply]

...perhaps your subconscious mind conjured this misinterpreted imagery after you heard an agronomist discussing ballistic dispersal? Nimur (talk) 18:00, 16 July 2018 (UTC)[reply]

It's more likely I once glanced at the Obama-era headline; ballistic dispersal is about making seeds fly, not embedding them in the ground when they land. (That I know of ... there's probably some crazy species out there I don't know about that leaves a vine growing out the body of some wretched herbivore... yummm, Shawn Ashmore...) Wnt (talk) 18:17, 16 July 2018 (UTC)[reply]

Guerrilla gardening has popularised the term seed bomb. See DIY: Make Your Own Wildflower Seed Bombs: "The instructions are simple enough, a bit like making chocolate truffles. Takes 30 minutes." Carbon Caryatid (talk) 20:36, 16 July 2018 (UTC)[reply]

https://www.sbir.gov/sbirsearch/detail/1207769 --Guy Macon (talk) 04:12, 17 July 2018 (UTC)[reply]

I'm surprised the seeds would survive the shock from explosions. I'd have thought it would cook the seeds.. Dmcq (talk) 08:21, 17 July 2018 (UTC)[reply]

A rail gun would avoid the explosion and greatly reduce the heat. It would, obviously, induce a heavy ionized field which may or may not affect the seeds. However, I've never seen any design at all for a rail "machine" gun. All functioning models I've seen are one-shot deals with a lot of setup between shots. 209.149.113.5 (talk) 17:09, 17 July 2018 (UTC)[reply]

Some seed varieties would probably survive. Some almost certainly wouldn't. This keen collector of home grown seeds can tell you that a normal bean seed won't survive the fall from a table to a concrete floor. (Probably why nature invented those nice packages for them that we call beans.) So I doubt they would survive a machine gun. HiLo48 (talk) 23:21, 17 July 2018 (UTC)[reply]

Not a machine gun, but a cannon was successfully used by John Murray, 4th Duke of Atholl to plant trees on an inaccessible crag near Dunkeld in Scotland in 1788. A special type of canister shot was devised by the artist Alexander Nasmyth, who was also an amateur inventor, and they were fabricated by a local tinsmith. The trees are still growing apparently. See On Planting by Cannon. Alansplodge (talk) 20:08, 19 July 2018 (UTC)[reply]

When Trans woman get breasts from hormones or surgery, can they feed babies breast milk?

What is best scientific answer to this question? Sphinxmystery (talk) —Preceding undated comment added 18:30, 16 July 2018 (UTC)[reply]

They can only do that after babby is formed. 173.228.123.166 (talk) 20:17, 16 July 2018 (UTC)[reply]

According to Male lactation, even some men can breastfeed. According to Witch's milk, even some babies produce this nutritious life-fluid. Carbon Caryatid (talk) 20:40, 16 July 2018 (UTC)[reply]

Implants would be of no use, and can even be problematic. Hormonal treatments would be necessary to induce lactation, just as Caryatid mentioned.--Khajidha (talk) 12:32, 17 July 2018 (UTC)[reply]

Gynecomastia is a common condition in which male breasts start developing the same as female breasts do during puberty. In some cases the enlargement disappears after a couple of years and in others it persists. It typically happens during puberty. If the man is obese the breasts may look like those of a typical woman. They can certainly produce breast milk. The cause may involve fluctuations in estrogens and androgens, but the male can have quite normal appearance otherwise. The cure is typically mastectomy, in that the mammary tissue is removed in a minimal operation. Since it is a cosmetic operation and the breast is not typically cancerous, removal of large amounts of tissue is not necessary, and the nipple is preserved. Edison (talk) 14:30, 18 July 2018 (UTC)[reply]

Horse chestnut sap causing blue colour

Following a recent discussion I have been trying to find information about the chemical reaction that is happening when young horse chestnut twigs are put into water and the sap causes a distinct bluish colour in the water. I have witnessed this effect on many occasions but the effect and its cause seems curiously absent from the web. Or perhaps I am inept. I wonder if there are any chemicobotanists or anybody in the house that might give me some direction or indication of the cause of the phenomenon. Richard Avery (talk) 22:45, 16 July 2018 (UTC)[reply]

This article about a closely-related species, Aesculus indica states that aesculin is the source of the blue color, which turns from clear to blue at the correct pH, see here. --Jayron 32 02:51, 17 July 2018 (UTC)[reply]

Thanks Jayron, that adds to the meagre info I have. Richard Avery (talk) 18:44, 17 July 2018 (UTC)[reply]

July 17

Impairment of dolphin function during sleep

I've heard that dolphins sleep one hemisphere of their brain at a time. Since the hemispheres of the human brain perform different complementary tasks (like, I think, the left side senses or controls the right side of the body/eye while the right side senses or controls for the other side); does that mean that one side of a dolphin's body is impaired during sleep? --129.215.47.59 (talk) 10:43, 17 July 2018 (UTC)[reply]

Your assumption that "the left side senses or controls the right side of the body/eye while the right side senses or controls for the other side" is incorrect. See Hemispherectomy and Ahad Israfil. Also see [15]. "The important functions our brain carries out are not farmed out to single distinct brain regions, but instead supported by multiple regions, often in similar but slightly different ways. If one structure breaks down, the others can pick up the slack."[16]

Jeeeee-zus. Peri-insular hemispherectomy has been developed to allow for seizure relief with minimal brain tissue removal. In this procedure, the surgeon aims to disconnect (rather than remove) the hemisphere, in order to minimize long term complications. What if you wake up from the operation to realize that you're the disconnected hemisphere? Wnt (talk) 20:00, 17 July 2018 (UTC)[reply]

Split brain patients, although they experience very interesting phenomena, appear to not experience "two consciousnesses". My guess is because they are still connected through the brainstem, particularly the reticular formation, which is central to consciousness. --47.146.63.87 (talk) 07:09, 18 July 2018 (UTC)[reply]

I had a look at that paper used to support there being a single consciousness and I believe the conclusion is junk. The findings they got are interesting but they have no relation to anything about consciousness. In fact it would help if they actually gave some criterion for consciousness being detected as being the same - but the results can all be explained by blindsight which people do not associate with consciousness at all - quite the reverse. Dmcq (talk) 12:30, 18 July 2018 (UTC)[reply]

Article about the general idea: lateralization of brain function. --47.146.63.87 (talk) 07:09, 18 July 2018 (UTC)[reply]

As for dolphins, see Dolphin#Sleeping. Also see [17][18][19] BTW, we (sort of) do it too.[20] --Guy Macon (talk) 16:03, 17 July 2018 (UTC)[reply]

While humans and other animals are forced periodically to stop all activity and sleep, dolphins have evolved alternate half-brain sleep as a means of keeping alert against predators (sharks) for more than two weeks. An experiment found that dolphins' echolocation sense was undiminished. In the future a dolphin may be fitted with a portable EEG backpack to learn more about its handling of complex tasks during the half-sleep state. Another experiment found that acquired information is transferred between the two hemispheres of the their brain. DroneB (talk) —Preceding undated comment added 16:17, 17 July 2018 (UTC)[reply]

Nutrition: How long does it take to add 10 kg (22 lb) to one's weight, while consuming 5000 kcal per day (by eating cakes)?

Current weight: 50 kg (110 lb).

Current height: 170 cm (5ft7in).

Health: good.

Sports: no. HOTmag (talk) 14:06, 17 July 2018 (UTC)[reply]

[21]. --Jayron 32 15:06, 17 July 2018 (UTC)[reply]

Thnx.

Resolved

HOTmag (talk) 18:26, 17 July 2018 (UTC)[reply]

Drowning spiders

Do spiders have any in-built resistance to water? How long does a spider take to drown? I mean ordinary small household ones, not huge furry ones like a tarantula. Thanks. 86.190.109.151 (talk) 18:20, 17 July 2018 (UTC)[reply]

Not by any means a full answer to the question, but see diving bell spider. Looie496 (talk) 18:59, 17 July 2018 (UTC)[reply]

It depends on the species, but remember temperature is crucial, since arthropods are ectothermic. I've been amazed how long insects can survive submerged in ice-cold water - literally hours! Wnt (talk) 19:57, 17 July 2018 (UTC)[reply]

Here's an interesting article about spiders in lab conditions seemingly drowning and then reviving.[22] ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:39, 17 July 2018 (UTC)[reply]

In my part of Australia the best known habitat for Daddy Longlegs spiders is the shower cubicle. (The first photo in that article is a perfect example of these cute little guys.) They seem capable of surviving all sorts of inundations. HiLo48 (talk) 23:31, 17 July 2018 (UTC)[reply]

Here is our article on this subject.John Z (talk) 04:28, 18 July 2018 (UTC)[reply]

With all due respect, the article assumes permanent immunity to rainwater events, provided there is a subsequent solar event each time that is sufficient to dry up "all the rain". Partial drying up of the rain might well reduce resistance and/or impair climbing ability. I'd suggest that some scientific, double-blind testing should be reported, preferably from a peer-reviewed tertiary source. And does this effect hold true only for itsy bitsy size, or does it also extend to bigger lactose-tolerant individuals?? I think we should be told. Martinevans123 (talk) 14:49, 18 July 2018 (UTC)[reply]

As chance would have it, I have been conducting informal, admittedly somewhat impressionistic tests of the reported tendency of arachnids to rescale climbs after being subjected to a hydrodynamically consistent deluge of water. Which is to say that, despite being, for the moment anyway, halfway across the world from Hilo, I too have been sharing my shower cubicle with a truly teeny Pholcidae, who has shown the utmost patience and tenacity in responding to my destructive showering habits and the attendant risks to life and web (I'd say life and limb, but she's lost one leg somewhere already, so clearly she's willing to suffer some loses in this regard; I call her "Lucky/#7" and no, shut up, that's not at all weird and no I haven't been accused of talking to bugs too much since I was a kid...).

Of course, all of that has more to do with spider mobility, endurance, and stimuli-response strategies than the OP's original inquiry as to drowning, so--just to prove what a hopeless stick in the mud I am--I'll now follow up my rare attempt here to get in on the humour with discussion of some of the spider physiology that is relevant to that inquiry. Specifically, all spiders who are ambush predators, rather than active hunters (which is to say, the significant majority of all spider species) have evolved a metabolic physiology that is consistent with this ecological niche. Most such spiders cannot be certain of how often their meals will arrive, so while waiting, they enter into states of subdued metabolic function. A happy side-effect of this, from the spider's perspective anyway, is that this aspect of their physiology (while generally believed to be a consequence of their adaption to their particular variation of a predatory ecological niche and the need to conserve calories over an extended period) means that they are also capable of making do on relatively little oxygen for stretches that would kill most other organisms at their level of complexity. This is of course true for a great many arthropods who specialize in long periods of stillness punctuated by rapid bursts of movement in response to certain stimuli. Snow ^{let's rap} 14:26, 20 July 2018 (UTC)[reply]

Ah ok. So, in simplistic terns..... "you can't drown 'em if they're hungry"?? Martinevans123 (talk) 14:31, 20 July 2018 (UTC)[reply]

Ownership of Ryugu and Ceres

Now that we've found this great big pile of fertilizer, we have to decide who is a thief for using it.

The recent mission to 162173 Ryugu seems like the sort of thing that might trigger the thing Obama signed in 2015 (see commercialization of space) creating a new sort of pseudo-property "right" for those who first exploit an outer space object. As a hazardous near earth object, I imagine returning metals from that site should be especially feasible. Also, the Dawn (spacecraft) mission also seems to have done much to scout out resources on Ceres (dwarf planet) - what struck my eye is that the white salt mountains [23] are apparently made of sodium carbonate and ammonium chloride, making Ceres a great place to send nitrogen into space cheap. Now, traditionally, there was not going to be ownership of such things (Outer Space Treaty), and I still don't know how this is going. Should we have a Japanese flag icon on the Ryugu article/infobox? Is it still debated whether one party can claim entire asteroids or minor planets? And to what degree should these scientific missions be taken as prospecting expeditions rather than pure science? Wnt (talk) 20:10, 17 July 2018 (UTC)[reply]

This 2010 episode of Big Picture Science - the official podcast of the SETI Institute - is entitled Space Race 2.0. Among the esteemed guests were Burt Rutan and a few others; the topics discussed included property rights law in the new era of spaceflight.

In my storied days of hanging around with space-weirdos, I've met a fair shake of characters who are very enthusiastic about property rights (and mining rights) for objects in outer space. I've met a few who tried to sell these property rights to the U.S. government, the duke of Luxembourg, and the billionaires who run Silicon Valley. It is my estimation that most of these fine entrepreneurial-spirited characters are comprised of that most fascinating dual combination: crank-scientist and con-artist. It doesn't mean that they don't get high-profile press coverage - just that they aren't really people who you ought to take seriously.

Regarding the topic: the reliable sources for our articles ought to be official statements by governments, space agencies, and if we're being generous, we could accept official press releases from commercial spaceflight entrepreneurs who have at least actually launched a real mission. (As of 2018, there are a lot fewer of those commercial spaceflight entrepreneurs than the mass-media would lead you to believe).

JAXA's website on the Hayabusa 2 space probe does not make any public assertion of any property ownership right. Real spaceflight engineers tend to be a realistic bunch who try to avoid making ridiculous statements. On the other hand, the folks who associate with the so-called "NewSpace" movement - the kind of space-groupies who talk about near-term space-colonialism and mineral ownership contracts - tend to be proponents of, or at least victims of, pseudoscience, counterfactuals, and general quackery.

Nimur (talk) 20:25, 17 July 2018 (UTC)[reply]

Space law, Outer Space Treaty, Commercial use of space, Treaty Clause. --Guy Macon (talk) 22:24, 17 July 2018 (UTC)[reply]

Under what legal or philosophical principle do these individuals claim to have property rights over space stuff that they could sell to the US Government or anyone else? Iapetus (talk) 10:10, 18 July 2018 (UTC)[reply]

If I could generalize, I would say that many enthusiasts embrace an analogy between extraterrestrial territory and the open range of the American West; they espouse a few bold and provocative ideas about "manifest destiny in space" that sound exciting and adventurous; they put together business-proposals by cherry-picking scientific data-points from reputable space-research; they can make the profit potential sound really incredible; and all this hubris lasts until anyone inquires about how heavy the life-support systems will need to be in the space-rancherias, or how we'll actually build them - right about when the project is mature enough to require an actual scientist or engineer. Then it collapses, everyone has a good laugh, and the investors eat the losses - or better yet, they sell it to a government who doesn't know any better. ...or they sell it to one whose ulterior motive is undisclosed but for its unspokenly obvious infatuation with commercially acquiring very large rockets.

The whole lifestyle is developed when the reader of science fiction takes certain fictions a little too seriously. It's hard to say when the "space cowboy" genre was invented, but we can surely call out a few key works: in the 1966 fictional work, The Moon Is a Harsh Mistress, Robert Heinlein lays out a political philosophy of libertarian idealism and the economic and political implications of moon-colonialism. I have actually heard this book cited in a sales pitch for an asteroid mining venture. In multiple distinct instances.

While such fiction can be entertaining and inspirational, it ought not be used as an actual model for real life: the book's details are fiction. Also, ... in that story, everybody dies, the space-government collapses, and the colonists get stranded on the moon, so even if we suspend our disbelief of the scientific details, it's a story about a failed space mining venture. It just goes to show that certain attention-deficient individuals can't even get to the last chapter of the fiction-book they idolize.

Nimur (talk) 14:15, 18 July 2018 (UTC)[reply]

July 18

Vickers Hardness Number Notation

why does vickers hardness value is represented as 4500HV without the load ? how do i read it ? what is the load ? help i found this on many websites — Preceding unsigned comment added by Kinetc ner (talk • contribs) 05:47, 18 July 2018 (UTC)[reply]

See Vickers hardness test. 173.228.123.166 (talk) 06:19, 18 July 2018 (UTC)[reply]

Calibrate radiation detector

"To ensure they got the right items, the specialists from Idaho brought radiation detectors and small samples of dangerous materials to calibrate them: specifically, a plastic-covered disk of plutonium, a material that can be used to fuel nuclear weapons, and another of cesium, a highly radioactive isotope that could potentially be used in a so-called 'dirty' radioactive bomb."[24]

Why did they need "small samples of dangerous materials to calibrate" the "radiation detectors"? Couldn't they just calibrate the radiation detectors before they left on their journey?

I originally raised this question in this thread. Bus stop (talk) 07:08, 18 July 2018 (UTC)[reply]

There are many different radiation detector instruments such as Scintillation counters and the commonest Geiger counter types that may give a readout in counts or radiation dose. An operator should always have access to radioactive calibration samples that allow confirmation that a particular instrument is working, identify its pickup range and demonstrate its different responses to a source and to background radiation. See Geiger counter and, for details of dose measurement Geiger–Müller_tube#Energy_compensation. The Ludlum 3030 pictured in the OP's cited article is a Scintillation counter instrument. DroneB (talk) 16:27, 18 July 2018 (UTC)[reply]

This is just a guess (if you read the article you will see that the government is trying really hard to stop us from finding out any details about this incident), but if you are going somewhere where you will be picking up some radioactive material, you really need two ranges of detection: [A] a high range to tell you if this is a situation where you need to evacuate the entire neighborhood and send in a robot with a lead box, and [B] a really sensitive detector that will tell you if you are leaving a tiny bit behind. [A] and [B] may be ranges on the same instrument or they may be separate instruments. Calibration of [B] really doesn't matter. The only answers you care about are "none detected at the most sensitive range" and "hey, I am getting a trace reading from behind this filing cabinet!" Calibration of [A] is fairly important, but verification that [A] is working and not broken is absolutely critical. Critical as in "a bunch of people could die if the high range of this meter was broken and didn't warn us of the danger." If it were me, I would bring along calibration sources suitable for both ranges and test the meter(s) before and after visiting the site. --Guy Macon (talk) 16:58, 18 July 2018 (UTC)[reply]

I found something that seems to be referencing why it may be necessary to calibrate the instruments upon reaching their destination:

"Modern LS counters offer the possibility of both qualitative and quantitative analysis of alpha and beta emitters with high precision and accuracy, offering at the same time low detection limits. As many other instrumental techniques, liquid scintillation spectrometry requires robust and reliable calibration to accurately measure radiation [2, 3]. However, the detection efficiency of the counting equipment will vary depending on a range of factors including radionuclide emission and associated energy, sample composition, scintillator and vial type. All these factors must be accurately quantified and corrected for during routine measurement. In addition, the detection efficiency will vary with time due to deterioration of instrument optics and periodic recalibration is therefore required. In order to address these issues the most commonly used approach is to calibrate the LS spectrometers using a set of standards of known activity and a varying amount of quench."[25]

The term "quench" is spoken of here:

"Liquid scintillation counting makes use of an intimate mixture of radioactive sample and detecting medium which translates atomic radiation into light flashes. The light intensity of such a flash is proportional to the deposited energy in a burst of radiation, but the constant describing this proportionality may change from sample to sample because of chemical differences in various radioactive preparations. This chemical loss in detection efficiency is known as “quenching” and needs calibration if one is to get quantitatively meaningful results from liquid scintillation counting. Many ways are available for measuring quenching correction, and these have been reviewed by Peng [1]."[26]

I can't say I fully understand any of this. Bus stop (talk) 01:22, 19 July 2018 (UTC)[reply]

What enzymes take place in glucose re-absorption?

I came across this question and answer in which states that there is a condition in which decreased activity of glucose reabsorption enzymes could be. I googled for "glucose reabsorption enzymes" and found a very few results, most of them are copy paste of this site and don't really have information about that. In addition I red the wiki article "renal glucose reabsorption" and yet I didn't find any reference for such enzyme. Do you have an idea what it is? --93.126.116.89 (talk) 13:24, 18 July 2018 (UTC) "[reply]

You'd be having difficulty because no ordinary person calls it an enzyme. SGLT2. Someguy1221 (talk) 20:36, 18 July 2018 (UTC)[reply]

mystery spider

Can anyone identify this spider? She lives in a big web on a bush in Oran, Algeria (near the sea). Maybe 6-8cm, including the legs. Thanks, Henry ^Flower 15:13, 18 July 2018 (UTC)[reply]

Try and drown it? This should narrow it down, apparently. Martinevans123 (talk) 15:17, 18 July 2018 (UTC)[reply]

Probably an argiope lobata - quite similar to this image. Mikenorton (talk) 15:57, 18 July 2018 (UTC)[reply]

Splendid, thanks (also for the word stabilimenta).

Resolved

Henry ^Flower 16:52, 18 July 2018 (UTC)[reply]

Perhaps the painting of the Mona Lisa could be said to contain stabilimenta, or would that be craquelure? Also, that spider appeared to have a thin-faced smile. Please see here in archives. Bus stop (talk) 14:33, 19 July 2018 (UTC)[reply]

Reference Desk Staff

What are the requirements needed to answer questions here? Limited Brain Cells (talk) 18:27, 18 July 2018 (UTC)[reply]

I don't believe there are any formal requirements and some of us are better than others in providing good-quality answers but to be on the safe side the inclusion of sources is generally a good idea so that anyone reading a response can verify your assertions. Bus stop (talk) 18:54, 18 July 2018 (UTC)[reply]

We have an informational wiki page, Wikipedia:About.

"Wikipedia is ... based on a model of openly editable content..." Like other pages, the Reference desk is "...written collaboratively by largely anonymous volunteers who write without pay. Anyone with Internet access can write and make changes to Wikipedia articles, except in limited cases where editing is restricted to prevent disruption or vandalism. Users can contribute anonymously, under a pseudonym, or, if they choose to, with their real identity."

Contributors here are volunteers who choose to help maintain the project. We are not "staff" in the sense that nobody hires us, manages us, or pays us, for our efforts.

Many of us carry credentials, but the general guidelines are summarized in our informational page on Wikipedia:Expert editors. Being an expert, in this environ, does not carry any special privilege, other than the enhanced ability to write well and to efficiently find and to cite sources.

Nimur (talk) 22:03, 18 July 2018 (UTC)[reply]

There are no requirements, anyone can do it, and many do. "If you have knowledge and the teaching instinct, here is a classroom of the world." 173.228.123.166 (talk) 22:33, 18 July 2018 (UTC)[reply]

Lead soldered kettle

I see people repairing kettles with what appears to be solder. Is that lead? Won't that end up in the boiled water? Anna Frodesiak (talk) 20:22, 18 July 2018 (UTC)[reply]

Some solder is lead-free, some has lead. Sagittarian Milky Way (talk) 20:28, 18 July 2018 (UTC)[reply]

The solder sold for pot repair is usually zinc. Someguy1221 (talk) 20:34, 18 July 2018 (UTC)[reply]

Thank you both. Next time I pass a kettle repair shop, I will see what he uses. If it is lead, it is bad, right? Many thanks. Anna Frodesiak (talk) 20:34, 18 July 2018 (UTC)[reply]

Probably? In the case of leaded glass, a food and liquids stored therein take hours to days to reach dangerous concentrations of lead (Lead_glass#Safety). So a lead slow-cooker would probably be disastrous. I have no idea though, if short-term contact can expose the food to a lot of lead if the lead is very hot. I mean, the safety tests with leaded glass were done at around room temperature, not boiling. I'd avoid it if it's lead. Someguy1221 (talk) 20:41, 18 July 2018 (UTC)[reply]

Wow. A lot of people use those kettles here. I do hope it's pure zinc solder. Anna Frodesiak (talk) 20:50, 18 July 2018 (UTC)[reply]

A US penny made after 1982 is nearly pure zinc plated with copper. It can be melted over a (non-electric?) kitchen stove in a spoon but the higher melting point and cost is why zinc is not the first choice for solder. I note that breathing metal vapors might not be harmless Sagittarian Milky Way (talk) 21:41, 18 July 2018 (UTC)[reply]

Soldering is done with solder, an alloy of tin and lead. Neither pure tin, nor pure lead, are much use as solders. Even now that leaded solder is prohibited for many tasks, the tin has to be alloyed with something else (BTW - don't fly on aircraft relying on lead-free solder for their electronics. The unreliability of unleaded solder has already started to kill people.)

Assuming a repairable "kettle" is made of brass or copper, then it's not much of a hazard if it's used to boil plain water. But either of these metals, used as a general cooking pan, is distinctly unsafe unless it's tinned (lined) inside with solder.

Leaded solder has a very long history and has largely been an insignificant risk. When vessels or pipes were made of lead, the lead from the solder alloy joining them wasn't an issue. Only in recent years, once we've largely eliminated lead exposure in the diet, has solder become at all significant as a component of the sources for it. As with lead plumbing, it also depends what your water is like and what you're cooking. Hard water is of very little risk with lead, as it deposits calcium minerals on it, rather than dissolving the metal (any metal). Soft water though, or something more acidic, such as pickling for preservation, and you have a much more serious exposure risk - and copper is perhaps worse than lead here, at least for acute toxicity. Andy Dingley (talk) 23:39, 18 July 2018 (UTC)[reply]

Airplanes still have lead in their gas - why would they bother taking lead out of the solder? Anyway, I'm going to have to call "citation-needed" on the claim that fatalities have been reliably attributed specifically to an electronic failure directly caused by the use of unleaded solder ... that seems like a pretty specific claim that warrants a reliable source to back it up. Nimur (talk) 04:24, 19 July 2018 (UTC)[reply]

Not for the passengers, but for the assembly line workers putting the things together. Greglocock (talk) 06:06, 19 July 2018 (UTC)[reply]

Not exactly death, but here is a reliable source for potential deaths: [27] --Guy Macon (talk) 05:58, 19 July 2018 (UTC)[reply]

That's only true for aviation gasoline, which you linked. Only piston-engine small planes use that; jet engines use jet fuel. Of course I still think it should be banned. --47.146.63.87 (talk) 06:51, 19 July 2018 (UTC)[reply]

Aviation (and other safety critical industries) has an exception which permits leaded solder in its electronics. However lead-free electronics has distinct long-term reliability problems (see tin whiskers), and the lead-free majority of components are finding their way into many products, even those requiring reliability. Andy Dingley (talk) 08:36, 19 July 2018 (UTC)[reply]

Thank you all. By the way, Andy, the kettles I see getting repaired here appear to be stainless steel or something. Definitely not copper anything. Anna Frodesiak (talk) 04:47, 19 July 2018 (UTC) [reply]

Unhelpful. Matt Deres (talk) 11:57, 19 July 2018 (UTC)[reply]

The following discussion has been closed. Please do not modify it.

I seem to recall from previous RefDesk posts that you live in the PRC. If true, my money would be on it being lead solder. Hey, what's a little irreversible brain damage between ~~peons and overlords~~ friends? --47.146.63.87 (talk) 06:51, 19 July 2018 (UTC)[reply]

Please do not insult China. We are not peons and the the government is not an overlord. If you came to China you would see how ignorant such a statement is. You geolocate to USA. If you are actually there, you might consider examining your arrangement. It's been looking a little like peons and overlords lately. Anna Frodesiak (talk) 07:30, 19 July 2018 (UTC)[reply]

That said, leaded solder is still widespread in China. Removing lead from consumer electrical products (like the idea of properly insulating or earthing them) is just not seen as so important in China. Andy Dingley (talk) 08:36, 19 July 2018 (UTC)[reply]

Hat this, please. Anna Frodesiak (talk) 07:31, 19 July 2018 (UTC)[reply]

I'm surprised to see stainless steel kettles being repaired. I would expect India to be doing this, possibly China, but very rare elsewhere. Stainless steel is not a ductile metal, so it's impractical to make a stainless steel vessel by hand, rather than using large powered machines. So countries (such as Turkey or India) where there's still a large market for hand-make vessels are largely making them from copper or brass, then repairing them later. Once stainless steel becomes widely adopted though, the manufacturing economy has shifted to factory production of one-use, non-repairable items on the Western model. India also uses a lot of thin stainless sheet for cooking vessels and tableware. This stainless sees far less hand repair afterwards - it doesn't need it (much harder to wear such items out than a copper pot) and it's also harder to do (soldering stainless is hard work and often unpleasant). I solder stainless steel a lot myself, but I do it by hard soldering (a gas flame) rather than soft soldering, at a lower temperature with a heated metal tool or soldering iron (which is usually a block of copper, not iron). The solder and flux I use is silver solder, which is expensive because of its silver content, and also (the older grades) quite toxic because it contains cadmium. You really don't want cadmium alongside food. Cadmium has largely gone from silver solder now, but that increases the silver content and price even more so. Even the flux, a fluoride compound, has aggressive fumes when heated. Andy Dingley (talk) 08:36, 19 July 2018 (UTC)[reply]

Video showing process using large corn kernels in a roadside machine in Haikou, Hainan, China.

Hi Andy. First, yes, China may indeed still use lead and be a bit behind the times. However, this repair thing is rare. We're seeing the very last of the walking knife sharpener, the small, kettle repair shop, and I haven't seen a puffed grain man in years. There are probably only half a dozen kettle repair shops in this city of 2 million, and they'll likely be gone for good in a couple of years.

So, understood about the solder. That is very interesting, actually, and seems a bit asbestosy, in terms of 'you shouldn't be near it'. The repairmen, by the way, just seem to fix teensy holes. Also, I think I saw them once take off a bottom and solder it back on. So strange, these kettles are cheap. Why fix them? I guess the old people are a bit stuck in their ways here and are used to fixing things to save money. Young people would never do that. Best wishes and many thanks for the thoughtful answers. Anna Frodesiak (talk) 18:01, 19 July 2018 (UTC)[reply]

July 19

Does gravity always point to somewhere in the Earth's core?

I know there are points on the Earth's surface where gravity points along a line that detectably misses the Earth's center of mass. But are there any where a line in the direction of gravity doesn't even go through the Earth's core? Neon Merlin 08:11, 19 July 2018 (UTC)[reply]

No, the Earth's gravitational field is nearly spherically symmetrical. Deviations from this symmetry are small. Ruslik_Zero 08:45, 19 July 2018 (UTC)[reply]

[e/c] :No. Assuming the Earth is a homogeneous density sphere, (which it is not) the gravity vector will always pass through the geocenter. However, since the Earth is actually a bit elipsoidic, (see Reference ellipsoid) there is a difference in angle between spherical and ellipsoid normals (Vertical deflection -- see also: geoid). This difference is very small, however, relative to the diameter of the Earth's core. Also, since the core is more dense than Earth's average, this will add even more "attraction" to the center. There are some gravitational anomalies (local variations of the gravity field) that distort the force vector angle, but doubtfully enough to bypass the core; there might be an artificial condition where this is not true -- perhaps standing right next to Fort Knox? —2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 09:05, 19 July 2018 (UTC) ... since your two questions are diametrically opposed (colloquially, not literally), the answers are "yes" and "no".[reply]

The core is really big, with a radius of 3,470 km, it would have to be a huge deflection (33°), which is highly unlikely - see vertical deflection, which talks about deflections up to 50 seconds of arc. Mikenorton (talk) 09:30, 19 July 2018 (UTC)[reply]

Guys, that's the kind of question where you need to show the numbers.

Gravity of Earth is the relevant article here. The two most important effects that explain local variations of gravity are (1) the centrifugal force due to Earth's rotation and (2) the fact Earth is not exactly round but slightly flattened at the poles. The article states that the combined effect is a 0.5% change in g between poles and equator ~~(this is why all space rocket launching pads are near the equator)~~. By comparison, local deviations are about 0.005% of g (5e-4 m/s2 max changes, g~10m/s2).

The exact details of how much of the variation in magnitude changes the direction of the gravity vector depending on the latitude need more calculus than I am willing to do, but fortunately very rough assumptions get us what we want. In the worst case scenario, the 0.5% change in g's magnitude comes from an additional pull perpendicular to g (this maximises the deviation). A bit of trigonometry (solve cos(theta)=1/(1 + 0.5%) for theta) tells us the deviation is less than 6° (by the way, this is higher than I would have expected).

On the other hand, Earth's inner core is seen from an angle of two times 10.8° (some more trigo with Earth radius = 6400km, core radius = 1220km). So even with all assumptions lined up in the worse case, we still get that the gravity vector will pass through the inner core. Tigraan^{Click here to contact me} 09:40, 19 July 2018 (UTC)[reply]

Indeed. The Schiehallion experiment measured deviations from the local zenith of around 11 seconds of arc. Similar (but less precise) measurements around Chimborazo measured deviations of 8 seconds of arc. Over a distance of 6360 km (radius of the Earth) these sizes of deflections result in a deviation of less than 1 km away from the geometric centre of the Earth. Gandalf61 (talk) 11:43, 19 July 2018 (UTC)[reply]

Re "(this is why all space rocket launching pads are near the equator)". The difference in gravitational force is not the main reason rockets are launched from near the equator. Rather, it's because the earth's rotation means the rocket is already traveling east at close to 1000 miles/hour even before it launches. The additional velocity means less fuel required. The hard part of getting into orbit is achieving orbital velocity, not reaching a specific height. [28] [29] — Preceding unsigned comment added by CodeTalker (talk • contribs)

Huh... I somehow thought that was the same effect, but of course it is not (speed in the geocentric frame of reference vs. centrifugal force in the terrestrial, non-inertial frame). Struck accordingly, see also discussion below. Tigraan^{Click here to contact me} 08:06, 20 July 2018 (UTC)[reply]

To dispel some very common misconceptions: spacecraft launch sites can be located anywhere on Earth. The geographic location of the launch site is selected for many reasons, not the least of which is orbital dynamics; but there are many other factors, including range safety, redundancy, and convenience - it's important to have easy access to a bunch of rocket scientists, who don't necessarily all want to live on the launch site! Here's a list of NASA's primary launch sites; but not all American orbital (and sub-orbital) launches are managed by NASA. Notably, yesterday a New Shepard 3 launched from West Texas, an operation that was largely conducted without overtly depending on NASA's money or help.

I would use caution before spouting anything about equatorial rotational inertia unless you've worked through the orbital flight dynamics equations - orbits aren't really that simple - and I can spout some counterexamples off the top of my head. For example I've been to spacecraft launch sites at Kodiak Island and Vandenberg Air Force Base: sites from which the spacecrafts can fly westbound or northbound or pretty much where-ever they want to fly. Quoting directly from NASA's website, "Kodiak Island is one of the best locations in the world for polar launch operations, providing a wide launch azimuth and unobstructed downrange flight path..."!

Nimur (talk) 18:33, 19 July 2018 (UTC)[reply]

Do they launch low-inclination orbits from Kodiak? Sagittarian Milky Way (talk) 19:51, 19 July 2018 (UTC)[reply]

With enough ΔV, you can get to any orbit! That maneuver would be called a "dog leg" on the launch trajectory, and it's expensive (you have to spend fuel to do it) - but any orbit is possible if the people buying the launch want to use their mass (and dollar) budget in that way. Nimur (talk) 22:22, 19 July 2018 (UTC)[reply]

Indeed. Likewise a launch from the equator that ends up going over the poles would require a dogleg. Not sure whether it would use more energy than was gained by the equatorial launch -- it feels like it should but I would have to do the math. --Guy Macon (talk) 23:45, 19 July 2018 (UTC)[reply]

Orbital inclination changed are ludicrously expensive in terms of energy. If they weren't, there wouldn't be separate low and high inclination launch sites. An extreme example, a LEO craft launched from KSC want to transfer to a 90 degree inclination polar orbit. Plane change delta v for circular orbits is :

\Delta {v_{i}}={2v\,\sin \left({\frac {\Delta {i}}{2}}\right)}

. Assuming a LEO orbital speed of 7 km/s, the delta v required for that plane change is 7.4 km/s again. Or almost as much as it took to launch in the first place. Of course, there are tricks to lower that, but it illustrates my point. Doglegging during launch is severely restricted by overflight considerations on most launch sites. Fgf10 (talk) 07:06, 20 July 2018 (UTC)[reply]

Maybe sort of related: shell theorem. Although the Earth isn't perfectly symmetrical, the deviation is pretty tiny given the scale of the Earth. The standard factoid is that the Earth is, to scale, smoother than a billiard ball. --47.146.63.87 (talk) 06:54, 20 July 2018 (UTC)[reply]

No. A pool ball is much smoother than the (whole) Earth would be if it were shrunk down to the size of a pool ball, though much of the Earth’s surface is indeed smoother than a pool ball. DroneB (talk) 13:11, 20 July 2018 (UTC)[reply]

July 20

Photon as "information"

Sometimes I hear photons described or used synonymously with "information". Can anyone help me understand or point me to resources that explain this comparison?

As an example, in a youtube video on the Black_hole_information_paradox, at around 3:45, the speaker states that, "The black hole radiates particles, mostly photons - that contain no information. Eventually the black hole must completely evaporate into those particles leaving no clue as to what fell into it in the first place."

I understand the evaporation and paradox aspects of what is being said, but am unclear how "information" and "photon" relate. — Preceding unsigned comment added by 128.229.4.2 (talk) 14:56, 20 July 2018 (UTC)[reply]

A photon is not information; a photon can be used to carry information, if and only if some property of the photon can be controlled - like when it gets emitted, or what its frequency is, and so on. Formally, that would mean that we can express this "controllable" property using a causal relationship to some other property; then, if we took a measurement of the output property, it would have carried information about the causative property that we did not directly measure.

In the case of an engineered system like fiber-optic communication, individual photons don't actually carry the information: instead, information is encoded into the rate of arrival of groups of photons, treated as an ensemble. The arrival of any one specific individual photon is called shot noise. The arrival of a whole lot of photons within a specific interval, per the engineered specification of the system, carries information.

There is a fun mathematical conundrum of quantum mechanics here - how can one single event be noise, but if we put two otherwise identical events together, they constitute a non-noise signal? This is the property of coherence. In real engineered systems, we use more than two photons so that we can build reliable machinery; but in the realm of theoretical physics or in the study of natural systems, we might investigate the behavior of this single-particle information-carrying behavior using the mathematical and analytical tools of thermodynamics; and we might construct testable hypotheses using the methods of experimental physics; and then we might use those tools to draw conclusions that apply to the more difficult realm of black hole thermodynamics.

Ultimately, when you hear a pop-science publication talking about why black holes do (or do not) emit "information," they are using loose terminology to describe the incoherent emission of radiated energy. Whether those statements are accurate, or valid, depends on the quality and currency of the documentary you're watching!

Nimur (talk) 17:10, 20 July 2018 (UTC)[reply]

There is something out there about the concept of physicality of information. I haven't found a layman explanation of it (I tried googling). Apparently somehow information is as "real" and permanent as particles of matter? There are Conservation laws but that article does not contain the word "information". Black hole information paradox kind of hints at it but seems to lack an explanation why it is a paradox. Any help on this for us non-quantum-theorists? Or am I chasing a red herring, in which case can you explain why the black hole information paradox is a paradox? 85.76.73.51 (talk) 17:28, 20 July 2018 (UTC)[reply]

The "paradox" is a way to express a disagreement about whether a property's measured state is statistically certain, or absolutely certain. Some physicists believed these words described distinct concepts; and certain specific mathematical models of the black hole provided an example where we could differentiate between the two conditions. As of the time of this writing, the consensus seems to be − there is not any paradox, because there is no actual way to distinguish these two conditions apart. (One of the very last peer-reviewed publications by Stephen Hawking was Information loss in black holes, (2005), in Physical Review - if you can read and understand that paper, you can understand the paradox and Prof. Hawking's position regarding its resolution... and if you can't read and understand that paper... well... you're one of many).

I mean, it's a little bit of a disservice that this "paradox" has been brought to the forefront of the popular conception of modern physics. It's a minor debate about the minutia of the problem. To really understand it, you've got to invest a lot of up-front intellectual effort. And if you actually do that, you'll find many more interesting things to spend your intellectual efforts on! Nimur (talk) 17:41, 20 July 2018 (UTC)[reply]

That photons are not information, but carry information is a helpful clarification Nimur. Thank you.

I also came across another video that says "Light not only interacts with matter, it is also altered by it, and can be used to gather information about the world around it, with almost no delay...". This helps me understand. 128.229.4.2 (talk) 19:05, 20 July 2018 (UTC)[reply]

Balance and vision

Does the human brain use vision to establish balance? Does a blind or short sighted person have worse balance? Would closing your eyes make you have worse balance? Clover345 (talk) 19:08, 20 July 2018 (UTC)[reply]

Yes, vision plays a role. In most people, the semicircular canals are the most important factor, and vision only plays a minor assistive role, along with proprioception. However, people whose semicircular canals are non-functional (this happens in a substantial fraction of deaf people) may have to rely entirely on vision to balance. See our Balance disorder article for more information. Looie496 (talk) 20:02, 20 July 2018 (UTC)[reply]

How germs get inside the body

I'm using "germs" as a collective term for viruses, parasites, fungi, and bacteria. They can all be called "microorganisms", but that name is a mouthful. So, I'm sticking with "germs" and "bugs". I am aware of the ways that germs get inside the body - by vapor, by food and water, by broken skin, and by intimate touching. What makes the inner lining of sexual body parts so defenseless against pathogens that some pathogens ONLY use this route to climb onto another individual? Perhaps, the vaginal walls, unlike skin, don't have layers and layers of protection. So, germs can easily pass through the cells or infect the cells. Take HIV, for example. There seems to be no reported cases of HIV being able to infect a person through contaminated food. So, HIV cannot survive in food or in the water supply or pollute the air. It can only spread by bodily fluids - using contaminated needles, breastfeeding, and having sexual intercourse. Also, unlike the digestive system, the vagina is not acidic enough to burn the bugs. And some bugs don't travel through air, because they can't. They can only travel by close contact, and sexual intercourse is a super-close contact. The man and woman during coitus are not next to each other. The man's penis is placed into the woman's vagina, and if sperm can travel up to the uterus, then so can bugs and germs, can it? That is literally inside an organ. This question is not about how a bug infects a cell, but how a bug - especially a bug that primarily relies on super-close contact - gets inside the body. SSS (talk) 19:11, 20 July 2018 (UTC)[reply]

@@ Line 518: / Line 518: @@
 Does the human brain use vision to establish balance? Does a blind or short sighted person have worse balance? Would closing your eyes make you have worse balance? [[User:Clover345|Clover345]] ([[User talk:Clover345|talk]]) 19:08, 20 July 2018 (UTC)
+:Yes, vision plays a role. In most people, the [[semicircular canals]] are the most important factor, and vision only plays a minor assistive role, along with [[proprioception]]. However, people whose semicircular canals are non-functional (this happens in a substantial fraction of deaf people) may have to rely entirely on vision to balance. See our [[Balance disorder]] article for more information. [[User:Looie496|Looie496]] ([[User talk:Looie496|talk]]) 20:02, 20 July 2018 (UTC)
 == How germs get inside the body ==