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December 16

Galileo pulse meter

According to this book, Galileo invented a pulse meter based on a swinging pendulum. By adjusting the length of the string of the pendulum, the user could alter its speed to match their heart rate. That particular speed would correlate with a particular length of string, and there was a scale measuring how long the string was at a particular time, thus telling you your heart rate.

My question is; how did the user insure that the pendulum maintained a constant momentum so that variations in speed could only come from variations in the length of the string? As I picture this in my mind, I imagine that the user would have just a few seconds to measure the patient’s pulse and adjust the pendulum accordingly, before the measurements became inaccurate. Puzzledvegetable (talk) 00:04, 16 December 2018 (UTC)

I don't know what your source exactly says but a pendulum has a nearly constant period and not speed. When the motion slows down due to friction and air drag, the period doesn't. Pendulum says: "The period depends on the length of the pendulum and also to a slight degree on the amplitude, the width of the pendulum's swing." If the source said speed then it probably meant period. PrimeHunter (talk) 00:30, 16 December 2018 (UTC)

@PrimeHunter: Thanks for explaining. I found a very helpful article online that clarifies how a pendulum works. According to explainthatstuff.com: "If there were no friction or drag (air resistance), a pendulum would keep on moving forever. In reality, each swing sees friction and drag steal a bit more energy from the pendulum and it gradually comes to a halt. But even as it slows down, it keeps time. It doesn't climb as far, but it covers the shorter distance more slowly—so it actually takes exactly the same time to swing. This handy ability (technically called isochronism, which just means "equal amounts of time") is what makes a pendulum so useful for timekeeping." Puzzledvegetable (talk) 01:29, 16 December 2018 (UTC)

Note that a metre is (almost exactly) the length of a pendulum beating seconds. 2A00:23C0:7903:B200:6D35:1B0:E2BB:692D (talk) 10:14, 16 December 2018 (UTC)

From 1789^{Citation requested} to 1889, the definition of the metre was one ten-millionth of the distance from the pole to the equator.

That's for the historical reason that on 8 May 1790 – The French National Assembly decided that the length of the new metre would be equal to the length of a pendulum with a half-period of one second. These days the second is defined as exactly the time for light to travel 299792458 metres in vacuum. DroneB (talk) 15:13, 16 December 2018 (UTC)

Huh? The why does our Metere arcticle say

"The metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole"?

Also see History of the metre. which says

"As a base unit of length, many scientist initially favored the "seconds pendulum" (a pendulum with a half-period of one second), but this was rejected when it was discovered that it varied from place to place with local gravity. A new unit of length, the metre was introduced - defined as one ten-millionth of the distance from the North Pole to the equator."

--Guy Macon (talk) 15:38, 16 December 2018 (UTC)

There is no contradiction here, as reading our Metre article, specifically Metre#Timeline will make clear. DroneB (talk) 19:55, 16 December 2018 (UTC)

I don't think that comment, with its useful links, needed to be in small type. However, it does not really address the issue Guy raises. More below. --76.69.46.228 (talk) 07:27, 17 December 2018 (UTC)

My choice of tiny type was for politeness. Specifically I posted a timely correction to my learned colleague Guy after he reacted to my post with an exhalation "Huh?" coupled with a misspelled link to a non-existing article that, had it only been found and read, would have revealed the "Huh?" to be a non-question. Regardless what "issue" IP User 76.69.46.228 thinks remains unaddressed here Guy Macon's [posted claim that the meridional definition of metre dates from 1789] can be challenged. I deduce that it is an error of false precision generated when Guy copied the globe image from History of the metre article with its underlying text hastily paraphrased from that article's lede summary, neglecting the detailed article content that supports 1791. DroneB (talk) 17:30, 17 December 2018 (UTC)

A meter today is the distance the light travels during 1s/299792458. And the speed of light is 299792458m/s Doroletho (talk) 23:24, 16 December 2018 (UTC)

Guy states above the reason why the "seconds pendulum" definition was rejected. According to The Measure of All Things by Ken Alder, these objections were already known in 1790 when the National Assembly was working on the law, so Talleyrand had wording put into it that said the length of the pendulum should be determined at 45° "or whatever other latitude might be preferred", with the French Academy of Sciences to establish a commission to execute the plan. Therefore the law of 1790 was more a plan for a definition than an actual definition, and I think this is why the 1791 definition is usually considered the first one.

Note incidentally that the "seconds pendulum" definition was rejected because it would be tied to a particular location and therefore might not be accepted worldwide, but the "quarter-meridian" definition that replaced it was also tied to a particular location, as it was specifically based on the meridian passing through Paris. But as Alder points out, the commission's chairman, Jean-Charles de Borda, provided a list of good reasons for this. To actually determine the length of the meridian, they would have to survey a sizable chunk of it, through country that was already well surveyed at the time, with both ends of the chunk at sea level, and passing through the latitude of 45°. Which meant a meridian through France from the English Channel to the Mediterranean. And when they actually sent a team to survey it (which is what the book is mainly about), the result was internationally accepted. --76.69.46.228 (talk) 07:27, 17 December 2018 (UTC)

I would put it a different way. It seems to me the key issue is whether there is any connection between the seconds pendulum definition and the later meridional definition. From what I can tell, neither the metre article nor the history of the metre article say there was say there was. The fact that some people came up with the seconds pendulum definition (or whatever you want to call it) is irrelevant if there was no concern about trying to approximate that definition with the new definition, and nothing in our articles suggest there was. While the fact these are similar may seem awfully coincidental, the fact that their definition was "one ten-millionth of the distance from the North Pole to the equator" and their decimalisation outlook and considerations of what would make a useful length makes it a lot less clear it was anything other than a happy accident. In other words, when the meridional definition was being designed, the designers could have said, 'we don't give a damn what definition people came up with before, we just want to choose something which works well'. By comparison, since then the redefinitions have generally attempted to keep the same length. I'm sure you're right that this is mostly because it was never an official definition but a working plan that was abandoned. So they had no real reason to try and approximate the older plan/definition, but later they actually had metre that people had been using for a while so changing the actual length in any significant way would have been insane. And all this means Guy Macon was right to question the claim being made. Nil Einne (talk) 15:51, 19 December 2018 (UTC)

What happens to an electrical device when it gets the wrong power?

Too much, and you can burn a fuse (or whatever). But what if you get too little, like connecting a 220V device in a 110V power source or one source with too much variation? Or what happen by the wrong Hz? I imagine my microwave oven, which sets its clock through the power, won't show the right time, but what else? What's the worst that can happen in terms of damage?--Doroletho (talk) 23:19, 16 December 2018 (UTC)

• It's complicated. There are many sorts of device, there are many failure modes. In general, "inefficient" operation leads to excess heat dissipated in the machine, and that can cause overheating and an insulation failure.

A 60Hz motor or transformer will have sheet iron laminations in its armature. The losses here increase with lower frequencies, so although many 50Hz machines of similar power work just fine throughout Europe on 50 Hz, an imported US motor designed badly for 60 Hz with no margin beyond that, will overheat. This is a common failure in imported workshop machinery.

A powerful 12V motor, such as a car engine starter motor, won't have enough power to turn the engine fast enough to start if its run under-voltage. This - mostly the tendency to run the starter for too long - is a classic example where a motor (normally only designed for brief use) will easily overheat.

There can also be problems with induction motors, where 'slip' becomes excessive. If the motor is adequately powerful to run at the correct speed, then it works fine. But under-voltage it may lack power and so run too slowly. This has a secondary effect where the 'slip', a difference between the physical speed of the rotor and the speed of the rotating field, becomes excessive. This increases the induced current in the rotor (induction motors transmit power to their rotors by induction, not through brushgear) and so the rotor may burn out. Normally a small reduction in speed acts as a feedback mechanism, so that the increased slip increases torque and causes the motor to safely speed up to its designed speed - however too much of this drops out of the controllable region and becomes a failure. Andy Dingley (talk) 23:31, 16 December 2018 (UTC)

Your microwave clock is probably controlled by a crystal, not the mains, unless you have an analog clock on it! I run my immersion heater off a 110V transformer in my 240V off grid house to reduce the peak load on the batteries, but it would take four times as long to come up to temperature. Greglocock (talk) 23:40, 16 December 2018 (UTC)

I had exactly that problem at a performance last week. My amplification for my upright bass, which had been very reliable previously, failed utterly; I was getting no sound. Had to play unamplified, not as planned. Turns out the problem is I had two wall warts in my system, one rated 12v 500ma, the other rated 9v, 1000ma. Of course, they had identical connectors. The device that wouldn't work -- a little tube preamp -- wanted the 9v 1000ma. Nothing died; but no sound. I hate wall warts. You should too. --jpgordon^{𝄢𝄆 𝄐𝄇} 05:10, 17 December 2018 (UTC)

December 17

Newest species

What is the newest animal species on Earth? Not the most recently discovered, but the most recent species that diverged from another species in the same family? Thank you.    → Michael J Ⓣ Ⓒ Ⓜ 22:43, 17 December 2018 (UTC)

See Species problem. There are many different ways to define what a species is, and there is no precise agreed-upon definition even among biologists. When considering geographically separated populations, deciding when these become separate species is quite arbitrary. Besides that, the genetic makeup of many species has never been studied, so there is also insufficient data to really answer this question. - Lindert (talk) 22:52, 17 December 2018 (UTC)

The 5 entries in the Category:Speciation events may be of interest. As Lindert suggests, our knowledge in this area is limited to what we have observed, which can only be a small fraction of all species that exist, and it can be quite difficult (and take a long time to determine) when studying a hitherto unseen species to determine how long it has existed. There is also the question of whether species created by artificial techniques such as hybridization count or not. {The poster formerly known as 87.81.230.195} 90.217.251.247 (talk) 00:15, 18 December 2018 (UTC)

Indeed, this is true; a hybrid species created by deliberate human action (oranges and grapefruits) might be disqualified, but there are plenty of temporarily deliberate/later reconsidered or accidental hybrid species like killer bees and these little guys. Even within species there can be separate groups whose hybridization causes real-world problems [1]. I do think that the mass extinction that is ongoing, with all its losses to posterity, will not plague people so much as evolution's vengeful creativity. But I can think of at least one more or less "new species" that is not a hybrid (that I know of), that being the mutant strain of Caulerpa taxifolia taking over the oceans. But it is hard to get a new species a brand new name, no matter what! I don't know if it's been thought of by those who do such things. Wnt (talk) 04:13, 18 December 2018 (UTC)

There's some discussion of this in an article on gizmodo.com. Rojomoke (talk) 09:33, 18 December 2018 (UTC)

Ah -- Haplochromine cichlids of Lake Victoria, a favorite example of recent speciation (of real accepted species, that is). I vaguely recall thinking there was still a bit of room for skepticism about "cheating" in the sense that multiple precursor species might have hybridized in the past, leaving the adaptive radiation to progress with some reservoir of pre-made pieces, but it is hard to exclude such things from any speciation event, and I haven't tried to chase down what came out of that idea any time recently. Wnt (talk) 14:16, 18 December 2018 (UTC)

There's also the case of Procambarus virginalis, thought to have formed around 1995: [2]. Not everybody agrees it's a separate species. PiusImpavidus (talk) 15:11, 18 December 2018 (UTC)

There are two new species of American goatsbeards (or salsifies, genus Tragopogon) that sprung into existence in the past century. J2088 (talk) 16:42, 20 December 2018 (UTC)

December 18

"Static discharge" circuit tech

I have a sense that electrical technology has progressed unimaginably in the past two centuries, yet with some notable exceptions the application of "static electricity" and "static discharge" has not (what I'm thinking of is more, perhaps much more, than about 4000 volts, with amperage so low as not to be more than a minor annoyance to humans). I know that static electricity circuits can be made easily for a lark [3], I know there's the ionocraft and even Van de Graaf generators used for X-rays and particle accelerators, but are there reliable, precise static electricity power supplies, perhaps pulsed, that you could safely touch (not high tension electric lines!), are there solenoids powered by static electricity, have people built relays and complex logic circuitry that uses it, and above all, can you generate an arbitrary waveform of ultra high voltage electricity (subject to the need to have some way to restrict total amperage) using small cheap components? Wnt (talk) 14:27, 18 December 2018 (UTC)

Are there reliable, precise static electricity power supplies, perhaps pulsed, that you could safely touch? Yes. They are called "hipot testers" and "ESD testers" and you can adjust the (high) voltage and (low) current up and down. Many of them put out a waveform with a rise and fall that mimics a static electricity shock.

Are there solenoids powered by static electricity? No. Too little energy.

Have people built relays and complex logic circuitry that uses it? Relays are just solenoids that activate switches, so no on that one. Modern logic circuits use transistors, which need to be protected from static electricity. Older vacuum tube and relay logic isn't so sensitive to damage, but there is too little erergy in static electricity to run either.

Can you generate an arbitrary waveform of ultra high voltage electricity (subject to the need to have some way to restrict total amperage) using small cheap components? If you want to include DC in your definition of "arbitrary" then no. If you are OK with AC only, just build a cheap low voltage arbitrary signal generator and step up the voltage with transformers (a cheap signal transformer will give you a signal suitable for driving a neon sign transformer). Or you can wind your own high voltage transformer if you really want cheap. --Guy Macon (talk) 17:34, 18 December 2018 (UTC)

Converting angular to linear velocity

I have a question about determining the linear (tangential) velocity of a point rotating with some angular velocity at a distance d from a center, and more specifically, the metrological aspects thereof.

As everyone knows, it's simple enough:

v = ω · d

as long as the angular velocity ω is expressed in radians-per-unit-time.

So my questions are:

1. What if ω is not in radians?
2. How do you resolve the unit discrepancy?

With respect to #2, as my high school physics teacher taught me lo these many years ago, it's not enough to get the right numeric answer, you've got to get the units right, too. And when you use the expression above, with angular velocity in a unit using radians, you end up with a result in units of (distance · radians) / time, while you presumably intended to get a conventional velocity expressed as distance/time. So how to get rid of the radians?

I have an answer, but I've never seen it expressed this way. I believe that a more explicit, unit-agnostic version of the expression would be

v = ω · 2π · d / ¤

where the 2π term is in there because we're obviously dealing with the circumference of a circle somehow, and where ¤ is the number of angle units in a circle: 2π if you're using radians, 360 if you're using degrees, or 1 if you're using full rotations (as in RPM).

So the question is not so much "does this work?". (It does, with the two 2π terms nicely canceling out if you are using radians.) Rather, does anyone else formulate it this way, and has anyone ever identified a "constant" (basically another name for 1) like my ¤? (I belatedly notice that the indispensable units program does have "circle" as a unit, which is heartening.)

This is basically a simpler version of the debates that play out when comparing MKS to the various flavors of CGS. (As it says at Advantages and disadvantages, "A key virtue... is that 4πε₀ is replaced by 1".) So what I think I'm asking here is, if the 2π and ¤ terms drop out (are replaced by 1) in the "simpler" radian-time-distance system, what's the more-complicated system that radian-time-distance is simpler than, and how is angular-to-linear velocity conversion expressed there? —Steve Summit (talk) 15:28, 18 December 2018 (UTC)

• I'm confused why you don't just convert angular velocity to radians-per-unit time if it were in some other unit. That seems like a trivial operation. --Jayron32 15:30, 18 December 2018 (UTC)

+1 on that. One thing to bear in mind is that radians and degrees are formally unit-less, they are ratios. What Steve's teacher said is true but unhelpful in this case. That is, if you do a dimensional analysis of an equation in radians, it'll give exactly the same answer as a dimensional analysis in degrees. You could even argue that the circle constant is already indicated by the choice of angular measurement. Greglocock (talk) 19:30, 18 December 2018 (UTC)

Note the bold Wikilink when I state your equation:

v = ω · d

where:

v = Tangential velocity

ω = angular velocity

d = distance from center of rotation

Dimensional analysis insists that an equation have the same dimensions on its left and right sides, which is the first part of "getting the units right". In this equation the units are those of v, the speed, which is LT^-1. That means "length/time" and you may meet that again in the form dx/dt called velocity, the derivative of position with respect to time if you take an interest in Calculus. You are free to select the actual units as long as they are consistent, as in these two examples:

v metres per second = ω radians per second · d meters (using metric units)

or

v feet per hour = ω radians per hour · d feet (using imperial units)

...or any other units of time and distance used consistently will work.

To your questions:

1. What if ω is not in radians? - Angular velocity ω has to be a unit of angle rotated per time. It provides only the T^-1 part of the dimension of the right side of the equation. These values are equal: 1 radian/second = 1/(2π) rotations/second = 57.296... degrees/second (approximate) so you are free to convert between them.

2. How do you resolve the unit discrepancy? - There is none when you realize that the equation is giving tangential velocity which must be thought of as conventional velocity at a point in time. Of course you don't get rid of the given fact that the motion over any finite time is not straight but in a curve, but that does not dictate a change of units. An object such as a bullet tumbling through the air has both straight-line and tangential velocities which one can add together if one wants to estimate the air resistance due to friction. DroneB (talk) 21:08, 18 December 2018 (UTC)

So the real issue here turned out to be that I had never thought of angles as dimensionless. I really thought they were more "real" units. (I just about argued with @Greglocock: for asserting that they were unitless ratios.)

@Jayron32: asked why I couldn't just trivially convert my angles to radians if necessary. That's fine if you're working with ordinary numbers. But I'm working with a system which deals with formally unitful quantities wherever possible. (It is somewhat akin to Boost.Units. The intent, among other things, is to avoid bugs like the one that doomed the Mars Climate Orbiter mission.) With this system, it's considered wrong to extract values as particular units and work with them as ordinary numbers -- that defeats the purpose of carrying the units around. With this system, I would have had to write (and the co-worker who originally wrote the code did write) the equivalent of

angular_rate.extract(radian/sec) * dist.extract(meter)

and this resulted in an ordinary number which had to be converted back to a unitful quantity by explicitly re-tagging it as meters. In our system, it's almost always wrong to extract raw values, perform math on them, and then convert back to quantities. I instructed the co-worker to replace

double v = angular_rate.extract(radian/sec) * dist.extract(meter)

vel = quantity(v, meter/sec)

with

vel = angular_rate * dist

But this then resulted in a dimensional mismatch, since it computed something with units of angle · distance / time. Our analysis of this failure (an analysis which, embarrassingly enough, tended to contradict my usual argument that unitful quantities are always easier and more convenient to use) resulted in the question I asked here. But it looks like the real bug is that our system treats angles as a distinct unit, incommensurate with scalars.

Thanks for everyone's answers. —Steve Summit (talk) 11:37, 19 December 2018 (UTC)

@Scs: I don't think it's wrong to give angles units. I am personally a big fan of making up units as necessary to annotate a calculation -- for example, when diluting a solution, you can put "mL conc." and "mL dil." and the calculation can be audited with units (converting molar into mol/ml whatever explicitly), whereas otherwise it is "just ratios" and people can make the most embarrassing errors if they're in a hurry. In your case, you can address this explicitly with the factor-label method, making the equivalences:

1 full rotation = 2 pi radians 1 full rotation = 2 pi d (which may be in inches or whatever; note "d" is a radius as you defined it)

So if we start at, say, 0.5 rad/sec rotation and a 4 inch radius,

v = (0.5 rad/sec) * (1 rotation/2 pi radians) * ((4 inch * 2 pi) / 1 rotation) = 2 inch/sec.

The impulse to skip the units is generally treacherous, because the intuitive process you want to do can generally always be written in units and otherwise you're just doing algebra in your head for the heck of it. Even some of the hard ones nobody does with units will give way to just a little thought, for example you can add (273 K - 0 C) to any computation because you can add zero to anything, and preserve units instead of making a special case. You could also specify some really weird things like + ln( mol/L) in certain calculations, though that takes more adjustment to fundamental definitions.

As an aside, I should say that by far the most interesting case to apply any of this to is Planck's constant. It is the fundamental unit of action, energy times time, but it has the units of angular momentum, but for light it is the linear momentum per wavelength, i.e. divided by frequency i.e. times time. Any path to an intuitive understanding of quantum mechanics has to depend on all that making sense in a metrological way, which seems to depend on an understanding of moment of inertia and mass... let's just say I haven't gotten very far as of yet with that. ;) But I feel sure it's important. Wnt (talk) 15:16, 19 December 2018 (UTC)

I know what you mean about "factor-label" (though I hadn't heard it called that). And indeed your (0.5 rad/sec) * (1 rotation/2 pi radians) * ((4 inch * 2 pi) / 1 rotation) ends up being pretty darn close to my ω · 2π · d / ¤ ! —Steve Summit (talk) 05:37, 20 December 2018 (UTC)

I should redirect Factor-label method to dimensional analysis which has a section on it. The key difference is that your formula tends to look kind of like a random series of operations, where ideally a factor-label computation should take only a few pieces of data (ideally, none, if you phrase it just so) and everything else involves multiplication by 1 or, rarely, addition of 0. In other words, one rotation is 2 pi radians, so you know you can multiply by that ratio, and the same is true for the circumference being one rotation, and you can even say that, for purposes of this computation, 0.5 radians is one second, in the sense that every time you have one occur you have the other occur, and so inevitably, the result is equal to 1 also, in some conceptual sense: 2 inches is what happens in one second. Wnt (talk) 15:25, 20 December 2018 (UTC)

Can Tapir's be ridden or domesticated?

Can a Tapir be domesticated and ridden?Naraht (talk) 22:34, 18 December 2018 (UTC)

By any chance, is this a veiled question about biblical literalism? If so, you might find this publication relevant: ..."the issue cannot be resolved by reference to normal scholarship," a statement that can be considered in isolation as about the most intelligent thing that can be said about the issue. (Please don't construe this as an endorsement of any of the madness or other conspiracy-theories associated with the horse/tapir topic).

In actual fact, tapirs are not commonly domesticated in any part of the world.

Nimur (talk) 01:31, 19 December 2018 (UTC)

Where are tapirs mentioned in the Book of Mormon? ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:42, 19 December 2018 (UTC)

As far as I can tell, they are not, by that name. However it does mention "horses" and "asses", neither of which are native to the New World, though there were horse species that survived possibly as late as 7600 years ago (according to Horse#Taxonomy and evolution). Apparently some Mormon exegetes identify these with tapirs or deer. That's just from a brief search; I don't remember ever hearing of this before, and I'm not sure I got it all right. --Trovatore (talk) 04:11, 19 December 2018 (UTC)

Joseph Smith might not have known there were no horses in the western hemisphere until our ancestors brought them over. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:28, 19 December 2018 (UTC)

From the Mormon point of view, that hardly matters; the angel Moroni would presumably have known. --Trovatore (talk) 04:30, 19 December 2018 (UTC)

Were there ever tapirs in the western hemisphere? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:27, 19 December 2018 (UTC)

Most tapirs are in the western hemisphere. Iapetus (talk) 10:39, 19 December 2018 (UTC)

D'oh! ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:06, 19 December 2018 (UTC)

If you go to the Creation museum you can see Jesus riding a dinosaur so I'm sure it's possible ;-) Dmcq (talk) 10:59, 19 December 2018 (UTC)

Probably more fun than riding a tapir. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:06, 19 December 2018 (UTC)

Since humans wiped out New World horses in the first place, there's no scientific way to rule out that some royal family might have kept some in captivity or on an isolated preserve/island etc.; I don't believe in the Book of Mormon to make that jump on its behalf but it can't be called unscientific if someone does, just a different choice of what historical sources to credit without other corroborating evidence. Wnt (talk) 15:23, 19 December 2018 (UTC)

Is there any indication of why they would have done that? ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:10, 19 December 2018 (UTC)

Of course not. I don't think they did do it. The point is though, if somebody in Nebraska hits a 2500-year-old horse skeleton with his shovel tomorrow, scientists will be skeptical, but they're not going to run around in circles yelling it's impossible. Some explanation would be devised. Wnt (talk) 04:24, 20 December 2018 (UTC)

Your alter ego said they did. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:59, 20 December 2018 (UTC)

Our article says human caused extinction is only one of the generally accepted theories. More to the point though, I admit I'm mostly unfamiliar with Mormon theology but it seems clear from this discussion we aren't just talking about random horses that just happened to survive, but domesticated horses. The generally accepted extinction date range is long before domestication, although I presume we have no indication they were ever domesticated in North America anyway, rather those domesticated elsewhere were brought over later.

So not only would they have had to survive somewhere a lot longer than commonly believed, but they would have been either kept despite not being domesticated, or these ones which happened to survive in the wild far longer than we are aware of would have had enough survivors to be domesticated, or they were domesticated a lot earlier in North America than elsewhere but we never found signs of that. And either way, despite this successful domestication, they would have still been allowed to die off. (I guess you can come up alternatives like them being brought over after domestication but no signs of this have yet been found and again they were allowed to die off.)

Besides us not finding signs of these horses, we also haven't found their chariots. This source [4] which mentions the verses does mention some non-LDS sources who believe horses did survive, generally that they never died out at all but later interbred with those brought over by the Spanish, although their evidence seems weak and I would expect we should have definite detection of such an occurrence in the genetic profiles of horses in North America within a decade or two if it really happened. Frankly I think we should have already found it [5].

BTW that earlier source also mentions tapirs, it seems that they do sometimes allow children to ride on their backs. But I'd note that from what I can tell, there's no mention in the Book of Mormon of people riding horses anyway. Instead while the horses were domesticated, the only indication of what they were used for is pulling chariots (of unknown purposes) and as food. Well even the chariot bit doesn't seem to be directly mentioned but the chariots and horses do seem to be associated with each other. (Incidentally is the elephant thing supposed to be before or after they moved to North America?)

Nil Einne (talk) 19:53, 20 December 2018 (UTC)

Thank You. It was for information in regards to that, but I am not a believer in the Book of Mormon as Scripture. Naraht (talk) 08:02, 22 December 2018 (UTC)

Is bad web typography a Sin? Andy Dingley (talk) 11:35, 19 December 2018 (UTC)

It's a multitude of Sin's. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:00, 20 December 2018 (UTC)

Yes, it is, how do I atone?Naraht (talk) 08:02, 22 December 2018 (UTC)

December 19

How many floating point operations and TB of storage would be needed for a good car crash test?

Is it a lot? Then a container ship crashing into another or something complex like that would be computationally expensive as hell. Or are auto regulators just crashing them in real life out of caution? Sagittarian Milky Way (talk) 00:09, 19 December 2018 (UTC)

You are talking about simulating car crashes? Why would anyone do such a thing? The expense would be far higher than crashing a car would be, even if computing resources were free. Just entering in the data for the shape and thickness of every part would be far more than a car. Then there is the liability cost; even if the simulation was perfect, would a jury believe that with the lawyers on the other side trying to confuse them? Would every jury believe it? --Guy Macon (talk) 01:37, 19 December 2018 (UTC)

In fact, IIHS wrote this year-2000 op-ed on the topic of the NHTSA Driver Simulator: Advanced driving simulator is costly, value is questionable.

Of course, computer modeling is important, but actual crash tests are also important.

Nimur (talk) 01:44, 19 December 2018 (UTC)

Those links seem to be about simulating the driving experience, not the crash. --Trovatore (talk) 20:28, 20 December 2018 (UTC)

For a few years I was employed under the same manager as was responsible for computer analysis of car crashes. The results are good enough these days that the physical tests are done to verify the CAE runs. The calibration for the airbags etc is done from the sensor signatures generated by the CAE test. Yes it is lots of data. Yes the computer tests take a while to run on supercomputers. The fidelity of the model used is a mesh size of about 1-3mm. The main programs used are LS Dyna and Nastran. The physical tests that are done by NHTSA and IIHS and NCAP and so on are to verify that the auto manufacturers are telling the truth and to provide an absolute number. The error is rarely more than 0.5 stars. These are crashes into concrete blocks, car vs car is rarely modelled. A test has to be reliable, repeatable, and, representative. Car vs car scores 1/3, car vs block scores 2/3. In practice car vs block seems to be pushing the casualty rate the right way. Greglocock (talk) 04:43, 19 December 2018 (UTC)

How expensive are individual runs? Could you test those two, car vs. standard guardrail, car versus highway divider, car versus moose, car versus jogger etc. and start getting composite pictures of overall safety? (I realize that economically the goal would be to get the best score on the test and never mind the real world, but I mean, potentially...) Wnt (talk) 15:28, 19 December 2018 (UTC)

Not amazingly expensive once you have the model. I don't know if they use the same models when they develop pedestrian safety, I'd have thought so. I'm not sure how to implement a composite picture other than the current approach which gives a single figure score made up of several categories. Greglocock (talk) 21:31, 19 December 2018 (UTC)

Why do we shake when we're angry?

Many people shake when they're angry. I looked for this question on Google and I saw many answers that said that it's because the activation of the sympathetic system (by the amygdala) which cause to flow of adrenaline. But I really didn't find the relation between the adrenaline and the shaking of the body muscles. So assuming that the shaking is from the adrenaline, I'm asking what's the relation between them? --ThePupil (talk) 00:12, 19 December 2018 (UTC)

Increased blood pressure might also figure into it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:43, 19 December 2018 (UTC)

See The effect of adrenaline on the contraction of human muscle -- one mechanism whereby adrenaline increases the amplitude of physiological tremor.[6] --Guy Macon (talk) 01:56, 19 December 2018 (UTC)

December 20

Do fish drink?

Well, do they? Is it accurate to speak of a fish drinking? If they don't drink, what do they do, exactly? FreeKnowledgeCreator (talk) 03:55, 20 December 2018 (UTC)

Googling "do fish drink" yields many items. This one from Quora, for example, says saltwater fish drink and freshwater fish don't.[7] ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:57, 20 December 2018 (UTC)

All aquatic organisms that are too large to meet their oxygen requirement by body absorption arrange water flow through their gills by action one cannot entirely call drinking or breathing. DroneB (talk) 18:51, 20 December 2018 (UTC)

This is kind of tangential to the question. Yes, all fish with gills need water flow over them to respirate. But, as stated in the link above, saltwater fish actually lose water from doing this through osmosis, because the seawater is saltier than their bodies. So, they drink water, just like you and me. Freshwater fish pull water into their bodies through their gills, because their situation is the reverse of saltwater fish. The excess water has to be excreted through urination. Since they take in plenty of water through their gills, they don't drink. --47.146.63.87 (talk) 21:55, 20 December 2018 (UTC)

Hmm, that generally makes sense, but not completely, and the sourcing is not exactly rock-solid. The part that doesn't make sense is that even freshwater fish presumably take water into their gut along with their food, and it's not clear how you distinguish that from "drinking". I could easily believe that they don't drink except incidentally to eating. --Trovatore (talk) 22:24, 20 December 2018 (UTC)

"Saltwater fish actually lose water from doing this through osmosis, because the seawater is saltier than their bodies. So, they drink water, just like you and me." -- But what are they drinking? They are drinking the same seawater, so they are actually getting into their system even more salt, so what is the point of that? --2001:16B8:118B:3800:903B:C589:11CC:913B (talk) 07:39, 21 December 2018 (UTC)

I was at an aquarium a few months ago, where a vet explained that in the wild, marine mammals get non-salt water from the foods they eat. I did not have a chance to ask if they had any sort of active transport for salt excretion. I would be interested to see a comparison of average body salt-content going up the food chain, on the assumption that a predator could trivially be more saline by exchange with the ocean but would be harder to lose salt. DMacks (talk) 08:35, 21 December 2018 (UTC)

A slightly better reference is here [8]. It starts to get into technical detail like osmoconformers and osmoregulators. For example sharks have high concentrations of urea and TMAO so they are as "salty" (osmolar) inside as out, so they don't have to drink for water balance. Freshwater fish don't want to drink (though they might anyway - they don't want to eat fishhooks either) because like us the more they drink the more they have to pee. With very watery urine they can set things to rights when they do drink, or absorb water through their gills, but I don't know if their pee can be more watery than water, or if this implies they have to take in ions from food, sediment, etc. to compensate... Even this reference, which is far more complete, doesn't seem to directly answer the question of how "complete" the reabsorption of Na+ and Cl- is, or just how "dilute" the urine really is. Meanwhile the salt water fish actually do drink because they lose water through their gills and have to make up for that. So they take in salty water to their digestive tract, then pee a lesser amount very salty urine for a net intake of water minus salt. Wnt (talk) 15:11, 22 December 2018 (UTC)

Mercury and gallium

Electronegativity and melting point of metals - rationale for post-transition metals

Mercury has a melting point of -39°C while the boiling point is 357°C; gallium has a melting point of 30°C and boiling point 2203°C. Is Mercury's low melting and boiling points are due to the same reasons? If so, how the boiling point of gallium so extremely high relative to its melting point? PlanetStar 05:51, 20 December 2018 (UTC)

Gallium and mercury are not in the same column of the periodic table. 62.49.80.34 (talk) 09:49, 20 December 2018 (UTC)

More to the point than simply not being in the same column is what that means. Transition metals with unpaired electrons tend to have higher boiling points (there is some simple discussion of that here. Gallium has one unpaired electron in its 4p orbital, while mercury has zero unpaired electrons. These unpaired electrons allow for the formation of stronger interatomic forces with neighbors, leading to a higher boiling point for gallium. Certainly this also has an impact in the melting point differences as well, but other factors may also come into play there (crystal structure, perhaps?). --OuroborosCobra (talk) 14:33, 20 December 2018 (UTC)

Look at aluminum and boron above gallium, they have higher melting points despite each having one unpaired p electron. The melting points decrease from boron to gallium, but after that going further down the group the melting points increase through indium, thallium, and man-made element nihonium, but boiling points decrease continuously all the way down. How is it that melting points decrease over these first three elements then increase the last three but boiling points decrease all the way from top to bottom? And what makes gallium to have so low of a melting point that it melts on a person's hand but other elements in that group don't despite all having only one p electron? Could it be that presence of filled electrons in the 3d orbital influenced the melting point of gallium? PlanetStar 02:58, 21 December 2018 (UTC)

According to the above cited gallium wikipedia article, the low melting point is due to Ga's tendency to form dimers, though it is not immediately clear why the other elements in its group do not form dimers.--Wikimedes (talk) 04:51, 21 December 2018 (UTC)

Quora has the answer about why gallium has the lowest melting point of the group despite it is in the middle of the periodic table column. PlanetStar 04:34, 22 December 2018 (UTC)

Quora's answers don't look exceptionally convincing to me, though I'm not sure I'll do better. But it should be clear that this region of the periodic table has a lot of low-melting compounds: the components of galinstan, which (debatably) melts more readily than water, include indium and tin which are relatively easy to melt (hence tin soldiers, which also involve lead, just below tin). Cadmium and zinc and thallium also melt fairly readily compared to most metals. So we more or less have two boundaries - one, the edge of the transition metals where mercury (and Cd and Zn) has (according to our article) a "pseudo-noble-gas configuration", and the other being the diagonal line where things like aluminum and germanium start to act less like metals, beyond which we get into covalent chemistry that is either hard as diamond or airy as oxygen depending on how the numbers work out. Our article on thallium sort of references the inert pair effect, a relativistic effect on the lower rows of the periodic table - I have no idea if this has the impact of sort of shoving thallium to the left on the periodic table, i.e. with higher melting point, due to the status of the s electrons, while perhaps pulling low-melting lead and bismuth into this general category. But it should be clear that the post-transition metals have a general trend to melt at low temperatures; that article gives more discussion and a lovely figure I've placed at right. Wnt (talk) 15:44, 22 December 2018 (UTC)

How many pregnancies at one time?

At any one time, roughly what percentage of women in the world aged between 18 and 50 are pregnant? -- Jack of Oz ^{[pleasantries]} 07:48, 20 December 2018 (UTC)

Googling that subject, the following US information turns up, which isn't a full answer, but it's interesting.[9] ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:52, 20 December 2018 (UTC)

Current rate of fertility (average number of children per woman) is current about 2.35 - which would mean each woman being pregnant for 21.15 months - which would probably need to be increased to allow for those pregnancies which do not result in a live birth. Over the 32 year span suggested (which may be too short, as in many parts of the world women start having children much younger than 18) that would mean the average woman spending just under 18% of the period pregnant. Logically, that would also mean that at any given time about 18% of them should be pregnant - perhaps 20% is you allow for the miscarriages, still births and abortions. Wymspen (talk) 13:01, 20 December 2018 (UTC)

I can't really see where the 18% comes from. 21.15/(32 x 12) = 5.5 %. Incidentally, I used a different method and found almost the exact same result (i.e. 5.5% excluding miscarriages and abortions). - Lindert (talk) 13:24, 20 December 2018 (UTC)

I didn't specify pregnancies that go full-term. -- Jack of Oz ^{[pleasantries]} 16:21, 20 December 2018 (UTC)

I know, that part is just easier to calculate. As far as miscarriages go, [this page] (I was not able to post the url, as the site is blacklisted, however it is a well researched article, titled "Making Sense of Miscarriage Statistics" and reviewed by an OB/GYN, with links to scientific studies) has some interesting statistics: 1) up to 75% of conceptions may end in misconception, although this also counts cases where implantation fails to take place, and many argue that pregnancy does not start until that point. After confirmed implantation, this number drops to 31% 2) After a woman discovers she's pregnant, the probability of a misconception is about 15%. Nearly all misconceptions occur in the first 12 weeks, children who survive this period have a 96-97% chance of surviving the pregnancy (naturally).

Based on the above, it's probably reasonable to say that the average lenght of a misconceived pregnancy is at most around 6 weeks. That would mean these pregnancies cumulatively account for +/- (31/69 x 6/40 =) 0.07 times the pregnancy duration of all succesful pregnancies. This would change 5.5% to (1.07 x 5.5%=) 5.9%

Stillbirths account for about 1% of pregnancies, so this is hardly statistically significant.

When it comes to abortion, statistics are undoubtedly incomplete, especially in countries where abortion is not legal/tolerated. That said, most abortion also take place in the first trimester. If 50% of pregnancies are aborted, at an average of 8 weeks, that would add (2 x 8/40 x 5.9 =) 1.2%, but it's probably less than that. This brings the total to 7.1 % (a rough estimate). - Lindert (talk) 17:26, 20 December 2018 (UTC)

Thanks, that's most interesting. -- Jack of Oz ^{[pleasantries]} 21:51, 21 December 2018 (UTC)

Besides not carrying to full term, you would also have to decrease the result by half a percent because of twin pregnancies. – b_jonas 23:26, 21 December 2018 (UTC)

Tuned response function.

I have interest in the equation that gives the amplitude of the current (or the voltage across the resistor) in a voltage exicted series RLC circuit but using only the parameters: Q and omega0,(Where Q is the quality factor of the complete circuit and omega0 is the undamped resonant radian frequency of the circuit). I need the equation to be a function of omega (the driving frequency),omega0 and Q only please. I have searched all over the web and all the books i can find. Yet I cannot find the formula for the amplitude against radian frequency. This is not homework but a personal interest. Its too hard for any homework and doesnt seem to be covered anywhere. Help!!!213.205.242.154 (talk) 23:45, 19 December 2018 (UTC)

Can someone ask that sparky spinner to look at this, He.she seems to be very clever.213.205.242.154 (talk) 23:47, 19 December 2018 (UTC) --213.205.242.154 (talk) 12:49, 20 December 2018 (UTC)

See RLC_circuit#Series RLC circuit that gives a 2nd order differential equation whose solution is a complex number because the current is not in phase with the applied voltage. At the resonant frequency V(t) = sin (W₀t) and I_R = V(t) Q / (L W₀).

At higher frequency than resonance W > W₀, I_R is smaller and lags the phase of V(t). At lower frequency than resonance W < W₀, I_R is smaller and leads the phase of V(t).

I_R is zero in these 3 cases:

• V is not time-varying i.e zero or d.c.
• V alternates at infinite frequency
• R is infinite

RLC filter describes applications of this second-order tuned circuit as an electrical filter. DroneB (talk) 18:25, 20 De6cember 2018 (UTC)

thanks but I need an equation telling me the amplitude of the response at any frequency only in terms of the circuit wo and its Q.

• I get this formula for amplitude of impedance of circuit as a function of input frequency ω. Assume a sinusoidal input. It also depends on resistance R. ${\sqrt {R^{2}+\left({\frac {\omega QR}{\omega _{0}}}-{\frac {\omega _{0}QR}{\omega }}\right)^{2}}}$ This ignores phase shift. Graeme Bartlett (talk) 11:15, 21 December 2018 (UTC)

Ah yes that's more useful even though it still contains R, i can get rid of that by changing to equation that gives the voltage across the R. In that case, R disappears and om left with an expression contain g only omega, omega0 and Q which was my goal. Thanks for helping me toward my goal.80.2.20.132 (talk) 22:24, 21 December 2018 (UTC)

You could just set R to 1. Then you can plot a graph. Using a logarithmic ω axis will make the plot symmetrical. Originally there were three parameters R L and C, but you only gave two (Q and ω₀) so there is still one needed. L and C can be written as a function of QR and ω₀. Then the formula I gave is just the impedance of resistor, inductor, and capacitor added, but since two are imaginary it is square root of the sum of squares. Graeme Bartlett (talk) 12:00, 22 December 2018 (UTC)

Direct vision repair

What precisely is this in the context of heart surgery, and what should it contrasted to? Ericoides (talk) 18:00, 20 December 2018 (UTC)

See Cardiac_surgery#Types_of_cardiac_surgery, SURGERY BY DIRECT VISION IN THE OPEN HEART DURING HYPOTHERMIA and AORTIC STENOSIS—Surgical Treatment Under Direct Vision, Using the Heart-Lung Machine. DroneB (talk) 18:34, 20 December 2018 (UTC)

Ah, OK. The Hypothermia pdf contrasts it to "feel". Thanks, Ericoides (talk) 19:02, 20 December 2018 (UTC)

activity coefficient as a function of membrane potential

If my solution near a transmembrane protein is locally more depolarized or closer to 0 mV with respect to the outside of the cell, would ionic interactions between chains of a protein by stronger or weaker? I'm trying to figure out how to use the Debye–Hückel equation here. Any advice? In this case, I'm being asked to brainstorm some novel mechanistic bullshit about hERG (that's honestly the standards of this assignment) for a "literature review" (lol) -- essentially, stuff that would violate WP:SYN if it were on Wikipedia -- but I ideally want to brainstorm some evidence-based bullshit.

Anyway, in popular explanations of the lysine-rich and arginine-rich voltage-sensing domains of voltage-gated ion channels to undergrads, as the membrane potential depolarizes, the positive membrane depolarizes. As such he positive potential "repels" the lysine/arginine gates away from the cytosol, inducing conformational change that opens the channel.

Recently, someone pointed out to me that there are several issues with this explanation. The first is that the conformational change happens when the membrane potential is at less positive, but still negative potentials, e.g. -40 mV. The second is that the lysine/arginine residues in most of these channels (I am writing about the hERG channel, a cardiac potassium channel) are in a very hydrophobic region; they are already poorly stabilized. I pointed out that for the potassium channels, the positive voltage-sensing gates "retreat" into a negatively-charged pocket of acidic residues. Thus, in my original conception, negative membrane potential serves as a substitute for stabilization for the pocket and competes for the pocket. When the membrane potential gets closer to zero, retreating into the pocket is now the only energetically stable state left.

However, when I looked at some of the PDB structures of the hERG channel (5VA2), we can see that many of the basic residues are actually close to many acidic residues on a nearby neighboring domain (S5), implying tightly coupled electrostatic interactions. How would changing membrane potential (from -90 mV to 0 mV) affect electrostatic interactions in a hydrophobic transmembrane region of the cell membrane, especially in an ion channel protein? Yanping Nora Soong (talk) 20:34, 20 December 2018 (UTC)

Fascinating assignment. What the heck is this for, a graduate course in biophysics or something? Violating WP:SYN is always to be encouraged, except where you'll get in trouble for it.

I haven't done the necessary literature review to even start looking at this properly, and I assume there has to be some context of what resources should be familiar here. But arguing off the top of my head, then looking at the figure in the article for a number, I'm thinking that a phospholipid bilayer is, what, maybe 36 angstroms of insulator, going by our figure? (I assume a better figure can be researched, if relevant) And in that 36 angstroms we might blow through as much as -90 mV of potential difference. So, I mean, if you had that kind of field over a full centimeter, you'd have -9,000,000 volts difference between the electrodes. We can imagine then that these proteins feel a lot of force. A full positive or negative charge moving by a full angstrom would be comparable to electron volts: -90 meV * (1/36) = -2.5 x 10^-3 eV, if I didn't do something stupid, which is like 28 kelvin degrees' worth of energy or 0.25 kJ/mol. Not bond breaking, to be sure, but a significant factor yanking positive bits one way and negative bits the other. I can't begin to fathom a way to model the effect on the structure aside from, well, compiling some computer program to calculate protein secondary structure from scratch and then adding code pulling/pushing on the charges. I suppose someone must have done it though... Wnt (talk) 02:24, 22 December 2018 (UTC)

I measured inter-residue distances in pymol and used the idea of the field inducing torque on charges linked to levers and pulleys on several domains (since glycines and prolines break alpha helices and would serve as fulcra -- thanks Ramachandran!) So rotating the S4 domain say, 15 or so degrees, results in yes thousandths of eV, but breaking an entire ionic bond between arginine and aspartate is on the order of eV. If I conceive of the ionic bonds as dipoles which the electric field then does work on, I get less unfavorable energetics with free energy changes on fractions of kJ and maybe a whole kJ if I'm lucky in how I frame my moment arm, but mutations in certain regions discussed in the literature (ie changing the lysines or arginines to aspartates) discuss open or closed states becoming more favorable by factors of up to 12 kJ/mol. I feel like I'm missing something. I mean the relative dielectric constant of the cell membrane being 5 would strengthen ionic bonds as well as the external electric field -- or am I wrong? I'm going to look at the literature a little more. Yanping Nora Soong (talk) 22:58, 22 December 2018 (UTC)

I could be totally wrong about this, but my thought is that dielectric constant affects capacitance -- the higher the constant, the more charge can be put on the plates of the capacitor, i.e., the aqueous surfaces of the membrane. Here I don't really care how many charges are on either side of the membrane, and certainly don't know, so I'm not measuring Coulomb force and not caring how much it is shielded by local dipoles. I only know the potential difference and the charge, and want an answer in electron volts or some interconvertible unit.

I'm not sure how you got to thousands of eV. My thought is that overall the protein won't have a lot of total positive or negative charges on it (once you cancel out the + and - on a helix or domain), and it's only being pulled by mV, so I don't see how you crack an eV of energy to be had. Maybe if there's some sequence like KRKKRKKRKK in there... but my feeling is you should recheck you didn't drop a "milli" somewhere. Wnt (talk) 23:10, 22 December 2018 (UTC)

December 21

claws, hooves, nails—or not?

Does any tetrapod with distinct digits – thus excluding (e.g.) snakes, whales, sea turtles – not have keratin structures thereon? —Tamfang (talk) 04:26, 21 December 2018 (UTC)

Probably frogs, see Frog#Feet_and_legs, except for some burrowing frogs, which have "keratinized tubercles".--Wikimedes (talk) 04:38, 21 December 2018 (UTC)

Thank you! Any mammals? —Tamfang (talk) 05:45, 22 December 2018 (UTC)

Danger, danger, danger

Statistically speaking, what is more dangerous: attempting to beat the water speed record, or fighting in the Soviet Army as an infantryman at the Battle of Stalingrad? 2601:646:8A00:A0B3:4C8F:175D:BDAF:23EC (talk) 08:14, 21 December 2018 (UTC)

You could compute it by dividing the fatalities in each by the total participants in each. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:06, 21 December 2018 (UTC)

That's what I thought, but can you point me to the sources for these numbers? 2601:646:8A00:A0B3:0:0:0:A5A2 (talk) 09:52, 21 December 2018 (UTC)

• They only fought Stalingrad once. Many of the major names for water speed records kept repeating their record attempts until it did finally kill them. One of the safest boats (in terms of successful runs) was Bluebird K7. Yet this was finally the boat that Campbell was killed in. It's little appreciated afterwards how old the boat was, and how long a successful career it had had beforehand.

So the figures for "risk per attempt" and "risk per racer" would be quite different. Andy Dingley (talk) 10:35, 21 December 2018 (UTC)

This Quora thread has casualty rates for Stalingrad. The German figure (94%) must include prisoners, although very few of those lived long enough to go home. Alansplodge (talk) 13:45, 21 December 2018 (UTC)

cox proportional hazard regression v multiple logistic regression

Hi all, I'm trying to learn about medical statistics but the difference between cox proportional hazard regression and multiple logistic regression is unclear to me. From what I've read: Cox proportional hazard regression model is used in survival analysis, e.g. it is used to determine the effects of variables such as smoking status on the survival of a group of people over a period of time.

In terms of multiple logistic regression, I'm not really sure what it is, the wikipedia article on it is Greek to me! According to one of my textbooks, it could be used in a retrospective study following an outbreak of a disease to identify factors (e.g. temperature on arrival to hospital, sex of patient) that might be associated with an increased risk of death. I'm aware that temperature is a continuous outcome measure where as sex of patient is binary.

To me, these 2 different medical statistics seem like the same thing, there must be some difference but I don't understand it...

If anyone can help with a brief explanation of the difference(s) between them I'd be very grateful. Please don't include formulas in your response if at all possible(!) as I am definitely not mathematically minded, I had enough trouble learning about T-tests! Thank you. RichYPE (talk) 09:30, 21 December 2018 (UTC)

Courtesy links: Proportional hazards model#The Cox model and Logistic regression. Loraof (talk) 20:50, 21 December 2018 (UTC)

• The proportional hazards model asks what is the probability that something happens at a certain time. Logistic regression can ask that same question, and in a different context it can ask what is the probability that something falls into one of two possible categories. Loraof (talk) 23:27, 21 December 2018 (UTC)

Many thanks. RichYPE (talk) 11:23, 23 December 2018 (UTC)

Is honey vegan?

is honey vegan? Blingeapper (talk) 12:22, 21 December 2018 (UTC)

(ec) No, assuming that you mean "can honey be used or eaten by vegans". Vegan means abstaining from the use of animal products. Honey comes from bees, and bees are animals. Bazza (talk) 12:37, 21 December 2018 (UTC)

And this is the mainstream vegan view, honey is not vegan. Abductive (reasoning) 14:57, 21 December 2018 (UTC)

And by "products" they include the result of an animal's labor, arguing that we would be enslaving the animal. IOW if you trained an animal to pick apples, those particular apples would not be vegan.

A further subtlety: for some vegans it isn't actually animals that are forbidden. They are concerned with suffering so the rule is "nothing with a central nervous system." Thus they are allowed to eat yeast and jellyfish. Others don't allow alcoholic beverages as being the product of yeast. Some use health-based arguments, arguing that plants are healthy to eat and animals not. That particular brand of vegan would reject fully synthetic meat that was never part of an animal. --Guy Macon (talk) 18:04, 21 December 2018 (UTC)

When I hear these debates about what "truly" vegan is about, I'm reminded of a colleague who considered himself a vegan, yet was a significant cigarette smoker. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:40, 21 December 2018 (UTC)

Ahah. What part of an animal did he smoke or is there some kind of a hidden point you're making in your post?--TMCk (talk) 23:15, 21 December 2018 (UTC)

Am guessing he smoked those humpy ones. Martinevans123 (talk) 23:29, 21 December 2018 (UTC)

I don't know. Luckily I was nowhere near when he would light up. But what's the point of being vegan if not to be healthy? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:36, 21 December 2018 (UTC)

I once bought some honey from an organic farm shop; the owner told me all about the health benefits of unblended, unheated honey, while he coughed and spluttered through his nicotine-stained teeth.... PaleCloudedWhite (talk) 23:47, 21 December 2018 (UTC)

"Fags are people too, you know." Martinevans123 (talk) 23:54, 21 December 2018 (UTC)

Baseball Bugs, if you're not already aware, our article at Veganism#Philosophy lists a number of reasons to go vegan, none of which are the health of the consumer. Matt Deres (talk) 14:42, 22 December 2018 (UTC)

It seems to have to do with harm to animals, and apparently harm to oneself is fine. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:06, 23 December 2018 (UTC)

Guy, I realise you're making a point about the diversity of opinion among vegans, but just to be clear: it's a very, very unusual vegan who would consider consuming a fungus like yeast to be non-vegan. They might avoid alcohol for other reasons, of course. Henry^Flower 21:48, 21 December 2018 (UTC)

"Yeasts are people too, you know." Martinevans123 (talk) 23:27, 21 December 2018 (UTC) [10]

I just did a bit more research (I had a vague memory about vegans and wine/beer) and it turn out that my memory about yeast was wrong. As you can see in our articles on Vegetarianism and wine and Vegetarianism and beer they most;ly have a problem with animal product used in manufacture -- and further searching turns up wine and beer makers who don't use animal products so they can sell to the vegan market. Thanks for helping me to clear up my misconception. --Guy Macon (talk) 23:45, 21 December 2018 (UTC)

Yup, it's the finings used to clarify the beer, at the end of brewing. This makes the yeast clump together, so that it can be removed. Traditionally isinglass was used, which is extracted from the swim-bladder of some fishes. In addition, some beers, such as milk stout contain adjuncts which are non-vegan. LongHairedFop (talk) 10:44, 23 December 2018 (UTC)

Contra Abductive, I don't think there's really a vegan consensus on honey. Some vegans accept it; some don't. The ones that accept it presumably don't consider insects to be the sort of "animals" they're concerned about.

I recently saw an article that made a moral argument in favor of vegans eating, not just honey, but insects themselves. The gist of the argument was that the evolutionary purpose of suffering was longevity, and insects were too short-lived for suffering to be adaptive, so insects presumably did not suffer. Given that vegetable farming imposes suffering on (for example) field mice, it was supposed to be better to eat the actual insects.

(I am not sure whether the author considered him/herself a vegan.)

I found the argument interesting, but not especially convincing. But the hard problem of consciousness inevitably comes up here. --Trovatore (talk) 08:40, 22 December 2018 (UTC)

Insects (and other invertebrates) are deliberately killed during the production of commercial food crops anyway - even organically grown ones - so any act of eating by a human, even those who consider themselves as 'pure' vegans, is likely to involve the death of animals. PaleCloudedWhite (talk) 08:57, 22 December 2018 (UTC)

The vegans I've met or read from who eat honey do so because beekeepers will tell you that it's an undeniably symbiotic relationship and anyone who says otherwise is either ignorant or delusional. Wild hives are inefficient crapshoots for all the reasons. You have to divide effort between looking for food, maintaining the hive, defending the colony from wasps; build too big and weather's gonna wash it away, build too small and everyone drowns in honey; build too close to food and you're just inviting bears and wasps and insecticides to find the hive. Human-made hives are extremely safe and reliable, are protected from predators, come with way more storage space than the bees could ever dream of, and are usually near lots of plants that the bees like. Bee keepers do everything they can to make sure that the bees are healthy and safe, and that does include collecting the honey because bees will stuff their hives so full that everyone gets trapped inside. Ian.thomson (talk) 06:31, 23 December 2018 (UTC)

Speculation about possible space travel

For our present understanding, even the 'closest' star is way too far to be reached with present technology within the span of a human life. However, things are not always how they seem to be. So, is there any not-yet-dismissed hypothesis that would allow human built spacecrafts, manned or not, to travel to any near star systems?--92.191.143.129 (talk) 17:37, 21 December 2018 (UTC)

Until somebody who knows what they're talking about comes along, try our Interstellar travel article, especially the Proposed methods section. Alansplodge (talk) 18:16, 21 December 2018 (UTC)

Atomic clock and standard time

According to atomic clock, its caesium standard is calibrated against ephemeris time, meaning an atomic clock is ultimately based on ephemeris time. But seemingly an atomic clock can also show old-school standard time for various time zones, like here. How can an atomic clock measure both of these times? 212.180.235.46 (talk) 20:03, 21 December 2018 (UTC)

You're conflating two different ideas. The first is the passage of time itself in your particular reference frame. That is, the length of the second, which in any particular reference frame is invariant in that frame. The other is the particular time any one clock should read (i.e. what should my properly calibrated clock read). Ephemeris time and standard time and the various solar times are clock times. These are calibrated against the standardized length of the second, not the other way around.--Jayron32 23:08, 21 December 2018 (UTC)

What kind of snake was put in the passenger's seat?

The clip starts at 6:30 on the YouTube video with "kDCtQcYES9Q" in the link. Thank you. 104.162.197.70 (talk) 22:42, 21 December 2018 (UTC)

The one in the cage looked to me to be an albino Burmese python. - Bilby (talk) 23:34, 21 December 2018 (UTC)

December 22

When we laugh which part of the autonomic system works?

When we laugh which part of the autonomic system works? Is it the sympathetic or the parasympathetics system that takes place in this case? --ThePupil (talk) 02:45, 22 December 2018 (UTC)

I am not sure that the autonomic system is at works at all when humans laugh. Although laughter episodes do have influence on it as all other emotional events. Ruslik_Zero 19:38, 22 December 2018 (UTC)

Looking directly at bright lights; what is the result called?

When you stare into a bright light and then look away, you experience the result of a sort of temporary bleaching of cells of the retina - what is that phenomenon called? Is there a single word or phrase to describe this? Thanks. --88.105.121.127 (talk) 06:39, 22 December 2018 (UTC)

Temporary blindness. One astronomer (as an experiment) deliberately looked at the sun for several minutes and lost his sight as a result (he feared permanently, but it later came back). After the 1999 eclipse hospitals treated a number of people who looked at it without filters. Some of these people still have sight problems. NEVER LOOK DIRECTLY AT THE SUN. 94.2.25.22 (talk) 08:09, 22 December 2018 (UTC)

Less dramatically, there's afterimage. Rojomoke (talk) 09:00, 22 December 2018 (UTC)

Photokeratitis is known by a number of different terms including: snow blindness, arc eye, welder's flash, bake eyes, corneal flash burns, sand man's eye, flash burns, niphablepsia, potato eye, or keratoconjunctivitis photoelectrica. DroneB (talk) 15:05, 22 December 2018 (UTC)

Nonpolar vs apolar

In chemistry, what is the difference between saying that some molecule is apolar versus that it's nonpolar? I'm asking mostly because on en.Wikipedia, the two words redirect to different articles right now. – b_jonas 12:32, 22 December 2018 (UTC)

They have exactly the same meaning. In addition nonpolar (apolar) molecules are usually hydrophobic, so the first redirect. It should probably be re-targeted for consistency. Ruslik_Zero 19:32, 22 December 2018 (UTC)

Just as a further detail that apolar/nonpolar should point to the Chemical polarity definition of the terms rather than the hydrophobe property, not all non-polar substances are hydrophobic. Or at best it depends if you consider structures that are transiently polar (even though on average non-polar), such as xenon that is a polarizeable single atom, or structures that can form strong hydrogen bonds to water, such as hexamethylenetetramine to give solvated polar clusters (is it still "the nonpolar molecule itself" that is present?). DMacks (talk) 06:32, 23 December 2018 (UTC)

Eccentricity needed to produce seasons without an axial tilt?

If the Earth had no axial tilt, how eccentric would its orbit have to be, if the perihelion and aphelion were to produce a cycle of seasons as intense with respect to temperature as the real Earth has around 45°N and S? NeonMerlin 22:28, 22 December 2018 (UTC)

I expect someone will be able to calculate the required eccentricity to produce a similar variation in insolation, but considerably more than the current value. There would, of course, be two summers and two winters per year. The exact climatic effects would be difficult to predict with any accuracy, but there would be a much greater temperature gradient from equator (impossibly hot?) to poles (much thicker ice cap). Dbfirs 23:23, 22 December 2018 (UTC)

There would not be 2 summers a year, the center of ellipses is not at the Sun. Sagittarian Milky Way (talk) 00:05, 23 December 2018 (UTC)

Sorry, you are correct, of course. My mental image was faulty. My only excuse for such a silly error is that it was late at night! Dbfirs 07:54, 23 December 2018 (UTC)

That article on insolation certainly conforms to all the checkboxes for user-hostility in math articles. It snows people under with an incredibly complicated derivation, then the moment it starts moving toward a conclusion, omits the conclusion and throws a curve ball with the ellipticity of the earth, then finishes with a numerical formula with no term for latitude. I honestly feel like one of the big textbook publishers has a couple dozen people on payroll whose job is to make sure Wikipedia math isn't usable across the board. Don't even try to fix an article like that -- my expectation is all you get is a tirade of threats of being banned for daring to suggest anything could be wrong with it.

Still, if you do what all proper peasants should do and beg the Google gods for a page from a properly copyrighted textbook [11] you'll get a prod toward a simpler explanation. You take the 23.5 orbital declination and subtract (summer) or add (winter) that value from the 45 degree latitude of the example. That gives 21.5 and 68.5 for the zenith angle at high noon. Now take the cosine of that and get 0.93 and 0.37 respectively - that is how much the light is reduced by the angle during summer and winter. The ratio of summer to winter is 0.93/0.37 = 2.53. To get that by eccentricity, the sun would have to vary in distance by the square root of 2.53 = 1.59, i.e. 59% further away in winter than in summer. (Plus the earth's minor eccentricity, which I doubt is simple addition but probably is negligible in the face of that) Now for these purposes it doesn't matter how big the ellipse is - we were only asked eccentricity, and any variation in light can be dealt with by turning the sun up or down afterward. So let's say the earth moves from (0,0) in summer to (2.59, 0) in winter with the focus at (1,0). Now if my recollection of what eccentricity is is right, we can take the center of the ellipse at (1.30,0) and calculate the ratio of (1.30 - 1)/1.30 and get 0.23. The article on orbital eccentricity says the ratio of aphelion and perihelion is (1+e)/(1-e) and that checks, though it would have been a royal pain to use it in a forward direction. So I'm going to go with a figure of 0.23, noting that this is only the hypothetical top-of-atmosphere insolation at the summer and winter solstice and may not reflect a real climate (since after all, an elliptical orbit is a lot of winter and a little bit of summer) Wnt (talk) 04:43, 23 December 2018 (UTC)

Thank you for the calculation. I was too tired to attempt it last night. Dbfirs 07:54, 23 December 2018 (UTC)