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September 10

What's the explanation for "Larger diameter axons have a higher conduction velocity"?

I read on khanacademy site "Larger diameter axons have a higher conduction velocity, which means they are able to send signals faster. This is because there is less resistance facing the ion flow. We have a lot of ions flooding into the axon, so the more space they have to travel, the more likely they will be able to keep going in the right direction.". The reason that this site brings it isn't understandable to me, because according to my logic many times the smaller diameter the faster fluid velocity. I have two examples for my claim: 1. Hypertension of the blood circulation. 2. A simple water pipe, as the diameter is smaller the flow is stronger and faster. So this clame that "Larger diameter axons have a higher conduction velocity, which means they are able to send signals faster" isn't understandable to me. What's the correct explanation for that? 93.126.116.89 (talk) 01:57, 10 September 2018 (UTC)[reply]

I don't know anything about axons, but in your water pipe example, the larger diameter pipe transports far larger volumes of water per unit time than the smaller diameter pipe, assuming other parameters like head pressure are held constant. A sudden reduction in pipe diameter (i.e. a nozzle) may result in a sudden increase in the flow velocity, but over longer pipe lengths that effect is opposed by increased drag against the sides of the pipe (due to the square cube law) which reduces velocity. 202.155.85.18 (talk) 02:36, 10 September 2018 (UTC)[reply]

We explain part of this at Length constant, but there's a lovely presentation at [[1]] that goes further. The length constant is pretty easily understood as the amount of the current that goes down the neuron versus the amount that escapes; the other relevant concept (from the link) is that "Each time an ion channel needs to open to recharge the action potential, this delays the propagation of the action potential by ~1 ms." Hence the evolutionary tendency either to make bigger cables (decreasing r_i) or else to insulate them (increasing r_m). Wnt (talk) 03:07, 10 September 2018 (UTC)[reply]

Electricity = a flow of electrons

Would it be correct or accurate if I'll defined "electricity" as 'a flow of electrons'? (I know what the article here says, but I'm asking specifically about this definition). 93.126.116.89 (talk) 03:45, 10 September 2018 (UTC)[reply]

No it really doesn't work like that. 173.228.123.166 (talk) 04:29, 10 September 2018 (UTC)[reply]

A flow of protons can also be an electric current carrier. But if the electrons and protons flow together they cancel each other out! Graeme Bartlett (talk) 07:39, 10 September 2018 (UTC)[reply]

A flow of positrons can also be a current carrier, as can a flow of ionic species within a solution...but for a relatively lay understanding of electricity, it's fine to describe it as a flow of electrons as that describes almost all of the electrical phenomena familiar to the average punter. 202.155.85.18 (talk) 07:44, 10 September 2018 (UTC)[reply]

Inside an ordinary metal conductor it is correct to describe an Electric current as a flow of electrons. But Electricity (see article) embraces both this and many other phenomena involving Electric charge, and with magnetism constitutes the phenomenon of Electromagnetism. DroneB (talk) 11:23, 10 September 2018 (UTC)[reply]

"A flow of charge" would be better. A flow of electrons is certainly electricity and it's the common one especially in metals, but so would be a flow of any charge carrier, including positive charges. Andy Dingley (talk) 11:42, 10 September 2018 (UTC)[reply]
"Flow of electric charge" is really the best definition, there are all sorts of electricity that do not involve flow of electrons, besides the ones already notes, P-type semiconductors have electricity that flows in the form of positive charge "holes" in the semiconductor. Of course, the actual Wikipedia article on electricity would have answered the question for the OP sufficiently, so I'm not sure why he didn't look there. According to that article "Electricity is the set of physical phenomena associated with the presence and motion of electric charge." That seems like a perfectly fine definition. --Jayron32 12:01, 10 September 2018 (UTC)[reply]
- The OP actually went out of his way to note that he has looked at the actual Wikipedia article on electricity. -165.234.252.11 (talk) 18:54, 14 September 2018 (UTC)[reply]

Fire has to have heat, fuel and oxygen?

I understood from the article fire that fire needs three things in order to exist: heat, fuel and oxygen. I have gotten some questions on it: 1) Is it always necessary to have oxygen? (I'm asking it because I saw this video on Youtube that says: "to create fire you need 3 things: some fuel, and oxidizing agent normally oxygen, and enough heat to raise the fuel to what known as ignition point.". It seems from his things that there are other oxidizing things that can cause to it. What are the other oxidizing materials for example that can cause fire? 2) Does any electricity take place while having combustion? (in other words there is a relation between the light that we see in an incandescent light bulb that generated by electricity to a combustion of a wood for example?) I'm looking for a relationship between electricity to any kind of combustion. Can I claim that any burning involves electricity characters? When people in ancient times took two stones or woods and rubbed them in each other it caused to ignition as I understand due to electricity in those things. 93.126.116.89 (talk) 19:24, 10 September 2018 (UTC)[reply]

Consider, for example, the act of striking a match. The match will flare, but if there is no oxygen present it will not burn. 86.133.58.126 (talk) 19:28, 10 September 2018 (UTC)[reply]

We discussed the theory behind fire - and we specifically discussed whether matches can burn in anoxic environments - almost one year ago today. Nimur (talk) 01:39, 11 September 2018 (UTC)[reply]

So that's why this sounded so familiar... Yep. See my comments from last time. shoy (reactions) 18:33, 11 September 2018 (UTC)[reply]

Light bulbs used to have a filament in a vacuum. The light produced is not a burning fire, it's simply that the passage of electricity through the filament heats it up, causing it to glow. 86.133.58.126 (talk) 19:34, 10 September 2018 (UTC)[reply]

They still do. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:29, 10 September 2018 (UTC)[reply]

No, mostly they don't. --76.69.47.228 (talk) 03:01, 11 September 2018 (UTC)[reply]

Interesting. What percentage is "most"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:06, 11 September 2018 (UTC)[reply]

Where I live, it's becoming difficult to find filament light bulbs. Supermarkets are hardly stocking them anymore. The country has moved strongly toward LED lamps. Akld guy (talk) 03:27, 11 September 2018 (UTC)[reply]

Assuming you mean ordinary household light bulbs, I don't believe this is much of the reason. I believe our article 76 linked to is correct, and incandescent bulbs of that sort were inert gas fill for a long time. (Halogen also started to become more common although there were always small light bulbs, inside a larger covering if designed as a replacement for ordinary A60/E26 bulbs.) What vacuum light bulbs still exist are specialist or very old ones. Our article mentions smaller lamps but AFAIK even torch light bulbs are usually inert gas. Xenon if they're fancy. I'm not sure about incandescent bulbs used in Christmas lights however. Nil Einne (talk) 10:01, 11 September 2018 (UTC)[reply]

"Fire" is not a scientifically rigorous defined concept. "Heat, fuel, and oxygen" is a good rule for most of the fires directly affecting humans - it's, IIRC, a rule that is taught to help people to avoid dangerous accidents with fire. But you can burn many things that burn in an oxygen atmosphere in a fluorine atmosphere (usually to much more spectacular effect) - it's just that fluorine atmospheres on earth are rare outside of laboratories. A famous combination for rocket fuels is Hydrazine plus nitric acid - what comes out the back of the rocket is certainly flames, but do you want to call this fire? --Stephan Schulz (talk) 20:54, 10 September 2018 (UTC)[reply]

Quoting myself from last year - "Flame, in the conventional sense, requires the three parts of the fire triangle..." In a "normal" fire, that would be your fuel (maybe some wood), and oxygen from the air, and ignition by a spark. In an abnormal fire, you might have a strange fuel - like amorphous boron or tungsten carbide; you might have a strange oxidizer - like nitrous oxide - and the heat of friction caused by boring a tungsten-carbide drill into a gas-pocket, resulting in an ignited BLEVE - a fiery hazardous material explosion. You can even get fire with no oxygen at all: instead of oxygen, you can burn with fluorine or chlorine - which is certainly not a safe thing to do at home!

As Stephan Schulz correctly points out, the term "fire", as we use it in day-to-day speech, is not really clearly defined. If we want a technically-accurate definition that meets our intuitive and normal use of the word, we might say that fire is any exothermic oxidation reaction that releases gases that are hot enough to incandesce.

From a practical perspective, we might defer to the definitions used by the experts: say, the National Fire Protection Association, a fire safety advocacy group in the United States. In their extremely thorough glossary of technical terms, they define "fire products": flame, heat, smoke, and gas; among the hundreds of definitions they provide for entities relating to fire, they also have some half-dozen definitions specifically for the word "fire," with excellent citations for each. For example, in one case, they define: "a rapid oxidation process, which is a chemical reaction resulting in the evolution of light and heat in varying intensities." In another usage, they define: "any instance of destructive and uncontrolled burning, including explosions."

The specialist - whether they're a fire-fighter or a physicist - might use the word "fire" with many different meanings in different contexts. The relationship between flame and electricity is also quite complicated: electricity can cause certain types of fire, and can be caused by certain types of fire (in the form of gases that get ionized by the heat of the flame). In the most common cases that apply to the study of fire, we would consider electricity to be a source of heat and/or spark for an otherwise conventional chemical flame - so you'd still need fuel (like a wooden material) and oxidizer (like air in the room). Here's one of the frightening famous Christmas Tree Fire Safety video from NFPA. Electric wires that are frayed or overheating can cause a huge conflagration in a real hurry, "with flashover occurring in less than one minute." When you reach flashover, your fire is so exothermic that it no longer spreads chemically, but actually ignites distant objects entirely via the emission of infrared radiation. Most humans don't really have a great appreciation of this fact - a fire that's about three inches in radius is controllable and extinguishable, but once it gets a little bit bigger than that - the physics gets weird, and the practical consequences get really bad.

Nimur (talk) 01:57, 11 September 2018 (UTC)[reply]

[is there] a relation between the light that we see in an incandescent light bulb that generated by electricity to a combustion of a wood for example? As explained above, light bulbs work by the path electricity -> heat (see Joule effect) -> radiation (see Blackbody radiation). For fires, it depends; there is an appreciable amount of blackbody radiation from soot particles etc., but in many cases it is due to intermediary reaction species undergoing chemiluminescence (that is why you can see blue flames in Bunsen burners, even though the flame temperature there is lower than 2000K yet blackbody radiation is blue for about 6500-7000K).

I also questionthe assumption that flintstone fires involve electricity. According to Flint#To ignite fire or gunpowder, which unfortunately has poor sourcing on that point (the only ref is [2] which I would not imagine to be very accurate scientifically), "sparks" are created by exposing reactive iron or iron sulfide to the atmosphere; we are talking about this spark, not that spark. Tigraan^{Click here to contact me} 08:27, 11 September 2018 (UTC)[reply]

A well-designed fuel-burning lamp from the Victorian age onwards is brighter and whiter than black-body radiation, but this doesn't usually involve chemiluminescence, it uses a gas mantle and candoluminescence. This is a device for holding tiny quantities of rare-earth elements so that they can be heated by the flame. They then (like chemiluminescence) produce colours of light which are bluer than the black-body colours, but they do it by physics and spectroscopy (and aren't consumed) rather than by a chemical reaction. Andy Dingley (talk) 09:49, 11 September 2018 (UTC)[reply]

There is a difference between oxidation (in the chemical sense) and fire. You can also have fires which don't involve any oxygen. But we live on a planet with a lot of free oxygen in the atmosphere, so that's by far the most common oxidiser, and so we tend to assume that it's the only one.

Look at some of the chemistry for liquid propellant rockets. These use a rapid combustion (i.e. a fire, and an oxidation) to release energy as mechanical thrust. They have to bring their own oxidisers with them, just because they need so much of it and it would be difficult to supply enough of it by scooping it from the atmosphere, not just because that also allows them to operate in a vacuum and so reach space. Many different sets of chemistry have been used to make rocket fuels, and there are several used for the oxidiser too. See liquid rocket propellant or read Ignition!. ISBN 0813599199. (neither of these wiki articles are very good, but Ignition! is excellent and newly reprinted). A popular oxidiser is liquid oxygen, because it's relatively cheap and safe and it works well. Unfortunately it has to be kept very cold to liquefy it, so it can't be stored in the rocket. So the military use nitric acid, or nitrogen tetroxide instead. There are also exotic chemicals like chlorine or fluorine compounds - these will certainly give "a fire" just like oxygen, if you did an experiment in an atmosphere rich in them. Andy Dingley (talk) 09:43, 11 September 2018 (UTC)[reply]

As far as a connection between the chemical reactions that we call "fire" and electricity, the two halves of the reaction mixture can be segregated such that in order for the oxidation reaction to proceed, electrons must cross through a conductive material. This allows us to extract work in the form of electrical energy. Such an arrangement is known as a fuel cell, the most common of which is based on the reaction of hydrogen combustion, but they can also be designed around the combustion of the regular hydrocarbons we more commonly use as fuels. What this illustrates is that there is an electrical interaction taking place in all combustion reactions (and, in fact in all chemical reactions) involving changes in the electronic structures of the atoms, ions and molecules in question, but without particular contrived situations being deliberately created to take advantage of the electron flows, the relationship to electricity is trivial. 139.194.67.236 (talk) 10:22, 11 September 2018 (UTC)[reply]

What parameters do you need to describe an audible sound?

Frequency and amplitude of the wave, duration, intensity? Is that all? --Doroletho (talk) 21:04, 10 September 2018 (UTC)[reply]

Wikipedia has some good information at Sound pressure and Decibel#Uses. Dolphin (t) 21:46, 10 September 2018 (UTC)[reply]

Depends what you mean by "sound". Describing or synthesizing the sound of a musical instrument would take many more parameters (in the old days you'd define a sound envelope by attack, sustain, release, and decay, at different frequencies and amplitudes. Most sounds would have a complex timbre or mixture of frequencies and still be perceived as one sound. - - Nunh-huh 22:22, 10 September 2018 (UTC)[reply]

Basically, I had human speech in mind. But I imagine music is also complex and well-researched, and there must be good references about this. --Doroletho (talk) 23:59, 10 September 2018 (UTC)[reply]

Free books! Julius Smith, a professor at the Stanford Center for Computer Research in Music and Acoustics, has made all of his textbooks available at no cost. He's a world expert on the practical mathematics to represent music and sound.

The starting point for a representation of a sound is a full waveform recording, which may be digitized; and from there, it takes a lot of math and science to compress the sound in a manner which is perceptually similar to the original waveform using as few parameters as possible. A good audio compression scheme can achieve thousand-to-one compression, or better, in ideal circumstances - in other words, you can describe a sound using just a few parameters. The more parameters you use, the more accurately you can re-create the original sound with minimum distortion; phrased another way, the more parameters you use, the more different types of sounds you can accurately and uniquely describe.

Nimur (talk) 04:40, 11 September 2018 (UTC)[reply]

...Regarding human speech: here's a link right to the chapter on the Vocoder, a review of one historically-important effort to parameterize human speech at Bell Labs. These books are great - they're thorough but simple enough to understand, and Julius cites more references cited than you'll probably read. Nimur (talk) 13:52, 11 September 2018 (UTC)[reply]

Properties of sound are often simplified to concepts like sound intensity (amplitude), pitch (fundamental frequency), and Timbre (related to waveform shapes). There are also psychological effects of sound, which include things like loudness. --Jayron 32 13:57, 11 September 2018 (UTC)[reply]

September 11

Planets with natural satellites with natural satellites?

Are there any planets (or so-called "dwarf" planets) that have natural satellites with natural satellites? As far as I know, there aren't any. But I've never heard anyone definitively say that there are none that we know of. A Quest For Knowledge (talk) 01:10, 11 September 2018 (UTC)[reply]

see http://curious.astro.cornell.edu/about-us/44-our-solar-system/the-moon/general-questions/104-can-moons-have-moons-intermediate Graeme Bartlett (talk) 01:19, 11 September 2018 (UTC)[reply]

We don't know of any. Most moons around planets have Hill spheres too small to support significant satellites, and our Moon has the added problem of mascons making many lunar orbits unstable. However there may have been some in the past. Rhea (a moon of Saturn) has been speculated to have rings, and the equatorial bulge on Iapetus may have been formed by a de-orbiting subsatellite. (While Iapetus has a significant Hill sphere, more than any other moon because of its size combined with its distance from its parent planet, it was tidally locked to Saturn, and therefore ended up rotating slowly enough that its subsatellite would have suffered significant tidal deceleration. This process could have happened on some other moons, but only on Iapetus and perhaps Oberon would the process take long enough that the equatorial ridge wouldn't have been obscured by later impacts.) Double sharp (talk) 01:32, 11 September 2018 (UTC)[reply]

We don't find such systems in our own solar system, and we probably won't find them elsewhere, because they are unstable ...for reasonable and realistic mass and distance parameters. In astronomy we have a special appreciation for the statistical likelihood of observing an astronomically-unlikely event amidst an astronomically large sample-size; but at this time, our best observational methods still do not allow us to see such detail as a planet's satellite except for those planets that are inside our own solar-system. Even our own solar system is sparsely explored, and we have very limited observations of our outer planets. So, it's unlikely we'll see such a moon-with-satellite within, say, the next few generations of human lifetimes.

A standard homework problem for students of astrophysics is to calculate the number of orbits (years) until an n-body system - such as a sun/planet/moon/satellite system - becomes unstable. Here's an example from Cornell University's Astro 3303 class. The hard part is making sure your numerical method isn't more unstable than the physical system! The standard method is unfortunately not suitable - it is this homework-problem that tragically results in the loss of mathematical naïveté for many an up-and-coming computational physicist. Nimur (talk) 04:52, 11 September 2018 (UTC)[reply]

It may be thinkable on an Polar orbit where the "moon-moon" would keep an equal distance to the moon and the planet, but it would remain a delicate balance act to stay there for billions of years. Even more close to impossible wonder would be the history how it got there, but then, our earth is a real wonder too with all the different, needed ideal conditions to support life, met on a single planet. --Kharon (talk) 05:04, 12 September 2018 (UTC)[reply]

Not only would it need to be in a polar orbit, but it would need to be in a planet-synchronous orbit (analogous to a sun-synchronous orbit) in order to maintain a constant distance from the planet's surface. To maintain stability of this orbit the tendencies for the orbital parameters to evolve would need to cancel one another. Over the periods of time relevant to the evolution of the solar system such an orbit would be vanishingly unlikely to remain stable. Changes in the moon's equatorial bulge or radiation pressure due to solar output changes could be significant enough to gradually lead to destabilization and a reduction in orbital inclination. 114.124.144.185 (talk) 06:27, 12 September 2018 (UTC)[reply]

Polar orbits would tend to be unstable to the Lidov–Kozai mechanism, in which inclination is traded for eccentricity. Double sharp (talk) 06:30, 12 September 2018 (UTC)[reply]

Nereid may be a binary satellite of Neptune according to this paper. 114.124.144.185 (talk) 05:50, 12 September 2018 (UTC)[reply]

Your link is to the mythological entity, the relevant article is Nereid (moon). {The poster formerly known as 87.81.230.195} 2.122.60.253 (talk) —Preceding undated comment added 17:15, 12 September 2018 (UTC)[reply]

That paper is very old, though: it's pre-Voyager. So this may have been refuted by newer data. Double sharp (talk) 08:12, 12 September 2018 (UTC)[reply]

Default human template

I have heard that the "default" human template is female, and in the (perhaps artificial) absence of testosterone during development a female body type will result, irrespective of even the sex-determining chromosomes.

However, is this status of "default" of any medical significance?--Leon (talk) 10:38, 11 September 2018 (UTC)[reply]

This "default" is due to the XY sex determination system used in mammals. The Y chromosome has relatively few active genes, mostly serving as a signal to activate the male pattern rather than the female. There are many more genes on the X chromosome. The different sizes (and, thus, different genetic contents) means that any gene form (allele) present on the X chromosome will be expressed, regardless of questions of dominant or recessive alleles. This makes certain genetic disorders (red-green colorblindness, hemophilia, etc) more common in males than females. --Khajidha (talk) 13:41, 11 September 2018 (UTC)[reply]

To elaborate for pedagogical value, only around half of humans have a Y chromosome, so obviously it can't contain any genes necessary for non-biological males. Conversely, the X chromosome behaves more or less like any other chromosome; most of its genes have nothing to do with biological sex or reproduction, since, as noted, there is no "trigger" to make a human fetus develop as female. The sex chromosomes evolved from a regular pair of autosomes; since only males inherit a Y chromosome, this means there's a massive evolutionary pressure to delete genes from said chromosome, which is what has caused it to become so small. In some mammals it consists of only the single TDF/SRY gene, which is the gene that triggers male development. --47.146.63.87 (talk) 19:28, 11 September 2018 (UTC)[reply]

I don't follow the evolutionary pressure bit. Why is there this evolutionary pressure?--Leon (talk) 19:35, 11 September 2018 (UTC)[reply]

Y chromosome § Origins and evolution: any alleles on the Y chromosome have a ~50% chance of hitting a dead end: if the possessor of the chromosome has only female offspring, the chromosome dies with them. This is why there's a single Y chromosomal Adam we can trace: the Y chromosome alleles from all other human males living at the same time have died out. Additionally, if a Y chromosome allele were essential for all members of the species—not just males—it would be lethal for any female offspring of the man carrying that allele, since they wouldn't have it. So, any genes that were on the X/Y chromosome's ancestral autosomes that are beneficial to the female phenotype tend to get removed from the Y, leaving only the copy on the X, which is inherited by both sexes. --47.146.63.87 (talk) 21:56, 11 September 2018 (UTC)[reply]

Yes, many if not most intersex conditions are the consequence of the interplay between components of the sex-determination system. For example, in androgen insensitivity syndrome, a fetus with one or more Y chromosomes will nevertheless develop a female phenotype, often with infertility. In this condition, the Y chromosome is present and functioning, but androgen receptors are defective, meaning they don't respond normally to testosterone. The gonads are triggered by TDF to begin developing as testes and secreting testosterone, but androgen receptors don't respond to it, so to varying degrees the body continues to develop along the "default" female pathway. --47.146.63.87 (talk) 19:28, 11 September 2018 (UTC)[reply]

All very interesting. Thank you!

A follow up question: I've just read something on X-inactivation, and noted the tortoiseshell cat as a typical example of how the differences between the two X chromosomes that females have can have an interesting effect. Is there anything as visually obvious as this that happens in humans?--Leon (talk) 21:10, 12 September 2018 (UTC)[reply]

As far as I am aware, no. X-inactivation doesn't mention anything. --47.146.63.87 (talk) 06:14, 15 September 2018 (UTC)[reply]

There can be phenotypic variation, but nothing so striking as that. Double sharp (talk) 08:12, 15 September 2018 (UTC)[reply]

Is there a material that it's 100% non electrical conductive?

We used to say that wood or other materials such as plastic are not conductive for electricity, but based on what I understand everything is conductive but some of the materials are low conductive while others are highly conductive, and all materials have a measurement on a scale of the conductivity. Is it correct? Is there no an exception for material that is 100% non conductive? 93.126.116.89 (talk) 15:18, 11 September 2018 (UTC)[reply]

Some sort of Superinsulator? DMacks (talk) 15:22, 11 September 2018 (UTC)[reply]

How much theoretical physics do you want to use in evaluating your answer? Even if no electrons flow, an electric current may still occur: the displacement current. This is not even one of those weird quantum-mechanical, "only-there-in-the-statistical-sense" concepts! Displacement current is a real phenomenon and is a key component of classical electrodynamics. So even if you had a material that were somehow completely able to block the flow of charged particles, you still could not preclude the accumulation of electric charge outside of the boundaries of that material - in other words, even if you had a perfect insulator, electric current would still flow, and the stuff surrounding the insulator material would function as a capacitor. In yet other words, even if you magically prevent matter (electrons and ions) from moving, by building a super perfect insulation material, it is a law of nature that the photons will still get through and carry your very real, very physical electric current without the motion of any electron or other charged particles - we might say this is spooky action at a distance (although it travels only at a finite speed) - and we'd be in good company - that was the title of Chapter 23 in one of the most important physics books ever written!

This ingenius insight is attributed to James Clerk Maxwell, who corrected the faulty Ampère's law by generalizing it into a more correct conservation law - and it is this very same generalization from whence all of general relativity ultimately derives. It is no coincidence that this equation is the one which defines the speed of light, whether you consider its speed inside a material or through a totally empty vacuum.

One must work one's way up in this world: here's a few good books to get you started:

Physics for Scientists and Engineers (Mosca & Tipler)
Introduction to Electrodynamics (Griffiths)
Classical Electrodynamics (Jackson)

...so you start with the advanced science-and-engineering stuff, and spend several years working your way up to the introductory material, and finally you read the really easy "classical" stuff. If you don't like those books, we also have a thorough list of textbooks in electromagnetism.

Nimur (talk) 16:31, 11 September 2018 (UTC)[reply]

Over what distance? It's a (surprising) aspect that something isn't a perfect insulator immediately, but the current falls off exponentially with depth. So something that you think of as an insulator (or in a related case, something that's opaque to light) will still transmit or conduct it, if it's in a sufficiently thin layer. Andy Dingley (talk) 16:59, 11 September 2018 (UTC)[reply]

That's technically correct that nothing is perfectly insulating, but it depends where you put the cutoff. Except in vacuum or maybe in a material at absolute zero, there is pretty much never zero free charge carriers, so any simple model (e.g. the Drude model) will tell you charges move (i.e. there is current) if there is an electric field. However, if you look at Electrical_resistivity_and_conductivity#Resistivity_and_conductivity_of_various_materials, you can see that the conductivity of metals is always above 10^6 S/m while that of common insulating materials is below 10^-6 (or 10^-4 if damp wood counts). The ratio between the two limits (worst conductor vs. worst insulator) is gigantic (10^10 to 10^12) - to put that in perspective, that is the same ratio as the height of Mount Everest to the width of a hair. If you were evaluating non-smoothness of Earth's surface, you would surely assume that lengths below the millimeter are outside your cutoff - you consider those as flat even if they are technically not perfectly flat. (This answer does not talk about semiconductors because my knowledge of those boils down to "here be quantum").)

You might also be interested in our article about electrical breakdown (whose most common manifestation is thunder inside "insulating" air). Tigraan^{Click here to contact me} 17:17, 11 September 2018 (UTC)[reply]

Gravity

What's the diff tween a gravity wave and a graviton? — Preceding unsigned comment added by 80.2.22.73 (talk) 23:35, 11 September 2018 (UTC)[reply]

A Graviton is a purely hypothetical part(icle) that some scientists believe exists. A gravity wave is actually more correctly a Time dilation-wave (also measured/noticed that way) that the mainstream of physical science decided to call "gravity wave", probalby because they assume such waves are caused when 2 black holes unite into one. --Kharon (talk) 04:09, 12 September 2018 (UTC)[reply]

A gravity wave is a wave in a fluid where the restoring force is gravity. This is the kind of wave that you see when wind blows on the ocean; if you're a meteorology nerd, this is also the kind of wave that causes certain high cloud formations. Here's a cool image of one from the NOAA Cool Image website at the Storm Prediction Center. Here's some more imagery from the MODIS satellite: Gravity Waves, from NASA Goddard. Oh, and here's a special issue of the peer-reviewed journal Atmosphere: Atmospheric Gravity Waves, the March 2017 issue, with just boatloads of science in it.

A gravitational wave is a relativistic phenomenon that has been theorized for a long time and only recently measured. These are very low-amplitude, self-propagating changes in the shape of the universe that occur when very very dense massive objects move. Ever since the theoretical math we call relativistic gravity was first studied - about a hundred years ago - we knew this should happen - but it was only 2016 when we first had instrumentation sensitive enough to measure this very tiny effect. For this achievement, and a lifetime of scientific contributions, the 2017 Nobel Prize in Physics was awarded to three scientists. Here is a video by some guy named Rainer Weiss hosted on Youtube, in which he just drones on and on about gravitational waves for like three quarters of an hour. If you can handle it, you'll glean little bits of wisdom: for example, gravitational waves don't just come from black holes - this other guy named Albert does a calculation for a tiny gravitational wave coming out of a passing train, but he said it was way too small to notice - praktisch verschwindenden.

A graviton is a mathematical description of the propagation of gravity as a localized, quantized amount of change. The math for this description does not work out very easily - so most scientists do not use this mathematical formulation. It is studied by certain communities of theoretical physicists. For a reputable source, here's a little bit of discussion about quantization limits on the LIGO - but there's more to worry about quantization noise, shot noise, photons, and phonons - these are far more practical concerns than any quantization limits of the gravitational wave itself. In fact, there's more gravitational noise from seismic vibrations - not because of the vibrations themselves (which are low frequency and can be easily measured and compensated), but because the compression waves cause mass density changes in the soil which then affect the conventional Newtonian gravity measured by the detector! The point is: no real scientist is measuring gravitational quantization; even if it did exist, it's way below the regime of what we can measure with today's experimental physics.

(It's almost as though we, mere denizens of the Wikipedia Reference Desk, can actually find free publications authored by professional experts who know about this stuff!)

Nimur (talk) 04:50, 12 September 2018 (UTC)[reply]

One central issue with all that is often overlooked tho. Its still unknown how gravity exactly works, as Nimur also circumscribe in his description of this graviton that may actually not exist in reality. Till now all science around gravity is actually better tagged as "phenomenology" than science. --Kharon (talk) 06:20, 12 September 2018 (UTC)[reply]

I'm sorry,... is it simply your own esoteric view that "all science around gravity" is not actually science, or can you cite a reference for that statement?

The Reference Desk is not a place to spout your own original pseudoscientific research. If you are not qualified to help respond to questions by finding encyclopedic-quality resources, you should not contribute answers to queries here.

Nimur (talk) 14:20, 12 September 2018 (UTC)[reply]

I think I see Kharon's point (and presume he's including phenomenology as science). However I'd also say that he was out of date. It's a fair description of the period from Newton to Einstein, but was invalidated by GR. Andy Dingley (talk) 15:13, 12 September 2018 (UTC)[reply]

GR describes the phenomenon of gravity but we don't have a theory of how it works (quantum gravity) the way we have a theory of electrodynamics. There's a ~ 10 minute youtube interview with Freeman Dyson[3] where he says there might be no gravitons or quantum gravity, and that gravity might instead be more like a temperature, a statistical property of bulk matter. I watched that recently and have actually been meaning to ask about the idea here. I see now that he also has a longer talk[4] so I guess I'll watch it when I get a chance. 173.228.123.166 (talk) 16:00, 12 September 2018 (UTC)[reply]

So you're broadly agreeing with my comments on Kharon's post, but seeing the "Till now" as much closer? I can go with that. Although even then, you're arguing 50-ish years vs. 100. Even post-GR theories have been around for some time now. Andy Dingley (talk) 19:36, 12 September 2018 (UTC)[reply]

Yes basically, afaict the "till now" extends to the present. GR is considered an unphysical theory because it's not quantized. And there are a bunch of approaches like superstrings that have too many loose ends to be considered theories the way QED is a theory. So at present, we do not have a physical theory of gravity. This is cool and hip, but it's still "out there". I don't understand much beyond the popular level, but the quantum gravity article describes some of the unresolved issues. 173.228.123.166 (talk) 21:05, 12 September 2018 (UTC)[reply]

September 12

Jellyfish

Can you assume that there are no jellyfish in the sea after the summer months (I Mean now and in the next month). Is that something restricted to the summer? I have south Spain in mind, other places on the Mediterranean might be interesting. — Preceding unsigned comment added by 37.252.180.169 (talk) 03:24, 12 September 2018 (UTC)[reply]

There is a Spain Travel forum post on that subject; you might try a query there: "Jellyfish summer 2018 - Spain Forum". www.tripadvisor.com. TripAdvisor. June 26, 2018. —107.15.157.44 (talk) 05:57, 12 September 2018 (UTC) ... Reports that I could find regarding beach closures in Spain due to jellyfish are dated April & May (2018).[reply]

I have found some random comments in travel sites too besides anecdotal evidence provided by locals. But I was wondering from a more scientific point of view. Does winter decimate jellyfish populations? 31.177.99.137 (talk) 13:16, 12 September 2018 (UTC)[reply]

If there were no jellyfish in the sea at all, where would the next generation of them come from? ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:57, 12 September 2018 (UTC)[reply]

I obviously mean on the sea shore. But even then, it might be possible that there's no specimen of some living being in winter, only eggs that will hatch in the next season. 31.177.99.137 (talk) 13:16, 12 September 2018 (UTC)[reply]

Thanks for clarifying. If it was obvious, I wouldn't have asked. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:21, 12 September 2018 (UTC)[reply]

In a sense, the next generation of jellyfish will come from polyps ! What we usually think of as a jellyfish is actually a jellyfish medusa - the final sexually reproducing phase in a complex life cycle. Medusae have relatively short lives compared to the polyps that bud them. Gandalf61 (talk) 13:24, 12 September 2018 (UTC)[reply]

"Patterns of jellyfish abundance in the North Atlantic" discusses reasons for seasonal variation of jellyfish in the North Atlantic. It looks as if in the open ocean, jellyfish populations peak with prey populations, whereas nearer shore (in the continental shelf area) they peak with surface temperature. (The paper also states that in the shelf area "advection and aggregation" affect jellyfish population, and this appears to be advection and aggregation of prey, which leaves me puzzled.)--Wikimedes (talk) 07:16, 13 September 2018 (UTC)[reply]

Advances in consumer facing industries

Why is it that consumer facing industries such as automotive, retail, personal banking etc seem to advance faster than corporate industries such as legal, investment banking, construction etc especially in terms of IT and digital? Clover345 (talk) 06:33, 12 September 2018 (UTC)[reply]

Buisiness and government will want to enter into long term contracts, perhaps using tenders. They also want stability and assurance in their IT systems, so they don't just want to take whatever is the latest that will mean they needs to change instructions and cope with a new bunch of issues. Operating system changes for example mean that applications that use them have to be changed, and then retested. There is a lot of expense in changing unnecessarily. Some industries are very conservative and may be regulated to avoid changes. This includes aviation. Graeme Bartlett (talk) 09:49, 12 September 2018 (UTC)[reply]

I'd say manufacturers strive to make consumer products that look shiny but fall apart in a couple of year. Industrial equipment, on the other hand, is made to last, often some decades, and it normally does not matter how it looks. --31.177.99.137 (talk) 13:24, 12 September 2018 (UTC)[reply]

Planned obsolescence is the tradeoff for products being relative inexpensive. If you want an industrial-strength laptop PC, for example, you're going to pay a lot more than what you would get at Best Buy. Related to Project management triangle. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:22, 12 September 2018 (UTC)[reply]

Quantum CAP Theorem

What are the limits on syncing up distributed Quantum machine learning?

I.e. has anybody done the math on a quantum version of the CAP theorem?

In short, given a swarm of killer robots, how do you ensure that they all learn together?

Hcobb (talk) 14:08, 12 September 2018 (UTC)[reply]

Fluid dynamics question.

If you have water flowing down a vertical steel pipe, and both the water and pipe were at 25 C. Now, if both the water and pipe were at 50 C, water would flow faster, because of this thing called friction. Change in viscosity with temperature. So my question is, which would flow faster, if the water were at 25 C and pipe at 50 C, or water at 50 C and pipe at 25 C. As far as I know, there is no difference with water flowing in a horizontal pipe, only vertical pipe. Thanks. 12.239.13.143 (talk) 18:17, 12 September 2018 (UTC).[reply]

If we can assume laminar flow i.e. no cross-currents perpendicular to the direction of flow, nor eddies or swirls, and that the fluid is incompressible and Newtonian, the empirical Hagen–Poiseuille equation will be useful, see Hagen–Poiseuille equation#Equation. It requires knowledge of the liquid's dynamic viscosity μ which is a function of temperature shown at Viscosity#Dynamic-viscosity. See the theoretical development of laminar Pipe flow at Hagen–Poiseuille_equation#Derivation and Hagen–Poiseuille flow from the Navier–Stokes equations. DroneB (talk) 20:53, 12 September 2018 (UTC)[reply]

I don't see how this is useful, my question was about temperature and not pressure. And I am not comparing different materials with same liquids, or different liquids with same pipe materials. Only same liquid and same piping material. Either way, I think the answer I was looking for is: cooler pipe cooling the hotter water, or cooler water cooling the hotter pipe - whichever is slower. And whichever answer that is, what are materials where the opposite is true, for different piping materials. 12.239.13.143 (talk) 22:56, 12 September 2018 (UTC).[reply]

While DroneB did miss the point of your question, I do not see what their answer has to do with pressure. (I also strongly doubt Hagen-Poiseuille applies for reasonable values of pipe diameter and flow speed for water.) The answer does make a decent job of explaining why temperature impacts viscosity (which impacts friction) but your original post seems to acknowledge that.

Friction is driven by the (viscous) boundary layer in the liquid near the surface, so what matters is the water's temperature. Now, of course, thermal transfer between pipe and water means that "the water's temperature" can hardly be fixed different from the pipe's (even if you try, water temperature near the pipe will likely not be at the regulation temperature), and that thermal properties of the pipe will eventually matter; but good luck on quantifying such an effect. Tigraan^{Click here to contact me} 11:28, 13 September 2018 (UTC)[reply]

This would be a pretty gnarly set of differential equations, one for heat transfer and one for flow, doable but tedious. In an ideal world where everything stays at a constant fixed temperature, you could set up a numerical solution with a computer program. In the real world, I suspect that the pipe and water would quickly come to temperature equilibrium, especially if the pipe is metal. shoy (reactions) 13:27, 13 September 2018 (UTC)[reply]

In order for the question to be "interesting but solveable" I would assume that the pipe is long and has large diameter...that means we have pretty good equilibrium of the pipe temp with the outer layer of water and a gradient towards the center that is at the supply temperature. That gets away from a pipe that is thin enough for temperature to equilibrate all the way to the center (making the question pointless). DMacks (talk) 15:26, 14 September 2018 (UTC)[reply]

I read somewhere that the maximum speed for rain drops is 19 mph. So does that mean, water falling down a vertical pipe - whether huge diameter like 10 meter, or 1 inch - neither water will fall more than 19 mph? I'd like to see some models for hot water falling down hot pipes vs. room temperature water falling down room temperature pipes, even for a pipe that could be an inch in diameter. 67.175.224.138 (talk) 16:27, 15 September 2018 (UTC).[reply]

According to the viscosity of water in different temperatures as listed here, the change is much more significant if the water temperature changes. Additionally Hagen–Poiseuille equation focuses on pressure, which is not very helpful for estimating flow speeds, because the actual limits on flow speed doesnt lie in pressure but in already mentioned flow state (laminar/turbulent) which in Fluid mechanics is measured/calculated in/by the Reynolds number which is better aka implies less resistance and thus faster flow for higher viscosity (as long as its not a Non-Newtonian fluid, which luckily (else flow is getting very complicated) water is only in its Slush-state. --Kharon). (talk) 11:26, 16 September 2018 (UTC)[reply]

Desire to raise legs

I am familiar with restless legs syndrome, albeit only from descriptions, and am almost certain that I am not talking about it!

Is there a name for the seemingly inexplicable desire to raise one's legs? Specifically, to a higher level than one's torso when lying down.--Leon (talk) 21:12, 12 September 2018 (UTC)[reply]

That's a new one, unless you're elevating them for circulation reasons. What have you found on Google so far? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:31, 12 September 2018 (UTC)[reply]

You might mention that to your doctor. If you also feel faint when you stand up, that is orthostatic hypotension and could be related. I've seen it claimed that sleeping with your head elevated is good for many reasons, so instinctually doing the opposite sounds slightly amiss. ObIncantation: we can't give medical advice here bla bla. 173.228.123.166 (talk) 06:50, 13 September 2018 (UTC)[reply]

Leon is not looking for medical advice, he is not even saying that he has a medical complaint. I wonder why anyone would suggest he see a doctor or suggest that the condition he asks about is "slightly amiss". I have been in nursing most of my life and have never encountered the idea that sleeping with your head elevated is good - although it is customary. Richard Avery (talk) 13:06, 13 September 2018 (UTC)[reply]

The OP should speak for himself. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:10, 13 September 2018 (UTC)[reply]

I'll speak for myself - I corroborate with Richard. I'm just curious. I'll add that this desire seems to be coupled with a general desire to get into strange bodily positions, but what I have already described is the most obvious manifestation of this.--Leon (talk) 16:17, 13 September 2018 (UTC)[reply]

Where have you seen this? ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:13, 13 September 2018 (UTC)[reply]

If not circulatory maybe it's psychological, from some kind of anxiety? Regarding thing about sleeping with head elevated, here's an example:[5]. Obviously not RS but it's an example of some of the (possibly bad) info that's out there. Actually a quick web search shows the author is a "medical anthropologist" who writes lots more such unorthodox stuff. So skepticism is warranted. 173.228.123.166 (talk) 17:01, 13 September 2018 (UTC)[reply]

September 14

Defibrillator units

I was watching an early episode of Law & Order (season 2, episode 5 "God Bless the Child") in which hospital staff use a defibrillator in an attempt to resuscitate a small child. The doctor holding the paddles instructs a nurse to set the device to "18 watts per second". Now I'm no brilliant physicist, but if I remember rightly, watts are already joules per second. That would make this unit joules per second per second which would be rate of change of power. I googled around and there are other sources that refer to watts per second as the unit for defibrillation such as this one (which seems to get the relationship between joules and watts wrt time backwards). Some other sources quote doses in watt seconds, which would make more sense, as that reduces to joules but the terminology makes it clear to the operator that the machine is delivering a power for a time period. Does anyone know how the units of defibrillators are normally used in a typical hospital setting? 114.124.175.125 (talk) 00:49, 14 September 2018 (UTC)[reply]

Here is a great review article from the American Heart Association: Defibrillation - 2010 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations. It's part of a whole series of scientific review, published in the October 2010 issue of Circulation (Vol. 122, No. 16), in which a panel of experts detailed the scientific studies and made recommendations for clinical use.

In scientific literature, defibrillation is characterized using several parameters: among them are the paddle type and placement; the total energy; the waveform of the shock; the number of shocks; and the energy level per shock, measured in Joules.

In a clinical setting - like a hospital - scientific accuracy might be sacrificed during common use. If the machine is an AED - an Automated external defibrillator - the operator might have limited or zero medical and scientific training. Though in many places, use of an AED is restricted to only those emergency responders who have certain levels of professional qualification - in other places, the recommended procedure is for the first person near the victim - trained or otherwise - to use the machine. So you can see how the operator might mess up some of the details of the physics.

"Watts per second" is a nonsensical physical unit, at least in the context of measuring an electrical shock during a medical defibrillation procedure. Even if we're generous and we assume the fictional character misspoke, and meant to say "eighteen watts-times-seconds," that's equal to eighteen joules, and it's not a meaningful or reasonable quantity of energy for a defib. Defib shocks are normally in the range of 100 to 300 joules. The duration of time that this energy is delivered is very short - different machines use different waveforms, but all the energy is usually delivered in the first 15 or 20 milliseconds. Normally this would be characterized by describing the energy (in Joules) and the waveform (by naming it, out of a small set of common waveforms like "Pulsed Biphasic Waveform" or "Biphasic Truncated Exponential Waveform"). If the user were a physicist and felt like wasting time during the emergency, they might convert to using watts as the unit of measurement, and compute somewhere between 1 and 2 kilowatts during the application of the shock.

As always, the easy way out is to forgive a little poetic license in a work of fiction - they shouted some technobabble for dramatic effect, and the show's writers probably spent less time researching the topic than I did just now. But hey, in addition to being a volunteer science-enthusiast, I'm also a volunteer emergency-responder and I like to know a little bit of theory in case it ever saves a few seconds during an emergency.

You can sign up to learn more about AEDs; a great resource that's probably available in your community is the Red Cross AED training class - they'll probably encourage you to get a CPR refresher too. "The average response time for first responders once 911 is called is 8-12 minutes. For each minute defibrillation is delayed, the chance of survival reduces by approximately 10%." Or, as I like to phrase it: the professionals are, by definition, the second responders to your emergency: you are the first responder - so why not take some time to prepare for it now?

Nimur (talk) 05:00, 14 September 2018 (UTC)[reply]

Eighteen joules is certainly a reasonable quantity of energy for a pediatric defibrillation (as implied by the original question). Generally the "dose" is 2 J/kg for the first attempt, so 18 joules is right for a 9 kg (20 lb.) child. - Nunh-huh 19:12, 14 September 2018 (UTC)[reply]

I second what Nimur said about the value of getting even minimal training. AEDs are widely deployed in public places now and stupid-easy to use. Some are just "slap the pads on two places on the chest--there is a pictograph on the pads themselves and it doesn't matter which goes where; press the big button and then follow the instructions that the device's voice tells you" (things like "call 911; hands off; shock delivered" and a metronome for chest compressions). And hands-only CPR is pretty simple too (plus a great soundtrack!). Some key AHA data are that the survival rate for cardiac arrest that occurs outside of a hospital setting in communities where AEDs are available and people have AED/CPR training is nearly 40%, vs <10% overall. Part of the basis for improvement is that 23% of those patients initially have shockable rhythms. DMacks (talk) 15:16, 14 September 2018 (UTC)[reply]

I agree that it's useful to be trained in AEDs (even a bonehead like me can follow their instructions), but they're entirely a side issue to the question. The OP specified that the scene took place in a hospital, not at the scene of a first respondent attempting to use an AED. Matt Deres (talk) 17:05, 14 September 2018 (UTC)[reply]

Coming back to the original scenario (thanks Matt Deres for keeping us loosely on track!), doi:10.1001/jama.2010.1576 has the interesting conclusion that "Among hospitalized patients with cardiac arrest, use of AEDs was not associated with improved survival." It had no statistically significant effect on those with shockable rhythms (and these accounted for a lower percentage of patients than out-of-hospital case) and a detrimental effect on those without shockable rhythms. They propose that a major effect is that AED delays CPR and other emergency treatment actions. A systematic review study[6] reminds that although AEDs in hospitals are not effective, the basis for comparison is normal external defibrilation (which is presumably promptly available in that setting). I haven't yet found data for effectiveness of non-external. DMacks (talk) 22:38, 14 September 2018 (UTC)[reply]

Did Prohibition Reduce Drinking?

Our article on Repeal of Prohibition in the United States says that:

Alcohol consumption declined dramatically during Prohibition.
Violent crime did not increase dramatically during Prohibition.
Organized crime did not increase during prohibition.

There are indeed some sources that support at least some of those claims,[7][8] but a `quick web search also finds:

So which view is supported by the sources? Or could it be, as one source says, "In truth, nobody really knows exactly how much alcohol consumption increased or decreased during Prohibition. The reason was simple enough -- people like Al Capone didn't pay taxes on their product and thereby report their production to the government. Licensed saloons became illegal speakeasies, and many common citizens took advantage of the high sales price of illegal booze by secretly manufacturing booze in their own bathtubs."? --Guy Macon (talk) 04:43, 14 September 2018 (UTC)[reply]

And don't forget the yeast-flavored grape juice that would "go bad" if you added sugar and then waited. Anyway, regarding at least the first point, it is true that the certainty on this is pretty shit, and scholars bicker over the flaws in any method, but as far as I can tell, all the indirect evidence points to a singular conclusion: alcohol consumption declined a lot. Both contemporary and modern estimates of illegal alcohol production and consumption are vastly below the surrounding time periods, arrests for public drunkenness declined by two thirds, deaths from alcohol related illnesses declined by 80%... I'd say that there are arguments that the mainstream view is wrong, or poorly supported by the evidence, and it's certainly true that all available evidence is circumstantial, but it seems pretty damned uniform in where it points: [9]. Someguy1221 (talk) 06:16, 14 September 2018 (UTC)[reply]

Deaths from alcohol related illnesses declined by 80%?

"Deaths from Alcoholism. In New York City, from 1900 through 1909, there was an average of 526 deaths annually attributable to alcoholism.

From 1910 through 1917, the average number was 619.

It plummeted to 183 for the years 1918 through 1922.

Thereafter, the figure rose, averaging a new high of 639 for the years 1923 through 1927.

Total deaths from alcoholism in the United States show a comparable trend, with the gradual increase resuming somewhat earlier, about 1922."

"These statistics should be qualified by the observations of Dr. Charles Morris, Chief Medical Examiner for New York City: 'In making out death certificates (which are basic to Census Reports) private or family physicians commonly avoid entry of alcoholism as a cause of death whenever possible. This practice was more prevalent under the National Dry Law than it was in preprohibition time' ".[10] --Guy Macon (talk) 07:15, 14 September 2018 (UTC)[reply]

80% decline is the figure from Gebhart, J. C., Statistical studies of enforcement and social effects, 1930, which is based on contemporary nation-wide statistics, though I can't find an online version. Specifically 5 per 100,000 persons per year prior, dipping to a low of 1 per 100,000 during. Notably, Gebhart was actually anti-prohibition, and believed certain causes of death were under-reported (indeed, it is today a point of contention with this type of measure that at the time, there was no consistent nationwide reporting of causes of death, and standards varied over time in particular places). Someguy1221 (talk) 07:31, 14 September 2018 (UTC)[reply]

And yet The Effect of Alcohol Prohibition on Alcohol Consumption[11] by Jeffrey Miron [12] of the National Bureau of Economic Research says "The overall conclusion of this paper is that Prohibition exerted a modest and possibly even a positive effect on alcohol consumption". So alcohol deaths dropped by a whopping 80% while alcohol consumption stayed about the same? Is there something extra healthy about bathtub gin? Or did Gebhart's 1930 figures simply reflect that during prohibition physicians avoided listing alcohol as a cause of death? --Guy Macon (talk) 12:32, 14 September 2018 (UTC)[reply]

The Miron study is however based entirely on the correlation between the number of deaths due to cirrhosis and alcohol usage (something the author somehow fails to mention in the abstract), since there is simply no real data on alcohol supply or demand in that period. The study does acknowledge one weakness of this method: cirrhosis is correlated mainly with heavy alcohol usage, and so may not be greatly effected by a decrease in casual alcohol consumption. A more solid conclusion from the study then would be to say that the number of heavy drinkers probably did not decrease significantly during prohibition. That is not to say that the total amount of alcohol consumed stayed the same. Also note that this is a working paper, so it has not undergone peer review (yet). - Lindert (talk) 13:13, 14 September 2018 (UTC)[reply]

Using cirrhosis as an indicator of alcohol consumption is an interesting idea. According to our article on it, worldwide 57% of cirrhosis is attributable to hepatitis, and 20% to alcohol consumption. In the US the (current) number is 40% alcohol -- probably because we have better treatments for hepatitis. I wonder whether those percentages hold in the 1920s and 1930s, and whether the incidence of hepatitis remained steady during that period.

Another interesting factor; a bunch of light drinkers consuming X amount of alcohol would result in less cirrhosis than a smaller number of heavy drinkers consuming the same amount. It's heaviy drinking that ruins your liver. I don't have any figures, but it is plausible that light drinkers were more likely to become nondrinkers once it became illegal.

There is also a matter of timing. Increased alcohol consumption doesn't cause an immediate increase in deaths by cirrhosis. It take a while to destroy your liver. A decrease in deaths by cirrhosis follows a decrease in alcohol consumption much quicker; livers that aren't yet bad enough to kill you start healing if you stop drinking. The two are certainly cause/effect related, but it isn't a simple one-to-one correlation. --Guy Macon (talk) 17:54, 14 September 2018 (UTC)[reply]

Death from cirrhosis can also go under-reported (if there is no autopsy). Ruslik_Zero 20:23, 15 September 2018 (UTC)[reply]

I wonder if the autopsy rate was different in the 1920s compared to the 1930s. The more I look into this the less I like the absolute certainty that is in our article. --Guy Macon (talk) 04:04, 16 September 2018 (UTC)[reply]

All of the 3 assumptions on Developments are based on official statistics, which seem most unfit to estimate black markets and their circumstances. Therefor any such assumption should be mentioned as "based on very limited official knowledge" due to their systematically hidden nature. --Kharon (talk) 10:59, 16 September 2018 (UTC)[reply]

There is an interesting article about similar anti-alcohol campaign. Ruslik_Zero 20:19, 16 September 2018 (UTC)[reply]

Internation standard

Is anyone having knowledge of international quality standard that are to be followed for equipment racks and enclosures. 112.133.223.2 (talk) —Preceding undated comment added 06:24, 14 September 2018 (UTC)[reply]

Try here: 19-inch_rack#Specifications 196.213.35.147 (talk) 06:56, 14 September 2018 (UTC)[reply]

Best also search for ISO-Norms (International Organization for Standardization). --Kharon (talk) 10:41, 16 September 2018 (UTC)[reply]

Unidentified farm crop

Can anyone help me identify the crop in this picture? Taken on 9 June at 36°20′58″N 76°59′53″W / 36.34944°N 76.99806°W / 36.34944; -76.99806; there were a lot of fields in the area with the same crop, and I can't remember ever seeing such a crop anywhere else. Nyttend (talk) 14:00, 14 September 2018 (UTC)[reply]

Looks like clary sage to me. 216.59.42.36 (talk) 16:40, 14 September 2018 (UTC)[reply]

To me too: https://www.ncfieldfamily.org/farm/on-the-scent-of-sage/ 194.174.73.80 (talk) 16:57, 14 September 2018 (UTC) Marco Pagliero Berlin[reply]

Another option is lavender, though the plants tend to form more rounded shrubs that you see in the OP's picture. Matt Deres (talk) 17:11, 14 September 2018 (UTC)[reply]

Per the clary sage article, "In the United States, large scale production is concentrated in northeastern North Carolina in the counties surrounding Bertie County, NC." This is just the next county north of Bertie. Thanks! Nyttend (talk) 17:19, 14 September 2018 (UTC)[reply]

September 15

Is there something that is non-inflammable 100%?

As I understood everything is flammable (includes rocks and stones as we can see in lava) but all of the materials in the world are kind of located on the scale of flammability and while some require a very low temperature to be flamed and to change form, other materials require a very high temperature (like stones) to be flamed and change form. Is it correct? or there are exception for totally non-inflammable materials? 93.126.116.89 (talk) 05:08, 15 September 2018 (UTC)[reply]

Combustion products are essentially non-flammable, such as carbon dioxide, water, etc. but I suppose in principle even those substances can be reacted to higher and higher oxidation states. 139.194.65.208 (talk) 05:14, 15 September 2018 (UTC)[reply]

By the way...flammable and inflammable have the same meaning. Non-flammable is the term for something that doesn't burn. 139.194.65.208 (talk) 05:16, 15 September 2018 (UTC)[reply]

Thank you, I really didn't know it. I corrected it. 93.126.116.89 (talk) 14:53, 15 September 2018 (UTC)[reply]

In principle, CO₂ and H₂O really are completely combusted, with C and H in their maximum possible oxidation states and O happy with a full shell. Trying to oxidise these further would either be completely impossible (H doesn't have any more electrons for anything else to take) or require more energy than any chemical reaction could give (trying to involve the 1s electrons of carbon). Double sharp (talk) 06:15, 15 September 2018 (UTC) (Answer struck based on Ruslik0's comment, raising something which I somehow completely forgot about: this answer is only accurate if we restrict ourselves to combustion in air.) Double sharp (talk) 03:38, 16 September 2018 (UTC)[reply]

I get what you are saying but H2O2 Greglocock (talk) 06:34, 15 September 2018 (UTC)[reply]

H₂O₂ is thermodynamically unstable and slowly disproportionates to water and oxygen, so it doesn't affect the statement. ^_^ Double sharp (talk) 08:07, 15 September 2018 (UTC)[reply]

Of course the H is in the same oxidation state in both water and peroxide, but the oxygen is in the -2 state in water but increases to the -1 state in peroxide. It is further increased to -1/2 in superoxides. 139.194.67.236 (talk) 13:00, 15 September 2018 (UTC)[reply]

Yes, but we're typically thinking of oxidising the other element in an oxide, not oxygen itself. Otherwise, we could further oxidise oxygen in all oxides just by decomposing them to their constituent elements. Double sharp (talk) 15:17, 15 September 2018 (UTC)[reply]

Water can burn quite well in atmosphere of fluorine. Ruslik_Zero 20:05, 15 September 2018 (UTC)[reply]

Hmm, good point. I guess I must have been thinking implicitly of combustion in air. I've struck my original answer and added a note explaining that it only applies to that case. Double sharp (talk) 03:38, 16 September 2018 (UTC)[reply]

@Double sharp: What you say is true, in any sane way, yet ... well, in principle, I could take any substance and convert it into a plasma. Then I could take oxygen and convert it to plasma. Then I could mix the two plasmas and they would be intermingled, no matter what, with some conceptual release of energy no matter what, because entropy. Therefore ... everything is combustible at a high enough temperature. ??? Wnt (talk) 21:51, 15 September 2018 (UTC)[reply]

Naturally, we have an article on this - Combustibility and flammability. It appears to confine the definition of flammable to the commonly understood concept of something burning in the presence of oxygen. It lists some non-flammable materials. Interstingly, they include Diesel fuel. Haven't read it all so as to get my head around that yet. HiLo48 (talk) 06:27, 15 September 2018 (UTC)[reply]

The article seems to indicate that diesel fuel is considered combustible but not flammable, because it must be heated above room temperature before it ignites. Double sharp (talk) 08:09, 15 September 2018 (UTC)[reply]

Just to point out that lava isn't burning, it's molten. Some rocks can be burnt, such as limestone when making quicklime. Although that's strictly thermal decomposition, rather than burning. Mikenorton (talk) 08:54, 15 September 2018 (UTC)[reply]

Interesting, but I'd like to know based on what do you say that lava isn't burning while we can see it red and everything that you put into it burn as well.93.126.116.89 (talk) 15:02, 15 September 2018 (UTC)[reply]

Melting and burning are not the same thing. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:34, 15 September 2018 (UTC)[reply]

The red/orange glow of lava is black-body radiation. The rock is so hot that it glows in the visible spectrum. This doesn't have anything to do with combustion. --47.146.63.87 (talk) 04:09, 16 September 2018 (UTC)[reply]

One obvious example of a rock that burns is coal. 139.194.67.236 (talk) 12:51, 15 September 2018 (UTC)[reply]

Coal and jet are rocks that can be set on fire, sometimes with interesting results. --Guy Macon (talk) 13:01, 15 September 2018 (UTC)[reply]

Can I conclude from the article that mentioned above above that liquids are the only non-inflammable substance, or there're are also solid materials that no mater what they'll not be burnt? Basically except for water I didn't find a specific solid material that is non-flammable. 93.126.116.89 (talk) 15:00, 15 September 2018 (UTC)[reply]

Any oxide is non-flammable. I can think of glass or quartz (SiO2) or corundum (Al2O3). Ruslik_Zero 20:03, 15 September 2018 (UTC)[reply]

Tin(II) oxide has a bone to pick with you. That's just one example - conventional burning is still possible for an oxidized material if it can still be oxidized even further by oxygen. Someguy1221 (talk) 03:56, 16 September 2018 (UTC)[reply]

Of course, carbon monoxide can also be burned, and is in fact the gas that is combusted in many pyrometallurgical processes. 139.194.67.236 (talk) 10:16, 16 September 2018 (UTC)[reply]

In the presence of pure oxygen a lot of unlikely substances can undergo combustion - steel cutting torches depend on this to convert steel to rust, thereby cutting it. Per mention above, there is a difference between temperature-induced incandescence (i.e., fresh lava) and actual combustion. The flames seen coming from lava are from the decomposition of organic material that the lava has covered, which combust. Acroterion (talk) 17:17, 15 September 2018 (UTC)[reply]

Funny, non of all the experts, who tried to answer here till now, who obviously have some remarkable deep insight into chemistry and/or physics, mentioned noble gases which are not only 100% "non-inflammable" but even widely used in the industry as Shielding gas (usually Argon) to even prevent any "burning" (aka Exothermic reaction based on Oxygen) from happening. --Kharon (talk) 10:32, 16 September 2018 (UTC)[reply]

Except numerous oxides of noble gasses exist such as XeO4. 139.194.67.236 (talk) 13:39, 16 September 2018 (UTC)[reply]

XeO4 is manufactured by Synthesis. That hardly counts as inflammable. Whats the other "numerous oxides of noble gasses" that exist according to you? I bet they are all synthetic. With your argumentative pattern you could as well claim that Bricks fly, since you could form them like a wing and add enough air flow to actually make them fly. --Kharon (talk) 14:01, 16 September 2018 (UTC)[reply]

Our Noble gas compound article is a good place to start learning about the various classes of compounds of them that exist. For your specific concern about "synthesis", I assume you mean other than simply combining, say, xenon and oxygen at some temperature and pressure and getting xenon oxide? See doi:10.1038/nchem.2528 for examples of exactly that. Given the difficulty in getting it to happen, I suppose it's "combustible" not "flammable", and given the scale on which the reaction is performed, there is presumably not an actual "flame". DMacks (talk) 14:13, 16 September 2018 (UTC)[reply]

@DMacks. "Some temperature"? I was actually most impressed that XeO4 explodes above −35.9 °C and started wondering how many hundred Million $ a laboratory probably would cost that would be able to do both, the synthesis and storage, like some casual task for the day.

Btw, have you actually read your source yourself. At least until it mentions "Diamond-anvil-cell experiments" in the second sentence of its description? --Kharon (talk) 21:47, 16 September 2018 (UTC)[reply]

Diamond anvil cell experiments are relatively cheap (well, the pair of diamonds are a problem) because they're small scale. This makes them cheap to perform, also safe to perform. The reaction quantities are so small that even energetic results are still manageable. Andy Dingley (talk) 22:09, 16 September 2018 (UTC)[reply]

Of course I read the article before writing about it. That's why I clearly stated that the scale was small and the conditions were non-ambient. Even the diamonds of diamond anvils are only a few $K if I recall. And long-term storage of materials only a few tens of °C below zero is trivial too. Dry ice is not expensice even for small amounts to the general public, and large amounts or LN2 or low-temp freezers are present in every even poorly-equipped lab facility I've seen. DMacks (talk) 01:49, 17 September 2018 (UTC)[reply]

Indeed, at least the lighter noble gases should really be completely non-inflammable. Helium and neon should qualify under any sane definition since they have no known chemistry; argon should also count, because inserting Ar into an HF molecule isn't oxidising anything. Krypton will react with fluorine, which may count as combustion by some definitions. Double sharp (talk) 01:59, 17 September 2018 (UTC)[reply]

September 16

Heating of solids

It's known that a temperature increase increases the speed of molecules/atoms. Since in solids molecules are tightly packed and tied by intermolecular forces of attraction, having little or no room to move, this means that they should experience very negligible to no temperature increase at all. So why do solids have different thermal conductivity and in general it's relatively easy to heat up a solid material? 212.180.235.46 (talk) 12:06, 16 September 2018 (UTC)[reply]

Actually solid water (Ice) is less dense than fluid water and altho that is rather unique that is enough to prevent setting a general rule of matter "packings". Also atoms and their state have almost no significance for thermal conductivity. The real significance lies in the molecular "static", aka their arrangement in 2 or 3 dimensions as crystal, net or string. The most thermal conductiv natural material for example is Diamond with 1000 watts per metre-kelvin (W·m−1·K−1) and the (known) most conductive artificial materials are Carbon nanotubes (3500 W·m−1·K−1) and (molecular 2-dimensional) Graphene (5300 W⋅m−1⋅K−1). So you see that thermal conductivity is much more complicated than just how atoms swing (aka move) more or less dependent on their temperature.

The third part of your question is dependent on the Volumetric heat capacity AND thermal conductivity, which again does not follow a simple rule and contrary is a very individual perk of materials in general. --Kharon (talk) 12:57, 16 September 2018 (UTC)[reply]

It's known that a temperature increase increases the speed of molecules/atoms.

That's true as a statement, but it's not useful as a model unless you start to consider the laws which relate these two things. In a gas, kinetic theory does claim, "a temperature rise increases the speed", but it does so by showing the temperature to be proportional to the energy of each molecule, not its speed (i.e. the square of its speed, from the usual relation for kinetic energy).

It's similar in a solid. Temperature is proportional to the energy, not the speed. You might find phonons worth reading. The usual simple approximations begin by modelling the crystal lattice forces as atoms on springs, with a mathematical treatment as simple harmonic oscillators. This still works fine for a crystal or metal with a rigid lattice, but keep thinking about the energy for each atom (much of which is going into displacing that spring), not just their velocity, as if they were a free particle in a gas. Andy Dingley (talk) 13:20, 16 September 2018 (UTC)[reply]

Metal identity

Can the likely identity of the metal in these terminal blocks be inferred from the colour variations of the metal? 185.230.100.66 (talk) 15:58, 16 September 2018 (UTC)[reply]

No. Those are screws you're looking at, not the blocks, and their colour is due to a coating on them, not the underlying metal.

The blocks inside are usually brass, but modern ones are becoming ever more cheaply made and might become steel at some point. They're usually tinned or plated to make their surface more corrosion-resistant and avoid poor contact problems. You can tell brass from steel easily with a magnet. It's quite likely that there are steel screws in a brass block.

These 'chocolate block' connectors are also becoming less widely used, in favour of connectors (such as the Wago range) with sprung connectors. They have a perennial reputation for poor contacts over time. Andy Dingley (talk) 16:57, 16 September 2018 (UTC)[reply]

This is the correct link to the Wago range of connectors. 194.174.73.80 (talk) 10:53, 17 September 2018 (UTC) Marco Pagliero Berlin[reply]

The surface appears to be Cadmium but terminal screws are almost never pure cadmium but rather cadmium plated. A magnet will tell you if there is steel underneath.

https://www.google.com/search?q=Cadmium+plating&num=100&tbm=isch will show you what cadmium plating looks like. --Guy Macon (talk) 17:55, 16 September 2018 (UTC)[reply]

It won't be cadmium. Cadmium is so toxic that even the Chinese have stopped plating things with it. Now it looks like cadmium, but so do many other modern plating and conversion coating processes. You can even get "super cadmium-looking" processes, for the car restoration crowd. Andy Dingley (talk) 18:12, 16 September 2018 (UTC)[reply]

Metallurgy is a very specialized Science and Metallurgists have a masters degree. They are also the highest paid specialists in material science, i learned by chance a long time ago. So you may have to pay the 500$ bill for the correct professional answer to your Question! Sorry, way above my pay grade. --Kharon (talk) 22:17, 16 September 2018 (UTC)[reply]

Then why do you keep answering questions here, if you have nothing to contribute? Andy Dingley (talk) 23:44, 16 September 2018 (UTC)[reply]

Makes sense to me. It keeps people from too easily believing answers posted by other people who are guessing. --76.69.47.228 (talk) 01:54, 17 September 2018 (UTC)[reply]

Obesity

Is it genetic or determined by what you eat?86.8.203.189 (talk) 18:31, 16 September 2018 (UTC)[reply]

Have you considered that both factors may be in play, and that there may be others as well, for example gut flora? Matters of biology are rarely simple. {The poster formerly known as 87.81.230.195} 90.208.172.36 (talk) 18:54, 16 September 2018 (UTC)[reply]

It can't be only genetics because anyone can starve to death and 3 pounds of butter has 12,250 calories. Sagittarian Milky Way (talk) 18:56, 16 September 2018 (UTC)[reply]

The answer is "Yes". ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:07, 16 September 2018 (UTC)[reply]

Some people cannot get fat no matter how much they eat. 86.133.58.126 (talk) 19:12, 16 September 2018 (UTC)[reply]

Jack Sprat, for example. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:15, 16 September 2018 (UTC)[reply]

See Obesity#Causes. PrimeHunter (talk) 23:02, 16 September 2018 (UTC)[reply]

Is the negative charge - the absence of the positive charge?

We used to say, based on the science - if I'm not mistaken, that the darkness is the absence of the light, because there're no photons at the medium of the darkness. True? So my question is about physics or chemical physics, is the negative charge is the absence of the positive charge? If it is, what is the explanation for that? (for example about light we say that there're are no photons but here in negative charge what is the actual absence in the micro-level?19:52, 16 September 2018 (UTC) — Preceding unsigned comment added by 93.126.116.89 (talk)

no, no, no. The attractive force is proportional to the negative charge times the positive charge, which can't be if the negative is just a lack of positive. Wnt (talk) 21:20, 16 September 2018 (UTC)[reply]

'Absence of charge' generally implies no charge. Only in some cases (where a negative charge carrier is expected) would it really be seen as implying a positive charge.

Charge is different to light (or mass). There are two forms of it, so there's a difference between 'negative' and 'absent' which doesn't arise for light.

The most common charge carrier (at least in discussion and description) is the negative electron (as electrons can travel freely in metals). But the 'natural' state of an atom is to be neutral (the number of positive and negative charges are equal). If a charge is removed, then yes, that's equivalent to gaining the opposing charge. So atoms in ionic bonding (how many molecules are formed) may easily lose or gain an electron (or two) to an adjoining atom; one becomes positively charged (an ion), one negatively charged. It's the electrons which move between atoms, not their protons, as the electrons are both less tightly bound and also lighter.

In semiconductors, both positive and negative charges are important. The idea of 'holes' is an importat one. It's just as important to account for a removed electron as it is for an excess electron. But this is the removal of an electron which was there, not merely the absence of one. Andy Dingley (talk) 21:55, 16 September 2018 (UTC)[reply]

Donated blood not clotting

Why does donated blood not clot? I thought, no air=no clot, but blood can clot inside our veins. Mix up some anti-coagulant into it? But, then wouldn't that be pretty inconvenient for recipients like accident victims and hemophiliacs? — Preceding unsigned comment added by 31.177.99.255 (talk) 22:14, 16 September 2018 (UTC)[reply]

I googled "why doesn't donated blood clot", and here's an answer:[13] ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:46, 16 September 2018 (UTC)[reply]

Yes, I saw that page too, when I googled it. It does not touch the topics of my sub-questions. --31.177.99.255 (talk) 22:54, 16 September 2018 (UTC)[reply]

Just enough citrate is added to the blood in order to chelate most of the calcium. Calcium (specifically Ca²⁺) is required for coagulation (factor 4 in the coagulation cascade), so without free Ca²⁺ the blood will not clot in the bag. When blood is then transfused, because there is little unbound citrate in the bag, there will be little effect on the plasma calcium concentration, and hence coagulation in the body is possible as normal. The kidneys can then effectively clear the citrate from the body, although in the interim it may have other biological effects. Klbrain (talk) 00:34, 17 September 2018 (UTC)[reply]

A reference for the actual amounts of citrate vs calcium in a donated unit would be important here. How much of the calcium is actually bound and how much free citrate remains? The plasma calcium concentration is also affected by dilution of the added no-free-calcium blood in the recipient. A donated unit is about 0.5 L and a person has about 5 L total volume, so if we are talking about someone suffering from blood loss, mixing one unit of whole blood with no Ca++ into "well less than 5 L" of whole blood is easily a 10% drop. If one really needs blood, it's obviously an acute situation and side effects or interactions with other conditions can be addressed later. Headed slightly off the OP's question, the citrate is also a potential problem for the donor in apheresis, where the blood is withdrawn, citrate added, certain components of interest removed, and the rest returned to the donor. That means dumping a bunch of calcium-depleted blood and possibly excess citrate into the donor for a several-hour period. pmid:26607494 is an interesting read. DMacks (talk) 03:13, 17 September 2018 (UTC)[reply]

Not a direct answer, but the citations in the "trauma" section of this review [14] presumably mention it at some point? That talks about standard practices in the management of bleeding during surgery. In brief, if someone comes in needing a massive blood transfusion after an accident, coagulation is very carefully monitored and a variety of infusions are available to keep the blood behaving normally. Someguy1221 (talk) 03:25, 17 September 2018 (UTC)[reply]

The American Red Cross notes[15] that there actually can be a possibly clinically significant amount of anticoagulant infused, although it is indeed metabolized promptly assuming normal liver function and circulation. And it concurs with my thought that that the transient drop in free Ca++ can be an acute problem. And it notes that the transient presence of citric acid and then the presence of its metabolic products can also be an acute problem (blood pH and Ca++-level effects) for those who have certain circulatory or metabolic problems. DMacks (talk) 03:29, 17 September 2018 (UTC)[reply]

September 17

@@ Line 358: / Line 358: @@
 : The blocks inside are usually [[brass]], but modern ones are becoming ever more cheaply made and might become [[steel]] at some point. They're usually [[tinning|tinned]] or [[electroplating|plated]] to make their surface more corrosion-resistant and avoid poor contact problems. You can tell brass from steel easily with a magnet.  It's quite likely that there are steel screws in a brass block.
 : These 'chocolate block' connectors are also becoming less widely used, in favour of connectors (such as the [[Wago]] range) with sprung connectors. They have a perennial reputation for poor contacts over time. [[User:Andy Dingley|Andy Dingley]] ([[User talk:Andy Dingley|talk]]) 16:57, 16 September 2018 (UTC)
+:: This is the correct link to the [[WAGO_Kontakttechnik|Wago]] range of connectors. [[Special:Contributions/194.174.73.80|194.174.73.80]] ([[User talk:194.174.73.80|talk]]) 10:53, 17 September 2018 (UTC) Marco Pagliero Berlin
 :The surface appears to be [[Cadmium]] but terminal screws are almost never pure cadmium but rather cadmium plated. A magnet will tell you if there is steel underneath.