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[
"Why do \"cold\" and \"hot\" burns feel the same to the touch of human skin?"
] |
[
false
] |
Burning is typically associated with heat or fire, but at times is also related to damage from extreme cold. What, why and how are the distinctions of extreme temp "burns" decided and what defines a "burn"?
|
[
"Because after a certain threshold, only neurons associated with pain are firing. The ones sensing hot and cold become irrelevant. So both sensations just feel like pain. And both hot and cold when extreme can cause tissue to die which may answer you burn question."
] |
[
"Sorry for being a little off-topic but I thought it worth mentioning that this is true for any perceptions. Pain has its own neural network and associated pathways. Thermoreceptors, mechanoreceptors etc. are all separate and distinct and do not respond to noxious stimuli (i.e. things that cause you pain). Once a stimulus reaches that point it kicks off the nociceptors (pain receptors) and you feel pain. So pain from an ice burn and pain from a thermal burn should feel the same. As should pain from whacking your thumb with a hammer and so on. "
] |
[
"Having smashed my thumb a disproportionate number of times, why do crush injuries feel warm? Is it because hot/cold burns kill cells locally where as crushes are deforming the tissue and damaging cells over a more distributed area?"
] |
[
"Why is cyanide an anion, but carbocations cations?"
] |
[
false
] |
[deleted]
|
[
"They're real, and they're sometimes stable, too. The triphenylmethyl cation is probably the most famous example."
] |
[
"Have you learned about formal charge? The difference between the two is that cyanide's carbon atom has a lone pair and the carbocation doesn't."
] |
[
"Is a carbocation a real thing or just a theoretical placeholder for demonstrating a mechanism?"
] |
[
"Why do some antihistamines make you sleepy?"
] |
[
true
] |
[deleted]
|
[
"First generation antihistamines (i.e diphenhydramine) cross the blood-brain barrier, and thus can affect the brain directly. While we call them \"antihistamines\" because they affect histaminergic receptors (which are responsible for allergic reactions , among other things), they also have other effects, such as blocking cholinergic receptors. The overall effect on the brain is sedating.",
"Second generation antihistamines were designed not to enter the brain as easily, and thus the brain effects, such as sedation, seen commonly in first-generation antihistamines are much less pronounced."
] |
[
"This. 1st generation antihistamines are full-blown psychoactive drugs, usually considered \"deleriants.\"",
"Eating 8-10+ Benadryl will get you high asf for 6 or so hours, but like... Not a good high: Itchy, confused, and sleepy but unable to sleep."
] |
[
"To discourage the curious, benadryl is not to be messed with. People can die from overdosing. It’s rare but there have been cases of children taking 5 adult benadryl tablets and never waking up, usually due to negligence or ignorance from the caregiver."
] |
[
"How would you prove to a skeptic that the earth is round, not flat, using only instruments made from common household materials?"
] |
[
false
] | null |
[
"Such hypothetical / speculative / open-ended questions are better suited for our new-ish sister sub ",
"/r/asksciencediscussion",
". Please consider reposting there instead."
] |
[
"You've misunderstood my question. It's not about whether the earth is flat. It's intended to elucidate fundamental facts and methods of astronomy, and also, possibly, the history of science and astronomy. I don't know the answer myself. I don't know if there is a good answer, but it seems an interesting question."
] |
[
"Sorry, my last response as the canned response I give to all questions that fall under one of the three question descriptions. In this case, the question is open-ended in that there is no one specific answer; it's really a discussion-based question. You're asking for people to come up with an experiment / demonstration. That's precisely what our sister-sub ",
"/r/asksciencediscussion",
" is for."
] |
[
"My eyes see in different colors. Why?"
] |
[
false
] |
My left eye sees in hues of red and my right eye sees in hues of blue. Now, I still see in full color, but its like my eyes were ran in photoshop to add 5% color. Sometimes it is more noticeable than others and can make me a bit dizzy. Not sure if it is relevant but I have heterochromia. Why?
|
[
"I have the same thing. I never really even thought about why, I just always kinda accepted it. My left eye see's yellows and reds far better than my right, and my right sees blues and greens better. I've never been able to find an explanation. This sounds like it could definitely be a reason for it though."
] |
[
"I have the same thing. I never really even thought about why, I just always kinda accepted it. My left eye see's yellows and reds far better than my right, and my right sees blues and greens better. I've never been able to find an explanation. This sounds like it could definitely be a reason for it though."
] |
[
"I'm no expert, but I'm pretty sure everyone has a blue/red tint on opposite eyes. Go ahead a try it. Close one eye for a bit ( like 30 seconds) and look around with the other eye, then alternate open/closed eye. I've asked random people to do this (family, friends) and they all have the same experience. "
] |
[
"Can thunderstorms affect a wireless signal?"
] |
[
false
] |
[deleted]
|
[
"Wifi and cellular systems use microwave radiation (like your microwave oven, except far far less power). Microwave radiation rips absorbed quite readily by polar molecules like water and fats. (this is how microwave ovens cook food, imparting the energy of microwave radiation into kinetic energy of water and fat molecules. Thunderstorms obviously come with a high amount of atmospheric moisture. It is no coincidence that your wireless devices suffer from decreased connectivity during thunderstorms. The moisture in the environment blocks the signal rather effectively due to the polar nature of water molecules. "
] |
[
"Rips=is. iPad typing, apologies. "
] |
[
"Ah yes. My apologies, this is correct, fats are not polar. They do still absorb microwave radiation and convert it to atomic vibration though."
] |
[
"Ask Anything Wednesday - Engineering, Mathematics, Computer Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"So I've been thinking about this one, there was this YA book I read a while back called Artemis Fowl and The Eternity Code",
"Basically it's an encryption system that is unbreakable because it creates a new language each time it does its thing. Is something like this possible?",
"I'm not sure if I'm even asking it correctly. Thanks"
] |
[
"Some expert can probably correct me/expand, but before all a precise definition of the cryto system is needed to evaluate it's security (security in the technical sense of computational hardness).",
"That said, for example say you and your friends generate create a language through some system, and use it for a while (and then some time later change it). If an enemy obtains an excerpt of your communication, even without knowing about the details of the generated language, will be able to make statistical guesses (inference) based on knowledge like frequency of certain words (pen, table, love, life, etc) and grammatical structure. An assumption often made is that the enemy will know the system that generates the languages, but won't know which language was generated (so he has some baseline to make guesses -- e.g. he may know all languages contain articles, or something like that) -- this is known as Shanon's maxim, \"The enemy knows the system.\". Even if he doesn't know the system, that part should (?) be easy, and the security should lie on the 'key' that generates each language.",
"Back to the generated language, you and your fellows need to communicate a short enough period such that the enemies analysis is guaranteed to fail. I'd say anything more than a single word communicated may be vulnerable (it will give off ",
" information, not certainty). But if you're communicating a single word generated from a language that's in turn generated by a more traditional crypto system, why not skip the language altogether (that's complicating and probably introducing vulnerabilities) in favor of a well trusted system, like a stream cipher (essentially plain text XOR cipher text)? I guess it's just a plot device."
] |
[
"I heard recently a new prime number was discovered. How was this possible? Was there a recent break through in mathematics or computing that led to it?"
] |
[
"Do operating theatres have to be a certain temperature in order to proceed with a surgery?"
] |
[
false
] | null |
[
"The room does not have to be a specific temperature, but the patient does. Remember, the patient is naked most of the time, and receiving chemical paralytic medications, so they can't shiver, and will quickly become hypothermic if left lying on a table in a 70-degree room. Being hypothermic will actually interfere with blood clotting, so it's a major concern during an operation. We have ways of trying to keep them warm (blankets, hot air blowers, infrared warming lights) but we often have to modulate the room temperature as well, especially for vulnerable patients like babies and burn victims who can't self-regulate very well. This is so important that, in the US, we actually have to take a temperature on every patient leaving the OR as it is a government-reportable quality metric."
] |
[
"Off the bat, there is a common misconception that it prevents bacteria growth. Just feel in your fridge and it is a lot colder than any operating room. You also don't want the patients body temperature to drop so you can't expose them to the cold for very long. But it definitely isn't cold enough to prevent bacteria growth.\nAlso consider the clothes and the stress of the surgeon. It may help keep sweating down if there are multiple layers or it is a tense environment.\nMy anesthesiologist said that he didn't care about the temperature in the OR when I said it was cold, so one can also infer that anesthesiologists and the surgeons have differing opinions in regards to temperature.\n",
"https://www.boundless.com/microbiology/textbooks/boundless-microbiology-textbook/culturing-microorganisms-6/physical-antimicrobial-control-69/low-temperatures-403-5323/"
] |
[
"It also depends on the type of operation. I just finished a rotation in a burn ward. All operations are conducted in a room at 37 degrees (civilization units) and with a humidifier, as patients without skin coverage and repeated rinsing the operation are prone to hypothermia and dehydration from accumulated bloodloss/evaporation (we have transfusions and IV fluids for that, but still). as a sidenote I can inform you that all personel are required to shower between operations, it gets HOT under the sterile gear!"
] |
[
"When a woman is pregnant does the baby follow the same sleeping patterns as the mother? Or can they have 2 separate sleeping patterns?"
] |
[
false
] | null |
[
"Fetuses are asleep almost all the time until third trimester, when they’re awake 2-3 hours per day. It’s unrelated to mom’s sleep, although people think it is because they notice their movement more when laying down and trying to sleep.",
"Edit - since this post became popular, I’ll add some info. ",
"Fetuses rapidly cycle between active states. We don’t know if that is sleep as we experience it, but they have REM activity like adults do when they sleep so it’s possible. ",
"Unlike adults, it is believed that they don’t have the muscle inhibition during REM that prevents movement, and therefore they move a lot in their REM phases. ",
"Here ",
" is an article that shows REM like patterns (actually the most active active state) occur in <6% of the time in 3rd trimester fetuses."
] |
[
"They burp and cough and yawn and chew on their hands and feet and roll around and do all sorts of stuff.... Well.. that's probably most of it."
] |
[
"I just thought fetuses were in a suspended animation state while they are in the womb. I would have never thought. Now, when they are awake are their eyes open and such?"
] |
[
"May longitudinal eletric field oscillations be considered EM waves?"
] |
[
false
] |
EM waves must be transverse because of the way the oscillations on electric and magnetic fields perpetuate each other as they propagate from the source. However, even without this mechanism, imagine this: You have two eletrically charged spheres near each other, each one being held on their place by a spring that allows them to move in the direction in which they are aligned (see drawing below). (this would be the system in the equilibrium state)(sorry for being lazy to draw the electric fields) The electric field both produces is strong enough to cause the other to oscillate if you move one of them. And then, you pull one of them, making it oscillate and making both work as oscillators coupled by the electric field. In this scenario, the variation of the field (that corroborates with the motion) occurs in the same direction they oscillate. And as nothing can propagate instantaneously, this oscillations must propagate through the space between both. So, it's an oscilation in the electric field, that's propagating between them and transfering energy from one to other. Why can't it be considered as an wave? Even if in a small scale, as it decays rapdly as the distance increases, differently from an transverse EM wave (like the very-low energy transverse EM waves that they would be producing during this). Other scenario i could propose to simply talk about the longitudinal variation of electric field would be the field in the front of an flat charged surface (like a thin metal sqare) as you change it's charge, making it positively and then negatively charged.
|
[
"But this is considering that both spheres would oscillate in phase with each other, isn't it? ",
"I'm considering i'm starting the movement by pulling one of the spheres abruptly, and not moving both simmetrically out of the equilibrium point.",
"Doesn't really matter, the spheres do not actually interact at all and neither do their respective fields (static or radiation), the above will apply to each separately.",
"Plus, if you had an similar system but now with an separation of 2 light-seconds and very, absurdly strong electrical charges (ignoring the problems about the energy density this would suggest), shoudn't one sphere start moving 10 seconds after you started moving the other spehere? ",
"Who is moving the spheres?"
] |
[
"Are you moving the spheres, or do you assume they move as the effect of some phenomena, or...? Are they dynamical or \"on-rails\"?"
] |
[
"But this is considering that both spheres would oscillate in phase with each other, isn't it? ",
"I'm considering i'm starting the movement by pulling one of the spheres abruptly, and not moving both simmetrically out of the equilibrium point.",
"Plus, if you had an similar system but now with an separation of 2 light-seconds and very, absurdly strong electrical charges (ignoring the problems about the energy density this would suggest), shoudn't one sphere start moving 10 seconds after you started moving the other spehere? Shouldn't the change in any eletrostatic field be perceived non-instantaneously by things around it? "
] |
[
"Would a lead jacket compensate for bone loss due to low gravity on Mars?"
] |
[
false
] |
I would think that you would lose a lot of bone density on mars due to the low gravity. Would a weighted jacket help?
|
[
"Yep, probably. Weight lifting on earth has been shown to increase bone density, and astronauts on space stations use bungee cords to force them down onto treadmills. I think anything that adds extra stress to your bones increases their density, and a lead jacket would do that on mars."
] |
[
"There are a few of reasons I do not think this would work/isn't a very feasible idea:\n1. The increased weight would only help to reduce decrease of BMD of lower body.\n2. The weighted jacket would change center of gravity of the body and would cause detrimental damages to bones during movement.\n3. Because weight is relative to gravity the weight experienced when standing versus jumping can be extremely different when wearing a weighted jacket.",
"\nSince weight on a planet is figured by using W=MassxG, during jumping, the acceleration of a body downward increases the force experienced by the knees. Due to a weighted jacket, this weight would be considerably more than our knees/bones could handle and again could cause damage to our skeleton. "
] |
[
"The weight experienced when standing versus jumping is always different. Look, it happens on Earth too and without a lead jacket. Amazing.",
"Due to a weighted jacket, this weight would be considerably more than our knees/bones could handle and again could cause damage to our skeleton.",
"He didn't say how heavy the jacket was. I think your only valid point so far is that it would change the center of gravity and put pressure in areas where it shouldn't. In order to spread out the effect you can wear a heavy suit to put extra mass on the arms, legs... etc. Spread it out proportionally."
] |
[
"Why do cells die from low oxygen?"
] |
[
false
] |
As far as found out from google, cells need oxygen to produce ATP , and necrose on low ATP levels. So why do cells do that? Why dont they just 'stand by' till they get more oxygen?
|
[
"There are certain processes that are required to maintain vitality and those consume ATP, some cells can't just switch off and on at will. On the other hand some bacteria create capsids when in unoptimal circumstances, this puts them in a \"low consumption state\" and they are known to survive low periods of time with little to no water and/or oxygen"
] |
[
"It's not true for all cells/organisms. But for mammalian cells, there are a number of biological and chemical gradients within the cell that must be actively maintained, on a permanent basis. Without an energy source (oxygen is the combustive of respiration) this homeostasis collapses",
"Eventually the proteins that make up the cell would start to degrade as well but that's a much slower process."
] |
[
"capsids",
"Do you mean spores?"
] |
[
"Are peripheral and central neurons structurally different?"
] |
[
false
] |
Do these neurons just serve different functions due to their location and connections, or is there something structurally different about them? I was reading about hot flatworms can remember things even after their brain is cut off and regrows, so I'm wondering if peripheral neurons could serve the same functions as CNS neurons, or if they are structurally different?
|
[
"So the thing with neurology and nerves are that generally speaking, everything is super specialised in their structure to aid in their functions, and there are many different types of nerves both in the periphery and in the CNS.",
"Let's look at peripheral nerves on their own, even before we bring central nerves to the mix.",
"For peripheral, I'll just crudely focus on motor and sensory neurons.",
"Structurally, most nerves will have a cell body, an axon, and dendrites that will form communications with whatever it is they need to form a communication with. They can also be classified as either unipolar, bipolar, or multipolar, and I'll give an example further down. ",
"Take a look at this image ",
"here.",
"Note the different position/size/structues of the cell body when comparing the motor neurone to the sensory neurone. The sensory neurone here is a pseudo-unipolar nerve, and the motor is a multipolar nerve, and these terms relate to both the structure of it, but also how many communications the nerve is able to have. Furthermore, the motor neurone will have a neuromuscular junction where it will communicate with whatever muscle it's attached to, whereas the sensory one won't have that. ",
"A sensory neurone",
" however, depending on where it is may have some other structures such as Ruffini or Pacinian corpuscles which are sensitive to stretch, and vibration/pressure respectively. These structures are found in the sensory nerve endings which innervate your skin, however they're not found within other deeper sensory neurones. ",
"Autonomic neurons are slightly different to these, but I won't go into too much detail as it can get quite confusing. ",
"Now before I get into the central nervous system, I want to point out that our nervous system in general isn't just made up of neurones. Neurones are the functional unit that carry the electrical impulses, however they'd be nothing without the supporting cells that aid them. In the peripheral nervous system, a prime example of this is the Schwann cell. This is the cell that is \"wrapped\" around the axons and it forms what's known as the myelin sheath. The myelin sheath is responsible for rapid electrical conduction. ",
"Now let's get into the central nervous system. The CNS is made up of loads, and loads of different types of cells. You have your basic neurons, and they can be all sorts of different polarity, and you have different subspecialised neurons in different aspects of the brain which do different things. An example would be the Lugaro cell which is found in the cerebellum. ",
"Central neurones also have a myelin sheath, however unlike the PNS ones which are formed from Schwann cells, the myelin in the CNS is made up of a type of glial cell called ",
"Oligodendrocytes.",
"I understand this is a lot of information, and it's just scratching the surface of the wonderful world of neuroscience, however I hope it's provided a little insight into the structure and function to nerves, and to answer your question: No. Peripheral nerves couldn't serve the same function as CNS neurones if we're talking about replacement; however if you're talking about simple electrical conductivity, then yes they work in very similar ways."
] |
[
"One day! I’m currently less than a year away from finishing my medical degree, and I have a real passion for teaching. I occasionally use Reddit for opportunities to explain stuff because it helps me consolidate my own knowledge as well. I’m really glad you found it useful, and thank you for the kind words. 🙂"
] |
[
"You need to write textbooks. That explanation was much easier to understand than anything I have read about the subject. Thank you."
] |
[
"From what perspective do we look at the Milky Way?"
] |
[
false
] |
Take for example. It's hard for me to explain exactly what I mean in just text, but what I'm trying to say is when we see the Milky Way in the sky like in the linked pic, which part of it are we actually seeing? My own reasoning (which isn't backed by any form of astronomy) would be that we are looking parallel along the plane the galaxy lies on, which is why it almost appears more like a line than a spiral. But I have no expertise in this field, just awe and wonder. Thanks to whoever helps clarify this for me.
|
[
"We are part of teh Milky Way and are located on one of its spiral arms (about 2/3rds of the way out iirc). So yes, the reason the Milky Way appears as a line is that we are looking along its plane, as we are within that same plane. "
] |
[
"The Milky Way is a flatish, spiral galaxy of which our solar system is a part of, on one of the outer arms. This is why it looks like a stream, or a \"Road of Milk\" going across the sky, because what you are seeing is some part of the plane of our galaxy. If you have access to a place with low light pollution, I recommend stargazing and trying to find the constellation Sagittarius. Looking at this constellation, you are literally staring into the center of our galaxy.",
"Here is a cool video which may sort of help illustrate this."
] |
[
"Check out ",
"Stellarium.",
" This is probably one of the best tools out there for learning about constellations and such. "
] |
[
"Which planet has the best \"moonlight\"?"
] |
[
false
] |
Now I know most planets with satellites (in our solar system) are gas giants with no real atmosphere. So they are unlikely to have any "night sky" at all. But I just want to confirm this
|
[
"If you're asking which planet has the ",
" moonlight, that's something we can answer objectively. It comes down to (a) how big is/are the moon(s), (b) how far away they are, (c) what fraction of the Sun's light they reflect, and (d) how bright the Sun is at this distance (i.e. how much light there is available to reflect).",
"My first guess is that Earth has the brightest moonlight, because the Moon is one of the biggest moons in the solar system, and it's far closer to the Sun than any other large moon, but we can look at the maths.",
"Jupiter has 4 moons larger than 1000 km (and none from 100-1000 km, apparently) - Ganymede, Callisto, Io, and Europa, the classic Galilean moons. Three of these (not Europa) are bigger than the Moon. However, Jupiter is 5x further away from the Sun than the Earth is, so the sunlight is 25x dimmer. The closest large moon to Jupiter's surface is Io, which is about the size and distance as our Moon is. Europa is about 2x as far away from Jupiter as our Moon is from Earth, Ganymede is about 3x, and Callisto is about 4x further away. Doubling the distance gives you 1/4 as much light, and you have another 1/25th as much light to start with, so they'll all be much dimmer than the Moon. Io apparently has a higher albedo than the Moon - it's much shinier, and reflects a higher fraction of light - but that's not enough to counter that it gets 1/25th as much light to start with. However, the total sky area of these moons does add up to more than our Moon has from Earth - if you're on a space station in low Jupiter orbit, you will see Io about as big as the Moon appears from Earth, plus several other moons visible as small discs.",
"Saturn only has one moon larger than 1000 km, though it has several moons from 100-1000 km. Titan is maybe 50% bigger than the Moon, but it's about 3x further away from Saturn than the Moon is from us, and sunlight at Saturn is like 90x dimmer than it is at Earth. So Titan (and several smaller moons) will be visible as discs. The total angular area may add up to be comparable to Earth's moon, but the brightness will be far less. Neptune has Triton which is a bit smaller than the Moon and at a similar distance, but the sunlight is getting even dimmer at that point.",
"Pluto (if you want to count dwarf planets) is actually really close to Charon though. From Pluto's surface, Charon looks 6x the diameter of the full moon as seen from Earth. It is of course incredibly dim because you're so far from the Sun, but that's actually the most moon-dominated sky in terms of angular area/\"solid angle\".",
"So yes, the Earth's surface gets more moonlight than any other planet in the solar system. But if you don't care about brightness, and only care about what fraction of sky is covered by moon, then Pluto/Charon actually wins, and Jupiter beats Earth too."
] |
[
"Thanks for the detailed answer. Yeah, I meant brightest"
] |
[
"Came expecting \"brightest,\" was pleasantly surprised with the bonus fascinating \"biggest\" that I didn't even know I wanted the answer to"
] |
[
"What is happening to these rocks?"
] |
[
false
] |
Pics: They are placed in a south-facing window in the Pacific Northwest (ergo: it's humid). They've been there for a few months, behind a curtain. I just discovered them today—what is making them decompose? I believe we found them on the shore of Flathead Lake, in Montana. Edit: a couple more pictures: (this one you can clearly see the layered rock has decomposed on certain planes)
|
[
"That's because there are several minerals, which may be contained within those rocks, that crumble when exposed to light. Soda Niter is a good example (also called Nitratine). Orpiment is another great example, which crumbles when exposed to light (and is ALWAYS in the presence of Realgar). Changes in humidity, heat, and light can result in an enhanced weathering effect on rocks in general. Limonite, which is contained in your last sample (Gertite as well) also powders when exposed to light, and can also change its color. These rocks are doing this because of their chemical composition. Studying the petrology of these minerals in detail shows that their structures are weakly bound together, and can be drastically altered when photons interact with inclusions or imperfections in the mineral surfaces. ",
"An example of such color change is in Tiger's Eye, a variation of quartz. This mineral exhibits bands of color, which are caused when light interacts with inclusions, or open spaces in the mineral's structure. These bands are called chatoyancy. A similar mechanism is involved with objects such as star sapphires, which, instead of forming bands, form stars, which is called asterism."
] |
[
"Physical weathering: specifically the interaction of heating in the window with high humidity levels infiltrating the porous material"
] |
[
"Why would they 'perspire' their material. That is, presumably, why it looks so odd—the way the matter looks like it is being 'pushed' out of the rock."
] |
[
"How do I use a fair 6-sided die to generate a random number from 1 to 100, with each outcome occurring with the same probability?"
] |
[
false
] | null |
[
"One idea is to let the roll-1 be a digit in the base-6 expansion of a number. So if the roll is ",
", record the digit ",
"-1. All integers from 1 to 100 can be expressed with 3 base-6 digits. So you need to roll the die 3 times.",
"Now, of course, it's possible to get numbers that are greater than 100. Indeed, there are 6",
" = 216 numbers you can get by this process. If you get any number greater than 100 just try again. (Or you can have the numbers 101 through 200 correspond to 1 through 100, and then only try again if you get a number from 201 to 215 or 0.) Then all numbers from 1 to 100 have an equal chance of being rolled.",
"For example, if your three rolls are (3, 1, 6), you record the digits as 205",
", which is equal to 77",
". If your three rolls are (5, 2, 3), you record the digits as 412",
", which is equal to 152",
" (which is 52",
" in our modified game). But if your three rolls are (6, 5, 5), you record the digits as 544",
", which is equal to 208",
", and so you try again. The chance of having to try again is 16/216 = 2/27, or about 7.4%. Thus the expected number of rolls is 3*(27/25) = 3.24. So you shouldn't expect to have try again too many times.",
"I'm sure there is probably some other very clever way, but that's the first that comes to mind.",
"Another option is to divide the numbers 1-100 into 5 equal groups (1-20, 21-40, etc.). Roll the die once. If you get a 6, roll again. Otherwise, your roll puts you in one of the 5 groups (roll 1 for 1-20, roll 2 for 21-40, etc.). Then divide your group into 5 more groups (so 1-20 is now divided into 1-4, 5-8, etc.). Roll the die a second time. If you get a 6, roll again. Otherwise, your roll puts you in a new subgroup (roll 1 for 1-4, roll 2 for 5-8, etc.). Then roll the die a 3rd time, rolling again if you get 5 or 6. Your final roll gives you the number in the final group.",
"So if your rolls are (3, 5, 2), ignoring any rerolls, that gives you the subgroups 41-60, then 57-60, then finally 58. The expected number of rolls needed to get a result is (6/5) + (6/5) + (6/4) = 3.9. You can probably modify the scheme by keeping track of your rerolls to determine later rolls, or maybe just by being cleverer about the divisions, to get a smaller expected number of rolls.",
" An interesting question is whether there is an optimal method (in the sense that it minimizes the expected number of rolls) and what that method is. Clearly any such method needs ",
" 3 rolls. Just 2 rolls gives you 36 possibilities, which is too few to distinguish between 100 numbers. But 3 rolls gives you 216 possibilities. My first method based on base-6 representations tries to \"waste\" as few of the 216 possibilities as possible by having each of the 100 numbers correspond to 2 possible roll configurations. But you have to waste 16 of them. So the question then becomes whether there is a method that utilizes those 16 wasted possibilities. I would not be surprised if 3.24 expected rolls really is the best you can do.",
"Generalize this method to the problem of using a ",
"-sided die to get a uniformly distributed integer from 1 to ",
". With my method, you need at least ",
" rolls, where ",
"[; r = \\left\\lceil\\log_d(n)\\right\\rceil ;]",
", which is the smallest integer ",
" such that ",
"[; d^r \\geq n ;]",
". Then the expected number of rolls for my method is",
"[; E = r\\cdot\\frac{d^r/n}{\\left\\lfloor d^r/n \\right\\rfloor} ;]",
"(Note that for ",
" = ",
", we get ",
" = ",
", and the whole thing simplifies to ",
" = ",
", as expected.)",
" Any method must have ",
"[; E \\geq r = \\left\\lceil\\log_d(n)\\right\\rceil ;]",
". But is the expression for ",
" above optimal?",
" The problem has been solved! ",
"See this post",
" by ",
"/u/ericGraves",
" and the follow-up comments.",
"(Note that the notation used in his post and below is slightly different from the notation I have used previously.)",
"If we want to use an ",
"-sided die to generate uniformly distributed integers from 1 to ",
", then the optimal method (in the sense that it has the least expected number of rolls) is a minor modification of the first scheme I proposed based on base-6 expansions, and the optimum number of expected rolls is",
"[; E = d\\left(\\sum_{j=1}^{\\infty}{jx_js^{-j}}\\right) ;]",
"where ",
" is the ",
"th digit in the greedy base-",
" expansion of 1/",
". In the case ",
" = 100 and ",
" = 6, we get an expected value of about 3.16, slightly better than my initial method that gives 3.24."
] |
[
"How about this for outside the box.",
"Throw the die onto a 100 spaced roulette wheel. "
] |
[
"I'm going to have to ask you to take a few steps back towards the box sir."
] |
[
"Gravity at the galactic scale"
] |
[
false
] |
We stars on the other side of the galaxy as they were 100,000 years ago. They should have rotated a fraction of a degree away from their perceived position in that time. Do we feel their gravity from their current position, or are we pulled in the direction of where they were in the distant past?
|
[
"That's not entirely accurate. While changes in the gravitational field do propagate at the speed of light, the field depends on both position ",
" momentum, with the net result being that the \"pull\" is toward their instantaneous, as opposed to retarded, position. So while we are \"feeling the gravity\" from where they were, the effect is to pull us toward where they ",
"."
] |
[
" As far as we know, gravity propagates at the speed of light. "
] |
[
"Well, I suspect it would assume ",
" motion, but really it's a hard question to answer: in talking about us being pulled toward them we're tacitly ignoring whatever might be causing them to not follow a straight-line path.",
"The only actual calculation I've ever seen on the matter is determining the path of a test particle in the simplified case of a single gravitational source moving in a straight line (including an argument that it holds in the case of accelerated straight-line motion), but my 3+1 dimensional geometric intuition tells me that the appropriate Newtonian approximation to the apparent instantaneous acceleration of a body is determined using the instantaneous position of all relevant gravitational sources. That is, if the inertial path of our gravitational source isn't a straight line, there must be some other gravitational source altering the path. Accounting for that source using linearity of gravitation (i.e., the Newtonian force approximation) suggests that we should be drawn toward its instantaneous position as well. Moreover, there should be a perturbative correction term due to the interactions between those two objects, and I suspect the net result would be that our Newtonian approximation should be toward the instantaneous positions of the sources ",
" accounting for their deflected motion."
] |
[
"Will the vaccine help an infected organism to fight the disease?"
] |
[
false
] |
The vaccine is used to prevent a healthy organism from being infected. But can it be helpful in other cases?
|
[
"A vaccine is essentially just something that helps train your adaptive immune system. Most people think of prophylactic vaccines when they hear the word vaccine, but there are ",
"therapeutic vaccines",
" as well. ",
"That's not to say if you have an active infection that any old vaccine will help cure it, it needs to be designed as a therapeutic vaccine. There are several already approved for use, and IMO it's going to be the eventual standard treatment for many types of cancers."
] |
[
"As others have said, vaccines are generally most effective when administered before exposure to an infectious agent, and they work by triggering an immune response which takes a few days to build up to a maximum and then provides long-term resistance (\"immunity\") to the true infection for months at least, and usually several years-life. This long-term immunity is mediated by memory B cells (and T cells).",
"However, \"vaccines\" (i.e. a moderate dose of part of/ an inactivated (\"dead\") form of the infectious agent) can also be acutely therapeutic, because they mobilise the immune system to attack the vaccine more intensely than the actual dose of the infectious agent should elicit. The antibodies that your body uses to attack the vaccine will also catch the real infection in the crossfire. As a result, you're likely to eradicate the infection before it takes hold and starts to give the most severe symptoms associated with that disease.",
"In fact, this is a major part of the post-exposure treatment of rabies, which is probably the most notable example: ",
"https://www.cdc.gov/rabies/medical_care/index.html"
] |
[
"anyway this Covid-19 it’s going to stay forever, It will be like a flu, we just have to live with it",
"This is not at ALL obvious or a foregone conclusion. In fact, there's plenty of evidence that corona viruses have a type of genome repair mechanism despite that fact that they are ssRNA viruses, though it doesn't look like it's well characterized. This is well outside my expertise but here's a couple articles where you can search for 'repair' that discuss it. ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3127101/",
" ",
"https://jvi.asm.org/content/81/1/20#sec-12",
"I also want to point out that it's unlikely that the vaccines being developed for this pandemic will be attenuated virus vaccines. There are generally better and safer methods nowadays such as inactivated or subunit vaccines and none of the vaccine development I'm aware of is going the attenuated route (but there are a ton of places trying so who knows)."
] |
[
"Do blind dogs make better scent hounds?"
] |
[
false
] |
The other senses of the blind are known to be heightened. Does this apply to dogs as well? If so, do blind dogs make better scent hounds, or does their lack of vision make them worse.
|
[
"In theory they might have better sense of smell, but in dogs, so much of their brain is devoted to scent already. I think having a tracking dog tripping over everything and slowing you down might not be worth that extra little boost. For dogs, smelling is what vision is to us. They hear a noise, they turn towards it not to see, but to smell primarily.",
"Sorry, my only source is my biology education."
] |
[
"Science and shit"
] |
[
"In terms of sight, dogs (and cats for that matter) are biologically limited by their lack of a light absorbing retinal pigment epithelium (RPE). In humans RPE works to absorb all the light missed by photo receptors to prevent the light bouncing back and hitting another receptor (light would bounce at all kinds of angles). This serves to heighten the acuity of human sight, but the trade off is we are terrible at seeing things in low light. Cats and dogs however do not have an RPE (or maybe they do just sans light absorbing capability, not sure) and thus the acuity of their vision is decreased. A photon that passes through their photoreceptors uncaptured will bounce back and could hit a different photorec. not corresponding spatially to the proper light source. But in exchange they preserve their subpar vision in low light enviroments. Their lack of RPE is also why their eyes look shiny in the night (its the light reflecting back).",
"Edit: The only source I have is my Nervous System class from a top tier university."
] |
[
"How much does personality really differ between sexes as compared to within-sex variation?"
] |
[
false
] |
I’m wondering about this because a common criticism of gay relationships is that men and women are complementary, but same-sex couples are not. However, it seems to me like sex is probably not a great predictor of complementarity. As far as personality goes, as long as there is significant overlap between the distribution of personalities for the sexes, it should be feasible to find complementary pairs both for homosexual and heterosexual couples. What I’m looking for is data that shows how much overlap there is between personalities for the sexes. Any related research would also be interesting :) Thank you!
|
[
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3149680/",
"TLDR they are largely overlapping curves. Men and women are more alike than different with the extreme ends of the distribution leaning heavily to one gender or another. \nExample, most men and women can average out to similar levels of disagreeable-ness, but take the most disagreeable person out of 1000 and it’s a man every time."
] |
[
"Even worse when the quote is how men can't understand women. Yeah Bill, it's real hard to understand them when they are unconscious"
] |
[
"It’s the statistical expression of the fact that humans aren’t very sexually dimorphic in the measured variable. There are some variables where the dimorphism is more pronounced. I believe forward cranking power (of the arm) is a good example of an instance where humans are actually pretty dimorphic (there is some but not much overlap of the bell curves)."
] |
[
"Why do some aircraft, such as the F/A-18, feature canted tail fins, despite also having \"flat\" horizontal stabilisers?"
] |
[
false
] |
The F/A-18 Hornet, among other aircraft features canted fins, as well as traditional "flat" horizontal stabilisers. Why is this? Why do the fins need to be canted? Why not just have them pointing straight up, at right angles to the stabilisers, or just have a traditional v type tail? There must be a reason but I can't put my finger on it. Anyone?
|
[
"I can't speak for any aerodynamic reasons, but right-angles such as between traditional vertical/horizontal stabilizers have a very high radar cross-section. Essentially it acts somewhat like a corner-cube and reflects a large amount of radio waves back to the transmitter. Military aircraft tend to like lower cross-section aircraft for obvious reasons. You'll notice that true stealth aircraft, namely the F-22 and the F-117 also implement this feature as one of many strategies to mitigate their radar cross-section."
] |
[
"Another partial answer is redundancy. Canted rudders provide some pitch authority, which may be sufficient to recover the aircraft in case of a stabilator failure. I've heard of of one case where a Rhino with an aileron failure had enough roll authority using differential stabilator to successfully trap on a carrier, and another where an F-35 with one of its stabs failed full down maintained control by mixing inputs from other control surfaces to make up for the severe nose-down pitching moment."
] |
[
"^ This. Also, I was curious about the anhedral geometry of the horizontal stabilator of the F4 Phantom.",
"\"After much wind-tunnel testing, it was found that the new McDonnell fighter would encounter severe stability problems at high speeds and would as a result probably be limited to speeds below Mach 2. In order to correct these problems, several important changes had to made. One of these was the application of 23 degrees of anhedral to the all-flying tailplane, which became known as a ",
". This gave the necessary degree of stability but still left the tailplane free of the jet exhaust. Another change was to the outer wing panels. The center section of the wing had originally been envisaged as a single unit spanning 27 feet from wing fold to wing fold. It was decided to give the outer (folding) panels twelve degrees of dihedral, and a dog-tooth leading edge was fitted. Another change was to the air intakes. The intakes had originally had a fixed geometry, but it was now decided to fit movable ramps to the sides of the air intakes. These ramps could be adjusted in flight to admit the optimal airflow to the engines at various speeds and angles of attack. These changes took time to incorporate in the design, and initial structural release was not authorized until December 31, 1956.\"",
"Credit",
"I suspect the same applies for aerodynamic reasons on the F/A-18"
] |
[
"Why do some people complain that their bones hurt when it rains?"
] |
[
false
] |
Usually It's people with old injuries. I've had broken bones, but I feel fine when the weather changes.
|
[
"Because the barometric pressure in the air drops, and the water in your bones can't equalize fast enough, they swell, and cause general achy-ness. ",
"Old injuries probably hurt more because when you break a bone, and it heals, it always heals a little more than it needs to to make it stronger in that area. So, there is more bone density in those people's bones than in normal people's bones, which means more swelling, and more achy-ness."
] |
[
"Nurses know their shit and don't get enough credit. :P"
] |
[
"Not a doctor, no. Just kind of a nerdy RN :)"
] |
[
"What do scientists think of the Harvard Landmark Study?"
] |
[
false
] | null |
[
"Like the other user said, it's a weird hypothesis that intelligence would lead to happiness. Even just from a purely statistical standpoint, a significantly above-average IQ puts you on the fringe of the population (due to the gaussian distribution of IQs). That marginalizes you and is unlikely to lead to happiness."
] |
[
"it's a weird hypothesis that intelligence would lead to happiness",
"It's like they were quite happy to completely ignore the idiom 'ignorance is bliss', which kind of breaks the irony meter."
] |
[
"Why would IQ be a good predictor of overall happiness? We are first and foremost social creatures, it's our bonds with others that help us thrive. Intelligence can tell us why we are sick or injured but it won't care for us when we are. If anything it may be preventative and help us avoid some misfortune, but not everything can be avoided. Sometimes bad things happen and there is nothing you can do...but relying on friends and family can get you through. That support is what matters."
] |
[
"When something becomes bleached from the sun, where does the colour go?"
] |
[
false
] | null |
[
"The color doesn't ",
" anywhere. The high energy ultraviolet radiation in sunlight simply destroys the molecules that give a particular object its color. Those molecules are colored because they interact with light, so they are naturally more susceptible to absorbing too much energy and having some or all of their molecular bonds broken."
] |
[
"Interesting! Thanks so much!"
] |
[
"Close.",
"Objects absorb electromagnetic radiation, \"darker\" objects absorb more EM radiation including more UV.",
"Objects have color because they absorb the wavelengths of visible light EXCEPT those we perceive as their color. The high energy UV changes the chemical composition and the object ends up reflecting more wavelengths of visible light and UV and appears faded over time."
] |
[
"Why does the sun look red as it nears the horizon?"
] |
[
false
] | null |
[
"Shorter wavelengths are blocked out the more atmosphere the sun has to travel through. ",
"This",
" graph is great for explaining the change in spectral response of the sun throughout the day. You can see that in the late afternoon (and of course at sunset) the solar spectrum is stronger in the reds (longer wavelengths)."
] |
[
"Sunlight passing through the atmosphere scatters off molecules of gas and other small particles. Because the strength of ",
"Rayleigh scattering",
" is inversely proportional to the fourth power of wavelength, shorter wavelengths like violet and blue light scatter more than the longer wavelengths (yellow and especially red light). The resulting sky color, which appears like a pale blue, actually is a mixture of all the scattered wavelengths. ",
"Conversely, glancing toward the Sun, and light that was ",
" scattered away — the longer wavelengths such as red and yellow light — are directly visible, giving the Sun itself a slightly yellowish hue.",
"The reddening of the sun is intensified when it is near the horizon because the light being received directly from it must pass through more of the atmosphere. The effect is further increased because the sunlight must pass through a greater proportion of the atmosphere nearer the earth's surface, where it is denser. This removes a significant proportion of the shorter wavelength (blue) and medium wavelength (green) light from the direct path to the observer. The remaining unscattered light is therefore mostly of longer wavelengths and appears ",
"."
] |
[
"It is not blocked, it is scattered. To me blocking implies absorption, which is negligible in the visible spectrum. "
] |
[
"Why does NADH and FADH2 give electrons at different points?"
] |
[
false
] |
So NADH donates its electrons at protein complex I but FADH2 donates its electrons at protein complex II. Why does this happen? Is it because FADH2 has less energy in its electrons and if so why does it have less energy even though it has the same amount of electrons as NADH. If NADH does have more energy how does it have more energy in its electrons then FADH2?
|
[
"Take a look at their structures: ",
"FAD, Wikipedia DE",
" and ",
"NAD+, Wikipedia EN",
"As you can see, there is a significant structural difference between those two cofactors - they would just not fit."
] |
[
"The Wikipedia article for ",
"Complex II",
" says that FAD is actually covalently bound to one of the enzyme's subunits."
] |
[
"What do you mean by protein complex I and II? Proteins have different binding sites for the specific cofactors they use meaning that they have specific physical pockets in their 3D structure where the appropriate cofactor can \"dock in\" and do its job. Also, usually, proteins do not receive electrons as they are catalysts, the substrate of the protein will receive the electrons, hydrogens or protons from NADH or FADH2. Apologies if I misunderstand the question but to me cofactors have nothing to do with energy, the proteins themselves (enzymes) reduce the activation energy driving the reaction - like any catalyst. "
] |
[
"In the context of Astronomy, we often hear that space contains gases and dust. What is space dust and what is it made of?"
] |
[
false
] | null |
[
"There are different kinds of space dust. Within the solar system, the dust tends to made of similar stuff as planets: iron and silicon oxides. In interstellar space, it tends to be made of organic molecules (hydrocarbons) and ice. The grains in the solar system tend to be a few microns in size. ",
"Here's a picture of one"
] |
[
"It absorbs light, making distant galaxies look redder and darker than they otherwise would. In the mid-20th century there was an apparent observation that the farther away a galaxy was, the bigger it was, which goes against everything we understand about the universe. Eventually it was realized the distance measurements were wrong because they weren't taking into account dust."
] |
[
"I think it's based on spectroscopy done by cosmic microwave background experiments, e.g. ",
"https://iopscience.iop.org/article/10.1086/303568/meta"
] |
[
"How can a photon have a position?"
] |
[
false
] |
[deleted]
|
[
"Actually photons don't have a well defined position. We describe them as excitations of fields, which have a parameterized spatial and temporal dependance, and if you try and write down an operator that describes a single photon position it doesn't work out. Either the proposed operator doesn't transform as a vector or the components don't mutually commute (both required to be interpreted as position), and it's been shown that there isn't an operator that satisfies both properties. ",
"source",
"Additionally, there are other observables that don't mutually commute for a single photon state, analogous to the position-momentum duality in the wave-mechanics picture of single particle QM. For example in the case of photon states, the electric field observable and the magnetic field observable don't mutually commute, such that every photon state is a quantum superposition of electric and magnetic field configurations. The mathematical definition of some of the more intuitive observables used in introductory single particle QM don't have immediately obvious definitions because we are a priori defining the photon states as creation and annihilation operators on a Fock state space."
] |
[
"Warning: When you read answers in this thread, keep in mind that the word \"photon\" is heavily overloaded in both scientific and lay usage.",
"Ok, forget \"photons\" for a minute. Consider a rope where I hold one side and you hold the other. If I give the rope a swing on my end, a pulse will travel down the rope to you. If I constantly swing the rope up and down I can set up a sinusoidal wave on the rope. In both cases I have excited the rope. In the first case with the pulse, the excitation has a particular position as it travels along, but since it's a localized pulse it doesn't have a single well defined wave length. In the second case of the sine wave, there isn't a single well defined position of the excitation, but there is a well defined wave length.",
"The story with light is ",
" the same. If you take the word photon to just mean \"an excitation of the electromagnetic field\" then you have not specified whether you mean a localized pulse or an extended sinusoid, or something in between.",
"In many scientific contexts we focus on one particular ",
" of the electromagnetic field which has a prescribed shape. For example, the fundamental mode of a guitar string looks like ",
"this",
". In those cases the word \"photon\" means \"excitation of the mode we're currently talking about\". So, if I say \"there are five photons in mode ",
" of the electromagnetic field\" then I'm assuming we know what mode ",
" looks like, and I'm saying that it is excited with five quanta of energy. In other words, the number of photons tells you the intensity of a specific mode."
] |
[
"Actually photons don't have a well defined position. We describe them as excitations of fields, which have a parameterized spatial and temporal dependance, and if you try and write down an operator that describes a single photon position it doesn't work out.",
"I would like to add to this because the answer might be confusing to some. Certainly we can write down a creation operator that adds one quantum of energy with all the field at a single point. This is done all the time in field theory books, normally called \"field operators\". For example, if ",
"_k annihilates a plane wave we also have",
"Psi(x) = sum_k ",
"_k e",
"which has well defined position. The article cited in the post parent to this one shows that this isn't the full story and that with the full theory you can't quite get a single point localization: there is an exponential tail around the center point."
] |
[
"How effective are plant seeds at sprouting?"
] |
[
false
] |
Given a certain plant that produces 100 seeds, how many would sprout into plants? Does this number change between families of plants, such as grasses and trees?
|
[
"This depends on a huge number of factors.",
"One thing you should take into account is the age of the seeds. seeds have a halflife and generally a certain percentage will die each year. This is a realy important factor for determining weed stress in agriculture.",
"To make stuff even more complicated you also have seed dormancy. Seeds often need signals like water, temperature or even physical stress before they germinate, but time is also important.",
"these factors are all different for families, species and even cultivars (plant breeders need to give the germination percentagefor each batch of seeds), and at any point in time a seed can be dormant, germinatable or dead."
] |
[
"Just to expand on the answers by ",
"/u/Fleur-de-lille",
" and ",
"/u/prettystupidstudent",
", germination rates can vary greatly even within families, orders, and genera (probably even within ecotype or subspecies). Dormancy is actually highly complex as a subject, and is hard to summarize in this kind of format. There is a good ",
"overview available at this link",
", which is excerpted from a textbook on plant physiology. ",
"In addition to the types of dormancy listed by ",
"/u/Fleur-de-lille",
", there are also primary and secondary dormancies, ",
"chemically controlled dormancies",
", and stratification requirements (specific lengths of time in cold, often moist soils). Some plant seeds (like many orchids) even require a fungal symbiont before the seeds will germinate (or an external sugar source), since they don't store enough carbon in their tiny seeds to grow successfully. So ",
"dormancy is broken by chemical signalling between the fungi when it infects the seed",
", the seed then germinates, and the duo (plant and fungus) grows as a mycorrhizal symbiotic partnership .",
"I study grasses, so I can make some generalizations on that group. Annual grasses generally produce more seeds (that are less dormant) than their perennial grass competitors (with, generally, more dormant seeds). This is largely to do with reproductive strategies (which ",
"/u/prettystupidstudent",
" hinted at): winter annuals (",
") often produce a lot of seeds with low dormancy (97%+ germination rates following inundation after 1-2 months of 'curing' in hot, dry conditions); perennials, especially those from arid environments like ",
", produce fewer seeds that are often ",
" dormant, so only a few percentage might germinate each year for 5 or more years after seed shatter. For ",
"Indian Ricegrass (",
")",
" from the Intermountain West, seed that is less than 5-6 years old often doesn't germinate at high enough levels to be significant, so seed is stored for commercial or restoration purposes for years before it is used. This is in contrast to a grass like cheatgrass (",
"), which may have less than 1% germination if stored in normal conditions for more than 5 years.",
"You can extend the length of time seeds will keep by storing them in cold, dry conditions. We often surface sterilize seeds (to get rid of external fungal pathogens), dry them, and then store in sealed containers at 4",
" C for years in order to maintain high germination rates. Store the same seeds at room temperature, and germination rates will oftentimes decline by 50-60% per year.",
": it varies greatly from plant to plant, and per-year germination rates can range from <5% to >95% in the same 'family' of plants (i.e., grasses). It depends on what sort of dormancy is appropriate for a particular life cycle and reproductive strategy."
] |
[
"It's actually quite hard to tell. I've germinated plants for experiments and normally I sow about 3 times as many as I need. One species will germinate at an 80% rate, while others would be more like 40%.",
"Germination rate, amount of seeds released and timing of seed release is totally dependant functional type, i.e. forb, grass, tree. ",
"Trees like oak for example have mast years, this means is that they don't release seed each year but they send out a mass of seeds when climatic conditions are optimal for germination and subsequent growth (In ecology this is called a ",
"K strategy",
") Once these seeds are germinated many environmental factors control the survival rate of the saplings, e.g. frost, distance from the parent tree, pest/ disease, drought. ",
"The germination rate of forbs and grasses depends on whether they are annual or perenial. This is partly due to the fact that whereas annuals live for one year and need to complete their whole lifecycle within the growing season, perenials do this over multiple years. However, the yeild of seeds tends to be more dependant on species type."
] |
[
"Does ISS have to increase speed after it's added more mass to remain in the same orbit?"
] |
[
false
] | null |
[
"No, mass can't be safely added to the ISS unless it has already matched orbits, so when a ship docks with it, they're already going the same velocity. The mass of the orbiting body doesn't enter into the equation when the mass is so small. "
] |
[
"No, if it's orbiting at x velocity before the new module is docked then everything will still be at x after the docking is completed. The velocity required to maintain orbit depends only on the mass of the body you're orbiting (i.e. the Earth) and the shape/size of your orbit - not the mass of your satellite/space station/whatever."
] |
[
"No. The above assumptions are correct, it does not depend on the mass of the satellite, but ",
" when compared to the central attracting body.",
"The mass of the ISS is negligible when compared to Earth so you can keep adding modules or dock several Soyuz/ATV/Cygnus/whatever and leave orbital speed the same.",
"The Moon's mass is not negligible, so in this case you not only have to consider the Earth attracting the Moon but also the Moon attracting the Earth. Orbital speed may have to change."
] |
[
"Why is LSD so powerful?"
] |
[
false
] |
[deleted]
|
[
"Not speaking to LSD specifically, but for a lot of drugs, a little bit goes a long way. Drug X, for example, might result in anti-depressant effects by reducing seratonin reuptake, but that doesn't mean the Drug X is causing that ",
". Drug X might be a ligand for Enzyme Y, which causes increased levels of hormone Z to be produced, and hormone Z is what causes the increased seratonin levels. Because of the signaling pathways, the amount of seratonin released might be very disproportional to the amount of Drug X ingested. ",
"To put that in other words, 1 molecule of drug X might cause 10 molecules of hormone Z to be released, and each molecule of hormone Z released causes 10 molecules of hormone Y (which is what is ",
" causing the effect of the drug) to be released. Thus 1 molecule of drug X can lead to the release of 100 molecules of hormone Y. This mechanism, extrapolated out to dozens or hundreds of steps, is how a very small amount of a drug can lead to very pronounced effects. "
] |
[
"\"US scientists looked up close at an LSD molecule bound to a serotonin receptor from a human brain. As it turns out, when LSD latches onto a brain cell's serotonin receptor, the LSD molecule is locked into place because part of the receptor folds over the drug molecule like a lid, and sealing it inside.\"",
"https://phys.org/news/2017-01-lsd-brain-cell-serotonin-receptor.html"
] |
[
"I've understood perfectly. Thanks for the answer! :)"
] |
[
"Why is \"gravity stronger in General Relativity than in Newtonian Mechanics\"? Is there an intuitive way to understand (at least as intuitive as relativity can be)?"
] |
[
false
] |
Specifically, for the Schwarzchild solution, the radial equation of motion for timelike geodesics looks like - A/r + B/r - C/r . I understand the A term is Newtonian gravity, the B term is some kind of centrifugal effect, but is there a physical way to interpret what the C term is?
|
[
"I think it’s much clearer if you look directly at the geodesic equation. From the point of view of a static observer (and pretending areal and proper distance are the same) then a purely radial motion looks just like Newtionian radial motion. ",
"That is the 1/r",
" term comes from the time dilation between the propertime of the infalling observer and the static one"
] |
[
"Can you point me to what exactly you’re asking about? The Newtonian force goes like 1/r",
", not 1/r."
] |
[
"Sorry I should have said what I wrote constitutes the effective potential (V(r)), which you get by doing something like this:",
"Taking the Lagrangian for the Schwarzchild solution to be L=g(dx/ds,dx/ds), with g as the Schwarzchild metric, then the Euler-Lagrange equation for the radial direction is (dr/ds)",
" = E",
" -1 + (some constant)xV(r)"
] |
[
"Are personal computers finite state machines?"
] |
[
false
] |
I Googled the question prior and got , however I don't fully understand everything past the first sentence. Why can a personal computer be considered more like a Turing machine then a FSM?
|
[
"A FSM is a machine with a finite amount of states, meaning that it can not represent infinity. This is true for your computer since it only contains a finite amount of data, whether that is 1 tb or a trillion tb, it is finite. Thus, a computer IS a finite state machine, it will run out of states given enough time. However, computer science is mostly a science of practice, and in practice, modelling infinity is not the same as obtaining infinite. You will take trillions of years to permute all the states of an average computer. This means, in practice, we model computers as Turing machines, since our computers in practice, has infinite states for trillions of years(probably more, but you can do the math on that). Thus, we can not actually verify that a computer is an FSM in practice."
] |
[
"Ok, so in response to your question (because the debate raging on in this thread is making my head hurt), yes, a computer is a finite state machine. ",
"In your link, the first answer discusses that your computer is a finite state machine in part due to the limits of it's computations before the end of the universe (ok, universe heat-death, whatever). ",
"However, the answer goes on to explain that while you can consider a computer a finite state machine, it's better to call it a ",
"Turing Machine",
", for sanities sake because of specific attributes that span both concepts. ",
"The debate in this thread talks about the semantics of a Turing Machine vs a finite state machine, because a finite state machine does NOT have unlimited states, while a Turing machine has an unlimited tape and unlimited run-time, but finite set of basic instructions."
] |
[
"Not quite. A linear bounded automaton is more powerful than a pushdown automaton, since they can decide context-sensitive languages."
] |
[
"Would the Stanford Prison Experiment yield similar results with people who have knowledge about the experiment?"
] |
[
false
] |
EDIT: I meant knowledge about the of the original experiment Of course this would be hard to answer, since as far as I know, there hasn't been an experiment conducted with these circumstances, although one could deduct from the results of other experiments in which the participants knew about the likely outcome of said experiment.
|
[
"I think he means the outcome, the experiment itself was conducted by participants that knew it was an experiment. But they didn't know the outcome at that time. A newer experiment would see different results, because the new participants know the outcome of the old experiment, so they might try to defy it."
] |
[
"Do you mean knowledge that the experiment was happening or knowledge of the outcome of the original experiment?"
] |
[
"This is what I was talking about, thank you for clarifying this for me. :)"
] |
[
"If most of conventional \"taste\" is actually smell, then why can something smell terrible but taste delicious?"
] |
[
false
] |
Specifically thinking about the durian fruit, which "tastes like vanilla pudding, but smells like the used underwear of someone you don't want to know". Knowing that taste is only composed of sweet, sour, salty, bitter, and umami, what accounts for the drastic difference between the experience of smelling versus tasting this fruit? Thanks!
|
[
"With the durian, in particular, it's more a case of ",
"a false smell",
" than a false flavor. Your tongue, with less complicated detectors, isn't affected and ignores the info from the nose. But your nose reacts more strongly, there are more than 50 different compounds that compose its scent... including 4 that were unknown to science. "
] |
[
"Wait what? There were 4 previously unknown chemical compounds that made up the smell of Durian?"
] |
[
"According to that article anyway. Looking at the ",
"study",
" they cited I found: ",
"So I think the Smithsonian's writers either read more of the report than the blurb, or overstated the number of compounds by one. I'm also not sure whether these were compounds synthesized or identified in a lab before being found in the durian, either. ",
"A quick search for the first one they mentioned brought up zero results: ",
"http://www.chemspider.com/Search.aspx?q=1-(propylsulfanyl)ethanethiol",
", though 2-(propylsulfanyl)ethanethiol was in their database. But for all intents and purposes, yes... it appears these were an unexpected discovery."
] |
[
"Why do we perceive three spatial dimensions?"
] |
[
false
] |
Is there a good reason for it? (I just read Flatland)
|
[
"I'm no string theorist, but I would venture to guess it is because we exist in a universe dominated by three spatial dimensions."
] |
[
"Because that's the number of dimensions there are. There aren't any more or fewer non-compact spacelike dimensions.",
"Can we ",
" a manifold with more or fewer non-compact spacelike dimensions? Of course; it's not even hard. But just because we can imagine something doesn't mean what we imagine is related in any way to reality, and in this case it isn't."
] |
[
"I'm going to go ahead and quote ",
"Barrow & Tipler",
" as they have a very pertinent commentary",
"The fact that we perceive the world to have three spatial dimensions is something so familiar to our experience of its structure that we seldom pause to consider the direct influence this special property has on the laws of physics ... It transpires that the dimensionality of the World plays a key role in determining the form of the laws of physics and in fashioning the roles played by the constants of Nature ... In 1955 Whitrow suggested that a new resolution of [the OPs question] could be obtained by showing that observers could only exist in such universes ... [Gurevich and Mostepanenko also studied the properties of universes with] all possible dimensionalities ... and concluded that \"If we suppose that in the universe metagalaxies with various number of dimensions can appear it follows our postulates that atomic matter and therefore life are possible only in 3-dimensional space\".",
"They go on to discuss the effects of N dimensions on gravitation (only N=3 leads to stable orbits etc), electromagnetism (only N=3 prevents reverberation and distortion), behaviour of trajectories, dimensional analysis, the brain, and a discussion of the possibility of more dimensions that are much \"smaller\" than the 3 we are familiar with."
] |
[
"According to the graph inside, the temperature of Earth's atmosphere fluctuates back and forth as you increase in altitude, how come?"
] |
[
false
] |
This is the graph I am talking about Also, why does the atmosphere seem to change linearly in the Troposphere, but in the other regions it doesn't?
|
[
"Short answer: different layers of atmosphere interact and distribute solar radiation in different ways. ",
"Lower levels of atmosphere transfer energy primarily through thermal conduction, in which hotter particles impart heat through contact with cooler ones. The surface of the earth absorbs most of the solar radiation that makes it through the atmosphere, which means that traveling upward 1) brings you farther away from the largest conductive heat source 2) lowers the atmospheric density so there are fewer particles transferring heat.",
"At a certain point (look up the thermosphere), radiative heat (direct photon absorption) dominates and the temperature rises due to intense exposure to solar radiation that is attenuated further toward the surface.",
"Futher out in space, you encounter very few thermally energetic particles, but are subjected to insane amounts of radiation. That is why satellites and the like have shielding and are covered with a reflective foil substance - to protect the interior of the instrument from radiation levels much higher than we would ever experience on earth (possibly short of nuclear fallout)."
] |
[
"Lower levels of atmosphere transfer energy primarily through thermal conduction, in which hotter particles impart heat through contact with cooler ones",
"This is false. Conduction is only important in a very small boundary layer (less than a meter) near the Earth's surface. Within the troposphere, energy is moved in the vertical dimension primarily by convection and radiation (recognizing that latent heat plays an important role in convection). What is usually referred to as the \"boundary layer\" in atmospheric physics (generally the bottom few kilometers of the troposphere) isn't a conductive boundary layer, it is a turbulent boundary layer."
] |
[
"Temperature changes approximately linearly in the troposphere because it tracks the ",
"adiabatic",
" ",
"lapse rate",
" (the temperature change a parcel of gas will experience if it changes pressure and density without exchanging energy with its surroundings). In the troposphere energy is exchanged vertically by radiation and convection. Convection is what happens when you have warm air underneath cold air: the situation is unstable and the air masses will try to switch places. However, when density and pressure vary vertically in addition to temperature, the line between stability and instability is not simply warm below cold, but is a more complicated function (",
"potential temperature",
") related to the adiabatic lapse rate. If the temperature drops with altitude much faster than the lapse rate the atmosphere will be unstable, and convective overturn will happen. If the temperature drops slower than the lapse rate, vertical heat transport will stagnate and the surface will warm up by absorbing solar radiation. (Remember that this is all on average: local temperature inversions and other deviations from the adiabatic lapse rate can and do happen all the time).",
"In the stratosphere, temperature increases again because of absorbtion of UV radiation by the ozone layer. Starting from the cold temperatures at the top of the troposphere (the tropopause), the UV absorption steadily adds energy to the atmosphere and increases temperature as altitude increases. Because this is a situation with warm air above cold, the stratosphere is stable against convection. This is why \"anvil\" thunder clouds exist, because convection gets shut down (for the most part) when storms try to penetrate into the stratosphere.",
"I do not know enough to talk about the mesosphere and the thermosphere off the top of my head."
] |
[
"Does it require more battery power to stream music using a data plan vs. using WiFi?"
] |
[
false
] | null |
[
"Hi BlistersOnMySisters thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
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", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Computing"
] |
[
"'Computing'"
] |
[
"If whales evolved from rat-like land mammals, how did their blow-holes develop and how did their size so substantially increase?"
] |
[
false
] |
This is a mammal I have difficulty in comprehending its evolution. Something so small affecting the emergence of something so large.
|
[
"First, we need to deal with a misconception. You say that there is an (apparent) lack of animals on a path to some major physical change, but here's the thing... how would you be able to tell?",
"If you take a snapshot of life on Earth at any given time, such as now, it won't look like many of the animals are on the path to a major change. They're all perfectly happy where they are, successful in their niches. If they weren't, they'd be dead, after all! If you happened to look at, say, a theropod dinosaur millions of years ago, you wouldn't see any clues that it was on the way to becoming a bird. Or at least, you wouldn't see any clues without the benefit of hindsight -- obviously its feathers and overall form would be a big clue, but only because you ",
" that its descendants will one day be birds. If you lived in that time, and had no advance knowledge of its ultimate evolutionary destiny, you wouldn't even suspect that in a few million years its descendants would be flying.",
"Maybe polar bears will be fully aquatic in a few million years, growing to the size of small whales and hunting dolphins. Maybe the dolphins that fish in extreme shallows will eventually re-invade the land. Maybe parrots will evolve human-like intelligence and develop vastly more dextrous feet. Rats might become predatory and grow to be ten feet long. Deer, after many years of dealing with the threat of roads, might become far smaller in order to require smaller ranges, and end up the size of chihuahuas.",
"None of the possibilities listed above should sound extremely far-fetched. Evolution has produced much bigger changes in the past. So if it's not at all far-fetched that ten million years from now there might be ten-foot-long giant predatory rats, how can you possibly say that a rat isn't in the process of transforming into something else?",
"Evolution is slow. Human lives are short. When you see only a tiny snapshot of a very long process, it looks like nothing is happening. Only with the benefit of millions of years of hindsight can we see the massive changes wrought by evolution."
] |
[
"Here's a fascinating tidbit from the Wikipedia blowhole article:",
"The blowhole of a sperm whale, a toothed whale, is located left of centre in the frontal area of the snout, and is actually its left nostril, while the right nostril lacks an opening to the surface despite the fact that its nasal passage is otherwise well developed."
] |
[
"Here is a wikipedia article and 2 discovery articles that will help you understand more about this topic. Although there are common rat-like ancestors, there are also better intermediate examples that were amphibious and maybe give a better resemblance.",
"\nOn the size thing, there are only speculations of course, but the most common theories involve the abundance of food and the skeleton adapting to water(less restrictions).",
"\nI can't find a reference to the blow-holes but if you look at the images of the skeletons and digital reconstructions of intermediate species you will notice that their nostrils start from the edge of their long noses and gradually goes further back which would give them some advantage being fully submerged.",
"http://en.wikipedia.org/wiki/Evolution_of_cetaceans",
"\n",
"http://news.discovery.com/animals/whales-dolphins/blue-whale-larger-than-ever-120131.htm",
"\n",
"http://news.discovery.com/animals/dinosaurs/how-dinosaurs-got-so-big-120131.htm"
] |
[
"If the universe was finite and there was an edge, what would happen if you went outside of it?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"It is hypothetical or speculative in nature. We do not allow hypothetical questions because questions that cannot be confidently answered with any available data often invite non-scientific speculation. For more information regarding this and similar issues, please see our ",
"guidelines.",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
". It might be too open-ended or speculative for ",
"/r/askscience",
". ",
"/r/AskScienceDiscussion",
" is also a better place for advice on education, book suggestions or general questions about working in STEM. Please feel free to repost there!",
"Please see our ",
"guidelines",
"."
] |
[
"/r/asksciencediscussion",
" is a toxic pool of iamverysmarts"
] |
[
"Well, it's too bad that you feel that way, because this question is not appropriate here."
] |
[
"When a supernova explode and collapse to a black hole, how much time does it takes from explosion to being a singularity ?"
] |
[
false
] |
Is the speed of the density increase constant, accelerated, decelerated ? In the time frame of a distant external observer
|
[
"The dying star doesn't really explode, it impodes. The singularity is formed as soon as the fusion power of the star can't stop the force of gravity from crushing the core. As the inner core shrinks and the singularity is formed it begins to eat the star but it can't handle the compression of the outer core. The outer core will rebound and blow the star apart. It only take a matter of seconds for this to happen once the singularity is formed. Only a star with 8x the mass of our sun has the mass to create a singularity and the supernova I'm describing is a type 2"
] |
[
"As the inner core shrinks and the singularity is formed it begins to eat the star but it can't handle the compression of the outer core",
"What do you mean by 'not handle the compression'? Wouldn't the singularity eat anything pushing inward?"
] |
[
"An accreting black hole does not eject anything from beyond its event horizon. The reason the accretion rate is not unlimited is that as matter falls onto the black hole, it heats up as it compresses and runs into itself. If enough matter tries to fall in all at once, it gets so hot that the pressure from its own thermal radiation is enough to prevent any more matter from falling onto the black hole. This is called the Eddington limit."
] |
[
"Is artificial gravity even theoretically possible?"
] |
[
false
] |
In nearly every sci-fi show or game or whatnot, the spaceship has an artificial gravity device on it that allows for everyone to walk around like normal. Even if we had some amazing technology with some kind of infinite power source, is it even possible to manipulate gravity like this?
|
[
"Yes. You can simulate gravity yourself with a simple experiment using centrifugal force. Get a bucket and fill it with water, make sure the top is open. Rotate your arm over your head and back to a resting position quickly making sure to move your arm in a fluid motion. ",
"Like this.",
"So what science is at work here? ",
"Centrifugal force",
" caused by the rotation of the bucket in a circle makes the water want to move in an outward direction. However, because the bucket has a bottom, the water is prevented from leaving. This is one of Newton's Laws of Motion that every action has an equal and opposite reaction. As the water pushes on the bottom of the bucket (artificial gravity), the bottom of the bucket pushes back on the water. This holds the water in place the way that our gravity does.",
"So if we made a space station that rotated, we would be able to produce artificial \"gravity\". A minor thing that could be both a blessing and a curse is that the farther from the center you are, the greater centrifugal force you would feel. So we would actually be able to control the levels of artificial gravity that the object would experience. We would be able to take people closer to the center to experience less gravity and farther from the center to experience more gravity.",
"However, I'm not entirely sure that's what you meant as we would be using centrifugal force and calling it gravity, not actually making gravity. According to Einstein, gravity is a body of mass' displacement of space-time. So in order for us to produce true gravity, we would have to take a large amount of matter and compress it into a small space. I'm not entirely sure how realistic it is because you can only compress matter so far before it would either turn into a singularity and produce a black hole, or begin to expand because its energy would be greater than its gravity, basically the idea behind the Big Bang. Another problem that we'd run into is that because it would take so much mass to produce Earth-like gravity, the space ship would weigh so much that you'd likely never get it into orbit. At least not in any cost efficient way.",
"EDIT: Added a statement.",
"EDIT 2: Added a hyphen. Sorry, I'm a slightly OCD when it comes to grammar."
] |
[
"If you've ever played Mass Effect you'd know what this guy is talking about. The Citadel simulates gravity by rotating, and it is a comfortable 1.02 standard G's on the Wards and a light 0.3 standard G's on the Presidium Ring."
] |
[
"As far as we know...no. However, you can exert forces that would be perceived similarly to gravity (to different extents) in ",
"several ways",
". Though again, none are currently viable for actual use on a spacecraft."
] |
[
"Whenever I buy a lottery ticket I remind myself that 01-02-03-04-05-06 is just as likely to win as any other combination. But I can't bring myself to pick such a set of numbers as my mind just won't accept the fact that results will ever be so ordered. What is the science behind this misconception?"
] |
[
false
] | null |
[
"I'm not sure if there is a name for this heuristic, but is has to do with our ideas about randomness and what we think a \"typical\" set of random numbers or events looks like.",
"Another example of this occurs when you ask people to simulate flipping a coin 100 times. In the sequence of heads and tails that they write down, people will include many fewer and shorter chains of repeating values than would be statistically expected. For example, people rarely write down a sequence of 8 or more heads or tails and usually don't have more than one such sequence. However, these are actually much more likely to occur in 100 flips than people expect and a computer would generate more and longer sequences. ",
"Edit: as others have pointed out, this is an example of the representativeness heuristic and gambler's fallacy."
] |
[
"Gamblers fallacy. It's also to do with misunderstanding that each event is completely independent of any that came before and any that will come after which is why such a combination is statistically just as likely as any other. Our intuitive understanding of chance is such that, once something has occurred, it is then less likely to reoccur. Obviously this cannot be true when each lottery event is essentially like having a clean slate. "
] |
[
"While it's true that 01-02-03-04-05-06 is just as likely to win as any other combination, you probably shouldn't choose that sequence, because it's likely that many other people have chosen the same sequence, and you'll have to split a top prize more ways if you win one. If you pick \"random looking\" numbers instead, your numbers are less likely to collide with someone else's random looking numbers."
] |
[
"Does the moon have any legitimate effects on behavior?"
] |
[
false
] |
[deleted]
|
[
"If it did, the phase would be the main independent variable and the effects would cycle over a month. The distance pretty much has no effect besides making the moon look bigger right now. Female hormones vary across that length of time, but that's not directly caused by the moon."
] |
[
"There's been ",
"some study",
" on this, both for human patients and animal patients. ",
"This study",
" seems to contradict you, saying that trauma rates were 2.1% lower than average on full moons (over a 36 year period).",
"It's got to be a tough thing to get confident results on, though, since you can never do any sort of blind study. Everyone has access to the state of the moon and knows society's preconceived notions of a full moon, so you can never be sure if people are unconsciously modifying their behaviour according to expectation."
] |
[
"I've read that men have periodic fluctuations in hormone levels too, with about the same frequency. I was trying to find a reputable study, but Google Scholar is all about daily LH signals and Google is full of old wives' bullshit."
] |
[
"What are p-values? What would it mean to go from a p-value of 0.05 to 0.005?"
] |
[
false
] |
A month ago, made waves by publishing that the standard p-value should be changed from 0.05 to 0.005. If my intro to statistics covered p-values, I have completely forgotten, and the description in the commentary is abstract for me. (cross-poted to and )
|
[
"EDIT for clarity: The proposal under consideration is about changing how we interpret p-values. So I need to go through what p-values are, then we can talk about the proposed change to a threshold called alpha that is used when we interpret p-values. ",
"The p-value is the likelihood of getting data at least as unlikely as the data you actually got, ",
". If you leave out any part of that definition, you are not talking about p-values and you will mess up in your reasoning (and I would ding you points on your exam, I used to teach intro statistics).",
"Null hypothesis testing is a probabilistic version of proof by counterexample. You assume something, you show that your data is very unlikely given that assumption, and that provides evidence that your assumption is false.",
"For example, you might assume that your drug is no better than placebo (is equally likely to cure patients). Then you administer the drug to a bunch of patients, and the placebo to a bunch more patients, and you compare how many patients were cured. ",
"If more of the patients who got the drug get better, then you have evidence against the null hypothesis that they're the same. ",
"But, if roughly similar numbers of patients were cured, then you haven't shown anything at all; maybe your drug isn't better, or maybe you just didn't have enough patients to prove anything.",
"The bigger the difference between the two, the smaller the p-value, because it's less likely the drug and placebo are the same if they cure different numbers of people.",
"The more people you have in the study, the smaller the p-value, because who gets better has an element of chance, and you might randomly have some placebo people get better on their own. ",
"If there's no element of chance, you don't really need p-values; it'll just be really obvious, since one thing is always better. P-values are for when you cannot tell by eye because there's too much data and the difference is too small, or when you want to prove the difference to someone.",
"In practice, we want to make up our minds at some point, even though this whole thing is probabilistic. To do that, we say that if the p-value is below a certain threshold (EDIT for clarity: this threshold is called alpha; the proposal under consideration is lowering alpha from 0.05 to 0.005), we reject the null hypothesis. If you designed your experiment right, if the null hypothesis is false, then some other hypothesis of interest must be true, and then your experiment will show support for that other hypothesis. ",
"Lowering that threshold is demanding more evidence before we are willing to reject the null hypothesis. It basically says how often we are willing to reject the null hypothesis when it's actually true. Going back to the drug example, if we insist on a p of 0.05, that means that out of every 20 drug trials ",
" EDIT where the drug isn't better than placebo, we'll average one study that incorrectly finds that the drug is better (a false positive). If we ask for a p-value of 0.005, then we'll only be wrong 1 in 200 drug trials. The threshold is essentially arbitrary; the 2 standard deviations thing is probably why that particular threshold was picked, yes, it makes it really easy to calculate since we can almost always assume an approximately normal distribution when doing these tests.",
"Given just how many drug trials are performed, that might be a good thing to do; we don't want to approve a drug that doesn't actually do anything! All drugs have side effects, and all drugs cost money, so drugs that don't do anything are bad.",
"Now, if you've been paying attention, you might note that the p-value just talks about the likelihood of the null hypothesis. And we don't actually care about the null hypothesis at all! We want to know if our hypothesis is correct, not if our null hypothesis is wrong. ",
"This is a fundamental limitation of p-values and the philosophy of statistics that spawned them, because that philosophy does not really believe in probabilities, only proportions. So it isn't about the probability of a study being wrong, it's about the proportion of studies that we're willing to accept being wrong in a certain way. Asking about the probability of a hypothesis is a nonsense question; hypotheses must be either true or false.",
"The other philosophy of statistics is perfectly happy to assign probabilities to hypotheses, with the probability representing our own uncertainty about whether the hypothesis is true or false. In reality, it's one or the other, but since we don't know, probabilities are a great way to measure our uncertainty.",
"Unfortunately the other philosophy of statistics often involves math that was untractable before computers, and the p-value philosophy had a very aggressive advocate, and so p-values became extremely popular, even though 99% of the people using them are using them incorrectly because they forget that the p-value is the probability of the data GIVEN THAT THE NULL HYPOTHESIS IS CORRECT. They leave off that part and just treat the p-value as the probability that the null hypothesis is correct. ",
"This ignores the probability of the null hypothesis given everything else you know, which is what you need to transform from what the p-value actually is to what people think it is. And if the hypothesis your testing is deeply unlikely to be true, which is extremely common since there are many, many possible hypotheses, then you need WAY more evidence before you decide to assign high probability to it, and just taking the p-value will mess you up rather badly. ",
"This is all also ignoring the fact that if you really want to reject the null hypothesis, you can just run 20 studies and one of them will come up rejecting just by chance (at a p-value of 0.05). Going to 0.005 would require 200 studies to get one to come up by chance. ",
"And there are many, many, ",
" ways to fiddle with your data to turn one dataset into 20 datasets, find one that rejects, and then not really talk about the other 19. Or to otherwise get a low p-value when you shouldn't. I've seen analyses where the math in a paper would reject the null hypothesis something like 60% of the time for totally random data. ",
"So, if we lower to 0.005, it will be harder to publish papers, because papers only get accepted if they say \"we rejected the null hypothesis (which is taken to mean 'my hypothesis was right')\"; saying 'we failed to reject the null' is taken as 'my study didn't show anything and was a giant waste of time'. Whether this would be catastrophic, I couldn't tell you; it will certainly be bad for labs publishing papers about results that aren't real."
] |
[
"I would add to this that lowering the alpha value (which is the cut-off for the p value; the point where you accept your hypothesis as true) from 0.05 to 0.005 not just only makes false positives less common (which is a good thing of course) but it also makes false negatives more common, where you conclude that your treatment had no significant effect, even though in reality it did have an effect. ",
"So choosing your alpha value is also a trade-off between getting false positives and false negatives. "
] |
[
"A p-value is the probability that the results achieved in the study were due to random chance. Usually p<0.05 is used as a threshold to determine if the study has significant results. This means practically that if the results the study showed have a higher than 5% chance of occurring randomly the study hasn't given any evidence that changes the current theory (which is why these studies aren't published which could also be a problem). ",
"5% was chosen because it's low but not unreasonably so. (And also because we seem to like 5 in our base 10 number system).",
"Changing it from 0.05 to 0.005 would be good in that results would almost certainly disprove currently held theories but the problem would be that such results (in some disciplines) might be quite difficult to get. For example, psychology research has almost a 0% chance of ever getting a study to have that low a p-value. Human bodies just can't be controlled as much as say a physics experiment which get up to 6 sigma (p<0.0001)."
] |
[
"Is the world running out of chemical formulas to create new antibiotics?"
] |
[
false
] |
[deleted]
|
[
"Not really. The possible theoretical chemical space is so vast as to be infinite for practical purposes. The \"druggable\" part of that space is smaller, but certainly not even close to being fully explored.",
"The reason why we don't have more antibiotics is a simple economic one: antibiotics generally don't make much money. Thus, pharma is not interested in pursuing them, which is fair - they are businesses after all.",
"The NIH is stepping in to fill the gap by funding more drug projects, specifically antibiotics and \"orphan\" diseases. We're still ahead of the bugs for now, and I guarantee you that many smart people are paying very close attention to the problem."
] |
[
"Thank you Ren, the exact answer and response I was hoping for, as it was a topic on debate between a workmate and myself. Is it so much so a problem, that if it were not for these philanthropic beings with the NIH, we would run out of viable combinations within a couple of generations, or do we have decades of stockpiling and potential combinations for mutated viruses that could pop up in the future?",
"Sorry for the in layered question, it's just you can't exactly ask a machine/search engine these exact questions."
] |
[
"Profitability is a big issue, but largely for reasons other than what you mention here.",
"The way it typically works is Professor Smith at State Technical A&T University discovers new potential drug (smithidone) on his NIH grant. Prof Smith gets a patent and founds an emergent biotech (Smithtech) to get cracking. He gets a technology transfer grant (like SBIR/STTR) and gets started on preclinical development. He publishes like crazy. Biological Industrial Global Partners (BIG-P) takes notice and buys Smithtech. Prof Smith goes back to his lab a wealthy man and BIG-P picks up where Smithtech left off.",
"Now BIG-P has to develop smithidone to the point where it can be prescribed. This means a lengthy and expensive process of preclinical work leading up through phase trials. It's a HUGE investment, and they won't have long before that patent clock starts ticking. And the patent clock is your window for return on investment. Generic manufacturers are chomping at the bit, ready to flood the market when that clock runs out.",
"And here is where antibiotics cause a problem. If you take Allegra, you take it pretty much constantly for 6 months out of the year. And if it works for you, you probably will never switch to Claritin. It's a cash cow; a constant revenue stream that only requires the conversion of one customer. If smithidone is the Next Best Thing in treating vascular disease, or macular degeneration, or erectile dysfunction, whichever customers buy into it are almost certainly going to stay with it. You only need one successful sale and you get brand loyalty for the rest of the patent life. One sale => hundreds of thousands of dollars.",
"But if smithidone is an antibiotic, that doesn't work. You get an infection, you take the stuff for a few weeks, and you're done. You may never take it again before the patent runs out. One sale => hundreds to thousands of dollars.",
"It's not simply a matter of BIG-P being greedy. It's largely a matter of what they can and can't do while keeping the company in the black. Yes, there are certainly internal problems with big pharma and how they run themselves; don't get me started. They certainly aren't innocent in all of this. But the current regulatory climate does throw up a big obstacle to this kind of work, largely in patents and FDA phase trials. "
] |
[
"When electrons jump from one atomic orbital to the next, how fast do they move?"
] |
[
false
] |
Electrons can only exist in defined energy levels, and cannot exist in an intermediate state. This seems to imply that the change is instantaneous. When an electron changes atomic orbitals, can it be said to have 'moved', and if so, how fast is that 'movement' if the jump is instantaneous?
|
[
"Good question. You may have heard of the Heisenberg uncertainty principle about how position and momentum of a particle have a bound, where the more precisely you know the location of a particle the less precisely you know the momentum. Well it turns out that energy and time also share an uncertainty relationship. So when you ask this kind of question things are kind of fuzzy. To change the energy, maybe you have a photon interact with the atom to excite the atom, or if the atom has an electron already excited, it could change its energy to a lower energy state and emit a photon. Stimulated emission can be very fast, picoseconds, perhaps Femto seconds, while spontaneous emission can be pretty slow. The time duration for the spontaneous emission can even be in the milliseconds if the energy level is very sharp, but often microseconds.",
"So if you know how precisely the energy level for a specific energy level you can get an idea of how long the electron would stay at the energy level. ",
"In terms of \"moving\" from one energy level to another, even though the probability distribution for the position of the electron has changed, at that instant the location of that electron hasn't changed. At least as precisely as you can determine what the position and momentum is anyway within the Heisenberg uncertainty principle."
] |
[
"It's not instantaneous. Take a two-level system, with a particle starting in the excited state. The wavefunction of the particle will have time dependence in the form of",
"exp[(Γ/2 - iE)t/",
"].",
"When you evaluate the probability density, you take the modulus of this quantity. The imaginary part of the exponential goes away when you take the modulus, and you get a probability density function for the excited state which decays in time like",
"exp[-Γt/",
"].",
"So the excited state de-excites with an exponential probability distribution as a function of time.",
"The characteristic timescale (and mean lifetime) is 1/Γ."
] |
[
"Well, the premise is in principle wrong. Electrons can and do exist in states without a clearly defined energy level, and in intermediate states. Nevertheless, electrons do change atomic orbitals.",
"The mostly complete story of atomic orbital transitions:\nThe electron begins in an upper orbital A. Because that is an energy eigenstate, the system will not change on its own. If it is slightly disturbed, for example by light or by another particle, the electron will move into an intermediate state that is a mixture of the original state and other orbital states. From there, it has a certain rate of decay to lower orbitals. Another intermediate step is not necessary, because essentially what you need is a small probability to find the electron in the lower orbital, and then the electron will sooner or later go there, release a photon and that completes the measurement process and collapses the wave function to the lower orbital state."
] |
[
"If an electron is 1/2000th the mass of a proton, how do they have the same magnetic force?"
] |
[
false
] | null |
[
"What do you mean by \"have the same magnetic force\"?"
] |
[
"2 protons = 2 electrons they have the same attraction forces...unless I'm missing something."
] |
[
"The proton and electron have equal and opposite electric charges. Their masses don't affect their electrostatic interaction."
] |
[
"How are atoms (which are made up of mostly space) affected if space is expanding faster than the speed of light?"
] |
[
false
] | null |
[
"The rate of expansion doesn't work like that. The units aren't km/s but km/s/Mpc. If you have two points at 1 Megaparsec distance, their apparent recession speed is 72 km/s (or something like that). So that speed is a factor of distance. That means no matter how how small that rate is, you can always find two points (sufficiently far away from each other) that are receding faster than c."
] |
[
"So what is it that's actually expanding?"
] |
[
"Space is expanding."
] |
[
"Is there a difference between the \"space\" between planets in a solar system, between solar systems in a galaxy, and between galaxies in the universe?"
] |
[
false
] |
Sure the distances are much greater, but do we know of any other properties that make "space" distinct in different parts of the universe?
|
[
"The amount of gas in different parts of space is different. No space is an absolutely perfect vacuum, it's all varying shades of gray. There's the solar wind near Earth, particles blasting in our direction coming from the sun.",
"In between stars, the stellar winds are weak, and there's gas called the interstellar medium.",
"In between galaxies in galaxy clusters, there's gas called the intergalactic medium.",
"All of these gasses come in different densities and temperatures, so in some ways, space can be identified by the gas that's found in it."
] |
[
"You might find ",
"this",
", ",
"this",
", and ",
"this",
" interesting. Dark matter (3rd link) is believed to be responsible for the large scale distribution of gas in the universe, including the interstellar medium (1st link)."
] |
[
"Differences in gravity, which means differences in 'bending'. "
] |
[
"Why do older people's veins look squiggly? Do veins and other internal body parts sag like our skin does?"
] |
[
false
] | null |
[
"You are partially correct. In old age, the elasticity of blood vessels decreases just like our skin. Additionally, you will notice that these squiggly veins appear on lower extremities, where the back-pressure is great in an upright posture. There are valves inside veins to prevent backflow. Eventually these valves can dysfunction, leading to the back-pressure being conducted all the way down. This further worsens the \"squiggliness\" and dilates the veins by stretching them out. These are called varicose veins."
] |
[
"I am a vascular technologist (meaning I use ultrasound to look at veins and arteries). I do a lot of vein mappings for people with varicose veins and this is a very good description of the physiology that occurs causing varicose veins."
] |
[
"OP is not asking about varicosities. - ",
"EDIT: I musta misread that. OP is asking for older people, so maybe varicosities, maybe not. If not, then the answer in non-varicose veins (like arm veins, which do get 'squigglier') is that the tissue around the veins gets floppier, and stabilises them less, so the veins become for tortuous. ",
"But I will leave this all here in case it is valuable -",
"Essentially veins only consist of thin connective tissue walls. They are not supported by smooth muscle like arteries are. Arteries look strong and straight, veins are soft and squishy.",
"Veins also contain blood at much lower pressures. Less than 40mmHg, arteries can have blood up to 2-300mmHg. This is why a venepuncture tourniquet closes off veins, but leaves arteries open.",
"Since the internal pressure is lower, outside pressure affects the shape a lot more. Muscles, fat and skin all provide pressure, and the veins divert accordingly.",
"Finally arteries are generally deep, surrounded by muscle and supported along bone. They have their own little sheaths of stiff connective tissue too. ",
"Veins are generally more superficial, and rest in fatty tissue, which can move. Which means the veins can move - try pushing one around, you should be able to move them by a cm or two.",
"All these factors add up to mean the veins really path around any obstruction. They will wrap around muscles, and over bones. Minor pressure changes will divert them. Arteries are less mobile, and in fact arteries leave impressions on the bones underneath them because they exert pressure back on the bone - you see smooth grooves along bones.",
"Interesting side note - veins are massively variable. Microevolution has been shown numerous times, with the general 'path' of veins changing during the time anatomy has been studied.",
"And yes, unsupported veins certainly sag. The big ones in the abdomen flop around a fair bit.",
"TL:DR - veins are soft and squishy for lots of reasons, and therefore path around obstacles like bones and muscles."
] |
[
"Imagine if the U.S. decided to divert 10%(72.13 billion) of the defense budget to science. What would be the most promising and necessary research, projects, and ideas they could effectively support?"
] |
[
false
] |
If we answered this and presented it as a worthwhile and necessary investment, we could use this to bring attention to the gross differences between defense vs. science expenditures. We could explain how one misuses resources and the other is an investment in the short-term and long-term future. Edit: Thank you all for your thoughts and discussion.
|
[
"Here's the problem: Just as 9 women can't make a baby in 1 month, throwing a ton of money at the problems won't make them magically be solved immediately. That said, if you want long-term, awesome and disruptive advancements, there are few better places to spend the money.",
"What I'd do with the money is establish funding for decently-paid, full time research scientists, and drastically reduce the number of postdocs. Due to the budget doubling and subsequent crunch over the past decade, there is a huge underclass of people with PhDs in hand who end up working 80 hour weeks for 38k a year in postdoc positions. They have to switch jobs every two years, while they wait for faculty positions to open up, only to be competing against 100 other applicants for each position. We could get much more productivity out of these people if we gave them a solid research position, paid them decently and let them work on science instead of stressing about applications and job prospects.",
" spelling"
] |
[
"You want more science? Make sure as many people in the word are as free from disease and hunger as possible. Make sure education is available to everyone. Yes I'd love a few extra bucks for my detector or pet projects, but the real way to improve science is to improve the world we live in. Only when people are free from ",
" trying to survive can they even begin to accomplish things like science."
] |
[
"Please note that the military does spend a lot of money on R&D, leading many fields of hard and soft sciences in the creation of what eventually becomes consumer technology. It's one of the reasons the budget is expensive, because they constantly push research and try to make it a reality, and that is very very expensive.",
"Sure their interest is largely the weaponization of the R&D, but that's another topic."
] |
[
"Mauna Loa not erupted since 1984; Kilauea has been erupting since 1983. Is it just a coincidence?"
] |
[
false
] |
Going by Wiki article on , it's currently in unusually long period of inactivity, while Kilauea is in unusually long period of activity. Are the two connected, or is that just a coincidence?
|
[
"Mauna Loa and Kilauea are thought to have a common magma source in the asthenosphere. Eruption activity on one volcano relieves pressure in the other, producing an alternating eruption pattern. Source: ",
"http://www.livescience.com/24262-kilauea-mauna-loa-linked.html"
] |
[
"IIRC, the general theory is that it's a hotspot in the mantle. As the crust moves over it, the volcano that formed the last island tends to shut down, and a \"new\" one forms, and makes a new island.",
"Which is why Hawai'i is an island chain, in the middle of nowhere.",
"Both volcanoes are on the same island, but the next one (when Kilauea shuts down), might be in the ocean."
] |
[
"Probably not unrelated. There's only so much magma coming up through Big Island, and the plumbing system below the south of the island is quite complicated. It's likely that the magma reaching Kilauea has been intercepted from the main Mauna Loa feeding system. This may well just be a short term thing."
] |
[
"Is seawater antiseptic? If not, at what salt/ mineral content is a liquid antiseptic,antiviral, etc?"
] |
[
false
] | null |
[
"My guess is those trace elements would be negligible. Let’s look at iodine first, one of the trace elements our body needs. You only need ",
"150ug of iodine a day.",
" In seawater, iodine is found at a concentration of ",
"0.05 parts per million.",
" This can be roughly converted to 0.05mg/L.",
"Doing some quick math: 150ug Iodine(1mg/1000ug)(1L/0.05mg) = 3L",
"You’d need to drink 3 liters of seawater to get your daily value of iodine, an element you really don’t need much of in your diet",
"I really like your question and I’m stuck in lab waiting for a reaction to finish. Don’t want to be ",
" productive on a Sunday so rather than update my lab notebooks and whatnot I might calculate some other trace elements as edits to this comment for funsies.",
"Also, keep in mind I’m not really even taking into account if the element in question is in a form that can be processed metabolically. You can look that up if you’d like.",
"Edit (Calcium): Calcium is at 400ppm. ",
"Recommended amount is between 1000 and 2500mg, so let’s use the low end.",
" So you’d need ",
" of seawater for your daily amount of calcium",
"Edit (zinc): zinc is at 0.014ppm. Daily lower recommended value is ",
"8mg.",
" You need a whopping ",
"Edit (iron): iron is at 0.02ppm and 19mg are needed. ",
"I think you get the picture"
] |
[
"So I just want to preface my answer by saying this isn’t really my field. Take it as you will",
"But different pathogens are going to have different tolerances to osmotic pressure. Gram-positive bacteria are more resistant to salt concentrations than gram-negative bacteria for example. And “naked” viruses are more resistant than enveloped viruses. ",
"This paper",
" found that staph (a G+ bacteria) could still grow in 15-20% NaCl solution. Seawater has a salinity of 3.5% by comparison, most of which is from NaCl",
"I’m having trouble finding similar studies for viruses but I’m also in a rush and gotta wrap this up. May edit my answer later. I’m sure these studies exist though. I’d speculate that naked viruses would be even more resistant to osmotic pressure thanks to the rigidity of their capsid, but again not my field so don’t take this as the truth.",
"So basically, salt content alone probably doesn’t make for good antiseptic, hence why they don’t just sell salt water spritzers for that purpose."
] |
[
"Related question: I've heard that every drop of sea water contains a little of every naturally occurring element on earth. Wouldn't a few sips of sea water once in a while be good for you with all those trace elements to top you up?"
] |
[
"Have humans gained any traits over the past 2000 years through natural selection?"
] |
[
false
] |
Since natural selection is a constant thing, I was just curious if anything has happened to our species since year 0(AD). No matter how weird or worthless, I wanna hear anything!
|
[
"The taller and smarter changes have happened too fast for them to be attributable to natural selection. They likely were mostly due to better diet, health care, and education."
] |
[
"We're getting taller and smarter than we were 2K years ago. It's hard to delineate those from improvements in medicine and diet though. Our skulls and brains are getting smaller and fewer people are growing wisdom teeth. Many populations have straighter hair and lighter skin due to being able to live in different climates to 2K years ago and avoid the sun.",
"Recently, many human populations have evolved to maintain the enzyme lactase after childhood which allows them to consume milk without indigestion. There is also the various anemic populations in Africa due to the advantage it poses in resisting malaria.",
"Not sure if I would call these \"traits\", but we're well on the way to being different to 2K years ago."
] |
[
"Depends on how you define humans in that question. If you mean humans and their internalized biome, i would say that human gut bacteria have gained significant traits since the industrial revolution, learning to cope with rich modern diets in addition to countless drugs, toxins and chemical pollutants. All the while supporting a complex multicellular being into an exceedingly old age. "
] |
[
"Change in enthalpy for transition of carbon in the diamond form to carbon in the graphite form is apparently a negative number (-453.5 cal). According to this, graphite is more stable than diamond, how’s that possible? Isn’t diamond supposed to be stronger and more stable than any other material?"
] |
[
false
] | null |
[
"At standard conditions (1 atmosphere, 20 degrees celsius), graphite is a more stable form of carbon than diamond. However, the energy barrier to cross means that spontaneous reordering of diamond into graphite is essentially negligible. This doesn't affect the hardness or other physical properties of the material. Indeed, an even less stable form of diamond, called ",
"lonsdaleite",
", is predicted to be even harder than standard (cubic) diamond."
] |
[
"Graphite is layered, with a hexagonal, strong bonds in each layer. Weak bonds hold the layers together.\nThe c-c lattice which makes up the diamonds structure is made of identical bonds. The change in enthalpy being negative indicates the reaction is exothermic. "
] |
[
"Mechanical strength doesn't necessarily correspond to phase stability. ",
"Another example is certain amorphous alloys. They're stronger than the corresponding crystalline structure because they don't allow easy dislocation glide, but they're also less stable than a crystal and need to be produced via extremely fast cooling from the liquid phase to prevent crystallization."
] |
[
"Why have we not revisited the idea of nuclear aircraft?"
] |
[
false
] |
I was thinking about this because I recently found out how much carbon emissions are released by . It seems to me that the biggest problem with nuclear aircraft was radiation shielding, but newer technologies like could compensate for that, right? Add to that the size of proposed and the compactness with which we have created modern , it just seems more feasible than in the past. Is there something I am overlooking, or is the airline industry missing out on a huge new market?
|
[
"Power plant for aircraft require an extremely high power-to-weight ratio [",
"1",
"]. The Boeing 747-300 requires ~1400 W/kg (ibid.)",
"A nuclear power unit would require a thermodynamic cycle to extract thermal energy from the reactor and convert it either directly to motive force or (less efficiently) to electrical energy used to produce motive force. While there are examples of research programmes into nuclear aircraft for the purposes of strategic bombing ([",
"2",
"], [",
"3",
"]), these projects were aimed at developing extremely high endurance aircraft, in the same manner as nuclear surface vessels, and both projects failed on the grounds of safety and economy.",
"In comparison, a high bypass ratio turbofan [",
"4",
"] is extremely efficient because it combines the production of thrust with the release of chemical energy from its fuel. New fuels for aviation, third generation biofuels and other hydrogen carriers, even hydrogen itself, present the possibility of low-emission and carbon-neutral aviation fuel. While current government efforts aim towards reducing dependence on imported oil, the same chemical techniques apply to biofuel feedstocks [",
"5",
"].",
"P.S. [",
"6",
"]"
] |
[
"Demron doesn't provide enough to shield against high energy neutrons or high energy gamma, which are the two main things that come out of a nuclear reactor. You need the equivalent of 4-6 feet of water to deal w/those, and thats extremely heavy to have on an aircraft."
] |
[
"Its very simple: The idea of a nuclear powered aircraft was only interesting when you wanted to keep planes with nuclear weapons circling routes for weeks at a time. With the invention of ICBM's, all of this didn't matter anymore.",
"Otherwise, the safety and shielding risk was terrible. Pilots used to get large radiation doses just from the reflection of radiation off the ground as they were about to land the one of the Aircraft Reactor Experiments."
] |
[
"Do spectral lines (emission or absorption) continue past the visible portion of light?"
] |
[
false
] |
I understand most of this topic I think. Quantized electron energy levels create shadows that you can see when you direct the light given off when the element is heated through a prism. But does it only correspond to visible light or are there more 'electron shadows' we can't see because its in the infrared or ultraviolet?
|
[
"Yes, there are spectral lines across the entire electromagnetic spectrum, and not just in the tiny region that is visible to humans. The existence of a \"visible\" portion of the EM spectrum is a result of the limitation of the human eye and not a fundamental aspect of EM waves in general. We can \"see\" the rest of the EM spectrum just fine using instruments. ",
"UPDATE: As others have noted, there are many different other types of transitions possible that create spectral lines besides electron transitions. There are also molecular vibrational transitions, molecular rotational transitions, and nuclear transitions. This is what I had in mind when I said \"there are spectral lines across the entire electromagnetic spectrum\". Still, electron-transition spectral lines spread across most of the EM spectrum."
] |
[
"So spectral lines are caused as these are the energies required to transition electrons between states. There is a maximum here, if you put in enough energy the elctron will escape the atom and become free. If I recall correctly for Hydrogen this is something like 13.6eV, which gives rise to the H-alpha spectral line - this is in the red part of the visible spectrum (its why things like the orion nebula appear red, the cloud consists of hydrogen gas which is constantly ionizing and reionizing, the reionization is emitting red light)"
] |
[
"Yes! Is is actually amazing that light visible to the human eye is only just a fraction of the whole electromagnetic spectrum!"
] |
[
"So we did this in my physics class and I don't understand why it worked"
] |
[
false
] |
We attached a cord to the cement at the bottom of a light pole, and hooked the other end to the back of my teacher's car. My teacher got several students to try and pull on the cord parallel to the ground and get the car to move. It didn't. Then he took one student and had them grab the cord and pull straight upwards (away from the ground), and lo and behold the car moved very easily. The car was in neutral the entire time. Why was it so much easier to move when pulling straight away from the ground as opposed to pulling straight away from the car?
|
[
"It's essentially leverage.",
"The students pulling on the car horizontally had to pull the rope one inch to make the car move one inch, but the student pushing the rope up had to move the rope further than an inch to make the car move one inch (exactly how far depends on the length of the rope). Look up an explanation of levers to understand why the difference in distances the students have to move the rope makes a difference in how much force is applied to the car."
] |
[
"Let's say the force F is needed (higher than the current tension in the rope) in order to pull the car.",
"If you pull it horizontally, you need to apply all of F which will be the tension in the rope then.",
"If you pull it vertically,you need to only apply T*sin(theta), where theta is the angle (close to zero) between the rope and the horizontal. Here T = F/cos(theta) ~ F as cos(theta) is ~ 1.\nMost of the force is applied by the pole on the rope (rope presses horizontally on the pole, so the pole applies a reactionary force on the rope)."
] |
[
"Did it look like this?"
] |
[
"What happens to the light/energy that's travelling faster than the universe is expanding?"
] |
[
false
] |
Energy can't be destroyed, the speed of light is 3,000,000m/s, and the universe is expanding at around 70,000m/s. Given those facts, light must constantly be travelling past the edge of the universe; what happens to it?
|
[
"Where did you get this number? The universe doesn't actually have a speed of expansion! What happens is that the velocity in which two points \"expand\" away from each other is proportional to the distance, and the proportionality factor is given by the Hubble parameter.",
"No matter how small the Hubble parameter is (it is very small today, so for small scales we don't see expansion), there will always be a distance after which the expansion velocity will be bigger than the speed of light, so the light will be trapped inside this bubble of expanding universe."
] |
[
"Can this also be scaled down, as in, is the distance between me and the other side of the room getting larger even by a minuscule ammount as time progresses? or is this only for body's seperated by a vacuum, or a set \"minimum\" distance?"
] |
[
"It is only for bodies which are not bound to eachother by ",
" of the fundamental forces. Gravity is the only force that matters on the largest scales, so it basically applies only to galaxies that are not bound gravitationally. So, for example, the Milky Way, Andromeda, and the Triangulum galaxy along with several dozen dwarf galaxies in our local cluster, these galaxies are all gravitationally bound and will eventually merge with time. However, all other galaxies are far enough away that they will expand away forever."
] |
[
"What exactly is, what I would call, \"leg bobbing\"?"
] |
[
false
] | null |
[
"Are we talking about a stereotyped movement that is ",
"? If that's the case, then it is very commonly used as a method of self-stimulation. Self-stimulatory behaviors are often seen (to a much, much worse degree than you're describing) in children with autism. However, what you're describing could just be indicating that the person is bored, or not getting as much stimulation as their used to. As long as (once the person is made aware of it) they can completely cease the behavior of their own volition, it's definitely normal."
] |
[
"I've been very curious about this for awhile. Not sure if the OP is talking about conscious or not, but I know for me it definitely starts out as a unconscious act. Most often, it goes unnoticed for a long time (possibly an hour or more) before either I notice it, or my foot moves to where I'm tapping something that makes a noise and a co-worker calls me out on it. I've noticed it's not uncommon for others in my office to do it as well, the not often for the same length of time.",
"If I notice I'm doing it and notice, I have the ability to completely stop if I feel like it and often do, though it most instances it does act as a form of simple self-stimulation so sometimes just let it go & it slips back into an unconscious \"twich\"."
] |
[
"I should have clarified. By conscious control I meant that you are able to stop it once you're aware that it's happening. Some people have tremors that they can't control due to various neurological disease processes (e.g., Michael J. Fox, who has Parkinson's disease), and that's a much different thing."
] |
[
"Is it dangerous to eat burnt foods?"
] |
[
false
] |
In this case, I had barbecued some chicken wings. The drippings caught fire and blackened the lot. The insides are cooked as normal, but the outside is blackened and tastes of char. Is this dangerous to eat? If so, why?
|
[
"First thing I found on google.",
"It's not dangerous the way speedballs or blindfolded skiing is dangerous. But it is unhealthy and harmful. "
] |
[
"I was hoping to get a slightly more detailed answer than:",
"\"A: Maybe. Some chemicals in burnt toast have been linked to cancer.\"",
"While I understand that overcooking of food will cause carcinogenic compounds to form, I was wondering just how dangerous these compounds are. For example, after eating X amount of it, would I begin to feel physically ill. What is happening immediately at the villi in my GI tract, or would this be an extremely long process involving oxidative stress?"
] |
[
"Potentially, but mostly if you ate it on a regular bases. Heat causes chemical reactions and some of those are carcinogens. These are present in any cooked food but the more cooked (I.e. The more charred) the more carcinogens there are. These can cause abnormalities such as tumors but these has really only been recorded in large doses over a prolonged diet, certainly not from a single meal in one sitting. The other thing to look at is there's very little nutritional value, most of the vitamins and minerals are destroyed. ",
"You'd be safe to eat the chicken wings (if you'd even want to since they might not taste good) but like smoking, it's definitely not a habit to get into. "
] |
[
"Does taking notes actually help us understand the content we’re learning (lectures, reading, studying)?"
] |
[
false
] | null |
[
"I did a paper on this in college. There isn’t any evidence that taking notes by Itself helps people learn better. ",
"It should be noted that taking good notes and reviewing them within a couple of days after taking them does seem to help. ",
"The only source I remember using in that paper (you may not be able to access the whole thing, I can because I work for a school): ",
"https://www.tandfonline.com/doi/abs/10.1080/0013188740160310"
] |
[
"I know for me, typing results in virtually zero retention. I can flow stuff through from my ears to my fingers easily. Actually handwriting and sketching results in far more retention."
] |
[
"The very act of typing something makes it stick in your memory better. Also, by choosing what information to write down you're analyzing and processing that information as it comes in which improves you're understanding of it."
] |
[
"Disassociation of Salts in Water"
] |
[
false
] |
Through all my years in Chemistry I was always taught that when a salt such as NaCl is put in water it dissociates into Na+ and Cl-. I know water is such a great solvent because of the difference in electronegativity between O and H, and thus its ability to form H-bonds. I also learned that intramolecular forces (ie covelent/ionic) bonds are always stronger than intermolecular ones (ie Hydrogen dipole and London dispersion). How does water break the ionic bonds between Na+ and Cl- in order to disassociate the salt when it can only interact through H-bonds? Are my assumptions correct or am I looking over a critical point?
|
[
"Whether chemical reactions happen is determined by their free energy. For constant pressure processes, like a salt dissolving in water, the Gibbs free energy is used. ∆G=∆H-T∆S. When the Gibbs free energy, ∆G, is negative the process happens spontaneously. (Note that this does not give you information about how quickly that process happens, that involves more concepts.)",
"The ∆H is that equation is the change in enthalpy. Enthalpy is a measure of the total energy of a system, such as its heat or ability to do work. Some chemical reactions release heat, and are termed exothermic. When heat is released in a reaction, ∆H is negative. For this example that would be the enthalpy of solvation for salt in water. For salt, the enthalpy of solvation is actually positive. This means that it takes energy to break apart the NaCl and put it into solution. ",
"Well how does this work, since we know salt dissolves!! The other part of the equation involves the -T∆S. ∆S is the change in entropy of a process. Entropy is roughly a measure of disorder in a system. Entropy increases when going from a solid to liquid, or liquid to gas. Entropy also increases when one substance decomposes into multiple products. When entropy increases, ∆S is positive. Luckily for us, when salt dissolves it leads to an increase in entropy since one NaCl formula unit turns into two ions, Na+ and Cl-. The entropy of solvation is large enough at room temperature that salt dissolves. The T in the equation is absolute temperature. If we could cool the solution enough, the entropy change would no longer be enough to make the overall Gibbs free energy negative and the salt would not dissolve. Fortunately water freezes before then. The application of this is that salts are less soluble in solvents at lower temperatures."
] |
[
"In a sense. the term -T∆S is literally an energy change exerted by entropy. In this case with the salt and the water it is much more thermodynamically favorable to increase the entropy of the system by dissolution of the salt, than the unfavorability of breaking the strong ionic bonds."
] |
[
"The ionic bond is breaking, check out this ",
"wiki",
" article. The first step of forming a solution is breaking the interactions in the solute. In the case of salts this would be lattice energy and the energy of the ionic bonds. Salts don't dissociate in the open because it is not energetically favorable. The last part of solution is the formation of solvent-solute interactions. The oxygens of water will coordinate around the positive cation, while the hydrogens will coordinate around the negative anion. This is a polar interaction that results in a lower energy system. Lower energy systems are thermodynamically favored. Not all salts dissolve, mainly because it is not favorable to break their strong ionic bonds and have water coordinate to the ions."
] |
[
"Will the Sun become tidally locked with Sagittarius A* in the future?"
] |
[
false
] |
[deleted]
|
[
"Thanks for making me check numbers, I was quoting from memory and totally wrong. Sgr A* is 4 million solar masses, which would be 0.0004% of the galaxy's mass (around 1 trillion solar masses). Which does make the \"insignifiant influence\" part way more obvious..."
] |
[
"Sgr A* is much to far away to exert any sort of noticeable gravitational effect on our solar system. Tidal effects are required to cause tidal locking and they fall off even faster (1/r",
" than gravitational forces (1/r"
] |
[
"The sun is orbiting the center of mass of the galaxy, Sgr A* just happens to be around there (and accounts for ",
" which is why it's considered as insignifiant for its gravitational influence on us)"
] |
[
"What do scientists mean by: X is the part of the brain responsible for Y?"
] |
[
false
] |
Where Y is a mental/psychological (as opposed to physiological) process. From what I can tell, they generally mean two things. (1) X is necessary for Y: based on the study of brain injury, it's clear that without X, the ability to Y is inhibited. And (2) activity in X corresponds with Y-activity: based on observing various neuro images, when a subject Ys, their X "lights up." To me this establishes (1) that X is a necessary condition for Y, and (2) that there's a robust correlation between activity in X and Y. I was just listening to Jonah Lehrer ( , ) on , who mentioned "the dorsolateral prefrontal cortex [...] which is closely associated with impulse control." And a basic google search turns up (Harvard Med School, emeritus) describing "the central importance" of the dorsolateral prefrontal cortex "in regulating many key aspects of consciousness, including attention, decision-making and voluntary action." I'm not sure how to interpret phrases like "X is closely associated with Y" (Lehrer), and "X is of central importance in regulating Y" (Hobson). I guess they sound to me like claims. But in other scientific disciplines, the standards for establishing causality seem to be much more stringent than (1) necessity and (2) correlation. For example, I know of Koch's postulates, required for establishing an etiological relationship between a microorganism and a pathology. In that case there is a more required than just necessity and correlation. Then again, maybe correlation is basically a first principle for neuroscience? If so, am I right that that makes it fundamentally different, methodology-wise, from other scientific fields? Anyway, I'm primarily interested in how actual investigators working in neuroscience fields think about such methodology/epistemology questions. Or is it just not something one thinks about all that much?
|
[
"I guess they sound to me like causal claims.",
"No and yesno. With current technologies and methodologies in the brain and behavioral sciences (e.g., fMRI, EEG, MEG, PET, SPECT) we can't infer too much causation. But, with appropriate experimental paradigms (i.e., setting up an experiment where you can manipulate an independent variable) you can infer ",
" level of causation. Also, through lesion studies (that is, people with portions of their brain damaged) you can infer that whatever behavioral or psychological deficits they have ",
" injury, is probably due to whatever region has been lesioned.",
"\"X is closely associated with Y\" (Lehrer), and \"X is of central importance in regulating Y\" (Hobson).",
"Both of those mean that when X behavior is tested for or measured ",
" imaging/lesioning Y region of the brain, the results are very consistent. For example, the DLPFC shows activity in lots of experiments where attention switching or executive control are required. ",
"If so, am I right that that makes it fundamentally different, methodology-wise, from other scientific fields?",
"Nope. Psych/Neuro and many, many other fields depend on experimental manipulation. If, as a researcher, you can design an experiment with a variable that you can ",
", you can infer, to some degree, that ",
" has a causal effect on ",
". ",
"Two examples for an experiment and an \"experiment\". In a task, all I ask is that you come into a well lit room with ambient noise (air conditioning, outside sounds) and comfortable temperature. I ask you to place your elbow, of your dominant hand, firmly down on the a table. Lift your forearm and hand upward so that it is perpindicular with the ceiling. Bend your wrist so your hand is ready to grasp at something falling from the ceiling.",
"I set up a mechanism to hold a ruler. This ruler is placed 1 inch above your hand (that is, the edge of the ruler; the other edge is now 13 inches away). ",
"At any random time, the ruler will drop. Your task is simply to catch it. I will calculate your reaction time and skill based on how much of the ruler falls before you catch it.",
"1) The experiment: I randomly assign half of my participants to have 10mg of caffeine. The other half receives a placebo. Everyone waits 45 minutes (that's how long caffeine takes to do its magic). After 45 minutes, you get ready to catch the ruler. ",
": Caffeinds, on average, catch the ruler faster than non-caffeinds.",
"2) The \"experiment\". Everyone comes in and performs the task. I also measure eye color of the participants. ",
": brown eyed people catch the ruler faster than non-brown eyed people.",
"In 2) it sounds easy to say that brown eyes ",
" faster reaction time. Maybe those people have superior vision? But since we didn't control the experiment we can only say that having brown eyes, in this experiment, is correlated with faster reaction time. In 1), however, we ",
" say that caffeine has a causal effect. The groups were manipulated specifically to find this out. We cannot say that caffeine ",
" causes it, but caffeine ",
".",
"In neuroscience, psych and cog studies, that's how it's (traditionally) done. Even inside of a magnet. Some of the most classic and repeatable cognitive psychology experiments just used to get repeated in fMRI. We use experiments that are well known and have strong effects, but now we get a bit more information. However, now, studies are designed specifically for being inside of a magnet. ",
"Nearly all statistical techniques in these fields are correlational. Causal effects are inferred through experimental manipulation. ",
"Or is it just not something one thinks about all that much?",
"If you're not thinking about these things, you won't last very long in the field. The neurosciences have seen a strong, strong presence of \" 'the fuck did you just do?\" in the past few years:",
"Voodoo correlations",
"Circular analysis",
"Pretending you tested interactions",
"(No) Control group skeletons",
" (very recent!)",
"And quite a few more. However, these aren't the norm, nor reflective of \"how bad things are\". ",
"So, if you set up an experiment properly, and then find out what part of the brain is active during measure, you can comfortably say that, yes, this part is involved in that behavior. But you can't strongly say it ",
". But, in all the imaging modalities there are considerable levels of noise (as opposed to signal). The best example is the cerebellum. The cerebellum, most people would say, is responsible for motor whatever. ",
"If you look at any fMRI paper (except in journals or articles specifically about the cerebellum) you'll notice something missing: THE CEREBELLUM. Literally. It's just gone. Why? It activates for many, many things and appears to be involved in too many things to make sense of. This is actually a limitation of the technology used, as opposed to the experimental designs. But at the same time, if we didn't have these technologies, we never would have known the cerebellum does so many damn things that we can't actually make sense of it anymore. And that's why it has entire journals dedicated to it.",
"It's also important to note that no neuronerd doing image worth their weight in Nature papers would ever say the know ",
" what the brain is doing or what brain region is ",
" a behavior. Not with these technogies:",
"MRI measures (para)magnetic properties of your body. fMRI measures the paramagnetic properties of blood ",
" metabolic functioning. That is, fMRI measures the garbage after the neuron party.",
"EEG & MEG measure electrical signals and magnetic signals, but these signals must be facing the electrode (a receiver) and dont' necessarily happen anywhere near the electrode itself. ",
"In TMS and animal studies, you'll have stronger statements leaning towards confident causation, but only after decades of working on the same regions. Never as a fresh-bearded academic."
] |
[
"I hate to ask you to do sociological speculation, but... What do you think most neuro/cognitive scientists would say: in principle, could we \"build\" a DLPFC (the functional equivalent thereof), ",
"Nope. Too science fictiony. "
] |
[
"I'll add a little something here as a neuroscientist who goes after a more direct but narrower analysis of brain function than the imaging/gross electrical studies mentioned by dearsomething. We're the electrophysiologists - we measure pretty directly the changes in electrical activity of small groups or even single neurons. ",
"Our experiments are cool because we get a lot more detail than the broader techniques dearsomething has so wonderfully described. However, in this we sacrifice scope - we're only able to look at the activity of individual neurons or small groups (around 10-20) at a time. As a lot of brain functioning, especially on the level you're refering to, occurs across large networks of neurons, it can be difficult to get a full picture of what these brain areas are doing with our techniques. So the work that dearsomething might do is complemented and strengthened by the more detailed view we can provide (and vice versa).",
"I'll give you a concrete example - we can record from single neurons using electrodes inserted into the brain of awake, behaving animals and correlate their activity with changes in the state of the neuron. This is especially striking in the visual system, where individual neurons will respond very specifically to components of a stimulus - direction of movement, contrast etc.So we can see more or less directly that these neurons are responsible for handling visual information - they are connected to a network that receives visual information and respond to a specific components of that stimulus. We can then insert electrodes into neighboring areas to map these responses and determine the borders of such areas. We also compare between animals to make sure that this is not just one wierd little creature with a strange brain. Then we can do the same for other sensory inputs to find and describe auditory or somatosensory ('touch' senses) regions for example. ",
"I can even take out sections of the brain from animals and record the fine-scale characteristics of neurons in isolation. This can give me important information on how this particular type of neuron could process information - how it might transform or modulate the inputs it receives and the limits of its computational abilities. ",
"So these methods allow us to build a really strong picture of how this neuron acts in a working brain, and how this is influenced by its own specific little characteristics. Then if that fits with the broader population/imaging studies we can start to talk with real confidence about what different areas of the brain do and how they do it."
] |
[
"Why is the Earth's freshwater supply diminishing?"
] |
[
false
] |
If our potable water is considered a renewable resource, why are we taught to conserve water? Think about it: we use the water, it goes to the sewage cleaning facility, and then back to our water taps. So why is it so suddenly (within the last 10ish years) that there has been a movement to save, save, save water? What's happening to our fresh water?
|
[
"it goes to the sewage cleaning facility, and then back to our water taps. ",
"This isn't quite right, most of our treated sewage does not get sent back to the water supply as it's not fit for drinking and we either drain it into the ocean or use it for irrigation and other non-drinking uses. Most of our drinking water is from rivers, glaciers, wells/springs, rain, etc. When there are droughts, we get less water back into our drinking water sources. "
] |
[
"The earth \"produces\" the same amount of freshwater that it always* has, what is changing is the amount of people that want to drink it and use it for bathing, cultivating land, etc.",
"more demand + same amount of water = shortages"
] |
[
"As others have said - waste water is usually put straight our to sea.",
"One of the largest problems is that in large parts of the world, the freshwater supply is not drawn from the recharged water cycle, but from deep aquifers which are not recharged. This fossil water - once gone - will not be replenished.",
"Even when active aquifers are used, there have been a large number of cases where the water is being extracted faster than it is replenished, leading not only to problems in the future, but the drawing in of saline water which poisons the aquifer."
] |
[
"Why do volcanic hotspots create a chain of volcanoes instead of a continuous ridge?"
] |
[
false
] |
Why do volcanic hotspots create a chain of volcanoes like for example the hawaiian island chain instead of creating a single continuous ridge?
|
[
"There are a few things to consider. First, is that if we look trails of volcanoes formed by hotspots, in many cases they do form (at least in small parts) things like ridges, e.g. if we used the classic ",
"Hawaiian-Emperor seamount chain",
" as an example and consider the bathymetry, we can see sections where there are semi-continuous ridges below the ocean, even if there are isolated and more prominent peaks that could make it look like there is less continuity than there is. However, at a larger scale we can see that your point still stands in that this, and other examples, do not form an unbroken ridge of volcanic rocks. This largely relates to two things, 1) non-constant rate of supply of magma and 2) the details of how magma plumbing systems work. ",
"Toward the first point, and again, using the Hawaiian-Emperor chain as an example, there is evidence that the rate of melting and thus production of magma has varied over time, e.g. ",
"this publication from the USGS",
". Changes in supply rate would obviously influence how much new material was being added to the surface through eruptions, which can contribute to the lack of continuity.",
"The other important aspect is that for all volcanoes (whether these are hotspot related or not), the lava that erupts at the surface is transported through a magma plumbing system, e.g. this ",
"review paper on magma plumbing systems",
". This basically reflects that it is actually not that easy for large volumes of molten rock to make it to surface and that the magma 1) often exploits pre-existing weaknesses in the crust and 2) tends to continue to travel along the same pathways until something changes that makes it preferable (i.e. more efficient) to travel along another path. If we put this in the context of a moving heat source (i.e. a plate moving over a semi-stationary hotspot), what this means is that once established, the magma plumbing system may preferentially funnel melt towards the surface via established routes (and out of established vents), even if the hotspot no longer directly lies under the vent. As translation continues, there will reach some point where it becomes 'easier' for magma to find new, more direct paths to the surface forming new vents, with progressively less material traveling through the old, established plumbing system. This ends up being reflected at the surface as more isolated eruptive centers (even if the supply rate is constant)."
] |
[
"Yes, that's an important contributor to the height (and areal extent) of Olympus Mons. Also important is the difference in flexural rigidity of the Martian lithopshere in the area under Olympus Mons compared to typical lithosphere on Earth, especially compared to oceanic lithosphere (i.e. the effective elastic thickness of the Martian lithosphere is generally thicker than most areas on Earth, allowing it to support larger loads without \"sagging\")."
] |
[
"So volcanoes like Olympus Mons on Mars are so tall because Mars lacks plate tectonics and the magma pools generally in one place?"
] |
[
"What are the scientific theories behind why Saturn's north polar storm is shaped like a hexagon?"
] |
[
false
] |
[deleted]
|
[
"This",
" article from the planetary society is one I found a while ago. It explains the theory BlueStraggler outlined quite well, and shows some nice pictures of some experiments done at Oxford University in support of it. ",
"This",
" is the original paper, unfortunately it's behind a pay-wall."
] |
[
"Some sort of oscillation in the weather patterns around that latitude that resembles a sine wave. North and south of that latitude the period of the wave doesn't sync, so it mixes and disappears. At the latitude where the period syncs, you get a standing wave, which happens to be 6 periods long in this case. Beyond that, I'm not sure if anyone has a good explanation of the causes of the oscillation."
] |
[
"Here's an interesting article on the topic:",
"http://physicsbuzz.physicscentral.com/2010/06/secret-of-saturns-hexagon.html"
] |
[
"Why does a picture of a spider or a weird insect scare me, but a picture of a more dangerous lion or bear not scare me?"
] |
[
false
] |
[deleted]
|
[
"Phobias are generally thought to be learned associations to certain things. Put another way, you have probably learned to fear spiders from your experiences in your day to day life. Whilst lions and bears may in reality be more dangerous should you encounter them, because you have not encountered them in your experiences it is likely that you have less of a fear from seeing these in pictures than you would spiders."
] |
[
"If I saw a larger-than-life size picture of a spider, I would most likely be even more terrified."
] |
[
"If I saw a larger-than-life size picture of a spider, I would most likely be even more terrified."
] |
[
"Can we predict a double pendulum?"
] |
[
false
] | null |
[
"The double pendulum is a completely deterministic system, it just behaves chaotically, meaning that small deviations in initial conditions lead to large deviations in the motion. If you know the initial conditions perfectly, you can predict exactly what it will do forever. But if there's any uncertainty in your initial conditions, eventually, your prediction of the motion will become wrong. And the \"wrongness\" grows exponentially with time."
] |
[
"If you start identical double pendulums from exactly the same initial conditions, they will do exactly the same thing forever. But that's not possible to do in real life.",
"Where is the chaoticness?",
"Here:",
"But if there's any uncertainty in your initial conditions, eventually, your prediction of the motion will become wrong. And the \"wrongness\" grows exponentially with time."
] |
[
"We can define them exactly mathematically. But experimentally, we can never reproduce the same initial conditions exactly."
] |
[
"How Accurate Is This Website?"
] |
[
false
] | null |
[
"About as accurate as saying that everyone should eat exactly 2000 calories a day. Everyone's body is a little different, with different requirements and strengths and weaknesses. Sleep is the same. Some people should aim for 9 hours, some people only need 6. "
] |
[
"And a few lucky bastards who genetically need hardly any sleep at all."
] |
[
"Not my field, but its saying you need 9 hours sleep (or any increment 1.5 less than that to have full sleep cycles) + 14 minutes of time to fall asleep. It seems to base this on your sleep cycle being 90 minutes=1.5 hours; hence 5-6 sleep cycles or 7.5 - 9 hours of sleep. Quick check on from ",
"NIH",
" says a sleep cycle getting to REM is 90 to 110 minutes on average, thus making the calculator not particularly accurate. (E.g., if your sleep cycles are 100 minutes long sleeping 7.5 hours you'll only get 4 sleep cycles with REM sleep.) Also its not really accurate that each cycle is the same length. (Look at the hyponogram diagram from ",
"NIH link",
".)",
"The psychology prof who coined the term \"power nap\" suggested strongly in a public lecture I saw that if you want to improve your sleep, don't wake up by the alarm--just get enough sleep and wake up naturally (and you'll be smarter and more productive all day long). (And if you need to use an alarm, definitely don't use the snooze button -- that's low stage sleep that doesn't really help at all). Everyone's sleep needs are different, though most everyone nowadays is sleep deprived."
] |
[
"If I ignite the smoke of a candle it burns down but not up, why?"
] |
[
false
] |
So there is this to light a blown out candle by igniting its smoke. But the smoke only burns downwards, even if I try to ignite it at the very bottom. Anyone know why?
|
[
"But if there is enough vaporized wax in the smoke to burn, why does it not burn upwards too? At least until the concentration becomes to low to sustain the reaction?"
] |
[
"But if there is enough vaporized wax in the smoke to burn, why does it not burn upwards too?",
"Best guess:",
"The heated air rises too fast pushing the vaporized wax & carbon too far out of the way to be used as fuel.",
"Get your camera. Set it too the maximum frames per second you can. Record yourself trying it both ways multiple times. Play it back in slow motion and note the differences in how the trail of smoke behaves to the flame."
] |
[
"I believe it's because the smoke isn't actually what is burning. Basically it is the vaporized wax that's catching so the fire is going to burn down towards the candle where the concentration of the vaporized wax is greatest."
] |
[
"Is space-time really just an aspect of the gravitational field ?"
] |
[
false
] | null |
[
"You've got it a little backwards. Gravitational fields are actually a derived aspect from the curvature field of space-time.",
"From this thread: ",
"http://www.reddit.com/r/askscience/comments/gpaha/what_causes_gravity/",
"Well it actually isn't really a force. It only looks like a force due to some really interesting properties of our universe. That's the current consensus. ",
"Let's start with a basic principle. We know that all observers must agree that light travels at c, the speed of light (in a vacuum). The resolution is to realize that because they ",
" agree on c, that they will disagree on measurements of distance and time when they're moving with respect to each other. Now when they're moving without acceleration, that is a ",
" case of relative motion, and thus the disagreements on measurements of space and time are described by... Special Relativity. And since each observer ",
" whether they are moving or the other, neither measurement of space and time is more ",
" true than the other.",
"When an observer accelerates though, acceleration ",
" be detected. (feeling pinned to your seat when flooring the gas, eg) And some new math needs to come in to play to describe the disagreements in space and time measurements for these accelerated frames. Particularly as the fact that you're accelerating means that you'll disagree with measurements that you made just a moment ago. ",
"Now let's switch gears for a moment and go back to that \"knowing you're accelerating\" bit. Imagine you're in a box. The box hasn't any windows. But you're standing on the floor of it. Could you tell if the box was sitting on the surface of the earth, or if it was being accelerated \"upwards\" by a rocket in some deep space (where it's not being gravitationally affected by any nearby masses). Suppose instead of standing you were floating around in the box. Are you floating around because you're in deep space away from mass and gravity, or because the box is in free fall toward some massive body? ",
"The answer is no. In both cases, there is ",
" difference between the effects of acceleration and gravitational effects. And this is where a theory about making sure that the speed of light is universal becomes a theory about gravity. You see the math we did above for the accelerating frame? (and by \"did\" I mean \"I mentioned and ignored entirely what it is\") Well you can construct an expression of mass and energy called the Stress-Energy tensor that is related to the ",
" of spacetime around it. All of those disagreements about length and time measurements between observers in relative motion become summarized in this curvature.",
"So now we go and do some \"physics.\" Newton's framework is a little too simplistic to work in for what we need to do, so we usually work in a slightly more advanced system called \"Lagrangian\" mechanics, or its very close relative \"Hamiltonian\" mechanics. In these mechanics frameworks, we have derivatives. Derivatives are rates of change with respect to something, like the rate of change of location with respect to time is velocity. Well now you have to include additional terms where you describe not only how an object's position varies in space and time, but how space and time vary with respect to... space and time. (Because of this curvature/disagreement over measurements issue). And when you include those new terms, gravity ",
" out of the equations. Even though you didn't put in a term for a force, or a gravitational potential energy. Gravity is an emergent property of this ",
".",
"And furthermore, this new gravity gets more things right than the old Newtonian gravity did. For instance, Newtonian Gravity couldn't correctly calculate Mercury's orbit, it was off by a ",
"very tiny amount",
". When General Relativity came along, it was able to answer the question within the experimental limits. ",
"If someone had ever thought to look at the positions of stars ",
" blocked by the sun during an eclipse, they would have noted that the position appears to shift just slightly. But light is massless, Newton's gravity can't affect it. And even if we fudge Newton's gravity by taking a massless limit, it's off by a factor of 2 from what General Relativity predicted. This was confirmed in the famous Eddington Expedition."
] |
[
"please feel free to ask for clarification. I'm just copypasting an old response. I'll try to write up in better detail after work."
] |
[
"Sorry I forgot about this post earlier. The wiki on stress energy tensor is actually pretty neat and useful, imo.",
"Anyway my thoughts on the graviton are as follows:",
"Keep fresh in your mind that gravitation is ",
" a force. It is a fictitious force, a force that arises out of choosing a non-inertial reference frame. That of ",
" free-falling towards the center of a mass (like standing on the ground). The common misconception about gravitons is that they're like \"photons of gravity,\" little particles zipping about saying \"hey there's a mass over here and it's pulling you by ",
". ",
"Gravitons (should they exist) are the photons of not gravitation, but ",
". So we have classical treatments of electromagnetism with just plain old electric fields and magnetic fields, right? But at the microscopic level, these fields are the result of many photons acting in concert that result in a classical smooth field. Much like water is a continuous fluid for all intents and purposes, even though it's actually made out of little molecules within it. ",
"The equations of General Relativity describe classical fields, like classical electromagnetic equations described classic electromagnetic fields. So the question naturally arises, \"Is the classical curvature field of GR actually the result of many little excitations/particles of curvature acting together to form a smooth field overall.\"",
"The answer seems to be... maybe. We haven't managed to make the maths work yet. But in a way we got lucky with E&M that the maths worked as easily as they did in the first place. A little renormalization and all these weird infinities disappear from the equations (you can kind of think of this as we can assume particularly high energy particles are very rare, and particularly low energy particles don't contribute much to the picture, so we can in a way, ignore both) - Well it turns out for GR, we can't show that those assumptions hold mathematically, so we're stuck with maths we can't solve. ",
"So my personal opinion is to wait. It really is too hard to tell one way or the other."
] |
[
"why do the planets in the solar system have a mostly circular orbit but far objects like ceres have highly elliptical orbits?"
] |
[
false
] |
Edit: my bad I confunded sedna with ceres, I meant sedna
|
[
"Ceres has an eccentricity of 0.075. That's not much more than Earths eccentricity. I think you are mistaking Ceres for a kuiper belt object, such as Pluto? Ceres is located in the asteroid belt between Mars and Jupiter. ",
"Anyway it is true that many trans-neptunian objects have quite large eccentricities compared to the objects in the inner solar system. The are many reasons for this. 1 major one are interactions between Neptune and the objects out there. It is thought that during the formation of the solar system everything started out in more or less circular orbits but then the large planets \"migrated\". The change in orbit of the larger planets would have then caused shifts in the orbits of smaller objects. ",
"For example Pluto is caught in a 3:2 resonance with Neptune",
" which likely gave rise to the higher eccentricity too. ",
"If you look at this graph",
" you can see many object in orange with a semimajor axis of 40AU that are in a 3:2 resonance with Neptune. There are more out there in red with a 2:1 resonance as well. There is large population of so called \"cubewanos\" sometimes also called \"cold population\". These are object with no apparent resonance to any of the larger planets. They also have lower eccentricities and lower inclination. Most of the cubewanos have inclinations <5° while plutoids have generally larger inclinations. Some other high eccentricity objects can have other causes for their eccentricites, such as collisions or chaotic motion, but in general most high eccentricities come from resonances with Neptune. \n",
"In fact while Neptunes influence caused other objects to have higher eccentricities its own eccentricity got damped because of the interactions.",
" It has an eccentricity even lower than Earth's.",
" ",
"\nEdit: Sedna is a special case. We don't know why Sedna has such an extreme orbit. ",
"There is some speculation that Sednas orbit was caused by interactions with a massive unkown planet.",
" But it is important that this is all entirely speculation. For now we really don't know why Sedna has the orbit that it has. ",
"u/_senpo_"
] |
[
"Ceres is the largest object in the asteroid belt. I think OP might have confused it with something else, maybe Pluto? But it is definitely part of the solar system and has always been. We know very few interstellar objects, actually ''Oumuamua' is the first and only confirmed interstellar object. Although there are a few other out there that are unconfirmed.",
"High eccentricities mainly come from resonances between Neptune and other objects. Collisions only caused small part of high eccentricities."
] |
[
"I'm not expert but I believe it would be caused by a collision. I'm fairly certain that Ceres is also believed to have originated somewhere other than our solar system. However a collision with another object can/would change the orbit of said object. Pluto would be similar with charon and their elliptical orbit. As I said not an expert so someone with an actually background in this please correct me or elaborate."
] |
[
"Could many dead languages be resurrected 'as is' -- with just terms for new discoveries added -- and still be as practical as any modern language?"
] |
[
false
] | null |
[
"I think you mean \"the early years of the last century\". Hebrew has certainly been in use as a modern language for more than 14 years."
] |
[
"I think you mean \"the early years of the last century\". Hebrew has certainly been in use as a modern language for more than 14 years."
] |
[
"That's really interesting. I did not know Hebrew had been revived so recently."
] |
[
"Is the string in a canter-leaver under tension or compression? - Teacher disagrees with the class can someone please explain"
] |
[
false
] |
Our physics teacher spent todays lesson trying to rationalize that the string in a canter-leaver is under compression while the class disagreed saying that if the string was supporting the beam from above then the string would be under tension not compression. Bellow are 2 diagrams showing the forces that the teacher stated where acting on the object and the workings that she tried to use to explain her reasoning. Can someone please explain why or why not the string is under compression. Links to images for reference Edit: thank you for all your responses, it has realy cleared up my understanding.
|
[
"Because that's the convention that mechanical engineers use",
"No it's not. My undergrad training is in mechanical engineering, I've worked as a mechanical engineer, and I've taught mechanics of materials classes. It's flat incorrect to say \"The string is under compression because it is being pulled apart at the ends\". It makes me cringe just to read it. (If you disagree, please feel free to provide a citation.)"
] |
[
"Oh wait, I think I figured it out.",
"The question you're asking is ",
" \"why is diagram 1 correct and not diagram 2\".",
"What looks like is being done is a combination of a free-body diagram with the picture of the object. If we look at picture 3, we see that diagram 1 is on the board, and immediately below that is a relief focusing on just the bottom right vertex. The string (under tension) is providing a force away from the vertex (toward the center of the string).",
"Similarly, in the upper left corner, the string (under tension) is providing a force away from the vertex (toward the center of the string).",
"You, ",
"/u/BenxRobbo",
", are misinterpreting these forces as being the forces acting ",
" the string (because they are drawn on the string) ",
" the cantilever, and if that were the case, they would be compressive forces.",
"However, that's ",
" what's being drawn; what's being drawn are the forces acting ",
" the string ",
" the cantilever.",
"Somewhere along the line, I am willing to bet that you were taught to draw compressive forces in the manner shown in diagram 1, and tensile forces in the manner shown in diagram 2, and are mistaking that scenario for this one, and I would further bet that your teacher didn't actually say the string was under a compressive force, but instead insisted that the arrows were correct. I'm also going to guess that this was either a TA or a new instructor.",
"Please let me know if I've got that about right."
] |
[
"The string is under tension: outside forces are pulling its ends apart. The arrows in the first diagram are a bit confusing: they indicate the force ",
", not the forces applied to the string. The string is pulling the tip of the beam up and to the left.",
"At the tip of the beam, the string is pulling up and to the left because it is in tension, the beam itself is pushing to the right because it is in compression, and the weight of the load applied at the end of the beam is pulling downward. The vector sum of these forces must be zero. The values of F1 and F2 calculated by your teacher are correct, for a 10 kN load applied to the end of a massless beam."
] |
[
"Have we ever whitnessed an impact of a non artificial object on the moon?"
] |
[
false
] | null |
[
"Yes, an impact was observed during the last eclipse",
"http://www.astronomy.com/news/2019/01/impact-on-the-moon-during-the-total-lunar-eclipse"
] |
[
"Many of them. There are many cameras pointed at the Moon to spot these events.",
"55 events found by ESA here",
"54 from a NASA program a while ago",
"A NASA follow-up program is at 435 candidates",
"and many more"
] |
[
"Wow, thank you!"
] |
[
"Aquagenic urticaria: Is it a real condition or media-hoax?"
] |
[
false
] |
[deleted]
|
[
"It's real, and a pain in the butt. I've had it since I was born. It's not simply water, in my case the problem is hot water. For example, every time I take a shower, all these red spots appear and it gets really itchy. Swimming is fine, as long as I don't move a lot, as sweat also makes it \"happen\". I'm 22 today, tried to find a cure, but no luck. Bottom-line for me is: I got used to it."
] |
[
"My aunt has it. Though not as bad as the girl from the last link."
] |
[
"How is this possible? You're allergic to water? The substance that all of your cells are made out of and require for sustained life?",
"I could imagine something IN the water reacting, maybe salts or fluoride or something. I have a REALLY hard time believing that pure distilled H2O would cause a reaction."
] |
[
"When your body is 'burning fat', (during exercise) what fat does it burn first?"
] |
[
false
] |
As in is the fat burnt localised to the muscles that require the energy? Also how is the fat 'burnt'? An oxidation process?
|
[
"You can NOT target fat loss.",
" For example doing lots of ab crunches will not make you lose more belly fat than doing something else (e.g. bicep curls). Genetics alone will determine which fat is burned off faster.",
"Furthermore your body will actually burn your ",
"glycogen",
" stores first while those are plentiful. Glycogen molecules are basically carbohydrate storage units, created in the liver but also stored in the muscle cells themselves. When your body eventually runs low on glycogen it will start burning more fat. It's always using both energy sources but the less glycogen you have left the more fat you will burn.",
"Glycogen is much easier to burn and replenish so that's always the first place your body looks for energy. This means it's important not to consume carbohydrates before working out, and you should also reduce your carbohydrate intake significantly at all other times too.",
"As to how the fat is burned:",
"from ",
"http://science.howstuffworks.com/life/human-biology/lost-weight1.htm"
] |
[
"This means it's important not to consume carbohydrates before working out, and you should also reduce your carbohydrate intake significantly at all other times too.",
"this is partially opposite to what people who are already in ketosis are doing ( the TKD diet ). they increase their carbohydrate intake (compared to their low levels on the diet) prior to exercise to maintain their endurance in workouts.",
"i suppose that depends on whether you are already on a low-carb diet or not."
] |
[
"Dogs4life's post is incredibly biased. It is far healthier for the vast majority of the population (basically anybody but epileptics) to eat at least a moderate carb diet.",
"It is best to eat some high glycemic carbs (such as an apple) about 45 minutes before a workout.",
"Fad diets like the ketogenesis don't teach you how to sustain a long term healthy diet."
] |
[
"Humans have huge brains. It's that the only thing we have going for us?"
] |
[
false
] |
I am always fascinated by the feats some animals can do, their amazing senses and evolution and adaptations. So... Besides our brains, do humans have any other kick-ass things that other animals would be jealous of?
|
[
"We sweat! This gives us very impressive endurance compared to most of the animal kingdom."
] |
[
"opposable thumbs, though some other animals have this as well. "
] |
[
"Bipedal motion and the ability to sweat makes us the best long distance runners.",
"Relevant: ",
"http://en.wikipedia.org/wiki/Persistence_hunting"
] |
[
"Massive space station's centrifugal \"gravity's\" effects on plants"
] |
[
false
] |
So, I hope this doesn't sound too sci fi, but, if a massive tubular space station were to be built (something along the lines of the spindle in William Gibson's Neuromancer; a long band of artificial sun in the middle, the ability to see straight across to the opposite interior surface) and there were big forests and such, would the trees growth be effected by the "spin gravity?" if the trees were big enough, and the tops grew closer to the center of the "spindle" space station, would they experience a different "gravitational" pull than the bases of the trees? would trees grow crazy in a gravity free environment for that matter? I know this is a bit of a muddled question, but any thoughts/insights are welcome.
|
[
"We are of course talking about angular motion.",
"For an object in uniform angular motion there is a constant angular velocity (radians per second).",
"--acceleration = radius x angular velocity",
"Say you built a giant cylinder with a radius of 1kilometre at \"ground\" level where there was a centripetal acceleration of 10ms",
"--angular velocity = square root( 10ms",
" / 1000m) = 0.1 radians s",
"If a tree grew to 50 metres tall the acceleration at the top of the tree would be:",
"--acceleration = 950m x (0.1s",
" )",
" = ms",
" = 9.5ms",
"For an object in uniform circular motion acceleration every time the radius halves the acceleration and thus the force felt for an object of the same mass is also halved. ",
"For our hypothetical 1 km radius space station I doubt that would affect trees very much. But for a 100m radius space station the effect would be quite pronounced, climbing a tree would get far easier as you progressed. What this would do to the tree's biology is debatable. "
] |
[
"He's asking about a hypothetical centrifugal space station probably of the order of at least 1 kilometre across. "
] |
[
"Considering how easily trees can break apart rocks and damage metal structures with their roots, it would be a phenomenally bad idea to grow them in a spaceship. If you think they're bad when they get into your sewer pipes, imagine what it would be like if it breached the ship's hull halfway to Jupiter.",
"I don't know how a tree would take shape in low or zero-g environments, though. However, here is an article about how moss grown on the space shuttle had formed into a distinctly spiral fashion:",
"http://www.redorbit.com/news/science/122510/growing_plants_in_zero_gravity/"
] |
[
"How will the James Web Space Telescope orbit AROUND L2 lagrange point?"
] |
[
false
] |
I've been reading up on the James Web Space Telescope and how it will orbit around the L2 point. I'm familiar with lagrange points and the balance of gravity which allows objects to be stable or meta-stable to have the same orbital speed around the sun as the Earth does while being in a different orbit "elevation", but how will the telescope orbit around the L2 point when there's not actually any attractor there? As I understand it, the L1, L2, and L3 points are the meta-stable ones, akin to a bowling ball being able to sit on top of a very small plateau on top of a peak. Move too far from the L plateau, and the ball will roll down the mountain into the nearest gravity well. The JWST orbiting around the L2 at a distance seems to me like it would be circling the mountain at a constant elevation contour line below the level of the plateau, without ever rolling down hill. In contrast, the L4 and L5 points, being stable points, would be more like a saddle bowl on the side of the mountain with a small lake in it. The bowling ball could orbit around those lakes in the bowl with centripetal force keeping them at a stable elevation, ignoring friction. Is it the same phenomenon with the L2 point? Is it actually a lake at the top of the mountain with its own little bowl? I suppose that would look more like a volcanic crater, but I digress. In such a case the ball would be rolling around the rim of the crater, but would not have to stay in the center of a small plateau. But being that case, how would the L2 be meta-stable and any different from the stable L4 and L5? Can anyone explain or point me to a good source? I've not been able to find anything Googling, but having the right term for the phenomenon might help. Thanks!
|
[
"If you look at the individual coordinates then the point is unstable in the radial direction but stable in the other two. Overall that makes the point unstable but it gives a plane where you can orbit.",
"https://en.wikipedia.org/wiki/Lissajous_orbit"
] |
[
"Have a look at ",
"halo",
" and ",
"lissajous",
" orbits. JWST will use a halo orbit. "
] |
[
"Excellent. That at least gives me the right term to use for Googling to get a better grasp. Thank you."
] |
[
"Water boils at about 7 degrees in .01 atmospheres. Could you cook instant ramen in this boiling water?"
] |
[
false
] |
This question was inspired by .
|
[
"The process of cooking food works through the application of heat. Therefore, temperature is what matters. Whether or not the water boils is not very important. If water boils at 7 degrees, then the food won't heat up beyond the temperature of a fridge and it will not be cooked.",
"This is why people bring pressure cookers when they travel to high altitudes. The lower air pressure lowers the boiling point of water, which means that in a regular cooking pot the water doesn't reach as high a temperature, slowing down the cooking process considerably. The pressure cooker increases the pressure in the pot, raising the boiling point of the water and therefore the temperature that the food is exposed to."
] |
[
"This is an experiment you can conduct yourself. The fact that the water is \"boiling\" at 0.01atm is irrelevant. Take some instant noodles, put them in cold water, and put that in your refrigerator and see what happens."
] |
[
"The denaturing of proteins requires heat. Putting them in water at 7 degrees under atmospheric pressure would be no different than putting them in water at 7 degrees at 0.01 atmospheres. Cooking of any kind requires heat, not pressure."
] |
[
"I may sound stupid asking this, but how come we can see massively coloured and detailed pictures of objects in deep space (galaxies etc.) But not of certain objects in our own solar system? (Sedna for example)"
] |
[
false
] | null |
[
"Galaxies are huge. Sedna is small.",
"Not only in physical size, but in angular size as well: they actually appear much, much larger in the sky than Sedna does. The Andromeda galaxy is as large as the Moon in the sky, while Sedna is so small as to be barely resolvable.",
"In other words, galaxies, compared to Sedna, are many more times bigger physically than they are farther away."
] |
[
"Ah that actually makes sense. Is that just because telescopes enhance the light that we can already see? And if we can't see the light from the smaller objects we wouldn't be able to see them at all? "
] |
[
"Well telescopes focuses light from a huge area onto a small one, in order to capture more light and details; that's just how they work. Keep in mind the distant galaxies we are imaging are producing their own light (and it's alot of it, from billions and billions of stars, some thousands of times brighter than our sun). Little Sedna is merely reflecting light from the Sun, which at it's distance is quite faint."
] |
[
"Are hex-shaped pixels better than square-shaped? Are they viable?"
] |
[
false
] | null |
[
"The answer is, for the most part, no. Here's an easy way to see why. This is how you draw a rectangle and a circle in a square grid:",
"X X X X X X _ _ X X _ _\nX _ _ _ _ X _ X _ _ X _\nX _ _ _ _ X X _ _ _ _ X\nX _ _ _ _ X _ X _ _ X _\nX X X X X X _ _ X X _ _\n",
"This is how you draw a rectangle and a circle in hex:",
"_ X X X X X _ _ X X _ _\n X _ _ _ X _ X _ _ _ X _\n_ X _ _ _ X X _ _ _ _ X\n X _ _ _ X _ X _ _ _ X _ \n_ X X X X X _ _ X X _ _\n",
"Which one looks better for rectangles? For circles? Now look at this website, your browser, your desktop, your file system, your word processor. Now tell me, what's more important, drawing rectangles or drawing circles?",
"Absolutely. Here's what most LCD monitors looks like under a microscope. ",
"http://imgur.com/PXPUqFI.jpg",
"Whoa! Where did all the bars come from? A single pixel is actually made up of 3 subpixels, each showing red, green, or blue that are so close together that our eyes can't tell them apart. A rectangular pixel grid actually looks like this (checkerboard to help you show pixel boundaries):",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"RGB",
"Let's take that same mass of subpixels and group them sliiiiiightly differently.",
"RGB",
"RGB",
"RGB",
"RG",
"BRG",
"BRG",
"B",
"RGB",
"RGB",
"RGB",
"RG",
"BRG",
"BRG",
"B",
"RGB",
"RGB",
"RGB",
"RG",
"BRG",
"BRG",
"B",
"Don't see it? Let's group a bunch of them together to make it more obvious.",
"RG",
"BRG",
"BRG",
"B",
"RG",
"BRG",
"BRG",
"B",
"RGBRGBRGBRGBRGBRGB",
"RG",
"BRG",
"BRG",
"B",
"What does that look like to you? Pretty much a hexagon, right? The difference in shape between that and a hexagon is smaller than our eyes can detect, because if our eyes could detect that difference it'll also detect the fact that your white pixels are just really closely grouped color ones. Boom, I just made your screen use hexagonal pixels and you didn't even need to buy a need laptop.",
"Now, can we somehow replace the rectangular subpixels with something different? Absolutely, in fact, there are more ",
"subpixel geometries",
" than the most common square one, and ",
"! Some of them are kind of hexagonal. So yes, it is possible to build a hexagonal pixel.",
" Hexagonal pixels are not really better if you want to draw rectangles, which is what all of our UIs are based off of. And yes, you can make hexagonal pixels, because pixels are actually lies, they're just even tinier subpixels that can only be different brightnesses of red, green, or blue."
] |
[
"Actually, hexagonal grids are square grids with odd and even rows offset by half a cell. So they're trivial to index and store. Interpolating the values isn't a huge deal, this is basic sampling and filtering theory. Both square and hexagonal pixel grids are ",
"voronoi diagrams",
", so linear approaches still work. GPUs nowadays already render a rectangle as two triangles for example.",
"Beyond basic bilinear filtering, even square grids require anisotropic filtering and other trickery anyway to look good. In pixel shaders, we use local derivatives and tangents, treating the discrete grid as a continuous function. The fact that it comes from square pixels and gets baked into square pixels is accidental, really."
] |
[
"With a bit of knowledge of how to write device drivers, you can, indeed, hack your monitor to use hexagonal pixels. Then watch as every program ever written tries to draw rectangular pixels and then go crazy as your eyes tries to piece together the squiggly horror that results."
] |
[
"What happens to the large object orbiting the black hole?"
] |
[
false
] |
Let's imagine the space station with its center of mass having sufficient distance and velocity, so it can orbit a black hole. However, station is very large, and some parts of the station are below the event horizon. What happens to them? Do they get torn apart? If not, does it mean that people can go below the event horizon, and then get back up? (I am absolutely sure that they do not, it however seems to be possible from classical point of view(gravitational force is not fully balanced by centrifugal force, but it is with additional station elasticity force/ floor reaction force))
|
[
"However, station is very large, and some parts of the station are below the event horizon.",
"No, they aren't. To an observer who's not actually falling toward the black hole, the event horizon is an impenetrable barrier. Nothing ever crosses a black-hole event horizon.",
"Do they get torn apart?",
"Say you have a ",
" gravitational field. That is, if you drop a test particle at any point in that field, it will accelerate in exactly the same way it would if you dropped it at any other point.",
"Now consider a long bar in that gravitational field. What is the difference in acceleration between the centre of mass of the bar and the ends of the bar? It's zero, obviously. We just got through saying the field is uniform.",
"But this is a contrived example; gravitational fields are ",
" uniform in nature. In particular, the gravitational field around a point source — and any spherically symmetric distribution of matter is treated as a point source from ",
" of it — is radial, and varies from close to the source to far from it.",
"So consider a long bar in any ",
" gravitational field, oriented such that it's pointing down toward the source of gravitation, and you will find that the centre of mass of the bar and the two ends of the bar want to accelerate differently. There's a ",
" on the bar, exactly as there would be if you and your best friend grabbed the ends and played tug-of-war with it.",
"In weak gravitational fields, this difference in acceleration between two nearby points is very slight, so the resulting stress on small solid objects is also very slight.",
"But the gravitational field around a black hole is not weak. It's strong. The closer you get to the black hole, the greater the difference in acceleration between the ends of a solid object and its centre of mass.",
"And in fact, as you approach the event horizon, that difference in acceleration goes to infinity. Meaning that ",
" any solid object reaches the event horizon, the stress between its nearest and farthest extents will have exceeded its intrinsic mechanical strength, and the object will have broken apart.",
"It's important to note that there's nothing magical about black holes that makes them tear things apart. The exact same phenomenon I've described here also occurs around ",
" source of gravitation. It's just that with objects of typical density, like the Earth and the sun and you for instance, you can't ",
" sufficiently close to them before encountering the surface. Black holes' surfaces are as close to their centres as it is physically possible for them to be, which means it's possible in principle to get so close to one that strong gravitational effects, which are not usually seen in everyday life, become significant."
] |
[
"…\"particles that eventually smack into the singularity\".",
"There aren't any."
] |
[
"The surface area of a black hole is proportional to its entropy. So as the entropy of a black hole increases, due to scattering interactions with matter and fields, its surface area also grows. When the entropy decreases, due to thermodynamic changes over time, the surface area gets smaller."
] |
[
"Can we ever know the exact position of a photon."
] |
[
false
] |
Ok, so I've only ever had an introductory physics course. According to Heisenberg's uncertainty principle, the uncertainty of the position of a particle times the uncertainty of its momentum is a constant yes? But according to relativity a photon can only travel at c. So our uncertainty with regards to it's momentum must be zero. Wouldn't that imply that we have zero certainty about it's position? I feel like I'm conflating and/or abusing concepts here. Can anyone enlighten me?
|
[
"The momentum of a photon isn't mass times velocity, but rather its frequency times Planck's constant divided by its speed. You can't measure the frequency with absolute accuracy."
] |
[
"Two things:",
"A photon's momentum is related to its wavelength according to p = h/λ, where λ is the wavelength and h is Planck's constant. Thus there is uncertainty in the photon's momentum since there is uncertainty in its wavelength.",
"We can't know ",
" quantity exactly. If you wanted to exactly know any physical quantity, you'd have to specify it to infinite precision. This means you would have to know an infinite number of ",
"significant figures",
" for that quantity. This would take an infinite amount of time to determine. Thus, any physical quantity has some small uncertainty associated with it. In fact, the uncertainty principle can be derived by treating physical quantities not as fixed numbers, but as the average value of a distribution function."
] |
[
"The uncertainty principle applies to photons in the same way that it does to regular particles. In this case, as already pointed out, frequency takes the place of momentum.",
"What this means is that light generally exists in little wave packets. A wave packet is a set of frequencies of light mixed together, and it travels around in space. It is also referred to a pulse of light. The pulse has neither a unique frequency nor a unique position. It is a smear on the frequency spectrum, and its spatial position is also a smear (in terms of probability, if you haven't heard of ",
" being used, look up uncertainty principle on the search).",
"The thing here is that as you make the frequency more certain, (you can pass the pulse through a filter that cuts of parts of the smear), the wave packet starts to spread out. You can actually see this IRL using a light detector that measures EM fields in space, and using a spectrometer to look at the bandwidth. You can also try making the pulse really sharp locally, but doing that requires you to add additional frequencies to the pulse.",
"You has done math ? Think of the fourier series of a dirac delta function."
] |
[
"Why do flies rub their limbs together?"
] |
[
false
] |
Sometimes when flies land I can see them apparently rubbing their front and back limbs together. Is this some type of self grooming?
|
[
"Please keep this kind of material out of AskScience. "
] |
[
"On-topic humor is the best kind of humor. Try to limit the rest of it",
"And above that is says:",
"focus on giving scientific answers to the question at hand."
] |
[
"To the side, it says \"On-topic humor is the best kind of humor. Try to limit the rest of it\" pretty on-topic, considering they look like evil monsters rubbing their hands together menacingly.",
"A quick google search of ",
"\"Why do flies rub their legs together\"",
" confirms the OP's suspicion on self grooming techniques. And to impress the lady flies by showing how well they can care for themselves, and I'm guessing baby flies.",
"sources ",
"wiki answers",
"straight dope",
"wikipedia of Housefly"
] |
[
"Can the stomach of an obese person hold more than the stomach of a regular person?"
] |
[
false
] |
[deleted]
|
[
"Yes. Its the same situation as people who get their stomach stapled. If they continue to eat the way they used to, it can stretch right back to almost normal size again."
] |
[
"For the most part, yes, but mainly because obese people are almost always obese because they eat a lot more than necessary and thus expand their stomach capacity that way. The bigger stomach essentially causes obesity (indirectly) rather than the other way around. If you were to somehow become obese without overeating, perhaps due to hormonal or metabolistic disorders, your stomach should be normal."
] |
[
"Interestingly while obese people are likely used to eating larger amounts than normal people, lean people are more able to greatly exceed their normal food intake. This is because the fat buildup around the midsection acts to restrict the expansion of the stomach.",
"So while an obese person will likely have a more stretched stomach than normal, a competitive eater who is lean is more capable than one who is obese."
] |
[
"If the flu adapts around the vaccine every year, why don't we let everyone catch the flu once and be done with it?"
] |
[
false
] | null |
[
"There's a few reasons: \n1) because it also adapts around whatever individuals in the population have had previously,\n2) there are lots of different strains of flu,\n3) immunity wanes, and\n4) flu kills a lot of people every year, and that's WITH flu vaccination in place.",
"Basically at all times there are loads of flu strains around - mostly in birds, a few in particular mammalian species, and a few that occasionally jump between species. Therefore even if we let everyone get the flu once, they would typically only be protected against that one strain (and maybe a few related ones). However, other strains would still be able to infect them. Even if we could somehow let all humans be exposed to all currently circulating human-infecting flu strains, one eventually would either pop in from another species or mutate to be able to infect us again.",
"The human side of things is that immunity is not a 100% thing (and isn't great in the first place in some demographics, particularly the very young and old), and that generally we don't want people dying from (somewhat) preventable diseases.",
"The more people that get flu shots the better!"
] |
[
"Great answer. Thanks!"
] |
[
"You're welcome!"
] |
[
"Some genetic mutations cause disease when inherited from the mother, but not the father. What is going on?"
] |
[
false
] |
Some genetic mutations cause disease when inherited from the mother, but the same exact gene sequences do not cause disease when inherited from the father. What causes this? I am guessing it has to do with genetic imprinting, and maybe epigenetics. Point me in the direction of the relevant Wikipedia articles, please. What happens if the mutation is sporadic? Is that the right term? Inherited from mother -> disease. Inherited from father -> healthy. What about the case where neither parent had the mutation, and this is a newly emerging mutation that first appeared in the child. Is sporadic mutation the right term for this? Is there another term? Can you link to any mutations which have this trait? Namely, can you list some mutations that are more likely to cause disease if inherited from one parent based on the parent's gender. Thank you. EDIT: I am only talking about autosomal dominant mutations, not sex chromosome mutations or recessive mutations. You can deduce this from my original post. For instance, you can deduce that I am talking about dominant diseases, not recessive diseases, because I say that the mutation causes a disease when it is inherited from only a single parent.
|
[
"Epigenetics and imprinting are at play in the case where different diseases are caused by inheritance from different parents. There are also diseases that are only inherited from fathers. The other post here so far describes X-linked inheritance, which is a different scenario than what you are trying to describe, I believe.",
"The classic genetics example is ",
"Prader Willi Syndrome",
" and ",
"Angelman Syndrome",
".",
"If a baby receives a copy of a damaged (in a specific way) chromosome 15 from their mother, they will have Angelman syndrome. If they receive a damaged or deleted copy of chromosome 15 from their father, they will have Prader-Willi syndrome.",
"This doesn't occur with all chromosome regions, because not all genes are imprinted (imprinted = silenced). With gene regions that are imprinted, if we inherit both \"working\" copies from each parent, we still only have one working copy physiologically, because the other one is turned off (imprinted). ",
"The specifics of how this causes disease can get very complicated, but basically it boils down to certain genes being turned on or off depending on which parent they are inherited from. When you combine this switching off with damage or absence of the other copy of the gene, that is when disease results."
] |
[
"This is exactly the answer I was looking for, thank you."
] |
[
"Epigenetics, as sasky_81 already explained well, certainly answer your conditions. There is another option, which you might not be expecting. Maternal effects (",
"Wiki",
") cause offspring to have the same phenotype as the mother, no matter what the father's phenotype is. This is because the egg/oocyte is full of maternally-derived mRNAs and proteins. There are many examples from ",
". For example, when female flies are mutant in the ",
" gene they have misplaced microtubules and abnormal cytoplasm streaming in the oocyte. (see Emmons ",
" 1995 9: 2482-2494 ",
"pdf",
"). This eventually results in abdominal defects in the embryo. These problems, caused by proteins from the maternal gene and deposited in the oocyte, effect the earliest stages of development and therefore have sustained effect on the offspring. However, if the male fly is mutant in ",
" there is no effect on the offspring. This is because the oocyte is already stuffed with functional proteins and/or mRNAs and the early developmental stages can occur correctly. Interestingly, the ",
" gene is similar to a gene in vertebrates (like us) that controls limb development.",
"And to address your second point, sporadic isn't the right term in this case. We say that the child has a ",
" mutation."
] |
[
"If I placed a cold pot into a cold oven, then turned the oven onto 350 degrees. Will the pot reach 350 degrees at the same time the oven does?"
] |
[
false
] | null |
[
"The heating element will heat up first, then the heat will radiate from there. It takes a lot of energy to heat a pot of water, so that will probably take longer to heat than the air in the oven."
] |
[
"Wait a minute. You could heat a metal pan much faster with a radiant element. Think of the sun heating your car. The surface will be much hotter than the air ever is."
] |
[
"Depends how technical you want to be. If you hear the air very slowly, they will stay almost the same temp the whole time. ",
"Technically though it's a no. Since the pot is being heated by convection, the air would have to be hotter than the pot to give heat to it. So the air would have to be slightly hotter than 350 to heat the pot to 350. ",
"The rate at which heat is transferred is a function of the temperature difference between the air and the pot. As the pot approaches the temp of the air, the rate of heat transfer approaches zero. ",
"Imagine taking a number and dividing it by 2 over and over. It never reaches 0. "
] |
[
"Are there ideas or knowledge about anything that would release more energy than nuclear fusion?"
] |
[
false
] | null |
[
"Matter-antimatter annihilation."
] |
[
"Matter-antimatter annihilation is a direct and ",
" conversion of mass into energy, so you can't get more energy out of a reaction than that unless you discover some even more exotic type of matter that interacts via a mechanism we haven't discovered yet.",
"I don't know about any steps in-between fusion and annihilation though."
] |
[
"Is that where it ends? And is there something between Matter-antimatter annihilation and nuclear fusion?"
] |
[
"How did domestication actually happen?"
] |
[
false
] |
[deleted]
|
[
"I cannot give you a general answer, but one that I found convincing in the case of wolves/dogs:",
"Wolves might have fed on human leftovers, at least the ones that were not too shy to go near human settlements. And the ones that were aggressive towards humans were more likely to be killed than the tame ones. So in the beginning there was probably no concious effort by humans to domesticate them, some wolves just adapted to living close to humans."
] |
[
"Sometimes referred to as \"self-domestication\"."
] |
[
"Russian scientists experimented with ",
"creating a domestic fox",
"."
] |
[
"Why does tapping a beer bottle on its top result in foam, but a standard 'cheers' tap doesn't do anything?"
] |
[
false
] |
I've seen this happen a few times: someone takes the bottom of their beer bottle and taps it on the top of another one, causing the beer to foam violently. Why doesn't this happen with a clink from the side? I would guess it has something to do with the vibration propagating down the sides, agitating the liquid enough to cause nucleation points to form. But if that was the case it seems like a clink from the side would do the same thing.
|
[
"I thought something like this too;",
"The glass is pushed down, the liquid lags behind \"in freefall\", pressure thusly drops, the glass jerks back up, and the pressure increases again.",
"Edit: On the other hand, this happens fine when victimized glass is placed firmly on a table as well. And it's seemingly always the bottom glass that foams."
] |
[
"I was skeptical of this as well.",
"I was talking with a buddy at a bar, and the best we could come up with is that the vibration from the top moves down the sides of the bottle at the same speed on all sides, meets at the bottom of the bottle, and then returns in the opposite direction with weaker energy. Possibly something about this forms the nucleation points, whereas a side clink's vibration isn't propagated from a symmetrical point (the bottle is symmetrical looking down from the top, but not from the sides). ",
"No idea if this is correct, though."
] |
[
"I was skeptical of this as well.",
"I was talking with a buddy at a bar, and the best we could come up with is that the vibration from the top moves down the sides of the bottle at the same speed on all sides, meets at the bottom of the bottle, and then returns in the opposite direction with weaker energy. Possibly something about this forms the nucleation points, whereas a side clink's vibration isn't propagated from a symmetrical point (the bottle is symmetrical looking down from the top, but not from the sides). ",
"No idea if this is correct, though."
] |
[
"If not even light can escape form a blackhole, how does radiation and energy leak out?"
] |
[
false
] |
[deleted]
|
[
"There are two things you might be thinking of... Neither of them is really radiation the way you might expect.",
"Radiation can be emitted when things slam into each other on their way around or into the black hole... That's what we often see as a jet of particles or radiation streaming outwards from the hole... But it doesn't come from inside.",
"The other mechanism is a bit harder to grapple with. Particles sometimes just pop into existence. These are usually paired with an anti-particle to keep all the conservation rules happy... and normally the pair will destroy itself again pretty quickly... But if one falls into the black hole and the other doesn't, you end up with a spare particle on the outside that looks like radiation coming out of the black hole (hawking radiation is what it's called)."
] |
[
"You'll hear a lot of answers - you have already - talking about particle-antiparticle pair production near the event horizon, and how one falls into the black hole and the other escapes. Those are decent answers because they're very intuitive, but the problem is they aren't exactly correct. Even Hawking (who uses that explanation in a lot of his popular books and talks) says this is one of the original Hawking radiation papers; it's a useful visual aid, but not a very accurate description of what's happening.",
"That's because what ",
" happening is a lot more subtle, and more abstract. It's due to the fact that the vacuum is not only not really empty, but it actually ",
" when the spacetime background it lives in changes. Spacetime does change due to the presence of mass and energy - this is exactly what gravity is. So if you have spacetime going through a change, then the vacuum before and the vacuum after aren't the same thing.",
"Let's say you have a star collapsing into a black hole, so that spacetime changes from one with a star in it to one with a black hole in it. Alternatively, you can think of the change occuring not in time but in space - near a black hole, spacetime is highly curved, but far away from it, it isn't. In either case, you have two \"phases\" that a black hole spacetime goes through. These two have different vacua, so that the vacuum in one turns out to be filled with particles in the other. In other words, what appears to be a vacuum near the black hole horizon, where spacetime is strongly curved, looks like a bath of radiation far away from the black hole where spacetime is more or less flat.",
"It's a bit abstract, as I said, but more accurate. This doesn't only apply in black holes, by the way; it's also responsible for the formation of all the structure in the Universe! Early in the Universe there was a period of rapid accelerated expansion called inflation. Inflation ended and the Universe went into a phase of decelerated expansion. The accelerating (inflationary) phase and the later decelerating phase have two different spacetime descriptions, so the state that was a vacuum during inflation suddenly, when inflation ended, was filled with fluctuations, because spacetime changed. These translated to fluctuations in density, which we can observe in the pattern of ",
"cosmic microwave background",
" radiation, and which later led to the formation of the cosmic web and galaxies within it as overdense regions collapsed under their own gravity."
] |
[
"The black hole has to repay the debt with its own mass of the escaped particle that came into existence."
] |
[
"My girlfriend asked me, and I told her to /r/askscience instead. So here: Why have animals shrunken over the course of evolution?"
] |
[
false
] |
[deleted]
|
[
"My understanding is that a number of factors are at play, including:\n1. Most recently, human predation has selected against large size in animals because of their high desirability in hunting. (see stellar's sea cow, the largest fish in the ocean, the buffalos, etc.)\n2. The largest animals have always had to be ocean animals, because of plain ol' gravity. The blue whale is STILL the large animal known to have ever lived on earth. \n3. Smaller animals may have more abilities to change food sources, find new habitats, etc--they may be more adaptable in certain ways and pass on those genes. See: The dinosaurs vs. the small mammals. ",
"Oh! Another possibility I just considered that may greatly color our perception of past \"massives\"--they are much, much, more likely the fossils to be found. "
] |
[
"can you be a bit more specific about which animals?"
] |
[
"That's not true."
] |
[
"When a person severs a body part like a finger , or part of foot and doctors are able to stitch it back on do the severed nerve endings and blood vessels reconnect? Or do they form new nerve endings,and blood vessels?"
] |
[
false
] |
[deleted]
|
[
"I have assisted at microsurgery for limb reattachment. Larger blood vessels and nerves are relatively easily brought together, but the nerve bundles within a nerve sheath can’t always be directed to the muscles they originally supplied. Many tiny blood vessels and nerves are sewn together with suture material so thin one can’t see it without a microscope. This kind of surgery can take 10-12 hours. Success depends on how ragged the injury was, the length of time the limb was separated, associated muscle damage and obviously the skill of the surgeon."
] |
[
"They're stitched back together with very fine suture. Unfortunately that doesn't stop the downstream axons from dying, it primarily functions to leave a tract of support cells for the neurons to use as they slowly regrow."
] |
[
"Individual nerve cells are hair thin, they're organized into bundles though. It's the thicker connective tissue that holds all the individual cells together that can be stitched together."
] |
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