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[
"What is that phenomena called when I pee in the toilet with a steady stream and a random drop seems to pop out from the toilet bowl (and land on the rim)?"
] |
[
false
] |
I know there's a name for this but I cannot remember it (not bad aim). Google search with the above question yields nothing helpful. Please help! Thanks!
|
[
"splash back or back splash? These are also names for guards in fountains and such to catch this."
] |
[
"Searching for 'rebounding water droplets' turns up a lot of related articles."
] |
[
"I believe that this is the scientific term for this phenomenon. At least, that's what all us grad students call it."
] |
[
"X-ray go through us, UV and visible light is stopped by us, and radio waves go through us; where is the cut off for radiation going through people?"
] |
[
false
] | null |
[
"Radio waves don't actually go through us, or, for that matter, food in a microwave, contrary to a commonly heard urban myth.",
"Only very high powered photons pass through us -- x-rays and gamma rays. And subatomic particles go through us, but with some chance for a collision along the way.",
"Neutrinos go through us, but they also go through the entire earth with little chance for an interaction.",
"So the cutoff for energy passing right through us is at or near the x-ray wavelength or higher (more power). All electromagnetic radiation of lesser power levels doesn't pass through us.",
"Photon energy increases with frequency (shorter wavelength). X-rays are composed of very powerful photons."
] |
[
"NIR penetrates deeper into skin than VIS, e.g. you can monitor brain flow transcranially. THz and mm/submillimeter-wave goes deeper still."
] |
[
"If the energy of the radiation matches a specific energy transition in the atoms it travels through, then it is strongly absorbed. For instance, the energy of visible light matches the transition energy between different electron levels in a low-atomic-number atom (",
"http://en.wikipedia.org/wiki/Bohr_model",
").",
"X-rays match the electron energy levels in the most tightly bound electrons of high-atomic-number atoms. That is why they will travel through tissue (Z = 6 or 8) but not bone (Z=20, calcium). This is also why lead (Z=82) is a good X-ray shield.",
"Radio waves are so low energy (long wavelength) that they don't really behave like particles at human-sized scales (remember particle/wave duality? ",
"http://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality",
"). The situation is more like being hit by a wave at the beach - the wave is so much larger than you that it just diffracts around you.",
"There are a few more examples. Microwave ovens are set to match the energy of magnetic energy levels in hydrogen atoms, so they are absorbed. Neutrons that match the energy levels of a nucleus are strongly absorbed. Any uncharged radiation that doesn't match a specific energy level is weakly absorbed, or scattered. So there is no real \"cut off.\" Some photon energies are very likely to be stopped, and most others pass through with minimal resistance."
] |
[
"Is the chance of winning the lottery on a ticket with in-order numbers the same as random numbers?"
] |
[
false
] |
Sorry if the title is confusing, I couldn't find a better way to phrase it. If 6 balls are pulled out of the lottery, is the chance of winning the same for increasing numbers in order and randomized numbers? For example: You pick your numbers in order to be: 1,2,3,4,5,6 or: 11,12,13,14,15,16 Or you pick random numbers to be something like: 24,11,14,3,27,35 Would you have better chances with the random numbers? I couldn't imagine the numbers being picked in order. It seems like the chances are a lot lower for that. But don't all numbers have the same chance of getting pulled?
|
[
"Both 1,2,3,4,5,6 and 24,11,14,3,27,35 have precisely the same chance of winning. Your evaluation of your chance of winning with 1,2,3,4,5,6 (extremely unlikely, like almost never) is closer to the correct chance and is how likely you should feel of winning with any combination you pick.",
"That said, there is a point of truth in what you've asked: the chance of a straight is much less likely than a non-straight. However, this is a lottery not roulette and you don't get to bet on straights against non-straights. You only get to bet on one set of 6 numbers and every set has precisely the same chance of winning."
] |
[
"Interestingly, while the numbers you pick don't alter your chances of winning, they do alter the amount you are likely to win. If the options are 1-60 for example, you have an equally high likelihood of winning if all of your numbers are over 30 as under 30. But people like to pick birthdays etc as lottery numbers meaning that there are likely to be more numbers in the drawer from 1-31. Thus, if those numbers do come up which is equally likely as any other combination, you are more likely to have other winners and thus a smaller prize pool. That's one example but there are others. I read a really interesting article a few years back on the subject. ",
"Tldr: you can't change the odds of winning but you might be able to increase the amount if you do win. "
] |
[
"Any set of numbers has the same chance of being drawn, but having randomly chosen numbers could be advantageous if you have a winning ticket. Depending on which lottery you are playing, the total prize money may well be split between all winning tickets. A lot of people pick regular sequences of numbers, so if you won with the numbers 1,2,3,4,5,6 you may well be sharing the prize pot with enough people that you don't get much money."
] |
[
"Why is iron attracted to a magnet, but chromium isn't?"
] |
[
false
] |
(Below 38 degrees Celsius, at least.) The explanation I've always gotten is, roughly, 'well, in chromium each atom pairs with another atom, cancelling out the magnetic field' (i.e. antiferromagnetism) - but this leaves a lot to be desired. Why do such pairings form in chromium but not in iron? And why do such pairings form in such a way to cancel out the magnetic field? On a large scale, it's energetically favorable for magnets to orient themselves such that their fields add - why is it any different on an atomic scale?
|
[
"Hi, ",
"wikipedia",
" has a decent (and much better than I could do in a reddit comment) explanation of how ferromagnetism (permanent magnets) work. To properly understand why in some atoms parings are made and others are not requires a decent amount of ",
"quantum mechanics",
" at the 2nd/3rd year undergraduate level. The topic is actually hard to find a good book on online, the closest I could find were ",
"these",
" ",
"three",
" on ",
"quantum magnetism",
".",
"To provide some quick hand-wavy answers:",
"Why do such pairings form in iron and not chromium?",
"Why do pairings cancel out the magnetic field?",
"Why is it sometimes more energetically favourable on an atomic scale to anti-align magnetic fields?",
"Here",
" is a good slideshow with some good books at the end (I can't find any of them online for free though)",
"I hope some of that is useful.",
"[Edit: Formatting]"
] |
[
"Why do pairings cancel out the magnetic field? All electrons have a magnetic moment (this is what gives rise to the magnetic field), it's orientation is dependent upon the particles' spin (either up or down). Due to the PEP, electrons in a filled shell will always pair up (one up and one down) and their magnetic moments will cancel. ",
"It is unfortunately one of those seemingly simple questions that are tremendously difficult to answer. Perhaps one has to give up on accuracy for the sake of simplicity. But I thought the pure chromium is in fact a spin density wave (SDW) metal rather than an insulating antiferromagnet. In this case, I suspect that the origin of SDW in chromium has more to do with the Fermi surface geometry (or broadly, electronic structure) of chromium in its paramagnetic state than the local exchange interactions."
] |
[
"The gist: electrons define magnetism as a side effect of quantum spin. The more electrons with the same spin (up) and no countering spin (down), the more magnetic the atom can be. Each orbital has two electrons in it - one of each spin. A valence shell has X number of orbitals in it, and each shell has more orbitals than the one before it and a higher energy level, but the higher the shell is, the narrower the energy level difference is between them. Each shell fills each orbital with an up electron first until the shell is half full, then the lowest orbital gets a down electron, then the next, etc. When shells' energy are close enough, adjacent orbitals in the nearby shells will also fill with up electrons before the down ones come into play. ",
"Iron is in this sweet spot where the electrons can fill out several orbitals with up electrons without being countered by down electrons, and, because of the properties of paramagnetism, these \"ups\" can be matched with the \"ups\" of surrounding atoms when a magnetic field aligns them. Basically this means that iron can be stably filled with electrons without filling any of the outer orbitals with two electrons, and interactions between these shells of ups induces the same direction of up in nearby atoms. When this happens, the magnetic field has multiple contributions from different atoms and forms a larger magnet, and can continue to align nearby atoms with the same properties. ",
"Chromium and other metals don't have as many \"exposed\" or disparate valance orbitals. Other metals usually have fewer exposed orbitals and/or the spins of the up electrons are mitigated by the spins of the down electrons in the same orbitals. ",
"Think of magnetism as a disparity caused by quantum spin. The field is created when the net quantum property of the sea of electrons in a magnetic chunk of metal is very up and wants some down. Non-ferrous metals don't have as much of an up/down disparity, so the sea of electrons have a balanced spin proportion and the field created by whatever imbalance is much weaker. All the electrons are paired and happy. ",
"Quick edit: I'm operating off of memory of knowledge I don't really use often, so please correct any lapses in vocabulary or understanding! ✌️"
] |
[
"Looking back in time at our children- Using telescopes? (Galaxies example)"
] |
[
false
] |
[deleted]
|
[
"A telescope can only pick up light that reaches it. It can't reach out and grab far-away light.",
"As you get into your spacecraft, the light reflected from you leaves Earth and starts traveling towards Kepler-22b. You take off at the same time, traveling at 99.9999999999999999999999999999% of the speed of light. The light that was reflected off of you as you boarded your spacecraft is still going to beat you there, because you're going slower than it."
] |
[
"Not unless you traveled faster than light, which is impossible according to our current understanding of physics."
] |
[
"(Faster the light, means we arrive there before light does, so we are arrive before time does), In that scenario, it would work, ok.",
"But say we were traveling 99.9% as close to the speed of light, without ever actually surpassing it. (Assuming we could) ",
"We reach the planet with my #nth grand child being born on Kepler, and he/she points a telescope at earth from Kepler",
"Maybe I am thinking about it wrong, is there some correlation between telescopes / the distance they view/ and time?",
"I am trying to explain my thought the best I can ><"
] |
[
"Why does all visible light travel at the same speed through a vacuum, but not through a medium?"
] |
[
false
] |
Additionally, does this apply for all other types of radiation in the electromagnetic spectrum? E.g. radio waves travel slower through a medium than UV waves?
|
[
"Alright thanks for clearing it up. Seems like I had some things mixed up there."
] |
[
"That's a misleading explanation, especially as the poster above you has the proper explanation (it excites other charged particles and the interaction between the emitted photons from them slows the group velocity). ",
"See the following from Sixty Symbols: ",
"https://youtu.be/CiHN0ZWE5bk",
"Also: ",
"https://en.wikipedia.org/wiki/Refractive_index#Microscopic_explanation"
] |
[
"That's a misleading explanation, especially as the poster above you has the proper explanation (it excites other charged particles and the interaction between the emitted photons from them slows the group velocity). ",
"See the following from Sixty Symbols: ",
"https://youtu.be/CiHN0ZWE5bk",
"Also: ",
"https://en.wikipedia.org/wiki/Refractive_index#Microscopic_explanation"
] |
[
"Why does the 5th (pinky) finger, have its own extensor but not its own flexor? Why do why need to extend it in isolation from the other digits?"
] |
[
false
] | null |
[
"It does have a flexor muscle, the flexor digiti minimi, which is part of the 3 intrinsic muscles of the pinky. The pinky needs to be able to extend and flex in isolation so it can cross and touch the thumb. If it wasn't for the opponens muscle, then we wouldn't be able to grasp items in the manner that we do now. This is from what I remember from my Kinesiology class. "
] |
[
"The hand is pretty complex and there are lots of factors that go into this answer. I'll try to explain this the easiest way possible. Basically, all your fingers have two main flexors and one main extensor. The muscles for these tendons are located in the forearm. The flexors are the FDS and FDP (flexor digitorum superficialis and profundis). The extensor is the EDC (extensor digitorum communis). these tendons all share one common muscle belly, this is to aid in gross motor movement (opening and closing your fist all together). The index and pinky finger have their own tendons as well, both for flexion and extension. This is to aid in fine motor movement (pointing, pinching, typing, etc). Now, the reason you have problems extending your ring (and middle to some degree) but not your index and pinky is due to several reasons. The simplest explanation of one of the mechanisms is that, even though all the fingers have a common muscle belly, the tendons of the middle and ring have an attachment to each other higher up in the hand. So when both muscles are flexed (during grip) this attachment helps pull the tendons closer together, thus improving grip strength. This is one of the few mechanisms your hand uses to keep your fingers tightly together while gripping, because loose fingers while trying to tightly grasp something would be worthless. The hand is pretty cool and there are a lot of other factors that go into this answer, but this is the easiest to understand without explaining the complex anatomy that is involved as well.",
"TL;DR: several tendons, one muscle belly, individual extension of ring and middle is less important than index and pinky, so the body connects them more tightly to improve grip."
] |
[
"Indeed--if it didn't have it's own flexor and extensors our musical instruments and keyboards would likely be arranged differently. ",
"The thing the OP is experiencing is reduced cortical representation of the fourth digit. Our brains dedicate fewer resources to the independent control of the third and fourth digit. "
] |
[
"Is there a way to pull carbon from the atmosphere in order to make useful products like carbon nanotubes and graphene, thus providing a useful item while also lowering greenhouse gasses?"
] |
[
false
] |
Bonus questions: Can you do this in a way without producing other harmful side effects, such as eating away the ozone? Is it possible for this to be monetarily profitable?
|
[
"So there are several parts to your question. First, it is possible to pull carbon out of the atmosphere, for instance with CO2 scrubbers. There are a number of different versions, some using passive adsorption and other reacting with CO2 to form other compounds.",
"Generally speaking, it would be... difficult and largely impractical to try and use scrubbers to combat carbon emissions, as many of these methods are less effective, and typically more expensive to achieve a desired level of impact, as compared to reducing the carbon footprint of a process by using green energy, renewably sourced materials, etc.",
"Now, as far as using recaptured carbon to produce graphene or carbon nanotubes, it would not work, at least not in an effective way.",
"Any processes which would convert gaseous carbon into something like graphite (a solid-state precursor to graphene) would be very cost- and material-intensive, and likely not worth it for the small output achieved.",
"While graphene and nanotubes are widely produced by CVD (chemical vapor deposition), these processes are extremely sensitive, and rely on the flow of two gases over a catalyst, typically nickel or cobalt.",
"The two gases are a carrier gas (ammonia, nitrogen, etc.) as the primary stream with a carbon source such as acetylene or methane. The carrier is just that, a carrier that does not participate in the reaction, but dilutes the carbon source to the correct concentration. The carbon source then reacts with the metal catalyst to grow carbon sheets, either in a flat 2-dimensional (graphene) configuration or in vertically growing tubes (nanotubes) depending on the structure of the catalyst material.",
"With current CVD techniques, you would have a very hard time producing graphene or carbon nanotubes from recycled/captured CO2. That being said, there is ongoing research to produce both materials from sustainable (or potentially sustainable) carbon sources such as camphor. However, so far there is still always a catch; you either have poor quality, poor efficiency, need some exotic, specialized reactant to make everything work, whatever.",
"But, it is possible that a future breakthrough allows for CVD growth of carbon nanomaterials from recycled atmospheric carbon. We're just nowhere near that point.",
"If that would be possible though, then there's still the question:\nIs it efficient enough to help reduce atmospheric carbon, or is it just an environmentally friendlier route to produce carbon nanomaterials as compared to CVD or other methods?"
] |
[
"There's already operational plants that pull it from the air, mix it with water and electricity and creates a hydrocarbon fuel that can be burned in cars. To pull JUST the carbon from the air, you gotta either separate it, and/or combine it with another compound, which you can remove it from. Creating a hydrocarbon fuel is probably the best thing we can do NOW. We can use solar and water to create \"gasoline\", which removes carbon from the air. It would be a self sustaining system, in that we pull carbon from the air to put it back in gas and then back to the air again. We only need a renewable source of energy like solar or fusion to power it."
] |
[
"The key thing here is energy everything is possible with enough energy but to capture more CO2 than the amount of co2 the capturing emmits think about energy and material. Many of these co2 caturing devices use massive fans wich need a lot of power"
] |
[
"If you windmill your arms in outer space, do you rotate or do you stay stationary?"
] |
[
false
] | null |
[
"You rotate for as long as your arms are kept spinning such that your total angular momentum stays the same as before."
] |
[
"what would prevent me from stopping my arms spinning and ending in a different orientation then I started? ",
"Nothing, you can totally do that. That's how cats turn to land on their feet when they're falling, and astronauts can also ... you know what, a video is worth a thousand words.",
"https://www.youtube.com/watch?v=VJcno_XL4RU",
"Your angular momentum remains zero the whole time -- so long as by \"you\" you mean your body ",
" your arms together."
] |
[
"No. If the total rotation of your body is zero, and part of it (your arms) is spinning clockwise, the rest of it will be spinning counterclockwise."
] |
[
"Do/Can \"equator-line-crossing\" hurricanes exist? if so, do they change their \"turning\" direction when changing hemispheres?"
] |
[
false
] |
Question is self explanatory.
|
[
"Is it possible? Well, sure, in theory. But hurricanes don't often form near the equator (because there isn't a coriolis force there, so normally cyclones cannot form). They ",
"can",
" form near there, but it's usually due to unusual effects. As far as crossing the equator: I can't find any examples (other than ",
"Agni",
", but details are sparse). However, if it did happen, the cyclone would indeed try to start rotating the other direction. It's quite likely, however, that the hurricane would dissipate (since it wouldn't have any cyclonic force to drive it) before that could happen, unless some external effects were sustaining it (in which case the Coriolis effect would probably have little or no effect anyways)."
] |
[
"It is a myth that water in different hemispheres spins differently down the plug, but the Coriolis effect does affect hurricanes. ",
"http://en.wikipedia.org/wiki/Coriolis_effect"
] |
[
"It is a myth that water in different hemispheres spins differently down the plug, but the Coriolis effect does affect hurricanes. ",
"http://en.wikipedia.org/wiki/Coriolis_effect"
] |
[
"When does evolution favor polygenic and monogenic traits?"
] |
[
false
] |
I ask because organisms tend to have a mix of both, but it seems to me that polygenic traits ought to be favored because they would be more resistant to disorders caused by unfavorable mutations. One unfavorable gene in a large system of genes has a relatively small impact on the phenotype compared to an unfavorable gene in a small system, where the change can cause large deleterious changes in the phenotype. But on the other hand there are plenty of monogenic traits. Is this 'just because', or is there an advantage to traits that are determined by relatively few genes?
|
[
"Well, its not that it favors one or the other, its simply a nature of the genetics of it. If a trait is based solely on one protein, its simply going to be monogenic because a single protein will only be encoded by a single gene. For example, ABO blood type consists of a single gene with 3 alleles. If you have the gene for the 'A protein,' you will make the 'A protein,' same thing with B, the 'O gene' doesn't encode for either, so you won't make either protein. This isn't something that requires multiple genes encoding for multiple proteins.",
"Polygenic traits are those that require multiple proteins, thus multiple genes. Things with a spectrum, like height or hair color, are polygenic traits.",
" Just because"
] |
[
"That's a good example of a trait that's just because.",
"I was thinking more about genes that regulate some metabolic pathway. Like a gene that codes for an enzyme, and there can be other genes that regulate the production of that enzyme, or maybe even alter the enzyme structure (if that's possible), or produce other proteins that help the process. I was wondering what drives certain systems of genes to be complex and others to be simple, and whether resilience towards mutations was a factor."
] |
[
"Well, there are other genes that affect everything. A single gene codes for a single protein (or some form of functional RNA.) There are proteins that do play important roles in the functioning of various other proteins and there are some proteins that require other proteins to work. Fatty acid synthase, for example, contains multiple enzymes, each one required to function for the whole enzyme complex to function.",
"Basically, there are a lot of interdependencies involved in the functioning of many proteins. A good example of how complicated it can get is with a genetic disorder called henylketonuria (PKU). PKU is typically caused by a mutation in the gene coding for phenylalanine hydroxylase (PAH), an enzyme that converts one amino acid into another. However, this enzyme is dependent on a cofactor, a chemical that helps the enzyme work, called BH4. Defects in the various genes that encode for 3 different enzymes can cause the depletion of BH4, preventing PAH from functioning.",
"Essentially, a mutation in a gene encoding for an enzyme that replenishes this one chemical can directly impact the functioning of a different enzyme leading to a genetic disorder.",
"I guess in that manner, there's no such thing as a monogenic trait. Every protein is ultimately dependent on another for functioning. Sometimes, the dependencies are straightforward, sometimes they aren't. Typically, its just the nature of the biochemistry involved. Like with PKU, PAH needs that cofactor to function, and that cofactor needs to be replenished. There isn't really any other way it could work that way.",
" Basically, its never very simple. Proteins encoded by one gene tend to be dependent on a lot of other proteins, thus a lot of other genes. With some traits, you can point to a single cause for a trait, like in ABO blood type, but even that has other proteins involved for it to truly function. Certain genetic disorders are caused by a dysfunctional enzyme, but that can be caused by either a mutation in the gene encoding for that enzyme, or a different gene encoding for another enzyme it requires. Basically, the complexity of a trait is more dependent on the biochemistry involved than an evolutionary advantage."
] |
[
"How far are we away from economical synthetic/In vitro meat?"
] |
[
false
] |
says, it could be competitive around 2050. It is stated that in vitro meat has a lesser environmental impact, requires less energy to produce and does not harm animals. Is In-vitro meat a realistic and sustainable alternative to common animal-meat? What main problems have to be overcome in the next decades? Can in vitro meat substitute todays animal meat, or will it only be a small niche?
|
[
"HI!",
"I'm going to have a rant here about ",
" meat.",
"First off, this shit comes up every few months on reddit, and the massive response is always really positive, and everyone looks forward to 2020, or 2050 or whatever magical date that is proposed to be the date when this shit is cost-effective. ",
"Let me burst that bubble. My background is biotech, which is where this kind of meat would end up, in the science world. In Biotech we grow lots of meat already, in massive, 10,000 litre vats that make tons of incredibly expensive medicines. We tend to use CHO cells, which are Chinese hamster ovary cells. They are great! I worked with them a lot, and they are basically one of the most retard-proof mammalian cells in the world. ",
"OK, so what are the problems facing artificial meat?",
" the cost. We can make cheap \"meat\" with fungus or whatever. People want 'real' meat though, which means mammalian cells. Which means very tricky growth. They have no cell wall, are delicate, and as the most efficient way to grow them is to use vats, they need a lot of careful aeration and feeding. Small scale is relatively easy, although you make very few cells. Large scale, massive costs, massive problems. Forget about antibiotic free meat for a start, you can't have large scale without tons of antibiotics, foam reducers and other 'chemicals' that would curdle the toes of your average meat eater. ",
"Another, and to me the major unspoken point, is FBS/FCS. Foetal calf serum, foetal bovine serum. Mammalian cells don't grow well without it. You either mince up baby cows and give the juice to the cells (see the redundancy?), or you spend insane amounts of money on very costly Swiss artificial sera which don't work very well. ",
" you have manufacturing scale. Have you, dear reader, ever grown mammalian cells and forgotten them in a T-flask? And then you go in and find a massively over-confluent sheet of flesh at the bottom of the flask? A slice of Henrietta Lakcs? That is what the goal is, and to make a full steak you need a BIG flask or vat. And to make enough meat to replace the meat industry, or even make a dent, you need a MASSIVE biotech industry to spring up. ",
" capital costs. And the problem with that capital cost, is the problem number 3...",
", is lack of a benefit. The problem is, cows are cheap. Cheap to look after, ridiculously so compared to growing cells. Every single piece of the cow is used, everything is sold and nothing, not even the shit, is wasted. While mammalian cell growth is as wasteful as hell. Cows make a ton of meat cells, with an ",
" defence against infection, while mammalian cell growth is as touchy as fuck about aeration dead spots, shear forces, infections or whatever. ",
"The search for ",
" meat is a ",
" search. I worked on a project for an artificial liver once, it is another one of those '2050' projects, but on that journey we will learn so much that we can use now. This search for an artificial steak is like that, it's a way to learn a lot about the whole field. However, the picture of a guilt-free steak they show you is just the hook for funding, imho. ",
"And to the inevitable retorts about how we will overcome these problems with future technology, please remember this is an industry that is currently worth absolutely ZERO. The recombinant protein industry is worth more than Africa. (",
", I checked and it's only around a tenth of the value of Africa, my bad, sorry Africa). If we got these problems sorted, it wouldn't mean a triumph for steak, but for Factor VIII. The two dudes working in a university lab, who are always quoted with these stories, aren't going to be breaking out the perfect serum free media, it's going to be Pfizer or whatever. ",
"Sorry to be a balloon popper. ",
"Just to add one more take on this! ",
"The thing is, Cows are excellent at turning the raw materials of water and grass, into meat. We want the meat. So we want to skip the cow bit. Meat is cells, and they want the raw materials to go through a lot of digestion. The entire premise here is that we somehow jump over all that digestion. We want to take cheap raw materials, and somehow make the cells eat that shit. The alternative, which is what we do now, is to get cows to eat it, take their blood, mix it with really expensive, really pure chemicals that cost tons, and give it to the cells. ",
"So what we want, is to either make cells that can deal with cheap raw materials, or make some machine that can turn grass or sugar beats or whatever, into blood, more or less. ",
"Hopefully, putting it that way makes it obvious that what we are after here, if we had it, would be massive. Cheap meat-in-a-vat would be a tiny detail compared to the technology we would be wielding in that future. "
] |
[
"http://www.guardian.co.uk/science/2012/jun/22/fake-meat-scientific-breakthroughs-research?CMP=twt_gu",
"2 independent researchers are working on it with different methodologies and are pretty close to a breakthrough. The price is the real problem."
] |
[
"How long would we be talking to get to, say, 120% of current beef prices with similar fat content? At that level, I'd probably switch over. I'm not a vegetarian, but I can understand the cruelty and environmental impact arguments, and would have a harder time justifying my current choices if this was an economical (though not necessarily cheaper) alternative."
] |
[
"What is the evolutionary advantage of an animal eating its young?"
] |
[
false
] |
[deleted]
|
[
"Howdy! This is a bit outside of my subject area, but I have ",
" background here in animal behavior. There are several good theories on why animals might eat or kill their young. For many birds, for example, it is to guarantee greater success of offspring within multiple egg clutches. ",
"If you read some of ",
"Sarah Hrdy's",
" work, she even goes on to show this behavior of infanticide in primates and even early humans. In the book Mother Nature (which is a fantastic read, by the way), she seems to suggest that early humans may have actually killed their young in some cases. The reason for this being that since human infants are such costly (both in resources and in time), there is evolutionary pressure to kill offspring when conditions are simply too harsh. ",
"It is easier, therefore, to simply wait until better conditions arise and attempt to have children again, as the initial inputs are much less costly than trying to raise a child in an environment where the odds are heavily stacked against you and may actually result in your ",
" mortality as well. Of course, this seems very controversial, as it is a very taboo subject in human research.",
"There has been some light evidence showing that even initial \"cuteness\" ratings of human infants are low, compared to other animals and even other primates at the same general \"life stage,\" showing that by separating initial attachment at birth (i.e. just born human babies being wrinkled and very \"un-cute,\" even to humans), this can allow for an interval of rational decision making about an incidence of possible infanticide."
] |
[
"There is one way I can think of that an animal might benefit from eating its own young: if an animal has recently spent much of its energy producing offspring, it may be in dire need of sustenance. If there are no readily available food sources, there are basically two possible scenarios: \n1. The parent dies, and is no longer able to take care of its young, which is then also likely to die. (In some species of insects, the parent is often eaten by its larvae, as an interesting alternative.)\n2. The parent eats its young, allowing it to survive and have the possibility of procreating in the future."
] |
[
"So... post-birth abortion?"
] |
[
"Why do we still detect background radiation from the big bang?"
] |
[
false
] |
Regardless of how long these microwaves took to reach us, wouldn't it have blown past us already especially if the event that generated it occurred in a very small volume? Is it bouncing around matter in the universe or being bent back around by gravity to make another pass at us, perhaps?
|
[
"Its not an afterglow like you think of the bright flash of a bomb exploding. It instead has to do more with the temperature of space. Its the leftover \"heat\" that occupies the space and we are detecting that black body emission.",
"You can think of it as everything start off super hot and dense and as space expanded thermodynamics says it must also cool. But since there was thermal energy there it cant just disappear and the temperature gets lower and thus the radiations frequency decreases. This radiation is constantly emitted everywhere. ",
"There are obviously warmer places but the vast majority of matter is emitting from all directions at this 3(ish) Kelvin."
] |
[
"Thanks. That makes a lot of sense. I was indeed thinking of it like a flash of light not a hot \"object\" cooling down by radiating heat."
] |
[
"Just to clarify, the microwave background is black body radiation emitted from the stuff that fills black or \"empty\" space? "
] |
[
"I heard a snippet on NPR that we are pumping so much water out of the Ogallala Aquifer that it is effecting the earths gravitational field. Can someone please explain this too me? How is it changing, why is it changing, etc."
] |
[
false
] | null |
[
"I was not commenting on the abuse of aquifers, just the abuse of scientific sounding language. Every movement of mass causes a change in gravity. Sublimation of snow every winter causes a change in gravity but we don't hear the evening news commenting on that. ",
"This is the same manipulative nonsense as referring to radio energy as RF radiation, which is only invoked by 1) scientists who understand what the words mean or 2) manipulative scum trying to stoke fear over WiFi or cellular towers.",
"If you can't make an argument based on facts, do not try and use words people do not understand to stoke fear - even if it might be a 'good cause'."
] |
[
"Gravity is a function of mass. Any movement of mass affects earth's gravitational field. If you move a shoe from one room to another, you affect the gravitational field. This is just the sort of 'framing' people use to generate anxiety or fear about specific causes. "
] |
[
"I agree. The real story is how amazingly sensitive the GRACE mission is for measuring gravity anomalies. The popular press (NPR included) often confuses the technical ability to make very fine measurements with the need to make those measurements relevant. The same thing happens with radiation and toxins. Just because we have marvelous machines that can measure concentrations down to picomoles, doesn't mean that such measurements are cause for concern."
] |
[
"What do we need to ingest water for?"
] |
[
false
] |
[deleted]
|
[
"Its a solvent, you need it to transport chemicals that would otherwise be a solid into and out of your cells."
] |
[
"It also aids in preventing macromolecular crowding from becoming a huge problem."
] |
[
"The main reason is because our kidneys require a lot of water to remove waste products from our blood. ",
"A human being ordinarily produces approximately 2 liters of urine per day, which means that you have to drink at least 2 liters of water per day. ",
"http://en.wikipedia.org/wiki/Ureotelic",
" ",
"http://en.wikipedia.org/wiki/Kidney",
" ",
"Humans also lose water through sweating. ",
"Maximum sweat rates of an adult can be up to 2-4 liters per hour or 10-14 liters per day ",
"http://en.wikipedia.org/wiki/Perspiration",
" "
] |
[
"What caused the moon to tilt slightly in the night sky?"
] |
[
false
] | null |
[
"What do you mean by tilt?"
] |
[
"I mean that when you look up to the moon, the line of shadow (phases) it creates isn’t always vertical or horizontal. Sometimes it tilts a bit."
] |
[
"The earth moon and sun do not lie on a perfect plane. Also, the angle of orbit of the moon relative to the earth changes. That is why we don't get a solar eclipse every day"
] |
[
"How close are we to the use of RNA drugs in humans?"
] |
[
false
] |
I have read the abstracts from a few papers lately with some promising results using RNA as a drug to selectively inhibit expression of unwanted genes. For example in or . These sound promising, but I wondered if anyone knows what barriers exist towards human application. For example, what is the route of administration? How can we get the RNA into the right cells. Will this cause immune problems?
|
[
"Hi there. I do undergraduate research in protein therapeutics and drug delivery. I've read some papers on such drugs as well. I think drug delivery itself is a huge area of research, let alone developing the drugs themselves. There many delivery methods, such as particles (often on the nanoscale), viruses (viruses inject their own genetic material into host cells; we can harness this by substituting the genetic material with the RNA drugs, for example), and tunable-release hydrogels.",
"Along with delivery methods, targeting is another big area of research. Most methods I believe try to harness some natural hallmarks of the human body. For example, I read a paper recently about particles that release their payload upon a change in shear stress/pressure. They argue that this could be used for targeting plaque in atherosclerosis (the hardening of the walls of the blood vessels will create a pressure difference in the local blood vessel area). ",
"You've also hit on the issue of immune responses, which can potentially be a problem whenever you introduce anything into the human body. One way to do this is to disguise the drug until it is needed. Researchers have created capsules of polymeric materials that do not illicit an immune response. "
] |
[
"If you could use these drugs to \"inhibit expression of genes\" couldn't you also reverse the effect and gain expression of good genes?"
] |
[
"Not in the application that the OP is talking about. His application refers to the selective destruction of transcribed RNAs to prevent or seriously downregulate expression of those genes."
] |
[
"Is there any reason for the increase in severe weather?"
] |
[
false
] |
Tornados, tsunamis, and hurricanes seem to be a lot more frequent and severe than it was say 10-20 years ago. Is there a reason for this or has it always been like this.
|
[
"The problem is that there is no obvious trend in the actual number of these events; patterns have shifted, clearly in part due to global warming, but it is far from obvious that the trend is unambiguously upward. ",
"Instead, the reporting of these tragedies had become more common, and the dollar damage has increased due to more building on the coasts and in other vulnerable areas."
] |
[
"All of these points are correct. There are still the effects of shear that may reduce hurricane formation, in addition to potential changes in the time pattern of formation that could lead to weaker storms. The modeling that uses is very sensitive to assumptions, results are inconclusive, and so there there is still a lot of uncertainty."
] |
[
"Some factors that bias our perception.",
"Journalism reporting it more because it's an easy story.",
"Doppler radar and satellites and other tech advances as well as the internet allowing anyone (including the journalists) to see and track every storm.",
"More people living in cities/regions with high flood danger because of increasing urbanization (most cities are near water, 50% of the world population lives in cities, will reach 70% around 2050) and flood insurance."
] |
[
"Why do bug bites and healing wounds itch if we're not supposed to scratch them?"
] |
[
false
] | null |
[
"Actually, pretty close I believe. The reason why bug bites are itchy is because the body releases histamine at the site of the bite as an immune response. The increased blood flow from the vasodilation flares up nearby nerve endings creating the itchy feeling. This is why hives are also itchy. "
] |
[
"Actually, pretty close I believe. The reason why bug bites are itchy is because the body releases histamine at the site of the bite as an immune response. The increased blood flow from the vasodilation flares up nearby nerve endings creating the itchy feeling. This is why hives are also itchy. "
] |
[
"I have thought that the toxin induces histamine release by our cells too, but apparently some spider toxins are actualy composed of histamines, see",
"http://www.sciencedirect.com/science/article/pii/S004101019700072X",
"I am assuming that the spider's normal prey is (a) smaller than a human (seems safe) and ( b) shamdoodled by the injection of histamines, which are potent vasodilators and neurotransmitters. Interesting that histamines would also work in (I assume) arthropods.",
"\n Thanks for asking the question DreyKevins!"
] |
[
"If it's possible to see galaxies and planets billions of light years away, how come it is not possible to see whats on the planets themselves?"
] |
[
false
] |
Shouldn't we already have the technology to determine what a planet's atmosphere is made of based on the light it emits? Using that information, we should be able to refract the light which blocks our view of the surfaces of the planets and truly search for life.
|
[
"We don't see planets billions of light-years away. The range of observed exoplanets is about 10 to 25000 lightyears.",
"We can use spectroscopy (absorption and emission) to determine atmospheric compounds in some exoplanets.",
"Form the most part, we do not directly image exoplanets, nor do we have the resolution to see their surfaces.",
"I don't think refract means what you think it means. "
] |
[
"As I said in another thread, planets in other solar system are very small on a cosmic scale and are positioned right next to a very bright light. It is hard to distinguish light from Earth-sized planets from the light from their star."
] |
[
"Essentially for the same reason that you can see an apple with your naked eye, but not the individual cells that make up the apple. Distant planets are just too small, in terms of the amount of sky they cover, to get an image of them with current telescopes. "
] |
[
"Is there a reason why the gay community was initially the first to be hit hard by HIV/AIDS?"
] |
[
false
] | null |
[
"Somehow I feel like this is the wrong lesson to draw from this."
] |
[
"A small number of gay men were ",
" sexually active and had a large role in spreading the disease. ",
"This guy",
" is notorious for being originally thought to be patient zero for HIV in North America. He claimed over 2500 sexual partners. Worse yet, the guy was a flight attendant and spread the disease all over the continent.",
"But aside from Captain AIDS up there, anal-genital intercourse has a higher HIV transmission rate than vaginal sex, and gay men at the time were more promiscuous than their straight counterparts."
] |
[
"I would add to this three things:",
"1) The gay community was hit very hard very early in the U.S., but that does not necessarily apply to other countries.",
"2) The AIDS epidemic struck after the development of antibiotics. Many STDs (particularly syphilis) had already become significantly less dangerous, and given that pregnancy is not a factor with gay sex, there were fewer incentives for gay men to avoid promiscuous and unprotected sex at that time.",
"3) Given that, during the nascent gay rights movement, being gay was in and of itself considered to be opposed to traditional sexual morality, it's not so surprising that unrestricted sexuality was seen as part of being gay. The internalization of stereotypes (both unfavorable and \"complementary\") is discussed in system justification theory (a limited overview: ",
"http://www.psych.nyu.edu/jost/Jost,%20Banaji,%20&%20Nosek%20%282004%29%20A%20Decade%20of%20System%20Justificati.pdf",
")."
] |
[
"Is there weather on the moon?"
] |
[
false
] |
I know there is space weather, but are there any "weather" effects that only occur on the moon?
|
[
"The Moon has no atmosphere, so I'm unclear in what medium lunar \"weather\" would occur, or what form it would take.",
"The surface temperature varies according to its solar exposure and local geology, ranging from 120 ± 5°C maximum at the equator dropping to about -150°C at dusk, and cooling to -180°C. just before sunrise after a two-week long night.",
"\n \n",
"Otherwise, the solar wind, occasionally modulated by the Earth's magnetic field, affects the lunar surface over time, so \"space weather\" is the closest thing the Moon has to weather as we know it."
] |
[
"Actually the \"lunar atmosphere\" does change slightly during the day, so I suppose you could call that \"weather\".",
"But we are talking about trace amounts of particles that are only slightly more dense than the interplanetary medium. So there would be no measurable effects that even slightly compare to the weather here on Earth.",
"https://en.wikipedia.org/wiki/Atmosphere_of_the_Moon"
] |
[
"They carefully planned the missions during the best time of day (lunar dawn). Also their suits provide some protection. "
] |
[
"Can I intentionally stop shivering?"
] |
[
false
] |
[deleted]
|
[
"There are several questions here...",
"Shivers are muscle spasms - usually you can stop them temporarily by either calming yourself (a few deep breaths) or by freezing the muscles (flex your abdomen and core - when the muscles are already flexing, they cannot shiver) but both of these methods are temporary. A better way to stop shivering would be to simply warm up. (Go to the bathroom and run hot water over your hands and wrists, the hands and wrists are good heat-exchanges between the blood and outside environment, so 60 seconds of hot water can raise your body temperature noticeably.)",
"It's possible to increase your heart rate by mental force alone. This is well documented, however increasing blood flow to certain parts of the body is probably not possible. (Emphasis on the probably, I'm no doctor)"
] |
[
"if you are truly freezing (ie hypothermic) DO NOT run hot water over your body, you will go into shock and die! rather, cover yourself in blankets, eat soup, drink some tea but do not expose yourself to such a rapid change in temperature"
] |
[
"This is true for extreme situations, however I thought we were talking about the average \"I'm in a really cold lecture hall and want to warm up\" kind of problem...",
"PS it also works in summer, use cold water to cool off."
] |
[
"What is in the vacuum of outer space?"
] |
[
false
] |
To clarify, what exists between, for example, to planets? There's no air or other gases (in most scenarios), so what fills the empty vacuum of space? It is my understanding that a perfect vacuum, an area in which literally nothing exists, is impossible, so by extension something needs to inhabit that area. So what exists in the void of space?
|
[
"Your understanding is what is only somewhat correct. Space is made up of a small, very countable, number of hydrogen atoms per cubic meter and some larger number of mobile particles like neutrinos and photons, though due to their nature, they do not change the properties of the vacuum that is space."
] |
[
"To be more specific, the space between stars have an average of 1 hydrogen atom per cubic cm. The space between galaxies has 1 hydrogen atom per cubic meter. For comparison the best vacuum on earth can achieve on the order of a ",
"thousand",
" particles per cubic cm. So space is called a 'vacuum' relative to what we know on earth, but it's far from a true vacuum. "
] |
[
"the atoms aren't dense enough to be able to absorb any significant number of photons, this is called an optically thin gas. it's the same concept of why we don't expect any head on collisions between stars when 2 galaxies merge, although the odds are different, the idea is the same. "
] |
[
"If you try to swallow repeatedly in quick succession, why does it become progressively more difficult to do so?"
] |
[
false
] |
This confused me as a child, and it seems strange that there is some sort of delay between 'gulps' when swallowing just air.
|
[
"Swallowing is a reflex, it has to be triggered. The four phases of swallowing are oral, oropharyngeal, pharyngeal, and esophageal. The sight of something or placement during the oral phase actually triggers the reflex through the muscles and production of saliva. Without this, it is very difficult to swallow and the reflex is very difficult to produce in succession without the oral phase. Think about chugging a drink of water/beer - you swallow successively because of the oral phase being present.",
"If you really want to try something different - stick out your tongue, hold it between your teeth, and swallow. Then do it again and again. This is called a Masako exercise and a lot of elderly and stroke patients have to use it to strengthen muscles. After a while, it gets damn near impossible.",
"Logemann is a really good source for this sort of thing if you want some heavy reading."
] |
[
"The question was about the increasing delay not the fact that there was a delay."
] |
[
"Thanks, this is a really informative answer. The Masako exercise is probably what I happened to be doing when first making this observation."
] |
[
"Does the effectiveness of sunscreen stop increasing when the SPF is higher than 30?"
] |
[
false
] |
I've been hearing that sunscreen doesn't actually get more effective at SPFs higher than 30, meaning that a 50 SPF sunscreen won't actually work better than a 30 SPF. Is this true at all and if so why?
|
[
"This mainly true. 50 SPF is technically better protection than 30 SPF, but only marginally - they each protect you from 98% and 97% of the sun's rays, respectively. Anything higher than SPF 50 is borderline ridiculous - an SPF 100 sunscreen still only protects you from 99% of sun's rays, even though you probably paid double for it.",
"Its also worth noting that sunscreen effectiveness is ONLY when you apply as much as the bottle tells you to. Applying high SPF sunscreen sparingly is basically as useless as using an SPF 8 tanning oil.",
"Sources: ",
"http://www.skincancer.org/skin-cancer-information/ask-the-experts/does-a-higher-spf-sunscreen-always-protect-your-skin-better",
"http://www.skincancer.org/prevention/sun-protection/sunscreen/sunscreens-explained"
] |
[
"Those numbers don't look as good as they actually are. A sunscreen that blocks 99% is twice as effective as one that blocks 98%."
] |
[
"Really? I don't understand sun and SPFs as well as I thought then... care to enlighten me?"
] |
[
"I have a question about Quantum Mechanics observation..."
] |
[
false
] |
Ok, I think I understand that unobserved an electron can exhibit both a wave and particle function, but observation causes it to collapse into a particle function (please shore up this probably incorrect knowledge) What I am interested in is how the electrons "know" that are being observed. What is it, specifically, about the observation that causes this collapse into one or another? What constitutes observation and what doesn't (if even a camera filming the event can collapse the electron function)? I'm a molecular biology undergraduate, so I'll understand complex scientific terminology, but am only really into physics/quantum mechanics as a "Popular interest" sort of thing.
|
[
"Observation in this sense requires interaction - ",
" interaction. ",
"This explains it",
" better than I could."
] |
[
"Ok, I think I understand that unobserved an electron can exhibit both a wave and particle function…",
"Not really. This trips up a ",
" of people new to the subject. If it makes you feel any better, it's harder to explain succinctly than it is to understand.",
"The metaphor I like to use is of an elephant. We can describe an elephant in a variety of ways: it's got a trunk that's similar to a snake, its legs are thick like trees, its take is a bit like a whip. But at the end of the day, an elephant ",
" It can be ",
" to other things, but if you were to say that it's a snake sometimes, a tree sometimes and a whip sometimes, or somehow all three at once, you'd be just plain wrong.",
"Particles are ",
" They have all of the characteristics of particles, and they behave like themselves. The fact that we can ",
" particles to waves or to little cannonballs or whatever doesn't mean that sometimes they're waves and sometimes they're little cannonballs, or that they're both at once.",
"…but observation causes it to collapse into a particle function…",
"For the same reason: no. That's like saying an elephant is a snake, a tree and a whip all at the same time, but when you grab its trunk it ",
" into being a snake. Total rubbish.",
"What I am interested in is how the electrons \"know\" that are being observed.",
"They don't, for reasons that should be a ",
" clearer now that we've done the elephant thing. Particles do what particles do. We can write down a lot of fancy maths to describe what particles do under different conditions, but we shouldn't let ourselves be tricked into the assumption that our maths ",
" the nature of the particles we're talking about. That's not how it works. If we have an equation that describes how a particle behaves under ",
" conditions but not ",
" conditions, it would be wrong to assume that when the particle leaves an environment in which ",
" conditions apply and enters an environment where ",
" conditions apply that it somehow ",
" from being something into being something else. All that happened is that our equation, which is a ",
" of the particle's ",
" became applicable where it wasn't before."
] |
[
"…I do enjoy learning about the theories (read: not the maths!)…",
"There aren't any theories about any of this stuff separate from the maths. We can't observe anything at that scale; we can only build mathematical models and compare them to the results of experiments.",
"That might be what's giving you such a difficult time. You're looking for something ",
" than equations, perhaps. There isn't anything else."
] |
[
"What causes louder sounds to travel further than softer sounds?"
] |
[
false
] |
I just wondered what the scientific explanation of it is.
|
[
"Higher volume sounds directly correlate to the amount of energy they contain. There are two main factors for sound diminishing over distance. The first is the simple quadratic diminishing that happens as the sound has to spread out over an area. The higher the energy at the beginning, the more energy it will have at any given distance away from its source (in comparison to a quieter sound). The second thing that causes sound to diminish over distance has to do with friction and resistance in its vibrating medium. The coefficient for this \"friction\" stays relatively the same regardless of the amplitude of the sound waves, so a louder sound would have a smaller percentage of its energy taken away over a given distance. Softer sounds get dampened more easily because the coefficient that diminishes them effects them more as a percentage of their total energy. "
] |
[
"Is this a strict inverse-square law? Also, why does sound travel further over water than over some other relatively unobstructed surface, like a parking lot?",
"EDIT: spelling"
] |
[
"Is this a strict inverse-square law? ",
"I'm not sure if you're referring to the decibel/energy relation, or the rate at which sound disperses over distance. ",
"If you mean the first, then ",
"this article",
" explains the relationship. ",
"If you mean the second, then it is an inverse-square relation (",
"source",
")"
] |
[
"How does the electron move to different energy levels without disturbing the charge of the atom?"
] |
[
false
] |
When an electron moves up/down an energy level, it jumps over a gap of empty space. In doing so, what actually happens to the electron? It obviously cannot be instantaneously transferred from one energy level to the other because that would break the universal speed limit, so for a very small fraction of a second, the electron must be removed from the atom, right? However, if this is true, would we not see materials break down very easily, such as aluminium, in photoelectric effect experiments? The electron moves to another energy level as it attempts to remove itself from the atom, and in doing so jumps a gap. Because this electron cannot be transferred instantaneously without breaking the speed of light, it must, for a fraction of a second, seize to exist, and so the charge of the atom would oscillate as electrons bump up energy levels. Am I completely wrong? Or is this something that should actually happen with our current atomic model?
|
[
"When an electron moves up/down an energy level, it jumps over a gap of empty space.",
"Electrons don't have well-defined locations in space. There are not \"gaps\" between the different bound state wavefunctions, they can overlap each other in space.",
"In doing so, what actually happens to the electron? It obviously cannot be instantaneously transferred from one energy level to the other because that would break the universal speed limit, so for a very small fraction of a second, the electron must be removed from the atom, right?",
"Transitions are not instantaneous. And if the electron is transitioning between two bound orbitals, it is never removed from the atom. The electric charge distribution of the atom ",
" in general change as a result of the transition."
] |
[
"Well-explained. Thanks! ",
"So the charge still exists whilst the electron changes energy level?"
] |
[
"That's correct."
] |
[
"Is the magazine, \"Popular Science\" credible?"
] |
[
false
] |
I've gotten Popular Science for a few years now but it's always felt they were more of a... kind of unproper scientific magazine, just jumping at stories to grab attention. Maybe I'm wrong but that's just how it feels. Also, could you suggest any good scientific magazines?
|
[
"Of all the popular science mags Scientific American probably does the best job because alot of its articles are written by actual scientists, about their own work."
] |
[
"Lets just say I don't think many scientist cite articles in Popular Science. ",
"SA is good. But I also really have to hand Arstechnica (owned by reddit's parent company) alot of credit. They do a great job in covering (atleat in physics) science articles, and always point you towards sources if you are further interested. They have some pretty good people on staff. "
] |
[
"That's not practical, most of them are not meant for laymen."
] |
[
"[Hypothetical] Steven Wright said. If you were in a vehicle traveling at the speed of light and you turned your headlights on, would they do anything?"
] |
[
false
] | null |
[
"Please see the FAQ"
] |
[
"Can you link me?"
] |
[
"You can find a bunch of posts by searching for \"speed of light flashlight\" or \"speed of light headlight\""
] |
[
"Are certain behavioral tics passed on genetically?"
] |
[
false
] |
I was talking to my sister some time ago when she pointed at the callous on my left index knuckle and said, "Um... why do you have that?" So I explained to her that I have a weird habit of lightly chewing on my knuckle while I use my computer/read a book/whatever. She then showed me her left hand and lo and behold, she had a callous in the same place, caused by the same habit! We aren't incredibly close siblings by any means -- I see her maybe once every few months (we live in different states). Is it possible that this habit is a genetic thing? PS. I should mention that I have two other sisters who do not do this. They are the youngest and oldest kids, with me and my knuckle-chewing sister being the middle kids. Also I'm the only boy, if that changes anything.
|
[
"Do either of your parents display this behaviour? Most likely it's a learned behavior from when you were kids, and not genetic. I personally picked up habits from my father this way including the way I sit and a distinctive way of tapping my fingers on a hard surface when being patient."
] |
[
"Just asked both of them and they said they do not. I looked at their hands as well. "
] |
[
"I dont know about 'tics' but certain behaviour traits have been bred into mammals (dogs).",
"There is a BBC horizon documentary on the the history of dogs and the relationship with humans. They travelled to a research centre in russia where they picked 2 of the most docile wild wolves and bred them and carried on this process for 50 years (many genrations) in the hopes of seeing how dogs evolved to become docile/friendly towards humans, they also bred another group, only this time with the most aggressive futures. Alas if they that aggressive behaviour can be past down through your parents.",
"In humans it might be a case of nurture rather than nature."
] |
[
"What present human behaviors are considered instinctual?"
] |
[
false
] |
Just curious about what behaviors we do that can be attributed to instincts. For example, the idea that men might prefer younger women because they are seemingly more fertile.
|
[
"Fear of snakes and spiders is probably inborn as well, as other primates seem to share it, even ones that have never seen a snake or spider.",
"Snakes yes. The instinctual fear of spiders and other insects is uniquely human. "
] |
[
"Fear of snakes and spiders is probably inborn as well, as other primates seem to share it, even ones that have never seen a snake or spider.",
"Snakes yes. The instinctual fear of spiders and other insects is uniquely human. "
] |
[
"\"Now all this together, combined with our conscious mind makes a complicated mess\"",
"The ",
"neuroscience of free will",
" suggests that even our conscious minds may be much less 'conscious' than previously thought"
] |
[
"Why does your brain need glucose to survive but when you eat a bunch of sugar, your body doesn't seem to like that and long term it causes all sorts of diseases?"
] |
[
false
] | null |
[
"Why you need glucose: Your brain (and all of your cells) rely on glucose to create ATP for energy. Because of the degree of specialization of neurons your brain is especially bad at creating energy (ATP) from things other than glucose, while your liver is great at it. It's true that you don't have to eat glucose AS glucose, your body (in particular your liver) can convert fat and protein into glucose molecules.",
"Why too much is bad for you: your body regulates cellular uptake of glucose by using insulin as a signal for cells to draw glucose out of the bloodstream. Have too much glucose in your bloodstream for too long and cells become less responsive to the high levels of insulin in your blood. Then the extra glucose stays in your blood and starts to bind to things randomly (the non-enzymatic glycosylation u_ironlenin already mentioned). That's the mechanisms by which diabetes kills you... blood vessels get hardened, you get poor flow to fingers and toes, and poor flow to the smaller vessels in your heart. "
] |
[
"First thing first: the brain uses glucose ",
", not ",
". Your blood-brain barrier contains specific pathways to transport glucose into the brain for use as energy, but your brain can also utilize ketone bodies in the event that there is not enough glucose. [This is the reason why people on Atkins diets don't die.]",
"Second, what we think of as sugar is often not simply glucose. Most of the time when people talk about sugar, they are talking about sucrose, a 1:1 combination of glucose and fructose. When you eat a large amount of sucrose, not only does the level of glucose in your blood spike, causing a whole bunch of complicated reactions, you also have a rush of fructose go to your liver, which almost invariably gets processed into a non-trivial quantity of VLDL-TGs (very low density lipoprotein triglycerides), which are just in general not good for you."
] |
[
"You're confusing dietary ketosis with ketoacidosis.",
"Ketoacidosis is a dangerous metabolic state where the body produces a very large amount of ketones. Most commonly happens in diabetics.",
"Ketosis is a metabolic state where your body use ketone bodies for energy. ",
"Dietary ketosis is controlled and benign. "
] |
[
"If DNA reflects aging due to telomere length, why doesn't the DNA in sperm and egg reflect the parents' ages?"
] |
[
false
] |
[deleted]
|
[
"The enzyme \"telomerase\" exists for exactly this purpose. Telomerase is active in developing embryos, and extends telomeres back to their original state (",
"Developmental regulation of telomerase activity in human fetal tissues during gestation",
"). Telomerase shuts off in newborns (actually a little earlier) and telomeres start shortening again at that point, but newborns start with a blank telomere state. ",
"Telomerase is also active during sperm development, so sperm have long (if not necessarily full-length) telomeres too. Ova are formed very early in development, so it's less of a problem there, but ova do have slightly shortened telomeres and (I believe) those are corrected during fetal development. (",
"Telomeres and human reproduction",
")",
"If you turn off telomerase, then successive generations of mice do have gradual telomere shortening. Mouse telomere biology isn't quite the same as human, but the same would probably be even more true in humans (who have much shorter telomeres than mice). (",
"Immunosenescence phenotypes in the telomerase knockout mouse.",
", and other papers.)",
"Remember that this whole elaborate system developed at least in part to prevent cancer development, so any anti-aging use of telomerase would need to overcome the whole, you know, dying of cancer issue."
] |
[
"Crossing over doesn't really effect telomeres. The answer to the OPs question is that telomerase becomes active in gametes, which can help to expand the length of the telomeres that were lost in the parental divisions. The other poster in this thread gave a good summary of this."
] |
[
"Because they're a new reconstruction of their already existing DNA. And only 23 chromosomes at that. These are for reproduction obviously and are made to interlock with another humans 23 to make a child. Their telomeres are still shortening. But their newly generated half DNA isn't because it's a new combination every single time. It's not as if the parents directly send out ",
" exact DNA copies to procreate. Else every child they had would be the same and would already have 25 year aged telomeres as you said."
] |
[
"Why would it be bad for us to kill all the mosquitoes?"
] |
[
false
] |
Seriously, why can't we just have the mosquito holocaust and get on with our (much happier) lives?
|
[
"Other species depend on mosquitoes. Spiders, frogs, etc.",
"Good read ",
"here",
"."
] |
[
"Excellent read, thanks for that. "
] |
[
"Speaking for arctic ecosystems: the food chain is very short there and it would collapse without blackflies and mosquitos."
] |
[
"Does every star have an Oort cloud and Kuiper belt, or are they idiosyncratic to our sun?"
] |
[
false
] | null |
[
"The terms \"Kuiper belt\" and \"Oort cloud\" refer to the specific regions that surround our sun, so in that sense they are unique to us, but similar features probably exist around other stars. I don't know that they've been observed, but since they're populated by such small objects there's no reason to think that just because we don't see them they're not there. We know almost nothing about our own Oort cloud!",
"The structure of our solar system is probably not unique at all. Our sun is a main sequence star, there are thousands like it that we know of that formed under similar circumstances. It's not hard to imagine that there are other stars out there with some rocky planets, some gas giants, and a bunch of asteroids and comets floating around the outside."
] |
[
"There is no reason to assume that our sun is unique in any way. It is probably a very common type of star/star system.",
"and by the way, we have never observed the Oort cloud, so it is not even proven that it exists at all. I mean we are very certain that it exists, we just haven't seen it yet. "
] |
[
"Ah, I see. I wasn't sure if they were common to all stars, or if certain events in our sun's past had caused the to form just around us."
] |
[
"How large would a black hole with, say, the mass of our star be?"
] |
[
false
] |
[deleted]
|
[
"The Schwarzschild radius for a black hole with the mass of the Sun would be about ",
"3 km",
"."
] |
[
"How those supermassive black holes at the centers of galaxies arise is an open question. Wikipedia has a decent summary of the topic; see ",
"here",
"."
] |
[
"How those supermassive black holes at the centers of galaxies arise is an open question. Wikipedia has a decent summary of the topic; see ",
"here",
"."
] |
[
"How much does efficiency drop when the heat exchange fins on the condenser get pushed in (fouled)?"
] |
[
false
] |
Is the drop linear in nature? Is there already an existing model that describes the efficiencies lost?
|
[
"I'd say it's \"non-algebraic\", i.e. that there is no closed formula that can exactly describe the phenomenon. There are just too many variables involved in how air flows around a complex shape.",
"As long as air flow is more or less laminar, i.e. slow, I'd guess that there is practically no effect of a minor kink at all - but as soon as the air is blocked, you have a serious problem. However, you'll not find a formula with some easy parameters. You'll have to simulate it, or do an experiment."
] |
[
"The efficiency drop in your picture will be minimal, and no, it is most certainly not linear.",
"The heat exchange here works mostly by convection, see ",
"here",
". The bent fins will impact the airflow, which itself is highly nonlinear."
] |
[
"So is it logarithmic? Exponential? Does anyone know?",
"I see a lot of these around that are fouled, as most people probably have - some minimally, and some pretty bad."
] |
[
"Why does everything in the universe tend to orbit in planes?"
] |
[
false
] |
Galaxies, black hole accretion disks, protoplanetary disks, planetary rings all have a disk formation. Is this because these systems are spinning? It seems strange to me that all the material "queues" up in a neat disk and doesn't skip the queue by "falling" off the sides of the disk towards the star/hole/planet.
|
[
"It doesn't queue in a flat shape. It averages out. ",
"Imagine you had a spherical system with a random distribution, eventually the average momentum would prevail, because each object acts on every other object through gravity. Many of the objects wouldn't be able to make the transition from their original velocities to the new, average velocity and in the process would lose enough momentum and fall into the object they orbit. ",
"What is leftover at the end, though, is a relatively flat orbits plane, with a relatively uniform average velocity. "
] |
[
"One thing I never understood is why the collapsing nebula's net angular momentum is non-zero. If the motions of the molecular could is random, should that yield zero or close to zero. "
] |
[
"Close to zero, though, is not zero. Keep in mind that 99(.8?)% of the matter in our solar system is in our sun. That's .2% (actually less, I think it's .15% or so) that had enough angular momentum, after it was all said and done and averaged out, to stay afloat (so to speak) and out of the sun. "
] |
[
"When two billiard balls make contact, what is the surface area of the billiard ball that is actually touching the other billiard ball?"
] |
[
false
] |
I'm more curious about this scenario when the billiard balls are simply touching in a stationary position, as opposed to having one billiard ball collide with another billiard ball. How do you measure that single point that "connects" the two billiard balls?
|
[
"That depends on how fast they're moving when they make contact. There's no single point here; besides the fact that billiard balls aren't perfect mathematical spheres, they deform on contact. Even if they seem rigid, no material is perfectly rigid. Or if you like, everything behaves like rubber balls to an extent, even steel, glass, concrete, rock. It's just that the elastic deformation is usually too small for you to see with the naked eye. ",
"Theory and experiment ",
"by this account",
", gives the deformation of the balls to be 0.3-0.35 mm when they collide at 7 m/s. Square that number and you'll have an order-of-magnitude estimate of the area, ~10",
" m",
" or so."
] |
[
"If both billiard balls start as perfect spheres, then this problem was solved by Hertz in the 19th century. ",
"Wikipedia",
" has the results, but not the derivations. The upshot is that the contact area is a circle of radius a, where a",
" = 3FR/(4E*). where F is the force holding the two balls together, R is the radius of the balls, and E* is the material stiffness of the two balls."
] |
[
"order-of-magnitude estimate of the area, ~10-7 m2 or so",
"For reference: That's roughly the ",
"cross sectional area of mechanical pencil lead",
"; between a pinhead (larger) and a human hair (smaller)."
] |
[
"Do planetary gravitational calculations assume an infinitely small point in space, or take into account the size and distribution of the mass of the planet?"
] |
[
false
] |
So I have little to no science background, beyond what I have picked up from wikipedia articles related to Episodes of stargate and too many hours reading and thinking about why I crash my ships in Kerbal Space Program. With that being said, how are the gravitational effects of a body, such as a planet or sun, calculated in relation to its size? I'm thinking that for a relatively small dense body, calculating its effect on another body at a relatively great distance would be a matter of calculating the effects of an infinitely small point with equal mass to the actal planet, with the same center of gravity. As if all of the mass of the planet were focused in a single mathematical coordinate in space, rather than distributed over several thousand miles of diameter. This seems like a simple equation, that the force between the 2 bodies would be calculated by their mass and distance, regardless of their respective size. How does this change for objects that are very close together? for example, calculating the pull of gravity of a person standing on its surface? From that distance, the distributiong of mass seems more significant, as it is not all focused in some far off single point, but distributed essentially on a plane that stretches out in every direction from the point where the person is standing, not just directly downward towards the center of the planet. Does that just get insanely complicated and a best estimate is used? Where this could get even more interesting would be calculating the influence of 2 very large, very dense bodies with no atmosphere passing extremely close to each other in space. Like 2 massive planets moving so quickly that they pass each other within a handful of miles without colliding. If the shape of each planet was irregular, it seems the gravitational interaction of various parts of the planet and the distribution of their mass would be crucial to understanding how their respective courses would change after passing. I imagine it would go far beyond the video game approximation of a planete, which would essentially be a massless solid sphere with an infinitely small center of gravity containing all of its mass, so the force of gravity just pulls directly to the core, no matter the distance to the surface. Another thought: how would this change the effect of gravity beneath the surface of the planet? If one were to theoretically dig a hole to the center of the earth, there would be no gravity felt except that of the sun and moon, correct? The planet's gravity would be pulling you equally in all directions from that point, essentially negating itself. Am I thinking of this right? edit: TLDR: In gravitational calculations, are planets big or small?
|
[
"In most simulations (using smooth particle hydrodynamics, I recommend the paper by Allison Sills et. al. 1998, or monahan 1992) masses are treated as point masses since reading the object as a distribution would be very computationally expensive. Also for a object which has enough gravity to form into a sphere the distribution is uniform enough that there would be no noticeable change by using a distribution instead of a point mass. That said, for small non uniform objects (like small asteroids) there may be some slight change by treating the object as a distributing. "
] |
[
"For a perfect sphere with evenly distributed mass, the gravitational field ",
" the surface of the sphere is identical to what would be produced by a point mass at the center - whether you're 1 inch outside the sphere or a million light years. If the mass is distributed asymmetrically or if the object isn't a perfect sphere, the field will differ from what the idealized sphere model would give you, but most stars and planets are so close it makes very little difference."
] |
[
"There's an interesting result from Newton's law of gravity that the gravitational field at radius ",
" due to a spherically symmetric body is exactly the same as that of a point mass at the center whose mass is the mass of the portion of the body with inside the radius ",
". ",
"Shell theorem.",
" The math of proving the theorem can be a little hairy, but it is a nice result to use when doing calculations.",
"The basic idea is that if you divide up the body (say Earth) into a bunch of small chunks and add up the corresponding gravitational forces on a person standing on the body, the resulting force is ",
" identical to what you would get if you just had a point mass at the center of the body. The differences are entirely due to deviations from spherical symmetry. A mountain here, a pocket of extra dense mantle there, etc. ",
"The take-away is that for most calculations and purposes, using the mass distribution and using the point approximation should give the same result, as long as the dominant masses are close to spherically symmetric."
] |
[
"How are electron spins read?"
] |
[
false
] |
I can't find an easy explanation that's part concept and part practice, and the wikipedia is more than I can absorb in 5 minutes. I'm looking for something like "an electron shoots down a tube, passes through a ________ which makes it do ________ and then it goes _________. Can it be "read" twice? How far can it travel before it is read? How about can it be kept running in a circle say, I wanted to read it, go home for the weekend, and read the same electron again later? I'm particularly interested in these secondary questions. best. Thanks for your time!
|
[
"http://en.wikipedia.org/wiki/Stern-Gerlach_experiment",
"Basically what you do is fire an electron through a magnetic field. Since the electron can be spin up or spin down, it is deflected either up or down, to produce two distinct patches on the detector. (",
"http://en.wikipedia.org/wiki/File:Stern-Gerlach_experiment.PNG",
")"
] |
[
"Charged things moving through a magnetic field are deflected via the right hand rule, i.e. perpendicular to the field lines, not towards the positive pole of the magnet. \nThe reason neutral atoms are used is so they can probe the magnetic effects, and not the electric effects of moving an ion through a magnetic field."
] |
[
"it is not an electron that is shot through the magnetic field(its an atom with an unpaired electron), if this were to happen you would only get a single deflection point which would be towards the positive pole of the magnet. "
] |
[
"How is the Carbon-13 isotope formed?"
] |
[
false
] | null |
[
"There are many ways to form carbon-13. What is the context you’re interested in?"
] |
[
"When it was first created, for example Carbon-14 was formed by cosmic rays, how did Carbon-13 come to be?"
] |
[
"The same cosmic ray reactions that produce carbon-14 can produce carbon-13 as well. Spallation on a heavy ion can produce anything lighter than the parent nucleus."
] |
[
"I know water pressure is only dependent on depth not width, but is there a lower boundary where this breaks down?"
] |
[
false
] |
If the water is only a molecule thick, would the water pressure still be the same?
|
[
"Is this assuming a free standing column of water? Otherwise I would imagine capillary action would take over and dominate at some width (like a 1mm wide tube)."
] |
[
"All those molecules are piled on top each others, like a bunch of mattresses, it's obviously very heavy at the bottom of that pile. What matters is not how wide those mattresses are, it's how many are piled on top of each other. Now the same applies for molecules!"
] |
[
"The fundamental equations of fluid dynamics is often formulated in terms of a single particle. In a closed system where you have a stack of water molecules the pressure would still be only dependent on the depth (or length)."
] |
[
"At different temperatures, things are differently attracted or repelled magnetically?"
] |
[
false
] | null |
[
"Helium-3",
" changes magnetic properties at extremely low temperatures; not exactly what you're looking for possibly, but very interesting!",
"You may be talking about the ",
"Curie temperature",
" - the temperature at which materials can lose their permanent magnetism.",
"There are several different types of magnetism that you may not have heard of before; ",
"this page",
" mentions that various magnetic properties change at different temperatures."
] |
[
"God bless you. Thank you very much."
] |
[
"Yes, definitely. For example the ferromagnetic properties vanish above a certain temperature, called Curie point. In general magnetic properties depends on how quantum states are populated. The population of quantum states is temperature dependent "
] |
[
"Why does Water evaporate at all when not boiling?"
] |
[
false
] | null |
[
"Consider what liquid water is. It's a collection of molecules bound together with hydrogen bonding. ",
"If a glass of water has air around it (which is normal), it has a gas above it which consists of a large number of gas molecules pounding it and hitting it at great velocity. Some of the gas molecules get deflected. Some of them get dissolved in the liquid. And some gas molecules push some of the liquid water molecules outward and into the air.",
"The picture we get from the human macroscopic scale is misleading. There isn't a static liquid unmoving, surrounded by a largely motionless gas. The gas molecules are hurtling around at around 500metres/second (around 1000mph) ",
"(Source)",
" and when they hit the surface of water molecules they can knock some water molecules up and out into the air."
] |
[
"Short answer, no.",
"There's something known as the ",
"vapour pressure",
" of a liquid, which is the pressure at which the gas phase is in equilibrium with the liquid phase (as many particles are evaporating as are condensing at any one time.",
"At room temperature (25 °C), the vapor pressure of water is 3.2 kPa",
" so the water would evaporate until it reaches that pressure.",
"Collisions with air isn't the only thing giving water molecules enough energy to leave the liquid phase. The temperature is a distribution of energies, so at any one time, some molecules have enough energy to become gaseous. Collisions also occur within the liquid as the molecules move around, vibrate and rotate against each other.",
"Edit: forgot to mention that a lower pressure will lower the boiling point. ",
"At 0.03 atmospheres, water will boil at 25 °C."
] |
[
"Thank you very much for the explanation :)"
] |
[
"In a combustion reaction, is it possible to stop the fire if you \"Add fuel to the fire\"?"
] |
[
false
] |
Combustion reactions usually produce CO2 and H2O as the products. So is it possible to have too much for a flame to handle and quench a flame? There it possible of having too much CO2 and H2O for a flame to continue combusting?
|
[
"The waste gasses won't really be the limiting factor. As a flame grows, the heat will cause enough convection currents to move the waste gasses away fast enough and replace them with oxygenated air. ",
"As an example of this taken to a large degree look up the Dresden firestorm. ",
"If there is a physical barrier preventing all the waste gasses from leaving, the fire will be damped down until it burns just fast enough to consume what oxygen it can receive. The physical barrier confining the waste gas and limiting the oxygen supply is the limiting factor-- this is why charcoal grills have adjustable vents. The vents limit the oxygen supply and let you adjust the rate of combustion and therefore adjust the temperature. "
] |
[
"Combustion reactions usually produce CO2 and H2O as the products. So is it possible to have too much for a flame to handle and quench a flame? There it possible of having too much CO2 and H2O for a flame to continue combusting?",
"This is a different question than your title asks. Too much waste products can indeed quench a flame quite easily, because it prevents fresh O2 from getting in to react."
] |
[
"So there is no way of removing a non-premixed flame other than depleting the fuel(methane) source?"
] |
[
"Recent advances in Navier-Stokes equations?"
] |
[
false
] |
Hi all, I'm just wondering if anyone knew of any current research that's looking into exact solutions to the full Navier-Stokes equations? Also, has any progress been made on solving the full NS equations at all? I know about reducing them to something solvable by considering the Reynolds number, but apart from numerically, it's my understanding that we haven't solved them yet.
|
[
"For reference, the Millennium problem about the well-posedness of the Navier-Stokes equations can be found at:",
"http://www.claymath.org/millennium-problems/navier%E2%80%93stokes-equation",
"One of the more recent results is due to Terence Tao from 2014/2016",
"http://www.ams.org/journals/jams/2016-29-03/S0894-0347-2015-00838-4/",
"https://terrytao.wordpress.com/2014/02/04/finite-time-blowup-for-an-averaged-three-dimensional-navier-stokes-equation/",
"He shows that an averaged version of the Navier-Stokes equations exhibits finite time blow-up, which suggests that either blow-up also occurs for Navier-Stokes or a much deeper understanding is necessary to show that this is not the case. "
] |
[
"I feel like exact solutions for systems of equations are getting fewer and farther between. This is because it is becoming easier and easier to solve these equations numerically. A lot of people just ask \"why bother?\" \nI have a model of the atmosphere that solves the N-S equations, and it is really complicated. The largest simplification that these type of codes make is assuming gravity = gradient in pressure in the radial direction and ignoring the other forces. 99.9% of the time, this is perfectly fine, but as we go to higher resolution, and try to capture things like convective instabilities (e.g., thunderstorms), this breaks down and models can't give the correct answer. But, in order to model it correctly, the fundamental approximation has to be changed and a huge section of the code rewritten.\nTLDR: It is really hard to solve the full N-S equations, even numerically."
] |
[
"Here",
"'s a good article on Navier-Stokes."
] |
[
"Would anyone be willing to help me learn some biophysics? I would like to know how much energy is expended from the firing of a neuron."
] |
[
false
] |
I have some training in physics from a military school. I'm kinda rusty but with some practice I can do stuff like find how much energy it takes to melt an ice cube, or something like that. I'm wanting to know how many joules of energy is required to get a neuron back to its ready state of firing. The resting po Some (hopefully) useful links I think the rough outline of what's going on is to get a potential energy difference of 65-70mV, we're going to need X amount of Joules to pump out X amount of ions to get that differential. I'm also curious to know how long it takes to convert sugar (I know there's different types so it may vary) into ATP.
|
[
"What you're looking for is the total wattage of the Na+/K+ pumps on a neuron. An action potential is primarily a passive activity since it uses Na+ and K+ concentration gradients. The Na+/K+ maintains this gradients by using 1 ATP to move 3 Na+ out of the cell and 2 K+ inside. The pump has to work even when there are no action potentials which is why they can often consume at least 50-70% of a neuron's ATP. There's also Ca2+ pumps but their role in RMP is less significant.",
"Unfortunately finding the power usage of a neuron's Na+/K+ pumps is going to be hard. The number of pumps vary significantly depending on the the type of neuron, and on a single neuron they are not evenly distributed. Neurons vary too much so you're not going to get a uniform answer. You're best bet is to pick one part of one type of neuron and search the literature for the capacitance per square micrometer. A giant squid axon or a nerve cell node of ranvier would be good places to start. You can assume that the potential difference is 65mV (although it's actually higher); and with capacitance and potential difference you can figure out the power. If you want Joules just remember the typical action potential lasts ~4ms. This should get you a baseline figure."
] |
[
"The point I was trying to make is that an action potential is, in terms of energy, practically free. What a neuron spends most of it's energy is to maintain an imbalance of Na+ and K+ ions. During the spiking phase of an action potential, aka depolarization; Na+ channels open and Na+ rush into the cell. During the return to resting state, aka hyperpolarization; Na+ channels close, K+ opens and the gradient causes K+ ions to rush out of the cell. (There is also a phase called afterhyperpolarization that technically does uses energy but it's small and complex and best ignored). It's the job of the Na+/K+ pump to keep K+ concentration higher and Na+ lower inside the cell, and the pump is always working. In fact the pumps work the hardest after an action potential, not during.",
"So in physiological terms it's somewhat incorrect to talk about the energy expenditure of an action potential. The ATP goes to maintaining the resting state, the action potential is free. ",
"However, in physics terms you are just moving a charge so it's not totally unreasonable to think of hyperpolarization as work. Hyperpolarization goes from about +40mV to -65mV, so you could use J = V*C with V = 105mV. For C just you'll need to find amount of amps expended during an action potential and set C = A*s with s about 2ms (the typical time of hyperpolarization). You can also find the capacitance of a neuron and set W = Cap*V",
" then just set J = W*2ms. But you must remember that an action potential occurs only on small sections of a neuron, so any reasonable answer must be Joules be square millimeter.",
"e.g. I've has some language and behavioral psychology but I never heard of ego depletion. It seems more in line with the depletion of neurotransmitters. The strange thing about neurons is that depletion of energy causes an increase in action potentials."
] |
[
"According to ",
"this article",
", section 3.2, the PMCA pump has a rate of 30Hz (which I'm pretty sure means 30 ions per second). Although the article it references says the turnover rate is 150Hz? I'm not sure which figure is better, although there are always outside factors that can affect capacity. The article does seem to mention that 1 Ca2+ transported for every 1 ATP used.",
"But either way you're correct that the role of the PMCA is less influential than NCX, and the NCX pump is a lot less influential than the Na+/K+ pump.",
"As far as your other question: you're correct that glucose levels have a big effect on executive functioning. I'm not really knowledgeable about how it works, but I doubt it would have much to do with action potentials. I would guess that impaired executive functioning during fasting has more to do with micronutrients and/or neuromodulator synthesis . But I'm probably wrong about this, you may want to ask ",
"r/neuro",
", or if you have access to a university library I'm sure there's a few books on the physiology of executive functioning."
] |
[
"Is there a universally accepted way to accurately measure or gauge an organism's level of consciousness?"
] |
[
false
] |
There are levels of consciousness from various organisms that varies from species to species, and even in a group of a particular species. For example, most animals are at the physiological level of Maslow's hierarchy of needs. Their main focus in life is to find the next meal, how to stay safe, and reproduce. Some aren't even self-aware and fail at recognizing itself in the mirror. My question is, have we accurately categorized species yet based on how conscious and aware they are of the reality around them? If so, how did we come up with a way of categorizing consciousness? E.g. Humans would be #1, followed most likely by primates, elephants, dolphins, whales, and some bird species like pigeons (not necessarily in that order.) Extending this question a step further, have we done this with just humans? Is our consciousness just based on our ability think and process information? Or is there some underlying mechanism like genetics that limits your IQ and ultimately how much information you are able to understand? Closest thing I can find related to different levels of human consciousness is this:
|
[
"Neuroscientist here, although nothing is accepted, one of the leading theories is that the unique information content in the brain can serve as a measurement, you can read about that ",
"here.",
"There are a number of other theories of similar flavour, such as the information complexity, or the fraction of connections that are causally related, you can read about these and a good summary of the field \n",
"here."
] |
[
"I think the above is about as solid of an answer as can be given from the cog neuro field. ",
"Since I'm a neural correlate kind of neuroscientist, I think ",
"Palmiter's work with dopamine deficient mice",
" is interesting. Without dopamine, the mice lose several behavioral characteristics that arguably make them conscious: like the ability to process information and respond appropriately to their environment. This is probably mediated by a loss of neural plasticity.",
"He also makes it a point to delineate consciousness in a neuroscience or philosophical perspective from consciousness in an anesthetic or medical perspective, which I think is important."
] |
[
"Short answer, no. ",
"We can ask whether animals have specific senses/sensations. For example, if an animal has ",
"nociceptors",
", perhaps this can be interpreted as the animal being capable of experiencing pain. ",
"We can ask what kinds of representations do animals have in general, like do they have a representation of time, space and number and can they act based on those representations. Monkeys (I forget what species) can be trained to select quantities of things in ascending order (1-2-3-4). When trained on a discrimination task (pick the larger group of things), they transfer to novel quantities (once they learn 1-2-3-4, they can answer whether 5<8). Desert ants do some sort of path integration in that they take a very windy path from their hill in search of food and then return to their hill in a straight line no matter where they end up.",
"We can also investigate whether animals have memories and what kinds of memories those are. For example, birds cache food and can remember what food they cached where at what time. This is very similar to human episodic memory.",
"There has been a lot of work in monkeys recently looking at social awareness (sense of ",
"fairness",
", ",
"cooperation",
", altruism etc.). Also, self-awareness (i.e., self-recognition) has always been a popular research topic in animal cognition. We can also look at complicated, goal-directed behaviors such as tool use (e.g., ",
"a Caledonian Crow bends a wire to make a hook to pull up a bucket from a tube",
").",
"Recently, there has been an interest in higher-level functions in non-human animals such as work on concepts, analogical reasoning, and understanding of physics (e.g., ",
"trap-tube task",
" (couldn't find a better video, sorry). ",
"The best we can do at the moment is make inferences from observable behavior. However, there's no consensus on what kinds of behaviors we'd have to observe before we could make that inference. Many of the behaviors listed above can be explained by simple associative learning. We don't have a quantifiable \"scale\" of consciousness.",
"See also this post:\n",
"http://www.reddit.com/r/askscience/comments/qxdfl/is_there_a_crossspecies_intelligence_scale/"
] |
[
"Is String Theory still a relevant Scientific theory?"
] |
[
false
] |
[deleted]
|
[
"It has yet to attain relevance.",
"However, a lot of very smart people think it will one day be relevant and that's why they're working on it.",
"If you want to read a polemic against string theory, check out ''The Trouble with Physics'' by Lee Smolin."
] |
[
"String theory has evolved past the Theory of Everything that is still prevalent in pop science. People often discuss Brian Greene's An Elegant Universe, which is an archaic way of thinking about string theory. I would avoid it. Unfortunately, there are few resources for the public that talk about the new uses of string theory and many that perpetuate the old. ",
"String theory is now thought of mathematical tool for doing calculations, no different than Lie algebras or Laplace transforms. ",
"The problem is that the study of string theory took up most of the financial resources of the physics community and many people who learned string theory learned something, but it definitely wasn't physics. But now they hold physics faculty positions. There are many bitter people out there who chose a field that was probably more rooted in reality, but not popular, and thus had to sit on the back burner while string theory couldn't keep the promises it made. ",
"Of course, this is how it works. Fields go in and out of vogue and people are left bitter. "
] |
[
"it's just so elegant and wonderful a solution that it almost has to be right",
"I think this is one of the biggest cognitive flaws physicists and other researchers make - that the ultimately correct solution to a problem should be beautiful and elegant.",
"But we need to critically think about ",
" we would view a solution as elegant. Take Einstein's theory of relativity. By anyone's opinion, a beautiful model. Now why is is beautiful? Because it was able to explain gravity in a manner which intrinsically makes sense to us based on our understanding of the world.",
"Our sense of beauty or simplicity, etc. is grounded on our everyday experiences. This means that for theories of things we work with or experience everyday, it may very well be a good idea to seek a model which appeals to our sense of 'beauty.'",
"For things outside the realm of our experience though, it makes no sense that their solutions should be 'beautiful.'",
"They are foreign to us. Since beauty is based on what is common and everyday and familiar, if anything, solutions to problems outside of our everyday experience will likely seem ugly and unwieldy to us.",
"Compared to relativity, quantum mechanics is a bizarre, non-intuitive beast. And if I had to bet on which will ultimately be shown to be inaccurate, I would bet on Einstein's model.",
"What we don't know is ugly to us."
] |
[
"Are rates of communicable diseases any different in countries where it is common to wear a face mask in public?"
] |
[
false
] |
There are some countries where it is extremely common for people to in public. And others where it is not common at all. Do those face masks really help anything? Do people get colds or flu less?
|
[
"To add to this, the disposable cloth masks are only rated for a couple hours max. So people that wear the same one for more than that are essentially getting the same protection as if you wore a linen cloth on your face. Which would only vaguely protect you from particles the size of dust.",
"A ",
"PM_2.5",
" (blocks as small as 2.5 microns) mask would be better, but most virions are in the 20 nm to 300 nm (0.3 microns). So they shouldn't block viruses with much regularity. All the masks will block a percent of the virions, just out of random chance.",
"edit: fixed a few grammatical errors"
] |
[
"Those face masks are NOT the type that would prevent ANY sort of bacteria/virus from getting in or out. They're mostly dust masks, for particles MUCH larger than germs. ",
"So, no, they don't help.",
"Not to mention that almost no one wears them correctly."
] |
[
"That's incorrect. Surgical masks ",
" been shown to prevent the spreading of disease, ",
" you're sick. It is true that it doesn't stop you from ",
" sick, but that isn't the point. The reason people wear the masks is to wear them while sick, to prevent the spread of disease to those around them. ",
"That's also ignoring the fact that, yknow, not everyone is just wearing a surgical mask? There are tonnes of different mask types, not just surgical masks you'd see a nurse wearing. Lots of them are ",
" made to be face fitting. So no, they aren't all wearing them incorrectly."
] |
[
"Does Space-time have an elastic modulus?"
] |
[
false
] |
For background (and to ensure everyone that I'm not entirely full of it) I'm an Engineering student specializing in Structural Engineering. I was thinking about the implications of gravitational waves and the fact that they exist makes me think that space-time and matter are two entirely different things that interact with each other--that matter and energy merely influence deformations in space-time and past that have no true interaction with it. This is somewhat analogous, in my opinion, to structural mechanics. It seems to me as though the bending of space-time due to mass/energy is similar to a bar of concrete or steel yielding in response to physical or thermal stresses. So my question is--should my intuition satisfy reality to a certain extent--what exactly is the relationship between the bending of space and time and mass-energy? I know that Energy is related to mass via c2, and that there are likely some considerable complications from the puzzling nature of time, but does a general relationship between the two (or four I guess) exist? If so, what is it?
|
[
"The relationship between the bending of space-time and mass-energy, as you say, is that the Ricci tensor minus its trace times the metric (where the metric is a 4x4 matrix that describes the pythagorean theorem through spacetime and the Ricci tensor is a differential function of the metric) is equal to a constant (8 pi G/c",
" ) times the stress energy tensor, which is an extension of the stress tensor from mechanics.",
"Spacetime does have elastic (and viscous) properties, which are manifested as gravitational radiation. I'm not sure you can easily ascribe a modulus to it, but the shear induced by a change in the distribution of mass is proportional to the second time derivative of the moment of inertia."
] |
[
"It will take me a bit to figure out what you are saying (thank god I took that linear algebra class), but thank you so much for the answer!! Would this shear that is experienced from the change in the distribution of mass be the cause of tides?"
] |
[
"No, tidal effects are caused by gradients in the gravitational field."
] |
[
"how did the water disappear on Mars?"
] |
[
false
] |
So, I know it didn't disappear per say, it likely in some aquifer.. but.. I would assume: 1) since we know water was formed by stars and came to earth through meteors or dust, I would assume the distribution of water across planets is roughly proportional to the planet's size. Since mars is smaller than earth, I would assume it would have less than earth, but in portion all the same. 2) water doesn't leave a planet. So it's not like it evaporates into space 🤪 3) and I guess I assume that Mars and earth formed at roughly the same time. I guess I would assume that Mars and earth have similar starting chemical compositions. Similar rock to some degree? Right? So how is it the water disappears from the surface of one planet and not the other? Is it really all about the proximity to the sun and the size of the planet? What do I have wrong here? Edit: second kind of question. My mental model (that is probably wrong) basically assumes venus should have captured about the same amount of H2O as earth being similar sizes. Could we assume the water is all there but has been obsorbed into Venus's crazy atmosphere. Like besides being full of whatever it's also humid? Or steam due to the temp?
|
[
"water doesn't leave a planet. So it's not like it evaporates into space",
"This is the part you're missing: it actually ",
" escape into space! ",
"There are actually ",
" of processes that cause atoms and molecules to escape a planet's atmosphere into space (",
"atmospheric escape",
"). There are thermal mechanisms (where individual particles in the upper atmosphere get hot enough to reach literal escape velocity). There is \"sputtering\" where particles of solar wind collide with atmospheric particles, again giving them a push to escape velocity, and the related \"impact erosion\" where meteorites do the same thing. And that's just scratching the surface, there are also more complicated mechanisms involving charged particles, and chemical conversions.",
"For Mars specifically, it is thought that over time, all of these factors had an impact. And while water molecules are heavy enough that their loss to space is a very slow process even on Mars, UV light breaking water molecules into their constituent hydrogen and oxygen, especially in ionic (charged) form, makes it very easy for those individual components (especially hydrogen) to escape into space.",
"To be clear: these same processes occur on Earth, ",
" ",
"/u/OlympusMons94"
] |
[
"Earth's gravity (and temperature) don't allow it to hold onto hydrogen significantly longer than Mars. Molecular oxygen, on the other hand, is too heavy to be lost to this same Jeans escape process from either planet. Atomic oxygen and water vapor can be lost from Mars this way. Though, other modes of escape do also lead to significant (atmoic/ionic) oxygen losses from both planets. Oxygen left behind after the hydrogen from dissociated water vapor escapes can oxidize minerals and this is one main theory for why Mars is red.",
"Magneric fields aren't just protective, either. To the extent they are, the \"strong\" part is very important. For Earth, one of the major processes responsible for atmospheric loss (especially oxygen ions) is actually the polar wind caused by the interaction between the magnetic field and the solar wind. On the balance, however, the ",
" magnetic field is protective. Mars' weak global magnetic field induced by the solar wond does provide some protection from sputtering. But the weak magnetic field is a major contributor to atmospheric loss. In addition, there are areas of the crust, primarily in the southern hemisphere, with remanent magnetization from the ancient dynamo that produce regional magnetic fields. These fields can pinch off and carry blobs of atmosphere away in the solar wind. Furthermore, even a weak intrinsic magnetic field on early Mars would have been more hurtful than helpful to the atmosphere (",
"Sakata et al., 2020",
").",
"But one should not have the misconception that a strong magnetic field is necessary to maintain a thick atmosphere. This is an old paradigm that has been significantly challenged over the past decade or so. Venus, with a very thick atmosphere, but without a strong instrinsic magnetic field, serves as a strak contrast to both Mars and Earth in these respects. Venus, however, has also lost most of its water.",
"The way we can estimate how much water a planet lost is by looking at the ratio of deuterium (the heavier of the two stable isotopes of hydrogen) to normal hydrogen (aka protium). The heavier deuterium is less likely to be lost, so a higher ratio of deuterium to protium (D/H) serves as a proxy for past hydrogen (and thus water) loss. Mars' atmosphere has a D/H ratio several times higher than Earth, implying significant (but not near-total) water loss/destruction. With that in mind, ",
"some recent research",
" suggests that a significant proportion, perhaps even the vast majority, of Mars' water may not have been lost ",
", but has been sequestered in crustal rock at hydrated minerals (",
"Scheller et al., 2021",
"). Regardless, Mars still has lots of water ",
", not only at the poles, but buried in mid- to perhaps low- latitudes as ground ice and dead glaciers.",
"Another thing is that the D/H ratio for Venus' atmosphere is ~100x that of Earth. There is ",
" H2O on Venus (notwithstanding any hydrated minerals in the interior), limited to trace amounts in the atmosphere. The runaway greenhouse in Venus' distant past would have evaporated/boiled the oceans. Venus also gets a lot more UV light from the Sun. Water vapor is much more susceptible to photodissociation than liquid or solid water. Earth's atmosphere and temperate climate keeps most of its surface water as liquid. As the Sun gets hotter, Earth's oceans will eventually evaporate.",
"Earth's ozone layer also protects the surface water from UV. Since this comes primarily from oxygen produced by photosynthesis interacting with UV, the end of life will likely exacerbate photodissociation of any remaining H2O. Venus and Mars have very little ozone in comparison (what they have is formed from the oxygen released by the dissociation of CO2 and water vapor).",
"Mars has been too cold to maintain liquid surface water for billions of years. The air pressure is also generally too low. Beyond the polar ice caps and seasonal frost belts of higher latitudes, the temperature is high enough for ice to be unstable, and sublimate directly to water vapor. Being buried by regolith can protect the ice indefinitely (hence the significance of buried glaciers and other ice).",
"u/MadstopSnow"
] |
[
"Nailed it.",
"UV light splits water into hydrogen and oxygen. The hydrogen is light enough that it escapes into space. The heavier oxygen bonds with minerals on the planet's surface, such as the iron compounds, turning them to rust, which explains Mars's red colour.",
"There's actually pretty significant ice at the Martian poles. That's because ice doesn't photo-disassociate into oxygen and hydrogen as easily as liquid and vapor H2O can, and also the ice at the poles is frequently covered and insulated by a layer of dry ice (aka solid CO2). There may also be significant ice frozen under Mar's surface.",
"The moon has traces of ice as well, but largely only in the deepest polar craters where the sun can't shine to photo-disassociate it.",
"Taking your examples 1) and 3) still further, all matter in the universe is about 80% hydrogen. The sun and the gas giants are all roughly 80% hydrogen, give or take 10%. The 4 rocky planets have almost no atmospheric hydrogen. That's because the rocky planets don't have enough gravity to keep their hydrogen. It floats up to the upper atmosphere and is whisked away by the solar wind and other processes. Ditto for helium, the second lightest element and the second most common form of matter in the universe and the solar system."
] |
[
"Why, when I drop water from the lid of my pot on-top of my hotplate, it beads up into a sphere, rolls around the hot surface, and eventually (~30 seconds) it evaporates?"
] |
[
false
] |
Why does it not immediately evaporate? Could it possibly be water impurities?
|
[
"It takes energy to change the water from a liquid into a gas. The evaporation is limited by how fast heat energy can be transferred from the hot plate to the water droplet. ",
"The drop balls up and rolls around because the water touching the plate is constantly turning to gas, expanding, and escaping out from under the drop. This actually further decreases the rate of evaporation by limiting the surface available for conduction.",
"edit: clarity"
] |
[
"It takes time for the energy from the hot plate to the water to transport. Water doesn't just suddenly rise to its melting point, well not all of the water does at the same time. So the molecules move around until all parts of it has reached the melting point and it evaporates."
] |
[
"Ok, thank you, that makes sense. I suppose my hot plate was not as \"hot\" as I expected."
] |
[
"Where did all the peanut allergies come from?"
] |
[
false
] |
[deleted]
|
[
"This Straight Dope article",
" may give you some insights into this. Anecdotally, there probably isn't an increase in actual incidence---with increasing awareness, so too increases the number of parents who claim their little Snowflake has an allergy because he/she didn't want a peanut butter sandwich. A pediatrician I know tells me that most allergies are completely made up by parents based on their children's likes and dislikes, with parents almost never making an effort to positively confirm the allergy."
] |
[
"Wait, what? People actually do this? As someone who will most definitely die if a peanut touches my lips, that's pretty insulting. "
] |
[
"Sadly, people actually do do this. The specific allergy I was discussing with my friend at that time was wheat gluten* allergy.",
"One family in particular had a child who was suffering from diarrhea. As we all know, the causes of childhood diarrhea are innumerable, as children are the main reservoir for most infectious ailments. However, at the same time as the diarrhea, the child was refusing to eat almost anything bready, favoring other foods as children sometimes like to do. The mother latched onto the idea that it was a wheat gluten allergy and took that out of the diet, and when the diarrhea stopped, decided that was all the proof she needed that her child was wheat gluten intolerant. She came to my friend demanding that he place his official approval on her diagnosis so she could have her child served special meals at school. When he said that he would have to do further testing before coming to such a diagnosis, she immediately went to another doctor. My friend is sure that she had no trouble finding a doctor willing to sign off on the allergy---an 'allergy' based off of nothing more than their child having diarrhea at the same time as going through a phase of not wanting bread. He tells me that this sort of thing happens all the time, usually with peanuts and other foods with strong, unique flavors.",
"*Wheat gluten, in case you are not aware of it, is in just about everything. It's in pretty much any wheat-derived bread and is used as a thickening agent and filler in many other foods."
] |
[
"What's the beef with Group Selection?"
] |
[
false
] |
I was reading last night about E.O. Wilson and his push for group selection. On it's face, his idea seems to be much more reasonable than kin selection. I read which was a little helpful, but the example seemed a little contrived, so was unconvincing. It seems like it over-values the impact of a lone selfish actor. I can understand the "realm of consequences" (for lack of a better term), where the benefits of altruism are limited geographically and limits the spread of the behavior to something less than "a population." But it seems more reasonable than kin selection, unless there is some mechanism I'm unaware of that organisms innately have for telling whether or not they're related to another organism.
|
[
"Well 8 upvotes, no downvotes. I know this is an issue for which many people feel passionate about (was anyone else surprised that no one mentioned kin selection in the \"what is the most controversial question in your field today?\" thread a few days ago?), and there is just too much information to cover. So I pose we go with the Socratic method and I'll get the ball rolling. I really do want to have this discussion because it is important and the debate is going to tow the field of evolution and animal behavior in the years to come, whether we like it or not.",
"OP, why do you think kin selection is unreasonable?"
] |
[
"The old explanation for why people acted so altruistically was what is called a \"missfire\". As the story went, way long ago we lived in such small groups that everyone was so related, we did not even need mechanisms to distinguish kin from non-kin, because we were all such close kin!",
"This has now shown to be a pretty poor explanation. Firstly, anthropological evidence suggests that the average relatedness in hunter-gatherer groups is not nearly kin enough to justify this, and that there was frequent interaction with strangers from other tribes. Secondly, because evolution is a ",
" process, even if we were all close kin, you would still expect us to preferentially treat our kids than our nephew, as that gives us a ",
" advantage. It is these shortcomings that leads many to suggest something else must be in play. That something else, which does a very good job of explaining modern altruism, involves group selection (as well as kin selection and reciprocity)."
] |
[
"I work in this field, so I feel a lot of the push back you seem to be tapping in to. Hopefully I can therefore answer your question as to where the beef is coming from.",
"There are a couple pushbacks, one I find more reasonable than the other.",
"The first is a reverse appeal to the naturalistic fallacy. Some people fear that if we are to demonstrate a genetic adaptation for the preferential treatment of group members, then we will be legitimizing racism, eugenics, etc. As you might have guessed, this is the rather annoying group of dissenters. Simply having evolved to act in a particular way does not make it ",
" to do so. These people do not attack the research scientifically, but instead despise it as a field because of what they (falsely) believe the implications to be.",
"The other group is far more principled, and I engage with them on a regular basis. A number of researchers believe that the game theoretic problem of altruism is ",
", and that it was solved a long time ago. They believe kin selection, direct reciprocity, and indirect reciprocity explain what we see. This was the view of most scientists for quite some time. However, anthropological evidence, as well as advances in game theoretic modeling cast doubt on the explanatory power of these 3 mechanisms. It seems that something else was needed, and thereby you see the re-emergence of group selection.",
"If you would like to read a short chapter covering (1) how people previously believed the cooperation problem was solved (2) why those explanations were insufficient, and (3) the new culture-gene coevolution explanation (which involves group selection), check out ",
"this chapter",
".",
"Let me know if you have any more inquiries on the topic!"
] |
[
"Is there a distance at which the human eye could see the Andromeda galaxy the way it looks on long exposure pictures? (with its full arms, colours etc.)"
] |
[
false
] |
I know that on Earth it's impossible, but I haven't seen evidence that outside of our atmosphere humans can clearly see Andromeda in all its splendor still. Which makes me wonder, is it even possible for our eyes to see it the way our telescopes and cameras can reveal it (maybe it's just too large and too much of the light is lost by the time it reaches us), and if yes is there a theoretical distance at which the human eye could capture its majesty?
|
[
"We are able to see one of Milky Way's spiral arms (the one we're in, of course!), which are much dimmer than the galaxy's core. \nIs it not safe to assume the same would be true if we were inside the Andromeda Galaxy, instead?"
] |
[
"It's not obvious by eye what you're looking at in the night sky is a specific spiral arm. Rather, you see a sum of the light from the disk, not of an individual spiral arm. If we were orbiting a star not in a spiral arm, or if there were many spiral arms between us and the center, the Milky Way would look very similar in the night sky if the density of stars was similar.",
"Definitions of spiral arms in the Milky Way is a tricky business because you have to know the positions of stars really well to see that there's a build-up. ",
"GAIA",
" will hopefully help improve our understanding."
] |
[
"I believe every object can be accurately resolved with any optical instrument (including our eyes) if you are at the right distance.",
"In astronomy, the minimum angular distance you can resolve with any optical instrument is given by the equation",
"x = 1.22 * lambda/D",
"where x is the minimum angular size you can resolve, lambda is the wavelength of light in which the observation is carried out (so in this case in the visible part of the electromagnetic spectrum), and D is the size of the lens aperture (which in the case of an eye would be its pupil)."
] |
[
"Is it possible to build up an immunity to allergens?"
] |
[
false
] |
Not food allergies but things like pollen and dander. If you are around something you are allergic to for long enough will you stop being allergic to it? Thanks for the amazing responses from everybody. Since it seems that building and allergen tolerance can vary widly from person to person I'm going to look into getting a HEPA filter,great idea gfpumpkins, and also look into seeing if an allergist is covered by my insurance and getting back on a shot regiment.
|
[
"Yes, but it depends.",
"Some people will react worse and worse every time they are exposed to an allergen, that is called Sensitization. ",
"Some people react better and better every time they are exposed to an allergen, that is called Desensitization.",
"Sensitization or Desensitization can occur with any allergen, including food allergies.",
"Its actually quite common, unfortunately, for people to try to desensitize themselves to an allergen, only to actually be making it worse and sending themselves into ",
"Anaphylactic shock",
".",
"People die from this ",
". Talk to your doctor. Don't go trying any self treatments or trying to desensitize yourself. ",
" Please note, I am not an expert. My knowledge of anaphylaxis and allergens is only from EMT training, and a few biology and anatomy classes.\n"
] |
[
"I believe I had some delicious beer available to wash it down."
] |
[
"This idea can be used for allergy treatment",
"Desensitization or hyposensitization is a treatment in which the patient is gradually vaccinated with progressively larger doses of the allergen in question. This can either reduce the severity or eliminate hypersensitivity altogether. It relies on the progressive skewing of IgG antibody production, to block excessive IgE production seen in atopys. In a sense, the person builds up immunity to increasing amounts of the allergen in question. Studies have demonstrated the long-term efficacy and the preventive effect of immunotherapy in reducing the development of new allergy.[55] Meta-analyses have also confirmed efficacy of the treatment in allergic rhinitis in children and in asthma.[citation needed] A review by the Mayo Clinic in Rochester confirmed the safety and efficacy of allergen immunotherapy for allergic rhinitis and conjunctivitis, allergic forms of asthma, and stinging insect based on numerous well-designed scientific studies.[56] Additionally, national and international guidelines confirm the clinical efficacy of injection immunotherapy in rhinitis and asthma, as well as the safety, provided that recommendations are followed.[57]",
"A second form of immunotherapy involves the intravenous injection of monoclonal anti-IgE antibodies. These bind to free and B-cell associated IgE; signalling their destruction. They do not bind to IgE already bound to the Fc receptor on basophils and mast cells, as this would stimulate the allergic inflammatory response. The first agent of this class is Omalizumab. While this form of immunotherapy is very effective in treating several types of atopy, it should not be used in treating the majority of people with food allergies.[citation needed]",
"A third type, Sublingual immunotherapy, is an orally-administered therapy which takes advantage of oral immune tolerance to non-pathogenic antigens such as foods and resident bacteria. This therapy currently accounts for 40 percent of allergy treatment in Europe.[citation needed] In the United States, sublingual immunotherapy is gaining support among traditional allergists and is endorsed by doctors who treat allergy.[citation needed]",
"Allergy shot treatment is the closest thing to a ‘cure’ for allergic symptoms. This therapy requires a long-term commitment."
] |
[
"I have heard it claimed that the current vaccination schedule for infants in the US hasn't been well tested for safety (heavy metals) & that each vaccine is generally tested in isolation. What is the best evidence for and against that claim?"
] |
[
false
] | null |
[
"Hi 60percentg thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Medicine"
] |
[
"Medicine"
] |
[
"How did they create a strain of X. campestris that grew on lactose instead of glucose?"
] |
[
false
] |
I was reading about Xanthan Gum, and the Wikipedia article reads, "Whey is composed mostly of water and lactose, so researchers developed a strain of X. campestris that would grow on lactose rather than glucose." How did they accomplish this? Did they just slowly replace the medium's glucose with lactose, with the bacteria evolving on their own?
|
[
"Under normal conditions, XC preferentially uses glucose as an energy source when they are both available. When lactose is used it is cleaved to produce glucose and galactose, thus an additional step in the growth pathway. Normally, XC has a low level of beta-galactosidase, the enzyme that hydrolyzes lactose into glucose and galactose, and gene that encodes its production is repressed in the presence of glucose. A strain was developed that highly expressed the promoter for the lacZ gene, which encodes the production of BG. If there is a high level of BG, the strain is able to utilize lactose and grow at levels similar to those strains that utilize glucose.\nSource: ",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC184322/",
"\n",
"http://en.wikipedia.org/wiki/Lac_operon"
] |
[
"But how did they do it? How does one \"develop\" a different strain of XC?"
] |
[
"First source: \"In this study, a beta-galactosidase expression plasmid was constructed by ligating an X. campestris phage phi LO promoter with pKM005, a ColE1 replicon containing Escherichia coli lacZY genes and the lpp ribosome-binding site. It was then inserted into an IncP1 broad-host-range plasmid, pLT, and subsequently transferred by conjugation to X. campestris 17, where it was stably maintained.\"\""
] |
[
"When large areas are logged I assume a lot of nutrients are being taken away with the wood... How are these nutrients replenished? If an area is logged for thousands of years, over time will it lack enough nutrients to grow healthy forests?"
] |
[
false
] | null |
[
"What about minerals like magnesium?"
] |
[
"C, O and H are in water and the air. S, N and P are sometimes limiting, but are present in soils and/or water or there are other ways they are incorporated (e.g. nitrogen fixing bacteria).",
"For other elements it depends, but many are relatively abundant in rocks and soil (Mg, Ca, Fe, Zn, Mo).",
"Scroll down to:\n1.1.3. Most common elements in soils\n",
"http://www.landfood.ubc.ca/soil200/components/mineral.htm#113",
"Just for comparison:\n",
"http://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth's_crust"
] |
[
"You must remember that plants can 'add' new energy to the environment via photosynthesis. Most nutrients can be synthesized by decomposers. As long as there is a basic food chain in set, the environment will heal."
] |
[
"I'm building a still. An experienced moonshiner I know recommends using copper (it evidently produces the highest quality liquor). Is there a health risk involved with ingesting alcohol that is exposed to copper at high temperatures?"
] |
[
false
] |
I want to make good shine, but I also want to make safe shine. Is copper toxic?
|
[
"Hmm...",
"http://www.google.com/search?q=copper+cookware+safety",
"http://www.google.com/search?q=copper+toxicity"
] |
[
"it's illegal, but you only get in trouble if you try to sell it"
] |
[
"it's illegal, but you only get in trouble if you try to sell it"
] |
[
"Based on the Voyager probe trajectories, is it possible to calculate where they will end up thousands or millions of years in the future?"
] |
[
false
] | null |
[
"Their trajectories out a few tens of thousand years are known, since they will remain in the Sun's gravitational sphere of influence for most of that time. ",
"Within a few hundred thousand years, the Sun will be an inconspicuous speck of light in the Voyagers' skies. Their future trajectory will be influenced by the masses they encounter: stars, gas clouds, etc. ",
"Since we don't knowing the mass, density, location, and velocity of all of these objects, it will not be possible to calculate anything better than a rough approximation of Voyagers' trajectories beyond this. ",
"And sometime in the next decade or so, the Voyager RTGs will finally weaken to the point that communication with Earth will cease, taking with it our only means of tracking them."
] |
[
"Does anyone know what their end of life sequence looks like? Do they just keep trying to transmit or go into a stasis, etc?"
] |
[
"I believe they're scheduled to run out of power in 2025.",
"\nThey're only really using fuel for turning around and occasional transmitting now, though, so it won't stop them from continuing on through space"
] |
[
"/r/askscience, are those \"flesh eating\" bacteria on the news really flesh eating?"
] |
[
false
] |
[deleted]
|
[
"Necrotizing fasciitis is most certainly real. It leads to a break down in the skin, hence being called \"flesh eating\" ",
" infections can be one cause of this disease, which I find interesting. You can have essentially the same bacteria causing multiple different diseases (strep throat and flesh eating?!?). It's an active area of research to determine if there are difference in the bacteria that result in some forms of infection and not others, and whether the host response plays a roll in how the infection plays out."
] |
[
"Necrotizing fasciitis can also be caused by ",
"."
] |
[
"It can be caused by a few bacteria. In relation to the news, it seems MRSA is being reported as \"flesh eating bacteria.\"",
"http://www.ncbi.nlm.nih.gov/pubmed/18005776"
] |
[
"This morning as I stirred my coffee it happened to be on a kitchen scale. I noticed that the weight of the spoon registered on the scale, even when I was holding it. Why?"
] |
[
false
] |
To confirm, I dipped and removed it several times while holding the spoon. Each time I dipped the spoon in (without touching the bottom) an extra 2g registered. Is it the weight of the spoon that registers or the weight of the displaced water? Why doesn't the spoon feel lighter when I do this?
|
[
"The coffee provides a buoyant force to the spoon, pushing it up, making it lighter in your hand. The counter to this force is added weight on the scale. "
] |
[
"~ 2 cm",
" of spoon displaces 2 mL of coffee. Buoyant force is the weight of the liquid displaced. Coffee's probably about ~ 1g/mL. Buoyant force should add about 2g to the scale. Numbers check out."
] |
[
"Why doesn't the spoon feel lighter when I do this?",
"A high school project estimated the average weight of a conventional teaspoon made of metal to be approximately 25 grams.",
"The material that the teaspoon is made of is dense enough that the lift produced is a small fraction compared to gravity, which is also why the spoon sinks instead of floating. The spoon only feels 2/25ths lighter (assuming your spoon weighs 25g) and that's a small enough fraction that it's difficult to feel the difference."
] |
[
"Why does water expand when it freezes?"
] |
[
false
] | null |
[
"Silicon, silicon dioxide, germanium, and other solids that have a tetrahedral structure also expand upon freezing for related reasons."
] |
[
"Silicon, silicon dioxide, germanium, and other solids that have a tetrahedral structure also expand upon freezing for related reasons."
] |
[
"Yes, the most common example you'll know is salting roads in winter. ",
"The sodium chloride salt 'blocks' the formation of the perfect crystal structure easily, and makes the freezing point lower than pure water (therefore it stays liquid at lower temperatures). Eventually the temperature will be low enough that the salt will be incorporated into the crystal lattice, even if it's not perfectly aligned. ",
"It also doesn't actually matter what the solute is, but salt is cheap. "
] |
[
"How do physicists use lasers to \"cool a cloud of atoms?\" I would think shining a laser on something would heat it up."
] |
[
false
] |
I read that phrase in this article and I don't understand how this is possible:
|
[
"Atoms absorb light at specific frequencies, and if you shine a laser at a frequency slightly higher than one of those, atoms that are moving faster towards the source will absorb due to the Doppler effect causing the frequencies to match. This selectively changes the momentum of only the faster atoms, lowering the average speed of the cloud."
] |
[
"Though laser cooling does seem a little counter-intuitive at first it works, and can be understood fairly easily. For a vapor of atoms, the overall temperature is related to the average velocity of the atoms by the Maxwell-Boltzmann distribution ",
"[1]",
", so to cool them, they just need to be slowed down. Light has momentum (p=hbar*k) ",
"[2]",
", so when an atom absorbs light, it gets a momentum kick in the opposite direction. If the atom happened to be moving towards the light source, generally a laser, it will slow down. This is where things get exciting. After absorbing the light, the atom will re-emit it at some point later in time and receive another momentum kick, so one might expect the atom's velocity to remain the same after undergoing an absorption/emission cycle. In reality though, the light will be emitted in a random direction, so after many cycles, all of the emissions will cancel each other out resulting in a change in velocity in the direction of the laser. Using 6 orthogonal lasers (2 counter propagating along all 3 spatial axes), the atoms can be slowed in all directions. ",
"This is a little simplistic, so I'll take things a little further. The light from the lasers is doppler shifted due to the motion of the atoms. Atoms only have very specific allowed transitions, so they can only absorb certain frequencies of light. It would make sense then that as the atoms slow down, the lasers will shift out of resonance with the atoms, and cooling will stop. This is dealt with by red-shifting the lasers slightly so that only atoms moving towards a specific laser will be cooled in that direction, and simultaneously applying a magnetic field and the proper polarization on the lasers to further restrict from which direction light can be absorbed and to shift the energy levels of the atom to allow for continued resonance despite an every changing velocity. The result is what is called a Magnet-Optical Trap (",
"MOT",
"), which traps atoms. There is a zero in the field at which the atoms are trapped. As they move from the center, the magnetic field shifts the energy level in the atom and allows absorption from the laser which will push the atom back towards the center. ",
"Using just the techniques listed above temperatures in the milliKelvin range can be achieved. Further optical or magnetic techniques can be used to go even cooler (see Compressed MOT, Sisyphus cooling, Evaporative cooling, etc.). "
] |
[
"and if you shine a laser at a frequency slightly higher than one of those",
"I think you mean a laser of lower frequency. A higher frequency laser will be absorbed by atoms moving away from the source."
] |
[
"Do mosquitos hide in predictable locations?"
] |
[
false
] |
I've noticed that if there's a mosquito in the room, and I swat at it but fail to kill it, it usually seems to disappear for about 30 minutes before it tries to come after me again. I'm curious how programmed or predictable mosquito behaviors are. For example, does it actually have a behavior like "if swatted at, lay low for 30 minutes before trying again?" Or am I just imagining the correlation? Second, if they do have a "hide" behavior, do they choose predictable locations? Do they prefer corners of the room? Areas with less light (do they even use light in making their decisions)? Do they go low to the ground? High on the ceiling? Do they use air currents and calmness to choose a spot? It seems like I usually find mosquitos hiding out in a shadowy corner near the floor of the room, which is infuriating because if it would just hang out in the open against the white, well-lit wall, it would be a lot easier to hunt them down. This correlation could definitely just be my own confirmation bias at play, though, so I'm curious if much is known on this topic. EDIT: Thank you for the lovely replies so far! I just wanted to clarify that I'm not actually that interested in *where* mosquitos hide in a descriptive sense, I'm more interested in how and "why" they make their decisions... like which senses do they use most (vision, smell, touch), and do they actually have different phases like hunting vs. hiding, or are they just sort of always doing the same thing and flying around aimlessly until they detect prey, then go for an attack? EDIT 2: Well this post blew up! You may notice that it's a bit of a comment graveyard... sorry but askscience has strict commenting policies and the mods had to remove most of the replies. The vast majority of replies were either 1) personal tips for hunting mosquitoes, or 2) personal anecdotes on where mosquitoes hide. Precisely one comment linked to an actual scientific research article (thank you !) showing that at the very least mosquitoes can learn to associate being swatted at with certain chemical odors, and then avoid the source of those odors (people) in the future. I didn't feel satisfied so I spent a few hours trawling the literature... turns out there's simply no research on this topic! We know a great deal about mosquito hunting behavior and how it finds its target, but seemingly nothing on hiding behavior. It's not even clear whether there exists a "hiding" behavioral program, or if they're just sort of always on the hunt and are just updating their attraction/aversion biases in response to swats, etc. However, after reading up on it I do think it's safe to say that the majority of the hunting/hiding behaviors are instinctual and not learned. It turns out adult mosquitoes are only alive and hunting for ~2-4 days before they stop and spend several days digesting + laying eggs (they typically repeat this hunt/rest cycle ~3-4 times before they die). Furthermore, a mosquito can collect all the blood it needs in one meal if left undisturbed, so in reality it typically only feeds on 1-5 people before stopping. Therefore, even though to us it seems like mosquitoes are constantly present and attacking us, from a single mosquito's perspective it may only ever encounter a few humans (less than 10) in its life cycle, and over the course of only a few days. That isn't a lot of data for the mosquito to "learn" with. So, if the possible answers to my original question are 1) it's random, 2) they have instinct-driven preferences for hiding, with a lot of variation between regions/species, or 3) they learn where to hide from experience, we can probably rule out #3.
|
[
"There is a wealth of research on mosquito behaviour but mostly in relation to the ones that spread diseases. ",
"This paper: ",
"https://www.researchgate.net/blog/post/mosquitos-learn-to-avoid-people-whove-swatted-at-them",
" shows that they 'learn' to avoided being swatted. From the article 'the insects’ ability to associate the smell of a specific human with the vibration of a swat may be a factor'.",
"In terms of resting it all depends on the species of mosquito. There has been a lot of research looking at the resting and feeding behaviour of the mosquitoes, mostly in relation to malaria prevention.",
"It can divided into two categories. An endophilic mosquito is one that rests indoors, inside a human dwelling, and an exophillic one is one that's rest outside. You also get some that will only bite outside and some that only bite inside.",
"I am unaware of any research about whether they always rest in the same place but my gut feeling is they don't. However asian tiger mosquitoes tend to hide in dark corners and behind furniture to avoid being seen.",
"EDIT 1\nUpdate:\nI am a mosquito biologist but i didn't have time to find and cite more sources. I love how much interest this question has raised! ",
"Behavioural research into mosquitoes has huge gaps especially when you go beyond the species that don't spread malaria. Much of it is based on host preferences ",
"Most mosquitoes do live short fast lives however some species in colder climate will overwinter. Here is a link the a paper on culex pipiens (common house mosquito) ",
"https://pubmed.ncbi.nlm.nih.gov/21476444/",
". How they pick their locations as far as I can see is unkown.",
"Resting behaviour is important in working out out effective mosquito nets and indoor residual spraying is ( this is where you spray an insecticide on walls and when the mosquito land it picks up some of it an dies). This paper ",
"https://pubmed.ncbi.nlm.nih.gov/23427653/",
" showa Aedes mosquitoes do have a preference to things like the colour of mosquito bed nets and horizontal versus vertical surface when it comes to resting."
] |
[
"There is some vague themes with some mozzies. ",
" species, for example, need to rest after feeding, and will typically head for the nearest wall to nap and digest for a bit."
] |
[
"The real wacky bit is watching the mosquito bite with an \"X-ray\" view. The \"needle\" on it's face is just a sheath, and the actual feeding apparatus is quite flexible. The sheath bends out of the way, the proboscis pierces the flesh and then... wiggles around till it finds a vessel. Up and down, left right, in out, twitch twitch twitch until it finally hits that channel and opens up to allow feeding. ",
"https://www.youtube.com/watch?v=MbXSPacvuak"
] |
[
"How deep is the magnetic North or South Pole?"
] |
[
false
] |
I assume the magnetic North and South Pole aren't positioned at the exact surface of the planet, just like how the poles in a bar magnet aren't exactly at the very ends of the bar, but a bit more towards the middle. If that's correct, do we know how deep they are underneath the surface? This question came to me as it was mentioned in Jules Verne's Journey to the center of the earth.
|
[
"From electromagnetism, magnetic fields actually have no source, field lines are entirely closed loops. If you followed a compass north you would reach the north pole, where the compass will fully point down into the ground. Continue to follow, and you’ll eventually reach the south pole. "
] |
[
"Well the convection of the Earth's molten outer core, which is driven by heat escaping from the inner core, creates earth's magnetic poles/magnetic field (this is the geodynamo theory...probably one of the cooler named things in Earth Sciences - here's a pretty cool computer simulation that does a great job describing the process ",
"https://www.nature.com/articles/377203a0",
"). So the 'source' is located within the inner core.",
"The field varies with time (and even switches polarity over Earth's history) and so does geomagnetic north. This later concept is referred to as magnetic declination, and is the different between our geographic north and magnetic north. But since the field is constantly varying with time the exact location is ever changing.",
"Hopefully this answers your question?",
"Also bar magnets have the strongest pole forces at their edges, and they get weaker towards the center.",
"Edit: Also Earth's magnetic fields are also strongest at the North and South Magnetic Poles, and weakest at the equator. This is why things like natural source magnetic surveying are more complicated at equatorial and polar regions."
] |
[
"Unfortunately not that I'm aware of. ",
"Here's the article without a paywall/login (sorry I tend to forget about journal paywalls due to university internet). ",
"https://websites.pmc.ucsc.edu/~glatz/pub/glatzmaier_roberts_nature_1995.pdf"
] |
[
"What exactly is 'shock', and how does one die of it?"
] |
[
false
] | null |
[
"\"Shock\" is medically known as Hypoperfusion, which is inadequate perfusion of oxygen to the body systems. ",
"There are a number of different ways that hypoperfusion can occur, such as a sudden, massive loss of blood (known as hypovolemic shock). Edit: removed some incorrect information here. See the clarifying comment below.",
"In simplest terms, shock is when oxygen doesn't get to the vital body systems necessary to support life. Without oxygen, cells (especially brain cells) will die very quickly. "
] |
[
"Not at 1 atmosphere of pressure, on air, no, it's not really possible to have an over abundance of oxygen in the tissues. One atmosphere of pure oxygen ",
"can result in hypercapnia (low CO2) in the blood",
", which decreases the breathing reflex, among other problems, but it's not likely to be fatal. Note, this is for adults, ",
"neonates",
" are a different story. ",
"Greater than one ATA of O2 pressure, can be increasingly hazardous. ",
"Oxygen toxicity",
" is a problem encountered by divers, ",
"this chart",
" gives the maximum operating depths of divers on gas mixes containing various concentrations of O2. It gives the maximum allowable partial pressure of O2, on the left column, from 1.2 to 1.6 ATA, the PADI recreational dive tables set a max of 1.4 for ",
"nitrox",
" divers, and under certain circumstances, the Navy has set a 2.0 ATA limit. The top of the chart gives the % O2 in the mix, so, match your max PP02, your gas, and find the max operating depth. ",
"As you can see, at one end of the chart, breathing 100% O2, the maximum depth is between 6-19 feet, while at 3% O2, a diver can go down to 1700 feet. "
] |
[
"A clarification/correction should be made:\nAnaphylaxis is a histaminergic reaction of the body in response to foreign proteins entering that the person has been sensitized to. The swelling of the airway and choking is due to angioedema (localized swelling due to increased extravasation of fluid) and causes asphyxiation (inability to ventilate the lung). ",
"Shock is specifically in reference to hypoperfusion of tissue either due to low cardiac output or low blood pressure or a combination of the two. He is correct that without proper organ perfusion you have \"end organ damage\" and vital organs (ie. - brain) will s be starved of oxygen and die.",
"Source: I'm a fourth year medical student. If you want I can name a textbook."
] |
[
"Graphing Help??"
] |
[
false
] |
Not sure if this is the best place to ask this, but I was wondering what kind of programs people use to present their data. I currently use , but I find it difficult to use and not very good looking... I have an idea for a graph that plots x, y, and z with x and y on the normal axes, but z as the size of the plot point (i.e. larger circle for larger value of z). Does that make sense? Can anyone help me out? Thanks, Reddit!
|
[
"depends on your range of values for Z",
"you could use prism if it is 8ish"
] |
[
"I don't use it personally, but I took an intro course on ",
"ggplot2",
" using R. Ever heard of it? It makes pretty graphs but takes a bit of syntax understanding to 'program' the graphs correctly."
] |
[
"Interesting... I'll give it a try... thanks!"
] |
[
"Why are deserts formed and is it possible for a desert to be permanently \"de-desertified\"?"
] |
[
false
] |
[deleted]
|
[
"So deserts are primarily created due to geography which blocks rainfall and prevents large areas of lush green vegetation from developing. ",
"De-desertification would be difficult, this is because it would always have to be heavily managed. There is no way for a greening of the desert to be maintained naturally without increased rainfall. And that would require extensive changes to the geography of surrounding regions. And the exact effects of these changes would be hard to predict."
] |
[
"Hadley cells are the reason for deserts. It is dry air riding at the equator and falling at 30°s, North and South. This dry air let's the land evaporate more moisture than it receives. ",
"Southern California farming techniques have transformed some desert areas, but needs constant upkeep. Using a dripper system, rather than sprinklers allows for less evaporation during watering and is more sustainable. ",
"In theory, this technique could be used if you have a large enough water source to pull from. But most large desert areas don't. So Cal pulls from the Colorado River.",
"Hope this contributed in searching for your answers."
] |
[
"Thanks a ton! This makes sense."
] |
[
"If you eat raw fruits with a total of 5g of sugar. Then you eat a piece of candy with 5g of sugar. Will your body know the difference when it is breaking them down?"
] |
[
false
] |
Is sugar, sugar no matter its source? Or is refined processed sugar (candy, soda, etc) not as healthy as natural sugars found in fruits?
|
[
"If we assume that the sugar composition (i.e. ratio of fructose, glucose, sucrose) of the fruit in question is identical to the other \"unhealthy\" food (which is a false assumption), the fruit will still be considered healthier due to the fiber content of the fruit. This often slows digestion, and as a result prevents rapid rises in blood glucose and subsequent increased secretion of insulin. Fructose, the dominant sugar in fruits, is recognized and metabolized differently than the glucose-fructose mix often found in many added sugars. Fructose will lead to lower insulin release as compared to a mix of glucose and fructose. There is evidence where ",
" high fructose loads can promote fat synthesis in the liver, though eating enough fruit to achieve this is rather unfeasible. "
] |
[
"Searched",
"Relevant ",
"discussion",
"Original question by ",
"Snapdr",
"Does the sugar I consume by eating, say, a banana or an apple, affect my body in a different way than the sugar I would take in from drinking soda or eating candy? Are fruits considered healthier because they are generally lower in sugar and contain more vitamins and nutrients than other snack foods, or is there something fundamentally \"better\" about the sugars and carbs you get from fruits? Mentally, I want to think eating 20g of sugar from an apple is somehow better for me than drinking 20g of sugar from soda, but I don't see why that necessarily should be the case.",
"Top comment courtesy ",
"theStork",
"Some of these other posts contain a bit of misinformation when in comes to processed sugars. CalmSaver addresses that it is harder for the body to regulate fructose metabolism, which is certainly true. Yet, many fruits have a higher fructose/glucose ratio than sucrose or high fructose corn syrup. Table sugar (sucrose) is a dimer of fructose and glucose, so it contains 50% of each. The most common verson of high fructose corn syrup in soft drinks contains 55% fructose and 42% glucose. By comparison, apples contain over 70% fructose (source).",
"The big difference ends up being quantity consumed. Fructose in small amounts isn't going to cause any problems (unless you have fructose absorbtion problems). However, soft drinks in particular contain large amounts of sugar and don't fill you up, promoting over-consumption. I am unaware of any studies indicating that high fructose fruits promote obesity; however, fruit juices are often just as bad as soda in terms of sugar composition. Fruit juice will have a few more redeeming qualities in terms of nutrients, but it still provides a very easy way to consume too many calories from sugar.",
"EDIT: I've been seeing a lot of arguments about whether HFCS and sucrose/other \"natural\" sugars have any significant health differences. Just to throw in my perspective, while a number of studies have shown that fructose may be bad when consumed in a very high ratio compared to glucose, all recent epidemiological reviews have failed to show any difference between the health effects of HFCS and sucrose.",
"1) Metabolic Effects of Fructose and the Worldwide Increase in Obesity ",
"http://physrev.physiology.org/content/90/1/23.long",
" “There is at present not the single hint the [sic] HFCS may have more deleterious effect on body weight than other sources of sugar”",
"2) The effects of high fructose syrup. (AMA) “Because the composition of HFCS and sucrose are so similar, particularly on absorption by the body, it appears unlikely that HFCS contributes more to obesity or other conditions than sucrose does” ",
"http://www.ncbi.nlm.nih.gov/pubmed/20516261",
"3) A critical examination of the evidence relating high fructose corn syrup and weight gain. “Based on the currently available evidence, the expert panel concluded that HFCS does not appear to contribute to overweight and obesity any differently than do other energy sources” ",
"http://www.ncbi.nlm.nih.gov/pubmed/17653981",
"4) Straight talk about high-fructose corn syrup: what it is and what it ain't. “Although examples of pure fructose causing metabolic upset at high concentrations abound, especially when fed as the sole carbohydrate source, there is no evidence that the common fructose-glucose sweeteners do the same. Thus, studies using extreme carbohydrate diets may be useful for probing biochemical pathways, but they have no relevance to the human diet or to current consumption. I conclude that the HFCS-obesity hypothesis is supported neither in the United States nor worldwide.” ",
"http://www.ncbi.nlm.nih.gov/pubmed/19064536",
"Relevant follow-up courtesy ",
"aphasic",
"Yeah, the bulking effect of the fiber also reduces the amount you're likely to eat. A 20 oz coke has almost as much sugar as FIVE apples. I don't know many people who casually scarf down five apples in a sitting, but people will pound a coke like it's nothing. The mind quails at what a Big Gulp from 7-11 contains, in terms of apple-equivalents.",
"I have seen basically no credible research that was actually rigorously done and proves beyond a shadow of a doubt that HFCS is in some way worse than other sources of fructose. I think the most logical hypothesis is just purely the amount of sugar consumed is responsible for negative effects. HFCS is cheap as hell, so it goes in EVERYTHING as a general flavor enhancer. Because of this, the average american ends up consuming a metric shit-ton of sugar. I don't think it's inherently more weight gain or diabetes promoting than any of the other possible sources of fructose, like apples, or honey. It's just no one ever really consumed those sources of sugar in the kinds of quantities people consume today. I even get kind of queasy at the thought of trying to eat five apples at once."
] |
[
"Sugar is sugar, but the fruit is packed with fiber the candy bar doesn't have. Fiber negates a lot of the negative reactions in your body caused by sugar. Search YouTube for \"sugar the bitter truth\" for more info. "
] |
[
"Question about why we and nearly all creatures display senescence"
] |
[
false
] |
All my life I've only heard two explanations for senescence. That it is either because of the inevitable accumulative damage of biological processes or the mutation accumulation theory of aging or a combination of both. In other words we die of old age because of metabolic damage that is an intrinsic side effect of being alive. Or we die because our genes don't care how we're doing after we have kids. So genes and genetic errors that kill us when we're 50+ never get fixed. However thinking about this there seems to be another theory that makes a lot of sense which I've never heard discussed: If a species fitness for its environment didn't decrease after it has reproduced the adequate amount then there would be no room in the environment for its children or its grand children. Assuming that the mortality rate for a creature in its prime is lower than that of a child, adolescent or a parent burdened with the care of either then if it didn't age evolution and with it the species ability to adapt to change would slow to a halt. At this point the species if extremely vulnerable to extinction should the environment change quickly. In addition if our non-senescent creature were in competition with a senescent creature the senescent creature would probably take over because it would evolve so much quicker. Therefor could it be that evolution is not simply apathetic to senescence but that it actually encourages it? It wold be nice if an evolutionary biologist could either: give me the name for this theory or tell me why it's wrong or right or unknown. EDIT: Also if the mutation accumulation theory of aging were correct wouldn't evolution favor extending the reproductive stage of life indefinitely? What's the point of menopause if not to prepare for killing the creature so that there is room in the environment for it's children. I mean in many creatures successfully spawning is an incredible and rare achievement. Once you have one of these superstars of your species why wouldn't you do everything in your power to allow it to reproduce for as long as possible? Why kill it?
|
[
"Some very interesting things along these lines have come out of Richard Lenski's work with the long term evolution project. Basically, it says that genomic flexibility is more advantageous than adaptation to a niche. This would make it less preferable for great-great-great grandma to still be cranking out offspring; it reduces the population's overall genomic flexibility, and therefore fitness. ",
"But basically, yes; you're right, but it's been thought of before...sorry. IIRC, it's called generational kin competition, and it balances with generational kin altruism and dispersal. Dispersal is going to a new environment; this is ideal as it allows the older generation and newer generation to both reproduce and grow, further increasing the genetic diversity of the species. However, dispersal capacity is limited; sometimes severely.",
"So, as you suggest, it becomes advantageous to make room for the new generation if the old generation is no longer increasing its fitness. Altruism kicks in here; a grandparent can increase his own fitness by caring for his kids' kids, but there's a diminishing return with each generation. Grandpa is less related to each subsequent generation, and his contribution becomes more diluted.",
"If you have an individual that no longer produces offspring, that individual can still contribute to their own fitness in a reduced way by taking care of grandchildren. But this has a drawback of reducing the population's genomic flexibility. However, if a given grandparent loses the ability to reproduce after a certain age, this drawback is gone and generational altruism is more advantageous. Now lifespan will be more determined by how long it takes to dliute the contribution of an older generation to their downstream gene carriers."
] |
[
"I'm not sure if I understand the question, then. Yes, what you describe above is a known phenomenon in certain species. ",
"In most species it's not a factor, though, because the pressures you describe never come into play. Predation, infection, injury, etc take out most of the older generation anyway, so the population pressure is only hypothetical. ",
"In the absence of this pressure, you get mutation accumulation and pleiotropy. "
] |
[
"Thank you,",
"A lot of great information there however I still don't feel satisfied. So my issue with the the mutation accumulation theory of aging was it seems that it only takes into account generational kin altruism (which suggest that longer life is preferable) and not generational kin competition (which suggest that shorter life is preferable). In other words it says that evolution will put a lot of effort in increasing the lifespan of creatures up until the point at which it no longer has enough of an effect on the survival of the genes it's passed on. After that it just doesn't give a shit. It does not seem to state that evolution actively seeks adaptations that kill the creature once generational competition becomes too detrimental to passing on genes. It appears to say that what ever happens after the important part of life is just random."
] |
[
"What are gluons, taus, neutrinos etc.?"
] |
[
false
] |
What is the deal with all of these subatomic particles and what meanings they have? I don't understand much beyond protons, electrons, and that quarks form protons and neutrons (just neutral mass).
|
[
"Gluons are the gauge bosons of the strong interaction. They're the field quanta of the field that holds baryons — particles made of quarks — together, and also to a lesser extent atomic nuclei.",
"The tau is the third-generation charged lepton. You can think of it as an electron, only more so.",
"Neutrinos are uncharged leptons. They're little bits of nothing that the universe uses to balance its accounting of angular momentum. They have no charge and essentially no mass, so if you think of them as the quantum of angular momentum, you'll have enough of the essence of the thing to get by."
] |
[
"I've been curating an ",
"r/sciencefaqs post",
" on fundamental particles. There may be some interesting reading in there for you. Perhaps if you start there and have some specific questions about certain particles and their properties?"
] |
[
"Don't get fooled into thinking the universe \"needs\" anything. But for example, consider the decay of a neutron. A neutron has either +½ angular momentum or –½ angular momentum; you have to have two decay products to conserve charge (one positive and one negative), but fermions have half-integer spin, so you need an additional half-integer spin particle in there to conserve angular momentum. That's where the electron antineutrino comes in."
] |
[
"Is there any possible sun-planet-moon configuration that would yield a full moon every night?"
] |
[
false
] |
As in is there a set parameters (i.e. orbital distances, mass ratios, etc.) that would cause the moon to be "stuck" in "full moon position"?
|
[
"I think the only way this would work is if the moon was trapped at the L2 Lagrange point, so that it orbited with the Earth but slightly farther out. This is an unstable orbit though."
] |
[
"Not quite. It would just need to be within 42,164 km which is the distance of a geostationary orbit, i.e. Has a period equal to 1 day. As the moon is smaller than this distance it is possible, but the tides would be something fierce for both bodies. "
] |
[
"Not quite. It would just need to be within 42,164 km which is the distance of a geostationary orbit, i.e. Has a period equal to 1 day. As the moon is smaller than this distance it is possible, but the tides would be something fierce for both bodies. "
] |
[
"If a chemical is a dermal sensitizer, does that mean that it will be incompatible as an implant material?"
] |
[
false
] |
[deleted]
|
[
"Yes. Implants that are not biological in origin (in which case they are tissue-matched or acellular and don't need any matching) must be what we call biocompatible, which means they are non-allergenic and nontoxic. Silicone and titanium are popular choices. Before a device is allowed to go to market it must undergo quite a bit of testing to ensure that it is safe to implant into a person."
] |
[
"To address your example directly, I believe that in practice \"silver allergy\" is actually an allergy to nickel. Silver jewelry often contains enough nickel to trigger a reaction in sensitive individuals. A medical implant made of silver would be expensive and I do not know of any actual use of silver in implants, but hypothetically a person with a nickel allergy should not have an implant that contains nickel, or an alloy of silver that contains nickel (I guess that's the answer you're looking for). ",
"This is why they use titanium and/or steel for orthopedic implants: they're hypoallergenic and relatively cheap to manufacture compared to silver or gold. Plus gold is pretty soft and wouldn't work well for holding together your bones!"
] |
[
"To address your example directly, I believe that in practice \"silver allergy\" is actually an allergy to nickel. Silver jewelry often contains enough nickel to trigger a reaction in sensitive individuals. A medical implant made of silver would be expensive and I do not know of any actual use of silver in implants, but hypothetically a person with a nickel allergy should not have an implant that contains nickel, or an alloy of silver that contains nickel (I guess that's the answer you're looking for). ",
"This is why they use titanium and/or steel for orthopedic implants: they're hypoallergenic and relatively cheap to manufacture compared to silver or gold. Plus gold is pretty soft and wouldn't work well for holding together your bones!"
] |
[
"I was taught that the brain's sulci and gyri exist to increase surface area because the skull limits brain growth. So what would a brain look like if it was grown outside of a skull? Balloon-like?"
] |
[
false
] |
[deleted]
|
[
"Even if a brain were just grown outside of a skull, it would still look like a brain that you recognize (or close to it.) It doesn't start folding in because it reaches the skull and bounces back, it starts folding in because that is how it's programmed to develop.",
"Some people are born with ",
"smooth brains",
" though.",
"Edit: spelling."
] |
[
"I'm not really sure how you would do this in an animal, considering everything kind of develops and grows in size in coordination so you couldn't really just remove the skull once it's grown and then expect the brain to keep growing or something. There are a few experiments which may give some insight though. For instance, a study a few months ago was published using ",
"iPS-derived brain organoids formed in a bioreactor",
". This method shows that even without the developing embryo, the cells that make up the brain were still able to form sub-cortical structures and cortical layers (although primitive). The only limitation was that once the brain organoid structure became too large, the necessary supplies couldn't reach the inner structures due to lack of vascularization. So one could argue that the brain does have an intrinsic ability to self-form and probably wouldn't just keep on growing past a normal human brain size.",
"\n Another idea would to just make a human-mouse or human-pig chimeric animal where the human cells make a contribution to the brain. Of course this is bordering on a thin ethical line, but similar experiments have been done. In ",
"this study",
"00007-6), ",
"http://www.cell.com/cell-stem-cell/abstract/S1934-5909(13)00007-6",
" the authors engrafted glial progenitor cells into a mouse brain and found that the cells were human-like (i.e. larger) even though they developed within the mouse. This suggests that our cells have an intrinsic ability to behave like they would in our body, despite being in a different environment. The same can be said in ",
"this study",
" where they took mice that were incapable or generating a pancreas (due to gene knockout) and injected some rat cells into the developing embryo. The rat cells were able to make the mouse's pancreas since the mouse couldn't. The cool part: the pancreas was the size of a rat's, despite being in a mouse's body. "
] |
[
"There have been a couple of papers this year that show some gyrus formation in mice after forced expression of particular genes: ",
"Fgf2",
", ",
"Trnp1",
"It's all sort of a novelty at the moment, though -- there's still a lot to learn about the process of gyrification."
] |
[
"Scientists of reddit, have you ever made or contributed to a scientific discovery?"
] |
[
false
] |
[deleted]
|
[
"Most research contributes to its respective field in a new but small way. With that said, you'll find that a lot of things \"discovered\" on a daily basis are very technical, and would have little to no relevancy to people outside of that discipline. For example, my research involves using numerical fluid simulations to model effects in basilar aneurysms. Not only do most people not understand the math, but the application of this work is extensible to only a hundred cases a year, many of which will be fatal. "
] |
[
"I discovered how to make normally 8 feet tall pole beans grow ",
"8 inches tall with the same yield",
". Here's what the ",
"internodes",
" look like.",
"I may have discovered that ",
"chlorophyll B",
" can fluoresce ",
". I'm still getting review on this one."
] |
[
"This illustration gives a general idea of how discovery works in the field of science",
"Most of it is baby steps, not something that has immediate profound implications."
] |
[
"Are there any wild animals that are showing signs of adapting to cars? IE: Looking both ways before crossing the street"
] |
[
false
] | null |
[
"Yes, in fact birds such as crows have been known to use cars to their advantage. They are able to learn when traffic stops and goes at lights and will then drop a hard nut into the road to be crushed by cars and wait for traffic to stop to retrieve the insides. So, not only some species adapting, some are using cars to their advantage.",
"However, it should be noted that some species can't or will not be able to adapt to cars and that wildlife pathways are very important."
] |
[
"In Chicago, coyotes have adapted to traffic. ",
"https://www.google.com/amp/www.chicagotribune.com/news/ct-downtown-coyotes-met-0117-20150116-story,amp.html?client=safari",
"\"The footage revealed coyotes astutely waiting on passing cars so they could safely cross streets, using sidewalks and other walkways, and even raising a litter of coyote pups in the top of a parking deck.\""
] |
[
"Hi FUCITADEL thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"The Large Hadron Collider can allegedly reach 4 trillion Kelvin, is this theoretical, are there repercussions of producing that heat?"
] |
[
false
] | null |
[
"It's not just theoretical, it actually happens. The \"repercussions\" are intended: to produce quark-gluon plasmas, hadronic jets, etc. using relativistic heavy ion collisions."
] |
[
"If you're thinking of repercussions as something you have to deal with and vent away, note that only a very tiny amount of matter gets to that temperature, and is thus not very harmful. If you magically had an atom that was 10",
" Kelvin in your room, nothing interesting would probably happen.",
"I would imagine the electromagnets used to get the atoms up to speed to produce these insanely high temperatures requires more heat management than the collisions themselves."
] |
[
"yes, however",
"exponentially more",
"\"more\", not \"exponentially more\". \"exponentially more\" isn't a thing. the word \"exponential\" designates a certain type of growth. not a \"large difference in magnitude\". "
] |
[
"How does insecticide work? Particularly for ants."
] |
[
false
] |
I just woke up to a disaster in my kitchen and nuked them all in roughly ten seconds. They stumble around a bit before dying completely. Can anyone explain what exactly is happening to these critters?
|
[
"The majority of ant insecticides are ",
"Pyrethriods",
". These, in general, cause paralysis through shutting down Na+ channels (these channels are important for passing nerve signals around your body).",
"Interestingly, they tend not to affect humans because we have more enzymes to break it down."
] |
[
"No. Borax is sodium tetraborate (as the hydrate). It is classed as a physical insecticide. I don't know the mechanism for sure, but it probably kills ants by dehydrating them or causing a fatal chemical burn."
] |
[
"No. Borax is sodium tetraborate (as the hydrate). It is classed as a physical insecticide. I don't know the mechanism for sure, but it probably kills ants by dehydrating them or causing a fatal chemical burn."
] |
[
"Why does touching one tine of a tuning fork stop both tines from vibrating?"
] |
[
false
] |
I was playing around with a tuning fork that I found today, and discovered that this stopped both sides from vibrating and ended the tone. Why doesn't the other side keep vibrating?
|
[
"If I remember right, the length from one tine, down and around the curve, and up to the other is proportional to the frequency of the note. When it vibrates, the wave is travelling the whole distance and bouncing back at the end of the tine. ",
"When you touch one tine, you're dampening the vibrations so when they return they aren't as strong and there for don't continue as long as if they weren't dampened. "
] |
[
"This answer is pretty correct. One modification.",
"the length from one tine, down and around the curve, and up to the other is proportional to the frequency of the note.",
"The length of the tuning fork is exactly one wavelength long.",
"You can see what I mean in this video.",
"Note that both ends of the tuning fork are moving back and forth at the same time. Also note that there appear to be no other bends in the tuning fork, indicating that there are no major vibrational modes set up in the tuning fork other than the vibrational mode for whatever note the tuning fork is tuned to. So, when you stop one tine from vibrating, you remove energy from the only major vibrational mode in the tuning fork and cause it to completely stop moving."
] |
[
"I worked for a while with the tiny quartz tuning forks used in watches. We would remove it from the can, and clamp one side down, and use the other side as a ",
"tapping mode AFM",
". It vibrated just fine, but at a different frequency, and a lower quality factor than the untouched fork.",
"Long story short, it's not that a tuning fork can't vibrate with just one tine, it's that this vibration loses energy faster. The tuning fork is, as you would hope, a finely tuned instrument. It's designed to have one fundamental mode, and when you tap it only that mode is excited. If you clamp down one side of the fork, you should be able to excite a single tine mode (I remember the single tine mode being half the tuning fork frequency, but I might be wrong about that), but it will damp out much faster than the unclamped fork since sound energy will be able to travel into the clamped tine and dissipate into the table you clamped it to."
] |
[
"Will a diesel semi truck explode?"
] |
[
false
] |
I'm watching the season 6 premiere of Burn Notice (yeah, I'm quite a bit behind), and about 10 minutes in, Michael stuffs a burning rag into what appears the be the gas tank, and the truck goes up in a fireball. Diesel is hard to burn...it's not gasoline after all. Would this actually work? Is it possible to cause a Truck's diesel tank to explode?
|
[
"Correct, however, what was described in the question generally will never happen. First, diesel has both a high flash point, and a high ignition temperature. When we burn diesel for training, we have to use a great deal of gasoline just to get it started.",
"Furthermore, there is very little oxygen in the fuel tank of a car or truck, if you ignite the fuel, the most that will happen is a brief flash, and a small fire coming from the filler cap. I have seen this many, many times. "
] |
[
"http://www.engineeringtoolbox.com/fuels-ignition-temperatures-d_171.html",
"For flash and ignition temps "
] |
[
"A tank of any sort of hydrocarbon fuel ",
" explode under the right circumstances. TV explosions are always way over-dramatized, and the likelihood of it happening like that is fairly rare in real life. ",
"For a explosion to happen, it is the fuel vapor and air mixture in the tank that ignites violently. There has to be just the right combination of low levels of fuel, temperature to have caused just the right amount of vaporization, and the right amount of air, too. For all fuels, there is what are called the upper and lower flammability limits, and this refers to the % of fuel in the fuel/air mix. ",
"http://www.gexcon.com/handbook/GEXHBchap4.htm",
"http://www.nrel.gov/docs/fy03osti/34817.pdf",
" [PDF]"
] |
[
"Why aren't satellites infinite sources of energy?"
] |
[
false
] | null |
[
"If you take energy away from a moving object, then it has less energy. Eventually it will stop moving, and you can no longer get anymore energy from it."
] |
[
"Well how do you propose to extract kinetic energy from the moon?",
"Some tiny fraction of the moon's energy is already being lost to ",
"tidal heating",
". But it would be an engineering feat to turn that directly into usable power."
] |
[
"Well how do you propose to extract kinetic energy from the moon?",
"Some tiny fraction of the moon's energy is already being lost to ",
"tidal heating",
". But it would be an engineering feat to turn that directly into usable power."
] |
[
"How to insects grow hair/fuzz when they have a hard exoskeleton?"
] |
[
false
] | null |
[
"Hello and very fun question! Many arthropods have hairs or spines that have many functions. They are connected to the arthropod via pores or sockets for larger spines within the exoskeleton (cuticle). I love spiders as an example of arthropod hair, so we're going to move in that direction as I explain what the hairs and spines are for as it relates to how they are connected to the spider. I'm on a panel with some friends at comic conventions and part of my talk is spider sense and how it relates to what Spider-Man is feeling versus what an actual spider feels (it's a blast!).",
"Hairs are specialized and allow the spider to interact with the environment around it, picking up cues and reacting accordingly. Different types of hairs have different jobs to do and all are attached to receptor cells, though the number of cells differs depending on the hair type/location. Spider hairs come in two categories: proprioreceptive and exteroreceptive. Proprioreceptive hairs are stimulated by the spider's locomotion - through joint movement or when a joint membrane moves over sensory hairs (",
"Eickweiler et al., 1999",
"). Exteroreceptive hairs are stimulated by the environment .",
"Bathellier et al., 2011",
"Barth and Höller, 1999",
"here is a photo",
"McConney at al., 2008",
"Albert et al., 2001",
"Here is an image of a spider's face",
"Foelix, 1970",
"Foelix and Wang, 1973",
"Cerveira and Jackson, 2012",
"Bell and Roberts, 2017",
"Bertani and Gaudanucci, 2013",
"Here is a photo",
"Isbister and Hurst, 2002",
"Aside from hairs, spiders also sense the world through slits and pits which are also connected to receptors within the cuticle. ",
"Here is a great drawing",
" from the Australian Museum of different sensory organs/hairs on a spider's leg. The splits in a spider's leg (lyriform organs) detect vibration. It's like having eardrums all over your legs! The pits sense humidity which is very important to arthropods as some desiccate easily.",
"Oh, another note on hairs! The Australian whistling spider (",
") rubs specialized hairs together on its chelicerae (mouthparts) to produce a whistling noise. Some other spiders in that family (Theraphosidae) can also do this (",
"Berge, 2003",
").",
"If you want to see some amazing microscopic images of spider hair and other parts up close ",
"here is a link",
" to an excellent PDF."
] |
[
"Oh! I'm so sorry, I forgot to mention their use! They allow for a better grip, even on smoother surfaces. So spiders that do a lot of active hunting and climbing need them to get around."
] |
[
"Great answer. It piqued my interest enough that I have to ask: what do the scopulae do?"
] |
[
"I heard about ~1.5% of our genome is exons. Were primitive organisms composed of so much \"junk DNA\"?"
] |
[
false
] |
[deleted]
|
[
"1) ",
"Noncoding DNA (aka Junk DNA)",
" has actually been shown to have a great deal of functionality. This isn't to say that we know everything that it does, but it certainly doesn't appear to be useless. Largely these regions appear to be involved in gene regulation, which is absolutely essential for making more complex organisms.",
"2) There does appear to be a preference for the expansion of genomes within higher organisms but this can be a valuable evolutionary trait as it allows for gene duplication and specialization.",
"3) Bacteria are well known for having very compact genomes, where most of the DNA codes for genes. I wouldn't necessarily call them more primitive than us, but simply less complex."
] |
[
"Another reason that evolution wouldn't have rooted out introns (reads: evolution does not select ",
" traits, merely doesn't select ",
" them) is that there is massive (relative) redundancy in the case of mutation of UV damage. The more DNA you have, the less likely a critical base pair will be damaged."
] |
[
"there is massive (relative) redundancy in the case of mutation of UV damage. The more DNA you have, the less likely a critical base pair will be damaged.",
"I've heard this before and I'm not sure if it is actually true. The mutation rate from UV light is dependent on how often a high energy photon hits a strand of DNA in the correct orientation. If you were to double the amount of DNA inside a cell and expose it to the same amount of UV radiation, I would expect the number of mutations to double as well since we have not changed the mutation rate."
] |
[
"How do we get Vitamin D from sunlight?"
] |
[
false
] |
I never really understood why, like do we have some special organelle in our cells that convert sunlight to vitamin D or is it something entirely different?
|
[
"It’s a photochemical reaction. ",
"There’s a chemical in your skin called 7-DHC that’s photochemically reactive to light between the wavelengths of 290 and 320 nm. These wavelengths are part of the sun’s spectrum and what is often referred to as UVB radiation. When 7-DHC reacts with UVB light, the product is dholecalciferol, also known as Vitamin D3, which is then carried to the liver."
] |
[
"Vitamin D3 sythensis is regulated by hormones in the skin. Simply put, when there’s a lot a vitamin D3 in the system, the body will stop producing vitamin D precursors. ",
"There’s also regulation later in the process. Vitamin D synthesis is also down-regulated by the FGF23 protein acting on a transport protein that mediates bone growth, NPT2. When there’s a lot of new bone cells, FGF23 it will inhibit NPT2 to regulate the process.",
"So while it may be possible, it is extremely unlikely to develop a Vitamin D toxicity from sun exposure."
] |
[
"So is this process continuous as long as you are in the sun?"
] |
[
"Why can completely paralyzed people often blink voluntarily?"
] |
[
false
] | null |
[
"Blinking is a motor function controlled by the facial nerve, the seventh cranial nerve. Cranial nerves come directly from the brainstem, bypassing the spinal cord. Cranial nerve reflexes are often used to assess levels of brain function (diencephalon, mesencephalon, and medulla). "
] |
[
"It's like as if all the network switches are down, but your face has a direct line to the server. Very interesting. Thanks!"
] |
[
"Or if your computer is the brain, you can't access the network but your speakers still work fine as they're plugged straight into the computer without passing the router. You don't have any Internet access, but can still communicate with your neighbors if you turn the volume up."
] |
[
"If a wave is cancelled out by another wave (destructive interference), where did the energy go?"
] |
[
false
] |
This question sprouted from trying to explain how noise-cancelling headphones work, but I also wonder about other waves. If two laser beams in a vacuum come out of a semi-transparent mirror, one half-wavelength apart, would only darkness emerge? But, energy cannot be destroyed. Where did it go?
|
[
"Whenever you have destructive interference in one place, you have constructive interference somewhere else, and that somewhere else is where the energy goes. In your example of the half-silvered mirror, if they're one half-wavelength apart on one side then they'll be in phase on the other side."
] |
[
"The positive energy of one wave is canceling out the negative of the other.",
"Energy is always positive -- even for antimatter and for waves. There is no \"negative energy\" in this situation. Hence the question of where the ",
" goes when you have interference."
] |
[
"The positive energy of one wave is canceling out the negative of the other.",
"Energy is always positive -- even for antimatter and for waves. There is no \"negative energy\" in this situation. Hence the question of where the ",
" goes when you have interference."
] |
[
"Why are Hydrogen(1) and Helium(2) highly abundant in the universe, while Lithium(3) and Beryllium(4) not that much?"
] |
[
false
] |
I came across the other day. I made a quick search but didn't find much. Can someone explain? Is it due to the state? Or due to their reactivity?
|
[
"Production of lithium from helium is highly ",
", meaning that it consumes massive amounts of energy instead of creating it. Secondly the fact that it's endothermic results in a significant ",
" that needs to be overcome, on top of the powerful electrical repulsion between nuclei.",
"The most likely way one would assume lithium would be produced is from a hydrogen nucleus colliding with a helium-4 nucleus. (2 protons and two neutrons), producing Li-5. ",
"Li-6, the first stable isotope, would need to be produced by fusion of deuterium (Hydrogen-2) with helium-4. Deuterium in the sun is only about 23 parts per million, because it tends to fuse more easily into highly stable helium, than bare hydrogen-1. So it's consumed almost as fast as it's produced.",
"Additionally producing Li-6 runs up against the ",
" mentioned earlier, making this process astronomically rare. ",
"In fact the majority of the lithium in the sun has probably been there since the sun's formation. Lithium, Berylium, and Boron are among the rarest elements in the sun.",
"Li,Be,and B are probably produced in outer space by ",
"Cosmic Ray Spallation",
" from much more common, heavier elements. Not produced by fusion in stars.",
"Berylium is likely produced from lithium-7 by neutron capture via the ",
"S-Process.",
" (PDF)",
"In fact, lithium-7 is much more common than lithium-6, because the latter is much better at absorbing neutrons.",
"Certain reaction in the sun involving hydrogen isotopes, end up producing high-energy neutrons. These neutrons may be absorbed by heavy elements in the sun. In some situations this converts them into higher elements through successive beta decays. In other cases this may produce lighter elements plus helium by triggering alpha decay."
] |
[
"Oh wow, thanks for your answer. Just some follow-up questions, what is this ",
" you talk about? Is it measured somehow? And what type of energy is it exactly?"
] |
[
"The energy barrier is usually a general term for the amount of additional energy required for a reaction to occur. The form in which the energy comes isn't exactly important, but it generally involves heat energy. You can measure the energy barrier of a reaction by adding energy and noting when it occurs, or performing the reaction in a calorimeter and marking the change in temperature."
] |
[
"Why does a vaccine have to be injected through a needle?"
] |
[
false
] |
If a virus, like Sars-Cov-2 can enter the body through orifices, why can't preventive medicine like vaccine? Wouldn't it be a whole lot nicer and easier to orchestrate if everyone could just get a nose spray "vaccine"? I'm sure if it were possible the brilliant minds of several scientists would've thought of it, so I know I'm not proposing something groundbreaking here, but I'm wondering why it is not possible.
|
[
"Lots of reasons:"
] |
[
"Regarding the first point, our mucous membranes are filled with enzymes called ribonucleases specifically because we don’t want RNA from the outside world getting into our bodies (as it could be a virus!). ",
"Injection gets around (some of) our normal anti-viral safeguards. ",
"https://en.m.wikipedia.org/wiki/Ribonuclease",
"Some viruses even encode ribonuclease inhibitors to suppress this defense mechanism."
] |
[
"to add what others have said, people are working on ",
"microneedle patches",
" that can be used instead of a direct injection"
] |
[
"How do the instruments of probes sent to the far reaches of the solar system not freeze/malfunction due to extreme cold and other issues?"
] |
[
false
] | null |
[
"They are engineered to withstand the conditions for the duration of the mission (and sometimes beyond) from the very beginning, by making them temperature-tolerant and warming those systems that need higher temperatures to operate. Have a look at what for example the ",
"ESTEC Labs",
" have regarding testing equipment under space conditions.",
"Typically these probes come with a radioisotope thermoelectric generator and similar heating elements, they essentially use a block of slowly decaying radioactive material (like plutonium) as a temperature and electric energy source."
] |
[
"Thermal management is a very important aspect of building spacecraft. Taken as a whole you have to deal with the energy received from the sun or other bodies via radiation, the energy lost to space via radiation, and the heat generated by the spacecraft itself and keep the instruments at a temperature where they can operate.",
"So even though you are in a very cold environment certain components like electronics could overheat just like the CPU in your computer can overheat if there isn't a heat sink. The heat needs to be carefully managed.",
"The way this is tested on earth is with a thermal vacuum chamber. This is a special vacuum chamber where the inside surface is kept at very cold temperatures using cryogenic liquids. "
] |
[
"One other thing to consider is that a lot of components of these probes will only work if they are very cold. WMAP, COBE, and Planck measure 2.7 K radiation. If they are warmer than that, their own thermal signatures will drown out the signal they are trying to measure. "
] |
[
"Why are many natural satellites in space found to be tidally locked or in a synchronous orbit?"
] |
[
false
] | null |
[
"Short answer, it's the most stable state, and they have been there a LONG time.",
"Natural satellites in less stable places have a habit of being knocked about by other objects. The effect can be subtle, but over long enough time periods can destabilise another body. This either sends it flying out of the system, flying into a body, or into a more stable orbit.",
"Wait long enough and everything settles down."
] |
[
"Thankyou"
] |
[
"Nature favors the stable. That is, we are more likely to see stable things than any particular unstable thing."
] |
[
"What am I really smelling, when I smell rain coming?"
] |
[
false
] | null |
[
"You are smelling ozone (O3), as well as something called 'petrichor'--the mixture of odiferous molecules that are are moved from surfaces into warm, damp air that tends to blow around before a rain storm. There is an SA article about this very phenomenon ",
"here",
"."
] |
[
"As a microbiologist, I can't let that answer sit without elaborating that the 'mixture of molecules' you and the article are referring to are (at least in part) created by ",
"Actinobacteria",
". The name of the compound is even means 'Earth Smell' in Greek! How cool. "
] |
[
"Additionally, your nose is more efficient at picking up smells when there is moisture present, hence why shower farts smell considerably more heinous than standard ones"
] |
[
"How does the anisotropy/transmission axis of polarizers work?"
] |
[
false
] |
So polarizers have optical axis that block or let through the corresponding polarizations of light, but it also depends on how much the polarizer is rotated, like shown in Malus's Law. Somehow, the polarizer isn't the same when viewed from all direction or otherwise the light transmitted would all be the same regardless of polarizer orientation, so what is it about the polarizer that makes it have a directional dependence on light transmission?
|
[
"Electromagnetic radiation is a vector, so its transverse profile has an amplitude AND a direction. (e.g. vertical or horizontal polarized light). For the same reason, a polarizer, as you mentioned, also has a direction. (often called s and p). You now need to 'match' these directions for the proper result you want. ",
"Or to put it in another way: You understood that a polarizer has a directional dependence. The same principle of directional dependence is valid for light, too. This is the reason, that you actually need polarized light to show how a single polarizer works ! The confusion may arise because a human cannot distinguish the polarization of light. At least not without some help of reflection or birefringent media.",
"\nIf you have two light sources, one polarized (in a certain direction) and one unpolarized, meaning the light in form of wave packets has random polarization directions, then both look absolutely identical for your eye. If you now place polarizers in front of them, you won't be able to change anything in the case of the unpolarized beam. You always have components in the random mix which match up the polarizer axis.",
"\nThe transmission of the polarized beam on the other hand will depend on the polarizer position. You can imagine that this beam travels with a coordinate system which has to somehow match the one of the polarizer. "
] |
[
"A trained eye in optimal conditions can actually detect polarized light. ",
"https://en.wikipedia.org/wiki/Haidinger%27s_brush",
" One of the easiest ways to do this is with a white LCD screen. The effect is extremely subtle, though."
] |
[
"A polarizing film consists of long molecules in a parallel orientation (like a picket fence). Electro-magnetic waves with polarization parallel to the long axis of the polarizing molecules are transmitted preferentially compared to EM waves polarized orthogonal to the main axis of the molecules. The latter orientation results in attenuation of the incident light."
] |
[
"Why does a star need to go supernova before it turns into a black hole?"
] |
[
false
] |
What does it get rid of or gain that it doesn't already have?
|
[
"Mackinstyle is more or less correct. A ball of gas that is big enough to ignite fusion (a star) will be in a state of hydrostatic equilibrium, where the push of the fusion resists the pull of gravity. When the fuel for fusion runs out, gravity dominates and it begins to collapse. But then the pressure becomes greater, so new fusion processes start, and this becomes a supernova if the star is big enough. The leftovers of this, as you know, may eventually become a black hole.",
"So to answer your question, when the star collapses towards a critical black hole density, it becomes hot enough that a supernova explosion happens beforehand. "
] |
[
"and then the black hole starts slowly losing mass in the form of Hawking radiation (unless it picks up more mass from rocks)"
] |
[
"This isn't my specialty, but my understanding is that the fusion reaction occurring in a star resists the inward pull of gravity. When a star has run out of matter to fuse, collapse can occur. Depending on the mass of the star at this point, a number of things can happen (black hole, neutron star, white dwarf).",
"It largely depends on the conditions of the star. A good place to begin is here: ",
"http://en.wikipedia.org/wiki/Main_sequence"
] |
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