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[
"Could you use thermochromic ink for tattooing?"
] |
[
false
] |
I saw this and it made me wonder about putting it into the dermal layer of skin: I've heard that early (pre-1800's) Japanese body suits used to have color changing properties.
|
[
"Why wouldn't the same approach with pmma work here?"
] |
[
"No - you can't. Thinks get a little tricky when the ink has special properties. Remember UV reactive ink? The first to come out turned brown. They finally found a solution - but it was to encase the ink in pmma - this allowed the ink to not come in contact with skin / body fluid.",
"Anyway, look at the chemical ingredient list in photo chromatic ink - it has a chemical list that contain a few that would easily absorbed by the body."
] |
[
"Because the mix of chemicals - the lab that makes the pmma inks here in the US said it would require significant advancements in encapsulation technology. ",
"Believe me they want the money - if they could deliver even a marginal, body safe product, they would."
] |
[
"Is it possible using software to determine the hardware circuits of a computer system?"
] |
[
false
] |
[deleted]
|
[
"Unfortunately no - and it's the same problem we have with our own reality. :) ",
"With any instruction you execute, the response returned may only be what the emulator you didn't/ couldn't know was running wants you to know. "
] |
[
"No, not even what you said. A computer can quite easily lie about quite a few things, and often does for backwards compatibility reasons.",
"There's nothing that says that a computer must allow software to interrogate it about its capabilities, either. It's perfectly possible to have a computer that has no straightforward way of asking how much RAM it has, other than trying to write to an address and seeing what happens, while accounting for that addresses might wrap around at some point.",
"In fact, the ability to figure out what's inside a computer is quite new. In the 90s and earlier configuration used to be a lot trickier because there wasn't an easy and convenient way of asking the computer what sound card it had inside. Code wanting to do autodetection had to very carefully try to poke at things to figure out whether there was a soundcard at a given IRQ, DMA and IO addresses, and hope that this wouldn't happen to send a signal to something else, which might get misinterpreted in some awful manner -- from a crash to disk corruption.",
"And then there's emulation, which can go really far. With console emulators you usually have the emulator not only emulate the hardware and instruction set, but also the timing and various hardware glitches. Some things like precise timing can be hard to emulate, but only for practical reasons, and not because it's impossible. An emulator could achieve absolute perfection and make it impossible for a program running inside to determine it's being emulated.",
"Now if you're familiar with virtualization, today most systems don't try to hide their existence, but even there you see this: If you assign a VM 1GB and 2 cores of a 64GB, 32 core machine, as far as the software running inside can tell, you only have 1GB and 2 cores, as well as a Cirrus video card and Realtek network card, neither of which you probably physically have, but that for whatever reason turned out to be convenient to emulate."
] |
[
"The software wouldn't know that it was indeed controlling a robot, rather then just being run on an emulator that emulates results from the \"robots\" investigation."
] |
[
"Youngest person to achieve atomic fusion: what has he actually done?"
] |
[
false
] |
If you haven't seen it in the news here is a link: I understand the basic principles of fusion, but how is this different to what governments are spending billions on? If it's so easy why aren't more people doing it?
|
[
"Fusion is easy, trivial even. But that's because it's easy to \"cheat\". Particles are small, by putting enough energy into small particles you can initiate fusion. One simple way to do this is to accelerate deuterium nuclei into deuterium or tritium nuclei. You can do this in a handheld device that runs off of wall power.",
"But these devices use far more energy than they produce. What we've been seeking with fusion research is a system that returns a surplus of energy. That's only possible by containing fusion fuel plasmas under high temperatures and pressures, which is a very complicated and difficult thing to do that requires state-of-the-art equipment. Currently we have only gotten to a barely break-even level of being able to operate fusion reactions which return as much energy as is used to create the conditions necessary for the fusion to take place.",
"Think of it like ... say, hydropower. It's easy to fill a sink with water at home, or to collect rain water in a barrel outside. But generating significant amounts of electrical power from water requires large reservoirs, dams, generators, and other special equipment."
] |
[
"I would first point out that the article says atomic fusion. Bad word choice, it should be nuclear fusion.",
"People have been doing nuclear fusion since the 1930s. It is actually is pretty easy to do. In the most basic definition, I can take a source of Am-241 and aluminum and create nuclear fusion since the alpha particle will combine with the aluminum isotope. That is typically not what is meant by nuclear fusion. Specifically they are talking about some form of hydrogen fusion. ",
"The kid made a device that fuses hydrogen to make neutrons. That isn't hard to do in terms of the science. We have been doing that for well over 60 years. It is impressive someone so young built a device. The main thing governments are working on is similar. They want to create nuclear fusion with hydrogen. The big difference for them is they want to create more energy from fusion than it takes to make the fusion occur. The experiment the kid did took more energy to produce the fusion than was released. That is nice if you want a good neutron source. However, if you want to make a power plant you need to have a reaction that is pseudo self sustaining. That is very difficult. "
] |
[
"Actually, making a fusion reactor is ",
"surprisingly easy",
", as ",
"Taylor Wilsen",
" will attest. The thing is, these reactors require loads more power than they put out, meaning you can't use them to generate energy. The ultimate goal of programmes like ITER is to change this, as once you have a viable self-sustaining reaction, you can start to harvest the energy given off to generate electricity. ",
"All those billions are going toward making a self-sustaining reaction viable (as in, doesn't need outside power sources to continue fusion once it's running)."
] |
[
"How accurate is radiometric dating? and other questions. Details inside."
] |
[
false
] |
I was reading through an article about the theory of young earth . (Someone linked it in an ) In the 15th citation they mention that radiometric dating is very unreliable. They reference a scientist, Claus Rolfs, and his paper . I tried searching around and I couldn't find much discussion about this actual paper or what he actually proved in his research. I do not want to start a discussion bashing the afformentioned young earth website (even if it is lunacy). If you want that I'm sure would be happy to have you. I'm just curious on how they twist science to meet their ideas and preconceived notions. Can someone explain radiometric dating and give insight into Rolfs' work on the subject? Maybe expand on how it could be misconstrued to fit the young earth believers theories.
|
[
"A quick note first is that New Scientist is not a peer-reviewed article. So I will disregard this article. The research by Rolfs et al. was published here ",
"http://iopscience.iop.org/0954-3899/32/4/007",
" . Looking at this in isolation it looks interesting. The problem is however that other groups have looked at this as well and failed to find the same results. Example: ",
"http://www.sciencedirect.com/science/article/pii/S0375947407006021",
" . So it would appear that the results of Rolfs et al. was a fluke rather than a new discovery. There is no reason to believe that the half-life of nuclei would change drastically at low temperatures.",
"All this said. Even if the results were true the young earth people have taken it out of context. The method described by Rolfs et al requires the alpha emitter to be encased in metal and cooled to very low temperatures (a few K). Even if it does get rather cold here in Sweden some time I have yet to experience temperatures below 200 K. "
] |
[
"There is going to be a lot of terminology involved so bare with me regarding definitions.",
"Radiometric dating is defined (by Wikipedia) \"is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates.\" ",
"For Radiometric dating we measure the \"half life\" of a isotope. Now when we say \"Half life\" in regards with Science, what we mean is the time for a isotope to half it's value. So with Carbon 14, it takes approx 5,730±40 years. So let's provide a hypothetical situation, say we start with carbon 14. In 5,730 years, Carbon 14 will half it's original value, going from a original percentage of 100 to 50. After that, in other 5730 (11460 years in total) it will half again! Percentage of 50 to 25. But what happens to the other 50, 75 %? It is converted into the \"daughter element,\" in this it is nitrogen. ",
"So why am I telling you about half lives? Essentially, not to overburden, but for radiometric dating, we can establish a date, given our knowledge of half lives. So if found some rock with 25% carbon 14 (isotope), we can deduce that it is 17190 years old. ",
"Now, Radiocarbon (carbon 14) is limited in it's accuracy. We only consider it valid from about 61,000 years and lower because the carbon amount becomes so small as an amount that measuring it is rather difficult. ",
"Now because Radiocarbon dating (Carbon 14) is only valid for up to 62,000 years, the young earth believers tend to state \"you can't measure that with radiocarbon with that piece of strata.\" And that is true, we can't and most importantly... we don't. We use the other forms radiometric dating. We measure other isotopes and their half lives. For example isotope Uranium dating which is valid from about 1 million years to over 4.5 billion years. Uranium(235) has a half life of 704 million years.",
"In addition there is exceptions to radiocarbon dating. E.g. reservoir effect. But this is knowledge realm of Science and declaring the inaccuracy of radiocarbon as a result of the reservoir effect has no validity as an argument. We can explain why carbon 14 is inaccurate in that case. ",
"I hope this made things easier",
"Edit: Here is a graph of half life to help understand the concept. ",
"http://earthsci.org/fossils/geotime/radate/c14.gif",
"\nThe red line is carbon 14 and the green line is nitrogen. See how over time carbon 14 percentage decreases? and as a result it is converted to nitrogen"
] |
[
"Good response. I would only point out that U",
" has a half life of 700 million years, but U",
" has a half life of about four billion years."
] |
[
"Basics of Speaker Design"
] |
[
false
] |
So far, I modeled the diaphragm of a speaker as a 2nd order spring damping mass system - and to maintain constant SPL (flat response in the human audible frequency range),the ideal diaphragm should have small mass & spring constant. What are some other factors to consider, and what makes a good speaker? What's the difference in approach between say like Sennheiser and Bose? Are there standard principles they follow? What exactly do audiophiles consider before buying audio equipment? Thanks
|
[
"Well, you were right to start with the barebones physics. Thiele and Small's research will give you more information on that should you wish to find it. They created equivalent circuit designs to model the mechanical and electrical behavior of speakers, like how the suspension of a speaker acts like a capacitor and the mass of the cone acts like an inductor, plus the effects of the voice coil inductance, etc. ",
"Some other factors that play a large part in speaker design are the materials of construction of the speaker (and how they can cause nonlinearities and variations in the frequency response). For example, a large woofer made of the traditional paper cone material will usually have a range of the frequency response where \"break up\" is encountered. This is when the cone stops moving like a piston, and starts flexing since the cone itself is resonating (not the cone-suspension system). ",
"In paper cones these \"break up\" resonances which are between 1 kilohertz and 5-10 khz are more damped than in metal cones. Metal cones are stiffer than paper so their break up ranges are usually higher in frequency than a paper cone of the same size, but since the metal doesn't damp resonances of the cone as well, their resonances are higher magnitude and accordingly, subjectively more annoying. When designing a 2 or more way speaker system (i.e. Woofer + midrange + tweeter) these break up ranges are attenuated by the crossover, which splits the signal into frequency ranges only sends each speaker driver the frequency ranges it can produce satisfactorily. ",
"There are \"full range\" single driver speakers that use various methods to obtain high frequency response such as reducing the cone mass, or using a whizzer cone which is a smaller and lighter cone within the main one that has an easier time reproducing high frequencies. If a speaker driver is small enough, (around 3 to 4 inches or less) it may not even need a whizzer cone since its mass is already low enough as not to act like a mechanical inductor, attenuating high frequencies. The cones of these small speakers are also small enough to put the resonant break up modes higher up in frequency, and of course the maker can choose the best cone material that reduces the noticeability of those resonances. ",
"As for what makes a good speaker, that is somewhat of a subjective question, but generally it means low distortion, flat (-ish) frequency response, and minimal resonances. The evaluation of a speaker can depend on these as well as the perception of the listener. For example, a layman and non-audiophile may not notice resonances as well as an audiophile or sound engineer with a trained ear. The same goes for distortion and variations in the frequency response. Audiophiles can consider any or all of these parameters when choosing a speaker system, but measurements or data on one will not tell the whole story. For example, a speaker system may measure nicely with a relatively flat frequency response, but it could be made with speaker driver(s) that have nonlinearities worse than average, causing more distortion. Resonances show up in the frequency response most of the time as a peak of varying width, but sometimes they don't, so everything should be taken into consideration. And to further complicate things, sometimes manufacturers and users use resonances to their advantage, in ways that a listener may or may not find suits their ears. ",
"Bass reflex speaker systems that use an opening in their speaker box (called a port, it is often a tube of some length) actually take advantage of the resonant system created by the speaker, the air in the box, and the air mass in the port. This can improve lower bass response that would be otherwise hard to achieve in a sealed speaker box, but since it is a resonant system, it doesn't decay instantly, so some may call the bass that comes out of a bass reflex system \"smeared\" sounding. The Q value of any resonance (which is determined by dividing the energy stored in the system by the energy dissipated in the system, per cycle) is related to how \"smeared\" a resonance can sound, since resonances with higher Q values don't dissipate as much energy per cycle as those with low Q values, and hence decay more slowly and are audible for a longer time. As a side note, bass reflex systems are mostly designed to be critically damped, with a Q value of .707, which minimizes ringing (the audible decay of a resonance). ",
"Full range speakers can also take advantage of cone break up resonances to extend high frequency response, though this method must be carefully applied as not to be audibly annoying (which is subjective anyway). ",
"(Note that the next section isn't really science, but I still wanted to answer OP's questions. Keep in mind this is from what I have gathered and accordingly should be taken with a grain of salt.)",
"I'm not sure about the different approaches of different manufacturers, but it does seem like most of them at least try to obtain a flat frequency response (again, depending on the application, for example partiers may want a huge bass boost, which can be designed in the speaker or added later electrically or in software with equalization [EQ], which allows you to adjust the frequency response using filters that can amplify or attenuate certain bands of frequencies.) as well as low distortion and minimization of non-useful resonances. Some manufacturers use EQ in their systems to heavily attenuate resonances (make them inaudible) or to try to flatten the response of the mechanical/electrical system they have already developed. Bose has a reputation for taking that route by using full range drivers in so many of their systems, and EQ'ing any shortcomings away as well as adding a modest bass boost. ",
"There are other things about speakers like directivity (how wide the beam of sound coming from a certain speaker driver or system is at various frequencies) and baffle step compensation that I won't cover here, but information on them can be found with a quick search. ",
"I hope this answered your questions and gave you some good starting information if you plan to research speaker design more. It is a bit complicated, like most things when you really delve into them, but I enjoy the hobby, learning about it, and sharing my knowledge with others. Good luck. ",
"edit: some words in paragraph 3, and second to last paragraph added. "
] |
[
"Lord knows I'm not going to get into the actual physics, but I will say this: Sennheiser don't make \"speakers\" - not room speakers, anyway :). ",
"Bose use a special engineering technique called \"Spending a ton of money on marketing\". Really, I would not be looking to Bose for speaker design tips. Their satellite systems are extremely poorly engineered (and have inspired, sadly, thousands of similar PC speaker systems): a tiny subwoofer (incapable of reproducing deep bass at volume) which has been stretched up into the midrange (where it sucks at doing the job of a midrange speaker), and tiny, tinny satellites (made from stamped cardboard drivers, like in a $5 radio). ",
"I understand why you mentioned Bose, though: they are simply the most visible thanks to their \"engineering\" skills I mentioned above...",
"Truth is...there is no perfect speaker. Not from a practical standpoint, anyway. Lord knows there are enough speaker designs out there...",
"I guess ideal speaker driver would:",
"Have an infinitely stiff cone.",
"Have zero moving mass.",
"Have suspension that is a) infinitely flexible when the signal starts, and b) infinitely rigid when a signal stops.",
"Have perfectly flat impedance from 20Hz to...infinity hertz.",
"This doesn't exist.",
"And at the end of the day, it's all subjective. There are guy who swear by behemoth multispeaker, multi-driver systems, and then the guys who want one Fostex driver in a precisely made tapered quarter-wave pipe.",
"Then there are guys who want \"dry\" bass, and \"wet\" bass.",
"And that's why, my friend, there are a ton of different speaker enclosures out there. Sealed (acoustic suspension) and ported are the two you're familiar with. There there's open baffle, TQWP, horn enclosures, sub and satellite, bandpass boxes...",
"More tomorrow, when I'm less sleepy."
] |
[
"Here's a model of speaker impedance I've seen used in several places:",
"---(R1)---(L1)---(R2,L2)---(R3,L3,C1)---\n",
"where objects within parentheses are in parallel with each other, and groups connected by --- are in series.",
"R1 is the voice coil DC resistance, typically about 80% of the quoted speaker impedance.",
"L1 is the voice coil inductance. (R2,L2) allow for additional shaping of the high-frequency impedance. If the amplifier is voltage drive (as opposed to current drive), then the increasing impedance at high frequencies means speaker output declines.",
"(R3,L3,C1) put a (usually narrow) spike in the impedance at the speaker's resonant frequency. For an '8-ohm' speaker, the amplitude of this spike could easily be 30-60 ohms.",
"Here are some example values which produce a reasonable impedance plot for some imaginary driver:",
"R1 = 7 Ω\nL1 = 35 uH\nR2 = 32 Ω\nL2 = 110 uH\nR3 = 30 Ω\nL3 = 3000 uH\nC1 = 400 uF\n",
"As for the ideal speaker, I think it's one which instantaneously moves, as a rigid body, to a position dictated by (and linearly proportional to) the signal amplitude (voltage) at that moment. It has no tendency to be pulled back to an equilibrium position."
] |
[
"Is Felix Baumgartner actually going to go supersonic, or is he just going to break the speed of sound at sea level?"
] |
[
false
] | null |
[
"Take a look at ",
"this graph",
". The speed of sound is significantly lower in the regions he'll be falling through."
] |
[
"Good ",
"article",
" about the whole setup.",
"Says he will reach 690 mph after forty seconds but will not experience a sonic boom because the air is so thin."
] |
[
"Thanks, that's exactly what I was looking for. Also, to clarify, the article states he WILL experience one, but the air is thin enough that it will be insignificant in damage and won't be a problem (...hopefully)."
] |
[
"Would I weigh the same if there was no atmosphere above me?"
] |
[
false
] |
[deleted]
|
[
"Any object immersed in a fluid experiences an upward (bouyant) force equal in magnitude to the weight of the fluid displaced by the object.",
"The atmosphere will provide a small upward force and make you weigh slightly less than you otherwise would. In a more dense fluid you'd weigh even less.",
"Say a human body has a volume of about 70 litres. The atmosphere has a density of about 1.2 kg/m",
" (1.2 g/l) at sea level. So atmosphere with mass of roughly 84 grams (about 3 ounces) is displaced by the average person, and their weight is reduced accordingly.",
"Edit - just to add",
"if I'm standing up then the atmosphere couldn't be \"pushing up\" on me from below my feet.",
"The upward force doesn't come from fluid below the object pushing up on it. It comes from the increase in pressure with depth in a fluid which gives rise to a net upward force."
] |
[
"This is wrong. Pressure is force applied equally over all sides. Gauss's theorem can be used to show that this exerts no net force on a body."
] |
[
"Gauss's Theorem only applies for infinitely small bodies though, the left/right front/back components of pressure on a body would be equal magnitude but the up/down would differ. This is what provides the buoyancy force skeesicks has described above."
] |
[
"If the coronavirus (or any virus for that matter) is so contagious and can be found on surfaces or in the air for long periods of time, then why do you need to swab so deep in your nasal cavity?"
] |
[
false
] |
I have not personally had a test for COVID-19 but I have seen the procedure. The swab seems to go much deeper than that of a standard flu test. If the virus can be found in most of our mucus membranes why do they need to swab so deep?
|
[
"You only need to inhale a handful of virus particles to catch the disease. Since the virus reproduces inside you, after a few days that handful becomes trillions. ",
"However, the test isn't sensitive enough to pick up tiny quantities of virus, and the virus does not reproduce in the test, so they swab where the highest concentration is likely to be to have the best possible chance of a correct result."
] |
[
"To continue this, our current PCR based tests tend to detect SARS-CoV-2 at around 250 genetic copies per mL. The earlier tests needed upwards of 2-3000. The LabCorp test that everybody was sending away for that took a week to come back is actually abysmal. So now they're looking at how well nares or oropharyngeal (nostril or throat) swabs work with lower limits of detection. The ASM has a decent relatively low-level article summarizing PCR testing for COVID-19.",
"https://asm.org/Articles/2020/April/False-Negatives-and-Reinfections-the-Challenges-of"
] |
[
"We use real-time PCR, rather than waiting for the PCR to run a set number of cycles (using fluorescent probes or PAGE and Southern blot to detect the product). We use fluorescent tags during the PCR and count the number of cycles before seeing a threshold. So the whole process goes way faster. We also use engineering controls like negative air pressure \"dirty\" rooms and biological safety cabinets to protect ourselves and the samples. But at the heart of it, it's the same as it always was, and likely will be for a long time."
] |
[
"How would I find the amplitude of the membrane of my kazoo?"
] |
[
false
] |
I have a cheap plastic I was messing around with when the question came upon me. I'll explain how it works briefly. The kazoo is a pipe you hum into. This causes a membrane (wax paper in my case, I think) to vibrate sympathetically and produce the unique sound. Let's say that I'm humming at 440 Hz and the wax paper has a diameter of .01m. How far up or down will the middle of the wax paper go? (Bonus: does this distance change based on the frequency?) I'm not sure how to approach this problem.
|
[
"Attach a tiny mirror to the membrane, perhaps use a fleck of aluminum from a shattered CD. Bounce laser off buzzing mirror. Measure peak-to-peak excursion angle, calculate amplitude."
] |
[
"440 Hz is the A above middle C"
] |
[
"440 Hz is the A above middle C"
] |
[
"What's the difference between Cocaine and Crack Cocaine, and what's a freebase?"
] |
[
false
] |
[deleted]
|
[
"The Cocaine white powder you are familiar with exists in the salt form of Cocaine Hydrochloride (Coc-H+Cl-).",
"Crack Cocaine is a free base, or conjugate base (deprotonated) form of Cocaine. It can be synthesised from Cocaine as such: Coc-H+Cl− + NaHCO3 → Coc + H2O + CO2 + NaCl",
"Furthermore, Crack vaporizes around 90°C which is much lower than cocaine hydrochloride at 190°C. This means the crack form can be easily smoked for an almost immediate high compared to snorting. Additionally, powder Cocaine burns and degrades if smoked."
] |
[
"Crack is not a concentrated source of cocaine. You can't get any more out of what you start with, so if anything it's less. This rumor might exist because smoking crack is likely going to give someone a much more intense high than smoking cocaine, but only because free based crack won't burn the active molecule before vaporizing it. That's why people make crack in the first place. Another factor may be the criminal prosecution process. For some reason (maybe you can guess) the punishment for crack possession is much much higher than that for cocaine of the same concentration. This has lead to significantly heavier sentences on individuals apprehended with crack (generally in poorer communities) than those with cocaine."
] |
[
"A lot of sources say that crack is a concentrated form of cocaine. \nCan you explain how combining cocaine with sodium bicarbonate (baking soda) causes the cocaine to be concentrated?"
] |
[
"Is there any scientific facts that back up this \"Superbrain Yoga\" phenomenon, or is all placebo effect?"
] |
[
false
] |
Here is a web page on it with a video: Of course, I'm already skeptical given that it is on a homeopathy site, but the video is of a local Bay Area newscast, which lends at least a bit of credence to the claims. Basically, you grab your earlobes and do squats. They interviewed doctors, teachers, etc. that say the people they work with "get smarter". Thanks.
|
[
"It seems safe to say, there is no scientific research to back it up. Searching pubmed finds no articles for \"superbrain/super brain yoga\" or variations. It seems relatively accepted that exercise has a causal link with overall brain function (personally not an expert) and some ",
"meta-studies",
" seem to indicate that generic yoga may be as effective as other forms of exercise.",
"The closest thing to research from a google search is a blatant advertisement from people trying to teach/sell you this method without a hint of objectivity. See: ",
"http://www.pranichealing-mkd.com/research/Superbrain%20Y%20research.pdf",
"Its pretty painful to read, contains multiple glaring errors, and no mention of statistical errors or attempt at serious analysis. Overall, I trust the research/data about as much as a middle school lab report.",
"For example:",
"In the third year of study, up to sixty-eight students in eight classes of eighth grade students were included in the study. ",
"So how many? A student was in the study or was excluded for some reason. What does up to 68 mean?",
"Experimental Group Performing superbrain yoga\nPerformance levels | 1st marking period | 3rd Marking Period\nPercentage of Proficient Students | 3.03% | 54.55%\nAdvanced Level | 0 | 2\nProficient Level | 8 | 13\nBasic level | 9 | 6\nBelow Basic Level | 3 | 0\n",
"Many things wrong with these numbers. If N=68, the numbers should have been 12% (before 8/68) and 22% (22%) after. I have absolutely no idea where the 3.03% and 54.55% came from. It seems made up. If you check the details on ",
"PSSA",
" (which seems to be the mandatory standarized test for her Pennsylvania 8th grade students) you see there are 4 categories (Advanced/Proficient/Basic/Below Basic) so it seems safe to assume that the number of students was 20 in the 1st period, and 21 in the 3rd period. That's a major design flaw, not excluding the student who changed groups.",
"Now with N=20 (before) and 21 (after), percentage of proficient students in initially was 40% and afterwards was 71%. Thus the percentage of proficient students increased by ~77%. (You don't just subtract -- you divide and find that the final students were 177% as good as the initial student; a percentage increase of 77%).",
"On further edit, it seems that the third year numbers are exactly identical to the second year numbers and largely just miscopied. Still I didn't list the second year numbers as I didn't know what to make of \"Total\" (is it the % proficient? Then it would be 40% (8/20) not 42.86% though roughly correct for the second group, but still the number of students changed unless they meant 9/21 (which would be 42.86%); e.g., they missed one proficient student in the before group. But still this shows a 66% increase due to SBY, while previously the year 3 control had a 125% increase due to nothing. I just don't trust the 3.03% 1st marking period results for the non-control group as not being a typo of some sort.",
"Control Group Not Performing Superbrain Yoga | 1st period | 3rd period\nPercentage of Proficient Students | 20.20% | 45.378%\n",
"No further breakdown of proficient/advanced/etc given.",
"The control group improved their percentage score by about 25 percent-points or increased by ~125%. Thus the control group appears to have improved slightly more, though its not statistically significant. E.g., just two less students in the experimental group starting not proficient would fix things. Any sensible person would interpret these results as saying there's a null finding.",
"Students experiencing SBY-proficiency levels improved by 51.52% over three marking period's ",
". Students not experiencing SBY performance levels improved proficiency over three marking periods.",
"Note she just subtracted percents when saying \"levels improved by 51.52%\" and couldn't remember how to properly pluralize the word \"period\". (Again, I have typos/grammar mistakes all the time in quick reddit comments, but they would very rarely make it through in work I try publishing of a research study.)",
"This doesn't demonstrate that SBY is bullshit, just has no real research (that I could find) supporting it. It seems reasonably plausible as a potential memory aid (e.g., if you were thinking of something to remember while doing a strange action). On Colbert's interview with Joshua Foer (the Moonwalking with Einstein author talking about memory competitions) gave tips for memorizing things by associating very weird things, though his examples were thinking of family members doing sexual/violent/disgusting things to stay in memory.",
"EDIT: Also the Dr Rajesh at the bottom of the page, has credentials ",
"elsewhere",
" listed as a MDS. The only credentials of those initials that make sense is Master of Dental Surgery (not Doctoral degree, so he shouldn't be calling himself doctor).",
"Further EDIT: Ok I watched the video and downloaded the PDF (which seems based on the same study above but laid out in article form with less access to their methodology or analysis of \"data\", though it confirms that it was the PSSA test). ",
"Eugenius Ang has three papers on pubmed dealing with the ultrasounds in the brains of mice (2 in 2003, 1 in 2006). You've managed to convince 1 medical doctor, a few teachers, and one postdoc. I'm most surprised about the post-doc, but not that surprised as I've said elsewhere there are plenty of stupid people with PhDs (and the medical doctor bit doesn't surprise me the slightest -- you can find MDs who are silly enough to promote basically anything). ",
"Nothing seems to be published about the research. The p=0.0001 seems especially bizarre. (3.8 sigma when group A increased by 25% and group B increased by 15% with sample sizes of 36 students) on a standardized test that gives you results in 4 categories? ",
"To do a proper study you would need to have one equally absurd control exercise (say do a jumping jack with your hands on your head) for at least one of the control groups, and need to fully publish the data in a clear and consistent manner in a peer-reviewed journal.",
"Disclaimer: Ignore panelist badge; this isn't physics, but also doesn't appear hard to debunk."
] |
[
"You may want to try ",
"r/skeptic",
" for this; however, I would venture that there is little evidence that supports 'superbrain yoga' outside of any benefits usually associated with exercise. "
] |
[
"If you cannot clarify your answer in excruciating technical detail, don't answer at all. This is to reduce layman speculation, which is generally not helpful."
] |
[
"If I plant two genetically identical acorns will the trees look the same or is the shape of the trees random?"
] |
[
false
] |
[deleted]
|
[
"Phenotype is a combination of genes and environment. If they had ",
" the same environmental conditions and genes (also factoring in random mutations through replication), they would look the same, but even a tiny difference can add up to a lot."
] |
[
"It's even harder. Even with identical conditions, the genetically identical acorns themselves will still harbor internal differences -- as will the details of their planting sites. Since these lead to differences in the first weeks of life, they can still profoundly change the resulting tree."
] |
[
"Lots and lots of the 'individual' plants you see day to day are clones of one another -- that is they share the same dna. And they grow at different angles and rates and with different branching patterns. So, neither, really. Which makes them unlike animals. They do this because plants are modular, with different structures being relatively independent, and so have more plasticity in form instead of having a set body plan. Instead they grow in response to their environment -- leaves and stems will grow toward light and roots will grow toward water and nutrients."
] |
[
"Does the holographic principle imply that the maximum information (in bits) contained within a spherical region of space must be less than or equal to its surface area in Planck length squares?"
] |
[
false
] |
I recall reading something to that effect somewhere, but the doesn't explicitly say that's the case, just that the maximum information is proportional to the surface area.
|
[
"Yes it does imply exactly that (or if not exactly that, then it's certainly proportional to the surface area, not the volume) and here's why.",
"Thermodynamics' second law says that entropy in a closed system must always increase. But what of black holes? Is it possible that they somehow could be used to violate the 2nd law? Physicists pondered this, they thought, what would happen if I took something that had very very high entropy (say a container filled with diffuse gas) and threw it into a black hole? If the container had higher than average entropy, the net entropy in the universe would decrease, no?",
"The answer, according to the holographic principle, is that black holes must be the fundamentally maximal entropy a given region can have. Intuitively, this makes sense, since no matter how one would rearrange the microstates inside the black hole, the external appearance would never change (since it's shielded by the event horizon). Given that black holes have maximum entropy, physicists figured out that the total amount of entropy of a black hole is equal to the number of Planck squares it would take to cover its surface area. This has deep implications.",
"Since black holes have maximum possible entropy, and since the total entropy of a black hole is equal to the number of Planck squares it takes to cover it, then the Planck square ",
" be fundamentally the smallest region of space that something can occur within. The reason for this, is logically that if black holes have max entropy, and if it takes a given number of Planck squares to surround this max entropy space, then each Planck square on the black hole's region must be entropy saturated. Since it contains the max number of entropy, principally ",
" can occur in a region smaller than a Planck square, since ",
" action that could occur within the Planck square could increase the region's entropy (but we've already said that our Planck squares contain max entropy).",
"Brian Greene explains it a little bit better than I do in his Fabric of the Cosmos book if you have access to it.",
"Oh, I didn't read your entire question. :) Yea, not sure if it's exactly less than or equal to its surface area, or just proportional, but the important part is that it's not proportional to its volume, but rather its surface area. I was going to delete all that stuff I typed up when I realized I misread your question, but I'll leave it just because it's pretty interesting :)"
] |
[
"Just going by what I read in the Wikipedia article, doesn't it mention it as at least 4 times the area, given Hawkings constant of proportionality ?"
] |
[
"Thanks for not deleting it, although I know nothing about physics I enjoyed reading this."
] |
[
"How can light travel in a vacuum?"
] |
[
false
] | null |
[
"The electromagnetic field exists everywhere, including in the vacuum of space (or any other vacuum). If there's no light, or EM radiation, at a particular location then the field has no energy there, and basically sits still. If there is light, this manifests itself as waves through the field. Since the field exists in vacuums too, these waves can travel through vacuums as well, uninhibited. "
] |
[
"It depends on the wave. Waves need a medium to travel through. With light, that medium is the EM field. Since the EM field is present even in a vacuum, yes, the waves can travel through a vacuum. ",
"Something like sound waves travel through air though. Since, pretty much by definition, there's no air in a vacuum, sound waves have no medium to travel through. So, unlike light, they can't travel through a vacuum. "
] |
[
"It depends on the wave. Waves need a medium to travel through. With light, that medium is the EM field. Since the EM field is present even in a vacuum, yes, the waves can travel through a vacuum. ",
"Something like sound waves travel through air though. Since, pretty much by definition, there's no air in a vacuum, sound waves have no medium to travel through. So, unlike light, they can't travel through a vacuum. "
] |
[
"Could any plants grow anywhere on Mars?"
] |
[
false
] |
[deleted]
|
[
"It would be difficult for plants that reproduce sexually to spread, but simple plants like algae, and even some colony organisms like lichens might find suitable conditions in isolated locations.",
"As for flowers and trees, the conditions on Mars are extremely dehydrating. They would quickly freeze and lose their water, so even if something like an alpine flower or a pine tree were prepared by wintering it beforehand, exposure to the Martian surface conditions would do it in.",
"As for compatibility with the soil, there are no bacteria or fungi to cycle carbon or nitrogen, and peroxides/perchlorates in the soil would make it deadly for plant tissues.",
"It's not a garden, nor will it be one soon. "
] |
[
"The main problem would probably be atmospheric pressure. The place on Mars with the densest atmosphere has about 1.2% the pressure of Earth's surface. I'm not sure what that would do to a plant but given that surface water isn't stable at that pressure, and multicellular plants need to do a certain amount of evapotranspiration anyway, I expect all the water would get sucked out of it pretty quickly."
] |
[
"It is believed some extremophiles could adapt to Mars and live comfortably. They've been tested in simulated conditions in labs. It's something being considered by terraformers. As far as we know it would be essential for setting up a carbon cycle. The problem we run into is what would happen to any native life we might encounter.",
"Before we seed Mars with extremophiles we need to know, as close as possible, what is already there. If we were to destroy an entire, novel tree of life the cost to our future as a species could be incalculable.",
"Every alien gene has the potential to do something terrestrial genes don't, or can't. Until we figure out an alien biome's potential, it is in our own best interest to keep it as pristine as possible.",
"This may be the great debate from 2030 on: how to proceed if we find native life on Mars, Europa, Titan, anywhere else in the solar system."
] |
[
"Why is mad cow/CJD transmissible to humans, but deer chronic wasting disease and scrapie is not?"
] |
[
false
] | null |
[
"The protein responsible for mad cow disease is, due to its structure, able to bind to some forms of the natural human prion protein and catalyse its conversion to the pathogenic form. Proteins responsible for other prion diseases in animals don't have the same affinity for human prion proteins. Answering in terms of \"why? is difficult. It depends what you mean by \"why?\" There's no fundamental reason why this is the case, it just sort of ",
". It's a mistake to think of things like this in terms of a goal or reason, nature at the fundamental level of biochemical interactions doesn't really have a goal.",
"Its like how we can catch some viruses from animals but not others. Some viruses are, due to the structure of their surface proteins, able to interact with host proteins across species, some are more limited. There's a whole thing about selective pressure to jump species, at least where viruses are concerned, but then you're starting to go off on tangents. Interesting tangents, sure, but it still only partially answers a \"why\" question and more \"whys\" will be forthcoming.",
"Kind of an unsatisfying answer, I accept, but its difficult to answer a \"why\" question like this. Beyond the fact that the structures happen to be compatible there's no real \"reason\".",
"There are some human variants of the natural prion protein that don't interact so well with the agent that causes mad cow disease and individuals who are homozygous for these variants appear less susceptible to acquiring mad cow disease. Most of the people who seem to have developed nvCJD from eating infected beef appear to share the same genetic variant of the human prion protein, while other variants are underrepresented among patients."
] |
[
"Most “why” questions are actually “how” questions in disguise. The difference is in adopting the intentional stance instead of the design or physical stances when thinking about the problem."
] |
[
"It’s likely cows eating scrapie infected meat led to prion disease in the cattle. So scrapie —> bovine spongiform encephalopathy —> vCJD in people. So almost like an indirect affinity?"
] |
[
"What is the difference between low-end and high-end vodka, chemically speaking?"
] |
[
false
] |
[deleted]
|
[
"Ethanol is ethanol. The source won't change the taste of the ethanol itself, just the impurities."
] |
[
"Here",
" is something that sums it up a little better than I can, but there are basically two parts to what makes a \"high end\" vodka. Part one being the recipe/method in which it is brewed, part 2 being the manner/number of times in which it is distilled. The more times it is distilled the closer it becomes to pure."
] |
[
"So when I mixed lab grade ethanol with lab grade water it was the best vodka ever created?"
] |
[
"Why is pre-fission uranium relatively harmless to humans but spent nuclear fuel must be locked away for hundreds of years?"
] |
[
false
] |
[deleted]
|
[
"Think about how nuclear fission works. You take heavy atoms and split them. The original uranium (U-235/U-238) used in a typical water reactor is a relatively weak alpha emitter overall. ",
"When you split uranium, you get two or three smaller fission products. There is a distribution of products that you can get (",
"https://en.wikipedia.org/wiki/Fission_product_yield",
"). But these smaller atoms are often formed with energy distribution states and neutron to proton ratios that are not along the \"line of stability\" and can be extremely radioactive. Additionally these fission products are all contained in the fuel rods, essentially being concentrated. ",
"The fission products are what tend to be dangerously radioactive. If you could separate the remaining U238/235 from the spent fuel, those portions are still very weak alpha emitters only. It's some of the new stuff that was created in the process that has strong radiation emissions. "
] |
[
"To add a bit more to this, it's not just that the smaller atoms are less stable and more radioactive, it's that their modes of radioactive decay involve the release of much more beta and gamma rays than uranium gives off. Those beta and gamma rays require FAR more shielding than alpha rays require.",
"The storage methods for used nuclear fuel rods have to take both the shielding against beta and gamma rays into account, as well as the other issue with such radioactive material: heat generation. If you've seen or read ",
", you've got the basics: radioactive decay can give off heat. Used nuclear fuel rods have so much radioactive material concentrated in them that they require constant, direct cooling for ",
" before they can even be stored in just the air. Without that cooling, the rods can melt themselves with their own heat and risk releasing all that highly radioactive material into the environment.",
"Edit: I wanted to add that there is a third issue with the products of uranium fission: they can be more chemically toxic than unused uranium fuel is. The chemical behavior of some fission products makes them more toxic, or makes them bioaccumulate in the body in specific areas (and they will then radioactively decay there and expose those specific areas, too)."
] |
[
"Once the uranium nuclei have undergone fission, they are no longer uranium nuclei. Fission reactions produce many lighter nuclides, many of which will be unstable.",
"Spent nuclear fuel contains some of these radioactive fission products. They need to be stored for a long time so that these radioactive fission products can decay away."
] |
[
"System Neuroscientists: What are your thoughts on people with magnetic implants who claim to \"sense\" magnetic fields?"
] |
[
false
] |
Related to this AMA: Maybe I'm missing something, but I cannot conceptualize on a physiological level what it is about a subdural magnet that generates transduction in the mechanoreceptors. Any peripheral nervous system neurophysiologists want to chime in here?
|
[
"I am not an electrical engineer or a physicist, so take what I say with a grain of salt.",
"We know that mechanoreceptors respond to pressure and vibration. This means that if you have a magnet in your fingertip (subdermal, so underneath the mechanoreceptors in your skin) and you approach another magnet, it makes sense that you will feel the pressure from receptors directly \"above\" the magnet as those cells get squeezed, and from mechanoreceptors around the magnet, as those cells get stretched.",
"In a changing magnetic field (like that observed in an AC line) the same forces and sensations are at play, except now you have the ability to sense vibrations as well. ",
"I'm assuming you know about the different types of mechanoreceptors, so I won't go into that. I think it basically comes down to the fact that electromagnetic fields are generated by a number of electrical devices and are capable of imparting kinetic energy to the subdermal magnets. This kinetic energy produces forces that are transmitted to the mechanoreceptors in the skin, which are already specially adapted for sensing pressure and vibration."
] |
[
"So then it is the vibration of the magnet that compresses/extends the cellular membrane of the mechanoreceptors in order for transduction to occur. I suppose that makes sense...except that the percept generated from, say, shifting magnetic fields generated from an AC current would do nothing but vibrate the magnets at a certain frequency, and with lines at 50 or 60Hz the Meissner corpuscles could pick up on that level of sensitivity, and I can't imagine the level of stimulation provided by the magnets could actually generate the types of perception people are claiming, for lack of a better run-on sentence.",
"I'm not calling bullshit here, I just wanted to understand the physiology of it all. I'm a central nervous system guy, and if these implant folks could actually detect the types of changes they claim to be, there must be some wild neuroplastisicity going on at the cortical level. "
] |
[
"I think they are maybe using overly generous language when they are discussing the perception provided by these magnets. I don't think there is any neuroplasticity or cortical re-wiring going on, I think its just that they are capable of sensing these vibrations in their fingertips. It makes sense to me that you could probe a magnetic field with these magnets and get a sense for its shape and strength."
] |
[
"Why is Xenon used to power ion thrusters instead of other noble gases?"
] |
[
false
] | null |
[
" It's the heaviest noble gas. It is also the easiest to ionize. ",
"The fact that it is the easiest to ionize is pretty easy to understand. You have to spend less energy turning the gas into plasma which is good for the efficiency.",
"So now the question is why would you want a heavier particle? People who are used to classical rocket engines know that a lighter particle can be accelerated to higher velocity than a heavier one with the same energy. And faster particles mean that you get a higher specific impulse (ie a lower consumption of propellant), which is what are looking for in general. ",
"The issue is that you only have a limited amount of electrical power available on board a spacecraft. And the electrical power is directly converted into the energy of the ion beam. You can write that the electrical power ",
"P",
"is proportional to thrust ",
"T",
", ",
"Isp",
" and thruster energy efficiency ",
"n",
":",
"P ~ T*Isp/n\n",
"So for a given power and efficiency, if you increase the Isp you have to reduce the thrust. This can be also seen in this ",
"graph",
". So if you choose a gas that gives you a lot of Isp you get very little thrust. That means that not only you take longer to perform you maneuver (orbit change or whatever) but you also have to take a less optimal trajectory.",
"So then the question is why don't we increase the power on board? If we just put more solar panels we could get both high thrust and high specific impulse! Then the issue is that solar panels and power processing units add mass! This reduces the acceleration for a given thrust and/or forces you to reduce your payload. Taking into account the mass of the power system and a set transit time we can actually rewrite the rocket equation:",
"M_payload / M_total = exp(-dV/Ve) - 2C*Ve/(n*dt)*(1-exp(-dV/Ve)\n",
"With ",
"M_payload / M_total",
" the ratio of payload mass over total mass including propellant and power system. ",
"dV",
" the delta V of the maneuver, ",
"dt",
" the time it takes to makes the maneuver, ",
"Ve",
" the exhaust velocity (basically the ",
"Isp * g",
") and ",
"C",
" the mass in kg per kW of output power of the electrical system. Taking realistic number for current technologies and a transfer from GTO to GEO orbit (what most commercial satellites with ion thrusters do) we can calculate the mass ration depending on the Isp and the transit time. This gives you this ",
"graph",
". ",
"Here you can see that for transit times between 4 to 8 months you actually want only 1000 to 2000s of Isp in order to get enough thrust and maximum payload mass to destination. This Isp range correspond pretty well with a xenon fed Hall thruster working at reasonable discharge voltages. Lighter gases gives you too much Isp!",
"Of course this is for a transfer to geostationary orbit with a commercial satellite that has to generate revenue as fast as possible. For interplanetary missions where the delta V requirements are higher and you are not as much in a hurry you might want higher Isp. But so far only 4 missions have used ion thrusters to do that so there is no real need to develop entire new systems with new gases that are harder to ionize."
] |
[
"I might have missed it as I’m reading on a phone, but another huge reason the heavier mass of Xenon relative to other noble gasses is that the larger atomic mass makes it easier to store a larger mass of propellant.",
"The pressure exerted by an ideal gas is P=nRT/V - so a mole of helium stored in any given volume will exert the same pressure on the container as a mole of Xenon, that has about 32.5 times as much mass.",
"Taking up an equivalent mass in Helium would either require many more storage tanks or much more robust tanks, either of which would greatly add to the mass of the spacecraft that needs to be accelerated."
] |
[
"You are totally right. As far as I know xenon is stored as a supercritical fluid around 150bars. So the ideal gas law doesn't quite work. I just checked on wolframalpah and it gives you about 2 kg/l for xenon. In the same conditions krypton is around 0.73 kg/l, argon 0.27 kg/l and helium 0.023 kg/l."
] |
[
"Why do muscles fatigue in a static pose if no work is being done?"
] |
[
false
] |
I've got ideas about why this might be the case, but I wondered if anybody could explain this to me. If I take a plank of wood, shove it in a wall such that it acts as a cantilever, and hang a weight off the end, I can be pretty sure that it will stay there indefinitely. Nothing is moving, hence no work is being done (beyond the initial deflection). If I take a bag of heavy stuff and hold it out to one side, I'll be able to hold it for a while, but eventually my arm will give up. What, biologically, is it about muscles that doesn't allow them to hold a stress for large periods if nothing is moving. Why is my body getting exhausted when there is no physical work being done? Am I misunderstanding something fundamental about the situation?
|
[
"The plank of wood is in a stable configuration. Although while acting as a cantilever there is tension and therefore stress on the bonds between lignin fibers and other structural aspects of the wood, there is no net input of energy to keep it rigid.",
"Your muscles require a net input of energy to maintain even a static contracted state. There are action potentials from motoneurons, recruitment of motor units, action of myosin and actin, and so on. If there were some mechanism which could simply ",
" your arm muscle into a certain place, it would indeed require no energy input or work. But there's no organic mechanism like that.",
"So while from a certain perspective there is no real work done on the weight, you are expending energy constantly to maintain the contraction of the muscle."
] |
[
"great answer. Just to add on as a side note, one of the notable differences between skeletal muscle and smooth muscle, such as that of the gastrointestinal tract and blood vessels, is that it is capable of \"locking\" into place and not require any more energy input. This is one of the aspects which makes smooth muscle more energy efficient than skeletal or cardiac muscle. "
] |
[
"Hm, I thought that in the contraction of the actin-myosin filaments, the binding of ATP caused the detachment of the filaments and that the depletion of ATP would then result in the inability to detach, such as what we observe in rigor mortis.",
"Would i be wrong to say that this is related to the fact that when we keep it 'stable', we're not actually fixing it there, but instead forcing the rapid contraction and release of multiple individual fibers?"
] |
[
"Why isn't garbage utilized more as a source of power?"
] |
[
false
] | null |
[
"Sweden is doing this, but was so efficient at reducing trash production, that they have had to import garbage, as reported ",
"here",
". Oslo has had ",
"this problem",
" as well, as have other places in northern Europe."
] |
[
"Because fossil fuel corporations control decisions involving the energy industry"
] |
[
"In short, economics. Trash is not free. There is a processing cost and collection costs. As a result you have to look at whether your cost per therm of energy is higher or lower than a different fuel source. As a simple comparison, natural gas (by my rough number crunching) has an energy density nearly 4,000 times that of a big Mac (my comparison trash of choice.). Natural gas costs about $5 per therm. That means that your trash has to cost you less than a tenth of a cent per therm in order to be economically competitive.",
"Dealing with trash is an important project for our society, but using it for energy is an incredibly inefficient source of energy and thus an incredibly inefficient way to deal with it."
] |
[
"Is lava flow laminar?"
] |
[
false
] |
I came across this video, and the question popped in my mind, like a giant, red, burning and deadly pimple:
|
[
"In theory, it can be either, but what we see in Nature on Earth today is ",
" very often laminar due to a relatively high viscosity (e.g., >1 Pa-s), low speed (e.g., 1 m/s) and small lateral scale (e.g., 1 m). These combine to give a ",
"Reynolds number",
" on the order of a thousand and often far less; the transition to turbulent flow occurs for Reynolds numbers of approximately several thousand. Try plugging in the numbers for the lava flow you have in mind!",
"Edit: ",
"recently posted"
] |
[
"This is counter to what is discussed in literature on the fluid dynamics of lava flows, e.g., the rather comprehensive review by ",
"Griffiths, 2000",
" which discusses that lava flows can be both laminar or turbulent (and both are observed) and the state depends critically on the both the composition of the lava but also the eruptive style, etc. Modeling of lava flows emphasizes that they are often laminar, but not exclusively, and that turbulent flow is expected for some ranges of real world conditions (e.g., ",
"Filippucci et al., 2010",
")."
] |
[
"Turbulence is dependant on the Reynolds number (Re = rho * V * L / mu ) which is the ratio of inertial and viscous forces.",
"The higher the Re, the more turbulent the flow is, so velocity definitely plays it's part."
] |
[
"How can we determine what dinosaurs looked like based just on the bones?"
] |
[
false
] |
I got into an argument with my friend who claimed that it was just guessing, and i don't know nearly enough about the process to make a valid argument against him. So basically the question is, how can we determine the skin type, organs, etc just from the bone structure? What process is used to determine these things?
|
[
"Well, \"just\" from bones we have gotten a lot of stuff wrong. If you go look through some of your \"old\" (like 90s) textbooks on dinos, you can see that how they look over time has definitely evolved. People probably have even put bones of dead dinos found near each other together, giving some really interesting results...",
"For example, T-rex is a great illustration where you have an dino go from nearly upright to more \"horizontal\". So we appear to have gotten it wrong at least according to how our understanding og their physiology changed. ",
"Generally people look at the \"living fossils\" and analogous animals for muscle structure and we can basically figure out a lot from what's around now. It \"should\" have a lot of similar features (ie. a brain, eyes, stomach, etc)",
"We have also found samples of soft tissue of dinosaurs ",
"Linky",
". \nThat's pretty cool (and quite rare). I don't know if we have other samples of say a dino with all the imprints of the organs (though there appears to be ",
"only one",
"), but a lot is conjecture."
] |
[
"Thank you for the reply, that clears up my confusion.",
"Unfortunately, you very much supported my friends argument that it is forever changing, so we don't really know for sure."
] |
[
"While a large deal of these reconstructions is quite speculative, some basic assumptions can be made based off of studying the correlation between morphology and bone structure in living organisms, and extrapolating from that. "
] |
[
"Do some materials cause precipitation of water at a higher rate than others (such as steel over glass)?"
] |
[
false
] |
A follow up question: is precipitation solely dependent on temperature differences? Thank you!
|
[
"Precipitation is basically rain, that happens because of water condensation in the atmosphere. There is hardly any glass or steel floating in the atmosphere so I am guessing you meant condensation. Which is the change of phase from gas to liquid. Some materials do promote condensation, and the brief following explanation is not only true for water but for any other gas. It is also true for the phase change from liquid to solid. ",
"The simplest case is the one you describe, the phase change from vapor to liquid. Imagine there is only vapor, not in contact with any solid. The first thing to establish is that at any given moment, there are vapor molecules (or atoms) becoming liquid. This process is called ",
", however, they have the same probability to evaporate again. That is a system in ",
". So for the phase change to occur you need to add energy (pressure, temperature, etc) to the system, this will take it out of equilibrium and cause any nucleus to ",
". Why is this energy needed? You are creating a new phase with a new surface, and it has to overcome the surface tension generated. When any nucleus reach certain size, it will continue to grow spontaneously. That is the simplest case.",
"Now what happens when there is a solid surface? This surface has a property called excess surface energy, that is the energy needed to create it. You could also see it as an atom or molecule not as bonded as the bulk ones. This causes an extra influx of energy into the system, and therefore some stable nuclei form on the surface. How important is the effect on the phase change? Depends on the interaction of both the gas/liquid and the solid. That interaction can be very different even if you are using the same material, depending on the geometry of the surface, its composition and even partial charge. ",
"This of course applied to water. The geometry of the surface could be interpreted as its roughness. So rough glass can help water condensation while polished metal won't. Then rough metal will help condensation and smooth glass won't. Then there is the fact that water is a polar molecule, so polar surfaces such as some organic materials will help condensation while non-polar materials such as teflon won't help it. ",
"In conclusion, it usually depends more on the physical nature of the surface rather than its chemical properties.",
"References:\n",
"Instrumental Methods in Electrochemistry, Ch. 9",
"Electrocrystallization. Fundamentals of Nucleation and Growth"
] |
[
"This is a great answer for describing the dynamics of two phase systems. However, I think it's missing an important part. In general metals are much better thermal conductors than any other class of materials. Metal vessels also tend to have thinner walls due to their ductility as compared to most ceramics and glasses. ",
"To use the example of a cup, given equal internal fluid temperatures, the outer surface of the metal cup will be cooler (assuming the inner fluid has a sub ambient temperature) than the glass one. This means that not only will the equilibrium be more in favor of condensation, but the initial rate of change of the system will also be faster in the metal case. All of that is assuming that nucleation is not a significant barrier. Usually unless the surface is created to be smooth it's not. "
] |
[
"Your last remark made me remember the phenomenom of supercooling, where the gas/liquid is placed below its condensation/solidification temperature but the phase change does not occur because there is not a favorable place for the first nucleus to appear. So for OP's follow up question, phase change is definitely not only dependent on temperature. ",
"Bonus: This ",
"video",
" of supercooled water."
] |
[
"If the Kuiper Belt and Oort Cloud contains billions of cosmic rocks, how do we know that probes such as the Voyager won't hit anything?"
] |
[
false
] |
I know the density of the Oort Cloud probably isn't that much, but isn't there still a pretty substantial probability that Voyager I will hit an asteroid or something?
|
[
"We don't know that the probes will be safe! This is a lesser problem than it might appear, however, because space is really, ",
" big. The popular image of a maze of enormous, moving rocks is pure movie fiction; while the density of objects is much higher than average, space is very empty so the average is extremely low. It would be extremely unlikely for a probe to pass near an object, much less hit I ."
] |
[
"No. There wasn't even much chance going through the asteroid belt.",
"\nIf you were on an asteroid in the asteroid belt, it would be hard to see any other asteroids without at least binoculars. In the kuiper belt and especially the Oort cloud, things are even much, much farther apart."
] |
[
"... object, much less hit I .",
"You didn't get to finish your sentence. It would be funny if you typed that from a spaceship that was hit by an asteroid."
] |
[
"What's your favorite unexplained natural phenomena?"
] |
[
false
] | null |
[
"Is there a way I can transfer the post there from mobile?"
] |
[
"Damn. Thanks anyways, kind redditor. :)"
] |
[
"Will do!"
] |
[
"Why does atomic radius decrease across the period?"
] |
[
false
] |
[deleted]
|
[
"I think the mistake you're making is that you're considering \"stronger attraction\" to be determined by the number of protons, when you should be thinking about charge ",
". Protons are held together by nuclear forces, which are much stronger than electromagnetic forces, so more protons means greater charge density, which means greater force. Thus in order for the electrons to cancel that resulting force, they must be more densely packed."
] |
[
"It's not about if the numbers of protons and electrons are equal.",
"It's about how attracted a given electron is to the nucleus. ",
"So for the outer electrons (which will determind the atomic radius) they are attracted to the nucleus by it's protons but repelled by the other electrons which partially cancle out (or shield) the positive charge at the nucleus. ",
"Electrons come in shells which you can think of as being increasingly far from the nucleus with each period you go down adding another shell.",
"When you're moving across a period you're adding protons to the nucleus so the outer electrons are more attacted to it and this is stronger than the increased shielding that happens when you add electrons to the same shell.",
"Where as when you add an aditional shell by going down the period atomic radius increases because the additional shielding from having another shell between the outer electrons and the nucleus is more significant than there being additional electrons at the nucleus."
] |
[
"to piggyback on this comment, You can get more information if you Google: \"why is osmium the densest element?\""
] |
[
"Extra Dimensions in String Theory"
] |
[
false
] |
So, there are a couple extra dimensions according to string theory that are just too "small" to see. I've seen pictures of the projections into 3-space of Calabi-Yau manifolds all over the place and just assumed that these little manifolds are peppered across our universe. Then I got to wondering what would happen if you were in a space between these little manifolds and realized that what I had envisioned was a bunch of separate dimensions contained within our 3-space, which I realized is total bull. So my question is: are these extra dimensions simply periodic spaces orthogonal to our regular 3 dimensions whose period is an extremely short distance? Like if you were to move through one of these dimensions you would travel however far that dimension's period is and end up back at the place you began while remaining at the same point in 3-space the whole time? Don't be afraid to get somewhat technical, I'm a third year physics undergrad.
|
[
"You should read about ",
"fiber bundles",
". The total 10-dimensional space is a fiber bundle, where the base space is 4-dimensional space-time, and the fiber is a 6-dimensional Calabi-Yau manifold. ",
"Just think of a torus: That is the total space of an S",
" bundle over S",
" Imagine the circle going through the center of the torus as your base space (we need not consider it as part of the total space--fiber bundles do not need to have a \"section\"). For each point along that big circle, there is a little circle that goes around the \"tube\" of the torus. (This is a ",
" fiber bundle, because in fact it's just the cartesian product of the base with the fiber. The Klein bottle is a ",
" S",
" bundle over S",
"Now you can think about your question, \"what would happen if I were in a space between the circles in the torus\"? You can see how it doesn't really make sense."
] |
[
"hmm interesting. I don't have much of a topology background; do you know of any resources that could give me an introductory background?"
] |
[
"Well, the short answer is to ask your adviser or some other professor who knows your background. It will probably be hard to read any proper introduction to fiber bundles, because a fair bit of background will be assumed (even if it's not strictly necessary).",
"To just get a basic sense of what's going on, you will want to know something about topology. Any basic introduction to topology will discuss products. Then you can already understand trivial fiber bundles, because those are just the product of the base B with the fiber F, along with the projection to B. That at least will give you a sense of how you can have a copy of F for every point of B. To get a sense of how things are more complicated in general, then you can think about a cylinder as a trivial fiber bundle over the circle, and then think about how the Mobius strip--which is not just a product--is similar, and how it is different.",
"To be in a good position to study fiber bundles, you would also want to study manifolds. There are a lot of motivating constructions and examples there, and the base and fiber are often assumed to be manifolds.",
"I should also add that fiber bundles are ubiquitous in math and physics--it's by no means just a string theory thing. Vector fields and more general tensors are sections of a vector bundle, which is a special kind of fiber bundle (the fibers are vector spaces, and they are \"glued together linearly\"). Gauge theories (AFAIK) are formulated in terms of a fiber bundle with something called a connection."
] |
[
"How does pyroelectricity work? In what real world applications can it be found?"
] |
[
false
] |
I've briefly read about pyro and piezoelectricity - I had trouble finding understandable applications. I gather it can be used to induce nuclear fusion. Moreover, at what temperature do pyroelectric crystals generate voltage? How feasible is their use in more common applications? Thanks in advance!
|
[
"I don't know much about pyroelectrics, but if you're interested in the general concept (thermal to electrical energy conversion), I'd suggest thermoelectrics as a much more robust field to explore -- there are already many applications of this effect in use today, and quite a bit of ongoing research into finding new, more efficient thermoelectric materials. "
] |
[
"For power generation, thermoelectric materials are limited by both the carnot efficiency ( (T_hot - T_cold) / (T_hot) ) and the material properties, which are quantified in terms of the \"figure of merit\" ZT. The material properties are generally the biggest limiting factor in the overall efficiency -- optimized TE generators can harness maybe 5-10% of the heat energy available, depending on a lot of factors. This field is relatively old but has only recently really expanded in the last 20 years or so. It will never overtake other energy sources as a ",
" way of generating useful energy, but it definitely has a place in boosting the efficiency of many existing processes. "
] |
[
"Ah, this is fascinating stuff. One of the motivations for asking this particular question was an interest in its potential use for energy recycling. I saw from the Wiki that power plants use thermoelectric generators for this purpose. I noticed \"low efficiency\" thrown around quite a bit - is this because of a lack of effective materials or does the process have inherently low viability to begin with?"
] |
[
"Why do depleted batteries bounce more than fully charged batteries?"
] |
[
false
] |
As seen in a recent gif on depleted batteries will bounce higher, but why?
|
[
"The chemicals inside the battery change state and different states react different to forces.",
"It's similar to raw/cooked eggs. The rotate VERY different. You can try it out. Rotate a raw egg (or try it) and then cook it and rotate it again. "
] |
[
"I asked this same question too! Check out ",
"this",
" comment. He or she linked a youtube video that explains it and is worth watching. They also linked the 2 half cells redox reactions and a diagram of the inner cylinder. Anyways a battery contains two half cells. Water is the product of the first half reaction, and it's also the reactant in the second half reaction. As the battery discharges water is produced in the first cell and then consumed in the second half cell. How much charge the battery has dictates the density of the 2 half cells and the battery's structural characteristics. I hope that helps!"
] |
[
"To add on to this: interestingly the less fresh an egg is, ",
"the more boyount it is in water."
] |
[
"If your main utility company were to temporarily shut down, how much time would you have between shut down and blackout at your home?"
] |
[
false
] |
I'm wondering if there's any "residual electricity" in the wires that could be used in this time and how substantial it is
|
[
"A few milliseconds. For a sole generator supplying you. There would be 1/2 to 1 cycle of energy (5-20ms) left as inductive or capacitive storage in the lines. This is actually a problem with opening a switch on the main line of a utility. That residual energy can cause voltage surges. But typically any particular generator going off line, simply throws that part of supported load to the remaining generators on the grid. So a shutdown may be accompanied by ",
"brown outs",
", then final shut down. That can be minutes to hours."
] |
[
"Ah okay, I knew electricity travels quickly and that there wasn't much storage along the line.. but I was wondering if the lines were sooo long that you might still be able to draw for a whole second or two before you were \"caught up\""
] |
[
"This is the answer I was looking for, thanks!!\nI thought about the \"delay\" like the concept of Light years; where the electricity has already left the source and the user gets to experience that electricity for a couple milliseconds before it ends"
] |
[
"Heisenberg Uncertainty Question"
] |
[
false
] |
[deleted]
|
[
"Begin with the uncertainty principle",
"Δ(x) Δ(p) > h/2π",
"So let's divide both sides by Δ(x) for reasons which will be soon obvious",
"Δ(p) > h/(2πΔ(x))",
"So let's just say Δ(x) is just equal to aλ where a is however close to 1 you want to be and say it's on the order of the DeBroglie wavelength. Because you said the uncertainty of position is on the order of the DeBroglie wavelength.",
"The DeBroglie wavelength is given to be:",
"λ = h/p. ",
"This brings us to Δp > h/(2πΔx) or Δ(p) > h/2πaλ.\nSubstituting in for λ we get Δ(p) > h/[2πa(h/p)]\nAfter simplifying we get Δ(p) > p/2πa",
"Assuming aλ is within half an order of magnitude of the DeBroglie wavelength, you get an uncertainty of momentum that is more or less within an order of magnitude of p."
] |
[
"Okay so I'll try and teach the math: ",
"Δ(x) is the uncertainty in x. One way to think of it is a change in x. \nLike how average velocity is Δ(x)/Δ(t). Which is your change in position over your change in time.",
"Defining some variables: x is just position of a particle. p is just the momentum of a particle.",
"So the uncertainties of these two quantities when multiply together must be greater than h/2pi where h is something very important in QM known as \"Planck's constant\" that governs the scope of a lot of quantum mechanical phenomena.",
"λ = h/p is just an equation relating a particles momentum to it's DeBroglie wavelength which follows from wave-particle duality. I can go more into that if you need to.",
"As for setting Δ(x) = aλ. that just came from the uncertainty of the position being \"on the order of\" or around the DeBroglie wavelength.",
"All the other math is just basic elementary and middle school arithmetic I believe.",
"If anything is still unclear I can answer. "
] |
[
"That's the craziest looking math I've seen so far on AskScience. I must learn what it means."
] |
[
"Over time, does a satellite naturally attain synchronous rotation? Pics in question to explain what I mean."
] |
[
false
] |
There are two scenarios shown . Does the satellite, with no initial rotation, naturally start to rotate as in image 2? Or does it maintain attitude as in 1, until otherwise acted on?
|
[
"In terms of natural satellites, yes. The moon and earth share this relationship. It's called 'tidal locking'."
] |
[
"Artificial satellites would do it too, given sufficient time."
] |
[
"AskScience: Why do we only see one side of the moon?"
] |
[
"Does the Milky Way Galaxy orbit something?"
] |
[
false
] |
Earth orbits the Sun, the Sun orbits the supermassive black hole at the center of the galaxy. Does the galaxy orbit anything? I realize that since the Universe is infinite and expanding then everything is technically at the 'center', but do all galaxies orbit some common center of gravity?
|
[
"Our galaxy does interact with other galaxies in our ",
"local group",
" to a certain extent. For the most part, it appears that the galaxies in the local group simply orbit a center mass for the entire cluster, but even the local group itself orbits a center mass for our local supercluster."
] |
[
"Again you are confused as to the definition of infinity. Infinity is not a limit. \"Infinity\" is a concept designed by mathematicians to explain something that would go on literally for the rest of eternity. ",
"No matter what number you count to, there is always one higher, so it goes on for as long as you can keep counting, and beyond. ",
"Now think of two distant particles in space. The distance in between two very far particles is a finite quantity, one second later, they are even further apart. One second later, even further apart. ",
"If your question is 'Why is the infinite universe expanding?' then I don't know the answer. My layman answer would be momentum from the Big Bang. Even this answer is probably too simplified to be correct. "
] |
[
"Well, it might not be. But it is at least 250 times the Hubble volume..."
] |
[
"In a magnetic hard disk, how are the servos that position the read/write head so accurate?"
] |
[
false
] |
With the data tracks as narrow as they are (on the order of a hundred nanometers or so wide), these servos must be incredibly precise. How do they achieve that level of precision?
|
[
"The tracks themselves have embedded information called servo codes that act like a map. The heads are moved by a voice coil motor and can read these codes and see how far they are from where they need to be and then adjust accordingly.\nCheck ",
"this",
" out."
] |
[
"It is a mixture of a few things.",
"Direct position feedback. As others have said, before you ever saw the hard drive there are servo wedges written to the disc. There is a big written in signal marking that it is the start of a servo wedge, then a physical position reference (This is Track Position X) as well as an analog signal allows the read head to understand how far away from its intended position it is. These wedges happen a bunch of times across the disc, so the head has feedback >25,000 times per second. After this servo wedge the data portion starts. After data portion another servo wedge and so on.",
"Feed Forward information. There are lots of sensors on the hard drive that feed forward information into the control system. This could be information like external vibration, current temperature, and many other signals. This information is used in the start of the plant to understand the amplification that should be applied to the feedback.",
"There is also the hardware that allows such fine control. ",
"Main Voice Coil motor. This is the main way to move the head, and every drive must calibrate itself to know exactly how much current will cause how much force onto the system. As the system knows its own inertia this allows you to calculate how much this will move the head, and how fast.",
"Secondary Actuator. Many high performance hard drives have a secondary actuator on the very end of the servo arm. This secondary actuator uses a Peizo Electric material to move the read/write head at an incredible precision and very high frequency. However the range is very small (micro inches)",
"Z-axis servo. There is also control of the head height above the disc. This is on the order of angstroms to nano-meters. Is is also controlled via a mixture of hardware design (the wing that flys above the disc) and firmware control (distorting the head to move the head up and down)",
"For a more indepth review of hardware you can take a look at ",
"Dual Stage Servo Control"
] |
[
"And then on top of that equalization and error correction are applied to the electrical signal coming from the read/right head."
] |
[
"Can you make an image ONLY a colorblind person can see?"
] |
[
false
] |
I remember the colorblind tests where the number would appear to a person with "normal" vision but not to a person who is colorblind. Can this test be reversed to create an image using the same principles, so that only a person who is color-blind could see it?
|
[
"Have you ever heard of the color-blind army men, chosen simply for their ability to spot camouflage? There are several articles about studies that have analyzed a possible evolutionary benefit to colorblindness. Why? For some reason, the color-blind seem to be much better at spotting camouflage. ",
"Here",
" is a link to an article that says the following: ",
"Some studies conclude that color blind people are better at penetrating certain color camouflages. Such findings may give an evolutionary reason for the high prevalence of red–green color blindness ",
"This",
" Discover link has a really interesting article about how wild color-blind capuchins in Costa Rica are better at detecting camouflaged insects than individuals with broader color vision. This gives the color-blind capuchins an advantage while insect hunting. You should read the article if you are interested, but to summarize I believe it mentioned that the color-blind were able to catch 20 insects an hour, while the capuchins with normal vision were only able to catch 16. ",
"Here is one quote from that article that you may also find interesting: ",
"One possible explanation for the color-blind advantage is that a reduction in color signals makes the differences in texture and brightness more apparent, so it’s easier to see past color camouflage, says Melin. ",
"Edit: I wanted to add that I know all of this because as a color-blind person, I wondered early on in my life whether or not there was any advantage to my condition :). So feel free to ask me any questions or take any tests you have found. Oh, also really interesting fact that kind of scares me...on that discover link, the pictures of the world in the middle and on the left look the exact same, with maybe a tinge of red in the middle of South America on the left one."
] |
[
"It's possible, but there are some caveats.",
"First, the key is adding distracting color information which obscures patterns in shading, but even differences in shading are visible to people with normal vision so it's just a matter of making something harder to see, not impossible to see.",
"Second, there are many different types of colorblindness, though some types are more common than others. I'm not sure if it would be possible to create an image that all individuals with different sorts of colorblindness would be able to make out (and would still be obscured for people with normal vision).",
"Here's a good one: ",
"http://www.moillusions.com/2012/01/reverse-color-blindness-test.html",
"And try this: ",
"http://colorfilter.wickline.org/?a=1;r=;l=9;j=1;u=www.moillusions.com/2012/01/reverse-color-blindness-test.html;t=p"
] |
[
"That is not correct. Colorblind people are more sensitive to differences in contrast than \"normal\" people. As a result, colorblind people are less often fooled by camouflage. Here are some examples:",
"Those with normal color vision or total color blindness should be unable to trace the line. Most people with red green color blindness can trace the wiggly line",
"People with normal vision or total color blindness should not be able to see any number. Those with red green color blindness should see a 45.",
"People with normal vision or total color blindness should not be able to see any number. Those with red green color blindness should see a 5.",
"EDIT - Clarifying: Colorblindness causes difficulty discriminating between colors, but actually enhances ability to discriminate shades. In other words, even if I can't see that these two red crayons are red, the difference between them is more apparent to me ... I can identify them individually where a \"normal\" person might see them as the same."
] |
[
"Mount Agung Volcano Eruption Megathread"
] |
[
false
] |
Hi all, Mount Agung on the island of Bali, Indonesia, has currently been undergoing eruptions. If you have questions about the specific eruption, volcanic eruptions in general, or related topics, feel free to post your questions below! Some relevant links:
|
[
"This is something that comes up a lot - there's actually some decent stuff in the FAQ.",
"However, to pracie;",
"Yellowstone has erupted hundreds if not thousands of times over the last 2 million years or so. Three of those eruoptions have been 'supereruption', where in excess of 1000 cubic kilometers of magma has been ejected. These occurred 2.1, 1.2 and 0.6 million years ago. So the intervals are about 0.9 and 0.6 million years. Two intervals is not enough to say there is any trend, and the range is enormous. For comparison Humans migrated out of Africa somewhere between about 0.12 and 0.06 million years ago.",
"So we can't tell you when to expect a super eruption. Almost certainly not in the lifetime of anyone within a dozen generation of you.",
"Most eruptions from Yellowstone are in fact rather minor and not really something we need to worry about either. Lava domes mostly. ",
"There is no way you can stop an eruption. The forces involved are simply far too huge."
] |
[
"Volcanic plumbing systems are complex beasts; there can be a multitude of interconnected magma reservoirs. As you depressurise one system there is potential to destabilise other parts of the system, which can trigger new pulses of activity We know of 3 or 4 eruptions from Agung in the last 200 years or so; 2 of them were large Plinian-type eruptions. The general consensus is that there has certainly been enough time for sufficient magma to accumulate for another large eruption. What we don't know is whether that magma is still mobile enough to erupt (e.g. has it cooled down or not?), or where any such magma sits in relation to the currently tapped magma reservoir system."
] |
[
"Every once in a while someone brings up Yellowstone's chance to erupt, but it's all people speculating at gatherings. This is why it's great to have experts in this field to ask questions to!",
"When can we expect a Yellowstone eruption as I am sure it's not an if but a when situation, how bad will it be and will we know ahead of time? If so, enough to get people to safety? Is there a way to stop or disrupt an eruption?"
] |
[
"Can one light wave cancel out another light wave?"
] |
[
false
] |
In my Physics class last night, my teacher talked about destructive interference and how it is possible for waves to cancel each other out. Is this true for all waves including light waves? If so, how come I (to my knowledge) have never come across or experienced a way to have one light source cancel out another light source.
|
[
"I'm sure you have come across it many times, you just haven't realised that's what you're seeing. See ",
"thin-film interference",
" for examples, and the ",
"iridescence",
" page has more. These include things like the colours in soap bubbles or puddles with oil spilled on them. A thin film causes the light to reflect at two surfaces. Different wavelengths of the light interfere in different ways depending on the thickness of the film. Some wavelengths interfere destructively while others don't so you get different colours."
] |
[
"Polarisation is not necessary for interference. Coherence is. This is why in the double slit experiment we insert a single slit before the double when using a thermal source like a light bulb. the light from such a source is coherent over a small area only, the single slit selects such a region. When using a coherent source like a laser the initial single slit is not necessary."
] |
[
"What happens with thin films is that you are seeing the superposition of 2 reflections. Light reflects of the top the film and light reflects of the surface below the film. If that film is exactly 1/4 the wave length then the light reflecting off the surface has traveled 1/2 wavelength further which makes out of phase with the light reflecting of the film. ",
"This picture",
" shows what's happening.",
"So now those 2 rays are both travelling towards you at the same speed, so now they merger in such a way that they are decontructively interfering with each other essentially cancelling each other out.",
"The reason you see a bunch of different colours from a thin film is because white light is not a single wavelength but a bunch of photons with all wavelengths of light. So the film will cause decontructive interference for only one of the colours, essentially removing that colour from the white light which makes it no longer white. For example if I shoot yellow light and blue light together I will see green light but if the thin film is exactly a quater of the wavelength of the yellow light then the film will cause the yellow light to decontructively interfere so now you can only see the blue light."
] |
[
"Is this derivation of F = dp/dt flawed for cases with variable mass?"
] |
[
false
] | null |
[
"You're wrong in the assumption that F=dp/dt was found using constant mass. That's why you are confused. But even then, does it really matter? Momentum is simply the product of mass and velocity. Whether one or the other, both, or neither is constant doesn't change that. It doesn't change F = dp/dt because dp/dt = d(m*v)/dt, which equals m*dv/dt + v*dm/dt per the chain rule. (Or, equivalently, m*d",
"x/dt",
" + dm/dt * dx/dt). If mass is constant, then dm/dt = 0 and the equation simplifies.",
"",
"As for relativity, that doesn't matter when we're talking at the Newtonian level. You include relativistic factors with velocity once you need to, but at \"low\" speeds it's negligible (i.e. difference is less than the significant digits of any reasonable measurement)."
] |
[
"ahh that makes more sense thanks"
] |
[
"Constant mass is a common simplifying assumption made that allows us to write F=ma. If the mass has some time dependence then properly applying the chain rule when you take the time derivative of momentum will give you the correct form of the force with a non-constant mass. For an example see the rocket equation."
] |
[
"Where did all the stars go?"
] |
[
false
] | null |
[
"The stars didn't go anywhere. They are hard to see when there is light pollution."
] |
[
"Light pollution? What’s a example"
] |
[
"https://en.m.wikipedia.org/wiki/Light_pollution",
"It just means that there are other bright lights around. You can't see very dim light when there is another bright source around. That's why you see few stars at night in a big city and can see lots of stars if you go into the countryside."
] |
[
"How would you fix something like the Guatemala sinkhole?"
] |
[
false
] |
Pic for reference: Do they just pour in a lot of dirt? Wouldn't that just become unstable again? If a sinkhole that size was there, wouldn't that mean that the whole city area would be in danger of falling into sinkholes? Is there anything they can do to prevent them from happening?
|
[
"I was mostly convinced that was photoshopped, then googled it. Blimey. From the article I read on it: ",
"Typically, officials fill in sinkholes with large rocks and other debris. But the 2010 Guatemala sinkhole \"is so huge that it's going to take a lot of fill material to fill it,\" Currens said. \"I don't know what they're going to do.\"",
"http://news.nationalgeographic.com/news/2010/06/100601-sinkhole-in-guatemala-2010-world-science/"
] |
[
"Before the sinkhole can be filled other problems need to be addressed. The city sits on unconsolidated soil that can easily be washed away, which, in addition to the tropical storms and heavy rainfall, likely added to the formation of this hole. The underground water system needs to be thoroughly inspected to detect if there are other places where something disastrous like this could occur.",
"As for filling it in, if this is what they decide to do, it would be quite an endeavor. In order to preclude large amounts of settlement in the surrounding area, the fill material would need to be placed in controlled lifts and compacted. In a hole this deep with vertical sides this is nearly impossible to do safely. ",
"I am interested to see how they go about fixing this."
] |
[
"Try ",
"/r/askengineers",
" "
] |
[
"If microwaves work by vibrating water molecules, why is it that my bowl is hot while my food is still cold?"
] |
[
false
] | null |
[
"Microwaves work by exciting rotational modes in polar molecules. Your bowl may be made of some other polar substance."
] |
[
"The bowl I was heating at the time was ceramic so that does contain polar molecules (typically). Is that why Styrofoam does not heat up in the microwave? Because it is nonpolar? "
] |
[
"That makes sense to me."
] |
[
"If you were standing on Mars, how bright would it’s two moons look in comparison to our Moon on Earth?"
] |
[
false
] | null |
[
"Phobos has ",
"40% the apparent diameter",
" if you are directly underneath, Deimos has ",
"just 6% of the diameter",
".",
"Their albedo is lower compared to the Moon by a factor ~2, and sunlight only has half of the intensity. Combined you have much smaller moons which also have a dimmer surface. Both moons are easily visible during the night but they are not as dominant as our Moon, and seeing Deimos during the day might be difficult.",
"Edit: Forgot the radius of Mars, which is important for Phobos."
] |
[
"Thanks for the reply. This was exactly what I was hoping to figure out. My little guy and I were talking about it being a disadvantage of living on Mars, but then he started wondering how much smaller and dimmer they would be. He feel asleep before you all replied, so excited to share this with him tomorrow. Cheers!"
] |
[
"Yes (",
"here is a picture with Earth and the Moon",
"), but Mars' moons are even darker."
] |
[
"What do storm clouds do that make them darker compared to regular, lighter clouds?"
] |
[
false
] | null |
[
"Simple answer... They're thicker. The dark grey you see in storm clouds is a result of the shadow of more cloud between it and the sun. Storm clouds usually have a large amount of cloud above them that you can't see from underneath, or close to the cloud. You do see it's shadow though, at the base of the cloud, obscuring most of the suns light from making the cloud appear white."
] |
[
"For an illustrative example, ",
"http://www.snopes.com/photos/natural/graphics/storm2.jpg",
"Notice how the surrounding clouds are might lighter than the bottom of that very thick, central storm cloud."
] |
[
"Oh boy that's a fantastic image. I wish they had that in 4k as to utilize it as my wallpaper."
] |
[
"What causes X shaped lines on the stream when I pour milk?"
] |
[
false
] |
I've noticed that when I pour milk (I think it's any liquid but its most obvious when I'm pouring milk out of the gallon container) that there are X shapes that form likes indented ridges on the stream that is pouring out of the mouth of the container. Why does this happen? You can see the lines that I'm talking about in this picture. Edit: Thank you guys for all the helpful answers! This has been something I've wondered about for ages, and I just used to go "eh, physics" but last night I spent a while looking up stuff about Rayleigh jet instability and waves instead of studying AP Chem, so that was pretty awesome.
|
[
"In general, fluid dynamic models are very difficult to describe using natural language. The mathematical interactions are so complex to model that fluid simulation is one of the major applications of supercomputers.",
"This case might be more simple, I honestly don't know, but it also might be extremely complicated to describe the \"reason\" for the shapes of streams in a moving fluid."
] |
[
"Let's look at the cross section of the milk as it falls into the bowl. Take the section right at the mouth of the carton and you have a triangle of milk, 2 edges from the walls of the carton and the third being the top surface of the milk. This is the best shape for the milk to be in because it minimizes surface area, which is what surface tension does.",
"As soon as it leaves the carton that triangular shape is no longer the optimal shape for the surface tension of the milk, now that it's falling through the air not touching any walls the optimal shape for that cross section is a circle. The edges are gone and nothing is supporting it, so circle is the best shape minimize surface area. So the surface tension pulls in the corners of the triangle to make it round. But because it keeps pulling until the instant the corners reach the circle it should be at, the section pulls in too far and it starts ",
"jiggling like a water droplet in space.",
"We can think of the cross section of the milk as a 2D jiggling drop of milk falling from the carton. In which case we can think of the stream of milk as a long line of 2D drops. And because (if you hold the carton in place) every one of those drops will be experiencing the same forces, they will all jiggle exactly the same way on the way down, making a stream of milk that bulges and dents as it flows but always stays the same shape. The Xs you're noticing are just where bulges in the jiggling drops happen to pass through one another and form an X shape in the stream.",
"I hope that helps, or if not then someone can better translate the idea."
] |
[
"This is the closest thing to the correct answer here.",
"We, fluid physicists, refer to this as Rayleigh jet instability. You can read about it in plain terms on Wikipedia here: ",
"http://en.m.wikipedia.org/wiki/Plateau–Rayleigh_instability",
"In the particular case of milk, which is a colloid, you get some additional \"non-Newtonian\" behavior of the fluid which makes it more interesting looking than just a regular Newtonian fluid. But this behavior is expected in all fluids in contact with another fluid."
] |
[
"Did all of the birds of today, flightless and those that can fly, evolve from a single Mesozoic dinosaur ancestor? Or are modern birds the ancestors of several different Mesozoic dinosaurs?"
] |
[
false
] | null |
[
"Yeah. Flight has been lost multiple times among birds. Penguins are a separate evolutionary branch from ostriches/emus that also lost flight."
] |
[
"It's possible that flight, or at least ",
"gliding",
" evolved in therapod dinosaurs a few times. Many of the small therapods were probably highly feathered little critters that flapped their arms about to help maintain balance and scramble up surfaces, and it's ",
" that several lineages independently got good enough at it to get briefly airborne. But all birds as we know them (the group ",
"Neornithes",
") are clearly descended from a single flying ancestor. A number of other branches off the bird tree didn't make it past the Mesozoic. It's ",
"unclear",
" exactly how many bird species survived the mass extinction, but the number wasn't large, and most of the diversity of modern birds appeared afterwards. "
] |
[
"This is not true, Archaeopteryx is not thought to be a direct predecessor of birds",
"https://en.wikipedia.org/wiki/Archaeopteryx#Phylogenetic_position"
] |
[
"I read so many science papers that conclude with \"correlation does not equal causation\". Why are such experiments conducted?"
] |
[
false
] |
This seems to be mostly happening in science dealing with human health. Is there a point in doing such experiments and the take away is just correlation? Isn't it similar to picking two random trends on Google Trends and showing correlation?
|
[
"The thing is, correlation ",
" imply causation, as long as the study is done correctly. If A and B are correlated, one of four things could be occurring:",
"Properly applied experimental techniques and statistical analysis may be used to determine that #1 is unlikely.* In that case, you're left with #2-4, which is more useful information than you had before. The caveat \"Correlation does not equal causation\" just means that we should not choose #2 or #3 to be necessarily true; #4 is also possible.",
"*That goes way beyond choosing two random trends on Google Trends. You'd want to alter either A or B or both and look at the effects, and also apply time series analysis to compare the size of the effects to what you might see just from random variation."
] |
[
"It's not an experiment unless some kind of intervention is conducted. Correlation is usually from observational studies. It is hard to change people's health, but relatively easy to observe what is happening with people's health. Correlation was used to discover that smoking was associated with lung cancer. Later led to understanding that there were causal mechanisms."
] |
[
"Correlation is usually a good hint to bring further study into an area that was ignored before. Linking two phenomenon that previously had no sign of being correlated opens the doors to important questions.",
"Also, statistical correlation is something slightly different from colloquial correlation."
] |
[
"It's a bit crude, but... Why does taking a dump feel so damn good?"
] |
[
false
] | null |
[
"Try a better title for ",
"/r/askscience",
" such as but not limited to: \"Why is my brain's reward center excited when I excrete?\" or \"Why does it feel good when I excrete?\""
] |
[
"Follow up question. Since males have a prostate, does the evacuation of matter from the posterior regions feel more pleasurable to them in comparison to females?"
] |
[
"With that it makes an easy enough way to answer,",
"Your body rewards you for pooping because it's essential to survival. Just as eating is rewarding.",
"As far as the allure for Anal sex, there is much more than the sensation of something moving around in the anus. As pain is exciting for some, and with this unantural movement pain can cause pleasure to some. And with that you open the idea that since sometimes pooping is painful (especially so with the abundance of food that causes a poor diet and a more constipated poop) the pain from pooping is pleasureable."
] |
[
"Why is it that some molecules can have two opposite effects?"
] |
[
false
] |
How is it that a molecule, such as prostagladin, can have two opposite affects on one type of tissue, i.e. it can cause both contraction or dilation of smooth muscle. Does it depend on the certain receptors expressed in the tissue or is it something to do with the different signaling pathways that might be active?
|
[
"One of the biggest reasons is definitely going to be different receptors. For any given signaling molecule, the effect of the signal is entirely determined by the receptor and what the receptor is coupled to. For example, there are both excitatory and inhibitory receptors for many neurotransmitters.",
"I'm not sure what you mean by \"different signaling pathways that might be active\", but the same receptor can be coupled to different signaling mechanisms. Many neurotransmitter receptors, for example, are coupled to proteins that act to increase or decrease production of cyclic adenosine monophosphate (cAMP). But depending on the cell, the effect of increasing/decreasing cAMP production will vary wildly."
] |
[
"The prostaglandins are a complex group of structures that share the basic shape. Side groups change their structure and action. Often two variants oppose each other.\nMore:\n",
"https://en.wikipedia.org/wiki/Prostaglandin"
] |
[
"To add to what others have said, while I do not know much about prostagladin, it is not uncommon for cells to express feedback loops, that limit the time of a response. While this is not directly what you asked, many drugs will feed into these cell switches. For instance, you may have one receptor that activates contraction on a short time scale, and another receptor that activates dilation on a longer time scale. This can create a negative, or a bistable feedback loop, preventing the cell from getting \"stuck\" in one state, although because these processes tend to work at different timescales, there is still a biological response for some initial time period. ",
"Somewhat related wiki article"
] |
[
"How are cannabinoids metabolized?"
] |
[
false
] |
What do they bind to in the blood stream and what is the detectable metabolite in urine?
|
[
"http://www.health.gov.au/internet/main/publishing.nsf/Content/health-pubs-drug-cannab2-ch47.htm",
"After smoking, the initial metabolism of THC takes place in the lungs, followed by more extensive metabolism by liver enzymes which transform THC to a number of metabolites. The most rapidly produced metabolite is 9-carboxy-THC (or THC-COOH) which is detectable in blood within minutes of smoking cannabis. It is not psychoactive. Another major metabolite of THC is 11-hydroxy-THC, which is approximately 20 per cent more potent than THC, and which penetrates the blood-brain barrier more rapidly than THC. ",
"Not sure about what it \"binds to\" in the blood, if that's even necessary.",
"THC and its metabolites are highly fat soluble and may remain for long periods of time in the fatty tissues of the body, from which they are slowly released back into the bloodstream. This phenomenon slows the elimination of cannabinoids from the body. ",
"From ",
"the wiki article",
", this seems to be fairly correct."
] |
[
"As far as I know cannabinoid receptors are some of the most common binding sites in your body with virtually every cell sporting them. So really it binds everywhere."
] |
[
"Not sure where your source is, but I found ",
"this",
". Your reply seems to be generally correct, but I was trying to find if red blood cells had those receptors too (seems that they don't).\nStill, cannabinoid receptors should clearly be widespread as they ",
"do cool signalling stuffs",
"."
] |
[
"How do Civil Engineers go about factoring in the curvature of the Earth when dealing with extremely long bridges?"
] |
[
false
] |
Engineering
|
[
"The Earth's curvature is fairly predictable so during the planning stages you can make pretty reasonable approximations of what the differences in height will be. Then, when it comes to actual construction, the areas are surveyed so you'll know the exact difference in height. In most cases, I'd bet that local variation and accuracy in the recorded ground height is probably larger than the difference caused by the curvature of the Earth.",
"An exception occurs in suspension bridges with extremely long spans, where you'll end up with towers that are not parallel to each other. The reason for this is not because the span itself needs to match the curvature of the earth, but because you want the forces on the tower to be transmitted directly into the Earth (i.e., they need to be parallel with gravity, not parallel with each other). An example is the Verrazano-Narrows suspension bridge, where the tops of the towers are about 1.5 inches further apart than the bases."
] |
[
"Is the 1.5 inches something that's planned for? That's 0.02% flatness across the side of the tower, right? (They're 693 feet tall)"
] |
[
"I'm a civil engineering major and I have never come across this in any of my classes. You could try asking ",
"/r/civilengineering"
] |
[
"Are all muscles contracting? As in there are no \"push\" type muscles?"
] |
[
false
] |
What about other species besides humans? And what are non-contracting (I'm assuming stationary) muscles generally used for?
|
[
"Yes, muscles can only ever contract themselves. Muscles can only be stretched with another muscle, a \"stretcher\". You will always have muscles working either way on most of the body's joints. The fingers are a bit different."
] |
[
"sphincter muscles (the round ones that control most digestive processes, the irises of your eyes) are a little different, in that sphincters “open and close” vs push and pull, so they don’t need a counterpart like a bicep has in a tricep in your upper arm or quadriceps and and hamstrings in your leg."
] |
[
"As for the second part of your question, there are not really non-contracting muscles, except those that are atrophied and thus not working or muscles that are not needed. Ligaments, tendons, and fascia, for example, provide the extra support without contracting."
] |
[
"[physics] - Where would I have to go on land (not water) to find earth's weakest point of gravity?"
] |
[
false
] |
I got conflicting answers. I was told any land point on the equator would be the place where gravity is weakest. However, I was told that there are some "hot spots" where gravity is even weaker. I would like to ad that even on other "physics" websites there is disagreement with conflicting citations:
|
[
"Based on the GOCE satellite, gravity appears weakest in Southern India.",
"http://news.bbc.co.uk/nol/shared/spl/hi/world/10/goce_gravity_field/img/goce_gravity_field_786map.gif",
"That axis is mislabeled though, the units should be milligal (1 gal=1 cm/s/s)."
] |
[
"Not as a human, no. Maybe with sensitive equipment."
] |
[
"If I could somehow travel instantly from Iceland, where it appears to be strongest, to Southern India, where it appears to be weakest, would I notice a difference?"
] |
[
"Is digital, lossless audio amplification possible?"
] |
[
false
] |
If so, is anyone working on it? If not, why not?
|
[
"It should be noted that you can't just \"raise\" the amplitude value without first looking at the entire file. If you do so, you risk hitting the upper bound and causing clipping. You first have to inspect the entire file to see how much the highest peak can be raised before hitting the maximum, then raise all sample points using the same ratio as (Maximum_Allowed_Amplitude)/(Highest_Original_Peak_Amplitude). ",
"The phrase \"proportional to the wave's position\" is confusing. You increase the amplitude value of each sample by the same multiplication factor. ",
"This process is as trivial to reverse as it is to do the first time, as long as you have a method to determine how much you want to reduce the amplitudes. If you don't store the value that you originally used, then it is virtually impossible to return the file to its original state. "
] |
[
"If by \"amplification\" you mean either compression or normalization then yes, there is nothing degrading about either of these processes, although they would be difficult to reverse. if you have a 48bit wav file and you want it to be \"louder\" you just \"raise\" the value for the wave at each time an amount proportional to the wave's position.",
"Lossy audio has thrown away data that can never be recovered. It is done in a way that is heard least by humans typically. This is actually altering the waveform into something that it wasn't originally."
] |
[
"I typed that way too late at night. You are right, if it is just an applied gain then you could reverse it (with roundoff errors) easily, but if it is something dynamic, like compression or normalization with a finite sample time, then it would be more difficult to determine what was applied where, and at what frequencies. Position, I just meant the value at that time slice, the \"position\" of the potential, speaker cone, whatever."
] |
[
"Why are vaccines traditionally given via injection vs a pill or other method?"
] |
[
false
] |
Has there been research into other delivery methods' efficacy? What would possible limiting factors be for pills or other ingestible versions?
|
[
"The oral route does not tend to be very good at delivering antigens to the immune system. You don't generally ",
" your immune system to respond to oral molecules: think about the general awfulness of wheat or peanut allergies. Your body not only tends to break down molecules for sustanence, but also has some tolerance-promotion mechanisms for molecules that make it through. These mechanisms can be overcome in some circumstances, but normally, the oral route just isn't the best.",
"It has been used in for some attenuated vaccines, which means vaccines that contain live virus that is less virulent (hopefully!) than the strains that normally cause disease. If these virus normally infect via an oral route, then that can be a good way to inoculate. "
] |
[
"Your immune system will not react differently to an antigen on the basis of its point of entry.",
"Actually, that's not accurate. There's a whole subset of research on mucosal immunology because the immune system has so many unique properties at mucosal surfaces. Within that area are labs that solely focus on one mucosal surface, such as lungs or intestines.",
" ",
"This suggests your immune system can recognise which orifice a molecule has come from; I think it's worth pointing out to other readers that this isn't the case.",
"The immune system does have some ability to recognize where an antigen was encountered. Dendritic cells that encounter antigen in the presence of retinoic acid(RA), which exist at much higher levels in the small intestine than anywhere else in the body, will uniquely prime T cells to home to the gut. The mechanisms behind this are covered more in depth in this ",
"review",
".",
"The same is true for skin and vitamin D. Dendritic cells which mature in the presence of high amounts of vitamin D will prime T and B cells to traffic to the skin. This and the effects of RA are discussed in this ",
"review",
" here.",
" ",
"We also know now of a certain type of memory cell, known as a T resident memory cells, which stay at the site of infection and can provide an incredibly fast response in the case of reinfection. There is a lot of exciting research being done on these cells right now, with the emerging notion that they may be even more important for immunosurveilance and early responses than circulating lymphocytes. \n",
"Here",
" ",
"are",
" ",
"some",
" reviews, all published this year, concerning this type of cells.",
" ",
"Are there, however, immune cells which only patrol the gut?",
"Yep, beyond the aforementioned resident memory cells, there are intraepithelial lymphocytes (IELs). A population of T cells that nestle in between epithelial cells of the small intestine to provide protection to the gut environment. They have to walk a tightrope between protecting against dangerous pathogens but not overreacting to less harmful or even helpful members of the microbiota. Failures in doing so are associated with diseases such as IBD, Crohns, and Celiac disease. \n",
"Here",
" and ",
"here",
" are reviews discussing IELs.",
" ",
"Which brings us back to OPs original question. All of these things, especially resident memory cells, mean there are labs interested in the importance of studying delivery technique for vaccines. ",
"Here",
" is paper I was able to find arguing that an aerial delivery method of flu vaccine is more protective because it generates a T resident memory response in the lungs. I can't find anything right now but know there are labs interested in oral vaccines as a way of generating more effective responses against pathogens that have an oral entry route.",
" ",
"I'll add that I typed this up in lab in between doing some benchwork. Some of these references I have read but others I haven't. I'll try to come back to this later and read this and can add more / replace them if they don't cover enough ground."
] |
[
"Your immune system will not react differently to an antigen on the basis of its point of entry. ",
"You don't generally want your immune system to respond to oral molecules.",
"If these virus[es] normally infect via an oral route, then that can be a good way to inoculate.",
"This suggests your immune system can recognise which orifice a molecule has come from; I think it's worth pointing out to other readers that this isn't the case.",
"Are there, however, immune cells which only patrol the gut? I'm not aware of these but I'm happy to be shown a reference which tells me about them. It was my understanding that they simply circulate in the general bloodstream."
] |
[
"Can God fuck a piece of cake and eat it afterward and have it NOT taste like cum?"
] |
[
false
] | null |
[
"Ah on second thought, per the 3rd bullet point could a mod please move this to AskScienceDiscussion?"
] |
[
"Ah on second thought, per the 3rd bullet point could a mod please move this to AskScienceDiscussion?"
] |
[
"Ah on second thought, per the 3rd bullet point could a mod please move this to AskScienceDiscussion?"
] |
[
"Does the size of an adult of a species affect the size of the gametes? For example, do elephants have bigger ova than humans? Do mice have smaller sperm?"
] |
[
false
] |
I'm also curious to know if smaller animals have smaller (ie: thinner) neurons compared to humans.
|
[
"I don't know about general trends, but fruit flies rather famously have the longest sperm in the world.",
"wikipedia"
] |
[
"Yes and no. There's a general trend that smaller animals have smaller parts, but this is not universal. Evolutionary pressures have a lot to do with it, and most of the time, we're not sure why an organism deviates.",
"For example: Squid have ",
"giant nerve axons",
".",
"This trend is less true for individual cells (like gametes). Larger animals are more made of more cells of a similar size than larger cells.",
"For sperm, there's a theory that larger sperm are present when there is higher competition (sperm physically competing in the female). ",
"This paper",
"(journal access required), shows that in mammals, this is the case, mammals with larger testes (related to sperm competition) produce larger sperm.",
"So its complicated, in general, yes, but there are lots of exceptions."
] |
[
"Couldn't find a comparison to humans, but for small mammals, body size and neuron size are coupled",
"source"
] |
[
"Why does it snow less near the coast?"
] |
[
false
] |
I've always been told it's because of salt coming off the sea into the air, which causes the snow to thaw, but this sounds more like an urban myth than actual science.
|
[
"It has nothing to do with the salt but it certainly does snow less in coastal areas. This is due to the ",
"Maritime Effect",
" which in a nutshell gives coastal areas more mild seasons. It snows less near the coast because it is in fact generally a few degrees warmer on the coast during the winter."
] |
[
"The Lake Effect",
" is actually the result of the colder inland air passing over the relatively warmer water then back over the colder land. The same thing can happen from the ocean.",
"This effect occurs on bodies of water of every size, it is just some bodies of water are not large enough for a noticeable impact to the local temperature. "
] |
[
"And cooler in the summer. This is because it takes more energy to heat up/cool down water than other similar substances. It's polarity means that it forms hydrogen bonds, which require more energy to break."
] |
[
"What's happening when my eye gets red?"
] |
[
false
] |
[deleted]
|
[
"The red lines you see are the blood vessels in the conjunctiva, a translucent tissue that covers all but the cornea in front of your eye. The conjunctiva prevents anything from going behind your eyeball, including contacts. When your eye gets irritated, dry, or detects a foreign body or substance, it becomes inflamed and the blood vessels dilate. Inflammation is a natural immune process, and your eyes are very sensitive and quick to react.",
"If your eyes become red often or for long periods of time, consult an eye physician. Red eyes can be pretty benign, but can also be secondary to seriaus diseases and conditioned.",
"As a side note, vasoconstrictor drops like Cleareyes and Visine can reduce the redness temporarily and are safe to use ",
". Chronic use can have a rebounding effect, causing your eyes to become more inflamed when the effect wears off. This encourages you to use it more, which causes more inflammation and a horrible cycle."
] |
[
"The irritation of your cornea causes a histamine response in response to a possible foreign object in the eye. This causes the blood vessels in the sclera (the white part) of your eye to dilate some and get more blood to the area, mostly in order to supply your tear glands with more raw material to make tears with. "
] |
[
"Thanks!"
] |
[
"Is PTHrP parathyroid hormone-related peptide or protein?"
] |
[
false
] |
Searching around I've found both used in academic literature, is one more correct than the other or are they completely interchangeable?
|
[
"Peptides are shorter than proteins. Peptides usually range from 2 to 50 amino acids while proteins range in the hundreds or thousands of amino acids. PTH is 85 amino acids long therefore is more accurately classified as a polypeptide."
] |
[
"Apologies, read your question correctly and halfway through typing the answer my brain switched to parathyroid hormone and only realised you were asking for parathyroid hormone related peptide. ",
"According to ",
"this",
" review article it has a variable amino acid length of 139 to 173 amino acid. I guess at this length both descriptions are acceptable"
] |
[
"Would the same be true of PTHrP?"
] |
[
"For how long will a bug survive if I swallow it whole?"
] |
[
false
] |
I just swallowed a fruit fly which had invaded my beer and I can't waste a single drop of it. I'm sure it's long gone by now, but how long did it survive? What if we upped the ante and considered a cockroach instead? Are there any non-parasitic multicellular animals which could survive the whole process and come out alive?
|
[
"It's quite unlikely that the fruit fly lasted very long once it hit your stomach. The sheer acidity of the digestive fluids would have dissolved most of the chitinous tissue within a minute or so. Even if you were to indadvertedly swallow an entire cockroach within damaging it, the chances of survival are quite low. Moreoever, it wouldn't be a pleasant way to go... it could potentially die by means of:",
"Dissolution in gastric juices",
"Haemolymph leakage due to breaks in the cuticle",
"Blockage of spiracles, thus resulting in suffocation",
"Starvation, if it somehow found a suitable microenvironment",
"Since these insects are in no way parasitic, they lack the essential adaptations to survive such conditions. There is however a group of organisms called facultative parasites that under normal circumstances can live independently, but will resort to parasitic behavior if the certain conditions are met. Soldier fly larvae, for example, normally develop in cow manure, feeding of the larvae of house flies. If they are for some reason ingested - say, from overripe fruit or undercooked meat - they can actually colonize the intestine and lead to myiasis."
] |
[
"Hint, there's a reason we have teeth. Chew your food! Things aren't supposed to be alive by the time they hit the esophagus."
] |
[
"Thanks for the hint! Henceforth I will chew my cockroaches well and good."
] |
[
"If men typically have more muscle mass than women doesn't that mean that they need more sleep than women to rest/repair/ and build muscle from daily activities?"
] |
[
false
] | null |
[
"No for a few reasons, recovering from exercise isn't the determining factor in how long we need to sleep. 8-9 hours of sleep is appropriate but substantially less than that is needed to recover from most exercise. Also, the differences in muscle mass and daily exercise load are more varied within men and within women than between men and women. In other words, there are plenty of women with more muscle mass and a higher daily training load than an average male. "
] |
[
"Just to be clear- sleep is a requirement for for brain functioning, for reasons that aren't completely understood. Muscle repair requires resting the muscle, or at least not high exertion, not necessarily sleep. "
] |
[
"I'd argue sleep is required for complete recovery for hormonal reasons. Insulin and hGH are important factors in recovery and their levels are affected in important ways by sleep. "
] |
[
"Is there a reason the \"gravity map\" lines up somewhat with the fault lines of earth tectonic plates."
] |
[
false
] |
gravity map, .
|
[
"This is exactly backwards. Mountains in either Free-Air or Bouguer gravity maps are lows, and the extensional basins are gravity highs due to the decompression and upwelling of hotter, more dense asthenosphere. This is seen in the Basin and Range in the Western United states as a wide rift example, the Llanos basin in Colombia near the Andes Mountains, and the East-Africa Rift in Africa. ",
"You will note that the Ural mountains in Russia, the Rocky Mountains in the western United States, and the appalachian mountains in the eastern United States are indicated as relative gravity lows. ",
"Because we don't know what kind of gravity map this is, I'm assuming is an uncorrected wide-band map, the mountains that show up as very large gravity highs are exactly where we would expect large amounts of intrusions from arc volcanism. Therefore, the gravity highs are not because it is a mountain (because mountains should be gravity lows) but are from the intrusives that are emplaced from the subduction zone interaction. ",
"The reason that you find these gravity highs near some of the plate boundaries is because of the interaction of volcanism and plutonism on those boundaries. "
] |
[
"I'm sorry, but I have to be adamant about this. It is not correct what you are saying. ",
"You will notice that all of the mountains that are showing up as a positive have either magmatic intrusions, or they have basaltic cores. Himalayans have a basaltic core called the Abor mafics. The Pontides in Turkey are a volcanic arc from the Cretaceous subduction of the Paleo/NeoTethys, and the southern margin is an accretion of ophiolites. The Andes are a volcanic arc, the Zagros are a conglomeration of basalts in the Neoproterozoic substrata, the Andes are a current Volcanic arc. The Carpatians have basalts and ophiolites, as does the Moravian Massif from the accretion of the Neo-Tethys oceanic closure. ",
"If we compare this to the mountain ranges that we know were deformed without prominent magmatism like the Appalachians, Urals, Greater Caucasus, Lesser Caucasus, Adjara-Trialet fold belt, and the Rocky Mountains, they show up as gravity lows. There is a direct correlation between the gravity signature and the type of mountain it is corresponding to. ",
"Again, we can prove that the highs correspond to denser materials being forced into overlying strata or that it corresponds to rift basins where there is asthenospheric upwelling. Take a look at the Basin and Range, East Africa, Black Sea, Llanos Basin, and the Red Sea Rift. All of them are extensional basins, and gravity highs. ",
"If we look at the Pacific, the positive anomalies align exactly with the Emperor Islands and the Hawaiian Islands, which is, again, what we would expect because of the emplacement of basalt. ",
"Gravity highs come from the emplacement of mafic, or denser than surrounding contiental country rock such as in volcanic arcs or places where the crust is thinning, and the density of the asthenosphere is able to be measured with gravity techniques. Whereas the lows are coming from the accumulation of less-dense rock, such as the deformation of continental crust into the aforementioned non-volcanic mountain ranges. So, what we are looking at is just a bulk gravity map with no corrections where the highs are areas of emplaced denser volcanic or igneous rocks, and the lows correspond to an overthickening of the less-dense continental crust. ",
"Gravity maps do not have resolution to see sinking oceanic plates at subduction zones, as if we wanted to measure the depth of the plate near that would correspond to the gravity high in the Andes, the oceanic plate would be at a depth of about 300 km. No gravity map has ever seen to that depth. "
] |
[
"Of course of course. Gravity is sensitive to only one thing, and that is density variations. Whether those come from mafic intrusions or mass deficits at the bottom of the crust, this is exactly what gravity is sensing. And yes, Bouguer maps are more useful for certain types of detections. Unfortunately, the GRACE data is so long wavelength that it cannot be topography corrected, so for now we're stuck with free air only. Its up to man power for now to fill in the gaps with ground based surveys."
] |
[
"Why do larger stars burn out faster than smaller stars?"
] |
[
false
] |
I understand that the larger stars have to to maintain higher temperatures to balance their additional gravity, and this consumes fuel much faster. I must be missing something, but I would think that the larger star as it burned through it's fuel would lose mass and require less temperature over the course of it's lifetime. Is it simply not burning off enough of it's mass?
|
[
"Indeed, [isolated] stars stay at roughly the same mass for their entire lifetimes before they stop burning hydrogen and they leave the main sequence. Let's estimate the mass lost by the sun in its main sequence lifetime.",
"Main sequence Lifetime = 10",
" yr",
"Luminosity = 4 * 10",
" erg/s",
"So mass change is (using E=mc",
" )... (4*10",
" erg/s) * (10",
" yr) / c",
" which gives, about 10",
" kg. However the mass of the sun is like 10",
" kg, so this is puny. The same will remain true for high mass stars as well."
] |
[
"Thanks for the mathematical explanation. I think I sort of brought myself to this conclusion as I was writing, it but still wanted to hear a panel member's precise answer. "
] |
[
"Stars do not \"burn stuff off\" in the way that a burning piece of wood or paper does.",
"What is happening in a star is that smaller atoms like hydrogen and helium are undergoing a process called fusion which essentially merges the nuclei together to form a heavier element.",
"Some of the mass from the smaller nuclei is released from the star as energy, but you only need a small amount of mass to release a large amount of energy (E=mc",
"Now in order to undergo fusion, the atoms have to be under enormous temperatures and pressures. The larger the star, the greater the pressures and temperatures which makes it easier for the nuclei to fuse.",
"Now as time goes on, the lighter elements can can easily undergo fusion are turned into heavier ones that cannot. In a heavier star, this process is faster and that is why they generaly \"die\" faster."
] |
[
"What is the Pauli Exclusion Principle and how does it manifest itself?"
] |
[
false
] |
[deleted]
|
[
"It says that two identicle particles whose angular momenta are odd multiples of half of Planck's reduced constant (fermions) cannot occupy the same quantum state. In practice, this means that electrons and protons can't overlap the same space, and electrons cannot all be in the same energy level of an atom."
] |
[
"I would say no. The Pauli Exclusion Principle is mainly a \"bookkeeping\" procedure of labeling electrons. Electrons don't interact because of this law but instead this law is in place to track where areas of high electron density (molecular orbitals) are located. Furthermore, solids are solids through atomic bonds, something that cannot be completely explained through the Pauli Exclusion Principle (it would not factor in entropy, for example), though the Pauli Exclusion Principle could help assess the properties of a solid on a quantum level."
] |
[
"Correct, the Pauli exclusion principle does not apply to particles belonging to different atoms - the upshot of which is that 2 electrons in neighbouring oxygen atoms can be in the same quantum state."
] |
[
"Are there any characteristics of people physical or psychological based on blood type."
] |
[
false
] |
I recently had an operation and I found out my blood group is AB +. Does blood type affect us as individuals.
|
[
"Lucky for you to be the \"universal receiver.\" But there aren't really any physical impacts of blood type. In fact, it's pretty much the go-to example of a neutral trait, meaning it has no impact (positive or negative) on fitness.",
"Edit: I missed the psychological aspect of your question. The evidence is mixed! ",
"Here",
" is a study that found AB to be the most \"tough-minded\" blood type, with A (my blood type!) being the most \"tender-minded.\" However, ",
"here",
" is a much more recent study that found no relationship between blood type and personality."
] |
[
"Your first paper ",
" of pseudoscience. The paper almost exclusively self-references, and non-self-references are to books, unpublished articles, and 'overview' articles, with little relation to the topic at hand."
] |
[
"True life. I thought it was worth directing the reader to, for interest. I tend to put less weight on research that's so old because I feel like it wasn't reviewed as thoroughly. Which is what I was trying to imply by saying \"here is a much more recent study\" and linking to the more legit one. I just figured since the research is out there, why not look at? It was relevant to the question."
] |
[
"How many particles in the universe?"
] |
[
false
] |
[deleted]
|
[
"So people always say there's like 10",
" particles in the universe or something like that.",
"For clarity, I believe that figure is the upper limit on an estimate for the number of ",
" in the ",
" universe.",
"But how many particles are estimated to be in the actual universe?",
"In order to estimate this, we need to know how big the actual universe is, and ...",
"I know we don't know the size of the universe",
"... since we don't know that, we cannot answer this question. :(",
"but assuming it's finite and we know what the expansion rate is would it be possible to estimate it?",
"Not knowing just the expansion rate, no. We would need to know ",
" it is. If we can determine an estimate for the volume of the entire universe some way, we could calculate it. But just knowing the expansion rate and the fact that it's finite does not give us enough information to derive what the volume would be.",
"Hope that helps."
] |
[
"Additionally, the number of particles changes depending on whether you are accelerating or not (Unruh radiation). There is no observer independent particle number."
] |
[
"Additionally, the number of particles changes depending on whether you are accelerating or not (Unruh radiation). There is no observer independent particle number."
] |
[
"Why does alcohol prevent my cola from foaming when poured over ice?"
] |
[
false
] |
When poured over ice, cola foams a ridiculous amount. As in, I pour a quarter of the glass and the rest is full of foam that takes almost a minute to disperse. Much more than if I pour cola in the same glass with no ice. Now I understand the reason for the foam is because the ice forms a surface for the bubbles to form, causing the quick release of carbon dioxide from the mixture (see: Diet Coke and Mentos). My question is why does adding an ounce of hard alcohol (say vodka or rum) before I pour the cola prevent the foam from building up? I thought maybe it was partially melting the ice cubes, smoothing the surface, but an ounce of room temperature water did not cause the same results. (Interesting note from my service industry days: fountain drinks don't foam nearly as much when poured over ice, I assume because they're much more watered down)
|
[
"Alcohol has low surface tension, so the bubbles end up popping much more rapidly, preventing much head from forming."
] |
[
"You can also see alcohol surface tension effects in drinks in other ways. When a drink is said to have \"good legs\" i.e. large rivulets around the glass when you swirl the drink, generally wine, around the glass, The size of the legs is governed by the alcohol content. This means the ever classy \"this wine has good legs\" translates to the less classy \"this shit will get you DRUNK, bitch\". "
] |
[
"Yes, it turns out surface tension is the basis of bubbles. It turns out that the bubbles in soda are caused by the dissolution of carbon dioxide into water forming carbonic acid. When held at high pressure carboic acid is stable but when you open up the can you reduce the pressure the carbon dioxide is no longer stable as carbonic acid so it decomposes to water and carbon dioxide. if you pour cola over ice it further reduces the solubility because the higher the temperature of water the greater the solubility is. So if you quickly reduce the temperature it forces the carbon dioxide out of the water. now you have a large volume of gas trying to exit quickly. Now nearly all sodas contain alot of sugar or sugar substitute, The sugar increases the surface tension causing the foam you see just like soap makes the bubbles you made as a kid. Ethanol (the stuff that gets you drunk) has a much lower surface tension than water, that is, the ethanol molecules dont attract each other as well as water molecules do. So since you added a good amount of something that lowers the attractivbeness of the fluid it reduces the number of bubbles that form. So the formation of bubbles in this case has less to do with the number of nucleation sites (the roughness of the ice) than it does with the surface tension. This is a very high level explanation and does not delve into the hardcore math involved but the theory holds all the way into more advanced fields like steel making which has been studied ad nauseum and makes for a solid theory."
] |
[
"How do some people walk away from being struck by lightning while others die?"
] |
[
false
] | null |
[
"The immediate-death effect of being struck by lightning is cardiovascular. The bolt essentially acts like a defibrillator. If a person's heart is still beating after being struck, they will likely be fine. The route the bolt takes through the body (ie, through the chest, or not) will determine if the person's heart is affected. Most other injuries from being struck by lightning are thermal injuries (both internal and external). The path of the bolt through the body as it makes its way to ground will determine that. "
] |
[
"I was told recently that If you somehow know you are about to get struck, say by noticing a static buildup around you, you should quickly lay flat on the ground. They justified this saying it would provide the shortest route through you to the ground and this would help save your life. ",
"Are there any facts or rationale to back this up?"
] |
[
"I've heard this advice as well, and though I've never seen any evidence to support it, it does make logical sense. Giving the bolt a 'target' in the form of your gluteals may help prevent the bolt from running through your chest. "
] |
[
"Exactly how many stars are contained in a 100 light year radius around Earth? Or, is there a tool to easily calculate/observe this kind of thing?"
] |
[
false
] | null |
[
"We don't know exactly, because we don't have a complete count of the most common type of star (red dwarfs) beyond 10-20 light years, because they are so dim. But we can count the sample of stars closest to us where we probably aren't missing any, and use that number to extrapolate the number of stars in the larger radius. Since 100 light years is small compared to the thickness of the galaxy's disk, the density of stars should not change much over that distance, so this estimate should be pretty accurate.",
"According to ",
"https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs",
" there are 60 stars within 5 parsecs (16.3 light years) of the Sun and 83% of them are red dwarfs. The volume of space within a radius of 100 light years is (100/16.3)",
" = 231 times larger, so there should be about 231 times more stars. 231 * 60 = ",
", give or take. About 11500 of them are red dwarfs."
] |
[
"very cool i didn't realize red dwarves are so dang common. Thanks"
] |
[
"About 512 G-type stars ",
"according to this site",
". This is arrived at by direct observation. You'll have to look at the other types individually (see list at the bottom under Other Information), as it doesn't give a total for all types together. "
] |
[
"Why do nuclear reactors not explode after starting fission?"
] |
[
false
] | null |
[
"Because they are not prompt critical, it's delayed neutrons that maintain a fission reaction in a nuclear reactor. See ",
"here",
" and ",
"here"
] |
[
"Sorry but this isn't true. Control rods would be useless in the event of prompt criticality, which is essentially what happens with a nuclear weapon. Control rods do control the reaction rate by absorbing thermal neutrons (ergo leaving fewer available to cause further fissions), but in current designs (with the exception of fast reactors) they operate by controlling the reproduction of delayed neutrons. ",
"It's the difference in type of neutron criticality that prevents reactors from exploding as they would in a nuclear bomb. Reactors need to be delayed critical rather than prompt critical, as prompt critical is practically impossible to control.",
"Source: Doing an Masters degree in nuclear engineering. "
] |
[
"In a bomb, the products from fission (such as free neutrons) meet other nuclei and trigger fission in them. In a reactor, there are things (control rods) in place that absorb many of these products before they can trigger another reaction. This leads to a controlled but sustaining reaction."
] |
[
"Altitude Sickness? How sudden can it take effect, what can happen?"
] |
[
false
] |
Hello again scientists! So, my latest question is pretty simple. Altitude sickness, how long does it take to have an effect? I'm finding online that it usually takes between 12-24 hours for somebody to feel ill due to a raise of over 8000 feet. Well, what if somebody were suddenly exposed to such an altitude!? What if, for instance, some massive giant were to scoop you up from the ground and raise you, miles above the surface and right up to his own face? Any info, random tangents, strange possibilities etc are more than welcome, thanks for takin' a look!
|
[
"The cabin altitude of most airliners when in the cruise is about 8000ft. For most healthy people being suddenly raised to 8000ft pressure altitude and spending many hours there is a complete non-issue. There are plenty of long haul flights over twelve hours and 17 hours is the longest scheduled service I’m aware of - I’m not hearing of any cases of altitude sickness amongst healthy people."
] |
[
"You should look up hypoxic hypoxia. It's a lack of oxygen from air surrounding you, and is regulated for in air law for altitudes of 12.000 feet and up. It can cause euphoria followed by death, a very dangerous combination."
] |
[
"Jet airliners do have their cabin pressure controlled. They typically cruise at about 40000ft and the cabin pressure is equivalent to about 8000ft (ie not cruising level and not sea level but in between).",
"Long term periods at up to 10000ft pressure altitude basically have no effect on healthy people - in fact about 2 million people live in La Paz, Bolivia which is about 12000ft up (although their physiology will become accustomed to the altitude).",
"As you go higher you may experience altitude sickness -often experienced by mountaineers. ",
"https://en.wikipedia.org/wiki/Altitude_sickness",
"Exposure to much higher pressure altitudes rapidly leads to hypoxia which results in unconsciousness or death. Such pressure altitudes would typically be experienced during a decompression of an aircraft. This is why emergency oxygen masks are fitted and the aircraft would make an emergency descent to 10000ft where people can breathe normally. Time of useful consciousness decreases with increasing altitude to as little as about 5 seconds.",
"https://en.wikipedia.org/wiki/Time_of_useful_consciousness",
"\n",
"https://en.wikipedia.org/wiki/Hypoxia_(medical)"
] |
[
"Joseph Postma: The Greatest Scientific Fraud of All Time?"
] |
[
false
] | null |
[
"We don't vet videos or blogs on this sub"
] |
[
"Would it be more appropriate to link to his book on the same topic? I can't type out his full physics argument in one post, what would be most appropriate to link to?"
] |
[
"Such posts are better suited for our sister-sub ",
"/r/asksciencediscussion",
". Please post there instead."
] |
[
"If the sun is white but appears yellow because of atmospheric scattering, why doesn't the moon also appear yellow?"
] |
[
false
] | null |
[
"The moon ",
" appear yellow or even red when it's low in the sky (or there are a lot of particulates). You think of the moon as white or pale yellow because usually when you see it it's high in the sky and therefore tending towards white. If you looked at the sun at solar noon (don't), it would look a lot whiter than you typically think of it. That's because the only time it's comfortable to look at or near the sun is when it's lower in the sky and therefore more yellowish/reddish."
] |
[
"Another reason the moon may look less yellow is that ",
"color vision is worse in low light conditions and blue light is seen more easily",
". "
] |
[
"Is it possible the contrast to the night sky makes it appear \"more white\"? "
] |
[
"Why isn't the deep sea frozen?"
] |
[
false
] |
I've heard somewhere that deep sea temperatures can be well below zero degrees Celsius. So, why isn't their a layer of ice in the depths of the ocean?
|
[
"You heard wrong: Deep-ocean water can be quite cold, but when we say \"quite cold\" we mean typically between ",
"0 and 3 C (32-37F)",
".",
"The deep ocean can be ",
" below 0C however, and there are ",
" three reasons why it does not freeze:",
"The ocean has a lot of dissolved salt and other materials, which lowers the freezing point to about -2C (28F)",
"If some small portion of water deep in the ocean started to freeze, two things would happen: First, this ice would be less dense than the water around it, so it would rise toward the surface. Second, the act of freezing actually warms the water around it ever so slightly, due to its ",
"latent heat of fusion",
", suppressing further freezing.",
"The rock beneath the ocean floor is warmer than the water, so the water in the deep ocean will be slowly warming, not cooling, if anything.",
"Edited for counting. I never said I was a mathematician. "
] |
[
"Salt + pressure."
] |
[
"Also, water is most dense at 277.15K, so water of this Temperature will sink."
] |
[
"Why did herbivorous dinosaurs get so large?"
] |
[
false
] | null |
[
"Why is almost always not a good question to ask of evolutionary biology as you will always get a hefty amount of speculation. Perhaps being large deterred carnivores the same way it does today, perhaps selective pressures just happened to lead to increases in size. "
] |
[
"The easy answer is that it was probably as a defense against predators.",
"But there is a concept under debate in evolutionary biology called \"Cope's Rule\", which describes the tendency for a lineage of animals to gain a larger body size over time. It's not clear if this is because there's an innate advantage to being larger, or if it's just because the majority of animals are small, so a new group is statistically more likely to come from a small ancestor, and as the group expands into new niches some will get larger. There have also been a few scientists, including Stephen Jay Gould, who argue that this isn't really a common rule and it's just due to our bias towards larger animals.",
"TL;DR good question."
] |
[
"The point that is might have evolved as a defense against predators is a valid idea. However, let me offer another point that is from the stance of trophic ecology. This can work in conjunction with the points brought up by ",
"/u/dblmjr_loser",
" and ",
"/u/loki130",
". ",
"In trophic ecology, you have ",
"different parts of the pyramid",
", with primary producers making up the base and some level of consumer (at the very least secondary) making up the top. This is representative of available biomass and the transfer of energy through the different levels. Although it's not terribly accurate, we were always taught all throughout my environmental science degree (and now in some of my classes in my oceanography degree) that there is a 10% efficiency. So only 10% of the that energy actually makes it to the next level. So it's actually much more efficient to feed at a lower level than higher up. That said, organisms have done well feeding on those higher levels. But since you can essentially have more energy at your disposal, you're able to do with it as you please (metaphorically speaking). In this case, you can increase the amount of biomass that is on your trophic level, either in the form of increased individuals in a population or increased size of individuals (Note: it's a little bit of both though. Ecosystems really enjoy the ebb and flow of things).",
"Think of it like money: Taking out taxes when you get paid acts as an intermediate level that leaves you with less money (in the now), so it's like you're on a higher trophic level. However, if taxes aren't taken out, then you have more money to work with. With that increase in money, you can buy a lot of cheaper, smaller things (increase the number of individuals in a population); buy a (or several) larger, more expensive item(s) (increase the mass of an individual, but limiting the number of individuals), or somewhere in the middle. ",
"But it works together with the evolutionary aspect mentioned in other answers. Not only do you want to maximize your efficiency, but it has to be done in a manner that allows genetic diversity and the survival of a species. This makes it sound like evolution is goal oriented, which it is not. But yeah, you get the idea. ",
"Also, this video of Fry from Futurama deciding on a Christmas present might also demonstrate it. Kind of. Sorry for the potato quality, but it was the only version that I could find.",
"Edit: Sorry if there are grammatical errors or I seem like I'm rambling. I'm taking a break from writing my prospectus, so my life is a bit jumbled right now."
] |
[
"Can we know anything about the older star that created our sun?"
] |
[
false
] |
the solar system (along with other stars) were created by a cloud of gas and dust formed by the nova of a previous star. is there anything we can learn or find out about what that "parent" star system was like? like.. theres gotta be some kind of evidence. Can we find clues as to what kind of planets were around it when this old star existed? what kind of star it was?
|
[
"There was no such thing.",
"Many former stars contributed material to what formed the Sun later, although most of the mass is hydrogen and helium that was never part of a star."
] |
[
"Interesting question. Best answers would probably be in the form of asteroid study - as these chunks of rock have undergone the least \"reflow\". Planets and moons have been heated, squeezed, whacked, and often subjected to billions of years of chemical reactions, so there's very little there. But asteroids are more pristine bearers of the original \"stuff\" that glommed together to make our current system."
] |
[
"hmm, is there at least a way to study star systems from our galaxy that don't exist anymore? i know theres some evidence leftover."
] |
[
"What are the dangers of using AAA batteries in place of AA?"
] |
[
false
] | null |
[
"This isn't a safety issue, but there's a battery lifetime difference. Duracell's spec sheets say that a AA Coppertop battery's output will drop below 1 V after 20 hours of use when connected to a 10-ohm resistor, whereas a AAA Coppertop battery will drop below 1V after just 6 or 7 hours. See Duracell's ",
"website",
".",
"AAA batteries may get hotter than AA batteries under comparable current loads, but I'm not sure.",
"I think the main issue would be the risk of a short-circuit."
] |
[
"The problem is the uncertainty of the wad of aluminum foil, not the batteries themselves. ",
"Your \"Standard\" sizes of batteries do all share the same voltage (1.5v for AAA, AA, C, D, etc.). In fact, you can buy adapters that will allow you to use smaller batteries for larger applications on most any website. Perfectly fine and safe to do.",
"Think of it this way; Take a couple old wire hangars, wrap them on the ends of an air conditioner power cord, and plug the the tips of the hangars into the socket. Sure, it might work, but you wouldn't assume its safe, right? Or, you could buy an extension cord and do the same thing. In this analogy, the wire hangars are the wad of aluminum, and the extension cords are a properly manufactured battery adapter."
] |
[
"What would cause the heat transfer to increase when using AAA? Less surface area?"
] |
[
"What did they think would happen before they set off the first Atomic Bomb?"
] |
[
false
] |
Did they know how big the explosion would be when you would try and split an atom? How is that calculated? Thanks Guys! (P.S. Big upvote to the mod team here. I love the constant moderation that keeps this community pure!)
|
[
"As was already mentioned, they had a descent idea on the yield for the first explosion (trinity). Keep in mind that trinity was a test explosion; it was not an attack of any sort. Data was collected from that and the formula to estimate an explosion was developed. (See wikipedia for the equation, its formatting is superior). Keep in mind that this is an estimate. It ignores a number a factors. The math (and design) for a modern day nuclear device is really complicated. ",
"http://en.wikipedia.org/wiki/Nuclear_weapon_yield#Calculating_yields_and_controversy"
] |
[
"There were two initial types of atomic bombs made, both for use as war-time weapons.",
"The ",
"Little Boy",
" uranium gun-type weapon worked by firing a subcritical mass of uranium at a stationary subcritical mass of uranium at the other end of the bomb. When the two parts collided they formed a supercritical mass of fissile uranium which then explodes. The scientists were confident that the design was simple enough to not need testing, so the first one to go off was over Hiroshima.",
"The ",
"Fat Man",
" bomb was a plutonium compression bomb, and it was a much more complicated device. They needed to test the idea, and that test was the trinity explosion. Basically, they wrapped a plutonium core with shaped high-explosive charges that had to go off at precisely the same time, causing a shockwave to compress the plutonium to a supercritical level and trigger the nuclear reaction."
] |
[
"Was it formulated to be an attack weapon from the start? Or was the idea to pursue the advancement of science? ",
"Along the same idea, any suggestions for good documentaries on the subject?"
] |
[
"When you donate blood or let's say an organ to someone, what happens to your DNA in those cells?"
] |
[
false
] | null |
[
"Red blood cells don't have a nucleus and therefore no DNA, so no issue there. Normally for blood donations, the white blood cells (which do have DNA) are removed. In the case of organs, the host cell DNA remains intact, which is why it is necessary to get a match between donor and host, and why immunosuppressive drugs need to be taken regardless."
] |
[
"So in theory would it be possible for the organ donors DNA to affect or cause a mutation to the hosts DNA? "
] |
[
"I don’t think DNA does that?"
] |
[
"Why do they say not to put a car battery on a concrete floor?"
] |
[
false
] |
The old wive's tale has been proven anecdotally that putting a car battery on a concrete floor kills the charge. Is there any science behind this or is it coincidental?
|
[
"Leaving a car battery on a concrete floor won't do anything abnormal to affect the charge.",
"The belief stems from an outdated set of circumstances that no longer exist. Once upon a time, battery casings were made from more porous materials - tarred wood, ",
"rubber",
", etc. - which were susceptible to degrading after exposure to the moisture coming from unsealed concrete. As the casing degraded, battery acid could leak out and water could enter the battery, causing the battery capacity to drop. ",
"With modern, plastic-encased batteries, the moisture-related degradation isn't really an issue on any meaningful time scales. ",
"(Incidentally, anecdotal proof is not actually proof.) ",
"edit: added source re: rubber enclosures"
] |
[
"This is the correct answer. However you would be \nSHOCKED how strong this myth is. I have been a Mechanic for 20 years now, and while I work for myself now, I spent 15 years working in all manner of shops. No matter how many times I explained this to my bosses, they ALL forced me to put a piece of wood under batteries whenever they were placed on the floor. Many shops will still actually have special wood panels just for this purpose. And I have sat down and explained to them that this is from the 20's and even then took quite some time to have any effect. Nope still with the piece of wood. Even now one of the guys who works for me swears by his little wood battery panel. "
] |
[
"Mechanically, newer cars don't require this at all. Manufacturers actually recommend not idling your car, as it wears out the engine. ",
"In reality, the when it's -25 or below out, I'm running my car for a good 20 minutes, just so my ass doesn't freeze to death. However, your car will heat up faster in motion, rather then sitting in your driveway."
] |
[
"Methylcellulose question"
] |
[
false
] |
If methylcellulose (citrucel) capsules are crushed, does this ruin the methylcellulose? The company says not to do it but wont tell me why, other than "it hasnt been tested."
|
[
"It doesn't chemically ruin the methylcellulose. Methylcellulose passes through your digestive system pretty much unabsorbed and attracts water in your colon. Crushing it won't change how your body processes it chemically, but it might make it work less effectively if it causes it to be more dilute in concentration by the time it reaches your colon. I doubt this would be the case though if you are just crushing it and drinking it as opposed to just taking a pill. "
] |
[
"Thank you so much!!! My 5-year-old daughter has to take a fuck-ton of this stuff because of a colon condition, and it's very hard for her. I'm always looking for ways to make it more palatable."
] |
[
"We aren't allowed to give out medical advice, so knowing you are asking because your daughter has a colon condition causes me to be conflicted. ",
"That being said, I will say this: There are many 'drugs' that you shouldn't crush, for many reasons. Some drugs for example have an enteric coating on them so they can pass through the stomatch largely unaffected and deliver their therapeutic dose further through the GI tract. If you crushed them, the acid in your stomach might destroy them before they can do any good. Similarly, if you crushed your citrucel it might not work quite as intended."
] |
[
"Underground ocean 3 times bigger than our own?"
] |
[
false
] | null |
[
"I'm not sure if there's been a more recent set of splashy articles, but when ",
"Pearson et al., 2014",
" and shortly thereafter ",
"Schmandt et al., 2014",
" were published in 2014, there were endless \"multiple oceans worth of water found in the mantle!\" pop-sci articles published, like ",
"this one",
" (and ",
" many others). Taken together, what these articles imply is the presence of hydrous minerals in the deep mantle (around and above the transition zone, which is approximately ~660 km below the surface). As described on ",
"this page",
", and perhaps obvious from their name, hydrous minerals are minerals that incorporate water into their structure. Common examples of hydrous minerals at surface conditions are gypsum and opal. In the case of the deep mantle, the likely hydrous minerals of note are ",
"wadsleyite",
" and ",
"ringwoodite",
". So in the same sense as if you were dying of thirst and found a big chunk of gypsum, your reaction would not be \"Hooray, I found water!\", describing the presence of hydrous minerals in the mantle as \"oceans of water\" is a bit hyperbolic. More so when you consider that the estimates from Pearson and Schmandt suggest <1% weight percent of these hydrous minerals, so in terms of the \"multiple oceans\" bit just highlights how big the mantle is (even considering the restricted region of the mantle where these hydrous phases exist) compared to the ocean. Schmandt et al., does suggest that the presence of these hydrous minerals may lead to some partial melting around the transition zone in some areas, but again, this is melted rock with some hydrous phases, not water.",
"Broadly, subsequent papers have expanded on details that arise from the two previously mentioned papers, for example: 1) the rates and fate of water entering the mantle from subduction zones (e.g., ",
"Wang et al., 2015",
", ",
"Cai et al., 2018",
", 2) the stability of particular hydrous phases at mantle temperatures and pressures (e.g., ",
"Ohtani et al., 2015",
", ",
"Walter et al., 2015",
"), or 3) more bulk estimates of the amount of water (as hydrous phases) in the solid Earth (e.g., ",
"Peslier et al., 2017",
"). That latter paper suggests that as a whole, the solid Earth may contain 18x as much water (by weight) as the oceans (though there are some ",
" error bars there, with their estimate ranging from 3x to 81x). All of these results are interesting, especially within the context of questions of how Earth got its water (with this amount of water and level of hydration of the mantle strongly suggestive of much of the Earth's water being present since early accretion as opposed to being delivered by comets and the like after accretion), "
] |
[
"That was such an interesting response. Thank you."
] |
[
"Thank you! Fun read"
] |
[
"Why don’t we explore different directions of space?"
] |
[
false
] | null |
[
"There are no planets in those directions"
] |
[
"But how do we know if we have not deeply explored that direction."
] |
[
"We can look in that direction without having to send a probe"
] |
[
"To what extent does the Pauli Exclusion Principle hold true regarding splitting of energy bands? No two energy levels are allowed \"in the same place\", but what if the sample was a single crystal the size of a basketball or larger?"
] |
[
false
] |
1 mg of iron has about 10 atoms, and the Pauli principle therefore requires that each separate energy level in the free atom split into some 10 levels in a 1 mg crystal. This means each of those electrons need to be in a different energy state, with the range of states so close to each other they're considered a band. I get this. Both sides of this crystal are considered "the same place". But it's pretty easy to grow single crystal samples that are extremely large (maybe not of iron, but of other materials like silicon). So if you had a chunk of silicon the size of a basketball or even larger, are of the electrons truly unique in energy? Does the electron on one end of the sample really know not to share the same energy level as the electron on the opposite side of the sample? Or is this just a mathematical construction that is truly an estimation, and we use it to make the maths work out better? The reason why I ask is because I've heard a professor say something similar regarding quantum mechanic equations we use for magnetism- they're all just really approximations, and to call them is incorrect. The way I initially argued with myself and told myself that this has to be true is the neutron star or white dwarf example. In a white dwarf, the electron degeneracy pressure is what supposedly helps the star maintain its shape without further collapsing. Meaning all of those neutrons must have a different amount of energy. But then I realized that even neutron stars can collapse into black holes, and not only that, but to me this doesn't prove that every single fermion in that star is in a different state, it just tells me that no near-neighbors can be in the same quantum state (energy and location).
|
[
"If you want to deal with continuous bands, it's easier to forget about split levels and instead start with an 'electron gas' model. (See e.g. ",
"these lecture notes",
") You'll find that the expression for the 'exchange energy' (the change in energy by taking the Pauli principle into account) is strikingly similar to that of the degeneracy pressure of a neutron star. (as it's largely the same thing, same model, different particle)",
"For a full derivation you'd have to see something like Parr and Yang's book ",
", but suffice to say that the Pauli principle is still there, even when you don't have discrete levels. (Edit: Note that the fundamental property here is ",
" i.e. that the wave function changes sign when you ",
" the coordinates of two electrons - including their spins. I.e. Ψ(x1, x2) = -Ψ(x2, x1), where x1 and x2 are spatial+spin coordinates. The Pauli principle is a result of this, but antisymmetry is the actual boundary condition you have to enforce on your wave function)"
] |
[
"Keep in mind that the actual Hamiltonian of this thing is really really really complicated. When you do the \"band\" approximation, you're actually doing a mean field limit that averages out some of the interactions. At the end, Pauli only cares about antisymmetry of the wave-function when you interchange coordinates of two fermions, so you won't be able to capture this just by looking at the energy of the electrons. In other words, I can have Hamiltonians which have an arbitrary number of degenerate states."
] |
[
"So as long as they're connected by atoms, no matter what, it's 100% true without a doubt and can be proven experimentally that they hold different amounts of energy? You answer isn't convincing at all."
] |
[
"How do you measure the Earth's core temperature?"
] |
[
false
] |
I was just wondering how we estimate the Earth's interior temperatures. Obviously we can't get that far, how'd we come up with exact numbers?
|
[
"One piece of evidence comes from seismic waves. The speed those waves travel depends on the properties of the matter that they are traveling through, including temperature. Also some kinds of waves cannot travel through liquids, which we can use to tell that the core is partially liquid. So it must be hot enough to make whatever it is that's down there a liquid, even under the immense pressure of all the stuff above it.",
"We can use other information to tell us what the liquid stuff is. Earth has a magnetic field, which probably means a liquid iron core. This also matches up with what we think the abundances of different elements are in the inner earth. We can use big compressor machines to do experiments at extremely high pressures and temperatures to determine how hot iron needs to be to melt.",
"Another piece of evidence comes from heat flow. We know that heat is leaving the planet's interior at a certain rate. This is controlled by how much the temperature changes from inside the earth to the surface, and on the material it's made of. We also have an idea of how much heat is being generated inside the planet by radioactive decay and other processes. So we know the heat creation rate, the rate at which heat leaves, and some ideas about what it's made of. This allows us to back out the temperature change with depth.",
"One more note-taking when you see exact temperatures cited on this, they're not accurate to one degree or anything. Maybe tens of degrees or a couple hundreds of degrees."
] |
[
"Earth has a magnetic field, which probably means a liquid iron core.",
"Is not necessary. It is an unfortunate coincidence that the core is thought to be iron and iron is magnetic at room temperature. It confuses a lot of people. No material can be magnetic at those temperatures, because they are beyond the ",
"curie point",
". Any molten material that has electrical conductivity (almost everything does) is all that is needed, along with differential rotation of the core versus the mantel. ",
"Dynamo theory",
".",
"But then this gives clues to the temperature of the interior as well."
] |
[
"We know it is made of iron predominantly, thanks to studies on the propagation of seismic waves. Iron is the only element that is abundant enough in the universe and closely matches the seismic properties of the earth's core: We know its density, we know the pressure, we know also that there is a liquid and a solid core (also from seismic waves, because some don't propagate on liquid), we know where both inner and outer core are. We can match all we know so far with known behaviour of iron under similar conditions, so using lab experiments we can estimate approximately the temperature of the core.",
"However, performing such experiments on the surface of the planet is a challenge, so the temperatures are not accurate, being 4000K to 7000K a good guess. If we knew the exact point where iron melts under such pressures, we would be able to pinpoint the temperature better."
] |
[
"What does \"cross tolerance\" mean in immunology?"
] |
[
false
] |
Myeloid-Derived Suppressor Cells Promote Cross-Tolerance in B-Cell Lymphoma by Expanding Regulatory T Cells I was skimming through the article but didn't quite get the gist of the paper. Do they mean that in the presence of MDSC, Treg has less of an immunosupressive effect on B-cells?
|
[
"I don't think it really \"means\" anything. I think what they're trying to say is that it promotes tolerance in more than one way: MDSC directly inhibit CD8 cells -- we've known this for a long time. Now it seems they ",
" directly activate and increase Treg cells, which is a tolerizing kind of cell, adding another layer of tolerance. ",
"The main gist of the paper is MDSC leads to activation of more Tregs, leading to decreased killing of the tumor.",
"Most interestingly, they propose killing off MDSCs with Viagra as a \"boost\" to cancer treatment. I LOL'd."
] |
[
"It's a tricky subject. Yes, we absolutely need to address suppressor cells (of all kinds) while also avoiding massive autoimmunity. (Shock isn't really the word you're going for here.)",
"I've seen papers recently for MDSC conditional knockouts that have just as much autoimmunity as scurfy mice, so we can't just get rid of them entirely. ",
"We're working on it. People spend all day every day just pondering \"how the fuck\" in this field. =)"
] |
[
"I saw the Viagra part too and I was like huh? ",
"Well, btw -- thanks for the explanations. Do you think it is a good idea to deplete MDSC/Treg for cancer/injury treatment? Though, patients can go into shock due to increased level of inflammation.",
"Edit: Also another question, does MDSC have any direct method of inhibiting B-cells or only just T cells?"
] |
[
"Are other animals born with disabilities like down syndrome etc ?"
] |
[
false
] | null |
[
"Animals can have genetic diseases, too. This happens all the time in pure-bred animals due to ",
"inbreeding depression",
". You'll see dogs with the equivalent of cerebral palsy because of this."
] |
[
"I know that askscience isn't the place for this kind of thing, but this is one of the ",
"funniest things I have read on the internet.",
" It's a great read if you've had a stupid dog."
] |
[
"Like what Tekmo said because of inbreeding some purebred dogs have what is very similar to an obsessive compulsive disorder in humans. Commonly they will chase their tails until they pass out from exhaustion.",
"http://www.petwave.com/Dogs/Dog-Health-Center/Mental-Disorders/Obsessive-Compulsive-Disorder.aspx"
] |
[
"What was the difference between splitting the atom and nuclear fission?"
] |
[
false
] |
Possibly a stupid question. Encountered something that said that . This confused me, because I thought . Am I missing something here? What specifically was discovered in 1938 -- just that splitting an atom could release a large amount of energy? If so, why was that not apparent when they first split the atom six years earlier?
|
[
"\"Splitting an atom\" is a non-technical phrase that doesn't really have any specific meaning, while \"fission\" is a technical term for certain kinds of nuclear reactions.",
"The reaction performed by Cockroft and Walton was",
"p + ",
"Li -> ",
"He + ",
"He",
"which could be considered ",
"Li(p,α), or it could also be considered proton-induced fission of lithium-7.",
"That being said, in non-technical literature (the kinds of places where you might find the phrase \"split an atom\"), the word \"fission\" is sometimes reserved for a specific subset of what nuclear physicists would consider fission.",
"Specifically, the fission reactions which are most useful for applications, which are ",
" fission reactions (or also spontaneous fission decays) of ",
" nuclides.",
"So the reaction above, which is induced by a proton, and not on something particularly heavy, would not fall into that class, even though nuclear physicists wouldn't have a problem calling it fission.",
"What Cockroft and Walton did was a big step for particle accelerator physics, and today many accelerators all over the world are used to perform nuclear reactions (in fact, there's still at least one Cockroft-Walton generator in operation at an accelerator that I'm aware of, despite many technological advances happening since).",
"However, the discovery that heavy nuclides could be made to fission using neutrons, generally releasing large amounts of energy, and could be made to do so in a neutron-multiplying chain reaction, is what implied the possibility of nuclear reactors and weapons."
] |
[
"Thomson believed that atoms were complicated vortices of many, many negatively-charged, low-mass \"corpuscles,\" which he believed were the Proutean \"fundamental particle\" of atoms. So he believed that he had discovered subatomic particles, but that there was only one subatomic particle. He believed these particles were held together by a diffuse positive force (the origins of which he never really speculated on to my knowledge). ",
"This is how he had his model of the atom drawn",
" (from a lecture he gave in 1905) — you can see it is actually not ",
" different from what would later come, except that obviously there are more subatomic particles and the bulk of the mass is in the nucleus (for Thomson's article to work, even relative low-Z atoms had to have ",
" of corpuscles). He spent considerable time trying to figure out what kinds of arrangements of corpuscles might be stable. The round area shows the boundaries of the diffuse positive force.",
"Thomson's atom is often misrepresented in media (to draw a bigger contrast with the Rutherford atom; unlike how it is normally depicted, the electrons are not meant to just be sitting there, but rotating in complex orbits), and physicists in his day were always quite lukewarm about his atomic structure speculations (they liked the discovery of the electron — but didn't think it necessarily justified his model). Rutherford famously disproved it in 1905, and disproved the idea that there was a single Proutean subatomic particle."
] |
[
"I would just add, as an historical note, that physicists were interested but not ",
" that if you accelerated protons to fairly high energies and shot them at other atoms, you could get interesting nuclear reactions. Going from p + Li-7 to He-4 + He-4 is interesting but didn't contradict how they thought about atomic nuclei at that point, and looked a lot like other nuclear reactions they were familiar with (e.g., the resultant products are just alpha particles, which they were familiar with through other reactions). As you note, it is just as easy to see this as causing alpha particles to be ejected, which was a pretty common thing to see in the early 1930s. ",
"Whereas using a low-energy (moderated) neutron to split a heavy nuclei (uranium) was very surprising. Not at all what they had expected to be the case, and it didn't really look like the kinds of decays they had seen before (they had not seen things bigger than alpha particles being thrown off by decays). They had previously expected that a neutron absorbed would just get added into the nucleus through capture (which does happen, of course), and that the resultant product might be radioactive, but its decays would be of the ones they had already seen (very small movements around the periodic table, not huge jumps). ",
"So that was very exciting just by itself, a revolutionary way to think about high-Z nuclei, and it really challenged their understanding of what was going on in the nucleus. This interest and surprise was even before they started to contemplate the chain reaction and its technological possibilities, which happened a few months later.",
"This is just one of the reasons that even in the historical scientific literature, the Cockroft–Walton experiment is regarded mostly as a triumph of the instrument (the generator) and not as something that dramatically changed their view of the atom."
] |
[
"How much better is the James Webb Space Telescope going to be than Hubble?"
] |
[
false
] |
Is it possible to take a Hubble photo, draw a rectangle on it, and say "JWST will have the same resolution on this little square"? Any other advances beyond resolving power?
|
[
"In terms of pure resolution it is difficult to compare. Angular resolution is a function of wavelength and the two telescopes observe at different wavelengths (JWST is primarily infraread, Hubble is mainly optical/UV). The angular resolution of the JWST is about 0.1 arcseconds at 2 micrometres, this ~ the same as Hubbles at 0.7 microns. That makes it about twice as good for the same wavelength.",
"This is purely due to the larger diameter mirror, resolution is directly proportional to mirror diameter so the increase from 2.4 to 6.5 is huge.",
"If you mean resolution as in image resolution, the increase won't be huge. JWST will take similar resolution images (32MP versus 16MP iirc) but Hubble already tiles extended sources from multiple images anyway, this practice can continue.",
"The larger diameter means larger collecting area, 5 times larger. This means 5 times more light can be gathered from the same object in the same time. A big advantage, that along with a wavelength change allows JWST to look at much fainter, younger galaxies.",
"In terms of wavelength, the two instruments are different rather than one being better. Like I said before Hubble was mainly in the visible/near uv at 300-800 nm with some IR capabilities up to about 3000nms (3 microns) JWST will just touch on red light at 700nm but will extend all the way down to something like 30 microns, basically covering the whole IR spectrum.",
"The positioning of the satellites will be different, Hubble is in LEO meaning a lot of heat from the earth/moon/sun lowers the precision of its instrumentation, this is part of the reason why it does not do much work in the IR regime. At the L2 lagrange point, the JWST will be able to shield most of the heat from these objects allowing it to operate much cooler increasing it's precision. The disadvantage here is that Hubble has received many upgrades and repairs - indeed you may have heard a huge failure in manufacturing left it's image quality pretty terrible until the first space shuttle service mission a few years later. JWST will not be able to be upgraded or repaired so it's operational lifetime will be a lot shorter."
] |
[
"Handy visual aid",
" courtesy jwst.nasa.gov"
] |
[
"The wavelength that these cryogenically cooled telescopes (Herschel 60-700 microns, AKARI was 2-180 microns) is even longer than the JWST. The longer wavelength the more influence temperature has on noise. This is why these telescopes had detectors that were as cool as 1K or so.",
"A big reason why JWST can stay cool is, like I mentioned, the positioning of JWST. A launch to the L2 point is more expensive, and unservicable but by putting the Earth, Moon and Sun all in a position where a Sun shield can block out them all makes a huge difference in the operating temperature of the telescope.",
"This will allow the JWST mirror to operate at something like 50K compared to the 70-85K of Herschel. ",
"The next generation far infrared telescope SPICA will use mechanical cryocoolers to get the mirror down from ~80K to ~5K, very impressive."
] |
[
"The coefficient of static friction is greater than that of kinetic friction. Why?"
] |
[
false
] |
I shelved this question back in intro to physics but it just came up again. What's the deal?
|
[
"This is how my physics teacher explained it to me:\nThere is no such thing as a completely smooth surface, they all have small bumps and cracks. So whenever you have one surface lying on top of another, their bumps and cracks slide into eachother, causing the static friction.\nWhen your object is already moving, not every bump gets to slide into a crack, causing less friction. (like when you're driving a fast car and there's a small gap in the road)"
] |
[
"Well, let's say the coefficient of static friction were less than that of kinetic friction. Then start applying more and more force to a body at rest. You'd reach the point where the force was great enough to overcome static friction, but it since the force wouldn't yet be enough to overcome kinetic friction it still wouldn't move. So it still hasn't really overcome static friction."
] |
[
"I'm no expert at these things, but I would guess that the timescale that the forces you describe act on is very small, far too small to cause the substantial difference between static and dynamic friction.",
"Could it not be macroscopic effects? At small spatial scales, those rough teeth, once moving over a bumpy landscape, are part of two vibrating masses, the energy of which comes from the force applied to overcome dynamic friction. With that localized relative motion, the \"teeth\" would have little opportunity to engage, keeping the coefficient lower."
] |
[
"Is there any way that the sandworms from Dune could actually travel through the sand like it is described in the books or would the sand be too dense a medium to move through?"
] |
[
false
] | null |
[
"Viscosity?"
] |
[
"http://cronodon.com/BioTech/Earthworm_locomotion.html",
"It should be fine. The real issue is how fast they go."
] |
[
"They sift sand plankton for nourishment. Little tiny plants and such."
] |
[
"AskScience AMA Series: We are paleontologists here to talk about Dakota the Dinosaur Mummy, AUA!"
] |
[
false
] |
Hello ! Dinosaur mummies preserve skin and other soft tissues, but how they fossilize has always been a bit of a quandry. It's generally thought that very rapid burial is required to protect remains from predators, scavengers, and other agents of decomposition. However, they often also appear desiccated, which usually takes long-term exposure on the landscape. Recent preparation on the Edmontosaurus mummy "Dakota" revealed the first evidence of predator activity on dinosaurian soft tissues and provided an alternate explanation for how these rare fossils form. You can read in PLOS One. Joining us today are: ( ) is a paleontologist at the University of Tennessee whose research focuses on the processes of fossilization, evolution, and biology, of crocodiles and their relatives, including identifying bite marks on fossils. Find her on Twitter @UglyFossils. ( ) is paleontologist and Lab Manager of the Johnsrud Paleontology Lab, with the ND Geological Survey. She worked on preparing part of the tail, foot, and body block of Dakota the Dinomummy. ( ) is the Senior Paleontologist at the North Dakota Geological Survey and Curator of the North Dakota State Fossil Collection. His research focus in on ornithischian dinosaurs, including specimens of Edmontosaurus like Dakota the Dinomummy. ( ) is a fossil preparator with the State Historical Society of North Dakota. She prepared the right arm, portions of the left foot, helped with parts of the tail, and is currently preparing the body block of Dakota the Dinomummy. We will be joining you to answer questions at noon ET (1600 UT), AUA!
|
[
"Without time traveling it's really hard to say for sure! The more specimens we get, and the more with soft tissue, the better our depictions get. Looking at historical paleo art is quite the trip - lumbering, kangaroo, skinny, bland, wattles, etc.. I agree though - there were a lot of dinosaurs that were shrink-wrapped in skin, without enough muscle mass. Toy companies fall victim to this a lot. You get really cool poses, better skin textures, but then they all look like they're starving. I've just ended up modifying toys for teaching purposes, thickening up the tail and haunches or adding fleshy bits when they're discovered.",
"\nFossils like Dakota really help change our artistic renderings - just look at the beautiful art by Himmapaan, ",
"https://twitter.com/Himmapaan/status/1450117335562563592",
" to see the perfectly chonky tail and haunch reconstruction. When we began cleaning the tail it became painfully obvious that where the lower chevrons / haemal arches end, there was still another 18-20\" of skin that needed filling.",
"\nSame with the hands - looking at the bones, especially the last bones of the fingers - some were unguals holding nails, while others were just phalanges with nothing special. Studying the bone I could see what I assumed were two nailed fingers, and two with nothing but pads. After preparation of the mummy hand, this was verified in-the-flesh."
] |
[
"How accurate are artists renderings for the true shape of these creatures? It always looks to me like they drew the body shape too close to the bones. I know the temperatures were such that they likely wouldn’t have needed fur or much fat, but do these fossils show us a more true shape?"
] |
[
"Brendan Fraser needs no warning. He is obviously immune to all possible dinomummy curses.",
"\nI wish we had had Brendan Fraser on our side the week the dinomummy went on display here, because we were NOT immune to the curse. Flights delayed and canceled, 6\" of water in the gallery, the electrical failed in the lab during tours... we had a whole list. It was bad."
] |
[
"Falling speed is independent of mass. Why is a heavy sled faster than a light one?"
] |
[
false
] |
[deleted]
|
[
"Because a heavier sled carries greater momentum, and is subsequently less affected by friction."
] |
[
"By Newton's second law f=ma",
"Gravitational force on the surface of Earth is given by f=m(9.81), ",
"so net acceleration is given by a=f/m=[m(9.81)]/m=9.81",
"Now then consider friction (whether due to air resistance or runners on snow).",
"a=(fg-ff)/m",
"As ff gets bigger acceleration gets smaller.",
"So what is ff a function of on snow?",
"ff=fn*mu",
"Where fn is a function of mass ",
"fn=(m)(g)cos(theta)"
] |
[
"Static friction (i.e. the friction between two non-moving objects) is dependent on the pressure between the objects (in this example the weight of the sled) whereas kinetic friction (i.e. the friction between two objects sliding against each other) is less dependent on the pressure between the objects, meaning that when the heavier sled moves, its friction is not substantially different from the lighter sled (all else equal, as my science teacher would say).",
"On top of the hill, the heavier sled has a higher level of potential energy than the lighter sled as the potential energy, U, can be calculated as m (the mass) times V (the gravitational potential, which is the same for the two sleds), so a sled that is twice as heavy as another sled will have twice as much potential energy at the top of the hill as the lighter sled and at the bottom of the hill it will have \"shed\" twice as much energy to convert into speed (the friction being the same), which means it will be faster."
] |
[
"Theoretically, can you gain energy through nuclear fusion then gain energy through fission of the same material?"
] |
[
false
] | null |
[
"Unfortunately, no. The energy we're gaining (to use to heat steam in a reactor, say) comes from the change in binding energy per nucleon in the nuclei we're working with. Here's a ",
"nice plot",
" of that quantity, with atomic number (number of protons) on the x axis.",
"Looking at that plot, what you can see is that the most tightly bound (most binding energy per nucleon) nucleus is iron. To the left of iron (lower mass elements) we can release some energy for our use by combining two light nuclei to make something heavier, closer to iron. That's what happens in stars burning hydrogen/helium/etc, which stops working at iron, even for high-mass stars that can burn things all the way there.",
"To the right of iron (higher mass elements) you have higher mass things, like uranium off there on the far right, which also have a little less binding energy per nucleon than iron does. So, you can get a little energy for us to use by splitting those heavy nuclei, to end up with two nuclei closer to iron.",
"So, sorry, no circular free lunch bar. :("
] |
[
"Iirc those are usually formed in supernovae when fusion isn't sustainable in a star."
] |
[
"There's an emerging set of data that strongly suggests that another very large contributor might actually be neutron star merging. Would still follow the r-process, just a different manner of getting there.",
"https://en.wikipedia.org/wiki/R-process#Astrophysical_sites"
] |
[
"What kind of steel makes magnets stronger?"
] |
[
false
] |
[deleted]
|
[
"Electrical steel is what is used in transformers and motors. It has high permeability and small hysteresis. You can also look up magnetic circuit to see how your fixture could be used to generate the highest field for the flux generated by the magnet."
] |
[
"Laminated steel is often used in those applications to reduce hysteresis, but those involve changing electric currents and magnetic fields. As I understand OP’s question there will be no electrical current (AC or DC) involved, only a permanent magnet. So I believe hysteresis is not a consideration. Please correct me if I am mistaken. ",
"Would any particular type of steel perform better than another with a permanent magnet, and are the performance gains enough to be worth a higher material cost and/or higher cost to machine it to fit the magnet?"
] |
[
"Non electric, permanent neodymium magnet ( a magnet in a blok of steel with a rope attached, to trow in the ocean an pull the rope back to retreave sweet treasure)"
] |
[
"What would Earth be like if it rotated on the ecliptic?"
] |
[
false
] | null |
[
"You mean if the orbit of the Earth lay in the ecliptic plane? It does in any situation where the Earth orbits the Sun (Edit: like in real life).",
"You mean if the rotation of the Earth had it's axis in the ecliptic plane? The seasons would be dramatic - like the entire planet was in the arctic circle. The equator would probably still be inhabitable: in two seasons it would have a fairly normal night day pattern, but in the other two seasons it would be sunset/sunrise pretty much all the time. Further away from the equator, the winters would be completely dark and freezing, and the summers would be impossibly hot. No part of the planet would be cold all year round because every part of the planet would spend time directly facing the sun.",
"You mean if the rotation of the earth had orbit perfectly perpendicular to the ecliptic plane? It would look much like it does now, except with no seasonal variation at all.",
"I hope one of those answers your question."
] |
[
"Diagram",
"I hope this makes sense. I've only described how the sun would look for the seasons on the poles and equator. There would be a sinusoidal gradient that gives the description in between. I've also mostly only shown the behaviour at the peak of each season - again the gradient in between follows a sinusoid.",
"Also, not being a meteorologist, I have no idea what the atmospheric patterns or water currents would look like or how they'd affect the weather. If anyone knows a meteorologist, I'd love to find out...",
"Thinking about it, I think the equator of this planet would be a picturesque place to live..."
] |
[
"Diagram",
"I hope this makes sense. I've only described how the sun would look for the seasons on the poles and equator. There would be a sinusoidal gradient that gives the description in between. I've also mostly only shown the behaviour at the peak of each season - again the gradient in between follows a sinusoid.",
"Also, not being a meteorologist, I have no idea what the atmospheric patterns or water currents would look like or how they'd affect the weather. If anyone knows a meteorologist, I'd love to find out...",
"Thinking about it, I think the equator of this planet would be a picturesque place to live..."
] |
[
"Traveling through the universe. [Big Bang] [Time Travel]"
] |
[
false
] |
Assuming that the phenomena of the Big Bang did occur. If there truly was a singularity that our universe existed in. Then, according to the theory, if you were to travel in the direction where this singularity once existed; would you be technically traveling back in time? Also how difficult would it be to determine where this singularity once existed, based off of the movement of surrounding galaxies? EDIT: Of course, to truly head back in time, you would need to travel faster than the speed at which the universe is expanding.
|
[
"No?",
"I really dislike the balloon analogy, but this is one case where it may be helpful. Imagine that you have this perfectly spherical balloon. The 2-dimensional surface of that balloon is all of space (we're dropping a spatial dimension so that you can picture it). The only directions in which a person living in this balloon can point are those along the balloon's surface. That said, they can still work out the \"radius\" of the balloon by seeing how far they have to travel to get back around to where they started. Now, let's say that the balloon is expanding. As it does so, the objects on it get further and further apart, right? And the people who measure the \"radius\" see that it gets bigger and bigger—you have to travel further and further to get back around to where you started. Now, let's run that backward. As you do so, all of the stuff on the surface gets closer and closer together, until you find that at some finite point in the past the balloon had ",
" radius—it vanishes into a point. Running forward again, we see that singular point (i.e., singularity) suddenly expand into a two-dimensional surface. That is, at all times ",
" the singularity, it's a two-dimensional expanding universe, but ",
" the singularity it's a true point with no non-zero dimensions."
] |
[
"the direction where this singularity once existed",
"That's not a real direction (unless you consider \"straight into the past\" a direction). The so-called \"Big Bang\" was not an explosion into an empty void, away from which all matter is now moving. Rather, it was the rapid expansion of all of space in such a way that every point got further away from every other point.",
"Also how difficult would it be to determine where this singularity once existed, based off of the movement of surrounding galaxies? ",
"The singularity \"existed\" everywhere."
] |
[
"That's what the analogy says, but it's not quite right (the balloon analogy is really only good for one or two things, but it can often mislead which is why I don't like it).",
"There are two main places where the balloon analogy fails here:",
"1) In the analogy, the two-dimensional surface is curved in a three-dimensional space. It's necessary that this be the case because all of our experience (indeed, all of the events for which evolution has prepared us to encounter) the only sort of curvature ",
" a \"two dimensional surface curved in three dimensions\". The thing is, as far as our mathematical descriptions are concerned, curvature is an intrinsic property. You can make a two-dimensional sphere without putting it in a three-dimensional space and it remains curved. Without any evidence to the contrary, that's what we think is happening in our universe: the spatial part is three-dimensional and curved, but ",
" sitting in a larger space.",
"4) That said, there is a fourth-dimension to our spacetime. It's just not a dimension in which we're curved (though it ",
" be curved; yay general relativity). It's ",
" not the direction \"toward the center\" (well, it sort of is, but it's complicated). The thing is, it's ",
" a spatial dimension. In the balloon analogy, the direction toward the center is a spatial direction, as it has to be because that's all we're capable of \"visualizing\". But time is ",
". It's connected up to the spatial dimensions in a way that differs from the way in which they're connected to one another. It's this odd coupling that gives us the fact that the speed of light is constant and all the associated effects like time-dilation and space-contraction.",
"That probably came out really confusing, but I don't know of a much better way to explain it. All of our experience has primed us to think of two-dimensional curved surfaces in a three-dimensional space, so trying to come up with an intuitive \"picture\" that describes an expanding, curved, three-dimensional space that's ",
" sitting in a larger space but ",
" connected to (and mixed with) a fourth dimension that's different is just something I don't know how to do. That said, I'm happy to attempt to clarify any of that."
] |
[
"What is Time ?"
] |
[
false
] |
What is time, and why does it occur. What would happen if there was no time ? How does it occur and is it something like a wave or something physical or none of these.
|
[
"So let's start with space-like dimensions, since they're more intuitive. What are they? Well they're measurements one can make with a ruler, right? I can point in a direction and say the tv is 3 meters over there, and point in another direction and say the light is 2 meters up there, and so forth. It turns out that all of this pointing and measuring can be ",
" to 3 measurements, a measurement up/down, a measurement left/right, and a measurement front/back. 3 rulers, mutually perpendicular will tell me the location of every object in the universe. ",
", they only tell us the location relative to our starting position, where the zeros of the rulers are, our \"origin\" of the coordinate system. And they depend on our choice of what is up and down and left and right and forward and backward in that region. There are some rules about how to define these things of course, they must ",
" be perpendicular, and once you've defined two axes, the third is fixed (ie defining up and right fixes forward). So what happens when we change our coordinate system, by say, rotating it?",
"Well we start with noting that the distance from the origin is d=sqrt(x",
" +y",
" +z",
" ). Now I rotate my axes in some way, and I get new measures of x and y and z. The rotation takes some of the measurement in x and turns it into some distance in y and z, and y into x and z, and z into x and y. But of course if I calculate d again I will get the ",
". Because my rotation didn't change the distance from the origin. ",
"So now let's consider time. Time has some special properties, in that it has a(n apparent?) unidirectional 'flow'. The exact nature of this is the matter of much philosophical debate over the ages, but let's talk physics not philosophy. ",
" we notice one important fact about our universe. All observers measure light to travel at c regardless of their relative velocity. And more specifically as observers move relative to each other the way in which they measure distances and times ",
", they disagree on length along direction of travel, and they disagree with the rates their clocks tick, and they disagree about what events are simultaneous or not. But for this discussion what is most important is that they disagree in a very ",
" way. ",
"Let's combine measurements on a clock and measurements on a ruler and discuss \"events\", things that happen at one place at one time. I can denote the location of an event by saying it's at (ct, x, y, z). You can, in all reality, think of c as just a \"conversion factor\" to get space and time in the same units. Many physicists just work in the convention that c=1 and choose how they measure distance and time appropriately; eg, one could measure time in years, and distances in light-years. ",
"Now let's look at what happens when we measure events between relative observers. Alice is stationary and Bob flies by at some fraction of the speed of light, usually called beta (beta=v/c), but I'll just use b (since I don't feel like looking up how to type a beta right now). We find that there's an important factor called the Lorentz gamma factor and it's defined to be (1-b",
" )",
" and I'll just call it g for now. Let's further fix Alice's coordinate system such that Bob flies by in the +x direction. Well if we represent an event Alice measures as (ct, x, y, z) we will find Bob measures the event to be (g*ct-g*b*x, g*x-g*b*ct, y, z). This is called the",
" Lorentz transformation",
". Essentially, you can look at it as a little bit of space acting like some time, and some time acting like some space. You see, the Lorentz transformation is much ",
" a rotation, by taking some space measurement and turning it into a time measurement and time into space, ",
" a regular rotation turns some position in x into some position in y and z. ",
"But if the Lorentz transformation is a rotation, what distance does it preserve? This is the really true beauty of relativity: s=sqrt(-(ct)",
" +x",
" +y",
" +z",
" ). You can choose your sign convention to be the other way if you'd like, but what's important to see is the difference in sign between space and time. You can represent all the physics of special relativity by the above convention and saying that total space-time length is preserved between different observers. ",
"So, what's a time-like dimension? It's the thing with the opposite sign from the space-like dimensions when you calculate length in space-time. ",
"We live in a universe with 3 space-like dimensions and 1 time-like dimension",
". To be more specific we call these \"extended dimensions\" as in they extend to very long distances. There are some ideas of \"compact\" dimensions within our extended ones such that the total distance you can move along any one of those dimensions is some very very tiny amount (10",
" m or so).",
"from here"
] |
[
"Time is directly related to change. If there was no time there would be no change, the universe would be in some constant state, and the only possible way to move in space (given there is space) would be at c. ",
"The best description that I've ever read (and I do believe it was here on ",
"r/askscience",
") described time as 'futureward' and 'pastward', just like forward and backward. If you imagine some location in three-dimensional space to be one term x, and plot a vector against time y, you will see that as you move in space you move in time at a velocity related to your velocity in space, until you reach the speed of light. In a fixed interval of time, as your change in distance increases the vector will approach horizontal. That is, moving in space without moving in time (aka the speed of light). This is where the notion that photons do not experience time comes from. ",
"This is my favorite way to think about relativity and time, and it may be that I have some incorrect notions. This is no area of expertise for me, but I am fascinated as hell by it."
] |
[
"That's an amazing answer.. So is there time on the very edge of our universe. Do scientist believe that once you get to the edge of our ever expanding universe is there time on the other side (I'm bad at phrasing this) "
] |
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