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July 17

Can Magnesium or Nsaid drugs inhibit muscle Metabolism?

Someone Anaerobically exercises his Limbs... After the workout his muscles keep to contract and he start's having Doms. Can taking Magnesium or Nsaid drugs (To ease this Dom's Pain) actually damage the Anabolic process he aimed to achieve by the workout? Thx. Ben-Natan (talk) 08:26, 17 July 2014 (UTC)

Fixed your link. --50.100.189.160 (talk) 08:47, 17 July 2014 (UTC)

?Ben-Natan (talk) 10:21, 18 July 2014 (UTC)

I'm sorry, we cannot give medical advice. --ColinFine (talk) 15:54, 18 July 2014 (UTC)

It's not a question for a medical advice - It's a question about Metabolism (particularly in Muscles). Ben-Natan (talk) 16:50, 18 July 2014 (UTC)

Is osmium blue?

Copper#Physical appears to state that Os is one of the four coloured metals (the others being Cs, Cu, and Au). Greenwood & Earnshaw on the other hand state that Cs, Cu, and Au are the only three coloured metals. So is Os coloured? If so, could anyone explain why it is coloured? Double sharp (talk) 13:30, 17 July 2014 (UTC)

There are several pictures of it on the osmium article (and another at [1]). It's variously described as "blue–white" or "blue–black". To my eye, it appears mostly like a generic meta, silvery with maybe a tint of a color, not as obviously colored like copper, gold, and highly pure cesium seem. DMacks (talk) 16:16, 17 July 2014 (UTC)

Judge for yourself the Osmium powder in this video which appears black in inert argon, but is said to oxidise to smelly, dangerous Osmium tetroxide in air. 84.209.89.214 (talk) 23:24, 17 July 2014 (UTC)

It's pretty clear that the samples in the article have blue highlights. The article says it is bluish. But is the blue the metal or just the oxide coating? I should add that I'm suspicious that if we are strict enough many other metals will be classified as "colored". After all, visually it seems like you can tell things like bismuth, lead, aluminum, and silver seem just a little different than the lovely metallic shade of something like mercury. But I've never actually looked at polished samples of those in a rigorously inert environment. It'll be interesting to see a good answer here. Wnt (talk) 22:01, 18 July 2014 (UTC)

Rain power ?

It seems to me that a type of hydroelectric power could be generated by using the gravitational potential energy of rain collected on rooftops. The most power could be generated where you have tall buildings with frequent rain. Such power generation would be intermittent, of course, so, like solar and wind energy, being able to sell it back to the electric company to reduce your bills might be the best approach. Does such a system exist ? StuRat (talk) 13:54, 17 July 2014 (UTC)

I suspect that the cost of the system would outweigh the savings. The Pumped-storage hydroelectricity article discussed a few questions above contains this calculation: "For example, 1000 kilograms of water (1 cubic meter) at the top of a 100 meter tower has a potential energy of about 0.272 kW·h (capable of raising the temperature of the same amount of water by only 0.23 Celsius = 0.42 Fahrenheit)."

Large buildings could use rooftop rain collection for Greywater collection, to prevent the need to pump water for toilet flushes to upper stories. The savings in the power bill would be higher than if it was used for generation, and the system would be much simpler. Our articles on related subjets don't have much to say about it - it would be interesting to know if any buildings are using that sort of approach. Katie R (talk) 14:14, 17 July 2014 (UTC)

I'm all but sure it does; my company captures and uses greywater captured via roof collection for warming the freezer floor and then washing out the delivery trucks. We'd probably flush the toilets with it afterwards, but it would be inconvenient to install the extra piping necessary. Matt Deres (talk) 15:09, 17 July 2014 (UTC)

It doesn't seem to be a viable method, if you do the calculations. Looking at this table, yearly precipitation is, depending on the location, at most ~3 meters/year. So one m² of roof surface gets 3 m³/year, which is 9.5 * 10^-8 m³/s. Each m³ at 1000 meters altitude has 1000 kg * 9.8 m/s² * 1000 meter = 9.8 * 10⁶ J of potential energy, so energy output is, on average 0.931 W/m² at 100% efficiency at 1000 meters altitude in a very rainy location. Even the cheapest solar panels will get you a great deal more power output per m². Buildings of more reasonable dimensions (~100 meters high), get less then 0.1 W/m² even without any losses. - Lindert (talk) 14:41, 17 July 2014 (UTC)

Since this system wouldn't preclude other uses of the roof, such as solar panels, I'm not sure that looking at it this way is the right approach. Presumably the infrastructure to drain the water off the roof is in place in any case, with the only additional cost being that of the water turbine(s)/electrical generator(s) at the bottom of the drains. So, the cost of those units should be compared with the value of the electricity generated. StuRat (talk) 16:59, 17 July 2014 (UTC)

A two story house would generate a few cents' worth of electricity per month. It would take centuries, more likely millennia, to pay for a generator. If you factor in maintenance it's a total no go. Googling for "roof hydroelectricity" and such will find people doing it as a hobby, but for anything serious it is a few magnitudes off, cost/benefit -wise. 88.112.50.121 (talk) 23:42, 17 July 2014 (UTC)

Who's talking about a two story house ? I asked about tall buildings, like skyscrapers. StuRat (talk) 02:56, 18 July 2014 (UTC)

Since the kinetic energy in the water derives from the height that the droplets are formed at (ie, where the cloud is at) - it doesn't matter how tall your building is. Collecting water into a big tank on the roof and letting it fall through a generator to ground level would waste the energy in the water at the moment of impact onto the roof. If you can collect THAT energy - then the total of energy gathered by the impact of the water on the roof PLUS the energy gained by releasing it to ground level is the same - regardless of the height of the building. That said, the speed of a falling raindrop reaches terminal velocity eventually - but still, that kinetic energy has to go somewhere - so the friction with the air is warming up the raindrop and you'd have to collect the microscopic amount of energy from the temperature of the raindrop being a fraction of a degree warmer than ambient air. But the numbers simply aren't there...there just isn't enough energy to be had to make it worth building a machine to capture it - and then have the machine sit idle all the time it's not raining hard enough to overcome the internal losses in the machine itself.

But let's consider just the flow of water off the roof of a 400 meter tall building (the Empire State Building, for example)...it has a roof area of 10,000 square meters. The rainfall in New York is around 1.2 meters per year. So 12,000 cubic meters of water per year fall through 400 meters. A cubic meter of water weighs 1000 kg. The total gravitational potential energy gathered by having that water flow through a frictionless pipe to a generator at ground level would be m.g.h which is 12,000,000 . 9.8 . 400 = 48,000 MJ...which is the amount of energy used by a typical US automobile in a year. So adding all of this stuff to the Empire State Building would allow ONE occupant to charge his electric car...assuming the system is 100% efficient and extracts ALL of the energy from the falling water regardless of it's speed and volume. Even a light mist of rain would have to generate energy. More likely, it would be not even half that efficient.

So it's not tremendous amounts of energy. But the real problem is that the energy comes all at once during a heavy rainstorm - then nothing for weeks more. You'd probably find that almost all of the usable water flow would come in a handful of big storms during the year - and your machine would have to have the capacity to work in the heaviest deluges. So you'd need a water turbine capable of generating all the energy that a typical car uses over several months over a period of a few hours. An incredibly rough estimate suggests that this machine would probably be a hundred times more expensive than a car engine - and can't really power a car - and that's using the rain energy from the fourth tallest building in the USA.

Some clever ideas just don't work - no matter how much you think they should. This is one of those. SteveBaker (talk) 05:25, 18 July 2014 (UTC)

RE: "Since the kinetic energy in the water derives from the height that the droplets are formed at (ie, where the cloud is at) - it doesn't matter how tall your building is." I have to disagree with your conclusion here. When it hits the roof it will lose any kinetic energy it had at that point, and I can't think of any good way to capture that energy, except maybe hanging some dirty laundry out and using the raindrops to wash them. So, at that point all that's left is the gravitational potential energy, which is dependent on the height of the roof. Note that it's not necessary to build a tank on the roof, it can flow down the downspouts as it always does. And cars are rather energy intensive devices, how about if we instead use the energy to power the adjacent apartments, or sell it back to the energy company, as I suggested ? A nice benefit of powering apartments is that they might be able to disconnect from the grid during storms, when power spikes are a risk. Also, you might not want to use equipment large enough to handle the maximum flow rate at the downspouts, just have a bypass for the excess, when the flow rate is too high.

Also, at my Mom's house, I installed a system to collect rainwater in a rain barrel, then slowly release it. This is to prevent a flooding problem whenever it rains. (Her drainage system just can't keep up with the rainfall.) Now this is at ground level, where the pressure is too low to be useful, but I could imagine a similar system in use atop tall buildings, where water is currently collected in tanks to prevent overtaxing the sewers during storms, then slowly drained. If such a system exists, then we could add a very small device to convert that gravitational potential energy to electricity, at a steady rate, at the bottom of the downspouts. StuRat (talk) 16:51, 18 July 2014 (UTC)

Using your Empire State Building calcs, I get 13333 Kwh, and I pay about $0.15 per Kwh, so that's $2000 a year. If we want the device to pay for itself in 5 years, we could thus spend around $10,000 for the device. Is that enough to pay for such a device ? StuRat (talk) 17:08, 18 July 2014 (UTC)

That calculation has been done before. - ¡Ouch! (^{hurt me} / _{more pain}) 10:10, 18 July 2014 (UTC)

That's using the relatively low pressure of a municipal water supply, not quite the same as the pressure from a high building. StuRat (talk) 16:36, 18 July 2014 (UTC)

True. And oddly, the xkcd guy totally missed that it was hot water, which should have opened a whole range of lunatic schemes up to him. Wnt (talk) 21:51, 18 July 2014 (UTC)

True. But my calculation isn't. It's still a non-starter. SteveBaker (talk) 23:48, 18 July 2014 (UTC)

What technically quest been bestly?

If world university science of humankind been began at simple to implex in all, what technically quest been bestly, which start at first from implex to simple technical or around another?--Alex Sazonov (talk) 16:51, 17 July 2014 (UTC)

That question is hard to understand. I'm guessing you meant "What are some examples of technology which has changed from simple to complex and from complex to simple". If that's what you meant, then almost all technology progresses from simple to complex. But we can probably find a few examples that moved in the reverse direction. One thought is space ships, sent to the Moon and other planets, which, when they carried humans, had to be more complex than later ones carrying a robotic cargo. One of my favorite examples of a simple technology which is still in use after thousands of years, despite far more technical solutions existing, is the plumb bob used to create a vertical chalk line. StuRat (talk) 17:02, 17 July 2014 (UTC)

You see StuRat, this is exactly what we're talking about. μηδείς (talk) 17:20, 17 July 2014 (UTC)

I have no idea what you're talking about, as I provided references. StuRat (talk) 17:42, 17 July 2014 (UTC)

Thank you StuRat! In Holly Bible always been sad that God been do all at implexly miracle materia to simplely miracle material, but human mind always been do as human think as from simple to implex. Why human always do around another that God? I seen, that all technically quests always been implex that they always must been do at decide God. As I know a science always been start at implex to simple if a science quest been implex, is it’s right?--Alex Sazonov (talk) 17:55, 17 July 2014 (UTC)

I can think of one example where science has a simpler solution than biology, the wheel. Compared with legs, that's a much simpler system. StuRat (talk) 18:06, 17 July 2014 (UTC)

As I know well the USA always decide now that simple technically decides always been bestly because the simple always been infective, is it right?--Alex Sazonov (talk) 18:11, 17 July 2014 (UTC)

I don't know if it's true or not, but there was a story that the US space program spent a lot of money to develop a pen that would work in zero gravity, while the Russians used a pencil instead. StuRat (talk) 18:19, 17 July 2014 (UTC)

Thank you StuRat. The USSR always been give a simple story technology for world. I been think, what is been always clever, the cognizing the world from implex to simple or around another?--Alex Sazonov (talk) 18:34, 17 July 2014 (UTC)

The story StuRat notes is false.[2] DMacks (talk) 18:37, 17 July 2014 (UTC)

False-ish. NASA didn't develop the Space Pen - but it did cost a private company quite a bit to develop. NASA actually paid an entirely reasonable price for a bunch of them. Moreover, the Russians didn't use normal pencils because the graphite they produce when you write with them floats around in zero-g and gets into the various switches and potentiometers in the controls causing potentially lethal problems. The shavings produced when sharpening a pencil would also be a nightmare to deal with. It's believed that they actually used a form of grease pencil - but those don't write very well on paper. So this is a really bad piece of mis-information, it makes NASA seem like they spent a fortune for something that wasn't needed - when in fact, they spent very little on something that truly WAS needed. SteveBaker (talk) 19:43, 17 July 2014 (UTC)

To make a long story short, the USSR used regular air while the USA used pure oxygen, in which carbon dust is extremely explosive. Even the solid graphite of the pencil and the wood could catch fire. There is only a minor issue in air (with 21% oxygen), and we're talking about the USSR after all (overstatement, though).

One could say, "The USA threw tax money at it and used the Space Pen and pure oxygen, while the USSR threw cosmonauts at it and used a pencil and ordinary air." (Both ended up with fatalities BTW; the Groeningesque cliché of "wave after wave of cosmonauts" is a huge overstatement.) - ¡Ouch! (^{hurt me} / _{more pain}) 10:31, 18 July 2014 (UTC)

Simple-to-complex-to-simple is a little tough to define. For example, consider something like a boat hull. Originally, early boat-makers probably just hollowed out a log to make a canoe or lashed together logs to make a raft...really very simple. Then, as time progressed we got those amazing pieces of carpentry that made 500 ton warships out of interlocking planks, beams, etc during the age of sail - the complexity in the design and implementation was immense. Nowadays, most small boats have a hull formed from a single piece of fibreglass. Arguably, the fibreglass hull is simpler even than a hollowed out log or a log raft...but "simplicity" here depends on the assumption that you don't include all of the work it took to make the glass into thin strands and weave it into cloth - and the chemistry needed to make the epoxy that turns that in to sheets of a solid material. The entire process is vastly complex - but the resulting boat hull is simplicity itself.

It's very easy to come up with things that have become very simple if you don't include all of the infrastructure it took to get you there.

A more extreme example of that would be that I can write a command on my computer, using the smallest movements of my fingertips that will search a repository containing the whole of human knowledge (well, more or less) to find out a piece of information that our ancestors could have spent a lifetime searching dusty old libraries to discover. Is that "simpler"? It's certainly simpler for me! But include everything about computers, the Internet and so forth - and you have the most complex thing that humans have ever produced.

SteveBaker (talk) 19:43, 17 July 2014 (UTC)

Thank you SteveBaker, do you mean that a science knowledge is been always simple but not implex, is it been mean that not never been implex quests in a science, they always been simple?--Alex Sazonov (talk) 20:37, 17 July 2014 (UTC)

Science is often able to swing back and forth between simple and complex. Take the ideas of how the stars and planets move:

• Early astronomers (who believed that the Earth was at the center of the universe) thought that the planets went around the earth in simple, circular orbits - riding around us on crystal spheres.
• But as more careful observations were made, they had to change that idea to have the planets move on wheels mounted inside those spheres - circles around circles...but these ideas had to get more and more complicated to try to fit ever more complicated observed motion to their original simple idea.
• When the really simple idea that the sun is really at the center of the universe was explored, suddenly everything got incredibly simple again - planets moving in circles around the sun makes the explanation very simple again.
• But they don't move in exact circles - the motion is really elliptical...so new math, new equations and more complexity was needed to explain that.
• Newton's theory of gravitation provides an explanation for why the motion is elliptical - and reduced all of the motion of all of the planets known at that time to simplest imaginable gravitational equation.
• But sadly, that isn't quite correct - and the way that the orbit of the planet Mercury gradually shifts can't be explained by those simple equations. It wasn't until the more complex theory of relativity came along that Mercury's orbit could be fully explained.
• Sadly, even relativity doesn't completely explain the motion of stars orbiting distant galaxies - or the motion of the galaxies themselves. For that we needed to invent the concepts of Dark Matter and Dark Energy...so things are getting more complicated right now.
• Many physicists expect that future work will eventually come up with a Theory of everything that will again reduce everything we know about absolutely everything into a single, simple equation. This may be the final end to this cycle - but it may not happen, there is some evidence that the universe simply isn't that simple.

Science is very often a cycle of coming up with a pretty good explanation for what we see in experiments - then finding situations that our explanation doesn't cover - then figuring out a more complicated explanation to cover those exceptions - then realizing that if you think about things in a slightly different way, it gets very simple again.

SteveBaker (talk) 04:44, 18 July 2014 (UTC)

Thank you for you SteveBaker. What was been, in all means a science always been given a implex or a simple decisions, but why in a science always been a implex method of knowledge which always been a science example at all?--Alex Sazonov (talk) 08:08, 18 July 2014 (UTC)

May be a science is been so simple, that a implex method of knowledge not been. May be a God is been a simple miracle and mind of human is been simple too, I’m don’t know what is been better a simple or implex!--Alex Sazonov (talk) 10:07, 18 July 2014 (UTC)

Even, in a simple science always been a implex method of knowledge, because implex method of knowledge in a science always been more scientifically, than simple method of knowledge, that’s why a science is not been even simple!--Alex Sazonov (talk) 05:44, 19 July 2014 (UTC)

Electricity - Blue colour?

Hi, why is current or electricity depicted in blue or purple color always? are they blue really? if so, why? thanks. — Preceding unsigned comment added by 122.174.34.155 (talk) 19:26, 17 July 2014 (UTC)

Electricity is the flow of electrons...not the electrons themselves - but their movement. So the concept of color doesn't apply. It's a bit like asking "What color is speed?" or "What color is the wind?". The depiction as blue probably comes about because sparks that are made by electricity jumping a gap through air are blue. A spark is the most obvious visual image of electricity - so that presumably explains this idea. But no, electricity has no color. SteveBaker (talk) 19:46, 17 July 2014 (UTC)

For a discussion of the various emission spectra that contribute to the characteristic electric blue color of electric discharges in air, see the article Ionized-air glow. Red Act (talk) 20:00, 17 July 2014 (UTC)

Just to clarify a bit based on Red Act's provided references. The blue or purple color we associate with electric sparks is NOT the color of electricity. It is the color we get from what is called the "emission spectrum" of the specific mix of gases in the air. What happens is that, in a spark across air, electrons in the molecules of air (mostly nitrogen and oxygen) are "excited"; that means they absorb energy (from collisions between the molecules and the free electrons in the "spark"). These electrons are in unstable states, so they have to release the energy they absorbed as a result of those collisions. When the release that energy back to the universe, they do so in the form of photons (light), and these photons are the blue glow. The exact color of the glow depends on the specific material being excited... air produces that characteristic blue glow, but neon gives a red glow, argon is purple, sodium vapor is yellow, etc. For more of a discussion about the mechanics of this "absorb energy-->get excited-->relax-->release photon process, see Bohr model. --Jayron32 21:54, 17 July 2014 (UTC)

And just for fun, I'll note that if the air were thinner, you would get yet another different set of colors. TenOfAllTrades(talk) 13:08, 18 July 2014 (UTC)

July 18

Electron = black hole?

The electron is assumed to be a dimensionless point particle since the electric repulsion between the parts of a finite-sized electron is supposed to be so strong that it would disintegrate. If so, then the electron is a tiny black hole: how long does it take for such electron-black-hole to evaporate due to Hawking radiation ? Antonquery (talk) 02:03, 18 July 2014 (UTC)

There's an article on this, black hole electron, but it's rather awful at the moment so don't read it.

Black holes in GR must satisfy q² + a² ≤ m², where q is the electric charge, a is the angular momentum, and m is the mass (all in natural units). Electrons violate this inequality by a factor of (from memory) about 10²¹. Therefore either they are naked singularities (no event horizon) or the GR calculation is wrong somehow. The simplest way it could be wrong is if there are large extra dimensions, but the LHC hasn't found any evidence for that.

Black hole evaporation conserves mass-energy and electric charge. There are (for unknown reasons) no charged particles lighter than the electron. Therefore electrons can't decay by Hawking radiation even if they are black holes.

It's not impossible for the electron to be a composite particle; it could be made of preons bound by a force like the strong force. It's hard to understand why its mass is so low in that case, but that's hard to understand anyway. Many preon models have been proposed over the years, but there's no experimental support for any of them. Elementary particles are not pointlike in string theory either. -- BenRG (talk) 02:54, 18 July 2014 (UTC)

An electron is not really a point particle. It's not really a finite-sized particle either. It does not necessarily have a precisely defined position in space, or size. You can describe an electron as a particle and use that model to talk about some aspects of its behavior. You can also just as well describe it as a wave and describe some of its properties that way. Both models are fully correct and equivalent. See Wave-particle duality.--Srleffler (talk) 16:16, 18 July 2014 (UTC)

Thank you for your answers, Antonquery (talk) 10:16, 20 July 2014 (UTC)

Experimental evidence for muscle microtrauma in exercise?

I've been hearing for a few decades that the reason muscle strengthening exercise works is that it causes small tears in muscles, and the resulting healed muscles are stronger than the original (roughly speaking). Has anyone actually observed these tears in exercised muscles and counted more tears than exist in unexercised muscles? Failing that, what other experimental evidence exists?--Wikimedes (talk) 03:59, 18 July 2014 (UTC)

DOMS is a good place to start. 86.164.27.197 (talk) 12:30, 18 July 2014 (UTC)

Evidence for myofibril remodeling as opposed to myofibril damage in human muscles with DOMS: an ultrastructural and immunoelectron microscopic study. suggests some of the physical evidence that is typically considered. 86.164.27.197 (talk) 15:13, 18 July 2014 (UTC)

Thanks for the reference. It's good to know that the hypothesis is being tested.--Wikimedes (talk) 01:09, 20 July 2014 (UTC)

Were ancient oceans orange ?

As I understand it, before there was oxygen in the air, micro-organisms released oxygen into the oceans, which reacted with iron which was then dissolved in large quantities in the water, to form rust (iron oxide), which then precipitated out. So, did this happen at a fast enough rate to visibly make the oceans rust-colored, if anyone had been around to see them ? StuRat (talk) 04:36, 18 July 2014 (UTC)

At modern rates of net primary productivity there would have been more than enough rust created to make the ocean surface appear visibly discolored. However, I don't think we can make anything other than wild ass guesses about what the rate of oxygen formation was during that early epoch. Dragons flight (talk) 10:42, 18 July 2014 (UTC)

I should think we could get a good estimate, based on the rate of iron oxide deposition on the sea floor, which can determined by taking core samples. StuRat (talk) 15:36, 18 July 2014 (UTC)

I thought that too, and immediately thought of banded iron formations, but our article states that it is unknown if the bands are from seasonal variation or some other process. That means we don't know how much time is represented by each band of iron, so I suspect it makes it hard to precisely estimate the iron concentration in the water that led to the formation. I think we need to attempt to track down references on estimated iron concentrations, then find information on what concentrations would cause noticable changes in water color. Other questions such as if the surface layers of the ocean had as much concentration as lower ones may be much, much harder to find information on. Katie R (talk) 19:09, 18 July 2014 (UTC)

The idea that electromagnetic radiations in the wavelength range 590-620 nm should be distinguished from other wavelengths by the colour name "orange" is a perception that humans owe to the long evolution of the colour-discriminating eye and early implementations of colour signaling by interacting organisms; for example, the orange of Agelas clathrodes elephant ear sponge signals its bitter taste to predators.

Oxygen began to outgas from the oceans 3–2.7 billion years ago, leading to the Great Oxygenation Event (an extinction event for anaerobic organisms) around 2.3 billion years ago. Thus the OP asks about the colour of oceans that neither eyes, nor Arthropods to have them, had yet evolved to see, existing under an unbreathable atmosphere of (probably) nitrogen, carbon dioxide, methane and (in a hypothesis about early greenhouse effect) Carbonyl sulfide and illuminated by the relatively weak young Sun. The question is moot. 84.209.89.214 (talk) 18:32, 18 July 2014 (UTC)

Not moot at all. Part 2 of my question would be if we can detect orange (water) oceans on exoplanets, and use that to infer that those oceans contain micro-organisms giving off oxygen, along with dissolved iron. The idea being to supplement looking for free oxygen in the atmosphere as a sign of life. The orange-ocean method would presumably work for earlier life forms than the free oxygen in the atmosphere method. StuRat (talk) 19:25, 18 July 2014 (UTC)

Well, usually the exoplanet hunters are trying to look for absorption in the atmosphere. Trying to detect the components in the oceans... well, the exoplanet transiting its star is essentially in a state of solar eclipse to us. There must be some light that reflects off the ocean on the near side and scatters in the atmosphere to us, but ... well, I've learned by experience not to say what's impossible for exoplanet hunters any more, but they will sure impress the hell out of me if they can do that one! Wnt (talk) 21:47, 18 July 2014 (UTC)

Part 2 of the question is expressed as a condition "if we can" rather than "can we?". Supposing that we can, and do, detect a WOE (wet orange exoplanet), these sobering expositions may cause SETI devotees to restrain their celebrations.

• Inferences from the prehistorical terrestrial biosphere only make sense if taken in full. So a WOE is a Waste Of Expectation unless it lies within Goldilock's orbital zone.
• The status of Drake's equation for the number N of civilizations in our galaxy who might have radio communication

$N=R_{\ast }\cdot f_{p}\cdot n_{e}\cdot f_{\ell }\cdot f_{i}\cdot f_{c}\cdot L$

as far as we know is still

$0=$ ∏ wild guesses

The WOE gives a little magnitude to the factor f_l (planets that actually develop life) but does nothing to f_i (life that develops intelligence).

• Anthropocentric loyalty requires us to shun contact with WOEs at distances 0 to 4 and >10 billion light-years which are Waste Of Energy distances, due to the alien intelligence not having had time to evolve yet or having had enough time to evolve, make guns and blow themselves up before Earth missionaries arrive. 84.209.89.214 (talk) 15:47, 19 July 2014 (UTC)

"Eupleridae", meaning

I want to know what that word means. It doesn't say. 174.22.238.66 (talk) 07:56, 18 July 2014 (UTC)

Eupleridae means a family of carnivorans endemic to Madagascar. If you are asking about the etymology, I suggest you visit the Language Desk--Shantavira|^{feed me} 12:07, 18 July 2014 (UTC)

Google scholar has references about Eupleridae and you may read the Wikipedia article. Eupleridae is also an entry in Wikispecies and is a family of carnivorans endemic to Madagascar and comprising 10 known living species in seven genera. 84.209.89.214 (talk) 12:10, 18 July 2014 (UTC)

(edit conflict) Well, I'd say that the name is pretty transparently from Greek εὖ ("well") and πλήρης ("full" or "filled up"). It's based on Eupleres, the genus name of the falanouc, which is just the two Greek words stuck together. I'm not, however, finding any indication of why the falanouc was considered "well filled" by some taxonomist (maybe he saw a particulary fat one?). Perhaps someone here can turn up the scientific paper in which the species was originally described. Deor (talk) 12:09, 18 July 2014 (UTC)

Whoah, wrong track! See wikt:eu- - the first part generally means "true" in taxonomies, as opposed to say "pseudo". To begin with, here's a reference to the creation of the name from Eupleres in 2005.^[3] Hmmm, except actually the word "Eupleridae" at least (no idea if it's a similar grouping) apparently dates to 1850. The name Eupleres was nonetheless first (as you'd expect) from Doyère, 1835.^[4] That's Louis Michel Français Doyère. From [5] I came to [6] which at least might be the actual source text, but in classic early 1800s style I'm not finding table of contents and it's all in... French. At this point I may take a break in hope that beneficent fairy folk will stop by and wave a magic healing wand at it to make it something other than... French. :) Wnt (talk) 12:57, 18 July 2014 (UTC)

In French books, tables of contents most often appear at the end, Wnt (at least nowadays; I'm not sure about the early 19th century). In this instance, there's a "Table Méthodique" back there, but I'm not seeing any mention of Eupleres in it, nor does the name seem to be mentioned in the book's section on viverrids (p. 183 ff.), where one might expect to find it. In any case, that book's just an overview of mammalian systematics that lacks any etymological information at all, from what I can see. The initial description of Eupleres must lie elsewhere. Deor (talk) 14:45, 18 July 2014 (UTC)

According to eol.org, the original description is in Doyère, P. 1835. Description d'un nouveau genre de mammifières carnassiers. Bulletin de la Société des Sciences Naturelles, 3: 45. That doesn't appear to be online. However, there is also myetymology.com, which claims (without sources) that the word is from eu (no meaning given) and pleres meaning "replete, or covered over; by analogy, complete". So Eupleres might mean 'completely covered'. I found some fairly convincing confirmation of this on Google Books in The American Journal of Science and Arts (1836), which contains this on p.192: "A new genus of Mammalia has been found ... which M. Doyère ... proposes to call Eupleres ... the sole of the foot being the only part free from hair." --Heron (talk) 21:20, 18 July 2014 (UTC)

I corrected a spelling in your post for clarity, Heron. The website says pleres, not pleures, referring to the same Greek word I cited above. (Pleur- would have something to do with the flanks or the ribs.) Deor (talk) 22:54, 18 July 2014 (UTC)

You're quite right, Deor. I didn't mean to disagree with you; it was just a typo. My fingers decided to auto-correct the unfamiliar pler- to the more familiar pleur-. --Heron (talk) 11:21, 19 July 2014 (UTC)

Good job, Heron! And no less than I deserved for suggesting someone else was on the wrong track without completing my own. Deor was actually not far off the mark; "completely covered" with hair then. If there's one thing I ought to know from biology it's that there are no laws. Wnt (talk) 21:42, 18 July 2014 (UTC)

Yes, Wnt, the only law is that the names have to be unique within a kingdom; otherwise, they are at the whim of the discoverer. Even jokes are allowed. --Heron (talk) 11:40, 19 July 2014 (UTC)

excellent. never would've guessed. thx. 174.22.238.66 (talk) 22:17, 18 July 2014 (UTC)

Help identifying a feather

I recently found this feather in a wooded area of southeastern Pennsylvania. I am unable to identify the bird that it comes from. The feather is a very bright yellow (more so than the photo may suggest) and is about 6 inches long. I am not aware of any yellow birds in the area that are large enough to have such a feather. (Though the bird may not appear as yellow as some parts of the feather itself, because it is the underside that is the yellowest, and the presumably more exposed top side has more brown.) Can anyone help identify this? Thank you. 108.52.245.122 (talk) 12:03, 18 July 2014 (UTC)

Very speculative, but note yellow-shafted Northern flicker. Wnt (talk) 13:06, 18 July 2014 (UTC)

I think you might be right. They live in this area, they are about the right size, and a Google images search finds plenty of pictures of the undersides of their wings which look bright yellow. Thanks. 108.52.245.122 (talk) 14:43, 18 July 2014 (UTC)

Disabling MANPADS

Since some countries cannot keep track of all their MANPADS (MAN Portable Air Defense Systems, i.e. Stinger missles), I am wondering if they could be made with an expiration date, much like landmines. However, since some will no doubt be stored along with other equipment or munitions, it would not be a good idea to simply detonate the warhead when the expiration date arrives. So I'm wondering if there is some chemical reaction that would render the explosive part of the warhead inert without causing an explosion or starting a fire. Yes, I know, there is a huge amount of energy stored in the warhead, but to me chemistry is mostly black magic, so maybe there is a way to do this. — Preceding unsigned comment added by 50.43.11.252 (talk) 16:13, 18 July 2014 (UTC)

Another approach would be to make the electronics fail after some period of time. A timer could go off after the designated time period, and detonate a micro-charge that would be just enough to burn through some wires or critical electronic components. Of course, the terrorists might be able to repair this or remove the charge before it detonates, if they are sophisticated enough. Using components that just naturally fail with age is another approach, and would be more difficult to prevent or repair, but there the timing would be less exact. In any case, the explosives and fuel could still be removed and used for some nefarious purpose, but probably won't kill as many people as if a plane is shot down.

I believe there is a great need for this, for example in Syria, where any weapons given to the rebels may well end up being used against civilians. StuRat (talk) 16:24, 18 July 2014 (UTC)

When components fail, it's not all that hard to simply replace them with newer (and more reliable) ones. A better (if expensive) solution would be to equip civilian aircraft with infrared jammers (what the hell, no article?!) to prevent the missile from guiding properly. 24.5.122.13 (talk) 19:57, 19 July 2014 (UTC)

These missiles are made to take down military planes. I am therefore more than a little skeptical about the claim you could harden civilian planes to resist anything but the most utterly obsolete weapons. Wnt (talk) 21:00, 19 July 2014 (UTC)

We have an article infrared countermeasure which mentions Israel is attempting to develop a laser based system for civilian aircraft to help defend against MANPADs which is what the question was about. MANPADs are of course mostly a threat on take off/landing and not when overflying, Nil Einne (talk) 21:12, 19 July 2014 (UTC)

Given that ALL aircraft have to take off and land somewhere, and that many civilian airports are both extremely busy in terms of traffic and inadequately guarded, a threat to civilian aircraft at takeoff and landing is definitely to be taken seriously. What if, for example, terrorists from Al-Qaida stake out the departure paths from several major civilian airports (JFK, LAX, Chicago O'Hare, Sea-Tac, etc.) and use Stinger missiles (plentiful from old Afghan stocks) to simultaneously shoot down several jumbo jets right after takeoff?! 24.5.122.13 (talk) 23:03, 20 July 2014 (UTC)

No chemical solution for this problem?

Identify a plant

Can anybody identify this plant, which is next to the hothouse in the Walled Kitchen Garden at Clumber Park? It is probably an exotic: the same bed contains specimens of Paulownia tomentosa and Echium wildpretii. I asked one of the gardeners (in another part of the garden, so it wasn't in sight at the time) and she thought it might be Tetrataxis, but she wasn't sure, and I haven't found a picture of that anywhere, so I don't know if that identification is even plausible.

Unknown plant

--ColinFine (talk) 16:16, 18 July 2014 (UTC)

A picture of Tetrataxis salicifolia which is listed as a critically endangered species shows a different leaf shape. 84.209.89.214 (talk) 17:16, 18 July 2014 (UTC)

I can't tell from the photo if the leaf margins and veination are right, but it reminds me of castor oil plant, see e.g. picture here [7]. Also I can't tell the context/ situation of the plant from the photo. Not sure why you think it's exotic, but the way it's poking out of the other hedge makes it seem like a weed to me... SemanticMantis (talk) 19:33, 18 July 2014 (UTC)

And in case of mispronunciation/transcription/slip-of-the-tongue errors, "Tetrataxis" could be confused for "Tetrapanax" (verbally, not botanically). See e.g. pictures at Tetrapanax papyrifer. It has a fairly similar leaf to your specimen, but I'm not sure that it would survive over winter in that location, even in a walled garden. It does apparently survuve in British Columbia, though... [8] SemanticMantis (talk) 20:30, 18 July 2014 (UTC)

Tetrapanax it is. Thank you, SemanticMantis. I actually thought she had said "Tetrapaxis" with a 'p', but I couldn't find that, and concluded it must have been "Tetrataxis". I actually thought it looked araliaceous, but didn't think of trying to look it up in Araliaceae. --ColinFine (talk) 23:23, 18 July 2014 (UTC)

thrombosis or sclerosis in the coronary veins

Can it be thrombosis or sclerosis in the coronary veins (usually they are only in the coronary artries)מוטיבציה (talk) 18:23, 18 July 2014 (UTC)

Yes, coronary venous thrombosis exists.[9] Red Act (talk) 18:34, 18 July 2014 (UTC)

Thank you מוטיבציה (talk) 01:05, 21 July 2014 (UTC)

"Do that thing with your eyes"

In Invasion of the Body Snatchers (1978 version), about 20 minutes in, Donald Sutherland asks Brooke Adams (actress) to "Do that thing with your eyes". She then wiggles the pupils back and forth rapidly. I can do the same thing. So:

1) What's this ability called ? It's similar to a saccade, but that's normally involuntary, and moves in all directions, not just horizontally.

2) How common is this ability ? StuRat (talk) 20:44, 18 July 2014 (UTC)

+1 here. I've seen others do it also; it's instinctive enough that I feel like it has to have something to do with the basic biology. Blatant speculation: It feels like there's some relationship with focusing nearer, crossing the eyes... I'm thinking somehow it's a set of saccades after a target that disagrees with itself due to the urge to cross the eyes; I think that because the disagreement is somehow tied to eye-crossing is why it is only left to right. Wnt (talk) 21:40, 18 July 2014 (UTC)

Yes, I find it much easier to do it when focusing both eyes on a finger placed just in front of my nose. StuRat (talk) 22:52, 18 July 2014 (UTC)

Over 30 years ago, 8% of "college age populations" could produce "voluntary nystagmus" according to Zahn JR (July 1978). "Incidence and characteristics of voluntary nystagmus" (J. Neurol. Neurosurg. Psychiatr. 41 (7): 617–23.) You can also find "voluntary flutter" or "voluntary ocular flutter". I guess you'd have to add "horizontal" to specify exactly what you're describing. (I can't do it, by the way, unless I'm looking straight out a train window). ---Sluzzelin talk 21:49, 18 July 2014 (UTC)

My optician used the term "voluntary nystagmus" when I inquired about it.--Gilderien Chat|List of good deeds 23:09, 18 July 2014 (UTC)

July 19

May be all science always been humanitarian?

If philosophy of science knowledge always been humanitarian, may been all science always been humanitarian?--Alex Sazonov (talk) 09:16, 19 July 2014 (UTC)

What do you mean? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:11, 19 July 2014 (UTC)

It might be better to write it in your own language and use google translate to change it to English. At least I normally understand that. I think it is a pity if people don't support the Wikipedia in their own language. Dmcq (talk) 11:19, 19 July 2014 (UTC)

There's no way working backwards from Russian you can assume this linguistic behavior is caused by translation mistakes, μηδείς (talk) 17:49, 19 July 2014 (UTC)

I think I know what he means, and I have this to say: Was the Manhattan Project humanitarian? Was I. G. Farben's research into nerve gases humanitarian? Was Alfred Nobel's invention of high explosives humanitarian? 24.5.122.13 (talk) 19:52, 19 July 2014 (UTC)

At least two of those (Manhattan Project, and especially much of Nobel's work) are often argued as a net humanitarian gain, either with the benefit of historical perspective and/or at their own time. Knowledge is not a moral thing; only how one uses it. DMacks (talk) 19:59, 19 July 2014 (UTC)

Does that make Nazi research into the atomic bomb humanitarian too? HiLo48 (talk) 23:55, 19 July 2014 (UTC)

If they had been destined to win WW2 in either case, then I suppose it could be argued that a quick victory, using nuclear weapons, that killed fewer people, would be better than a longer, more deadly war. Of course, if they just murdered everybody after they won anyway, then there wouldn't be any benefit. StuRat (talk) 03:20, 20 July 2014 (UTC)

Will, the philosophy of science knowledge in all technical is been always humanitarian too?--Alex Sazonov (talk) 08:36, 20 July 2014 (UTC)

Thank you, Hayne. Beisbol bean berry good to me. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:21, 20 July 2014 (UTC)

To philosophy of science is amoral, meaning neither moral (humanitarian) nor immoral (evil). That is, the goal is just to seek knowledge, and whether that knowledge is good or bad for humanity is irrelevant. StuRat (talk) 19:36, 20 July 2014 (UTC)

Recommendations for textbook on galactic astrophysics ?

I have just read and enjoyed Gravity's Engines by Caleb Scharf and would like to read a more detailed book on the same subject. Can anyone recommend an undergraduate level text covering galaxy formation and evolution, active galactic nuclei, supermassive black holes, dark matter etc. ? I know this is an area of active research, so something that is up to date and includes latest observations and developments would be good. I am comfortable with undergraduate level mathematics and physics. Not looking for a popularisation - Scharf ticks that box nicely - or pretty pictures - I can get those from APOD. Thank you. Gandalf61 (talk) 09:58, 19 July 2014 (UTC)

I think you will find The Astrophysical Journal of interest. Abstracts of its articles are free at the website, though to read them in full you need to pay or join a subscribing library. Caleb Scharf has written widely cited articles in The Astrophysical Journal. 84.209.89.214 (talk) 13:59, 19 July 2014 (UTC)

The Astrophysical Journal is a research journal that publishes highly technical research papers. You'll need a degree to understand the contents of individual articles and you'll need to spend a lot of effort on synthesising the contents of many articles into something like an overview of the current status of a field of research. Not recommended for the lay person. A book that I like and that covers most of the topics mentioned by Gandalf61 at an accessible but not too simplistic level is "Extragalactic Astronomy and Cosmology: An Introduction" by Peter Schneider. There are others, of course. --Wrongfilter (talk) 17:38, 20 July 2014 (UTC)

Improvement to Cosmological Inflationary Model?

One of the aspects of current inflation that can be recorded in our modern universe is that it is only increasing in speed with time, which as I understand was the opposite expected behaviour until not too long ago. Of what evidence or idea does the early Cosmic Inflation theory still hold validity? As I've researched, the "Metric Expansion of Space" model defines that the universe still underwent that abrupt inflation and expansion at the moment of the Big Bang, then slowed down over the next 8 billion years, then began accelerating about 5 billion years ago. This would look something like this graph for the Inflection Point article:

Inflection point.

which is more or less a graphical deviation of an otherwise straight-line, and therefore possibly a misinterpretation of data on the Scientific Community's behalf.

I still feel the existence of an "inflationary epoch" to not be a necessary or appropriate model. If inflation is only increasing with time, is there really anything stopping it from always having been that way since the moment of the birth of the universe? Is there any observable data that says the early universe couldn't have existed as is postulated, but for millions or even billions of years rather than the established fraction of a fraction of a fraction of a second? Fbushnik (talk) 19:06, 19 July 2014 (UTC)

Value of the Hubble Constant including measurement uncertainty. Vertical units are (km/s)/Mpc.

Modelling of the expanding universe is initially based on the observable constant $H_{0}$ in Hubble's law v = H₀D. If $H_{0}$ were really constant, the age of the universe could be resolved simply by extrapolating the present rate of expansion v back in time to a Big-Bang moment 13.7 billions of years ago. Such a finite universe lifetime seems to explain both Olbers' paradox (black gaps show between the stars) and the residual background radiation. The vast timescale rules out reliable direct observation of the rate of change, if any, of $H_{0}$. Observations of Type Ia supernova now suggest an Accelerating universe (see article). Models attempting to explain accelerating expansion include some form of dark energy, dark fluid or phantom energy and lead to different estimates of the age of the universe. See the diagram at Hubble's law#Ultimate fate and age of the universe. 84.209.89.214 (talk) 22:26, 19 July 2014 (UTC)

The accelerating expansion of the universe due to dark energy is not the same as inflation. They're theoretically similar, both being apparently caused by a spin-0 field of some sort, but there's nothing to suggest that they're related beyond that. There is no evidence that the rate of the accelerating expansion is increasing with time. What is happening is that the density of ordinary matter (and dark matter) is decreasing, and a few billion years ago it fell to the point that its gravitational attraction was no longer enough to counter the gravitational repulsion of the dark energy that had, apparently, always been there. It's not certain that this is the right model, but it's the simplest model that fits all of the data so far.

It's not true (or not known to be true) that inflation only lasted for a fraction of a second. The observed smoothness of the universe only gives a lower bound on the duration of inflation. There's no theoretical reason to think it didn't last for much longer than that. It could have lasted for billions of years as far as anyone knows. -- BenRG (talk) 23:37, 19 July 2014 (UTC)

I'm not a great fan of Occam's Razor, but I have to wonder how one measured Hubble constant (with substantial disagreements in the measurements) can support the proposal of two separate mysterious universe-wide repulsive forces active at the same time. Wnt (talk) 11:50, 20 July 2014 (UTC)

Support for the ΛCDM model comes primarily from the cosmic microwave background, the luminosity-redshift relation of supernovas, and baryon acoustic oscillation, not from one measured Hubble constant. Ned Wright's cosmology site has some details.

The universe-wide repulsive force is predicted by general relativity if there is a spin-0 field with a nonzero value in the vacuum (VEV). GR is known to be very accurate, and spin-0 fields with a nonzero VEV are known to exist (the Higgs field and the QCD vacuum). A lot of the appeal of the inflationary / dark energy model is that it doesn't require new physical laws, just new fields of a familiar type. -- BenRG (talk) 16:05, 20 July 2014 (UTC)

Chemical disposal of chemical weapons

As some of you probably know, phosgene can be made harmless by reacting it with a solution of caustic:

COCl₂ + 4 NaOH → 2 NaCl + Na₂CO₃ + 2 H₂O

and cyanide gas by chemical (e.g. catalytic) oxidation:

HCN + 5/2 O₂ → HNO₃ + CO₂

My question is, what other chemical warfare agents can be made (relatively) harmless by selective chemical reactions (other than by high-temperature incineration, which would be sort of "cheating" because it's non-selective)? 24.5.122.13 (talk) 20:15, 19 July 2014 (UTC)

Most mustard agents and nerve agents seem reactive towards water or aqueous-caustic. Many of their biological properties are based on a similar reaction with various N and/or O nucleophiles. DMacks (talk) 20:33, 19 July 2014 (UTC)

See, for example, doi:10.1021/jo01175a018 discussing the rates and mechanisms of hydrolysis of some nitrogen mustards. DMacks (talk) 20:48, 19 July 2014 (UTC)

Thanks! I was pretty sure that mustard gas would hydrolyze in alkali solution like it actually does -- wasn't sure about nerve gases, though, because I didn't remember their structure. 24.5.122.13 (talk) 22:45, 19 July 2014 (UTC)

Wave interference - What´s happen with their energy ?

My doubt is about light/wave interference and their energy. I have read all the posts about waves and I didn’t find any reference about wave energy when interference occurs.

I don´t know if it is a dumb questions but I would like to ask you a question that is bothering me and I dont know how to explain.

If two waves meet at a point and from there we have a completely destructive interference, what happen with original energy that was transported (contained) by each wave ?

In other way, Could we have light wave interference, with phase deplacement, in such way that light will disappear ? In such case what will happen with energy ?

Futurengineer (talk) 22:07, 19 July 2014 (UTC)futurengineer

"Destructive interference" when travelling waves interact means that the net deviation (which may be brightness, electric potential or sound, depending on the type of wave) is zero at that point. Each wave continues in its own direction and likely there will be constructive interference between the waves at a different location. But in neither case has any energy been destroyed or constructed, only the local observation is affected. For simplicity assume small sinusoidal waves in a linear medium where no intermodulation of the waves occurs. 84.209.89.214 (talk) 22:40, 19 July 2014 (UTC)

Agreed. To see this for yourself, fill the tub with an inch or two of water, and poke the water with fingertips at two different locations, simultaneously. Waves will spread out from each point, and pass right through each other. StuRat (talk) 03:13, 20 July 2014 (UTC)

In the general case where the waves are not spatially correlated, then the energy will redistributed, but the total energy is conserved. The waves may interfere destructively in some places, in which case the energy density could be locally reduced to zero. However, the waves will interfere constructively in other places, and in those places the energy density is greater than sum of the energy densities of the two waves. This is because the energy depends on the square of the amplitude, and the square of the sum of two amplitudes is greater than the sum of the squares. For example, if the waves have equal amplitude at a point where they constructively interfere, then the amplitude at that point is twice the amplitude of that of either wave, but the energy density is locally four times the energy density of either wave. The cold and hot spots average out, so that it turns out that energy is conserved (this is half the answer). --catslash (talk) 18:34, 20 July 2014 (UTC)

In the special case where the interfering waves are spatially correlated (such as two plane waves of the same amplitude and same wavelength travelling in the same direction), then the source of one wave (say the second), will continually be opposed (in the case of constructive interference), or assisted (in the case of destructive interference), by the field of the first wave. This means that the second source may be working abnormally hard (radiating more energy than usual), or may actually be absorbing energy, and so energy is conserved even though the total energy in the interfering waves does differ from the sum of the energies in the separate waves (still not a complete answer). --catslash (talk) 18:56, 20 July 2014 (UTC)

Another point worth mentioning is that anything that obeys both the wave equation and conservation of energy consists of a pair of fields (or a field having at least two components). For example a sound wave consists of a pressure wave and a particle velocity wave, while a light wave consists of both an E-field (electric) and and H-field (magnetic). Both parts of the wave carry energy. For the sound wave, the medium holds energy both by virtue of being compressed and due to its local kinetic energy. In the case of interference between waves travelling in opposite directions (a standing wave), constructive interference of the pressure waves (or E-field waves) occurs at the same locations as destructive interference of the particle-velocity waves (or H-field waves) and vice versa, so that the total energy density is everywhere the same. --catslash (talk) 23:04, 20 July 2014 (UTC)

July 20

How thick is the skin of a balloon?

I realize that the thickness would depend on the material, and how much pressure was inside, but I'm wondering what the range is. I'm talking about an ordinary children's party balloon. I'm thinking an uninflated balloon could be several thousandths of an inch thick and it would get thinner as it was inflated. How thin could it get before it fails? One one-thousandth? A ten-thousandth? Less? — Preceding unsigned comment added by 50.43.11.252 (talk) 22:51, 19 July 2014‎

Party balloons...dunno. Similar looking things used for some scientific/medical purposes are described here as being "12mils" thick...about 0.3 millimeters...which is probably about what the party balloons are.

When you inflate them, every time you double the diameter of the balloon, the wall will have four times the surface area...so the thickness of the wall ought to be four times thinner. The thickness of the wall is inversely proportional to the square of the diameter of the balloon. So if a 3cm diameter (uninflated) balloon might get up to 30cm diameter when fully inflated - so we would expect it to be 100 times thinner. That would be three thousandths of a millimeter...three micrometers. That's about the same as the thickness of a human hair...which seems awfully thin to me. I'm suspicious of the validity of this estimate...but I don't see how it could be much different than that.

Incidentally, I doubt the failure of the balloon directly relates to the overall wall thickness. There are bound to be weak spots in the latex that give way long before the overall thickness of the material gets too thin to hold the pressure - and we know that a microscopic flaw (like a pin-prick) rapidly propagates to a large tear. This video: https://www.youtube.com/watch?v=idfvjbScXJM shows you how they're made - basically they dunk metal molds of the uninflated balloon into a tank of liquid latex - so the thickness of the material isn't going to be all that uniform either across the whole of one balloon - or from one balloon to the next.

SteveBaker (talk) 03:46, 20 July 2014 (UTC)

Ref. Desk vs. YouTube challenge on the same question

What is the thickness of the rubber just before bursting? Why do the air-filled balloons break at the top while the last one with some water inside breaks at the bottom? 84.209.89.214 (talk) 11:18, 20 July 2014 (UTC)

Well, if the balloon was perfectly uniform, I'd say that the pressure at the bottom of the puddle of water is higher than the pressure at the top of the balloon because the weight of the water is added to the air pressure. It seems like it would be a tiny difference - but if the balloon were completely uniform, that would be the first place to go. But there are other possibilities. Balloons get hot as they stretch - and the water would conduct that heat away creating a thermal gradient that might affect the elasticity...there are MANY possibilities. However, I'd guess that it was mostly coincidence. I don't think balloons are manufactured carefully enough to ensure that they are that perfectly uniform. SteveBaker (talk) 15:19, 20 July 2014 (UTC)

I think the shape of the balloon is a factor in bursting. A favourite party game when I was a lad, was to blow up a balloon until it burst, and sausage balloons where always much more difficult than round ones. I think zig-zag sausage balloons might be easier to burst than straight sausage. Modelling balloons are very difficult to blow up to bursting point. I can inflate them by mouth but when I used to model at fetes I used a pump, partly in interests of hygiene but also to save my body, although it is quicker to inflate by mouth. I guess they have thicker skins than party balloons. --TrogWoolley (talk) 14:44, 20 July 2014 (UTC)

Pre-CPR resuscitation

Early- and mid-20th century films sometimes depict a pre-CPR method of resuscitation, in which the body is laid on the back, the arms put at the side, and then moved behind the head before being returned to the side; this is repeated until the person breathes or (thought this isn't often shown in the films) until the resuscitator gives up on the hopeless case. What do we call this method? Nyttend (talk) 03:06, 20 July 2014 (UTC)

At History_of_cardiopulmonary_resuscitation I see the idea of lifting the arms, but that sounds like "up in the air" not "along the ground to behind head" as you describe. Anything you find, please add a note to that article. DMacks (talk) 03:25, 20 July 2014 (UTC)

There's also a mention at Cardiopulmonary resuscitation#History. HiLo48 (talk) 03:30, 20 July 2014 (UTC)

Yes, I was thinking of the lifting-in-the-air; I wasn't describing moving the arms along the ground. Think vaguely of the motion backstroke swimmers use. Sorry that I missed the history section in the CPR article; I looked for it and somehow completely failed to find it. Nyttend (talk) 04:16, 20 July 2014 (UTC)

That's because this material belongs in the article on artificial respiration, which came before CPR. Or maybe the two articles should be merged. --50.100.189.160 (talk) 04:45, 20 July 2014 (UTC)

I was taught this every time I refreshed my First Aid at Work qualification because it is useful in cases where the patient is believed to have ingested poison per ora or where there is a lot of blood round the oral area and you are worried about oral transmission of disease. --TammyMoet (talk) 08:43, 20 July 2014 (UTC)

Ca and K sorbates?

what does it mean? [10] --84.108.213.48 (talk) 07:27, 20 July 2014 (UTC)

I think I had understand : Potassium sorbate + Calcium sorbate, but I need to read it again. thanks --84.108.213.48 (talk) 07:31, 20 July 2014 (UTC)

Yes, that's right --50.100.189.160 (talk) 09:49, 20 July 2014 (UTC)

Number of employees at the Russian Federal Space Agency

How many employees does ROSCOSMOS (the Russian Federal Space Agency) have? Thanks. --Schweinchen (talk) 13:47, 20 July 2014 (UTC)

Voltage divider - question about current

Suppose I have a device that draws 1 A at 6 v and I have a 12 v supply so I make a voltage divider with two 1 Mohm resistors. Now I can have 6 v across my device but how could it draw 1 A through that 1 Mohm resistor? This was completely neglected at school (a long time ago). 78.148.105.159 (talk) 15:34, 20 July 2014 (UTC)

it can't. whatsmore, any load except very small ones (several megaohms) will upset the divider because of how parallel resistances add. That's why voltage dividers are never used as sources of voltage (except in transistor stages, to provide bias voltage to the base, but then the base only draws microamps (huge base-emitter resistance), so it's OK). if the device draws 1A at 6V, then you could connect it through a 6 Ohm series resistor, which would drop 6 V and dissipate 6 W (!) of power as heat, but that's also "suboptimal." If the voltage is AC, one could use a simple stepdown transformer. DC requires the use of DC-DC converters, such as the 7806, which is a linear regulator (there are other conversion methods, such as when you have an oscillator generate a square wave with an adjustible duty cycle, then smoothen the voltage out with a capacitor, or by generating a sinusoid which is then power-amplified and fed into a transformer etc) Asmrulz (talk) 17:35, 20 July 2014 (UTC)

The LM7806 regulator is a good suggestion. It will deliver fixed 6V whether a load (up to 1A) is connected or not and it will tolerate a short circuit. But note that when the device takes 1A, the device and the regulator are each dissipating 6 Watts. Therefore the regulator which comes in a TO-220 package should be bolted to a Heat sink. If you know the thermal resistance of the heat sink, say 3 deg C/W, then in this application the regulator runs at 6 x 3 = 18 degrees above ambient temperature, which is reasonable. Read the application note for other information such as the pin connections and the capacitors that should be soldered close to the regulator to ensure stability see Fig 4. 84.209.89.214 (talk) 21:32, 20 July 2014 (UTC)

Don't use a voltage divider as a power supply, because it's inefficient, it's sensitive to imperfections in your (probably non-) ideal voltage source; and even if it works, it loses a lot of energy to resistive heating. Real power supplies that source large currents do not use voltage dividers to set the output voltage. Nimur (talk) 17:37, 20 July 2014 (UTC)

Voltage divider#Loading effect mentions this problem, but I added another mention earlier in the article since it seems rather important. -- BenRG (talk) 17:40, 20 July 2014 (UTC)

What do insect bites do to your skin tissues?

Bites by many insects result in rashes, which may last from hours to few weeks. What do insect bites do to your tissues? For the ones that take a few weeks to completely clear up, what makes recovery take soon long? What's happening when your tissues are recovering from an insect bite?

For those which aren't trying to harm you, like a mosquito, it's often a bacterial infection. The mosquito injects a blood thinner so it can avoid clotting while drawing blood, but that's also full of bacteria and viruses. Having microbes injected directly into the blood vessel is one of the worst places for it, since it can't be ejected by bleeding, as in a normal cut, or killed off by free oxygen, in the case of anaerobic bacteria, or removed/killed by washing and sterilizing the wound. At that point, it's up to the immune system to counter the infection.

For those which are trying to harm you, like venomous spiders (not technically insects), the venom may work by any of a number of methods. In any case, first the venom must be diluted to the point where it no longer causes damage, then the damage must be repaired. StuRat (talk) 16:35, 20 July 2014 (UTC)

Even a non-infectious mosquito bite can cause an allergic reaction, which believe it or not is called Skeeter syndrome. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:12, 20 July 2014 (UTC)

Good point. Note that many of the same problems I noted above also apply to an allergen injected directly into a blood vessel, such as the inability of bleeding to wash it away. StuRat (talk) 17:23, 20 July 2014 (UTC)

• Typically there are two types of reaction from blood-sucking flies and mosquitoes. The first and subsequent bites will from a histaminic which will be local swelling, redness and itching due to the response to the direct tissue damage of the bite. If the body forms antibodies to chemicals in the flies' saliva, in later bites, some minutes after the initial red, pimple-like reaction, the skin will become raised and hardened in the shape of a coin or a pancake. This is called induration, and is caused by white blood cells responding to the presence of activated antibodies. Odly we lack an article on induration. μηδείς (talk) 17:36, 20 July 2014 (UTC)

• Beware those bites shaped like a con. That sounds serious. :-) StuRat (talk) 19:31, 20 July 2014 (UTC)

Unless you're goining to start paying me Stuart, don't expect me to notice things the spelczeck doesn't. μηδείς (talk) 23:01, 20 July 2014 (UTC)

Salt poisoning

Our hypernatremia article mentions salt poisoning as one possible cause. However, we have no article on that. Is salt poisoning simply consuming so much salt in a short time period that your body is unable to compensate by drinking water and urinating salt, in order to bring the sodium balance back to normal ? If so, how much salt intake causes this ? For example, according to this nutrition menu from Chili's, ordering a full order of Texas Cheese Fries as an appetizer followed by a Margarita Shrimp Bowl for the entree and a Molten Chocolate Cake for dessert will result in about 12 grams of sodium: [11]. So, would this cause salt poisoning, if consumed within an hour, by a 200 pound man ? How about a 100 pound woman ? StuRat (talk) 19:28, 20 July 2014 (UTC)

This page has the Center for Disease Control recommendations for sodium intake. At Wikipedia, we cannot diagnose whether or not any action you or someone you know has taken or plans to take would cause a medical problem. Only a doctor would. --Jayron32 19:42, 20 July 2014 (UTC)

That's not particularly helpful, as it deals with chronic excessive sodium intake, and I asked about an acute overdose. And I believe you can state whether a particular level of sodium intake would cause medical problems in a theoretical individual. For example, is there an LD50 value for sodium ? StuRat (talk) 21:25, 20 July 2014 (UTC)

I'm also interested in knowing what the minimum sodium intake is. I believe the 1.5-2.3 grams stated in the previous link is the range for maximums. StuRat (talk) 21:29, 20 July 2014 (UTC)

How can we know that electrons cannot be broken down into smaller constituent parts

Just tell me how? OsmanRF34 (talk) 20:58, 20 July 2014 (UTC)

We can't know for sure. We can however state that there is no verifiable evidence that they can be. If you want absolute certainty, you won't find it in science... AndyTheGrump (talk) 21:01, 20 July 2014 (UTC)

See preon. Wnt (talk) 21:05, 20 July 2014 (UTC)

What is the difference between ECG and Monitor?

What are the main differences between ECG and monitor? מוטיבציה (talk) 21:28, 20 July 2014 (UTC)

An electrocardiogram can be displayed on a monitor and/or recorded on paper tape. The paper tape version traditionally had the advantage of allowing quicker access to recent data which had scrolled off the monitor. However, modern systems both electronically record the data and hopefully allow rapid access to recent data, but it's still hard to get quicker than paper tape. Paper tape does need to be changed periodically, however. In a third world hospital, where power disruptions are frequent, paper tape records may also be more reliable. StuRat (talk) 21:37, 20 July 2014 (UTC)

July 21

Time loops

Could time loops actually exist in real life? Clover345 (talk) 00:05, 21 July 2014 (UTC)

Probably not, but existing theory doesn't currently completely rule out that possibility. There do exist solutions to the Einstein field equations which contain closed timelike curves, but those solutions generally require circumstances which have never been observed, and hence may never exist. See also Chronology protection conjecture. Red Act (talk) 01:54, 21 July 2014 (UTC)

Hello everybody, I have some questions about the history of the EKG, and I would like to know the answers. 1. In the book "Dubin: rapid interpretation", written that "Galvany knew that the closing circle between two metals to dead frog's leg, creates an electric current". According to this thing, if someone takes a gold and silver for example (two different metals), his legs dance... but it does not happen in the reality. if so, what is the explanation for the things that mention above? 2. There written too "Koliker and Muller recover that when putting a motor nerve of grog's leg on a beaten heart, then the leg moves according to the beats", it does not clear to me what kind of heart he's talking about, Is it talking about human heart, and how they did that (what is the way they did it to approach to the beaten heart in order to make their research? מוטיבציה (talk) 02:39, 21 July 2014 (UTC)

Some history questions about the ECG development

Hello everybody, I have some questions about the history of the EKG, and I would like to know the answers. 1. In the book "Dubin: rapid interpretation", written that "Galvany knew that the closing circle between two metals to dead frog's leg, creates an electric current". According to this thing, if someone takes a gold and silver for example (two different metals), his legs dance... but it does not happen in the reality. if so, what is the explanation for the things that mention above? 2. There written too "Koliker and Muller recover that when putting a motor nerve of grog's leg on a beaten heart, then the leg moves according to the beats", it does not clear to me what kind of heart he's talking about, Is it talking about human heart, and how they did that (what is the way they did it to approach to the beaten heart in order to make their research? מוטיבציה (talk) 02:40, 21 July 2014 (UTC)