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[
"Would impacting Mars with its smaller satellite, Deimos, cause a substantial change to Mars's atmosphere?"
] |
[
false
] |
With all the subsurface ice being discovered on Mars recently, it seems a large influx of energy could be used to vaporize it and start a green house effect. Has impacting Mars with asteroids been evaluated as a possible tera forming strategy?
|
[
"I think there are probably larger problems with terraforming Mars than introducing a lot of water vapour into the atmosphere by de-orbiting Deimos.",
"The lack of a magnetosphere is one which can't really be overcome and would seriously hinder any sort of Earthlike-ecosystem that hadn't been radiation hardened.",
"In terms of creating an atmosphere (regardless of trying to get an ecosystem started), it's not enough to generate an atmosphere - you need to retain it!",
"I would also expect that in an impact of that magnitude, Mars may also lose quite a lot of material into space due to it's relatively low gravitational pull - which is one of the reasons for it's thin atmosphere, it has a hard time clinging onto it's atmosphere, especially without a magnetosphere to ward off the worst of the solar wind.",
"Also, as gases warm up, their molecules move faster and can more easily escape into space. By warming Mars' atmosphere, you would ",
" the rate of atmosphere loss!",
"But that's by the by, because smashing Deimos into the planet may well vaporise much of the ice, but it would also throw a lot of dust, rock and other planetary material up into the atmosphere which would cause global ",
" - the opposite of what you're trying to achieve!",
"So in brief. If you don't ruin the planet entirely, you're going to plunge it into a deep winter. Once the rock and dust falls out the atmosphere it may start to warm up, and in doing so, increase the rate of atmospheric loss until it reaches an equilibrium point... which is where it is right now."
] |
[
"The lack of a magnetosphere is one which can't really be overcome and would seriously hinder any sort of Earthlike-ecosystem that hadn't been radiation hardened.",
"The magnetosphere plays a minor role in protecting the ground on Earth from space radiation. It does have a longer-term role where it prevents atmospheric erosion by the solar wind, but we're talking hundreds of millions of years until significant effects can manifest.",
"The bulk of the radiation is filtered by the atmosphere itself and the harder forms of UV are blocked by the ozone layer."
] |
[
"Deorbiting Deimos would probably work by removing about 40% of its orbital velocity, which is 1.3km/s. Given it's mass of about 1.4762*10",
" kg then deorbiting it would take about ",
"95gigatons of TNT equivalent",
" of energy or about 950 ",
"Tsar Bomba",
" bombs at maximum yield (100 megatons each).",
"Maybe a cheaper option would be to crash it into Phobos and have the debris rain down on Mars."
] |
[
"How does hearing work in animals with good hearing?"
] |
[
false
] |
I don't think being able to see well can really be a hindrance, and a super sensitive nose probably isn't a big deal either, but what about hearing? If an animal can hear really far/low volumes, does that mean everything at "normal" volume is deafening? Or is it not as simple as a simple multiplier being cranked up?
|
[
"Neuroscientist here! First, about vision and olfaction (smell): Highly acute senses can be more burdensome than you might think. ",
"Take vision, for instance: having good vision is actually kind of expensive, because of the brainpower required. Your brain consumes a lot of energy (about 25% of your resting metabolic rate is due to your brain), and a decent chunk of your brain (basically the entire occipital lobe) is dedicated to processing visual inputs. Turning the output of your photoreceptors into something you can \"see\" is actually not easy. Take the example of the famed mantis shrimp.. it has many more types of photoreceptor than we do, but in practice it's actually WORSE at telling colors apart than humans, because it lacks the neural circuitry to process that information into a usable form.",
"Likewise, a more complex olfactory bulb (the chunk of brain tissue that sits above your nasal passages and initially processes smells) has a cost too. Your olfactory system has only a few hundred unique receptors, but can recognize millions of smells by the specific ",
" of olfactory receptors they activate. That takes additional processing power too. ",
"As for hearing: ",
"In terms of sensitivity to very quiet sounds, one thing that animals with this kind of sensitivity tend to have is big ears for sensitive, directional hearing. A bigger ear can concentrate more sound onto the eardrum, and also improve directional hearing, which is really important for being able to hear faint sounds in an environment that isn't perfectly quiet. If your hearing were totally non-directional, it would be really hard to tell sounds apart. This is actually a problem that it ISN'T possible to solve just by having more neurons for processing, although that helps."
] |
[
"Well, part of the answer is that they can turn their head away from the source of the noise (since their hearing is often highly directional). But there are also mechanisms for damping loud sounds while maintaining sensitivity to quiet ones.",
"One such mechanism is the ",
"acoustic reflex",
", which involves tiny muscles in your inner ear tightening to dampen movement of the middle ear bones when you hear a loud sound. ",
"Another mechanism for controlling loudness has to do with",
"outer hair cells",
" in the cochlea. Inner hair cells are what actually turns vibrations into electrical signals (and vibrations that are too strong can break these hair cells, leading to hearing loss), but outer hair cells actually act as selective amplifiers that amplify quiet sounds, which helps detect quieter sounds without making stronger sounds too strong. ",
"So, animals do tend to have ways of partially blocking out too-loud sounds, although there is certainly an upper limit on how much can be blocked out."
] |
[
"Very insightful thank you. I'm still wondering however, if they hear everything maddeningly loud all the time, or they can somehow tune out noises they don't want to hear."
] |
[
"What is the most widely accepted theory in the scientific community as to how life started on earth?"
] |
[
false
] | null |
[
"I think you need to clarify, do you mean single celled life, anaerobic, sea life, mammals or some stage in between?",
"I assume you are talking about the transition from chemical to protein through abiogenesis? If so, wikipedia has a good article discussing current popular theory:",
"https://secure.wikimedia.org/wikipedia/en/wiki/Abiogenesis"
] |
[
"Tricky proposition there....",
"At what point during abiogenesis did it stop being chemistry and start being biology? Was it a hard line or a big grey area? I would argue the latter. All biology is subject to evolution, no physics is subject to evolution, but chemistry? It's in the middle. ",
"Take those hypothetical micelles in the primordial soup. They start off as a film of some kind that wraps back around itself to seal off an inside an outside; a ball. Some factor of that film allows certain things to pass to the inside where they can react and form more of the film-stuff. This increases the rate at which the film builds and the ball grows. As it grows, it becomes more likely that the ball will break, forming two new balls. Now because the inside volume has decreased more than the perimeter, it becomes easier to absorb more precursors and therefore grow faster. So it splits again. Something changes the chemistry slightly for one set of these balls, and that species will grow faster or slower than the rest.",
"EDIT: I'm a biochemist, but that last bit there is 100% conjecture and hypothesis. Widely accepted conjecture, but still conjecture AFAIK."
] |
[
"The most widely accepted hypothesis (it's too much to call it a theory, perhaps) is that life began in a soup of complex molecules as RNA strands. It's possible for RNA bases to form naturally under the right conditions, so it's conceivable that a short RNA polymer could also form, such a thing would tend to facilitate copies of itself being made (as well as the mirror image base-pairing wise). Eventually mutations that lengthen and change the base pairs of strands would lead to various chemical properties beneficial to reproduction (notably the catalysis of the formation of RNA bases) and from there it would evolve to fully cellular life one step at a time."
] |
[
"Would an octopus, or any other sea creature with tentacles, have a dominant tentacle?"
] |
[
false
] | null |
[
"It seems they actually do: ",
"http://www.3sat.de/page/?source=/nano/natwiss/145556/index.html",
" (sorry. it's german but here is the google tanslated version: ",
"http://translate.googleusercontent.com/translate_c?hl=de&rurl=translate.google.de&sl=de&tl=en&twu=1&u=http://www.3sat.de/page/%3Fsource%3D/nano/natwiss/145556/index.html&usg=ALkJrhhy9yNBqNunkIcbQzJPckLN9GFx5w",
")"
] |
[
"I do not know about octopuses but starfish lead with a 'dominant' arm, but dominance can change throughout the day. Dominance is decided by which arm receives the strongest positive stimulus (e.g. food particles). For some species, dominance seems more fixed and rarely changes.",
"A little bit about starfish:",
"http://accessscience.com/content/Asteroidea/056600",
"http://www.jstor.org/pss/4532796"
] |
[
"Google says \"probably\", here's an NPR link: ",
"http://www.npr.org/templates/story/story.php?storyId=92398531"
] |
[
"Why does protein from crustaceans look so different than land meat?"
] |
[
false
] | null |
[
"A muscle is not made of 'a protein'. Proteins are molecules after all, and even big molecules are VERY small.",
"Muscle tissue, like any other tissue, is made of cells and extracellular matrix. How it feels and/or tastes is dependent on a huge number of factors. There will be some chemical differences, but for the most part, the building blocks are the same but just arranged differently. Just like a rhino's horn and a duck's feathers are both mostly composed of keratin."
] |
[
"All muscles are made of some combination of the proteins actin and myosin. Invertebrate and vertebrate muscles have different structures than each other so will have different qualities, including appearance. Other differences between animals such as blood type will also impact what muscles look like. But even land meat can look significantly different from each other. Beef and chicken do not look much the same after all."
] |
[
"How can the same protein look white amd mushy vs red and tough?"
] |
[
"Does temperature affect the half life of an isotope and the amount of radiation it releases?"
] |
[
false
] |
Since colder atoms vibrate more slowly, would this change the amount of radiation it releases?
|
[
"Check this out:",
"\n",
"http://www.whoi.edu/cms/files/1972AnRevNucSci22p165_68424.pdf",
"\nThis Annual Review of Nuclear Science published a paper on a large summary of effects of altering nuclear decay rates. The top of page 193 would be most relevant for your question: ",
"Except in the vicinity of phase transitions, such as have just been discussed, the effects of temperature changes on capture and conversion rates should be of modest size, and may be characterized in much the same way as temperature dependent Mossbauer isomer shifts (168, 227). The volume effect, due to thermal expansion, will be similar to that found in pressure studies. There may be specific\neffects of changing rms vibrational amplitude, from squeezing of wavefunctions and, in polar environments, from high-frequency electric fields. The purely kinematic effect of second-order Doppler shift (232, 233) will play a much smaller role here than for the isomer shift.",
"\nByers & Stump (149) have compared the 99mTc decay rate at room temperature with that for \"normal\" Tc metal at 4.2°K, and found an effect of about one part in 10",
" , with the decay faster at the low temperature. ",
"So to summarize that quick example, Technetium decays 1.0001x its room temperature rate at near absolute zero."
] |
[
"You vastly misinterpreted that last sentence. one part in 10",
" means an increase of 1.0001 times more. ",
" 10000"
] |
[
"Ahah, thought that seemed odd; was in a bit of a rush. Edited, thanks!"
] |
[
"If a guy with 20/20 vision wears another guy's glasses, does he see what the other guy sees without glasses?"
] |
[
false
] | null |
[
"No, he doesn't. Let me explain how, I'll try to keep it simple but ask away if I don't explain something satisfyingly.",
"There are 2 major types of refractory anomaly called myopia and hyperopia (not counting other stuff like presbyopia and astigmatism for simplicity sake). These 2 are generally caused by a mismatch between the strength of refraction happening in the front of the eye and the size of the field of projected light in the back of the eye. In more simple terms, it's caused by variations in the length of the eye bulb so that the light arriving on the retina (the portion of your eye with the light receptors) is too \"scattered\" and has a bad resolution. Myopia is the inability to properly focus on objects far away from your eye, the eye bulb is usually too long and the plane of \"sharp projection\", the focal point, lies in front of the retina. Hyperopia is the inability to properly focus on objects too near to your eye, the eys bulb is usually too short and the focal point lies behind the retina. ",
"See this diagram for reference",
".",
"Soooo how does this relate to your question? Depending on what type of refractory anomaly you have, we use different types of lenses to correct these. We want to shift the focal point onto the retina so that your visual acuity is increased, and we accomplish that by manipulating the refraction in the eye. For myopia, we want to push forth the focal point, so overall we want less refraction - thus, we use ",
" (or biconcave lenses) for our glasses. For hyperopia, we need to increase the overall refraction, so we use ",
" (or biconvex lenses).",
"So imagine our glass wearer has myopia - without glasses, he only sees objects in front of him clearly, but distant objects are not sharp. The lenses in the glasses are scattering lenses so that the focal point in the glass guy's eyes shifts from inside the eye bulb to the back of the eye bulb, the retina. Give these glasses to a 20/20 person. Because the glasses are scattering, what happens that the focal point now shifts from the retina of the eye to ",
", because the refracted light is now not collected enough. This person doesn't see like glass guy without glasses, but exactly the opposite: he is now far sighted and can't focus on close objects, but only far away objects, so we have induced hyperopia in him. The exact inverse happens if glass guy's glasses had collecting lenses for hyperopia.",
"TL;DR If glass guy is near sighted 20/20 guy becomes far sighted and vice versa"
] |
[
"Thanks a lot for this explanation!"
] |
[
"So does this mean you can see what the other guy sees by turning the glasses backwards and looking through them?"
] |
[
"If the asteroid (2005 YU55) that just missed Earth scored a direct hit instead, what type of damages are we talking about?"
] |
[
false
] |
Would it be an extinction event for human beings? Winter for the next 100 years?
|
[
"Impact Calculator - Welp, there goes my workday."
] |
[
"Impact Calculator - Welp, there goes my workday."
] |
[
"On the debris of the Earth is an engraving of screaming humans encrusted with diamonds. It is of highest quality. "
] |
[
"If carbon dioxide is only 0.0391 percent of the atmosphere, how does it have such a big impact on climate change?"
] |
[
false
] |
Hi everyone, I have a teacher who believes that humans are not to blame for climate change and that climate change is not a real thing due to the fact that carbon dioxide only makes up a very small part of the atmosphere. I have tried to research this, but found conflicting results. Can you please help me to find an answer?
|
[
"People often mistakenly conflate abundance with importance (not just with climate science, but with a lot of things). Consider this: iron makes up only about 0.006% of the mass of an average human. Yet, it is completely essential for us to live (without it the hemoglobin in our red blood cells can't transport oxygen). So any argument that something is unimportant simply because it's not abundant is not valid. "
] |
[
"Your very absolute statement that ",
" argument based on lack of abundance implying lack of importance falls flat if I can provide an example where it isn't true: one cyanide molecule won't kill you so abundance does matter in ",
" systems.",
"You're misreading my argument. I said ",
". The argument: X is unimportant because it is rare, by itself, is never a good argument. To use your example, we have a pretty good knowledge of how different doses affect people, this is ",
" evidence that tells how how important, exactly the amount of cyanide ingested by someone is to their survival. That being said, the mass of cyanide required to kill someone is a negligable fraction of their body mass, so it would be ridiculous for a coroner to say, \"the cyanide in this person is well under a percent of their body mass, so it can't be what killed them\". ",
"I'm not saying abundance ",
" matters. I'm saying using abundance of something ",
" to discount its importance is a bad argument. My example of iron illustrates this perfectly. It's because of its specialized role that its importance to life has nothing to do with its relative abundance in the body compared to other elements. Similarly, it is the specific properties of carbon dioxide that make it a potent greenhouse gas, even at a low fraction of the total gas in the atmosphere. "
] |
[
"It's true that CO2 is a \"trace\" gas in the atmosphere. Ask your teacher if they'd be willing to drink water with a \"trace\" amount of arsenic. Then ask if they'd be willing to drink water with ",
" the \"trace\" amount of arsenic...It's still a trace amount, but can have significantly destructive effects. CO2 in the atmosphere is no different.",
"Morever, CO2 isn't the only gas that contributes to climate change (specifically global warming). Sulfur hexafluoride (SF6), for instance, has nearly 24,000x the impact on global warming than CO2, and SF6 is used as an insulating gas in high voltage networks...all over the world.",
"Methane contributes to about 25% of our global warming impact, primarily from the burning of natural gas. These all add up, and given that we're the ones using technologies that directly emit these molecules into the atmosphere, it's pretty difficult to lay the dicks at someone else's doorstep."
] |
[
"If you add more nitrogen to the air, but don't take any oxygen away so you just raise the pressure, does a candle burn the same or whorse?"
] |
[
false
] |
Basically nothing changes. Everything is the same. You don't take anything away. Just add nitrogen. How does it affect burning?
|
[
"It means you need a bit more energy to heat up air. It makes things burn a bit worse.",
"In the opposite direction: Fire burns a bit better if you remove all the nitrogen.",
"A pure oxygen atmosphere is only really dangerous if it's at atmospheric pressure or higher (see e.g. Apollo 1)."
] |
[
"The air is roughly 21% oxygen, 78% nitrogen and the rest is argon and other gases. ",
"If we simplify to say that the air is 20% oxygen at 1 atmosphere (atm) of pressure, we can say the oxygen has a partial pressure of 0.2 atm. (20% of 1 atm) ",
"If we were to add more nitrogen so that the pressure is now 2 atm, we would still have 0.2 atm of oxygen - the oxygen has the same partial pressure which means oxygen molecules will bump into our candle flame just as often as in normal air. ",
"Our candle will probably burn the same based off this alone. ",
"In reality, the extra nitrogen will be heated up as well and ‘steal’ some of the heat energy from the candle’s flame, so the flame will be a bit less ‘fiery’ and there will be a limit as to how much nitrogen you can pump in."
] |
[
"I remember this argument in undergrad - I can see where the the other posters are coming from from a theory perspective but on a practical basis they are incorrect - you alter the fuel-oxidant mix by adding nitrogen and this can suppress fire even without removing the oxygen. I know fire suppression on board a submarine works this way - things can reignite later but the nitrogen burst controls the fire long enough for the sub to surface and use more effective (but not life-supporting) means.",
"https://www.nist.gov/system/files/documents/el/fire_research/R0000296.pdf"
] |
[
"In vitamin supplements they often provide 100% of the RDA or more. Why do they only contain 2% of potassium?"
] |
[
false
] | null |
[
"Hi ASIMOVSAGAN thank you for submitting to ",
"/r/Askscience",
".",
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"Hi ASIMOVSAGAN thank you for submitting to ",
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".",
" Please add flair to your post. ",
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] |
[
"The Earth and Venus have an atmosphere. Our moon does not. Mars has a thin one, but Saturn's moon Titan has a thick one. How does Titan manage to hold onto a thicker atmosphere than Mars?"
] |
[
false
] |
It surely cannot be just gravity. How does Titan maintain its atmosphere where the moon and Mars cannot?
|
[
"What the other commenters say is not quite correct. Titan can hold its atmosphere because of its atmospheric composition and its low temperature. The magnetic field has only a small part in this. Basically what determines if an object can hold an atmosphere is if the components of an atmosphere can excell the escape velocity. Titan is very far away from the sun so the temperature in the atmosphere is rather low. The atmosphere also mostly consists of Nitrogen, which is comparatively heavy. Heavier atoms and molecules need more energy to reach the escape velocity. Colder temperatures mean lower thermal velocities. These two factors mean that Titan can hold a substantial atmosphere while the Moon and Mars cannot. They are both much closer to the sun and have much higher temperatures. Mars does not have a lot nitrogen in its atmosphere either. ",
"Unlike what the other commenters say, ",
"\nA quote from a recent ",
"research paper",
":",
"We find that the solar wind is not a strong driver for the rate of atmospheric ion escape.."
] |
[
"Being further out from the sun and protected by Saturn's magnetic field help curtail nonthermal escape, but probably the most important factor is that Titan is very cold. The reason low-gravity bodies tend to lose their atmospheres is due to Jean's escape: A given gas at a given temperature will have a random distribution of velocities for individual particles around a mean, and some small portion of the gas near the top of the atmosphere will, by chance, exceed escape velocity and be lost to space. The closer the average gas velocity is to escape velocity, the faster gas is lost. Both the moon and Titan have similar escape velocities, but because Titan is much colder the average gas velocity is much lower."
] |
[
"The moon is too light, too close to the sun, and without a magnetic, field any atmosphere it has is stripped off almost immediately.",
"It’s a similar situation with Mars, but being a bit farther out and having higher gravity, Mars can hold onto a bit more against the solar wind. Plus, it’s atmosphere is mainly carbon dioxide, which is heavy and harder for the solar wind to kick away.",
"Titan is a different story. The Saturn system orbits about 9 times farther from the sun than Earth, so solar wind isn’t much of an issue. Plus, Titan orbits mostly within the edge of Saturns Magnetic field, which induces a field in Titan and protects it from any lingering solar wind. Titan also orbits pretty far out, so theres not much gravitational disturbance from Saturn. All these factors combined means there’s nothing really trying to get rid of Titan’s atmosphere, and it likely hasn’t shrunk much since the Saturn system formed."
] |
[
"If a door has three hinges, are the forces on each hinge (top, middle, and bottom) identical?"
] |
[
false
] | null |
[
"Let me make a few assumptions about your question first: Let's say that the door is uniform in density/weight, is open, it is not moving or being touched, the hinges are all connected to the frame and door leveled and are not offset in distance from the frame or door more than their own thickness, and when you ask about the forces acting upon each hinge you are asking about the forces felt from the weight of the door in any direction. ",
"I'll address two scenarios, one where the hings are improbably exactly the same distance from each other on both the frame and the door and equidistant apart with the middle hinge at the door's center of gravity CG, and second a real world, more likely scenario with miniscule differences in distance and spacing on an average door. Tldr: the total force vector on each hinge would be different in both cases. ",
"Let's say that the hinges connected at the door and on the frame are exactly the same spacing, the true total force vector (so amplitude force and direction) would be different on each hinge because the center of gravity of the door (fairly centered, offset slightly towards the handle) is offset from the three hinges by different amounts. All three hinges would feel a downward pull, but the highest hinge is also experiencing an outward (from the wall) pull as the torque of the weight of the offset CG wants to rotate the door away from the hinges, the middle hinge pretty much a downward only pull as it is at the pivot point so to say if it was at the same height as the door's center of gravity. And the lowest hinge would experience an inward to the frame and downward force. Image there was only the top hinge, the door would want to swing inwards, on the plane of the door, to the wall towards that bottom hinge. If only the top two hinges were there the top would feel a stronger downward and outward force, the middle would feel a downward and inward force.",
"More than likely the door is not perfect. In this case all hinges again will feel different forces, but without measuring or observing them it is hard so say at which hinge the imperfection lies (say you can see a gap in the hinges themselves - this could tell you that hinge is not feeling any downward force from the weight on the door, and may only be feeling an inward or outward force from the door's CG offset as explained above). At the least 1 of the 3 hinges will feel the downward force of the door as one is all that's needed really to hold the door up (like only one nail will hold a board to the wall if nailed in). And at the least 2 of the 3 hinges should feel the pull and push of the door's CG offset. Likely all three hinges will feel a little bit of both forces and act similar to the perfect scenario above (so assume all three hinges touch between the door and frame's connection), with the highest hinge feeling a downward and outward force, lowest hinge a downward and inward, and the middle force a downward and either out/in/none directional force if it were higher/lower/or at the same height as the door's CG."
] |
[
"It is interesting to note that it is ",
" to ",
"not have the three hinges evenly spaced from the top and bottom",
", for mainly aesthetic reasons. It turns out that evenly-spaced hinges will look, from the usual eye-level perspective of somewhere between the middle and the top hinge, to be skewed towards the bottom, which is why many hinges are designed to be placed closer to the top."
] |
[
"In fact, one of the hinges is likely taking most of the weight. The two halves of each hinge are linked to the door and the door frame in a very stiff way. It would be enough to move the door side of a hinge a very small amount up or down to cancel the vertical load it supports, or, to the contrary, make it support all the load (by lifting the other two). Since the hinges are not positioned with such great precision, the latter is exactly what happens: the system is ",
"hyperstatic",
". That's for the vertical load. Since the door hangs by one side, there is also a bending load, which translates into equal and opposite side forces on the top and bottom hinges."
] |
[
"I am teaching about graphs - What are some of the most important graphs in scientific history?"
] |
[
false
] | null |
[
"The results from ",
"COBE",
" would be my pick. The data points matched the theorised curve pretty much exactly, showing that the Universe used to be very hot everywhere - a very strong argument for the Big Bang theory."
] |
[
"This would be my pick as well. ",
"Here's",
" NASA graph and explanation. The correspondence is so strong that it's impossible to tell the curves apart visually."
] |
[
"Thanks! That's awesome :) "
] |
[
"What would the most average person be like?"
] |
[
false
] |
[deleted]
|
[
"European coloration is quite rare on the global scale, so your average person would be:",
"*hermaphodite",
"*dark hair",
"*dark eyes",
"*mid-toned skin",
"*since average features are the most attractive, this person would be be quite popular! ",
"In computer face averaging tests, women with averaged faces have been shown to be considered more attractive"
] |
[
"This is not typicality, this is plurality. It's a shame NatGeo doesn't understand this distinction."
] |
[
"Is that like the difference between Mode and Mean? Yea, I was slightly disappointed with their findings too. I was hoping for a composite sketch every ethnicity in the world. "
] |
[
"Can you date the age of earth without the use of radioactive isotopes?"
] |
[
false
] |
This is in relation to Hubble's law, and if they were able to date the age of earth during the discovery of redshift. My professor stated how initial measurements of hubble's constant were proven faulty since the earth would be older than the universe. However, during Hubble's time radioactive dating wasn't used.
|
[
"Well there are several methods that were tried and were wrong, very wrong.\nYou can ",
"read about them here",
". It includes methods ranging from thermodynamic cooling to salinity of the ocean.",
"Edit: Salinity wasn't actually included in the article, but it was one of the faulty methods used. It just doesn't appear here."
] |
[
"I agree. the answer is basically, no. All other methods will just supply upper and lower bounds, and very poorly at that."
] |
[
"First, we can use the age of Sol as an upper bound for the age of the Earth. Sol has a certain chemical composition that is directly related to its age - as the sun burns, it turns hydrogen into heavier elements at a rate determined by how bright it is, and we can measure what elements are in the sun by the light it gives off.",
"For this you'd need to know how much helium there was before the first stars formed, which basically means you need to know details of the big bang theory, which wasn't an option at the time. The actual helium abundance is a lot higher than what stars can produce in 10 Gyr, so this is crucial. I doubt they knew that the sun was a star of the third generation, too.",
"PS: I don't think they knew the necessary nuclear physics to calculate the fusion rate either."
] |
[
"Does the universe have a charge?"
] |
[
false
] |
[deleted]
|
[
"Here is a ",
"previous discussion",
" on this subject. The general consensus is that the universe is charge-neutral."
] |
[
"Assuming our theories of baryogenesis are correct, all subatomic particles are formed by random quantum interactions that obey the laws of physics--the most relevant to this discussion being conservation of charge.",
"EDIT to clarify: if a charged particle pops into existence out of empty space, an oppositely-charged particle ",
" be made at the same moment. Anything else would violate an empirical law of physics."
] |
[
"I don't know if I should make this it's own post. But why is this and how did scientist come to find this out?"
] |
[
"Is my thinking on this thought experiment right? (dry ice in a balloon)"
] |
[
false
] |
If I put some dry ice in a balloon and put it on a balance what would you predict would happen to the reading on the balance as the dry ice sublimes and fills the balloon? Initially I would think that the balance reading would stay the same as the same amount of stuff is on the balance. But then think that the balance reading of 0 includes the air pressure on the balance . As the balloon expands it is displacing the air above the balance. Now CO2 is denser than air. So would the balance reading actually increase?
|
[
"Actually, it would decrease. The mass does not change, but the it will have bigger volume and the Archimedes' principle applies."
] |
[
"The balloon's weight would not change. The Archimedes force would increase (pulling the balloon up). Since the balloon is static, the reaction force would decrease slightly.",
"How precise is your scale? I estimate that the reading would drop by slightly more than 1 gram for every litre that the balloon's volume increases."
] |
[
"Never seen it sold in any petrol stations near where I live. Why would they sell dry ice?"
] |
[
"Why do soft drinks/ beer taste so much better ice cold?"
] |
[
false
] | null |
[
"For beer, its because the beer you are (probably) used to drinking, american lagers, taste bad. At cold temperatures, you get less flavor, more cold refreshment. As the temperature increases, you start to take more of the flavor of the beer, and in the case of your typical american lagers, are not good flavors. ",
"Good beers, on the other hand, you want to taste the flavors, and depending on the style, will be served between 40-60 degrees. ",
"Here's an excerpt from ",
"http://craftbeertemple.com/",
"Most beers have an ideal serving temperature. There’s a chart below outlining which styles are served at what temperature, but as a general rule the temperature at which to serve a beer is correlated to the strength of the beer. As beers go up in alcohol, they are generally drunk at a warmer temperature. This is because stronger beers often are sipped slowly, and enjoyed for their complexity of flavor and aroma while weaker beers are often consumed for refreshment. For no style is this more apparent than American macro lagers, which are generally drunk so cold that you can’t taste them. There’s a reason those big brewers want people to drink their beers at tongue-numbing temperatures. As they warm up, they don’t taste very good. ",
"EDIT: when I say \"American Lagers\", I'm only talking about coors, miller, bud, etc... Europe has some great beers, overall, we make the best beers here in the good ol U.S of A. "
] |
[
"That explains why the entire marketing of Coors Lite is based around it being cold. They have gone as far as temperature sensitive labels to let you know when it is cold enough to be able drink the stuff."
] |
[
"Part of the explanation is carbonation. Gases generally (including CO2) become less soluble in water at higher temperatures. Ice really does serve a purpose because it makes the carbonation stay in the drink the longer the temperature is near zero C."
] |
[
"Electrical Theory: What the hell are vars?"
] |
[
false
] |
Look, this is embarrassing. I am an actual power plant control room operator and feel like I'm pretty good at it. This is the white whale of my knowledge; wtf is a var and why do I need to push vars out? Or maybe the term is Power Factor? Or Imaginary vs Apparent vs Real Power? All these terms have been used to explain it to me, but I can't wrap my mind around it. The closest someone has gotten is that it's back pressure on the grid, but I don't understand the cause of it. Any help is greatly appreciated.
|
[
"var means volt ampere reactive, wich is the unit of imaginary power. Imaginary power is (to use the most easy formulation) all power that is only present to change electric and magnetic fields.",
"For example a pure capacitor always has a current proportional to the change of voltage (C",
"di/dt=v)",
"if you hook up an ideal inductor to a alternating source it will cause it to have pure imaginary power because all of it is used to change the magnetic field, if you have a resistance in between the power will be shared between real (ohmic) losses and imaginary (inductive) losses and those together are called Apparent. Capacitive and inductive losses can compensate each other (capacitors cause negative imaginary parts)",
"If you look a sine signal and try to plot the change rate for every point in time you'll end up with a sine that is shifted by 90 degree or pi/2 radians. sin(x) derived is sin(x+90°).",
"and now the cause: electric motors and transformers have large inductivities and therefore cause the current and voltage to get out of phase. There are large synchronous generators hooked to the grid without a turbine, to control the amount of phaseshift.",
"The topic is a little too large for a short anwer, if you really want to understand it you should grab a book about complex alternating current calculation."
] |
[
"The equation to describe the behavior of an inductor is V(t) = L dI(t)/dt, essentially Faraday's Law. ",
"Assuming I(t) takes an exponential form like ",
"/u/RobusEtCeleritas",
" , and inserting your assumption of I(t) into the differential eqn, you will find that V is out of phase from voltage by pi/2.",
"Since Power(t) = Real( I(t)*V(t) ), and if your phase difference between V and I is pi/2, P(t) averages to 0 over the whole wavelength. On the other hand, if phase diff is pi/2<φ<0, then you get a sum of real and reactive power. In the case of φ = 0, then all power is real and no reactance exists in the circuit. "
] |
[
"What I'm understanding best is your last statement and I think what trips me up the most. What the heck is causing the phase shift in regards to induction motors or transformers? People keep trying to explain that it has to do with a field collapsing, but what does that actually mean?"
] |
[
"Are rod cells also used in photopic vision?"
] |
[
false
] |
There is a plenty of sources that states that cones are used to see colors under well-lit conditions (photopic vision) and rods are used under low-light levels, because they're more sensitive (scotopic vision). However, I can't find anything, whether rods are also used in good light conditions. (I'm sorry for any mistakes. English is not my mother tounge.)
|
[
"The photopigments in the rods react faster than they can be recharged in bright light, meaning they get depleted. This is why after entering a dark area from a bright area, it can take up to half an hour for your night vision to kick in fully.",
"https://en.m.wikipedia.org/wiki/Rhodopsin",
"There are people with a congenital disorder that makes them lack all types of cones, and only have rods. They have very poor eyesight and need to wear very dark sunglasses to see anything at all in daylight conditions."
] |
[
"This is such interesting info, thank you!"
] |
[
"What is the name of that congenital disorder?"
] |
[
"Can cancer be \"Transplanted\"?"
] |
[
false
] |
I'm no doctor, but I know that cancer can't be transmitted through means like sneezing or exchange in body fluids like other diseases, but I always wondered what would happen if one could extract cancerous tissue from one person and then put in someone else's body. would the cancerous cells "infect" the other guy? what special conditions would there have to be if it is even possible?
|
[
"This is done experimentally in rodents as a model in research. It's super-effective.",
"In your scenario it wouldn't be as effective because of tissue mismatch, but it would still work in a lot of cases (if not most). Part of what makes cancer so cancer-y is that the tumor cells are assholes and don't listen when the immune system tells them they should FOAD",
" (which is how the immune system usually deals with grafts of foreign tissue). There would almost certainly be some kind of inflammatory response, and that would cause some problems.",
"But if you had cancer cells that are a good match for the target, or ones that are resistant to this kind of clearing, then yes, I'd say it's possible.",
" Fuck Off And Die"
] |
[
"In my research we inject A549-luc lung cancer cells into the vertebral bodies of rats in a single metastasis model. We have to do this in athymic rats, since rejection of the transplant does occur and causes ",
" immune response that usually causes the death of the animal. ",
"I can only speak about cancer transfection in rats. In humans I'm not sure about what sort of immune response would occur. "
] |
[
"What you describe is mediated through apoptotic pathways, which are usually broken in cancer tissue. IgG-assisted complement might kick in at some point, but that may or may not happen. The presence of tumor antigen may not be strong enough or \"found\" in the right ways."
] |
[
"To what extent is decrypting something an act of creation?"
] |
[
false
] |
[deleted]
|
[
"The act of decryption is not creation on the ground that only the original can possibly come out -- the same data that was encrypted, not changed in any way. So it's not creation, it is duplication, like a dry copy or a photograph.",
"No court that understands the issues will buy the idea that decryption represents creation. It's not plausible.",
"There are two possibilities:",
"The decryption recreates the exact, unchanged original, so it is not creation.",
"The decryption creates something other than the original, but this would indicate a failure of the process, an unintended outcome.",
"So this doesn't seem to be a legitimate argument.",
"For the sake of argument lets say everything was accomplished using TrueCrypt. Though, if the answer really does depend on the software package one chooses, I'd appreciate someone pointing that out.",
"All lossless compression and encryption methods should be the same -- they all must reproduce an exact copy of their inputs, or they have failed. So there is no reason to specify which program is in use."
] |
[
"and my favorite xkcd comic about people being wrong on the internet ...",
"Mine too, although it 's hard to choose among the great candidates.",
"Surprisingly, my initial question may end being very pertinent depending on the approach I choose.",
"Yes -- but be prepared for the response that an intermediate file is not necessary, it's only a gimmick to support a particular kind of argument.",
"Surely the fact that an intermediate encrypted form has no essential role is material to the question and to the argument.",
"I emphasize I am taking this strong position only to keep you from thinking that an argument that relies on an intermediate encrypted form has any technical substance."
] |
[
"and my favorite xkcd comic about people being wrong on the internet ...",
"Mine too, although it 's hard to choose among the great candidates.",
"Surprisingly, my initial question may end being very pertinent depending on the approach I choose.",
"Yes -- but be prepared for the response that an intermediate file is not necessary, it's only a gimmick to support a particular kind of argument.",
"Surely the fact that an intermediate encrypted form has no essential role is material to the question and to the argument.",
"I emphasize I am taking this strong position only to keep you from thinking that an argument that relies on an intermediate encrypted form has any technical substance."
] |
[
"Do hybrid and electric cars actually reduce overall human carbon emission?"
] |
[
false
] |
Obviously I'm no scientist, but it seems to me that since a large portion of our electricity is produced by burning coal and other fossil fuels that electric cars are more of a "not in my backyard" solution. Along with the fact that a car burning, say a gallon of gas would use that energy more effectively than what you'd get for that gallon burning in a powerplant after it gets sent by wire to where you charge it. So unless your power supply comes directly from a clean power plant, you still have roughly the same carbon footprint. Am I incorrect in this way of thinking?
|
[
"Starting with regular hybrids, those don't plug into the grid at all, so the coal argument is irrelevant. Plug-in hybrids do, but they are a very small subset of hybrid cars. Compared to normal cars, ",
"hybrids do, in fact, have a lower lifecycle carbon footprint than normal cars",
".",
"Now, as for electric cars, there are two nuances that are important to understand:",
"Emissions-wise, not all fossil fuels are created equal. If you refer to ",
"the IPCC and Benjamin K. Sovacool's work",
", you'll find that on a per-kWh basis, natural gas runs a distant third to oil and coal. The mix of fossil fuels in the electrical grid includes a sizeable portion of natural gas, which means that electric cars can burn fossil fuels, and still be less polluting than normal cars.",
"The exact emissions of the electric car depend on the local electrical grid mix. As per the lifecycle analysis from the UCLA in the first link, if you look at a place with a high proportion of renewables such as California, electric cars incur 50% less carbon emissions over their full lifetimes compared to a normal car. Of course, if you take the multiplier given for the US average electrical grid mix, the electric car still gets about 20% lower lifecycle emissions compared to normal cars. Still, given that ",
"60% of the US population live in places where the per-mile emissions of electric cars are even lower than that of a Prius",
", electric cars are most certainly less carbon-intensive than normal cars for a majority of the population."
] |
[
"Glad to hear you found my work helpful! There's an enormous amount of misinformation surrounding electric cars, so I do my best to fight the misinformation.",
"Without knowing what state you live in so I can look up the local electrical grid mix, it's impossible to answer that question. However, if you take a look at the map produced by the Union of Concerned Scientists above, you can find the average MPGe ratings by electrical grid. As a general rule, if you live on the east coast or the west coast, the electric car is going to be less carbon intensive than even a 60 MPG motorcycle in operations. Anywhere else, and the motorcycle would be the better option."
] |
[
"I'm sorry, I just glanced at that one initially. I live in Louisiana, so its perfectly equl here(except way more fun). And I used to live in Alaska. That 126 mpg figure is pretty mind blowing."
] |
[
"Саn Тrаіnіng tо Весоmе Аmbіdехtrоus Іmрrоvе Вrаіn Funсtіоn?"
] |
[
false
] |
[deleted]
|
[
"Not that we know of. There have been some studies that showed differences in specific types of performance for left handed and right handed people. To my knowledge, there has been no conclusive research showing improved performance due to ambidexterity. In fact, developmental issues and reduced performance in some functions seem to be related to ambidexterity.",
"https://www.scientificamerican.com/article/can-training-to-become-ambidextrous-improve-brain-function/",
"https://www.ncbi.nlm.nih.gov/pubmed/20338681",
"Source: Experimental psychology student"
] |
[
"What if you only started learning it as an adult? "
] |
[
"It would definitely be an interesting research question, but as far as I know and could find in the research databases, there is no conclusive evidence in this area. I'll ask my professor(s) and get back to you."
] |
[
"Why is it called the 'special' theory of relativity?"
] |
[
false
] |
[deleted]
|
[
"Accelerating reference frames just make things more complicated but they are fine in special relativity.",
"The special case is no gravity = flat spacetime."
] |
[
"The “special” case is flat spacetime. That means no gravity, but you can have accelerating frames of reference."
] |
[
"Einstein's original paper outlining the special theory of relativity just called it the \"theory of relativity.\" It dealt with flat spacetime (Minkowski space) and covered everything to do with Lorentz symmetry (relative velocity, length contraction, time dilation, relativity of simultaneity, etc.) but it did not address gravity at all.",
"Later, this \"theory of relativity\" was ",
" to include curved spacetime, and this new more all-encompassing theory was called the \"general theory of relativity.\" Then the original theory of relativity falls out of the new general theory as a special case (the case where spacetime is flat and there is no gravity), so it is distinguished from the general theory of relativity by calling it the \"special theory of relativity.\"",
"An easy mnemonic that you can use to remember the main difference is: ",
"pecial relativity deals with relative ",
"peeds, while ",
"eneral relativity also includes ",
"ravity.",
"... some say it's because it only describes events that unfold in inertial frames of reference.",
"Both special and general relativity deal with inertial reference frames, and both can also handle accelerated reference frames as well.",
"The difference is that in general relativity, ",
" frames are treated as ",
" frames in a curved spacetime. In special relativity, you can in principle model gravity as a separate field in flat spacetime, but then gravitational acceleration is a proper acceleration caused by a real force and is not just inertial motion that appears as a pseudo-force.",
"Hope that helps!"
] |
[
"If we would go to the moon today - using and bringing with us the technological capabilities we possess now - what would differ from our missions some 40 years ago?"
] |
[
false
] |
What would we be measuring? Would we be looking for different things than back then? And so on...
|
[
"Insulating the wires powering the oxygen tank agitators thats for sure."
] |
[
"For one thing, due to how politics have changed in the past 40 years, today's missions would have to be much ",
" safer. There was a very real possibility that the Apollo 11 astronauts wouldn't make it back from the Moon. Nixon had a ",
"speech",
" prepared and everything. Hell, they had to jam a ",
"ballpoint pen",
" into the dashboard to get the lander started after the ignition switch broke off. ",
"They still went because America was having a dick measuring match with the Russians. If the Americans were going to win the \"space race\", they had to act fast. It was so close in fact, that the Russians launched a ",
"probe",
" three days before Apollo 11 launched. They would have been the first to successfully bring Moon samples back to Earth had their probe not crashed into the Moon's surface.",
"Long story short, there is a lot that could have gone wrong 40 years ago, and a mission like that would not have been approved today.",
"Not sure if that answers your question, but I always find Apollo facts interesting."
] |
[
"A good resource is the Lunar and Planetary Institute. This might be a good starting point: \n",
"http://www.lpi.usra.edu/lunar/strategies/",
"But you should also look at NASA's Planetary Science decadal survey: \n",
"http://solarsystem.nasa.gov/multimedia/downloads/Vision_and_Voyages-FINAL1.pdf",
"There, the actual planned missions to the Moon are outlined. There are two big ones: the Lunar Geophysical Network and Lunar South Pole-Aitken Basin Sample Return. The Geophysical network is pretty obvious: we want to know about the interior of the Moon, and seismometers could help make that happen. It could provide a huge amount of data for a long period of time that would help us understand how the Moon formed. The SPA basin is notable for being the largest impact crater on the Moon, and as a result, it exposes rocks at the surface of the Moon that would normally be buried quite deep. ",
"It is important to note that most of the objectives that are scientifically interesting can be achieved by robots. Robots are also cheap compared to humans, and NASA just took a pay cut, so that is what will continue to happen. ",
"There are a lot of other gains in our knowledge of the Moon that guide other research concerns. Generally, our knowledge of the Moon and of the Solar System has increased exponentially since the 1970's. We didn't have the Lunar Cataclysm hypothesis at that time, but now we are almost certain that a Mars-sized body impacted Earth about 30 million years after Earth was 90% finished accreting. That is one reason why we want to sample the Lunar interior -- all of our samples from the Moon that we currently know are from the surface, and so our models may or may not work once we know what the Moon is like at depth. ",
"We are also learning that the Moon is not quite as dry as we once thought, so a big concern is figuring out exactly how much water and exactly where it is on the Moon. If we found a reasonably large source, long-term habitation might be possible. ",
"Also, the Moon's geological history goes back much farther than Earth's. The oldest rocks on Earth are 4 billion years old, so we have a 500 million year gap after the beginning of the solar system where geology is not recorded. The Moon does record that time. So we can learn a lot about impact processes. Of particular interest is the Late Heavy Bombardment, which happened somewhere in the range of 4.2-3.9 billion years ago, but we don't have too much direct evidence of that. If we could get accurate ages on some craters on the moon, we would be a long way to properly constraining both the timing and magnitude of the event. ",
"We also have only a limited understanding of Lunar volcanism. If we could go back to the Moon, we could learn a lot more about the volcanic activity there, including the timing of the events. This is another method of probing the interior of the Moon. The only way that recent volcanism is possible is if there was a reservoir of magma near to the surface in recent times, which has implications for how quickly the Moon cooled after it formed. ",
"And also, we have never had a human land on the far side of the Moon (as an aside, it isn't the \"dark side,\" since all sides get to be dark, depending on the time of the month). ",
"So there is a lot to be learned on the Moon! We definitely need to go back. What I listed here is just scratching the surface of what could potentially be learned by further exploration. "
] |
[
"What factors contribute to the acoustical activity (or lack thereof) of a piece of material"
] |
[
false
] |
Obviously there's the two most basic - longer and/or thinner = lower pitch, shorter and/or thicker = higher pitched - but what about factors determining timbre, sustain, pureness of tone, etc. In other words, why does a piece of leaded glass crystal dinnerware make a different sound than a metal cymbal or a wooden xylophone key?
|
[
"Shape and density are the biggest factors (in wires, tension and length are the most important). The pitches you get when you hit something are due to a natural instability in the object.",
"The natural vibration frequencies can be calculated, and are called \"modes\". The first (fundamental) mode is the lowest frequency and also the one that comes across the loudest. The other modes are all considered overtones. If you take shapes that aren't simple (like aircraft wings), these can be frustratingly difficult to determine. But strings are pretty straightforward.",
"So the fundamental frequency is \"the note\" that you hear. If you play a middle C on a trombone and a piano, the pitches are identical but they sound different. The difference in sound (timbre) is due to the difference in overtones. The higher frequencies of vibration make the instruments seem different even though the fundamental is the same.",
"The actual nature of the different vibrations is really interesting; in a metal bar, you hear several main virbations. If you put your hand on the end of the bar after you hit it, one of the pitches will go away because you stopped it from expanding and shrinking lengthwise.",
"Percussive sounds are not necessarily like pitches; they don't have a set frequency or timbre and they don't sustain at all. Instead of a vibration from a natural instability, the're actually single pressure waves caused by a collision. If you hit two sticks together really hard, you'll hear a click sound and two extremely short pitches. The click is a single bump from the collision, and the pitches are the very short-lived vibrations of the sticks. Cymbals actually have pitches, but the modes are really similar in magnitude and are extremely dissonant, so it sounds like a bunch of noise, and the initial percussive sound is really important."
] |
[
"There are a lot of things about a material that lead to the sounds it can make. The two biggest are wave speed and geometry of the object. The geometry determines the wave shapes that the object can support (often called modes). For circular geometries you can expect modes that look like bessel functions, for rectangular geometries the modes look like sine waves. Regardless of what the modes look like, though, the object itself will oscillate sinusoidally creating a tone.",
"The wave speed will determine the frequency of those modes. An object might have multiple wave speeds, each corresponding to a different form of motion. A solid metal rod, for example, will have one wave speed associated with longitudinal waves (the bar compressing), another wave speed associated with shear waves (the bar bending), and another associated with rotation. Putting mode shapes and wave speeds together, you can find all of the frequencies associated with an object.",
"That only answers part of your question, however, since knowing the frequencies of harmonics only tells you so much about the sound. The initial amplitude and rate of decay of the modes will make a big difference for how the object sounds.",
"Initial amplitudes for the harmonics is relatively simple, since it's really associated with how you are creating the sound in the first place. For example, if you hit a xylophone key, where you hit the key is going to determine which modes are initially excited. If you are playing a reed instrument, the frequency of vibration for the reed is going to make a difference.",
"To understand the rate of decay for the modes you really need to start looking into the chemistry and the structure of the materials. The decay essentially comes in when processes turn sound into heat, and the differences for each harmonic either have to do with the time scales or length scales of those processes. Viscosity plays a part, thermal transport plays a role, molecular relaxation is involved, etc. For example, the crystal dinnerware rings more than an analogous piece of unleaded glass because the crystal has a more regular molecular structure. A metal key from a glockenspiel rings \"truer\" than a wooden xylophone key because metal can deform with less loss to heat."
] |
[
"The first three paragraphs are good stuff. Unfortunatly for me, they're good stuff I already knew, but still good stuff. ",
"I have to disagree with you on your discussion of percussive sounds though. ",
"This video says more than I ever could about the range of percussion musicality beyond \"hitting two sticks together really hard.\"",
". Terry Bozzio (from Korn) is guest performing with Zappa Plays Zappa, with his monstrous drum kit that's specifically built with the ability for \"playing melody\" in mind...the 13 drums on the left are tuned to a chromatic scale, then 10 on the right tuned in pentatonic (two octaves), and a series of chromatic cymbals and gongs. ",
"Also, bells, xylophones, glockenspiels, and a host of other percussion instruments (shit, piano is technically a percussion instrument...it's just a stringed percussion instrument) that go beyond dissonance and crashbangboom sounds...would love more information about this realm of instrument design and craft. "
] |
[
"Question about gradual paralysis"
] |
[
false
] |
[deleted]
|
[
"It could be Guillain-Barre syndrome. I'd get it checked. I had a friend that almost died from it."
] |
[
"The suggestion of GBS was probably based on the fact that it was an ",
" paralysis, which is very characteristic of GBS. So knowing where and how they were affected would be an important element in coming up with a diagnosis.",
"Progressive paralysis is usually indicative of an on-going pathological condition, not some trauma in the past. It's possible, although unlikely, that the trauma may have been the initial insult that has started an auto-immune disorder specific to nerves, in which the most likely diagnosis would be Multiple Sclerosis. MS is pretty rare (<0.1%), though. What I suspect is more likely is that the trauma is unrelated, as most nerve damage that occurs as the result of trauma doesn't really have the pattern of getting better then getting worse. ",
"Could you say more specifically as to what has been going on?"
] |
[
"The suggestion of GBS was probably based on the fact that it was an ",
" paralysis, which is very characteristic of GBS. So knowing where and how they were affected would be an important element in coming up with a diagnosis.",
"Progressive paralysis is usually indicative of an on-going pathological condition, not some trauma in the past. It's possible, although unlikely, that the trauma may have been the initial insult that has started an auto-immune disorder specific to nerves, in which the most likely diagnosis would be Multiple Sclerosis. MS is pretty rare (<0.1%), though. What I suspect is more likely is that the trauma is unrelated, as most nerve damage that occurs as the result of trauma doesn't really have the pattern of getting better then getting worse. ",
"Could you say more specifically as to what has been going on?"
] |
[
"What does it mean, in a physical sense, to break symmetry when refering to the Higgs mechanism?"
] |
[
false
] |
I get breaking the mathematical symmetry of the standard model, and i understand the anecdote about a ball falling from a hat or bottom of a wine bottle like shape and thus breaking the rotational symmetry of the object, but i don't understand what this means in the physical/quantum sense. What symmetry is being broken in the system? Is it the symmetry of a guage boson, if so what does that mean? Just looking for some sort of picture i guess of what this looks like in the physical world (if that even makes sense). Thanks for your time.
|
[
"First, abandon the idea of particles and think of excitations of a field. That is, a field is something that has a value at all points in space. Some fields are scalar; their value at every point is a simple number. Some fields are vector; their value at ever point has a number and a direction. The vector bit is important for the math, but I'm going to hand wave it away for now. ",
"A particle is then the field jiggling at some point with a definite value. The jiggling is what we think of as a particle. But really, it's just a field bouncing up and down at some point. Different modes of excitation correspond to different modes of excitation. So if the field jiggles ",
" it's particle A, if it jiggles ",
" way, it's particle B. ",
"If the field is a scalar field, its excitations are called Goldstone bosons. If the field is a vector field, its excitations are gauge bosons. The two are different, but the exact differences aren't important for this ham handed explanation. ",
"The Higgs field is a scalar field with four modes of excitation. That means if the field is jiggling, it could jiggle in such a way to produce any of four different types of Goldstone bosons. Because the field is symmetrical and scalar, these are all spin 0 massless particles. ",
"The electroweak field is a vector field with four modes of excitation. Again, the jiggling field produces four different types of gague bosons. But because the field is symmetrical and vector, these are all massless, but have different charges and spins. ",
"Now the fun begins. These two fields permeate all space. Pick any point literally anywhere and there's a Higgs field and a electroweak field there. Jiggle the Higgs and there's a Higgs Goldstone boson there. Jiggle the electroweak field and there's a weak gauge boson there. Both particles are massless. ",
"Now here at last is the trick. The Higgs field is sticky. If you jiggle the weak field, it isn't just the electroweak field that's excited, its the Higgs field as well. Jiggle the Higgs field and the electroweak field jiggles as well. Excitations of the electroweak field provoke excitations in the Higgs field as well. But not for all excitations. Because of the way things mix together, three of the four excitation modes of the Higgs field stick to three of the four excitation modes of the electroweak field. Instead of a pure jiggling of the electroweak field, you get a mixed state of a jiggling Higgs and electroweak field. ",
"So we have three mixed excitation modes. These are the W",
" W",
" and Z",
" particles of the weak field. Since they're excitations of a gauge field, they are still force carriers. But because they have a bit of Higgs stuck in them, they're massive. One of the excitation modes doesn't mix in with the Higgs and remains massless. That's our friend the photon. ",
"But that leaves one particle out. Three of the four Goldstone bosons that represented the jiggling Higgs field have been eaten by the electroweak field to become the massive W",
" W",
" and Z",
" bosons. But there's still one Higgs boson left. And that is the imfamous Higgs boson itself. ",
"Which leaves the mass of the Higgs boson to explain. As near as I understand it, this boson interacts with itself, giving rise to its own mass. Scalar field weirdness, I think. ",
"Hope that makes some sort of sense."
] |
[
"Incidentally, for a fantastic popular level description of the development of electroweak theory, the Higgs field and the people involved, read ",
"The Infinity Puzzle",
" by Frank Close. ",
"Also, you'll run into something called 'mixing angle' when studying this. In my simplified analogy, the mixing angle is the coupling strength between the Higgs field and the electroweak field. In the real theory, it's a bit more complex, but serves the same purpose."
] |
[
"Very easy to understand thank you, however i still don't get what \"breaking\" the symmetry means, is it because the higgs \"sticks\" to gauge boson that makes them unsymmetrical and thus massive? Or is it better to completely forget about symmetry in natural terms and simply say the higgs breaks the standard model equations mathematical symmetry and this is seen in nature by the higgs sticking to these bosons?"
] |
[
"On 'Frozen Planet' David Attenborough said some birds migrated 11,000 miles for food. How do they know how to do that, and where to go?"
] |
[
false
] |
[deleted]
|
[
"I'm sure there are more knowledgeable folks here who can provide a more comprehensive answer, but ",
"there is evidence",
" birds navigate over such long distances in part by being biologically sensitive to the Earth's magnetic field. In other words, they have a built in compass. ",
"As for where to go, in at least some species, it is a learned behavior passed down from adults to chicks. This had been one of the problems faced by conservationists seeking to actively breed endangered species back from the threat of extinction. We can fertilize and hatch eggs, and to some extent serve as surrogate parents. But people don't migrate. One effort to address this has been pioneered by ",
"Operation Migration",
", using ultralight aircrafts to lead/guide artificially hatched birds along known migration routes. Their story was fictionalized some years ago in a movie called ",
"Fly Away Home",
"."
] |
[
"I'm confused. Does the question ask on how birds are tracked or how they migrate? "
] |
[
"Ah I see... how do they do it? through natural selection over millenia"
] |
[
"Why are CRT monitors at 60Hz flickery, while CRT TVs at 60Hz seem just fine?"
] |
[
false
] |
I realized that when I watch a movie on a CRT TV, it doesn't seem flickery, even though the NTSC standard is 60Hz. However, if I set a CRT monitor to 60Hz, it seems to flicker a lot. Why is this?
|
[
"Remember you would sit much closer to a desktop computer CRT monitor than you would to a TV, and focus on detail that's much smaller than any text would be on a television.",
"So I think you would notice the flicker more with your ",
"peripheral vision",
", which is more sensitive to movement. This used to be a trick with CRT monitors -- look just to the side of it and you can see the screen flicker (at, say, 75Hz) but you can't see it if you look dead-on."
] |
[
"Part of the flickering is caused by you thinking that you're seeing it, because it's a desktop monitor.",
"The main reason why you're not seeing it on a TV, is that the TV very rarely has a perfectly still image for you to focus on. Your eyes are compensating for the lack of movement, by focussing on the still harder."
] |
[
"A lot of CRT TVs operate at 100-120Hz, even though the input is 50/60Hz, by displaying each frame twice. You could definitely see flickering on older TVs before they started doing that."
] |
[
"If my sunglasses have yellow lenses and reflect yellow light, why does everything appear yellow when I look through them?"
] |
[
false
] |
[deleted]
|
[
"The glasses actually absorb blue light, which means any light that goes through them looks yellowish. The reflections shouldn't be yellow, they probably just appear that way because the glasses let through a lot of yellow light that gets mixed with it. To test this you could look at a blue object in the reflection in a dim room where only the blue object is lit, it should still appear blue in the reflection (but not when looking through the glasses). "
] |
[
"The reflections shouldn't be yellow",
"Actually, that's what happens if something absorbs the blue light - whatever it lets through is yellowed and anything it reflects is yellowed too, because the blue has been absorbed."
] |
[
"Sunglasses lenses have two different properties: reflectance and absorbance and they can in principle be independent of each other. You may coat the lenses with a thin reflecting layer that reflects some part of the spectrum. However that still doesn't completely determine what goes trough the lens to you eyes - they could have chosen the lens material to filter out everything but yellow - then some yellow light will be reflected and the rest will go through, while all other colors will either be reflected or absorbed."
] |
[
"If I play music at the same volume on two speakers then will the overall volume of the music increase?"
] |
[
false
] |
[deleted]
|
[
"It is the dB scale. Equivalent Power = 10×log (10",
"+10",
" +...). Humans ears won't equate it to a volume doubling until it is 6-10 dB."
] |
[
"When you have two noise sources it will be louder. It is essentially the same thing as having two light bulbs next to each other.",
"It does not add up directly though - it won't be twice as loud. If you have two noise sources with a sound level of 100 dB each the total will be about 103 dB."
] |
[
"The important thing to know here is that \"loudness\" is a perceptual quality of sound, not a physical property. The apparent loudness of a sound is related in very complicated ways to the physical properties of the sound. Even for simple sounds like sine tones, the loudness depends on frequency as well as power -- the relationship is called the ",
"Fletcher-Munson curves",
". ",
"The dB math expressed by the poster above is correct only for physical measurement - dB SPL is a unit of physical power, not perceived loudness. Loudness is measured in ",
"sones",
". Of course ",
"/u/longerthanuthink",
" is correct on the direct answer: yes, your two speakers playing the same thing are louder than only one speaker. It's not an auditory illusion.",
"As you can see from those curves, we could create an equation to model them but it's not a simple one.",
"And once you get to more complex sounds like music, cognitive effects start to come into play. For example, people that don't like rock music perceived it to be louder than people that do, ",
"in one study.",
"(Source: I have a Ph.D. in psychoacoustics and audio signal processing from MIT)"
] |
[
"From the perspective of a cell in the human body, how big would hydrogen look?"
] |
[
false
] |
[deleted]
|
[
"A cell is about 100 microns and a hydrogen atom is about 10E-5 microns. It would still be microscopic even if the cell were the size of a person."
] |
[
"Right. A typical human cell sits around 20um or so, and we can easily see them under 5-10X magnification. "
] |
[
"Right. A typical human cell sits around 20um or so, and we can easily see them under 5-10X magnification. "
] |
[
"Why do matrices raised to the power of 0 always give the neutral?"
] |
[
false
] | null |
[
"Your proof that A",
" = A only shows that it's true for n > 0.",
"It's not always true that A",
" = 1 for all matrices.",
"A",
" = A",
" = AA",
", which only has meaning if A is invertible. And if it's invertible AA",
" = 1. For a singular matrix like ",
"your example",
", A",
" isn't defined."
] |
[
"Yeah I see, that bothered me, because at my University they said that that exact matrix is also 1 when raised to 0. ",
"However, your answer makes me wonder about mathematical induction. If I prove that inductive step is true for n+1, did I only prove it for positive numbers (or numbers greater than the base at least). Should I prove for n-1 as well to prove for negatives?"
] |
[
"Proof by induction is only intended to hold for natural numbers. I guess it could be extended to include all integers."
] |
[
"How did early astronomers know that those slightly brighter dots of light were planets? How did they know the order of the solar system?"
] |
[
false
] | null |
[
"What distinguished the planets from the stars for ancient astronomers was not their brightness, but the fact that some objects were always in the same relative positions to each other in the sky, while others moved around and could be found near different stars at different times. The ones whose positions were fixed were the ",
" and the ones that moved around were the ",
". (In fact, the word \"planet\" comes from the Greek word for \"wanderer,\" reflecting this property.)",
"Of course, people did not know what the physical properties of the planets and stars were in terms of their composition and such, but did know that they behaved differently in the sky."
] |
[
"Also, this would have been obvious to people, not something that only astronomers would discern after study. In the industrial age we've largely lost the night sky as a constant companion. Most people do not realize just how dark a moon-less sky is at night without any artificial illumination. It's incredibly dark, you can't see where you're going, you can only barely make out shadowy shapes. But the night sky is an awesome sight. Given that it's night about half the time, and humans don't sleep half the time humans would have spent a considerable amount of time outside in the dark. They were familiar with the stars in the sky because they saw them so often. And since the classic 5 planets are not only fairly bright but move substantially across the sky over the course of a single year, it would have been obvious and well known public knowledge that there were some particular stars which moved, while the rest stayed fixed relative to each other."
] |
[
"Planets are not necessarily always the brightest dots in the sky- Mars for example varies from a nondescript brightness to being one of the brightest things in the sky (based on if it's far or close to Earth), which is why its sudden brightnesses were attributed to its being a harbinger of war. What gives them away is that they are stars that move, and in a ",
" obvious way if you know your constellations- my friends always amaze that I can look up and spot a planet and ask me how I know what it is, for example, but it's just something I can know without looking up from years of experience.",
"Interestingly though yes, the ancient astronomers had the order of the solar system pretty well worked out as early as ancient Egyptian times (excepting of course the part where they thought the sun went around Earth!). This isn't so hard to do because while the little motions of planets were hard to explain, ie ",
"epicycles",
", the further away ones ",
" move more slowly. So they had the order right, ie Mercury, Venus, the Sun, Mars, Jupiter, and Saturn.",
"Uranus and Neptune were discovered in modern times via telescope... though it should be noted that Uranus can just ",
" be seen with the naked eye if you pay attention. However, there is no record of ancient astronomers ever spotting it."
] |
[
"How do we know about other dimensions if we can only understand the first three?"
] |
[
false
] |
I just don't really understand how people gather information about dimensions that we can not physically see.
|
[
"You can definitely treat time as a fourth dimension"
] |
[
"Try reading the book Flatland. It's a little dry, but a quick read. If you can imagine how a sphere would appear to a two dimensional being, you can imagine how a 4 dimensional object would appear to us "
] |
[
"Four."
] |
[
"I've obviously heard of people being born without hearing and sight, and less commonly smell/touch, but can we be born without other senses like proprioception or our sense of time without brain damage being a factor?"
] |
[
false
] |
To elaborate: is there a way someone could be born without being able to "feel" time or "feel" the position of things in relation to their body (knowing when they're about to touch their nose if their eyes are closed, etc.).
|
[
"All of these can occur. Anosmia is a lack of smell, which can potentially lead to life threatening situations (can't detect when food is bad, gas is leaking, smell of smoke, etc). While I haven't researched in people missing a sense of taste, they would encounter many of the same problems.",
"Problems with priopreception and nociception (pain) are going to be neurological in nature, and can coincide with other neurological abnormalities. As you can imagine, these two can be exceptionally dangerous as both of these senses are necessary for day to day functioning."
] |
[
"I apologize for not posting an article, as I am on my phone, but-",
"\nThere was a case fairly recently where a girl was born without any ability to feel pain. Her parents had to constantly watch her because she would never cry if she was sick or had somehow hurt herself. Other than an inability to feel pain, she was a normal, fully functioning child.",
"So yes, being born without the ability to feel pain is possible, just quite rare."
] |
[
"This disorder is called CIP, or congenital insensitivity of pain, it's often associated with in the inability to feel heat and cold as well."
] |
[
"Why do diesel engines blow black smoke when you turn them on but blow white smoke when you accelerate?"
] |
[
false
] | null |
[
"So the coloration of smoke is a basic indicator of the fuel ratio. Black smoke is more apparent on a cold start due to the intentional over-richening of the mixture. As part of the cold start cycle, injectors will put more fuel in than ideal in order to compensate for the lower internal temps. It also has the nice effect of brining the engine up to operational temp quicker.",
"Now, black smoke isn't \"bad\" per say, but it just means that a portion of the fuel is unburnt. This can either be intentional or unintentional. In a turbo diesel setup, you tend to want to stay on the slightly richer side of the spectrum of air/fuel ratios. This isn't ideal for power, but it's more of a safety thing... going rich just means you run less efficiently, going lean could mean you burn up your internals. It's cheap insurance to stay rich(er). ",
"White smoke is either an indicator of water in the mix (vapor) or raw fuel dump. So, really the smoke shouldn't be white at operating temps - if anything, it should be on the blacker spectrum. Blue smoke is burning oil, which is usually an indicator of bad rings (which is another by product of running rich...fuel wash) or seals if it's a turbo diesel."
] |
[
"I don't know how cold it is at OP's place right now, but when the weather is cold, since the air is pretty much saturated with water vapor, the water produced by the combustion simply condensates when it comes out of the exhaust, making \"white smoke\". This applies to both diesel and gasoline engines."
] |
[
"Another reason to run richer mixtures is that (Taken from basic aviation knowledge) is that it means the engine runs a bit cooler than if it were run leaner."
] |
[
"How do caterpillars maintain basic bodily functions as they transform to butterflies within the chrysalis?"
] |
[
false
] | null |
[
"When a caterpillar forms a chrysalis to metamorphose, despite common misconception, a suite of enzymes doesn't literally digest the body down to a rich fluid to reform anew from scratch. Only some of their organs do that; the rest remain largely intact and simply undergo radical remodelling via cells undergoing programmed death to be replaced by other rapidly dividing cells. A chrysalis is not quite just a bag of protein goop.",
"With this in mind, how does a caterpillar survive? Let's break it down:",
" A developing chrysalis clearly needs some sort of gas exchange taking place to keep breathin'. All insects breathe through teeny pores that line their bodies called ",
"spiracles",
", which lead into long tendril-like tubes that penetrate deep into the body, carrying oxygen. Thankfully, during metamorphosis, this respiratory system remains intact (even through a bit of renovation), allowing the developing butterfly to continue breathing throughout.",
" Unable to forage for food, a stationary chrysalis is at risk of running out of energy - after all, it uses a considerable sum to forge a new body. However, before enclosing itself in a hard outer shell, the caterpillar spends almost all waking moments gorging itself, storing up an enormous amount of energy as body fat. During metamorphosis, it's this stored fat that's broken down into the requisite resources needed to survive; a chrysalis can lose over half its weight during the entire process, as this fat is broken down.",
" As with the spiracles that provide oxygen and remove carbon dioxide, a series of malpighian tubules remove excretory waste - albeit in this case not outside the chrysalis. They're likewise retained through much of metamorphosis and release concentrated nitrogenous waste into an isolated subsection along where the caterpillars intestines once hung about. When the butterfly emerges, it releases all of this, well, poop and bits of old caterpillar carcass as a red fluid out the abdomen, known as meconium. Finally released of this debris of its past experience, it can stretch its wings and fly away.",
" ",
" ",
" ",
" ",
" ",
" ",
" ",
" "
] |
[
"Fascinating read, thanks for the answer 👌🏼"
] |
[
"At the Houston Museum of Natural Science butterfly center there is a huge, three pane display section where they have dozens of species of butterflies hatching. There are easily a hundred in there at any given time and they hatch all day. I used to love going in and watching kids marvel at a butterfly fighting out of its chrysalis, then take a huge, gross dump right before their eyes. "
] |
[
"A \"biohacker\" with a PhD in biophysics says he's modified his DNA with CRISPR. What's the reality of this?"
] |
[
false
] |
Article here:
|
[
"Editing DNA with CRISPR is absolutely possible. But it kinda depends on what he means by \"modifying his DNA.\" Sure, you can change it in a test tube, or even in a living cell. But changing the DNA in every cell in the human body is still an impossibly tall order.",
"That day will come. But we're years, if not decades, away from it."
] |
[
"Not to mention CRISPR-Cas9 had an insanely high off target reads. You’re basically risking screwing up other parts of the genome to edit one gene. A new CRISPR-Cas13 is more promising but we’re a long way from true gene editing. "
] |
[
"Which is not a very difficult or dangerous thing to do. Two MSTN genes that are pretty isolated. ",
"Difficult part is delivering the knockout to enough cells to make a difference in myostatin release. "
] |
[
"Are spurting fountains of blood due to swords hacking off limbs or heads realistic? If not, how much blood would be involved in a sword fight?"
] |
[
false
] |
Aside from Monty Python, Shogun 2 is releasing a "blood pack" to add more blood to the game. Which made me wonder, I know in the historical records they talk about rivers of blood, which I can see as feasible, I mean look at what happens during a whale slaughter. But I'm curious exactly how much blood would be spilt on an ancient battlefield in a sword on sword clash. Like if you cleave somebody's head in half, or slice their neck or arm or leg off. Etc. Like we see demonstrations on the deadliest warriors, but those are inert meat bags filled with blood, not a living thing with a beating heart.
|
[
"Blood squirting is feasible, if it's arterial blood, but a river? Perhaps in a mass death. The tide at Normandy beach was red for days after the invasion."
] |
[
"It's definitely possible with arterial spurts. If you see videos of people whose throats were cut and had an artery in their neck severed you'll notice that blood spurts everywhere when their heart beats. I assume it's the same with removing limbs, thought it's incredibly unlikely that it's quite as drastic, and hilarious, as Monty Python makes it seem."
] |
[
"Yes its realistic. ",
"http://www.liveleak.com/view?i=05ebe688b1",
" VERY NSFL"
] |
[
"Does the expansion of the visible universe cause some sort of exaggeration in the apparent distances between distant objects because their light is coming from a time when the universe was more compact?"
] |
[
false
] |
[deleted]
|
[
"I'm not ",
" sure that I understand your question. But I ",
" one answer might simply be to point out that determining the distances to other galaxies is ",
" a trivial exercise. The way one might guess — parallax, the same method you'd use to triangulate the distance to a reference point on the surface of the Earth — is useless outside our own galaxy, and in fact largely so within our own galaxy, since the angles involved are so miniscule.",
"One thing that helps is the fact that the distance between luminosity and distance is a trivial and universal one: If you know how bright something is in absolute terms, and you know how bright it appears to be when you look at it, then you know how far away it is. The challenge, then, is identifying things of known absolute brightness and then searching the sky for them. In this way we can measure the distances to a wide variety of objects at various distances, to within our own galaxy all the way out to modestly distant galaxies.",
"But no matter what, you're still looking at ",
" of some form or fashion. If you know what frequency of light you're looking at, and can compare that to the frequency it was when it was emitted, then you can figure out how long the light took to get here. But pay attention to that: the result of a redshift calculation like that gets you back units of ",
" You know how much ",
" the light took to get here … which of course translates trivially into units of distance in a static universe, but not so in an expanding universe. One must jump through a few hoops to convert lookback distance — which is simply the time it took light to reach us converted to units of distance — into actual comoving distance, which is the distance the object would be from us if it were possible to freeze time and erect a colossal stack of rulers from here to there. Then there's ",
" which is similar to comoving distance except it varies over time, so while the comoving distance from here to Galaxy X is a constant, the proper distance depends on when you're talking about.",
"I'm sorry this is so confusing, but the truth is it's simply complicated. On the other hand, it's not like it's important at all to anyone but a cosmologist; it's really vitally important that you know your way back home from the pub down in the village, but nobody's ever going to need to navigate between stars much less between galaxies, so it's really quite academic."
] |
[
"What you're describing is the difference between the comoving distance and the proper distance which you can read about ",
"here",
"."
] |
[
"Thanks!"
] |
[
"At the hardware level, how do computers multiply numbers together?"
] |
[
false
] |
I was learning about [adders](en.wikipedia.org/wiki/Adder_(electronics)) and I tried thinking how computers multiply numbers together. I haven't seen anything like an adder that works for multiplying, and the only way I could think of was looping the number through the adder a ton of times, for example, 5x3 would be 5+5+5. But trying to do that with two numbers that are both 10 wouldn't really work whereas my phone can do it instantly. So how do they do it?
|
[
"A simple algorithm works by using the binary representation of one of the numbers (which is easy because numbers are already stored in binary inside the computer). For example, if b is 00100011 in binary then:",
"a * b = a * 00100011 = a * 00100000 + a * 00000010 + a * 00000001",
"Now, multiplying binary number a by a binary number of the form 1000.…0 works by adding zeros to the end of a:",
"a * b = a00000 + a0 + a",
"And now you have a simple addition."
] |
[
"The simplest way is exactly how you mentioned; successive addition. An internal register holds the number of additions to make (one of the operands) while another holds the value to successively add (the other operand). once the correct number of additions have taken place, you have your result. This, as you rightly say, is quite difficult for large (infinite) numbers.",
"However, remember that computing works on base 2, and the size of an integer is finite. for example, a 32-bit machine will only be able to multiply numbers less than 2",
" so we know, in your suggested algorithm, it will take 2",
" successive additions to calculate the maximum multiplication possible.",
"We can simplify though. Because integers are base 2, any multiplication by 2 is actually a logical left shift. i.e. all binary digits move left 1, and the MSB becomes 0. using this, we can simplify the successive addition algorithm to ",
"result = operand1;\nfor (i = 0; i < 32; i++) {\n if (operand2 & (1 << i))\n result += (operand1 << i);\n}\n",
"i.e. for each set bit in operand 2, add operand 1 shifted left by the set bit's position. this gives us only 32 operations to carry out instead of 2",
"Furthermore, if complexity of design is no problem, all of these 32 operations can happen in parrallel in the ALU, so we result in a huge 32 integer addition. of course, this is not recommended as it is a waste of chip space.",
"There are also methods of approximation, whereby you calculate the nearest power of 2 of both operands, use whichever is closest to the power of 2, and logical shift the other operand according to this value. and then add/subtract the difference between the power of 2 and the original operand. e.g.",
"100001 * 111 = (100000 * 111) + (1 * 111) = (111 << 5) + (111 << 0) = 11100111\n OR \n100001 * 111 = (100001 * 1000) - (100001 * 1) = (100001 << 3) - (100001 << 0) = 100001000 - 100001 = 11100111\n",
"There are more ways of implementing this, and is a very interesting topic. If you would like to read more, there is a book called Computer Systems Organization and Architecture by John D. Carpinelli that delves into the world of processor design. He introduces a lot of great ideas for custom core designs. I would greatly recommend that book, and a cheap Altera/Xilinx FPGA development board (I personally have an Altera DE1 for playing with).",
"P.S. Apologies for the bad explanations/examples. But if you think this is confusing, stay away from division. haha."
] |
[
"Hmmm, that's ",
" algorithm that uses binary, it's not necessarily how a modern CPU uses it. A primitive Multiplier would use something like ",
"Booth's algorithm",
", a more modern one would use something like ",
"Wallace trees or a Dadda multiplier",
". And, of course, these are integer algorithms, for floating point math (or floating point operations in generally), there's an entirely different part of the CPU dedicated to that that uses entirely different methods."
] |
[
"If hummingbirds have such high food demands, what do they do when flowers aren't blooming?"
] |
[
false
] |
see title
|
[
"They only drink nectar to give them the energy they need to hunt the bugs. ",
"The insects are their primary source of nutrients. ",
"The sugars in nectar and, well, sugar (in your hummingbird feeder) give them the calories they need to hunt for insects. They usually feed in the morning and evening, and especially in the evening they use those calories to carry them over to the next day. ",
"Source: ",
"http://www.hummingbirds.net/feeders.html",
" , and watching the little suckers outside my window every day.",
"Side note: I've seen people wring their hands over \"white sugar\" in hummingbird feed (seriously... people are crazy). Don't do that: your problems with 'refined carbs' aren't hummingbirds problems. They need that sweet sweet sugar to survive. "
] |
[
"They also eat bugs, which isn't all that well known. They can also lower their body temperature to burn calories more slowly."
] |
[
"They migrate to where the flowers are in bloom."
] |
[
"What do physicists mean when they say that gravity is the weakest of the four forces?"
] |
[
false
] | null |
[
"It means exactly that: out of the four forces, gravity is the weakest one. Gravity only seems strong because we live right next to a giant mass of rock and experience gravity all the time. When an entire planet worth of gravity is opposed to a small fridge magnet worth of magnetic force, the fridge magnet usually wins. That's how weak gravity is."
] |
[
"Per particle, gravity produces a much lesser force and is overpowered in all local contexts.",
"The entire gravity of earth isn't enough to overpower a common magnet holding an object up, it's not enough to overpower the strong nuclear forces of the nucleus. However, the strong force is short ranged, the electromagnetic force cancels out on net (every proton tends to have an electron nearby) so over longer distances and with extremely large amounts of mass gravity is dominant."
] |
[
"That's not electromagnetism, that's Pauli exclusion; electrostatic repulsion has basically no effect on making something solid, or else positively charged objects would be less solid than neutral ones. ",
"For a better example, a two-inch fridge magnet is able to completely overpower the gravitational pull of the entire Earth."
] |
[
"How far off the moon would it take for one to be to not get drawn back to the surface because of gravity?"
] |
[
false
] |
This post...- ...got me thinking. If an astronaut were to jump off mount hadley in the picture, would they just float back down to the ground safely? Actually, that's kind of two different questions because I assume it's a lot further from the surface than mount hedley..? But hey! enlighten me :)
|
[
"There was a similar post about this recently. This may help.",
"http://www.reddit.com/r/askscience/comments/q88lw/how_small_would_the_moon_need_to_be_for_someone/"
] |
[
"Very much farther than any mountain on the moon =P\nThere are a set of points where the gravity of the moon and earth balance exactly. These are the Lagrange points. You can google them. There are actually Lagrange points between the sun and earth as well. Very interesting places to put a refueling space station"
] |
[
"How far off the moon would it take for one to be to not get drawn back to the surface because of gravity? ",
". With no velocity, no distance is great enough to avoid falling back. With enough velocity, the surface is high enough to assure no return to the surface."
] |
[
"I've often heard that leaving your cellphone plugged into a charger even though it's fully charged is bad for its battery life. Is this true? What about for laptops?"
] |
[
false
] |
Or is this something that only happened with old battery technology? Most people I know leave their laptop and cellphone charging overnight even if it's fully charged.
|
[
"Some companies don't design this into a system.",
"Lithium ion batteries ",
" overcharge protection because overcharging can cause thermal runaway, so I don't know what sort of laptops won't have this feature. Are there many laptops that don't run on lithium ion batteries?"
] |
[
"What I mean is that some companies don't utilize advanced battery protective features.",
"It's impossible. Either you terminate the charge early (and in addition have better battery life when measures in charge-discharge cycles) or you have to switch into the constant voltage/delta I mode to \"top\" the battery. When lithium battery is overcharged it starts to get really hot and then blows up. There is no middle ground."
] |
[
"There two ways to technically do it.",
"1) Charge the battery. When full, run off battery until X% discharged. Repeat.",
"\n2) Charge the battery. Bypass the battery.",
"Some older laptops used (1), which burns charge cycles and is generally not good. The better solution is (2)."
] |
[
"Zeno's Paradox"
] |
[
false
] |
[deleted]
|
[
"Put simply, just because there are infinite points to reach before reaching a key, that doesn't mean that reaching all of them will take infinite time. This is because while there are infinite points, they are also infinitely close to each other.",
"Wikipedia",
" has copious links to various historical and current answers to this question."
] |
[
"In the same way that you are able to move at all, given that between every point that you could choose and your finger, there are always infinitely many points.",
"If space isn't discrete. It is unknown if space is discrete, but the assumption is that it is continuous."
] |
[
"Numberphile has a great video about this: ",
"Zeno's paradox"
] |
[
"Why do LCD monitors have fixed refresh rates?"
] |
[
false
] |
Why wouldn't an lcd monitor just be able to draw at whatever rate the image data is coming in at?
|
[
"This is an appropriate question for askscience.",
"Anyways, a fixed refresh rate makes sense for LCDs. They hold their images between refreshes, so they don't \"flicker\" like CRTs do. You want the entire LCD screen to refresh at the same time, to eliminate \"tearing\" of the image, but you don't know exactly how fast the image will be coming it. So the solution was to create a maximum frame rate, and to always refresh at that rate.",
"A variable refresh rate wouldn't have any real advantages, except for possibly very minor energy savings."
] |
[
"Why not? It's along the same lines as \"does whitening tooth paste really work?\". Already the majority of questions in this subreddit are physics specific."
] |
[
"While I understand where you're coming from, I assume that there are engineers that are able to tell you the ",
" behind why LCD's currently do not (or can not) draw whatever rate the image is coming into. There are a number of other questions on ",
"/r/askscience",
" that I wouldn't call strictly science; but they have received a number of helpful replies that answer their questions through science, even though the question wasn't asked in such of a way.",
"Also, I don't know of many manuals that explain the why the company decided to do such a thing. I'm assuming its fairly rare."
] |
[
"Is it possible to get yourself sick again by drinking out of the same water bottle you had drank from when you were sick?"
] |
[
false
] |
My roommate could be trolling me, he got me thinking it was possible, but it sounds retarded.
|
[
"If you get sick your adaptive immune system will build antibodies to that sickness antigen, if you are exposed to the same germs after your immune response to that same germ is started you can get infected but your body will be much much quicker in helping you"
] |
[
"Chances are if you were sick and drank from a bottle by the time you were better again any bacteria etc that was left on the bottle will be long dead. "
] |
[
"Well, I wasn't going to post since I didn't have any sources handy, but what is already here seems no better, so:",
"Although it is possible, it is quite unlikely. Most bacteria do not survive long outside of a nutrient rich environment (like you!) and someone correct me if I'm wrong, but I think viruses also tend to degrade with time. Assuming I am correct about the virus decay then you are pretty safe.",
"What would have to happen for you to reinfect yourself is for enough of the virus or bacteria to survive to infect you for longer than you had extra antibodies to fight them off. Basically, when you fight off a disease successfully you are temporarily vaccinated against it. ",
"If the \"germ\" lasts longer than the \"vaccination\" sure, it could happen, but if you are talking about real-world senerios, you should be okay. ",
"If you had something really serious, I wouldn't risk it anyway though. Or if you have a weakened immune system. "
] |
[
"Could a piece of decaying radioactive material, properly contained in lead to make it's rad levels safe for humans, be used to heat eg. a house for many years, if placed in the floor?"
] |
[
false
] |
I've heard that decaying radioactive material creates heat. I'm not sure if this requires a controlled reaction or not (ie. in a reactor core), or whether heat output could cause criminality if something generating it was sealed in lead. Does AskScience know why this has never been tried? Is it the radiation problems, nobody would want one in their house, or something else?
|
[
"Sure, The plan you describe would work wonderfully, but there are some things to keep in mind.",
"First, the actual amount of heat generated would either be very little, but last a long time, or the opposite, with a great amount of heat being produced, but it will wane quickly.",
"The radiation would not cause any problems. You could either pick an isotope that only emits alpha and beta particles, which can be stopped quite easily, or use very thick lead. (if you choose the alpha/beta, make sure to pick isotopes with decay products that only produce alphas and betas as well)",
"Science has done this, if you open up your scenario a bit. Many space missions have used ",
"RTGs",
" to power their electronics and to heat up the equipment that doesn't like to be frozen solid. The best example of this is the recent Mars rover, Curiosity."
] |
[
"The heat is generated by radioactive decay. It is an uncontrollable physical breakdown of a radioactive isotope. No special reactions are required, other than whatever reaction you use to create the original radioactive material you are going to use in the first place. Your basic idea is sound in premise, but here are some issues to actually doing this in practice, even if shielding is involved.",
"First is licensing of nuclear material. For a radioisotope to release enough heat for it to warm a floor, you require a special nuclear material license from the NRC. Now if a company properly designed and got a license from the NRC, it could be generally licensed (similar to glow in the dark tritium exit signs), but that would require showing that it would not fail and break during reasonable postulated events such as fire or seismic in such a way that it would release its radioactive material or contaminate the area.",
"Second issue is the amount of material required. If you look at Curiosity, it generates just over the power required to run a single 100W standard light bulb, and its RTG is rather large in size. In order to generate thermal energies required to keep a floor warm or heat a house you need a large amount of shielding in addition to whatever the NRC requires (or whatever country you are in), in addition to the amount of special nuclear material to generate that heat. It would be very cost prohibitive.",
"And the third big issue I can think of off the top of my head is you have no way to 'turn it off'. Radioactive decay is uncontrollable. If we could control it, Fukushima and Three Mile Island would not have been issues as both plants had meltdowns due to radioactive decay. In fact, if we could control radioactive decay, nuclear power would have no real downsides as we could simply turn off the radiation and heat being released by nuclear waste, and it would no longer require special casks or fuel to cool and and shield it. All that aside, during summer time you have no way to turn the heat off other than to move the material to another location, which, if its installed all under your floor, is not going to be a trivial thing to do.",
"Anyways, cool idea and great question, and who knows maybe in a few hundred years when the war with robots scorches the atmosphere and we need another heating source, we'll use this (in fact, in the Matrix the 'heat source' for the human city Zion is geothermal, with the heat coming from the radioactive decay of elements in the earth's core). But I personally don't forsee us using this during the fossil fuel age."
] |
[
"\"its\""
] |
[
"Why do hear little clickity clacks for a few minutes after I turn off my car from a long drive?"
] |
[
false
] | null |
[
"I'm not sure exactly which \"clickity clacks\" you are referring to, but it is most likely metal that was hot from the engine running, but is now cooling down and contracting. As metal contracts (or expands) it can make noises -- similar to the \"clacking\" that an electric baseboard radiator in your home will make when it is turned on and just starting to warm up (or cool down)."
] |
[
"That's possible, but most likely it's the exhaust system, since it gets comparatively hottest."
] |
[
"Asked my mechanic once, this was it, the exhaust system cooling causes those pings, clicks, and clacks. "
] |
[
"Metal melted to liquid, then what?"
] |
[
false
] |
So I know when most metals (Iron, Aluminum, Tin) are heated to a certain temperature they melt and become liquid, but what happens if we keep heating the liquid? Does it boil? Does it evaporate? If it does become a gas, what happens when we continue to heat that?
|
[
"Metals behave like all other matter. Like ice, they will melt, then boil. ",
"If the metal is an alloy or compound of some other metals, first, that will break down (if it hasn't already) and then the metal will ionize. Ionization means that the electrons become disassociated from their parent nuclei because they have too much energy relative to their parent nuclei to remain bound to them electrically. "
] |
[
"So metals melt, vaporize, and ionize like any other materials, this much is clear.",
"However, I'm not sure what you mean by \"break down\" for alloys. The phase diagram of most alloys includes a homogeneous liquid phase for all compositions (e.g., ",
"PtAl alloy",
", ",
"parent article",
"). That is, the alloy melts to a single liquid alloy. (Many alloys with mercury, called ",
"amalgams",
", are liquids.) ",
"In my ten minutes of looking I haven't found an alloy phase diagram which includes a vapor phase, but nanoparticles of alloys can be prepared by heating a powder of the bulk alloy with a laser until it vaporizes, then cooling the vapor in a controlled fashion (LVCC, ",
"source",
"; ",
"pdf",
").",
"Neglecting the ionization result of extreme heating, I'm not sure that \"break down\" is necessarily correct for an alloy. It may melt, vaporize, and condense like a pure metal."
] |
[
"Here is a video demonstrating that, using UV light to cast a shadow from the vapor.",
"https://www.youtube.com/watch?v=lpZF88fqrl8"
] |
[
"Is wind chill convection or conduction?"
] |
[
false
] |
I always thought wind chill was the motion of the air against skin that caused increased heat loss, is this not an effect at all? Is this also conduction? From what I understand now wind chill is caused by the wind disrupting any insulating pocket of air, is this the case?
|
[
"If anything the motion of the air rubbing against your skin is heating you. Just not enough to make up for the steeper temperature gradient it is creating. When there's no wind you build a cocoon of hot air that insulates you better than your own skin. If it's windy you keep heating cold air since it's constantly replaced with newer cold air. ",
"With no wind you could take convection into account. If you're naked, the hot air will rise and colder air will fall on you basically. That's why having a good blanket is nice."
] |
[
"Convection (in physics/fluid dynamics, not meteorology) is typically defined as heat transfer caused by moving liquids/gasses. This is sometimes split in free/forced convection, with forced convection indicating that the movement of the fluid is caused by an external force (wind, a fan, etc..) Conduction is the heat transfer that takes place in solids and stationary liquids/gasses. Thus, wind-chill is mainly convection, although things like increased evaporation and such also play a role."
] |
[
"So, the heat is lost via convection because the air is moving, or the air is moving because of convection?"
] |
[
"Why is candle wax transparent when melted but opaque when cool."
] |
[
false
] | null |
[
"I has to do with crystallization in the wax. When solid, the long alkyl chains align and crystallize, and these crystallites scatter light which leads to higher opacity. When heated, the crystallites melt, and the resulting amorphous liquid no longer scatters light."
] |
[
"I wonder if it's similar to tap water being clear as liquid yet cloudy as ice?"
] |
[
"I suspect you're getting downvotes because you didn't contribute directly to the question, just offered a potential analogous situation. I think it's a fair point though. "
] |
[
"Why do moles grow such long hairs?"
] |
[
false
] |
Some moles grow hairs much longer than the surrounding area, why?
|
[
"They're called terminal hairs and we don't really know why they grow longer than normal hairs. They do appear to be influenced by hormones during puberty; so it could be that the mole hair follicle has a slightly different base level of receptors, or interacts differently with the bodies normal hormone levels."
] |
[
"Also to note, if your mole has hairs in it, then suddenly loses the hairs it is worth getting that mole checked. ",
"A process that kills hairs in a mole can be an early sign of a melanoma, as the melanoma damages the surrounding normal tissue architecture, killing the hairs."
] |
[
"Why are they called 'terminal'? That doesn't sound very nice."
] |
[
"If the earth 'wobbles' on it's axis, do geosynchronous orbits 'wobble' with it?"
] |
[
false
] |
Do sattelites in GS orbit follow a flat orbit, or do they wobble with the tilt of the earth? Would this have implications for a possible space elevator?
|
[
"The \"wobble\" that occurs of Earth's axis is so slow (over the course of 10s of thousands of years) that it shouldn't affect the geosynchronous orbits in any meaningful way. That being said, yes - over the course of those 10s of thousands of years, the orbits will shift to maintain their geosynchronous positioning."
] |
[
"You have to remember that the satellites are already being affected by so many other forces and are constantly having to be repositioned within a box with a 70km side length."
] |
[
"I was thinking of the \"Chandler Wobble\" ",
"http://en.wikipedia.org/wiki/Chandler_wobble",
"\nwith a period of 7 years - even though it's small, the distance to the GS orbital would make for a pretty big arc, no?"
] |
[
"Can you \"overdose\" on lemon?"
] |
[
false
] | null |
[
"We don't offer diet advice. If you have concerns, you need to speak to a medical professional."
] |
[
"It's not a diet. I don't need help on diet. I think you made that assumption because I've used words \"detox\" and had daily plan. ",
"Can lemon juice in larger quantities have negative impact on your body?",
"What would happen if I ate 3-5 lemons for a month?",
"Would eating 5 lemons a day for an extended period of time acidify my stomach?",
"What are the the effects of overdose and underdose of citrus acids and vitamin C?",
"Overuse of acids from fruits (like lemon) can be bad for your teeth. Can it also be bad for your digistive system?",
"Which do ",
" as having nothing to do with diet? "
] |
[
"\"Diet\" by definition is what you eat, and yes, this is about diet. We don't offer diet or health advice. If you're asking \"Is this bad for me?\" then it's not appropriate for ",
"/r/AskScience",
". Please feel free to read the subreddit rules before submitting. "
] |
[
"Why are vegetables (mainly green ones) supposed to be good for you?"
] |
[
false
] |
Everyone is always saying how healthy green vegetables are for you, but what do they contain that could make them healthy? Usually, people will say vitamins, but if you already take a multivitamin that covers your needs, would extra vitamins and minerals in vegetables provide any extra benefit? Excluding fiber, it seems like they are mostly devoid of macro-nutrients like carbs, proteins, and lipids.
|
[
"1) a multi vitamin may be a start, but it isn't all your nutritional needs; infact you might just be wasting most of it making your piss more expensive",
"2) they are high in folic acid, and colored veggies usually are a sign of anti oxidants",
"3) every cell everywhere has a lipid bilayer, so there will still be lipids in plants, as well proteins make up much of what things are."
] |
[
"I understand that the plants are made up of proteins and lipids but I think they may be indigestible: the nutrition facts for celery (",
"http://en.wikipedia.org/wiki/Celery",
") and broccoli(",
"http://en.wikipedia.org/wiki/Broccoli",
") show very negligible amounts of those macronutrients per weight. I believe folic acid is vitamin B, and I see that not every daily value's worth of vitamins is covered by multivitamins (",
"http://www.biossential.com/images/multissentials/multissentials-supplement-facts.jpg",
"). I guess my real question is what (besides fiber) is there in green vegetables that you can't get in multivitamins."
] |
[
"(1) Fiber.",
"(2) Vitamins and Minerals. You could get these from multivitamins, but why would you pick the ",
" delicious way of getting these things? As highintensitycanada mentioned, a single multivitamin a day might not cover your needs.",
"(3) Antioxidants. Again, could get some from multivitamins.",
"Really, though, some of the benefit of veggies is from what they ",
". One of the signals telling someone they're full is how stretching of the stomach. Better for a big eater to feel full after a salad+philly cheesesteak, than to need two cheesesteaks to feel full. Generally, the more veggies consumed, the less salt and fewer calories consumed.",
".",
"As an aside, let me pick at the phrasing of your question a bit, ",
"Everyone is always saying how healthy green vegetables are for you, but what do they contain that could make them healthy?",
"Well, it's more that people carefully observed the world, and found that you'll be healthier if you eat vegetables than if not. It's based on this that people looked more carefully at ",
" this was the case, and discovered that there was such a thing as vitamins. The history and discovery of vitamin C is a good example ",
"(and the wikipedia article is a short, fun read)",
". The way you asked the question (and maybe I'm just reading too much into it), seems like you won't believe that veggies are healthy unless someone can explain from the bottom-up, why. It's odd since the science went in exactly the opposite direction: You split people into two groups, and feed one of them veggies. Which group is healthier at the end? The veggie group. This (with enough replications of that sort of experiment, observations of restricted diets, like aboard ships in the 1700's which lead to inferences about Vit.C, etc.) closed the question of \"Are veggies good for you?\" with a \"Yes!\". It's still an interesting topic as to ",
", of course, but (for instance) you shouldn't change your diet based on the (in)ability of internet strangers to give you a good answer."
] |
[
"Why do we get headaches for so many different ailments? Why is it such a common occurrence?"
] |
[
false
] | null |
[
"headache is pain or discomfort in the head or face. Headaches vary greatly in terms of the location and intensity of the pain, and how often the headaches occur. The brain tissue doesn’t have pain-sensitive nerve fibers and doesn’t feel pain. But, other parts of the head can be responsible for a headache including:",
"A network of nerves that extends over the scalp",
"Certain nerves in the face, mouth, and throat",
"Muscles of the head, neck, and shoulders",
"Blood vessels found along the surface and at the base of the brain"
] |
[
"Well exactly my point. Why is it always a headache and not something more clear of \"I need more fluids\" or \"I need caffeine\" type message (obviously not a typed message clarity but just something a bit more defined than headache)"
] |
[
"Well exactly my point. Why is it always a headache and not something more clear of \"I need more fluids\" or \"I need caffeine\" type message (obviously not a typed message clarity but just something a bit more defined than headache)"
] |
[
"Why do we use the 12-number system when speaking of time?"
] |
[
false
] | null |
[
"Babylonian math",
", which used base 60. We also have 360 degrees in a circle to thank for that."
] |
[
"As far as benefits, the only one I can think of is it is easier to break up 60 or 12 into thirds than any decimal based systems. If an hour were split into 100 \"deciminutes\" some of the results would not be as nice as our traditional 60 minute system.",
"1/2 hour = 30 minutes or 50 deciminutes",
"1/3 hour = 20 minutes or 33.33333... deciminutes",
"1/4 hour = 15 minutes or 25 deciminutes",
"1/5 hour = 12 minutes or 20 deciminutes",
"1/6 hour = 10 minutes or 16.66666... deciminutes"
] |
[
"The Sumerians used Base 12 to count because they could use the three segments of the four fingers of a hand. That's most likely how they got 12, and originally only counted daylight hours. There's also conjecture that 12 comes from the number of lunar cycles in a year. The Egyptians divided the daylight into 10 hours and then added one at each end of twilight, and marked their sundials accordingly. I believe JimboMonkey1234's Base 60 explains how hours were subdivided into minutes and correspondingly, seconds as technology allowed the ability to more accurately measure the passage of time.",
"The simple answer as to why we don't use decimal time or any other funny system is just because, \"we're used to it.\"",
"Edit...forgot to add, it was the Romans that most likely gave us two sets of 12 hours instead of using a single set of 24, although they used to count ",
" to noon instead of up and resetting."
] |
[
"Why is the time a medicine stays in your system measured in units of half-life?"
] |
[
false
] |
It seems strange to me that medicine is measure in the time it takes half of it to leave your system. Would it not be better to just say that a medicine will be completely out of your system in 20 hours than saying that half will be out in 10? Is it not roughly linear like that?
|
[
"Because when there is less medicine left, it takes longer to leave/dissipate. ",
"Think of it like a large tank of water with a hole at the bottom. The water will start to flow out of the hole pretty quick at first and then it would gradually slow down because less water above the hole would mean less pressure to push it out. "
] |
[
"Because when there is less medicine left, it takes longer to leave/dissipate. ",
"Think of it like a large tank of water with a hole at the bottom. The water will start to flow out of the hole pretty quick at first and then it would gradually slow down because less water above the hole would mean less pressure to push it out. "
] |
[
"Because when there is less medicine left, it takes longer to leave/dissipate. ",
"Think of it like a large tank of water with a hole at the bottom. The water will start to flow out of the hole pretty quick at first and then it would gradually slow down because less water above the hole would mean less pressure to push it out. "
] |
[
"I need some help applying to graduate schools"
] |
[
false
] |
[deleted]
|
[
"Go to the school's site and look at all the professors research interests, that should give you a guide to what they skew towards.",
"When I applied to grad schools, I basically started with the US News top 50 list, crossed off schools in places I wouldn't want to go, and then looked at the research interests listed for the professors and put how many profs in each field in a spread sheet. Then I chose a bunch, well spread out in rank and whose research interests fit my own.",
"You could also ask your professors, they were helpful in insuring I had a proper ranking spread and offered insights into the departments you wouldn't get by looking at numbers (eg yeah the geometry group at university of X is small, but its got Prof. Y, who is all you really need, etc)",
"If you don't already know about it, ",
"http://forum.thegradcafe.com/",
" is a good grad school related forum."
] |
[
"I'm a PhD student in Australia (bioinformatics), and this seems quite different to how it seems to be done down here. Typically here, you'll contact the potential professor/research group leaders directly and talk/email/coffee with them, before any thought of applying via the university. We have no coursework in PhDs though, and many fewer universities.",
"I think it bears remembering though, that your relationship with your supervisor is the most important thing about choosing a lab - more so than the exact research project suggested. It's likely this will change a fair bit after you do all of your background reading/lit. review anyway.",
"Ask existing PhD students what the potential supervisor is like! They'll generally be bitter enough to tell the truth... ;)"
] |
[
"For mathematics, there aren't labs that you have to choose as an entering student, this could be different for the OP's case, which would mean that contacting professors is much more important. I didn't contact any professors at my chosen universities before I applied anywhere, for better or for worse."
] |
[
"Can you know the age of a single atom?"
] |
[
false
] |
I know you can estimate the age of many objects by looking at it's carbon 13 ratio. But can you know the age of a single atom? is it easier for larger atoms such as gold?
|
[
"Nope. Atoms are indistinguishable from one another. Two C-13 atoms look the exact same. Even assuming you know the decay constant exactly, it only means you have a knowledge of the likelihood of decay. Assume you have a single U-238 atom. It has a half life of 4.5 billion years. How would you go about measuring its age? All we know is that a sample will have half of the atoms decay within 4.5 billion years on average. With very small samples dominated by Poisson statistics, who knows. Maybe all will decay before 4.5 billion years, or maybe none will. You cannot tell the age of a single atom. "
] |
[
"It doesn't always exist in a superposition. The wave function does collapse. You can say there are two atoms if they are not in a superposition. "
] |
[
"I was under the impression that under quantum effects, atoms don't even have identities. That is, that one cannot say \"this atom\" or \"that atom\" as doing so really doesn't make sense at a quantum level.",
"Is that correct? If so, could you elaborate on that a bit?"
] |
[
"What are the effects of adding rock salt to a cooler full of ice?"
] |
[
false
] |
Background: I know some fishermen who do this, because it melts some of the ice, and the resulting liquid in there is as cold as the ice, and it quickly freezes the fish placed in the cooler. These same fishermen claim that the resulting slurry stays cold much LONGER than just a cooler of ice without the salt. They've done no experiments with timing it, they just make the claim. I understand the salt melting the ice, and the resulting slurry being partially liquid and the liquid being as cold as the solid. What I don't understand, or even BELIEVE, without some explanation is that he mass would stay cool LONGER in one form or another. It's as if they're saying that by adding salt, they've removed even more energy (heat) from the mass. Sounds wrong to me. Am I missing something?
|
[
"Ice in equilibrium with (pure) water will stay at 0 degrees C. No higher and no lower. If you add salt to the water, the equilibrium temperature will decrease. So a brine ice mixture can be lowered below 0 degrees C. This lower temperature system would \"stay cool longer\" because it is colder.",
"It's as if they're saying that by adding salt, they've removed even more energy (heat) from the mass",
"Melting is an endothermic process. This process will \"remove\" heat via bond breaking in the ice. So by adding salt to the water and lowering the equilibrium temperature, the system will respond by melting some of the ice. This consumes energy and lowers the temperature until equilibrium temperature is reached.",
"EDIT: To clarify a misconception, an observed decrease in temperature does not equate to the \"removal of energy from the system\" (when simply adding salt). A decrease in temperature can occur when there is a transfer of kinetic energy to potential (when ice melts endothermically). Regardless, in the water-ice system the temperature is not actually proportional to kinetic energy. That is only the case in an ideal gas."
] |
[
"It's the transfer of heat that's important.",
"The goal is to transfer heat away from the fish.",
"In the cooler, the fish is part of \"the environment\" that the melting ice will transfer heat from. ",
"The materials that the cooler is made of aren't good for transferring heat and there's not much else in the cooler except for a bit of air. So most of the heat must come from the fish. If the cooler were a hypothetically perfect insulator and a vacuum, then all the heat would come from the fish.",
"If the cooler were a hypothetically perfect insulator and a vacuum, then the ice would not have anything to get heat from and it could stay the same coldness forever.",
"It's really intuitive for us to think of mixing temperatures: half a glass of cold water plus half a glass of hot water equals half a glass of warm water. But that's not the concept we're dealing with so try to put it out of your mind.",
"Don't think of the ice like a bit of a mooch. If it were a mooch, it would take a little bit of of the fish's heat in a similar to the way the two glasses share their heat and both come out warm... or like a friend who goes out for pizza with you but doesn't pay their share but still eats a normal amount of pizza.",
"Instead, you need to remember that phase change from solid to liquid is really very expensive in terms of the amount of heat it takes. So think of the ice as water that is heavily indebted to it's environment. On its own, water will pay off its big loan slowly as it gradually gathers heat.",
"And then think of salt as the loan shark who shows up at water's door with a baseball bat and says \"Look at you walking around dressed as a solid! You're paying off all that debt now!\" Salt forces ice to pay back the solid debt suddenly. So water looks around and there's not much heat in the cooler except for fish.",
"And fish says, \"How much do you owe anyway? I'll give you what I've got since there's no other option.\" But the amount is way more than the fish expected. But the fish has good credit and pays off the loan in full anyway. But this puts the fish in debt. It now has even less heat than the water. The fish will be colder than freezing. It will be in deep heat debt.",
"The fish will cool more suddenly and will freeze more deeply with this method (and as a result of the fish cooling more deeply, it will stay cold longer.",
"It's all counterintuitive unless you get your head around the idea of phase change forcing outsized debt on the fish."
] |
[
"By adding salt to the water you are increasing the number of dissolved particles in the water (this is quantitated as the molality of the solution). This decreases the freezing point of water and therefore the temperature of the ice/water mixture because it will always equilibrate at the freezing point of water as long as there is both ice and water present in the mixture. This is known as \"freezing point depression\"."
] |
[
"If an astronaut travel in a spaceship near the speed of light for one year. Because of the speed, the time inside the ship has only been one hour. How much cosmic radiation has the astronaut and the ship been bombarded? Is it one year or one hour?"
] |
[
false
] | null |
[
"You get the full year's worth of radiation.",
"From an outside point of view, we see that time is dilated and the astronaut is moving very slowly inside their spaceship. But we see the spaceship take a full year to reach its destination, and gets hit by all this radiation along the way.",
"From the astronaut's point of view, there is another effect - length contraction. From their point of view, the reason it only takes an hour to reach the destination is because the distance has shrunk down by a huge amount. So, from the astronaut's point of view, they still have to move through the same amount of \"stuff\" - interstellar gas, radiation, whatever - it's just that this \"stuff\" is packed really close together, and the astronaut hits it all really quickly.",
"Of course, it's not all that simple - you have to deal with redshift and all that - but it does often work out that length contraction and time dilation basically cancel out, and that can allow different reference frames to not contradict each other."
] |
[
"You get the full year's worth of radiation.",
"Wouldn't it be a lot more? If I get hit by distant starlight, I don't care much. If I get hit by starlight that's blue-shifted into gamma-rays - that's not very healthy.",
"So the physiological effects should be a lot more than just the accumulation of the year's worth of radiation.",
"Edit: Here's a cool video by Carl Sagan which should answer many questions I got:\n",
"https://www.youtube.com/watch?v=lPoGVP-wZv8&t=202s"
] |
[
"Right - like I said, it's not quite as simple as my first explanation implies."
] |
[
"Why is Coulomb's law so close to inverse square?"
] |
[
false
] |
I was reading a physics text recently that mentioned that early on, experiments showed that Coulomb's law was inverse square to a very high degree of accuracy. I'm wondering why the power would be so close to 2, and if there is any deeper theoretical justification for that. Does QED offer an explanation of why Coulomb's law is a good approximation, or perhaps correct the value?
|
[
"Just in terms of the experimental limits, the results don't suggest that the force law is something very close to two but slightly different, but rather that it is experimentally consistent with two to within a certain accuracy (",
"~10",
"). The search for a deviation from two yields a null result."
] |
[
"At very short distances, the force law is no longer simply 1/r",
" due to charge screening effects a/k/a scaling of the coupling constant."
] |
[
"fishfly is correct. One needs to add to Git's argument two facts:",
"Then the argument works. These facts are important, because the weak nuclear force violates the first, and the strong nuclear force (QCD) violates the second."
] |
[
"Why do different species of birds sound different? Is it learned or is it to do with their physical makeup?"
] |
[
false
] | null |
[
"for nearly all bird the sound of their tweeting is genetically determined. a good example is the cuckoo... it is raised by non related foster parents but tweet in their typickal cuckoo-way. \nsome species can adapt and learn new sounds. eg. parrots, ravens, starling, etc. can learn to talk. there is also a bird that mimicks sounds from its surrounding to attract females. see ",
"http://www.youtube.com/watch?v=bfGImXX-sDs"
] |
[
"it's a mixture of both. the vocal organ of birds is different then ours: we mammals use vocal chords whereas birds have the so called syrinx: its a hollow organ at the base of the trachea. sound is modulated by vibrations of the walls of the syrinx (called membrana tympaniformis) and the pessulus (sits at the forking of the trachea. check out wikipedia for a schematic picture and a more detailled description. the anatomy give the limits of the sound while the genetic program tells the bird how to use the syrinx."
] |
[
"Thanks for the reply! Do the genetics determine the bird's physical makeup or the way it uses the same parts as others? If that makes any sense"
] |
[
"Does anyone have a good, intuitive explanation of what the word entropy means?"
] |
[
false
] |
I know that it's related to the amount of information needed to define a system, but I can't find a satisfying definition. From Wikipedia: "...entropy is defined as the amount of additional information needed to specify the exact physical state of a system, given its thermodynamic specification." What does it mean by 'given its thermodynamic specification'? What is entropy and why is it higher in more disordered systems?
|
[
"This is the purely thermodynamic point of view :",
"'Given its thermodynamics' implies that quantities like pressure, volume and total internal energy of the system are known. However, this does not constitute complete knowledge of the system because thermodynamic systems are generally composed of 10",
" atoms or so and there are many combinations of the position and velocities of these atoms that will give you the same set of thermodynamics variables.",
"This gives you some freedom in choosing the exact state of a system given the thermodynamic variables, because you are free to play around with a huge set of variables. Alternatively, given only the thermodynamic variables, you are ignorant of the states of this vast number of atoms, and entropy is a measure of this ignorance.",
"For example : if you specify a very low temperature and pressure, the range of velocities you can assign to the atoms is constrained and you end up with fewer variables to choose from, leaving you with a low entropy. At larger temperatures, you have a lot more variables to play with, implying larger entropy.",
"This way of saying this is flawed though, because entropy is a more basic quantity than temperature. You first measure the freedom you have in assigning non-thermodynamic variables and use that a measure of temperature.",
"Imagine you have a barrel filled with 10",
" red balls and a similarly large number of serial numbered boxes. Given the constraint that on an average, each box contains three balls, how many ways are there of filling up the boxes ? Lets call this number N1. ",
"Assume now that you add a bunch of blue balls to the mix. You end up with a larger number of distinct ball configurations that satisfies the three balls on an average criterion. This is because you can do things like create new configurations by swapping a blue and a red ball between two boxes.",
"Disorder is any lack of uniformity. Decreasing uniformity increases the number of possible configurations. Simple example :",
"Lets say you have two identical electrons and you know the velocities are v1 and v2. All you can do is assign v1 to one and v2 to the other and be done with it, just 1 configuration possible. ",
"You now discover that they belong to atoms located on opposite sides of a wall. One of them on the right (R) and the other on the left (L). This lets you have two configurations: (L:v1,R:v2) and R:v1,L:v2).",
"The first part is equal to both electrons being on the same side of the wall. Making them have distinct positions 'creates disorder' and opens up more configurations. More configurations = more ignorance. More ignorance = more entropy.",
"Say you have two systems that you are totally ignorant about, one has 10 and the other has 100 configurations. If someone asked you at gunpoint to predict the configurations that they are in, the best you can do is guess. The probability that your guess works is 1/10 in the first case and 1/100 in the second. Obviously, the first guess is 'better' than the second because its more likely to be correct.",
"Entropy is a measure of how bad our ability is guess correctly the state of a unknown system. The larger the set of configurations of the system, the worse our guess will be."
] |
[
"I don't agree with Marsupial's need to cite sources in this case. This concept is basic and found in an introductory text to physics or thermodynamics. It would actually be somewhat silly to find a random undergrad text just to cite it as a source for obvious common knowledge.",
"An unpaneled response is perfectly well distinguishable from speculation, especially for a basic concept. One simply needs to determine if the response is correct."
] |
[
"Entropy is a way of measuring how reversible a process is. If a process is fully reversible without external energy input then it creates no entropy. If it is not reversible and requires energy input (or more energy than can be extracted from the original process) to reset to its inital state then it creates entropy.",
"EDIT: I didn't like the example I put here. Does someone have a good comparison of a reversible and irreversible process?",
"So, if a system is disordered then it has undergone many irreversible processes i.e. it was once in order and then things happened to it as time passed, and not all of those were reversible, therefore it is now more disordered (aka the entropy has increased)."
] |
[
"Are there species with more than 2 sexes?"
] |
[
false
] |
In humans the X and Y chromosomes decides the biological sex. Are there any species where theres more than 2? I found previous discussions where birds were said to have 4 genders and 2 sexes, but I would guess its still only 2 chromosomes at play. I wanted to know if there can be more.
|
[
"In the evolutionary literature, \"sexes\" are defined in terms of different sized gametes (egg/sperm). There are many forms that unequal gametes can take, but we don't observe a third \"intermediate\" gamete in any species. Presumably, sperm and eggs are well optimized for their differing roles/benefits (mobility and cheap production vs. providing energy and structures to the embryo), and a medium-sized one would have the costs of both without most of the benefits.",
"However fungi, which have equal-sized gametes (though they are not really what you'd normally consider \"gametes\") can have many ",
"mating types",
", determined by one or more genes. In species with two mating types, + and - are often used instead of female and male, to denote the DNA receiver and donor, respectively. However, some species have many mating types, and only need to find a fungus with a different type than their own (at each mating type gene).",
"For example, the mushroom ",
" has two mating type genes, with one having over 300 possibilities and the other 64. This leads to a documented 23,328 distinct mating types. A ",
" individual would be capable of reproducing with just under 23,000 of these types!"
] |
[
"Very true, but those are intersex conditions which are often pathological and don't result in a discrete and distinct sexual phenotype. "
] |
[
"Are you talking about ZW-sex determination? Not all birds are ZW and also a few other organisms such as insects, some lizards, etc. are also ZW-determined. While it is true that ZW does have two main sex chromosomes at play, do not confuse the number of chromosomes with the number of discrete sexes. For example, the platypus has 10 or so sex chromosomes. Also, of course there are XY species that can have three sex chromosomes (although this is often considered a disorder).",
"The only known types of sex-differentiation are the XY, ZW, UV, and haplodiploidy exhibited by insects. I also believe some lizards are parthenogenic. Of course there are environmental factors as well that participate in sex determination, mainly temperature. In addition, whether or not you consider hermaphroditism a \"third\" sex is mainly an issue of categorization. Gender is an entirely different matter."
] |
[
"We are scientists from the Society of Vertebrate Paleontology coming to you from our 75th annual meeting. We study fossils. Ask Us Anything!"
] |
[
false
] |
Hello AskScience! We are members of the . We study fossil fish, mammals, amphibians, and reptiles — anything with a backbone! Our research includes how these organisms lived, how they were affected by environmental change like a changing climate, how they're related, and much more. You can learn more about SVP in or . We're at our 75th Annual Meeting in Dallas, Texas and we're here to answer your questions. Joining us are: : Dr. Adams is the Curator of Paleontology and Geology at the in San Antonio, Texas. He specializes in the diversity and biogeography of crocodile relatives in Texas. : Dr. Pritchard studies the early history of the reptiles that gave rise to lizards, dinosaurs, crocodiles and birds. Mr. Borths works on the evolution of carnivorous mammals and African ecosystems. He is a postdoctoral researcher at Ohio University. Find them on Twitter @PastTimePaleo. : Dr. Drumheller is a paleontologist at the University of Tennessee whose research focuses on the processes of fossilization, evolution, and biology, of crocodiles and their relatives, including . : Dr. Gold studies brain evolution in relation to the acquisition of flight in dinosaurs. She is a postdoctoral researcher at Stony Brook University. : Jess studies alligatorine systematics, morphology, biogeography, and ecology as well as dicynodont morphology and extinction survival. She is working on a dissertation at the University of Iowa and will soon be joining the staff at the University of California, Riverside as a museum scientist. : Caitlin is a current graduate student at UCLA. She studies the evidence left on bones by mammal behaviors and environments, such as hunting injuries of Ice Age predators. She has also done some sticky experiments with a modern tar pit. : Dr. Wilberg studies the functional morphology of the snouts of crocodiles and their fossils relatives. He is a postdoctoral researcher at Stony Brook University. We will be here at 11am ET/10am Central to answer your questions. See you then!
|
[
"Adam Pritchard - A vehement no and a cautious yes. Ross doesn't seem to spend much time reading about paleontological discoveries, traveling into the field, or engaging in actual research. He's too busily engaged in relationship drama with Rachel to really read much into therapsid evolution.",
"HOWEVER, I distinctly remember an episode where he actually gave a seminar about the importance of CAT scanning to paleontology. This was in the mid-1990s, looong before CT scanning become a standard paleo-tool. So THAT ONE SCENE suggests that Ross was actually ahead of the curve on science!",
"Also, there is a real paleontologist named David Schwimmer. That is all."
] |
[
"100 duck sized horses, because then I might be able to look into growth patterns, natural variation, and all sorts of other things that require a larger dataset. - S. Drumheller"
] |
[
"I could have sworn you went extinct in the Cretaceous... It's good to know you are alive and well. Also, props for being able to type with such tiny forelimbs"
] |
[
"Why is the water clearer in the caribbean than in the Gulf of Mexico?"
] |
[
false
] |
I'm spending my honeymoon in the British Virgin Islands. The water here is absolutely beautiful. It's very clear and you can see very deep. Whenever I spend time on the beaches of the Gulf of Mexico, the water is much darker and you can't see deeper than a few feet at most. Is it simply different plant and animal life? Is it pollution? What is it that makes the waters of the Gulf of Mexico beaches so much darker than the beaches of the Caribbean?
|
[
"The Caribbean is much more nutrient-poor than the Gulf. The Gulf is heavily affected by the nutrient input coming from the Mississippi dumping water filled with nutrients and other particles picked up from traveling over land. The Amazon delta is the same way. There is also less circulation in the Gulf, so the nutrients tend to stay in the gulf. In water with more nutrients in it, there is not only more general crud floating in the water, but also more plankton and other microscopic organisms that are allowed to flourish with the nutrients. In the Caribbean, water is much more nutrient-poor. Any body of water with decent coral populations is nutrient-poor. Since nutrient-rich water is more cloudy, corals, which rely on energy produced from sunlight by their photosynthetic endosymbionts, cannot survive and outcompete algae. The introduction of excess nutrients, often caused by increased runoff due to logging or coastal building, is called eutrophication. It is one of the more prevalent threats to corals. The open ocean is typically crystal clear since it is essentially a nutrient desert. "
] |
[
"Where in the Gulf of Mexico are you referring to?",
"I live in New Orleans and can tell you the silt and mud that comes out of the Mississippi is so vast that it stretches all the way from mid texas to beyond gulf shores so you've got to go a bit beyond that to hit the really clear waters. "
] |
[
"Mainly Gulf Shores. That makes a lot of sense, actually. Thanks!"
] |
[
"Why do we need to postulate the presence of dark matter? Wouldn't unexpected astrophysical phenomena simply indicate that our understanding of gravity in inadequate?"
] |
[
false
] |
It seems to me to be a great jump to postulate the existence of a new type of matter in response to astrophysical observations not lining up with predictions as dictated by current theory. Would not the more parsimonious response be to work on modifying the theory? Do we really need dark matter to explain our observations?
|
[
"People seem inordinately bothered by dark matter. Dark matter is evidence that our understanding of gravity is good, not the other way around.",
"Let me begin with another situation. You hear your doorbell ring, yet when you go to look, there's no one there. Do you suppose that there must be something new electrical force that only shows up in doorbells or do you figure somebody rang the bell and then left?",
"Or imagine you see a star's light showing oscillations in its wavelengths, up a little bit then down a little bit, in a regular pattern. Do you imagine that these particular stars are governed by some new force observed nowhere else in the universe, or do you figure that you've detected the influence of a planet -- which would produce exactly this effect as it orbited the star -- even though you don't have an actual image of the planet? That's exactly how the first exoplanets were discovered.",
"Or imagine you see a loss of energy and momentum in a decay process. Do you imagine energy and momentum conservation should be tossed aside, or do you recognize that there is a particle you've not overtly detected carrying that energy and momentum? That's exactly how the neutrino was discovered.",
"Or imagine you see the stars near the center of our galaxy undergoing elliptical motion around nothing that you can see. Do you suppose there is something wrong in our understanding of motion, or do you conclude that there is a massive object you can't see at the center of our galaxy, around which things are orbiting? You conclude the latter, and have evidence for the black hole at center of the Milky Way.",
"Dark matter is evidence that our understanding of gravity is really, really good. Remember, general relativity has survived a range of tests, from the orbital mechanics of the solar system and tides on Earth all the way up to cosmological behavior of the universe and the merger of black holes. Positing dark matter ",
" the parsimonious approach, because it turns out that we can explain a host of phenomena--the motion of galaxies, the motion of stars within galaxies, gravitational lensing around galaxies, and features of the cosmic microwave background radiation--if there is additional matter that interacts gravitationally but not otherwise (or perhaps also via the weak force).",
"If our models of gravity were wrong, positing dark matter would not be expected give us results consistent with all these quite varied observations. ",
"I'll add that we know that not every particle feels every force -- electrons don't feel the strong force, for example--but every kind of object is subject to gravity. Therefore, there is nothing particularly peculiar about something that does not interact via any force other than gravity. (And, since dark matter may interact via the weak force, that would put it in the same category as the neutrinos, which feel the weak force and gravity, but not the strong or electromagnetic force.)"
] |
[
"We infer the presence of things from their gravitational influence all the time -- the exoplanet and black hole examples were precisely that, and for a great classical example, the presence of Neptune was inferred from deviations in the orbit of Uranus. Which is more natural: that the orbit of Uranus needed a new effect to describe it, or that there was another planet tugging on it?",
"The point is that, yes, there are things that wouldn't behave as we expect without dark matter, but once you put dark matter in, everything fits. What are the odds that what we're missing would exactly mimic the behavior of the gravitational influence of matter but not be matter? "
] |
[
"As a physicist working in a completely different field, I appreciate your answer so much.",
"People tend to forget that everything we measure or experience is generally ",
", but their measurable effect. Even for very ordinary things like when you reach your cup of coffee, you are guiding yourself trusting the knowledge that those electric signals produced in your retina mean something.",
"The existence of dark matter is not less reliable because it is based on a much complex theory rather than your experience. In fact, it completely the opposite because it is based on experimentally verified, peer reviewed studies.",
"Of course it may be wrong. It has happened numerous times. But that's how science is made. ",
" The best we can say is that the present theory explains everything we managed to measure until now."
] |
[
"Why is there so much diversity of life in the ocean, when all \"sea creatures\" are evolving in the same place?"
] |
[
false
] |
There are a ton of different and very diverse species of life in the ocean (jellyfish, sharks, dolphins, seahorses, crabs) but they are all evolving in the same place (correct me if I am wrong). What conditions or variables make them evolve differently?
|
[
"Good question! Let me take a stab at it. It's late, and I'm drunk - so expect this to be scattered slightly.",
"The answer lies in the fact that they inhabit different ",
"ecological niches",
" - essentially, a niche is the role they play in the ecosystem. ",
"Even though all of the life is evolving in the ocean, two parts of the ocean can be dramatically different from another - such as a shoreline vs. deep sea. And just like how two parts of the ocean can be different, the roles that species play can be different.",
"Natural selection is going to try to maximize success for organisms - and if they all evolved to do the exact same thing, they'd have a lot of competition to deal with, so different organisms are going to try to fill different roles in the ecosystem to try to minimize competition and try to maximize success. ",
"Take this for example: (let's pretend organisms get to choose how they evolve)",
"You're a new organism in a pond full of sea sponges. Sea sponges filter feed - they \"suck\" in water and take the nutrients before shooting it back out through their main tube (the ",
"osculum",
" ) ",
"So why wouldn't you just be a sponge like everyone else? The answer is that ",
". Think about it - if you're a sponge, you have to compete with ALL THE OTHER sponges for the finite amount of nutrients in the water.",
"But what if you became a creature that ate the sponges? You wouldn't have to compete with anything for your food! This is why diversity happens - because it is ",
" to be diverse - it allows you to fill new niches and try new strategies. ",
"A crab is adapted to be able to efficiently feed on algae and molluscs, sponges are adapted to efficiently filter feed, sharks are adapted to efficiently be able to prey on other creatures, etc.",
"Let me know if you have any questions."
] |
[
"The ocean is massive and the earth is 70% water. You could ask the same question about the diversity of life on land and consider that evolving in the \"same place\". But in both environments there are many different variables that put selective pressures on the different species that inhabit them. In the ocean, there are temperature, pressure, and light changes as your depth increases. ",
"Think of the ocean as consisting of many layers. The top layers where the sunlight penetrates (called the photic zone) the temperatures are higher and the pressure is much lower. At the bottom of the ocean the sunlight is scattered and it's effects are diminished (called the aphotic zone) causing much lower temperatures and higher pressures. These variations in the environment on such a large scale lead to the diversity of life we see today."
] |
[
"Yeah, so picture you're an organism in an environment that's saturated with those sponges (this probably wouldn't happen either, but baby steps!). ",
"You're a sponge, and you undergo a mutation that makes you have to compete LESS with all the other sponges. You're likely to be more successful than the other sponges in the ocean because you have more food availability now (aka it's not being competed over). ",
"Since that organism is more successful, that mutation will theoretically spread via natural selection until it's no longer beneficial (there is now just as much competition as the other method). This is called ",
"frequency-dependent selection",
", but that's a bit off topic. Just realize that the mutation is successful because it doesn't have to compete as much - but that will change as more organisms do the same thing, so one mutation isn't going to dominate, but instead they'll reach some kind of equilibrium or ",
"evolutionarily stable strategy",
".",
"If another mutation happens that introduces another way to reduce competition, that will proliferate as well. If multiple mutations happen, different splittings will happen - in a few thousand generations you could have 20% using strategy A, 20% using strategy B, and so on for C, D, E. ",
"If a mutation happens in the A group, it could split further.. ",
"5% doing method A1, 5% A2, 5% A3, and so on - you can start to see how the different organisms are splitting - we now have 8 different strategies to try to get food from the 1 we began with. Our diversity has increased!"
] |
[
"How exactly does alcohol induced heart failure cause tiredness and breathlessness?"
] |
[
false
] |
I can't get my head around the exact mechanism for these two symptoms occurring. Is it just because the heart is weakened and therefore less blood is going to the muscles (tiredness?). But with breathlessness there must be an element of the oxygen/carbon dioxide transfer between the lungs. Could someone clarify in as much detail as possible please.
|
[
"I think there are a couple of reasons... As the heart fails, fluid backs up in the lungs. This decreases the volume of airspace available for exchange. In addition, though, this adds to the weight of the lungs and a decrease in its compliance so the work of breathing increases. The latter contributes to the fatigue. Fluid begins to collect in other spaces (legs, etc.) that can make movement more difficult. I suspect there is also a psychological contribution to fatigue from the shortness of breath. "
] |
[
"Thanks. Would you be able to be more specific in the mechanism of fluid backing up and the decrease in volume? Is it to do with an inflammatory response of the lungs caused by the build up of blood in the left ventricle? "
] |
[
"Let's go through it one step at a time. Alcohol causes a dilated cardiomyopathy meaning over time the heart muscles stretch out which at the same time thins them out. Because it stretches out, it holds more blood in its chambers, but the fact that it is thinned out (aka it has less muscle per cm",
" ) means the heart can't exert the force necessary anymore to move all the blood it is holding. So what happens to that blood that doesn't get moved out of the heart? This is where you get lungs problems.",
"Take a look at the right flowchart of this image",
". Basically blood flow is: body --> right heart --> pulmonary arteries --> lungs --> pulmonary veins --> left heart --> body.",
"That blood that couldn't be moved out of the heart because it is so dilated gets backed up. First, it will just stay in the heart. But remember that blood is continuously passing through, so slowly more and more blood with back up. Now, there is so much blood backed up, that it starts getting backed up in the pulmonary veins. Eventually, it will end up engorging all the vessels in the lungs with backed-up blood. And with all that pressure in the pulmonary vessels, some of that fluid in these evessels will leak into the alveoli of the lung. Now you become short of breath because all these alveoli are filled with fluid which disrupts normal gas exchange."
] |
[
"If iron makes blood red, what would make blood other colours?"
] |
[
false
] |
I think some spiders have green blood due to copper, but are other colours found in nature, or even possible?
|
[
"hemocyanin",
", which contains copper, is blue.",
"hemerythin",
", which has iron, is pink.",
"chlorocruorin",
" also has iron and is sometimes either green or red."
] |
[
"Other colors can found in nature, and they can be caused by....the iron in your blood! It's not just the presence or absence of iron that causes teh color of blood, the color is also strongly effected by the oxidation state of the iron. The ",
"color of hemoglobin",
" is determined in part by whether there is oxygen bound to the heme group or not. This color change is actually a key tool for measuring how much oxygen is in your blood. However, the color difference, while easily measured, is kinda subtle to the naked eye.",
"For more dramatic color changes, there is a ",
"famous example",
" of a family in rural Kentucky with a rare genetic disorder which meant their hemoglobin, and therefore blood, appeared blue rather than red."
] |
[
"To go along with the explanation others have given, here's a ",
"pic",
" to show the subtle difference between the two."
] |
[
"What will happen to a rock floating through space as the universe goes through heat death?"
] |
[
false
] |
I understand that in an isolated system entropy tends to increase, but I’m having trouble picturing what an increase in entropy of a space rock would look like. Is a space rock constantly losing molecules on its surface as time goes on, and eventually there’s no rock left and the molecules also break down? How would the bonds holding the surface molecules to the interior break apart in a vacuum? A rock in a vacuum seems so permanent from my perspective but I know surprising things happen over huge timeframes. Thanks a lot for reading.
|
[
"In a conventional heat death scenario, the rock cools off asymptotically to absolute zero, any defects in the crystal lattice will anneal away until it is almost a perfect crystal, atomic diffusion morphs it into a perfect sphere (the minimum energy shape gravitationally), and eventually quantum tunneling will allow nuclear reactions to convert all atoms into iron nuclei. If it is silicate rock specifically, these will mostly be nuclear fusion of oxygen to silicon and silicon to nickel which then decays to iron-56. The exact timescales of each of these processes depend very sensitively on the mass of the rock and it's exact thermal evolution, and many of these processes can take hundreds of orders of magnitude longer than others. ",
"Now, since you asked about entropy I'll write three more paragraphs. ",
"This process probably sounds like it doesn't involve much 'disorder', with the rock becoming nice and round and having a perfect lattice made pristinely of one element. This probably doesn't really jive with how you understand entropy though and that's because people often focus on the 'disordered' part of entropy. That ends up confusing people because entropy is so much more. Worse still, it's a plain English translation of more detailed mathematical expression that tends to create confusion when mixing colloquial ideas and the more rigorous definitions of terms. This isn't your fault, I'm just trying to prepare you to accept a new definition of entropy. ",
"Entropy is a thermodynamic quantity just like temperature or pressure. This quantity is a little more nebulous than temperature since you can't measure it with your finger tips, but it's very similar. One of the definitions of entropy (which is again poorly translated into plain English and won't give you the full understanding, but is good enough for our purposes) is related to the ability of the energy to do work. This is different than potential energy, which is a measure of how much energy is present. In terms of the second law, entropy increasing is equivalent to saying the universe is losing the ability to do work with its energy. ",
"Entropy tells us whether or not the energy present has the capability to change things about the system. Take the crystal defects as one example. As the crystal settles into its ground state without any crystal defects, this seems on its surface like a 'loss' of disorder or a decrease in entropy (which would violate the second law). But really, there was energy available there- perfect crystals are low energy states while defects are 'excitations' in a sense. Clearing out the defect releases some small amount of energy and once it's 'spent' this way you can't 'use' it later (for example, to fix a defect). While the configurational entropy has decreased, the kinetic/vibrational entropy has increased. The rock heats slightly and then radiates away a handful of photons before coming back to thermal equilibrium with the universe and the net result is that the entropy grows."
] |
[
"Thank you for taking the time to type this out"
] |
[
"👉😎👉"
] |
[
"problems with alcohol help?"
] |
[
false
] | null |
[
"Hi FJNK12 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, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" 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.",
" ",
" "
] |
[
"Hello,",
"We can't advise you about this here."
] |
[
"and on what subreddit then?"
] |
[
"What does being cold feel like, its not painful, but what about it makes it uncomfortable?"
] |
[
false
] |
[deleted]
|
[
"There are receptors on the surface of cells that are activated by changes in temperature. These receptors allow ions to move across the cell membrane when changes in temperature occur, essentially generating an electric current that is detectable by the nervous system and interpreted as a sensation of cold or hot depending on which receptor(s) are activated.",
"For example, the receptor/ion channel TRPV1 is involved in sensing heat, and can also be activated by capsaicin (the compound producing the “hot” sensation from hot peppers), and TRPM8 is involved in sensing cold, and can also be activated by menthol (the compound producing the “cold” sensation from mint)."
] |
[
"So interesting. Thanks!!"
] |
[
"This is way deeper than I ever thought I'll know. Thanks!"
] |
[
"How sensitive is a dog's sense of touch on the pads of it's feet or through it's fur?"
] |
[
false
] | null |
[
"Veterinary Technician here. The pads of dog paws are much like the pads of our feet. When we walk around barefoot often, they get calloused and rough, whereas when we are not barefoot often, our feet are softer and more sensitive. Dogs who go on walks/hikes/are outdoors often will have tougher pads, while the smaller/indoor only dogs will have incredibly soft paws that can damage easily. Therefore, a dog's sensitivity on its paws varies depending on their paws. Through its fur, dog skin is a different story. They are definitely not nearly as sensitive on their skin as us. There are certain areas that that you can poke with a needle that they won't even feel, like in between their shoulders, or directly into their bladder through the abdomen (to obtain a sterile urinary sample). However, it can often depend on the breed, or just dog in general. Certain dogs are just more reactive than others when it comes to skin/paws."
] |
[
"I've seen a dog wimper in pain cause it's owner was walking it on pavement in the heat of the day."
] |
[
"Skin has pressure sensors and tickle sensors, amongst others, so the pressure doesn't transmit through a callous while vibrations still do.",
"\"pressure doesn't transmit through a callous while vibrations still do\" You understand how that statement kind of contradicts itself right? "
] |
[
"How does the Earth retain its magnetic field despite the high temperatures in the core?"
] |
[
false
] |
[deleted]
|
[
"The Earths magnetic field is not the result of a solid-stade magnet in the core. It is rather the result of the rotation of the solid metal inner core in relation to the liquid metal outer core, which generates an electro-magnetic field. The process in not unlike an electric dynamo."
] |
[
"The exact behavior and processes at work are still under study, and there is still quite a lot of research going on the finer détails; so the jury is still out on this one. As you can imagine, \"access is problematic\" as they say...",
"I'll link you to some research on the topic, but keep in mind this reasearch area is still fluid and we probably wont be seeing the definitive paper anytime soon:",
"http://www.nature.com/nature/journal/v389/n6649/full/389371a0.html",
"http://sites.pmc.ucsc.edu/~glatz/pub/glatzmaier_roberts_pepi_1995.pdf",
"https://books.google.ca/books?hl=fr&lr=&id=96APl4nK9lIC&oi=fnd&pg=PR13&dq=Earth+core+magnetic&ots=O6aZs5Q63n&sig=oKn43KkGj1UJvuo9inX7D8K46uQ#v=onepage&q=Earth%20core%20magnetic&f=false"
] |
[
"The Earth's magnetic field is created through a dynamo. Dynamos are really cool, and they're (for example) how we make electric power -- but the easiest way to understand them is a little different than you picked up in high school physics. Instead of thinking about ",
" being induced in a dynamo (the practical application of the dynamos in power plants), think about the ",
" in the dynamo.",
"The way a dynamo works is that magnetic field lines are hard to move through conductors. You can see that effect in ",
"youtube videos like this one",
", where people drop powerful magnets through copper pipes. The reason they're hard to move is that moving a magnet past a conductor induces an electric current in the conductor -- and that induced current has its own magnetic field. There's a nifty cancellation in the math, and that secondary field happens to be exactly the right strength and shape to make the magnetic field lines themselves stick to the conductor. In a perfect conductor they would be held fixed forever. In a real conductor, the induced current decays slowly, so the lines slooowly retract through the material. That's why the youtube video above works that way -- the magnet is held in the pipe by its own magnetic field, and it can only move as fast as the induced currents decay, inside the copper pipe.",
"The easiest dynamo to make is a ",
"homopolar generator",
": just a disk of metal, with a horseshoe magnet wrapped around it. When you turn the crank on the generator, the disk moves past the magnet, and field lines (that would normally go straight from the north pole of the magnet to its south pole) get swept sideways by the metal disk. ",
"In a liquid conductor things get even weirder. If you start with a tub of, say liquid mercury or seawater, place a magnet near it, and then stir the fluid -- you'll stir the field lines too, and end up with a tangled mess of magnetic fields. Each individual field line stretches like taffy in a taffy puller, and gets longer and more complex as the stirring happens, until the whole volume of the fluid ends up full of densely tangled magnetic field lines. If you stir the mercury or seawater fast enough, you don't even need an initial magnet -- quantum fluctuations in the magnetic field will cause small field lines to form, and these small fluctuations get stretched and grow rapidly until the fluid is highly (and more or less randomly) magnetized. That's true even for the homopolar generator -- you can make a ",
" homopolar generator that uses an electromagnet coil instead of a permanent magnet. The only trick is you have to turn the crank fast enough for it to \"strike\" itself.",
"Of course, filling a material with strong random magnetic field is the same thing, more or less, as filling it with electric currents to produce that magnetic field -- which is why the power company spends so much effort making dynamo action happen inside their equipment. They divert those currents into transmission lines to power your computer in return for money.",
"In the core of the Earth, there is a large liquid sea of nickel-iron, which is conductive. The metal isn't rotating uniformly, it sloshes around a bit -- driven by Earth's rotation and by convection from internal heating. That leads to it becoming magnetized. The magnetic field in there is highly complicated, but only the largest-scale, simplest part of the overall pattern is visible at the surface of Earth."
] |
[
"When I close my eyes, am I flexing or relaxing my eyelid?"
] |
[
false
] | null |
[
"You're not doing anything to the eyelid; what you are doing are flexing/relaxing muscles connected to it.",
"Now the general rule for muscle antagonism applies here: so opening ",
" closing eyes involve ",
" relaxation of one muscle and contraction of another (similar to the relationship between your biceps and triceps).",
"Specifically, ",
"this is the muscle",
" that opens the eyes; its contraction pulls back the eyelid. It is opposed by ",
"this muscle",
"; its contraction closes the eye."
] |
[
"This one?"
] |
[
"You are contracting the ",
"orbicularis oculi muscles",
" when you forcibly close your eyes."
] |
[
"Are we aware of the location of neurological signals relative to the brain?"
] |
[
false
] |
Let' say you get an itch on your thigh. You are aware that the itching sensation came from your thigh, but how? I assume that specific nerves correspond with locations all over your body. Now let's say you close your eyes so that you cannot visually see the location where the itching is coming from (your thigh). You can still accurately find that spot with your arm and itch it, without any visual feedback. How can your brain understand the coordinates of your thigh and how much it has to move your arm so that you can itch it? How come you can tell exactly where your limbs are with closed eyes?
|
[
"Let's say I took a vibrating tuning fork and held it against your little toe. The sensation of this area of your body is covered by a specific dermatome (",
"http://en.wikipedia.org/wiki/Dermatome_(anatomy)",
"). So, all of the sensation you feel there will go back to one level of your spine (",
"in this case S1",
"). The message will then be passed into a specific column of your spinal cord called the ",
"gracile fasciculus",
" which picks up nerve fibers in a uniform fashion as it goes up your spinal cord. ",
"Look at ",
"this image",
". The gracile fasciculus is the blue part in the back. The part labeled \"sacral\" is where the nerve impulse from my tuning fork is being carried up your spinal cord. ",
"This signal will be carried up your brain stem through your thalamus until it ends up in your somatosensory cortex. This is where your brain realizes that you have felt something. Information from different areas of your body correspond with specific areas of this cortex. ",
"This",
" picture shows how different body parts are mapped onto the brain. The ",
"blue area",
" of this image shows where this mapping is occurring in your brain as a whole. ",
"Different areas of your body have different amounts of real estate dedicated to it in the cortex. The ",
"humunculus",
" shows by exaggeration what body parts have more area in your brain. ",
"Ok, so now we know where the signal came from. How do we know where it is in space? ",
"Proprioception",
". This is your ability to tell where both your arm is and where your little toe is. It is one of your senses (like pain, temperature, or vibration), and happens to be carried by the posterior part of your spine (where the gracile fasciculus is) for the example of conscious proprioception. (Your cerebellum is the big player in unconscious proprioception). ",
"TL;DR: You feel a signal. That signal goes to a specific area or your brain. Proprioception allows you to know where your different body parts are."
] |
[
"There are receptors for several different kinds of stimuli (pain, hot, cold, light touch, etc) all over your body. These receptors send signals toward the spinal cord via synapses (connections between neurons), and then usually on to the brain. Each receptor serves a certain space on your skin (the surface area that the receptor serves depends on location on the body - smaller surface area, thus, finer discrimination, in the hands and face, and larger surface area, thus, less discrimination, say, on the back). The nerves are ultimately tied to the ",
"primary somatosensory cortex",
" (the outer layer of the cerebrum in the parietal lobe). Each area of the cortex corresponds to a different part of a body. These connections can be drawn as a map, called a ",
"homunculus",
". This map shows which body part connects to which part of the cortex.",
"When you close your eyes you can still find the spot that itches without visual feedback because we have something called proprioception - a mental map of our body position. It is due in part to the unique connection between sensory nerves and the primary somatosensory cortex. It allows us to do things like scratch an itch without looking at it or walk around in the dark without falling over. We have all these nerves sending signals to our brain about the current state of our limbs and our body, allowing the brain to create this mental map of where our body is even when we can't see it. When you drink too much, your proprioception can fail (this is why a cop might ask you to close your eyes and touch your nose). "
] |
[
"So is this proprioception responsible for amputees knowing where their \"arm\" is after it is amputated? As in, they feel where it is?"
] |
[
"How many percent of the incoming radiation from the sun are emitted by earth?"
] |
[
false
] |
I recently took a multiple-choice exam where this question came up. The 'correct' answer turned out to be 100%, but this doesn't sound right to me. I know that the Stefan–Boltzmann law says, two black bodies are in thermal equilibrium if the emitted power is equal. However earth is not a black body and some of the incoming energy is transformed into other forms of energy (i.e. photosynthesis etc.), right? So 100% cannot be the correct answer since this would violate conservation of energy. Is that correct or am I seriously mistaken?
|
[
"It's very, very close to 100%. Photosynthesis accounts for a relatively tiny amount of energy absorption, and is just about a net-zero game anyway, because most plants will eventually be eaten or burned, converting that chemical potential energy back to heat.",
"So unless your multiple choice test had answers like 99.9999% or 100.0001% answer, 100% is the closest."
] |
[
"The question, as I interpret it, was asking how much of the incoming radiation to the Earth gets re-emitted. Since the Earth is in thermal equilibrium (in broad strokes, i.e. its average temperature over long periods of time doesn't change much), it must be re-emitting the same amount.",
"What you're missing is that while the Earth's cross-section to solar radiation is indeed the area of a circle, pi r",
" , its emitting surface is 4 pi r",
" . "
] |
[
"That doesn't sound right, because the Earth also has an internal energy source from radioactive decay. If the sun provides about 1400 watts/m",
" to half the planet and the Earth is about 20 Celcius then it radiates about 400 W/m"
] |
[
"How can cheese be \"aged\" so long, but when it's in my fridge for longer than a few weeks it goes mouldy?"
] |
[
false
] | null |
[
"Aged cheese wheels have something called a \"rind.\" Rinds are most obvious on a cheese like brie. Some cheeses are also waxed on the outside (think Gouda.) It's basically an outer dehydrated shell that is maintained by the cheesemakers, and either one certain type of edible mold is allowed to flourish on it (like brie,) or it is wiped with saline regularly to keep mold from growing on it (cheddar). Once you penetrate the rind (slice the cheese into blocks) and stop maintenance, the \"inner\" non-dehydrated cheese is susceptible to mold it picks up from the environment.",
"Source: I'm a professional cheesemaker."
] |
[
"Mozzarella!"
] |
[
"What’s your favorite kind of cheese to make?"
] |
[
"How small can a star be?"
] |
[
false
] | null |
[
"In terms of mass, objects below 80 times the mass of Jupiter are not big enough to ignite hydrogen fusion and are classified as brown dwarves. Objects below about 12 times the mass of Jupiter are not hot enough to fuse deuterium.",
"In terms of radius, neutron stars are extremely dense and can be below 10 km in radius despite being similar to the sun in mass. White dwarves are in between, about as massive as the sun but about as wide as the Earth."
] |
[
"I think it's worth noting however that bodies such as white dwarves and neutron stars do not function at all like our sun does. ",
"In active stars like our sun, additional thermal energy is constantly being generated through fusion reactions. However, in white dwarves and neutron stars, no fusion reactions are taking place. This means that while these bodies may still be very hot and bright, they are slowly but surely cooling as they radiate away their remaining thermal energy. ",
"To be clear, such bodies are usually very hot from a fusion-driven past and/or from gravitational collapse/compression.",
"It is also interesting to consider that these inactive stars are so small ",
" there is no fusion occuring. Our sun is so much bigger than a white dwarf because the energy released by fusion reactions couteracts the force of gravity pulling the sun together. However, in white dwarves and neutron stars, since the weight of the body's material is unbalanced in the absence of energy released from fusion reactions, these bodies collapse into a smaller shape. ",
"How small they become is limited by their mass and strange degeneracy pressures that I'm not qualified to describe... If you're interested, perhaps someone could expand... ",
"This wikipeida article",
" is a decent start."
] |
[
"You may be interested in ",
"this lecture",
", it's all about brown dwarves, 'rogue' planets and other small, dim bodies."
] |
[
"Are sound waves effected by other sound waves?"
] |
[
false
] | null |
[
"Yes, sound waves can interact with other sound waves through destructive and constructive interference. If the frequency match in phase and pitch, then they would be amplified. If they differ in phase, then they would cancel each other out. ",
"It is how noise-cancelling headphones work ",
"http://en.wikipedia.org/wiki/Active_noise_control"
] |
[
"Usually? No. Sound waves that are small compared to atmospheric pressure obey the principle of superposition. That is, the sound field from two sounds together is equal to the sum of the sound fields created by those waves individually.",
"However, if sounds waves become very loud, they can become strong shockwaves, and strong shockwaves don't obey superposition. Shockwaves absorb smaller waves that they come across, they heat up the medium, and they move faster the more intense they become. Shockwaves are, by definition sound waves, but they are so much louder than normal that they behave differently.",
"Why is this? Essentially it's because normal sound waves are so outrageously small. The sound from a jackhammer at 1 meter away is 2 Pascals. But compared to atmospheric pressure at 101,000 Pa, the sound only accounts for 1/50000th of the total pressure. And that's for a sound that would normally be perceived as being pretty damned loud. For the sound of a normal conversation, the acoustic pressure would be measured in parts per million of atmospheric.",
"Only when sound waves are comparable to atmospheric pressure do they start interacting with each other's motion. And by that time, you're dealing with shockwaves that can damage property or cause instantaneous hearing damage.",
"Of course, this is to say nothing about constructive and destructive interference. Technically, waves that interfere in that way aren't actually interacting. Those waves still follow the principle of superposition."
] |
[
"To add a small explanation to this: when a physicist says \"something affects something else\" they mean that the two things change due to the interaction. We would say that sound waves that merely interfere do not interact: two sound waves that move in perpendicular directions and interfere at some location simply move through each other and come out the same they came in without any change in frequency, direction, etc.",
"At the location of interference, the waves may add in ways that a layman would probably consider as a strange effect of the waves taken together that isn't there when they are alone, and therefore would say the sound waves affect each other. A physicist wouldn't.",
"In addition to interference, and conditions where the pressure wave can not be considered a perturbation anymore, there are other true interactions of sound waves, but they do not happen in gases. In solids or liquids, two sound waves may combine to form a third sound wave with a different frequency and momentum. This process is called phonon-phonon scattering (or three-phonon process). There are even stranger higher-order effects but I doubt this is what the OP was asking about."
] |
[
"If I get my epigenome sequenced, can I only get a representative sample of my epigenome if I got tissue samples from every region of my body?"
] |
[
false
] | null |
[
"It depends on what you want to use it for. If you are trying to detect a disease or pre-cancerous cells, then you need to sequence every at-risk tissue (which for a non-specified cancer, would be every one). If you are just curious about epigenome heredity, then inherited epigenomic elements should be present in every cell."
] |
[
"I would take those epigenetic elements with skepticism however. Since they are, by definition, epigenetic, they are prone to modifications that alter the expression levels on this persons genes. So, even if he does get samples from each tissue, they are likely to be less stable over time and would therefore not be very useful in the long run.",
"I do, however, think this information would be useful to 'measure' this individuals epigenetic state in order to see what good there is and what bad there is (for example, if their epigenetics have induced some predisposition to obesity and they plan on preventing obesity by altering their diet and, hopefully, they epigenetic makeup)."
] |
[
"I agree. This was a difficult question to answer without understanding what the application was. Epigenetic elements can be very transient and they serve tons of different roles in biology on several different timescales."
] |
[
"Can anyone ID this weird animal?"
] |
[
false
] |
[deleted]
|
[
"Praying mantis egg case (after hatching), I think. "
] |
[
"Ootheca",
".",
"Mantids and cockroaches lay oothecas, although some give live birth.",
"Cockroach egg sacs typically are not adhered to a surface, but are usually carried around by the female until hatching takes place.",
"Mantids usually deposit an egg case that adheres to wherever it is laid."
] |
[
"You're welcome. Always happy to ID a bug-related thing!"
] |
[
"Space Battle with Today's Technology?"
] |
[
false
] |
I was rereading Ender's Game, and I started thinking about what would happen if, today, an alien species attacked us (a la the Buggers). Would we just be completely overwhelmed? Do we have any weaponized systems that could stand a chance, or would we be able to build anything in time? I assume the alien civilization would be far more advanced than us.
|
[
"If they can just accurately chuck rocks from the distance of the moon then the earth has no chance. ",
"They can easily take out nearly all our space infrastructure with (dumb) pebbles or even sand. We can't even get anything out of low orbit without massive work.",
"A few nations have the capability to take out satellites in low orbits but that's about all the space warfare capability in existence. ",
"Anything higher is perfectly safe from anything we can do from earth. Anyone who controls the high ground has a huge amount of options to harm people on the earth."
] |
[
"A good example of warfare from the moon is Robert Heinlein's The Moon Is A Harsh Mistress. Absolutely excellent battle in that book."
] |
[
"To talk about something like this there are two things we should be considering; how far this race has traveled to get here, and how complicated it is to travel such a long distance. We should be able to assume that based on our observation methods of space, and that we haven't found any other civilization out there yet that this species has some sort of FTL (faster than light) technology. This alone, regardless of how the species has developed culturally, is enough to indicate that a war with this race would be pathetically one sided. FTL technology is just such an advanced idea that it would mean even \"simple\" things like weapons, medicine, and observational tools would have also developed to a level that would vastly out preform our technology. Our only real defense would be nuclear weapons and missile based weapon systems, and even these might not have any affect. "
] |
[
"Why exactly do refracting lens magnify electromagnetic radiation?"
] |
[
false
] | null |
[
"They don't really magnify it like you might be thinking... They're not making something small into something bigger (ie., less energy into more energy). They're simply redirecting the things coming into the lenses into a smaller area. That's focusing."
] |
[
"Yup. It's like how a shovel can turn a bunch of sand on the beach into a big pile. It didn't make more sand, it just moved it over here. Now there's less of it over there, but you got a big pile, and that's what you wanted. "
] |
[
"They superimpose the signals by bending the path the signal takes so more of the signal is found in the same area. This is the general idea for a concentrating lens. ",
"If however the lens characteristics are of the divergent type the signals will be diffused over a wider angle and appear to be weaker.",
"Neither method magnifies the radiation.",
"Refraction does work across a wide range of electromagnetic radiation. Certainly from radio, IR, Visible light and UV all the way to X-rays depending on the dielectric/medium that is used for the lens."
] |
[
"Why are moles often the site of skin cancer? Doesn't more melanin mean more protection from the sun?"
] |
[
false
] | null |
[
"No science background so I may get kicked off this thread but...",
"Moles are usually the result of your skin cells having a small mutation that results in small, abnormal growth. Many moles aren't dark in the way that you're referring and just look slightly reddish. Other similar mutations are sometimes referred to as skin-tags (according to my dermatologist). The darker ones may over produce melanin as well. Being that many types of cancers are a simply a cellular mutation that go haywire, a mole is a perfectly reasonable place to look for potential issues. This is also the reason many people seem to get more moles as they grow older. Their skin cells aren't quite as good at reproducing and have small mutations.",
"My two cents... Someone with more science-y jargon should take it from here."
] |
[
"Geneticist here, and that is a good answer! To expand on that, the defining characteristics of all these various skin lesions are the type of cell affected, how it's affected, and which layer of skin the cells are in.",
"While melanin does protect from UV exposure, a mole, or \"nevus\" in medical terminology, has already suffered from genetic mutation. Specifically, and typically, the mutations within a mole cause the cells to divide more than they are supposed to.",
"Moles are often sites of cancer because uncontrolled cellular growth is one of the prerequisites for cancer, which means these cells are closer to cancer than ordinary cells. You could interpret this to mean that whatever protective effect is provided by the melanin is more than overwhelmed by the increased likelihood of becoming cancerous in the first place.",
"If the cells that constitute the mole include melanocytes, the mole will typically appear black or blue or brown. Moles consisting of other cell types can indeed have different colors, including red or pink or just your own ordinary skin tone.",
"The difference between a mole and a freckle, in case you are wondering, is that a freckle simply represents a region of overly sensitive melanocytes that produce more pigment than average. The cells themselves are not growing abnormally, as with a mole."
] |
[
"The \"more melanin\" in moles that progress to cancer are often due to abnormal proliferation of melanocytes (the cells that produce melanin). In the case of moles that progress to melanoma, the melanocyte proliferation has been caused by DNA mutations caused by repeated insult from UV radiation. So in short, the cells comprising moles that progress to cancer have already undergone mutation and are abnormally proliferating. ",
"Having said that, it's important to remember that not all moles progress to cancer. Moles that are at high risk of being cancerous are initially identified based on the ",
"ABCDE",
" criteria, which takes into consideration factors such as the uniformity of color within the mole, the regularity or irregularity of the mole's border, the symmetry or lack-there-of of the mole, the diameter of the mole, and how the mole changes over time (it's \"evolution\"). "
] |
[
"since the comoving distance remains constant, is the observable universe a shrinking sphere, when looked at in this comoving frame?"
] |
[
false
] |
I'm trying to wrap my head around the observable universe concept, and faster than light speeds etc. And an answer to this question would help with that. Also, why is the OU always displayed as an oblong sphere, rather than a perfect sphere. Does it have to do with the, I'm guessing, flat side being on the axis towards the center of the universe (=location of big bang) and the top-sides being the direction to the galaxies that have a velocity vector more parallel to earth? thanks in advance!
|
[
"Maybe it just adds some artistic expression, or because people expect it to look like that, or because you're looking at a sphere spread out into a 2D surface, maybe even because it's easier to see objects that aren't hidden behind things in our own galaxy so the distribution of known objects is a bit skewed . The observable universe, as we understand it, is a perfect sphere, the edge is the greatest distance that we could ever travel, or the greatest distance that light can reach us from. There is no one axis towards the center of the universe, you are the center of your observable universe, and no direction towards the Big Bang. The Big Bang happened everywhere, so every location can be said to be the center of the Big Bang, as far as we can tell."
] |
[
"the big bang happened everywhere",
"This is weird (not saying wrong!) :) ",
"I always envisioned the big bang happening, throwing away matter in all directions eventually. with all matter being spread out moving away from the center of the explosion (but, if i understand you correctly, the big bang was a tiny dot exploding, with nothing around it. so, per definition, that dot was everything with nothing around it. not even vacuum.) it is just that tiny dot expanding, with all processes that happened, leading to the formation of the universe as we know it today.",
"Then again, even with this point of view, there has to be a center of that expanded dot, no?"
] |
[
"It sounds like you're thinking of the Big Bang as a stone dropped in a puddle and everything expanding away from that point. It's more like a balloon getting blown up, our universe is the surface of that balloon, every point is expanding away from every other point. The universe was infinite when the Big Bang occurred and it continues to expand in every direction. "
] |
[
"Is there any species where unfertilized eggs can sit dormant for a long time, similar to spores?"
] |
[
false
] | null |
[
"I'm not entirely sure what you have in mind, but eggs in human females just sit around... Oocytogenesis is complete before birth. "
] |
[
"I'm thinking of fish, where they lay eggs that are fertilized externally. Is there ever a situation where eggs are laid that can be fertilized significantly later?"
] |
[
"I don't know of any species that has this ability with ",
" eggs.",
" ",
"But there are ",
" species where fertilized eggs stop development and exist in suspended animation (diapaused embyros) until external conditions are right to continue developing/hatching. ",
"In fish its more often seen in species that exist in desert pools or temporary water sources. For example, the fertilized eggs of ",
"annual killifish",
" can pause development at different stages, and diapaused eggs can completely dry out for ",
" and stay viable, until rehydration triggers the rest of development and hatching. ",
"For reptiles, ",
"many species have the ability to delay or suspend development in fertilized eggs.",
" For example, eggs of snake-necked turtes can survived (diapaused) for up to a year after being laid. Their fertilized eggs are laid underwater or in soaked soil and development doesn't start until the water level drops enough to allow air access to the eggs - they need the extra oxygen available in air to grow.",
"In birds, I don't know of anything quite so extreme. Some species will delay incubation until the last egg is laid in the nest, so earlier eggs do not begin development until they get the consistent warmth from a parent starting incubation. The very first egg laid may suspend its development up to a week or more.",
"Mammalian eggs are retained within the female's body. Even so there are many mammalian species which exhibit similar ",
"embyronic diapause.",
" This is either seasonal (animals may breed in the fall, diapause embryos during the winter, and resume development in the spring), or a result of hormone levels in the mother.",
"There are way more examples of developmental diapause in animals, especially if you look at invertebrates and microscopic organisms."
] |
[
"Why are most people right handed?"
] |
[
false
] |
Why are most people right handed? Is it due to some sort of cultural tendency that occurred in human history? What causes someone to be left handed instead of right? And finally if the deciding factor is environmental instead of genetic, are there places in the world that are predominately left handed?
|
[
"So I actually study handedness on a day to day basis and I will try to cite some of the newer research that has been coming out. Most of what I've found thus far is behind pay walls as many of the articles are very new and I've heard most of this research at conference presentations up to this point.",
"So there seems to be some research out there suggesting that handedness preference is actually genetic as develop while in the womb. ",
"Example paper - behind pay wall, sorry",
". There has been a history of research showing infants in the womb will tend to use one hand or the other early on, but over time as they develop they begin to use both. I have also been told (I do not have a citation for this) by one of the professors I work with (who has been research handedness for close to 30 years) that there was a study done showing when you first put an infant down after delivery their head tends to flop to one side and the side of the head flop is strongly correlated with their hand preference, the theory being that the side of the dominant hand is developing sooner and is thus slightly heavier. If all of this is true, then there aren't cultural factors playing into a person's natural handedness and it probably has more to do with how the brain has evolved to lateralize some tasks more to one side or the other.",
"However, just because culture doesn't shape something prenatally doesn't mean other environmental factors cannot. As some people have pointed out there are some studies from the 80's suggesting babies in a high stress pregnancy are more likely to be left-handed, although the one review i've found so far suggests the relationship is pretty weak ",
"Citation, again sorry for pay wall",
". More recently research seems to be focusing on hormones and other chemicals present during fetal development that may play a role in shaping handedness. ",
"This study",
" (yay full text!) suggests maternal smoking and low Apgar scores* can significantly increase a child's chance of being left-handed. Other studies have focused on hormones, specifically testosterone, suggesting low levels of testosterone are more likely to lead to left handedneed ",
"Citation 1, sorry pay wall",
": ",
"Citation 2, pay wall again",
". The most recent research I have seen looking at testosterone and handedness look at second to fourth digit ratio, which some research has shown correlates to prenatal oestrogen and testosterone exposure ",
"citation",
". I do not think the research looking at the 2D:4D ratio and handedness has been published yet, but IIRC it fits with people showing lower testosterone exposure (based on 2D:4D) were less strongly right-handed.",
"So i've talked about all of this genetic and prenatal exposure, but I haven't touched culture yet. Cross-cultural handedness is not something I have studied much beyond knowing some cultures think being left-handed is evil or the sign of the devil, or whatever it is they believe exactly. Even in the US there was a period in time when children were taught to be right handed because it was unacceptable to be left handed. From a functional stand point, if you use your non-dominant hand enough especially from a young age you should be able to make yourself fluent enough with that hand to consider it your dominant hand. So a lefty raised from birth to be a righty could end up identifying as right-handed and using their right hand on a day to day basis. However, this does not mean the underlying brain structures that differentiate handedness will necessarily change. ",
"There is a growing body of research out there showing differences in the size of the corpus callosum between mixed and strong handers. Since I have changed terminology I will explain why. Most people who research handedness have started to move away from using the left vs right distinction as it turns out it is more of a gradient. Some people will only use their dominant hand for everyday tasks and some will use both equally, even if they self-identify as one hand or the other. So people who only use their dominant hand are strong handers while people who use both are mixed handers. Mixed handers have a larger corpus callosum than strong handers (",
"Witelson, 1985 - I have the full text offline if someone wants it",
"). In my opinion, I do not think retraining someone even during childhood would change the size of the corpus callosum so in some ways your handedness is permanent, even if your use of hands changes.",
"*[Definition of Apgar from the article: Apgar score is a standardized, simple and reliable measure \nto assess the health of a baby using a three-point scale to \nassess five parameters (skin color, pulse rate, reflex irritability, muscle tone, breathing). Total Apgar score ranges \nfrom 1 to 10, whereby 10 means desirable, almost ideal \nhealth of a newborn. Newborn babies with Apgar scores \nless than 7 are considered to be at health risk, and usually \nrequire specialized medical attention]",
"tl;dr Handedness appears to be genetic w/ prenatal environmental factors playing a role in the final determination of handedness. Cultural influences may change someone's outward handedness, but I dont believe there is any research showing this changes the underlying brain structures that change as handedness changes."
] |
[
"One common theory, as to how handedness affects the hemispheres, is the brain hemisphere division of labor. Since speaking and handiwork require fine motor skills, its presumption is that it would be more efficient to have one brain hemisphere do both, rather than having it divided up. Since in most people, the left side of the brain controls speaking, right-handedness predominates. This theory also predicts that left-handed people have a reversed brain division of labor.",
"That is a theory from ",
"wikipedia",
". The article mentions a couple other theories, including one that untrasounds while in utero could promote left-handedness.",
"(edited out accidental chinese characters)(and again)"
] |
[
"More theories on the promotion of left-handedness.",
"A 1988 survey found that in 30 of 33 publications, infants who had undergone birth stress were significantly more likely to be left-handed. Lower Apgar scores — a measure of a baby's overall condition at birth — have been clearly associated with left-handedness. A 1987 study found that more than a third of 4-year-olds who had been born prematurely were left-handed. Another found that more than half of children born with extremely low birth weights — a full 54% — were left-handed. In total, left-handers are twice as likely as right-handers to have had a stressful birth",
".\n"
] |
[
"Rotating spacecraft, artificial gravity problem."
] |
[
false
] |
If I am not mistaken, the "rotating spacecraft" solution to artificial gravity uses centripetal force to keep its inhabitants on the ground. Even if this simulation of gravity is perfectly matched to that of the earth, what would keep someone or something from flying due to weightlessness if it was knock off the surface?
|
[
"Objects in motion tend to remain in motion. If something is moving tangentially at a high enough speed, and then jumps, it's still moving at that speed tangentially."
] |
[
"If I were standing at the surface and jumped straight up, wouldn't I be weightless? I understand that I would move along with the surface, but one of the great things about earth is that it exhibits a pull on its inhabitants. I can't fathom why this artificial gravity would exhibit the same pull."
] |
[
"I can easily picture water in a bucket, however, I am still struggling. I think a hypothetical situation would help explain it. If I were stationary some distance away from the surface of the sufficiently big rotating cylinder and I were to throw a ball the same velocity a human would fall out from a distance of a meter; would the ball return to me or \"fallback\" to the surface? ",
"I am guessing that it would be something in between as it doesn't have the rotational(maybe) velocity that a human would have. But I think a clearer picture would help illustrate the forces at work here."
] |
[
"It's been about 5 years since the Mochizuki's ABC Conjecture proof was originally published. What's its current status?"
] |
[
false
] | null |
[
"Relatively recently, one of the few who claim to understand how the proof works put out a brief summary to help guide those who are trying to decode it. ",
"This summary is 300 pages long.",
" More people are beginning to get an understanding of it, and it has been determined that, correct or incorrect, the ideas in the paper are groundbreaking and worth study, but it is still pretty far from being verified or put into a journal.",
"Here",
" is the article, if you want to see what a summary looks like. I have some technical exposure to anabelian geometry, how it works and what it's about, and it all looks like gibberish to me (though, I'm not working on verifying the proof)."
] |
[
"Just to add some perspective:",
"Mochizuki published some really important articles proving several important cases of Grothendieck's anabelian conjectures in the middle of the 1990's, which are quite hard and technical and relies on several previous articles that are also quite technical.",
"He has since then devoted two decades full-time to extend and generalise these results and methods in several directions, and has found what he believes to be \"the essence\" of the phenomena.",
"And after working on a really hard problem for 30+ years and not really getting that much attention, he announced a proof of the abc conjecture, which has made a big splash. A lot of people with various degrees of expertise wanting to read it found themselves with a long backlog of technical exposition to catch up with to be comfortable with this proof, and very few people have tried and succeded at doing that."
] |
[
"I don't know much about pure mathematics at research level, but would it be possible to get a computer to verify the proof?"
] |
[
"Do we really need the Id?"
] |
[
false
] | null |
[
"I'll answer your question, but won't release it to the general sub. First of all, I have to note that the conceptualization of Freud's psyche (Id, Ego, Superego) is outdated. Modern psychologists/psychiatrists no longer recognize it as a valid concept. ",
"That said, psychoanalysis does still exist in the form of psychodynamic therapy. Freud--or a modern-day psychodynamic therapist--would likely answer your question this way: Your Id is your animal brain. It is what tells you what makes you happy. It makes you seek food, shelter, love, sex--all the things that you need to be fulfilled. Without the Id, the ego and superego would cause you to float through life unfulfilled and never satisfied. The Superego seeks only to live by the laws of civilization, and therefore doesn't care if the Ego and Id are happy. Just as the absence of the Superego would allow the Id to run quite literally rabid, the absence of the Id would allow the Superego to completely dominate. The key, in Freud's view, is balance: allow the Id to dictate what you need to survive and thrive, while allowing the Superego to dictate how to assimilate to society. That's the Ego's entire job."
] |
[
"According to Freud, there were two ways that humans seek satisfaction: the basic, primal instincts of the Id (that I described above) and the moral and civil supremacy--the ability to fit into civilized society--that satisfied the Superego. Most often, these were in conflict with each other. For example: You find that you're sexually aroused. The Id tells you \"Go have sex with something. Doesn't matter how, take it by force if you need to.\" That's clearly against the laws of society and morals, so the Superego tells you to abide by those laws at all costs, even to the point of foregoing sexual activity. This causes the Id to push harder for sex, and it becomes a vicious cycle. The Ego's job is to find a happy medium: satisfy the Id's need for sex while remaining morally righteous to appease the Superego. ",
"Note that both the Id and the Superego have positive and negative aspects. Neither one is \"good\" or \"evil\". Also note that, in Freud's view, letting either the Id or the Superego \"win\" too much leads to mental instability. An over-zealous Id without a balancing Superego leads to all sorts of nasty behaviors, including psychopathy. A Superego that never allows the Id satisfaction leads to feeling unfulfilled and can bring on anxiety, depression, mania, and the like. ",
"Disclaimer: None of the above is actually how the mind works. I'm speaking from an exclusively psychoanalytic viewpoint, and this structure of the psyche has been almost entirely discredited."
] |
[
"Well, plausibility does not equate to accuracy.",
"The simplest answer is that the personality--what Freud called the 'psyche'--is far more complex than to be distilled down to three main drives (morals, satisfaction, and balance). Personality psychology continues to struggle to find a theory that adequately describes all of the nuances, motivations, and needs that contribute to the development of a personality, and those that are currently accepted are far more intricate than Freud's model."
] |
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