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September 29

alpha particles in nucleus

I have heard that the the neutrons and protons in the nucleus are sometimes combined into alpha particles. But the article seems to imply that bosons don't feel the nuclear force, or at least not as well as fermions do. Is this why alpha decay happens, because the nucleus doesn't have the nuclear force to hang on to it?144.35.45.70 (talk) 02:50, 29 September 2017 (UTC)[reply]

Which article are you referring to? Looie496 (talk) 03:49, 29 September 2017 (UTC)[reply]

An Alpha Particle is simply an ionized helium atom. Alpha decay is the expulsion of a helium nucleus from an unstable heavy element, called "decay" for historical reasons, but not really decay into a different type of particle in the same way as lone neutron decay into a proton, an electron, an antineutrino and a gamma ray. μηδείς (talk)

Alpha Radiation or its main source Alpha decay would be the proper articles. Cluster decay however comes closest to answering the question tho it does not go into such detail in Quantum mechanics to mention individual particles. --Kharon (talk) 04:46, 29 September 2017 (UTC)[reply]

I think the OP is thinking too hard about the nucleus really looking like a cluster of colored balls all glued together, as classic pictures in most textbooks show it. The nucleus does't look like that. Insofar as it looks like anything, it looks like a fuzzy sphere, not unlike an atom would look if you could look at it (that is, if vision at that scale has any meaning, which is a debate for another day). The fuzziness may be denser than the fuzziness of the electron cloud, but it's still basically an impervious cloudy structure. When we say that the nucleus undergoes alpha decay, we say that it emits a helium nucleus, which is to say that a new nucleus is formed, that of helium, and the remaining nucleus has lost a mass and charge equivalent to that helium nucleus (ignoring, for the sake of this discussion, binding energy/mass, etc) That doesn't mean, however, that if you looked at that original nucleus, you could identify discrete neutrons and protons, or that those discrete particles "broke off" in any meaningful way. If you think about alpha decay like that, you run into real problems using the same explanation for beta decay. After all, where is the electron in the nucleus? The classic lie to children explanation is that a neutron in the nucleus turns into a proton by emitting an electron. Which is only sort-of correct, and works because it makes the picture easier to understand. The next question you may be asking is "where in the nucleus was that electron". Was it in the neutron? No, classically, neutrons conists of three quarks, none of which are electrons. Well, maybe electrons are themselves made of quarks, or gluons, or some other particle we know to be in there? No, near as all models can tell, electrons are fundamental particles which means they don't have any finer structure, they aren't made of parts. So, if the electron didn't exist in the nucleus, and there are no parts of electrons in a nucleus with which it could be built, what then? By what mechanism does beta decay happen? The answer is shut up and calculate. By which to say, quantum mechanics does not behave by the same rules as newtonian mechanics, so stop trying to make it work that way. To say that protons and neutrons exist in a nucleus is true, but only in the sense that they are a useful model to explain concepts like nuclear decay and atomic mass and charge and stuff like that. When you start treating them as objects unto themselves as though they were little lego bricks you could just pluck off and build new things out of, you start to introduce things into your model which do not match reality. If your model is that bad at matching reality, throw away the parts of the model that don't work. And the part of the model where we expect these particles to behave like little hard balls is the part which we need to abandon. --Jayron 32 16:29, 29 September 2017 (UTC)[reply]

I think we can be a bit more generous to the OP. An alpha particle is indeed a type of boson, because it has a net spin that is an integer. In principle bosons can be packed at arbitrary density, but as our boson article explains (or at least tries to explain), other factors may come into play that prevent that from happening. Such is the case with alpha particles: the strong forces that their components feel prevent them from coming too close together. Looie496 (talk) 17:00, 29 September 2017 (UTC)[reply]

That's true, but as you note the concept of boson has limited utility here. There are lots of nuclei one could construct which are boson; it's trivial as any even-nucleon nucleus (such as C-12 or a deuteron) is also a boson. However, since the composite particles (protons and neutrons) that make up the nucleus are fermions, one gets the unreasonable task of deciding which is more important to consider when describing the properties of such a nucleus. You do get wierd physics when boson nuclei interact (such as in a Bose–Einstein condensate). --Jayron 32 17:35, 29 September 2017 (UTC)[reply]

I fell in love with the Atomic orbital concept once i learned to understand it, because it also works so well in explaining molecular bindings and their resulting geometry and function aka chemistry. Id say its also a very good approach to understand nuclear physics. So i would recommend to ignore the quarks and focus on that instead to learn how matter "works". --Kharon (talk) 16:59, 29 September 2017 (UTC)[reply]

Pretty much this^^^^ --Jayron 32 17:35, 29 September 2017 (UTC)[reply]

Pantothenic Acid and Biotin

Do large doses of Pantothenic Acid (say, 500mg a day) cause Biotin deficiency in humans? I've read conflicting reports that they compete for the same absorption mechanism and so an excess of either can cause a deficiency in the other. But I've also read that they require each other for the other to be absorbed and used. I'm confused and can't seem to find a straight answer to this question. Thanks for your time. OrvilleVoyager (talk) 17:20, 29 September 2017 (UTC)[reply]

I see no studies on PubMed for humans. I do see studies on rats, mice, and bulls. The only one with a very conclusive result involved increasing both Pantothenic Acid and Biotin while reducing Folic Acid. The result was an increase in cancer risk. As of 2008, my nutrition textbook states that there have been no conclusive studies on Pantothenic Acid or Biotin supplements. Instead, B-complex vitamins are used, which include both. 209.149.113.5 (talk) 18:56, 29 September 2017 (UTC)[reply]

"Large doses of pantothenic acid do not cause symptoms, other than (possibly) diarrhea. There are no known toxic symptoms from biotin." Source: https://medlineplus.gov/ency/article/002410.htm

I am wondering why anyone would take large doses of Pantothenic Acid supplements without taking any Biotin supplements. Most people just take a B Complex supplement, which contains both. Also, large doses of either do nothing except create expensive urine. --Guy Macon (talk) 19:48, 29 September 2017 (UTC)[reply]

Design engineers

Many site and project engineers have to be reactive, for example if a problem arises on site or an incident occurs. Is design engineeeing less reactive? Or is it possible the design engineer could also be called in if something goes wrong on site? 94.10.178.193 (talk) 20:01, 29 September 2017 (UTC)[reply]

The work of a Design engineer is information intensive and unless (s)he takes care to deliver all necessary information and skill, (s)he remains liable to be called upon to solve problems that arise later in manufacturing and implementation of a project. The documentation accompanying a piece of technology is often the only means by which the user can fully understand said technology. Blooteuth (talk) 20:43, 29 September 2017 (UTC)[reply]

Both. For instance the Millennium Bridge at first swayed from side to side due to well understood resonance. It was much easier then for the design team (using real data) to then add dampening correction. This would have been difficult and more expensive to do at the conceptual stage before the bridge had been built. Architects tend to be conservative, even when creating something new. The counter lever roof on the original Wembly stadium was new on that scale but the principles had already been proven on a smaller scale. Even the largest domed-roof is only a cement version of an Igloo. A sky scraper using new construction techniques on Manhater Island was found to be unsafe, but its short comings were rectified, negating the neead to demoish it. Yet, as always some architects get is wrong... Ronan Point and Tacoma Narrows Bridge etc. Aspro (talk) 20:58, 29 September 2017 (UTC)[reply]

"Even the largest domed-roof is only a cement version of an Igloo." But surely the builders of the Pantheon had never seen an igloo. CodeTalker (talk) 21:56, 29 September 2017 (UTC)[reply]

It's not even true. An igloo is a circular cantilever. Some domes (which are thinner, but require centring during construction) are circular arches. Andy Dingley (talk) 22:10, 29 September 2017 (UTC)[reply]

Design engineers are usually called in as second or third level support when a problem arises with a product after it is in use. This is nearly universal practice with software products, and also with complex or custom physical products. -Arch dude (talk) 02:46, 30 September 2017 (UTC)[reply]

As a design engineer in a car company I spent hours each week working on problems on the assembly line with my parts, and would also get involved in recalls and technical service bulletins. Greglocock (talk) 07:15, 30 September 2017 (UTC)[reply]

are neurons specific to a single neurotransmitter?

I've been trying to self educate myself about the brain, neurons, etc. My background is computer science and I have a decent understanding of artificial neural networks. One question I'm not sure about that seems rather important is: how specific is a neuron to a neurotransmitter? I.e., does each neuron only respond to and/or take input from a single neurotransmitter, or can neurons respond to neurotransmitters in different ways (e.g., dopamine might excite neuron x but serotonin inhibit it). This seems to me to be an important differentiator between ANNs and actual neural networks. Are there other major differences (or would that take a book to respond to)? Thanks. --MadScientistX11 (talk) 22:24, 29 September 2017 (UTC)[reply]

Almost every type of neuron responds to a wide variety of neurotransmitters. In fact, almost every type of neuron releases multiple neurotransmitters. The only real restriction is Dale's principle, which says that a neuron releases the same set of neurotransmitters at all of its output synapses -- and even that has exceptions. You're right that simple ANNs don't capture this aspect of real neurons. There are more sophisticated types of ANNs that do, as described in our biological neuron model article, but they are of more interest to biologists than computer scientists. Looie496 (talk) 23:03, 29 September 2017 (UTC)[reply]

Looie's got it right, and you also have to consider that a specific neuron can accept stimuli from scores of other neurons that themselves react to different neurotransmitters. We are at the beginning of understanding the brain. Endocannabinoids were only recognized as neurotransmitters in the last decades of the last century.

Look at the plethora of designer drugs that coroners can't even detect as the underground drug industry outruns them. Neuroplasticity, and positive feedback (short term) and negative feedback (long term) and refractory period are not necessarily directly related, but may be of interest, and lead to other links such as SSRI's and serotonin syndrome may be of interest. There's also neuron and action potential and synapse.

I won't waste your time with more links, I have to go get me some dopamine. μηδείς (talk) 03:44, 30 September 2017 (UTC)[reply]

@Looie496: and @Medeis: Thanks a lot. That cleared up my confusion, excellent answers!! --MadScientistX11 (talk) 18:00, 2 October 2017 (UTC)[reply]

September 30

Oxirane excited state

How much higher in energy is the excited state of oxirane, wherein the molecule can be considered an ethylene complex of an oxygen atom, than the ground state? Plasmic Physics (talk) 00:03, 30 September 2017 (UTC)[reply]

@Plasmic Physics: I don't really understand the distinction you're making there, but here is the IR spectrum and here is the UV-vis spectrum. 1/ 3800 cm-1 = 2630 nm , so there is quite a gap between this and the 182 nm the UV-vis spectrum given begins at, but if the absorptions in the UV-vis spectrum peaking at 156, 159, 171, 173 are what you want, then you'd think the energy might be around hc/lambda, i.e. (from photon energy) 1.2398 eV um / (.156, .159, .171, .173) um = (7.94, 7.80, 7.25, 7.17) eV. Not at all sure this first-principles approach is correct though. Wnt (talk) 20:19, 30 September 2017 (UTC)[reply]

I don't see the reasoning behind your ab initio approach, but I do see an interesting peak in the IR spectrum between 1750 and 1500 cm⁻¹, that would correspond nicely to the double bond in an ethylene ligand. This would seem to suggest that the excited state forms a significant proportion of a sample in thermodynamic equilibrium, which would mean in turn that the energy level is not that much higher than the ground state. The distinction that I'm trying to make is that the excited state involves more pi-bonding character than does the ground state, by either occupying the π-LUMO, or vacating the π^*-HOMO. Plasmic Physics (talk) 22:47, 30 September 2017 (UTC)[reply]

@Plasmic Physics: I'm still not really sure what state you're looking for, but my impression is that infrared absorptions are basically vibrations of the bond - though I should admit I don't know what those are in orbital terms. A double bond in that region is absolutely normal for IR spectra. But my impression is that genuinely breaking bonds, or switching from HOMO to LUMO, requires serious visible or UV radiation. See e.g. [1]. I mean, I believe you use UV light to make an otherwise antarafacial sort of ~~Diels-Alder reaction~~ (cycloaddition, really) work by putting one of the aromatic compounds into the excited state. Wnt (talk) 19:32, 1 October 2017 (UTC)[reply]

I'm not sure how to describe the state without using the molecular orbital concept. Although, the coordination should look similar to Zeise's salt. Yes, IR-spec asseses bond vibrations, but an individual spectrum makes no distinction between unique species or states of an individual species present. This why a reference spectrum is taken and subtracted from the sample spectrum. I've done plenty of IR spectroscopy, and I can't say that a double bond vibration is normal, if the carrier is aliphatic. This is not really cycloaddition since the molecule doesn't actually break appart to reform, it's just an internal electronic rearrangement, like what happens in the methanium cation. Plasmic Physics (talk) 05:51, 2 October 2017 (UTC)[reply]

Hmmm, ethane has a 1.54 angstrom bond length while ethylene oxide is at 1.46. According to Dewar–Chatt–Duncanson model the bond lengths of bound ethylene goes from 1.33 angstrom to 1.34 angstrom in Zeise's salt to 1.43 angstroms in a random ? nickel compound they mention. But I certainly don't understand all considerations, starting with whether the strained bonds of ethylene really curve, and whether that curve makes the bond shorter as the crow flies without actually changing its order. I also don't know if the IR band can be explained simply that the "stiffness" of the three-membered ring, with each member having two bonds close to each other, merely equals that of a double bond. So I don't know if calling ethylene oxide a complex of ethylene is merely a matter of groping the elephant and writing the same interaction different ways. But my expectation would be that if you can make an excited complex that is described by having different bonds between the atoms, that this is a bond-breaking operation at some level and should take UV-vis levels of energy to do. Wnt (talk) 10:14, 2 October 2017 (UTC)[reply]

I see, that makes much more sense. Plasmic Physics (talk) 10:35, 2 October 2017 (UTC)[reply]

Highest survivable temperature

What is the highest temperature a human has ever survived? 2601:646:8E01:7E0B:D403:68F1:A297:C74A (talk) 01:47, 30 September 2017 (UTC)[reply]

[2]. --Jayron 32 02:19, 30 September 2017 (UTC)[reply]

That's only body temperature, but what about environmental temperature? I'd say that it would be pretty close to the point at which you start to choke from the fluid in your lungs. However, what if you had respiratory gear that controlled the temperature of the air that you inhale? Plasmic Physics (talk) 03:00, 30 September 2017 (UTC)[reply]

You'll need to be able to define the Q more precisely to get a precise answer. Some factors:

1) Humidity. The lower the humidity the hotter temps we can survive, due to evaporative cooling from sweat.

2) Wind. Wind can actually make things worse at high temps, as it blows away the air near the body which has been cooled (by the conduction with the body and evaporative cooling) and replaces it with hot air.

3) Time. Obviously high temps are more survivable for short time periods.

4) Body mass. A larger body will take longer to heat up than a small one, due to the square-cube law.

5) Sunlight versus shade. In sunlight, clothing matters a lot, and loose-fitting white clothes may be best.

6) Activity level.

7) Availability of water, especially cool water, to drink. StuRat (talk) 02:58, 30 September 2017 (UTC)[reply]

OK, here are more details:

1) Humidity: Low due to extreme air temperature.

2) Wind: Convection only from rising air and combustion products, and from fresh air being sucked in.

3) Time: More than a few seconds is the only limitation (I'd say 1 minute or more).

4) Body mass: How much does a typical firefighter weigh?

5) Sunlight: None, but radiant heat from the fire may be a factor.

6) Activity level: Standing and spraying with a fire extinguisher, moving as needed.

7) Water: Available, but the water may have been heated a great deal by the fire.

8) Miscellaneous: The person is wearing full turnout gear (not a fire proximity suit), but has lost his breathing gear.

2601:646:8E01:7E0B:D403:68F1:A297:C74A (talk) 05:05, 30 September 2017 (UTC)[reply]

Guinness Book of World Records (voluntary, briefly): 400°F naked, 500°F heavily clothed. Sagittarian Milky Way (talk) 05:20, 30 September 2017 (UTC)[reply]

That low? Don't people sometimes go inside lit brick kilns, coke ovens, locomotive fireboxes, etc. (wearing fire proximity suits, which is not the case in my scenario, that is true) to make repairs without having to wait for the fire to die down? 2601:646:8E01:7E0B:D403:68F1:A297:C74A (talk) 12:38, 30 September 2017 (UTC)[reply]

Well I don't know how long that test was exactly. Or if the clothing was even reflective. It may have been broken by now. Also I don't know if firefighters wear thermometers which would be the only way to tell if the air temperature+radiative heat contribution of the fire, walls etc. averaged over their whole body exceeded that. That record might not be in the book anymore because Guinness has sucked for a long time. Many interesting records that rarely change like sweetest chemical or biggest locomotive are replaced by useless things that happened that year like most hours singing Lady Gaga on a roller coaster and biggest underwater rap battle. Sagittarian Milky Way (talk) 15:32, 30 September 2017 (UTC)[reply]

Americium oxyrhenide is the sweetest chemical. μηδείς (talk) 23:00, 30 September 2017 (UTC)[reply]

In relation to body mass: it's not as simple, because thinner bodies will also tend to more efficiently dissipate heat. If it is still possible of course (if the environment does not transfer more heat to the body than the body can transfer it to the environment including by sweat). Large bodies tend to cope better with cold. Also of interest which was not mentioned would be heat shock. —Paleo Neonate – 06:15, 30 September 2017 (UTC)[reply]

For how long can someone stand directly in front of a steel furnace with the hatch open and no protective gear? Plasmic Physics (talk) 08:04, 30 September 2017 (UTC)[reply]

In this scenario, the person DOES wear protective gear -- specifically, a firefighter's turnout gear minus the breathing mask (which he lost somehow, maybe by falling through a hole in the floor). 2601:646:8E01:7E0B:D403:68F1:A297:C74A (talk) 12:38, 30 September 2017 (UTC)[reply]

I'm thinking you'd have to specify an air pressure - humans can theoretically survive explosive decompression for brief intervals (I'm not sure if the remarkable story of JAT Flight 367 applies, though it certainly might expand my notion of the possible). And temperatures in the thermosphere and outer space can be ... outlandish. I mean, in theory a person in a space activity suit might survive with their skin exposed to temperatures of thousands of degrees for prolonged periods ... I think. Wnt (talk) 20:26, 30 September 2017 (UTC)[reply]

Thermosphere? Are you kidding? In this case, the air pressure is normal (29-30 inches of mercury) -- I think I kind of implied this by saying that the person doesn't have breathing gear (so if the air was that rarified, he'd die from suffocation before the temperature could do anything!) And BTW, explosive decompression has nothing to do with this -- it does NOT make the air temperature go up, in fact the temperature goes DOWN because of the Joule-Thomson effect. 2601:646:8E01:7E0B:D403:68F1:A297:C74A (talk) 02:18, 1 October 2017 (UTC)[reply]

Hmmm, doesn't sound like I'm talking about what you're talking about here. Wnt (talk) 19:36, 1 October 2017 (UTC)[reply]

Right, I'm talking about high temperatures at normal atmospheric pressure (as I said, I kind of implied this by saying the person doesn't have breathing gear, and also by saying that things are on fire -- which they wouldn't be in a near-vacuum such as that in the thermosphere!) 2601:646:8E01:7E0B:D403:68F1:A297:C74A (talk) 01:10, 2 October 2017 (UTC)[reply]

How would one detect a magnetic monopole at a distance?

This Forbes blog post https://www.forbes.com/sites/startswithabang/2017/09/28/is-the-inflationary-universe-a-scientific-theory-not-anymore/#7f436605b45e talks about detecting magnetic monopoles, presumably at great distances. (It dismisses the notion they even exist.) If they did, how would they be detected? Thanks. μηδείς (talk) 03:31, 30 September 2017 (UTC)[reply]

This isn't an area I know much about, but I don't see that it says it's expected we can detect them at great distances. Instead it seems to be saying that under some theories without inflation, there should be a lot of monopoles, enough that we should have observed them by now but inflation provides an explanation for why we haven't. It greatly reduces the expected density such that it's entirely plausible we still haven't found one. The author appears to be suggesting that inflation isn't the only explaination, it's possible the theory they should exist is just wrong. Our articles Inflation (cosmology)#Magnetic-monopole problem and Big Bang#Magnetic monopoles and Magnetic monopole#Grand unified theories seem to say the same thing (including that others have said something similar to the blog author about our theories of them existing just being wrong). BTW the very next section of the last article Magnetic monopole#Searches for magnetic monopoles discusses various ways to look for them and also seems to support the previous points. Nil Einne (talk) 12:57, 30 September 2017 (UTC)[reply]

Yes, I did get the point that inflation might have spread them out so much as to be rare, but the original article seems to imply that even if there were only one in the observable universe it would be detectable (without outright saying this, or explaining how). I also read our entire article, including the section "searches for magnetic monopoles" before posting this, but it spoke of inducing currents in wires, not some sort of observable far-off phenomenon like a black whole. That's what I am wondering, would they be detectable somehow on cosmic scales? Or only like particles in a neutrino detector? The Forbes blog implies without actually saying it that they would be detectable even if there were only a very small number of them. μηδείς (talk) 13:30, 30 September 2017 (UTC)[reply]

Again, I don't see that the Forbes articles implies that "even if there were only one in the observable universe it would be detectable" or even "they would be detectable even if there were only a very small number of them". Yes there is one brief mention of single monopole in an image caption, but no where does it seem to imply we would have found that single one. It also says We do not, however, see any of them which seems to be simply saying we haven't definitely found any, even though we should have if they were as abundant as some theories predict. (Our articles do suggest the maximum possible density of monopoles based on current research, so I guess it does depend on what you mean by very small number. I'm assuming the Forbes article was written accepting this research although it only really barely touches on it IMO.) Could you explain what parts lead you to believe that it's trying to suggest we would have found them even if there was only a single or or "very small number"?

To me it seems to be saying the same as our articles are saying. 'We aren't seeing any magnetic monopoles. Inflation supporters say this is because under inflation they're so rare this is to be expected. An alternative hypothesis is that our theories on how common they would be without inflation are simply wrong. In fact, perhaps it's completely expected they don't exist even without inflation.'

Actually it seems to me it's specifically implying that we can't detect only one, or probably a few. If it were claiming we could detect only one, then it would be saying or at least implying that 'clearly we are wrong, since we know there isn't even one based on research', But instead it just offers an alternative hypothesis and don't say or imply 'this is definitely correct, since we are are extremely confident there are no monopoles'.

The only thing it really says about monopoles other than we haven't found them and possible reasons why (either because inflation is correct or because our theories on how many monopoles there would be are wrong), is that we haven't found evidence for grand symmetry but the actual search for this was primarily looking for proton decay rather than anything to do with monopoles. Actually if I understand the last sentence to do with monopoles correctly, it's even acknowleding that mostly even supporters of inflation don't consider the monopole problem as compelling evidence for inflation which again seems to be semi supported by our articles.

BTW, I just realised the third link above if incorrect, I meant Magnetic monopole#Grand unified theories 2. Also I admit I only really read the beginning and the part to do with monopoles then searched the rest to look for any other mention. So if the article talked about monopoles in other sections without meaning the word, I would have missed that.

Nil Einne (talk) 16:29, 30 September 2017 (UTC)[reply]

The article did say that if symmetry breaking were true, there would be one monopole in the observable universe. On what basis is this claim made or to be verified? Should I just give up? Inflation has always seemed like an unfalsifiable premise to me. But I only took up to Physics 202. μηδείς (talk) 19:09, 30 September 2017 (UTC)[reply]

You'd detect a magnetic monopole in the same way you'd detect any other monopole! Measure the magnetic field and estimate a best-fit for a spherical harmonic decomposition and look for a non-zero coefficient for the first term... which we never see!

A monopole would satisfy certain mathematical properties. We have fancy equations to express those properties using very few words - for example, non-zero divergence. So, you'd measure the field, and you'd observe its mathematical properties, and you'd look for any deviation from normally-observed properties. So far, this specific type of deviation has never been seen, and there isn't any good reason to expect it. You would literally have better luck looking for electrons that deviate from normal electrons by carrying a positive electrical charge, because there are a few places in the universe where that rarity actually exists.

Nimur (talk) 17:02, 30 September 2017 (UTC)[reply]

Nimur! Why are you yelling at me! If I understood this already, I wouldn't have asked! And if I hadn't read up on the subject here, I wouldn't have asked! (An unmarried Pollack!) μηδείς (talk) 19:09, 30 September 2017 (UTC)[reply]

I use exclamation points for emphasis, not because I mean to yell at anybody. I apologize.

If I may misquote Herman Kahn, [3], I apologize for my prolific use of typographical emphasis (!!). I do it in spite of many admonitions from friends and colleagues and in full awareness that many people will find it irritating. I feel, however, that some readers will find it helpful. Nimur (talk) 19:37, 30 September 2017 (UTC)[reply]

NP! :) μηδείς (talk) 20:46, 30 September 2017 (UTC)[reply]

https://arxiv.org/abs/astro-ph/9412053 Count Iblis (talk) 23:20, 30 September 2017 (UTC)[reply]

[ec] (Haven't read Iblis' yet) Am I to understand monopoles would be subatomic? Wouldn't the r² law simply make them indetectable unless they were in your lap? μηδείς (talk) 00:37, 1 October 2017 (UTC)[reply]

Monopolonia? Jak gdyby byli więcej niż jedną Polskę!

The above translates as "Monopolonia? As if there were more than one Poland!" Blooteuth (talk) 02:29, 1 October 2017 (UTC)[reply]

When I worked in the post department of a famous bookshop we had to type the first word of the name of the firm raising the order on the invoice in capitals. On one occasion I also added it as the first word of the address. The order, for a customer in New York, was raised by "Polak's Frutal Works" [4]. One afternoon the manageress told me a customer had come in, asked for who had typed his invoice, and said he had said he had come over from New York to fight with me but I had just gone to lunch. Then I was called to the general manager's office. He asked me "Have you ever come across the word 'Polak'?" I thought for a minute and said "no". He said "It's a derogatory word for a Polish person, like 'Limey' for an Englishman. You wrote it all over a customer's address label. When the postman delivered the book he said 'Look what they call you in London!'" When I saw the label I explained who had raised the order and he said "You did the right thing". 81.147.142.152 (talk) 08:55, 1 October 2017 (UTC)[reply]

The changing magnetic field created by a single monopole has the effect of introducing a relatively long-lived electric current in any conducting loop that it passes through. A simple circle of wire is sufficient for this effect. A magnetic dipole passing through the loop does not have the same effect. In order to detect such a current you need a sensitive current detector and ways to eliminate interference, but both technologies are well developed for scientific research. So, basically, you lay out a large loop of wire, hook up some fancy measurement equipment, and wait for a monopole to fly through your loop. Monopole studies often imagine that the monopoles will be coming at high speeds from space. The larger the loop, the smaller the expected current, so there are some trade-offs when deciding the size of your measurement device. However, after observing for a while, the failure to see any monopoles can be interpreted as a limit of the flux of monopoles in the neighborhood of your detector. For a given assumption about the average monopole speed, a flux limit can then be translated into a density limit for our region of space. Without too much effort one might conclude that there are fewer than 100 relativistic monopoles in a volume the size of the Earth. However, for more powerful limits one is likely to turn to other types of studies. Dragons flight (talk) 02:18, 2 October 2017 (UTC)[reply]

Question about the SUNRISE and SUNSET on equator of Earth?

Planet earth not only rotates about its axis but also orbits around the sun once every 365.25 days. Ignore the obliquity of the earth's axis which is more related to the seasons. Days and nights on the equator of the earth are nearly the same; 12 hours each say e.g., Seri Lanka.

For simplicity, lets days and nights are 12 hours each on the equator of the earth throughout the year.

Bird’s Eye View Observer of Picture sees

• SUNRISE in the autumn equinox and SUNSET in spring equinox on his RHS

• SUNSET in the autumn equinox and SUNRISE in spring equinox on his LHS

Thus Bird’s eye view shows a difference of 12 hours when SUNRISE in the autumn equinox takes the position of SUNSET in spring equinox on earth - vice versa and the same is applied to summer and winter solstice. Sunrise and sunset take their original positions when the earth completes its orbit around the sun.

This means, each day, sunrise is lagged behind approximately by 1 min and 24 hours in one year (12 hours in six months as explained above)

If the presented model in the Picture is truly accepted worldwide then why don't we notice such effects in our daily life unless I missed something important?2001:56A:7399:1200:8CC4:755D:4DBC:A90A (talk) 04:17, 30 September 2017 (UTC)EEK[reply]

I think you are referring to sidereal day vs. solar day. A real day is 23 hours, 56 minutes and 4.something seconds. The reason this is not noticed is because right is winter constellations and left is summer constellations and this is how you'd tell. (technically a sidereal day is not exactly one rotation, a stellar day is but it takes 26,000 years for the two to be off by 1 day). Sagittarian Milky Way (talk) 04:31, 30 September 2017 (UTC)[reply]

No, I am not referring to sidereal day vs solar day as days and nights in my questions are still remain the same but lagging behind every moment when the earth changes its position in its orbit around the sun.

Yes, you are referring to sidereal day vs. solar day. The reason we don't notice is that all timekeeping in everyday life is based on the solar day. Sidereal days are only important if you're interested in observing the stars, planets, etc. --69.159.60.147 (talk) 06:10, 30 September 2017 (UTC)[reply]

When you say "sunrise is lagged behind approximately by 1 min" I think you mean 1 degree. The sun's position along the ecliptic (orbit) can be expressed in degrees or time measured eastward from the vernal equinox (Right Ascension). This is tabulated in almanacs - you can see the daily change here [5]. 82.14.24.95 (talk) 11:55, 30 September 2017 (UTC)[reply]

The question was: "why don't we notice such effects in our daily life...?"

Aren't you paying attention to the sky, the stars, and the planets? If you watch them each day, you will notice that they rise and set at different times because the Earth is moving relative to the sun; some of them wander around in the sky and some even look like they're moving backwards; these are not purely-theoretical ideas and you don't need special technology to notice these occurrences. All you need is a keen attention to detail.

Probably the easiest object to notice, if you live on Earth, is the Sun; and next, the moon; watch how the moon rises at a different time each day. Once you've intuitively developed a sense for its pattern - which will take about a month to see through the cycle - next, start watching for the planet Venus - it appears to move much more slowly, and you'll need nearly one whole Earth year to notice its variations. Finally, after you've developed such patience, you can really begin to notice that the stars rise and set at a different time each evening - but the change is very slow.

Some older astronomy books - the ones that assume all the readers live in Northern Europe - write about "summer" and "winter" constellations. The "winter constellations" are stars that rise just after sunset, but only in the winter time. In summer, those same stars are still in the same general spot - but they're overhead only after sunrise! If you recognize those constellations, you absolutely notice that the Earth moves around the sun.

As of the time I write this, Orion is becoming easier to see - as long as you live like a diurnal mammal on the northern half of planet Earth. The stars themselves have not moved very much - but because the constellation appears high in the sky only a few hours after sunset, now - say tonight at around 8:30 PM - is a good time to spot it. If you watch this group of stars for the next six or twelve months, you'll see that every day, they rise a little bit later... And if you live elsewhere in our universe, you'll see your own set of constellations that are easier to see during certain seasons.

Saturn is up, too... right now in California, we can watch Saturn all day long (except we have to work around that pesky blue sky problem). Saturn sets just after sundown, so if you wanted to watch it for long, you'd have to put another observer in Australia, on the other side of the Pacific (where the sun and Saturn go, right after they set in California).

Of course, the sun hasn't gone anywhere - we say that the sun has set, but in reality, it's the Earth that has spun! If anything, it is me and you and the entire Pacific Ocean - we're the ones who have rolled away from the stars and planets that used to be over our head, and no power in the universe can stop us!

So, why doesn't our OP notice the effects they describe? Effects of living on a round planet that moves in space, surrounded by other round planets that also move in space? Evidently, the OPs aren't looking hard enough... the effects are everywhere!

Nimur (talk) 16:05, 30 September 2017 (UTC)[reply]

The most obvious example of this is the planet Venus. It's many a time been mistaken for a flying saucer or an aircraft. You see it in the evening as the "evening star" and then it disappears and comes back as the "morning star". Eventually the ancients worked out that both apparitions are of the same object. 82.14.24.95 (talk) 18:51, 30 September 2017 (UTC)[reply]

This took longer for Mercury I think. Evening or morning Mercury was called Hermes in Greek and the other one was called another god. Sagittarian Milky Way (talk) 19:47, 30 September 2017 (UTC)[reply]

Day is longer than night everywhere because the sky is bigger than the ground to an observer. This is due to the curvature of the Earth. If you were standing on a tiny planet the size of a basketball, you would have nearly all day and hardly any night. Abductive (reasoning) 20:18, 30 September 2017 (UTC)[reply]

This is called horizon dip. Actually for many people the sum of these factors makes more difference: atmospheric refraction: adds about 4 minutes, Sun is 31.5 to 32.5 minutes wide: adds about 2 minutes, Sun usually doesn't drop straight down: exaggerates the above factors. At middle latitudes these sum to over a tenth of an hour. (half at sunrise and half at sunset) Sagittarian Milky Way (talk) 21:41, 30 September 2017 (UTC)[reply]

First of all thank all for your interest and replies. I thought my question was easy to understand for illuminate but let's try this way.

AE = Autumn equinox

WS = Winter solstice

SE = Spring equinox

SS = Summer solstice

Take a point “A” on the equator of earth at sunrise at AE. Now follow this point “A” during the rotation of the earth about its own axis while orbiting the sun. Let's assume first earth is stationary and rotating about its axis only not revolving around the sun. To the Bird's eyes view observer point, “A” always takes its position again when an earth completes its rotation about its axis. Now

There are two different types of the motion of earth according to the accepted model.

1- Rotation of the earth about its own axis

2- Revolving of the earth around sun in its orbit

Both “1” and “2” are independent of each other. Try with an educational globe. Thus the image of the earth is the same in all AE, WS, SE and SS position. So point “A” can be seen in

AE @ Sunrise

WS @ Midnight

SE @ Sunset

SS @ Noon

Example: If sun rises at “A” at 0600 on Sep 01 in AE position then on the equator

Sun rises at 05:59 on Sep 02

Sun rises at 05:58 on Sep 03

Sun rises at 05:57 on Sep 04

Sun rises at 05:56 on Sep 05

Sun rises at 05:55 on Sep 06

Sun rises at 12:00 in its WS position

Sun rises at 18:00 @ in its SE position

Sun rises at 24:00 @ in its SS position

Sun rises again at 06:00 @ AE (When the earth completes its orbit around the sun)

Thus days and nights in my questions still remain the same but lagging behind every moment when the earth changes its position in its orbit around the sun. I hope I have explained things clearly enough to understand. Please correct me if I am wrong.2001:56A:7399:1200:ED04:E934:3CEF:873A (talk) 02:13, 2 October 2017 (UTC)[reply]

There's not enough room for something to change 1 minute per day and add up to 24 hours in 1 year. There are 1,440 minutes in a day, it'd take about 4 minutes per day. Also your explanation is going in opposite directions. Time is determined by the Sun. The left and right don't matter for time (except sidereal time which determines what constellations are up). The longitude of the Equator that's at sunrise on the fall equinox will not be at sunrise on the next fall equinox. It'll be about noon because the year is a whole number of days plus 5 hours 48 minutes and 46 seconds long (give or take a few minutes because 12 lunar months is only 354 days, the planets jiggle the Earth-Moon system's orbit around the Sun a little and so on) Sagittarian Milky Way (talk) 02:45, 2 October 2017 (UTC)[reply]

So all you are asking is "What is the sidereal time at sunrise?" Noon sidereal time is when the vernal equinox is on the meridian. Be clear in your mind as to the difference between the vernal equinox as a direction in space and as a date on the calendar. The "right ascension" (of the sun) mentioned above is the sidereal time at midnight solar time. Now, on the equator on 23 September (the autumnal equinox) the sun will rise at 06:00 by both sidereal and solar time because the vernal equinox culminates at midnight (it being halfway round the orbit from the autumnal equinox). Every day the stars rise about four minutes earlier by solar time (which means the sun rises about four minutes later by sidereal time). Consequently, by the winter solstice the sidereal time of sunrise has advanced to noon, by the vernal equinox to 6 P.M., and by the summer solstice to midnight. We don't notice all this because our clocks are set to solar time, however astronomers do notice it because the sidereal time tells them where to point their telescopes, and it's also an ingredient in the formula by which they derive Greenwich Mean Time from celestial observations. 81.147.142.152 (talk) 09:35, 2 October 2017 (UTC)[reply]

Something has gone awry here. If a body has right ascension X, the sidereal time when it is on the meridian is X. So at the vernal equinox, (when the sun has right ascension of 0h), the sidereal time at solar noon is 0h. Or to put it another way, the sidereal day begins when the vernal equinox ("place") (which we can call the "first point of Aries" to avoid confusion) is on the meridian. The sun's right ascension increases by about four minutes per day. So the relationship is:

                                                      Sun's Right  Sidereal Time   Sidereal Time                
                                                      Ascension    at Solar Noon   at Sunrise 
Vernal Equinox (21 March)                                 0 h           0 h            18 h
Summer Solstice (21 June)       sun has moved 90° E       6 h           6 h             0 h  
Autumnal Equinox (23 September) sun has moved 180° E     12 h          12 h             6 h
Winter Solstice (21 December)   sun has moved 270° E     18 h          18 h            12 h

Right answer, wrong reason. 92.8.220.234 (talk) 19:29, 2 October 2017 (UTC)[reply]

Here is confusion why one can’t notice aforementioned lagging on our mechanical clocks in the representation of Sidereal time Vs Solar time

Sidereal time reckoned from the motion of the earth relative to the distant stars – so its still relative to earth. The position of the sidereal time keeping observer (on earth) also change when earth changes its position in its orbit around the sun

The position of observer "O" in Bird’s eye view of the modeled diagram is fixed in space and therefore the interpretation of "O" is more accurate than observing star moment up in the sky from earth.2001:56A:7399:1200:2016:33DE:67DE:8B48 (talk) 22:27, 2 October 2017 (UTC)Eclectic Eccentric Kamikaze[reply]

Why is the sea level of the Pacific ocean different than the sea level of the Atlantic ocean where the panama canal is?

But the same where Cape horn is? ScienceApe (talk) 20:53, 30 September 2017 (UTC)[reply]

Because the prevailing winds, and hence current, can blow around Cape Horn but not over the Isthmus of Panama? We learned this back in 10th grade History when it was discussed why President Grant wisely chose in a moment of sobriety not to use H-Bombs to simply blow a lock-less waterway through the territory. μηδείς (talk) 21:12, 30 September 2017 (UTC)[reply]

Your ignorance is showing. President Grant, h-bombs, it is to laugh. Abductive (reasoning) 21:13, 30 September 2017 (UTC)[reply]

Yes it's laughable. Ulysses S. Grant b. 1822, POTUS 1869 - 1877, d. 1885. An H-bomb was not available until after completion of the Manhattan Project 1942 - 1946. Blooteuth (talk) 02:23, 1 October 2017 (UTC)[reply]

Ignorance? At least ScienceApe is trying, rather than drinking whiskey. That counts for something in my book. μηδείς (talk) 22:50, 30 September 2017 (UTC)[reply]

If you read our Panama Canal article it says that the difference in levels is due to "differences in ocean conditions such as water densities and weather" which is cited to [6]. Richerman (talk) 23:41, 30 September 2017 (UTC)[reply]

Yes, winds and currents being other terms for "differences in ocean conditions such as water densities and weather". I appreciate the confirmation.

Now, about why Grant didn't decide to use H-bombs...or did he? μηδείς (talk) 00:30, 1 October 2017 (UTC)[reply]

"Was it 'over' when the Germans bombed Pearl Harbor?" ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:11, 1 October 2017 (UTC)[reply]

It was'nt the Germans but their allies, the Japanese who did the Attack on Pearl Harbor. --Kharon (talk) 15:46, 2 October 2017 (UTC)[reply]

I'll stand by Bluto Blutarsky's world view.[7] ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:05, 2 October 2017 (UTC)[reply]

Some readers here may not understand that this stupid subthread is alluding to a real proposal of the 1960s. See Operation Plowshare#Proposals. --69.159.60.147 (talk) 18:22, 1 October 2017 (UTC)[reply]

Who you calling stupid? Jesus,, the Grant/H-Bomb BS was a joke, but I do assume people who've gotten an educationn to age 16 would know t'were a friggin joke. μηδείς (talk) 14:56, 2 October 2017 (UTC)[reply]

U.S. Grant was a rough-hewn character. Sometimes he would get angry and holler "Hell!" Otherwise known as dropping an H-bomb. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:05, 2 October 2017 (UTC)[reply]

Can I just have a straight answer instead of troll answers? ScienceApe (talk) 03:54, 1 October 2017 (UTC)[reply]

I googled "pacific ocean higher than atlantic at panama canal" and there are many results. This one, from The Straight Dope, may be interesting.[8] If not, do that google yourself and see which answers you like. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:02, 1 October 2017 (UTC)[reply]

Short answer, the Earth isn't flat and oceans don't behave like a puddle on the sidewalk. Ocean currents, winds, etc. cause the local height of the ocean's surface to vary. For instance, it's higher at the Equator because it bulges out due to Earth's rotation. The land at the Equator does this too. --47.138.161.183 (talk) 07:22, 1 October 2017 (UTC)[reply]

The Earth bulges out thing is already taken into account with mean sea level. That's why the equatorial Andes aren't the highest point in the world. Sagittarian Milky Way (talk) 07:49, 1 October 2017 (UTC)[reply]

As to the difference in water density mentioned above, see Why is the Atlantic So Salty from Columbia University. Alansplodge (talk) 11:59, 1 October 2017 (UTC)[reply]

The most important factor for most parts of the ocean is the long-term average wind flow, which also affects surface currents. Water flows downhill, to good approximation, but if winds consistently blow water towards the land then on average the water piles up a little higher at that coast. Conversely, if winds consistently blow away from the coast, then they carry a little bit of the water away from the coast and sea level there is, on average, slightly lower than one would expect. The deviations often amount to less than a foot across basins that can span hundreds or thousands of miles. Dragons flight (talk) 07:08, 2 October 2017 (UTC)[reply]

"Wind flow" is repeated in answers here, but not ocean current. The ocean current is west-to-east on both sides of the canal. You can easily do a mini-experiment in a pool or tub. Put your hand in the water to create a strip of land separating two bodies of water. Since it is hard to make the water flow, move your hand instead. If you move it right to left, you will see water on the left side rise and water on the right side fall. That is exactly what is seen on the two sides of the canal. 209.149.113.5 (talk) 14:24, 2 October 2017 (UTC)[reply]

According to this, sea level is about 20 cm higher on the Pacific side of Panama than the Atlantic; if there were a canal without locks, there would be a steady flow from the Pacific to the Atlantic, augmented by tidal currents because the tides have opposite phase on the two sides of Panama. The two oceans can keep water flowing indefinitely in a giant Siphon connecting tube; could this be the basis of future free hydroelectric energy for Middle America? Blooteuth (talk) 21:48, 2 October 2017 (UTC)[reply]

My understanding was the Suez Canal is in a similar situation, though its flow varies in direction by season. But these canals... well, they're like really flat rivers. I mean, the first power plant was at Niagara Falls, involving a large amount of water falling a very long distance (around the falls indirectly, that is; they never quite nerved themselves up to literally eradicate them for a power generator, just turned them down a lot). So it is really scraping the bottom of the barrel to get to this; it's way worse than damming the mighty lower Mississippi in oxbow country. On the other hand, if you could make a canal a mile wide and a mile deep maybe you'd have something, since the volume could be huge. Wnt (talk) 22:21, 2 October 2017 (UTC)[reply]

October 1

CO2 fire extinguisher vs. burning office cubicle

OK, so we know what happens in a CO2 fire extinguisher in terms of thermodynamics and chemistry:

1) When the valve is opened, the liquid CO2 (which is in equilibrium with the vapor inside the tank) is propelled through the valve by the pressure of its own vapor (thermodynamic changes are negligible in this process);

2) As the liquid CO2 passes the valve, it instantly flashes to gas because of the reduced pressure, and cools because of the latent heat of vaporization;

3) The gas undergoes free expansion to many times its original volume, and cools further because of the Joule-Thomson effect;

4) As the gaseous CO2 cools, it hits its sublimation point, and part of it turns into flakes of dry ice;

5) When the gaseous/solid CO2 mixture hits the fire, it instantly stops the combustion reaction by displacing oxygen, thus stopping the generation of heat by the fire (so now only the heat energy already present in the burning fuel must be dissipated); and

6) The cold CO2/dry ice mixture also absorbs some heat from the hot fuel by the sublimation of the dry ice and the heat exchange with the cold CO2 gas (however, this effect is much less than for water).

Which brings up a few questions:

A) Is the above sequence of events correct?

B) I've done some VERY rough calculations, and come up with a ballpark figure that 1 mol (44 grams) of CO2 from a fire extinguisher absorbs about 6.7 kJ of heat as its temperature goes up to 100 C, and that at 100 C the cloud of CO2 can extinguish fires within a radius of 0.625 m of its center (approximating the CO2 cloud as a sphere, and assuming that 25% of the available oxygen must be displaced to stop combustion) -- are these figures in the right ballpark?

C) Suppose you're spraying CO2 from a full fire extinguisher at a typical office cubicle which is on fire and equilibrated at cherry-red heat (about 800 C) (because everything else in the office space is on fire as well and equilibrated at the same extreme temperature) -- how much CO2 is needed to extinguish that cubicle and cool it down to 100 C (assuming that this happens so rapidly that heat transfer from the rest of the room is negligible), and is this even possible with a CO2 fire extinguisher? (I don't know how the firefighter can survive such temperatures -- maybe he's standing just outside the room and spraying through an open door, so he's not exposed to the full heat.)

2601:646:8E01:7E0B:D403:68F1:A297:C74A (talk) 02:49, 1 October 2017 (UTC)[reply]

I don't think CO₂ extinguishers work that way, or at least not primarily. I think the primary mechanism is the separation of the heat from the fuel by displacement as the stream of gas from the extinguisher blows the heated combustion products away. In a self-sustaining fire heat gassifies the solid fuel and the gassified fuel burns, causing heat and completing the cycle. This is why you are instructed to "aim at the base of the fire" and " sweep from side to side" (quoting from the instructions on my extinguisher). -Arch dude (talk) 03:35, 1 October 2017 (UTC)[reply]

See a comparison of carbon dioxide and Halon fire extinguishing systems. StuRat (talk) 04:14, 1 October 2017 (UTC)[reply]
- That appears to be a comparison of a Halon flood system with a CO₂ flood system, not a hand-held extinguisher. A flood system (apparently) needs to raise the CO₂ concentration of the flooded volume to above about 34%, which reduces oxygen availability to the fire. This is a different mechanism. -Arch dude (talk) 21:38, 1 October 2017 (UTC)[reply]

CO₂ extinguishers don't deliver either liquid CO₂ or dry ice, unless you hold them upside down. They work by a simple gas blanket excluding O₂. Andy Dingley (talk) 10:47, 1 October 2017 (UTC)[reply]

The primary efficiency of CO₂ extinguishers is to break the fire triangle thus removing atmospheric oxygen rather than heat. Heat radiates away pretty quickly, yet the CO₂ blanket needs to be maintained until the risk of further combustion has subsided due to radiation. This doesn't apply though to aluminum/magnesium etc., fueled fires because these metals being highly reactive can sequester the extinguishers oxygen (from the CO₂). Nitrogen gas can be used against these fires as it again denies the fuel it necessary oxidant. Thus, braking once more the triangle. Note also, if one is having to use that much CO^{2 one is in danger of asphyxiation oneself. Aspro (talk) 14:42, 1 October 2017 (UTC)}[reply]

I had thought that CO₂ extinguishers had a secondary cooling effect, but this article says: "Danger - This type of extinguisher does not cool the fire very well and you need to watch that the fire does not start up again". Alansplodge (talk) 15:06, 1 October 2017 (UTC)[reply]

Really? The only way the heat dissipates in this scenario is by radiation, and the cold CO2 has negligible effect on it? Then I guess in my scenario the cubicle wouldn't cool at all (because everything else around it is also on fire and glowing red-hot, so the heat would radiate into the cubicle as fast as it radiates away) -- so the firefighter would have to keep spraying it constantly just to keep it from reigniting, and as soon as the CO2 runs out it would catch on fire again! 2601:646:8E01:7E0B:D403:68F1:A297:C74A (talk) 01:15, 2 October 2017 (UTC)[reply]

Yes, CO₂ extinguishers are designed for use in the early stages of a fire, not for when the whole building is ablaze. Dbfirs 13:25, 2 October 2017 (UTC)[reply]

Mars in 2024

An article in WSJ Sept 30-Oct 1 pg B1 titled: "Musk's Mars Shot: To Red Planet by 2024." It means 7 years from now! Briefly, he proposes building a fleet of capsules larger than superjumbo airliners and sending them to Mars, perhaps even in 2022! He claims he figured how to pay for the project but it is not my concern. Does he think about radiation protection? This NASA website[9] is very vague about the current state of technology. No numbers are offered. At the end of the article they mention hydrogen-rich materials. It is water! So, will they fly to Mars in an aquarium? This Wikipedia article[10] gives a radiation comparison chart. The major point I want to make is what to do on Mars? It is a dead planet with no energy anywhere. The Sun is too far away, no tectonics, no wind energy. If they get there they need a nuclear power plant to bring with them. They need to generate heat since the place is so cold, sometimes below $100^{o}$ Centigrade[11]. OK, they got there and what is next? --AboutFace 22 (talk) 22:23, 1 October 2017 (UTC)[reply]

You would need to take a lot of water with you, in any case, both to consume directly (because recycling is never 100% and there's very little water to be had on Mars), and also it could be split to create hydrogen and oxygen. So, putting the water tanks on the outside of the crew compartment for additional radiation shielding might make sense. Of course, there would be far more fuel, at least most of the trip, so surrounding the crew quarters with that might make sense, too. This sounds extremely dangerous, in general, but in this case, if the fuel tanks bursts they are going to die anyway.

I believe solar power could still work on Mars. Sure, there's less sunlight at that distance, but there's also few clouds (except maybe an occasional dust storm) and no trees to block the light. Power production would be modest, of course. StuRat (talk) 22:40, 1 October 2017 (UTC)[reply]

Storing the water and other water-containing supplies around the outside of the living quarters as radiation shielding has indeed been a standard design feature in manned Mars mission vehicles for years. {The poster formerly known as 87.81.230.195} 2.217.210.199 (talk) 18:27, 2 October 2017 (UTC)[reply]

The history of rovers, Opportunity and Curiosity clearly showed that the energy that can be had from the Sun is infinitesimal. They are able to crawl a mile in a year or so and go into hibernation in the winter. --AboutFace 22 (talk) 00:07, 2 October 2017 (UTC)[reply]

Mars is between 1.4 and 1.7 times as far from the Sun as Earth is, so the solar insolation is between 1/2 and 1/3 that of Earth. I wouldn't call that "infinitesimal". It means a solar array has to be 2-3 times the area of one on Earth to generate the same power, although as StuRat says, the lack of clouds and the much thinner atmosphere may reduce that somewhat. The rovers needed to carry their solar arrays with them, limiting the possible size of the array. Even on Earth, solar powered cars are just barely possible with current technology, but stationary solar arrays can generate significant power. Martian dust storms shouldn't be discounted though; a dust storm can last for months and greatly reduce insolation. CodeTalker (talk) 00:41, 2 October 2017 (UTC)[reply]

The linked article says that a thinner atmosphere increases solar insolation - also a lack of clouds would be beneficial to a solar array, not detrimental. I think StuRat made that last point. 81.147.142.152 (talk) 09:15, 2 October 2017 (UTC)[reply]

Ah, I think that the poster is saying that the size of the array can be reduced in these circumstances. 81.147.142.152 (talk) 09:17, 2 October 2017 (UTC)[reply]

See The Martian - it is fiction, but I believe it has a high degree of technical accuracy. The protagonist (Watney) uses a combination of a RTG for heat and big solar panels + rechargeable batteries for electrical power. Gandalf61 (talk) 10:56, 2 October 2017 (UTC)[reply]

I want to know what they are going to do on Mars once they arrived. Any long term plans? --AboutFace 22 (talk) 10:49, 2 October 2017 (UTC)[reply]

There are several possibilities:

0) Since most plans I've seen involve pre-landing supplies with robotic ships, they would then need to go and collect those supplies. Supplies would need to continue to arrive afterwards, as a truly self-sustaining Mars colony would not be possible initially, and they would need to go collect those, too.

1) Dig an underground bunker, to protect from radiation (the thin atmosphere won't stop it all). Perhaps the lander can then be flown into the bunker and covered up.

2) Deploy a greenhouse to grow food.

3) Deploy a communications array to talk with Earth.

4) Deploy a solar panel array.

5) Keep a daily e-journal and send it home. This would be important to monitor their mental health, among other reasons.

6) They would need to regularly do medical self-exams. Hopefully, they could deal with some minor problems, like excising skin cancer, setting a broken bone, or pulling an infected tooth.

One thing I wouldn't think they would need to do is exploration, since unmanned rovers can do that, and they probably can't travel far to investigate anything interesting the rovers find, and such travel would be dangerous (exposure to radiation, space suit tears far from the base, etc.). Something else they wouldn't need is a latrine, since human waste would have water extracted from it then used as fertilizer. Also note that many tasks would take far longer than on Earth, if they involve donning a space suit first. StuRat (talk) 13:21, 2 October 2017 (UTC)[reply]

Its definitively doable. The odds are actually a lottery win in cosmic comparison. I am just an amateur fanboy for "space science" but, far as i have read and no matter the hunt for Exoplanets has only just recently started with Kepler (spacecraft) in 2009, it's already very clear by now, that there are not so many systems with 2 habitable Planets, not to speak of one of them being a paradise or 1000 trillion $ lottery win in sense of habitability. So its only a question of time till we send first settlers there. Maybe a Billionair wants his name in the history books, maybe politics starts a new race to space, maybe it takes another 100 years.. whatever.. it will happen. --Kharon (talk) 15:34, 2 October 2017 (UTC)[reply]

It's not all that difficult to keep a Martian base comfortably warm using only thermal energy from the environment. You need a heat pump and the heat pump can itself be powered by temperature differences in the environment, e.g. between the surface and below the surface. With only two heat reservoirs , you need an external power source to drive the heat pump, with 3 heat reservoirs at 3 different temperatures (the Martian base, the outside environment and the environment at some depth below the surface), that's not needed. Count Iblis (talk) 20:21, 2 October 2017 (UTC)[reply]

Or you could just put a bunch of mirrors on the hills and trust that neither wind nor Martians will steal them away. Wnt (talk) 22:25, 2 October 2017 (UTC)[reply]

Most of what @Kharon attributes to the future Martians can be accomplished here on Earth. In catacombs under the city of Rome or even in New York there is plenty of room to enjoy underground life. It is my understanding that there is no underground heat on Mars, there is no tectonics thus there is no heat. --AboutFace 22 (talk) 00:17, 3 October 2017 (UTC)[reply]

The sources of underground heat on a planet are:

1) Residual heat from the formation of the planet. Since Mars is thought to be as old as the solar system and is somewhat smaller than Earth, nearly all that heat would have dissipated to space by now.

2) Tidal heating. Since Mars has only a couple tiny moons, that won't be much there.

3) Radioactive decay. This should be the major source of heat on Mars, I suspect. Should have lots of heavy elements there to decay, mainly in the core.

4) Heat from sunlight that seeps underground. Sunlight will be less significant on Mars than Earth. StuRat (talk) 00:28, 3 October 2017 (UTC)[reply]

I notice that our Space-based solar power article says "A considerable fraction of incoming solar energy (55–60%) is lost on its way through the Earth's atmosphere by the effects of reflection and absorption". If accurate, and assuming that negligible solar energy is lost passing through Mars' thin atmosphere, that means that the available solar energy on Mars is practically the same as that on Earth's surface. It's actually slightly higher than on Earth when Mars is at perihelion (10% - 25% higher than on Earth) and slightly lower when Mars is at aphelion (15% - 25% lower). CodeTalker (talk) 03:21, 3 October 2017 (UTC)[reply]

True if talking about solar panels, but not if talking about heating Mars, because you have to take night into account, too. Earth's thick atmosphere acts as a blanket at night, especially when cloudy, while heat would radiated unencumbered into space at night on Mars. You can somewhat see an indication of this on Earth deserts, where the dry air doesn't hold in heat as well as elsewhere on Earth, and temps drop more dramatically at night. StuRat (talk) 05:47, 3 October 2017 (UTC)[reply]

October 2

Earaches

Quoting Ear pain#Primary ear pain:

Ear pain can be caused by disease in the external, middle, or inner ear, but the three are indistinguishable in terms of the pain experienced.

Why? Are all the pain-sensing nerve endings located in one place, so they can't tell where the problem is? Nyttend (talk) 01:46, 2 October 2017 (UTC)[reply]

More likely the few nerve endings aren't distinguished in the brain. Many areas of the body have the nerves lumped together, when it didn't make much difference, in our evolutionary past, where the pain was. After all, what would you do differently depending on where in the ear the pain was, and how would knowing where in the ear the pain was improve your survival chances ? (There's a test where you place one or two tines on the arm, and try to tell which is which, and this shows we don't have the ability to distinguish which you might expect.) StuRat (talk) 01:52, 2 October 2017 (UTC)[reply]

References explain this differently. I'm reading (1) the inner ear has no pain fibres The structures of the inner ear (i.e., cochlea and semicircular canals) are innervated by cranial nerve VIII (vestibulo-cochlear), which has no pain fibers. Therefore, most pathologic processes of the inner ear do not produce pain.¸and (2) the nerves in the outer ear are shared with other remote sites on the body making it difficult to know where along these long nerves is the stimulus causing the sensation of pain. The sensory innervation of the ear is served by the auriculotemporal branch of the fifth cranial nerve (CN V), the first and second cervical nerves, the Jacobson branch of the glossopharyngeal nerve, the Arnold branch of the vagus nerve, and the Ramsey Hunt branch of the facial nerve. Neuroanatomically, the sensation of otalgia is thought to center in the spinal tract nucleus of CN V. Not surprisingly, fibers from CNs V, VII, IX, and X and cervical nerves 1, 2, and 3 have been found to enter this spinal tract nucleus caudally near the medulla. Hence, noxious stimulation of any branch of the aforementioned nerves may be interpreted as otalgia. 70.67.222.124 (talk) 20:20, 2 October 2017 (UTC)[reply]

I'll reluctantly agree with Stu. When they had to remove two thirds of my colon, I first went to a urologist, thinking it was a bladder issue. Pain and touch sensors are not very specific internally. My cousin had a ruptured appendix for over a week--normally fatal--but lived through the sepsis. μηδείς (talk) 14:38, 2 October 2017 (UTC)[reply]

It's probably worth while to link to the Cortical homunculus, though it doesn't seem to deal with internal organs. AndrewWTaylor (talk) 17:00, 2 October 2017 (UTC)[reply]

Applying coloured print to silicone?

A lot of programs I use have handy keyboard shortcuts but I use so many different programs that I just can't remember the majority of the shortcuts. My favourite solution would be one of those $2000 USD Optimus Maximum keyboards with an OLED display inside each key which changes depending on what program you're using. However, I'm a baller on a budget and the best I can afford is this $1 USD silicone keyboard cover which I was thinking I could put shortcut symbols onto and then swap with others when changing application. The problem I want help to solve is how to apply the symbols cheaply but in an aesthetically-pleasing way. The only way I can think of is to print them out on paper and cut them out and glue the little squares inside the cover but there's nothing aesthetically-pleasing about that. Are there other ways to cheaply apply coloured print to such silicone covers?

Buy an alphabet stamp kit. Available at most craft stores. Abductive (reasoning) 03:39, 2 October 2017 (UTC)[reply]

I'd just write on them with permanent marker, but then, I have neat printing. StuRat (talk) 05:07, 2 October 2017 (UTC)[reply]

"Permanent" ink wouldn't stick to silicone (at least not for long). ... Apparently, the only ink that sticks to silicone is silicone ink : [12] — 2606:A000:4C0C:E200:E19A:1892:B4DC:8315 (talk) 07:37, 2 October 2017 (UTC)[reply]

The ink will last a lot longer if you write it on the inside - especially if you can carve a small groove and fill it with ink (maybe with a sharp-pointed pen like a fineliner.) Smurrayinchester 07:49, 2 October 2017 (UTC)[reply]

For that you will not just need neat printing, but neat mirror printing! -- Q Chris (talk) 07:58, 2 October 2017 (UTC)[reply]

Laboratory-grade markers will work on a variety of surfaces where more common "permanent" markers rub off. The brand I'm familiar with is VWR [13], but you can find others. I've never tried them on silicone so I can't swear whether that will work, but it is what I would try (of course, I also happen to have VWR markers lying around). Dragons flight (talk) 08:32, 2 October 2017 (UTC)[reply]

I suspect they will work. This product Staedtler Lumocolor permanent special 319 specifically says it's for use on silicone [14]. It's available at various crafts or office supply stores so you probably don't even have to find someone who'd sell single quantities of labroratory equipment to random people [15] [16] [17] [18] [19]. It's even on Amazon [20] but the price there seems a bit out of wack. Nil Einne (talk) 13:28, 2 October 2017 (UTC)[reply]

Let us know if you try. VWR markers have some pretty amazing powers of penetration, but silicone seems pretty resistant. It is practically irresistible force vs. immovable object, or at least ought to be . But actually, I remember that VWR markers could still be resisted by plastic. I mean, you could take your RNase-free Northern blot (on nitrocellulose) and heat-seal it with a radioactive RNA probe in what I think was a polyethylene sleeve, and then, to make sure you keep track which probe is which, you could write on the outside of the polyethylene to permanently and prominently label the Northern blot inside the bag, without getting any counts at all on your marker or anything else. But the bag itself would only take the faintest trace of color from this operation. Wnt (talk) 00:57, 3 October 2017 (UTC)[reply]

And, I suspect that a punch-type stamp wouldn't 'take' (too "rubbery"). 2606:A000:4C0C:E200:E19A:1892:B4DC:8315 (talk) 07:46, 2 October 2017 (UTC)[reply]

Print them on little squares of adhesive plastic, using a print process that resists abrasion. £20 label makers do this quite well. Andy Dingley (talk) 08:35, 2 October 2017 (UTC)[reply]

If alphabet or alphanumeric is all you need, I suspect you could find mirror image alphanumeric stickers. How well they'd stick to the silicone I'm not sure but it might be well enough that'll last if you're careful Nil Einne (talk) 13:31, 2 October 2017 (UTC)[reply]

Article on pubmed

In this paper on pubmed about decreased testosterone levels in biotin deficient rats it states "Biotin treatment of biotin-deficient rats reversed this condition". Could anyone with access to the full text tell me how long it took for the biotin treatment to reverse the decreased testosterone levels? Could you also tell me if there were any effects of biotin deficiency that were not reversed by the biotin treatment? Thank you for your time. — Preceding unsigned comment added by 125.164.134.97 (talk) 17:22, 2 October 2017 (UTC)[reply]

If you look up the URL on Sci-Hub, you have access to this paper. I call this an interlibrary loan from friends in Russia. Some will call this "piracy"; the same people called ResearchGate appropriate a few months ago, and now are ready to call them 'pirates' too unless they arrange a special censorship interface. [21] At each moment in time the life of a slave is a shameless theft from his master, so learn to be shameless.

Now as for the data, the rats were fed a biotin deficient diet for 7 weeks, then injected intraperitoneally with 20 micrograms of biotin for 6 days and killed one day after that. This treatment restored testosterone partially (13.63 +- 3.42 to 70.68 +- 9.35 vs. 103.37 +- 8.65 for controls. It rather mysteriously caused cholesterol to go up to 1.73 in biotin-deficient rats given biotin, vs. 1.35 to 1.39 for all other conditions - biotin deficient and control and testosterone-treated! A clue is that the biotin-deficient rats had 1335 for cholesterol in testis vs. 923 micromol/gram in control, but the value for the treated rats is not given. Presumably the excess store of cholesterol rapidly dribbles out??? They say an acetyl CoA carboxylase deficiency causes cholesterol to accumulate because acetyl CoA is shunted to a malonyl CoA pathway, but don't ask me to explain why it takes to the bloodstream once biotin is restored! 14C-leucine incorporation to proteins was fully restored from 32 to 40 pmoles/mg protein, same as controls. Bear in mind though that this is a small, limited study that cannot possibly show that all effects of biotin deficiency are reversible because they only looked at this much. Wnt (talk) 22:53, 2 October 2017 (UTC)[reply]

If you dip a cube of metal, plastic, glass or nonporous ceramic/rock in

diarrhea infected with the hardest to rinse deadly germs, how long would you have to rinse it with a showerhead before the top becomes food-grade clean and you could lick it? Apologies for the stupid question that I just thought of for some reason. (the water is not hot enough to hurt microorganisms, the drain is fast enough that there isn't much of a pool there, the cube is not water glass, radioactive or the left 2 columns of the periodic table, it's small enough to be inside the heavy flow zone and the block and showerhead isn't moved (except possibly a little twitch as showerheads sometimes do when turned on)) Sagittarian Milky Way (talk) 21:58, 2 October 2017 (UTC)[reply]

Sterilization (microbiology). Forever, rinsing with cool water is NOT a form of sterilization. If you want to perform a science experiment, you need to measure the D value of your technic.

The aim of sterilization is the reduction of initially present microorganisms or other potential pathogens. The degree of sterilization is commonly expressed by multiples of the decimal reduction time, or D-value, denoting the time needed to reduce the initial number $N_{0}$ to one tenth ( $10^{-1}$ ) of its original value.^[1] Then the number of microorganisms $N$ after sterilization time $t$ is given by:

{\frac {N}{N_{0}}}=10^{\left(-{\frac {t}{D}}\right)}

.

The D-value is a function of sterilization conditions and varies with the type of microorganism, temperature, water activity, pH etc.. For steam sterilization (see below) typically the temperature (in °Celsius) is given as index.

Theoretically, the likelihood of survival of an individual microorganism is never zero. To compensate for this, the overkill method is often used. Using the overkill method, sterilization is performed by sterilizing for longer than is required to kill the bioburden present on or in the item being sterilized. This provides a sterility assurance level (SAL) equal to the probability of a non-sterile unit. 110.22.20.252 (talk) 23:39, 2 October 2017 (UTC)[reply]

References

^ "Guidance for Industry: Biological Indicators". United States Food and Drug Administration. 4 October 2007.

...

What a spectacularly scientific question, User:Sagittarian Milky Way.

You know, you might enjoy reading the works of the esteemed Ayatollah Khomeini. Although he is most well-known in the western world as a proponent of militant theocratic revolution, if you ever actually read any of his books, you’ll find that most of his actual writing pertained to his pronounced and well-referenced opinions about how much water you have to use to scrub various types of filth away. It is not entirely unsurprising, given the long cultural legacy that evolved a special relationship with water in the desert ...cleanliness is next to, well, you know.

When the revolution puts you up against the wall, and circumstances are beyond your control, you can scrub yourself clean without wasting a single drop of water.

There’s some kind of recurring eschatological/scatalogical theme in there, somewhere...

Nimur (talk) 15:51, 3 October 2017 (UTC)[reply]

See our articles Oligodynamic_effect, Antimicrobial_properties_of_copper, Antimicrobial_surface, and for more detail see properties of nine pure metals: a laboratory study using Staphylococcus aureus and Escherichia coli, and this recent Nature review article Antimicrobial activity of metals: mechanisms, molecular targets and applications

TLDR: many metals have an intrinsic ability to disrupt and kill many microbes. This fact has been used since antiquity [22], but fully understanding and applying these effects are currently an important and active area of research. SemanticMantis (talk) 17:18, 3 October 2017 (UTC)[reply]

Get h without h20

Suppose I have no water. What is the easiest way to make hydrogen? I'm not looking for smartass answers like buy it on Amazon. Since hydrogen is in all carbohydrates, I figure that there must be some way I can mix common household goods to extract hydrogen. — Preceding unsigned comment added by 2600:1004:B145:B4FB:E9FF:D136:CD9A:87BE (talk) 22:43, 2 October 2017 (UTC)[reply]

Hydrogen-containing acid and metal produce a salt and hydrogen. This may not be the easiest way. Sagittarian Milky Way (talk) 23:03, 2 October 2017 (UTC)[reply]

Also see hydrogen production. Most current production is from fossil fuels. —Paleo Neonate – 23:41, 2 October 2017 (UTC)[reply]

Conceptually, any combustion reaction will convert compounds of C, H, and O into CO2 and H2O in proportion to the C and H present. This water, from any source, can then be used to make hydrogen as desired. (Ideally, I suppose the electricity comes from a generator run by the combustion reaction...) Wnt (talk) 00:51, 3 October 2017 (UTC)[reply]

Alternatively, cracking (chemistry) can convert many hydrocarbons into mixtures that contain hydrogen + smaller hydrocarbons. Wnt (talk) 00:49, 3 October 2017 (UTC)[reply]

The easiest way would be to drop iron filings into acid (this was how the French and others made hydrogen for balloons when there were no other methods of hydrogen production yet). 2601:646:8E01:7E0B:D403:68F1:A297:C74A (talk) 01:13, 3 October 2017 (UTC)[reply]

Victorian aviation balloons were filled by reacting scrap iron, usually high surface area iron filings, with acid. Look at photographs for observation balloons of the US civil war, there are some good photos around.[23] The reaction was done in wooden barrels carried on wagons. These wagons had to have their iron fittings replaced with bronze or lead ones, owing to their corrosion from the acid fumes. Andy Dingley (talk) 11:59, 3 October 2017 (UTC)[reply]

Been too long (45 years) since chemistry. I was trying to do a feasibility test. Assume that I have iron filings and vinegar - two things that I could likely get easily just about anywhere. It seems to me that if I were to try to separate the hydrogen and then burn it to make water, I would be much better off distilling the vinegar to separate out the water. Perhaps I'm misreading the question and it isn't about trying to get hydrogen to make water. 209.149.113.5 (talk) 15:10, 3 October 2017 (UTC)[reply]

All of the methods appear to use water in some form. The big industrial approaches react steam (water) with natural gas or coal. Methods using acid and metal have water in the acid. -Arch dude (talk) 15:43, 3 October 2017 (UTC)[reply]

"Since hydrogen is in all carbohydrates, I figure that there must be some way I can mix common household goods to extract hydrogen."

Not necessarily. Consider the energy aspects. Andy Dingley (talk) 17:15, 3 October 2017 (UTC)[reply]

October 3

More firefighting Q's...

1) Are Novec 1230 fire extinguishers likely to be found in airport terminals?

2) How much heat can 1 mole of Novec absorb from a burning object at 800 C, and how many moles of it does a typical fire extinguisher contain?

3) Suppose I substitute a Novec extinguisher for the CO2 one in my previous scenario (trying to extinguish a burning office cubicle at 800 C and cool it down to 100 C) -- how much Novec must be expended to achieve this (assuming the cooling is rapid enough that heat transfer from the rest of the room, which is also at red heat, is negligible), and is this even possible with Novec?

2601:646:8E01:7E0B:D403:68F1:A297:C74A (talk) 01:08, 3 October 2017 (UTC)[reply]

They're used, but in flood systems, so not in human-occupied spaces. You find them in server rooms or machinery spaces. The regulations are very tight on mixing these flood systems with humans - you either have to disable the flood system when humans are in there, or the humans have loud warnings to evacuate before it goes off - and those systems are only used where there's a risk of explosion that would destroy the building (it's worth the risk of suffocating people if they'd be killed by an explosion anyway).

Again, these materials are used to extinguish a fire chemically, by blanketing or by chemical reaction. They're not intended for use by simple cooling.

They're used in three main scenarios:

Expensive equipment. So it's a safe blanket that's easy to clean up and doesn't react with warm materials. You can flood a room full of money and only damage the one rack that was actually on fire. Note that cold gases can cause damage by thermal shock.
Dangerous materials. They're a fast knock-down to energetic materials that you really don't want on fire. An installed flood system is deployed far faster than a human team reaction, or bringing extinguishers to it.
Difficult to extinguish materials. The ability to block the chemistry of the fire reaction can be useful to extinguish things that can't otherwise be extinguished by simple cooling or blanketing. Note the difference between inert sodium bicarbonate powder extinguishers for BC fires and ammonium phosphate that is acidic, reactive and can extinguish ABC fires (but will leave a corrosive residue). Fluids like Novec (I know nothing of Novec itself) are inert at low temperatures, limiting cleanup damage, but reactive at high temperatures.

You don't need to extinguish such a fire by cooling it, because you had installed an expensive flood system with an expensive fluid, which extinguished the fire before it became so hot that its simple total heat was a problem. Hot fires (as total heat in a volume, not temperature) are extinguished with water, because nothing else is available in the quantities needed to deal with a big fire.

If you're on site, you can extinguish potentially serious fires with a tiny CO₂ extinguisher, just because you were quick on the scene. Even better when is automatic.

If you're not on site, and have to travel to it, serious fires will be big by the time you get there. That's why it's nearly always time for water.

To answer your specific questions needs textbook figures that I just don't have handy. But I don't think they're even needed here, because your basic premises - that these fluids operate only by cooling - aren't correct. Andy Dingley (talk) 11:56, 3 October 2017 (UTC)[reply]

The article Fire extinguisher clearly states that Novec works by cooling as well as by blanketing/chemical reaction -- and your assertion that hot fires always require water is not correct, because if there's live electrical equipment in there (as in the cubicle farm I described), then water cannot be used. 2601:646:8E01:7E0B:D403:68F1:A297:C74A (talk) 12:27, 3 October 2017 (UTC)[reply]

Efficiency of jet engine

Suppose a jet passes $r$ kg/s of matter at a velocity $v$ m/s. Then the force on the jet is $F=rv$ N (I think). Now, suppose you want to configure $r$ and $v$ so that the engine is "efficient" in the sense of using a small amount of power for the given force $F$ . Basically, is it better to have small $r$ and large $v$ , or large $r$ and small $v$ ? My guess is that the power used to pass the propellant is ${\frac {1}{2}}rv^{2}$ W, because each second, you're passing matter which has kinetic energy of ${\frac {1}{2}}rv^{2}$ J: that means you have to give the propellant ${\frac {1}{2}}rv^{2}$ Joules every second, or expend ${\frac {1}{2}}rv^{2}$ watts. Substituting my first equation, that would equate to a power of either ${\frac {1}{2}}{\frac {F^{2}}{r}}$ or ${\frac {1}{2}}Fv$ watts. That would suggest that it's better to have large $r$ and small $v$ if you want to minimize power. Is this logic sound? PeterPresent (talk) 02:53, 3 October 2017 (UTC)[reply]

Nope! It's really hard to compute the relation between the thrust (force) and the power for a jet engine. In fact, it's as hard as doing rocket science. You can try to deduce a relation from first principles of kinematics, but your equation is bound to be incredibly inaccurate because it fails to account for all the complications of airflow.

The math you used might apply to some toy problems in continuum mechanics like computing the energy budget for a chain falling off a table, or for bulk material getting accelerated as you continuously pour it onto a conveyor belt... this is the sort of problem that is concocted to torture physics graduate students, but it's not a practical equation, and it's not particularly useful as a practical approximation to real-world aerodynamics.

You might want to read our article on specific impulse; thrust; and jet engine.

For a practical overview of how this works, read Chapter 5 of the Pilot's Handbook of Aeronautical Knowledge; for a theoretical overview, Aerodynamics for Navy Aviators (Required Thrust and Power, pg. 96; and principles of propulsion, pp. 104-112). The latter reference actually starts with your exact equation and develops it into an equation more familiar to the engineers who build jet engines. They do so by introducing η (eta).

Our Wikipedia article used to have this great picture, two airplanes tied to a tree; it's not a wonderfully sound explanation; but the metaphor is potent - the relationship between power expended by the engine, and thrust that actually develops, is subject to aerodynamic inefficiency. The aerodynamic effieciency-factor can range all the way down to 0% - so it's not something you can casually neglect!

This is exactly why engineers use the specific impulse to examine engine efficiency; and they use the drag coefficient and the lift-to-drag ratio to examine the aerodynamic efficiency. For large jet engines, there are many separate types of efficiency losses, and many distinct regimes of operation; so you can't summarize all of engine efficiency into a single parameter.

I might observe, for example, the recent trend toward high bypass turbofans. That trend seems to indicate that on the whole, it's more efficient to move more air at subsonic speeds, than to try to move a small jet of air at hypervelocity. But on more thorough consideration, this is not a generalizable rule; it's easy to find counter-examples. For example, one of the first maneuvers taught to aviators is slow flight - the regime of "reversed command," in which slowing down the aircraft requires adding engine power. More fuel is spent, and the aircraft goes slower! Aerodynamics - it's not intuitive!

Nimur (talk) 04:32, 3 October 2017 (UTC)[reply]

The OP might find this explanation to be helpful: Why Planes Don't Fly Faster. --Guy Macon (talk) 08:08, 3 October 2017 (UTC)[reply]

The formula

f=rv

is quite accurate for a rocket engine in a vacuum, but for a jet engine you have add a slightly lower mass flow of gas flowing in at a lower speed at the front end of your engine, in addition to the other difficulties of fluid dynamics which make finding analytical solutions impossible most of the time. I'd say that jet engines are much harder than rocket science. But qualitatively, it's quite easy to see that a larger flow at a lower speed gives a more efficient engine: you put less kinetic energy in the jet for the same momentum. The momentum of the jet is what gives you thrust. The high bypass ratios of modern jet engines are there to increase efficiency. PiusImpavidus (talk) 11:02, 3 October 2017 (UTC)[reply]

But, lower speed means flow that is less laminar, so less of the momentum you impart is in a useful direction. When you measure thermodynamic energy budgets for a jet engine, is it useful to consider the work output if the work is spent moving turbulence, instead of the vehicle? Nimur (talk) 13:49, 3 October 2017 (UTC)[reply]

The OP may find the Ramjet article interesting. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:54, 3 October 2017 (UTC)[reply]

How does the Portuguese man o' war eat

Our article has lots of info about how it stings and tons about the gas filled sail, but doesn't explain how it actually eats the things it stings. Presumably, they'd normally float away, so do the tentacles grab them and pull them to some kind of mouth or do they grab them and eating parts of the tentacles get to work? --84.19.47.96 (talk) 09:06, 3 October 2017 (UTC)[reply]

This National Geographic video shows the process. -- ToE 09:29, 3 October 2017 (UTC)[reply]

Complex roots by numerical methods

Which numerical method is best for finding the complex roots of a given algebraic equation? 14.139.241.85 (talk) 16:21, 3 October 2017 (UTC)[reply]

Refilling Glycogen Stores

According to various sources (although somewhat lacking in the Wikipedia article) the liver can store ~100 grams of glycogen and the muscles can store ~400 grams. As each gram of glycogen has 4 calories, this means in total a hypothetical persons body can store ~2,000 calories in glycogen.

Lets say that hypothetical person has a daily total caloric expenditure of 2,000 calories to maintain their weight (ignore water weight here since 1 gram of glycogen binds to 4 grams of water so water weight will fluctuate by 2 kilograms).

If they depleted their liver and muscle glycogen through exercise, a ketogenic diet, or starvation and then ingest 4,000 calories of carbohydrates in a single day, does that mean that 2,000 calories of the ingested carbohydrates will go directly to glycogen stores and the remaining 2,000 will be used by the bodies metabolism? Meaning in effect that despite consuming double their required daily intake, they do not put on any fat? 209.40.170.84 (talk) 16:42, 3 October 2017 (UTC)[reply]

I'm not sure if you will find any studies on that, but it seems unlikely that fat production would be 100% shut down. I could believe it would be reduced somewhat, yes, but entirely stopped, no. However, if stored fat is also turned into glycogen by some method, then effectively, this could be the case. StuRat (talk) 17:14, 3 October 2017 (UTC)[reply]

Anti-biotics questions.

1. Some anti-biotics advertise as killing gram-negative bacteria as good as gram-positive bacteria. Are there any anti-biotics that advertise as killing gram-negative better than gram-positive? Or should I say, what % of anti-biotics kills gram-positive better, what % both equally, and what % kill gram-negative better.

2. If something is both an anti-biotic and a anti-viral, what would it foremost be classified as? I just asked a chemistry professor who worked in the pharmaceutical industry, designing drugs, he say he never heard of a medicinal drug that can do both, so I guess I should instead ask, are there any drugs that are both anti-viral and anti-biotic at the same time? I note that Wikipedia's antiviral article says most anti-virals unlike anti-biotics, are used for killing/treating 1 virus at a time. But it wouldn't surprise me if some anti-viral are also have some anti-biotic. The anti-biotic article, says that "A limited number of antibiotics also possess antiprotozoal activity," so. Thanks. 12.239.13.143 (talk) 17:46, 3 October 2017 (UTC).[reply]

Big science equipment - rolled on wooden trunks?

Does anybody know the story behind this picture? It shows a large magnet of the Mirror Fusion Test Facility in 1981, probably prepared for transportation on a road made out of logs. Was is really transported so low-tech? At those times SPMTs were already known.

Thanks for any help.--Stephen Doe (talk) 16:08, 2 October 2017 (UTC)[reply]

Looks like somebody went over budget and had to make due. :-)

One thought is that it won't do much bouncing around, this way. If the equipment is extremely sensitive, and time is no object, and perhaps the money involved in a more high tech solution is an issue, this approach might make sense. StuRat (talk) 17:00, 2 October 2017 (UTC)[reply]

I've taken over this question, since I don't believe in any coincidence.--Spmt6 (talk) 18:03, 3 October 2017 (UTC)[reply]

[1] "Guidance for Industry: Biological Indicators". United States Food and Drug Administration. 4 October 2007.

[1]