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[
"Can somebody explain gravitational slingshots to me?"
] |
[
false
] |
[deleted]
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[
"Gravitational slingshots allow spacecraft to 'steal' some momentum from planets and increase their speed (relative to the Sun) while using very little fuel.",
"Consider Jupiter, a frequent tool for gravitational slingshots. Relative to Jupiter, a spacecraft comes in with some speed v, then Jupiter's gravity deflects it to a different direction (say, back the way it came) ",
" (by conservation of energy). Now, the trick is that we don't so much care about the speed of the spacecraft relative to Jupiter, but rather relative to the Sun, and Jupiter is moving pretty fast relative to the Sun! If the alignment of the slingshot is correct, the spacecraft can then get a boost of up to ",
" Jupiter's speed relative to the Sun.",
"Relative to Jupiter: v----> (Jup) ~~~~~ <----v (Jup)",
"Relative to Sun: vS----> <----vJ (Jup) ~~~~~ <-------------vS+2vJ <----vJ (Jup)",
"(Short computation: if the speed of the spacecraft relative to the Sun is vS, and Jupiter's speed relative to the Sun is vJ, then the craft's speed relative to Jupiter is v=vS+vJ towards Jupiter. This gets flipped around to be vS+vJ ",
" from Jupiter, and converting this back to the Sun's frame, becomes vS+2vJ away from Jupiter.)",
"The point is that a gravitational slingshot is essentially half an orbit relative to a planet's frame of reference, but viewed from the Sun's frame of reference, the spacecraft picks up a lot of speed. And, note that this gain in speed required (ideally) zero fuel, because all of the work was done by Jupiter's gravity. (In reality some amount will be required for course adjustments, etc.)"
] |
[
"Imagine there's a truck driving towards you and you throw a bouncy ball at it. How fast does it bounce back? Ideally, it's the speed you threw it plus twice the speed of the truck. From the truck's reference frame, the ball (and everything else) was moving very quickly in the direction of the back of the truck. Now the ball is moving that quickly forwards.",
"Gravitational slingshots are the same idea. They're just using gravity instead of bouncing. Your satellite goes behind the planet and then curves back. It ends up moving the same speed relative to the planet, but much faster relative to the sun."
] |
[
"Another way to think of it is this. When you fall towards a planet, let's say it takes 10 hours to reach the lowest point. If you then burn fuel or position yourself so that the planet follows it's orbit away from you, then it may take only 9 hours to ecape the sphere of influence. Because you spent less time leaving then you did falling, you don't lose all of the velocity that you gained falling towards the planet. This can only occur when passing through a body's sphere of influence in a hyperbolic orbit (an open orbit where you will not continue past the planet rather than get captured). "
] |
[
"Does light undergo \"acceleration due to gravity\"?"
] |
[
false
] |
If you drop/horizontally launch an object near the surface of the earth, its y axis velocity changes at a rate of about 9.8 m/s If I "launched" a beam of light at the surface of the earth, would its y axis velocity also change at a rate of 9.8 m/s
|
[
"Actually, the beam of light will bend exactly ",
" as you would calculate using the classical acceleration, due to relativistic effects. That's still immeasurably small, however. We do observe that sort of bending for starlight around the sun, and for gravitational lenses, for instance. "
] |
[
"\"Classical\" can also be taken to mean nonrelativistic, though \"Newtonian\" is probably the more common (or at least less ambiguous) word."
] |
[
"What number do I use for the mass of the light?",
"There's no need to use anything for the mass of light, since all bodies fall at the same rate ;) Just use the Newtonian value of the acceleration due to gravity, apply it to your light ray, and find the angle by which the Earth's gravity bends it. The result will be half the GR result."
] |
[
"Can we utilise metal pathways and boots to simulate gravity in space?"
] |
[
false
] |
[deleted]
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[
"Not easily, or not well. We can use magnets to adhere to surfaces, so you could walk around on the metal with fairly small magnets. However, the magnetic force works over a much shorter distance than gravity, meaning that if you were to jump, you would either just fly off or need unreasonably powerful magnets to pull you back down. You can see this yourself by noting how close to a metal surface you have to get with a magnet before it snaps to it.",
"As for exercise, you could probably come up with some way of involving magnets in exercise, but running isn't really one of them. Generally elastic is probably a better bet. Here's an astronaut exercising with a \"weight\" machine: ",
"http://phys.org/news/2015-11-astronauts-space.html"
] |
[
"Adding to that, even if you found the way to make it work so that astronauts can walk comfortably, it still wouldn't prevent the health problems related to microgravity (bone mass loss, muscle mass loss and compromise of the immune system)."
] |
[
"thanks for the clear insight✨"
] |
[
"What causes flexibility in humans?"
] |
[
false
] |
I've heard the muscles/tendons/ligaments/etc. physically get longer when people are able to stretch further, but I feel like there must be more going on. Like what's happening at a cellular or biochemical level when you stretch that leads to you having more flexiblity?
|
[
"Your body has a stretch reflex. Proprioceptors reside in the parallel with the muscle tissue. These receptors sense the muscle length and tension. When the muscle gets to a certain \"stretch\", then the \"stretch reflex\" is activated, causing the agonist muscle (i.e. the one being stretched) to contract/resist.",
"Now, with stretching, you essentially de-sensitize (is that a word?) these receptors, so that they fire less and less for the given length. over time, this allows increased stretching of the muscle and an increased range of motion for the joint.",
"Hope this helps. If you have any more questions I can continue to try and help, specifically if it relates to injury/performance (I am majoring in Kinesiology). Cheers!",
"Edit: Forgot the Good 'ol Golgi's! The golgi tendon organs (GTO) are located at the origin and insertions of the muscle (i.e. the tendons). They actually help the muscle to relax, for if the contraction is too forceful, then damage will be done. ",
"If you look in to PNF stretching (proprioceptive neuromuscular facilitation) then that deals with increasing flexibility by activating these GTO's. Basically, you contract against a resistance (e.g. a partner holding your leg) for about 10 seconds. Then you, relax your leg as your partner pushes it further, increase its range of motion due to the GTOs stimulation and subsequent muscle relaxation. This process may be repeated for additional gains in range of motion. (Keep in mind this is acute range of motion gains. Long term gains would require long term stretching)",
"I also believe the muscle energy is similar to PNF stretching, although I have no background in that, so maybe someone else could chime in."
] |
[
"Thanks! So from what you've said, is it at least theoretically possible to \"trick\" your muscles into being really flexible? Like say you were so inflexible you couldn't get your hands past your knees, but there's nothing fundamental about your muscles that's preventing you from doing splits? If the proprioceptors and GTOs are tricked correctly you would be able to? I hope that makes sense."
] |
[
"Patients under general anesthesia are much more flexible than they are normally, due to the inhibition of receptors mentioned above. So it's possible. "
] |
[
"What do hospitals do with cancer tissue after it is removed?"
] |
[
false
] |
I assume it probably goes to research treatment, but how does that actually work in practice?
|
[
"At least ",
"one famous cancer",
" was made immortal and is used for research in thousands of labs around the world."
] |
[
"they put it with all the other biological waste and incinerate it.\nAlthough if they think it is usable like say for med school use they will keep it. I cant say specifically if this happens with cancer tissue.\nThere are other things like umbilical cords which are filled with a high level of stem cells, you can actually sell it."
] |
[
"It is sent to a cellular pathology laboratory for examination by a pathologist who will issue a report that will confirm the diagnosis, determine the prognosis and help guide if further treatment (and what treatment) is required. Some of the material (processed paraffin blocks and microscope slides) will be stored in the laboratory for future reference/research if required and the rest of the material is usually incinerated after a few weeks of the pathology report being issued. In some circumstances, tissue will be retained for specific research purposes with consent of the patient."
] |
[
"Is the ability to make the decision to not reproduce unique among humans?"
] |
[
false
] | null |
[
"Armchair zoologist here, but aren't panda's notorious for being too lazy to reproduce?"
] |
[
"the end result is that they're deciding not to reproduce in zoos.",
"I think that's too strong a conclusion - they're simply deciding not to have sex."
] |
[
"Mate selection isn't just common, it is practically existent in almost all animal species (and I say almost because I will acknowledge that there ",
" be exceptions).",
"Sexual selection is incredibly important to evolution."
] |
[
"Are organs sensitive to touch?"
] |
[
false
] |
If I could somehow touch one of my organs, would I feel it? I can push on any muscle or organ and I only feel it on my skin. But at the same time, liver shots exist which seems to me that you they do feel pain. I’m guessing organs only cause you pain during acute trauma and not regular activities but I’m curious what the truth is.
|
[
"Touch sensors (discrete for pressure, vibration, temperature etc) are different from the proprioceptors like stretch or pressure sensors in internal organs, they inform different parts of your brain. So a real \"touch sense\" only applies to skin and mucosa (think mouth, nose, rectum etc).",
"Nerve endings sensing pain are another, different type of receptor, those exist in almost all organs (but not in every tissue). The brain for instance doesn't have them, only the vasculature, the 'wrapping' = meningues and the skull. Once you've reached the brain, it can't feel touch or pain if you avoid the vessels. Syphilis or other brain infections are painless."
] |
[
"I just learned that syphilis infects the brain. I thought it just made your balls rot or something."
] |
[
"That explains Krendler's lack of response to the intracranial probing of Hannibal Lecter."
] |
[
"Why are black holes thought to be singularities with infinite?"
] |
[
false
] |
If a supernova that doesn't have infinite density collapses into a black hole then how can a black hole form that has an infinite density? Could black holes be points or areas that just have enough mass and therefore enough gravitational pull to not let light out, but not an infinite amount of mass? I feel like this could be true for other reasons to, including different sized black holes. If a bigger supernova collapes then it could form the center-of-galaxy supermassive black holes. But if all black holes have infinite density then how can some be supermassive and some be 100x smaller?
|
[
"First, the term \"black hole\" refers to the region bounded by the event horizon. Thus, black holes have finite density.",
"The singularity itself could possibly be described as having infinite density, but (1) that's just a natural consequence of squeezing a finite amount of stuff into a point of zero dimension and (2) we don't really know what happens to matter when it's compressed into that small of a volume so it's not technically correct to say the singularity is \"expected\" or \"predicted\" to have infinite density. Rather, we don't have any models that accurately describe the behavior of matter under those conditions, so we can't ",
" predictions about its behavior there. In other words, there's really no reason to suspect that the singularity one finds in classical relativity corresponds to an actual physical ",
"."
] |
[
"It's usually just called the singularity."
] |
[
"Edit: Also, supermassive black holes aren't necessarily \"bigger\" than other ones. They just have a bigger event horizon.",
"A black hole is a region of space bounded by an event horizon. Since a supermassive black hole is more massive and has a larger (event horizon) surface area than a stellar mass black hole, it makes sense to say the supermassive black hole is \"bigger\" than the stellar mass black hole."
] |
[
"Absolute zero"
] |
[
false
] |
So i was just in chemistry class today (senior year high school) and we were talking about absolute zero. Can someone explain the concept to me; the teacher was saying that things such as processors would be able to function easier because it would essentially have a straight path. But at like -50° F don't things start to not function .... my teacher didn't know the answer, granted he is new, but it'd be great to know
|
[
"Resistance doesn't become zero at absolute zero - many metals (including copper) have residual resistance that is constant and nonzero at low temperatures, not decreasing (discussed ",
"here",
"). And for materials that do reach zero resistance at sufficiently low temperatures (superconductors), they typically do so well above absolute zero. Absolute zero doesn't really have any special relationship to resistance."
] |
[
"The temperature of an object is (essentially; more in a bit) the average kinetic energy of its particles. Kinetic energy is 1/2",
"velocity",
" and is strictly non-negative, as mass and velocity",
" are positive. So, when you have no kinetic energy, you cannot get colder, and we call this absolute zero. Temperature and energy are related by Boltzman's constant.",
"You can't reach absolute zero for a few reasons. First, temperature is by definition an equilibrium (think \"time-averaged\") property of a system, so if there is any chance that an outside disturbance will impart energy to a system, it is not at absolute zero. ",
"A classier definition of temperature is the partial derivative of energy with respect to entropy; that is, temperature is a measure of how much disorder changes when you input energy. So, hot things don't change much with the input of a unit of energy as compared to cool things. So why can't anything reach absolute zero? Because an input of any arbitrarily small amount of energy would have an infinite change in entropy, which is absurd. ",
"But, more fundamentally, quantum physics tells us that systems have \"zero point energy\" and cannot ever be truly at rest. Why? Who knows. We observe this to be a truth of nature, and it can only be derived if you are willing to assume something else; the Shrodinger equation is the most concise thing to assume (the real word here is \"axiom\")."
] |
[
"Funny enough, while resistivity in metals decreases with temperature, and in some cases goes to zero resistance well before 0K, semiconductors in computer processors would not function at too low of temperature. The dopants used to change the conductivity of a semiconductor would no longer have enough thermal energy at low temperatures to ionize. It's call freeze out."
] |
[
"Did the Hunga-Tonga explosion produce a significant overpressure at the spot on the other side of the earth where the shockwave converged?"
] |
[
false
] |
I'm wondering if locations on the exact opposite side of the Earth from major volcanic eruptions are at some kind of risk for e.g. having their windows blown out. The thought was triggered by .
|
[
"[Edit - this response is to the idea that there is an ideal antipode and windows getting blown out - see response below to the more general question] No - the idea behind your question is spot on though. In a perfectly uniform spherical system this is what you would expect.",
"However, the Earth is not a sphere, and neither the land surface nor atmosphere are uniform. As a result, arrival times are different in different directions from the source. And energy has been greatly dissipated by this point, so there is not enough energy to cause damage."
] |
[
"To the title question: yes, three times. ",
"Here's an amazing video:",
" the top panel shows a computer simulation of the propagating air pressure wave from the Hunga-Tonga explosion. The bottom panels show actual air pressure measurements at several locations (Hawaii, California, the Carribean, and southern Spain. The Spain station is very close to the opposite side of the world from the Tonga volcano.)",
"The pressure wave was seen traveling past each spot, passing through the antipode in northern Africa, and continuing its trip around the world. It went all the way back to Tonga and back out again for a second round-the-world trip, and then a third. Sensitive instruments were able to see the wave passing around the globe at least three times.",
"However, the answer to the question in the text of your post is no, the waves were not large enough to do any damage on the far side of the world. The pressure change was much less than what you'd get from a gentle breeze blowing against a building, and would be impossible to notice except with sensitive instruments.",
"Because the Earth is not a perfect sphere, and has mountains and stuff, the waves don't all line up when they arrive at the antipode, so the wave response there is only slightly larger than it is everywhere else."
] |
[
"The oblateness of Earth is ~20 km difference in radius, far larger than mountains, and it's everywhere not just in a few mountain ranges."
] |
[
"Is it better to accelerate or decelerate through a turn than to maintain constant speed? (Why?)"
] |
[
false
] |
I distinctly recall my high school physics teacher telling us this would be more important when we were older. I certainly forgot the specifics of this as soon as we left class, but the idea has stuck with me and pops into my head regularly when going around long turns...
|
[
"Neither. For a maximum non-slipping turn you would not apply any power to the wheels, and only use them for turning. Any additional power reduces the amount of force that the tires can use to turn the car.",
"However this is the case only in a non-slipping turn, with only the static friction of the tires vs the road considered. In a tire slipping turn, it is very different and depends on the road conditions and the type of car. When someone does \"drifting\" or a handbrake turn they are slipping tires."
] |
[
"But turning ",
" acceleration, and hitting the gas pedal is a bad thing if it causes your tires to skid. The real question is whether OP should be pressing on the gas pedal, the brake, or neither in order to get a better minimum turning radius at a given speed without losing traction.",
"I think the answer is \"neither\", though I'd have to do some more research. Braking ",
" you hit the turn can sure help though, if you're going too fast to make the turn without slipping."
] |
[
"Fastest way through a curve is late apex - brake as late as possible turn sharp shortly after the apex and hit the gas. Less time braking, more time on the gas. This is taught at nearly all motorcycle road racing courses, and if you watch racing, you can see it in action. On a side note, this is a good technique (late apex) for regular driving as well, as it lets you see farther through the curve, giving you greater response times in the event of something unexpected.",
"That said, the physics depend on the vehicle. Fundamentals:\n1) In the middle of a turn, you want to maintain traction so that no tires start slipping.",
"\n2) Acceleration performs a bit of a weight transfer - under acceleration, weight shifts towards the rear, and vice versa for deceleration. ",
"For a motorcycle, the contact patch of the rear tire is larger than the front. As a result, the front tire will start slipping earlier than the rear if both are experiencing the same force. The rule of thumb is 60:40. You want 60% of the weight on the rear tire on a turn, and 40% in the front. To do this requires accelarating to effect the requisite weight transfer.",
"For a pickup truck, you have a different situation. Due to the fact that there is considerably less weight in the rear of the vehicle, the rear tires will start slipping before the front when experiencing the same forces. I don't know if there is a rule of thumb in this situation, however you do need to transfer weight to the rear of the vehicle so that there is more weight on the rear tires, and the means by which this is done is acceleration.",
"If you have tires of equal width, and the weight balance of the car is 50:50, then you will want to maintain constant speed through the turn. In an ideal scenario where friction could be ignored, this would mean you wouldn't need to accelerate. In the real world, your car will want slow a little due to friction, so you will need a slight amount of acceleration (gas) to maintain constant speed."
] |
[
"If I blended everything I ate, would it make a difference?"
] |
[
false
] | null |
[
"Actually, it's not the juice that's coming out. The juice is just stimulating your bowels to \"clear room\" since you have food incoming. Some foods do this better than others due to their nutrients, but it's a general response to new food in the stomach/upper small intestine. When you make a bowel movement it's not the new food coming out, that normally takes a couple of days (on average).",
"Normally I wouldn't make this correction, but being in askscience I just wanted to clarify, sorry if I'm being a little anal (hehe, anal, poop)."
] |
[
"A difference? yes - saliva contains amylase which is necessary to breakdown starch (which is high in modern carbohydrate laden diets). The grinding action of the molars and the manual manipulation of a bolus of food around the mouth facilitate a) salivation b) coating of the food bolus with saliva allowing amylase to do its job.\nThe pancreas also produces some amylase but from memory the salivary glands produce proportionally more. ",
"The act of chewing (and taste sensation) also \"primes\" your distal digestive tract (in this instance everything after your oesophagus) for digestion. There are numerous secretions at various points along the gastrointestinal tract which allow for digestion and absorption (and in the case of water and some ions - secretion depending on your health) which don't just happen because of a magical \"because\" but rather several different signals and feedback and feedforward loops. ",
"Assuming you're talking about blending things like bread and potato and not just chocolate and milk then yes - the comparatively undigested starch would potentially have an effect on the amount of water absorbed in the colon making your stools loose. ",
"Edit: clarity"
] |
[
"What? Complain about non-science and then go on to make a statement based on a guess? The whole purpose of the digestive process is to break down the food, blending is just like chewing - only way better. The enzymes released by blending in no way detract from the quality of the food, in fact it could only aid digestion and increase absorbtion of nutrients. "
] |
[
"Is there a map of the known universe as it \"is\" vs what it \"was\"?"
] |
[
false
] |
Every time I see that cool 3D map of the universe, it is prefaced with, "we are looking into the past". While that's cool and all, we do know the location, approximate distance, and approximate direction of travel and speed. Has anyone ever "advanced" the map to where everything is (or should be) positioned today?
|
[
"Except in a few special cases, we can't even confidently predict the motion of three objects or celestial bodies, let alone billions of them -",
"we can write down equations which describe the motion of the sun, the planets and any spacecraft flying about between them. ",
"If we simplify the solar system and consider only the sun and the Earth we can solve the equations analytically. That means we can find a simple solution which predicts exactly where they'll be at any point in time given information about their positions and velocities at some starting point. This problem is known as the two body problem and the solutions describe the familiar eliptical orbits of the planets known since the time of Kepler.",
"Unfortunately, when we add a third body to our equations of motion, such as a spacecraft lost in space between the Earth and the sun, we can no longer find an analytical solution. The equations are unsolvable. This problem is known as the three body problem of celestial mechanics and remains the subject of research today.",
"- ",
"https://plus.maths.org/content/mathematical-mysteries-three-body-problem",
" ",
"The gravitational three-body problem has been called the oldest unsolved problem in mathematical physics. ...",
"In many cases, even slight deviations in the way we set up a three-body scattering experiment will lead to a complete different outcome. ",
"- ",
"https://www.ids.ias.edu/~piet/act/astro/three",
" "
] |
[
"The simple answer is that it's not so simple. We do have the approximate location and velocity of many things in the universe at the time we see them at, but not even close to the entire universe, and the fact that it is only approximate would make any simulations we create very inaccurate."
] |
[
"Wow. I had no idea it was that complex. Thanks for the information:)"
] |
[
"What purpose does inflammation serve in immune response"
] |
[
false
] | null |
[
"Inflammation does many different things. On the one hand, it directly drives anti-pathogen measures. On the other, it is the connector between innate immunity and adaptive. Both aspects are about equally important. ",
"Inflammation happens when there’s tissue damage, or when cells detect common features associated with pathogens. The local cells start releasing soluble substances including cytokines and chemokines, which drive the effects of inflammation. There are both positive and negative feedback pathways involved, leading to a rapid ramp up and (when the problem is resolved) rapid ramp back down. ",
"The obvious things we see (redness, swelling, fever, pain) include the direct anti-pathogen measures. Cells in the neighborhood become resistant to viral infection. Cells like neutrophils, that can attack bacteria directly, move in. There’s more blood flow, bringing in more such cells. The cytokines diffuse through the body, leading to systemic effects like fever. All these things act very quickly (seconds, minutes, hours) and hopefully limit the immediate infection. ",
"The other thing inflammation does is recruit B and T cells and their drivers like dendritic cells and macrophages. B and T cells are adaptive immune components and are more effective and longer lasting at recognizing and destroying pathogens. They take days to ramp up (less, if they’ve seen the pathogen before) and the details and precise nature of the inflammation (that is, the exact mix of cytokines and chemokines) helps control the precise nature and extent of the B and (especially) T cell response. ",
"This is wildly, wildly simplified. Inflammation isn’t even a single college course, it’s a career."
] |
[
"There's a fun new video by Kurzgesagt on the subject of the immune system that mentions this, at around 3:45.",
"https://youtu.be/lXfEK8G8CUI",
"Keep in mind that the video speaks very confidently on subjects that are still debated by science, but they do explain a good interpretation pretty well.",
"The explanation they give is that the body uses the swelling as a means to send many complement proteins into the area that will fight infections."
] |
[
"well itch is a completely different system which basically is present to hide the pain of swelling (in this case at least)"
] |
[
"Why does metal fuse without oxide layers?"
] |
[
false
] |
I recently found out that metals will fuse together just by touch if they are lacking an oxide layer. I have searched around about this but what I am really wanting to know is why this occurs. I mean what causes this to happen with this type of solid specifically?
|
[
"Metals fuse without oxide layers because the surface of both the metals before fusing had undergone surface reconstruction. Surface reconstruction is the rearranging of atoms in a different orientation than that of the bulk crystalline periodic structure. It takes energy to create a surface of any material. By placing to oxide free metals together, usually in a vacuum, they will cold weld because the lowest energy state is that of the crystalline material."
] |
[
"It's because the metals have no way of knowing what the \"edge\" of the substance is. We know that if we put, say, copper atoms in the same place, they'll combine together; this doesn't stop happening if you have two groups of copper atoms that have already aggregated. The only reason it doesn't normally occur is the oxide layer.",
"I can't speak about all other materials, but it's not just metals-you can get contact welding in glass that's very clean as well. (Or, at least, I think I remember something the Feynman Lectures that said so.)"
] |
[
"I think yours is the only response that beings to address the heart of the question: why does the metallic material bond together but not the oxide?",
"Extending your line of thought, is it because metallic bonds allow for freer movement of atoms and electrons, in contrast to the stiffer ionic bonds of the oxide? So the atoms of both metallic surfaces are capable of orienting themselves in an arrangement conducive to bonding.?"
] |
[
"Does the inverse square law for waves (EMF, Acoustic) hold true at the microscopic level? Is the energy at a picometer away from the source really the square of the energy at 2 picometers?"
] |
[
false
] | null |
[
"The inverse square law is only true for a point-sized source. If you have a thin but infinitely long glowing line, the light intensity goes like 1/r over the distance to the line. If you have an infinite large glowing plane, the light intensity is constant no matter the distance (moving away from it decreases the light intensity from each spot but brings more spots into view).",
"For a finite-sized source the relation will be more complicated, but generally somewhere inbetween. If you have a big glowing ball and you are a picometer from the surface of the ball, it looks more or less like an infinite plane, so the light intensity will approximately not change with the distance.",
"Another way to visualize this is to think of it in terms of field lines: imagine lines coming out from the surface of the object, ",
"like this",
". The field strength is the density of lines. If you are close to the surface of the sphere the lines near you are mostly parallel, so moving a little bit doesn't change the field strength. If you have a point-shaped source (like the plus-sign in the picture), then even when you are close to it the field lines are diverging, so you get the inverse-square effect. If you have an infinite plane, then the field lines are parallel throughout all space, so the field strength is constant everywhere."
] |
[
"In a given solid angle cone you get a larger area of the source as you move away."
] |
[
"moving away from it decreases the light intensity from each spot but brings more spots into view",
"Can you elaborate on what this means? Every point on a plane can draw a straight line to any point above that plane without self-intersection, which means that all points on the plane are \"visible\" from any point above it."
] |
[
"Why don’t we have vaccines for all Herpes Viruses?"
] |
[
false
] |
Ok so I hope I don’t sound like a complete idiot, keep in mind I have very little medical knowledge. So we have vaccines for shingles and chicken pox, which are herpes viruses. However we don’t have a vaccine for Cold sores, Genital Herpes, or Mononucleosis (also a herpes virus). Why is this? I know they are obviously different mutations but they all stem from the same viral tree. Is this something that the medical community is working on or is it a lost cause to find an umbrella Herpes vaccine?
|
[
"Vaccines work by training your immune system to respond to the pathogen. Herpes simplex virus 1 and 2 (the kinds that cause cold sores and genital sores) are immunoevasive, which means that they have a mechanism to avoid destruction by your immune system. As your immune system begins to respond to the virus, herpes will hide inside nearby nerves (but not destroy them like other tissue). Normally, virus-infected cells are detected by your immune system and destroyed by cytotoxic T cells, but your nerve cells have ",
", which means your immune system does not attack them. Herpes lies there in a dormant state until a biochemical stressor (high stress, hormonal changes associated with menstrual cycles, new medications, etc) cause them to pop back out and reinfect the nearby tissue. Also, since nerves don’t move around, this is why herpes almost always reappears in the same location. It just pops in and out of the same hidey hole."
] |
[
"It’s not for lack of trying. These vaccines have been in the works for about 100 years but they keep failing the clinical trials. Sometimes the vaccine itself has too many side effects - I remember there was some neurotoxicity - and other times the resulting antibodies weren’t robust enough to eliminate the virus, which is pretty darn good at evading our immune system in the first place. Remember that vaccines simply stimulate our immune systems to produce antibody production without catching the full blown disease so that if/when we are exposed, our immune system can have an immediate response to a virus before it can reproduce successfully."
] |
[
"One main factor is cortisol. The \"stress hormone\". It actively supresses your immune system to conserve energy."
] |
[
"I just bought a new microwave oven and it came with a metal rack. You can't use most types of metal in a microwave, so why is the rack okay? Maybe the shape or the composition?"
] |
[
false
] |
Has microwave technology changed?
|
[
"Metal objects with points will cause electrical arcing. The rack that came with your oven will not. It's the same technology, it's just the shape of the metal makes it safe for use inside the oven. "
] |
[
"Does that mean that metal spoons are microwave safe because they don't have points?"
] |
[
"yes, and forks will arc."
] |
[
"I have a question about Schrödinger's cat."
] |
[
false
] |
Wikipedia states this as an example of quantum entanglement. Now I Understand why it is quantum supposition. After a certain about of time the probability that the nucleus has decayed is high enough that it both has and hasn't and only collapses to one state on observation. But why is this quantum entanglement? I thought that was when you had two linked things in supposition and so when you observed one then the other immediately collapsed too. What is the other thing here?
|
[
"The classic Schrödinger's cat experiment doesn't really demonstrate entanglement. Entanglement usually refers to a situation where a single system---described mathematically by a single wavefunction---is separated somehow into (what we normally think of as) two systems. The math, however, demands that the two systems must still be described by a single wavefunction. And thus, that they must share some sort of property.",
"A ",
"typical example",
" is splitting a single photon into a pair of photons. The resulting photons invariably have correlated polarizations. Depending on how you do the splitting, the photons will have either the same polarization or perpendicular polarization, every time. That is, if I have the one photon, and you have the other, then the following \"if-statements\" holds (assuming we've entangled our photons to have the same polarization):",
"If I measure my photon to have up-polarization, then when you measure your photon, you must find that it has the same property.",
"If I measure my photon to have down-polarization, then when you measure your photon, you must find that it has the same property.",
"You could, I suppose, in principle, generate an example of entanglement from Schrödinger's cat. The idea is that the radioactive atom and the cat, via the diabolical mechanism, form a single system, described by a single wavefunction. If you then separated them the right way, you could have an atom/cat-in-a-box entangled system. If I had the atom and you had the boxed cat, then the following \"if-statements\" would hold:",
"If I measure my atom and find that it has decayed, then when you open your box, you must find a dead cat.",
"If I measure my atom and find that it has not decayed, then when you open your box, you must find a live cat.",
": accidentally a word. Thanks, Arcs_Of_A_Jar."
] |
[
"Keep in mind that \"Schrödinger's cat\" is not a serious interpretation of quantum mechanics, it is an attempt to concoct a thought experiment to discredit (or at least expose the limits of) several of the leading interpretations of quantum mechanics at the time."
] |
[
"I think you accidentally a word in your cat analogy at the bottom there."
] |
[
"Are spiral galaxies accretion discs for supermassive black holes?"
] |
[
false
] |
[deleted]
|
[
"No. The supermassive black hole at the center of a galaxy has virtually no interaction with the rest of the galaxy not near the centre."
] |
[
"Depends on the galaxy, but for the Milky way, the amount of mass in baryonic matter is roughly 10",
" solar mass, and the black hole is roughly 10",
" solar mass, so about 0.001%. And then there is about 10 times as much dark matter as regular matter, so about 0.0001% of the total mass."
] |
[
"Speaking as an astronomer, I would informally characterize about 99% of astronomers in being ",
" in the existence of dark matter, as there is a ton of other evidence for it as well. "
] |
[
"Is there a limit to how large marine life could become?"
] |
[
false
] |
Besides the obvious factors such as finding enough food. I know that land animals can only get so big (though I don't know any exact range) because of both gravity and oxygen levels, but are there similar limitations for aquatic life? And if so, can I get a ballpark estimate for how big some kind of ocean leviathan could get?
|
[
"Since you didn't mention any sort of phylogeny, no, there is not limit to how large marine \"life\" could become. This is including superorganisms of fungi and plants though. There is theoretically no limit to the size of a single fungus, or say a massive algal bloom caused by a single organism could be. (I'm not a marine botanist, I'm sorry.) ",
"For example, take ",
"the largest organism on earth is (supposedly) a fungus in Oregon.",
" I can't see much reason why a similar organism couldn't be inhabiting a large volume of the ocean at this very moment. The ocean floor has much less variable conditions, and may be the perfect environment for a single, massive ancient (or ",
"archeum",
".) There's a wealth of nutrients in the form of ",
"marine snow",
" and niche environments for these kinds of big, creepy guys.",
"Of course, when you're asking about largest organism, one must also ask where one draws the distinction between something being a single organism and being a collection of genetically identical organisms. Likewise, there is no limit to how far a single bacterial colony could stretch, but one may not like to call a cloud of genetically identical bacteria a single lifeform. ",
"Me: I'm a graduate biochemist. If you're more interested in limits on animals in particlular, I'm probably not the guy to answer your question. I'm also drunk."
] |
[
"Considering the fact that the OP was mentioning gravity and oxygen levels as limitations for terrestrial animals, I think that he meant his question to be a little more specific than \"life\". My interpretation would be that he wants to know about vertebrates.",
"Aside from finding enough food, I would guess that there is a theoretical limit based on oxygen requirements and the limitations of a breething organ (lungs/gills). There was a publication in Nature in 1997 about how a breathing organ needs to have branches etc, written by West i believe? That publication probably contains some math that could be used to find some sort of rough answer. Aside from that, I guess there would be a question of whether or not it is marine if it is standing on the bottom and reaching up in the air. So I guess this animal would have to be more shallow than the depth of the sea. ",
"I think the question should be specified a lot more, before it would make any sense to try and find an answer. "
] |
[
"One other thing to consider is density. Bony fishes and mammals can only get to a certain size before the amount of bone in their skeleton causes them to sink. This is particularly problematic for air-breathing mammals. This is why whale skeletons are so diminished. Also, looking to larger bony fishes (such as the mola), the skeletons have become mostly cartilaginous. ",
"Another thing to think about is that most of the largest and highest performing fish are sharks, with cartilaginous skeletons too (whale shark and mako, respectively).\nThe amount of oxygen that these organisms need is easily up-scaled through the relatively inexpensive process of increasing the surface area of the oxygen-exchange system. "
] |
[
"What's the difference between d^2 x(t)/dt^2 = -x(t), and idx/dt=-x(t)?"
] |
[
false
] |
In this specific case, it's only true when d x(t)/dt =idx/dt, but is there a more general connection? The two equations give the same solution set.
|
[
"The two equations give the same solution set.",
"Not quite. The general solution to the first is x=c*e",
"+d*e",
", or equivalently x=a*cos(t)+b*sin(t). The general solution to the second equation is just x=c*e",
". This is not surprising, since second order (homogeneous) differential equations will generally have two linearly independent solutions, while first order equations will only have one."
] |
[
"It's the same difference between the two equations x",
" +1 = 0 and x-i = 0",
"While i is a solution of both equations, they are not the same equations. More specifically, the first equation has two solutions (i and -i) while the second one has only one solution."
] |
[
"Suppose idx/dt = -x(t), or you could write it as dx/dt = ix(t). Then d",
"x/dt",
" = idx/dt = i",
"x(t) = -x(t). So the second equation implies the first. But the first does not imply the second. d",
" sin(t)/dt",
" = d cos(t)/dt = -sin(t), so it fits the first equation, but not the second."
] |
[
"How do plants die? Is there an exact moment when they simply die?"
] |
[
false
] |
Do they die simmilar to animals, or in a completly different way.
|
[
"Plants die cell by cell as opposed to animals that ",
" go from a state of being alive to death like when the heart stops. For example with plants if almost the entire plant is dead but you still have a bit of healthy root it would be possible to replant that root and it could grow into an entirely new plant. This is how you clone a plant.",
"I've though about this a lot and I like the analogy of digital versus analogue signals. Digital signals (animals) are unmistakable on/off or 1/0.. there is no in between. But a plant can have a % of cells that are still alive similar to how analogue signals are identified by intensity/frequency of the signal."
] |
[
"To ",
"define death",
" in a multicellular organism is not as simple as you make it seem. A heart stop doesn't equate to immediate death in most meanings of the term.",
"Alongside that difficult question, animals like some starfish can also regrow complete bodies from a single arm, for example.",
"So, yes, plants usually have much higher regenerative capabilities than most animals. But in both cases it is very difficult to define an \"exact universal moment of death\".",
"EDIT-spelling, punctuation and stuff...."
] |
[
"Agreed.",
"I think the true cause of the perceived difference is mostly because animal cells tend to rely more heavily on a more complicated support mechanism. Plant cells need water and minerals but not much of either, and they are capable of making their own sugars using light. Cut off the \"tap\" -- the connection to the rest of the plant-- and they can go a while before running out of resources. ",
"Contrast that with animal cells, especially in vertebrates and large inverts. They need a constant supply of sugar and oxygen from the blood (or other circulatory fluid). Cut that off and they'll suffocate and starve a lot faster than most plant cells will die off from lack of water and nutrients."
] |
[
"Can all matter be ionized (become plasma)?"
] |
[
false
] | null |
[
"Roughly speaking, it will dissociate into atoms, then the atoms will be ionized, as you increase the temperature."
] |
[
"Yes."
] |
[
"How would that work with things that a a mixture of multiple things. Let's say a chocolate bar?"
] |
[
"Is it theoretically possible to control radioactive decay?"
] |
[
false
] |
Could one speed up the rate of decay by stimulating an unstable nucleus without causing a chain reaction? For example, if an element decays by electron capture, could one bombard the nucleus with electrons to have a stimulated decay instead of a spontaneous decay? Also, I used electron capture as an example but my question is a general one.
|
[
"I was wondering if theoretically there were safer and faster methods of processing radioactive waste instead of waiting for them to decay to stable elements on their own, preferably without starting a chain nuclear reaction or generating too much gamma radiation."
] |
[
"I was wondering if theoretically there were safer and faster methods of processing radioactive waste instead of waiting for them to decay to stable elements on their own, preferably without starting a chain nuclear reaction or generating too much gamma radiation."
] |
[
"Rate of decay is constant for elements, however it is possible to cause nuclei to emit particles or otherwise partially disintegrate. For example, in some neutron experiments, neutrons are produced through proton bombardment of tungsten, which emits neutrons during the process."
] |
[
"Can someone be colorblind in one eye?"
] |
[
false
] |
[deleted]
|
[
"In the visual pathway, colour is interpreted early on in the visual cortex (V1 specifically) using inputs from both eyes. In this sense, colour is encoded once information from both eyes has been combined. However, if only one eye lacks colour-sensitive photoreceptors (cones) for whatever reason, then the brain will only have this colourless information to use if the functioning eye is closed. If both eyes are open, then it is likely that the individual will see in full colour given that the brain is capable of sufficient plasticity to omit the wavelength information encoded in the defective eye"
] |
[
"Great response, thank you! I have a better understanding of this now!"
] |
[
"I actually have very, very mild color blindness. I can't tell the difference between very dark blues and black with either eye. I also see colors more vibrantly with my right eye. With my left, they are all a little bit more dull. I would assume that this is due to some problem with the cones in my left eye."
] |
[
"At noon on Dec. 21 a beam of sun shines through a window. It lights up spot X on the center of an adjacent wall. We know the Lat-Lon and elevation of the window and wall. Can we predict where on the wall the sunlight would strike for any given time and day of the year? With what degree of precision?"
] |
[
false
] |
Let's assume that: The window frame and walls are insignificantly thick. In other words, the window frame, sill and thickness of that wall will not interfere. The beam on the wall will take the shape of the window, albeit distorted. Consider one corner of that shape to be the spot X which we're tracking. (This should be simpler than trying to predict how the shape would distort as angle of incidence changes.) Our location coordinates are provided and limited by a standard consumer-grade GPS like those found on smart phones. The time and dates above were selected arbitrarily. We're close to sea level and not more than 5,000 km from the equator. EDIT: Lots of good information below. Thanks to all for the direction. Still wondering if anyone is able to come up with a formula, where we just need to plug in the variables. Any takers? (Please forgive me if what I'm requesting is a monumental task. I just don't know...)
|
[
"In fact you can. When you were done, you'd have constructed an Analemmatic sundial. ",
"http://en.wikipedia.org/wiki/Analemmatic_sundial"
] |
[
"Here",
" a handy demonstration of the motion of the sun throughout the year. Put your latitude to whatever you want, the time is set to noon by default but you can change that too if you want. Then you can drag the arrow on the calendar to change the date and see where the sun will be on that date at the chosen time. At the bottom left corner turn on show analemma too to see the track the sun will make.",
"It even has the stick figure standing and its shadow, so you could think of the head of the shadow as spot X, it's just on the floor instead of on the wall. It'll make a similar figure as the analemma but just projected on the floor. It would work similarly for a wall. Play with the latitude and time of day and the calendar a bit and you should get a pretty good feel for the motion of the sun."
] |
[
"Thank you; that's very interesting. I'll need to spend some more time playing with it. Hopefully I'll be able to form a general conceptual understanding of the relationships of the sun, window and point X. "
] |
[
"When it is cold enough outside to see my breath, why can I not blow smoke rings?"
] |
[
false
] | null |
[
"This is anecdotal but I've definitely blown steam rings in the cold, was just doing it yesterday. Its harder and fainter but doable."
] |
[
"When it's cold outside, the air in the atmosphere condenses into water vapor - thus we have \"smoke\". More accurate would be vapor.",
"When you smoke, the chemicals leaving your breath isn't only air/water. It consists of many more elements that make it denser. Because the smoke actually has density IN RELATION to the air, it is more malleable and doesn't immediately diffuse into the surrounding air particles. ",
"Essentially, it isn't the same stuff creating the \"smoke\" clouds."
] |
[
"I know you can blow rings with water vapor. While I was unable to find any photographic or video evidence of people doing it with only their breath in cold weather, I found a few instances suggesting it was possible but that it requires very stable air. So try it in a small enclosed space like a car. "
] |
[
"What happens if I shoot one single photon to a semi-transparent mirror?"
] |
[
false
] |
We can create single-photon laser emitter [1], and half-transparent mirrors can be created with very good accuracy. My question is: If I (multiple times) send a single photon to a 50% semi-transparent mirror, will I always get the same result (like the photon will always either pass through the mirror or be reflected)? [1] -
|
[
"Any one of the photons will either pass through (transmit) or reflect; there is no partial transmission or partial reflection when talking about individual quanta.",
"Of the multiple photons, 50% of them will transmit and 50% will reflect, so you won't get the same result each time."
] |
[
"It's a little more complex than this. The photon's wavefunction will split into two pieces, one transmitted and one reflected. So the photon, as a wavefunction, will both reflect and transmit at the same time. You are not really splitting a photon in half though, because both the reflected and transmitted parts are just pieces of one unified photon wavefunction. If you then try to measure the location of the photon, you will only measure it as having been completely reflected or completely transmitted. The wavefunction collapses to one of these possibilities upon measurement. If you repeat this many times, you will find the 50% of the photons collapse to the reflected state and 50% collapse to the transmitted state. This is more than semantics as the wavefunction splitting can lead to interference effects that would not show up if photons were simple balls that completely reflected or completely transmitted.",
"I assume you know this, or even implied this, but your comment seemed overly-simplified to me."
] |
[
"The photon's wavefunction will split into two pieces",
"I've not heard a photon as having a wave function. could you clarify what you mean by this? I've only ever heard of wave functions as being associated with quanta of matter, not energy."
] |
[
"Question regarding the big bang, quantum field theory, virtual particles, matter dominance, and the end of the universe."
] |
[
false
] |
A brief background of my limited understanding: As I've learned from Steven Hawking and Lawrence Krauss, our current understanding is that random quantum fluctuations happened to cause the big bang; that these same random fluctuations in the quantum field are also what is responsible for spontaneous virtual particle/antiparticle pair creation which causes black holes to eventually evaporate; and that the spontaneous creation of these particles is allowed because the existence of (+one) balances the existence of its opposite-in-every-way (-other), and in sum they are zero. Now to the questions! Thanks!
|
[
"Virtual particles are due to the uncertainty principle. Because of that they can exist for a short time. What happens with hawking radiation is that due to the uncertainty principle the virtual pair can exist, and quantum mechanically they event horizon is not perfectly defined. This lets one particle \"escape\" and the other fall into the BH and annihilate matter inside. In this way the BH evaporates. ",
"Now as far as whether or not our universe is due to quantum fluctuations? Who knows its a conjecture. I am not even sure if someone has done any math/can do any math. Its my understanding that you have to have a quantum theory of gravity before you can even say anything. So while I don't think 1&2 can be answered, I am going to say, no probably not. For 3, what you are talking about is baryogenesis. The current idea is that there was some small preference for matter, and it therefore dominated. This is one of the biggest mysteries in physics today. ",
"For 4, IF there was an \"anti-universe\" I am pretty sure conservation would require it to have the same global structure as our own, certain laws of physics actually depend on what the global structure is. "
] |
[
"If both the universe and virtual particles spring into existence from nothingness via the same mechanism, do their similarities end there?",
"The similarities continue. A virtual particle pair can remain in existence as long as it doesn't violate the mass-energy bookkeeping of the universe. For a virtual particle pair, this can be a very short time.",
"But for the universe as a whole, the protection against violating mass-energy conservation is more systematic -- it has to do with a balance between two kinds of energy:",
"Positive mass-energy, the energy of mass and of the kinetic motions of masses.",
"Negative energy, that is to say, gravitational potential energy.",
"If the universe began by giving masses a certain velocity called \"escape velocity\", the required balance between positive mass-energy and negative energy is achieved, which allows the universe to continue to exist.",
"It is thought by some that the Big Bang gave masses this particular velocity, other think this velocity was provided by the hyperinflation phase immediately after the Big Bang. In any case, it seems that masses have this mutual recession velocity now, this one unique velocity able to create a net zero mass-energy.",
"Here is the equation for gravitational potential energy:",
"[; \\displaystyle e_p = -G \\frac{m_1 m_2}{r} ;]",
"Here is the equation for kinetic energy:",
"[; \\displaystyle e_k = \\frac{1}{2} m v^2 ;]",
"Here is an equation that combines both kinds of energy:",
"[; \\displaystyle e_t = \\frac{m_{1} r v^{2} - 2 \\, G m_{1} m_{2}}{2 \\, r} ;]",
"And here is the equation for escape velocity:",
"[; v_e = \\sqrt{\\frac{2 G M}{r}} ;]",
"If one processes the math, one discovers that escape velocity exactly cancels the two kinds of energy. On a large scale, the recession velocity of masses only needs to average escape velocity. Local deviations don't matter as long as the average is maintained and net mass-energy remains zero.",
"Is it plausible that the beginning of the universe was just a pair-creation event of much greater magnitude?",
"That is the current thinking,, and the above exposition provides some of the details. ",
"Here is a more detailed exposition.",
"Could there be a virtual anti-universe floating out there, and could this explain why matter dominates in ours (assuming anti-matter dominates in the other)?",
"No, the particle-antiparticle picture is fulfilled at the cosmological scale using positive and negative energy. Also, it is a good idea to avoid invoking invisible universes to solve physics problems -- although this doesn't stop people from doing it. In this case, there's no need.",
"It is said that the ultimate fate of the universe boils down to whether our local universe is open, flat, or closed. But would this possibility modify that? ",
"Yes, because escape velocity by definition means the universe's geometry is flat.",
"None of the foregoing takes dark energy into account -- this changes everything from the present forward. But the early history of the universe had mass-energy densities so much higher than they are at present, that dark energy played either no, or a very small, part in the initial mass-energy balance being described."
] |
[
"I am not an inflationary cosmologist, so I can't talk sensibly about the universe at extremely early times, but I do think that the analogy of virtual particles is generally taken too far.",
"Virtual particles are simply a bookkeeping device in quantum field theory. They are not, in a strict sense, really particles at all.",
"In a quantum field theory, say quantum electrodynamics (QED), the electron field can be thought of as the surface of the pond, and a particle (electron or positron) as a localized ripple traveling along the surface. One feature of quantum field theory is that the surface of the pond cannot be perfectly still - there is a minimum amplitude to the ripples everywhere on the pond. The photon field is another type of ripple that interacts with the electron ripples.",
"So lets say that you have an electron moving about by itself, and you want to calculate how it behaves. You cannot make the calculation exactly, you have to make an approximation. Let's say that S is the thing you want to calculate. You can only calculate a series of terms like this:",
"S = S0 + S1 + S2 + S3 + S4 + ...",
"You have to calculate an infinite number of terms to get S exactly, but as the terms get smaller, you can get a good approximation by calculating the first few.",
"Richard Feynman found a way to simplify getting this calculation correct by coming up with a clever system called ",
"Feynman Diagrams",
". Each piece of each term is represented by a diagram, with an electron going in, and an electron coming out.",
"For S0, we have zero vertices - there is just a line representing the electron moving along.",
"For S2, we have two vertices - and what you draw is a 'virtual' photon being emitted by the electron and then absorbed. One vertex for the emission, and one for the absorption.",
"For S4, there are many diagrams that you have to calculate is one where the electron emits a virtual photon, and then that photon converts to an electron positron pair, the pair annihilates to create a photon, and then that photon is absorbed by the original electron. If you draw it you get four vertices.",
"So what actually happens as the electron moves along is the sum of all these diagrams.",
"In the case of the black hole hawking radiation, the black hole is just emitting particles and losing mass. This is possible because the electron and other fields around the black hole, even though there are no actual particles, is still 'ripply', and when you do non-standard quantum field theory in the curved spacetime around a black hole, you end up with the black hole emitting a sort of thermal radiation. ",
"In the language of Feyman diagrams, you see particle antiparticle pairs being created when you run the calculation. But they are nothing more than calculational tools."
] |
[
"Why are we not photosynthetic?"
] |
[
false
] |
I'm assuming, based on the fact that we never incorporated chloroplasts (we being humans), that it is unfavorable evolutionarily, if that is a fair assumption, why is that?
|
[
"I can think of two evolutionary reasons.",
"First, it just doesn't produce enough energy for a mobile organism with a high metabolism.",
"Second, photosynthesis has two functions, the production of ATP for energy, and the conversion of CO2 to sugar and eventually other hydrocarbons. Since we get our sugars from eating plants, this would be a wasted metabolic pathway."
] |
[
"We are to a limited extent, as our skin will produce Vitamin D when exposed to UV light. ",
"Source"
] |
[
"You're making the common mistake of assuming evolution has a goal and that its goal is to make us more and more advanced or adopt a wider array of biologic tools. This isn't so. Our ancestors never incorporated, end of story. It might be favorable for us, today, to have done so, but it's not what happened. We can only really make judgment calls on whether a particular adaptation is beneficial after the fact, after the environment has changed, after we've undergone some sort of competition. Adaptations aren't MEANT to be useful in future crisis, they just are or are not."
] |
[
"What prevents whales from getting the bends?"
] |
[
false
] |
How can aquatic mammals rapidly and deeply dive safely?
|
[
"There are a couple things going on here: First, risk of decompression illness is much greater when you breathe compressed air. When you just hold your breath, there's not a high risk.",
"Second, there's recent evidence suggesting ",
"that whales do in fact have decompression damage",
"."
] |
[
"I'm not sure how you meant that statement but I want to stress to ",
" hold your breath while SCUBA diving."
] |
[
"Your lungs can explode.",
"Air is a gas and is compressible; at a certain depth underwater the air will be at a certain volume. If you breathe in compressed air at a certain depth, hold your breath, then ascend, the air expands because there's less pressure at shallower depths. ",
"I'm probably mangling that a bit, I'm just a diver =)."
] |
[
"In the future will it be possible to implant a working third eye?"
] |
[
false
] |
[deleted]
|
[
"The eye and vision work very specifically through specific neural connections in the brain. Think of the brain as a jumble of wires connected very specifically to allow specific function. The brain is \"wired\" in a very specific way and changing just one thing could affect many different things.",
"To add an eye you would first have to structurally alter the skull to create another eye socket (not probable). You would then have to find a donor eye (or manufacturer one through something like stem cells). you would then have to \"wire\" that new eye into your current brain in a specific way as to what you you wanted the eye to do. None of these steps are very feasible.",
"Probably not. It's just too complicated to add something completely new to an existing brain artificially."
] |
[
"there is a similar story about a",
" man who lived after having a pole go through his skull and through is frontal lobe",
". The brain retains neural plasticity which is it's ability to change and create new neural connections, however it has it's limits. These stories are more evidence for our brains to be able to compensate for something we lack due to damage. In these examples their brains are compensating the best they can for what they lack. It's an entirely different concept for the brain to go through a change as large as installing a fully functioning sensory organ that isn't supposed to be there."
] |
[
"there is a similar story about a",
" man who lived after having a pole go through his skull and through is frontal lobe",
". The brain retains neural plasticity which is it's ability to change and create new neural connections, however it has it's limits. These stories are more evidence for our brains to be able to compensate for something we lack due to damage. In these examples their brains are compensating the best they can for what they lack. It's an entirely different concept for the brain to go through a change as large as installing a fully functioning sensory organ that isn't supposed to be there."
] |
[
"Do Organelles Just Float Around in the Cytoplasm of Cells?"
] |
[
false
] |
I know the Mitochondria in Plant and Animal cells floats around in the Cytoplasm, but do other organelles do, like the Nucleus, Vacuoles, ER, etc? I would guess so, but isn't cytoplasm jelly like? How exactly do the manage to move around?
|
[
"Actually, organelles, including mitochondria, don't simply float around the cell randomly... Cells have a highly structured cytoskeleton, which provides spatial and mechanical functions. Microtubules, for example, one of the three cytoskeleton constituents, determine the positions of membrane-enclosed organelles and direct intracellular transport, along with accessory proteins, which include motor proteins (such as kinesin and dynein).",
"Source: Alberts, Bruce; et al. (2014). Molecular Biology of the Cell (6th ed.). New York: Garland Science. ISBN 978-0815344322."
] |
[
"There is a fantasic animation made ",
" for Harvard students by some company about this:\n",
"http://www.studiodaily.com/2006/07/cellular-visions-the-inner-life-of-a-cell/",
"Someone edited out the parts with motor protein walking along the microtuble, in the background you can see how there is a network of cytoskeleton everywhere in the cell:\n",
"https://www.youtube.com/watch?v=y-uuk4Pr2i8"
] |
[
"A bit off topic but I would like to add that these animations only depict the cytoskeleton, motor proteins, the cellular membrane and vesicles during transport.",
"Videos like that are great if you want to study intracellular transport mechanisms, but it leads many people to imagine cells as mainly empty water bags. However in reality the cytoplasm is tightly packed with all kinds of stuff. David Goodsell made some mind blowing illustrations that emphasize that point, here are some of them and it is easy to find more.",
"http://mgl.scripps.edu/people/goodsell/illustration/public"
] |
[
"How does bioluminescence work on a biological level?"
] |
[
false
] |
Is it mostly found in deep water marine life?
|
[
"Luminescent organisms produce a pigment (called ",
"luciferin",
") that can undergo a chemical reaction with oxygen that gives off light. During the chemical reaction, an electron drops from an excited state to a lower energy state, causing a photon to be emitted.",
"This reaction is slow unless catalysed by an enzyme (",
"luciferase",
"); the activity of luciferase can be controlled in a variety of ways (different in different organisms). This is how the light is switched on and off.",
"Fireflies and glow worms are another common place to find bioluminescence, as are certain fungi, but yes, it's most prevalent in deep sea creatures."
] |
[
"Also, many organisms bioluminesce because they have special organs that basically \"farm\" bioluminescent bacteria. The organism themselves cannot fluoresce but they harbor bacteria that do. Its a pretty neat symbiosis. "
] |
[
" (a G- bacterium) uses ",
"quorum sensing",
" to activate its oxygen-dependent light-emitting ",
"luciferase",
" proteins, which allows clusters of the organism to act as on-off switches to each other. It does this by secreting small chemical messengers, to let nearby bacteria know that they have neighbours.",
"If there is not enough secreted signal nearby, the transcriptional regulation factors controlling luciferase will fail to transcribe and no energy is wasted. If there is a big enough party of ",
", then they'll all turn on their lights at the same time to produce a visible effect even at the macroscopic level."
] |
[
"Is it really possible to build up a tolerance to toxic chemicals like cyanide/arsenic?"
] |
[
false
] |
This might just be a Hollywood legend, but it is really possible to build a tolerance to extremely toxic compounds despite the fact that less than a gram could kill the average person?
|
[
"In theory yes ",
"The body produces proteins called Metallothioneins which bond to dangerous chemicals and substances in order to protect your organs from damage.",
"They aren't produced in large amounts normally which is why you can die from taking large doses of hazardous chemicals. In theory you could condition your body to increase production of Metallothioneins which would allow you to ingest higher doses of hazardous chemicals.",
"One example are the ARSONIC EATERS of Upper Styria, Austria. Back in the 1800s there was a population of peasants living in Austria that were ingesting large amounts of Arsenic because they believed it had positive health benefits. They had been doing this for quite some time and had managed to live.",
"Now can it be done? Possibly, Should it be done? In all honesty trying to become immune to anything like that by ingesting it would have more negative effects than positive.",
"Positive: You may be able to ingest more of a hazardous chemical which would mean you could survive if someone tried to poison you.",
"Negative: Arsenic increases the risk of many forms of cancer so even if you can survive a surprise poisoning you would probably get cancer and die anyway."
] |
[
"I've read stories on people who live in areas with unusually high arsenic deposits. Places like some parts of Mongolia and especially Bangladesh. Some of these people deliberately ingest it by sucking on and eating stones found around the area that are high in arsenic. They build up a tolerance. I did see some pics (I think it was in an old National Geographic mag) where the extremities of their hands and feet were discoloured (especially under the nails), as is one of the classic signs of arsenic poisoning.",
"I've heard (and I'm dubious) that some people are somewhat immune to doses of arsenic that would kill most. The example given was Rasputin. I can also say that I personally tried to poison a goanna (that was eating my ducks' eggs) with arsenic and I failed miserably. I put over a gram of arsenic powder in water and injected it into an egg. The fucker most certainly ate it and I thought that was that. Weeks later, I find the same one climbing up the tree I had seen it in before. "
] |
[
"Honey badgers can be bitten by cobras and survive"
] |
[
"Why are some viruses only transmitted by blood/sex and some only by saliva"
] |
[
false
] |
Reading about HIV I got wondering it's not transmitted by spit? What's special about blood and sex fluids that saliva lacks? And then I realised that the cold & flu are transmitted by coughing/sneezing (presumably saliva) and I've never heard anyone get the flu from sex. Why do some viruses get transferred by some methods while others get transferred by others?
|
[
"Viruses rely on receptors on the outside of cells to recognize cells (and gain entry into them). Different cells have different receptors, and so different viruses recognize different types of cells. ",
"The same way that a lock pick will not get you into a door with a digital keypad, and a circuit analyzer will not get you into a door with a regular key lock."
] |
[
"It's going to vary virus by virus, but let's start by offering an alternative to the hypothesis that you've offered (what does saliva lack to allow infection) to think about \"does saliva contain anything that might inhibit viral replication?\".",
"At least for HIV-1 it seems saliva contains certain properties that inhibit replication. ",
"Some",
" ",
"studies",
" have provided evidence that a protein, called \"secretory leukocyte protease inhibitor\", is responsible for a good deal of saliva's resistance to HIV-1 infection. ",
"But what are some other general differences between saliva and blood? pH, water content, enzymes (lysozyme, peroxidase etc), antibodies etc. Any of these factors could prevent viral replication (or conversely may be hijacked and required for replication). And of course the kind of cell that is infected is going to come into play as well (i.e. kidney cells are not likely to be part of your saliva)."
] |
[
"Viruses come in all different shapes and sizes. Some are wrapped up nicely in a protein coating, some have different shapes of different protein shells, some are made of DNA while others are made of RNA. Because of all this variability, different types of viruses can only survive in different conditions. Some viruses can only tolerate so much heat, or get destroyed by certain enzymes that only exist in a certain part of our body. Some viruses die very quickly when exposed to open air (like HIV) whereas the flu can remain on a door handle ",
"for days",
" and still make you sick. This is why you can get the flu through touching a door handle, then touching your face, but the same won't happen if there ",
" on a door handle. "
] |
[
"Are there populations of people that exhibit better mental health than others, and have they been studied?"
] |
[
false
] | null |
[
"If a population that small were to have the same suicide rate as in the US they would only have one suicide every 10-15 years. Since they are a small, homogenous community that have been infrequently observed I don't know if we can really extrapolate a lot from this fact. "
] |
[
"If a population that small were to have the same suicide rate as in the US they would only have one suicide every 10-15 years. Since they are a small, homogenous community that have been infrequently observed I don't know if we can really extrapolate a lot from this fact. "
] |
[
"Some extracts from the Wikipedia page on the Pirahã:",
"The Pirahã people are an indigenous hunter-gatherer tribe of Amazon natives, a subgroup of the Mura, who mainly live on the banks of the Maici River in Brazil's Amazonas state, in the territory on Humaitá and Manicoré municipality. As of 2010, they number 420 individuals. ",
"As far as the Pirahã have related to researchers, their culture is concerned solely with matters that fall within direct personal experience, and thus there is no history beyond living memory. One of the strongest Pirahã values is no coercion; you simply don't tell other people what to do.[5] There appears to be no social hierarchy; the Pirahã have no formal leaders. Their social system can thus be labeled as primitive communism, in common with many other hunter-gatherer bands in the world, although rare in the Amazon because of a history of agriculture before Western contact. Pirahã build simple huts where they keep a few pots, pans, knives, and machetes. They make only scraping implements (for making arrowheads), loosely woven palm-leaf bags, bows, and arrows.[3] They take naps of 15 minutes to, at the most, two hours throughout the day and night, and rarely sleep through the night.",
"They often go hungry, not for want of food, but from a desire to be tigisái (hard).[7] They do not store food in any quantity, but generally eat it when they get it.[3] Pirahã have ignored lessons in preserving meats by salting or smoking.[3] They cultivate manioc plants that grow from spit-out seeds and make only a few days' worth of manioc flour at a time.[3] They trade Brazil nuts and sex for consumables or tools, e.g. machetes, gunpowder, powdered milk, sugar, whiskey. Chastity is not a cultural value.[5] They trade Brazil nuts, wood, and sorva (rubbery sap used in chewing gum) for soda-can pull-tabs, which are used for necklaces.[3] Men wear T-shirts and shorts that they get from traders; women sew their own plain cotton dresses.[3] ",
"Their decoration is mostly necklaces, used primarily to ward off spirits.[8] The concept of drawing is alien to them and when asked to draw a person, animal, tree, or river, the result is simple lines.[9] However, on seeing a novelty such as airplane, a child may make a model of it, which may be soon discarded.[10]",
"According to Everett, the Pirahã have no concept of a supreme spirit or god,[11] and they lost interest in Jesus when they discovered that Everett had never seen him. They require evidence based on personal experience for every claim made.[5] However, they do believe in spirits that can sometimes take on the shape of things in the environment. These spirits can be jaguars, trees, or other visible, tangible things including people.[12] ",
"Their language is a unique living language. Unrelated to any other extant tongue, and based on just eight consonants and three vowels, Pirahã has one of the simplest sound systems known. Yet it possesses such a complex array of tones, stresses, and syllable lengths that its speakers can dispense with their vowels and consonants altogether and sing, hum, or whistle conversations.",
"The language does not have words for precise numbers, but rather concepts for a small amount and a larger amount. The language may have no unique words for colors. "
] |
[
"For Practical Purposes, do Black Holes Remove Energy from the Universe?"
] |
[
false
] |
From a practical standpoint, is something within a black hole still part of the universe? To my knowledge, the only way the contents of a black hole interact with the rest of the universe is through gravity. Any thermal or light energy within a black hole does not interact with the rest of the universe (Unless energy produces gravity?), thus can it really be said that all of the contents of a black hole are part of the universe? Yes, they are within the universe, but if they do not interact with the universe, they cannot be observed, and don't really exist from the viewpoint of the rest of the universe. So, when a black hole captures energy, is it still part of the universe, for practical purposes? Or is it now more or less removed?
|
[
"Things that fall into a black hole won't themselves re-enter the rest of the universe. But, the black hole itself can still release energy either through quantum-mechanical Hawking radiation, or by interacting gravitationally with other objects (including other black holes). As a concrete example, the recent gravitational wave signal detected by LIGO was produced by two black holes merging and releasing a total of ~3 solar masses of energy in the form of gravitational waves. Nothing from inside the horizons leaked out, but some of the energy of the black holes---which was stored in the gravitational field ",
" the horizon---was released."
] |
[
"So, if there's gravitational energy, where does it come from? Does matter lose mass in the form of gravitational energy? Eventually, will all matter deteriorate into gravitational energy?",
"Also, if heat energy turns into gravitational energy by enterring a black hole, does that reduce entropy?"
] |
[
"That's basically right. It's hard to define a total energy in general relativity, especially for a black hole, but by at least one good definition the black hole is ",
" gravitational energy. Things that fall in just become gravitational energy instead of whatever they were before. Some of that energy is stored outside the event horizon and can therefore be released, e.g. when merging with another object."
] |
[
"Why do I have a specific taste in my mouth when I'm taking a small nap on my table/couch and awaken suddenly?"
] |
[
false
] | null |
[
"No, I don't mean that.",
"That's a very specific taste when I'm feeling very exhausted, take a mini-nap for 3-4 min during work and being awaken suddenly.",
"That doesn't happen when I'm exhausted and just go comfortably to bed.\nI thought it was something chemically that \"puts me to sleep\""
] |
[
"I know what you mean, to me it only happens while actualy naping, this doesnt occur when sleeping normally at night. "
] |
[
"'It's as if a cat urinated in your mouth while you were napping'",
"Mystery solved."
] |
[
"When scientists talk about consciousness, are they referring to the subjective experience of perceiving the world, or the ability to be self aware?"
] |
[
false
] |
[deleted]
|
[
"A self driving car is aware of its physical location with respect to everything else. I am self aware because I am aware of my thoughts in addition to external stimuli. I don't think we have any evidence to suggest that cars have this. Calling them self aware, and saying they have a subjective self because they have a self in their names seems silly "
] |
[
"Well this is a very complex question. Actually there's a semantic and philosophical discussion about what consciousness is. \nIn general lines, consciousness is the ability to experience or know an external or internal object. However, as Velmans said, the disagreement on the definition of the term might mean that people are talking about different things when they talk about consciousness, or that it is an umbrella term."
] |
[
"Christopher Koch and Giulio Tononi (who are generally considered serious and rigorously scientific scholars of consciousness) I think generally ask more about the first thing. That is, the subjective \"phenomenal\" self (which is a dirty philosophy word that's poorly defined but most people have an intuition of what it refers to). For Tononi this is a pragmatic question since his work addresses a very real problem:",
"people waking up in the middle of surgery and suffering immensely and being unable to communicate their pain.",
"Part of the reason this can happen is that there is (currently) no perfectly objective \"consciousness meter\". We have intuitions that tell us a chair is not conscious, and a 3-year old child probably is, but no objective way of measuring it.",
"So, consciousness is that state of mind that is (for lack of a better word) capable of ",
" or ",
" things.",
"The ability to then reflect back and know that you are ",
" and ",
" might be some kind of metacognitive thing on top of consciousness. But that's just me speculating.",
"Also, this is getting away from your original question, but I can't help myself... if an objective measurement of consciousness could be shown* to be accurate, then it would bear upon many outstanding moral questions, such as the mental states that fetuses or animals are capable of having.",
"*It's worth noting that some philosophers do not think it is possible to do this. They think there is an uncrossable \"explanatory gap\" between the kinds of things science can show and the solution to the 'hard problem' of consciousness. I understand their viewpoint, but feel that if the neuronal correlates of consciousness can be sufficiently pinned down through experimentation then it doesn't matter if we can't come up with a perfect scientific explanation as to why some matter is conscious at all."
] |
[
"Would it be possible to synthesize a functional blood cell with little/no iron? Or would iron be required to have functioning hemoglobin from the start?"
] |
[
false
] |
For people with disorders such as sickle cell anemia / thalassemia (major), frequent blood transfusions ultimately cause toxic build-up of iron. While chelation is possible to some extent, it's a restrictive, physically taxing and expensive process. Rather than pay for these treatments, I was wondering if a blood cell could be synthesized without the iron found in standard donor cells, which would allow the synthesized blood to be a direct treatment, and allow the patient to receive much more as well. However, I don't have a clear understanding of how much iron is inherent in the cell's construction vs. absorbed by the cell after formation for use. Could anyone please elucidate?
|
[
"In principle one could design a cell with hemocyanin (using copper) instead of hemoglobin(using iron) oxygen carrier. I suspect that this would require immunosupprssion, however as this protein is not endogenous to humans. Hemocyanin is hemoglobin surrogate in arhtropods and the reason their blood is blue (from oxidation state +II).",
"However, sveral other blood substitutes are under development."
] |
[
"Iron is the ‘active ingredient’ of red blood cells. Red blood cells are little sacks of haemoglobin, and the body places a single iron atom at the centre of each molecule of haem",
" (heme) which makes it able to carry oxygen molecules and get rid of carbon dioxide (and makes red blood cells red). So you’d have to re-engineer or replace this whole mechanism to make a non-iron based blood replacement."
] |
[
"Quite right! I wrote “molecule of haem” when visualising it in my mind but thought it looked wrong and changed it to ‘haemoglobin’ without checking. Have made the correction above. Thanks for that."
] |
[
"Can some infinities be larger than others?"
] |
[
false
] |
“There are infinite numbers between 0 and 1. There's .1 and .12 and .112 and an infinite collection of others. Of course, there is a bigger infinite set of numbers between 0 and 2, or between 0 and a million. Some infinities are bigger than other infinities.” -John Green,
|
[
"Yes. For instance, the set of real numbers is larger than the set of integers.",
"However, that quote is still wrong. The set of numbers between 0 and 1 is the same size as the set of numbers between 0 and 2. We know this because the function y = 2x matches every number in one set to exactly one number in the other; that is, the function gives a way to pair up each element of one set with an element of the other."
] |
[
"When talking about infinite sets, we say they're \"the same size\" if there is a bijection between them. That is, there is a rule that associates each number from one set to a specific number from the other set in such a way that if you pick a number from one set then it's associated with ",
" one number from the other set.",
"Consider the set of numbers between 0 and 1 and the set of numbers between 0 and 2. There's an obvious bijection here: every number in the first set is associated with twice itself in the second set (x -> 2x). If you pick any number y between 0 and 2, there is exactly one number x between 0 and 1 such that y = 2x, and if you pick any number x between 0 and 1 there's exactly one number y between 0 and 2 such that y = 2x. So they're the same size.",
"On the other hand, there is no bijection between the integers and the numbers between 0 and 1. The proof of this is known as ",
"Cantor's diagonal argument",
". The basic idea is to assume that you have such an association and then construct a number between 0 and 1 that isn't associated to any integer."
] |
[
"I've always like this explanation, it seems to help get the concept:",
"\n",
"Look at this picture",
". The inside circle is smaller than the outside one. Yet they both have the same amount of points on them. For every point on the inside circle there is a corresponding point on the outside one and vice versa. ",
"*Edited for clarity",
"\nEDIT2: If you're into infinity check out \"Everything and More - A Compact History of Infinity\" by David Foster Wallace. It's fucking awesome. Just a lot of really interesting info about infinity. Some of it is pretty mind blowing."
] |
[
"Do black holes interact with the electromagnetic field? If so, what kind of interaction?"
] |
[
false
] |
[deleted]
|
[
"Black holes can have net electric charge (say, if it had been constructed entirely out of protons and no electrons), in which case they interact with the electromagnetic field just as a charged particle would. It's important to note that while a (classical) black hole has no memory of what fell into it (e.g. protons) it DOES (and MUST) remember their electric charge. Energy, angular momentum, and charge are the only things a black hole remembers of what falls in (see ",
"no-hair theorem",
").",
"More interestingly (in my opinion at least) electromagnetic fields interact ",
" with black holes; the most significant effect being that charged black holes produce their own EM field which has its own gravity and modifies the structure of the black hole. There is a maximum charge that a black hole can have before its singularity becomes exposed (without an event horizon) and these 'extremal' black holes are important theoretical objects even though most astrophysical black holes are almost certainly electrically neutral."
] |
[
"Whar exactly do you mean that the EM fields interact gravitationally? Is it that they change that energy tensor thing?"
] |
[
"Exactly: the EM fields contribute to the stress-energy tensor (a measure of the mass and energy density), which is responsible for curving spacetime in GR."
] |
[
"When a diabetic hypo's, why do they not switch to burning ketone-bodies, like a runner who 'hit the wall'"
] |
[
false
] | null |
[
"In short, they do in fact switch to ketosis, but, as the other posts explain, its not as easy as just getting ketotic and switching back out again. In such an insulin low state, a diabetcs body cannot get glucose into their cells, which triggers ketosis. However, whereas a runner can just drink some glucose and get out of it, a diabetic cannot because of their lack of insulin. in time and if uncorrected with aggressive hydration and insulin, a diabetic in dka, or diabetic ketoacidosis, will eventually slip into a diabetic coma from the unchecked acidity of the ketone bodies filling up their blood. It is for this reason that a lot of dka patients aremanaged in a highly monitored setting, whether it be an icu or a step down unit."
] |
[
"Diabetic ketoacidosis is a common complication of diabetes, and as many of the posters here state it is associated with an absolute insulin deficiency and a ",
" blood sugar level. My impression is that the OP is asking why do ketone bodies not form when a diabetic becomes hypoglycaemiac.\nThe answer here is that they do, but that in itself is not usually sufficient to prevent the hypoglycaemic efects. My guess is that a part of it would be that hypoglycaemia occurs far more quickly and profoundly in diabetics, probably because the commonest cause woudl be a relative insulin overdose.\nIn non diabteics, the commonest causes of ketosis are excess alcohol intake and starvation, and both of these will have a more gradual onset . "
] |
[
"In a brief nutshell, it is my understanding that they have a high insulin resistance. The Insulin essentially \"ties up\" the fat cells that would normally be used for energy; ketosis. Unfortunately the body can sometimes resort to eating muscle and organs because the energy rich fats cells are not accessible due to the insulin resistance. Please correct me if I am wrong, but that is my understanding of it. ",
"Also, people with type 1 diabetes can experience ketosis, whereas those with type 2 rarely do."
] |
[
"How to remove glycol based contaminant from metal substrate without damaging substrate?"
] |
[
false
] |
working as a temp for a semi-conductor company... boss told me to figure this out. how to remove glycol based contaminant from metal substrate without damaging substrate. the substrate would primarily be either stainless steel or aluminum. also if there is a test to determine if all the glycol based contaminants are removed i'd greatly appreciate it.
|
[
"What kind of glycol?",
"If its short chain the ethylene glycol or propylene glycol Why not just boil it off. If it's longer chain use ethylene glycol to dissolve it then boil off the residue.",
"Also, do your own work"
] |
[
"hey entropy.. thanks for the help\ni only ask because i've been instructed to post on scientific community forums for the help, but thought that it'd be quicker to get a response from here... seeing as how there are some very intelligent people here"
] |
[
"lol just giving you a hard time. You may wish to phrase your problem more precisely if you want quality answers. Glycol doesn't refer to any specific chemical compound I can find but a class of compounds, maybe even you mean PEG? Also by contaminant do you mean like a thick buildup or more like a monolayer and how clean does the substrate have to be at the end. All these things could have a bearing on the process you might want to use."
] |
[
"How does the energy compare with fusion of larger atomic nuclei to the fusion of hydrogen atoms?"
] |
[
false
] |
I think that the potential energy would have to be higher for large nuclei to fuse, but would this also mean the energy released would also be higher? Thank you for any responses!
|
[
"You can calculate the Q-value for any nuclear reaction ",
"here",
"."
] |
[
"The Q-value of a nuclear reaction is the energy released during the reaction due to a change in the rest mass of the particles. During a nuclear reaction, mass is converted to another form of energy (generally kinetic energy of the products). This is given by the famous E=mc^2.",
"",
"The Q-value is then the change in mass during the reaction: Q=(m_final-m_initial)*c^2. To convert from mass units to energy units, the conversion is roughly 931 MeV/amu, where amu=atomic mass units.",
"",
"A positive Q-value denotes reactions which produce kinetic energy (exothermic) due to a decrease in total rest mass and they readily occur at any initial energy. A negative Q-value denotes reactions which increase in total rest mass and require initial kinetic energy equal to the Q-value in order to occur (endothermic reaction).",
"",
"The Q-value of a nuclear reaction may equivalently be seen as a change in binding energy of the constituents due to the reaction. However, binding energy is a little less intuitive. You can read more about it ",
"here",
"."
] |
[
"Can you explain this with a bit more detail?"
] |
[
"Could zero point energy theoretically be applied to humans?"
] |
[
false
] | null |
[
"Zero point energy is not \"theoretical\" in the sense I think you mean it. We know for sure the it exists; it's a very straightforward consequence of quantum mechanics.",
"Zero point energy can never be a \"limitless supply of energy\", because by definition, it's the minimum energy that a given quantum system can possibly have. You cannot remove it, because by definition it's the lowest possible energy that that system can have."
] |
[
"I think what I meant to say is the theoretical application of the energy. I do know that indeed exists, but the usage and harnessing of said energy is what I'm deeming as theoretical"
] |
[
"\"Harnessing\" zero-point energy is impossible."
] |
[
"Why can't you have fusion products with an atomic mass greater than that of iron?"
] |
[
false
] | null |
[
"You ",
" have fusion reactions which create arbitrarily heavy known nuclides, however the Q-values can be negative.",
"Can you give a specific example of a reaction you’re talking about?"
] |
[
"But surely, if this is the case, there are fusion reactions with positive Q-values which produce nuclides heavier than those of iron (simply by considering the change in binding energy per nucleus) and should therefore occur in the cores of main-sequence stars."
] |
[
"Any reactions that ",
" happen in stars ",
" happen to some extent. It's an oversimplified picture to just consider a few fusion reactions happening in stars. In reality there are ",
" reactions that can and do happen in stellar burning."
] |
[
"Can metals evaporate? If so, can the gas be condensed back into solid metal?"
] |
[
false
] |
[deleted]
|
[
"Yes they can. In fact, ",
"this is a common technique used to deposit thin films of metals."
] |
[
"This is one way that mirrors are made, yes. Aluminium is evaporated and deposited on the back of a piece of glass, and then covered with a protective layer. "
] |
[
"Like mirrors in the back of glass? "
] |
[
"Why does my AC Power Adapter make clicking and humming noises?"
] |
[
false
] |
I understand that electricity causes vibration, etc... and thus certain noises. But what specifically is going on inside that box between the plug and my laptop that causes audible clicks and humming noises?
|
[
"As a former electrician and current electronics geek, your power supply should not be making clicking sounds or humming. Typically these problems have to do with the power supply capacitor (the power is rectified, filtered through a large filter capacitor and then buck converted to a lower DC voltage at high frequency). I'd get a new power supply soon."
] |
[
"Thanks. It is an iGo, which has been reviewed pretty well, but now I'm nervous. Could it \"fry\" my laptop?",
"I should probably stop holding it up to my ear, too."
] |
[
"I'd have to hook it up to my oscilloscope and look at what's going on at the voltage output to answer that question."
] |
[
"Silly magnets, why is this not possible?"
] |
[
false
] |
[deleted]
|
[
"So if you take two magnets oriented so they attract each other, they'll accelerate and snap together. The amount of force they exert to attract each other is the same amount of force it will take to then pull them back apart. You're car scenario may approach a stationary magnet and accelerate towards it, the inertia of the car will continue it moving forward, once it passes the threshold of the magnet and continues along it's path it will still be attracted to the magnet and pull the car back towards it, sucking energy from that inertia and slowing it down.",
"Another way to look at it is if you have a soapbox car, no engine, just free spinning wheels. It's at top of a hill, and the road is a series of equally high and steep hills that move forward like a wave. The car will speed up down the first hill, hit the bottom, slow down on the way up the next hill barely crest the top, speed up down the next hill, slow down up the next hill, and so and so forth. Once you then take into account friction of the road, tires, air, etc; If the hills are all equal, it won't make it over the first hump, it'll just pendulum to a stop at the bottom of the first hill. With the magnets, the car will just comes to a rest directly above one of the stationary magnets. ",
"tl;dr: magnets attract each other, but it also takes force to separate them."
] |
[
"That's more or less the concept of a mag-lev.",
"\n ",
"http://en.wikipedia.org/wiki/Maglev_(transport)"
] |
[
"Maglev works similar to this, but it uses electromagnets, and as the stationary magnet on the train gets closer, the electromagnet will turn off, then possibly reverse polarity so that the stationary magnetic doesn't cause a loss of forward momentum by attracting in the opposite direction, and in the case of reversed polarity, it will cause the stationary magnetic to be repelled, giving more forward momentum."
] |
[
"Why do we \"Weigh\" things in kg,g,and mg, if grams are units of mass? If I've got some powder on a scale and it reads 40mg, is it actually calculating the weight and then dividing it by 9.8 to tell me the total mass of the powder on the scale?"
] |
[
false
] | null |
[
"Why do we \"Weigh\" things in kg,g,and mg, if grams are units of mass?",
"We measure mass by exploiting Newton's 2nd law: F=ma. The acceleration due to earth's gravity at its surface is about 9.8 m/s",
", so we can measure an object's mass by measuring the force gravity exerts on it and then dividing by 9.8 m/s",
" (using F=ma --> m = F/a). If you know the force on earth's surface (ie weight) then you know the mass, and vice-versa.",
"If I've got some powder on a scale and it reads 40mg, is it actually calculating the weight and then dividing it by 9.8 to tell me the total mass of the powder on the scale? ",
"Yes."
] |
[
"The mass of something has two effects: it resists acceleration, and it attracts other things by gravity. To measure mass, you have to measure one of these two effects. An ordinary scale measures the force of gravitational attraction of the object to Earth. If you used your Earth-calibrated scale on another planet, you'd get the wrong results.",
"You might be able to use a low-friction rig, like an air-hockey table, or mag-lev to float an object, then push it with a known force and see how much the object accelerates. This would work regardless of the force of gravity, whatever planet you're on."
] |
[
"Congratulations, you've just repeated what I said but less intelligibly. "
] |
[
"Is it possible to \"carbonate\" liquids with other gasses?"
] |
[
false
] |
What is special about carbon dioxide? can we use other gasses to "carbonate" a liquid instead? If so why c02. If not why can't we.
|
[
"Many gases (like N2 and O2) dissolve in water. But carbon dioxide is special because it doesn't just dissolve, it ",
" with water to form carbonate and bicarbonate ions:",
"CO2 + H2O --> 2 H",
" + CO3",
"CO2 + H2O --> H",
" + HCO3",
"This releases hydrogen ions into the water, making it acidic, which is why carbonated water is tart.",
"This reaction removes CO2 ",
" from the water, making room for more to dissolve in: as a result, you can pack ",
" more CO2 in water than you can other gases. Like, 100 times as much!",
"This means that beverages made with CO2 are a lot bubblier than ones made with, say, nitrogen. Guinness beer, for instance, is nitrogenized rather than carbonated: that's why it has less \"head\", tiny bubbles, and less tartness than other beers.",
"There are a few other gases that react with water when they dissolve: two good examples are sulfur dioxide (SO2) and ammonia (NH3). However, if you try to make a beverage out of them they will kill you, so CO2 is the best choice for drinkmaking."
] |
[
"You can aerate water with tons of stuff. We just don't see it in faily life because a CO2 is readily available, tries to \"leave\" water under normal atmospheric pressure (giving it that nice bubbly), and not going to harm you when ingested. ",
"I constantly aerate water at home, with my aquarium. A pump agitates water, which dissolves air into it. My aqualife needs the O2 in that dissolved air to survive."
] |
[
"Absolutely. In many places they are making ",
"beer",
" with a nitrogen/CO2 mix to decrease the size of the carbonation bubbles.",
"Carbon dioxide is unique though as it chemically reacts with the water, forming carbonic acid. This allows for much greater quantities to be dissolved in the liquid, as well as adding the acidic tang we associate with carbonated drinks."
] |
[
"If a person eats junk food with a stuffy nose, will their brain receive the same chemical reward as it would when they can taste normally?"
] |
[
false
] |
I was eating chips with a cold and was wondering this.
|
[
"Oral Doctor here! [That sounds wrong]\nTo give you a short answer: The brain receives the same impulses as it would without a stuffed nose. However, your brain interprets it as being tasteless. Smell is 70-80% of the taste.\nThe impulse is the same but the feedback is different because of the lack of information.\n(English not my first language)"
] |
[
"So this would mean that you receive less of a \"reward\"?"
] |
[
"I don't really know what you mean by reward?\nIf reward means how strong a taste is, then yes. Because you can't smell it it has 70% less taste."
] |
[
"Evolution by randomness or necessity?"
] |
[
false
] |
[deleted]
|
[
"\"It doesn't makes sense for me Evolution by randomness. Maybe a combination of both? I don't know.\"",
"It's this. Evolution via natural selection itself is ",
" random. Like, not at all. This is a common misconception. Instead of a lottery, it's a game played where the ",
" players tend to 'win'.",
"However, to use analogy, during this game, when players, say, start each round with a new set of cards, though they usually start with the deck they finished with last time, sometimes a random card gets swapped out for another. This is what we call 'variation'. Suddenly a player might find that the strategy they used last game can no longer work; they lose and unceremoniously get kicked off the table. Bad luck. In contrast, sometimes a new card allows a player to try a new strategy, thus enabling them to wreck the competition. When this happens, they make it to the next round and they get to keep this card. ",
"That's the 'randomness' aspect of the process of evolution. What's more, in this analogy, the rules of the game change, like, every ten rounds or whatever, and so the 'meta' is always in flux. A hand that might work for a few rounds might suddenly find itself outta' luck with a new rule change. However, if a player was lucky enough to have other options in the deck, or be handed a useful new 'random swap', they can play a new strategy and still make it.",
"As an aside:",
"I always thought that Evolution is by selection. I mean, giraffes, for example, need to be taller to reach taller trees. So, next generation of giraffes will be taller than the old ones, but no by randomness, because they need it. Need to be taller to reach food.",
"What you're describing is a little along the lines of the debunked ",
"Lamarckian selection",
", as opposed to ",
"natural selection",
". Giraffes don't \"want\" to grow longer necks to reach higher branches. Going with the above, some pre-giraffe-beasties just randomly got handed a card that gave them an extra +3 to neck length. They therefore had a chance to play better during the 'bonus points for reaching higher branches' rule set, got more points, and that +3 neck length card stuck around. Hence giraffes. There's no ",
" involved; evolution is ",
".",
"Players don't plan for future rounds. All they can do is play the best game they can this round. A new rule change in the future might make the current strategy useless, or make some underutilised cards way more viable. In any case, the players can't foresee this and plan ahead. They just gotta' hope the cards they're handed (i.e. take with them) will help them win.",
"In reality of course, it's an awful lot more complicated. The cards represent individual nucleotides in a deck ('genome') containing several billion. And as you point out, some cards can only be played if other cards are played in tandem: Giraffes, for example, needed to play multiple cards to play their particular 'long neck success' strategy. And that's not taking into account what, like, other players are up to... Eek!",
" It's a game where randomness can change what you start with (variation), but the best players always win (selection)."
] |
[
"Also, most of the time that single card that got swapped out doesn't make any difference at all. It was a minor change that wasn't ever part of your play strategy. Many rule changes later it may become an advantage or disadvantage, or it might forever remain some unimportant variant between your deck and the players around you."
] |
[
"So... evolution is basically a game of War but with Mao rulings?"
] |
[
"Why are sunburns warm to the touch?"
] |
[
false
] |
My forearms were sunburned today. When I press my cheek against the burn, it feels warmer than if I touch it to a non-burned area. What are the physiological reasons behind this?
|
[
"Your body sends an increased amount of blood to area of the burn in order to heal it. The blood is warm, so the skin above it feels warmer. "
] |
[
"No, you break out in shrubs."
] |
[
"There are 5 'cardinal signs' of inflammation: heath, pain, redness, swelling, and loss of function. The first are the classical signs, described by Celsus, while the loss of function was later added."
] |
[
"Is there a limit to how big planets can potentially be?"
] |
[
false
] |
Is there by any chance a planet as big as our sun or even bigger? What's the largest planet known to man at this present time?
|
[
"Yes there is. At about 13 times the mass of Jupiter a planet will be reclassified as a brown dwarf. These can fuse deuterium at their core for a brief time. At about 8% the mass of the Sun that brown dwarf will become a red dwarf star."
] |
[
"The limit would still be the Chandrasekhar limit. Your big ball of iron would collapse into a Neutron star or a black hole under it's own gravity. "
] |
[
"'Planet' and 'star' is a human classification. If there is a super rare event that someone artificially put thousands of giant ball of iron together then sure, it will collapse into some object similar to a neutron star due to gravity. But the newly form object could not be considered a 'star' because historically it did not go through the fusion phase. Also, if the mass is comparable to the star it is orbiting around, then they will just start orbiting around each other base on some barycenter. ",
"But can the event happen naturally? Unlikely. "
] |
[
"If golf balls have dimples on them to make them more aerodynamic then why don't cars or planes have them too?"
] |
[
false
] | null |
[
"Because golf balls are so short compared to a car or plane, drag is dominated by sperating flow behind the ball. By using dimples to trigger a turbulent boundary layer, speration can be postponed thus reducing drag. ",
"Cars and planes are longer more narrow bodies and drag tend to be dominated by skin friction drag. In this case, maintaining a laminar boundary layer is possible. Things change a bit as you reach transonic speeds.",
"The Wikipedia entry on drag has a good diagram right at the top showing this effect. We talk about Reynolds number to describe which regime we are in."
] |
[
"A few reasons come to mind:\n1. Different Reynolds number regimes. Golf balls are a different size and shape than cars or planes, so the turbulence transition enhancement from dimples would be different. \n2. There have been some studies on on this (and related hump back whale fin ridges), and some showed that there may be a slight benefit for certain cases. However, the higher manufacturing costs, no benefit in some cases, and poor aesthetics (who wants to drive a car that looks hail damaged?) make it not viable. ",
"Source: am aerospace engineer"
] |
[
"And to expand, while cars and planes may not (commonly) have dimples on them, they often use other devices to induce a turbulent boundary layer to inhibit boundary layer separation. ",
"Vortex genertors",
" which acheive a similar results as dole ball dimples are seen in both planes and race cars."
] |
[
"Why are we so interested in Europa and Titan, but have heard so little of Ganymede?"
] |
[
false
] |
From a layman perspective anyways. I was just reading about it, and it looks like an even candidate for life with Europa, but I haven't seen any mission planned to it or anything... Edited for clarity. Edit2: there is a mission planned!
|
[
"I'm not sure why you say that it seems like a better candidate than Europa. Europa is the stronger candidate for having a subsurface ocean, and its outer layer is entirely ice rather than being a rock/ice mixture like Ganymede and so many other bodies. Titan is interesting for a variety of reasons, partly because it actually has a thick atmosphere (surface pressure is even higher than on Earth), because it has liquid on the surface and thus probably something similar to Earth's hydrologic cycle, but with methane instead of water. It's atmosphere contains a variety of simple organic chemicals, and is conducive to the presence of complex organic chemicals as well. "
] |
[
"I haven't seen any mission planned to it or anything...",
"So by interest you mean exploration? Actually ESA is planning a mission to Ganymede: ",
"http://www.esa.int/Our_Activities/Space_Science/JUICE_is_Europe_s_next_large_science_mission",
"The same mission is planned to perform two Europa fly-bys before achieving its final orbit around Ganymede. What I'm not sure about is whether this is actual interest in Ganymede, or simply possibility of exploring it because radiation is not as high as ",
"on the surface of Europa",
"."
] |
[
"Well, the history here is an odd one...",
"Originally there was going to be a joint NASA/ESA flagship mission to Jupiter's moons, the ",
"Europa Jupiter System Mission (EJSM)",
". Flagship missions are the largest, most expensive class of spacecraft (Cassini was the last flagship). This thing was planned to include an American Europa orbiter, a European Ganymede Orbiter, and possibly even a Russian Europa lander.",
"After NASA's budget cuts to outer planet exploration at the beginning of this decade, it started looking like it wasn't prioritizing the mission properly. So, ESA decided to go it alone, effectively canceling EJSM and starting their own project, ",
"Jupiter Ice Moons Explorer (JUICE)",
", which ",
" have Ganymede as the main focus.",
"In the meantime, NASA has since down-scaled its jovian moon aspirations and they're now considering the ",
"Europa Clipper",
" spacecraft, which is essentially a cheaper version of the Europa orbiter that would have flown on the EJSM. Although this Europa Clipper is still only in \"proposed\" status (unlike JUICE which is in full-scale production), after talking to some of the higher-ups in charge of planetary exploraiton at NASA I'm pretty convinced that Clipper will happen."
] |
[
"Are carbon-based lifeforms the only plausible type of lifeforms?"
] |
[
false
] |
Given different environments, could life develop to use something besides carbon as their primary element for their organic chemistry? (presumably one as versatile as carbon, with 4 valence electrons)
|
[
"It's been asked quite a few times if you search for it. To repeat what I've said then: Not really. ",
"Carbon-carbon bonds are simply more stable than (say) silicon-silicon ones, and while the environment does affect the overall stability, the relative stability is more or less the same. Carbon's always better. There are many more stable carbon compounds than silicon compounds, and under a wider range of conditions. Just looking at the number of valence electrons is a much too simplistic understanding of chemistry. It works to explain why silicon and carbon both form dioxides - but is quartz and dry-ice really similar? Not really. ",
"In terms of more sophisticated theories of chemical bonding, silicon and other third-row p-block elements have 3d orbitals contribute in its bonding. Hence why SiF6",
" exists but not CF6",
" for instance. You definitely can't drop in silicon as a replacement for carbon and expect similar bond strengths and such properties. (The aforementioned d-orbital hybridization being the reason why silanes are much less stable and act quite differently from hydrocarbon alkane chains) ",
"Biology only uses a relatively small number of elements, which doesn't really match their prevalence on the Earth's surface/atmosphere. (from that perspective, silicon is much more abundant) I wouldn't necessarily expect other life forms to have the exact same elemental composition as life on Earth, much less use DNA/RNA/proteins and so forth. But it seems quite a stretch to assume that they'd not use carbon, which is definitely the most versatile element around under any conditions. To me, that sounds more like imaging something different for the sake of being different, rather than because we have good reasons to. ",
"Chemistry ",
" only exists in a relatively limited range of conditions. At high temperatures, molecules (in particular big ones) will break apart, too low temperatures and things will become solids and chemical reactions won't happen. Too low pressure and you won't have liquids, but at extremely high pressures things will solidify again (and at extremely high pressures, probably turn into some kind of weird metallic soup)."
] |
[
"Yes, \"Life, but not as ",
" know it\" is a sci-fi trope. As I said, non-carbon based life is stretching it as far as I'm concerned, so non-",
" life is just an idea that's just far too vague and speculative for my tastes. It's best left as science-fiction without trying to give it some scientific rationale, as any such theory would probably be far too speculative to qualify as good science.",
"\"Impossible\" is too strong a word, but I don't really think such a thing exists. I'd love to be proven wrong on that, of course. But it'd still be a wild-goose-chase to try to find ways that such a thing might be possible. (To draw an example from history, nuclear physics showed that you could turn certain other elements into gold. But those centuries people spent doing alchemy was still largely wasted time. Science doesn't advance by looking for what we'd like to be true, but by working from what we know. The farther you deviate from what's known, the more likely it is you're wasting your time)"
] |
[
"I'm sorry, but this has been debunked in two recent studies",
"here : ",
"http://www.sciencemag.org/content/337/6093/467.abstract",
"\nand here : ",
"http://www.sciencemag.org/content/337/6093/470.abstract",
"and noone believed the original NASA paper anyway, DNA incorporating arsenic would have severe stability problems"
] |
[
"Hot objects in space."
] |
[
false
] |
Heat travels through converction. If I were to take a brick of lead, and stick it in the over to let it heat up, then remove it. It is going to cool off to room temperature over some time period as it radiates it's heat energy into the air surrounding it, and the surface it is resting on. What if I did the same experiment in a vacuum? Would it remain hot for a longer period of time as there is little, if any medium for it to radiate heat into?
|
[
"Heat travels through converction. ",
"Convection, radiation, diffusion are the main ones.",
"If I were to take a brick of lead, and stick it in the over to let it heat up, then remove it. It is going to cool off to room temperature over some time period as it radiates it's heat energy into the air surrounding it, and the surface it is resting on",
"So far so good, but convection usually only occurs in fluids.",
"What if I did the same experiment in a vacuum? Would it remain hot for a longer period of time as there is little, if any medium for it to radiate heat into?",
"It wouldn't lose heat from diffusion, but it would from radiation. The amount of power that it radiates is proportional to its temperature to the power of four. But yes, it would take longer to cool down. It's the same concept as a thermos: there's no heat diffusion across the vacuum layer."
] |
[
"You're mixing up convection and radiation. Convection is when the heated body comes in contact with a medium (such as air) and give energy off to it.",
"Radiation (infrared, if we're talking about heat, or Black body radiation in the more general case) happens independent of any medium - and that would be the dominating process in space. You don't need anything to ",
".",
"That said, I'd still guess that the cooling process would take a longer time - think of water in a thermos bottle. (But I'll admit that I haven't thought that through, so maybe someone else can contribute.)"
] |
[
"Would it remain hot for a longer period of time as there is little, if any medium for it to radiate heat into?",
"You only mentioned one of three kinds of heat transmission:",
"Convection, by way of gas molecules",
"Conduction, by way of solid vibrations, i.e. \"phonons\".",
"Radiation, by way of the electromagnetic field.",
"The next time you are standing out in the sun, being warmed by it, remember that there is a vacuum between you and the sun, and remember this conversation."
] |
[
"Why is more than half the world's oil located in the Middle East, geologically?"
] |
[
false
] |
I'm specifically asking about oil formation in terms of geological factors, etc. I am not at all asking about anything to do with politics, economics, etc.
|
[
"Oil (and coal) get their beginnings in places where life flourishes but frequently gets buried without access to oxygen. Places like swamps and river deltas. The organics that are buried then start moving around due to plate tectonics and make trips, and over millions of years, sometimes to locations that have absolutely no life. Like Antarctica, and underneath deserts.",
"Having oil be so concentrated underneath that specific region does not indicate that it was that specific region that hosted the life, or necessarily any life. The fact that there's so much of it in that single place only indicates that there was a large concentration of tropical life on ",
" continuous continent millions of years ago."
] |
[
"The ocean floor is as much subject to plate tectonics as much as any other part of the crust.",
"The organics are buried due to various events, tectonic ones included, and in those anaerobic conditions are broken down into fossil fuels of various sorts depending on the exact conditions. These buried reserves are then at the mercy of geological movements. "
] |
[
"The ocean floor is as much subject to plate tectonics as much as any other part of the crust.",
"The organics are buried due to various events, tectonic ones included, and in those anaerobic conditions are broken down into fossil fuels of various sorts depending on the exact conditions. These buried reserves are then at the mercy of geological movements. "
] |
[
"Why do we sometimes refer to creatures by their scientific names as \"genus species\" and sometimes \"genus species species\"?"
] |
[
false
] |
For instance, . The title of the page calls the animal elaphe obsoleta; the picture caption calls it elaphe obsoleta obsoleta. As a secondary question, is my capitalization there correct, or should genus names be proper nouns?
|
[
"This indicates a subspecies or variety. Genus should be capitalized always."
] |
[
"Awesome, thanks very much. I'm glad I know that now."
] |
[
"All species and genus names should also be italicized (unless handwritten, then underlined)."
] |
[
"External intelligent entities, mathematics and further communication"
] |
[
false
] | null |
[
"Hi there! This question would be perfect for ",
"/r/AskScienceDiscussion",
" due to the speculative nature of any answers that would be provided.",
"Cheers!"
] |
[
"can you move it? I will I have to repost it?"
] |
[
"Repost. We don't have fancy tools to move posts because the admin don't love us. "
] |
[
"Does receiving a blood transfusion give you immunity to viral illnesses that the donor has had (and recovered from)?"
] |
[
false
] |
I have looked for an answer to this but most information seems to talk about blood type compatibility issues which is not what I am asking. To refine my question, these would be conditions that you had not been previously exposed to. Put another way, do antibodies or the body's knowledge of how to make specific antibodies persist in the blood and work in isolation?
|
[
"It only has to do with the amount of antibodies present in the blood (usually need a larger than normal amount), if you spike the donor with antibodies then yes, but only for a certain amount of time. It's called Passive Immunity."
] |
[
"If you receive a large number of antibodies from someone you might get temporary protection from some infections. Up until those antibodies were degraded and lost. ",
"To gain a permenant immunity from a blood donor you would instead likely need a transplant of activated mature B and T lymphocytes from the donor. IIRC theses activated cells reside in your lymphatic organs and aren't just free floating in the blood. "
] |
[
"It is also worth pointing out that such transplant of mature B and T lymphocytes would be very likely rejected by your immune system. ",
"In most cases the relationship between donor and host immune systems is pretty hostile. E.g. after transplantation of bone marrow the cells of donor are attacked by the host immune system while the immune cells from the donor`s bone marrow attacks the host body. This is called as Graft-versus-host disease and it is actually used as treatment option for some types of leukemia. "
] |
[
"Would it be possible for two people to grow together if they both were to cut off a hand/finger and then hold the wounds together?"
] |
[
false
] |
Assuming blood types and so on are identical.
|
[
"Ignoring practical issues like being able to brace the wounds together for the weeks it'd take to heal, you would have to go beyond just matching blood type--the two people would need matching HLA haplotypes or else each person's immune system would try to reject the other person's tissues. (There may be ways around this, for example if each person were put on immunosuppressants.) Perhaps it could happen with identical twins, whose HLAs would be perfect matches."
] |
[
"Somewhat related question: if I cut off both of my hands and held the wounds together, would the same thing happen (get one continuous \"loop arm\")?"
] |
[
"Many people with damaged or burned hands have them sewn inside their abdomen. There they heal and new growth takes place."
] |
[
"On average, and not including direct human intervention, how do ant colonies die? Will they continue indefinitely if left undisturbed? Do they continue to grow in size indefinitely? How old is the oldest known ant colony? If some colonies do \"age\" and die naturally, how and why does it happen?"
] |
[
false
] |
How does "aging" affect the inhabitants of the colony? How does the "aging" differ between ant species? I got ants on the brain!
|
[
"Ant colonies can die off in a variety of ways. Mites, other forms of parasites, ant wars, death of the queen, lack of food or sugar or water, predators, disease, and so many more. A colony can usually grow proportionate to its amount of resources, and room to roam. I am not sure how old the oldest ant colony is, but many colonies in captivity have survived for many years. Most colonies with only a single queen only last until her death. This is due to the fact that queen alates(young queen ants and their male equivalents) participate in yearly nuptial flights when they leave to mate. Male alates die right after this, but female alates that do make begin an entirely new colony, with only a few eggs to start. There are some species of ants that can have several queens however, and if the acclamation of the new queen goes well each time theoretically a colony could live forever.",
"-an ant enthusiast."
] |
[
"When ants colonies fight. A lot of ants are highly territorial and will battle over resources and territory."
] |
[
"Can you please elaborate on these \"ant wars\"?"
] |
[
"AskScience AMA: We are scientists from the team that recently discovered a malaria protein with the ability to target many different types of cancer. Ask us anything!"
] |
[
false
] |
Hi Reddit! We are Dr. Mads Daugaard, Dr. Nader Al Nakouzi, Chris Wang, and Gunjan Kumar from the Vancouver Prostate Centre. We are part of the group that recently published a study detailing the use of a malaria protein, VAR2CSA, as a new and novel way of targeting cancers. Cancer and the placenta show many similar characteristics. However, scientists have spent decades trying to find biochemical similarities between placenta tissue and cancer. Together with our colleagues from University of Copenhagen we discovered how malaria uses VAR2CSA to embed itself in the placenta and how the same target is present on cancer cells. Based on that discovery we immediately saw its potential to deliver cancer drugs in a precise, controlled way to tumors. New and novel ways of targeting cancers are needed in order to combat the disease. With a recombinant version of VAR2CSA, we hope to develop a promising therapy for a broad spectrum of different cancers. We will be answering your questions at 1pm EST (10am PST). Ask Us Anything! Edit: Hello Reddit! Thank you all for the wonderful questions, we are here to answer what ever question you have for us for the next hour. Ask away! Edit 2: Hi All! Thank you all so much for all the questions again, we had a blast answering everything we can. However, we must be go back to work now! We will come back through out the day and answer more questions when we have time. THANK YOU FOR YOUR INTEREST :D
|
[
"Hello!",
"I'm a newly started Danish student from Aalborg on 1. semester in Medicine with Industrial Specialization. I wish you the best of luck with your project! I have a few questions:",
"What do you think the odds are, that this will end up as a major breakthrough? I'm curious about the odds of it working for humans, as I've heard it worked on mice.",
"There's been tons of stuff like \"Cure for cancer found!\" in the news over the years which (obviously) haven't been true, and this has made most average people lower their expectations for anything alike. Specifically, it was easy to see all the hate and disappointment in the comment sections of the articles of your discovery, where most people believed it was a lie. Do you think anything needs to be done about this, and if yes, what? Additionally; Does the public's opinion on this even matter?",
"I'm fascinated by the work, but I'm curious what field it's in, as I have just started on my bachelor. For my candidate, I can choose between translational medicine and biomedicine, and I'm wondering which one of these best describes your work.",
"What does this discovery feel like for yourselves, personally? Pride, increased curiosity, happy, et cetera?"
] |
[
"1) I think the odds are pretty good! The main concern is safety and whether there will be any unforeseen side effects. \n2) I completely agree on your concern here, but I think the critique should be directed towards the media. The problem is that the media wants to sell news papers. We have been very careful in our press releases going out from UBC and UCPH saying that our potential new treatment will take 2-4 years before first human dose.\n3) Well, it is a merge between two different research fields - Parasitology and Cancer biology. In our case, we brought expertise together in Malaria research from UCPH and Cancer Research from my lab at UBC.\n4) I am definitely proud, but I also have a strong feeling to get on with the next phases of these studies. This is just the beginning and we can use this technology for diagnostics, but also for immunotherapy applications. This is all something that we are working hard on now. \nThank you for your questions. Mads"
] |
[
"When will we see this tested in real patients?"
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"I'd say we don't know enough of the brain to be able to do that, but we ",
" know enough about technology to be able to do that. ",
"If you gather enough data, for example by using electrodes, you can use machine learning to decipher this data, without relying on the actual knowledge of how the brain is processing this information.",
"\nFor example, ",
"this study",
" used machine learning to be able to tell what someone was seeing, and when that person was seeing that thing. Granted, there was a 2-fold choice, either houses or faces, but the principle can be applied to more difficult distinctions. ",
"In fact, those principles are sometimes already aplied in real life. ",
"Brain Computer Interfaces, BCIs",
" - great review - are computers that read signals from the brain in order the help people act out things they might not physically be able to do. ",
"Finally, ",
"this",
" is an older, article about reconstructing what people saw in movies from their brain activity. However this used fMRI, so would not really be applicable to real life situations. The results however, ",
"were very interesting",
" and another sign that the principle is already being used, we just need to work it out. "
] |
[
"I'd say we don't know enough of the brain to be able to do that, but we ",
" know enough about technology to be able to do that. ",
"If you gather enough data, for example by using electrodes, you can use machine learning to decipher this data, without relying on the actual knowledge of how the brain is processing this information.",
"\nFor example, ",
"this study",
" used machine learning to be able to tell what someone was seeing, and when that person was seeing that thing. Granted, there was a 2-fold choice, either houses or faces, but the principle can be applied to more difficult distinctions. ",
"In fact, those principles are sometimes already aplied in real life. ",
"Brain Computer Interfaces, BCIs",
" - great review - are computers that read signals from the brain in order the help people act out things they might not physically be able to do. ",
"Finally, ",
"this",
" is an older, article about reconstructing what people saw in movies from their brain activity. However this used fMRI, so would not really be applicable to real life situations. The results however, ",
"were very interesting",
" and another sign that the principle is already being used, we just need to work it out. "
] |
[
"No. I'll give an example from a much simpler animal, the fruit fly. Fruit flies have 51 compartments to their sense of smell, called olfactory glomeruli. Every fly has the same 51 glomeruli, and if you could measure the activity of these brain areas, you would know what they fly is smelling. So far so good.",
"Then the information from the glomeruli are sent to a bigger group of approximately 2000 cells, called Kenyon cells. The Kenyon cells are where memories are stored in flies, so that's where you'd want to look to do what you're asking about. And here's the thing: the connections from the smell areas to the Kenyon cells are 100% completely random. The Kenyon cells essentially turn each smell into a random, hopefully unique, barcode. So even if you could measure the activity of all of the Kenyon cells simultaneously, you would still have no idea what the fly was smelling. Only by watching a fly sniff every odor of interest could you make a map of what the Kenyon cells mean, and the map is different for every fly.",
"So, to sum up: we know exactly how the fly smell system is wired, but we still can't figure out what smell memories the fly has in principle, never mind in practice. And the human brain is literally one million times more complex than a fly brain (10",
" vs. 10",
" neurons), and we don't know nearly as much about it. So, while with great effort we might be able to tell if a person has seen the same thing twice, but we will never be able to read memories directly out of the neurons/synapses."
] |
[
"If you dropped batteries into a glass of water, and put a balloon on top.. would the balloon fill with Oxygen? If not, what would happen?"
] |
[
false
] | null |
[
"Water certainly does split, I'm not sure where you're getting your information or maybe I don't understand?\n",
"Water splitting",
"In 18 megaohm water you certainly wouldn't see much, but tap water has plenty of ions to keep the resistance low."
] |
[
"Water certainly does split, I'm not sure where you're getting your information or maybe I don't understand?\n",
"Water splitting",
"In 18 megaohm water you certainly wouldn't see much, but tap water has plenty of ions to keep the resistance low."
] |
[
"You can't just mix hydrogen and oxygen together and make water. It takes additional energy to force the electrons to bond. "
] |
[
"If 100% of the population smoked cigarettes on a daily basis, would evolution cause us to become 'immune' to the carcinogens?"
] |
[
false
] | null |
[
"I would have to say no. Most of cigarettes lethal affects occur after multiple decades of their use. The cancer caused from smoking occurs after our reproductive years so any benefit one would gain from a mutation that resisted the carcinogens would not alter their reproductive success.\nEvolution only occurs when a genetic mutation increases ones ability to have viable offspring. As potential cancer obtained from smoking has no effect on this outcome it give no selective pressure, and therefore no evolution would occur."
] |
[
"Evolution only occurs when a genetic mutation increases ones ability to have viable offspring.",
"True, but I'd caution that 'viable' doesn't just mean healthy at birth, it also means that the offspring themselves grow up and reproduce. Humans invest a huge amount in rearing both their children and grandchildren, and societal factors punish those with sick relatives. Having to take care of sick parents instead of studying/socializing, having no financial support from parents because they're paying medical bills, having no living grandparents to help raise/support you, could all make someone less likely to succeed in finding a good mate and therefore make them less 'viable' offspring.",
"I'm not necessarily saying that this would be a strong enough selective pressure to make us immune to cancer, but it shouldn't be dismissed without careful consideration."
] |
[
"This sort of thing actually happens. Maybe not with a payload as comprehensive as that of a cigarette. My example is a type of lemur in Madagascar. It eats the root of a bamboo that grows there that actually contains cyanide. This particular species of lemur evolved an ability to metabolize cyanide and this bamboo is part of its diet.",
"My point is that animals are known to evolve ways of coping with common poisons, but I think the example you gave would be too acute and the exposure would be to too broad a range of carcinogens to evolve an adaptation."
] |
[
"What is the difference between a single-cell organism and a cell in our body?"
] |
[
false
] |
I know there is a large variety of types of cells, but.. Can you say that our bodies are just a large colony of single-cell organisms working together?
|
[
"Can you say that our bodies are just a large colony of single-cell organisms working together?",
", yes. But that's a bit oversimplified. There are plenty of single-celled organisms that work together and divide labor in a similar fashion, but at the gene expression level it works quite differently.",
"The cells in our body all share the same genetic code (aside from some notable exceptions: haploid cells like sperm and egg cells which are jumbled up half-versions of the same genetic code, and the T and B cells of the immune system, which actually deliberately recombine and/or mutate small portions of their genes.). But each tissue has a specific function, so a lot of the genome is \"turned off\" in any given cell - the only things that remain \"turned on\" are the genes necessary to keep it alive and perform one of thousands of roles. The mechanics are very complicated, but suffice it to say that it's not as simple as the way single-celled organisms divide labor. Those organisms perform different functions based on the molecular signals they receive, but they retain the ability to perform any and all functions as soon as a different signal comes along. Human body cells, once differentiated, ",
" go back.",
"So it's more like a city full of people with specific college degrees doing jobs they're trained for and so they can't switch between jobs, whereas a \"colony of single celled organisms\" is more like... I don't know, a stage production in which the actors were able to trade roles whenever they felt like it."
] |
[
"Single celled organisms, such as yeast or most bacteria, are capable of surviving and multiplying independently. Each cell can sufficiently gather all the nutrients it need to survive and can divide indefinitely.",
"We are multicellular. Although we are made of many individual cells, a cells from our liver would not be able to survive in the outside world. Granted, we can grow some types of human cells in a lab, however they will eventually stop dividing ",
"Some organisms live in what are considered colonies. They can exists on their own however they survive better as a colony. Some bacteria and simple eukaryotes display this."
] |
[
"Each single-cell organism has to carry out all of its own life processes in order for that cell to survive. They sometimes live together in colonies, but if their friends (clones of themselves) die, they can carry on without them.",
"In contrast, even the simplest multi-cellular organisms have specialized, differentiated cells that depend on each other in order to survive within their organism. Their friends are not clones; they know certain \"skills\" that the cell would be helpless without.",
"Easy rule of thumb: single-cell organisms are ",
". Cells in our body are ",
"."
] |
[
"I just learned about foreign accent syndrome, when brain damage makes it sound like you have a foreign accent. Do those who suffer from it actually speak with an accent from one they know or is it just the new speech patterns that come with the syndrome making it sound similar to an existing accent?"
] |
[
false
] | null |
[
"I'll answer this with the caveat that this is a very rare condition ",
"(<20 cases worldwide to date)",
" and with an etiology that is not perfectly understood. ",
"The basic idea is that after a stroke regions of the brain are damaged that result in a changed prosody. Most of the time, the change in speech pattern becomes close to but does not perfectly correspond with another accent (not necessarily one known to the patient). The current thinking is that observers hear this atypical speech and attribute it to an accent that they are familiar with, even if there are inconsistencies."
] |
[
"I think the syndrome is far more common than is reported. I've seen 3 cases in 5 years of working with brain injured patients. The patients I've seen are actually using a foreign accent, and when cued to speak with their American accent, being Americans, they will do so for brief periods before they forget and lapse into the foreign accent. I haven't seen any satisfactory explanation for the phenomenon to date."
] |
[
"No, it's a change in the way they produce speech which just seems to sound (to some speakers) like another specific accent. The man who gained an Irish accent after a stroke would not have sounded Irish to an Irish person. "
] |
[
"Can someone explain the science behind this video of a water bottle instantly freezing?"
] |
[
false
] | null |
[
"It's called supercooling."
] |
[
"To crystalize into ice water needs a nucleation point. Once you have some ice in there it's easy to make more crystals, but it's hard to form that first crystal due to the entropy loss. Ice is a lot more ordered than water.",
"If you hit the water hard, say by pouring it, you provide a nucleation site for crystal growth.",
"http://www.youtube.com/watch?v=cYj_vqcyI78",
"You can see something similar here. They provide a crystal to start the process up and it grows a lot faster."
] |
[
"I agree, that the water is supercooled, and in beer for example it's the drop in pressure when opening the bottle.",
"I know of pure water not freezing and then when the bottle is slammed on a table, it freezes. As fas as I know this is because of a pressuredrop in the top when the water rushes down in the slam.",
"But I don't see anything there that initiates the crystallisation."
] |
[
"Can moving water wear down a diamond?"
] |
[
false
] | null |
[
"I think you are talking about a situation where a natural diamond is on the surface of a riverbed. I don't have any answers for you there, but a study in 1993 investigated rain-like erosion properties of diamond. Here is a link to the publication: ",
"http://www.smf.phy.cam.ac.uk/Publications/Strength%20papers/390StrSewardDRM2.pdf"
] |
[
"Rocks in the water would have to be extremely sharp and moving very fast.",
"They don't need to be particularly sharp nor fast.",
"Breaking a diamond into smaller diamonds is relatively easy depending on the angle of impact. Despite their hardness, diamonds have cleavage and are brittle. Every heard of somebody chipping their diamond ring? Or of diamonds getting scuffed up in daily wear? It's pretty easy to do. Hardness ≠ toughness. And diamonds are not really impressive on the toughness scale.",
"http://findmyrock.com/2012/09/24/difference-between-diamond-hardness-vs-toughness/",
"http://en.wikipedia.org/wiki/Material_properties_of_diamond#Toughness"
] |
[
"Rocks in the water would have to be extremely sharp and moving very fast.",
"They don't need to be particularly sharp nor fast.",
"Breaking a diamond into smaller diamonds is relatively easy depending on the angle of impact. Despite their hardness, diamonds have cleavage and are brittle. Every heard of somebody chipping their diamond ring? Or of diamonds getting scuffed up in daily wear? It's pretty easy to do. Hardness ≠ toughness. And diamonds are not really impressive on the toughness scale.",
"http://findmyrock.com/2012/09/24/difference-between-diamond-hardness-vs-toughness/",
"http://en.wikipedia.org/wiki/Material_properties_of_diamond#Toughness"
] |
[
"Is it possible to keep a cell phone charged longer by using stray electromagnetic energy and a broadband antenna?"
] |
[
false
] | null |
[
"Yes, there has been some research: ",
"http://www.eetimes.com/electronics-news/4195530/Nokia-working-on-energy-harvesting-handset",
"However, you can't harvest too much energy that way (unless if you are near a big radio transmitter or something).\nSome megawatt radio transmitter can even light up lightbulbs. There was a village near such radio station, and people were complaining about all kind of strange things (can't find the link now)."
] |
[
"This is an anecdote, but your answer is correct so I hope I'm not against ettiquete:",
"A family friend of mine used to work with radios, and there's a picture of him standing in front of a transmitter with a florescent tube, which is lit way the fuck up. Radio waves are energy in the air, and that can be transfered. Solar power is just enery being made from visible 'radio' waves. However, you'd have trouble getting enough energy to do much with them unless you're really close to a high power transmitter, and especially if you are limited to a certain frequency range. I don't know if its possible to capture a very wide range of frequencies easily or not...but that would certainly net you more energy."
] |
[
"In theory, yes. But in 99.9% of cases the tiny amount of energy you harvested wouldn't make any kind of noticeable difference. Check ",
"this",
" out for an idea of what kind of energies we're talking about here. "
] |
[
"Is it true that women with - RH factor miscarry + RH babies and why or why not."
] |
[
false
] |
[deleted]
|
[
"Not quite the same question, but I answered a ",
"similar question in a thread recently",
", along with ",
"another similar one before that",
".",
"Take a look through those two threads"
] |
[
"I thought the shot was a vaccine against RH+ antibodies ... Usually, the first baby will be fine, but if this occurs again, the mother will have RH+ antibodies which will destroy the baby's blood cells if I remember correctly. If the shot isn't used, the baby might need to be completely emptied of its blood after birth and reinjected with donor blood. Well that's from my college courses."
] |
[
"I thought the shot was a vaccine against RH+ antibodies ... Usually, the first baby will be fine, but if this occurs again, the mother will have RH+ antibodies which will destroy the baby's blood cells if I remember correctly. If the shot isn't used, the baby might need to be completely emptied of its blood after birth and reinjected with donor blood. Well that's from my college courses."
] |
[
"If the Earth was condensed to the size of a peanut, and it turned into a black hole, would the black hole be stable?"
] |
[
false
] | null |
[
"Yes. The Hawking temperature would be some 2 hundredths of a Kelvin, while the CMB is hotter at 2.7 K. The black hole gets more power in that it radiates out."
] |
[
"You need to go a tad smaller. Try it yourself, set the Hawking temperature equal to the CMB temperature and find the mass of the black hole."
] |
[
"Wow!",
"I thought tiny black holes \"evaporated\" really fast via Hawking Radiation. I assumed one this size was well within the going ",
" range in short order. Guess I am off by a few magnitudes of size.",
"Learned something new today. Thanks!"
] |
[
"How did spacecrafts in 1960s transmitted photos of space and the moon when digital photography had not been invented yet?"
] |
[
false
] |
What I am missing here?
|
[
"They used analogue photography, e.g. TV cameras."
] |
[
"Whoa, whoa. Define \"digital photography\" because my parents were watching fast moving photography in the 1960s in their living room. We tend to call it television. The technology that powered television powered these cameras. Yes, it was an analog process, but it was 100% electric and sending analog signals is the same technology as digital signals. Its just analog is prone to noise, lacks error correction, and because of the lack of proper compression - uses more bandwidth.",
"It looks like you think digital photography is the only way to send electronic visuals. This is not correct. Analog methods were used."
] |
[
"Your claim that they used film is grossly incorrect, for many cameras in use in the late 1960s, there was no film involved. For example:",
"https://en.wikipedia.org/wiki/Apollo_TV_camera",
"http://www.myspacemuseum.com/apollocams.htm#A11%20B&W",
"There was also no film involved in the Venera cameras which were developed in the late 1960s and (for the successful missions) sent to Venus in 1970-1975.",
"https://en.wikipedia.org/wiki/Venera",
"http://www.mentallandscape.com/C_CatalogVenus.htm",
"The Venus link above also has information on the Soviet cameras on their Mars orbiter, which used a solid state imager (like a primitive analog CCD) and recorded to ",
", not film."
] |
[
"When a dog sniffs around for a place to poo, what is his criteria?"
] |
[
false
] | null |
[
"It depends on the dog's social status and current mental state. In general, higher-status dogs will use their feces to cut other dogs off from certain areas. Lower-status dogs will try to keep their feces out of the way in order to avoid upsetting a higher-status dog (or in the case of domestic dogs, a human). But a dog that is particularly upset might use its feces more aggressively, putting it somewhere it knows will cause upset."
] |
[
"Essentially, it treats humans like other dogs and then figures out its status based on how those humans treat it. Generally, they will consider themselves lower in the pecking order, but if they are spoiled they may think they are in charge."
] |
[
"Essentially, it treats humans like other dogs and then figures out its status based on how those humans treat it. Generally, they will consider themselves lower in the pecking order, but if they are spoiled they may think they are in charge."
] |
[
"Were mental illnesses suchs as depression as common 100 years ago? If not what's the main cause that they are more common today?"
] |
[
false
] | null |
[
"We can't answer that question, because the modern definitions and characterizations of mental illnesses are ",
" recent--like, the 1980s (when the DSM-III came out). There aren't reliable, large-scale epidemiology studies before that era--at the very earliest, the data goes back to the mid-century.",
"When we take something like depression, writers back even in ancient Greece noted that sometimes people seem to be extremely sad/down for extended periods of time, well out of proportion to \"normal\" responses. Of course, they thought it was because they had too much black bile in the body and/or they were possessed by demons. One hundred years ago, Freud was publishing his first books on \"melancholia.\" "
] |
[
"Some mental illnesses are caused by environmental factors (lead comes to mind). Others could go undiagnosed or ignored. When you are struggling every day to not die, most people were living short miserable lives. Others still would get you locked in an insane asylum or killed for devil possession. "
] |
[
"Is there any source at all for this claim?"
] |
[
"What is oscillating in an electromagnetic wave?"
] |
[
false
] |
What I'm trying to ask is that if waves formed in the ocean are oscillations/vibrations of the water particles and sound is the oscillation/vibration of air particles. What is actually oscillating to form an electromagnetic wave. I think I'm phrasing the question wrong or I've just misunderstood the concept of electromagnetic waves.
|
[
"You are basically asking \"through what medium do photons propagate?\" Waves in the ocean propagate through water, sound waves propagate through air (or anything else really). But it turns out photons don't need a medium to propagate. The confusion stems from the fact that EM waves seem to have all the properties of other waves that we understand more intuitively.",
"Your question confounded physicists for many years. Much effort was spent trying to determine what the medium was - they called it the \"luminiferous ether.\" The ",
"Michelson-Morely experiment",
" was the first conclusive proof that there was no ether.",
"What is interesting is that the properties of light that fall out of Maxwell's equations. If you insert the proper conditions, you can arrive at a solution whereby an oscillating electric field gives rise to an oscillating magnetic field. This magnetic field then gives rise again to the electric field, and these oscillating fields travel through space. ",
"This figure from wikipedia",
" demonstrates this.",
"So, to answer your question, since magnetic and electric fields do not need a medium, photons do not require a medium to propagate."
] |
[
"The electric and magnetic field vectors are oscillating."
] |
[
"An electromagnetic wave is not a stream of particles, it can be considered a stream of photons but I don't think you need to involve wave particle duality to understand the idea behind an em wave. ",
"If we are talking about a wave we are talking about something which oscillates in space/time. In a water wave we have the height of the water about a mean. In a sound wave we have variations in pressure/density about a mean. In an electromagnetic wave we have variations in the electric and magnetic fields. ",
"Just like in a water wave we can measure these variations. Put a charged particle in the path of the wave and it will experience a force that oscillates it up and down. This is in fact what happens in an antenna, the radio wave oscillates the electrons in the aerial up and down which we detect as an oscillating current/voltage."
] |
[
"How do avalanche beacons work, and why do they follow flux lines?"
] |
[
false
] |
I feel that I understand the basics of radio beacons, but I don't understand how avalanche transceivers figure out direction. If you had 3 antennas I assume you could do some rough triangulation to get the direction, but avalanche beacons don't give the exact direction, they "compute distance and direction" from "the emitted dipole flux pattern" (per Wikipedia). Where does come from, and how is it used? I thought that radio beacons transmit uniformly in all directions, giving a spherically symmetric electromagnetic field. And why aren't several antennas used to directly get the direction through triangulation?
|
[
"I thought that radio beacons transmit uniformly in all directions",
"This is not correct. The pattern in your diagram is that of a simple dipole antenna, what you get from electric current oscillating back and forth along a straight wire. See ",
"this",
" for an explanation. ",
"This",
" is a better image."
] |
[
"Could you explain what causes the dipole pattern and how the pattern can be used to find the direction to the transmitter?"
] |
[
"Consider what tao observers see when a charged particle accelerates (linear motion).",
"An observer along the motion hardy sees anything happen.",
"An observer perpendicular to the motion sees a change of the direction of the electric field. This change, perpendicular to the line of sight, is the radiation field.",
"So, the strength of the radiation is proportional to sin",
"theta, where theta is measured away from the direction of the charge's acceleration."
] |
[
"Screw Thorium, why are we not using Toroidal Fusion reactors now?"
] |
[
false
] | null |
[
"Quite simply: they don't work yet.",
"I am a fusion physicist; I work at the JET site, though on a different tokamak (",
"MAST",
").",
"To get deuterium and tritium (the most likely fuels for a commercial plant) to fuse, the plasma has to be at a temperature of about 100 million K. In order to have a self-sustaining fusion reaction, we want the plasma to stay this hot - that is, we want to be heating it faster than it can cool down. And if we're going to be using it to produce power, we want it to be heating itself. This, we can do. We can get plasmas hot enough that they undergo fusion. The big difficulty is how quickly they want to cool down.",
"So, how quickly do plasmas cool down? It's not too hard to calculate this, if you assume that the only way heat is going to get out is by diffusion. People did this in the 60s, and worked out that you could get a self-sustaining fusion reaction in a device about 30cm across. Brilliant! We'll definitely have fusion in the next 30 years!",
"Except, when they built these devices, the heat got out much quicker. This is because the plasmas in their devices were turbulent and turbulence can move heat much quicker than diffusion. Think about a cup of tea, when you add a drop of milk and let it sit there, it takes a long time for the milk to spread out throughout the cup. What happens when you stir it? The milk very quickly disperses throughout the tea. The same thing happens in tokamaks. Except, instead of a spoon stirring the plasma, we are ",
" strongly heating it, mixing it up, making it turbulent.",
"Turbulence is one of the greatest unsolved problems of modern physics. If you solve it, there's a couple of nobel prizes and clay medals in it for you.",
"Of course, there's a whole bunch of other reasons they don't yet work, but we're currently building ",
"ITER",
" in the south of France which should solve (or help solve) some of our problems. "
] |
[
"Two Main reasons:\nPhysics and Engineering.",
"Firstly, engineering: These things are super hard to build. We need very carefully made reactors to confine something as hot as 100000000K. We still aren't sure if we can do all the things we need to be able to do to run a working power plant. Things like remotely replacing the irradiated inside of the reactor vessel, having material that won't be destroyed by the very energetic neutrons coming out of the reaction or breeding the tritium needed to fuel the plant.",
"Physics: We still have no real coherent theory that explains what is going on inside a fusion plasma. We don't really understand the way particles are transported inside the reaction, how and why certain disruptive instabilities are formed and controlled and how various forms of MHD turbulence mess things up."
] |
[
"We need more vespene gas",
"In all seriousness though the fusion problem has gone from always being 30 years away to being 10 years away. ",
"I've been to a few talks on tokamack fusion concepts. The problem seems to be sustaining the reaction while extracting energy. ",
"All of them are good ideas and in fact the first ones were invented by our good friend prof. P.T. Farnsworth. ",
"They all suffer from implementation problems stemming from the fusion cross-section of the constituent atoms. "
] |
[
"How do cassette adapters transfer the sound output from my phone to a magnetic encoding readable by the play-head?"
] |
[
false
] |
[deleted]
|
[
"The trick is that there's no real conversion needed. ",
"You record on a tape by changing a magnetic field near the tape. You play a tape by running it past a magnet to detect the changes. ",
"You get sound from a speaker (or headphones) by changing a magnetic field in the speaker coil. You pick up sound from the air by letting the air pressure move a diaphragm to make a changing magnetic field in the speaker coil.",
"In all of these cases, the sound is \"encoded\" the same-- it's a simple analog waveform. When you listen to music on headphones, the electrical signal wiggles the magnetic field in the headphones, which moves the speaker cone to make sound. If you just take your headphone output and connect it to a small magnet, then place that next to the tape player's head-- it just works, because all you're doing is wiggling the magnetic field in time with the music. When you play a normal tape, the moving tape does the same thing-- it's magnetized, and as it slides by, it wiggles the magnetic field in time with the music. No conversion needed.",
"TL;DR: A tape wiggles a magnetic field in time with music as it moves by. A headphone output wiggles a magnetic field to move the speaker cone. A tape adapter is a speaker without a cone, so it just wiggles a magnetic field in time with the music... like a moving tape."
] |
[
"The tape had iron oxide particles which can be magnetized as they pass through a magnetic field, in the same way that you can magnetized a sewing Needle by rubbing it against a magnet. As the current through the head changes in response to the audio signal, some of the oxide particles will be oriented one way, some another. When you play the tape back, as the oxide particles pass by the head, they induce a carrying current in a coil of wire. The cassette adapter kind of cuts out the middleman of the tape. Perhaps a better way of thinking about is to think of the combination of the adapter and the head in the tape player as just a transformer. A carrying current in the adapter creates a carrying magnetic field which induces a current in the head of the tape player."
] |
[
"The cassette adapter doesn't have an actual ribbon, it's a spinning head that doesn't store data like the ribbon does. Electrical signal from your device gets runs to the \"write\" head of the cassette adapter. That means the magnetic field output by the write head changes with the signal, and the read head in your cassette player reads that in real time just like it would for a ribbon passing."
] |
[
"Why do wet dogs smell so bad?"
] |
[
false
] |
It seems odd to me that there is a unique smell that virtually all dogs have when wet that is completely absent when they are dry. What's the scientific account?
|
[
"First of all, what actually makes something smell?",
"\nMolecules have to leave the smelly objects and get to your nose through the air and that means that these molecules must be very small and volatile. That's to say they must be easily evaporated. The chemicals that make dogs smell are mostly what we call volatile organic acids and they are produced by bacteria from the fats that are breaking down from sweat; and that's maybe why we find these body odours unpleasant. They signal a presence of bacteria and decay and death to us.",
"\nTheir [dogs] skins mostly have Staphylococcal bacteria, which don't produce much in the way of a smell at all, but they've also got some yeasts too which are really pongy.",
"\nBut why does the smell seem worse when the dog is wet? Here, I think we have to go into some physics. The amount of evaporation of a substance is related to the concentration of the compound on a surface it’s evaporating from and the amount of compound that's in the air, just above the surface. \nSo how might that change when it’s wet? Well, if the organic acids are dissolved in water on the fur of the wet dog, as the water evaporates, the concentration of those smelly acids increases, so they'll evaporate more, so there are more molecules in the air for us to smell. ",
"A bit of evaporation can effectively amplify the amount of volatile chemicals that emanate from a dog’s skin, and Dr. Williams thinks it’s the same effect that causes that damp earth smell when it rains. It may also alter how dogs interact with each other when they're wet. So, if you have a dog, watch to see if it sniffs differently at other dogs on a dry day versus a wet one...",
"Source: ",
"http://www.thenakedscientists.com/forum/index.php?topic=40705.0",
"Sorry if I quoted wrong, never done it before"
] |
[
"I thought dogs didn't sweat. Have I been living a lie all this time?"
] |
[
"Is that saying that the concentration difference between the substance on the skin and the substance in the air is greater when the substance on the dog is dissolved in water than when it is not? Wouldn't dissolving it in water decrease the concentration? How could the difference be any greater than when the substance on the surface is not dissolved in anything? If the concentration difference is the only reason for the extra smell, I don't understand. Please ELI5."
] |
[
"What domestic or wild animal provides the most efficient kilogram to kilogram, gram to gram, conversion from eating grains/plant based material to meat, or do all herbivores have equal ratios?"
] |
[
false
] | null |
[
"This is measured as the ",
"feed conversion ratio, or FCR",
", which is calculated as kilograms of feed per kilograms of body weight (or sometimes carcass weight, dressed weight, etc). Exact FCR will depend on what the feed source is - a cow eating corn has a lower FCR than a pasture fed counterpart since the corn is more energy dense. Generally speaking, fish have low FCRs - the wiki link cites 1.4-1.6 for tilapia - followed by chickens around 2-2.1, pigs are in the 3-4 range and cattle average around 9. The substitution of chicken or fish for beef therefore has a big impact on your overall FCR as a human. This time of year it's also relevant to point out that ",
"FCR changes with age",
" - it's quite low in young and adult animals and peaks in juveniles - so eating immature animals (like lamb) is less efficient than eating young adults."
] |
[
"How do we factor in farming practices and conditions? For example, a cow fed corn grown commercially in Indiana almost certainly has a higher net impact than a cow grazed on marginal land in Montana that would otherwise be agriculturally unproductive."
] |
[
"This can get really complicated depending on how detailed you want your analysis to be:",
"All things equal, the corn fed animal will produce more meat faster, hence the prevalence in modern food chains, but corn fed production is not sustainable in the long term, especially as global per capita meat consumption is rising.",
"This analysis",
" is rather biased in perspective, but it is fairly thorough, and ",
"they do describe their methodology for setting values to each factor",
"."
] |
[
"What impact, if any, would the growing of hemp have on the medical community?"
] |
[
false
] |
Hypothetical world: Hemp is legalized and being grown across the States. Hemp growers will grow both male and female plants because they need the stalks and leaves, not the bud. Assuming fertilization of the plants happens within the fields regularly: Would this then lead to some sort of evolution to the plant?
|
[
"I'm not sure what your question is. Evolutionarily growers have been selecting for generations for better quality and more potent plants. In terms of impact on the medical field, there would be less chronic pain management nonsense to deal with and an easier time managing nauseated cancer patients. "
] |
[
"As you said, the current selection goes more for quality of the plant, or THC levels. But hemp growers would most likely just be going for things like height and density of the plant assuming they want to grow more plants in the area they have."
] |
[
"Sure, maybe if they're just trying to maximize yield per acre. But customers are often driven more by considerations of shall we say refined quality and delicate flavors. I think we'd see more of the vineyard model, with a recognizable high end producing intentionally limited quantities of expensive bottlings for connoisseurs willing to pay extra for a luxury product; as well as a low end for the mass middle class market and an even lower end for hobos. "
] |
[
"What causes the relativistic contraction of the innermost electron orbitals of heavier elements, given that electrons don't actually \"orbit\" the nucleus with a given velocity?"
] |
[
false
] |
I've been trying to grasp what's going on with the so-called that cause the contraction of the electron orbitals of heavier elements, and a lot of what I have found online talks about the greater nuclear charge of said elements causes the innermost electrons to travel at relativistic velocities, which in turn causes their mass to increase and orbital to decrease. This seems to fit the Rutherford-Bohr model for electronic orbitals, though it was my understanding that this model has long been superseded. Instead, electrons exist as wavefunctions of probability around the nucleus. If they were to move around the nucleus they'd radiate energy and their orbits would rapidly collapse. nation? If my understanding is correct, then presumably the notion that contraction is caused by the electron approaching is flawed? Is there a more cogent explanation?
|
[
"An orbital represents a standing wave, so you are right that it does not change with time. However, the electron still has angular momentum and kinetic energy in an orbital. This might seem contradictory, but we only need the values for these quantities to be constant with time, they don't need to be zero. The average velocity must be zero of course, since the electron remains in place, but that isn't the same as saying the average speed of the electron must be zero.",
"You can ",
" think of an electron in an orbital as obeying the virial theorem, where if the total energy is -E, the potential energy is -2E and the kinetic energy is +E. Therefore, the lower the total energy of the electron gets the more kinetic energy it has. This is also true of the orbit of planets - close orbits have more kinetic energy even though they have less total energy than a similar mass planet in a larger orbit.",
"Rather than asking if the speed is close to c, we can focus on the kinetic energy and the rest mass. If the kinetic energy becomes large compared to the rest mass of the particle, then relativistic effects become important in your calculations. For a hydrogen atom, the ground state is -13.6 eV, giving a kinetic energy of +13.6 eV, which is very small compared to the mass of the electron (0.51 MeV/c",
"). But this energy scales with Z",
", so for a massive element with Z=100 (Fermium) that has a single electron, you get a kinetic energy of 13.6*10,000 = 0.136 MeV. That is now a pretty large fraction of the rest mass of the electron. Therefore our back of the envelope calculation suggests that relativistic corrections are going to be important for the lowest orbitals of heavy elements."
] |
[
"You can roughly think of an electron in an orbital as obeying the virial theorem",
"In terms of expectation values, it ",
" obey the virial theorem."
] |
[
"If my understanding is correct, then presumably the notion that contraction is caused by the electron approaching c is flawed? Is there a more cogent explanation?",
"It's basically correct. You're right that the picture of electrons zipping about in nice well-defined orbits around the nucleus is incorrect, but that doesn't mean that the electrons are stationary. Many people often conflate the constant electron probability distribution with the electrons being at rest. Just like we can write down the wave function and find the probability distribution telling us ",
" the electron is most likely to be, we can also find the probability distribution that tells us how much momentum it is likely to have.",
"Given that this is a probability distribution, it's not immediately obvious how to apply relativity, but ",
"relativistic quantum mechanics",
" combines the two and allows us to determine precisely what happens. The gist of it is that the wave function itself gets contracted by an amount dependent on the expectation value of momentum."
] |
[
"What does it mean for a photon to have \"more energy\"?"
] |
[
false
] |
Gamma ray photons are more energetic than visible light photons which are more energetic than microwave photons. What does "more energetic" actually mean? More what? They all travel at the same speed, and are massless, so there's no additional kinetic energy. I don't think frequency has much meaning when you're referring to an individual photon (or does it?). A gamma ray photon has more than a microwave photon?
|
[
"Frequency ",
" have a meaning in this case. Higher energy, higher frequency. A blue photon has more energy than a red photon.",
"Another way to think about it is what happens to a system that absorbs a given photon. If it absorbs a higher energy photon, it will see a greater increase in its energy."
] |
[
"Another example: if a photon hits an atom and knocks out an electron, that electron will be moving faster if the photon has higher energy."
] |
[
"It is kinetic energy. Without going into too much detail, since i'm late for class, when you get into really small massless particles, they in fact do have kinetic energy, though it is not related to the mass. This is part of quantum physics. The kinetic energy is related to the frequency, which fr gamma ray is much higher than for visible light. Therefore, they have more kinetic energy. "
] |
[
"What made scientists decide to start smashing particles together at high speeds?"
] |
[
false
] |
Most people (of this sub, at least) know of the LHC and that high-speed collisions of particles can produce particular kinds of particles, but how did it start? What did scientists expect to find by smashing particles together at extremely high speeds, and why did they expect that? Moreover, why did the first scientists believe it would help answer fundamental questions about physics and the universe? Thanks!
|
[
"In 1905 Einstein proposed the concept of photons, particles of light with energy proportional to their frequency (E = h f , where h is Planck's constant). Light waves with a higher frequency will have a shorter wavelength (the more cycles which pass by per second, the smaller that each cycle is in length). For example, X-rays have a higher energy then visible light, which means X-rays have a shorter wavelength. ",
"Waves with a shorter wavelength allow us to probe smaller objects precisely. This is why, in daily life, light is much better for determining precise positions of objects than sound is; the larger wavelengths of sound cause it to diffract around corners and interfere with itself, while (on human scales) light essentially moves in straight lines and gives us more precise information about what we're looking at. ",
"So with photons, we have that energy is inversely proportional to the distance scales that we can probe. It took another 20 years after Einstein for people like Shrodinger and deBroglie to propose that matter had wavelike properties, and just as with light the particles with more kinetic energy have shorter wavelengths. ",
"Over the decades, this inverse relationship between energy and distance scales proved to be a very deep fact of nature. It appears throughout quantum physics, and in relativistic physics objects with a large kinetic energy (relative to an observer) will appear to undergo length contraction (relative to an observer). So ultimately the answer to your question is that building particle accelerators with access to higher energy scales allows us to probe the universe at smaller distances, which is how we pursue the ancient idea of the Greek atomists to reduce nature to it's smallest components."
] |
[
"I'm not sure what kind of electromagnetic frequencies we can get up to nowadays, but a simple reason is that you can accelerate protons (or electrons) over and over again. So you can keep adding energy to them. There are limitations to this if you're using a circular accelerator, but for a linear accelerator you can in principle keep adding energy indefinitely. ",
"With a photon (particles of the electromagnetic field) once you create it then it's really hard to increase it's energy. So instead of increasing its energy incrementally up to some really high value you have to go all the way up to that high energy all in one shot."
] |
[
"I'm not sure what kind of electromagnetic frequencies we can get up to nowadays, but a simple reason is that you can accelerate protons (or electrons) over and over again. So you can keep adding energy to them. There are limitations to this if you're using a circular accelerator, but for a linear accelerator you can in principle keep adding energy indefinitely. ",
"With a photon (particles of the electromagnetic field) once you create it then it's really hard to increase it's energy. So instead of increasing its energy incrementally up to some really high value you have to go all the way up to that high energy all in one shot."
] |
[
"Do fish hold their 'breath' when pulled out of water, in the same way we hold ours when we go under?"
] |
[
false
] |
Do fish right before they're removed or voluntarily remove themselves from water have a big intake of oxygen (in the same way a human takes a breath before submersion) to sustain themselves while out of their natural environment? If yes: comparing to humans (and other species) storing air in their lungs, how do fish do it?
|
[
"Fish can still extract oxygen through gills if water can still run over them. Technically you can run water through a hose over their gills perpetually and they'll still live. This is how fish surgery tends to be done.",
"The key is making sure water is moving across the gills to work their counter-current exchange mechanism. Out of the water, they can't pull or push water on their gills.",
"So, they are still breathing when you pull them out because wet gills still allow for some exchange to occur, but it's so inefficient at that point that gas exchange becomes quite restricted, causing oxygen deprivation to occur. ",
"Gill filaments also collapse out of the water because they are not buoyant in air, and there's no structural support for the filaments. Rub your finger through gills and you'll notice they are feathery; each individual strand of gill is a filament that is supposed to be supported by water, which is not when out of the water. Thus when water is not flowing through them the gill filaments fall down, and the collapse further decreases the surface area where gas exchange can occur. This is why we recommend people NOT pull fish out of the water unless you have to take a hook out or you're moving them from system to system. Gills take a little bit to unstick even if you throw them back right into the water, and in that time they are stressed because they are taking in less oxygen. "
] |
[
"Yeah sure!",
"Here you go, a fish surgery at the Vancouver Aquarium!",
" Notice the water is pouring over the gills, not into the stomach. This is so the fish can still gas exchange while under anesthetic.",
"So, there's myriad reasons for fish surgery. It seems funny that we'd be doing surgery on a fish rather than eating it. But, there's definitely some necessity for fish surgery if the animals are in captivity and these happen to be 1) rare species, 2) species that are trying to breed, but mechanically something went wrong (the video has some egg-bound ovaries or something going on in the reproductive tract that needed immediate surgery), 3) species that are deemed important in some capacity, 4) doing surgery for things like parasite loads and other invasive, exploratory analyses.",
"Also, some surgery happens for tagging purposes. This is called ",
"intracoelomic implantation",
" and is usually reserved for long-term telemetry and biologging studies where we are concerned about the long term survivability of a tag.",
"I'm not a veterinarian, but fish surgery doesn't happen as often as this would be implied. However, there are a lot of uses for it."
] |
[
"The don't really hold their breath as they don't have lungs to hold it in. For the majority of fish they force oxygenated water across their gills, which have a capillary network that allows for the exchange of oxygen and carbon dioxide. Your lungs have basically this same network, we just suck ours into our lungs versus the air passing directly through, which allows us to hold a little extra in reserve until the oxygen within is depleted.",
"When fish come out of the water their CO2 builds up just like our's and oxygen decreases in the blood, eventually starving the brain. "
] |
[
"If you know how many people are in a store at a set starting time, and you know the rate at which people are entering and leaving the store, can you calculate the average amount of time that a customer spends in the store?"
] |
[
false
] |
Imagine that a store opens at 9am and closes at 6pm. If you know: (a) the number of customers in the store at noon; (b) the rate at which customers enter the store (e.g. customers/sec); (c) the rate at which customers leave the store (e.g. customers/sec); (d) that the store is empty at 6pm; Can you calculate the average amount of time that a customer spends in the store between noon and 6pm? Does it change things if your data goes all the way back to 9am, when the store opened and was empty? What if you are only given (b) and (c) above, can it still be calculated? This feels like an obvious and intuitive hypo that has been a topic of debate at my workplace. Can it be solved at all? If so, can it be done algebraically, or is more advanced math necessary (i.e. differential equations)?
|
[
"Knowing the rates that people enter and exit the store (whether constant or as functions of time) and the number of customers you start with (initial conditions), you could set up an ODE to describe the amount of people within the store at a given time. ",
"In the simplest case of constant rates, it would be formulaically identical to the \"in-filling/emptying water tank\" problems that most people look at in their first semester differential equations courses, and would have a nice algebraic solution.",
"But this, of course, doesn't address the question at hand.\nIn my mind, the amount of time which passes for each customer between entering and leaving the store is a random variable sampled from some form of exponential distribution. Whether this distribution can be usefully parameterized by only the information you described is something that I need to think about further."
] |
[
"The answer is ",
", without any other assumption on the model, and with closed formulas (no simulation is needed). You need the data (a)-(c).This comes from a inversion of summation.",
"I'll use some LaTeX formulas. To visualize them, you can copy and paste them into an online editor (for instance ",
"here",
"), after deleting the $$.",
"We are given: ",
"A number ",
" of people present at noon;",
"An starting time (for instance, noon), which I'll assume to be ",
";",
"An closing time, which I'll denote by ",
" (in your case, T=6h);",
"An input function ",
" which describes the rate of entrance of people (in people/unit of time);",
"An input function ",
" which describes the rate of exit of people (in people/unit of time).",
"I'll also use two functions:",
"the population ",
" is the number of people in the store at time $t$;",
"the total time ",
" spent by the person ",
" in the store.",
"Then, in the whole day, the number of people who pass through the shop is:",
"$ N + \\int_ 0^ T I(t) dt.$",
"The average time a customer spend is the total time spent by all the customers, divided by the number of customers, i.e.:",
"$ \\overline{D} = \\frac{1}{N + \\int_ 0^ T I(t) dt} \\sum_{\\text{people} \\ x} D(x).$",
"The total of man-hours the patrons spend in the shop in an afternoon is:",
"$ \\int_ 0^ T P(t) dt = \\sum_{\\text{people} \\ x} D(x).$",
"In addition, at all time $t$,",
"$ P(t) = N + \\int_ 0^ T I(t)-O(t) dt.$",
"Therefore,",
"$ \\overline{D} = \\frac{1}{N + \\int_ 0^ T I(t) dt} \\int_ 0^ T \\left( N + \\int_ 0^ t I(s)-O(s) ds \\right) dt. $",
"After some simplifications, it becomes:",
"$ \\overline{D} = \\frac{1}{N + \\int_ 0^ T I(t) dt} \\left( NT + \\int_ 0^ T (T-t)(I(t)-O(t)) dt \\right). $",
"If you have all the data starting back from the opening of the store, then you can take the initial time as 9am, the final time as 6pm (or 0 and T=9h). Since this is equivalent to taking $N = 0$, the formula becomes somewhat simpler, and you don't need to know the number of people at noon:",
"$ \\overline{D} = \\frac{\\int_ 0^ T (T-t)(I(t)-O(t)) dt}{\\int_ 0^ T I(t) dt}. $"
] |
[
"The way it's usually done is by simulation. You give a starting situation and just add the number of people entering/leaving each second.",
"Now, if you want something more advanced (let's say not a fixed rate of people arriving, some costumers spend longer time on the store, etc.), you do need more advanced math, including differential equations.",
"This is called Queueing Theory and it's still a quite active area of research.",
"Here is the wikipedia entry, not the most accesible thing ever but gives some overview on the problems involved in more advanced models.",
"edit: forgot to add the mentioned entry.. ",
"http://en.wikipedia.org/wiki/Queueing_theory"
] |
[
"When the last black hole in the universe evaporates and explodes, what happens to that radiated energy?"
] |
[
false
] |
A model of the future universe predicts that, after trillions upon trillions of years into the future, all the stars have exhausted, all matter has accumulated into black holes, and the black holes themselves evaporate. When the last black hole in the universe radiates away, there are no other structures in the universe to interact with those fluctuations. What happens to that last bit of energy? Does it simply diffuse through the impossibly vast, cold, empty universe? Does that mean that there will always be some amount of energy (and information?) that persists?
|
[
"Just like most other radiation and stable particles (only a very small fraction will fall into black holes) it will just fly through the universe forever. The expansion of the universe will separate all these particles from each other."
] |
[
"The expansion of the universe will separate all these particles from each other.",
"It'll also leech off photon and kinetic energy. If proton decay were a thing, the situation would get even 'worse' as with each decay, yet another share of the energy content of the universe would become subject to this cosmological redshift..."
] |
[
"Angular momentum is a good point."
] |
[
"How do new born babies survive starvation for several days under rubble?"
] |
[
false
] |
[deleted]
|
[
"I would like to point out that most babies do not survive such conditions - the cases pointed out here are exceptions."
] |
[
"The layers of fat provide nutrition. Its their life fat-ket"
] |
[
"you only notice something when it hits and not when it misses."
] |
[
"What happens if you eat or drink something without waiting 30 minutes after using fluoride mouthwash?"
] |
[
false
] | null |
[
"Try to imagine all life as you know it stopping instantaneously and every molecule in your body exploding at the speed of light. Total protonic reversal. ",
"No, seriously. It's just because we want to give a generous amount of time for the fluoride to absorb into the enamel of our teeth. Fluoride is safe; it's in our drinking water. ",
"http://www.ada.org/sections/scienceAndResearch/pdfs/patient_72.pdf",
"http://www.ada.org/fluoride.aspx"
] |
[
"it is naturally in our drinking water",
"before anyone comes in here and hits you with something stupid"
] |
[
"You ingest fluoride which passes the blood brain barrier with ease.",
"Does it matter though? Probably not, since one cup of water contains roughly the same amount of fluoride as a bit of toothpaste or the leftovers of mouthwash and we ingest that all the time everyday (unless you drink bottled or well water).",
"The worst thing that will happen is your food will taste odd I suppose."
] |
[
"Can sudden bursts of loud noise (specifically through headphones) cause significant hearing loss?"
] |
[
false
] |
I am a music producer and I work with studio headphones on. A new piece of equipment that I use has a sensitive volume control and a few times now I have accidentally turned it to 100%. Obviously I knocked my headphones off each time as quick as I could, but could these instances contribute to significant, permanent hearing loss?
|
[
"The external noises you hear come from sounds waves entering the ear canal. These waves are physically transmitted to the inner ear, where they bend tiny, hair-like structures called cilia on \"hair cells.\" As the cilia bend, they transmit signals to the brain, and this information is processed, giving you the experience of sound. ",
"Extremely loud noises, including the ones you described, can damage the hair cells and prevent the cilia from bending properly. This can eventually lead to irreversible damage and subsequent hearing loss over time, usually with the person losing the ability to hear high-frequency sound first.",
"The exact mechanism of how loud noise can lead to hair cell death and eventual noise induced hearing loss (NIHL) is still under heavy investigation in the field. Some recent theories involve the production of reactive oxygen species (ROS), but the risk is certainly a mix of both environmental exposure and genetic factors. "
] |
[
"It would be much easier to answer this question if you could approximately tell us the dB level of the sound at 100% volume, or measure it even, since you're a music producer after all. Hearing damage is worse for higher frequencies and higher volumes, so the more you can tell us the better."
] |
[
"I don't have the equipment available to measure the output decibel level. This would be hard to do even if I knew the output from my computer because I can't account for the monitor headphones."
] |
[
"Does water get any more slippery as it approaches the freezing point? i.e. Does driving on wet roads that are 33F pose any more risk of sliding than roads that are, say, 40F?"
] |
[
false
] |
[deleted]
|
[
"I don't know about water, but as the temperature drops, the road surface and your rubber tires harden up, which reduces the amount of traction they can provide to you.",
"You can see this in action at a drag race. Racers will do a burnout just before their race, to heat up the tires, increasing traction. Cold tires are less \"grippy\". You can see this in other race types, too. If there is a \"caution\" in effect, and they have to drive slow for a bit, a lot of them will slalom side-to-side to keep the tires warm via friction. ",
"Combine this with an already wet road, and it can become quite slick. ",
"Source: Motorsport enthusiast"
] |
[
"When rubber warms up it becomes softer and easier to deform. This allows the rubber to better deform around the small imperfections in the road and this increases traction. So if you have colder tires they deform less on a small scale and consequently have less grip on the road surface."
] |
[
"when the rubber ties harden up at lower temperatures, why does that reduce traction? Is it because the surface area of the tires that come in contact with the road is less since the cold condenses things?"
] |
[
"How much more energy does a hairy human expend growing hair than the same body without [much] hair? Is it a metabolically meaningful amount?"
] |
[
false
] |
For example, in my case, a 6'1" 230 lbs. 46 year old hairy male. Thanks.
|
[
"Hair grows in stages and at the last stage stops growing, so there is an upper limit to hair growth that varies from person to person. The reason I mention this is that your question seems to mostly be about body hair, which unless you shave or wax is already at it's final stage for the most part and thus wouldn't matter metabolically. Now if you were to have a brazilian (yes they can do it for guys) then you would have to regrow the hair but hair is made from keratin something already present in large quantities as it also makes up your nails and the outer layer of your epidermis so I doubt it would be metabolically meaningful."
] |
[
"Producing the hair in the living parts of the hair follicle must have a metabolic cost, regardless of whether or not the end product, ie the hair itself is no longer \"living\"."
] |
[
"I would actually expect the extra hair growth to result in a net energy surplus for the body. Anorexics and other people who are starving will grow a very fine hair all over their body called lanugo (newborn babies also have this). Lanugo provides a kind of blanket to maintain body temperature in the setting of lost subcutaneous fat. So this is a bit of an extrapolation, but I would expect that hairy people would have a lower basal metabolic rate than non-hairy people, all other things being equal."
] |
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