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[
"Guitar question: Why do the harmonics on the 5th fret and the 17th fret have the same exact pitch?"
] |
[
false
] |
[deleted]
|
[
"Pinch harmonics (where you put your finger slightly on the string) are created by cancelling out the fundamental frequency of the string so that the dominant harmonic frequency at that location takes its place. This is done by putting your finger at one of the harmonic frequency's \"nodes\", seen ",
"here",
"You can see where the pitch repeats itself along the neck, this is due to the wavelength of the harmonic along the string."
] |
[
"(Gets guitar...) They don't. The 5th fret harmonic is the same as the 24th fret harmonic. The 24th fret harmonic is the same as playing a note on the 24th fret normally, and is 3 times the frequency of the natural 5th fret note. 3 times the frequency translates to an octave and a 5th or 19 frets, and 5+19=24.",
"The 17th fret harmonic (plenty of distortion required) seems to be equivalent to the (hypothetical) natural 36th fret note. Most playable harmonics will be equivalent to another note because the harmonic frequency will be a small multiple of the frequency of the note played naturally, and small multiples are covered pretty well by 12 notes in an octave (see ",
"Equal temperament",
")"
] |
[
"I made a little drawing to help illustrate what I'm talking about",
"These are drawings of a picked note, a higher picked note, the 5th harmonic, and the 17th harmonic.",
"Remember, the pitch of the note is determined by the frequency of the wave created by the string when you pick it. When you just fret a note and pick the string, you're basically putting the string into a half sine wave. When you fret a higher note, you are increasing the frequency of the wave, and therefore increasing the pitch. When you fret a lower note, you decrease the frequency, and therefore decrease the pitch.",
"When you first pick the string, waves of all frequencies at once sound out. That's called the attack. After the initial fraction of a second, most frequencies die out, except for the one that can resonate on the string. That's why picking the note and a hammer sound differently, because a hammer doesn't produce nearly as much attack.",
"Harmonics work differently however. By just putting your finger lightly on the string, you are allowing waves to resonate that don't have a frequency of half of the length of the string anymore. Because of the shape of the sine wave, you allow frequencies to resonate that don't have any amplitude where you have your finger, so the whole string resonates. ",
"So, when you play a harmonic on the 5th and the 17th, you are creating a dead spot that is the same distance from the end of the string. You're dividing up the string in the same way, so waves of the same frequency resonate."
] |
[
"Between foam, liquid, or bar, what is the best type of soap for handwashing?"
] |
[
false
] | null |
[
"Bar soap.",
"Further, antibacterial soap of any kind is ",
"raising concerns",
"00723-0.pdf) as a possible contributor to the spike in resistant bacteria.",
"Good old naturally derived bar soap doesn't just kill germs; it sucks them into it's gooeyness, then repels water, so you can rinse all the bad germs off your hand and down the drain.",
"A $1 bar of soap will have the same hand-cleaning efficacy as any other fancy or more expensive cleaner, if used properly (lather well, let soak for at least 20 seconds, but even longer with vigorous scrubbing like ",
"Alton Brown demonstrates",
" is best). It is also important to rinse the bar and store properly in a clean soap dish (clean the dish often!) and replace the soap before it's a nub - bar soap is cheap!"
] |
[
"I prefer ",
"this one",
" because it includes interesting information about ",
" soap works, why it doesn't need to be \"antibacterial,\" and why simply washing your hands is more effective than using hand sanitizer. ",
"Plus before he was made to edit it, it had a funny joke at the end."
] |
[
"I prefer ",
"this one",
" because it includes interesting information about ",
" soap works, why it doesn't need to be \"antibacterial,\" and why simply washing your hands is more effective than using hand sanitizer. ",
"Plus before he was made to edit it, it had a funny joke at the end."
] |
[
"What is the most recent case of natural selection introducing a new widespread trait in any organism?"
] |
[
false
] |
I'm particularly interested to know if there's any in humans, but otherwise any organism.
|
[
"Definitely not the 'most' recent, but ",
"some elephant populations are increasingly being born tusk-less.",
"Historically, an elephant's tusks were ",
"a mechanism for digging and fighting",
" and an elephant with longer and stringer tusks would have a significant advantage. However, with the current high demand for ivory, this advantage is of diminishing value compared to the risk that the animal in question will be poached."
] |
[
"Antibiotic resistance in various bacterial pathogens, such as ",
"MRSA",
" and ",
"MDR-TB",
" is the obvious example.",
"White nose syndrome in bats and chytridiomycosis in amphibians are also both driving selection within some affected populations (although they're also driving high rates of extinction in others).",
"Fishing is driving selection on many fisheries, leading to smaller adult size, higher fecundity, and lower boldness in fishes with significant fishing pressure.",
"There are probably plenty of other examples but these are all off the top of my head."
] |
[
"There's also the ",
"famous example",
" of a moth in the U.K. with light- and dark-colored phases. The dark phase became more common in sooty industrial areas because it was better camouflage, while the original light-colored phase remained common in cleaner more rural areas."
] |
[
"Why does drinking water get rid of the stabbing pain in my heart?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"medical advice",
"/r/AskScience",
"Please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"This is also a question based on an personal or isolated event, which is against our guidelines: ",
"https://www.reddit.com/r/askscience/wiki/quickstart/askingquestions"
] |
[
"This is also a question based on an personal or isolated event, which is against our guidelines: ",
"https://www.reddit.com/r/askscience/wiki/quickstart/askingquestions"
] |
[
"Would it be possible to have an Earth sized object composed completely of water? If so, would the core be a type of exotic ice?"
] |
[
false
] | null |
[
"If you had an earth-sized mass of water, its core wouldn't be composed of the same ice you see regularly. There are a variety of named structures of ice, but at high pressures it's mainly ice VII, VIII, X and XI. Beyond these, there are also amorphous ices of various densities (interestingly, not just one amorphous ice: there's LDA, HDA and VHDA). Martin Chaplin's website is a good resource: ",
"http://www.lsbu.ac.uk/water/phase.html",
"EDIT: Sorry, the amorphous ices I mentioned are in the GPa range whereas ice X and XI are in the TPa range. ",
"EDIT: Chaplin, not Chapman."
] |
[
"Ice is a solid form of water, and its molecular structure can be amorphous (see LDA/HDA/VHDA ice) or crystalline (regular repeated units). Ice VII, VIII, X and XI fall under the latter: They are solid forms of water with different crystal structures. Look at ",
"Martin Chaplin's website",
" for pictures of their structures. The real-life ice IX is nothing like what's described in cat's cradle though. In fact, it's only stable at low temperatures and high pressures. ",
"EDIT: Chapman-->Chaplin"
] |
[
"Generally you can synthesize them in a lab, but the temperatures and pressures required can be, shall we say, ",
" for humans. You could probably see it through a viewing glass. As for what you'd see, it would depend on which structure you're considering. I can't say for sure since I'm on the simulation end of things. I would expect to see a colourless crystal. Possibly opaque, possibly clear. If anybody knows what these structures look like, I'd be happy to hear."
] |
[
"At what point does a dialect become a language?"
] |
[
false
] | null |
[
"You're getting a lot of comments here but no one with linguistics flair is leaving any, so let me offer the view from within the discipline, as a practicing linguist who works heavily in dialectology and doing exactly the kind or work where this is most applicable:",
" None. It is not a linguistic reality that there's a line that a variety of speech crosses during its development at which point you can then say \"A-ha! Now it's a language\".",
"Are German and Dutch languages? Yeah okay. Are they dialects of Germanic? Alright, sure. These are sociopolitical concepts, not linguistic ones, and there's a good chance that anyone who's making the clear claim that X and Y are dialects of the same language, or that X and Y are different languages, that person has some motivation outside the science of linguistics. There's another agenda there, which isn't to say that's a bad thing, but it's not based in linguistics."
] |
[
"It's not ",
" a bad way to describe it, and one might still say \"now they're different languages\". It's just not a scientific or objective way to describe it. ",
"Mutual intelligibility has a number of significant problems ",
"which I mentioned in a comment here",
". So even if it were possible to consistently and objectively determine mutual intelligibility (which it's not), that judgement will still not reflect a lot of deeper linguistic realities that would justify leaving that aside. For example, you have what are called dialect continuums, where a person from location A can understand B and kinda understand C, and then someone from D can understand C and E without any trouble, but then maybe the guy from E can't really understand A. You have an unbroken chain where neighbours have similar enough dialects that you wouldn't call them languages, but then at the ends of that continuum, there's not really much mutual intelligibility.",
"For this reason, mutual intelligibility shouldn't be the most important criterion for making such a distinction."
] |
[
"Max Weinreich said something similar: \"A language is a dialect with an army and navy\".",
"He said it in his native Yiddish, and for me it sounds exactly like German."
] |
[
"Does sound travel faster when it is raining compared to when it is not?"
] |
[
false
] |
Sound ravels faster in water than in air, so would sound travel faster when it is raining out than when it is not? (Or possibly simpler, would sound travel faster in a humid environment than an arid one?)
|
[
"For your first question (does rain increase sound speed), the answer is no.",
"The effect of rain on sound speed is relatively small, because the water is such a small component in the air. If it even did have an effect, it would actually be to ",
" the sound speed, because the water increases the effective mass of the air without appreciably changing its compressibility. Since, c=√(B/ρ), if B stays the same and ρ increases, then c goes down.",
"For humid air, the answer is yes, but probably not for the reason you'd suspect. The soundspeed for a gas (or gas mixture) is given by c=√(γRT/M), where γ is the ratio of specific heats, R is the universal gas constant, T is the temperature in Kelvin, and M is the molar mass. Interestingly, the molar mass of water is actually ",
" than that of air. This raises the sound speed in air! However, the ratio of specific heats for steam is also somewhat lower than air, which does offset the change a touch."
] |
[
"It depends on the wavelength of the sound. If the water droplets are small compared to a wavelength, the sound will just sort of...ignore them. If the droplets are large compared to a wavelength, they'll cause scattering. If the droplets are resonant, they'll strongly absorb the sound. Acoustic wavelengths range from 2 cm ~ 20 m, and rain drops are usually smaller than a cm, so that means the waves just ignore the drops."
] |
[
"That's awesome. Thanks for answering a question I had been wondering about for a while."
] |
[
"I noticed that myself, my cat and my dog all yawn. Does this mean that we all share a common ancestor that yawned?"
] |
[
false
] |
I know that some evolutionary features can develop over and over independent of one another, but just how common is it?
|
[
"The last common ancestor between humans and carnivores was ",
"something like a shrew",
". Here is a youtube video of a shrew yawning: ",
"http://www.youtube.com/watch?v=rO6k1-NYJto"
] |
[
"The last common ancestor between humans and carnivores was ",
"something like a shrew",
". Here is a youtube video of a shrew yawning: ",
"http://www.youtube.com/watch?v=rO6k1-NYJto"
] |
[
"Convergent evolution is pretty common, so it's a bit hard to tell. I doubt the answer is conclusively known, since we can't tell if something yawned by looking at fossils or DNA. I would guess a single origin for mammals, though. "
] |
[
"Do dogs like/dislike or even perceive music?"
] |
[
false
] | null |
[
"Do they perceive it as organized sound?"
] |
[
"The only animals I ever see that visibly perceives and enjoys music are birds. ",
"http://www.youtube.com/watch?v=N7IZmRnAo6s",
"Music must have an effect on other animals: ",
"http://www.washingtonpost.com/wp-dyn/content/article/2009/09/06/AR2009090601990.html",
"But it looks like birds enjoy music similarly to us.\n",
"http://www.youtube.com/watch?v=N7IZmRnAo6s"
] |
[
"Music is just certain types of sound. Dogs can certainly hear. So yes, they perceive music. Are you asking if they have a conception of it as any different than any other types of sound?"
] |
[
"Why is there no freshwater coral?"
] |
[
false
] |
I'm surprised to find out that with all the abundance of life underwater, there's still no freshwater coral. Can anyone explain why it would be so difficult for coral to live in fresh water?
|
[
"I'm NOT an expert here, I can only speculate, but maybe it has to do with the fact there are fewer dissolved ions in freshwater, and I know carbonate ions are needed for forming their rigid parts, their skeletal structure so to speak. (same goes for lots of shelled marine life).",
"Edit: pH may be a factor too. Too acidic and creatures relying on dissolved carbonate may have trouble forming their hard body parts."
] |
[
"Speaking in ignorance; wouldn't that rule out freshwater clams and stuff too?"
] |
[
"Obviously freshwater mollusks do exist. Maybe mollusks get their minerals from a different source than just the water around them (food?).",
"Again, I was just speculating.",
"Maybe it has to do with the fact that rivers are always unidirectional in flow, so corals can't ever evolve to settle there, they'd always migrate downstream. Corals are symbiotic with zooxanthellae algae that live inside them. Maybe the problem is that this algae fundamentally can't survive in salty conditions. Or maybe it's this algae would be competing for an already occupied ecological niche it can't win, something occupied by a freshwater algae? I know corals (or maybe the algae living in them) are very sensitive to temperature fluctuation. Maybe terrestrial water systems have more temperature variation than marine ones?",
"I'm just tossing out ideas, not any hard assertions."
] |
[
"Are there any animals which have benefited from human dominance of the planet?"
] |
[
false
] |
The only ones I can think of off the top of my head are city-dwelling pests such as rats and pigeons, but then again I know nothing about rat/pigeon population pre-civilization, so I could be wrong there.
|
[
"Dogs - or rather their wolf ancestors... In order to gain protection and a constant supply of food from the human communities at the time, the dog ancestors evolved to look less menacing (i.e. Increasingly cute), display loyalty and an offer of companionship. "
] |
[
"If you're just looking at straight population counts, it could be said that domestic livestock, like cattle, pigs, sheep, chickens, etc. have benefited from human dominance. If you are considering quality as well as quantity of life in the term \"benefited,\" then it's harder to make that case. ",
"Certainly, as others have said the animals we domesticated to keep as pets, such as cats and dogs, have benefited, as have urban pest species and the invasive species we have introduced to certain areas. "
] |
[
"Human dominance has caused \"benefits\" for a number of species through habitat transformation and invasive species introduction. As you mentioned, the destruction of native habitat and replacement by urban settings has allowed certain species to flourish (pigeons, rats, etc). Introduced exotics (rats, cane toads, starlings, etc) can be very successful and out-compete native species.",
"But, the \"benefits\" for a species have come after (or resulted in) a much greater loss of total species diversity."
] |
[
"Does higher brain plasticity also mean that you loose neural connections faster?"
] |
[
false
] | null |
[
"Not necessarily. Neural plasticity has to do with many more factors than just losing neural connections. For example, researchers have found that existing neural connections can be strengthened and weakened through processes called LTP and LDP. This does not necessarily mean the neural connection is lost completely or formed, but rather that the existing connections are made stronger and weaker through neural activity. These are key processes in learning and forgetting. Check ",
"this",
" source for more information on LTP.",
"But, synaptic plasticity does mean losing neural connections in some cases, particularly in the womb and early in life. For example, the visual system, when formed in the womb, contains hundreds of thousands (maybe even millions) of extra neural connections. If you'e ever heard the term \"nature vs. nurture,\" that is a key process here. As the visual system is stimulated with what your eyes see early in life, some of those neural connections are strengthened, and some are weakened and end up being lost completely. This is how humans gain the ability to see - neural connections in the visual system are refined so that the region of the brain that processes visual input only receives the most important signals for producing the things we see to create our vision- binocular vision, color vision, ability to see movement, among other things. See ",
"this",
" source for information on visual development.",
"Neural connections to muscles are also in great excess when you are born. As the muscles become used more often after you are born, the less active connections to the muscle end up being removed, until only one connection is made to the muscle. It's a \"winner takes all\" scenario - the single most active connection wins complete control over the muscle in the end. This is why babies and toddlers have difficulty with coordination of movement. There are many extra neural connections that must be removed during this period of high neural plasticity. See ",
"this",
" source.",
"It's widely accepted in the neuroscience community that synaptic plasticity decreases as we age, meaning that activity from sensory input as well as other things are crucial during early years (under the age of 8 or so). During this time, periods of neural development called critical periods cause permanent changes to be made to the brain (when plasticity is high), that persist throughout life. During these critical periods, neural plasticity is generally high, which means neural connections are much more susceptible to being formed, strengthened, weakened, or even lost completely. See ",
"this",
" source.",
"Though, in certain regions of the brain, neural plasticity remains high throughout adult life, and in this context, a high neural plasticity means that neural connections can be formed faster. For example, the adult hippocampus (a structure of the brain responsible for formation of memory, for simplicity's sake) makes about 700 new neurons ",
". In the context of the rest of the adult brain, that number is exceptionally large. And, new neurons inevitably mean new neural connections are made. A study done on London taxicab drivers found that the hippocampi in their brains were significantly larger than the average test subject (see ",
"this",
"). Before the days of reliable GPS technology and smartphones, taxicab drivers had to memorize street names, locations, etc. and so the high plasticity of the hippocampus allowed them to do so (by forming new neurons and hence more neural connections). See source for the first paragraph.",
"So, to bring it all the way around (",
"): neural plasticity can mean that connections are lost, but it can also mean connections are made. It really depends on the context. Also, increased neural plasticity does not necessarily mean that connections are \"lost faster.\" That also depends on the context, as well as time period in question.",
"Also, I want to add that a lot of things in this post are greatly simplified - a Reddit comment simply can't do all of these amazing processes due justice."
] |
[
"To expand, LTP and LTD are more long-term forms of plasticity because both these processes are involved in altering dendritic spine length and shapes (for example). Most plasticity is actually more short-term. Not all synapse LTP and LTD follows Hebbian law either, but there are always exceptions when talking about the brain. Lol Plasticity is more than just LTP and LDP, but those two are the classic examples.",
"Great job and trying to answer that mammoth of a question!"
] |
[
"Great point! I made sure to include things other than LTP and LDP (my point on development of the neuromuscular junction as well as visual development). Synapses can be removed via spontaneous activity in the LGN as well as elsewhere prenatally (at least from what I remember) which kind of sort of follows a Hebbian scheme I guess. I suppose development of the neuromuscular junction follows a Hebbian scheme as well. ",
"I also want to point out that LTP and LDP can be short term processes as well. ",
"This",
" paper utilizes optogenetics (LTP) to induce fear conditioning in mice. They were able to extinguish the memory only a matter of hours later through LDP. So, while LTP and LDP can very well be long-term processes, they definitely can be short term as well.",
"I couldn’t think of anything else, but then again, I’m only a third-year neuroscience student in college, so I’ve got a lot to learn!"
] |
[
"Is it possible for one sun to orbit a larger sun?"
] |
[
false
] |
[deleted]
|
[
"Yes."
] |
[
"Absolutely -- these are known as binary stars and they come in many different shapes and sizes. In fact, one type of supernova (type 1A) are caused by a white dwarf orbiting around a larger red giant star and accreting matter from it.",
"Interestingly, most star systems in our galaxy (and presumably other galaxies) are binaries; so our sun being on its own is a relative rarity.",
"Also, to clarify: it's very, very rare for two stars to actually pass close enough to each other to interact; space is so large that the probability for a collision or interaction between two stars is very low. As a result, binary stars often form together out of the same molecular cloud."
] |
[
"Technically, no because they orbit a common barycenter. Then again, so does the Earth and the Moon. The barycenter between the two is about 1700 kilometers from the core, while still within the Earth itself. ",
"http://www.astronomycafe.net/qadir/q665.html"
] |
[
"Does earth's specific gravity facilitate life or do all the other variables dictate that life would have prospered anyway and adapted to almost whatever gravity our planet had.?"
] |
[
false
] |
i.e. is our gravity also in a Goldilocks zone?
|
[
"It's like a puddle that became sentient. The puddle says the hole it's in seems designed and perfect as it could not fit in any other hole. We all know that the puddle confotmed to the environment. This is how life works on earth, it grew to fit the environment. We can see radically different trends based on historical conditions via fossils.",
"This means life would indeed adapt to different levels of gravity. There is limits on what life as we know it would have formed in and adapted to. We don't really have reason to believe life can form without an atmosphere so a minimum bound is likely. This minimum bound would depend a bit in the planet in question and the magnetic field present to protect an atmosphere. There is definitely an upper boundary as pressure and heat come up to a point that interferes with the chemical reactions we associate with life ",
"So in a way, there is a goldilocks zone but it's likely fairly big. But we're also the water in the puddle, we are fit for the environment we live in, the actual puddle was not designed for us. Our life would not be the same if the puddle was a different depth or shape."
] |
[
"Yes & No",
"Gravity doesn't directly impact the development of life, marine organisms largely disregard gravity. However, a certain amount of gravity is necessary to maintain an atmosphere (Mars lacks that minimum threshold and so lost it's atmosphere)",
"Once this minimum threshold is met, it's less important than other factors until the gravity becomes so great that it exceeds biological limits (using our biosphere for predictions, obvs). However, between those two extremes the gravity may shape how organisms evolve. Low gravity worlds may support more airborne life, while high gravity may see more squat, powerful life and emphasis on marine life over terrestrial. Same goes for plants, expect tall tree-analogues and brush on low gravity worlds, and short stubby brush on high gravity worlds"
] |
[
"Mars has an atmosphere. It used to be thicker but didn’t lose it because lower gravity. It’s magnetic field diminished over time as the core cooled. The smaller magnetic field allowed solar winds to strip a lot of the atmosphere away. If it had no atmosphere we wouldn’t be able to land crafts/rovers with parachutes and the helicopter we sent there wouldn’t be able to fly."
] |
[
"Why does yellow exist on the light spectrum but not pink?"
] |
[
false
] |
Just read an article about how pink does not exist on the light spectrum, but our brain creates it to signify that it's "not green" Here is the link: . In essence it's saying that we only have red, green, and blue cones in our eyes, and when your red and blue cones fire but not green, your brain in a way "creates" purple. However, we also can't "detect" yellow. It appears when our red and green cones fire. Yet for some reason we call yellow "real" because it appears on the light spectrum. However, that doesn't make any sense to me, all that means to me is that the wave length between blue and green fires both my blue and green cones. For all I know the "yellow" section is just a mix of green and blue light. In other words, why does yellow exist if we can't even detect it, but pink doesn't just because it's not on the spectrum? Seems like they are doing the same thing to me.
|
[
"To understand, look at ",
"the color response curve of the 3 types of cones we have in our eyes",
". The x-axis is the wavelength of light going into the eye, and the y-axis is how strongly the cone \"fires\" based on that wavelength. Their peak response roughly correlates to blue, green and red, which is why we call the cones by those names. ",
"Yellow light has a wavelength of about 580 nm. If you look at the chart, that makes the green and red cone fire about the same, and the blue cone doesn't fire much at all. Our brain interprets those signals as 'yellow'. ",
"But pink is different. We see pink when the red cone and the blue cone both fire strong. There is no wavelength of light which can cause that. Magenta and brown are similar- they are caused by cone responses which no single wavelength of light can produce. ",
"And so that's the difference between what we call \"real\" colors and those which we don't. Real colors are any color which can be produced by a single wavelength of light, non-real ones are ones which require a blending of different wavelengths. "
] |
[
", non-real ones are ones which require a blending of different wavelengths",
"I think we will soon be in a position to perform the following lunatic experiment: edit a human genome with a transgene which encodes an inducible synthetic photopigment (an engineered opsin that responds at maybe 700). Let the human grow up normally. After a certain age (say... 18, when nervous system development is finished), give them tetracycline to turn on expression of the transgene in their cones.",
"Observe the result. I'm genuinely curious at whether this person will report an expansion of experienced subjective qualia or whether they will simply see more \"shades\" of colors they already know. The fact that the brain can create a synthetic label we call \"pink\" for something that doesn't actually exist suggests that entirely 'new qualia' are perfectly possible. Which then leads to the question of how many new qualia you can jam into each sensory system. I mean, none of this insanity will resolve the hard problem of consciousness but it might give clues.",
"And in case anyone thinks I'm just a complete nutjob:\n",
"https://en.wikipedia.org/wiki/Gene_therapy_for_color_blindness"
] |
[
"The fact that the brain can create a synthetic label we call \"pink\" for something that doesn't actually exist",
"Saying \"it doesn't exist\" isn't quite right, unless you mean that in the \"no colors exist\" sense, since color is your brain's lossy three-value model for an infinite number of frequency and intensity combinations.",
"But the \"pink\" response is triggered by real-world things. It's as real as green or yellow or blue or red-- it just can't be made with a single frequency."
] |
[
"Is it possible to not have a sense of humour?"
] |
[
false
] | null |
[
"Some diseases, such as Obsessive Compulsive Disorder, depression, (there are studies both ways) and Parkinson's Disease may reduce the sense of humour.",
"http://www.ncbi.nlm.nih.gov/pubmed/7886167",
"\n",
"http://www.ncbi.nlm.nih.gov/pubmed/22000944",
" "
] |
[
"Please keep discussion:",
"Civil\n\nOn topic\n\nScientific (i.e. based on repeatable analysis published in a peer reviewed journal)\n",
"www.reddit.com/help/faqs/AskScience"
] |
[
"Please keep discussion:",
"Civil\n\nOn topic\n\nScientific (i.e. based on repeatable analysis published in a peer reviewed journal)\n",
"www.reddit.com/help/faqs/AskScience"
] |
[
"AskScience AMA Series: My name is Thankful Cromartie, and I led the detection of the most massive neutron star ever (to date). Ask me anything!"
] |
[
false
] |
Hey AskScience! My name is , and I'm a graduate student at the University of Virginia Department of Astronomy and a Grote Reber Doctoral Fellow at the National Radio Astronomy Observatory in Charlottesville, VA. My research focuses on a special class of neutron stars called millisecond pulsars. Yesterday, a paper I led along with my colleagues* in the North American Nanohertz Observatory for Gravitational Waves ( ) collaboration was published in Nature Astronomy. It details our measurement of what is very likely the most massive neutron star ever detected. The source, called J0740+6620, weighs in at 2.14 solar masses. In short, this result was obtained by observing a general relativistic effect called in a pulsar-white dwarf binary system with the telescope, and combining that data with five years of NANOGrav observations of the pulsar. No other neutron stars have measured masses that exceed 2 solar masses outside their 1-sigma confidence intervals, so we're really excited about this result! The main motivation behind these kinds of measurements is to constrain the very poorly understood neutron star . The paper can be found , and a more accessible summary of it that I wrote for Nature Astronomy. You can find me on twitter . I'll be answering questions between 3:00 and 5:00 pm ET (19-21 UT). Ask me anything about pulsars, using them to detect gravitational waves, the neutron star equation of state, observational radio astronomy, astrophysics grad school, or anything else you're curious about! *I want to especially highlight my close collaborators on this work: Dr. Emmanuel Fonseca at McGill University, Dr. Paul Demorest at NRAO Socorro, and Dr. Scott Ransom at NRAO Charlottesville. EDIT: I'm going to be answering questions for a while after 5pm. This is fun!
|
[
"I mean, I guess I’ll ask the obvious because I am super curious - what’s the story behind your name? Was it your name given at birth, or did you choose it?"
] |
[
"Haha, I should have been more prepared for people to be so interested :) It’s actually an old family name! My full, legal name is Hannah Thankful Cromartie; my parents literally picked it off an old (1700s) family gravestone in eastern NC (where my family settled after leaving Scotland). In first grade, I started going by my middle name because there were too many Hannahs in my class. Here’s a chart for the weirdly curious/doubters ",
"http://www.cromartiefamilyassociation.com/docs/CromartieChartdraft9.29.08.pdf",
". TMI?"
] |
[
"How smooth is a neutron star ? I read somewhere that a millimetre sized “starquake” on the surface would release deadly gamma rays. Have we detected such events ?"
] |
[
"No Electron Spin?"
] |
[
false
] |
[deleted]
|
[
"The \"spin\" of electrons, 1/2 and -1/2, is an intrinsic property of electrons. It does not describe the movement of electrons around the nucleus."
] |
[
"First, you have to understand that \"spin\" is a bit of a poor name- the electron is not actually spinning, the electron has angular momentum which is in the direction that an electron would have if it were spinning. This \"spin\" is an intrinsic property of electrons (and in fact, of most matter). ",
"The fact the electrons have spin = 1/2 is in fact very, very important for all of physics and chemistry. It turns out there are 2 types of particles in the universe, bosons and fermions. Electrons are fermions (all particles with spin = 1/2 or 3/2 or any half integer are fermions) but if it had spin = 0 it would be a boson (all particles which have integer spin, 0,1,2... are bosons). If electrons were bosons, they would no longer follow the Pauli Exclusion Principle. This means that all of the electrons, no matter how many, could occupy the first shell (be in the 1s state). Thus, all chemical reactions would basically cease, because chemical reactions take place because of unfilled electron shells. Without needing different shells, the concept of unfilled shells would cease to make sense. "
] |
[
"Yes, I would agree. Electronic structure is central to chemistry. If electrons suddenly became bosons, all of chemistry as we recognize it would fall apart."
] |
[
"Why do small stars live much longer than big stars?"
] |
[
false
] | null |
[
"Bigger stars have more mass → more gravity → higher internal pressure → hotter → burn faster.",
"More precisely, ",
"the lifetime of a star on the main sequence scales roughly as M",
"Yes, bigger stars have more fuel, but they burn through it much faster."
] |
[
"The quote is actually, “The flame that burns Twice as bright burns half as long.”\n-Lao Tzu, Te Tao Ching",
"Just modernized is all."
] |
[
"Also, smaller stars have convection through which allows them to burn all of their hydrogen. Stars as big as the sun or larger do not burn all of their hydrogen fuel before going further up the element chain because they hydrogen can get to the core to fuse."
] |
[
"Assuming both volumes are equal, if I add cold water to hot water, and hot water to cold water, will they cool/heat at the same rate?"
] |
[
false
] | null |
[
"Semi-layman answer (I worked in a college fluid physics lab, but many years ago as a high school internship):",
"How are you adding the liquids to each other? Are you mixing the fluids together? If not, I would imagine they would mix at different rates (because of the complex fluid interactions, and the fact that the hot water would rise). When you add cold water to hot, the hot water will rise up, mixing with the cold water, If you add hot water to cold, there will be less mixing. Therefore, all things equal, I believe adding cold water to hot would generally hit equilibrium sooner than the other way around. "
] |
[
"If you mix them perfectly, then yes. ",
"Note that the density of water is somewhat complicated (",
"it is actually most dense at 4 degrees C",
"). At room temperature cool water is slightly less dense than warm water however. ",
"Basically, if you add cool water on top of warm water the system will be unstable and tend to 'mix' it self. ",
"This",
" is a really cool discussion on lighter fluids supporting or pushing on denser fluids. So in some ways, adding cool water on top of hot water will cool/heat at a faster rate.",
"In almost all situations, the relative densities will hardly contribute to the transfer rate. I thought it was merely a cool situation to mention as it crops up in many situations."
] |
[
"No problem, I was a bit hurried while typing it up, but the general concept is this:",
"1) Heat transfer is aided by large surface areas or mixing zones (this is why heat sinks have fins)",
"2) Diffrent geometric configurations can lead to diffrent rates of heat tranfer not only in the short run and the long run.\\",
"It may be interesting to examine situations where water is super cooled or heated and so on, depending on why you are interested."
] |
[
"I've been reading about Portuguese man o' war, a colonial organism. Each species is completely dependent on each other. Could I be considered colonial composed of just single celled organisms?"
] |
[
false
] |
Man o' war:
|
[
"I think his analogy is not to humans and our bacteria, but to humans and our cells."
] |
[
"A good place to start thinking about the differences between colonial organisms and multicellular organisms is their respective definitions. Colonies are defined as groups of organisms that closely associate but, if separated, are capable of survival on their own (I'm paraphrasing for the sake of brevity). Considering your different tissues in this respect makes it clear that separating your cells out (even in a medium that allows for continued existence) would still make it so that they could not reproduce or grow without substantial intervention. Of course there are other differences: for example how a unified biological organism develops and differentiates at the cellular level versus how a colonial organism (like Physalia physalis) becomes whole by a budding process for each of its different organisms (or zooids). This paper covers a lot of the developmental biology of these types of organisms: ",
"http://www.brown.edu/Faculty/Dunn_Lab/assets/Dunn_Wagner2006.pdf",
" ."
] |
[
"A little clarification:",
"A man-o-war is one species, not many. It is many individuals or \"zoids\" attached together. It would be like getting a hundred people and duct tapping them together and say \"survive\". In the man-o-wars case each individual has a job: \"One of the polyps, a gas-filled bladder called the pneumatophore (commonly known as the sail), enables the organism to float....The other three polyp types are known as dactylozooid (defence), gonozooid (reproduction), and gastrozooid (feeding).[11] These polyps are clustered.\"",
"Your analogy about humans and our other bacterial symbionts is a bit different. In this way we provide these bacteria a place to live (our gut, mouth etc.) and they provide us with services like breaking down our food. Of course some bacteria that live on us are harmful but we usually fight them off. That is why most cuts don't become infected. But we are one species and the bacteria are many. Also, while we may help each other out we are not the same type of unit as the man-o-war working together to survive."
] |
[
"How are protein folding rates related to protein stability?"
] |
[
false
] |
[deleted]
|
[
"They are not at all related. Stability is a thermodynamic parameter, which means it is path-independent. Folding rates are kinetic parameters, which depend on many molecular details."
] |
[
"The rate of protein folding and the stability of a folded protein are only linked indirectly. They both have to do with energy minimization and entropy maximization, but a protein might quickly fold into a local energy minimum that is ultimately less stable than its lower energy, global minimum. This is one major reason why the heat-shock protein class evolved, precisely because the first equilibrium point reached is not necessarily the best."
] |
[
"http://www.nature.com/nature/journal/v475/n7356/images_article/nature10317-f1.2.jpg",
"That figure is a good one showing what he is describing. To add on, a protein may quickly fold into a misfolded conformation, that is neither more or less stable (thermodynamically), but is in fact an aggregate which the cell must clear.",
"Think of each energy minimum as a conformation in which the protein might get trapped (as in a well). Energy is then needed to climb out of the well and transition into another state. Chaperone proteins help with this. "
] |
[
"When is a tree considered dead and do trees die of old age?"
] |
[
false
] |
I'm know trees don't just fall over and die like animals do (atleast from old age) but some trees are still considered dead. I've read that some trees can live up to thousands of years.
|
[
"Heartwood in most trees is dead tissue that serves just a structural role. It can be rotted away without affecting the health of the tree, but not everybody understands this and they are likely to describe the tree as being dead."
] |
[
"There is also the concept of \"negligible senescence\" where by some species do not appreciably age after reaching maturity. Giant tortoises are an example and continue to be able to reproduce their entire life. This is due to adaptations that reduce oxidative stress caused by free radical damage. ",
"Some flatworms, called planaria, appear to have the ability to endlessly regenerate telomeres. Essentially, this means that their cells can undergo mitosis indefinitely, with old decayed cells dying and being constantly replaced. ",
"Woody plant cells generally provide two functions, structural support or vascular function. Neither particularly require a lot of energy, so oxidative stress is less than in animal cells. Cells that undergo high amounts of activity, such as photosynthetic cells and reproductive structures usually die off in deciduous plants, but the slowly dividing woody cells can last for a long time. Plants are also capable of cloning, in fact, there is an entire aspen forest that is made up of one cloned plant, and may be thousands of years old. "
] |
[
"There is also the concept of \"negligible senescence\" where by some species do not appreciably age after reaching maturity. Giant tortoises are an example and continue to be able to reproduce their entire life. This is due to adaptations that reduce oxidative stress caused by free radical damage. ",
"Some flatworms, called planaria, appear to have the ability to endlessly regenerate telomeres. Essentially, this means that their cells can undergo mitosis indefinitely, with old decayed cells dying and being constantly replaced. ",
"Woody plant cells generally provide two functions, structural support or vascular function. Neither particularly require a lot of energy, so oxidative stress is less than in animal cells. Cells that undergo high amounts of activity, such as photosynthetic cells and reproductive structures usually die off in deciduous plants, but the slowly dividing woody cells can last for a long time. Plants are also capable of cloning, in fact, there is an entire aspen forest that is made up of one cloned plant, and may be thousands of years old. "
] |
[
"Stupid question: Is dough considered a solid or a liquid?"
] |
[
false
] | null |
[
"The definition of liquid is that it must have a fixed volume but no fixed shape, so I think it is clear that dough (the one in your bread dough picture) is closer to solid than liquid because it has a fixed shape (i.e. it doesn't automatically take the shape of a container). ",
"Just because dough is very pliable does not mean it is a liquid; think of metals that are very malleable in their solid form.",
"EDIT: It would be a solid if you classified it into the main 3 categories but it might be better classified as an amorphous material."
] |
[
"Dough is probably best classified as a colloidial gel. The small starch granules and other particles are suspended in water within a polymeric matrix of proteins to form a gel. Think of Jello, is it a solid or liquid?"
] |
[
"They are both amorphous materials, and don't fit perfectly well into solid or liquid."
] |
[
"How would this type of jaw surgery be performed? (Link in text)"
] |
[
false
] |
Xpost from : My mind is slightly blown. What is the nature of her condition, and how is it fixed so spectacularly?
|
[
"Severe overbites/underbites can be fixed with a ",
"bilateral sagittal split osteotomy",
" - basically they saw your jawbone off, move it, and screw it back on in the proper position. I had this done a couple years ago. "
] |
[
"The recovery wasn't bad. I was in a lot of pain for the first couple days, but I was also on a lot of drugs :-) The surgery causes nerve trauma, so my entire jaw was almost completely numb. My mouth was rubber-banded shut using the brackets from my braces (this was all related to orthodontic treatment) so I was on an all-liquid diet for a few weeks, which kind of sucked. It took several months before I was able to chew tough foods. ",
"I did have a tiny bit of permanent nerve damage on the left side of my chin. I can feel when something touches that side of my face, but sometimes the sensation isn't localized, so say I touch something hot to my lip, I might feel it an inch or two down onto my chin. My lip occasionally tingles. That all sounds worse than it really is, though, I hardly notice it anymore. Besides, the results were totally worth it. "
] |
[
"I too had this done. It's not that uncommon, I don't think. At least, I've met others. Mine was done in 1986, so it's not super new either. Lost like 40 pounds, it was awesome. My nerve damage is on the right, though.. interesting. Be careful if you get numbing shots at the dentist on that side.. my nerve is in a slightly different place than they expect and I've had 4 shots before they find it, and that stuff makes one's heart race pretty bad.",
"Edit: wait, my nerve damage is also on the left. I'm so used to it I forgot!"
] |
[
"Without the expanding force of fusion reactions, why don't gas giants get smaller?"
] |
[
false
] |
With stars, the outward pressure of fusion and the inward pressure of gravity eventually equalize, but gas giants don't have the outward pressure. Why don't they collapse in on themselves?
|
[
"There is an outward gas pressure. This is the same reason it is hard to compress a basketball down to the size of your palm. Gas pressure increases when the volume it occupies decreases (and temperature is held constant). Gravity acts to decrease the volume of the gas, and a balance is achieved when ",
"hydrostatic equilibrium",
" is reached by creating a pressure gradient."
] |
[
"They do shrink. Once the gravitational pressure gets high enough, electron degeneracy causes them to shrink a bit. So they would appear smaller than they would below the limit, while being more massive."
] |
[
"What ends up being important here is how much mass the body has to exert gravitational pressure with. If the pressure is such that the body never favors deuterium fusion, and thus never has thermonuclear fusion as a source of outward pressure, it's a gas giant. If the cloud of gas contracts sufficiently to support deuterium fusion, but not hydrogen fusion, the body is a brown dwarf, and will produce some light and heat for a few million years. If the the cloud has enough mass to contract to the point that hydrogen fusion becomes favored, then the body is a star. So a gas giant is a star with no fusion, a brown dwarf exhibits the easiest forms of fusion (fusion processes below hydrogen burning), and star burns hydrogen."
] |
[
"How Does Gravity Affect Single Particles?"
] |
[
false
] |
Does a single particle (like a hydrogen atom) in a vacuum fall like a macroscopic object in a relatively weak gravitational field (like the Earth's)? Or maybe does its position expectation value change like -(1/2)gt ? ELIundergrad if possible, and thanks!
|
[
"Gravity does affect individual particles. There have been some experiments to test how Newtonian gravity affects quantum systems (looking for interferences with cold neutrons passing through different gravitational potentials, etc.). I think Sakurai goes over the details in his QM book."
] |
[
"We actually have a really good idea how things work in a weak gravitational field, thanks to Newton and Einstein. It's only when you get close to black holes when you need to include quantum gravity corrections, which are messy and less understood."
] |
[
"Just to follow up on the \"How\" part of OP's question: We do not know. For all other forces we have this picture of force-mediating particles: photons, Z,W-bosons, and gluons for electromagnetic, weak, and strong force, respectively. This we have a very detailed understanding of (the Standard Model). For gravity we have a ",
" \"graviton\" that would do something similar, but we have no idea of ",
" it would interact with other particles."
] |
[
"What makes one feature dominant and other recessive?"
] |
[
false
] |
I want to know why some features in genetics are dominant and can overcome this recessive ones, how they do this, what is the difference between them?
|
[
"This is a broad oversimplification, but one key difference here is loss of function vs gain of function. ",
"Take the ",
"Melanocortin 1 Receptor",
". This protein is a receptor that when triggered, most notably from skin damage through UV radiation, converts phaeomelanin, a reddish-yellow pigment responsible for freckles, into eumelanin, which is a darker skin tone, i.e. tanning. ",
"In some cases, there is a mutation that inactivates this protein, preventing skin tanning from happening, resulting in a person becoming a redhead. However, since there are 2 copies of it on each set of the chromosome pair, one from each parent, a person with only one mutant copy would still have normal skin tanning as the other one works. However, if both copies have mutations, then that person wouldn't tan normally, hence a recessive feature. Again, there's a lot of caveats and nuances here, so remember this is more of a broad brush. ",
"Other alleles are dominant because you gain 'function'. One such example is a mutation that causes ",
"achondroplasia dwarfism",
". A growth factor receptor, FGR3, is mutated in this case where the receptor is overstimulated, causing abnormally high signaling of that pathway. When that happens, skeletal growth is affected, causing the individual to have dwarfism."
] |
[
"The problem with hair color is it's a polygenic trait, so simple Mendelian descriptions like that do not fully represent the situation.",
"Edit: ",
"Here",
" is a GWAS that found a bunch of sites involved in determination of hair color. It's particularly complex for various shades of blonde and brown."
] |
[
"In the case of individuals with dual MC1R mutations in almost all cases the individual would have red hair, with some potential exception for albinism, etc.",
"That is not correct. They would more often have light brown hair. This is due to poor penetrance of many MC1R variants.",
"As the study above states:",
"Although 93% of individuals with red hair carry two MC1R variants, these make up only 15% of people who carry two MC1R variants. The majority of people with two variants have blonde (15%) or light brown hair (41%)."
] |
[
"I pull a tray of ice cubes from the freezer. Why are some of them opaque and some of them almost brilliantly clear?"
] |
[
false
] | null |
[
"The clear ones have higher transmittance than the opaque ones. This is because there are fewer regions of different materials within the ice, like air bubbles. Remember that light rays are scattered at the boundaries of materials (e.g. the air bubble- ice transition) due to the differing indices of refraction. So in an opaque ice cube, there are more air bubbles for the light to scatter off of, while a clear cube will allow the light to be transmitted. "
] |
[
"It has to do with how fast the water freezes. The ice cubes that froze quickly will be opaque, while the ice cubes that freeze slowly will be clear.",
"Here is why:\nFirst, if you look carefully you will see that the \"opaque\" part of the ice cube is actually many tiny bubbles. This is because there is gas (air) dissolved in water. Warm water can hold more dissolved gas than cold water, so as water cools it releases the dissolved gas.",
"What happens is when water is frozen slowly, there is plenty of time for all of the gas to escape the water, and the ice cube will have no bubbles in it, thus being clear.",
"When water is frozen quickly, the gas may get released, but the water above it might already be frozen, so there is nowhere for it to go. it stays trapped in the ice cube as bubbles, which causes it to be opaque."
] |
[
"I can only think of one reason and that is morphology of the ice-crystals. Morphology describes the form of a crystal and the morphology describes the physical properties of your crystal. If the morphology is different, the physical properties are different. This fact is very important if you make solid (crystalline) pharmaceuticals. You can change the morphology by adding additives, contaminations so to say. Since you do not use destilled/de-ionized water you always have contaminations in form of different salts and also dust since you are not working in a dustfree area and this is what will in fact change your morphology which will therefor change your physical properties like transparency. "
] |
[
"What physical differences are there between a marathon runner and a non-marathon runner (regular person) of roughly the same stature?"
] |
[
false
] |
It's much easier for me to understand the differences between a regular person and a strong person / heavy lifter. But what about the differences between a regular person and someone with a lot of endurance? My thoughts have been about: Better usage of the lungs?; more mitochondria? Less fat to carry?; more capillaries? I would assume the amount of blood was the same - but maybe not the same proportions of cells? A stronger heart, so more blood pumped per beat (Cant remember the word)?
|
[
"I am assuming that you are referring to an exceptional endurance. There are two main types of muscle tissue in muscle and a third in cardiac muscle. The straited muscle also called slowtwitch and unstraited muscle called fast twitch. Fast twitch is what burst strength comes from. Slow is for endurance.",
"Good Marathon runners also have anatomical differences too. There is a general difference in anatomy regarding limb length vs body length and tendon length, heal and hip mechanics. A longer calcaneus, your heal bone, gives you a longer and quicker lever for your foot. A narrower foot also allows for a quicker transfer of weight from the outside of your foot to the inside and the big toe joint.",
"A narrow pelvis is a factor too. A narrow pelvis changes the gives a better 'Q' angle or the angle relationship between the road and the ground. A narrow pelvis will make for quicker transfer of body weight from one side to the other. ",
"The longer the upper and lower parts of a leg will give you better 'Pop' mechanics. This is the hop that puts a runner up in the air while the lower while the foot pushes them forward. A longer upper leg carries the weight more forward when swinging under their body and up when they rise above vertical in front of the body. ",
"Anatomic make up in the biggest difference. There are plenty of heavier people with a huge amount of endurance. My mother where I got my extremely high percentage of slowtwitch. She is a short big boned person that could drag a tractor tire across North America.",
"I have been out of the loop for 2 decades and am not confident in my descriptions regarding the biomechanics. Any better description of this would be appreciated."
] |
[
"Just for clarification, there are some inaccuracies in what you've said, perhaps just a mistake.",
"Also, to answer OP well, a bit of background:",
"There are three types of muscle in the body: Skeletal, smooth, and cardiac muscle.",
"The muscle that propels us during exercise and under our voluntary control is the skeletal muscle (think biceps, quads, etc). It is striated, not straited, for clarification. This means that when you look at the muscle under the microscope it looks like it has stripes on it. Wiki \"muscle striation\" to understand why. It involves how muscles are able to contract.",
"Simply, striated muscle can be divided into two categories - Slow twitch (ST) and fast twitch (FT).",
"Compared to slow twitch (ST) muscle, fast twitch (FT) muscle contains a higher amount of the anaerobic cellular machinery needed to make energy quickly. Lactic acid is produced as a by product and oxygen isn't used. FTs are the muscle fibers that predominate when you're doing activities requiring a lot of strength. But, when lactic acid accumulates faster than the body can buffer it, you feel \"the burn.\" \"The burn\" is the acidity of the lactic acid starting to wreak havoc with the operating conditions within the cell.",
"Slow twitch (ST) muscle has comparatively more aerobic capability, a metabolic pathway that is more efficient but takes longer to ramp up. Once it's initiated though, it shares energy production with the body's fat burning machinery for endurance exercises more than 20 mins.",
"To answer OP:",
"You are right in a few of your assumptions. Endurance training does effect a few physiologic adaptations, including an increased number and size of mitochondria, increased vasculature to the skeletal muscles and pulmonary areolae, and quicker initiation of aerobic glycolysis and betaoxidation.",
"As far as endurance athletes hearts, their left ventricles (the chamber that pumps to the systemic circuit) tend to be hypertrophied, with increased ",
" leading to increased ",
". The body tissues are refreshed quicker with more blood, and more oxygen as a result.",
"Endurance athletes proportion of plasma in their blood increases, improving thermoregulation.",
"Obviously, the muscles used most frequently will become bigger. They include the quads, hamstrings, calf muscles, and glutes.",
"Pulmonary adaptations aren't particularly necessary, since a person's ability to keep the red blood cells and plasma saturated with oxygen is perfectly fine in a healthy, albeit untrained, individual. The modifications that allow great endurance stem more from the muscle tissues' increased ability to use oxygen and buffer lactic acid more effectively than non trained individuals.",
"Endurance runners tend to carry less fat because when exercising past about 20 minutes, the body's fat burning metabolic pathway ramps up (beta-oxidation) to start converting the triglyceride from your adipose tissue into useable form for energy production. As long as the individual doesn't overdo the eating between exercise bouts, they'll likely carry less fat than a comparable untrained individual.",
"One other important thing regarding endurance adaptations as it regards slow and fast twitch muscles. People are genetically endowed with more or less FT or ST muscle...Elite athletes in sprinting will be on the far end of the bell curve as far as their proportion of FT muscle fibers. Marathoners will have more STs. The two different muscle fibers actually look different under a microscope. That being said, anyone can maximize their potential by chronically overexerting themselves in the exercise they'd like to improve at.",
"Hope that helps.",
"Source: Taking exercise physiology right now, getting an A at the moment :) Wish me luck."
] |
[
"That makes great sense. If we had to compare a regular person (non-fit) with him again 12 months later ready for marathon, what would the differences be? Muscle composition as you mentioned. Anything else?"
] |
[
"Is there a limit to the number of pathogens our bodies can produce antibodies for?"
] |
[
false
] |
Since B cell lymphocytes are responsible for antibody creation, I assume the answer to this question is "the number of B cells in your body," but is there a theoretical limit to the number of distinct antibodies our bodies can create?
|
[
"First of all, B cells starting being unique, but when their services are needed, each unique cell multiplies. So total number of B cells is greater than the number of distinct antibodies you can produce.",
"Second, each distinct antibody can react to multiple antigens, so the total number of antigens you can respond to is greater than the number of antibodies you can produce.",
"Third, each pathogen has many antigens, so the total number of pathogens you can respond to is less than the total number of antigens you can respond to.",
"Then, B cells, when activated as part of active immune response, undergo maturation, during which the antibodies they produce become more selective. As a result, mature B cells can respond to fewer antigens than immature B cells.",
"And finally, B cells by themselves don't do much; for most immune responses, they have to be activated by T cells. As a result, the total number of pathogens you can respond to is not just about your B cell diversity, but also your T cell diversity — and that's not even counting pathogens which are picked up by innate immunity (like macrophages) which also have the ability to stimulate B cells.",
"In short: yes, but it's complicated."
] |
[
"Also, B cells are constantly produced from our bone marrows, so every day we get new ones with new specificities."
] |
[
"Totally agree with everything you wrote, but I'm not sure I agree with the conclusion that there is a theoretical limit to how many pathogens/antigens we can create antibodies for. At least what I've learned as a medical student is that the diversity of the T/B-cell with V(D)J recombination is sufficient to always have an answer to whatever antigen the environment throws at us. But drawing conclusions like these is always dangerous when it comes to science so your answer is true in a theoretical sense but not realisticly."
] |
[
"Why do energy drinks make me sleepy?"
] |
[
false
] |
Over the years I've drank every name brand energy drink on the market and not one has given me energy. In fact, most have made me sleepy. I'll feel a flutter in my chest for about 20 seconds... and then I feel as if I just finished working double-time. Is there a reason why my body would reject liquid energy and cause the opposite intended effect? Edit: Thanks for the answers, guys! Interesting stuff. You really are the best.
|
[
"(LAYMAN) Perhaps it's this:",
"Paradoxical Reaction"
] |
[
"Someone will have to elaborate but it is due to the insulin response due to the high sugar content."
] |
[
"Nocebo effect",
" perhaps?",
"What I mean is, if the effect is immediate, then it is most likely psychological. You expect to feel tired, therefore you do. You may have created a subconscious association from a past experience when you were in a fatigued state and drank an energy drink.",
"If, on the other hand, it happens an hour or more after ingestion you're probably 'crashing' from a rapid drop in blood glucose levels and reduced seretonin and catecholamine activity from caffeine withdrawal."
] |
[
"Do elements in the Earth's core settle in homogeneous bands?"
] |
[
false
] |
I was wondering if elements in the molten portion of Earth's crust can be found together in layers like we see when you pour oil in a glass of water or if they are mixed up by a type of convection process.
|
[
"Yes! The interior of the Earth is differentiated, like a glass of oil and water. And it is due to the same principle of varying densities.",
"In the beginning, the solar system was a disk of gas and dust surrounding what would become the sun. This cloud was more or less homogenous (except that the gasses and other volatiles were concentrated on the outside) and so the planetesimals that accreted out of it were also homogenous. But this accretion and compression generated an awful lot of heat, and so these planets and planetesimals started out as big, molten balls of rock and metal floating around in space. In this liquid state, it was easy for the heavy metals like iron, gold, and uranium to sink down to the core. The lighter carbons and silicates floated to the top. The outer surface of the crust exposed to space began to cool, forming the crust. The mantle of the Earth is also more or less solid, although it is still very hot and does convect over very long timescales. The only truly liquid portion of the earth's interior is the outer core. The core itself is solid, having been \"pressure frozen,\" or forced into being a solid due to the extreme pressures that exist 4000 miles down."
] |
[
"it was easy for the heavy metals like iron, gold, and uranium to sink down to the core. ",
"and yet, there is thought to be very little, if any uranium in the Earth's core at all. Despite being extremely dense, it is strongly a lithophile element, readily combining with silicates thus being concentrated in the mantle and particularly the crust. This is how we are able to mine uranium ore for nuclear energy at all, we certainly wouldn't be able to extract it from the core. ",
"Your answer would be more complete with an aknowledgement of the role that chemical solubility of the elements into common Earth phases and minerals plays."
] |
[
"Thank you!",
"The core itself is solid, having been \"pressure frozen,\"",
"Would that mean, to the best of our knowledge, the core is layered like a jaw breaker, or was it \"pressure frozen\" too fast for that to occur?"
] |
[
"Do fundamental particles exist in 16 dimensions, but we \"experience\" them in only 3? How can dimensions be folded up inside other ones?"
] |
[
false
] |
[deleted]
|
[
"I can't really comment on the 16 dimensional stuff since I'm not a string theorist, but I have a good analogy to understand the 'curled up dimensions'.",
"Consider a long string or cable. When you hold it in front of your eyes you can see it has multiple dimensions. There is the length of the string, and there is the roundness to it; as in if you were small enough to be sitting on the string you could move around it in a circular fashion and not just along its length. Hence at that scale you can see there are 2 dimensions to the surface of the string. You could walk in a straight line down its length, or you could turn 90 degrees and walk around the body of the string.",
"However consider this same string held several feet away from you. If you had never seen this mysterious object before and could only view it from this relatively large distance you would conclude it one has 1 dimension, it only has its length, there is no thickness to the string! That second dimension to the string is 'curled up' at a smaller scale and only by magnifying the string does this new dimension become apparent.",
"Obviously we cannot possibly understand how these 13 other curled up dimensions would look because we live in a 3 dimensional world, the concept of another spatial dimension is beyond comprehension. However I hope my analogy has helped to understand the idea of curled up dimensions.",
"edit - wording"
] |
[
"Well, right now we have no evidence of these extra dimensions. String theory is still just a theory with no testable experimental predictions nor any experimental proof. So with that being said I can't really reference anything in the physical universe that we know possesses these curled up dimensions.",
"Theoretically, ",
"Calabi-Yau Manifolds",
" are supposed structures of 6 curled up dimensions. These are used in superstring theory."
] |
[
"Well, right now we have no evidence of these extra dimensions. String theory is still just a theory with no testable experimental predictions nor any experimental proof. So with that being said I can't really reference anything in the physical universe that we know possesses these curled up dimensions.",
"Theoretically, ",
"Calabi-Yau Manifolds",
" are supposed structures of 6 curled up dimensions. These are used in superstring theory."
] |
[
"Does stellar wind cause dust and gas to collect in stable pockets in the interstices between stars?"
] |
[
false
] | null |
[
"Like millions (well, Re~10",
" - 10",
" ). The viscosity is very low.",
"It definitely behaves like a fluid on interstellar scales. The mean free path might be something like ~100 AU (~1 light-day), and the mean time between collisions might be years to hundreds of years, but in galactic astronomy we're dealing with time-scales of millions to billions of years, and length-scales of light-years to millions of light-years, so the fluid approximation actually works fine."
] |
[
"Stars do inflate bubbles of hot high-pressure moderate-density gas, but you don't get stable pockets in between the stars: these bubbles are still small compared to the size between stars. The Voyager I probe actually passed through the \"Heliopause\" in 2012, and passed out of the bubble inflated by the wind. The distance to the heliopause is less than a light-day, which is much smaller than the 4 light-years to the next closest star.",
"So the overall picture is that most of the volume of the Milky Way's disc is taken up with interstellar gas, and that stars are just small bubbles within it. Additionally, the interstellar gas is very turbulent (mostly from supernovae), so it mixes around fairly quickly, and you don't get long-term stable clumps of high-density gas forming."
] |
[
"Additionally, the interstellar gas is very turbulent",
"It’s dense enough that it still behaves as a fluid? What’s the Reynolds number for interstellar gas?"
] |
[
"Why is that photons can \"feel\" no time?"
] |
[
false
] | null |
[
"That's a really misleading way of wording it, but you used practically-audible finger-quotes, so I assume you get that.",
"Imagine two events in spacetime: one at which a photon is emitted, and one at which a photon is absorbed. We'll call the emission event ",
" and the absorption event ",
" We'll further say that events ",
" and ",
" are both observed from the same reference frame, so we only have to deal with one set of coordinates. If you want, you can imagine that ",
" happens on one side of a laboratory, and ",
" happens on the other side some tiny fraction of a second later.",
"The proper time along an inertial trajectory through flat spacetime in one-dimensional Cartesian coordinates is:",
"² = –",
"² + ",
"²",
"This is a special case of the normal formula for proper time, which is a path integral. Since the trajectory we're considering here is a geodesic, we can reduce the integral to a simple algebraic expression.",
"To solve this equation, we need to know ",
" and ",
" If we know ",
" the spacelike separation between the two events — the separation as measured with a ruler — ",
" the timelike separation — the separation as measured with a clock — we can compute the other one trivially. How trivially? ",
" trivially:",
" = ",
"But wait, you might say. How can that equation be valid? The left side has units of time, and the right side has units of length!",
"Well, that's the thing about doing problems in spacetime. You never use any units of measure ",
" than ",
" Before doing any actual computation, you always convert ",
" to meters, by applying the right conversion factors. We measure time in meters, we measure mass in meters, we measure density in ",
" of ",
" … it may seem arbitrary and convoluted, but trust me, it's really the right thing to do.",
"So for a ray of light — and again, this is ",
" that applies ",
" to a ray of light ",
" — the timelike separation between the emission and absorption events is exactly equal to the spacelike separation between the events. If, in our experimental apparatus, the distance between the source of light and the detector is exactly five meters, then we know the ",
" separation between the emission and absorption events will ",
" be five meters. In other words, ",
" = ",
" = five meters.",
"So now we can just plug those values for ",
" and ",
" into the proper-time equation, and we get:",
"² = –(5 meters)² + (5 meters)²",
"Or, in other words, ",
"And of course, the same will be true of ",
" separation. Regardless of how far apart the emission and absorption events are, the proper time between them ",
" will be exactly zero.",
"And since proper time is equal to the time that would be measured by a clock moving along the given trajectory, we can say that photons don't age.",
"The equations for doing this same demonstration in curved spacetime are quite a bit more complex, involving the components of the curvature tensor and so forth, but the equation always comes out the same: zero. That's why the trajectories that light follows between any two events in spacetime are called ",
" because the proper time along those trajectories is always exactly zero everywhere, in every reference frame."
] |
[
"If I could fix toasters, I'd have a working toaster right now."
] |
[
"I tried. It just got brighter."
] |
[
"In a quote from the linked article from Nature “we describe the genomic profile and early transmission dynamics of Omicron, highlighting the rapid spread in regions with high levels of population immunity.” How does Omicron “spread” in area without high levels of population immunity?"
] |
[
false
] | null |
[
"In areas without high levels of immunity omicron will spread even more rapidly. The idea behind vaccinations was originally to stop the chain of transmission. We now realize that probably won’t happen since the community infection rate is very high. Instead we are hoping that vaccines will prevent severe illness. An unvaxed person would get more sick, be more infectious for a longer period of time thereby potentially infecting more people."
] |
[
"Isn't it also how this particular virus replicates in the upper airways where antibodies aren't readily available?"
] |
[
"You have to remember there are different types of antibodies (t-helper cells, b-helper cells, neutralizing antibodies etc.). The vaccine was never going to provide sterilizing immunity like they do with measles. But they do afford some level of protection even with more replication happening in the upper airways. To what exact level I don’t know and would have to consult the literature which is currently in preprint."
] |
[
"Do multiple electrons exist during superposition?"
] |
[
false
] | null |
[
"So you're asking about a ",
" electron in a superposition state? Then yes, it's really in both places at the same time.",
"But it's still just one electron, not multiple."
] |
[
"Thanks, that makes sense now!"
] |
[
"What do you mean?"
] |
[
"How often do viruses mess with the adaptive immune system?"
] |
[
false
] |
My understanding is that essentially every virus capable of causing an infection in a human has some means of messing with the innate immune system so as not to immediately be wiped out by it. But how common is it for viruses to have non-structural proteins in their genome that are targeted at messing with the adaptive immune system?
|
[
"It’s mainly the large DNA viruses, like adenoviruses, herpesviruses, and pox viruses, that modify the adaptive immune system. Smaller viruses, including most of the RNA viruses, tend to focus on the innate immune system primarily. Presumably the DNA viruses have enough extra room in their relatively large genomes that they can target both innate and adaptive. ",
"One of the earliest immune evasion approaches was identified in human adenoviruses, several of which have a protein that physically binds to MHC class I and prevents it from reaching the surface where it can interact with T cells. This was actually discovered before MHC function was properly understood, so there were several years when it wasn’t clear why it did this. ",
"Then it was shown that herpes simplex has a protein (ICP47) that also blocks MHC function, but by this time it was clear how this would lead to immune evasion, and this opened the floodgates. It now seems that virtually every one of the tens of thousands of herpesviruses has some means of adaptive immune evasion, probably an important part of their lifestyle (I.e. lifelong infection in spite of strong immune responses). ",
"Pox viruses also have a wide range of T cell inhibitors, but also have some antibody diversion molecules. Some herpes viruses also have Fc binders but it isn’t as widespread. ",
"It’s been surprisingly tricky to show how important these evasion strategies are. They’re so widespread and functionally conserved that they must be critical, but they tend to have surprisingly minor effects in standard models of pathogenesis, which probably says that standard models are missing important factors. ",
"This is a huge field and this is a super simplified overview. Further reading -",
"Immunoglobulin superfamily members encoded by viruses and their multiple roles in immune evasion",
"The Roles of Host and Viral Antibody Fc Receptors in Herpes Simplex Virus (HSV) and Human Cytomegalovirus (HCMV) Infections and Immunity",
"Poxvirus Immunomodulatory Strategies: Current Perspectives",
"New Insights Into the Structure of the MHC Class I Peptide-Loading Complex and Mechanisms of TAP Inhibition by Viral Immune Evasion Proteins",
"Herpesviruses Placating the Unwilling Host: Manipulation of the MHC Class II Antigen Presentation Pathway"
] |
[
"If a virus wants to replicate in the body for more than a week, it’ll have to interact with the adaptive immune system and the viruses that are able to develop ways to avoid detection will be more successful at getting spread. So I’d say lots.",
"One way is by not getting seen by T cells.\nOur healthy cells constantly show pieces of their insides to patrolling T cells by randomly loading bits of whatever is inside them into MHC (aka HLA, depending on the species) molecules that can be ‘read’ by T cells. If the cell is virally infected, some of those pieces that get loaded are viral and the patrolling T cells can recognize this as a foreign/dangerous thing and then try to kill the infected cell. Evasion mechanism: Some viruses can force cells to lower their expression of MHC molecules to try and fly under the radar. Failsafe: low MHC is recognized as weird by an innate immune cell called a natural killer (NK). Evasion counter-mechanism: To get around this, some viruses have a protein the looks like MHC to turn off NKs, but can’t present anything to keep T cells from turning on.",
"Also, I’m not sure if this is part of your question exactly but viruses that have chronic infection courses are all about balance with adaptive immune cells. They are probably slower replicators, so antigens are present but low, and the constant low antigen exposure takes advantage of our own immune brake mechanism and T cells start expressing proteins that limit their activity."
] |
[
"That’s not adaptive immunity, which is limited to T and B cells."
] |
[
"Are fingerprints genetic at all? Would you be able to tell that someone is related to another person if their fingerprints are similar?"
] |
[
false
] | null |
[
"They're genetic, but they're also heavily influenced by environmental factors in the womb. ",
"For example, identical twins have different fingerprints. ",
"The foundation is genetic but it variations are introduced before birth. "
] |
[
"Families often have similar overall fingerprint patterns such as loops or whorls but the small points of minutia that law enforcement uses to distinguish between fingerprints for identification are different.",
"There are also some trends in fingerprint patterns in ethnicity, but not enough to be useful in any way.",
"Law enforcement cannot reliably predict family relation using fingerprint patterns.",
"Fingerprints form in the womb at about the 10th week of estimated gestational age and their shape is influenced by genetics, hand-position of the fetus, salinity & ph level of amniotic fluid and other factors. Specifically, fingerprint ridges form along lines of nerve endings called papillae and it is all of the above factors that determine the position of the papillae and then the fingerprints just form on top of them.",
"Identical twins have the same DNA and they might have similar fingerprints, but they are not identical.",
"Note that in law enforcement, there should never be such a thing as an \"80% match\". Fingerprint examiners will provide either a match or no match. If 80% of a print is similar to another one but there are some unexplainable details, then the examiner must determine it to not be a match.",
"Also note that due to a similar concept to the 'infinite coastline paradox', as fingerprint scanners become more detailed and better-quality prints are being compared, the differences between two fingerprints also increases.",
"However, all persons with Down Syndrome have a similar horizontal crease across their palm. Not everyone with this crease has Down Syndrome and there appears to be no correlation between having this crease and any predisposition for having children with Down Syndrome - but everyone with DS has the same crease."
] |
[
"A great deal of conditions (depression, diabetes, intelligence, etc.) have a genetic component and an environmental component so that many are not really well correlated with one alone. For instance, we know that if the mother has had previous male children, her future male children will be more likely to be gay."
] |
[
"Why does our heart beat at the rate that it does?"
] |
[
false
] |
This question really is -- Why don't our bodies have a higher dilation of the veins as a default and beat around 20-30 BPM instead of the 60-80 BPM? Or alternatively, why don't our bodies have a higher constriction of the vasculature and beat at 140 BPM or so? Thanks in advance!
|
[
"Yes and no. It depends on the site of the body.",
"Many blockages, especially in the heart and in the larger arteries in the brain, are due to clots blocking flow.",
"In the kidney, constriction of the blood vessels can essentially starve the kidney of oxygen and kill it. Things like epinephrine (adrenaline) are used to maintain blood pressure in very sick patients, but can damage the kidneys by this mechanism."
] |
[
"Not a doctor, but IMHO if your vasculature was further constricted, wouldn't that increase mortality rates by increasing potential blockages?"
] |
[
"First, arterioles, the smallest arteries with a muscular wall, are the main controllers of blood pressure. Veins mostly affect blood return to the heart",
"The quickest complete answer I can give:",
"Blood pressure is a function of the heart and of the vessels. Both are regulated by multiple systems to tightly regulate blood pressure. The important thing to keep in mind is that it is the ",
" or MAP that is crucial for our organs to receive adequate blood flow. You can approximate the MAP by taking",
"2/3*Diastolic BP + 1/3*Systolic BP ",
"Your organs do not care what the heart rate is, only the MAP.",
"Since you have two variables you can change (heart and vasculature), you could, as you note, adjust them to compensate for each other, and maintain MAP. The reason we live with our heart rates where we do is because it is the most efficient way to do it.",
"I can't get into detailed cardiac physiology right now, but for the heart to pump efficiently, the ventricles need time to fill up with blood. When our heart rates increase, the cardiac cycle is shorter. The reduction in length is due to a shortened diastole, that is, the passive filling of the ventricles. If your heart rate gets too high, the ventricles don't have time to fill properly, and it's a very inefficient pump. Note that different size hearts take more or less time to fill. Rodents frequently have pulses around 200 bpm, because a small heart fills more quickly. Elephants have pulses around 30.",
"So why can't the heart rate safely go down to say, 20 in a person? Well, the heart produces beats of blood flow, but organs want a constant stream of flow. To allow for this, the large arteries are elastic. Think of the aorta as like a balloon. Every time your heart beats, it puts a 'breath' into the balloon. Even between beats, there is pressure in the balloon because of the elasticity.",
"Basically, the aorta can only be so elastic. So if your heart rate got to 20, the aorta would have already given up the pressure it had (the balloon is empty), and your brain lacks blood flow. Larger animals have bigger aortas, and can accommodate more volume in their balloons."
] |
[
"If one of the main reasons for inaccuracy in firearms is the effects of recoil on the shooter, why are gun barrels not vented on the top, so gas could be expelled upwards, fighting the jerk of recoil?"
] |
[
false
] | null |
[
"They are, it's called porting. But, most of the people who will pay to have their barrel ported are trapshooters and such, and most guns already have vents that porting might fuck up."
] |
[
"I didn't know that, thanks"
] |
[
"No problem brother, I'm a trapshooter myself, and my shoulder would be horribly bruised and I couldn't hit shit with anything longer than a 30\" barrel because of the upkick. Asked my coach about that and he had me meet a guy who ported my barrel for 50 dollars. Best addition ever to my gun."
] |
[
"Chemically, what makes high-efficiency detergents better/required for HE washing machines?"
] |
[
false
] |
From what I've read, the major difference in detergents between regular and high-efficiency is that HE detergents reduce suds to prevent pump failure in HE washing machines. Is this just due to the addition of an anti-foaming agent or is there more to it than that?
|
[
" \nBorax\nCitric Acid\nDiethylenetriamine Pentaacetate (Sodium Salt)",
"\nLiquitintTM Blue",
"\nAmylase\nMannanase\nPectinase\nProtease",
"\nDisodium Diaminostilbene Disulfonate",
"\nSodium Hydroxide",
"\nPolyethylene Glycol\nPolyethyleneimine Ethoxylate",
"\nBenzisothiazolinone",
"\nCalcium Formate\nDimethicone\nEthanolamine\nSodium Cumene Sulfonate\nWater",
"\nAlcohol Ethoxylate\nAlcoholethoxy Sulfate\nLinear Alkylbenzene Sulfonate\nSodium Fatty Acids",
"\nBorax\nCitric Acid\nDiethylenetriamine Pentaacetate (Sodium Salt)",
"\nLiquitintTM Blue",
"\nAmylase\nMannanase\nPectinase\nProtease",
"\nDisodium Diaminostilbene Disulfonate",
"\nSodium Hydroxide",
"\nDiquaternium Ethoxy Sulfate\nPolyethyleneimine Ethoxylate",
"\nCalcium Formate\nDiethylene Glycol\nDimethicone\nEthanol\nEthanolamine\nPolyethylene Glycol 4000\nPropylene Glycol\nSodium Cumene Sulfonate\nSodium Formate\nWater",
"\nAlcohol Sulfate\nAlcoholethoxy Sulfate\nLauramine Oxide\nLaureth-9\nLinear Alkylbenzene Sulfonate\nSodium Fatty Acids",
"\nDisodium Distyrylbiphenyl Disulfonate",
"So, what are the differences and what do they do? The builders, Colorant, Enzymes, Brightner, and pH Adjustment are the same.",
"The polymers are different: HE is polyethylene Glycol, while regular is Diquaternium Ethoxy Sulfate, but it turns out the regular has the polyethylene glycol listed under the processing aids, so really , it's the regular that has something in it that HE doesn't. This is just a surfactant different, probably related to the solubility of this particular soap.",
"The HE has Benzisothiazolinone as a biocide, where the regular doesn't have a biocide. This is probably added because front-load washers have a tendency to develop mold do to not being aired out as well. ",
"You'll notice both have dimethicone, with is the defoamer. They probably have different amount sof it, without knowing the exact formula it's hard to say. ",
"TLDR; It looks like they use a different surfactant package and add a biocide, so it isn't a defoamer addition that is the difference!"
] |
[
"Would it be possible that the HE just contains less water/filler?"
] |
[
"Certainly, the ratios of ingredients are probably different, but how much would be guesswork with out a lot of analysis. Just based on the amount of material you add this may be the case, however, Front-load washers use a lot less water, so to have the same concentration of detergent in the water you'd expect to add less anyway. "
] |
[
"Why is coffee cup calorimetry constant pressure and bomb calorimetry is constant volume?"
] |
[
false
] |
Like the question asks, what pressure is being constant in a coffee cup calorimetry? The pressure inside the cup or the air pressure outside? Either way, why is the pressure not changing? Similarily, is the volume of the reaction chamber being referred to when we say constant pressure or is its the external insulating jacket? Thank you
|
[
"The coffee cup is not airtight, so the pressure is just atmospheric pressure. A bomb calorimeter is pressurized and tightly sealed so that the gas produced cannot expand, so the volume remains constant and the pressure inside goes up."
] |
[
"Thank you for your help!"
] |
[
"Like the question asks, what pressure is being constant in a coffee cup calorimetry? The pressure inside the cup or the air pressure outside?",
"Either way, why is the pressure not changing?",
"The pressure inside the cup is dictated by the air pressure outside the cup because there's a relatively large opening at the top of the cup. Any pressure changes inside the cup will quickly equalize with the air pressure outside the cup, and nothing you do in a coffee cup calorimeter can meaningfully influence the air pressure outside the cup, so in practical terms the pressure is constant.",
"Similarily, is the volume of the reaction chamber being referred to when we say constant pressure or is its the external insulating jacket?",
"While neither is likely to change, it is the volume of the reaction chamber that is important."
] |
[
"What is the name for the mixed particle that photons form when moving through a medium?"
] |
[
false
] |
So I know that the absorption/emission explanation for light slowing down in a medium is wrong, and I somewhat understand the other explanation. But for the life of me I can't recall what exactly the quasi-particle that is formed during the interaction is called. I've checked the FAQ on the subject, but the only names I've found are "polariton" and "phonon", which I don't remember reading in previous explanations. Is there another name, or is my memory just faulty?
|
[
"Polariton.",
"Also mentioned in the ",
"FAQ"
] |
[
"It's a polariton under a certain set of assumptions. Though the term polariton has multiple definitions and takes different meaning depending on community. But really it's best in almost all cases to treat it classically using Maxwell's equations in a medium. Even in quantumy scenarios like modelling spectroscopy and such the actual light is modelled classically and its propagation into the medium dictated by the requirements of Maxwell's equation at the interface. Keep in mind that the wavelength of visible light is about a 1000x longer than the spacing between atoms. Even in XRD where this isn't the case much is treated classically, see for example Bragg's Law."
] |
[
"Also, be sure not to confuse them with polarons."
] |
[
"Why is it that listening to music at a certain volume hurts my ears in a quiet room, but listening to it in an airplane at the same volume doesn't bother me at all?"
] |
[
false
] |
I'm just using music as an example. If I accidentally turn on music in my headphones at full volume in my room, I get a physical pain in my ear because of how loud it is. On an airplane, I need to play my music at full volume to even hear it, and it doesn't bother me at all. Why is this? Does the ambient noise make a difference? If so, how? Thank you!
|
[
"In the airplane, you're probably protected by the middle ear's acoustic reflex. According to ",
" 3e, this mechanism is activated by sounds above 75 dB(SPL) and, within 60-120 ms, starts attenuating frequencies below 1kHz by 12-14 dB. There's more information at ",
"Wikipedia:Acoustic reflex",
", although the numbers given are a little different."
] |
[
"3 responses and nobody mentioned the tensor tympani muscle? Aww, well let's check the wiki link on Acoustic reflex, I haven't heard of that specifically. Oh! ",
"When presented with a high-intensity sound stimulus, the stapedius and tensor tympani muscles of the ossicles contract. The stapedius pulls the stapes (stirrup) of the middle ear away from the oval window of the cochlea and the tensor tympani muscle pulls the malleus (hammer) away from ear drum. The reflex decreases the transmission of vibrational energy to the cochlea",
"Hooray! It was in the top answer all along :-) "
] |
[
"Does the acoustic reflex physically reduce damage? It seems like that is what the article says, but this is a foreign topic for me so I wasn't sure... Thanks!"
] |
[
"What Is In a Modern Day Cigarette and Why Is It So Bad For You?"
] |
[
false
] | null |
[
"A lot of carbon monoxide, hydrogen cyanide, carbon black, polyaromatic hydrocarbons, to name a few. All of these things are unhealthy to inhale.",
"EDIT: Source? Ran an IR on smoke of a cigarette."
] |
[
"They don't put it in there. It's a by-product of the combustion. Hydrogen cyanide is a gas (in my climate at least), and would not keep in the cigarette."
] |
[
"Why cyanide?!",
"How would that help the flavour? Or anything for that matter?"
] |
[
"How does adding energy to an e- move it to an orbital further from the nucleus?"
] |
[
false
] |
I understand that electrons in higher orbitals have higher potential energies, but I dont understand what it is that changes in an electron that having a higher energy moves it further from the nucleus.
|
[
"It is absolutely not the same! Electrons are nothing like satellites; that's a fiction told to people in order to avoid getting into quantum mechanics. If electrons were orbiting like satellites then they would radiate energy and quickly crash into the nucleus. Electron orbits are more like states of particular resonance."
] |
[
"It is the same way that an object placed on top of a ladder has more potential energy. The nucleus and the electron attract each other just like a rock and the earth attract each other. (Except with electromagnetic force instead of gravitational)",
"Moving the electron to a higher orbital requires that some energy be expended to counteract the force that attracts the nucleus and electron together, this is stocked as potential electric energy."
] |
[
"Electrons are attracted to the nucleus by an inverse square law, like satellites are to the planet. Quantum physics makes electrons not be exactly like satellites, but they aren't nothing like satellites."
] |
[
"If the winter solstice is the shortest day of the year, why is it that the coldest days seem to be during January/February?"
] |
[
false
] |
Also, why is it so much colder 20 days before the March equinox (e.g. March 1) than 20 days after the September equinox (e.g. October 10)? This is all pertaining to the northern hemisphere, of course. Reposting this question since it didn't receive a response yesterday.
|
[
"It has to do with the daily energy budget: how much energy is incoming from the sun per day vs. how much energy is outgoing from the earth per day. The sun supplies a lot of energy (mostly in the form of visible light which gets absorbed by the ground) during part of the day, and the earth is continuously re-radiating some of that energy (in the form of infrared light) back into space during the day and night. A graph of the daily incoming vs. outgoing radiation would look something like ",
"this",
". By that chart's example, there is a net gain in energy (which translates to an increase in air temperature) from shortly after sunrise to a couple hours before sunset. This is why the high temperature of the day typically occurs in the mid-late afternoon, not at solar noon. The daily temperature curve lags behind the solar energy curve by a few hours.",
"You could imagine a similar energy balance curve happening on an annual time scale, but we'll have to make a change to what the solar energy supply curve looks like. There would be no \"sunrise\" or \"sunset\", but you would see a minimum of solar energy supply happening on the winter solstice (December) and a maximum on the summer solstice (June). How that would balance out with the earth's outgoing radiation will cause the temperature curve to lag behind the solstices by about a month. So, average temperatures in the hemisphere will be coldest in January and warmest in July."
] |
[
"I was going to say:",
"Think of warmth like money the sun deposits in a bank account, which always has money going out as well as coming in.",
"Sunlight reaching the ocean or land warms the Earth. But the warm ocean or land also give off heat, which escapes out into space as infrared energy. This is why it almost always grows cooler at night.",
"When days are short during the winter, more heat is leaving than coming in. Even as days begin growing longer, more heat continues going out than coming in until maybe late January, depending on the place, when more heat finally begins arriving than leaving, and days start to warm up. ",
"But your explanation is way better."
] |
[
"Thanks. I wish I could find you all a chart that shows annual incoming and outgoing energy curves, but hopefully you can imagine it well enough.",
"Best I can do is show the ",
"incoming and outgoing energy as a function of latitude",
". With the annual change in seasons, the surplus area would oscillate such that the majority of it would be located in one hemisphere for half a year, then the other hemisphere the rest of the year. There will always be a surplus of energy near the equator and a deficit near the poles.",
"Then a good question to ask would be, why don't the north and south poles collapse to near absolute zero and the tropics catch on fire? You can thank ocean currents and the ",
"winds of the atmosphere",
" for transporting that energy from the tropics to the poles."
] |
[
"Why do we hear static on speakers or headphones when we are about to get a phone call or text message?"
] |
[
false
] |
When my phone is near my speakers or headphones, I hear a series of static noises in quick succession of one another right before I receive a call/SMS, sort of sounds like a beep. Why does that happen?
|
[
"But why only during the connection procedure? Once you get the call there's not a sound. ",
"Is the initial connection much higher power, perhaps, and the transmitter and receiver drop to a low-power mode once they've established the parameters of the connection?"
] |
[
"The circuit in your speaker acts as an antenna that picks up the signal and plays it out. "
] |
[
"The receipt of a call or SMS causes the circuitry inside the phone to produce electrical noise, which is coupled into the speakers. If this happens with passive headphones that aren't plugged into the phone or anything electrically connected to it, your phone is throwing out extreme amounts of RFI. Crappy iPod dock type speakers (i.e., all such speakers) could be susceptible to moderate RFI.",
"The most likely culprit for radiated noise is the power draw of the radio and CPU changing when they wake up and have to do work. If the power supply current return path is different from it's arrival path, that encloses an area. And a loop with a varying current in it radiates. ",
"If the headphones or speakers are ",
", noise can easily couple into the high-impedance input side of the line-out/headphone jack audio amplifier, if it is poorly designed or if it's on a separate chip and the board layout is poor. You will hear this effect with many cheap USB audio devices, if you plug another USB device into the same hub. The earlier versions of the Raspberry Pi also had severe problems with this."
] |
[
"Are moths and butterflies able to cross breed like tigers and lions?"
] |
[
false
] |
I know that lions and tigers can make and produce sterile offspring. Do moths and butterflies have that same ability? They seems close enough genetically but what factors would limit them?
|
[
"I suspect you'll have to be more specific as there are thousands of species of moths and butterflies, which are an order, whereas lions and tigers are species within the same genus. ",
"If you mean if an arbitrary moth and an arbitrary butterfly, then almost certainly not. They diverged 56 million years ago, with hugely varying chromosome counts even within their clades."
] |
[
"All moths are equally distant from all butterflies and vice versa. They split from each other before splitting into the many species that exist today. It's similar to asking if there's some dog that's close enough to breed with some cat."
] |
[
"There are ",
"moth x moth",
" and ",
"butterfly x butterfly",
" hybrids at least. Species boundaries are never that rigid.",
"For a very rough comparison, monarchs and peppered moths share an order the same way you and capuchin monkeys share an order if not more. 56 million years is a lot from the perspective of a butterfly."
] |
[
"Why does rotating a spaceship create artificial gravity?"
] |
[
false
] |
I understand the idea of angular momentum and centrifugal force, but I also understand (I think) how relativity factors into physics, and the aspect of artificial rotational gravity that I don't get is how we can say for sure that the spaceship is rotating and not everything else. If everything else were rotating, then you wouldn't feel centrifugal force, would you? In empty space, there would be no way to detect the rotation, so how would you feel it?
|
[
"Short answer: Not everything is relative. Acceleration is absolute, and you can determine that the spaceship is spinning instead of the universe specifically because you can measure its centrifugal force. At every event in spacetime, there exists a special set of reference frames which are inertial (i.e. freely falling) and all others feel fictitious forces such as the centrifugal or gravity.",
"The long answer is very long indeed and not strictly known. Newton claimed that space is absolute and \"proved\" it with his famous Bucket Thought Experiment, in which he claims that in a universe completely empty of all matter except for water in a bucket, that the state of rotation of the bucket can still be determined by examining whether the water has climbed its walls or not.",
"Later, philosopher Ernst Mach disagrees with Newton, but doesn't consistently say what he thinks will happen to the water in the bucket. Sometimes he seems to think that the water will never climb the walls, and other times that the answer is unknowable since we have no empty universes. What he does say is that he believes that which reference frames are inertial has something to do with the large-scale distribution of mass in the universe. ",
"Mach's Principle",
" is never formally stated, but his idea that all motion, including acceleration, is relative, strongly influenced Einstein.",
"But Einstein, despite this Machian influence, did not make Mach's Principle an axiom of Relativity. Instead, he was pleased to report to Mach that Relativity had effects which seemed to satisfy it, such as ",
"Frame Dragging.",
" ",
"Today, most Relativists do not believe that Relativity is Machian, although certain special solutions might be. But it's hard to tell, because the Principle is never formalized, and there are multiple ways it might be stated, some of which apply to GR and others which do not. So if in general, GR is not fully Machian, then in some sense we are back to the bucket experiment: inside the spaceship with closed windows, you know it is rotating because you can circumnavigate the floor all the way around, and thus deduce that a centrifugal force is acting."
] |
[
"What makes acceleration absolute, though?",
"The fact that an accelerometer (a mass on a spring) on board the spaceship will register it (by expanding in the direction away from the acceleration).",
"What happens if the universe only contains one wheel? Would there be any way to determine whether it's spinning or not?",
"I don't know, Dr. Mach. I suspect accelerometers on the rim of the wheel will still expand and reveal the rotation, but I don't know."
] |
[
"What makes acceleration absolute, though? If I am accelerating away from something, from my reference frame it seems that that thing is accelerating away from me.",
"Does it have something to do with the fact that an accelerating rocket is expending energy doing so?",
"What happens if the universe only contains one wheel? Would there be any way to determine whether it's spinning or not? All else applying, the lack of any reference would imply it doesn't spin. But as soon as you fire a thruster to accelerate it, it would accelerate relative to the jet, no?"
] |
[
"How Did We Discover Bi-209 Is Radioactive?"
] |
[
false
] |
Given that its half-life is so ridiculously long, what led us to find out that Bismuth isn't actually stable? Did we "get lucky" and happen to witness some decay, or are there analytical ways to determine an element's radioactivity without needing to observe anything? If the latter is the case, what prompted us to do this for bismuth?
|
[
"Are there analytical ways to determine an element's radioactivity without needing to observe anything",
"There are ways to roughly predict whether an element would be radioactive, but getting an actual quantitative result to any precision is not possible from first principles using theory, and even numerical methods will be at best very approximate."
] |
[
"https://en.wikipedia.org/wiki/Bismuth-209",
"Bismuth-209 was long thought to have the heaviest stable nucleus of any element, but in 2003, ",
" at the Institut d’Astrophysique Spatiale in Orsay, France, discovered that 209Bi undergoes alpha decay with a half-life of approximately 19 exayears ",
"https://pdfs.semanticscholar.org/ba53/1ef1775a61bed94674aefa1fce81a75f9bca.pdf",
"We detected a-decay of 209Bi using the scintillating bolometer\ntechnique. The earlier scintillating bolometers used CaF2(Eu) and a\nsilicon photodiode, glued on the crystal, as the light detector9. After recording an initial high-resolution a spectrum within a microtarget (a 1-mg diamond bolometer at 1.3 K, ref. 12), we introduced a ‘heat-and-light’ pair of bolometers, with 300 mg of scintillating CaF2(Eu) at 130 mK (ref. 8). ",
"As part of our development of more massive scintillating bolometers (Fig. 1c) for the Dark Matter search experiment ROSEBUD, a 45.7-g BGO (Bi4Ge3O12) bolometer exhibiting unusual discriminating properties at 20 mK was checked at Orsay for contamination at high energy (Fig. 2): this crystal had already shown a strong 207Bi contamination13. Thanks to their high quenching factor, a-particles could be perfectly separated from events induced by cosmic rays "
] |
[
"Mass of Bi-209 = 208.9803987 amu",
"Mass of alpha = 4.00260325415 amu",
"Mass of Tl-205 =204.9744275 amu (decay product)",
"208.9803987 - (4.00260325415+204.9744275) = +0.0033679 amu",
"Since the mass of the parent Bi-209 is heaver than the mass of the decay products, it is a reasonable assumption that the Bi-209 is radioactive. Also since the decay energy of the alpha is 3.1 MeV (take the mass excess and use E=mc",
" and convert the units), this is pretty low for alpha decays so we can be pretty certain it will have a very long half-life.",
"See slide 12",
"https://en.wikipedia.org/wiki/Geiger%E2%80%93Nuttall_law"
] |
[
"If the solubility of CO2 decreases as temperature increases, then why is global warming causing ocean acidification?"
] |
[
false
] |
I've read that the CO2 becomes less soluble in water the hotter it gets, but I've also read that the ocean is absorbing more CO2, causing its pH to decrease. Are both of these statements true? If so, how?
|
[
"For simple solutions, the relationship between the partial pressure of a gas and the concentration of it in a solvent is proportional, ",
"p = kc ",
"This is called Henry's law. k can be a function of temperature. For CO2, k becomes smaller at higher temperatures, so at the same partial pressure, less gas can dissolve. However, the amount dissolved always increases with the amount in the air.",
"Even though the solvency of the gas can decrease, we can still dissolve more total gas by simply pumping up the atmospheric concentration."
] |
[
"The ocean is not yet saturated with CO2. As the partial pressure of CO2 in the atmosphere increases, more dissolves in the oceans. ",
"If the oceans were saturated, they would lose CO2 as they warmed. "
] |
[
"There's a bit of chicken-and-egg going on here. The temperature rise is being driven by elevated atmospheric CO2 levels. It's the CO2 concentration in the atmosphere that's driving the increased concentration in the sea, not the temperature. Eventually, if the sea temperature rises enough, it'll start releasing CO2 again, making the problem much worse! However, as others have pointed out, we're below the saturation point at the moment."
] |
[
"How long was a day on Earth 300 million years ago?"
] |
[
false
] | null |
[
"Still exactly 1 day :)",
"But as compared to a different reference standard for time, such as an atomic clock, the earth used to spin a bit faster. The influence of the moon causes tidal braking of around 2.3 ms/century. So 300 million years ago, that would be around 2 hours. So it would be a 22 hour day instead of 24 hour day."
] |
[
"He said it was 22hrs instead of 24. So, 300,000,000 *22/24 = 275,000,000",
"Idk what that has to do with anything though. "
] |
[
"The Earth was spinning faster, but what about its orbit around the sun? Was a year the same amount of time?"
] |
[
"I was just introduced to this 'miracle' product that frankly has set off red flags, but I don't have the background to dispute or verify the claims."
] |
[
false
] | null |
[
"What is the product called? Do you have any other information?"
] |
[
"OK, this looks potentially legitimate (but probably not actually effective). Although the website calls the linkage \"saline\" which means salt, what they show is actually a \"silane\" which will indeed link a molecule to a surface through a stable, lasting bond. So that part is legit. The second part is based on some mysterious long chain that will disrupt bacterial membranes. This is also a reality. There are many peptides, proteins and polymers that kill bacteria by disrupting membranes. So far, so good. The problem with such a product is that a bacteria has to physically contact the surface for any effect to be observed. In a typical surface contamination (a sneeze, a water splash from a toilet, a drop of blood, salmonella contaminated chicken juice...) the vast majority of the contents of the droplet will never contact the surface, even after it dries. This approach has been shown to work to prevent biofilms, for example, in surgical implants. But as for decontaminating a surface, I doubt that it will have much effect in real life situations. I am a professor and this is my research area, by the way."
] |
[
"And I am the one who asked for a link. Ooops. Sorry. What i mean is that the compound linked to the surface will have to physically contact a large part of a bacterial cell. That means the bacterium will have to be within about 0.01 micrometer or less of the modified surface to be affected because that's how long most antimicrobial polymers are. If a water droplet is 1 millimeter high then the killing zone is 1/100,000th of the droplet thickness. The rest of the drop is unaffected because it is not in contact with the layer. When a droplet dries, there will dissolved stuff like salts or other dissolved substance. When these precipitate upon drying they will coat the surface, blocking most bacteria from contracting the surface. Even a sample with lots of bacteria will be mostly unaffected because the dead cells will fall to the surface and will block it from killing the rest.\nNow where this approach might do better is on cloth (like bandages). These materials are porous and there are lots of surfaces that bacteria could contact once they have entered the cloth.\nI have made a note of the product name. I would like to test it. Right now, my lab is not doing surface decontamination. Next time we do that, we will buy some of this stuff and test it."
] |
[
"Soap/shampoo can be any color but the suds are always white. Can someone explain?"
] |
[
false
] | null |
[
"They're diluted when used. The bubbles, being on the micron length scale, also scatter visible light making the foam look white. It's why milk is white and not transparent. For smaller dispersions of particles, bubbles or emulsions smaller wave lengths of light are scattered more intensely and so they can appear bluer in colour - all whilst the components themselves aren't necessarily blue coloured."
] |
[
"Not air bubbles but extremely tiny particles. They're so small, gravity doesn't really affect them in a solution so they can stay suspended sort of indefinitely.",
"But if you leave your milk in the fridge for a few weeks because you accidentally forgot to dump it before going on vacation, you can actually start to see the tiniest bit of separation at the top"
] |
[
"Milk is white because it is filled with microscopic air bubbles?"
] |
[
"In time dilation, time passes faster the further an observer is from a large center of gravity. So on the surface of the earth, time is faster than the center of the earth. Does this have any effects in geological time scales on different theories such as plate tectonics, continual drift, etc?"
] |
[
false
] |
[deleted]
|
[
"Actually, the gravitation in the center of earth is zero.",
"The acceleration in any direction due to gravity is zero at the center of the planet, but you are still within a gravity well, so clocks still run slower compared to someone outside that well."
] |
[
"There is no such thing as \"real\" or \"normal\" time. Time dilation for one object can only be considered relative to the time perception of some other object. That's why it is called the theory of relativity."
] |
[
"The time dilation due to Earth's gravity is about one part in 10e9. If no part of the Earth ever moved, then over the 4.5 billion year lifetime of the planet, the rocks at the very core are about 4 years \"older\" than the rocks at the surface.",
"This difference is so small that it has no effect on anything at all."
] |
[
"How fast could we get a spacecraft going with current tech?"
] |
[
false
] |
I know there are a lot of theoretical, untested drives out there, so for the sake of this, let's limit this to any technology that could actually make it's way into space and propel a spacecraft within the next 10 years. With the best available drive, and the hardest planetary sling-shotting we can muster, how fast could we actually send something sailing through space?
|
[
"I don't believe there's a known answer for this. It comes down to what percentage of the space craft you are willing to use to devote to fuel. The higher the percentage, the faster you can go. The achievable speed is purely Newtonian. If you eject 50% of the mass, then you would be traveling at the same speed as the nozzle velocity. If you then eject 50% of the remaining mass(total 75%), then you would be traveling at twice the nozzle velocity, ejecting 87.5% of the mass would give you three times the nozzle velocity and so on.",
"But in practice, no one would build a space craft that does not have a cargo load so no one would find out. And you are also limited by the minimum size of the space craft itself including the fuel tank and engine."
] |
[
"You're referring to a ",
"Bussard ramjet",
". Unfortunately, the drag and subsequent deceleration caused by gathering fuel exceeds the acceleration gained by expending said fuel. This nets out to deceleration, unfortunately. At least, these were the findings of Zubrin in and Andrews back in the 1980s (the article discusses this). This may have changed, so if anyone can make further commentary on that, it would be pretty awesome. "
] |
[
"Chemical rockets wouldn't be able to match even the most basic nuclear powered rocket. The energy released by chemical reactions per kilo of mass is too low. If money and safety were no concern, you could create a spacecraft using a number of experimental components. These have been built and tested in labs on Earth, but not used in space yet.",
"SAFE-400",
" A compact 100kW nuclear reactor.",
"VASIMR",
" A high specific impulse electrically powered engine. Fires Argon gas at 50km/s",
"SAFE-400 weighs 1200kg, lets use 2 of those to power a 200kW VASIMR.",
"A 200kW VASIMR engine only weighs 300kg according to wiki.\nThat's about 3000kg so far if we make some allowance for structural components.\nI'll add on an extra 5000kg for cooling radiators at this point because the amount of heat generated by this setup will be very significant and I don't believe the figures I've read include adequate cooling.",
"The thrust of the VASIMR engine is a mere 6N so this craft would have to be launched into orbit by chemical rockets and possibly assembled there. However (if my calculations are correct) with a specific impulse of 5000s it would expend a mere 0.3g of fuel each second. The nuclear reactors will have dropped to half power after about 25 years so lets assume we only want to accelerate for that length of time. We need to bring 236,500kg of fuel for the mission. Add on an extra 10% for tankage and we get a total of 260,000kg for fuel plus 8000kg for propulsion for a total of 268,000kg. ",
"The puny thrust level of 6N will only accelerate our craft at 0.000022m/s/s initially. As the mass of the fuel drops over the years it will gradually allow more acceleration. If my rough guestimate is correct this would give a top speed of 31km/s after accelerating for 25 years. That's about twice as fast as New Horizons which I believe is the faster man made spacecraft to date."
] |
[
"Energy loss of a bullet - free swinging target vs fixed"
] |
[
false
] |
Hi, An post led to question and it's follow-up comment. Summarised in essence ; a 50 caliber round failed to penetrate a free swinging steel plate at 200 yards. A question was raised about the difference if the target were fixed. A supposition was given that the transfer of energy was over such a short period that the free-swinging nature wouldn't change the total energy transferred much. My question to you, is what would the energy loss be? Is the assumption of the speed of impact playing a part, accurate? Enquiring minds must know! TIA
|
[
"50 BMG is used in the video."
] |
[
"Just adding that it would highly depend on the .50 cal used and what weapon it's fired from. Kinetic energy is proportional to velocity squared.",
"Examples: ",
"A .50 cal Hollow-point 325 grain Action Express round fired from a Desert Eagle pistol with a 6\" barrel will have a muzzle velocity of 398 m/s (1 666 J).",
"A .50 BMG (12.7×99mm NATO) 800 grain Barnes round fired from a sniper rifle with a 45\" barrel will have a muzzle velocity of 882 m/s (20 195 J)",
"http://en.wikipedia.org/wiki/.50_Action_Express",
"\n",
"http://en.wikipedia.org/wiki/.50_BMG"
] |
[
"It's still a big difference between different cartridges of 50 BMG. Regular cartridges are designed ",
" to pierce through targets, but to be absorbed by the tissue of the target. When firing at a steel plate a regular bullet scatters and much impact energy is lost.",
"The 50 BMG Armor Piercing round should penetrate 0.75\" armor at 500 meters (",
"http://www.inetres.com/gp/military/infantry/mg/50_ammo.html",
"). In the video they used regular bullets, .50\" armor and a distance of 200 meters.",
"As for the actual question, I can't answer it with certainty. It looks like a lot of energy was lost as transfer of momentum in ",
"video",
". But as I said, regular bullets aren't designed to pierce through armor."
] |
[
"Why have insects and reptiles more readily developed poisonous/venomous capabilities than mammals or birds?"
] |
[
false
] |
I understand that there are very few poisonous/venomous mammals and no venomous birds. Why have these species shunned a useful defensive technique? Is it that they were able to survive well enough without the need to use it?
|
[
"Most of evolution is pressure-based; if you have have nothing killing you...you don't need to adapt. Insects tend to be the food source for many different animals. As such, they are exposed to much more pressure to adapt protection. They also reproduce wayyy faster/more plentiful than mammals, which lends to more chances for adaptations to occur."
] |
[
"no venomous birds",
"That's actually not true. The ",
"hooded pitohui",
" of Papa New Guinea is poisonous. ",
"Here's",
" a pretty cool video done by the guy who discovered it. He goes into detail about the toxic compounds they found."
] |
[
"My most educated guess would be the size of the prey and has virtually nothing to do with defense since most venomous animals prefer to flee rather than bite. the reason it deals with the size of prey is that the smaller the organism, the faster it motabolizes making venom alot more applicable for hunting small prey, such as insects and rodents. it takes seconds for venom to kill a rodent, it can take hours or days to kill large prey and thats plenty of time to flee and die which leaves the predator without a meal, sharp teeth work better for larger prey since you can kill them without chasing them all day after theyve been bitten."
] |
[
"Will flickering the lights (or turning them on and off really fast) actually cause a fire / short circuit?"
] |
[
false
] |
I remembering being told as a kid never to flick the lights on and off rapidly because it could cause a fire. My roomate just flickered the lights in my bedroom and now I'm typing this message.
|
[
"Nah, not really.",
"Flicking the light switch on and off rapidly has a number of effects, which I will try to deal with individually:",
"Remember that a dimmer is, in fact, just a \"glorified switch\" that turns the light on and off so quickly we cannot see it — and they do normally not cause fires, do they?"
] |
[
"If you want to get entirely technical the light bulb is turning off 60 times per second anyways it happens so fast the filament stays heated (in incandescent) .So flipping it on and of wont really hurt the bulb,except maybe the electronic ones. The switch would be the main concern, that you may break something mechanical."
] |
[
"Incandescent bulbs have much lower resistance when they are cold, as such a much higher current flows through them before the light appears. This can stress the wiring, the switch and the bulb causing something to fail. Comparing two scenarios where in one the bulb is just on and in the other you are flicking it on and off every few seconds, the latter will stress the system more and is more likely to cause some sort of failure. Overall the probability of actual fire should be pretty low."
] |
[
"Why can't we think in \"dream time\" when we're awake?"
] |
[
false
] |
This morning a sound woke me up (almost instantly, in a second or two) in that time I had a dream that would take about 30sec-1 minute if it were playing on TV.
|
[
"Time doesn't pass any differently while you're dreaming or awake. You might perceive or remember it differently.\nMore info:\n",
"http://indianapublicmedia.org/amomentofscience/time-passes-dreams/"
] |
[
"Thanks! I love askscience:)"
] |
[
"1) Recall Bias. When you're awake, you're not experiencing the dream. You're just remembering what you can of the dream, leading to biases in perspective.",
"2) Perspective bias: We can 'think' faster if we want to: eg. I could speed up a video I saw earlier as I remembered it. I could also make up a story spanning one minute in one second. Thus, we can change the 'speed' of a memory or idea, but not reality. When we're in the dream, we experience it in the 'dream' time frame. This is what you remember. Then when you wake up, you experience everything in the 'reality' time frame. The difference in what you feel now and what you remember you felt is what causes this split.",
"tl:dr;\nit could be one or all of:\n1)Recall Bias\n2)We can control the 'speed' of thoughts/memories, and that is just what a dream is leading to time frame perspective difference\n3)Faulty Memory"
] |
[
"Are there gemstones on the moon?"
] |
[
false
] |
From my understanding, gemstones on Earth form from high pressure/temperature interactions of a variety of minerals, and in many cases water. I know the Moon used to be volcanic, and most theories describe it breaking off of Earth after a collision with a Mars-sized object, so I reckon it's made of more or less the same stuff as Earth. Could there be lunar Kimberlite pipes full of diamonds, or seams of metamorphic Tanzanite buried in the Maria? , if you're bored and looking for something to do in the next ten years or so...
|
[
"The ",
"surficial geology of the moon",
" is relatively simple compared to Earth, the Lunar highlands are predominantly ",
"anorthosite",
" and the Lunar maria are predominantly ",
"basalt",
". On Earth, neither of these rock types are associated with common gem minerals (EDIT: unless you consider olivine a gem mineral, then sure, basalts have tons of olivine, but not usually gem quality, for that you usually need mantle xenoliths, which I suppose could exist in the Lunar maria basalts, but to my knowledge, I don't think we've found any in our limited sampling of the moon). Anorthosites are relatively rare on Earth and one of the few places we find them on Earth are in ",
"layered mafic intrusions",
", e.g. ",
"Bushveld",
" or ",
"Stillwater",
", which are commonly rich in a variety of metals (e.g. chromium, paladium, etc) but not so much in things we usually consider 'gems'. ",
"A lot (not all) of gem minerals are associated with either metamorphic rocks or igneous environments which are related to various plate tectonic processes. E.g. ",
"garnets",
" are almost exclusively metamorphic (there are rare igneous garnets, though I've only ever seen igneous garnets in very felsic igneous rocks, which you would not find on the moon), ",
"corundum",
" (i.e. ruby, sapphire) is often metamorphic but also can be found in a variety of igneous rocks, ",
"beryl",
" (i.e. emerald, aquamarine) is mostly found in felsic igenous rocks (again, not expected to exist on the moon) or metamorphic rocks, and as you mentions, diamonds are often associated with ",
"kimberlites",
". We wouldn't really expect many of these rocks / environments to exist on the moon as it lacks/lacked plate tectonics, thus the various mechanisms required to generate the minerals we consider gemstones likely did not exist on the moon.",
"Caveat to above, lunar geology is most definitely not my specialty and I've done as much as I can in my career to avoid petrology / mineralogy, so I will happily defer to someone with more expertise in these fields if someone with relevant knowledge wants to chime in."
] |
[
"Considering the impact hypothesis, a large portion of the material that accreted to form the moon was ",
"molten",
", thus at least at the surface there is no material that is preserved 'solid bits of Earth', for lack of a better term."
] |
[
"If the processes that form gems on earth are not present on the moon, could there be gems left from the origin of the moon's material makeup? The prevailing theory as I understand it is that the moon formed from a collision with the earth. Could there be gems formed on earth and launched into space to coalesce into the moon?"
] |
[
"What is the difference between Deep Learning and Artificial Intelligence?"
] |
[
false
] |
What is the difference between Artificial Intelligence vs Machine Learning vs Deep Learning?
|
[
"You can argue the toss a little about the exact definitions but I'd style it like this :",
"Artificial intelligence : See this link - ",
"https://www.reddit.com/r/askscience/wiki/computing/ai_definition",
"Machine Learning : the branch of computer science and (computational) statistics which deals with developing statistical models and algorithms which can self-parametise (learn) on a dataset. The learning here is the idea that the model will discover the correct weights for the model in a purely algorithmic fashion and with minimal human input. Largely with a view for clustering, classification and regression tasks. Common algorithms in the field include neural networks, support vector machines, Nearest neighbour clustering, n-dimensional regression, Decision Trees, back propagation, genetic algorithms and many, many more",
"Deep learning : the subset of machine learning which deals with deep models, mostly neural networks. These are models which have unusually large representational spaces. In neural networks this typically means more than 1 hidden layer and many nodes in each hidden layer. Because deep networks have very many parameters to train they typically require very large datasets to successfully train"
] |
[
"Artificial intelligence : the branch of computer science which deals with making machines which display intelligence. One goal being a machine which displays human-like, general intelligence. Our current attempts make extensive use of machine learning algorithms because we can use these to make decisions and decision making is likely central to intelligent thought.",
"No, this is not the goal of the field. Read our ",
"FAQ",
"."
] |
[
"Fair point, I should have left it styled as agent as I originally wrote, I'll just swap in your link."
] |
[
"Can someone explain how voltage and current have a phase difference in ac circuits containing inductors and/or capacitors?"
] |
[
false
] |
So a couple of things I don't understand: What is happening? In circuits that involve capacitors, I've learnt that current leads voltage. But how does that work? Does complex impedance have phase difference? I know that V=IZ, and if V doesn't have a phase difference (taking V as the starting reference point) and I does, does that mean the Z must have an opposite phase difference? What does that mean physically? (I realise that this isn't exactly the clearest question, but I'm hoping someone will understand)
|
[
"It happens because there is some energy stored in the capacitors and inductors. ",
"For example, if we put a current through an inductor, the inductor will store energy as a magnetic field. If we stop the voltage source that gave the inductor its field, the inductor will try to maintain its current using the magnetic field as a power source. In that instant, the external power source will give 0V, but there will be some current, because the inductor is generating that current, not the power source.",
"With a capacitor the same thing happens. The capacitor stores energy and then creates a current with that energy when the voltage source goes to 0.",
"The impedance is constant, and it has value and phase. The value is a measure of the absolute admitance of the system - I/E we put x volts RMS in the circuit and we measure y amps RMS. The phase specifies how delayed is the current waveform from the voltage waveform. We use complex numbers in the impedance because that way we can use the good old Ohm's Law with little change: V (complex) = I (complex) * Z (complex)"
] |
[
"For the purposes of this post I will be assuming all signals are sine waves and the voltage function has no phase offset. It makes things a little easier to talk about if we state from the outset that ",
"v(t)",
" at t=0 is our zero phase reference.",
"What is happening? In circuits that involve capacitors, I've learn't that current leads voltage. But how does that work?",
"The equation that models ideal capacitors is ",
"i(t) = C*dv(t)/dt",
" where ",
"i(t)",
" and ",
"v(t)",
" are time-varying current and voltages. The ",
"C",
" is the capacitance of the particular capacitor and is a scalar value.",
"This leads to the notion that current leads voltage because at t=0 we find that ",
"v(0) = 0",
" but with a positive derivative. This means the current is some positive value and we say the current waveform is ",
" of the voltage waveform because from our zero phase reference the current is \"above\" it in phase. This continues to work if you add a constant phase offset to the voltage (ie voltage starts at some arbitrary point of the sine curve at t=0) but it just makes it messier to discuss.",
"You may notice that it's kind of an arbitrary distinction because you could say that the current doesn't lead by X degrees but instead lags by 360-X degrees. This is completely true mathematically but convention has arisen that capacitors lead so that's what the literature will phrase it as.",
"Does complex impedance have phase difference?",
"Sort of. If we limit ourselves to sinusoidal signals we can adopt the terminology of ",
"phasors",
" to describe impedance while handling the phase characteristics that will appear when you apply a sine wave input. This allows us to replace the nasty time-derivative relationships of capacitors and inductors with complex numbers and vectors. In this system the angle of the vector away from the real positive axis represents phase.",
"If we take ",
"V",
" to be a sinusoidal voltage signal and our phase reference we can transform it into phasor form by stating that it is a complex number of the form ",
"(A + B*i)",
". Since we have defined it as our zero phase reference we can state that it is entirely on the real positive axis and so will be written in the form ",
"(A + 0*i)",
" ie no complex component.",
"If we know that the current ",
"I",
" leads the voltage V by 90 degrees (ie ",
"I",
" is of the form ",
"(0 + B*i)",
", 90 degrees difference than ",
"V",
" in the complex plane) then we can use complex division to work out that ",
"Z = V / I = -i * A/B = (0 - A/B*i)",
".",
"\nThis tells us that the impedance (in phasor form) has no real component and exists entirely in on the negative complex axis, and this is precisely the behavior expected of a capacitor whose impedance is calculated by the following: ",
"-i / (2*pi*freq*C) = (0 - i / (2pi*freq*C))",
"This is a real roundabout way to answer your question because it's coming down to an issue of terminology: Do complex impedance have a phase ",
"? No. Do complex impedance have phase ",
"? Yes. The actual phase difference itself will depend entirely on your input signals and what you define to be zero phase.",
"What does that mean physically?",
"Using the language of phasors we can see that physically the complex impedance phase characteristics are a way to model any network of RCLs as a single complex number wherein the angle of the complex vector away from the real axis will determine the phase difference in the current from the voltage or vice-versa.",
"This is a really hard topic to put into words because all the vector addition and division really lends itself to drawing instead of text. Let me know if this makes any sense at all or if you need more specific examples, I'm trying to find some good references to link to but coming up short."
] |
[
"Sietis's answer is very good and probably better than what I can come up with.",
"If impedance has phase-like characteristics, does that mean it fluctuates like a wave?",
"In phasor form the impedance itself isn't changing when only using capacitors and inductors; the impedance of these components only depends on frequency which in this case is fixed. The complex phasor expression of an impedance won't change over time for any RLC network.",
"By phase-like characteristics I mean that the impedance will impart a phase change on the input signal, not that the impedance itself will change.",
"I am completely incompetent when it comes to linear circuits/electricity.",
"Sucking at something is the first step to being sorta-good at something :)",
"Did you get anywhere with finding decent references? Any would be welcome!",
"Only textbooks I'm afraid. The wikipedia articles on phasors is quite dense and most other online readings I've found assume a sturdy basis in complex math. I would ",
" recommend picking up a cheap textbook that covers basic circuit analysis if you really want to dive in because I don't know any other way to teach it without a huge amount of pictures :( Maybe the folks over at ",
"/r/AskElectronics",
" can come up with some better analogies or explanations!"
] |
[
"If a huge and dense enough amount of coherent light was emitted, would it create a black hole traveling at the speed of light?"
] |
[
false
] |
[deleted]
|
[
"A system of photons all moving in the same direction has no invariant mass, so you can Lorentz-transform into a frame where they have arbitrarily small energy. And in such a frame, it's clear that they should not form a black hole.",
"And, a black hole has mass so it can never move at c.",
"But anyway, it's in principle possible to create a black hole purely out of light, you just need to make sure that it's not all moving in the same direction.",
"If you have two photons moving in opposite directions, this system has nonzero invariant mass. ",
"So you can imagine an inwardly-moving spherical shell of photons all converging onto a single point. When the invariant mass of this system is within its Schwarzschild radius, in theory a black hole could form. This is called ",
", but it's never been observed."
] |
[
"I'll take a stab at an estimate. The shortest pulsed laser system has ~ attosecond width, and I've worked with systems capable of 10s of femtosecond pulses, so lets assume a 1 fs laser pulse. Also assume that the lasers are firing from all directions inward, to approximate a spherical shell of light.",
"The invariant mass of the photons would be just E/c",
" = m, since there is no net momentum. The mass ",
" of a black hole with Schwarzschild radius ",
" is given by M = Rc",
"/2G where ",
" is the gravitational constant. The radius ",
" will be the width of the laser pulse, 1 fs*c = 300 nm. The required mass for a black hole of this size is 2E20 kg. The total energy of all the pulses will then need to be 1.8E37 J, or about 1500 times the energy released by the sun per year. Even if we shrink our pulses down to 1 attosecond then it's the total energy released by the sun in 1.5 years.",
"It would probably be hard to secure enough funding to pull that off."
] |
[
"If you have an unlimited budget you could in theory make a black hole by piling up the money from that unlimited budget. Now all you need to do is make a currency out of photons and there you go."
] |
[
"Does it make a difference (to weight loss efforts) if you were to eat an extra 10,000 calories in one day, or an extra 1,000 a day for ten days?"
] |
[
false
] | null |
[
"“I never ate that much,” Phelps said. “It’s all a myth. I’ve never eaten that many calories.”",
"Said Phelps: “I wish. It’s too much though. It’s pretty much impossible.”\n",
"http://www.thebiglead.com/index.php/2012/05/11/michael-phelps-legendary-12000-calorie-a-day-diet-is-a-myth/"
] |
[
"As a side note, it would be extremely difficult for most people to eat an extra 10,000 in one day above what they are normally used to. This would be the equivalent of eating 10 dozen eggs, or 12 sticks of butter, or 18 Big Macs. Many people would get sick and throw up before managing to consume that much extra food."
] |
[
"I watched a youtube video of a guy drinking 20,000+ calories of olive oil. Probably found it through Reddit. Wasn't a good idea, but clearly it can be done.",
"EDIT: Here's ",
"the video"
] |
[
"Can someone please explain why this is wrong to me? Someone is trying to show me \"proof\" that Earth is not round AND that Earth does not move. (link in the text)"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"\"Sorry, flache-erde.bplaced.net has been blocked due to to it being a suspected malware site. \"",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"I'm in the United States, on my work computer so I presume whatever site-blocking software my company uses picked up on it. ",
"But anyways critical thinking websites also encounter opposition though... :-) No wonder they get banned^",
"I'm sorry you feel that way. When I get home I'll try to remember to check it out. But honestly, if anyone is willing to believe such an easily disproven, ridiculous conspiracy, then there's very little hope that any amount of evidence short of sending them to space will persuade them (and maybe not even that)."
] |
[
"I'm in the United States, on my work computer so I presume whatever site-blocking software my company uses picked up on it. ",
"But anyways critical thinking websites also encounter opposition though... :-) No wonder they get banned^",
"I'm sorry you feel that way. When I get home I'll try to remember to check it out. But honestly, if anyone is willing to believe such an easily disproven, ridiculous conspiracy, then there's very little hope that any amount of evidence short of sending them to space will persuade them (and maybe not even that)."
] |
[
"How would one calculate if striking a metal shell would deform it, penetrate it, or not deform it (in the context of striking armor with a weapon)?"
] |
[
false
] | null |
[
"This is not a straightforward thing to just calculate on paper. It's like asking whether a fall from a certain height will break a watermelon. It depends on too many factors (like how high is the fall, how elastic is the floor, what part of the watermelon hits first, and what's the overall shape and material properties of the melon?) and many of those things will change dynamically over the course of the collision. ",
"In practice, you would use something like finite element analysis software to take a CAD model of your armor and simulate its deformation under different loading configurations. This has been used successfully to simulate things like bullets hitting composite armor."
] |
[
"This is not a direct answer to your question, but in practice this question is answered through experimentation, not calculation. If you were implementing a high-level simulation or a game you could then use experimental values to determine the behavior of objects in the simulation.",
"Vehicle or structural armor ",
"is commonly rated in mmRHA",
", or millimeters of Rolled Homogenous Armor. This is a specific type of solid metal armor that was in use during WW2. While modern armors use different materials and techniques, they can still be rated in millimeters penetration of RHA. ",
"For example, the turret of the M1A2 Abrams tank is estimated to have around 1000mm RHA equivalent armor, even though the actual dimensions are probably 50-75mm thick. Each surface of the tank has its own thickness rating, as armor is allocated strategically to reduce overall weight and increase maneuverability. ",
"Note that these ratings are for a right-angle shot directly perpendicular to the armor plate. In reality most shots will come in at an oblique angle (and armor on tanks is commonly sloped to exaggerate these angles). The dimensional thickness of an armor plate may be 3 inches, but the effective thickness of a projectile's path through the armor may be calculated to be 4 inches because it's travelling through extra armor as a result of the angle. Then the effective mmRHA value of the armor plate needs to be suitably increased. For example, if our 3 inch armor plate has the 1000 mm RHA rating above, and the angled path through the armored plate results in a 4 inch path, then the effective resistance to penetration would be 1333 mm RHA. ",
"I'll also note that guns are also rated in terms of their mm RHA penetration. ",
"An example table is here.",
" This allows a knowledgeable gunner to make smart decisions about what targets they can realistically engage with their weapon. It is also common to provide data for penetration of other materials as well: mm penetration of concrete, brick, soil, etc. ",
"Personal armor is rated differently. The most common classification here is classification by standard. For example, a \"Level III plate\" as defined by the National Institute of Justice is required to stop six rounds of 7.62x51mm M80 ball ammunition, provided each shot falls more than two inches away from a previous shot. This standard can be extrapolated to other rounds and situations in different ways, but is not an exact science. The 5.56x45mm NATO is a significantly smaller round, so a Level III plate should stop at least six rounds given the assumption above, but it's impossible to say whether it may or may not perform better than six rounds. A 7.62x54r is ballistically similar enough that a Level III plate will probably perform the same as specified. It's not clear what happens against a larger round though. A .30-06 has around 10% more energy than the 7.62x51mm- does this penetrate completely? Does it behave the same? We can't really estimate based on the standard."
] |
[
"In Structural engineering, deflection is based on the support conditions, geometry of the material, the force, youngs modulous of the material. ",
"There's a relation for metals that stress/strain of the material will revert back to its original geometry. That relationship is the Youngs modulous. (E) = Stress/Strain. For your typical steel, its 29,000 KSI. (using imperial units). Any stress/strain within that window are considered 'elastic'. Once the 'load' or force is beyond the yield capacity of the material. The material is undergoing Plastic deformation. With testing you can determine the yield stress of the material, but a lot of it is already published. For your typical steels, 36 KSI is the yield capacity. When the stress of a material is beyond its yield capacity, it will not revert back to its original geometry, ie, it will deform. As you continue to increase the stress, you'll eventually reach the ultimate capacity and the material will rupture. ",
"Depending on the size of your metal shell, the force and how you impact your plate, you might be able to hand calculate some affects. The more 'complicated' your impact scenario is, the more analysis and likelyhood you'll need a computer for modeling."
] |
[
"I just started running. My friends insist I should run on my toes, not my heels because it's \"better\". Any science behind this?"
] |
[
false
] |
I get inconsistent answers when I ask why, ranging from the vague "It's more natural" to the nonsensical "that's what cats and dogs do". Running on my toes makes my arches ache, but I could just be an out of shape pansy. If it makes a difference, I generally run on treadmills. Thanks, science reddit!
|
[
"Just recently, in fact:",
"http://www.ncbi.nlm.nih.gov/m/pubmed/22217561/",
"The study looked at repetitive stress injuries in HS cross-country runners. Those that had forefoot strikes had lower injury rates versus heel strikers. ",
"This one:",
"http://www.ncbi.nlm.nih.gov/m/pubmed/22217565/",
"Found that efficiency was the same between the two types of foot strikes.",
"Long-distance runners tend to have very short strides with high rates of turnover. This encourages landing on your forefoot when your foot is directly below you."
] |
[
"Toes? No. Balls of your feet, yes."
] |
[
"Former DI Runner. I don't have time to find the references for you but here's what I've learned:",
"Running barefoot or in racing shoes (which don't have built up heels), top African distance runners tend to land on their forefoot or midfoot, allow the rest of the foot to come down, then push off their toes again.",
"This is more difficult to do in trainers with bulky heels, because that bulky heel causes it to strikes earlier than it otherwise would.",
"Injury rates for people who run this way may or may not be lower overall, BUT, people who ",
" into it have a MUCH MUCH HIGHER INJURY RATE than either group. Achilles injuries are especially common for these people. Please don't completely change your running style all at once, transition into it slowly (if you'd like to give it a shot)."
] |
[
"Can egg born animals have twins?"
] |
[
false
] | null |
[
"https://extension.psu.edu/programs/4-h/projects/poultry/embryology/teacher-resources/faqs",
"Yes. It is a rare occurrence. When two chicks hatch from the same egg, the egg usually has two yolks. Usually, one embryo out competes the other and only one chick survives to hatch. Many time both embryos die before hatch.",
"We have no knowledge of Siamese twin chicks ever being hatched. The development of twin chicks from a single-yolked egg."
] |
[
"Actually, the development of viable twin chicks from a single-yolked egg has been observed twice, once in domestic chickens (Nalbandov 1942) and once in pigeons (Levi 1941)."
] |
[
"Siamese twinning does happen in reptiles. Two headed snakes are known from many species (",
"the san diego zoo had one",
"), and two headed turtles ",
"have also been found",
".",
"In these species you can get twins, too, though they don't make the news in the same way."
] |
[
"Impractically conditioned brain"
] |
[
false
] |
[deleted]
|
[
"There's this phenomenon with trying to break a habit called resurgence. Resurgence is when you've stopped doing X, but suddenly you start doing X again. This time it's a little easier to stop doing X, but then it comes back again. This happens multiple times before a habit is truly gone. So don't get discouraged when your bad habit comes back. ",
"read this"
] |
[
"It's certainly possible, just takes a good degree of willpower and self-control, which is where most people fail.",
"I don't know of the scientific backing behind this but a rule of thumb is that it takes about a month to change a habit. "
] |
[
"Well it really depends on the type of habit and how you are trying to change it. You can stop chewing your fingernails and don't feel agitated about it in 3-4 days.",
"Stop getting distracted by interesting things can take MUCH longer than a month though, even if you work on it."
] |
[
"How are routers capable of handling multiple devices at once on the same wifi network? Wouldn't there be some kind interference between all of the devices?"
] |
[
false
] | null |
[
"The transmission protocol that is in use in most wifi routers is IEEE 802.11. WiFi uses a half duplex transmission mode meaning that messages are transmitted and received on the same frequency. The problem that you have guessed is that two transmissions may collide with each other causing a failure. This is actually a relatively common thing with WiFi access points that have a lot of connected devices, but this is actually fine because 802.11 provides a collision management protocol. ",
"We first must understand how wifi devices send information. All data sent over the network comes in discrete packets rather than a continuous stream. This is incredibly useful because it allows devices to continually check how the data was transmitted, retransmitting any packets that were lost. When a device sends a packet of information, it then listens for an acknowledgement response from the destination device. If it does not hear this then it knows that the receiving station did not hear its data. It will then retransmit its message after a certain amount of time, but ",
" the channel is clear. Thus if two devices end up \"stepping on\" each other, or transmitting at the same time, at least one of them will not hear an acknowledgement and will retransmit once the channel is clear. ",
"All of this behavior is defined under the Distributed Control Function mechanism. The fact of the matter is that collisions actually happen all the time on a lot of wifi routers, but because of the ingenious invention of packet protocol and collision management systems, the end user is virtually unaware of any of this. "
] |
[
"Well put. Of note, the protocol specifies a random wait time in the case of a collision. This makes it so that two devices don't keep colliding with each other."
] |
[
"The router sends out each packet with an address. If your device gets a packet not addressed to you, it discards it. Your device will only keep packets addressed to you.",
"You might think, well what if I hack my computer to accept other people's addresses, couldn't I just snoop on them?",
"Yes, yes you could. That's called wifi sniffing. ",
"The way to protect yourself against sniffing is to use encrypted connections. So, if you are browsing reddit with https instead of http, your information is encrypted and when someone else grabs your packets they won't be able to read what you are doing."
] |
[
"Why do certain medications need to be taken during dinner, after dinner, etc? What makes the difference? How harmful is it to not do it at the specified time?"
] |
[
false
] | null |
[
"A lot of it has to do with interactions with other drugs and eithfood and withtgewau the body breaks down the drug so you actually get it. Medications that have to be taken before food generally need the acid of the stomach to break them down for absorption. Medications that need to be taken with or after food generally cause nausea or need to be absorbed and broken down in the small intestine so as to not be destroyed by stomach acid. Some medications need to be spaced from each other as they can make the effects of other medications stronger or weaker.",
"The harm of not taking them as scheduled really depends on what the medication is. Of it's a take eithfood because it could cause nausea and you don't have nausea as a side effect from it, then it's very little harm. If it's taking all of your morning meds together with breakfast instead of one before and the rest after and the one that's supposed to be taken before interferes with your medication to keep your heart rhythm normal if taken together, it could be pretty harmful. Most circumstances fall somewhere between these 2 examples tho that it may not be super harmful but you just aren't going to get the benefit of the medication"
] |
[
"All has to do with how it breaks down in the body, and in some cases, whether or not nausea is a common side effect. (Eating with those medications sometimes calms that effect.)",
"Not crazy harmful, but not as effective as they could be."
] |
[
"Because of your stomachs high pH its tissue lining is constantly renewing itself so your stomach acid isn't everywhere in your body (this is usually three days). When you take some tablets like paracetamol without eating it breaks down your stomach lining faster than it can renew itself causing internal bleeding and making you very ill. With paracetamol its in high amounts or over time i am not to confident about other drugs."
] |
[
"Of all the academic and/or professional studies done about RISUG, the male contraceptive, what can consumers expect in the next 5 years? 10 years? Further?"
] |
[
false
] |
I read an article recently about RISUG, the male contraceptive that allegedly lasts 10 years or more with 100% effectiveness. As a young man in my 20s, I was wondering, based on academic and professional research, whether or not it is safe, viable for production, or likely to become available anytime soon. I want kids in the future, but not yet, so something like this (read: 100% effective, but reversible) is quite intriguing. Here's the I read.
|
[
"The issue is that the clinical testing required by the FDA to ensure efficacy and safety are extremely expensive, but the potential for making a profit selling that kind of contraception is basically nil, so alternative sources of funding for the clinical testing are needed to move forward."
] |
[
"The FDA can grant \"orphan\" status to drugs that treat certain diseases where the return on investment for bringing those drugs to market isn't very high. Orphan drugs get certain benefits including longer patent life to give more time to recoup money. If the FDA were to extend orphan status to male contraception then companies may be more willing to try and bring it to market. "
] |
[
"Orphan drug status in the U.S. requires that the disease affect less than 200,000 Americans."
] |
[
"Which single species accounts for the largest portion of earth's biomass?"
] |
[
false
] |
Also, since some population models predict human numbers rising to 15 billion this century, will this change our rank in terms of biomass and what are the environmental effects of having so much additional water contained within ballooning human biomass? Source:
|
[
"That might well be true, but bacteria aren't one particular species. Actually it's not clear if bacteria even HAVE species in the way that animals and plants do."
] |
[
"The ",
"AntBlog has a good answer to that question.",
"TLDR: By mass, cattle beats human, weighing about twice as much. Lots of krill, but probably they only weigh as much as humans."
] |
[
"Have no clue as to whether Stephen Gould knows what he's talking about; but he makes the case that bacteria may have more biomass than plants and animals.",
"http://www.stephenjaygould.org/library/gould_bacteria.html",
"But new discoveries in the open oceans and Earth's interior have now made a plausible case for bacterial domination in biomass as well.",
"[... many comments points suggesting this ...]",
"surprisingly, total bacterial biomass (even at such minimal weight per cell) may exceed all the rest of life combined, even forest trees, once we include the subterranean populations as well. "
] |
[
"Do \"lazy eyes\" expand a person's field of vision or is vision unaffected?"
] |
[
false
] | null |
[
"I have a lazy eye, I can confirm this is the case. I do not see one larger \"picture\", but one view at a time (usually my left as the lazy eye is mostly blinded as well)."
] |
[
"I have a friend with a lazy eye, and he told me that he sees two separate pictures and he can only pay attention to one at a time. (Normally, the brain combines the pictures from both eyes and makes a single 3D picture.) So, I believe that even if the overall field of view that his eyes are seeing is larger, it doesn't expand the area that he's able to watch because he can only pay attention to one eye at a time.",
"I don't know if this is universal for people with lazy eyes."
] |
[
"And confirmed again as a wearer of a lazy eye.",
"I primarily see from my right eye, and my left eye has been little more than peripheral for almost all my life. I'm taking steps to correct the vision and doing exercises to try and force the brain to complete the connection, but this will very likely take a long time to make it work. So I'll keep trying but not expecting.",
"And to clarify a bit on ",
" we don't see a wider FOV is simply double vision. Our brains are wired to take in 2 images as stereo. If that stereo image isn't true (such as one eye not pointing in the same direction as the other) then it causes double vision. And this hurts. A lot. So, the brain figures out which is the best (or truer) image of the two and then shuts off the input from the other. Sometimes we are lucky and it doesn't shut it off entirely, but instead just ignores the input. ",
"Since there's a small range of reasons why we have lazy eyes, as well as different types (one or both eyes facing the nose, one or both eyes facing the wall, and vertical turns as well), sometimes combined with impaired vision in either eye, I could end up being this a very, very indepth post. I've been doing a lot of research on it and have been looking at whatever ways I can to help rectify the problem shy of surgery. I'm not averse to surgery at all to fix it, rather I can't afford the surgery AND the time off work I'd need to take until I can see properly again. Nevermind the complications from correcting a horizontal ",
" vertical turn.",
"For more info, you can start off with Wiki and work out from there."
] |
[
"Do neurons have their own genome?"
] |
[
false
] |
My AP Biology always said that all the cells in a your body have the same DNA but a few articles on the internet like this one ( ) say that neurons often have different ones and even unique to a specific neuron. So who is right?
|
[
"Good question. All cells in your body start off from the same genome. Every time a cell divides, that genome gets replicated. DNA replication in humans is really, ",
", long-slow-whistle-sweet-baby-jesus accurate. But it's not perfect. ",
"This guy",
" did the math, and estimated that every time the genome is replicated, you get about 1/3 of a base pair change. Or rather, every three divisions you get one change. So if you plucked any two cells out of your body at random and compared their genomes, there's a pretty good chance that they won't have them ",
" same genome, even if they both descended from the same, original zygote. ",
"The paper you linked to reports that neurons, which can live for decades, accumulate mutations over their lifespan. That's really cool! But since the cells they're studying don't divide, they don't replicate their genomes, so that's not really an option for acquiring base pair changes. That paper also reports that the source of those mutations is likely not from DNA replication but from ",
". The idea is that every time DNA's double helix is opened to transcribe a gene, the bases of DNA are briefly more susceptible to mutation. ",
"Your teacher wasn't wrong, they were just simplifying things for the sake of understanding. Your teacher was right, but that paper is probably more right. "
] |
[
"To be clear, most cells do not in fact contain the exact same DNA pattern. One simple reason: mutations. All DNA will undergo natural mutations. This article is saying that neurons have a high rate of mutations. So yes, their genome is different than a heart cell. But the heart cells genome are going to be different than liver cells. To extend it, epigenetics also change how the DNA is read. ",
"more information about mutations: ",
"http://www.nature.com/scitable/topicpage/genetic-mutation-441",
"epigenetics: ",
"http://www.pbs.org/wgbh/nova/body/epigenetics.html"
] |
[
"The reason to that (from what I understand) mitochondria has their own DNA is that they are organelles then? Does this mean they can differ this same way or are they unique?"
] |
[
"Why are some cooling towers at power plants \"hyperboloid\" shaped?"
] |
[
false
] | null |
[
"Just from the structural side, a 'hyperboloid of one sheet' (which is the kind of hyperboloid they are) can be constructed of straight segments on two biases, cris-crossing. Depending on the eccentricity of the hyperboloid, each straight member crosses several of the ones in the other direction, this allows it to be very resistant to buckling. Using a hyperboloid you can make a rather tall and wide clear space without the need for internal ties to keep the walls from bowing out under the weight. Similarly the structure is very resistant to wind loads because it basically turns a side load into internal torsion and shear."
] |
[
"Here's a picture",
" that helps visualize the design. "
] |
[
"From the functional side:",
"-those cooling towers have fill material in them which the water is sprayed onto and trickles down. This has the effect of increasing the surface area of water available to make contact with the cooler air and increasing the effectiveness of the tower. The wide base of a hyperboloid tower allows for a large amount of fill material to be inserted at the bottom, maximizing the surface area",
"-those towers are natural draft cooling towers and have no fans to move the air through them. They are large and move large amounts of heat from the water to the air. They transfer enough heat to the air that the buoyant effect of the hot air rising is enough to pull enough air through the tower to properly cool the water. This reduces the operational cost of the tower because you don't have to spin fans, but that amount of heat transfer also requires a massive amount of air. Since the air isn't moving all that fast (compared to forced draft towers), there has to be a lot of area across which the air can enter the tower. The bottom of the towers are open to the atmosphere to allow the air to enter and their large diameters mean there's plenty of open area at the bottom to allow air to move into the tower.",
"-The now heated air has picked up not only heat, but has become saturated with evaporated cooling water. This water is expensive for the plant to constantly replace, so removing as much of the water from the air as possible before it leaves the tower is desirable. The shape of the tower means that as the hot wet air rises through the narrowing body of the tower, it is forced to speed up due to the constriction. When it reaches the narrowest portion of the tower where it begins to widen, it starts to encounter the cooler air from outside of the tower. The speed it picked up in the narrower sections then helps to ensure that it mixes well with the cooler air from outside the tower. The goal is to cause some of the evaporated water in the air leaving the tower to condense out as rain and fall back into the tower. The widening shape of the top of the tower not only serves as a place where the air leaving the tower can mix with the air outside the tower, but it also acts as a funnel to catch as much of the condensing water as possible to return it to the cooling loops."
] |
[
"I think I may be experiencing something called derealization. Can anyone tell me about it?"
] |
[
false
] |
[deleted]
|
[
"Your doctor. Also, it will take more than one visit for any doctor to seriously consider the claims. "
] |
[
"As the other person said, go to a better doctor. Also remember that a traumatic event is anything that traumatizes you. I know that sounds redundant, but an incident that may seem completely harmless to others can still leave lasting psychological damage. Again, if it's a problem for you see another doctor."
] |
[
"No need for you to apologize, your concern is understandable and it's good to ask for outside help/advice. I hope someone in this field sees this thread.",
"I'm certainly not even close to being any kind of expert in this field, but in my personal opinion (backed by some life experience with a similar issue), I think you might have some form of PTSD from an event in your childhood. This is all anecdotal, but I had a very frightening experience as a child and I had some problems with dissociation, I suppose. Whenever something very bad or stressful happened, I felt like I was non-physical, some sort of invisible thing floating around the room, watching my physical body react (or not). I didn't know why this was happening, until my early twenties, when my mother randomly brought up a topic that triggered my brain to remember a traumatic event that I had \"blacked out\" and then I had a meltdown. I know a few other people who had similar situations, too. Now that I've sorted out my past (to some extent) and made some peace with it (continuous work in progress), these occurrences have become rare. I don't think I've had this in 3-4 years, now. ",
"You might have a similar problem, but it also sounds like you are currently mildly depressed. Are you feeling burnt out on school? Are you feeling really pressured by something/someone?",
"I highly recommend speaking with a reputable therapist who understands your situation and has worked with others with these issues. Keep looking, not every therapist is good, of course... and not every therapist has experience with every type of mental/emotional issue, either. Don't give up and if you need to take a medical leave from university for a semester, do it before your grades tank. ",
"I wish you the best, please take care of yourself. "
] |
[
"Is there any way to describe the right-handedness of a coordinate system without resorting to hands?"
] |
[
false
] |
[deleted]
|
[
"The ordered triple <",
", ",
", ",
"> is a right-handed basis of ",
" if and only if det(",
", ",
", ",
") > 0. This is the only definition of right-handed."
] |
[
"The definition ",
"u/Midtek",
" gave is the correct definition and the one we use in higher level mathematics. But usage of this definition assumes some comfort in determinants which is not strictly necessary here.",
"One of the reasons left-handedness is different from right-handedness is that you cannot go from your left hand to your right hand with just rotations and translations. But you can if you allow reflections. ",
"In math-speak, we would say that any transformation sending your left hand to your right hand must also change orientation. Rotations and translations do not change orientation but reflections do change orientation. The example ",
"u/Midtek",
" gives where you swap the x and y-coordinates is another example of a transformation that changes orientation. ",
"If we are explicitly given a map, then we can measure the change in orientation through the sign of the determinant. ",
"So to describe right-handedness, we do not need to resort to hands. We just need to define which maps change orientation and which do not. So property 13 here is key. ",
"https://en.wikipedia.org/wiki/Determinant#Properties_of_the_determinant",
" ."
] |
[
"The ordered basis ",
" the coordinate system. <",
", ",
", ",
"> is not the same as <",
", ",
", ",
">"
] |
[
"In the long run, is worldwide income/wealth inequality increasing, decreasing, or fluctuating around a mean?"
] |
[
false
] |
[deleted]
|
[
"The details will of course vary from country to country. In Europe for example, the biggest trend is that inequality has been lower in the 20th century than at any point over the past few centuries. However, on shorter time scales, inequality has both increased and decreased.",
"To get a better sense of these fluctuations, let's take the specific case of France. ",
"This chart",
" shows how wealth inequality has evolved over the past two centuries. As you can see in the 1800s the situation was more or less unchanging with the richest 10% owning about 80% wealth. Their share slowly rose until the start of the 20th century when it rapidly fell. The fall was directly due to the destruction of the two world wars as well as changes in taxation and structural changes in the economy. For much of the twentieth century wealth inequality decreased until about the 70s. At that point you see inequality creeping up a bit, which is still were we are now. The latter effect is a bit controversial, but key contributions came from a slowing economy and the rise of highly payed managers (e.g. CEOs) who could invest their earnings. ",
"For other countries, the situation is very similar in Sweden, as ",
"shown here.",
" Indeed, the French case is pretty representative of Western Europe. On the other hand, in the US the situation ",
"looked like this",
". The key takeaway from the American case is that historically inequality was a bit lower than in Europe, but at the moment it's on the rise much more quickly than in Europe."
] |
[
"I second this book recommendation. It's a great overview of the history of economic inequality.",
"To summarize Picketty's argument in the simplest of terms, inequality tends to be higher over time because the rate of return on capital investments is higher than the rate of economic growth. People that already have a good deal of wealth are able to invest it and generate more income than people working off of wage labor (i.e., you need to have money to make money.) When economies grow quickly, this effect is reduced as the new wealth is constantly being created - therefore pre-existing wealth is less important. When economic growth slows, less new wealth is being generated and the people that already own large amounts of capital benefit more relative to everyone else. In the 20th century the World Wars and the Great Depression effectively destroyed much of the world's existing capital. When combined with the economic booms that followed economic policy changes in the mid-20th century, this reduced the importance of existing capital relative to income, which in turn reduced economic inequality. As economic growth began to slow near the end of the 20th century, the importance of capital relative to income increased, as did economic inequality.",
"If true, this is rather depressing as it indicates that economic inequality is the default state of affairs in modern capitalist economies, and the \"middle class\" societies of the 20th century are the exception rather than the rule. As you said, Picketty's proposed solutions are controversial, but he does a great job both explaining the math behind these processes and presents copious amounts of empirical evidence to support his conclusions."
] |
[
"Some of the responses here are not correct. ",
" wealth inequality is most definitely decreasing.",
"This is because globalization (e.g. immigration, trade, internet, etc) has made it possible for people to exchange goods and services across national borders in a way that just wasn't possible before. ",
"This means that where you're born in the world has less of an impact on how much you can expect to earn. Don't get me wrong, it's still by far the biggest determining factor, but not nearly as much as it used to be.",
"If you look at where the fastest growing economies are, they're virtually all in the developing world. An annual economic growth rate of 4% would be considered outstanding in America, but very disappointing in Rwanda. Developing countries are catching up to developed countries, not falling further behind.",
"I should point out that even though ",
", income/wealth are becoming more egalitarian, they're actually becoming less equal ",
". This isn't a contradiction; worldwide inequality can decline even if it increases within every single country in the world.",
"To illustrate this point: If a middle-class Mexican earning $10K per year immigrates to America and becomes a lower-class American earning $20K per year, income disparity has actually increased in both countries, even though globally it decreased."
] |
[
"Does the infinite multiverse theory assume that in addition to every possible scenario existing, every impossible scenario also exists?"
] |
[
false
] |
I'm having a hard time reconciling the concept of infinity with the idea of complete improbability. According to (one of the many) multiverse theory, there should exist an amount of alternate universes, thus there must be one for every conceivable outcome to have taken place since "the beginning". Following this reasoning there must be one where I chose to wear blue socks today instead of white, one where I chose to eat baked beans instead of broccoli with dinner, etc. But is it also believed that there are universes with impossible outcomes? Is there a universe that has been completely parallel up to ours for all of time up until right now when suddenly the Earth turns into an umbrella, or my left arm begins speaking to me with an Australian accent? How can every outcome exist when so many outcomes are impossible within our conceivability? edit: Wasn't sure what to tag this under (math maybe?) so I put physics, let me know if I should change it.
|
[
"The short answer is no. If a particular scenario is by definition ",
" then it ",
" come about. However, given enough time, ",
", but still possible, events can take place.",
"But to understand why this is the case it would help to review the argument you are proposing more fully.",
"No doubt, the model you propose is some variant of a universe infinite in time and space, which can be subdivided into pockets which are independent of each other and limited in volume. The ensemble of particles within each 'pocket' is either in thermal equilibrium or near thermal equilibrium, characterised by a finite temperature.",
"Now, since we have a set of 'universe', i.e. collection of particles (let us assume that they are classical microscopic partiucles, for convenience) confined in a particular volume, there is a total number of arrangements that these particles can occupy within that given volume. This set of configurations is the phase space for each universe.",
"Now, consider the universe under time evolution. With time, the universe will either evolve into a periodic pattern (i.e. when it begins at some state, it will inevitably return to that state after a finite peroid of time, and as the rules of time evolution are deterministic, or at least preserve the distinctions between different states, it will continue to follow this pattern with some period) or it will not, i.e. it will continue jumping from one state to the next. However in the second case it is bound to occupy every region of the phase space; eventually it will return to a state arbitrarily close to one it has already occupied. In infinite time this will happen infinitely often.",
"This whole story is an outline of the concept of ",
"Poincaré recurrence",
".",
"However, it is important to stress that even the improbable states must be part of the phase space of the system and that the rules of time evolution must connect these states to the somewhat more probble ones. So truly ",
" states, states that violate the laws of physics, will never occur.",
"I could go on to talk about how this concepts aaplies to our universe, ",
"Boltzmann brains",
" and associated paradoxes, and list the different ",
"multiverse hypotheses",
" but I think this is enough for now to kickstart some discussion on the topic. Essentially, givent a finite 'volume' of possible states and infinite time or space, and chaotic time evolution, every permutation is bound to arise infinitely often."
] |
[
"First there's no such thing as \"infinite multiverse theory\"",
"What you are thinking of is ",
"the Multi-World Interpretation of Quantum Mechanics",
". ",
"From that it ",
" be noted that this pertains to ",
" not your choice of sock color, nor your dinner selection. So unless you use some kind of quantum mechanics-die to make decisions for you, it's entirely irrelevant to macroscopic \"choices\" you make.",
"That being said, let's reiterate the \"measurement problem\" of quantum mechanics. What exactly is occurring when I ",
" an object? The long-traditional view has been that quantum mechanics doesn't play nicely with big macroscopic things like measurement equipment, so the thing being measured stops behaving like a ",
" quantum state, and acts more like a classical thing when it's measured.",
"But ",
"Everett",
" and others thought maybe something else happens. Which I'll reframe in maybe more contemporary language. When a measurement happens the quantum particle interacts with some other quantum particle. The electron with spin emits a photon of some energy. The energy of that photon is correlated to the electron's spin. But that photon is quantum too, so we can say that it's just a correlated quantum particle. ",
"That photon interacts with a single electron in our measurement box, but you can frame it that now the electron is merely ",
" with the initial electron. This electron bumps an atom, tangling more particles into the correlation with the initial electron's state. A whole cascade of correlated actions later, and our dial reads out ... something. But whatever the dial reads out is correlated to the superposition of that first particle. ",
"... so what if all the particles of our measurement machine are all one big quantum system afterall, and they are now in a superposition of states equal and correlated to the superposition of our measured particle? It doesn't mean there's multiple copies of our machine out there... just... multiple states it's in.",
"And there's really no special thing about human minds, either, so now our mind is in a correlated superposition, depending on what we saw on the dial. ",
"Maybe all measurements of coherent quantum systems are really just adding a new degree of superposed states to all the stuff that is \"measuring\" them. ",
"But remember, your mind isn't magic, it's physics. One state of a superposition can't influence the other state. You can't \"remember\" the other state of yourself that measured spin down, when you remember spin up. You have no way of accessing those memories because the chemistry of your brain is correlated to whatever the particle was.",
"Anyways, back to the original question. Since no measurement will show something physically impossible, none of the states in our \"universal wavefunction\" will be physically impossible states. There may be many/infinite correlations between superpositions of portions of that wavefunction, but none of them lead to impossible results."
] |
[
"First there's no such thing as \"infinite multiverse theory\"",
"Far outside mainstream scientific opinion (actually, outside of science entirely) is Max Tegmark's ",
"Ultimate Ensemble",
" theory, which could reasonably be called an \"infinite multiverse theory\".",
"Also:",
"Since no measurement will show something physically impossible, none of the states in our \"universal wavefunction\" will be physically impossible states.",
"You have to be very careful here -- many things that we'd naturally call \"impossible\" are actually \"vanishingly improbable\" (and an event occurring with zero probability is not the same thing as that event being impossible.)"
] |
[
"Would it be possible to survive inside a blue whale for a short period of time?"
] |
[
false
] |
Slightly ridiculous question, I know, but it just got me thinking. Lets say you somehow find yourself inside the mouth of a blue whale. Could you survive for minutes? Hours? Is there somewhere where water doesn't breach, and is there any oxygen there?
|
[
"The inside of their mouths are filled with water and whale spit. There is no air in there, so you would survive as long as you could hold your breath, then pass out and inhale whale mouth juice and drown. So minutes is the answer."
] |
[
"According to this ",
"article",
":",
"The blue whale also incidentally consumes small fish, crustaceans and squid caught up with krill."
] |
[
"\"Despite the size of its mouth, the dimensions of its throat are such that a blue whale cannot swallow an object wider than a beach ball\" - en.wikipedia.org/wiki/Blue_whale"
] |
[
"What was the first domesticated animal?"
] |
[
false
] |
And does it differ area from area; did the humans in Mesopotamia domesticate one animal and those living in South America some other first?
|
[
"We currently believe ",
"dogs",
" were the first animals to be domesticated, around 15,000 years ago, but that date is fuzzy. It may have happened multiple times in different places, but we also have no good way to tell for sure. Dogs predate other domesticated animals by thousands of years, and seem to have spread all over the world, even to the ",
"Americas",
", before the next domestication event (sheep) took place. This makes sense -- agriculture and permanent human settlements are far newer than 15000 years old, (about ",
"11000 years old",
"), and pretty much every other domesticated animal is either livestock or had/has a secondary agricultural purpose."
] |
[
"I'd be surprised if this wasn't the case... I can't see a lot of impetus for a person, in a world where domestication isn't even a concept, to go out and trap literal wolves. We think cats domesticated themselves too, by choosing to voluntarily hunt near granaries in human settlements where rodents were more densely populated. Perhaps it's not a surprise that we regard these two species as friends moreso than with other domesticated animals?"
] |
[
"There is some debate whether humans domesticated dogs, or dogs domesticated themselves. Wild dogs may have invited themselves into human groups, rather than humans actively capturing wild dogs."
] |
[
"Why is it telephone calls broadcast on radio programmes still sound muffled and dodgy?"
] |
[
false
] |
Phone call quality between mobile handsets or even VoIP have reached a point where everything's pretty much crystal clear. Why is it when a phone call is broadcast over the radio, it sounds bad? I feel like the technology to make the call sound like the person speaking is physically present in the studio should already exist.
|
[
"The technology required to produce high quality sound from an extremely small receiver does exist. The problem is that it isn't exactly cheap. Remember that phones aren't designed to produce high quality audio. They're for personal communication. When we make a call, the speaker at the other end isn't designed to resolve high fidelity sounds. This would make it somewhat pointless to install a top notch microphone when the average phone isn't going to differentiate the difference. It would also notably bump up the price.",
"Additionally, think about where a talk-show host is broadcasting from. If you've ever seen the room they sit in, the whole thing is designed to reduce an ambient noise and cancel out any sound reflecting off of the walls. Most are also soundproof, so noise from anywhere outside of that room is muted. There are also differences in the microphones they use and how they work. This all results in an ultra-crisp sound.",
"There are bluetooth microphones which are designed to produce high quality sound. Note, however, that they're massive in comparison to those found in the average cellphone. They're also not very cheap.",
"Takeaway message: It's a cost-benefit thing. Increased sound quality versus functional sound quality. If you want to do an interesting contrast, listen to the difference in sound quality from a radio show if you listen to it from your phone's speaker instead of a run-of-the-mill radio."
] |
[
"You have messed up the frequencies a bit. The Nyquist frequency of a telephone is 4 kHz indeed, that means the sampling frequency is 8 kHz. OTOH, 44.1 kHz is the sampling frequency of an audio CD, the Nyquist frequency being 22.05 kHz.",
"I hope this clears up any doubt about it."
] |
[
"It's the ",
"nyquist bandwidth limit on the telephone system",
"; it's much smaller than that of the studio equipment."
] |
[
"Does volcanic magma originate in the Earth's core?"
] |
[
false
] |
Has the magma that erupts from volcanoes come from the core of the planet via a rupture in the mantel? If so, what prevents more of the core, which I understand is under around 30 million psi of pressure, from spewing forth? What is lava's "coagulant?" Just heat/pressure loss?
|
[
"Virtually all lava erupted at volcanoes is derived from partial melting of either the crust or the upper portions of the mantle. Even in mantle plumes, which are theorized to originate at the core mantle boundary and produce hotspot volcanism in places like Hawaii or Iceland, the actual melting does not occur until the material in the plume reaches the crust or shallow mantle (i.e. rocks in the plume are hotter than the surrounding mantle and thus more buoyant, but still solid). ",
"The reason for the melting of a rock and formation of a liquid (magma) is a function of both temperature and pressure, with the melting temperature increasing with pressure. Check out this ",
"page",
" and scroll down to the \"Making Rock Melt\" section. If you look at the phase diagrams, which simply chart the temperature and pressure conditions for an ideal rock to melt, you can see that under normal conditions, the geotherm (the increase in temperature and pressure with depth for a parcel of rock) is always is in the solid phase, thus the crust and mantle are solid. Going down in the earth (so moving along the green line representing the geotherm, to melt a rock and form magma, you need to (1) add heat at a constant pressure/depth (which can happen, but is not common) to move the conditions to the right and into the solid+liquid phase, (2) move the rock up fast, decreasing the pressure but keeping the temperature high (it needs to move fast so that it doesn't cool through conduction with the surrounding cooler rocks or (3) change the conditions such that the phase change occur at a different temperature/pressure, which in the earth usually happens through the addition of water. Mechanism 2 produces magma seen at rifts and hotspots and mechanism 3 produces volcanism at subduction zones."
] |
[
"Awesome explanation! Thanks!",
"I can't wait to check out that link and graph when I get home.",
"Do we know what kinds of phenomena move rock upward at the speeds required for mechanism 2 to occur?"
] |
[
"This made me think of a question: If I had a container with ten pounds of water and a thousand pounds of oil on top of it, the oil would, of course, float. If I were to open a channel through the oil to the water, say a straw, wouldn't the mass of the oil be enough to push the water up through the straw?",
"Intuitively it seems like it would, maybe it would require some suction to get it started, but that also seems like it would sink back down and come back up the straw which implies perpetual motion, which makes me doubt the results of my little thought experiment."
] |
[
"How is blood type determined?"
] |
[
false
] |
[deleted]
|
[
"Its pretty easy to measure blood type. You can use antibody binding to test for presence of A or B antigens in your blood.",
"If you have only A, then you are type A.\nIf you have only B, then you are type B.\nIf you have both, you are type AB.\nIf you have none, you are O."
] |
[
"And how do they find the resus ? What this even mean ?"
] |
[
"Rhesus, aka Rh has an antigen called D. It works the same way as with the ABO system, you use antibodies for the D antigen(anti-D) and check if there is a reaction or not."
] |
[
"Why does general relativity cause asymmetry in spectra-graphs?"
] |
[
false
] |
A professor told me this, but I cannot find any papers or videos on it. Why does it create an asymmetrical "tilt" in peaks on spectras?
|
[
"Maybe you're thinking of ",
"gravitational redshift",
"?",
"Gravitational redshift results in the shifting of spectral lines in response to gravity (e.g. a photon moving upwards on Earth loses energy and becomes redder) and/or the expansion of the universe (photons coming from far away appear redder because their wavelength has been stretched by the expansion of spacetime).",
"Einstein argued with a simple thought experiment that gravity must affect the energy of light. Suppose it ",
": launch a photon of energy E upwards to a great height, then convert it into a massive particle (via E=mc",
"). Drop the particle; it gains energy from falling in the gravitational field. Then at the bottom convert it back into a photon of greater energy and launch it back upwards. Rinse and repeat and get as much energy as you like. Since we know energy must be conserved, Einstein reasoned that the photon must, contrary to the assumption, lose energy on the way up.",
"It's a key prediction of general relativity, and it's been tested both on Earth (",
"Pound-Rebka experiment",
") and cosmologically.",
"Edit: ",
"see below",
" for a nice discussion of conservation of energy in GR."
] |
[
"But it's very nearly conserved in the systems that nonabeliangrape is referring to. Close enough that the thought experiment is still valid.",
"Of course, general relativity isn't really about thought experiments - those are just to help understand things more intuitively. You can do the calculations - using the same exact equations which tell us how conserved or not conserved energy is in an expanding universe - to get the same result quantitatively."
] |
[
"Conservation of energy (mass is included in this) only holds when physics doesn't depend on time. This is a consequence of ",
", which links symmetries of physics to conservation laws.",
"Here's a nice example. Take the expanding Universe, which pretty clearly depends on time. Consider a ball of photons, or light particles, expanding with the Universe. As the Universe expands, the total energy in that ball ",
", because each individual photon is being ",
" and losing energy."
] |
[
"Question about refraction."
] |
[
false
] |
[deleted]
|
[
"The full equation you're talking about is c/n = f*l, where f is the frequency, l is the wavelength, c is the speed of light, and n is the index of refraction of the material. The frequency f (which is directly related to the energy of the light) doesn't change. So if some light enters a medium it's velocity and wavelength will change, but it's color (frequency) will not. Note that when people talk about light of some wavelength (like \"520nm light is green\") it is implicitly assumed they're talking about the vacuum wavelength. "
] |
[
"They detect the energy of the photon. It's a shortcut to refer to the energy of a photon by its wavelength, because nanometers is a more relatable unit than something like eV. The implied assumption when doing so is that you're talking about the wavelength in a vacuum."
] |
[
"They detect the energy of the photon. It's a shortcut to refer to the energy of a photon by its wavelength, because nanometers is a more relatable unit than something like eV. The implied assumption when doing so is that you're talking about the wavelength in a vacuum."
] |
[
"Why are the cave drawings of France, which are older than the Native American Southwest rock art, so much more sophisticated and accomplished?"
] |
[
false
] |
The cave drawings of France, such as the Chauvet cave, is being dated at 28 to 40 thousand years ago. Why are they so much more artistically accomplished than the Native American Southwest rock art (13-15 thousand years?), which seems consistently crude by comparison? I’m not asking this in a judgmental sort of way, but I’m wondering if there has been any speculation on what it says about the meaning of the drawings or about the people who drew them.
|
[
"r/Anthropology",
" might be able to help you."
] |
[
"\"they are so much more artistically accomplished\" - can you provide source/images that formed your opinion? I found images on IMHO similar level."
] |
[
"I don't agree about the artistic value. The Native American art however had rather significant symbolic use and value. So you are likely seeing less art and more message. The cave artist was likely drawing deer, the Native American was likely presenting a religious message to a specific deer god. Or telling a story and stories require more constrained symbols."
] |
[
"I am a staunch supporter of Nuclear Power. Can someone give me a few reasons why nuclear power is NOT viable?"
] |
[
false
] | null |
[
"The ",
" resistance to nuclear power is a major problem. It's been that way for decades and is unlikely to go away.",
"Given the anti-science trends in the US, it's likely to get worse, not better."
] |
[
"a small mistake kills thousands and the environmental ramifications are disastrous - Fukushima being the most recent example.",
"Using LNT (a conservative method) to approximate health impacts of the Fukushima accident, there will be somewhere on the order of 10-100 excess cancers to people outside of the workers. Using a threshold method to estimate it, no one will get any cancer as a result of Fukushima.",
"On the other hand, in the US every year tens of thousands of people die to health complications brought on by fossil fuel pollution. This is an EPA estimate. World-wide, the number is around 300,000/year - mainly due to China's coal fired plants. There is no \"accident\" that is causing these deaths, it's just business as usual.",
"Why in the world does coal get a free pass in these discussions? I shouldn't have to state this every time :(."
] |
[
"Somewhat related, and also interesting to read, is David MacKay's book, ",
"sustainable energy - without the hot air",
". I recommend the whole book, but the chapter on nuclear power is a good read as well when talking about the numbers. "
] |
[
"My pretentious rules for pluralization of units..."
] |
[
false
] |
So for a long time now (I've got a BS and MS in physics, working on a PhD) I've always believed that one should only pluralize units when the magnitude of the quantity is greater than one. So for example, "0.5 meter" as opposed to "0.5 meters". I was just explaining this to someone and realized I don't remember where I got this idea, and some minor googling didn't bring anything up. My thought process is that if you have less than one of something, the unit should not be plural. Am I just a total asshole or is there actually a convention on this?
|
[
"Hipstre, pleeease."
] |
[
"Myself, I'd say \"half a metre\" or \"0.5 metres\". I only tend to use the singular for exactly one of a thing. Any mutliple, even multiples less than one, just doesn't sound right without the plural."
] |
[
"Alley's Craft of Scientific Writing, doesn't go over this topic specifically, but does include a place where he writes",
"\"... the eruption of Mount St. Helens in 1980 had an ash plume that reached 19,000 meters and dispersed 0.67 cubic kilometer",
" of material into the atmosphere ...\".",
"This goes with what I intuitively do. For integer objects I have negative one cats, zero cats, one cat, two cats, etc. For real number objects that are measured with errors (or specify precision), I always pluralize. E.g., 0.5 meters, -0.5 microCoulombs, 1.0 hours, and 2.1 liters."
] |
[
"Knowing the mass of a star, is there a maximum allowable distance of orbit?"
] |
[
false
] | null |
[
"In an isolated 2 body system (that is there is nothing else in the universe) there is no maximum distance.",
"In reality the answer will be the Hill sphere of the star in relation to the nearby stars. In less technical jargon, the maximum distance will be dependant on how far you can travel from the star before the gravitational influence of another star (or other object) becomes dominant."
] |
[
"how much thought is there on the concept of gravity being perhaps not exactly the inverse square of the distance at all distances, and how that might explain a portion of the dark matter and dark energy problem?"
] |
[
"They could remain in orbit and not collide (depending on a lot of other physics like how each object evolves in time)."
] |
[
"Two Drones Flying Away From Each Other Along the Equator; Does the Earth's Rotation Affect the Length of Ground Covered By Each Drone?"
] |
[
false
] |
Sorry if this has been asked before, it's difficult to come up with an appropriate search term. If two identical drones, hovering a foot off the ground, are placed back-to-back on the earth's equator (parallel with it), and each is then propelled forward along the equator (i.e. directly away from each other) at a fixed speed, would one travel "further" than the other given the direction the earth is rotating? By "further" I mean relative to the surface of the earth, as opposed to a direct ass-to-ass measurement of the drones from their starting point to the end point, which would obviously be the same for each drone. To keep it simple, let's assume there are no other factors involved (such as variable wind resistance, sunlight/time zones, anti-drone activists with shotguns, that the equator of the earth isn't a perfectly smooth surface, etc.) This feels like a physics 101 question, but I was educated in science by a rotation of substitute teachers whose actual area of expertise was P.E. or Home Economics, so I'm learning all of this stuff by the seat of my vast adult pants. Thanks for reading/answering/directing me to previous threads which cover the same question!
|
[
"Two quibbles: \"Variable wind resistance\" doesn't make much sense in this context. \"Variable wind\" does.",
"\"Fixed speed\" is meaningless unless you specify with reference to what. Ordinarily, an aircraft flies at a fixed ",
": i.e., speed with reference to the airmass.",
"The rotation of the earth will have zero effect on the distance traveled, ",
". But wind will indeed affect it.",
"If an aircraft is flying east at 100 mph, into an east wind of 10 mph, it will make 90 mph over the surface of the earth; another one, flying in the opposite direction, will make 110 mph.",
"If you meant zero wind, with both drones flying at the same airspeed, then they will cover exactly the same distance as seen by an observer on the ground."
] |
[
"So, here is a fun way to visualize the problem with the question:",
"Take 3 drones to a point on the equator. Set 1 to travel east to west at a speed where it will fly around the world in 24 hours. Take the second drone, set it to fly west to east around the world in 24 hours. Set the third to hover. Now wait and watch. To you, drones 1 and 2 will cover the same distance in the same time while the third drone hasn't moved. ",
"But, at the same time you have a friend that was hovering over the north pole, letting the world turn under him. He looks down and sees something completely different: drone 1 will appear to circle the earth twice in that 24 hour period, drone 3 (the one you set to hover) will circle the earth once, and drone 2 will appear to hover.",
"Reference frames matter. "
] |
[
"Damn, this is what a lack of education looks like; I can't even formulate the question correctly because I don't know the most basic terms! 🤦",
"Thanks for the clarifications/answers, they've helped me get to grips with the whole thing."
] |
[
"When prey is swallowed whole, what can kill it once it is in the digestive tract?"
] |
[
false
] |
This photo propmted the question: What would kill the frog once it is swallowed by the fish? What other ways to prey meet their end inside the gut of large predators? Whale? Snake? Chameleon? Other examples you might know?
|
[
"Most animals have many mechanical and chemical means of digesting their food after being swallowed whole. I believe frogs and other reptiles have hard bony structures towards the back of their throat that crush living organisms that pass through. They also have strong digestive acids and enzymes which begin to break down these animals rather quickly."
] |
[
"Is that what the frog in the linked picture is sitting on?"
] |
[
"Not exactly sure. Looks like the frog is just situated in that fish's throat. ",
"That fish likely has pharyngeal teeth that would break that frog down though",
"."
] |
[
"Phosphorus can make 6 covalent bonds?"
] |
[
false
] |
I was reading my text book and I found the molecule PF6 . Which is supposed to have an octahedral shape. I can't understand how phosphorus, which has only 5 valence electrons, can bond with 6 atoms of fluorine.
|
[
"Fluorine is extremely electronegative and will bond like crazy to anything it can, and phosphorus can also 'expand it's octet' meaning electrons can move up from the 3p orbital to the 3d orbital which can accommodate more bonds. These two factors help make the six bondson phosphorus more stable. For comparison fluorine also bonds with xenon to make xenon tetrafluoride, and xenon has no valence electrons."
] |
[
"You say that like you think he doesn't know. He clearly means no 'free' valence electrons. The fact that it has a closed shell and will still react is the relevant information, don't be pedantic."
] |
[
"You say that like you think he doesn't know. He clearly means no 'free' valence electrons. The fact that it has a closed shell and will still react is the relevant information, don't be pedantic."
] |
[
"Does the speed of light limit the speed at which molecules vibrate, and if so, does this mean there is a limit to how hot something can be?"
] |
[
false
] | null |
[
"Does the speed of light limit the speed at which molecules vibrate",
"Yes. ",
"and if so, does this mean there is a limit to how hot something can be?",
"No. There is not limit to how much energy an object can have from relativity. As a particle approaches the speed of light, its energy will grow without limit, i.e. it appears to require an infinite amount of energy to accelerate a particle to the speed of light. In a simple model of a non-interacting gas, the temperature is proportional to the average kinetic energy of the particles, so the temperature could be arbitrarily large even if the particle speed is always less than the speed of light.",
"There may be other, possibly yet unknown, physics that puts an upper limit on temperature, and certainly we know that a complete theory of quantum gravity would be needed to describe systems above the plank temperature, but that goes beyond classical relativity."
] |
[
"Yes, in principle a system with sufficient internal kinetic energy could form a black hole. The temperature of a system actually contributes to its rest mass! "
] |
[
"Shouldn't a black hole form as energies reach absurd levels?"
] |
[
"Are nocturnal animals active for longer periods in the winter?"
] |
[
false
] |
Are nocturnal animals generally active as long as it's dark outside? Or do they tend to keep similar hours regardless of the proportion of light and dark in a day? Like, the sun goes down around 1700 right now where I am, will wolves become active as soon as it is dark, or will they wait until around 2200 when the sun would set in the summer, or something completely different?
|
[
"Your question isn’t as straightforward as it seems because many animals aren’t strictly “nocturnal”, different populations of them may tend to be active at different times for different reasons other than just night/day (such as local human activity, weather/temperature, availability of food during a particular time of year). ",
"Here is a 2-year study of several different mammals in Japan based on camera traps, showing that some animals shift their activity patterns seasonally: ",
"Seasonal and Diel Activity Patterns of Eight Sympatric Mammals in Northern Japan Revealed by an Intensive Camera-Trap Survey",
"Interestingly, instead of being more active at night when winter nights are longer, some crepuscular (normally active at dawn and dusk) animals such as deer became more diurnal in winter— the authors hypothesize that it’s because winter nights are cold so it’s better to be active when the sun is up. ",
"For wolves specifically, since you mentioned them, they are one of those species that is highly adaptable and not always strictly nocturnal or crepuscular. There is some good discussion of that in this article: ",
"Daily Patterns and Duration of Wolf Activity in the Białowieza Forest, Poland",
"This causes dissimilarities in activity patterns of wolves from different study sites: wolves were nocturnal in Italy (Ciucci et al. 1997); nocturnal with a tendency to bimodal activity in Spain (Vilà et al. 1995); active throughout day and night in Ontario, Canada (Kolenosky and Johnston 1967); and most active from 2200 to 0600 h in summer and from 0700 to 1600 h in winter in Alaska (Fancy and Ballard 1995).",
"The sources are clickable in the linked article if you want to learn more! ",
"These authors found their particular wolves remained basically crepuscular year round, and believe that weather and prey availability/behavior affect their activity patterns more than human activity nearby or other factors, but they specifically call out that in other parts of the world, different circumstances apply and you end up with different results. ",
"Also from the same paper:",
"If wolves adapted their behavior to avoid direct contact with humans, they might have become less active during the day. Indeed, wolves studied in mountainous agricultural regions of Spain and Italy with human densities of 20–30 inhabitants/km2 hardly moved during daylight (Ciucci et al. 1997; Vilà et al. 1995). In Alaska, where human density is low, wolves moved during 50% (Peterson et al. 1984) of the daylight. In forests of Minnesota, where human density in the wolf range was 1.5 inhabitants/km2 (Mladenoff et al. 1995), wolves moved during 28% of the daylight in winter (Mech 1992). In the Białowieża Forest, persecution does not seem to have caused wolves to reduce their activity and movement in daylight, perhaps because our study area is mostly covered by forest. In Italy and Spain, where <40% of the area in the wolves' home ranges was forested (Ciucci et al. 1997; Vilà et al. 1995), there may not have been enough cover for daylight movement. Human activity therefore does not seem to significantly influence temporal activity patterns of wolves in regions where they have the opportunity to avoid direct contact with humans.",
"So you can see there’s not just one simple answer to your question!"
] |
[
"Very interesting! Thank you."
] |
[
"thank you so much for the detailed response man it was such an interesting rabbit hole"
] |
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