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[
"How does a computer/device know how much battery life it has left?"
] |
[
false
] |
I was just thinking about this. Curious about what type of measurement is used to measure time and life.
|
[
"There are basically two ways to do it. Either you measure the voltage on the battery, and calculate remaining charge based on the discharge curve, or you route charge going into and out of the battery through a low-resistance shunt, and measure the voltage drop across the shunt to get the current draw, and count coulombs into and out of the battery. ",
"The first solution is cheaper and less accurate, and the second method is more common in applications where the cost of the battery is small in relation to the cost of the product (I.e. laptop batteries and smart phones)."
] |
[
"I designed a circuit that did this while doing another project, but it was just to have a quick battery indicator for the project so this is just how I did it once, not industry practice. Battery powered electronics of any complexity must use voltage regulators to produce a nearly constant voltage or voltages from the varying voltage provided by the battery. Batteries rated as 7.2 V would be 8 V with a full charge, and my circuitry worked off 5 V.",
"It included a microprocessor with a free analog-to-digital pin, so I put in a high-resistance voltage divider with equal resistors to generate a voltage half of the unregulated battery voltage. This was because the microprocessor is limited to working with 0-5V. The analog-to-digital input read in this voltage and it was available as a number of millivolts (after multiplication by a scaling factor) to be queried by my status command.",
"Typically the batteries would have a discharge curve where they started off with a high voltage that quickly fell to nominal, lingered around there slowly decreasing for a while, and then dropped quickly as they were depleted. So from the voltage readings you see how in a consumer device a percentage could be estimated- you'd probably have a more well-designed measurement circuit than an inaccurate voltage divider, and there's small inaccuracies for various reasons, but it works."
] |
[
"This is actually how it's done for a lot of low-cost devices. Works well for disposable batteries, but not for lithium-ion batteries, which have a flatter discharge curve. "
] |
[
"How is the universe infinite, if it started small and continues to expand?"
] |
[
false
] |
If we assume something along the big bang theory is approximately correct, and that the universe is still expanding from a singularity that exploded billions of years ago... then we can say, perhaps a few milliseconds after the initial "explosion", the universe was rather small. For the sake of argument, let's say at X time after the event, the universe was 100 miles in circumference. Then, at some time later, it is 1,000 miles in circumference. And so on and so on as it continues to expand. This begs a couple of questions. What is the universe expanding into? And, how is it infinite if it's a measurable size at a given point? Doesn't the fact that it had a beginning, and will likely have an end, mean it is not infinite? I know the stock answer is that nothing extends outside the universe. But, how do we know that for sure? Why can't there just exist an unknown emptiness, and our universe is merely comprised of all the "stuff" filling the emptiness from our particular explosion. And, that perhaps the emptiness is full of other universes separated by vast expanses? Much as different galaxies are separated by interstellar space within our own universe, how do we know our entire universe doesn't exist in similar manner just on a much bigger scale? Aren't we a bit too small to see the whole picture?
|
[
"we can say, perhaps a few milliseconds after the initial \"explosion\", the universe was rather small.",
"That doesn't necessarily follow. It's entirely possible for the entire universe to have \"begun\" in a singularity, but to have been infinite at ",
" times after the initial singularity. See ",
"here",
" for an analogy involving am infinite, expanding, one-dimensional universe that exists as a singularity at time zero.",
"What is the universe expanding into?",
"Nothing, so far as we know. Even if it's finite, there doesn't have to be an \"outside\".",
"Doesn't the fact that it had a beginning, and will likely have an end, mean it is not infinite? ",
"First, no; see above. Second, there's no reason to assume it will \"have an end\".",
"how do we know that for sure?",
"Well, we ",
" know for sure. However, all of the evidence we have is ",
" with there being no outside, so hypothesizing that there ",
" an outside isn't particularly helpful: it's an unnecessary extra hypothesis that doesn't in any way add to our current understanding of the universe.",
"how do we know our entire universe doesn't exist in similar manner just on a much bigger scale?",
"Well, we know that's true of our ",
" universe, but if our ",
" universe is inside something larger then either we're really just calling the wrong thing \"the universe\" or it's got more than three spatial dimension in which case my previous comment applies."
] |
[
"Did you look at the post to which I linked? There I described an infinite string of balls that, despite having no region \"outside\" (there is a ball at all integers), expands. All \"expanding\" means in this context is that the distance between any two points gets bigger. So, for example, imagine you have an infinite grid of 1x1 squares. Now stretch each square to be 2x2. You still have an infinite grid, there was no outside, but your space has expanded."
] |
[
"Did you look at the post to which I linked? There I described an infinite string of balls that, despite having no region \"outside\" (there is a ball at all integers), expands. All \"expanding\" means in this context is that the distance between any two points gets bigger. So, for example, imagine you have an infinite grid of 1x1 squares. Now stretch each square to be 2x2. You still have an infinite grid, there was no outside, but your space has expanded."
] |
[
"Can anyone be a scientist or do you have to have an official B.S. (Bachellor of Science) and publish a in a \"peer-review\" journal to be a scientist?"
] |
[
false
] | null |
[
"There is a major difference between these things: ",
"1) Doing Science",
"2) Publishing Scientific Research",
"3) Making a living as a Scientist ",
"I guess the first question is how you are defining scientist. If it's anyone who does science, than obviously no degree is needed. Children do science all the time. Anyone who works with their hands does. Anyone who cooks or bakes does. Design an experiment, execute it, observe the results, and take them into account when you do it next time. Learn from what you see. ",
"Publishing scientific research is a different story. It is very hard to get published with no reputation, and no laboratory or research group to back you up. Without such a peer group, you don't have anyone to guide you through the writing and submission process. Is it possible to do it alone? Sure. But it's damn hard. Thus you're more likely to be able to publish if you're attached to a research group or laboratory. And if you're attached to one of those, you're probably already got a degree, or you're working on one. Also, a lot of liberal arts colleges give out BAs for science degrees. Doesn't make sense, I know. But there are plenty of Biology and Chemistry BAs running around doing science and publishing stuff. ",
"To make a living as a scientist, you definitely don't need a degree. There are a lot people involved in science, from all walks of life. It's harder to get an interview, let alone a job in the sciences without a degree in the field, or something related. However, it's definitely possible. I know plenty of IT people who are the foundation research groups are built on, and who get their names on every publication because of that. Some have a BS, some other degrees, some no degrees. "
] |
[
"You certainly don't need a B.S. to be a scientist. It just will likely be harder to get published in a peer-reviewed journal. This, though, would depend on your record and reputation as well as the specifics of what you are trying to publish."
] |
[
"A scientist is someone using the scientific method. For some reason, our society seems to want to treat scientists like priests five hundred years ago...people with a special knowledge unattainable by the general public. That's BS. Wasn't that long ago our scientists were writers and politicians and businessmen as well.",
"That being said, you're probably going to have reputation and credibility problems in the same way someone who passes the bar exam without a degree from a reputable school will have problems getting hired by a law firm. We are a society that values credentials. "
] |
[
"Looking for papers dealing with behavioral changes via microorganisms"
] |
[
false
] |
Hello, I'm trying to find a paper dealing with behavioral changes via mircoorganisms. examples: Cordyceps alter ant behavior via interferring with pheromones, but I have never been able to find said paper. I know some microbes affect light receptors, to attract the the host to light. (can't recall any genus names off the top of my head) However, I can never find the papers that show this/study the mechanism. Can anyone here help me out?
|
[
"http://www.jstor.org/stable/3496014",
"http://schizophreniabulletin.oxfordjournals.org/content/33/3/752.abstract"
] |
[
"\"The mechanism of action by which T. gondii alters rodent behavior is unknown.\"",
"Dang. No wonder why I can never find it. but, it's still good fun reading material. ",
"Thanks for the links! I owe you one."
] |
[
"Well that article is from 2007; maybe they found something since."
] |
[
"Why do Microwave ovens set to low cycle high/off in intervals instead of steadily using lower constant power?"
] |
[
false
] |
I have always wondered when microwaving foods why operating at 50% power for example the food is cooked at 100% power for 50% of the time instead of 50% power 100% of the time. Is it a functional effectiveness? cost saving? Why not supply 500w instead of 1000w?
|
[
"Microwave ovens utilize a device called a cavity magnetron to produce the electromagnetic radiation used to cook your food. The basic gist of how this device works is similar to how blowing air past the top of a bottle creates sound, only with electrons instead of air. If the voltage isn't high enough, then the resonance required for it to operate doesn't occur. Cutting the voltage in half will result in a device that just produces a little heat, and no radiation. Cutting the operating cycle in half produces the desired effect.",
"Pulsed operation is very common in electronics as a means to produce varied output, as it's generally easier to control. However, there are always side-effects of doing this, like noise from the pulsing itself. Your food doesn't care about this noise, so it's considered acceptable."
] |
[
"This is exactly right. To add a bit more information. you can change the power output in two ways, by varying current, or by varying voltage. Voltage was mentioned above. The magnetron used to produce the microwaves needs a certain voltage to work. if you change the voltage, it stops working. ",
"You can also vary the current (to some degree) which the magnetron will accept however this requires circuitry to provide this varying current based on required power output. Now in electronics, varying voltage is easy and efficient and small. Varying current is not. In order to generate a power supply that can limit output current you need to use much larger, more inefficient and expensive components which would raise the cost of the unit. since pulsed operation works just as well, and requires none of the complicated constant current power supply malarkey it is used instead and the entire issue is moot. "
] |
[
"Panasonic claims that their Inverter microwaves can actually sustain lower power levels. How does that work? "
] |
[
"Are there competing scientific theories to Darwin's Theory of Evolution?"
] |
[
false
] |
Besides the magical and religious interpretations of literature, has anyone published or hypothesized scientific theories that conflict with Darwin and his theories? Where can I find good information on them?
|
[
"Nothing that is legitimately taken seriously. Darwin proposed natural selection, but Evolutionary Theory is now the product of thousands of different researchers over decades. Darwin didn't even present natural selection by himself, Sir Alfred Russel Wallace discovered it independently.To be honest, evolutionary theory is now the bedrock of whole disciplines of study and has been and is still proven every day even in mundane experiments. It's taken for granted that it's correct in legit science"
] |
[
"Totally. Learning that natural and sexual selection are not the driving forces for the evolution of new species would be like discovering that probability is wrong and dice are not random or that natural decay is not reliable and we don't know how old anything is. Total chaos."
] |
[
"Not really. The general principle of change in allele frequency over time driven by natural selection is accepted by almost all biologists. ",
"There are disagreements, to a degree, about whether it is a gradual or a \"punctuated\" process. Punctuated meaning periods of genetic stability \"punctuated\" with periods of rapid evolution. Darwin was an advocate of gradualism and this is by far the favoured explanation to this day. So in that sense punctuation is a \"competing\" theory. But punctuation relies on the same basic principles and is taken as a hypothesis worthy of being taken seriously by most biologists even if they disagree, unlike the supernatural explanations you mention."
] |
[
"What is the easiest example of dual nature of light?"
] |
[
false
] |
How do I understand the duality of nature of light?
|
[
"Photoelectric effect shows its particle like character, interference patterns show its wave like character.",
"(Remember, both are just models of reality. Science describes models of reality, not reality itself. Those models have applicability in some circumstances but not in others. We are medium sized beings (on the order of metres) who have evolved to look at medium speed animals (on the order of metres per second), and can see things of medium size (on the order of millimetres to kilometres). Our brains haven't evolved to look at or understand very small objects which are dominated by quantum mechanical effects that our brains struggle to understand as we find them intuitively difficult.)",
"Essentially the ",
"photo electric effect",
" shows that light can be thought of as discrete separate parts called photons. And ",
"interference patterns",
" are evidence of wave like character."
] |
[
"This is really cool. However, the Crookes radiometer doesn't rotate due to pressure due to the momentum of light, but due to the interaction between air molecules and the hotter side. Your link states as much. So I'm pretty sure the Crookes radiometer can be explained with classical physics."
] |
[
"Yeah you're right. He asked for the easiest example and I suppose that covers both characteristics in one experiment. "
] |
[
"How do animals without parental figures know what species to mate with?"
] |
[
false
] | null |
[
"Animals without parents have the ability to recognize each other either visually, chemically (olfactory), or auditorily - same as animals that experience parental care.",
"Even though an animal may not be raised with parental care, they were still likely briefly exposed to an adult or their siblings (this is of course not the case for every animal, we'll get examples further down). This would give those newborn animals visual cues as to who they should be looking for in a mate.",
"Sea turtles, for example. The female lays eggs in the sand and leaves them to their fate. Young turtles hatch together in a group though, so they receive visual cues from each other. Many species of snake would be another example (some lay eggs and leave them, others are live births) or lizards. Sea turtles would also have the chemical cues from their mothers from the eggs they hatched out of. We'll talk chemical cues next, in birds.",
" ",
"If you have an animal without siblings that hatches alone they will have a residual chemical cue from their mother on the egg they just hatched from (they all have to be egg examples, as live birth exposes the offspring to at least the female briefly either giving a chemical cue or a visual cue from the birthing process). I honestly cannot think of one example where an animal lays a single egg and then leaves it. That's very risky for the survival of that one egg.",
"I think the best example here is the ",
"Brown-headed cowbird",
" (",
"). This species is an ",
" or an animal that must (obligate) parasitize another host's nest in order to reproduce (",
"more on that in this ",
" article",
"). Brown-headed cowbirds never raise their own chicks. Another example would be the Striped Cuckoo or really many species in the Cuckoo family ",
" (where we get the term ",
" from). ",
"So the brood parasite lays their eggs in a host nest, say a Yellow Warbler (I've seen this in action when studying endangered grassland birds). The Yellow warbler raises that cowbird chick, but though the cowbird is around the Yellow warbler parents it is remembering the chemical cue from its egg and does not try to mate with Warblers. As a side note, the cowbird chick usually hatches first then kicks all the other eggs out of the nest. The host adults end up feeding it to adulthood none the wiser (",
"not my image, but this is what I've seen in the field",
"). ",
"If we go back to cowbirds, males sing for females and females are attracted to those songs even though they were not raised with other cowbirds. Instinct is an incredible thing. Cowbird females that are not attracted to male cowbird songs do not get to mate as often and eventually we are left mostly with receptive females.",
"There's also body language which is processed in the brain and tells the animal the sex of what they are looking at (chemical cues, sometimes visual), how fit they are, and if they are the same species (or close enough! Some animals do mate with other species). The neuroscience part of it can get pretty heavy. ",
"If you're interested in that there was a Science Daily article about it in mice."
] |
[
"You've got that mixed up, mules are a hybrid between donkeys and horses. Donkeys and horses (and Zebras) all belong to the same family, Equidae. They are all equally related to each other. They have differing chromosome counts which is why we get sterile offspring. Their interbreeding primarily happens due to human meddling, but there is some natural horse and donkey matings.",
"As I stated in my original comment, sometimes we get inter species breeding. This is likely due to confused cues, either visual or chemical or a combination of both. Interspecies mating has also been observed as a stress outlet and as a dominance display. ",
"Looking at cue confusion in your example, donkeys and horses are so closely related they may be giving off chemical and visual cues that are close enough to trigger a copulation response. Sometimes things get a little muddy when animals only diverged from a common ancestor a short time ago."
] |
[
"Extant primates are not at all as closely related to each other as Equines are, so I would not expect them all to be attracted in the same way as your example (other than humans and chimps). Primate is an Order, three taxanomic jumps above Genus Equus, for Equines (my apologies I think I said family before which is also true but animals of the same genus are even more related). ",
"If we look at humans and chimps, we had a common ancestor 6 million years ago. Horses and donkeys had a common ancestor around 4 million years ago and did not diverge very far given they do belong to the same genus. Humans belong to genus ",
" and chips to ",
". Even if you want to say chimps should also belong to Genus ",
" they are still 2 million years different than us and far enough away where the cues may no longer work or they might, it's not something we test on humans. I think humans and chimps was a bad example. Let me give another, if you want to take humans out and sub in another primate, Lemurs, we're still talking a common ancestor between chimps and lemurs happening about 43 million years ago. Chimps and gorilla divergence happened about 10 million years ago, for more context. All a fair difference than 4 million years ago if Equines."
] |
[
"Why does the James Webb telescope sun shield use layers with significant separation instead of a single multilayer insulation sheet?"
] |
[
false
] |
The James Webb sun shield is complex, and requires intricate mechanisms to allow for the precise tensioning of 5 layers of thin material to ensure separation. Why could it not use a single sheet of multilayer insulation in which the layers are separated by a mesh as per conventional satellite insulation? This would only require tensioning of a single sheet and therefore be simpler to implement.
|
[
"Just to add to this the shield is bent slightly with each layer smaller than the last allowing for IR light to be reflected at angles that will move it down the shield and ",
"out into space",
"."
] |
[
"The sun shield is there to block the sun's rays which will heat up the telescope, this you already know.",
"But that sun shield will get hot, and will start to emit infrared on the other side of it. So you add another layer, but that will get heated by the infrared of the previous layer, and so on and so on.",
"Between the layers of heat shields, the radiator, and everything else, the actual telescope will be kept at the -218c that they're targeting for the satellite's instruments to work as designed."
] |
[
"Ah, thank you! This is the key piece of information I was missing which allows it to perform better than multilayer insulation."
] |
[
"Why do we see double when drunk ?"
] |
[
false
] | null |
[
"Your eyes converge to varying degrees depending on how far away the object they are focusing on is (you can easily test this by focusing on your finger and moving it back and forth in front of your nose.) When you get drunk, the very fine control of the muscles of your eyes gets a little sloppy, so they don't converge the right amount and the result is a double image (similar to what you might get intentionally crossing you eyes and looking at a distant object.)"
] |
[
"part of the explanation is loss of good motor control. the other part is that many of us have an underlying imbalance in how the two eyes point at things; if this imbalance is always manifest, we call it a tropia, but if it's usually hidden it's called ",
"phoria",
". a phoria is considered latent so long as the oculomotor system can fully compensate for it, but when you're drunk or maybe just really tired (e.g. I have a small phoria, and if I stay up really late reading, pushing against drowsiness, I eventually have to close one eye in order to read..), this control decreases and the phoria becomes manifest. then, the two eyes will be pointing in different directions than intended, and you'll see double."
] |
[
"It's a combination of things. Others have mentioned convergence, but another pieces of this puzzle is the vestibuloocular reflex.",
"The semicircular canals in the ear are a form of gyroscope. When you get drunk, the fluid becomes lighter, sending faulty signals. (The brain itself also starts sending faulty signals, but it's a lesser effect). ",
"These signals tell your brain to twirl your eyes in their sockets around the direction you're looking in. This is supposed to keep the image on your retina with up being in the opposite direction to gravity. ",
"You can see this in action if you look closely in a mirror at your eyes and tilt your head from side to side. ",
"(This is also what causes the spins)."
] |
[
"In winter bugs like spiders, flies and mosquitoes, seemingly die off. How is it that after the winter they're able to come back in such numbers? A layman would think the winter would cause an extinction of some insects."
] |
[
false
] | null |
[
"Insects survive the winter months in a variety of different ways. Some migrate, like birds and other animals, to warmer climates from which they will return at the end of winter. Others can enter a sort of hibernation. A lot of insects will \"overwinter\" in some sort of non-adult stage of development, either as an egg, pupae, larvae, etc. This requires the young insects to be deposited somewhere warm and with relative shelter, deep underground or in the foundation of a building. Their genetics allow them to enforce this infantile stage of development until weather conditions permit."
] |
[
"Many types of insects lay eggs before winter and then die off and those eggs hatch in the spring and give life to a new generation of bugs ",
"https://www.google.com/amp/s/www.washingtonpost.com/lifestyle/kidspost/ever-wondered-where-do-bugs-go-in-winter/2019/04/18/f09b3a10-563d-11e9-814f-e2f46684196e_story.html%3foutputType=amp"
] |
[
"So if you had a few very cold months, a few warm weeks and more very cold months you could kill much more insects and have a nicer summer?"
] |
[
"Does iron stop being attracted by magnets when it gets hot enough?"
] |
[
false
] | null |
[
"Above the Curie temperature, it just becomes paramagnetic rather than ferromagnetic. So still attracted by external magnetic fields, but much more weakly than in the ferromagnetic phase."
] |
[
"Interesting, thank you. I had wondered if it went both ways after learning the curie temperature is how cheap rice cookers work."
] |
[
"To expand on the other answer. There is a competing interaction between the energy in magnetic dipoles and an external field.",
"\nAs temperatures get higher the magnetic dipoles become harder to magnetise because their energy exceeds the orientating energy of an external field (plainly put), so a stronger magnetic field would be required in order to achieve the same magnetisation."
] |
[
"How far from the Sun would you need to be before you could safely look at it with the naked eye?"
] |
[
false
] | null |
[
"This has been asked before.",
"http://www.reddit.com/r/askscience/comments/qzkgd/how_far_away_from_our_sun_would_you_have_to_be_in/",
"http://www.reddit.com/r/askscience/comments/nz6qh/at_what_distance_from_the_sun_is_it_okay_to_look/"
] |
[
"One thing the previous questions didn't include - no matter how far you go, the brightness per solid angle doesn't change.",
"If you assumed that you had perfect lenses in your eye, then the intensity on the specific rods and cones that received the sun's light would be the same at any distance. The question of which metric matters is for biologists. From the other questions, however, I gather that bulk heating matters, which means that distance would matter. At a far enough distance, we can safely assume that our eye isn't a perfect lens so it will smudge the light beyond the solid angle that it should occupy, or else be smaller than our eye's functional pixel size. This is why it's safe to look at stars.",
"This principle of constant power per solid angle is also used in Olbers' Paradox. If the universe were both static and infinitely old, the entire sky would be of about the brightness of our sun."
] |
[
"You don't mention a period of time which is clearly integral to your question. You also don't mention what \"safely\" is defined as nor \"naked eye.\""
] |
[
"Why don't hydras die of old age?"
] |
[
false
] | null |
[
"Ok, sorry I need to interject here. ",
"/u/inkheartandwings",
" is mostly incorrect (Sorry!)",
"Hydra don't die of old age because their cells don't senesce. Plain and simple. It is unknown how they maintain their telomeres. It is thought that hydra avoid aging in part due to a gene called ",
". ",
"A good example of this phenomenon is the ability of hydra to regrow limbs/parts of their body after injury. Again, this adds to this idea that they consist of mostly stem cells or stem cell-like cells.",
"While it is true they have a life cycle that generates many medusa, it is not particularly relevant to the question of immortality.",
"For those interested, here is the life cycle (as I described in another comment):",
"It's sperm + egg --> fertilized egg/blastula --> planula ---> polyp. ",
"The polyp can asexually reproduce to make tons of the same medusa or two medusa can sexually reproduce to make a fertilized egg which goes through the above process.",
"Edit: So the ELI5 answer simplified it a bit too much to the point where another user pointed out that it sounds like ",
"/u/punkrockscience",
" and I are disagreeing--and we're not. ",
"These cells, found mostly in the region below the head, continue to differentiate and divide throughout the life of the animal. Old cells are constantly being sloughed off at the ends of the tentacles and the base of the body, to be replaced by new cells freshly produced from division of the i-cells from the center.",
"This is an important clarification."
] |
[
"Wait, I thought this was a joke. What the fuck is a hydra? Aren't they mythical creatures with 9 heads?"
] |
[
"I'm probably going to explain this incorrectly but from what I recall when studying them in bio class, you are dealing with a very simplistically constructed animal. ",
"You can think of hydras' life cycles as a continuing change between two phases. The first is called a madusae (sounds like madusa) phase. At this point the look pretty much like tiny jelly fish and find a surface to attach and grow. This larger phase is called the polyp phase. At this point the hydra will start reproducing simply by budding and creating more madusae. ",
"Again this is only possible because on a cellular level these creatures are very simple, not requiring an emmense amount of energy to survive. "
] |
[
"If superman were to keep running faster and faster, would he fly off the earth eventually?"
] |
[
false
] |
My friends and I are having a discussion about whether or not, for example, an entity such as a sci-fi era plane could theoretically travel fast enough to "fall of the earth" as it were. The opposing argument is that rockets fly upwards for a reason, but isn't this the ideal? If someone runs fast enough, wouldn't they just fly off the earth and eventually leave orbit at an angle and tangent respectively? Thanks!
|
[
"Yes. Once he hits the ",
"escape velocity",
" (which is really the escape speed, no vector direction implied), then he will leave orbit."
] |
[
"A potentially negative issue would occur before he actually reached escape velocity. As each stride got progressively longer he would essentially be jumping hundred of feet each step and it would be harder and harder to make sure he didn't hit something and then aim for the next step. Depending on how long it would take to actually get to escape velocity, he could do this out in middle of the desert, as the damage from sonic booms would prevent this from happening in populated areas."
] |
[
"Also air resistance would be a problem as he's have to reach escape velocity starting from a horizontal plane.. running on flat land. This means he's have more air resistance to over come .... unless he ran up a huge ramp.... like Mt. Everest. This presumes he's relying solely on running and not flight or jumping.",
"The other problem is that as he runs faster and faster, he's eventually lift off the ground, loosing his friction to accelerate fast enough to achieve terminal velocity. Again presuming that he's not jumping, just running. the air would keep slowing him down each time he started to get up into to the air."
] |
[
"Are fears hereditary?"
] |
[
false
] | null |
[
"I'm taking the question to ask if simple phobias are hereditary. That is, if one of your parents was terribly afraid of dogs, then are you likely to inherit the same fear of dogs.",
"The answer to this is no.",
"There is some heridetary component to simple phobias and other fear/anxiety disorders. The exact percentage is hard to pin down and varies from one type of fear to another. For example, ",
"this relatively recent",
" found 25-37% heritability of phobia/fear liability. This is not a very big effect if you think that the environment may end up explaining as much as 75% of heritability. ",
"This article",
" also cites a number of works that support a genetic role in needle phobia. One trend in this research is that while there is a genetic component, it's not specific. Most of the effects are found when type of phobia is ignored, which suggests that the heridetary component is a predisposition to develop fears/phobias, but is not specified in any way.",
"/u/Mrman53",
" mentions a \"primal instinct\" against spiders, snakes and sharp teeth. I haven't encountered the sharp teeth bit before, but there appears to be something special about spiders and snakes. There is a hypothesised ",
"preparedness",
" to become afraid of certain kinds of stimuli. This is based partly in the finding that specific phobias tend to cluster around certain stimuli, and the finding that those same type of stimuli condition and extinguish differently in the lab. These stimuli appear to include snakes, spiders, heights and violations of peripersonal space (among potentially other stimuli).",
"The important thing to keep in mind is that this view only supposes that we are primed or prepared to become afraid of these type of stimuli, not that we are born afraid of them. This maintains that there is still an important role that the environment can play in the form of learning. Without this, preparedness would not be able to explain how it is that people are able to use snakes and spiders are sources of food."
] |
[
"Good articles, could the eating of spiders and snakes be part of a hierarchy of needs situation where the need to eat is more important than the fear of spiders?"
] |
[
"Possibly, but that doesn't explain why people ",
"still eat spiders",
" when other food is readily available. Same goes for other predatory foods such as alligator/crocodile and snakes.",
"The idea of heridity is also not able to account for the lack of specific phobias for mushrooms/fungi, which are more lethal in some parts of the world than snakes and spiders (i.e., Sweden)."
] |
[
"How does a wild animal population naturally recover from an STD outbreak?"
] |
[
true
] |
Wouldn’t a population be perpetually infected and/or die off as a result of STIs? In the case of animals that engage in casual sex or polygyny, I’d expect STIs would be even more easily spread. This NCBI article concludes that extinction events due to an infectious disease is relatively unusual… Without any anthropogenic intervention, hepatitis could easily wipe out troops of bonobos. An outbreak of syphilis would wreck havoc in a pod of dolphins. There may be survivors that recover and possibly develop a resistance…. provided they don’t get reinfected, the disease doesn’t mutate, their reproductive organs aren’t compromised, etc. So, what’s the science behind a species surviving from an STD outbreak in the wild kingdom?
|
[
"It’s very much the same science as any other diseases, STIs just tend towards more chronic infections and lower rates of transmission. Diseases spreading through populations are often described using mathematical models that take into account births and deaths of the hosts, and the proportion of susceptible, infected, and resistant hosts in the population over time. The game for the disease is to keep a pool of susceptible and infected hosts large enough to maintain itself. The only difference in STIs is they have a very structured way of moving hosts from the susceptible group to the infected group, but otherwise the maths is the same.",
"If you imagine a new disease appearing in a small group of animals, if the damage it causes is excessively high then the group rapidly dies like in the examples you gave. This massively decreases the number of susceptible and infected hosts in the population and it’s likely the pathogen goes extinct. Too few symptoms in the host and the pathogen can’t transmit efficiently, causing the proportion of infected to fall to 0 over time. Once again the pathogen goes extinct.",
"This middle-ground of virulence, where the pathogen is nasty enough to cause symptoms and spread, but not so nasty it incapacitates/kills it’s hosts and exhausts all opportunities to transmit, is called the trade-off hypothesis. Pathogens can’t know what their optimum level of damage is in advance, they either evolve towards it in time or they go extinct.",
"That’s the pathogen side of things, the host population may also have some individuals that are naturally resistant to a new infection by random mutation (most commonly they have mutated versions of proteins on their cell surfaces that prevent pathogens from entering them). This means, in the event of a very damaging disease appearing, some hosts start off in the resistant group before the disease has even started, and survive despite the disease killing all hosts in the susceptible and infected groups. Their offspring are also likely to be resistant too, which can revive the host population over time and avoid extinction.",
"So going back to your question, species can avoid extinction during outbreaks of new diseases either through the disease not being too damaging (or evolving towards less damage if it started off excessive), or through existing resistance in some of the hosts by chance."
] |
[
"This is an excellent response. I did a lot of mathematical epidemiological modeling in undergrad, so this is exactly how I think about the issue as well.",
"My question - is the key factor controlling the spread of STDs simply that the rate of interaction between entities is too low? If we're talking about coronavirus, an interaction = we shared the same air space for 2 minutes. For syphilis = we had sex. STDs are also unlike other illnesses we commonly encounter like the flu in the sense that you don't automatically enter into the recovered group after 2 weeks. Once you have syphilis, unless treated, it stays with you, and it only starts wreaking real havoc on your body after around 3 years. 3 years is a long time to have the opportunity to spread it, which would make you think the R0 value would be quite high. But its clearly not, so my thought is that this hints towards the rate of sexual interaction being so low that it doesn't automatically become an epidemic everywhere it shows up."
] |
[
"Unfortunately I can't quote my source because it's a book I don't have with me (",
"The Origin of AIDS by Jacques Pepin",
") but there have been deceased tribes of some primates found who were theorized to have been wiped out by variants of SIV, the simian immunodeficiency virus - that is, the non-human primate equivalent of HIV. Additionally, both HIV and SIV have evolved to become less lethal over time."
] |
[
"How is hearing protection from impulse noise different than that from continous nose?"
] |
[
false
] |
Hi,I'm curious if someone with background in audiology and/or hearing protection could explain the following:
|
[
"The question I have is following: how was that limit established and how accurate it is?",
"The most commonly cited work is this:",
"Taylor, W., Pearson, J., Mair, A., & Burns, W. (1965). Study of noise and hearing in jute weaving. ",
", ",
"(1), 113-120.",
"Basically, looms are loud, produce predictable, constant noise, and weavers in that era stuck to one job for life, so you could track hearing loss VS exposure. Office workers in that area acted as a control.",
"",
"Could I blast my ears everyday with let's say 103dB of noise for exactly 3 minutes and expect no hearing loss whatsoever? ",
"As with everything healthcare related, noise-related hearing loss happens on a bell-curve. There will be those who are exposed to loud sounds for life and don't have hearing loss, and vice versa. You could expect no hearing loss, but it's not a guarantee.",
"",
"How many dB of noise reduction is needed for complete safety in that case? ",
"As mentioned above, probably no such thing as complete safety. Also depends on how much you shoot.",
"",
"Is it enough if the shooter uses earmuffs that reduce the noise by let's say 30dB - from 170dB to 140dB and if so, how do we know it's safe and won't cause damage over the course of years or decades?",
"We don't know it is safe, but it's a guideline. More protection is also better than less protection, in the case of gun noise. Personally, if I shot a lot of unsuppressed guns, I'd be wearing muffs on top of plugs. Also, depends on how much you shoot.",
"",
"Is there a limit, on how many shots could a shooter take in such case before damage to hearing occurs, in spite of using hearing protection and if so, how can that limit be established? ",
"You can detect noise-induced hearing loss in young adults nowadays, I think the last figure was something like 1/6 of all young adults having measurable noise-induced hearing loss. With better workplace guidelines, most noise-induced hearing loss is recreational, so mainly music and guns. However, if someone out there is doing this experiment, I haven't heard of it."
] |
[
"There is a difference between acoustic tolerance to impulses versus steady-state sound that are spread out over time. The brain/ear has an automatic reflex mechanism whereby if very loud sounds are detected the muscles in the middle ear “lock up” so that they don’t transduce too strong of mechanical energy to the inner ear, causing damage. But an intense impulse doesn’t give the reflex enough time to detect & respond, so impulses are much more dangerous to the auditory system in terms of raw magnitude exposures than continuous sounds."
] |
[
"Hearing loss in very noisy environments is a crazy problem. On military flight lines, for instance, people usually wear two sets of ear protection at the same time and can still suffer hearing problems. If sound intensity is large enough, it can damage your hearing by traveling through your open mouth into your Eustachian tubes or even up the jawbones."
] |
[
"I can't visualize how cords tangle themselves? Does any research exist on how it happens?"
] |
[
false
] |
I have searched through a few databases, but haven't found any research on it.
|
[
"Spontaneous knotting of an agitated string",
" is a neat paper dealing with knots. Starting at page 4 is more along the lines of what you want with the section \"Simplified model for knot formation.\" There are also a few sources referenced in that section (particularly Adams CC 2004 ",
") that might interest you for further reading.",
"I feel like reddit introduced me to this paper about a year ago. so i shall keep the annual tradition going."
] |
[
"There certainly is, here's a video about it: ",
"http://www.youtube.com/watch?v=lNWEuMJCMEk",
"Dorian Raymer and Douglas Smith won an ig noble prize for their research."
] |
[
"nice! thanks for this....watching right now"
] |
[
"What is the mechanism by which an atom or molecule conveys smell? (x-post from r/chemistry)"
] |
[
false
] | null |
[
"A molecule acts on receptors in the nose. \"Olfaction\" or smelling is something not completely understood (at the molecular level) as the receptors have not been mapped out completely. Essentially its a lock and key mechanism that allows certain molecules to bind to receptors. "
] |
[
"An answer I posted in another thread:",
"Olfactory receptors are exceedingly complex. Compared to three cone cells for color vision in the eye, it is estimated that humans express ~400 olfactory receptors. Each odor receptor can detect a variety of structurally related compounds. Furthermore a compound can trigger more than one receptor. So as you can see, there is essentially a limitless variety of possibilities by which an odor molecule (or molecules) can trigger the final combined signal to the brain. This discovery was so revolutionary that it garnered the scientists who discovered it the Nobel Prize!",
"Check out this link for more background (I know it's wikipedia, but it has references to a couple of pretty sweet primary literature publications)",
"http://en.wikipedia.org/wiki/Olfactory_receptor",
"Great paper on combinatorial odor sensation:",
"http://www.ncbi.nlm.nih.gov/pubmed/10089886"
] |
[
"So then, how many receptors do we have? Wouldn't there be a limited amount of smells we can smell? Only so many locks for all of the keys."
] |
[
"I can't seem to find a definitive conclusion to the safety of Genetically Modified Organisms for human consumption. Can someone please clear out the fog?"
] |
[
false
] | null |
[
"This Wikipedia entry",
" summarizes the controversies surrounding GMOs really well. According to the article:",
"There is broad scientific consensus that food on the market derived from GM crops pose no greater risk than conventional food.[1][2][3][4][5][6] No reports of ill effects have been documented in the human population from GM food.[3][7][8] ",
"In fact, for Bt-type crops, the pesticide use on crops is significantly lowered. So, humans end up ingesting fewer pesticides. This is not a major problem in developed countries but ",
"in developing nations its a serious serious problem",
". It also says later",
"Advocacy groups such as Greenpeace and World Wildlife Fund have concerns that risks of GM food have not been adequately identified and managed, and have questioned the objectivity of regulatory authorities.",
"To put the broad picture in perspective, a significant number of scientists now are convinced that GM foods are ok. They equate the argument about GM foods with the argument that scientists have with, say, Republicans in the US who believe in creation over evolution. No matter how much evidence there is, the latter group refuses to recognize evolution as a fact. Same thing with the environmentalists. Despite a broad scientific consensus on safety of GM foods, radical environmentalists are failing to recognize it as true.",
"However, a major cause of concern regarding GM foods is gene flow to non-GM organisms. The above Wiki entry says the following:",
"In July 2005 British scientists showed that transfer of a herbicide-resistance gene from GM oilseed rape to a wild cousin, charlock, and wild turnips was possible....On 18 August 2006, American exports of rice to Europe were interrupted when much of the U.S. crop was confirmed to be contaminated with unapproved engineered genes....A study published in 2010 by scientists at the University of Arkansas, North Dakota State University, California State University and the US Environmental Protection Agency showed that about 83 percent of wild or weedy canola tested contained genetically modified herbicide resistance genes, and they also found some plants that contained resistance to both herbicides, a combination of transgenic traits that had not been developed in canola crops.",
"A lot of labs are working on solving this problem. This poses little concern to human health (your question) but it does have environmental repercussions."
] |
[
"But it's important to know that, in the US, the FDA must still approve any new GMO, and they do their full analysis regardless of the speed of scientists making changes. The safety net is just as tight as ever."
] |
[
"An argument could indeed be made that way. However, it is always a question of whether benefits outweigh the costs. Studies suggest there are no ",
" effects. Also, GMOs are, in fact, beneficial to the health and environment in many ways. Again, check out ",
"this section on the Wiki article on GMOs",
". Some of the benefits and uses include:",
"Improved shelf life, Improved nutrition, Stress resistance, Herbicide resistance, Pathogen resistance, Production of biofuels, Production of useful by-products, Drugs, Materials, Bioremediation",
"providing wide-ranging benefits to human health, nutrition and environment. Agreed, there are challenges to be met, but that's what science is for. ",
"It also needs to be noted (kinda off-topic) that GMO crops are not the magic wand to all agricultural problems. In developing countries, there are bigger problems - reduced size of land holdings, low yield/hectare, absence of electrification and irrigation, massive agricultural waste , massive losses during transportation and storage, corruption and hoarding of food grains etc. No matter how many GMOs is used, we are not going to solve the problem of world hunger if these problems persist. GMO crops are only part of the solution."
] |
[
"Are there any other known viruses that are as similar as SARS-COV-1 and SARS-COV-2?"
] |
[
false
] |
[deleted]
|
[
"You should ask if there are any known viruses that do ",
" have similarly close relatives. It’s virtually universal to have phylogenetically close family members and essentially every family of viruses has clouds of relatives that are similarly related. Look at ",
"lyssaviruses",
" or orthomyxoviruses like the thousands of subtypes of influenza A/B/C/D, or look at herpes simplex 1 and 2 or ",
"filoviruses",
". ",
"In general it is more a question of semantics than anything, there’s a huge cloud of viruses circulating among various populations, and you shrug and arbitrarily draw a line and say well, I guess that’s one virus type and that’s another - but it’s just a choice, you could say that SAR and MERS and SARS-CoV-2 are the same virus and it would be just as reasonable as other choices.",
"I know that to the vast majority of the population, having never thought about viruses in their lives, COVID-19 and SARS-CoV-2 seem new and strange. I can’t overemphasize how ",
" this virus seems to a virologist. It’s utterly generic, doing standard virus things in a normal virus way just like the average virus."
] |
[
"\"I can’t overemphasize how ordinary this virus seems to a virologist. It’s utterly generic, doing standard virus things in a normal virus way just like the average virus.\"",
"Why has the global response been so extraordinary?"
] |
[
"Because it has high transmissibility, relatively high morbidity and mortality, and an immunologically naive population to infect."
] |
[
"What happens in the area where nuclear weapons are tested underground?"
] |
[
false
] |
Does it create a giant cave? Is there just a giant glass sphere from the heat/energy? Is that where the aftershocks come from, from the sphere collapsing? I've always wondered because in videos like below, they say the land permanently rises, what is put there to hold it up?
|
[
"The explosion breaks up rocks, so they take up more space and allow fluids (water) to move into those spaces. This forms a mound that can remain for an extended period of time. For larger, deeper tests this can extend into the ground water and provide a link which was not otherwise present (the aquifer usually being isolated somewhat from the surface)."
] |
[
"The explosion breaks up rocks, so they take up more space and allow fluids (water) to move into those spaces. This forms a mound that can remain for an extended period of time. For larger, deeper tests this can extend into the ground water and provide a link which was not otherwise present (the aquifer usually being isolated somewhat from the surface)."
] |
[
"There's a full ",
"report here",
" \"Evaluating the Effects of Underground Nuclear Testing ...\"",
"Some of their conclusions:",
"\"Scoping calculations show that if low permeability rocks surround underground nuclear tests, \nwhich initially pressurize the disturbed zone, an elevated hydraulic head mound may be created \nand sustained, even beyond the disturbed zone, for a substantial amount of time. For deeper tests, \nand particularly large tests, this zone of initially elevated hydraulic head may extend down into \nregional aquifer rocks. Also, such tests may create a high permeability conduit from the cavity \nto the regional aquifer, depending on the size of the cavity and the post-test permeability. It is \npossible that fluids originating near the external boundary of the disturbed zone, and maybe even \nfrom within the cavity, will eventually move into the regional aquifer. The existence of high \npermeability rocks, such as fractured welded tuffs or carbonate aquifer rocks within this zone of\npressurization would cause the overpressure to dissipate rapidly if they are not altered \nsignificantly during the test. \""
] |
[
"Is there any living human subspecies?"
] |
[
false
] |
I've just read an awesome book by Tom Knox called The marks of Cain that was inspired by this topic so my question is: Is there any known living human subspecies in world right now? If not, how long would it take for evolution to make one?
|
[
"There used to be ",
"many subspecies of humans",
": the extant ",
", which is what we are, ",
", which are commonly referred to as the Neanderthals, and ",
", who lived about 160,000 years ago in Africa. There are ",
" different species in the genus ",
", but I'm being literal in that the above mentioned species are classified as humans.",
"The Neanderthals were thought to be a different species from modern humans, but it turns out that most living humans today (with the exception of Africans) contain Neanderthal DNA. And since the Cro-magnon humans and Neanderthals could interbreed and produce viable offspring, they are considered to be humans. And the youngest Neanderthal specimen is dated to have lived 30,000 years ago (but there has been some evidence that they survived up until 24,000 years ago).",
"So no, there are not any still alive today. But it was not that long ago that at least 3 human subspecies were living on this planet at the same time."
] |
[
"Interesting: ",
"according to Wikipedia's definition",
", if Neanderthals and Cro-magnons interbred, then they weren't subspecies - they were just part of the same species."
] |
[
"Going by Wikipedia's definition of ",
"subspecies",
" (essentially a sub-group that would be capable of interbreeding with the rest of the species but for geographical or other factors that prevent it), there are no living human subspecies. The Aboriginal population of Australia might have qualified as one before Europe \"discovered\" them, although it's not at all certain that they were genetically isolated after the initial colonization of the continent around 50,000 ybp or so."
] |
[
"When does a piece of bubble gum turn from calories gained to calories expended?"
] |
[
false
] |
If a piece of how many chews until I start burning calories in excess of the 50? For instance, if I chew it for an hour am I burning calories at that point? And another question I just thought of.... Anyone know if the 50 cal value is if a person swallows the gum or just chews it?
|
[
"I read once that chewing gum burns approximately 11 additional calories per hour, depending of course on the person. In this case, it would only behoove you to chew the gum if you planned on keeping it going for 5+ hours. ",
"If you eat sugar free gum like extra, for example, which is 5 calories per stick, you may find yourself in a calorie deficit more quickly. However, the amount of calories ingested or burned from. Chewing bubblegum is very net negligible, so I wouldn't worry too much about it. "
] |
[
"If you take account of the appetite suppression qualities chewing that has been reported in some studies I imagine it could have a reasonable effect on weight loss. "
] |
[
"Bouncing off of the original question. I'm sure we've all chewed 2, or 3, maybe even 4 pieces of gum at once, and I'm sure we all noticed it gets harder and harder to chew. So my question is; When we chew more than one piece of gum, although you add more calories, does it burn exponentially more calories for every piece of gum?"
] |
[
"What preoccupied the minds of the first humans to gain consciousness?"
] |
[
false
] | null |
[
"We have no way of knowing"
] |
[
"Yet or forever?"
] |
[
"How would one ever know?"
] |
[
"Has a Formula One car got enough down-force to go round a loop-the-loop, considering it has a very low ground clearance and therefore the loop would have to be massive?"
] |
[
false
] | null |
[
"One - Shameless plug for ",
"/r/Formula1/",
"Two - ",
"It's been done with a hatchback",
"Three - You may have noted that in the above video example the car couldn't maintain driving upside down, and this is what the claim with the F1 car is all about. F1 cars easily produce more downforce than their weight so they can yes stick to ceilings if not for...",
"Four - The cars aren't made to work upside down.",
"Edit: Found a source, though not for F1. The Panoz DP01 Champ Car weighs 1565 pounds +/- driver weight variance as per the 2007 sporting regulations - ",
"Source",
". The car produces 5700 pounds of downforce at 200mph - ",
"Source",
"."
] |
[
"Oil starvation - oil sprayed into the heads and undersides of the pistons relies on gravity to return to the sump. If the engine is upside down, oil will collect in the heads and under thr pistons, the sump would run dry, and the crankshaft journal bearings would seize. Bang!"
] |
[
"The rules specify a standard \"driver weight\" amount. Actual drivers have an annoying habit of not being cookie cutter clones for the rule book, that's what he means by \"driver weight variance\"."
] |
[
"Some carnivores have this notch near the front of their upper jaw that interrupts the tooth row. I can't seem to find any satisfying reason for why it's there. Anyone got an answer?"
] |
[
false
] |
The only examples I've found so far are in reptiles like crocodiles and a couple of dinosaurs like Spinosaurus and Dilophosaurus. I've seen it referred to as a "subnarial gap" in dinosaurs.It seems like it's there to make space for larger teeth in the lower jaw to poke up through an overbite but I'm curious as to why that kind of jaw shape would be advantageous. Perhaps something to do with catching fish? I really haven't a clue. EDIT: It's a new day and I've done a little more looking around for answers. Found a really interesting paper on fish dentition that suggests having larger teeth at the front of the lower jaw could be to assist in capturing elusive prey. That makes a good deal of sense to me at least. When an animal bites, it moves the lower jaw a lot more quickly than the upper one as it's not got an entire head attached to it. So some large teeth at the front of the lower jaw would likely be useful to puncture smaller prey during the bite and prevent them from escaping before the upper jaw engages. To have this provide a meaningful advantage for larger predators, the jaw has to be quite long (both for increased jaw speed and to make it significantly easier to catch with the front of the mouth than the back) and the prey has to be quite small (so that the greater bite force at the back of the jaw isn't needed to maintain a hold) so this morphology seems only likely to show up in fairly specific niches. I think I'm satisfied with this answer, but if anyone has something to add, or is unconvinced by this explanation, by all means say something.
|
[
"Evolutionary traits do not need to be advantageous to continue to exist. ",
"The ones that put the animal at a disadvantage are likely to eventually disappear. But the ones that have no real effect either way often stay around."
] |
[
"Tbh I'm not sure that I buy that.",
"Jaw structure and dentition is going to be a major factor in a predator's fitness. If this kind of notch conferred even a slight reduction in fitness, even something like slightly reducing skull integrity or bite force, it would be selected against quite quickly in evolutionary terms. I'd imagine that this would be especially true for larger animals like these, where the larger stresses on the skull would incentivise a more solid structure without potentially weakening notches.",
"I can't see a morphology like this showing up in multiple lineages without it providing some significant advantage."
] |
[
"They stay around as vestigial traits, but for a trait to be selected ",
" it needs to give some advantage. So the question then becomes, why is it so prevalent? Even on animals which aren't descendant from the ones mentioned in the OP."
] |
[
"Why is it assumed there was a mass extinction of the dinosaurs?"
] |
[
false
] |
[deleted]
|
[
"They disappeared suddenly from the fossil record. They weren't completely eradicated. It seems more likely that there were food shortages due to the ash cloud caused by a meteor strike, blocking out the sun and reducing the availability of plant matter, thus disrupting the food chain. These food shortages would have had a greater effect on large animals as smaller animals can better survive on bits and bobs found through scavenging. Because of this, all large dinosaurs died out leaving the smaller, already bird-like dinosaurs as well as the small burrow dwelling mammals to repopulate the niches left behind."
] |
[
"Wouldn't a mass extinction of the dinosaurs have resulted in the eradication of their DNA so that nothing could have evolved from them, like birds are thought to have?",
"TL;DR: Birds did not evolve from dinosaurs, birds are dinosaurs. ",
"\"Among the features linking theropod dinosaurs to birds are the three-toed foot, a furcula (wishbone), air-filled bones and (in some cases) feathers and brooding of the eggs.\"",
"If you look at this it gives you an idea of how complex this group was. Now, only the birds made it past the K-T boundary (65 mya - birds evolved before the extinction of the other groups of dinosaurs, but they did undergo further evolution after that time radiating into the many species we see today). Birds didn't come from dinosaurs...they are dinosaurs. They just survived and had many more unique adaptations after the K-T extinction event. (FYI Birds are contained in the last offshoot group within the theropods called avialae in this ",
"chart",
")\nSome adaptations were already present in the theropods - like feathers and hollow bones, and birds took advantage of these in unique ways compared to other offshoot groups in the ",
"theropods",
".",
"Archaeopteryx is thought to be the first fossil we have of a primitive bird which is capable of powered flight, and it was alive well before the K-T boundary (Archaeopteryx lived in the Late Jurassic Period around 150 million years ago). ",
"Now I must clarify, that while archaeopteryx is certainly though to be a primitive bird, it may not be a direct first ancestor of all living birds",
". It may be an offshoot group of theropod dinosaurs. To my knowledge this is an ongoing debate.",
"For more information see: avialae is a clade (group) of dinosaurs containing their only living representatives, the birds (Aves), and the most immediate extinct relatives of birds. Archaeopteryx may or may not be included.",
"Edit: ",
"This evolutionary history of birds may also help you",
"Edit: how was their DNA able to be passed on and share similar traits with modern day species of birds?",
"Since birds are dinosaurs, they already have dino DNA. No need to pass it on in the sense that you are thinking of.",
"Its also important to understand that the dinosaur groups was around for many hundreds of millions of years, but within that time species only typically lasted around 2 million years. Meaning, there were many extinctions and diversification events within the time frame of the dinosaurs but none were so widespread and destructive as the extinction event at the end of the cretaceous (K-T boundary). There is tons of evidence for a sudden and massive extinction event at this time, most but not all dinosaur groups present at that time went extinct. The most notable exception were the birds. "
] |
[
"A mass extinction definitely ",
" happen. This has to be, since for millions of years you have dinosaurs and then suddenly (geologically speaking) you don't anymore.",
"It could have been climate change, it could have been a meteor, it could have been a flood (ಠ_ಠ), it could have been ",
"aliens",
". No one is seriously sure what caused it to happen.",
"There have even been other mass extinctions. This doesn't mean that ",
" on earth died... it just means that a ",
" of things died. This leaves room for rats in holes tiny dinosaurs with feathers to become humans and birds.",
": Forgot where you mentioned gradual climate change. Like I said that is also a possible mechanism for a mass extinction, but the only evidence we have to work off of is on a geological time scale (as in about a million years, and that is only more recent times, so think more like a few million years at best) this means that there could have been a climate change over a few million years that big things like dinosaurs just couldn't cope with while small buggers were fine with it. The problem is that this million years of change results in a very small layer of rock that we can't be quite sure of it's beginning and end time-wise.",
": Also, a meteor hitting causing the extinction would not have caused it in the way portrayed in popular media. It wouldn't have been like you nuked the entire surface of the planet and instantly incinerated everything. Don't get me wrong, that totally happened at the impact site and for a ",
" large radius around it, but not the entire globe. The meteor would however have caused long term climate issues, think \"nuclear winter\". Junk gets in the atmosphere blocking out sunlight and cooling the planet down. Or possibly trapping more sunlight and heating the planet. But the big thing is that the dinos didn't die in one day regardless of how they died. They died over a fairly long time period be that a million years or ten thousand."
] |
[
"Will flowing water and stagnant bodies of water freeze the same way and at the same rate?"
] |
[
false
] |
When it gets chilly, my family runs the tap at night to prevent our pipes from freezing. It's something we've always done, but I've never understood why it works. This got me thinking about the way water freezes in nature. If there is a flowing stream and a stagnant pond in the same area, affected by the same freezing temperature, will they freeze at the same rate? Additionally, will the flowing stream freeze in a different pattern than the stagnant pond?
|
[
"AFAIK, you run the faucets in winter because home plumbing, is not as well insulated/heat regulated as it would be coming from the grid/watertowers/reservoirs.",
"If water sits in a pipe that is 32°F or below, it will freeze when it reaches that temperature, moving or not, but when you run the water, you are moving water from a warmer source as mentioned before, through your pipes and back into the grid.",
"Again, afaik, water will freeze at 32°F (at STP) regardless of its motion. There’s some pretty beautiful pictures of frozen waterfalls that are rather bizarre to see."
] |
[
"Thank you. That was a helpful answer. :)"
] |
[
"Happy to help friend, stay tuned though. Someone else may give a better answer or correct something I got wrong :)"
] |
[
"Quantum question about spin..."
] |
[
false
] |
I am trying to understand a little about quantum mechanics for fun but, I am slightly confused about one thing so far .Lets say we have prepared a a bunch of electrons so that they are all facing one way by using magnets then we rotate them by switching on another magnet. Lets say we rotated it 90 degrees. Now from what I understand is that some of those electrons will flip and some will not therefore we will get radiation of a certain amount from 50% of the electrons turning because we use probability. The thing I cant understand is how come we don't know that they all, not half, turned buy 90 degrees therefore putting out a lower energy amount? (I'm not sure if this is clear please tell me if it is not)
|
[
"The situation you described is more of a classical picture because you assume that you know all three components of the spin. In actuality, you do not. Even if you know one component, you can't claim to know the other components."
] |
[
"Okay, I think I better understand your question.",
"Susskind assumes that there is only one electron. When you talk about the use of multiple electrons, it is only useful insofar to make the idea of the probability meaningful. You can prepare multiple electrons the same in separate experiments, and half the time they will flip, half the time they will not.",
"Electrons, if they flip in that manner, will always release the same amount of energy. Doing just one experiment will release some energy, but in order to get results that are consistent with quantum, you need a large ensemble of experiments."
] |
[
"U can make this question meaningfully however by considering just one component of the spin, the question is is still valid with this adjustment",
"Im not really sure what your getting at with the last part of the question, perhaps you would like to elaborate a bit",
"Perhaps this will help. When you prepare an electron with the z-component of spin in, say, the \"up\" configuration. You can ask what is the probability of observing the spin being \"up\" along the z-axis, and the answer is 1, and every experiment will say that the spin is up (you prepared it like this so it should remain this way). However you could look at another observable, say the x-component of spin of an electron prepared in this way. It turns out that half of the experiments will say its up and half will say its down. Just note you can't ask both questions at the same time though (Pauli matrices do not commute). This is the physics of the \"Pauli matrices\" and their eigenvalues",
"Also if you interested in this type of physics, I recommend starting with plane polarized light, it's the exact same physics but much easier to visualise."
] |
[
"What happens to the fructan in garlic when burnt?"
] |
[
false
] |
[deleted]
|
[
"Fructan is an oligosaccharide, essentially, it's a big chain of fructose molecules joined together. During cooking, those big chains are randomly broken into smaller and smaller chains or random length. It's exactly the same as trying to cut a string into small pieces by only using random cuts.",
"This is one reason why beans make people flatulent. It's really difficult to break those big chains into individual pieces - you mostly just end up with a lot of small chains. Instead, you want to rinse out as many chains as possible and not bother trying to smash them up.",
"Frying does decrease the amount of all oligosaccharides (including fructan). It is a function of cooking temperature, time and any pre-treatment.",
"Very very very crudely, frying beans for 5 minutes @ 190°C will ",
"decrease the oligosaccarhides down to about 50-75% of initial concentration",
".",
"Black garlic may be interesting to try. ",
"Temperature is used to break the fructan chain into fructose sugar",
" and it drops by about 15%. Black garlic tastes quite sweet.",
"IMHO - stick with your elimination diet for at least a week to observe changes. It can take anywhere from 12-72 hours for food to move through your digestive tract."
] |
[
"Thank you for the help!"
] |
[
"Here's ",
"an article that reports",
" their own and previous experiments showing that the amount in other foods drops significantly when cooked at a high enough temperature for long enough. Unfortunately they don't report the temperature the samples got to during the cooking so it's hard to know how to figure out whether your garlic cooking process is adequate to do the same thing but it seems likely."
] |
[
"If evolution occurs over a long period of time, how and why do the individual creatures adapt themselves?"
] |
[
false
] |
[deleted]
|
[
"how does it occur in that specific giraffe's lifetime?",
"It doesn't.",
"Since the evolution occurs over such a long period of time I don't understand how it occurs in individual creatures, and therefore at all.",
"Individuals in the population will have mutations that benefit them slightly, for instance, a giraffe precursor happens to be born with a slightly longer neck. He is more successful, and his genes are more widely spread. You now have a population of animals with a slightly longer neck. Continue that until neck reaches silly proportions.",
"But then why did they develop those traits in the first place?",
"They develop randomly through mutation and recombination. Most mutations are deleterious, but occasionally one pops up that provides an advantage."
] |
[
"(not a biologist but studied it in university)",
"Creatures don't choose to evolve. Evolution happens when you have two things: variation and selection. For example, in the arctic you'll have a bunch of rabbits of varying fur colours. The darkest rabbits are the easiest for predators to see, so they tend to get eaten, leaving more light coloured rabbits that camoflauge in the snow. Over time, the arctic rabbit population gets whiter. They didn't choose to whiten, it just happened due to variation and selection.",
"To understand the mechanism of variation and how these traits are propagated, you'll have to get into the molecular biology of it."
] |
[
"Am I saying this correctly?",
"That's a reasonable explanation. If you want to learn more, check out these. They are crucial to an appreciation of evolution.",
"http://en.wikipedia.org/wiki/Natural_selection",
"http://en.wikipedia.org/wiki/Genetic_drift"
] |
[
"Why is breastfeeding so difficult and unintuitive for many women? Why aren't humans like other animals that seem to do it with ease?"
] |
[
false
] |
It seems that many new moms and babies have to struggle to learn this basic function. How does this make sense evolutionarily?
|
[
"It seems that evolution conspired to make breastfeeding something that has to be learned for all primates. There are studies that show monkeys, chimps and apes all have to be shown how to breastfeed successfully. Humans are in that group as well, and because of modern life we have other problems that confound what should be easy. "
] |
[
"Do you mind linking a reference? It sounds like an interesting paper to read."
] |
[
"A correllary question would be: do new mothers in societies where toplessness is common have less problems than in places like the US, where women can't casually expose their breasts?",
"IOW, maybe young females in most species are used to seeing adult females help their babies \"latch on\", Cows just have to stand still, but calves are born ready to walk; apes have to hold newborns close and encourage them in certain ways. American human mothers, however, may have never seen strangers hold a newborn to their breasts - and our babies are born more helpless than most animals'. It might take a lot of learning through observation to get the fine details right.",
"Dunno."
] |
[
"Why do bubbles form after you mix soap/cleaning detergent/shampoo with water?"
] |
[
false
] |
Relevant:
|
[
"Soap acts as a ",
"surfactant",
". Surfactants go between the interface of two phases, in the case of soap, water and air. Normally chain molecules, one side of the chain has a higher affinity for air, and the other a higher affinity for water, sit between the two, and they make the two phases happier to stay near each other.",
"Because it's not trying to exert as much energy to get away from the water it can get trapped underneath a layer of surfactant and water."
] |
[
"Surfactants actually lower the surface tension of water; the polar/ionic ends of the surfactants interact with water, disrupting hydrogen bonding. I believe this might just be an issue of wording in your sentence but I just wanted to clarify that to anyone curious about it."
] |
[
"Yeah that is my bad. Tutoring O-chem this semester so forgetting some of my surface chem."
] |
[
"Is it better to spit out phlegm when coughing, or is it fine to just swallow it?"
] |
[
false
] | null |
[
"Depending on how sick you are, if you swallow too much phlegm it can make you feel nauseous from the volume of mucus entering your stomach. It definitely won't make you any sicker though. Phlegm is coming from your lungs (delicate and very vascularized) and going to your stomach (tough and extremely acidic) where pretty much everything is going to be broken down extensively.",
"I think my microbiology professor said that receiving benign exposure to broken down pathogens in your stomach can help jump-start your immune system (idea behind oral vaccines), but if you're at the productive cough stage, chances are your immune system is already on high alert and producing B-cells and antibodies to whatever is making you sick."
] |
[
"Just to play devil's advocate: if we're advising people to search ELI5 before asking questions, why not just have them search google and do away with the subreddit altogether? Surely there's a simple enough explanation for most of these questions available on google...",
"EDIT: I thought this post was submitted to ELI5. It makes a lot more sense for people to search AskScience before posting than it does to ask them to search ELI5 before posting."
] |
[
"Just to play devil's advocate: if we're advising people to search ELI5 before asking questions, why not just have them search google and do away with the subreddit altogether? Surely there's a simple enough explanation for most of these questions available on google...",
"EDIT: I thought this post was submitted to ELI5. It makes a lot more sense for people to search AskScience before posting than it does to ask them to search ELI5 before posting."
] |
[
"Why do spicy foods like horseradish sauce or wasabi clear your sinuses?"
] |
[
false
] | null |
[
"Most commercially produced \"wasabi\" is actually horseradish paste with green coloring added.",
"Genuine wasabi is related to horseradish, but it's very difficult to cultivate, even under ideal conditions. You aren't likely to find it outside of japan.",
"The spiciness of horseradish, wasabi, radishes, mustard, and other members of the mustard family (brassicacea ) is due to a class of reactive compounds called ",
"\"Isothiocyanates.\"",
" ",
"In the case of horseradish and mustard, the most potent compound and the one produced at the highest concentration is called Allyl Isothiocyante. Although several other ITC's are produced as well.",
"Allyl Isothiocyante is a fairly small molecule that easily evaporates. So when you eat horseradish, your body heat evaporates some of the compound and it travels up your nose and throat passages as a gas.",
"A-Itc stimulates a pair of ion channel proteins called TRPV1 and TRPA1",
"TRPV1 is normally responsible for sensing pain and excess heat. So when A-Itc reacts with these channels on sensory nerves, it produces a painful burning sensation. It fools the nerves into thinking things are too hot.",
"TRPA1 is normally responsible for sensing mechanical stress, and also pain thereby. So A-Itc fools the nerves into produces a tickling, stretching sensation. It makes it ",
" like your nasal passages are opening up, but that's merely an illusion.",
"The nervous system responds to this by stimulating mucus glands in the nasal passages and the tear glands in the eyes to produce extra fluids.",
"TRPV1 also responds to capsaicin found in chilies. Although capsaicin is chemically unrelated to A-Itc. Capsaicin is a large-sized oily compound, which is not very water soluble and doesn't evaporate easily. That's why chili peppers tend to affect the mouth, tongue, and throat and have a bit of a \"delayed effect.\" ",
"Since capsaicin only affects TRPV1, it produces the burning heat, but not the stretching and tickling feeling.",
"While mustard and horseradish travels up into the nose and sinuses and takes effect almost immediately, because A-Itc is a fairly small compound."
] |
[
"Wow, thanks for the explanation. "
] |
[
"Wow, thanks for the explanation. "
] |
[
"Where/how was the first cell created? According to cell theory?"
] |
[
false
] |
According to cell theory, cells are not spontaneously made but instead produced from other cells. How was the first cell created?
|
[
"As ",
"u/AsAChemicalEngineer",
" said, we do not know. And there may have been more than one primitive cell that emerged from non-cellular material. However, all life on earth appears to be descended from a common ancestor cell."
] |
[
"Ph.D in biology here. \"We don't know\" is correct, however, we have really good hypotheses. Interestingly, we don't \"know\" anything for sure in science.... we just have varying degrees of trust in our hypotheses. So, read on...",
"What you're talking about is called \"abiogenesis\" --the process of life arising from non-living materials.",
"Here are a few great links that will provide you with the answers you're looking for: ",
"http://www.ncbi.nlm.nih.gov/books/NBK9841/",
"http://evolution.berkeley.edu/evosite/evo101/IIE2bDetailsoforigin.shtml",
"http://www.newscientist.com/article/dn17987-how-life-evolved-10-steps-to-the-first-cells.html#.VNt0__nF-MI",
"The first cells needed to accomplish three tasks: 1) copy information (likely RNA precursors), 2) perform basic catalytic functions, and 3) extract energy from the environment and put it into a chemical form. It is largely thought to have been a biochemical (rather than biological) process. ",
"None of the current hypotheses are satisfying. Researchers are actively working to recreate abiogenesis in the lab, however none have been successful yet. "
] |
[
"As already mentioned we don't know how but we do know the when (roughly); it must have occured some time between 3.5Billion and 4.5Billion years ago.",
"It's roughly belived that self-replicating molecules (probably RNA) appeared before cellularisation occured. How cellularisation occured is widely debated and there are a number of theories with little evidence in the favour of any one."
] |
[
"Why do radiologists always keep it dark in the room where they take x-rays? Does visible light affect the x-ray exposure?"
] |
[
false
] | null |
[
"The region of the patient's body that will be exposed and visualized through x-ray based imaging is commonly shown in the room by a light beam projected from where the x-rays originate. By keeping the room dark, a radiologist or x-ray tech can see whether the patient is properly positioned with respect to the beam.",
"The light beam also allows the radiologist to adjust the beam so that it focuses on as small a region as possible without missing the anatomic structures of interest, a process known as \"collimation.\" Collimating the beam reduces x-ray photon scatter, which in turn improves image sharpness. It also reduces patient exposure."
] |
[
"For the most part, the image on the film is not due to x-rays striking the film but due to the x-rays striking a phosphorescent screen that surrounds the film.",
"Depends on the film. Some types of film are sensitive to visible light and use phosphorescent screens. Other types are sensitive only to x-rays (e.g. GafChromic, which undergoes a polymerization reaction). "
] |
[
"Ignore the stuff about films. If we are talking about Radiology in a developed country, the imaging is done digitally using one of two types of detectors. Both types of detectors have a low sensitivity to the visible spectrum, and have a protective cover anyway. Even old fashioned film was kept in a cassette, so the light in the room was not a problem.",
"The real reason the room is kept dark, is because the region that is going to be irradiated is indicated by what is referred to as a \"light beam diaphragm\", and the light sources used aren't very powerful. Hence to get a good idea what you are taking a picture of, it's best to have a bit of mood lighting.",
"A second reason is that the processing/viewing areas are often in low light for optimum viewing purposes, so some radiology departments tend to keep all the lighting at the same level.",
"Oh, and it's usually a Radiographer or Radiology Technician that perform plain xray examinations, not a Radiologists. "
] |
[
"How does qubit work?"
] |
[
false
] |
[deleted]
|
[
"As far as I know, qubit is a term in quantum computing, where some information can be 1, 0",
"A qubit can have more states than that. It can be in infinitely many states that can be visualized with a sphere that has the |0> state on one pole and the |1> state on the other. This sphere is called Bloch sphere and looks like ",
"this",
". ",
"It's important to note that while there are infinitely many states, the qubit will collapse into either the |0> or the |1> state upon measurement. The closer its state was to the e.g. |0> pole before measurement, the more likely it will collapse into the |0> state upon measurement.",
"So it's not so easy to understand why such a qubit should be any more useful than a normal bit, as it also comes with only two measurement outcomes just as the regular bit. You can however use their fragility and the way that you can manipulate them for secure key distribution and you can implement algorithms with them for problems for which we know no efficient classical algorithm."
] |
[
"It is important to realize a qubit still ends up being a 1 or 0 in its output (when it is measured).",
"What makes it different from an ordinary bit is the way it can be manipulated before it is measured. ",
"For instance, a single bit can only be switched: 0 to 1 or 1 to 0. Single qubits can be controlled in more complicated ways like putting a 0 state into a superposition of 0 and 1."
] |
[
"Qubits are based on quantum mechanics. If you have a particle with two different energy levels, 1 and 0, and perturb it with a magnetic field, then you don't know for sure whether the particle ends up in the 1 or 0 state until you measure it. By choosing the magnetic field correctly, and entangling multiple qubits together, we can manipulate qubits with gates, somewhat analogous to the NOT, AND, OR, etc. gates of classical computing. It's all based on the probability of qubits ending up in the 1 or 0 state at the final measurement."
] |
[
"Do phosphorescent/fluorescent materials glow in daylight?"
] |
[
false
] |
I've read up a little bit on fluorescence and phosporescence, but I don't definitively have an answer to this - I have a pair of shoes which are partly glow-in-the-dark. Even in somewhat dim light they seem to not glow the least bit, while in the dark they are remarkably bright. So is it the case that the glow is simply masked/overpowered by other ambient light, or is it that the material actually can't emit unless it is dark? As far what I've read goes, the way glow-in-the-dark things are made is with a combination of something like zinc sulfide (phosphorescent) and sodium fluorescein (fluorescent), since that way the result has the delayed emission effect from phosphorescence, and the brightness from fluorescence.
|
[
"Yes; its also easy to test, get a glass of tonic (as in gin and tonic), and hold it up next to a piece of white paper. There will be a tinge of blue this is the fluorescence caused by the UV in sunlight. I you do this inside with a normal light bulb the tonic will not have this faint colour. ",
"the reason that it look faint is as you say its over powered by the natural light. "
] |
[
"That's a really cool picture - so let me ask you something unrelated - what constitutes a \"healthy\" plant, as far as amount/distribution of chlorophyll goes? Is the one above healthy?"
] |
[
"Thanks; to make sure - is this definitely also the case with phosphorescence?"
] |
[
"Is there a reason why phone screens are made of glass and not something harder to crack, like plastic?"
] |
[
false
] | null |
[
"Glass is harder and isn't scratched as easily as plastic. This at least was the reason ",
"Apple",
" screens were made from glass. "
] |
[
"Apple wanted to use artificial sapphire, but couldn't get a supply cheap enough. BTW super market laser scan windows are made of sapphire. It is the next lowest hardness on the Mhos scale from diamond. Harder than quartz. They really need it there, where all manner of things are dragged across them every day.",
"Edit: some ",
"other manufacturers",
" are trying to compete with sapphire.",
"Windows used in supermarket laser barcode scanners and other high volume barcode scanning applications are subject to scratching from objects such as glass bottles and other packaged goods when their barcodes are scanned, resulting in reduced read rate, poor read accuracy and lower productivity. Our patented EVERSCAN superhard windows exhibit extreme diamond-like properties that will last the life of the scanner, allowing authorized OEMs to offer a lifetime warranty.",
"The performance of EVERSCAN is similar to sapphire scanner windows at a fraction of the price. Unlike sapphire windows, however, EVERSCAN can be produced in any size to meet the demands of new system designers or to replace scanner glass in existing scanners. DIAMONEX can provide this product in quantities suitable for scanner equipment manufacturers or grocery store chains."
] |
[
"That's very interesting, apparently it's also used on some Apple Watch screens."
] |
[
"Why are volcanic erruptions causing volcanic winters even though they emit CO2?"
] |
[
false
] |
Hello, student here, dealing mainly with climatology and GIS. Recently I've had a quarrel with a client at the shop I am working at. He denied climate change so I tried to talk to him about it. I couldn't answer the question you see in the title. Now that I think about it I am guessing that volcanoes emit volcanic ash, sulphur dioxide and other gasses AND CO2. So the CO2 gets into the atmosphere and it does contribute to warming, but the ash cloud prevents the energy from reaching the earth. Is it correct or am I confusing something here? Also, another question of his wnich confused me was about the CO2 effect on warming. He said that the if the CO2 blocks radiation, then it should also block incoming radiation from sun. So it would block some of incoming radiation, and some of the earth's radiation and it should even out. I know that's not the case, but my courses don't teach ANY physics, even those dealing with climatology and climate change, so my understanding of these issues is very poor considering I am a student related to the subject. But I want to learn :( I did try to get a grasp of some basic university level physics on my own (tho failed miserably at that), so I would love you to provide a reasonably detailed explaination. I'd like to know what happens, how and why. I would gladly be also directed to any articles that deal with this issue. In advance, thanks for help :)
|
[
"The volcanic ash prevents part of the solar radiation from reaching the lower layers of the atmosphere where we live. Hence, decreasing the temperatures, as you said. It can stay in the stratosphere for a very long time (=rain doesn't clean it). Look the Pinatubo eruption up.",
"The radiation from the sun is absorbed and reemited by the atmosphere. Same happens with the thermal radiation by the earth, but in different wavelengths. The increased CO2 increases the absorption of radiation inside the atmosphere. You could see it like this: if the radiation in a given wavelength is not absorbed at all by the atmosphere, it reaches the surface. Depending on the albedo of the surface at that wavelength, part (or almost all) of it goes back to space all the way out. \nIf you have an absorber, be it CO2 or water vapour, the radiation ",
" in the atmosphere and is reemited ",
", thus causing a warming. The higher the concentration of your absorber, the greater the warming. CO2 doesnt block radiation like a mirror. It absorbs it and reemits in all directions (not just back to space)"
] |
[
"I'm glad you're confused about this stuff--it means your brain juice is flowing!",
"/u/CrustalTrudger",
" provided a ",
"great response",
" to a ",
"recent thread",
" on the topic of volcanic emissions of CO2 versus anthropogenic CO2 emissions. The quick answer is that the sulfur dioxide aerosols released by volcanoes find themselves in the upper atmosphere, where they can ",
"efficiently block out incoming radiation",
". However, these tiny particles are cleaned out of the atmosphere by rain within a few years, which ends there short-lived effect on climate. It's called a volcanic ",
" to imply that the event is ephemeral. CO2 released by volcanoes can contribute to longer-term warming, but is overridden by the aerosols on the short term.",
"The case of greenhouse gases reflecting incident radiation is always a topic of conversation among my students, and a valid question before you learn the details. Energy from the Sun arrives at Earth primarily as ultraviolet radiation (UV light), which is ",
"high-energy",
" for our purposes here. ",
"About 30% of that energy",
" is reflected right back into space by the clouds and Earth's surface, about 20% is directly absorbed by the atmosphere, and the rest (50%) is absorbed by the Earth's surface, warming it up. ",
"Here's the neat trick: the Earth's surface then re-emits some of it's absorbed energy. Because some of the energy is used to warm the land and oceans, there is only going to be some fraction of the incoming energy left over to shoot back up towards space. The energy level of this re-emission places it in the infrared part of the ",
"EM spectrum",
", which is what we feel as heat (",
"check out a heat lamp",
"). Gases in the atmosphere can absorb and reflect this IR radiation more efficiently than UV radiation, so the net result is that the air above us warms up a bit more and the clouds zap some of those heat waves back toward the Earth's surface, where the heat is again absorbed. These atmospheric gases trap energy much the same way that panes of glass trap heat in a greenhouse. It's warmer in the greenhouse for the same reason that it's warmer on Earth than in outer space. ",
"ELI5 version: High-intensity stuff flies toward Earth, some of which pings off the globe, some gets sucked up, and some gets ",
" and then leaks out again. The leaking energy can't make it back out of the atmosphere (the greenhouse), so it has to ping around until it's absorbed by the clouds or the globe.",
"tl;dr: Volcanoes shoot out SO2 aerosols, which only cool the climate for short durations. CO2 works on longer time scales. Not much UV energy from the sun is reflected by GHGs. The GHGs trap heat that is first absorbed by Earth and then re-emitted as IR."
] |
[
"But wait, window glass is opaque to light of infrared wavelengths, so your car gets hotter and hotter. Now substitute car windows with CO2 and that's how the greenhouse effect works on the globe.",
"This is actually a super common misconception. It's understandable because, believe it or not, the \"greenhouse effect\" is a misnomer: actual greenhouses (and your car) heat up because of suppressed convection, not the greenhouse effect. This is similar to the way that a blanket keeps you warm, and is quite different from the actual greenhouse effect in the atmosphere.",
"If you do an experiment where you ",
"replace the windows of a greenhouse with panes of salt",
" (which is transparent to both visible light ",
" thermal infrared), the greenhouse will heat to almost the exact same temperature as if the panes were made of glass.",
"Confusingly, though, atmospheric heating ",
" caused by the greenhouse effect."
] |
[
"Humans and chimpansees diverged some 6 million years ago. This was calculated using the molecular clock. How exactly was this calculation made?"
] |
[
false
] |
Please be very specific but understandable to laymen. I want to understand how divergence dates are estimated by use of a specific example.
|
[
"Molecular Clock Hypothesis tries to estimate how far apart organisms are evolutionarily by means of using specific proteins. Some proteins, such as cytochrome c (present in almost all organisms) seem to have a fairly consistent time between neutral mutations, meaning that if most mutations are neutral (have no effect on fitness), and if they occur at more or less regular intervals, you can estimate how many new mutations you should see in a generation. ",
"Thus, by measuring the number of mutations in that protein from the time when two now distinct species had the same or very similar versions of these proteins, one can theoretically estimate the time these species diverged. There are several limitations of this process, like fossil prevalence, generation time and metabolic rate, among others. So while it may not be a perfect process, it's not without its uses."
] |
[
"One of the coolest methods I know is the use of endogenous retroviruses as molecular clocks to date divergence between species. First off, what is an endogenous retrovirus? HIV is a retrovirus and all retroviruses incorporate their DNA into the DNA of the host they infect. If a retrovirus does this in a sperm or egg cell, and then these cells give rise to a baby --> voila! all subsequent descendants from that baby have this endogenous retrovirus in their DNA (this has happened a lot over our history and ~8% of the human genome is endogenous retroviruses).",
"So how do they work as clocks? When they integrate into your DNA, these viruses have two identical LTRs (long terminal repeats). These LTRs then accumulate mutations independently over evolutionary time scales. Given that we know the (very low) mutation rate of DNA polymerase (the enzyme that copies our own DNA for cell division), we can calculate how long ago the endogenous retrovirus entered our DNA. ",
"For your specific question, there are 7 endogenous retroviruses shared between humans and chimpanzees. Using their LTRs as molecular clocks one can calculate how long ago we diverged. I'll defer to a molecular biologist for the details of these calculations. Hope this helps and at the very least prompt some people to read up on endogenous retroviruses - we are all part virus!"
] |
[
"I'm an evolutionary anthropologist!",
"They compared the genomes of humans and chimps, estimating the total number of divergences (changes). Then they calculated the average number of mutations (changes) in one generation (by comparing the genes of parents and children). ",
"Then they performed the following calculation: \n[(Number of total divergences)/2]/(mutations per generation)\nto determine how many generations have passed since the divergence of humans and chimps. (They divide the total number by two because the divergences represent changes accumulated in both the chimp genome AND the human genome, whereas you want the number of generations for just one species, since they're happening simultaneously.)",
"Now that they have the number of generations, they convert that to a time by multiplying that number by the average generation time - that is, the age at which a parent has a child (the average child, not first or last). ",
"So basically, find out how different the genomes are, find out how many mutations happen per generation, and calculate how many generations have passed. Then multiply by the number of years a generation is.",
"Finally, they corroborate it with fossil evidence. We can date fossils using isotope dating, so if we have fossils for all the \"intermediate\" species dating back to a common ancestor for two species, we can get a good timeframe for their divergence. The problem with fossil evidence is that it's actually very limited for non-human apes. We have a good fossil record for the human lineage, but not for the chimp, gorilla, or orangutan lineage. The next closest primate that has a really good fossil record is actually macaques (a type of monkey), so calculations are often checked against the macaque record. For a long time, our ape calculations actually didn't jive so well with the macaque record.",
"Something interesting happened in 2012 (I could be misremembering the year). Scholars named Scally and Durbin proposed that the calculations had all been incorrect because they had used generation time for ",
". Larger animals tend to have larger generation times (bigger animals have kids later, take longer to mature), and extant modern apes are generally larger than their ancestors. Therefore the \"generation time\" variable was decreased a little, and these guys' new calculations fit better with the macaque evidence. ",
"Edit: wording"
] |
[
"How is glass made, which is a mirror from one side, and a window from the other?"
] |
[
false
] | null |
[
"You basically coat one side of glass with a reflective coating (thin, semi transparent reflective material like aluminium). This is done very sparsely, so the reflective molecules don't cover half of the glass.",
"The glass works as normal and people see each other, but if the surrounding area on the side with the coating is brightly lit, the reflective material does what it does best, reflects. The reflection is far brighter than what you see through the glass, and it dominates your eyes.",
"No such mirror exists which is a perfect mirror on one side and a window on the other."
] |
[
"The one-way-mirror isn't actually a one way mirror. It's a trick of the lighting. Glass reflects a fair bit of light anyway so just keep the interogation room bright so that a lot of light reflects off of the glass and the observation room dark so that not much light gets into the interogation room. That way, someone inside will mostly only see their reflection. You can amply this effect by partially silvering the glass too. ",
"Anyway, here's a picture."
] |
[
"A mirror that you have at home is typically a thin layer of metal, typically aluminum, that has been layered onto a sheet of glass. The process is called ",
"silvering",
", since silver used to be more widely used. If you make the thickness of the aluminum very thin, you will ",
"reflect less light and allow more light to pass through",
". A one-way mirror, or half-silvered mirror, will aim for less than 100% reflection.",
"Now, if the mirror reflects 50% of the light, then you might think you should be able to see through it all the time. In a sense this is true. But if the room on the other side is very dark, then your reflection will be so much brighter than the room behind the glass that the reflection is all you see. If you are in the dark room, the opposite is true.",
"Even plain glass reflects a little, so you can see a similar effect in your windows at night if it is very dark outside. From the inside, you can't see outside easily because of your bright reflection. From the outside, it is very easy to see into the house."
] |
[
"My Pyrex baking dish exhorts the user to both \"Avoid sudden temperature changes\" and \"Always preheat oven.\" That seems like a contradiction. What property of the glass accounts for this?"
] |
[
false
] |
Taking a dish from a refrigerator (roughly 38F) and placing it directly into a preheated oven at 400F seems like a worse "shock" than placing it into a room temperature oven and slowly bringing it up to temp. Yet, the instructions clearly indicate otherwise. What gives? Happy Thanksgiving, to those celebrating.
|
[
"They probably mean dont do things like take it from the oven and put it in the sink with water. The dish will heat up slowly in the oven because air is a poor conductor of heat...but if you take it from the oven and run water over it, water is a much better conductor so the dish will cool rapidly and could crack."
] |
[
"Pyrex today is made of tempered glass. Pyrex used to be a low thermal expansion borosilicate glass, according to Wikipedia. Now glass subjected to a fast change in temperature breaks because glass is a thermal insulator. If you cool a surface of the glass quickly, you induce a large variation of temperature along the inside of the glass, which for a dish can be pretty large. The cool side will shrink, but the hot side won't. This will cause stress inside the glass dish, which can be enough to break the glass. Since original Pyrex had a low thermal expansion, it would induce lower stresses and not break. Tempered glass is a resistant glass that is already stressed in a way to make it more resistant. It also breaks into very small pieces when shattered. However it still expands or contracts enough to break when subjected to sudden large temperature changes."
] |
[
"Do you know if anyone makes cookware like the old Pyrex?"
] |
[
"Are electron bonds \"real\"?"
] |
[
false
] |
I understand basic chemistry and how atoms share electrons to complete their shells. Are the bonds real, or are they a figure of speech/an analogy? I prefer to think that the atoms are held together by their electric field acting on the electron which is in a potential well, am I losing any detail or rigor because of this? Thank you.
|
[
"On the bottom left of ",
"this image",
" is an atomic force microscopy image of a pentacene molecule. The brighter the colour, the stronger the interaction between the molecule and a little pointy tip. As you can see, there are regions between where the atoms are where the tip feels attraction. As to whether those are \"real bonds,\" it comes to how you interpret formalism."
] |
[
"You can't look at the electron as a tiny ball. In quantum mechanics it can't be interpreted as living at a definite position or travelling in some nice orbit. The electron is in fact spread out over the entire molecule.",
"Eventually that level detail won't be sufficient to understand chemistry, though it should be okay if you're at the early highschool level. If you have a double bond, it actually ",
"forms in blobs on either side of the first, central bond",
" (note that both sides constitute ",
" bond). This is why double bonds ",
", since the bond takes more energy to be broken than normal random jiggles will provide (at low enough temperature anyway. high temperatures screw with chemical bonds all the time). An explanation of two electrons sitting on either side, tugging on each other through an electrostatic potential could not account for this."
] |
[
"They're as real as much as you put stock into the math correctly describing the system. The bonds represent low energy configurations of electrons between multiple atoms--the evidence for such bonds is about as strong as the evidence for cells or gravity."
] |
[
"Why does the moon seem to have significantly more craters at the poles?"
] |
[
false
] | null |
[
"Some of that is in the word \"seem\", like the moon seems to be bigger when at the horizon. It isn't actually bigger, but a trick of perception. The angle of view at the poles mean you're seeing more land in a smaller area of view.",
"Here's a good video about the Moon's craters: \n",
"https://youtu.be/mCzchPx3yF8"
] |
[
"Take a piece of paper and draw some uniformly distributed random dots on it. Look at it straight on representing the equatorial view. Then tilt the paper 89 degree to represent the polar region view. You will perceive that the dots to be much more dense on the polar view even if they are the same paper you are looking at. And for fun, tilt it 180 degree. What do you see? ",
"So, angle of view can give different perceptions of the same exact object."
] |
[
"You see a circle, but on a sphere the center of the circle is closer to you and the edge is further away. A (for example) 100 km² square patch of the moon in the center of your field of vision will appear to be more or less square, while the same sized patch near the horizon will appear to be much smaller in one dimension. But both patches will contain roughly the same number of craters, therefore causing the smaller-seeming patch's crater distribution to appear much more condensed.",
"Edit: The previous poster's example with a flat plane may make more sense if you think of a model of the moon made out of polygons, especially the low polygon-count models in Playstation 1 or N64 games. Each polygon is one of the planes from their example, with the ones towards the edge having a greater tilt."
] |
[
"Why do nuclear bombs create a 'mushroom' cloud?"
] |
[
false
] | null |
[
"Whenever a less dense substance moves through a more dense substance, it creates instabilities and vortices like those created in a mushroom cloud. This is known as ",
"Rayleigh-Taylor instability",
". ",
"In the case of a nuclear weapon, the fireball is very hot and much less dense than the air around it — this is why it rises. However, as it rises it cools and encounters friction with the air. This causes the \"ball\" to flatten and turn into a torus surrounded by mushroom cap. The stem is caused by the hot fireball sucking up dirt from the ground into it; if the bomb is detonated at a high-enough altitude, ",
"a stem does not form",
". "
] |
[
"I'm too lazy to go looking, but FYI there are plenty of youtube videos of non-nuclear explosions of various sizes producing mushroom clouds. "
] |
[
"There are actually two things happening in a mushroom cloud. The first is a large, spherical explosion. Energy and matter move outwards in all directions. ",
"There are no issues moving up, forward, backward, left or right. Going down isn't going to happen. There might be a crater formed, but a lot of that energy is going to reflected up. So in general, you will have a net amount hot gas flowing straight up, like jet.",
"So now you have a hot jet of gas flowing up into a cold atmosphere. It can over come the resistance up to a certain point, then turbulence starts to eat away at the jet and large eddies (ie, the mushroom top) start to form. "
] |
[
"Why doesn't the midpoint formula(divided by 3 instead of 2)find thirds of lines?"
] |
[
false
] | null |
[
"Why should it? If (",
"+",
")/3 is ostensibly the endpoint of the first of the three equal-length subintervals of [",
", ",
"], then it must be the case that ",
"-",
" = 3*(",
"+",
")/3 = ",
"+",
", i.e., if and only if ",
" = 0.",
"If ",
" < ",
", then the length of any of the ",
" equal-length subintervals of [",
", ",
"] is (",
"-",
")/",
". So the endpoint of the ",
"th subinterval is",
" = ",
" + ",
"(",
"-",
")/",
" = [(",
"-",
")",
" + ",
"]/",
"This reduces to a multiple of the simple average of ",
" and ",
" only when ",
"-",
" = ",
", or when ",
" = ",
"/2. In other words, one of the endpoints of the ",
" equal subintervals of [",
", ",
"] is a multiple of the simple average of ",
" and ",
" only when ",
" is even and only for the midpoint of the interval."
] |
[
"Well, the reason that you divide by 2 is not because its length is divided by 2 but because we take the average of 2 points. So if you want a third, you don't divide by three because you aren't looking for the average of 3 points, which is what you seem to be suggesting by doing the math that way. ",
"So the halfway point is:",
"a+(b-a)/2 = a+b/2 -a/2 = a/2 + b/2 = (a+b)/2",
"In word: the point halfway is 'a' plus half the distance between 'b' and 'a'; (b-a)/2",
"For the point a third away:",
"a+(b-a)/3 = a+b/3 - a/3 = 2a/3 + b/3 = (2*a+b)/3"
] |
[
"Sorry, could you explain in layman's terms?"
] |
[
"Is data sent through the underwire wires in the ocean sent digitally or is it modulated and sent as an analogue wave?"
] |
[
false
] |
I just cant understand how so much Internet traffic could flow through that one wire. I would assume it would be sent as a wave and be demodulates at the other side so that you could do frequency multiplexing. Or is it time domain multiplexing and everything is just sent as 1's and 0's?
|
[
"Optical fiber can carry lots and lots of data thanks to ",
"wavelength division multiplexing",
". Basically, different data streams are sent as different colors of light. This can be done even with simple on/off signaling."
] |
[
"Ultimately, ",
" long-distance data transmissions use an analog carrier. For instance, digital cellular telephone transmissions are analog, but the analog encodes a digital signal. Which is an encoded version of an analog signal (at least, the voice part). ",
"Pure digital transmission is used over short-distance links, such as a buss within a PC, or even within a microprocessor chip. Although with the transition to SERDES (Serial/DeSerial) busses, this is starting to change. ",
"Undersea data cables these days are mostly optical. They are arguably digital...the data is transmitted as bright/dim binary information. (Of course, we can think of the light transmission as a wave,and usually do. So you could also argue that this is analog at its heart.) Data streams are broken up,serialized, encoded and sent on a single wavelength of light, but one fibre can carry multiple wavelengths simultaneously. And the cable is made of bundles of bundles of fibres, resulting in very high bandwidth for the cable as a whole. ",
"There has been work to use more (directly) analog techniques to transmit data over optical networks, but I do not believe these have ever been deployed in commercial undersea cables. "
] |
[
"So bright/dim as in 0's and 1's being directly sent down the wire, no modulating the signal with a carrier wave?"
] |
[
"Theoretically, what is the largest object a human being could move, disregarding weight, before air displacement becomes too great?"
] |
[
false
] |
I think the title sums up the question just enough. I thought of this lifting large empty cardboard boxes at work.
|
[
"Theoretically the answer is infinity.",
"If we ignore gravity (weight) then F=ma. With \"a\" approaching zero and \"m\" approaching infinity the force required is approaching zero.",
"Then again \"air displacement\" is meaningless so I have no idea what you mean."
] |
[
"If you are talking about the viscous adhesion, it is proportional to the velocity at which you are lifting the box., so you should be fine as long as you go slow enough.",
"For reference the force is given, for a circular plate (and for a small gap between the plate and the floor) by:",
"F=-6 * pi * mu * V * (R",
" )/(4 h",
" ),",
"where mu is the viscosity, V is the upward velocity of the plate, R is the plate radius, and h is the gap between the plate and the floor.",
"This comes from the Reynolds' lubrication equation. I'd link a reference, but there dooesn't seem to be a good one online. Any textbook on tribology or low-Reynolds number fluid dynamics should have a derivation."
] |
[
"You can move any size object, if only by a tiny amount. Air resistance increases with speed, so if you keep it slow you can still move it."
] |
[
"Is there a point near a black hole where the amount of gravity is pulling with the exact same force that light is moving away from it, rendering the light in a stand-still, only view-able from within that distance?"
] |
[
false
] |
In other words, would there be a point where the black hole would actually be an extremely bright light?
|
[
"Can you go into more details about this? Are there diagrams or equations used to represent this phenomenon? The idea of photons in orbit is fascinating "
] |
[
"Can you go into more details about this? Are there diagrams or equations used to represent this phenomenon? The idea of photons in orbit is fascinating "
] |
[
"Light cannot stand still in any reference frame. If you're the observer who falls into a black hole, you see nothing special until the point where you reach the singularity. You don't even know when you've crossed the event horizon because the event horizon at R=2GM is no more a special place than crossing at R=4GM, R=10GM, R=22.3917GM etc. If you're the observer who sees someone falling into a black hole, you see them slowing down more and more because light eventually takes an infinite amount of time to reach you. But it is not the same as light standing still as in \"light not moving\" or \"moving with speed 0\"."
] |
[
"Can Somebody Please Explain This? (Question Inside) x-post from /r/AskReddit"
] |
[
false
] |
I posted this to awhile back and did not get a response. Help me, ! While reading some of the goofs for The Core (2003) on . I was reading one of the factual errors: " As a body enters the interior of a large mass, such as the Earth or any other planet, the force of gravity begins to decrease at a linear rate, and reaches zero at the center of the planet. Although the ship is hovering above the inner core, and is therefore not at the exact center of the earth, the gravitational force would be nearly zero, so the actors should be able to float around the ship as if in orbit. As is, they walk around as if under the influence of normal gravity experienced on the surface of the Earth." I can't seem to wrap my head around this. I guess I would think that gravity would become more intense near the center of an object because that is where the densest elements would be, right? EDIT: ANSWERED! Thanks, everybody!
|
[
"When you are outside the Earth, the attractive force between you and the Earth is as if your are being pulled toward the middle of the Earth. However, once you enter the Earth, there is matter all around you exerting gravitational attraction on you; if there is the same amount of material on your left and right and at the same distance, then the forces pulling you left and right cancel out. If yo're at the center of the Earth, there will be (approximately) the same amount of matter in each direction from you and at the same distance, so the forces will cancel out."
] |
[
"Well, I'm glad I asked. It seems so simple when it's spelled out, I kinda feel stupid for asking! Could there possibly be any instances where this is not true? For instance, what if the object was not a sphere?"
] |
[
"I believe all statements anastas made would still be true, just if you replace \"center of the Earth\" with \"center of mass\"."
] |
[
"How do they get consent for testing medication/vaccination specially made for children?"
] |
[
false
] |
If they want to make Covid vaccination for very young children, they have to test it first. To get volunteers, they need consent. Obviously a 5 year old can not give consent legally (I assume), so how does this work in the medicine industry? Obviously the parents have to give the consent, but the test could endanger the child. So giving consent to a test run that is not really needed for the child could be looked at as child endangerment. How does this work?
|
[
"It’s complicated. Here’s an article on the topic (",
"Testing vaccines in pediatric research subjects",
") - a decade old, but as far as I know not much has changed. One point -",
"parents actually have less than a straightforward power-of-attorney in making choices regarding their children’s participation in human subject research [3]. The regulations actually limit what studies the parents may actually enter their children. The parents are not simply acting in place for their children but instead have a limited role. Instead, as stipulated by the 45 CFR 46, the Institutional Review Board (IRB) acts in loco parentis with children by prohibiting children’s participation in studies it would permit for adults. In all of these, 45 CFR 46 not only calls for parental permission but also the assent of the child when appropriate.",
"So (as least as I understand it) a parent’s permission is ",
" but not ",
". A parent’s refusal means No, but if an independent board doesn’t also agree that a study is acceptable for children the parent can’t override that."
] |
[
"That makes sense. Thanks."
] |
[
"Theyll be having the same trials of the same mRNA vaccine in children whose parents consent. After seeing the efficacy of the last vaccine trials with adults, there will be a lot of parents excited to possibly be getting their child the vaccine first. (There will be control groups with placebos)"
] |
[
"In what ways does dark matter interact with other dark matter?"
] |
[
false
] | null |
[
"Gravitationally, which keeps it loosely clumped together through space. It's possible that it interacts through the weak force, but this is currently unknown. Obviously we would have a better answer if we knew what dark matter was made of."
] |
[
"(Assuming WIMP dark matter) It does, but because it doesn't interact via the strong or EM forces it can't collide with other matter (including other dark matter) (or at least almost never collides with itself), or lose energy via emitting light, it can't lose energy, and will thus carry on out the other side. ",
"As an analogy - imagine a pendulum - at the top of it's arc it has lots of potential energy and no kinetic energy. As it swings through it's lowest point it has lots of kinetic energy and no potential energy. As it swings to the top on the other side the KE is converted back to PE and so on. In the everyday world the pendulum will slow down over time - something is removing energy from the system - in this case mainly drag due to collisions with air molecules. If we remove the air then the pendulum will swing for much longer. If we remove all methods for the pendulum to lose energy (eg frictionless hinge, perfectly rigid components) then it would swing for ever. ",
"Thus, going back to the dark matter, overall you are left with a 'cloud' of dark matter that stays roughly the same size over time. The fact that there is any variation in the density of dark matter implies there are some interactions that allow for energy loss, and by looking at the level of clumping of dark matter in the universe (inferred from measurements of galactic rotations) you can get an idea for what the likely interaction cross-section is (it's very small). "
] |
[
"What balances gravity? How does it not fall onto itself indefinitely?"
] |
[
"How come we can see our planet so clearly in the 'Pale Blue Dot' photograph?"
] |
[
false
] |
[deleted]
|
[
"The other planets and Sun were not in frame. They used a narrow angle camera pointed at the Earth. They had separate pictures of other planets taken during the same photo shoot. Some planets could not be photographed at all due to being too close to the Sun.",
"This page has a detailed breakdown of how the photos were taken and the planet's relative positions at the time.",
"http://www.nasa.gov/mission_pages/voyager/voyager-20100212.html",
"Related cool factoid, NASA took the pictures of the outer planets first because they thought that pointing the camera too close to the Sun might blind the camera and prevent them from shooting more photos."
] |
[
"FTA they used a narrow-angle camera for the photo (and for a similar photo of venus). The wide angle shot contains the regions where both planets are as well as the sun (though in the wide angle shot the planets are not visible)",
"http://en.wikipedia.org/wiki/File:Solar_System_Portrait_-_View_of_the_Sun,_Earth_and_Venus.jpg"
] |
[
"Perfect, thanks for this."
] |
[
"How do scientists continue to discover new species?"
] |
[
false
] |
I am particularly refering to land species, but in general. Also, are we finding anything bigger than a thumbtack anymore?
|
[
"Keep in mind, \"discovering\" isn't the same thing as \"scientifically cataloging\". It's unlikely there are species that have ",
", but there aren't armies of biologists swarming every corner of the earth to study/classify them. So just because something hasn't been discovered in the sense of being added to the pantheon of \"known\" species, doesn't necessarily mean it's been actively hiding from view. "
] |
[
"Niche species, that inhabit very small isolated environments. Also species that closely resemble other species and may have escaped notice previously. And ultimately, there's just a lot of species out there and we can only count them so fast.",
"Also, are we finding anything bigger than a thumbtack anymore? ",
"For an example, here's a small antelope described in 2010.",
"http://www.naturalsciences.be/active/sciencenews/archive2010/antilope/index_html/"
] |
[
"Also, more and more species are being genetically sequenced or further studied. From the studies, we have learned that what was once categorized as one species is really two or three or more, so they are separated out. For others, biologists who study something like, say, ants may find a new species out in the field."
] |
[
"Is the correct energy of a confined particle related to n^2 or 1/n^2?"
] |
[
false
] | null |
[
"ok so the potential mainly describes the energy spacing the particle can have?"
] |
[
"ok so the potential mainly describes the energy spacing the particle can have?"
] |
[
"Is the hamiltonian somehow different for an electron in an finite square well compared to an electron bound to a nucleus? Wouldn't the potential be the only thing that is different?"
] |
[
"Can light collide with itself?"
] |
[
false
] |
If I shined two torches which crossed paths, is there a chance the photons would hit each other and bounce off? See the link below for a detailed diagram I've composed to help explain the experiment.
|
[
"Quantum particles don't really \"bounce\" off of each other. Particles are actually waves and interact with each other based off of their properties. Since photons have no charge, for normal, low energy systems they will not interact. However, if you have a higher energy system they can. You can look up two photon physics for a better explanation."
] |
[
"So when two photons occupy the same point in space, is it like when two ocean waves intersect and the intersection point gets twice (actually a little less) as high?"
] |
[
"Yes.",
" It's very unlikely for two photons to collide though, and this has never been directly observed.",
"Also, \"collide\" isn't exactly what you think when dealing with quantum physics. Basically, the two photons can cause a particle-antiparticle pair to be created and reabsorbed, resulting in the photons moving in different directions."
] |
[
"How to tell the difference between \"Very Coarse\" and \"Coarse\" when identifying igneous rocks?"
] |
[
false
] |
Alright, so in my Geology lab we've been looking at igneous rocks when the professor starts to show different samples, I always get confused between Porphyritic and Pegmatic. I was just wondering if there was an easier way to tell the difference between the two other than looking at countless samples.
|
[
"Pegmatites contain ",
" large crystals - several centimeters across at least.",
"Porphyritic and pegmatitic are also not simply a difference in size. A porphyry has at least two distinct crystal sizes - usually a fine grained groundmass, with larger phenocrysts of one or two minerals. A pegmatite is made up of large crystals, with no requirement for a finer groundmass."
] |
[
"To confirm - a rock can be ",
" pegmatitic and porphyritic, correct?"
] |
[
"Yeah, I don't see why not."
] |
[
"When I open a non-text file with a text editor a bunch of symbols and text appears, where does this come from?"
] |
[
false
] |
[deleted]
|
[
"Every file on your computer is stored in binary, that is, as a sequence of 1's and 0's; those 1's and 0's are called bits. If you open a file in a text editor, each byte, or string of eight bits, gets mapped to a character (sometimes multiple bytes are used for a single character), which includes the usual upper and lower case letters, numbers, and symbols that you see on your keyboard, as well as some more obscure symbols, which depend on which character mapping your text editor uses - that is, ASCII, or one of the various unicodes, etc. A character mapping basically says, when you see the byte 01100001, display an a. 01100010 = b. Etc...",
"It appears to be gibberish, because it's not being read in the format in which it is intended. Kind of like if you fired a shotgun at a metal plate, and gave it to a blind person to read as braille. It wouldn't make any sense. But if you gave it to a forensics expert, they might be able to tell you what type of shot you used, how far away you shot it from, etc.",
"Basically, the answer is, from the character map that your text editor uses."
] |
[
"From the file. All files contain just a sequence of bytes, and then it's up to the program that reads the file to make sense of it according to some specific file format that defines what the bytes mean. Text editors don't usually check whether the content of the file looks like sensible text, they just assume you know what you're doing."
] |
[
"As you might know, computers store data in binary, that is 1's and 0's. Each text file has a specific encoding, that means that chunks of data, usually 8 1's or 0's are mapped to a letter. So for example, 00000001 could mean 'a', 00000010 is 'b' etc. So if you open a file that is not meant to be a text file, the editor interprets the \"random\" data as letters, dividing the file in chunks of 8. \nSome file formats are actually text BTW, for example HTML files are just text and opening one with a text editor will result in readable text. "
] |
[
"Why do we get hungry sooner after a small, high-calorie meal than after a large, low-calorie meal even if the net caloric content is the same?"
] |
[
false
] |
[deleted]
|
[
"Hunger is a physiological response to a range of chemical markers in blood changing, such as depleted blood glucose and reduced blood amino acid content. When you eat, you trigger a number of chemical pathways, such as through stretch receptors in the stomach wall, which stimulate secretion of gastric juice, and G cells activated by food proteins, that secrete gastrin triggering the release of a range of peptides and hormones.",
"The long story short, stretch receptors will be activated to a greater extent by a larger volume of food, regardless of caloric content, which in turn will trigger the release of greater quantities of huger-suppressing hormones such as Cholecystokinin, which act to stop the hunger reflex from being triggered for a period of time. The presence of more proteins and other chemicals in low-calorie foods will activate more G-cells too, in turn inducing more hormone and peptide release",
"Hence, the greater volume of food will in effect make you feel 'fuller', even if caloric content was the same, due to the food volume and protein makeup of the food acting to induce greater hormone release",
"For a good paper on the topic,",
" refer to this"
] |
[
"Calories have very little to do with hunger/fullness. Imagine eating 1 pound of lettuce-you would feel very full for almost no calories. But if you ate 400 calories of butter and sugar you wouldn't feel very full. Volume (usually from water and fiber) make us feel full acutely. Protein and fat (but not their calories) usually make us feel satisfied in the longer term due to chemical signals they induce. "
] |
[
"A small, easily digestible meal won't sit in your stomach for as long, and once your stomach is empty you will start to get hungry again."
] |
[
"A math question with multiple probabilities"
] |
[
false
] | null |
[
"This question would be more appropriate in ",
"/r/learnmath",
" or ",
"/r/cheatatmathhomework",
".",
"You can multiply and add probabilities according to the rules of ",
"conditional probability",
".",
"For this problem, you have a 1 in 2 chance of getting heads followed by a 1 in 4 chance of selecting a red ball plus a 1 in 2 chance of getting tails followed by a 1 in 2 chance of selecting the red ball.",
"The total chance of selecting a red ball is then (1/2)*(1/4) + (1/2)*(1/2) = 1/8 + 1/4 = 3/8 = 0.375."
] |
[
"Is this a homework question? If so, please try ",
"/r/HomeworkHelp",
" instead.",
"Guideline 2.8:",
"AS is not here to do your homework for you."
] |
[
"No, I am a math nerd. :P",
"I was just thinking about answering a question \"There's a 50% chance I'm 50% sure, but there's a 50% chance I'm 75% sure. How sure am I?\" This just sounded like a more suitable question."
] |
[
"How did Ole Christensen Rømer calculate the speed of light?"
] |
[
false
] |
I understand that he used the orbit of io but I seriously don't get how it's orbit or precived orbit can change based on distance alone since the sun is constantly emitting light and all orbits are constant. I could see how it could be calculated if the sun sent light in pulses, what am I missing?
|
[
"I understand that he used the orbit of io but I seriously don't get how it's orbit or precived orbit can change based on distance alone since the sun is constantly emitting light and all orbits are constant.",
"They had quite accurate predictions for when io would disappear into Jupiter's shadow, and when it would reappear on the other side.",
"However, Rømer noted that the observations were slightly off from the predictions in a cycle which corresponded to Earth and Jupiter's distance.",
"He realised that if Jupiter is further away, the light would take longer to reach us, and we'd see the eclipse events later than usual. Conversely, if Jupiter is closer, we'd see them earlier.",
"By comparing the specific timing of the anomalies against the Earth-Jupiter distance, he predicted that light travels at about 220Mm/s.",
"The wikipedia article goes into a lot more detail"
] |
[
"His measurements simply weren't accurate enough for a better result.",
"Yes, if you repeated the same method today, you'd get a significantly more accurate result - especially if you leveraged existing history of observations of Io rather than making your own fresh ones."
] |
[
"One issue back then was the time-keeping. The relative shift is just 1 in 10,000, so you need a clock that is much better than that. If a clock is off by 1 second per day (1/86,400) this is a relevant error source already.",
"You have to determine the time when Io enters the shadow with a precision much better than 1/10,000 of its orbit, or 15 seconds. Io needs about two minutes to move by its own diameter, in addition the half shadow (from the finite size of the Sun) corresponds to about 4 minutes of its orbit. Io gradually gets dimmer over 6 minutes, and you want to find some time of that process with a few seconds uncertainty at most.",
"Today atomic clocks have no problem with time-keeping better than one part in a billion and better telescopes help with the observations of Io - we could even use spacecraft orbiting Jupiter.",
"In practice we don't need to use Io any more. We can use the signal travel time of spacecraft at Jupiter. There are the pulses OP was looking for."
] |
[
"I recently read an article by Ioannidis titled \"Why Most Published Research Findings Are False\". Do you, as a scientist, feel that this is a very significant hindrance to your field? How do you deal with it?"
] |
[
false
] | null |
[
"What field is that that you're in, if you don't mind my asking?"
] |
[
"This is a much bigger problem for science journalists and their readers who read a publication and believe or portray it as absolutely true whereas a scientist views it only as evidence."
] |
[
"Essentially the paper explains the statistical problem of ",
"the prosecutors fallacy",
". Briefly, if you have some procedure which can detect a relationship when one does not exist at some rate (say 0.05) then you apply this procedure over and over randomly looking for the relatively rare true relationship, then most detected relationships will be false positives. ",
"However, I'm not aware of a great many scientist who discover their results by performing enormous numbers of statistical test until something finally shows up. In the end, most scientists (at least in my fields of interest) show their results through multiple independent methods, and statistics are often more of a nod to the scientific form rather than a necessary part of the argument in the paper. Of course, there are some papers that follow a logical process closer to what the authors describe (I would call them fishing expeditions) but the majority of papers don't follow this procedures, at least IMHO. "
] |
[
"When do cells with epithelial characteristics first appear in embryonic development?"
] |
[
false
] | null |
[
"Are you asking for flies, frogs, mice or humans? And what do you define as epithelial characteristics? Epithelium is ectodermal lineage, those cells start to differentiate away from mesoderm and endoderm very very early. In mice it’s about 7.5 days after fertilization, and mice have a 21.5 day gestation period. For humans, I’m not sure but by week 3 you got some ectoderm on you. If you’re an embryo."
] |
[
"Follow-up question: is senescence exclusive to ectoderms during organs and vestigial structures like limbs and digits formation?"
] |
[
"Humans. I put a flair on the post, sorry I will specify next time. ",
"Thank you a lot, my guess was also around gastrulation."
] |
[
"Does rain fall for a long distance as distinct drops, or do the drops constantly recombine on the way to the ground?"
] |
[
false
] |
How far do individual raindrops fall? Do they remain relatively unchanged on the way to the ground, or are they constantly re-forming in mid air?
|
[
"There are 2 different types of rain depending on your cloud type. Stratiform clouds will produce a constant rate (continuous rain) with same type of rain drops while cumiliform clouds will produce a larger and various size raindrop (mostly tropical type showers).",
"To answer your question though, rain drop form inside the cloud in a process we call \"Collision and Coalescence\" where the drops combine. Once the drop gets heavy enough it descends to the ground, so yes once it starts falling it remains relatively the same size. ",
"To answer how far, it depends on the base height of the cloud. Most cumiliform bases in the tropics are about 1500ft-3000ft while stratiform cloud bases can vary from 1000ft up to 7kft-10kft (at which point your precip can be freezing rain/snow depending on the height of your freezing temp).",
"Source: I'm a WX Forecaster"
] |
[
"What is WX?"
] |
[
"Abbreviation for \"Weather\""
] |
[
"Can you become addicted to placebo?"
] |
[
false
] | null |
[
"In the sense of a physical addiction I would have to say no. Physical dependence requires the drug to be integrated into the body (or change the body) to the point it can't function normally without it. Addiction comes from trying to avoid the withdrawal symptoms associated with physical dependence as taking more of the drug gets rid of these negative symptoms so it becomes a negative reinforcement.",
"Placebo effects on the other hand rely on giving the individual an inactive substance and allowing their expectations about its effectiveness to help the individual. Since the placebo is an inactive drug it is not going to physically change the body meaning there will not be withdrawal symptoms if you stop taking them. No physical symptoms means no negative reinforcement and no physical addiction.",
"Physical addiction is not the only kind of addiction as people can also become psychologically addicted to substances. Psychological dependence is the belief that the drug is needed to continue a feeling of emotional or psychological well-being. Doing a quick literature search I was not able to find any studies looking at psychological addiction to placebos. I would say i'm skeptical that someone would become psychologically addicted to a placebo as it relies on the individual believing the treatment is doing something to help them. As a result I wouldn't think you would use a placebo for any sort of long-term treatment (although i'm not a doctor so maybe some of them have) as eventually they would realize the placebo isn't really doing anything if their symptoms keep returning."
] |
[
"Do you think it could be addictive in the same sense that gambling can be addictive to people with impulse control disorders? It seems that psychiatrists regard it as a disorder instead of an addiction, but the symptoms can be very similar. Needing larger stimulation, withdrawal, irritability, lying, frequent thoughts or preoccupation with the subject.",
"I wonder if an impulse control disorder could be triggered through a placebo effect. It seems plausible to me that if you gave someone cocaine (but it was a placebo), and they got \"high\" with it, then they could develop an \"addiction\" to a placebo."
] |
[
"I would definitely say it is possible. For example, in ",
"Munchhausen Syndrome",
" patients are obsessed with the advice and attention of doctors. They are severe hypochondriacs in every sense of the word, even so far as to go beyond the defined levels of a hypochondriac. If a hypothetical scenario were to occur where doctor gave in to such a patient,and ended up giving her some sugar pills and making her pay standard price for them (the ethicality being questionable at this point, anyone care to comment?) i imagine the patient would covet these magic pills."
] |
[
"How does a hydrocolloid bandage actually work?"
] |
[
false
] |
I’ve tried to Google this but I can’t really find a straight answer and I don’t necessarily trust the very basic explanations given on Tiktok. Thank you!!
|
[
"Wounds like to have a kind of protein soup on top of them which is protected from germs and provide optimal protection for the regrowth of new cells. Hydrocolloid plasters provide a perfect medium for the wound to develop a soft protein rich gel which allows for the perfect conditions to regrow cells."
] |
[
"They mimic the environment of a scab or blister to protect the injured tissues, keep the tissue from drying out and cracking (opening up more places for infection to set in) and basically keep the area sterile while healing takes place."
] |
[
"There are various types. During my MS I was at a lab where a postdoc developed such a product. His was based on ",
"hydrophobically modified chitosan",
", where hydrophobic groups crosslink with components of blood to form a gel network. This ",
"stops bleeding quickly",
" and isolates the wound from contamination, allowing healing to proceed.",
"In general, other hydrocolloid bandages also aim to form some kind of hydrated gel to seal the wound."
] |
[
"If there was a way to have a person born blind have an \"eye\" transplant to see, would their brains be able to process images?"
] |
[
false
] |
[deleted]
|
[
"would their brains be able to process the images they see or would that be too much for them and drive them insane or severely depressed?",
"I can't speak for the exact scenario you mentioned, but Oliver Sacks wrote about a similar scenario in his book, An Anthropologist on Mars (Chapter 4, ",
"). The subject was a 50 year old gentleman who developed severe cataracts at six years old, and was effectively blind for most of his life. He received cataracts surgery at 50, and his vision was more-or-less restored (it wasn't 20-20, but it was apparently decent).",
"In doing so, however, he started experiencing problems. When he first opened his eyes after surgery, the world was a mess of colors to him. He couldn't recognize any shapes, he didn't know what objects he was looking at. He started making connections (\"that tan bluer from where the voice is coming must be a face\"), but it was a learning process, and he had difficult taking objects as a whole. He'd see parts, and the parts would run together. He had difficulty understanding perspective; he had difficult recognizing objects seen at new angles; he had difficulty putting letters together to form words; he had difficulty corresponding colors to their names. He could eventually do these things pretty passably, but it was never natural, never comfortable.",
"He fell into a depression and other illness; his work as a masseur became foreign to him after seeing his clients for the first time; he still only really \"understood\" an object if he closed his eyes and felt it with his hands. Sight had virtually no meaning to him, especially in visually cluttered spaces.",
"Eventually, he lost his eyesight again for reasons not fully known (though it was theorized that seeing light for the first time in half a century caused excessive damage to his eyes), and he was much happier with his blindness. It was all he had known for most of his life.",
"It's an interesting read."
] |
[
"Pawan Sinha, at MIT, does essentially this. In India, there are lots of children born with cataracts who are essentially blind (they can process light/dark, but not much else).",
"He has a project that removes the cataracts, providing them with mechanically intact vision for the first time. Then he studies their visual perception. The answer is -- it's complicated. Their brains ",
" adapt, it does ",
" drive them insane, and they're not severely depressed. But they don't have fully intact vision (I don't think any of them ever get close to 20/20), and they process objects in really atypical ways (e.g., if you show them a line drawing of a square and circle overlapping, they don't see it as square and circle, but rather IIRC, 3 discrete objects.)",
"Here's his TED talk: \n",
"http://www.ted.com/speakers/pawan_sinha.html",
"You can find out more about his research by searching for Project Prakash"
] |
[
"\"At First Sight\" Starring Val Kilmer was made from the book i believe. the story above matches the plot of the movie rather closely.",
"http://www.imdb.com/title/tt0132512/"
] |
[
"What is the mathematical function for getting a negative reciprocal?"
] |
[
false
] | null |
[
"-1/x"
] |
[
"Ah thanks so it is just -f(x)",
" ?"
] |
[
"The negative reciprocal of ",
" is -1/",
"."
] |
[
"Why are humans one of the only animals to have so much of the \"whites\" of their eyes showing?"
] |
[
false
] |
It occurred to me today that almost all other animals (at least the ones I could think of quickly) hardly have any of the "whites" of their eyes showing. It also occurred to me I have no idea why that would be. So, my question(s): Why do we have so much more of the whites of our eyes showing than other animals? Is there some sort of advantage to this? Maybe the answer is "just because that's how it is"... and if so, fine. But I figured I would at least post the question to see if there's an answer out there. Thank you for your time.
|
[
"My understanding is that it evolved under selection pressure related to social function, as part of a mechanism for communicating mood, intent, and to help direct others' attention or reveal where one's own attention is directed.",
"http://www.ncbi.nlm.nih.gov/pubmed/10652522",
"\"Do the eyes have it? Cues to the direction of social attention.\" (Langton SR, Watt RJ, Bruce I I., 2000).",
"The article is available for free via Google ",
"here",
"."
] |
[
"Interestingly, while dogs don't use this manner of communication themselves, they recognize it in humans."
] |
[
"Interesting question. This guy was wondering the same thing, thought this article might provide some food for thought, assuming it wasn't your inspiration...",
"http://www.nytimes.com/2007/01/13/opinion/13tomasello.html?_r=0"
] |
[
"Are we sure that an emitted photon is only absorbed once? Could it not be absorbed once on average? (and sometimes be absorbed several times)"
] |
[
false
] |
Forget about the photons being lost into space. Assume the emitted photon is emitted in a closed space. What I'm really interested in is an experiment that could point this out. Side questions: What about the theory in quantum physics? The photon wave function collapse when it is absorbed, right? Can we detect a photon without absorbing it? What about an electron? An ion without it losing or gaining (even temporarily) an electron or absorbing/emitting a photon? What are the techniques to detect a single photon absorption/emission ? What about the photons produced by an electronic apparatus (radio, cell phones...)? Is there a way to get single photon absorption around those frequencies? I think the answer is no, at least at room temperature where the energy of the photon would be lower than the energy of thermal radiation photons.
|
[
"I think you better stick to the theory. You seem to know it.",
"Somewhat. I'm an engineer and I know classical physics well. But quantum mechanics, I only studied as an amateur, and what I know I'm not confident that I understand it well.",
"Because what you are asking indeed violates energy conservation. Suppose that indeed it only happens on average once. Then you can excite an atom without consuming the photon. Were would the energy for the excitation come from?",
"Indeed violating energy conservation is very disturbing to me too. But there could be a lower level interaction that would force the energy conservation on a global scale (yeah deus ex machina I know). And the instantaneous collapse of a light-years wide wave function is also very disturbing to me! That's why I'm interested in an experiment that shows for sure that a photon is only absorbed once.",
"For example, such an experiment could be something like this: take a source of photons that emits on average a photon every second or so. Put detectors all around it that detect an important part of all the photons absorbed. Look for the number of simultaneous absorptions. But maybe there are experiments (for example in particle accelerators) where it would definitely have already be noticed if one emitted photon could be absorbed several times, that's what I'm looking for; empirical proof that could completely lift those blasphemous, energy-conservation violating ideas from my mind.",
"In the double slit experiment, you just put any kind detector before one the slits. Could be as simple as scintillator paper. Why bother will fancy, non-absorping techniques? Detect the photon and be done with it. It is about the double slit and the interference, not about the type of detector.",
"I'm talking about the detector that counts the particles going through each slits.",
"Wikipedia says:",
"If, for instance, any device is used in any way that can determine whether a particle has passed through one slit or the other, the interference pattern formerly produced will then disappear.[citation needed]",
"It's about knowing what collapses the wave function and what doesn't. If the wave function collapses there is no interference. What I'm interested in is what does and what doesn't collapse the wave function. I would like a formal definition of what a measurement in quantum mechanics is."
] |
[
"I think you better stick to the theory. You seem to know it.",
"Somewhat. I'm an engineer and I know classical physics well. But quantum mechanics, I only studied as an amateur, and what I know I'm not confident that I understand it well.",
"Because what you are asking indeed violates energy conservation. Suppose that indeed it only happens on average once. Then you can excite an atom without consuming the photon. Were would the energy for the excitation come from?",
"Indeed violating energy conservation is very disturbing to me too. But there could be a lower level interaction that would force the energy conservation on a global scale (yeah deus ex machina I know). And the instantaneous collapse of a light-years wide wave function is also very disturbing to me! That's why I'm interested in an experiment that shows for sure that a photon is only absorbed once.",
"For example, such an experiment could be something like this: take a source of photons that emits on average a photon every second or so. Put detectors all around it that detect an important part of all the photons absorbed. Look for the number of simultaneous absorptions. But maybe there are experiments (for example in particle accelerators) where it would definitely have already be noticed if one emitted photon could be absorbed several times, that's what I'm looking for; empirical proof that could completely lift those blasphemous, energy-conservation violating ideas from my mind.",
"In the double slit experiment, you just put any kind detector before one the slits. Could be as simple as scintillator paper. Why bother will fancy, non-absorping techniques? Detect the photon and be done with it. It is about the double slit and the interference, not about the type of detector.",
"I'm talking about the detector that counts the particles going through each slits.",
"Wikipedia says:",
"If, for instance, any device is used in any way that can determine whether a particle has passed through one slit or the other, the interference pattern formerly produced will then disappear.[citation needed]",
"It's about knowing what collapses the wave function and what doesn't. If the wave function collapses there is no interference. What I'm interested in is what does and what doesn't collapse the wave function. I would like a formal definition of what a measurement in quantum mechanics is."
] |
[
"I doubt that you are going to find what you are looking for.",
"You're probably right.",
"Perhaps you have access to the text book \"quantum mechanics\" by Bransden and Joachain?",
"Not really... Maybe I'll buy it on amazon... But I already have so many books to read. I'll add it to my TOREAD list.",
"I gave you the standard answer, you already knew the standard answer. You now have a reference. Nothing more I can do, I am out. Good luck.",
"Thanks anyway. Even if you didn't give me an empirical evidence, as you know the subject much better than me, your confidence that the standard answer holds is already quite convincing."
] |
[
"Why do things proceed toward equilibrium?"
] |
[
false
] |
Why exactly do particles, atoms, molecules, temperatures, whatever, continue to react and change until equilibrium is acheived? I cannot think of a reason that I've been taught in chemistry, physics or biology courses. Thanks a bunch
|
[
"OK, lets get temperature out of the way first.",
"Temperature equilibrates because of the second law of thermodynamics, which states that a system will end up in a state of maximal entropy. The highest entropy state is the one with the most degenerate microstates. This is the famous Boltzmann Equation (S=k.lnW) and is the cornerstone of statistical mechanics. The degeneracy term means it is always preferable for the temperature to be the same across the entire sample.",
"Now in Chemistry we aren't just concerned with Entropy, we are also concerned with Enthalpy (this is how much work we can get something to do by making and breaking some bonds too), which can help us work against that pesky second law of thermodynamics.",
"In Chemistry (and Biology) we consider reactive a system to be in equilibrium when the sum ",
"activity coefficients",
" both sides of our chemical equation are equal. The simplest cases are for homogenous reactions where all reactants and products are dissolved in solvent, when we can work with concentrations. However the same principles apply to heterogenous chemistry (you can start with ",
"Raoult's Law",
" and add complexity from there)."
] |
[
"Perhaps, what Im asking then, is why the 2nd law of thermodynamics works. Being a chemistry major, I understand the Enthalpy approach a little better, but heres an example of my frustration:",
"2Na + (Cl)2 = 2(NaCl)\nwhy? because the Cl2 electrons will grab an Na, thus breaking both original bonds and forming 2 new ones. \n why? Because Cl is highly electronegative.\n why? because its a small atom with 7 valence electrons. \n why does this make it reactive? because it wants an octet.\n why? because its the most stable orbital configuration.\n why? actually Ill look into this, thanks for trying to help haha my brain is a mess.",
"I may just be questioning in the same way as \"why is the universe held in a fabric of space-time\" when the answer is likely \"it just is\", doesnt really need a reason I suppose "
] |
[
"I can't tell you why the 2nd Law is what it is. I had an extended argument on here about it with someone some time ago. They said 2nd Law is because ",
", I said maths is a tool we use to describe our universe and doesn't tell us why anything is the way it is. You can decide whether you agree with him or me.",
"As for the rest, you know the answers. Stable orbital configurations are ultimately just low energy solutions to Schrodinger's Equations. Why? Well ultimately the orbital energies are a balance of attractive and repulsive terms as well as a few other terms like a degeneracy term and an electron pairing term. None of these necessarily have trivial mathematical solutions, but that doesn't mean that a Chemist doesn't know the answer from our collective empirical knowledge."
] |
[
"What don't we understand about water?"
] |
[
false
] |
I was just watching a television show on The Science Channel called "Wonders of Life." The host of this show was talking about how life on earth depends on water. (duh) But then he said something like, "I've heard it said we can never understand biology until we fully understand water." Which got me wondering what we don't understand about water. I mean it has a basic molecular structure, we understand hydrogen bonds, we understand how this makes it a polar molecule and why that makes it an excellent solvent etc. etc. So what are the remaining mysteries of water we have yet to work out?
|
[
"for more information on how proteins fold due to hydrophobic effects, you can take a look at ",
"foldit",
", a videogame set up so you can help scientists by trying to optimally fold a protein."
] |
[
"One thing thing that was being researched at least recently is the hydrophobic effect- the repulsion between water and non-polar substances such as oil. In chemistry they say \"like dissolves like\", but the actual dynamics of substances mixing or repelling at the molecular level is more complicated. Important questions are, for example, how to measure the strength of the hydrophobic effect and what its dependence on temperature is. The hydrophobic effect determines how proteins fold, so it turns out to be relevant to understanding biology. "
] |
[
"Some interesting points here: ",
"http://www.newscientist.com/article/dn18473-the-many-mysteries-of-water.html#.Um-MalNZhdM",
"I also remember reading an article a few years ago explaining how water boils to an unprecedented level of detail which was previously unknown to science."
] |
[
"Since swamps produce huge amounts of methane gas, is there any sort of chance of one catching fire?"
] |
[
false
] | null |
[
"There are occasional small flames or lights on swamps, where a steady stream of methane has gotten lighted by a static spark. The volume of methane mixed with oxygen is too small however for the fire to spread.",
"Most methane evolves and \"flies away\", so there's no large accumulation at the surface (as opposed to large deposits of natural gas)",
"So no, an entire swamp will most likely never spontaneously catch fire"
] |
[
"alright, cool. I was just wondering if any natural phenominon was connected to that. What would these flames be called cause I'm interested in seeing a photograph of this."
] |
[
"Well, ",
"here",
"'s a mockup. I can't find any real pictures. Peter ackson also used some fakes in ",
"\"the two towers\""
] |
[
"What causes the natural heating and cooling of the earth? What causes ice ages?"
] |
[
false
] | null |
[
"As gradientso alluded to, one of the primary drivers of long-term climate cycles are called \"Milankovitch cycles\". These cycles result from the slight imperfections in the Earth's orbit. The ",
" of the orbit is how elliptical the orbit is, the ",
" is how much the Earth's tilt varies (between 22 and 24 degrees) and the ",
" is the direction the Earth's axis points relative to the stars. Like a little gyroscope, the Earth wobbles about its axis.",
"These three geometric properties vary over time with different periods, the three different year lengths that gradientsyo mentioned. Each property slightly changes how much energy is received at the Earth, which in turn affects the weather systems So the primary driver of long-term variability is in the geometry of the Earth-Sun orbit. In fact, one could line up the level of solar insolation as a function of these three \"wobbles\" with the temperature record going back a million years and find a close match. ",
"Here's one",
" (not peer-reviewed). As a first-degree approximation, it looks pretty good.",
"Now, what causes the dramatic \"ice ages\" that we see in the rock record? The small changes in solar insolation have a tendency to result in out-of-control changes, through a process called ",
", which you may have heard about already. An example: the \"albedo effect\" (how reflective the Earth's surface is) has a positive feedback, because ice reflects the most solar energy of all the surfaces, and as the Earth heats up, the ice melts, so less energy is reflected, so more is absorbed, so the Earth heats up, so ",
" ice melts... The same process can happen in reverse, and indeed many scientists think that once a certain level of ice coverage is reached (around 60 percent of the Earth's surface), the Earth will quickly cool as it reflects so much of the incoming solar energy and the rest will freeze too. These positive feedback loops are present in a lot of places in the Earth system, including a couple that gradientsyo pointed out.",
"One of the most relevant questions to ask about long-term climate change relates to mass-extinctions. Probably the worst possible effect of the modern warming trend is a mass extinction triggered by excess CO2, but how likely is this to happen? For the five major mass extinctions in Earth's history, we've found evidence correlating the extinction even to a massive influx of CO2, usually from volcanics. The Earth warms, the ocean rises, the deep upwelling is shut off, and ocean anoxia kills most sea life. Scary, right? Of course, this theory is just one (some scientists still believe a meteor killed the dinosaurs) but it does paint a pretty dire picture. Long-term climate change can come from the Sun and orbital geometry, but it can also come from processes on Earth.",
"If you have any more specific questions, I can try to answer them; I have a pretty deep understanding of these processes."
] |
[
"Thats exactly what I said. Maybe my wording was slightly unclear. Consider a 1km by 1km area at 60* N and 60*S. In summer the area at 60N recieves more solar radiation per day than the exact same latitude in the southern hemisphere. That is what I meant by amount of Solar Radiation/Area/time."
] |
[
"Ok you're both partially correct and partially wrong. A better way to think about the cause for seasons is that the hemisphere which is experiencing summer is tilted towards the sun, so gets more sunlight per day. (At this distance, sunlight is very evenly distributed, so \"falling over a larger area\" doesn't make sense: if a larger area is exposed to sunlight, more energy is absorbed.)",
"Have a look at this:\n",
"http://en.wikipedia.org/wiki/Seasons#Causes_and_effects",
"For the rest of the things, volcanoes, ice ages etc. which I think are the more interesting question, I don't have any expertise."
] |
[
"What happens if we delay the second dose for AstraZeneca vaccine to 12+ weeks after the first one?"
] |
[
false
] | null |
[
"It improves the efficacy. ",
"https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00528-6/fulltext",
" \"Modelling analyses showed an increase in vaccine efficacy after two standard doses from ",
".(95% CI 33·0 to 69·9) with an interval of less than 6 weeks to ",
" (60·3 to 91·2) with an interval of at least 12 weeks.\"",
"We are not really sure why. One possibility is that it's due to the body having more time to get over the vector immunty problem. But mRNA vaccines like Pfizer also reported better results with a longer delay. It is quite possible that the 3-4 week interval selected for fast trial results is not optimal for overall vaccine efficacy. Or it's possible that the vaccine just get more protective over time, both Johnson and Johnson and Sinovac reported improvements if you measure months later. Most likely a combination of all those reasons."
] |
[
"It’s common for delaying boosters to lead to higher-quality immunity. One important reason is probably that as B cells are pruned following the first exposure, the highest-affinity B cells last longest (as they can compete best for remaining antigen) and over time they’ll become a larger component of the second response. ",
"Of course the problem with delaying boosters is that you have a much longer period during which you have much lower immunity (from the first vaccination only) before you gain slightly higher immunity from the second shot. Is the eventual higher immunity more beneficial than the added weeks of higher risk? Only math can answer that, and it will depend on the precise details of all of those."
] |
[
"Could it also be possible to give the higher risk people, who got it early, a third booster when everyone else has got their second?"
] |
[
"Why does sliced roast beef sometimes have an iridescent sheen on the surface?"
] |
[
false
] |
[deleted]
|
[
"This effect was just recently described in an ",
"Optics Picture of the Day",
". Quick description: the cellular structure of the meat has a repeating pattern, which can produce interference effects in the reflected light. Some other pages on the site describe ",
"iridescence from clouds",
" - check those out for a better description of how interference can lead to spatial color patterns."
] |
[
"This is an immaculate answer, thank you."
] |
[
"I too have been puzzled by this same effect with Canadian bacon. There are irregular patches of iridescent rainbow patterns on the cut faces of the meat. Is this a property of the meat, the slicing, or something else altogether?"
] |
[
"Is molten metal still electrically conductive?"
] |
[
false
] |
Is molten metal still electrically conductive?
|
[
"Stuff dissolved in water is often great for conducting. In pure water, small amounts will dissociate, which can also conduct electricity. Pure H2O doesn't, though."
] |
[
"To some extent yes, but not really. As you apply energy (heat) to any atom the electrons jump to higher energy shells. With the outer most shells mimicking being stable, the material is less likely to accept and transfer electrons. Hence a rise in resistivity. It depends greatly on the exact metal and the temperature. Some metals at high temperature can become open to conduction while others become closed to it. "
] |
[
"Deionized means that you take the ions out. Namely the dissolved metals and non-metals.",
"You typically do this by distilling. You can dissolve more things in the water that aren't ionic compounds, like glucose. This would result in something that is deionized and not conductive."
] |
[
"Help providing a satisfying explanation for a friend (Quantum)"
] |
[
false
] |
Hi AskScience, the other day I was talking to my friend (a 3rd year undergrad chemistry student) and he was saying that he doesn't like quantum mechanics as an explanation for natural phenomena. I was hoping someone could provide an explanation of certain things in a way better than I could. He made points that if a particle "could technically be anywhere in the universe at any time" (referring mostly to electron probability functions in orbitals), it would violate the speed of light. Also, when thinking about the double slit experiment with electrons and how matter can exist as a "wave," he asked how that distant bodies that have never been observed can have gravitational effects on us etc. These seem to me to be misunderstandings of the subject matter, but I figure someone else would be able to explain this better than I could.
|
[
"It's kind of a dickish thing to say, but first of all one must acknowledge that it doesn't matter whether one \"likes\" a scientific theory or not, but whether it makes reliabe predictions.",
"You may not \"like\" special relativity, but it explains why we can see long traces of ionizing radiation in a ",
"Cloud Chamber",
", although these particles are extremely short-lived - and many other things.",
"You may not \"like\" general relativity, but it gave a ",
"consistent explanation for the perihelion precession of Mercury",
" and without it, ",
"GPS wouldn't work.",
"Equally, you may feel uncomfortable with the way quantum mechanics describes reality, but the fact of the matter is that it ",
" describe a whole range of phenomena correctly and with immense precision.",
"That doesn't mean that either of said theory ",
" reality - but they describe known aspects of reality well and without too many prior assumptions, and they can make a number of pretty accurate predictions.",
"What's your friend's alternative?"
] |
[
"The propagator for a particle propagating outside its light cone falls off exponentially (Peskin and Schroeder ch 2.4 if you want the derivation) which holds for scalars, so it doesn't need an antiparticle."
] |
[
":("
] |
[
"Is genetic diversity beneficial or detrimental in an organism and it's species' survival?"
] |
[
false
] |
[deleted]
|
[
"In the simplest terms, greater genetic diversity will likely lead to greater adaptability as the environment changes. Therefore, a species with a high genetic diversity will be more likely to survive changes in the environment, and/or have new species branch off in the selective pressures are right.",
"To bring this into terms relevant to disease/health: the greater the diversity of certain immune related proteins (i.e. MHC/HLA proteins, TCR or BCR) the more likely it is that individuals will have a greater natural immunity to any given new infection. For this reason, the species with greater diversity for these genes will be more likely to survive."
] |
[
"Not an answer, but cheetahs actually have ",
"remarkably low genetic diversity",
", which seems to be the result of a population bottleneck (dramatically reduced population size) about 10,000 years ago. "
] |
[
"Simply put: too much or too little diversity is detrimental. ",
"If you don't have enough genetic diversity your species might become extinct after a change. For instance a parasite or a fungus in a bee population is detrimental for that population since there is very little diversity in a bee (or ant) population. If you have enough diversity, one or maybe more individuals could have a better defense against that parasite of fungus and thus repopulate after 'almost extinction'. This is called an evolutionary bottleneck, which is what supposedly happened to the cheetahs a long time ago. So cheetahs in fact have very little genetic diversity making the cheetah an easy target for extinction!",
"Too much genetic diversity may cause too much difference between two individuals so that they can't copulate anymore. ",
"If you have just enough genetic diversity (caused by temporal segregation or mutations in the DNA of organisms for instance) you have the benefits of protection against extinction as well as against too diverse individuals."
] |
[
"If we absolutely had to for some reason, how long would it take NASA to have an old shuttle fueled and ready for launch?"
] |
[
false
] | null |
[
"lets assume it's a rescue mission to the ISS.",
"They'd be dead before we could get a shuttle up there. The Soyuz capsules would probably be their best bet.",
"The space shuttles have all been decommissioned, and they'd have to basically be re-built to make them flight worthy. Atlantis is at the Kennedy Space Center Visitor Complex. Discovery's at the National Air and Space Museum. Endeavor is at the California Science Center in LA."
] |
[
"The Soyuz modules are launched fairly often between ",
"unmanned Progress flights",
", which carry supplies and manned ",
"Soyuz flights",
", bringing new crew. It looks like they go to the ISS about once every couple of months on average.",
"http://www.theatlantic.com/infocus/2012/03/decommissioning-the-space-shuttles/100271/",
"That article has some images of decommissioning the shuttles. In that process, the computers are removed, the airlocks are removed, dozens of maneuvering thrusters are removed, the main engines themselves are removed, and everything is replaced with replicas for public display.",
"The shuttle launch platform has been reconfigured for use with other spacecraft in the future and would need to be rebuilt to launch the space shuttle again.",
"The shuttle orbiter bodies that we have are basically shells after being stripped, and for the last 2 years or so, the manufacturing and maintenance processes to support space shuttle flight have been winding down. ",
"Some 3200 workers were laid off",
" at the end of the shuttle program, and NASA would need to re-hire at least some of them.",
"To get a shuttle running again, you aren't looking at a number measured in days or weeks. You're looking at a number measured in months or years, and costs in the billions or tens of billions."
] |
[
"they'd have to basically be re-built to make them flight worthy",
"How long would that take? If the Soyuz capsules weren't ready..."
] |
[
"How is asthma medication made?"
] |
[
false
] |
So, very recently, I wanted to learn how rocket fuel was made. I did some googling, and learned all the chemical processes needed to create materials to create experiments that make more materials that eventual create rocket fuel. In the process however, I learnt how to make a lot of dangerous chemicals. So today, I was curious how asthma medication was made, but I couldn't find a single source anywhere on how it's made, I've only found the chemical names. Is it a trade secret or something else? It's just confusing for me that given some time I can learn how to make rocket fuel, but not asthma medication.
|
[
"There's various different classes of asthma medication - inhaled corticosteroids, beta agonists, leukotriene modifiers. That's why you can't find a direct source on how it is made. Also, compared to rocket fuel, we are getting into really complex chemistry here, so you need to know what to look for. But I fear it won't be easy to understand without a thorough grounding in organic chemistry.",
"Here is an overview on corticosteroids, for example: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2650492/"
] |
[
"All that stuff is patented and patents are public. If you plug the name of a substance into Google patents or into a serious patent database like ",
"Espacenet",
", you'll find all of them."
] |
[
"All that stuff is patented and patents are public. If you plug the name of a substance into Google patents or into a serious patent database like ",
"Espacenet",
", you'll find all of them."
] |
[
"Is capsaicin responsible for all spiciness?"
] |
[
false
] |
Is capsaicin responsible for everything we perceive as spicy? Wasabi vs. curry, for example... the effect is notably different (nose vs. mouth).
|
[
"Nope, capsaicin is but one piquant. Wasabi, mustard, horseradish etc. contain ",
"allyl isothiocyanate",
", and black pepper has ",
"piperine",
"."
] |
[
"A white russian?"
] |
[
"What about hydroxy-alpha-sanshool? Sichuan pepper\nLink ",
"http://en.wikipedia.org/wiki/Sichuan_pepper"
] |
[
"How do people with permanent pacemakers/defibrillators go with being tazed? Does damage occur to the devices? Do people without them potentially go into an arrhythmia?"
] |
[
false
] | null |
[
"i have an ICD. Getting tazed is not common here in Switzerland. I guess the devices could be damaged. Magnets are much worse. ",
"The tazing itself is bad for the heart. It isnt likely to cause arhythmia for people without damage to their hearts. But it may cause damage itself making people more inclined to get arhythmia long term.",
"here is a study - indeed the devices are fine.",
"https://pubmed.ncbi.nlm.nih.gov/17491105/",
"so it can cause the device to trigger and deliver its own shock. Apparently getting shocked by the icd is like getting kicked by a horse. It can cause PTSD.\n",
"https://www.jacc.org/doi/full/10.1016/j.jaccas.2020.04.057"
] |
[
"That being said, I have asked police I know about this and I was told that the tazer actually shocking a person is relatively uncommon, depending on where you live it's not a frequent occurrence, it also can be caught or stopped by clothing."
] |
[
"That being said, I have asked police I know about this and I was told that the tazer actually shocking a person is relatively uncommon, depending on where you live it's not a frequent occurrence, it also can be caught or stopped by clothing."
] |
[
"I have a chance to ask Stephen Hawking a question next week. What's a question that you'd like Stephen Hawking to answer?"
] |
[
false
] | null |
[
"Ask him if he believes that cryonic suspension is a feasible way to bridge the gap between the current state of medical technology and the future in which radical life extentension is possible. ",
"He has stated that he believes that aliens could use cryonic suspension to allow them to travel across the vastness of space but he has never commented publicly about human use of cryonic suspension to my knowledge. This seems strange to me given his own medical challenges. "
] |
[
"probably because it has only been posted for six minutes..."
] |
[
"Ray Kurzweil is a sensationalist hack. I strongly suggest against. "
] |
[
"How would we know anti-matter if we saw it?"
] |
[
false
] |
In the article posted the following is said: "The whole world is made almost entirely of normal matter, with only tiny traces of antimatter. Astronomers have looked right to the edge of the visible universe and even then they see just matter, no great stashes of antimatter. Physicists just do not know what happened to all the antimatter, but this research can help us to confirm or rule out some of the possible explanations." When we peer out at the cosmos, how can we tell that what we are looking at is matter and not anti-matter?
|
[
"You know how you can have a sink full of water, then drop some food colouring into it? It doesn't instantly go entirely pink (or whatever). Instead, you see an interface where the water that doesn't have any food colouring in it meets the water that does. And it's very pretty and fun to watch, but that's not the point right now.",
"The point is that if there were an antimatter structure of some kind in the universe — a galaxy, a solar system, whatever — there'd be an interface where the antimatter-dominated volume meets the matter-dominated volume.",
"And we'd see ",
" of very energetic gamma radiation screaming at us from that interface in a way that'd be just impossible to miss."
] |
[
"That's not at all a stupid question; it is in fact quite a clever one.",
"However, while your thinking is right, the scenario turns out to be implausible in the extreme. In order for pair-annihilation gamma radiation to be redshifted into the microwave band, the source of that radiation would have to be moving away from us at a relative velocity of I-don't-feel-like-doing-the-maths-right-now-but-pretend-I-typed-the-number-nine-for-several-minutes-here percent of the speed of light."
] |
[
"I'll be the idiot this time, and ask the really stupid question.",
"If a photon-emitting source is moving away from me as it emits the photons, I am told that the photons appear to be lower energy than they would be otherwise. IOW, light emitted from receding objects appears to be red-shifted.",
"If such a matter/antimatter interface existed, but was receding from us at a prodigious rate, presumably the gamma ray photons emitted from the interface would also be redshifted. ",
"We are in fact bathed in absolute shedloads of radiation, but it's microwave radiation. It's everywhere. It's called the Cosmic Microwave Background.",
"Could the source of the CMB be matter/antimatter collisions occurring at an interface that is receding from us at such an inconceivably prodigious rate as to redshift the resulting gamma radiation all the way into the microwave spectrum?"
] |
[
"Look at this gif, then please help me to understand why gravity doesn't pull the slinky down straight away from the bottom"
] |
[
false
] |
I don't get it. How's it just... hovering or whatever.
|
[
"The source video",
" can answer this question for you."
] |
[
"Ok so the best way to explain this is to think of it as two separate events, one has ONLY spring contraction, NO gravity, and the other has ONLY gravity, and NO spring contraction. Then, combine the two events, and you get the result. Here is a little drawing I made to animate ",
"Imgur",
"Basically, the center of gravity/mass (I don't know which one, its been a long time since physics) should fall just like any other object. Therefore, as the spring contracts, its center of mass also gets closer to earth. It just so happens that the movement of the lower half of the contracting spring and the movement of the center of mass towards the earth are almost perfectly matched until the point of full contraction, at which the spring falls like a normal object. Looking at the only the bottom of the spring, it looks like it doesnt move, but if you imagine where the center of mass of the spring would be at each point, it falls just like any other object. If this doesn't make sense, I can explain further."
] |
[
"It's not a force due to human pulling. It's a force due to the nature of the spring. Springs have a \"rest length\" that they are at if no forces are acting on them. That is, if you put a slinky horizontally on a table and let it go, it will naturally contract to its ",
".",
"Slinkys only stretch when a force acts on them. You can pull them or just hold them vertically and let gravity pull. If you hold the top of the slinky, gravity will pull the bottom down. The bottom will fall until it stops, and the slinky is stretched. ",
" Does gravity stop pulling on the bottom of the slinky? No. Gravity is still pulling. But there is ",
" force, the \"spring force\" that arises when the slinky is stretched. This force increases when the length of the slinky increases. Mathematically, ",
"F = -k*x",
"Where x is the distance the slinky has stretched and k is some constant which depends on the material (k will be different for plastic vs metal slinkys). This force is always opposite to the direction of stretching.",
"This \"slinky force\" is pulling the slinky together. It is pulling the top down, the bottom up.",
"When he lets go of the slinky, this spring force is ",
" because the slinky is still stretched. Only when the slinky is ",
" will the force stop. So the bottom of the slinky only falls after the slinky has compressed back to its rest length."
] |
[
"What would happen if you injected different liquids directly into your bloodstream?"
] |
[
false
] |
I know that hospitals and ORs will use saline IVs, and that's fine, but what about other liquids in the bloodstream? For example, If someone were to inject plain water into their bloodstream would it do anything, would it be different if it was deionized water? What about if the liquid is acidic, ph 2-4, and what about basic, 10-12? I know that blood is a buffered solution and can handle some pH changes, but I don't know to what extent. I wondered about this after I saw from South Park.
|
[
"Hospitals use isotonic saline, pH 7.4 to avoid problems with injections. If plain water were to be injected into the blood stream, it would cause an osmotic imbalance and cause the cells circulating to try and balance their salt content with the salt content of the fluid they are in. This would result in the cell taking in water and lysing (blowing up). Bad stuff. If different pH solutions were injected, proteins in the blood would be denatured (this means that they would fold in a different manner than normal) and most likely non-functional. Bad stuff.",
"To try and answer your question of volume it would take to make injecting water/unbalanced pH solutions into the blood, that is a more difficult question to answer as it would depend on what exactly you are injecting. "
] |
[
"Generally, IV solutions want to be isotonic (~290mOsm) and at around pH7.4 to be compatible with blood plasma. If solutions are not isotonic, they can create osmotic stresses on rbcs, causing lysis. Low pH's can also directly damage cells and proteins circulating in the blood. With that said, here's some information on when people ",
" use them for IVs.",
"Here's a study done in rabbits:",
"The effect of repeated induced intravascular hemolysis upon the blood of rabbits was studied in the following manner: ",
" slowly into the marginal ear veins of 6 rabbits at 48 hour intervals. [...] After various intervals following the repeated injections of water, there was a ",
" However, despite continued repeated injections the erythrocyte count ",
" There was a slight to moderate poly-chromatophilia and anisolcytosis with an occasional normoblast and hemacytoblast. The number of reticulocytes showed a slight increase; the highest figure was 7 per cent. ",
" than in the number of erythrocytes.",
"So in this paper, hypotonic solution injection did cause some degree of hemolysis via osmotic effects, but without any major harm.",
"Apparently, IV infusions of distilled water were once used to treat hematuria (bloody urine) in sickle-cell disease patients, according to this ",
"really old paper that is not digitized so only the abstract is available",
":",
"Transient cessation of hematuria also occurred repeatedly after an infusion of distilled water. This phenomenon may be related to red cell expansion and dilution of S-hemoglobin and supports experimental evidence that a critical concentration of S-hemoglobin is a prerequisite for sickling.",
"This even older (1914!) book",
" describes some of the parameters in the hemolysis, but again shows no anemia as a result.",
"IV HCl is sometimes used to correct for metabolic alkalosis (by directly adding more acid to the body). Uptodate says",
"HCl is usually given as an isotonic solution (150 meq per liter) over 8 to 24 h. It can be infused into a major vein (since HCl is very corrosive) or into a peripheral vein if the HCl is buffered in an amino acid solution and given with a fat emulsion ",
"This page",
" says:",
"The addition of 100 milliequivalent/liter hydrochloric acid to normal saline produced a pH of approximately 1.5. [...] Hydrochloric acid solution should be administered through a central venous line to prevent ",
". Do NOT infuse via a peripheral vein! Injection of HCl into a peripheral vein may cause extravasation and can produce severe tissue necrosis.\nSolutions for infusion should NOT exceed 0.2 N (increased risk of hemolysis and increased venous irritation). Concentrations >0.1 N have been reported to cause corrosive effects, even when administered through a central venous catheter. "
] |
[
"Not refuting you just going to clarify. We do inject sterile water into pt's as some medicines do not mix well with saline. This is normally only used to put a powdered medicine into a solution. The same is done with hypotonic/hypertonic solutions. Some medicine mixes better and gets better effects depending on the solution. Some medicines mostly infusions are mixed into a 5% dextrose solution. Also the saline we use is 0.9%. Once again just trying to add a little information. "
] |
[
"What is happening in our lips/mouth that causes spicy foods we eat to feel hot or \"spicy\"?"
] |
[
false
] | null |
[
"According to ",
"this paper",
", capsaicin (the substance responsible for the feeling of heat) activates pain receptors, specifically causing the body to experience the feeling of heat.",
"Interestingly, mammals experience heat from capsaicin, but birds do not. This may be an evolutionary adaptation. It keeps mammals from eating the fruits of the pepper plant but allows birds to eat them. Birds travel farther than mammals do, thereby carrying the seeds they've ingested to new places. As a practical matter, this means that you can keep squirrels out of your bird feeders by adding cayenne pepper to the bird seed. "
] |
[
"Is the spice actually causing any damage when it activates the pain receptors or is it doing so without any damage? Can I eat a pepper hot enough to burn my tongue or hurt me?"
] |
[
"Capsaicin itself is not corrosive. It doesn't cause chemical burns or anything. It can cause temporary inflammation and irritation, like if someone gets pepper spray in the eyes. But it does this by essentially tricking the nerves into sending pain signals, not by causing actual damage. I'm referring here to short term, immediate damage; I can't speak one way or another about any long term effects."
] |
[
"How strong would a magnet need to be to affect the iron in a person's blood?"
] |
[
false
] |
If you had a strong and large enough magnet, could it lift a person just by the iron in their blood?
|
[
"You'd have to understand Gaussian field theory to make sense of any answer, but first know hemoglobin is only weakly affected by magnetic fields. Even an MRI, which has an extremely strong magnetic field, ",
"barely interacts with blood",
"."
] |
[
"Haemoglobin is diamagnetic if it's carrying oxygen and paramagnetic if it's not.",
"Also note that the diamagnetic response of the water in your body drowns out any response from haemoglobine, since there's just a LOT more water in your body."
] |
[
"Well, you could levitate people magnetically, but not by the mechanism you are thinking off.",
"To understand why, we need to look into how molecules interact with magnetic fields. There are two components to this: the paired electrons are repelled (diamagnetism) by the magnetic field, while unpaired electrons are attracted to it k(paramagnetism). In most biologically relevant molecules, there are no unpaired electrons. If a transition metal is present, thee can be one or more unpaired electron. Even though there is many more paired electrons, the paramagnetism is so much strong that the molecule overall is attracted to magnets. ",
"Paramagnetism isn't very strong. To get something like the effect of metallic iron, you need more than just that. What you need is ferromagnetism. This works like paramagnetism, but the individual atoms affect each other, leading to a much stronger effect.",
"Now, the iron in blood is not metallic. At most, it is paramagnetic. Most other tissue is diamagnetic, and overall, the diamagnetism wins. So you can levitate e.g. ",
"a frog",
" with magnetism, but it works by repelling the frog, not by attracting it. You could do the same with a human, but the magnetic field would have to be much, much stronger."
] |
[
"How is speciation possible for sexual reproductive organisms?"
] |
[
false
] |
What is the logic that leads to 2 viable members of the new species having the ability to mate and produce offspring vs members of the species from which they came? This has always been the question whenever I went over evolution in school. I understand that most developments of new species happened in isolated areas so the distinction of when exactly the organism became a new species is usually relatively unimportant but it has always been something that I could never get a clear answer on.
|
[
"Speciation isn't a discrete thing. A good example of this is a ",
"ring species",
". Just because A can mate with B and B can mat with C doesn't mean that A can mate with C. Speciation occurs when two groups are separated enough that they gradually drift apart until they are no longer interfertile. But there's still a point where only some members of one group are fertile with some members of the other."
] |
[
"The topic of chromosomal rearrangements and speciation is much more complicated than that \"article\" suggests. The human chimp rearrangement probably isn't a great example. There is a solid one in Drosophila that does appear to be caused by rearrangements though. This is also only one type of molecular mechanism that is theorized to cause speciation. "
] |
[
"I don't know how many ring species exist laterally, but every single species is a ring species temporally. A breedable population isn't formed. You start with one. Then you slowly change their genes together until they can no longer mate with the original group. But since they're all pretty closely related at any given point in time, they can always all mate with each other."
] |
[
"How do meteorologists calculate wind chill or “feels like” temperatures?"
] |
[
false
] | null |
[
"There is actually a wind chill formula that is typically used (it's different depending on where in the world you are, there is no standard).",
"In the United States we have one",
"T= 35.74 + .6215(Ta) - 35.75 v",
" + .4275 (Ta) v",
"Where T is the final, (Ta) is the air temp (f), and v is the wind speed in mph.",
"Australia has a far more complex one, involving humidity as well as wind velocity and ambient temperature.",
"The American model only works under certain temperatures and in low humidity, the Australian one has a wider range."
] |
[
"Edit: Somehow I skipped entirely over the wind chill, which is the \"feels like\" measure you actually asked about. This response is about the heat index, which is another \"feels like\" measure. Sorry. ",
"This is called the heat index, and it's a subjective attempt to combine the effects of humidity with heat. The human body's primary cooling mechanism is through evaporation of sweat, and high humidity can dramatically slow this evaporation. The result is that the same temperature that's comfortable at 50% humidity can be sweltering or even dangerously hot at 90% or 100% humidity. The goal of the heat-index scale is to approximate, for a given temperature and humidity, how hot you would feel at \"normal\" humidity. Accurate scales try to take into account many other variables, such as how much heat is lost from your body via respiration and direct thermal radiation. ",
"For example, if it's 90 degrees F outside and \"normal\" humidity then the scale should say it \"feels like\" 90 degrees F. If it's 90 degrees F out and it's 70% humidity then ",
"NOAA says",
" it \"feels like\" 105 degrees F.",
"The key observation is that we want to estimate how fast your body loses heat. If you assume a constant heat input to your body from your metabolism, then the heat shedding rate determines your apparent temperature. If you shed heat faster then you'll reach equilibrium at a lower skin temperature and lower apparent temperature. If you shed heat slower then you'll feel hotter. ",
"In a perfect world we could measure how fast your body sheds heat under various temperature and humidity conditions. However, the world is full of complications. There are tons of variables that affect how your body sheds heat, so the heat index equation makes a whole lot of assumptions in order to try and model an average person under average conditions, and then have this model be at least somewhat meaningful no matter where you are. ",
"Some variables relate to the person. ",
"NOAA's model",
" assumes you're 5 foot 7 inches tall and weigh 147 pounds- this is important as an estimate as your total body surface area, and more surface area means you can radiate heat more easily. They assume that 84% of your body is covered by clothing. They assume you're walking at a pace of 3.1 miles per hour (which governs the total heat input from your metabolism). There are many such variables, see the link above for details.",
"Then, there are variables that relate to the environment. For example, NOAA assumes a 5 knot wind.",
"All this is boiled down into a model that takes five variables in order to estimate the total heat transfer away from the body.",
"So now we can determine whether any two weather conditions have the same \"apparent temperature\" by estimating how much heat your body loses in each condition. If your body loses the same amount of heat in conditions A and B then that means that A and B feel about the same. If your body loses more heat in A than B then A is going to feel cooler, while if your body loses less heat in A than B then A is going to feel warmer."
] |
[
"The vast majority of convective heat transfer constants are empirically derived and as such are really ugly weird numbers. Wind chill is an effort to correlate the difference between heat transfer off a person in still air compared to the heat transfer of moving air and as such is subject to those same types of odd correlations and coefficients.",
"I don't know precisely how the wind chill formula was derived as I don't work in that field, but that type of very precise coefficient is pretty common for other derivations of convective heat transfer rates for specific objects and shapes."
] |
[
"If a codon is only 3 bases long, what does the rest of mRNA molecule do?"
] |
[
false
] |
[deleted]
|
[
"It’s also worth adding that the bits of mRNA that don’t encode proteins are also very important to processing ",
"Some non coding regions of mRNAs form things called internal ribosome entry sites (IRES). The ribosome can bind to these and start translating from this point instead of the start of the molecule. This means that one mRNA can be used to make different protein sequences (because the IRES can have a different reading frame). ",
"DNA contains introns and exons but the introns are spliced out before the mRNA is made into proteins. The mRNA can be spliced in multiple ways to produce different sequences that will be read by the ribosome to produce different proteins."
] |
[
"An mRNA strand is made up of lots of codons, each codon codes for 1 amino acid. Though there are some noncoding segments that get cut out I believe in post transcriptional processing",
"An mRNA molecule would look like this",
"- CCU - CUU - GGC - UAG",
"",
"And the corresponding protein strand would look like this",
"- Proline - Leucine - Glycine - stop",
"",
"Proteins have a lot of amino acids in a chain, that's what allows them to form useful, and different structures.",
"",
"Post transcription tRNA processing is probably best answered by someone else who remembers better, Ribosomal RNA is interesting because it has a large section of RNA to interact with the mRNA and tRNA it catalyzes. The rest is amino acids to make the protein portion.",
"",
"--I hope this helps at least answer some of your questions for the time being"
] |
[
"Alternative splicing (removal of specific introns) is one of the reasons why humans have a relatively short genome but a huge amount of genetic diversity. For example, if on an mRNA molecule you have A-B-C, where ABC are exons with introns in between them, that could be expressed in 7 different ways (A, B, C, AB, BC, AC, ABC) all of which result in different proteins."
] |
[
"Why can't we absorb oxygen through our skin? What's the point of lungs?"
] |
[
false
] |
[deleted]
|
[
"The outer layers of our skin are mostly dead cells, plus there's a fair bit of material there to protect us from the environment. However, there probably is some diffusion of gases across the barrier of the skin, just as our skin can absorb water or other substances. The amount of oxygen absorbed and CO_2 emitted by our skins is not very significant however, simply because the surface area of our skin is so small.",
"An average sized human has skin covering a surface area of around 2 m",
" The surface area of the interior of the lungs, on the other hand, is upwards of 50 m",
" Even if our skin was every bit as good at moving oxygen in and CO_2 out as the surface of our lungs, our lungs would still do almost all of the work because their surface area is so much larger. ",
"As for why lungs exist... A tiny organism might be able to rely on diffusion through it's skin, but as the size of organisms increase the volume of tissue increases faster than the surface area over which gases can be exchanged. At some point you need to compensate for the reduced surface area to tissue volume ratio, and lungs are one way to do that."
] |
[
"All folded up and crumpled, the lungs are, but all the little nooks and crannies of your lungs if completely unfolded can add up to 50m",
" ",
"Think of it like taking a giant sheet of 7m x 7m paper and crumpling it up to the size of something like your lung interior. Now you see how 50m",
" can fit inside your chest and have that much surface area, still, right?"
] |
[
"Lungs' lining is very thin and moist. Skin is very not thin and dry. Being very thin means that your lungs can very effectively transport oxygen into your body, but it also means that pathogens can easily cross from your lungs into your body. Being moist makes your lungs an excellent breeding ground for pathogens.",
"If your skin was as thin and moist as your lungs, it would be too fragile for you to survive — between walking and touching things and wearing clothes, you would damage it almost instantly, at which point pathogens would invade your body and kill you.",
"Meanwhile, your skin is dry (which is inhospitable to pathogens) and thick (which makes it harder for them to get inside, especially if you have no open wounds), which makes it an excellent protective layer against mechanical damage as well as biological attackers, but terrible at exchanging gasses. ",
"When people get severely burned, what happens is that their skin is destroyed and the moist, fragile underlying layers are exposed to air. Then they get an infection and die. That is what having external lungs would be like."
] |
[
"Why do women have two breasts when, on average, they have one baby at a time?"
] |
[
false
] |
Also, why not three or four?
|
[
"Think about why you have to rotate your tires, but with tits."
] |
[
"Because you'd never get any work done."
] |
[
"Most mammals have twice the number of nipples as the average litter size."
] |
[
"Is it in any way possible to reverse a black hole?"
] |
[
false
] |
Would it be possible to remove mass from a black hole, making the gravititional pull too weak to "maintain" a singulariry? What would happen?
|
[
"If they're small enough, they actually do this on their own. We think that quantum fluctuations near the event horizons of black holes cause them to emit mass/energy in the form of Hawking Radiation. For big black holes, this happens really slowly, (many-times-the-age-of-the-universe-slowly) but the smaller they get, the faster they evaporate. Exponentially faster. Eventually, we think they explode, and people are looking for the energy released in such events. In the last second of their life they should emit 100000 times more energy than the largest bomb ever built. We don't, however, have a complete description of the end of a black hole's life, which would need a quantum theory of gravity, which still eludes us."
] |
[
"Just to clarify, these quantum fluctuations happen at the event horizon of the black hole. Therefore the radiation produced is proportional to the surface area of the black hole. You can think of the mass of the black hole being proportional to the volume and the rate at which it is turning into Hawking Radiation being proportional to the surface area. The volume divided by the surface area would represent the life expectancy of the black hole. The larger the sphere, the higher this number is. Therefore, the larger the black hole, the longer it will last.",
"This should explain ",
" larger black holes last for a longer time.",
"The life expectancy of big black holes is ridiculously long. As viscence pointed out, it's many times the age of the universe, but with many, we don't mean 10. We mean 8*10",
" times as long. And that's for a black hole with only 2 solar masses.",
"The math behind the life expectancy of a black hole is actually quite simple. If you want, I can talk a bit about that.",
"(this is aimed at Blackbabygsus, you definitely already know this, viscence)"
] |
[
"Basically, since the temperature of a black hole (or rather, the Hawking radiation associated with it) increases as the hole gets smaller, which causes the hole to shrink faster, and thus keeps looping, the last moment of its life is its most energetic.",
"Along with that, the process is very directly converting the hole's mass into radiation, so it is perfectly efficient, via E=mc",
"Anyway, once you work it out, at the last second of the hole's life, it still has a mass of a few hundred tons - all of that will be energy a second later. Our biggest bombs are still in the range of a few grams of mass converted, total. "
] |
[
"When a tree (or other land plant) is immersed in water, what does it die of?"
] |
[
false
] |
Let's pretend the water only just covers the tree/plant, so light is still available. Does it suffocate due to lack of oxygen? Does the water leach essential chemicals out of leaves? Both? Does the water just block enough light it starves?
|
[
"Plants need oxygen to metabolize the sugars they have produced all day. They do proportionately more of this at night to put the stores energy to growth, and maintenance. Unless they are adapted to aquatic life, they can’t access the oxygen their mitochondria need."
] |
[
"Many terrestrial plants are surprisingly resistant to flooding, surviving months and even years. The lack of oxygen is what would kill them, but they produce that given light. ",
"Here",
" is a source. Light is a major deciding factor in the lifespan of submerged organisms because with it comes photosynthesis and oxygen production. Since it isn't a closed system, some of the CO2 produced from respiration would be lost to the environment and would not be available for photosynthesis. This causes eventual biomass loss and death."
] |
[
"Some plants have evolved to be tolerant of flooding. In the Amazon the water can rise 50ft (ca. 15 metres) in the wet season and young trees survive. Other plants can die in a day or two being immersed in water."
] |
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