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Contents
- 1 April 4
- 2 April 5
- 2.1 Nuclides undergoing nuclear fission
- 2.2 MHD and nuclear reactors coupling
- 2.3 Arduino: RGB LED lights and Resistors
- 2.4 Solubility
- 2.5 Voltage drop over fully open transistor?
- 2.6 Why is Fresh-water Fishing mostly so poor in Winter? (I'm sure there are exceptions)
- 2.7 How does lactulose cause flatulence ?
- 2.8 Gravity detector
- 2.9 Bacterial victim
- 2.10 Reaction with ice
- 3 April 6
- 4 April 7
- 4.1 Rotating sphere
- 4.2 how is this happening?
- 4.3 Sharks' food choice - surfers vs. scuba divers
- 4.4 Covalent bonds
- 4.5 what % ethylene is polyethylene made of?
- 4.6 How many notes can the average human sing?
- 4.7 How to dissolve the chemical that wrecks circuit traces?
- 4.8 Outpatient procedure complication and mortality rates
- 4.9 Washing clothes
- 5 April 8
- 6 April 9
April 4
Special relativity. Simultaneity 2
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Ok. There is no observers, just clocks showing something on their faces. In Special relativity. Simultaneity we showed :
in frame ε clock from ε shows on its face:
in frame ε clocks from ε' show on their faces (from left to rigth):
Suppose, when light reaches walls, clocks on walls are reseted to zero, so . Reseting of clocks is the result , so must be seen from all frames, so in all frames clocks on walls must show zero if light reaches them. Then: and . and . and . and . So at start in frame ε clocks from ε' show on their faces (from left to rigth): , , . How to check this? I have tried to use Lorentz transformations for time , but got absolutely different result. Hind clock when shows , is situated in ε in point and also in ε' in point , but also it can be represented as . So . Why? Or backwards: ; . By subsituting , : . Why ? But I don't want to use coordinate. I like to imagine that time in moving frame is slowing down through explanation by primitive clock made from vertical rod and mirror https://upload.wikimedia.org/wikipedia/commons/8/8f/Reference_desk_Science160404140000.PNG . Is there same intuitive explanation for desynchronization? |
Light path analysis and consequences
Null result of Michelson–Morley experiment extrapolation |
37.53.235.112 (talk) 05:49, 4 April 2016 (UTC)
- Time in a moving frame is not "slowing down", it is proceeding at the "normal" rate. From an inertial frame that is moving relative to the original moving frame (or "stationary" by some ad-hoc definition), time is observed to be running more slowly, but this effect is symmetrical because time in the "stationary" frame is observed to be running more slowly when observed from the moving frame. It is only when one frame (either of them) accelerates to match the speed of the other that a twins paradox appears. Perhaps someone else can explain how your equations work out? Dbfirs 11:02, 4 April 2016 (UTC)
- Symmetry of time is certainly claimed by special relativity, however general relativity lays claim to an asymmetry that exists (and it's an asymmetry that I view as being much more important and fundamental). For instance, if on one hand, a rogue twin planet Krypton, which is like our own, was moving very near the speed of light, their communication systems hibernate with, say, just one computation per week and therefore incapable of processing any interactive communication data we may wish to share with them during their brief passage with us though our inner Solar System (within the orbit of Pluto). They would be "dead on arrival". On the other hand, we could interactively observe them, probe their planet with radar, etc. in excruciating detail during the brief encounter because we are unaffected and are almost at rest with respect to the CMB rest frame, which is likely the ultimate arbitrator of what constitutes the fastest clocks. -Modocc (talk) 13:08, 4 April 2016 (UTC)
- I follow http://www.feynmanlectures.caltech.edu/I_15.html . Please, write answers using materials which do not go beyond sections 15-1 ... 15-6.37.53.235.112
- [after edit conflict]Alas, according to SR, your intuition is incorrect for a very simple reason: you are incorporating classical velocity addition with your primitive photon clock and not the relativistic temporal and spacial transforms which are derived independently. Not a bad idea though and consistent with absolute simultaneity and distances :-), but it is very much inconsistent with the reference frame invariant lightspeed of your photon, which according to Einstein, requires relativity of simultaneity as well as length contracted distance (length contraction) that the light travels and is frame dependent. Thus relativity goes well beyond the classical paradigm. The book "Einstein's Theory of Relativity" by Max Born may be a bit dated, but from it I learned the basics of how its nonEuclidean worldlines were developed many years ago. -Modocc (talk) 16:08, 4 April 2016 (UTC)
- I follow http://www.feynmanlectures.caltech.edu/I_15.html . Please, write answers using materials which do not go beyond sections 15-1 ... 15-6.37.53.235.112
- Symmetry of time is certainly claimed by special relativity, however general relativity lays claim to an asymmetry that exists (and it's an asymmetry that I view as being much more important and fundamental). For instance, if on one hand, a rogue twin planet Krypton, which is like our own, was moving very near the speed of light, their communication systems hibernate with, say, just one computation per week and therefore incapable of processing any interactive communication data we may wish to share with them during their brief passage with us though our inner Solar System (within the orbit of Pluto). They would be "dead on arrival". On the other hand, we could interactively observe them, probe their planet with radar, etc. in excruciating detail during the brief encounter because we are unaffected and are almost at rest with respect to the CMB rest frame, which is likely the ultimate arbitrator of what constitutes the fastest clocks. -Modocc (talk) 13:08, 4 April 2016 (UTC)
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- you are incorporating classical velocity addition We can use classical velocity addition for approach velocity and we should use relativistic velocity addition for object velocity. Just write what formulas are wrong in my 1st question. 37.53.235.112 (talk) 16:40, 4 April 2016 (UTC)
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- @Modocc: Your explanation is confusing at best. The whole idea of relativity is there's no difference between how we see Krypton and they see us (how we see the CMB is something else!). We see their clocks ticking slowly and they see our clocks ticking slowly. The solution to this staring contest is that sooner or later, one party accelerates and comes back again, and is revealed to be the "true" slowed party. Or else both parties keep moving apart and their record of each other's light just keeps getting more and more out of date. There's a graphic in Twin paradox - the "simultaneity planes" change angle when you accelerate, i.e. "the same time back on Earth" takes as abrupt a jump forward as your rocket engines will allow (could be backward if you accelerate away faster). But of course, unless you're in possession of an ansible, those simultaneity planes don't really physically exist - they don't mean anything because no information or substance can follow any of those spacetime paths. Wnt (talk) 15:34, 4 April 2016 (UTC)
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- Whatever reference frame one wants to invoke to solve the paradox involving time doesn't actually matter. The fact is that when we accelerate matter, particles' contract and their lifetimes increase, but with consequences. Do that to a rocket or planet so it is fast enough then with regard to a staring contest then the rocket or Krypton cannot interact with us while it is in close proximity to us, its computers are simply aging too slow with respect to the laser light we can bounce off it and that we observe as it passes us by. The fact that such asymmetry exists is the whole point of the paradox. --Modocc (talk) 16:28, 4 April 2016 (UTC)
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- That's why I wrote above that the twins paradox appears whichever frame is accelerated to match the other. There is still symmetry, because the "rest frame" could be accelerated to match the velocity of the "moving frame" and the same paradox will appear except that the age difference will be reversed. Dbfirs 18:21, 4 April 2016 (UTC)
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- Krypton is nearby from Earth's perspective for the same amount of time as Earth is nearby from Krypton's perspective. They can investigate us as much as we can investigate them. It's a symmetric situation. You seem to be suggesting that we have longer than they do because we're moving at a slower speed relative to the CMB. That's incorrect. -- BenRG (talk) 06:22, 5 April 2016 (UTC)
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- In case I wasn't clear, I assumed that Krypton was initially accelerated relative to our Milky Way when it was hypothetically created and that it is now moving almost, but not quite, at the speed of light (this is just a thought experiment. I'm not saying that it even possible, but its something to think about) when we encounter it. Now we know that our computers can process a few serial computations per clock cycle, so lets figure ten gigahertz to give us a benchmark here. It takes about 33,000 seconds of elapsed time for light to traverse the orbit of Pluto and in that time our computers can do a lot of data crunching during our encounter with weak short-range signals (such as with our land-based radar) that are aimed at the rogue planet as it passes us by. Now let Krypton's velocity be such that its 10 gigahertz computers are time dilated to only 1/30,000 clock cycles per second. Then at this speed, during our 33,000 second encounter, their computers' clocks can cycle only once and their weak signals will be fewer in number too. -Modocc (talk) 07:28, 5 April 2016 (UTC)
- Similarly, Krypton's observations of Earth will be hopelessly distorted, with our computers appearing to run ridiculously slowly. Dbfirs 08:32, 5 April 2016 (UTC)
- A stark uncompromising asymmetry would exist however, for real time computations are required by the radio telescopes' tracking computers and their computers could barely perform a single computation during the entire crossing of our solar system and both our ability to perform and their inability to do likewise are reference frame invariant. Modocc (talk) 04:44, 6 April 2016 (UTC)
- I don't understand the lack of symmetry that you claim. Krypton's computers run at normal speed in their reference frame. Dbfirs 19:11, 6 April 2016 (UTC)
- @Modocc: you've specified a time dilation factor of γ = 10 GHz / (1/30000 Hz) = 3×1014, which corresponds to a speed of √(1 - 1/γ2) ≈ (1 − 6×10−30) c. Assuming Pluto is around 16,500 light seconds away from us, and Krypton passes close to Earth, Earth-bound telescopes won't see Krypton pass the orbit of Pluto until 16500(c−v) ≈ 0.1 yoctosecond before it passes Earth. (They will see it in the form of a concentrated beam of gamma rays that will probably sterilize the Earth, but never mind.) If Earth scientists send a radar beam to probe Krypton's surface a nanosecond after it passes us, the beam will return to us about 10 trillion years later, and will be redshifted by a factor of about 4×1029.
- So it is not true that Earth-bound scientists will have lots of time to investigate Krypton. Of course, they will most likely spot Krypton's arrival before it gets to Pluto. If they notice it 1 second before it passes us, they'll have seen it at 1025 times the distance of Pluto, which seems implausible but maybe not. That would give them 1 full second to send radar signals to it which will all bounce back within that second (blueshifted by a factor of 4×1029).
- Krypton will have exactly the same opportunity to investigate us, since this is a completely symmetric situation. The symmetry of reference frames is the most important thing about special relativity. -- BenRG (talk) 19:25, 6 April 2016 (UTC)
- Well, yes, detection of Krypton's existence is also important before we would be making any observations at all:
thus simply let Krypton emit significant electromagnetic radiation ahead of it (we can do the same for them) and then we will get to track them and observe them for the full range of our active radars, but their radars will be dysfunctional with regard to the task. [see a better strategy below] This is because we are the stay-at-home twin for most of the inertial mass around us has been nearly at rest for billions of years and so our watches differ from theirs and time in physics is what clocks measure. If my own twin takes a trip and returns he will have completed fewer tasks than I have, perhaps only a few weeks worth compared to my years worth, thus our performances are asymmetric even though the naive Lorentz transformation preserves spacetime symmetry. --Modocc (talk) 21:16, 6 April 2016 (UTC)- But if you accelerate to match your fast-moving twin's inertial frame, it will be you who has completed fewer tasks because you will be younger than your twin. I still insist that the situation is symmetrical. Dbfirs 21:38, 6 April 2016 (UTC)
- If Krypton is the stay-at-home twin that would be true, but since I specified that Krypton was accelerated initially then I would simply be
rejoiningjoining him for the first time as an older man (although we are physically the same, we would have to be born in different places) when I crash land on his planet in a hail of gamma rays. :-) BenRG made a really good point about the lead distance involved and although the numbers can be tweaked (I'm not a big fan of playing with them much) a more robust strategy to recording their passage I suppose would be to have numerous active pulsed radars that continuously cover the sky much like we do with our weather radars. It is a very large volume of space to cover, but perhaps more feasible and likely than the origin of a massive Krypton (which, being our twin, would have their own matrix of radars). -Modocc (talk) 00:50, 7 April 2016 (UTC)
- If Krypton is the stay-at-home twin that would be true, but since I specified that Krypton was accelerated initially then I would simply be
- But if you accelerate to match your fast-moving twin's inertial frame, it will be you who has completed fewer tasks because you will be younger than your twin. I still insist that the situation is symmetrical. Dbfirs 21:38, 6 April 2016 (UTC)
- Well, yes, detection of Krypton's existence is also important before we would be making any observations at all:
- A stark uncompromising asymmetry would exist however, for real time computations are required by the radio telescopes' tracking computers and their computers could barely perform a single computation during the entire crossing of our solar system and both our ability to perform and their inability to do likewise are reference frame invariant. Modocc (talk) 04:44, 6 April 2016 (UTC)
- Suppose Earth knows in advance that Krypton is coming and starts sending out radar beams 33000s before Krypton reaches Earth, so that the first beam bounces off Krypton just as it crosses Pluto's orbit. Those beams are sent over a period of hours, but since they travel at c just like any other light, they all arrive back in the 0.1 ys interval between seeing Krypton cross Pluto's orbit and Krypton passing Earth. Of course, no equipment could record the signal in that time, but we could imagine faster computers (or a less ridiculous gamma factor).
- To be fair, you must allow Krypton to start sending signals 33000s before the meeting by its proper time. For large γ the Doppler shift factor is roughly 2γ. So those signals will reflect off Earth over a period of about 33000s / 2γ ≈ 55 picoseconds (of Earth proper time), and will be received by Krypton over a period of 55ps / 2γ ≈ 0.1 ys (of Krypton proper time), just before the planets pass each other.
- The fact that Krypton accelerates and we don't is an asymmetry in your scenario. But it only accelerates when it's far away, and by assumption, it can only investigate us (and we it) when it's nearby. Physics is local; the universe doesn't remember who accelerated in the past. When Earth and Krypton are near each other, an exact symmetry of nature (Lorentz/Poincaré symmetry) exchanges them, so the situation is symmetrical. -- BenRG (talk) 03:09, 7 April 2016 (UTC)
- "To be fair, you must allow Krypton to start sending signals 33000s before the meeting by its proper time"? It takes precisely 33000 times a gigahertz number of computer cycles for that to happen, thus those signals would have to begin at a far greater distance from us than Pluto which is but approximately one half of their cycles away by my earlier calculation above and since they are just about almost physically identical to us and are therefore sending similar signals they should be considerably weaker upon arrival.. or am I missing something important here? -Modocc (talk) 03:52, 7 April 2016 (UTC)
- Yes, it starts long before they reach Pluto's orbit (the trip from there to Earth takes only 55ps by their clocks), but the light doesn't travel farther in any Lorentz-invariant sense. With respect to Earth's rest frame, you could say that relativistic beaming prevents the light from spreading as much as you'd otherwise expect over such a long distance. With respect to Krypton's rest frame, Earth is 33000 light seconds away when they send the first signal, and Pluto's orbit is only 16mm closer.
- (If there is background dust comoving with Earth, Krypton's signals will travel through a lot more of it and be attenuated more by that. But if there is background dust then the relativistic dust bombardment will destroy Krypton long before it reaches Earth anyway. This scenario only works in a perfect vacuum.) -- BenRG (talk) 05:27, 7 April 2016 (UTC)
- "To be fair, you must allow Krypton to start sending signals 33000s before the meeting by its proper time"? It takes precisely 33000 times a gigahertz number of computer cycles for that to happen, thus those signals would have to begin at a far greater distance from us than Pluto which is but approximately one half of their cycles away by my earlier calculation above and since they are just about almost physically identical to us and are therefore sending similar signals they should be considerably weaker upon arrival.. or am I missing something important here? -Modocc (talk) 03:52, 7 April 2016 (UTC)
- Similarly, Krypton's observations of Earth will be hopelessly distorted, with our computers appearing to run ridiculously slowly. Dbfirs 08:32, 5 April 2016 (UTC)
- In case I wasn't clear, I assumed that Krypton was initially accelerated relative to our Milky Way when it was hypothetically created and that it is now moving almost, but not quite, at the speed of light (this is just a thought experiment. I'm not saying that it even possible, but its something to think about) when we encounter it. Now we know that our computers can process a few serial computations per clock cycle, so lets figure ten gigahertz to give us a benchmark here. It takes about 33,000 seconds of elapsed time for light to traverse the orbit of Pluto and in that time our computers can do a lot of data crunching during our encounter with weak short-range signals (such as with our land-based radar) that are aimed at the rogue planet as it passes us by. Now let Krypton's velocity be such that its 10 gigahertz computers are time dilated to only 1/30,000 clock cycles per second. Then at this speed, during our 33,000 second encounter, their computers' clocks can cycle only once and their weak signals will be fewer in number too. -Modocc (talk) 07:28, 5 April 2016 (UTC)
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- and also in ε' in point – I think everything before this is correct, and this is wrong. In the original setup the primed clocks showed t' on their faces, but in your revised setup they show an offset from that (specifically ), so you should have . That should agree with the result from the Lorentz transform (with ). -- BenRG (talk) 23:48, 4 April 2016 (UTC)
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- I think I'm hopelessly misled. Why ? How to calculate them (suppose light flash never occurred , so no synchronization was ever made)? Why in all frames result of experiment is same, but indication of clocks (which also is result of some processes inside clock) are not? 37.53.235.112 (talk) 18:04, 5 April 2016 (UTC)
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- You wrote "hind clock when shows , is situated [...] in ε' in point ". This means that at , the clock reads .
- The clock is at rest wrt ε', so it ticks at the same rate as the coordinate time of ε'. So if it shows at , then it must show at every time.
- But you also wrote "in all frames clocks on walls must show zero if light reaches them". So the hind clock shows when the light arrives. So when the light arrives. But this is clearly wrong: the light is emitted at and doesn't travel infinitely fast.
- So there is an internal contradiction in the assumptions you made about the behavior of the clock (or in the assumptions I made when reading). Which part is wrong depends on what thought-experiment you meant to describe. I think what's wrong is the idea that at , the hind clock reads . This was true in your previous Ref Desk thread, when that clock was set to show on its face at all times. But now it is set to show when the light arrives. Since it has the same worldline and ticks at the same rate as in your previous thread, the time it shows in this thread differs by a constant offset from the time it showed in the last thread. The offset is . In the last thread it showed at and at when the light arrived, but now it shows at and at when the light arrives. In the last thread it showed at , but in this thread it shows at . -- BenRG (talk) 00:44, 6 April 2016 (UTC)
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Ok. Then we have next
* because θ is not variable, θ is just literal representation of digits. |
You wrote "hind clock when shows , is situated [...] in ε' in point ". This means that at , the clock reads .
The clock is at rest wrt ε', so it ticks at the same rate as the coordinate time of ε'. So if it shows at , then it must show at every time. But you also wrote "in all frames clocks on walls must show zero if light reaches them". So the hind clock shows when the light arrives. So when the light arrives. But this is clearly wrong: the light is emitted at and doesn't travel infinitely fast. So there is an internal contradiction in the assumptions you made about the behavior of the clock (or in the assumptions I made when reading). Which part is wrong depends on what thought-experiment you meant to describe. I think what's wrong is the idea that at , the hind clock reads . This was true in your previous Ref Desk thread, when that clock was set to show on its face at all times. But now it is set to show when the light arrives. Since it has the same worldline and ticks at the same rate as in your previous thread, the time it shows in this thread differs by a constant offset from the time it showed in the last thread. The offset is . In the last thread it showed at and at when the light arrived, but now it shows at and at when the light arrives. In the last thread it showed at , but in this thread it shows at . -- BenRG (talk) 00:44, 6 April 2016 (UTC) |
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When do clocks show proper time ? |
37.53.235.112 (talk) 05:00, 6 April 2016 (UTC)
- and are lines in spacetime. The reading of a clock at is its reading at the intersection of its worldline and the line .
- The lines and intersect only at the origin , so the only way a clock can show the same reading at and is if it passes through . The two "middle" clocks in this setup do pass through , but the hind and front clocks don't. The hind clock passes through before , and the front clock passes through before .
- In your table, the clock readings at are correctly given as , and the clock readings at are correctly given as and . But .
- I don't understand what you mean by . -- BenRG (talk) 18:06, 6 April 2016 (UTC)
- I don't understand what you mean by -- It's clock's proper time. E.g. -- proper time of hind clock at start, -- proper time of hind clock when light reaches it. Also I don't know what is worldline, so don't understand this part. Clock shows something when it is situated in some place in space. When clock is situated in some place , it can be in point or . So it must have same readings. As I wrote readings are such letters as and . But absolutely unclear for me which readings must be equal what other readings and when. E.g. you wrote that when . What time corresponds with this? ? Why then reading of hind clock does not coincide? 37.53.235.112 (talk) 18:54, 6 April 2016 (UTC)
- I never wrote , or if I did it was a typo. You defined (I think) to be the hind clock's reading at t=0. It's not the hind clock's reading at t'=0, because the hind clock crosses t'=0 at a different time (an objectively different point in spacetime, and also a different proper time).
- The best way to understand this sort of thing is with a spacetime diagram. I'll attempt one in ASCII.
- I don't understand what you mean by -- It's clock's proper time. E.g. -- proper time of hind clock at start, -- proper time of hind clock when light reaches it. Also I don't know what is worldline, so don't understand this part. Clock shows something when it is situated in some place in space. When clock is situated in some place , it can be in point or . So it must have same readings. As I wrote readings are such letters as and . But absolutely unclear for me which readings must be equal what other readings and when. E.g. you wrote that when . What time corresponds with this? ? Why then reading of hind clock does not coincide? 37.53.235.112 (talk) 18:54, 6 April 2016 (UTC)
rear of train front of train (and hind clock) (and front clock) v v ^ / / | / /,, <-- t'=0 later / ,,/’ / ,,’’ / earlier .../.....@...../.... <-- t=0 | /,,’’ / v ’’
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- The point marked @ is . The lines and are angled differently (relativity of simultaneity). The clocks read on the line , but not on the line . There is no single well-defined "time at the start" because there is no single well-defined "start" of this experiment. Does that help? -- BenRG (talk) 19:42, 6 April 2016 (UTC)
- Does that help? No because it's rotatings. As I wrote, I did not study rotatings yet and I will not study rotating specially.
- You defined (I think) to be the hind clock's reading at t=0. Yes, it's reading of hind clock of moving coach ε' in coordinate system of ε. So reading in coordinate system of ε' must be . But you use same notation just saying it's different (but it's impossible as is number e.g. , and cannot be sometimes ). It is confusing. And one more thing is unclear: if hind clock is situated in some place of space, it's no matter what coordinate system is applied, so in both systems readings must be same (coordinates may be different). Yes or no? 37.53.235.112 (talk) 05:46, 7 April 2016 (UTC)
- The point marked @ is . The lines and are angled differently (relativity of simultaneity). The clocks read on the line , but not on the line . There is no single well-defined "time at the start" because there is no single well-defined "start" of this experiment. Does that help? -- BenRG (talk) 19:42, 6 April 2016 (UTC)
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- Yes, the readings are the same, the coordinates are different.
- My diagram is just a picture of the scenario you set up. (Except that I left out the light beams because the diagram was cluttered enough already.) The horizontal and vertical axes are x and t respectively. I didn't introduce any new rotating. I did say the Lorentz transformation is like a rotation, but you are already doing Lorentz transformations (and doing them correctly).
- The reading on a clock at some particular spacetime point doesn't depend on reference frames. For example, I could add numbers to the diagram showing the readings on the clocks:
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/ / / /,, <-- t'=0 / ,-10 / ,,’’ / ..-7.....@....-13... <-- t=0 /,,’’ / -10 /
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- and those numbers are objectively correct. They wouldn't change if I drew this diagram using x' and t' instead:
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| | | | ˙-7. | | ˙˙.. | ,-10,,,,,@,,,,,-10,, <-- t'=0 | ˙˙.. | | -13. <-- t=0
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- The numbers aren't in exactly the same places but all of the relationships are the same. The readings on the t=0 line are −7 and −13, the readings on the t'=0 line are both −10, and −10 is above −13, and so on.
- Yes, it's reading of hind clock of moving coach ε' in coordinate system of ε. – That doesn't really make sense. "The reading of the hind clock at t=0" makes sense (it's −7). "The reading of the hind clock when the light reaches it" makes sense (it's 0, not shown on this diagram). But "the reading of the hind clock in the coordinate system of ε" doesn't make sense. You need to be more specific about what time you're talking about—for example, by giving a value of t.
- I think that with these numbers, you'd say and . But I'm still not sure what you mean by . Is it ? -- BenRG (talk) 06:28, 7 April 2016 (UTC)
- Yes, it's reading of hind clock of moving coach ε' in coordinate system of ε. – That doesn't really make sense. I imagine as reading on hind clock seen from ε at start (start in ε is ) and virtual observer's eye is almost touching hind clock (but of course this eye is not moving with hind clock). is reading on hind clock seen from ε at moment light reaches hind clock () and again virtual observer's eye is almost touching hind clock. I understand that difference between and equals , but I'm not sure how to calculate independently from , and what other readings (besides ) influenced by .
- But I'm still not sure what you mean by . Is it ? Yes, for this numeric example. This is what is called "proper time", right? I imagine as reading on hind clock seen from ε' coach at start (start in ε' is ) and virtual observer's eye is almost touching hind clock (but eye IS moving with hind clock). In first thread Special relativity. Simultaneity I thought -- all 3 clocks in ε' coach were synchronized at start. 37.53.235.112 (talk) 10:04, 7 April 2016 (UTC)
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- Okay, I think I understand all of your symbols now. In the previous thread, indeed . But in this thread you changed the rules by saying "when light reaches walls, clocks on walls are reseted to zero". I assume you don't mean that they were literally rewound to 0 from whatever higher value they were showing (if so, all your other calculations are wrong). I think you meant that they counted down from a negative value to 0. In that case, , since the elapsed proper time from t'=0 until the light arrives is .
- In any case, I still think my first comment in this thread was correct. You said the hind clock, when it shows the numerical value on its face, is at . And that isn't true. It was true with the clocks set as they were in the previous thread. It isn't true with the clocks set as they are in this thread.
- The clocks are in the same places in spacetime in this thread as in the last thread. Only the values they show on their faces are different. And they are always different by exactly L'/2c. The clocks tick at the same rate, they are just set to different initial values, in this thread versus in the other one. In the previous thread, the hind clock showed on its face at . In this thread, it shows on its face at , and it shows on its face at . Behind all the complicated symbols, it's a very simple situation. -- BenRG (talk) 07:19, 8 April 2016 (UTC)
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You said the hind clock, when it shows the numerical value on its face, is at . It was not statement , but assumption as I'm not sure it's true (even for previous thread). I've taken it from previous thread (see Remark).
Correct? Let's check. Hind clock at start is situated in ε in point and in ε' in point . ; . What's next? What to substitute in and what should be compared with result? |
Special relativity. Simultaneity.
In your problem, say the light is emitted at (0,0) (in either coordinate system). It reaches the walls at , or equivalently . Your first clock has the parametric equation (x,t)(τ) = (0,τ), which you can plug into the Lorentz transformation to find (x',t')(τ). To find the digital reading of that clock at a particular (x,t) or (x',t'), you just solve for τ. Your other three clocks have the parametric equations (x',t')(θ) = (0, θ) and (x',t')(θ[]) = (±L/2, θ[]), and you can plug those into the Lorentz transformation to find (x,t)(θwhatever). Any question you have about what someone sees at a given (place,time) can be answered in this way. They are simple questions about coordinate geometry. -- BenRG (talk) 19:58, 29 March 2016 (UTC) |
37.53.235.112 (talk) 12:02, 8 April 2016 (UTC)
OK. According your suggestions we have:
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we will substitute x' and t' and should get next
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After substitution:
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Why result doesn't match with highlighted equation? 37.53.235.112 (talk) 18:02, 9 April 2016 (UTC)
Composition of Antarctic tephra
This block of tephra is located at Brown Bluff, Tabarin Peninsula, Antarctica. The dark specks appear to be Alkali basalt (per Skilling, 1994). Can anyone help identify the composition of the matrix material? Many thanks in advance.--Godot13 (talk) 17:30, 4 April 2016 (UTC)
- Hard be to certain, but the deposits at Brown Bluff and other locations within the James Ross Island Volcanic Group are mainly formed in lava deltas topped by subaerial lava flows Skilling (2002) erupted into an englacial lake. If this block is part of that, then we're looking at a lump of hyaloclastite breccia, with both clasts and matrix made up of shattered basaltic glass. Mikenorton (talk) 17:50, 4 April 2016 (UTC)
- Mikenorton- Many thanks!--Godot13 (talk) 17:56, 4 April 2016 (UTC)
Shadows
Is it true that a shadow is a tangible representation of nothing? Meaning that a shadow is not a thing but it exists independent of humans. A shadow can travel faster than the speed of light, and besides the particles occupying the space of a shadow, the shadow itself has no mass/energy? 2601:204:C003:57A5:B517:938E:2F62:3EA0 (talk) 20:25, 4 April 2016 (UTC)
- A shadow is an area of reduced light due to some object blocking some of the light source(s). ←Baseball Bugs What's up, Doc? carrots→ 20:30, 4 April 2016 (UTC)
- Yep, I've always wondered about a shadow being able to travel faster than the speed of light, due to the angle at which a shadow can be caused. Apologies for the previous answer which has nothing at all to do with your question. The Rambling Man (talk) 20:36, 4 April 2016 (UTC)
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- I don't think shadows are things in and of themselves but the manifestation of other things that are things in and of themselves (ie light/objects)...does this make sense??68.48.241.158 (talk) 20:41, 4 April 2016 (UTC)
- Shadows are a product of light and objects, so it doesn't make sense that a shadow would "travel" faster than the light that's accompanying it. ←Baseball Bugs What's up, Doc? carrots→ 20:51, 4 April 2016 (UTC)
- I don't think shadows are things in and of themselves but the manifestation of other things that are things in and of themselves (ie light/objects)...does this make sense??68.48.241.158 (talk) 20:41, 4 April 2016 (UTC)
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- It can sometimes be useful to look at the speed of "negative reality", like how quickly an electron hole can travel, or how quickly "coolth" spreads from a cold object. In the case of looking at how quickly a shadow moves, this could be important for things like a sundial. StuRat (talk) 21:13, 4 April 2016 (UTC)
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- There is a lot of very wrong science wrapped up in such a very short quantity of discussion here!
- Shadows do not "travel faster than the speed of light." Maybe the best place to start reading is our article on propagation delay; but I think it would be helpful to go back and read our article on light, wave, and shadow to help you re-center your understanding around the way scientists actually study these topics.
- The original question also touches on more philosophical ideas about the absence of substance (in this case, rather, the absence of photons...) Well, you might also enjoy reading about horror vacui - but you should understand up front that this is a pre-scientific philosophical idea that is largely refuted by careful study of modern theory and experiment. As you have arrived to the science reference desk, you should follow up that reading by looking at our article on the vacuum, and on electromagnetic radiation, which we now know may propagate in a vacuum. This concept can be a bit baffling, but pay careful attention to the way scientists define their terms, and you will find that the modern explanation is very consistent with experiment.
- Nimur (talk) 21:21, 4 April 2016 (UTC)
- A "shadow", like the dot made by a laser pointer, isn't an object. It's, well, a concept. You can take a laser pointer and wiggle it across the surface of the moon, and in theory, if it's perfectly collimated, that little dot might break the lightspeed barrier. But of course "that dot" is different photons from one instant to the next. They say you can never step in the same river twice ... same about a laser pointer dot, or a shadow, since the one is different photons each time, and the other is the lack of different potential photons each time.
- Inevitably group velocity and phase velocity will come up, though they're not very directly related. The concept though is that there are things that aren't things that can go faster than light. Wnt (talk) 22:06, 4 April 2016 (UTC)
- TANGIBLE (adj.) means capable of being touched, from Latin tangere "to touch". The OP has surely never touched a shadow and may not have read Shadow#Propagation speed in the article they already cited. Since there is no actual communication between points in a shadow that projects over a large surface, the shadow's edge cannot convey information between those distances at any speed. AllBestFaith (talk) 13:29, 5 April 2016 (UTC)
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- Consider a star that's, say, ten light years distant. It is constantly emitting photons. Any photons hitting us were emitted about ten years ago. Now suppose some large, dark object passes between us and the star, maybe hallway between us, i.e. five light years away from each of us. The photons already more than five light years away from the star will continue on their merry way toward us. The dark object will, at least temporarily, block that stream of photons, thus putting the star in shadow from our perspective. But we won't observe that phenomenon until about five years after it happened. So, NO, shadows do not "travel" faster than light. ←Baseball Bugs What's up, Doc? carrots→ 13:53, 5 April 2016 (UTC)
- The answer above by Wnt is correct and informative, but let me enlarge on it slightly. It is thought to be impossible for matter to travel faster than the speed of light, but there is no prohibition whatsoever against a phenomenon traveling faster than the speed of light. For an easy-to-visualize example, think of a wave on the water making contact with a straight shoreline. The smaller the angle between the wave and the shoreline, the faster the contact point will move. There is no upper limit to its speed: as the angle approaches zero, the propagation speed of the contact point increases without bound. Looie496 (talk) 13:57, 5 April 2016 (UTC)
- No, it isn't correct. A shadow can't "travel" any faster than the photons it's blocking. ←Baseball Bugs What's up, Doc? carrots→ 14:11, 5 April 2016 (UTC)
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- I think you're using that term differently than most people. For example, most people would say that the shadow of a hawk travels across the ground, or the shadow of the Moon travels across the Earth during a solar eclipse. But your use of "travel" is that a shadow travels only away from the Sun in these cases. Wnt (talk) 14:46, 5 April 2016 (UTC)
- I don't follow. Shadows "travel" only in relation to the light source and the object causing the shadow. ←Baseball Bugs What's up, Doc? carrots→ 19:27, 5 April 2016 (UTC)
- The technical term for gathering in special buildings to look at moving shadows is cinematography from Greek kinein "to move" + graphein "to write". AllBestFaith (talk) 21:55, 5 April 2016 (UTC)
- I don't follow. Shadows "travel" only in relation to the light source and the object causing the shadow. ←Baseball Bugs What's up, Doc? carrots→ 19:27, 5 April 2016 (UTC)
- I think you're using that term differently than most people. For example, most people would say that the shadow of a hawk travels across the ground, or the shadow of the Moon travels across the Earth during a solar eclipse. But your use of "travel" is that a shadow travels only away from the Sun in these cases. Wnt (talk) 14:46, 5 April 2016 (UTC)
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What about THIS???? you only have to watch the first 2-3 minutes or so 199.19.248.20 (talk) 00:43, 6 April 2016 (UTC)
- OK - speed of movement of a shadow. Let's put together a thought-experiment. Let's take a laser with a pencil-thick beam - and let's put an opaque black dot onto the exit window of the laser so that it casts a circular beam of light with a 'shadow' in the center of the beam. The laser is on a stand that allows us to rotate it really quickly. If I place this contraption vertically above my (infinitely large and perfectly flat) desk, shining the laser downwards, I'll see a shadow on my desk cast by that black dot. As we rotate the light from the vertical towards the horizontal, the center of the shadow moves from being vertically below the laser to being infinitely far away to the side. Since we can rotate the light from vertical to horizontal in a fraction of a second - but the shadow moves from being right in front of me to being infinitely far away in just a couple of seconds - it's tempting to say that it moves faster than the speed of light.
- But that's not true.
- The light from the laser is what defines the edges of the the shadow - and that light can't travel faster than light. So no matter how fast I rotate the lamp to "move the shadow" from right in front of me to being a million miles off to my right - the light from the laser can't travel that million miles to define the edges of the shadow at anything faster than the speed of light. The shadow moves at speeds approaching (but never exceeding) the speed of light.
- OK - so we need another thought experiment. Instead of projecting the shadow onto a flat desk, let's project it onto the inside of a vast sphere...an entire light-second in radius. If I'm standing in the center of the sphere - then I see the light reflected back at me from the sphere with a two second delay. If I suddenly move the laser from shining on the sphere to my right - to shining on the sphere to my left - then two seconds later, I see the light disappear from my right side and a fraction of a second later, it'll reappear on my left...and the shadow moved with it. So the "shadow" did indeed track all the way across the sphere in that tiny fraction of a second (albeit with a two second delay). It travels a distance of pi light-seconds in the time it took me to spin the laser around...which is *way* faster than the speed of light.
- But the problem here is that this shadow isn't a constant 'thing' - it's the absence of photons, but it's the absence of different photons when it's pointing in one direction versus pointing in the other direction. It's like driving along a freeway with a beige Volvo estate wagon a mile ahead of you. Suddenly it turns off of the freeway, out of sight. Simultaneously, you notice in your rearview mirror, a different beige Volvo estate wagon drives onto the freeway a mile behind you. Do you now conclude that the absence-of-a-Volvo travelled faster than the speed of light?
- SteveBaker (talk) 16:36, 6 April 2016 (UTC)
Tigers smarter than lions?
This might be just a bit of useless and potentially wrong trivia, but when people claim that tigers are smarter than lions, could it be that they are right? If yes, how could that be measured? AFAIK, brain size alone won't let us conclude about the intelligence of an animal. But where could the information bit come from?--Scicurious (talk) 20:58, 4 April 2016 (UTC)
- One of the predictors of intelligence is the degree of social integration, as social structures require a lot of intelligence to navigate (when to act submissive, when to dominate, when to fight). Since lions are social animals and tigers are not, that would seem to mean more intelligence is required of lions. StuRat (talk) 21:10, 4 April 2016 (UTC)
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- hard to say, all kinds of philosophical problems involved....is a dog smarter than a tiger because it can be trained to do things for humans but tigers can't?? or are tigers smarter because they can't be conned into doing things for humans?? you can look at behavior and behavior differences but the interpretation of smartness is inherently subjective...look at controversy over IQ....ants might be the smartest if look at how successful they are in terms of numbers etc...humans might be the dumbest..or the smartest as can use tools like crazy...but maybe dumb as the use of these tools may lead to their demise...idk...68.48.241.158 (talk) 21:15, 4 April 2016 (UTC)
- There are lots of ways of assessing animal intelligence, but usually scientists don't make claims about animals being "smarter" than another or terms like "intelligence" which is very broad and poorly defined. Rather, they talk about memory, learning, path finding and many other more specific things that are slightly more amenable to experimental or observational quantification. Our article Animal_cognition has some info and refs on methods. Here are a few books that give overviews of how we measure intelligence in animals, why animals are intelligent, etc. [1] [2] [3]. They are not feline specific, but we do have cat intelligence which gives this [4] scholarly article comparing the brains of lions to tigers. I might search a bit more later for more specific refs. You may also enjoy ref 3 and others at Portia_fimbriata, which describe how this spider can do things that smart lions do, like breaking line of sight to make a detour around prey, so as to approach it from a better angle. In the mean time, I suspect user:Snow Rise might have something helpful to add. SemanticMantis (talk) 21:17, 4 April 2016 (UTC)
- Also, a strike against tiger intelligence is that they refuse to jump over a wall of white fabric, even when cornered and facing death. For some reason they have a very strong instinct not to jump into something unfamiliar, even when doing so could save their life. StuRat (talk) 21:21, 4 April 2016 (UTC)
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- I wonder where you get this information from StuRat. I always do. Scicurious (talk) 22:24, 4 April 2016 (UTC)
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- StuRat to his credit quotes accurately from a source that is rife with spelling mistakes. A good convention in such quotations is to insert sic in brackets at misspellings; it stands for sic erat scriptum "thus was it written" and is a way to be scrupulously fair to both the present reader and original writer. Example: "...roles of white cloth...where[sic] laid out..." AllBestFaith (talk) 13:07, 5 April 2016 (UTC)
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- Sounds apocryphal to me, but who knows. But what you said was "For some reason they have a very strong instinct not to jump into something unfamiliar, even when doing so could save their life." Which sounds doubtful to me. I think if the tiger felt under stress, it would go over (or through) the fabric if that were the only option. This source makes it sound more like they bounded the an area such that it made it more convenient for the the tiger to take another path, to where they lay in wait. Two very different images, if you ask me, even if we assume either to be accurate.. Snow let's rap 06:23, 5 April 2016 (UTC)
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- Animals can sometimes be fooled relatively easily - for example, these painted "cattle grids". I suspect that if the tigers were sufficiently motivated, they would have jumped over the cloths. It was probably very skillful animal handling that allowed this method to be used. DrChrissy (talk) 16:57, 5 April 2016 (UTC)
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- Yes, the virtual cattle grids are another good example of what I mean. A smarter animal would notice they aren't quite the same as real cattle grids, and test them out with just one hoof. When they determined that they could walk on it, they would then have learned the difference and remember it. Getting back to the Q, lions do seem confused by the wild stripes on zebras, so that might be a mark against them. StuRat (talk) 17:21, 5 April 2016 (UTC)
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- But do we know whether tigers are similarly confused by the motion dazzle of the zebra stripes - it's just not black and white (sorry, could not resist that!). More seriously, because the zebra is able to confuse the lion, does that mean the zebra is more intelligent than the lion? Obviously not, (because the stripes are not part of any conscious effort) but I think it indicates the lack of usefulness of trying to apply "intelligence" to species other than humans. DrChrissy (talk) 17:45, 5 April 2016 (UTC)
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- @DrChrissy: and @StuRat:, you're both a bit out of date on your Zebra thinking. See this 2014 Nature Communications paper concluding "there is no consistent support for camouflage, predator avoidance, heat management or social interaction hypotheses" [6]. Rather, they conclude there is strongest support for the stripes being useful in avoiding ectoparasitism. Obviously this is not the be-all, end-all answer, but it's hard to get more authoritative than a comprehensive Nature paper from just a few years ago. SemanticMantis (talk) 19:19, 5 April 2016 (UTC)
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- Actually, I am well aware of that hypothesis. The function of the stripes is, in my opinion, not yet settled. I actually think they might be multi-functional, but you are correct to point out to other readers that motion-dazzle is not the only possibility. DrChrissy (talk) 19:42, 5 April 2016 (UTC)
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- I'm fairly confused though. If you accept there is no consistent support that zebra stripes even help with lions, why do you think it confuses tigers. I'm sure someone has fooled around with tigers and zebras, but if we can't even get enough evidence that it helps with lions, it seems unlikely we have anything even close to useful for tigers. (I believe there are some who suggest tigers may also use motion dazzle, but even if that's true I'm not sure there's any reason to think it's for other tigers as opposed to their prey.) Nil Einne (talk) 07:28, 6 April 2016 (UTC)
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- I've just read the Nature paper and I am not convinced it discredits the motion-dazzle hypothesis. The paper really has only one comment on this.
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- Across contemporary ecosystems in Africa, where lions have been subjects of repeated detailed study, lions capture zebra in significantly greater proportions to their abundance
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- but this leaves the question - what proportion would be captured if the zebra did not have stripes? Regarding the insect deterrent hypothesis, I am also left with another question. If this is so effective, why have no other animals (e.g. antelope) evolved something similar? DrChrissy (talk) 13:32, 6 April 2016 (UTC)
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- By the way, did you know that some sheep in the valleys of Wales completely trump lions and tigers in intelligence. They have learned to curl themselves into a ball (like a hedgehog) and roll over cattle grids to get to the more luscious grass on the other side. Please note, I meant to post this 4 days ago. ;-) DrChrissy (talk) 17:04, 5 April 2016 (UTC)
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"Measures" of intelligence (please note the scary quotes) are totally, totally dependent on the questions you ask and the way in which this is investigated. What would you like to know? Is the hunting behaviour of the tiger more plastic than that of the lion? Can tigers solve human derived puzzles quicker than lions? Do circus tigers learn "tricks" more quickly than circus lions? It all depends on the question asked and the way we try to determine the answer. Unfortunately, so many studies on animal "intelligence" are clearly locked firstly within an anthropocentric world, and then secondly our own limitations of trying to investigate this. How do we objectively measure whether a tiger is more intelligent than an earthworm? If we can not answer that, then we can not measure whether a tiger is more intelligent than a lion. DrChrissy (talk) 23:11, 4 April 2016 (UTC)
As others have noted already, the question is problematic as phrased because "intelligence" is not an empirically quantifiable value. That is to say, despite the way we idiomatically reference it (especially with regard to our own species) it's not a substance or unidimensional quality or process that lends itself to measurement. Part of this is innate; to the extent that "intelligence" is seen as a desirable quality, there will always be a propensity towards reductionism in order that it can be seen as a uniform quality that is more present in some than others. But this mistaken concept got kicked into overdrive in the pre-modern and early modern history of the biological sciences, in order to justify the hierarchical structures that many "learned" men wanted to presume, particularly with regard to racist and gendered notions of innate superiority. I don't mention this just as a general aside either--these beliefs were central to the development of notions like IQ, and the tests that purported to evaluate a "general intellect". Proponents of this variety of psychometrics have tried hard to excise the bias from these tests since, but many cognitive scientists believe the very concept upon which they are predicated (a general measure of intelligence) is flawed beyond repair and based in a lack of understanding of the modular mind.
Now, bringing this back around to animal behaviour, the complexities become even more pronounced when we try to compare species. You can test for performance on certain tasks, but then your are necessarily bringing your value judgments into what intelligence is best typified by when you select the tasks for "general" intelligence. That's not to say you can't measure changes in the concept of general intelligence; if a given individual or generation raises in performance on all kinds of task, largely across the board, you know that intelligence has become "superior" in the sense. But there are too many different types of behaviours and faculties when it comes to cognition to say which is going to prove most vital or advantageous to a given individual in the longterm, in an open system like an eco-system or a social system. And to compare the needs and environment of two different animals that are alike only that both are cats and apex predators misses the functional meaning of intelligence. cognitive researchers (and sometimes social psychologists) call this "situated intellect" (and also a principle of environmental psychology), while sociobiologists (and EP and sociobiology really are the same fields as seen from either the anthropocentric/narrow or zoocentric/broad lens) call this the animal's "behavioural niche". You might even say that all animals with substantially developed brains have a "cognitive niche", but that term is already applied to in a related but distinct sense to describing ones of the ecological niches that humanity fills.
But it goes further than the species level, because what turns out to be "smart" behaviour varies not just by the species but by the individual and their circumstances. What is the "intelligent" solution in the aggregate? If its the type of decision that leaves the animal best off in the long run, the animal doesn't know what that's going to be--even if we, or it, could even put together an accurate or concrete notion of what "best off" would be for it. Indeed, most species won't even necessarily ever recognize the long-term consequences of its actions, especially if the "decision" and the outcome are separated by a bit of time. But the decisions that the animal makes are tailored to ecological/environmental demands the members of its heritage during its evolutionary past. But even if you are asking which species is more "intelligent" with regard to adapting to unexpected circumstances, you'd have to qualify the conditions very carefully to decide which was "more intelligent" in this regard. Ultimately you'd have to have a lot of experience studying the ethological nature of both species just have an informed decision, and even then you'd have to pass your opinion along subjectively; there'd be no one empirical measure you could use. If they naturally cohabitated in a certain region, you could at least measure their success in their survival rates, but you can't even do that here. Snow let's rap 06:11, 5 April 2016 (UTC)
- Which species is closer to extinction? ←Baseball Bugs What's up, Doc? carrots→ 13:45, 5 April 2016 (UTC)
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- There are different (sub)species of each, but according to the infoboxes at lion and tiger, the tigers are currently more threatened. While I appreciate a little teleological thinking, that does not tell us much of anything about intelligence, though it may tell us something about their Ecological_resilience. SemanticMantis (talk) 14:06, 5 April 2016 (UTC)
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- But not even much about that, since both species live in drastically different ecological contexts, with different degrees and forms of habitat displacement, prey reduction, interruption of reproductive habits and other population stressors. The populations of asiatic lions and most tiger species are so reduced now, I don't think they co-exist anywhere in the world, making comparison of their circumstances an apples and oranges affair. That line of inquiry raises another issue, actually--namely that you get substantial variation of behaviour between subspecies. Snow let's rap 20:15, 5 April 2016 (UTC)
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- @BBB: That's a ridiculous point of comparison. Which are closer to extinction, Polar Bears or House Flies? Your conclusion: House flies are more intelligent than polar bears? That's meaningless. Turn brain on before posting! SteveBaker (talk) 20:49, 5 April 2016 (UTC)
- The trouble with direct comparison of intelligence is that behavior is often evolved to match environment. Why won't a tiger jump a white sheet? Well, maybe it's just stupid - but maybe it's evolved to avoid jumping into hidden snow banks for some deep and subtle reason that we've failed to comprehend? It's easy to label weird behaviors like this as "stupid" - when in reality, we just don't have the intelligence to understand them ourselves.
- Why is it that your stupid dog spins around in a circle before (s)he poops? It turns out that dogs prefer to face North or South when they poop - and spinning around helps them sense the earth's magnetic field more easily [7]. Are dogs stupid for doing this - or is there something they know that we don't? Maybe they are smarter than we random-direction-pooping humans?
- The root problem here is that we simply do not have a reasonable definition for the word "Intelligence" - and the closest we ever get to having a means to measure this vague thing is the IQ test - which more or less defines "Intelligence" as "The ability to get a high score on an IQ test".
- So when it comes to animals, not only would it be hard to compare different species against some fixed standard - but it's also impossible to come up with a fixed standard that has much real-world significance.
- So how do we define as "intelligence"? "That which humans have but other animals and computers have less of!"
- For example, we'd say that humans were more intelligent than chimpanzees. But teach a chimpanzee to the digits 1 through 9, then place those digits in random order on a computer screen and have the subjects remember the positions of each digit and to recall them in numerical order. Sounds easy - but chimpanzees are much better at playing this game than people are[8]! If this is a measure of intelligence then chimpanzees are smarter than humans - and at a game that we invented! I'm old enough to remember when beating a human at chess was regarded at the pinnacle of intelligence...until Deep Blue beat Kasparov...then it was winning Jeopardy! (well, Watson nailed that one pretty effectively)...and then playing Go...but since a week or two ago, computers beat us all at that too. We have the Turing test - but to pass that, the computer has to adequately pretend to be a human...which takes us back to "Intelligence is that thing that humans have" - which is cheating! Computers are fast edging towards passing the Turing test - so now we're looking for another reason why we can't call them "intelligent".
- Consider the Clark's nutcracker - which can hide tens of thousands of nuts around it's territory - then, nine months later, flawlessly retrieve them as needed and without hesitation...even when they are buried under feet of snow. Humans can't manage to hide more than a dozen or two without losing track. Over short-term memory, even cats have better memories than we do! These things are mental capabilities that are beyond what humans can do...yet we persist in moving the goal posts to preserve our feelings of superiority!
- Clearly humans DO have a breadth and depth of skills and mental capabilities that no other animal (nor machine) can come close to matching - but defining what that thing is eludes us.
- So asking whether a Lion or a Tiger has more of some indefinable thing is entirely meaningless. First define what the word means, and how to measure it - then we'll tell you who has the most of it.
- SteveBaker (talk) 20:49, 5 April 2016 (UTC)
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- Surprised no one here has mentioned Encephalization or Brain-to-body mass ratio. Our page has the ratio for Lion (1:550) but I can't find Tiger after a brief search. Yes it's imperfect and has glaring exceptions, but as a "starting point" it's better that "the question is meaningless".. Surely we CAN compare 2 animals and decide a Raven is smarter than a housefly, the question is a tiger smarter than a lion might be much "harder" to resolve, but doesn't mean it's meaningless. Ultimately, the animals might be similar enough to say there is more overlap then we can't reliably distinguish between the two for that metric. Vespine (talk) 23:30, 5 April 2016 (UTC)
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- Well yes, of course we might all be inclined to agree, as an impressionistic matter, that the raven is "smarter" than a house fly. Certainly we can see that it has a vastly more complex CNS and has something much closer to the kind of problem-solving capabilities we recognize as more similar to human cognitive capabilities. But that's not what the OP asked about; he wanted to know if there were specific and concrete measures by which two relatively closely related (at least when compared against the raven-fly scenario) could be judged with regard to "intelligence". And the short answer is, no not really, though you could (theoretically) get performance measures if you narrow the question to a specific behavioural task in a specific environmental context. That said, brain to body mass ratio is an interesting phenomena, but once again, it only makes sense as a vaguely defined trend; when you look at the particulars of this supposed correlation, it breaks down all over the place. Snow let's rap 01:48, 6 April 2016 (UTC)
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- What is the evidence that a raven is "smarter" than a housefly? Can a raven land upside down on a ceiling? Rather than looking at brain ratios etc, we first need to define what "smarter" means. Once we agree on that (Ha!) We can devise questions and studies to answer those. DrChrissy (talk) 13:09, 6 April 2016 (UTC)
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- What is the evidence that a raven is "smarter" than a housefly? I think this kind of statement is bordering on solipsism, how could we possibly know anything? Oh the despair. IMHO it's actually not that hard. For example, it doesn't take "intelligence" to land on a ceiling, in fact, a study was done which examined how a fly does it, and all it has to do is reach up with it's front legs and sticky feet do the rest. Vespine (talk) 22:27, 6 April 2016 (UTC)
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- Yes, of course I already knew how houseflies managed this - I was asking the question in a way that would indicate how the question posed about "intelligence" determines the answer and therefore the futility of asking the question. StuRat has now posed the suggestion that tool-use indicates intelligence. Tool use by animals tells us that ants will drop stones down the burrows of rival colonies. And there are other examples of tool-use by invertebrates, but again very dependent on the definition of "tool-use". DrChrissy (talk) 22:42, 6 April 2016 (UTC)
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- No, you misquoted me. I did not state that tool use indicates intelligence, I stated that "the ability to reason a solution to a novel problem" does. That solution may, or may not, involve tool use. In ants, presumably any tool use is an evolved instinctive behavior, and not to a novel situation, as competing any colonies have existed as long as ants have. StuRat (talk) 17:21, 7 April 2016 (UTC)
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@StuRat Apologies for misquoting you - it was not intentional. With regards to ant responses to novel situations, you might care to look at this problem solving in leafcutter ants, Atta colombica.[1]
- Other examples of invertebrates responses to novel situations include include -
- Social transmission of information during the waggle dance of honeybees.
- Idiothetic orientation by spiders, i.e. they memorize information about their previous movements.[2]
- Detour behaviour in which spiders choose to take an indirect route to a goal rather than the most direct route, thereby indicating flexibility in behaviour and route planning, and possibly insight learning.[3]
- Conceptualisation in the honeybee, Apis mellifera.[4]
- Numeracy in the yellow mealworm beetle, Tenebrio molitor,[5] and honeybee.[6]
References
- ^ Dussutour, A., Deneubourg, J.L., Beshers, S. and Fourcassie, V., (2009). Individual and collective problem-solving in a foraging context in the leaf-cutting ant Atta colombica. Animal Cognition, 12: 21-30
- ^ Seyfarth, E.A., Hergenroder, R., Ebbes, H. and Barth, F.G. (1982). Idiothetic orientation of a wandering spider: compensation of detours and estimates of goal distance. Behavioral Ecology and Sociobiology, 11: 139-148
- ^ Template:Sherwin, C.M., (2001). Can invertebrates suffer? Or, how robust is argument-by-analogy? Animal Welfare, 10 (supplement): S103-S118
- ^ Avargues-Weber, A., Dyer, A.G. and Giurfa, M., (2011). Conceptualization of above and below relationships by an insect. Proceedings of The Royal Society B-Biological Sciences, 278: 898-905 doi:10.1098/rspb.2010.1891
- ^ Carazo P., Font E., Forteza-Behrendt E. and Desfilis, E., (2009). Quantity discrimination in Tenebrio molitor: evidence of numerosity discrimination in an invertebrate? Animal Cognition, 12: 463-470 doi:10.1007/s10071-008-0207-7
- ^ Dacke, M. and Srinivasan, M.V., (2008). Evidence for counting in insects. Animal Cognition, 11: 683-689
- DrChrissy (talk) 17:48, 7 April 2016 (UTC)
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- "I'd go with" ≠ "empirical measure". We're not talking about whether anyone has a right to a "reasonable" subjective impulse as to what constitutes remarkable intelligence, relative or otherwise, especially if it meshes with with the semantics of their impressionistic/fuzzy logic definition for the term. The OP was inquiring about empirical measurement. And the answer, notwithstanding the question being steeped in a deeply complex cognitive inquiry, is that no, there is no real way to determine with scientific clarity that a tiger is smarter than a lion or vice versa. Nor indeed that a raven is smarter than a housefly. If that makes me sound solipsistic, well I understand what Vespine means to say by that, but coming from a scientific perspective, I don't know of a single sociobiologist who I think would make the claim that they could "prove" that. They might talk about the relative complexity of the nervous system or the behaviour itself, or they might talk about whether the task was accomplished with working memory or by a previously observed instinctive reaction, whether it required novel pattern analysis or was a conditioned response, whether the animal could (or had to) learn the behaviour socially, or whether it could add a new step to the process to meet new necessities, ect, ect. But no serious researcher is going to say "this animal is X order of magnitude or Y% greater than this other species in terms of intelligence."
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- Again, just avoid running this circle one more time, the argument is not that "you shouldn't say, as reasonable shorthand, that an iguana is smarter than an ant." But if you want to prove that statement as empirical fact...well you better be a revolutionary in the understanding of animal and human make-up on par with Charles Darwin in his day, with a bit of Carl Sagan's gift of gab mixed in, because you're going to have to advance our understanding of the mind and the brain lightyears in order to be able to come up with one unified measure that defines "intelligence" such that great thinkers all over the world, greatly divided over basic questions about the nature of cognition and intelligence all nod and go "Yup, that's it, alright. Oh, what do you know, Johnson, looks like I've an intelligence rating of 354.7 Vesps. You're only 320.1. So....now we know that, don't we Mr. Nobel laureate?!" <------"Vesps" used in good humour! :) Snow let's rap 04:45, 7 April 2016 (UTC)
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- THIS paper takes a reasonable stab at a mathematically solid definition of intelligence. However, it depends on a few uncomputable measures - so it's not something that can be practically tested - and a lot of people who work in the field do not agree with it. SteveBaker (talk) 15:18, 7 April 2016 (UTC)
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April 5
Nuclides undergoing nuclear fission
What nuclides beside U, Th, can undergo nuclear fission? The nuclear fission article seems not to specify a list of fissionable and fissile nuclides. Can bismuth and palladium, for instance, undergo fission?--5.2.200.163 (talk) 10:44, 5 April 2016 (UTC)
- Please see Fissile material. Did you consider an internet search for "fissile elements" before asking here?--Phil Holmes (talk) 11:03, 5 April 2016 (UTC)
- I find the article you mention not very informative. It mentions fissile rule and centers on actinides. Other elements beside actinides and other ways of triggering fission are not mentioned. I have considered a gogle search, again not very informative. I've read somewhere (don't remember where) about elements like bismuth and palladium fissioned by deuteron beam collision.--5.2.200.163 (talk) 11:20, 5 April 2016 (UTC)
- Also nuclear fission does not specify many details about fission reaction mechanisms and triggering possibilities.--5.2.200.163 (talk) 11:20, 5 April 2016 (UTC)
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- You're right - that article could do much better. The topmost graph answers your question, but turning the low-res little dots into element and isotope is ... laborious. We should have a real chart that excludes the long gray band and just focuses on where there is data (if that indeed is all the data that is available, which seems odd) Wnt (talk) 14:40, 5 April 2016 (UTC)
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- I would even go so far as to say every atom except Hydrogen-1 can undergo fission, although it requires bombardment with some rather high energy particles to make it happen in stable isotopes. So, I assume they meant to ask about spontaneous fission. StuRat (talk) 19:38, 5 April 2016 (UTC)
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MHD and nuclear reactors coupling
What are the requirements for the coupling of nuclear reactors with MHD generators in order to convert nuclear heat directly into electricity?--5.2.200.163 (talk) 10:47, 5 April 2016 (UTC)
- Big Pipes. Greglocock (talk) 19:54, 5 April 2016 (UTC)
Arduino: RGB LED lights and Resistors
If we want to link 5 of 5V or 3V RGB LED to Arduino, how many resistors should i get? and how many Ohm does single resistor have to be? hellllpppp — Preceding unsigned comment added by 195.94.247.199 (talk) 11:23, 5 April 2016 (UTC)
- What happens when you type [ Arduino: RGB LED lights and Resistors ] in the Google search box? --Guy Macon (talk) 16:27, 5 April 2016 (UTC)
Solubility
How is the solubility of a substance, say a salt, influenced by another salt? Is the solubility the same when dissolving a salt in a saturated solution of other salt comparatively to dissolution in pure solvent(water)?--5.2.200.163 (talk) 11:32, 5 April 2016 (UTC)
- What happens when you type [ How is the solubility of a salt influenced by another salt? ] in the Google search box? --Guy Macon (talk) 16:29, 5 April 2016 (UTC)
- Common-ion effect may come into play, depending on the identity of the other salt. --Jayron32 16:41, 5 April 2016 (UTC)
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- I see this discussion and I wonder how the above said aspects can be quantitatively characterized? Is the mixture of the two solutions an ideal mixture or not?--89.122.39.86 (talk) 08:26, 8 April 2016 (UTC)
Voltage drop over fully open transistor?
I've made a [schematic for a circuit] which uses two PIR circuits to control some LEDs (either PIR sensor will activate the LEDs). A couple of resistors and a capacitor slow the opening and closing of the transistor so that the LEDs fade on and off. Can anyone advise the voltage drop over a 2N2222 transistor that is fully open? The LEDs accept 1.8-2.2 V. --78.148.105.117 (talk) 12:31, 5 April 2016 (UTC)
- If by "open" you mean not passing current (when VB = VE = 0V), the voltage drop across the transistor collector-to-emitter is the whole 6V supply. The 2N2222 is a common NPN switching transistor with hFE >75 @ IC =10 mA. Datasheet here. The HC-SR501 Body Sensor Modules that you use seem to deliver maximum 3.3V outputs; that suggests an inadequate 1V approx. to the LEDs after voltage drops in the 1N4001, division by 7 k ohm resistors, and VBE. The 470µF capacitor in your circuit diagram is an electrolytic type that should be shown with correct polarity. The power dissipated in the transistor would be maximum and equal to the power in the LEDS if its emitter could supply 3V to the LEDs. Ptot in 2N2222 must not exceed 500mW so the LEDs should draw somewhat less than 160 mA. (If by "open" you meant the fully conducting state, VCEsat of the 2N2222 is about 0.4V ). AllBestFaith (talk) 14:26, 5 April 2016 (UTC)
- Damn! I meant closed! Thanks. I'm not sure I'm using the symbol properly either. The base is where the signal goes right? The 6V is meant to be shared across the LEDs when the transistor is closed/on. The 3.3 V is meant to be delivered to the transistor to tell it to turn on. 78.148.105.117 (talk) 15:13, 5 April 2016 (UTC)
- The base is ... where the base is. Refer to our article on bipolar junction transistors for an introduction. To be clear, it is possible to design a single transistor amplifier that places the input or output signal on any of the terminals of a transistor. Most commonly, though, the convention is to use the base as the input signal, because this yields the most desirable current gain. This is called the common emitter configuration, and it is popular for lots of general purpose circuits like simple audio amplifiers or simple current drivers. Not all amplifier circuits need high current gain, so other configurations exist for different applications. Nimur (talk) 15:18, 5 April 2016 (UTC)
- Unfortunately the OP drew a transistor in Common collector (known as "emitter follower") arrangement where there will be no voltage gain, and VE cannot be more positive than VB. This seems to be a case of wanting several functions together i.e. (i) an OR-logic combination of the two sensor outputs, (ii) slow ramp switching on/off and (iii) a driver for 9 LEDs. There are better circuit solutions for these functions e.g. (i) a standard CMOS device such as MC14071, (ii) an Op amp integrator with (iii) a high-current output stage respectively. A designer would enquire why the ramp switching is wanted (reasons could be to reduce transient loading of a power supply shared with something else, or to prolong the life of incandescent bulbs but that's not necessary for LEDs) and (s)he would consider a Switched-mode power supply especially if the total LED power is large. Advantages of the more complex switched mode is that little power is dissipated by the driver since its output transistors are mostly fully on or fully off, and the ramp dimming function is easily done by varying the switching Duty cycle. AllBestFaith (talk) 19:13, 5 April 2016 (UTC)
- Hi. I've rearranged the circuit a lot. The reason for the fading is to make the light look more like a flame coming on and going off. [[http://everycircuit.com/circuit/4523679919112192 This is part of the circuit - I'm trying to make the on phase switch on more slowly but I don't seem to be able without reducing the final voltage/brightness. The first switch simulates the PIR sensor coming on and the second switch is just to drain the capacitor to reset the circuit for the simulation. The problem is that I can only make the light fade-on take longer by simultaneously increasing the delay before any light shows at all. Thanks for any advice. 78.148.105.117 (talk) 21:24, 5 April 2016 (UTC)
- Unfortunately the OP drew a transistor in Common collector (known as "emitter follower") arrangement where there will be no voltage gain, and VE cannot be more positive than VB. This seems to be a case of wanting several functions together i.e. (i) an OR-logic combination of the two sensor outputs, (ii) slow ramp switching on/off and (iii) a driver for 9 LEDs. There are better circuit solutions for these functions e.g. (i) a standard CMOS device such as MC14071, (ii) an Op amp integrator with (iii) a high-current output stage respectively. A designer would enquire why the ramp switching is wanted (reasons could be to reduce transient loading of a power supply shared with something else, or to prolong the life of incandescent bulbs but that's not necessary for LEDs) and (s)he would consider a Switched-mode power supply especially if the total LED power is large. Advantages of the more complex switched mode is that little power is dissipated by the driver since its output transistors are mostly fully on or fully off, and the ramp dimming function is easily done by varying the switching Duty cycle. AllBestFaith (talk) 19:13, 5 April 2016 (UTC)
- The base is ... where the base is. Refer to our article on bipolar junction transistors for an introduction. To be clear, it is possible to design a single transistor amplifier that places the input or output signal on any of the terminals of a transistor. Most commonly, though, the convention is to use the base as the input signal, because this yields the most desirable current gain. This is called the common emitter configuration, and it is popular for lots of general purpose circuits like simple audio amplifiers or simple current drivers. Not all amplifier circuits need high current gain, so other configurations exist for different applications. Nimur (talk) 15:18, 5 April 2016 (UTC)
- Damn! I meant closed! Thanks. I'm not sure I'm using the symbol properly either. The base is where the signal goes right? The 6V is meant to be shared across the LEDs when the transistor is closed/on. The 3.3 V is meant to be delivered to the transistor to tell it to turn on. 78.148.105.117 (talk) 15:13, 5 April 2016 (UTC)
Why is Fresh-water Fishing mostly so poor in Winter? (I'm sure there are exceptions)
Fish don't hibernate, so it has to eat and swim around same as any other season. Some fish can't even breathe unless they are on the move. Not sure if this applies to fresh-water fish, but maybe it does. Anyway, it has to eat and it has to exist same as any other season, so why is fishing so poor in winter?
2A02:FE0:C711:5C41:3155:1744:AA32:2C45 (talk) 15:28, 5 April 2016 (UTC)
- Fish are cold-blooded animals, so their metabolism slows down in cold weather. Therefore fish use less energy and don't have to feed as often in winter, and thus are less likely to take the bait. - Lindert (talk) 16:09, 5 April 2016 (UTC)
- (edit conflict)Doesn't it depend on what sort of fishing? Fly fishing will be more successful when there are more flies around in summer, but other fishing techniques are possibly better in winter? Freshwater fish can breathe when at rest relative to the river bed just by relying on the flow of water past their gills. Dbfirs 16:14, 5 April 2016 (UTC)
Thanks guys, for answering 2A02:FE0:C711:5C41:D448:2C0C:836:8174 (talk) 14:02, 6 April 2016 (UTC)
What happens to dissolved oxygen in the water when the lake is completely frozen over ?
I would expect the level to steadily go down, since there's no air in contact with the water at the surface to replenish the supply. Wouldn't the fish then use up the oxygen, converting it to carbon dioxide ? Or are there enough plants in freshwater lakes so that the oxygen cycle is self-sustaining ? StuRat (talk) 16:19, 5 April 2016 (UTC)
- Completely frozen over as in "a layer of ice on top, with no gaps" or as in "ice down to the bottom of the lake"? --Jayron32 16:42, 5 April 2016 (UTC)
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- Can it be ever so cold that a lake is frozen down to the bottom? --Scicurious (talk) 00:49, 6 April 2016 (UTC)
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- A shallow lake is not a lake, but a pond. These can freeze all the way down, but I do not believe a lake can be completely frozen. Scicurious (talk) 11:01, 6 April 2016 (UTC)
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- Sometimes. Depends on who does the defining. --Jayron32 14:38, 6 April 2016 (UTC)
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- Whoever named Shallow Lake apparently disagrees. StuRat (talk) 17:45, 6 April 2016 (UTC)
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- Why is it that water freezes on the surface of a lake but not below it?, Why Fish don’t Freeze in a Frozen Lake and Lake Vostok. I've not come across a lake frozen to the bottom during the last 40+ years in the Arctic. CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 02:37, 7 April 2016 (UTC)
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Thanks guys, for answering... Ops, wrong post. Sorry. Was meant for the one above. 2A02:FE0:C711:5C41:D448:2C0C:836:8174 (talk) 14:00, 6 April 2016 (UTC)
How does lactulose cause flatulence ?
It's an indigestible sugar used to treat constipation (among other things). So, if it isn't digestible, what generates the gas ? StuRat (talk) 19:20, 5 April 2016 (UTC)
- It's a stool softener. What it does is draw water into the stool, thus expanding and softening the stool and replacing the gas contained within the stool with water. All that gas gotta go somewhere... --TammyMoet (talk) 19:43, 5 April 2016 (UTC)
- Lactulose is metabolized in the colon by bacterial flora, see Lactulose#Mechanism of action.Fermentation is the name of the metabolic process that converts sugar to acids, gases or alcohol. It occurs in yeast and bacteria, and also in oxygen-starved muscle cells, as in the case of lactic acid fermentation. AllBestFaith (talk) 19:44, 5 April 2016 (UTC)
- See also Flatulence#Production.2C_composition.2C_and_smell. ---- LongHairedFop (talk) 19:47, 5 April 2016 (UTC)
- Lactulose is metabolized in the colon by bacterial flora, see Lactulose#Mechanism of action.Fermentation is the name of the metabolic process that converts sugar to acids, gases or alcohol. It occurs in yeast and bacteria, and also in oxygen-starved muscle cells, as in the case of lactic acid fermentation. AllBestFaith (talk) 19:44, 5 April 2016 (UTC)
- As others have noted, lactulose's medicinal usage (and veterinary usage; its common as a no-fuss/easy on the metabolic pathways treatment option for constipation in certain mammals) is directly a result of the fact that it is not digested or absorbed in the upper gastrointestianl tract. When it reaches the lower tract, it becomes a readily-available form of sustenance which can greatly increase the numbers of various bacterial species within your gut's microbiota. In metabolizing the sugar, these gut flora change the pH of the stool mass and, through osmotic differential, pull water across the intestinal wall, the sum result of which is fecal matter with more water content and a greater volume, both of which make stools easier to pass and also create greater stimulation of the voiding reflex. Snow let's rap 20:49, 5 April 2016 (UTC)
Gravity detector
Hi, on a TV programme I saw demonstrated a gravity detector supposedly sensitive enough to detect people moving around nearby (within a few feet). The man demonstrating it moved from side to side in front of it, and the signal from the detector appeared to oscillate in sync with his movements. Is this really feasible, or would a detector that sensitive be overwhelmed by background noise? 86.161.61.41 (talk) 20:04, 5 April 2016 (UTC)
- Simple gravimeters have been known for centuries. See Cavendish experiment for one of the famous early experiments in detecting the strength of a gravitational attraction between relatively small masses. Modern gravimeters are more sensitive and transportable. --Jayron32 20:10, 5 April 2016 (UTC)
- With regards to background noise, consider that a person weighing 80 kg at two feet from the sensor has about the same effect as a 8000 kg truck at 20 feet (gravity decreases with the distance squared). Hence I'd say that background noise could be a problem in some locations, but if the immediate vicinity of the sensor is not too eventful the scenario you describe is entirely feasible. - Lindert (talk) 20:22, 5 April 2016 (UTC)
- What about larger terrestrial and celestial events? 86.161.61.41 (talk) 20:53, 5 April 2016 (UTC)
- Even though the gravitational effects associated with those things are large compared to what the sensor is measuring (e.g. the moon has a much larger gravitational pull on the sensor than any person standing a feet away), the time scales for these events are of a completely different order. Because these larger events happen so slowly relatively speaking you can still see the immediate effects of people moving by the sensor. - Lindert (talk) 21:18, 5 April 2016 (UTC)
- I see, thanks. 86.161.61.41 (talk) 22:55, 5 April 2016 (UTC)
- Even though the gravitational effects associated with those things are large compared to what the sensor is measuring (e.g. the moon has a much larger gravitational pull on the sensor than any person standing a feet away), the time scales for these events are of a completely different order. Because these larger events happen so slowly relatively speaking you can still see the immediate effects of people moving by the sensor. - Lindert (talk) 21:18, 5 April 2016 (UTC)
- What about larger terrestrial and celestial events? 86.161.61.41 (talk) 20:53, 5 April 2016 (UTC)
- The LIGO detectors are incredibly sensitive. Your observation about background noise is correct; Neil deGrasse Tyson talks here about the signs they have around the facilities telling you to drive slowly to reduce interference. --71.110.8.102 (talk) 23:04, 5 April 2016 (UTC)
- That may be more for mechanical vibration than gravitational disturbance? 86.161.61.41 (talk) 00:04, 6 April 2016 (UTC)
- Yes, LIGO is very sensitive to mechanical vibrations. I once heard a talk discussing the sources of noise that LIGO has to deal with, and it included many ridiculous problems including: tides caused by the moon, continental drift, weather patterns, and apparently tumbleweeds hitting the side of the building (so they erected fences to catch the weeds before they got too close). Dragons flight (talk) 07:03, 6 April 2016 (UTC)
- That may be more for mechanical vibration than gravitational disturbance? 86.161.61.41 (talk) 00:04, 6 April 2016 (UTC)
Bacterial victim
Viruses notoriously infect us eukaryotes. Are prokaryotes spared this affliction? Jim.henderson (talk) 20:25, 5 April 2016 (UTC)
- In fact, there is a specific word for viruses that attack bacteria: bacteriophage. Nimur (talk) 20:38, 5 April 2016 (UTC)
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- Ah. Thanks. And I should have phrased the question as to not invite a double negative. Jim.henderson (talk) 20:42, 5 April 2016 (UTC)
- Also, you need to phrase your comment not to include a split infinitive. Only jesting!--178.101.224.162 (talk) 00:09, 6 April 2016 (UTC)
- Ah. Thanks. And I should have phrased the question as to not invite a double negative. Jim.henderson (talk) 20:42, 5 April 2016 (UTC)
- There are even virophages! Nobody gets a free pass. :) But honor among thieves means that more of them are simply satellite viruses. Wnt (talk) 11:30, 6 April 2016 (UTC)
Reaction with ice
Does sodium react with ice? What are some values of the reaction rate?--213.233.84.20 (talk) 21:03, 5 April 2016 (UTC)
- It reacts quite violently with water. So if the ice melts.....--178.101.224.162 (talk) 00:29, 6 April 2016 (UTC)
- If there is any reaction at all, that would melt some of the ice, which would react more, and melt more ice, in a chain reaction until all the ice was gone. And I would expect there would be some reaction at first, since ice still sublimates into water vapor even at low temperatures. StuRat (talk) 00:42, 6 April 2016 (UTC)
- It would actually be an interesting experiment if you got some very cold sodium and pressed it up against some very cold ice. I don't mean like -1c, i mean like -20c or something. I'm actually not sure you could really guess what would happen from fundamentals, without actually trying the experiment... I agree water sublimates into vapor but that is VERY VERY slow at very low temperatures. A single ice cube can take a month or more to sublimate in a freezer, not sure that would be enough to really "set off" the reaction, sodium is only the 2nd alkili metal. Vespine (talk) 02:02, 6 April 2016 (UTC)
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- Interesting question. There must be a some values of the reaction rate. Do a thought experiment: place some ice in vacuum chamber with a clean unoxidised piece of sodium. The ice (on recsiving any heat) will sublimate. That water vapour will create a 'protective' film of hydrate on said lump of element preventing further ingress of water vapour. Decrees vacuum (ingress persure) enough and the the vapour pressure increases and penetrates the protective film. Thus creating heat – which if sufficient, will cause frozen water to change state. At temperatures of boiling helium I doubt anything will happen, perhaps not even at boiling nitrogen because too much heat is being lost to the rest of cryogenic vessel. So, the reaction must depend on temperature and pressure -with a cut off point where nothing happens. --Aspro (talk) 20:25, 6 April 2016 (UTC)
- Interesting aspect suggested about a thin film of the surface of the ice formed by sublimation. I think the problem reduces to the presence or absence of a water layer on the surface of the ice. Can sublimation form such a thin layer?--89.122.39.86 (talk) 08:37, 8 April 2016 (UTC)
- Interesting question. There must be a some values of the reaction rate. Do a thought experiment: place some ice in vacuum chamber with a clean unoxidised piece of sodium. The ice (on recsiving any heat) will sublimate. That water vapour will create a 'protective' film of hydrate on said lump of element preventing further ingress of water vapour. Decrees vacuum (ingress persure) enough and the the vapour pressure increases and penetrates the protective film. Thus creating heat – which if sufficient, will cause frozen water to change state. At temperatures of boiling helium I doubt anything will happen, perhaps not even at boiling nitrogen because too much heat is being lost to the rest of cryogenic vessel. So, the reaction must depend on temperature and pressure -with a cut off point where nothing happens. --Aspro (talk) 20:25, 6 April 2016 (UTC)
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April 6
That automatic camera timer
I don't know what it's called. You set it for 10 seconds and run back into the frame to be in the shot.
Is there a camera that does that but then keeps taking pictures every 5 seconds or so for a while?
Anna Frodesiak (talk) 03:08, 6 April 2016 (UTC)
- Self timer. Now with digital cameras, I can't imagine any type of time-delay or timing pattern of multiple images can't be accomplished. But I'm not familiar with commercial cameras in general, so I have no idea what's available (vs what could be programmed on a smartphone or other custom device). DMacks (talk) 03:17, 6 April 2016 (UTC)
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- Hi DMacks! Thanks for the feedback. But now I am totally confused. :) I don't know the difference between a digital camera, a commercial camera, and a custom device. As for "accomplished", I think it either has the setting or not. Cheers. :) Anna Frodesiak (talk) 03:31, 6 April 2016 (UTC)
- I read "a camera" to mean a preconstructed object whose primary purpose was to take still protographs (the thing we called a "camera" that used to have a roll or disc of film but more recently instead uses digital processing...not "the camera feature now seemingly present in every portable device, phone, and computer). A digital camera has a lot of on-board embedded processing available, more than just the mechanics of a button connected to a shutter. Once you have electronic control and don't need to do anything physical internally to "take a picture", you can have an electronic controller fire the "take a picture" electronic actions any time using some circuit. The old cameras had a fixed 10-second timer, but with a pure electrical system, one can have any one-time or repeated timing pattern one likes by using some custom-designed circuit or bit of software programming. So "it can be done". But I don't know of "a camera" that actually does it. But using a more general piece of hardware that happens to be able to take photographs, (for example, "a phone that has a camera in it"), it's easy to write a program that uses that camera function (again, on any arbitrary schedule). It's easier on "a smartphone with a camera" than with "a camera object" because the actual programming interface is available (anyone can write an app), instead of only having the few buttons and built-in software or interfaces that a camera-object's manufacturer decides to make available. As others have noted below, there actually are camera-objects that have this feature already and/or make the interfaces available for third-party controllers. DMacks (talk) 04:55, 6 April 2016 (UTC)
- Hi DMacks! Thanks for the feedback. But now I am totally confused. :) I don't know the difference between a digital camera, a commercial camera, and a custom device. As for "accomplished", I think it either has the setting or not. Cheers. :) Anna Frodesiak (talk) 03:31, 6 April 2016 (UTC)
- intervalometer is the device that you are looking for.
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- Not quite what you are after but some Canon DSLR cameras have wifi (I have a 6D) and you can get an iphone app which lets you use your phone to remotely trigger the shutter. It's really awesome, you can even see the camera's viewfinder on your phone and change the settings. The only thing you really have to do at the camera is "frame" the shot (you can't "move" the camera with the phone), then you can do the rest with your phone. When I want to take a group shot, I just hold my phone behind my back, or behind someone/something else and trigger the shutter a bunch of times. Vespine (talk) 04:02, 6 April 2016 (UTC)
- Also, any of the "more expensive" remote shutter trigger probably has the options you need, for example this canon remote control does everything you've asked, from a different site the unit's features include a self-timer, long-exposure timer, interval timer and the option to set the number of shots in a sequence. . Vespine (talk) 04:06, 6 April 2016 (UTC)
- Not quite what you are after but some Canon DSLR cameras have wifi (I have a 6D) and you can get an iphone app which lets you use your phone to remotely trigger the shutter. It's really awesome, you can even see the camera's viewfinder on your phone and change the settings. The only thing you really have to do at the camera is "frame" the shot (you can't "move" the camera with the phone), then you can do the rest with your phone. When I want to take a group shot, I just hold my phone behind my back, or behind someone/something else and trigger the shutter a bunch of times. Vespine (talk) 04:02, 6 April 2016 (UTC)
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Holy moly. I seem to always ask questions that draw very complicated answers. I just noticed that all cameras seem to have a self timer that takes just one shot and then you have to walk up to it and set it again. A bit silly, if you ask me. Multiple shot capability should be standard on all cameras. I imagine it would be very well received and quite a selling point. And I-phones don't seem to have any self timer at all. Thank you all kindly for the thoughtful replies. I am sorry to ask such questions. Anna Frodesiak (talk) 06:33, 6 April 2016 (UTC)
- Most digital cameras also have an option to record video, although often at reduced resolution, but that might work in some cases. Of course, the first few seconds will be you starting it and running back to the group to be photographed, and the last few seconds will be the reverse, but you can edit that out later. You can also pull stills out of the video later. StuRat (talk) 06:57, 6 April 2016 (UTC)
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- Thanks, StuRat. I guess that would be sort of okay. Now, if your camera could do multiple timed images, say, every 5 seconds, wouldn't that be useful and fun? And wouldn't you get lots of great photos out of it? :) Anna Frodesiak (talk) 07:02, 6 April 2016 (UTC)
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- The problem with that is that you would need to hold your pose for a long time, not blinking, etc. They would need to add some type of audio or visual cue to tell people when the next frame will be taken, in order to avoid that issue. The remote trigger also solves that problem. StuRat (talk) 07:05, 6 April 2016 (UTC)
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- Why hold the pose? Everyone would have 5 seconds to get it together and then the little light or beep would go and zam, another photo. I think it would be bags of fun and produce a choice of 5 or 10 great pics. So, if they had it, would you use it? Anna Frodesiak (talk) 07:11, 6 April 2016 (UTC)
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- No, it would be too restrictive for me. Every 5 seconds we would have to get into a good pose, be careful not to blink, etc. More likely most of the shots would be bad because somebody would be moving, not looking at the camera, have their eyes shut, be talking, etc. Of course, there is such a thing as "candids", where you take pictures without posing. But those tend to generate a large volume of pics with only a few being worth keeping. StuRat (talk) 07:32, 6 April 2016 (UTC)
- StuRat, I think you would love it. Maybe every ten seconds with a light just before. After several photos everyone would start to crack up and the photos would get really good. Anna Frodesiak (talk) 08:02, 6 April 2016 (UTC)
- No, it would be too restrictive for me. Every 5 seconds we would have to get into a good pose, be careful not to blink, etc. More likely most of the shots would be bad because somebody would be moving, not looking at the camera, have their eyes shut, be talking, etc. Of course, there is such a thing as "candids", where you take pictures without posing. But those tend to generate a large volume of pics with only a few being worth keeping. StuRat (talk) 07:32, 6 April 2016 (UTC)
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- Note that professional photographers photographing subjects like models used to have a setting that would take a pic, say, every second. They held onto the camera while using this setting, though. As I mentioned above, this did generate a large volume of pics, and only a few were "keepers". StuRat (talk) 07:36, 6 April 2016 (UTC)
- If your camera does support taking photos at sufficient intervals (at 5 seconds apart or whatever) and of sufficient quantity, then you could just start taking photos and delete the ones at the beginning. The only issue would be that there may not be any indicator before each photo. Nil Einne (talk) 07:40, 6 April 2016 (UTC)
- Every second, sure. But that's that "...work with me baby, come on, feel it..." type of thing. So, sure there would be hundreds with a few keepers.
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- That whole idea of setting the camera to 10 seconds and rushing in front to join the others for a single snap seems very old fashioned. Surely an option string of 10 photos with 10 seconds between would be an improvement. Anna Frodesiak (talk) 08:02, 6 April 2016 (UTC)
- I'm fairly sure there's quite a few cameras which do allow setting the interval. After all, it's used for time lapse photography although 5 seconds is a bit short for most time lapse. Anyway in terms of your later point AFAIK the most common option nowadays is that the camera will take a burst of several photos after the timer with the possible ability to set the number of photos but not an interval (it's intended to be a burst not time lapse) with the hope that one of them will be good despite people blinking etc. If this doesn't work it'll probably be possible to combine different photos so it's also useful in that way. I think your specific option is less common because if you're going to take a seperate shot most people would prefer to set it up first. Nil Einne (talk) 08:42, 6 April 2016 (UTC)
- Okay, that makes sense. But set it up first and someone has their eyes closed and you have to run back and set the timer again. That is what this was all about. Also, that smartphone burst thing seems to make too many photos. Many thanks for answering yet another annoying Anna question. :) Anna Frodesiak (talk) 08:47, 6 April 2016 (UTC)
- I'm fairly sure there's quite a few cameras which do allow setting the interval. After all, it's used for time lapse photography although 5 seconds is a bit short for most time lapse. Anyway in terms of your later point AFAIK the most common option nowadays is that the camera will take a burst of several photos after the timer with the possible ability to set the number of photos but not an interval (it's intended to be a burst not time lapse) with the hope that one of them will be good despite people blinking etc. If this doesn't work it'll probably be possible to combine different photos so it's also useful in that way. I think your specific option is less common because if you're going to take a seperate shot most people would prefer to set it up first. Nil Einne (talk) 08:42, 6 April 2016 (UTC)
- That whole idea of setting the camera to 10 seconds and rushing in front to join the others for a single snap seems very old fashioned. Surely an option string of 10 photos with 10 seconds between would be an improvement. Anna Frodesiak (talk) 08:02, 6 April 2016 (UTC)
Aside: I'm typing and suddenl "y" is a "z" and my full colon is an "E" with two dots on top. Why? I'm typing this in a notepad and pasting it here. Help! :) Anna Frodesiak (talk) 07:48, 6 April 2016 (UTC)
- Never mind. Someone in IRC helped me with that. Anna Frodesiak (talk) 08:00, 6 April 2016 (UTC)
- The OP did not state which model of camera they have. CHDK concentrates mainly on Cannon but other brands are being worked upon. It give you full control over the cameras firmware. It included setting time lapse and multiple images. It will even calculate the hypo-focal distance like professionals do, to give a better focused group shot. Warning. It requires one knowing how to switch on a computer, down-load, instal a program and to own a digital camera.--Aspro (talk) 12:08, 6 April 2016 (UTC)
- This Youtube clip describes how to down load, instal and select time laps for whatever intervals you so desire. Canon CHDK Hack Tutorial: RAW, HDR, and Time Lapse Does a lot else as well. Keep it on a spare SD memory card until one gets used to all the options. No sensible Canon camera would want its owner to not to have one.--Aspro (talk) 12:51, 6 April 2016 (UTC)
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- Other models are available! I have a digital Pentax (medium price range - not a professional model). I can adjust the settings of the timer such that the shutter can remain open for as long as I want. I can set it to do this multiple times, with each exposure made after an interval which I also set. So, I can set the camera to open the shutter for 20 secs, every 1-minute, and continue to do this for 3 hours. This is how we get those wonderful pictures of stars appearing to circle in the sky called Star trails. DrChrissy (talk) 13:46, 6 April 2016 (UTC)
- @Anna Frodesiak: The answer is you can set the timer on a 2 to 10 second interval on a modern DSL camera like e.g. Canon 1200D.--TMCk (talk) 14:36, 6 April 2016 (UTC)
Thank you thank you thank you! This is exactly what I'm after. I've been using this horrid Sony Cyber-shot DSC-T700 and am trying to persuade family to let me get a better one. Every time there is a timer group photo, I have to run back after each shot and set it again because someone had to be a joker. This interval thing would be poifect! I will look into the cameras you've suggested. Many, many thanks, DrChrissy, TMCk, and everyone else too!! P.S. Lovely Star trails! Anna Frodesiak (talk) 23:09, 6 April 2016 (UTC)
- Anna, I did not mention that my camera also has a remote control device. So, I can put the camera on a table/tripod, focus and frame it on my friends, then turn on the remote control function on the camera. I can then rejoin the group, pose, then press the button on the remote control device and it takes our group photo. I can do this for as long as I want without having to return to the camera. I can also set a delay (e.g 2 secs) so that I have time to hide the remote control in my hand or behind my back - otherwise all the photos have me pointing a small plastic device at the camera! Happy snapping. DrChrissy (talk) 23:17, 6 April 2016 (UTC)
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- Yeah, this kind of thing is pretty standard on higher-end cameras. I have an almost decade-old Canon that has "continuous shot" and remote control. The tl;dr answer to the original question is that you need to look at professional or "enthusiast" cameras, not the cheap low-end ones. --71.110.8.102 (talk) 19:29, 7 April 2016 (UTC)
- I'm glad to hear it's standard on some cameras and hope it becomes standard on all. After all, it's programming, so no extra cost really, therefore no real reason to omit the feature from cheapos. Thank you for the feedback. Anna Frodesiak (talk) 21:35, 7 April 2016 (UTC)
- Hi DrChrissy. A remote control, yes. I had one of those on a Sony Handicam. I still think auto-timer offering 5 shots at intervals would be liked by customers. Cheers. Anna Frodesiak (talk) 21:35, 7 April 2016 (UTC)
- Yeah, this kind of thing is pretty standard on higher-end cameras. I have an almost decade-old Canon that has "continuous shot" and remote control. The tl;dr answer to the original question is that you need to look at professional or "enthusiast" cameras, not the cheap low-end ones. --71.110.8.102 (talk) 19:29, 7 April 2016 (UTC)
- Happy to help. BTW, if you want to check a camera's more detailed features (like the timer modes), check the model specific user manual online ;) --TMCk (talk) 00:08, 7 April 2016 (UTC)
- Good suggestion, TMCk. Thank you. I will try. I doubt they will have an advanced search feature to allow me to find models with that. I will probably end up going through camera descriptions one by one. Anna Frodesiak (talk) 21:35, 7 April 2016 (UTC)
Harvest energy of downwards escalator
I'm getting very interested in escalators (because I currently spend about a quarter of an hour a day on escalators in the Kyiv metro system). [I was amazed to learn from the escalator article that the term to 'escalate', as in wars etc., comes from the machine.]
The article mentions that most escalators use AC motors. I wonder if a downward escalator could be so crowded - say with two people on every step - that their weight exceeded the friction and the escalator would have to be braked or governed? And if this were the case, would it be efficient to couple its mechanism to the upward escalator?
Hayttom (talk) 12:48, 6 April 2016 (UTC)
- Hey, Haytttom, interesting question! It seems the answer is "yes, some escalators use something akin to regenerative braking." Here [14] is a scholarly article on energy efficiency in escalators (and elevators), and mentions regenerative braking in a few places, as well as things like optimizing counterweight. They claim that highly efficient escalators (and elevators) can use 80% less than their old-fashioned un-optimized counterparts. This paper is more about metro systems as a whole [15], but does have some interesting stuff about how escalators fit in to the big picture. Finally the E4 project [16] has a mission of studying and improving efficiency in lifts and escalators, though their web presence is a bit thin. SemanticMantis (talk) 14:12, 6 April 2016 (UTC)
- I've never felt the need for downward escalators to begin with, as I only get tired walking up stairs, not down. But, I understand that architects like the symmetric look of one up and one down escalator. I always thought the down escalator could work without a motor, just using the weight of the passengers and a mechanism like a thick fluid to limit the speed. This would mean it would stop when nobody was on it, and small people might not be heavy enough to overcome friction and move it, but then they could just walk down. Can anyone put some numbers on this, and let us know what kind of frictional forces we must overcome ? StuRat (talk) 16:09, 6 April 2016 (UTC)
- I can't see any easy way to use a counterweight on an escalator. I'd have thought it should be possible to link an up escalator with a down escalator and so only have to cope with the difference in weight between people going up and down. I guess regenerative braking is easier though. Dmcq (talk) 17:37, 6 April 2016 (UTC)
- Sorry, my mistake. I've added "and elevators" to my post to clarify that I (and the article I linked) was talking about both. SemanticMantis (talk) 18:35, 6 April 2016 (UTC)
Water ballast cable cars (→de:Wasserballastbahn) operate similar to Your idea and have less friction per passengers than current escallators. The Steffturbine has a high efficiency and might fit it when using people instead of water. Elevators use a counterweight. The oversized alnd filled counterweight makes the passive system of a water ballast cable car operate. --Hans Haase (有问题吗) 08:31, 7 April 2016 (UTC)
Wind and solar power
Can wind and solar power combined ever match the power output of current fossil fuels such as oil and natural gas, to power large cities such as Los Angeles or London?--WaltCip (talk) 13:59, 6 April 2016 (UTC)
- Read Renewable energy in Germany and see if it leads you to any conclusions. --Jayron32 14:34, 6 April 2016 (UTC)
- Renewable energy in Denmark also has some interesting data. --Jayron32 14:35, 6 April 2016 (UTC)
- This is excellent reading. Thanks.--WaltCip (talk) 14:42, 6 April 2016 (UTC)
- There is far more solar energy available than would be needed to power our cities. In some areas, there is also sufficient potential wind power. To fully replace fossil fuels, these technologies would need to be combined with some form of large-scale energy storage technology to provide power at times when the sun doesn't shine and wind doesn't blow. There is no reason humanity couldn't go 100% solar and wind, but right now it would cost more than fossil fuels which is often the limiting factor unless adoption is driven by government mandates or incentives. Solar cells are getting cheaper, but still cost more than fossil fuels in most cases. Wind turbines can be cost competitive with fossil fuels in areas with consistent strong winds but less so in areas with intermittent or weak winds. Large scale energy storage is also still pretty expensive in most areas but can be done. Dragons flight (talk) 14:54, 6 April 2016 (UTC)
- This site has an interesting map of the land area required using solar alone (not counting wind, hydro, geothermal). Rmhermen (talk) 15:18, 6 April 2016 (UTC)
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- The trouble with the "X costs more than Y" argument is that we very often fail to include all of the costs. It's quite possible that the cost to construct a coal power station and to mine the coal to fuel it for (say) 50 years will be less than to construct and operate a wind power plant with the same capacity over the same period. But if you include a fair share of the cost of shoring up ocean wall defenses due to sea level rise due to the coal plant's excessive CO2 output - then the economic argument gets shakier. But how should we price the loss of the polar bears - or the impact of all of the ash mounds left by the coal plant - or the loss of human life due to the dangers of coal mine accidents? So economic arguments only get you so far. However, there is great difficulty with using this extended economic argument as consequence of the way human societies have formed. If (say) mainland China doesn't have much issue with coastal flooding, then it feels a lower price for coal power plants than an island nation like Indonesia - where sea level rise is a critical factor in their survival. But each country makes the decision on how to price and regulate coal power plants, even though the global climate is something that we all share.
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- Energy storage is certainly a big issue with many kinds of renewable sources - but those costs can be mitigated by beefing up our energy transmission capabilities. Sure, the amount of wind available in one particular area may be intermittent and somewhat random - but the average amount of wind available over an entire country, or an entire continent, should be much more predictable. So if you can efficiently move energy around, you can average over space instead of using storage systems and averaging over time. Averaging over domains (solar/wind/tidal/geothermal) gets you an even more predictable output.
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- SteveBaker (talk) 15:24, 6 April 2016 (UTC)
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- Not to derail the topic, but it bothers me that China is able to get away with a lot of environmental catastrophes (the smog and traffic in Beijing are rated as among the worst in the world) and not be held accountable for them the same way other developed nations are.--WaltCip (talk) 15:50, 6 April 2016 (UTC)
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- They are still considered a "developing" nation, but the pollution is becoming a concern to them, too, at least the obvious pollution, like smog. London and New York City had their periods of horrible pollution, too. It's a variation on tombstone mentality, where they weren't willing to do anything about pollution until it affected them personally. StuRat (talk) 16:17, 6 April 2016 (UTC)
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- At ~$8,000 per capita, the GDP of China is still below the world average (~$10,000) and far below the traditional developed countries (US, Europe, etc.; $30k-50k). In terms of pollution, China situation's today is reminiscent of the US situation in the 1960s when after a long industrial expansion pollution had become widespread and a populist political backlash was starting to drive reforms. If they follow the American example, we might expect to see dramatic improvements in China's environmental situation over the next 10-20 years. For example, the US cut regulated particulate emissions in half during the first decade after the passage of the 1970 Clean Air Act. Dragons flight (talk) 19:10, 6 April 2016 (UTC)
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- If you're just talking about haze or air pollution in cities, it's sort of weird to single out China as is often done. Sure China is terrible, but most data shows Indian cities tend to be worse on average e.g. [17] [18] although it's obviously difficult to make comparisons given the varying ways measurements are done, data is made available etc [19]. Still at a minimum what data there is suggest there's no reason to think of the situation in Chinese cities as some sort of extreme barometer, at a minimum both Chinese and Indian cities should be considered and possibly others [20]. (Of course air pollution in cities can depend not just on pollutants but weather the Asian brown cloud article sort of touches on that and while local pollution is generally a factor, as the Southeast Asian haze has shown so to can pollution from neighbours.)
In terms of overall environmental issues, to give an example India is worse than China in the Environmental Performance Index [21]. Economically China is obviously at a far greater level of development which shows in things like the higher levels of GHG (although still far less per capita than places like the US, UK, Australia and NZ), however with Modi's make in India and other campaigns there's fair concern what this means for the future and whether India will deal with it better or worse than China [22] [23] [24].
As the other commentators have touched on and my comment did as well to some extent, a key factor the fact is that China or India both of which are still developing nations by most definitions, are at a significant different level of development from whatever developed countries you're thinking of. Most of the developed countries did similar things or worse (albeit since they are smaller often on a smaller scale) at some stage of their development.
The "learn from us" mantra is all fine and well, but it doesn't necessarily resonate with government or citizenry when it's likely to mean a significantly less or slower development and as plenty of examples have shown it's not like developed countries are particularly willing to pay to protect the environment during other countries development (and for large countries like India or China, they probably couldn't really afford to make that big a dent anyway).
Or to put it a different way, hold to account at what stage? While there are some grumblings about historic issues, there isn't really much of a serious suggestion to hold developed countries to account for their historic environmental issues (except perhaps from their own citizens). In a number of ways, particularly in regards to deforestation and GHG emissions, developing countries now are actually normally facing more strigent expectations than the developed countries faced during their development.
- If you're just talking about haze or air pollution in cities, it's sort of weird to single out China as is often done. Sure China is terrible, but most data shows Indian cities tend to be worse on average e.g. [17] [18] although it's obviously difficult to make comparisons given the varying ways measurements are done, data is made available etc [19]. Still at a minimum what data there is suggest there's no reason to think of the situation in Chinese cities as some sort of extreme barometer, at a minimum both Chinese and Indian cities should be considered and possibly others [20]. (Of course air pollution in cities can depend not just on pollutants but weather the Asian brown cloud article sort of touches on that and while local pollution is generally a factor, as the Southeast Asian haze has shown so to can pollution from neighbours.)
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- The news reports that India is much worse than China are basically based on a lack of information. As of 2015, China only provided WHO with PM10 data and only for select cities as of 2010. Since 2013, China has been monitoring more cities and collecting the more health-relevant PM2.5 data but those figures have not yet found their way to the WHO. If one looks at the PM2.5 data, China and India are much more similar. China should actually occupy about half the slots on the top-25 most polluted cites, and go as high as #4 on the list. WHO is expected to release an updated list later this year. China and India are both major problems, though for different reasons. China's biggest problem is coal, whereas India has a huge biomass burning problem. Dragons flight (talk) 14:07, 7 April 2016 (UTC)
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- Regarding including all the costs. This is known as life-cycle assessment and is related to Whole-life cost and impact assessment. Specifically addressing these ideas with respect sustainability issues, here [25] is a nice overview of life cycle analysis from the Illinois Sustainable Technology Center. SemanticMantis (talk) 18:19, 6 April 2016 (UTC)
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- There is no good or efficient manner to store large quantities of energy...and the ability to do so isn't on the horizon...so when wind doesn't blow or sun doesn't shine...this is actually a major problem for wind and solar..68.48.241.158 (talk) 18:36, 6 April 2016 (UTC)
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- Walt, it's not a method of creating energy, just of storing energy from some other source. For example, solar panels that create too much electricity when the Sun is up and none at night. During the day, the excess would be used to pump water to the high reservoir, while at night the water falling from that height would power turbines, like in conventional hydroelectric power plants/dams. StuRat (talk) 01:01, 7 April 2016 (UTC)
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- It costs energy, but that doesn't negate the utility of the idea. Nothing is free, and especially not energy storage. The costs are often worth it. Pumped-storage_hydroelectricity is our article that StuRat should have linked if he's going to bother talking about this stuff on the reference desk. I know that we have an article on that and how to find that article but not everyone does, so it's just common courtesy to provide wikilinks if we want to actually help people at the reference desk. Okinawa_Yanbaru_Seawater_Pumped_Storage_Power_Station is a good example of pumped-water energy storage, and there are even schemes to store energy by pushing rail cars full of gravel up hills [26] [27]. Energy storage and List_of_energy_storage_projects are also highly relevant to this thread. SemanticMantis (talk) 19:09, 6 April 2016 (UTC)
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- (edit conflict) In practice, usually 70-75% efficient round-trip. So everything else being equal pumped-hydro will probably make the electricity at least ~35% more expensive. However, since the wholesale cost of electricity often already varies by more than 100% due to time-of-day load variations, this is probably acceptable. The biggest limitation of pumped hydro storage is that it is only easy to implement in areas with existing reservoirs or where the terrain makes new reservoirs relatively easy to construct. Other technologies, e.g. NaS batteries, compressed air, flywheel energy storage, etc., will probably make more sense in terrains that don't readily support pumped hydro. These things are entirely possible if one is willing to pay the associated costs. Dragons flight (talk) 19:10, 6 April 2016 (UTC)
- There's been some discussion about electric cars as a form of distributed storage. The cars get charged up at night when there tends to be a surplus of generating capacity -- sometimes utilities literally give away nighttime electricity to maintain their base generation load. Then the cars are driven during the daytime. Shock Brigade Harvester Boris (talk) 00:45, 7 April 2016 (UTC)
- (edit conflict) In practice, usually 70-75% efficient round-trip. So everything else being equal pumped-hydro will probably make the electricity at least ~35% more expensive. However, since the wholesale cost of electricity often already varies by more than 100% due to time-of-day load variations, this is probably acceptable. The biggest limitation of pumped hydro storage is that it is only easy to implement in areas with existing reservoirs or where the terrain makes new reservoirs relatively easy to construct. Other technologies, e.g. NaS batteries, compressed air, flywheel energy storage, etc., will probably make more sense in terrains that don't readily support pumped hydro. These things are entirely possible if one is willing to pay the associated costs. Dragons flight (talk) 19:10, 6 April 2016 (UTC)
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- I strongly recommend reading, and understanding, the ebook/website linked to from here. Basic conclusion is that for the UK you need nukes if you are trying to actually reduce CO2 output. In my opinion Renewables are useful without extra storage up until X % contribution to generating capacity, X is certainly not a simple number to calculate, 20 might be a place to start, to be generous. The problem with storage is all the good hydro sites have gone, and nothing else is cost effective at current base load prices. Greglocock (talk) 18:45, 6 April 2016 (UTC)
- if you're not afraid of nuclear power generation than "renewables" are a complete and utter waste of time, money, and effort....but perhaps nuclear power is indeed something to be afraid of....(if your receiving govt subsidies to run your solar panel business, than "renewables" are wonderful)...68.48.241.158 (talk) 21:05, 6 April 2016 (UTC)
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- No nuclear power station has ever been economically viable without massive public subsidies, including limits to the liability of owners for accidents and radioactive waste. And even assuming that nuclear power can be made "safe" in the first world (although Fukushima is not a good sign), it does not scale out. Who wants nuclear power plants in Nigeria, Libya, Iran or Somalia? --Stephan Schulz (talk) 21:23, 6 April 2016 (UTC)
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- the political/regulatory cost have made them economically difficult at least in USA...but in and of themselves there's nothing that even comes close...a single plant can power half a million home, night/day/wind/no wind....there's nothing that comes close....renewables aren't even in the conversation, particularly since you can't count on them at any given time....68.48.241.158 (talk) 21:31, 6 April 2016 (UTC)
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- Solar power towers using molten salts, heat up more than needed. So there's capacity to drive turbines over night. Using the kalina cycle, can make even more efficient. --Hans Haase (有问题吗) 07:56, 7 April 2016 (UTC)
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- I think StS has touched on two key points. Particularly when I lived in Malaysia I was often somewhat favourable to Indonesia or other such countries when it came to complaints on environmental or other such issues from people from developed countries (generally the West). But I don't think there was ever a point of time when I was favourable to Nuclear power in Indonesia and I don't think this attitude is uncommon among Malaysians or other regional neighbours. (The other environmental issue which annoys most would be the Southeast Asian haze, although companies from neighbours like Malaysia are probably a contributing factor to the issues in Indonesia.) In fact, I'm not really sure if I ever even trusted Malaysia to use nuclear power, and I definitely don't now. Nil Einne (talk) 13:48, 7 April 2016 (UTC)
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Does kosher/halal beef taste different due to drainage of blood?
An older person I know has been having a lot of trouble appreciating steak and other meat lately. She keeps complaining it all has a "liver" flavor. From a master's thesis I found on the topic [28] there is some indication that hemoglobin level in the meat matters, as it is a source of free iron that causes degradation while cooking (cooking temperature is also a factor, and various other things). It cites this for that, which I haven't accessed in full, that talks about liver flavors being a combination of metallic and fishy taste; I suppose the source must have some discussion.
Anyway, I just want to back up, go in the front door here and ask: are people aware of any evidence that kosher/halal meat, from which blood is drained as thoroughly as possible, has a different flavor of any kind from other meat? Of course, searching online finds people who say yes - in the past I had assumed this was boosterism, and a double-blind test with a sufficient sample size wouldn't find people able to tell. But finding real data is tricky on this.
FWIW, I already suggested she might try it and see - it can't hurt, unless you happen to be a cow. :) But I am just wondering if there's any science on it. Wnt (talk) 14:01, 6 April 2016 (UTC)
- I'm guessing you searched google scholar for longer than the 4 minutes I did? I didn't find any proper controlled experiments either. I did find one potential lead though: I would try to contact these folks [29] at the Halal Products Research Institute. Seems they do perform/fund real science published in good journals. If anyone knows about the existence of the studies you're looking for, I bet they do. SemanticMantis (talk) 14:18, 6 April 2016 (UTC)
- And to approach from another tack: what about cortisol? Here [30] is an article from The Atlantic discussing how animals with higher cortisol levels and less humane treatment might taste worse, and here [31] is a scientific article talking about Malaysian Halal standards [32], including maximum cortisol levels. Still no good studies on taste, but I think cortisol must be a conceptually viable route to different taste in halal/kosher meats. SemanticMantis (talk) 14:25, 6 April 2016 (UTC)
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- We have an article on the PSE meat referenced. But it's a good search term - with it I found [33] which makes all kinds of totally unexpected statements about kosher meat. Their results are that the loss of blood is actually not any larger in kosher meat. But they find the meat loses less water, is tenderer, is a different color than the conventional meat. So kosher treatment seems to make much more difference than I'd imagined, even while not having the effect I expected. Wnt (talk) 14:55, 6 April 2016 (UTC)
- Before considering the possibly different flavour of the meat, you might consider the effect of age on the human sense of taste. My mother has been complaining for a long time that the food doesn't taste as good now as it used to. To me it all seems fine - and I think the fact of her being 100 may be significant. 217.44.50.87 (talk) 15:44, 6 April 2016 (UTC)
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- Do you have a source that confirms how growth rate of foodstuffs affects flavor and nutrition? 91.155.193.199 (talk) 00:44, 7 April 2016 (UTC)
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- Here you go: [34]. The book referred to at that link is The Dorito Effect: The Surprising New Truth about Food and Flavor. StuRat (talk) 04:29, 7 April 2016 (UTC)
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- Conventional livestock slaughter is usually a 2-stage procedure. The animal is first rendered unconscious by, e.g. a stun gun. The animal is then immediately killed, usually by exsanguination. My thought here is that the removal of blood is likely to be very similar to the kosher and halal methods, and therefore unlikely to have any influence on taste. To WNT, people of the Jewish faith do not eat pork, so there is no such thing as kosher pork and PSE is therefore not an issue - I think. DrChrissy (talk) 15:47, 6 April 2016 (UTC)
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- The first line of that article says "beef and poultry" also. But I think it's not technically an issue for another reason, which is that they say it's only 3% of meat, or anyway, not more than 10. Nonetheless, the "exudative" is reminiscent of the differences in water loss during cooking in the study I cited above, so it might be the extreme case of a broader phenomenon. (but I don't know that) Wnt (talk) 17:25, 6 April 2016 (UTC)
- Suggestion: If she doesn't care for the taste of meat any more, and we know meat is unhealthy anyway, maybe it's time to explore more vegetarian options. Might keep her alive and healthy longer, too. Or she can avoid red meat and stick with things like fish and chicken, if she still likes those flavors. StuRat (talk) 17:38, 6 April 2016 (UTC)
- Ah a question about food, one of my most favourite topics. Yes your taste buds may be getting less sensitive but I think your asking about why the meat itself doesn’t taste like it used to. The whole reason for bleeding meat, was it kept longer (and did not develop those off flavours) before the days of refrigeration. It was also hung for 4 or more days for rigour-mortis to pass. These days the cow walks in to the abattoir one morning and is vacuum packed by lunch time. The vacuum packed meat today is not bled and undergoes what is euphemistically referred to a 'wet curing' because it is more profitable for the food (?) industry. Find a family butcher that can supply properly hung meat (or order it over the internet). Ask for 'Dry Cured Aged' meat. If they can't supply AGED then dry cure yourself in the fridge. The link give some directions: How to Dry-Age Beef at Home Finally, always roast at a very low temperature (like Grandma used to do). The British award wining chef Heston Blumenthal gives guidance on the best temperatures and cooking times for most common cuts but you will have to google it. --Aspro (talk) 21:22, 6 April 2016 (UTC)
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- Thorough and cooking temperatures are two different things. Its like the pasteurisation of milk. 161°F (71.7°C) for 15 sec or 145°F (62.8°C) for 30 minutes. A proper low temperature meat roast takes 4 to 5 hours to bring out the full flavour (for some meats like fowl it need to be higher -so check). Otherwise we would not be here today, because our grandmother would have poisoned everyone. --Aspro (talk) 21:53, 6 April 2016 (UTC)
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- Yes e.g. beef is safe at 145°F internal temperature [35]. You could in principle get it there by setting your oven to 146°F, which would indeed be a very low cooking temperature (this is not recommended as a cooking technique, but it illustrates the point). We also have a whole article on Low-temperature_cooking. But none of this is really relevant to the OP's question, it is rather relevant to Stu's shoot-from-the-hip comments on topics with which he is unfamiliar. SemanticMantis (talk) 21:59, 6 April 2016 (UTC)
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- I would (have) gone lower for beef to 122 °F. Of cause this is assuming one uses a meat thermometer and calibrate it – (dip in boiling water and add a few degs for safety). Some ovens are better than others, so don't rely on you ovens temperature gauge.. Think this is New River Restruant's philosphy as well. And they give cooking times and show photographs of the results. --Aspro (talk) 22:33, 6 April 2016 (UTC)
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- Well your "warning" was useless because you gave no refs and not even any numbers! You asserted that cooking at low temps is unsafe. That is patently false. Millions of people cook at low temps safely every day. It is true that there is some relation between temperature and food safety of meat. It is true that some temperatures are considered too low by safety authorities. It is true that all this can be clarified with a simple reference, which you could have given if you spent
306 seconds googling (I timed it) instead of typing your first vague and unclear reaction. 14:50, 7 April 2016 (UTC)
- Well your "warning" was useless because you gave no refs and not even any numbers! You asserted that cooking at low temps is unsafe. That is patently false. Millions of people cook at low temps safely every day. It is true that there is some relation between temperature and food safety of meat. It is true that some temperatures are considered too low by safety authorities. It is true that all this can be clarified with a simple reference, which you could have given if you spent
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- Don't think SM signed his last comment above. Anyway
StewStu, page 4 does not give the cooking times. Also, the Serving Temperature refers to the recommended safe Serving Temperature (is that tautological ?). In restaurants and buffets, the food is already cooked but often displayed for 'long periods' in areas where cold air currents can cool some it down to levels were bacteria can multiply very fast. I am not denying the fact that, given the right conditions they exhibit exponential growth. So 'cooked' food 'on display' needs to be kept at higher temperatures. As an example from the other end: Consider the fridges in commercial restaurants – modern hygiene standards require them to be 'fan assisted' because in a busy restaurant the doors are constantly being opened and shut – much like an oven door. They need fans to quickly bring the temp back down in a way that is not considered necessary for domestic fridges. So for commercial offerings where the food is not to be consumed immediately (within approx 15 mins) – other hygiene guidelines apply. So, for those reasons, page four is not a valid reference to 'safe cooking' temperatures.--Aspro (talk) 16:38, 7 April 2016 (UTC)
- Don't think SM signed his last comment above. Anyway
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- It appears to be a reliable source (the USDA). As stated "Cook foods to the recommended safe minimum internal temperatures listed below", and 145°F was the min listed for beef roast. Your suggestion to cook at 122°F is never going to get the interior temperature above 122°F (do you need a source to prove this, too ?). And the fact that food can be unsafe in other ways in no ways cancels my point that cooking at 122°F is unsafe.
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- And my stating that there is some temperature too low to cook food safely didn't need a ref precisely because I didn't assign a number to it. A specific number would require a source, but the general statement is so patently obvious that it does not. Meanwhile, you ignored the ref provided and instead gave dangerous food prep advice that you would have known not to give had you found a ref, or at least read the ref provided by SM. StuRat (talk) 17:06, 7 April 2016 (UTC)
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- Yes. I did read though SemanticMantis's reference and took delight from it. But going back to the OP's question. I was pointing out that if he wants to rediscover the full flavour of yesteryear, then try s-l-o-w roasting -which takes time and so kills the bacteria in the process. I also made the comparison with the different times for full pasteurizing milk vis temperature. The need for a calibrated meat thermometer. Guidelines are advised (not set in concrete) for the common Joe (or more probably Jane). I also made reference to Heston Blumenthal. Did 'you' read that reference? “He advocates scientific understanding in cooking, for which he has been awarded honorary degrees from Reading, Bristol and London universities and made a Fellow of the Royal Society of Chemistry. He is a pioneer of multisensory cooking, foodpairing and flavour encapsulation.” So not exactly a naïve amateur, wouldn't you agree? Here is one of his recipes for slow-roasted rib of beef. It states for 'rare' -cook at 50ºC. Being old fashioned, that means to me 122º F -as I stated above. If you want an even better reference – I can give one of the best of all. I and my forbears thrived on s-l-o-w roasted joints every Sunday, with fruit pie and home-made custard (now commonly called crème brûlée, made without pasteurized eggs – oh shock and horror) for deserts!--Aspro (talk) 18:56, 7 April 2016 (UTC)
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- An honorary degree is of no value in establishing credibility. But, even if I accept him as an expert on food taste, that in no way makes him an expert on food safety. Some people do prefer rare, or even raw, meats, fish, eggs, etc., but those do carry significant health risks, especially for the elderly and otherwise immune-impaired. Restaurant menus in the US state as much (at least here in Michigan they do). StuRat (talk) 03:10, 8 April 2016 (UTC)
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- Pasteurized eggs? DrChrissy (talk) 19:54, 7 April 2016 (UTC)
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- Yes, restaurants now are requested by some health and safety Jobsworths to buy safe, quality assured, pasteurized eggs in cartons. And please no jokes about Cleopatra asking if she wanted her bath of asses milk to be pasteurized – when she only wanted it up to her chin.. I like eating, so I make dam sure that I get invited into the kitchens as often as possible to see what goes on behind the scenes. A lot of restaurants look great, from the clientele point of view, but some, back stage are food-poisoning-outbreaks waiting to happen. There is nothing difficult or underhanded in this approach. A good proprietor is only too happy that you take an interest. His staff like it too – they are getting recognition for once, by someone that appreciates their skills and long hours of toil in a hot sweaty kitchen. If one doesn't ask, one doesn't get to see. It also makes life more interesting and of course, I always have my camera ready. Its a win-win.--Aspro (talk) 21:09, 7 April 2016 (UTC)
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- Well I learn something every day here. Never heard of pasteurised eggs before. Here in the UK, producers are not allowed to even wash eggs in water as it is feared this can can dissolve faecal contaminants through the shell and into the egg contents. Just as a slight aside, here in the UK there seems to be a growing demand for raw milk (i.e. non-pasturised). Sounds like a TB problem waiting to happen and a further excuse for badger hunting. DrChrissy (talk) 21:49, 7 April 2016 (UTC)
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- Yes, restaurants now are requested by some health and safety Jobsworths to buy safe, quality assured, pasteurized eggs in cartons. And please no jokes about Cleopatra asking if she wanted her bath of asses milk to be pasteurized – when she only wanted it up to her chin.. I like eating, so I make dam sure that I get invited into the kitchens as often as possible to see what goes on behind the scenes. A lot of restaurants look great, from the clientele point of view, but some, back stage are food-poisoning-outbreaks waiting to happen. There is nothing difficult or underhanded in this approach. A good proprietor is only too happy that you take an interest. His staff like it too – they are getting recognition for once, by someone that appreciates their skills and long hours of toil in a hot sweaty kitchen. If one doesn't ask, one doesn't get to see. It also makes life more interesting and of course, I always have my camera ready. Its a win-win.--Aspro (talk) 21:09, 7 April 2016 (UTC)
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- As an aside also: Raw milk (which comes in green top bottles) can only come from dairy herds that are currently 100% TB free. The greater risk is from over crowded housing – a breading ground for TB. In Southall, England it has become an epidemic – not because of milk but landlords allowing overcrowding of cheap and squalid accommodation. Many of their tenants come from countries where TB is not treated properly so bring the disease in with them. So it is a profit issue. UK strains of TB can be treated with antibiotics but these new imported strains are more antibiotic resistant, due to some foreign counties not having the health-care services to ensure that the full course of treatment is complied with. In the UK it is the unregulated movement (sale) of cows between farms that enable TB infected cattle to infect other cattle. So coming back to your point. DNA analysis suggests strongly that TB was primarily just a human disease. However, as primitive man advanced (?) and turned to animal husbandry, they passed it onto their cattle. The cattle in-turn passed it on to Broke the badger. So now we know who the Patient Zero's are (i.e., humans) perhaps Brock should really be thinking about culling us.--Aspro (talk) 23:02, 7 April 2016 (UTC)
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Does it make sense to talk about temperature of particles?
Can the concept of heat be applied to photons, electrons, and protons? — Preceding unsigned comment added by Scicurious (talk • contribs) 23:33, 6 April 2016
- Do you mean individual particles, or large collections of them?
- Thermodynamics is a fundamentally statistical discipline. It studies only the random component of the behavior of systems. So it really doesn't usually make much sense to speak of the temperature of an individual particle. But you can certainly speak of the temperature of a "gas" of electrons, or of the photons in an evacuated chamber acting as a black body. --Trovatore (talk) 00:04, 7 April 2016 (UTC)
- Yes, except for photons, would be expressed as velocity (m*v^2 is temperature). As above, it's statistical but also used to calculate collision rates. Example would be an Argon plasma at a certain temperature will have different velocities for electrons and the Argon ion. The different masses means that for the same temperature, the particles have different velocities and different collision rates. A Langmuir probe is a device used to measure that temperature in a plasma. Photons in a vacuum don't change velocites so temperature refers to a black body model. See Color temperature for black body radiators and "Correlated Color Temperature" in that same article for emitters that are not black body radiators. --DHeyward (talk) 04:25, 7 April 2016 (UTC)
- Well, that doesn't work for an individual particle. As I said, it's only the random part that counts. If you have a blast of particles all moving very fast in the same direction, it doesn't make them hot. And so you really can't make a lot of obvious sense out of the notion of the temperature of an individual particle. Maybe if you don't know its energy, but you know it's sampled from a Boltzmann distribution or something, it would make some sort of sense to describe your lack of knowledge in terms of a temperature.
- Moreover, temperature is not simply related to kinetic energy per particle. That only works for monatomic ideal gases. For anything else, it's a lot more complicated. --Trovatore (talk) 05:44, 7 April 2016 (UTC)
- As I said, it's a distribution. Average velocity is a measure of temperature. Collision rates are averages. The fact that it's an average, though, doesn't change the measurement of temperature. Even thermal conductors have an average and distribution. Evaporative cooling is based on average and deviations of individual molecules. Plasma physics are very dependent on average energy. Debye length is about density and temperature, not deviation. Solutions are provided for Boltzman distributions and that is standard theory, but it's not required as it can be solved for any distribution. A blast of particles is not the same as a contained set and in that case both relative velocity distributions and burst energy are relevant especially if they hit a stationary target. I didn't disagree with you, I just provided examples where temperature is used as a metric. Langmuir probe was one such application and it's underlying causes are rather independent of the measurement. You can even apply it to some solid state distributions where junction temperature affects the length of transition. Thermoelectric effect is a solid state version of Debye length and describes average particle energy against a built-in electric field. It's an "average" but no one argues that a thermocouple doesn't measure temperature even though every carrier has a different energy. P/N junctions also have Vbi and the effective mass of "holes" and electrons makes the depletion region length different in equally doped semiconductors. The absolute length of a P/N space charge region is temperature dependent with kT/q as a standard descriptor as a constant that varies only with average temperature.. --DHeyward (talk) 08:03, 7 April 2016 (UTC)
- Also, it's rather intuitive that the distribution is dependent on density and material. Anyone that's been in a 68F office vs. a 68F ocean knows that carrier-transport/collision-rate is much greater in the ocean even if the temperature is the same. --DHeyward (talk) 08:18, 7 April 2016 (UTC)
- Well, average velocity is not a measure of temperature if there's only one particle. Not in general, really, either, but that's a different discussion. It's not clear to me whether the original question was talking about gasses of particles, which can clearly have temperatures, or individual particles, which really can't. --Trovatore (talk) 17:35, 7 April 2016 (UTC)
- For a slightly different take on the temperature of a particle, see Neutron temperature. Jim.henderson (talk) 00:23, 8 April 2016 (UTC)
April 7
Rotating sphere
While I don't begin to understand the equations at Frame-dragging#Mathematical derivation of frame-dragging, I don't see anything there that looks as if it is modelling the messy atomic nature of real-life matter. It looks too mathematically "exact". Do the equations assume an idealised kind of perfectly smooth and uniform matter? If so, how can one even in principle determine whether a perfect sphere of such matter is rotating or not, given that the sphere rotated through any angle is completely indistinguishable from the original? 86.161.61.4 (talk) 01:56, 7 April 2016 (UTC)
- We can tell the sphere is rotating or stationary by its effect on the surrounding region of spacetime; that is even though the sphere itself is perfectly symmetrical, and thus visually indistinguishable whether it is rotating or not, the effects on the surrounding region of spacetime are detectable and measurable, and can be used to deduce the axis, direction, and speed of rotation of the object in question. The Kerr metric describes how so. --Jayron32 02:02, 7 April 2016 (UTC)
- Thanks, well I understand that is what the frame-dragging equations say, but I still have a hard time understanding how it is even defined whether the sphere is rotating when, as I say, the sphere rotated through any angle seems completely indistinguishable from the original in every respect (assuming granularity of real-life matter is not modelled). Is the "frame-dragging" the only way that the rotation can be detected? I suppose since we are talking about a hypothetical type of matter, it would possibly depend on other hypothesised properties of the matter, but if it is perfectly uniform in every respect then I don't really see how hypothesising other properties would help. 86.161.61.4 (talk) 02:35, 7 April 2016 (UTC)
- I don't genuinely understand general relativity, but note that a moving mass generates gravitomagnetic force. Gravity waves and gravity and gravitomagnetism are all aspects of some big messy tensor math. When a sphere turns that contains mass, it induces fields around it vaguely like how a continuous loop of current in a superconductor generates a magnetic field. I don't actually have any idea how accurate that metaphor is or how far it goes, but at least it should illustrate that the sphere isn't really homogeneous. Wnt (talk) 02:46, 7 April 2016 (UTC)
- Thanks, well I understand that is what the frame-dragging equations say, but I still have a hard time understanding how it is even defined whether the sphere is rotating when, as I say, the sphere rotated through any angle seems completely indistinguishable from the original in every respect (assuming granularity of real-life matter is not modelled). Is the "frame-dragging" the only way that the rotation can be detected? I suppose since we are talking about a hypothetical type of matter, it would possibly depend on other hypothesised properties of the matter, but if it is perfectly uniform in every respect then I don't really see how hypothesising other properties would help. 86.161.61.4 (talk) 02:35, 7 April 2016 (UTC)
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- In the absence of gravity, you could throw a tomato at it and see what happens to the stain, or scratch it and see what happens to the scratch, or hit it with a hammer and see how the sound waves propagate. If it's frictionless, rigid and indestructible, then maybe there is no way to tell and maybe there's no meaningful sense in which it is rotating. But perfectly rigid objects can't exist in special or general relativity because of the light-speed limit. In general relativity, you can't have rotation without frame dragging (as far as I know), so the field is enough to distinguish a rotating from a non-rotating sphere. -- BenRG (talk) 03:45, 7 April 2016 (UTC)
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- Bounce light off of it and you'll get a different doppler shift depending on whether you are shining light on the part rotating towards you or the part rotating away. (Assuming the magic sphere reflects light anyway.) Push on it and gyroscopic effects will affect the result, etc. Even for a smooth classical mass, there are definite differences that one could measure. Dragons flight (talk) 07:56, 7 April 2016 (UTC)
- @Dragons flight: If a sphere is perfectly smooth, light would either have to reflect from it or transmit through it. Either way, I'm not clear that the Doppler shift would come into play. I would ass-u-me that the reflection off a moving mirror should be the same as from a stationary one? Wnt (talk) 16:48, 9 April 2016 (UTC)
- A photon reflection is properly understood as occurring in the rest frame of the mirror. A mirror moving at velocity v, relative to the observer, will appear to change the frequency of the light be a factor of in the low velocity limit. Such effects are small but reliably measurable. Different parts of a rotating mirror ball which show a different amount of doppler distortion due the surface velocity at the point of the reflection. Dragons flight (talk) 17:41, 9 April 2016 (UTC)
- @Dragons flight: If a sphere is perfectly smooth, light would either have to reflect from it or transmit through it. Either way, I'm not clear that the Doppler shift would come into play. I would ass-u-me that the reflection off a moving mirror should be the same as from a stationary one? Wnt (talk) 16:48, 9 April 2016 (UTC)
- Bounce light off of it and you'll get a different doppler shift depending on whether you are shining light on the part rotating towards you or the part rotating away. (Assuming the magic sphere reflects light anyway.) Push on it and gyroscopic effects will affect the result, etc. Even for a smooth classical mass, there are definite differences that one could measure. Dragons flight (talk) 07:56, 7 April 2016 (UTC)
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- It's not representing anything atomic. It's macro field equations generally applied to black holes but are also seen in any rotating mass. Rotating sphere's have symmetry but when it is so massive that the rotation induces a change in space-time around the object. Normally we think of conic solutions for gravity and solve for the static field. In simplified way, the rotation changes the static field and that change forces the body to follow the rotation. That's "frame dragging" as the reference frame is dragged around the rotating body without any angular momentum being supplied by the reference fram. That defies Newton mechanics where rotation doesn't affect attraction and it's also more than simply adding mass/energy to the rotating body. It appears to physically alter space-time and all matter/energy have dynamic solution based on rotation and their location within the ergosphere. The effect is greatest at the sphere's equator and disappears at the poles. I believe it also means that point-mass models fail GR for rotating black holes as do singularities. The rotating mass has a volume and the disappearing affect at the poles is how jets are formed. Lense–Thirring precession is frame dragging with more familiar masses. It's written more intuitively than the complex equations surrounding black holes and shows that rotating bodies with volume and mass can be identified with a gyroscope. --DHeyward (talk) 07:14, 7 April 2016 (UTC)
- In the Einstein field equations, the rotational motion enters through the energy-momentum tensor which has a component for mass or energy density but also components for mass or energy fluxes. Icek~enwiki (talk) 10:16, 9 April 2016 (UTC)
how is this happening?
what is going on here scientifically speaking? how has this remained in this state for so long? if you google image it there's even people sitting on top of it...Old Man of the Lake 68.48.241.158 (talk) 05:28, 7 April 2016 (UTC)
- There is a suggested answer in the first reference given in the article (from which, incidentally, at least some of the article is plagiarised): Some have suggested that when the Old Man slipped into the lake, he had rocks bound within his roots. This might naturally make him float vertically, though no rocks appear to still be there. At any rate, the submerged end could become heavier over time through being waterlogged. Acting like the wick on a candle, the shorter upper portion of the Old Man remains dry and light. This apparent equilibrium allows the log to be very stable in the water.. HenryFlower 05:58, 7 April 2016 (UTC)
- 26 feet is below the waterline, 4 feet above. That volume below the waterline must displace the entire weight of the log. The weight below the waterline seems to be concentrated in the lower section. That places the center of mass far below the surface and makes it stable. Unless there is a change in mass, it's very stable. --DHeyward (talk) 09:24, 7 April 2016 (UTC)
So, how long could this go on for? how did it begin? rolled in there and first floated horizontally? how will it eventually end?68.48.241.158 (talk) 12:15, 7 April 2016 (UTC)
- If the waterlogged wood is denser than the wood that's out in the air, then it's easy to see how it remains stable. If it was firmly attached by roots to the bottom of the lake - yet close enough to the shore for the top to be poking out of the water, then the section that's below water would become waterlogged - and therefore denser than the top part - and when the roots eventually gave way (possibly in a storm or something), it would float away in the current position.
- In future, what happens depends a lot on the nature of the lake water and the above-water climate. In some conditions, wood can remain underwater for centuries and still be relatively intact. If so then we'd expect the top section to gradually erode away. This would result in the tree gradually rising in the water to maintain equilibrium. If the newly exposed (waterlogged) wood dries out fast enough, then the tree would gradually move upwards to compensate for the loss of above-water wood - the log would probably remain stable for decades or longer. But if the below-water wood starts to decay and slough off at a higher rate than the above-water wood goes away - then the entire tree will slide slowly underwater - until it's sufficiently water logged to sink completely. Various combinations of above and below water decay could produce other results.
- SteveBaker (talk) 19:19, 8 April 2016 (UTC)
Sharks' food choice - surfers vs. scuba divers
Do sharks avoid biting scuba divers (maybe due to the neoprene suit)? All attacks I read about seem to be against surfers. Wouldn't it be easier for a shark to bite someone who is underwater? --Scicurious (talk) 11:54, 7 April 2016 (UTC)
- Not if they're in a shark cage. ←Baseball Bugs What's up, Doc? carrots→ 12:37, 7 April 2016 (UTC)
- These may help you in your research: [36] and [37] and [38] and [39] and [40] The last one looks most promising, it seems to be a database of known shark attacks, which would allow one to categorize attacks by type of sharks, where and when the attack occurred, etc. --Jayron32 13:04, 7 April 2016 (UTC)
- The hypothesis I've heard is that, from below, surfers on paddle boards look like seals, so sharks attack in a case of mistaken identity. They rarely actually eat a surfer, and this seem to support the idea that it's not intentional predation. StuRat (talk) 16:58, 7 April 2016 (UTC)
- On TV shows I've seen about sharks, they reiterate what you're saying. It's as if the shark takes a bite out of you and thinks, "Oh, that's not a seal", and goes swimming off looking for other prey, oblivious to the screams of the victim. ←Baseball Bugs What's up, Doc? carrots→ 18:30, 7 April 2016 (UTC)
- And let's not forget to note that shark attacks on humans are altogether rare. And in most attacks that do happen, the shark doesn't want to eat the human. They're either defending themselves or their territory or mistake the human for a prey animal. --71.110.8.102 (talk) 19:37, 7 April 2016 (UTC)
- They're afraid of the bubbles (until habituated). 78.98.62.173 (talk) 20:38, 7 April 2016 (UTC)
- I don't know this, but I'd assume a shark can tell a lot more about a human under the water than one on top of a board. Wnt (talk) 16:51, 9 April 2016 (UTC)
Covalent bonds
I'm a high school student. We've learned that Covalent bonds form exclusively between Non-Metals and Ionic between Metals and Non-Metals. However, a question came today on what type of bonds are present in TiCl4 (Titanium(IV) Chloride). What should be the answer? — Preceding unsigned comment added by Imad Sawal (talk • contribs) 12:45, 7 April 2016 (UTC)
- What you're learning is called a heuristic or a "rule of thumb". The main purpose of the learning you are doing in your class is to train you to learn how to apply abstract rules (like "nonmetal + nonmetal = covalent bonds") to specific situations, (like "What kind of bonding would you predict would happen in TiCl4"). Pedagogically, students usually need to learn the basic principles of abstract thinking like that (of the type "If A then B, If B then C. Now, Tell me about the relationship between A and C), that is just applying abstract rules to specific examples. Actual deep Chemistry content is still delivered, but at a very superficial level. The next thing you would be taught is more complex heuristics, such as electronegativity, which is still a heuristic rule, but a more complicated one than the "nonmetal + nonmetal = covalent" rule (in this case, it is "If the difference in electronegativity between the elements is below a certain threshold, the bond is covalent). Now, that's a more complicated rule, but it's still a rule of thumb, and still doesn't get down to the deep understanding of exactly what a bond is, and what makes a covalent bond work. After you had learned that, THEN you would go into concepts such as molecular orbitals and valence bond theory and hybridization theory and start to get into the behavior of electrons at at the basic level, and then you would be expected to use those principles to be able to determine the sort of bonding that is happening. This type of learning model, starting with the simplest (easiest but most inaccurate model) and building towards the complex (hardest to understand but more accurate model) is called Instructional scaffolding, or sometimes derisively as the Lie-to-children, not in the sense of being misleading, but in the sense of simplifying complex concepts at the early stages, to prepare the learner to better understand the more complex concepts at the later stages.
- If that was too TL;DR for you, here's the simple explanation: If your teacher taught you that "nonmetal + nonmetal = covalent" and "metal + nonmetal = ionic" and that is all they taught you, then for this task, they expect you to apply that concept to the problems they gave you. Whether or not at this point such thinking is correct in all cases is irrelevant to the educational task, because they are building towards something more complex you should learn later. --Jayron32 13:17, 7 April 2016 (UTC)
- Chloride is the anion (negatively charged ion) Cl− found in common salt NaCl. Wikipedia has an ar-ticle about Titanium tetrachloride a volatile liquid with industrial uses, whose molecular formula (TiCl4) might be read as tickle. AllBestFaith (talk) 15:55, 7 April 2016 (UTC)
- Indeed. I know the correct answer because I have two chemistry degrees, and by the end of my Freshman year of college, I had been taught quite enough information to know how to work that out. That's not the question the OP asked, which was more about what their teacher expects as the "correct answer". We would need to know on what basis the teacher is assessing the student, and what the purpose of the lesson is. --Jayron32 17:24, 7 April 2016 (UTC)
- Just a question: In University senior year, do they still label them "orbitals" or is the Lie-to-children thing still applied :) --DHeyward (talk) 07:21, 8 April 2016 (UTC)
- No, the word "orbital" is still used, even though electrons don't properly "orbit". The language is what the language is, etymological fallacy and all. All chemists use the term, they just understand that electrons are not little rigid balls carving circular paths around the nucleus. --Jayron32 09:43, 8 April 2016 (UTC)
- Just a question: In University senior year, do they still label them "orbitals" or is the Lie-to-children thing still applied :) --DHeyward (talk) 07:21, 8 April 2016 (UTC)
- Indeed. I know the correct answer because I have two chemistry degrees, and by the end of my Freshman year of college, I had been taught quite enough information to know how to work that out. That's not the question the OP asked, which was more about what their teacher expects as the "correct answer". We would need to know on what basis the teacher is assessing the student, and what the purpose of the lesson is. --Jayron32 17:24, 7 April 2016 (UTC)
- Chloride is the anion (negatively charged ion) Cl− found in common salt NaCl. Wikipedia has an ar-ticle about Titanium tetrachloride a volatile liquid with industrial uses, whose molecular formula (TiCl4) might be read as tickle. AllBestFaith (talk) 15:55, 7 April 2016 (UTC)
- Honestly, if the OP is really interested in learning about chemical bonding from the horse's mouth, they could do no better than to pick up a copy of (or read it for free online) The Nature of the Chemical Bond by Linus Pauling. That work is the sine qua non of the subject, and really, everything in a modern HS or College chemistry textbook that has been said about bonding for the past 50 years or so is basically taken straight from Pauling's mouth. The great thing about The Nature of the Chemical Bond is that, for what is a pretty dense topic, it's quite readable and understandable. Pauling, besides being perhaps the most brilliant chemist in history, was a pretty good writer as well. He does get into some deep mathematical analysis, but his prose is understandable even to the lay person with little mathematical background; that is if you skim the math and trust that he's smarter than you and know what he's doing, his conclusions based on that Math are written in fairly plain and understandable language, and it's quite easy to get all the basic principles of bonding even if you don't have much background in the subject. --Jayron32 00:58, 8 April 2016 (UTC)
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- Taking Jayron's cue: the expected answer, given the rules, is ionic; but lo! in real life it's covalent. So there must be something more going on than the rules suggest, etc. 'Scuse me whilst I go & read some Pauling & eat Vitamin C like sherbert. --Tagishsimon (talk) 03:46, 8 April 2016 (UTC)
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- Indeed. The thing with TiCl4 is that all the heuristics would get it wrong, even electronegativity. Even comparisons to other Ti (IV) compounds. TiO2, Titanium (IV) oxide, is a clearly ionic high-melting crystaline solid. TiCl4 is a liquid, so clearly covalent. And yet they both contain Titanium (IV), and Chlorine and Oxygen are very close in terms of electronegativity, the difference is not nearly enough to explain the huge game in bond character. Real chemistry is messy. --Jayron32 13:21, 8 April 2016 (UTC)
- The PubChem database entry for Titanium(IV) chloride shows a 2D structure of charged atoms but lists 5 covalently-bonded units consistent with a non-polar tetrahedral structure. Further, TiCl4 is soluble in toluene and chlorocarbons, as are other non-polar species. However, from a high temperature mixture with other metal chlorides the Titanium ion can be extracted by electrolysis, [41] AllBestFaith (talk) 16:11, 8 April 2016 (UTC)
- Indeed. The thing with TiCl4 is that all the heuristics would get it wrong, even electronegativity. Even comparisons to other Ti (IV) compounds. TiO2, Titanium (IV) oxide, is a clearly ionic high-melting crystaline solid. TiCl4 is a liquid, so clearly covalent. And yet they both contain Titanium (IV), and Chlorine and Oxygen are very close in terms of electronegativity, the difference is not nearly enough to explain the huge game in bond character. Real chemistry is messy. --Jayron32 13:21, 8 April 2016 (UTC)
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what % ethylene is polyethylene made of?
what % ethylene is polyethylene made of?
polyethylene is what resin is made from, polyethylene is the main material in plastic bags. — Preceding unsigned comment added by Joro613 (talk • contribs) 12:49, 7 April 2016 (UTC)
- I'm not sure I follow the question. The question is either 100% or 0% or something in between, depending on what you mean. Let me explain the three possibilities
- polyethylene is a polymer made up of ethylene monomer units. Since there is only one monomer unit , ethylene, and nothing else polyethylene is 100% ethylene. (in contrast, nylon is composed of two alternating monomer units, so could be said to be 50% of one and 50% of the other, I suppose).
- That being said, the final product should contain none of the original ethylene. It's a chemical reaction that creates polyethylene out of ethylene units, so the final product (the polyethylene) has already reacted and thus there's none of the ethylene left. So the answer could be "0%"
- THAT being said, the actual reaction that turns ethylene into polyethylene isn't as simple as leaving a bunch of ethylene around and letting it become polyethylene on its own. There are several different steps along the way, various other chemicals are used to react, etc. So, if you take into account the other chemicals in the reaction mixture that GETS you from ethylene --> polyethylene, it would be some other % of the total amount of the reaction mixture.
- So, first you'd need to clarify which of those amounts you are really looking for. --Jayron32 13:25, 7 April 2016 (UTC)
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- Polyethylene (a solid) is made from Ethylene (a gas) either by Coordination polymerization or by Radical polymerization. Both the plastic and the gas are organic Hydrocarbon compounds of Carbon and Hydrogen atoms with covalent bonds. The Wikipedia articles linked here can serve well as an introduction to Organic chemistry. AllBestFaith (talk) 15:34, 7 April 2016 (UTC)
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How many notes can the average human sing?
I know I can sing at middle C and two octaves above middle C. Is this normal? 140.254.136.179 (talk) 16:57, 7 April 2016 (UTC)
- The Wikipedia article titled vocal range would be where you should start researching the answer to your question. --Jayron32 17:19, 7 April 2016 (UTC)
- Two octaves is not bad I suppose. Minnie Ripperton could do five octaves. Depends on the trousers if you are a man.--178.101.224.162 (talk) 23:22, 7 April 2016 (UTC)
- Example videos: Maria Carey (5 - 7 octave), Tim Foust (5 octave), (9 octaves ?). AllBestFaith (talk) 01:23, 8 April 2016 (UTC)
- Yes, these men had exceptionally long trousers as well as exceptionally wide vocal ranges. --DHeyward (talk) 07:59, 8 April 2016 (UTC)
- Yes what? Castrati to whom your "these men" links are neither average humans, normal nor noted for wide vocal range. The article notes that the lower part of the voice sounds like a "super-high" tenor. AllBestFaith (talk) 14:26, 8 April 2016 (UTC)
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- You asked how many notes, not the range of the voice. Given that there are an enormous infinite of gradations between one tone and the other (called being flat, or off-key by musicians) you could probably manage a few thousand very slightly different notes (though it might not be called singing by everyone). 217.44.50.87 (talk) 10:40, 8 April 2016 (UTC)
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- We assume the OP intends different pitch notes. In Western song music the Equal temperament scale of 12 intervals (11 notes) per octave is standard. Arab singers can use twice as many intervals per octave but are not noted for wide vocal range. AllBestFaith (talk) 14:11, 8 April 2016 (UTC)
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- Based on my personal experience as a choral singer, two octaves is pretty typical, maybe a bit larger than the average amateur singer.
- As the vocal range article mentions, there are different ideas of what it means to "sing" a note. Probably many people can squeak or grunt into an amplified microphone over many octaves. Here's a video of Matthew Curtis actually singing beautifully over three octaves. That's more than most people can manage. Julie Andrews, famous for her wide range, had a useful range of three octaves and change ([42]). (She's still alive but I think her range is smaller now.) -- BenRG (talk) 16:47, 8 April 2016 (UTC)
Vocal range and acoustics are a huge field of research, with variances and qualities of both populations and individuals well studied, but in searching for a direct answer to the OP's question, I was surprised at the dearth of sources directly on point as to the "average range". Its probably a result of the fact that researchers recognize the complexities A) of the sort raised by BenRG above as to what it means to properly sing a note, B) the question of innate capability between realized potential (this article speaks to that issue briefly), and C) the difficulty of a getting a testing group reflecting the true human average, controlled for environment and natural variance.
Still, I did find this paywalled source (which unfortunately does not reflect much of anything of its findings in its abstract...) and this, for what little clarity they can provide. This source is more about the relevant musical theory than any specific empirical measurements, but it does have some relevant observations. Note also that we have Category:Singers with a three-octave vocal range, Category:Singers with a four-octave vocal range, Category:Singers with a five-octave vocal range, Category:Singers with a six-octave or greater vocal range--though you'll want to check the refs on the articles for the individual singers before you look at any of them as exemplars of the range they are purported to have. Snow let's rap 19:46, 8 April 2016 (UTC)
How to dissolve the chemical that wrecks circuit traces?
What chemical does one use to get rid of the damage with the green/blue color to circuit board traces that EEVblog #696 shows at 8:07 ? It should be possible to have something that react with the attacking chemical and binds to it harder than the underlying copper trace. Removal by braiding is likely to just make the damage worse. Bytesock (talk) 18:19, 7 April 2016 (UTC)
- The "attacking chemical" is actually ordinary Verdigris and the "underlying copper traces" are gone. Google "remove verdigris" for general info on removing verdigris. That being said, if you remove the verdigris, there won't be anything left. Instead google "repair pc board traces". --Guy Macon (talk) 19:39, 7 April 2016 (UTC)
- The green colour of the circuit board shows that it most likely and certainly is epoxy fibre. The protective coating spayed over the top of the PCB (printed circuit board) would perhaps be a two-part polyester resin (for this 1984 era) . The chemicals that dissolve polyurethane resin may also attack the epoxy. Which means it will lift the copper tracks from the board. Just have to go back to basics. See you see this site for help and advice :Coating Removal, Identification of Coating--Aspro (talk) 20:21, 7 April 2016 (UTC)
Outpatient procedure complication and mortality rates
Anyone know of a single source for outpatient procedures' complication and mortality rates? I have a list of 8 procedures I'm interested in. Was trying to find a single source before going to look up each individual procedure (e.g., liposuction, wisdom teeth extraction, etc.) I found http://riskcalculator.facs.org/ but it seems to be only for more major surgeries. If anyone knows, I'd appreciate it. Please ping me in reply. Thanks! EvergreenFir (talk) Please {{re}} 22:09, 7 April 2016 (UTC)
- @EvergreenFir: Hard question as I would look at different sources depending on whether it was an absolute mortality rate or a comparative rate to inpatient care of the same procedure. Comparative is difficult because the rates change (i.e. an outpatient procedure may have no waiting list, with a 10% post-op mortality rate, an in-patient identical procedure may have a 3 year waiting list with 20% dying before the procedure and a 1% post-op mortality rate - what would you compare?). The other question would be whether it's directly attributed to the procedure (i.e. "die on the table") or whether it includes post-op complications such as infections. Do you have more details? --DHeyward (talk) 08:26, 8 April 2016 (UTC)
- @DHeyward: Honestly would be fine with any, so long as it was consistent and I could compare procedures apples-to-apples. Would prefer both "die on the table" and long term, but would settle for either. For complications, same thing. As for wait list, I'm interested in post-procedure only. EvergreenFir (talk) Please {{re}} 17:41, 8 April 2016 (UTC)
- UK's NIH might be my first choice for data. They have waitlists and they are now trying to move to more outpatient care which is more difficult and should have more scholarly papers. The U.S. data overall would be harder to compare apples to apples because it's generally not random difference in method or recent or controlled. Patients getting inpatient service are sicker, generally, in the U.S. as insurance companies set some of the service standards and approve admissions (e.g. a person who gets an inpatient abortion is likely to be an emergency or complications while the normal procedure is outpatient but I doubt there is any scholarly data that could reasonably be used for mortality rates comparing inatient vs. outpatient, it's just normal vs. emergency - I was looking for that type of data a few weeks ago so that's why it popped into my head). Next choice would be VA but they don't often publish and use industry standards (the wait list is just a bonus). Let me look fore som NIH data. --DHeyward (talk) 18:17, 8 April 2016 (UTC)
- It's not clear to me that OP wants to compare inpatient to outpatient at all. E.g. the example of wisdom teeth - isn't that almost entirely done outpatient? If there's no need to compare inpatient to outpatient, then many more data sources become available. I was interpreting the "apples-to-apples" to mean the same method was used to assess complications for wisdom teeth extraction and liposuction, not a method to compare wisdom teeth between inpatient and outpatient procedures. SemanticMantis (talk) 19:22, 8 April 2016 (UTC)
- Just outpatient is fine. I'll check out NIH though EvergreenFir (talk) Please {{re}} 03:13, 9 April 2016 (UTC)
- It's not clear to me that OP wants to compare inpatient to outpatient at all. E.g. the example of wisdom teeth - isn't that almost entirely done outpatient? If there's no need to compare inpatient to outpatient, then many more data sources become available. I was interpreting the "apples-to-apples" to mean the same method was used to assess complications for wisdom teeth extraction and liposuction, not a method to compare wisdom teeth between inpatient and outpatient procedures. SemanticMantis (talk) 19:22, 8 April 2016 (UTC)
- UK's NIH might be my first choice for data. They have waitlists and they are now trying to move to more outpatient care which is more difficult and should have more scholarly papers. The U.S. data overall would be harder to compare apples to apples because it's generally not random difference in method or recent or controlled. Patients getting inpatient service are sicker, generally, in the U.S. as insurance companies set some of the service standards and approve admissions (e.g. a person who gets an inpatient abortion is likely to be an emergency or complications while the normal procedure is outpatient but I doubt there is any scholarly data that could reasonably be used for mortality rates comparing inatient vs. outpatient, it's just normal vs. emergency - I was looking for that type of data a few weeks ago so that's why it popped into my head). Next choice would be VA but they don't often publish and use industry standards (the wait list is just a bonus). Let me look fore som NIH data. --DHeyward (talk) 18:17, 8 April 2016 (UTC)
- @DHeyward: Honestly would be fine with any, so long as it was consistent and I could compare procedures apples-to-apples. Would prefer both "die on the table" and long term, but would settle for either. For complications, same thing. As for wait list, I'm interested in post-procedure only. EvergreenFir (talk) Please {{re}} 17:41, 8 April 2016 (UTC)
Washing clothes
This is a SERIOUYS QUESTION> What is the best way of washing clothes in order to remove those unsightly marks on certain undergarments? I cant find anything in the pedia to answer this Q. --178.101.224.162 (talk) 23:19, 7 April 2016 (UTC)
- I would recommend stain removal soap. And soaking in water. Graeme Bartlett (talk) 23:55, 7 April 2016 (UTC)
- Depends on the stain I suppose... non-chlorine bleach (usually hydrogen peroxide) will get most organic-based stains out when used with detergent (thinking poo, blood, mold, etc.). I find that the Resolve stain stick (looks like a deodorant stick) works very well for old grease/oil stains. That might help for the stains bras sometimes get. Jezebel has a lovely article about getting panties clean (link). EvergreenFir (talk) Please {{re}} 23:56, 7 April 2016 (UTC)
- For really soiled stuff like diapers, Grandma used simple washing soda and borax followed by vinegar. It didn't bring them up 'brilliant white' because the don't contain any bluey colour chemical enhancers but they were clean. After the diapers have been rinsed in clean water, wash in dilute vinegar (washing soda is chemically basic, so this helps to neutralize what’s liquid is left in the cloth and makes it feel softer – which what you want next to a baby's bum). You can wash them in modern detergents after though, if you wish (but the modern detergents cost more per wash). Note: Some modern detergents work at low temperatures but washing soda and borax needs water to be very hot. Not marketed today because its too cheap and 'unbranded.' Being unbranded no corporation would be willing to spend the high cost of advertising for something they can not claim to be their own unique product. Sham, when its so much cheaper and effective.--Aspro (talk) 00:17, 8 April 2016 (UTC)
- Think reusable nappies (diapers if you are American). It is normal for them to get faecal stains. Buy a tub of nappy cleanser, and follow the instructions. It should work fine unless your diet contains a lot of strong artificial colourings. (I suspect your initial question didn't get taken seriously because you used the slang expression "skid marks"). 217.44.50.87 (talk) 08:55, 8 April 2016 (UTC)
April 8
Bread slice missing middle
I was nearing the end of a bag of sliced bread (branded, factory-made, bought at a major supermarket), and found that the second last piece (the piece before the end) consisted only of three edges edges (i.e. it was missing the middle and one edge) - more than just the crust, but most of the middle was gone. It looked torn, definitely not cut by a blade. The bag was closed with the original plastic clip, and there were no holes in the bag. I can't guarantee that the clip 100% securely closed the bag, but as far as I remember it was closed. The previous day I had taken two slices that sat above the odd slice in question, and they were fine. I think I would have noticed if the next slice was odd, but can't be sure. The last piece in the bag (the end) was intact.
What could have caused this? Some possibilities I thought of are: (i) at some point previously I had left the bag open and a mouse had gotten in and out, but then it would be odd for it to dig down to the second piece before last, eat it, and not disturb any of the others; (ii) there was some manufacturing error and that piece came like this; (iii) the bag was not securely closed the previous day, and a very nimble mouse or something smaller had gotten in during the night and eaten the bread; (iv) bread eating mould of some kind? The bread was a few days past its "best before" date. --PalaceGuard008 (Talk) 08:55, 8 April 2016 (UTC)
- Possibly a damaged blade in the slicing machine. 217.44.50.87 (talk) 08:57, 8 April 2016 (UTC)
- (ii) is definitely your answer. The bread could have been torn while slicing for some reason, or it could have been baked that way I suppose (an air bubble in the dough). shoy (reactions) 13:51, 8 April 2016 (UTC)
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- Perhaps the original Loaf had an oversize void due to uneven Leavening caused by inadequate mixing of the Bread dough. Mouse infiltration leaves tooth marks, crumbs or stools. AllBestFaith (talk) 13:54, 8 April 2016 (UTC)
- I had a squirrel come down my chimney and attack a loaf of bread. It was fascinating what he did with it. He formed it into mouth sized balls, presumably planning to transport it back out by mouth. Then I showed up and ruined his plans by evicting him from my house and getting a chimney cap. StuRat (talk) 19:18, 8 April 2016 (UTC)
"Engagement length"
What does the "engagement length" indicate in ISO 965? There are many standard screws and nuts that go above and below this range, so what happens when you use such a combination? Let's say I try to seat a M2 screw 4 mm into a threaded hole, exceeding the "engagement length" range of 1 to 3 mm, what happens then? Will the thread strip? Or it is likely to get stuck or something? Johnson&Johnson&Son (talk) 10:25, 8 April 2016 (UTC)
- Google "engagement length of bolt" and take your pick of the explanations on offer e.g. [43] "One of the main guidelines in designing fastener joints is that the length of thread engagement should be long enough so that the bolt will break rather than strip the threads in the tapped hole". Richerman (talk) 10:47, 8 April 2016 (UTC)
- ISO 965 is used for pass/fail Acceptance testing of ISO threaded fasteners so it is desirable to set both minimum and maximum values for the engagement length that can be difficult to establish exactly but is critical for testing breaking strength. However the quoted maximum engagement length does not bear on usage and nothing bad happens if it is exceeded, as routinely happens with the long nut illustrated. AllBestFaith (talk) 13:37, 8 April 2016 (UTC)
Psychology study that involves perception of pain of another person
I remember that there was this psychology study that involved a person tapping on something. If the person heard another person in the room answering the question wrong, then the other person seemed to be shocked literally. What was this study? 140.254.77.187 (talk) 17:36, 8 April 2016 (UTC)
- Perhaps the Milgram experiment. Sean.hoyland - talk 17:39, 8 April 2016 (UTC)
- The Milgram experiment.--TMCk (talk) 17:41, 8 April 2016 (UTC)
Engineering Physics
Light from a broad source source is obliquely incident on a thin transparent plate. Find the expression for the effective path difference between part of a ray reflected from upper surface and part that suffers reflection over surface internally . — Preceding unsigned comment added by 1.39.15.220 (talk) 19:28, 8 April 2016 (UTC)
- Okay, I did it. Now you do it...seems like it's your homework not mine. DMacks (talk) 20:27, 8 April 2016 (UTC)
- Depends on the thickness of the plate and the angle of incidence I would say. Any help?--178.101.224.162 (talk) 01:57, 9 April 2016 (UTC)
- Just draw the path of the internally reflected ray. It forms two symmetrical right triangles. You can calculate the angle and hence the length of the hypoteneuses (don't forget to use Snell's law to take refraction into account - within the glass, the angle of the ray is different from outside the glass). You know the length of one side. The rest is sine and cosine applied repeatedly, I think. Wnt (talk) 16:57, 9 April 2016 (UTC)
- On second consideration I realize I don't know... it's a matter of philosophy. :) The thing is, not only does the refracted light bend differently; it also moves more slowly than the light in vacuum. For most interesting measures of the path difference, like the spreading of a pulse laser when it bounces off the thing, you're measuring the time of transit, not the distance in glass + distance outside of glass. But that would be wrong since it's not truly the length... or is it? As I understand (the problem being, I don't), there are grand unified theories, M theory etc. that present electric fields as being a curvature of space, and the light is not really slowed, it just appears slowed as it wends and weaves through the fields of atoms. And so its squiggly path is exactly what the time suggests, and so the "length" of the path in glass should be multiplied by this time factor. But is curvature in space actually a part of distance? Wnt (talk) 17:10, 9 April 2016 (UTC)
Do hens ever reach a point where they are passed their egg-laying days?
Or do they lay eggs as long as they live? 140.254.70.33 (talk) 21:35, 8 April 2016 (UTC)
- Are you talking about commercial egg laying birds or non-commercial birds? Commercial egg layers in the UK are usually kept for only 62 weeks as their egg production then starts to decrease. In some countries, including the US, the birds are force moulted (deprived of food and water for many days) which stimulates the hens to increase their egg laying again. This may happen several times. Let's not forget, these commercial birds lay approx 300 eggs per year whereas a non-commercial hen might lay only one clutch (e.g. 6) of eggs each year. DrChrissy (talk) 21:44, 8 April 2016 (UTC)
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- And in Britain, where there is a Royal Society for the Prevention of Cruelty to Animals, but merely a National Society for the Prevention of Cruelty to Children, there is the British Hen Welfare Trust, which enables members of the public to re-house hens past their laying days. "They are approximately 17 months old when we collect them from farms, and are off to slaughter because they are deemed no longer commercially viable as they may be laying fewer eggs." Carbon Caryatid (talk) 22:00, 8 April 2016 (UTC)
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- Yes, I should have mentioned that. When the commercial hens start to decrease their egg laying, the producer makes a financial decision to get rid of them. These are often called "spent hens". If people get spent hens, these often initially stop laying (probably because of the stress of the change of habitat) but very, very often start laying again at the usual pattern (they lay an egg each day for 7 days then miss a day). DrChrissy (talk) 22:12, 8 April 2016 (UTC)
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- I meant that, in some ways, British sensibilities afford more value to animals than to children, and therefore it isn't surprising that there is a specific organisation to enable well-wishers to be kind to chickens. Carbon Caryatid (talk) 16:13, 9 April 2016 (UTC)
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- See A Modest Proposal (yes, I do realize it's satire). StuRat (talk) 16:55, 9 April 2016 (UTC)
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- The RSPCA got its "Royal" title in 1840, thanks to Queen Victoria. The NSPCC also has a royal charter, even if it doesn't use the word in its name, and the Queen is in fact the patron of both charities. 217.44.50.87 (talk) 18:12, 9 April 2016 (UTC)
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- Hens may slow down and stop egg production temporarily during the winter cold and they might also stop if they get sick, but otherwise no. My friend had a bird that lived and laid eggs for at least 9 years. This [[44]] website mentions a hen that did so for 17 years. Modocc (talk) 20:19, 9 April 2016 (UTC)
April 9
Source of ammonia in life science lab?
What is a source of ammonia in a life science lab that might be used, for example, to clean an oven? --78.148.105.117 (talk) 13:13, 9 April 2016 (UTC)
- I don't know why you need a life science lab. I can buy ammonia for cleaning at my local grocery store.--Jayron32 13:23, 9 April 2016 (UTC)
- Are you asking what lab activities might incidentally create ammonia fumes in that lab ? If so, the obvious answer is cleaning, specifically with glass cleaners, which often contain ammonia. It's also possible that some experiment might create ammonia. StuRat (talk) 15:25, 9 April 2016 (UTC)
- Chemicals in laboratories are purchased from any number of sources, such as Sigma-Aldrich. --OuroborosCobra (talk) 15:42, 9 April 2016 (UTC)
- This question is too unclear to answer. Ammonium hydroxide for most lab uses is highly concentrated and its fumes should NOT be inhaled. Using it to clean an oven would require substantial dilution in a well-ventilated area. Confusing the two could lead to severe injury, and I think it might also damage the oven (I don't know that). this source says 14-15 M for lab solution and 5% (NH3) for household; doing the calculation they suggest, I get 17 g/l is 1 M and so 50 g/l = about 3 M, or 5x diluted, but PLEASE DO NOT RELY ON THAT because neither source nor calculation is guaranteed here. Just buy your cleaner at the store, and do not fool with lab ammonia for anything but real chemistry. Wnt (talk) 16:42, 9 April 2016 (UTC)
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- What about solid ammonium bicarbonate? Ah, here we have solid ammonium chloride! Perfect! I heard I can just leave this to evaporate in the oven and do all the cleaning by magic 192.41.128.212 (talk) 18:54, 9 April 2016 (UTC)
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- Lab ammonia? Chemicals do not care what their destination is, they just are. Any lab is going to either order the proper concentration and purity for their specific use, or be able to dilute down from a concentrated source. If I do not need HPLC grade purity for whatever work I am doing, I do not spend the money on HPLC grade. I don't know of anything called "lab <insert chemical name here>." Nor would I order already diluted HCl for almost anything (unless I really really need 1.000N HCl), I have a supply of glacial that I dilute down to whatever I need for either experimental or cleaning usage. --OuroborosCobra (talk) 17:51, 9 April 2016 (UTC)
Handedness and cheek concavity
I am interested in finding reports of evidence either for or against the hypothesis that left-handedness is correlated with concavity of the right cheek (more than the left cheek), because of the right cheek being supported by the right hand while the left hand is writing; and vice versa. Where can I find such reports?
—Wavelength (talk) 18:46, 9 April 2016 (UTC)
US college admission through standardized tests alone
Does any US college admit students through standardized tests alone, either for undergraduate or graduate studies? The list of standardized tests in the United States confirms that there are plenty of options to choose from. Doesn't any college trust those test enough? --Scicurious (talk) 18:55, 9 April 2016 (UTC)
- unless this has changed recently, Harvard requires neither high school diploma nor standardized tests for admissions...and there are instances of Harvard admitting unusual but gifted people who have neither...68.48.241.158 (talk) 19:39, 9 April 2016 (UTC)