Wikipedia:Reference desk/Archives/Science/2013 September 14

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September 14

Solar eclipse

Here's a question I've been meaning to ask for a long time: When I watched the annular solar eclipse two years ago, I saw many people try to watch it through ordinary sunglasses (which, as you probably know, are completely inadequate for this task). Which got me wondering: Is there usually a local increase in eye-related complaints immediately after a solar eclipse? (No, this is not medical advice -- I used welding goggles, so I had no eye problems afterward.) 24.23.196.85 (talk) 00:39, 14 September 2013 (UTC)

Solar eclipses aren't annular, they occur far less often than once a year. μηδείς (talk) 01:26, 14 September 2013 (UTC)

"Annular eclipse" is a type of partial eclipse where all of the Moon is covering the Sun, yet the Sun isn't covered 100%, there is an annulus around the Moon that is not covered by the Moon. Count Iblis (talk) 01:51, 14 September 2013 (UTC)

(I think Medis is thinking "annual" rather than "annular" - but annular eclipses do happen at roughly yearly intervals at some place in the world - they aren't that rare. This site lists annular eclipses in 2012, 2013 and 2014 - but none in 2011 and 2015.)

This site has reports from hospitals in the area of eclipses (it's not clear whether they were annular - but the damage likely occurs before the eclipse gets to the annular stage - so the results are probably similar for less-than-total eclipses. They found 45 eye injuries in one case and 58 in another - in each case at just one hospital. So we'd have to guess that the overall damage in the path of the eclipse is probably in the hundreds of people. It seems that roughly half of the people who showed up at the hospital eventually recovered fully - while the remainder were still seeing ghostly after-images at least 15 years after viewing the eclipse. But much will depend on the educational and technological level of the people in the path of the eclipse. In a modern society, with comprehensive news coverage - people should be aware of the dangers - but out in the back-of-beyond, when the eclipse just suddenly and unexpectedly happens - I'd expect the number of victims to be vastly higher. SteveBaker (talk) 02:33, 14 September 2013 (UTC)

Medeis might be making a punny funny. "Annular" means ring-shaped. "Annual" means yearly. Given that a year is a "ring" of sorts (i.e. a "cycle"), it's tempting to try to link the terms together, but according to EO they come from different roots. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:53, 14 September 2013 (UTC)

Hmm, I hadn't thought of that. I read it and thought she was serious, and I was pretty surprised. I have to remember to use <small> for jokes even if I think it's obvious I'm joking; someone else might not be sure. --Trovatore (talk) 07:50, 14 September 2013 (UTC)

This is precisely why we ask people to refrain from joking until at least one decent answer has been provided - and to use the small font when you do. Medis is well aware of this - I think it was probably just a mis-reading of the question. SteveBaker (talk) 12:43, 14 September 2013 (UTC)

I am sorry, I simply couldn't resist. I'll hat this section. μηδείς (talk) 17:02, 14 September 2013 (UTC)

See also "Eclipse eye damage reports rise" news item following the last total eclipse visible in the UK in 1999. I expect it could have been much worse as there was full cloud cover over much of the country. Alansplodge (talk) 08:01, 14 September 2013 (UTC)

Although it turned out that there were only 14 actual cases of solar retinopathy in the UK following the 1999 eclipse, according to UK hospitals assess eye damage after solar eclipse published in the British Medical Journal; "In one of the more serious cases the patient had reportedly looked at the sun for around 20 minutes without protection". There's no accounting for stupidity. Alansplodge (talk) 09:44, 14 September 2013 (UTC)

Bad eyesight question

A guy in my programming class has to hold his cell phone within about 3" of his eyes for him to see it. He squints quite a bit when he does it. He also has some sort of tech assistance as well because as I saw him using it, it had large icons and only displayed part of the desktop on the screen at any point. He had to move the desktop around with his thumbs to choose various icons. Yet he watches my teacher lecture just as I do, i.e. with no visible impairment. I don't know if he wears contact lenses but he doesn't wear glasses. I have 20/20 vision and have never taken a big interest in various sight issues but I'm curious as to what may be the issue with this guy's eyes. Could it be any of a large number of things or what? Note: This is not a request for medical advice, I don't plan on treating this guy, I'm not planning on harvesting his eyes for some cruel medical experiment, I am not talking about "my friend" when I actually mean myself, I'm just curious. That's it. Thanks, Dismas|^(talk) 02:25, 14 September 2013 (UTC)

Have you asked him? He might be just watching the blob that the teacher looks like to him. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:47, 14 September 2013 (UTC)

Nope. I don't know him. Too much of an introvert to just ask some dude why he squints at his phone. Dismas|^(talk) 03:41, 14 September 2013 (UTC)

He could well just have limited vision. As long as he can hear the lecturer, and knows the convention of the "paying attention" body language, he will be looking at him in the same way that you would, but possibly not actually seeing much at all. If an image is up close, he might be able to see some it, and thus the squint at the enlarged phone screen. You could always just ask him if you can help with anything; you might learn something specific that way. Bielle (talk) 04:41, 14 September 2013 (UTC)

Does he seem to be able to get around otherwise? Any trouble finding his way in or out of the room, or the desk? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:39, 14 September 2013 (UTC)

Consider the size of a human compared to the size of text or icons, and the different importance in distinguishing small details. I'm nearsighted (astigmatism), and if I can't tell a "j" from a "b" or "k", it's worth squinting for, if I care to read it. But it's not vital to see a teacher's pupils or whiskers to listen along and follow the blurry-yet-still-obvious human shape across a black (or white) board. InedibleHulk (talk) 07:06, 14 September 2013 (UTC)

See Visual acuity for our relevant article. Incidentally, "20/20" is not perfect vision, it just means you don't need glasses. Normal human visual acuity is around 20/16 to 20/12. Tevildo (talk) 11:30, 14 September 2013 (UTC)

Hyperopia ("long-sightedness", aka "far-sightedness") means that you can focus on distant objects with ease - but cannot focus on things close up without appropriate vision correction. If this person has the wrong prescription of glasses or contacts - or simply doesn't own such things - then what you describe is precisely the results you'd expect. I'm sure there are other possibilities - including that his vision is bad at all ranges but simply manages to cope with everything being out of focus at all ranges - but I'm fairly sure you'd have noticed that. SteveBaker (talk) 12:40, 14 September 2013 (UTC)

I see people do this all the time. My wife uses her iPhone like that on many occasions, for example. Vision can be a tricky thing; just consider the folks who need glasses, but don't have them, or need bifocals, but only have regulars, or need trifocals, but only have bifocals. While the text on a phone can be quite bright and sharp, it's very small, to the point where looking at it (even with glasses on) can be difficult if you're not at exactly the right length. This chap might have contact lenses to correct his long distance vision, but those lenses now make his up-close vision worse . Matt Deres (talk) 13:50, 14 September 2013 (UTC)

Another problem that even people with perfect vision have is that primary colors are focussed at different depths due to the fact that the lens of our eyes has different refractive indices at different wavelengths. For "normal" objects, there is rarely a pure color - so you can get a sufficiently sharp image despite that. However, on synthetic displays - and particularly with icons and other GUI elements - designers use a lot of 100% saturated colors. When they do that, the closely adjacent blocks of violently different colors defeat the eye's "autofocus" capability and the result is a blurry image. This effect is much worse when the display is close to your eyes - which is more often the case with cellphones than with other kinds of display. Designers for those systems would be better off using pastels and earth-tones rather than bright primaries...but they are continually fighting the problem that in bright sunlight, the displays get very washed out - and pushing the contrast higher helps that...hence they use a lot of primary color. As cellphone and tablet displays get brighter, hopefully we can return to a more muted color palette and life will be easier! SteveBaker (talk) 14:56, 14 September 2013 (UTC)

That's very interesting; I wasn't aware of the cause of that phenomenon with the contrasting primary colours. I experience that sometimes, especially with bright blue and red, where the blue lettering, say, will appear to dance and judder on the page. Used to get it all the time with the covers of colouring books when I was a lad. Would you get the same problem using black/white contrast instead? That would increase the contrast and would use rods rather than cones. Matt Deres (talk) 15:05, 14 September 2013 (UTC)

Blue and Red (being at opposite ends of the spectrum) produce the strongest effect - I'm quite sure that's what you're seeing. With black and white, the various frequencies that make up white are focussed at different depths, but somehow our brains compensate for that - but with pure red and blue, (which is something that just doesn't come up in nature) - we don't seem able to handle it. SteveBaker (talk) 18:09, 14 September 2013 (UTC)

It may be interesting. It would be even more interesting if anything Steve said was correct. He's got it horribly wrong. While the human eys optical system does have some chromatic aberation, as the difference is focal length for different colours is termed, it's not too bad, and due to the way the retina-brain system works, it is quite unimportant. It is quite unimportant for basically two reasons: we do not see detail in colour, and the brain is able to compensate for chromatic aberation, as explained below.

The human vision system gets its fine detail from the total light intensity, not from any one colour. When analog TV was developed, this was taken advantage of - analog TV works by transmitting a high resolution black and white image (termed "luminance") and a low resolution image in each of red, green, and blue primary colours, all 4 of which are added together in the TV receiver to reconstruct the composite colour picture.

When you look at a black object on a white background, you can see sharp edges because the eye/brain system works on the total light instensity change on the whiete/black transistion. When you look at (say) a pure red object on a black background, you still see the sharp eges, because the eye doesn't care whether its red or green or purple, it's working on the intensity edges.

The retina is most sensitive to wavelengths in the middle of the visual range. So wavelengths at the colour extremes don't contribute much in a composite image to the intensity as decoded by the retina.

Colour aberation can cause coloured lines to be displaced slighly on the retina. From this you would expect to see a thin white line on a black background as a red and green line next to each other. However the brain automatically compensates and re-merges the lines. It can do this because for any given eye, the compensation required is constant for any given object distance. And the brain knows the distance.

The eye/brain system's "autofocus" works by adjusting for the sharpest edges - the sharpest perceived intensity edges - with considerable "pre-tuning" from the object distance which the brain is able to determine from the scene context and the convergence angle of the eyes required to merge the left and right images. It thus nearly always does not matter if a block of one saturated colour is next to another block of saturated colour, because the retina detected light intensity will nearly always be different in each block. Where two colours has the same retina detected intensity, focussing will be a little harder, especially if teh scen context does not give any clue as to range, but as we can't see in colour sharply it doesn't matter. And where it happens, there will almost always be somewhere else nearby in the image that will provide the intensity (luminence) change.

The difference between a saturated colour and a non saturated colour is that the non-saturated colour has a percentage of ALL other colour wavelengths added to it. White, which is all wavelengths at equal strength, is a total desaturation. This all means that it is desaturated colour objects that are hard to see clearly, not saturated colours - the opposite of what Steve said. As of course any engineer that has designed display systems knows: they go for saturated colours (eg the almost monochromatic red or red light emitting diodes) or just black and white, because both are the clearest to see, not desaturated colours.

However, for those who wear spectacles, colour aberation can be a problem, particularly if they work with computer graphics and CAD. Especially for high refractive index glass (often chosen for cosmetic reasons as it makes for thin lenses for near-sighted people), chromatic aberation of the spectacle lenses can exceed what the eye-brain system can handle. For natural scenes and not too bad a degree of prescribed correction, the brain usually soon learns the new image displacement and re-compensates.

121.215.38.161 (talk) 02:53, 15 September 2013 (UTC)

If you poured Coca Cola onto a frog, does it cause distress and death?

I am not planning to do this, just for the record. But I remember that some kid I went to high school with poured Coca Cola on a frog and it went crazy for a few moments then died. What happened here? Does Coca Cola 'burn' a frogs skin? Does the fizz from the drink cause distress? --Mathmmaats (talk) 10:44, 14 September 2013 (UTC)

Our frog article points out that frogs have glandular skin with all sorts of specialized secretions that are vital to the frog - it's not at all unreasonable that the acidity of the coke would do something bad here. Frog skin is also semi-permeable - meaning that things can pass through it MUCH more easily than (for example) human skin. So your instincts on this (that coke is kinda harmless when poured onto human skin) are totally misleading when it comes to frog skin. I don't know for sure that this is enough to result in distress or possibly death to the frog - but it's certainly not entirely impossible. I'd also note that not all frogs are equal. Some have adaptations to help them live in very dry environments, others have waxy rather than slimey secretions - and their skin is very different from frogs that do not have that adaptation. Our article also says that many frogs are able to absorb water and oxygen directly through the skin - and perhaps absorbing a weak acid - or something laced with CO2 instead of oxygen - would be fatal to them. SteveBaker (talk) 13:44, 14 September 2013 (UTC)

Performing the "experiment" by yourself seems to be useless and cruel. OsmanRF34 (talk) 16:41, 14 September 2013 (UTC)

As stated above I will not be performing this experiment. --Mathmmaats (talk) 17:54, 14 September 2013 (UTC)

Yeah, Osman, have a little read of OP's very first line. What is wrong with posters who can't even take the trouble to read a short and simple post before slamming "Send" on their keyboards? Myles325a (talk) 03:26, 16 September 2013 (UTC)

antidotes for sodium fluoroacetate

Sodium fluoroacetate says "Effective antidotes are unknown". However, as far as I know in China we use acetamide to treat fluoroacetate poisonings and it is said to be "very effective". Can anyone tell me whether there are effective antidotes for sodium fluoroacetate?--Jsjsjs1111 (talk) 11:59, 14 September 2013 (UTC)

I suspect (without evidence) that the term "antidote" is intended for substances that directly counteract the poison. It's possible that the acetamide is only used to treat some of the symptoms of poisoning. This is an odd claim though - neither our article on acetamide, nor any of the usual chemical databases that I could readily access, list any effects on the human body - either positive or negative. This lack of information on the substance as a drug makes it an unusual choice. SteveBaker (talk) 12:32, 14 September 2013 (UTC)

Are you perhape thinking of sodium fluoroacetamide instead of Sodium fluoroacetate? While our article doesn't mention it, I think sodium fluoroacetamide poisoning can be somewhat counteracted by acetamide [1], [2] (refers to rats), [3] (note that the later source is a Chinese chemical seller). Before I read the last source, my hypothesis was that fluoroacetamide is most likely metabolised to fluoroacetate to some extent hence fluoroacetamide toxicity arises from the same mechanism as fluoroacetate toxicity and could be partially counteracted by giving acetamide to compete and drasticly limit the metabolism of fluroacetamide to fluoroacetate, similar to the way ethanol is given for methanol poisoning. The Chinese source while far from an RS suggests something similar except that it suggests fluoroacetamide is metabolised to fluoroacetic acid. It seems to me it would make more sense to give acetate for for fluoroacetate poisoning yet I suspect that won't work considering the significance of acetate (i.e. giving an overdose of acetate will probably kill anyway) and the fact you're too far down the metabolic chain considering the apparent inhibition strength (meaning you have to drasticly reduce fluoroacetate metabolism not just limit it a bit). Nil Einne (talk) 16:53, 14 September 2013 (UTC)

The original poster is correct in principle, though I'm not sure if something like acetamide is truly an antidote. (The goal is to slow the poison rather than neutralizing it; nonetheless, it is something "given against" poison) [4] The idea is that sodium fluoroacetate gets drawn into the citric acid cycle and jams it (read the article for details). So far as I know fluoroacetamide should work the same way - the tail end is removed from either in favor of the CoA. The purpose of acetamide and other treatments such as ethanol is simply to provide the citric acid cycle with more input material, which would compete with the poison for preference. (I suppose that just having eaten a fatty meal before the exposure would be helpful in the same way - haven't verified that) I have not chased down the details of the substrate specificity of pyruvate dehydrogenase to see whether certain compounds would have preference, but I assume the use of acetamide on actual humans implies it was the best examined at the time. Wnt (talk) 20:14, 14 September 2013 (UTC)

Thank you! I guess Wnt's right. But regarding the definition of "antidote", it is stated in the antidote article that ethanol is the antidote of methanol.--Jsjsjs1111 (talk) 11:44, 15 September 2013 (UTC)

Good point! On further consideration, I suppose this is the only workable way to decide the semantics, on the basis of what the medical practice is, rather than any more rarefied notion in theory. Wnt (talk) 14:25, 15 September 2013 (UTC)

Marine Fossil

Does anyone know what this fossil is? I am guessing some sort of scallop or mussel - it was found at Kettleness near Whitby.--Gilderien Chat|List of good deeds 18:54, 14 September 2013 (UTC)

Hmm, it looks like one of the two shells from some type of bivalve, with the hinge visible at the bottom. It's oddly non-symmetrical, but that could be due to distortions caused in the rock over millions of years. In particular, it looks like the lower, left side has been stretched out. StuRat (talk) 03:00, 15 September 2013 (UTC)

Indexing my technology company on Wikipedia

How can I have Wikipedia Index my technology company, including our products, history, website, etc.?

Thanks

J.Pamelia, CEO EZCO MEDICAL SYSTEMS EZ COURSES.ORG http://www.ezcourses.org— Preceding unsigned comment added by EZCO MEDICAL SYSTEMS (talk • contribs) 21:01, 14 September 2013 (UTC)

Become notable enough earn it. Also see what Wikipedia is not, in particular that it's not a directory. WegianWarrior (talk) 21:16, 14 September 2013 (UTC)

This isn't really the right place to ask, but the key thing to note is WP:GNG, which lays out the basics. Have good third party sources reviewed the company's activities? Newspapers, magazines, reviews of the industry, that kind of stuff. Wikipedia covers things after other sources have written about them. Also be warned that there is a great confusion and controversy about WP:COI - people make perhaps unrealistic policies, while others badly abuse the system. Done improperly, you could end up getting a bad image out of this so be careful. The gold standard is that you set up a page User:(Your handle)/My draft article and get a third party to review it and move it into mainspace. I say (Your handle) rather than EZCO MEDICAL SYSTEMS because I fear you're about to be told that this isn't a proper username (Wikipedia takes all kinds of aliases, but it wants accounts to be used by one person who is responsible for everything, not a group of people who can pass the buck at each other, nor does it want trademark lawsuits over who holds the name) Wnt (talk) 22:24, 14 September 2013 (UTC)

To state that simply, get mentioned for notable accomplishments in books or periodicals outside trade magazines and advertisements. If, for example, you build a better mousetrap, and Time Magazine does an article on you, you are set. μηδείς (talk) 00:16, 15 September 2013 (UTC)

"In nature, on average, only one baby makes it to adulthood, per parent."

I'm having trouble understanding this statement, made by Thomas R. Holtz, Jr.. Wouldn't that mean that the Earth's biomass is not increasing at all? Wouldn't that mean that a very large number of species are going extinct simply by having a less than average number of surviving offspring? Surtsicna (talk) 22:19, 14 September 2013 (UTC)

The premise appears to be that the carbon cycle is working with a fixed amount of material (largely though not entirely true in the long run), and that the average size of organisms is not decreasing, and that the amount of biomass in organisms that don't count as "babies" or "adults" (bacteria?) remains a constant proportion. Wnt (talk) 22:27, 14 September 2013 (UTC)

Sure, the biomass of a given species will wax and wane, and some will go extinct. Mathematically speaking, if there were considerably more that one offspring reaching reproductive age on average for each member of every species, then biomass would exhibit positive exponential growth, and accelerate quickly to unreasonable sizes (e.g. the carbon and raw material limits mentioned by Wnt). However, if that number is less than one on average, then everything is (perhaps slowly) headed to extinction, and all the biomass eventually goes away. So saying that each individual gives off one offspring on average is a fair statement, if you take the long enough view and ignore a lot of details (also careful on the phrasing, we don't want to condition on the assumption that an individual is a parent). Surely human populations have been skyrocketing, as with our commensal species. But this is at the expense of a lot of other biomass, and it remains unclear how long out species and society will last on evolutionary, let alone geological time scales. All this reasoning does imply (or assume, depending on how you look at it) a global biomass that doesn't change too much when averaged over relatively long time scales, i.e. barring dramatic shifts in climate, etc. See also logistic growth and carrying capacity for related information. SemanticMantis (talk) 23:42, 14 September 2013 (UTC)

On the long term, it doesn't make sense. Unless you believe that all the number of individuals is stable, for every species. Either he meant "at least one individual" or I don't know what he means. Can you provide the source of this assertion: "In nature, on average, only one baby makes it to adulthood, per parent." ? Google point to this page. Maybe the quote is not authentic.OsmanRF34 (talk) 23:52, 14 September 2013 (UTC)

diversity in number of existing genera

There's no need to or point in going into abstruse side issues. If a population is not growing or shrinking, then on average two parents have two children that survive to reproduce, or one child to replace each dying individual. μηδείς (talk) 23:58, 14 September 2013 (UTC)

That's mathematics and simple logic. What's the point of saying this at all? OsmanRF34 (talk) 00:00, 15 September 2013 (UTC)

Oddly, a lot of people find this extremely hard to grasp, as I know from taking an upperlevel class on ecological modelling. Extra credit. What's the only thing you know every single one of your ancestors accomplished? μηδείς (talk) 00:08, 15 September 2013 (UTC)

Then, there should be a Holtz's principle in biology. OsmanRF34 (talk) 00:09, 15 September 2013 (UTC)

I think Medeis is hinting that this hypothesis is not nearly as profound as it might seem at first. And you have to include various conditions to make it work. Consider the bacteriophage, a virus (i.e. an organism of sorts) that can have as many as 900,000,000 individuals in a mere thimbleful of sea water. And a lot of the extinctions in recorded history have been due not to "natural" environmental pressure, but rather due to human behavior ranging from indifference to deliberate slaughter of a species. It occurs to me that the author of that statement should give credit to the one he probably got the idea from, Blood, Sweat & Tears ←Baseball Bugs ^{What's up, Doc?} carrots→

This is standard population ecology and population dynamics. Population 1 equals population 0 plus births minus deaths plus immigrants minus emigrants. If change is zero and migration is zero then births equal deaths. This is easiest to see in populations with discrete annual generations, but it applies in all cases, as well as humans. The math was worked out by the 1930's, so no credit to Holtz. See also population genetics. μηδείς (talk) 00:28, 15 September 2013 (UTC)

Note: in the above I was taking this as a statement about the average of all species. Where individual species are concerned, clearly some will go extinct and others have long-term success, becoming families, orders, and in the fullness of time, perhaps one day even supplanting most other organisms in existence. But even if these factors apply, the effect is small: for example, suppose that there are two organisms now, and one day 560 billion tonnes of biomass will be almost all composed of 1-kg organisms of this type. Well, that 250,000,000,000,000-fold increase in numbers is roughly 2⁴⁸, so if this evolutionary revolution takes only 48,000 years, that still means a doubling of numbers every 1000 years. If these organisms have an average of 100 years generation time, that means the number of offspring averages around the tenth root of 2, or 1.07 per parent. But if it takes more than 48,000 years to drive all other species extinct, if the lifespan is shorter than 100 years, if the organisms are larger, etc. it all makes that number even closer to 1.00 Wnt (talk) 04:06, 15 September 2013 (UTC)

It is a reasonable assumption that if the total biomass of the earth has increased over time, the number of individual animals and non-clonal organisms may have increased. The number of genera has been increasing due to the increasing variety of flowering plants, which is much greater than that of the non-flowering plants during the age of reptiles. The number of insect species has increased over that time, with each plant being said to have its own species of beetle, and each beetle its own species of parasitic wasp, and so on. It seems reasonable to assume this means a steady increase in the number of individuals over time. Obviously the colonization of the land would have had that result. μηδείς (talk) 17:40, 15 September 2013 (UTC)

Flagellum-driven vehicles

Throughout microbiology a flagellum appears to be the greatest thing ever. Swimming animals don't use them, but this might be due to the limitation that they aren't set up to easily have a body part rotate around and around. So... how well does a flagellum work if well engineered for use with a sub, ship, plane, airship, etc.? Are there examples where people have tried their best with it, and how does it measure up? Wnt (talk) 22:32, 14 September 2013 (UTC)

It's a question of scale and the relative viscosity of water at different scales. See Reynold's number. Someone versed in physics can probably give a better answer. μηδείς (talk) 00:02, 15 September 2013 (UTC)

Agreed. While it could work at a macro scale while moving through a rather thick liquid, we tend not to encounter those much. However, at a smaller scale, even water behaves like a thicker fluid. The way in which water bugs can stand on the water shows this effect. So, to move microscopic nanobots through water (or blood, etc.), flagella may work well. StuRat (talk) 02:53, 15 September 2013 (UTC)

I understand about the viscosity, but I'm not so clear on how quickly the alleged inefficiency sets in with increasing scale or decreasing viscosity. Even if a flagellum-driven vehicle were a toy operated in honey, seeing it in operation, and how engineers would try to optimize it, would still be a really interesting learning experience. Surely someone must have tried? Wnt (talk) 03:18, 15 September 2013 (UTC)

I think the difficulty in replicating a flagellum mechanically is a problem, too. We might well make some form of one, but getting the whip action just right would be difficult. It's analogous to, in flight, using flapping wings versus fixed wings. While people have played around with ornithopters at least since Da Vinci, none of them have ever been a practical form of human transportation.

I believe scientists are working on an artificial jellyfish, though. There the bell contracts together, rather than multiple flagella which must work together, somewhat simplifying things. The idea would be to use it to sneak a camera or other payload close to an enemy, who would think it was a normal jelly. StuRat (talk) 07:27, 15 September 2013 (UTC)

Sorry, I didn't mean to restrict consideration to things that can transport humans. With ornithopters there are lots of examples. And the engineering challenge is what would make it interesting to see what people come up with! Wnt (talk) 14:59, 15 September 2013 (UTC)

Googling "flagellum-driven robot" resulted in this relevant link, as well as this link in which reference 144 seems to address the question. As others have stated, it appears to be feasible only on the microscopic scale. --NorwegianBlue ^talk 17:13, 15 September 2013 (UTC)

These were interesting links. The former source suggests there is still more uncertainty than I would have imagined about whether the scale of a flagella-driven vehicle has any effect on its efficiency - the main issue being whether the Reynolds number of the fluid at a given scale permits the use of other methods of inertial propulsion such as fins. They still seem to fall well short of being optimally engineered for their size, however, even so far as helical properties. Wnt (talk) 14:47, 17 September 2013 (UTC)

It might work for macroscopic object as well, because you are free to use a large number of microscopic flagella. Count Iblis (talk) 16:03, 17 September 2013 (UTC)

heart acceleration

What causes the human heart to accelerate? Or put another way: what are the actions or materials that cause a human heart to beat faster? --66.190.69.246 (talk) 23:59, 14 September 2013 (UTC)

The release of adrenalin and the stimulus of the sympathetic nervous system. μηδείς (talk) 00:11, 15 September 2013 (UTC)

And, of course, this is done because the body detects a need for a faster heart at that time. This can be, for example, if performing difficult physical activity, where the muscles need more oxygen than usual. Moving the blood more quickly helps to meet this increased need. The anticipation of the need for physical activity can have the same result, say when facing a fight. Unfortunately, this last mechanism seems rather defective in humans, such that just being worried about some possible future threat causes your heart to race now. Other animals tend to only worry about the immediate future, and thus it's not a problem for them. And humans apparently haven't been worrying about the distant future long enough for our bodies to have evolved the ability to distinguish between an imminent threat, where a rapid heartbeat is required, and an eventual threat, where it is not. StuRat (talk) 02:48, 15 September 2013 (UTC)