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[
"What is uncertainty principle and what is it's significance?"
] |
[
false
] |
You want to see an electron. What do you do to see that? You shoot some photons aka light on it to 'see' it and this causes the electron to get more unstable and hence it becomes impossible to track down its original "position". Hence, the uncertainty. This is what is given in our science textbooks. It seems like it is dumbed down to it's basics. Can someone please give a more elaborate yet easy to understand explanation of the uncertainty principle and explain it's significance in physics?
|
[
"The uncertainty principle is a mathematical consequence of the way that position and momentum are related in quantum mechanics. Here is a slightly more accurate (but still handwavy) picture:",
"A particle with a definite momentum has a definite (de Broglie) wavelength. Something with a definite wavelength essentially has to look like a sine wave (via the Fourier transform, if you're curious.) But a sine wave looks basically the same at all spatial positions, so there's no information about ",
" the particle is.",
"On the other hand, if you know exactly where the particle is, you have no real way of assigning it a wavelength (since there aren't two points to measure between) and therefore you don't know its momentum.",
"The mathematical formula that expresses this is:",
"(uncertainty in position) * (uncertainty in momentum) >= hbar / 2",
"where hbar is the reduced Planck constant, which is (kind of) a measure of \"how quantum\" the real world is."
] |
[
"It's important to remember that the uncertainty principle is just one of many (experimentally verified) ",
" of quantum theory.",
"You're correct in that the idea that \"the observer affects the observed\" is a bit simplified. It's more than that. If you prepare a system for measurement, you're going to get a statistical distribution. The uncertainty principle can deal with ",
" systems and not be able to pin down both the position and momentum to arbitrary accuracy. You don't have to measure one after another for uncertainty to be applicable.",
"Quantum statistics are weird for many reasons (mainly the fact that imaginary numbers are involved), and Heisenberg uncertainty is just a manifestation. "
] |
[
"I never quite got it, until your sine wave example. Thank you, oh person of science"
] |
[
"What does the band of muscle at the back of the head do?"
] |
[
false
] |
I've been looking at the muscle anatomy of the head and I'm confused. There's a band of muscle at the back of the head in between the ears and I don't know what it does. The area surrounding it seems to be mainly composed of tendons so I'm not sure why this muscle is there. Does anyone know?
|
[
"I assume you're referring to the occipital belly. Some believe that the occipital belly, at the back of the skull, and the occipitofrontalis muscle, at the front of the skull, are essentially the same muscle, but others classify them as two separate muscles. As far as I know, the occipital belly muscle helps move the scalp back and that's about it, so it could be part of the muscular system that helps us create facial expressions (since pulling down on the back of the scalp would also move the front of the scalp)"
] |
[
"I’ve heard several of the facial muscles being referred to as vestigial. These come from ancestors that could wave their ears and such to (I’m presuming) ward off flies."
] |
[
"This makes a lot of sense. My very nearsided family has always talked about how we think wearing glasses makes you more aware of these muscles because you often wiggle/pull your ears back to pull your glasses up, which seems like it may be the only real function of the vestigial trait"
] |
[
"How do scientists determine the gravitational pull of exoplanets?"
] |
[
false
] | null |
[
"Whether or not we know the gravitational pull of an exoplanet depends on how we detect it. For most exoplanets, the best we can get is an estimate of size by observing how much of a star's light is blocked when the planet passes in front of it. But without knowing the planet's density, we can't know its mass, which is what we need to figure out its gravity.",
"The primary method we have for determining the mass of an exoplanet is the radial velocity method. When we observe stars, there are dark absorption lines (from various atoms) in their spectra. We know where these lines are supposed to be. If a star is moving toward or away from us, then light coming from the star will be squeezed or stretched respectively by the Doppler effect, which shifts the positions of the spectral lines.",
"If we notice that a star's lines move back and forth very regularly, we can infer that it is being nudged by another object in orbit of it. If we can't see another object and the star is only being nudged a little bit, then it's probably an exoplanet. The duration of this cycle is the exoplanet's year. The maximum shift in a line corresponds to the star's speed. These two pieces of information tell us what effect gravity is having on the system, from which we can estimate the mass of the whole system (star+planet). If we already know the mass of the star (estimated based on its spectral type, say), then the difference is the mass of the planet."
] |
[
"These two pieces of information tell us what effect gravity is having on the system, from which we can estimate the mass of the whole system (star+planet).",
"No. Radial velocity measurements are sensitive to the mass ratio, or more precisely (planet orbital speed)*(planet mass)/(star mass). The mass of the star has to be estimated based on its type, size and temperature. The orbital speed comes from the orbital period and the mass of the star."
] |
[
"Bleh, you're right. I got lazy at the end and didn't quite remember the math that takes you from star speed and exoplanet period to exoplanet mass. Momentum is conserved, which sets up the ratio you spelled out. Kepler's third law (or Newton) and the period get you the planet's orbital speed. Thanks for catching that."
] |
[
"What produces the whistling sound you hear when a large bomb is being dropped or a firework is going off, etc?"
] |
[
false
] |
[deleted]
|
[
"Fireworks are designed to whistle, they basically have whistles built into them for effect which create sound as they rush through the air.",
"In war films and documentaries the sounds of falling bombs etc. are not necessarily authentic, but are added afterwards to help communicate the story. Oftentimes the original footage is silent. Some bombs and attack aircraft have had whistles or sirens added to them to increase the terror inflicted on the enemy. Most famously the German Stuka dive bomber of WWII with their distinctive shriek."
] |
[
"Bombs have a safety device which is unscrewed by a small propeller when they fall through the air. This keeps them from exploding if the plane crashes. And the propeller makes the whistling sound.",
"And as ",
"u/scroam",
" pointed out, fireworks are designed to whistle."
] |
[
"Would you also count the doodlebugs or V2 rockets in this? They made a loud noise until their engines stopped. Then the psychological terror kicked in as you waited to hear where it hit. "
] |
[
"Why does torque point where it does in a spinning wheel?"
] |
[
false
] | null |
[
"Right, so how does it translate to the real world? Why does a symmetrical wheel appear chiral?"
] |
[
"Right, so how does it translate to the real world? Why does a symmetrical wheel appear chiral?"
] |
[
"My original question...\nForget torque, why is the direction of the angular momentum the way it is out of two possible, seemingly impartial, directions? Hell, even electromagnetism is applicable to this question, but a spinning object should be less \"mystifying\" so I didn't even mention it."
] |
[
"How can light be both a wave length and particles?"
] |
[
false
] | null |
[
"If you think ",
" weird, how about electrons? They're both waves and particles too.",
"On one level -- \"it just is\". On another...",
"It boils down to something in the philosophy of science, called ",
". It turns out that the concepts of \"particle\" or \"wave\", convenient as they are for learning, don't really correspond with actual categories of thing that are found in the real world. The common example of a mismatched category is the imaginary colors \"bleen\" and \"grue\" - say, bleen things might appear blue on odd-numbered days and green on even-numbered days, or vice versa. You can describe the world of color perfectly adequately in terms of those colors, but it would be more awkward than using the familiar ones you're used to. That's because most things aren't really bleen or grue by that definition, so you might say \"The sky is bleen on odd numbered days, but grue on even numbered days, how can it change colors like that so routinely?\". ",
"The concepts of particle and wave are sort of like the colors bleen and grue -- they don't match, exactly, with how the Universe itself behaves, so objects in the Universe (like light) have some of the characteristics of each."
] |
[
"A good rule of thumb is that ",
". This means that any interaction with matter - absorption and emission - must occur in discrete chunks of ",
" which we call photons. For all other cases, it's often simpler to think of light in terms of EM waves.",
"Light is an electromagnetic wave - it is a changing electric and magnetic ",
" that move through space together. Waves are fundamentally a way that ",
" moves through the universe. Waves are often (always?) associated with some type of field (like the electric field).",
"Put another way - the ",
" transferred between light and matter is quantized, but the field is classical (non-discrete) object."
] |
[
"This is not correct. The field is also quantized - its components obey uncertainty relations. See ",
"this",
" (technical article).",
"Example: One cannot know both the amplitude and phase of an electromagnetic wave with arbitrary accuracy. This affects the design of gravitational wave detectors (",
", the ",
"LIGO",
" interferometer)."
] |
[
"I am currently taking Ranitidine (which sells as Zantac in the USA). Why are the pills so sweet to the taste?"
] |
[
false
] | null |
[
"Lots of pills are sugar-coated to mask unpleasant taste."
] |
[
"Is it Children's Chewable Zantac?"
] |
[
"Sure beats a spoonful!"
] |
[
"PHYSICS: Are there events between atomic or subatomic particles where the collision is not perfectly inelastic?"
] |
[
false
] |
Are there events between atomic or subatomic particles where the collision is not perfectly inelastic? This may be a silly question but my searches haven't given me a satisfying answer. Thanks! Also I'm new to posting on AskScience and couldn't figure out how to apply a field to the question. Sorry. Edit: nvm
|
[
"Honestly, I'm not sure I've ever heard \"perfectly inelastic\" be used to describe a collision that was not macroscopic.",
"A perfectly inelastic collision means that the maximum amount of kinetic energy is removed from the system by the collision. In the case of colliding rubber balls, this means the balls stick together when they collide. Some energy is used up deforming the rubber, some energy is lost to heat, etc.",
"If you collide two hydrogen atoms though, you can get an inelastic collision because some of the kinetic energy the hydrogen atoms had can be used to excite electrons. In some sense, two hydrogen atoms can collide and stick together as a hydrogen molecule, but the process of forming the molecule releases energy, so this doesn't fit the definition of a perfectly inelastic collision either.",
"So I believe every collision between atomic/subatomic particles can be classified as elastic or inelastic (but not perfectly inelastic). You get elastic collisions between particles with no internal energy levels (electrons, photons, etc.), and you can get inelastic collisions between particles that have energy levels that can be excited by the collision (atoms, nuclei, protons, etc.). Elastic collisions are also possible with the latter set of particles.",
"Because inelastic collisions probe the energy levels of the particles, they can be used to probe the internal structure of these particles. For example, inelastic collisions were used to figure out that protons were actually composed of quarks.",
"Sorry for the long-winded answer. Let me know if you still have any questions."
] |
[
"Thank you so much for taking the time to answer! \nNo worries on how long you answer was, it was thorough. Which is good. ",
"I do have an additional question regarding the energy levels of electrons and photons. You mentioned that they have no internal energy level... Do you think you could elaborate on this? Is it because photons are massless that they can't have energy in and of themselves but do have energy when exerted upon exterior particles...",
"Again thank you for your time. "
] |
[
"Very helpful, thank you. ",
"My understanding is that once you move beyond fundamental particle we have no measurable evidence so theories like Super String Theory take hold of possible structures. Would you happen to know if the vibrating strings described in this theory are attributed any mass or energy level? In which case this theory would state that fundamental particles may vary in their internal energy... Or are the \"strings\" in the theory in reference to more of a plane or dimension? "
] |
[
"Does synesthesia hamper the sense it manifests in?"
] |
[
false
] |
Say you have a synesthesia where you see the letter A as red. You are shown a paper with a yellow A and a blue A. Can you tell that the letters are of different ink colors? Is it as easy and quick as compared to one with no synesthesia? Do you expererience both colors, only semantic or only visual or do you experience a blend or mix of them?
|
[
"I can always see what color letters are printed in. Like as I'm typing this, my words are clearly white. Usually the colors I see from synesthesia manifest as a translucent highlight around the word or the color would feel like it's encasing my brain. (Wonderful description, I know.) If letters or words are printed in a color that doesn't match up with my brain colors, it'll make me feel nauseous because the colors are oh so very wrong in my brain. I also won't be able to \"see\" my brain colors that well. The association is still there, but it would feel like my brain colors and the color actually on paper are fighting."
] |
[
"Does the fighting happen visually and is there pain involved?",
"Does it help if the whole word is one color?"
] |
[
"The fighting happens semantically or psychologically. Like, for example, McDonald's is usually printed in a bright yellow, but my brain wants to see it as turquoise and red. Since the yellow is so strong and actually there, it'll cause a disagreement in my brain and it'll make it harder for me to see my brain colors on the word.",
"And there is some pain. I'll get a bad nausea feeling, along with a mild headache.",
"It is easier to see words printed all in one color. If each individual letter is in a different color and my brain finds each and every color wrong, it will give me something close to sensory overload"
] |
[
"How can I calculate the weight of a cubic meter of fat?"
] |
[
false
] |
I understand that there are different fats, I have no further knowledge of the type of fat... how can I roughly calculate the weight per kg / Tonne / cubicmeter? Thanks for any help, I don't know where to start on this one...
|
[
"Weight per kg is exactly one kilogram.\nWeight per metric ton is exactly 1000 kg.\nThe cubic meter is the only challenge. \nHere's what I found: ",
"http://www.aqua-calc.com/page/density-table/substance/animal-blank-fat-coma-and-blank-bacon-blank-grease",
"\nAccording to this, the answer is 870 kg for bacon grease type fat."
] |
[
"You don't ask the question very well, but I'll avoid unhelpful flippant answers and try to guess your intent.",
"First off, if you know the density of fat, you multiply that by a million, because density is per milliliter, and there are a million milliliters in a cubic meter (100 x 100 x 100). That gets you the number of grams and dividing by 1000 gets you the number of kilograms.",
"So googling the density of things lets you answer these questions accurately.",
"You can estimate an answer to questions like this pretty easily, if that is what you are getting at. The question you ask yourself is, does it float?",
"The density of water is 1.0, so that's a million grams or 1000 kg per cubic meter. If something barely floats it will be a little less than that, and if it barely sinks it will be a little more.",
"I can use this to guess, for example, that the mass of a cubic meter of wood native to my locale will be maybe 700-1000 kg depending upon species and how wet it is.",
"With regard to fat, you can ask yourself whether you think it sinks or floats, and if you had answered \"it barely floats\", you could have estimated the answer provided by didzisk pretty closely with nothing more than your brain."
] |
[
"Thanks. It's not about floating though. The grease separater gets disposed in cubic meters, but I have to report the data in tonnes / kg."
] |
[
"Is there a reason why we can't invent a device to objective measure pain level?"
] |
[
false
] |
I imagine if there was a device that could actually tell you how much pain someone is in, that would have a world changing effect on everything we know. Is there a reason why this is not feasible? What are the limitations to creating such a device?
|
[
"Pain can't even be defined, let alone measured.",
"Seriously, try to define pain!",
"In the end it doesn't really matter because pain is a subjective experience. It doesn't matter what caused the pain, only how much you are in and that's pretty well measured by asking the patient 'on a scale of 1-10, 1 being no pain and 10 being the worst pain imaginable'."
] |
[
"I think fMRI (functional Magnetic Resonance Imaging) can tell how much pain a person suffers. They are expensive. "
] |
[
"Well I was wondering because surely something is occurring on a physiological level, even if pain was subjective, isn't there anyway to measure what physiological changes are occurring?"
] |
[
"Are telescope images of objects such as galaxies that are hundreds or thousands of light years across, are they distorted?"
] |
[
false
] |
My thought process is that if you look at a galaxy from an angle that would put one end of the galaxy dozens if not hundreds of light years closer to us than the furthest end, would that mean that we are looking at a distorted image?
|
[
"They are, but only by an imperceptibly small amount. Stars in the outer edge of a Galaxy will be moving at about 200 km/s. Their light takes about 100,000 years to cross the galaxy. So in that time stars on the far side will have moved about 70 light years, so ~1/1000th of the entire galaxy's size."
] |
[
"Ah, I know what you mean.... interesting. In principle, yes. But: Huge (spiral) galaxies like the Milky Way or Andromeda are about 100.000 lightyears across. That of course that the part of the galaxy that is closer to us, is also older* than the part which is further away.",
"On cosmic time scales, 100.000 years is nothing. So the galaxy that is observed has the same look and the same properties everywhere.",
"Very good question!"
] |
[
"Parallax measurements only bring you out a couple of hundreds to a thousand or so lightyears, because the measured angle gets soooo small, that our best telescopes can not measure it."
] |
[
"Why does a television's signal strength increase while I'm touching the antenna?"
] |
[
false
] |
It's happened on numerous occasions and I was curious as to why it happens. I also wanted to know how to emulate this without having to touch it to keep the signal strong.
|
[
"By touching the antenna, you are effectively increasing the size of the antenna. And while bigger isn't always better, this does allow TV signals to be picked up more clearly in some cases. (It could just as easily make it worse, but how often are you touching the antenna when the signal is good?)",
"You could try extending the antenna with an unwound metal coat hanger, which may help. Or get cable."
] |
[
"If the reception is already good, you might end up adding some unwanted noise to the signal. The antenna is (almost) perfectly tuned so any change will be for the worse."
] |
[
"Let's see if this gets past the mods, it's hilarious yet accurate in a way."
] |
[
"Do celestial bodies have decaying orbits?"
] |
[
false
] |
[deleted]
|
[
"If there is nothing else going on, the emission of gravitational waves makes orbit decay over time. Apart from black holes and neutron stars close together, the timescale of this process is much longer than the age of the universe. It will become relevant, but only in the very distant future. Eventually most of the objects in a galaxy get ejected from random fly-bys and the rest falls into the central black hole."
] |
[
"Phobos, one of Mars's moons has a decaying orbit:\n",
"what the ESA says:"
] |
[
"For planets and moons the main migration is tidal and so bodies tend towards what is known as tidal equilibrium (circular orbits with aligned spin-orbit axis). This effect can increase or decrease orbital distance (depends on a number of things such as spin and orbital speeds as well as on the convective emotion inside the body). Tidal equilibrium subtly includes effects that indirectly act on the orbital evolution such as magnetic breaking (acts to slow the spin of one body) and stellar mass loss (acts to increase orbital separation of one body from the body losing mass).",
"So it really just goes both ways (as in an increase or decrease of orbital separation, in some cases one follows the other) as the real end point is a circular orbit not any orbital separation."
] |
[
"Why is there a very high-pitched sound coming from my CRT television? What is making it?"
] |
[
false
] |
Not sure if this falls under Physics or Engineering.
|
[
"The frequency that the CRT puts out is a direct function of the refresh rate of the screen and the number of scan lines on the screen.",
"If you take 29.97 (the refresh rate of an NTSC signal) * 525 (the vertical resolution of an NTSC signal) = 15734, which is the frequency of the tone produced by the TV. ",
"Source. ",
"http://en.wikipedia.org/wiki/Cathode_ray_tube#High-frequency_audible_noise"
] |
[
"I can confirm that all CRT monitors make this high pitch sound no matter if it is a television or a radar display. I can walk into a room and immediately tell if one is on while others in the room can not."
] |
[
"Only some people can hear this noise. All CRTs TVs make the noise (That I've been around anyway), if the OP only hears it on his TV, then it would be a capacitor going, if not and he hears it on others, then it's the refresh rate of the TV.",
"How come they all sound the same pitch?"
] |
[
"How come similar latitudes north and south don't experience the same climate?"
] |
[
false
] |
Base on it seems like southern hemisphere locations which are equidistant from the equator are not as cold as their northern counterparts. What causes this?
|
[
"There are ",
" influences on climate besides latitude. At the gross scale and for this observation, the primary reason is the relative proportion of a given latitude that is land vs ocean, where the southern hemisphere has more ocean on average. ",
"Continental climates",
" generally have larger temperature ranges than the climate over large bodies of open water, i.e., the ocean."
] |
[
"Human geography (which sounds like the class you took) and physical geography (which sounds like the class the poster is describing) are typically two different courses. An intro geology course might also cover some of this, but depending on the course, climate might be a relatively small component."
] |
[
"If you could I would encourage you to take a geography class. They should cover this in great detail. It’s incredibly interesting to me and it sounds like it would possibly be to you as well. ",
"Yeah at a macro level, latitude matters, hemisphere matters for timing, but then as you zero in on the nuances of an area, proximity to shoreline, altitude, the prevailing ocean currents that are nearest, amongst so many other things, give rise to a local climate. ",
"If you do a deep dive on “Mediterranean climate” you might get a decent idea of the forces at play in the info you find."
] |
[
"When and how did we learn the position of the planets in the solar system?"
] |
[
false
] |
For example in what year did we found that Jupiter is the 5th planet from the Sun? How did we learn that Saturn was similar in size but even further and in the 6th position?
|
[
"Although I'd like to encourage more history of science questions here, I'm not sure how many answers you might get. If you don't get an answer, you can also try ",
"/r/askhistorians",
", ",
"/r/historyofscience",
", or ",
"/r/philosophyofscience"
] |
[
"As soon as people realized the planets orbited the Sun it is pretty obvious. The time for one orbit is easy to find by watching the planets for a while and you get relative distances by assuming the planets have somewhat smooth motion in space. At the time of Kepler people had quite good relative distance measurements already (allowing Kepler to find a relation between orbital period and time), so at the very latest by then.",
"This is a 2500 years old model",
". It has Earth as center, but even back then people recognized a relation between distances and orbital period. It has Mercury, Venus, Sun (instead of Earth), Mars, Jupiter and Saturn in the right order just with the wrong object as center."
] |
[
"You may be interested in ",
"this",
" page which gives all the details of timelines of discoveries of planets and other objects in the solar system.",
"As a side point we may not have discovered all the planets as there is still the open question of it planet x actually exists or not."
] |
[
"Does putting Vitamin E lotion on your skin actually do anything?"
] |
[
false
] | null |
[
"I did a pubmed search for articles with \"topical vitamin E\" in the title. There is a paper that showed that it reduced UVB (but not UVA) skin damage in swine skin, when combined with a commercial sunscreen, compared to the sunscreen alone. Other than that, studies looking at potential benefits for surgical scars, doxorubicin-induced oral mucositis, and something called \"yellow nail syndrome\" have all been negative."
] |
[
"In addition, many sunscreens contain vitamin E as Tocopheryl Acetate. Just look among \"inactive\" ingredients."
] |
[
"Do you strictly mean rubbing liquid vitamin E on your skin? Or a lotion that has been fortified with the vitamin?"
] |
[
"I have a keen interest in martial arts but want to know how is this possible? What's the trick? Can anyone here explain what is happening here? [Sorry its a video link]"
] |
[
false
] | null |
[
"(Oh hey, something on AskScience I'm actually qualified to talk about!)",
"I trained martial arts in China for two years in my early twenties. I lived as the only foreigner in a school amongst a bunch of super hardcore dudes, some of whom were part of the school's performance troupe. I've seen a 15 year old boy, no more than 120lbs, do the spear-in-the-neck trick. I also saw a slight, 16 year old girl get the sticks broken on her limbs and torso.",
"I saw numerous exhibitions of \"unusual feats of strength and skill\" which were almost always attributed to qi/chi. In every single case there was always something that seemed off -- I'd played around with card tricks before so was very attuned to acts of misdirection and such. I went there having watched videos like the one linked, thinking that there was a possibility some of this stuff was real. I came back home being quite certain it was all bullshit.",
"The people doing these things are in insanely good shape. They usually train 30-50 hours a week, and most of the guys who get to the exhibition level start when they're 4-7 years old. They are hard as fucking rocks, but I assure you they have no magical powers-- if anyone here had trained 40 hours a week for 15 years from a young age, you'd most likely be able to do some of the same things. Others have gone over why the physics of what's shown in this video don't necessarily kill someone-- as long as they're in good enough shape.",
"I got a chance to see behind the curtain while I was there-- while these sort of guys are training. They practice those little \"qi\" embellishment movements in the mirror, and have coaches pick apart their grunting technique. I don't want to devalue the incredible physical abilities of them-- it was truly awe inspiring to see what that much dedication can do for/to the human body, but when it comes to these demonstrations, it's just as much about showmanship as physical abilities. ",
"Rather than thinking of these people as 'spiritual warriors', just think of them as circus performers, and it begins to make a bit more sense.",
"As for the actual qi thing, everything I was taught, and everything I saw, I can fairly confidently say that \"concentrating your qi\" is merely an analogy for concentrating your attention to your lower abdomen area (and visualizing any movements that involve your core) while expanding your diaphragm extremely hard.",
"PS - While I'm at it, let's go over this whole 'Shaolin' thing. Shaolin was an abandoned temple until movies made it popular in the 1980's, then it became a huge industry. Most of the original style was lost when the temples were destroyed and outlawed during the ",
"Great Leap Forward",
". Now, there are something like 180 schools in the town surrounding the old temple, with ~100,000 students; the largest school has over 30,000 students alone. The higher-ups in the Shaolin temple are not monks, they're businessmen with shaved heads and robes. They have fancy pads and pricey cars, know nothing of the martial arts, and don't ascribe to any of the religious tenets-- I got to eat dinner with one of them once-- he had two prostitutes with him, ate meat, and drank heavily. The next day I saw him with two different prostitutes. It's all marketing. Huge business."
] |
[
"They calculated the \"force\" based solely on the speed of the bat. That's not a measurement that would pass any kind of scientific scrutiny."
] |
[
"They calculated the \"force\" based solely on the speed of the bat. That's not a measurement that would pass any kind of scientific scrutiny."
] |
[
"How much does centrifugal force counteract Earth's Gravity?"
] |
[
false
] |
Would a person weigh less closer to the equator? Would it be possible for a planet the size of Jupiter to spin so fast that its gravitational pull is the equivalent of Earth's?
|
[
"0.3% at the equator."
] |
[
"Reread the question; it's legit."
] |
[
"You do weigh less near the equator, but it's mainly because the earth is bulged out near the equator so you're further from the center of mass. I suppose the rotation does affect your weight, but it's a very small correction. "
] |
[
"Why are blood cells red/white?"
] |
[
false
] | null |
[
"Interesting. Well thank you for explaining!"
] |
[
"Red blood cells contain the oxygen-carrying molecule hemoglobin, which contains iron. White blood cells, however, have no hemoglobin. The iron in the hemoglobin makes the red blood cell red, and since the white blood cell doesn't have any, it's not red."
] |
[
"Oddly enough, some of your \"white blood cells\" aren't white at all. Eosinophils have a pretty distinct \"fire-engine red\" color, due to certain granules they posses. Mast cells and Basophils appear purple due to their granules, and lymphocytes (T and B cells) appear quite purple/bluish because they have a very small amount of cytoplasm and a large nucleus comparatively. The majority of these colors come from different uptake of the stain, but staining is almost always used to visualize cells."
] |
[
"How much larger would Earth's diameter have to be before life would be affected by being that distance closer to the sun?"
] |
[
false
] | null |
[
"The habitable zone for our solar system, for an Earth-like planet, is approximately 0.99AU to 1.688AU ",
"according to the study done by Kopparapu et al. 2013 ",
".",
"If we take the lower limit and expand such that we're 0.01AU closer to the Sun, that would make Earth's radius increase from 6371 km to 1,502,349 km. ",
"Note the radius of Jupiter is 69,911 km, and the radius of the Sun is 695,500 km, so this scenario is ridiculously unphysical.",
"edit - words"
] |
[
"The distance between the Earth and the Sun varies by about 3% over the year, and these changes have less of an effect on the weather than the seasons. 3% of Earth's orbital distance is over 700 times its own radius."
] |
[
"For those curious, the earth is closer to the sun during the southern hemisphere's summer than the northern's"
] |
[
"COMPUTERS: When you take an image off of one machine, and apply it to another (using ~Acronis) How similar are the machines/OS's/HDD's on a low level?"
] |
[
false
] |
We use it at my company and we are interested!
|
[
"Disk imaging software typically does a byte by byte copy of the original disk, so the HDD should be near identical after copying a disk image. Granted there will be small differences -- e.g., one HDD may have different number of platters, etc and map stuff to different locations. Also if you use an old hard disk there may be certain sector/blocks that are no longer used (e.g., checksums were failing in that block so the hard disk controller stopped using them) and writes elsewhere instead. ",
"Similarly, there may be underlying differences in the technology (e.g., SSD drive at a low level is quite different than HDD)."
] |
[
"At the level where data is read/written, it may or may not be identical depending on the software. Different imaging programs work differently. For example, a desirable piece of functionality in such a program is the ability to apply a disk image to a different capacity disk than it came from (as long as the used space in the image is smaller than the destination disk capacity). Most imaging programs have functionality like this; it's useful and relatively simple to implement. In order to do this, the software needs to be able to understand the file system in use so that it can create an empty file system (format) on the destination disk, then read the individual files out of the image and copy them to the disk. In this case, the files themselves will be identical, but the layout of the files on the surface of the disk is highly unlikely to be the same. I'm not familiar with all of the various imaging options, but I doubt that too many of them make much of an attempt to preserve file ordering; the operating system doesn't care about it.",
"Assuming that an image was written to a disk so as to be block-for-block identical to the original information, at the level of the physical sectors on the disk platters, it is quite unlikely that the information is identical. Maybe if the data is written to a disk of the same capacity, manufacturer, model, revision, and lot number... maybe. Hard disk platters spin at a high rate of speed under the read-write heads, which have to move in order to seek specific sectors, so there's a (small) latency involved. This means that sectors which appear to be contiguous are likely spaced around the platters at regular intervals. Basically, if it takes X fractions of a second to read a sector, the next sector in line will be placed a certain distance away based on a function of the track circumference, rotational speed, and X. The firmware on the disk's formatter board handles all of the timing and abstracts everything away for you, so that from ",
" perspective the data will be identical, but the internal representation will be highly specific to the disk hardware and firmware."
] |
[
"From a software point of view, the machines are pretty similar (assuming the hardware is close).",
"The main differences will be the hard drive serial number and network card MAC address."
] |
[
"Will the Covid vaccine go to people that have caught Covid already?"
] |
[
false
] |
Since the vaccine just gives your body a little piece (mRNA) of the virus would catching the actual virus do the same thing for your body? Making people that have caught Covid and survived immune to the virus since their body has already dealt with the virus and knows what to look for. I remember around June - July that nobody was sure if you became immune once you caught Covid. but with this vaccine and how it works, it would make sense that you would be immune after catching covid. So with that, has anyone heard of "Covid survivors" getting the vaccine? Or am I wrong in thinking you'd be immune after catching Covid?
|
[
"We don’t know how long natural immunity to COVID (that is, immunity after natural infection with wild virus) lasts, and probably the answer is something like “between three months and thirty years, depending”. Several studies have found long-lasting immunity following clinical cases of COVID, but there are also a handful of cases of repeat infections. ",
"The bottom line is that natural immunity probably",
"So though there’s no official guideline yet, it’s been suggested that (for now) COVID survivors not get the vaccine for 90 days after they recover, given that vaccine is in short supply. After 90 days, they would be put in the same priority baskets as everyone else. ",
"Over the next few months we will probably get a better idea of what proportion of recovered patients are immune for various lengths of time, and decide if 90 days is the right period or not. And as vaccines become more available, there will be less concern over sparing it and recovered people will be put in the standard lineups.",
"The A.C.I.P., which makes recommendations to the Centers for Disease Control and Prevention about vaccine distribution, said at a meeting on Wednesday that people who had not been infected should get priority over those who contracted the virus in the past 90 days.",
"“At some point we’ll need to figure out whether 90 days is the right number,” Dr. Maldonado said. But for now, “people who have evidence of infection recently should probably not be vaccinated at first in line because there’s so little vaccine available.”",
"—",
"‘Natural Immunity’ From Covid Is Not Safer Than a Vaccine"
] |
[
"Obviously it needs to be tested. But there’s certainly precedent for vaccines giving better immunity (e.g. HPV vaccines) and it should be both obvious, and supported by data, that the natural immune response to SARS-CoV-2 is extremely variable and not very predictable (though mild and asymptomatic infections tend to cause shorter, weaker immunity) - whereas, again obviously, vaccines can be more consistent and predictable."
] |
[
"Thank you for your concise and helpful answer. I was wondering the same since I've had it and had a confirmed positive."
] |
[
"What is that faint \"vortex\" you sometimes see called or caused by?"
] |
[
false
] |
Sometimes when I look at the sky (or some other uniform area) I see a 'vortex' in the center of my vision. It is akin to that starfield screensaver on old Windows computers. Does anyone else ever see this? What is it called? PS Sometimes in the dark I also see noise. To me, it looks like a huge conveyer belt of very tiny SpaghettiOs (red colored too!). Is that a known phenomenon as well?
|
[
"Haidinger's brush",
"? ",
"That, being an artifact of polarized light in the sky, would not show up in just any blank area."
] |
[
"Hmm, that is an interesting phenomenon, but it's not quite what I see. In my case, the vortex is quite animated, as if you have the sensation of patches of vaguely greyish shapes traveling inward into a point."
] |
[
"Here is a starting point:",
"http://en.wikipedia.org/wiki/Closed-eye_hallucination",
"By the way, I see the exact same thing. As far as I know, not many people see it. I am not sure if this is because they cannot, or because they simply don't notice it."
] |
[
"Do all stars have the same photospheric composition?"
] |
[
false
] |
I googled this question and only received vaguely related articles and blog posts. I would assume the photospheric composition of a star changes whit the different stages of a stars life cycle (O to M classes) but I would like to know for sure rather than accept false information.
|
[
"For a main sequence star, the outer layer generally remains constant until it reaches the red giant phase.",
"Red Dwarfs would steadily grow in helium as convection currents mix their core with the outer layers.",
"If the star is between .4 and 4 solar masses, the star will undergo a set of thermal pulses where it ejects large portions of its atmosphere, this will certainty change its composition. After this point it will retain a core of carbon, oxygen, and neon and will become a white dwarf."
] |
[
"It depends on the chemical environment in which the star has formed. The photospheric composition represents roughly the composition of the initial cloud of gas that formed the star. This composition may vary from one star to another, depending on the enrichment its initial cloud has received from stellar winds/supernovae etc, but they are similar for neighbors stars that originate from the same molecular cloud.\nThis composition mainly depends on the age of the galaxy and the age of the universe. Young galaxies and in the early universe, metals are almost absent because the interstellar medium received no feedback from already-formed/dead stars.",
"Not really the question, but star classes (O to M) do not correspond to stages in their life cycle. They are different kind of stars, defined by their mass/luminosity/temperature, O being the largest and hottest, while M are the smallest and coldest."
] |
[
"We do also observe changes over the star’s lifetime. Some red giants have significantly more carbon or other elements in their outer regions due to deep convection zones bringing up fusion products from the interior. It’s not a huge amount in absolute terms, but it can cause a pretty significant change in the spectrum. "
] |
[
"Evolutionary advantages of viruses?"
] |
[
false
] |
I'm currently watching BBC Horizon - Are We Still Evolving and they are discussing viruses. A virus is effective at producing copies of itself and thus pass on it's gene via evolution. The thing that troubles me is fatal viruses. If fatal virus kill their host, there is technically a point when viruses will run out of hosts before it learns to jump to a new species. Would that not make it a disadvantage to be a fatal disease? Of course there is a complex interplay between viruses evolving possible host species as well as hosts evolving defense mechanisms, but it seems that if a one species, fatal virus existed, it would spread rapidly killing the host species and killing the virus itself due to lack of hosts. Is the interplay so complex that the death and defense of each species balance each other out? Won't one organism eventually lose given enough time or does evolution work too fast to have this happen?
|
[
"On one hand is a virus that infects and goes to a high serum titer (uncountable zillions of copied viruses in the blood, semen, gut, mucous, and tissues) causes enormous systemic symptoms and sheds everywhere through diarrhea, vomit, coughing, etc. This virus will spread fast and very likely impair or kill the hosts it infects.",
"On the other is a virus that infects slowly and subtly over years with only a sparse presence in tissues and fluids that could lead to its transmission. This virus will spread very slow and likely have far less acute impact on the host's health.",
"Obviously there are \"in-between\" strategies, but grossly, there is always a balance between these strategies. For every bug's pathophysiology, the infection process optimizes based on selection and descent with modification (like always).",
"Ebola hemorrhagic fever is easily the most terrifying viral infection to me, because it infects quickly, kills quickly, and is virtually impervious to medical therapy (in \"The Hot Zone\" the author is told the only known cure is to consume an entire bottle of whiskey the night after an exposure). ",
"But an Ebola virus epidemic runs its course quickly and then disappears as quickly as it starts. So where does it come from? It comes from bats, probably. And in bats it does not cause hemorrhagic fever. It's quite possible that the Ebolavirus natural history has been one of epidemic spread through primates (or other mammals) then establishing endemic reservoir populations in bats and so on, back and forth throughout its history.",
"HIV infection classically has two phases. First, an acute phase with high viral titer and peak infectivity over the course of days to weeks. This ends once the host's body mounts an effective immune response. Then there's a chronic phase, when the virus kills the hosts immune system and the viral titer slowly creeps up as the immune system impairment continues.",
"As it turns out, HIV has an opportunity to spread during both phases. The first because the titer is so high, the second because its duration is so long."
] |
[
"Ebola virus",
". Thats why its so rare. 'coz its so fatal. It manages to only come up as short outbreaks, and scientists suspect also that the only reason why it even persists is because its main host is not primates but some other species where its not so dangerous.",
"But your question is right: fatal parasiticism is not a good way of evolving, and most such viruses (like HIV) if I'm not wrong are extremely recent in evolutionary history (some not more than thousands of years) and don't have that much of a chance. They can surely not destroy the entire population this way (without themselves becoming extinct) but more importantly this gives a great disadvantage (not full disadvantage; latent asymptomatic infections could mean the disease will persist in-spite of the hosts dying) but some scientists theorize that these parasites are just new species evolving towards symbiosis (or at least not killing the host off) and them killing the host is just an unfortunate side-effect that even they probably don't want."
] |
[
"Here's a couple of advantages off the top of my head:",
"1) If you were going to insist that they're around because they add some sort of advantage, you could make an argument that they promote allele diversification. Viruses, especially retroviruses are responsible for a good fraction of gene duplication and subsequent drift.",
"2) Cross-protection and immunity to other viruses. Closely related viruses make proteins that shut down the production of other viral particles from other closely related viruses. Once you've developed an immune response to one member of a viral family, you've probably developed an immunity to other members of the family. Edward Jenner's cowpox vaccine to prevent smallpox comes to mind.",
"Evolution is a never ending arms race. You have to keep running faster to just stay in place. There's a school of though that says that viruses which kill their hosts off too fast or frequently (like Ebola or the 1918 pandemic flu virus) burn themselves out and never get to spread widely and stay around. "
] |
[
"Where and how did the Spanish flu start, and what caused it to spread so rapidly?"
] |
[
false
] |
I know that ww1 was a major contributor for the spread of it but what else, and I keep finding different theories on what animals caused it, some say horses and some say pigs. So reddit please help me out here.
|
[
"This was posted on Reddit a few months ago and, if iirc, the ",
" answer is....",
"It seems to have begun in a rural area of Kansas. It would've stayed there, for the most part, if not for World War 1. Infected young people went to boot camps and shared the flu. Then most of those people were transferred to other bases, and spread it there. Eventually, the soldiers went to war overseas and the flu was given to our allies AND to our enemies. Whenever anyone went home, the flu tagged along."
] |
[
"The exact origin of the 1918 Spanish Influenza is unclear. There is some evidence that it may have emerged in rural Kansas in early 1918 and spread from there due to the movements of soldiers enlisting, training, and being sent overseas. There are other proposed possible origins, including China in 1917 or France in 1916, but this ",
"paper by Barry",
" notes that the outbreak follows a clear path out of Kansas through the movement of troops and concludes that Kansas was the likely source of the origin. ",
"As for the genetic origin, research into that is also ongoing. Genetic studies have indicated that it may have originated as an Avian virus and jumped directly to humans, but there is also some evidence that there may have been a intermediary host like pigs before jumping to humans."
] |
[
"The reason it spread so fast initially, is most likely because the people getting infected (especially soldiers) were living in extremely close quarters and probably didn't use any hand sanitizer (cause it wasn't around, just so no one gets confused).\nWhen it spread in the countries there were a lot of injured people, poor nutrition because of war, many people shared a toilet with the whole house of apartments because plumbing wasn't so common and so on.\nThe reason it's called the spanish flu although it didn't come from Spain was, that Spain was neutral. It discussed this new illness that killed so many people in the newspapers. Since all the other countries were at war and apparently didn't have a working news system anymore, the people heard about it from Spain. Therefore, they called it the spanish flu."
] |
[
"Why are planets and moons spherical? I haven't seen any planets that are oddly shapes so far. Similar thing to asteroids, why are they not as perfectly spherical as planets?"
] |
[
false
] | null |
[
"A sphere is the most compact form of matter\n So any large lump of matter will tend to form a sphere as gravity pulls everything to the center of mass, packing it as tightly together as possible ",
"Slightly smaller masses like most asteroids or smaller moons (Martian moons Phobos and Deimos for example) can still maintain their more random shapes. But if we had the technology to gather up the asteroids and bring them together, the resulting lump would become more and more spherical as we proceeded, no.matter how unevenly we added material."
] |
[
"Any rock bigger than about 300 km diameter, will have enough gravity to pull itself into a sphere."
] |
[
"Any rock bigger than about 300 km diameter, will have enough gravity to pull itself into a sphere."
] |
[
"Why do some of my wife's favorite foods nauseate her now that she's pregnant?"
] |
[
false
] |
I know that this is not uncommon. In my wife's case, she loves barbecue. Pulled pork, brisket, slow smoked, the whole bit. But, now she's pregnant and even thinking about slow cooked pig is enough to get her feeling sick. What's the physiological reason for this? What evolutionary purpose would this serve?
|
[
"From an evolutionary perspective, \"morning sickness\" is thought to serve a protective function for both the mother and the fetus during early pregnancy. Before we had such luxuries as pasteurization and proper food storage, foods such as meat were more likely to contain parasites and pathogens, and toxins in strong-tasting vegetables, than blander foods. These would be most harmful during early pregnancy, when the basic steps in organogenesis occur (i.e. first ten weeks or so). This is the period of maximum sensitivity to teratogenicity since not only are cells differentiating rapidly, but damage to developing tissues and organs becomes irreparable - exposure to teratogenic agents during this period has the greatest likelihood of causing a structural anomaly.",
"Further, the mothers body during pregnancy is in an immunosuppressed physiologic state, such as to prevent rejection of a fetus that is \"half-foreign\" tissue by the maternal immune system - creating an immune-privileged environment for ingested pathogens/parasites to infect and spread.",
"Though, if its any comfort to your wife, it usually lets up for many women past the first trimester.",
"And the chances of her getting a parasite from your brisket are slim. Unless you're doing it wrong. In which case, hey survival of the fittest."
] |
[
"Thanks. Well known phenomenon, happens to many if not most women. I've never heard an evolutionary explanation, but it makes a lot of sense."
] |
[
"As Iheartgogurt said, while morning sickness early during pregnancy is normal, severe morning sickness, or ",
"hyperemesis gravidarum",
" is not typical or beneficial. It is thought that this could be caused by an infection with a bacteria that can live in the stomach called ",
"Helicobacter pylori",
". Some researchers suggest that women looking to become pregnant are screened and treated for H. pylori before becoming pregnant to prevent this."
] |
[
"Is it possible that all (or all but one) elements exhibit radioactivity in all isotopes?"
] |
[
false
] |
Bismuth was thought to be a stable element for a long period of time until it was found to be very weakly radioactive. Although the decay rate is more or less insignificant for all practical purposes, it still exists. Is there any physical law that states that certain isotopes will never decay, or is it possible that all elements are radioactive (or decay to the simplest element possible), but their decay rates aren't detectable?
|
[
"I wish there were a place where we could ask expert scientists about things."
] |
[
"Would the existence of proton decay imply that all isotopes can eventually decay?"
] |
[
"Every element has at least one radioactive isotope. Some heavy elements have no stable isotopes. But there are some nuclides (about 300 of them) which will truly ",
" decay, to the best of our current knowledge.",
"There is no law against them decaying per se, but we've never observed them decaying, and have no reason to believe that they do."
] |
[
"Why are self antigens not considered foreign?"
] |
[
false
] |
Antigens are usually thought of as something foreign causing an immune response, then why doesn't our body attack our self antigens. If we have self-antigens that are tolerated, then they aren't really antigens, since they don't cause harm? I'm confused Thank you
|
[
"Something is not an antigen by itself. To a bacterium, its antigens are just proteins that do something. To our immune system, an antigen is something that an antibody binds to, either free floating or on a T-Cells membrane (that‘s how they detect antigens). Self-antigens are just normal (surface) proteins that the immune system responds to in autoimmune diseases, thereby causing all kinds of symptoms. The term doesn’t make a lot of sense without autoimmunity."
] |
[
"The field generally does refer to \"self epitopes\" as \"self antigens\". Epitope refering to a specific peptide sequence and antigen referring to an epitope that is recognized by the immune system. Immune cells are recognizing and tolerant to self all the time. Autoimmunity is obviously the outlier. \nTo maybe more completely answer OPs question, when T cells develop in the thymus, they are shown literally every single protein epitope that the body can make (overriding normal epigenetic regulation). The ones that recognize self are either killed or turned into regulatory T cells. Regulatory T cells can also be induced later in life to food, gut microbes and fetal antigens during pregnancy. To further prevent autoimmunity, every nuclear cell in the body is presenting their own self peptides on the cell surface to prevent being accidentally killed. And mutated tumors that try to avoid being killed by not presenting their mutated peptides are also killed by a \"lack of self\". Hope that helps!"
] |
[
"But wouldn't that just be an epitope?"
] |
[
"Why do babies have a distinct baby smell?"
] |
[
false
] |
Why is it that babies all smell pretty much exactly the same when all adults smell a different kind of foul (without any deodorant/perfume/cologne)? Is it because we load them up with baby powder? I'm sure not all parents do that(but maybe it's hidden in their items, like diapers?), so I can't figure out why they all smell very similar. Basically, I'm asking if there is a biological explanation behind their smell?
|
[
"http://www2.citypaper.com/columns/story.asp?id=2139",
"It seems men may like it even more than women. As a man, I can say babies do smell great. I can see this helping to change behavior from hunting and mating to taking care of a child. A trait like that could be selected for by evolution in the very care-intensive human child."
] |
[
"Was the study measuring the father's response to the smell or random men's response? I ask because I, and every other non-father I know, find the baby smell repulsive, and being in the presence of babies stressful and unpleasant. An infant seems to induce as much stress in me as it induces love in the mother - to the point that I can't exactly identify any cognitive process which explains the repulsion. I've always sort of assumed it was an evolutionary conditioned response of some sort. "
] |
[
"(just being silly here) What if his trait would have provoked his ancestors to murder other men's babies? Thus if he even makes one kid, and he kills everyone else's babies, he wins!"
] |
[
"Do people with tetrachromacy perceive electronic displays differently?"
] |
[
false
] |
So I've been interested in for a while now, and while fiddling with my monitor settings, a thought occurred to me: The pixels of LED monitors are made up of red, green, and blue LEDs. If someone with tetrachromacy can see a fourth primary color, would trichromatic monitors seem to display the wrong colors to them? For instance, if they took a photograph with a digital camera and then viewed it on the screen, would the colors be "off" from what they see in reality?
|
[
"Yes in theory - a tetrachromat by definition would need four fixed primaries to match an arbitrary target color (like something they see in the world).",
"But as far as the literature is concerned, ",
"there's evidence for a single tetrachromat",
" (and it's not perfectly convincing, though that is a cool paper)."
] |
[
"That's true, but RGB only allows for each color to be emitted at 256 discrete levels of intensity, which ultimately results in an inability to fully reproduce every visible color. The link I provided demonstrates that clearly "
] |
[
"Well for one, RBG monitors despite showing all of the primary colors cannot actually reproduce all the colors we can actually see as shown here ",
"http://en.m.wikipedia.org/wiki/Color_space",
". So even for those with only the three standard cones see colors on a monitor in a more limited way than in real life. As CCDs only encode RGB data, then a 4th primary color would be lost however it likely wouldn't be much more noticeable than what is lost for everyone "
] |
[
"Do foods have different caloric values for different animals?"
] |
[
false
] | null |
[
"Not a full answer to your question, but an example: Humans cannot digest cellulose, the main components of the cell wall in plants. Some animals like Cows however can (with the help of all their stomachs and their microbiome). Thus the nutritional value of plants like grass is vastly different between cows and humans.",
"As for the energy derived from simple sugars like glucose, this will be very similar among all animals, since the machinery and proteins responsible for these processes are virtually identical in closely related species like other vertebrates.",
"Edit: Typo and clarification"
] |
[
"Yes, exactly. Cellulose is a complex sugar and humans cannot break it down, it is indigestible for humans (fiber). Cows can break cellulose down, and those broken down sugars can then support the Cow's growth."
] |
[
"Yes, exactly. Cellulose is a complex sugar and humans cannot break it down, it is indigestible for humans (fiber). Cows can break cellulose down, and those broken down sugars can then support the Cow's growth."
] |
[
"There is a video of a man folding a piece of paper with a hydraulic press 7 times. The 7th time seems to essentially break the piece of paper, what happened here?"
] |
[
false
] |
Here is the video I'm referring to.
|
[
"After a quick literature search, the answer appears to be rather boring and straightforward: most likely what happened was the following:",
"1) Paper is largely made up of a forest of irregular ",
"cellulose",
" fibers, ",
"as shown here at high magnification",
". When pressure was first applied, the fibers became compacted together, but their internal structure did not significantly change. ",
"2) A further increase in pressure caused rapid local heating. ",
"3) The heating led to ",
"pyrolysis",
", i.e. a messy series of reactions that we throw together under the umbrella term \"decomposition.\" In the end what was probably left was a mess consisting of fibers in domains with different packing, some plastic-like patches, and bits of what is essentially char. ",
"The best source I could find was ",
"this paper",
" where they could study how you can try to transform cellulose into a plastic. As the introduction explains:",
"But when heating pulp or paper, the common experience is that they rather reveal incineration than plastification",
"These researchers observed a similar result when they just subjected cellulose to uniaxial pressure (i.e. pressing it on one axis, like in the video). It was only through a careful combination of laser irradiation, pressure, and torque that they managed to transform the fibers into compact glassy disks.",
"link"
] |
[
"Citations?",
"Edit: No idea why I'm being downvoted here. The video shows something really interesting and all the answers so far are basically speculation.",
"Edit: Well I guess the votes have swung the other way now. Thanks Science fans!"
] |
[
"Except the press didn't shatter it. Rather, it seems to have momentarily liquefied it, and when it resolidified, it did so into a more brittle substance. "
] |
[
"Please explain what \"quantum tunneling\" is, and why does it happen."
] |
[
false
] |
I only know one thing, that companies that make processors like Intel, AMD, Nvidia and others have trouble making processors smaller than a few nanometers (smallest now is about 22nm as far as I know, I personally posses a 32nm one) because at that scale a phenomenon called "quantum tunneling" causes electrons from transistors to jump wildly across the circuit (correct me if I'm wrong). Why does this happen?
|
[
"Take an egg carton and cut off the top. Then put a marble inside one of the dimples. No surprise, the marble will stay there forever because it doesn't have enough energy to jump over the top and into another dimple.",
"Now, shrink everything down to the size of electrons and nuclei. The marble represents the electron and the egg carton represents the potential landscape that the nuclei of atoms set up for the electron to move in.",
"At this tiny scale, a funny effect happens in which the marble can hop into another dimple, ",
"! This is quantum tunneling.",
"Thin film transistors consist of a thin layer of oxide that separates a metal and a semiconductor. The oxide acts as an insulator. As transistors shrink, this oxide layer has to as well. When it gets too thin, the effect of electrons tunneling across the insulator becomes a huge problem. The insulator isn't acting like one anymore."
] |
[
"I think in your analogy the bullet still has enough energy to punch through the wall even when its thinned. Tunnelling is stranger than this. It is as if without shooting the bullet, you gently place the bullet right up against the wall, and later, you find that it is on the other side!",
"The bullet is the electron, and the wall is some very thin film oxide say. Extremely tiny length scales.",
"I'm not really sure I understand all your followup questions though, so let me know if the following is what you are interested in.",
"All particles behave as if they have a wave-particle duality. It follows from the ",
"de Broglie relationships",
". However, the crucial thing is that this duality only matters when you have something extremely tiny, like an electron. It won't be observed for everyday objects, like baseballs. It doesn't mean that scientists haven't tried to push the boundary of testing wave-particle duality. I think the largest object shown to have this property are a molecules of C60.",
"Your example with light going through thin objects reminds me of ",
"evanescent waves",
". Tunnelling is very analogous to it."
] |
[
"Quantum tunneling occurs when some quantum object crosses an energy barrier that it shouldn't be able to cross classically. For example, if we think of a bowling ball as our particle and a hill as our barrier then if you roll the ball towards the hill, the ball will either roll up to the top of the hill and back down the other side; or it will roll partways up the hill, stop, and then roll back down the hill in the opposite direction. It will either cross the barrier or be deflected, in other words. The easiest way to predict whether the ball makes it over the hill is to compare its initial kinetic energy and the potential energy it would have at the top of the hill (assuming everything is frictionless). If the initial kinetic energy of the ball is greater than the potential energy at the top of the hill, then the ball will roll over the hill. Otherwise, it won't and it will be deflected.",
"In the quantum case, where the bowling ball is replaced by an electron and the hill is replaced by a transistor, the situation is identicle to that described above except for two differences. Instead of the gravitational force creating the energy barrier, the electrostatic force between the electron and the abrupt change in the electronic structure of the atomic lattice in the transistor produces the energy barrier. ",
"The second difference is quantum tunneling! If the electron has more kinetic energy than the potential energy of the transistor barrier, it will cross through the barrier just as in the case with the bowling ball. However, if the kinetic energy is less than the energy required to cross the barrier, the electron will not neccessarily be deflected. Instead, it has some non-zero probability of \"tunneling\" across the barrier and making it to the other side regardless. It is as if the bowling ball only had enough energy to make it halfway up the hill, but instead of rolling back down the hill, it decides completely at random to tunnel through the hill without stopping, and then rolling down the other side. We don't see this happening because the tunneling probability for macroscopic objects is outrageously small.",
"So, why does tunneling happen? It happens because electrons aren't particles. They are both particles and waves simultaneously that, for some reason, obey the Schroedinger equation and if you solve that equation for the case of an electron traveling towards a finite energy barrier, you get a non-negligible probability of the electron crossing the barrier even if it has lower energy than the barrier. Giving reasons for tunneling beyond that is rather speculative."
] |
[
"What exactly is happening when someone uses skin lotion/moisturizer?"
] |
[
false
] |
I guess I’m asking how skin cells interact with the chemicals in the lotion and where those chemicals go once they’re “absorbed”.
|
[
"While the answer depends on several factors (including what's getting applied to the skin, where on the body it's being applied, what vehicle (or topical agent type - think cream, lotion, ointment, foam, etc) is being used, and what the composition/active ingredient(s) are in that vehicle), let's start with the basics and move from there. ",
"If we're talking about things applied for the purpose of moisturizing, the goal is less about direct hydration and more about preventing excess water loss. Preventing water loss from the skin is super important: in fact, it's a primary function of the stratum corneum, the topmost layer of skin that is made of protein-rich cells that have lost their nuclei (colloquially referred to as \"dead skin cells\"). You can think of these cells as the 'bricks' of our skin: holding them together like 'mortar' is a lipid-rich layer full of things like ceramides, sphingolipids, and more. ",
"On the daily, we run into tons of stuff that can disrupt either the bricks or the mortar of this layer: dry weather, friction, caustic topicals or agents, skin diseases, you name it. When the barrier's weakened, there's more points through which water can exit this skin. This escape, called 'transepidermal water loss (TEWL)', is ultimately what results in dry skin. ",
"By applying moisturizing agents, you're essentially putting an external 'mortar' on the stratum corneum: this decreases TEWL, and helps to 'rehydrate' skin by making sure excess water isn't lost to the environment. ",
"As for 'chemical absorption', it all depends on the properties of those chemicals. The rate-limiting step for absorption from the skin is the stratum corneum: if something has a hard time passing through a lipid-rich environment, it's not going to pass through here so easily. Meanwhile, if you're trying to treat a condition that starts deeper down in the skin, having agents that can readily diffuse through the skin's top layers to exert their effect would be ideal. ",
"Hope this helps!"
] |
[
"Yep, there's a difference! 100% oils or waxes are called 'occlusives', meaning they form an inert barrier right on top of the skin that completely blocks TEWL. While great at keeping water in, they can be a bit messy to apply - think of petroleum jelly and the like. ",
"Conversely, lotions are vehicles made of oil ",
" water, generally using the help of emulsifying agents to keep things together. As a result, they're thinner, less greasy, and generally easier to apply and remove. By virtue of their composition, you can also blend things into lotions that help with their moisturizing potential: some are called emollients (generally, these are lipids like fatty acids or cholesterol that can bulk up the 'mortar' mentioned above) and others are known as humectants (agents that can \"pull\" water into the stratum corneum due to their charge - think glycerol, urea, hyaluronic acid, etc.). ",
"In short, true occlusives completely block water loss. Meanwhile, lotions may not be as good at this effect, but they can have things added into them that help decrease TEWL."
] |
[
"The top layers of your skin are dead skin cells, lightly adhering to the layers below. One they dry out, there is a lot of space in between. Moisturizer gets sucked into this space, so you end up with a more adhesive matrix of dead cells in oil. Still dead though."
] |
[
"Hand sanitizers claim to kill ~99% of bacteria. Does this mean that 1% of the population of all strains survive? Or does it mean that 1% of the strains of bacteria will always be impervious to alcohol?"
] |
[
false
] |
[deleted]
|
[
"Alcohol kills bacteria exponentially. I don't remember (read: google couldn't find) the precise numbers, but after x amount of time, 90% are dead. After 2x that time, 99%, 3x, 99.9%, and so on. As you can see from that math, you'll never 100% sterilize something using alcohol - at least not in a practical way. However, as far as getting germs off your hands, 99.9% is good enough. You're not looking to sterilize your hands (which is impossible), you're looking to cut down the risk of infection.",
"The 10% survivors in each instance aren't resistant, they're just lucky. Maybe they didn't get the full exposure to the alcohol, they had a little extra water in them, or they were in a clump. To make a terrible analogy, it's like randomly spraying a crowd of blind, deaf people with a machine gun. Some will survive, not because they're bulletproof, but because they were lucky enough not to get shot. If you keep shooting, you'll kill more and more over time.",
"Also, while alcohol kills everything, it doesn't efficiently kill everything. Bacterial spores, bacteria with thick capsules, and nonenveloped viruses are fairly resistant to alcohol. For this reason, alcohol is never used as the only method when something needs to be completely sterile - we use fire, 10% bleach, formaldehyde, gamma rays, or autoclaving instead.",
"Sources/further reading:",
"CDC",
"Nifty review paper",
"What we do in the lab when it absolutely, positively has to be 100% sterile"
] |
[
"Fire is 100% effective ;)"
] |
[
"Fire is 100% effective ;)"
] |
[
"why does bar soap lather differently when it's nearly gone?"
] |
[
false
] | null |
[
"Here is the answer from a soap maker. When soap is made commercially it hardens and crystalizes from the center out. The seed crystal that forms originally for the crystalline structure of the soap to form around it has a different structure and makeup, IE the core of the soap is different than the fatty exterior. "
] |
[
"The most likely explanation I can think of is that, the more you expose the soap to tap water, the more it exchanges sodium ions for calcium and magnesium ions that are in the water. This effect should increase with water hardness (a measure of the concentration of calcium and magnesium ions in tap water).",
"http://en.wikipedia.org/wiki/Hard_water#Effects_of_hard_water"
] |
[
"Can you show that this phenomenon actually exists?"
] |
[
"Why do I cough whenever I clean my ears?"
] |
[
false
] |
So, every time I clean my ears with Q-tips, I cough, sometimes rather violently. Sorry if this is a stupid question, but can someone please explain this?
|
[
"More specifically.",
" It's called the Ear-Cough or Arnold Reflex. One of my small contributions to Wikipedia was adding this very subject (self-serving pat on my own back, I know)."
] |
[
"You're digging too deep and stimulating the ",
"vagus nerve",
". "
] |
[
"Listen to this man, I'm just a physicist ... "
] |
[
"\"Greenhouse gas levels highest in 3 Million years\". Okay… So why were greenhouse gases so high 3 million years ago?"
] |
[
false
] |
Re: Carbon dioxide concentrations in the Earth's atmosphere are on the cusp of reaching 400 parts per million for the first time in 3 million years. The daily CO2 level, measured at the Mauna Loa Observatory in Hawaii, was 399.72 parts per million last Thursday, and a few hourly readings had risen to more than 400 parts per million. ''I wish it weren't true but it looks like the world is going to blow through the 400 ppm level without losing a beat,'' said Ralph Keeling, a geologist with the Scripps Institution of Oceanography in the US, which operates the Hawaiian observatory. ''At this pace we'll hit 450 ppm within a few decades.''
|
[
"At the risk of spamming this across reddit today (I posted it ",
"here",
" in response to another post), the IPCC's Paleoclimate chapter does an excellent job of explaining changes in climate during the past, and their implications for modern climate change:",
"http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch6.html",
"From that chapter:",
"Changes in CO2 on these long time scales are thought to be driven by changes in tectonic processes (e.g., volcanic activity source and silicate weathering drawdown; e.g., Ruddiman, 1997)."
] |
[
"There are several ways:",
"Stable isotope ratios of growth rings in speleothems (stalagtites and stalagmites);",
"Stable isotope ratios in oceanic foraminifers (for which we have time series reaching back several tems of MY);",
"Direct measurement in gaseous fluid inclusions in both ice-core, vadose zone cements, evaporites, speleothems, etc.;",
"Stomatal density variation on fossil leaves;",
"and others."
] |
[
"The question isn't about natural or normal or not. Its about the ability for human civilization (and other species, though there will be big winners and losers among them) to live happily under the rapid change. Human civilisation wasn't around 3 myo, and will likely suffer immensely if the world rapidly changes to be that way again.",
"No-one says cancer is natural and therefore not a problem. We don't only worry about Anthropogenic Cancers like those caused by pollutants. Why do we entertain arguments like that with climate change?"
] |
[
"How are viruses and bacteriophage affected by convection currents and Brownian motion in regards to adhesion?"
] |
[
false
] |
[deleted]
|
[
"Consider that the bacteria is not a perfect sphere, it lacks a uniform density. It is not an attribute-less particle like is expected for Brownian motion.",
"Right, and small nonspherical bodies don't actually orbit the sun because ",
" can only happen between spherical objects or point masses. ",
"All you are doing here is making arbitrary linguistic prescriptions which are completely divorced from actual usage in the literature.",
"The usage you suggests gives a vague sense of superior scientific rigor but actually greatly diminishes the usefulness of the term \"Brownian motion\" and is implicitly opposed to using simplified models to describe complicated real world phenomena.(which some might say is what science is about.)",
"Beyond this ill-gotten sense of superior rigor your responses here contain no meaningful claims or insights.",
"First you make the spurious claim that viruses and bacteria are at a scale where brownian motion is not significant, then when you realize this claim is false your argument devolves into a combination of layman speculation and arbitrary redefinition:",
"The movement you are calling Brownian is actually just the result of bacteria being bombarded by other molecules. That very fact means it CANNOT be truly Brownian.",
"Here I think you are imagining that relatively large molecules(you say \"other molecules\" as if to imply they are comparable in size to bacteria? You don't find many molecules that big, so what not say \"particles\"? ) are bombarding the bacteria in order to get significant motion and therefore the motion can not be considered Brownian.(which you presumably think is required by definition to involve small bombarding molecules or maybe single atoms in which case none of the classic Brownian motion examples are actually forms of Brownian motion according to you.)",
"You are just defending your original false claim with arbitrary redefinition combined with speculation. \nI can't imagine you have any experience allowing you to estimate the size of the particles involved so it seems to me you have just assumed that the molecules involved are so large that the definition of Brownian motion does not apply. ",
"In fact you don't even give a reference for how this free parameter of particle size relates to your definition of Brownian motion or to the threshold you think is required to see motion of the bacteria, you don't know anything about these limits independently but you somehow seem to know that there is a particular relation between them such that your claims are correct. This is an elaborate way of making a circular argument.",
"Imagine the inflatable balloon at a stadium with many, many people hitting it as it passes. This is Brownian.",
"You could just link to the section of the wikipedia page where you probably just read that:",
"http://en.wikipedia.org/wiki/Brownian_motion#Intuitive_metaphor"
] |
[
"I get that your latest point(this is after you finished with the claims about scale and energy which were vague to the point of lacking all content) is that flexible bodies which change shape over time and as a function of interactions with water can not be perfectly described by a Wiener process. This is a trivial point(and pretty much irrelevant for the purposes of this thread) and does not justify all the arbitrary claims and linguistic prescriptions you have made.",
"Why? Because proteins aren't going to change shape or properties significantly during the course of being bombarded by water. Cells will. That is the cut off.",
"Changes in shape as a function of bombardment mean that the process is not strictly a ",
" or a ",
" but it may be still successfully modeled as one for many purposes depending on the magnitude of the changes. Again, the paper linked to by OP that you apparently didn't look at gives an example of this.(Please at least skim the paper linked to by OP, I have a better link here: ",
"http://www.pnas.org/content/105/47/18355.full.pdf",
" )",
"They model a bacterium as a sphere attached to a helix and were able to make useful predictions using a Brownian model.",
"If the changes in shape become significant enough that the ",
" is no longer a good model, you could always attempt to modify the model to account for this and appropriately call it an example of Brownian motion, just not the ",
".",
"If you have any real information about how a body of a certain modulus diverges from the standard Brownian process I would be very interested to hear it.",
"If you are saying is that a particle will diverge critically from a standard Brownian process at some modulus in particular, and you believe this modulus is at about that of a cell or bacterium, I would like to know how you know this. ",
"If instead you agree that the loss in standard Brownian accuracy as a function of decreasing modulus has no critical inflection points in particular I must note that you don't have any reference point as to what threshold on accuracy is good for OP purposes, and therefore your claim that cells or bacteria are at the \"cut off\" is not meaningful."
] |
[
"All I argued is that is isn't a strict Brownian function. Not that modelling it as such is not feasible. Just that you have to make the simple distinction on definition that what we are describing may have merit modeled as such, but the two are not simply the same.",
"The OP claimed that viri and bacteria underwent Brownian motion. I disagreed, arguing that they do not, even if it looks very similar. I never once said that modeling them as such had any value, positive or negative.",
"My response was to point out an important misnomer to the lay-community. At no point did I debate the usefulness of the model, because it clearly is there. But for people who do not understand the finer details of what is going, terminology is PARAMOUNT. If they understand why this isn't a strict Brownian process, they have gained one piece of knowledge. You make a clear argument, as does the paper, that using Brownian models offer some value, which I don't disagree with.",
"Please reread my argument. You inferred a number of statements I had no interest in making and assigned a causation different from my own. The PNAS paper basically just says that the influences on a small swimming bacteria can be successfully approximated using a Brownian model. That is it. It offers some insight into in vitro factors. If you feel that is sufficient to make a statement about an in vivo system, that is your choice. I see no conclusive data that supports the notion that a Brownian model, standard or otherwise, holds any value in actual biological situations, which is what I believe the OP was asking.",
"I see your points and hope you feel I have replied sufficiently."
] |
[
"What gives a steel cable so much more tensile strength than a steel rod?"
] |
[
false
] | null |
[
"I thought for sure someone would give you the answer. But I saw lots of just dead wrong answers, like a cable doesn't have higher strength than a rod, that it's more flexible, or that it's denser. But tensile strength, which is the same thing as ultimate tensile strength for a wire, is fracture load divided by true area. The question asked why the wire has a higher strength than a rod. The poster didn't mention alloys, so let's assume the rod and the wire are of the same material. (This is not necessarily true, as a wire may very well have higher carbon content and that could be an additional answer. Steel is a material class, there are many kinds of steel commercially available.)",
"The answer is that wire is cold drawn to a much higher extent than a larger diameter rod. Steel is like most metals, in that there is a marked increase in strength when you deform it. Drawing increases the wire's strength, and also reduces its ductility (measured by strain to failure). Materials scientists will explain this by noting that the microstructure of a cold drawn material has smaller and more elongated grains, and therefore dislocations in the metal crystals have a harder time moving, interfere with each other, and get pinned at grain boundaries very quickly."
] |
[
"Metallurgist here: the general rule of metals is that beating the shit out of them (or forcing them into shapes, like a wire) makes them \"stronger\".",
"By \"stronger\", we mean that you need to apply more stress (= force per unit of surface area) before it deforms or breaks. Ceramic is pretty strong, which is why you can't break a ceramic plate with your bare hands (but you could potentially bend a metal plate, depending on the metal and your workout routine). But it usually comes at a price, since stronger stuff tends to be more brittle (which is why you can bend metal but not ceramic, which will plainly break). Anyhoo, deforming metals makes them stronger.",
"Why? Because all metals* are made of crystals, i.e. regular arrangements of atoms in neat little rows, a basic pattern repeating billions and billions of times. When you pull on it, or squeeze it, or bend it, you are essentially asking these atoms to move. Have you ever played with ",
"these little magnetic balls",
" and tried to dislodge them? What happens is, because of all the magnetic forces in play, the balls can really only \"jump\" from one stable position to another, either aligned with the other balls, or halfway between, but never in a random position. I'm simplifying, but atoms act about the same; when you pull or push or squeeze them, they'll roughly stay in the same regular configuration, except some of the atoms will be one position \"off\" compared to the rest. That's what in the business we call a ",
", and that is the main mechanism through which metals deform.",
"But here's the thing: every time you introduce a dislocation, it's essentially a kink in the system. And as far as Mother Nature is concerned, if the system has a kink in it, then it's not in its most stable energetic state: it's a bit off-kilter, just by a fraction of almost nothing. And that means it makes it ever so harder to introduce the ",
" dislocation nearby, because now when the atoms move, they have to deal with the already existing one. Think about it as trying to cut through a crowd: if the whole crowd is in neat rows, it's easy; but if one row is like half a step off, you'll have to move a bit more, push with the elbows a bit, i.e. exert more energy. And if more and more rows are placed in off positions (one could say... ",
") you're gonna have to really push your way through, and kick and elbow and generally fight to make way. You're gonna have to exert more energy. You're gonna have to, well, apply more pressure. The crowd is \"stronger\". That's why deforming crystals makes them gradually harder to deform, and that's why wire, which has been deformed to all hell, is very strong.",
"*Some metals are ",
" crystalline, but 99.99% of the ones encountered in construction are."
] |
[
"Can you explain this like I’m not a materials scientist?"
] |
[
"With the winter in North America being so long and cold this year, have any invasive species expanding northward been set back? E.g. Southern Pine Beetles?"
] |
[
false
] |
I remember reading which stated that there were issues with pine beetles migrating north. I'm wondering if this cold winter has mitigated the problem, and whether there are any other cases of invasive species whose impacts may have been temporarily mitigated by the cold.
|
[
"A couple of studies have concluded the cold weather has put a serious knock down, but not eradication, the emerald ash borer and asian murmurated stinkbugs ",
"http://www.washingtonpost.com/national/health-science/winters-freeze-stopped-ash-borers-and-stink-bugs-cold-but-theyre-primed-for-a-comeback/2014/03/02/93a7fe8a-9fbb-11e3-9ba6-800d1192d08b_story.html"
] |
[
"Aside from the cold weather, are there any potential predators that might be able to migrate north alongside of them?"
] |
[
"Not sure if resilient. They didn't get all the trees, and cones were left on ground. They took things out pretty quick. Copper-Basin TN is where I am talking about. The sapling hardwood trees (Oak, Hickory, and Poplar) took off with all the pine trees down or rotting.",
"If really concerned make a journal and document changes in your area. I am going by my memory. "
] |
[
"Why has early detection of diseases via dogs not found widespread use in medicine?"
] |
[
false
] |
I have heard how dogs can detect diseases such as cancer or now covid with a surprisingly high accuracy. However I have not seen widespread use of dogs in such a manner.
|
[
"Consistency issues.",
"In some cases, researchers don't know exactly what chemical compounds the dogs are detecting. That remains a hurdle for training better sniffer dogs but also for designing better detection devices.",
"Competition with AI detection devices. Robots are pretty good at this stuff too, plus they work 24/7 and can usually do high-throughput.",
"Difficult to move dogs around - easy to move tiny vials of samples. Standard clinical or pre-clinical testing is very robust and efficient. \n Compare to that it's more difficult to collect/store/analyze samples of breath, sweat, smelly socks or whatever the dogs are smelling.",
"Trained service dogs cost anywhere from $20k-$50k each. Sometimes higher still. For them to work, a patient needs to visit a clinic that owns a dog or present a dog with a sample. There will be a limit to number of patients per day, per dog. That means cost per test gets very high.",
"Reject dogs and test-on-demand. Ethical questions are breeding dogs do tasks like this. Usually a lot of dogs fail training, and then what? OR how long per day can the dog do tests before it gets fatigued. False positives and false negatives.",
"Skepticism remains high in medical community. Historically, everything is moving to robots and controlled lab testing. Moving back to animals seems like an odd quirk that will quickly be replaced by an AI sensor."
] |
[
"I would guess the skepticism of the medical community is only compounded by that of patients who would likely take the news that a dog has sniffed them and decided they've got cancer about as well as a kick in the teeth. As humans, we quite like our official and complex processes; the more official and complex it seems, the more likely we are to believe."
] |
[
"The studies look good",
"https://journals.sagepub.com/doi/abs/10.1177/1534735405285096",
"",
"But, its not like they have dogs just sniff 1000 people and try to find breast cancer. That wasnt done, and presumably wouldnt have just a high success rate. So basically the studies arnt well controlled to demonstrate this is actually applicable to a REAL clinic. Like you couldn't just put a cancer sniffing dog in your waiting room at the PCP office"
] |
[
"If I'm standing in a completely red room that has a white light source, will a green ball appear black to my eyes?"
] |
[
false
] |
So from my understanding, the reason a red object appears red to us is that it absorbs all visible light frequencies except for red, which it reflects. This goes for all pigments/light combinations. For the sake of this question, lets say that the green ball has no direct line to the white light source, so that all the light hitting the green ball has to bounce off of something red first, thus becoming "red filtered." I suspect that the green ball will still appear green. What am I missing here?
|
[
"Human vision takes a lot illumination into account when deducing color. That is if a lamp is yellow it doesn't that much make you change your opinion on the color of the objects it illuminates. There is a neat optical illusion picture where a object projects a shadow on a chess board. If you compare pixel by pixel the black square in light and the white square in shadow are the exact same color. However for human experience that is different enough that for most it would not cross their mind that they are the same color.",
"This is a psychological effect rather than a physical one.",
"If you entered such a room there would not be any difference for the ball to actually be black than actually be green. It would also be the same thing to just have the walls glow red without any white light source.",
"However if you for example first see it with direct white to green contact which is later broken your brain is smart enough that it realises that the situation is still consistent with the ball remaining green and because color changers are the exception rather than the rule its a decent guess that its still green (or its a better guess than that it suddenly turned black)."
] |
[
"Here's a link to the illusion you mentioned: ",
"http://web.mit.edu/persci/people/adelson/images/checkershadow/checkershadow_illusion4med.jpg"
] |
[
"The only thing you're missing is that most objects in reality will reflect some level of all wavelengths of visible light. Sure, it might be predominantly reflecting red, but those walls will still reflect some measure of other wavelengths too."
] |
[
"How will E.T. see us ?"
] |
[
false
] |
We have been transmitin television waves for some years as seen in this . So, if there is a planet with intellengent life in that range, they should be able to watch our TV signals. But a) Will they have to point their anntenas to exactly our location (or maybe our location 50 years ago) ? b) Will the signal be strong enough to receipt it ? c) Are we doing the same with every new planet the Keppler discovers ? Are we trying to "watch" them ?
|
[
"Man, I feel so much more comfortable about my crush on you right now..."
] |
[
"Good lord. Where even to begin. It's entirely true that there really are women working in science. Everything else I can think of about that novel is pure imagination."
] |
[
"Once you get out to a distance of about three light years, terrestrial radio and television signals are attenuated to the point where they cannot be distinguished from noise.",
"The closest star is more than four light-years away.",
"So no, there are no little green men watching Hitler open the Olympic games."
] |
[
"How does time near the speed of light work for two different frames of reference?"
] |
[
false
] |
Ok, so I know the classic example of an astronaut leaving earth traveling at near the speed of light and then returning to find that time has passed much quicker on earth than in his speedy spaceship. However, in my astronomy textbook it says that if there are two bodies moving relative to each other and each body had its own clock, both clocks would appear to be ticking slower than the other, depending on which frame of reference you take. So, my question is this: Wouldn't the people on earth be traveling at near the speed of light relative to the astronaut and thus be experiencing time at a slower rate from their perspective than the astronaut?
|
[
"Ah this is the classic ",
"twin paradox",
".",
"Special relativity states that reference frames that are uniform are equivalent. i.e. they are either traveling at a constant speed or stationary. ",
"The thought experiment is: if you are on a bus that's traveling at a constant speed, it is indistinguishable from if you are stationary. You can construe yourself as being stationary and the whole world is moving backwards at the constant speed.",
"But the moment the bus accelerates or decelerates, you will be jolted forwards or backwards (this leads to general relativity, beginning with the equivalence of accelerating frames and gravity). ",
"So in this case, the astronaut has to accelerate out, decelerate ",
" make a round-about change in direction. The people on Earth stay stationary relevant to the astronaut and experience no such accelerations/decelerations/change of direction. The two reference frames are no longer equivalent.",
"This proves to be an simplification - more details are provided in the link above."
] |
[
"This is the reason that the ",
"twin paradox",
" is called a paradox. The astronaut on his journey will see time progress slowly on earth- however, when he turns around to come back to earth, he changes his frame of reference. When he changes frame of reference, many of his coordinates get relabeled. In a sense, he sees the earth experience a whole lot of time at once.",
"Of course, there's nothing discontinuous about what the astronaut actually -observes-, when we write 'sees' we mean that the astronaut corrects his observations based on the speed of light. The astronaut -observes- time passing faster on the earth when he travels back towards it, because he's travelling into the oncoming light beams. When he corrects for the distance between him and the earth, however, he finds the same thing he found on the way out, that time is passing more slowly on the earth than for him.",
"The wikipedia link has more material about this under the 'resolution' section.",
"Edit: It seems I was beaten by an equivalent explanation. Perhaps I shouldn't write responses while travelling close to the speed of light."
] |
[
"Just want to say that you don't need general relativity to resolve the twin paradox. Special relativity can handle the accelerating bodies."
] |
[
"How do we assign time values (in seconds, years, etc.) to events that occurred long before the earth began rotating and orbiting the sun? And are those estimates given in our present fame of reference or the local reference frame?"
] |
[
false
] |
When I hear that something happened X seconds or years after the Big Bang, I always wonder how that number was arrived at, when seconds and years are based on events that didn't begin to happen until just a few billion years ago. It seems like these figures could be derived from something like the hyperfine transition of hydrogen, but even hydrogen atoms didn't exist until 380,000 years (there it is again) after the Big Bang.
|
[
"First I'm going to be pedantic and say that the second is determined in terms of transitions of a Cesium atom, not Hydrogen. To actually answer your question though, even though Cesium certainly didn't exist in the earliest moments of the universe we still know how long those events took because we have made calculations based on things that we can observe in terms of what ",
" exist at the time (much of this data comes from the cosmic microwave background), and how those things acted based on the universal physical laws we know to be true. So while the events of the first second after the big bang did not literally happen in \"the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom\", we can say that if there WERE a Cesium-133 atom there, the events would have occurred in that period.",
"Also, the the times are in the local frame because, once again, everything we know is based partially on observed data but mostly on calculations that are done in the frame of the event."
] |
[
"Why does the hydrogen need to exist before you can use it as a measurement?",
"It's almost like saying I don't have a meter stick with me, so using the metric system to measure distances is therefore invalid."
] |
[
"Wow. That was exactly the kind of answer I was hoping for. Thank you."
] |
[
"How are program installer files so much smaller than the program they install?"
] |
[
false
] |
In order for it to install something, all of the data has to be there, right? So, how does it work?
|
[
"In some cases, the installer may hold a compressed version of the data. The installed files are decompressed, so they take up more disk space.",
"However, the compression factor usually only gets to about 2 or 3 for typical software. If you're seeing a much larger discrepancy than that, then probably what's happening is that the installer actually downloads the rest of the necessary data during the installation process. You could check for this by disconnecting from the Internet and then running the installer, and seeing if it still works."
] |
[
"This, and I'll add that install programs these days often are a channel to grabbing the real data from some authorized location on the internet. In other words, not all the data has to be there if you have an internet connection.",
"You install a small program, a \"download client application\", that creates a connection to the cloud to get the program you want, and that client application then downloads and installs it. "
] |
[
"Another common one you'll see with some of the big apps, like Office, is it's preinstalled and locked out, the installer just unlocks the existing application (and doesn't actually install anything, except maybe a start menu icon)."
] |
[
"Making it's rounds on Facebook: Sodium Fluoride added to our drinking water is poisoning us. Any truth to the claims?"
] |
[
false
] |
I'm not a scientist, but I immediately get skeptical when someone cites a "holistic medicine" website to prove their claim. The following has been posted on quite a few of my friends' walls and I am just wondering if the claims have any real substance. Offspring of pregnant animals receiving relatively low doses of fluoride showed permanent effects to the brain which were seen as hyperactivity (ADD-like symptoms). Young animals and adult animals given fluoride experienced the opposite effect -- hypoactivity or sluggishness. The toxic effects of fluoride on the central nervous system was subsequently confirmed by previously-classified government research. Two new epidemiological studies which tend to confirm fluoride's neurotoxic effects on the brain have shown that children exposed to higher levels of fluoride had lower IQs. A study published in Brain Research shows that rats drinking only 1 part per million fluoride (NaF) in water had histologic lesions in their brain similar to Alzheimer's disease and dementia. All pics are for sharing... so if you wish to use them to help spread the truth, please do! ♥ Reached the 5,000 limit so here's my other page... Feel free to share your posts! UPDATE: This is my first time using , and I am extremely pleased with the quality of these responses. Keep up the good work!
|
[
"Some personal informatio:\nI work with large amounts (kg quantities) of NaF for the past year in the form of FLiNaK (NaF-LiF-KF) fluoride salt. I've inhaled it a ton. I've definitely had more than 1 ppm in me. ",
"Some scientific information:\nThe MSDS says the oral lethal dosage for 50% of humans is: 71 mg/kg. That's much more than whats in water.\n",
"http://www.alfa.com/content/msds/USA/11561.pdf",
"No information on when it becomes harmful.",
"Around the lab we don't worry about it too much."
] |
[
"http://www.sciencedirect.com/science/article/pii/S0022113905002599#sec3.5.1",
"A lot of the health effects are inconclusive. The population data supports the fact that it is generally safe, but it can cause a well documented cosmetic defect known as dental fluorosis."
] |
[
"This is perfect. Thank you so much!"
] |
[
"Why are neanderthals considered a seperate species to humans if we were able to breed with them and produce fertile offspring, to the point that a large percentage of modern human DNA is derived from neanderthal DNA?"
] |
[
false
] | null |
[
"Species is a pretty mushy term and there is many species where things are just species because we want them to be or find it useful. ",
"Like a polar bear and a black bear can breed but no one is super interested in making them the same species because it's more useful to just pretend because they are different enough. "
] |
[
"To expand on this, human paleontology in particular is rife with named species that probably should not have their own name. We don't have DNA for the vast majority of them (Neanderthals are recent enough to be an exception), so everything is based on anatomical differences, and many of these differences are really small and could easily be explained by normal variation within one species. ",
"The Dmanisis skulls",
" are a great example of significant variation within a single hominid population. Had they been found at different sites, it's likely they would have multiple species names (and some people still argue that they're different species despite all coming from the same context)."
] |
[
"Species definitions vary, but typically feature reproductive isolation as part of the definition, not outright reproductive incompatibility. i.e. if two populations don't typically encounter each other (on separate islands maybe) they might be considered species even if, were we to artificially put them together in a zoo, they might successfully breed. Hence Ligers from tigers and lions doesn't compromise lions and tigers being separate species, because typically they ",
"don't share a common geographical range",
".",
"The ambiguity of species definition goes the other way too - I suspect a chihuahua would need to invent a step ladder before mating a great dane, but we call them both dogs...",
"TL;DR The natural world doesn't have hard boundaries they we'd like it to, plus the actual technical definitions of species typically aren't what people think they are."
] |
[
"If cold-brewing coffee takes nearly 12 hours, would continuous mechanical stir/agitation significantly accelerate extraction?"
] |
[
false
] |
For example, putting water with coffee grounds into something like a slurpee machine then letting it run for a while? Or, for an even more vigorous stir, a mixer? If this does indeed accelerate extraction, can we take some wild guesses on how much faster the process could potentially be? Does the possibility exist that with sufficiently energetic stirring, one could obtain similar results to the 12-hour "static" process in a matter of minutes?
|
[
"Generally, stirring the solvent speeds up whatever is going on in it. If you place a sugar cube in water, it dissolves rapidly at first but then as the water around it becomes saturated the dissolution slows down as molecules diffuse away from the sugar cube. Diffusion happens rapidly over short distances but slowly as the molecules go farther. ",
"Stirring helps the diffusion and makes the liquid homogeneous throughout the whole container. This being said, it's obvious that the substances in the coffee grounds would dissolve faster in the water.",
"This is a simplified version of this scenario - if we had pure chemicals we dissolve in a solvent. ",
"However, since we're talking about extraction, we also have to take in account how fast these molecules go from the coffee grounds to the water phase. This is not my area of expertise, so I can't say for sure. If the extraction happens slowly, the time it takes the molecules to diffuse might not have much effect on the total time of extraction. Then there would be no significant acceleration of the whole process.",
"If you want to know more about this kind of extraction there's a method called maceration used to extract crude chemical mixtures from solid phase (fx plants) into a solvent (fx water or ethanol). When doing maceration you place the solid in a solvent and let it stand for a period of time but shake/stir it occationally.",
"(Sorry if anything is unclear, English is not my native language)"
] |
[
"Not minutes but faster. But for something like coffee there are other complexities. The issues involved are how fast something comes out of the grounds into solution and the amount of stuff in the water at the time. The more stuff that has dissolved in the water the longer it takes to extract. That is why stirring helps since it causes the grounds to come into contact with more water. (That is worded badly.) ",
"But with coffee we care about how fast and what gets extracted. That is why different methods of brewing coffee give a different flavor. So stirred cold brew might taste better or worse (or just different) from non-stirred. A 6 hour brew might need lots of stirring but taste great. Or horrible."
] |
[
"It seems that every cold-brew method I've read about is essentially some form of maceration (as opposed drip coffee, which is percolation). Intuitively, the maceration speed of a stirred \"solution\" should increase many times over a static one, but I'm specifically interested in the behavior of compounds found in coffee."
] |
[
"Why doesn't the sun have a metal core?"
] |
[
false
] |
Or does it? I realize the metals may not be liquid or solid, but seems to suggest that the metal composition of the inner and outer layers of the sun are roughly the same, suggesting it doesnt' have a metal core. But the same article suggests the sun isn't churning out elements from its center because it is radiative, rather than conductive. Shouldn't it have quite a bit of the heavier elements that were floating around the solar system while the planets were forming?
|
[
"A bunch of it did end up in the sun, 2% of the sun's mass is heavy elements, not 2% of the total heavy elements in the solar system are in the sun. Huge difference ",
"Here",
" is a pie chart comparing the masses of the different objects in the solar system, notice anything?",
" post originally said what it says now, managed to confuse my self changed it to something wrong, and then changed it back. The point is the mass of the sun dwarfs the masses of the other objects in our solar system. For reference the sun is roughly 300000 times as massive as the earth is!! The mass of the heavy elements in the sun is orders of magnitude greater than the earths total mass even."
] |
[
"The sun indeed was born with some metals. Gravitational settling would tend to make the heavier elements \"sink\" (I am not saying that heavier things fall faster; that is not how gravitational settling works).",
"There is a timescale associated with gravitational settling. I actually don't know what physical parameters control that time scale (obviously density, temperature, and composition; but I don't know ",
").",
"Apparently gravitational settling is not particularly efficient (though I haven't studied the metal distribution throughout the sun).",
"The core is definitely enriched with Helium, though!"
] |
[
"Well, I can accept that they'd spin off all across the solar disk, but I'd think at least a ",
" of the metals would have ended up in the sun."
] |
[
"How do Hard drives of the same physical size have different memory capacity?"
] |
[
false
] |
Say you have a 2.5" laptop HDD. How do HDDs of the same physical size, (such as 2.5" or 3.5") have such varying memory capacities? I know there are different numbers of platters but you can't really fit more than 4 in a standard case i would assume. Is the servo for the read arm just more sensitive? If this is true, can a lower capacity HDD be "recycled" into a higher capacity one by slapping on a higher resolution read arm servo and special drivers?
|
[
"There are several different factors. One of course is the number of platters. But the magnetic medium on the discs, the field strength of the write heads, the sensitivity of the read heads, the placement accuracy of the heads, platter vibration, etc. all determine the raw bit density that can be put onto a platter. ",
"One great example of this is that several years ago, the industry transitioned from making the magnetic domains be oriented vertically instead of horizontally, greatly increasing the bit density that could be put on a platter. Nowadays they are doing things like using thermally assisted writes to give the write head more \"zing\". ",
"Then you have some other effects, such as the actual encoding scheme used, the error detection/correction schemes incorporated, etc. that influence the total byte capacity possible for a drive. That is to say, you don't get the total raw bit capacity divided by 8 as the number of potentially usable bytes....some bits are lost as \"overhead\". ",
"After all that, you have manufacturing defects. The drive's controller can mark out some sectors as \"bad\" and not use them, thereby allowing discs that are not 100% perfect to still be sold. ",
"Then there's Marketing, but I won't attempt to explain that. "
] |
[
"And what are the differences in production cost when you build a 500gb hdd vs. a 1000gb one?"
] |
[
"Also, how different (if at all) is the design? "
] |
[
"Why is \"clean coal\" technology so difficult? What are the limitations?"
] |
[
false
] |
[deleted]
|
[
"Aren't most of the byproducts too heavy to be released into the air ",
"The main byproducts of the combustion of coal are CO2 and H20. The lesser products include SOx (various states of oxidized sulfur). All of these are \"released into the air.\"",
"\"Clean\" means scrubbing the exhaust of coal-fired industry of these components (not the water, of course)."
] |
[
"One other thing is that mining coal is incredibly dirty and is not addressed whatsoever with the \"clean coal\" technology. Coal also has big pools of fly ash that have been known to spill and leak thousands of cubic meters of sludge all over the land."
] |
[
"Clean coal is easy on a technical level but if it costs more than solar or wind its not very useful."
] |
[
"Why does biodiesel produce less emissions than petrodiesel?"
] |
[
false
] |
I imagine it must have to do with the chemical structures of the different molecules, but I can't find anything that confirms this.
|
[
"Oh, well there are likely to be fewer sulfur compounds in the total process. The sulfur doesn't really get to your tank of gas but it is a part of the oil that comes up that needs to be cleaned out. Although nowdays most of the sulfur is extracted and used rather than just burned into the atmosphere anyways. Essentially every hydrocarbon that you put into an engine will be a hydrocarbon+O2 -> CO2 + H2O reaction."
] |
[
"It produces less CO2 emissions. Because the carbon comes from plants, where it comes from the CO2 in the air. So no net CO2 emission.",
"Digging coal/oil up out of the ground and burning it ",
" lead to a net increase in CO2."
] |
[
"Oh. I guess I just misinterpreted the information I was reading. I assumed that they meant it produced less CO2 and other kinds of dangerous emissions. I'm less impressed with biodiesel now. Thanks for clearing that up for me. "
] |
[
"Effects of solar gravity..."
] |
[
false
] |
Does the gravity of the sun counteract the gravity of Earth to any degree? If so, is there sun based gravity conflicting with the Earth's affecting us at daytime when we are facing towards, i.e. being able to jump a few millimeters higher and the opposite at night? Would this effect be more pronounced for example on a moon of Jupiter where the large body is much closer?
|
[
"Solar gravity is negligible compared to Earth's gravity for a person on Earth. The acceleration due to gravity at Earth's surface is 9.81 m/s",
" . The acceleration due to the sun's gravity for a person on Earth's surface is",
"(Gravitational constant)*(mass of the sun)/(distance from Earth to the sun)^2\n",
"which is approximately ",
"5.9 * 10",
" m/s",
". So the effect of the sun's gravity on us is about 1000 times less than the effect of Earth's gravity on us."
] |
[
"Moreover, you need to remember that the Sun is pulling Earth too almost as much as it pulls you. Think what will happen if you hold a bowling ball and have a lego figure \"standing\" on the under side of it and then drop both. Earth pulls the both of them just as much and they'll stay together. Similarly the Sun pulls both the Earth and you with that 5.9*10",
" m/s",
" so that's not the difference you'll experience in gravity.",
"But there is still a small difference. Since the centre of Earth is about 6370 km (the radius of Earth) further from the Sun than you are, the Sun pulls Earth a tiny bit less than it pulls you, and this is the effect you'll experience. It is ",
"(Gravitational constant) * (mass of the sun) * ( 1/(distance from ",
" of Earth to the sun)",
" - 1/(distance from ",
" of Earth to the Sun)",
" )",
"which comes out as 5*10",
" m/s",
" . Note that this is the exact same mechanism that causes the tides, it's just that the gravity of the Moon causes about twice as big a difference as the gravity of the Sun."
] |
[
"Another way of putting it is that the Earth itself is orbiting the sun, so it is essentially in a free fall around the Sun, along with everything on it. It's kind of like the way you feel weightless in a free-falling elevator. So, the tiny differences in gravity (the 5*10",
" m/s",
" you calculated) that the Earth and something on the Earth's surface experience come from the differences between what you feel and what is pulling the Earth, but your post explains that better than anything I could come up with."
] |
[
"Found this on the beach and can't identify what it is. Help?"
] |
[
false
] |
[deleted]
|
[
"I am pretty sure it is not wood (or petrified wood)."
] |
[
"It looks like a really worn clam shell, possibly ",
", which can grow quite big. I remember finding these a lot in North Carolina"
] |
[
"It seems way too heavy and rocky to be wood, even impregnated with something. It's also wearing away in a pattern that I don't ever see on driftwood."
] |
[
"Why does drinking methanol (CH3OH) cause blindness while drinking ethanol (CH3CH2OH) doesn't?"
] |
[
false
] |
Even though the difference between the two is only one carbon.
|
[
"The compound causing the blindness is actually not methanol, but formic acid, created from methanol in a metabolic process called toxication. Formic acid is a nerve toxin that acts through damaging mitochondria, and the optic nerve seems to be particularly vulnerable to its toxicity. Though, with doses only a little above the dose that can lead to blindness (that is, about 15 ml), toxicity extends to the whole organism with potentially lethal outcome. ",
"Fun fact: the antidote to methanol poisoning actually is ethanol. Poisoned individuals are being kept at about 1 per mille, for about a week, by means of infusion."
] |
[
"In principle, yes. You want to keep the oxidising enzymes busy while the methanol is eliminated in another way that does not yield formic acid. "
] |
[
"Diverse, or none at all. If the methanol is not metabolised, it will be excreted through the urine and maybe stool in it’s original form. Takes long though, it is quite lipophilic and thus can freely diffuse. "
] |
[
"What is the physical state of victims of cardiac arrest after being woken up?"
] |
[
false
] | null |
[
"I used to be on the code blue team when I worked in acute care hospitals and no, the person who has been revived after a cardiac arrest doesn't just get up afterwards. They generally look quite shocked afterwards and are taken to ICU because their condition will be guarded until they're stabilized. I forget the exact statistic but we were taught only 11% of people who suffer a witnessed cardiac arrest (another person seeing the patient go into cardiac arrest and starting a code blue) actually go back to the level of functioning (mentally/physically) that they were prior to the cardiac event."
] |
[
"Cardiac arrest often causes or is caused by damage to the heart muscle (typically, part of the heart isn't getting enough blood/oxygen and starts to die).",
"It takes a week or so for this damage to heal (as much as it's going to - it's common for some portion of damage like this to be permanent.)",
"In the meantime, its advisable for the patient to stay as quiet as possible (in fact they might not be ",
" to do normal physical activity.)",
"--- ",
"You could roughly compare this to ",
"\"I've sprained my ankle\"",
"- \"Well, you should let it rest for a while until it heals.\""
] |
[
"usually after a cardiac arrest a person is quiet confused (if not unconscious) due to the fact that brain's (as well as the other organs) is not well maintained during , then the patient is placed under surveillance in a intensive care unit, since the cardiac arrest is prone to occur afterward (especially if the cause is not taken care of or it it's still unknown).",
"After this they just continue saving the world or whatever they were doing before",
"yeah, i know what you mean...just for the sake of the plot."
] |
[
"How close can two stars be without absorbing each other or colliding? Is there a standard distance that makes them a binary system?"
] |
[
false
] | null |
[
"I would love to see an artists rendering of this."
] |
[
"I would love to see an artists rendering of this."
] |
[
"I read the Wikipedia article but I guess I'm not all that smart. Does this mean that theoretically a body such as a moon could one day turn into rings around a planet if it moved within the Roche limit?"
] |
[
"If I could physically manipulate atoms, how much force would it take to smash or combine two?"
] |
[
false
] |
The question is hard to word properly, and I can't help but think I'm misunderstanding how atoms work, but imagine if I was somehow able to hold a hydrogen atom in one hand, and a couple oxygen in the other. With impossible accuracy, would I be able to clap them together and make water or even function as a particle accelerator/smasher? I remember reading a while back that the force of the LHC is something like a mosquito running into you, so it got me thinking about if it would take a similarly weak physical force to smash atoms together if only we could actually manipulate them at that level. A related question that might be the basis for my misunderstanding is if combining hydrogen and oxygen (or any other combination) could even be done physically or of it's some other quirky feature of atoms that wouldn't work if simply smashed together.
|
[
"So would smashing two whole atoms together just make a tiny explosion, and would I be able to produce the force necessary with my hands? ",
"I wasn't really thinking about specifically what the LHC was doing, just that the energy was related to something as small as a mosquito hitting me. That got me thinking about if two atoms could be smashed together with a fairly weak physical force, if only I had a hammer capable of smashing two of them together. ",
"So ok, switching to what the LHC is actually doing; if I could hold a proton in each hand and clap them together, would I be the most powerful accelerator in existence, or is the force I'm able to produce still far too weak? ",
"I guess my overall question is about how strong the repelling force of atoms is, and if that force could be overcome with a toddler using a sufficiently accurate chisel. I know the collective of the force keeps me from being able to walk through a wall, but that's obviously a few billion trillion trillion of them."
] |
[
"Warning: Not a particle physicist.",
"First, for colliding hydrogen and oxygen to make water, that's not exactly what happens. When you add a certain amount of energy to hydrogen and oxygen (the activation energy), they are able to break up and recombine to form water and heat. This reaction is not a direct collision, it happens because the electrons move around and form bonds. ",
"The thing to remember is that your original question was a collision between whole atoms (nucleus and electrons). But the collisions in the LHC are just the ionized nucleus.",
"The force of the collision is often measured in electron volts. It's a measure of energy and is based on how fast the particles are going when they hit.",
"The LHC is trying to run 14TeV collisions between two protons. Converting units, that's only 2*10",
" joules....a very tiny amount of energy. However, because these particles are so small, the protons are travelling close to the speed of light. These speeds are able to reproduce the quark gluon plasma that existed right after the big bang. "
] |
[
"From what I understand it's more about the speed you can clap rather than the force.",
"The repelling force of charged particles like electrons is based on ",
"coulomb's law",
". Basically the equation says that the repelling force approaches infinity when you get really really close together. Although, with that much force, weird stuff starts happening. (Like the link in aqwin's post)",
"Also, \"toddler using a sufficiently accurate chisel\" is my new favorite phrase."
] |
[
"How deep in the ground can we find microbial life?"
] |
[
false
] |
The soil microbiota has a very important role in many processes such as nitrogen organication, the production of methane and so on. Is there true limit in depth we can find microbes or are extremophiles able to basically colonize the whole crust?
|
[
"Multicellular life has been found up to ",
"3.6 kilometers deep",
" and microbial life ",
"at temperatures of 102C",
". It's reasonable to suggest that life might be found even deeper.",
"There are probably a few limits to consider:",
"We're not sure if life can survive in environments above the boiling point of water (the 102C temperature of the deep ocean microbes was below the boiling point due to the extreme confining pressure)",
"The ",
"brittle/ductile transition",
" in the crust places a hard limit on how far down water and nutrients can percolate in the brittle layers because the rocks here fracture. Below the transition, rocks begin to behave in a plastic manner, meaning any cracks that do form are quickly sealed by rock fusing them shut again.",
"The depth to which nutrients can percolate and remain at levels to sustain life. This is probably dependent on groundwater flow, and how deep water can flow into the crust isn't well understood."
] |
[
"Correction: It's 122 deg C at around 200 times pressure at sea level, still liquid phase of water. ",
"http://www.pnas.org/content/105/31/10949.full.pdf",
" (from wikipedia)"
] |
[
"As long as there is an energy source and it's physically possible for bacteria to make it down there, I don't see why not. ",
"Crust is ~40km thick and we've only ever drilled 12km down, so it will be a while before we can ever verify it either way. We've found them present 3km down, and the super deep borehole projects were interested in geology, not biology. But really, we can't really prove that they don't exist at a given depth.",
"There are, however, some limitations we can and predictions we can make about what sorts of subsurface environments can support lithoautotrophs:\n",
"http://onlinelibrary.wiley.com/doi/10.1111/j.1574-6976.1997.tb00318.x/full"
] |
[
"Is the military myth true that you don't hear the artillery/mortar shell that kills you?"
] |
[
false
] |
this was inspired by another question that was asked that if an atomic bomb went off near by you wouldn't see, feel or hear it. So I was just curious if there was any scientific evidence that could prove whether or not you would hear the mortar/artillery shell that kills you.
|
[
"It's no myth. Most artillery shells travel faster than the speed of sound. You, or the area near you, get hit before the sound reaches your ears.",
"Personal experience. While at field artillery school at Fort Sill Oklahoma there was a battery practice firing nearby. The shells passed directly over our position before impacting several thousand yards away. We learned to look up immediately upon hearing the gun fire. We could actually see the shell pass silently overhead. A number of seconds later we could hear the sort of crackling sound the shell made while passing through the air, just like in the movies I add. ",
"The point of all of that is if we were the target we would have been hit before we even knew that a gun had been fired."
] |
[
"You probably wouldn't hear the explosion that kills you, the shock wave would probably kill you before anything.",
"Artillery and mortars are fired at high angles, usually, the sound takes the shortest path. Indirect fire rounds go way up and then come down, they may leave the tube traveling faster that the speed of sound but because they take such a long trajectory to get to the target you can usually hear the thump of the gun and the whistle of the round even if the round lands very close to you. There are many different type of rounds too, that can change things too.",
"I'm no scientist but I did have mortars walked over my position while I was in Iraq, I was in a concrete tower within 50 feet of the impacts and could most certainly hear the round being fired and the whistle of it as it cut through the air.",
"edit: if the firing angle is low enough you won't hear it like CanonFan says. Also, my MOS was 13B Cannon Crew Member."
] |
[
"You're ",
" underestimating the amount of energy released in a nuclear blast. You will be ",
"."
] |
[
"How does Aspirin inhibit platelets but other NSAIDs don't?"
] |
[
false
] |
Both ASA and NSAIDs such as naproxen or ibuprofen inhibit COX and prostaglandins and all that business but ASA inhibits thromboxane release of platelets and decreases their aggregation. Is it COX 1 vs 2 or is it more complex than that? What makes ASA so special? TL;DR Whats the molecular mechanism behind ASA inhibiting platelets and but other NSAID don'
|
[
"The other NSAIDs do inhibit platelets. It depends upon the ratio of COX1 to COX2 activity of the NSAID. Aspirin, naproxen, ibuprofen are all anti-platelet due to COX 1 inhibition, but aspirin is an irreversible inhibitor of COX1 and so the duration of effect is longer (the lifetime of the platelet). For ibuprofen the anti-platelet effect is reversible - it lasts as long as the dug is in your system (a few hours)"
] |
[
"One extra thing, even the so called \"COX-2\" inhibitors should be more accurately named \"mostly COX-2\" inhibitors because all the NSAIDs inhibit both COX-1 and COX-2. The COX-2 inhibitors mostly inhibit COX-2 but they'll also have a small amount of COX-1 effect. Likewise of the older nonspecific COX inhibitors may also have a degree of effect on COX-2. Naproxen, a COX-1 inhibitor, \"traditional\" NSAID, also has a particularly large effect on COX-2. ",
"So almost all the NSAIDs prolong bleeding time. However aspirin is also shown to reduce cardiovascular events (like heart attack) which is why people take it. AFAIK the other NSAIDS haven't been shown to reduce cardiac events and it's not clear what happens if a person is taking both an NSAID and aspirin. It's probably worse - that is, taking an NSAID with aspirin interferes with the action of aspirin in reducing cardiac events."
] |
[
"Sweet thanks"
] |
[
"Reasurance theorem? Mutual masturvation of primates?"
] |
[
false
] | null |
[
"Hi gigilo_down_under thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
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] |
[
"How many bloody things do i need to add to a post? Question marks, flairs... im on the Android app. With no ability to edit headings"
] |
[
"There isnt a flair for zooology"
] |
[
"Are the same type of cells found in humans relatively the same size across all humans, or do they vary in size? Similarly, are the same type of cells the same size across species, and other animals, e.g. is a liver cell in a dog the same size as a liver cell in a cat?"
] |
[
false
] | null |
[
"Not sure about \"regular\" cells but spermatozoa very in size a lot comparing different species. I did research on fish reproduction and sizes would vary between fish species, though they would be somewhat similar. They differ a lot from other species I also did a bit of research on or saw on the field such as dogs, pigs, bulls and dolphins (and those would be different between each other too, no only on size but in morphology)."
] |
[
"Different types of blood cells (red and white) tend to be the same size across a species unless there is pathology. This is why we can have machines that do automated cell counts, and also why they can be wrong with disease (I.e. leukemia). Cell sizes and morphology vary quite a bit between different species, so our veterinary lab equipment needs to be set for each species to be accurate. I looked at tons of blood smears from to do differential cell counts on different animals in a zoo during vet school because no lab automated count would be accurate. I would love to have a veterinary pathologist weigh in on cells from different organs, because I have very little experience with this"
] |
[
"There's obviously a lot of variation in cell size within an organism and even within a tissue. You have neurons with a 2 meter long axon, but also neurons of less than 10 micrometer total size. But this does not correlate with animal size, so smaller animals don't have smaller cells, they just have fewer of them.",
"As for your specific example, hepatocytes -liver cells- are relatively uniform in size and between mammals they are more or less the same size."
] |
[
"Electromagnetism is generally presented as wave phenomena. What is the particle (photon)-based interpretation of wireless communication, or of two charged particles repelling each other?"
] |
[
false
] |
I've just completed a mid-level university course in electromagnetism under electrical engineering, covering uniform plane waves, transmission lines, antennae, waveguides, optical fibres, etc. The entire subject matter was presented by interpreting a disturbance in the electromagnetic field as a wave, e.g. for a basic plane wave, the electric field strength and direction could be given by: E(x,y,z,ω,t) = A e e e . Similarly, we are shown that a charged particle creates a disturbance in the E field, and hence will exert a force on other charged particles. My question is, how should I think about these phenomena as an interaction between matter via photons? I understand that matter particles can be considered in a quantum sense to be entirely described by a wave that represents the probability of that particle's superposition collapsing to that point. Does a similar understanding apply to photons? If so, how does this wave (which seems to be a lot like a field to me) relate to the electric and magnetic fields as I understand them now? And if particles are constantly shooting photons at each other to convey the effects attributed to the electric and magnetic fields, where does the energy for these photons come from? Maybe related, or maybe I am reading the wrong discussions -- I have seen some talk online of electrons having a "cloud" of virtual photons. How can this possibly work if photons travel in a straight line and always at c? Cheers
|
[
"In principle, interaction of matter via photons ",
" the interaction of charged objects through changes in EM fields.",
"Let's say you have some static distribution of charge in some volume of space. This distribution generates constant electric fields with constant energy that we might as well call 0. Now, if you change the charge distribution (either by reconfiguring it, or simply by pouring more charge in/taking some of it away), the electric field changes. The consequence of finite velocity for propagation of information and the fact that the change in charge distribution costs energy, is that now you have a EM wave traveling through space (a specific case would be the plane wave), carrying the energy. Once it reaches some other point in space, it will interact with the charge distribution there, changing it and exchanging some of its energy.",
"The gritty details of consequences of quantum mechanics on this process are something, that I'm not sure I would be able to explain (quantum field theories aren't very intuitive), but the gist of it is that the charge distribution can't assume any form, but only discrete states (like, for example electrons in atom can't just fly around to their liking, but are always found in superposition of infinite, but not continuous, set of allowed states).",
"To give you a semi-classical, completely wrong example (that at least hints in the right direction):",
"Imagine you have a semi-classical electron just sitting in there in constant electric field - which is completely against uncertainty principle, but that's beyond the point right now. If you send an disturbance thorough the field (an EM wave), the electron would change it's state (if the disturbance would be periodic, like your plane wave, the electron would start to shake with it), absorbing some of the fields energy.",
"Quantum mechanically, the electron can't be shaking at arbitrary frequency, so to get it from the ground state (it just sitting there) to some excited state (shaking), you have to give it a very specific amount of energy through the EM wave - and that amount of energy hidden in the disturbance of the EM field is what we call the photon.",
"If we wanted to give up the semi-classical pretence, we would need to use quantum-mechanical description of the electron. That doesn't mesh well with classical fields, so you need to find a way to describe the EM field in a similar way. This is done by a formal process called second quantization, during which the photons emerge (mathematically speaking).",
"In this formalism, interaction between particles (electrons) can be mediated by arbitrary number of interaction particles (photons), provided the process obeys conservation laws, that's why they are called virtual. An example would scattering of two electrons. [EDIT: ",
" Let's rather not talk about localisation of the collision], they \"collide\" by exchanging a virtual photon, which transfers the momentum between them (like in this ",
"Feynman diagram",
" where two particles with momenta p1/p2 collide through a mediating particle with momentum/quasi-momentum k).",
"As for the cloud of virtual photons, that's mostly a formal thing. The idea is that vacuum and single-particle states have to behave as such (meaning there can be no interaction in the mathematical description of their dynamics). This necessitates introduction of terms to the Hamiltonian that look as if the electron had a cloud of photons around itself."
] |
[
"I may not have have understood some of your post, but I hope I will answer your question.",
"Actual photons are definitely described by a wave function, but not really the quantum-mechanical kind. The problem is that quantum-mechanics doesn't work really well with the concepts of absorption and re-admittence, and definitely not with the concept of an object moving at the speed of light. But, when you focus your energy onto a single photon, it does infact obey a wave-equation, but it is governed by quantum field theoretic mechanics, with a Dirac-type equation, rather than a simply Schrodienger-type formula.",
"This",
" paper is good for the basics, and as noted in the paper, the equation is essentially the Neutrino wave-equation adjusted to a different spin, and gives you an equation, which you can solve to see exactly hows your photon wave looks! So when you have an actual interaction mitigated by a proton, you have three waves (the source, the target, and the photon) overlapping and destroying at every interface!",
"Now, that said, regarding virtual photons, there is no such semblance. Virtual photons are better thought of as a tool, rather than a physical thing. They \"exist\" when we expand an exponential function into it's Taylor series, and then begin to notice that certain terms have a Dirac delta function that fixes the momentum between two points, so that the two points have \"interacted\". The analogy there is just for the toy theory of the free boson, but the analogy continues: they exist mainy as a approximate and computational measure. As such, the really don't have a physical interpretation, since they don't even follow simple equations like mass conservation, see ",
"this",
". So in the actual interaction, we have mitigation by \"concrete\" virtual photon particles, that exist in a single place, and obey more or less no equations.",
"This \"cloud\" generates the electromagnetic force, and has a density function leading to the regular Maxwell and Coulomb equations, but it is not a probability function per se, only a representation of the electromagnetic field itself, which satisfies an \"wave\"-equation, but totally unrelated to the photon one above.",
"tl;dr Photons have an wave-equation, just as any other particle. Virtual photons, which actually mitigate the force don't, since they are more of a construct, they just have a density function which fictitiously represents the electromagnetic field interactions."
] |
[
"So a photon is really just virtual?"
] |
[
"What happens when you go without sleep?"
] |
[
false
] |
Is it true that you can 'go crazy' if you go too long without sleep? How long would that take if it is possible? What is the mechanism by which this takes place? And how long would it take someone to die without sleep?
|
[
"The longest any one person has stayed awake without the use of any stimulants was 11 consecutive days. Supposedly, people have broken that record, but none of them have been scientifically verified. The individual suffered from moderate sleep deprivation symptoms, but did not die, nor reported any long-term issues as a result. It depends on the individual on how long it would take to 'go crazy'. Some of the symptoms of sleep deprivation include hallucinations, but some people may not experience these, so it's hard to give a blanket statement that would apply to every single person."
] |
[
"Theoretically, yes. Though I'm not sure if such a study has been performed. I'd be willing to bet that if stimulants had been used in the aforementioned study, the subject might have been able to stay awake much longer. Constant administration of methamphetamine would probably do the trick, but of course you're looking at a ton of physical and psychological side effects that no IRB would ever be willing to approve of such a study."
] |
[
"Very extreme cases of insomnia can limit your sleep entirely for years ",
"Al Herpin",
" , ",
"Thai Ngoc",
". Also, studies have shown that it's not the actual lack of sleep that makes someone go \"crazy\" but the lack of the REM stage of the sleep cycle. I recently read a study (that must have been performed in the 1970s) where the subjects were immediately awoken once rapid eye movement was recorded. Over time, the subjects seemed to have resembled a dissociative fugue state. "
] |
[
"Question on perpetual motion"
] |
[
false
] |
[deleted]
|
[
"Nobody really disagrees that a system into which you're pumping energy indefinitely can sustain motion indefinitely. However, that's not what \"perpetual motion\" has come to mean.",
"Perpetual motion machines are those that can produce more energy than they consume. Your friend is not proposing one of these. So your friend is not perpetrating a scam, he's simply proposing an expensive, boring, but feasible use of an electromagnet."
] |
[
"I don't think he's using the magnet to power the rod - I think it's there as a magnetic bearing. ",
"And if you have something spinning on a frictionless bearing in a perfect vacuum, yes, it will spin forever. But that's still not a perpetual motion device any more than any space junk floating forever in space is a perpetual motion device for the reasons you stated."
] |
[
"Yeah, its possible for something to move forever if the energy in the system doesn't change forms. But thats a highly ideal (and useless) scenario."
] |
[
"How do you calculate the motion resulting from a sound wave?"
] |
[
false
] |
In other words, lets say you have a sound wave at a known pitch, amplitude, etc, going through an object of known mass, etc. Is it possible to calculate the size of the resulting vibrations? If so, how? Thanks.
|
[
"What you're essentially asking is how does a sound wave in air behave when it becomes a soundwave in a material. Well in many ways, it's a similar process to how light interacts with materials. In this, you can even reach a quantum description of sound in materials in the form of ",
"phonons.",
"How these waves will behave depends on the dispersion relation of the material. Some frequencies will travel at different speeds within the material and some will get absorbed and ",
"attenuated quicker than others.",
" There's also the case of resonance, where the sound wave is completely absorbed by the material and converted into mechanic motion.",
"The mathematical approach can be quite in depth and it really depends on what sound regime you're dealing with and what kind of model you want to you. "
] |
[
"Thanks for responding. Is it safe to assume the frequency of the vibrations in the material is equal to the frequency of the vibrations of the air particles? If a sound wave carrying a pitch of middle C (ie, 261.6 cycles per second, no harmonics) goes through air, then a wall, then through more air, is it all vibrating back and forth 261.6 times per second?",
"\nThanks again."
] |
[
"Frequency is always constant with waves. The wavelength and velocity change."
] |
[
"Why does my coffee look like this?"
] |
[
false
] | null |
[
"Hi wandering_grizz thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
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" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"‘Chemistry’"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"listed in our wiki!",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"If it takes time for nerve impulses to reach your brain and be processed, is your body in the future as compared to your conscious?"
] |
[
false
] | null |
[
"Yes!"
] |
[
"That is also correct. Especially when you consider the fact that information from different senses is processed at different speeds (e.g. auditory is faster than visual, pain, especially from far away limbs takes a (relatively) long time to reach your brain). Also consider the fact that a lot of information that we detect unfolds over time and is not instantaneous such as motion (change in light intensity in a region of space over time) etc. As a result, the brain has to sometimes fill in what was going on a moment ago based on the information it is currently seeing. In perception this is called \"postdiction\" and you can find a few examples with a Google search."
] |
[
"I feel like this has big implications; we're not living in one point in time, but in a period in time. ",
"Am I coming at this from the wrong angle? "
] |
[
"Why do some parts of the body seem to be more prone to cancer?"
] |
[
false
] |
I'm especially thinking of breast cancer and cervical cancer in women, what makes those parts so vulnerable?
|
[
"Cervical cancer is actually less common--the reason it's often emphasized is that many instances are preventable.",
"In general, the most common cancers are in areas that are subject to rapid cell turnover, are acted on by hormones that impact growth, and are exposed to environmental compounds that cause either cell death or direct mutations to DNA, because these give a tissue more chances to accumulate mutations.",
"The most common cancers in women are breast, lung, and colorectal (aside from nonmelanoma skin cancers). Breast cancer is usually but not always in the epithelial cells lining the milk ducts--a layer that turns over quickly--and since breasts are a secondary sexual characteristic and important in childbearing, breast tissue is acted on by reproductive hormones--for example, in some women they actually change in size many times during their lives, even without childbearing. There may be additional reasons, as this is not my exact field of study, but in and of themselves those would predispose a tissue to be a more common site of cancer."
] |
[
"Here's a ",
"list of the most common cancers",
" divided by men and women and ethnic group. You can often see interesting environmental trends. You'll note, for example, that while colorectal and breast tend to be common in women across ethnic groups, stomach cancer tends to correlate with high salt diets. ",
"I'm not sure how the rate of turnover in milk duct epithelial is affected by milk production, except to say that obviously it makes sense that it would be lower without milk production, but I haven't read much research in this area and can't do anything more than speculate and note that epithelial layers are in general characterized by lots of cell turnover. I'd ask my cousin, who used to study breast cancer, but she's on a plane right now.",
"Lung is so high generally because of smoking. I'm not sure about mouth cancer, honestly, except that it also correlates highly with smoking and with chewing tobacco. But passage of hazards through the mouth is generally quite transient with the exception of chewing tobacco, while they mill around in the stomach (which has the added factor of the acidic environment) for quite some time."
] |
[
"Women who have breastfed are actually at lower risk, ",
"http://onlinelibrary.wiley.com/doi/10.1111/j.1582-4934.2005.tb00350.x/abstract"
] |
[
"What is the smallest theoretical size a nuclear fusion reactor capable of 'breakeven' could be?"
] |
[
false
] |
[deleted]
|
[
"Went looking for a small design I saw a while ago and came across this fairly well done blog post:",
"http://www.ialtenergy.com/spherical-stellarator.html",
"The UST-1 is the design I saw, smallest I've ever seen. And the guy that makes it is such a pure engineer it gives me hope. ",
"edited since I found his presentation, looks nice actually. "
] |
[
"There is the reactor size and the then there is the support stuff. In the NIF holorum and the Z-machine wire net, the reaction device is millimeters in size, but the external drivers are gigantic and weigh many tons."
] |
[
"The holorum is millimeter sized. I've toured the NIF and seen one. The reaction after being hit by the lasers stops a few tens of nanoseconds after the initial compression and fusion. The plasma has not grown by much more than a few more millimeters. The chamber to do this in on the other hand is meters across. I consider the \"reactor\" to be just the holorum capsule. The rest is just drivers and support infrastructure."
] |
[
"What can I put on ice such that a second layer frozen on top will separate easily?"
] |
[
false
] |
I'm planning an ice sculpture but can't build it where I want to present it, and since it's going to be very heavy, I'd like to be able to separate it into layers. If I freeze the first layer, then smear something hydrophobic (butter?) on the ice before filling up the rest of the mold, will they be easily separable? What are other common household hydrophobes? (I hope this question is sciency enough...)
|
[
"How about a physically intact barrier like wax paper or saran wrap? If those aren't tough enough you could do polyethylene sheeting (trash bag material, if thin. you can get thicker at hardware stores) or even something like a tarp."
] |
[
"I look forward to this thread helping me store individual cooking size portions in my freezer. ",
"If I may request some answers more generic than OP's specific scenario (sculptures)?"
] |
[
"I immediately thought of painting drop sheets, which I imagine are polyethylene as well."
] |
[
"What is morning breath and what causes it?"
] |
[
false
] | null |
[
"Bad breath (and even body odor) in general is caused by bacteria. On the tongue, the back is relatively dry and not really affected by brushing, rinsing, etc. This creates a very pleasant environment for bacteria to thrive, and they produce malodorous compounds, which accounts for the vast majority of bad breath. This is more noticeable in the morning because there has been very little activity in your mouth for 8 or so hours, allowing the bacteria to do their thing undisturbed. In order to get rid of the odor, you have to get rid of the bacteria. You can use a tongue scraper or even your toothbrush, you just have to get back there. "
] |
[
"So despite my brushing and flossing, there is still too much bacteria build-up while I'm sleeping? Is this due to food in the diet, (like too many simple sugars) or are there multiple factors?"
] |
[
"Right, sort of. It's not that you're doing a bad job or anything, it's just that normal brushing and flossing doesn't reach the back of the tongue, and that's where all the bacteria hang out. It's not that they're building up, but they secrete smelly compounds, so the longer you leave them there to do their thing, the more smelly stuff they will put out. Make sense? Mints, toothpaste, mouthwash, etc... they just mask the smell, but don't get rid of the bacteria, and that's the only way to truly get rid of the odor. ",
"There are multiple factors. Eating sugar before bed isn't a great idea anyway, and it's definitely discouraged, but it doesn't really change the odor situation. It's due to a build up of old food remnants, dead cells and even post-nasal drip, which are all things you can't get rid of. Rinsing with a diluted solution of hydrogen peroxide after you brush and floss wouldn't really hurt, and it may even help to whiten your teeth (I'm not a dentist, so don't quote me on that one). There's tons of lymphatic tissue back there that likes to kill bacteria and stuff, but if you've had your tonsils removed, that could be a contributing factor. "
] |
[
"How Do Inward-Rectifying Calcium Channels INCREASE \"Resting\" Potential In Pacemaker Cells?"
] |
[
false
] |
I understand that less inward-rectifying Ca2+ channels is responsible for the higher mV "resting" potential of pacemaker cells (and consequently keeps the fast Na+ Channels inactive), but how does that make sense? The inward-rectifying Ca2+ channels are responsible for uptake INTO the cells. By having less of them, would it not mean that there are less positive Ca2+ ions going into the cell, thus the charge would be MORE negative? Additionally, as a bonus question, would the decrease in intracellular calcium due to less of these channels affect the rate /force of contraction, given the need for Ca2+ to release calcium from the SR via CICR?
|
[
"Where did you come by these ideas? If they have come from a lecturer then perhaps I am wrong but from my understanding pacemaker cells function differently to how you suggest. I will use cardiac pacemaker cells as an example which will hopefully help explain.",
"If you scroll down to figure 4 here (",
"https://courses.lumenlearning.com/suny-ap2/chapter/cardiac-muscle-and-electrical-activity/",
") you can see a trace of the pacemaker cell membrane potentials. ",
"As you can see the membrane potential slowly increases up to about -40mV before a rapid increase up to around +5mV and then a more gradual decrease back to -60mV. This can basically be divided into 3 parts.",
"Part 1 is called the pacemaker potential (this is the slow increase from -60mV to -40mV). This is mainly determined by two things, the potassium leak current and the funny current (sometimes called the pacemaker current). The potassium leak current is the slow efflux of potassium ions which decreases as time goes on. The funny current is the continuous inflow of sodium ions. ",
"Combine these two factors and it’s pretty obvious why the potential gradually increases. A gradual decrease in Potassium efflux + a steady increase in intracellular sodium causes the inside of the cell to become more positive (depolarised). ",
"Part 2 is the upstroke (the rapid increase from -40mV to +5mV). Pacemaker cells have L-type calcium channels which are the most important here (although the funny current does also increase). These channels open more slowly but stay open for longer than other voltage-gated calcium channels you may have come across. This is the reason that this increase is still slow when compared to depolarisation of axons.",
"Part 3 (slow return to -60mV). This is effectively repolarisation of the cell and occurs due to closure of the calcium channels, opening of the potassium leak channels and inactivation of sodium channels. Additionally the activity of sodium/calcium exchanger and sodium/potassium pump work to return the membrane potential to its ‘resting’ state of -60mV.",
"I hope that made everything more clear, if not then please let me know if you have any further questions"
] |
[
"Great info in there. I'm relatively familiar with the phases of the action potential. What I'm referring to is (supposedly) why the \"resting\" potential is -60 rather than -80 or so. I've read it's because there are less inward-rectifier potassium channels, but that doesn't make any sense to me."
] |
[
"Do you have the source for that? If I can see that it might help me to explain your question better.",
"The reason why the membrane potential is as it is will be a consequence of the dynamics of all the channels involved."
] |
[
"Can someone explain what's exactly going on in yesterday's Astronomy Picture of the Day?"
] |
[
false
] |
This is the picture that I mean: Apparently, there was a solar eclipse on 1st September and it is a time lapse shot of the same. However I don't quite understand how this time lapse shot worked. My doubts: Is that the sun we're seeing in different phases? It looks like the moon to me! Why does it look like the moon? If that indeed is the sun, then what is the bright yellow object in the lower left corner of the image? (I still feel the white object in phases is the moon and the sun is in the lower left hand corner. But then the 'lunar' eclipse makes no sense!) Would highly appreciate if someone with knowledge in photography/astronomy can enlighten me what is going on in the photo.
|
[
"Yes, it is the sun. It \"looks like the moon\" because the sun is VERY bright and these photos were shot with VERY dark filters which allow the camera to actually capture the detail of the sun and not a big bright orb as you are used to seeing in photographs.",
"Yep, that is the sun, I am guessing at sunrise.",
"It's a time-lapse, and you are seeing multiple shots of the sun across the sky. Likely a cloudless day would be my best guess.",
"How it was made: The photographer shot 68 frames exposed/filtered to capture the detail of the sun for the eclipse. Those 68 photos (or at least the sun from those 68) were then overlaid on a 69th photo right at sunset, which is why you only see one yellow sun in the corner and no clouds streaking across the sky (also looks like a cloud-free day)"
] |
[
"I may be mistaken, this isn't so much as a 'time-lapse' as a photographically altered image, solar eclipses typically last 7 minutes in totality (that's the circle of light 19 images down). ",
"So, what's happening?",
"Yes, that is the sun, no it's not in different 'phases' as much as it's undergoing an eclipse. It looks like the moon because the images have been taken with filters so the actual sun disk is visible, as a disk, it has the same (similar) angular size as the moon. You can tell it's not the moon because a new moon isn't generally lined by a ring of light.",
"The last image (and the foreground) is the final picture they took but they didn't use a solar filter so you don't just see the disk but all the light.",
"This is indeed a time-lapse but each individual shot of the sun (the dots tracking down from top right to bottom left) is 4 minutes apart 4.5 hours worth of images (68) have essentially been cut out and placed onto a single photo, hence there are no clouds, that is part of the foreground and is only a single photo.",
"Sorry if that's confusing, it's quite a strange but very satisfying image."
] |
[
"Yes, the foreground from all the other shots would be entirely black because of the aforementioned dark filter :) ."
] |
[
"Why haven't any plants evolved the ability to move around, crawl walk or otherwise?"
] |
[
false
] |
[deleted]
|
[
"Because there is no evolutionary pressure to do so. They already have a perfectly well adapted means of travel, their seed dispersal mechanisms. ",
"There isn't an \"extreme advantage\" to movement. Movement is an extremely expensive operation. There are plenty of animals who move as little as possible. Cats are good example, they sleep up to 20 hours a day. ",
"If you move around a lot you need a lot more energy, which means you need to be easily able to pass food into your cells. In animals there is only a cell membrane, which is weak and breaks easily thus requiring more energy to repair. But plants have cell walls which are much harder to pass food through but much stronger and thus dont require the same amount of maintence. Its a balancing act. It isnt as simple as saying movement is better.",
"Plants do have structures similar to muscles and nervous systems. There has already been a post about venus fly traps. They are also capable of communicating to other plants when under attack and the other plants can beginning activating their ",
"defenses"
] |
[
"Movement is extremely energy costly. The energy that a plant would need to expend in order to move to a \"better\" location would be extremely higher than the energy it would gain.",
"http://what-if.xkcd.com/17/",
"Is a good breakdown of how much energy an animal (cow in this case) could gain from photosynthesis. It amounts to about 4% of the required caloric intake of cows. ",
"This basically answers your second point as well, the process of getting energy from the sun is no where near efficient enough to allow for plants to grow complex energy consuming organs. A human brain consumes 25% or more of our energy, and even in a typical vertebrate it consumes between 2-8%. That is a huge amount when you do not get that much energy to begin with."
] |
[
"Some plants do have the ability to move, think tumbleweed for example. Other plants instead of moving take advantage of more of their surroundings. Venus flytraps eat bugs to get essential nutrients, and cactus have evolved protections against extreme weather and dryness for example. "
] |
[
"How did sleep evolve so ubiquitously? How could nature possibly have selected for the need to remain stationary, unaware and completely vulnerable to predation 33% of the time?"
] |
[
false
] |
[deleted]
|
[
"It also should be noted that remaining stationary and unaware is the ancestral state for animals and all multicellular eukaryotes.",
"Awareness and behavior are fairly remarkable evolutionary innovations, really."
] |
[
"I don't know the answers to most of your questions, but I just want to point out that for something to evolve \"ubiquitously\", it only really needs to evolve once, in a common ancestor. And if it seems to have obvious maladaptive disadvantages, it must have some other adaptive advantage.",
"EDIT: So these threads might help:",
"What happens during sleep that gives us \"energy\"?",
"how complex does an animal's brain have to be in order for it to need sleep?",
"Why do we get short-tempered and easily stressed when we don't get enough sleep?",
"Do simple organisms 'sleep'?",
"Why do we require sleep?"
] |
[
"This is an obvious, but very interesting observation."
] |
[
"When they mapped the human genome, what is that? If everyone has different genes, was the mapped genome one person or an average or a \"perfect\" one?"
] |
[
false
] | null |
[
"Everyone's DNA sequence is different. Even identical twins may be slightly different due to gene copy number variations, or due to mutations occurring during development. However, on average, about 99.5% of our DNA is similar to all other humans. Since the human genome is about 3 billion base pairs long, the variation between individuals is about 15 million base pairs.",
"When they \"mapped the human genome\" as you say, they mapped the genome of particular individuals. The Human Genome Project was the first to do so. They don't reveal the names of their volunteers who provided the DNA, but obviously it was some person (or small group of people).",
"Since then, people have full-sequenced thousands of genomes, so we have individual genomes for thousands of people. By \"full sequence\" I mean sequencing the entire haploid genome (not DNA tests offered by internet companies such as 23andme which only partially sequence the genome and look for particular markers).",
"Also, when we say \"full sequence\" we mean \"almost full\". There are still some small regions which are unsequenced due to technical difficulties. The last I read, there were ",
"about ~100 gaps in the euchromatin (the DNA that is loosely coiled) which remain to be sequenced",
", and quite a few more in the heterochromatin. But these are very small parts; the majority of the human genome has been sequenced.",
"There is no \"perfect\" genome. When we do comparisons, for example, comparing your DNA sequence to some standard, we use the Human Reference Genome, which is maintained by the ",
"Genome Reference Consortium",
". It's made available through various sites, for example, ",
"UCSC Bioinformatics",
", or ",
"Genbank",
".",
"The reference genome is not homogenous. Different chromosomes (and different parts of chromosomes) may have different coverage. For example, chromosome 7 may consist of the sequences of 14 volunteers, while chromosome 15 may consist of the sequences of 30 volunteers (not necessarily the same volunteers as the other group). The current reference genome keeps changing as more people are sequenced and more data becomes available. The last reference genome I'm aware of was ",
"GRCh38",
", though there may be newer ones.",
"As for how they're used, it's up to the investigator to determine what makes sense. For example, you could \"average\" the genome for a particular population (pick the commonest polymorphisms at different loci and call them standard). Or you could keep each person's genome separate, if you were studying the variability in a particular gene. It depends on the purpose of the study."
] |
[
"Not very different at all. IIRC, human DNA and chimpanzee DNA is something like 98% identical. Remember though, that our genome contains about 3 billion base pairs, so that 2% difference is actually 60 million base pairs. Between two different humans, DNA is over 99% similar, but that <1% is still millions of base pairs and is responsible for all our differences."
] |
[
"The biggest implications are its uses for identifying where exactly certain genetic mutations come from, and what genes do what. While we may look drastically different to one another, the genes that make up our appearance are minuscule in comparison to the number of genes that control everything else that makes us human. That being said, it doesn't really matter who the genes come from, the sequencing is simply dependent on the sample DNA being human. \nI believe the DNA used was from a randomly selected male in New Mexico but don't quote me on that. "
] |
[
"Is it possible for a single volcanic hotspot to create features of the Yellowstone hotspot (specifically, fertile plains due to ancient ash beds) and the Hawaiian hotspot (specifically, island building)?"
] |
[
false
] |
I'm working on a new world building project, and one of the major ideas of the region I'm creating is a volcanic hotspot creating a volcanic archipelago (much like Hawaii) across an inland sea or a large oceanic bay. However, I'm wondering what the land would look like on the adjacent land where the hotspot had been active before moving under the water. I understand that a typical shield volcano doesn't really produce huge clouds of ash, instead producing lots of lava which builds land. Something like Yellowstone, on the other hand, erupts explosively, leaving a large caldera that can later be filled in, creating fertile lands like the plains of Idaho. Do these features ever appear from the same hotspot? How are these related to volcanoes on islands like Monserrat, which, while capable of land building, also seem to erupt explosively? Finally, could a hotspot capable of island building exist under a continent, or is it factor of thinner oceanic crust? How thin would continental crust have to be to have such a volcanic system exist?
|
[
"well, first we have to discuss what a hot-spot actually is. A hotspot is not material travelling from deep, it's a thermal anomaly from the D\" that transmits thermal energy to the surface in a very concentrated area. ",
"When this thermal energy reaches the crust, one of a few things can happen: You can end up with a hotspot trace on oceanic crust, where because of the chemical composition of the sea-floor (basalt) the resulting magma will be very thin and not very viscous. If it were over continental crust, however, the addition of Si makes the magma much more viscous and gloopy, which is why you end up with explosive eruptions rather than flowy eruptions. ",
"Montserrat is not made from a hotspot, at least not as far as they have determined from the geochemistry as of yet. The reason it can be capable of landbuilding and explosive eruptions again comes down to the geochemistry of magmas and the interaction between that magma composition and the existing landscape and internal geology. ",
"Your final question is answered above concerning what a hot-spot actually is. "
] |
[
"The size of the hotspots are just about the same. The reason that the hotspot trace on a continent is 'larger' because of the composition of the continental crust. Instead of spewing out a less viscous material as soon as it is heated, it heats up a much larger area. ",
"You can theoretically make an island chain and a mountain range from the same hotspot, but it's not going to be a mountain range that will be created by compressional tectonics, more of a chain of volcanoes (so they will erode quite quickly). "
] |
[
"Ok, so a couple of followup questions. What happens to a hotspot of Hawaiian size when it travels across a continental plate? I assume that the Yellowstone supervolcano's hotspot is a dramatically larger/deeper anomaly then Hawaii's hotspot.",
"I was originally hoping it would make sense to end up with a mountain range on the hotspot track, which appears to have happened with the Anahim Volcanic Belt (",
"http://en.wikipedia.org/wiki/Anahim_Volcanic_Belt",
"). Does it make geologic sense to have mountains like that on the continent and then islands offshore on the same hotspot track?"
] |
[
"Is pregnancy between the ages of 35 and 40 really a considerably higher risk?"
] |
[
false
] |
I've always heard that pregnancy over ages 35 (often called Advanced Maternal Age) is significantly more dangerous for both the woman and the baby, due to the higher risks of miscarriages, preeclampsia, gestational diabetes and decrease in fertility rates (as said , and , for example). But, I watched this , from "Adam Ruins Everything", which provides evidence that the risks of getting pregnant between the ages of 35 and 40 don't increase as much as warned by the majority of doctors. So, what's the truth about pregnancy after 35? If women could have babies until they were 40 without taking any more risks, it would be better to their careers.
|
[
"Genetic counselor here. The historic reason for 35 being the magic number is that when amniocentesis was first introduced, the risk of a complication due to an amnio was the same as the age-related risk of the baby having Down syndrome. ",
"Now, the risks of amnio are significantly lower (ultrasound guidance, practice, etc.), but the age 35 thing has stuck. ",
"The risk of chromosome abnormalities goes up every year older a women gets; there is not some magic jump from 34 to 35. This risk is due to the higher chance of nondisjunction, which can occur when splitting up the chromosomes in the egg, as a women ages. If nondisjunction occurs, the woman passes on either too many or too few chromosomes to the fetus (Down syndrome is an extra chromosome 21, while Turner syndrome is too few X chromosomes in a female).",
"I cannot speak as much on the other pregnancy risks, so I'll leave that for the physicians on here."
] |
[
"“Advanced paternal age” (not sure how this is defined, possibly > 40?) is associated with an increased risk of de novo mutations and specifically an increased risk for dominant FGFR and Noonan spectrum disorders. ",
"These are rare conditions however, so the overall risk to the fetus is lower than having a chromosome difference in a fetus of a 40 year old woman for example. ",
"Source: I’m a genetic counsellor. Too lazy to pull a paper."
] |
[
"Just adding to this, nondisjunction can happen on lots of chromosomes, but many of them won’t thrive and spontaneously abort. You might just experience a heavy period, and you try again. We hear about chromosomes 21, 18, and sometimes 13, because those chromosome errors can still be compatible with life and be brought to term."
] |
[
"Do electric cars have a measurable weight difference after they deplete their batteries?"
] |
[
false
] | null |
[
"2 micrograms, for the Tesla Roadster."
] |
[
"As far as I know you apply it just like in any other case, for example a spring weighs slightly more when compressed due to the (relatively tiny) energy it is storing."
] |
[
"Only those with fuel cells, since they use atmospheric oxygen as one electrode (whether they get heavier or lighter depends on whether they exhaust reaction products into the atmosphere or retain them as solid or liquid)."
] |
[
"Would it be possible to condense all daily nutrients into a single block of food?"
] |
[
false
] |
You often see in Sci-Fi (maybe just 50s B movies) in the future people eating food that's just a cube. I know each person is different even the two genders have different caloric requirements but could it actually be possible to have all daily nutritional requirements concentrated into a small block?
|
[
"It would certainly be possible since we can list them out and could just homogenize them together. The problem comes with actually using it as our only source of sustenance. There are a lot of writings that discuss (mostly) NASAs research into minimization of food for long-haul space travel. (Mary Roach's book \"Packing for Mars\" is excellent.) There turns out to be a lot of psychological issues with not having what our bodies consider traditional meals over time."
] |
[
"Nutraloaf",
" is(was?) served in prisons as punishment. "
] |
[
"It already exists, and zoos and medical labs feed it to their monkeys and chimps. It's called Purina Monkey Chow. ",
"(I've tried it and tastes horrible)",
"Purina makes a wide variety of nutritionally complete foods for various sorts of mammals. They also have Pig Chow and Carnivore Chow (I did not try those...). ",
"Ref: I worked in a monkey lab and did 2 internships with the zoo nutritionists at National Zoo and Brookfield Zoo."
] |
[
"Does low blood sugar have an effect on blood pressure?"
] |
[
false
] |
[deleted]
|
[
"You should ignore that answer entirely. That’s some Ancient Greek level understanding of science right there, meaning it’s entirely wrong. I’m not sure if ",
"/u/bugsybunny14",
" just thought they’d give it their best guess or what, and it’s a shame because the question is a good one. I’ll post a reply to your question in just a moment."
] |
[
"Glucose (sugar) tends to be really sticky. It especially likes to stick to proteins, and this process is called glycation. It's hard to undo glycation, so high levels of blood sugar over time will continually glycate protein components of different organ systems. Glycation is not harmless, because the addition of these particles ultimately will impair the intended function of whatever is being affected. The kidneys are tasked with filtering the blood and thus will encounter lots of glucose. The kidneys play a crucial role in regulating blood pressure, so damage to the kidneys over time can lead to increased blood pressure. I'm sure there are other widespread issues as well that contribute to this"
] |
[
"Eating less sugar does not really cause low blood sugar, at least in the way you're probably thinking about it. The body has an extremely sensitive and complicated way of maintaining adequate blood sugar and will make it if necessary from carbohydrates, proteins, and fats elsewhere in the body, mostly in the liver. So taking in less sugar in a 24 hour period will not cause your blood sugar to be significantly lower the next day and therefore acute changes in sugar intake will not cause acute changes in blood sugar or blood pressure by any direct mechanism that I can think of (dangerously low blood sugar can cause low blood pressure because the rest of the body basically shuts down, not because of the sugar itself).",
"Not eating at all will not affect your blood sugar significantly until these stores run out in days to weeks. Truly low blood sugar causes rapid deterioration in mental status and can lead to seizure, coma, and death quickly. The most common cause of truly low blood sugar is excess insulin, not starvation/sugar sparing. For an interesting story demonstrating how dangerous this is, read about ",
"Sunny von Bülow",
".",
"What you're reading about is probably related to the long-term effects of having HIGH blood sugar, i.e. diabetes. Diabetes causes damage to the walls of blood vessels and the kidneys, which play a major role in blood pressure regulation. In a basic sense, when the blood vessels in the kidney are damaged, there is less blood flow felt by the kidney, so it tries to fix it by raising the blood pressure. Controlling high blood sugar can slow this vascular damage and lower blood pressure."
] |
[
"Sperm... Apart from being male or female, does each sperm carry a unique genetic makeup or would I be this good looking whichever sperm got there first?"
] |
[
false
] | null |
[
"A normal male human has 23 pairs of chromosomes. Each sperm will get one of the two chromosomes from each pair. Which means there are 2",
" different combinations (2",
" = 8,388,608), barring genetic defect and potential mutations."
] |
[
"Each sperm is different. They carry some general basic stuff. For example let's say you are heterozygous for widows peak. It is possible that one sperm has the dominant while the other the recessive allele. There's more to the mechanics of variation in sperm production, I don't remember it all too well from last semester. "
] |
[
"Recombination/crossing over during meiosis would most likely produce this variation. It wouldn't be very fun if all sperm cells were the same."
] |
[
"Would the geographic center of a tectonic plate be the least earthquake-prone spot on that plate?"
] |
[
false
] |
Or is it more the makeup of the underlying rock that makes an area less likely to experience quakes, regardless of how close it is to a fault line? Or perhaps a combination of both?
|
[
"Not necessarily. To understand why, we need to think a bit more about how plate tectonics works. The idealized view of a tectonic plate is a portion of lithosphere that is internally rigid and non-deforming that moves coherently with all of the consequences of its motion (i.e. deformation, earthquakes, etc) occurring along its edges, i.e. at the boundaries between plates. However, it's important to realize that the interior of plates are under stress, indeed their ability to be under stress and remain rigid and thus transmit stress is key to the way plate tectonics work as the forces driving plate motion occur primarily along the edges of the plate. If the plate was not rigid enough to transmit the stress being applied to the edge of the plate, the plate would not move. Think about the difference between pulling on an edge of a block of wood vs (trying to) pull on the edge of a dollop of yogurt.",
"With that in mind, for an idealized plate there would never be any deformation or earthquakes (which in the simplest sense is the reflection of the applied stress and resultant accumulated strain overcoming the internal strength of a material, specifically overcoming the frictional strength of a planar discontinuity, i.e. a fault, in that material) anywhere but directly along the plate boundary. However, real plates are not ideal, primarily because they are not homogeneous. The important heterogeneity in this case is not necessarily different rock type as you hypothesized, but rather the presence of old faults, which represent planes of weakness within the interior of plates. If the transmitted stresses are oriented correctly with respect to the orientation of these preexisting faults, then eventually enough strain may accumulate across that fault to cause an earthquake, i.e. ",
"an intraplate earthquake",
". The location of these faults will depend on the geologic history of the plate, not expressly the position within the plate, so if there was a preexisting set of faults in the exact geographic center of a plate, then this area would be more likely to have intraplate earthquakes than other places without preexisting faults. A classic example of an intraplate earthquake is the ",
"New Madrid",
" seismic zone which generated a sequence of large (~M7.0-7.5) earthquakes in the early 1800. This seismic zone is related to the presence of a very old set of faults that were part of a continental rift zone that originally formed ~750 million years ago."
] |
[
"The response above is only a partial answer. The likelihood of an earthquake to occur is not only controlled by the presence of faults and the stress state, but also by the strain rate, i.e. by the rate at which the plate is being deformed. We know from earthquakes that are induced by oil and gas operations that the plate interior of the North American plate is very close to earthquake failure, and that faults do exist to cause earthquakes. The difference to plate boundaries is the low strain rate. If the strain rate is high,as in California, faults get reloaded after an earthquake more rapidly, say every 100 to 1000 years, whereas faults in plate interiors may only get reloaded every 100,000 years or so. Thus, locations away from active plate boundaries have a lower earthquake risk."
] |
[
"Good point, strain rate does play an important role. Though it's worth pointing out that in some places it's been argued that intraplate seismic zones have comparable strain rates to plate boundaries (albeit still on the low end), e.g. ",
"this paper",
". Similarly, going off just estimation of hazards, these types of regions have similar seismic hazard even though they are in the interior of plates, e.g. ",
"the New Madrid seismic zone has similar hazard as areas directly along the San Andreas",
". Such intraplate seismic zones are generally still a bit of mystery, but popular ideas often focus on some property (besides just the presence of preexisitng faults) that causes their strength to be reduced, e.g. ",
"elevated temperatures",
", which allow for the higher strain rates."
] |
[
"AskScience Panel of Scientists"
] |
[
false
] |
Calling all scientists! Please make a top-level comment on this thread to join our panel of scientists. The panel is an informal group of Redditors who are professional scientists or amateurs/enthousiasts with at least a graduate-level familiarity with the field of their choice. The purpose of the panel is to add a certain degree of reliability to AskScience answers. Anybody can answer any question, of course, but if a particular answer is posted by a member of the panel, we hope it'll be regarded as more reliable or trustworthy than the average post by an arbitrary redditor. You obviously still need to consider that answer here is so check sources and apply critical thinking as per usual. You may want to join the panel if you: You're still reading? Excellent! Here's what you do: We're not going to do background checks - we're just asking for Reddit's best behavior here. The information you provide will be used to compile a list of our panel members and what subject areas they'll be "responsible" for. The reason I'm asking for top-level comments is that I'll get a little orange envelope from each of you, which will help me keep track of the whole thing. Here's a good chance to discover people that share your interests! And if you're interested in something, you probably have questions about it, so you can get started with that in . isn't just for lay people with a passing interest to ask questions they can find answers to in Wikipedia - it's also a hub for discussing open questions in science. I'm expecting panel members and the community as a whole to discuss difficult topics amongst themselves in a way that makes sense to , as well as performing the general tasks of informing the masses, promoting public understanding of scientific topics, and raising awareness of misinformation. As long as it !!! EDIT: Thanks to ytknows for our fancy panelist badges! :D
|
[
"I bet this is giving the Grammar Nazis fits right now."
] |
[
"Position: Research scientist (postdoc)",
"General field: Astronomy",
"Specific field: Extragalactic astrophysics, observational cosmology",
"Research interests: Galaxy evolution over cosmic time, star formation in the distant ('high-redshift') Universe, the connection between gas behaviour and star formation rate."
] |
[
"PostDoc Experimental Particle Physics. Currently on ATLAS , did PhD on IceCube."
] |
[
"Why do we get a feeling in our gut/chest when experiencing very strong emotions?"
] |
[
false
] |
For instance, when experiencing embarrassment, nerves... Love. Is this just an accident, a biproduct of our physiology; or is there an evolutionary reason for it?
|
[
"The gut has more nerve endings than the brain, and a much higher concentration of neurotransmitters which help to regulate gut function. A flood of neurotransmitters such as serotonin and norepinephrine, caused by strong emotions and resulting in a temporary increase in gut neuronal activity, is likely the cause of these sensations."
] |
[
"I study a region of the brain called the insular cortex for a living. It is intimately involved in both the perception of bodily states and emotional awareness. The predominant theory among my colleagues is that the two are linked.",
"The first real question is, \"what are emotions, and why did they evolve?\" This is an impossible question to answer definitively, but it is still worth theorizing about. Emotions are generally tied to events which positively and negatively reinforce concurrent behavior. Love and attachment mediate evolutionarily useful bonding behavior, disgust tells us what to avoid (potentially for health reasons), happiness tells us when we are sated, etc. All of these emotions are reflections of our motivational state.",
"If emotions are to be motivational, it makes sense that they would be tied to a system that already deals with motivation, e.g. the system that monitors the physical state of the body. If you require nutrients, the body already has a system to make you feel hunger as a physical sensation in your gut, rather than as an abstract notion in your mind. In fact, it's hard to imagine emotion ",
" acting in this way, because it is very likely evolutionarily \"older\" than abstract thought. It is my professional opinion that emotions evoke/are reflections of physiological sensations so that they can more readily motivate action than they would were they ineffectual in bringing about arousal/satiation."
] |
[
"Maybe ",
"this",
" thread and ",
"this",
" thread on ",
"/r/askscience",
" can answer some of your questions"
] |
[
"Why can't a charged object be approximated by a point charge at the object's \"center of charge\"?"
] |
[
false
] |
When we were learning about gravity in Physics, we learned that an object can be treated as if all of its mass is concentrated at its center of mass. Since gravity and electromagnetism are both inverse square laws, why can't we treat charge this way as well?
|
[
"A spherically symmetric charge distribution ",
" be approximated in this way, as long as the observation point is outside the object."
] |
[
"A spherically symmetric charge distribution has exactly the same electric field as a point charge. ",
"For a non-spherically symmetric distribution, you can still approximate the field by a point charge. For any charge distribution with a net charge, Q/(k r",
" ) is the leading term in the multipole expansion."
] |
[
"If it’s spherically symmetric, it’s still the same.",
"If not, you can expand in multipoles. At short distances, higher multipoles will become significant, and the approximation will break down."
] |
[
"What is the highest grade a wheeled vehicle could climb theoretically?"
] |
[
false
] |
Scenario: vehicle on Earth, no artificial down force
|
[
"If you have enough centripetal acceleration, you can drive through a loop-de-loop, or (usually diagonally) ",
"around a near 90-degree slope",
". ",
"If you're moving very slowly, then your options are going to be a little more limited."
] |
[
"Theoretically, anything up to but not including 90 degrees (perpendicular to the ground) is possible, with unbelievably sticky tires and an almost impossibly low center of gravity.",
"In reality, above about 30 degrees of incline, gravity starts to make things a bit difficult."
] |
[
"As long as the vertical sum of the normal force vector and the friction force vector exceeds the force of gravity, it will climb.",
"The vertical friction is directly related to the normal force, and the normal force is just the force of gravity times the cosine of the angle of the slope.",
"Theoretically, as long as the cosine of the angle isn't zero, it is possible. That means anything up until exactly 90 deg. At 90 deg the normal and friction forces are zero.",
"Of course the center of gravity would have to be low enough to prevent itself from falling backwards, but that doesn't change the answer."
] |
[
"What is \"Metallic\" taste?"
] |
[
false
] | null |
[
"When you touch iron or copper (and to a lesser extent zinc and some other metals) and then smell or taste metal on your hands, you're sensing a chemical called ",
"1-octen-3-one",
".",
"The role of 1-octen-3-one in the taste of metal was only determined recently (2006). Full paper:",
"http://onlinelibrary.wiley.com/doi/10.1002/anie.200602100/full",
"This chemical is formed by \"skin lipid peroxide reduction and decomposition by low valence metal ions\". So you're not tasting metal but a chemical formed from human skin oils/sweat in the presence of metal. It's theorised that this smell is related to our ability to smell blood which forms the same chemical in contact with skin.",
"However...",
"Tasting metal is a common symptom which may be caused by colds, dental problems, nutrient deficiencies, problems with medication or a large range of conditions that cause distortions in your sense of taste:",
"http://en.wikipedia.org/wiki/Dysgeusia"
] |
[
"Neither – the taste they have in common is not metal or blood but another chemical made from body oils/sweat in the presence of metal or blood."
] |
[
"It's theorised that this smell is related to our ability to smell blood which forms the same chemical in contact with skin.",
"So blood doesn't taste metallic, but metal tastes like blood?"
] |
[
"How do E&M instruments which require extreme precision account for the Earth's magnetic field?"
] |
[
false
] |
From what I know, Earth's natural magnetic field is constantly changing, although the changes are extremely small. (Except for when it "flips".) So how does an instrument account for this? You can't just "zero it out" like you can with a mass scale, because it might change afterwards, right?
|
[
"You can't just \"zero it out\" like you can with a mass scale, because it might change afterwards, right?",
"Earth's magnetic field (1) is weak enough and (2) changes slowly enough that it can effectively be \"zeroed out\" for many experiments. In order for Earth's magnetic field to be problematic your experiment would need to be sensitive to fields in the ~0.05 mT range (Earth's typical magnetic field strength) with fluctuations many orders of magnitude smaller than this, would need to last over a very long period of time on the order of decades to see such fluctuations, and would need to be difficult to recalibrate the sensors. I can't think of any such experiments off the top of my head -- did you have something more specific in mind?"
] |
[
"This is actually an issue for people developing very sensitive magnetometers. I believe there's a group where I work actually dealing with nT field measurements. They need to use mu-metal chambers and specific materials inside the chamber so as not to produce unwanted fields."
] |
[
"While you can't 'zero it out' at the sensor unit, you can subtract noise of any kind from a data set if you have some way of measuring JUST the noise (i.e. 'everything that isn't the thing you want to measure').",
"Shield one sensor against the thing you want to measure, and compare the reading from that against the sensor that CAN detect the thing you want to measure."
] |
[
"How do you weight things in zero g?"
] |
[
false
] |
Lets say two hundred years from now you make a quick trip to "Geostationary Quality Foods" for the roast you're making for the holiday seasons up in your spankin new space station mansion and you buy some turkey breast by the pound. How on Earth (well, actually "how in space" I guess) are they supposed to weight it to charge you?
|
[
"Put it at the end of a spring balance of known length and swing that turkey... For a certain given spin rate (angular velocity) you will read a force that is proportional to the mass. Yay centripetal acceleration."
] |
[
"Well... implementation details :-P",
"You can always fix instruments to minimize disturbance. You can constrain the string to one axis using a cylindrical of some sort around it. You can tie your turkey to a rigid spring whose vibrational axis has be confined to a single axis by a smooth sheath. You could use the vibrational period of a long rigid bar.... stuff like that. In general, the such devices called an inertial balance.",
"Here's a NASA guide to help teachers introduce the concept to an introductory science class. ",
"http://www.nasa.gov/pdf/315957main_Microgravity_Inertial_Balance.pdf",
"You can also go the other way and take a reference mass with you (instead of a reference beam/spring/whatever) and then measure other masses gravitationally using a torsion balance. It still blows my mind that that device not only worked, but it worked accurately enough in the shed of some 16th century Englishman to actually derive the gravitational constant (and hence measuring the mass of the earth...).",
"http://en.wikipedia.org/wiki/Cavendish_experiment"
] |
[
"Remember 'weight' is just a measure of the force produced by a mass being accelerated by gravity. So you are really just looking for the mass of the object.",
"Mass equals force divided by acceleration. So basically they could add a force to the turkey and see how much it accelerates? You could still tell how massive an object would be by moving it around in your hands and feeling how easy it was to accelerated it back and forth. "
] |
[
"Is it possible to cancel out AC current the same way sound gets cancelled with an inverse wave?"
] |
[
false
] |
I was wondering since both AC and sound are waves. I know that the way sound cancelling headphones work is by simply playing an inverse wave of the sound it is trying to cancel. This way the two waves cancel each other out, and silence is formed. Are we able to do something similar with ac current where we would match the frequency to "cancel" any current?
|
[
"/r/AskScience",
" frowns upon short answers but yes, yes you can. AC signals have a phase that varies in time and space and to a good approximation can superimpose and constructively or destructively interfere with other AC signals. In fact in most power system the base AC signal is a superposition of three sinusoidal AC signals all offset in phase by 120 degrees from one another. This is what is called \"three-phase power\" which you can read about here:",
"https://en.wikipedia.org/wiki/Three-phase_electric_power"
] |
[
"In fact in most power system the base AC signal is a superposition of three sinusoidal AC signals all offset in phase by 120 degrees from one another.",
"No it's not, the three phases are sent on different wires.",
"Three sinusoids, offset in 120 degree increments, would completely cancel if combined via superposition."
] |
[
"Well, each sine wave starts on a separate wire, but they all cancel out on the shared neutral, so there's minimal load over that line assuming a balanced load; otherwise you'd need a need a neutral line 3x the capacity of each hot line."
] |
[
"How do we know the mass of quarks when it is impossible to separate them from each other and not knowing the binding energy?"
] |
[
false
] | null |
[
"The particle data group has a section on ",
"quark masses",
". This is a notorious problem, both conceptually and experimentally.",
"Defining and evaluating quark masses is most challenging for light quarks. The basic idea is to find ways to relate observed hadron masses, and the differences and ratios thereof, using theoretical tools such as chiral perturbation theory, lattice calculations, or sum rules. Look at formulas (71.10) in the link above for instance. The current best estimates are given by the two references below",
"Up and down quark masses and corrections to Dashen's theorem from lattice QCD and quenched QED",
"Up, down, strange and charm quark masses with Nf = 2+1+1 twisted mass lattice QCD",
"People work hard to separate the binding energy.",
"I should add that ",
" is really a poor use of the term, since it is usually defined as the potential energy of individual components after being separated. Since quarks are confined, the concept of binding energy is ill defined here."
] |
[
"We can picture a proton as 3 valence quarks (up, up, and down) switching their respective colors by exchanging gluons between one another. These gluons can in turn themselves split into quark-antiquark pairs, and can even radiate gluons. The process repeats, and the extents of this process depends on the scale of the observation. ",
"So we have the notion of valence quarks, as defining the quantum numbers of the hadron they constitute, as well as additional sea partons generated by the interaction, and the extent of the sea partons depends on \"how close\" we look. If we attempted to make a classical analogy, the \"potential energy\" would be contained in the \"sea\" which would represent the interaction field between the valence quarks. In this case, the valence quarks retain their \"true\" or \"current\" masses of a few MeV, and most of the hadron mass is contained in the sea or \"potential\" or \"binding\" energy.",
"Another idea is that of \"constituent quark\". Usually when people talk about \"constituent quarks\" they are not thinking in terms of \"current\" or \"true\" quarks. People who talk about \"constituent quarks\" would refer to the previous quarks as \"naked quarks\". The view of constituent quark models is to insist that the baryon is really made up of exactly three quarks, and that the sea \"dresses\" those quarks. The constituent quark mass is about a third the mass of the baryon, as they have acquired a \"cloud of virtual particles\" around them.",
"Those are basically the two views which are common on how to think about the hadron masses. People have strong opinions on which is better. "
] |
[
"For heavy quarks (charm, bottom) the hadron mass is dominated by the heavy quark so it is relatively easy.",
"The top quark decays before it hadronizes, here we can actually measure its mass directly.",
"See the other comment for the light quarks."
] |
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