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[
"Help with orbital hybridization."
] |
[
false
] |
[deleted]
|
[
"The answer I'd give you changes depending on why you want to know. My ",
"/r/askscience",
" answer is that hybrid orbitals are a lie we tell students before they actually learn molecular orbital theory, and that they are only useful as a heuristic to predict molecular and lone pair geometries.",
"The answer I'd give to one of my current students is that they are combinations of orbitals that reconcile the fact that p-orbitals are oriented 90 degrees apart, yet molecules like methane have bonds that are 109.5 degrees apart. The hybridization scheme is based on the steric number of the central atom in question."
] |
[
"Methane and Nitrogen are both sp3.",
"Methane has 4 bonded pairs of electrons and so it forms a tetrahedron. this shape requires sp3 hybridised carbon.",
"Nitrogen has 3 bonded pairs and one lone pair. so it is essentially a tetrahedron (but the lone pair \"squashes\" the 3 bonded pairs down a bit more) which also requires sp3 hybridisation.\nOne of the hybrid orbitals is just occupied by a lone pair though"
] |
[
"Methane and Nitrogen are both sp3.",
"Methane has 4 bonded pairs of electrons and so it forms a tetrahedron. this shape requires sp3 hybridised carbon.",
"Nitrogen has 3 bonded pairs and one lone pair. so it is essentially a tetrahedron (but the lone pair \"squashes\" the 3 bonded pairs down a bit more) which also requires sp3 hybridisation.\nOne of the hybrid orbitals is just occupied by a lone pair though"
] |
[
"Can astronomers watch anything at all happen over time, or are the timescales so large that the universe looks like it's on pause?"
] |
[
false
] | null |
[
"Depends on the type of astronomer. If they observe the solar system, they can obviously see changes from day to day. If they observe stars, and that means the Milky Way, because all observable stars are inside our own galaxy, I'm not entirely sure, but I believe they could measure changes on time scales of years. ",
"This is with respect to star positions. If they look for extrasolar planets, they often measure the luminosity of stars which can vary when a planet is moving in front of them. This happens over days. Then there are pulsars, which are sort of like cosmic light houses. Also, binary stars, whose orbital frequency is measurable. And of course super novae, exploding stars in other galaxies that become brighter than the entire galaxy for a few days or so.",
"If they observe the position of other galaxies, the Universe looks pretty much static, even though there are some recent efforts to do ",
"real time cosmology",
", where they hope to be able to measure changes on the order of decades. This would mean to literally watch the Universe expand."
] |
[
"Other things that can be observed in a reasonably short time frame:",
"\nVariable stars, which fluctuate in brightness, with a period ranging from a couple of hours to a few days.",
"\nStars orbiting a supermassive black hole, as seen in the center of the Milky Way. This takes a couple of years. ",
"Gif here.",
"\nPulsars, which are fast rotating neutron stars, which send periodic radio waves on a scale of a few seconds. ",
"More here.",
"\nAnd of course, as ",
"/u/leberwurst",
" said, anything close by, things like the movement of planets, moons, comets, sun activity and stuff like that.",
"\nBasically the further you look, the less acitivity you can see, though supernovae have been observed in other galaxies, but that should say more about the power of supernovae than anything else."
] |
[
"Why, just this week, a new supernova began appearing. It's currently in the process of brightening and will peak in the next few days. Of course, the star went nova long ago but the light is just reaching us now.",
"source"
] |
[
"Is there a way to protect electronics against EMP blast (without using faraday cage)"
] |
[
false
] |
[deleted]
|
[
"You seem to be confusing things. A vaccuum tube is an electronic component typically used in high power amplifiers; it has nothing to do with electronic shielding. Tanks and jets are largely formed of continuous metalic bodies and so are implicitly Faraday-shielded. As far as buildings go its a fairly simple matter to embed the concrete with conductive mesh that serves the purpose (though I have no idea if Military installations actually do this)."
] |
[
"In the sentence right after, it says \"other components in vacuum tube circuitry can be damaged by EMP\". So while vacuum tubes may be less susceptible to damage than transistors, there are still all sorts of other components that can be damaged. ",
"The concrete isn't serving any protective purpose, its the embedded mesh that provides the shielding."
] |
[
"In the sentence right after, it says \"other components in vacuum tube circuitry can be damaged by EMP\". So while vacuum tubes may be less susceptible to damage than transistors, there are still all sorts of other components that can be damaged. ",
"The concrete isn't serving any protective purpose, its the embedded mesh that provides the shielding."
] |
[
"Do earthworms sleep or have some sort of circadian rhythm?"
] |
[
false
] |
I know they have some sort of hibernation but don’t know if they actually sleep.
|
[
"Research with deep burrowing species, such as Lumbricus terrestris (the lob worm), demonstrates that during a 24-hour period, activity is greatest from dusk until dawn. This is not surprising, as these creatures possess photo-receptive cells (even though they have no eyes) and therefore only surface to feed and mate under cover of darkness. During less active periods of the day, their oxygen consumption has been shown to be at its lowest, but only physiological experiments could determine the level of nervous activity at these times. During adverse soil conditions, such as drought, certain species (there are 28 different types of earthworm in the UK) enter a dormant state known as dispause. Within the soil the earthworms form a mucus-lined chamber, in which they curl into a tight ball in order to prevent moisture loss. They remain in these chambers until more favourable soil conditions prevail. If earthworms do 'sleep', it must be during such times when all other behaviours cease.",
"Edit: this is the ",
"source"
] |
[
"Hey, this seems fine since it’s a multi paragraph direct quote from the researcher, but in general, I would not trust scientific research published on the guardian or any major media (CNN, FOX, NBC) that isn’t direct intact full paragraph quotes from researchers. Media loves to get the big picture of research dead wrong. I’ve had a news story where my sentence “these toxins can kill breast and colon cancers at low doses but are poor candidates for a therapeutic because they are just as toxic to non cancerous cells but they are interesting because they are resisted by another cancer cell line even at really high doses when other toxins we’ve looked at of this type are not resisted at all.” Was turned into craftmacaro shows that “toxins [cure] breast and colon cancer at very low doses...”. I’m sure you’re aware, but just in case others who see your post aren’t, make sure you dig deeper into any non-peer reviewed sources talking about scientific breakthroughs. Journal articles are best, longer, unbroken quotes from the research authors are usually ok, but remember that what a media source can twist to make more exciting, they will."
] |
[
"Hey, biologist here. My dissertation is focused on venomous snakes which are much different from worms despite their shared lack of legs, but I teach physiology and mammal circadian rhythms in our universities physiology class so I might be able to shed some useful insight. ",
"Before I get into anything else this paper is awesome: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5090016/",
"It’s a review of a lot of research done into the rhythms of things that are typically 24hr in animals in “rhythmic” zones where the day night cycle is 24 hours in “arrhythmic” zones (polar, deep sea, deep subterranean, caves). And there are fascinating variances, deep sea fish seem (though limited data is a factor) to have 24 hour feeding cycles which set them on a 24 hour circadian rhythms due to the depth of their prey even though the fish themselves are never directly impacted by the light or heat changes between day and night. Some polar animals seem to have 30 or 17 hour variances or an absence in any kind of circadian rhythm to melatonin spikes since polar light cycles get increasingly variable and eventually are not even a daily occurrence. However, it seems that earthworms likely do have a circadian rhythm based on evidence of other low depth subterranean life as well we C. elegans.",
"The stuff I didn’t think was as interesting as that paper: ",
"First thing to distinguish is what you mean by circadian rhythm? The idea is almost synonymous with the sleep cycle in humans but it can also refer to any biological/genetic/cellular/protein expression shifts that have 24 hour light/dark cycle that is endogenous (basically it has to originate from reactions that occur within the organism, if we injected a worm with a stimulant in the morning that would make it not endogenous... replicating a light dark cycle that mimics what they encounter in the wild would be ok, and that’s actually one of the second qualifiers for a circadian rhythm is that it is entrainable oscillations that are typically dependent on light/dark or heat/cooling cycles that occur on a 24 hour cycle because of day/night). These rhythms, once set, continue to function even in the absence of 24 hour recurring stimulus like light and heat from the sun... so basically, do they have an internal clock that keeps running even when they don’t have 24 hour recurring sensory or physiological input.",
"First, sleep in the sense that humans and other mammals might experience it (REM, dreams, brainwave frequency amplitudes in different areas, increased cerebrospinal fluid flow, possible removal of accumulating unwanted products from hardworking neuronal cells like beta-amyloid, postulated increases microglial activity, and many other hypotheses) is not the only circadian rhythm. But if you’re asking if we have evidence earthworms and humans do the same things during “sleep” the answer in most cases is no because we have such different physiologies of our nervous system, vascular systems, and immune systems. By the definition of something that’s occurring on a 24 hour oscillation influenced by an internal solar clock. Plants, animal, fungi, and even certain types of bacteria have shown circadian rhythms so it wouldn’t be surprising if worms did too. From a little research not getting specifically into earthworms yet, at least some do.",
"So for earthworms there’s not a ton of research that I could find, but flatworms, C. elegans, ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2953526/#!po=85.0000",
" were shown in 2010 to have at least a few genes that were tied to a circadian cycle, some influenced by heat and some by light and seemed to have an effect on behavior as well. At least there is some strong evidence for it. Earthworms, while they spend most of their lives underground, but they do have photoreceptors, perhaps mainly so they can avoid exposing themselves to sunlight and the threats it brings. However, earthworms, as ectotherms, are certainly going to be reliant on temperature for certain things, especially in more temperate zones. Those in... say... Ecuadorian rainforests might have warm soil with minor fluctuations near the surface year round... but those in Canada are likely going to be pretty strongly influenced by the warming and cooling of soil by the sun. I haven’t found a direct primary source my university has a subscription too for earthworms specifically, but I would put money on there being at least some proteins and genes that are controlled in a manner that fits the definition of a circadian rhythm... and I’d make an educated guess that some behaviors would be tied to a 24 hour cycle as well.",
"As an aside, it seems that someone has decided this is a good teaching question ",
"https://bioone.org/journals/The-American-Biology-Teacher/volume-71/issue-2/005.071.0210/Darwin-Earthworms--Circadian-Rhythms--A-Fertile-Field-for/10.1662/005.071.0210.short",
"\nI don’t have access to the journal but if you reached out I’m sure they’d share a pdf with you if they ever published on it. I’ve never been denied a full text request for a paper by an author, nor have I ever denied someone a full text request for a paper I’ve authored, so if the contact information is still good and you don’t get caught in a junk mail filter...I’d say your chances are good."
] |
[
"What causes a burning sensation when you get salt in an open wound?"
] |
[
false
] | null |
[
"It is just basic electrophysiology. When you have an open wound, the solution around nerve fibers is directly accessible. Nerve fibers work via gradients of sodium and potassium inside vs outside the cell. If you really boost the sodium concentration outside the cell, it becomes hyperexcitable. Now, it is a wound, so C fibers (nociceptors) are going to be active anyway. The salt is going to act like an amplifier. ",
"It is different from the case of lemon juice, which alters the local pH. The C fibers are directly sensing the pH and sending a signal that your brain interprets as pain. "
] |
[
"So, will salt work as an amplifier for any sensation? If you were feeling cold, and then somehow magically introduce salt to the nerves in the cold area, would you feel super cold? "
] |
[
"The pain sensation originates from nociceptive receptors (nociceptors) on the dendritic ends of sensory neurons. There are many subtypes, but the relevant one here is the chemical subtype, which contain environment-sensing channels, such as TRP. These channels respond nonselectively to ion gradients. The addition of NaCl creates a sudden change in the preexisting ion gradient that causes the dendrite to fire. The subsequent action potential results in the sensation of pain at the level of the CNS."
] |
[
"Why is that Cesium is a liquid below it's melting point?"
] |
[
false
] | null |
[
"Cesium is not a liquid at room temperature. I am not quite sure what makes you think that. In special circumstances you might be able to supercool it but this is really an edge case."
] |
[
"I just googled it and wikipedia says that it is liquid in room temperature, hence my question."
] |
[
"Wiki says ",
"which makes it one of only five elemental metals that are liquid at or near room temperature",
"28C is near enough room temperature."
] |
[
"Has a computer ever had a scientific discovery completely on its own? (Ex. Something humans can't explain etc)"
] |
[
false
] | null |
[
"Kinda, yes. Depends on what you mean by explain.",
"Genetic algorithms are being used all the time these days, and they come up with crazy results that no human would have thought of, and are usually incomprehensible. They make no sense at all but still work.",
"Perhaps the most striking example I'm aware of, in 1996 Adrian Thompson used an ",
"FPGA",
", a piece of hardware that can be physically changed by software, and a genetic algorithm to create a circuit to perform a rather complex task, detect tones and even words.",
"After a while, the circuits evolved to perform the task exceptionally well, but they relied on fringe effects, asynchronous responses and other things that are extremely difficult to simulate, predict, let alone use for a task. These circuits involve loops that do nothing other than be around in order to create electromagnetic couplings to tune the actual circuit. It's fascinating stuff.",
"All of this was found by a computer operating on a physical system by trial and error, and selecting and breeding the configurations that worked a little better. The algorithm explored combinations of circuit that no human would ever conceive of or could have a chance to model in advance. So in a sense, the computer discovered something novel and incomprehensible.",
"Similarly, people have been using these algorithms to create antennas. NASA has tried it before ",
"Sources: ",
"the paper by Thompson",
", ",
"another paper",
", some ",
"writeup at Damn Interesting",
" and ",
"Discovery Magazine",
"."
] |
[
"I would not say never, the field of ",
"automated theorem proving",
" is a very active area of research. ",
"One of the complications with automated theorem proving is that computers are unable to assess the \"elegance\" of the theorems computed. In short, many results have been discovered, but their \"importance\" is difficult to quantify."
] |
[
"Never.",
"Computers have been used, though to fill out brutally complex mathematical proofs, with a huge number of possible classes examined one by one. The first (1976) proof of the Four Color Theorem is an example of this - the mathematicians reduced the problem down to 1,936 separate classes of map, and ground through them all computationally. That made it very unfeasible for humans to check it, but it's not something that a computer came up with, any more than a chisel comes up with a sculpture.",
"The closest thing to what you're talking about would probably be something like genetic algorithms, where you configure a problem as something that can be solved by combinations of individual modules, and you let these mix, match, and mutate \"generation by generation\", each time selecting the ones that seem to be doing a better job on the problem. The end result of such a process can look pretty odd, and definitely not something that a person would have come up with on their own."
] |
[
"On average, what percentage of their contribution to GDP are workers paid in the United States?"
] |
[
false
] |
I’m going to try and describe my question/thought process in terms of things I know, so forgive me if a lot of what I say is obvious to anyone who’s studied economics. I took a business economics class last semester where we learned about mutually exclusive alternatives (MEAs). I’ve been thinking a lot about workers wages in terms of MEAs. When deciding where to invest money, a company establishes what’s called a ‘Minimum Acceptable Rate of Return’. I don’t know how that’s determined, but generally speaking an individual or entity can invest in mutual funds and make about a 7% ROI in the long term. I know that probabilistic risk plays a huge part in decision making, but let’s just keep it simple. This means that any investment that doesn’t make a 7% ROI is a waste of money and that includes workers wages. I would think then, that most workers are paid about 90% of their contributions to GDP...or company revenue...or something. I’m a capitalist to the bone, but if we stray much farther from that I would say that the average worker is definitely being taken advantage of. Maybe contribution to GDP isn’t the thing to measure against, but is my thought processes generally correct? And do we know what percentage GDP (or whatever the appropriate metric is) workers are paid on average? Thanks.
|
[
"You need the mean, not the median, for the multiplication result to have any meaning. The first reference I found indicated the mean U.S. household income in 2018 was $90K. Multiplied by 128.6M households yields a $11.6T total, or 60% of the GDP figure you quoted."
] |
[
"This is a hard question to properly answer, but to a rough first order approximation:",
"The median personal income in the US is ",
"$63,179.",
" There are ",
"128.6 million households",
" in the US. That means workers make roughly $8.1 trillion per year.",
"The US GDP is $19.3 trillion, so workers are paid roughly 42% of the US GDP."
] |
[
"I disagree. If we're trying to estimate something about the typical worker, then using a mean that's skewed by the handful of people that make tens or hundreds of millions per year makes the result meaningless when talking about the typical person. The median, while not perfect, is much more representative of the average of the distribution of salaries with those high-earning outliers removed."
] |
[
"Why is it impossible to balance a needle on its point in such a way that it stands that way alone without a magnet?"
] |
[
false
] | null |
[
"Yes."
] |
[
"A perfect needle on its tip is in an unstable equilibrium. In practice, situations like this are hard to achieve."
] |
[
"So, the \"perfect circumstances\" can be calculated, but not created?"
] |
[
"Will you be weightless if the resultant gravitational pull on you is zero?"
] |
[
false
] |
An Irish physics examination asked: Where will an object will be weightless between the earth and the moon? The answer given was that it will be weightless when the gravitational pull of the earth = the gravitational pull of the moon. My understanding of the term 'weightless' is that an object is weightless when the only force acting on it is its weight (resulting in free fall). However, in the scenario above, there are 2 separate weights acting on you which balance each other, leading to a resultant force of zero. If this is weightlessness, it seems to imply that I am weightless if I stand still on the ground, as the resultant force acting on me is zero. Was the answer given in the exam wrong? Or is the object actually weightless? Edit: Here is the exam for those who are interested (Question 6(iii)) In the original post, I should have mentioned that this is the exam that Irish students take at the end of their second-level education (usually at age 18) so I'm not looking for answers which refer to the theory of relativity.
|
[
"Now that you have posted the exam, I am willing to say unequivocally that the exam is wrong, regardless of whether we ",
" consider Relativity or not. The question asks:",
"A spacecraft carrying astronauts is on a straight line flight from the earth to the moon and after a while its engines are turned off. At what height above the earth’s surface will the astronauts experience\nweightlessness?",
"The answer to this question is ",
" \"the height at which the engines are turned off.\" The question is not asking about forces or gravity. It is asking about the astronauts', and I quote again, \"experiences.\"",
"The astronauts experience weightlessness (they float freely about the cabin) as soon as the engines are turned off, and their experiences never change for the entire rest of the trip, so long as the engines stay off. There is no way for them to know (i.e., their ",
" never can tell them) experimentally when the two gravitational pulls are equal. Nothing in their experience inside the ship can tell them this. No experiment on board the ship can tell them this. Period, end of story.",
"This, by the way, is a terrible, terrible question. The word \"weight\" is fraught with difficulty in physics as you can see and should never be used in an instructional setting. Turning the engines off does not result in a \"straight line trip\" to the Moon, etc. The authors should have their wrists very firmly smacked with a meter stick."
] |
[
"I prefer your understanding of weightlessness - an observer feels weightless if they are in free fall.",
"However, you could say the exam is pedantically correct. Weight is usually defined as the force of gravity on an object. Therefore, you want to find where the object has no force on it in the Newtonian sense - this is at some point between the Earth and the Moon. Then, for any observer at rest or moving with a constant velocity with respect to the Earth-Moon system, the object exhibits zero coordinate acceleration. There is no local experiment that the object could perform which would determine that it is \"truly weightless\" in this sense; it would need to determine its position and motion with respect to the Earth and Moon first.",
"If this is weightlessness, it seems to imply that I am weightless if I stand still on the ground, as the resultant force acting on me is zero.",
"I think the trick is that the normal force isn't gravitational, so it doesn't count as a \"weight\" force. Your exam truly is playing dirty."
] |
[
"For some reason I never realised that weightlessness occurs as soon as the engines are turned off. Thank you very much for your answer, I found it to be the most straightforward and informative."
] |
[
"Is there a legitimate, applicable solution to safe nuclear waste storage?"
] |
[
false
] | null |
[
"There is no 100% safe way to dispose of nuclear waste.",
"Nor is there any 100% safe way to dispose of thousands of other very hazardous non-nuclear industrial waste products.",
"So there isn't anything special about nuclear waste, except it is easier to frighten children with it. In fact, in some ways, nuclear wastes is better...radioactive materials eventually stop being radioactive. Mercury and cadmium are poisonous forever."
] |
[
" hasn't seen Superman III...",
"Really, there's no totally foolproof way to get rid of the stuff and we can't be sure it's going to stay put."
] |
[
"The best way to deal with nuclear waste is to use a nuclear fuel cycle ( e.g., ",
"http://en.wikipedia.org/wiki/Thorium_fuel_cycle",
" ) that \"burns\" radioactive elements as completely as possible, so that the stuff left over isn't very radioactive. ",
"This is also important to avoid hitting \"peak Uranium\" 100 years from now."
] |
[
"How did Chinese officials know to look for a novel virus in the early days of the SARS-CoV-2 outbreak?"
] |
[
false
] |
What triggered the search to determine the specific virus? Is there some sort of protocol in place that catches these things? Maybe I’m naive, but I’m impressed with how quickly China was able to determine it was a new virus given how common and broad the symptoms are.
|
[
"This is standard public health. Public health systems are things that no one notices during normal times, but that are constantly watching for this sort of thing. When something looks abnormal, there are processes to escalate surveillance and start looking for causes. ",
"I think the first English-language report was to the WHO (which is one clearing-house for this, but not the only one), which announced Jan 5",
"On 31 December 2019, the WHO China Country Office was informed of cases of pneumonia of unknown etiology (unknown cause) detected in Wuhan City, Hubei Province of China. As of 3 January 2020, a total of 44 patients with pneumonia of unknown etiology have been reported to WHO by the national authorities in China. Of the 44 cases reported, 11 are severely ill, while the remaining 33 patients are in stable condition. ",
"—",
"Pneumonia of unknown cause – China",
"The bland language here should be a clue that this is ",
". If you follow public health announcements, there are constantly reports of local clusters of pneumonia or neurological problems or diarrhea or whatever. There are similar announcements probably weekly. Most of them turn out to be “normal” - influenza, or some known disease, or maybe nothing - just a random cluster. ",
"But they all get followed up, and there’s a standard toolbox to look at these sorts of things. There’s a brief description of the Chinese organizations that respond to these kinds of things in ",
"Use of National Pneumonia Surveillance to Describe Influenza A(H7N9) Virus Epidemiology, China, 2004–2013",
":",
"Since 2004, the Chinese Center for Disease Control and Prevention (China CDC) has conducted surveillance for pneumonia of unknown etiology (PUE) to facilitate timely detection of novel respiratory pathogens, such as severe acute respiratory syndrome (SARS) and avian influenza.",
"The specific response is summarized in the initial (English-language) report of the disease:",
"In late December 2019, several local health facilities reported clusters of patients with pneumonia of unknown cause that were epidemiologically linked to a seafood and wet animal wholesale market in Wuhan, Hubei Province, China.11 On December 31, 2019, the Chinese Center for Disease Control and Prevention (China CDC) dispatched a rapid response team to accompany Hubei provincial and Wuhan city health authorities and to conduct an epidemiologic and etiologic investigation.",
"—",
"A Novel Coronavirus from Patients with Pneumonia in China, 2019",
"So the bottom line is that there are organizations and groups who do this all the time, and no one notices. ",
"It’s possible that China was especially quick to catch this, because of their previous experiences with SARS and various avian influenzas (note that their PUE group specifically noted those). But we’ve seen similarly rapid identification of the clusters of avian influenza in humans in Mexico, The Netherlands, Canada, and the US (and by the way if you didn’t notice that there were recent avian influenza outbreaks in humans in Mexico, Canada, the US, and the Netherlands, the public health organizations you don’t know about say You’re welcome), so I don’t think China is extraordinary - virtually all public health organizations are excellent."
] |
[
"Well thought out and rapidly sourced intel, great post."
] |
[
"Thank you for the thorough response! I’m glad to hear the various public health agencies are good at what they do."
] |
[
"Why does staring at a moving optical illusion and looking away cause what you're looking at to appear to be moving?"
] |
[
false
] |
For example, the illusions in
|
[
"It's known as 'The Waterfall Effect'. The simple explanation is that the nerve cells detecting movement get tired, and when you look away, the brain overcompensates and creates the illusion of motion where there is none. ",
"Find out more: \n",
"http://psylux.psych.tu-dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/html/motion_aftereffect.html"
] |
[
"I remember when guitar hero came out, and I didn't like playing it because after I would look away from the screen, my vision was swirly and triply for a few minutes "
] |
[
"Yes it is adaptation. Specifically many aspects of visual processing are computed as ratios in the nervous system. Motion detectors (called correlation detectors) are directionally tuned, and velocity tuned, and higher levels of visual processing compare output of these detectors to determine the motion of objects. Prolonged exposure fatigues the cells (fatigue=adaptation) so that after removal of the stmulus, they don't just return to their baseline firing rate but are firing less than baseline. Because the neurons that detect movement in the opposite direction are still firing at the baseline spontaneous rate, the ratio favors the \"opposite direction\" neurons, interpreted as motion in that direction."
] |
[
"If I chose a random bit of my computer's hard drive and flipped it from a 0 to a 1 (or vice versa), what would happen?"
] |
[
false
] | null |
[
"Nothing - on your hard drive this happens all the time. Data on hard drives is written with error correction encoding. During every write to a hard drive, a few 'extra bits' are also written. These 'extra bits' are cleverly calculated so that whenever one (or more) data bits get corrupted during a read operation the error is identified and corrected. There is actually some very deep mathematics behind this process.",
"References:\n",
"http://en.wikipedia.org/wiki/Hard_disk_drive#Error_rates_and_handling",
"http://en.wikipedia.org/wiki/Forward_error_correction"
] |
[
"Depend on which bit.",
"If you chose a bit from a bitmapped image, one of the pixels in that image would be a different color when you viewed the image. This could be not even noticeable (if you changed 0xFFFFFF to 0xFFFFFE, for example, that one pixel would go from pure white to just barely grey) or if you chose a different bit (0xFFFFF to 0xFFFF7F) it might be very noticeable since you'd change a white pixel to yellow. Or 0xFF7FFF would be purple.",
"If you changed a bit in a JPEG-encoded image, you'd likely mess up an entire 16x16 block of the image. Would be much more noticeable.",
"If you changed a bit of an executable program you could easily cause the program to crash when it reached that point. For example, if you changed the address in a JUMP instruction, the program would go to some random address rather than where it was supposed to go. Let's say you messed with a bit in a video game program and it was supposed to jump to the section of code where it calculates your score, but instead with the new mangled address it jumps into the middle of an image file and tries to execute the bytes in the image is if they were machine language instructions. This would almost certainly just crash the program.",
"Keep in mind that many of these things have error checking built in - a bitmap image, JPEG, or executable program might have a checksum so that it can detect when it has been corrupted. An executable program can't simply jump to any memory location it wants because the operating system only allows it to access memory allocated to it. If it tries to go to a random memory address you will just get a page fault and crash."
] |
[
"Most file systems and even file formats have some level of error resiliency. Consider that most hard drives are still of the spinning variety rather than solid state. They are mechanical devices which can suffer from mechanical problems. Also, a lot of the basics of filesystem design were developed many years ago when hard drives were much more prone to failure than they are now. Those designers planned for various failure conditions because they were a part of life.",
"Your computer probably deals with single bit errors almost constantly, but you don't notice because the error correction does its job. However multiple bit errors can cause data corruption. This is why companies usually store data on disk arrays joined together with RAID, ",
" have backups of that data. The RAID helps prevent the failure of any one disk from destroying data and the backups help prevent data loss due to situations RAID can't protect against, like accidentally deleting a file."
] |
[
"Do other stars follow an orbit?"
] |
[
false
] |
[deleted]
|
[
"To a first approximation, we can say that everything in the universe that has mass \"follows an orbit\". ",
"(Though every orbit is perturbed by the gravity of other objects that have mass.) ",
"-",
"Our Sun orbits around the center of our galaxy, taking about 225–250 million years to make a round trip.",
"With perhaps a very few exceptions, the other stars in our galaxy - whatever their size - similarly orbit around the center of our galaxy. Stars in other galaxies orbit around the centers of their galaxies. "
] |
[
"Sure, and these binary and multiple stars are also orbiting around the center of our/other galaxies."
] |
[
"Yes, so the answer to the question is yes, on multiple scales! Nothing is so massive that it is not influenced by gravity. "
] |
[
"Why are lithium, beryllium and boron so rare?"
] |
[
false
] |
Compared to heavier elements like carbon, nitrogen, and oxygen?
|
[
"Elements are forged in stars. Moderately massive stars make C/N/O easily and for a decent chunk of their lifetimes in ",
"a cycle named after those elements",
", but they don't spend much time making beryllium, boron or lithium. To paraphrase ",
"Neil DeGrasse Tyson",
", when stars die, they unleash their guts on the universe, and so their CNO rich guts wind up everywhere, including your backyard and your lab bench. And you. Read up on ",
"stellar nucleosynthesis",
"."
] |
[
"I think it's less that they \"don't spend much time\" making Be B or Li, and more that those elements are very easily fused into more massive elements, so in any star which is capable of making C, those three will get fused out in short order and the net product of the star will include very little of them."
] |
[
"All elements heavier than hydrogen ultimately come from stars that underwent fusion for millions/billions of years and then exploded to release their fused elements into a new solar system. The lack of Beryllium, Lithium, and Boron has to do with this fusion process occurring inside the star.",
"You probably know that the primary fusion of stars is the combination of Hydrogens to form Helium. This happens when a Hydrogen-2 (1 proton, 1 neutron) fuse together to form Helium-4 (2P, 2N). Once Helium-4 is formed, those heliums can try to fuse together, but when they do, they make an extremely unstable Beryllium isotope, Beryllium-8. This has a half life in the range of femtoseconds and immediately undergoes alpha decay which splits back into two Helium-4 atoms. (Lithium and Boron have related problems.)",
"This leads to the question how can we have heavier elements if Beryllium decays? Every star is a balancing act between the explosive outward force of fusion reactions and the crushing inward force of gravity. Once the star begins to run out of Hydrogen fuel, gravity starts to win and the star crushes down a ways. This makes the core more dense and even hotter, which allows for fusion to occur even faster. Fusion can happen so quickly now that when Beryllium-8 forms, it can immediately react with another Helium-4 to form Carbon-12 before the beryllium has a chance to decay. Carbon-12 is a stable isotope and thus an even numbered element is born. Carbon can then fuse with Hydrogens to undergo the CNO cycle.",
"The decay processes can get quite complicated but ultimately even atoms will be more abundant than odd atoms because of the fusion with Helium.",
"Notes on the Nuclear Physics of Stars"
] |
[
"When you get cancer, is most of the pain focused on the area that you have cancer in? Or does the pain spread out across the body regardless of the origin of cancer?"
] |
[
false
] |
[deleted]
|
[
"Excepting brain cancer, pain in cancer is frequently due to disruption of the normal anatomy which produces local pain that may be so severe or vague it feels like it’s spreading. For example, liver cancer can stretch out the sac that surrounds the liver (its capsule) and produce excruciating pain, but since the nerves inside your body aren’t as god at locating pain as the ones in your skin, the brain could misattribute that pain to pretty much the whole belly. As another example, bony metastases from prostate cancer usually cause pretty bad local pain in the bone they’re invading, which is worsened by injury to said weakened bone. "
] |
[
"Part of the reason for bone cancer pain is the interruption of TRP receptors which fire when the body is exposed to a thermal stimulus. Disruption in the TRP channel lead to firing at core body temperatures, thus constant and relentless pain. Note that modern pain medications don't function via a mechanism to alleviate bone cancer pain."
] |
[
"Just to add to your answer, tumors can also directly impact major nerves, which can cause pain in otherwise healthy areas of the body."
] |
[
"Why is it that an animal can go years without any form of brushing their teeth, yet if a human tried that, their teeth would rot?"
] |
[
false
] | null |
[
"Animals and humans have a very different diet. Our diet consists of much more sugars and other things that cause tooth decay, which is why we have to clean our teeth to maintain a healthy mouth."
] |
[
"Looking up if animals get dental diseases, I found ",
"this book",
"... ",
"Animals can develop caries and periodontal diseases, just like humans! ",
"Look up pictures of animals' teeth - they don't always look healthy! ",
"There are a significant amount of deep cleans and extractions done by veterinary dentists... ",
"EDIT: ",
"This",
" looks like dog teeth to me, and that's a combination endo-perio lesion. Considering it affects the adjacent teeth too, I think it's primary periodontal disease. ",
"TL;DR Animals ",
" get away with it... we just don't know about it because they can't tell us. Even if humans do stop brushing their teeth for years, plenty don't die because the infection drains into their mouth... we just have a hell of a time cleaning up the mess by the time they come in."
] |
[
"What about monkeys and other fruit eating species? Don't they eat tons of sugars through fruit?"
] |
[
"What is the sound made by fires?"
] |
[
false
] |
Where does the sound of fire come from exactly?
|
[
"You're probably thinking of the crackling sounds that comes from burning wood. Wood has pockets of moisture in it, and fire boils that moisture and increases the internal pressure in the wood, causing it to crack. The cracking wood is where the sound comes from.",
"A fire like a bunsen burner doesn't make any sound other than the gas coming out of the nozzle."
] |
[
"Op could also be thinking of a fire's roar, which comes from thermal expansion (think of it like wind turbulence)."
] |
[
"It probably still would. Air trapped in the wood might expand enough to crack it. "
] |
[
"Do pilots have to take the Earth's rotation into account during North/South flight?"
] |
[
false
] |
My question mostly stems from my understanding on inertia. For example, if you too a ball straight up in the air while on a moving train, to ab observer not on the train the ball will have a parabolic flight pattern. Extrapolating to airplane flight: Say a pilot is flying from South Africa to Poland (same time zone). Does he/she just have to point the aircraft due north and fly straight? Or do they have to aim towards China, and by the time they get that far north the earth will have rotated such that Poland has rotated into place? Basically, at what point does the plane "escape" being affected automatically by the earth's rotation (train example) and have its own independent inertia?
|
[
"It isn't just the earth that moves, but also the atmosphere moves with it at the same rate. So when a plane flies through the atmosphere, the whole system is rotating as a whole at the same rate (earth + atmosphere) so the net effect on flying times is zero - DIRECTLY. ",
"INDIRECTLY the rotation of the earth has some effect on the winds, whose average speed ultimately depends on the Earth's spinning as well but the dependence is indirect. The airplane flies in the atmosphere and wants to reach a particular speed relatively to the air mass. So, if the air mass is moving West, the plane moving in the same direction will reach the destination faster than flying opposite to it.",
"In addition, ",
"Coriolis effect",
" has a very important and very indirect effect on air travel because it alters winds, weather, and in particular the direction of the jet stream. As for direct effects on the airplane, it is very small."
] |
[
"The air rotates (more or less) with the earth (otherwise we'd have very massive winds). The aircraft flies through the medium so the air carries it. If there were no air, a flying device like a rocket would have to take into account the rotation of the planet in such a flight."
] |
[
"The Coriolis force it acts 90° to the wind direction causing air to turn right in the northern hemisphere and to the left in the southern hemisphere. As altitude increases wind speed increases due to less surface friction and increases direction (10° to 50° depending on surface roughness) in the northern hemisphere, the reason it increases direction is because the surface of the earth slows down the Coriolis effect so it 'turns' less to the right than it would above the friction layer. E.g. if you are at mean sea level on a location in the N-hemisphere with rough terrain the wind speed could be 10 m/s coming from 120° but at 5000 feet on the same location the speed could be 20 m/s coming from 150°, same example but at the southern hemisphere the wind speed would increase the same way but the direction would 'back' at higher altitudes, so the wind would still be 20 m/s but coming from 090° at 5000 feet. The magnitude of this effect also varies depending on latitude.",
"However the rotation of the earth (among other things) causes the directional gyros and the IRS/INS system (Think old school GPS based on gyros) to lose accuracy over time. This is also affected by different latitudes but at it's highest it is 15° per hour for the directional gyro (360°/24 hrs = 15° per hour.)"
] |
[
"Is there a reason that the superposition \"works\" in so many situations, or is the fact that so many physical properties are representable by a linear system a happy coincidence/approximation that is backed up by experiment?"
] |
[
false
] |
Is there any reason to believe that we're simplifying things by assuming that so many properties of the universe are linear? I know that chromatic forces aren't linear, so why should so many other things be? On a personal level, it bothers me how convenient it seems. (resubmitted - the last one got blocked because it wasn't tagged)
|
[
"We don't really assume that so many properties of the universe are linear. We know now that many of the linear forces we deal with on a daily basis (i.e. Newtonian gravity and electromagnetism) have higher-order corrections that are nonlinear. Newtonian gravity was superseded by General Relativity (a fully nonlinear theory of gravity) and Maxwell's equations were superseded by Quantum Electrodynamics (which predicts higher-order nonlinear corrections to Maxwell's equations, for example see ",
"here",
"). ",
"The forces that mediate the interactions of large, low-temperature objects (like us) are Newtonian gravity (low-energy limit of GR) and Maxwell's electromagnetism (low energy limit of QFT). It's no accident that these forces both obey the superposition principle and are long-range. The main reason we don't see the much more powerful color forces in our daily lives is that the color force fields are nonlinear and, as a result, the fields attract themselves forming ",
"flux tubes",
" between two quarks, with enough ",
"residual strong force",
" to hold protons and neutrons in the nucleus together (similar to how the Van der Waals force mediates attractions between molecules). "
] |
[
"Imagine some system doesn't obey the superposition principle, and some property f is an arbitrarily complex function of some parameter x. On some small enough interval the function is constant. You can make a better approximation on some interval by including a linear term. Of course, you can keep going and include quadratic terms and so on. This process is called a taylor series expansion of the function f. Sometimes the linear term is 0, and you might need to include higher terms before you get anything interesting at all. Other times, the linear term might just be a horrible approximation on the interval you're interested in. But often the linear term will be good.",
"Special relativity is a good example of a more accurate theory which can be approximated at low velocities by this kind of an expansion. Addition of velocities is linear in pre-relativistic physics (i.e. with galilean transforms) it's not in special relativity, but as long as the velocities that you're dealing with are much less than the speed of light the galilean transform is a very good approximation. ",
"Just to carry this a little bit further you can also look at the expression for energy, which in isn't 1/2mv",
" in relativity, but once again doing the approximation at low velocity you get E = mc",
" + 1/2 mv",
" + ....\nAgain you see the approximations at work, though this time the linear term is 0 so you get an apparent quadratic form in the low velocity regime.",
"This is one example, but honestly it happens all the time. Very often we simplify things and get linear rules out of it. But often the corrections to the simplification are exceedingly small in the regime we're interested in. For example the addition of two parallel velocities: if both velocities are 100m/s the full special relativistic expression gives vtot ~ 200 m/s * 1/(1+9",
" ). So the correction is at the trillionth of a percent level."
] |
[
"Thank you. I didn't think to look whether GR was nonlinear. I also didn't know about that property quantum quantum electrodynamics. ",
"I know that Newtonian gravity is an approximation of GR gravity. Is the electrodynamics I learned in school a \"pretty good\" approximation in the same way? Or are the rules seemingly totally different at smaller scales?"
] |
[
"Do defibrillators just \"reset\" irregular heartbeat rhythms or do they \"restart\" a stopped heart as well?"
] |
[
false
] |
Afaik, the human heart relies on electrical signals from 2 nodes in the heart to maintain a regular rhythm. It makes sense that an electric shock can reset the irregular rhythm into a regular one. During my grade 12 biology class, my teacher said that fixing irregular rhythms is the ONLY purpose of the defibrillator. He also said that all medical emergency situations portrayed in the media are inaccurate because defibrillators do not work on a person that's flat-lining since there is no rhythm to reset. From what I can understand from Wiki, this seems to be the case. Yet, yesterday in the news there was an report on a teenager that was hit by a puck during a hockey game and his heart stopped. A paramedic and a doctor in the stands tried to use a defibrillator from the hockey rink on him first but it was out of batteries, so they performed mouth to mouth and chest compressions instead and resuscitated him. When an ambulance arrived, they used a defibrillator on him. Now I'm left wondering if my high school teacher was mistaken and that defibrillators can "restart" stopped hearts as well as resetting irregular rhythms. Any answers would be appreciated. Thanks in advance.
|
[
"What you describe sounds like ",
"commotio cordis",
" which is a disruption of heart rhythm due to some sort of traumatic impact (i.e. a hockey puck, or the steering wheel in a car accident). It sends the heart into a very bad rhythm which could be reversed by defibrillation. This may be why they tried to use a defibrillator on him. ",
"There can be some misconception about what is meant by when a heart stops. If you can't feel a pulse, it doesn't mean the person is flatlining. These very bad rhythms can have uncoordinated heart muscle contraction which isn't very good at pumping blood, so therefore you can't feel a pulse, but the heart isn't flatlining. "
] |
[
"Only in the movies can they restart a heart. They are used to reset an irregular heartbeat."
] |
[
"Thank you for your patronizing sarcasm. I'm not sure what you're trying to prove.",
"Here's the scenario: you find a person down in the field. There is no pulse. You have no means of determining the underlying cardiac rhythm. It is not unreasonable to say, in a colloquial sense (again this is not a medical term), that the heart has \"stopped,\" given that there is no forward blood flow. It would not be fraudulent, in this scenario, for a physician to document \"cardiac arrest\" and death, without proving the absence of v-fib or v-tach, or any form of pulseless electrical activity."
] |
[
"Are human fertility rates affected by population density?"
] |
[
false
] | null |
[
"So, for context, I recently learned that there are a species of Arctic ground squirrels in which the females reproductive success is affected directly by the density of the squirrel population, rather than by availability of food. I was wondering human reproduction acted in any similar way."
] |
[
"In a hunter-gatherer tribal society fertility rates are regulated by lactation/milk production.",
"When a woman is lactating, due to hormonal factors, she is less like to ovulate and become pregnant",
"When food is plentiful children are weaned off breast milk earlier, ovulation returns, and a woman is more likely to become pregnant",
"When food is scarce, children are breast fed longer, and a woman is less likely to become pregnant",
"Thus in a society living more naturally in accordance with nature there are inherent lactation feedback mechanisms that can regulate population size ",
"Source: ",
"Biology class a long time ago",
"Also: Effect of breast-feeding patterns on human birth\nintervals, P. W. Howie and A. S. McNeilly, Journal of Reproduction and Fertility ",
"<PDF>"
] |
[
"Which while fascinating unfortunately doesn't really answer the question."
] |
[
"How does an axial compressor create more pressure?"
] |
[
false
] |
I'm actually in the math-heavy design stage to build an actual mini axial gas turbine. There are reasons why a centrifugal one is used as part of a turbocharger, but the scientific challenge really got to me. I'm even building an extra 4-axis lathe to mill the blisks for it. Anyways. I have no problems with the design of the blades or the velocity triangles. BUT EVERY book about fluid dynamics or turbomachinery OMITS THE EXACT causal link of how a stator (if the compressor is of such design) creates pressure. It usually vaguely talks about the stator being a diffusor, but on the same time the flow area of the annular stream continually grows smaller and smaller through the compressor. In other words: How does it work that a flow is diffused (subsonic design) and at the same time the flow area is reduced. Obviously this can't work the way I describe the question, but the phrasing of the question is well formed to exactly depict how much I understand and what's still missing. So, what exact characteristic of the stator (is it the curvature, the thickness, the nozzle spatial geometry,...) causes the pressure to rise from the velocity AND how do I bring this in accordance of the steady reduction of flow are throughout the compressor? I REALLY appreaciate an answer as not even fluid dynamic books really get this specific and just generalize that point.
|
[
"This is an interesting question: one I have spent close to a lifetime pondering. I am a retired compressor research engineer. This is a corollary question to the age old “why do pumps pump?”. That is, why doesn’t the fluid stop and reverse course and go back out the front of the pump? ",
"The aerodynamics of compressors are uber complicated and it is easier to outline the challenges/difficulties rather than the mechanism of compression. That is, your question is well put. ",
"The goal, of course, is (usually) to gain static (thermodynamic) pressure (in both blade rows). Basically a ram/inertia effect comes into play (especially) in the first rotor (of course, it continues to play a roll in every blade row). To try to simplify things I focus on the key flow physics: ",
"So the rotors impart KE to the fluid while also (and in concert with) diffusing the flow (to gain static pressure Ps). The stator diffuses the flow (in a prescribed manner) in order to convert the KE into Ps. It is a balancing act in order to gain Ps while also maintaining uniform flow that is fit to flow into the following rotor. Flow separation in the stator decreases the flow area and so defeats the diffusion process, that is the flow speed increases (with reduced area) rather than decreases in that case. I’ve uber simplified in order to describe the basic flow mechanics.",
"E: in a well designed compressor the area goes down (thru the machine) bc the density (and Ps) is increasing. In general the axial speed of the air is approximately constant. The idea there is to reduce flow losses."
] |
[
"If I understand your question correctly, you actually answered it in your question :>",
"At an energy level the kinetic energy is converted into potential energy. The rotational flow is converted to an axial acceleration which is converted into pressure by the narrowing effect of the stator. That's if I understand your question. It is the same property that creates lift in an airplane wing. Your fluid dynamics books should cover this pretty well."
] |
[
"I think you might be the one cracking the egg so to speak.",
"I understand what you're writing. I think your answer is exactly where I am standing right now knowledge-wise. The question is: How does the reduction in flow area not sabotage the diffusors (rotor blades and vanes)? There can either a diffusion OR a constriction, but seeing schematics, it's always a constant flow area reduction if you look at the whole compressor and a diffusion on the blade- or vane level. It fells like I almost got it."
] |
[
"Are energies in general relativity \"relative\" or \"absolute\"?"
] |
[
false
] |
Within quantum mechanics, energy zeros are arbitrary and only energy differences affect the dynamics of a system. Shifting the energy higher or lower will simply cause a rotation of the global phase of a system. However within general relativity energy warps space. If I add a field of constant energy field over the whole universe (with no spatial variation) does this alter dynamics within the universe? I feel at zero time after this change it does not since the gravitational field from this extra mass will cancel out at every point (except at the boundaries). However, after some time passes the extra energy field may be attracted to other masses and this uniformity will break down and then the energy field will start having an effect? It seems therefore that energy is an absolute quantity, but I am not sure about my analysis. This seems quite profound to me that there could be this difference between our two most fundamental theories of how the universe works. If there is a zero of energy, what is it? Does this relate to the cosmological constant etc?
|
[
"Since energy density enters into the stress-energy tensor and the field equations are non-linear it should be no surprise that the absolute sign of the energy does matter. For instance, consider the stress tensor for a perfect pressureless fluid (a matter dust). If the energy density is 0 and the spacetime is diffeomorphic to R",
", then one solution is the Minkowski metric. But if the energy density is positive, then one solution is the FLRW metric, which exhibits Hubble expansion.",
"There are also several energy conditions you can impose on the spacetime to guarantee certain desirable properties (e.g., global hyperbolicity). All of these conditions are inequalities involving various contractions of the stress tensor or products of the stress tensor and arbitrary vector fields. This reflects the importance of the sign of the energy density (and other components of the stress tensor) in determining the solution."
] |
[
"The Aharonov–Bohm effect still relies on the differences between potentials at different points in space to work, not because of a global potential change at all points in space. ",
"Also as I understand it the zero point energy that comes from quantum field theory is not sufficient to account for the value of the cosmological constant. Edit: Also why does the gravitational field change when you add a constant energy density field? I assumed a test mass in this field would experience no net force."
] |
[
"The Aharonov–Bohm effect still relies on the differences between potentials at different points in space to work, not because of a global potential change at all points in space. ",
"Also as I understand it the zero point energy that comes from quantum field theory is not sufficient to account for the value of the cosmological constant. Edit: Also why does the gravitational field change when you add a constant energy density field? I assumed a test mass in this field would experience no net force."
] |
[
"Why do humans find many animals cute instead of tasty looking?"
] |
[
false
] |
Is it some evolutionary glitch? Is it genetics passed down from our ancestors to motivate us to domesticate animals? Curious what the reason is.
|
[
"Evolution doesn't have infinite precision to work with. The failsafes against killing human infants are extremely strong because the outcome if they fail is so catastrophic; if you weaken them enough (or install enough loopholes or whatever) to let you kill other infant animals, the odds go up that you'll accidentally kill an ugly baby (or whatever), and that cost outweighs the benefits of a few ducklings in most situations."
] |
[
"This makes sense. But it raises the question: human beings have no difficulty distinguishing between human and non-human animals. Baby animals easy prey. Why wouldn't our \"baby love\" failsafes incorporate the distinction between human and non-human?",
"Is it simply that this situation just didn't come up enough to exhibit selective pressure? (A hunter spares a baby rabbit because it's cute, then dies of starvation - that seems extremely unlikely).",
"Or is it because there are selective pressures in favor of sparing young animals (sustainability? was that even an issue way-back-when?). Or some other reason?"
] |
[
"This makes sense. But it raises the question: human beings have no difficulty distinguishing between human and non-human animals. Baby animals easy prey. Why wouldn't our \"baby love\" failsafes incorporate the distinction between human and non-human?",
"Is it simply that this situation just didn't come up enough to exhibit selective pressure? (A hunter spares a baby rabbit because it's cute, then dies of starvation - that seems extremely unlikely).",
"Or is it because there are selective pressures in favor of sparing young animals (sustainability? was that even an issue way-back-when?). Or some other reason?"
] |
[
"What is the difference between the different types of silicon in a transistor?"
] |
[
false
] |
[deleted]
|
[
"N-type has excess electrons, P-type has missing electron \"holes\" in the crystalline structure. Usually silicon is doped with a small amount of another material to make it N-type or P-type. The type of dopant determines whether it is N-type or P-type."
] |
[
"This will be simplified.",
"If you look at silicon on the periodic table, you'll see that it's in the second column of the p-block along with the other Group IV semiconductors. Stripping this whole entire subject down to the bare bones, the elements in this column have 4 valence electrons (2s",
" and 2p",
" ). These valence electrons play a role in the electrical conductivity of semiconductors.",
"\"n-type\" doping is easy to explain. If you look at elements from Group V, just to the right of silicon, you'll see that they have an extra valence electron (2s",
" and 2p",
" ). Let's take phosphorous, for example. If we were to substitute a single phosphorous atom for a silicon atom in a huge chunk of silicon, the phosphorous would still want to bond with these other silicon atoms. However, the issue is that this phosphorous atom had an extra electron that it usually holds onto, and this isn't necessary for bonding with the Si atoms. ",
"Here is a picture",
". See that lone electron? That electron is free to conduct about the structure rather than stay bonded to the Si atoms, meaning the conduction of the material will increase. The more P atoms (edit: P for phosphorous, not for p-type doping!) we add to the Si network, the more free electrons we have, and the more conductivity we'll get.",
"What about \"p-type\" doping? Well, sometimes people have a little more difficulty understanding it, but really it's the reverse of what happens above. If we were to take an element from Group III, such as boron, you'd notice that they're short an electron compared to Si. But we're still able to substitute a B atom for an Si atom inside a chunk of silicon, and it still bonds with the silicon. The only thing is, now we're short an electron: look at the ",
"left side of the diagram",
". The tricky part is, this hole can migrate through the structure just as the electron did in the previous example. People get confused on this. When I first heard this I asked the professor, \"How can a hole migrate? A hole isn't ",
", it's the lack of something.\" He told me I can think of the hole as a severed bond in the lattice, and this severed bond migrates throughout the structure. But the broken bond, this hole, also has a charge to it. It has a positive charge with respect to its surrounding. It has to be positive, because with a normal bond there would have been a negatively charged electron in its place. We're missing that negatively charged electron, therefore we gain a positive charge.",
"So there's n-type and p-type doping in a nut shell. N-type doping uses excess electrons to carry negative charge, and p-type doping uses \"holes\" that carry a positive charge."
] |
[
"If you think about how a transistor works, it has to maintain an 'off' state even when there is a voltage applied between the source and the drain.",
"What does this mean? Simply that the area between the source and the drain must be non-conductive when off, and conductive when on (as controlled by the gate).",
"Now the question is, how do you alter the resistance here?",
"By drawing or removing electrons to the depletion layer you can change the resistance locally thus placing the transistor in an on or off state (or somewhere in between).",
"Where do these electrons come from? Well from the dopants!",
"By adding elements with one more electron than silicon (N-dopants) or one fewer electron than silicon (P-dopants) you can essentially create an area which has excess or fewer electrons. This will cause for an easier creation of a conductive band in the depletion zone when your gate switches the transistor on.",
"http://britneyspears.ac/lasers.htm",
" This site is a surprisingly good introduction to the concepts required here "
] |
[
"Would a spherical shell rotated about 3 orthogonal axes simultaneously feel an evenly distributed outward pressure?"
] |
[
false
] | null |
[
"Any arbitrary rotation of such an object can equivalently be described as a rotation about a single axis. Whatever angular velocity vector you can construct in your initial coordinate system, I can pick a coordinate system where one axis lies along that direction. Then the angular velocity has a nonzero component in only one direction.",
"And the outward centrifugal force in a co-rotating frame points normal to that axis. So it's not uniform in all directions, if that's what you're asking."
] |
[
"How would you rotate a rigid body about two (let alone three) perpendicular axes? Imagine a globe spinning about the X-axis, and then you give it a smack in the positive X direction, so as to spin about the Y-axis. The globe wouldn't be spinning about both axes simultaneously. It would be spinning about a new axis of rotation somewhere between the X and Y axes. "
] |
[
"Ok here's a thought experiment. Suppose you have a rigid sphere. You put three marks on it : two on the equator, about 90 degrees apart, and one on the poles. I claim that no matter how you spin the sphere, you cannot get all three points to have equal centripetal force directed away from the center of the sphere.",
"Why is this? Well, for each point, the centripetal force is perpendicular to the direction of motion of that point. For the two points on the equator that's easy. Spin the sphere so it rotates on its axis, and the points are moving along a big circle of rotation. The normal force is away from the center of the rotation.",
"But now how can you simultaneously get the point at the pole to experience the same force? That would mean that point is also moving perpendicular to the direction of the force. The point would have to be moving towards the equator - but we said it's a rigid sphere, so the points can't be moving relative to each other on the surface of the sphere.",
"You can add all the axes you want, but you can't change the fact that each point on the sphere is only accelerating in one vector at a time. And in a rigid sphere, you'll find you can't get all the points on the sphere to accelerate so that the normal force is outward via rotating the sphere."
] |
[
"Which is more effective at cooling a room in a house: Pointing a fan in (pulling cool air in) or pointing a fan out (pushing hot air out)?"
] |
[
false
] | null |
[
"If you want it to feel cooler, you want the fast moving air to pass by your body, displacing the warm air just above your skin. When a fan is pointed towards you, the colomn of moving air is tighter than when it is pointed away from you. Blowing cold air at you will feel cooler than blowing warm air out, even if the total exchange of heat energy for the house is the same."
] |
[
"Right. It depends on where you get to put the fan and whether there are other vents in the room/house. If you only have a floor fan, and no other openings, blow cold air in.",
"For greatest efficiency, bring the cold in the bottom and hot out the top. A fan can be used in a number of ways to help this."
] |
[
"Right. It depends on where you get to put the fan and whether there are other vents in the room/house. If you only have a floor fan, and no other openings, blow cold air in.",
"For greatest efficiency, bring the cold in the bottom and hot out the top. A fan can be used in a number of ways to help this."
] |
[
"Has there been any research into removing the need for the human body to sleep?"
] |
[
false
] |
It's my understanding that the reasons why humans sleep are pretty vague. I think with all the advancements in the next 20 years, that this could be one of them.
|
[
"Yes actually, though it is not with any documentation that I bring forth this information, (though google may bring something) the U.S. military has experimented with sleep replication supplements. I have heard first hand from soldiers (Marines, if I remember correctly) being test subjects for this drug while on active duty. Basically, a pill is taken once every eight hours and the need for sleep is quelled substantially for up to a week at a time.",
"At the same time though, I was told that being awake for that long still messes with your head in that you perception of time becomes rather messed up.",
"EDIT: I found a document pertaining to the drug Provigil and military use.",
"http://www.thecrimson.com/article/2002/11/7/one-pill-two-days-no-sleep/"
] |
[
"I take that drug for narcolepsy. It is very interesting and very effective and really a godsend. You have no idea (or maybe you do if you have narcolepsy) how terrible it is to feel partially asleep, your brain tired and aching for sleep during the day, not quite fully awake, your whole life. If you've ever driven and been sleepy but you have to force yourself awake, it is very similar to that, almost painful to maintain concentration when you get extremely fatigued. It is almost like living in a dream. ",
"Yes continuous exposure to the drug can remove the ability to sleep. I tried to take it once like the fighter pilots do and see what it was like! Things get very strange the longer you take it, but you do stay awake and I can see how they say you can maintain your ability to perform your duties at pre-deprivation levels for 40 hours or so. I think longer than a few days and you'd go completely insane. :) Whatever \"ordering of your brain\" that sleep does, starts needing desperately to be done, is the best way I would describe it. "
] |
[
"The main effects of sleep deprivation are damage to brain processing,; so memory and learning capability is effected and damage to the immune system.",
"Are there any permanent cognitive effects from semi-routine sleep deprivation? "
] |
[
"Would it be possible to create a stable, artificial ring around our planet (any celestial body, really)?"
] |
[
false
] |
[deleted]
|
[
"It would be very challenging but is entirely possible. You'd be hard pressed to find enough materials without some serious off-world mining and you'd need a much larger global economy than we currently have."
] |
[
"Relevant: ",
"Larry Niven's Ringworld and problems with it",
". "
] |
[
"Actually, rings of mass around a sphere wouldn't do stable equilibrium. It would be very possible to position the ring so that the forces on it are zero (so it would be in equilibrium and not move). But if it gets pushed a little bit, we would have to realign the position with thrusters or something or gravity will pull it farther out of the way. ",
"TL;DR: points in orbit are stable, rings are unstable and require correction to prevent it drifting out of equilibrium, and uniform spherical shells don't experience any net gravity from the mass inside them."
] |
[
"How does \"escape velocity\" work? Isn't any speed escape velocity as long it isn't zero?"
] |
[
false
] |
I mean, if a space ship moves at a constant 20kph upwards, won't it eventually leave the Earth? And since you get farther and farther away from the Earth by every kilometer you move, the escape velocity and the gravity should slowly decrease, right? So when the space ship reaches a height of maybe 100km, it will be much easier to escape the Earth. If that is the case, "where" does the escape velocity apply? At sea level?
|
[
"A ship that's moving at a constant speed upward is under power. It's being dragged down by gravity, and yet it's still moving upwards without losing speed. That means it's under propulsion, an engine is at work, energy is being spent in fighting gravity.",
"Escape velocity is a different concept. It's the speed you give to an object ",
", like throwing a stone. Your arm gives the stone it's initial velocity, but once you let it go, the stone is not being powered anymore.",
"Escape velocity is like asking \"if I were to throw a stone up in the air away from the earth, how fast would it need to go so it just keeps rising forever and never comes back?\" What's happening here is that you are giving the stone some initial velocity, and this velocity continues to fall as gravity tries to pull the stone back. The force of gravity decreases the higher the stone goes, the farther away from earth. So you're basically asking \"how fast must I throw this stone so that it can reach a point where earth's gravitational potential diminishes to zero?\" This point is mathematically an infinite distance from earth, meaning the stone will never return to earth.",
"So, to summarize - escape velocity applies to ",
" objects - i.e., objects that are given some initial velocity but then are let go, like a thrown stone. Objects that are under power throughout their motion can keep rising at any arbitrary velocity against gravity, provided they remain under power."
] |
[
"That's correct. Just to contribute with some vocabulary:",
"escape velocity applies to ",
" objects",
"In aerospace engineering, these are called ",
". The term is an analogy to a bullet, meaning that the only forces acting on the projectile are gravity and, at most, air drag."
] |
[
"I actually answered some of this question in the context of black holes ",
"in this post",
".",
"You are absolutely right that as long as the ship has an acceleration that is ",
" greater than the gravitational acceleration, then the ship will escape to infinity. The ship might be going at literally a snail's pace, but it will escape. In fact, at any distance from Earth, the ship may never even reach escape velocity at that distance.",
"The escape velocity at a distance ",
" from the center of mass of a spherically symmetric gravitating mass ",
" is",
"v",
" = √[2GM/R]",
"(Technically, it's not a velocity, but just a speed.) This is the speed that a ",
" object needs to escape to infinity. A free object is an object that is subject only to gravitational forces and is not undergoing a proper acceleration, say from an engine thrust. So, if the ship just happened to be a distance ",
" from the planet's center, it would have to have a speed of at least v",
" to escape the planet's gravity. (If you start on the surface of the planet, there are some other considerations, like atmospheric drag or the rotation of the planet, but we are ignoring those factors in this formula.)",
"Of course, as you noticed, the ship could just accelerate, in which case it may escape to infinity at any speed it wants. You also correctly note that the required escape speed decreases with distance from the planet. So it is possible for the ship to throttle the engine in such a way to never go faster than the required escape speed for whatever distance the ship is currently at.",
"If that is the case, \"where\" does the escape velocity apply? At sea level?",
"When we talk about \"the escape speed\" of a planet, we usually assume: (1) the planet is approximately spherically symmetric, (2) the distance ",
" is the radius of the planet, and (3) the object is projected vertically upwards, so as to ignore any of the planet's rotation. Of course, if the planet is not spherically symmetric, then the escape speed is not the same at all points on the surface. So if you want to be more precise, we can talk about the escape speed at different points on the surface, or just give an escape speed based on the average radius. The difference between the Earth's polar and equatorial radius is only about 0.34% though.",
"The rotation of the Earth actually matters more. Since the Earth rotates, the ",
" of the initial velocity also matters. For a given latitude, an object launched tangentially from Earth to the east requires the least escape speed (relative to Earth) and an object launched tangentially to the west requires the greatest speed. The required tangential speed also decreases as you approach the equator and increases towards the poles."
] |
[
"Does honey really have antibiotic or antibacterial properties? If it does, what causes it to be either antibiotic or antibacterial?"
] |
[
false
] |
I've heard this mentioned several times about how honey is either antibiotic or antibacterial. What exactly is in honey that makes it antibacterial or antibiotic? I hope this isn't a stupid question...
|
[
"One of the more clearly understood aspects of honey is that it's very hygroscopic, due to its high sugar content. Most bacteria can't survive for very long in honey, because the honey will pull all the water out of the bacteria and kill it.",
"Edit: ",
"Here's a link",
" that gives a basic overview of five different antibacterial / antibiotic properties that honey has. (High sugar concentration is the only one I've heard multiple times, which is why I mentioned it without a source.) The article is a condensed, easier to read form of ",
"this research article",
", which has been published in the journal for the Federation of American Societies for Experimental Biology."
] |
[
"Just to be sure, we're talking about putting bacteria directly into a bath of honey. Eating honey will not clear up your infection.",
"To be fair, putting bacteria in a lot of things kills them."
] |
[
"I doubt that's been tested. Even if it worked, you'd have to keep the instrument in the honey for a period of time.",
"Even then, before you could use the instrument, you'd have to clean the honey off, which depending on your method of cleaning could re-contaminate. Indeed if you had another way of getting the honey off of the instrument without recontaminating, then why not just use that method in the first place and skip the honey?"
] |
[
"Minimal Human Contact - Side Effects?"
] |
[
false
] |
I understand this is a broad question but what kind of side effects would you encounter from distancing yourself from society for a really long period of time? I guess an example would be if you were in prison and you were put in solitary confinment with nothing but books for 10 years what sort of state of mind would you come out with. (For the sake of argument the books are scientefic, non-fiction).
|
[
"I just finished a fantastic documentary by National Geographic on solitary confinement. Many of those guys were in Ad Seg for a decade or more. ",
"Basically what happened was the development of anti-social behaviour, anxiety, fear, etc. One inmate being interviewed through glass noted it was his first sit-down conversation with someone in 4 years. ",
"Another man said he was released after 8 years of SC and snapped the first week out because the paranoia was so intense he feared his life. He attacked an innocent guy in a grocery store who he believed was following him... and promptly returned to SC in prison.",
"They showed an experiment on a rat that was kept in a SC situation for just 2 weeks - when it was let out to roam free, it scaled the walls only as if it were afraid of the big empty room even though there was clearly no threat."
] |
[
"In children at least there is a disorder called non-organic failure to thrive (NOFFT). It's a psychosocial disorder in which children are seemingly healthy with no discernible biological causes, don't grow at the same rate or mature physically as other children. This extends to intellectual development as well. It seems to stem from lack of physical contact and interaction with other people. They also talk about failure to thrive in the elderly. I'm not sure about those of us in between the two age extremes, but I imagine it's similar to the flu, those two age groups are most susceptible. There are lots of pathologies seen to coexist with antisocial behaviors and both seem to exacerbate each other. You would likely experience distrust of others and paranoia perhaps some cognitive lags at best, and at worst possible failure to thrive, maybe death. "
] |
[
"can you tell us the name of this documentary? please."
] |
[
"How do strong forces pull things from far away?"
] |
[
false
] |
I heard that strong forces pull things stronger from farther away, and that these forces are so strong that nuclear forces are basically the residual spill-off from them. How is it possible that something can get stronger from farther away? Wouldn't that pull everything into a certain range?
|
[
"The effect you're referring to is known as ",
"color confinement",
". The force felt doesn't increase with distance, but it is approximately constant. However, this occurs in bound groups of quarks (either a quark and antiquark pair, which is a meson, or three quarks or three antiquarks, which are baryons and antibaryons respectively), not between any quarks. The residual force which binds, for example, protons and neutrons in an atomic nucleus together ",
" diminish strongly with distance.",
"Also, if you try and separate bound quarks, you would pretty quickly put enough energy in to produce new quarks, and thus you'd be left with two separate particles rather than one stretched but still bound particle."
] |
[
"Actually, the strong nuclear force is unique among the fundamental forces of the Standard Model in that it gets weaker as you get two particles which are affected by it closer together. This is known as ",
"asymptotic freedom",
".",
"The only particles which are affected by it are ",
"quarks",
", such as the up and down quarks that comprise atomic nuclei. On the other hand, ",
"leptons",
", such as electrons and neutrinos, are unaffected by the strong force.",
"While I won't feign intimate knowledge of ",
"quantum chromodynamics",
", the model which dictates how the strong force behaves, asymptotic freedom is one of the facets of the strong force which greatly interests high energy physicists.",
"EDIT: Fixed backwards description of asymptotic freedom. Many thanks to Sentynel for pointing it out."
] |
[
"it gets weaker as you get two particles which are affected by it further away from each other",
"That should be the other way around - it gets \"asymptotically weaker as ... distances decrease\" (from the article you linked). In other words, quarks are free to move around within a hadron, but as you separate them beyond, the energy of the binding gets increasingly large. See ",
"this HyperPhysics page",
" and my answer on color confinement."
] |
[
"If light cannot escape from a black hole, wouldn't the objects being pulled in be going faster than the speed of light?"
] |
[
false
] | null |
[
"Sort of.... the thing is, you can't measure distances and speeds ",
", i.e., looking at spacetime as a whole. From that standpoint they're dependent on the coordinates you choose. The only physical way of defining distance is ",
". In other words, observers near each other can measure their distances, before they get so far apart that the effects of gravity (i.e., the curvature of spacetime) become important.",
"Locally, no speeds can ever go faster than light. But that's fine: inside a black hole, you'll never measure your neighbors exceeding that speed. From a local perspective, all speeds inside a black hole are below the speed of light.",
", when you look at those speeds from a global perspective (which you can only do theoretically, mathematically - it's not possible in practice), they all tend inwards towards the center of the black hole. No matter what direction you look like you're going locally, forwards or backwards, left or right, from the global point of view, ",
" inside the event horizon points inward towards the black hole."
] |
[
"Once you're past the event horizon, that's it. You're done. There's no coming back--not ever. And it's not just about speed. ",
"General Relativity says that mass can warp spacetime, and the more massive something is then the more it warps spacetime. ",
"The singularity in a black hole takes \"massive\" and turns it to 11. So you can imagine that warping of spacetime that goes along with that is also pretty extreme. ",
"It's so extreme that beyond the event horizon that every direction gets bent toward the singularity. ",
" direction. Forward, backward, left, right, up, down--they all point toward the singularity. ",
"That's why nothing that crosses the event horizon can come back. Once it's inside the ",
" of 'away' from the singularity ",
". Any movement at all will go in a direction that points toward the singularity. It's the only direction that exists."
] |
[
"Look at it this way: If you were stationary at 5m outside of the event horizon, and a nuclear bomb exploded 5m past the event horizon, you wouldn't even know that there was an explosion, as none of the matter, light, or radiation would reach you."
] |
[
"what would happen if you threw a paper aeroplane in space?"
] |
[
false
] |
Would it just keep moving in the direction you threw it until I hit a solid object? Edit 1: my phones saying there are 9 comments, but only showing/messaging me about 1 of them so apologies to anyone else that commented if there was/is actually 8 more comments! Edit 2: I woke up and reddit had fixed that glitch and this was on the front page of ! Thanks everyone, there is some good viewpoints and videos here demonstrating interesting stuff in space!
|
[
"Even from a PC browser, this thread only shows two comments, but says 13. Reddit dun broke.",
"For your answer, though, if you threw it in \"deep\" space, nowhere near any large gravitating bodies, it would just keep going until it eventually hit something (or got caught by something's gravity). If you threw it ",
" near Earth, it would start falling toward the ground just like any other object does. Things like satellites and the ISS can only stay in orbit because they move forward at the same rate they fall - Pretty damned fast (the ISS has an orbital velocity of five miles ",
")! And even then, they need periodic corrections to keep them at the right speed and altitude.",
"Even if you could somehow throw your paper airplane hard enough, it would almost certainly disintegrate from the force needed to get it up to speed."
] |
[
"Even if you could somehow throw your paper airplane hard enough, it would almost certainly disintegrate from the force needed to get it up to speed.",
"Unless it's already traveling at that speed, like if an ISS astronaut made a paper airplane and just let go of it outside)."
] |
[
"I really wish there were more videos of simple zero G experiments like this. I want know what fire looks like in space. I want to see what it looks like when you flip a coin. I want to play with a gyroscope. I want to go to space. "
] |
[
"Why are DNA bases and RNA bases so different? How can removing a single hydroxyl group have such a large impact?"
] |
[
false
] |
Considering the other groups in DNA bases I would expect that the hydroxyl group would be rather insignificant, yet DNA bases exhibit different chemical properties as opposed to RNA bases (ex: they're more stable) So why does removing this one hydroxyl have such a big impact on the molecule as a whole?
|
[
"RNA can rarely be double stranded, but yes the OH of RNA makes it much less stable than DNA. This is because the OH group can actually attack the 'backbone' of the RNA strand. Basically, RNA is capable of tearing itself apart while DNA isn't.",
"Also, RNA is much less stable in the environment than DNA because RNA is supposed to be temporary, and is commonly used by viruses. Thus as a recycling/protection measure, RNAses are ",
"."
] |
[
"This is a good question that I have had to think about a lot in my research. Besides being less stable (covalently) than DNA, RNA can also (1) fold into ",
" stable secondary structures and (2) binds a very different set of proteins in the cell. ",
"Why does one little OH group have such big differences? Well, despite the 2D representations of the sugar group you are used to seeing, there is actually ",
"some \"pucker\"",
" to the 5 atom ring. The pucker in the ribose is biased to adopt a C3'-endo configuration, while in deoxyribose the the pucker can adopt a wider range of configurations.",
"The pucker has a large influence on how the duplex comes together. In RNA, the molecules adopt an ",
"A-form configuration",
" while DNA can adopt several configurations but is usually found in a B-form configuration. Since A-form matches the pucker of the ribose, that makes A-form RNA duplexes more stable than DNA duplexes in A-form or B-form.",
"The stability of RNA duplexes has many consequences. One, it means it take more work to split RNA duplexes apart. This might be part of the reason DNA is used to store genetic information more frequently - it is easier to access. But it also allows single stranded RNA to fold into more complex shapes, since small pieces of the single stranded RNA can form short duplexes that are stable. Folded RNA molecules can even have ",
"catalytic abilities",
", just like proteins do. The ribosome is the most impressive example of this.",
"Now, as far as the chemical stability of RNA, this is well understood. The OH group can lose its hydrogen (especially at high pH). The charged oxygen left over can then hydrolyze the phosphate bond. So while the change from H to OH might not look like a big difference on the printed page, it has a very different activity. "
] |
[
"Someone will post a better answer but, I believe the differing molecule configuration of the OH group cause the RNA to be less stable because its more vulnerable to hydrolysis? also its only single stranded as well and not a strong double helix like DNA. \nNot the best answer, its been a few years out of school"
] |
[
"Diluted red wine changes color at a certain concentration. What's happening here?"
] |
[
false
] |
[deleted]
|
[
"You wouldn't be comparing against phenolphthalein - rather, you should be comparing it to ",
"litmus",
" - which belongs to the same class of chemicals found in your wine, known as anthrocyanins - which is red in acidic solution and blue in basic solutions.",
"The main concept behind a dye as a pH indicator relies on the electronic structure of the protonated and deprotonated states. Organic dyes consist of large, conjugated systems, and the general rule is the larger the system, the larger the wavelength of light it will absorb. A benzene ring generally absorbs in the UV region, and larger rings will push the absorption down to the visible range. The conjugated system will be disrupted, either from being protonated or deprotonated, thus shifting the peak absorption wavelength and producing a colour change.",
"For example, in ",
"phenolphthalein",
", in acidic solutions (excluding pH < 0) it is colourless. If you examine the structure at those pH, you'll see that the three phenyl rings are separated. However, when deprotonated, you can see a double bond on one of the rings that link to the central carbon, connecting the conjugated systems and shifting the absorption maximum down from UV to blue/violet, leaving the intense pink colour you observe."
] |
[
"Well, a quick scan on wiki has turned something up.",
"http://en.wikipedia.org/wiki/Phenolic_content_in_wine",
"Its most likely the colour change of anthocyanins in the wine. Heres a ",
"journal",
" your chemist friend may be interested in reading, but without having a sample of your specific wine its hard to know exactly what compound it is."
] |
[
"I don't know what your chemistry background is, but if the pigments in the wine form a solution that behaves according to the Beer-Lambert law you should see a simple lightening of the color, so it could be a chemical deviation (",
"http://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law#Deviations_from_Beer-Lambert_Law",
", or google Beer's Law deviations) of one or more pigments present. "
] |
[
"Is it possible to create \"Anti-Atoms\" with Antimatter ?"
] |
[
false
] |
So I know that antimatter consists of positrones and anti-protons wich are basically the same as protons and electrons just with opposite charges. So i wondered if there is a possibility that these two can form an "anti-hidrogen atom" and if so if they can form bonds and create "anti-H2" and other molecules (Im not aware of an anti-neutron, so I think that we cannot create more heavy atoms). I know it would be useless because matter and anti-matter annihilate each other but it is interesting if an "anti chemistry" would exist Edit: Thanks for all the replies I know now that I was pretty stupid but now I know that anti-neutrons and anti-atoms exist
|
[
"Yes, and ",
"it has been done for decades now",
".",
"if so if they can form bonds and create \"anti-H2\" and other molecules",
"Theoretically, yes.",
"Im not aware of an anti-neutron, so I think that we cannot create more heavy atoms",
"Antineutrons do exist."
] |
[
"Matter neutrons contain matter quarks; these would annihilate with the anti-quarks in the anti-proton. So, one would need anti-neutrons to create heavier anti-atoms."
] |
[
"As mentioned we have created anti-hydrogen atoms already.",
"To create anti-hydrogen molecules you need enough of the atoms together. That is very challenging, but possible in principle. ",
"Here is a proposal",
".",
"Antineutrons exist and we create them routinely in particle accelerators. They are not charged, however, so we cannot capture and contain them in any useful way. That's also why you don't hear about them.",
"Collisions of heavy ions produce anti-deuterium, anti-tritium, anti-helium-3 and even anti-helium-4 once in a a while, but these products are very rare and they fly in random directions with a high energy. Capturing some of them would be extremely challenging."
] |
[
"Why do we sleep?"
] |
[
false
] |
Besides the obvious, we are tired, is there any other reason why we need to sleep? I should be sleeping now but that question has taken over my head.
|
[
"AFAIK a lot of body functions are only performed when we are asleep. Such as skin, teeth and nails nutrition and cell renewals. \nThat is why people with insomnia suffer hair falls and nails damages, because their body doesn't have the chance to renew these cells."
] |
[
"This is still very much an open question, but here's a few key features:",
"Sleeping lets your brain \"defrag\" itself, sort of like a computer does",
"Sleeping lets your brain physically clean itself",
"Sleeping lets your brain focus on processing complex stimuli without distractions of waking experience"
] |
[
"I know this late, but none of the answers so far explain why we sleep. And I researched a bit and it turns out we don't know yet. We know that when we sleep, we do some important functions which we don't do while we are awake( we don't know why ).",
"So yeah, it's still a mystery. "
] |
[
"Does Neuro-Linguistic Programming (NLP) Have Any Scientific Basis?"
] |
[
false
] |
My dad took a bunch of courses in it and has a bunch of 'certifications' in NLP. However the claims it makes to me sound ridiculous and I think the affect NLP may have is no more than a placebo. In addition things like using it to reading people so well sound a bit bogus too - this is just anecdotal but my brother is a compulsive liar and my dad constantly assures us that he was telling the truth just to be screwed over again. Whats more is I have never seen classes or modules dealing with NLP in any psychology courses. you'd have thought that if NLP lives up to its claims that it would be a highly taught and researched topic.
|
[
"I think its fair to say the claims made exceed the evidence for those claims. The ",
"scientific reasoning doesn't appear particularly sound",
", and what little direct experimentation there has been doesn't seem to support the case for its efficacy.",
"This is not to say there's nothing to the connection of language, thought and behavior and its possible utility in therapy. It just looks like whatever that utility was happened to be exploited unscrupulously very early after its discovery, leading to discrediting of the theory.",
"I would seriously doubt any practitioner's claims, and I would highly doubt that any course you would take for \"certification\" would be scientifically grounded."
] |
[
"It is complete and utter scientific garbage."
] |
[
"I only have a word of a Ph.D. psychologist who has some sort of training/certification in NLP. He says it's crap, I didn't inquire further."
] |
[
"What would it take to annihilate all life from earth and can it be \"achieved\" by humans?"
] |
[
false
] |
I mean like every single organism, extermophile bacteria, etc.
|
[
"We're still trying to find the limits of sustainable environments - for example ",
"http://rsta.royalsocietypublishing.org/content/369/1936/516.short",
"Because we have identified lithospheric bacteria at substantial depth, the only way to be ",
" sure is to completely annihilate the crust and atmosphere. That would involve a similar impact to that which formed the moon. However, several astrobiology theories suggest that ejecta from these kinds of impacts are viable transporters of microbial life elsewhere, so there's no reason to suppose you would kill off everything."
] |
[
"This is ",
"/r/askscience",
"."
] |
[
"Yep - that's the belief. e.g. ",
"http://journalofcosmology.com/Panspermia9.html",
"\n",
"http://www.springerlink.com/content/h171534701359381/",
"From the abstract of that last paper: \n\"The data suggest that in a scenario of interplanetary transfer of life, small rock ejecta of a few cm in diameter could be sufficiently large to protect bacterial spores against the intense insolation; however, micron-sized grains, as originally requested by Panspermia, may not provide sufficient protection for spores to survive.\""
] |
[
"[Neuroscience, Molecular Biology, Medicine] How bad are small doses of MDMA for the brain and body? What are the long-term and negative side-effects?"
] |
[
false
] |
1.) What is the current scientific understanding of the mechanisms and short/long term effects of low-dose MDMA use? 2.) Has there been any research on potential interactions between prescription psychostimulants and low-dose MDMA use? 3.) What structures might undergo the most stress/damage? I've read research about how methamphetamine modulates mitochondria functioning, causing lactic acid build-ups. Is a similar effect to be expected from MDMA? 4.) What sort of difference in damage and side-effects can be expected between inhalation (low dose, rapid onset) and ingestion (high dose, long duration)? Thanks for your (informed) answer, and please remember to keep replies free of medical advice or speculation! :)
|
[
"1) MDMA works on the serotonergic system in your brain (among others) which causes downstream effects in other monoamines (dopamine, norepinephrine) as well ",
"here",
". Short-term effects of MDMA use are sweating, increased body temperature, increased blood pressure and pupil dilation. It causes increased euphoria but the other psychological effects vary based on the individual ",
"here",
". Long-term effects in humans may include a neurotoxic effect in the brain, potentially due to serotonin depletion, but this is primarily shown in primates and not humans. If there is a neurotoxic effect, this may disappear after years. More research is being done now. ",
"here",
"2) There is very little research on the interactions of low-dose ecstasy and prescription stimulants. However, based on the fact that both work on the serotonin system, it is suggested that there could be an additive effect between MDMA and these drugs, which could lead to a higher risk of serotonin depletion and neurotoxicity ",
"here",
"3) Areas: ",
"amygdala, striatum and hippocampus",
" It has been hypothesized that MDMA forms free radicals, which may or may not destroy cell membranes ",
"here",
"4) Oral administration of the drug will undergo first-pass metabolism, meaning that less of the drug will be absorbed into the system. However, whatever long-term damage there may be will remain the same between oral and inhalation routes of administration, since the main side effect seen with MDMA is serotonergic depletion, which occurs after the drug has been absorbed into the bloodstream and passes the blood brain barrier ",
"somewhat explained here",
". Inhalation obviously provides the additional side effect of potential lung damage and, since it has a more rapid onset, could cause more issues with hyperthermia, etc. since it is such a sudden change, but other than that, both routes will provide pretty similar \"damage.\"",
"Keep in mind that the majority of the studies done in the field are done with moderate to high doses and usually with chronic use. The neurotoxic effects are typically seen with higher doses and longer durations. I know you asked about low-dose, but research is scant on that due to that not being a priority for public health. ",
"Edit: crazy link"
] |
[
"bleh, not sure Terrence McKenna is the best source for an academic answer."
] |
[
"bleh, not sure Terrence McKenna is the best source for an academic answer."
] |
[
"Why don't modern ships use sails?"
] |
[
false
] |
[deleted]
|
[
"Shipping companies are looking into using kites attached to ships to help supplement the engine.",
"As for the historical reasons sails fell to steam, it's mostly speed and reliability. They're really cool and I spend a lot of time studying them, but they're complicated and a pain in the ass."
] |
[
"Usually the answer to any question like \"why doesn't a major corporate entity use XXX technology\" is that it isn't cost effective. I'm certainly not an expert on shipping, but here are some reasons I can brainstorm.",
"-Wind powered ships are slower, and wind is less reliable than an engine.",
"-Sails would greatly interfere with the usual method of loading/unloading super-massive container ships.",
"-Wind energy may not be dense enough to move a massive container ship",
"That said, it looks like some people are looking into it - there are a bunch of mentions of this kind of thing if you google search for ",
"wind powered container ship"
] |
[
"Here's an article from a couple years ago: ",
"http://www.nature.com/news/2008/080208/full/news.2008.564.html"
] |
[
"Does downloading a podcast make my phone heavier?"
] |
[
false
] | null |
[
"Depending how pedantic of an answer you want, maybe. \"Heavier\" is not the same thing as \"has more mass\". If you flip a bit, you're changing the charge of some memory element somewhere, so there is probably a minuscule change in charge or magnetic fields, which will push or pull a tiny bit more on the ambient fields, e.g. the Earth's magnetic field, so a scale measurement would change (if the scale could read such a ridiculously tiny change). Holding it in your hand, though, you'd never notice.",
"Then again, if the podcast is compressed well enough, it probably has a nearly 1-1 ratio of 1s and 0s, so maybe it averages out to (near) zero effect?"
] |
[
"No. The data of the podcast is represented on your phone by a bunch of switches. Turning the switches from off to on doesn't make the switch weigh any more or less.",
"On a side note, when your battery is dead it will weigh a tiny bit less than when the battery is full."
] |
[
"In principle this is correct, but it depends on the exact nature of the switches (depending on how they work, some switches contain more energy/mass if off than on). In practice phones use ",
"flash memory",
", which works by placing electrons into a floating gate to turn that bit off, which means a set of all 0 will have more electrons and therefore more mass than all 1s. So, whether the podcast will take make the phone heavier or not depends on the state of the flash prior to downloading. We can fairly safely assume the podcast has ~50% 1s and 50% 0s, so if the flash had been \"zeroed\" prior to the downloading (i.e. contained all zeros), the podcast would actually result in the phone weighing less. More likely, the cells were in a random state prior to the download, so there'd (on average) be no difference, but it's basically impossible to say either way."
] |
[
"Pretend we have a second moon, basically identical to our current one, orbiting perfectly on the opposite side of the planet as our own. Would we still have tides?"
] |
[
false
] | null |
[
"Tides are caused by the gravity gradient of the moon across earth; stronger gravity on the near side causes a bulge (water moves toward the moon), weaker gravity on the far side causes another bulge (water moves away from the moon). If there's no gradient, you don't get tidal forces. I'll look at local force of gravity at the earth's surface in three places for each the single moon and double moon case: Closest to the moon, furthest from the moon, and 90 degrees off to the side.",
"Some assumptions: The earth is rigid, doesn't spin, and the moon(s) orbit aligned with the equator. This makes the math much easier and I don't think invalidates the result. Please correct me if wrong here (or anywhere else).",
"Mass of earth: 5.97219e24",
"Mass of moon: 7.34767e22",
"Distance from earth to moon: 384400000",
"Radius of earth: 6371000",
"Case 1: Single moon. Some pretty simple and messy Matlab, which calculates the force due to gravity from each body, then does the vector addition. There's some screwiness with signs because of all the squared terms, I think I have them all correct.",
"G = 6.67384e-11;\nRmoon = 384400000;\nmearth = 5.97219e24;\nmmoon = 7.34767e22;\n\n% points to calculate\nx = [-6371000 0 6371000];\ny = [0 6371000 0];\n\n% distances\nxmoon = Rmoon+x;\nymoon = y;\nrmoon = sqrt(xmoon.^2 + ymoon.^2);\nrearth = sqrt(x.^2 + y.^2);\n\ngmoon = G*mmoon./(rmoon.^2);\ngearth = G*mearth./(rearth.^2);\n\n% vector addition...\nthetamoon = atand(ymoon./xmoon);\nthetaearth = atand(y./x);\ngxmoon = -gmoon.*cosd(thetamoon);\ngymoon = gmoon.*sind(thetamoon);\ngxearth = gearth.*cosd(thetaearth); gxearth(3) = -gxearth(3);\ngyearth = gearth.*sind(thetaearth);\n\ngx = gxmoon + gxearth;\ngy = gymoon + gyearth;\n",
"Results are accelerations toward the center of the earth (m/s",
"gravity on moon side: 9.81957",
"gravity 90 degrees away: 9.819610",
"gravity on far side: 9.819641",
"The nice gradient we would expect.",
"Case 2: Two moons",
"The only additions to the code are:",
"gxmoon2 = -fliplr(gxmoon);\ngx = gxmoon + gxmoon2 + gxearth;\n",
"Gravity on \"moon side\" (left in previous): 9.819607",
"Gravity 90 degrees away: 9.819610",
"Gravity on \"far side\" (right in previous): 9.819607",
"The force of gravity is now relatively constant.",
" Lunar tides would be near zero. There would still be solar tides; these are about 20-30% the strength of lunar tides."
] |
[
"I looked at the problem analytically (as opposed to numerically as you have done) and my results indicated that the tidal forces would double. ",
"See my top level post",
"."
] |
[
"It looks to me like the tidal forces would double.",
"Below I've linked to the equations calculating the force on the \"left\" (L) side of the Earth, the center (C) of the Earth, and the \"right\" (R) of the Earth due to moons A and B, and then taking the difference:",
"diagram",
"page 1",
"page 2",
"(Note: I've assumed for diagram simplicity that the moon orbits at Earth's equator. This is not quite true in actuality: the orbit plane of the moon is slightly inclined relative to the equatorial plane of the Earth.)"
] |
[
"Does gravity on the earth's surface vary throughout the day?"
] |
[
false
] |
[deleted]
|
[
"Gravity does vary very slightly throughout the day, but certainly not enough for your bathroom scales to notice. The acceleration on your body from the Earth is about 9.8 m/s",
" . From acceleration from the Moon on you from Earth is about ",
"0.000035 m/s",
" . So if you weighed 70 kg (~150 pounds), the Moon could increase or decrease your weight by 0.0003 kg (or 0.0006 pounds). ",
"So why did you weigh a different amount? Because (most) bathroom scales are only accurate to a couple of pounds. You could weigh yourself repeatedly, once right after each other, and you would likely get different weights. "
] |
[
"The Moon pulls the scale with almost exactly the same acceleration as the person standing on the scale. Think about this, you jump from a diving tower holding a brick above your head. Earth pulls the brick down with an acceleration of 9.8 m/s",
". Is the brick pushing you down and making you fall faster? Of course not, it's not pushing down on you at all because you're both being pulled down by Earth by (almost exactly) the same amount.",
"Notice the almost exactly. What you really want to figure out is the difference in Moon's gravity between the scale and the person standing on it, i.e. how much the gravity of the Moon changes between that one metre separating the scale and the (centre of mass of the) person. And that's somewhere around 2*10",
" m/s",
", so several orders of magnitude smaller than what you calculated."
] |
[
"You have a funny way of asking questions. Your boyfriend was incorrect in explaining your apparent weight gain as a change in the gravitational force you were feeling. He was not incorrect in saying that gravitational forces do chance, though.",
"In any engineering situation where the mass needs to be accurate to 1×10",
" % or less, you would need to care about this. I'm not sure what sort of situations that would be, though."
] |
[
"Can two samples of the same size, with the same mean and standard deviation, contain different values?"
] |
[
false
] |
No right? I feel like the answer is no but something is nagging me about it, and it may be such an obvious question which is why I can't find anything online. I thought I would ask here.
|
[
"Sure they can. It would be quite silly if you could reconstruct a whole sample of hundreds (say) degrees of freedom from just two.",
"For example, let ",
" = sqrt(5/2), that is about 1.5811. Then the two samples",
"have the same mean and standard deviation. However if you keep calculating higher order sample ",
"moments",
"#), eventually you should run into one that is different. In this case the two samples above have the same first, second and third moment, but different fourth moment. If the sample size is ",
" then two different samples must differ somewhere among the first ",
" moments."
] |
[
"There's a fun little piece of math trivia called ",
"Anscombe's quartet",
". For different sets of numbers that were maliciously constructed to have the same aggregate statistics, but look completely different when plotted. Not only do they have exact matches for the sample mean and standard deviations, but also match a few other statistics to several decimal points.",
"The entire point of descriptive statistic measures like mean is to be a ",
": instead of looking at the real data, you're looking at a simplified version. Instead of looking at the full spread of numbers, you're going to look at a Normal distribution that more-or-less approximates the real data that you measured. This is inherently a lossy compression that loses detail; that's kind of the point, to simplify things enough to be able to study them analytically. It's a necessary consequence that several different measurements will \"look\" the same.",
"In fact, this is ideal: if you take two measurements from the same distribution, you would hope that the mean and standard deviation will match even if the individual measurements don't. In practice there will be a small amount of variance, but the ideal is that the descriptive statistics can match even when the individual measurements do not."
] |
[
"Thank you! I ended up asking this on stack exchange as well, and the degrees of freedom answers help this make sense to me."
] |
[
"What happens to protons when light is polarized?"
] |
[
false
] |
[deleted]
|
[
"Could it be that you meant \"photons\"? "
] |
[
"Assuming OP meant \"photons\"... and further assuming OP has heard of the wave/particle duality...",
"Electromagnetic radiation usually travels as a transverse wave. The wave's orientation is the same thing as its EM fields, which are perpendicular to the direction of travel.",
"When you linearly polarize an electromagnetic wave, you restrict the fields to a single plane.",
"Linear polarization isn't the only option, though ",
"Read more yourself, if interested."
] |
[
"I understand the wave perpendicular to the direction of movement is then restricted to one dimension, but I was curious if there was any noticeable effect on individual photons. "
] |
[
"Could any artifacts of an ancient civilization survive on Venus?"
] |
[
false
] |
I've often heard that Venus could be considered within the "Goldilocks zone" of the sun, but that its extreme greenhouse effect and corrosive atmosphere precludes the possibility of life as we know it. However, assuming the atmosphere was not always like that, if a humanoid civilization of relative technological parity to our own once existed there, would any of its artifacts survive under current atmospheric conditions?
|
[
"What a very interesting question, to answer it we have to consider several things; firstly any life that may have existed on Venus would have most likely existed several billion years ago when we suspect there may have been liquid water on the planet so we are talking about a huge length of time between any existence of life when artifacts would have been created and when we would discover them. Secondly, in the time between when we believe there may have been liquid water on venus and now, the planet has undergone tremendous geologic and meteoric activity so any artifacts that may exist on or just below the surface may have either been destroyed by meteor impacts or have been buried under solidified volcanic magma. Thirdly, the local weather on venus is an issue as well; it is well known that sulfuric acid does rain down toward the surface from the thick atmospheric clouds but the thing is that due to the high surface temperatures the sulfuric acid rain evaporates before it even hits the ground. What is more likely to cause damage to any potential artifacts that would be brought to the surface through various means is the Venusian wind. While the winds themselves are relatively slow moving (only a few kilometers per hour) the atmosphere is so thick and full of dust, anything that would be recognized by us as coming from an ancient civilization would be rendered unidentifiable or quite possibly destroyed due to erosion.",
"So for the purposes of your question lets assume that an artifact was able to survive buried under the surface having been untouched by volcanic, meteoric, or local weather activity it is possible for an artifact to survive barring that it is made out of certain materials. Lets draw a parallel to artifacts we have found here on earth. Pottery is one of the most often found type of artifact found because it is made from what is essentially dirt and since dirt doesn't really corrode (yet it can disintegrate back into dirt through being exposed to water or simply being pulverized) it is quite likely to survive. This same parallel would hold true for glass since glass is refined silicon dioxide (a rock) it would also be very likely to survive on the surface of Venus as it does here on earth. ",
"It could also be very likely that refined metals would survive as well due to the low oxygen content in the atmosphere (no oxygen, no oxidation. read:rust) it is possible for them to survive assuming they aren't destroyed by a billion years of soil erosion. ",
"Plastics could have also survived assuming that they weren't melted due to the high temperature on the surface but if they were buried under the soil and protected from the high temperatures it is possible that they could survive. ",
"What also has to be considered is the catastrophic event that ended life on the planet. If is was a meteor that destroyed all life as we know it on the planet then it is likely that nothing would survive. If the extinction event were simply a runaway greenhouse effect and all life on the planet for lack of a better word just cooked and died then it is quite likely that some artifacts would have survived.",
"But again there is most likely to be billions of years between any life on the planet and now and most likely we would not even be able to find any evidence simply because the length of time is too great and our archaeological know how simply is not advanced enough to find anything.",
"Source: anthropologist as well as a space buff"
] |
[
"That's an amazing answer! I hope other people read it for its thoroughness, even if they don't share my weird obsession with Venus."
] |
[
"How far we're looking back also makes a difference. Venus is sufficiently volcanically active that it undergoes basically a complete resurfacing every 300-600 million years. "
] |
[
"Are women predisposed to be vocal in fright or is it a result of social conditioning?"
] |
[
false
] |
I was playing Laser Tag and remarked on the different reactions of men and women to being surprised. I then thought of the conventional horror movie stereotypes and wondered if there was a disposition for women to be more vocal in fright or if, from these movies and other sources, there was a societal expectation for women to scream.
|
[
"http://en.wikipedia.org/wiki/Vociferation#Emotional_motivation",
"Both men and women scream when frightened."
] |
[
"The comments here are deleted for two reasons.",
"(1) Layman speculation: For some reason half the population seems to think they have something to say on evolutionary psychology. Please only answer if you really know what's going on.",
"(2) People asking \"why is everything deleted?\": Our rules have been set in stone for quite some time now, and I don't think there is much more we can do to make it clearer - there is even a section beneath the comment submission explaining that we delete layman speculation. There's no need to restart the meta-discussion in every thread with deleted comments."
] |
[
"I think the things deemed incorrect are listed on the right."
] |
[
"How close to Earth could a black hole get without us noticing?"
] |
[
false
] | null |
[
"It depends on the mass of the black hole. A black hole with the mass of, say, a person (which would be absolutely tiny) could pass through the Earth and we'd be none the wiser. If one with the mass of the Sun passed by, well, the consequences would be about as catastrophic as if another star passed through - our orbit would be disrupted, and so on.",
"The important thing to remember is that black holes aren't some sort of cosmic vacuum cleaner. For example, if you replaced the Sun with a solar-mass black hole, our orbit wouldn't be affected at all, because its gravitational field would be pretty much exactly the same. Black holes are special because they're ",
". If you were a mile away from the center of the Sun, you'd only feel the gravity from the Sun's mass interior to you, which is a tiny fraction of its overall mass. But if you were a mile away from a black hole with the Sun's mass, you'd feel ",
" that mass pulling on you, because it's compacted into a much smaller area."
] |
[
"Generally this is correct, but i wan't to add that a black hole with a mass of a person would evaporate pretty much instantly due to Hawking readiation and therefore wouldn't be able to pass the earth."
] |
[
"When you get objects that small, the concept of 'impacts' needs to be considered. The Schwarzschild radius of a 70kg black hole is ~10",
" m, which is 10",
" times smaller than a single proton. I don't think we can necessarily expect it to interact in the same way as a macro-scale impactor."
] |
[
"How do stimulants such as nicotine, caffeine or amphetamines suppress your hunger?"
] |
[
false
] |
Does it make some people feel temporarily satiated because it regulates, or triggers a leptin response?
|
[
"That is a rather incomplete answer that doesn't account for the physiological actions of chemical binding to receptors or blood glucose levels.",
"You're not accounting for that fact that nicotine, caffeine, and amphetamine all trigger adrenaline release since they are adrenergic stimulants. Adrenaline release causes release of glucagon which is hormone that causes release of glucose from the breakdown glycogen stores in the liver. ",
"Coffee by itself can supress hunger through PDE inhibition. Breakdown of glycogen is enhanced by the presence of caffeine since it inhibits an enzyme called phosphodiesterase (PDE). Inhibiting PDE prevents breakdown of the second messenger triggered by glucagon and causes a sustained release of glucose to the blood stream."
] |
[
"That is a rather incomplete answer that doesn't account for the physiological actions of chemical binding to receptors or blood glucose levels.",
"You're not accounting for that fact that nicotine, caffeine, and amphetamine all trigger adrenaline release since they are adrenergic stimulants. Adrenaline release causes release of glucagon which is hormone that causes release of glucose from the breakdown glycogen stores in the liver. ",
"Coffee by itself can supress hunger through PDE inhibition. Breakdown of glycogen is enhanced by the presence of caffeine since it inhibits an enzyme called phosphodiesterase (PDE). Inhibiting PDE prevents breakdown of the second messenger triggered by glucagon and causes a sustained release of glucose to the blood stream."
] |
[
"As someone who works in the greater neuroscience community, I can endorse this comment as correct. I would provide a source but I'm actually at work now and it would be hard to find a single one, likely a book chapter is needed for enough references.",
"As for how to test this, all of this neurochemistry/behavior work is pretty tough going often requiring elegant mouse(or rat) models to painstakingly show the importance of certain brain regions in reward/response loops. Right now the biggest breakthrough in answering these questions is to use ",
"optogenetics",
" to allow for direct stimulation of these neurons (and pathways) with light. Another way you can test this is to directly insert a thin needle/port system into the brain and dose with dopamine or dopamine inhibitor and expose the mouse to a stimulus either +/- drug condition (nicotine, caffiene, etc) and observe the response of the mouse behavior to the stimulation or inhibition of the dopaminergic neuron populations in the region of interest. It's as hard as it sounds to do correctly. We can also directly attach electrodes to individual neurons in those populations to measure each neurons response to an event (a technique called patch/clamp) which can also be used (best probably done in brain slice cultures, which is when we culture a living slice of the brain in a petri dish so we can actually see and visualize the living neurons of the brain)."
] |
[
"Are there any scientific studies demonstrating the difference in magnitude of the placebo effect on skeptics versus believers? If so, what are the results?"
] |
[
false
] |
For example, if you compared the effects of say essential oils on the headaches of 100 skeptics versus 100 non-skeptics, would there be statistically significant variances between the two groups? I consider myself a skeptic so maybe my bias is showing with the wording here, but I'm genuinely curious to know what the difference of the placebo effect is on people with different levels of belief.
|
[
"Respectful Insolence",
" has a good take down of Kaptchuk's methodolgy, and I suspect that similar problematic methodologies are used in many of these small studies.",
"For instance,",
"Participants were recruited from advertisements for “a novel mind-body management study of IBS” in newspapers and fliers and from referrals from healthcare professionals. During the telephone screening, potential enrollees were told that participants would receive “either placebo (inert) pills, which were like sugar pills which had been shown to have self-healing properties” or no-treatment.",
"So, Kaptchuk is not necessarily recruiting a cross section, but recruiting people who believe in placebos and will self-report positively about placebos, regardless of the efficacy or lack-there-of."
] |
[
"There have been ",
"a number of small studies in recent years",
" regarding so-called \"open-label placebos,\" where participants are literally told \"the pill we are giving you is a placebo, it has no medical value.\"",
"Again, these are small studies (so the effect ",
" disappear in larger studies, ",
"several of which are currently underway",
") but the preliminary results have demonstrated the placebo effect for conditions like ",
"irritable bowel syndrome",
", ",
"allergic rhinitis",
", ",
"ADHD",
" and ",
"neuroses",
" ",
" when the patient has been told that they are only being given a non-functional placebo. Patients show both reduction of symptoms and improved mental quality of life at rates similar to patients who believed they ",
" be getting a pharmacologically-active substance. In the allergy study, patients who were better informed during the study about the placebo effect showed even greater improvement in mental quality of life.",
"So, while again cautioning that these results are preliminary, and lack both the large sample sizes and long-term follow up that more robust study would be able to provide, there are early indications that neither deception nor ignorance are a necessary component of the placebo effect, and that fully-informed patients experience the effect just the same as (or even stronger than) patients who don't know. And while that's not ",
" the same scenario as \"skeptic vs. believer\", I feel like there's enough overlap between \"essential oil skeptic\" and \"patient fully-informed that the pill they are taking has no medical value whatsoever\" that some inference can be made."
] |
[
"Right, so Kaptchuk is actually measuring the impact in \"believers\" (referring to OPs question), and is finding similar levels of improvement to more generally informed studies (which contain a good cross-section of \"believers\" and \"skeptics\"... ignoring any bias of the demographic of people who participate in drug trials). So he's not actually showing that knowing doesn't effect the placebo effect, but that the placebo effect happens equivalently no matter the cross-section of skeptic/believer patients.",
"So there's your answer as it stands, ",
"/u/premeditatedsleepove",
" . But clearly needs more research, with clearer definitions of those groups."
] |
[
"Why are the black boxes in airplanes physical devices that have to be found after an accident instead of just a thing that sends wireless data to a set location?"
] |
[
false
] |
[deleted]
|
[
"Well first off, they were invented long before wireless backups were possible. It was for a long time the only way to ensure that information was preserved. Second, damaged equipment could interfere with sending that information. If the antenna is struck by lightning and melts, the computer will still try to send information, but it won't go anywhere, and that information is now lost. Having a physical copy of the data, set in an mostly indestructible box, is the most effective way to ",
" the data is preserved. ",
"It's like, if you have a netflix account, you can watch movies. Unless the internet is down. Or netflix is down. Or you've reached your cap by your provider. Or any number of other things. ",
"If you have a physical DVD, you can watch it any time, regardless of the condition of your connection. The physical media cuts out a step that could go wrong in the transmission of the information. ",
"Or, another example might be, imagine you are writing a novel. You store your novel on Google Drive. You don't have a local copy, nevermind a physical copy, and Google Drive goes down. Or you have no internet. Or you're somewhere where the internet is crummy, or you forgot your password, or your account gets hacked, or google decided to just delete your files, you're SOL. The information is at the whim of countless scenario's and circumstances that could go wrong. But if you have a physical local hard copy, you haven't lost anything and you don't need to worry about any of those scenarios where your information might be lost. "
] |
[
"Aircraft mechanic here...",
"General electric and Rolls Royce are currently able to perform what you are talking about with some of their engines. They are actively monitoring flights and advising airlines to change engines or parts whenever possible in order to avoid minor or catastrophic failures.",
"I have had multiple instances where I ask my supervisor why we are changing this engine component when all tests are showing it's working fine. and the response is usually \"Engineering advised we perform this change\" and its immediately no contest... just change the part.",
"Boeing and airbus are currently implementing reporting systems on their aircraft that use global satellite connections and cannot be turned off with a simple circuit breaker pull.",
"Most of this technology was already in the works but has been pushed even harder after the MH370 flight went missing."
] |
[
"There is a PBS documentary on Netflix US right which talks about some of the \"live\" monitoring systems in place (I believe this one focuses on RR). It is called City in the Sky, worth the watch for OP I think.",
"Also to add my $.02 from my time researchig in reliability. The US DoD is working on a project to have sensors monitor the health of a ",
" aircraft from nose to tail; along with a live satellite data connection to relay any anomalies detected to a control room. Most failures can be detected by sensors weeks or months before they would catastrophically fail, meaning they would be able to ground the plane and fix it before anything bad happens. ",
"This also would replace the need for periodic maintainence of their aircraft, which typically takes it out of the air for a month out of the year. Thats a lot of money saved, as they only stop flying when needed.",
"Why isnt it already in production? This all takes ",
". Each part in the plane comes from a different manufacturer, and each needs to have sensors implemented in it to predict failures. The project has a goal of 2050 - and that is for military aircraft and not commercial aircraft. But the commercial industry (hopefully) wont be far behind. "
] |
[
"How are concepts or memories formed and stored in the brain?"
] |
[
false
] |
I’m trying to understand how concepts are stored in the brain. From what I understand a certain strand of information is repeated by a group of neurons until they create a sort of bond where the same action potential is repeated. Every time you activate this group of neurons the are reinforced (such as studying).
|
[
"Best theory I've ever seen is connectionist theory, in other words neural networking theory.",
"A neural network is a type of computer, really a computer cluster. Where a bunch of really simple computers are hooked together so they compute in parallel, and they are densely interconnected so they are able to influence each other, meaning the output of one is the input for another. How *much* one node influences another is the question. The gain is variable and adjustable, and the ability of a network to adjust that gain between any two given nodes is how the thing is able to store information. Learning is the process of adjusting those connections.",
"Just to look at the brain, that does appear to be how it's wired up. Neurons are simple processing units that are massively interconnected and wired up in parallel. They communicate with each other using neurotransmitters, and the gain does appear to be adjustable. Artificial neural networks act a lot like brains, seem to learn the same way. Seem to make the same mistakes too.",
"If so, memories won't physically be stored anywhere in the brain, they won't be found written anywhere. Information will be manifested as a pattern of activation, that is regenerated on the fly in response to some kind of stimulus.",
"I'll have to rely on the computer types to pop the hood and explain the math to you, but from the perspective of a neurologist, I get the feeling they are all over it. To be clear, there are different types of memory. As for contextual or explicit memory, I'm convinced this is it. There are other kinds of memory. Working memory may well be spatially \"written\" at least temporarily. But connectionist theory explains a lot about how the brain works. Even up to a highly conceptual level. Over on the zen forums, for example, people tie themselves into knots over \"dualism,\" a tendency to see the world in terms of opposites. \"There are two kinds of people in this world\" is a dualistic statement, for example. If you understand how connectionist theory works -- as a system of classification, that is based on how this is similar to that, but different from the other thing -- you begin to see that dualism is an artifact of how we are wired, that it's very hard for a brain to tackle problems any other way. Which gets at some of what Kant was worried about. And Jung; both took dualism to task in their own way. So, connectionist theory correlates with how the brain is wired, and arguably correlates with the subjective phenomenology of thinking, so... hats off to the computer theorists, I think they nailed it."
] |
[
"The current most widely accepted theory is, as the other commenter described, that memories, knowledge, skills, etc. are encoded in the brain by changes in the connections between neurons. For very simple associations (e.g. if you learn that a particular tone is associated with another stimulus like a puff of air in your eye) this is easy to grasp: We can hypothesize that some neuron that responds to the tone becomes connected (or, more strongly connected) to some neuron that responds to the puff of air. For more complex concepts and memories, it's not as easy to imagine how it works, but it's probably based on similar principles. "
] |
[
"/u/brainmindspirit",
" has an excellent answer. I'd like to discuss some other aspects.",
"Long-time storage of information depends on the modification of neural synapses. So there has to be new gene expression and protein synthesis to alter synaptic connections on a long-term basis.",
"The Arc protein",
" is very important in this regard. It has been described as the master regulator of this process. Earlier this year, ",
"two different labs came to the same conclusion at the same time",
": Arc is essentially a virus. It forms a capsid (a protein shell) containing mRNA (genetic instructions) that is released from one cell and picked up by another.",
"Memories are viral. What does this mean? At this stage, we don't know. But it will be interesting to see what we'll learn in the next few years.",
"Let's take a step back. So Arc is important for re-structuring synapses and making sure memories last. But how is it decided what memories actually get to last?",
"Enter the process of ",
"Behavioral Tagging",
". It makes sense that that you need to have some sort of value signal. Something that tells you that it's worth remembering.",
"As it turns out, dopamine and noradrenaline can provide these signals. Dopamine is well-known to most, even though its portrayal in popular culture is nearly always misleading or plain wrong. Dopamine is not a \"feel-good chemical\". It's a utility signal. It signals ",
"Reward Prediction Error",
": the discrepancy between expected and actual reward. Noradrenaline has been suggested to code for what's been called ",
"unexpected uncertainty",
". Expected uncertainty reflects normal variability. It means your model of the world has accounted for this already, so it's nothing to be surprised about. Unexpected uncertainty means that there's something new--something you don't already know.",
"One way I like to think of this is in terms of environments and resources. Organisms have to solve what has been called the exploration-exploitation trade-off. Should you stick to your familiar environment and extract the resources you already know about, or should you explore a new environment that could potentially harbour even better resources (or, alternatively, threats)?",
"The involvement of dopamine and noradrenaline becomes obvious in this regard. You need to remember what the environment is like. You need to remember where you came across resources. These are important bits of information.",
"This is where it gets interesting. It turns out that these maps of environments are also used to map ",
". First, let's look at the idea of cognitive maps.",
"In the 30s and 40s (at least in the U.S.), behaviorists were the predominant figures of psychology. The central idea was that of reinforcement. Animals learned by associating stimuli and responses. Behavior could be reinforced by favorable outcomes. Today, it's obvious that their ideas about learning was all about dopamine. Edward C. Tolman was somewhat of a non-traditional behaviorist in that he didn't think it was too bad to theorize about mental states. He led a team of rats through a maze. One team was rewarded while the other just hung out. Later, he tested them both on their ability to find their way through the maze. He founded that they performed equally well. So it couldn't be all about reinforcement. Now, in hindsight, it's obvious that this can be attributed to noradrenaline. They formed maps. Cognitive maps.",
"The Nobel-prize winning research team, the Mosers, often refer to Tolman when explaining their findings. As you may have heard, they shared the Nobel prize in medicine or physiology with John O'Keefe for their work on grid cells. John O'Keefe discovered hippocampal place cells. They fire whenever an animal is in a specific location. The Mosers discovered entorhinal grid cells. Grid cells take into account speed and head-direction and are arranged in a hexagonal pattern so that their firing patterns can be used to chart the environment. They feed into the place cells. Place cells usually begin to respond heavily to particular locations when biologically significant events occur (such as finding a juicy reward). So it fits really nicely with the idea of maps and resources.",
"Excitingly, it seems the brain encodes physical and abstract space in much the same way. Traversing your mental models of abstract concepts is analogous to moving about in your environment.",
"This brings us to an interesting recent paper by DeepMind. They suggest that the hippocampus encodes ",
"Successor Representations",
". This means that place cells don't just tell you that you are in location A, but also that location A leads to location B. This is important, because this means that the value of a future location can affect the value of a current location.",
"An interesting way to think about this is by way of an analogy to gravity. Imagine a three-dimensional grid pattern. You can explore this environment. When you come across something good, a valley is formed. When you come across something bad, a hill is formed. It will take extra effort to climb the hills in future, and less effort to slide down the valleys.",
"It turns our my comment got a bit too long, so I'm splitting it into two."
] |
[
"What is the chemistry behind toilet bowl cleaners that change color when the surface is \"clean\"?"
] |
[
false
] | null |
[
"I was a chemist at a production plant which produced one of the major brands of toilet bowl cleaners that does this. It's a gimmick and nothing more. Water soluble dyes are added to toilet bowl cleaner during production. When the cleaner mixes with the water in the toilet, the dilution causes a change in pH which allows the dyes to transition from one color to the other. ",
"If you want a good cleaner at a reasonable price, look for one with between 9 to 15 percent hydrochloric acid and has a decent viscosity. We added acid stable thickeners to some blends. With those you get the advantage of high acid content with a product that clings to the bowl surface. Just be sure to use good ventilation when cleaning with these products and never ever mix other chemicals into the bowls such as bleach containing products, caustics like Comet, or anything else. This will result in chlorinated gases being produced in a relatively small room. The toilet bowl cleaner has surfactants that will do just fine in combination with the acid. "
] |
[
"I really like one product called Greased Lightning. It's an all purpose cleaner that does a great job, but be careful what surface you use it on. Glass cleaners are pretty generic with usually a bit of ammonia, isopropyl alcohol, streak-free surfactant, and blue dye. Store brands are good here. The Lysol and The Works toilet bowl cleaners are good, but make sure it's a thickened formula. Scrubbing Bubbles does a good job in my shower too. I also like one called Kaboom for the shower, though you still need to scrub. I'm old school though, I still like Comet or Ajax with bleach to scour the tub and tiles when it gets bad. With a Scotch-Brite pad or one of those plastic mesh scrubbers. ",
"Avoid the \"green\" products unless you literally want to pour your money down the drain.",
"But do remember - do not mix chemicals, only use one chemical at a time, and be sure the door is open with the vent fan running. If you need to, put a box fan in the doorway or open a window to ensure air circulation."
] |
[
"It's good to wait a bit just to let the active chemicals do their job. I usually spray those things first, then clean the sink or mirror while I'm waiting. "
] |
[
"Can fish see clearly outside of their aquarium?"
] |
[
false
] |
Since their eyes are accustomed to focus under water, does looking through air look like looking through water without googles looks to humans?
|
[
"Actually, it is like looking into water with goggles to humans. The refractive index between the eye and the medium is what counts for focus. This is why only a very small air space between human eyes and water allows for clear vision. Since the fish have water in contact with their eyes, as they are accustomed, their visual acuity is undiminished.",
"Fish react to visual stimuli outside aquaria. This includes the \"fight\" response for male bettas near reflective surfaces, or other males, as well as other activities such retrieving food. Octopuses will exit aquaria to attack prey crabs if they are within line-of-sight."
] |
[
"That makes perfect sense. So, if they were taken out of the water, their vision would get blurry?"
] |
[
"Presumably yes. If you like, I will dig up a primer lesson on refractive index as it applies to air/water interface."
] |
[
"Explain to me what the deal is with the Higgs boson?"
] |
[
false
] |
Specifically, I know that it's supposed to give matter its mass. What I don't understand is how matter could fail to have mass. Are we saying that without the Higgs, matter would just be energy and therefore massless? Are other bosons inherently massless? Please help me understand.
|
[
"See ",
"this",
" that I wrote in another thread. It is not the Higgs boson that leads to mass, but the value of the Higgs field that permeates the vacuum.",
"And yes, the various fields would be inherently massless if there were no Higgs field. It is worth knowing, though, that protons and neutrons get most of their mass from the strong force interactions holding their quarks together, and not from the intrinsic mass associated with the quark fields."
] |
[
"I'm not really sure why there is all the fuss about the higgs. It's just the last hole to be filled in the standard model - had the things been discovered in a different order, we'd be talking about a different one."
] |
[
"The Higgs Boson doesn't give matter mass. It merely confirms the existence of the Higgs field. It's the Higgs field's non-zero value in a vacuum that give mass to all the particles it intersects with. A more detailed explanation of this phenomenon is available ",
"here",
". I ",
" you read this as it clarifies this issue significantly. "
] |
[
"Why are 64 bit binaries larger than 32 bit ones?"
] |
[
false
] |
They're almost always larger but why? They're not directly referencing memory address so I can't think why they need to be bigger. Can anyone shed some light?
|
[
"The number of memory offsets in the binary should be fairly small. Also, x64 keeps most immediates at 32 bits.",
"The real reason that x64 binaries are bigger is because of the REX prefix. Anytime you want to use one of the new registers (R8 to R15), or do a full 64 bit operation (default is 32 bit) - you need a REX prefix.",
"That makes 64 bit code, on average, anywhere from .5 to 1 byte larger per instruction (using SSE instead of x87 is also part of that larger average)."
] |
[
"The compiled binary data is most certainly storing memory addresses and memory offsets! The reason why this makes the binary larger is very simple: The data used to store such addresses and offsets takes up 64 bits each as opposed to 32 bits."
] |
[
"Have a look at eabrek's reply, I can confirm it's more accurate."
] |
[
"[Biology] Since hypoxia typically occurs at extreme altitudes due to the thinning of the atmosphere, would a person get \"hyperoxia\" if they were to descend to the depths of the Marianas Trench, (if the water were removed, and open atmosphere were available to breathe)?"
] |
[
false
] |
I was just watching a documentary on National Geographic about "The Oceans Drained", and this question popped into my head. Let's say we COULD drain the ocean, (for the sake of this question, life on Earth wouldn't cease to exist, and the atmospheric content remained identical to today). If a person were to go to the bottom of the bottom of the Marianas Trench, and attempt to breathe, would they suffer from getting too much oxygen, or get crushed by all the weight of the atmosphere pushing down on them?
|
[
"You would not be crushed by air pressure, humans aren't balloons, we are open to the environment. People get crushed in deep water because the air in your lungs and other lumens can't resist the pressure from water outside your body. But at a great depth of air your body would have little trouble equalizing the pressure. By the logic stated in the above answer people would explode at the top of high mountains. Also, to contribute to the original question, we had a study in which we gave athlete supplemental oxygen at a concentration that mimicked ≈15,000 feet below sea level. They were always exercising and never had it for more than 8 minute on-1minute off for a few hours and we saw no ill effects except some people had accelerated heart rate at rest. "
] |
[
"This question has a few components: the environmental/earth science side and the human physiology side.",
"For a brief idea about the physiology: oxygen toxicity caused by increased O2 partial pressure is well documented and understood. The most common causes are iatrogenic (caused by a medical intervention) like hyperbaric chambers or artificial ventiliation, or recreational, in the context of scuba divers.",
"Oxygen partial pressure at sea level is 21 kPa. (It comprises 21% of the atmosphere at sea level, where air pressure is 100 kPa.) Oxygen toxicity can start occurring at pressures as low as 50 kPa, but the higher the pressure, the more risk.",
"The body systems more susceptible to oxygen toxicity are pulmonary (lungs), central nervous system (spine and brain) and the eye (especially in newborns). The mechanism seems to be the accumulation of oxygen free radicals which interfere with normal intracellular metabolism. Further exposure can lead to structural damage to cell components and eventually to the DNA.",
"http://en.wikipedia.org/wiki/Oxygen_toxicity"
] |
[
"For comparison: At 10,900 m below sea level (with no water), the atmospheric pressure would be 285 kPa. This is a partial O2 pressure of about 60 kPa - not deadly, but not good for you in the long run."
] |
[
"I have been told that antibiotics can decimate someone's gut flora. Do the affected bacteria eventually repopulate, or can the make-up of one's guts be permanently altered?"
] |
[
false
] |
How do (presumably) competing strains of bacteria respond to antibiotics, and what happens to them in the long term?
|
[
"To speak to one specific example, a c. dificile infection is a potential consequence of antibiotic use. The antibiotics basically wipe out the native gut flora that would ",
"normally keep the c-diff infection in check",
", resulting in significant overgrowth of the pathogenic bacteria. While c-diff specific antibiotics can be used to treat most cases, refractory cases are sometimes treated with a ",
"fecal transplant",
" to re-seed the gut microbiota."
] |
[
"The problem is that it's ubiquitous, meaning it's pretty much everywhere. You're probably breathing it in as we speak. So you take your antibiotic, it kills everything, and clostridium enters your system with nothing to stop it from adhering to your gut."
] |
[
"Well, that's what antibiotics do. They kill bacteria. Some strains are more prone to specific antibiotics than other.\nOur gut flora comprises lots of species, not dangerous under normal circumstances. It prevents more dangerous species from getting more \"influential\" - it interferes with their growth. Most of those species are gram-negative and facultatively anaerobic. They feel really good in our intestine, thus their growth is quite intense.\nVarious antibiotics are effective against specific types of bacteria and they differ in spectrum. When we decide to use an antibiotic ( to treat other infection ), which is also really effective against our G- flora, e.g. aminoglycosides, we may encounter some problems with G+ species', such as Clostridium difficile, overgrowth. In fact, C. difficile is known to produce various toxins, that our intestine doesn't really dig. That's why we can sometimes experience a condition called post-antibiotic diarrhoea. Generally speaking, our gut tries to get rid of those vicious creatures. Doctors can help by providing specific treatment aimed at those species that do us harm. In our case that would be prescribing an antibiotic that is effective against G+, anaerobic bacteria, such as metronidazole and withdrawing the first one. Probiotics may also help bringing it back to previous state.",
"I am aware that my answer is not that comprehensive, but i hope it shed some light on this matter :)"
] |
[
"Can food be charred to where it will not be digested or adsorbed?"
] |
[
false
] |
Can food be cooked to the point where the body is unable to absorb it for nutrition?
|
[
"Interesting question. This is educated speculation, but yes I would think that once food has burnt through there will be no more nutritional content (in the sense of energy, micronutrients like calcium would still be present). In fact, a bomb calorimeter (which IIRC is the gold standard for measuring the number of calories in food) does just this, it burns/combusts food in a controlled environment with lots of oxygen to see its calorie content. Calories in fact are just another form of energy, and when you burn or combust things, you are releasing their stored chemical energy (which is also in fact what the human body does, albeit at a super-controlled cellular level)."
] |
[
"Can food be cooked to the point where the body is unable to absorb it for nutrition?",
"Of course. If, for example, you were to heat a vegetable or piece of meat in a sealed environment (i.e. where the cooked food cannot react with oxygen in atmospheric air), then you would create charcoal out of your food. Charcoal is comprised, mainly, of carbon - which isn't digested by your body - you would just pass the carbon through your digestive system (and creating really really dark poo)."
] |
[
"Are you familiar with heterocyclic amines formed during cooked meat? Is this the same a charing?"
] |
[
"Why does the taste of ice cream change when thawed and refrozen?"
] |
[
false
] |
I'm not crazy am I? Surely someone else have noticed this!
|
[
"Note: this is not speculation, this is the true answer:",
"ELI5:",
"Ice cream tastes good because you have fine particles of ice cream in a large mixture. However, if you leave it open for a long time, or if you melt and refreeze, the ice cream particles will coalesce, making it harder for you to mix the flavors homogenously in your mouth and it will overall taste grainy and unpleasant. ",
"ELIamAMaterialsScientist:",
"When ice cream is made, it is purposefully made to have extremely small 'globules' of ice cream. When the globules are small enough, the ice cream tastes very smooth and rich, and the flavor blends together very homogenously. ",
"Unfortunately, small globules are a metastable state. As you leave the ice cream for a long time, the small globules will combine into bigger particles (coarsen), and the water will also phase separate, making its own ice crystals. This is why ice cream left for a long time tastes pretty nasty, and there are usually ice shards scattered about randomly. This is the process of moving toward thermal equilibrium. Actually, small globules have high surface area to volume ratio, and with that comes surface energy. Surface energy is always positive, and in the process of reducing free energy, the grain boundaries coalesce and ",
" to reduce the total amount of surface. ",
"The same process happens when you melt and refreeze ice cream, except you are freezing from the melt, and so you are skipping the metastable state and going straight for the thermodynamic ground state. ",
"The same thing happens with fine chocolate too - good chocolate is tempered in a metastable state that melts precisely at 98 degrees F, so it melts very nicely in your mouth. However, if you let chocolate sit, or if you let it melt and resolidify, it will move to its thermodynamic ground state, which will bring the melting temperature up to > 100 F, making it insoluble, crumbly and brittle. "
] |
[
"I think it has to do with the way ice cream is made from the start. I'm not sure if this is correct but my understanding is that ice cream is made similar to how icees or slushees are made. As in they move the material around as they freeze it. This seems like it would do nothing, but in the end it gives the substance a different texture. Idk about the taste though, that I'll leave to someone with the right expertise to handle."
] |
[
"I'm not a member of the panel or anything, but I'll throw out a hypothesis seeing that I'm a chemical engineer. ",
"First, I assume by \"thaw\" you mean melted (or almost melted). When the ice cream is thawed, it is overall at a higher temperature, thus the metabolic rate of the microbes in the ice cream increases. This causes them to consume more carbohydrates (e.g. sugar) in the period of time where the ice cream is thawed, thus directly affecting the taste of the ice cream. "
] |
[
"How big would a planet have to be before the gravity is too strong for humans?"
] |
[
false
] |
As title says
|
[
"a similar question was asked on a thread some time ago, and this begs the question to define the \"too strong for humans\". 5g is the limit where humans black out, but at 2-3G the heart would have to work overtime to send blood to the head, probably blood clots would appear in legs and chronical back pain would appear. i don't think we'd have the same life expectancy if living in 3g conditions",
"/ source - i read something similar on the internet"
] |
[
"G = 6.7e-11 m",
" kg",
" s",
"M_earth = 5.9e24 kg",
"M_me = 6.4e1 kg",
"Dist = 6.4e6 m",
"F = ( G * M_earth * M_me ) / Dist",
"F = ( 6.7e-11 * 5.9e24 * 6.4e1 ) / (6.4e6)",
" = 6.2e2 Newtons",
"F = 620 Newtons",
"G = 6.7e-11",
"M_earth = 5.9e24 kg * 125 = 7.3e26 kg",
"M_me = 6.4e1 kg",
"Dist = 6.4e6 m * 5 = 3.2e7 m",
"F = ( G * M_earth * M_me ) / Dist",
"F = ( 6.7e-11 * 7.3e26 * 6.4e1 ) / (3.2e7)",
" = 3.1e3 Newtons",
"F = 3100 Newtons",
"Regular earth: 620 Newtons",
"Regular earth x 5 = 3100 Newtons",
"5x radius earth = 3100 Newtons",
" If you increase the radius of a planet by a factor without changing density, the gravitational force between an object on the surface and the planet will increase by the same factor.",
" Basically when you increase the radius by a factor, you're doing this to the formula for force",
"If the density remained the same, the mass would be M_normal * factor",
"F = ( G * M_normal * M_me ) * factor",
" / (Dist * factor )",
" ",
"F = ( G * M_normal * M_me ) * factor",
" / Dist",
" * factor",
"or ",
"F = [ ( G * M_normal * M_me ) / Dist",
" ] * factor",
" / factor",
"which is",
"F = [ ( G * M_normal * M_me ) / Dist",
" ] * factor"
] |
[
"I'm just going to post this"
] |
[
"Why is Bragg's law empirically correct?"
] |
[
false
] |
(worded as a question now). In x-ray diffraction, Bragg's law states the relationship between the lattice spacing of a crystal and the wavelength and incidence angle of incident radiation to that crystal. I understand the proof of the law (it's just geometry), but I have a few question's about why it works in practice: Why is the incidence angle equal to the diffraction angle? Why do photons see the diffracting planes of atoms as "planes," when the EMF around the atoms in the crystal isn't planar? What properties/fields causes a diffraction event? More generally, for any interaction between a photon and any particle with mass, which fields are interacting? What is the extent of the "trail" of a photon? How far ahead of one photon can another in-phase, parellel, and laterally near photon be, while still interfering with it constructively (or destructively, if out of phase)? Why do powders produce clear diffraction lines? In a material with millions of randomly oriented crystals, why do clear diffraction lines at any angles exist (suggesting that the planes of randomly oriented crystals favor a specific orientation)? Sorry if this is too specific. I also don't know quite what discipline this falls under.
|
[
"These are all some of the best questions I've seen posted here in a long time, and I feel bad that I can't really give them as good a treatment as they deserve. I hope someone else can call me out on my bullshit below, because odds are good I get something wrong. ",
"Why is the incidence angle equal to the diffraction angle? Why do photons see the diffracting planes of atoms as \"planes,\" when the EMF around the atoms in the crystal isn't planar?",
"Because it is spherically symmetric, so what matters is where we find the \"scattering center.\" Basically when particles/light scatter off of different scattering centers, the geometry of the scattering centers (the spacing and lattice of the atoms) will determine what angles will yield constructive and destructive interference, giving maxima at very specific angles, which line up with the planes of atoms in the material. ",
"The angles that make for constructive interference will have to line up with the planes",
", because otherwise there will be considerable destructive interference. That gives you your Bragg condition. ",
"What properties/fields causes a diffraction event? More generally, for any interaction between a photon and any particle with mass, which fields are interacting?",
"Bragg scattering is just a straight forward application of scattering theory. Things (ie particles) interact via some force (so there is a potential between them) and in this case it's the electrostatic potential. ",
"What is the extent of the \"trail\" of a photon? How far ahead of one photon can another in-phase, parellel, and laterally near photon be, while still interfering with it constructively (or destructively, if out of phase)?",
"Well remember that photons are wave packets, so they are spread out over some space. ",
"Here's an example of electron interference that captures the gyst of it (pay close attention to the blue spots on top of the animations, those capture the particle amplitudes fairly well).",
" In general, they have to be fairly close in order for the interference patterns to be noticeable; by fairly close, I mean their separation is on the order of their deBrogle wavelengths. ",
"Why do powders produce clear diffraction lines? In a material with millions of randomly oriented crystals, why do clear diffraction lines at any angles exist (suggesting that the planes of randomly oriented crystals favor a specific orientation)?",
"Powder diffraction (which is a technical term I believe) is quite different from Bragg scattering, as you noticed. In the powder, you assume that every possible grain structure and size is present, so your diffraction pattern just ends up being the diffraction pattern of your average grain size, which would be a halo. You're basically doing diffraction from a circular aperture. "
] |
[
"your diffraction pattern just ends up being the diffraction pattern of your average grain size, which would be a halo",
"Not at all. Powder diffractometers still measure the diffraction between lattice planes, which is why we can use them to determine crystal structure. With powders, you assume that all possible grain ",
" are present (the grain shape/size has effects on the shape of the peaks, but you'll still get diffraction data from a sample of uniformly sized and shaped grains), so that when your x-ray source and detector are positioned at an angle that satisfies the Bragg condition for any lattice plane, there are some grains in the correct orientation to produce a peak."
] |
[
"It's important to note that Bragg's law is a result of ",
" planes, not planes of atoms. It is the periodicity of the crystal lattice that is responsible.",
"Bragg's law isn't actually a geometric argument, the geometry is just a simple interpretation. Bragg's law is actually derived from the Laue equations.",
"These are just common misconceptions, hopefully it'll help you understand it a little better! There are probably people much more qualified than I am to specifically answer your other questions."
] |
[
"I have a hypermobile tongue and no frenulum..."
] |
[
false
] |
[deleted]
|
[
"How can you swallow your tongue if it's attached at the other end in your mouth?"
] |
[
"its really long and flexible and can flip over itself and down my throat."
] |
[
"I'm not quite sure what you mean by \"swallow\" then?",
"Are you asking if people have choked on it?"
] |
[
"How do other baryons behave inside atomic nuclei?"
] |
[
false
] |
Neutrons decay in free space, but are apparently stable inside some atomic nuclei. In other nuclei protons decay. Are there theories or experiments describing how the stability of other baryons are affected? I've found quite a few interesting papers on hypernuclei which I am working through, but very little more easily digested material. Also the papers I have read so far have all discussed the properties of the nucleus itself, mostly binding energy, but not the affects on the constituent baryons. It seems to me that if the half-life of neutrons can be increased by 10 times, then a lambda baryon which usually decays in under a nanosecond might last for a more human scale timeframe, seconds or years, or even be effectively stable. I also see that the additional binding energy in light nuclei when a hyperon is added is up to around a tenth the mass of the strange quark, which suggests to me that it will be energetically favourable for the strange quark to decay even if the entire nucleus is then left unstable, but is near enough in scale I would expect some change to the decay. Has there been research on heavier hypernuclei, like iron or lead? Thanks.
|
[
"I've found quite a few interesting papers on hypernuclei which I am working through, but very little more easily digested material.",
"Yes, this is what you're looking for. It's a relatively young area of research, and obviously a lot of it is theoretical rather than experimental. We understand QCD very well, but it's hard to calculate the properties of many-body systems directly from QCD. That's why when you look in the literature, only very light hypernuclei have been studied so far. Instead of starting from QCD, one can use an effective nucleon-lambda interaction to do \"ab initio\" calculations of light hypernuclei, but then that requires an understanding of how nucleons interact with lambda baryons.",
"As for how other baryons behave in nuclei, they do basically the same thing that nucleons do. They undergo short-ranged interactions with nearby particles via the residual strong force. They occupy some set of orbitals, just like nucleons do. Although other baryons are not identical to nucleons, so there is no Pauli exclusion principle between nucleons and hyperons. The simplest observables that a theorist would try to calculate about some nucleus (hyper or otherwise) are binding energies, charge radii, etc. That's why you see theory papers calculating binding energies for hypernuclei. It may seem like a \"boring\" observable, but it's the first step for a nuclear structure theory to be able to calculate the binding energy."
] |
[
"Thanks. ",
"There's nothing boring about this, quite the opposite it is so interesting I just wish there was more information to find. ",
"Should I ask again in 10 years or 40? "
] |
[
"Hopefully the field will be much more developed in 10 years. There isn’t much introductory literature available, unfortunately. "
] |
[
"Why is non-dairy coffee creamer so flammable?"
] |
[
false
] | null |
[
"No. Powders are really only especially flammable as fuel/air mixtures. And when they catch they have a lot of flash but don't exactly have a lot of sustained flame. If they catch anything else on fire it's generally only stuff that is also already extremely flammable, and even then it's hit or miss. So it wouldn't make a reliable tinder."
] |
[
"It's not particularly more flammable than similar materials like flour, corn starch, or sugar. Non-dairy creamer is processed to have a specific particle size and contains non-caking agents designed to make it flow easily, which makes it easy to be used in an explosion but that's also true of other things, such as corn starch."
] |
[
"It is the same reason coal mine dust and grain dust is so flammable. There is a tremendous amount of surface area so fire travels incredibly quickly.",
"Grain fire explosion",
"Coal Dust fire",
"Upper Big Branch Mine"
] |
[
"When a T-cell (T lymphocyte) differentiates into the Killer T cell, Helper T-cell, Suppressor T-cell, and Memory T-cell, why doesm't the function of the Helper T-cell and Suppressor T-cell cancel each other out?"
] |
[
false
] |
I know that the Helper T-cell stimulates the other T-cells (and B-cells) alerting them to go congregate together and go fight the tumor, but doesn't the Suppressor T-cell inhibit the T-cells (and B-cells)? What am I missing here? These two actions seem to contradict each other. Does the Suppressor T-cell only activate when a certain number of Helper T-cells have been produced? Are the ratios of Helper T-cells to Suppressor T-cells 1:1 or skewed? I'm not sure what I'm missing here. The Helper T-cell must be doing work since our immune system does fight tumors from within.
|
[
"I know that the Helper T-cell stimulates the other T-cells (and B-cells) alerting them to go congregate together and go fight the tumor, but doesn't the Suppressor T-cell inhibit the T-cells (and B-cells)?",
"Yes",
"",
"What am I missing here? These two actions seem to contradict each other.",
"You're not missing anything. They act in opposition, just as many, many regulatory systems in the body do.",
"",
"Does the Suppressor T-cell only activate when a certain number of helper T-cells have been produced?",
"We actually do not know much about Treg cell activation and function, and they are quite a few competing hypothesis out there. We do know that they (probably) are activated via TCR interactions with antigen, just like normal T cells. They can themselves be suppressed in areas of infection.",
"",
"Are the ratios of Helper T-cells to Suppressor T-cells 1:1 or skewed?",
"They are very skewed towards Th subtypes. There are expections, like in tumor environments, where the Treg population can grow considerably large relative to the entire CD4+ population.",
"",
"I'm not sure what I'm missing here. The Helper T-cell must be doing work since our immune system does fight tumors from within.",
"They are thought to only dampen the magnitude of an adaptive response, but not suppress it completely. But in fact, many tumors do recruit Treg cells to suppress effector cell functions to activities below than what would be considered effective."
] |
[
"Not completely sure, but it sounds like a feedback mechanism. If T cell activation continued to activate T cells, nothing would ever cause the reaction to stop. Activating suppressor T cells would keep immune reactions from going out of control. I'll be learning about this more in the near future, but this is my best guess"
] |
[
"Yes! This your reasoning is correct. This a big factor. In fighting influenza, protocol 1 is to search, kill, destroy the virus whereas protocol 2 is to turn on the breaks and cool the immune system off once the virus is gone. An out-of-control immune response can be deadly, and is thought to be responsible for the young, otherwise healthy people who died during the swine-flu outbreak a few years ago. Death by cytokine storm."
] |
[
"Does hair go grey or grow grey?"
] |
[
false
] |
I’ve got a long beard, there are some greys in it, I’ve pulled them all out before so either they are going grey or they are growing much faster than I thought (I think my beard has gotten to it’s natural length as I have not perceived extra length in the last year or so, but it never seems to thicken up or anything). I’m just intrigued if the greys are growing out of my face grey or if otherwise coloured hairs are losing their colour?
|
[
"Hair grows grey. Melanin in your hair follicles give it color, and the amount can vary over your lifetime (and strand to strand). If you think of kids that are blond but then darken in their teenage years, you're basically seeing the graying process in reverse. There are a lot of variation in mekanocytes and the amount they deliver, but typically over time their ability to produce melanin is reduced and strands get lighter in color. ",
"Also, as a side note hair only grows for 3-5 years, so it can only be so long. Those people with crazy long hair down to their feet have a rare genetic anomaly that keeps their hair in growth part of the cycle for much longer."
] |
[
"Your hair doesn’t turn grey, it grows in grey. ",
"It becomes a slightly different texture, so the colored part may snap off, but the only way to lose color in your hair after it’s grown out of your skin is to bleach it somehow. (Whether with sun or chemicals or something else that isn’t coming to mind)"
] |
[
"It's really about the amount of melanin in the hair...blond hair has some melanin, white does not."
] |
[
"Why do certain things you eat cause your stomach to make that churning/rumbling noise? What's going on?"
] |
[
false
] |
Is it gas? And if it is then why do other foods that give you gas not do it?
|
[
"The name of this sound is actually called \"peristaltic sound,\" and is simply the sound of the food being pushed through the small intestine in a process called \"peristalsis.\" The same contractions of the muscles occur while you are hungry, which create the audible indication of hunger."
] |
[
"You would be unlikely to hear liquids moving around. If you can hear it, there are gases involved, either gases you swallowed, or methane and hydrogen generated by bacterial action on indigestible carbohydrates. These can include fructose, lactose, and sorbatol for some people, and complex carbohydrates found in beans, peanuts, and plants in the cabbage family."
] |
[
"I have this issue recently too. I noticed it has been happening more often recently... should I change my diet or what should I do about this? "
] |
[
"When water leaves or enters a body of water from a point source, does the entire surface level decrease instantly or is there a gradient?"
] |
[
false
] |
For example, when water is withdrawn from Lake Meade at various water intakes; does the entire surface of Lake Meade decrease at the same time, or is there a wave or gradient effect? Same goes for water being added, such as filling a pool with a garden hose at the bottom of one end.
|
[
"When water leaves a body of water from a point source, there is a gradient. To provide an example for this, when you drain a bathtub, the water is drained out of the tub in a vortex. However, since the volume of water is large, the vortex and the gradient that it causes is unnoticeable. You would see a decrease in the surface level that seems to occur instantaneously across the uniform surface; even so, there is a gradient. ",
"To apply this to Lake Meade, should water be withdrawn, there would be a concave gradient above the source of water withdrawal. However, given that the volume of water is extremely large, the gradient is invisible to the naked eye. Similarly, if you fill a pool with a garden hose from the bottom, there would be a concave gradient above the source of water input."
] |
[
"More generally, matter never spontaneously moves ",
" a gradient of some type (e.g., force or pressure)."
] |
[
"The entire basin does not instantly adjust when water is added or removed from a specific area. In general, the rest of the water in the basin won't \"know\" that any water has been removed until the information propagates to that location. This type of information (height of the upper surface) generally propagates in the form of waves. The type of wave depends on the time and space scales of the problem. For a water body such as Lake Mead, the information that water is being removed would spread via surface gravity waves. As the waves first arrive a the remote locations, this would be the first information they receive that something changed downstream regarding the water removal/addition. The equilibrium adjustment to this change would not happen immediately but over the course of arrival of a long series of wave trains. ",
"In a larger body of water, such as an ocean basin, the effects of the earth's rotation are important so the types of waves are physically different. The waves which carry information around the ocean basins are primarily ",
"Rossby",
" and ",
"Kelvin",
" waves. These are planetary-scale waves not visible to the naked eye and vary on time-scales of weeks to months.",
"Currently there is a huge Kelvin Wave adjustment occurring in the tropical Pacific. An El Nino is forming and one of the first signs is a large Kevlin wave propagating eastward along the equator. In normal conditions, the winds pile-up a big pool of warm water in the western tropical Pacific. If those winds were to weaken, that big pile of warm water is then free to spread about the rest of the basin - completely equivalent to the notion of suddenly adding a bunch of warm water to the western tropical Pacific. That oceanic adjustment to the sudden increase in water marks the beginning of El Nino and begins with the fastest planetary waves, the equatorial Kelvin waves, propagating that information eastward along the equator, taking a few months to cross from West to East. "
] |
[
"Why is there such a large strength gap between Electromagnetism and Gravity?"
] |
[
false
] |
Is there anything that explains the enormous disparity between the gravitational scale and the typical mass scale of the elementary particles? In other words, why is gravity so much weaker than the other forces, like electromagnetism? A simple magnet can pick up a paper clip off a table if it is relatively close, yet the entire earth is pulling it the other direction. Is there anything in physics that helps us understand why Gravity is so weak?
|
[
"No. This is one of the great unsolved problems of theoretical physics, called the hierarchy problem. People have different theories for explaining it, like supersymmetry, large extra dimensions, brane-world scenarios and so on, but none of these are truly convincing and there is no experimental evidence for any of them. So it is still a mystery, really. People hoped that the LHC would find something, like supersymmetry, or even extra dimensions, which would then help us understand it, but so far no luck. "
] |
[
"I never understood why this was considered a problem. Aren't both G and the fine structure constant free parameters, so there's no known way of defining what they ought to be in the first place?"
] |
[
"It might not be a problem, but there seems to be something that needs explaining there. The fine structure constant, and the corresponding constants for the strong and weak force are all numbers roughly of order 1. The gravitational coupling constant is around 10",
" If you think about these constants as being picked at random, the chance of one of them being so very close to zero is very, very small, so it seems too beg for some explanation. There is also an argument about the mass of the Higgs boson, which states the problem differently and where it is somehow clearer that one needs some explanation, but to explain that you really need to know some quantum field theory. Or you can read wikipedia here: ",
"http://en.wikipedia.org/wiki/Hierarchy_problem#The_Higgs_mass",
" "
] |
[
"Greenland ice melt reporting has me worried, what are ramifications of this year's melt?"
] |
[
false
] | null |
[
"In a very general sense, one year / season of event data is not something to be overly concerned with, but this is still quite troubling more in that it's pretty much in line with a series of recent papers suggesting that the melting of the Greenland ice sheet is accelerating, e.g. ",
"Graeter et al, 2018",
" and ",
"Bevis et al 2019",
". Acceleration of the melting of the Greenland ice sheet is of course important in terms of more contributions to sea level rise, but personally I find it more concerning within the context of its potential to destabilize the ",
"Atlantic meridional overturning circulation",
". There's been work to suggest that destabilization/shutting down of AMOC (driven in part by injection of freshwater, like melting Greenland) could have quite disastrous effects for society, e.g. ",
"Hansen et al 2016",
" and that the AMOC may be more prone to destabilization than commonly thought, e.g. ",
"Liu et al 2017",
". The potential for destabilization of the AMOC remains contentious, e.g. this ",
"Atlantic article",
" does a nice job of discussing this in layman's terms and refers to the two papers I just linked to (with some notes of caution in terms of interpreting those results from others quoted in the article).",
"EDIT: For those interested, you should also check out the answer in this thread by ",
"/u/Grifwin",
", as they provide some other good points in terms of 'tipping points' with regards to ice sheets and the stochastic nature of individual seasonal measurements compared to long term averages."
] |
[
"Thank you for bringing this up. If one ocean flow is disrupted the entire climate will change, and we have no clue how. Less warm water flowing north and less cold water flowing south, the temperature changes could be devastating."
] |
[
"Annual melt estimates in general are pretty susceptible to the stochastic nature of our climate. Where we might get crazy melts one year we might see very reduced melt estimates for the next, this is a common interference of climatologists when we try to remove the natural variability to ascertain the longer time climate change trend. That being said longer term trends are now sufficient and pronounced enough to see decadal climate change linked to anthropogenic perturbation of natural climate cycles.",
"",
"What is interesting about Greenland ice melt is that the current volume of ice can contribute up to 7m s.l change if it begins to irreversibly retreat. This ice melt has been reported to of increased by up to 6x the rate since the 1980s ",
"Mouginot et al., 2019",
" which is pretty scary stuff! It is also worrying because there are tipping points for particular ice sheets, whereby once a particular threshold of melt has occurred positive feedbacks take over and the resultant ice sheet loses it's stability and collapses. Unfortunately for us tipping points on Greenland (and West Antarctic Ice Sheet) are very low, around 1.5C for Greenland ",
"Pattyn et al., 2018",
". Understanding the timescales of these ice sheets to collapse, their susceptible `tipping` points, and their resultant influences on the ocean-climate system is a tricky topic that we are slowly getting better with understanding. So under the various emission estimates of ICPP and the target of 2C feeling fairly lacklustre it is a worrying scenario for those of us worried about climate change. Especially since the 7m of Greenland ice sheet sea level rise when combined with West Antarctic Ice Sheet collapse can provide up to 20-25m of global sea level rise. This sea level projection will directly affect populations of low-lying coastal inhabitants thought to number more than 600million. (tried to find reference - will update)",
"",
"One good example of how dynamic Greenland is came from the Greenland Ice Sheet Project, which found that Beryllium10 a cosmogenic nuclide, formed from direct sunlight, was found in quantity beneath the Greenland Ice Sheet. This was attributed to a major collapse of the ice sheet over the last 1.1 million years ",
"Schaefer et al., 2016",
", where carbon dioxide levels have fluctuated between 180-280ppm with some deviations towards 400ppm. Yesterdays carbon dioxide level from Mauna Loa observatory was 416ppm and will likely carry on increasing for our generation. Scary stuff when put in perspective."
] |
[
"If a patient is given full nutritional support, what is the actual cause of death in Rabies?"
] |
[
false
] |
So I watched an extremely sad video of a man with rabies who seemed to be conscious up until the day before he died. Which, made me think, I've never understood the actual mechanism that rabies kills you by if your body is provided the water and calories it needs through hospital support. Could someone clarify it for me?
|
[
"Scientific answer here. Rabies actually has been cured four times using the ",
"milwaukee protocol",
".",
"First some details. Rabies is a capsulated rhabdovirus, it is rod shaped or bullet shaped in terms of microscopic shape. It has an RNA genome with code to create only a few proteins. It has it;s own RNA-dependent RNA polymerase. One major important product that rabies virus creates is the G protein, which codes for the spiked glycoprotein envelope, which covers the bullet shaped virus. ",
"(sorry, I failed at that) I'm a second year MD-PhD student and this is actually on my neurology exam in about 5 hours, so I hope I get this right :D",
"Rabies is a virus which has a particular affinity for neurons. This is important because neurons can often have extremely long axons. By way of analogy, consider a phone call from CA to NY. If there's a telephone line, that's the axon. Rabies can use neurons to travel from the periphery up into the brain. ",
"G glycoprotein is both good for us and bad for us. It's initially BAD because it allows the virus to interact with nicotinic acetylcholine receptors on muscle as well as ganglioside. G also allows interaction with CD56, a surface protein on neurons. You can forget the names of the proteins or the acronyms, just know rabies invades muscle or neuron cells using the envelope, made of glycoprotein, tricking our cells. ",
"Once the virus enters the cell, the cell realizes that something foreign has entered the environment, does not recognize it, and sends the particle to a cellular organelle called a lysosome, which uses acid and enzymes to breakdown unneeded or unwanted materials for recycling or presentation to activate the immune system. ",
"Unfortunately, acid allows the envelope on the virus to fuse with the membrane of the lysosome. Consider two globs coming together in a lavalamp, only both are hollow, and one is inside the other. ",
"As the membranes fuse, the contents of the virus actually escape the lysosome, while the envelope is lost. The virus gets to work making proteins, which are disguised as human proteins. The virus can travel 8-20 mm per day up an axon. The farther the animal bite from your brain, the more time you have to get help and supportive care (although without care death occurs 2-3 days after neuro symptoms begin (contrast w/ 10 if supportive care is available).",
". Remember how lysosomes can also be used to activate the immune system? Well G protein elicits a neutralizing antibody response (meaning one that doesn't just result in stalemate, but destroys the infection and results in immunological memory). ",
"The problem is that by the time antibodies are present, the virus is already in the brain and it's likely too late. If one were to look at the pathological brain findings at autopsy, the findings are actually extremely non-specific. The prevailing theory is that the immune system actually ends up causing lethal amounts of collateral damage. It can be very difficult to diagnose rabies if the patient neglects to tell you there was an animal bite. ",
"In the Milwaukee protocol (which has succeded 4 times and failed a hell of a lot more), the notion is to induce a coma and try to protect the brain from the raging battle being waged by the immune system. It's extremely costly financially, the treatment can be very lengthy from a time-perspective (the first patient cured spent 76 days in the hospital) and it's unknown if this is actually working the way we think it might be. The doc who developed it actually believes that he got lucky and the successful patients had unknown variants (mutated versions) of rabies.",
"If you get to a doctor before neurologic symptoms (odd behavior, hallucination, seizure, hydrophobia - fear of water, muscle spasms, furious anger which gives way to total paralysis and death usually secondary to cardiac or respiratory arrest) you will likely do very well, prognostically. ",
"The prodrome comes next which lasts 2-10 days. If you don't get treatment now you're about to be in trouble. Next is the neuro stage, and once antibodies are detectable in blood, you are likely already beyond saving. "
] |
[
"Actually to my knowledge, no. Nerves are not all the same, even those of the sensory variety. Some are for deep pressure, others light pressure, others pain, vibration, temperature, proprioception (the sense that allows the sober version of you to close your eyes and touch your nose), and nociception (general word for pain, commonly used to describe caustic injury - the root word is noxious, I believe).",
"All of these different nerve endings are found not only at different layers within the skin, but (depending on body location) will have at least some degree of overlapping receptive fields. Let me explain the concept of receptive fields using a baseball analogy. If there's a fly ball heading towards the outfield right in between the center and right fielder, both of them are able to catch it. One neuron needs to yell 'I got it!', and this process not only ensures the two players don't both go for the same ball, but also allows your brain to better determine precisely where the stimulus is coming from. ",
"To explain what I mean when I say 'to some degree', I have an experiment for you to do with a partner. Shut your eyes, and ask your bestest bud to lightly touch the palm of your hand with two pencils (with a point, but not sharp obviously.). Have your pal start out by putting both pencil tips right ontop of each other. With your eyes closed, ask your friend to lift the pencils up, separate them by a half inch, and place them back on your palm. Try to determine the minimum distance between the two pencil points such that you are able to tell (with eyes closed) that there are actually two pencil tips, not one. Assuming you have no nerve damage and no one is cheating, you will be able to tell that there are two different locations where you feel pressure points with only a very small distance between the two points. ",
"Now ask your friend to do the same thing with you again, but on your back -- maybe in between your shoulder blades. You will find that a much larger distance is required before you can tell that there are two pressure points. What does this mean? It means your hand is equivalent to the \"infield\" and your back is equivalent to the \"outfield\". We have evolved to be able to discriminate sensory information much more precisely when we use more sensitive areas of the body. It's not hard to imagine how that might be an advantage. The palm of your hand is the infield, where a fly ball can be easily caught by the pitcher, the catcher, short stop, or the third basemen. In between your shoulder blades is the outfield, where we don't need that many eyes on the ball. ",
"With that in mind, let me answer your question and explain the relevance. In order for an area to go completely numb, especially on the external skin, many neurons would need to be knocked out of the picture. These neurons are located at different depths within the skin, and the cell body of the neuron (as opposed to the receptive organ) is often not present in the same location as the receptive field. Your TV antenna sits on top of your TV, to use another analogy, and breaking off one of those old fashioned rabbit ears not only leaves you with one remaining, but also leaves you with a working television which the antenna is resting upon. ",
"Enough analogies. Here's some more science. Rabies belongs to a family of related viruses called ",
"rhabdoviridae",
". Within this family, there are multiple subfamilies or genera. Lyssavirus (derived from the greek word for rage) is the pathogen that causes the rabies we all know and love. Vesiculovirus is another related virus which causes vesicular stomatitis virus in farm animals (inflammed and dry mouth which also has fluid filled cysts present, called vesicles). Vesiculovirus can cause flu-like illness in humans who are sufficiently exposed. ",
"\nRhabdoviridae replicate by budding off from the host cell. For many members of the rhaboviridae group, this kills the cell. Budding of rabies does NOT kill the cell. Without serious structural or mutagenic damage, a peripheral neuron is likely to survive and regenerate -- partially because the cell body is often far away. The continued survival of the cell is another reason the pathological findings at autopsy are so nonspecific. It's like you can smell the smoke and feel the heat but someone forgot to write 'fire' into the script.",
"It is entirely possible that the bitten area goes numb as you have described, but I would be quite surprised if this was directly the result of the virus. This is not an area that I feel comfortable answering definitely. To speculate, it's more likely the result of a local immune response. One of the major ways that we fight off viral infection is by killing the cell which has been infected and basically destroying the body (dead infected cell) using macrophages, large white blood cells that eat, engulf, and destroy foreign/waste material (usually).",
"I hope I answered your question. Rabies was not on my test this morning (because I know the topic too well, and that's med school for ya..), but I scored well :)"
] |
[
"Rabies virus causes widespread inflammation of the brain and other parts of the central nervous system. This causes all sorts of neurological problems, including paralysis and loss of consciousness, and it's those that kill you."
] |
[
"Einstein birthday megathread"
] |
[
false
] |
Hi everyone! Today is Albert Einstein's birthday and we're here to answer all of your Einstein-related questions. His most famous achievement is arguably the development of the in 1915. General relativity is an extremely well-tested theory of gravity, with implications for mechanics, astrophyiscs, cosmology, and more. It has been a hot topic lately with the direct detection of . Besides his work in gravity, Einstein was known for a great many other things. In 1921 he received the Nobel Prize in Physics for the discovery of the . He also worked on thermodynamic/statistical physics (such as and ), the famous , , , and more. Feel free to ask all of your Einstein-related questions!
|
[
"Out of respect, please do not joke about Stephen Hawking's passing."
] |
[
"Out of respect, please do not joke about Stephen Hawking's passing."
] |
[
"Things Einstein contributed to besides relativity:",
"-understanding atomic dimensions through viscosity",
"-relating atoms to viscosity and Brownian motion (the Stokes-Einstein relation)",
"-understanding the photoelectric effect in terms of discrete photons",
"-developing the electromagnetic theory that allowed the laser to be invented (probably his biggest technological contribution)",
"-particle statistics of bosons aka Bose-Einstein statistics",
"-implication that quantum mechanics would imply entanglement at a distance",
"-a stable solution to the Friedmann equations that was totally wrong for our universe",
"-an experiment (that's right!) to determine the electrical charge of objects",
"-a lot of stuff about classical unified field theory that ultimately went nowhere",
"-many papers (mostly in German) on the history of physics",
"and a whole bunch of other stuff he isn't famous for."
] |
[
"Is the BioNTech/Pfizer vaccine 'Open-Source'?"
] |
[
false
] |
Hello everyone, I recently read . This article links to the BNT162b2 mRNA sequence provided by the WHO. From my understanding this sequence contains the whole 'logic' of the vaccine. So i wonder if this sequence is enough information that (given that you have the required money/machines/base materials etc.) 'everyone' could mix the vaccine? Or is there some secrets information required for producing the vaccine which is kept secret by BioNTech/Pfizer?
|
[
"The RNA \"source code\" is public. The manufacturing processes used to manufacture the vaccine (create the RNA sequence, encapsulate it in lipid nanoparticles, etc.) ",
"are protected by both patents and as trade secrets",
"."
] |
[
"Compulsory licensing exists in many countries, and of course the whole point of the patent system is that the process is published. It's unusual in the US for a compulsory license to be imposed, but more common elsewhere (for example, India has done it for several drugs to improve availability there). Trade secrets are secret by definition and there is no compulsory licensing scheme, but a government in principle can force its way into almost anything within its grasp. It's not like most people would be willing to do prison time to protect their employer's intellectual property.",
"The thing is, these vaccine manufacturing facilities aren't everywhere just sitting around waiting for the government to give them secret sauce. The facilities and level of expertise necessary to safely and effectively produce biologicals meant for human use are relatively uncommon, and it's generally both easier in the short term and safer in the long run for governments to obey their own laws and let people keep their intellectual property and pay for vaccines than it is to try to seize knowledge or facilities. ",
"There have been authors who have called for compulsory licensing if necessary",
" because of course if anything warrants compulsory licensing, it's a public health emergency like COVID-19.",
"But this is all a bit off topic here."
] |
[
"I wonder - what did he (or you, for that matter) base this claim on? I'm asking this neutrally - this is something that I've heard in discussions about him (with people emphasising economic reasons for his choice) and I would love to get a more round view of things if possible. Thanks :)"
] |
[
"Xenotransplantation: What determines what animals can participate?"
] |
[
false
] |
Hello. :) I’ve come across the concept of using pig hearts for transplants, but not many other animals in general. This got me wondering: What is the scientific reasoning was for choosing pigs as opposed to a different animal like a cow, or some other? I wasn’t sure whether the flair would fall under human body or biology. :)
|
[
"Mainly organ size, but also what kind of antibodies the animal have and if they’re compatible with human immune systems - it has been said the history of transplantation is the history of immune suppression; tackling rejection is the holy grail of transplant medicine and ",
"the reason for using these “gal-safe” pigs, which are bred to not have a sugar on the organ cell humans react to",
"."
] |
[
"Pig hearts have been considered as a potential source of transplant organs for humans for several reasons. One of the main reasons is that the size and structure of a pig's heart is similar to that of a human heart. This makes it easier to transplant a pig heart into a human without requiring significant changes to the recipient's blood vessels and other tissues.",
"In addition, pigs are widely available and can be easily raised in large numbers, making them a convenient source of transplant organs. They are also relatively similar to humans genetically, which reduces the risk of transplant rejection.",
"While it is possible to transplant organs from other animals, such as cows, into humans, the success rates for these types of transplants are generally lower due to the differences in size and structure between the donor and recipient organs. Additionally, transplanting organs from other animals can carry a higher risk of rejection and other complications. These factors make pigs a more attractive option for organ transplantation."
] |
[
"Also some potential alternatives, like chimpanzees, are ruled out for ethical and practical reasons."
] |
[
"what happens to the millions of silent mutations that make inactive proteins? why don't we still have a ton of them?"
] |
[
false
] |
Random mutations only very rarely result in changes in a protein that improve its usefulness for the cell, yet useful mutations are selected in evolution. Because these changes are so rare, for each useful mutation there are innumerable mutations that lead to either no improvement or inactive proteins. Why, then, do cells not contain millions of different proteins that are of no use?
|
[
"In genetics, a silent mutation is one which doesn't have an effect--it either doesn't change the amino acid sequence, or if it does, it switches to one similar enough not to change function. If a mutation is silent, by definition it's not breaking the gene product. (And these do accumulate quite a lot.) You seem to be talking about deleterious, or negative, mutations.",
"First of all, cells do get these. Sporadic mutations happen all the time. They cause congenital defects so severe that the fetus spontaneously aborts (by some estimates, most pregnancies end in early miscarriage), they cause genetic diseases mild enough for the fetus to come to term but which kill in infancy or the childhood or teen years, they cause milder disorders which people live with throughout their lives or which have later onset, they're recessive and lurk in the background until you have kids with someone with a mutation in a similar or the same gene, or there's another gene which performs a similar function and picks up the slack. Sometimes, these mutations happen in the adult tissues and aren't passed on--and a fraction of those times, you get cancer. ",
"And the human genome as a whole is riddled with broken genes, even some which are broken in all people. These are often called pseudogenes, but they're the remnants of genes that used to work. For example, the ancestors of primates used to be able to make vitamin C. Long ago, in the lineage leading to primates, the gene was broken. Now we have to eat vitamin C or we get scurvy. "
] |
[
"Mutations that aren't useful don't have any advantage over other organisms, whereas directly useful mutations will lead to greater numbers of the recipient organism.",
"So the population of a species inevitably has useless mutations as a rarity, rather than an evolutionary debris. Besides, racking up too many would undoubtedly cause some harmful effects."
] |
[
"Based on the way you asked the question, I'm going to assume there are two issues you're not taking into account.",
"The first is that functional proteins are needed for survival and reproduction. If a protein isn't required, then yes, it will get mutated into oblivion. And you can see that in the genomes of species in cases where a certain gene became superfluous for one reason or another.",
"However, the vast majority of genes are needed for survival. Without a functional copy, the organism dies and doesn't spread its genes. Therefore, while deleterious mutations are more likely, you don't see them because they don't get passed on to future generations. This is what natural selection is based upon.",
"Furthermore, you need to consider the genome as a whole. It's expensive in terms of biological resources to maintain a large genome. Every time you need to replicate the genome, you need more nucleotides and more energy. Selection favors smaller genomes, so you won't have millions of nonfunctional copies for that reason alone.",
"And, without going into too much detail, there's an entire field devoted to studying why genomes look the way they do. For instance, sometimes organisms can simply double their genomes and become polyploid. If you look at these genomes over time (by looking at related descendents) you can see something interesting happening: fractionation. This is a process where one of those genome copies is preferentially degraded over time (like, lots and lots of time), and eventually you end up back at approximately the original state. There are lots of other cool things, but suffice it to say that useless stuff tends to get purged from genomes, especially non-functional genes."
] |
[
"Is there any evidence that \"sugar rushes\" actually occur?"
] |
[
false
] | null |
[
"But a change in diet might help with ADHD. ",
"NPR",
". ",
"Journal",
".",
"I've also read somewhere that eating candy can help you concentrate (temporarily, of course), essentially acting as a stimulant. Carbs also trigger the release of insulin, letting tryptophan through to be converted into serotonin and then melatonin, which makes you sleepy. "
] |
[
"But a change in diet might help with ADHD. ",
"NPR",
". ",
"Journal",
".",
"I've also read somewhere that eating candy can help you concentrate (temporarily, of course), essentially acting as a stimulant. Carbs also trigger the release of insulin, letting tryptophan through to be converted into serotonin and then melatonin, which makes you sleepy. "
] |
[
"In social psychology they taught us much of the supposed \"sugar rushes\" children have are actually due to the environment. For example, a child at a birthday party in a new environment surrounded by other children and activities will naturally be more stimulated, though parents usually fall back on the old \"the cake is making Johnny hyper\" excuse."
] |
[
"Do people dream while they are unconscious or in a coma?"
] |
[
false
] |
[deleted]
|
[
"I spent a little less than six months in a coma from December 1999 to June 2000. I basically felt the same as I would if I went to sleep one night and woke up the next morning (of course, when I did wake up I wasn't entirely convinced it really was the year 2000).",
"I don't believe I had any dreams either."
] |
[
"Fake answer: you've seen the end of Inception?",
"Real answer: they don't feel anything, in literature reports and my personal experience. The person I spoke to about it extensively described it as bewildering to wake up months in the future."
] |
[
"I wouldn't assume that she is blatantly lying, but what I find more likely is that her brain convinced her either just as she was entering or just as she was exiting the coma that she had been conscious for the duration, and had seen something miraculous.",
"Of course, it is very difficult to argue with personal experience, especially if the person is likely to reject science in favor of angels."
] |
[
"Can we fix the blind spot?"
] |
[
false
] |
I saw a billboard for the 2012 Camry that touted its "blind spot detection" technology. Is such technology even needed? Couldn't we just add a third set of mirrors positioned to give the driver a view of this spot? I put this in because I'm assuming this is somehow not possible due to some geometrical constraint. I mean, if it were possible...wouldn't auto manufacturers much rather make simple mirrors instead of relatively complex technology?
|
[
"You're right. You can even buy little stick-on mirrors that have a convex shape, allowing you to see the presence of something in the blind spot. But that doesn't sell cars. Telling people that they have a radar that keeps their family safe does."
] |
[
"I was afraid this would be the answer..."
] |
[
"I've used ",
"Multivex Mirrors",
" on one of my cars and they are awesome (although their website is awful). They are stick-on glass mirrors that are flat nearest to the car and curve as they reach the outside. ",
"Edit: formatting"
] |
[
"Few questions about the nature of conciousness, the process of thinking and the senses."
] |
[
false
] | null |
[
"See our FAQ on the topic.",
" All the best!"
] |
[
"Thanks! Should i remove the post?"
] |
[
"Nope, I already did. Also, if you delete your own posts it will make it more likely that your future posts will get marked as spam, so I wouldn't recommend deleting it."
] |
[
"Are some traits inherited more dominantly from either the mother or the father?"
] |
[
false
] |
Someone claimed that baldness was inherited from the mother, and to look for the trait one should look at the persons (boys) uncles on his mother's side. I have no idea if this is true - but if it is, or other traits are inherited either from the mother or father, which such traits are the ones most well-known? And how can it be?
|
[
"Someone claimed that baldness was inherited from the mother, and to look for the trait one should look at the persons (boys) uncles on his mother's side.",
"This isn't completely true, because baldness is polygenetic, but there is a scientific reason for saying this.",
"Most human chromosomes are the same in men and women. You have two of each of these. But X and Y chromosomes differ depending on sex. Men are XY (one X and one Y) and women are XX (two X chromosomes).",
"This matters because some important genetic determinants are encoded on the X chromosome.",
"Typically, a recessive gene means that the gene is associated with a loss of function of a gene product. In other words, the recessive gene codes a protein that doesn't work right. The good news is that you have a backup of that chromosome, and if it has a functioning gene, then you can still make that protein (half of it, but usually half is plenty). That is why carriers of recessive genes don't have the recessive trait.",
"With X and Y chromosomes, some recessive genes on the X chromosomes will affect men. This is because they don't have a second X chromosome. So if you have a baldness gene on your X chromosome, you don't have a backup. You are going to go bald.",
"So where does a man get his X chromosome from? He gets it from his mother (the father gave him his Y chromosome, and made him male). And where did the mother get her X chromosome? Well, she definitely got one of them from her father (the father didn't give her the Y or she would be male).",
"So, if a woman's father is bald, you know that she carries at least 1 copy of the baldness gene in her X chromosome.",
"Some examples of X-linked recessive conditions:",
"Multiple types of hemophilia",
"Duchenne Muscular Dystrophy",
"Red-green color blindness"
] |
[
"Mitochondria are solely inherited from the mother. Thus ",
"mitochondrial diseases",
" are inherited mother-to-child."
] |
[
"Very good answer, thank you!"
] |
[
"If protons become neutrons by the process of beta+ decay, how come a proton has a lesser mass than a neutron?"
] |
[
false
] |
As I understand it through the process of beta positive radioactive decay one element becomes another yet they have the same atomic mass. Ergo a proton becomes a neutron. In this process a positron and a neutrino exit the nucleus. Both of these have mass. Yet a neutron has a mass of 1.00727647u, a neutron has a mass of 1.00866491u, a positron is equal in mass to an electron therefore .00054858u. I don't know the mass of a neutrino I know they have mass. This math doesn't add up. Also as an add on why does a C12 have a mass of 12u when it has 12 nucleons and each nucleon has over 1u mass?
|
[
"A ",
" proton cannot β",
" decay into a neutron because of the mass difference.",
"The thing you're missing here (with regards to the ",
"C thing too) is that a nucleus is a bound state. Nuclei sit in a potential well caused mostly by the strong interaction. The potential is lower than the case of all the nucleons being free particles. Therefore a stable, bound nucleus has lower mass than the sum of free nucleons.",
"See ",
"binding energy",
"."
] |
[
"A proton can only decay into a neutron if it is more energetically favourable -- if the nucleus with the neutron would have less total energy than the same nucleus with a proton instead. This can happen because the proton also has electric charge and will repel other protons in the nucleus. The binding energy for the nucleus may be greater with the additional proton than with the neutron because of this.",
"So it ends up that the energy of the proton ",
" is greater than the energy of the neutron. This isn't always the case; it's generally only the case when the proton to neutron ratio is higher than a certain amount. If it is higher, then beta+ decay occurs and protons convert to neutrons; if it is lower than another certain amount, then beta- decay occurs and neutrons convert to protons. If it's between those two amounts, it is stable (at least with respect to beta decay).",
"Also as an add on why does a C12 have a mass of 12u when it has 12 nucleons and each nucleon has over 1u mass?",
"This is a good related question -- it's because the binding energy of the system is subtracted from the total energy of the system's constituents. The binding energy is the energy you need to add to the system in order to disassemble it. Since the disassembled system has greater energy than the bound system, the bound system ends up with less energy than the sum of its unbound parts. This difference in energy is called the \"mass defect.\" Different nuclei have different-size mass defects, and if there is a beta+ decay path from a nucleus with a large mass defect to one with a smaller mass defect, and the difference between the mass defects is greater than the difference in mass between a proton and a neutron, then the decay can proceed since the resulting nucleus will have a lower total energy than the initial nucleus.",
"Hope that helps!"
] |
[
"So for the mass we just have to plug into E=mc",
" and have mass be just another form of energy?"
] |
[
"Why is it that snowflakes are practically two-dimensional?"
] |
[
false
] |
Of course they aren't actually, that would be impossible, but why is it that the crystal grows outwards in two dimensions but not the third nearly as much? In other words, why are snowflakes nearly flat, rather than spherical or cubed or hexahedronal?
|
[
":",
"There are actually a bunch of other shapes such as needles and prisms, ",
"see here",
". These different shapes form under different temperature and water saturation. It just so happens that our atmospheric conditions often favour the formation of plates.",
":",
"Firstly, it's important to understand the bare crystal structure of ice. It looks something like ",
"this",
". The arrangement of molecules and their intermolecular bonds makes it into a hexagonal prism. This prevents some shapes such as cubes and tetrahedrons, because they lack the correct symmetry of the crystal.",
"Secondly, different faces of the lattice have different atomic spacings, different energies, and different thermodynamic stabilities. Water molecules attaching to the top/bottom of the cylinder and attaching to one of the hexagonal faces will experience different interactions. These interactions are favoured by different temperatures/pressures. Where axial growth is favoured, needles-like crystals are produced. Where lateral growth is favoured, plate-like crystals are produced.",
"Thirdly, the branches on a snowflake are formed because of more complex physics. The branches is also known as ",
"dendrites",
", which is observed in a range of metals and crystals other than ice. Dendrite formation is ",
" heavily dependent on temperature and pressure. These branches also grow independently of each other, which means the branches are usually not symmetrical.",
"Lastly, the ice crystal is not in equilibrium with its surroundings, and it heavily depends on how long it is allowed to grow, and many water molecules it can gather on its way down. This determines the size of the crystal. Low-lying clouds give snow, but some clouds can produce updrafts that send the initial snow-flakes up again to collect more water. As these crystals aggregate, their geometries become less distinctive, and eventually fall out of the sky as hail (spherical).",
"So, in summary:"
] |
[
"Can you expand on the lack of symmetry? I have always been under the impression that snowflakes often are (at least superficially) symmetric.",
"Furthermore, snowflake photography suggests that most snowflakes are more self-similar than they are to other snowflakes from the same cloud (",
"example",
" and ",
"example",
"). I understand that photographers will be biased towards more beautiful, symmetric images, but surely if the majority of snowflakes were not symmetric it would be more difficult to get these kinds of photos?",
"Other dendritic growth processes also show a little symmetry (",
"such as SCN growth",
") and some theoretical research suggests rotational symmetry should be common in dendritic growth (",
"source",
")."
] |
[
"The symmetry he's referring to, I believe, is on a very small scale, not referring to the whole snowflake, but to it's building blocks. ",
"Basically, you can only make certain overall patterns with a specific shape."
] |
[
"What is the strict difference between micro-evolution, macro-evolution, and speciation?"
] |
[
false
] |
[deleted]
|
[
"microevolution and macroevolution are extremes on a continuum of evolutionary change. MIcroevolution typically refers to changes in gene frequencies in a population over time scales that ",
" ",
" can measure. Macroevoution generally refers to large scale changes between species that occurs on geological time scales (millions of years). Speciation is the division of a single species into two (or more) subsequent species. "
] |
[
"Ring species",
" made all of your questions make sense to me when I first learned about them."
] |
[
"Conceptually, every species that has ever existed was new at some time. ",
"Precisely defining species and when they begin is challenging though because species are human constructs that are properties of populations (not individuals) over time, poorly defined (no one definition works for all species) and fluid (gene flow and interspecific hybridization occurs a lot). "
] |
[
"Could the theory of relativity have been proven without a solar eclipse?"
] |
[
false
] |
Einstein's theory took around 20 years to prove because they needed a solar eclipse and a clear sky with good equipment and so on, in order to test the theory. Could there have been any other way to prove it 100 years ago?
|
[
"Gravitational lensing",
" was another prediction but I believe this was harder to detect since it wasn't until 1979. ",
"Also check out ",
"Tests of General relativity"
] |
[
"The first laboratory test of general relativity - and, as far as I'm aware, the first test done without the aid of a solar eclipse - was the ",
"Pound-Rebka",
" experiment in 1959, which tested gravitational redshift (the phenomenon of light emitted in weaker gravity gaining frequency in stronger gravity). This is often described as having been done in a \"tower\", but the building it was done in is four stories, with an attic extension above the fourth floor and a loft above that; the experiment was done between the loft and the basement - 74 feet in all.",
"That was a whole 40 years after the first eclipse used to test GR (which in turn was only 4 years after Einstein produced his theory.)"
] |
[
"It's kind of amazing to think that the only reason Einstein was as famous as he was, is because we just happened to live on a planet that had just the right sized moon and an anomaly that happens every few years or so."
] |
[
"Very difficult-to-formulate question about how the human eye processes visual information: do we process things in order based on what we are focusing on rather than the entire field of vision?"
] |
[
false
] |
I want to try and explain this phenomenon a bit better (I'm not even sure if it's real or an optical illusion), so I'll be as detailed as I can. I'm experiencing something weird with reflected light and the way my brain is trying to process it and I'm not sure if there have been any experiments done that might address it. I am curious if this is due to how our brain evolved to use our entire field of vision while focusing on specific points and is basically limited by the amount of information it could process per unit time. I just read something about Eagles having a higher "Nyquist Rate" and wonder if that has any relevance to what I'm getting at here, but more on the software side and less on the hardware, if you get what I mean. The main reason I am asking is because of the potential applications for neuroscience and AI. Mapping the human mind based on how many bits of information we can process at a given moment, what we have to focus on, the stimulus/reaction delay for things in our focus vs. things in our periphery, etc. Thanks in advance for reading this long-winded and poorly-worded question, and if you need me to explain what I'm experiencing in better detail, I'll do my best.
|
[
"A few points of clarification... you're asking about your internal process of perceiving the stimuli? And that your focus seems to create an internal perception of de-synchrony?",
"I only ask because Potter and colleagues (2014) revealed that the brain can process and interpret images presented to the eyes for as little as 13 milliseconds. For simplicity, we'll round C up to 300000000m/s and we'll round 0.013 down to 0.010. So light going 30000000m/s for 0.010 seconds means you cannot distinguish visual onsets of light sources within 3000000m."
] |
[
"And that your focus seems to create an internal perception of de-synchrony?",
"Yes this. It's consistently de-synchronized as well, i.e. the timing between perception of Lights A and B flashing seems to be virtually the same. It's as if my mind is ready to process the information coming from the side that I'm focusing on, and is \"surprised\" by the light on the opposite side, causing a very minor perceived delay in its processing."
] |
[
"No expert in any of the topics mentioned, but any chance some of the differences noticed are due to there being more rods in the periphery of human vision which are more perceptive to light? One of the reasons averted vision is a technique used by astronomers to spot faint stars you cannot see when directly looking at them because of the higher cone to rod density in center focus of human vision. Just a thought"
] |
[
"What are those things floating around in my vision?"
] |
[
false
] |
I see little outlines of shapes in my vision, Almost exactly like when you look at organisms in a microscope. What are they?
|
[
"http://en.wikipedia.org/wiki/Eye_floaters"
] |
[
"Debris from several possible sources (such as collagen fibrils, remains of the hyaloid artery which appears and regresses during fetal development, clumps of calcium, blood cells that have leaked into the eye etc) in the vitreous humour that makes up the body of your eye casting shadows onto the retina. What is quite cool is often people that have them don't see them as the brain adjusts to ignore them. "
] |
[
"Thank you, This is exactly it!"
] |
[
"Could we use entangled photons to learn about the inside of a black hole?"
] |
[
false
] | null |
[
"Nope"
] |
[
"Care to explain why?"
] |
[
"You cannot send information with entangled pairs, black hole or not."
] |
[
"Oil is a huge potential source of energy, so why haven't bacteria been eating it all?"
] |
[
false
] |
It's frequently in warm locations/not necessarily that far down, but they haven't even eaten the accessible oil
|
[
"Metabolism depends on the existence of a gradient of chemical potential. There are organisms that can thrive solely on ferrous iron by exploiting its oxidation with aqueous oxygen. A large, highly reduced, organic compound like oil stores lots of energy, but in the absence of a suitable oxidizer there is no way to release that energy and no way for an organism's metabolism to function. So being that most oil forms where there is no significant source of oxygen, my guess is that oil-eating bacteria have never had a good enough niche in which to thrive. There definitely are bacteria that consume oil though, so what's left has been either inaccessible due to lack of oxygen or excessive heat/pressure, or simply existed in greater quantities than they could finish before we got our drills down there."
] |
[
"The biggest issue with oil metabolism is that it's difficult to break the C-H and C-C bonds of an alkane. This is simple enough when, say, operating a car, but life doesn't operate very well while on fire. In order to be useful in a biological sense, a useful enzymatic method needs to be employed to get a molecule's precious energy.",
"Fatty acids are quite similar to oil (alkanes) in that they're composed mostly of saturated carbon--that is, carbon saturated with C-H bonds. However, fatty acids have a carboxylic acid group at one end of the molecule, and this provides a \"handle\" for enzymes to grab onto (via coenzyme-A). This allows the fatty acid to be shuffled to the right places for the right chemistry to be done. In addition, this carboxylic acid chemically activates the cleavage of C-H bonds, lowering the energy barrier for oxidation of these molecules and thus energy extraction. Finally, this activation+handling allows for this oxidation to be done in a very controlled manner. Oil--simple alkanes--have no such \"handle\", and no such activator. They aren't easily oxidized in a controlled manner to generate chemical energy.",
"So, although energy-rich, alkanes aren't very easy molecules for life to work with, and evolution hasn't selected them to be workhorse energy molecules for anything other than Hummer-limousines."
] |
[
"Bacteria break down oil when it leaks out into more habitable environments...there are many bacteria which make their living breaking down oil at natural seeps (or manmade spills, for that matter) all along the floor of the Gulf of Mexico, for example. Oil eating bacteria are apparently are found down in some oil wells as well, where they can break the stuff down into methane. "
] |
[
"Do muscles burn more calories just by being sore?"
] |
[
false
] | null |
[
"Similarly, in what ways can your baseline resting caloric consumption be increased?"
] |
[
"Building more muscle will raise your BMR but I have no idea what percentage of a difference it actually makes. This is actually what led me to find out if a sore muscle burns more calories than a resting one. "
] |
[
"Muscle tissue does require more energy for upkeep than fat tissue, but the difference is not that great as some people like to believe. It's pretty much impossible to measure exactly, but you have to put on a few kilos of muscle tissue to make a statically significant difference."
] |
[
"Andromeda Collision"
] |
[
false
] |
I've been told that the Milky Way is on a collision course with the Andromeda galaxy, but I've also heard that all the galaxy's are moving away from each other, how does this work?
|
[
"Cosmological expansion only causes things that are already sufficiently far apart to expand away from one another. For things that are relatively close to one another, like the galaxies in the Local Group, the behavior is much more closely approximated by the standard picture of attractive gravity.",
"In other words, gravitationally bound systems (like galaxy groups) don't experience cosmological expansion. It's only when you consider widely separated galaxies that you find the distance between them increasing due to expansion."
] |
[
"Basically the gravitational force is much stronger than the expansion force of the universe. Only if the distance between two objects is sufficiently large, then the objects will move away from each other.",
"In billions of years our cluster of galaxies will be the only thing visible to us in the sky. Without a telescope there wouldn't be much different as the stars keep are kept together by gravity.\nThe galaxies that are far away will have moved so far away that we can't see them anymore."
] |
[
"Maybe less. ",
"We can still see back 13 billion years ago, to when the first galaxies were forming."
] |
[
"Why does the tip of a javelin tilt towards the ground when reaching the ground?"
] |
[
false
] |
Hello reddit, I watched the olympics yesterday and saw some javelin throwing. Now the thing that puzzled me a bit is that the tip of the javelin at the beginning of the flight (when it's released by the athlete) points towards the sky. But during flight the javelin tilts to the front and at about its maximum height it's completely horizontally. After that point the javelin's tip tilts even more to the ground so that when it finally hits the ground, the tip goes in first. With my (vey basic) understanding of physics I would have thought that every part of the javelin is accelerated to the ground with the same force. Thus the relative position (tip higher than the rear part) shouldn't change during the course of the flight. Obviously this is not so and I read somewhere that the tip was made heavier than the rear part in order to make the javelin descend faster. Can you tell me where I am wrong or what other forces I am missing in my understanding of the flight? Kind regards
|
[
"That's not how gravity works."
] |
[
"Because of ",
"pitching moment",
". The tip does ",
" always tilt towards the ground though, if it's a bad throw."
] |
[
"Yes that's the perfect explanation, my beef with the parent comment is that it didn't explain why (center of gravity in front of center of pressure) but instead just said that there was a pitching moment, which doesn't explain anything. Also, the wiki page involves aerodynamic center and other aerospace jargon which doesn't apply to this much at all and would only serve to confuse the OP. "
] |
[
"How plausible is the idea/concept that someone might die (or whose death my be accelerated) by heartbreak?"
] |
[
false
] |
Also: Do you know that feeling you get in your chest/heart when something emotionally damaging occurs? Sometimes you'll think of a really sad thought and you don't cry but your heart feels almost like it's tightening/collapsing into itself. What is biologically occurring when that happens? Is that a direct link to emotional processes that transpire in the left side of one's brain, or is your brain fooling you into believing that your chest is tightening? Though the question may raise some concern, please know that I only ask out of curiosity. I'm recovering from depression, but I'm at a really good point in my life at the moment - so no worries needed here!
|
[
"Extremely plausible",
"http://scienceline.org/2006/08/ask-schrock-heart/"
] |
[
"Question: Could this be related to the stories in medieval legends where maidens would 'swoon and die'?"
] |
[
"Thanks!"
] |
[
"What environmental factors affect hair color?"
] |
[
false
] | null |
[
"\"Nature vs. nurture\", I love it!",
"In addition to the obvious example of sun bleaching, I have heard that the food you eat can affect your hair color. We have two pigments that determine hair color, one for black / brown hair and one for blonde / red hair. Your hair color depends on the different concentrations of these two pigments. The concentration is affected by the breakdown of certain amino acids (unfortunately I don't remember which one). My point is that certain foods contain more of this amino acid than others, and if I understand it correctly, this is what happens when the hair gradually changes color.",
"I see now that this was pretty pointless since I don't remember any of the details, I'm sorry"
] |
[
"That's a more interesting answer than I expected. I'm at work now but I'm going to look into it more. "
] |
[
"okay, tell me if you find out. this has made me more curious than I first thought:P"
] |
[
"What happens at the source of carbonated bubbles in a glass?"
] |
[
false
] |
[deleted]
|
[
"The bubbles form at spots of leftover bits of dust or grime or whatever that didn't get cleaned off fully. The cleaner the glass is, the fewer bubbles you will see.",
"Bubbles have a hard time forming on glass itself because the CO",
" doesn't have anything to \"stick\" to in order to form a bubble. The CO",
" will come out of the drink whether there are bubbles forming or not, but for a bubble to form, you have to get a bunch of CO",
" to sit in the same place, which is hard to do on a clean glass surface.",
"In other types of cup, especially the cheap plastic ones, you can see bubbles sticking to the side of the cup but not going up. This is because the coating they use is hydrophobic, so the liquid prefers to \"stick\" to a bubble than to the side of the cup. I believe that bubbles can form on plastic surfaces because plastic is generally less \"smooth\" than glass, so bubbles can coalesce in the little imperfect spots."
] |
[
"Pint glasses in Pubs in the UK have a bunch of nobbly bits on the bottom (not glass) so the bubbles form there and stream all the way to the surface making it look a nice lively pint...."
] |
[
"Those spots are so-called \"nucleation points\", which are usually small scratches or pieces of dust. The CO2 forms there because it is able to \"stick\" there more easily than the rest of the glass. The next time you drink a fizzy beverage, try sprinkling a little bit of sugar inside. The sugar provides nucleation points for the CO2, and causes it to bubble up a little. This is also why mentos cause fizzy drinks to bubble over."
] |
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