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|---|---|---|---|---|---|
[
"Did cannonballs spin and exhibit the Magnus effect?"
] |
[
false
] | null |
[
"Yes. Cannonballs were fired from smoothbore cannons, so they would develop some random spin when fired. The Magnus effect then caused the cannonball to veer off target.",
"http://pencilcricket.blogspot.com/p/magnus-effect-in-leg-spin-bowling.html?m=1"
] |
[
"Imperfections of the ball/barrel and inconsistency of the blast (the powder won't ignite at the exact same time and would be unevenly packed down)."
] |
[
"Imperfections of the ball/barrel and inconsistency of the blast (the powder won't ignite at the exact same time and would be unevenly packed down)."
] |
[
"What is the most current description of a vacuum?"
] |
[
false
] |
I'm aware that a vacuum in space is not truly empty, as shown by the Casimir effect and other experiments. What exactly is a vacuum then, and does this affect how physicists view real matter? I'm particularly interested in something I read that described a vacuum as being nearly infinitely dense and that real particles exist only when an excitation in a field "knocks" the particle out of the vacuum. Here is the quote I'm going off of: In the 1930's Dirac proposed that the vacuum was a near infinitely dense sea of particles in which all of the possible quantum states were filled. Matter as we know it, is what exists in quantum states above the vacuum. When a particle is knocked out of the vacuum, it leaves a hole called an anti-particle. Strong electromagnetic fields can effect the interactions of electron positron pairs which alter the observed electromagnetic field. The effect is called vacuum polarization and it has been experimentally observed. Is the above quote correct?
|
[
"The best current description (and this describes everything we've observed in terms of high energy physics) is that spacetime is filled with quantum fields. It turns out that quantum states of these fields correspond to a number of particles with particular properties. e.g. we may excite the electron field to have 1 particle with a particular momentum.",
"Excitations of these fields (i.e. particles) behave and interact with other excitations of this and other fields according to very particular rules. We use experiments like LHC to continually verify this.",
"We are also able to generate these rules from even simpler rules/models (representation theory of Lie algebras, and gauge symmetries). Some of these rules have issues and we've postulated the existence of additional fields (Higgs field(s), supersymmetric fields) to explain them. The LHC will help us better understand the existence/behaviour of these fields."
] |
[
"It is indeed possible, and was recently ",
"demonstrated",
"."
] |
[
"I'm sure my question will be well off-base, but as I have absolutely no education in these matters, I'm willing to ask the stupid question in order to be educated:",
"Granted, I don't really understand what you mean by quantum fields, but the way you phrased your answer makes me curious if it is possible to excite these fields to essentially 'generate' particles? Or does it mean that introducting particles to the field is the only way to excite it?"
] |
[
"Dear Reddit, blacksmith needs advice on a sundial."
] |
[
false
] |
I am an apprentice blacksmith and i have been asked to make a Sundial as a 100h project. It is to be exhibited at the 15-17 June, hopefully I will sell it there as well. I don't want to make this post too lengthy so here is the question: What is the angle of the gnomon in relation to the ground? I live outside Warwick (Warwickshire) in the UK, the latitude 52 degrees 16 minutes and 48 seconds north. Now i don't consider myself stupid, however, for some reason I cannot wrap my head around this. I know the dial plate needs to be 90 degrees to the gnomon as this will align it with the equator. I have also heard that 55 degrees should work pretty well but I have no idea why. Hopefully I asked the proper subreddit. I'm sorry for the bad English, it's not my native language. Have a smashing day!
|
[
"The angle of the gnomon with the horizon should be equal to the latitude. This way, on average, it will be about perpendicular to the Sun and will cast the strongest shadow. You can build the dial plate perpendicular to the gnomon (like ",
"this",
"), or parallel to the horizon (like ",
"this",
"). Depending on the orientation the locations of the lines on the dial plate will change, though."
] |
[
"The angle of the gnomon alone is not the only thing that's important for you. Its the relationship between the point of the gnomon and the marks indicated on some surface. That, plus orientation to north, is all that geometrically defines a sundial. Any arbitrary angle btw the ground and the gnomon, and btw the gnomon and the surface, could be used and would be irregular, but not incorrect. This is why sundials are ",
"numerous in their taxonomies",
".",
"As indicated by user Spatula, regular angles could be horizontal or inclined at latitute. (I would add that 'inclined at latitude' refers to the angle btw the ground and the projection surface. If the gnomon pointer is straight and normal to the projection surface, then the angle btw the ground and the gnomon is the compliment of latitude. Avoiding using the compliment, you can also say that the angle of the gnomon is latitude from vertical/observer zenith.)",
"I would imagine the difficulty in constructing a sundial to be in annotating sun positions and paths on the projection surface. Documenting the position of the sun requires time, and 100 hours won't give you a complete picture of the sun's apparent excursions. 8760 hours will (if you consider yearly variations in sun positions to be negligable). Predicting the position of the sun is easier, but could require significant precision in manufacturing, depending on your particular use for the sundial. Without any suggestion to your skill, blacksmithing is not typically considered a high precision process. ",
"Here's the value for your creative side. Regular angles for the gnomon and projection surface are used for standarization and readability (when sundials were used for time keeping) but can be defined by each sundial object on its own terms, and can remain readable if properly annotated. You are not limited by the form of standard sundials, only by your means for documenting or prediciting the cast of the sun on your form. ",
"Try using the sun tool in google sketch up to plan this project. ",
"In increasing orders of continued enthusiasm for this topic, I recommend looking up: apparent solar motion, NOAA's sun position calculators, Jantar Mantar, and the astrolabe.",
"*edit- Splatula"
] |
[
"Upvoted for correct answer. I have an excellent book on sundials, called \"Sundials, their construction and use\" by R Newton Mayall & Mrgaret W. Mayall, Sky Publishing Corp, P.O. Box 9111, Belmont, MA 02178-9111. It was originally published in 1938, but there have been several re-printings. Pretty much a definitive reference on the subject, with everything you'd need to know."
] |
[
"What are these tiny creatures that keep appearing on my window sill (on the inside)?"
] |
[
false
] | null |
[
"Try ",
"/r/whatsthisbug"
] |
[
"oh thank you, didn't know it existed...should i delete this post?"
] |
[
"Probably makes sense to delete it here, and just post on ",
"/r/whatsthisbug"
] |
[
"Are LCD monitors more or less stressful to our eyes compared to CRT monitors?"
] |
[
false
] |
over a given time span, which would be more stressful/strenuous to our eyes?
|
[
"No expert here, but after some googling this is what I found. Eye strain is not necessarily caused by the monitor (LCD or CRT), but rather by staring at a fixed spot for extended periods of time and not blinking enough.",
"Link",
" and ",
"link2",
" \nfor more info"
] |
[
"This is a supposition based on personal experience, sourceless.",
"Then you should have stopped right there and not commented."
] |
[
"This is a supposition based on personal experience, sourceless.",
"Then you should have stopped right there and not commented."
] |
[
"Is there a certain area of the body that is more susceptible to changes in temperature?"
] |
[
false
] |
For example, if one wanted to cool down and had an ice pack, what part of the body could he place the ice to make his body cool down the fastest? Is there a certain part that controls our sense of temperature more than the other parts?
|
[
"For example, if one wanted to cool down and had an ice pack, what part of the body could he place the ice to make his body cool down the fastest?",
"Place the ice pack on an area which exposes a lot of veins and arteries. This will stop the cooling being mostly localised, because of the blood which is circulating.",
"I don't know about which parts might affect your ",
" more, though."
] |
[
"The face is perceptively more susceptible and triggers different responses to cold than a lot of the rest of the body. In terms of actual cooling ability, armpits and behind the knees provide the best options."
] |
[
"The palms of the hands are the best place to cool down your body temperature from because they have a large number of blood vessels near the surface. Instead of an ice pack though you should use something around 70 degrees Fahrenheit (I think that's the number) as this will prevent your blood vessels from constricting from the cold."
] |
[
"What is the biological basis for physical sensations related to your \"third eye\" (that space on your forehead between your eyebrows)?"
] |
[
false
] | null |
[
"You can make many places on your body seem to tingle just by attending to them. Nothing special. Your brain just naturally ignores a lot of these sensations when you are not attending to them explicitly."
] |
[
"But it ",
" special. Maybe that happens a tiny degree but nowhere near as strong. There's no way I could do this with like...a random spot on my upper arm, or my belly button, or the back of my hand."
] |
[
"We can't answer why you specifically have some kind of experience, but anatomically there is nothing special about the spot on between your eyes"
] |
[
"Why do camera recordings get digital artifacts when receiving physical strain(during impacts, for example)?"
] |
[
false
] |
Like this:
|
[
"The artifact you see is from a packet loss: the video is encoded blocks by blocks and then transmitted. Because losing adjacent packets (blocks of data) is likely, blocks are shuffled so that we lose less ",
" blocks, and it looks less crappy. There are ways to conceal losses but when they're too numerous, blocky artifacts happen.",
"So it is not the sensor that fails, or even the compression itself, but the writing to memory or the transmission, which may be affected by big shocks, but tbh while I do know that it happens I don't know why :)"
] |
[
"The shock can momentarily cause connections to break. Then remake. All electronics use connectors to attach things together. They are spring loaded. So a large enough shock can cause the spring loaded connections to bounce."
] |
[
"I think this isn't actually a physics question, it's a computer science question! Modern video encoding algorithms don't store ",
" the details about a scene: they pick and choose what's most important for the eye to see, and store a certain amount of information about details and changes in the scene per second. In the case of your linked video, this cuts the rate of data transmission from about 80 megabytes/sec to maybe 1 megabyte/sec. ",
"For slow-moving scenes, there's only a little bit of detail to describe, so this method can capture it all and your eye won't notice. But if the scene being filmed has a ",
" of changes that occur very quickly -- an explosion, or the camera gets bumped, or in this case a blast of spray -- the algorithm can't describe it all in the limited amount of data available: it does the best it can, but a lot of the fine details are dropped out, so you get a blocky picture."
] |
[
"What evidence is there that there is a smallest particle? Is it possible that even the smallest particle we know about could be composed of smaller particles, composed of even smaller particles ad infinitum?"
] |
[
false
] |
I understand that elementary particles are supposed to be 'elementary', because they have no measurable internal structure. But could it be that we are just unable to measure an internal structure made up of ridiculously small particles? And if that is the case is it theoretically possible that even those particles have internal structures of even smaller particles? Is there evidence against this, if so what is it? EDIT: So basically as I understand it. Nobody has any fucking clue.
|
[
"From the outside it would indeed seem theoretically possible but let me expand upon this quickly in two ways.",
"The internal structure of protons and neutrons (well all hardons, particles made up of quarks) is not just a result of theory there is ",
"experimental evidence",
" that they are made up of quarks. There is no such evidence for quarks. Now you might say lack of evidence is not evidence of lack, very true.",
"This brings in the other point. There is a very successful theory that describes most of particle physics. You may have heard of it, it is called the ",
"standard model",
". Now this theory is a tremendous theory, it describes the fundamental forces (barring gravity), it describes how objects gain mass and it describes all the particles. It predicted the existence of quarks before any evidence of them existed. It also predicted many other particles and effects that have since been spotted. Overall on the scale of wrongness, the standard model is very close to being right. It has quarks as fundamental particles.",
"This isn't to say it has to be right, there could be some deeper theory beyond the standard model. This deeper theory could postulate a quark internal structure, this may result in new predictions which turn out to be true, verifying we were wrong about quarks. Who knows what we will \"know\" in the future. For now though, we have no evidence to suggest we are wrong and quarks are made of something smaller, furthermore we have successful theories based on the fact that they are indeed fundamental particles.",
"So, possible? yes. Plausible?...not fit to judge but I don't know if anyone thinks so."
] |
[
"The internal structure of protons and neutrons (well all hardons, particles made up of quarks)",
"Pretty sure you meant hadrons, but that is a hilarious typo."
] |
[
"A particle physicist's dirty talk:\n\"I'll show ",
" a hadron!\""
] |
[
"AskScience, can someone please explain this weather-radar anomaly?"
] |
[
false
] |
Is it just a radar anomaly or something more sinister? This showed up about a month ago. Haven't seen it again since.
|
[
"Out of curiosity, do you know what date and time this screen capture was taken? I would like to compare it to raw radar data, because I think there was an issue with the radar in Warner Robins, Georgia at this time making the odd circle. The map you are looking at is a composite reflectivity image of all of the WSR-88D Level III radar data which is the \"clean\" version of data compared to the Level II data which is raw. Contrary to what others have said, this is not a mass bird migration occurring throughout the Southeast.",
"Radars scan in two different modes, a \"clean air\" mode and a \"precipitation\" mode. The difference between these modes is that a clean air scan sends out fewer pulses in order to maximize the range of the radar and rotates more slowly to obtain a higher resolution, compared to precipitation mode. Clean air mode is most likely the mode that all of the radars in Texas, Oklahoma and the rest of the Southeast are in.",
"Clean air scans can be used to detect birds, insects, dust, moisture and boundaries. If you continue to watch the radar tonight in Austin, Texas for example, you will notice these rings begin to grow. Since the sun has set, temperatures are cooling off and getting closer to the dewpoint temperature, so the air is becoming more saturated and thus the radars are picking up moisture in the boundary layer.",
"Finally, an inversion layer is probably going to establish tonight. Typically, temperature decreases with height but sometimes it will actually increase with height. This inversion will bend the radar beam downwards towards the ground, so it will end up detecting more ground clutter and thus show anomalous propagation.",
"Edit: Replaced Peachtree City with Warner Robins.",
"Edit 2: The large circle in Georgia is due to a malfunctioning radar that had issues with data quality, that has since been recently repaired by the National Weather Service. The other circles throughout the South and Southeast are explained above."
] |
[
"Birds form concentric circles when migrating?"
] |
[
"Birds form concentric circles when migrating?"
] |
[
"The movement of rotating things and the movement of a weight hanging on a spring and can both be described with sine waves. What does rotate in a mass/spring system and what does oscillate like a spring in a rotating system?"
] |
[
false
] | null |
[
"The other two comments are correct, but i wanted to try to give you some mathematical insight as to ",
" the two things are described by the same mathematics.",
"The crucial feature of a spring (or a pendulum, or ...) is the existence of a ",
", which is ",
". In math, this looks like ",
" = -",
" ",
", where ",
" denotes the force, ",
" describes how strong the force is, and ",
" is the distance from the 'rest' position. The negative says that the force wants to push the object back towards the equilibrium position. In other words, if the spring is compressed, the force wants to make the spring expand again, and if the pendulum is on the left, then gravity wants to make it swing back to the right. Also, the more compressed the spring is, the harder it fights back.",
"Now, Newton's second law says that ",
" = ",
", where ",
" is mass and ",
" is acceleration. That is, forces make things accelerate. Remember that acceleration is the second time derivative of position. If the position changes with time, it has a speed, and if the speed changes with time, there is an acceleration. Conversely, speed means a changing position, and acceleration means a changing speed. Let me write this like this: ",
" = ",
"', and ",
" = ",
" = ",
"'', where i'm using the prime to mean the time derivative.",
"Combining these two, you have ",
" = -",
" = ",
". The crucial thing here is that the acceleration ",
"'' is directly proportional to, but also opposite in sign to, the position. If the object is at the rest position, then there is no acceleration. If the object is a little way off centre, then it will accelerate a little bit when you release it. And if it is a long way off, then it will accelerate a lot. ",
"So, thinking it through, if you release the object at some displacement, it will start to move towards the centre. As it does, it keeps picking up speed, but the actual acceleration decreases as it gets closer to the centre. As it passes the centre, its acceleration is instantaneously zero; it's velocity maxes out as it passes the centre. But then immediately it starts to decelerate. The deceleration gets stronger as it moves further past the centre point. In fact, the deceleration almost perfectly mirrors the previous acceleration, so that the object ultimately stops at the same distance from the centre as you released it, before springing back in.",
"This is called simple harmonic oscillation, or simple harmonic motion.\nAnd the real point is that you will get this behaviour whenever the acceleration is proportional to the displacement: ",
". when ",
"'' = -",
" ",
".",
"Mathematically, the one and only solution to this equation ",
"'' = - ",
" is for ",
" and ",
"'' to be described by sine or cosine. Why? Well, you can see ",
" this is true by remembering that the derivative of cos ",
" is -sin ",
", and then the derivative of sin ",
" is cos ",
". So the double derivative of cos ",
" is - cos ",
", and the double derivative of sin ",
" is -sin ",
". But the fact is that this is not only one potential solution, but it is also the only possible solution, because math.",
"So, long story short: any situation in which ",
"'' is proportional to ",
" will be described by trigonometric functions; that is, by sin and cos. It doesn't matter ",
" that proportionality exists, the mathematical description will be the same.",
"As a counter example, you could also imagine a situation where ",
"' is proportional to ",
". Say ",
" is the number of members of a population where the more people you have, the more births you have, so the more the population grows. In this case, the only mathematical solution to the differential equation ",
"' = ",
" is an exponential, of the form ",
" = ",
" exp ",
". That is, you get exponential growth (or decay) whenever the time rate of change depends on the value at that time. "
] |
[
"Circular motion can be described by sine and cosines. ",
"Here's an animation I created explaining that",
". So that's the connection. The two phenomena are related by the same functions. That's all there is to it, pretty much."
] |
[
"So, why is the position (along an axis) of a point that rotates about a pivot point proportional to the second derivative of the position of said point? "
] |
[
"How much is Iceland's climate and temperature affected by the Iceland hotspot?"
] |
[
false
] |
I know that the main reason for Iceland's very mild climate is the North Atlantic Gulf stream, but since Iceland is right above a volcanic hotspot, I assume that volcanic activity in some way adds to Gulf streams effect. Am I right about this, and to which extent does it affect the climate?
|
[
"The heat flow to the surface due to volcanic activity on Icealnd is insignificant compared to the solar energy input.",
"This paper:",
"HEAT FLOW FROM THE EARTH'S INTERIOR: ANALYSIS OF THE GLOBAL DATA SET",
"Describes the heat flow from the iinterior as 65 and 101 mW/M",
" for the land and ocean respectively. By comparison, the sun is ",
"240 watts of solar power per square meter",
"The sun contributes more than 99.5% of the heat to the surface of the earth. ",
"Even locally in such places a high-latitude Iceland, with concentrated local volcanic heat input, it is still a small value. The ",
"global heat flow map shown here",
" has maxima of 350mW m",
" , which is at least 2 orders of magnitude less than the solar heat input. Sorry, I don't have a reference for the annualized solar heat input to Iceland."
] |
[
"If we look at the bare bones of the argument, it is infinitely dependant on the hotspot, as without, the climate would be very much like the North Atlantic and very little like an island. "
] |
[
"Geology student who recently visited Iceland here,",
"Not much more to add -- but the main utility of the hotspot is to harness the geothermal energy related to it. I believe Iceland is the only country in the world not dependent on fossil fuels that has an excess of energy, and they are trying to find out ways to export it.",
"And Iceland can sure get really cold up on the glaciers! Haha, even in the summer months."
] |
[
"A question about intersteller travel and navigation"
] |
[
false
] |
I was (not) watching some show about space last night as i was trying to fall asleep and had a thought maybe you all can help me wrap my mind around. Let's say somehow tomorrow we find/are given/discover a method of space travel that would allow you to get in a ship and go explore any star in our galaxy (or others). Somehow your ship can move across the vast expanse of space in a timely mannor. My question has to do with navigation. When we plan a trip to say Mars, we can figure out what path to take by doing the math for where we are and where Mars is and adjust for where it will be when we get there right? How could we do this with a distant star? One thats light took years just to get to us? Can we track the movements of a distant star well enough to to "jump" to a point near it and on the correct plane or better yet near a planet? I know it's dumb to bring movies into this, but in films ships always "jump" across space to a just outside of a planets orbit where they can then pilot down into the atmosphere. If we had such a ship, is there anyway we could figure out where to go?
|
[
"Astronomers can track star movements across the sky and can estimate distances pretty accurately. As long as you had those two pieces of information for your destination and knew how long it would take to travel that distance (to adjust the flight path for the illusion of a distant star's location in the sky) you could navigate accurately. If a star is moving more or less perpendicularly to the way you're traveling to it, and provided you had faster-than-light travel, you would see the star rapidly moving across the sky the closer you got to it. Look up Red Shift some time."
] |
[
"One option is to use ",
"pulsars to define cosmic location",
". Individual pulsars are readily identifiable by their rate of spin (pulsation)."
] |
[
"Could we calculate it so you could put your ship to within a hundred miles of the surface of a planet on the other side of the milky way?",
"I guess i got overwhelmed (as i often do when confronted with the sheer number of stars in our galaxy) last night thinking about the complexity of navigating a ship between hundreds of billions of stars with such vast space between them. ",
"Another question: if you fucked up and jumped to a spot thats not in any solar system, could you stand a chance at finding your current location based off of the stars you see? "
] |
[
"Is the \"Island of Stability\" possible?"
] |
[
false
] |
As in, are we able to create an atom that's on the island of stability, and if not, how far we would have to go to get an atom on it?
|
[
"The current theoretical best estimate for the location of the island is Z = 114, N = ",
" 184. We have produced some isotopes of the element with Z = 114, but they have less than ",
" 184 neutrons.",
"The nuclides near and at the island of stability may exhibit enhanced stability relative to their neighbors on the chart of nuclides, but they will not truly be stable.",
"Unless nuclear forces do something totally weird and unexpected at high A, the alpha separation energies for all of these species will be negative relative to their ground states, so they will always be able to alpha decay, if nothing else.",
"Technologically and logistically, we are far from being able to reach the island of stability. We don't know of any nuclear reaction mechanism which would allow us to produce nuclides so neutron-rich, for such high atomic number."
] |
[
"Since supernovae produce all super-heavy isotopes, couldn't we make the argument that if the island of stability exists, we should see the corresponding spectral lines in a fresh supernova, but not if the island of stability does not exist?",
"Or are we talking about the difference between half-lifes of microseconds within the island versus half-lifes of nanoseconds outside of it? In that case even if the supernova produces these isotopes, they won't be visible for any appreciable amount of time."
] |
[
"We don't know whether superhevay nuclides are produced in non-negligible quantities in supernovae. We have no reason to believe that species near the island of stability are produced. But yes, even in the island of stability, the lifetimes could be very short on practical timescales."
] |
[
"How would I go about making an electromagnet stronger than the average man?"
] |
[
false
] | null |
[
"/r/AskEngineers",
" is probably the most suitable place to ask about this. The answer is most likely that it is possible, but there are a lot of practical considerations that makes it pretty complicated. For once, you'd need a powerful electromagnet, which is big. Thus, its probably easier to hide the magnet on the table and just have a metal place in the box."
] |
[
"Can you think of a feasible alternative?"
] |
[
"My initial idea would be something that latches onto some hinges that pop out of the box. But it would be kind of hard to rig everything so that you could put the box down and have the latches automatically come out. "
] |
[
"In a vast universe, is it possible that a solid gold planet exists?"
] |
[
false
] |
Edit: What a great discussion! A lot to think about here, especially regarding the implications of infinity. So it seems that the verdict is that yes, it is in reality POSSIBLE for this to happen, and though it would be incredibly unlikely that a planet consisting of only a single type of ANY element would exist, in a truly infinite universe, this scenario SHOULD occur at least once! Now for extra credit, does that mean that a solid gold planet would exist an infinite number of times?!?! Thanks again for all the great comments everyone!
|
[
"It's really really unlikely. Gold is produced in highly energetic events like supernovae that come with a lot of accompanying matter. ",
"On a lower energy chemical scale, gold binds to iron really well (which is present in the same events) and makes it highly unlikely to get a planet made purely of gold. "
] |
[
"Hydrogen is the most common element in the universe by a fair margin at about 75%. Jupiter is already about 90% Hydrogen, so it seems that that would be the most plausible.",
"Especially if there was a gas giant around a first generation star before most of the other elements were formed."
] |
[
"A metal is a material where the electrons in the outermost 'shell' of the atom interact with the rest of the material in a way that they are not bound to single atoms any more. The silvery appearance of most metals is a direct consequence of this physical fact. ",
"Some materials that aren't metals can become metallic (metal-like) when compressed to a very large degree, and hydrogen is one of those. Hydrogen becomes metallic at about 10",
" bar of pressure, and because of this reason (correct me if I'm wrong here) we haven't made macroscopic amounts of it, so it's hard to gauge exactly how it looks and interacts.",
"Phase diagram of hydrogen",
"(edit: 10",
" bars instead of Pa)"
] |
[
"Is it possible to find the algorithm for a random number generator by studying the sequences it produces?"
] |
[
false
] | null |
[
"For the sake of brevity, we will talk neither about the seed, i.e. the number that is given to the algorithm to bootstrap its pseudo random generation process, nor the environment it is executed in, and from which it can draw some randomness (time, temperature of the CPU, etc.). We will only talk about a deterministic pseudo random generator.",
"There is only a finite amount of information in the algorithm. You can more or less (discarding a whole lot of important details) map it to the size (in e.g. MB or kB) of the program file.",
"Therefore, the pseudo random number generator can only output a certain amount of random numbers before it starts giving away information about itself.",
"The mathematical notion that ties the output of a program to what we may informally call its true information content is called the Kolmogorov complexity.\n",
"https://en.wikipedia.org/wiki/Kolmogorov_complexity",
"The way in which we measure the information contained in, say, a program output is stronly tied to its randomness, it is called the entropy, or Shannon information:\n",
"https://en.wikipedia.org/wiki/Entropy_(information_theory)",
"You want to have a program whose output has a lot of entropy, i.e. is random, but you don't want to store this output as is on the disk (this would be a one-time-pad, it is an unbreakable means of encryption but requires the transit of huge amount of secret data), you want to store a program that will compute this at runtime.",
"The problem is that there is a lower bound on the Kolmogorov complexity of a true random string, that is more or less the length of the string itself. This is bar some pathological case where the execution environment is defined as containing the random string you want to output. There is no way to minimize the Kolmogorov complexity in general.",
"That is why you can not zip a file twice for example.",
"Note that the output of a program does not need to repeat itself. For example you could output the digits of pi or of any irrational number and never repeat yourself, but the Kolmogorov complexity of pi is finite: you can write a program that outputs digits of pi, and this program will fit in a finite amount of memory.",
"How to actually guess the structure of the algorithm is another can of worm. The naive approach is tied to one of the fundamental problem of Computer Science: the Halting Problem:\nIf you try to enumerate all programs of reasonable size, and run them to see if their output match the one of your mystery algorithm, then you will find that some programs never terminate. And some other terminate after a reaaaaaaaaally long time. The problem is that the amount of time you have to wait before you can stop a program because it will never terminate is literally uncomputable, it is called the busy beaver number:\n",
"https://en.wikipedia.org/wiki/Busy_beaver",
"You will never know if you have the algorithm you search, and are just not patient enough to get the answer, or if you are just watching an endless loop...",
"Practically, though, there exist a variety of attacks: you could try to learn how to predict the output with machine learning techniques, you can try to gain insights on the probable implementation using clues (which algorithms are commonly used, which system is this running on, can I time the execution of the algorithm...).",
"All those side-channel attacks are the reason why crypto system are very hard to implement in practice, as the tiniest of error can bring the whole thing down."
] |
[
"That was a really interesting read! I'm pretty sure it went in one eye and out the other but while it was in there, I found it really informative."
] |
[
"/u/linschn",
"'s answer is great from a theoretical perspective, but from a practical everyday perspective, I think there's an equally interesting answer.",
"First, there are two kinds of pseudo-random number generators (PRNGs): cryptographically secure (CSPRNG), and non-cryptographic (PRNG). The short answer is that in practice, we design CSPRNGs specifically to not have the property you mention: knowing the partial output of a CSPRNG should not allow you to compute or learn anything else it has or will output. In fact, a stream that comes out of a CSPRNG is meant to be practically indistinguishable from true random. This means that if you have a set of CSPRNGs, they should also be indistinguishable from one another, as they should all look truly random. In fact, if you had some way to distinguish CSPRNGs from one another, you'd have an attack that showed those CSPRNGs were actually not secure (i.e. distinguishable from random).",
"Now for the hard question: do we have actually secure CSPRNGs in practice? It turns out we're not really sure! We have many strong candidates, and many that have remained secure in practice for decades despite incremental advances in breaking them. On the other hand, we have seen popular CSPRNGs fail: in recent history, RC4 is a good example; RC4's output was weakly but detectably biased from random, making it unsuitable for use as a stream cipher.",
"On the other side, there are CSPRNGs that are designed with a backdoor, such as DUAL_EC_DRBG. In this case, the NSA created a seemingly-secure CSPRNG that to a naive observer appeared to produce an output indistinguishable from random. However, shortly after its standardization, some clever cryptographers speculated that if the NSA knew a relation between two particular parameters in the algorithm (these parameters themselves being chosen by the NSA), then the NSA (and, in theory, only the NSA) would have the ability to compute future outputs from the supposedly-CSPRNG given its current output. This speculation was later confirmed to be true in the Snowden documents. Nonetheless, you'd be hard-pressed in practice to distinguish DUAL_EC_DRBG outputs from any other CSPRNG, unless you had the secret key generated by the NSA (in which case, it would be trivial)."
] |
[
"Why do carbon dioxide levels cause climate change when it was all originally drawn from the environment in the first place?"
] |
[
false
] | null |
[
"The carbon is being released due to burning of fossil fuels.",
"This carbon was removed from the atmosphere during the Carboniferous geological age (~360-300 million years ago), before the dawn of the age of dinosaurs.",
"When stored underground this carbon was not contributing to the greenhouse effect, and do not increasing global atmospheric temperature.",
"To give you an idea of what things were like before the carbon was locked away, at the start of the Carboniferous global temperatures were 6 degrees C above pre-industrial levels (Paris agreement aims for < 2 degrees C), and sea level was 120m above current."
] |
[
"Some of the CO2 currently in the atmosphere used to be trapped in the earth in the form of trees, coal, natural gas, other hydrocarbons, ect. Since it was trapped in those things, it had a very different effect on the environment.",
"Humans came along and found out that we could burn these things to make our lives awesome. Generate power, build things, generally increase the standard of living for nearly every person on the planet.",
"Unfortunately, that moved the CO2 from in the ground to in the air, which did happen naturally but not as fast as humans have started doing it. The natural environment has a hand full of ways it can remove CO2 from the air but because of the increased speed of CO2 going into the air caused by humans, those methods have not been able to keep up. So excess CO2 builds in the air, unable to be removed, and acts as a green house gas which traps heat from the Sun not allowing it to dissipate into space."
] |
[
"Today’s CO2 levels are some of the lowest in earth history. It’s been that way for about a million or so years. ",
"Plants have taken what was about 2400 ppm down to about 300-400 ppm by locking it away. Plants starve if the CO2 is less than about 200ppm."
] |
[
"Noise Cancelling Technology + Radiation Will it work?"
] |
[
false
] |
[deleted]
|
[
"Optical waves and sound waves behave very similarly and both exhibit destructive and constructive interference. Interferometers can give you destructive interference at one point (at the cost of constructive interference at another point).",
"Doing this \"real time\" like is done in headphones by employing some sort of feedback is not feesable though. Optical cycles occur at such a high frequency that you can't feed back fast enough to have a \"real time\" type of radiation canceling scheme.",
" I just found out that the OP was asking about radiation that can kill you (like from a nuclear reactor). In the answer above I was assuming the OP meant radiation as in any form of electromagnetic radiation (light)."
] |
[
"To address this to the concept of nuclear radiation you might be better off thinking of radiation as particles in this case. All you have to do is stop the particle, which is what lead walls and thick concrete do. In theory you can fire other particles with exactly the same momentum at the radiation particles and stop them, but this is extremely difficult."
] |
[
"OH...OH GOD oh no I horribly misunderstood your question then. You were talking about nuclear radiation like from a nuclear reactor. ",
"I was talking about radiation meaning any form of light. Please discount my initial response."
] |
[
"Would flipping your body every 30 seconds for an hour get you just as tan as lying on both sides for 30 minutes each?"
] |
[
false
] | null |
[
"There are two ultraviolet lights at work in tanning: UVA and UVB. UVA causes the oxidation of melanin present in the skin, which causes a short term darkening of the skin. UVB triggers the production of melanin (which takes around 72 hours to have an effect).",
"\nAlthough these processes are very different, they do both respond to damage from UV radiation, and the damage it causes is immediate and proportional to time (so it doesn't need to 'build up' before it begins having an effect). All this comes together to mean that it doesn't matter how you flip, but that it is the total elapsed exposure for each part of your skin that alters the tan."
] |
[
"so being tan is skin damage?"
] |
[
"It's caused by skin damage and is the body's mechanism to protect itself. We don't have a permanent tan because we also need to use the light for vitamin D (so can't just block it all using melanin)."
] |
[
"How are bats' organs adapted to sleeping upside down?"
] |
[
false
] |
I know why they sleep upside down and that tendons in their legs "cramp up" to make sure they hold on pretty tight. But how are their internal organs arranged? Doesn't blood flow to their brains like in humans turned upside down?
|
[
"Humans are close to 2m tall. Bats is close to a quarter of that. This basically means that they only have to deal with a quarter of the pressure difference a human does.",
"They probably have some adaptions in addition."
] |
[
"Only the largest bats (some of the fruit bats) are that big. Most bats are mouse sized or squirrel sized. So yeah, they're dealing with a tiny fraction of the pressure difference that a human would experience. "
] |
[
"If the bat is roughly a quarter of the human's demensions, wouldn't that equate to about 1/64 the pressure, due to the square-cube law? "
] |
[
"Is it possible to \"make it rain\" in the literal sense (not urban)?"
] |
[
false
] |
If possible how is this done? Side effects?
|
[
"Cloud seeding",
" has been shown to give a 10% increase in precipitation. Not exactly a mad-scientist-style weather control machine.",
"There really are no side effects since the clouds are seeded with such a small amount of silver iodine dust. The increased exposure is 2 orders of magnitude less than the normal amount. "
] |
[
"I thought every attempt at this just lead to a hurricane being redirected somewhere else."
] |
[
"I recently saw half of a short film/documentary[?] by the BBC and Discovery Channel called \"Superstorm\" in which they were attempting to precisely control the direction of hurricanes --I don't know how much fiction it is but according to it, China successfully did deviate a hurricane to the Gobi desert or something like that."
] |
[
"Does compression effect the electrical conductivity of a material?"
] |
[
false
] |
Not necessarily to the point of trauma, but does pressure alter the flow of electrons through, let's say, copper in any meaningful way?
|
[
"Yes it does. However, there isn't a clearcut relationship. For example, noble metals like copper and silver get more resistive under pressure, whereas tin and indium get less resistive. And that's just metals, the simplest conductors. When you get to nonmetals and semiconductors and ionic liquids and whatnot it gets even more complex."
] |
[
"Exactly.",
"\nThis phenomenon is exploited in sensing technologies. The resistance in a conduit is manipulated by the stretching of the materials, giving a signal reading that can be interfaced to read a real physical value. It is well known, and largely exploited. But like our other friend said already, different materials have different properties."
] |
[
"It does indeed, to add to ",
"/u/iorgfeflkd",
", straining silicon in order to enhance its electron mobility is actually a huge part of modern computer chip designs. Strain in that case isn't coming from \"compression\", as you may be thinking (i.e. by putting a weight on it), but rather by growing the silicon on top of another material whose lattice constant (i.e. atom-to-atom spacing) is just a liitttttlllleee different than silicon. As a result, the Si material that grows, provided it is only a thin layer, ends up having a built-in tension to it, and this enhances mobility. This allows the transistors that make up modern computers to switch faster and produce less heat (which is the crucial limiting force in chip technology)."
] |
[
"Is there a set amount of energy in the universe?"
] |
[
false
] |
Due to the conservation of energy, where energy cannot be created or destroyed and only converted from one form to another, would that mean that there is a set amount of energy within the whole universe?
|
[
"Actually no. Conservation of energy predicates on time-translation symmetry. But our universe is expanding, so it lacks such symmetry. In more mathematical term, there is no time-like Killing vector in Friedmann–Lemaître–Robertson–Walker metric, the metric modelling our expanding universe. Consequently there is no well-defined \"total energy\" in our universe."
] |
[
"On small scales and in \"flat\" spacetime, energy is conserved. When you get to larger scales and take expansion into account then conservation of energy can no longer be applied."
] |
[
"So does this mean that energy on large scales can diminish but not increase? Does the energy released in the big bang represent the upper limit on the energy in our observable universe?"
] |
[
"Under what circumstances will a star collapse?"
] |
[
false
] | null |
[
"Interestingly, not all stars that explode do so from collapsing. Lighter weight white dwarf stars (which began their lives as stars less massive than the approximately 8 solar-masses needed to form a neutron star) with companions can add mass over time and enter a period of runaway fusion reactions which blows the star apart, this is a Type Ia supernova. Stars heavier than roughly 8 solar masses will all end their lives in some dramatic way, but exactly how things work out varies depending on the details.",
"For \"ordinary\" massive stars when fusion ends after the formation of Nickel-56 in the core the inner core will be supported only by electron degeneracy pressure but the core will get heavy enough to overcome that pressure, form a neutron star and throw off a Type II supernova explosion in the process. Sometimes the end result won't be a neutron star but a black hole instead, and there actually isn't a firm cutoff of masses, it's a somewhat non-linear effect.",
"For extremely massive stars two other phenomena can become more dominant than mere pressure. As the cores of such stars heats up it glows in various wavelengths depending on temperature. At some temperatures the glow is so energetic that it extends not just into the UV or the x-ray spectrum but even further, into the range where individual photons have more energy than the combined rest-energy of an electron plus a positron. The light from the glowing core will actually cause matter/anti-matter pair production inside the star. The positron will quickly find a nearby electron and annihilate with it, re-producing high energy gamma radiation, but during that brief period of time the energy that had been produced from fusion reactions was not contributing to maintaining the pressure of the core. As the core heats up, even more of the thermal energy will spend a period of time in the form of electron/positron pairs. This is a runaway feedback loop because the star will begin to collapse while the temperature increases as the thermal pressure is lowered. Very rapidly enough energy will have been released from fusion reactions to completely gravitationally unbind (explode) the star. This is a pair-instability supernova.",
"For even more massive stars the glow from high temperature matter in the core can become so bright that it begins to blow apart atoms in a process called photodisintegration. This uses up thermal energy and the result is that the star cannot halt its collapse into a black hole, though it can still produce a supernova or hypernova explosion despite the formation of the black hole in the core."
] |
[
"A star will collapse when gravity is sufficient to overcome the outward force usually created by the star during its lifetime. This usually occurs after the star has fused hydrogen and helium into heavier elements such as carbon, oxygen, and iron, around the end of the lifetime of the associated star. The outcome of this gravitational collapse depends on the mass of the star; above a certain threshold, the star will collapse into a black hole. Otherwise the star, having shed its outer layers, will become a white dwarf and meet a comparatively calmer end."
] |
[
"above a certain threshold, the star will collapse into a black hole. Otherwise the star, having shed its outer layers, will become a white dwarf and meet a comparatively calmer end.",
"There's a pretty big mass range in between these two that results in the formation of neutron stars as well.",
"The processes that form white dwarfs don't involve core collapse, as far as we can tell (well, ",
"maybe",
" there are ",
"some",
" that ",
"do",
", but that isn't observationally settled yet)."
] |
[
"Does cold water extinguish fire more effectively than hot water?"
] |
[
false
] | null |
[
"It's negligible. Yes the entire purpose of putting water on fire is too remove the heat source side of the 3 sides of the fire triangle (heat source, fuel, oxygen). However, most of this energy transfer occurs as the water turns to steam (so I am told, I do not know the particulars of this). And therefore, the effect of using cold vs hot water to fight the fire is therefore negligible. Yes it is more efficient, but its <1% gain due to the steaming process having such a large advantage in this cooling effect."
] |
[
"Even if we ignore the heat absorption from changing water to steam, ",
"an ordinary candle burns at temperatures over 1,100 °C / 2,000 °F",
". Compared to that, the difference between hot and cold water is still negligible."
] |
[
"When we're applying water to a fire we're not trying to take away the heat source, most of the time we are actually trying to take away the fuel source. The argument is when using water what we are trying to do is cool the fuel, so that it can't reach its ignition point, this in turn reduces the amount of sustained chemical reaction (fourth side making up the the fire tetrahedron). My point is, with your 2000 degree candle, we're not fighting 2000 degree flames (heat source), we're fighting the ignition point of the wick/wax (fuel source) which is prolly 400-500 degrees. If we can keep that down we'll snuff out the fire by not providing any fuel."
] |
[
"Can an open reading frame be expressed without a stop codon"
] |
[
false
] |
Say you have a start codon and the required promoters but there is no stop codon, and some other mechanism stops transcription, could you have a functional gene?
|
[
"Yes. Yes is the answer to your question technically, however let me start with some definitions to be sure I am answering the question you are really asking. A gene is the common term for the part of the DNA that gets transcribed through the process of transcription. What we most commonly think of are protein coding genes. These are transcribed then translated to make a protein. However, a gene doesn't have to be protein coding. There are genomic regions that get transcribed, but don't get translated. For example, there are many genes that encode entities that function as RNA molecules. These are transcribed from DNA into RNA, but are not translated. They are still functional, they play a regulatory role as an RNA molecule. Since they are never translated into a protein, they don't need stop (or a start ) codons. Most of the ribosome itself, which translates the RNA into protein (where an RNA needs the start and stop codon to be properly processed) is made of these enzymatic RNAs. So the technical answer to your question is yes, you can have a functioning gene without a stop codon.",
"If you are asking only about protein coding genes, these do not need to have a stop codon to be transcribed into RNA, but do to be their properly functioning protein. It is possible for them to be processed by the ribosome. What typically happens is that the ribosome will just keep going along till it hits the next stop codon or runs out of RNA. This usually results in a nonsensical protein and can cause problems for the cell."
] |
[
"Let me look around, these would be pretty old. I do know of several people who have done it accidentally. It is something you are warned about when cloning. It is one of those things that is so common a mistake a paper on it would not be accepted.",
"Here",
" is something that may interest you, it is about stop codon readthrough. In this case, where special signals in the sequence occur, the ribosome can ignore certain stop codons to make different isoforms of proteins."
] |
[
". the stop for transcription are the ",
"termination bases",
". mRNA are further modified before translation, removing introns. They wrap and fold and are subject to degradation. A very large mRNA would likely be unstable and not usable for the ribosome. Now lets say teh revers the termination sequence is before any stop codon. the protien would be truncated-- short."
] |
[
"How does CPR work?"
] |
[
false
] | null |
[
"It really depends on the situation.",
"If someone goes into cardiac arrest, there is the possibility time lapse between the arrest and someone initiating CPR. Every second that goes by without CPR is a second those organs are starving without oxygen. If the arrest is witnessed, and CPR is quickly initiated, the chances improve.",
"The big issue though is why did the patient go into cardiac arrest in the first place? CPR is just an artificial means of breathing and circulation. It is not curing the problem.",
"If an otherwise healthy patient goes into an abnormal rhythm, loses a pulse, gets some CPR, and is quickly shocked back into a normal rhythm, odds are decent that the patient could have a favorable outcome.",
"However, if someone suffers a huge myocardial infarction and loses a pulse because his heart is severely debilitated, CPR won't cure that problem. The patient would need treatment for the cause of heart attack. Otherwise CPR is just delaying the inevitable."
] |
[
"http://www.kingcounty.gov/healthservices/health/news/2013/13090401.aspx",
"http://en.wikipedia.org/wiki/Seattle_%26_King_County_Emergency_Medical_Services_System",
"http://www.komonews.com/news/health/King-County-may-be-the-best-place-to-have-a-heart-attack-210592381.html",
"That top link is particularly relevent, as it's straight from the county public health office. Keep in mind that I'm talking about where I'm at, as it says in that report the national average is closer to 10%."
] |
[
"I read your links, and it makes me slightly nervous that you are attributing that 57% cardiac arrest survival rate to CPR. First, none of what you posted mentions traditional CPR at all, furthermore, that survival rate is not from compressions/breaths CPR, but to early and effective defibrillation, and likely to a competent dispatch system, and rapid transport. I've been in the fire service twenty years now, and survival rates are increasing for cardiac events everywhere, because of the availability of AED systems in public places, homes, and on nearly every emergency apparatus. You're saving lives, and that's commendable, but your CPR skills aren't the reason. "
] |
[
"Would it be possible to create a larger scale experiment of a straw holding water?"
] |
[
false
] |
So if u put something over the top of a straw as it is in water, could u then create the same scene but say 10 times larger. Would this work? would the force of gravity pull it down?
|
[
"Excellent question! The bottom surface of the water in the straw (with water above it and air below) would be an unstable surface if not for surface tension. That is to say, although it's in equilibrium (if the surface were PERFECTLY flat and it were in a hypothetical zero-vibration environment nothing would happen), it's subject to something called the Ralyeigh-Taylor instability which means the surface gets exponentially wavier and wavier until the air bubbles up through the water and the water falls out.",
"So the Rayleigh-Taylor instability would make the situation unstable, but the surface tension of water stops waves/ripples from forming on the surface, making it stable again.",
"So there is a maximum width for the straw, which you could determine experimentally!"
] |
[
"In fact, we can do even better than this! Based off of the discussion of the linearized Rayleigh-Taylor instability in the Wikipedia article, I find that the maximum wavenumber of an unstable mode is sqrt(g * density / surface tension). Since I think the correct boundary conditions mean you have to have at least one half-wavelength (so one side goes up and the other down - this is the part I'm least sure about), the minimum width of a tube such that there is an unstable RT mode is pi * sqrt(surface tension / (g * density)), which in the case of water turns out to be 8.4 mm!",
"So, assuming my boundary condition reasoning is correct, if you have a normal-sized straw less than 8.4 mm in width, it ought to hold water without it dribbling out, but in a larger tube the surface would be unstable and the water would dribble out as the air bubbles up. (I'm sure the calculation isn't very accurate because of interaction with the walls of the tube, but it should definitely be in the ballpark).",
"If my boundary condition reasoning is wrong and you actually need a whole wavelength rather than a half, it's 17 mm instead. Either way, this agrees with our observations that the water stays in a straw, but falls out of a big drinking glass or bucket.",
"Note that if you use a fluid with less surface tension, like oil or something, or maybe even water with a bunch of detergent in it, it won't even work with a straw."
] |
[
"For fun let's calculate the critical width for some different liquids:",
"Water: 8.4 mm",
"Water + 11% ethanol (similar to wine): 6.7 mm",
"Vegetable oil: 6.0 mm",
"Ethanol: 5.2 mm",
"Hexane: 5.2 mm (gasoline is similar)",
"Liquid helium: 1.6 mm",
"Liquid nitrogen: 3.3 mm",
"Mercury: 8.0 mm"
] |
[
"Lorentz Transformation into a superluminal frame"
] |
[
false
] |
Using the laws of special relativity, we can show that if an airplane was travelling at a superluminal velocity in one frame another frame would exist where that plane is travelling backwards through time. My question is, what would happen in the frame of the plane itself? The Lorentz factor in the denominator would suggest it is travelling through imaginary space and time as it sees itself. In the context of special relativity only, is this correct, or is there a better interpretation?
|
[
"What you're describing is just the argument for why this is impossible. It would violate causality - a fundamental assumption of relativity. Therefore, if you want to consider superluminal velocity, you are no longer working with relativity."
] |
[
"How does what he's saying violate the Lorentz transformation"
] |
[
"We throw out the solution because its physically inconsistent with our expectations, but there is nothing mathematically forbidding an object with superluminal velocity in special relativity, correct? Isn't that what a tachyon is, at least hypothetically? If this is the case, then for a \"non-moving\" reference frame the results obtained from my superluminal plane don't, at least superficially, seem to contradict any sacred principles -- it moves in real space and forward in real time, maintaining (I think) causality as we expect it. I can switch to a different reference frame, however, where the plane seems to move through real space but backwards through time. Though this obviously violates causality, at least I can put some physical meaning to it through the mathematics. However, what happens in the frame of the plane itself seems unclear to me as it appears to move through complex space and time. I don't know how to put a physical interpretation on it, or if it's even possible to put a physical interpretation to this.",
"From my (limited, erroneous, first-year grad-student) understanding of special relativity it appears that an object cannot exceed the speed of light because to actually get to the speed of light one would need to supply it with infinite energy. Are there other reasons in special relativity to believe that the speed of light cannot be exceeded as well?"
] |
[
"What causes the throbbing in my head during a bad headache?"
] |
[
false
] |
[deleted]
|
[
"Typically headaches are caused by blood vessel inflammation in the dura of the brain. The dura is one of the most highly innervated areas of the body. These inflamed blood vessels are prone to spasm and tend to spasm severely with rapid changes in blood pressure (ie standing)",
"Therefore the combination of dense innervation (lots of pain receptors) plus spasming vessels = pounding or throbbing headaches."
] |
[
"The vascular theory of migraine has problems. For one thing, blood vessels routinely dilate and constrict without causing pain. And experiments in which blood vessels in the head and neck were artificially dilated by infusing saline solution failed to induce migraine-like symptoms.",
"Migraine headache is accompanied by vascular dilation in the head and neck, but that doesn't necessarily mean the vascular dilation causes the headache pain. There are other logical possibilities; it could be a third, underlying factor causes both the vascular dilation and the headache pain.",
"Adenosine, an endogenous (originating within the body) neurochemical, is the likely culprit:",
"vascular dilation <— adenosine —> headache.",
"Why standing can aggravate headache pain: Standing produces a drop in blood pressure in the head. The nervous system reacts to that drop in blood pressure by dilating blood vessels in the head and neck. This it accomplishes by releasing adenosine from neurons (nerve cells). The released adenosine dilates blood vessels in the head and neck in order to maximize the blood supply, and therefore the oxygen supply, to the brain, in order to prevent a shortage of oxygen supply to the brain, which could cause unconsciousness (blacking out).",
"Unfortunately that same released adenosine can also aggravate headache pain."
] |
[
"Adenosine.",
"Adenosine is the endogenous (originating within the body) neurochemical that causes headache pain and associated vascular dilation."
] |
[
"The \"face\" of the moon is always visible because of tidal locking. Are there any other common examples of this phenomenon that might help a rube like me to understand it?"
] |
[
false
] | null |
[
"Good question. ",
"Think about tides on earth. As the moon rotates around the earth it pulls a bulge of water around with it. It doesn't just effect the wate though, the moon also pulls the solid surface of the earth a little bit more on the closer face than on the other side.",
"A similar effect happens because of the earth's gravity on the moon, with the earth pulling the side of the moon that faces it. ",
"If the moon's spin was different from its orbital rotation (ie if we saw it spinning round from our perspective), then there would be a different section of the moon's surface experiencing greater pull. This section would constantly be changing and would cause massive tidal forces which would cause heating and friction.",
"Basically over time, it has settled into the most stable position. Nature typically does this - there is a saying \"nature is lazy\". For example: a ball is more likely to be at the bottom of a hill than the top because it is more stable there.",
"The most stable formation for the moon is effectively no spin (ie although the moon in spinning, this rotation matches it's orbit round the earth so that the earth and moon are tidally locked, and to an observer on earth the moon appears not to be spinning).",
"Ninja edit: ",
"There is some good information on this physics page here on todal locking",
". It concludes:",
"\"the fact that the rotational period of the Moon and the orbital period of the Earth-Moon system are of the same length is not an accident. Presumably this was not always true, but over billions of years the tidal coupling of the Earth and the Moon has led to this synchronization. In the case of the Earth-Moon system the synchronization is not yet complete. The Earth is slowly decreasing its rotational period and eventually the Earth and Moon will have exactly the same rotational period, and these will also exactly equal the orbital period. At the same time, the separation between the Earth and Moon will slowly increase in just such a way as to conserve angular momentum for the entire system.",
"\"Thus, billions of years from now the Earth will always keep the same face turned toward the Moon, just as the Moon already always keeps the same face turned toward the Earth. We will encounter other examples of such tidal locking in other pairs of objects in the Solar System\""
] |
[
"A semi-related fact: there are no maria on the lunar far side. Recent publication says that the maria (which are volcanic outflows) are the result of Earth's glow when the Earth was still molten, causing the lunar near side to also stay hot millions of years longer than the far side. ",
"article"
] |
[
"Because it's had lots and lots and lots of time to act on the water. It's like pushing someone on a swing. You give them a little bit of a push, but with the right timing (resonant frequency) the small pushes add up until the person is swinging with a much larger amplitude than the initial push alone would have done. In the same way the drag on the moon caused it to get tidally locked and is causing the Earth to become tidally locked, it's been resonating the oceans by sloshing them back and forth basically.",
"Gravitational acceleration from the moon on close side is approx 3.83e-5 m/s",
" (",
"http://www.wolframalpha.com/input/?i=mass+of+moon+*+newton%27s+gravitational+constant+%2F+%28distance+to+moon+-+radius+of+earth%29%5E2",
") while the acceleration on the far side of the Earth is approx 3.57e-5 m/s",
" (",
"http://www.wolframalpha.com/input/?i=mass+of+moon+*+newton%27s+gravitational+constant+%2F+%28distance+to+moon+%2B+radius+of+earth%29%5E2",
"), which is about hundredth of a hundredth of a percent of Earth's gravity (since one is going up and the other is going down, the total difference is about 7e-5 m/s",
" in the magnitude of the acceleration, compared to roughly 10: six orders of magnitude different).",
"But resonance over a long period of time is a powerful thing."
] |
[
"What happens to one's body after orchiectomy?"
] |
[
false
] |
I'm a 24 year old heterosexual male who has no intention of building a family or dating girls but instead dedicating my life to science and other pleasures. I'm interested if there are any negative side-effects (even the smallest one possible) of orchiectomy. Since I'm not interested in what most people want from life, I would be much more productive and focused on my interests if I had no sexual desire. Thank you.
|
[
"For those wondering, here is a ",
"link",
" explaining what an Orchiectomy is.",
"Edit:\nLayman speculating, I believe you would have a hard time finding a doctor willing to perform this procedure unnecessarily."
] |
[
"I agree that most doctors would be reluctant to perform this operation on an otherwise healthy man. They would probably require you to visit a psychologist and get approval from the hospital's ethics board before performing it."
] |
[
"It doesn't look like we are going to get a well detailed or scientific answer here. I applaud you for your decision, I have often thought of doing the same thing, but I fear the shadow of my time has grown too long while I played in the pools of destruction. I would encourage you to try to find other, similarly themed people; or if you were to find a mate (which would be good because although you might not want to you seem to be good gene stock for the next generation) who shares your views of science.",
"As for the changes to your body, there would be hormone level changes which might affect your physical appearance, hair and voice as well; as well as the effects on motivation and activity choice. Do you think that perhaps with meditation you can try to still your body so that the mind may be free?"
] |
[
"How Might Universal Expansion Affect Black Holes?"
] |
[
false
] |
I just had a field day with Wikipedia on the subject of black holes, so you'll have to forgive my layman' understanding of the subject. As I understand it, expansion will, at some point (assuming acceleration continues) lead us towards a "Big Rip" that will tear apart structures when expansion overcomes the strength of a given force holding that structure together. I also know that as space expands, the universe cools, so I would assume that once a given black hole reaches it's equilibrium point because of that, it will start shrinking (ignoring any matter that may still be falling into it). My question is, specifically, concerning the "direct" effects of expansion on a black hole, rather than its surroundings. So, would a "Big Rip" scenario rip up a black hole too? (If so, what would the fireworks look like? That energy has to go somewhere, right?) Or is the black hole itself immune to the ripping effect inside it's event horizon? (Or is it "apparent horizon" now? I don't quite remember how that one was resolved) Could expansion somehow accelerate the evaporation of the black holes? (If I remember right, the Rip, if it happens, will occur much sooner than the expected lives of most black holes, even in an empty universe scenario) [edit] Fixed some spelling.
|
[
"IIRC: black holes are expected to evaporate before any such \"big rip\" would occur."
] |
[
"As far as I remember, the Big Rip's most optimistic date is a meagre 103 billion years away (10",
" -ish years), where the expectant lifespan of black holes with only a single solar mass (most are far bigger than that) is the the order of 10",
" -ish years. I don't even think there's a name for that! And keep in mind that the evaporation rate is INVERSELY proportional to the mass of the black hole SQUARED (anyone want to crunch the numbers on the expected time for a super massive one? Billions of solar masses must be ridiculous). And ALSO keep in mind that most black holes aren't even shrinking yet! (The CMB is feeding them enough energy to outweigh evaporation)"
] |
[
"oh well so it is. I was mistaken in thinking about the big rip vs. just the general accelerating heat death of the universe. I guess the answer to your question probably depends on the nature of dark energy then. I don't know much about those two scenarios. I think some recent data suggested one scenario was more likely than the other, but I can't recall which it was."
] |
[
"Why is styrofoam squeaky?"
] |
[
false
] | null |
[
"There was a good answer to a very similar question ",
"here",
" a few months ago:",
"Styrofoam is mostly air, and is otherwise walls of the polymer polystyrene. The reason that it is so squeaky is that when something rubs against it, on the microscopic level, there is a \"stick-slip\" interaction between the surface of the box and, say, your finger. When you \"stick,\" friction compresses the small bubbles (walls) of the polymer, and when you \"slip,\" your finger moves to a new spot. In this time, your finger is off of the surface, and the bubbles that you compressed now expand, contract, expand, contract, and do this at the frequency (-ies) that you hear the squeak. It is loud because the entire box effectively acts like a resonator- the energy dissipated from the scene of the \"stick-slip\" causes secondary oscillations from neighboring bubbles.",
"Dip your finger in grease, which will cause less of the \"stick\" when trying to recreate the squeak. No sound, right?",
"This is all based on friction between the \"sticky\" polystyrene and (using a musician word here), a mallet."
] |
[
"There's a name for the effect: stiction",
"http://en.wikipedia.org/wiki/Stiction"
] |
[
"That name is proof that scientists can have fun too."
] |
[
"Why does voltage increase when the resistance increases?"
] |
[
false
] |
Correct me if I'm wrong but I think that's what happens but I don't understand why it works like that.
|
[
"The V = IR law we learned in school has a lot of analogies to other physical phenomena, like fluid flowing through a pipe.",
"Voltage is like pressure",
"Resistance is like the width of the tube",
"Current is like...well...the current, the speed of the fluid",
"If you imagine, increasing the resistance by decreasing the width of the tube makes the fluid passing through the tube have a higher pressure (considering fluid flow stays the same). ",
"If fluid flow can vary, or if fluid pressure is invariable (like liquid, an incompressible fluid), then an increased resistance will cause increased current instead (like squeezing a water hose to make the water spray out faster)."
] |
[
"Thanks that goes in to more detail. I understand it now. Thanks again"
] |
[
"I think of current more like the volume of water, not the speed. All electricity moves at the same speed. ",
"It all depends on what you hold constant. If you increase resistance in a normal circuit powered by a constant voltage source, like a battery, you will therefore decrease the current. If you want to maintain a constant current while increasing resistance, you will have to increase voltage. "
] |
[
"What variables make some viruses deadlier than others?"
] |
[
false
] | null |
[
"Most of the deadlier viruses display a certain type of homing behavior in specific groups of human cells through epitope matching on viral structures, like surface glycoproteins. This makes certain viruses difficult to control and eradicate by your immune system. For example, HIV uses Th4 lymphocytes and macrophages as its main replication reservoirs, which are crucial in maintaining and coordinating immunological function via release of cytokines. By disabling T-cell mediated immunity, it leaves your body particularly susceptible to infections and tumors, as no inflammatory cytokines can be produced, leading to inadequate immunity. ",
"Other viruses like the filovirus ebola does the opposite, wherein infected monocytes undergo an OVERproduction of cytokines, leading to an induced septic state, damaging endothelial cells and increasing permeability of blood vessels, leading to catastrophic bleeding.",
"Yet still, certain types of viruses are able to use its own or the host's cellular machinery to produce things that downregulate inflammation, or act as decoy signals which bind important inflammatory mediators. ",
"Some viruse classes (e.g. herpesvirus) steal a portion of the host cell's surface phospholipid coat as as the virion buds the cell, making it harder to be detected by the patrolling white blood cells (think of it as wearing a camouflage suit). On that note, herpesviruses can actually travel retrograde along nerve axons and take up refuge inside what are called sensory ganglions, where it remains dormant, until the host environment becomes more favorable (immunosuppression due to chronic stress, smoking, diabetes, etc.), at which time it reinitiates replication and manifests as either another outbreak or shingles, in the case of varicella zoster. In its dormant state, herpes is almost non-immunogenic and can remain stable for decades or more (hence the joke herpes lasts longer than diamonds).",
"Last thing I want to mention: certain types of viruses (like HPV, Epstein-Barr, anf HTLV) are also capable of causing cancer. Research is being done on their pathogenesis, but current literature suggests it's a combination of viral oncogene products (e.g. E6, E7, TAX, REX proteins), increased host cell turnover rate, immunomodulation, and in the case of retroviruses, incorporation of viral DNA into critical tumor suppressor genes. ",
"BROADLY speaking, all of these sort of viral \"behaviors\" are called \"virulence factors\", and there are far more than what I can describe here. Viruses are incredibly fascinating and terrifying at the same timeI. If you are interested, I recommend you look into it some more."
] |
[
"For example one may target more important cells like the immune system. Whereas another may target the resperatory sytem.",
"These are not variables, but specific behaviors as a consequence of the genotype.",
"Variables would include, in this context, for example, e.g. RNA mutation rate with defined mutations beneficial to the viral pathogen according to the selection pressures, etc..",
"Variation in RNA Virus Mutation Rates across Host Cells"
] |
[
"It would be in the genetic information carried in the virus, deadly viruses carry instructions to self replicate and destroy the body in the process. As such some viruses are more harmful because they contain instructions that are better. For example one may target more important cells like the immune system. Whereas another may target the resperatory sytem. Whilst both could kill you, targeting the immune system is more dangerous."
] |
[
"Is there a commonly accepted theory on how life evolved from single celled organisms to multi-celled organisms, or is it a complete mystery?"
] |
[
false
] | null |
[
"This is an odd way to formulate the question, but we can take a stab at a satisfactory answer. Multicellularity has evolved numerous times, multicellular organisms are not one lineage. The genus Chlamydomonas has developed lineages which differentiated cell types only to eventually revert back to unicellularity, while other lineages, like the closely related Gonium genus, have developed into a stable multicellular lineage without reversion.",
"This type of development is not conducive to the development of 'one commonly accepted theory' - each organism is different, and the nature of any historic development of multicellularity in the ancient past will always be uncertain. But, to be sure, the mechanisms by which multicellularity are developed and expressed are ",
"extremely well understood",
". One common path to multicellularity involves two functional steps:",
"the ordered division of one cell to generate a number of cells that are organized in a predictable fashion.",
"the differentiation of cell types within an individual organism.",
"That is all that is required, pretty simple when you think about it. A unicellular organisms ordinarily undergoes the multi-step process of cellular division in order to result in two copies of the same cell, which then go their separate ways. In order to become a multicellular organism all that is required is that the division be incomplete, resulting in a cytoskeletal superstructure or extracellular matrix which binds both the dividing cell and its progeny into a single unit, if these cells then perform exclusive but complementary functions this organism is now multicellular. ",
"The textbook excerpt that I linked above is extremely detailed, it will walk through several organisms to show the different levels, and potential stages of development, for the expression of multicellularity. The process is sufficiently well understood that we can take unicellular lineages and ",
"induce the development of multicellular colonies",
" over time."
] |
[
"This depends, to a great degree, on what exactly one considers to qualify for multicellularity. I cannot provide a definition that will be satisfactory to all people in the field. ",
"I think we could refer to the nature of some ",
"desmids",
" where an isthmus divides a single cell into two distinct functional compartments which share a nucleus. Is this a 'bicellular' organism? No, but it is illustrative of a certain continuum which we are trying to pin down with the term multicellular.",
"Members of the order ",
"volvocales",
" which are discussed in great detail in the textbook that I previously linked exhibit many different types of multicellularity. It is possible that there is an individual which is just two cells, but I am not aware of one which is specifically characterized in this way. ",
"This may be an arbitrary addition, but very many multicellular organisms were, at one point in their life cycle, just two cells, but this is due to the nature of cell division not the nature of the evolution of multicellularity as a characteristic of organisms. As to the idea of a 'clump of attached cells sharing nutrients', it might be best to refer you back to ",
"this text",
" because the characterization may not be representative of how we understand these organisms to have developed. "
] |
[
"Thanks for the answer! Would you say then that the first multicellular organism only had two cells? Or would it have been a clump of attached cells sharing nutrients? "
] |
[
"If I am standing still on earth, how fast am I moving from a third person universal standpoint."
] |
[
false
] |
I know I'm sure it has to do with inertial frames and relativity but this problem has stumped me for a long time. Accounting for earths rotation, revolution around the sun, the solar system floating through our galactic arm, the entire galaxy rotating, and gravitational interactions between galaxies how fast are we really moving if a person were watching you outside of gravity's hold.
|
[
"You still have issues with how you define a stationary observer. I believe that you could make a case up to the galactic level to defining the galaxy center as stationary, but above that I believe that it would be difficult to justify defining a reference frame as stationary."
] |
[
"The view point you're talking about doesn't exist. ",
", ",
"here's a site",
" that will probably give you what you're looking for."
] |
[
"yes, that site is very helpful but like they said at the end, those results are just added together, they have nothing to do with vectors :(. As for the view point. If you were say at the exact place where the big bang happened and not moving at all, everything would be moving away from you so you could use that as a universal reference right?"
] |
[
"Is there any evidence that playing a frequency similar to that which our brains interpret would cause it to temporarily change?"
] |
[
false
] | null |
[
"Are you asking whether human bodies have some kind of resonant frequency in the way that, for example, a wine glass does? I don't really understand your question."
] |
[
"My bad. That is a very good point. In that case, would the human body have a resonant frequency? If it does, is it possible to find out what it is? Will it have multiple resonant frequencies? ",
"Thanks for your response :)"
] |
[
"I think OP is just taking about Abby effects on the body from specific frequencies. There are a lot of different ways for this to happen though. The aforementioned resonance frequency as well as the brown note (mythbusters), effect of high amplitude frequencies outside hearing range, frequency patterns changing brain waves. ",
"less related are high frequency white/pink noise causing agitation as well as sound based weapons/deterrents. ",
"This could be a big discussion...."
] |
[
"How far back in history would I have to go before people couldn't understand the modern english I speak?"
] |
[
false
] | null |
[
"It looks as though the comments so far are suggesting around the time of Chaucer, and they seem to be doing so based on how intelligible ",
" Middle English is to a modern reader. However, this is misleading; English pronunciation has changed much more than our spelling has. Looking at the written text is NOT a good way to judge, at all! ",
"That said, the answer to your question is going to depend on how strictly you define \"understand,\" because (a) it's a continuum, and (b) it depends on your own ability to cope with an unfamiliar accent/dialect. (Have you ever been in a classroom where half the people couldn't understand the TA, and the other half didn't see what the problem was?)",
"If I had to choose I would pick some time during the latter half of the ",
"Great Vowel Shift",
". This was a series of changes in the pronunciation of English that shuffled around the vowels significantly. Before the Great Vowel Shift, many English words were pronounced with completely different vowels than they are today. This process started ",
" Chaucer, and ended before Shakespeare.",
"Here",
" is a page with audio of people reading Old and Middle English poetry in reconstructed pronunciations, with a lot of Chaucer. Personally, I don't think it's very understandable at all, although I can pick out a few pieces. (Lots of words, fewer sentences. Concentrating on picking out words makes it harder to interpret the stream as a whole.)",
"As a side note - while it is true that we don't have recordings of people from Chaucer's era speaking, and that there are some remaining questions, on the whole we are pretty confident about how they were pronounced. It's not just complete guesswork; linguistics does have methodologies for reconstructing historical pronunciations.",
"EDIT: ",
"Here",
" is a page with side-by-side audio of Middle and Early Modern English. If someone told me that they could understand most of the Middle English without knowing the passage and without prior practice, I would be quite skeptical. Early Modern English is by comparison practically the same as what you speak now. Of course, in a scenario of being dumped in the streets in 1380s England, how tolerant would people be of you asking them to repeat? Communication can be cooperative, and if you grant that pantomime, slow speaking, repetition, and such are part of your scenario of \"understanding,\" then you may be able to get by.",
"Though you might have some trouble if you want to buy some ",
"egges",
", depending on where you end up.",
"EDIT 2: Why was I not prepared for the flood of comments about how it's actually understandable? I wish I could do speech perception experiments on everyone who's said it's easy, because you might be a group of stellar performers.",
"EDIT 3: GUYS, THE BEOWULF PASSAGES ARE TRANSLATIONS. "
] |
[
"I would just like to add that even the excellent audio links you provided under-demonstrate the actual difference between spoken Modern English and earlier varieties, because those recordings are of Modern English speakers reading ",
" language slowly and carefully. If you were to drop in and talk to your average Aethelrad, they would be speaking much more quickly and with much less care. You could go back farther and still be able to understand a poetry reading than you could to have a conversation at a pub."
] |
[
"As a foreigner who has learned English as their third language and now speaks it fluently (living in the US), I'd be curious to find out if there have been studies about near-native speaking foreigners understanding these type of recordings better.",
"I'm curious, because anecdotally, I actually understand all of these recordings just fine, but then again, my personal experience is rather biased since I also talk with a lot of English speaking people from India, Ireland, Scotland, England, and all over the US on a regular basis. So, I'm also wondering if this could be because I am so well versed with so many modern English accents."
] |
[
"Why don't the tides bring the moon closer to the Earth?"
] |
[
false
] |
[deleted]
|
[
"To put it colloquially: ",
"Imagine the moon suddenly went twice as fast. Its speed would be so large it would \"overshoot the corner\", escape earth gravity and float further and further away from earth.",
"Imagine the moon suddenly lost all its speed. It would no longer orbit, but fall straight down."
] |
[
"A spacecraft in orbit that accelerates forwards ends up in a higher orbit. Even if you fire forwards/downwards at an angle. You increase the energy and angular momentum, which leads to a higher orbit. Same for the Moon.",
"For an idealized circular orbit the radial force doesn't even matter for orbital changes. It just determines the distance/velocity relation but not changes in the orbit."
] |
[
"Because it increases energy and angular momentum.",
"The radial force is not strong enough to keep the Moon on its circular orbit at the increased velocity. A trajectory that is curved less goes to a larger radial distance."
] |
[
"Does anyone know the Emissivity of Molten Aluminum?"
] |
[
false
] |
I can find all kinds of charts for oxidized, polished etc, but not molten.
|
[
"12% at 700 C\nSee ",
"this book",
", page 57."
] |
[
"Emissivity is usually provided as a number between 0 and 1. Like a percentage is. Emissivity of 0 is a perfect reflector, emissivity of 1 is a perfect black body. "
] |
[
"It was in the book that ron_leflore pointed to in the first response of this thread. 12% (or 0.12) at 700C. "
] |
[
"How does the body create so much mucus so fast and where is it stored?"
] |
[
false
] |
[deleted]
|
[
"You have specialized cells in all of your mucus membranes (mouth, sinus, GI tract, etc.) called goblet cells. They are interspersed within the cells that line the cavities and are always producing mucus to lubricate and protect the surrounding cells. When you have an infection, mucus production is sped up as a form of protection to try and keep the bacteria/virus out of the tissue (specifically out of your blood). It is especially ramped up in your sinuses because the mucus there will either be blown out of your nose or flow down your pharynx, into your esophagus, and then digested (destroying the included infection) in your stomach."
] |
[
"No you should. Your body views your sinuses, mouth, GI tract, lungs, ect. as external areas because they are open to the environment. By blowing your nose you are increasing infectivity to other people but what your body cares about is to keep the infection in its \"external\" environment. (if it's bacterial, the contagious aspect of the infection is real low unless someone directly transfers it to their membranes).",
"Think of an infection like a war. In war, you want to keep your enemy as far away from your vital resources (brain, heart). Your front line is your mucus membranes and skin. They are physical boundaries. To keep the integrity of your physical boundaries intact, you need to keep the enemy from sitting on the same spot and breaking through (just like the fortress in LOTR Two Towers). You blowing your nose and your membrane brushing (mucociliary movement) mucus into your stomach.",
"If the infection breaks through the physically barrier, inflammatory response and immune response rush to the break to try and kill the infection now in the tissue and to patch the breach. This is why you see those disgusting sores when you see MRSA YouTube videos. Your body has given up on patching the breach and is now trying to surround the infection to isolate it from the otherwise healthy body. This is known as an abcess.",
"Let's say that their fiction is really virulent or you are immunocomprimised and the abcess now fails. You know have the infection free in your body and once it hits your bloodstream, it has free access to all of your tissues except the CNS (brain). This is known as bactermia. Your body keeps fighting the infection but now it has access to almost all the corners of your body.",
"Let's say that your immune system just can't keep up with the infection now. The infection now has free run in your body except the CNS. Your body is now in septic shock and your blood pressure is really low because you have inflammation (increased fluid in tissues) throughout your body. This is the last step before death (the fall of your fortress).",
"I pulled the CNS out because there is the blood brain barrier that keeps your central nervous system separate from the things in the blood. If you have an infection in your CNS (the most common being meningitis which occurs with certain bugs and the patient is either immunocomprimised or there is a breach in your blood brain barrier or lining of the CNS (dura mater)."
] |
[
"This is a good answer. :)"
] |
[
"How does gravity work in a Dyson sphere?"
] |
[
false
] |
Let's say that a Dyson sphere has the same mass as Earth with the same circumference. If you were on the inside surface would gravity pull you toward the center of the sphere or toward the surface?
|
[
"This is why Ringworlds are more likely constructs than Dyson spheres. You can spin up a ringworld for artificial gravity."
] |
[
"The gravity inside a spherical shell of uniform density vanishes. No matter where you are, gravity pulls you from all directions, resulting in a net force of zero (this is a lot of handwaving, as it works only for a spherical shell, but I think you get the gist). That is, the Dyson sphere would have no effect whatsoever on gravity inside it."
] |
[
"what would happen to the atmosphere in a spinning Dyson ? "
] |
[
"Can fish survive in carbonated water, or would they suffocate?"
] |
[
false
] |
Would there be any other side effects if the carbonation is not grounds for suffocation?
|
[
"Saltwater fish?"
] |
[
"Saltwater fish?"
] |
[
"/u/divestrong",
"'s post says \"saltwater are less salty than the surrounding water,\" and ",
"/u/NegativeX",
" is just trying to clarify divestrong meant saltwater fish."
] |
[
"If electrons in an atom are actually in probability clouds instead of a set orbit, then how can London Dispersion Forces exist?"
] |
[
false
] | null |
[
"Electrons don't have to be discrete particles for the dispersion to occur. They can change the shapes of the \"probability clouds\" of electrons in other molecules, though, because electromagnetic forces still very much come into play in quantum mechanics.",
"LDF actually relies on quantum mechanics."
] |
[
"The orbitals are very dynamic. Just because the Bohr model of an electron orbiting around the nucleus is wrong that doesn't mean that the electron distribution doesn't change as molecules move around and interact with each other. "
] |
[
"Yap. Orbitals have distinct shapes that we can/have calculated, so it makes total sense that the shape could be altered by an external field."
] |
[
"Are the risks associated with vaccinating against tetanus greater than the risk of contracting the disease?"
] |
[
false
] |
I am very pro vaccination; however, my hippy friend is always posting shit against vaccination on Facebook. She did make a fairly good point (if it's true). "You get 5 doses by age 6. Side effects include swelling of entire limb (1/30), vomiting (1/50), seizure (1/14,000) and permanent brain damage (1/1Mill.). 50% occurs in folks over the age of 50 with an average of under 30 cases per year. Which led me to wonder what kind of chances of getting tetanus are? That is 1/10Mill. So you have a higher chance of permanent brain damage than actually getting tetanus."
|
[
"The reason why there's a 1/10,000,000 chance of tetanus is because vaccinations have helped lead to eliminating tetanus in countries that vaccinate. ",
"Also, seizures and brain damage can be the result of a pre-existing condition. That's always a possibility. But there isn't any real evidence stating there is a link between those hyper-severe issues and the vaccine. The ",
"CDC",
" states so. Although if your friend is a real hippie, like that, she might not listen to what a gov't agency has to say. ",
"Vaccines are why we don't have horrid rates of preventable diseases and conditions. ",
"Babies, especially, need every chance to build their immunity, as it develops during the first year. A mother's body can only do so much. ",
"And with tetanus having a 20% mortality rate, a swollen limb and sour stomach are not too bad. "
] |
[
"That's the way I understand it. People who don't vaccinate weaken our herd immunity. This is why it angers me so much. I understand there will be stupid and ignorant people and I've stopped caring as I know you can't change them.",
"But it really heats me up when their ignorance can potentially harm my child. It's where I draw the line, so I speak my opinion on the matter regardless if I lose a friend or not."
] |
[
"There's an episode of House that kind of explains it. Probably not the most credible source, but they did their research for the show.",
"Usually people who don't vaccinate claim it's government conspiracy for health care profits and chemicals. And if they do know what a vaccine is, they don't understand why it's effective. ",
"And that's the dangerous thing. Non-vaccinated children can still be a serious health risk to those who are. "
] |
[
"With current technology, how high can we build a skyscraper."
] |
[
false
] |
Theres lot of talks about space elevators and etc. How about a spiral road to space? haha yea pretty stupid, but i can still dream.
|
[
"I heard that we don't really have a material that is strong enough to support itself to construct a space elevator. Can you provide any evidence one way or another?"
] |
[
"I heard that we don't really have a material that is strong enough to support itself to construct a space elevator. Can you provide any evidence one way or another?"
] |
[
"Limiting factor is definitely structural. It's not the height that matters, though. It's the shear force. A tower of any height is going to be affected by wind. The elasticity of the material has to be enough to hold the mass of the tower in place when the bottom is anchored in place and the top is being blown around - but not so elastic as to allow anything dangerous to happen. The forces involved are not small - iirc, as you go higher, wind speed norm can be 200kph or higher?",
"[edit: kpw->kph ]"
] |
[
"Does octave equivalency show any sort of property in physics, or is it a completely perceptual phenomenon?"
] |
[
false
] | null |
[
"Yes. First thing to understand is timbre. When you play a note, you hear a collection of frequencies. The note you're playing is the loudest frequency but there are other more quiet frequencies being produced concurrently. This is what gives an instrument's tone character, and makes a flute and a trumpet sound different. ",
"Take a flute for example. You can model it as a cylinder of air open at one end, and write out the harmonics. These are shown in the figure labeled \"",
"Harmonics of open air column",
"\". When you play an A4 at 440 Hz, that's the loudest frequency - but the timbre comes from other allowed harmonics. Frequencies playing at 880Hz, 1320Hz, 1760Hz, etc. with power decreasing as you go farther from the fundamental at 440Hz. ",
"Let's go up an octave. When you play an A5 on the flute, what a surprise! The fundamental frequency is now at 880 Hz, with harmonics at 1760Hz, 2640Hz, etc. When you overlay those two, you notice some of those timbre frequencies line up, and the sounds \"agree\". Not all resonators follow this principle, but in general strings that aren't suspended at weird points and cylindrical air columns do. ",
"440 ",
" 1320 ",
" 2200 ",
" ...",
"\n",
" ",
" ",
" ..."
] |
[
"Pitches an octave apart are in 2:1 ratio with respect to their frequencies. This is true of all octave intervals. The brain experiences then as similar because their information content (in terms of pitch) ",
" very similar."
] |
[
"This is an excellent explanation and what I was going to say. If you listen to pure sine waves at octave intervals, you can hear it, but not as definitely as in an instrument, and this is specifically because of the shared overtones you hear on top of the pitch."
] |
[
"Why must a vacuum be 'filled'?"
] |
[
false
] |
This is something that's always bothered me. I understand the idea of a vacuum and suction, but I always wondered why it happens. Why is it that a vacuum cannot exist beside matter? What is it that causes nature to fill the vacuum? Lastly, where does the energy to facilitate the movement of the matter come from? It seems to me that it is quite literally that is pulling the matter into the vacuum, and I can't make sense of it.
|
[
"Random movement of particles results in a transition of molecules from a place with high density to a place with low density.",
"Let's assume that there are two enclosed regions - one is filled with air and one is a vacuum. In the one filled with air, the air molecules are colliding with each other and with the walls. Now let's imagine we open a hole between these two regions. The molecules that collide with the walls and other molecules continue to do so, but the molecules with trajectories towards that hole have nothing to collide against. So they travel to the other region. This continues until we reach an equilibrium between the two regions - that is, until the number of molecules traveling from one to the other is equal in both directions.",
"As an analogy, imagine a supermarket. In the morning, it is empty. People enter, and the number of patrons in the market increases (higher pressure, reduces the vacuum). Over time, those patrons will finish their shopping and leave, while more will come in. Eventually you will reach an equilibrium and the number leaving will be approximately the same as the number entering.",
"In the case of the molecules in a vacuum, what makes them \"enter\" is simply momentum - an object will travel in a straight line until affected by a force."
] |
[
"There is an unbalanced force of air on the opposite side of your hand. ",
"\"Suction\" is actually an emergent phenomenon, it isn't a real force. What is happening is that there is higher pressure on the opposite side of your hand, and the unbalanced force of the multitude of particles striking your hand on that side pushes your hand towards the vacuum."
] |
[
"Why does a vacuum literally suck onto my hand if i were to suck the air out of a bottle, and put my hand on it.",
"Is that just air pressure?"
] |
[
"What is the most habitable celestial body besides Earth? If we had the technology, what would the best celestial body be to move to?"
] |
[
false
] |
This is obviously inspired by NASA and SpaceX wanting to get to Mars. SpaceX want to inhabit Mars but as it seems like a hellish place to live, what other celestial body's are out there that are closer to Earth. There are so many factors here like does the body have a thick atmosphere, magnetic sphere, water and breathable air. Has there been study's of the many celestial objects we've observed to find out which one is the most Earth-like?
|
[
"rotating habitats inside the holes we’ve drilled in asteroids to mine them",
"it protects from radiation, provides the precisely desired artificial gravity, and is way easier to transport to/from than the gravity well of a planet",
"plus there’s way more room in the solar system for these habitats than there is on the surface of all the planets"
] |
[
"Few asteroids are likely to have the structural strength to hold together under rotation. You'd probably want to process the material into something more robust and cohesive."
] |
[
"no asteroid rotation is required",
"cylindrical rotating habitats within holes drilled in asteroids from mining doesn’t turn the asteroids"
] |
[
"What is going on in this picture?"
] |
[
false
] | null |
[
"I am going to take a stab at this, and offer a hypothesis. The arm does not move in straight lines, but in arcs. I would assume that as the hand is moved down, there is a tendancy for it to also move toward a natural position in front of the shoulder. If this is the case, then the only scratches directly below the reader would be due to people who stood in line with it. If they stood to the left, then it would scratch the left (as the hand moved toward the shoulder) and standing on the right would scratch the right. If I were a spiffy science type I could then do a statistical analysis on the scratch pattern to see if it fit the distribution one would expect for this behavior. Also I could get some friends (left clueless so as not to ruin the experiment) to swipe a card while I watched carefully, taking notes on the position of the shoulder relative to the reader, and where the card struck. I would also make sure that said friends were selecting my favorite beverage when they slid their card, since science makes me thirsty."
] |
[
"Right-handed vs Left-handed people?"
] |
[
"This is on the right track. It's probably a combination of where you are standing when you swipe your card (directly in front of the machine or offset), and whether you use your left or right hand to swipe.",
"Just as an experiment, hold your arm out in a \"swiping\" position, and try to recreate the mechanics of making a completely vertical motion. I find that the swiping motion of my arm goes both down and towards my torso; as my elbow lowers, it naturally ends up closer to my rib cage. ",
" I'm no biomechanist, but I do frequent soda machines."
] |
[
"What is happening when we focus on one particular noise?"
] |
[
false
] |
[deleted]
|
[
"Auditory Scene Analysis",
" is a branch of cognitive psychology, I believe. Like you said, humans are able to focus on specific streams in a loud environment. Also, humans are able to cue in to ",
" conversations that were previously not being listened to. This is called the ",
"Cocktail Party Effect",
". Imagine vacationing overseas, being at a noisy cafe, chatting with somebody, and suddenly you hear the name of your hometown coming from a table near you. You weren't paying attention, there is really no reason why all your attention should suddenly go to this other conversation, but it does. ",
"All we know is that auditory processing is a lot more complex than just analyzing a stream of sound (bottom-up processing). Certain things are actively attended to (your name, personally relevant details) which is called top-down influence. My answer to your question would be \"pending more research\". "
] |
[
"I've noticed that when there's nobody with me, I can turn the tv way down and still catch everything that's being said. If there's a noise though, it takes a few seconds to get back on track. It's pretty interesting how much processing goes on when you hear."
] |
[
"Yes, I can be in a very crowded, distractingly loud environment, but if somebody says my name, I can hear it clear as day. I didn't know there was a name for it."
] |
[
"Is reading on a higher resolution display (such as Apple's Retina Display) any better on your eyes then reading on a display with lower DPI or is the difference purely aesthetic?"
] |
[
false
] | null |
[
"For the sake of this post, lets assume we are looking at text with the same font size on both screens, but one is obviously a bit more pixelated (say, comparing a PDF at 100% zoom on an iPad 2 vs. an iPad 4). "
] |
[
"It's mostly the size and not the DPI that matters if you are getting a headache from reading too much on your screen(also the light from your screen compared to the light around the screen), unless you are having a REALLY low resolution.",
"If you have high resolution then many texts will be smaller than normally, so you would need to make it bigger normally."
] |
[
"As long as you have a decent resolution, it's size of the font that matters, not super high resolution. Eye strain is worse when reading small text."
] |
[
"Why don't we feel pain we haven't noticed yet?"
] |
[
false
] |
If I scrape my knee and don't realise it's bleeding, it won't hurt until someone points it out later. And then it REALLY hurts. If I saw myself get damaged though and therefore have some level of assumption that it's going to be damaged, I can feel the pain already. It's just kinda funny, whats the point of a 'damage attention alert' system if we have to already perceive the damage before it goes off?
|
[
"Pain has unusual perceptual qualities compared to other sensory inputs. It is significantly gated by things like attention and anxiety. There are lots of reports of fairly significant injuries being sustained in sport or battle that are largely unattended until the sport or battle alert lessens. ",
"The point of the 'damage attention alert' system may be that if you are attending heavily to something else, modest damage can wait. "
] |
[
"When we're talking about intensive stuff like sports or battle, isn't adrenaline also a factor in this?"
] |
[
"People use the term \"adrenaline\" generically to refer to a heightened state of arousal/attention caused by some context. In that sense, yes. In a chemical sense, no, as the blood-brain barrier is essentially impermeable to adrenaline from the adrenal glands. Because it cannot impact the central nervous system, it has little impact on the gating of pain by attention. "
] |
[
"How does the iterative process that provides Graham's number not violate the pigeon hole principal?"
] |
[
false
] |
[deleted]
|
[
"How would it violate the Pigeonhole Principle? ",
"Do you mean \"Why can we describe Graham's Number, even if we can't write it down in base 10?\" This comes down to the meaninglessness of decimal expansions and the power of mathematical notation and human invention.",
"Decimal expansions tell us next to ",
" about a number. There are no intrinsic properties of numbers that depend on how we write it in base 10, base 2 or any other base. Rather, decimal expansions give us information about how the base number views other numbers. The base 10 digit expansion of a number tells us more about 10 than it does that number. For instance, the number of zeros at the end of a decimal expansion tell u show many powers of 10 go into that number. The final digit of a number tells us the remainder of this number after dividing by 10. The base 10 expansion tells us how 10 views a number, but doesn't tell us anything intrinsic about a number.",
"You commonly hear people ask if primes are different if we write them in different bases. The answer is definitely No. We learn almost nothing about a number based on it's representation in base 10, decimal expansions are different ways to look at numbers but don't tell us properties like primality.",
"A related concept are ",
"p-adic Numbers",
" which create numbers by looking at their expansion via prime numbers. But the created numbers tell us about the prime that we're expanding with respect to, rather than anything about the actual numbers.",
"So the fact that we can't write Graham's Number in base 10 is just a property of the smallness of 10 compared to the size of Graham's Number. That's it. Compared to 10, Graham's Number is so large that the decimal expansion is too big to write down. You could also see it as a smallness of the universe compared to Graham's Number, the physical universe is too small to be able to represent Graham's Number. But these are properties of 10 and properties of the universe, not Graham's Number.",
"This is where the power of mathematical notation and human creativity/invention come into play. The universe is so small that it can't contain Graham's Number, but math is not of the universe, so we're not going to let that stop us! Using up-arrow notation, we can represent very large number using a small number of symbols. Each symbol carries behind it tremendous power. How do extend the idea of multiplication being repeated addition? Or exponentiation being repeated multiplication? We can extend this in concise ways to higher order things via up-arrows. We can then concisely assign large quantities of up-arrow date via the g(k) notation of which Graham's Number is g(64). ",
"Graham's Number has a ton of information. So much information that the universe can't contain it. But that can't stop us from finding ways to construct and express it concisely. Heck, in Base Graham's Number, Graham's Number is 10."
] |
[
"Could you outline your reasoning? I don't know why you would think that.",
"Graham's number is \"compressible\" in the sense that it has a relatively small Kolmogorov complexity(for a number as big as that): you can write a computer program that computes it and is way shorter than actually writing the number out. (The Kolmogorov complexity of a string in a given computer language is the length of the smallest program in the language that outputs the string)."
] |
[
"It's a property of the number, but nothing intrinsic about it. You're comparing how it looks compared to 10 rather than discussing properties of the number. ",
"Intrinsic properties of a number include whether it's prime or not. Slightly related, how many primes divide the number. The sum of the divisors of a number. Whether or not it is a Perfect Number. And so on. None of these things depend on how we write a number down, it just depends on what that number actually ",
". The sum of digits of a number is a property of what base we write it in. Whether or not it is palindromic is a property of how we write it and what base we write it in."
] |
[
"Is it possible to invent an engine with the same efficiency as the Carnot cycle?"
] |
[
false
] |
I know the Carnot cycle is the maximum efficiency in which any cycle could have, but is it possible to even achieve that in an engine?
|
[
"The short answer is no. The Carnot efficiency is, as you said, the maximum efficiency that a heat engine can have. It assumes that things like friction, wear on moving parts, vibrations/sounds induced in the engine, etc do not exist. These things will always be present. Friction is certainly not going anywhere, since an engine is generally going to be moving/turning something. The Carnot efficiency is a limitation placed on us by the laws of thermodynamics, it tells us how good our engine could be if we made it out of frictionless, infinitely strong, infinitely stiff material. "
] |
[
"At that point the assumptions behind the model of a heat engine go out the window. Quantum effects allow you to get around various classical laws in very controlled conditions."
] |
[
"I can't find a mention of efficiency in that article."
] |
[
"Would Spacetime Curvature Affect Gravitons?"
] |
[
false
] |
I've always been confused as to how to reconcile gravity being a pseudo-force (space curvature) with a quantum mechanical idea of gravity. If gravity IS just curvature of spacetime, would gravitons still move through it? Or is gravity just affecting objects in some non-fluid space in a way that makes it SEEM like space is curving?
|
[
"There's been several historical approaches to handling gravity quantum mechanically and the general consensus is that any effective spin-2 massless field theory is by default a theory of gravity",
"It's better than that. There's exactly one massless spin-2 theory (which is local, 4D, ghost-free, etc.) and that is nothing other than general relativity."
] |
[
"There's been several historical approaches to handling gravity quantum mechanically and the general consensus is that any effective spin-2 massless field theory is by default a theory of gravity (this is the position a lot of string theories take since they have such fields--therefore a lot of string theories are by default quantum theories of gravity--and there's some good theoretical justifications for this). In the Feynman lectures on Gravitation he derives Einstein's field equations from first assuming a quantum theory and deriving the classical result--in this interpretation, gravity acts on objects (and itself!) on flat-Minkowski spacetime (aka Special Relativity), the geometrical interpretation that spacetime is literally bending and changing from mass-energy distributions (stress-energy tensor) isn't brought up until late in the lecture. Feynman wasn't the only physicist to de-emphasize the geometrical interpretation in favor of a more particle centric viewpoint and Weinberg wrote a pretty good textbook formally enshrining this.",
"However, most physicists use the geometrical interpretation by default and textbooks like Wald and Misner-Wheeler-Thorne (lovingly nicknamed the black bible) and others start with the geometrical view from the get-go. There's some reason for this, the geometrical interpretation is quite beautiful mathematically and it's essentially a complete description of gravity. Most people know it is probably not the whole story and thus it's been a highly active area of research for decades and will remain so for decades to come.",
"Edit: To note, the derivation of spin-2 fields are often characterized by problems which prevents it from working in all the situations it should, such as in renormalization of say loop diagrams. Partially this is why they haven't caught on--as mentioned before string theories can attempt to solve this by introducing degrees of freedoms via \"strings.\""
] |
[
"There's something I've never quite understood about the quantum gravity discussion; does the particle-based interpretation of gravity replace the geometric interpretation as the actual \"story\" of what's going on in the universe? Or is it more that the geometric explanation of gravity occurs as a consequence of the quantum theory?"
] |
[
"Why, when you continue to burn ash, do the ashes eventually change from black to white?"
] |
[
false
] |
Whenever you burn wood, plants, or other organic material, the residual carbon becomes black ash. However, if you continue to burn that material, eventually the ashes will turn white. What are the mechanisms involved in further combustion of the material that result in the ash changing from a compound which essentially absorbs all photons in the visible spectrum making it appear black, to a compound that largely scatters light in the visible spectrum appearing white? Thanks!
|
[
"If you have something black during a combustion process that‘s not ash but the remaining carbon. The carbon reacts with oxygen in the air to form carbon dioxide, a gas. Ash is the product of oxygen reacting with everything not containing carbon: calcium, magnesium, and a few other metals. The oxides of those metals (reaction products with oxygen from the air) are usually white in color and do not become gaseous at usual combustion temperatures. That is why this is what‘s left at the end of burning something and why it is white."
] |
[
"Interestingly, most of these are basic oxides, meaning that they form very alcaline solutions in water. This was exploited in ancient times to prepare soap from fat."
] |
[
"It's important not to mix up terms here. What you get after combustion are oxides: Na2O, CaO, K2O, MgO, etc (probably some superoxides as well, but I digress). These are not oxidants, because the metals are in very stable oxidation states. But they are very reactive towards water: the oxide anions \"steal\" protons from water, giving hydroxide ions as product.\nSpecifically, in the case of K2O, the reaction would be something like: K2O + H2O ➡️2K+ + 2OH-. The hydroxide ions then react with triglycerides in the saponification reaction."
] |
[
"If time is relative to speed, what happens when we stop moving?"
] |
[
false
] | null |
[
"Which means that the spacecraft moving away from the earth in one direction would have time slow more for them as they accelerated than the spacecraft flying in the opposite direction.",
"Nope! The effects of time dilation are also relative. In other words, if you're an observer on Earth looking at the clocks on each spacecraft, all that matters is the relative speed between the clocks and the observer. It does not matter at all what Earth's speed is relative to any other reference frame. If you look at the equation for ",
"kinematic time dilation",
", note that the velocity term v is ",
". That is, it doesn't mean some velocity relative to \"absolute space\" - because such notion doesn't exist.",
"So there is no such thing as \"moving relative to space itself\". \"Space\" isn't a physical thing - it is a metric by which we use to measure distances. This means it is absolutely dependent on the reference frame you're using."
] |
[
"You can find many past threads by ",
"doing a quick search",
".",
"...if you could be perfectly still relative to the universe?",
"There is no such a thing. Speed is always relative, and there isn't really a \"reference frame of the universe\". For example, if I'm driving past a lemonade stand, the girl sitting there will see the car travelling at, say, 50 km/hr relative to her. But to ",
", sitting in my car, the car is not moving at all. I'm at rest relative to the car. Neither reference frame is more \"correct\" than the others.",
"So ",
", you are answering your own question. You are experiencing time while you are at rest, because you're always at rest in your own rest frame. Nothing special happens - time flows normally at one second per second, as it does in everyone's rest frame."
] |
[
"Speed is always relative, and there isn't really a \"reference frame of the universe\". ",
"I understand that everything is moving in space, and there is no way to observe space itself to see if it has its own point of reference because anything we can observe is matter moving through space.. But saying that all speed is relative sounds like a self contradicting statement? ",
"Let's say for the sake of argument that we create hundreds of thousands of spacecraft capable of reaching near the speed of light and fit each of them with an atomic clock, and we have a control clock on earth. They are all sensitive enough to measure the differences in time created by the different speeds they travel. you then fire all of those spacecraft off to slowly accelerate to light speed in different directions in an expanding sphere away from earth. Earth is moving through so space, so the control clock on earth should be effected by the same equation that the spacecraft are. Which means that the spacecraft moving away from the earth in one direction would have time slow more for them as they accelerated than the spacecraft flying in the opposite direction. Wouldn't that give us some idea what direction the earth is moving relative to space itself? And couldn't that then be used to figure out what velocity in what direction we would have to go to be \"stationary\"?"
] |
[
"I'm learning about Henrietta Lacks right now, but have a question about the HeLa cells"
] |
[
false
] |
[deleted]
|
[
"There can be the accumulation of mutations in the cells that get propogated with each generation. These are what caused the cells to turn cancerous in the first place and that hasn't stopped just because the cells are in vitro. ",
"Also, as cells are grown for a long time in culture there are other non-genetic changes. Different genes are expressed and regulated at different levels than before. This effect is a constant source of consternation for cell biologists.",
"Research into aging and mortality certainly has benefited from studying immortal cell lines. It's too bad the whole problem would be easier if we were all made of cancer cells. "
] |
[
"I think you'd like this wikipedia section on ",
"immortalized cell lines",
". There are actually several cell lines like this and they're used for production of biologic pharmaceuticals.\nKeep in mind that HeLa cells are cancer cells, so they're not a kind of cell you would want living & reproducing forever in your body. I'm not sure what you mean by the use of the cells as a fountain of youth. If you explain the idea a little more, I might be able to tell you why it would or wouldn't be practical."
] |
[
"I'm wondering of we can learn anything from them in order to manipulate our own cells to live longer/continute dividing and surpass the limit (I forget what the limitation is called) that we understand cells to have. "
] |
[
"Does the placebo effect work on infants?"
] |
[
false
] |
[deleted]
|
[
"First, different fields use the term 'placebo' and 'placebo effect' differently. Psychology tends to use it in the strictest sense - a neutral intervention that produces a positive change due to the ",
" of treatment in the patient (a negative change is called a ",
"nocebo effect",
", btw). Medicine tends to use it in a broader fashion - natural physiological processes that lead to good health are labeled a 'placebo effect' due to the fact that change is observed in a control group which received a placebo treatment. This, however, excludes the possibility of people getting better on their own.",
"For example, in one ",
"study",
" Johns Hopkins researchers examined whether diphenhydramine (Benadryl) would help infants (6-15 months) have fewer sleep interruptions. Despite anecdotal evidence, the researchers advised that physicians stop prescribing antihistamines for infants with sleep difficulties because, \"Benadryl was no more effective than placebo in helping the children to remain asleep during the night\" (they found that giving kids Benadryl helped them to fall asleep faster, but not stay asleep any better). ",
"They use the term 'placebo' here to indicate that the control group was given an inert substance for a blind trial control (the parents would likely not participate in the study if they knew they were giving their infants something useless). The problem arises when you consider that the infants could not perceive the treatment. This is a vital component of the placebo effect. (In fact, 'placebo effect' is a bit of a misnomer. It should actually be labeled a 'placebo response,' since anything that has a direct effect technically is not a placebo. But that is neither here nor there for your question.) Since the researchers observed some improvement in sleep functioning with the group given a placebo, they label is a 'placebo effect,' without regarding that they may have naturally improved regardless of the administration of a placebo.",
"In short, no. Infants cannot perceive treatment, and so any change noted would have to be concluded to have occurred ",
" rather than ",
". If you want to split hairs, since an infant cannot perceive treatment, then technically you ",
" given them a placebo."
] |
[
"Thank you for responding!"
] |
[
"In medicine, use of a placebo control is done to rule out quite a few different explanations for improvement. If the only thing involved was regression to the mean, placebo treatment wouldn't be necessary, as a no-treatment arm would rule out such.",
"Placebos work to blind patients to whether they're in the treatment arm or the no-treatment arm. One of the things people forget, though, is that placebos also work to blind people administering those treatments! If you're looking for a certain effect, you're more likely to find it. Imagine you get a bunch of nurses together to take blood pressures, nurses who know who's in the treatment arm and who is not, and you tell them, \"Well, what we're really hoping for is that people in the treatment arm show lower blood pressure than people that aren't.\" Is it any surprise when you hear what you were asked to be told?",
"That's part of the reason why placebo controlled trials are important in studies with infants. However, that's not the only reason. This study ",
"http://www.jpeds.com/article/S0022-3476%2899%2970428-2/abstract",
" shows infants in the placebo arm showed improved outcomes as compared to a no-treatment arm.",
"Is that proof of the placebo effect in children? Well, kind of. It's as good as you're going to get. In fact, it's in large part the same evidence we have for the placebo effect in adults: comparison of placebo treatment with no treatment. But you have to keep in mind that there are more possible reasons for a difference between placebo and no-treatment than patient psychology. In particular, it is impossible to fully double blind between placebo and no-treatment. Placebo treatment still means a caregiver paying attention to a patient when they might not during no treatment.",
"The problem arises when you consider that the infants could not perceive the treatment.",
"That's not quite correct. Infants CAN perceive treatments, in that they can perceive, for instance, heel sticks, needle jabs, etc. (Believe me, it would be a lot easier if they were incapable of perceiving treatment.) In fact, one explanation (of many, but the placebo effect probably is a combination of several different effects) is that of conditioning, and it's just as possible to condition infants as it is to condition adults.",
"It's not true that there's no reason infants could demonstrate a placebo response. (It's not hard to find any number of skeptical medicine blogs enumerating those reasons, although those blogs are awfully light on sources.) We don't understand the placebo effect well enough to be able to say what you need to be affected by placebo!",
"Unfortunately, the answer is we don't know. ",
"http://books.google.com/books?id=i5sC0fUKY-MC&pg=PA120&lpg=PA120&dq=placebo+effect+in+neonates&source=bl&ots=bQifM40vvn&sig=5_MHP1KLzssAfWknfEmyRs2io94&hl=en&sa=X&ei=m8M-T6bpDOfSiALX14GGAQ&ved=0CFwQ6AEwCTgK#v=onepage&q=placebo%20effect%20in%20neonates&f=false",
" "
] |
[
"How small can nuclear power plants become?"
] |
[
false
] |
I know that the Nimitz-class and the Gerald Ford-class aircraft carriers use nuclear power in order to meet their energy needs. This makes me wonder: if it is possible to fit a nuclear power plant on an aircraft carrier, how small can nuclear power plants become right now? Are there any developments now that can make these power plants become smaller in the future?
|
[
"They're small enough to fit in nuclear submarines and the basements of apartment buildings, the submarine case being of interest as they operate as completely sealed units with magnetic torque couplings to manipulate their internals through sealed walls. ",
"Are there any developments now that can make these power plants become smaller in the future? ",
"Yes, but the most active centres of this research will be places like the US & the UK Navy Research establishments and their like - good luck getting any specific answer from them. National security entails them being coy about size, power outputs, and future developments either planned or currently in the works."
] |
[
"This is kind of a trick question. When people talk about the nuclear in nuclear power plants they are really talking about fuel. See most power plants tend to use the rankine cycle as there basis for generating power(",
"http://en.wikipedia.org/wiki/Rankine_cycle",
"). This cycle in its most simplistic form the rankine cycle only needs four parts to run (boiler,turbine,condenser,pump). So a \"functioning\"(it would produce power but would not safe for people to run) nuclear power plant can be as small as the smallest rankine cycle set up. (For a reference on how small a rankine cycle could be ",
"http://www.youtube.com/watch?v=17wokE7XKnI",
")"
] |
[
"The ",
"Toshiba 4S Nuclear Battery",
" is pretty small although I haven't heard anything about it since the 2011 Tsunami and subsequent de-nuclearization of Japan."
] |
[
"What's the difference between a proton and a Δ+ baryon?"
] |
[
false
] |
I've been reading about quarks recently and I came across the Δ baryons. The Δ+ has the same component quarks as the proton, but a different angular momentum (3/2). How / why does this happen and what makes it different from a proton?
|
[
"It's not that they have different angular momentum, they have different isospin. Isospin isn't as fundamental as regular spin, which is associated with angular momentum. Instead isospin has to do with the properties of the strong nuclear force.",
"The delta particles were predicted and discovered long before the quark model was suggested. Deltas all have roughly the same mass, so the conclusion that they represent different states of the same particle wasn't so crazy. However, it turns out that they are really excited states of proton and neutron because they have the same quark content. We only describe them as different particles because they are so short-lived and because the nomenclature for baryons is largely historical.",
"Isospin is still a useful concept, as it describes the partial SU(2) symmetry of the Strong force. It turns out that in the full quark model isospin symmetry is just an aspect of flavor - different quarks have different isospin contents.",
"I'm sorry if I'm unclear - but you're skirting up against questions that can only be fully answered mathematically using quantum field theory."
] |
[
"Astronomy|Star Formation|Galactic Evolution",
"That is an impossibly cool tag."
] |
[
"For the technically minded, it may be worth adding that the proton and delta+ have the same isospin projection, but they're part of different multiplets.",
"For the less technically minded, describing the delta+ as an excited state of the proton is probably good enough..."
] |
[
"Can the common house fly(Musca domestica) see window glass?"
] |
[
false
] |
Well flies keep flying into my window every minute or so. There isn't a major difference of light between inside and out, and there isn't any smell that would attract them inside my house.
|
[
"there isn't any smell that would attract them inside my house.",
"That you can readily detect. Flies, especially the more highly derived ones, are quite capable of picking up on very minute olfactory cues. "
] |
[
"True.... "
] |
[
"A family friend of mine swears by filling up a sandwich ziplock baggie with water and hanging it by your doors or windows. She says that the water confuses the flied because of their strange eyesite and helps repell them."
] |
[
"Are all galaxies moving in the same direction? If not why?"
] |
[
false
] |
So me and a friend of mine (who is an astronomy major) were sitting around talking about the universe and galaxies and some stuff he was explaining to me didn't quite make sense and I was wondering if a experienced astronomer could enlighten me. From what I understand the universe is constantly expanding from a central point from the big bang or huge cosmic explosion or what have you, but at the same time our galaxy is also moving toward another galaxy, the Andromeda galaxy, while it is also moving towards us. So I guess my question is are both of our galaxies flying in one direction but at the same time moving closer together? Like if you were to throw two magnets in a single direction and they link up in the air? or is our galaxy or the Andromeda galaxy moving at a slower rate than the other and one is simply catching up? Also are all galaxies really moving away from a central point or do we have any evidence that some might be moving in the wrong direction and how would this be proven? I'm sorry if this is a lot and if I'm not asking a very clear question but I just can't seem to get this question out of my head and I would love a good explanation to some of these questions.
|
[
"From what I understand the universe is constantly expanding from a central point from the big bang or huge cosmic explosion or what have you",
"There is no central point. The Big Bang wasn't an explosion. See the ",
"FAQ",
". It was an event in which the whole universe began uniformly expanding. All points started receding from all other points, because additional space was being created in between them. This wasn't matter traveling through space, this was space itself spreading out.",
"The universe is thought to be infinite, or at least so obscenely large that it can be easily mistaken for infinite. Galaxies tend to have some random intrinsic motion relative to nearby galaxies, this is known as \"peculiar velocity\". Within galaxy groups and clusters (like the Local Group, where we and the Andromeda galaxy reside), galaxy motions are dominated by their gravitational attraction toward each other, and that is what is pulling us and M31 (Andromeda) toward each other."
] |
[
"Stars and galaxies moving away from us seems weird and very earth-centered, but its actually not.",
"I will use the overly-used example to illustrate this: consider a balloon. You can draw a grid on the balloon. Since you can choose two axis, you know each grid points have their coordinates, for example (0,1) or (15, 12). Now if you blow air in it so that it expand, every grid points are moving away from each other; no matter which point you choose, you ALWAYS see points leaving you! So, there isn't a special \"central points\" in the universe (balloon) and what you see happens everywhere. If you are standing on Jupiter (which you can't really stand on but leave it with that), you will see every galaxy moving away from you. If you stand on some planet in another galaxy far far away from us, you will still see all galaxies moving away from us, including milky way. \nJust like standing on one point on the balloon, suppose there are galaxies in every grid points, and they stay still on the grid point, then when balloon expands you see they moving away from you. This is the concept of homogeneous expansion.",
"Of course, the galaxies didn't just stay still on every grid points; they rotate, they move around a bit, but in general the moving speed is far smaller than the grid expansion speed. That's why we almost always see redshift (moving away). In rare cases, if there's a galaxy close enough to us and happen to rotation in a direction toward us, we can observe blueshift instead! We have to be very lucky though, it really have to be close enough and just happen to be moving toward us when it rotate around some bigger objects.",
"I think current observed blueshift objects are like only dozens, and we observe tons of millions of redshifted galaxies already."
] |
[
"This never made sense to me though. Taking the balloon example, as you add air the balloon gets bigger and all the points move away from each other (I get that). However, everything is then moving away from the center of the balloon, or the point at which the balloon was the smallest. How is it then incorrect that there is no \"center\" or central starting point to the big bang?"
] |
[
"If I put a rock in say water, would it ever dissolve like a cube of sugar due to diffusion so I'd have a glass of rock water?"
] |
[
false
] |
Edit: assuming that the glass and the surrounding environment stay the same eternally.
|
[
"That depends on the Ksp of whatever mineral makes up the rock, the size of the rock, and the volume of water."
] |
[
"It really depends on the rock, and on how big it is compared to the volume of water. If you dropped a chunk of halite, which is just table salt, in there, it'd dissolve pretty quick, unless it's a big chunk in a small glass, in which case it might eventually reach saturation. Some carbonates, such as limestone, will probably dissolve a little bit, enough to taste, but I'd be surprised to see a whole rock dissolve. Silicates--granite, basalt--will barely dissolve, if at all. Ice is technically a rock, too, so you could say any water is rock water if you want to."
] |
[
"No. Eventually the water would be saturated with as much of the rock as it could possibly dissolve and the system would reach a state of equilibrium, where atoms were deposited back onto the rock at the same rate at which they were dissolved. You can see the same thing with sugar, where if you put enough sugar in a glass of water it will stop dissolving."
] |
[
"What is the most efficient method of removing contaminating bacteria and viruses from a person?"
] |
[
false
] | null |
[
"In what context? Does the person still need to be alive afterwards? Simply incinerating the person would certainly remove all contamination.",
"If the bacteria/viruses are only on the skin, then they should be relatively easy to remove with soap and water (or bleach if needed).",
"If the person is already infected, then antibiotics/antivirals are probably the best option. However, these will not completely remove all of the microbes."
] |
[
"I'd say the most efficient way would be for the person to have already been immunized against the bacteria or virus, so that the immune response just gets rid of them.",
"However, I feel like that answer is kind of cheating. So lets say you didn't pre-immunize. The methods will be different for bacteria and viruses as they're very different entities. ",
"For bacteria, the most efficient way would probably be a combination of strong, specific antibiotics and the immune response. If you didn't care about the normal flora, I'd say just use a strong, broad-spectrum antibiotic that you know works against the bacteria you're trying to get rid of. At the same time, you might boost the immune system with an immunization against the specific bacteria.",
"For viruses, you'd probably do a combination of antivirals and the immune system. Certain antivirals only work on certain viruses, and not all viruses have an antiviral that works on them. In that case, the most important thing is to get the immune system going, so I might immunize with the infecting virus proteins or an attenuated virus. For some viruses you can use interferon, which is a cytokine of the innate immune system that starts an anti-viral response in cells. However, interferons wreak havoc on the body and don't work for all viruses (some can counter interferons).",
"I hope this helps!",
"Edit: Oh, and for viruses I might infuse with antibodies."
] |
[
"Yeah I agree completely. For some viral infections that lack vaccines, monoclonal antibody treatment has been helpful for improving disease outcomes for things like ebola, but its not what I'd call fully efficient."
] |
[
"If the immune system \"learns\" and \"remembers\" viruses, how and where is this information created and stored?"
] |
[
false
] |
My understanding of vaccines is that we take "dead" viruses, and inject them into the body so that our immune systems can learn to fight them before we first get them. My guess is that somehow the white blood cells (?) adapt to the virus somehow, but in what way? Do they unzip parts of DNA like cells do when they replicate? What would they even do with these pieces of DNA or whatever information they learn? ie. how does that information help them kill the virus? Do they then go and hide out until later waiting for the next infection?
|
[
"To simplify greatly, there are immature immune cells present in your body. Certain types have \"hypervariable\" regions which, for complex reasons, are able to develop with incredible diversity on a molecular level. Enough diversity that virtually any complex protein (which are absolutely essential for life but are incredibly complex and based upon certain patterns) can be matched to a hypervariable region of some small subset of immature immune cells. ",
"When a certain antigen (epitope technically, but antigen is a word most people know) is widely present in your body (like during an infection), this induces the clonal proliferation of immune cells which have hypervariable regions which are able to respond to that antigen. This proliferation has a far greater degree of mutation than normal cell division, which ensures that new cells which are best able to respond to the antigen are selected for. The cells with the best response to the antigen thus reproduce the most. ",
"Most of the cells produced to combat a given antigen die off quickly if the antigen is no longer present. However, a select few remain which do not directly combat infection, but retain the affinity for that antigen. They stick around, and if that antigen is encountered again, they quickly begin clonal proliferation, ensuring a full blown infection will not occur. "
] |
[
"This is a good answer. The \"hypervariable\" regions ",
"/u/mstrgrieves",
" mentioned is not an easy concept and topic to understand, but this is essential to recognizing and combat any past, present, and future infections. To put an insanely high number to the amount of hypervariable combinations possible, it is estimated that 3 x 10",
" combinations are possible. That is 300 billion combinations! ",
"If you're interested to learn more check out the ",
"wiki",
" on V(D)J recombination. Unfortunately I could not find a very simply diagram showing how it works that wouldn't require additional explaining."
] |
[
"Good question! To continue to trend of simplifying the vastly dynamic and complicated world of immunity, the body \"practices\" in that you have cells that present antigens (called professional antigen-presenting cells, or APCs) to your developing B- and T-cells all the time. The ones that recognize your self-antigens are targeted for programmed cell death (apoptosis), and do not survive to become mature and active. Antigens are presented on a type of protein complex called MHC, which is unique to you (because again, there are a vast number of combinations that are used to form MHC). When an immune cell binds an APC with your MHC and a self-antigen, it is given a cell death signal and does not proliferate. Cells that strongly bind your MHC with a foreign antigen are upregulated in order to fight the infection.",
"Also, while V(D)J recombination is arguably the most important process, it's not really unique to the development of memory cells. Another important process by which you develop very tight memory cell-antigen affinity is through ",
"somatic hypermutation",
". But the general idea that your antibodies develop very specific binding for a particular antigen is really the takeaway",
"EDIT: I recognize that I am using antigen and epitope interchangeably, but that's purely to make this a little bit clearer."
] |
[
"How long might it take for humans to evolve significantly enough to see noticeable differences from humans today, either physically or mentally?"
] |
[
false
] | null |
[
"It depends on how you define \"evolve.\" We are taller than we used to be just 100 years ago (and live a hell of a lot longer on average) and we are also much more knowledgable as a society as a whole than we were just 20 years ago. You may have also heard recently the population growth in India predicted to succeed China in total population.",
"If you are interested in seeing human's with telepathic abilities or tails then I'd look up the incidence of autism. It is highly correlated to having smart parents which is very intersting."
] |
[
"What about intelligence? Certainly it's a complex thing and difficult to understand, but do you see cultural or social systems leading to an interbreeding of more intelligent members in any way (for example isn't it encouraged in some countries for academics to intermarry)?",
"Would it therefore produce perhaps over the course of thousands of years, a subculture of sorts with a greater evolved intelligence level?"
] |
[
"What about intelligence? Certainly it's a complex thing and difficult to understand, but do you see cultural or social systems leading to an interbreeding of more intelligent members in any way (for example isn't it encouraged in some countries for academics to intermarry)?",
"Would it therefore produce perhaps over the course of thousands of years, a subculture of sorts with a greater evolved intelligence level?"
] |
[
"How does the body know if a gene is recessive or dominant?"
] |
[
false
] |
[deleted]
|
[
"First of all, genes are not dominant or recessive; alleles are. ",
"If you are unfamiliar with the terms, then allele is roughly a specific thing that you might have in your DNA (such as \"blood group A\") where as a gene is a set of specific things you might have in your DNA (such as \"blood group\"), but a gene does not specify which one of those you actually have.",
"To extremely simplify things, you have two alleles for each gene, one of which you inherited from your mother, and one of which you inherited from your father.",
"For example, if you mother has two \"blood type A\" alleles, and your father two \"blood type B\" alleles for the \"blood type\" gene, you will have one \"blood type A\" allele and one blood type B\" allele for the \"blood type\" gene, which will result in your ultimately having the AB blood type.",
"(This is an example of co-dominance.)",
"Your body turns alleles (which contain genetic information) into proteins (which have specific function within your body).",
"If you have two alleles (X and Y) for gene #1, where X codes for the normal (functional) protein and Y codes for a useless (non-functional) protein, then X is usually dominant to Y because your body will end up producing about half the usual amount of protein, which will usually be enough for it to function properly, so the fact that you have Y will be essentially irrelevant. Only if you have two Y alleles (and no X alleles) will you be completely deficient of that protein → Y is recessive and X is dominant.",
"But if you have two alleles (A and B) for gene #2, where A codes for the normal protein and B codes for a dangerous protein, then A is usually recessive and B is dominant, because your body ends up manufacturing a dangerous protein, and you typically only need a little of a dangerous protein for some bodily function to be affected. In that case, even if you have a single B allele, you will be affected → B is dominant and A is recessive.",
"If you assume in these examples that X and A are normal alleles (also known as wild type) and Y and B are rare mutations, and also that there are no other known alleles for genes #1 and #2, then you might say that Y is a recessive mutation and B is a dominant mutation. ",
"But the more accurate way to express this is, as I said above, that for gene #1 X is dominant to Y and for gene #2 A is recessive to B. That allows you to talk about situations in which you have multiple alleles, where you might see situations where P is dominant to Q which is dominant to R, or K is recessive to L and M which are co-dominant to each other, etc etc. "
] |
[
"A small nitpick. Your dangerous protein example would be referred to as dominant negative. "
] |
[
"Well, it doesn't really, it basically just does as it is told. Both genes are there in each parent, it's just to what probability will the dominant alelle be expressed and how fully will it be expressed. I know that's not the most helpful answer. Could you maybe rephrase your question?"
] |
[
"Why does Earth's iron core generate a magnetic field?"
] |
[
false
] |
Also, what is special about the specific directions of the north and south poles?
|
[
"We do and we don't. We know that earth generates a magnetic field. We know that this magnetic field changes polarity intermittently. ",
"The thing we don't know is WHY. The popular theory (known as Dynamo theory) theorizes that the earth's core (inner and outer) is made of iron and nickel. Because the outer core spins ever so slightly around the inner core, this spin is thought to power the magnetic field. HOWEVER (and maybe somebody can correct me) They have yet to show how one can make iron and nickel at 3000 C produce a magnetic field. These temperatures are WAY beyond the curie point for these materials, so it remains a mystery. Though a dynamic system like a liquid is likely to explain why the poles are able to reverse, it is still not proven how this occurs. ",
"These things are not PROVEN most because it is nearly impossible to replicate these conditions, or even be totally certain of particular ideas about the core (namely exact composition, pressure, temperature). ",
"I know a bit about this, but we really need a geophysicist! HALP!"
] |
[
"Iron in the outer core rotating is basically what causes it. If you want you can read about it in more depth.",
"http://en.wikipedia.org/wiki/Dynamo_theory"
] |
[
"The magnetic field is generated by moving currents inside the outer conductive metallic core. These most likely are driven by convection produced by the the release of heat due to solidification of the inner solid core. ",
"Here",
" is a reasonable summary. The spin of the inner core and of the layers outside the outer molten core probably play a very small role, if any, in producing the magnetic field. The fact the core's temperatures is well above the Curie point is irrelevant, except as noted, it precludes the magnetic field from being due to some sort of permanent magnetism. There have been experimentally produced ",
"dynamos in large masses of molten sodium",
" (also see ",
"here",
"), which do undergo ",
"spontaneous magnetic flips",
"."
] |
[
"Is there an inherent difference between a nuclear explosion and a conventional explosion other than radiation released?"
] |
[
false
] |
Someone posted a photo of operation Minor Scale Where large amounts of explosives were used to simulate a small nuclear explosion. My question is, other than a lack of radiation released, does detonating a nuclear weapon actually equate well to the equivalent amount of explosives. Does a 300 kiloton nuclear warhead explode the same way 300 kilotons of TnT would?
|
[
"interestingly, our current nuclear warhead design (as far as a lay person can tell) seems to be:",
"Chemical reaction (conventional explosives) compress fissile material driving a fission reaction. That fission reaction then (through a rather brilliant design, I think) drives a fusion reaction. But that fusion reaction mostly exists to compress a new fissile fuel as well as provide neutrons to that reaction. The overall energy from fusion in a thermonuclear bomb is relatively small compared to the fission explosion."
] |
[
"A conventional explosion relies on the electromagnetic force; the energy stored in chemical bonds is released through a variety of methods - but fundamentally, it is the breaking of chemical bonds that is the energy source. ",
"A nuclear explosion relies on the Weak Force (or perhaps more appropriately, the interaction of the Weak and Residual Strong Forces). These forces don't really even exist on the distance scale that the EM force uses. The energy stored in the nucleus of an atom (in the form of the binding energy that keeps the protons stuck together despite their electric charge) is released by introducing an instability to the nucleus (vis a vi a neutron with some kinetic energy). ",
"They are fundamentally different processes on a microscopic level. ",
"Other than the radiation release, is there a difference: yes. The type of energy released is different. Per explosive unit (so we're talking about one nucleus or one molecule of explosive), the energy of the nuclear explosion is much, much (10",
" times) higher. This higher energy, confined to a smaller space, results in a different 'flavor' of energy being emitted. A nuclear explosion transmits a lot of energy in very high frequency ranges (UV, x-ray, gamma, particle radiation). A chemical explosion does not do this. When you say \"other than the radiation released\" I understand what you're trying to say, but it's important to note that much of the effect of a nuclear weapon is this radiation. ",
"Now, if you neglect this anyway, essentially what you are looking at is a very large amount of energy confined in a very small space. Thermodynamically, what happens next is obvious: the energy disseminates from that point very, very rapidly. In that regard, yes, a chemical and nuclear explosion are the same. But don't discount the high-energy aspect of the nuclear explosion - there is a large amount of energy that, rather than being transmitted as 'blast effect' (shock wave, heat, etc) is transmitted as radiation and ",
" behave the same thermodynamically (eg, intense heat will be emitted by the nuclear weapon because of the energy density - this will cause very serious flash burns that aren't present or are present at a much lower level than on a chemical explosion - these heat effects happen near-instantly, because they are carried away at the speed of light - it takes much longer for a blast wave to travel through the ground or atmosphere and carry the fireball of a chemical explosion with it). ",
"EDIT: I opened with the word \"No\" and I'm not entirely sure why. "
] |
[
"In a sense, to simplify for OP, could you say \"A nuclear explosion is much, much brighter per kiloton\" using \"brighter\" oversimplified to imply visible and ir/uv/xray/gamma photons?"
] |
[
"What would be the immediate effects of a supervolcano eruption at Yellowstone?"
] |
[
false
] |
...I don't mean a piddly one like the eruption 70,000 years ago, I mean a full-scale eruption along the lines of the one 640k years BP. Who is in range of the blast radius, and how far out and in what directions does the deadly ash cloud go? Does the eruption set off already-volatile faults in California? Alaska? Asia? What about the poisonous fogs? Does the East coast survive? West coast? Midwest? How about Boise? Billings? There are articles talking about 10 years of problems, but I'm wondering about the first 10 .
|
[
"Well everybody nearby would die, and a large region would get covered in ash. In 1883 a massive volcano exploded in Indonesia and there was so much ash in the atmosphere that the whole world experienced a temperature decrease for a year. I imagine this would be worse."
] |
[
"This actually contains one of the reasons I asked this question. They say \"tens of thousands would die.\" After explaining how a chunk of Earth roughly the size of Oahu would be atomized and blown into the stratosphere with sufficient ",
" to make it a permanent fixture of the air for a decade they go on to note that \"tens of thousands would die.\" There's 8,000 people in Cody, WY, 71 miles away. So we're saying that Cody and the rest of it's municipal school district are the only people who are going to be immediately killed when this thing goes off? That seems like sugar-coating a catastrophe to me."
] |
[
"Nom nom sweetastrophe nom nom"
] |
[
"(Astronomy) Why is the sun white?"
] |
[
false
] |
I've heard that the sun is white, and that the atmosphere makes it look yellow, but it's surface temperature of about 6000 degrees Celsius would place it as a yellow star in the HR diagram. Is the sun not white then?
|
[
"The HR diagram was created in 1910 when we knew much less about stars and their spectral power distributions. The color range on the diagram was arbitrarily based on visual observations. There are a lot of traditional holdovers like this in astronomy that remain because they don't really get in the way of the science. ",
"You're correct that the sun is white but appears yellow or orange due to atmospheric scattering. "
] |
[
"The colors on the HR diagram are exaggerated. Most mid-range main sequence stars would look white in real life, as we can see when we observe stars at night (though admittedly that sample is biased towards larger, brighter stars)."
] |
[
"oh ok"
] |
[
"Why did NASA use a skycrane to deliver Curiosity to Mars?"
] |
[
false
] |
How did NASA come to the conclusion that the skycrane was the best way to land a heavy rover on the Martian surface? What were some of the other strategies considered for the EDL (entry descent and landing) of Curiosity and why weren't those used instead?
|
[
"It should be noted that the EDL system used by the Mars Exploration Rovers, Spirit and Opportunity, was by necessity very elaborate as well:"
] |
[
"It's atmosphere is too thin to use a parachute and ",
". ",
"Can you explain the bolded part? I don't understand why the thickness of Mars' atmosphere would preclude the use of rockets to land. "
] |
[
"It's atmosphere is too thin to use a parachute and ",
". ",
"Can you explain the bolded part? I don't understand why the thickness of Mars' atmosphere would preclude the use of rockets to land. "
] |
[
"[Physics]Can ALL physics be represented mathematically?"
] |
[
false
] |
Sorry for such a simple question, a quick google didn't give me what I wanted. I have been working in computer simulation with physics engines and got to wondering, are there any psysics that don't have a definate mathematical equation to represent it?
|
[
"Just a protip: you don't need to type \"[Physics]\" in your title because you can add it with the \"flair\" button after you post. I've gone ahead and done that for you. It'd be nice if more submitters would do this since it makes it easier for experts to home in on their questions. (Right now the moderators are just tagging most things ourselves.)"
] |
[
"Oh I was wondering how that was done. I thought it would automatically color it if I wrote it that way. Thank you."
] |
[
"We've yet to find something we can't approximate through math.",
"There's a few problems for which there aren't very good closed forms, even in simple Newtonian mechanics."
] |
[
"Why is biomedical research to computationally expensive, and what exactly is being 'researched'?"
] |
[
false
] |
[deleted]
|
[
"There are at least two large, inter-related fields: one is bioinformatics, which involves high-level comparison/interpretation/extrapolation of genetic data. The 2nd is molecular simulation, where the three-dimensional structure/function of macromolecules such as proteins or nucleic acids can be predicted and/or calculated (from experimental data) and/or simulated. ",
"These are the very simple descriptions of these fields, but both involve calculations that are computationally expensive"
] |
[
"For computational biology (bioinformatics), the data sets are very, very large - they could be the entire human genome, or the output from some short read sequencing. The data often lists the nucleotide or amino acid makeups of a certain item - such as our genome (ie, ACTTTGCTGCTA, except many, many times longer). These data sets can be gigabytes, even terabytes large. Considering that the algorithms used to manipulate the data into something readable / meaningful (such as with Needleman-Wunsch (used to align different sequences), which is O(mn) (basically quadratic growth)) have complexities that are, at the very least, linear, doing this sort of computaional work is very expensive. As such, scientists need really powerful computers to do work in any decent time frame. ",
"The machines themselves are not discovering new things - it is humans that are looking at the computed data for statistically significant similarities and differences that occasionally turn out to be something scientifically significant."
] |
[
"Similiarly for molecular simulation the complexities are vast. For example, protein folding simulations ideally take into account individual atoms, including the surrounding water molecules. ",
"Then the algorithm itself would be a numerical iteration where you start with an initial \"push\" to the starting configuration\n1. calculate the resulting force on the individual atoms of the protein\n2. calculate the acceleration due to the force\n3. move a VERY small time step forward and numerically integrate the acceleration to arrive at new positions/velocities\n4. repeat as many times as possible before project deadline",
"Basically the large number of molecules and the large number of timesteps add up fast"
] |
[
"If Titanic had not sunk 100 years ago, could it still be used as an ocean liner?"
] |
[
false
] |
[deleted]
|
[
"With proper maintenance, yes. There are much older ships than it that are seaworthy.",
"However, whether it would be economically feasible is an entirely different story. Maintenance and operating costs are probably much higher than a modern cruise ship, and those only increase with age. There's likely a point at which it would be cheaper to build a newer and more efficient ship."
] |
[
"Medina. Built for Mallory Line. Completed 1914. Last reported in service with Good Books For All as a floating ministry/bookshop. It was announced in November 2009 that she would be withdrawn from service on 31 December 2009 after surveyors discovered that she needed major repairs. In March 2010 she was handed over to her new owners, BizNaz Resources International Pte Ltd in Singapore who planned to preserve her under the name Doulos Phos and operate her as floating hotel/restaurant.\n",
"http://www.allatsea.co.za/oldestships.htm",
"In theory She could, ",
" The ship was taken care of and cared about. In reality though a few things would have happened by now.",
"http://www.frommers.com/articles/7331.html"
] |
[
"It would have most probably been stripped of its steam turbines and received a diesel makeover because of the more than double efficiency of the latter, as companies ",
" care about money. Other than that, only if it would have received proper care, because boats and the sea are not friends."
] |
[
"How do I explain the density of the observable universe in an easy to understand way?"
] |
[
false
] |
In the aftermath of a discussion I found the density of the observable universe through wolframalpha (I assume there will be different views on the validity of this number, and although not my primary concern here further insights would be interesting too), but I really struggle coming up with a couple of easy to understand similes since the number is so low. This might be a little different than the usual questions here, but you guys are usually amazing at giving relatable and easy to understand examples, so if you feel like it, have a go :-) (or point me to a better subreddit if I'm trampling all over some rules here)
|
[
"Maybe give a term such as, \"it would take this number of houses (or square feet (assuming a certain height)) to give one breath of air\". "
] |
[
"Can't you just say that for the most part it's a vacuum? 1 O atom in a swimming pool, if it were enclosed, would qualify. "
] |
[
"I really don't think there are. To explain a density, you have to explain it as a mass divided by a volume. If you want a mass that is everyday familiar, you wind up with a volume that is too big to be everyday familiar. If you want a volume that is everyday familiar, then you wind up with a mass that is too small to be everyday familiar."
] |
[
"Is there an extreme level(high or low) that would disable smell or taste?"
] |
[
false
] |
[deleted]
|
[
"You mention that if a room is dark people will go blind. I read that researchers were having people learn Braille and used a group of students wearing sleep masks to cover their eyes so they were \"blind\". They left them on for a few weeks and learned Braille. When they took the masks off they actually couldn't see, and as they regained their eyesight the forgot how to read Braille. Their brains used the existing neural pathways that they were no longer using for eyesight to learn Braille. Crazy how the mind works."
] |
[
"This is also \"state-dependent memory\". When you learn something under a specific condition, it would be easier to recall when you are placed in the same condition. Indeed, it's very interesting stuff."
] |
[
"Closing your eyes isn't the same thing as having a mask on for an extended period of time. I mean, you can see light through your eyelids."
] |
[
"Can we mine the moon?"
] |
[
false
] |
Is there resources there that we can harvest and ship back to Earth? It seems if we want to whole world to be advanced, we will definitely need more resources, because the way we live now is destroying the planet, and not even the entire planet is advanced. I don't understand why the government doesn't try and spend money on improving technology and make it more green. It seems just most companies pick up the tag as Green, to make them better to people, and are really just fighting over consumers. The biggest problem will probably be the cost/power of shipping it back to earth. But if the government would fund programs to research that stuff, not just spend it on retarted shit. idk, it feels like everyone is looking down to try and fix their problems, when we should be looking up.
|
[
"Is there resources there that we can harvest and ship back to Earth?",
"Sure. Near the top of the list is ",
"helium-3",
" : \"The abundance of helium-3 is thought to be greater on the Moon (embedded in the upper layer of regolith by the solar wind over billions of years) \"",
"Helium 3 is a potentially very powerful fusion fuel for future, hi-tech power generating methods.",
"idk, it feels like everyone is looking down to try and fix their problems, when we should be looking up.",
"Perhaps. But spend a minute thinking about the transportation costs."
] |
[
"This leaves us with only one option: preemptively nuke the moon."
] |
[
"This leaves us with only one option: preemptively nuke the moon."
] |
[
"[Space] If all the stars in the night sky appeared at the same brightness to us on earth, would the entire sky be light?"
] |
[
false
] |
Would there be any dark patches, or do stars (there are a lot of them) fill in all the gaps?
|
[
"You might be interested in this wiki-article:",
"https://en.wikipedia.org/wiki/Olbers'_paradox"
] |
[
"If you apply this to every star in the observable universe there would not be any patches. There are 100-500billion galaxies out there, and on a scale as large as this, our universe is almost perfectly uniform. Our nigth sky would be compleatly filled without any noticable spots or holes. And saying that stars in our galaxy would appear dim in contrast is very big understatement. Stars in our galaxy would be compleatly invisible in contrast."
] |
[
"If you apply this to every star in the observable universe there would not be any patches. There are 100-500billion galaxies out there, and on a scale as large as this, our universe is almost perfectly uniform. Our nigth sky would be compleatly filled without any noticable spots or holes. And saying that stars in our galaxy would appear dim in contrast is very big understatement. Stars in our galaxy would be compleatly invisible in contrast."
] |
[
"If swelling/inflammation is our body's method of sending essential blood cells and nutrients to a site of damage, why are most treatment efforts after, say, an ankle sprain concentrated on reducing swelling?"
] |
[
false
] |
[deleted]
|
[
"Hey, so it seems no one is really answering your question, so I guess I'll take a stab at it. I'm a human biology major, and while I may not have the credentials as most people have on here, we definitely discussed the subject of inflammation quite thoroughly, and I believe I can answer your question.",
"Basically, when you have an injury (let's use your example of an ankle sprain) the first thing the body does is release histamine, which causes the capillaries to dilate and swell up, and this increases blood flow and also temperature (so that's why your ankle gets swollen and kinda warm). The reason for this is that the heat can inhibit the growth of some pathogens (say if you got a small cut), and the increased blood flow will bring in more white blood cells to the site quicker. Then the incoming white blood cells release signals called cytokines to call even more cells to the rescue that can help rebuild broken tissue, and when they're all together they need to drain out the dead cells into the lymphatic system (which doesn't have a beating heart to make fluid move, so the dilation helps). At the end, the waste product that results needs to be drained, and if you ice the region it kind of just delays the process. Icing does help to relieve pain and it does bring the swelling down a bit, but generally your body knows what it's doing and it doesn't really need to be iced. According to some articles I just looked up, they mentioned icing may be good in the event of a brain injury (to prevent a secondary injury), but that's not really what we're talking about here.",
"This ",
"Journal of Athletic Therapy",
" conducted a study on the outcome of putting ice on a soft tissue injury, and the results were generally that ice did help with pain, but did not help with the healing process. We need the swelling to help our body heal itself. ",
"Anyway hope that helped, and maybe anyone else can chime in with more information."
] |
[
"The primary reason to reduce swelling is to prevent additional damage caused by pressure on the cells. In a traumatic injury, the increase of fluids into the interstitial spaces(especially confined spaces) can cause physical damage to the surrounding tissues. Additionally, the swelling increases localized pressure, which can actually reduce or prevent blood flow to and from the affected area. A severe form of this can be found in ",
"compartment syndrome",
".",
"In minor injuries, say in the ankle sprain you suggested, the resulting consequences of not treating the swelling are likely to be minor, but in severe cases the result can be the aforementioned compartment syndrome, which can cause the loss of a limb.",
"In fact, the use of RICE is generally only for the first 24 hours to prevent further injury. After around 24 hours, heat can in fact be used to dilate local vasculature and encourage fluid flow out of the affected area."
] |
[
"Ive always wondered the same thing about the fever response, if its not dangerously high, >103°, is it just for patient comfort? "
] |
[
"Is there a diamond equivalent for silicon?"
] |
[
false
] |
I understand that silicon shares certain properties with carbon. Can it arrange itself into a diamond-type structure?
|
[
"Yes. Silicon is already naturally occurring (or I should say ",
"naturally arranges itself",
" ) in a diamond structure. Unlike carbon which occurs mostly in its graphitic form at ambient pressure. ",
"There are also ",
"P-Si",
" which is easier to produce than monocrystalline silicon.",
"There's also ",
"A-Si",
" (amorphous silicon) which is not really naturally occurring but it can be useful for some applications. ",
"To my knowledge there is no \"graphitic\" form of silicon. It simply does not like to form hexagonal structures like graphite. I am not entirely sure why though. "
] |
[
"The qualitative explanation for the non-existence of a graphitic allotrope of silicon is the fact that pi-bonding is relatively weak for elements below the second row of the periodic table. In the diamond structure, each atom has 4 sigma bonds. In the graphite structure, each atom has 3 sigma bonds and one pi bond."
] |
[
"There is indeed a \"graphitic\" form of silicon. Its single layers are called ",
"silicene",
", but contrary to graphite the structure is slightly bucked and not completely flat."
] |
[
"Would doing a belly flop into a pool filled with a non-newtonian liquid such as ketchup hurt more or less than would water?"
] |
[
false
] | null |
[
"Ketchup should hurt less, since it's sheer-thinning and at an appreciable belly flop speed, the viscosity will be lower than water. That initial impact is where most of the pain comes from, and in the case of ketchup, that impact is smoothed out."
] |
[
"shear thinning"
] |
[
"Cornstarch with water would be close to jumping on asphalt. "
] |
[
"Does the radiation from the sun/sun's radiant energy change over time?"
] |
[
false
] |
Are there any differences in the composition of the radiation from the sun in it's early days and the present? Also as the sun ages/dies, will the composition change?
|
[
"Yes, very much so. Here's a star migrating over a ",
"Hertzsprung-Russel diagram",
". The vertical axis is luminosity, from darkest to lightest, and the horizontal axis is temperature, from hottest to coolest. Most stars, like our sun, are on the \"main sequence\" depicted as the black line. The way the sun moves throughout its life is depicted by the white lines. During the formation of the earth, known as the Hadean Epoch, the sun was hotter. It has since cooled down a bit, and it will continue to cool bit by bit until it burns off its hydrogen. Then, several billion years from now (I think around 6), the sun will burn off all of its hydrogen and undergo a violent \"helium flash\", where it begins to burn helium into elements like carbon and oxygen, and it will expand into a red giant as internal pressures overcome gravity. Due to its larger surface area, it will be more luminous despite being cooler. Once it burns through its helium there will be a brief stage where it combines lighter elements into heavy elements as it dies, eventually completely shedding its atmosphere in a nova, leaving behind a small, hot white dwarf, the end of the white line."
] |
[
"Thank you. This was very helpful."
] |
[
"also, the sun's energy output increases by about 10% every billion years. This means that as time goes on, the habitable zone around the sun gets pushed a little farther out. Maybe someday in the future, the Earth will look a little more like Venus as the sun cooks us into a delicious, sulfuric, greenhouse mess."
] |
[
"Marine biologists use submarines with bright lights to film deep sea creatures, many of which have very large, sensitive eyes. Are the retinas of these animals damaged by these lights, and do they try to avoid the subs?"
] |
[
false
] | null |
[
"Marine Biologist here, to answer your question the most truthful answer is \"we dont know\". Thats due to a lack of research, species specific responses and difficulty of accessing the deep sea. But that's not very fun or elaborate.",
"An interesting report here",
" covers most of the bases. It seems in most species, bright light exposure temporarily removes the ability to respond to light stimuli. After some time to re-acclimate, the fish respond normally again. That would obviously vary with species, intensity and exposure time etc. ",
"The only true permanent damage stems from UV exposure which wouldnt be emitted by ROV sub white lights. ",
"EDIT: Reworded to avoid taser like vocabulary"
] |
[
"Do we know what spectrum their eyes actually \"care\" about? I know when I go deer hunting I can wear LED headlamps and it doesn't bother the deer in the wee hours of the morning whereas if I was wearing a Halogen lamp they would avoid me like the plague. "
] |
[
"Thats another \"we dont really know\" question. However, we do know that no surface light reaches past 200m, and anything from 100-200m will only receive blue light.",
"Our current understanding is that fish would be seeking out that far reaching blue light, especially if the species is vertically transient. We also know that things bioluminesce at depth, which is most commonly blue or green as these wavelengths travel best in water as we just described. Unless you're a malacasteid, which is an exception and can see and emits red light.",
"So most likely a red light would be least intrusive but also crap for photos."
] |
[
"Why is Plutonium considered to be so dangerous?"
] |
[
false
] |
It has a very long half life so it's not throwing out a lot of radiation, yet it is still considered to be bad.
|
[
"Plutonium isotopes that have a long half life are not considered deadly for their radioactivity as much as their toxicity. Plutonium is incredibly toxic, even a small amount can kill you/seriously mess you up if ingested. In fact, in this regard, the long half life actually makes the situation worse because it doesn't degenerate for a while, thus increasing its chances of being absorbed into a biological system. "
] |
[
"In fact, in this regard, the long half life actually makes the situation worse",
"If its lifetime would be so short that it would decay notably while in the body, then its radioactivity would be a problem. You wouldn't win."
] |
[
"You wouldn't win.",
"When ingesting it. We would certainly win when it comes to the safe disposal of it."
] |
[
"Subtractive colors: Does a yellow filter just let yellow wavelengths through, or does it let green and red through?"
] |
[
false
] |
Are there different kinds of yellow filters? If a yellow filter only let yellow wavelengths through, then when it was stacked with a magenta filter, no wavelengths should get through... (rather than red)...?
|
[
"Depends on the filter. There's sunglasses that can treat colorblindness by being very selective on which wavelengths they let through. A perfect yellow filter would just look opaque, since almost no light would be exactly the right wavelength."
] |
[
"Ordinarily yellow filters let through the wavelengths that we see individually as red, orange yellow and green in large amounts. If they didn't they wouldn't work for subtractive mixing. In the same way, bright yellow objects like lemons and yellow paints reflect wavelengths throughout the ROYG range in large amounts, not just the wavelengths that individually appear yellow."
] |
[
"There are indeed many different kinds or of yellow filters. Your thinking is actually along the right track. If you have a perfect yellow filter that only allows yellow wavelengths to pass, say for example it passes 100% of light from 565-575nm, but completely blocks all other light, it would become black when stacked with a perfect blue filter that only passes light from say 410-480nm.. Perfect filters like what I described here don't exist perfectly, but there are notch and pass filters that have quite sharp light transmission curves that pass more than 90% of light in a given range while keeping all other wavelengths pretty darn blocked.",
"In the case you proposed, where you stack a yellow filter on a magenta filter, well, you get magenta by subtracting green and passing blue and red. Since yellow is right on the border between green and red, whether or not this filter combination would result in black depends on the precise wavelength ranges transmitted by each filter."
] |
[
"Educating myself on the MCAT topics. Recommended reading?"
] |
[
false
] | null |
[
"The MCAT prep books are not terribly good for you - they are based more on the principle of ",
" you first year concepts than actually teaching you. The answers to the practice questions often include explanations, but they may only include key words designed to jog your memory, without ",
" explaining them. After all, the books are there to get you through the MCATs.",
"For example, they might just tell you that polar aprotic solvents favour SN2 reactions over SN1 as a rule that you should remember, without explaining the mechanisms behind the two reactions.",
"I'd say pick out first-year textbooks on all the topics and do your own reading. Go through the required textbooks for the courses in your university to see what kind of books they use.",
"There is also ",
"MIT Open Courseware",
" and ",
"Khan Academy",
" that are great for introductory concepts in university courses."
] |
[
"For Ochem, check out ",
"Ochem as a second language I and II",
". It goes over your basic concepts including orbital theory, nomenclature, mechanisms, NMR, etc with pretty good explanations to help get the concepts across. I used this as supplemental material to my real ochem book. Also, if you want to learn more about ochem, check out the ",
"ACS Ochem Prepbook",
"; this is the prep book for the ACS exam. It does a good job refining and testing your knowledge. If you don't have basic inorganic chemistry knowledge then start there following the same \"as a second language\" books.",
"Physics books you can really pick up any, but I'd suggest sticking with ",
"-calculus based physics. UCLA has a non-calculus based physics series for life science majors who weren't engineers. It was split into three books over three quarters, which is what I used, and they were pretty easy to understand. I'm not sure where you could get your hands on the books. If you're in LA, check out ",
"www.bruinwalk.com",
" or check out the ucla subreddit.",
"This",
" is a great biology book and does a great job going over a lot of the biology concepts.",
"I used ",
"this",
" book for biochem. It's very dry and detailed so might not be what you're looking for.",
"Calc, I'm not sure. Any book should do.",
"Lastly, check out khan academy on youtube. He does an awesome job covering a lot of concepts that the MCAT tests."
] |
[
"I think your best approach would be to read one of the MCAT prep books. I used the Princeton Review CBT book and I believe it was pretty thorough in its material. The point of these prep books is to review concepts that are expected to be known on the exam, but without going into to much depth because it to be understood that you have already learned these concepts in depth.",
"I used ",
"this book"
] |
[
"How did scientists estimate the age of Earth before the advent of radiometric dating?"
] |
[
false
] | null |
[
"There were a lot of different attempts that largely relied on estimating the rate of something and then extrapolating that to estimate the age of the Earth, i.e. there is Y quantity of this, it changes at X rate today, we'll assume it started at Z condition has always occurred at X rate and from there we can estimate how long the process has been happening. Some notable examples/categories:",
"A variety of people used the generations of people discussed in the christian bible and some estimation of the average lifespan to estimate when the world was created (e.g. Kepler, Ussher, Lightfoot). These kind of border on scientific since even though they were based on a religious text, they were applying a form of logic to try to use said text to make an estimate.",
"A common, more clearly scientific, pre-radiometric dating way to estimate the age of the Earth was from cooling rates. Assuming that the Earth started out molten and knowing something about cooling rates of various materials, you can estimate how long it would take for a body the size of the Earth to cool (with some big assumptions). Notable examples of this were undertaken by Comte de Buffon and Lord Kelvin (and both Newton and Liebniz kind of dabbled in this, but weren't as direct in terms of actually producing a formal estimate of the age). ",
"Another common attempt was using the salinity of the ocean (the so-called \"salt accumulation clock\"), i.e. we know the salinity of the ocean on average, we can measure the rate at which salts are delivered to the ocean via rivers, and if we assume the ocean started off as entirely fresh water, we can estimate how long it would take to build the salt concentration we observe. A variety of people did these types of calculations, including Edmund Halley (same Halley as the comet), T. Mellard Reade, and John Joly. ",
"There were estimates made based on orbital mechanics and dissipation of tidal friction between the Earth and Moon. George Darwin (son of Charles Darwin) and Lord Kelvin both used these lines of reasoning to estimate the age of the Earth.",
"The most consistent mechanism across history though was trying to use the thickness of sedimentary rocks to estimate how long it took for them to accumulate. The Greek historian Herodotus presented some estimations based on sediment deposition rates of the Nile. There were a flurry of these types of estimations in the late 1800s with one of the most complex being put together by Charles Walcott. Other notable estimations using this technique came from J.D. Dana and others.",
"Pretty much all of these estimation techniques missed the mark by at least a few billion years, largely because of incomplete understanding of the processes (e.g. heat from radioactivity dramatically changes the cooling rate of the Earth, non steady delivery of salts to the ocean plus a variety of mechanisms for dissolved loads to be removed / sequestered, or that the sedimentary record includes lots of gaps of erosion and non-deposition, etc). There are lots of sources out there that go through much of this in a lot of detail, the above was mostly taken from the introductory chapter of the \"Geochronology and Thermochronology\" textbook by Reiners et al."
] |
[
"Pretty much all of these estimation techniques missed the mark by at least a few billion years, largely because of incomplete understanding of the processes",
"But in the nineteenth century context their answers usually served to advance the scientific conversation, they discredited the Biblical creation story, at least way the story was commonly interpreted at the time. Also, their ages provided with more than enough time for Darwin's theory of Evolution to make sense, because people knew it had to be a very slow process. Even if they estimated the Earth to be billions of years younger than it actually is, that still left them with hundreds of millions of years."
] |
[
"Poorly.",
"One estimate was based on the estimated age of the sun, which derived by assuming that the sun was powered by gravitational collapse, since nobody knew about nuclear fusion. So they got a figure between 20 and 100 million years. Likewise the cooling rates of the Earth, which would have been way off since they didn't know about heating caused by radioactive decay, which would keep the interior of the planet hotter for much, much longer."
] |
[
"Does the Earth gets bigger trough the Seafloor Spraeading ?"
] |
[
false
] |
Today in school we learned sth about plate tectonics and the seafloor spreading. But does the Area of the earth gets bigger because of the Seafloor Spreading ? (srry for my bad English)
|
[
"No, new seafloor (oceanic lithosphere) is created at ",
"mid-ocean ridges",
" but this, on average, is balanced by seafloor being destroyed at ",
"subduction zones",
", meaning that the surface area of the Earth is constant (but this destruction and creation of oceanic lithosphere are the primary mechanisms driving the motion of the plates)."
] |
[
"No, because old sea floor is pushed back down into subduction zones where it melts again, at about the same rate that new seafloor is created and spreads out.",
"Anyway, even if this didn’t happen, there is only a finite amount of material that makes up the earth. The earth couldn’t get bigger without new material being added to it from outside. Edit: Or if some process happened that made the material already making up the earth less dense."
] |
[
"Thx"
] |
[
"How far can the Earth actually move towards or away from the Sun and still be okay?"
] |
[
false
] |
I was always told that if it were to move even 10 feet then we would all die. I know this isn't true but what is the exact distance that the Earth's can get from the Sun and still be habitable by humans?
|
[
"I was always told that if it were to move even 10 feet then we would all die. ",
"This is a myth especially common among Christian communities, the insistence that any tiny deviation in the Earth-Sun distance would obliterate life on the planet being convenient for argumentation about the Earth having been created for our survival by some higher power. ",
"The truth is that the Earth-Sun distance varies by over 5 million kilometers throughout the year on its normal (elliptical) orbit, and the resulting changes in living conditions are too small to notice, being eclipsed by the effect of axial tilt creating the seasonal cycle."
] |
[
"This is referred to informally as the ",
"Goldilocks",
" zone after the fable. It extends inward for our solar system to about Venus and extends past Mars.",
"While such drastic orbital changes would undoubtedly wreck our climate, these represents the regions where it's plausible to find a temperate planet. It's speculated that Mars for instance was vastly more Earth like in it's early history, but it failed due to it's small mass and the solidification of its core."
] |
[
"The Earth's orbit is not a perfect circle, it varies between 152.10 million kilometers and 147.10 million kilometers, so 5 million kilometers, from the sun. The difference we feel in weather between the two is completely overshadowed by the effects of the earth's tilt."
] |
[
"[chemistry] Why does Cl- not form Cl2 in water?"
] |
[
false
] |
I work in water treatment but I'm not a chemist. I'm seriously considering further education because the more I learn the more I want to know. I use drop-test kits and a typical water sample can contain 30ppm Cl- (chloride) , 0.3ppm ClO- (free chlorine) and 0.4ppm Cl2 (total chlorine) What stops the Cl- from becoming Cl2? Why does my total chlorine test kit not pick up the chloride? What would have to change in order to make the Cl- form covalent bonds and become Cl2? What are some good sources of information on water chemistry?
|
[
"Cl- is a chloride anion. It has a negative charge because it has one extra electron in its valence shell (it would've gained this by forming an ionic bind, a bond where one atom gives up an electron entirely, typically a metal). ",
"Water is a polar molecule so ionically bonded compounds such as NaCl can disassociate into there constituent cations and anions (Na+ and Cl- respectively in this example) ",
"So if two chloride ions approached they would repel each other because they are both negatively charged. In the exact same way that the negative ends of two magnets would repel each other.",
"However if two elemental atoms of Chlorine were to collide they would both seek to fill there valence shell by each sharing one electron amongst both of them forming a covalent bond and thus a Cl2 molecule.",
"If you're thinking about studying Chemistry I couldnt recommend it enough. Science is totally dope"
] |
[
"Yes, if the Cl- ions want to form neutral Cl atoms (or essentially Cl2) then they need to find a species that would happily take their electrons away. As it turns out, in water alone there aren't any species that would rather the electrons than chlorine.",
"Electrolysis is one way to remove the electrons in a controlled manner to produce Cl2. This requires energy input as we are trying to escape an energy well - pulling electrons away from their desired locations on an electronegative species."
] |
[
"This doesn't really explain why chloride couldn't be oxidized to chlorine, one way or another; that has to do with electronegativity."
] |
[
"If oxygen is thought to be the \"enemy\" of food, and can cause certain foods to spoil, how would an oxidizer like sodium nitrate cause meat to NOT spoil?"
] |
[
false
] |
It seems counter intuitive, help me understand! Thanks.
|
[
"Because nitrite was found to inhibit the growth of C.botulinum (Reddy, Lancaster, Science, 19 August 1983: Vol. 221 no. 4612 pp. 769-770) "
] |
[
"Oxygen is bad because it allows bacteria to grow. Bacteria consume nutrients in the food and can be toxic to the human body. By itself, oxygen isn't bad at all, but it just has the secondary effect of promoting aerobic bacteria to grow. That's why vacuum-sealing processed food helps to keep it from spoilage. Of course, not all bacteria require oxygen to grow, so eventually all food spoils.",
"Nitrate is an oxidizer which means it can undergo a chemical reaction that is toxic to these bacteria, and can inhibit the growth of bacterial colonies. Just because it has oxygen in it does not mean that that oxygen is present in the same form as diatomic oxygen found in the air. They have very different chemical properties that are not useful to the bacteria that require oxygen to grow."
] |
[
"Sodium nitrite is actually the main preservative used in cured meat. Nitrate is converted to nitrite in the food, and it's the nitrite that does the job. Actually, it does several jobs: it binds to hemoglobin and preserves the red/pink color, it affects the taste (the characteristic \"sausagey\" taste of cured meat), and most importantly, it acts as an antibacterial.",
"The biggest worry is ",
", the species that's responsible for botulism. It's an anaerobe, i.e., it grows without oxygen, so the center of a sausage is just perfect. Nitrite inhibits the germination of the spores (by an unknown mechanism as far as I know), and also keeps existing bacteria from producing the toxin. It also has growth inhibitory effects on many other species, which cuts down on off-odors and other kinds of spoilage."
] |
[
"Do we ever see instances of infidelity among species that have been identified as \"mate-for-life\" types?"
] |
[
false
] | null |
[
"Yes! In fact, there is a huge difference between sexually monogamous (individuals only mate with their SO) and socially monogamous (pairs will live and associate together and take care of their young together, but will mate with other individuals). There is fairly strong evidence that sexual monogamy doesn't actually exist. It seems that species we once thought were completely sexually monogamous (mating for life) would occasionally sneak away from their partner to copulate with other individuals. ",
"From an evolutionary standpoint, it makes sense that the individuals who mate with as many others as possible would be able to spread their genes better and thus that behavior would continue. There are, however many evolutionary advantages to forming a monogamous pair, so a balance is formed between the two behaviors. "
] |
[
"There's a whole section in the book Dr Tatiana's Sex Advice To All Creation about this. The author is the evolutionary biologist Olivia Judson. It's an interesting book, I'm enjoying it. She gives TONS of interesting examples behind the evolution of sex and the sexual practices of different creatures. ",
"She cites that before the 1980s it was thought that 90% of bird species were monogamous at least during the mating season but that turned out not to be the case after better genetic testing techniques were discovered. ",
"Gibbons were once thought to be monogamous and are not. ",
"The problem Judson says is that most studies that look at the mating habits of species don't study said species for more than one mating season or only observe a small number of 'families'. So many species that may appear monogamous, may not be at all.",
"Monogamy tends to only evolve when it is in the best interest of both males and females of a population. Obviously, if the only surviving children are those from a monogamous partnership, those genes get passed on.",
"She looks at reasons why monogamy may occur in nature, and gives an interesting example of mantis shrimp, which she argues is the Danger Theory of Monogamy. Monogamy will tend to endure in a species if it is too dangerous to travel to find a partner. The mantis shrimp has a soft body and females are hard to come by. Two adolescent mantis shrimp will stick together and dig a burrow together from which they hunt. They will never leave the burrow, and can stab passing prey from within. As adolescents, they secrete a mucus which they use to stabilize the sand of their burrow. Interestingly they lose the ability to produce the mucus to build a new burrow once they've aged to a certain point. This leaves them in the same burrow with the same partner for the rest of their life as it's too dangerous to leave. Hence, they remain monogamous and produce offspring with the same traits. ",
"It's an awesome book. I could fill the TIL section with crazy examples she has and cites. "
] |
[
"Male angler fish have no infidelity. You can't exactly cheat on your SO when you're fused to her and everything but your testes has atrophied down to nothing."
] |
[
"When looking in a mirror, do animals understand that they are looking at themselves?"
] |
[
false
] | null |
[
"Some do! This is actually a common test of animal intelligence: ",
"the Mirror Test",
"Unsurprisingly, several species of apes pass the test, but so do dolphins and orcas, Asian elephants, magpies, and according to one study at least three species of ants."
] |
[
"Ants? How on earth would you even objectively asses that? "
] |
[
"Ants don't have sophisticated vision but they do have vision. It's a good sense for not bumping into things."
] |
[
"Why can't we treat depression (or just become happy) by actually injecting serotonin?"
] |
[
false
] |
I've heard that our happiness is purely controlled by our dopamine and serotonin levels, and that depression is mostly a lack of serotonin. Depression is currently treated using SSRIs which control the uptake of serotonin by the body. But why can't we just supplement our serotonin levels to achieve this more effectively?
|
[
"Couple issues.\nFirst, a physical barrier. Serotonin (5-HT, 5-Hydroxytryptamine), cannot cross the blood brain barrier (BBB) the BBB is a physical boarder that separates/filters what components of our blood can reach our brain. ",
"http://en.wikipedia.org/wiki/Blood%E2%80%93brain_barrier",
"Serotonin isn't one of these (but variation of Serotonin have been synthesized which can! ",
"http://onlinelibrary.wiley.com/doi/10.1111/j.1460-9568.2008.06201.x/pdf",
")",
"Second, a barrier of knowledge. When it comes to how the biochemistry of the brain relates to behavior and moods we have very little basic understanding. For example. Serotonin works because it is a ligand for a receptor in neurons ",
"http://en.wikipedia.org/wiki/5-HT_receptor",
". The problem is, there are many types of these receptors, and we don't really know what they all do. They are expressed in different brain cell types and may have different functions (not all of which is triggering or inhibiting depression)",
"So simply pouring Serotonin in the brain is not the solution. We need to know specifically which parts of the brain regulate mood in response to serotonin, which parts of the brain release the serotonin, and how much serotonin is the right amount. "
] |
[
"\"I've heard that our happiness is purely controlled by our dopamine and serotonin levels, and that depression is mostly a lack of serotonin.\"",
"You often hear this, but neither part is quite true. Neurotransmission is not a simple process. The monoamine hypothesis has been firmly shown to be lacking, and does not represent current psychiatric research. SSRIs do indeed increase synaptic serotonin levels in a matter of hours, but as they take weeks to take effect, the actual mechanism of action must involve something further downstream. For that matter, while standard antidepressants do have benefits, particular in more severe and/or chronic depression, many patients do not respond to them. Depression remains complex and poorly understood.",
"As to your question, 5-HTP is a precursor to serotonin, which crosses the blood-brain barrier and is converted to serotonin in the brain. It has been tried as an antidepressant, and small studies have sometimes reported benefit on par with standard antidepressants, but I haven't seen anything convincing."
] |
[
"I don't think that SSRIs work the way you think they do. The name serotonin re-uptake inhibitors doesn't refer to diet or the blood. When serotonin is released from nerves in the brain, the serotonin then interacts with it's receptors, producing multiple effects in multiple nerve types, one of which is improving mood. For a signaling molecule to be specific, it can't persist forever in space between the nerves, so it get's taken up (re-uptake) by the nerves that release it, or destroyed by enzymes.",
"By inhibiting serotonin re-uptake, the concentration of serotonin at the signalling junction stays higher and lasts longer. The theory is depression is a result of either low serotonin levels or low receptors, either of which would be improved by blocking re-uptake. Almost all signalling molecules are re-used for different pathways and purposes. These other targets don't interfere with each other because the signalling molecule is released locally and then taken back up. Giving people systemic serotonin would stimulate all these other pathways and have awful side effects. Part of the side effects from existing SSRIs is this increasing of serotonin in signalling outside of the depression/mood system.",
"The bottom line is just adding the signalling molecule in bulk to the brain rarely fixes the problem. The exception would be Parkinson's disease, where adding back dopamine orally crosses the blood-brain barrier relieves some of the symptoms. Partly this is due the fact that dopamine producing cells are slowly dying off, but not gone completely in the beginning. So the signalling can still go up and down, with some baseline supplementation from outside. It's still not perfect. Right after a dose of dopamine, large movements are easier, but fine movements are poor. As it wears off, fine movement improves, but large movements worsen. Later in the disease, when there is very little dopamine being made by the few remaining cells, just adding more dopamine from outside stops working at all. At the same time, when the level of dopamine production gets low enough, the other functions of dopamine on mood and memory break down and these people can become quite violent, and again, adding back dopamine from the outside doesn't help."
] |
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