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[
"Physically, what could this black orb near the sun be? (video)"
] |
[
false
] |
The video depicts a Jupiter-sized black orb siphoning something off the surface of the sun, then zooms away. You can cross-reference images and data from SOHO (solar and heliospheric observatory) with the dates to see that these are in fact authentic images. BLACK ORB: SOHO: From the size of the object, would it be moving at the speed of light? It's absolutely massive. Does anyone know what the hell this is?
|
[
"Here's ",
"a paper",
" authored by NASA researchers (et al) that talks about coronal prominence cavities, and includes some images of some past cavities that are every bit as large as this one."
] |
[
"So what? Why not explain why you think it's correct or challenge the guy and win him over to your opinion?",
"The explanation was offered. He dismissed it without any reason. It is not anyone's obligation to win him over. Nobody cares whether he understands or believes the explanation or not - especially when he is so quick to dismiss what was offered on no grounds.",
"He's perfectly at liberty to dismiss it, and it's rude to just downvote him for being skeptical.",
"It is not rude. Just as he is free to dismiss a perfectly good explanation on no grounds whatsoever, I am free to dismiss his dismissal on no grounds whatsoever.",
"That's just berating him for being unorthodox, and I don't like church and \"believer\" mentality on a forum like this. It's hypocritical and disgusting.",
"I have not berated him. He received downvotes not because he was being \"unorthodox\", but because he was being irrational and unscientific. There is no church and believer mentality here. We go where the evidence goes. If you don't trust the explanation, feel free to offer an alternative. If it is sound, it will be accepted. As simple as that. No need to get worked up over this."
] |
[
"I'm pretty sure NASA explained this in a video on YouTube already. There were posts about this a while ago. Search for it and you'll find it."
] |
[
"How long does it take, on average, for a human to develop scurvy due to a total lack of Vitamin C?"
] |
[
false
] |
How long does it take, on average, for a human to develop scurvy due to a total lack of Vitamin C? I know Vitamin C is basically everywhere in most diets of the world. However, in a "what-if" scenario, how long would a human have if he or she was devoid of any Vitamin C intake to develop the disease of scurvy. I assume there are records of this due to the old sailing ages of exploration from Europe to the Americas and circumnavigating the globe for trade. Not to mention modern science probably having a deep understanding of the disease nowadays.
|
[
"Lots of responses with people pontificating about things but no one answering the question.",
"\"Symptoms of scurvy generally develop after at least 3 months of severe or total vitamin C deficiency.\"",
"http://dermnetnz.org/systemic/scurvy.html"
] |
[
"Meat also contains some vitamin C.",
"I'm sure some populations don't get the ",
" amount of vitamin C, but there's a difference between getting a sub-optimal amount of something, and having so low an amount that it makes you actively sick."
] |
[
"Meat, specifically meat from carnivores, often has enough vitamin C. Many animals can synthesize it on their own.",
"The issue is that Vitamin C breaks down very easily, so you need to eat fresh meat that hasn't been overcooked or processed."
] |
[
"How can a speaker produce more than one sound at a time?"
] |
[
false
] |
I can visualize how a speaker can make a sound by vibrating at a certain frequency, but how can it create more than one sound at the same time? It can't vibrate at two different frequencies can it? Am I wrong about how speakers work? Edit: Thanks for the answers!
|
[
"Oh man, what a good looking question.",
"The answer is that sounds are waves, which have the property of ",
"superposition",
". This means that the ",
" wave coming from a multitude of sources is simply the addition of all the sound waves coming from each of those individual sources. ",
"What a speaker does is play the 'summation' sound wave. This is how you can get more than one 'voice' at a time. ",
"What is more interesting is how you can save sound waves. You could save each individual wave, but that becomes quite a laborious business. Instead, what you can do is save sounds as contributions from some basic sound waves, such that when you add the basic sound waves in varying amounts, you can make ANY sound. ",
"The only way to make this example intuitive is the following: Consider any point on an x-y plane. You can get to this point by going some in the x-direction, plus some in the y-direction. In this sense, a vector <1,0> and a vector <0,1> can be used to generate the entire x-y plane. ",
"These vectors are called ",
". Amazingly, waves also have 'basis waves'. You can use a large combination of basis waves, in varying contributions from each basis wave, to make the sounds of ANYTHING. This procedure is called the ",
"fourier transform",
". It's usually shown as that oscillating bar graph in music vizualizations. Like the x-y plot, if I add some of basis wave 1 to some of basis wave 2 plus some of basis wave 3 etc etc., I can make any sound in 'sound phase-space'. "
] |
[
"Allow me to illustrate this with a ",
" crude ",
" ",
"and now accurate drawing",
". EDIT: The original gives you an idea of multiple waveforms, but as ",
" pointed out, is ultimately incorrect. The new drawing is identical to my followup to this comment.",
"NOTE: While I do not possess any variety of FT analysis software, this should get the general idea across. Quick hack in GIMP :/",
"NOTE 2: It's actually far more complicated than the image makes it to be, since the bottoms of each wave would cancel the top, and vice versa.",
"Imagine that this very small (only a few cycles) sample includes the following instruments:",
"Ignoring (from a musical perspective) harmonics, overtones, etc., assume that each instrument, when played, results in the generation of a single frequency. ",
"While each instrument outputs a unique frequency on its own, when combined, the summation of all waves is what would be recorded by a standard microphone (and your ear!). The combination of waves is also what would be replicated by a speaker.",
"Your mind is capable of discerning individual frequencies, of course - in that you are able to focus on distinct sounds.",
"Regardless, a speaker is not only able to reproduce a single frequency at once, as not all sound consists of a sine wave of a single frequency."
] |
[
"I Forgot! I ",
" own FT analysis software (Sonar 7, DAW/Sequencer). I did one MUCH better -",
"ACTUAL visualization of the resultant waveform consisting of 4 different frequencies",
".",
"So, OP - combine that with the basic image in my previous post, and the resultant waveform at the bottom is the actual result."
] |
[
"Is eating grains bad for us? Is a \"paleo\" diet better for our health?"
] |
[
false
] |
I am considering the paleo diet/"lifestyle", eating mostly proteins, vegetables, and cutting out processed and fast foods. I have been doing research on the subject, but I thought I'd come here to see what scientists have to say about it. Thanks.
|
[
"please no personal anecdote. That is not a scientific answer to the question. Scientific answers only please.",
"Edit: my reply to bib4tuna, since apparently that's already downvoted to oblivion too:",
"attempted to fix the below.",
"Books are notoriously unreliable where the author cherry picks data to support their hypothesis, so no, a book is not a peer-reviewed scientific source. It does not count. Nor do documentary films. Peer-reviewed science only.",
"I am proud of everyone at least that nearly everything was downvoted to just about zero. Thank you guys for helping to maintain quality.",
"edit 2: ",
"Textbooks are okay."
] |
[
"In terms of health, you would be hard-pressed to claim that grain-free diets are the key to healthy lives. When you look at the ",
"zones",
" around the world where people live the longest, they all eat grains (and refined grains in the case of the Okinawans). So, grains are clearly compatible with healthy lives and therefore are not always \"bad for you.\"",
"Eating grains can certainly be part of a balanced, healthy diet. The issue here is ",
" and ",
" of grains and carbohydrates in general. The Food Guide Pyramid suggested that we eat ",
"6-11",
" servings of carbohydrates per day until it was recently updated to reflect the ",
"paradigm shift",
" in the field of nutrition. In the new ",
"MyPlate",
" guidelines, grains occupy a portion of our diets closer to 30% compared to the more standard 45-60%. This vacuum is to be replaced with more fruits, vegetables, and oils. ",
"Now, some people who prescribe to the paleo diet might claim that all grains, including whole grains are unhealthy. They would argue that all the ",
"research",
" regarding the benefits of whole-grain consumption is reflective of a substitution away from refined grains. Put in other words, replacing the refined grains with vegetables cooked in oil (isocaloric) or roast beef might yield similar reductions in atherosclerotic lesions. Furthermore, they would claim that substitution away from whole grains to non-starchy vegetables and meats would yield even better outcomes. This is largely unsubstantiated. The data seem to claim that low-carb/high-fat diets and high-carb(whole grains)/low-fat diets are both significantly better than the standard American diet (high-carb(refined)/high-fat) ",
"1",
" ",
"2",
". But we already knew that intuitively.",
"All this has been talk about outcomes such as obesity, diabetes, and heart disease, but there is emerging research relating to carbohydrates and aging. Cynthia Kenyon has a great ",
"TED talk",
" regarding her research on insulin and aging. This field builds off the findings that ",
"prolonged caloric restriction significantly increases health and longevity in animal models",
". Kenyon argues that the cause of the increased longevity may be gene regulation by insulin. She continues to claim that one can achieve the benefits of caloric restriction without starving by reducing insulin levels. This can be done with a paleo/low-carb diet, but it would be more difficult to do with a high whole-grain diet.",
"TL;DR There is little or no data to suggest that grains are inherently \"bad for you.\" However, it is likely that ",
" grains are indeed \"bad for you.\" Read the ",
"wiki article",
"Replacement of refined grains with either whole grains or oils/meats/fat appears to be beneficial in reducing risk of CVD, diabetes, and obesity. It is very difficult to determine what the ",
" diets for all humans is, but you can be sure that a diet low in refined grains is generally healthier than one high in refined grains. "
] |
[
"your pedantry is spot on. I was being overly general. Thanks for the catch."
] |
[
"Why is earth's orbit elliptical and not round like that of a revolving ball attached to a string?"
] |
[
false
] |
I know the Kepler's law of planetary motion but still whats the reason its not perfectly circular orbit?
|
[
"No real-life orbit is ",
" circular. Circular orbits are a special case of elliptical orbits where the two foci of the orbit coincide. ",
"There are many ways to make an unstable orbit, and there are many ways to make a stable but elliptical orbit. There's only one way to make a perfectly circular orbit, and that's by setting up the initial conditions such that the orbit velocity always balances the force due to gravity (or by adjusting an elliptical orbit to be circular, which is just as hard). This means you need to start your orbit at ",
" the right speed -- if you're a single meter per second away from that number you'll end up in a stable but elliptical orbit. "
] |
[
"A better question is, why would it be circular? There are infinite ways to make an elliptical orbit but just one very specific way to have a circular one."
] |
[
"You're correct, I meant to signify that it was speculation about qualifying an absolute statement (\"No real-life orbit\"), since it's not proven that there are no perfectly circular orbits. I attempted to identify one condition that could enable an achievable circular orbit (planck length), but agree that it was misleading or confusing. I've removed it."
] |
[
"How is it that we can figure out properties of planets and stars that are so far away?"
] |
[
false
] |
For example, apparently there is a planet made of diamonds extremely far away. How did someone figure that out when all they really had was a high powered telescope and no way to confirm its properties?
|
[
"There's a variety of techniques that are used to gather various properties. Some of the key ones:",
"1) Doppler Radial Velocity Measurements. The planet and star orbit around a common center of mass, so as the planet goes around the sun, the sun moves a little bit too. Just like how the frequency of sound from a train changes as the train passes you because of it's velocity with respect to you, the light from a star shifts frequencies very slightly as the planet and star move around each other. We observe this shift over an orbit and can map out the planetary orbit (assuming we know the star's mass), and this gives us the planet's mass.",
"2) Transits. When a planet goes in front of a star (think Venus last month), it blocks a tiny bit of the light from the star. This is really hard to detect from the ground, except in the case of giant planets, but is easier to detect from space. Telescopes like Kepler look for these regular, periodic shifts in the star's light when transits occur, and then can determine the radius of the planet based on how much light is blocked (assuming you know the radius of the star.",
"3) Transit Transmission Spectroscopy. This guy is the future. People look at the light from the sun + planet, and then wait for the planet to move behind the star. When that happens they look again, and can only see the light from the star. The difference between these two is the light from the planet (which is a really tiny signal!) With this, you can study the planet's atmosphere, deduce what elements might be in it and what ratios, the temperature, etc. Similar studies can be done when the planet is in front of the star. This is really hard- the first atmosphere around a planet was detected only 10 years ago, and this field is more or less in its infancy still (although advancing quickly).",
"There are a couple other techniques, but these are the big ones."
] |
[
"This does not really answer the question. What he wants to know is how they for example know there is liquid water on a certain planet, or what kind of other elements are present and in which quantities. "
] |
[
"astronomers use ",
"spectrometers",
" to determine things like these"
] |
[
"Why does your voice get deeper as you go without sleep"
] |
[
false
] |
I was watching a show about sleep deprivation, and noticed as the participants went without sleep, their voices substantially deepened. They even mentioned it a few time's but gave no indication as to why. Is there science here?
|
[
"The vocal chords need rest as does the rest of the body. When fatigued, they dont respond as well and vibrate at a lower rate, resulting in a lower pitch. Mucus health can affect this as well. Unhealthy thick mucus can have a similiar affect. Drink a glass of water first thing in the morning to rehydrate and see what happens to your voice."
] |
[
"I'm not going to speculate, but if I may also add to this, why do our voices sound deeper when we first wake up?"
] |
[
"I'll try that! Thanks For the knowledge! :-)"
] |
[
"What are the logistical problems with installing a waterwheel connected to a turbine and generator half way down a big waterfall to create a never ending source of electricity?"
] |
[
false
] | null |
[
"Isn't this just ",
"hydroelectric power",
"?"
] |
[
"Yeah basically. But hydroelectric requires a massive undertaking of landscaping the environment, and it is usually not a massive amount of water falling at a time (could be wrong about that)"
] |
[
"Hydroelectric plants are built where there is a very large volume of water flowing, otherwise they wouldn't generate much energy. Some of them do in fact take advantage of natural falls."
] |
[
"Does the age of the universe really influence the gravitational constant?"
] |
[
false
] |
[deleted]
|
[
"He's probably referring to Dirac's ",
"large numbers hypothesis",
", which posits that various constants, including the gravitational constant, change over cosmological times.",
"It wasn't based on any physical arguments but rather on numerological ones: various physical \"constants\" could be arranged into ratios that were all huge, but all looked related to each other. For example, a lot of these ratios were very nearly 10",
" . One of the \"constants\" used in these ratios is the age of the Universe which, of course, varies quite a bit over time. So to maintain these coincidences at all times - rather than us living at some special moment - these constants must also vary with time.",
"Starting right around ",
"1961",
" this inspired some work on modified theories of gravity in which G ",
" vary over time. Typically you promote G from a constant to a ",
" which can vary over time (and even space), and see what happens. Most of these theories are very strongly ruled out by observations, however, and the ones that remain are so close to Einstein's theory of gravity (which is where we started) that they don't add anything new or especially compelling.",
"The search does continue to this day for theories of modified gravity and more generally varying constants, although Dirac's large number hypothesis is no longer really a major motivation. These days it's explaining ",
"the acceleration of the Universe",
" that motivates us to see if gravity might behave differently than we expect at cosmological distances."
] |
[
"Thank you. I think that was what he was referring to."
] |
[
"It wasn't based on any physical arguments but rather on numerological ones: various physical \"constants\" could be arranged into ratios that were all huge, but all looked related ",
"Is this similar to \"the Earth is almost exactly 500 light-seconds from the Sun; for it to be such a round number can't be a coincidence\" kind of thing? ",
"(Of course that ratio is dependent on the definition of a second, so the \"coincidence\" is that whoever defined the second picked that particular value.)"
] |
[
"How does light get 'sucked into' a black hole if it has no mass?"
] |
[
false
] |
[deleted]
|
[
"It doesnt get \"sucked in\", it continues in a straight line through space - the difference is that space curves ",
" a blackhole....this space curvature is what we call ",
"."
] |
[
"In Newtonian gravity, mass acts on mass to produce gravity, so in that context, it is indeed puzzling. In general relativity (our current best theory of gravity), the presence of matter curves spacetime (this is the black hole in this case), and particles (massless or massive) follow straight lines on this curved spacetime (which then look like curved trajectories)."
] |
[
"First, gravity isn't a change in curvature, it is the curvature.",
"Anyway, it's because it's curvature of space",
". In ordinary flat, gravity-less spacetime, an object at spatial-rest relative to some inertial frame at an initial time will not move in space in that frame. It will, however, continue to move in time. We can plot this on a spacetime diagram by calling the up-down direction time and the left-right direction space. Then the path of such an object is just a vertical line. An object moving at a constant velocity would be a straight line at an angle, so that as time increases its position changes. What happens when you add a mass to this picture is that a path that starts out vertical becomes bent (really all paths are bent, but we're talking about things that start at rest). It starts out vertical, but as you move up the diagram (forward in time) it bends toward the mass. To an observer at rest in this reference frame, this looks like the object starts at rest and accelerates toward the mass."
] |
[
"Why is it easy to become addicted to things, but hard to quit?"
] |
[
false
] |
I ask this because it seems that if you do something once sometiimes, you'll want more. For example if you look at porn a few times you may become addicted, or if you try a cigarette a couple of times your body may crave more. But if you want to quit it's really challenging, why is that?
|
[
"The basic explanation is that addiction taps into a natural part of the brain's reinforcement processes. For example, you are thirsty. You want water. You drink. then you are not thirsty anymore. ",
"The addiction creates a new need. You take nicotine. The ventral tegmental neurons fire action potentials at high rates for 10s of minutes. These reinforce all the activities that preceded smoking. Now, repeat a pack a day for a month, or 6000 rounds of reinforcement. Now, those neural circuits are as important to you as the neurons that sense thirst. You smoke. They become active. Some 10s to hundreds of minutes later, they are crying out that you need a smoke, and everything that was reinforced from smoking (playing with something in fingers/lips, lighters, walking outside a building, etc) makes you want to smoke even more. ",
"The key here is that the addictive substance activates the brain's reinforcement pathways in an unusually powerful way. Powerful enough to create a need for the addictive substance. Powerful enough that after quitting, all joy for everyday rewards is blunted for a long, long, time. "
] |
[
"Extinction Burst is a good term for further reading on this, basically that's the phrase for when you're trying to break an addictive habit (or any conditioned response), where your brain goes full force into forcing you to reinforce that habit."
] |
[
"Habits die hard. You get into an addiction, then your mind and body gets in synch with the addiction. you're entrenched in it; your subconscious gets used to the rhythm. When you want to quit there is a backlash; an inertia which prevents instant withdrawal. Hence many addicts experience difficulty in suddenly stopping the habits. A slow and steady weaning produces better and permanent results. This helps the body and mind realize in reality that you want to quit."
] |
[
"Why do people smile or laugh when in bad/sad situations that one shouldn't laugh in?"
] |
[
false
] |
Such as telling someone a loved one died.
|
[
"Most of the time, normative individuals (that is, people that are not diagnosed with some mental disorder or do not exhibit some outlying trait) exhibit predictable emotional reactions to stimuli. For example, when someone's loved one dies, we ",
" them to exhibit sadness, grief, loneliness, vulnerability, etc. As I've stated in a few other answers I've given, these emotional reactions serve an important purpose: they allow the individual a safe way to express stress. Moreover, they inform the individual--and others in their social group--of their environment and circumstances. This is fundamental to the social nature of humans: we know that a loved one has died and we can predict how an individual may be reacting, and provide support for them (or receive support ourselves).",
"However, there is a phenomenon called ",
" (or ",
") ",
", wherein a person exhibits some emotional reaction that is, well, incongruent with their current status. For example, someone laughing when a loved one dies, or becoming scared when shown affection. There are many, many reasons someone could exhibit inappropriate affect, and I will not attempt to list them all here. But some of the more common causes are:",
"As you can see, some of these causes are temporary and minor (such as momentary anxiety), while others are more serious or long-lasting (such as psychosis). ",
"Great question!"
] |
[
"Thanks a bunch for the answer!"
] |
[
"I guess the part about anxiety is the most familiar one. If people are experiencing anxiety in a social situation, or about their own feelings, they might laugh to diffuse tension or divert attention. Like people who are afraid of being angry might laugh when they feel anger (functioning like a secondary emotion). So in this sense the laughing, or the maladaptive secondary emotion could also be called a ",
" just like good ol' Freud saw it.",
"But it's not only their own emotional reactions that people might want to mask with laughter. There might also be uncomfortable social situations which makes people want to laugh. For instance, if someone is announcing to a room of people that someone in the school has died, people may laugh because they're used to doing that to ease social tension. Or they're afraid of laughing, which may paradoxically provoke uncontrollable laughter."
] |
[
"Why does copper darken ? I'm guessing oxidation, but seeking further explanation."
] |
[
false
] |
I just moved to a new house about 2 months ago. My mother has some gold plated jewellery made of brass or bronze(not sure which, but it contains copper). She's been complaining that the jewellery has darkened because of some bad omens. I would like to explain to her that it is because of the natural process of oxidation. Could someone me understand what exactly is happening. Edit I forgot to mention that she's been claiming that the jewellery has suddenly darkened in the last 2 months.
|
[
"The coating is protecting her items. Nothing \"bad\" about that. You can also electrolytically reverse the process and give her some good omens(?) instead. "
] |
[
"Copper will oxidize to form a reddish copper(I) oxide layer, and in moist conditions will form various copper hydroxide and carbonate compounds (these are the blue-green patina you see on old copper roofs). If the copper turned black/gray, a more likely cause is formation of copper sulfide after exposure to hydrogen sulfide in the air or another source of reduced sulfur. (This is analogous to the ",
"darkening of silver",
" after contacting a hard-boiled egg)."
] |
[
"So you're suggesting that there are some sulphur compounds in air in the house. Any ideas on possible sources ? "
] |
[
"I've heard of genetically engineering bio-luminescence into non-bio-luminescent animals. Is this a simply done task now? What tools would I need to make a species, say... ants, bio-luminescent?"
] |
[
false
] | null |
[
"Not even close. ",
"Ants are VERY complex, in that you would first have to study their rearing behaviour, you'd have to get hold of some ant enbryos, figure out just how in the hell the particualr ants you are working with behave, then isolate some eggs and sperm, THEN breed yourself a queen, then figure out how to make the queen glow, then make sure your luciferase/whichever other colour producer/pigment is expressed in the queen, and make sure it is expressed in the workers, then make sure you can even aimtain a breeding population of the genes. ",
"Hymenoptera are RIDICULOUSLY complicated to work with. your best bet is to make something like a cockroach (even that is stretching it) glow. Its possible, but there are VERY few model organisms at the moment, and you'd best stick to fruit flies, else you're going to be studying ants for the next few hundred years. Drosophila melanogaster is your best bet because we know a shitload about it. The problem with ants, is well, they are full of shit, they are like the british, they've bot a queen, and a king whose a bit of a layabout, and the workers are nothing like their queen because she is a german, and changing the queen is not neccesarily going to change the workers and vice versa, and changing the workers is not going to get you a new head-german, and then if you change the queen she'll smell funny and the layabout king will mistake her for lunch as will the workers, and it's just not fucking worth it. Stick to making glowing dogs. Glowing dogs Won't invade America and ruin a thousand collective picnics. ",
"Hes right about the frogs. Just make frogs glow. Its different for EVERY animal and you have to know quite a lot about each animal first, like you need to know whereit keeps its 'colour genes' is it in the basement or the attic? Is the attic where the basement should be? Is it even shaped like a house? so you'll first need to sequence a whole genome which is going to cost you quite a lot, i'd say about $10000 for a good sequenceing including methylation etc, annd then you'd need to get to work trying to figure out a good way of getting the DNA you want into the cell and hoping it will work based on how you tried to stick it in there. so basically you'd need a team of people who give enough of a crap about making this frog glow who are willing to take a LOt of time to get it all workign. Its still VERy hit and miss, you are usually going to make about 1000 non-glowing super expensive frogs before you make a single glowing one, leading to a great deal of frog genocide, until you make a frog that does glow and then you don;t even know if's its going to have kids that are even alive, so the best answer to this question is, you've got better things to do. "
] |
[
"Not even close. ",
"Ants are VERY complex, in that you would first have to study their rearing behaviour, you'd have to get hold of some ant enbryos, figure out just how in the hell the particualr ants you are working with behave, then isolate some eggs and sperm, THEN breed yourself a queen, then figure out how to make the queen glow, then make sure your luciferase/whichever other colour producer/pigment is expressed in the queen, and make sure it is expressed in the workers, then make sure you can even aimtain a breeding population of the genes. ",
"Hymenoptera are RIDICULOUSLY complicated to work with. your best bet is to make something like a cockroach (even that is stretching it) glow. Its possible, but there are VERY few model organisms at the moment, and you'd best stick to fruit flies, else you're going to be studying ants for the next few hundred years. Drosophila melanogaster is your best bet because we know a shitload about it. The problem with ants, is well, they are full of shit, they are like the british, they've bot a queen, and a king whose a bit of a layabout, and the workers are nothing like their queen because she is a german, and changing the queen is not neccesarily going to change the workers and vice versa, and changing the workers is not going to get you a new head-german, and then if you change the queen she'll smell funny and the layabout king will mistake her for lunch as will the workers, and it's just not fucking worth it. Stick to making glowing dogs. Glowing dogs Won't invade America and ruin a thousand collective picnics. ",
"Hes right about the frogs. Just make frogs glow. Its different for EVERY animal and you have to know quite a lot about each animal first, like you need to know whereit keeps its 'colour genes' is it in the basement or the attic? Is the attic where the basement should be? Is it even shaped like a house? so you'll first need to sequence a whole genome which is going to cost you quite a lot, i'd say about $10000 for a good sequenceing including methylation etc, annd then you'd need to get to work trying to figure out a good way of getting the DNA you want into the cell and hoping it will work based on how you tried to stick it in there. so basically you'd need a team of people who give enough of a crap about making this frog glow who are willing to take a LOt of time to get it all workign. Its still VERy hit and miss, you are usually going to make about 1000 non-glowing super expensive frogs before you make a single glowing one, leading to a great deal of frog genocide, until you make a frog that does glow and then you don;t even know if's its going to have kids that are even alive, so the best answer to this question is, you've got better things to do. "
] |
[
"I had a guy like you in my old lab. ",
"I miss him."
] |
[
"Are STIs/STDs transmitted immediately?"
] |
[
false
] |
If someone is infected with an STI/STD and has unprotected sex with someone who doesn't have it, is it transmitted immediately, the second of penetration? Or is it like the longer intercourse lasts, the more likely the chances of transmission?
|
[
"Also, if you stab someone in the hand with an HIV infected needle, how long do you have before cutting off their hand/arm wouldn't stop the infection from spreading to the body?"
] |
[
"Most STDs are transmitted through contact between mucosal surfaces. The infectious particles obviously can't move instantaneously, as they have to move across several barriers. Longer periods of contact and, more importantly, contact between areas with any defects in the mucosal surfaces, will increase the chances of transmission."
] |
[
"Well, the infection rate for a hollowpoint needle stick is only about 0.3% for HIV. You would probably be better off just starting prophylaxis with antiretrovirals."
] |
[
"Besides explosive size, what exactly is the difference between novas, supernovas, and hypernovas?"
] |
[
false
] | null |
[
"A nova requires a white dwarf (the core of a dead star) and a nearby normal star. If the nearby star gets too close, it will start ",
"transferring its own mass onto the white dwarf",
", and that mass will swirl around the white dwarf in an \"accretion disk\". The mass will also fall onto the surface of the white dwarf, and if it gets hot enough it will start nuclear fusion (making heavier elements from smaller elements, releasing energy) and explode as a nova. This is a smaller explosion that will leave the white dwarf behind.",
"BUT! If enough mass falls onto the white dwarf, the white dwarf itself will begin nuclear fusion (as opposed to just the accretion disk). If this happens, it will destroy the white dwarf in a much larger explosion, a type Ia supernova.",
"Another type of supernova is called the type II supernova. This is when a star with a lot of mass uses up all of its fuel and dies. High mass stars can make heavier and heavier elements through nuclear fusion, up to iron. Once iron is made, it won't make heavier elements in the core. So, once the core has too much iron, that iron won't be able to support itself under its own gravity. The core will collapse, and the star will explode as a type II supernova. That collapsed core of the type II supernova can create a neutron star (more dense than a white dwarf) or a black hole.",
"A hypernova is basically a larger, more extreme version of a type II supernova, and it will create a black hole.",
"Edit: Where fusion takes place in a nova."
] |
[
"Small correction, a nova does not happen in the accretion disk, but in the boundary layer on the surface of the white dwarf. ",
"The progenitor of Type Ia supernovae is still debatable, though recent research suggests that the double degenerate channel, in which 2 white dwarves merge, is what happens instead of the single degenerate channel, in which a single white dwarf accretes matter from a companion. Evidence also suggests that a white dwarf undergoing nova eruptions actually ",
" mass as more matter is ejected from the nova than was accreted to ignite it. Recurrent novae were long thought to be a likely progenitor for Type Ia supernova, but they've largely been ruled out by the observations showing net mass loss."
] |
[
"We know iron to be the heaviest element that stars can make (stably) because it is the ",
"nucleus with the highest binding energy",
". Above iron, fusion requires energy; below it, fusion releases energy. By fusing iron, therefore, the star will ",
" energy, not create it, which will cause it to contract, increasing pressure, causing more fusion, absorbing more energy, causing more contraction, etc. The star's core then collapses. "
] |
[
"Skin fusing to surfaces: how the fuck?"
] |
[
false
] |
[deleted]
|
[
"Just to clarify, \"lack of airflow\" should be \"lack of blood flow.\" For those curious about this problem, read up on ",
"bedsores",
", a major problem with patients staying long-term in hospitals. "
] |
[
"It wouldn't even require abrasion. The combination of constant pressure, lack of airflow and constant moistness is enough to compromise the skin's integrity. Then there's the additional moisture, ammonia and bacterial growth aided and abetted by the urine and feces that are present and being squished into the same sofa (or whatever)."
] |
[
"when your skin is healing, it can form a layer over whatever is covering it, similar to what your skin does if you get a splinter. i don't know if you have ever had an injury that needed medical gauze, but when you put that stuff on, if you leave it on too long (like a day or two), your skin starts to heal over it. my guess is that the same thing happened here.",
"in this case i am guessing abrasion from having his skin rubbed against the chair's fabric is what caused his skin to be damaged in the first place."
] |
[
"Can you put a deciduous tree in a greenhouse (or similar climate control) and it never hibernate?"
] |
[
false
] |
...or do deciduous trees to hibernate and lose their leaves?
|
[
"You could have a deciduous tree with a \"chilling requirement\" in a greenhouse without hibernation for a few years, but it would be a sickly tree that would essentially die of exhaustion. Also it is almost impossible to force these trees to reproduce without a chilling period, as shown in this paper by the horticulture research institute: ",
"http://www.hriresearch.org/docs/publications/JEH/JEH_1991/JEH_1991_9_1/JEH%209-1-1-4.pdf",
"Source: I tried/failed to raise oak trees indoors"
] |
[
"There are several species of tropical deciduous trees. These do not hibernate, although they may (depending on the tree) require a dry season.",
"here is a discussion of tropical deciduous trees: ",
"http://ntsavanna.com/deciduous-trees-in-the-tropics/"
] |
[
"You could have a deciduous tree with a \"chilling requirement\" ",
"What does this mean? "
] |
[
"Why are carnivores generally more intelligent than herbivores?"
] |
[
false
] |
Dolphins and primates have the highest brain-to-body ratio and are usually called one of the smartest mammals. Octopi and squid are the smartest invertebrates. A large part of these animals diet, with the exception of primates being omnivores, is from other animals. Is this because they eat other animals, or is there some other reason?
|
[
"There are some nutrients not found in abundance, or at all, in plants that herbivores need to synthesize themselves, for example, cholesterol, vitamin d, vitamin b12, car nosing, creatinine, etc. There are also nutrients that are in greater abundance in a herbivorous diet. I suppose it could be argued that things like DHA and b12 support brain function and then draw a correlation to intelligence, but it would be tenuous. After all, the animals that are being eaten to gain these nutrients produced them just fine"
] |
[
"In general, it requires more cognitive power to hunt something than it does to avoid being hunted. Predators need to be able to plan routes of attack, select which animal would be easiest to catch, adjust their course of attack on the fly, possibly communicate with other pack members to have a coordinated effort. This requires a bit of higher order logic",
"On the whole, herbivores strategy is to either hide or run away.",
"This is far form a hard and fast rule though. Primates are omnivores, as are ravens and other corvids. Parrots are largely herbivorous, Pigs are omnivorous to herbivorous, rats are omnivorous. All these animals are generally considered very intelligent. "
] |
[
"Both? There are animals there, they are a source of nutrition, things evolve to take advantage of that. Carnivores get a lot more energy from a smaller volume of food, and they expend large amounts of energy in a short time instead of small amounts all day to obtain that nutrition. It IS a biological advantage to fill an empty niche. "
] |
[
"What’s the deal with this new “signal we’ve never seen before” from space?"
] |
[
false
] |
I don’t have the article handy but I’m sure many of you have seen it floating around. Obviously the need in me would love for this to be different (you know what I mean) but I’m sure it’s some natural phenomenon we just haven’t seen yet. What is our current best guess?
|
[
"Mostly because we keep finding new stuff and it keeps having a non-alien explanation. ",
"Pulsars are a great example-- they are basically lighthouses in space, incredibly regular repeating signals. The first pulsar discovered was somewhat jokingly named LGM-1 (for Little Green Men)... ",
"The other problem with \"it's probably aliens\" is essentially the \"god of the gaps\" problem-- every unexplained gap in physics can be explained as \"Well, God made it that way\", but that doesn't move physics forward. So: new weird signal in space is assumed to be some sort of natural phenomenon and theory is thrown at it until something sticks. It's possible we'll find something where the right explanation is \"aliens\" -- but we need to eliminate other possibilities first."
] |
[
"Completely with you on that, I just find the psychology around our beliefs of what's out in the wider universe quite interesting. There's a strange blend of exceptionalism, hope, irrationality, fear and all sorts of other things.",
"Personally I'm sure life of some description has, does or will exist somewhere other than this planet. But I very much doubt we'll ever see any evidence of it as it will be too simple or too far away.",
"Natural phenomena are the only things that realistically can or ever will produce enough energy to reach us in a measurable way."
] |
[
"Because aliens don't exist or because its unlikely to be complex life capable of creating anything that would send a signal of any description that would reach us?"
] |
[
"Is reading a book, and listening to an audio book similar enough to say you \"read\" an audio book?"
] |
[
false
] | null |
[
"This is something I would also like to know as I listen to a lot of trade books in the car while travelling and have wondered if its ",
" actually planting the information into my head or I'm a just listening like a song. "
] |
[
"What exactly do you mean by \"doing anything\"?"
] |
[
"Fixed, on my phone."
] |
[
"Change of buoyancy when changing from solid to liqiud?"
] |
[
false
] |
Hello everyone A few days ago i saw an interesting video: a guy put some liquid spermaceti (whale fat) into a tube, closed it and put it into cold water. At first it was floating, but with time it turned liquid because of the cold water and, much to my astonishment, started to sink!. After that, he poured hot water into the cold water, which made the spermaceti turn liquid and floating again. Now what I learned from physics school in class is that buoyancy is equal to the gravitational force on the mass of the water that got pushed away. So why is the tube floating/sinking depending on the state of its content? Shouldnt the buoyancy stay the same because the tube doesn't change size? Also, when water gets colder, its density increases (everything was above 4°), when anything it should be more buoyant, no? TL;DR: no change of volume, no change of mass. only change is density and temperature, why is the spermaceti turning into a solid (by adding cold water) making the whole tube sink and the other way round, the spermaceti melting (by adding hot water) making the tube float?
|
[
"This is demonstrating one-half of a classic lesson on thermal expansion.",
"The Oceanography Society produced this excellent lesson book ",
"Teaching Physical Concepts in Oceanography, an Inquiry-Based Approach",
". It contains several demonstration, all of which are valuable for understanding how the ocean works. However, one in particular is perfect for this question:",
"On page 40 you will see an image of two water filled beakers; one cool, one warm. In the cool beaker, an aluminum rod floats and a plastic rod sinks. In the warm beaker, the plastic rod floats and the aluminum rod sinks. Your spermaceti-filled tube behaves the same as the plastic rod.",
"So, yes, there is a change in volume and thus density for the warm/cool water and also for the warm/cool tube. All materials expand or contract to some degree when heated/cooled; some more than water, some less."
] |
[
"Well we have 2 things going on here. First most substances are denser (shrink) as a solid compared to a liquid (ice outstanding). So as it freezes it would become more dense and sink. ",
"However if the tube is truly a constant volume this can work another way. Water changes density as it changes in temp (warmer less dense) and so things that float in cold water can sink in warm. ",
"example"
] |
[
"the density of the water changes, not the tube or its content"
] |
[
"Where Do I Get Science Posters?"
] |
[
false
] | null |
[
"Hi physicsking thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"This isn't the right sub for this question. Try ",
"/r/asksciencediscussion",
" maybe"
] |
[
"thank you. I will submit it there"
] |
[
"Why can't a mountain be higher than 49,213 feet? What happens at that height?"
] |
[
true
] |
[deleted]
|
[
"I don't know the source of that calculation, but it was almost certainly merely an estimate based on someone's quick calculation. I can't find a single mention of that number through Google Scholar, or any other place on the web, which makes me even more dubious of that claim (and there is simply no way it could be determined to the accuracy of a single foot, which the number implies).",
"The current best model is that due to a suite of factors, mountain growth is limited to about 10 kilometers (30,000 feet or so), with the most prominent mountain loss occurring after about 5 kilometers. Multiple factors come into play with mountain growth, and the entire picture is fairly complicated.",
"The first factor is that mountain roots can be lost \"relatively\" easily if they extend deep enough into the mantle. For every kilometer of height a mountain has above the mantle, it has 5-7 kilometers of depth into the mantle. So a 5 kilometer mountain may extend 30 kilometers into the mantle. See ",
"this image",
" for an illustration. As the mountain root grows, a significant portion of the mountain can, in effect, be \"eroded from below\". As material is eroded from the root, the entire mountain must drop in elevation in some way in order to balance out the buoyancy force.",
"The second factor is that as pressures and temperatures build up underneath a mountain, faults become much more common and at depths can begin behaving in a ductile manner. This makes it much harder for mountains to increase in elevation. For an illustration of this, ",
"check out these two profiles of two mountain ranges",
". The top one is from the Himalayas, and the bottom from the Andes. Despite the fact these two mountain ranges involve vastly different volumes of rock, they both roughly reach the same maximum elevation. This shows the propensity for mountain ranges to grow \"outward\" rather than \"upward\" past a certain point in elevation.",
"Another factor is climatic. More relief means more surfaces for erosion to work upon. The Himalayas may be uplifting at one of the fastest rates on the planet, but due to the large mountain range there they also have some of the largest monsoons on the planet. Besides rain erosion, glacial erosion is also thought to play a major factor in maximum mountain height (termed the 'glacial buzzsaw'). Glaciers are fantastic erosional machines, that kick in past the snowline on mountains. This correlates well to where we see mountains start losing much of their mass (see ",
"this image",
" for an illustration of the relationship between snow lines and mountain morphology). Interestingly, the highest peaks of mountains do increase in elevation under the influence of glaciers, but this is likely temporary and in the long run glaciers are widely accepted as having a limiting role in mountain growth.",
"There are other factors that play into this as well. There is a proposed 'aeolian buzzsaw' (wind erosion) that may limit mountain growth at high elevations as well (there has been some work showing significant wind downcutting on the Himalayas, for instance). What limits mountain growth is still an area of active research, with lots of interesting theories, tests, and findings all the time!",
"Regardless, I just can't possibly see how the 49,213 figure is justified. My guess is it came from a 'back of the envelope' calculation that only accounted for a few factors, and is likely very far off from the true mountain elevation limit."
] |
[
"This is an excellent and comprehensive answer. I would only supplement it with the fact that 49,213 feet is 15,000.1 meters. So someone has calculated it as roughly 15km, it's then been converted into feet, and someone made the error of assuming the number was real.",
"It's really important to note that if the input data only appears to be accurate to the nearest km, the output answer should also have been stated to this similar accuracy (so 49000 feet). Even better would have been if the original number had got some +/- error stated. This is a really common error made by people, and for those of you not already familiar with it, it's worth getting used to spotting it."
] |
[
"My favorite illustration for explaining this to laypeople is the story of a museum employee telling visitors that a ",
" skeleton is 65,000,012 years old. When asked how such an exact figure could be arrived at, he explains that the skeleton was 65 million years old when he started working there 12 years earlier."
] |
[
"What is the environmental and long term climate impact of the recent Chile volcano eruption?"
] |
[
false
] |
I'm curious as to the temperature variations and long term effect the Calbuco volcano eruption will have on the local environment as well as further away.
|
[
"Locally a big impact mostly from falling ash an air pollution. However globally, I doubt we'll see much impact unless this continues for several months. It is located around 41 S, so not near the tropical regions. For volcanoes to have a global cooling effect, they usually need to be erupting in the tropical region.",
"Above the tropics, the stratosphere's circulation features rising air, which pulls the sulfur-containing volcanic aerosols high into the stratosphere. Upper-level winds in the stratosphere tend to flow from the Equator to the poles, so sulfur aerosols from equatorial eruptions get spread out over both hemispheres. These aerosol particles take a year or two to settle back down to earth, since there is no rain in the stratosphere to help remove them. However, if a major volcanic eruption occurs in the mid-latitudes or polar regions, the circulation of the stratosphere in those regions generally features pole-ward-flowing, sinking air, and the volcanic aerosol particles are not able to penetrate high in the stratosphere or get spread out around the entire globe. ",
"http://www.wunderground.com/climate/volcanoes.asp"
] |
[
"Chile is the country. Chili is the food. A chili eruption hopefully does not even leave the house."
] |
[
"The large volcanic effects that we have seen in the past are due to particulate matter being thrown up far enough to leave the troposphere and get into the stratosphere (some 20km to 40 km in altitude), where the SO2 can form sulfate aerosols, and this can spread globally. These enhanced aerosol layers can have climate effects.",
"I don't know anything about the Chile eruption, but it probably does not penetrate into the stratosphere, so there will be minimal global climatic effects, though still could have significant \"local\" effects.",
"EDIT: now less humorous "
] |
[
"Is there a reason for the majority of the world's land mass to be above the equator?"
] |
[
false
] | null |
[
"No. There's no distinction between North and South. It's just happenstance. Mars, for instance, would be basically all ocean in the North, and basically all land in the South, if you poured a bunch of water onto it."
] |
[
"I'm guessing what he wants to ask is if there is a known reason why there is much more land on one side of the equator than there is on the other.",
"Perhaps Pangaea was in the northern hemisphere or more in the northern hemisphere? (I have no idea at all...)"
] |
[
"No. It's just a result of continental drift. In fact, during the Devonian Period, ",
"Earth's landmass was mostly in the southern hemisphere",
"."
] |
[
"Why does the sound of a spoon hitting the side of a glass cup lower in pitch as I mix instant coffee grains into water?"
] |
[
false
] |
Basically, I drink coffee most morning and I've noticed that the sound that a spoon makes as it hits the side of a glass full of water when I swirl it around has a certain relatively higher pitch to it. When I add instant coffee grains, the pitch gradually lowers until settling on a certain noticeably lower pitch when the grains are completely dissolved.
|
[
"The water now has a different density. Sound travels at a different speeds depending on the medium( ie, stuff it's in, in this case, your coffee). That is why you can here digital watches underwater while swimming in a pool. Knowledge is power!"
] |
[
"I've experienced similar results when stirring cream/sugar into reheated/microwaved, 8 hour old coffee, but not while the coffee is fresh -- that is to say, tapping a spoon on a glass of fresh coffee after adding cream/sugar results in a higher pitch than stirring cream/sugar into reheated coffee. While I agree that adding cream/sugar to your coffee changes the density and the sound it emits, if the temperature of the coffee is roughly the same between the two scenarios, as is the consistency of the coffee itself, why do the two sound different under similar circumstances? Temperature differences of the glass/cup being used compared to the temperature of the fluid (cold glass, hot coffee; microwaved hot glass, hot coffee)?",
"Edit: This has bugged me for years... Seriously... I MUST KNOW WHY!!!"
] |
[
"Fantastic, thank you so much."
] |
[
"Sleeping is such a waste of time. Science : are there any researches/studies going on that will allow us to stay awake at all times and not crash?"
] |
[
false
] |
We sleep for a third of our lives. So for 90 years that you will live, you will waste 30 years of it asleep... What a waste.
|
[
"It may be a waste in terms of productivity, that you're not physically doing anything, but I don't think it's a waste in the sense that your body does a lot of housekeeping style stuff during sleep, and completely avoiding it is probably not a great idea. You can adjust your sleep cycles like some people and make a 36 hour day for yourself, for example, but completely being devoid of sleep is another thing entirely.",
"Phallic pointed out modafinil, which has been notorious in university circles in the UK as being used by students to pull all-nighters for essays and cramming for exams. Whilst short term use can be beneficial to mental acuity, but there are a lot of side effects as ",
"arabidopsis points out",
". Avoiding sleep for one night may just make you tired the next day and you end up 'crashing' or even sleeping normally, but being on it constantly is unlikely to be a good idea. Your body needs sleep at some point in time."
] |
[
"I'm doubtful that a simple chemical solution to sleep is possible for one reason - almost all complex animals do it. Being unconscious for a third of each day is such an evolutionary disadvantage that anything that reduced or removed this need would almost certainly be selected for."
] |
[
"I'm sorry, but if I interpreted the question correctly then I don't think you quite answered it entirely. I'm sure the OP (and everyone, for that matter) realizes that sleep is necessary to our body what with all the restorative functions that it provides.",
"However what I think he's asking is if there is any way to bypass the need for sleep by coming with a solution (be it chemical, nanotechnological, etc) that provides all the benefits of sleep without actually sleeping.",
"Now I'm no expert (yet; I am currently a student of biochemistry) but as far as I know there is very little we understand about sleep and about the brain as a whole. We know the secondary benefits that sleep provides (like alertness, better memory, etc) but we don't know the mechanism that causes it. So my answer to the OP is that we are very far away from seeing a sleep-eliminator in the marketplace, but once we understand more about the brain it could very well be possible. "
] |
[
"How do 2 particles get entangled?"
] |
[
false
] |
i've been watching videos and reading up about a bunch of cosmology and quantum physics stuff and am trying to wrap my head around entanglement. i understand for 2 particles that are entangled, when you measure the spin (or other quantum characteristic) on one you instantaneously know what the spin on the other is, regardless of their separation. I watched a video where they showed a process of measuring entangled photons by splitting a diagonally propagating laser beam with polarizers, so that when two photons split, and they measure the polarization of one of the photons, they knew the other. but how/when are particles entangled? do you only get entanglement when a particle splits somehow, or can two nearby electrons be entangled somehow? TL;DR does entanglement only happen when 2 particles are created together and are somehow linked, or can 2 non entangled particles somehow become entangled? if so, how?
|
[
"The specific answer will quite strongly depend on the details of the system which you consider. However, I will try to give you widely applicable explanation.",
"Let us start with what entanglement actually is. To talk about entanglement, we always have to consider systems which can be divided in parts (In this case, these parts would be your two particles). We can now try to describe the physics in this multipartite (fancy word for many parts) system the simplest way imaginable, by just trying to use local wave functions (lets call them f1 and f2) to describe everything. This means that the total wave function, F, will be a product of the local ones (F = f1xf2). F is now the total wave function of system. If we now assume that we have a second such possible wave function (G=g1xg2), quantum mechanics tells us that we can make a superposition such that F+G is a new wave function (up to normalisation - this is a technical detail, no need to worry). The main point of quantum entanglement is that this F+G is a valid wave function that describes my system, but I can in general ",
" find any product of local wave functions f3 and f4 such that F+G = f3xf4. This implies that entanglement is a special type of superposition in systems which have a special structure (i.e. they consist out of multiple parts).",
"Now they question would be rephrased as, how do we generate such superpositions between wave function of the form F = f1xf2 and wave functions of the form G=g1xg2? Ultimately you will always need some nonlinear effects or interactions. ",
"The former can be considered as for example the case where you shoot a highly energetic photon into a special type of ",
"crystal",
" and photons of lower energy come out. Due to conservation laws, these photons have to fulfil some conditions and this ultimately leads to entanglement. Similarly, there are well-know decay processes which emit entangled photons (I believe they used ",
"these processes",
"). ",
"Interactions are a bit more subtle, because things usually get quite complicated. There are for example ways of inducing entanglement between coupled dipoles (which may be applicable to some molecules) which can be described by something which is known as the Dicke model. In general you may argue that entanglement is even something generic when particles interact, let me just cite ",
"a review",
" here:",
"After they have interacted, quantum particles generally behave as a single nonseparable entangled system.",
"There is simply no reason to assume that a wave function structure like F = f1xf2 would remain intact once you particle 1 and particle 2 are interacting with each other. You may say that interactions just start \"mixing\" all these different products of local wave functions together until you have something which is more like f1xf2+g1xg2. ",
"The main problem is, however, that it is very difficult to protect the entanglement against decoherence. This is relevant when your particles also interact with the outside world, which forces the particles to get entangled with their huge environment. This ultimately decreases the entanglement between our two particles of interest and will actually make entanglement vanish quite rapidly.",
"Quantum opticians will tell you that you can also generate entanglement by \"",
"squeezing",
"\" light (from a laser for example). This is however a bit of a subtle debate, because this squeezing as such is not necessarily a quantum phenomenon. Nevertheless, I think it is safe to say that with what is called \"multimode squeezing\" you can generate EPR states.",
"Finally, let me point out that entanglement is actually not very well-defined for indistinguishable particles. In literature, the literature on this topic is a bit messy and there seems to be no real consensus (for the experts, the fact that you always have to consider the the system is invariant under permutations of particles leads to some ambiguity).",
"I tried to make it somewhat understandable, but it is quite difficult without going into (mathematical) details. I hope it at least gives an impression. ",
"edit: I will just add one more reference, although they are not really intended for the layman: ",
"Physical Realizations of Quantum Information"
] |
[
"Do I understand it correctly that the entanglement between two particles actually happens naturally all the time, and the real problem is to prevent the two particles from also getting entangled with the environment?",
"In other words, the tricky part is to get \"two, ",
"\" particles entangled?"
] |
[
"so my understanding of what you described is that entanglement is a quantum property of a system in which the system parts interact with each other. in your example, the two parts of the system have a wave function (F=f1+f2) and (G=g1+g2) and once they interact, you are then able to describe the system as =(f1+f2)+(g1+g2) but not as = (f3+f4) is this sort of correct? Can you explain where f3/f4 came from?",
"No, here I might not have been clear enough. Let me rephrase it: Since you are a chemist, let me try to phrase it in a chemistry language and assume that these two parts are molecules. So the system consists out of molecule 1 and molecule 2. Each of these molecules have a whole bunch of excited states (vibrational, rotational, electronic, etc.) and let su focus on the electronic degree of freedom (be mindful, I am changing the notation a bit compared to my last example). Molecule one has a ground state g1 and an excited state e1, for molecule 2 we label these g2 and e2 respectively. ",
"Let me focus on molecule 1 for a moment. A priori, this guy can actually be in a whole set of different states: There may be the g1 or e1, but it can also be in a quantum superposition of states, e.g. (e1+g1)/sqrt(2) [I will include normalisations to make things clearer]. These superpositions mean, roughly speaking, that when you do a measurement of the energy, you have a finite probability to measure the ground state energy and also a finite probability to measure the excited state energy. Assuming that I can forget about higher excited states states or other degrees of freedom, I can write the general state of my molecule as a superposition of g1 and e1, leading to f1 = a g1 + b e1, with |a|",
" + |b|",
" = 1. So even if you only consider two electronic states, you ca prepare your system in infinitely many of these superpositions.",
"Good, now let us include molecule 2, for which we can make a same type analysis. Now, we can start playing a game. For example, if both are int their ground states, we can just describe the combined system as \"g1 x g2\" (note that \"x\" is supposed to be a product, actually it is a ",
"tensor product",
"). Now, you could excited molecule 1, so the state would become \"e1 x g2\", notice that nothing changed to the description of molecule 2. Now I can in addition excite molecule 2 and get \"e1 x e2\". All the things I did, allowed me to just remain within a framework where I essentially describe the state of the one molecule and the state of the other molecule and just \"multiply\" (again, technically this is a tensor product) them to get the full state of pair of molecules.",
" ",
"What this entanglement formally means is that we cannot find any state f1 (see above), a superposition of the ground and excited state of molecule 1, nor any f2 (the analog for molecule 2) such that",
"\n (e1 x g2 + g1 x e2)/sqrt(2) = f1 x f2.",
"\nBy definition, an entangled (pure) state cannot be written as a tensor product of local wave functions. ",
"Notice that I also explained you a method to generate entanglement, but one which is not so straightforwardly implemented in an experiment. Above, I mentioned several other methods to generate entanglement, such as interactions. In this context, the molecules may have a strong dipole-dipole coupling. In that case, when we start from \"e1 x g2\" and let the pair of molecules evolve over time, to wel see is gradually change into a state like (e1 x g2 + g1 x e2)/sqrt(2), since the energy is coherently transferred back and forth. The problem with this molecular scenario is two-fold: first of all, you will have ah very hostile environment in most models, which will quickly drive you to a framework of rate equations (think of Marcus or Förster theory) rather than coherent transfer. A more fundamental question lies in how useful it is to call this entanglement. Usually people look at these problems on the level of e.g. an excitonic manifold and there, you just have a single exciton and entanglement language is not very appropriate.",
"Moreover, let me now emphasise that the descriptions of the states as such need not be limited to just two parts of just two energy levels. Entanglement is just a very general mathematical structure that occurs whenever I can separate my system in several constituents. They only problem is that, whenever these constituents are also talking to the outside world, that this structure is extremely versatile and just vanished ",
" quickly.",
"In my first post, the \"f1 x f2\" and \"g1 x g2\" (\"x\"-tensor product-, not \"+\") were intended to indicate something like e.g. this product state of ground state of molecule 1 and excited state of molecule 2, but in a more general way.",
"I hope I clarified things a bit more? The issue with entanglement is that is is hard to go beyond some popular science PR language without going into the details of the math, so i find it hard to explain things without using too much math.",
"It seems the issue with describing it like this is that if anything besides those two particles is introduced into the system, then further entanglement can be introduced, is this correct? ",
"If you describe it on the level of the system and the surrounding jointly, I think this is not a bad picture. It is a bit more subtle, because we usually have no idea about this environment and more or less \"integrate it out\", which implies ultimately that everything what happens there is out of reach and is washed out in our mathematical description.",
"As in, the further the particles are separated, the more potential to decay the entanglement is introduced. This sounds like entropy may play a part in this.",
"The distances are quite small, once the particles are far away compared to the correlation length in your environment (which is usually extremely short), you can say that each particle sees a separate environment and the entanglement between the two particles is \"dissipated away\" (I dislike this kind of descriptions a little, but without further math I cannot come up with anything more accurate). ",
"Entropy does actually play a very crucial role in entanglement theory. There is some stuff ",
"here",
", but if you do not really know mixed states et cetera, I think it will be hard to go into that. "
] |
[
"What evidence is there for WIMPs?"
] |
[
false
] |
Weakly Interacting Massive Particles are the currently favored theory for dark matter but they feel very similar to neutrinos. What evidence is there to convince scientists that dark matter is simply more neutrinos than expected, but another more massive particle (or particles) that has yet to be discovered?
|
[
"There are particle detectors at the DAMA/LIBRA, CoGeNT, and CRESST experiments that all register small dark matter signals. They have evidence but not conclusive evidence."
] |
[
"The difference between neutrinos the sort of WIMPs that are hypothesized to constitute dark matter is that dark matter WIMPs would not be traveling at relativistic speeds (which is why they can form gravitationally bound mass halos), whereas to the best of our our knowledge, essentially all neutrinos travel at relativistic speeds. Also, based on our neutrino detections, there are not enough of them to account for dark matter."
] |
[
"None yet. It's all theoretical math that seems to support the observed data. We're hoping to find evidence from the LHC when it gets to higher energies (and a few other facilities). But we might not find any evidence, in which case it could be back to the drawing board for a whole new idea.",
"Here's a really current article on the state of ",
"dark matter."
] |
[
"Dr. John Hagelin on the science of consciousness and the unified theory. Pseudoscience?"
] |
[
false
] | null |
[
"I have a B.S. in biophysics and spent ~ 1 year learning a cursory level of research neuroscience during lab rotations so I'll give you my opinion of this until someone more qualified responds.",
"He is using quantum theory (which is abstract in the first place) to make his philosophy scientific. The glaring flaw to me in his argument is he has used elementary particles as a starting point and then starts saying 'abstract' and 'this unifying theory' to then leap and say that since string theory unifies everything then we are all unified. What he has done is taken a theory (which isn't accepted by all physicists) and then saying that the theory proves a philosophy/theology. I'm not against using science as an explanation in favor of religion, in fact I believe it is necessary, but rather than starting at his theology and saying \"I believe this because\" he has presented his theology as science. His presentation of consciousness is not testable and thus not science. So I would say it is pseudoscience."
] |
[
"Consciousness has no current operational definition and all theories are probably as valid as each other, yet equally bogus. I have removed this question because the aspect of consciousness cannot really be answered scientifically, though, the aspects of cognition that are said to contribute to consciousness can. If you'd like to rephrase your question, please feel free to message the moderators."
] |
[
"Yeh I thought the response to this would be as such. I was just interested if there was any more info people had on this. I see this can't really be answered scientifically so I'm not sure how I could rephrase it..."
] |
[
"\"Two-thirds of the people who have ever reached 65 are alive today.\" Can this really be true?"
] |
[
false
] |
I saw this at the airport on an HSBC ad. I have trouble believing that, out of the dozens of billions (more?) of humans who have ever lived, two-thirds of those who made it to 65 and lived to tell the tale are alive now. Especially considering that "average" life expectancy was artificially shortened in prior centuries by high infant mortality rates. Is it really so?
|
[
"First, an answer to your partial question",
"The common statement: \"more people alive today than have ever lived\" is false as far as I am aware. (And as far as ",
"wolfram alpha is aware",
", stating that there have been about 100 billion people ever) ",
"I can imagine though, however, the possibility that since we are are reaching older ages with the technology available to us today, that this statement might be \"more\" true... I wouldn't discredit it right away, but i think it might be a little bit exaggerated, and heres why:",
"Given facts such as:",
"In the United States the proportion of people aged 65 or older increased from 4% in 1900 to about 12% in 2000. [",
"Citation",
"]",
"And in the entire world we are sitting at ",
"~ 7.9% of 65 and older",
" currently. So this would mean we have about 550 million seniors. Going back to your statement, it would require that out of the other 100 billion people who are not living anymore, only 250 million of them could have reached age 65... This seems small to me, but we have to look at what life expectancy has been historically. (I had a hard time finding any reliable sources for curves like this... but here is a rough idea of what i keep seeing (not from journals)) Curves of life expectancy in the past have looked like ",
"this",
". (Sorry, I can't find a reputable source for this data... if someone else can, please link it!)",
"Essetnailly unchanging, until the development of science and technology, and then exploding. This gives more possibility to the \"0.25% chance of reaching age 65\" that is a requirement for the 2/3 statement that OP posted... So as a whole... I see it as viable... but, I would probably feel more comfortable with a statement such as \"Most likely, 1/3 of the people who have reached 65 are alive today.\" (with some confidence levels thrown in... definitive statements like the one originally posted throw up red flags to my science self)"
] |
[
"Don't forget that huge infant mortality rates were a large part of low life expectancy in the past. I'll try to find the interactive graph that showed age breakdown for each year.",
"edit: ",
"here",
", I really love this graph"
] |
[
"I've been spending the last three weeks going over survival analysis, and I think seeing such an expertly presented hazard curve and survival curve just made me spooge myself. (Why can't they always come out this nice in the literature?)",
"As an aside, funny how on some years the hazard at t=98 is greater than at t=99. Probably meaningless, but amusing to see."
] |
[
"Has Rosetta significantly changed our understanding of what comets are?"
] |
[
false
] |
What I'm curious about is: is the old description of comets as "dirty snowballs" still accurate? Is that craggy surface made of stuff that the solar wind will blow out into a tail? Are things pretty much as we've always been told, but we've got way better images and are learning way more detail, or is there some completely new comet science going on? When I try to google things like "rosetta dirty snowball" I get a bunch of Velikovskian "Electric Universe" crackpots, which isn't helpful. :\
|
[
"Doesn't look like anyone has chimed in yet, and this is getting a lot of votes. So let me just say this for now:",
"Rosetta got there 3 months ago and Philae landed ",
".",
"Scientists have had the data from the lander in their hands for less than a week, and whatever science Rosetta is doing from orbit is just getting started (and the really exciting stuff is going to happen as the comet gets closer to the sun and we can watch how things change when you shine more light on it).",
"Science is not an instantaneous process. It takes many, many months/years to properly analyze all the data and figure out exactly what it's telling you.",
" after scientists have had plenty of time to process the data, understand its limits and systematic errors, compare it to everything we knew before, and figure out how this new data fits in with/changes our perspective of comets as a whole.",
"Scientists have been waiting 10+ years for this data, they are very excited, and you have no idea the absolutely insane hours over the next couple months some of them will work without getting paid any overtime just to push out initial findings. But the bigger picture is going to take years to sort out. ",
".",
"Edit: I say 3 months just because that's my bet on the turnaround time to get the first/coolest results pushed through ",
" or ",
" with a minimal/expedited peer-review process. Then the bigger picture/more detailed analyses will start to trickle in more slowly.",
"Edit 2: As ",
"/u/maep",
" brought up in a ",
"comment below",
", it appears that the American Geophysical Union (AGU) Fall Meeting in San Francisco will have a Rosetta results session. You can view ",
"all the abstracts here",
". ",
" They will be preliminary results and not peer-reviewed yet, but that will be the day you'll start to have a sense of what the most exciting science seems to be from the first part of the mission."
] |
[
"I'd like to know what exactly the data is. Temperature readings? Are ground samples being taken and analysed? I mean, I don't even know what else to ask. Why is the probe their in the first place? What do they plan to learn? ",
"Sorry for the ramble of questions. I just realize how little i know about what's happening. "
] |
[
"If you want detailed information, the ",
"ESA FAQ page",
" is probably your best bet to get up to speed.",
"I think the basic answer is that it's there to try to get as detailed information about what comets are made of and how they're structured. A lot of the data is going to be spectroscopic which can tell you the composition of the comet and what sorts of material is getting ejected as it starts to heat up when it approaches the sun.",
"How do the volatiles leave the surface and form the coma and tail we associate with comets? Which molecules start to be ejected from the surface when? How complicated and which organic molecules are there floating around on comets? What's at the core of the comet? Is it a rubble pile or are things more densely packed than that? Is the water from the comet consistent with being the same water we have on Earth and support the idea that Earth's water was delivered by comets?"
] |
[
"How does a superfluid have a viscosity of 0? If you held some in your palm would it flow through you (temperature notwithstanding)?"
] |
[
false
] | null |
[
"Contrary to the conventional notions on what constitutes a superfluid, 'zero viscosity' is not achievable in the so-called 'superfluid' state of helium 4, or 'He-II'. In practice, there is always a very low but finite value in the bulk shear viscosity, about 13 microPoise, which occurs somewhere between 1 to 1.5 K . As temperature is lowered below the lambda transition point, the viscosity drops quickly to the point where it is so low that it becomes difficult to measure. But at some point there is a marked increase in the shear viscosity with further decreasing temperature. This occurs despite the fact that the normal fluid density component that gives rise to both viscosity and finite entropy is rapidly decreasing with temperature. So one would ordinarily expect the the viscosity would go to zero only as T goes to zero. What appears to happen instead is an effect from the increasing mean free path of the collective states associated with the diminishing normal fluid component. These states become limited by the physical dimensions of the viscometer itself, and the true 'bulk' viscosity is no longer measurable, and the 'effective viscosity' becomes independent of the mean free path. This leads to the observed increase in the effective shear viscosity as temperature goes to zero."
] |
[
"Picture little fluid bodies as pushing and pulling one another. When they push or pull front to front- in the direction of motion- it's an inertial effect. When one moves and the other is carried as if they were \"holding hands\" it's a viscous effect."
] |
[
"Picture little fluid bodies as pushing and pulling one another. When they push or pull front to front- in the direction of motion- it's an inertial effect. When one moves and the other is carried as if they were \"holding hands\" it's a viscous effect."
] |
[
"What color is the dress? Why do some people see blue and black and some people see gold and white when looking at a single image of a dress?"
] |
[
false
] |
We've heard the clamoring for explanations as to why people perceive so very differently. Sometimes it's blue and black, sometimes it's gold and white. We've heard that it's even "switched" for some people. We've had our experts working on this, and it's surprisingly difficult to come up with a definitive answer! Our panelists are here to offer their thoughts. These are possible explanations from experts in their fields. We will not be allowing anecdotes or layman speculation; we'll be moderating the thread as always and removing comments that do not follow our guidelines. To reiterate: They are not acceptable answers on and will be removed.
|
[
"(Reposting from the other thread)",
"Hi! me and some other grad students have been discussing this for the last half hour. It's likely due to some kind of colour constancy illusion, where some people are perceiving the context to be something like \"lit by blueish daylight\" and others are perceiving it to be something like \"under yellow department store lights.\" In the former case, your brain will try and get the objective (if such a thing can be said) colour by subtracting out the blue as a shadow, and in the latter case it will do the same thing for the filigree by subtracting out the yellow as a reflection. This is a common illusion in psych : ",
"See here",
". but it's not seen that often 'in the wild,' even though your brain does this constantly. "
] |
[
"Do you have a reverse of this. I only see blue black and want to try to get it to flip."
] |
[
"For the people that only see a white dress. ",
"This is close to what other people are seeing as a blue/black dress.",
" I got this image by just editing the brightness and contrast of the image. Maybe getting this view of the image will help you flip the colors. I see a white dress most of the time. After I stare at the altered image for a while, if I go back to the original, it looks black and blue. I guess seeing the dress one way helps your brain correct the image in that direction."
] |
[
"How much tuna is OK per week/month?"
] |
[
false
] |
With so little fat and so much protein I could go on a tuna-only binge for a few weeks to get extra lean. My question is can this be done without risking harmful effects like mercury buildup? Or can I eat tuna from the can for the next two months?
|
[
"Here are the ",
"EPA/FDA recommendations",
" for women who are pregnant, may become pregnant, or are nursing, as well as children:",
"Eat up to 12 ounces (2 average meals) a week of a variety of fish and shellfish that are lower in mercury.",
"Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish.\n Another commonly eaten fish, albacore (\"white\") tuna has more mercury than canned light tuna. So, when choosing your two meals of fish and shellfish, you may eat up to 6 ounces (one average meal) of albacore tuna per week."
] |
[
"And I see that you're letting a popular diet run away with you just because someone with the title of doctor endorses it, whereas my recommendation is the current consensus of my field as a whole. And I'd bet I can find someone with the title of Doctor who supports pretty much any crackpot theory you can think of.",
"The current consensus could change, but only if a lot more research is performed. Low-carb certainly is a hot research topic these days because (just like calorie restriction) there ",
" an understood reason why ketogenesis leads to weight loss, but there are many unhealthy downsides of low-carb diets, too (ever wonder why you are told to drink so damn much when on a low-carb diet? It's because of the gout, uric acid kidney stones, bone loss, and more that I mentioned before); in contrast, no one denies that moderate calorie restriction and exercise is a healthy way to lose weight and keep it off long-term. ",
"They both can work, but I said I was recommending the healthiest, least risky way."
] |
[
"Don't worry, I know there is evidence that keto works great for weight loss and insulin resistance. If, in the future, I have a patient who had consistently failed to be able to restrict calories/exercise and wanted to try ketogenesis for weight loss, I would provide him/her with the good and bad evidence on both types of diets and counsel him/her on how to try ketogenesis healthily (i.e. lots of extra water, vitamin supplementation, and regular bloodwork just to make sure nothing is getting out of whack). Trust me, there is absolutely tons of research going on right now about both the effectiveness/healthiness and risks/unhealthiness of ketogenic diets. In ten or twenty years, the consensus recommendation could be different from what it is now...we'll just have to wait and see where all the evidence takes us. For the time being, there is a reason why the current consensus is what it is, and that is years of accumulated evidence about exercise and moderate calorie restriction leading to weight loss, reduced inflammatory markers, increased longevity through transcription of various survival genes, etc... like I said, there is lots of evidence to go around, so I didn't intend this to be a big argument, since it will just be a ton of typing for everyone with nothing gained on either side. I was just giving the current consensus recommendation on the healthiest way to lose weight."
] |
[
"Are the charges of the proton and electron exactly opposite? If so, why?"
] |
[
false
] |
Do the two particles have charge of exactly equal magnitude (just opposite sign)?
|
[
"Yes, they are of exactly equal magnitude. Why this should be the case is an interesting question, to which we do not have a full answer. There are three approaches to this question that I can outline.",
"Before doing so, let me note that electric charge tells you how strongly a particle feels the electromagnetic force, so constraints on the magnitudes of the charges should arise from some properties of the electromagnetic force.",
"The proton is made of three quarks (2 up, charge +2/3; 1 down, charge -1/3; total charge +1) while the electron is, as far as we know, a fundamental particle of charge -1. So the question really becomes whether the quark/electron charge ratios should be exactly 1/3 or -2/3.",
"The first constraint on these charges comes from something called ",
". The electromagnetic and the weak forces combine into a single force called the electroweak force. In order for the corresponding theory to be mathematically sensible, there are certain equations the charges of the particles have to satisfy (both the electric charges and the analogous properties for the weak force). So this imposes a constraint on the relative charges of the electron and the quarks, and the known charges satisfy this constraint. So this is a consequence of an established theory.",
"There are two other speculative approaches to this problem.",
"One is ",
". If the electromagnetic, weak, and strong force can be embedded in a single force, then it will automatically follow that the electric charges of all particles will be integer multiples of some basic electric charge. Every force is governed by some symmetry structure, and if there is a single simple symmetry structure underlying all the forces, this symmetry would enforce that constraint on the electric charge.",
"The other is the possible existence of magnetic monopoles. Dirac observed in 1931 that if magnetic monopoles existed (objects that were isolated north or isolated south poles), then it would necessarily follow that all electric charges would have to be integer multiples of a fundamental charge. This follows from the properties of quantum angular momentum.",
"One final note is that in many situations, grand unified theories predict the existence of magnetic monopoles, so although the mathematical origins of the constraints from unification and the presence of monopoles are different, they can dovetail together quite nicely."
] |
[
"\"Grand unification\" is the term we use to describe the unification of the non-gravitational forces. Gravity certainly is fundamental, but gravity has a mathematical structure that appears to be rather different from that of the other forces. On the other hand, the strong, weak, and electromagnetic forces all have a common mathematical structure, and quantum mechanical versions of these all make sense.",
"Gravity, on the other hand, we don't know how to quantize. So we can speak meaningfully about a quantum grand unified theory, but not yet about a theory that unifies all the forces including gravity.",
"Incidentally, there are ideas about how one might unify gravity and the other forces, but these involve more speculations than a grand unified theory requires, and lead to theories we are not yet sure how to formulate successfully at the quantum level."
] |
[
"Quarks in hadrons are not bound together by the electromagnetic force, they are bound by the strong interaction. I like your last sentence. We actually have no idea why a proton should have the exact same charge magnitude as an electron, one hypothesis is that if there are many universes with varying laws of physics, then ours is one where atoms may form (charge of p = charge of e). If atoms did not form, then we would not be here to observe the nice charge symmetry of protons and electrons."
] |
[
"Are LEO satellites visible with the naked eye?"
] |
[
false
] | null |
[
"Oh yes! The most famous satellite visible to the naked eye is the ISS. Depending on how the sunlight is getting reflected by it or its solar panels, it can even appear brighter than Venus with an apparent magnitude of roughly ",
"-5.9",
". Other LEO objects can reach similar magnitudes, depending on how much light they reflect in the right way for you to see. When the conditions are right, it can even happen that you can spot the ",
"reflected light of a satellite in geostationary orbit",
", although this is extremely rare."
] |
[
"I was actually out waiting for the ISS to fly over and I saw the satellites. At first I thought it was space junk. Hey, it was 5:50am lol. "
] |
[
"I was actually out waiting for the ISS to fly over and I saw the satellites. At first I thought it was space junk. Hey, it was 5:50am lol. "
] |
[
"Why can't we use integration in carbon-13 NMR?"
] |
[
false
] |
The normal answer is because only around 1% of naturally occuring carbon is carbon-13, so there is normally only one C-13 atom per molecule. But this doesn't seem satifactory because surely for a large enough sample the ratio of C-13 atoms in the different environments in all molecules would match the ratios of the carbons in different environments in a single molecule... What else is going on or have I misunderstood?
|
[
"I think relaxation time plays also a role.\nDifferent carbon types (sp3, sp2,...; carbonyl vs alkene,...) won't have the same relaxation time and if in your pulse sequence you don't wait for full relaxation then integration may not be reliable.\nN.B. That is also true for proton (and certainly most of other nuclei)."
] |
[
"Well that actually is part of the answer. The reason a 1% abundance ruins our ability to perform integration is that when we actually go to collect a C-13 spectra we have a very high signal to noise ratio compared to H-1 or other NMR spectra of abundant isotopes. ",
"If you have ever seen a C-13 spectra that hasn't been a averaged over thousands upon thousands of measurements you'll notice something about the base line",
"http://www.bmrb.wisc.edu/metabolomics/standards/Methanol/nmr/bmse000294/spectra_png/13C.png",
"It's a mess. This is because when we measure the spectra the signal is so weak (it is proportional to population) that it barely stands out above the natural noise that is present in these measurements. We often have to use various techniques which improve signal strength which in themselves can introduce error. ",
"In contrast with H1 the strength of the signal, because H1 is the dominant isotope, is huge compared to the noise.",
"http://nmr.chem.ucsb.edu/protocols/P31_H1dec.png",
"As a result there is a very large experimental error with determining the area under the curve in the C-13 case versus the H-1 case and while it may be possible to remove this error, the effort for the amount of information gained may not be worth it. Especially when other techniques or other isotopes can give us much of the same information without the hassle. ",
"I wouldn't doubt if some poor soul has had to try to integrate a C-13 peak, but I'm glad I haven't ever had to do that. "
] |
[
"A few reasons, but probably the biggest is because we usually decouple C",
" spectra, which distorts the peak heights and removes the proportionality between peak area and number of atoms.",
"More here:",
"http://www.chem.wisc.edu/areas/reich/nmr/05-hmr-01-integration.htm"
] |
[
"melting point depression: how does it work?"
] |
[
false
] |
the first lab I did in organic chem was a melting point lab. In it we combined solid cinnamic acid and solid uric acid, both crushed, and the melting point of the mix was less than either of the two compounds while they were pure. I can understand if the two were in liquid form, and how the intermolecular forces would be disrupted and the melting point would be lowered, though I don't get how two solids can be mixed and still get the same effect. can someone explain this to me?
|
[
"The mixture of solids can actually be described thermodynamically in the same way as an aqueous solution mixture. The regular solution model of thermodynamics treats chemical interactions on a global average scale, without specifically describing the atomic interactions. Two contributions, from the increased entropy and enthalpy are taken into account - both of which can depress the melting point.",
"The picture, microscopically, is that the dissimilar molecule bonds in this case have lower energy states than either of the pure component bonds. This then lowers the energy necessary to cause the melting phae change."
] |
[
"I didn't know that regular solution theory described phase transitions! That is interesting!"
] |
[
"Phase transformations are described by a (energy) difference between states. The regular solutions model is capable of decribing a \"solid solution\" state which covers most simple liquids and metals. ",
"The same concept can be extended to describe oxides and semiconductors using lattice theory. (each lattice site is taken to be a solid solution that may interact via lattice dynamics)"
] |
[
"If dry ice is made of CO2, and CO2 is transparent, why does it produce a white fog?"
] |
[
false
] | null |
[
"It's tiny droplets of liquid water condensed by the extreme cold of the dry ice - just like you can see your breath when you're outside on a cold day. "
] |
[
"Ah, so the fog is made of the water, not the co2. In that case, I thought water had to heat up to make vapor, not cool down. What gives?"
] |
[
"Ah, so the fog is made of the water, not the co2. In that case, I thought water had to heat up to make vapor, not cool down. What gives?"
] |
[
"Positive and negative ends of battery same as positive and negative charge?"
] |
[
false
] |
My understanding that in electricity, one end provides electrons and the other end doesn't. Not sure which is positive and which is negative in this case. Is this the same thing as the positive charge that a proton possesses and the negative charge an electron has?
|
[
"In conventional battery labeling, the positive terminal is the source of high-energy electrons (electron donor) and the negative terminal is where low-energy electrons go (electron acceptor). ",
"In today's circuits, charge carriers (that is, particles that are responsible for moving charge around and doing the work of the circuit) are electrons. Protons do not move energy around the circuit.",
"So no, positive and negative in battery terminals are not related to electron and proton charge in any way other than that they both have two opposite things, one of which is labeled with + and the other with -."
] |
[
"I don't think that's quite right. The convention for electrical current is that it flows from the positive to the negative terminal. This was determined before we discovered electrons are the carrier of electric charge, so while we often describe current as traveling from the positive to the negative terminal, the individual electrons actually travel from the negative terminal to the positive one. "
] |
[
"When a battery is not connected to a circuit there are a surplus of electrons located at the negative terminal and a shortage of electrons located at the positive terminal. While the battery is performing work in a circuit, electrons move out of the battery at the negative terminal, then move through the circuit, and move back into the battery at the positive terminal."
] |
[
"How did the \"Mother Lode\" vein of California gold develop?"
] |
[
false
] |
And why did it end up concentrating where it did? I have a very basic understanding that it was deposited there as tectonic plates collided and formed the Sierra Nevada mountain range, but where was the gold and in what way was it distributed before the plates collided? (I'd love to learn as much as you can tell me about the process, these are just a few questions that I hope are covered in a broader answer. Thank you!)
|
[
"160-165 million years ago, as North America trudged slowly west, there was ",
" in its way. This was probably (but not ",
") an island arc, chilling out minding its own business as an entire continent rolled towards it. And eventually, in painfully slow-motion, the North American plate collided with the islands (and the tectonic crust beneath them), thrusting them (and the seafloor around them) up into what would eventually become a big chunk of the Sierra Nevada mountains.",
"The heat and pressure of this collision—which ultimately fused the chunk of island crust to the North American plate—created lots of heat, lots of pressure, and lots of fissures.",
"Now deep in the earth's crust and under the ocean, the rock is usually under a lot of pressure. There's seawater in the rock, just like there can be groundwater in rock on land, but it too is under a lot of pressure. And should you add heat (either because the rock is being pushed down into the mantle, or magma is upwelling against the rock) the water becomes hot and pressurized. Further, being rich in chlorine ions, the seawater infused in the rock is chemically better at dissolving certain minerals, like gold, out of the surrounding rock. So even if there's only a little bit of gold spread out in the rock, the hot pressurized underground seawater can dissolve large amounts of it.",
"As the fissures opened up, the mineral-rich underground water—formerly under intense heat and pressure—was able to flow out of the surrounding rock into the fissures and rise toward the surface. The cooling and depressurization precipitated the minerals out of the water, including the gold, creating \"cracks\" of solid gold and quartz and so-forth wherever a new fissure formed. With every new fissure came new escapes of hot steamy mineral-rich water, and new precipitated gold veins. The fissures kept accumulating more and more thin cracks of gold, over and over, for many, many years.",
"As these gold-filled fissures were gradually exposed by erosion and weathering, flakes of underground gold could be washed downstream, which 160 million years later would lead prospectors back up to the original seams of the Mother Lode."
] |
[
"That's a fantastic answer, and very interesting, thank you!",
"Can I ask a couple follow-up questions to understand a few things better?",
"So the hot, pressurized water carrying the dissolved gold up toward the surface was also carrying other minerals with it that were also dissolved out of the rock? And when cooled and depressurized, ",
" minerals would also form some kind of \"veins\" or other concentrations elsewhere, depending on the minerals' properties?",
"Can I infer that the Mother Lode gold originated from the island crust rather than the North American plate, since that vein is located distinctly on the west side of the mountain range?",
"Was there anything remarkable about the tract of rock from where the gold originated, as far as the ",
" of gold it contained, before the whole collision process occurred? Or would any ol' plot of crust produce a similarly sized deposit of gold, given similar conditions (amount of heat, pressure, size of \"impact zone\" of collision, duration of collision, etc.)?"
] |
[
"You're welcome!",
"this process can happen pretty much instantaneously"
] |
[
"Is brilliant green (zelyonka) actually an antiseptic?"
] |
[
false
] |
I don't think this is used in Western countries, but nations that were part of the former USSR seem to still use a as a wound treatment (similar to/as well as iodine). It's something I grew up with and never really thought about, but when I looked it up today, I'm not really understanding if the dye itself has any active ingredients. Per my understanding, over-the-counter zelyonka is just the brilliant green dye crystals dissolved into diluted alcohol, so... Is it only antiseptic because of the alcohol? Or does the brilliant green actually have antiseptic properties on its own?
|
[
"It’s been used as an antiseptic since WW1. It’s not been widely used or studied in the west. I could find one ",
"note",
" published to the British Medical Journal in 1916 about its use in the WW1 theater.",
"I see some references to it being effective against gram positive bacteria and seems to be a component of the “triple dye” applied to the umbilical cord after it is cut to encourage it to fall off and prevent infections in newborns."
] |
[
"Not directly related but maybe lending credence to the potential benefits of dyes in medical usage, there is another dye (phenazopyridine) that is used as a medication to provide pain relief during urinary tract infections. It ends up coloring your urine a very bright orange."
] |
[
"Interesting! Thanks for the info, I'll look up those to learn more 😁"
] |
[
"How do bats avoid confusion on the frequencies they make?"
] |
[
false
] | null |
[
"Bats will actually alter their frequency based on surrounding bats so that each of them will have a unique frequency. Typically one will shift upward and the other downward but how exactly it plays it isn't understood entirely. The technical term for this type of behavior is Jamming Avoidance Response. This may not be the only factor in avoiding confusion, but it seems to be a major player.",
"Source",
"Source #2"
] |
[
"this is copy pasted from an answer i gave a couple months ago:",
"Yovel et al (2009) found that bats can identify individuals by their voice - very similar to the way you can tell your friends voices apart!",
"Some of it also has to do with the timing of the signal - bats have muscles around their ear bones that actually tense up when the bat produces their own noise (so they don't damage their ears!) which effectively makes them deaf for that part of a second.",
"Lastly, bats often do not echolocate when in a group. When exiting a group roost en mass, the bats know their cave so well that they do not need to echolocate to find their way around. it's only once they're outside of the cave and away from each other that they start echolocating. (as a side, this is what makes catching wild bats really easy for research! setting up a net by their cave mouth is perfect, because they are not using echolocation to look for anything around the cave, as their mental map is set. the net is a total surprise!)"
] |
[
"Though it's not a direct answer, I hope it may be considered relevant. I don't have credentials personally, but Richard Feynman does.",
"Richard P. Feynman Talks About Waves",
" ",
"Give him a minute to get going. Note, he's talking about light waves, not sound waves. But if you're thinking about this kind of thing you might still find his analogy helpful. "
] |
[
"Was the Chernobyl graphite radioactive due to induced radioactivity?"
] |
[
false
] |
Hi Just watched HBO's Chernobyl series for the 2nd time (wow that is some good TV) and I was a bit puzzled about why the graphite blocks were so radioactive. Is it simply because they were coated in fission products, or were did they become radioactive themselves as a result from induced radiation from being present in the core? I'm wondering the same about things like the 'Chernobyl claw'. Is that still radioactive because of induced radioactivity while it was working near the exposed core? Thanks
|
[
"During normal operation, the fission products should remain contained within the fuel and not really mix with the moderator material, but the moderator itself will be activated due to all the neutrons around in the core. So the fission products make up the bulk of the radioactivity in the core, but activation of the moderator/coolant occurs as well.",
"However when there’s an explosion like there was at Chernobyl, the fission products go everywhere and contaminate things as well.",
"So the answer to your question is really both."
] |
[
"Beside the damaged fuel contaminating the graphite, even in normal operation graphite reactors (RBMK for Cherobyl, but also Magnox/AGR, or UNGG), the graphite is naturally activated by the neutron flux. Even without an accident, handling gaphite fresh from the core by hand would be \"detrimental to your health\". ",
"To be precise, more than the carbon itself making up the graphite, the issue arises more from the ",
"impureties",
" in it. As you can expect, with time, purer and purer graphite was techically acheivable, so old design (RBMK, UNGG, Magnox), suffered more of such issues than latest ones (AGR). This is a major issue for decomissioning. ",
"The claw is hazardous because of its contamination, it did not get activated."
] |
[
"The main objective of a nuke remains the blast. Make a big boom that destroys stuff.",
"\nAll the material of the bomb (the fuel but also the casing itself) is activated (to various levels) by the intense neutron flux and fall down as fallouts, aka radioactive contamination adding the \"bonus\" of area denial for the enemy and heavy burden of soon to be quite sick people to take care of.",
"\n",
"Salted bombs",
" are concepts where activation prone material is purpusefully added to the bomb to enhance this \"contamination\" effect. ",
"Activation of land structures isn't a big contributor.",
"\nHowever, ",
"neutron bombs",
" design are conversely optimised to have a low burst but high radiation flash, the objective being then to kill the meatbags with minimum destructions of infrastructures. But even then, the gamma radiations rather than the neutrons do most of the work (plus if you want to take over a city, you don't want it to be shining radiations). ",
"All that to say that even with bombs, the activation will mostly be from the bomb itself (salted or not) than from other objects."
] |
[
"How is the power of nuclear weapons increased?"
] |
[
false
] | null |
[
"So most nuclear warheads in the current stockpile are of the Teller-Ulam design. You have a small(ish) fission primary, which initiates the whole thing. This creates the conditions necessary for fusion in the secondary. The neutrons produced in the secondary, in turn, cause fission in the natural uranium casing that surrounds the whole device. In most thermonuclear designs that have been fielded, the yield is about 50:50 from fusion and fission.",
"Based on what is in the open literature, and what we've seen in the history of testing, the Teller-Ulam design can be scaled arbitrarily large by adding more and more stages. So if you wanted a stupidly large warhead, you could \"just\" keep adding more fusion stages.",
"An example of this is the Tsar Bomba that was built and tested by the Soviets. While not a practical weapon (it was built in the grand tradition of various other oversized Russian things, like the bell and the cannon), it is the largest device ever detonated, yielding 50 Megatons. To reduce the fallout from it, they omitted the Uranium casing, so 97% of its power was derived from fusion. With the Uranium casing, it probably would have yielded 100 Megatons.",
"Now, one of the things that you have to understand, is that larger weapons aren't always better. You're far better off sending in multiple smaller warheads rather than one big one. It's bad enough that to get a 10 fold increase in blast radius, you need a 1000fold increase in warhead power. See ",
"here",
" for an interesting article on this concept. The other reason why you'd want to deploy multiple smaller warheads is it's harder to defend against a bunch of small ones, and they're easier to build and deliver than a big one."
] |
[
"It's bad enough that to get a 10 fold increase in blast radius, you need a 1000fold increase in warhead power.",
"The rule of thumb for blast scaling, as an aside, is that to increase the blast radius by a factor of two, you need to increase the yield by a factor of eight. Thermal effects work a bit more efficiently but it is still not a good trade-off. The key issue here is that the weight of a bomb increases almost linearly with its yield — even the most efficient weapons will get you around 6 kilotons of output per kilogram of bomb weight, so you're making it heavier and heavier without much increasing the effective damage."
] |
[
"Nuclear weapons work by releasing energy from nuclear fission reactions, and often nuclear fusion reactions.",
"Increasing nuclear fission bombs is a matter of making sure more material undergoes fissioning before the explosion of the bomb decomposes itself. This can range from increasing the efficiency of the reaction to just increasing the amount of fuel (which has to be done carefully so that the bomb can't go off prematurely). The largest pure-fission bomb, the Ivy King test, used a ",
" of enriched uranium in a very efficient arrangement and got half a megaton's worth of energy out of it.",
"Other ways to increase inefficiency involve things like having tiny amounts of fusion reactions, which produce neutrons that cause more fissioning. ",
"For thermonuclear weapons, a fission bomb's energy is used to compress and ignite fusion reactions, which in turn can produce neutrons to ignite more fission reactions, even in otherwise \"inert\" depleted uranium.",
"Making a big thermonuclear bomb is just a matter of increasing the amount of fusioning and fissioning you do. It is not hard to scale up the explosive power. For thermonuclear weapons, there is literally no real limit to the practical explosive power of the bomb — it just becomes heavier and heavier, and thus harder to \"deliver\" to a target. The largest weapon design I have seen seriously studied by US weapon designers had a projected yield of 10,000 megatons. That's a single bomb with 500,000 times the power of the Nagasaki bomb. It was never built.",
"More difficult, and more useful from a \"delivery\" standpoint, is scaling down the volume and mass, while still getting a respectable amount of explosive power (increasing the efficiency). There are several apparent tricks that are used by weapons designers to do this, so you can fit ",
"10 human-sized warheads onto one missile base",
", but they all come down to engineering tweaks (e.g., using a spherical fusion component surrounded by highly-enriched uranium, for an extra boom with only a minimal volume). ",
"This is more or less what the more advanced thermonuclear warheads look like today",
", if you had them in cross-section. They are just very efficient in terms of the yield-to-weight ratio and their mass/volume; this level of nuclear weapon technology was more or less achieved by the USA in the 1970s (with some very small optimizations in the 1980s). Each of those warheads has an explosive yield of \"only\" 475 kilotons (24X the Nagasaki bomb), but they are present in such numbers (and on highly-accurate missile platforms) that destruction of a target is still easily accomplished. "
] |
[
"Is it possible for there to be some sort of extra-terrestrial species who's time moves at a different \"speed\" than ours? (I'll try to explain in text)"
] |
[
false
] | null |
[
"Time is just a measurement tool, like distance. You can call a meter anything you like, but it's still the same distance in the same frame of reference. Same with time. How we comprehend it is another thing I suppose."
] |
[
"Right, time is a measuring tool. I'm curious about comprehension though. Is something like mentioned above beyond current human understanding?"
] |
[
"I guess it's possible for something to not notice the speed of time like something else. "
] |
[
"Computer Radiators: Actually a sensible idea, or pie in the sky that's inefficient?"
] |
[
false
] |
Been reading this article, and the idea seems sound: instead of radiators, have a computer system designed like a radiator that is a part of a network to crunch stuff, and as a side-product you get heat. As a layman with no idea, this sounds sensible as ideas go, but what do our Engineering and Computing sciencers think?
|
[
" It works, but is probably not very practical.",
" Computers generate heat and do so very efficiently. Practically every joule of energy you put into a computer ends up as heat coming out of one of its components. So the idea to use a computer instead of a regular electric radiator is quite natural.",
"The developments described in the article involve customers buying a computer-radiator system, installing it in their homes and have companies pay for the electricity in order to run computations on the machines.",
"The first problem is the summer. Little to no heating is needed in this period in large parts of the world. The article mentions a system where the server has an exhaust leading through the walls to take the heat away when it's not needed. This puts considerably constraints on the location where the server can be placed in the house and will involve additional work and costs to create this exhaust system. The other option is to simply turn the device off, but that would mean that the computational power of the network is almost non-existent in summer, which is very undesirable for companies seeking to use this network.",
"The next issue is the protection of the hardware and the data. The machine is said to be tamper-proof and the data encrypted, but you can bet your money on it that there'll be people trying to hack the device and see what kind of creative things can be done with it. As a company using this network for computation, you would have to break up your problems in such a way that they are heavily parallelized and the computation of one step does not depend on the outcome of another. Furthermore the requirements on completion time and the sequence in which different parts are completed should be relatively loose, since you never know when specific machines are not available due to outages or simply being turned off.",
"Finally, there is the issue of longevity. 5 years from now, computer hardware will have evolved considerably and the same computation will probably be available at much lower energy cost. Why would companies then still use server-radiators that were purchased years back and are relatively inefficient compared to the latest and greatest. This requires customers to upgrade to a new model every few years in order for their radiators to still be an interesting place to run computations on.",
"Because of these limitations, I don't see this idea taking off. But technically speaking, it's totally feasible."
] |
[
"Computers generate heat and do so very efficiently.",
"If your primary goal is to heat your house, then that's not quite true. Computers can give you at most one joule of heat for every joule of electricity. That's ",
". A heat pump can get you 2-3. ",
"In some places (Norway) resistive heating is illegal because its 100% efficiency is deemed too bad."
] |
[
"In some places (Norway) resistive heating is illegal because its 100% efficiency is deemed too bad.",
"Not true, you can buy all kinds of resistive heaters in Norway, and using them is not illegal. There might be some kind of regulation regarding office complexes or something that I'm not aware of, though.",
"Source: I'm Norwegian."
] |
[
"Does stomach size have an effect on gaining weight? Is it possible to have a run away effect from eating a few large meals in a row, leading to less feeling of satiety?"
] |
[
false
] |
[deleted]
|
[
"Appetite and satiety have far less to do with gastric expansion than you might think. There are two deep-brain structures in the hypothalamus that seem to govern a large proportion of appetite and satiety. The lateral hypothalamus is the structure that fires when you're hungry and eating, but after you eat for a while, it begins to fire less and the ventromedial hypothalamus starts to fire. In animal models (i.e., rats) when you lesion (ablate, damage) the lateral hypothalamus, the animals tend to lose about 10% of their body weight. When you lesion the ventromedial hypothalamus, the animals gain an enormous amount of weight. ",
"Kelley Brownell at UPenn did studies decades ago wherein he inflated balloons in people's stomachs to see if gastric expansion would influence appetite and satiety, and he found that it played a small but significant role (something like 10-20% of appetite and satiety?), but that the rest of the story was far more complicated than just gastric expansion. Between insulin/glucose ratios in the blood and a host of other hormones and neurotransmitters, appetite and satiety are immensely complicated and still not as well understood as many other biological processes.",
"When you influence one part of appetite and satiety (say, stomach stapling or lap bands to decrease stomach volume), you do get a reduction of body mass, but that effect can be moderate or temporary, because the human body has evolved to EAT. In our environment of ancestral adaptation, we sometimes had to alternate between feast and famine, so when food was readily available, we pigged out on it. For evolutionary reasons, it makes a lot of sense for our bodies to have multiple redundant systems to encourage eating! Like the rats that had their lateral hypothalamus damaged -- they still ate enough to stay alive!",
"Anyway, that's my two bits."
] |
[
"You can't simply eat your back to your old stomach size. Gastric surgery (for the purpose of weight-loss) involves either bypassing parts of intestine or removing part of the stomach entirely. While it is true that perhaps 25% of patients will experience weight regain staring 1-2 years after surgery, they will still be below their starting weight. Also, this effect is strongly linked to failure to maintain a proper post-surgery diet. "
] |
[
"The stomach is designed (and by designed I mean molded through natural selection) to constantly expand and contract as food enters and leaves. The stomach expanding is just one of the many signals that tells the brain it's time to stop. The stomach will only remain expanded as long as there is large amounts of food in it. Once its emptied the stomach will return to normal size.",
"So to answer your question no, not really."
] |
[
"I hear news about about coral reef loss all the time, but are we seeing any coral growth in new/existing areas?"
] |
[
false
] |
[deleted]
|
[
"Coral reefs take a very, very long time to form. Think thousands of years. They also mostly require clear, shallow water and they are very sensitive to temperature. So the reefs we ",
"know about",
" are a fairly comprehensive list. The best strategy thus far has been to introduce ",
"farmed coral",
" into existing reef structures. Coral that grows 2cm per year is near the maximum in terms of speed of growth, so without us artificially speeding it up the situation would be worse. However with ocean acidification becoming a problem, it's not likely we can keep up with the decline."
] |
[
"I did a little paper on this a few years back, it was pretty basic but I learnt a few things on this subject. The oceans are a massive carbon dioxide sink and much of the carbon dioxide in the air is sucked up by them, and as the carbon dioxide increases in the atmosphere more and more is deposited into the oceans to balance everything out. Carbon dioxide dissolved into the water reacts to form carbonic acid which further breaks down into hydrogen ions (which accounts for the increase in hydrogen) and bi-/carbonate ions (which are actually an important building blocks for the shells/exoskeletons of aquatic life that are being affected by acidification). The increase in dissolved carbon dioxide has already increased the pH in surface ocean water by around 0.1, which is actually significant considering that around a 30% increase in acidity."
] |
[
"I did a little paper on this a few years back, it was pretty basic but I learnt a few things on this subject. The oceans are a massive carbon dioxide sink and much of the carbon dioxide in the air is sucked up by them, and as the carbon dioxide increases in the atmosphere more and more is deposited into the oceans to balance everything out. Carbon dioxide dissolved into the water reacts to form carbonic acid which further breaks down into hydrogen ions (which accounts for the increase in hydrogen) and bi-/carbonate ions (which are actually an important building blocks for the shells/exoskeletons of aquatic life that are being affected by acidification). The increase in dissolved carbon dioxide has already increased the pH in surface ocean water by around 0.1, which is actually significant considering that around a 30% increase in acidity."
] |
[
"Why do people never forget how to ride a bike once they've learned?"
] |
[
false
] | null |
[
"The fear of falling is the main reason why it's hard to learn in the first place. You need a certain amount of speed to keep it upright, but a higher speed = a more painful experience if you fall. So the tendency is to want to start off slowly, causing a wobbly ride. The intricate details of which gear to use, how to pedal properly, to brake without flying over the handlebars, those could probably be forgotten.\nWhat \"clicks\" in your head is that you actually have more control over the bike if you get it moving a little faster, and less if you slow down. This is such a simple cognition, and something you won't forget. "
] |
[
"This guy forgot how.",
" Although that's because he retrained on a backwards bike. I don't know what it would take from just not riding it."
] |
[
"As a few people have commented, you ",
" forget how to ride a bike. You can train yourself out of it, or you can just let the knowledge lapse from disuse (it happened to me). So I think we need to back up and start by asking, why do people ",
" you can never forget how to ride a bike once you've learned? Is there any psychological or kinesiological research supporting that statement? Naturally, I don't know if there is, but hopefully a panelist in a relevant subject does."
] |
[
"Would it be possible to create a type of artificial air that is heavier than natural air and use it to create a breathable atmosphere on the moon?"
] |
[
false
] | null |
[
"No. ",
"Earth's atmosphere",
" (which we can breathe) is approximately 78% nitrogen and 21% oxygen (and 1% other gases). The essential component which we need is Oxygen, Nitrogen is essentially chemically inert. Oxygen and Nitrogen are both diatomic molecules, and so they weigh about the same at the same pressure. Because they weigh about the same, they keep mixed in the atmosphere.",
"If we were to replace the 78% Nitrogen molecules with a much heavier, denser inert gas, and placed this gas mixture on the moon, then because of their significantly different weights, the two gases wouldn't mix but separate into two layers. The Oxygen would be the upper layer, and we couldn't breathe the other gas (comprising the surface layer) on its own.",
"If we want to have colonies on the moon, the most promising approach might be to utilise ",
"lunar lava tubes",
", such as ",
"this picture",
" appears to show.",
"Lunar lava tubes may potentially serve a role as enclosures for manned habitats. Tunnels larger than 300 metres (980 ft) in diameter may exist, lying under 40 metres (130 ft) or more of basalt with a stable temperature of −20 °C (−4 °F). These natural tunnels provide protection from cosmic ray radiation, meteorites, micrometeorites, and ejecta from impacts. They are shielded from the variations in temperature at the lunar surface, which would provide a stable environment for inhabitants."
] |
[
"When did obama die/leave the white house?"
] |
[
"No. Like hal2k1 mentioned mixing due to density may be a problem, although if there is sufficient wind it may not be. The real problem is that the moon's gravity is not strong enough to retain oxygen due to heating and solar wind imparting enough kinetic energy to achieve escape velocity. The result is that, even if perfectly mixed, the atmosphere would be continuously depleted of oxygen even if the other gas is heavy enough to remain. "
] |
[
"What is happening on the cellular level when you rub lotion into your skin, and why is it good for you?"
] |
[
false
] | null |
[
"When you say lotion you can mean one of a few different things. Products known as ",
"emollients",
" are lipid (fat) heavy solutions that restore barrier function to disrupted skin. Another sub-class of \"lotions\" are humectants, which hydrate the skin by trapping water. Generally speaking, the lotion (vehicle) has little/no activity at the cellular level, however you do see changes in the thickness of some epidermal layers and changes in the relative proportions of components of the extra-cellular matrix. ",
"Other functions of lotions are to deliver various medications into the skin, and they're generally formulated to best serve as vehicles for the medication in a addition to being emollients/humectants. Other than that we can change qualities in the vehicle based on where on the body it will be used. Different vehicles are required for the scalp/hair, as opposed to the face, ect. "
] |
[
"NO MORE HOSE JOKES. Please. "
] |
[
"There's also been some great research showing that lotions containing nanoparticles are able to get through the skin and move into the blood stream. If there's any interest, check out the work done in the ",
"DeLouise Lab",
" at the University of Rochester."
] |
[
"When it's bright out, and your pupils constrict, why isn't our field of vision reduced?"
] |
[
false
] |
because there is a smaller 'hole' for it to enter the eye through
|
[
"I'm an engineer, not a biologist, but I believe that the optics of an eye are close enough to the optics of a camera to give a good answer. The aperture diameter of a camera determines the amount of light it receives and its ",
"depth of field",
", but not the field of vision (well, not how you're thinking).",
"Pinhole cameras",
" have been made to the size of ",
"aircraft hangars",
" from a quarter-inch pinhole aperture, though the exposure time was more than half an hour. The reason that this is possible is that you can think of all the rays of light that enter a pinhole as forming a cone: the rays from any angle in the outside world that happen to hit the aperture naturally make a cone. This is one parameter that defines the field of view: what the aperture can capture. There is no focus in a pinhole camera, which is one of the interesting features: it creates scenes where ",
" is in focus, and there is no depth of field. The light rays expand again into a cone that strikes the retina or the film. This also defines the field of view: the area of the sensor. The cone is therefore \"very wide\" from the world, squeezes though a very tiny spot (with a perfect pinhole it would be ",
"), and spreads out again to shine onto the surface. It's like a \"conical hourglass\" shape of light. There's a 2d image of this on that Wikipedia page with a tree being projected in a pinhole camera.",
"Pinhole cameras get these cones by just whatever light happens to be exactly incident to the pinhole, but cameras with lenses (and our eyes) can effectively widen the area that captures the light with the forward facing surface of the lens and cause much more light to exit the back of the lens. Therefore, a larger lens means more gathered light: a pinhole camera uses no lens, but a big lens can direct much of the light that hits it ",
", widening the area of incident light that it can capture.",
"You can understand how this spot focus works if you've ever used a magnifying glass to focus the sun's rays. Light is very capable of being squeezed into tiny locations. This center of focus is small enough that your iris doesn't normally come close to cutting it off entirely. Rather, the iris determines how much of the incident light gets in: it's more like the \"light volume control\" rather than a curtain.",
"The role that the aperture size plays is in depth of field: this is where the light that's not directly in the center of focus becomes blurry. Think about the same small-aperture case above, where there's a single in-focus collection of light rays that go right through the center of the iris and onto the retina. Now, when you open the retina and increase the aperture, you add more cones all around the periphery that add up on top of each other, lending a blurry mix of light around the center of focus. Each point in the opening is contributing a light cone, in other words. Open the aperture more, and you add even more mixed light cones that add blurriness. Since the center of the image is where the lens is causing the light to be focused, the center is in focus (all the cones near the middle hit the retina more precisely), but the light cones around the edges are unfocused: they land more haphazardly on the retina.",
"Finally, we can extend how this works in the pinhole camera to a camera with aperture and no lens: the pinhole camera excludes every ray of light that doesn't pass through its hole at the center of the 2 cones, which lends itself to a sharp picture. If there is no lens and the pinhole is widened, the whole image is blurred just as the outsides of the images on a wide-aperture camera is blurred. Eventually you mix the light up so much that you just see brightness instead of an image, which is why windows don't normally project the outside scene on a wall.",
"This is hard to describe in words - we used diagrams in the physics classes when I learned this - but the net effect is that whatever is directly under the center of focus gets the sharp image, as it's not superimposed with additional light cones. The wider the aperture, the more light cones you can add together, so the blurrier the image gets to the periphery.",
"This means that, as your iris widens, your image becomes blurrier around the edges and brighter - good for dark rooms (or when you're surprised and need to see everything). It also accounts somewhat for why our visual acuity is reduced in dark rooms: we're literally getting a blurrier image. When your iris narrows, your image becomes more focused but dimmer."
] |
[
"For most pupil sizes, the visual field is not affected, for the reasons listed in the other comments.",
"But when the pupil gets smaller than 3mm, it does have negative impact on the threshold visual field. The threshold visual field is a way of measuring \"how bright/big does a stimulus have to be for someone to see it 1/2 of the time\". It's what ophthalmologists typically measure when we do visual field testing.",
"http://www.ncbi.nlm.nih.gov/pubmed/1544786"
] |
[
"The image of what you see is projected on to the back of the eyeball, at the retina. All the light from any point you are looking that passes through any part of the lens is focused onto a point on the retina. The size of the pupil just affects the brightness of the point."
] |
[
"When we squint our eyes we tend to see things better. Why?"
] |
[
false
] |
[deleted]
|
[
"Squinting our eyes increases ",
"Depth of Field.",
" That is the range which things are acceptably in focus. You get the same effect when you look through a pinhole in a piece of paper.",
"It's also why you get eyestrain in a dimly lit environment. Your iris is wide open and your lens has to work extra hard to keep everything in focus."
] |
[
"Agree with comments above, but I also would like to add a quick side note. Ophthalmologists and Optometrists use this a quick and dirty test to assess blurry vision. If you come into my office complaining of blurry vision, I take your visual acuity twice. Once normally, then once with a pinhole covering your vision. If your vision improves with the pinhole, then you just need glasses. As ffca said, when you squint you block most incoming light except the light going directly to your macula (the most sensitive part of your retina) without the optics/physics of your eye refracting it. "
] |
[
"When an individual is squinting or looking through a pinhole, he is eliminating or reducing refractive errors. Most of the light will be passing through the center of the cornea and lens as straight light rays parallel to the axial length, with most refraction being eliminated from the equation altogether."
] |
[
"Are Animals able to reflect themselves ?"
] |
[
false
] |
[deleted]
|
[
"Yes and no, animals have genes that tell them what to do, how to do it, and when to do it. Using your bee example, bees have genes that tell them things, such as how to communicate and obey their queen. So I would have to say YES they did build hexagons but that they PROBABLY WERE perfect hexagons. This shape probably won't change. If they were using a hexagon shape and it has worked this long they probably have it mastered and know that it works great. Much like they shape of a fence, we know that vertical works the best and probably won't change that. I know that was a dumb example but the point is that evolution and gene changes have occurred since the first bee. If they were using hexagon shapes in the beginning then it would have changed if it was a bad shape design. This all depends on what shape they used in the beginning. I personally think they used this shape. And if they thought it was a bad idea they would have changed it in the past MILLIONS of years.",
"Hope this helps. "
] |
[
"I'm afraid I need some clarification. What do you mean by reflect themselves? Are you referring to assessing the quality of their work and trying to do it better next time?",
"I think biology is science too. Don't worry, this is the right place to ask. "
] |
[
"Yes, built a square comb, see it wont work well and next time try another form. And on top of all, give this to the next generation of bees. *bee-o-logy "
] |
[
"Confused about the energy release of hydrogen through fusion"
] |
[
false
] |
[deleted]
|
[
"You need to account for the fact that helium is lighter than 2 protons + 2 neutrons, due to its ",
"nuclear binding energy",
". You also have to be careful with the masses of electrons; 1 H1 is not the same as 1 p, and there are also positrons produced which annihilate some of the electrons.",
"You want (4 × H1 - 1 × He4)c",
"I always get my mass values for individual isotopes from ",
"the Atomic Mass Evaluation",
", to avoid any problems with the ",
"atomic weight",
" that chemists use which is the average over the naturally occurring isotopes. The masses in the AME are of neutral atoms, which is what you want here, because that will keep track of the electrons and positrons for you."
] |
[
"E = (H x 6 - He x 4 - p x 2)c2",
"I'm confused by that step. Can you explain how you got there?",
"The stages of nuclear fusion from hydrogen to helium are not that simple.",
"Check out the full proton-proton chain ",
"http://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain_reaction"
] |
[
"Yes. The whole point behind fusion is that heavier elements do not have a mass of the sum of their individual nucleons - the change in mass is where the fusion energy comes from."
] |
[
"Mirrors and angle of reflection"
] |
[
false
] |
At the atomic level the surface of a mirror (or prism) must look something like a bunch of overlapping spheres (of electromagnetic forces?) lying the same plane. In comes a photon from some direction, why does it reflect along the normal of the plane rather than being scattered somewhat randomly. The only thing I can come up with is that a photon viewed head on is much larger than the molecules that typically make up a mirror so that the photon sees a planar surface rather than a lumpy one. Am I even close?
|
[
"Disclaimer: Undergrad physics major currently taking electrodynamics.",
"The specific frequency and therefore the wavelength of the wave is important for reflection.",
"In conductive materials, light will excite electrical oscillations in the material. These oscillations absorbed the energy of the wave and re-emit the energy as new light. If the light is very high frequency, then the electrons will not be able to oscillate fast enough (smaller wavelength) to absorb the energy, and the light will pass through the material.",
"In non-conducting materials such as glass, reflection has to do with the speed at which light passes through the material. If I understand correctly, this also has to do with light being absorbed and re-emitted by atoms. This process is more complicated than in conductors.",
"So in some way, one can think of it as a matter of size; however, it may be more clear to think of reflection as light interacting with charged particles and being re-emited. I am personally looking forward to others responses."
] |
[
"If a photon is going to be absorbed and then emitted the configuration of the electromagnetic fields must somehow \"remember\" the angle of incidence and compute a reflection angle. That seems plausible if the the photon interacts with many atoms. However my understanding is that a photon dances with a single electron at a time and in that case I don't see how a single electron can \"remember\" the incidence direction."
] |
[
"To clarify, when light enters a medium it causes charged particles to vibrate (regardless if it is an electron or not). If their exists a mode of vibration in the material near the frequency of light, then most of the energy is absorbed and the material is not transparent to that frequency of light. The material does not \"remember\" the direction of propagation.",
"However, if there is no mode of vibration close to the frequency of light then our martial is transparent. The vibrating particles will re-emit light at the same frequency but with an offset phase. The sum of all the waves will form a new wave with the same frequency and direction but slower. The system \"remembers\" direction this way.",
"Note that the geometry of materials actually can determine the modes of vibration. E.G. diamonds and graphite are made of the same materials.",
"Furthermore, this is what leads to different frequencies of light having different indexes of refraction, the mechanism behind prisms.",
"Please feel free to ask anything else or gripe if I got something wrong."
] |
[
"How do unhatched chicks breath through the shell?"
] |
[
false
] |
[deleted]
|
[
"The short answer is the egg shell is permeable for O2 (there are little pores that allow gas exchange.) ",
"Gas exchange in and out of the shell is the least interesting part though (how does the chick breathe without lungs?)",
"https://www.npr.org/2018/04/17/602860545/how-birds-to-be-get-oxygen-inside-eggs"
] |
[
"Good question! If you remove the eggs, this can actually cause the birds to try and nest again. Nest get found by predators, destroyed, etc, if it’s early enough in the season and they lose the nest, they just try again. If you leave the eggs, they’ll keep sitting on them and they just never develop, they’re basically duds. They sit on the eggs, the eggs never hatch, and they don’t make a new nest. At the end of the summer, the parents just migrate like they normally would."
] |
[
"The eggs do need a certain amount of humidity. If they get too dry that is bad as well. However, you aren't too far off about too much being bad. One common method for controlling populations of geese (I think our local zoo did it when the peacocks really got out of control) is removing the eggs from the nest, dipping them in some kind of oil, usually corn oil, and then putting them back in the nest. The oil blocks the pores and gas exchange can't happen anymore. The eggs just don't develop."
] |
[
"Why is the same side of the moon always facing Earth? Is this common among satellites?"
] |
[
false
] |
I know that it's called tidal locking when an orbiting satellite always shows the same side. Is Earth's moon unique in its behavior? Or is tidal locking just a common side effect of orbit?
|
[
"Tidal locking is a common side effect of orbit. In fact, the tidal forces on the Earth exerted by the moon are slowing the rotation of the Earth, causing the days to get longer (by a very small amount). Eventually, the Earth will be tidally locked with the moon (the moon will then be in geosynchronous orbit).",
"The Earth also has tidal forces from the sun, but the tidal forces from the sun are much weaker than the tidal forces from the moon. Without the moon, the Earth would eventually tidally lock with the sun (if the sun didn't explode first).",
"Where there are sufficient tidal forces there is tidal locking. The smaller object tidally locks first.",
"The moon gets stretched along the line from the Earth to the moon, and the lowest energy configuration is for the elongation to stay along that line. If the moon rotated more quickly, there'd be a torque due to tidal forces attempting to keep the elongation along the line of gravitational force (assuming the elongation takes longer to relax than the moon does to rotate the elongation away from the line of gravitational force)."
] |
[
"Yes, planets that are close to their star should be tidally locked (or in some other spin-orbit resonance, like how Mercury rotates three times for every two times it orbits the Sun)."
] |
[
"Since there are tidal forces from the sun, would if be possible for a planet to lock itself into place (one side permanent daylight, the other night)?"
] |
[
"What would be the environmental impact of eradicating mosquitoes entirely?"
] |
[
false
] | null |
[
"According to ",
"this article",
", there are few obvious downsides, since the ecological niche occupied by mosquitos would be filled by other species. ",
"Ultimately, there seem to be few things that mosquitoes do that other organisms can't do just as well — except perhaps for one. They are lethally efficient at sucking blood from one individual and mainlining it into another, providing an ideal route for the spread of pathogenic microbes.",
"\"The ecological effect of eliminating harmful mosquitoes is that you have more people. That's the consequence,\" says Strickman.",
"It's worth noting that several large-scale efforts to eradicate specific mosquito species from local areas (e.g., by dispersing vast numbers of sterile males) have been conducted, with little perceivable impact on the local ecosystems. ",
"This diatribe",
" from Slate.com has some examples."
] |
[
"What do mosquito larvae eat before they grow large enough to fly around sucking blood?"
] |
[
"Worth noting that male mosquitoes never eat blood - it's only the ladies that do, and only for reproduction. Otherwise they all eat nectar. "
] |
[
"Do animals get jetlag the way humans do? Do they recover in the same way and in the same time period?"
] |
[
false
] | null |
[
"This",
" article highlights the fact that our circadian rhythms are programmed centrally by light - and that it involves ",
"epigenetic",
" changes. The feeling of jet lag is a disruption in the light cycle, and returning to a normal light-dark cycle is needed to \"fix\" our internal clocks/relieve jet lag.",
"If the circadian clocks of animals are regulated in the same way, then it would be reasonable to assume that they can experience similar feelings of jet lag."
] |
[
"My god you just asked a mouthful - that could easily be the topic of someone's doctoral dissertation.",
"I have no idea, maybe someone else will know. Definitely an interesting question but I don't know any data about it."
] |
[
"So which animals are similar(where on the evolutionary tree did this start and who is on it)?, and for the ones that are not, how do they experience jetlag?",
"Edit: Spelling."
] |
[
"Can hyenas become domesticated through selective breeding and eugenics?"
] |
[
false
] | null |
[
"Just a point of information: Hyenas aren't canines, they're feliformia (cat like). ",
"http://en.wikipedia.org/wiki/Feliformia"
] |
[
"Damn, I keep confusing them with canines because of their look. Editing the text now."
] |
[
"Given enough time, couldn't any animal be domesticated using the methods you mentioned? I am being naive there?",
"It is possible to keep hyenas as pets in their current state - I'm sure we're all seen the pictures floating around on the internets. I've heard that they will be quite obedient while they see you as the alpha in the situation but if they catch you so much as limping then shit can get ugly."
] |
[
"Of what significance is an angled frame of reference in spacetime?"
] |
[
false
] |
I once read that for objects traveling near c, their frame of reference becomes angled such that what is considered the future for a stationary object becomes "now" in front of a moving object. Are these slices only used to determine the order in which event cones affect the moving object, or can they further be used explain effects such as time dilation, change in length, and chance in mass? Also, does this effect show that our perceived flow through time is an illusion? Thanks in advance, this subreddit is phenomenal.
|
[
"It sounds like you're referring to Minkowski diagrams. They're just illustrations, and they do not preserve lengths or right angles. That's why they make things look stretched and angled.",
"and change in mass?",
"That does not happen. It was once fashionable to teach it that way even though it's incorrect, but that has fallen out of favour.",
"Also, does this effect show that our perceived flow through time is an illusion?",
"No."
] |
[
"I'm not quite sure I understand your question, but anything which determines the order which events are perceived will also have to predict time dilation and such."
] |
[
"They can be used to explain time dilation and length contraction. You wouldn't ",
" to, because representing those effects on a 2D representation of a Euclidean projection of the actual geometry is difficult, but you ",
".",
"Change in mass doesn't meaningfully happen in general, and nothing in physics shows anything about time being an illusion."
] |
[
"It seems to be an established fact that our planet is undergoing climate changes, but is it conclusively proven that this is due to human activity?"
] |
[
false
] |
In the media there has been numerous reports about how our environment is changing, which seems evident and indisputable. I have not ever seen any evidence to suggest that this was caused by human activity and in fact a few months ago it was suggested that we could be headed towards a small ice age because the suns activity was about to go to an all time low. In addition I have heard people make claims regarding the temperature on other planets in our solar system, suggesting that they follow our fluctuations, thus nullifying any correlation between human activities and climate change. Could someone please present the facts in an easily accesible format, preferably with links?
|
[
"I don't know how you could have ",
" the evidence suggesting climate change was partly caused by human activity, unless you've just been ignoring all scientific articles about it for the past 20 years.",
"Currently people are consuming about ",
"3 cubic miles of oil equivalent per year",
", which adds about 36 billion metric tons of CO2 into the atmosphere that wasn't there before. In 2011, CO2 concentration was up to ",
"390 ppm",
", compared to around ",
"270 ppm in preindustrial times",
". ",
"Fortunately ",
"CO2 has a pretty small effect on the temperature",
". If the Earth had no atmosphere at all, the average temperature would be about 60F (33C) lower than it is now, and of that CO2 contributes maybe 4F or 5F (2C or 3C). The revised IPCC climate sensitivity for CO2 is about ",
"2.3C for doubling CO2 concentration to about 540 ppm",
". We're currently up by about .8C with a 44% increase.",
"So it's only 0.8C, or around 1.4F increase so far, doesn't sound like a big deal. But ",
"the poles heat up the most",
", and they have a big effect on global weather. That's why scientists prefer to call it ",
" rather than ",
", because it may not be that much warmer, but the weather effect can be significant."
] |
[
"Oh, nice, our most active climate misinformer is back from ",
"/r/climateskeptics",
" with yet another misleading wall of text.",
"To keep it short, ",
"here's",
" our most recent (and link to previous) \"discussion\" showing the multiple flaws in your arguments.",
"A short answer to your recurring but seemingly more recent talking points: Spencer and Braswell's paper is plainly wrong, not just \"disputed\". It was known to be wrong even before it was published. Lindzen and Choi have similarly been proven completely wrong. Incidentally, both Lindzen and Spencer are known AGW denialists paid by the fossil fuel lobby, via neoliberal \"think\" tanks. Spencer is even on the board of the infamous Marshall institute, a denialist frontrunner also known for lobbying for Tobacco companies against smoking regulations.",
"On your long-term, supposed indirect effects of solar activity: Before 1970, the solar activity combined with comparatively little CO2 correlates nicely with temperature. You usually use this to show the sun's effect on climate. Past the 70s, the sun's activity has decreased but temperatures have gone up steeply. All of a sudden, apparently, this can well still be a solar effect, albeit an indirect one. Pray tell where this indirect effect was before the 70s if the correlation was so good. Does this mean there was no direct effect? "
] |
[
"It doesn't. The temperature trend for the AMO (if it is indeed a real oscillation, which is not yet certain) is flat, while temperatures have been increasing.",
"You really do persist in that misrepresentation, don't you? Do you understand what a linear trend superimposed on a sine wave means? Compare ",
"temperature",
" with a very simple ",
"function",
". In essence curve-fitting, but there's a physical basis for it in the form of AMO. The first term is the warming trend, and the second represents the oscillation. If this kind of oscillatory signal exists in the temperature record, the actual warming trend would be well under 1 degree celcius per century, hardly dangerous.",
"That is inaccurate. The 1970-2000 warming was higher.",
"According to Phil Jones",
", \"The 1860-1880 period is also only 21 years in length. As for the two periods 1910-40 and 1975-1998 the warming rates are not statistically significantly different (see numbers below).\"",
"There is some difference, yes, but in essence they are of equal magnitude and speed.",
"In any case, the effect of CO2 is not linear, and aerosols do have an impact, so it's not a valid argument to look at this and say \"see, the two trends are too similar, it can't be CO2.\" That is simply not a logical argument.",
"Of course not, and I never said as much. I just said that the similarity of the two warming periods is something to consider, especially considering the last 10-15 years of little to no warming which would fit with the 30-year cyclical warming/cooling trends. It is possible that the earlier warming was natural and the latter one CO2-induced and both just happened to be of a similar magnitude and speed."
] |
[
"By my understanding of Special Relativity going really fast makes an object super massive and gives it a strong gravitational pull. How close to the speed of light can we realistically propel an object and would going at that speed cause the object to act like a \"pseudo black hole?\""
] |
[
false
] |
And if going at that speed did cause an object to act like a "pseudo black hole" would the object be able to significantly disrupt the orbiting bodies of any solar systems it passes?
|
[
"You are going at .99999c right now relative to cosmic muons.",
"Velocities are not Lorenz invariable, thus they are only defined relative to a frame of reference.",
"Plus, the increasing of mass when approaching c is an outdated model.\nNowadays, it is believed that the kinetic energy, not the mass increases. "
] |
[
"\"The kinetic energy increases when you accelerate an object.\"",
"I think that's kind of obvious...",
"Regardless, your answer doesn't really give me much information I know how to think about. What would happen to a planet if an object going as fast as we can realistically propel an object were to pass close to the planet?"
] |
[
"The constancy of light causes the decrease of acceleration.",
"If you are interested in the math, ",
"here",
" is a derivation of the Lorentz Transformations. "
] |
[
"Why is it that there is such dense deposits of things like gold in certain regions of the world but others there isn’t in other places?"
] |
[
false
] | null |
[
"Impact events have indeed directly formed some major ore deposits, as well as generating large crustal disturbances and participated in at least one major extinction. There are other, more common geological processes which also lead to formation of ore deposits though, and it's perhaps worth pointing out that those involving 'meteoric' water don't pertain to meteorites (the study of which is often referred to as ",
"), but to water derived from precipitation. ",
"Impact formed ore deposits are also not to be confused with the fact that many ores of economic interest contain elements that were originally delivered to the crust by meteorite impacts. A substantial proportion of the precious metals in the mantle and crust are derived from meteorites that impacted the protocrust during the early stages of Earth evolution, but after the differentiation of core and mantle, which concentrated certain elements (like gold) into the core. So gold and platinum that is mined from ore deposits on the Earth's surface today ultimately had an extraterrestrial origin (the planet's original inventory of these elements being locked away in the core), even though they were likely concentrated to form the deposit by more common geological processes. ",
"None of this is to say your answer had anything wrong with it, just adding in some details for anyone else reading. "
] |
[
"Various elements of economic importance are concentrated by geological processes, these usually involve superheated fluids circulating within the crust. This can cause certain elements to become dissolved within the fluid, if this happens continually over a wide area and then conditions change and the fluid dumps a load of elements that mineralise into veins on a fault plane or fracture, or a stock work of very fine veins within a host rock then it can form a deposit worth extracting. ",
"Some of the strategically important metals, such as Fe, Al, Mg, Ti, and Mn, are abundantly distributed in the Earth’s crust (i.e. between about 0.5 and 10%) and only require a relatively small degree of enrichment in order to make a viable deposit. Fe and Al for example, need to be concentrated by factors of 9 and 4 respectively, relative to average crustal abundances in order to form potentially viable deposits.",
"Gold is particularly rare among the metals that we make extensive use of; average crustal abundances are in the range 4–5 parts per billion (ppb) and even though ore deposits routinely extract these metals at grades of around 5 g per tonne, the enrichment factors involved are between 1000 and 1250 times. ",
"Deposits formed from circulating fluids associated with a rising magma diapir in the crust or with volcanism are a very prospective category of gold deposit type, termed epithermal deposits. The term epithermal refers to those that formed at shallow crustal levels (i.e. the epizone). Studies show that epithermal deposits typically form at temperatures between 160 and 270 °C and pressures equivalent to depths of between 50 and 1000 m. There are two contrasting styles of mineralization that are now recognized in epithermal deposits, and these are referred to as high-sulfidation and low-sulfidation types. These terms refer specifically to the oxidation state of sulfur in the ore fluid, the chemistry and pH of which also relates to the nature of alteration associated with each type. The two terms do not relate to the abundance of sulfur, as this is highly variable in each deposit type, but in you might see “high sulfur” and “low sulfur” in some texts talking about epithermal deposits - these have been equated with high-sulfidation and low-sulfidation respectively. ",
"A hot, acidic, saline ore fluid, carrying gold as an Au(Cl)₂⁻ complex, could be derived directly from the subjacent magma and move directly up into the alteration zone. Ore precipitation would occur as a result of mixing and dilution of this fluid by cooler meteoric waters. Alternatively, it is suggested that Cu and Au are initially removed from the magma in the vapor phase and that these metal charged gases mix with heated ground waters circulating around the intrusion to form a low salinity fluid in which gold is transported as Au(HS). This fluid would then precipitate metals by boiling in the near surface environment, or mixing with meteoric waters, or both. ",
"All magmas contain the constituents that, on crystallization, combine to exsolve discrete fluid and vapor phases. Most magmas will exsolve substantial quantities (up to several wt%) of water, as well as an order of magnitude or so less of carbon dioxide, and these are the two dominant magmatic hydrothermal fluids. Water in particular has the ability to dissolve significant quantities of anionic substances, in particular Cl−, which in turn promotes the dissolution of other alkali and transition metal cations. The magmatic aqueous phase can exist as a liquid, vapor, or homogeneous supercritical fluid. The process of H₂O saturation can be achieved in two ways, either by decreasing the pressure of the system (called first boiling) or by progressive crystallization of magma (second boiling). \nH₂O saturation is particularly relevant to ore forming processes during the emplacement and crystallization of granitic magmas at moderate to shallow crustal levels. This environment gives rise to the formation of a wide variety of important ore deposit types including porphyry Cu and Mo deposits (that stockwork of fine veins throughout a rock), polymetallic skarn ores, granite related Sn–W deposits, and the family of volcanic related epithermal Au–Ag–(Cu) deposit types. Many metals will partition strongly into the liquid or vapor that forms on H₂O saturation and, in such cases, mineralization accompanies the alteration of host rocks, both within and external to the intrusion. Flux of fluids and vapor from the magma and their subsequent circulation are dependent on the permeability of the surrounding rocks, and may be modified by boiling related hydrofracturing. H₂O saturation and boiling in volcanic environments, producing significant volumes of volatile rich vapor, is conducive to the formation of epithermal deposits. High- and low-sulfidation epithermal deposits reflect end-members in a continuum of magmatic-hydrothermal processes that progressively incorporate more non-magmatic waters as the volcanic system wanes, or as one moves away from the volcanic center. ",
"There are also ore deposit types that are the product of fluids unrelated to a magmatic source. The processes of weathering can be responsible for the in situ enrichment of Cu, as well as other metals such as Zn, Ag, and Au, in many deposits that occur at or near the surface. The process is generally referred to as supergene enrichment and is a product of oxidation and hydrolysis of sulfide minerals in the upper portions of weathering profiles. ",
"Placer minerals are those that concentrate at the bottom of a flow due to their higher density, and so are naturally high density minerals which are resistant to chemical weathering. Placer deposits of gold, platinum, copper and zircon may therefore accumulate in the inside bends of rivers, in natural hollows, at the break of slope in a streamer at the base of waterfalls, or at beaches along the edge of a large body of water. This occurs particularly when there are porphry deposits or ore rich veins in the source rock upstream. "
] |
[
"I dont know about all areas, but some rich metal deposits are caused by massive meteor impacts. ",
"I read about a Canadian city called sudbury, which was basically founded for mining. ",
"A massive meteor impacted millions of years ago, and melted a large amount of the ground. ",
"This allowed the dense materials (like metals) to coalesce together and form large deposits."
] |
[
"What happens to alpha radiation once it hits a barrier it can't cross?"
] |
[
false
] | null |
[
"It slows down, grabs onto some electrons, and jus becomes a normal helium atom."
] |
[
"So it's neutralised for lack of a better word? There's no more radiation because it's no longer unstable?"
] |
[
"Neutralized, yes. Alpha particles are never unstable, but once it loses most of its energy, it's no longer ionizing radiation."
] |
[
"Can things truly go in a \"straight line\" when traveling in space?"
] |
[
false
] |
[deleted]
|
[
"According to the general theory of relativity, these orbits ",
" straight lines (geodesics). A cannonball following a ballistic trajectory is also traveling along a line-of-shortest-distance through spacetime."
] |
[
"No. The trajectory of the cannonball, which looks parabolic from the perspective of an observer forced upwards by the ground, is a straight world-line. Space is curved such that its path is straight. It is the electromagnetic force from the ground (upon impact) that wrenches the cannonball from its true path. Your notion of \"straightness\" is aphysical and meaningless. "
] |
[
"No. The trajectory of the cannonball, which looks parabolic from the perspective of an observer forced upwards by the ground, is a straight world-line. Space is curved such that its path is straight. It is the electromagnetic force from the ground (upon impact) that wrenches the cannonball from its true path. Your notion of \"straightness\" is aphysical and meaningless. "
] |
[
"When we learn a new language are we learning it differently to how we learn our first language (instead of adding meaning to words, translating words that we already know into the new language)?"
] |
[
false
] | null |
[
"While most people around me were studying child language acquisition, I took the road less travelled and studied adult language acquisition (at this point, most scholarly studies in this field are mine, thankyouverymuch).",
"The first part of the answer is we all learn differently. And a second (or third or seventh) language is no exception. The second part of the answer is we're ",
" differently.",
"I've lived several different places, learning the language as I went. Costa Rica, Norway, The Netherlands, Italy, France. And I also taught at a language immersion summer camp where kids and teenagers were shipped off to the middle of the woods where their counselors all spoke the target language. Something strange happened with those kids, and eventually with me when I went and studied art conservation in Italy. We got ",
". Really tired. It was a summer camp, a couple dozen excitable kids packed into bunk beds and I thought it would be a chore getting them to be quiet after lights out. What I found was that ten minutes before lights out, at least half of them were sound asleep. I turned the lights out, a few silent whispers for a couple minutes, and then silence.",
"Fast forward a couple years, I was a 20 year old with grant and scholarship money living in Florence. What happened at 10 PM on a Friday night? I put on my sexiest outfit, mixed myself a martini, sat on the couch, and woke up eight hours later after a good night's sleep.",
"Why? Because our brains work overtime. We're identifying patterns, picking out phrases and filling in the rest from context. The same thing we do all the time, but this time it's ",
" and ",
". It's like the graphics card in your computer— it's powering the monitor and GUI, doing the usual, what it can do easily— and then you fire up Crysis 3 with maxed out settings and you realize your computer fan is going full blast. When you speak your native language, you don't hear or even recognize everything said to you, but you understand it. With a new language, you're running Crysis 3 with maxed out settings.",
"That's assuming, however, that you're learning Italian in Italy. You start out translating, but eventually you know enough to start listening in. As you listen in, you stop translating and start ",
". Like a kid. Tell a child, \"Someday you'll be a great astronaut, but for now you don't have the wherewithal to go into space.\" Does that child know what 'wherewithal' means? No, but they know what you're saying.",
"As part of my research, I asked Americans with minimal, societal knowledge of Spanish to translate the phrase, \"",
"\" They'd tell me they don't know any Spanish, but yet most of them asked the same question: \"What does ",
" mean?\" Not only did they figure out the rest of the sentence (some didn't know ",
", however), but they knew ",
" was one word. A good portion of ",
" knew that it was a verb.",
"Now let's say a German student takes a first year Japanese class in grade school. They're translating, yes. But after, say, a year, the usual stuff (\"Hello\", \"Quiet\", \"How are you?\", etc.) are no longer translated. As a kid, we do this naturally because we have to. As adults, we're much more reluctant to take a new language at face value— we have to pick it apart. But it's not a bad thing, we're not doing anything wrong, it's actually quicker and easier to learn the ol' \"Repeat after me\" way since our brains have been set in one language for a very long time. We can't start fresh, having your mom point to herself and say, \"Mom\" and starting from there.",
"So yes, we learn differently. At first. But at some point if we want to become fluent, we have to go back to kid-mode and just figure out with brute brain force."
] |
[
"Amazing response!\nI'm fluent in Spanish and English, and I'm trying to learn Chinese. This post hit home. After I read about the \"extrapolating\" vs. \"translating\", I knew this was relevant. I find that when I see a new word in English or Spanish, it's not a big deal. I can understand even if some words in the sentence are unknown. On the other hand, if I encounter a single word that I don't know in a sentence in Chinese, I panic and I have no idea what it says. Especially, in Chinese, when I translate a newly learned word into English, I supposedly learn the meaning, but I don't know how to implement it into other situations, especially if it has complex usage or something other than a noun. Maybe if I was spending a long time in an immersive environment, I could pick up these kinds of \"extrapolating\" skills native speakers had..."
] |
[
"very interesting read thankyou, I fully understand the mechanism you describe, even though I speak only one language I learned how to read Morse code (at a 'fluent' speed), there is a step where you just hear the sound and the process is automatic you hear ._ and you write down \"a\", it is not long that words and even phrases are instantly understood without any process of translation. I also think much of it would be due to 'context' that you may not understand the word, but you understand the context of it. I also see parallels in touch typing, where to go from thinking about what finger to move for a certain key, do just thinking about the letter and its done."
] |
[
"Trying to teach high school science students about rockets! Anybody experience with water rockets, help us out."
] |
[
false
] |
[deleted]
|
[
"I used to get the sport water bottles with the pop top, fill them 3/4 full with water, drop in a piece of dry ice, and wait for it. The pressure builds up as the co2 goes to a gas and then the top pops open and water propels the bottle across the room. This is probably not the safest for school, as I have seen a few bottles explode."
] |
[
"A coke and mentos rocket would be a much safer alternative."
] |
[
"http://i.imgur.com/uJFsc.png",
"Basically it is a piece of wood with a hole in it for a copper tube to go thru. This was then fed thru the center of a big black rubber cork. There were 4 eyeleted screws in the wood around the cork in such a way that a \"tuning fork\" looking metal thing could slide thru the eylets and secure the plastic rib on the neck of the bottle. This whole thing is elevated with like 12\" 4x4 pieces (so you don't destroy the grass with all that water). The aircompressor (yellow) is attached to the copper tube. viola"
] |
[
"What's causing the strange ice behavior in this video?"
] |
[
false
] |
via :
|
[
"Hi there, since this is a crosspost linked to a very popular video on Reddit at the moment, I figured I should welcome some redditors unfamiliar with AskScience.",
"Welcome to AskScience! We have a few specific rules on this subreddit, you can find them on the sidebar that way --->",
"In a nutshell, please do not respond with personal anecdotes or speculations. Please stay on topic, even though you might have a funny tangent to get that sweet sweet karma (you can post that ",
"joke here instead",
"!).",
"Thanks",
"AskScience Mod Team"
] |
[
"The water, under pressure from the weight of the ice above it, is shooting out of cracks in the ice, and the air temp is cold enough to instantly freeze the water. The new ice lands on top of the other ice, increasing the weight of ice and therefore the water pressure. The water jets out and freezes, and the cycle repeats. "
] |
[
"This is not true. This is simply candle ice that is being pushed onto shore/piling up due to the movement of the ice behind it. I assume the ice movement is due to wind. "
] |
[
"Cryptography: Why can't a one-time pad be half as long as the plaintext?"
] |
[
false
] |
[deleted]
|
[
"The key to a one-time pad is to have a perfectly random key that is never used again. The key your proposing is no longer random, if I guess the original key (0101) I now have your new key (00110011). In practice, what you would do is use two different keys to encrypt the message such that the length of the two keys covers all the plain text you're interested in."
] |
[
"Actually, a 'true' one time pad cannot even be brute forced, since if it was truly random, then your output is truly random, and as you brute force through every possible combination, -every- possible clear text will also appear, with no way of knowing which one is correct. "
] |
[
"It's ",
" easier to guess a key of length n than a key of length 2*n. We're talking computers and GPUs and devices that can do a trillion operations in the time it takes you to (literally) blink."
] |
[
"What mechanism dictates that a particular medications will reach the correct brain region and cells without targeting other brain regions?"
] |
[
false
] |
How can we be so exact in target and location with medication? For example: If a particular substance binds NMDA receptors then how do we control the dynamics so that it binds to the NMDA receptors in the amygdala and not the NMDA receptors of prefrontal cortex?
|
[
"Nothing. If the drug crosses the blood brain barrier into the CNS then a drug will be available to all receptors. In fact, it'll be distributed through the whole body where the organs like the liver (mainly) and kidneys will metabolism it. Depending on how fat soluble it is (like thc) it'll be distributed in body fat.",
"So you probably know the drug is like a key and the receptor is a lock. Well, there's many subtle differences in receptors subtypes so the group of NMDA receptors are similar, but there'll be different glutamate agonist subtypes. This is where the affinity for subtypes comes into play. Each drug acts differently at different subtypes. Take LSD for example; there's well over 15 different serotonin receptors, and each is bound to at different affinities, and can act as a full agonist, partial, or an antagonist (and similarly, and inverse agonist, though we're getting technical now)",
"The take home point is every drug is a cumulative effect of its effects on the receptors subtypes"
] |
[
"Unfortunately drugs aren't as exact as you make them. A perfect drug would have no secondary effect; if they result in other than the intended effect, it is because of unintended interactions with other receptors.",
"Secondary effects may also occur due to an unwanted distribution of the drug. First generation antihistaminic, for example, caused dizziness because they easily crossed the blood-brain-barrier, instead of antagonising only the peripheral histamine receptors."
] |
[
"Then what causes a particular group of neurons of the brain to respond to a drug more so than another group of neurons? Receptor density on a given neuron region? ",
"Sorry if I am misunderstanding. ",
"Thanks"
] |
[
"Could it be theoretically possible to use an atom to store more than one bit of information by reading and rewriting the electron orbital configuations?"
] |
[
false
] | null |
[
"No. The electrons will always fall back to the lowest energy state."
] |
[
"When you ask how an \"atom\" can store information, you have to consider it as a system. The definition of information requires numbering the meaningful number of distinguishable states. This necessitates considering an atom as part of a system.",
"Once you have accepted that, you can use an atom to store all kinds of information given its context in a lattice, its interaction with streams of photons, and in many other ways.",
"It is also important to remember that quantum systems properly can store information in the form of qubits, the quantum analogue of classical memory which tend to have many interesting properties that scientists are very interested in harnessing."
] |
[
"Could qubits aid in classical computers or are they only applicable to quantum computation?"
] |
[
"How can a material remain radioactive after it has been exposed to radiation?"
] |
[
false
] |
I was watching TV today and the topic of the Fukushima nuclear accident was brought up on the news and the reporter had mentioned "radioactive water" which got that way from exposure to radiation from the Fukushima nuclear plant. I just wanted to know how a substance, such as water, can remain radioactive just because it was exposed to either alpha/beta/gamma radiation. What is the mechanism that makes this work? For example, if I expose a glass of water to a bunch of xrays or gamma rays, why is that water no longer safe to drink? How does radiation stay within the substance?
|
[
"It's important to recognize the difference between radiation, and radioactive material.",
"Radiation is the particles and waves which are emitted, which can be ionizing or non-ionizing. ",
"Radioactive materials are atoms which are unstable and emit radiation.",
"Some types of radiation can cause other materials to be radioactive. But in the case of Fukushima, the water itself is not what is radioactive. The water came into contact with the melted core material. The melted core material IS radioactive. Some of the melted core material dissolves in the water, and now the water carries the melted core material with it. So the water itself is clean, but it has dissolved radioactive materials and particles with it.",
"If you were to use ion-exchange and other types of filtration to separate the radiaoctive particles from the water, the water would come out clean and virtually non-radioactive."
] |
[
"As was said, the water is merely contaminated with radioactive materials, but some elements can become radioactive through neutron activation, from being exposed to a neutron flux in a nuclear reactor or explosion . \n",
"http://en.wikipedia.org/wiki/Neutron_activation"
] |
[
"Devil's advocate question: then why do they store all the contaminated water instead of just filtering it? "
] |
[
"How is it possible that neanderthals bred with humans?"
] |
[
false
] |
I happened across this which says that neanderthals bred with humans. I had thought that when species bred with other species then the offspring were unviable or sterile, but the article suggests the dna still exists within the human population? edit.. link to the original
|
[
"This is precisely why they're often classified as a subspecies (",
" to our ",
") rather than a separate species.",
"Interspecific hybrids",
" (breeding between two different species) is sort of a fuzzier matter than the textbook definition of species lets on. It can certainly ",
" for two closely related species (there are even a few examples of intergenus, or even interfamilial hybrids), and we've been doing it for thousands of years (mules). What makes them inviable, and thus considered separate species, is that their offspring are generally sterile (but even that is fuzzy)."
] |
[
"You have to keep in mind that the whole idea of a \"species\" is an artificial construct that humans have created to try to describe living things in the natural world. People spend entire careers trying to determine the distinctions between recognized species, or describing new ones. If you get down to single-celled organisms, bacteria can be exceedingly difficult to fit into the traditional understanding of species."
] |
[
"Not always. Different degrees of hybrid have different success breeding together. Humans and neanderthals were very, very similar. Female Yak-Buffalo hybrids are fertile."
] |
[
"X-Ray crystallography"
] |
[
false
] |
Is it fair to say, "in x-ray crystallography, we're looking at the x-ray shadows of atomic radii in crystals, in the same way that you're looking at the x-ray shadows of atomic radii in bones when you get an x-ray at the doctor's office"? Further- can anyone give me an easily understood demonstration of x-ray crystallography in use? To me it's just dots in pretty radii, I feel like I have to do a lot of hand-waving to explain it to my students because my own understanding is so vague. By demonstration I mean, two or three images of the x-ray crystallography of a simple crystal that I can then compare to its structure to make sense of it. Basically once we have the atomic radii, I'm great from there, but I'm pretty unclear on how we got it from x-ray crystallography.
|
[
"While I'm going to wait for one of our x-ray crystallography experts to give you a detailed answer, I'll start off with this:",
"\"in x-ray crystallography, we're looking at the x-ray shadows of atomic radii in crystals, in the same way that you're looking at the x-ray shadows of atomic radii in bones when you get an x-ray at the doctor's office\"?",
". You are ",
" looking at the shadows of the atomic radii. The reason x-rays are absorbed by heavy elements is because x-rays excite the core electrons (typically 1s-2p depending on what atom). This doesn't work for lighter elements (like carbon) because there aren't enough protons to provide a deep enough potential energy well.",
"X-ray crystallography is a diffraction technique. ",
"Wikipedia",
" does an awesome job of explaining the basics of how diffraction in general works. You might also want to look at the ",
"Young's double slit experiment",
".",
"Because of this, I don't think you can just look at an x-ray diffraction pattern and line it up with a structure unless you have a good intuitive understanding of ",
"Fourier transform space, or q space, or 'reciprocal lattice spacings'",
" (there seem to be a bunch of different names for this)."
] |
[
"They are not the same thing. Bear with me:",
"First, if we could visualize proteins with some kind of microscope, we could. However, light or electron microscropes cannot directly see things at that resolution. Therefore, we must use physics.",
"You know when you shine light through a diamond, and it scatters? That's because diamond's a crystal - a highly ordered arrangement of the same carbon molecule over and over again. The light that's shining through's is roughly coming in the same direction. The refraction generates the split pattern of light.",
"Let's look at a simple cubic lattice. Let's say two atoms are 2 angstroms apart (both parallel to the ground). The light we're using also happens to be 1 angstrom in wavelength. Photons comes directly down (perpendicular to the surface), hit each molecule, and are reflected in every direction. This essentially makes these two points the \"slits\" of the double-slit experiment. ",
"A crystal built with many atoms arranged 2 angstroms apart, so each one of these gives a similar \"double-slit pattern,\" thereby increasing the strength of the original image on an x-ray photographic slide.",
"Of course, in a square lattice, atoms are diagonal of each other as well. Therefore, there is another different \"double-slit\" pattern along another axis. ",
"On the x-ray photographic slide, we see the resulting pattern and, through mathematics that reverse what physics did, infer that the two atoms were 2 angstroms apart and 2*sqrt2 diagonal - therefore a square.",
"A crystallography crystal's the same thing, basically - an ordered collection of proteins (for example). Except there are a lot more atoms. That's why once we get a x-ray diffraction image, it takes a very powerful computer program to re-assemble the original complex molecule.",
"The REASON we use X-ray is because it has very short wavelength. The shorter wavelength enables us to detect things are a finer detail - essentially detect a smaller difference in distance between two atoms. We also use X-ray lasers (light coming in from the same direction, same wave phase) to give a crisper image."
] |
[
"Cool. So since the section where we teach 'em optics, wave particle duality et cetera comes much later, I'm probably starting to exit the remit of this class, here. I suppose I'll wave my hands about x-ray diffraction, and teach it in detail next year after they've had Optics.",
"Thanks :)"
] |
[
"A common question about Horava's (and others') Theory of Everything"
] |
[
false
] |
I recently read about Horava's modification of General Relativity that seems to be a good candidate for a Theory of Everything: And the same question popped up in my mind that I also have about every other serious attempt at a ToE: Does Horava's theory or any other serious attempt at a Theory of Everything (loop quantum gravity, string theory, etc.) allow for faster than light movement or communications?
|
[
"I don't know much about Horava's theory, but string theory still has the speed of light as the speed limit. There are some theories (mentioned in ",
"the bottom section",
") that include a speed of light that is energy dependent."
] |
[
"Experimentally it is well established the c is the local speed limit of matter with positive mass (and the speed that massless particles travel at). FTL travel could be achieved by having wormholes, but most do not believe these solutions to GR could be macroscopic or stable. ",
"I don't feel like reading into this theory, but if anyone wants to read more: check out the arXiv links at the bottom of the ",
"wikipedia page",
" "
] |
[
"Makes me want to learn the details of this stuff just so I can understand it. What's the point of being alive if not to understand the framework by which existence is possible."
] |
[
"Simple question about Aldosterone, pressure, and volume in the kidneys"
] |
[
false
] |
One the effects of aldosterone is The overall effect of aldosterone is to increase reabsorption of ions and water in the kidney -- ( ) However, Boyle's law says that pressure and volume are inversely proportional, so my question is: how does it can it possible that both pressure and volume to rise?
|
[
"Ahhh, this is a good question!",
"The reason lies in the fact that the body's circulatory system is half elastic really. If you do not increase the size of the system, and push more volume into that system, you will increase the pressure. It is by this active process that the blood pressure and volume are increased.",
"This is really only the tip of the iceberg.",
"Aldosterone is released by angiotensin II, which is released by angiotensin I.",
"You might find this ",
"page",
" helpful.",
"The truth is that increasing volume means that we're putting more fluid into the circulatory system, it's not a jar though, it's elastic, it has muscle that can expand and contract to allow for extra fluid, by controlling both the muscle tone of the arterial system and increasing the circulatory volume, blood pressure is increased.",
"Sometimes it's easier to understand this if the opposite is posed: If you cut someone's arm off and let them lose a half gallon of blood, will their blood pressure drop?",
"The respiratory system and the kidneys are actually inextricably linked for very important reasons (acid-base balance) so that's why I know this!"
] |
[
"No, it simply makes the arterioles constrict. The issue here is that you're trying to relate a law about gases to liquids. ",
"By constricting the arterioles it makes the SVR (Systemic Vascular Resistance) higher, and the systolic (active or higher portion) of the blood pressure higher. Putting more volume into the system will typically increase the diastolic (passive or lower/resting portion) of blood pressure.",
"Keep in mind that blood pressure consists of two numbers. 120/80 is very common and what you could think of here. Of course, MAP (Mean arterial pressure) will be increased by either of these, albeit in different ways, because MAP is 1/3 Systolic BP + 2/3 Diastolic BP."
] |
[
"Not that I can find. I think there are too many variables when considering solids or liquids, since both can contain a volume of gas inside their structure, and thus won't necessarily act predictably of their own according.",
"Not to mention that density and compressability varies wildly from substance to substance (albeit less so with liquids than solids) as well as the solubility they allow for, and their own densities."
] |
[
"Geography: What would the climate of the various parts of Pangea have been like? Especially the dry heartland?"
] |
[
false
] | null |
[
"Relevant: ",
"http://www.reddit.com/r/askscience/comments/1dbcoy/panthalassa_was_the_giant_planet_wide_ocean/"
] |
[
"Twas modelled in the following studies (below), although there are some discrepancies between inferred climate and in-situ data from observed palynological assemblages.",
"Overall and unsurprisingly: large parst of gondwana and Laurussia had quite arid desertic climate with upper average dayly temps in the 30 to 40 range. However, seasonal effects were important, notably as bitterly cold average daily summer temps in proto-Gondwanaland (then in the southern hemisphere) as well as monsoons along the eastern gondwanan coast. You can wheedle a lot more detail out of the papers themselves:",
"http://www.ipgp.fr/~fluteau/UIA/articles/7_fluteau-pangea-climate.pdf",
"http://www.geo.utexas.edu/courses/387h/Lectures/term_Erin_Eastwood.pdf"
] |
[
"unless they were migratory I suppose, as the Buffalo or the cariboo. Although they could have been migratory whether they were warm or cold blooded, now that I think of it."
] |
[
"Quantum Entanglement, what about quantum physics makes it work?"
] |
[
false
] | null |
[
"The ansible was based off of the misconception that most people have about entanglement. That somehow one particle reaches out across space and touches the other particle and tells it how to be.",
"The reality is a bit more simple. Suppose you have a particle with no angular momentum. It decays into two particles, each with angular momentum. You have no way to know which particle has which, but you know ",
" that they're in opposite directions because they sum to zero. If you measure either one, you now know which one the other is pointing, but you can't use that to send information at all.",
"So next comes the bit of quantum mechanics that's useful. Because these particles haven't been measured, they exist in a superposition of states. THey are simultaneously up and down/back and forth/left and right. What I can do with my particle is rotate it some (say by 90",
" ), which changes these relationships between them. I measure my particle and phone you up and tell you my result. You measure your particle and between the two measurements, you can calculate which rotation I performed. What we have now done is a perfectly encrypted message. My measurement on its own, tells you nothing. Someone tapped into our line gets no information out of it. Your measurement on your particle, same thing (say it was intercepted in shipping, and measured; in fact, this measurement would destroy the superposition and you'd be able to notice so you could immediately tell me to shut up about my measurement so I don't leak my half of the message). But the two halves together are a nice encrypted channel."
] |
[
"It's not that they're \"invisible gears.\" It's that the two particles are each ",
" of one system. That system must have net angular momentum zero (in my specific case example). But you have no information about which particle points which way. There are two ways to interpret this:",
"The first way is kind of like your invisible gears. In this model (known as local hidden variables) there is some ",
", some unknown quantity that exists that tells each particle about their relative orientation (what my rotation was). In this model, when I rotate my particle, it instantaneously \"tells\" the unknown quantity, the hidden variable in your particle, how I rotated mine, and your particle responds with the right kind of measurement. We don't like this, because there's an instantaneous transmission of \"something\", even if it's not a thing that can be meaningfully called \"information.\" (You can't use it to communicate, for example).",
"The other hand says that these particles truly have no ",
" state (or a state defined by a true superposition, rather than some hidden real thing that can tell up vs. down). In this case, the true superposition allows for my rotation to affect all possible states of my particle and that measurement then comes from the superposition (apparently) collapsing to a specific state for me. That state can interpret the measurement on your particle, also in a superposition, to tell you the rotation I performed.",
"Neither of these is known to be \"more correct\" than the other, they're ambiguous. But we're inclined to think that locality holds (no superluminal transmissions of any kind) and that the quantum world is just truly \"fuzzy\" without real deterministic states."
] |
[
"at a very very rough first glance: yes. it seems that they're saying maybe somehow somewhere we'll get access to those hidden variables and use them to send ftl messages. Well ftl messaging gets wonky with observers moving relative to each other, because it doesn't keep time ordering correct. It can be future directed for one, but past directed into the other, leading to temporal paradoxes."
] |
[
"Say we built an unbroken train around the Equator that could reach relativistic speeds. How does it appear to an outside observer as it approaches light speed?"
] |
[
false
] |
[deleted]
|
[
"I believe you have proposed something very similar to the ",
"Ehrenfest Paradox",
". The train would have to break at a certain velocity because the relativistic effects would stretch it faster than the speed of sound in the train could respond."
] |
[
"Oooo, I like this one. Let's paint it yellow. Then, when it approaches relativistic speeds its color will shift out of the visual spectrum and it disappears."
] |
[
"the relativistic effects would stretch it faster than the speed of sound in the train could respond.",
"Isn't the rate at which the relativistic effects stretch it dependent on the rate of acceleration? If so, couldn't you just make sure to accelerate it at a low enough rate so that it didn't stretch faster than the speed of sound in the train could respond?"
] |
[
"Why do people blame vaccines for links to Autism?"
] |
[
false
] |
I guess I was wondering what the actual argument used against vaccines was, and what evidence, if any can back it up?
|
[
"There was a 1998 study published in the Lancet (which has since been ",
"retracted",
") that is commonly cited. There have been some other correlations identified, but prevailing medical evidence right now suggests that vaccinations are safe. "
] |
[
"The above is absolutely correct. An additional factor is that the diagnosis for autism cannot be reliably made until the child is a toddler (Wikipedia has 14 mths to 3 years and I don't know enough to narrow down the age range).",
"What that means is that the parent will have a child who may be acting a bit strangely and be told that \"children develop at their own pace\". The parent will continue with vaccination while becoming increasingly concerned about their child's development.",
"From the parent's perspective, they will \"suddenly\" be told that their child is autistic and this sudden diagnosis will cause them to seek out the nearest significant event to blame it on. (source: an otherwise rational friend of mine is utterly convinced vaccines harmed her child and made him autistic even though her sister recalls the mother being concerned early on).",
"TL;DR: confirmation bias tends to lead parents to blame unrelated events for the negative diagnosis"
] |
[
"The fraudulent study was by ",
"Andrew Wakefield",
"is a British former surgeon and medical researcher, known as an advocate for the discredited claim that there is a link between the measles, mumps and rubella (MMR) vaccine, autism and bowel disease, and for his fraudulent 1998 research paper in support of that claim"
] |
[
"Why is water boiled in power plants as opposed to other liquids?"
] |
[
false
] |
E.g those with lower boiling points. Surely this would mean less energy is required to cause evaporation and therefore generate electricity.
|
[
"Wouldn't the amount of energy harvested be the same regardless of the temperature of evaporation? In which case it doesn't matter which liquid is used, therefore engineers would use the cheapest available, water. "
] |
[
"E.g those with lower boiling points.",
"Just the opposite!",
"The theoretical maximum ",
"efficiency of a heat engine",
" such as a generator is:",
"1 - T_c / T_h\n",
"where T_c is the cold reservoir and T_h is the hot reservoir. The cold reservoir in a power plant is typically ambient temperature (water from a river, for example). To maximize efficiency, you want the hot temperature to be as hot as possible so that the T_c/T_h term goes towards zero.",
"Thus far, water's practical advantages (it's cheap, non toxic, etc.) and its good-enough thermodynamic properties have made it the dominant coolant in power plants. You can use other coolants with higher boiling points, such as molten salt. ",
"Here are some pros and cons of that.",
"Remember that you don't have to just accept water's boiling point at normal atmospheric pressure (known as a \"boiling water reactor\"). You can pressurize it to raise the boiling point and thereby increase efficiency (a \"pressurized water reactor\")."
] |
[
"Do you have a news article for this? There no way a plant fire and explosion with liquid sodium could be covered up without the press knowing."
] |
[
"What mechanical motion of the body can exert the theoretical maximum amount of force?"
] |
[
false
] |
For example: even though the swinging of a golf club makes a golf ball travel farther than kicking a soccer ball, is there really more force being exerted on the golf ball through the swinging motion? What motion (swinging, throwing, kicking, etc.) produces the most force?
|
[
"I'm also interested in how much average power produced during the clean movement by certain weightlifter, for ex:",
"http://www.youtube.com/watch?v=QPO0LuDxXUE",
" So I found this:",
"4786 watts for a 110 kg lifter.\n",
"http://www.livestrong.com/article/406603-olympic-weight-training-stats",
"Now compare this to other type of movements."
] |
[
"There's a difference here between force and power. Raw force is the same as \"what's the maximum weight one can lift\", and it would probably be either a squat in a smith machine or a leg press - i.e. something which uses large muscle groups and doesn't need much stabilizing. ",
"Power on the other hand is about how fast force can be applied - can't really guess here. ",
"As for the golf ball, it's yet something else: impulse, which is speed times mass. In case of a golf club, it matters how fast the club's \"business end\" is moving, and how heavy it is - the momentum will be transferred almost completely to the golf ball. The easiest way to increase momentum is to have a longer club, this way you can apply more power at the handle and translate it into speed at the opposite end."
] |
[
"Discovery channel did a series on different martial arts kicks and their power, on iPod but just YouTube it, also Bruce lees side kick produced extreme amounts of power. Sorry I can't provide links :( \"martial art tricking\" artists also generate extreme power through their kicks. Though never have been tested as. Far as I know."
] |
[
"Is there a way to shield a magnetic force by placing something between two magnetic objects?"
] |
[
false
] |
Like if you had a magnet attracting an object, and you placed something between the magnet and the object, could you decrease the attractive force?
|
[
"Magnetic fields (forces are caused by magnetic fields) cannot be blocked, no. That is, there is no such thing as a magnetic insulator.",
"A major reason for this has to do with one of Maxwell's Equations, implying that there are no magnetic monopoles. That is, where as you can separate electric monopoles (positive and negative charges) such that an E-field never has to terminate on the opposite charge, you cannot do this with magnetic poles. There do not exist any magnetic monopoles. There is no such thing as \"magnetic charge.\" All magnetic field lines MUST TERMINATE on the opposite pole. Because of this, there is no way to stop them -- nature must find a way to return the magnetic field lines back to an opposite pole.",
"However, magnetic fields can be re-routed around objects. This is a form of magnetic shielding. By surrounding an object with a material which can \"conduct\" magnetic flux better than the materials around it, the magnetic field will tend to flow along this material and avoid the objects inside. This allows the field lines to terminate on the opposite poles, but just gives them a different route to follow.",
"You might want to check out:\n",
"http://www.lessemf.com/faq-shie.html#Lead-Copper",
"\nWhich does a good job to answer your question directly."
] |
[
"You can use materials with high magnetic permeability (Permalloy to name one), which more or less captures the magnetic field. This is however much more the case and effective for closed containers, that are sometimes stacked one into another like Matryoshka puppets..."
] |
[
"Im not an expert but I’ve read that magnetic or electric fields can’t get any deeper than 100nm into superconducting things. (Meissner effect? I think?) so if you build a box out of superconducting material the inside should be free from magnetic or electric fields, if there is nothing inside that creates them?"
] |
[
"In the show Lie to Me, the main character has an ability to read faces. Is there any backing to that idea?"
] |
[
false
] | null |
[
"The idea is based off the theory that people produce \"microexpressions\" that last fractions of a second, with the assumption being that we can read these microexpressions subconsciously. However, further study found that professionals trained in microexpressions had no higher odds of success than random chance. It's a debunked theory at this point."
] |
[
"This is a good answer.",
"As a social worker (msw) we are intensively trained in applied communication. If there's no incongruence between observable actions, stated actions, mood and affect, then there's no way to tell if someone is lying. This is why it can be very important to have collaterals as sources (family members etc). ",
"Hypothetically let's say sometimes there are micro expressions after a lie. Theres no way for you to differentiate the micro expression from random facial movements/reactions to internal or external stimuli.",
"Edit:",
"I do not have time right now to log in and collect research articles but at face value this appears to be decent for further reading:",
"https://www.psychologytoday.com/us/blog/spycatcher/201112/body-language-vs-micro-expressions"
] |
[
"University Psychology Professor here (33 years).",
"Nope. No peer reviewed support for determining the veracity of statements a person makes by reading their faces. Doesn't work.",
"But also Lie Detectors are also pure theater. Cannot be used in US courts, no validity. Used as an interrogation tool."
] |
[
"Radiocarbon Dating, How does one calculate what the original amount of carbon was?"
] |
[
false
] |
My understanding of Radiocarbon Dating is pretty basic but from what I know you take find the amount of carbon-14 in the sample and use its half-life to calculate the original amount of carbon was. What I don't understand is that if one uses the half-life to calculate, you can keep doubling that to infinity. How do scientists know when to stop?
|
[
"C-14 is formed in the upper atmosphere. It reacts with oxygen to form CO2, and get distributed throughout the ecosystem. So long as an organism continues to taking in carbon from its environment, its C-14 \"supply\" will be continuously refreshed, and the ratio between C-14 and regular carbon (C-12) will remain roughly the same.",
"But when it dies, it stops taking in C-14, which then starts to decay. For a new sample, there should be amount 1 C-14 atom for every trillion C-12 atoms. For a sample 5600 years old, that ratio is 1:2 trillion, 11,200 1:4 trillion, etc.",
" We measure the ratio of C-14:C-12, and compare it to what it was originally "
] |
[
"This is right. I'm commenting just to add ",
"this",
" image to accompany your explanation.",
"Also, I want to highlight the point that the Carbon-14/Carbon-12 ratio is fairly constant. That seems to be the point that OP missed. Since it is constant we already know the original ratio of what is being analyzed."
] |
[
"For the most part, yes, but there are some exceptions, like the Old Carbon problem.",
"Some aquatic organisms live near limestone, which slow leeches its carbon into the water. Since this will be very old carbon, the resulting ecosystem will be disproportionally C-14 deficient. "
] |
[
"How many diseases can we develop immunities for?"
] |
[
false
] |
I know that our immune system can essentially "remember" certain types of diseases to respond rapidly to them. Is there a limit to the number of diseases we can develop an immunity for?
|
[
"From a basic immunology point of view, humans can generate around 5 x 10",
" distinct antibodies (immunoglobulins) via the adaptive immune system that use VDJ recombination, Junctional Diversity and Somatic Hypermutation. Of course, not every combination will be successful, so people generally say around 10 billion. ",
"It’s for this reason that the adaptive is slower to start once the innate triggers it — making the best and most specific antibody to the antigen takes multiple tries. ",
"Scientists estimate that there around 10",
" environmental antigens in the world. So in that literal sense, we can be covered.",
"Of course, not every microbe will trigger the adaptive immune system and thus, prevent the need to generate a new antibody. The innate immune system can wipe a microbe before triggering the adaptive immune system and prevent the process that makes antibodies for immunological memory. ",
"Please correct me if I’m wrong. It’s been a while since I’ve taken intro immunology!"
] |
[
"The compliment can be considered ",
" Compliment systems act to enhance immune responses, namely the antibodies and phagocytic cells.",
"The compliment can be subdivided, broadly speaking, into 3 pathways:",
"Alternate and Lectin pathways are mainly innate processes. ",
" pathway is activated when a protein, C3B, binds to a pathogen surface, and leads to the recruitment of other \"C\" proteins. Alternate is usually first to act. They can be used for pathogens that you've never been exposed to. On the other hand, ",
" are proteins that recognize very specific sugar patterns on the surface of bacteria, fungi, etc.",
"After binding of the lectin ",
" the C3B protein, it can then lead to the formation of a protein complex that perforates the pathogenic cell membrane. They can increase the efficacy of phagocytosis. They will also recruit inflammatory cells. ",
"The Classical pathway involves ",
" and is last to act.",
"Let’s say you have already been infected and fully recovered from a particular pathogen.",
"The second time that ",
" pathogen comes, circulating antibodies (specifically IgM and IgG antibodies; these will be in the blood constantly) will be able to quickly bind to that antigen, form a membrane attack complex, which then leads to many effects, such as the perforation of the invading cell membrane, facilitate opsonization (making the pathogen more susceptible to phagocytosis), and recruitment of inflammatory cells.",
"The 2nd time that same invading pathogen comes, the immune system will have a ",
" time clearing it due to the classical compliment system, since your body has formed an immunological memory for it.",
"In this case, the classical pathway is ",
" as the antibodies are always present in the blood and ready to activate the compliment system.",
"Its for this reason that I say its ",
" ",
" and ",
"."
] |
[
"The innate immune system can wipe a microbe before triggering the adaptive immune system",
"Is part of the 'innate immune' compliment?"
] |
[
"How were heavier elements than iron created?"
] |
[
false
] | null |
[
"There are other nucleosynthetic processes, like the r-process, the s-process, and the p-process, which produce the heavier elements.",
"Here",
" is a table of the dominant production mechanism for each element."
] |
[
"Hi! Doesn’t the explosion itself from the ensuing supernova create heavier elements as well?"
] |
[
"Thank you! That does answer my question"
] |
[
"Can an ECG read voluntary muscle contraction ?"
] |
[
false
] |
From my understanding of how ECGs work, wouldn't an ecg reading pick up the action potential generated by skeletal muscle contraction in the same way it picks up the electrical impulse caused by the heart muscles ?
|
[
"Yes, it's called an EMG."
] |
[
"An ECG does tend to have background noise from chest movement. To measure skeletal muscle contractions you would use an EMG. (Which can have surface leads like an ECG, or have standard leads which involve piercing the skin with a needle electrode and measuring nerve impulses directly from the muscle.)"
] |
[
"Moving around a lot can definitely make an ECG harder to interpret. Even breathing can cause weird stuff on an ECG. Those are called \"artifacts,\" and whoever is interpreting the ECG has to figure out what to attribute it to. They'll always attempt to keep interference to a minimum, but there will be external input showing up on an ECG. As to your question, a significant amount of chest movement, like if the patient is shivering, would definitely show up. Take a look at this article, it's very user friendly. ",
"https://www.aclsmedicaltraining.com/blog/guide-to-understanding-ecg-artifact/"
] |
[
"Animals that camouflage themselves - how do they know?"
] |
[
false
] |
I feel like every question I ask here is derp, but here goes: I wonder about animals that camouflage easily - how aware are they that they are doing so? I assume the majority of the answer is that they evolved to be great at camouflage, but at any point is it known to be a conscious thing? Would an insect that resembled the leaf of a particular plant, if given a choice, gravitate toward that one for safety? Is it that they evolve to resemble the plants that they are most likely to hang out on (ex: their food source) and that's all there is to it? Would a pink fish choose a pink coral to hide in over a white one? What about higher animals? Does a brown rabbit know that it's harder to see in brown grass than in green?
|
[
"A pink fish probably became pink because it probably hangs around pink coral a lot. After these fish evolves pink scales, some may have also hung around white coral, but those ones may have been more likely to be eaten. This promotes pink fish staying near pink coral.",
"As for whether or not it's conscious, we can't determine universally, and even then it's difficult. A fawn's mother is likely to hide their child in shady grassy area and it's likely to know this is where it's safest, but we'd have a hard time determining whether or not it knows its spots are the reason why. For something dumb like a fish it's highly unlikely they're conscious of what they should chill by (pink coral) to improve survival. Instead, the pink fish that survive longer have evolutionary bred instinct to chill there."
] |
[
"The octopus biologist ",
"on NPR",
" says that for octopi it's a delocalized system; the cells merely react to whatever they're near, without any coordination by the brain."
] |
[
"I believe its all about survival. ",
"This video is a brief explanation on it",
". Imagine organisms as totally mindless, moving creatures that just eat, breed, and poop. The ones who have the 'safest' genes (Ie. Brown frog vs green frog in a brown swamp) will survive. They have no opinion in the matter. "
] |
[
"What is happening when a computer generates a random number? Are all RNG programs created equally? What makes an RNG better or worse?"
] |
[
false
] | null |
[
"RNGs use some algorithm to decide on a number which is based on the some previous number (or more over a large set of previous numbers) this is why all RNGs need a seed to get started, they need some way to generate the first letter. How you get that seed is a bit of a different discussion.",
"Now not all RNGs are equal, there a few ways to make how random it is, one is to use a chi-squared method to see if the distribution is random (ie normally you want a uniform distribution). You can also plot the current number as a function of previous numbers (known as a k-space plot) the higher dimension you can graph in without some pattern emerging the better. Finally you can look at the period of the number generator, the number of numbers you must generate to begin seeing a pattern emerge. For a very good generator like the mersenne twister method the period is 2",
" -1 numbers (so you should never see the same number pattern appear for practically all situations)",
"Edit: spelling "
] |
[
"Some great answers here talking about what makes a good pseudo-RNG. I'm going to tell you about a bad one.",
"In Pokémon Red, Blue, and Yellow, when the player encounters a wild Pokémon, the species is determined by comparing a random value between 0 and 255 to a lookup table for the current location. For example, the game might make a Rattata appear if the number in question is 0 to 127, Nidoran♀ if the number is 128 to 216, Spearow if the number is 217 to 242, and Nidoran♂ if the number is from 243 to 255.",
"The Gameboy has a weak processor and it runs games at 60 frames per second. Rather than running a random number generator 60 times per second while the player is walking through areas where Pokémon are found, the \"random number\" predictably increases by one 30 times per second. This might have been a reasonable solution for some applications, but when it comes to generating random Pokémon encounters, it has a problem: The RNG loops every 8.53 seconds, and in some circumstances, the length of a battle can be very close to that time. This means that a player can have a series of encounters with the same Pokémon because the RNG is returning a similar result every time. "
] |
[
"There's an implicit assumption in the vast majority of these answers that computer random number generators are ",
", and that random number generators must be implemented in ",
" unless you hook the computer up to a physical hardware random number generator.",
"That just isn't true, and in fact computers have been generating random numbers using much more sophisticated techniques.",
"The most recent advancement is that since 2012, all new Intel processors ",
"include a hardware random number generator built-in",
". It uses a hardware entropy source that is believed to be impossible to predict or bias within the limits of today's technology.",
"Even if your computer doesn't include a hardware random number generator, your operating system provides functions that use external sources of entropy. For example, Linux uses ",
"timestamps from the keyboard, mouse, network, and disk",
" as a source of entropy.",
"We call these inputs sources of entropy because they're highly unpredictable - but they don't give us other desirable properties of random numbers, like uniformity. We want all numbers to be equally likely.",
"To spread out the entropy through all bits of the random number so that all of the bits are equally likely to be either one or zero, a cryptographic hash function is used - for example, Linux uses SHA-1. This results in a ",
"cryptographically secure",
" random number - one that guarantees that there's no polynomial-time algorithm that could predict the next bit or recover previous values in the sequence.",
"Not all applications need random numbers that good. But it's a myth that ordinary computers can't generate good random numbers. They can, and they do. If they didn't, attackers would be trying to attack flaws in random number generators to break encryption."
] |
[
"How many degrees of the FOV (in human sight) is color?"
] |
[
false
] |
Is color generally only "recorded" by the fovea? If not, how large is the area where we sense color in terms of size of cell structure, and more importantly: how many degrees of vision does this constitute?
|
[
"You get colour vision outside of the fovea, though how far out depends on what you're discriminating and how big it is. ",
"This article",
" cites work that finds colour discrimination as far as 90° out:",
"They found that subjects could detect chromatic bars out to at least 50° on the nasal horizontal meridian, and temporal chromatic contrast out to at least 90° on the temporal horizontal meridian."
] |
[
"So my peripheral vision around my nose is not in color? "
] |
[
"Right, chromatic bars is one thing, but has anyone tried with lower contrast material, like TV images, photos, or something similar?"
] |
[
"Does the amount of plastic in contact with a substance change how much chemicles are leached into that substance?"
] |
[
false
] |
So say I have an entirely plastic water pitcher and a mostly stainless steel water pitcher with a small plastic window; assuming the plastics are the same and that they leach something, would the water in the mostly stainless steel pitcher have less chemicals leeched into it? (Assuming same amount of water)
|
[
"Assuming you have a plastic that leaches chemicals, and the plastic does not run out of those chemicals, both bottles will experience the same amount of leaching. The end product will be water containing the same amount of leached chemicals. ",
"However, the rate of leaching will be much faster if the fully plastic bottle. "
] |
[
"The concentrations would only be the same at equilibrium if the amount of leached compound was insignificant compared to the total concentration of whatever chemical is being leached from the plastic, though. Eventually that assumption would no longer hold, and more of the leeched compound would be present in the all plastic pitcher. "
] |
[
"Yes, I made clear that assumption in my comment. "
] |
[
"Energy of a wave is proportional to its amplitude. Energy of a photon is proportional to its frequency. How do those two propositions \"connect\"?"
] |
[
false
] |
[deleted]
|
[
"This was one of the big concepts in the early days of quantum mechanics. You might look up the story behind the photoelectric effect. The short version is that a light wave has total energy built up in discrete units (photons). You can think of the amplitude of a wave as being proportional to the number of photons it is composed of. Since each photon carries a chunk of energy, the total energy of the wave is proportional to the amplitude. However, the energy of each ",
" photon is proportional to its frequency. This doesn't mean that the total energy of the wave is necessarily proportional to its frequency, unless the number of photons is held constant. For example, you could have two waves with the same total energy but different frequencies, it would just mean that the low frequency wave would have to have more photons than the high frequency wave."
] |
[
"It may be worth adding that the classical limit of an electromagnetic wave requires a non-trivial limit. Others have already said that the energy is proportional to the number of photons N, but it is also proportional to ħ. It turns out that the classical limit involves taking ħ to zero and N to infinity such that ħN is fixed.",
"I say this is nontrivial because the energy of the quantum system involves ħ, and the ħ is a dimension-full constant which cannot be taken directly to zero. Rather then discussing electromagnetic waves/photons, let's just discuss a one-dimensional simple harmonic oscillator (photons/light of a given frequency are actually just a particular case of this with some ugly constants added in that I'm too lazy to think about right now). This can be described either classically of quantumly with the Hamiltonian",
"H = (1/2)p",
"/m + (1/2)mω",
"x",
"If you don't know what a Hamiltonian is, it doesn't matter, but the point is that this describes an oscillator, and a solution to the classical equations of motion (usually called Hamilton's equations for this approach but they're really just F=ma where F=-dH/dx in this case) is",
"x(t) = A cos(ωt)",
"So it describes a particle oscillating with amplitude A and frequency ω. The total energy is given by",
"E = mω",
"A",
"/2",
"Now if you solve this problem quantum mechanically the way you usually do in an undergrad quantum course, you usually learn about the states which have definite energy, and from this perspective the classical limit still seems rather mysterious. You find that you have a set of discrete states which have energy ħω, 2ħω, 3ħω, 4ħω, etc. When the SHO is applied to electromagnetism, this is interpreted as a state with 1 photon, 2 photons, 3 photons, etc. However, as first noted by Schrödinger a few months after publishing his famous equation, the correct states for the classical limit are the ",
"coherent states",
", which are a linear combination of definite energy states. Interestingly, these states have the minimum uncertainty allowed by Heisenberg's uncertainty relation. As usual in quantum physics, quantities like position and energy are actually not well-defined, but you can calculate an average position and average energy. In a coherent state where the average of the \"number of photons\" in N, the average values of position and energy are",
"<x(t)> = sqrt(2ħN/mω) cos(ωt)",
"<E> = Nħω",
"We can compare these to the classical values, and we find that a classical wave with amplitude A is really a quantum wave with \"photon number\"",
"N = A",
" (mω/2ħ)",
"in the limit that ħ goes to zero, N goes to infinity, but we keep fixed",
"ħN = A",
" (mω/2)",
"I should also note that in this same limit, the probability distributions for x(t), E, and all other quantities of the coherent states all become very sharply peaked around these average values, to that the states become classical in that you no longer need probability distributions. Basically, as I said before, these states saturate the Heisenberg uncertainty principle, meaning the product of the uncertainties is proportional to ħ, so they go to zero as ħ goes to zero.",
"Note that a crucial point in all of this is that quantum mechanics has an extra dimension-full constant, ħ, which means that the quantum oscillator problem has an intrinsically defined length scale given by sqrt(ħ/mω)."
] |
[
"It doesn't make much sense to talk about the energy of an ideal classical wave, since ideal classical waves are infinite in extent and thus would have infinite energy. We can, however, talk about the energy per unit length of a classical wave. We can think of such a wave as a bunch of simple harmonic oscillators moving in sequence. The equation of motion of a simple harmonic oscillator is",
"x(t) = Acos(wt)",
"where A is the amplitude, w is the angular frequency (f/2pi), and the phase is taken to be zero (since it won't matter for these calculations).",
"Now the energy of a simple harmonic oscillator is given by ",
"E = 1/2kx",
" + 1/2mv",
"where k is the spring constant. We can work out what the spring constant must be for an SHO with frequency w. Remember Hook's law",
"F = -kx",
"so",
"k = -F/x = -ma/x",
"a = d",
" x/dt",
" = -w",
" Acos(wt)",
"therefore",
"k = mw",
"Also",
"v = dx/dt = -wAsin(wt)",
"so we get",
"E = 1/2mw",
" (Acos(wt))",
" + 1/2m(-wAsin(wt))",
"= 1/2mw",
" A",
" ((cos(wt))",
" + (sin(wt))",
" )",
"= 1/2mw",
" A",
"So the energy of a simple harmonic oscillator, and therefore the energy per length of a classical wave, depends on amplitude ",
" frequency. ",
"As has already been pointed out, the energy of a single photon is proportional to frequency, and we can think of the amplitude of light as being proportional to the number of photons (ie. intensity), so the total energy of some amount of electromagnetic radiation will be proportional to both the frequency and intensity of the radiation. "
] |
[
"Why are Birds sub-grouped under Reptiles and not in their own unique standalone class like Amphibians?"
] |
[
false
] | null |
[
"When we classify animals today we base their relationships on a shared evolutionary history. The taxa we name must consist of a common ancestor and all of the descendants of that common ancestor. It's called a monophyletic group. Any other type of group is arbitrarily excluding descendants and won't actually reflect their shared evolutionary history. ",
"We determine these relationships using different sources of data, including DNA and the morphology of living and fossil organisms. Groups are united by features that they share and that are unique to them (or \"derived\"). They will also possess traits that are present in other groups and are \"ancestral\". It's not always straightforward, because things like convergent evolution can happen.",
"Reptiles were traditionally defined by what they're ",
": they were animals that lay hard-shelled eggs (amniotes) that ",
"aren't mammals or birds",
". The term \"reptile\" was used to classify cold, scaly animals into a group, but that completely ignores how they're all actually related. Even some groups more closely related to mammals were considered reptiles, so if you wanted to include everything classically referred to as a reptile in a monophyletic group, you'd just have a group with ",
"every amniote",
", including mammals and birds. If you make the group more restrictive but exclude birds, you're not including all the descendants of the most common ancestor shared by all reptiles. And it seems silly when you think about things, like the fact that we know ",
"crocodylians and birds are each other's closest living relatives",
". Saying crocs are reptiles but birds aren't doesn't change that fact, but choosing to ignore that relationship makes it harder to understand the evolution of these groups. Once you start to look under the hood, you see incredible similarities between birds and other reptiles. Birds are dinosaurs, through and through, and it's really cool.",
"I do want to caution you based on how your question is phrased. Unless you're looking at an independent derivation of life, there's no \"standalone\" group. There are lots of hierarchical taxonomic groups, and birds certainly form a monophyletic group. ",
"It's funny that you considered amphibians to be your counter example, because they're ",
" monophyletic! There are amphibians that are more closely related to amniotes than they are to other amphibians. You can't make a monophyletic group that includes all amphibians but excludes tetrapods (",
"this page",
" has some decent discussion about it). Even ",
"Lissamphibia",
", the subgroup of amphibians that contains modern amphibians like frogs and salamanders, might not be monophyletic! Edit: although the consensus view is that Lissamphibia ",
" monophyletic - the issue between molecular and fossil data seems to be largely resolved! ",
"TL;DR: The owls are not what they seem. "
] |
[
"Well, if you're not a morphologist, then it probably would seem like guesswork. It's...not. ",
"The vast majority of species that have existed are extinct. Morphology is a crucial component in the study of the relationships of life in earth, evolution, ecosystem change, you name it. "
] |
[
"The latest research, based on a stem-caecilian from the Triassic, reconciles the fossil and molecular evidence by concluding ",
"lissamphibians are monophyletic",
"."
] |
[
"Can multiple planets exist in the same orbital path?"
] |
[
false
] |
My understanding of planetary formation is that a disc of material eventually coalesces in a singular object, but is it possible that it happens in one or more locations in the same orbit? Could there be two planets on opposite sides of a star orbiting in sync? Could earth have a twin behind the star that we never see?
|
[
"Some scientists theorize this is how we got our moon.",
"We had a planet close to the same orbital path that got a little too close one day and the two masses collided, on enveloping most of the other and the remains kept as our moon"
] |
[
"Janus and Epimetheus share orbits around Saturn. Yes they are moons not planets, but it's not that hard to imagine planets doing the same. If it happened within our Solar System (and was independent of us evolving - it was) then it should have happened in many other places.",
"You do not need an exact match, very similar orbits are sufficient. As the inner (faster) object approaches the outer object it is pulled forward, reaching a higher (slower) orbit while the outer object gets pulled backwards, reaching a lower (faster) orbit, so the two objects recede again. Once the faster object moved ahead by almost one orbit the process repeats."
] |
[
"If there is a significant size difference between the planets, the only possible stable orbiting solution is at one of the ",
"Lagrange points",
". Jupiter has a collection of trojan asteroids at its L4 and L5 points. The opposite side of the star, you are referring to, is called the L3 point.",
"Because protoplanets change their mass and orbit during accretion, there is unlikely to be a second protoplanet that forms at precisely the same orbital path."
] |
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