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August 20

Are engineers scientists?

Ignoring personal opinions about the definition and limits of each; just considering concrete decisions - like grants, fellowships, or prizes - do engineers count as scientists? Hofhof (talk) 01:53, 20 August 2016 (UTC)[reply]

What do you mean concrete decisions?--Savonneux (talk) 03:58, 20 August 2016 (UTC)[reply]

That is, when someone has to draw a line as to who gets rejected or accepted. I mean when it comes down to apply and receive a grant for scientists, or a prize for the best minority female scientist, would engineers be considered a part of the scientists? Hofhof (talk) 04:13, 20 August 2016 (UTC)[reply]

"Science" grants are infinitely broad in what each one could possibly be for, they aren't the exclusive domain of scientists though (anything practical tends to be an engineering problem). The difference between engineering and pure theory is just that, engineers are mostly concerned with applied science (how do we use science to solve this problem) and "scientists" are mostly concerned with the purely theoretical.--Savonneux (talk) 04:28, 20 August 2016 (UTC)[reply]

While it's true that engineers are concerned with how to use science to solve problems, it's not true that scientists are mostly concerned with the theoretical. They also do empirical observations, such as observing fossils or supernovae, and they do experiments. Then they or other scientists come up with theories to explain the observations and results. Loraof (talk) 16:00, 20 August 2016 (UTC)[reply]

Agreed. The person asking seemed to want a sort of differentiation so I was trying to show the only one. Anyone who applies rigorous logic to a thesis is technically a scientist.--Savonneux (talk) 00:24, 21 August 2016 (UTC)[reply]

The problem is that the word engineer is very difficult to define. The man who comes to repair my washing machine calls himself an engineer, but so do the men who designed and built the space shuttle and the new Forth road bridge. In the USA the driver of a train also calls himself an engineer. Some may deserve to be called scientists - others probably do not. Wymspen (talk) 14:05, 20 August 2016 (UTC)[reply]

Origin of "engineer":[1] ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:31, 20 August 2016 (UTC)[reply]

I'm in A BIG CITY and I can't see the stars at night due to light pollution. If there was a...

I'm in A BIG CITY and I can't see the stars at night due to light pollution. If there was a countrywide powercut, how long would it take for the light pollution to go away? and the stars to be viewable? Like, would it be instant or would it take several years? Since light is really fast I can't understand how it would stay in the sky for very long once the lights went out. Please explain. — Preceding unsigned comment added by 200.94.21.194 (talk) 14:28, 20 August 2016 (UTC)[reply]

A tiny fraction of a second after the power cut, most of the light pollution would vanish. A small amount would remain because of emergency generators etc, but the effect would appear instantaneous. Air pollution is a separate factor to consider in some cities. Dbfirs 14:42, 20 August 2016 (UTC)[reply]

Do note that the afterglow of many kinds of lights (like high pressure sodium streetlights) would take minutes to dim to invisibility. Car headlights might be the biggest source of light pollution in a blackout, unless there's been a significant increase in generators now than during the 2003 blackout. Besides air pollution, blackouts often happen in heat waves when there might be a lot of haze. Sagittarian Milky Way (talk) 01:39, 24 August 2016 (UTC)[reply]

See Light pollution for our article; Adaptation (eye) might also be useful. Although the light pollution would be gone as soon as the power went off, it would take some time (about 20-30 mins, according to our article) before the observer's eyes could take full advantage of the darkness. Tevildo (talk) 14:56, 20 August 2016 (UTC)[reply]

I'm not so sure if you'd necessarily need 20-30 minutes or how strong the effect would be. Our Accelerating dark adaptation in humans seems in some ways better then the adaptation one, but even so, both primarily talk about moving from high illumination to low. If you were indoors in a light room, you may need 20-30 minutes. But how significant would the effect be if you were already in a dark area of the city (i.e. where there are no lights clearly visible). Sure the sky would still be bright, but I'm not sure how big the difference would be after adaptation for 20-30 minutes. If you were sleeping in a dark room with your eyes closed, provided you're careful when getting out (i.e. red light etc), the difference would probably be even less. So IMO the issue may be less related to light pollution but more what you were doing before. (Or in other words, it's quite similar to if you're living in an area with minimal light pollution except that you can't normally predict when a nationwide powercut will happen.) Nil Einne (talk) 15:31, 20 August 2016 (UTC)[reply]

Thing is that the difference between optimal dark adaption and partial dark adaption is only going to be noticeable when you try to spot hard to see objects at the very limits of visibility, like spotting M81 with the naked eye. Count Iblis (talk) 17:10, 20 August 2016 (UTC)[reply]

Supernova ice ages and artificial substitutes

I've been reading articles lately [2][3] that suggest that supernova debris, as evidenced by iron-60, might have set off the Pleistocene ice age. There is some mismatch - the iron-60 started 2.7 million years ago, and continued for a million years, but why isn't the correspondence exact, or at least entirely inclusive of the glaciated period? How viable is this idea. And if it is viable .... how much material are we talking about here? I shouldn't think a supernova 300 or more light years away would rain down very much matter on Earth to increase its cloud cover. So is it possible for humans to cook up a space probe that does the same thing, as a sort of geoengineering to counter excessive global warming? (Not that I'm suggesting this is necessarily a good idea... sometimes I wonder if the 'Gaian' purpose of humans was to look around and figure out how to clear out all that nasty ice...) Wnt (talk) 18:57, 20 August 2016 (UTC)[reply]

Ok, this is a really back of the envelope calculation, and I could be off by several orders of magnitude. They are hypothesizing a supernova 300 light years away, ish. Let's pretend it's a big star with 8 solar masses. Even if we pretend the entire mass of this star explodes outward, the earth will only catch a small fraction of the material. How small? Well, by the time the blast front reaches earth, it has spread out over a spherical region 300 light years in radius, and the space in that surface occupied by the earth is only 1e31 of the whole, so that's the fraction of the star we capture. That would be about a kilogram of material. Now, maybe Earth's gravity will pull in some material that is not headed directly toward us, but these particles are moving very fast, so probably not a whole lot more. I think even if I'm way off on some things (if the star is closer, or bigger) it's still going to work out to a truly negligible amount of matter. I honestly just don't see how this could possibly affect Earth's weather. Now a much much closer supernova, however (less than 50 light years) could make a noticeable dent in the ozone layers, and the effect on plankton could have some long-range ecological consequences. Someguy1221 (talk) 10:00, 21 August 2016 (UTC)[reply]

This is why there shouldn't be that much kryptonite on Earth. Terrestrial planets must be at least ~10⁵ times smaller than 8 Sun masses so there should only be a few grams of kryptonite in the entire world if Krypton exploded anywhere near the speed of Alderaan. Sagittarian Milky Way (talk) 20:16, 21 August 2016 (UTC)[reply]

what is this filter?

hello, in the discrete-time PLL example here there are these lines:

% Implement a pole-zero filter by proportional and derivative input to frequency
filtered_ersig = ersig + (ersig - lersig) * deriv;
% Keep error signal for proportional output
lersig = ersig;

In simple terms, what kind of filter is this (other than pole-zero and, I assume, FIR, as it doesn't use past output samples)? Apparently what the filter does is that whenever there is change, it creates an "overshoot" in the direction of the change and then settles on the new value. Is it then a high-pass? Thanks in advance! Asmrulz (talk) 20:06, 20 August 2016 (UTC)[reply]

A cursory search suggests that a 'pole-zero filter' is an approximation of a Butterworth filter, which our article describes as a theoretical ideal for a "maximally flat magnitude filter". 2606:A000:4C0C:E200:296A:CC64:7945:8C5F (talk) 03:47, 21 August 2016 (UTC)[reply]

That's not quite right... a Butterworth filter is a specific type of filter. "Pole-zero" is a design methodology to create a filter by placing poles and zeros - mathematical constants in the denominator and numerator of a transfer function. One can use pole-zero analysis to build a filter of any specific type. A "pole-zero filter" is any filter whose properties were designed by placing poles and zeros explicitly, instead of computing them using some other method. Every filter has poles and zeros: but many times, because we have a different analytical technique, we may choose not to concern ourselves with the values of the poles and zeros. In this case, the author described this code-snippet "pole-zero filter"; I would call it a "PD-controller"; but in any case, those comments are just a little bit of English language verbage to help motivate this very small mathematical sub-expression of the larger PLL system. Nimur (talk) 14:11, 21 August 2016 (UTC)[reply]

The code excerpt is meaningless without context - but if you look at the full code in the article, it makes a little more sense. This is a digital filter, and it saves state, so although the history (previous samples) aren't explicitly stored, the filter is using their values.

The filter is neither a high-pass nor a low-pass filter. Instead, it outputs a control signal whose magnitude and sign are proportional to frequency error. A reference signal, of known frequency, is compared to an input signal, of unknown frequency. This particular implementation uses the trick of edge-detection, using a digital, bitwise comparator to trigger the edge detection; and it keeps a running sample-counter to estimate how synchronized the two signals are - in other words, how coherent their phases are. In the analog world, we would use a totally different method.

Mathematically, any filter that converts a frequency to a different frequency (in this case, to a "dc" control signal) is definitionally non-linear: loosely speaking, frequency is not preserved. You can not think in terms of "frequency" pass-bands. This is not a low-pass, high-pass, or band-pass filter: it is a filter whose output depends on input frequency (and phase) in a nonlinear fashion.

This is a complicated bit of code - and it stores digital state in many variables, including the signal flags and the "it" (iteration counter) variable. If we want to throw mathematical terminology at this software implementation, we could say that because these state-flags allow us to compute results that are related to previous samples, they are functions of the derivative of the input signal. Although the code doesn't directly compute and store the derivative (difference between current- and previous- sample), the algorithm does make implicit use of the derivative.

Again, if you tried to formally write out that relation, it would be a non-linear differential equation - and what this software filter does is to try to numerically solve it! Like all non-linear differential equations, the solution is only valid in special cases: if you fed a junk input signal in, with really high noise levels or just completely the wrong frequency content, you could cause the PLL to fail to converge (and this is a real thing that does actually happens in real-world electronics applications)!

Nimur (talk) 14:11, 21 August 2016 (UTC)[reply]

Thank you so much! I think I "get" it (to the extent it's possible to "get it" without the theory and the associated math.) I'm just (still) trying to make an all-digital PLL as a hobby project (that I could flash onto the ATtiny.) I wrote a simulation in which I incorporated bits and pieces from the code in the PLL article. It seems to work well (I'm not trying to replicate the 4046 chip.) Even frequency multiplication works if I put a divider in the "feedback path." Thanks again! Asmrulz (talk) 20:02, 21 August 2016 (UTC)[reply]

Are all PLLs actually PID? That not all PID have frequency as the controlled quantity, is obvious, but from cursory googling, noone seems to discuss PLL in terms of PID, and no PLL block diagrams I've seen contain explicit P, I and D sections, like here. Asmrulz (talk) 20:28, 21 August 2016 (UTC)[reply]

No, it is possible to build a phase-locked-loop circuit that does not use a PID controller at all, but uses a different type of digital controller. It is also possible to build a PLL that is completely implemented in analog circuitry. For example, in the analog world, we can build a PLL using a varactor (if we want to pretend like it's 1970!), or using a voltage-controlled oscillator or using a Miller topology feedback control amplifier. In digital designs, PIDs are a fundamental building-block: it's such a convenient, commonplace design methodology that you will surely see it in lots of places. Moral of that story: learn the theory and practice of PID controllers really deeply, and learn to recognize the implementation and the behavior of PID controllers; because they show up as tiny building-blocks inside lots of more complicated systems.

Once you get really good at the math and the theory, you will be able to turn any control equation into an "almost-equivalent" PID controller... once again, "PID" is really just a design-methodology that lets us write a specific type of equation - a second-order digital control transfer function - in a standard, canonical form. Once the equation is in standard form, we can use shortcuts to solve for its behaviors and estimate its properties, and we can "plug and chug" into standard software or hardware implementations. That is meant to be easier than finding full solutions to the stability and control equations for every single sub-problem you encounter in a complicated design.

Nimur (talk) 20:52, 21 August 2016 (UTC)[reply]

August 21

Different number of heart valves in the heart sides

I've taken the liberty of transferring this question from Wikipedia talk:Reference desk Wnt (talk) 02:06, 21 August 2016 (UTC)[reply]

Is there any logical explanation why in one side of the heart (right) there are 3 valves -triquspidal, while in the second side (left) there are 2 (mitral)? Tov17 (talk) 21:56, 19 August 2016 (UTC)[reply]

This discussion has been closed. Please do not modify it.

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

You should post this Q to the Science Desk. This is the talk page where we discuss problematic questions. StuRat (talk) 22:01, 19 August 2016 (UTC)[reply]

When you're there, they may explain that the heart has only four valves, not five. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:43, 19 August 2016 (UTC)[reply]

If you provide an answer when someone asks in the wrong place, you not only encourage more misplaced questions, you encourage others to answer in the wrong place. Please stop doing that. --Guy Macon (talk) 03:24, 20 August 2016 (UTC)[reply]

And, more importantly, please stop giving wrong and unreferenced answers to questions which you are obviously unqualified to answer. The human heart has six valves: the bicuspid valve, the tricuspid valve, the aortic valve, the pulmonic valve, the coronary sinus valve and the eustachian valve. The eustachian valve has no known function after birth, leaving five functional valves in the normal human heart. Additionally, about 80% of people have a vieussens valve of the coronary sinus, which could be counted as a sixth (or seventh) heart valve.--William Thweatt ^Talk^Contribs 05:12, 20 August 2016 (UTC)[reply]

Four "main" valves, as noted in Heart valve and two other valves as you note. As to the OP, there's nothing stopping you from moving the question there yourself, if you're so concerned about it. Also, amidst your nannyistic scolding, you did not actually answer the OP's question. Way to go. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:55, 20 August 2016 (UTC)[reply]

I suspect the question that the OP meant to ask is the one answered at [4]. - Nunh-huh 08:36, 20 August 2016 (UTC)[reply]

Indeed, thank you. Tov17 (talk) 17:45, 20 August 2016 (UTC)[reply]

What the OP tried to ask is why the tricuspid valve has three leaflets while the bicuspid valve has two. The tricuspid separates the right atrium and ventricle while the bicuspid separates the left atrium and ventricle. Well, the answer is that it's complicated - we don't know the full network of biological and regulatory processes behind morphogenesis of any system in the level of detail needed to really give "why" type answers to these sort of questions with confidence. We can say that they're different and show particular factors which if altered might alter whether they are different, but I'm skeptical we've even gotten to that point, though properly I ought to look it up. But in this case the situation is a little weirder and a little simpler - the number of leaflets or cusps in the tricuspid can vary from two to six. Here's a reference that argues they are fundamentally divided in two: [5] So the difference in the anatomy is subtle - subtle enough that it might readily be ascribed (but this would be purest speculation, and probably wrong) to properties like how much resistance there is from lungs versus somatic tissue, or asymmetric development of the heart as a whole. Wnt (talk) 02:15, 21 August 2016 (UTC)[reply]

This discussion has been closed. Please do not modify it.

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

You and Nun-huh have it right. Macon and FGF do not. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:13, 21 August 2016 (UTC)[reply]

Yes, the OP was confusing number of valves with structure of valves. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:22, 21 August 2016 (UTC)[reply]

The OP wasn't confused at all. He made it crystal clear which part of the heart he was talking about. You simply didn't bother looking up "tricuspid" and "mitral" before answering. --Guy Macon (talk) 21:45, 21 August 2016 (UTC)[reply]

You're wrong, I did. And the OP agreed that Nunh-huh's link answered his question - which you didn't bother trying to do. So shut your own valve. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:57, 21 August 2016 (UTC)[reply]

The OP explicitly mentioned the vales they were asking about. The question was unambiguous. You were clearly wrong. Stop answering questions you haven't got a clue about. It wouldn't hurt to look up the word 'civility' while you're at it. Fgf10 (talk) 22:08, 21 August 2016 (UTC)[reply]

You, lecturing others about civility? That's funny. You pop in here to fire shots at others rather than answering the OP's questions. You're of no use here. Go back to ITN and nominate some more frauds for the "recent deaths" column. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:23, 21 August 2016 (UTC)[reply]

"The most hostile group was the one with high but unstable self esteem. These people think well of themselves in general, but their self-esteem fluctuates. They are especially prone to react defensively to ego threats, and they are also more prone to hostility, anger and aggression than other people.

"These findings shed considerable light on the psychology of the bully. Hostile people do not have low self esteem; on the contrary, they think highly of themselves, But their favorable view of themselves is not held with total conviction, and it goes up and down in response to daily events. The bully has a chip on his shoulder because he thinks you might want to deflate his favorable self image."

Source: Roy F. Baumeister, Evil: Inside Human Violence and Cruelty, p 149

--Guy Macon (talk) 22:34, 21 August 2016 (UTC)[reply]

The perfect description of someone who comes here to attack other editors. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:05, 21 August 2016 (UTC)[reply]

You're literately making no sense at all. The question was already correctly and exhaustively answered (no thanks to you) in the end. I'm not even active on ITN any more. I think you might need a holiday away from here. Can some passing admin just close this nonsense down? And preferably refer BB to ANI while they're at it....? Fgf10 (talk) 23:46, 21 August 2016 (UTC)[reply]

I applaud you for abandoning ITN. But before you return to the ref desk, if ever, be sure to come here for the sole purpose of answering an OP's question. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:53, 21 August 2016 (UTC)[reply]

Using plastic glove as condom

Can you still get a girl pregnant if you use a plastic glove as condom? — Preceding unsigned comment added by 107.214.148.164 (talk) 18:53, 21 August 2016 (UTC)[reply]

Even regular condoms are no guarantee against pregnancy, though they reduce the odds. But when used with spermicida foam, it's very near zero percent chance. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:20, 21 August 2016 (UTC)[reply]

What about plastic gloves used with spermicide? — Preceding unsigned comment added by 107.214.148.164 (talk) 19:25, 21 August 2016 (UTC)[reply]

Just get free condoms somewhere. The condom won't be like 3 inches long either. Sagittarian Milky Way (talk) 19:46, 21 August 2016 (UTC)[reply]

Condoms are specifically tested to make sure that they are strong enough not to tear or leak when used during sexual intercourse. Rubber gloves are not tested for that, so are less likely to be safe. Wymspen (talk) 20:23, 21 August 2016 (UTC)[reply]

Some limited info here [6] Nil Einne (talk) 21:29, 22 August 2016 (UTC)[reply]

There are actually a lot of gloves that are sold without any strong guarantee against breakage. The usual idea with lab gloves is merely to keep something sanitary given gentle usage, where not keeping it sanitary is no big deal. Often they're labelled as being for "comfort" or such, rather than being surgical gloves. Our article on Medical gloves talks about people who do double-gloving even with high-quality latex gloves. Some people who do work where glove integrity would be critical, like using hydrogen fluoride solutions, actually do without gloves but simply wash their hands after each and every potential contact because they fear the effect of an unseen leak. I can tell you for sure that with the usual cheapest-of-the-lot lab gloves that people use for non-critical scientific procedures, holes are not even uncommon. Of course, condoms aren't entirely impenetrable either, but at least they're designed to do one thing and do it as best as possible. Wnt (talk) 20:56, 21 August 2016 (UTC)[reply]

Add to it that plastic gloves (or the powder within it) are not tested for allergic reactions when used this way. Latex gloves and latex condoms are also made from a different type of latex. Llaanngg (talk) 20:59, 21 August 2016 (UTC)[reply]

In short, "no glove no love" is not meant to be literal. The same can be said about putting on your sombrero. :) Wnt (talk) 17:02, 23 August 2016 (UTC)[reply]

August 22

probabilistic sampling path planners

Besides Probabilistic road map and rapidly growing tree (RRT), what other algorithms fall under the probabilistic sampling category of path planners in robotics?117.206.48.169 (talk) 14:29, 22 August 2016 (UTC)[reply]

I would put any statistical estimator, like a Bayesian state estimator or a Kalman filter in that category.

There isn't a "correct" taxonomy of algorithm styles; different authors and researchers have different insights into the problem-space, so they may place various methods in the same category for a variety of reasons.

So - why do you need to categorize these algorithms in the first place? Are you looking for comparisons and contrasts? Reference implementations? Practical examples or case-studies?

Nimur (talk) 16:28, 22 August 2016 (UTC)[reply]

Extreme track and field

How fast could a human run 100 meters with a 30 mph tailwind and the fastest reasonable track profile? Let's say that slope cannot exceed 45° anywhere and the human must use a running motion the whole way and stop without assistance or falling down. A slope change to flat or uphill to aid stopping is allowed. Distance is measured by how far the center of mass goes cause 1 meter of steep slope is only ~0.7 meters horizontally. Sagittarian Milky Way (talk) 23:14, 22 August 2016 (UTC)[reply]

Given the effect of a steep slope (and of a strong wind) on a human's balance, my suspicion is that it would probably slightly slower than Usain Bolt manages on the flat. Wymspen (talk) 09:10, 23 August 2016 (UTC)[reply]

Wouldn't that mean a moderate or slight slope is fastest? 30 mph wind isn't that balance disrupting. I did this in Hurricane Sandy (downhill) and literally could not slow down until I discarded the umbrella built for two. I stopped from being dragged into traffic without dropping the other (smaller) umbrella. The wind was probably at least 40. Sagittarian Milky Way (talk) 09:44, 23 August 2016 (UTC)[reply]

This article may help you with your research. --Jayron 32 11:56, 23 August 2016 (UTC)[reply]

Double the speed means quadruple drag which requires eight times the power to overcome. (I may be off slightly) Drag equation I wonder if they took that into account.--Savonneux (talk) 13:08, 23 August 2016 (UTC)[reply]

There is a lot of research in the field of running and human mechanics. What you appear to want is the maximum speed at which a human can move his or her legs fast enough to keep up while applying enough downward force to remain in an upward position. If the legs do not move fast enough, the person will trip. If there is not enough downward force, the person's torso will get closer to the ground, causing a foot to drag, causing the person to trip. I am partial to Dr. Peter Weyand's work. Depending on conditions, he has placed the top running speed of a human between 40 and 50mph. The 40mph is technically possible for a very tall and genetically perfect running human (in other words, nearly all legs). The 50mph limit is based on the maximum speed a human can quickly move his or her legs back and forth as well as the time required to transfer a downward force from the leg to the ground. You can see a summary of biological running limitations here, but it isn't one of his better publications. 209.149.113.4 (talk) 18:35, 23 August 2016 (UTC)[reply]

A tailwind could certainly help, provided the runner could adjust to it. But I would think any significant downward slope would be counterproductive, as it would mess with the runner's balance. As we saw in some of the recent Olympic footraces, some of them had trouble staying balanced even on a flat surface. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:42, 23 August 2016 (UTC)[reply]

I think with practice, the downward slope would NOT be a hindrance. It would be a hindered to someone trying to run UPRIGHT, but the "trick" would be to throw yourself down the slope and "balance" to the ground you are running on, not to the horizontal, so that gravity effectively starts "adding" to your forward vector. The extreme example is how a skate boarder can thrown them self down a half pipe and essentially "balance" on a vertical wall on the way down. Vespine (talk) 22:27, 23 August 2016 (UTC)[reply]

This is definitely something that sources are needed for; on the other hand, some direct experience would be invaluable also. I can look through stuff like [7] but, well, it's like explaining sight to a blind man. They suggest that runners putting in "even effort" will go faster downhill. But definitely their bodies have to deal with more impact, because the gravitational potential energy is being dissipated in their tendons and muscles, essentially. Wnt (talk) 01:53, 24 August 2016 (UTC)[reply]

Pure anecdote, but in my experience of having a steep hill between my college and the train home, it's much easier to keep your balance by skipping than by running. Unfortunately, it's very difficult to slow down (or, in fact, to not accelerate) until you hit the flat, since the skipping motion doesn't permit any balanced deceleration, and transitioning to a run just makes you fall over. MChesterMC (talk) 08:07, 24 August 2016 (UTC)[reply]

Skipping should slow you down. The first contact, per foot, pushes forward to create the skip. The second contact pushes back to accelerate. It is likely that you can achieve the same speed by just running. A benefit to skipping is the increase of vertical force. The first contact acts as a sort of pole vault, giving the torso upward velocity. As I mentioned above, from many decades of compiled running research, the two issues with high speed running are moving the legs back and forth (there is a maximum limit to how fast a human is capable of contracting and relaxing leg muscles) and maintaining enough distance between the torso and the ground (if 100% of energy was used for horizontal momentum, vertical momentum would be lacking and the person't torso would get lower and lower to the ground until running was not possible). 209.149.113.4 (talk) 19:01, 24 August 2016 (UTC)[reply]

August 23

Overview of true flies mimicking wasps and bees

Hoverflies are known for mimicking powerful hymenoptera like wasps and bees. But they are not the only true flies doing so. Other examples include several soldier fly species. Two questions:

Can an overview be given which fly families include hymenoptera-mimicking species?
Would a layman, not familiar with the specific species, call such a mimicking fly probably a "hoverfly", even if it does not belong to this family?

Beetles, butterflies etc. using this mimicry are not included the question. --KnightMove (talk) 15:29, 23 August 2016 (UTC)[reply]

The Bombyliidae fit the bill. Mikenorton (talk) 15:45, 23 August 2016 (UTC)[reply]

In my experience, laymen don't often know the word or concept "hoverfly". If they do, then sure, they may well apply it to bee-looking flies outside the Syrphidae. But some people use the common name drone fly, some may use the term bee fly to pseudo-incorrectly refer to a Syrphid, etc.

Acroceridae is another Dipteran family with some bee mimics, as is Asilidae. Together with they Bombyliidae Mike mentions and the Syrphidae you mention, I think that covers all the mimics that I already knew about. Here is an interesting article on behavioral mimicry of honey bees in some Syrphidae spp. [8]. Here [9] is an article that discusses a few different bee mimics, and looks at their relative similarity, frequency, and potential benefits. This paper [10] discusses some of the interplay between bees, their mimics, phenology, and birds. I am unable to find a list of Dipteran families in which presumed hypmenopteran mimics occur. SemanticMantis (talk) 21:36, 23 August 2016 (UTC)[reply]

Well, I thought that picture was a hoverfly, until I looked it up, so I suppose that's one instance of someone calling such a mimicking fly probably a "hoverfly". I suppose it would depend on how similar the non-hoverfly mimics were to hoverflies (unlike the one here, the pictures on the soldier fly page don't look much like hoverflies to me). Then there's behaviour - hover flies hover, hence the name. Do soldier files and other mimics also hover? If so, I expect a lot of people would mistake them for hoverflies. If not, well, maybe fewer would. Iapetus (talk) 11:39, 24 August 2016 (UTC)[reply]

Dark clouds

How thick must a rain cloud or thunderhead be in order to completely block sunlight and reduce the ambient illumination from normal daytime levels to nautical twilight levels? (Assume that the sun is 45 degrees above the horizon.) 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 23:21, 23 August 2016 (UTC)[reply]

Define "thick"? Do you mean the droplet density inside the cloud, or the vertical dimensions of it? They both would be factors in the ability to block sunlight, and they both could be defined as "thickness". Indeed, the sunlight blocking ability of clouds is likely due to a number of factors, and isolating any one is likely difficult. --Jayron 32 01:30, 24 August 2016 (UTC)[reply]

The vertical dimensions, given a typical droplet density for these two cloud types. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 03:02, 24 August 2016 (UTC)[reply]

This document discusses the concept in general terms (search for the word "clouds") and references another NASA document called a "Clouds Fact Sheet" that may be promising. --Jayron 32 10:40, 24 August 2016 (UTC)[reply]

August 24

Does the International Space Station have enough radiation hardening to survive outside LEO?

According to International_Space_Station#Communications_and_computers, there are ~100 regular Thinkpads on board, so those won't survive outside LEO for sure. But I'm unable to find out:

1. Whether those ~100 Thinkpad on the ISS are mission critical or not. Maybe they're just there for the various scientific missions and are not critical to the functioning of the space station.

2. Whether the mission critical computers on the ISS have enough radiation hardening to survive outside LEO. Pizza Margherita (talk) 00:29, 24 August 2016 (UTC)[reply]

ISS only orbits at an altitude of ~400km which is within even the ionosphere. Low earth orbit extends out to about 2000km, so I doubt ISS is intentionally "hardened" to survive outside of LEO. It's intentionally hardened to survive precisely where it is. Whether it actually "would" survive outside LEO or not is a different question. Earth's_magnetic_field#Magnetosphere extends out at the "short end" to 65,000km, so even well above LEO I don't think the "radiation" is much worse, AFAIK it only gets really bad once you get outside of the magnetosphere. Discounting CMEs. Vespine (talk) 02:45, 24 August 2016 (UTC)[reply]

"Whether it actually 'would' survive outside LEO or not is a different question." Yes, that's the question I'm asking. Pizza Margherita (talk) 03:05, 24 August 2016 (UTC)[reply]

Well that's a question of "probabilities". Like I said, I don't think the radiation outside of LEO is dramatically different to the radiation at the normal orbit of the ISS, at least until you start reaching the upper levels of the magnetosphere. So undoubtedly everything would survive for some time, including normal laptops. I'm not sure why you say "those won't survive for sure"? What's your reasoning for that? I don't think anything would necessarily "fry" immediately even if you took it out of the magnetosphere. How long on average would a regular laptop survive in space? Well we didn't take any laptops to the moon so I don't think anyone has done the experiment. Vespine (talk) 04:17, 24 August 2016 (UTC)[reply]

This is a bit outside my wheelhouse (and more importantly, not referenced) but my understanding is that ambient solar radiation in the space that Earth's orbit occupies is more than substantial enough to fairly well guarantee that a non-shielded device like a laptop would be rendered non-operational instantly, if moved outside the magnetosphere (indeed, probably well before you cleared what is considered the outermost edge of the magnetosphere). As you say though, LEO is a more nuanced, probabilistic question with quite varied answers depending on the specific circumstances. It's also worth mentioning, in looking at the scenario the OP proposes, that the station itself is shielded, as an essential safeguard of the health of the crew and redundancy on protection of critical hardware--although this protection is variable by module and even at its best allows for significantly higher levels of radiation exposure compared to a typical terrestrial context. Snow ^{let's rap} 08:10, 24 August 2016 (UTC)[reply]

Whether the station will survive is a different question from whether the inhabitants of said station will survive. What is your definition of LEO? If you shift up to >1000 km, you're in the inner van Allen belt. Both electronics and inhabitants would be fairly swiftly fried in there (yes radiation is dramatically different there than in LEO). If you leave the Earth's magnetosphere altogether, you'd have both increased background radiation from cosmic rays, and be very much at increased risk from solar events, such as CMEs. The ISS is not designed for these. Have a look at the specialised computer required for BEO work, see Mongoose-V for one. There are significant other issues as well. For instance, the thermal management of the station is designed for LEO, that is regular alternation between orbital day and night. The (near-)constant sunshine in higher orbits would most likely overwhelm the thermal control system. Lastly, it would be a short trip for anyone in the Station, even if all the above wasn't a problem, as no resupply is possible with current craft at above LEO. Fgf10 (talk) 07:15, 24 August 2016 (UTC)[reply]

Metabolism

What is the average age that metabolism starts to slow down, ignoring lifestyle etc and only considering the physiological aspects of the human body? 82.132.220.29 (talk) 19:09, 24 August 2016 (UTC)[reply]

@@ Line 196: / Line 196: @@
 ::::This is a bit outside my wheelhouse (and more importantly, not referenced) but my understanding is that ambient solar radiation in the space that Earth's orbit occupies is more than substantial enough to fairly well guarantee that a non-shielded device like a laptop would be rendered non-operational instantly, if moved outside the magnetosphere (indeed, probably ''well'' before you cleared what is considered the outermost edge of the magnetosphere).  As you say though, LEO is a more nuanced, probabilistic question with quite varied answers depending on the specific circumstances.  It's also worth mentioning, in looking at the scenario the OP proposes, that the station itself is shielded, as an essential safeguard of the health of the crew and redundancy on protection of critical hardware--although this protection is variable by module and even at its best allows for significantly higher levels of radiation exposure compared to a typical terrestrial context. [[User:Snow Rise|'''''<font color="#19a0fd">S</font><font color="#66c0fd">n</font><font color="#99d5fe">o</font><font color="#b2dffe">w</font>''''']] [[User talk:Snow Rise|<sup><font color="#d4143a">'''''let's rap'''''</font></sup>]] 08:10, 24 August 2016 (UTC)
 :Whether the station will survive is a different question from whether the inhabitants of said station will survive. What is your definition of LEO? If you shift up to >1000 km, you're in the inner van Allen belt. Both electronics and inhabitants would be fairly swiftly fried in there (yes radiation ''is'' dramatically different there than in LEO). If you leave the Earth's magnetosphere altogether, you'd have both increased background radiation from [[cosmic rays]], and be very much at increased risk from solar events, such as [[CME]]s. The ISS is not designed for these. Have a look at the specialised computer required for BEO work, see [[Mongoose-V]] for one. There are significant other issues as well. For instance, the thermal management of the station is designed for LEO, that is regular alternation between orbital day and night. The (near-)constant sunshine in higher orbits would most likely overwhelm the thermal control system. Lastly, it would be a short trip for anyone in the Station, even if all the above wasn't a problem, as no resupply is possible with current craft at above LEO. [[User:Fgf10|Fgf10]] ([[User talk:Fgf10|talk]]) 07:15, 24 August 2016 (UTC)
+== Metabolism ==
+What is the average age that metabolism starts to slow down, ignoring lifestyle etc and only considering the physiological aspects of the human body? [[Special:Contributions/82.132.220.29|82.132.220.29]] ([[User talk:82.132.220.29|talk]]) 19:09, 24 August 2016 (UTC)