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[
"What is stopping video games from using dynamic motion synthesis instead of canned animations for simple actions?"
] |
[
false
] |
I'm fascinated every time I see real-time demos of dynamic motion synthesis, where characters have a simulated bone/muscle structure and intelligently maintain balance and perform actions without predefined animations. A few examples: Games industry has had physics-based ragdolls for quite some time and recently some triple-A games have used the Euphoria engine to simulate bits of movement like regaining balance, but I haven't seen any attempts to ditch animations for the most part in favor of synthesized, physics-based actions. Why is this? I'm assuming it's a mix of limited processing power, very complicated algorithms and fear of unpredictable results, but I'd love to hear from someone who has worked with or researched technology like this. I was also looking for DMS solutions for experimenting in the Unity engine, but to my surprise I couldn't really find any open-source efforts for character simulation. It seems like NaturalMotion is the only source for such technology and their prices are through the roof.
|
[
"Caveat: I don't work in this directly, but I develop physical simulations and have some knowledge on control theory and recently went to a research talk on analyzing animal biomechanic reactions.",
"First, the equations of motion of the models you see are basically N coupled differential equations, where N is the number of joints in your model (say around 10 in your videos). In and of themselves this is relatively trivial to compute, hence realistic-looking ragdoll effects.",
"The hard part is what those videos reference as \"AI\". Consider someone pushing you in the chest: if it's relatively weak you just kind of sway back and get back to equilibrium. If it's more forceful, you'll actually lift a foot and move it behind you to regain balance. The biological guts of this action is an incredibly complex function of your senses and conscious and unconscious decision making -- mathematically it's highly non-linear to the point that direct simulation of the process is out of the question. So you have to come up with very sophisticated models of the decision making process leading to the reaction of a given body, which is a very active area of active research outside the video game community.",
"See this popular video of Boston Dynamics' \"Big Dog\".",
" The reaction and control algorithms taking place in that machine are very complex."
] |
[
"Yes, ",
" and other animals can do that, and you're incredibly good at it compared to any robot/automated system in existence. Humans walk, sprint, crawl, climb mountains, climb ladders, play sports, lift heavy objects, perform delicate surgery, pick their noses, use tools, and adapt to wildly different tasks without ever having to give much thought to their mechanical motions.",
"Instructing a computer on how to do all these things is a different problem altogether, and is immensely difficult."
] |
[
"Combine ",
"/u/Overunderrated",
"'s reply with two facts",
"1) A lot of the in-game physics you enjoy in games are so complex that they're already being processed by your GPU (using something liks PhysX) just like the entire environment is being rendered by your GPU. ",
"2) Now consider that in gaming, 60fps is the bare-minimum for good game play. So, to make those extra-realistic physics practical, you need to be able to complete computations for every object 60 times per second. A bunch of those objects will be interacting which will make it even more complex. Graphics rendering can take advantage of the fact that a lot of what's obscured or off-screen doesn't need to be rendered or considered (a lot can be pre-rendered as well). With physics, you can't cheat nearly as much. Even objects behind you need their calculations run because they could be rolling down a hill and hitting you from behind. ",
"Finally, when you see demos, realize that they probably aren't real-time. They were probably built on a big rendering-farm. It could have taken an hour to build that 1 minute clip. "
] |
[
"Why is the light coming from my laptop screen polarised?"
] |
[
false
] | null |
[
"And here's a video with your answer.",
"Basically, the monitor works because the light is polarized."
] |
[
"Yessir. And those of us who like polarized lenses while driving to reduce glare get screwed by cars with LCD displays, such as the one for my gas tank, in-car clock, stereo system display, Nav, etc etc. -_- "
] |
[
"To be fair to LCDs, this is a lack of will on the part of manufacturers rather than an inherent limitation in LCD technology. Not only can normal LCDs be manufactured in such a way that they are visible from all normal driving positions, but ",
"wave plates",
" can be incorporated in the design to make LCDs that are visible from all angles while wearing standard polarized glasses."
] |
[
"With planets like Jupiter that have multiple moons, do the moons ever collide? Or is there something in the way they orbit that keeps this from happening?"
] |
[
false
] | null |
[
"When you have multiple moons, this is the notorious n-body problem (more generalized than the 3-body problem). You can't solve these problems exactly, so you can never truly rule out a collision in the distant future. There is even a possibility that Mercury or Venus might crash into Earth. (That is billions of years away, so nothing to lose sleep over!) ",
"That being said, the three inner Galilean satellites (Io, Europa and Ganymede) are in a 4:2:1 orbital resonance. Meaning Io orbits 4 times for every 2 orbits of Europa and 1 orbit of Ganymede. This resonance helps the moons to be self correcting in their orbits. They will be gravitationally nudged back to a stable state. However the other moons in the Jupiter system we can't say the same thing and possibly in the future they may collide.",
"Also orbital resonance can be destabilizing, but after billions of years, those objects have mostly been kicked out. There are some subtleties, so I'll let you read the following.",
"http://en.wikipedia.org/wiki/Orbital_resonance"
] |
[
"The orbital distance (how far away they orbit) is different, but there is nothing specifically to prevent moons from crashing into each other. The history of the cosmos is filled with celestial bodies colliding (or own moon, for example is thought to have been formed when a very large object collided with earth)."
] |
[
"Thanks! Was just a thought I had and I appreciate your taking the time to answer. :) Interesting stuff."
] |
[
"Why is it that a vaccine like J&J can reduce severity of Covid-19 even in cases where it doesn’t provide full immunity?"
] |
[
false
] |
The trials indicated that full immunity varied by country, probably due to the different strains. But it was effective at reducing severity across the board at similar rates, regardless of strain. Why does that happen?
|
[
"Vaccines elicit more than just antibodies. They can also stimulate the differentiation of T cells that recognize the antigens (the proteins of the virus) and these help coordinate the immune response as well as destroy infected cells.",
"For the virus SARS-CoV-2, how quickly the T cell reaction can respond is critical to how severe the disease can get. A rapid response often results in no or few symptoms, while a delayed T cell response can result in an uncoordinated immune scramble that results in severe illness and/or 'long COVID'.",
"Vaccines that attenuate disease but don't prevent infection are common. The vaccine for shingles is given to people who have a latent varicella virus infection (after childhood chicken pox); it prevents the disease from flaring up."
] |
[
"We don’t know why. Two possible, not mutually exclusive reasons: reducing viral load, and protection focused on the lungs and organs rather than the nose and throat. ",
"Reducing viral load is pretty obvious. If you have enough immunity to handle x amount of virus, and you’re infected with 2x, then you’re still infected but only with half as much virus as your neighbor. Usually to have a really major impact on disease severity, you’d look for a 10x reduction or more and it’s a little harder to imagine that kind of tuning, but it’s certainly possible. ",
"Like many respiratory viruses SARS-CoV-2 can infect much of your respiratory system, and usually first infects your upper respiratory tract (nose and throat) before spreading down to the lungs and then potentially throughout the body (",
"SARS-CoV-2 Reverse Genetics Reveals a Variable Infection Gradient in the Respiratory Tract",
"). The nose and the lungs are treated differently by the immune system, with mucosal immunity being important in the upper respiratory tract and systemic immunity kicking in for the lungs. Vaccines (and probably much of the natural immunity as well) probably make more systemic than mucosal immunity, so potentially what’s happening in these (rare!) cases of vaccinated people being infected, is that the virus can infect the nose and throat, leading to mild symptoms, but is blocked from getting deeper (preventing severe lung involvement). ",
"Other factors could also be involved, and we need to await actual research on this."
] |
[
"https://en.m.wikipedia.org/wiki/Polyclonal_antibodies#:~:text=Polyclonal%20antibodies%20(pAbs)%20are%20antibodies,each%20identifying%20a%20different%20epitope",
".",
"Heres a simplified example:",
"Pretend the protein on the outside of the spiky coronavirus is a square shape and is able to connect to the cell receptor, allowing it into a cell.",
"Then the virus evolves to something more like a rhomboid.",
"The vaccine not only produces antigens with perfect square shapes, but also some variations, like rhomboids that will match the evolved virus' protein. ",
"This is why the efficacy of the virus is not dropped to 0% when battling against new variants, and probably why severity is reduced."
] |
[
"What generates the recoil in a railgun?"
] |
[
false
] |
[deleted]
|
[
"This is covered by Newton's Third Law of Motion.\n",
"https://en.wikipedia.org/wiki/Newton's_laws_of_motion",
"For the projectile to travel forward, the \"gun\" must experience the same force in reverse. No matter the mechanism - bullet in barrel, linear accelerator, or rail gun."
] |
[
"Another difference is that for conventional artillery, it just isn't the projectile that gets accelerated but also the propellant gases."
] |
[
"Another difference is that for conventional artillery, it just isn't the projectile that gets accelerated but also the propellant gases."
] |
[
"What could this object seen close to the sun on nasa telescopes be (5th May 2012)"
] |
[
false
] |
Display: slideshow for the movie * Telescope: Behind COR1 Start Date: 20120502 End Date 20120505 search button. ''''''''''''''''''''''''' Appears on 2nd may 2012 at 19.15 image becomes pixelated on 4th may 2012 at 00.05 but object still visible. up until this point each image is 5mins separated, but from 00.05 the next image is 02.05 then hourly after that until 6th may 10.05 that is the last image available at the moment from the nasa site,and the object is still there. ....................................... perhaps someone could explain what sort of telescope creates these images. Is it a satelite or space station or ground based. the sun does not appear to be rotating , so is the object orbiting the sun along with the telescope. I found this video which seems to explain these kinds of shapes but I am not sure.
|
[
"How can we tell that it's an object close to the sun if the picture is 2d and there are no other angles?"
] |
[
"Reminds me of \"dust doughnuts\", an artifact caused by small particles on the CCD or whatever device is used in the coronograph in question. Typically you would take an exposure with the aperture covered then subtract this so called \"flat field\" from the image to eliminate artifacts like this. Here are some examples of \"dust doughnuts\" for comparison.",
"[1]",
"\n",
"[2]"
] |
[
"This is exactly what I was going to say - glad someone else thinks so, too (and bonus points for using ds9).",
"If there's dust inside the optics, it's going to scatter sunlight. Normally this would appear as a bright point, but because the optics are focused at infinity, it ends up imaging the primary objective mirror/lens. ",
"Essentially the donut you're seeing is the illuminated primary optical component of the spacecraft. The dark central circle is the central obstruction...in most telescopes it's the secondary mirror, and in Lyot coronographs such as STEREO it's the occulting disc. If you take any centrally obstructed telescope (e.g. Newtonian, Cassegrain, Ritchey-Chretien, etc.) and tune it out of focus, stars will have this exact same donut shape."
] |
[
"Could it be that babies cry when they are born because the oxygen in the air is oxidating them and it hurts?"
] |
[
false
] | null |
[
"Hi mantis6660 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:",
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"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
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" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Human body"
] |
[
"Human Body"
] |
[
"What causes the magnet/iron files experiment to have well-defined lines?"
] |
[
false
] |
[deleted]
|
[
"The rotational ordering arises because the filings are polarized by the magnetic field and align themselves with the magnetic field lines. The positional ordering likely arises from interactions between filings -the N of a given filing is attracted to the S of the next filing, etc, so the lowest energy state is for them to be lined up rather than evenly distributed."
] |
[
"Iron has a high ",
"magnetic permeability",
". It gets magnetized and you end up with a locally-stronger fields around the filings. ",
"So an evenly-distributed dust of filings will attract and lump together until the the point where the closest filings are too far away for its field to pull them over."
] |
[
"I'll preface this by saying that I am a senior in Electrical Engineering studying electric motors currently. So if I am off on anything in my explanation, I'd appreciate someone helping me to deepen my understanding.",
"There is a thing called magnetic flux, that by definition is leaving the north end of the magnet and entering the south end. This can be thought of as creating a ",
"magnetic circuit",
" with the north as a high potential and the south as the low potential. The magnetic flux in this instance is the \"current\" of the circuit. The next thing to be understood is ",
"reluctance",
". It is analogous to the resistance in an electrical circuit. ",
"Starting with the poles as boundary conditions, the filings line up with the field lines (not discrete but continuous in number) because this is the lowest energy state as iron has a much lower magnetic reluctance compared to air. This is similar to how current follows the path of least resistance. This is also the reason a compass lines up pointing to north. There is also a maximum packing concentration around the poles based on the cross sectional area of the filings.",
"The next step is to see that the lowest energy state for the other iron filings is to line up with these initial packings on the poles. This creates continuous paths for the magnetic flux to follow. This also creates the gaps you are seeing as the iron filings are limited in amount in a particular area and tend to clump into lines to create continuous paths.",
"As another note, gaps in the lines displayed by filings usually occur in this experiment as there is a certain amount of friction between the iron and the surface it's resting on. Sometimes this is enough to counteract the magnetic pull."
] |
[
"Why do coffee beans in a bag with a one way degassing valve appear to shrink wrap themselves in the freezer?"
] |
[
false
] |
This is a really simple question that I'm perhaps making complicated. Fresh roasted coffee is often stored in laminated, moisture proof, sealed bags with a one way degassing valve. As I understand it this is to protect the coffee from oxygen, while allowing the CO2 that fresh coffee beans give off to escape. I've noticed that when these bags get placed in the freezer and cool, they end up appearing to be shrink wrapped as if in a vacuum around the coffee beans. I understand that the volume of gas in the bag dramatically decreases, and hence I'd expect it to have far less volume in accordance with Charles law, just like a balloon would appear deflated in the freezer. What I don't understand is why this relatively inelastic bag in the freezer to have such a strong vacuum in it, such that the contour of each of the coffee beans contained within is obvious, and the surface becomes irregular as the beans are tightly hugged by the shrunken bag. The frozen bag has the feel of a solid brick, rather than loose beans, even though when the bag is opened, the beans are not frozen to one another. Other sealed bags with no valve in the freezer do not seem to exhibit this tendency, and there is a decent amount of headroom in these bags. That said, I can't say I've put a lot of room temperature, sealed stuff directly into the freezer, so perhaps this is incorrect, and the valve is a red herring. So, does the valve have anything whatsoever to do with this?
|
[
"Yes, I believe so.",
"I'm a biologist, but I'm not uncertain if the one-way valve can selective between oxygen and carbon dioxide. Most likely it's suppose to keep off the moisture while allowing gas to escape (like a Gore-Tex jacket).",
"With that assumption of the one-way valve (gas can go out, but not in), I can hazard a guess what happened.",
" the relative temperature between the inside and the outside of the bag is irrelevant, please see my response to ruper1920."
] |
[
"Your explanation might be correct (if the pressure of a room-temperature gas and a freezing gas is sufficiently different), but the one way valve is indeed to keep oxygen out but allow CO2 to escape. This is because when coffee is roasted, CO2 is generated but trapped in the bean's structure. This CO2 seeps out for a few days in a process called ",
". Brewed coffee will not taste as good during this time, and a sealed bag with no valve might actually burst.",
"Fun fact: my experience is that if you want to brew some fresh coffee right away, you should grind it and let it sit for an hour, and this seems to accelerate the outgassing process. Coffee that is roasted and immediately brewed tastes weird and bubbles in a funny way as it's mixed with water.",
"(I roasted my own coffee for about a year--yep, card-carrying hipster here.)"
] |
[
"I guess my point is that the valve is actually not selective to the types of gases, but only allows gas to escape but not enter."
] |
[
"Have there ever been any undiscovered elements in a meteorite or other object that has landed on earth?"
] |
[
false
] |
What I mean is, has there ever been an undiscovered material from space that has landed on earth. Does the earth's atmosphere burn the majority of elements before the material lands?
|
[
" elements, no. All known elements have either been found naturally on earth or synthesized here.",
"There are, however, some very rare elements, like iridium, gold, platinum, and other heavy metals that are found in much higher concentrations in asteroids than in the crust, due to the fact that the majority of those metals sank into the core when the Earth was forming. "
] |
[
"It seemed to me like the point of the question was have we ever found an element that only exists extra terrestrially, and since all stable elements are found on earth or have been synthesized then no there aren't any alien elements. "
] |
[
"The problem is that stuff constantly falls from space to earth, so pretty much anything you find in asteroids is already all over earth, in the residual spattery bits of previous asteroids.",
"EDIT: I can think of a historical example though. The earliest use of iron was removing pure metallic iron from fallen meteors and using it to make things. The technology to smelt iron from ore didn't exist yet, but some asteroids are essentially pre-smelted. So at the time this was a new, unknown element which was pretty impressive for making, eg, swords or what have you."
] |
[
"We have found Moon rocks on Earth, and even Martian rocks on Earth, what are the chances we will find Earth rocks on the Moon or Mars?"
] |
[
false
] | null |
[
"In a way, ",
"that's already happened."
] |
[
"A ",
"recent paper",
" by Hara et al. has shown that there should be scads of rocks from the Earth on the Moon and Mars and many other solar system bodies, and even rocks that have likely made it to other star systems.",
"In their paper, Hara et al. modeled the number of rocks that would have been ejected from the Earth and made it to various bodies after the huge impact the Earth endured 65 million years ago (see ",
"here",
" for more information on that impact).",
"They found that huge numbers of rocks made it to the Moon and Mars. They calculate that between 50 million and 1 trillion rocks wound up on the Moon, and between 20 million and 40 billion ended up on Mars.",
"Even if you are not someone who reads technical papers, you can look at Hara et al.'s paper for Table I on page 3, which summarizes their results of how many Earth rocks from this one impact event would have wound up on various bodies in the solar system. There is also a nice journalistic account at ",
"this location",
"."
] |
[
"Thank you for the informative post. "
] |
[
"Are all stables isotopes naturally occurring?"
] |
[
false
] |
I was wondering if there are any entirely synthetic stable(i.e. non-radioactive isotopes). For instance, a stable isotope of iron that does not occur naturally but has been synthetically produced? Edit: just noticed the title has a typo. "Stables"🤦
|
[
"From the fact that actinides like uranium are naturally-occurring, we can deduce that natural nucleosynthetic processes can reach at least that high in mass (~240). The heaviest stable nuclide is lead-208.",
"So any stable nuclide can be produced somehow in nature. I'm not aware of any stable nuclides which don't occur naturally on Earth, albeit possibly in small amounts.",
"As for the possibility of heavier stable nuclides that we don't yet know about (for example, the ",
"), I'll reference our ",
"FAQ",
". But in summary, it's unlikely that there are any stable nuclides that haven't been discovered yet."
] |
[
"There is always the odd process here and there that produces them.",
"As an example, if you only consider the main fusion processes then you won't see any stable beryllium and boron appearing in them. They are produced when high energy particles hit larger nuclei and split them. They are very rare in the universe, but still common enough on Earth to have commercial applications."
] |
[
"While theoretical elements in the island of stability may not be stable in the sense that they will decay, it's likely that they're half-life is long enough (if we were able to synthesize them) that they would be effectively stable, right?"
] |
[
"Faster than light communication, and particle physics"
] |
[
false
] |
Let's say you have a very long pole, actually, the length is arbitrary, but anyways... You have a pole, and a laser parallel to it, at the end of the pole you have a light sensor and a touch sensor. When you push the pole, the laser is turned on at the exact same moment. Could the touch sensor be activated before the light reaches the end of the pole, and the light sensor on the other side? The pole does not move faster than the speed of light, but could the chain reaction of the atoms pushing off of one another reach the end faster than the light? My question is, (besides say, quantum entanglement) can you transmit information faster than the speed of light, by not physically moving matter faster than the speed of light? After thinking about this, I can see one major problem. The EM force carrier particles that let the matter within the field know that there is an electromagnetic force acting on it would have to travel faster than the speed of light for this to work. Photons are EM force carriers, so they obviously cannot travel faster than the speed of light (photons == light particles). I have an extremely basic understanding of physics and general quantum physics concepts, so my logic may have fallen apart much earlier. I guess this leads me to my last question (Though it seems I have been answering them by myself already): what prevents a massless particle from traveling faster than the speed of light? And then, how can it have any energy without mass? (e=mc I am a high school student, so please don't mock me if I am making blatant errors. Instead, let me know where I am wrong so I can learn. That also entails using terms that I will understand, hopefully. Thanks.
|
[
"Your \"major problem\" is the answer. The force that is transmitted in an object travels at the speed of sound in the object. The fastest that speed of sound can ",
" be is the speed of light. (usually it's much much slower) ",
"what prevents a massless particle from traveling faster than the speed of light? ",
"There are a couple of ways of approaching this. One is somewhat more algebraic and we realize that if v>c momentum, p=sqrt(some negative number). Square root of negative numbers are called imaginary numbers. So in this case, this means your momentum must be imaginary. ",
"The other way to look at it says that velocity maybe isn't the most fundamental thing, but the hyperbolic arctangent of the velocity called the ",
"rapiditiy.",
" This goes to infinity as v->c. The reason it may be \"more fundamental\" is that when you add velocities relativistically you have to use a messy formula. But you can directly add rapidities of two things.",
"And then, how can it have any energy without mass? (e=mc",
" )",
"Because you've only learned part of the equation. The full equation is e",
" - (pc)",
" = (mc",
" )",
" , where p is, again, the momentum of the object. Thus when m=0, e=pc. For massless particles, E=h*frequency, and p=h/wavelength.",
"Here's our ",
"r/sciencefaqs",
" on the ",
"rod question",
" and one on ",
"light being massless",
". Hope this all helps! good luck!"
] |
[
"Entangled particles only remain so if no forces break the entanglement. My changing the spin of one, you break the entanglement, and the other one does not change."
] |
[
"Entangled particles only remain so if no forces break the entanglement. My changing the spin of one, you break the entanglement, and the other one does not change."
] |
[
"If having blond hair and blue eyes is determined by recessive genes, why do so many Scandinavians have blond hair and blue eyes?"
] |
[
false
] |
I live in France and blond hair and blue eyes are less common here. However, I've been to Copenhagen and Oslo multiple times and there are . Why?
|
[
"I think some people conflate \"recessive\" with \"rare\", when those are really separate concepts when talking about genes. "
] |
[
"Because they have a high frequency of the blue eye alleles. It is a misconception that the recessive trait would decrease in frequency through time and eventually go extinct. This would appear to be the case at first glance, because if a blue eyed person were to have offspring with a brown eyed person they are more likely to have children with brown eyes (the exact frequencies depending on the genotypes of parents). But in reality the allele frequency of the genes remains the same through generations in the population and thus the frequencies of blue-eyed and brown-eyed individuals remain the same. It takes selective pressure to change allele frequencies and it appears that in the higher latitudes there is no selective advantage to darker skin and brown eye phenotypes. ",
"This misconception was widely held even among the geneticists for a long time until the mathematician Hardy cheekily showed it to be wrong in 1908. This idea is now widely know as the Hardy-Weinberg equilibrium.",
"http://en.wikipedia.org/wiki/Hardy%E2%80%93Weinberg_principle"
] |
[
"It's probably a ",
"founder effect",
" coupled with a sexual selection. My guess would be that Scandinavians are descended from a relatively small number of founders, one or several of which contained genes for blonde hair and blue eyes. Over time, if blonde hair provided a fertility advantage it would have been selected for. Maybe viking men thought women with blonde hair are super-hot and therefore they end up having more babies with higher status men which leads to better nutrition for their babies. ",
"Once the recessive genes are more common, then blonde hair and blue eyes will be common. ",
"The other possibility is that it's linked to lighter skin pigmentation, which gives better vitamin D production in the low-light northern latitudes. It might be a combo of both, too."
] |
[
"What are the rings that form around a mushroom cloud in a nuclear explosion?"
] |
[
false
] |
There are some really good ones starting at 1:23 in this video: What causes these?
|
[
"The rings are clouds of condensation. Large explosions or any kind cause areas of high and low pressure in the air. In areas of lowering pressure, the air can cool below it's dew point and water vapor condenses into a cloud. As the air returns to it's normal temperature do to an increase in pressure, convection or warming from the explosion, the clouds vanish.\nThe rings are layered to to differences in humidity, pressure and temperature.\nThe lack of humidity and high temperatures may be why they do not appear in tests in arid areas."
] |
[
"Cool. Thanks!"
] |
[
"Is this basically the same phenomena that causes contrails behind airplanes?"
] |
[
"Generally, if you were to take the latitude of a location in the northern hemisphere, and the equivalent absolute value distance from the equator in the southern hemisphere, are these temperatures the roughly the same in their respective summers and winters?"
] |
[
false
] | null |
[
"Generally, no. The Southern Hemisphere has much more ocean than the Northern. The proximity of a point on land to a large body of water is usually a good indicator of its temperature extremes (excluding factors like mountain ranges and strong currents). This is because water is very slow to warm up/cool down compared to land and the air that sits over it. Generally islands and coastal regions experience warmer winters and cooler summers than places away from the ocean. "
] |
[
"It is actually quite the opposite. Warm waters tend to move away from the equator towards the poles and warm the more extreme points on earth. The gulf stream is a great example of this."
] |
[
"Absolutely. The Gulfsteam current carries warm water to Europe which gives it abnormally warm weather for the latitude it's at. Similarly, the Humboldt current in the Eastern Pacific carries cold water up the West Coast which is why places like San Francisco can be so chilly. If you've never seen it, check out ",
"NASA's Perpetual Ocean",
"."
] |
[
"In movies, people smash their head on someone else's head unfazed. Can anyone do that? Doesn't it cause fairly equal damage?"
] |
[
false
] |
Just wondering...
|
[
"It largely depends on impact area. Two people who whack their heads by accident usually both recoil in equal amounts of pain.",
"Someone who is actively attacking with a headbutt will try to strike with the forehead, and aim for specific target areas. The nose, for instance. It breaking, and the victim's head snapping back means the victim has absorbed most of the force, leaving the attacker with less pain.",
"That said, it's still dangerous, and both martial arts schools I attended typically discourage head attacks if you have any other option. Aim wrong or the defender moves wrong, and you will ring your own bell."
] |
[
"Big motherfucker came at me, bro. I said \"Get out of my grill, bro.\" He was all aggro, bro, grabbin my lapel and slobberin', bro. \"What're you gonna do, about it?\" So, I looked at the stars. Said, \"This.\" Then I looked at my shoes. And somewhere between, his nose turned to lasagna. Bro."
] |
[
"Big motherfucker came at me, bro. I said \"Get out of my grill, bro.\" He was all aggro, bro, grabbin my lapel and slobberin', bro. \"What're you gonna do, about it?\" So, I looked at the stars. Said, \"This.\" Then I looked at my shoes. And somewhere between, his nose turned to lasagna. Bro."
] |
[
"What is the medium between synapses? And what force if there is any, pushing neurotransmitters into receptors?"
] |
[
false
] | null |
[
"The synaptic cleft, which is the space between the pre- and post-synaptic structures, contain extracellular fluid which in many ways resemble the fluid surrounding the rest of the neurons. It is roughly 20-40 nm in width, which is just shy of the size of the vesicles that release neurotransmitters (50-250 nm) ",
"source",
".",
"There is no force 'pushing' neurotransmitters, rather all transport post release happens by diffusion. I.e.: the concentration of neurotransmitters in the released vesicle is so high that the neurotransmitters automatically disperse throughout the synaptic cleft.",
"If you want to read up on either the ",
"synaptic cleft",
" or ",
"diffusion",
" wikipedia is a great place!"
] |
[
"From what little I know of this: The synaptic cleft is really really small, no broader than the width of the vesicles that bring the neurotransmitter to presynaptic membrane. The vesicle attaches to the membrane and then it gets stretched out ('exocytosis'), pushing its contents into the cleft. Given the small distance involved, getting across the cleft to the receptors is probably mostly (or entirely) a matter of kinetic energy.",
"I don't know if the synaptic medium is any different from extracellular fluid around other parts of the neuron..."
] |
[
"What about drugs? I’d assume they find their way into the synapse through diffusion too but wouldn’t this require really high concentrations? "
] |
[
"Why does Earth have the highest density in the solar system?"
] |
[
false
] |
By this list, Earth doesn't just have just have high density, but actually has the highest in the entire solar system. Is that just coincidence, or is there some deep reason, anthropic or otherwise?
|
[
"No, the Moon is only a bit less dense than the Earth, and it is so much less massive (about 1% the mass of Earth) that adding it back into the Earth wouldn't reduce the density significantly. More massive objects are simply more efficient at compacting themselves."
] |
[
"No, the Moon is only a bit less dense than the Earth, and it is so much less massive (about 1% the mass of Earth) that adding it back into the Earth wouldn't reduce the density significantly. More massive objects are simply more efficient at compacting themselves."
] |
[
"The inner planets are more dense than the outer planets, because during formation of the Solar System, more volatile elements could not condense closer to the Sun, hence rocky inner planets and gas giants farther from the Sun.",
"As far as why Earth is more dense than Mercury, Venus, or Mars: Earth has more iron and nickel than the other three terrestrial planets, and also the highest mass (which helps compress the mantle and core). Mercury has a high iron content, and is very close in density to Earth."
] |
[
"Why are the blue lights of police cars so visible?"
] |
[
false
] |
[deleted]
|
[
"What do you mean? Those lights are incredibly bright, and are built within reflective lenses designed to be as visible as possible. They are bright because they are built that way. Plus, they are flashing, or moving, and the eye tends to lock onto moving objects."
] |
[
"The new lights are often LED lights, and I've found in purchasing LEDs that the blue and white have higher mCd (milli-Candela: brightness) rating than reds and yellows of the same variety. My guess is either the material used to make the blue LEDs produces brighter light than the reds, or it has something to do with wavelength and red and blue being on opposite ends of the spectrum (maybe higher frequencies mean brighter light for the same current?)"
] |
[
"I think in my case when comparing two different colour options for the same LED this isnt true.",
"I think it has more to do with the ",
"band gap",
", possibly meaning that blue has the largest (or smallest) band gap meaning for the same current more photons are released making them brighter"
] |
[
"If neutrons are electrically neutral why isn't the universe filled with free neutrons?"
] |
[
false
] |
My assumption is that free electrons have a tendency to bind with protons as atoms so that is why we don't see free protons as much.
|
[
"Free neutrons are unstable. A free neutron decays with a half-life of about 10 minutes, generally into a proton, an electron, and an electron antineutrino."
] |
[
"There are already a lot of protons and it costs some energy to add more, which is what will happen if a neutron decays into a proton. The energy cost keeps it stable."
] |
[
"Sorry, I meant to ask you this...",
"What is it about being bound in a nucleus that stabilizes the neutron so that it won't ever decay (at least not for billions of years)?"
] |
[
"If a black hole is infinitely small and dense, how could there be bigger black holes?"
] |
[
false
] | null |
[
"The \"size\" of a black hole can be specified by its mass, or the size of the event horizon (a sphere whose size is such that anything that passes within this sphere is trapped by the hole).",
"There can be microscopic black holes all the way up to those whose mass is millions of suns."
] |
[
"It depends on what you define as the density of the black hole.",
"Since, in theory, a black hole is a ",
", a mass occupying an infinitely small amount of space, you could say that the density is infinite and that would be true for every black hole.",
"You could also say that a black hole of mass M has a non-zero volume V defined by its event horizon and say that the average density in the space it occupies is simply M/V. Going by this definition, since the volume of a sphere is V=4/3 pi r",
" and the Schwarzschild radius that defines the event horizon is r = 2GM/c",
" (r proportional to M), the density scales as ~1/M",
" and so larger black holes (ones with large masses) are less dense than small ones. A stellar black hole of mass ~10",
" kg would have a density of ~10",
" kg/m",
" while a supermassive black hole of mass ~10",
" kg (about a billion solar masses) would only have a density of ~100 kg/m",
"."
] |
[
"For example, the list of every whole number must have twice as many items in it as the list of every odd number.",
"You are right that there are different sizes of infinity in some mathematical systems, but you are totally wrong about the rest. The size of the set of all whole numbers is identical to the size of the set of all odd numbers. There are multiple ways to prove that, but one trivial way is to take the list of all whole numbers, then apply the operation <*2 + 1>. This will turn every whole number into an odd number, with a 1:1 mapping between the two. Both sets are the same size.",
"The set of all whole numbers is a smaller infinity then the set of all real numbers though. There can be no 1:1 mapping between the two.",
"Regardless, this doesn't really apply to black holes at all."
] |
[
"What is the mechanism by which a virus dies outside a host cell--and what happens to the RNA inside?"
] |
[
false
] |
I've read lots on what soap does to viruses (so cool!), but I can't seem to find anything about how simply being outside a host cell long enough renders a virus inert, and I'm especially curious what happens to the genetic material inside once that happens. Does something else grab it up, or does it just wither to nothing? E.T.A.: The subject line should read "RNA/DNA inside."
|
[
"If a virus is ripped apart by soap, the genome will be exposed to extracellular nucleases that will chop it up really quickly. ",
"Radiation inactivation, like with gamma or UV, will cause major genomic damage that may allow the virus to enter a cell, but never replicate to produce new viruses.",
"Fixing chemicals like formalin will essentially lock the virus proteins in place. Essentially paralysis for the virus so that it cant change its shape which is required for function."
] |
[
"Thank you so much! This is super helpful.",
"One more question: if a virion just sits on a surface like cardboard (I saw SARS-CoV-2 takes about a day to go inert on cardboard), what causes it to go inert if it's not directly in the path of, say, sunlight (for the UV)?"
] |
[
"That's a great question. In the absence of obvious factors like UV, direct heat, or chemicals, I'm not too sure. Some brief reading suggests that humidity can affect the proteins on the surface of viruses in a way that basically renders them dysfunctional. All viruses contain a little bit of cell juice, so dessication may affect them as well. Cardboard may draw water out of s virus as well as have some chemicals involved in processing."
] |
[
"What exactly is chloroform and why does it make you pass out?"
] |
[
false
] |
[deleted]
|
[
"The first question is easy. The second question is hard.",
"Chloroform is a chemical with the formula CHCl3 (one hydrogen atom and three chlorine atoms bonded to central carbon atom in a tetrahedral shape). In the classic \"bad guy drugging someone\" scene during movies/TV shows, you usually see a rag filled with chloroform. This is because the liquid chloroform in the rag is evaporating into the gas phase which the victim inhales.",
"An exact understanding of consciousness is one of those open and unsolved \"holy grail\" questions of neurology/neurobiology. How exactly anesthetics operate is a subject of great debate. The best answer on chloroform I have seen is by Patel et. al (citation below). They show evidence that supports the idea that chloroform activates a potassium channel, rending the nerve cells unable to conduct a signal. One way cells communicate by varying concentrations of ions like potassium, so by \"flat lining\" the potassium levels, no information is coherently being transferred between cells. ",
"This lack of cooperation and signal transduction between your nervous systems/brain is what could cause someone to pass out. ",
"Citation: ",
"http://www.nature.com/neuro/journal/v2/n5/full/nn0599_422.html"
] |
[
"Nothing about this is correct. This reaction does not happen, and phosgene is a chemical weapon, not an anesthetic, and chloroform can ",
" make someone pass out."
] |
[
"Nothing about this is correct. This reaction does not happen, and phosgene is a chemical weapon, not an anesthetic, and chloroform can ",
" make someone pass out."
] |
[
"How come mothers can host babies of a different blood type yet have issues receiving blood from others?"
] |
[
false
] |
[deleted]
|
[
"Maternal and fetal blood do not normally mix. Maternal blood is pumped through the ",
"maternal blood vessels in the placenta",
", where nutrients and oxygen are allowed to diffuse into the fetal bloodstream due to the close proximity of fetal vessels. There are a number of ",
"fetal anatomic features",
" that work together to make this system work, as the fetus will be obtaining oxygen from the mother rather than its lungs. The expansion in maternal blood volume and cardiac output is simply a consequence of having to perfuse not only her normal organs but also divert a significant amount of bloodflow to perfuse the uterus and placenta, which then feed into fetal circulation - but they do remain separate.",
"Typically having a baby with a different blood type is not an issue. However, a Rh negative mother (eg O-, AB-, etc) can become sensitized to the Rh antigen if her fetus is Rh positive, resulting in complications for future pregnancies. This usually occurs as tiny volumes of fetal blood (<0.1mL) enter maternal circulation and trigger formation of anti-Rh IgG antibiodies, which can then cross the placental barrier in subsequent pregnancies and cause hemolysis (destruction of fetal red blood cells). ABO alloimmunization is less commonly an issue - for a variety of reasons the antibodies associated with Rh factor are more prone to cross the placenta and cause disease (they are IgG rather than IgM, and fetal rbcs express more of the Rh antigen). There are a few other high-risk antibodies associated with fetal hemolysis (eg anti-Kell)."
] |
[
"I think it's a matter of semantics. The fetus is inside the woman's body, but there is no strict medical definition of \"part of the body\", per se. The fetus is indeed simultaneously separate from and intimately related to the mother."
] |
[
"Anti-Kell in the maternal blood? So Kell antigen on fetal red cells?"
] |
[
"Mars is red because of the iron oxide present in its soil. What is preventing us from separating the Fe from the O, using the O for breathable air, and the Fe to build habitats for us to live?"
] |
[
false
] |
Chemistry class was 12 years ago. I have no idea how difficult the process is to separate the two.
|
[
"IMHO one of biggest problems to run a Mars colony would be the shortage of energy. There are no hydrocarbons to burn and no oxygen to burn them with. Solar power is between one half and one third of that on Earth (depending on the Martian season), and a hypothetical colony would use most of its energy for heating the habitat on such a cold planet.",
"There are several methods for separating iron from oxygen, but they are energy intensive. That is already a problem on Earth, it will definitely be worse on Mars. Some relatively energy efficient methods include reduction with carbon monoxide or hydrogen (or both). ",
"https://en.wikipedia.org/wiki/Iron#Industrial_production",
"But then you'd have to obtain hydrogen and carbon monoxide on Mars. Hydrogen can be obtained from water (which is present underground in some Martian locations) via electrolysis, but this requires a lot of energy as well. Carbon can be obtained from atmospheric carbon dioxide, most likely this will be done using hydrogen as a reducing agent.",
"I'll let chemists answer if there is a better method of obtaining carbon monoxide via reduction. What I know about is the Sabatier reaction which produces methane and water from carbon dioxide and hydrogen (it is a known method in space engineering to recycle oxygen for human respiration). It is slightly exothermic (i.e. it releases a little bit of energy), but the process as a whole requires energy because of hydrogen production.",
"All of this is not even counting the energy required to heat the iron ore up to 2000°C.",
"Nobody said living on Mars would be easy."
] |
[
"These challenges make me wonder why the fixation with Mars. The cost vs rewards and risks don't seem favorable.",
"Why not very large space stations. Then the moon. If we can do that well then venture out further. "
] |
[
"Just a side note from someone unexperienced in the field, Mars does have some winds particularly near sundown and sunrise as the heat from the sun and the cold soil. Could possibly lead to wind turbines.",
"\"There are no seas on Mars, but there are areas where the thermal inertia of the soil changes, leading to morning and evening winds akin to the sea breezes on Earth.[\"",
"https://en.wikipedia.org/wiki/Climate_of_Mars#Wind",
"https://science.nasa.gov/science-news/science-at-nasa/2001/ast31jan_1/"
] |
[
"In-depth AC Current questions"
] |
[
false
] |
I have a hard time understanding AC current. I would like an indepth explanation as to: The more detail the better! I read the wiki and it wasn't exactly what i was looking for. Edit: I forgot one question :) Thank you,
|
[
"How it works",
"Fundamentally, it's not so different from DC. Current tries to flow around a circuit, from positive to negative. In AC, the positive and negative change places periodically (hence \"alternate\").",
"We usually generate AC via an alternator, which is very similar to a motor, only opposite ;) It converts rotational energy into electricity. Imagine a permanent magnet rotating within a coil of wire. The ends of that coil are your AC source, and the voltage/current (I'm gonna say voltage from here to save typing) alternates because the north/south of the magnet alternate. If you draw a diagram of magnetic field lines, you'll note there are a higher density at the ends (poles) of the magnet. When these parts are moving past the coil, you will see peaks in the voltage. The voltage looks like a sine wave if you plot it against time - again, a direct result of the changing magnetic field that is moving past the coil windings (assuming constant rotation speed, centred in the coil, etc).",
"How do the electrons themselves move in the wire/circuit",
"I don't know the fine details here. Electrons flow in the opposite direction to 'conventional current' (ie. from the -ve to the +ve), but their actual movements are more complex. It's not as simple as ping-pong balls flowing down a hose.",
"how it differs in function and efficiency from DC",
"AC is easily and efficiently converted to different voltages by transformers. DC is not.",
"AC is very useful to drive motors because of the sine-wave shape of the voltage. ie. It was made by spinning a magnetic field in a circle, so it's very easy for it to generate a magnetic field spinning in a circle.",
"AC is very ineffecient to transmit under water. \nAC is also not as effecient as DC to transmit via copper wires (see: skin effect), but we can solve that by using multi-stranded cables, and since this effect is proportional to frequency it's not that big of a problem for mains power."
] |
[
"How it works",
"The source generates an electromotive force(EMF) which changes polarity at some frequency. This causes the electric field in the conductor to change direction. I am not sure if this is the kind of answer you're looking for, but have a look at what nalc wrote :)",
"How do the electrons themselves move",
"If you really want to understand electricity, you should look into electromagnetism. But the very simple explanation is that the electric field generated by the source, makes the electrons \"jump\" from atom to atom. When the field is changed, the electrons jump the other way.",
"How it differs in function and efficiency from DC",
"Well, there are several advantages to AC over DC, as well as some disadvantages.",
"AC is easier to transform into larger or lower voltages, depending on the need. This was true in the old days, when the power distribution systems were created. However, today, with switch mode supplies, this is not really valid anymore. ",
"Another advantage to AC is that the current in the line is zero at some point during the cycle. This allows for easy disconnection of a cable/switch, where a DC would carry a (constant) current, creating a larger possibility of arching between the terminals of the contact. However, this only applies for high voltages.",
"In a power transmission line(or any other circuit for that matter) there will be some parasitic capacitance. A problem with AC is that it needs to charge and discharge this parasitic capacity at each cycle. In the european case, its 50 times each second. This ofcause decreases the efficiency of the power line, as some energy is lost to this. But its seen as accecptable in most places. However, in under-sea cables, where parasitic capacitance is much higher than in normal power lines, this becomes a problem. The solution is to use DC in those cables. The problem with DC lines is that the conversion from AC to DC, and then the conversion back to AC require some sophisticated equipment. While it is easy to convert DC stuff at relative low currents/voltages with switch mode converters, it becomres more troublesome with large voltages and currents."
] |
[
"Roughly, current is caused by an electric field. The valence electrons, or \"outer\" electrons of the atoms that make up the conductor are the least strongly bound to their position, and (in metals) can move through the lattice fairly easily. Electrons, being charged particles, move due to the field. They bump into things a lot. Some of the collisions they undergo impart momentum to the lattice. At this point you may hear the word \"phonon\" being used, which refers to the quantized momentum in the lattice. The vibrations that arise in the metal are also known as heat. This is a loss of energy from the electric field into the heat of the metal, or resistance. "
] |
[
"Is it possible to have very vivid false memories?"
] |
[
false
] |
So a good while ago, I had a traumatic experience where I was blackmailed during a conversation with 3 people/strangers that I met somewhere. Ever since, I have been medicated for severe anxiety and depression and it ruined my life. After 3 years of digging, I still can’t find a trace of these individuals. Nothing, zelch. I was on both adderall and diazepam at the time and i was a bit exhausted/sleep deprived. I am starting to question if the conversation even happened. I recall the memory with extreme clarity. Is it possible to have full on vivid and traumatic false memories?
|
[
"What you are describing would be a hallucination rather than a false memory. A memory of a hallucination would be as vivid and traumatic as the hallucination was itself, because you are remembering something that you felt actually happened to you. "
] |
[
"also this is sometimes an issue in marriages / relationships where a spouse may feel like \"x did such and such\" when it never happened. ",
"many men will probably attest to angry wives that wake up after a bad dream where they think their spouse did something to them, but I think that is the lighter of the cases.",
"it can also be common among childhood memories among siblings which get constructed different than reality"
] |
[
"Yes - check out things like the \"lost in the mall\" study where a false memory is implanted into people.",
"https://en.wikipedia.org/wiki/Lost_in_the_mall_technique",
"Some suggest that vivd false memories could come from dreams where we mix the dream events into real life.",
""
] |
[
"Why can i see light even though my eyes are closed?"
] |
[
false
] | null |
[
"Yes it is passing through your eyelids. "
] |
[
"Does it still affect your eyes well being? "
] |
[
"Yes -- staring into the sun is bad, even with your eyes closed, even with sunglasses."
] |
[
"Why is the Sun composed solely of all the elements with a 1:1 proton/neutron ratio? Discarding the lightest and heaviest."
] |
[
false
] |
Also, what makes Fe so special? Do all stars share this composition?
|
[
"Well, when you throw out 75% of the sun's composition you're already being a bit picky-choosy.",
"The sun tends to made out of elements with low atomic number, because elements with high atomic number are made by dying stars, and the sun is alive. Small nuclei tend to have the same number of neutrons and protons because having an asymmetry raises the energy of the nucleus somewhat, because the Pauli exclusion principle forbids them all from having the lowest state, and symmetry between protons and neutrons lets most of the particles be in as low a state as possible. For larger nuclei, more neutrons are required to keep the mutually repulsive protons separated from each other, and this outweighs the symmetry term. (obviously this is a fairly handwavy description of nuclear physics). Aluminum is the first element (13) where the most common and stable isotope has more neutrons than protons.",
"Iron-56 is the most stable isotope, because it balances the energetic advantages of large and small nuclei.",
"Different stars have different \"metallicity\" which is a term meaning \"the fraction of elements heavier than helium.\""
] |
[
"Aluminum is the first element (13) where the most common and stable isotope has more neutrons than protons.",
"Lithium-7 and beryllium-9 would both like a word with you... And the lithium, at least, is pretty significant for stellar fusion paths.",
"Edit: Boron-11 is also the most common isotope."
] |
[
"Nickel 62 is the most stable isotope in terms of binding energy per nucleon.",
"Iron 56 is lighter on a per nucleon basis because it has a higher proton/neutron ratio."
] |
[
"Planck's quantum hypothesis proves that a body can't emit radiation beyond a certain frequency, but this still means that it will emit waves in ALL THE POSSIBLE FREQUENCIES below this limit. So wouldn't the body still be losing energy at an infinite rate?"
] |
[
false
] |
Or am I misunderstanding something?
|
[
"Your first sentence is simply not true. A blackbody emits at all frequencies. Where did you get that there is an upper limit?",
"As per your last question, just because it emits at all frequencies it doesn't mean the energy is infinite. The total intensity is the integral of the spectral insensity per unit wavelength. In symbols:",
"I = integral of dλ B(λ) from 0 to infinity",
"Where B (λ) = dI/dλ and dI is the intensity emitted between wavelength λ and λ+dλ.",
"Planck's hypothesis allows you to calculate a form for B(λ) (the blackbody spectrum) which is such that the above integral is finite, even though you integrate over an infinite domain. Instead, the older Rayleigh-Jeans law provides a B(λ) whose integral diverges when integrated down to λ-> 0 (ν -> infinity), which is the ultraviolet catastrophe. That's why under Planck black bodies actually ",
" emitting the infinite energy they should have in the classical theory."
] |
[
"You are simplifying the ",
"ultraviolet catastrophe",
" a little, but I think I understand why you are confused. For any finite volume of space, there are only a finite number of frequencies below the \"limit\" (even if that finite number can get really big when we think about large volumes), so that is why there is only a finite amount of energy. ",
"The easiest way to think about it is by considering the thermal spectrum in a cavity (i.e. a photon gas) in one dimension (imagine a very narrow and long black tube). The boundary conditions specify that the EM field goes to zero, so it can only be excited at certain frequencies, just like a ",
"vibrating string",
". If the tube has length L, you can have a wavelength of: ",
"lambda=2L, 2L/2, 2L/3, 2L/4, etc. ",
"And those wavelengths correspond to frequency modes of:",
"f= 1c/2L, 2c/2L, 3c/2L, 4c/2L, etc.",
"Thinking about frequencies is nice because they all line up with integers in this case. Now, each frequency mode can be excited independently, and by the equipartition theorem we expect there to be kT worth of energy on average in each of them. If you ask what the total energy is, then you get kT*infinity, because there is an infinite number of modes! So, there is the ultraviolet catastrophe in a nutshell.",
"What Planck did was specify that each mode can only oscillate in discrete energy steps of:",
"dE = h*f",
"So the energy in a given mode could be 0, hf, 2hf, 3hf, etc. with the relative probability of each one given by the Boltzmann distribution. That means that each mode has a different average energy that we can derive from the Boltzmann distribution and the partition function:",
"<E> = dE / (exp(dE/kT) -1)",
"Now, when dE is much smaller than kT, we can approximate that as kT. But when dE is much larger than kT (i.e. at the high frequencies), the average energy starts to shrink well below kT, decreasing exponentially. An exponential function never goes to zero, so there is still a little energy at those higher frequencies, but after a while it becomes very unlikely to find a photon at those high energies. When we sum over all the modes, we find the total energy is now a finite number. In other words, we sum over an infinite number of modes but the sum converges to a finite number.",
"If you work in three dimensions instead of 1, then you have to worry about more total modes, and we should have multiplied the result by 2 earlier to take into account the two possible polarizations of light, but you still get a finite sum. You also get the correct blackbody spectrum.",
"Another important point: If I increase the size of my box, I have to consider even more modes, so the total energy goes up. Is this another catastrophe? No, because the total energy scales exactly with the volume of the box, so the intensity of the radiation inside is the same. There is just more radiation in a bigger box. If the box is the size of the whole universe, then this calculation predicts the exact spectrum and energy density of the cosmic microwave background. That does contain a huge amount of total energy, but it is spread out far enough that nobody is going to get fried by it.",
" added text to make it clear that finite modes assumes a finite volume of space. In practice, the difference between a very large volume and an infinite volume won't make any detectable difference here.",
" I wrote this elsewhere, but since many people seem to make the mistake I want to write it here too:",
"Some of you are worried that there is a finite but astronomically low probability that a photon with an energy greater than the internal energy of the blackbody could be produced. So does Planck's law violate the conservation of energy? No, it does not. The important distinction is that Planck's law is not calculated for an isolated blackbody, it is calculated for a blackbody at fixed temperature. Fixed temperature means that the blackbody can absorb heat from the environment, which is idealized as an infinite reservoir at temperature T. Because the reservoir is infinite, any amount of energy could spontaneously travel to the blackbody and create a massive photon. That would be statistically unlikely but it wouldn't violate energy conservation. Now, a real blackbody isn't going to be able to emit these photons because infinite reservoirs don't exist. But the probabilities in that region are so close to zero that there are very few practical reasons to worry about it."
] |
[
"Here's a concrete example of your question. Take a 1 kg lump of iron and treat it as a blackbody. The specific heat of iron is 0.45 J/(g K) so at room temperature, this lump of iron has 0.45",
"293 J ~ 60,000 J = 4e23 eV of heat energy. If this lump of iron dumped ",
" of its heat energy into one massive photon, what would be that photon's frequency? ",
"Frequency = energy/h-bar and after doing unit conversions, it works out to roughly 6e38 Hz. By comparison, poking around, the most energetic photons ever seen are from a massive ",
"active galaxy",
" and have energies of roughly 1.2e12 eV, which correspond to frequencies of 2e27 Hz. The ",
"most energetic subatomic interaction ever observed",
" was 3e20 eV (frequency 5e35 Hz if it were a photon). So our hypothetical photon would be be a ",
" more energetic than the photons produced in the most violent explosions in the universe, and even a thousand times more energetic than the most energetic subatomic event ever observed.",
"The reason for this is that, as ",
"/u/crnaruka",
" explained, the light is being emitted by electrons in the object. Heat energy means that the atoms and molecules are moving around, so they're vibrating and running into each other. These interactions push electrons into higher energy states. The electrons then decay into lower energy states, emitting photons. These photons are black-body radiation.",
"Black-body radiation emerges from a sort of atomic \"friction,\" so the energies where we use Planck's law should be characteristic of the average molecular energy. Since the total heat energy of a macroscopic object is the ",
" of ",
" of molecular energies, we wouldn't expect Planck's law to be useful in that range, to that object. In other words, it is fantastically unlikely for every single electron in that lump of iron to drop to its ground state all at once, and for all the photons thus emitted to coalesce into a single photon (is that even possible?).",
"(By the way, returning to the example I started with, there are roughly 10",
" atoms in 1 kg of iron. This means at room temperature the ",
" energy of each atom is on the order of 10 eV. Since the photons emitted correspond to energy lost, and they won't lose all of their energy at once, the energy of emitted photons will be a tiny fraction (1%?) of the average molecular energy. That gets down to something like 0.1 eV. Frequencies and wavelengths of photons at that energy are 10",
" Hz and 2 um, which means we should expect to detect photons squarely in the infrared range.)",
"edit WHOAH GOLD! Thanks!"
] |
[
"What resolution is real life in?"
] |
[
false
] | null |
[
"Do you mean something like temporal or spatial resolution of the eye?"
] |
[
"I mean a tv has a set pixel resolution regardless of how well your eyes are. If you if you took a real life image how many pixels can you say it has in comparison?"
] |
[
"The terms you are using are still a bit too unclear for someone to be able to answer your question.",
"By \"real life\" you seem to mean observer independent, so I guess you just mean the universe? ",
"A pixel is a \"picture element\" so maybe you mean what are the elementary units of the universe? ",
"I guess the answer might depend on what level you're looking at and who you ask: a physicist might say atoms in which case I believe the estimate is something like 10",
" A chemist might say it's at the level of molecules, an astronomer might say stellar bodies, someone (philosopher?) might say objects. ",
"Perhaps you can try to explain what kind of format you expect the answer to this question to have and then it would be easier to answer."
] |
[
"How much does viral load contribute to the severity of symptoms for COVID-19?"
] |
[
false
] |
Have there been studies on this yet? For those that have said they had mild symptoms, was this mainly because they were infected with a small amount of virus vs. Someone who say inhaled a lot of virions? Or are severity of symptoms independent of viral load and strictly based upon immune system?
|
[
"Your question has two questions within it: 1. does viral load contribute to severity, and 2. does the dose of virus from the initial infection contribute to severity. These are two separate questions.\nQuestion 1: as far as we’ve seen, patients with worse symptoms typically present with higher viral loads in several studies. However, this is still a relatively new and ongoing pandemic with a variety of factors that may contribute to both severity and viral load, particularly different genetic backgrounds from across the world, so this is still being investigated. \nQuestion 2: this is harder to answer, both for me and for scientists (so far). Generally speaking, in vivo mouse studies or in vitro cell culture studies can be easily used to attempt to answer this question: throw different sized doses and see what happens. For most viruses higher initial dose usually reflects with higher severity, and it is so far suspected that COVID-19 is no different. There are exceptions of course - Epstein Barr virus has more difficulty establishing latent infection of B cells with too high of a dose for example. As far as I’ve seen this question has not been directly answered as of yet though with SARS-COV-2. We can’t exactly determine the dose people receive and for ethical reasons we can’t test it on people, but a mouse model would address this nicely.",
"TLDR; higher viral load seems to correlate with worse symptom severity but we don’t know just yet the doses for SARS-COV-2 in people to correlate with worse outcomes and so on for sure."
] |
[
"Nothing to cite although I believe the data is available and could probably be found with a Google search, but I have read that a) more severe symptoms correlate with a higher viral load and b) lower viral loads and difficulty detecting via PCR correspond with milder clinical symptoms.",
"However - whatever is found should be taken with a grain of salt. Some people, like children, may just have some level of inherent resistance, where the virus replicates with difficulty and the host shows little or no clinical signs. In others who are more susceptible, like the elderly, the virus is able to replicate very efficiently and symptoms are severe.",
"What I'm saying is don't try to correlate a low viral exposure to fewer symptoms, or a high viral exposure to more severe symptoms even if that seems to be the case. It's going to be much more complicated than that. Most people are probably exposed to a dose within 1-2 log viral titers and symptoms still vary widely."
] |
[
"Of course. Viral load is basically a determination of how much virus is in a given sample at a given time of reading. For example, I test how much virus you have right now in a sample from up in your nose - that will tell us your viral load. The viral dose on the other hand would be the amount of virus that you are first given that leads to infection or not. Imagine here how much virus you breathed in when I sneezed on you last week."
] |
[
"If an increase in green house gases causes an increase in temperature due to more heat being radiated back to earth why doesn't the increase cause more heat to be radiated back into space from the sun?"
] |
[
false
] | null |
[
"Greenhouse gases reflect infra-red radiation mostly. The light form the sun is ",
" effected by this. So when light from the sun hits the earth it warms it up, as the earth warms it emits infra-red radiation, it is this infra-red radiation that is reflected back to the earth by the greenhouse gases. For more info see ",
"the greenhouse effect"
] |
[
"Cheers mate that clears it all up"
] |
[
"Yeah. Think of your car. Light goes in the window, heats up the black dashboard, which heats the air in the car, then the heat builds in the car because hot air cant go through the window."
] |
[
"Why do people pace back and forth when they're thinking really hard about something?"
] |
[
false
] |
I know I do this, and I start doing it without even thinking about it. Does it help you concentrate somehow?
|
[
"I don't know if there is any literature on the subject out there, but one possible reason may be less about thinking and more of a physiological response to the stress or anxiety that comes along with it. We tend to use rocking or rhythmic patterns when trying to regulate. (You can look into research on stress regulation methods)",
"So it's not you think better, it helps you calm down which lets you think better."
] |
[
"Walking stimulates the hippocampus, which generates new neurons - likely because your ancestors often needed new brain-space to cope with new environs reached by walking."
] |
[
"Having trouble finding any scholarly articles (mostly because \"pacing\" is a broadly-used word), but I'm pretty sure that pacing is a type of stress coping mechanism, such as nail biting, foot-tapping, and self-touching. I'll see what citations I can come up with."
] |
[
"Why must you wait 28 days after testing positive for covid before getting the vaccinne?"
] |
[
false
] |
The current guidance in the UK is that you must wait 28 days to get ur vaccinne if you have tested positive and I'm just wondering whether there is a scientific reason for this? Also, would there be negative affects if an asymptomatic (but covid positive) person gets vaccinated?
|
[
"It’s nothing to do with “immune system resets” or anything like that. It’s just to make sure you don’t infect people when you go to get vaccinated. ",
"Here’s CDC guidance:",
"Vaccination of people with known current SARS-CoV-2 infection should be deferred ",
". This recommendation applies to people who experience SARS-CoV-2 infection before receiving any vaccine dose and those who experience SARS-CoV-2 infection after the first dose of an mRNA vaccine but before receipt of the second dose.",
"While there is ",
", current evidence suggests that the risk of SARS-CoV-2 reinfection is low in the months after initial infection but may increase with time due to waning immunity.",
"—",
"Interim Clinical Considerations for Use of COVID-19 Vaccines Currently Authorized in the United States",
"28 days is a safe period to be sure that an infected person is no longer infectious. That’s all there is to it."
] |
[
"I just graduated from medical residency from a large Chicago hospital. When the vaccines came out earlier this year, we were encouraged by hospital administration to get the vaccine regardless of if/when we contracted COVID.",
"I would also like to add that even before COVID, in medical practice, there are very few reasons ",
" to give a vaccine, and being sick or recently sick is not one of them. Really the only major one is if you had previously had an allergic reaction to a vaccination. Sometimes parents will ask us if it's OK for their kids to get vaccines even if they were sick recently/are currently sick/are currently febrile, and the answer is usually \"It's totally fine for them to get a vaccine now, but if you'd like to come back in a few days when they're feeling better we can give the vaccine then.\"",
"The other top level answers in this thread are nonsense. I'll never understand why people give their opinions on subjects they know nothing about."
] |
[
"Mainly to allow time for the immune system to reset*. 28 days is enough time for the infection to be completely over and all virus expelled from the body. It means the immune system can focus fully on the vaccine so your immune response will be better. It also makes it beneficial as the vaccine dose will act like a booster to the immune response generated by the infection - if you had both antigens in your system at the same time, you wouldn't get this boost.",
"It's possible that there could be negative effects, but realistically it's unlikely. If there was a real threat to health here, they'd test people before jabbing them and tell people to self-isolate after the jab for a few days. ",
"Edit - the word \"reset\" here is clumsy. I in no way mean that the immune system returns to some kind of starting position. Merely that it is no longer busy dealing with the previous antigen."
] |
[
"Why is there more steam from boiling water *after* I turn off the burner?"
] |
[
false
] |
Gas burner, if that makes a difference. Just something I've always found curious.
|
[
"You're on the right track! It doesn't have anything to do with the type of burner you're using, just that it's on and then gets turned off. Since steam is actually invisible, what you can see is when the vapor cools enough to form small droplets in the air. When you've got heat being pumped into the water, that steam coming off can be well in excess of the boiling point, keeping it invisible. As it gets farther from the source of heat (the burner, via the now boiling water) the steam can cool down and small droplets can form. Often this is far enough away and the steam has spread out enough that you don't really see many droplets. When you remove the heat source, the water molecules coming out of the liquid phase have less energy than they had before. That means that they will cool down a lot quicker and make it look like the water is producing more steam, when in reality it's actually cooler water vapor condensing closer to the water than it was before."
] |
[
"My ",
" is that the Gas burner increases the condensation point (?) in the air by heating it up. When I turn off the burner the water vapor is emitted at about the same rate, but the air is cooler allowing me too see it. ",
"Would be interested to know if this is a well-understood phenomena with a more robust answer. :)"
] |
[
"I was just wondering this the other day while making some mac n cheese. Thanks for the great answer, wish my timing was always this good."
] |
[
"Why can we treat AIDS but not cure it?"
] |
[
false
] |
[deleted]
|
[
"HIV, the causative agent of AIDS, is a retrovirus. Part of the retroviral life cycle is the synthesis of DNA from its viral genome and subsequent incorporation into your own genome. From here, it can go two ways depending on the activation state of the cell: it can either just lay dormant (or quiescent), or its genome can be actively transcribed/translated by the host cell machinery and produce more virus.",
"One major problem is that quiescent cells form a reservoir for the virus in our bodies. Our immune systems cannot recognize these cells as being infected because they're not actively producing virus and presentation of viral antigens is either turned off or significantly reduced. These quiescent cells can persist for years, if not decades, and subsequent infections or other events can activate them, allowing the virus to spread once again.",
"Current drugs prevent certain steps in the viral life cycle, so by keeping HIV+ patients on these antiretrovirals, their viral load is suppressed and spread of the virus will not occur, however we have no real way of flushing out the viral reservoirs from our body (the cells that have had the HIV genome incorporated into that of the cell and remain quiescent).",
"So essentially, we can prevent the virus from spreading, but we can't get rid of all the cells that are already infected. This is why when patients are either taken off antiretroviral therapy or who adhere poorly to the daily medication requirements, viral loads will quickly rebound due to random activation of quiescent infected cells, and the infection of new ones. Not to mention the fact that HIV reverse transcriptase (the enzyme responsible for turning its RNA genome into DNA) has no proofreading capability and its genome is highly mutable, leading to drug resistance and immune system evasion."
] |
[
"It's certainly possible! Though I can't think of one off the top of my head, I believe that a strain of human papillomavirus has been shown to be vertically transmitted in germline DNA (but don't quote me on that). As you said, there would need to be no observable effect, and when viruses establish latency, such as papillomaviruses are wont to do, they can establish this latency in dividing cell types and are theoretically capable of being passed on from generation to generation.",
"The human genome, and the genomes of all eukaryotes for that matter, are littered with the remains of endogenous retroviruses or other integrating viruses from our evolutionary history. Therefore, we know it CAN happen even if we don't have any current examples of it. Importantly, the DNA they incorporate into our own genome can mutate so as to become noncoding. If this happens, it is under no selective pressure, so it's free to mutate - perhaps into a protein-coding gene or as a transcript for micro RNA (miRNA). This way, it can potentially provide a novel function for us in our evolutionary future. An example of this is thought to be the gene for placentin. This is involved in the differentiation of trophoblasts, and the development of the placenta. It's believed to have originated from a virus."
] |
[
"Even though this has nothing to do with the OP, since you're a virologist, I'm going to ask anyway. Are there any examples of viruses which can infect the germ-line cells and show up in future generations of people without any observable effect on the person initially infected in the first place?"
] |
[
"Is E85 sustainable even in the short term?"
] |
[
false
] |
Where I live in Temple, TX an HEB opened a gas station this week and they're selling E85 @ around $2.60 a gallon. People were lined up 10 cars deep at . Now I'm sure a good portion of these people where there for regular gas which they were selling @ $2.99 (gas has been about $3.25 here). Regardless, My question is that if the demand for E85 raises significantly, is it even possible for the demand to be met in the short term? The research I've done on E85 says that it is an inefficient bio-fuel that is only being produced because of corn subsidies keeping the price of corn artificially low, and that we don't have enough farmland in the entire country to support a total e85-based fuel economy.
|
[
"•Bio fuels (when burnt in an engine) may produce less carbon emissions than regular gas/petrol but they still produce a fair amount",
"It depends on the biofuel, but if you allow me to use Brazillian ethanol made with sugar from extant brazilain farmalnd and fertilized with inorganic nitrogen reduced with electrolysis derived hydrogen, it is completely carbon neutral. The probelms you cite with biofuels producing carbon emmissions stem entirely from systems where some inputs from fossil fuels are unavoidable, which will not be the case soon once fossil fuels are too expensife to fit anywhere in the supply chain.",
"•They are generally derived from cereal crops. This means they compete with human food demands and will thus push up the global price of cereal crops. This will inevitably mean a lot of people in the developing world end-up being priced out of staple foods resulting in malnutrition, starvation.",
"The IEA recently admitted that they had exaggerated previous predictions about the ostensible food vs fuel issue which in the first place had been something mostly manufactured by the lobby of the Grocery Manufacturers of America. The food vs fuel issue is mostly inconsequential when taken in a global perspective.",
"•Farming of cereals (and other staples) not suitable for biofuels will switch over to those that are suitable, further squeezing food prices.",
"This is not an argument against biofuels. Right now, food proces today rise and fall on the price of gasoline. As supplies dwindle food prices will get higher and higher until the point where they uncouple from the price of gasoline. In Brazil, where half of thier transportation fuel is sugarcane derived ethanol, this even has already happened. The working economic strategy is to sell either sugar or ethanol depending on which ever product gives the most profit. No matter what, food prices will always be linked to whatever the cost of the current transportation fuel is.",
"•The increased demand for cereal crops will result in more deforestation in places like the Amazon and Indonesia",
"This is true, but again, without any viable alternatives with an energy density that can compete with biodiesel, this may be the sacrifice we'll have to make to avoid outright population control or global war.",
"•The carbon cost of deforestation, production and distribution easily outway the carbon savings when burnt in an engine.",
"This figure has also been greatly exagerrated. 70-80% of the CO2 on the planet is cycled through marine algae, not terrestrial forests, a key metric which was overlooked in the studies that modeled the carbon sinks of the rainforests. There is also the fact that even complete desertification of all of South America would release less stored CO2 to the air than complete consumption of all remaining fossil fuel reserves. Pick your poison.",
"There is nothing \"bio\" or \"green\" or ethical about biofuels. The only motivation for these fuels is that currently they cost slightly less than regular fuels. But the knock-on effects of mass popularity will be catastrophic.",
"Who cares if its green or cheap? That's not what its about. The oil is going to run out one day soon, but the world is still going to need transportation fuels. Electric power for this purpose is still a joke, and mass transit via eletrified rail just isn't feasible. The only thing left that can work with existing infrastructures which is anywhere close to useful as a fossil fuel substitute is biofuel."
] |
[
"I don't know about E85 specifically, but as far as \"bio\" fuels are concerned they must surely rank as one of the worst ideas in human history:",
"There is nothing \"bio\" or \"green\" or ethical about biofuels. The only motivation for these fuels is that currently they cost slightly less than regular fuels. But the knock-on effects of mass popularity will be catastrophic. ",
"Worst. Idea. Ever."
] |
[
"Even given the transportation costs. I've actually never heard of any industrial process that did not suffer diminishing returns on the top end of the economies of scale and increasing returns on the bottom end, so yes, biofuels will see this but then again, fossil fuels do too. Most of the models I've seen do predict the diminishing returns to happen at an earlier point in the arc than for fossil fuels, and that is largely why a global solution will require lots of other transitions. That is, no more heating homes with oil, no more generating electricity with oil, and lots more wind, nuclear and tidal power for electricity. Cynically, I expect we'll stop burning fossil fuels until they are simply gone (and not because we collectively can agree to stop dumping CO2 into the air). Practically this means we'll be burning coal and natural gas for a couple of decades after the oil runs out, so that will help the transition somewhat, and allow the biofuel economy some time to mature before it has to take on the really heavy lifting, but there is no scenario where this all doesn't happen in fits and starts. The scale curve will not be smooth and there will be frequent price volatility in fuels for decades to come. With that said, we're just at the beginning of the early part of the curve, and we're already seeing the increasing returns on the economies of scale and as a trend that should continue for some time.",
"As a last note, I should say that I'm not defending ",
" biofuels. Some of them are good and some of them are plain stupid."
] |
[
"What's the difference between ultrasound and echocardiogram?"
] |
[
false
] |
[deleted]
|
[
"Here’s a good article that describes the different types of echocardiograms. The quick answer is that an echocardiogram is a specialized ultrasound. There are several types of echocardiograms however including some that are done by feeding equipment down the patient’s throat. Why more expensive? Because cardiology.",
"https://www.webmd.com/heart-disease/guide/diagnosing-echocardiogram"
] |
[
"Echocardiogram is just an US of the heart. Originally used the same machines, but now the echocardiogram machines are more advanced in terms of software designed to measure blood flow, etc. ",
"Echo is more expensive compared to a gall bladder US for example because it’s a longer test where the operator have to look at each valve, measure flow and pressure gradients, etc. while on GB it would take 5 mins to see if there is stones or not and measure wall thickness. ",
"A long time ago when these machines were a brand new invention the terms US and echo were interchangeable."
] |
[
"The idea is the same. Why is the echocardiogram more expensive? It's about the same as a difference between a spectrometer and a spectroscope.",
"You can get a nice ",
" if the spectrum with very inexpensive equipment. But when you require data to analyse the spectrum, determine exact intensity of each wavelength, you'll need more advanced and expensive equipment. Same with the study of the heart."
] |
[
"What is it about being suddenly woken that often prevents you from clearly remembering the next few moments?"
] |
[
false
] |
[deleted]
|
[
"Firstly: does this actually happen? I don't think it does in my subjective experience.",
"If it does happen to many, I would ",
" that it's related to the complexity that is human consciousness. We have 'awake' and 'asleep' but within and between those there can be many differences in what the brain is doing and your level of alertness."
] |
[
"ive always had quite a degree of difficulty in remembering anything from most woke-me-up phone calls. the feeling is strange, its like a tip-of-the-tongue moment, i ",
" things were said but can't actually remember what it was. this effect occurs regardless of whether or not i go back to sleep or hop in the shower."
] |
[
"It happens to me ",
". My alarm will go off, I'll get up, cross the room, shut it off, and go back to sleep shortly thereafter. Sometimes I'll be woken by a phone call and not recall the conversation or associated time whatsoever. According to people that interact with me during these times, I'm alert & rational. If I wake up, do something, and go back to sleep shortly thereafter, the chances of me recalling the something are quite low."
] |
[
"[Biology/Medicine] Shouldn't Toxoplasma Gondii be a Bigger Deal than it is?"
] |
[
false
] |
[deleted]
|
[
"my lab works on T gondii infections, particularly in reactivation.",
"T gondii infects (mice, cats, humans) and usually goes quite for a really really long time. in a very few people, either due to severe infection or immune suppression, it reactivates, and can cause brain inflammation, but by the time that happens, the reason for the immune suppression is far more dangerous than t gondii in the brain."
] |
[
"Unless you're immune compromised, very young, or very old, toxoplasma isn't really harmful to humans. In addition, there are already available treatments.",
"It is being researched quite a bit though, you should check out Sapolsky's recent work."
] |
[
"there are a number of treatments for toxoplasmosis; pyrimethamine, sulfadiazine, sulfamethoxazole, and sulfisoxazole are the ones specifically labeled for that indication by the FDA.",
"\"nobody cares about it\" because generally speaking if you're not immunocompromised your body will fend off this infection fairly easily and you won't have to worry about the crazy things you hear about in the news every once in a while. those times you do hear about T. gondii suicide or other strange behavior are most likely going to be rare cases with other precipitating factors. there has been some research which may link infection to suicidal behavior, but it has not been confirmed as of yet.",
"every single hospital will ask pregnant women if they have a cat at home, and will likely make them get rid of it (at least for the duration of the pregnancy) to avoid transmission to the fetus. so really anyone who has had a child or worked in a hospital should have at least had the opportunity to learn about it."
] |
[
"How do we know how it will take around 5 billion years for our sun to turn into a red giant?"
] |
[
false
] |
We've been looking at stars for such a small amount of time how do we know the length of time between changes, or is 5 billion just a very rough estimate?
|
[
"Even though we've been observing stars for a small amount of time, we've been observing a lot of them. Think of an alien observing all humans for a few days. Not long enough to observe an entire life cycle, but long enough to determine what the average lifespan is. (Grossly simplified since human life spans have many more unknown variables.) Astronomers can find stars of similar masses, luminosities or ages and determine relations between them. Also for our sun, we know how long it's been around and knowing the physics of the interior (how much energy is being produced, how much hydrogen remains...) we can make a very good estimate of when the Sun will become a red giant. Do we know it will die on a Tuesday, no. But we can be confident to within a few hundred million years at least.",
"http://en.wikipedia.org/wiki/Stellar_evolution",
"http://en.wikipedia.org/wiki/Sun"
] |
[
"So how do we know the ages of the stars we see?"
] |
[
"If we just observe some given star which is in the ",
"main sequence",
" phase of its lifetime, we actually don't know its age very well at all, unless we can get some pretty robust measurements. Once a star leaves the main sequence, it goes through a very interesting path on the Hertzsprung-Russell diagram, moving through subgiant and red giant and Asymptotic Giant Branch and Horizontal Branch, and we can accurately date stars in those phases of their life.",
"Our knowledge of physics lets us accurately calculate how long it takes a star of a given mass to fuse its available supply of hydrogen (and for more massive stars, to fuse helium also), and so when we see a population of stars that formed together (globular clusters are an excellent laboratory for this, since they are tightly bound groups that formed at a very similar time), we look at what the most massive stars still remaining on the main sequence are (since heavier stars burn faster and brighter and thus live shorter), and since we know their main sequence lifetime, we can calculate how long ago the population formed."
] |
[
"How do the drills used for oil mining deal with torque?"
] |
[
true
] |
[deleted]
|
[
"Watch \"Oil Drill Animation\" on YouTube\n",
"https://youtu.be/fl8L4qSqSqE",
"Generally speaking, the teeth of the drill bit are driven by forced liquid called \"mud\" (which also acts as a preventative to keep the reservoir pressure from shooting out of the ground - higher pressures require more dense mud). ",
"The Drill String (pipe) is suspended by the derrick (roughly) to prevent all the weight of all the pipe to be exerted on the drill bit. Drillers keep a constant watch on \"Weight on Bit\" / Rate of Penetration (among many other things to watch out for to prevent a blowout). "
] |
[
"Glad to. There's so much more involved. Another \"real life\" rig in action can be seen here : ",
"https://youtu.be/HtLOXyoB9Ko",
" ",
"It's very dangerous, hard, and yet exciting work. ",
"A good crew \"tripping\" pipe (going in and coming out of the hole with the pipe) is exciting, but hard and dangerous work. The pay is usually very good. If you can cut it, it's a very nice lucrative career (electrical, mechanical, subsea, other specialties). ",
"If you're interested in more videos, just search *how to drill an oil well *. There'll be land based rigs and offshore rigs. I've never worked on a land rig. "
] |
[
"Glad to. There's so much more involved. Another \"real life\" rig in action can be seen here : ",
"https://youtu.be/HtLOXyoB9Ko",
" ",
"It's very dangerous, hard, and yet exciting work. ",
"A good crew \"tripping\" pipe (going in and coming out of the hole with the pipe) is exciting, but hard and dangerous work. The pay is usually very good. If you can cut it, it's a very nice lucrative career (electrical, mechanical, subsea, other specialties). ",
"If you're interested in more videos, just search *how to drill an oil well *. There'll be land based rigs and offshore rigs. I've never worked on a land rig. "
] |
[
"Do all medical experiments still use a control group?"
] |
[
false
] |
It seems like we would already know what happens to a person with untreated pancreatic cancer. It seems like not giving someone with a terminal illness in a drug trial a possible life saving treatment would be unethical if we already know without any treatment what will happen.
|
[
"Drug development follows a more-or-less defined progression of phases. Not all phases are set up to see if a drug is effective though, initially you want to find out how the drug is metabolized and what kind of doses can be tolerated. For this you don't need a control group. ",
"As far as large randomized control trials go (Phase III usually), what is given to the control group depends on the goals of your study and what is deemed ethically allowable. If you are researching a drug to help extend the life of end-stage cancer patients that have exhausted all other options, then a placebo control would be reasonable. If you are investigating a treatment for a new treatment for a disease with a pre-existing treatment option, you can either have the control group receive the standard of care therapy or even more conservatively give both groups the standard of care and have just the experimental group take the new drug in addition to that. ",
"Similar to phases in drug development, the implementation of new surgical techniques can also follow a set progression described as the ",
"IDEAL framework",
", while there is still an emphasis on randomized trials in surgical innovation (with the control being the standard surgery), you usually first want to prove feasibility and safety. Even after doing so, to randomize groups may also be non-ideal versus comparing to historical outcomes depending on the situation."
] |
[
"No, neither has it ever been the case that all medical experiments always use a control group (there are different study designs). In the case of your example, however: the effectiveness of a treatment is often researched using a control group. The reason this is done is that you want to investigate the difference a new treatment makes. Only knowing the treatment works, but not how it compares to other more conventional treatment, makes it difficult to convince doctors and health insurance companies (and me, would I be a patient) to use your new treatment.",
"So, no, patients in a control group will not be untreated, but rather treated in a conventional way. If I want, for example, to introduce a new therapy for pancreatic cancer, I'll need to know exactly what would happen if I would ",
" use this new treatment (but rather the old, conventional one), in order to investigate the actual effect of the treatment.",
"You're right in saying that we kind'a know what happens with the conventional therapy (it was researched before introduction as well), but there is a 'rule' not to use the same research population twice, so the results of that study should not be used again. Why? A research population should represent the total population (all people with pancreatic cancer) as well as possible. However, by chance the population you choose could be, for instance, luckier than average and survive longer. If you would use this population over and over again to validate new treatments, the 'luckier than average' keeps influencing research results. So, to prevent this, a fresh, uninvestigated group of patients is required."
] |
[
"Does that mean that someone who has participated in a research trial for New Treatment A and had no benefit would be unable to later test out New Treatment B, even though it could potentially save them? Would they be required to wait for NTB to be tested and made available first, or does the rule against using the same research population only apply to the conventional treatment group?"
] |
[
"How can scientists know that the intergalactic space has a density of one molecule per cubic meter?"
] |
[
false
] |
[deleted]
|
[
"Well you can look at the non-absorbed parts of the spectrum. Like each atom only absorbs specific small bands, \"lines\" usually, of the overall spectrum. So just look where the lines aren't and you can see how bright it \"should\" be. ",
"We can even do more advanced stuff, like for very very distant sources... we know that distant stuff is redshifted by the expansion of the universe, meaning that different absorptions at different distances, even of the same element, leave a different \"fingerprint\" in the spectrum, the ",
"Lyman Alpha Forest",
". This is how you can make a map of where clouds of gas are throughout the universe, even if that gas itself isn't visible."
] |
[
"Enlighten us, please?"
] |
[
"B is us right? So how do we know the original intensity of the light as it left A if all we can see is its intensity after passing, or not passing through the amounts of matter we are trying to estimate?"
] |
[
"Would a dinosaur be able to survive in Earth's current atmosphere?"
] |
[
false
] |
Let's pretend that we can clone a dinosaur (or snag one with a time machine, or whatever); would the dinosaur be able survive in our atmosphere, or would it suffocate?
|
[
"oxygen levels then were at 26% compared to 21% today. I would assume 5% would not be significant enough to suffocate a dinosaur considering life today exist at different altitudes with lower amount of oxygen the higher you are. ",
"Source"
] |
[
"lower pressure means less air to breathe. The percentage levels remain the same but the physical amount of oxygen is less at higher altitudes."
] |
[
"This is probably a dumb question, but is there a significant difference between oxygen levels at sea level and a mountaintop? I was under the impression that the most significant change was the pressure. A 5% change seems (to me, a layman) like a substantial change. "
] |
[
"Knowing that hackers can use radio waves to hack phones, is it possible that humanity will be attacked by advanced AI in different star system?"
] |
[
false
] | null |
[
"Such hypothetical questions are better suited for our new-ish sister sub ",
"/r/asksciencediscussion",
". Please consider reposting there instead."
] |
[
"Thank you for your reply. I assumed there would be clear answer telling me that electromagnetic waves can't hack military grade equipment as it's shielded or something else wild but specific.",
"\nI did re-post this question to ",
"/r/asksciencediscussion",
" and will delete my post here.",
"\nI hope you still get this message, I'm not sure how reddit works with messages."
] |
[
"Got the message! Cheers!"
] |
[
"If all of the mass in the universe was to be inside of one black hole right now would the event horizon be larger, smaller or the same size as the universe is right now?"
] |
[
false
] |
also if this was possible would this effect the rate at which the universe expands (especially if the event horizon of this black hole is larger than what the universe is right now)
|
[
"That black hole cannot form. In fact, that mass is already inside its own Schwarzschild radius: if you do the calculation that radius is about equal to the radius of the observable Universe, so you can tell already something doesn't add up.",
"An intuitive understanding for this is perhaps as such: the uniform distribution of matter that we see in the observable Universe continues on at least for a good bit beyond the cosmological horizon. All points of the Universe are mostly identical and none is special. This matter beyond the horizon pulls on you as much as does the matter inside. The overall effect is that this can make the Universe itself expand or contract (depending on the proportions of the various types of energy you can have in your Universe) but you cannot seal off one part of the Universe from the rest of it with an event horizon (which is what a black hole is) because that contradicts the fact that all points of the Universe are equal and are to be treated equally. "
] |
[
"How would an observer distinguish between a bog-standard universe and the interior of a very large and diffuse black hole?",
"Latter has a singularity in the future of any observer in finite proper time, former doesn't. The latter also isn't isotropic.",
"As i understand it, once you've crossed the event horizon, all paths 'out' vanish, and all vectors aim toward the singularity. ",
"Not a correct way to phrase it: all timelike ",
" lead to the singularity. Vectors are not the point and they don't work like you'd expect them to in a curved space. The philosophy behind is correct fo courwe.",
"In a black hole with a mean density similar to our universe, wouldn't this mean that the singularity would be little more than an abstraction, and attempts to cross beyond the event horizon be exactly as absurd as attempts to exit a normal universe?",
"No idea what that means. I'll just note the local density at any point of a black hole is zero.",
"Further, since the Schwarzchild Radius increases with in-falling mass in such a way that the mean density of the black hole decreases, from the perspective of an observer inside a universe-scale black hole wouldn't this simply appear as if the volume of space in their universe-hole were ",
"?",
"No, because ",
"1) the volume of space measured by infalling observer in the inside of the black hole is actually infinite and has nothing to do with R",
" ~ M",
"2) the expansion of the Universe is given by a second order equation you cannot reproduce in this way. Actually, the space in the black hole interior is stretching in one dimension and shrinking in two, and there is a singularity to this at a finite time in the future - it's not really like what is going on in our Universe.",
"3) expansion =/= inflation",
"TL:DR; perhaps the interior of a black hole is indistinguishable from a \"regular\" universe? (Although falling into one may still be unpleasant until the geometry flattens a bit.) ",
"It is really completely different"
] |
[
"Static gravitational fields (the ones that give Newton's law) don't travel. They are instantaneous. "
] |
[
"Stem Cells and regeneration"
] |
[
false
] |
I am curious about stem cells and regeneration from damage. For the sake of discussion lets imagine a hatchet wound to a quadriceps muscle, right in the muscle belly so there is no need to worry about nerves, ligaments, or tendons. Could stem cells be injected via syringe or some other method into the wound to accelerate the muscle/skin repair? How much faster would it heal? If this is impossible, is it due to inherent limitations in how stem cells work or just limited by where we have the technology today?
|
[
"I'm not a stem cell researcher, but I noticed no one has given you an answer so I can give you a little information.",
"Stem cells and regenerative medicine is a huge field as you might imagine. There is nothing that would prevent stem cells from being used in this capacity in principle, but it's tricky. It's a matter of understanding and technology right now; once we've learned more we can re-evaluate the position but ",
"it does look promising",
"!",
"Here are some technical issues. ",
"First, what is the source of the stem cells? Will we harvest them from an individual or will they be ",
"grown in a lab",
"? Right now one of the main things holding us back is that is is difficult to keep a stem cell as a stem cell -- as soon as you take them out of their niche (a place they are happy to be), they change and don't have the same properties that make them so useful. Also, if the source of the stem cell is different from the individual receiving the cells, there are immune/rejection issues to get around. ",
"Second, if we had the stem cells, ",
"how would we make sure they become the right type of cell when we put them in a damaged area",
"? This usually depends on the signals the cell receives from its environment (niche) and we don't fully understand the process, which is called differentiation. Additionally, in the case of muscle cells, we have to make sure the new cells can integrate into the muscle tissue structure since it isn't just a bunch of independently functioning cells.",
"Lastly, and this is related to the second point, how would we make sure the stem cells last long enough to help repair the injury? You have to know where to put these cells so you don't get stem cell loss while promoting the correct path to the correct cell type. ",
"We can do this kind of stuff with bone marrow transplants for blood cells, for example, in which case we know where to get the cells (compatible donor), know where to put them (marrow) and know they will repopulate the cell type we want. ",
"I provided as many muscle-relevant links as possible for the issues I brought up."
] |
[
"Thank you for the clarification, I was envisioning stem cells as a raw biological material that could be used as a sort of wound spackle in the this case, which would dramatically improve healing time. "
] |
[
"I work with stem cell niches, so I can briefly elaborate on XIllusions' answer. ",
"Adult stem cells in the body are essential to the generation of short-lived cells, and are held in tightly controlled environments called \"niches\". For instance, the adult stem cells that produce reproductive cells, called germline stem cells (GSCs), live in the testes or ovaries of an animal. These GSCs can replicate through mitosis and create two daughter cells, one of which stays a GSC while the other becomes a non-stem cell precursor to sperm or egg cells. In drosophila (fruit fly) testes, the GSCs and a type of GSC-helping stem cell called cyst stem cells (CSCs) are restricted to a structure of cells called the hub. If the GSCs and their companion CSCs are forced from the hub, both types of adult stem cells will differentiate into non-stem cells just like the aforementioned sperm-fated daughter cells of the GSCs.",
"I can't really answer the question because I don't know enough about adult stem cells in muscles and skin. If such stem cells did exist, they would require specific niches to function properly, so it may not be as easy as simply injecting them into the wound. Notice I refer only to adult stem cells, as I also don't yet know enough about embryonic stem cells to describe their properties."
] |
[
"Is it possible for binary planets (2 planets orbiting each other) to exist ? Why haven´t we found one ?"
] |
[
false
] |
Hello ! Binary stars and asteroids exist. Is it possible for a planet the size/mass of the earth to exist in a binary state, having another planet of roughly the same size orbiting it. Like a moon, but both are roughly the same mass.
|
[
"Pluto and Charon are in this configuration."
] |
[
"(",
" Pluto's not a planet. ",
")"
] |
[
"We haven't found any binary planets because a 'binary planet' would by definition not be a planet: they haven't cleared their orbit."
] |
[
"If I took a picture of a sunrise over the ocean and a sunset over the ocean, is there anyway for someone else to tell which picture is which?"
] |
[
false
] | null |
[
"You are technically correct, the best kind of correct.\nYou're still a dick though."
] |
[
"Not for certain, but you can often make a good guess.",
"Over the course of the day, the sun heats the air and evaporates water, creating clouds and fine suspended water droplets. The humidity, and droplets scatter blue light, making the sunlight that reaches your eyes redder. At night, the water condenses and the air dries and clears.",
"So sunsets tend to be redder and cloudier, sunrises more yellow and clear. But there's enough variation in daily weather that it's not a sure thing."
] |
[
"With a long exposure time, it might be possible to infer which direction the sun is moving.",
"The colour of the sky is caused by Rayleigh scattering. When the sun is near the horizon, the light is traveling through denser atmosphere and for longer, which filters out the higher-frequency colours. Depending on where the picture is taken, tides and air temperature could have a periodic effect on the barometric pressure such that the air scatters more or less light for sunset or sunrise. (You'd probably need a series of pictures to find a pattern though.)"
] |
[
"Zoologists: How do animals keep their teeth clean?"
] |
[
false
] |
I imagine there'd be great evolutionary benefit to dental hygiene. So what methods, if any, have animals developed to keep their teeth clean?
|
[
"Gnawing on hard materials can help break off tartar. This doesn't ",
" persay, but it does help. So carnivores will gnaw on bones for various reasons and an added side effect is this mild tartar removal. It can lead to tooth fractures though (so be careful giving bones to your pups)",
"Rodents require constant gnawing to combat the constant growth of their incisors, but again, this isn't really cleaning.",
"Mammals are really the only animals that need to worry about dental care however as we have special teeth! Many other groups don't have teeth, or have constantly refilling teeth. Although many groups do have special needs, such as birds beaks need care. Mammal teeth are special because they occlude eachother, allowing for chewing. This means we only get two sets though, and when we lose adult teeth they're gone for good.",
"Most animals will experience some tooth decay as they age however, and it can be a serious issue. This is also why you should take your pets in for dental cleanings!",
"Hopefully this was helpful!"
] |
[
"Very well said, the only think I'd like to add is that most animals don't live nearly as long as humans, so most mammals die before before their teeth totally disintegrate due to cavities."
] |
[
"Yeah! That is also a very important fact. Also good to note that a lot of carnivores don't chew as much as swallow so issues with their teeth may be less noticable"
] |
[
"Where did the mass that set off the Big Bang come from?"
] |
[
false
] |
[deleted]
|
[
"To ask what happened \"before\" the big bang is ill-defined. The big bang was, for all intensive purposes, the (chronological) start of the universe. There is no \"before\", there is no \"from what\". The best we can hope to do is craft theories (which are independently validated) that might give us a theoretical \"glimpse\" at time zero, but there are no (serious) contenders. At any rate, we will never be able to make observations or conduct experiments to validate any such claims."
] |
[
"You're right, forgive my poor choice of words. In essence, yes, the Big Bang was, as it were, the beginning of time. However, for such an event to be possible there had to be mass in the first place, correct? I'm not trying to make a point or go on some sort of ill-advised and nonsensical crusade. Just curious if there are any speculations and/or working theories that this layman can read up on. It's a question that's been on my mind for a while."
] |
[
"However, for such an event to be possible there had to be mass in the first place, correct?",
"What do you mean, ",
"? The big bang ",
" the beginning. There is no \"before\". The mass/energy that existed after the big bang have always existed ",
"."
] |
[
"Is there physical differences between blood types?"
] |
[
false
] |
If I put a drop of blood under a microscope could experts be able to say what type it is? Is there a visible difference? What does A,B, O etc actually mean? And what does the positives and negative’s mean? Thanks
|
[
"There are 4 main types of blood: A, B, AB, and O. Any one of these 4 types can be + or -.",
"On the surface of the blood cell there are proteins called antigens. The important antigens for this explanation are: A antigen, B antigen, and Rh antigen.",
"Someone who has A antigens on their blood cells would be type A. Someone who has type B antigens on their blood cells would be type B. If you have both A and B, you're type AB. If you have neither A or B, you have type O. ",
"Rh antigen decides if you're + or -. If you have the Rh antigen, you're +. If you don't, you're -.",
"So for example, someone with only B antigen and no others would be B-. Someone with A,B, and Rh antigen would be AB+. ",
"The reason it's important to know this is because your body recognizes your cells by recognizing the cell surface antigens on your cells. If a foreign cell surface antigen is detected, your body will attack that cell. So for example, if you have A- blood, you can only recieve a blood donation of O- or A- blood. You can get O- because there's no antigens for your body to recognize as foreign (no B or Rh). In contrast, someone with AB+ blood can receive blood from any blood type, but someone with O- can only receive O-, despite being a universal donor (anyone can receive O- blood.)"
] |
[
"Very tiny. A blood cell is around 7-8um across (there are 1000 um, micrometers or microns, in every millimeter). A surface protein is probably around the 10s of nm (nanometers, there are 1000 nm in every um) large. So roughly a thousand times smaller. ",
"It is relatively easy to see cells with a microscope. With a light microscope you generally cannot see proteins because they are too small. Microscopes are limited by something called the diffraction limit, which is usually around 0.25um (or 250nm).",
"However you can see much smaller structures with an electron microscope and could presumably “see” surface proteins in that manner.",
"You could also use a stain or dye which colors the cell based on what surface proteins are present. You wouldn’t directly see the proteins, but you could differentiate blood type based on an indirect visualization (the color)"
] |
[
"Depending on how you dye/stain the cell, yes. The surface proteins are distributed all across the surface. So if you use a dye which only sticks to those proteins it would color the whole surface of the cell. ",
"There are ways of binding dyes to targeting moeties, like antibodies, that only stick to one type of target. So you could theoretically make different batches with different colors of dyes and bind them to different targeting moeties so only blood cells with that group get stained that color. ",
"There are way, way, way easier and more practical ways to type blood though. So I don’t know that anyone would actually go through the work to do this or what it would accomplish. Just saying this is a way to achieve what the OP asked about and actually see a clear difference under the microscope."
] |
[
"Could the setting of Venus visibly affect the brightness of the whole sky?"
] |
[
false
] |
Let me give a bit of context. I'm a fan of historical novels of Patrick O'Brian, set in the early 19th century. O'Brian is generally known for his careful attention to historical and scientific detail. In the third book of the Aubrey/Maturin series, , there's a scene set on a ship that's sailing in the South Atlantic, south of the equator. There's a bet on whether one of the characters can read at night just by starlight and phosphorescence from the waves. The crucial detail is that they're waiting for Venus to set because then, it is claimed, the starlight is diminished. Allow me a brief quote: ‘We are waiting for the agreed moment, sir,’ said the chaplain. ‘Perhaps you would be so good as to keep time and see all’s fair: a whole bottle of pale ale depends upon this. The moment Venus sets, Dr Maturin is to read from the first page he opens, by the phosphorescence alone.’ ‘Not footnotes,’ said Stephen. [...] At this speed the frigate’s bow-wave rose high, washing the lee head-rails with an unearthly blue-green light and sending phosphorescent drops over them, even more brilliant than the wake that tore out straight behind them, a ruled line three miles long gleaming like a flow of metal. For a moment Jack fixed the glowing spray as it was whirled inboard and then across the face of the foresail by the currents from the jibs and staysail, and then he turned his eyes westwards, where the planet was as low on the horizon as she could be. (the emphasis is mine) Some friends of mine who're astronomical amateurs, but certainly more knowledgeable about astronomy than me, claim that this is definitely impossible; Venus's setting cannot have such a huge effect as to make it so "the starlight distinctly lost in power". Since Venus is the evening star, they say, its setting could indicate the coming darkness, but it can't have the immediate effect as described in the book. Are they right? Is O'Brian here completely wrong? Could you give me an explanation and maybe some data?
|
[
"Venus is in fact bright enough that someone with good night vision can read by it.",
"However, the story is unlikely. As an object gets lower on the horizon, you are looking through more of the atmosphere and the object gets dimmer. This is called atmospheric extinction.",
"At 5",
" , Venus loses about 3 magnitude, making only about as bright as Jupiter.",
"At 1",
" , it would lose 7 magnitude, and be no brighter than an ordinary star.",
"And at the horizon itself, where \"the round glow touched the sea\", it would lose 11 magnitude, and be right at limit of human naked eye visibility.",
"So there would be no sudden change...Venus would slowly lose most of its brightness over many minutes, and would be almost unnoticed as it dipped below the horizon."
] |
[
"Just to be clear, the question is \"Does Venus significantly brighten the night sky?\""
] |
[
"That depends a lot on the phase of the moon, doesn't it?"
] |
[
"If big cats don't purr, then what's going on in this video? (Link in text)"
] |
[
false
] |
See, I've always been told that the thing that separates big cats from small cats is that small cats can purr while big cats can't (with the exception of the cheetah). So what's going on That sounds like purring to me. He's clearly happy. Cats purr when they're happy.
|
[
"Well as most science information tends to be spread around, what you've been told is ",
" true. ",
" big cats can purr, like ",
"cheetahs, lynxes, pumas and more",
". But others, notably in Pantherinae, make purr-like sounds which aren't actually purrs and these include lions, leopards, tigers, and jaguars.",
"You can differentiate between a purr and a purr-like sound by listening for breaks. A true purr persists during the whole respiratory cycle, whereas the situation with the leopard in the video it only occurs during exhalation."
] |
[
"No, all the cats you mentioned belong in separate genuses, none of which are in Felis. Lynx is its own genus and Puma is its own genus."
] |
[
"Lynxes and pumas are Felis. They're small cats. "
] |
[
"What are the biggest scientific discoveries of the past 30 years?"
] |
[
false
] |
When I think of major scientific discoveries since 1900, most that come to mind are from before I was born: relativity, quantum mechanics, transistors, the double helix, the big bang, etc. There are probably some ideas that haven't been around long enough to be recognized for their true importance, but what ideas or discoveries in the past 30 years will future generations regard with the same respect as the ones I listed above?
|
[
"Hard to say one discovery is bigger than another. Here are some off the top of my head; obviously this list is biased towards my interests; e.g., advances in biology/chemistry aren't listed.",
"The universe is expanding at an accelerating rate.",
"The universe is 13.7 +/- 1% years old, made of 4% baryons, 23% dark matter, and 76% dark energy.",
"Neutrinos can oscillate resolving the solar neutrino problem and ensuring neutrinos have mass.",
"Discovery of the W / Z bosons, and top quark.",
"Mapping of the human genome.",
"All the images from Hubble/Chandra/Compton/Spitzer observatories",
"Aspect's experiments verifying no local hidden variables allowed in quantum mechanics, resolving EPR paradox.",
"How CFCs destroy ozone and increase UV light.",
"Better understanding of global warming.",
"Creation of Bose-Einstein Condensation",
"\"High\" Tc Superconductors.",
"1+T superconducting magnets that can be used for particle physics and MRI",
"Superfluidity in Helium 3",
"Quantum hall effect",
"Fractional quantum hall effect",
"Nanophysics; discovery of graphene",
"Scanning tunnelling microscope/ Atomic Force Microscopy, etc."
] |
[
"They're inventions, not discoveries."
] |
[
"I'll add a couple:",
"figuring out how to amplify/sequence/clone DNA on the cheap",
"genetically modified and transgenic organisms"
] |
[
"How is it that both SSRIs and SSREs are both effective antidepressants, despite having the exact opposite mechanism of action?"
] |
[
false
] |
Selective Serotonin Reuptake Inhibitors (SSRIs) supposedly increase the extracellular level of serotonin, while Selective Serotonin Reuptake Enhancers (SSREs) supposedly do the exact opposite. Yet both classes of drugs have been effectively used as antidepressants. What's going on here? This seemingly paradoxical effect makes me wonder if perhaps we're getting this entire mechanism of action wrong. It's commonly believed that SSRIs treat depression and anxiety by increasing serotonin levels, which makes us feel better. In other words, more serotonin = better. But it's also known that SSRIs can often make things worse before they slowly get better. What if the real cause of eventual relief is of serotonin receptors after being inundated with extra serotonin? What if serotonin is actually causing the problem? This theory would explain why SSREs (or more specifically Tianeptine, the only SSRE currently on the market) have a much faster onset of action... they're addressing the problem by reducing serotonin levels. In other words, too much serotonin = bad, and SSREs attack this issue directly. Of course, this is all a wild conspiracy theory on my part, and I'd love for someone to prove me wrong and explain how all this really works. What say you, AskScience?
|
[
"Theyre not necessarily opposite function. Ssri's increase the amount of serotonin in the synapse, which allows more serotonin to saturate receptors. Ssre's however, despite their name, do not increase serotonin to be removed from the synapse, they increase the sensitivity of serotonin receptors, meaning more serotonin is taken up which would other wise not be utilized by the receptors. "
] |
[
"This review will answer where we're at with depression theories and how we think tianeptine (SSRE) works... ",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2902200/",
"The real fact of the matter is the science of most mental/neurological disorders goes way beyond neurotransmitter issues. However, our current treatments are only at this neurotransmitter stage and it's a large focus of researchers to try and find new, better targets that get more at the root of these problems.",
"Also, focusing on neurotransmitters becomes a problem because a) most of their networks heavily intertwine, and b) there are many mechanisms of up-regulation and down-regulation that aren't exactly fully understood.",
"Just to address your theory, tianeptine still takes a couple weeks to have an effect. If it was just a matter of serotonin being a problem, this effect would be within a few hours. Also, things like reserpine (which deplete serotonin) would cause relief from depression, which it doesn't. Generally, it's found to do the opposite.",
"Let me know if you have any specific questions...it's a vast (but very interesting) topic!"
] |
[
"From what I've read, and this is by no means my field but I have studied some of these mechanisms, simply put, we have no idea. Some antidepressants work, some don't, some do very different things in different people, and many people often become attenuated and need dosages need to be increased medications switched etc. Many people struggle for years going from drug to drug until finally finding one that is effective. If anyone has a better answer I would also love to know."
] |
[
"electromagnetic shock waves"
] |
[
false
] |
if an object surpasses the speed of sound, the shockwaves produced (accumulation of wave fronts) create a sonic boom. how is the equivalent of electromagnetic shock waves handled? because aren't electromagnetic waves governed by c?
|
[
"Nothing can ever go faster than c, since it is the speed of light ",
". ",
"However, in materials, the speed of light is actually reduced by the material's index of refraction, and is given by v=c/n. If an extremely energetic particle moves faster than the speed of light for that material, the particle can produce ",
"cherenkov radiation",
", a type of \"electromagnetic sonic-boom.\""
] |
[
"your welcome. I'm going to use the wave model to explain the slowing of light in a material. ",
"The speed of light in vacuum can be written as c=(wavelength)x(frequency). The frequency of light stays the same when going between media (since the wave has to be continuous across a boundary). This means that wavelength of light in a material is different than in vacuum (or air), and we can write (wavelength/n). The speed of light in our material is now v=(wavelength/n)x(frequency)=c/n, so we see that the speed of light is reduced when going through a medium. In vacuum n=1 and we return to the scenario where v=c."
] |
[
"ok right, ive read about cherenkov radiation and its really cool, but is this because the (whatever medium) atoms absorb the light as energy then re-emit the light when returning to the lower energy state?",
"how are EMP's relevant in this discussion?"
] |
[
"How does a CPU physically work?"
] |
[
false
] |
[deleted]
|
[
"Hi, Intel engineer here,\nI just tried to type out a very simplistic example....and ended up getting longer and longer. But to try and sum it up: We have hardware (rtl - register-transfer level logic) and software in combination to tell the cpu what to do. on a very simple scale, if a pin is logic high (1 or vcc for example), then do blah. That blah coulde be an inverter, logical operator, etc. So the cpu just follows all of the finite state machine and combinational logic that we have programmed it to and gives results based on input, default states, etc. Its a hard question to answer simply without getting into detail."
] |
[
"Hi, another computer engineer here. I have some free time so let me expand on OP's explanation.",
"Let's start from the ",
"MOSFET",
". A MOSFET is an electronic switch; you can think of it as an open or closed switch for our purposes and ignore its use as an amplifier for now. There are two types of MOSFETS: NMOS and PMOS. NMOS conducts when the gate voltage is high, and PMOS conducts when the gate voltage is low. ",
"So from these two types of switches, we have the foundations of modern digital circuits: the CMOS. In a CMOS circuit, every NMOS transistor is complemented by a PMOS transistor. For example, look at an ",
"CMOS inverter",
" and note the characteristic symmetrical CMOS diagram. Two more transistors and we can transform the inverter into a NAND or NOR gate. This gives us ",
"functional completeness",
".",
"Once we have a functionally complete set of logic gates, we can implement any combinational logic function. This type of logic can be fully described by a truth table. If we have input set(X), then we get output set(Y) and so on for every possible set of inputs. Combinational logic function is memory-less, and only takes into account the current inputs to produce the outputs. So things like adders, multiplexers, and decoders are combinational.",
"A circuit without memory by itself can't be used implement finite state machines, so we need storage elements. A basic storage element is a flipflop, constructed from a bi-stable core with forcing and gating inputs. For example, a basic D-flipflop has inputs D, Clk, and outputs Q and Q'. D is the forcing input; it forces the bi-stable to assume a certain value. Clk is the gating input; it controls whether D can take effect. More useful D-flipflops have a reset or set which forces the bistable to assume 1 or 0 regardless of the Clk input.",
"Now that we have both combinational logic and memory elements, we can construct state machines. A state machine is a physical realization of a finite state machine: It starts at a predefined state, and given a sequence of inputs, advances through states in a programmed manner. The combinational logic determines what state the machine transitions into (next_Q) given a set of inputs (I) and the current state (Q). The clock determines when the memory elements of the state machine store the next_Q as the state (Q).",
"So from these parts, we can construct a CPU (a really complex state machine. edit: a Turing machine really). Let's look at a very simple single-cycle CPU with a SRAM for instruction memory, another SRAM for data, and a pair of registers (two banks of flipflops). The \"single-cycle\" refers to how at the start of a clock cycle, the CPU takes the state (stored in RAM or registers) and a single instruction (also stored in RAM) to produce an output (written out to RAM or registers) by the end of the same clock cycle. This type of CPU is typically a starting project for CompE undergraduates.",
"A single cycle CPU is made of very simple circuits:",
"Let's first put down our program counter (PC) and an instruction register (IR) . An PC counts up from the starting point of the program (in SRAM addresses). Certain inputs to the PC lets it assume different values than n+1... say n+k where k is taken from a instruction to \"go ahead k instructions\". An IR is simply a bank of D-flipflops that holds the current instruction that is being executed. In a single cycle processor, it updates from the SRAM on every rising clock-edge. So in summary, the PC tells the instruction SRAM which address to read and the IR captures the output of that SRAM. ",
"The contents of the IR is fed into the instruction decoder (ID). For our purposes, the ID can be a set of combinational logic functions. Each function produces an output that tells a certain part of the CPU (usually the multiplexers) what to do. The ID's output would determine which register to read from or write to, or which logic function that an ALU needs to execute, what data goes into that ALU, whether to advance the PC by 1 or k, and a host of other functions (read/write to SRAM being one). Note that the ID outputs control 'selection' functions which maps very neatly to multiplexers.",
"A way to think of it is that a CPU computes many next states simultaneously and the instruction determines which next state is taken (written register or data SRAM). By iteratively executing instructions (as the PC ticks up) until we hit a HALT instruction (that tells the ID to tell the PC to keep its value and disable all writes), we can say that the CPU has ran the program to completion. The output resides in the data SRAM or registers if so inclined. ",
"That's how a simple CPU interprets the electrical signals going into it: lots and lots of multiplexers, some memory elements, and a handful of combinational logic functions. More complex CPUs have things like pipelining, out-of-order instruction, caches, and multiple execution threads, but that's just muddling the point. "
] |
[
"Well to answer the last part of this question, it's all based on the logical circuits that are in the CPU itself (see ",
"Logic Gates",
"). These are circuits that take certain inputs (a set/combination of 0's and 1's) and produce certain outputs. These outputs are determined based on \"truth tables\" - tables that show the exact outputs that will result in certain inputs. We are guaranteed to always have those results (except if there are voltage problems or if the chip itself is dead... we can ignore those problems for the most part). All of these results can be expressed with ",
"Boolean Algebra",
".",
"Now, we can use these logic gates to create flip-flop gates. These gates have different properties based on which one we use; we can have some that toggle on/off, some that save state (used for RAM), and some that have different functionality. In any case, these are also combined with logic gates to create more complex systems (like an ",
"Arithmetic Logic Unit",
") that are themselves combined with other complex systems to create a CPU.",
"Ok, knowing this, the inputs that we throw at the CPU are what we know as an \"instruction set\". By putting in a set of inputs, we have a guaranteed functionality that will execute. Depending on the prior data stored in the registers, this will affect the output received and where the data is stored. But all of these are using circuits to send the data at the proper place.",
"Examples of logical circuits:",
"http://adamwsonu.files.wordpress.com/2010/03/quizcircuit.png",
"http://www.elmhurst.edu/~pturcu/2007-2008/ELM/it228-82/binAdd_files/binAdd.gif",
"http://liblcs.sourceforge.net/four_bit_shiftregister.jpg"
] |
[
"Why does the reaction H2 + O2 produce H2O rather than H2O2?"
] |
[
false
] | null |
[
"Oxygen has 6 of 8 electrons in its outer electron shell. Having 8 electrons in the outer electron shell is a favorable (i.e. stable) configuration. ",
"H2O looks like this with \":\" representing shared electrons:",
"H:O:H",
"In this configuration, O shares two of its 6 electrons with the H atoms and the H atoms share their one and only electrons with the O atom. The end result is that the H atoms have two electrons in their outer shells (both shared with O) and O has four shared electrons (with 2 being shared with each H atom) and four unshared electrons for a total of eight electrons in its outer shell. This is favorable. ",
"Compare the favorable electron state of H2O to that of H2O2. The molecule H2O2 contains 14 outer-shell electrons, but how can the atoms share electrons (i.e. bond) in such a way that the H atoms have 2 outer-shell electrons and the O atoms have 8 outer-shell electrons? The molecule would look like this:",
"H:O:O:H",
"This molecule is fine in theory, but O atoms are relatively electronegative and consequently \"pull\" electrons with more strength than atoms with less electronegativity. Thus, instead of sharing electrons with an equally greedy atom (i.e. another O atom) it is more favorable to form two bonds with H atoms because they are less electronegative. "
] |
[
"It's the way the shells, or how the electron orbitals are shaped. One form is more stable than the other, which in this case H2O is more stable than H2O2. It's why the lable on the H2O2 sign says \"keep out of sun\". The energy from the sun is enough to break the H2O2 into H2O and O2"
] |
[
"What's already been said, especially the bit about the low amount of energy required to decompose hydrogen peroxide. The synthesis of water from hydrogen and oxygen gas gives off a lot of energy (look up hydrogen balloon explosion) and that energy would be enough to decompose any hydrogen peroxide formed, giving off oxygen, which would then react with more hydrogen, and continue on."
] |
[
"Why does drinking coffee make me pee faster than if I drank the same volume of water in the same time period?"
] |
[
false
] | null |
[
"Actually, you are thinking of alcohol. ",
"Caffeine, on the other hand, can act as a mild diuretic by triggering ",
"dilation of the afferent arteriole",
" and increasing the amount of filtrate produced... It is also possible caffeine may decrease some Na+ reabsorption. Either way, more filtrate could mean more urine / loss of water.",
"However, in healthy individuals ",
"this does not lead to fluid loss",
", presumably because ADH/aquaporins will reabsorb all that extra fluid downstream."
] |
[
"My mistake. It has been a while since I dusted out the old cobwebs. Thank you for the correction."
] |
[
"The caffeine acts as an inhibitor for antidiuretic hormone which causes your kidneys to absorb water. Since it is not taking water in for your body, it is expelled.",
"Bonus: The dehydration caused by caffeine can actually make your hangovers worse, so drink water not coffee."
] |
[
"why does bleach feel \"slimy\" on your skin, particularly when you try to wash it off with water?"
] |
[
false
] |
[deleted]
|
[
"The bleach breaks apart the lipids of your skin cells and turns them into fatty acid salts. In a nutshell, the top layer of your skin is turning to soap."
] |
[
"That's not quite what he said. He was saying the bleach was turning the top layer of your skin into 'soap', but soap does not do the same thing to the top layer of your skin. Soap is a surfactant, which means that it helps to lower or break the surface tension of water. Basically, it lets water pickup stuff off your skin that it normally couldn't."
] |
[
"That's not quite what he said. He was saying the bleach was turning the top layer of your skin into 'soap', but soap does not do the same thing to the top layer of your skin. Soap is a surfactant, which means that it helps to lower or break the surface tension of water. Basically, it lets water pickup stuff off your skin that it normally couldn't."
] |
[
"Why do lots of low clouds have flat bottoms?"
] |
[
false
] |
I see this all the time. Giant crazy clouds that spread in every direction, but flat on the bottom.
|
[
"Clouds that form very low to the surface tend to have flat bottoms for two reasons: firstly, clouds normally form above what's called the \"boundary layer\", which is the level at which turbulent surface winds give way to even and horizontal atmospheric winds. This lends to a flattening out of the second factor: the lifted condensation level, or the \"cloud deck\". This is the point at which rising warm air cools to the point of condensation due to the process of adiabatic cooling, which is the natural tendency for air to cool as it rises in elevation. When the air that's rising from the ground hits the dew point, or the temperature at which the air saturates, it forms a cloud. This cloud forms even with the earth with a flat bottom due to horizontal and even winds blowing about above the boundary layer.",
"That's the best I could do from my smartphone"
] |
[
"AcerRubrum got it mostly right. The \"boundary layer\" comment isn't really relevant to this question, but the LCL (lifting/lifted condensation level), is the level at which a parcel of moist air begins to condense. The atmosphere generally cools with height, and a parcel of moist air lifted to a certain height becomes saturated and condensation can occur. Of course, different clouds have different moisture contents, so they might form at higher/lower LCLs than other nearby clouds."
] |
[
"I mostly wanted to illustrate that the winds above the boundary layer run mostly horizontal to the surface, rather than turbulently when mixed by the land surface. And you're right about different cloud types. Low clouds tend to be denser with higher moisture contents due to higher pressure if I remember my meteorology correctly."
] |
[
"Is the brain sexually dimorphic?"
] |
[
false
] |
I recently got into a discussion with a family member about wether or not the brain was sexually dimorphic or not, and they sent me that claim to demonstrate that the brain isn't sexually dimorphic at all. Are the articles accurate in their claims?
|
[
"People often make a rather annoying error of thinking that if there is some difference between men and women that means all men are something and all women are something else. And on the other hand people dismiss gender sex differences because “not all women/men”. Both of those ideas are fallacious. ",
"I like to use the height as an example because it’s relatively non controversial. Men are taller, that’s a biological fact, but that doesn’t mean every man is taller than every woman. Similarly there are differences in brain structure and function but that doesn’t mean you can reliably tell if some brain belongs to a man or a woman like you couldn’t say if someone is a man or a woman if you only knew he/she is 1.73m tall. ",
"One of the articles you linked showed this well. Their classifier was able to recognize the gender from brain measurements with 86% accuracy in cis gender subjects. That is a good accuracy but clearly many women have a brain that looks more like male average and vice versa.",
"Edit: so in the discussion you were in, if they argued that there is no sex or gender differences in the brain they are very likely wrong. If they argued that average differences between men and women can’t have basis in neural structure and function they are very likely wrong. However if they argued that you cannot make generalizing statements like “women are not good at this because their brain is different” they are right."
] |
[
"The articles are peer-reviewed, collaborations between respected scientific institutions, they present their data with conclusions...",
"Were you asking because these articles are counter to biases you may already hold? If so, consider why you may have these biases."
] |
[
"While I agree with you on the first part, I find the second a bit harsh. A lot of earlier studies came to the conclusion that the brain structures of the genders differed significantly from eachother, so I understand why that belief is still ingrained.\nAlso all these studies agree that there are brain forms that are typical for male and female. Only that the overlap is so big that saying they count as sexually dimorphic is the wrong conlusion.\nSo to answer your original question: yes, they prove that the brain is not sexually dimorphic. But to your defense: there are brain types that are extremely rare in one gender but not the other."
] |
[
"How can electrons move through a superconductor without any Joule effect ?"
] |
[
false
] |
Last time in class we started talking with the teacher about superconductors and he just said that one of the current challenge was to find a material that has superconduction proprieties , because we would be able to transport electrical energy without loosing it. When I asked him if it was near 0 or actually 0 joule effect he stated that there was NONE joule effect , when I asked him how could this even be possible he told me that he was not a specialist of this field and so that he wouldnt say something wrong. So now i'm asking it to you! How is this possible?
|
[
"Short answer: We're not completely sure.",
"Longer answer: The BCS theory of superconductivity attempts to explain a number of effects by postulating that if we take a crystal lattice of some form and have electrons moving within it, under sufficiently bizzare conditions, they start becoming correlated. An electron tugs on the atoms of the lattice a tiny bit and that created a minor charge imbalance which subtly rearranges other electrons which now depend on this imbalance to be in its state but that causes other imbalances which... you get the idea. Now usually none of imbalances really have a global effect. But in the superconductive case, the electrons start pairing off, and act as a new \"composite\" particle (the same way that electrons pair of against nuclei and you can treat this new \"atom\" as a composite particle that's neutral) called Cooper pairs. These composite particles are not some new novel \"real\" particle but they do have bosonic properties - i.e. they stop behaving in accordance with Pauli's exclusion principle. More and more and more electrons end up condensing into this sort of joint \"cult\" where electrons start pairing of and their entire state gets intertwined. You can't just change the state of one of them without changing the state of the rest of them. You can't just \"thermally excite\" or \"collide\" with one of them and get away with it. You need to spoil the entire thing at once which requires a bunch of energy.",
"Note that this is a vague recollection of superconductivity that I remember from college. It was heavily emphasized that this theory doesn't explain the mechanism behind how high temperature super conductivity worked or how modern exotic superconductors work. It's an area of open research.",
"TL;DR: It really is 0 Joule effect. We're not sure why. Learn physics and help scientists figure it out."
] |
[
"To give a little more background on what is and isn't known: once you have electron pairing, all aspects of superconductivity are very well-understood. In fact, the Russian Landau-school physicists were basically only missing this key ingredient in the early 50s, but had otherwise developed a completely correct picture of superconductivity. BCS came up with the idea and theory of electron-pairing in metals, and even gave a great justification of how pairing could occur (phonons/lattice distortions) which was consistent with all observations up to 1987 (except maybe heavy fermions?). So \"low-temperature superconductors\" have a totally satisfactory, non-controversial description.",
"The issue with high-Tc is not that we don't understand superconductivity in general (electron pairing = zero resistance), it's that we don't completely understand how pairing occurs in these materials. The temperatures aren't consistent with lattice effects, and these materials are not metals, but rather insulators, often with magnetic order and strong repulsive Coulomb interactions. The result is an enormous number of competing theories and experiments, and a lot of drama."
] |
[
"What you're referring to in your second sentence is ballistic transport and it's not the same as superconductivity. There are very small silicon transistors today whose size (several or tens of nanometers) is smaller than the mean free path of electrons, but they are not superconductive. ",
"Even without scattering events, there is an inherent nonzero resistance associated with ballistic transport. The resistance essentially comes from the limited density of states in the conductive material (",
"Wikipedia source",
"). In superconductors, however, the resistance is actually zero. As far as I know, superconductivity is also a lot more complicated.",
"Edit: added link"
] |
[
"Is there a limit to the resolution of images a spy satellite could capture?"
] |
[
false
] |
I'm interested to know the answer to this. I work with spatial data, and the big satellite provider, Digital Globe, can provide imagery with pixels of around 0.5 m. This is a US government imposed limit, I think. What is the theoretical limit of the resolution of an image captured from space, either from a spy satellite or that . I'm guessing it is limited by atmospheric distortion, but this can be modelled and solved for in post processing, right?
|
[
"The diffraction limit of an optical system is: theta = 1.22*lambda/D, where lambda is a wavelength, like 500 nm, and D is the diameter of the objective. So if something had a 2.5 meter objective, and was at 350 km altitude, it would be able to see features 8.5 cm across.",
"edit: And then there's ",
"the Membrane Optical Imager for Real-Time Exploitation, or MOIRE",
"."
] |
[
"... it would be able to see features 8.5 cm across.",
"This is inaccurate. You would be able to distinguished two points which are more than 8.5 cm apart. It is not like you would be able to see a CD because it is 10 cm across.",
"Each point (on earth) would give rise to a ",
"Airy pattern",
" on the image sensor. This is a result of the diffraction of the light though the aperture of the lens. If the points are too close (less than the 8.5) the two airy patterns would merge and you would be unable to distinguish them. The formula (theta = 1.22*lambda/D) comes from the criterion, that the airy pattern must be so far apart that the first ring of the two airy patterns do not touch."
] |
[
"This is interesting question. ",
"I'm assuming that you talk about resolution that can be achieved with single image. Oversampling (taking multiple pictures over time) together with signal processing could increase the resolution from what is theoretically possible with single image. There is also all kinds of wicked signal processing techniques that could stretch what is possible with straight forward optics. For example: ",
"compressive sensing",
" that can be used to build ",
"single pixel cameras",
"If I remember correctly, FAS has estimated that NRO has satellites with 10 cm resolution. Actual resolution is of course secret. "
] |
[
"According to Einstein, time, length, and mass are relative. Is there any unit of measurement that is not relative to the observer?"
] |
[
false
] |
I'm just wondering it there is a non-relative unit of measurement, since time, mass, length, and the speed of light are all relative to the observer. Or do we measure all things "relative to point (X,Y,Z) at the surface/center of the earth/solar system/galaxy/local group?
|
[
"The old way of doing relativity made mass a variant quantity, with m = gamma * m_0, with m_0 being the \"rest mass\". Then momentum was given by p = m * v like normal. There is a relativistic invariant here too, which would be m / gamma. That quantity doesn't have a special name afaik. ",
"The more modern way takes mass as an invariant quantity, but sets p = gamma * m * v. ",
"The difference is really just one of definitions. But the modern way is considered easier to work with. "
] |
[
"Care to clarify the mass part? In OP's question, he states mass as a Lorentz-variant property. I'm curious as to which it is. ",
"Although he/she also says the speed of light is dependent upon the observer, which is not true"
] |
[
"Care to clarify the mass part? In OP's question, he states mass as a Lorentz-variant property. I'm curious as to which it is. ",
"Although he/she also says the speed of light is dependent upon the observer, which is not true"
] |
[
"Why does most of the attention for alternative fueled cars center around electric batteries, and not hydrogen?"
] |
[
false
] |
I know that several years ago I was seeing a lot of news surrounding hydrogen fuel-cell cars, but recently it seems like cars running off of electric batteries have gotten all of the attention and research. I know that hydrogen can be dangerous, but is that the reason that they aren't being developed? It seems like all of the complaints against electric (short range, long recharge time, poor responsiveness) would be solved by using hydrogen.
|
[
"Hydrogen fuel cell technology is still advancing but there are some definite drawbacks that are hard to escape.",
"Firstly, hydrogen isn't a very good fuel for transportation energy. It has a terrible ",
"energy density",
" compared to batteries or liquid fuels, even when massively compressed. If we did use compressed hydrogen tanks then your car would be transporting a very heavy tank around that has significant rupturing potential. Fueling stations would need to keep huge compressed hydrogen tanks or operate small scale compressors at each pump, neither of which is attractive.",
"Hydrogen is also not the easiest thing to produce. Theoretically we could set up hydrogen production/fueling stations that use solar panels to electrolytically split water, but that is quite energy intensive and I don't think we could manage large scale production that way. The way we generate most of our hydrogen currently is through reformation of methane (natural gas), and if we are bothering to do all that we could just use compressed natural gas in a more traditional combustion engine anyway. Additionally, a lot of current generation fuel cells require extremely pure hydrogen (at least free of CO that comes with reforming) or the catalysts get poisoned.",
"Lastly, the current fuel cell technology is just too expensive compared to gasoline or batteries. The current high efficiency catalysts are typically platinum group metals which are extremely expensive. Work is being done on cheaper and more robust catalysts but we aren't there quite yet.",
"So what is on the horizon? Plenty of research is still being done. New methods for storing hydrogen that can be more dense than straight gas compression are in the works, using crazy solids that hold hydrogen atoms extremely densely at low pressures. New cheaper membrane materials for low temp polymer electrolyte fuel cells (PEM, also proton exchange membrane) are being developed and solid oxide fuel cells that operate at high temps with cheaper catalysts are being improved. Stepping away from hydrogen, we can also run fuel cells with methanol, ethanol, propane and other hydrocarbon feedstocks that have much better energy densities than hydrogen gas."
] |
[
"The hydrocarbon sources, still produce CO2 emissions though correct? So the main reason we're looking at switching to alternative fuels is still applicable to these."
] |
[
"There could (not a chemical engineer, here) be reactions that turn hydrocarbon sources into other carbon compounds, and release hydrogen gas. Ie, the carbon would be stored away (sequestered) in some form, like a solid compound, and so not go into the air."
] |
[
"Human powered energy?"
] |
[
false
] |
This is a serious question and if it is not possible I would love to know why. Why couldn't you take a large amount of people, preferably overweight individuals (the US has plenty), stick them on an excercise bike, and pay them a stipend for the amount of wattage they produce? Seems like to me you are denting the job/energy market, curing plenty of diseases (reducing healthcare costs) by getting people in shape, and producing clean energy. I noticed on the excercise bike this morning, while watching tv and playing on my phone mind you, I was producing 70 watts. What's wrong with this idea?
|
[
"Been asked a few times. Essentially, there are gyms that run this gimmick. But at the end of the day you don't produce enough for it to be worthwhile."
] |
[
"From an energy perspective, this is a very inefficient way to produce electricity. Humans get their energy from food and we are very inefficiently turning this energy into mechanical energy. You would get more energy by just burning the food directly and converting it in electricity. On top of that it cost a lot of energy to produce the food in the first place. Depending on the diet of a person it cost 10-20 calories worth of energy to produce 1 calorie worth of food. So by doing this you are actually losing energy."
] |
[
"Let's say you're Lance Armstrong and you hammer out 500 watts for an hour. The total energy output is 0.5kW-hr, which costs about 5 cents when you plug something into the wall.",
"So the best cyclists in the world can produce about 5 cents/hr in energy output.",
"In the process he's burning over 1500 calories."
] |
[
"Is there a energy limit for a single photon?"
] |
[
false
] |
Is there a limit for how much we can supercharge a single photon? If so, what is it, and how does it compare with the amount of energy we use to, for example, throw a ball? How short would the wavelength be?
|
[
"As the amount of energy in a photon depends on the observer, there can be no such limit. Imagine that there was such a limit that an observer would measure the maximum energy of a photon. And then imagine that this observer accelerated towards the photon. What would happen? Unless the photon increases in frequency, we would violate the conservation of energy for the observer-photon system. So such a limit can not exist."
] |
[
"But what happens when the wavelength of the wave reaches the planck length, does it continue to shorten if an observer accelerates toward it and sees is blue shifted?"
] |
[
"Yes. The planck length is not anything like the resolution of the universe."
] |
[
"How does salt kill a slug?"
] |
[
false
] | null |
[
"Hello! This is a very straight forward answer. When you dump salt on a slug it draws the water out of its body and the slug dies from dehydration. This is due to osmosis, as you probably remember from grade school science courses. Slugs really need to maintain high levels of water content in their bodies in order to survive so even a little loss can be detrimental. We don't know if they feel pain or not, but if you put salt on a slug they move away from it and produce a lot of mucus in order to clear their skin off. I would never recommend it for slug control."
] |
[
"I recommend deterrents like copper tape or metal slug fences around your plants. You can also use sheep wool pellets in your garden as a repellent (replace when wet, they stop working). You could also plant plants in the area you don't mind sacrificing to the slugs, like yellow mustard, lettuce, cucumber, zuccini or strawberries among others. The last resort is trap and release elsewhere. They like terracotta pots and wooden boards, shady areas. I'd use lettuce as bait."
] |
[
"Oh I see, so that's why. What would you recommend then?"
] |
[
"Can animals enjoy music?"
] |
[
false
] |
[deleted]
|
[
"I know a lot of birds enjoy dancing to music and some sing a long. ",
"https://www.youtube.com/watch?v=5DYFHHjSxAA"
] |
[
"I'm not a biologist, so take everything I say with a healthy pile of sodium chloride, but I've heard that music has significant connections to human speech and its patterns. So \"human\" music wouldn't make sense to animals."
] |
[
"Another interesting question, thought the answer is probably very complicated, why do we enjoy music? Its just a bunch of sounds, but it can evoke a pretty strong response in our brains.",
"First of all, cool reddit. Music has such a strong and deep resonance with humans because it was through music that it is believed by most anthropologists, that we formed our very first form of communication. Probably originating from imitation of animals (bird songs etc). Obviously this was a very powerful and enlightening moment for the human species, the beginnings of organised, complex communication. Not only opening up new doors for us in the survival sense, but also in the bonding between a man and a woman, when we moved onto the next level of being able to express sounds in a way that helped garner attraction from the opposite sex, like a lot of animals do. This are two incredibly emotionally monumental moments in our history, and though we've moved on to organised words and letters, the biological memory of where this enlightening came from hasnt left us yet. ",
"As for soundwaves themselves, you have to remember that the entire universe is effectively made up of soundwaves. Every\"thing\" in the universe is a potential medium for sound. The mechanical vibrations that can be interpreted as sound are able to travel through all forms of matter (gases, solids, plasmas, liquids). Although sound cannot travel through a vacuum, because it requires a medium. Sound has a very personal connection with whatever the vibrational waves are interacting with, because essentially, your eardrum, or even your entire body, is becoming intrinsically intertwined with the vibration, this is a powerful thing when you think about it. As to why certain sounds frequencies are perceived as more pleasant than others, I think thats going slightly too deep for a xmas eve, maybe tommorow :)."
] |
[
"What would it take to make a telescope that could see details on a hypothetical planet orbiting the closest stars?"
] |
[
false
] | null |
[
"Quote from my answer to this question: ",
"http://www.reddit.com/r/askscience/comments/n3mx1/could_an_astronomer_tell_me_if_kepler_22b_would/",
"So, if you mean see features of the planet itself, then the answer is we would not be able to see any direct features. (Hubble telescope cannot even really resolve features of pluto, they tried and you can see some pictures ",
"here",
") ",
"The formula relevant for the question you are asking is the ",
"formula shown here",
" for angular resolution. Theta ~= 1.22 lambda/D. ",
"James webb will be 6.5 m in diameter compared to Hubble's 2.4 m diameter primary mirror. ",
"This means it will have maybe 3x the resolving power at the same weavelengths, so its now at the point that it might be able to image pluto for instance, but definitely not the planet.",
"Now! All of that is not to say we cannot get more information about the planet from this. We would be able to measure intensity and spectrum curves from telescopes pointed at kepler 22B, and we would therefore be able to determine more features. Maybe determine if water is in the atmosphere (by seeing some wavelength absorption / emission), maybe we could get better estimates for mass and radius and such based on periods of oscillation and such. So there is still lots to be done, but unfortunately, there is no way to visibly resolve it at this time. ",
"(Numbers for numbers sake: It would require a telescope with a primary aperature/mirror with a diameter of about ",
"2200 km",
" to be able to resolve it comparable to the images we have of Pluto from hubble) ",
"For your question specifically, Proxima Centauri is the closet star at 4.2 light years. So to get pictures like those of pluto linked above, you would need a telescope with an aperture 16 km in diameter. So pretty massive. It makes more sense that we will develop some linked VLA style array of telescopes to be able to do this at some point, but as I'm not an astronomer or anything, i cannot give you a sense of the timeline for this. "
] |
[
"Yes it was, but the formulas and such still hold, just now instead of the \"2200 km\" it becomes 16 km in diameter for the telescope. (Compared to Hubble which is 2.4 m, and James Webb's 6.5 m diameters. )"
] |
[
"if I understand correctly, that last link is if it were 600 light years away?"
] |
[
"Exactly how does an influx of sodium ions create saltatory conduction in a myelinated axon?"
] |
[
false
] |
The lecturer in my neuroscience class today said that electrons associated with the Na ions make a circuit that goes from one Node of Ranvier to the next. The Na ions are not diffusing down the axon themselves. He also said it was a physical chemistry question that he wasn't qualified to answer. I am hoping someone can explain it fairly simply to me or else provide links to a good explanation. Thanks!
|
[
"I assume, from context, that you understand how the action potential travels down an unmyelinated axon. The individual sodium ions do not diffuse down the axon, but their concentrated positive charge pushes other positive ions away and pulls negative ions towards them. This creates a wave of positive charge that travels away from the sodium channels on the inside of the cell. This positive charge on the inside of the cell membrane pushes away some of the positive charged ions on the outside of the cell membrane, reducing the voltage difference that the Na-K pumps set up. This is what triggers the next set of voltage gated channels to propagate the action potential. ",
"However, those positive ions moving away from the outside of the cell membrane create a charge which neutralizes and slows down the wave of potential moving down the inside of the cell. In simple terms, the \"gap\" created in the positive charge outside the cell creates drag on the wave of positive ions inside the cell. In physics terms, the cell membrane create a capacitor which stores some energy and then releases it a split-second later, slowing conduction. ",
"By thickening the cell membrane with myelin, the ions on the inside and outside of cell are further away and influence each other less. This means less charge is stored across the myelinated membrane, and more charge can immediately travel down the axon. In physics terms, the myelin decreases the capacitance of the membrane and the myelinated section acts more like a simple wire, instead of a string of capacitors like an unmyelinated axon."
] |
[
"By thickening the cell membrane with myelin, the ions on the inside and outside of cell are further away and influence each other less. This means less charge is stored across the myelinated membrane, and more charge can immediately travel down the axon. In physics terms, the myelin decreases the capacitance of the membrane and the myelinated section acts more like a simple wire, instead of a string of capacitors like an unmyelinated axon.",
"Nicely done. I've seen numerous professors fail to explain that properly, and talk about it \"insulating\" the axon and various other silly things. "
] |
[
"The dispolarization of that segment at the membrane causes an electric field that reaches the next ranvier node, provided the influx is big enough to cause that, and this is the stimuli for this next node to start the influx of sodium."
] |
[
"Are there ocean dead zones where there is little or no life activity? If so why do they exist?"
] |
[
false
] |
[deleted]
|
[
"Absolutely. ",
"Consider a typical oceanic water column of about 3.5 km. The overwhelming majority of living critters are found within the photic zone, which ends at an average depth of about 200 m. Within this zone, all of the necessities of life are present: an energy source and nutriments. However, light from the sun cannot reach beyond this 200 m zone, so biological productivity decreases abruptly. Still 3.3 km to go.",
"Some critters will spend part of the day below the photic zone and have a daily vertical migration to get to rich food sources from the surface, before retreating to deeper waters where the likelyhood of predation is reduced. A lot of these daily migrators are plankton sized, and stay within a few hundred meter of the photic zone. ",
"Below this, life is scarce. It is not quite a dead zone in the formal sense of the word, but the combined presence of some of the more basic necessities of life (nutriments and an energy source) is not there. Consider this a biological desert. The main source of food is dead organic matter (mostly plankton) raining down from the surface. This may be degraded by bacteria on the way down, which may take a few days. Significant food resources, such as whale falls, are scarce and just \"passing through\".",
"Next stop is the ocean floor, 3.5 km down. Here is the final resting stop for that rain of organic matter from the surface. This allows for the (relative) concentration of this organic matter in a single locale. There is more life here than in the intervening 3 km between here and the surface. The food chain for the most part depends of this rain of dead plankton; this is the land of bottom feeders and detritivores, with a few predators which pick upon the benthos. ",
"Very locally, you'll find extraordinarily lush oases of life tightly clustered around hydrothermal vents. These are exceptional, and constitute a parrallel food chain where the input of energy is not from the sun (no matter how far removed) but from chemical energy transported by the Earths heat transfer system. A lot of these critters depend on symbiotic relationships with specialised bacteria and archea, and live off methane, sulphate, sulphuric acid, or some other energy source.",
"So, in retrospect, you'll find that most of the water column, from a few hundred meters of the photic zone to the ocean floor, is pretty much a biological desert with little biological productivity."
] |
[
"While ",
"/u/Gargatua13013",
" focused more on the ecologic zones of the ocean, I think OP was asking more about dead zones in the sense of anoxic/hypoxic dead zones, so I'll try to clarify.",
"Basically, when nitrogen or phosphorus levels in a region of the ocean get too high, usually from fertilizer runoff or industrial pollution, massive bacterial population explosions occur (usually cyanobacteria). The same can also occur for algae. These massive bacterial/algal blooms are accompanied by a mass die-off once the nutrient sustaining them runs out, and since bacteria can replicate at incredible rates and are very short lived, usually a bloom will explode into existence and then die off within days or weeks. The dead bacteria/algae then decay, which is a process that consumes oxygen. As a result, oxygen levels in the surrounding region of ocean can become depleted in a matter of days, which results in complete annihilation for any fauna living there. Ocean animals still need to breathe! There are some deadzones that have been recorded over areas as large as 800 square kilometers.",
"Interestingly enough, massive anoxic events are hypothesized to have been partially responsible for many of the ecological collapses during the Permian-Triassic extinction. A wide part of Siberia at the time was undergoing massive volcanic activity and releasing thousands of tons of sulfur and carbon dioxide into the air. The sulfur gets absorbed by the ocean and reacts with water to produce sulfuric acid. Sulfur-based bacteria bloomed worldwide. This process was accelerated by global warming from increased CO2 in the atmosphere, since bacterial blooms thrive in warm water. The result was devastating for marine life. There is a reason why many climatologists, geologists, and biologists are calling the Anthropocene \"the sixth extinction event\". Humans are supplying the greenhouse gases to warm the planet, and replicating the same conditions that caused mass die-offs millions of years ago (and that's not counting the countless species we've exterminated through more direct methods)."
] |
[
"For basic everyday use these two words are synonyms although historically I believe one was an adjective and the other a noun. Today they both can be used interchangeably as nouns; at least in American English. "
] |
[
"Why are fathers around the world referred to as some variation of 'papa' or 'baba' in a lot of different countries?"
] |
[
false
] |
When was it collectively decided that that was what we referred to fathers as?
|
[
"archydarky's comment about the history of languages is correct but there is a more fundamental and interesting (but also more speculative) theory:",
"The word for father is some variation of papa or baba for the same reason that the word for mother is commonly some variation of mama or baba; those are some of the first sounds that human babies make as they begin ",
"babbling",
". ",
"The cute version of the explanation is that the parents' vanity makes them assume that their child's first \"words\" will be referencing one of them. ",
"A more objective explanation is that, while the baby is entirely dependent on its parents, it is in the child's and the parents' best interest that the it have a means of getting their attention which does not involve crying loudly (drawing predators, etc.) as early as possible. So they begin to make the association (most likely without consciously realizing it) very early with the sounds which the baby is capable of making (ba, ma, da) with the things it needs to communicate (primarily, \"Dad/Mom, pay attention to me!\")."
] |
[
"The Mama/Baba phenomenon is NOT an Indo-European phenomenon!",
"Versions of 'Mama' for mother and are found all over the world.",
"In Semitic languages (Arabic ",
"), Basque isolate (ama -mother), Dravidian languages (Teluga ",
"), indo-Aryan languages (Bengali ",
"), East Asian languages (Korean informal ",
" and Mandarin Chinese informal ",
"), East African languages (Swahili ",
"), South African languages (Xhosa ",
"), South American native languages, (Quechua ",
"), North American native languages (Cree ",
"), Trans–New Guinea languages (Kabon ",
") and lots, lots, lots more. ",
"The same applies for baba for father. ",
"see ",
"/u/thergoat",
" 's comment below, the explanation is biological, not philological. The labial consonants are very almost universal throughout the world's human languages as is the open 'a' vowel, they are the first syllabic sounds human babies usually produce in the babbling stage of language development and so are the first sounds that parents will interpret as semantically meaningful from their baby. ",
"This paper gives a thorough debunking of the common-ancestor word hypothesis for mama/papa: ",
"https://www.sussex.ac.uk/webteam/gateway/file.php?name=where-do-mama2.pdf&site=1"
] |
[
"The Mama/Baba phenomenon is NOT an Indo-European phenomenon!",
"Versions of 'Mama' for mother and are found all over the world.",
"In Semitic languages (Arabic ",
"), Basque isolate (ama -mother), Dravidian languages (Teluga ",
"), indo-Aryan languages (Bengali ",
"), East Asian languages (Korean informal ",
" and Mandarin Chinese informal ",
"), East African languages (Swahili ",
"), South African languages (Xhosa ",
"), South American native languages, (Quechua ",
"), North American native languages (Cree ",
"), Trans–New Guinea languages (Kabon ",
") and lots, lots, lots more. ",
"The same applies for baba for father. ",
"see ",
"/u/thergoat",
" 's comment below, the explanation is biological, not philological. The labial consonants are very almost universal throughout the world's human languages as is the open 'a' vowel, they are the first syllabic sounds human babies usually produce in the babbling stage of language development and so are the first sounds that parents will interpret as semantically meaningful from their baby. ",
"This paper gives a thorough debunking of the common-ancestor word hypothesis for mama/papa: ",
"https://www.sussex.ac.uk/webteam/gateway/file.php?name=where-do-mama2.pdf&site=1"
] |
[
"Our eyesight is almost always stable. Do we have something close to 'Optic Image Stabilisation'?"
] |
[
false
] | null |
[
"Yes we do - we have the ",
"vestibulo-ocular reflex",
". It's an extremely efficient piece of hard-wiring in our brains and ears and eyes that moves your eyes almost instantly in response to changes in head position. If I remember correctly, as few as three neurons are involved in keeping your eyes stable. They can even rotate in response to a head tilt, although I'm not quite sure what's advantageous about that since they obviously can't rotate more than a few tens of degrees.",
"Our brains also do clever things like \"switching off\" your visual perception when you flick your eyes to a new position, in order to stop you getting disoriented and/or seeing blurred images. Your consciousness then \"fills in\" the missing time, which results in ",
"chronostasis",
", otherwise known as the stopped clock illusion."
] |
[
"Here's an experiment you can try at home: close one of your eyes. Now, gently wiggle the open eye by softly pressing down on your eyelid. Your vision should wobble. So here's the question: why doesn't our vision wobble when we move our eyes to look at something? Shouldn't this happen? How is our eyesight stable?",
"As it turns out, our brain cancels out this wobbling motion whenever it's caused by our eye muscles moving our eyes. The part of our brain that tells our eyes to move sends a copy of this signal to our vision centers, telling them to subtract the perceptual motion generated by the movement of our eyes. ",
"In case anyone is wondering, this signal is called an efference copy, and the way it works is summarized in a paper titled ",
". And the general term for this kind of process is ",
"predictive coding",
". So our brain definitely has something close to Optic Image Stabilization, and this example is only one of many."
] |
[
"Just saw ",
"this Steve Mould video",
" on the subject. He starts by teaching you how to move one eye without moving the other, but the majority is pretty good science. He talks about the things you mention as well as ",
"smooth pursuit",
" which is what enables you to follow a moving object smoothly. "
] |
[
"Does molecular geometry have any significance?"
] |
[
false
] |
So I was looking at the wikipedia article about molecular and atomic geometry and was wondering what role they play. For example what can we know about molecules and atoms simply from their geometry? Can we know what bonds will form? Do they literally fit together like legos based on their shape (in any dimension)?
|
[
"Absolutely! There are tons!",
"One big influence is on the polarity of the molecule. Essentially, more asymmetrical molecules (like water) have areas that are more positively charged and areas that are more negatively charged. This means that the molecules will attract each other more when in a group compared to more symmetrical molecules like ",
"benzene",
". This affects lots of things, like melting/freezing points, what kind of substances it can and can't dissolve, and others.",
"Another one is the shapes of crystals formed by those molecules. Water often forms ",
"hexagonal crystals",
" because of its shape and the types of bonds that can therefore form between water molecules.",
"In biology and biochemistry, proteins are incredibly important and varied molecules made up of incredibly long chains of smaller molecules called amino acids. A big part of what makes proteins unique and do the work they need to do in the body is the ",
"shape they fold into",
". In those images, each of those ribbon/string-looking things in the images represents a long chain of amino acid molecules. The reason they fold into those particular patterns is due to the geometry of the specific component amino acids, and the way the different parts of those molecules interact with each other in ",
"various geometric configurations",
"! ",
"I'm sure there are many, many more examples of how molecular structure is important for the properties of substances that I can't think of right now."
] |
[
"There is an entire branch of chemistry completely dedicated to symmetry applications of molecules. By understanding symmetry of molecules you can predict how that molecule will behave in spectroscopy (IR and Raman). As well as how that molecule will react.",
"We can also use symmetry to know ligand field diagrams of metal-ligand complexes. The process being:",
"Chemical formula ---> VSEPR (or crystal structure) ---> point group (what group of symmetry elements they share) ---> field splitting (based on metal, ligand and symmetry).",
"There is an application with crystallography, however, I know it exists but not how it works."
] |
[
"The shape of a molecule helps to determine its properties.\nFor example, carbon dioxide is a linear molecule. This means that co2 molecules are non-polar and will not be very soluble in water (a polar solvent).\nOther molecules have different shapes. Water molecules have a bent structure. This is one reason why water molecules are polar and have properties such as cohesion, surface tension and hydrogen bonding.",
"Source: ",
"https://socratic.org/questions/why-is-molecular-geometry-important",
" "
] |
[
"AskScience AMA Series: I'm Dr. Paul Knoepfler, stem cell and CRISPR researcher, here to talk about how you might build a real, fire-breathing dragon. AMA!"
] |
[
false
] |
Hello! I'm , stem cell and CRISPR researcher. My 17 year old daughter Julie and I have written a new book about how you might try to make a real, fire-breathing, flying dragon or other cool creatures like unicorns using tech like CRISPR and stem cells. We also satirically poke fun at science hype. We're here to answer your questions about our book, the science behind it, and the idea of making new organisms. AMA! We're planning to come online at noon Eastern (16 UT), AUA! EDIT: Here's a post where I discuss a review of our book by Nature and also include an excerpt from the book:
|
[
"Overly simply stated, I understand that CRISPR can selectivly find/replace bits in a given genome, right? So wouldn't creating a \"New\" property like breathing fire require an existing and perfect model of both the original host ánd the property to be added?",
"I can imagine that changing bits here n there would potentially have unintended or unforseeable outcomes."
] |
[
"It's much more efficient to make genetic changes in sperm/eggs and then let those be carried naturally into all or nearly all the cells of the adult vs. trying to engineer a trait into cells in an adult. However, it might be possible to make traits in adults via something like CRISPR if you can deliver it into enough cells. You might have to use a viral approach such that if you transduce say 20% of cells in a given tissue to try to make a trait change, then those cells would themselves make more of the same virus to infect their surrounding cells and so on. Or you could use something kind of like a gene drive but at the cellular level."
] |
[
"You don't need an existing model, but that would be really helpful. For instance, since we have thousands of models of flight, it'd be much easier to engineer flight in a new creature. Or we could even start with a creature like a bird that already flies. Engineering fire, an entirely new trait, by contrast would require more work and luck. But as we talk in the book some creatures like Bombardier beetles and electric eels could be very helpful in terms of giving us ideas and biological templates to build on. There would definitely be unintended consequences though so you are right on that."
] |
[
"Can you survive on the surface of Mars wearing a Scuba suit/gear? (minus the fins)"
] |
[
false
] | null |
[
"If anything, a lack of pressure is the problem. Humans can't survive anything less than 1/3 atmosphere (height of Mt Everest I believe). Space suits are pressurised (why they look puffy). ",
"Some info about this in this show ",
"http://www.reddit.com/r/Documentaries/comments/24eu9p/pbs_nova_can_we_make_it_to_mars_2011/"
] |
[
"If you were wearing a wet suit that offered enough compression I bet it would be possible."
] |
[
"Could a human survive with an airtight facemask (with air supply), googles, (earplugs?) and warm clothing?"
] |
[
"Why do we have to cry when we are sad or hurt?"
] |
[
false
] |
Is there any biological use or psychically use to it or why would the body use water for crying?
|
[
"First of all, I guess we should specify that two things usually go on when we cry: there are tears, and there is noise, and that noise can be seen a lot more liberally in children, who have no social reason to inhibit or retard their cries. Anyway, with that in mind we should probably consider the reasons a person may cry.",
"One reason we cry is when we are in pain, and you'll see this in both humans and animals. Crying allows us to vocalise our pain, and let others know that we are experiencing it. The difference between us and animals in this regard is the tears. Not a lot of animals will well up and shed tears when they cry, but we do. Even our closest evolutionary buddies like apes and chimps don't actually shed tears when they cry, though they do have tear ducts which are used in lubrication of the eye.",
"So that brings us on to crying as an emotional response. This is something quite unique to us as humans. Some animals will coo and wail when they experience what we can only assume is \"sorrow\" for example, when losing a mother or father, but not shed any tears. ",
"It has been suggested that crying for emotional reasons is something we do for reasons as simple as that it allows us to more clearly and readily communicate our emotional state to others, prompting them to provide us with support or assistance. The maternal instinct that some mothers experience isn't negligible in this regard either.",
"Michael Trimble wrote an entire book on crying, called \"Why humans like to cry: Tragedy, evolution and the brain.\" Sadly, I was only able to read parts of this during my psychology training, but I do recall a point he made which has resonated with me several times in life. He pointed out that as we have evolved, we have become more and more aware and educated about who and what we are, as humans. We grew to understand that other people have similar thoughts and feelings to us, and we learned that we were able to empathise with others because of this. However, sometimes emotions are difficult to express with language and words, because of their complexity, and so crying and laughter are both very fitting communication devices to help people understand how we feel.",
"This ended up being long and rambling, and I apologise. But this is a topic that is fascinating, and I hope you learn everything that you want to!"
] |
[
"Thanks for the long and great explanation! :) ImI find psychology also very interesting!",
"BTW, do you know / is there a simple explanation why men usually cry less than women? Is there a use or - just why? "
] |
[
"I have no training or experience in biology/psychology what so ever, just read it somewhere, that men tend to cry less, because of the way they are raised. They must be the MAN, the strong one, to protect themselves and the loved ones. They cannot show weakness. That is the reason why if a man experiences something wrong, he usually reacts with anger. Women on the other hand were raised to care, to love, to take care of the loved ones, tend to them if needed, support them. That is why if a woman experiences something wrong, they react with emotions (crying). Men are driven by reasoning, logical thinking (observe every aspect of the situation, weight out the possibilities, and make a decision). Women are driven by emotions, they get attached to a lot more things and more strongly in life then men, they usually go after their heart than logic and reasoning."
] |
[
"How do we know that humans interbred with neanderthals rather than just got the genes from a common ancestor?"
] |
[
false
] |
How do we know that humans interbred with neanderthals rather than just got the genes from a common ancestor?
|
[
"The evidence comes from looking at different populations of modern humans. The neanderthal alleles are found only in those populations that left Africa and were in contact in Europe with neanderthals. The African populations that did not come into contact with neanderthals lack the alleles. So it's the geographic pattern of genetic diversity that is the smoking gun."
] |
[
"Also we have neanderthal nuclear and mitochondrial sequences from fossils to compare. It's worth pointing out that all of our genes were inherited from our common ancestors with neanderthals. The sequences diverged over time (as all sequences eventually do) and therefore we can infer neanderthal ancestry to those sequences that are very similar to neanderthals yet different from the rest of human sequences."
] |
[
"All non-Africans are supposed to have ~1-3% neanderthal alleles. This happened 40-80 thousand years ago.",
"Sources ",
"here",
" and ",
"here"
] |
[
"Why is laughter contagious?"
] |
[
false
] | null |
[
"Because it's largely a social reflex"
] |
[
"Is it a matter of mirror neurons then?"
] |
[
"Not sure if it's been traced to them specifically, but they almost certainly play a role."
] |
[
"Do Lithium ion batteries gain weight when they are charged?"
] |
[
false
] | null |
[
"If you're thinking of some excess of electrons or such, then the answer is no. Batteries don't charge by grabbing a hold of electrons - they do so by transporting electrons from one compartment to another. For more about how a battery operates the ",
"Wikipedia article",
" is a good place to start.",
"Now, from a strictly pedantic standpoint, a system with higher potential energy ",
" have higher mass, due to the mass-energy equivalence. In that sense, a charged battery, having higher electrochemical potential, would therefore have higher mass."
] |
[
"What do you mean? I don't understand the context of your question."
] |
[
"Yes. Anything which gains potential energy (in this case chemical potential) gains an equivalent mass coming from the famous mass energy equation.",
"However ... let's take the Hiroshima nuclear bombing. That whole explosion took on the order of 1 gram of mass. 1 gram was equivalent to all that energy.",
"Now imagine the difference in the amount of energy you're charing into your battery and the amount of energy in such a nuclear explosion.",
"Does charging a battery increase it's mass? Yes.",
"Does the mass increase exist on any meaningful (or even measurable) scale? No.",
"Doing some rough estimates that my Laptop has a 100 watt-hour battery. It should weigh about 4 nanograms more when fully charged. That's about 40 red blood cells."
] |
[
"If sound is the vibration of the air, and the state of matter is determided by how much it's molecules vibrate, can sound melt something?"
] |
[
false
] |
Even if you'd need a impossibly high pitch, is it theoretically possible? I feel like I'm forgetting something very important about how heat works.
|
[
"Yes, ultrasonic welding is a method of solid state welding where the material such as plastic between two parts are melted together. The sound vibrates at a high frequency, at the low kHz, to heat up the plastic where it is pressed together in a vice or a press. No glue or soldering needed to meld them."
] |
[
"Yes! I work in product design with a focus on injection molded plastic parts and ultrasonic welding is a robust and reliable permanent assembly method. In designing parts for USW there are actually very specific geometries that are utilized in order to focus the vibratory energy directly into the weld area, as to only melt the polymer in the weld region rather than the entirety of the part. The designer also needs to account for where the molten polymer will flow once it becomes viscous. This ends up looking like a tongue and groove joint, where the tongue has a triangular cross section, and the groove being typically rectangular but with an equivalent cross sectional area as to completely 'fill up' with molten plastic. ",
"Fun fact: the part of the tool that contacts the product and produces the sonic energy for the weld is actually called a 'horn'. A very scientific term for a noise maker. "
] |
[
"Yeah, any sound over time can potentially damage your ears. It's just the way life is. It's like looking at too many bright objects, coloring your hair, scratching your skin. Stimulus over time wears out the receiving subject. ",
"That being said, it's not like you put your ear directly in front of the horn. It's a concentrated shot. Like those air smoke cannons. It's well engineered to prevent leaks. The energy in the vibrations gets absorbed by the plastic which causes it to melt. Any leakage means loss of vibration which means loss of energy which means less productivity. Of course factory workers would still wear ear muffs and safety glasses and insulated gloves, just per OSHA rules."
] |
[
"Are trinary star systems possible?"
] |
[
false
] |
[deleted]
|
[
"Yes, there are triple star systems, and also quadruple, quintuple, etc. However, they tend to arrange in subgroups. Say you have a triple system with components A, B and C. Probably you'll have A and B orbiting together closely one to the other and the C component orbiting both A and B from far away, as if A and B were a single star. The reason for this is that a configuration where A, B and C all orbit one another is very unstable and sooner than later one of the components would get flung away.",
"EDIT: Typo."
] |
[
"You don't even have to go too far to find an example of this - Alpha Centauri is the closest star system to the Sun, and has exactly what SantiagusDelSerif just described. Alpha Centauri A and B orbit their shared center of gravity every 80 years or so, while Proxima Centauri orbits that same center of gravity every 550 000 years."
] |
[
"For the most part, you can take a stable binary pair and replace one of the stars with a much more closely orbiting pair. Basically a small binary system orbitted by a more distant cousin. This first somewhat unintersting kind of trinary system is relatively common. There is believed to be a more interesting trinary orbit in which all the stars follow the path of a figure eight. This has never been observed but simulations suggest it should be stable for at least a few billion years. Some expected stable multistar orbits can be seen ",
"here"
] |
[
"What came first, dogs or cats?"
] |
[
false
] | null |
[
"The problem is when do you call a dog a dog if you don't include domestication? For example:",
"\"Although mDNA testing suggests an evolutionary split between dogs and wolves around 100,000 years ago, no specimens prior to 33,000 years ago are clearly morphologically domesticated dog\"\n",
"link",
"As for assuming cats came earlier because of \"superior\" senses. You have to remember that evolution is not goal-oriented. In whatever environment cats were in, those adaptations were necessary. Dogs had far different needs, such as running in packs and not climbing trees. Retractable claws are not \"better\" than dog's claws, they are jsut different.",
"EDIT: According to ",
"this",
" their common ancestor was about 55.7 million years ago, if that helps at all."
] |
[
"I accidentally a word in my original question (that I'll go fix now) but I meant to say that I assumed cats would come LATER because of higher scenes. ",
"Also I guess I should clarify that I was wondering about the split between canis and felis. You link looks really interesting and I'll have to check it out when I can get to a real computer (i.e. not my phone) "
] |
[
"I'm assuming that between 100kya and 33kya 'dogs' were just wolves that had learned to follow humans around but hadn't joined the pack yet, so to speak. Is that on track?"
] |
[
"AskScience AMA Series: I am a leading researcher in the areas of cannabis plant science and plant physiology at Volcani Agriculture Research Center, in Israel. My name is Nirit Bernstein and I am researching cannabis plant sciences, and the best ways to grow medical cannabis, Ask Me Anything!"
] |
[
false
] |
Medical cannabis is a fast growing field and researchers are delving into the implications of cannabis for medical purposes. Israel hosts one of the world's leading primary research facilities in the area of medical cannabis. I was the first scientist in Israel to study the plant-based science of medical cannabis. I and my team work to advance the academic and applied science of the cannabis plant. Their objective is to develop basic and practical knowledge of secondary metabolism in health-beneficial plants, including cannabis, to contribute to human health and food security, while protecting the environment. Here are some links to some of my research: I will be available at 12 PM PT (3 PM ET, 19 UT), Ask Me Anything! Username:
|
[
"Is there any scientific evidence that flushing plants (feeding only water or decreasing concentration of hydroponic solution) before harvest does anything useful to the final product?",
"Is there any scientific evidence that leaving plants in total darkness for ~24-72hrs prior to harvest increases cannabinoid concentrations?",
"Is there any scientific evidence behind the \"white ash\" test, in which growers seem to believe that cannabis that creates white ash is higher quality or has different mineral content?",
"Can you speak to the chemical process that is occurring when Cannabis is cured? (e.g. after drying, putting cannabis into air-tight, humidity controlled buckets to allow moisture content to become uniform).",
"Is there any evidence for supplemental UV lighting to increase cannabinoid concentrations?"
] |
[
"What is the biggest science misconception about the cannabis plant?",
"And what has your research told you about the best way to grow it? Is it sustainable to still farm it outdoors as the world gets warmer or will future cannabis farms be in fully controlled environments?"
] |
[
"Is the industry headed toward whole-plant cultivation, or cannibinoid isolation and processing for individual benefits? I assume pharma is pushing for the latter outcome, but the former is more scalable and socially equitable. Which is more beneficial from a science perspective?"
] |
[
"Is there anything alive in the soil 100 feet below ground level?"
] |
[
false
] |
Let's say you're drilling around 100' deep. Is there going to be any bacteria in the dirt/clay thats brought up? Is it completely sterile?
|
[
"Bacteria have been found ",
" below the surface. And that is not a limit of life - it is a limit of how deep we searched systematically. Some of them live from radioactive decays, as long as there is liquid water once in a while and the temperature range is fine they can survive, no contact to the surface necessary."
] |
[
"There are bacteria in the ",
"Yellowstone Grand Prismatic Spring",
" that ",
" to live above the boiling point of water."
] |
[
"https://www.newscientist.com/article/dn10336-gold-mine-holds-life-untouched-by-the-sun/",
"https://en.wikipedia.org/wiki/Desulforudis",
"Radioactive decays produce H2 molecules and some sulfur compounds, the microbes found 3 km below the surface use this to live."
] |
[
"Is energy physical?"
] |
[
false
] |
Can energy be described as a physical "thing" or is it more accurately regarded as a behavior/quality of a physical thing? I am a science buff - even by the standards of casual geeks - and I am under the impression that the smallest physical "things" are little vibrating "strings" of energy (you can already tell that answering my question may involve clearing up misunderstandings I have from too many Science channel shows). Does that mean that energy has a physical form? Is the observation of energy like the observation of a of nature is it an observation of a of nature? Is it more like the gravity involved when an apple falls or is it more like the apple itself? ...maybe I should have done this as an ELI5 v__v
|
[
"Energy is a number that you can calculate. It's a number that usually if you calculate it ",
" and calculate it ",
", the number stays the same between both of those times. ",
"Moreover, you calculate energy like E=((mc",
" )",
" +(|",
"|c)",
" )",
" , where m is the mass of the thing, and ",
" is its momentum, a measure of its motion."
] |
[
"Can energy be described as a physical \"thing\" or is it more accurately regarded as a behavior/quality of a physical thing?",
"It's more accurately regarded as a property of physical particles or systems; a property that is absolutely conserved in local interactions, and is related to rest mass, momentum, and other properties, allowing those other properties to be more easily calculated, which makes it very useful for making those properties how we want them to be (especially in the context of doing work, which is the context in which energy was originally conceived).",
"I am under the impression that the smallest physical \"things\" are little vibrating \"strings\" of energy (you can already tell that answering my question may involve clearing up misunderstandings I have from too many Science channel shows)",
"You should definitely abandon that impression. String theory, while it's a beautiful mathematical theory that has taught us much about mathematics, unfortunately now requires more fine-tuning to match observations and experiments than it was originally proposed to resolve, and so is now generally thought of as a useful mathematical framework but not likely to be a correct description of nature.",
"Does that mean that energy has a physical form?",
"No; and in any case, in string theory, strings aren't \"pure energy,\" energy is a property that strings/systems have (just like it's a property of particles/systems), it's just that the strings are replacements for particles.",
"Is the observation of energy like the observation of a law of nature is it an observation of a thing of nature?",
"Both. Measuring the energy of a particle or system is making an observation about a property of that particle or system, and that property obeys certain laws (such as a conservation law) which makes it useful for understanding how it interacts with other systems.",
"Is it more like the gravity involved when an apple falls or is it more like the apple itself?",
"Neither. It's more like the weight of the apple. More specifically, there is an important relationship (I think you know it) between the apple's energy, and its rest mass and momentum, and therefore its weight. And it's part of the quantity that relates the apple itself to gravity; the apple's gravitational field is determined in part by its energy."
] |
[
"Thank you for your time, this cleared things up nicely. "
] |
[
"Is it possible to see sound waves?"
] |
[
false
] |
[deleted]
|
[
"I'm not sure if this is the kind of thing you were interested in, but you can set things up to allow you to visualize sound waves. Check out ",
"Ruben's tube",
"."
] |
[
"I've always wished to do this project:",
"Audible sound is soundwaves between 16 and 16000hz. Any sound you hear is a mixture of one or more of these waves in more or less amplitude.",
"Visible light is radio waves from 400THz (red) to 800 THz (violet). Any color can be represented by a mix of the basic red, blue and green colors.",
"Imagine a very narrow focus directional microphone. It records the sounds, and displays it into a single color: low frequency sounds will be more red, high frequency sounds will be more blue-violet, the amplitude of the sound will be reflected on the brightness of the color. Mixed sounds will be represented like mixing the colors of each frequency, so a complex sound would be grayish or brownish.",
"Now picture an Array of those microphones. Each outputs one pixel, and it makes a grid of color of the sound.",
"With that you could record some fantastic videos of someone playing a music instrument. Imagine that the microphone directed to the mouth of the instrument would show a brighter, clearer sound, while other areas would just have a more general gray noise. You could probably see the sound bouncing out from echos and actually see the acoustic.",
"It seems a perfectly doable project, but I've never seen it. There is a very interesting technique, ",
" ",
"Schlieren photography",
" (thanks nurse spy!) which you can photograph air density, which is fantastic, but not what I'm describing.."
] |
[
"That sounds amazing. I would be very interested to see something like this."
] |
[
"Do lions (and other cats) have spikes on their penises?"
] |
[
false
] | null |
[
"Yes."
] |
[
"Google image search does wonders my friend. ",
"NSFW"
] |
[
"Lions and other cats also have spikes on their tongues to help separate meat from bone. "
] |
[
"Are household appliances perfectly efficient in winter (because all waste heat just heats the house anyway)?"
] |
[
false
] | null |
[
"In a lot of places, heating with gas (by furnace) is cheaper than heating electrically, so it might not be perfectly efficient from a cost perspective.",
"Also, a lot of work goes into designing a heating system for a home so that heat is distributed somewhat evenly. Heat coming from appliances probably isn't going to be as evenly dissipated. To give an extreme example, having one source of heat in a corner of your home will require more energy to maintain your home's climate than having a whole system of ducts which aim to evenly heat your home, because an uneven climate loses more heat to the outside environment."
] |
[
"I think OP was more saying that the appliances are going to be wasting energy via some of the energy they use ending up as heat no matter what you do, so in the winter, they contribute (however slightly) to heating your home, and thus, there is no 'waste' at all, making them 100% efficient because every single bit of energy that goes into them gets used in some useful way. If your TV uses X amount of energy and 95% of that goes to powering the screen and speakers and such, but 5% of that energy ends up as waste heat, then its only 95% efficient. But, during the winter, that 5% that ends up as heat will contribute towards the overall heating of your home, thus meaning that it isnt 'wasted' energy because it still serves a useful purpose and therefore, since 95% of the energy that goes into the TV is useful in powering the screen and such, and 5% is useful in that it add a tiny bit of heat to your home, and thus your HVAC has to do a tiny bit less work, it is 100% efficient."
] |
[
"Part of the problem here is that efficiency has a specific meaning in thermodynamics and the OP is not using it in thst context. I think he is simply observing that the heat normally regarded as waste heat is actually useful in heating the room. This has nothing to do with the devices efficiency. It just good use of a waste product."
] |
[
"Is It Possible Our Universe Is Inside A Black Hole?"
] |
[
false
] |
[deleted]
|
[
"In short, yes there are theories on this. The holographic principle ",
"holographic principle",
"I can't link the papers i've read as you can usually only get them with subscriptions or through a university library log in etc... but a quick google search will get you things like this:",
"black hole holo article",
"When investigating times close to the big bang, the issue is that the Physics of today has it's limits. As you have said, as you look further and further back in time everything gets closer and closer together until we would hit the theorised singularity. However, there exists the Planck length which current physics cannot probe beyond t_p at roughly1.6 times 10",
" metres and that leads to the correspongind Planck time of roughly 5.4 times 10",
" seconds. This latter being the shortest time after the big bang we could investigate (this is still way before the inflation stage of the universe). To probe beyond this time we need a theory of quantum gravity. So we cannot directly investigate the very first moment of universe creation.",
"Alternatively, string theory ( or M-theory \"master\"/\"membrane\" theory: which was created as there were serveral different string theories and someone realised they were all just variants of the same thing) suggests an ",
"Ekpyrotic Universe",
" which points to universes not starting from singularities at all but from clashing branes! This would not support your black hole idea. The membrane theory introduces a new \"brane tension\" term into the Friedman equation (one of the main cosmological tools cosmologists use to describe the universe) and current studies are investigating whether or not we can see signatures in gravitational waves in oreder to observe interactions between branes.",
"So I suppose that though I cannot answer whether a singularity at the centre of a black hole in one universe is where another universe \"Big bangs\" from....there is some proposed interaction between universes using the idea of branes. Perhaps what you talk of IS where they interact but I am not aware of any concrete evidence of this.",
"(On a side note, one theory of the faster than speed of light neutrinos involved the neutrinos hopping between branes and rejoining our brane to beat the light to the target!! WTF OMG!!!!)",
"Bit of a Cosmological rant but hope it will give you some leads for your curiosity to follow. I'm studying for my Physics masters and had a lecture on this stuff yesterday (It's currently the only module I don't fall asleep in!). Stopped lurking on reddit and wrote this over my breakfast expecially for you, ENJOY! :)"
] |
[
"The holographic principle does not actually say the universe is in a black hole - it just says it's sorta analogous.",
"Plus, we don't even know if the universe started from a singularity anyway."
] |
[
"Asked previously: ",
"http://www.reddit.com/r/askscience/comments/kbvdv/is_there_any_scientific_evidence_for_the_idea/",
"Our universe really is nothing like a black hole. A black hole has a centre, while our universe does not appear to. Also, there are no stable orbits inside a black hole - ",
" beyond the event horizon has to be going towards the singularity, no matter how fast it's going.",
"Black holes don't erupt when they get enough mass. They can \"leak\" a little mass through Hawking radiation, but the more massive the black hole, the slower it goes. Any astronomical black hole is so large that the cosmic microwave background gives it more energy than it leaks out anyway. It's completely not analogous to an atomic explosion."
] |
[
"Calling all physicists, especially those who are an expert in 2-d circular kinematics"
] |
[
false
] |
Ok, Reddit, I hate to do this but this is my last resort. I am calling in the big guns to help me answer a friend's physics question homework. I haven't taken kinematics in awhile so I am a bit rusty so I will detail the question out, there is no diagram. I spent literally like 40 minutes on this question and this is as far as I got. See question below. An automobile enters a constant 90 meter radius of curvature turn traveling at 25 m/s north and exits the curve traveling east. The car completes the turn in 5.4 seconds. Assume the speed of the car can be modeled as a quadratic function of time. Ok so here is what I did. I modeled the velocity equation, (the professor told us that the function of speed and velocity can be used interchangably). We are required to figure out initial and final values of arc length, velocity, acceleration, angular velocity, and angular acceleration. v(t) = a(t) + bt + c plugged in initial conditions t(0) and simplified the velocity function to v(t) = a(t) + bt + 25 so for the final value of velocity equation I have v(5.4) = a(5.4) + (5.4)t + 25 I used derivation to figure out the function for acceleration which I got to be: (ac is acceleration since a is already used) ac(t) = 2at+b and using initial conditions I found the initial acceleration equal to: ac(0) = b and final value of acceleration to be ac(5.4) = 10.8+b and finally I used integration of the velocity function to get the function or arc length equal to (I used the equation s = r(x) where x is equal to theta, s = arc length and r = radius, in radians to figure out arc length) 90s(t) = a(t) / 3 + b / 2 +25t. Using initial conditions I simplified initial arc length to 0 and final arc length to be equal to 52.488a + 14.58b = 70.686 after simplifying by figuring out final arc length to be 70.686 by using trigonomtery to figure out that the car did an exact quarter of a circle arc. And that is as far as I got, I have 3 equations with 4 unknowns and no idea how to figure out the rest of the data. Any help would be greatly appreciated, time is a issue here, it is due in about 6 hours.
|
[
"r/homeworkhelp"
] |
[
"Did not know that subreddit existed, just posted the question there too, thanks !!"
] |
[
"you're welcome "
] |
[
"Caffeine came from plants. What evolutionary advantage does caffeine provide for plants?"
] |
[
false
] |
[deleted]
|
[
"This ",
"interesting article",
" describes a study concluding that caffeine in the ",
" genus can act as an attractant for bees. I haven't read the source study yet.",
"This ",
"2007 paper",
" describes the use of caffeine as an insecticide, and outlines the general view of caffeine as a defensive secondary metabolite against insect herbivory. Given the similarity in CNS mode of action in caffeine to other well-known plant produced insecticides (nicotine, pyrethrins) and synthetic pesticides (nenicotinoids), I would think caffeine developed as an insect deterrent. ",
"Presumably, if more studies support the \"bees are attracted to ",
" species' flowers because of caffeine\" hypothesis, that would change the way we think about some secondary metabolite evolution. Would be quite interesting to have a chemical produced by plants which serves such divergent roels: to attract a pollinator; and to repel an insect herbivore."
] |
[
"The first paper is about caffeine in coffee seedlings. 1) it's more concentrated than it would be in the environment, and 2) your statement was about competeing plants. The second paper is about caffeine occurring in leaves, etc. Which is, at best, a first step to showing that allelopathy is possible. ",
"Neither of those papers was about allelopathy. Allelopathy has only been documented in a couple of species (and even those have people that don't really think that's what's going on). To make the claim you're making, you'll need either a study showing reduced growth of other species in soils with coffee litter compared to growing in similar conditions without coffee litter.",
"edit: word"
] |
[
"Here you go.",
"EDIT: Oh, and ",
"this",
", but it's behind a paywall. "
] |
[
"What would be the consequences for the neighbouring areas of the Atucha Power Plant in Argentina if it underwent something similar to other known nuclear disasters?"
] |
[
false
] | null |
[
"'Accident analysis' in design space is broken down into four categories. This doesn't include severe/significant accidents like Fukushima, as they are outside of the plant's design.",
"The four categories are normal operations and transients, anticipated operational transients (things that are expected to happen at least once a year but are not normal. no fuel damage allowed), abnormal operational transients (things that may happen once or twice in the plant's lifetime, very minimal fuel damage allowed, but any radiation release is in the plant's operating bounds and not their accident bounds), and the final category are postulated and design basis accidents (also called limiting faults) and are expected to never happen in the plant's lifetime. These accidents are considered worst case scenarios, and as such, they bound all other accidents. ECCS is designed around protecting against design basis accidents. Limiting faults allow certain levels of radiological release, and may require up to a 10 mile evacuation zone and up to a 50 mile \"plume ingestion pathway\" where wildlife and agricultural products must be destroyed. Each nuclear plant's Emergency Preparedness Program is required to function in the unlikely event of a design basis accident.",
"For accidents, they are readily detectable. Firstly, reactor protection system will actuate on parameters which could challenge the reactor core. RPS will initiate the scram, and set off a cluster of alarms in the control room. The operators, during the event, have data systems and annunciator/alarming systems which prioritize the alarms and code them based on priority and severity. There are monitoring systems for radiation, temperature, pressure, level, etc. ",
"Looking at the worst case event, a loss of coolant accident (LOCA), this involves a break of the largest pipe in the reactor coolant system (typically a 30\" or larger pipe for most plants). The water pours out into the containment. In a fraction of a second, this condition is detected at the reactor is immediately scrammed. It is assumed that simultaneously with the LOCA initiation, that all offsite power is lost, and as such, a LOCA signal automatically fires off an emergency diesel generator start signal. The DGs start up in emergency mode and as soon as they are capable, the load sequencer then begins starting up ECCS (emergency Core Cooling System) pumps, one at a time, from high pressure to low pressure, to ensure that it doesn't overload the diesel generator. The first set of high pressure safety injection pumps comes on and injects within 30 seconds, and is enough to prevent fuel melting. The fuel cladding may have slight cracks, as it is allowed to reach up to 2200F, but it will not have gross failure. As the pressure decreases in the reactor, the low pressure safety injection systems and accumulators will also inject to re-cover the fuel with water, or at least maintain a minimum spray. Water initially is injected from a storage tank, and the water which spills out from the reactor goes to the containment sump system. Once the water tank is empty, the ECCS systems will use the water from the sump system, spray it over the fuel, and let it spill back into the sump, creating a closed loop system (recirculation cooling). The containment will have a spray system activate to make it rain in the containment and reduce pressure and temperature, and one of the decay heat removal pumps is started to take some of that sump water and cool it before re-injecting it, which ensures the water temperature decreases. The system is designed to function for at least 30 minutes with nearly no operator action. The radioactive gases in the containment would be vented to secondary containment, where it then passes through a system of cleanup filters before being released. Under design conditions only a small amount of material is released (similar to the TMI accident). The number of expected cancers and/or deaths within 40 years for people exposed would be a on the order of <10-<100. ",
"This is a design basis accident however. If you want to look at worst case events, look at chernobyl and fukushima. They clearly show what happens when a plant is allowed to operate outside of its design basis, or with inadequate design basis, combined with systemic issues and human performance errors.",
"If you have any more questions feel free to ask."
] |
[
"Just some context: the ",
"plant",
" is by a river, some 100 km upstream from Buenos Aires. What would be the risk to the city?"
] |
[
"Thanks for the Link, I couldnt find it in English."
] |
[
"If the Sahara desert starts receiving 100 inch of rain per year, would it eventually become a forest?"
] |
[
false
] |
Assuming no humans goes in there and start messing with things, of course. If it does become a forest, how long would it take?
|
[
"Absolutely. I don't know who these folks are who are saying no.",
"With available water, pioneer species could move in and a unique community of primary succession could start. You would have a temperate rain forest fairly quickly.",
"Fun Fact:",
"Some climate scientists project that in a warming earth, changes in the fluctuations of the tropical rain belt could cause it to settle over the sahara causing a phenomenon called \"Saharan Greening\". This would be catastrophic because it would mean less rain for sub-saharan africa which would mean famine."
] |
[
"I do not agree with this in the slightest.",
"Of course it couldn't happen instantaneously, but there are plenty of plants, fungi, and lichens that can grow in poor soils with enough water. With 100 inches of rain per year, the sahara would be one of the most productive places on earth. I would venture a guess that a forest of some sort would emerge within 100 years."
] |
[
"It takes more than water. Consider all the worry regarding topsoil runoff. With enough runoff, a forested area can experience desertification.",
"So, with rainfall alone? No. With rainfall and nutrients? Yes. Topsoil is required for plant growth."
] |
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