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[
"What is the difference between highly composite numbers and superior highly composite numbers?"
] |
[
false
] | null |
[
"http://mathworld.wolfram.com/SuperiorHighlyCompositeNumber.html"
] |
[
"This was one of the explanations I couldnt understand lol, but thank you"
] |
[
"If you can pinpoint more precisely what part you're having trouble with, please submit a new question. Cheers."
] |
[
"What percentage of our universe is believed to be dark matter?"
] |
[
false
] |
Also, why doesn't the dark matter and regular matter annihilate until one or the other is gone?
|
[
"Dark matter represents ",
" of the energy content of the Universe (dark energy is 73% and baryonic matter 4%).",
"why doesn't the dark matter and regular matter annihilate until one or the other is gone?",
"Why would they annihilate?"
] |
[
"You're thinking of anti-matter, not dark matter. They are different. Dark matter is not yet fully understood, and hasn't been directly observed. Anti-matter we can make in a particle accelerator, and we know a lot about it. You were probably asking about the latter."
] |
[
"Do dark matter and regular matter not annihilate upon cantact with each other?"
] |
[
"Why don't we use solvents on kidney stones?"
] |
[
false
] |
[deleted]
|
[
"You can dissolve certain kinds of stones. Uric acid and cystine stones can be dissolved by making the urine more alkaline. This can be as simple as giving someone sodium bicarbonate (baking soda). Note: DO NOT DO THIS ON YOUR OWN. SEEK MEDICAL ATTENTION IF YOU THINK YOU HAVE A STONE. ",
"Meanwhile, calcium stones (the most common type) are not very soluble in any pH range that your body can handle. So we don't try to dissolve those. "
] |
[
"Source? With the right chemistry you can do some pretty amazing things."
] |
[
"Something that would dissolve a kidney stone would also dissolve your urethra. "
] |
[
"Does thinking require calories?"
] |
[
false
] |
Obviously your brain requires calories to stay alive and to function, but does increased concentration require an increase in calories?
|
[
"Increased brain activity increases metabolic demands and burns more calories, yes. ",
"However, you have to be careful - thinking brilliant or difficult thoughts may not necessarily be the thing that increases brain activity the most, you may get the same effect by thinking about a sports game or fantasizing about sex. ",
"Indeed, the process of 'concentrating' usually involves shutting down potentially interfering thoughts so you can only engage the parts of your brain needed for a particular problem, and therefore may actually decrease overall brain activity.",
"So the answer is, yes it does, but not in an intuitive or predictable manner."
] |
[
"http://www.reddit.com/r/askscience/search?q=thinking+calories&restrict_sr=on",
"Asked and answered."
] |
[
"I will agree that areas of the brain that are being activated will definitely increase metabolic demand (temporarily?), however, I'm not really convinced that this would translate into anything beyond a negligible amount of calories burned. Even if it was prolonged heavy concentrating.",
"The other threads on this topic mention chess champions burning large amounts of calories during their matches, but again I can't seem to find any actual proof of this."
] |
[
"When falling from a great height, what is the best position to assume to minimize injury?"
] |
[
false
] | null |
[
"Slight tilting of the body to prepare for rolling later, better to one side. Mostly vertical, arms up, if you hold something throw it downwards at some point, preferrably shortly before impact or right after feet touch. Pull arms down after contact, prepare for hitting with your butt and arms, depending on height.",
"This way your mass center is as high as possible when you make contact, and it is as low as possible when you stop moving, thus allowing for maximising the time of deceleration and hence reducing average force exerted. Throwing any objects downwards helps to reduce the momentum. Ideally your one leg should be up like a ballet dancer when you make contact but it is impractical and impossible to quickly put it down and bear load. Arms and legs are expendable, while head, spine and internal organs are not."
] |
[
"And do whatever you can to roll.",
"\nEven a slight angle to start a roll might been the difference between big-splat and splat-splat-splat..."
] |
[
"It is important to note that you want to land on the side of your legs and butt, and roll to one side. You do ",
" want to land straight onto your butt; ",
"this woman learned this the hard way.",
" WARNING: video is NSFL; no gore, but death."
] |
[
"Is 70% of the human immune system located in the gut?"
] |
[
false
] |
I see a lot of probiotic advocates making this claim, but I can't seem to find any credible sources to back it up. I figure with the thymus gland, bone marrow, lymphoid tissue, etc. odds are pretty low this is true. Does anyone have any idea for sure?
|
[
"I would say 70% is overreaching but the gut does have a large proportion of immune cells. According to \"Characteristics and functions of mucosa-associated lymphoid tissue.\" (Croitoru and Bienenstock, 1994), the mucosa-associated lymphoid tissue (MALT) contains approximately half of all the lymphocytes in the immune system. 'Lymphocytes' comprises NK cells and also all the effector cells of your adaptive immune system (T and B cells). So you can rephrase that to say approximately half of your adaptive immune system is found in MALT and you won't be that far off.",
"So ",
"what comprises the MALT",
"? That would include gut-associated lymphoid tissues, Peyer's patch, isolated lymphoid follicle, mesenteric and cervical lymph nodes, and the nasopharynx- and bronchus-associated lymphoid tissues. The last two will not be relevant to this question but the others can all be considered to be associated to the gut. I do not have the exact number but it will be safe to say that at least a third of all your lymphocytes can be found there."
] |
[
"Awesome, thanks for the detailed response. I guess taking into account MALT, as well as the length of mucosa tissue in the GI tract, 70% seems feasible."
] |
[
"im not correcting, but i'm gonna be one of those guys... heh heh heh",
"The Skin is actually the biggest immune barrier and is where the majority of immune cells live. This is the \"correct\" answer you give on tests and in books. With that being said, typrix is correct in the locations of various MALTs and peyers patches. The next locations would be bone marrow(naive B-cells cells), thymus(naive T-cell), and lymphatics(mature and naive cells). One can also interpret immune system differently(innate vs adaptive) so that can change the answer slightly, but thats a nonissue here. ",
"You have to remember that the GI system is mouth to ass, and this is at least 30-40 feet(considering most people have a small bowel of 20-30ft). On top of that, this region has the most surface area of any part of your body and it is the only opening to the inside of your body(not counting ears, nose, eyes, the mouth is the main contributor). Having various immune complexes in this region and in large quantities is one way the body can ensure its protection from pathogens and invaders. "
] |
[
"I thought anti-matter had nothing to do with anti-gravity?"
] |
[
false
] |
I specifically remember even panelists here saying that same thing. That antimatter just means anti-CHARGE, not gravity. then what's all this about? How antimatter responds to gravity remains a mystery, however; it may "fall up" rather than down. One significant difference between the two may be the way they interact with gravity - antimatter may be repelled by matter, rather than attracted to it.
|
[
"It has nothing to do with \"anti gravity\" in the sense of cancelling gravity. What they mean in that article is that antimatter would \"fall up\" in a matter gravity field. ",
"The CPT symmetry of the laws of physics is widely accepted. This means that if you reverse charge (C), parity (P) and time (T) all laws are symmetric. If this holds true, antimatter ",
" interact with gravity just as matter does. ",
"However, it might be that this symmetry does not hold true and that antimatter either has a \"negative gravitational charge\" and would then repel matter. It might also interact slightly different with gravitational fields. Only experiments can determine if the theoretical construct is indeed correct.",
"edit:",
"http://en.wikipedia.org/wiki/Gravitational_interaction_of_antimatter"
] |
[
"This means that if our current understanding of antimatter is wrong and instead of acting like normal matter, anti-matter repels matter with the same magnitude and on top of that you could put anti-matter into a magical tank (and the antimatter has more mass than the tank -- we'll neglect buoyancy) then, yes, the tank would fly upwards."
] |
[
"Does that mean if I can hold a large enough concentration of antimatter in a tank (presumably with magic magnetic walls) then the tank will fly up like a helium balloon?"
] |
[
"Why are some alloys better for some musical instruments than others?"
] |
[
false
] |
Bronze is good for cymbals while brass is good for horns while steel is good for certain drums. Obviously certain combinations "sound better" as time and tradition has shown but, scientifically speaking, why is this so?
|
[
"Different metals behave differently when forces are applied to them (be it by percussive nature, or by the air itself). One measure of this is the Young's Modulus. Simply stated, the higher the modulus, the stiffer a material is.",
"You can see ",
"here",
" that brass/bronze are similar, whilst steel is much stiffer - making it better for cymbals."
] |
[
"Thanks for responding:",
"Only cheap/beginner/toy cymbals are made of brass while high quality cymbals are made of bronze. As a drummer, I notice a huge difference in quality going form brass to bronze. If their stiffness is so similar, as the modulus values show, then why such a difference in quality? Is stiffness the only thing that matters here?"
] |
[
"There are various things which one could consider when differentiating metals - I just couldn't find any values easily online, so it wasn't really worth mentioning.",
"Density - (perhaps) obviously, two identically shaped cymbals made of two metals of different density will sound different. The heavier one will resonate will fewer high frequency overtones and so sound lower in pitch.",
"Bulk Modulus - this describes how the material responds to pressure. This is important for cymbals as they are being struck by the sticks."
] |
[
"If herd immunity exists and is important, why don't more adults get vaccinated? Not all vaccines give life long immunity."
] |
[
false
] |
I'm trying convince my sister to vaccinate her kids, but she is reluctant. She gets all these anti-vaccine articles from a facebook group and gives them to me. 'See, I told you vaccines are dangerous!', she says. I have been able to debunk all articles so far, but it takes so much energy. (Most of the time she doesn't even read the article, she just reads the comments on fb saying how this article proves this or that, and I have to prove them wrong...) Anyway, I believe that if I can answer the question in the title, I might be able to convince her to vaccinate. This is the one thing I can't really find a good explaination for. I believe in vaccines, but the last vaccine I got was some 20 years ago, which means that I might have lost some of my immunity. To prove my point to my sister, I will get re-vaccinated, but I don't think that is very common (at least not where I live). So again, if herd immunity is important, how come so few adults get re-vaccinated? Please help me convince my sister to vaccinate my nieces!
|
[
"I'll try to explain it. I'm a doctor but my English is not perfect. Some vaccines don't need to be repeated, and some does. This is because some give immunity for life (like hep A or Hep B) but other like difteria/pertussis/tetanus vaccine needs to be repeated. This is particularly important if you have little kids that doesn't have the vaccine yet. I hope I made myself clear."
] |
[
"In the case of Tetanus at least there can be no herd-immunity anyway since it is not contagious.",
"Anyway OP, you can't force her, but stay cool and provide facts. For example Unicef info like this: ",
"http://www.unicef.org/pon96/hevaccin.htm",
" or the history of smallpox, one of histories feared diseases that was thankfully erradicated by vaccinating: ",
"http://en.wikipedia.org/wiki/History_of_smallpox"
] |
[
"There are some vaccines that are lifelong like MMR that help make you immune to those diseases. These diseases are pretty stable and you don't find mutations like you do with influenza, which is why you have different flu vaccines every year. Vaccines like MMR and polio are lifelong where things like tetanus (lockjaw) need to be boosted every ten years due to issues with white blood cell activity. Now for people who have supressed or compromised immune systems from either disease or cancer will need other boosters which is why herd immunity is important. If one of her children ended up needing chemo it would be so vital that everyone else around her child be safe from disease as his/her chances of dying from nearly anything are much higher than normal. "
] |
[
"Why is quadriplegia/paraplegia irreversible?"
] |
[
false
] |
I know that some spinal cord injuries are reversible and some are not. For those who have spinal cord injuries that result in irreversible quadriplegia/paraplegia, what has gone wrong that medicine cannot fix yet/ever?
|
[
"I was going to write a nice summary but then I found ",
"this",
" website and it honestly gives a fantastic description of the processes that occur following acute spinal cord injury.",
"In a nutshell though, your spinal cord is made up of the axons (think of them as your brain wires) connecting your muscles to your brain. When there's an injury, and the spinal cord is ruptured, these axons can be damaged or severed completely. This is a problem as they are not very good at growing back. The damage further causes the loss of myelin (think wire insulation that shields the electrical impulses travelling up the axons) so that nerve impulses don't travel well, or at all, along the spinal cord. There is then an inflammatory response that causes more damage, and the axons often just fire off impulses endlessly effectively killing nerve cells (excitotoxicity). Cells that usually support and wrap around the axons (glia and oligodendricytes) then start to form a scar at the injury site and may actively prevent axon regrowth. Blood vessels are also damaged, so parts of the spinal cord can die off due to lack of blood flow/blood pressure changes.",
"This all causes paralysis and loss of sensation because the axons that are cut, damaged or otherwise killed are responsible for carrying motor commands to your muscles and sensory information back. The reason it's often irreversible is this:",
"Imagine you get a fibre optic cable and cut a bit of it. You can imagine how hard it would be to reconnect that. Nerve fibres are much finer, numerous, and more delicate than that. It's impossible to manually reattach it. This is also because they aren't really individual wires so much as tubes filled with special fluid and proteins and cellular machinery. So once you break them open it all spills out and can kill the cell if it doesn't heal over. Once it's healed over, how do you stick it back together? We can't.",
"In really severe cases there's nothing to be done although the idea behind newer therapies (like stem cells) is to grow new nerves from the beginning to replace the severed or damaged ones. But it's the most insanely complicated wiring system imaginable - innumerable contacts from the brain through the spinal cord out to the exact right muscle or sensory cell and back again. We can't just put them in, we have to convince the body to act like it did when it first made them so it can connect everything properly. And that's really tricky to do in adults for a whole host of reasons.",
"I'll stop here because this is getting a bit long, but I hope it gave you some of the info you were after."
] |
[
"Not really, because as I explained, if the cells don't outright die, then they heal up the broken ends and a glial scar may prevent regrowth. The best option is to convince the body to regrow entirely new nerves from scratch. This is literally the work of thousands of labs worldwide.",
"I'm having trouble explaining the complexity of the spinal cord. Have a look at this extremely simplified cross-section ",
"here",
". Now look at what each major grouping of nerves is responsible for at each level of the spine ",
"here",
". Each of those little subsections has literally tens of thousands of nerve axons. You can't reattatch them all. ",
"And it's not only that - the spinal cord isn't ",
" like a bunch of wires. Here's a stained cross-section of the spinal cord. Each level of the spinal cord contains little circuits looping between sensory inputs and muscle inputs and outputs that help control muscles subconsciously (reflexes and simples muscle movements). And further (from the wiki article):",
"Each segment of the spinal cord is associated with a pair of ganglia, called dorsal root ganglia, which are situated just outside of the spinal cord. These ganglia contain cell bodies of sensory neurons. Axons of these sensory neurons travel into the spinal cord via the dorsal roots.",
"Ventral roots consist of axons from motor neurons, which bring information to the periphery from cell bodies within the CNS ",
". Dorsal roots and ventral roots come together and exit the intervertebral foramina as they become spinal nerves.",
"The gray matter, in the center of the cord, is shaped like a butterfly and consists of cell bodies of interneurons and motor neurons. It also consists of neuroglia cells and unmyelinated axons. Projections of the gray matter (the “wings”) are called horns. Together, the gray horns and the gray commissure form the “gray H.”",
"The white matter is located outside of the gray matter and consists almost totally of myelinated motor and sensory axons. “Columns” of white matter carry information either up or down the spinal cord.",
"I hope that explains it - basically the spinal cord isn't just a bunch of nerve axons, it has little local neuron networks up and down the whole length. Plus associated ganglion, and support cells and inputs and outputs everywhere. And even if it was as simple as rewiring, and given it were possible to reattach damaged axons (I'm not sure how you could do it) it would still be impossible to reattach so many nerves correctly."
] |
[
"This is great! Can you also explain a little more about how, theoretically, these problems could be fixed? If a computer program could map how to reattach the 'wires' on an individual patient, could machinery accomplish reattachment?"
] |
[
"Do super massive stars have a goldilocks zone?"
] |
[
false
] |
And if so, how long would a year be on a planet within the zone?
|
[
"Every star, regardless of supermassiveness, has a Goldilocks zone. ",
" ",
" ",
"The size of the star just affects where the zone lies (how far from the star). Also, the luminosity is more important than the size though they are usually correlated. Some scientists suggest the type of star (more like its class or composition rather than size) can affect the habitability of a planetary system.",
"https://en.wikipedia.org/wiki/Circumstellar_habitable_zone#Spectral_types_and_star-system_characteristics"
] |
[
"It's also kind of hard to pinpoint what exactly a goldilocks zone should be. I mean the zone that Earth itself is in is only habitable because Earth has its own protection (Ozone layer, magnetosphere...). If Earth had more protection, the zone would be closer to the sun, and vice versa. How much lee-way should the definition of goldilocks zone have for that?",
"And some stars definitely don't have what we'd consider a habitable zone, for example brown dwarfs that don't emit a lot of energy, so all their planets are barren ice-balls."
] |
[
"Also, the Goldilocks zone may not be a constant, particularly not on geological timescales, for a few reasons. For one, high mass stars are typically short-lived, evolving rapidly through the CNO cycle, making their lifespan more on the order of millions of years rather than billions.",
"For two, these stars are often quite variable thanks to large swings in the radius, and as a factor of this the luminosity.",
"This is all ignoring the fact that high mass stars are volatile in other ways, often shedding mass in ways that would not be conducive to live in their solar system."
] |
[
"How fast can the human body travel with and without the assistance of a machine."
] |
[
false
] |
The reason I say without is because this is a completely hypothetical question. I was just curious if a human could run at extremely high velocity how fast could he go before the pressure on his body is too much (excluding the fact that his legs would be destroyed under the strain and whatnot)? Also I want to know how fast we can go with the assistance of a machine. I googled it and I was told the only limit is the speed of light (with the whole infinite energy impossibility thing) but I wanted to know how far can we go with the assistance of some device to negate some of the strain on the human body and a engine that can go infinitely fast. Also I would like to know the answer for both on Earth and in space (don't know if it would make a difference). Please let me know if any of my questions seem befuddled or too abstract so I can change it or narrow it down.
|
[
"A human is just a lump of matter. So in space (IE vacuum) the highest velocity you can get to is indeed the speed of light c.",
"In a fluid like the air we are sitting in now (yes air is a fluid), there are drag forces. I don't know the pressure to puncture flesh, but with assistance the velocity you can achieve before damage is basically the drag force per area (pressure). The drag goes up like a",
"V",
" + c*V",
" ... ",
"As far as how fast you can go without a machine, I guess the only non machine act you can do is jump off a cliff and then minimize your surface area. You will then reach a terminal velocity where the drag force balances gravity. ",
"A quick google (",
"http://hypertextbook.com/facts/JianHuang.shtml",
") turns up 50-70 m/s for skydiving. So about as fast as a normal car's top speed. "
] |
[
"Speed is not the problem, it's acceleration. Ignoring other factors, you could accelerate to hundreds of thousands of miles per hour if you accelerated slowly. As for how fast the human body can run, ",
"this",
" might be a good read."
] |
[
"Speed is a problem in a fluid, because the drag can either burn you up or rip you apart."
] |
[
"Could dangerous radiation from depleted nuclear reactor cores be harvested?"
] |
[
false
] |
I hear all the time about the problem of long term storage of radioactive materials, and understand that the yield can't come close to the original yield, but why don't attempts to store the waste include attempts to harvest low yield energy? Do they?
|
[
"You're having a cookout when you notice that the lid of your grill is quite warm to the touch. Why don't you find some way to harvest that waste heat to cook another couple of hamburgers?",
"Same thing."
] |
[
"For the broader question, we do: they're called ",
"Radioisotope Thermoelectric Generators",
". Basically, your intuition is correct: the heat produced by radioactive decay, when run through a thermocouple, generates electricity, making a sort of nuclear battery. Here's the thing: the strength of RTGs is that they can provide reliable power autonomously for long periods - that's why they're used for things like powering satellites, or remote automated facilities like modern lighthouses (the Russians were big on this design). These needed to be left alone for long periods while still being powered, but ",
" - RTGs generally only generate a few hundred watts or less, even for large ones.",
"So, for one, designing these things for broader use as power generation really isn't efficient, as their output is too low to be meaningful for civil use. Secondly, RTG fuels are carefully selected for their radioactive properties. Spent fuel from a fission reactor generally is too dangerously radioactive (and often toxic and corrosive to boot) to try monkeying around with them to build an RTG, especially when you're only talking about a few measly watts of power - it's simply not worth the cost, and is simply far safer and easier to go for reprocessing and safe storage."
] |
[
"This doesn't concern \"re-using radiation\" in a strict sense, but I think it is what your question was getting at. ",
"I think that you should look at nuclear fuel reprocessing, or more generally, closed nuclear fuel cycles. \"Spent\" nuclear fuel still contains more than 90% of it's original nuclear energy. This energy cannot be harvested in a conventional reactor, because as the fission process produces heat (and thus energy) it produces decay products which are neutron \"poisons.\" These poisons vigorously absorb neutrons, and slow the nuclear reaction. Eventually this poisoning effect renders the fuel useless - it must be removed and replaced with new fuel. In the USA, currently, that's the end of the road for the fuel. It goes into a pond, then dry-cask storage, followed (eventually) by terminal disposal (e.g. Yucca Mountain Waste Repository). ",
"Many nuclear powers (France, UK, Japan, soon China) recycle this fuel, by removing it from the reactors, and conducting chemical purification to remove the undesirable elements in the \"spent\" fuel. At this stage, other fissile materials can be added into the mix (forming MOX - mixed oxide fuel). Weapons-derived plutonium, which has been oxidized, can be used to create MOX fuel - this is what the DOE wants to do with the 34 metric tons of plutonium that the US has pledged to destroy in arms reduction treaties. ",
"Once the fuel has been reprocessed, it can be re-used in conventional reactors. Of course, the preceding discussion has omitted the use of heavy-water reactors, such as the Canadian CANDU reactors. These designs can essentially use the waste product from conventional light-water reactors (what the US exclusively uses for power generation) without any processing or other modifications.",
"Of course, this lunch ain't free. To do reprocessing, you have to move nuclear fuel all over the country. And pack/unpack it. This naturally involves higher doses to rad workers. The risk of nuclear weapons proliferation is heightened when using MOX fuel, as you're working with 80-90% pure plutonium oxide at one stage. ",
"Cheers, here are some links:",
"MOX",
"Reprocessing",
"The CANDU reactor",
". Check out the \"Fuel Cycles\" section."
] |
[
"What is a headache?"
] |
[
false
] |
[deleted]
|
[
"There are different kinds of headaches Click on each link for more information about causes and more information:",
"Cluster headache",
": A cluster headache is one-sided head pain that may involve tearing of the eyes and a stuffy nose. Attacks occur regularly for 1 week to 1 year, separated by long pain-free periods that last at least 1 month, possibly longer.",
"Tension headache",
": A tension headache is pain or discomfort in the head, scalp, or neck, usually associated with muscle tightness in these areas.",
"Migraine",
": A migraine is a common type of headache that may occur with symptoms such as nausea, vomiting, or sensitivity to light. In many people, a throbbing pain is felt only on one side of the head. Some people who get migraines have warning symptoms, called an aura, before the actual headache begins. An aura is a group of symptoms, including vision disturbances, that are a warning sign that a bad headache is coming."
] |
[
"seriously"
] |
[
"What is a google?"
] |
[
"How much closer to and farther from the sun could Earth's life survive?"
] |
[
false
] |
If the distance from Earth to the sun were greater/smaller, how much closer to and farther from the sun could life on Earth survive?
|
[
"I think another thing to note about this question is that \"life\" needs to survive and not necissarilly humans. I.e. single celled bacteria would count in this example and there are a large series of extermophiles that could exist under very broad conditions."
] |
[
"The distance between the earth and the sun is 1 AU (150,000,000 Km), the outer limit of our goldilocks zone is 1.37 AU, the inner 0.95 AU. This should give you an idea."
] |
[
"That doesn't sound like it will be very good for us as the sun's luminosity continues to increase."
] |
[
"How do batteries work?"
] |
[
false
] | null |
[
"Have you checked out the ",
"Wikipedia page",
"? Is there a particular part you want further elaboration on?"
] |
[
"For basic concepts like this Wikipedia is no more error-prone than textbooks or other sources. The concepts are well-established and easily corroborated."
] |
[
"For basic concepts like this Wikipedia is no more error-prone than textbooks or other sources. The concepts are well-established and easily corroborated."
] |
[
"What exactly causes a person to be homosexual?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"I appreciate the source of useful information, but in what way is my question less specific than all the other ones on this sub?"
] |
[
"We try not to release questions whose answers can be found with a google search / on wiki. If you have a more in-depth question following up on something you've read there, that's fine. "
] |
[
"How is the metamorphosis of a caterpillar into a butterfly currently explained by darwinian evolution? or science in general?"
] |
[
false
] | null |
[
"Are you asking about how metamorphosis increases an organism's fitness or how its mechanism evolved physiologically/genetically? It's important to note that there's nothing at all special about the metamorphosis of caterpillars to butterflies compared to the rest of the insect kingdom. The vast, vast majority of living insect species go through the exact same process. Think about it: Flies start out as maggots, turn into a pupa, and emerge as radically different winged adults -- its the same process. Ditto for beetles, wasps, ants, mosquitoes, bees etc. This process: from often \"wormlike\" larva to a somewhat immobile pupa (the chrysalis in a butterfly) to a very different adult all through successive stages of molting is called \"complete metamorphosis.\" Other insects like dragonflies and cicadas undergo \"incomplete metamorphosis,\" meaning they start out as \"nymphs\" that are fairly different from the adults but eventually they molt into their adult stage without ever transitioning through a pupa stage. ",
" ",
"Still other insects like mantises, cockroaches, and grasshoppers have young that are only slightly different from the adults (usually the only difference is the babies don't have full wings and their proportions are different). ",
"Sorry for all that but before looking at how or why a lifestyle evolved I think its really helpful and interesting to look at the various \"intermediate\" versions of that lifestyle that exist throughout the spectrum of closely related organisms. ",
"Regarding metamorphosis: Scientists aren't very sure why complete metamorphosis evolved but the fact that it is so widespread suggests that it has very significant survival advantages. One frequently suggested theory is that complete metamorphosis is advantageous because adults and young of the same species occupy very different niches and therefore are not competing for the same food and other resources. For example, caterpillars eat leaves while the butterflies feed on nectar. This means there can be more of the same species in the same area meaning these organisms can leave more descendants and hence be favored by selection. ",
" ",
"Also, breaking up the life cycle in this way is thought to help the larvae and adults specialize and get better at surviving with their respective rolls and diets. Caterpillars and other larvae can \"focus\" all of their biological systems on eating, growing, developing, and getting better at consuming whatever plants they feed on (caterpillars of course grow very large and eat constantly, butterflies and moths don't grow at all once they emerge from their chrysalis) The butterflies by contrast, can \"focus\" more on mating and laying eggs. Since each stage can devote more of its development and resources to these specific tasks, each can be better optimized for what they're specializing in compared to if these different tasks had to carried out at the same time in the same body type. Some moths take this to extremes: a few moth species don't even have mouths or digestive systems once they emerge from the cocoon. This adult stage exists for no other reason than mating and reproducing and no tissues, resources, or energy have to be invested in anything but reproduction. ",
"It's like if you had to build one car to do two completely different things: towing heavy cargo loads and racing -- in this case one car probably wouldn't be able to carry out either function as well as vehicles that are optimized and solely dedicated one ",
" the other.",
" ",
"Tl:dr Metamorphosis may let insects switch between bodies best specialized to very different kinds of tasks.",
"https://www.scientificamerican.com/article/insect-metamorphosis-evolution/",
"https://www.ncbi.nlm.nih.gov/pubmed/10519548",
"https://www.nicholls.edu/atemplet/Bio108HomePage/Chap20.html"
] |
[
"Thank you for the lengthy write up and sources."
] |
[
"I'm not sure this answers OP's question. I read it more as 'how did metamorphosis, involving forming a protective shell and basically dissolving the body to reform into something almost completely different, evolve?'. An excellent question, I'm quite curious if there are any insects that appear to exhibit an intermediate phase of that evolutionary cycle."
] |
[
"What is the difference between the second law of thermodynamics and the law of conservation of energy?"
] |
[
false
] | null |
[
"Yeah that's it. ",
"The average entropy of a system increases, but there can be local temporary decreases."
] |
[
"No.",
"Perpetual motion involves getting energy from nowhere. Even without the second law of thermodynamics, a \"perpetual motion\" machine is impossible."
] |
[
"IIRC yes, its probability based, kind of. there is a small chance that if you have two touching bodies of the same temperature, that one heats up and the other cools down. but you have to keep in mind the scale of probabilities that this happens. I dont have real numbers here, but the probability of such an event is incredibly low, like 1 : 10",
" or even 1: 10",
" In comparison: the number of atoms in the universe is about 10"
] |
[
"How do the seasonal viruses survive to the next season? Do they go inactive or spread to different parts of the world?"
] |
[
false
] | null |
[
"Well the viruses themselves are unaffected by seasons. In fact near the equator viruses that we consider to be seasonal, such as influenza, are prominent throughout the year. From what I've read the reason northern areas have a flu \"season\" is due to people's immune systems being weaker in colder weather and that the flu season corresponds to when children are in school. Children tend to be less hygenic and have weaker immune systems compared to adults. So, when a virus spreads in a school it spreads rapidly and parents become infected from their children who then infect co-workers. It's a complicated question to explain entirely and these are simply ideas as to why we observe viral seasons but the weather itself doesn't determine a viral season and the viruses are not inactive just because it is warmer."
] |
[
"Isn't it true that cold weather doesn't actually weaken immune systems, but rather that the cold weather forces people into closer proximity indoors causing a higher likelihood of infection?"
] |
[
"There is also a hypothesis that lower humidity in the winter makes mucus membranes more hospitable to pathogens."
] |
[
"Why do we say we share 99% of our DNA with chimps, but 50% of our genetic material with our parents?"
] |
[
false
] |
[deleted]
|
[
"These refer to two different things. In the case of your parents, you get physically get 50% of your DNA from each of your parents. In the case of chimps, you don't physically get your DNA from chimps, but the information in your DNA is 99…% the same as the information as the information in chimp DNA. The information in your DNA is ",
" 99…% the same as the information in each your parents' DNA. "
] |
[
"Careful with your wording....Humans did not evolve from chimps, and they are not our ancestors. We share a common ancestor with chimps that was more similar to both humans and chimps than we are to eachother."
] |
[
"Careful with your wording....Humans did not evolve from chimps, and they are not our ancestors. We share a common ancestor with chimps that was more similar to both humans and chimps than we are to eachother."
] |
[
"Is there any evidence that some single-celled organisms evolved *from* multi-cellular organisms?"
] |
[
false
] |
I think it is assumed that life started out with microorganisms which combined into more complex organisms. But I have read that amoebas have complex genomes by certain metrics -- would this "extra" information potentially be the result of them have once been part of something more complex and perhaps such organisms could be made to differentiate into more specialized cells?
|
[
"A commonality among all I know are that they are parasitic descendants of the host species -- that is, infectious cancers that became transmissable parasites.",
"First is ",
"Canine transmissible venereal sarcoma",
". They are cancerous cells that became a sexually transmitted disease several thousand years ago. Over the years they have lost quite a bit of their canine genetic material, being single-celled organisms instead of wolves/dogs. So, they are no longer genetically canine (unlike a typical cancer), but rather a different species.",
"Another example is ",
"(Tasmanina) Devil facial tumors",
". Also, an ",
"infectious leukemia in clams",
".",
"For a different type of example that's not quite single-celled is a ridiculously reduced jellyfish that causes ",
"whirling disease",
" in trout."
] |
[
"If I remember correctly, a few years back a group of scientists managed to get yeast to live in a more cooperative, multicellular fashion. That could have suggested that yeast may once have acted more in that way. You could try finding that article.",
"Hope that was some of what you were looking for, and sorry for being so vague."
] |
[
"You were downvoted, but this is totally correct.",
"Here's the paper",
"http://www.pnas.org/content/109/5/1595.full"
] |
[
"Reddit, What Happens When Lightning Strikes the Ocean?"
] |
[
false
] | null |
[
"Chilean here. Electric lines shut down automaticly in earthquakes, so you'll have 99 problems, but electricity ain't one of them. Lines are restored within hours."
] |
[
"This",
" might give a clue. The skin effect basically says that most of the energy associated with the lightning strike will dissipate through the surface of the water. I understand it says AC, but with something like a lightning strike the assumption behind alternating current would probably still hold. It is a strike that pulses to a high voltage, then a sharp decrease in voltage because the lightning strike is over. "
] |
[
"From a ",
"diving website",
":",
"Scientists know little about what happens when lightning hits water. The electrical current probably spreads in all directions, weakening as it spreads out. Since large numbers of dead fish aren't found after thunderstorms move across bodies of water, the current probably weakens in short distances.",
"My own experience: I was diving during a thunderstorm a couple of months ago in Thailand. The divemaster told me it's entirely safe at 20-60 feet, which I believe - the current would dissipate by the inverse square law, so by the time its down there it shouldn't be very high. He said lightning strikes on the ocean are extremely rare. He pointed out that being on a boat during a storm is probably slightly more dangerous, which I also believe. He told me if the storm had started before we left, he would have aborted because of this. "
] |
[
"Is it possible that massless particles don't experience time dilation or length contraction?"
] |
[
false
] |
If spacetime curvature is a consequence of the presence of mass, is it possible that massive particles are the only ones that experience these spacetime-curving phenomena? I know this is a rather odd question, and I'm pretty sure I'm missing something, so please explain to me what I'm misunderstanding. My understanding of neutrino oscillation is that the fact that they have time to oscillate means that they experience time in the first place and therefore must have mass. This would allow them to be massless like the Standard Model says they should be and still oscillate.
|
[
"Light bends in a gravitational field, which has been pretty well-established over the last century, so it's definitely not true that massless particles don't feel the curvature of spacetime.",
"The chain of logic is more or less like this. The presence of mass ",
" curves spacetime, and then all particles move on \"straightest line\" paths within that spacetime, which is what we see as gravity.",
"Note that I said mass ",
" energy. That means that even massless particles will contribute to spacetime curvature - in simpler terms, they'll gravitate - because they have energy. In fact, for the first 80,000 years or so of the Universe's history, light (which has since become the cosmic microwave background) was so energetic and so densely packed that it was the major source of gravity in the Universe, more than gas, dark matter, and so on combined."
] |
[
"You're conflating two ideas. Time dilation and length contraction are a consequence of ",
" relativity, in that they describe how different observers moving with different velocities will measure the same quantities. This applies even in perfectly flat spacetime, and the properties of the particles in that spacetime have no bearing on it. When people say that massless particles \"don't experience time\" what they really mean is that there's no frame-independent way to define a \"proper-time\" parameter for those particles. If a massless particle were to oscillate, it would necessarily be a violation of special relativity.",
"Spacetime curvature as a result of the presence of energy is covered by ",
" relativity. As others have pointed out, massless particles, which all have non-zero energy, will contribute to the curvature of spacetime and be affected by it."
] |
[
"No, it's not. If massless particles decoupled from the curved component of spacetime, they would not be affected by gravitational fields, but they are. ",
"That's not even relevant to time dilation and length contraction, though; those things arise from special relativity, which doesn't involve spacetime curvature."
] |
[
"How do we know that the speed of light in vacuum is the best measure of c ? Or what is the refractive index of the vacuum?"
] |
[
false
] |
As I understand it, the speed of light in a transparent material is c/n ,where n is the index of refraction in the material. The index of refraction depends on a bunch of things like how light interacts with electrons in the material. Roughly the more electrons light sees, the slower it goes. According to quantum mechanics, the vacuum isn't really empty; it is full of virtual particles. So shouldn't the vacuum have a small index of refraction. And the speed of light in vacuum that we measure, c', would be less than the real speed of light, c. Neutrinos are weakly interacting, so they would "see" fewer electrons, or whatever particles. Maybe they could travel closer to the real speed of light, c, than light itself. I'm sure people more experienced with the relevant areas of quantum mechanics have already done these calculations. Would a discrepancy between the speed of light in vacuum that we measure and the real speed of light be large enough to account for the faster than light neutrinos of recent experiments?
|
[
"Something rather similar was asked ",
"yesterday",
". \nSo first off: Virtual particles aren't really 'real'. Which is why they're called 'virtual'. They're a way of visualizing (through Feynman diagrams) the contributions in a perturbation series in (perturbative) quantum field theories. ",
"So any attempt to think up a descriptive physical theory in terms of virtual particles is dead-on-arrival. Virtual particles describe the math; The Feynman diagrams, which are drawn according to specific \"rules\". So if you're talking about virtual particles, it better be ",
" you did the calculations. (In other words, prepare to show your Feynman diagrams) Anything else will likely lead you dead-wrong, because 'virtual particles' don't always work the way ordinary ones do, even within this formalism (They're allowed to be ",
"off-shell",
", violating special relativity and conservation of energy). ",
"On an even more basic level, QED and most quantum field theories are (special-) relativistic. So I don't see how you could use them to derive c or prove that light travels at a speed other than c. ",
"As for the topic of refractive index, light actually ",
" travels at c. Refractive index is a bulk property which describes the 'effective' speed of light in that material, as the light is absorbed and re-emitted by the material's response to it, which occurs in a finite amount of time. "
] |
[
"I guess the speed of light and related constants like permittivity and permeability of free space are just what we measure them to be.",
"Well, they wouldn't be 'fundamental constants' if we knew some way of deriving them. There's a redundant number of them, but nobody knows which ones are more fundamental than others. Is it c? Or the permittivity/permeability? Or perhaps the fine-structure constant? Or maybe the Rydberg constant? ",
"the first time someone is measuring the speed of light accurately using something other than photons or properties of electro-magnetism. ",
"There's no measurement of c involved. They're just measuring the time it took. But you can't measure c in any way independently of electromagnetism. It's basically a property of the electromagnetic field, in some way. ",
"By the way, could you recommend a mathematically sound intro to QED? ",
"Well, Zee's book (\"QFT in a nutshell\") is pretty good. Or at least very popular."
] |
[
"Well, that was the most realistic possibility for the results from CERN, if the data turns out to be correct. That for some reason the speed photons travel is a tiny bit slower than the ultimate speed limit of the universe. ",
"The idea that even vacuums have an index of refraction is interesting. The one that I heard was that photons weren't entirely massless and thus don't travel at exactly c."
] |
[
"How are the listed side effects of drugs determined?"
] |
[
false
] |
For example, if someone in a clinical trial starts taking a drug and develops lung cancer, how is it determined whether or not lung cancer is a possible side effect of the drug or the person would have developed it anyway?
|
[
"They are compared to the placebo in the same trial. Example: in a trial of 1000 patients for drug X (500 placebo, 500 active drug) 10% of patients on the active drug reported nausea vs only 6% on placebo, we would most likely consider that a true side effect of the drug and not just resulting from unrelated factors. ",
"This is where sample size and a variety of other statistical factors come into play. Some drugs been recalled over postmarketing side effects that did not show up in clinical trials; either due to insufficient sample, different patient population, etc."
] |
[
"Thanks, I always wondered if they just used some algorithm to predict it or if they just gave it to a thousand people and waited to see how many stroked out of had a heart attack. Scary stuff! "
] |
[
"So when it says there is a risk of stroke, heart attack etc, they actually sit and wait until people die before identifying that potential reaction? "
] |
[
"Can positrons create magnetic fields similar to elektrons ?"
] |
[
false
] | null |
[
"Yes."
] |
[
"What happens if they interact ? "
] |
[
"Lots of things can happen when an electron and a positron interact. They can scatter elastically, they can form bound states (positronium), they can annihilate, or undergo various other reactions."
] |
[
"What's the most expensive part of launching a spacecraft?"
] |
[
false
] |
Disregarding the initial cost of constructing a shuttle/rocket, what are the expenses, or more specifically the greatest expense that comes into play when launching a spacecraft into orbit or beyond? I've always assumed that it's the tremendous amount of rocket fuel they must go through just to break free of Earth's gravitational influence (though I suppose if they're just going into orbit they're still very much under its influence). And I guess if it is the fuel a good follow up question to this would be: are there any cheaper alternatives that are available/being tested/hypothesized? My curiosity on this came about when a friend mentioned and I couldn't help but wonder how mining resources from other celestial bodies could ever be profitable as long as we have to expend a tremendous amount of resources just to get there and back.
|
[
"Fuel is pretty cheap. The problem is that you need so much of it that you have to shave every ounce of weight off your structure and engines in order to be able to make it to space. This means that your safety margins need to pretty small, leaving little room for error and uncertainty. ",
"To reduce this uncertainty, you need to spend a lot of money on engineering analysis, tests, quality assurance, inspections, etc. Some of these are non-recurring (only done once), but a lot of work still has to be done for each launch. "
] |
[
"I'm no expert, but as far as I am aware, the most difficult part of getting a spacecraft in space is, as you inferred, getting into orbit, and the cost and quantity of the fuels involved, as we lack an alternative form of thrust (that doesn't only work in a vacuum) capable of lifting such heavy loads with the forces required.",
"One way innovative companies are looking to get around this problem is SpaceX's approach on the Skylon with their ",
"SABRE Engines",
".",
"Edit: Link knavery"
] |
[
"if you don't have a very efficient spacecraft in terms of weight, you'll have to increase the size to store more fuel, which increases the weight. it's a nasty loop.",
"for an 40k aircraft, decreasing the weight by 1 pound will yield a roughly 7 pound weight saving.",
"source: aerospace engineer"
] |
[
"Sleep Grogginess?"
] |
[
false
] |
Why do we wake up groggy from sleeping for a long time? Wouldn't it be more biologically advantageous to wake up alert and ready to function? Thanks for any answers in advance!
|
[
"It might be worth clarifying exactly what sort of grogginess you're asking about here as it varies massively between people. Some simply cannot function in the morning, but others (myself included) are really quite functional as soon as they wake up. It seems almost everyone is groggy at least to some extent though... but anyway, consider:",
"When woken from some outside trigger like a noise, you can be instantly awake, alert, and ",
" active. One example of this which happens to me regularly is a knock at the door in the morning, which usually means a parcel for me. Somehow knowing that it's important I instantly get to the door so I don't miss my mail, when I'm sleeping and someone knocks on the door, I wake instantly, literally leap out of bed into my clothes and am opening the door downstairs 20 seconds later. I can't even move that fast normally!",
"So as far as an evolutionary/biological advantage goes, we can wake up alert and ready to function ",
".",
"Otherwise maybe it's simply not as much of an advantage over having a \"normal\" set of sleep cycles to which I believe the grogginess is related."
] |
[
"That sudden awakeness where you can jump out of bed and into action is thanks to a burst of adrenaline.",
"It's actually quite interesting when that does and doesn't happen - as really it's \"meant\" for dangerous situations where you would wake and jump straight into fight or flight.",
"For my above example, it triggers when there's a knock on the door, even if I'm \"expecting\" it, however if I set an alarm then it simply doesn't, I'll just slowly wake up and turn it off (then probably go back to sleep!) The funny thing about that is that I don't usually set an alarm and knocks at the door are actually a more common way of me waking up.",
"I would guess it's down to me having the notion already in my head that I don't want to be asleep when someone comes to the door, I almost fall asleep worrying that I will miss a parcel the next morning so I would postulate that what triggers this response is somewhat \"programmable\".",
"By the way, if your alarm doesn't wake you up, I would suggest changing to a different alarm clock - if you use your phone, change the melody it uses. It could work, at least for a while!"
] |
[
"A very good point! I was talking about the grogginess relating to when you wake up and feel mentally/physically slowed. And actually, now that you bring it up I've never really thought about how alert I've felt after being woken up by something that I'm not used to! (Sadly, my alarm clock doesn't count. It doesn't wake me up half of the time >.>...)"
] |
[
"How do trees know when to shed their leaves in the fall, and begin re growing them in the spring? How does this process work?"
] |
[
false
] | null |
[
"The trees or any plants that lose leaves or petals are categorized as deciduous. \nPlants are living organisms, and like humans they have hormones, which in plants are referred to as, phytohormones. Hormones are technically chemical messengers, they transfer signals from one cell to another. Those signals have to do with development of the organisms, such as formation of the roots, stems, leaves, and fruits on a plant; and that is a very general idea of what hormones are for.",
"Auxins are type hormones that regulate growth in plants (they are not the sole type of hormones responsible for the growth). During fall the leaves start to produce less auxins and abscission layer forms between the petiole and stem, causing the leaf to fall. So, basically, the high production of auxins keep the leaf attached to the stem.",
"Trees do keep a track of time. When the night time gets longer during fall the trees know that it is time to start dropping the leaves, even if the weather is still warm. When the spring comes the nights get shorter and so the trees start to bloom. Some other plants \"keep track\" of cold days and blooms when it gets warmer. ",
"So basically blame the growth hormones and their activity for leaf abscission and formation. "
] |
[
"I feel like the other answer missed the point. The question is not how do the leaves fall off, but how do the trees know when to tell the leaves to fall off.",
"I must confess that my knowledge of plant biology is limited, but what I do know is that there are pigments called phytochrome and cryptochrome that detect light. Specifically, when phytochrome is in its ground state (Pr) (think of this as its default or \"off\" state), it preferentially absorbs red light. When it absorbs red photon(s), it undergoes a rapid conformational change and now preferentially absorbs far-red (i.e. infrared) light (this state is known as Pfr), so you get the reaction Pr->Pfr. Pfr appears to have some sort of regulatory role, perhaps as a signaling molecule, and it modulates gene expression. I'm not familiar with cryptochrome, but I assume it something similar.",
"For most flowering plants, the critical factor is not the amount of daylight, but the length of night that they are exposed to. Therefore, as the length of night increases in fall, there is less Pfr produced in a day, so overall gene expression is different than when the nights are short. This altered gene expression leads to the series of events that cause the leaves to shed."
] |
[
"Those trees in the tropics which are deciduous tend to lose their leaves when it dries out, rather than when extended periods of darkness cause chemical changes."
] |
[
"Could a cat drink from a straw? And let's say if it could form a seal around the straw with its lips, could it create suction? Please help settle a debate."
] |
[
false
] | null |
[
"They suckle from their mother. "
] |
[
"Is that true though? According to one comment in that discussion, ",
"[...] as with most animals that cannot form suction with their mouths, the teat is stimulated to release milk by the kitten's licking and they basically lap up the milk.",
"What I want to know is, is that true, or ",
" they suck anyway?"
] |
[
"They can suck. I've had my finger sucked on by a kitten. Here's a video of one sucking on a bottle (you can even hear the suction break a few times): ",
"http://www.youtube.com/watch?v=y5FSgQ81kos",
" A bottle doesn't release milk until it's sucked on."
] |
[
"If we had a Duodecimal (12-base) number system, would the prime numbers be in the same place?"
] |
[
false
] | null |
[
"The primality of a number is a property of the number and not of its representation in any given number system; if you list the numbers in order starting with 1, then the second, third, fifth, seventh, eleventh, and so on numbers listed will be prime, regardless of what symbols you use to identify those numbers."
] |
[
"the same way you do math now, you just have two extra symbols.",
"say your numbers are 0123456789@&. the number you think of as 10 is @ and 11 is &. The number you think of as 23 (2 tens and 3 ones) is now 1& (1 dozen and 11 ones). you have a couple extra rungs to memorize on your multiplication tabls but that's the only difference"
] |
[
"'red red' goes into 'green green' green times",
"FTFY"
] |
[
"Can a material be thermally conductive but not electrically conductive?"
] |
[
false
] |
Even theoretically, if not physically.
|
[
"Yes, physically:",
"Monocrystalline synthetic diamond enriched to 99.9% the isotope ",
" C has the highest thermal conductivity of any known solid at room temperature: 3320 W/(m·K).",
"Absent significant substitutional impurities, diamond is a very good electrical insulator with room temperature resistivity in the range of 10",
" to 10",
" Ω·m ."
] |
[
"Theoretically it's certainly possible, just consider a material which does not have any charged particles.",
"In real systems, many materials have their electrons tightly bound to their nuclei, so at low energies you cannot excite any electrons and you have no electric conductivity. But lattice vibrations (called phonons) can still carry heat through the system, so you can have thermal conductivity but not electric conductivity. Technically, if you hit these objects with a large enough electric field, you will eventually excite some electrons and cause some conduction of charge, but you can sometimes ignore this for all applications depending on the material."
] |
[
"Yes. Very possible. In fact many such materials exist and have unique uses - such as replacing a metal when you want to conduct heat but not electricity. Just google \"heat tape\" or \"thermally conductive plastic\" for examples"
] |
[
"How is a recessive allele kept from being active if the allele on the other Chromosome is dominant in a recessively inherited trait?"
] |
[
false
] |
It's really hard for me to grasp how autosomal or gonosomal inheritance would look like on a molecular DNA level. What is the difference between a recessive gene and a dominant gene DNA wise? And how does a gene "know" if it needs to be active or not.
|
[
"A gene doesn’t “know” anything. It all depends on how that gene is expressed, regulated, or otherwise exerts control over the target cells’ function(s). Dominant in this respect means that the gene’s effect is phenotypically observed while the effect of the recessive gene is not (as much) evident."
] |
[
"To add to this. An example of how dominance can occur is through haplosufficiency. This means that if one would be heterozygous on a certain locus (Aa), the 'a' would lead to a dysfunctional protein, but the one 'A' copy is enough to continue the biological process of interest. So one would need to be 'aa' and go below a certain threshold of functionality of the protein in order to see any phenotypic effect. This still works if 'a' is not dysfunctional but only partially or just differently, it would just depend on the threshold of when the presence of the allele will have phenotypic effects."
] |
[
"I know that genes don't know anything that's why I put it in quotation marks.\nEdit:\nThat sounded more passive aggressive than it should have.\nThank you for your answer! :)"
] |
[
"Can the melting point of a substance ever differ from the freezing point?"
] |
[
false
] |
It seems as if they are inseparable.
|
[
"Ideally, for a pure substance there is no difference, but in practice, everything is impure to some extent, which creates a range of temperatures over which melting and freezing takes place. The solid-liquid phase transition of an impure substance takes place over the range of temperatures between the so-called ",
"solidus",
" point and ",
"liquidus",
" point. The observed melting (or freezing) range will depend on the impurity concentrations, and the degree of solubility in each phase. In practice, its hard to prepare a substance with a melting range less than 0.1 mK between liquidus and solidus. But if one limits the transition to greater than about 10% and less than 95% melted fraction, this range can be much more narrow. The most reproducible fixed point temperature standards, such as those realized via ",
"triple point cells",
" are used under such restrictions."
] |
[
"In a ",
" substance (see comment by ",
"/u/qwerty222",
" for a discussion of mixtures), there ",
" be a difference if you're talking about the experimentally observed temperatures of melting and freezing. These phase transitions (especially freezing) in practice occur under non-equilibrium conditions. Thus, a pure liquid can be supercooled to below its ",
" freezing point before it crystallizes, while a crystal can under some circumstances remain solid for a short time as it is heated above its ",
" melting point.",
"Furthermore, even equilibrium freezing/melting temperatures can differ, depending on the history of the sample. Very small (or sharply pointed) crystals have a lower equilibrium melting point than do very large (or flat) crystals. Moreover, a process known as Ostwald ripening or grain coarsening can cause the average size of a population of crystals to grow at a fixed temperature (the smaller crystals shrink, while the larger crystals grow, due to the difference in chemical potential caused by the curvature of the crystal-liquid interfaces). The upshot is that you can form (freeze) very small crystals at one temperature, and anneal the crystals to allow them the grow in size, thus acquiring an equilibrium melting point that is larger than the original freezing point.",
"So called ",
" (difference between freezing and melting temperatures) can also be caused by molecular additives that bind to the surface of the crystals (e.g., anti-freeze proteins that bind to ice crystals).",
"Tl;DR: Although conventional wisdom says that in pure substances, the melting point and the freezing point occur at the same temperature, reality is more complicated."
] |
[
"It is important to distinguish three things:",
"A given real material is usually a mixture. That means, there is a thermodynamic equilibrium for freezing of a sub-mixture of this mixture. Likewise, for a frozen mixture, its complement is the first to melt. For polymers and their gels, it is common for the apparent melting point and freezing point to differ substantially, for tens of degrees, depending on composition. This is because polymers consist of molecules of multiple molar masses, which are technically different substances. Also, for substances that are \"pure\", the real purity is often something like 99%, which is definitely not 100%.",
"For the distinction between thermodynamics and kinetics, for a material to freeze, it must undergo the reaction of crystallization or solidification. This has its own kinetics. For a simple molecule, it is usually pretty fast, but for polymers, it can take even months for a material to relax to its thermodynamic ground state.",
"For \"frozen\", gels don't necessarily have just \"solid\" and \"liquid\" states, since they don't actually crystallize. This means, there isn't that much of melting point but a \"sol-gel transition point\" where the storage modulus (quantifying elasticity) is equal to the loss modulus (quantifying plasticity, or ability to flow). In effect, this softening from a stiff, fully elastic material from a flowing liquid can take tens of degrees, with a smooth transition between them."
] |
[
"How does an ant find its way back to the nest?"
] |
[
false
] |
[deleted]
|
[
"By following their own or other ants' pheromone trails. ",
"Trails are volatile, and cumulative with use. Also, long-term use optimizes trails."
] |
[
"I think OP is asking how the first ant can find its way home. My understanding from learning the Ant Colony Optimization algorithm is that at first a lot of ants gets out of their nest at the same time; some return, some don't.",
"Being a successful path, the pheromones of those who return get used, the trail gets stronger, it keeps being used, and so on until finally the trail is optimized."
] |
[
"I think OP is asking how the first ant can find its way home.",
"By following his own trail, or residual trails from the day before.",
"that at first a lot of ants gets out of their nest at the same time; some return, some don't.",
"I think in reality all of them return."
] |
[
"Why, when the Europeans colonized America, did more natives die from new European diseases rather than the opposite, which was the case during the colonization of Africa?"
] |
[
false
] |
It's well known that when colonizing America diseases such as Small Pox were spread among natives and ravaged the population, usually unintentionally, but I recently learned that when colonizing Africa, however, it was the Europeans who struggled with diseases such as Yellow Fever and Malaria. Were there any noticeable reason for these different outcomes? (I'll probably end up in but I thought I'd come here first.)
|
[
" is a decent introduction to this question. But the theory given by Diamond is not necessarily true.",
"This",
" is a long write-up that considers the epidemic question in particular. In short: his hypothese that cities and domesticated livestock are necessary to develop lethal diseases is on shaky ground at best.",
"Furthermore, it appears that some diseases ",
" go the other way. In particular, ",
"tuberculosis",
" has been ",
" not so conclusively shown to originate from the ",
" many areas (see ",
"/u/jamimmunology",
" below). ",
"Syphilis",
" may have originated in the Americas as well."
] |
[
"Africa and Europe are close enough that communicable diseases can travel easily between them, so Africans had already been exposed to the diseases brought by Europeans. The diseases that the Europeans struggled with, like Malaria and Yellow Fever, are dependent on local factors, such as requiring particular (usually tropical-specific) vectors like mosquitoes to spread, which meant that these diseases never spread to Europe. So when Europeans arrived, they were highly susceptible."
] |
[
"Here's my understanding:\nFirst, remember that the Americas had been isolated from the Old World prior to colonization. Second, remember that Africa actively participated in trade with Eurasia. Third, Africa is a tropical continent. In the Americas, Europeans brought in many new diseases that the natives had never been exposed to, like smallpox, as you mentioned earlier. However, in Africa, the Africans were already immune to many of the Europeans' diseases, but the Europeans weren't immune to African diseases. According to Jared Diamond, Africa's tropical environment makes it a great place for microorganisms. Think about how hospitals are always cold to sterilize everything.",
"So, basically, in Africa, the Europeans met more new diseases than they introduced, whereas in the Americas, the Europeans introduced more new diseases than they met.",
"Hope that helps!"
] |
[
"How are “bits” stored in computer memory?"
] |
[
false
] |
How are “bits” stored in computer memory? Surely a memory isn’t a vault where 0s and 1s are locked. So what IS memory exactly? Additionally, memory-as-abstraction is understandable but how do tape, CD (metal), and “solid state” store anything? Please humour me here as I am really perturbed. I have understood basics of Panpsycism but not computing. I don’t do well if I do not get an expansive bird’s-eye view, and I haven’t got one in electronics and computing. So further additionally, 1. Is “Computing” and “Computer Science” a hard-science or rather a technique/ heuristic/ culture/ convention/ framework/ art? Was computing/ computer science “invented” or “discovered”? 2. Is there a book that explains - even if superficially - EVERYTHING about computers - from voltage, to bits, to memory, to assembly, to code, to machine learning, and now biological and quantum computing? 3. Can computers be coded in binary - or rather by taking a switch and turning it on and off with a certain rythem? 4. What are assemblers? 5. How were programming languages made? If programming languages are made on preexisting programming languages then how were those preexisting programming languages made? 6. Can new computer architecture be made? 7. Why is Silicon so special? 8. Why is computing and coding so English-heavy? Many thanks!
|
[
"In a simple computer, memory state will be represented by a literal \"is current sufficiently flowing here\" check. If it is it's one value, and if it isn't it's another. ",
"1 Hard science. Software Engineering can be a bit softer.",
"3 Which computer? There is at least one that exists that works like that, but your everyday personal computer does not.",
"4./5. In processor design there are \"instructions\" that make the CPU perform a specific operation. These instructions are bits/bytes with optional parameters. If you were to make a simple computer, you could \"force\" the instruction through manually flipping bits.",
"Programming languages compile down to something that sends the CPU the instructions it was built to understand. Assembly is fairly close to the instructions a CPU supports. Although, it's far more complex with modern CPUs because x86/amd64 CPUs don't usually run the instructions like older x86 processors - the instructions themselves have become an abstraction/high level language for a far more complex underlying system.",
"Instructions and their parameters are simply bits/bytes/numbers parsed",
"6 New computer architectures are made all of the time, but this question needs more clarity. Most computer architectures are based on the von Neumann architecture. Read up on it a bit, wikipedia's overview is fine, it will answer many of your questions!",
"7 Silicon is an excellent semiconductor. To define semiconductor, let's look at two extremes that wouldn't work well for a processor. Metal, which lets current flow freely through it, and plastic, which doesn't let any current flow through. A semiconductor allows you to control the flow.",
"8 Historically, not so much. You programmed older computers with numbers, perhaps on a punch card, and there'd be a sheet telling you the instructions and their inputs. In modern day, where it originated from and English being the defacto language of the academic world. Another factor is a relatively simple character set that is supported across many languages and scripts. Supporting more complex character sets is a non-trivial problem.",
"The most visible example of simple computers in 2019 are minecraft redstone computers. Watching some videos or reading up on those will go over pretty pure implementations of simple processors. If you wanted to learn without the abstraction, you'd likely learn about gates, registers, and alu (arithmetic logic unit). At that point you could figure out how to build your own simple computer. Looking for \"8 bit computer tutorial\" or something could also be useful."
] |
[
"I have understood basics of Panpsycism but not computing.",
"Good grief.",
"A 0 or 1 is an abstraction of a physical state of a soild-state device, usually a Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) during logic operation (i.e. \"computing stuff\") and either a series of them in a specific pattern to make a memory cell, such as DRAM or SRAM, for fast memory and something in a persistent state in a floating-gate transistor for \"long term\" memory (the basis of SSDs)"
] |
[
"Silicon is special because of its place on the periodic table. It is able to act as both a conductor and an insulator, both passing electrons but also able to prevent them from being passed, depending on the physical arrangement of its atoms. This allows it to be used for “transistors” — physical structures that can be switched between a conductive and resistive states, using “gates” and latches. The basic building blocks of all digital computing are “and”, “or” and “exclusive or” gates. Silicon allows you to make these gates really really small. You can also build them out of dominoes, plumbing, or just about anything else, but they will be significantly larger and slower."
] |
[
"Can there be a physical description of consciousness? How could quantum physics help explain it?"
] |
[
false
] | null |
[
"Yes but the brain is too complicated for us to know what it is yet. Give it a few decades. It's unknown whether quantum effects play a role, but based on the energy of synapses I'd say no."
] |
[
"You could have a physical description of ",
", and call it \"consciousness\". In fact, many biologists do. But the lay concept of consciousness just isn't defined well enough to give a physical description of it as a whole.",
"It is very unlikely that quantum physics can help explain it. If our consciousness were connected to quantum mechanics, that would be convenient philosophically (among other things, it would make free will and determinism compatible). But neurons aren't really small enough to do any sort of quantum processing, so from all we know any property of our minds cannot be linked to quantum behavior."
] |
[
"I have a question for you: Can you imagine an experiment which would empirically distinguish between the presence of consciousness and the absence?",
"This is a good trick to play to determine whether the question you are asking actually makes any sense. Try it with free will, \"perception\", life-force, and any other mystical wishy washy concepts you don't understand. ",
"As for QM, it is not mystical, or somehow philosophical. I recommend you to this ",
"extremely good introduction for the lay-person"
] |
[
"[Paleontology] What were lizards like when dinosaurs walked the earth?"
] |
[
false
] |
More specifically, what were lepidosaurs like during the Mesozoic Era? I looked into it and found out that dinosaurs and birds are archosaurs, whereas lizards and snakes are lepidosaurs. It made me wonder what kind of lizards were around in that era. If the question is too general, feel free to give your favorite examples.
|
[
"The biggest difference is probably that mosasaurs, which basically are weird monitor lizards, existed. Another difference is that, during the Mesozoic, snakes were still losing their limbs - hence you have a bunch of fossil snakes with two (or, in the case of ",
", four) limbs. Otherwise, regular anatomical variation aside, Mesozoic lepidosauromorphs were pretty same-y."
] |
[
"With lepidosaurs and some other reptiles, you're not going to notice extreme differences between now and the Mesozoic. They likely looked the same as they do today. However, the tuataras, primitive lepidosaurs, were shown to have some anatomical changes since its origin. Some crocodilians as well. ",
"I can't remember off the top of my head what primitive crocodile answer had that were lost (I think it was a feature in the skull?), but some forerunner crocodilians such as Sarcosuchus couldn't do the death roll like extant crocodilians of today due to some difference in skull structure."
] |
[
"Sarcosuchus most likely swallowed prey whole, according to ",
"this article",
"."
] |
[
"Is there a possible scenario where two events, A and B, can occur as: A then B, A and B simultaneously, and B then A, all using three different relativistic frames?"
] |
[
false
] |
Say two events occur: A and B. Is it possible to have a frame R experience A then B, a frame R' experience A and B simultaneously, and a frame R'' experience B then A, all within our universe of physics? I am unsure if this would imply that it is simply three frames with three different accelerations, or if one frame would require time to be moving in the negative direction. EDIT: Thank you for the well put responses.
|
[
"Let's answer this in SR. Forget about GR.",
"Given two events A and B, we can consider the invariant spacetime interval between them:",
"(Δs)",
" = -(Δt)",
"+(Δx)",
"+(Δy)",
"+(Δz)",
"The notation \"Δt\" means the difference in the time coordinate between the events, and similarly for Δx, Δy, and Δz. The two events can be classified into three categories (assume that A and B are different events):",
"Timelike separated events are those events for which a massive particle can, in principle, travel between them. Lightlike separated events are events connected by a light signal. Spacelike separated events are events so far apart that not even a light signal could have traveled between their spatial locations in the required time. Note that the number (Δs)",
" is the same in all reference frames. So if A and B are timelike separated in one frame, they are timelike separated in all frames. (Similarly for lightlike and spacelike separated events.)",
"Now to answer your question:",
"The temporal order of A and B is the same in ",
" reference frames IF AND ONLY IF the events can be joined by a signal traveling at or below the speed of light.",
"There are some other interesting properties these events must satisfy:",
"If A and B occur at the same space location in the frame ",
" (from which it follows that A and B are timelike separated), then their temporal order is the same in all reference frames and the least time separation between A and B occurs in that frame ",
".",
"If A and B occur at the same time in the frame ",
" (from which it follows that A and B are spacelike separated), then there is no limit on their time separation (it can be any real number) and the least space separation between A and B occurs in that frame ",
"."
] |
[
"TLDR:\nYes it can happen. In fact, it's usually what happens with things that you think of as happening \"at the same time\" but in different places."
] |
[
"'Arrival of light from an event' is not what the relativity of simultaneity is about. This is trivially different for different observers even in Newtonian mechanics. SR is about the ",
" event, not the received light; in other words, if you receive light at time t from a distance d, you then compute that the event happened at t-d/c. All of the (relatively stationary) observers in your example ",
" the events A and B to happen simultaneously even though the light reaches them at different times.",
"This issue, which seems like a silly semantic difference, is one of the most common stumbling blocks for understanding relativity!",
"(Also, yes, GR complicates the scenario somewhat, because you have to specify how you are determining the time and position of distant events. The basic picture of time/light/spacelike separation is preserved, but not with the same simple formulas.)"
] |
[
"If you could look further enough into the night sky in two different directions and saw the early universe, would the same objects be visible?"
] |
[
false
] |
I recently read somewhere recently that if we had a really awesome telescope capable of looking far enough into the night sky, we would be able see the very early universe being formed. From that I began thinking: the further we look into space, the more time will converge because of the laws of physics... so wherever we look we will start to see the same things appearing - we are literally looking through the curvature of space, as the expansion of the early universe reverses, right? But if I had two of these fantastic telescopes and pointed them in different directions, will the same objects be visible through both telescopes due to the convergence? If no, why not? If yes, is this a phenomenon or just a feature of space time? Must apologise if this sounds a little nooby to those answering, my terminology must really be lacking!
|
[
"I recently read somewhere recently that if we had a really awesome telescope capable of looking far enough into the night sky, we would be able see the very early universe being formed.",
"We have these. Unfortunately the very early universe was opaque so light can't travel through it.",
"I'm not sure about the rest of your question. What do you mean by time converging?",
"The universe is most likely infinite and flat (parrallel lines dont' converge). The observable universe is a sphere of light that has had a chance to reach us."
] |
[
"I think he might be under the assumption that by looking \"into the past\" you're also looking \"towards the centre of the Universe\", or something to that effect."
] |
[
"Yes. But still, even if we were to view the opaque early universe, wouldnt it be of a smaller surface area? If so, wouldnt space time be bending to accomodate this viewing from our position as it would be literally a window into the past, therefore you could see a lot more than what would normally be visible?",
"I'm trying to wrap my head around the concept of space-time here."
] |
[
"Is there a remnant of the womb in males in same way the clitoris and penis are related?"
] |
[
false
] | null |
[
"Well, since other answers already point out why your question is wrong, I should probably give an answer to the question you meant to ask about equivalencies. There's quite a lot to explain but you can read the appropriate chapter in an embryology book or this will have to do. before anyone tells me off, there are probably some mistakes, yes, this is a simplified overview.",
"the urogenital system - look at that word. yes, their developments are very closely linked; kidneys and reproductive tracts. We can't talk about one without talking about the orther. Kidney development goes through 3 stages. The pronephros appears and then quickly disappears in week 4 of development. It's basically vestigial. The mesonephros appears during the end of that week and is the next stage. It has tubules called mesonephric ducts which attach to the bottom of the mesonephros and act as the collecting ducts for the filtrate from it. The next and final stage is the metanephros which become the permanent kidneys but we won't go into that.",
"At about the same time as the mesonephric tubules develop, parallel tubules develop which originate from about the same place called paramesonephric tubules. Even though the mesonephros is the 2nd stage of kidney development, when the metanephros takes over its job, the mesonephros develops into the gonads. Well, some of it does. The rest degenerates. ",
"So now for the development of the reproductive tracts. The mesonephros has two outgrowths to it which become the gonads (i.e. testes in males and ovaries in females). The rest of the mesonephros shrinks around the gonads when its degenerating.",
"If you're male, the mesonephric ducts will stick around and the paramesonephric ducts will degenerate. If you're female, the opposite happens. This is important in answering your question about the uterus 'equivalent' in a male as you'll soon see. ",
"In males, the mesonephric duct becomes the epididymis, vas deferens and the related tubules around it which carry sperm away from the testis. In females, it withers away to leave remnants which don't really do anything, called the epoophoron, the paraophoron and occasionally left in the vagina, something called Gartner's cyst. So yeah, look those up if you're interested.",
"Now for the paramesonephric ducts (here's where I answer your question). In females, they fuse (you have two because of symmetry remember) at the base and the septum between them degenerates to leave a space which then gets bigger and becomes the uterus. The rest of the unfused paramesonephric ducts become the fallopian tubes and their ends lie next to the ovaries. The base actually extends out and also forms the top 2/3 of the vagina (remember that the vagina is the muscular tube not just the opening). So that's where the uterus comes from - the paramesonephric tubules. What happens to them in males? Well, they degenerate to leave just two remnants: the appendix testis and the prostatic utricle. The appendix testis is a little lump on the top of the testis so you won't be able to see that, and the prostatic utricle is a tiny pit in the prostatic part of the urethra so you won't be able to see that either.",
"Answered [clumsily]?"
] |
[
"The penis (or clitoris) can't really be considered a \"remnant\". The both develop from a common structure, and they grow into one or the other depending on the sex of the person.",
"The uterus, Fallopian tubes, and upper vagina develop from Mullerian ducts in an early female fetus. Hormonal differences in male fetuses cause these ducts to disappear.",
"TL;DR - No, there is no \"male uterus\""
] |
[
"There can sometimes be some remnants of the paramesonephric duct (the embryonic structure that gives rise to the uterus aka the meullarian duct) in men. The remains are mostly just tiny, cyst like remnants in and around the vas deferens/epididimus and are of little to no consequence. We only know they exist because one time someone got a cancer in it, and the pathologists couldn't place the tissue type."
] |
[
"What are some of the smallest animals in the world that spend their life together as a family?"
] |
[
false
] |
[deleted]
|
[
"Ants and wasps are probably a good contender. There are some very small ones and each colony is one big family.",
"edit:",
"here ya go",
"Dicopomorpha echmepterygis is a parasitic wasp in the family Mymaridae. ",
" Females are 40% larger. The eggs and larvae of this wasp are considerably smaller than the adult.",
"This species from Costa Rica is an idiobiont parasitoid of the eggs of a lepidopsocid barklouse, Echmepteryx hageni. ",
"; similar life histories can be found in the wasp family Trichogrammatidae, also in the superfamily Chalcidoidea."
] |
[
"Here are some primates",
" - monkeys that live in family groups.",
"\"Father\" + Mom + kids. Everyone helps raise the youngest in what is known as cooperative breeding. Humans are cooperative breeders as well. "
] |
[
"Portuguese man o' war"
] |
[
"How do fingerprints regenerate?"
] |
[
false
] |
I cut my finger recently and I noticed that the fingerprint was regrowing to exactly how it was beforehand (obviously, since fingerprint recognition would be a bit useless if we didn't). So how does the body regenerate something (not just fingerprints) so accurately?
|
[
"Fingerprints are the result of dermal ridges between your dermis and your epidermis (see ",
"dermal papillae",
"). Skin growth, on the other hand, occurs as the basal layer of the epidermis (so it's right above the dermis). This means injuries that are superficial enough not to damage the basal layer (e.g., minor scrapes and abrasions) will not affect the fingerprint.",
"However, some cuts can get pretty deep. If you don't take care in stitching your wound up, you can in fact misalign your fingerprints such that the ridges no longer flow continuously across the scar tissue. You can see some examples ",
"here",
" (PDF)."
] |
[
"Mildly not suitable for life? That seems contradictory."
] |
[
"Mildly not suitable for life? That seems contradictory."
] |
[
"Is it possible to know long after-the-fact if a person ever had CoViD-19, even if they were largely asymptomatic and never got tested while they were an active case?"
] |
[
false
] |
[deleted]
|
[
"You could test the blood for antibodies, though we don’t know which test works well, we don’t know that antibody-based defenses are actually what’s clearing the virus, we don’t know how long antibodies last. ",
"Technically, given unlimited funds and a research lab, you can test to see if your T-cells respond to SARS-CoV-2 antigens. ",
"But in reality, we don’t have a great way to tell if you’ve had it with any confidence. And even if we did, and we found you had antibodies or active t-cells.....we wouldn’t know how effective those would be against a new infection or how long those protections would lasts",
"There’s a lot we don’t know."
] |
[
"I know they were using the Abbott antigen test as it’s super fast. There were some questions about the accuracy of the test.....but there are questions about that for all the tests",
"The Abbott test looks for virus protein, so if you had it weeks or months ago you should not have any virus particles in your body."
] |
[
"I mean it’d be nice to know what test they use in the White House. I watched Dave Pourtney and his crew go in and they had results in 5 minutes"
] |
[
"Do some galaxies in the universe have smaller orbiting galaxies like a moon or satellite?"
] |
[
false
] | null |
[
"Yes! Our galaxy, the Milky Way, does. There are many smaller galaxies that orbit the Milky Way, ",
"see here for a list",
". ",
"The two best-known satellite galaxies of the Milky Way are the ",
"Large",
" and Small Magellanic Clouds. These small galaxies are so close and distinct that you can see them with the naked eye in the southern hemisphere. "
] |
[
"As do two close neighboring galaxies, Andromeda and Triangulum. It is thought that all galaxies have orbiting dwarf galaxies. Also, these dwarf galaxies are occasionally absorbed into the galaxy they orbit."
] |
[
"To visually add to this, here's an image of the Andromeda Galaxy, and two of its satellite galaxies"
] |
[
"Why there are no blue people, green people, etc., when there are blue birds, green birds, etc.?"
] |
[
false
] |
Mammals and even monkeys have a range of different colors and patterns. But the great apes are "monochrome". Why is that?
|
[
"Mammals and even monkeys have a range of different colors and patterns. ",
"You say that, but in truth, mammals only produce two types of pigment; eumelanin (black-brown pigment) and pheomelanin (reddish-yellow) - which is why, with little exception, almost all mammals have a sort of 'earthy' colouration. There are no green mammals",
", no purple mammals, and almost no blue mammals - the latter only appearing ",
"blue in parts",
", not due to any pigment, but by a physical phenomenon known such as the ",
"Tyndall effect",
" or coherent scattering, where light is scattered in the skin by very fine collagen fibers n' cellular structure. ",
"As it happens, all tetrapod animals (everything with four limbs) rely only on these two coloured brown-ish n' yellow-red-ish pigments, and the symphony of colouration you see in, say, amphibians and birds is likewise due to taking advantage of some physical light scattering phenomenon. Green frogs, for example, combine the Tyndall effect, to produce blue, with yellow pigmentation (from pheomelanin) in their skin, to look green. Many birds, alternatively, use ",
"microstructures",
" within their feathers to scatter light in particular ways to produce green or blue colour and ",
"iridescence",
".",
"So why don't mammals take advantage of these scattering phenomenon more often to become as colourful and resplendant as their ",
"bird",
" n' ",
"cold-blooded",
" contemporaries?",
"Well, turns out mammals were nocturnal for an incredibly long period of their evolutionary history - going right back beyond the dawn of the dinosaurs. For this reason, mammals lost two of the four genes that encode for colour vision in tetrapods, leaving them with very poor colour vision - which most mammal groups still retain to this day. Unable to see colour as, say, we do, there's little selective pressure on most mammal groups to therefore don the rainbow and strut about in style. Instead of colour, mammals therefore rely on shading and patterning as a means to both camouflage (tiger stripes, leopard spots) or display (skunk stripes).",
"Colour vision has however reemerged in a few mammalian groups - which leads us back to primates. If you're primarily feeding on fruit and leaves, it's important to be able to distinguish when a particular foodstuff is ripe and ready to eat and no longer bitter and poisonous, and the best way to do that is often via colour. Hence why monkeys and other primates see and utilise colour.",
"As for why we and the other great apes don't have ",
"fabulously blue butts à la the mandrill",
", well, rather unsatisfyingly, there simply was never any selective pressure for us to start considering that sort of thing as attractive. Like most mammals, including most primates, we stuck to the usual brown-yellow-red-ish eumelanin-derived hues.",
"Perhaps though, if we started preferentially banging people who look maybe slightly a bit blue, we might just manage to populate the Earth with blue men in a million years or so. It ",
" possible! Da bu dee da bu da... ",
" ",
" ",
" ",
" ",
" ",
" "
] |
[
"Is the greenish tinge in the sloth due to algae growing in its fur?",
"Yup! I mentioned that at the very bottom of my post. ",
"Sloths and various algae have co-evolved a rather novel symbiotic relationship, which itself is host to a surprisingly diverse ecosystem contained almost entirely within the fur of the beast. Three-toed sloth hair itself has evolved to promote algal growth sites, containing grooves and cracks allowing algae to take hold. ",
", a green algae found nowhere else but sloth fur, quite happily takes up residence; providing camouflage in return for shelter and a decent amount of water (sloth fur is like a sponge and retains moisture for lengthy periods of time).",
"The tangled algal fuzz is then home to a variety of wee critters, including ",
", a moth that, again, lives entirely on and around the bodies of sloths. Almost unbelievably, it's the existence of this moth that might explain why sloths, rather strangely, climb down from the trees about once a week to poop on the ground in one of several favourite spots (instead of taking a dump in the canopy and letting it just fall away). These moths, which live in the fur, lay their eggs in sloth dung and wouldn't find it if the sloth just let it go any old place. By coming down to the ground, revisiting the same ol' poop sites, the sloth encourages the moths to successfully lay their eggs, returning to pick up the hatched young next time it visits. By promoting the moth lifecycle, the sloth itself gets positively infested with 'em - which is good for the sloth as when the moths die, they provide essential nutrients to the algae growing in its fur, thus promoting fresh green growth and the success of its own camouflage.",
"Nature is ",
" sometimes!",
" ",
" ",
" "
] |
[
"Awesome answer, thanks! I had no idea that even frogs and monkeys use structural color instead of blue and green pigments."
] |
[
"How did we discover that atoms like carbon and oxygen and many others came from high mass stars?"
] |
[
false
] |
[deleted]
|
[
"We read the emission spectrum from the stars, which show that those elements are present in stars. Also, heavier elements can only be originated by fusion, and we only know that to happen in stars.",
"And the Big Bang didn't create any atoms, it created the fundamental particles, which once the universe had cooled enough, where able to get together and form hydrogen, helium and a very little amount of lithium, as it's just simpler to make these (you dont need to cluster as many particles), especially hydrogen as it's simply a proton and an electron.",
"Later, when stars formed, the ridiculous gravitational forces allowed hydrogens to become helium, heliums to become carbon, etc."
] |
[
"To expand on this, the process of forming these early atoms is called ",
"Big Bang Nucleosynthesis",
". More or less, it become favorable to make certain combinations of particles as the temperature of the universe decreased. (If it is too hot then it is not energetically favorable to be for example Deuterium (1 proton 1 neutron) rather than a free proton and a free neutron.) The reason why you don't see every atom made from this process is that once you get to larger atoms the reactions become unstable and decay back into their constituents so quickly that they can't go on to form even more complex atoms. The only way to overcome this hurdle with basically just hydrogen and helium is through nuclear fusion which is made possible by stars."
] |
[
"http://en.wikipedia.org/wiki/Stellar_nucleosynthesis#History"
] |
[
"Is there a science to bidding at auctions? Should you bid hard and fast to avoid others getting the rush of feeling like its theirs or wait for the last second to strike? What's the optimal strategy and does it depend on situation?"
] |
[
true
] |
[deleted]
|
[
"In an ",
"English auction",
", the best strategy is to continue bidding in small increments until the price reaches your personal value for the item. If you're buying a horse and it would be worth $1000 to you, bid up to $1000 then stop. It sounds stupid, but that's the optimal strategy.",
"The only trick is that if you don't know the true value of an item, you may be able to get information about its value by watching how others bid. In this case your strategy is still the same, except that you update your valuation as the auction progresses.",
"The optimal strategy assumes that the other bidders are rational, which is often not the case. Many people will get an emotional attachment to the item or feel rivalry against other bidders, so it's best to avoid any emotional engagement at all with the other bidders. It only takes one rival to bid up the price, so even if you can somehow scare away most of the other bidders, any tiny risk of attracting a fighter makes it not worth it. It's better to be cold and disengaged."
] |
[
"As pure game theory your strategy is optimal, but in most auctions, the bidders are humans, and as such have a biased rationality that will make them do some systematic errors. Exploiting these errors could lead to a more efficient strategy than one assuming that the other bidders are approximations of perfect rationality."
] |
[
"Editted. Let's say it's a run of the mill house auction."
] |
[
"Does an equation exist which is used to calculate the melting temperature of compounds?"
] |
[
false
] |
Does an equation exist which is used to calculate the melting temperature of compounds? Research tells me that melting temperature is determined by the ion and covalent bonding, but that was all that I could find. If there is such an equation, could you please provide a link to the source to confirm? Thanks in advance for any guidance. This is needed for the production of a prototype for a new type of battery cathode.
|
[
"Although we can predict that a phase transition should exist quite often, the specific temperature for the transition is, in general, non-universal. Even knowing the basic reasons for the solid-liquid transition, it is generally a collective behavior, meaning that simply knowing the building blocks isn't enough.",
"In condensed matter, we can make approximations to get an estimate for the transition temperature (e.g. spin wave theory), but even for toy systems these approximations are uncontrolled, and can be fairly far off.",
"Often to find the transition temperature we require numerical simulation, and that is expensive. There are probably some guidelines / rule of thumb from metallurgy or applied material science, those might give you a good starting estimate."
] |
[
"IIRC You can calculate the boiling point of a compound via the Clausius-Clapeyron relation, so long as you know the latent heat of vaporization. (",
"https://redirect.viglink.com/?format=go&jsonp=vglnk_148378206159912&key=6afc78eea2339e9c047ab6748b0d37e7&libId=ixn1hd7j010009we000MAb7tgzjdf&loc=https%3A%2F%2Fwww.physicsforums.com%2Fthreads%2Fcalculating-the-boiling-point-of-water.304437%2F&v=1&out=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FBoiling_point%23Saturation_temperature_and_pressure&ref=https%3A%2F%2Fwww.google.com%2F&title=Calculating%20the%20boiling%20point%20of%20water%20%7C%20Physics%20Forums%20-%20The%20Fusion%20of%20Science%20and%20Community&txt=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FBoiling_point%23Saturation_temperature_and_pressure",
") From my humble opinion (~6 years of physics) I would say classical thermodynamics is a very empirical field (trying to match experiments, find working relations, might be missing fundamental 'why' for the sake of 'well it works') and it was really the exploration into the 'why' which birthed Quantum Mechanics. A detailed course in Condensed Matter (aka solid state physics) will eventually describe a manner in which to calculate the heat capacity (dU/dT) in a material given its lattice structure, but that's actually the most detailed explanation of a theromdynamic property I've seen in the context of your question. It's a fairly long winded story which doesn't really answer your question so I won't drag on. "
] |
[
"The melting point is the temperature at which the Gibbs free energy of the liquid and solid phases are equal. Calculating those would involve the so called entropy and enthalpy of mixture as a function of the temperature. For that one would need to know the exact structure of the solid material and how ordered it is. ",
"If you wanted to predict the structure too, you would need to consider every possible structure and find the one with the lowest Gibbs free energy(that would be really hard).",
"Even with the structure it's hard to get the temperature dependence right. Also I'm assuming you know the exact composition of the material. Small impurities would typically lower the melting point. Bigger ones would alter the structure.",
"If you wanted to measure the melting point instead, it would be best to melt the material first, then slowly let it cool while measuring the temperature. At the melting point, the temperature will remain constant for a short time for the first time. This will also get you the temperatures of other possible phase transitions below the melting point. Those might also be of interest, since they could change the behavior of your material making it unfit for a cathode at temperatures way below the melting point."
] |
[
"Why aren't Higgs bosons everywhere? (And a few other related questions.)"
] |
[
false
] |
The Higgs field permeates all space, and all fermions in the universe (that we know of) (I think) have mass, so where are all of the Higgs bosons to maintain that field? And on a related note, since Higgs bosons everywhere, are there possible unintended consequences of smashing particles together to make one? Finally, do we know (or think) that the Higgs field extends throughout the entire universe, or are there potentially Higgs-free zones where particles lack mass?
|
[
"Higgs bosons don't maintain the Higgs field, nor do photons maintain the electromagnetic field, etc. These particles are excitations of their respective fields. The fields exist whether there's a particle there or not. ",
"Not really. We have a pretty solid idea of what the Higgs boson is like. We could, of course, be wrong about something or have yet to discover something new about it, but that's unlikely. ",
"The Higgs field is an all-permeating field. That description was redundant, though; a field, by definition, exists in all space and time. There's no escaping it. "
] |
[
"Be careful when you say the Higgs boson \"maintains\" the Higgs field. This isn't really a good description of what the Higgs is or does.",
"Like others have mentioned, the Higgs boson is just an ",
" of the Higgs field. Similarly, there are other gauge bosons which mediate their respective forces. However, and this is the important part, particles do not need to interact with Higgs boson to interact with the Higgs ",
".",
"In the standard model, all the fundamental forces are ",
" by the gauge bosons which \"carry\" their respective force, but that is different from the Higgs interaction, which gives most particles mass because the Higgs field has a non-zero expectation value. "
] |
[
"To add to owl's comment, The Higgs boson is unstable. It decays ",
" quickly compared to human detectable timescales.",
"Broadly speaking, the LHC deduces the existence of the Higgs (and many other unstable particles) by examining the decay products very carefully over a large number of collisions."
] |
[
"As scientists, what things do you wish your physics/science teacher had told you in high school?"
] |
[
false
] | null |
[
"A bit of a boring one to start with but it was surprisingly late in my education before I realised just how important maths (or math if your american :P) is in science. Maths always seemed so abstract and pointless to me in my early education. Then I realised that you can't do science with out a good mathematical grounding and so then I put the effort in to learn it and actually enjoyed it in the end. I think I was lucky and realised this just in time but many of my friends didn't and as time went on, found science subjects more and more difficult. And so these people didn't carry on into further science education, not because they aren't interested but because they don't have the mathematical skills required.\nSecondly, as a biologist, I wish I was told what DNA and genes are and how their code creates proteins a lot earlier. We were always given vague ideas about how DNA is in the nucleus and this controls the cell but I'm sure I could have understood it earlier if explained properly. This may also help to dispel common misconceptions people have about genetics. \nAlso, teach evolution! Try to show them the overwhelming evidence as simply as you can and hopefully they will be able to come to their own conclusion. I'm from the UK so this isn't much of a issue here fortunately but if you're in the fundamentalist parts of america, this is important. Also, if you want to inspire the younger generation, show them anything to do with NASA. NASA is awesome. Tell them that they can go out and see the ISS flying over head. Show them videos of what it's like to orbit earth, the moon landings and pictures of what it's like on mars from the curiosity rover. If that doesn't get them interested in science I don't know what will :)"
] |
[
"Calculus, dimensional analysis. The importance of understand concepts as opposed to memorizing formulas or equations. Applications to the real world for the lesson you are teaching. Applications of maths as you teach it(Like show how integrating a velocity curve is useful when you teach integration) "
] |
[
"Thanks for your reply. I'm from Australia, so evolution is not such a controversy in the classroom here. I've done a few workshops on how to explain DNA, so it's good to know how important the explanation is. Good tip about NASA, I've got a few HD orbits from the ISS. Beautiful."
] |
[
"Steep hill > car in front starts rolling back > move forward to meet it or stay still?"
] |
[
false
] |
[deleted]
|
[
"It depends on how fast you're going when you meet it, if you decide on that route. The other car will have a velocity like ",
". So basically the longer it's rolling backwards, the faster it's going. But if you're far back, and you have to accelerate to meet it, your combined speeds might be higher than they would be if you hung back. If you were skillful enough to accelerate then decelerate the correct amounts, you might come out ahead. If you're driving a stick you could even accelerate up to meet bumpers and then roll back a little to decrease the impact.",
"Maybe the best solution would be to get as close to the front car's bumper as you can before they start rolling back."
] |
[
"Would it be better to let the bumpers meet while you're in neutral, then slowly use both vehicle's brakes (or just yours, if theirs went out) to slow the descent?"
] |
[
"Regardless of the science, the police might fault you for running into him."
] |
[
"Why do we as humans often times feel he need to feed wild animals such as birds and fish when we get nothing in return?"
] |
[
false
] |
Obviously there's the "because we enjoy it" answer but I guess my real question is why do we like to feed animals that we aren't keeping as pets when there is nothing in it for us?
|
[
"Do you think that feeling compassion towards animals accelerated/facilitated domestication?",
"And if so, would that count as a selection pressure (i.e. altruism towards animals would be advantageous rather than just a side effect)?"
] |
[
"Do you think that feeling compassion towards animals accelerated/facilitated domestication?",
"And if so, would that count as a selection pressure (i.e. altruism towards animals would be advantageous rather than just a side effect)?"
] |
[
"I'd like to add a few things to this. First, this behavior has also been noted between other species of animals, which is not surprising if there's a biological basis for this behavior in humans. Second, there is an assumption in the question that we get nothing from it, but to the degree which satisfaction is derived from the activity there certainly is something we get from it. Internal drugs, by which i mean naturally occurring neurochemicals, can be rewards in themselves. Finally though it's not the answer OP wanted, why we enjoy it is not a truly answerable question. While I buy H2C2O4's answer, like all evolutionary psychology we can't structure an experiment which actually proves it. These just-so stories, while convincing, have historically been quite suspect."
] |
[
"how do those headphones/microphones work that they use on helicopters, how can people talk without all the helo noise coming through as well?"
] |
[
false
] | null |
[
"The older passive noise canceling headphones have insulated earpieces pushed hard against your head.\nDavid Clark, one of the popular brands of headset manufacturers, are sometimes called David Clamps from forcing the earpieces against your ears.",
"The microphones are muffled and filtered such that you need to really speak up to be understood and even then it’s hard to pick out what they’re saying. Older versions even clamped a microphone to your throat.",
"New active noise canceling headsets have sound processing computer chips and amplifiers built into the earpieces. They use the microphone to detect ambient noise and actively produce the “anti-noise” into the earpieces.",
"Similarly the microphone is actually multiple microphones which detect the noise coming from the microphone pointing at your mouth and compare the noise coming from the other microphones and filter out the noise signal accordingly."
] |
[
"Old technology is a noise cancelling microphone that acoustically subtracts the ambient noise from the signal very near the person's mouth. Now, that can be done electronically, or a combination.",
"https://en.wikipedia.org/wiki/Noise-canceling_microphone"
] |
[
"Actually you can make a mic that is preferentially sensitive to distance, not just direction. That's what has be used for many decades in that application. Now electronic noise cancelling is used as well. Hypercardioid or supercardioid mics are great, but there are better choices for this.",
"https://en.wikipedia.org/wiki/Noise-canceling_microphone"
] |
[
"Is there any evidence to suggest that using birth control for a long period of time would delay the onset of menopause?"
] |
[
false
] |
It is my (perhaps flawed) understanding that menopause begins when the female body runs out of eggs. It is also my (again, perhaps flawed) understanding that birth control prevents the release of eggs. So would someone who started and consistently used birth control at 16 end up going through menopause later than someone who started at 24 or someone who never used birth control at all?
|
[
"Women have hundreds of thousands of eggs, running out of eggs is not the concern. The concern is as women age, follicles either are released or die. The decrease in follicle count and corresponding hormone levels account for menopause. The aging process still affects follicles even if they're not released. It is possible to undergo menopause while actively taking birth control; it's even possible for BC to mask the symptoms of menopause. "
] |
[
"Looks like no:\n",
"http://www.webmd.com/menopause/features/menopause-age-prediction?page=2"
] |
[
"Very interesting, thanks for the reply. My girlfriend and I were discussing this this morning and we didn't know if it had to do with hormonal changes or number of eggs or something else. "
] |
[
"I keep hearing about outbreaks of measles and whatnot due to people not vaccinating their children. Aren't the only ones at danger of catching a disease like measles the ones who do not get vaccinated?"
] |
[
false
] | null |
[
"Sadly, no. Unvaccinated people are indeed at the highest risk, however, while vaccines are very effective, no vaccine is 100% effective. Most childhood vaccines protect between 85 and 99 percent of the population. For some reason, ",
"a small percentage of folks who are vaccinated do not develop immunity",
". This hasn't traditionally been much of an issue because with the vast majority of the population vaccinated for a particular disease, we develop \"",
"herd immunity",
".\" The more folks are vaccinated, the harder it is for a disease to spread, and so epidemics become less likely. ",
"Another issue (though not strictly what you asked) is that some children cannot receive the vaccine. Often this is because they have a compromised immune system thanks to a genetic disorder, or active cancer treatment. While these children cannot receive the protection of the vaccine, they ",
" indeed receive the protection afforded by herd immunity. Unfortunately, as more people choose not to vaccinate their children, immunocompromised are put in particularly bad risk. In the case of measles, these children",
" have up to a 50% mortality rate",
". ",
"/r/askscience"
] |
[
"Also, even healthy babies don't usualy get their MMR until 12-15 months of age, so they're vulnerable. "
] |
[
"After the late 1980s outbreak, an MMR booster was added to the regimen when it became clear that one MMR vaccine was not sufficient. While most younger people have probably had two shots, older people who have not had two shots may also be vulnerable. "
] |
[
"Where does the energy to keep Europa's ocean liquid come from? Conservation of energy question."
] |
[
false
] |
[deleted]
|
[
"I would explain it, but wikipedia does a good enough job"
] |
[
"As Europa comes slightly nearer to Jupiter, the planet's gravitational attraction increases, causing the moon to elongate towards it. As Europa moves slightly away from Jupiter, the planet's gravitational force decreases, causing the moon to relax back into a more spherical shape. The orbital eccentricity of Europa is continuously pumped by its mean-motion resonance with Io.[23] Thus, the tidal flexing kneads Europa's interior and gives the moon a source of heat, possibly allowing its ocean to stay liquid while driving subsurface geological processes.[13][23] The ultimate source of this energy is Jupiter's rotation, which is tapped by Io through the tides it raises on Jupiter and is transferred to Europa and Ganymede by the orbital resonance",
"Wow, that was more complicated than I expected but well explained. Thanks for the link."
] |
[
"It sounds more complicated than it really is. In truth, it's exactly the same mechanism that causes ocean tides here on Earth. Just more so, because we're dealing with larger masses and stronger gravitation."
] |
[
"Black Holes/Neutron Stars-Hot or cold?"
] |
[
false
] |
If matter gets so tightly packed or compressed to infinity in ther case of Black Holes the matter particles wouldn't have room to move or vibrate, yet inuitivley I would think it''s hot as you-know-where.
|
[
"The accretion disk around a black hole can get quite hot as the infalling material is accelerated to relativistic speeds and friction becomes significant.",
"The black hole ",
", however, is generally rather cold. ",
"Wikipedia",
" has the relevant equations for the Hawking radiation temperature of a Schwarzschild black hole (which is close enough for most every day calculations), from which you can see that a solar mass black hole has a temperature of around 0.00000006 K—well below the background temperature of empty space (arising from the cosmic microwave background). And the temperature of a black hole actually ",
" as its mass increases. "
] |
[
"Wrong. Those are the only ",
" properties. The temperature is dependent on those properties.",
"http://en.wikipedia.org/wiki/Black_body#Black_holes"
] |
[
"Thanks for the correction."
] |
[
"How does the cell understand the DNA code?"
] |
[
false
] |
I asked my teachers this in school, but on one gave me a normal answer. To a computer, a code 1010101100101 for example could only be understood because it is programmed with it's definition, or "dictionary" if you will. Just like in a forgoten language, any word would be completely useless without its translation or definition. So my question is, how does the egg for example process the DNA to make a human piece by piece. Where are these definitions for the sequence stored? If it's in the DNA itself? But..then...what? Every time I think about this, my brain kind of brakes.
|
[
"one could argue that all life is is a series of a near infinite amount of chemical reactions occurring simultaneous in response to each other. Probably not the answer your looking for, but I hope you understand that some people devote their entire life to the way only a handful of proteins interact and their purpose. And the possibilities of different proteins that ",
" be manufactured is infinite"
] |
[
"The central dogma of molecular biology is DNA codes for RNA, which codes for proteins. Everything in your body is the result of things coding for proteins that interact with the world. Proteins do everything from copying DNA to digesting food to building bodily structures.",
"So how does DNA -> RNA -> protein? DNA and RNA are made of roughly the same building blocks that like to bind each other in a predictable way. A \"G\" will always bind a \"C\", and an \"A\" will always bind a \"T\" in DNA or a \"U\" in RNA. So, if you split two strands of DNA apart, you can easily transcribe a piece of RNA by just following those rules. For instance, TAC in DNA would pair with AUG in RNA.",
"To go from RNA -> protein, all cells have organelles called ribosomes that translate RNA to protein. These work by feeding a strand of RNA through 3 bases at a time. Ribosomes recruit molecules called tRNA that have 3 bases on one end, and a specific amino acid on the other. These tRNA always carry the same amino acid for a given 3 bases. For example, from AUG mRNA above, a tRNA with TAC would bind. TAC always carries an amino acid called methionine with it (and also happens to be the beginning of every protein before processing). Feed a whole mRNA through, and you get a string of amino acids, AKA a protein.",
"As it happens, nearly every organism on the planet uses the same code for RNA and proteins. AUG codes for methionine in almost every organism on the planet, and starts almost every protein ever made by anything."
] |
[
"But my question is, where are the definitions for the sequences stored.",
"For RNA/DNA, it's in chemistry. G's and C's (or A's and T's) exist in such a way that they really like to bind to each other. You can pull them apart, but they'll always go back together the same way. So, you'll always get the same sequence from the same piece of DNA.",
"For RNA -> protein, not to be circular, but it's coded for in DNA. DNA makes an RNA molecule that binds itself in such a way that it folds up to only bind a specific amino acid. As for where the first tRNA came from, nobody really knows. We do know that pretty much every organism on the planet shares the same genetic code.",
"It's certainly possible for an alien organism using DNA to use some different universal code. We don't know of anything specific that says AUG innately codes for methionine, with all life on earth it just happens to. For you, your body interprets the code this way because every organism for the last 4 billion years has done it this way - it's just the way things are done on Earth.",
"There are some funky organisms that have very slight variations in the universal genetic code, but they're not that significant."
] |
[
"Is there anything particularly special about our solar system's position in the galaxy that helped to facilitate the formation of life?"
] |
[
false
] |
For instance, if we were closer to the galactic core, would it be more likely that there would be too much harmful radiation ("cosmic rays") for life as we know it? Or if we were further out towards the edge of the galaxy, might we not have abundant enough heavy elements from nearby supernovae? Or am I thinking about this incorrectly, and life is relatively equally likely on any rocky world with liquid water, regardless of its position in the galaxy?
|
[
"Yes",
", If we had been closer to the center of the galaxy, the earth would have been hit by supernova explosions more often, which would have inhibited the formation of higher life forms. On the other hand, the abundance of heavy elements is believed to be lower in the outer reaches of the galaxy, which would probably prevent the formation of rocky planets like the Earth.",
"On the other hand, stars can migrate from one part of the galaxy to the other during their lifetime, which complicates the whole issue immensely.",
"Edit: I am not an astrophysicist, so dont take my amateur opinion as gospel."
] |
[
"Wouldn't an abundance of heavy elements actually facilitate the formation of rocky planets? However, ",
"This article",
" states that the inside of Jupiter is actually composed of a mixture of elements instead of layers of less dense ones on top of denser ones, which shows that traditional planetary formation theory could be wrong and could be left out of this discussion.",
"Another reason that the Sun's position in the galaxy helped the formation of life is that it was in a less dense region of stars in the galaxy compared to the region around the core. If a star passed closely to the Sun more often than it does in this area in the galaxy, then the orbit of earth could be change by the passing star's gravitational pull, which could cause the climate to change greatly over a relatively short period of time. Most life that would be alive on the planet would likely be killed any time this happened."
] |
[
"I know of two books, \"Rare Earth\" and \"Privileged Planet\", that cover this question (Note: the authors of \"Privileged Planet\" have clear religious motivations, but \"Rare Earth\" is entirely secular)."
] |
[
"Any basis in the \"use a diamond to break reinforced glass\" trick that moriarty performed on this week's Sherlock?"
] |
[
false
] |
In this week's episode of BBC's Sherlock, Moriarty stuck a tiny piece of diamond onto a glass casing and then struck the diamond with a fire extinguisher. Later on lestrade and sherlock commented that Moriarty was only able to break the reinforced glass because he employed the help of the diamond. I know that diamonds are very hard objects, but I thought that only meant it is more resistant to deformations (such as scratches). I thought the energy of the impact is what determines the amount of damage dealt, not the strength of the weapon. (Stronger weapons only enable more energy before shattering/breaking) I find a hard time believing that fire extinguisher would have shattered if not for the tiny diamond.
|
[
"It's a matter of pressure - force over area. If a fire extinguisher can't break the glass, concentrating all that force over a small point with a diamond can help.",
"It's the same concept when you cut with a knife. You can try to push down on a slab of meat with your bare hand - and succeed in only giving your Angus steak a good massage. The knife concentrates that force and allows you to cut it."
] |
[
"Indeed. Thieves break the ceramic from sparkplugs and use it to shatter the tempered glass in car side windows. Ceramics are similarly very hard and, when broken, incredibly sharp.",
"Difficulty in breaking a car window with a blunt object: ",
"https://www.youtube.com/watch?v=L91_K-s4pMM",
"\nWith a bit of ceramic:\n",
"https://www.youtube.com/watch?v=y83UQ9ljTlE"
] |
[
"I didn't see the episode, but sound like he's making something like a window breaking hammer, like this:",
"http://www.lifehammer.com/",
"Something similar was also used on a Mythbuster show.",
"http://mythbustersresults.com/episode72",
"(no endorsement intended, was unable to find a better link)"
] |
[
"How much erosion does the international space station experience as it moves through the upper atmosphere?"
] |
[
false
] | null |
[
"Would being worn away by dust and suchlike be considered erosion? Is that sort of thing a concern for the ISS?"
] |
[
"Would being worn away by dust and suchlike be considered erosion? Is that sort of thing a concern for the ISS?"
] |
[
"I doubt that atmospheric dust would get as high as the ISS, which orbits at around 200 miles above Earth's surface. In atmospheric terms, dust is actually quite heavy and tends to fall out of the sky within at maximum 20ish days. That part I can find a ",
"source",
" for."
] |
[
"Why do fusion reactors use vacuums when fusion happens in the Sun under extremely high pressure?"
] |
[
false
] | null |
[
"We’ll never be able to achieve the pressures in the core of the sun in a terrestrial reactor. And such high pressures aren’t necessary anyway.",
"The thermonuclear reaction rate has a much stronger dependence on temperature than on pressure. It’s linear in the density, which is proportional to the pressure, with fixed temperature. But it’s generally some power law in the temperature, so ~ T",
", where p is some fairly large positive power.",
"So your plasma can be at a much smaller pressure, but a moderately larger temperature, and still get the same reaction rate per particle as you’d have with a stellar temperature and pressure."
] |
[
"It should also be noted the fusion rate in the sun is rather low. The power output is a few hundred watts per cubic metre in the solar core; the sun owes its enormous total power to its enormous volume.",
"The main factor in our fusion reactors (and bombs) achieving much higher power density is that we use deuterium and tritium fusion while the sun is powered by hydrogen-1 fusion. Hydrogen-1 fusion is much much slower."
] |
[
"The heat output of the sun per volume is actually less than the human body. The sun is just HUGE."
] |
[
"What is going on in the bodies of people with asymptomatic Covid-19?"
] |
[
false
] |
For the approximately 33% of Covid-19 positive people who have no symptoms (but can still transmit the disease), what is actually happening in their interactions between their immune systems and the virus? If they can transmit the disease to others, the virus must be replicating in their cells; why does this not hammer them with the usual symptoms such as coughing and fever?
|
[
"The symptoms you get from COVID aren't due to the virus directly. It's due to your immune response against the virus which causes leakage of your capillaries and tissue damage as your immune cells release cytotoxic metabolites. In asymptomatic people, that response just is more muted and doesn't cause as much cell damage so you don't actually feel symptoms. You're still fighting it off - it's just you're doing it silently."
] |
[
"You’re right on the first vaccine. Your immune system mounts a response that, put succinctly, results in the expansion of cells that can recognize an antigen (i.e. spike protein or other viral proteins) and induce an immune response. The second dose (and boosters) challenge these cells to properly respond to the same challenge and maintain (or increase) the number of cells that can respond. Because these cells are present and can rapidly recognize and respond to the foreign antigen/pathogen, the body can more rapidly fight off the infection and prevent symptoms from occurring. Your immune system is essentially ramping up silently, but that isn’t a perfect analogy. However it’s a decent way of conceptualizing it."
] |
[
"So,if you onlu have symptoms after vaccination one,but not two and three,is your immune system revving up silently,or throwing in the towel?"
] |
[
"Uncertainty in position allows a particle to tunnel from one position in space to another, could uncertainty in time (Energy-Time uncertainty) allow a particle to tunnel from one instance in time to another?"
] |
[
false
] |
[deleted]
|
[
"The energy-time uncertainty principle is different from the others. Usually, you have observables in quantum mechanics which have some sort of probabilistic distribution, and the normal uncertainty relation is given as",
"σ",
" σ",
" ≥ something",
"where σ",
" is the standard deviation of the distribution describing A, and \"something\" depends on the properties of the observables A and B. (\"something\" can be zero, where the uncertainty principle just tells you that standard deviations are positive; it can't be negative).",
"But time is not an \"observable\" in the technical sense I gave above, because there is no probability distribution for the time of the system, so there's no standard deviation. The time is just a parameter which the probability distributions of all the observables depend on. This basically answers your question: time cannot \"tunnel,\" it doesn't have a distribution and can't \"collapse\" etc.",
"So what is the correct statement about the energy-time uncertainty principle? It is the following: Consider any observable (once again, in the sense I have in the first paragraph) B. Now consider the energy, E. The following is true:",
"σ",
" σ",
" ≥ (ħ/2)|d<B>/dt| ",
"Here, <B> is the average value (mean) of the observable B. If the average value of B doesn't change with time, then there's nothing interesting to say here. But if B is changing with time, then there will always be an uncertainty relation between E and B.",
"Let's think about what this means physically. If you have a system where some observable B is changing, then the energy of that system must not be well-defined - instead there is some spread. This must be true, in particular, for any unstable system, since an unstable system is defined as one which is changing w.r.t. some observable. So unstable systems have some distribution of energies which must satisfy",
"σ",
" Δt ≥ ħ/2",
"where Δt = σ",
"/|d<B>/dt| is sometimes called the \"time uncertainty.\" You can think of Δt as the approximate time it takes for <B> to change by an amount σ",
". If this amount of time is large (which happens for stable systems with long lifetimes), then the energy uncertainty is small. Vice-versa, if this amount of time is small (e.g. in unstable systems), the energy will have a very large spread. "
] |
[
"Could there be some weird setup where σB could tunnel, which I guess would be more like tunneling to a different state or something than like tunneling through time per say?",
"Yes, this can certainly happen. The point is that the tunneling rate can often be approximated as what I called 1/(Δt) in my above post.",
"In non-relativistic QM, I think you can have instantaneous tunneling (in that limit, σ",
" goes to infinity). Of course, our universe is relativistic, meaning the Hamiltonian H is such that a measurable observable cannot tunnel outside of its light cone."
] |
[
"That's a great explanation, particular for my level of knowledge of Quantum Mechanics.",
"Could there be some weird setup where σB could tunnel, which I guess would be more like tunneling to a different state or something than like tunneling through time per say?",
"Or just in general, from how I understand uncertainty relations in quantum mechanics (which is limited for sure), it seems that because of the wave nature of the equations there's always a small possibility they could tunnel to a different state, so could any confinement to particular states, combined with this uncertainty and wave-nature, produce some instantaneous change in state?"
] |
[
"Theoretically and still staying in the rules of science of what we know to be facts, is time travel possible?"
] |
[
false
] | null |
[
"The short answer is that we don't know. There are consistent solutions of general relativity that do seem to allow closed time like curves. However, they all seem to require things that don't look physically possible. So for example, ",
"if one has an infinitely long rotating cylinder",
" then time travel becomes possible. Similarly, people have suggested using ",
"wormholes",
" but that would require matter with some extremely strange properties (essentially negative mass). ",
"There's a secondary issue also, which is that there's reason to think that any device allowing closed time like curves would actually self-destruct. See ",
"this paper by Stephen Hawking",
". Right now this looks likely, but the details run into difficulties that can likely only be addressed with a unified theory that combines quantum mechanics and general relativity, which we don't have right now. "
] |
[
"Forward in time, yes. Backwards, no.",
"By going faster than a reference point, time starts to flow slower for you or otherwise said, time starts to speed up for everyone else.",
"Every reference point is equal, so you can imagine a car being stationary while the entire universe moving underneath it.",
"Other than that, we don't know anything about moving backwards through time"
] |
[
"There are plenty of ways this can be resolved - for example, if, hypothetically, wormholes were possible and could lead to time travel, it would still be impossible to travel to a point before wormhole time travel technology was developed (since you wouldn't have a wormhole to exit from) - hence, there is no contradiction when we observe that we have not yet seen evidence of visitors from the future."
] |
[
"Is there any correlation between a person having vivid imaginary friend/s as a child and growing up to have MPD/schizophrenia?"
] |
[
false
] | null |
[
"As far as I can find, not really. There doesn't seem to be a lot of literature in this specific area, but if someone else has found some better resources, feel free to add on to my answer here.",
"Imaginary friends (often called \"imaginary companions\" or ICs in the research) are very common. Not only that, most research indicates that they're largely healthy. An IC gives a young child the chance to work on social skills and essentially practice for person-to-person relationships that they will have as they age. They give kids an external focus for their thoughts and feelings, and parents often (anecdotally) report that ICs help their kids to communicate their problems and fears.",
"On a more longitudinal note, it has been shown that children with vivid imaginary friends are more likely to engage in self-talk as they age, even when the IC disappears. There's a whole debate about the pros and cons of self-talk and how it affects mental health, but that's beyond the scope of this answer.",
"Finally, while I don't think there's a correlation between imaginary friends ",
" and mental illness, there may be a more specific connection. I found a case study concerning a young girl with schizophrenia (source 3 below) who had a \"dominating\" imaginary friend. My understanding from their study was that having a specifically negative imaginary friend or an imaginary friend which does not disappear by adolescence could be a sign of mental health issues. It's not a conclusive relationship by any means, but considering how it relates to your question, I wanted to include it.",
"TL;DR Imaginary friends are good for young children. However, if they are consistently negative or don't go away as the child ages, it ",
" indicate mental health issues.",
"Davis et al., (2014). Children with Imaginary Companions Focus on Mental Characteristics When Describing Their Real-Life Friends, ",
"Brinthaupt and Dove, (2012). Differences in self-talk frequency as a function of age, only-child, and imaginary childhood companion status, ",
"Shapiro et al., (2006). A Dominating Imaginary Friend, Cruelty to Animals, Social Withdrawal, and Growth Deficiency in a 7-Year Old Girl With Parents With Schizophrenia, "
] |
[
"Wow!! I wasn’t expecting this strong of an answer!! Thank you for your help ☺️"
] |
[
"Honestly, the intro section to the second article I cited gives an excellent overview of the self-talk literature. I would start there (if you can access it) and follow some of their citations if you want more info. In case you can't get the full article, I can hit some highlights below.",
"They mention a large amount of research into the positives of self-talk. These include rehearsal of information, self-guidance, goal monitoring, and on and on.",
"There are negatives associated with self-talk as well. Self-talkers (especially frequent ones) are likely to self-criticize and maintain a negative stream of conversation when they talk to themselves. They tend to be largely self-focused individuals, so on and so forth.",
"There is a Self-talk Scale (STS) which has been developed to examine the frequency and way in which someone talks to themselves.",
"There's definitely an interesting discussion happening with regard to self-talk, and it's not at all an open-and-shut case. Hopefully these points can get you started."
] |
[
"What determined the color of rocks, how random is it, and are their traits at all correlated?"
] |
[
false
] |
Rocks (aka, everything, the ground, right?) seem to really vary in color. They range from an orange tan all the way down to a cool purply grey, I think. What determines the change in color? For example, rocks in the desert always look all orange, but then rocks in the mountains look sort of grey. Or is this just lighting, and I'm missing the point? Also, if rocks are indeed colored depending on their type, is there any trends based on their attributes? Or is it completely random? Are darker rocks tougher/harder? Thanks!
|
[
"The colour of rocks is determined by the minerals they contain. Desert rocks appear orange because they have been extensively weathered, turning their various iron-containing minerals into iron oxide (rust). Mountain rocks are fresher, as uplift and erosion is constantly exposing new rock. ",
"There's no real correlation between colour and properties. It isn't \"random\" either, it depends on the minerals in the rock. Quartz and calcite are both light-coloured, but one is hard and the other is soft. For sedimentary rocks, it also depends on how well the grains are cemented together.",
"If you're interested in learning about rocks, try picking up an entry-level textbook. I can recommend \"Earth: Portrait of a Planet\" by Stephen Marshak. "
] |
[
"Thanks! This was very helpful."
] |
[
"Seconding the book recommendation. That was the intro textbook I used in undergrad."
] |
[
"How did people make programs for programming without programs for programming in the first place?"
] |
[
false
] |
I mean, at first there were basically computers which were machines for counting numbers, and then, all of a sudden, people created stuff to write code. How’d they do it?
|
[
"Here's the core of it:",
"https://en.m.wikipedia.org/wiki/Bootstrapping_(compilers)",
"At first, they'd program the program steps by directly coding in the series of zeroes and ones that forms each operation the computer CPU can perform.",
"Then, they used that to make something that would substitute three letter acronyms that are easier to remember than eight zeroes or ones. This is called compiling. You take the easier to read language and turn it back into ones and zeroes. ",
"Eventually, they used those that (assembly language) to write a compiler for the c language. Then they rewrote the c compiler ",
". So at that point you have a program that can compile other programs, but one of the programs it can compile is a copy of itself. This made it easier to manage and add features.",
"This is the grossly oversimplified history of course, since there have been many computers with many languages and I skipped the really old ones that used physical punch cards to program them..."
] |
[
"We solved three basic problems: storage, computing, and logic.",
"We figured out how to control a number of 0s and 1s, store those values in memory, and manipulate that. We then assigned a value system to what a sequence of these mean (in our fictional example, 0011 means 'a', 0011 means 'b'). We can then create a predictable output 1s and 0s, and use math to calculate things.",
"The rest is just repeating this over and over and over again, which is what we've done. We've just created big 'yes'/'no' systems, and shrunk it all down into microchips. As we do this, we can create tiny routines that do even more complex things. We then reuse things that we've already created to make even more complex things. So, we end up with a list of things like this:",
"Program 1) Ability to add acquired.\nProgram 2) Ability to multiply acquired.\nProgram 3) Ability to change the sign of a number acquired.\nProgram 4) Use Program 3 with Program 1: Ability to Subtract two numbers acquired.\n....\nProgram 349) Use Program X, Y, Z: Ability to calculate angles in a triangle acquired.\n....\nProgram 698) Ability to solve calculus acquired.",
"You can go from there to create the ability to store language, and then create text programming languages that are still very core to the ways we work with 1s and 0s, just with more processing time. We then use that new language to create a new more complex language, now called an operating system. The languages we program have to work on whatever operating system is working with the processor language underneath. But then you can create ways again to use old programs to create new ones."
] |
[
"Thanks! \nNow it starts making sense to me"
] |
[
"If the nature of sexual attraction comes from natural selection and the desire to create healthy babies, why am I more attracted to a skinny woman than a muscly woman?"
] |
[
false
] |
For example: I find this: more attractive than this: even though the latter is more likely to produce healthier, stronger, and genetically superior offspring than the former.
|
[
"There are two different questions you are asking. One is why you are more attracted to feminine looking women (without huge bulky muscles). The second, which is implied, is that the bulky muscle women are better suited to create healthy babies.",
"This second assumption is wrong. Women with large muscles often have higher testosterone levels. If those muscles are clearly defined, as in the picture you linked, they probably also have less fat. Both of those factors are actually less conducive to having a healthy baby.",
"High testosterone causes fertility problems in women, as does having too little fat. The ",
" of fat is also important. Men usually find fat around the hips to be more attractive than large bellies. It so happens that fat around the hips is rich in DHA, which is precisely the kind of fat that's needed to produce large-brained babies. Human babies have unusually large heads (and brains), and making such babies is much easier for women who have sufficient fat around their hips.",
"So by selecting for a woman with \"normal\" looking muscles and a larger hip-to-waist ratio, you are actually selecting for women who are more fertile and more capable of producing healthy babies.",
"It's important to remember that big muscles doesn't necessarily mean \"healthy\", biologically speaking. The woman in the first picture looks perfectly healthy to me. So long as the muscles are toned and used to activity, not flabby, it wouldn't make her any healthier if they were twice that size. Her hormonal levels are probably more conducive to keeping her heart healthier than the more muscular woman's. Again, those higher testosterone levels aren't very heart-healthy.",
"There is a normal variation among women, just as there is among men. There's nothing wrong with exercising, it does women good, just as it does men good. All women don't start with the same level of testosterone either. So there will be a range of body types and musculature. But if you pick the more extreme examples, such as women with very bulky muscles and low body fat, you will find that they probably started off with more testosterone to begin with, even if they take no hormone supplements to build those muscles. This can be good for bodybuilding competitions, but it's not a better body for producing healthy kids than a woman with smaller muscles and a more female-looking figure."
] |
[
"Thank you this was very helpful."
] |
[
"May have to do with mating. Natural selection doesn't only evaluate for healthy children. A woman who has masculine features may have assumed a masculine role in society, and may be less capable of raising a family for those reasons. She may also be less submissive as those muscles could have developed from an excess of testosterone historically.",
"Something along those lines. "
] |
[
"What occurs in the brain during an out of body experience?"
] |
[
false
] | null |
[
"The current understanding of neurophysiology is that the parietal lobe is the part of our brain that gives us our sense of self and physical body-ness. Things that that disrupt the function of that part (permanent traumatic injuries or temporary effects of drugs like ketamine) are able to induce out of body experiences."
] |
[
"The tempero-parietal junction is a brain region particularly associated with out-of-body experiences. It has been suggested it is responsible for syncing up inputs from different senses (vestibular, visual, somatosensory/proprioceptive), and that a disruption of this integration leads to the out-of-body experience. ",
"At least, that is the leading hypothesis. ",
"https://scholar.google.com/scholar?hl=en&q=imaging+out+of+body+experience&btnG=&as_sdt=1%2C11&as_sdtp="
] |
[
"They are well documented medically. They're not that uncommon as a side effect of general anesthesia. "
] |
[
"How much power does it take to drive an LCD display?"
] |
[
false
] |
Not counting the backlight, signal processing, etc. how much power is needed to change the state of a single LCD pixel? What about to keep it in the same state? How does this scale to larger displays?
|
[
"Since each pixel is basically a tiny capacitor the power consumption is very low. From one 15 inch panel datasheet I found a power consumption of 500 mA (all white) to 750 mA (all black) at 3.3V. That's for 1024x768x3. So overall power/sub pixel is close to 1 micro watt for black. Some of that (maybe most) is dissipated in the row and column drivers and the 2.3 million TFT switches. "
] |
[
"This is an order of magnitude too high. Nearly all of that is for the backlight. Old LCD watches with reflective screen can run for years. ",
"Take a look at a reflective matrix screen running 128x128. They have a power draw of 55uA with 16,384 active pixels.",
"That is less than .003uA per pixel at 4.5V, or 13 nanoWatts."
] |
[
"None of the figure I quoted was for backlight. It was from a Chi Mei datasheet. \n The monitor is 1024x768x3. The number includes driving circuits. I said the actual pixels were less."
] |
[
"How does a Tree decide to make a branch."
] |
[
false
] |
Trees, and bushes, seem to make a crotch at varying lengths. This picture shows us varying length branches but they all seem to be close to a similar length: . Also, some branching among trees seems quite a lot different such as this tree: . When does a tree "decide" to make a branch? What mechanism decides the length of the branch before it forms a new branch? Why are branches roughly the same length "per generation" where older branches seem about the same length, newer branches seem about the same length, and very young branches appear as the same length? What is the branching process called? Is there anything seasonal that causes branching or more branching?
|
[
"There are groups of cells on plants called meristems, which are similar to stem cells in animals. The meristem is an undifferentiated mass of cells, from which new organs grow. ",
"Each plant has a shoot apical meristem at the top of the main stalk. As the topmost cells of the apical meristem divide, they push push themselves up higher and higher. At the lower boundary of the meristem, cells differentiate into plant tissue. Every once in a while, the plant will produce a new leaf (alternate or spiral). The time between production of new leaves is called a phyllochron. At each leaf node, there is a an organ called the axillary bud between the petiole (leaf stem) and the main plant stem. The axillary bud is, in fact, a meristem, itself. This is how you end up with a stalk with a meristem on top, and regularly spaced meristems along its length. ",
"Now comes the fun part. The apical meristem produces an important plant hormone called auxin (You already have heard of the synthetic version of this -- 2,4-d a.k.a. agent orange), which is carried down to other meristems (the axillary buds) by the xylem tissue. This hormone prevents the differentiation of the axillary buds, keeping them dormant. This phenomenon is called apical dominance, because the top meristem prevents branching. In most small plants, this is why we see one main stalk with several leaves. In those plants, the apical meristem will eventally differentiate into a sex organ (flower). This is also why we prune rose bushes, because cutting off the apical meristem disrupts the flow of auxin, and causes all of the axillary buds lower down on the shoot to begin branching. Eventually, the topmost bud will enforce its own apical dominance, but with the benefit of having produced many branches that are now unaffected by the auxin it produces. ",
"In trees, and other branching plants, we have another effect called incomplete apical dominance, in which the auxin produced by the apical meristem doesn't make its way all the way to the lowest buds in large enough concentration to inhibit them. This causes buds that are a specific distance from the meristem to start branching. In effect, this ensures that the apical meristem, and all the brand new leaves just below it, are never shaded by branches, and also ensures that trees take on a triangular shape, so that each branch isn't blocked by one above itself. "
] |
[
"Follow up answers: ",
"What mechanism decides the length of the branch before it forms a new branch?",
"Same as with the apical meristem. A branch is basically a new tree growing off the trunk of the old one. ",
"Why are branches roughly the same length \"per generation\" where older branches seem about the same length, newer branches seem about the same length, and very young branches appear as the same length?",
"Hopefully the answer is clear from my explanation. It's because branches that are lower down started growing earlier.",
"What is the branching process called? ",
"Branching",
"Is there anything seasonal that causes branching or more branching?",
"No. Branching can be induced by removal of the SAM (shoot apical meristem). This is how coppicing and pruning works. The branching process is tied to the overall growth of the plant. ",
"Also, auxin inhibits the abscission (falling off) of leaves and other plant organs near the meristem. This is why many trees and other plants have leaves near the tips of branches. Auxin is also present in the sunny side of a plant stem, and inhibits growth there as well. This causes the other side to grow, essentially bending the stalk to face the sun. "
] |
[
"In short, your answer can be explained by ",
"Phyllotaxis",
". ",
"Essentially, a plants growth is determined by their genes. ",
"The growth of stems and roots has been shown, by cross-section analysis, to be radially symmetrical.",
" Which is to say, they grow most likely grown randomly and/or in response to stimuli. ",
"The growth of new stems, leaves, lateral roots, and flowers is based on specific patterns; alternate; opposite; whorled; and spiral, depending on the species.",
"For most temperate species, new buds are grown on the branches at the predetermined intervals over the summer and grow for the following season.",
" ",
"1) Brooker, Robert J. \"An Introduction to Flowering Plants.\" Biology. Whitby, Ont.: McGraw-Hill Ryerson, 2010. 766-67. Print.",
"2)Kershaw, Linda. \"Amazon Prime Free Trial.\" Trees of Ontario: Including Tall Shrubs (Lone Pine Guide): Linda Kershaw: 9781551052748: Amazon.com: Books. Lone Pine, 5 Jan. 2001. Web. 12 Jan. 2014."
] |
[
"Can you no longer enjoy science fiction because you know where the author is just dead wrong?"
] |
[
false
] |
Examples would be things like FTL travel, human interplanetary settlement, time travel, a host of things relating to genetics, AI- and other computer science-related faux pas. Can you suspend your disbelief and view the work in a universe with different physical rules, or do these "mistakes" just piss you off?
|
[
"I love science fiction. ",
"Can you suspend your disbelief and view the work in a universe with different physical rules, or do these \"mistakes\" just piss you off?",
"This. What ",
" bother me is when the fictional universe is internally inconsistent in its logic."
] |
[
"It's worst for me with TV shows like CSI or Bones. They're my guilty pleasure and really make my science hurt. "
] |
[
"Agreed. Consistency is the main thing. Additionally, things like FTL travel are often just a plot device to move things along and not integral to the plot. This makes them easier to ignore/accept in a book."
] |
[
"Do you sweat if you are submerged in hot water?"
] |
[
false
] | null |
[
"Yes. Sweating is a reaction to heat, not to lack of water on your skin. It doesn't work particularly well when submerged in water, but that doesn't stop your sweat glands from doing what usually works."
] |
[
"Used to play water polo. It’s really easy to get dehydrated cause you don’t realize how much you are sweating. "
] |
[
"Short answer, yes. Your sweat receptors do not actually take into consideration the presence of liquids already on the skin.",
"Extended answer; ",
"Sweating is mediated by head heat receptors (located in the hypothalamus) and skin-based peripheral heat receptors (located in, well, the skin). ",
"The skin and head heat receptors together set the ",
" for thermoregulation in the hypothalamus. Core temperature is constantly compared to this set point via central heat receptors. If core temperature rises above it, no matter the source, those C-fibres will increase their firing rate and sweating will begin.",
"Now, sweating is a pretty simple cooling tool; the basic idea is to increase cooling by having water evaporate off of your skin efficiently (1 gram of water evaporation requires 2400kJ of energy!).",
"Once your heat-sensitive fibres begin to detect a heat increase, they will increase their firing rate. This will cause a sympathetic signal ending in acetylcholine release- which will stimulate eccrine glands all over the skin to begin sweating.",
"So you'll begin to sweat- and probably quite quickly, as animal tissue tends to conduct heat a lot more easily than water. The same physiological function is at work as would be if you were walking in a desert or a sauna or a bread oven (shout out to my boy Charles Blagden).",
"So, water on the skin or not, your sweat pores wouldn't stop excreting sweat- and if it's not having the desired cooling effect, assuming no medical interventions, they're not going to stop until a) you dehydrate or b) the water/your body cool down enough that sweating is no longer necessary.",
"It's the opposite of shivering, in a way. Both are body-temperature dependent thermoregulatory mechanisms. Just as you'd shiver if you sat down in an icy cold bath, you sweat if you're submerged in a hot one.",
"Another decent comparison is spending time in a sauna. The highly humid environment results in useless sweating- your skin gets wet, but it doesn't evaporate and you don't actually lose that much heat. That doesn't stop your body from producing sweat, however, it's why saunas (and hot tubs) can dehydrate you (or cook you, if they're warm enough; see the 2010 sauna championship death) if you spend too long in them.",
"Source;"
] |
[
"How are the ends of a ski lift cable joined to make a complete loop?"
] |
[
false
] |
Was skiing today, and a friend and I were wondering how they make the steel cable into a complete loop. We didn't notice any particular joint while watching the cable for a while, though we could certainly have missed it. Also relevant, what are these things made of, specifically?
|
[
"Unwrap the strands that make up the ends of the rope, for a couple of meters on each end. Cut off half of the strands from each end. Wrap the remaining strands together to form one same-thickness rope again. Weld the ends. The strength is mainly in the friction of the strands being wrapped around one another. If the splice is long enough, the frictional forces can be stronger than the regular strength of the wire rope.",
"If you notice a painted spot on the ski lift cable, that's the join."
] |
[
"Your question has already been answered in prior replies, but I wish to share a bit of what I know about cables to earn upboats.",
"There is some subtlety to cable design principles that are particularly important to the application of lifting skiers up a hill. For one, lift cable strands are twisted. This twisting of strands around each other does two things. ",
"Firstly, when the cable is wrapped around the bullwheels (huge pulley wheels at the ends of a chairlift) the twisted configuration places each strand sometimes closest to the center of the bullwheel and sometimes at the furthest radius to the center of the bullwheel. In a sense, if you were to lay a cable straight and paint a single strand a bright color, you'd see it transcribe a mild sinusoid across the bundle, oscillating from one side to the other. This twist period must be shorter than half the circumference of the bullwheel. Because the length of each strand oscillates between minimum and maximum radius on the bullwheel, each strand is NOT stretched or compressed as the bundle is made to wrap the bullwheel. Conversely if the bundle was not twisted, with each strand parallel to every other, the inside most strand (strand contacting the bullwheel) would be placed under compression and the strand furthest from the bullwheel center would be stretched. This is a non ideal loading scheme which would result in fatigue loading of individual strands. You'd also get increased abrasion between strands. Not to mention a uneven loading across the bundle cross section which would be a less efficient use of the material.",
"Secondly, the twisting increases the friction between strands. This is extremely important as each strand has enough friction to it's neighboring strands that they can support each other in case a strand breaks or is otherwise compromise. In the case of an untwisted multi strand cable, the strength of the entire bundle is determined by the number of intact strands across it's entire length. With negligible friction between strands, a strand that has been broken can transmit no tension between your loading ends. When you're dealing with a few miles of stuff, the probability of a break in a given strand starts to get pretty high once you run the thing for years. In the case of the twisted cable, significant friction is developed between strands. A broken strand cannot transmit load across a break, but neighboring strands can pick up the load at the immediate zone of the break and pull on the sides of the intact strand away from the break. This means that a break in a strand does not make the strand a dead load carrier for it's entire length. As long as you do not have a collection of strand failures concentrated in the same zone, long twisted cables will generally give you very close to the breaking strength of a perfect short section even if every strand has one or multiple breaks spread through the bundle."
] |
[
"If you watch the ski lift episode of World's Toughest Fixes (great show, on Netflix streaming), you can see the guy do this. There are only a handful of people in the world that know how to do this.",
"It isn't widely practiced anymore, but in the age of sail, every ship would have a few sailers capable of ",
"unbraiding rope and splicing it into a loop, without a knot.",
" You can google \"rope splicing\". This is the same thing, using much more rigid cable, plus welding."
] |
[
"Combustion"
] |
[
false
] |
Sorry if this is not up to the standards of the normal questions, I'm still in high school. Someday I plan on making it to the same point as many of the people here but I have not to this day. So my question is, why do things combust? Recently we've been learning about states of matter and molar enthalpy of fusion and vaporization and I've been wondering why somethings combust rather then turn to a liquid. (It sounds stupid when I say it out loud but I really am curious) Any answers are appreciated! Thanks :) EDIT: The category is chemistry but I'm not sure that is exactly the right field. Sorry about that.
|
[
"Some groups of chemical bonds are simply less stable than others and love to react with oxygen.",
"Take a candlestick for example. The wax is mostly made of hydrocarbons, which in turn, is mostly a bunch of carbon-carbon bonds and carbon-hydrogen bonds. These chemical bonds turn out to be less stable than carbon-oxygen bonds, and hydrogen-oxygen bonds. As a result, there is a tendency built in already for these substances to react.",
"When you light a candle with a match, the heat breaks up a few of these C-C and C-H bonds, freeing up some chemical fragments to react with oxygen. These fragments eventually produce water, carbon monoxide, carbon dioxide, and soot. The exact mix depends on the details of the burning.",
"This initial rearrangement of chemical bonds is exothermic. This is a very important point. Heat is released, so that other chemical bonds can be broken and recombined with oxygen, which then releases even more heat in a self-sustaining (or even uncontrolled) way. A classic combustion reaction involves heat, fuel, and an oxidiser. Remove any one of these and the reaction will stop.",
"The heat is necessary to kick start the chemical reaction. Almost all chemical reactions require some form of energy to get them started. In an academic setting, this \"heat\" doesn't necessarily have to be something that is at high temperature. It could be an intense source of light, for example.",
"There isn't anything special about oxygen, it's just the most common oxidizer that we encounter. It would be possible to burn a candlestick in fluorine. In this situation, the combustion would be very vigorous because fluorine is an even stronger oxidizer than oxygen. It's so strong of an oxidizer that practically anything that comes into contact with it burns on contact. We are very lucky our atmosphere is not made of fluorine!",
"The fuel is a source of chemical bonds with energy stored in them. Once they are broken and rearranged, this energy is released. Sometimes you have oxidizing chemical groups directly bonded to the C-C and C-H bonds. It's as if at the molecular level there were standby oxidants at hand, ready to burn anything at the slightest provocation. Certain flammable substances and explosives share this characteristic. It's one reason why these combustion reactions are very dramatic."
] |
[
"Combustion tends to be an entropy-driven process. In most applications, large molecules are blown up into smaller molecules = higher entropy. Same goes for the phase transition from liquid to gas. Also, combustion products are usually very stable molecules."
] |
[
"I forgot to answer why these combustion reactions do not turn a solid into a liquid. The reason is that combustion products tend to be gaseous. Even in cases where water is produced, it first exists as a vapour which subsequently condenses into liquid form. The fragments of molecules reacting together to make water carry a lot of excess energy. Often, this energy is enough to keep things vaporized."
] |
[
"Is there a way to find the equation of a random curve?"
] |
[
false
] |
e.g. if I took a pencil and drew on some paper, could we express that curve as a function?
|
[
" to fold in a couple of great contributions from some other commenters.",
"The vast majority of smooth curves don't have \"closed-form\" equations, meaning that you can't write an f(x) in terms of simple functions like polynomials (x, x",
" x",
" ...), exponentials (e",
" trig functions (sin(x), cos(x), ...), and so on. In fact, a random scribble on paper isn't likely to be a proper function at all, because it would fail to be a one-to-one mapping that satisfies the vertical line test. As several point out below (",
"/u/idc2011",
", ",
"/u/darksoulisbestsoul",
" and others), though, you can parameterize a such a scribble as the set of functions {x(t), y(t),...}. So anything below would apply to these individual functions. (If you'd like an algorithm for finding the parameterizations, I'm afraid I can't help you there. Wolfram Alpha does a pretty great job, though.) ",
"Nearly any smooth function can be written as a (generally infinite) series of terms in a set of ",
". Polynomials form one such basis, so you'd be able to write your curve as",
"f(x) = A_0 + A_1 x + A_2 x",
" + ... + A_n x",
" + ...",
"Now all you have to do is find the set of coefficients A_0, A_1, ... in order to have an equation for your curve. For a randomly-drawn curve, there will be a lot of them, so this is best done using a computer. In fact, there will typically be an infinite number of terms, so you'll never be able to find all of them even with a computer. You can get an arbitrarily good approximation of your curve, though, by computing as many as you need to get \"close enough.\"",
"This polynomial expansion is called the ",
"Taylor Series",
" of the curve. Sort of. My background is physics, where we call all polynomial expansions \"Taylor Series\" (",
"), but \n",
"/u/functor7",
" has a great point below about the distinction.",
"The set of sines and cosines of different frequencies also form a popular set of basis functions; an expansion in terms of them gives you your curve's ",
"Fourier Series",
". Fourier Series work best for functions that display periodicity, like sound waves. I mention them because lots of people are familiar with Fourier analysis and might like the connection to stuff they already know, but they probably won't be best for modeling a random, non-repeating function.",
"For that matter, polynomials aren't typically your best bet, either, as the aptly-named ",
"/u/stoptalkingyourwrong",
" points out :). I was glad to see him/her and several other posters (like ",
"/u/samclifford",
", ",
"/u/DataLaird",
") mention splines, because I've used ",
"b-splines",
" for curve-modeling, and they are in fact the bomb for arbitrary smooth-curve fitting. I didn't bring them up because they're a little more complicated, but in essence they provide an alternate polynomial basis for the expansion. The Wikipedia article (linked) is a good place to start if you want to learn more.",
"If you're more curious about the mathematics of the Taylor Series, ",
"/u/dxdydz_dV",
" has a fantastic post below that you should read. There's tons of other great information in the comments, too. I have to walk away now, because I really do need to get some work done today, but thanks to everyone for the instructive discussion!"
] |
[
"f(x) = A_0 + A_1 x + A_2 x",
" + ... + A_n x",
" + ...\nThis polynomial expansion is called the Taylor Series of the curve.",
"Just for completeness, that is actually the MacLaurin series, i.e., a Taylor expansion around 0."
] |
[
"Finding the exact equation won't be possible except in very specific situations (e.g. a straight line). But in many cases, you could approximate it to arbitrary accuracy (or in reality: a level of accuracy limited by how accurate you can measure the coordinates of points on the curve).",
"Note that between any pair of distinct points you can draw precisely one straight line. This line fits with the equation:",
"y = a x + b",
"for unique values of ",
" and ",
". If you take three points on your curve, in such a way that they're not all on the same straight line, there is a single parabola, given by",
"y = a x",
" + b x + c",
"that can be fitted to cross all three points. If you take four distinct points that do not lie on a parabola, you can fit a single cubic function. And this process can be repeated for larger and larger sets of points.",
"The more points you take in your sample, the more precisely the approximating polynomial function will match the original curve. The requirement here is that the curve has at most a single y-value for each x-value and that it is smooth enough (specifically: infinitely differentiable). If either of these requirements is not met, then this process will fail to give an accurate approximation at some point.",
"The equation you end up with is a polynomial of the order of the number of sample points minus one. So if you take 10 sample points, you'll end up with a 9",
" order polynomial (y = a x",
" + b x",
" + ...)."
] |
[
"What does it mean when physicists refer to several additional \"small\" dimensions?"
] |
[
false
] |
I've just reread a couple of Hawking's books, and I can't figure out how to conceptualize additional dimensions. Three spacial dimensions plus time as a fourth seem straightforward enough (though obviously not always easy to visualize), but what does it mean to speak of additional dimensions that are "small" or "curled up"? How exactly are they different from the 4 space-time dimensions? You can measure a particle's relative position or velocity in space-time. Does that particle have a coordinate in each of the other existing dimensions as well? If dimensions are "small", does that mean they are local, or do they exist throughout spacetime?
|
[
"Easier to visualise is a universe with one \"normal\" spatial dimension and one small one. Picture a very long and narrow piece of paper, say 100m by 1cm. Let's call the long dimension North-South and the short one East-West. Now roll it up in the E-W dimension to form a cylinder 100m long.",
"The surface of this cylinder now represents a two-dimensional universe, with one of its dimensions wrapped up small. Any particle in this universe will lie somewhere on that surface, and it will have a coördinate in each of the NS and EW dimensions; the latter only ranges from 0 to 1cm, and a particle at 0 and a particle at 1 are in exactly the same place.",
"Now, if this universe has some kind of creature which can't see anything small than 1m, it will never notice that the second dimension is there at all. It'll believe it lives in a 1-D universe, and all the equations it comes up with to describe how particles behave will include just one spatial dimension. But a creature who can see anything down to 1mm in size will be acutely aware of the second dimension, and their physics will look quite different.",
"For instance, imagine a particle that acts like a torch, emitting light in all directions at a constant and equal rate. In one dimension, it doesn't matter how far from it I stand: I'll always see exactly half the light if I face towards it. But in 2-D the luminosity falls off as you move further away from the source since the light spreads out. In this universe the light would behave in one way at scales of 1m, in the second way at scales of 1mm, and in an intermediate way at scales around 1cm (since the light is spreading out but you're also seeing light that's wrapped around the side of the cylinder and returned to you). A full set of physical laws would need to take all three regimes into account.",
"Returning to our own universe, we just have to add extra full and maybe compact dimensions. It becomes much harder to visualise, but the nature of each individual dimension is just like the two in the rolled up paper universe. And its effect on physics is somewhat analogous: because a force like gravity 'spreads out' into space, gravity will behave slightly differently in a universe with one (or more) wrapped up dimension than in a simple universe with only 'big' dimensions.",
"Edit: Our 'big' dimensions don't actually have edges like a piece of paper 100m long. Really you should probably think about an infinitely long cylinder, or else just ignore the ends of it as not relevant to the analogy."
] |
[
"but what does it mean to speak of additional dimensions that are \"small\" or \"curled up\"? How exactly are they different from the 4 space-time dimensions?",
"What we mean by \"small\" is that the symmetry groups describing translations in those directions are \"compact.\" What compactness means is that if you go far enough in a compact direction, you get back to where you started. Rotations of solid bodies form a compact group, because after rotating by 2*pi you're back where you started. Similarly, directions on the surface of a sphere are compact: if you travel for long enough in a given direction, you get back to where you started.",
"So the thought to stringy or Kaluza-Klein models is to consider (an) extra dimension(s) which fields or strings are allowed to propagate in, but their \"size\" (how far you can move in those extra directions) is smaller than around 2*10",
" meters (1 TeV",
" ).",
"You can measure a particle's relative position or velocity in space-time. Does that particle have a coordinate in each of the other existing dimensions as well?",
"Classically yes, but from a quantum mechanical standpoint, these other dimensions are so small that particles are kind of smeared through this entire other dimension. In KK models, for example, typically there's an infinite number of ways they can be smeared out, each having a different amount of energy, which would look to us like, for example, an infinite number of excited electrons each with higher mass than the last.",
"If dimensions are \"small\", does that mean they are local, or do they exist throughout spacetime?",
"They would exist throughout spacetime, in the same way that the three spatial dimensions we know of exist throughout spacetime.",
"EDIT: unrelated, but can anyone tell me how to cancel superscripts without putting a space in?"
] |
[
"Check out ",
"this post",
" from 11 days ago."
] |
[
"What properties determine the density of elements?"
] |
[
false
] |
[deleted]
|
[
"Crystal structure, atomic radius, and atomic mass determine density. ",
"Depending on how you make the crystal lattice, there's a different amount of 'empty space'- this is called the '",
"Atomic Packing Fraction",
"'. For this purpose, we can treat the atoms as little balls with fixed radius. From here, we can calculate the number of atoms in a given volume, and therefore the mass per volume. ",
"Why some metals form one structure over another is a very complicated question. "
] |
[
"In OP's specific example, gold has a face-centered cubic structure (like oranges stacked at a grocery store), which is the most efficient packing of spheres. Uranium has an orthorhombic crystal structure (atoms are arranged like a rectangular prism), which is less dense."
] |
[
"Metals are made up of many crystals called 'grains'. A crystal is a repeating array of atoms- semiconductors are crystalline, metals are crystalline, ceramics are crystalline (e.g. minerals), sometimes polymers are crystalline (though it's the chains that are organized in a structure, not individual atoms)"
] |
[
"Askscience, is the idea that male and female brains develop differently debunked, disproven, or simply out of vogue?"
] |
[
false
] | null |
[
"They do develop differently",
". So no, no, and I dunno, maybe?"
] |
[
"I'd just like to add, almost every complex animal species has at least ",
" differences in behavior between males and females (in regards to mating and offspring care if nothing else) without anything like a culture influencing them. So, if humans were one of the only species ",
" any such differences, that would be a very strange and unlikely result which we would need a very strong theory to explain. Being the same is not at all the 'natural' state."
] |
[
"Male and Female brains are washed with different hormones during pregnancy, which stimulate and inhibit growth in certain areas of the brain. So no to all three."
] |
[
"How come some cuts and scrapes don't bleed, but still form scabs and scars?"
] |
[
false
] |
Sometimes a cut will go deep enough to be very sensitive, but not deep enough to cause bleeding. If it never bled, why does a scar still form?
|
[
"Such cuts/scrapes do not penetrate deep enough to affect any small arteries and veins. However, these cuts etc do rupture capillaries and lymph vessels which is deep enough to cause a release of interstitial fluid (which contains clotting factors and proteins which help form scabs/scars). "
] |
[
"Small nitpick. Serous fluid/interstitial fluid does not contain clotting factors. These are ",
". Rupturing small capillaries with plasma leak (we're talking ",
" - only wide enough for 1-2 RBC's to pass through at time), is likely the source of these proteins. ",
"Then the usual progression through hemostasis occurs, which begins with platelet activation at the site of injury. Platelet activation being necessary for a key step in the clotting cascade (the release of Factor V). "
] |
[
"So the clear fluid that comes out is blood plasma, and the reason you see mostly plasma is because the capillaries are so small as to only let out a few red blood cells at a time? That's awesome! "
] |
[
"What is it exactly about chronically high blood sugar levels that leads to insulin resistance and type II diabetes?"
] |
[
false
] |
I thought it was a matter of insulin receptors being downregulated because they aren't needed in normal quantities when the body is awash in insulin all the time; receptors are fewer and fewer until finally there aren't enough and you get insulin resistance. My friend, who apparently knows a bit about it, says that that's not the case, the receptors get "numb" and unresponsive to insulin. I know he's not so stupid as to think they get numb, I think he was putting it in a way he thought I would understand, but it didn't really explain anything. Any help?
|
[
"What comes first, the chicken or the egg?",
"Is blood sugar chronically elevated do to insulin resistance, or did it cause it?",
"Fact is it is not exactly understood just yet, but most medical doctors would say you have it backwards. Insulin resistance CAUSES chronically elevated blood sugar, rather than vice versa as you described. "
] |
[
"I would assume that to some extent it's a positive feedback loop, where higher blood glucose levels lead to more insulin resistance which leads to more glucose in the blood and so on, but surely the initial cause is high sugar intake or else why would diet be both the demonstrable cause and cure? In other words diet is known to cause it and diet corrections can control and even cure it so it's the result of diet. Surely it's not chicken and egg, the etiology is known.",
"But my question isn't what causes type II diabetes, my question is what changes do insulin receptors undergo so that they are \"resistant\" to insulin? Are there fewer of them after time, or do their numbers remain constant but due somehow to constantly being bombarded with insulin they become less likely to initiate whatever pathway they use to take in glucose, or what? "
] |
[
"Diet is not a demonstrable cause and cure. Body weight is however. My personal opinion is that the pancreas sees the blood glucose, and produces the correct amount of insulin for a healthy body. However, If you weigh 2x what a healthy person does, that means effectively the produced dose of insulin is only half as potent.",
"Are diet and body weight closely related? You bet. But they are very much not the same thing."
] |
[
"Does the energy from Sunlight change the Earth?"
] |
[
false
] |
With all of the energy that the Earth absorbs from the Sun, is this changing the chemical structure of our planet? Does the Earth radiate it back out?
|
[
"With all of the energy that the Earth absorbs from the Sun, is this changing the chemical structure of our planet?",
"Yep. You, for example, just like practically every lifeform, are one of the chemical objects on Earth which wouldnt' exist without Sun energy."
] |
[
"Ultraviolet radiation from the sun leads to the ozone layer. "
] |
[
"Your question is a bit too vague...",
"It provides most if not all of our energy. We get some from inside the Earth and I don't know the details, but by and large, everything comes from the Sun. In this context, I don't mean humans when I say 'we', I mean life in general.",
"The Sun's radiation (heat) causes the weather patterns, for example, rain, clouds, wind, sea currents and waves.",
"The food chain relies on it heavily. I'm sure you know how plants need sunlight. Well you know about food chains? Most animals if you follow the food chains down, animal eating animal, eventually rely on plants being used as a food source. And of course plants and trees provide homes if not food. And of course there are exceptions to this such as animals living at/close to the ocean floor where there is no sunlight and the surface could be frozen up for all they care.",
"Did your question mean something to do with the chemical make up of the atmosphere or the physical structure of the Earth?"
] |
[
"What happens to precious stones at exceptionally high temperatures (say 800-1000 degrees Celsius)?"
] |
[
false
] |
After watching the cremation video posted earlier on the Videos subreddit, and seeing the breakdown of flesh and bone, I was reminded of the last episode of MST3K where an emerald necklace was shot (yes, shot) into a body, and the body was cremated. The emeralds came out looking just fine, which always puzzled me. My question is, given the high temperatures associated with a crematorium, would the precious stones be converted back to carbon, or would they some how prove more resistant to the heat? I know some precious stones are essentially created THROUGH judicious use of heat and pressure, but what would happen to already processed stones set through those temperatures? From the research done on cremation, the average human body takes approximately 2-2.5 hours. I'm assuming this would make a bit of difference in the end product.
|
[
"metallurgist here"
] |
[
"Hang on, now. Diamond may very well melt at 3,547 degrees celsius, but with 20% oxygen, they combust at 800",
" C",
"source"
] |
[
"The melting points of precious stones",
" are usually quite a bit above the cremation temperatures you mentioned."
] |
[
"If the Universe is infinite, does that mean that the Joker and Spock are playing chess on the Millenium Falcon right now?"
] |
[
false
] |
[deleted]
|
[
"No. There are different levels of infinity.",
"For instance, there are an infinite number of real numbers, and an infinite number of integers. But there are more real numbers than integers.",
"So just because you have something that is \"infinite\", doesn't mean that all possible outcomes are true.",
"http://en.wikipedia.org/wiki/Cardinality_of_the_continuum"
] |
[
"Yeah, except the cardinality of the evens is the same as the cardinality of the naturals. So, really, no.",
"Integers are countably infinite, and reals are uncountably infinite. See: ",
"http://en.wikipedia.org/wiki/Countable_set",
" and ",
"http://en.wikipedia.org/wiki/Uncountable_set",
" respectively."
] |
[
"Yeah, except the cardinality of the evens is the same as the cardinality of the naturals. So, really, no.",
"Integers are countably infinite, and reals are uncountably infinite. See: ",
"http://en.wikipedia.org/wiki/Countable_set",
" and ",
"http://en.wikipedia.org/wiki/Uncountable_set",
" respectively."
] |
[
"What properties would an antimatter star have?"
] |
[
false
] |
[deleted]
|
[
"It would have the same properties as a regular star. However, if there was a region of space where things were made of antimatter, at the interface between that part of space and our matter part of space, there would be a massive amount of gamma radiation being emitted from all the annihilations, which we don't see."
] |
[
"That would be very exciting because it means a lot of physics needs to be rewritten."
] |
[
"Would that happen if antimatter is gravitationally repulsive to matter?",
"Edit; Is it possible that antimatter and matter naturally seperate out - is kinda what i mean... doesnt ahve to be gravity since you already confirmed it would have the same properties as a regular star."
] |
[
"How does Mars look from the Moon, assuming that the Moon is at the point in it’s revolution where it’s closest to Mars?"
] |
[
false
] |
[deleted]
|
[
"In 2003 Mars was at its closest it will be to Earth for a while, at a minimum distance of 55.76 Gm. The Moon orbits Earth at an average of 384,400 km (or 0.3844 Gm). Meaning if everything lined up, the moon was 0.69% closer to Mars than the Earth was. Essentially no difference. Space is mind-blowingly large."
] |
[
"Sure, but to a bare eye it’s still going to be just a bright orange-ish point of light even at opposition."
] |
[
"Here is an interesting website that helps realizing how wide the distances between planets really are : ",
"http://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html"
] |
[
"What's the difference between inductive reactance vs. capacitive reactance?"
] |
[
false
] |
I'm studying impedance on AC circuits, and I'm having a hard time with these terms. I understand the resistance concept in DC theory, but just can't wrap my head around the AC resistance theory
|
[
"The difference is in the frequency response. You know reactance extends the DC concept of resistance (towards a change in current) to the case for AC, and so fundamentally the concept is the same.",
"In an inductor as frequency of the input signal increases so does the reactance, linearly in fact. In a capacitor the effect is an exponential decrease as frequency increases - you will frequently hear reference to caps as being shorts to high f and opens to dc."
] |
[
"AC Resistance isn't really resistance, it's \"reactance\" -- and therefore, it's \"reversable\" in ways you may not yet fully understand. ",
"",
"Consider that DC always flows from + to - (or - to +, depending on your feelings) -- but AC flows \"both ways\", therefore; ",
"When AC goes through a capacitor, the frequency (or time in a positive or negative reference) determines the amount of charge that can collect on the physical capacitor plates before the flow reverses direction and the cap 'discharges' (but not in the same DC way, exactly.) The size of the plates (the capacitance) is also a factor for consideration, in terms of surface area. ",
"[[ In math terms; 1/2pifC -> the 2*pi describes the signal, the f and C are the frequency (rate of current exposure to the plates) and capacitance (physical size of the plates) ]] ",
"",
"When it goes through an inductor, the frequency determines the length of time a field is created and destroyed, which changes the flow of current through the device and therefore, appears as 'resistance' ",
"[[ Again 2*pi is the AC signal, and f L is the frequency and inductance value that determines the field created ]] ",
"",
"Note: You will likely soon learn that you can use these two phenomenon in parallel to your advantage; i.e the tank circuit.",
"",
"Hope this helps.",
"",
"Source: Brains from college. (Electronics Engineer, working at a top 10 public university in the US) "
] |
[
"Also; Noticed you also mentioned impedance; ",
"Impedance (for example, an audio amplifier) requires matching of load and source, this is to ensure there is no reactance occurring between signal transfer, ensuring maximum power transfer. (Check out Max power transfer theory which will require your future considerations when doing anything RF related.. )",
""
] |
[
"Do Tachyons Exist?"
] |
[
false
] | null |
[
"There is no evidence to suggest they exist and no reason to suspect that they do, and a number of problems that would arise if they did exist. A few years ago there was some hubbub about faster than light neutrinos, which was an erroneous measurement caused by a loose cable."
] |
[
"Tachyons don't exist in any sense; a tachyonic state or mode in general indicates that what you believe to be the vacuum is not the vacuum.",
"Technical:",
"Tachyons don't exist as particles:",
"In specific a tachyon would be a real particle with negative mass squared, meaning the 4-momentum is spacelike and satisfies the constraint P",
" = - |m",
"|, which puts it on a one-sheeted hyperboloid. This is connected and through a Lorentz boost we can arrange the energy (the actual total energy) to be negative. This means there are one-tachyon states with energy lower than the vacuum, which is in contradiction with the definition of vacuum.",
"Tachyons don't exist as FTL correlations:",
"The VEV of the commutator of two spacelike separated observables is zero (standard proof). This means that while virtual particles can be tachyonic, no real transfer of information can happen FTL.",
"A tachyonic field theory does not feature tachyons:",
"Finally, if you try to build a field theory with a negative m",
" mass term, you get that φ=0 is not the vacuum, so that the theory undergoes spontaneous decay to the true vacuum, which you should make sure exists for the theory to make sense.",
"And sorry for this dump of technical jargon; last time I was not precise enough in language and I got buried in comments claiming special relativity is not in contradiction with tachyons. It isn't, but it's not the point. Tachyons are in contradiction with relativity + quantum mechanics."
] |
[
"Yes, except that if you could emit and receive such particles, you could send information using them, and that would break causality, since there would always be a reference frame in which the emission and reception happened in reverse order. So basically, with superluminal communication you automatically get a way to send information to yourself back in time and that's not good.",
"Maybe there could be tachyons that couldn't be controlled and therefore wouldn't allow for sending information, but I'm not sure if there aren't other problems then."
] |
[
"Why does my nose get watery when I eat something really spicy?"
] |
[
false
] | null |
[
"Your airways are constantly producing very large glcyoproteins (proteins covered in long chains of sugars) called mucins. These are very sticky, water-binding molecules that function to protect the airways. Mucins are generated by specialized cells in little \"bubbles\" in the cells. These bubbles are prepackaged and stored. When mucus is needed, the \"bubbles\" are transported to the cell surface where they fuse with the plasma membrane and dump their contents out into the airways. The quantity and type of mucins released depends on where you are in the airway, and the physiologic state (irritated, infected, inflamed, etc) of that region of airway. ",
"But these are very thick, viscous proteins. If they are released by themselves, you would get a very thick and viscous goo. So, packaged in these \"bubbles\" along with the mucins are other molecules that stimulate the release of water into the airways. The water functions to dilute the mucus. The quantity of water is also regulated.",
"So you have two parts to mucus production: The release of mucins and the release of water.",
"The function of mucus is to keep the airways clear of foreign material. So, as you might imagine, one of the things that will cause localized increased mucus production is the presence of a physical object (e.g., a speck of dust). This response is mediated (in part) by nociceptive (damage-sensing) sensory neurons. ",
"When these neurons fire, they stimulate the specialized mucus-producing cells to release those little \"bubbles.\" This stimulation is regulated, and will only occur in the region where the object has been detected by the sensory neurons. This results in the release of mucins and the release of water into the airways. ",
"Capsaicin has the ability to \"short-circuit\" these neurons, making them fire. ",
"This is essentially a drug effect; you are taking a drug that causes your body to respond in a way that it normally wouldn't. ",
"There are two main differences in the capsaicin response and the \"normal\" response. First, capsaicin will not be a localized effect. When you eat a chili pepper, some of the capsaicin is aerosolized and gets spread over a relatively large area of the airway. Second, capsaicin is kind of oily...it is more soluble in fats than it is in water. So, when you try to wash it away with a water-based rinse (like mucus), it is not cleared very rapidly. Therefore, pushing water through the area where capsaicin is won't do much to clear the capsaicin. So the effect is prolonged.",
"So capsaicin gives you a longer-lived response put over a larger area.",
"Mucin is hard to make. It's a big protein, and making big proteins takes time. Pushing it out is quick. The molecules that stimulate water production are small and easy to make, and often stored in very large quantities. In fact, one of these molecules is ATP (yes, the same ATP), and the cells have huge quantities of that in reserve. You deplete the mucin relatively quickly. You don't really deplete the water secreting part.",
"The end result is that you get a sudden depletion of the mucin component of mucus, but the water secretion keeps going....and you get a thin, watery mucus. "
] |
[
"This was one of the most detailed responses I've ever read on this sub, so thank you for that. And thank you for explaining it in terms I could understand!"
] |
[
"When spicy food burns, your body dumps out all the snot it can. Then when the snot runs out, but it still burns, your body dumps out water to try to fix the burning."
] |
[
"Does bloodletting eventually reduce the ratio of pathogen to blood in the bloodstream, and if so, why is it not effective in weakening a pathogen's attack on the body?"
] |
[
false
] | null |
[
"Usually when you have an infection that circulates via the blood (viral, bacterial, parasite), it's pretty well dispersed throughout your circulatory system. In this case, even if you extract blood, the ratio of pathogen:blood for all intents and purposes will not change.",
"Now, what will change is the absolute burden of pathogens on your body. But this is still not an effective treatment since pathogens can easily replicate and regain its population. Bacteria (E. coli) can replicate as fast as doubling its population every 20 minutes. So from this, bloodletting is not a viable treatment.",
"Furthermore, several infections also establish reservoirs such as abscesses outside of the circulatory system. Bacteria often do this, whereas viruses can reside in immune cells (HIV), bone marrow (HIV), neurons (varicella) etc. This is an additional reason why a blood-targeted approach is not viable."
] |
[
"Actually, exchange transfusion is still suggested as a treatment option for severe malaria; see the ",
"CDC Guidelines",
", for exactly the reasons you mention."
] |
[
"Thanks for your response. When I thought of the question, I assumed that the pathogen was both evenly dispersed and restricted to the circulatory system, which I now realize isn't fair. Given my assumptions, at first no change of ratio would be possible. But what if the pathogen doesn't reproduce as fast as your blood? My next question then would be, are there any pathogens that are restricted to the circulatory system, and reproduce at a slower rate than blood cells?"
] |
[
"Is there a particular type of tree that can naturally convert co2 more efficiently than other trees?"
] |
[
false
] |
which can then be planted in condensed urban environments.
|
[
"In general, broadleaf trees (as opposed to needleleaf trees) tend to have higher maximum photosynthetic capacities. If they are not resource limited, they can sequester more carbon. ",
"What is also important to consider is how long carbon will be sequestered from the atmosphere (carbon residence time). Needleleaf trees tend to decompose more slowly due to their nitrogen content and carbon stability in the tree tissues, making them less degradable. They also tend to be longer lived, but it really depends on the environment that the tree is in. The boreal forests (northern latitudes) are dominated by needleleaf trees because it is colder. Most of the carbon is stored in soils because there is less microbial decomposition. In the tropics, there is a lot more primary productivity (growth), and there are no needleleafs in the tropics, but it is warm and rapid nutrient cycling, so much less carbon stored in soils in most locations. There are exceptions... a peat bog was discovered in the Congo and it stores a lot of carbon. "
] |
[
"The earliest form of photosynthesizing life would by far be the best to utilize for reducing CO2 and temperature. I'm talking about cyanobacteria. They were responsible for the first long freeze of the Earth, when they came into existence during Earth's hot, carbon dioxide-rich environment. They could be easily cultivated and used to begin undoing the damage we've done, and as a preventative measure against future excessive heat and/or CO2."
] |
[
"Trees are carbon sinks. They can release their carbon back into the atmosphere if they are burned or die and are completely decomposed (a process that takes a long time), but until that happens they store carbon and \"sequester\" it outside of the atmosphere. Using trees as carbon sinks is a \"temporary\" fix only in so far as everything is temporary."
] |
[
"Why are FM radio frequencies always listed with odd decimals (.1, .3, .5 etc instead of .2, .4, .6)?"
] |
[
false
] | null |
[
"The RF spectrum was divided up into various bands for various uses by the FCC. The band for FM radio transmission is 88 to 108 MHz.",
"From there there's a limit to how much information you can carry in an FM channel of a given band. It turns out that having channels that are 200 KHz wide gives a good tradeoff between having lots of channels and having good quality, so that's what is used.",
"To divide the spectrum up into even parts without wasting any you start with 88.0-88.2, then 88.2-88.4, and so on. This means that they're all even-to-even decimals.",
"The carrier wave in an FM transmission should be the center of the band, so for 99.6-99.8 you'd choose 99.7. Since all bands run even-to-even the center is always an odd decimal. "
] |
[
"Well, the decision was made to cap FM radio at 19kHz bandwidth, as typical adult hearing peters out at around 19kHz. In the later FM stereo standard, a difference signal was transmitted 38kHz above the main Left+Right signal, and a 19kHz pilot tone (to lock the oscillators) was also transmitted.",
"The 200kHz channel spacing actually has more to do with the state of analog filtering in the era when the standard was developed, rather than how much bandwidth was actually required to transmit the signal."
] |
[
"It turns out that having channels that are 200 KHz wide gives a good tradeoff between having lots of channels and having good quality",
"FM theoretically takes an ",
"infinite bandwidth",
". But like all things in engineering, they made a tradeoff. Deciding how much distortion, for how much bandwidth to allow."
] |
[
"Vast swathes of North America used to be an ocean, the Western Interior Seaway. If this is true, why are those lands not salted and inhospitable like other dried saltwater bodies that have left behind only barren salt pans?"
] |
[
false
] | null |
[
"They are! Almost all North American halite (rock salt) mines rely on the salt deposited during this period.",
"It's just that there has been fifty million years of deposition since then, meaning the salt is quite far below the present surface."
] |
[
"Sedimentation.",
"Almost all the salt flats and dried lake beds that we see now are in low lying areas surrounded by hills or mountains. Over time, sediment washed down from those areas will cover the salt flats and you'll have at first a thin layer but eventually a layer of silt and clays and topsoil hundreds or even thousands of feet thick.",
"The Rocky Mountains, which made up the western shores of the WIS covered what we now know as the Great Plains with vast amounts of rich topsoil."
] |
[
"We can walk out our back door and dig up 2-4\" of top soil and there is still sand underneath from when we were an ocean. Our well water still has high saline content (is still okay levels for drinking). We live at 10,000 feet in the Colorado Rockies.",
"Edited to add - there are still saltwater springs that bubble up in the valley we live in as well. Again, at 9500-10000 feet altitude."
] |
[
"Can a computer perfectly emulate itself?"
] |
[
false
] |
How about if I disregard the perfectly?
|
[
"If turing complete, yes."
] |
[
"Although this is true for all operations that the computer can do, if we take the idea of a \"perfect emulation of itself\" far enough, the emulation would not have the same amount of RAM and possibly hard disk space available, and of course it would be slower (that doesn't count).",
"So \"perfect\" emulation only when hardware limitations don't count. Otherwise you could emulate a computer in a computer in a computer in a computer in a computer... ad infinitum."
] |
[
"You could make the argument that the computer (by virtue of existing) is already emulating itself perfectly. Kinda like how you can't really emulate yourself because anything you do is by definition yourself.",
"If you mean can a computer perfectly emulate a ",
" computer, then for certain definitions of 'perfectly' yes it can be done. You're not going to get a 'perfect' emulation in the sense that you can't emulate the hardware from the quantum level and up, but it's entirely possible to emulate the logic employed by the target system; this is acceptable since in 99.99% of cases all we really care about is the logic and not the hardware."
] |
[
"What's the fastest moving physical object we've observed in the universe?"
] |
[
false
] | null |
[
"At that speed, in a year-long race between a photon and the particle, the particle would fall behind only 46 nanometers, or 0.15 femtoseconds (1.5×10−16 s); or one centimeter every 220 000 years",
"Important to note that the year would need to be measured from the same reference frame as the one from which the particle's speed is measured at 0.9999...c.",
"From the particle's perspective, the 46 nanometer gap happens almost instantly, because the photon still moves away from it at the speed of light. "
] |
[
"A good candidate would be the ",
"oh-my-god particle",
". From the article:",
"The Oh-My-God particle was an ultra-high-energy cosmic ray (most likely a proton) detected on the evening of 15 October 1991 over Dugway Proving Ground, Utah.",
"\n[...] translating to a speed of approximately 0.9999999999999999999999951c. At that speed, in a year-long race between a photon and the particle, the particle would fall behind only 46 nanometers, or 0.15 femtoseconds (1.5×10−16 s); or one centimeter every 220 000 years",
"I remember to have read that, from the particle frame of reference it only takes one month to cross from one edge to another of our observable part of the universe."
] |
[
"I take it you are not counting massless objects as physical particles? If you are, then the answer would be all massless particles, since they all travel at the speed of light.",
"If you only want to include massive particles, then neutrinos would probably answer your question. We haven't measured their mass accurately yet, but most evidence points to them having mass. Measurements of their speed tend to be around, or indistinguishable from, c, which makes determining their mass (or if they have it) tricky.",
"The ",
"Oh-My-God",
" might interest you as well."
] |
[
"Does the brain completely recover from a hit?"
] |
[
false
] |
I do boxing for fitness and once in a blue moon I do sparing. Usually we try not to fully hit each others head, just touch it without any force but today some idiot I was asked to spare with hit me hard. Does the brain fully recover from this? Or is there damage done that will never heal?
|
[
"Generally the brain will recover from a hit pretty easily. A concussion can cause some damage to the brain, but will generally recover with minimal issues. Several concussions, or not dealing with a concussion properly could lead to more severe issues. ",
"Recently we've discovered something called CTE. It's a brain disorder common among high tier athletes that suffer from a lot of head trauma. Basically CTE causes something similar to alzheimers, but can also lead to more aggressive and suicidal behavior. CTE symptoms don't show up until your around 40-50 though."
] |
[
"thanks a lot for the answer. If I may ask, those minimal issues, I read they are accumulative, does that mean they last forever? what is actually there now? some sort of scar tissue, dead cells? I it even right to say, everytime you get hit in the head, your cognitive functions slow down?"
] |
[
"Indeed. It depends on the severity of the hit and how intense the inflammatory response was. These factors determine how much extra phosphorous is now available to the Tau proteins, which usually help construct the microtubules within neurons. Overexciting these Tau proteins with too much phosphorous (released by the hit) can cause them to dysfunction and cause \"neurofibrillary tangles\", which are generally considered to be irreversible.",
"OP -- You may want to consider ingesting >200mg of cannabidiol (CBD) before and after your sparring rounds, as recent research has shown that it can prevent Tau proteins from becoming overexcited. For more reading on CBD and Tau, I strongly suggest this article: ",
"https://learn.woahstork.com/cannabis-science/cbd-for-cte/"
] |
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