Wikipedia:Reference desk/Archives/Science/2016 June 12

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June 12

Biomedical engineering

If biomedical engineering is such a growing and expanding field, why does its job market not seem to reflect this? 2A02:C7D:B965:D700:889D:7ADD:268E:DBAD (talk) 01:49, 12 June 2016 (UTC)

What's your source for that assertion? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:02, 12 June 2016 (UTC)

If five people were working on something last year, and it has gone up to 20 people this year, that is very rapid growth or expansion - but still only a very small number of jobs. Wymspen (talk) 11:21, 12 June 2016 (UTC)

Electromagnetism related elementary confusion

what is the relationship between Flemings left hand and right hand rules and Amperes swimming rule.The link http://www.gyroscopes.org/papers/Engineer%20through%20the%20looking%20glass.pdf gives some clues. Will someone explain how these rules are infact closely related.Please also explain Lorentz forces relation with these rules Ampere rule is much older compared to Flemings why was flemings rules discovered late. What is the relation between Faradays paradox and these rules.Please provide other links elucidate the intricate link betwween these apparently different rules.They are closely related especially between any of of Flemings rules and Amperes swimming rule150.107.177.17 (talk) 05:42, 12 June 2016 (UTC)

They both describe relationships between triplets of vectors in 3D space. The triplets can left- or right-handed leading to left- or right-hand rules. Ruslik_Zero 08:50, 12 June 2016 (UTC)

Here are links to articles about the rules you mention. Right-hand rule. Fleming's left-hand rule for motors. Ampère's circuital law may be expressed as a swimming rule: "Let the observer imagine himself to be swimming along the wire in the direction of the current and facing the needle, then the N pole of the needle will be deflected towards his left hand." The French physicist André-Marie Ampère lived 1775 - 1836. John Ambrose Fleming 1849 - 1945 would have encountered Ampère's work in the lectures at Cambridge University of James Clerk Maxwell around 1877. Lorentz force is the combination of electric and magnetic force on a point charge due to electromagnetic fields. See also Faraday paradox. AllBestFaith (talk) 09:07, 12 June 2016 (UTC)

My take on the left and right hand rules would be more like this: the rule for a generator suggests how motion induces an electric current and hence a magnetic field. The same motion in a motor also induces an electric current and magnetic field, but in the opposite direction; i.e. it consumes the existing electromagnetic energy. Or you can consider current and field in the same direction in each case, but the result in the generator is to produce a motion in the opposite direction (consuming the motion) while in a motor it is to produce one in the same direction. Note though that both the left- and right-handed rules recognize that the same electric current produces the same magnetic field - that's not where the polarity changes. Unlike electric fields, where there are different carriers, AFAIK the magnetic field is absolutely symmetrical, the sign of the effect depending only on whether Ampere decided to write about the North pole or the South pole. (If you happen to have some magnetic monopoles of different masses depending on their sign, feel free to show them off!) Wnt (talk) 10:59, 12 June 2016 (UTC)

There is no experimental evidence that magnetic monopoles exist. AllBestFaith (talk) 23:23, 12 June 2016 (UTC)

Can anyone identify this insect?

Picture

Location: Missouri, USA

I've been finding a fair number of these in my apartment recently. They're very small, a couple of millimeters in length at the most (hence the low-quality picture too...sorry!). I've mostly found them in my bed, although that may just be because they're so small and it's hard to notice them except against a white background such as my sheets. However, they don't appear to be biting, or at least aren't leaving any marks. Does anyone know what these are? And, bonus question, how best to get rid of them? Thanks. Shearedlettuce (talk) 06:50, 12 June 2016 (UTC)

Possibly some form of Thrips? Beyond actions to filter the air supply to your apartment, I fear that you'll have to learn to love them. --Tagishsimon (talk) 11:13, 12 June 2016 (UTC)

It's hard for me to make much out in that picture, even whether it has three pairs of legs. But the overall body shape, and, perhaps, my hallucination of "something" extra near the back end makes me wonder if it is a collembolan or "springtail". See [1] which says they infest living spaces but don't bite, which agrees generally with your description. The test of this idea: can you see if there is any sort of "spring" structure at the back end, or can you tell if they jump for long distances (that site says 10 centimeters at a time)? Wnt (talk) 11:13, 12 June 2016 (UTC)

Aha, I'm pretty sure this is it. I had indeed noticed the jumping, but didn't realize that was what was going on. Thanks! Shearedlettuce (talk) 20:57, 12 June 2016 (UTC)

If they were bedbugs, you would certainly know it. Still, having critters crawling all around does not seem like a good thing. You should call your Orkin man or the equivalent and get an evaluation. Or, if you're renting, ask your landlord about it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:19, 12 June 2016 (UTC)

Well, technically, we're not here to give advice; that's up to the person. Even the Orkin site I linked said that getting rid of dampness was the most important thing! Wnt (talk) 11:29, 12 June 2016 (UTC)

Presumably, they're eating something. A professional should be able to figure out what they are, what sort of hazard they pose (if any), the best way to deal with them, and while he's at it maybe what it is they're using for food - on the theory that if you zap them and also deprive them of their food source, they're less likely to come back. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:34, 12 June 2016 (UTC)

I shouldn't argue over what advice to give save that we shouldn't be giving advice. Of all the people who frequent this place I'd expect you to agree with that! Wnt (talk) 16:56, 12 June 2016 (UTC)

"See a professional" is acceptable. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:58, 13 June 2016 (UTC)

End of the World

Just a few minutes ago the environment correspondent of the Guardian on a TV debate about the end of the world on The Big Question claimed that humanity could not actually destroy the world. She said that we might destroy ourselves or end biodiversity, but the world would still go on in some form. Well...interesting question...if we really wanted to destroy the world for some obscure reason do we currently have the technology to achieve that? Well perhaps not destroy the actual planet, but could we find a way to completely wipe out life on the planet, perhaps by removing the atmosphere and letting solar radiation in? SpinningSpark 09:43, 12 June 2016 (UTC)

Runaway greenhouse effect would seem like the leading candidate to me, and it is still widely claimed to be unlikely if not impossible. Wnt (talk) 10:44, 12 June 2016 (UTC)

As the question itself suggests, there needs to be a more precise definition of what "destroy the world" means. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:17, 12 June 2016 (UTC)

Letting off the entire stockpile of nuclear weapons ought to come pretty close - though I guess the cockroaches might survive even that. Exploding them all in the main volcanic zones should increase the effect. Wymspen (talk) 11:25, 12 June 2016 (UTC)

It would be interesting to see an estimate of the TNT power (megatons or whatever) for all the nukes in the world, compared with the estimated energy release of the average erupting volcano. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:31, 12 June 2016 (UTC)

Not even close. The total yield of all nuclear weapons on earth is almost certainly less than 10 gigatons of TNT ([2] says 5 gigatons). By contrast, the Chicxulub impact released 100 teratons, over 10,000 times as much energy, and it did not even kill off all the mammals or birds. CodeTalker (talk) 16:44, 12 June 2016 (UTC)

I think we have a Loyal Officer here. :) But no, nuclear winter shouldn't kill all life on Earth, and the fallout from nuclear weapons doesn't have that much of a long term effect - consider how many nukes have actually been exploded already on this planet! Cracking open a volcano is going to take a hell of a lot more than a nuclear weapon, though I'd guess if you do some determined drilling down into a supervolcano like Yellowstone and try "fracking" the whole thing with a string of nukes you might have a chance. But ... the Permian extinction already tried something worse, at the Siberian Traps. And the Deccan Traps, perhaps. (Both are debated as bolide vs volcanism as the cause of the extinction, but the volcanism definitely happened in each case) I mean, Bikini Island is still there, still inhabited by anything but worry warts who don't want to catch cancer. Wnt (talk) 11:38, 12 June 2016 (UTC)

I think we could do it by letting a huge asteroid impact the Earth. To alter the course of a huge asteroid we could use a method similar to what I've proposed here. It won't work as well as deflecting an asteroid to make it miss Earth, but it might still work with more effort. Count Iblis (talk) 16:32, 12 June 2016 (UTC)

As mentioned, "world" is a vague term. Does it mean simply human civilization, Earth's entire biosphere, or the entire physical planet? Here's an interesting page that looks at methods of actually physically destroying Earth, or at least making it no longer a planet. The original poster suggested removing the atmosphere. This might kill off all land life, but life in the oceans would go on. There originally was no ozone layer on Earth, which is the thing that absorbs most incoming ultraviolet light; it was created by the photosynthetic life that pumped oxygen into the atmosphere. Also the atmosphere will gradually be replenished by outgassing from the crust and oceans unless you set something up to keep removing it. Asteroid impacts wouldn't kill all life, which we know because they've happened. To kill all life on Earth, including life in deep sea vents, you'd probably have to melt the entire crust. To accomplish this, you'd need to either smash something big into Earth—say, the Moon—or send Earth into the Sun, or close enough to melt it. This is perfectly doable; you just need to have some patience. The page I linked talks about this a bit: you can fling chunks of the Earth into space, or use massive bodies like asteroids as gravity tractors. In either case the objective is to alter Earth's orbital trajectory. Or you could do it to the Moon if you decide to smash the two together. --71.110.8.102 (talk) 03:09, 13 June 2016 (UTC)

This user Advices all to read upon the scale of destruction in apocalypse how of allthetropesFAMASFREENODE (talk) 07:07, 14 June 2016 (UTC)

Do you have a link to whatever it is you're talking about? ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:41, 14 June 2016 (UTC)

What an idiot. See for yourself:documentation. 50.253.212.229 (talk) 13:34, 14 June 2016 (UTC)

Well, I may be an idiot, but I'm smarter than you'll ever be. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:28, 14 June 2016 (UTC)

FYI, FAMASFREENODE (talk · contribs) is now indef'd. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:32, 14 June 2016 (UTC)

maggot infestation

Every morning my cat's large drinking water bowl (outside) is absolutely full of maggots. I check it before I go to bed and its fine, the next morning when I let my cat out, her bowl is full of maggots. The bowl holds a good pint of water so you can imagine when it is full of maggots there are hundreds in there. I don't understand why they are being laid in water and if the eggs are laid overnight, how come they have hatched into 1centimeter maggots by morning? How can I prevent this happening? Where are they coming from and why my yard - none of my neighbours have this problem. Please help if you can Linda — Preceding unsigned comment added by 87.102.81.74 (talk) 11:05, 12 June 2016 (UTC)

Probably a good idea to bring your cat to a vet, and bring some of the "maggots" as well. Flies are probably laying eggs in the bowl. It may be a good idea to wash the bowl thoroughly, and replace the water 2-4 times a day (empty it completely!). Keeping the bowl away from feces, moving it from its original location and keeping it as cool as possible may also help. It may be a good idea to check the area where your cat lives; it may be eating rotting flesh or its own poop and when it drinks water the "maggots" fall into the bowl. Oh, and check your pet food. For more, Google "maggots water bowl". The Quixotic Potato (talk) 11:44, 12 June 2016 (UTC)

I'm wondering if these are rat-tailed maggots which migrate in over night. They look distinctive. If so, placing the drinking bowl, on a box, coffee table etc., or relocating it might solve the problem. I don’t see any reason to go dusting the area with borax or anything else as they are not usually a problem. Cats have a very high level of hydrochloric acid in their stomach so don't get over alarmed by Intestinal Myiasis Caused by Eristalis tenax. Still, it might be worth getting pussy checking out by a vet.--Aspro (talk) 15:23, 12 June 2016 (UTC)

I thought of rat-tailed maggots too, which are the offspring of hoverflies. Rattailed Maggots from North Carolina State University says: "Drone flies have never been implicated as disease vectors... Chemical control is rarely necessary" (a drone fly is a common type of hoverfly). Alansplodge (talk) 17:28, 12 June 2016 (UTC)

They could also be mosquito larvae, which are something of a health hazard, but one would expect the OP's neighbours to have the same problem. A photo would help us to identify them, of course. Tevildo (talk) 22:28, 12 June 2016 (UTC)

It would be interesting for us to get some feed back from the inquirer. Here on help desk we often feel like we are stabbing in the dark from too little information. If the poster can give us an update, that will be appreciated. Also, don't think we answered Where are they coming from and why my yard - none of my neighbours have this problem. . Think the answer may be that poster is fortunate enough to have a yard that supports some biodiversity. Thus, eggs are laid in places were there is something to recycle. From there, the growing maggots migrate to still water (cat's bowl) during the night. The resulting flies, that they metamorphose into, go on to lay eggs in places were the maggots have something to recycle again. To brake this cycle of nature doing its wonders, one only requires to hire a contractor to concrete over the whole garden. As those flies are good pollinators too, so this sterilisation of their/your/our habitat would leave the world poorer place, me thinks. Therefore, localised infestations such as these are to be welcomed rather than eradicated. It provides a win-win situation for the cat too, as maggots attract shrews and shrews are a healthier diet than modern cat foods (which contain the wrong ratio of amino acids required to keep a cat healthy). Instal a cat-flap so s/he can enjoy a few late night take-ways. --Aspro (talk) 20:06, 12 June 2016 (UTC)

Signal delay from a transoceanic live broadcaster

What's the actual signal delay (in seconds) between a transoceanic broadcaster like CNN or some Japanese TV and receiver watching live on the other side of the ocean (both the TV signal and internet broadcast, assuming internet connection is good enough to watch without lags)?--93.174.25.12 (talk) 13:15, 12 June 2016 (UTC)

Probably very low order of seconds, but may be difficult to generalise since the delay is cumulative over the chain of equipment through which the signal passes. See this article on satellite latency, for instance. --Tagishsimon (talk) 13:41, 12 June 2016 (UTC)

Radio signals have same as speed of light. Encoded digital, encorder and decoders delay by the converting pocedures. Steaming digital, store and forward buffering also delays. Sattelite uplink and downlink have longer distance than a ship on the ocean, but ships can't reach light speed. In a satellite, uplink and downlink usually are idenical signals, handled by a frequency mixer to generate the transmitted signal directly from the receiver output. No decoding is necessary, like in a superheterodyne receiver or Low-noise block downconverter in a statellite dish, an intermediate frequency is mixed. Digital signals allow buffering an delaying without losts of quality. A some warmakers propagate and dictate hate, provocation can be taken from any information of screen where watchers become eyewitnesses and blend the seed of propaganda into the picture. For that reason, it might be possible, secretsevices drop provocating pictures. --Hans Haase (有问题吗) 14:16, 12 June 2016 (UTC)

Why are the last two sentences here, Hans? Dbfirs 20:23, 12 June 2016 (UTC)

A delay of 10 minutes has other reasons. It is too shot to play a recorded video tape or somilar and too long for any live broadcast. --Hans Haase (有问题吗) 05:58, 15 June 2016 (UTC)

Box turtle ID

What subspecies is this specimen? Photo is at 37°31′34″N 88°4′55″W, southeastern Illinois; File:Box turtle distribution map.svg says that both carolina and ornata are found in the state. I'm guessing that it's carolina (half a mile away is Kentucky, where the map says only carolina is found, and presumably Illinois ornata is more common farther northwest), but I can't tell reliably enough from photos on Commons. Nyttend (talk) 14:42, 12 June 2016 (UTC)

I am not an expert but I looked at Google Images and it seems the shield pattern looks more like a carolina than a ornata. The Quixotic Potato (talk) 07:22, 13 June 2016 (UTC)

The fact that there is such a stark dividing line between species which happens to correlate perfectly with state borderlines strikes me as unlikely. shoy (reactions) 13:49, 13 June 2016 (UTC)

That's not quite the case. The map is a graphical representation of textual documentation in its source, which lists the states in which each subspecies is found, without saying where in the state each subspecies appears. If this were in eastern Indiana (both subspecies), where only an imaginary line separates it from Ohio (carolina only), it would be obvious. The issue here is that Kentucky is on the other side of the Ohio River, which at this point is more than 1km wide (picture), so I wondered if the river might be a barrier between subspecies. Nyttend (talk) 14:11, 13 June 2016 (UTC)

The Ohio River as a barrier seems likely, but OTOH there's no river that separates Indiana and Ohio, so why the species line divides there is a mystery to me. You would think that if they were already in Ohio, there wouldn't be any real reason for them not to be in Indiana and Illinois. shoy (reactions) 16:42, 13 June 2016 (UTC)

The color for Indiana and Illinois says that both carolina and ornata are in those states, while the color for Ohio says that it's only carolina. Probably the ornata population for Indiana is restricted to the western part of the state, so by the time you get to eastern Indiana it's exclusively carolina. The starker divide is between Wisconsin and Michigan, which have only ornata and only carolina respectively. Perhaps the WI/MI border region has no turtles at all, so there's no real chance of them crossing the border? Nyttend (talk) 18:17, 13 June 2016 (UTC)

It is probably not very difficult to contact the authors of that PDF, and in my experience people who publish data like this are very helpful and they will try to explain how they got their data and how to interpret it. The Quixotic Potato (talk) 20:08, 13 June 2016 (UTC)

Where can I find information about "the proteins in biological membranes and their role"?

Where can I find information about "the proteins in biological membranes and their role"? ans second maybe some of you can explain what is the relation of this topic to biophysics course? (it should be in biochemistry as far as I know) 93.126.88.30 (talk) 16:14, 12 June 2016 (UTC)

I never saw a great deal of meaning in these terms; there is no real separation between chemistry and physics. But biophysics might be interested more in membrane rafts, lateral diffusion rates of membrane proteins within restricted domains on the cell surface, membrane potential and action potential and such, dynamics of cell fusion and exosome formation maybe ... though to be honest, I'm really not very sure of any of this categorization. Wnt (talk) 16:54, 12 June 2016 (UTC)

You can find information about membrane proteins in the membrane proteins article. Llaanngg (talk) 17:26, 12 June 2016 (UTC)

Flywheel against perpetual motion machine

Comparing the movement of a perpetual machine with a flywheel, would the first spin the in the same way than the latter? For example, would this perpetual motion machine's speed be affected when one of these arms topples to the right? That is, does it matter if a flywheel is not symmetrical? --Llaanngg (talk) 17:24, 12 June 2016 (UTC)

This design for a "perpetual motion machine" looks worse than a plain wheel. Because those arms stiffly outstretched on the right are, presumably, not bouncing up and down, I think there has to be an inelastic collision when they smack out to the stop. Which, of course, actually consumes energy above the unspecified, and possibly very small, amount of friction at the pivot. Wnt (talk) 17:58, 12 June 2016 (UTC)

See the article Perpetual motion that explains why a perpetual motion machine is not possible. The same image appears in the article. AllBestFaith (talk) 23:12, 12 June 2016 (UTC)

The question is about a comparison between perpetual machines (which are some peculiar flywheels) and usual flywheels. --Llaanngg (talk) 23:39, 12 June 2016 (UTC)

I imagine a balanced flywheel would have very much a constant angular velocity, whereas the PM machine as illustrated above would have an angular velocity which oscillated, increasing as a result of a flailing arm falling, and decreasing until the next one falls. --Tagishsimon (talk) 23:45, 12 June 2016 (UTC)

A flywheel is not just any wheel; it is a wheel which is basically there for its mass and, therefore, a significant amount of angular momentum when turning. I think of it as being a mechanical buffer. For example, in an internal combustion engine engine using pistons, I believe the flywheel helps smooth out the impulses generated when each cylinder fires. Similarly, when a (usually single-cylinder) steam engine uses a flywheel, the flywheel keeps things going even though the cylinder is only "firing" once (or, if double-acting, twice) per revolution.

Now, it's intellectually perilous to talk about how a perpetual motion machine "works". But, if the machine in the picture "worked", and if the levered masses actually drove the wheel around, and if the motion was therefore in any way jerky, and if the wheel was made more massive than it otherwise needed to be, so as to serve as a flywheel, then I believe we could say that it would tend to smooth out the impulses of the falling masses, also.

In other words, in the terms of the question, I think the machine illustrated is mechanically "asymmetrical" in more or less the same way that piston engines usually are, but that the flywheel concept could smooth out the asymmetry in about the same way, also.

But, even more so than usually, in the case of perpetual motion machines, caveat emptor. —Steve Summit (talk) 07:34, 13 June 2016 (UTC)

Is it less efficient (inherently more energy-lossy) if the axle of a flywheel is not at the center of gravity? For example, would a metal bar attached at its end be worse than one attached at its middle, assuming same moment of inertia, in terms of energy storage or practical concerns other than possibly needing a stronger axle to avoid wobble? DMacks (talk) 13:11, 13 June 2016 (UTC)

In physics, it makes no difference as all bearings are perfect. In engineering though, it's a horrid unbalanced design and would never be used (except for something deliberate, like balancing a piston engine). Andy Dingley (talk) 13:28, 13 June 2016 (UTC)

About what I figured (including the physics/engineering dichotomy:) Thanks! DMacks (talk) 13:35, 13 June 2016 (UTC)

What is the meaning of "physical characteristics" in the following sentence?

If you had a task to write about "The electric field, its physical characteristics", what would you understated about "physical characteristics of electric field"? is talking about the definition or formula or what? It's interesting me how people around me understand this task.93.126.88.30 (talk) 18:52, 12 June 2016 (UTC)

Physical characteristics of the electrical field include its value, direction and how it changes with time. Ruslik_Zero 19:35, 12 June 2016 (UTC)

Can you give an example please? 93.126.88.30 (talk) 20:20, 12 June 2016 (UTC)

static field or alternating?--178.104.157.88 (talk) 01:11, 13 June 2016 (UTC)

Antiphotons

Is there such a thing as Antiphotons? — Preceding unsigned comment added by Soul trainer (talk • contribs) 19:36, 12 June 2016 (UTC)

A photon is it's own antiparticle. Dbfirs 20:20, 12 June 2016 (UTC)

User:Dbfirs is correct. The short answer to "are there anti-photons" is "yes", but the disappointment here is that anti-photons and photons are the same particles. [3] The Quixotic Potato (talk) 21:33, 12 June 2016 (UTC)

Are there any other particles without a separate antiparticle? Sagittarian Milky Way (talk) 13:35, 13 June 2016 (UTC)

There is a table in Standard Model#Total particle count which lists known elementary particles and whether they have a pair antiparticle or they are their own antiparticle. 91.155.193.199 (talk) 15:10, 13 June 2016 (UTC)

I, er, just deleted that section. The table is still at Talk:Standard Model/Archive 1#Total particle count, but I think it is not especially meaningful. If you look at the kaons, you'll see that
K⁰
and
K⁰
are antiparticles of each other, while
K⁰
_L and
K⁰
_S are antiparticles of themselves—despite the fact that
K⁰
_L and
K⁰
_S are the same particles as
K⁰
and
K⁰
. Similarly, the
W^±
are antiparticles of each other, but the fundamental W bosons are their own antiparticles in the same sense as the other gauge bosons. And when people say that Majorana neutrinos would be their own antiparticles, they don't mean that there would be fewer particle types, just that it would make more sense to work with a different particle basis analogous to
K⁰
_L and
K⁰
_S. -- BenRG (talk) 04:12, 15 June 2016 (UTC)

WP has a List_of_particles#Bosons. Those that have a neutral charge (like photons) are neither.--Aspro (talk) 22:41, 13 June 2016 (UTC)

Calculating MBV - answer checking

This is the question: "Calculate the value of minute blood volume (MBV) in liters (l) if stroke-volume (SV) is 70 ml and heart rate is 80 beats/min.". My answer is: 70*80=5.6L. That's true? 93.126.88.30 (talk) 21:45, 12 June 2016 (UTC)

Cardiac output says yes. --Tagishsimon (talk) 22:08, 12 June 2016 (UTC)

What does the letter f/q in this formula stand for?

In this formula of the electric field, there's a formula: E=f/q. what does the letter f and q stand for? 93.126.88.30 (talk) 22:41, 12 June 2016 (UTC)

They are defined in the line immediately above the formula:

"The STRENGTH of such a field at a point in space is defined as the force exerted on a positive charge at that point, divided by the magnitude of the charge"

Rojomoke (talk) 23:00, 12 June 2016 (UTC)

(ec) From the OP's link, with initial letters in bold for clarity: The STRENGTH E of [an electric] field at a point in space is defined as the Force exerted on a positive charge Q at that point, divided by the magnitude of the charge, that is, $E=F/Q$ AllBestFaith (talk) 23:04, 12 June 2016 (UTC)