:::Ah, gotacha. Thanks, that clarifies it. [[User:Scala Cats|Scala Cats]] ([[User talk:Scala Cats|talk]]) 18:36, 23 June 2017 (UTC)
:::Ah, gotacha. Thanks, that clarifies it. [[User:Scala Cats|Scala Cats]] ([[User talk:Scala Cats|talk]]) 18:36, 23 June 2017 (UTC)
:Also note that the type of pinhole camera lacking a lens might still have a glass cover over the pinhole, to prevent dust from getting in. [[User:StuRat|StuRat]] ([[User talk:StuRat|talk]]) 17:55, 23 June 2017 (UTC)
:Also note that the type of pinhole camera lacking a lens might still have a glass cover over the pinhole, to prevent dust from getting in. [[User:StuRat|StuRat]] ([[User talk:StuRat|talk]]) 17:55, 23 June 2017 (UTC)
::Really? In the very unlikely circumstance of dust being a problem, wouldn't the shutter adequately serve that purpose?--[[User:Mrs Wibble-Wobble|Mrs Wibble-Wobble]] ([[User talk:Mrs Wibble-Wobble|talk]]) 18:37, 23 June 2017 (UTC)
== Blocking gravity waves? ==
== Blocking gravity waves? ==
Revision as of 18:37, 23 June 2017
Welcome to the science section of the Wikipedia reference desk.
The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
Why is francium so unstable? The article doesn't explain. Google found me a Prezi presentation ([1]), but first off that's not a reliable source for expanding the francium article, and secondly it doesn't explain why many isotopes of related elements, e.g. 238U with 54 more neutrons than protons, are so much longer lived. Nyttend (talk) 12:31, 18 June 2017 (UTC)[reply]
Island_of_stability has some general info on how people have tried to understand stability of stuff with high atomic numbers. I don't think it gives a direct and simple answer to why francium has a short half life, but lots of good relevant information and theory is presented. SemanticMantis (talk) 15:33, 18 June 2017 (UTC)[reply]
At a low level, it isn't very surprising - I mean, it's not like technetium sitting in the middle of the periodic table. It comes in a rogues gallery near the tail end of the known stable isotopes, between astatine and radon on one side and radium and actinium on the other. There is one little clump of stable isotopes after that - thorium, protactinium, uranium, neptunium, plutonium (protactinium and the latter two aren't all that stable, but at least you can take a picture of a big lump of plutonium, though somebody might have to kill you afterward). Wnt (talk) 17:21, 18 June 2017 (UTC)[reply]
Minor note: you noted that uranium-238 has 54 more neutrons than protons. Yes, that's what makes it relatively stable. Neutrons, just like protons, attract other nucleons through the nuclear force, but, since they're electrically neutral, they don't repel other neutrons or protons. Hence, neutrons are essential for stabilizing nuclei with higher numbers of nucleons. The neutron–proton ratio of stable isotopes goes up with increasing atomic number, for this reason. --47.138.161.183 (talk) 21:24, 18 June 2017 (UTC)[reply]
That is absolutely not the full story, or else heavier uranium isotopes would be even more stable. You need to take beta decay into account; too few neutrons and a few protons will want to turn into neutrons to increase binding energy, but too many neutrons and some will want to tun into protons for the same reason. In the middle we have the line of beta stability, a sort of "Goldilocks zone" for the nucleus. There are also regions of increased stability against other decay modes: here alpha decay and spontaneous fission are also important.
In the case of thorium and uranium, the beta-stable and alpha-stable lines coincide, and nuclides like 232Th, 235U, and 238U have not much of a desire to decay. Astatine and francium have a big problem because the lines do not coincide in that region: you will find that the most stable isotopes of At and Fr towards one decay mode quite readily suffer the other one.
Admittedly this explanation just puts the question one step further back. Why does the beta-stability line dive into a region of alpha instability just past Pb and Bi? The reason is because doubly magic 208Pb has a very stable closed nuclear shell, so much so that the energy gap between the highest occupied and lowest unoccupied proton and neutron shells is very big. Alpha decay thus ends up releasing enough energy and being energetically feasible, and thus if you look at a chart of nuclides the alpha-decay region appears to suddenly explode from polonium onwards. (Why Po and not Bi? Because making the alpha particle from Bi requires breaching the full subshell for both protons and neutrons. 210Po is less inhibited because emitting the alpha gets us back to the filled proton shell, and because both start and end nuclei are zero-spin; it is easier to form the alpha when the nucleons that form it are already paired the right way.) The same thing happens, though with much longer half-lives, in the lanthanide series once the closed shell of 82 neutrons is surpassed.
As a result, stability is greatly depressed until Th and U with their semi-closed shells at 142 neutrons and 92 protons. (Already the alpha- and beta-stability lines are not quite in sync; the most stable isotopes 232Th, 238U, and 244Pu can suffer double beta decay, and from Cm onwards spontaneous fission from the overly large Coulomb repulsion of protons puts an end to the island. But the region of alpha-stability is less skewed to the neutron-rich side than it is around astatine and francium.) Double sharp (talk) 06:31, 19 June 2017 (UTC)[reply]
Yellowstone national park super explosion
Would the eclipse which could be total in Wyoming put enough gravity on the hot magnma underneath yellowstone and make supervolcanos to destroy America? Can the fracking make it even worse? Thankyou! 64.134.238.170 (talk) 18:26, 18 June 2017 (UTC)[reply]
Total eclipses visible in Wyoming have, probably, happened multiple times since the last eruption 630,000 ago without any consequences. Ruslik_Zero18:29, 18 June 2017 (UTC)[reply]
No. Absolutely not. A geographic location is totally eclipsed every few centuries on average. I don't know about fracking. And I'm on the East Coast but Wikipedia's news ticker is on my watchlist and I saw "Yellowstone national park super explosion" new section and 1 reply and was like oh my God. Sagittarian Milky Way (talk) 19:02, 18 June 2017 (UTC)[reply]
No, because eclipses do not have a significant effect on gravitional effects on Earth. It's just not fundamentally different from any other spring tide. Even then, the maximal effect is a perigean spring tide, which occurs three or four times every year (far more frequent than eclipses), and the August 2017 eclipse does not coincide with one. The maximal totality duration for August 2017 is about 2:40, substantially less than the possible maximum of around 8 minutes of totality. Finally, the inclination of the lunar orbit with respect to Earth (about 5°) means that even when the moon is maximally angled away from directly overhead, some 99.6% of the theoretical maximal gravity pull is still oriented along the vertical — that's the key bit to explain why the fact that it's an eclipse (and directly overhead) simply doesn't matter for gravitational purposes. — Lomn19:26, 18 June 2017 (UTC)[reply]
But wouldn't the tides suck more molten rock into the caldera? Scientists seem to be unconcerned because the caldera is only 10% molten rock, but tides could increase that. 144.35.114.222 (talk) 16:51, 20 June 2017 (UTC)[reply]
June 19
Why does the squirty hand soap dribble in hot weather?
There are no stupid questions, right? :D So: I have a squirty hand soap, i.e. plastic bottle with a vertical tube that dispenses the soap when the top is pressed down. Recently the weather has been hot (for the UK: high 20s ºC; and that part of my house is a heat trap), and I keep noticing that some of the soap has drooled out on its own. Is there some heat-related explanation for this? Equinox◑00:58, 19 June 2017 (UTC)[reply]
I doubt expansion matters here. Likely the viscosity is rising with the temperature and the dispenser starts leaking because its not build to keep such highly viscose content. Easy to test. Put some of that soap into a glass and put the glass into hot water. Then check if it becomes more "fluid" when heated up. --Kharon (talk) 03:41, 19 June 2017 (UTC)[reply]
Agreed. The viscous friction normally keeps the thick fluid from the last use in the tube, but when it becomes thin, then gravity can pull it down. StuRat (talk) 04:22, 19 June 2017 (UTC)[reply]
@Kharon: Rihgt! That's easy to test: replace the liquid soap with water and see how the device behaves (in normal temperature and in heat; when pumped and when left alone). Then replace water with glue or with plasticine and see again. Correlate results with temperature and with viscosity. --CiaPan (talk) 12:30, 19 June 2017 (UTC)[reply]
I don't think that test would work, because with water it would flow completely out of the tube right away, as opposed to being thick enough to stay in there initially, and later becoming liquid enough to dribble out. StuRat (talk) 17:29, 19 June 2017 (UTC)[reply]
Using water (with food coloring over a paper towel) will prove that after pumping completes, there is still water in the tube. It drips out. If water remains in the tube after pumping, then we have to decide if it is reasonable that soap remains in the tube after pumping. Add gelatin to the water to get it between the consistency of the liquid soap and plain water. Does it still remain in the tube and dribble out? Keep increasing the consistency of the liquid. If you prove that soap remains in the tube after pumping (which makes sense), then you put the soap on a small cold dish with a thermometer and slowly heat it up. At what temperature does it start to get runny? Is it low enough that the ambient warm air could cause it to be runny? If so, you've demonstrated that soap remains in the tube and it is runny in the warm air. So, there is no need for gas expansion to explain the observation. There could be gas expansion - but it is not necessary and, in reality, gas expansion is a one-time thing. It would expand, dribble out some soap, and then be done. It won't dribble out soap every time you use the container. 209.149.113.5 (talk) 13:53, 20 June 2017 (UTC)[reply]
I put it down to thermal expansion, try loosening the pump from the top of the bottle (undo the thread a bit) and it will stop doing it! works every time for me here in Brisbane. 49.197.176.179 (talk) 07:33, 19 June 2017 (UTC)[reply]
Seconded: it's a matter of pressure, caused by thermal expansion of gas. The same way the Moka pot works. See the animation.
In a coffe pot the hot vapour presses water below, which escapes upwards through the internal vertical tube. The same way hot air in a soap bottle presses the liquid soap which escapes upwards and drips outside. --CiaPan (talk) 10:13, 19 June 2017 (UTC)[reply]
The coffee pot is an analogy, not an exact parallel. Try reading CiaPan's last sentence: air expands considerably when warmed, easily enough to create in the sealed, partially air-filled bottle a mild overpressure sufficient to force some soap through the pump mechanism. {The poster formerly known as 87.81.230.195} 94.12.79.194 (talk) 18:24, 19 June 2017 (UTC)[reply]
The Moka pot effect is due to the change in volume of the contained gas, not the liquid. It's easy to calculate the change in pressure, using the ideal gas law. Assuming the container is air tight and doesn't change its volume, the pressure of the gas is proportional to the temperature, expressed in Kelvin. So, for example, if the temperature increases from 15 C to 32 C (288 K to 305 K), the pressure increases by 6% (17/288). At standard atmospheric pressure of 14.7 psi, the increased pressure would be about 0.9 psi. If the soap tube is 3/8 inch in diameter like the one I just measured, it has a cross sectional area of 0.11 square inches, so the force on the liquid in the tube would be about 0.4 Newtons (1.6 ounces). That seems like sufficient force to move the gelatinous soap. How much would actually be extruded from the nozzle would depend on the volume of the contained gas, since the pressure decreases as the air expands into the tube. CodeTalker (talk) 23:08, 19 June 2017 (UTC)[reply]
Actually, the air won't expand into the tube. In the top-plunger design described by the OP, the tube extends (almost) to the bottom of the (partially) soap-filled bottle, so until the soap is (almost) entirely expended, the end of the tube will always be submerged in soap, while the (heat-expanded) air is exerting overpressure on the soap's top surface.
Sorry, I expressed that poorly. I meant the pressure decreases as the volume of the trapped air expands, due to the soap (not air) being pushed into the tube. CodeTalker (talk) 15:41, 20 June 2017 (UTC)[reply]
A possible contributory factor is that there must be something of a one-way valve effect allowing air into the bottle, otherwise as soap is expelled the air in the bottle would develop underpressure/partial vacuum and work against the pump mechanism, and the bottle (if flexible plastic) would tend to contract. Fluctuating ambient temperatures will then tend to "pump up" the internal pressure. {The poster formerly known as 87.81.230.195} 94.9.80.133 (talk) 14:49, 20 June 2017 (UTC)[reply]
Why does Earth keep getting nearer and nearer to the edge of the "habitable zone"?
The idea of a habitable zone, a part of a solar system where liquid water can exist, is deceptively simple. After all, habitable for what kind of planet? But I cannot for the life of me figure out the NASA graphics with the green habitable zones that keep putting Earth nearer and nearer to the edge. Like [2] Figure 6 -- I mean, their bright green non-"optimistic" habitable zone would seem to have Mars more squarely in it than Earth! (I think this estimate comes from here, but I don't see that much explanation of the logic... while liquid water may have flowed on Mars once, under what conditions was that?)
I just don't get it. From first principles, I'd think a non-optimistic habitable zone would be about the width of Earth on the diagram. Maybe you can broaden it on the basis that a planet might be a bit bigger or smaller than Earth, have a bit more or less CO2, a bit more or less water and so on. It's true that the Sun was fainter before (faint young Sun paradox), but it's also thought to be the case that there was a snowball Earth as recently as 600 million years ago, and that this lack of insolation was something that held back development of life. We ourselves came out of an Ice Age, and our culture seems to think it can take a six-degree-C increase in temperature over the next century and scarcely even complain. So where does the asymmetry come from? Does a habitable zone include underground Martian brine? Because I'd think there's a chance you could find brine in a cryovolcano on Pluto, so is that habitable zone? Why wouldn't we be able to postulate a planet in the position of Venus with a thinner atmosphere and a high albedo that is no warmer than Earth, but still has seas? Wnt (talk) 21:48, 19 June 2017 (UTC)[reply]
Life has existed for approximately 4 billion years, but we're near the end "In about one billion years, the solar luminosity will be 10% higher than at present. This will cause the atmosphere to become a "moist greenhouse", resulting in a runaway evaporation of the oceans. As a likely consequence, plate tectonics will come to an end, and with them the entire carbon cycle." Count Iblis (talk) 22:55, 19 June 2017 (UTC)[reply]
We almost missed having stable liquid water, actually: if you look at circumstellar habitable zone, you will notice that even at 0.98 AU calculations (see the recent Kopparapu 2013 paper) show that an Earthlike world (which would need to have similar quantities of liquid water – that seems a plausible general assumption) would receive enough insolation to slowly boil off the oceans. Then the water vapour in the air would be split into hydrogen (lost) and oxygen by solar ultraviolet radiation, and the entry of carbon dioxide into the atmosphere ends up going unchecked. Venus followed this route, and if the Sun was a little bit brighter (as it soon will be) we would too.
Mars is far enough away from the Sun that this problem does not apply. Instead, its problem is that it is too small and lacks a strong magnetic field, so its original atmosphere was stripped away by the solar wind and the water all froze. An Earthlike world at Mars' orbit may not have such a big problem. In general, the obstacles at the hotter side are more difficult to surmount than those on the colder side: the Kopparapu paper places the upper limit around the orbital distance of Mars. Double sharp (talk) 07:53, 20 June 2017 (UTC)[reply]
An additional factor is that Mars is apparently too small to have maintained tectonic activity, which apparently ceased there around around 2 billion years ago. On the Earth this causes atmospheric gases and liquids that have been chemically combined into the surface rock to be subducted and then recycled via vulcanism: on Mars, however, the rock-absorbed gases and liquids remain 'entombed' in the now-static crust. {The poster formerly known as 87.81.230.195} 94.9.80.133 (talk) 15:06, 20 June 2017 (UTC)[reply]
Venus has infact a much higher albedo (0.75) then earth (0.3). Nevertheless its around 450 °C there. Its much to close to our sun. Also a habitable zone orbital position does not guarantee a habitable planet. It only implies a good chance for one. Many other properties can make it unhabitable. From toxic gases, vulcanic activity to an eliptic orbit around the sun, allot can be wrong. We need much more than the right temperature and some water. I dont understand what edge you refere to in the nasa diagram. As noted below our 3 planets are only put there as reference. --Kharon (talk) 10:24, 20 June 2017 (UTC)[reply]
Yes, a lot more can go wrong. The border at about 0.99 AU merely alludes to how it can go wrong in one specific way (becoming a Venus), and the habitable zone merely states where things might not go wrong. It is quite possible that the border just outside the orbit of Mars is overoptimistic; at the very least it shows that planetary size is another way in which things might go awry. Double sharp (talk) 10:34, 20 June 2017 (UTC)[reply]
Here is the paper I have been referring to. While it is true that we appear closer to the inner edge than we might really be, there is generally much less wiggle room at the inner edge than the outer edge. Earth would then look like a perilously borderline case, while Mars would almost certainly have been habitable had it been Earth-sized. Double sharp (talk) 10:52, 20 June 2017 (UTC)[reply]
Earth has been much hotter, apparently without going greenhouse
@Double sharp: Thanks for pulling up the paper! Albeit I find myself inhospitable to its content. So far, I see that they assume a 6.5 atm surface pressure, a fixed assumed stratospheric temperature of 200 K, and ignore the effect of clouds entirely ... then come up with the notion of a "moist greenhouse" that depletes all the water via a very sharp-edged set of curves for stratospheric content if surface temperatures get just slightly higher than on Earth. Now this is indeed alarming in that they show a curve where at a nearly constant Seff only slightly above 1, the surface of the planet gets more than 50K hotter - it suggests utter catastrophe awaits us with global warming, for example. But a problem I have with that theory is that we did that with the Paleocene-Eocene Thermal Maximum and nothing very significant happened. I mean, it wasn't long enough for a "moist greenhouse" to do much, so we don't know that, but we know the surface temperature didn't go completely insane and roast everything.
So I'm tending to reject the validity of their model to some degree; yet there is one thing I will admit... yes, the Earth has all the water it can have. I mean, I'd think it seems possible there was even more water at some point but it raised the level enough that some of it got lost to space - fine tuning us right smack dab on the inner edge of the "habitable zone" where Earth can exist. And by the same token, if Earth started losing water to "moist greenhouse" until it was 1/3 ocean and 2/3 land, surely the level of water vapor in the stratosphere would go back down again, no? Also, what about the magnetic field? Couldn't that drastically expand a habitable zone against slow atmospheric loss, just as its lack put Mars, it would seem, inside the inner edge in reality?
Comparing Venus and Mars seems to understate the importance of carbon dioxide. Earth has 0.0004 atmospheres of CO2; Venus has 90. It's hotter than Mercury on average, but I'm not convinced it has to be that way. I don't know what the CO2 level on Mars was when it had liquid water flow - if that was ever water and not a dense brine. So I'm just not buying all of this ... but the drastic moist greenhouse definitely seems worth keeping track of anyway, just in case they have something there. Wnt (talk) 11:44, 20 June 2017 (UTC)[reply]
Earth's case may have been complicated by the development of life. An aspect of the Gaia hypothesis is that, due to evolutionary-like feedback mechanisms, the Biosphere has tended to modify Earth's atmosphere in ways which moderate temperature extremes, to its benefit. {The poster formerly known as 87.81.230.195} 94.9.80.133 (talk) 15:13, 20 June 2017 (UTC)[reply]
We have to bear in mind that cloud feedback will cool the planet's surface down, and that given the minuscule increase of Seff needed for this, it may well have been cancelled out by the minuscule increase of the Sun's luminosity since that thermal maximum. So perhaps, given how close to the edge this seems to be, we could have gone that far up then and have had things return to normal; but if we did it now, the prospect of creating a positive-feedback loop and going the way of Venus seems more likely.
The reason why Venus is the way it is is because the water all evaporated away even before the CO2 got there to such a degree. Actually that is the first reason; the CO2 levels were only held in check by buffer reactions when the water was still there. Then it boiled off, and a few billion years later, here we are. Double sharp (talk) 15:25, 20 June 2017 (UTC)[reply]
@Double sharp: I found a chart with the temperatures in Oligocene (now included at right) - which marked the beginning of the permanent glaciation of Antarctica. It makes it apparent that the PETM was actually a small blip on a larger pattern ... why that pattern is as it is I have no idea. I mean, common sense says there has to be an upper limit, but I'm thinking that upper limit has nothing at all to do with the model in the paper. Wnt (talk) 18:04, 20 June 2017 (UTC)[reply]
The idea is that with this amount of effective insolation, the cycle can go up and down without problems, as things are balanced correctly. If you go too hot, for examples, the clouds of water vapour that form will cool the planet back down through their high albedo. The habitability limit the authors impose is when the cycle breaks down and there is nothing stopping the water vapour from accumulating without end. The authors acknowledge this and note that 0.99 AU is probably a little too pessimistic. But I would note that the authors also impose a standard Venus-style greenhouse limit, and it comes out at about 0.97 AU. So even if you disagree with the conservative estimate, the habitability zone still ends up not going very much past Earth, while going quite a distance past Mars.
In fact, it seems that because of radiative warming from CO2 clouds (again) and the possibility of using other greenhouse gases as well, you could extend the habitability zone another 0.2 AU at least past Mars' current orbit. I wouldn't dare to include Ceres in it as a few early speculations suggested, though. Double sharp (talk) 23:33, 20 June 2017 (UTC)[reply]
I think you're taking these estimates a little too literally. There are so many variables and processes we don't fully understand that any of these models are ballpark guesses at best. As for what the "habitable zone" includes, I think the article is pretty clear: the area where persistent liquid water on a planet's surface is possible. As the article notes, this concept dates back to the 1950s. It's easy to forget that back then we knew practically nothing about other Solar System bodies, apart from them being rocky or gaseous. (Fans of classic science fiction will be familiar with Venus and Mars being depicted as slightly more extreme Earths. It wasn't until the '60s and '70s that probes started giving us a clear picture of what other planets and moons were like.) As we now know, there may be environments suitable for life outside of a star's "habitable zone", so maybe we should rename it the "Earthlike zone" or something else more accurate. --47.138.161.183 (talk) 00:29, 21 June 2017 (UTC)[reply]
Yes indeed, they are all guesses, and the only vaguely reasonable thing we can say is that at some point things get Venus-like and at some point they get Mars-like, while shrugging our shoulders on where exactly this happens. I mention Kopparapu because he is recent and stands about midway between the historical optimists and pessimists, and gives a rough ballpark of the obstacles that may be expected at the extremes, but we should take all of this with about a mole of salt. The phenomenon Wnt refers to, minus all the authoritative-looking markers, would simply be to say that it seems to be rather easy to end up like Venus, which while plausible still needs more empirical data that is of course not going to be very forthcoming.
I think we focus on the water habitable zone because we know for a fact that life is at least possible in it. Whereas we don't know enough about other biochemistries: it could be that methane and ammonia are acceptable substitutes, but it could also be that there is some sort of obstacle that we just don't know about yet. So the focus on water comes out of caution. Double sharp (talk) 02:39, 21 June 2017 (UTC)[reply]
@Double sharp: Your comment on the natural cycles above may have some sense to it, but did they really refer back to the PETM to decide what the habitable zone was? But it gets me thinking that there ought to be a scientific way to infer how close we are to some catastrophic greenhouse effect (moist or otherwise). Basically, the Kopparapu group claim that there is a curve of Seff vs T that goes almost horizontal if S (I'll leave off the subscript from here in) goes just a little higher than it is now. So dS/dT goes practically to zero, or dT/dS to near infinity. But we ought to be able to infer those values directly from variations in the geologic data! We have the Milankovitch cycles to tell us exactly how much the insolation changes over time, and we can look at how much those cycles affected temperature of the Earth's surface when it was high versus when it was low. Based on this we should be able to integrate a real T(S) function and then fit polynomials to it to extrapolate what actually happens. I should say though that at a far lower level of analysis, just eyeballing the data figure I posted above, and assuming the variations (whatever their cause, definitely not Milankovitch cycles) are about constant, I don't see the temperature numbers getting wild and looking to explode off the top of the chart every few million years when it is hottest. Wnt (talk) 19:16, 21 June 2017 (UTC)[reply]
If you're referring to Figure 3(c), I think the scale makes it a bit difficult to see, but the start of the horizontal region does not appear to be close to our current 288 K on a human scale, even though with such a wide range on the x-axis of course it will look pretty bad. Figure 3(d) shows that water vapour in their model doesn't start accumulating in the stratosphere until around 340 K, which seems a lot more plausible given that we never went anywhere near that, and seems to fit the position on the graph given. But thanks to the self-reinforcing nature of the greenhouse effect, and the rate at which T ought to increase with increasing Seff, I can believe that we avoided disaster by what looks like a large amount from the temperature perspective (since we never get anywhere near 340 K), but a small amount from the distance-from-the-Sun perspective. Double sharp (talk) 05:53, 22 June 2017 (UTC)[reply]
Health effects of sulforaphane
Cruciferous vegetables are healthy and that may be because of sulforaphane. But sulforaphane is destroyed by cooking so I don't understand how one can invoke the observed health effects in people who eat more cruciferous vegetables, because most people don't eat these vegetables raw. Broccoli sprouts contain more sulforaphane, but even in that case, you need to apply the right amount of heat for the right amount of time to get the most out of it, see here. Count Iblis (talk) 23:20, 19 June 2017 (UTC)[reply]
Well eating them raw will preserve the substance. But there are probably other health benefits for cooked vegetable such as vitamins, and fibre. Graeme Bartlett (talk) 00:24, 20 June 2017 (UTC)[reply]
Sulforaphane may or may not be specialty healthy, our article looks rather skeptical on this. Meaning cooking may makes no difference on a close to nil effect.
other possibilities includes
Sulforaphane are produced AFTER cooking and eating, from some others components that survive cooking
active substance may not be sulforaphane itself, but some other substance produced when sulforaphane is destroyed, while the cause of this destruction (cooking or digestion) do not really matter
I see a bunch of numbers at sites like this (though they'd have to be checked) - apparently platinum is higher than mercury at its melting point, and sulfur is higher than water. Near room temperature you can get anything from mercury-like surface tension to less than olive oil out of an indium-gallium alloy, I think it was in base, depending on applied charge. [3]
It would be interesting to see more of a theoretical overview of this. At a liquid's melting point, it almost has enough bonding to be locked into a solid. So why are some at a low surface tension and others at a high surface tension, based on different levels of cohesion between particles of the liquid? I assume there's some aspect of "flexibility" involved but I admit I have no clue on this one. Wnt (talk) 12:03, 23 June 2017 (UTC)[reply]
Yes. This page describes three different methods for converting carbonyls to thioketones. Although those methods are given in general terms, not for specific compounds. I don't know if the amide groups of urea would interact with the other compounds used in those methods. Someguy1221 (talk) 01:46, 21 June 2017 (UTC)[reply]
The examples on that page (two different reagents, two variations of the recipe for one of them) all say that certain amides are viable. But for the specific example of urea to thiourea (not regular amides, and not more complex structures containing these substructures), hydrogen sulfide can do it after an initial treatment with various metal oxides at a few hundred degrees celcius.[1]DMacks (talk) 03:31, 21 June 2017 (UTC)[reply]
References
^CN patent 101602702, "A production method of thiourea from urea", issued 2009-16-12
What mug material would make it hardest for soda bubbles to resist their buoyancy?
Teflon-coated diamond? Oil-coated glass? How would I know. The cup has vertical, smooth sides and is at sea level on Earth. Which material would make it easiest for the bubbles to resist their buoyancy? Sagittarian Milky Way (talk) 22:23, 20 June 2017 (UTC)[reply]
1) If you just want to prevent bubbles from rising, then preventing them from forming is one way. A lack of nucleation sites is one way to accomplish this, with very smooth sides and a pure liquid.
2) If, on the other hand, your goal is to have lots of bubbles sticking to the sides, then the above approach won't work. Here a container with "pockets" to catch the bubbles might help. StuRat (talk) 13:23, 21 June 2017 (UTC)[reply]
2, where it takes the most force to dislodge the bubbles (i.e. banging it on the table) and the opposite of 2 - which would look cool if they rise fast without percussive help but otherwise have no practical use. Perhaps something hydrophobic and smooth but not so smooth that there's no nucleation sites? Would they rise still in contact with the sides even if adhesion could be zero (since it's perfectly vertical) or would they break contact with the side out of a desire for spherical shape or because of turbulence if the adhesion was low enough that it wouldn't have resisted their rise much? Sagittarian Milky Way (talk) 20:14, 21 June 2017 (UTC)[reply]
It may be noted that one of the things the physicists had to consider before the Trinity test was whether it might ignite a nuclear chain reaction in the atmosphere. They were able to rule this out, but as it says in the article, "Enrico Fermi offered to take wagers... on whether the atmosphere would ignite, and if so whether it would destroy just the state, or incinerate the entire planet." (Emphasis added.) --76.71.5.114 (talk) 07:13, 21 June 2017 (UTC)[reply]
Tendons and ligaments are classified under muscular or bone system?
Tendons and ligaments are classified under muscular system or bone system? Basically they are not bones or muscles and that's why I have doubt. 93.126.88.30 (talk) 02:17, 21 June 2017 (UTC)[reply]
This sounds like a urban legend or fictional thing, but I guess it won't hurt to ask. Is it true that when a person dies, the last thing they see gets imprinted in the eye and the image can be retrieved somehow?
This was used as a plot point in Saint Seiya (manga only, the eye thing does not appear in the anime) by the character Black Swan.
(I tried to Google this, but keywords like "... image eye last thing seen death ..." got mostly pages about the completely unrelated notion that we see our whole lives past our eyes when we die.) --Daniel Carrero (talk) 07:32, 21 June 2017 (UTC)[reply]
Your hunch was right. The opsins in photoreceptor cells are degraded rapidly after being photoactivated by incoming light. This makes sense if you think about it. Your eye has to "refresh" in order to update what it's seeing. The membrane potential of the cell also rapidly resets to its resting state; furthermore, following death, the cell will deplete its energy reserves, the cell's ion pumps will stop working, and its membrane potential will dissipate. --47.138.161.183 (talk) 08:12, 21 June 2017 (UTC)[reply]
Almost all organic cells keep functioning for a while after an Organism is regarded dead. Else organ transplantation operations, from victims of accidents that subscribed to be donor in case of death, would not work. So this imprint theory is completely made up nonsense as usual in movies and shurely much more so in japaneese ones. --Kharon (talk) 07:00, 22 June 2017 (UTC)[reply]
What on earth is dicotyledonous wood? I came across the term while researching for draft:Akal Wood Fossil Park. There's no WP article about it and Google search mostly yields research papers only which are largely unintelligible to lay readers. A book search also failed to turn up any explanation for what it is. 223.227.109.162 (talk) 13:53, 21 June 2017 (UTC)[reply]
Obviously it's wood from a dicot, rather than a monocot. However, is it a term in any sort of use?
I checked my usual source for all such, R. Bruce Hoadley's Understanding Wood. It's not in there. A thorough check might also cover the US Forest Products Handbook. So although woodworkers are deeply interested in wood structure and distinguish between species, let alone hardwood and softwood, there's no evident distinction for dicots and monocots. Timber species are almost all dicots, the only monocots I can think of for commercial timber production would be the woody palms and bamboo.
From the context, I think that this is a palaeontological question, not a timber question. The point is that monocots are seen as "early" plant in a geological context and the dicots as "later". Their fossils are also identifiable by species, thus then (indirectly) categorizable as either dicot or monocot.
AFAIK (I may be wrong here, I'm no botanist, just a carpenter), there is no specific timber or fossil structure that shouts out "dicot", any more than other differences between species (there are some common differences between softwood and hardwood as groups). So a botanist still has to identify down to a finer detail than "monocot", such as "a palm" or "a bamboo" before identifying to the group level. But if the distinction is interesting as a fossil one, then they might be doing just that. Certainly identifying fossil species from structure, seeds or pollen grains is an important discipline. Andy Dingley (talk) 14:34, 21 June 2017 (UTC)[reply]
I think, most xylologists and foresters and botanists would not consider e.g. bamboo to be be true wood anyway. While our article doesn't call normal wood, dicotyledonous wood, it does have section on monocot wood, indicating its sort-of-wood status. So I suspect dicotyledonous wood is being used here as sort of equivalent to "true wood", and this is useful verbiage (Edit,see below) to distinguish from monocot fossils that may also be woody. SemanticMantis (talk) 16:56, 21 June 2017 (UTC)[reply]
And to clarify further: " there is no specific timber or fossil structure that shouts out "dicot", any more than other differences between species ", I don't think that's true. I think if a paleontologist had a small bit of bamboo fossil and a small bit of coinfer dicot fossil, they could immediately distinguish the two. The growth of monocot "wood" is very different, they don't have the same tissue structures. See here [5] for some discussion of differences, and e.g. here [6]. One easy detail is that monocots won't have growth rings. SemanticMantis (talk) 17:22, 21 June 2017 (UTC)[reply]
Monocots (for the most part) don't produce wood. Nor are monocots the most primitive angiosperms, the claim above is not even close. The Magnoliids are usually called dicots, and they along with a few other minor groups are the oldest angiosperm clades. They produce wood, unless they are herbaceous. The two crown clades of Angiosperms are the monocots and the Eudicots which are equally recent. Conifers also produce wood, so it is not unique to Angiosperms.
Basically, dicot wood in the broad sense is what we think of as hardwood, and include wood from the Magnoliids and the Eudicots, but excludes wood from the conifers and monocots. It's a taxonomically invalid (polyphyletic--like calling whales fish) grouping, but it is useful in forestry and woodworking.
Of course there are the articles wood and secondary growth. There's also Plant Biology, Raven, Evert, and Eichorn which gives an encyclopedic view of the biology of the Plantae proper as well as other organisms such as fungi and protists historically treated as part of botany from an evolutionary and physiological standpoint.
Nobody said monocots were primitive, so I'm not sure what or whose claim you're referring to. But I do think you're right that coniferous wood would be excluded from "dicot wood", so I've stricken the "true wood" bit above, because it's confusing. For the rare occurrence where it comes up, "dicot wood" is basically synonymous with "hardwood" SemanticMantis (talk) 15:02, 22 June 2017 (UTC)[reply]
From the context, I think that this is a palaeontological question, not a timber question. The point is that monocots are seen as "early" plant in a geological context and the dicots as "later".
That's why it's called timber. True wood is a form of secondary growth, where new layers grow over old ones yearly from secondary meristem. Monocots do not increase in girth this way, having lost the ability, hence coconut timber is a granular pithy material, not true wood. Functionally it can replace wood, and has some excellent qualities, as can bamboo. But biologically neither is true wood, with annual rings, as found in the gymnosperms, magnoliids, and eudicots. μηδείς (talk) 18:22, 23 June 2017 (UTC)[reply]
Solar eclipse hype
Today on the CBS Morning News Charlie Rose said "A total solar eclipse will cross the United States for the first time in 99 years." That would at first blush seem to mean no "total eclipse" in any US state since about August 1918. I have seen this August 2017 eclipse similarly hyped elsewhere. It seems like every decade the newscasters tell us there is about to be the first such eclipse in umpty-ump years and there won't be another one in our lifetimes, as if we have no memory of previous eclipses. The article List of solar eclipses visible from the United States lists "total eclipses" which crosses the US.Neglecting annular and partial eclipses, it lists the most recent one as the Solar eclipse of July 11, 1991 and says Hawaii (by then long since a US state) saw a total eclipse. It lists Solar eclipse of February 26, 1979 whose article says there was a total eclipse in five US states. It lists Solar eclipse of March 7, 1970, whose article's map appears to show totality across several east coast states. It lists Solar eclipse of July 20, 1963 whose map appears to show totality crossing at least Maine. It includes the Solar eclipse of June 30, 1954 which had totality over several northwest states. It says about the Solar eclipse of July 9, 1945 that "The path of totality crossed northern North America, ..." and a semi-legible map shows the path crossing several northwest US states. It says the Solar eclipse of August 31, 1932 hit the NE US and the map seems to show a couple of NE states in the path. The Solar eclipse of April 28, 1930 hit the northwest US states. The Solar eclipse of January 24, 1925 produced a total eclipse viewable in New York City. The list claims the Solar eclipse of September 10, 1923 hit the SW US, but the fuzzy map and the article about the eclipse imply the totality missed the US. Then we get to the 99 year eclipse: The Solar eclipse of June 8, 1918, which crossed many states from the northwest to the southeast. But how can they dismiss the eclipses of 1991, 1979,1970, 1963, 1954, 1945, 1932, 1930, and 1925? From 1918 to 2017 inclusive, there have apparently been 11 total eclipses visible in one or more US states, for an average of 8.9 years. What am I missing here? That is more often than some people trade cars. Do astronomers endorse this hype? Edison (talk) 14:25, 21 June 2017 (UTC)[reply]
The 1925 eclipse was pretty cool. A scientist asked people what street they were on and whether they saw totality and 100% saw it above 96th Street and 0% saw it below 94th Street (or something similar). 1 street is only 264 feet. Sagittarian Milky Way (talk) 21:06, 21 June 2017 (UTC)[reply]
One news story added the qualifiers "first total solar eclipse to cross the United States from coast to coast in nearly a hundred years" which seems accurate, but so far as one's personal experience, you just see it in one place (absent pacing it from inside a Concorde as was once done)., and the sense of wonder is not much greater to know that many others can see it too. Yet Rose said he had "never seen one, and little wonder, since there hasn't been one in a hundred years" which seems to be nonsense. Edison (talk) 14:48, 21 June 2017 (UTC)[reply]
Correct, that's the big thing here. coast to coast, more states, more 'potential observers within reasonable travel distance' than in a long while. 1918 was somewhat comparable to this event in terms of the track. So 'for the first time in 100 years' is somewhat accurate in that regard, but it should be noted that the 2045 event will be similar (longer even). So yeah, it's a bit of hyperbole, but then, that's the news. For anyone outside Hawaii, NYC, or the North West, there is a big chance that you have not had this good an option to observe a full eclipse in your lifetime before. Esp. because modern times has made travel this cheap. —TheDJ (talk • contribs) 15:17, 21 June 2017 (UTC)[reply]
BTW, as having personally observed a total eclipse in France when I was in my teens, I would advise any and everyone to take any opportunity you can to observe it. It's one of the strangest experiences I ever had. Will never forget it. —TheDJ (talk • contribs) 15:28, 21 June 2017 (UTC)[reply]
Solar eclipse of February 15, 1961. I remember it as a deep partial eclipse. My mother saw a total one - for practically everyone in Britain 11 August 1999 was clouded out, and the one before that was 30 June 1954 (also visible as total in the United States). Our article Solar eclipse of August 11, 1999 could do with some work - it claims it was "the first visible in the United Kingdom since 29 June 1927". 79.73.134.123 (talk) 16:11, 21 June 2017 (UTC)[reply]
Few saw the '91 umbra in America because the average July sunniness of Baja vs Hawaii made many people plan to fly or drive to the tip of the Baja desert to see it and by the time the weather report showed it was more likely to be seen in Hawaii than Mexico flights to Hawaii were probably pretty expensive. In the end the desert of Baja California had lots of cloud and the tropical rainforest of Hawaii saw the eclipse. Sagittarian Milky Way (talk) 16:17, 21 June 2017 (UTC)[reply]
Yes, if suitably manufactured. In the UK it has long been sold as "Non-brewed condiment", diluted and coloured with caramel, as a substitute for malt vinegar. "Vinegar", if sold under that name, must be made by brewing (or at least fermentation). NBC uses industrial acetic acid. It is cheapest (if you're buying acetic acid for industrial workshop use) to buy these "acetic acid pickling vinegars" in gallon jars, rather than a chemical reagent-grade acid.
This sounds like normal "white vinegar" we use in the U.S. It is the most common vinegar and apparently can use either foodstuffs or petroleum as a starting material although the industry claims not to be aware of any company making food-grade vinegar from petroleum.[10] It seems in the UK, malt vinegar may be the main type in use and laws do not allow certain other products to be labeled as vinegar: non-brewed condiment. Rmhermen (talk) 17:24, 22 June 2017 (UTC)[reply]
Yes, and you could pickle with it, but it would be a bit nasty if used "alone" (emphasis in title). A typical pickling solution would include salt and other seasonings. Matt Deres (talk) 20:08, 22 June 2017 (UTC)[reply]
June 22
anal sex & hygiene
a. What measures (or cleaning routine) are taken to keep the rectal region clean ? How sexually engaged couple makes sure that there are no remaining excretions behind ? Is an enema required each time they commence love-making ? b. Is the issue of remainings age dependent ? Namely, natural cleaning processes are more efficient when we're younger ? c. A few years ago, as I remember, I saw somewhere in Wikipedia (through 'external' or 'see also' ?) some guide regarding this issue, medically & hygienically. Any ellaboration is welcome. בנצי (talk) 15:07, 22 June 2017 (UTC)[reply]
Also see under point 3 in this Article in the cosmopolitan. Seems google thinks cosmopolitan-readers practice this allot :D. Doubtfull if "amateurs" always take as much care and you can be shure todays media would reveal if both ever did any seriouse harm to anyone - i remember reading about people needing surgery after "working" themselves up with big objects in that area so anything alike oddly ironic would have made headlines too. I also read there are far worse (medically & hygienically) frequently practiced kinks in human sexuality. --Kharon (talk) 17:15, 22 June 2017 (UTC)[reply]
The Wikipedia article about Anal sex has general information but it is not a how-to guide. However it links to an external guide that concludes "The most important pieces of advice anyone can give on anal sex are: lubricants, condoms, and patience." Blooteuth (talk) 07:56, 23 June 2017 (UTC)[reply]
There are a lot of things I've seen written about this topic that don't seem to add up. For example, I have no idea how the logistics of prison rape are supposed to work when it is done this way (and certainly I've seen sources that say it is). Are the victims forced to prepare in advance, or do the guards see one guy crying with a soiled uniform in the rear, and another with a soiled uniform in front, and just smile and keep going about a good day at work? And there are authors like Norman Mailer who seem to engage in flights of fancy, or at least, fantasies that omit anything unappealing. Wnt (talk) 11:57, 23 June 2017 (UTC)[reply]
Preparing is not mandatory at all, and I confirm it does not get messy very often, even without any preparing. But many people like to prepare. Here is a very detailed description with drawings of how to thoroughly prepare (not safe for work) : [14] --Lgriot (talk) 15:50, 23 June 2017 (UTC)[reply]
Free Neutrons making dark matter
I have a doubt. Please clear it. Can neutrons interact with electromagnetic radiation or electromagnetic fields? I am thinking that as neutrons have no net charge, they don't interact (I may be wrong). So I have a thought that free neutrons (like a diffuse gas) may contribute to majority of dark matter. (The reason for my doubt is that neutron stars can produce radio waves). So my major question is that can slow and diffuse free neutrons interact with electromagnetism considerably? Please help me.--G.Kiruthikan (talk) 17:51, 22 June 2017 (UTC)[reply]
The origin of this doubt : Majority of normal matter is Hydrogen. Hydrogen's majority don't have neutrons. If neutrons were produced in roughly same number as protons, I think the rest of the neutrons could not make a nucleus and may be diffuse forming the dark matter.--G.Kiruthikan (talk) 17:58, 22 June 2017 (UTC)[reply]
Neutrons are not elementary particles. The net charge is practically zero, but it is made up of charged particles. It does interact with electromagnetic fields. A simple experiment shows this. Shoot a beam of neutrons through a strong electromagnetic field and it will separate into two beams. 209.149.113.5 (talk) 18:34, 22 June 2017 (UTC)[reply]
The charge on a neutron is zero within the limits of experimental accuracy, so it is not affected at all by an electric field. The magnetic component of an electromagnetic field is what affects the path of the neutron. Dbfirs20:05, 22 June 2017 (UTC)[reply]
Some of the above might be confusing, so I should emphasize that as far as I know nobody expects to see any small amounts of charge on a particle - it is believed that all free particles have multiples of the elementary charge and quarks have multiples of 1/3 that amount. The charge does not vary with reference frame like other parameters in special relativity, so you can't get partial charges at a point in space by shooting things past each other either. I have no idea what kind of awesome mathematics can be invoked to explain that quantization, but I think no one expects to find a fractional charge on a neutron if they look really hard. Wnt (talk) 20:21, 22 June 2017 (UTC)[reply]
Only neutrons traveling at super relativistic speeds could survive for a long time. But even these will be turning into high energy protons and electrons that would be easily detectable. However it is quite easy to make dark matter from matter contains neutrons. If there were many free floating Earth or moon like objects floating between the stars they would be dark. However these might be detected by gravitational lensing or eclipsing stars. Graeme Bartlett (talk) 08:56, 23 June 2017 (UTC)[reply]
This seal is there to cover the hole that is underneath. When a PCB has been assembled the soldering flux is washed off and the seal prevents this fluid from getting into the hole and damaging the buzzer. The seal also mutes the loudness, which in some applications may be desirable. The innards of these devises are also affected by moister etc., and thus its life can be prolonged by leaving the seal in place (at the expense that it operates more quietly). Also note, the circle with the + sign within it, aids quick identification of the positive terminal; although this should be obvious from the length of the leads. Aspro (talk) 22:28, 22 June 2017 (UTC)[reply]
Whoops... Completely missed answering your question. One does not need to remove it. The manufacturer of the buzzer leaves the choice to its customers – but only afterwashing. Aspro (talk) 23:00, 22 June 2017 (UTC)[reply]
June 23
Random chance, probability, and predictability
In chemistry, I once learned that the exact locations of the electrons are not known (and probably not important anyway), but the probability of finding the electron at a particular point can explain why something bonds with another. Then in statistics, I learned about probabilities, which then made me think of randomness. In a realistic setting, what is randomness? While in theory "random" means "everything is equally likely", how is this practically possible? If one writes a personal name on an index card and repeats the process for 50 index cards, each having an unique name, and then puts all the cards in a Black Box and shakes the Black Box, then it may seem random that a random card will be drawn, but in reality, the card at the top may be more likely to be drawn than the card at the bottom. Maybe "randomness" is the "unknown"? If one doesn't know or expect something, then it's "random"? Another case is when a teacher lists the students "randomly". Practically, the students may race to the teacher and line up. Whoever's first in line may just happen to be closest to the teacher to begin with or be the fastest person in the room. The last student in line may be the slowest person, or because he/she can't find any open spots, may be forced to be the last in line. At what point is something "random"? At what point is something "biased" or has some sort of tendency/correlation? 50.4.236.254 (talk) 00:37, 23 June 2017 (UTC)[reply]
This is trickier than it may appear. Probability and statistics of discrete events (i.e. probability of a 2 dice roll being a seven (1 in 6) verses a 2 (1 in 36)) is different than quantum location where the distribution is a fundamental construct of the particle. Temperature of a gas is the mean of the temperature of individual particles and processes like evaporative cooling and sublimation work on the principle that particles are discrete. An electron in the orbital is a completely different construct that is described in models as a distribution and probability but lacks discrete components that can be separated to define the distribution. It is not a collection of random individuals but the distribution is a fundamental part of the particle. --DHeyward (talk) 01:05, 23 June 2017 (UTC)[reply]
There several definition of randomness, yours is one of them. "all results are equally likely" is another definition, perfectly legit provided (big caveat!) you have a correct definition of "result" (ie: equal chance for a dice to produce 1-6, which is correct, vs equal chance for a dice to produce 1 or not, which is not). Unfortunately those 2 definition do not means exactly the same. Gem fr (talk) 14:00, 23 June 2017 (UTC)[reply]
Your question is hard, and not solved. There are different definitions of randomness, that do not exactly overlap. A system perfectly deterministic, but chaotic and hence unpredictable ( n-body problem or Double pendulum for instance), can be said random because unpredictable, or NOT random because prefectly determinist.
I would recommend determinism and Bohr–Einstein debates for the famous "god don't play dice" quote and implications. Also maybe Hidden variable theory: obviously in your student example, there are hidden variables (proximity and sprinting abilities), so the order is not random, but pseudorandom. It could however be argued that those variable are themselves randomly distributed, meaning the result is random. But it is no longer, if the teacher is well aware of these abilities, meaning he actually choose the result, hence it is not random. When you think of all the things that make you shift back and forth between "it's random" and "it's not random", you end up at classical Antoine Augustin Cournot's definition of randomness (i just wonder why it is neither in his article nor randomness) « Encounter of two independent causal series ».
for instance : a first series of causes made you arrive somewhere, sometime; an other series made a bus arrive at the same place at the same time. The more common causes there are, the less random (the more biased) your encounter with the bus is. With enough knowledge of the causes, your encounter could be perfectly predicted (or explained afterward and then appear it HAD to happen), but would nonetheless stay random (according to this definition) provided they stay independent.
Rubbing alcohol is isopropyl alcohol. Drinking alcohol contains ethanol. What happens if flour (with added water) is left fermented on the kitchen counter for a very time and then the fermented liquid is used to make beer, which is then used to clean stuff? Will ethanol still work as effectively as isopropyl alcohol? Is it safer to use ethanol than isopropyl alcohol simply because you can ingest it safely? If you add a lemon wedge or slice to the ethanol solution, then will it smell like lemons too? 50.4.236.254 (talk) 00:53, 23 June 2017 (UTC)[reply]
Ethanol does make a good cleaner, beer and wine is usually only between 4-15% ethanol. The other stuff in beer and wine will make whatever you want to clean dirtier than before you started, defeating the purpose. Neutral spirits, such as vodka or moonshine can be used to clean things, though: [16]--Jayron3201:05, 23 June 2017 (UTC)[reply]
Isopropyl alcohol is more toxic to humans' central nervous system than ethanol but it's not that toxic. It'd take about a half shot to be toxic. Methanol is more toxic. Now that's some dangerous stuff. Even so, if the thing being cleaned is 50.4's mouth, using 70% isopropyl alcohol is a bad idea even if you spit it out immediately. The mouth will instantly desiccate and take days to heal. Alcoholic mouthwash is designed to not do that. Sagittarian Milky Way (talk) 02:03, 23 June 2017 (UTC)[reply]
I'm surprised no-one has mentioned Deglazing (cooking) where wine is used to dissolve the gunge off the pan after frying some meat, especially if the meat has been coated in a seasoning with flour. Dmcq (talk) 10:41, 23 June 2017 (UTC)[reply]
1. (Just to double check) Can a pinhole camera contain a lens element?
Assuming the answer is no, then:
2. Are these[17] really pinhole cameras? I can see a little glass-like reflection from little hole. And this site[18] sells what appears to be the cone-like tip of the camera, and it clearly contains a very large lens element.
Note that I'm not suggesting the seller is misrepresenting his product. Linguistically "pinhole camera" certainly covers all miniature cameras, regardless of operating principle. He has every right to sell it as a "pinhole camera". I'm just interested in learning about the operating principle behind these cameras. If they're not true (scientifically speaking) pinhole cameras then how come the front lens elements can be made so small? Is there a limit to how small the front lens elements can be before performance is unacceptably degraded? Scala Cats (talk) 01:16, 23 June 2017 (UTC)[reply]
Yes, diffraction. This is the same reason why a telescope lens has to be at least 115.8 millimeters wide to look as sharp as 20/20 vision at 60x magnification. Almost certainly not coincidentally, this is almost 60 times the width of the human pupil in the daytime. Sagittarian Milky Way (talk) 02:09, 23 June 2017 (UTC)[reply]
There are two completely different things that are called "pinhole cameras".
The first uses a pinhole instead of a lens. It is characterized by having everything in focus no matter how close or far it is, and by requiring a huge amount of light (typically full sunlight, fast film, and long exposures). Example: https://www.amazon.com/Ilford-Obscura-Pinhole-Camera-Only/dp/B00I9Z2PD8/
The second uses lenses, but configured in such a way that you can drill a pin-sized hole in a wall with a cone-shaped space behind it (there is a tool for that) and then take pictures of the inside of the room, hopefully without anyone noticing the pinhole your camera is looking through. Example: https://www.amazon.com/Vanxse-Pinhole-Security-Microphone-Surveillance/dp/B012K4VP5W/
"The second uses lenses" That's what my first question is getting at. Do those tiny cameras that use lenses actually qualify, scientifically speaking, as a pinhole camera? Because the article starts off by saying "A pinhole camera is a simple camera without a lens". I not sure whether that means "A pinhole camera is commonly constrction without a lens" or "A pinhole camera is defined as a camera that uses a pinhole instead of lens" Scala Cats (talk) 17:44, 23 June 2017 (UTC)[reply]
Also note that the type of pinhole camera lacking a lens might still have a glass cover over the pinhole, to prevent dust from getting in. StuRat (talk) 17:55, 23 June 2017 (UTC)[reply]
(My apologies if I missed this in the article gravitational wave.) Suppose a planet is near enough to its star that the view of a distant source of gravitational waves behind the star is completely blocked everywhere on the planet.
Is the planet affected by gravity from the distant objects?
Could detectors on the planet detect the gravitational waves from the distant objects?
If either of the answers is yes, then how? Can gravitational waves go through solid light-blocking objects like the nearby star?
No, and I can think of a number of reasons why gravity and its waves don't interact and disperse like other interactions. But you mustn't take my non-expert, truth-seeking and somewhat semi-random reference desk contributing wordy word for it today though... for I looked and found this to be asserted on the APS website here: [19]. I could go on (since I'm psyched I'm likely to go on a tear right now though so I'll refrain). --Modocc (talk) 18:35, 23 June 2017 (UTC)[reply]
![[4]](https://s-media-cache-ak0.pinimg.com/originals/1f/54/a0/1f54a0e81754fed447de87d830b57891.jpg){kind=link}
![[8]](http://i.imgur.com/oA4MZrG.jpg){kind=link}
Resolved![[18]](http://i.imgur.com/AXesjtD.jpg){kind=link}
