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[
"Why does the interaction between two magnetic fields creates force?"
] |
[
false
] |
like the force between two magnets
|
[
"Do magnets work this same way? I understand the intrinsic magnetic moments of the atoms that align and create a magnetic field, but how do they interact with other magnetic fields?",
"Edit: I'm sorry if im not being very clear"
] |
[
"I think I understand you clearly. The answer is that the electron magnetic moment also feels a force due to an external magnetic field. In a permanent magnet, where the moments all align, the whole magnet has a net magnetic moment, and this moment feels the force. It might help to consider the magnetic moments as tiny current loops, and a current loop will feel a force due to an external magnetic field dependent on their relative orientation.",
"Doing any calculations on this becomes extremely messy, but thinking of bar magnets as effectively being current loops gives you the correct qualitative picture."
] |
[
"The Wiki article on the ",
"force between magnets",
" covers the basics and can lead you to more advanced topics. I mostly think about the problem in terms of ",
"magnetic dipoles",
".",
"If you know some physics/vector calc, I could direct you to lecture notes: ",
"http://farside.ph.utexas.edu/teaching/em/lectures/lectures.html"
] |
[
"Are there any inherent issues with using tank tracks at high speeds?"
] |
[
false
] |
Are tracks inherently limited to relatively slow speeds due to mechanical issues or is it more because the vehicles themselves are heavy? Even the fastest tracked vehicles such as the M18 Hellcat, the BT-7 or the FV 107 Scimitar weigh multiple tons due to armor, armament and other equipment. The question is, would it be feasible to create a "tracked sports car" with a lightweight chassis, a powerful engine and not much else to weigh it down or would issues with the tracks themselves (friction? wear?) effectively limit its speed?
|
[
"Googling a bit, I noticed the ",
"Ripsaw",
" unmanned light tank---apparently the prototype can do 0-65 mph in 3 seconds, and and according to ",
"this article",
"The original speed goal for Ripsaw was approx. 80mph, but the Howe brothers have discovered that driving UGVs remotely can get scary and precarious at speeds above 50mph. According to Geoff Howe, 50mph is scary enough, and they don’t see a tactical need at present to go faster with a UGV, although that decision would ultimately be up to the U.S. military if they adopt it. ",
"So it seems at least the designers thought that 80 mph would be possible for a tracked vehicle."
] |
[
"I think this question assumes a cause and effect relationship between using tracks and going slow in a massive vehicle. There is a relationship between them, but I think it goes the opposite direction that you seem to think.",
"The reason to use tracks instead of tires is to spread the force from the weight of a vehicle over a larger contact area. A larger contact area means there will be less pressure on the ground, and so you'll be less likely to dig yourself in when traveling over soft ground.",
"The reason not to use tracks is that they're massively less efficient, both in terms of rolling resistance, and in maintenance burden. Both of those are mostly due to complexity, as a track system will have many more moving parts than a set of wheels and tires.",
"So a vehicle designer will usually prefer wheels over tracks, if they're at all practical. You only need tracks if you're supporting ",
" of weight (as with, say the NASA launch pad crawler vehicle that carried the Saturn V and Space Shuttle) or if you're operating on very soft ground (like a lot of construction equipment and snow grooming machines). Armored military vehicles like tanks are in both categories, as they're heavy due to their armor, and the need to be able to go off road in bad conditions."
] |
[
"Last part should be F=ma to accelerate the tank or apply a force to overcome resistance would be a lot more than the road could take. E=MC",
" only come into play if the tank approaches light speed."
] |
[
"Killing germs..."
] |
[
false
] |
I don't have much info on this topic but I would like to know what happens after a germ is dead? Does it have a body and if not what is it? Lastly if it does then what happens to the body?
|
[
"To add to what's already been said, the act of killing pathogens in your body can result in more disease. One example is the ",
"Jarisch-Herxheimer",
" reaction, in which the rapid lysis of spirochete bacteria results in toxin release and subsequent fever/chills/myalgias from inflammatory cytokines."
] |
[
"Yes, it has a body. If the bacteria are killed inside an organism (like a human, for example), they will be eaten by some specific immune cells and decomposed by some enzymes that they synthesize. This is called phagocytosis. If the germ is killed outside the body, by using alcohol, for example, it will also break down and probably be wiped away, or eaten by other microorganisms, like house dust mites."
] |
[
"There's a body, kind of, generally, like a popped balloon. The membrane of the bug will probably hang around a while, as will the cell wall. The internal components will generally leak out into the environment as the membrane and wall break down. Most of the \"stuff\" will either get dispersed, react with other things in the environment (e.g., oxygen) or get eaten by scavengers. ",
"Your body will still respond to the bacteria \"corpses\", too. There are chemical signals on the cell wall, membrane, and internal components that will trigger inflammatory responses even after the bug is long dead."
] |
[
"Are dolphins afraid of death? Or, are other species aware of their own mortality?"
] |
[
false
] | null |
[
"The short answer is that we're really not sure. Some researchers say that evidence suggests that some species do, while others claim that we are just anthropomorphizing them. The two big problems associated with this question are 1) death is not observed in the wild very often, so it's hard to gain a lot of reliable data and 2) it's very hard to understand what an animal is thinking or feeling without being able to truly communicate with them. For example, if you were an alien researcher sent to study whether or not humans could comprehend death, and to you our language was just a series of grunts, would you ever really be able to find out just by observing our behaviour after a death occurred? Some funeral practices, such as ",
"famadihana",
" performed by the Malagasy people, would even suggest that we don't. That being said, there is some evidence that some species may at least understand that death is a sort of final parting, and have ",
"some kind of awareness of death",
" . ",
"Chimpanzees were seen to give pre-death care to a dying female, check for signs of life after death, and then exhibit mourning behaviours ",
"[1]",
". Dolphins have been shown to exhibit different behaviours depending on whether or not the death was sudden (i.e. killed by another animal) or after illness ",
"[2]",
". Elephants have been shown to pay homage to deceased members and even have what coud be considered funerals ",
"[3]",
". Of course none of these behaviours definitely mean that these animals can fully comprehend and understand death, but they do suggest that there could be some understanding in other higher order, longer lived species. "
] |
[
"I'd like to extend this with a question as well. If they aren't, why do they feel fear when something attacks them?"
] |
[
"We can't really know what another creature thinks, feels, or understands, until we can communicate effectively with that creature. We can guess, and anthropomorphize, but there is no way to know. Luckily, we have finally gotten off our high horse enough to realize other species might be worth communicating with. We may know, someday."
] |
[
"I have a question about double-blind experiments"
] |
[
false
] |
So the way I understand it, the purpose of a double-blind experiment is to prevent the experimenter from hinting at the "right" answer to the subject. How can he hint at information he doesn't know? But then I thought, well, that almost makes the experimenter his own "subject"; he has to get the vials from someone. Would that someone not be able to telegraph information just as easily? If the only one who "knew" which was which was a computer, that would certainly alleviate my concern, but in cases where that's not possible, do my concerns even have merit, or am I missing something? Is there a certain amount of information hiding that's just considered "good enough," even if it's not perfect?
|
[
"The whole point about double-blind experiments is exactly that - the experimenter cannot \"hint at information he doesn't know\".",
"Now it's possible that when the researcher gives two bar-coded drugs to the experimenter, he'll say \"be careful with the one on the left, it's expensive!\" But normally that's not the case. The researcher can just drop off the vials in one envelope, each with a bar code. All the experimenter can deduce from that (or any subconscious signs) is that something expensive is in those envelops.",
"If you ",
" want to be careful, don't even be in the same room as the experimenter. Tell him to pick it up from a secure box.",
"At any rate, this one degree of removal from the subject is often enough."
] |
[
"he has to get the vials from someone. ",
"He doesn't have to interact with that person, though. They could just label and package the vials, and leave them on the experimenter's desk."
] |
[
"Check out the ",
"wikipedia article",
" for some more info on this."
] |
[
"Is the fabric of space-time fixed or fluid?"
] |
[
false
] |
As far as I can tell there seem to be three competing theories as to the microscopic structure of the fabric of space-time: lumpy (quantum packets of energy), silky (strings) or foam (quantum foam). Some (e.g. Einstein) argue that there is no such thing as a "fabric" at all, even though this is always the preferred visualisation (e.g. space-time expanding from the Big Bang, ripping in the Big Rip, planets curving the sheet of space-time etc.) Now, do particles with mass (e.g. me) move THROUGH (swimming in a pool), or ON the hypothetical fabric (a projector image on a wall)? E.g. I recall string theory saying that a particle is just a specific vibration of a string. When the particle moves, is the string moving with it, or is the vibration passed to the next string? (I guess this basically comes from the "flatland" visualisation, where I always took Mr. Flat to be moving on the stationary background fabric.)
|
[
"The fabric is just an analogy. There's no actual fabric."
] |
[
"Ok, so that means I take my strings with me wherever I go?"
] |
[
"As ",
" notes, it's not really a fabric. The way we actually describe spacetime is by noting the distance between two neighbouring points in a particular region (this is called the metric, and can be considered to be a function of two points in spacetime).",
"You might expect the distance between two equally separated points to be the same no matter where you are in spacetime, but that's not the case. You might also wonder if our choice of co-ordinates affects this distance - the answer is it doesn't, because the metric itself changes under changes of co-ordinates.",
"You might wonder what counts as neighbouring - they can't be overlapping, but I mentioned they must be in a particular region. Thanks to calculus and smooth functions, this has a well-defined mathematical meaning, the two points should be infinitesimally close.",
"And finally, you might wonder what I mean by separation of points - the distance between two points in 3d space is easy to understand, but in 1 dimension of time and 3 dimensions of space (or, (3, 1)-spacetime for short)? First, points in (3, 1)-spacetime are events. The quantity the metric measures has physical significance as the time a clock would register if you moved from one event to the other",
" (no matter how you got there).",
": assuming it was possible to do this movement without travelling faster than the speed of light. "
] |
[
"Do your nerves send a message to your muscles directly when you experience pain?"
] |
[
false
] |
I attempted to look this up but wasn't having a very lucky Google day. I remember reading that when your nerves "sense pain", it's almost as if they bypass your brain completely and will send a message like "MOVE YOUR HAND OFF THE HOT PAN" directly to the muscles. It makes sense because when you experience pain it's as if your body reacts automatically. Is there validity to this?
|
[
"Yeah, it's a reflex arc. Pain is sensed by your peripheral nerves, these sensory nerves then synapse in your spinal cord onto motor neurons, which in turn go back to the muscles and contract them to draw them away."
] |
[
"This is exactly it. You have some neurons that go directly to your spinal cord (or in some cases, skips the spinal cord entirely), synapse (connect) on another neuron (called an interneuron) which then a) sends a signal to the brain letting it know something's going on and more importantly b) sends a signal (via yet another neuron) to your extensor muscle to chill the fuck out and another signal to your flexor muscle to kick itself into gear. That's your simple withdrawal reflex and also explains why you withdraw from a stimulus before you even feel pain. (\"Oh shit that's going to hu- ow ow ow\"",
"While we're at it: rubbing an area that's painful actually does help, because it generates more action potentials (the things that basically run the whole show) which act to inhibit (basically drown out) the other ones being used for pain. "
] |
[
"Thanks for the input."
] |
[
"They say that to test String Theory, we need to build a particle accelerator as large as out galaxy. Is it a technical limitation or a fundamental one?"
] |
[
false
] |
[deleted]
|
[
"It's a little of both. With how we currently probe high energy regimes, there is a fundamental limit to the energies we can obtain from collisions, related to accelerator designs (including size). But it is, pedantically, a technological limitation, because the science doesn't say \"the only way to test string theory is to use your current understanding of accelerator physics to build a very large accelerator,\" rather it says \"if you want to avoid building a very large accelerator, you need a breakthrough in how you probe very high energy regimes.\""
] |
[
"There's wakefield accelerators, which are smaller and way more efficient. They work by using a laser pulse to create very strong electrical fields in plasma. Electrons then ",
"surf this wake",
" to very close to the speed of light.",
"That can't test string theory, but a GeV particle accelerator that fits in a single room is kind of neat. "
] |
[
"\"if you want to avoid building a very large accelerator, you need a breakthrough in how you probe very high energy regimes.\"",
"Are there any breakthroughs being made in that regard?"
] |
[
"If a woman's on birth control that stops her menstruating once a month, will she remain fertile for longer?"
] |
[
false
] |
My girlfriend is on a birth control regime where she only menstruates once every three months. From what little I understand of fertility in women, you've got pretty much a set number of ova and once you run out, you hit menopause and can't conceive. Since she only has 4 periods a year instead of 12, does that mean she'll hit menopause later?
|
[
"That makes sense biologically (and is why nulliparity is thought to contribute to earlier menopause). However, this is not always supported by epidemiological studies. ",
"This study",
" found that history of oral contraceptive use significantly ",
" the risk for ",
" menopause (defined here as prior to 49yo), while parity did not.",
"Ever-users of OC in our study had a mean age at menopause of 45.7 years (SD 6.00 years) while never-users' mean age at menopause was 47.2 years (SD 5.50 years).",
"It goes on to explain:",
"It is known that OC use and pregnancy disrupt the ovulation cycle. Whether this contributes to a later age at natural menopause is disputed. We found that ever-use of OC was significantly associated with early rather than later natural menopause. We have no obvious explanation for this finding, thus it is important that others investigate this. A Dutch cohort study found that ever-users of OC had a significantly later natural menopause than never-users (mean 51.2 years, SD 3.29 vs 50.1 years, SD 4.16; P < .01). In contrast to these findings, the Massachusetts Women's Health Study did not find an association between ever-use or duration of OC use and age at menopause."
] |
[
"So essentially the answer is \"No, but we're not sure why\"? "
] |
[
"This isn't true, contraceptives can prevent menstration as well. They essentially trick the body into hormonally thinking it's already ovulated, and perhaps even implanted, so it won't shed the lining of the uterus until the dosage is stopped or changed. Hence why the most common OC schedules include a week of placebo, or no pills."
] |
[
"Is it known when/where Rh negative people first appeared, or have they always been around?"
] |
[
false
] |
I stumbled upon a clickbaity article claiming that 'Rh negative people are aliens' and a bunch of other nonsense, so I started looking around and it turns out there isn't much info online about the 'genealogical history' (probably not the right technical term for it) of Rh negative people. A quick look at the Wikipedia page for tells me it's mostly European lineages that are Rh negative, so intuitively I would think that a mutation occurred in Europe at some point, but this is really just a guess. Is there currently any consensus about this?
|
[
"There are theories out there that Rh negative individuals have overactive immune systems which help to protect them against some viruses. An evolutionary advancement maybe? But on the other hand, that same overactive immune system can lead to autoimmune disorders. You can't win for losing."
] |
[
"Do you have any peer reviewed sources for this? "
] |
[
"Can you prove it?"
] |
[
"Even though we see different structures at different spatial scales of astronomical observation, why do many of us believe cosmological models which inherently assume homogeneity and isotropy?"
] |
[
false
] |
Been a while since I read about FLRW cosmology, but this question bothered me then. Am I wrong and people don't believe these models anymore? I know background radiation has the properties mentioned in the question, but aren't cosmological models supposed to be global descriptions? Clarification would be great thanks!
|
[
"Because we do see homogeneity and isotropy on the largest scales, larger than about 100 Mpc.",
"The simplest example is the cosmic microwave background. It looks like ",
"this",
". It's full of structures, spots that are hotter or colder than the average. But they're only hotter or colder by about a part in 10,000. If we had a more honest color scheme, it would actually look more like ",
"this",
". The CMB is pretty much entirely 2.725 K, with only the tiniest of fluctuations on top. If you're interested in a more rigorous test of the CMB's isotropy than \"look at the map!\", here's the ",
"Planck 2013 result",
". (Planck's released updated versions of most of its papers this year, but this one still not yet. From what I hear that paper is imminent, and since it's taking so long it might be that there's some interesting news, so stay tuned on that front.)",
"We've also been able to test homogeneity and isotropy for a few decades with large-scale structure, i.e., with the distribution of galaxies. Pretty much every search for deviations from homogeneity and isotropy comes up empty; see ",
"here",
" for a recent example, and ",
"here",
" for a review."
] |
[
"Beyond a particular scale (known as the end of greatness, about 300 million lightyears), large scale structures from smaller scales are effectively homogenized and isotropized. ",
"Basically the term \"large scale\" is very relative in this context. The structure is large scale when compared to our own galaxy, but not large scale when compared to the observable universe."
] |
[
"This",
" is a helpful graph. Even before the CMB we can see the strength of structures starting to flatten out at large sizes."
] |
[
"If I'm moving in a circle or an ellipse, am I changing direction? If so, am I expending energy?"
] |
[
false
] | null |
[
"Yes, it’s changing direction, but its energy is not necessarily changing."
] |
[
"But how is it possible to change direction without expending energy? Doesn't that involve doing work?"
] |
[
"Nope. Changing direction without changing speed doesn't change the energy of the object (assuming there's no direction-dependent potential energy).",
"As for work, the infinitesimal work done in some infinitesimal amount of time is equal to the dot product of the force and the displacement. For an object moving in a circular orbit in some central potential, the force and the displacement are perpendicular, so the work done between any two moments in time is zero."
] |
[
"How has the magnetic reversal of poles affected the evolution of life?"
] |
[
false
] |
This has been asked by someone else, but the answers were rather unsubstantial and not particularly well-sourced. Anyways, during physics class today we discussed how the the magnetic poles reverse and how it occurs every 700k years. We also discussed how during such a reversal, the radioactivity going through atmosphere would increase. In addition to this, we also discussed how certain animals use magnetism to know where to migrate to. So my question is this: wouldn't this reversal increase the mutation rate of evolution (due to the change in the atmosphere) and wouldn't it disrupt many migrating animals? And, if so, what kind of affect has this or hasn't this had on the evolution of current animal life?
|
[
"There is certainly speculation about what happens to the biosphere during magnetic reversals, where the Earth's magnetic field can drop to about 10% it's current strength. The increased impact of energetic particles on the biosphere during reversals is considered negligible by most, as the main shield against harmful radiation of solar and cosmic origin is the atmosphere, not the geomagnetic field/magnetosphere. However, it is thought that secondary effects may have a more profound impact on conditions for life, including holes in the ozone and increased cloud formation.",
"Most studies that I have read trying to link reversals to mass extinctions have come up with inconclusive results. Apparently, we just don't see a great correlation between extinctions and reversals, and there are usually better explanations for the extinctions.",
"Good source/further reading ",
"here",
".",
"As far as migratory animals goes, I am not sure what the effects would be. Speculation: The geomagnetic field changes in strength and orientation reasonably significantly even during polarity chrons, so animals which use magnetic fields for navigation have probably evolved the ability to supplement their abilities with other migratory techniques, which might help them during reversals."
] |
[
"There has been speculation that species origination rates would increase during reversals; but the record isn't really good enough to prove disprove it. In theory, more ionizing radiation coming through the atmosphere will increase the rate of mutation.",
"Basically, the increased proposed rate of extinction may be matched by increased speciation. ",
"You are definitely correct that there isn't anything in the literature that provides strong correlation between the two."
] |
[
"the magnetosphere handles extra bursts of radiation, like in solar flares and wind. but common constant radiation bombardment is handled by the atmosphere, like you said."
] |
[
"How can solid or gaseous elements by themselves become electron donors? Can shining light on the element or any other feasible process actually work? Can we bypass the electron affinity energy requirement and have the electrons donated?"
] |
[
false
] |
[deleted]
|
[
"produce electrons",
"It's not quite accurate, the electrons are excited by light and released from the atoms.",
"But yes, depending on the definition of \"light.\" X-ray photons will certainly release electrons from many things including noble gases. See: ",
"https://en.wikipedia.org/wiki/X-ray_photoelectron_spectroscopy"
] |
[
"Absolutely, there ",
" ways to calculate how much (actually, which wavelength) of light is needed to ionize (eject) an electron from a given element/molecule. Experiments exist too, like the above mentioned X-ray photoelectron spectroscopy (XPS).",
"Edit: The wavelength of the incident light decides if you're able to eject electrons. The RATE at which the light arrives (the number of photons per unit time) dictates how many electrons you can eject (if any)."
] |
[
"Thank you! So there could also possibly be a way to calculate how much radiation and light would be needed, in order to eject electrons from let's say, oxygen, correct? So we could still apply this to a non-metal in order to be properly aligned with the photoelectric effect."
] |
[
"Why does biology \"not make sense\" without evolution?"
] |
[
false
] |
I've often read this in articles about why evolution is true, but no one really explains why this is so. How does biology as a whole fall apart without evolution?
|
[
"I'm not sure how to properly answer this as I'm not really sure what you do or don't know so I'll go as simply as possible.",
"I think what the statement means, in it's current usage, is a lot of the things we understand about animals, plants, etc make sense when viewed through the framework of evolution. For instance, every critter on earth uses the same genetic code, coding for more or less the same amino acids (there are a couple of exceptions that have more than 20 aa), this makes perfect sense in light of evolution and descent from a common ancestor. Without it, there is really no good reason why this would be true. Or take the premise that every protein, or chain of proteins that are used in our bodies are made up of smaller protein bits (motifs) or proteins that are used elsewhere. This makes a lot of sense when you look through the evolutionary perspective that each pathway/protein is built out of bits and pieces of other pathways/proteins. Without evolution this really doesn't make sense.",
"Or look at the species level. Australia has a bunch of mammals that use old school (evolutionarily speaking, the baby half develops then crawls up to a pocket to fully develop) methods of birth. This makes sense in light of evolution (Australia was isolated for a very long time). This does not make a lot of sense without evolution. (You could argue that a 'maker' optimized them to Australia, but then why are rabbits kicking their asses).",
"Or look at physiology, the panda's thumb, our tails, or whale's feet bones. All of these make sense in light of evolution, without it, why would we have a bunch of useless (but mostly harmless) bits just chilling out. (Especially, when you look at DNA, there is a HUGE amount of DNA that seems to do nothing more than space things properly and a lot of DNA that is almost certainly just viruses that got stuck in our DNA.) ",
"Or look at non-optimized processes, human birthing is really hard and often fatal, so is hyena birthing. This makes sense in light of an evolutionary process that has not really had time to optimize such things, it really doesn't make a ton of sense otherwise.",
"Evolution has a ton of explanatory power, it explains how many things exist and allows us to understand the relations of proteins, genes, and species. It gives us a frame of reference in which most of biology is built. If you pulled away the frame, none of the relations or links between animals would make sense. If evolution were magically eliminated, all these links and understandings wouldn't make sense."
] |
[
"Because there is a metric ton of whack \"design\" in biology, like the fact the the eye in vertebrates has a blind spot because the vein passes through the retina rather than being attached behind it. This is, we know now, a result of the repurposing of an earlier structure rather than an intentional design feature, which is evidence for evolution, as is the fact that it differs between vertebrates and invertebrates (the latter of whom appear to have inherited a better variation). Take evolution out of the picture and you'll be left scratching your head trying to make any sense of how this situation could have come about.",
"Biology is littered with similar examples, vestigial structures, and all kinds of other \"evolutionary baggage\" that really only make sense in an evolutionary context -- individuals inherited slightly modified structures, but not in any \"optimal\" kind of way. Once you know a few of these facts, any notion of \"intelligent design\" seems completely ridiculous.",
"So you start thinking in terms of evolution and all these little seemingly unexplainable things start falling into place along with all the big things like: How do species arise and why are their structures (fins, wings, hands) so structurally related? Why did some species survive while others did not? It opens up a vista of understanding that is not accessible through any other viewpoint, and you start to see that evolution is what makes everything we observe in biology sensical. Then you realize that evolution is indeed the fundamental and unified theory of biology, and that without it, seemingly none of our observations make any sense."
] |
[
"We aren't very certain about gravity, or how or why it it exists. we just know we can measure it and know how it effects some things.",
"You've just described ",
". There's nothing about gravity that's more mysterious than any other phenomenon."
] |
[
"How big would LaGrange Point L4 (or L5) be... Are we talking 100s of metres or miles?"
] |
[
false
] |
I've read that they are like a gravity bowl, catching dust and trojan asteroids. Just wondered how 'big' would this bowl be? Seems like an ideal place(s) to build a massive space station.
|
[
"The Lagrange point itself is just that - a point, of zero size, but the L4 and L5 points are special in that there can be stable orbits around them. The points are ‘hilltops’ of maximum gravitational potential, which does not sound stable, but due to the orbital dynamics, when it starts so ‘slide’ off the hilltop in one direction, the nature of orbital dynamics makes it come back, allowing satellites to achieve Lissajous orbits without needing to expend any energy on stationkeeping. ",
"A bit more detail on the stability of the orbit: suppose that the satellite started to ‘slide’ off in the prograde direction - this would result in it gaining velocity, but in an orbit, a gain in velocity causes the size of the orbit to increase, and larger orbits take longer to complete a revolution, so the satellite does not escape, but rather moves in a stable (though complicated) path around the Lagrange point, forming a Lissajous orbit. This same correction happens whichever direction off of the Lagrange point the satellite goes, so if the satellite has a small enough velocity relative to the Lagrange point, it remains ‘trapped’."
] |
[
"How large can the orbit be? "
] |
[
"I don’t know any hard numbers, but very large. For example in this ( ",
"https://commons.m.wikimedia.org/wiki/File:InnerSolarSystem-en.png",
" ) image of the asteroids orbiting Jupiter’s L4 and L5 points (they are the green ones) it is apparent that they are very widespread, so it seems that as long as there is not too much excess energy to eject it from the orbit then it can stay in that orbit out to a very large distance. Of course, this depends on how big the host bodies are in comparison to other bodies in the vicinity. Jupiter can maintain them out to a large distance because it is the biggest planet - the inner planets exert only a slight perturbation on Jupiter’s Trojan asteroids due to their small mass, and the outer planets are rather far away to exert much of an effect."
] |
[
"I read that when the light of Betelgeuse’s anticipated supernovic explosion reaches earth, it will create two weeks of perpetual daylight. Is this true, and if so, will that have any lasting effect on fauna?"
] |
[
false
] |
[deleted]
|
[
"it will create two weeks of perpetual daylight",
"That's definitely a huge overstatement.",
"Betelgeuse currently has an apparent magnitude of about 0.5 (though it's somewhat variable), and an absolute magnitude of about -6 (how bright it would be if it were 32.6 light-years away). Betelgeuse will likely become a Type II supernova, which generally have absolute magnitudes of around -17. ",
"That means Betelgeuse will increase in brightness by 11 magnitudes (about a factor of 25,000x), so from our perspective on Earth, it will increase from magnitude 0.5 to -10.5. That's definitely bright, but for comparison...",
"The Sun is magnitude -26.7, so a Betelgeuse supernova would be some 3 million times dimmer than that. ",
"The Full Moon is magnitude -12.7, so a Betelgeuse supernova would be some 8 times dimmer than that.",
"Now an apparent magnitude of -10.5 is bright enough to cast very faint shadows at night (much the way a near-full moon can), and you could spot it in the daytime sky as a dot in the blue sky, but it's nowhere near the brightness to create \"perpetual daylight\"."
] |
[
"The Sun passes approximately 16° north of Betelgeuse around the end of every June. If Betelgeuse goes SN in June, we won't get to see much at all. Even at magnitude -10, that's just too close to the Sun. ",
"If it occurs at any other time of our year, it will be visible as a modest white dot in the blue sky during daytime, and a blazingly bright object (hundreds of times brighter than Venus) after sunset, or before sunrise."
] |
[
"Betelgeuses arc in the sky is roughly the same as the sun. So yes, if were it in line with sun at the time of its explosion then you would mainly see, at best, just a dot in daylight. Ideally it will arrange to explode when it's at the complete opposite."
] |
[
"Electromagnetic induction - Alevel stuff."
] |
[
false
] | null |
[
"Just being more precise: The aluminum ring originally experienced no magnetic field. The magnetic flux was zero. When the AC supply is turned on a magnetic field is created. Now you said yourself that a change in flux causes an induced emf. Lenz's law informs us that this induced emf causes a current whose magnetic field opposes the change in magnetic flux. When the AC supply causes the field to flip directions, the induced emf will also have to flip to oppose this new change in flux. Ad infinitum.",
"if it were just a dc supply the ring would jump then fall back down. Internal resistance would eventually eat up the current. with ac the fields keep switching."
] |
[
"The electromagnet is hooked up to an AC supply: that causes the field it generates to alternate (since the direction of the current alternates). That in turn creates a change in flux through the aluminum ring, which causes the levitation."
] |
[
"It's because the B field was initially 0. So, the flux, B*A = 0. When you apply the AC current through the wire loop you generate a B field so the flux is B*A (where A is the area inside the aluminum coil). Hence change in flux. ",
"The reason why the current is AC is because if it were DC then the induced current in the ring would eventually die off due to resistance and settle on the wire coil. With AC, the B field is always changing so this doesn't happen. The current does decay but very quickly the whole system changes and a new current in the opposite direction is induced.",
"The iron core just magnifies the field. For the purpose of physics ignore it. It's just an engineering thing."
] |
[
"When I mow my lawn, am I damaging insect life? How badly am I messing with an ant colony?"
] |
[
false
] | null |
[
"This is closely related to the topic of my MS thesis actually. The research I did (in hay, not lawns, but still) suggested that mortality due to the mower itself is actually pretty low. On the order of maybe 10%? Most of the changes caused by mowing are due to habitat loss. If there's other unmown vegetation nearby that can meet their habitat needs many insects will move there; otherwise they will have to move farther and have higher rates of mortality. "
] |
[
"You are most definitely killing thousands of bugs. In a square foot of grass there are hundreds, if not thousands of bugs. You probably don't slice very many, but you are sucking them up and crushing them in your bag. If you mulch, you probably kill a lot less, just suck them up and shoot them out. You probably won't affect an ant colony very much. Even if you kill hundreds of thousands you're not damaging the colony much. Ant colonies are underground, so cutting your grass won't damage their home.",
"I would like to mention that when I mention killing thousands, I'm not talking about grasshopper, mantis, cicada sized bugs. I'm talking about mostly tiny gnats, spiders, mites, ants, and other tiny bugs that live in the grass."
] |
[
"I'm talking about mostly tiny gnats, spiders, mites, ants, and other tiny bugs that live in the grass. ",
"Aren't these animals small enough to survive a trip through a lawn mower? I've vacuumed up and released spiders before that survived, surely something as small as a mite can make it?"
] |
[
"Could sound waves be used as an insect deterrent?"
] |
[
false
] |
From my basic understanding of physics, sound waves should effect the flight of small insects. Does this happen to a large extent? Could, for example, mosquitoes be prevented from flying by either a very strong sound signal or one at a specific frequency?
|
[
"It wouldn't knock them out of the sky, but there are insects that can \"hear\" at ranges above humans, and there are devices that can screw with their heads and confuse/scare certain insects away by playing very high frequencies (sort of like a dog whistle).",
"You have to remember that a flying insect also has to be able to handle wind, and, as you probably know, even just a light breeze can be felt more easily than a sound wave."
] |
[
"there are insects that can \"hear\" at ranges above humans, and there are devices that can screw with their heads and confuse/scare certain insects away by playing very high frequencies (sort of like a dog whistle)",
"There are a lot of devices on the market which claim to work on this principle. However, a 2010 ",
"Cochrane review",
" (pdf) examined the available evidence on Electronic Mosquito Repellents, and found that:",
"EMRs are not effective in repelling mosquitoes and should not be recommended or used."
] |
[
"I am not sure about insects, but mosquito larvae can be killed with sound waves."
] |
[
"Does aluminum-coated roofing insulation work better than matte insulation?"
] |
[
false
] |
I have recently been exposed to a lot of information about building materials. One debate which came up more than once deals with roofing insulation. Some of the water vapor barriers used under drywall in Poland have a reflective aluminum coating. The marketing materials as well as some people in the construction industry say that this causes it to insulate better. Barring the added thickness of the aluminum, would a reflective coating make the material a better insulator? Please keep in mind that drywall gets attached directly to this, so there is no radiation heat that I can think of which could be reflected. Can someone set this debate straight?
|
[
"As you imply, a reflective foil coating will only make a difference with regards to radiant heat. As such, foil coated insulation can make a minor difference with regards to insulation placed inside attic spaces -- the type you place on the floor of an attic, or on the floor and walls of attic crawlspaces. ",
"The problem is, using such a coating is mostly counter productive. In order to have any effect, the foil must be on the hot side of the insulation. It will do nothing at all if it is placed against a wall or ceiling. But, the proper place for a vapor barrier is between the living space and the insulation. Placing a barrier on the hot side of the insulation will trap moisture, which will degrade the insulation over time. The minor gain in thermal efficiency is quickly outweighed by the harm it causes to the insulation."
] |
[
"Note that the \"proper\" place for a vapour barrier depends on the climate.",
"In cold climates, you are correct. In hot, humid climates, you want the vapour barrier between the insulation and the outside world, to prevent warm humid air from outside condensing inside the wall as it encroaches into a cooler, air-conditioned space."
] |
[
"I did some research with regards to radiant barriers as an undergrad, and one thing that a lot of people might not realize is that while you reduce heat gains from the sun in the summer, you actually increase heating requirements in the winter. In the north, you can actually raise your annual utility bill by installing a radiant barrier. If you lived somewhere like Florida or Arizona though, a radiant barrier could potentially be cost effective. In general, addition of aluminum will make something a better insulator, it's just that in winter it does more to keep radiant heat from the sun out than heat from your house in."
] |
[
"Will the JWST sun sheild unintentionally act as a solar sail?"
] |
[
false
] |
I have heard of the concept of solar sails before and am curios (tried searching the subject) if the JWST sun sheild will unintentionally act as a solar sail and need to some how be accounted for and off set.
|
[
"Yes it will. They even have a small flap on one end of the spacecraft, which is there to help offset the small acceleration from the sun shield.",
"That flap is actually the latest thing JWST deployed earlier today.",
"https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html"
] |
[
"The flap probably adds to the the sail effect - but keeps it balanced (no spinning). The force is like a few grams, but that can add up over time. They counteract by keeping the thing on the “downside” (back to earth) gravitational slope of the L2 point, and occasionally boost up a little closer.",
"EDIT - Better description I just read by someone else: ",
"https://www.reddit.com/r/jameswebb/comments/rs42pj/i_understand_why_its_going_to_l2_but_why_do_a/hqk0arj/?utm_source=share&utm_medium=ios_app&utm_name=iossmf&context=3"
] |
[
"Well, most of the force will not add up over time. They're just trying to compensate for the part that would add up.",
"If you just have a flat sunshield orbiting the sun and rotating just enough to always be perpendicular to the sun, then the force would not add up over time and shift the orbit. But it's not perfectly flat and it won't be perfectly perpendicular to the sun, so there will be some component of the force causing an acceleration that would add up. It's just pretty complicated due to the way the JWST orbits. Also it can deliberately spin (yaw) to see more of the celestial sphere."
] |
[
"Is it possible for a deaf person to have tinnitus? If so, how does it work?"
] |
[
false
] | null |
[
"I am an MD and I have had tinnitus for several years. It is correct, that tinnitus i more a phenomenon of the brain than of the ear (it has been shown, that the \"sounds\" of tinnitus, typically ringing, does not at all behave like sound perceived by the ear). I consider tinnitus an inapropriate cerebral processing of sound information, a filtering defect. Initiated accidental, by stress or after trauma to head or inner ear, you start to focus on sound information, that normally would be filtered or damped by the several neurological circuts of the brain before reaching consciousness. It annoys you, which in turn makes the brain focus even more on the tinnitus sound. In the end the noice may be perceived as unbearable by some. Tinnitus, I think is present in every person, especially, if the person has a hearing impairment (the amplifier of the brain is turned to a higher level, due to the lack of sound). You can learn to handle your tinnutus, just as you normally perceive wearing a pair of trousers (or some other garment): for most of the time you are not truely aware of your trousers, then sometimes you are, and then it's like, \"aha, I am wearing trousers, so what...\". These days I perceive my tinnutus on and off, but it almost never bothers me, even if it is quite loud."
] |
[
"I am an MD and I have had tinnitus for several years. It is correct, that tinnitus i more a phenomenon of the brain than of the ear (it has been shown, that the \"sounds\" of tinnitus, typically ringing, does not at all behave like sound perceived by the ear). I consider tinnitus an inapropriate cerebral processing of sound information, a filtering defect. Initiated accidental, by stress or after trauma to head or inner ear, you start to focus on sound information, that normally would be filtered or damped by the several neurological circuts of the brain before reaching consciousness. It annoys you, which in turn makes the brain focus even more on the tinnitus sound. In the end the noice may be perceived as unbearable by some. Tinnitus, I think is present in every person, especially, if the person has a hearing impairment (the amplifier of the brain is turned to a higher level, due to the lack of sound). You can learn to handle your tinnutus, just as you normally perceive wearing a pair of trousers (or some other garment): for most of the time you are not truely aware of your trousers, then sometimes you are, and then it's like, \"aha, I am wearing trousers, so what...\". These days I perceive my tinnutus on and off, but it almost never bothers me, even if it is quite loud."
] |
[
"Some earlier attempts at curing tinnitus involved severing the auditory nerve completely, essentially causing the person to go deaf if they weren't already, and this only cured tinnitus about half the time.",
"So yes, not only is it possible for deaf people to have tinnitus, it is possible for someone with tinnitus to become deaf and still retain the tinnitus.",
"source",
" "
] |
[
"Is there an increasing occurrence of significant earthquakes or just an illusion of such caused by the information age?"
] |
[
false
] | null |
[
"Major earthquakes have remained constant in number, while (edit for clarity:) ",
" of minor earthquakes have increased in number over the years",
". The increase in minor earthquakes can be explained at least in part by increased monitoring and communication."
] |
[
"Right, I should have been more clear: the number of ",
" minor earthquakes has increased.",
"I don't think a proper study has been done on this, which is why the USGS doesn't state that it's definitely an artifact of better monitoring. It could be there are natural cycles of smaller earthquakes, or that they actually are on the rise. We've only been collecting really comprehensive global seismological data for about 20 years."
] |
[
"Can you give us some unbiased sources on this?"
] |
[
"What is exactly happening during a panic attack?"
] |
[
false
] |
I've had panic attacks on-and-off for several years and have yet to fully understand the biological happenings inside my body during an attack other than I feel like I want to run off a bridge with dynamite strapped to my body. I've had people tell me it's a glitch in the fight-or-flight response, that my brain is unable to process the stress being placed on it, my body is dumping it's supply of adrenaline, and a dozen other explanations. Can someone explain biologically what the hell is going on during a panic attack?
|
[
"NIH to the rescue",
"The \"fight or flight\" response is essentially right. When you experience intense fear stemming from a panic trigger, your sympathetic nervous system goes into overdrive. If you were a human in the wild and a lion started chasing you, the same or similar symptoms would occur: increased heart/breathing rate, trembling, sphincter release,etc.,",
"etc.",
" ",
"It's important to understand the symptoms of a panic attack so that your symptoms do not add to your anxiety. Hope these links help a little. ",
"Source: Biomedical engineer"
] |
[
"A lot of people think that panic attacks need to have a reason or some type of high stress situation so they make sense. For example, I have a panic attack before a flight because I fear flying. ",
"This is not true for all panic attacks. Sometimes it is a simple change in your bodily sensations that triggers a panic attack. Let me break it down this way: ",
"Your heart rate changes randomly, and those with panic disorder are generally very aware of their bodily functions. When a random heartbeat seems out of the ordinary to someone with Panic disorder, they may begin to worry about it and what it means (i.e. is something wrong medically?). They may not even realize at first that they worried about it, because what follows happens so fast and it ends up just being a blur of experience. So, they notice the change in heart beat, begin to worry, and this worry increases the heart rate. Then you may experience sweating among other symptoms that are perpetuated by the anxiety. ",
"In summary, panic is always in your head, and is generally a lapse in logic by wrongly analyzing bodily functions. No one has ever died from a panic attack. "
] |
[
"As an anxiety sufferer, I can confirm the \"very aware\" part. My anxiety increases when I wear a button-up shirt because I can feel the weight of the buttons on my chest. It also increases your awareness of eye floaters, which most people have and don't pay attention to. When I sit motionless, I can feel both my heartbeat and my body's \"essential tremor\" (why you can't hold your hand absolutely still). When I look at the moon in the sky, I can see it move. This one caught me off guard when I first discovered it. My eyes have become so aware that I can visually sense the movement of the moon through the sky in a couple of moments.",
"Anxiety is like getting all the super-human strengths that you don't really want. Your body becomes hyper-sensitive to the everyday stuff that most people have learned to ignore or aren't aware of. All day, it gives you discomforting stimulation and magnifies every little bodily discomfort and unpleasant thought. God forbid you experience the slightest chest discomfort for whatever reason. It'll be magnified to the point where you become convinced that you're dying."
] |
[
"Why does a higher thermal conductivity in the core lead to later inner-core formation?"
] |
[
false
] |
I am confused--intuitively, it feels like higher conductivity would cool the core faster, and so we'd get an inner core. But in the literature a higher conductivity is always given as a reason for a core (it's never really explained). Can anyone explain what's actually going on? What am I missing here? Thanks!
|
[
"Higher thermal conductivity --> less vigorous thermal convection --> slower core cooling --> later inner core nucleation",
"Cooling of Earth's molten core prior to inner core nucleation is thought to have been dominated by thermal convection. (In the present era with a growing inner core, compositional convection, from light elements remaining in the outer core and rising, is though to dominate.) In the more general case, considering a planet with a core that wasn't convecting (and thus lacked a dynamo) over most of its history, (e.g., Mars and maybe Venus) this would be associated with a more slowly cooling core, unlikely to nucleate an inner core at all.",
"Higher thernal conductivity inhibits thermal convection, which is more efficient than conduction for cooling the core. The steeper adiabatic gradient resulting from higher thermal conductivity tends to produce a thermally stratified layer (e.g , ",
"Pozzo et al. (2012)",
"), where heat flow is dominated by conduction down the adiabat, preventing thermal convection. Note that in the ",
"Rayleigh number",
" (Ra), thermal diffusivity, which is directly proportional to thermal conductivity, is in the denominator. A higher thermal conductivity reduces the Rayleigh number. Conceptually, Ra is the ratio of the times scales of diffusive (comductive) heat flow to convective heat flow. A faster (shorter time scale) conductive heat flow reduces Ra, and thus reduces the ability to convect, while lower conductive heat flow allows convection to dominate."
] |
[
"Thank you for that detailed response. I was suspecting that high conductive efficiency would still be less efficient that convection. Convection cooling the core faster, despite the core having lower thermal conductivity, does make sense."
] |
[
"Higher conductivity gets the heat to the core-mantle boundary where it can drive convection in the mantle, and therefore delivery of new materials to the c-m boundary and thence to the core. Keep the heat in the core and all you get is a hot core and cooler mantle with less convection and lower temps resulting in different material composition and solubility of various minerals."
] |
[
"Do you think there are too many laws restricting scientific research? Or not enough laws pushing research?"
] |
[
false
] |
[deleted]
|
[
"Others believe that scientific knowledge is growing too quickly and should be slowed by more laws restricting scientific research.",
"Perhaps one could think that in the 1940s, but now that we've gone 60 years without nuclear war breaking out I think we're in the clear.",
"It's not that the laws are in the way of science (the exception being that stem cell issue in the US), it's that there's not enough money devoted to basic research."
] |
[
"It's not so much the laws restricting scientific research for the most part (things like stem cell research being the exception), but rather the lack of sufficient funding. Nowadays, only a small percentage of grant applications will get funded, and basic science research even less so.",
"While there are lots of regulations with research (e.g. animal use and care), the most limiting factor is availability of funding."
] |
[
"In response to argonaute's and iorgfeflkd's comment on funding limitations on basic science reserach: I completely agree, especially now a days with large corporations no longer pursuing in-house research for the sake of research (e.g., Bell Labs, Kodak, IBM, 3M, Westinghouse, etc.). It's all become, \"when will this become profitable, and how\", instead of, \"let's see what comes of this\"."
] |
[
"What is the cause of the artifactual lines commonly seen on doppler radar images?"
] |
[
false
] |
What causes this and can we infer anything about weather from them?
|
[
"Not an expert in doppler radar but I deal with a lot of imaging artifacts.",
"This page",
" lists some interesting Doppler radar artifacts. If the spikes are pointed directly towards the radar receiver, it is almost certainly an artifact. ",
"This paper",
" deals with a \"clutter spike rejection algorithm\" to deal with with buildings in the vicinity of the transmitter, so it could be the spikes in your image are just from tall buildings nearby."
] |
[
"Those spikes are actually just post processing artifacts in the display, they don't actually represent any radar phenomenology. "
] |
[
"There are a large number of different types of clutter/false returns in radar images. The ones you linked to look like foreign transmitters."
] |
[
"What are the neurological or psychological differences between the auditory hallucinations of voices, e.g., as in schizophrenia, and a persistent negative internal monologue in one's own inner voice?"
] |
[
false
] |
[deleted]
|
[
"Schizophrenia by definition means that the person doesn’t differentiate reality. When a person is not schizophrenic, s/he knows that the internal voices are part of their own thoughts; a schizophrenic person doesn’t know what’s real and what isn’t. "
] |
[
"Mostly yes in that they are both internally generated. I worked with adults with schizophrenia for 6 years, but they were medicated. Still they couldn’t control the voices and they crowded out their other thoughts. The voices often gave commands or made paranoid statements and made it very difficult for people to concentrate. They couldn’t reason the voices away or distract themselves. Some of the folks used headphones to try to drown them out. So not only the interpretation but also the persistence and their disconnection from what was really happening. "
] |
[
"Do all internal monologues, regardless of their interpretation, classify as hallucinations?",
"Hallucinations",
" are perceived to be external. In that sense, they differ from ",
" monologues which are not perceived to be external.",
"Are the voices their own, or are they foreign?",
"What do you mean by ",
" and ",
"?",
"To add to ",
"/u/MoonEagle3",
"'s comment, hallucinations are not always confused for reality. Individuals with ",
"Charles Bonnet syndrome",
" are usually aware that their hallucinations are not real, but they nevertheless mimic \"real\" perceptions."
] |
[
"In the 19th century, the concept of ether was disproven, but the Higgs field sounds a lot like ether to me. How are they different?"
] |
[
false
] | null |
[
"The main feature of the ether is that it created a universal reference frame as the medium in which light traveled. In order for it to work it had to be possible to tell how fast you were moving with respect to the ether, for example by comparing the speed of light rays traveling in different directions with respect to yourself.",
"The fact that it was a field that permeates the universe was not the fact that was disproven, and indeed all of modern particle physics is based on the idea that fields permeate the universe. None of these fields, however, have the property that they create a preferred reference frame. It is never possible to do an experiment that tells you how fast you are moving with respect to the Higgs field, for example."
] |
[
"The reference frame explanation made it clearer for me. Thank you."
] |
[
"Field has a value for each point in space and time. Easier example than Higgs field is the electromagnetic field "
] |
[
"Why are large primes often published in the format of a*2^n +/- 1, such as 3756801695685 · (2^666669) ± 1?"
] |
[
false
] |
Is this a more clear notation to put these numbers in because it reveals something about the filter applied to the natural numbers to find primes? Why is it that prime numbers tend to be right next to numbers which can be divided by two so many times?
|
[
"The reason why a lot of the large primes are of the form a*2",
" - 1 is because there is a really fast ",
"test",
" to determine if that sort of number is prime or not. There is also a really fast ",
"test",
" for the primality of primes of the form 2",
" - 1 which are called ",
"Mersenne Primes",
". ",
"Edit: ",
"Math stack exchange question on this topic",
"Take a look at the Wiki page on ",
"largest prime numbers",
" and ",
"primality tests",
"."
] |
[
"This answers why there is at least one factor of two in the questions, but not why, as in the above example, the number which the prime is next to can be divided by two 666669 times. If you break down the number into its factors, and exponents of those factors, then the exponent over 2 is so much greater than the other numbers. How come?",
"With regards to the display, I must not have made myself clear. Why isn't the more convenient format something like a * 3",
" +/- 1. What is special about the base-2 system?"
] |
[
"This is the answer I was looking for, thanks!"
] |
[
"What kind of bug is this?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/whatsthisbug",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"sorry about that, thanks for the suggestion!"
] |
[
"No problem! Good luck."
] |
[
"What exactly causes myocardial hypertrophy?"
] |
[
false
] |
For instance, hypertension can result in left ventricular wall hyperthropyz but what mediators are exactly in play here?
|
[
"The largest mediator at play is repeated damage to the heart tissue, leading to scarring and enlargement of the walls. High blood pressure produces increased vascular stress in the heart, causing inflammation and damage. Unlike skeletal muscle, the heart never stops to rest and heal, so the damage is more likely to be repaired via less-than-ideal means, like building up additional tissue. ",
"This",
" abstract gives a good summary of the processes that lead to myocardial hypertrophy and hyperplasia. (The full text is behind a paywall, sorry.)",
"The underlying inflammatory processes behind myocardial hypertrophy aren't perfectly clear, though there's ",
"evidence",
" that cytokines and damage in the microvasculature play a major role. This abstract: ",
"http://www.ajconline.org/article/S0002-9149(97)00749-2/abstract",
" is pretty good, too. (Sorry about the lack of a properly formatted link, parentheses in the URL borked it up.)",
"This is not to be confused with ",
"hypertrophic cardiomyopathy",
", a genetic heart defect causing abnormal thickening of the cardiac walls. "
] |
[
"I don't think that there will be a common mechanism as there are different types of hypertrophy. ",
" (thickened wall) occurs due to chronic pressure overload of the ventricle, for instance in the case of chronic hypertension. From Laplace's Law, wall tension is reduced with increasing wall thickness.",
" (bigger chamber, wall not so thickened) is more associated with volume overload. There is usually a mix of concentric and eccentric hypertrophy and there are many different conditions that can cause hypertrophy. Because cardiac hypertrophy is a diverse condition and I think you will struggle to find a common mechanism.",
"Narrowing the discussion to hypertensive cardiomyopathy is sensible. We know that hypertension is associated with concentric hypertrophy and we assume that this is a causal relationship. Histology shows myocyte and fibroblast proliferation, and the mediators that may be involved are ",
" (which mediate fibroblast proliferation) and growth hormone, thyroxine, and pressure/volume loading (which are involved in myocyte proliferation). This leads to enlargement of cardiac myocytes and fibrosis - hence the thick, stiff, non-compliant ventricle of the hypertensive patient.",
"The ",
" (\"AT-2\") seems to be important in the pathogenesis of hypertensive cardiomyopathy (knocking out the AT-2 gene in mice stops left ventricular hypertrophy and fibrosis due to pressure overload).",
"There are also ",
" (perivascular fibrosis, and thickening of media). I'm not sure of the clinical significance of this - but I'd guess that this contributes to the fibrosis of the ventricle.",
"There is also ",
" of the cardiac myocyte. Again I don't know the significance of this. Maybe it is involved in the transition between compensated to decompensated heart failure. ",
"It seems reasonable to assume that the myocyte proliferation is physiological (at least initially) and the fibroblast proliferation is more likely to be pathological. ",
"There are some recent papers about the molecular targets and regulators for cardiac hypertrophy if that is more what you are after - but that is getting too detailed for me. ",
"Finally don't forget that there can be genetics factors that lead to hypertrophy. The classic example is hypertrophic obstructive cardiomyopathy (\"HOCM\"), aka \"familial hypertrophic cardiomyopathy\", and the genes involved have been identified."
] |
[
"Tachycardia is caused by activation of beta adrenergic receptors in the myocardium. Prolonged activation of these receptors leads to predominantly an eccentric hypertrophy, now known as dilated cardiomyopathy. ",
"In clinical settings, chronic cocaine or methamphetamine use will cause this. ",
"So, yes it causes damage that can be distinguished from the effect of hypertension. "
] |
[
"Solar Flares, should I be worried?"
] |
[
false
] | null |
[
"It's mainly just hyped up, however, a solar flare can indeed knock out a power grid, but only extremely rarely, and usually just by tripping circuit breakers. In March 1989, one of the most powerful storms in modern days occured. It knocked out Quebec's power grid for ",
"9 hours",
".",
"If, for some reason, some unbelievably powerful event occurred, and the world's power grid got knocked out by the fluctuations, it would simply take the amount of time to repair the damage, which would probably be mainly circuit breakers and the occasional blown transformer. "
] |
[
"Solid answer, but could you point us to some sources for the amount of damage solar flares could cause and how easily reparable the damage would be?"
] |
[
"A solid reply. I'd just like to add that ",
"Coronal Mass Ejections",
" (CMEs) are more often responsible for disruption of electronics on Earth, not solar flares.",
"SDO, one of NASA's solar observatories, caught a beautiful shot of one a month or so back. ",
"Here it is",
" with an image of the Earth super-imposed to demonstrate scale."
] |
[
"What is the difference between work and play in our heads?"
] |
[
false
] |
Why is it that doing something like managing spread sheets is boring, and something like playing an MMO is engaging? Or that we hate to do menial factory work of repeating the same action over and over, but we like to play rhythm games like DDR etc.? It seems like the approximately the same action, but working ten or twelve hours a day can lead to stress and poor health while I'm sure many people would have no problem playing games for that long.
|
[
"\"Play\" activities generally have some sort of payoff that triggers a release of dopamine and endorphins in your brain. \"Work\" activities become a daily grind because you lose that payoff step through repetition. When you play DDR you immediately get the reward when the song ends, when you do factory work you get your reward two weeks later in the form of a check. \nPlaying video games will kill you just as surely, you'll just enjoy it more.",
"tl;dr\nYou're in a big ",
"Skinner Box",
". It's all about when you get the treat."
] |
[
"Anecdotally I know people in the service industry have a hard time leaving just because of that. (they usually get tips at the end of a shift) "
] |
[
"As a game design student I encountered the great book Man, Play and Games by R. Callois last year and I would highly recommend it as I think it should answer your question or at least give you some insight on this matter.",
"http://en.wikipedia.org/wiki/Man,_Play_and_Games",
"To put it short, if I remember correctly, It's all about the fact that games/play create a separate world with simple rules to comprehend and to follow. There's nothing of value being produced in the game world therefor, we don't get the stress related to producing. You can always escape your responsibilities in a game by leaving the game world, be it football, basketball or an MMO. But the moment we start getting paid or produce anything of value for our play it stops being a game/play. (I guess that's where the problem lies with educational and serious games in general, hehe)",
"If there's someone here that is more familiar with R. Callois' work then please chip in because my memory is not as good as I had hoped."
] |
[
"Can we learn things while we sleep?"
] |
[
false
] |
I see videos on YouTube that are a few hours long and are meant to be listened to while sleeping to help learn the language. Does watching these videos help do anything while sleeping?
|
[
"It is pretty unlikely that you have the capability to learn while sleeping like that. It has been theorized that your brain spends your time sleeping to unpack the information from the day and store it, so it may not be able to learn additional information because it is already at capacity.",
"However, this is a subject of study and there are many of us that would like to be able to retain, process and internalize knowledge both faster and during periods of sleep."
] |
[
"There are movies and shows in which a character sleeps with a tape that he is learning, but that is all bogus."
] |
[
"Sources? I've actually read a couple studies that suggested there is some level of learning/retention with certain methods. ",
"Pretty sure it's impossible to \"watch a video\" while sleeping, though!"
] |
[
"With no atmosphere to carry a pressure wave, would a nuclear bomb be very effective in outer space combat?"
] |
[
false
] |
The way I'm thinking of it, the nuke would propel its own matter outwards very quickly (which wouldn't amount to much) as well as a lot of heat and radiation (which spaceships are already good at handling). Also, how well would a nuke work for excavation if buried in a Lunar cave? How well would they really work?
|
[
"I helped perform the calculations on the EMP Commission Report prepared for Congress. You are correct. A nuke exploded in space (not near the atmosphere) will not create an EMP in the traditional sense. "
] |
[
"Your intuition is correct, more or less.",
"Project rho has a good analysis of nukes in space: ",
"http://www.projectrho.com/public_html/rocket/spacegunconvent.php#id--Nukes_In_Space"
] |
[
"Nuclear bombs don't explode in the same way chemical explosives do.",
"A conventional explosive undergoes a chemical reaction that produces a lot of hot gas very quickly. A nuclear bomb undergoes a fission chain reaction, producing a lot of high-energy particles, x-rays, gamma rays, etc. which then heat the surrounding air and cause it to expand explosively. Certainly they do vaporize themselves into hot gas, but this is only a very small part of the explosion.",
"My guess for your hypothetical bomb next to a ship would be that the pressure wave of the bomb vaporizing itself would be pretty much inconsequential next to the pressure wave of the rapidly-heated air in the spaceship expanding and/or heat damage to the structure of the ship. I don't even want to think about what the radiation and high-energy particle pulse would do to the crew, assuming any survived.",
"One other point - spaceships (or at least, current ones) are not that great at handling heat or radiation, especially not the kind of extremely sudden heating and high-energy radiation a bomb would produce and double-especially not if they have a human crew on board. Proper radiation shielding is too heavy for spaceships and heat can only be managed through (very slow) radiative cooling."
] |
[
"is the Geiger counter not an observer in the Schrödinger's cat experiment?"
] |
[
false
] | null |
[
"Yes. That is exactly the point of the thought experiment. Schrodinger was trying to point out how silly it was to talk about 'Observers collapsing the wavefunction' in quantum mechanics, when it is much more useful to talk about 'measurements collapsing the wave function'. If a human observer were required in order to collapse the wavefunction, then you could set up an experiment where a cat is both alive and dead at the same time, which is obviously absurd."
] |
[
"Schrödinger's cat isn't an experiment. It's a metaphor that was constructed to demonstrate how ",
" quantum mechanics was when the principles were first being discovered. Now it's a metaphor used to demonstrate how ",
" those principles are, despite their being true.",
"Basically, the metaphor is constructed in such a way that the ",
" — the thing that can be measured by experiment — is the cat's aliveness-or-deadness. Until the measurement is made, the cat's state has to be described as a linear superposition of alive and dead. Why? Because that's the only way to get mathematical predictions that match experimental results. Not experiments on ",
" obviously, but experiments involving individual quanta. If you want to predict the outcomes of your experiments, you have to describe the states of quanta as linear superpositions of mutually orthogonal, measurable states. This is weird but true, is the whole point of Schrödinger's cat today."
] |
[
"this question is okay in my book. "
] |
[
"Advice for Parasitology Paper"
] |
[
false
] |
Hello , I am currently taking a parasitology course as a part of my biology major in college. We need to write a research paper on a parasite that was not covered in class. Any advice on some interesting ones? We have covered the important parasites in the genera Trypanosoma, Leishmania, Giardia, Entamoeba, Naegleria and Plasmodium. We have also covered Toxoplasma gondii and many flatworms and nematodes. I feel like all the ones of interest have been covered already. Thanks in advance! Note: Cordyceps has been taken already unfortunately.
|
[
"Look for behavior-altering parasites! Frighteningly fascinating. I wanted to suggest toxoplasma gondii, but a few minutes of googling yields a few possible alternatives. Like ",
"Hymenoepimecis argyraphaga",
"- a wasp that lays its larva on a spider, which then inject chemicals into the spider to alter its brain and make it build them a cocoon. Or ",
"dicrocoelium dendriticum",
", which forces infected ants to climb to the tips of grass so they can be more easily eaten (and the parasite's lifecycle continued). Or ",
"hairworms",
", which can force infected grasshoppers to jump suicidally into water."
] |
[
"How about ",
"Scabies?"
] |
[
"Well Dicrocoelium is my personal favorite but looks like you can't do that one. ",
"You can do things like Echinococcus granulosas (Google 'hydatid cysts') or Dracunculus medinensis (this is the one that pokes through your leg in water; also the 'snake' on the medical logos). Or try something that's zoonotic (spread from animals to humans and vice versa). "
] |
[
"If black holes do not emit any light. Why isn't it obvious if there is a super massive black at the centre of a galaxy? Surely there would just be a massive region of space with absolutely nothing present?"
] |
[
false
] |
[deleted]
|
[
"You can blot out the sun with your thumb, right? This is because of perspective. Things look smaller at greater distance. Well, the sun is only eight minutes away. The center of the Milky Way is 28000 ",
" away. The reason we don't see a big black spot in the sky is because in those 28000 lightyears, there is a ",
" of other stuff in between here and there."
] |
[
"This. As a DIY example:\nTake a basketball, paint it black, and put it 2 miles away from you (someone who cares can correct for scale). Now fill that 2 miles with flashlights pointed at you. Can you see the basketball?"
] |
[
"825,000",
" miles away.",
"Or 3.7 times farther than ",
"The Moon",
"."
] |
[
"Are there any cases where the sudden absence of a species had an effect of the function and economy of that area?"
] |
[
false
] | null |
[
"The collapse of the northwest Atlantic cod population in the early 1990s had a massive economic impact on the economy of eastern Canada.",
"https://en.wikipedia.org/wiki/Collapse_of_the_Atlantic_northwest_cod_fishery"
] |
[
"Since I don't see it mentioned yet, China did a little (/s) experiment back in the mid-1900s... Changed quite a bit. Sparrows, in particular, turned out to be much more important to the ecology than they had anticipated.",
"https://en.wikipedia.org/wiki/Four_Pests_Campaign",
"Edit - Added a /s just in case."
] |
[
"Look into wolves in Yellowstone.",
"\nHumans took them out. (Think it had something to do with making Yellowstone a more human friendly place.). Decrease or predators lead to increase of prey.",
"\nThe prey eats up more of the environment. And things start to change from there.",
"\nSupposedly, reintroducing the wolves helped undo some of the damage, but I'm having a little bit of trouble finding sources to back that up. "
] |
[
"What are the smallest measurable unit of time, and smallest theoretical unit of time and at what interval of time are universes “split” in the theory of infinite universes?"
] |
[
false
] | null |
[
"Astronomy"
] |
[
"Astronomy"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
" because of its open-ended or speculative nature. Please feel free to repost there!",
"Please see our ",
"guidelines",
".",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Is the phylogenetic (evolutionary) tree a mathematical tree (acyclic connected graph)?"
] |
[
false
] |
All the diagrams that I've seen in posters and textbooks seem to say that phylogenetic tree is a acyclic connected graph. However, I couldn't find any literature or articles that claims such relationship. This question can be rephrased as can two separate evolutionary path can result in similar (same) genetic composition? If so, has it been observed anywhere? (I'm guessing assumes affirmative to my question but I could be wrong.)
|
[
"Even if two lineages converged independently on identical genetic makeup (and this is pretty much impossible) they still wouldn't converge on the graph. This is because phylogenetic graphs don't measure ",
" similarity, they measure actual lines of descent. In practice, genetics is a large part of how we figure out lines of descent, but genetics isn't what the tree is about. Despite being genetically identical, properly speaking the ones descended from species A should be on the branch from A, and the ones from B should be on the branch from B. ",
"That said, it ",
" theoretically possible for branches to fuse back together. This occurs when two species hybridize to form a new species. Common ways of dealing with phylogenetic trees and cladograms don't handle this very well or ignore it (which isn't ",
" an issue)"
] |
[
"Phylogenetic trees are indeed directed, connected acyclic graphs. Specifically they are dendrograms as child nodes may only have 1 parent. ",
"With regards the question \"could 2 evolutionary paths converge on the same results\"? In theory yes. In practice never. And even if they did converge on the same solution 2 populations of organisms with a unique evolutionary history would be maintained as separate entities in a dendrogram.",
"On my phone so it is hard to give a more complete answer atm."
] |
[
"You need to make a distinction between gene trees and species trees. Gene trees follow the evolution of a single locus (assumed to be non-recombining). That kind of evolution is acyclic or what's called dichotomous branching since as other comments here have mentioned, the chance that mutations could give rise to the same sequence in two lineages is generally statistically insignificant.",
"However, most of the phylogenies you see are species trees (or taxon trees) in which the multiple gene trees are combined to infer the phylogenetic history of whole genomes. The tips may be inidividuals (i.e. real genomes) or they might be populations, species, families, or some other larger taxonomic group. They are not individual alleles, though, which is what the tips of a gene tree are.",
"When hybridization happens, taxon trees become cyclic or what's called reticulate in phylogenetics. Most phylogeneticists still pretend like it's not a big problem for phylogenetic inference because in old ways of thinking, it's mostly only immediately adjacent lineages (sister taxa) that hybridize and hybrids are ephemeral (they don't give rise to new populations). It's now clear that hybridization happens even between deeply diverged lineages that may have internal divergence along the lineage prior to hybridization. It's also well known that hybridization can in fact lead to new lineages either as hybrid speciation or as biogeographic recontact. So reticulate phylogenetics is one of the major areas of research in phylogenetics right now.",
"Recent advances in sequencing polyploid genomes have made it possible to very accurately map out the hybrid history of allopolyploids, which are species that arise as a result of hybridization. ",
"Some really cool recent work in ferns",
" is taking this all the way and creating reticulate trees. That's sort of an oxymoronic term, but as someone who does this work myself in forest tree taxa, I like to point out that real trees are also not always dichotomous branching, insoculation is when two branches of a tree fuse together, so we could call these new cyclic phylogenies insoculated trees."
] |
[
"What are gravity anomaly maps and how do they work?"
] |
[
false
] |
I've been reading up on the Chicxulub crater and saw that, besides cenote locations, there aren't any real visible impressions on the earth's surface of the crater/peak rings. The best way to visually observe the crater is looking at a gravity anomaly map. I've tried researching what exactly a gravity anomaly map is and what it's measuring/how it gathers that data. I can tell it has to do with mass, but how would that make it different than topography maps? And how does gravity play into that? I'm just having a difficult time with fully grasping how gravity anomaly maps work.
|
[
"Things with mass have a gravitational field around them. Higher masses have stronger gravitational fields.",
"Density is a measure of how much mass is in a given volume of thing. Different rocks have different densities. AS s result of this, if you ahve lots of dense rock beneath a location there is a higher gravitational force in the area than if there's loads of less dense rock.",
"Additionally, gravity decreases with distance from an object. So things which are shallow have a stronger effect on surface gravity than things which are deeper. And if you have a hill or a valley you have a relative difference in how strongly things like the earth's mantle and so on impact things. ",
"So, for any given location on the planet we can go and measure the gravity and say how far it deviates from what would be expected on an \"average\" earth. This is a gravity anomaly. There are two main types - the Bouguer anomaly and the free-air anomaly, depending on if they correct for the mass of rock between sea level and wherever you're standing or not. There's lots of stuff we could go into here, but it goes a bit beyond the scope of the question. This image gives you a decent idea of how the different anomalies respond around different types of large-scale tectonic feature: ",
"https://en.wikipedia.org/wiki/Gravity_anomaly#/media/File:Gravity,_geoid_anomaly_synthetic_cases_with_local_isostasy_2.gif",
"The result is that we can go and measure gravity at different locations, and the value will vary depending on what is going on beneath the surface. It is particularly sensitive for looking at thinning of the crust, such as that you get near big impact craters. Exactly what the map is telling you will depend on whether its a Bouguer or Free Air anomaly map."
] |
[
"Gravity meters are super accurate pieces of equipment. They can measure tiny variations in gravity from place to place. ",
"To give an example, earth's average gravity on the surface is about 9.81 m/s",
" , or 981 Gal. A decent gravity meter can measure with about 0.000005 Gal precision. These things are usually based on having a very precisely known weight inside a chamber on a sporting, then using laser or similar systems to measure how much that weight is attracted to the Earth below it. ",
"We've been using similar techniques to measure the mass of things like mountains since the 1700's. ",
"https://en.m.wikipedia.org/wiki/Schiehallion_experiment"
] |
[
"Thank you so much for the detailed response, this really helps!",
"I wonder then if the crater of Chicxulub had more mass and density due the the impact. The story of how those scientists pieced that location together and its significance in the earth's history is super intriguing and I fell down the rabbit hole last night. I didn't even know we were able to measure gravity anomalies, so that's pretty cool!"
] |
[
"Who has a greater epigenetic contribution, the mother or the father?"
] |
[
false
] |
My limited understanding of epigenetics is that it refers to changes in gene expression, not due to changes in the DNA itself but instead via mechanisms such as DNA methylation and histones, and that these changes may be heritable. It is therefore possible for behaviors during an individual's lifetime to alter the gene expression of that individual's offspring. As far as I can tell, both parents contribute to epigenetics. I was wondering, since the sperm and ova are quite different, are the epigenetic changes equally well preserved for both parents? To put it another way, does the prior lifestyle of either parent have a greater bearing on the gene expression of the child?
|
[
"I think you're asking the question too early - we only know a handfull of imprinted genes, in which the gene from one specific parent is always disabled. ",
"But yes, epigenetic changes are equally well conserved, in that you always get one set of marks from your mother, and one set from your father - however, which parent's epigenetic marks make the greater impact is something we won't know for a while.",
"Source: work in an developmental epigenetics lab as a bioinformatician."
] |
[
"Sure - first, it's important to know that there are more than one type of epigenetic modification. There are modifications done on the DNA itself (methylation of cytosines, generally), and there are modifications done to the histones around which DNA is wrapped. ",
"While DNA methylation is often used for repression, the histone marks are all over the map - some are used to promote transcription, others to repress it. Of course, it's important to note that when you're discussing histone marks that upregulate genes, the marks are upstream of the gene - not within the gene itself. (Transcription requires that histones be removed from the body of the gene, obviously...)",
"As for the machinery, there are a LOT of different things going on - so it's possible for a represor's binding site to be methylated to down-regulate expression as well. Cells do tend to reuse machinery a lot, and we're just starting to get a good grasp on what those proteins do."
] |
[
"Sure - first, it's important to know that there are more than one type of epigenetic modification. There are modifications done on the DNA itself (methylation of cytosines, generally), and there are modifications done to the histones around which DNA is wrapped. ",
"While DNA methylation is often used for repression, the histone marks are all over the map - some are used to promote transcription, others to repress it. Of course, it's important to note that when you're discussing histone marks that upregulate genes, the marks are upstream of the gene - not within the gene itself. (Transcription requires that histones be removed from the body of the gene, obviously...)",
"As for the machinery, there are a LOT of different things going on - so it's possible for a represor's binding site to be methylated to down-regulate expression as well. Cells do tend to reuse machinery a lot, and we're just starting to get a good grasp on what those proteins do."
] |
[
"Where are we right now in the research on longevity? What are the major obstacles to overcome?"
] |
[
false
] |
I remember reading about how they managed to extend the life of C. Elegans by quite some bit a bunch of years ago. What interesting developments or discoveries on slowing down the aging process have been made since then?
|
[
"I did Human Genetics at UCL in 2009 and received lectures from one of the leading researchers in Biogerontology - the subject you're currently interested in. He loves the C. elegans and just mentioning the name of it brings me back.",
"I believe at the time (3 years is long research time) they found several protein markers in the pathway of ageing and mutating these proteins led to lifespan almost doubling. They still have not found a common pathway, which is believed to link all these markers together. They might have by now but I wouldn't know. He speculated that ageing is the pathologic basis of all diseases, i.e. if we cure ageing, we cure cancer, osteoporosis, macular degeneration, Alzheimers and all other diseases of old age.",
"It is still an interesting prospect and many of these proteins are conserved across species (they would map it to fruitflies and mice with varying levels of success). I can't remember much else, it was a while ago and 3 years is a long time.",
"In response to one of the other comments made below, telomere length is no longer 'in vogue'."
] |
[
"Too much to easily summarize; I'd suggest browsing the last couple of years of archives at Fight Aging!, as that's a running commentary with links to papers and articles as they appear:",
"http://www.fightaging.org",
"Here's a 2011 retrospective:",
"http://www.fightaging.org/archives/2011/12/a-look-back-at-2011.php",
"I will say that slowing aging will have little to no practical end result for most of us, and thus more research should go into reversing aging by repair of the known and identified forms of damage that cause aging:",
"http://www.sens.org/sens-research/research-themes",
"Repair is useful to the old, while slowing the rate of damage accumulation is not."
] |
[
"Overcome to achieve longevity. If death is part of natural selection, you could argue that consciousness focused at artificially altering our genes for longevity would be, too. But the discussion is moot as that is a question of morality rather than science.",
"I'm not sure that the link is very much on topic either, but regardless it's a seriously interesting one and something I've been thinking a lot about too. That's an interesting blog altogether, is it yours?"
] |
[
"How do rocket scientists calculate the trajectories of rockets/satelites?"
] |
[
false
] |
For example, how do they calculate a launch trajectory so precisely? With things like air resistance, air pressure changes, and even the minute changes in gravity as you pass over different patches of earth. Furthermore, how do they account for all the gravitational influences of the planets while flying through space? There seem to be so many variables that any calculations would be impossible.
|
[
"I am an Aerospace Engineer by schooling, and you are talking about control theory.",
"Very well understood ",
"orbital mechanics",
" and ",
"aerodynamics",
" give the engineer very well exactly what is expected. The engineer can configure the machine to put the right forces in the right directions at the right time. Right direction, right force, and right time means that these three things solve the orbital mechanics and the aerodynamics equations for the system.",
"However, there is also a highly studied sub-field on how to correct for errors and for the unexpected. It is called ",
"closed loop control",
" and works by measuring your current status (position, velocity, accelleration, mass, direction, time, whatever), comparing it to where you want to be, and then adjusting your control surfaces, engines, mass, or whatever is in the system to compensate.",
"If you want to be very skillful in this field, learn differential equations. Everything in this field is solving systems of equations whose variables interact. The matrix notation and basic functions make these interactions intuitive with enough practical application."
] |
[
"A lot of those forces are not actually that significant (with the exception of air resistance, which can be and is calculated). The forces of other planets are practically negligible unless a spacecraft is doing a flyby, at which point gravitational acceleration is then easily found with g=GM/r",
" Gravitational inconsistencies on Earth are again not very significant, and in the end the rocket and spacecraft can \"make up\" for flight deviations.",
"No launch ends up on an absolute \"perfect\" (or planned) trajectory. Most satellites in Geostationary orbit have to undergo \"stationkeeping\" anyway, or performing \"burns\" (could be with cold thrusters) to keep a proper position and velocity."
] |
[
"yes. when more detailed measurements are needed (GPS satellite orbits), ground based measurements are used. "
] |
[
"Can computation be done without energy loss?"
] |
[
false
] | null |
[
"Landauer's principle asserts that there is a minimum possible amount of energy required to erase one bit of information, known as the Landauer limit: kT ln 2",
"Another way of phrasing Landauer's principle is that if an observer loses information about a physical system, the observer loses the ability to extract work from that system.",
"http://en.wikipedia.org/wiki/Landauer%27s_principle"
] |
[
"reversible computing",
"Just to be clear, reversible computing is a ",
". There is no reason to think it can't be realised, there is a lot of literature behind the fundamentals, but there is still a substantial amount of engineering problems waiting to be solved. All that is available in the references from the page you linked to, of course. :)"
] |
[
"With ",
"reversible computing",
" it is possible to beat Landauer's principle, though"
] |
[
"What stops micro chips in humans from being rejected by the body similar to splinters or other foreign bodies?"
] |
[
false
] |
[deleted]
|
[
"Thanks for the response :D"
] |
[
"I have experience with surgically implanting radio telemetry tags in the abdomen of different species of fish, they're made of metal encased in a cylindrical tube of clear hard plastic. Multiple times I've taken them out of fish (living and dead) that have had them in for a year or two. What I've found is that their bodies actually absorb the object and begin calcifiing and attaching flesh to the object. I have no idea if that's the same with humans but it happens in fish."
] |
[
"Thanks for the question prompt OP. Very educational all around! "
] |
[
"Hey Reddit, what fragrance most effectively cuts/counters the smell of formaldehyde/cadavers? [x-post from AskReddit]"
] |
[
false
] |
Some folks in AskReddit suggested I post here as well to get some lab rat opinions. My girlfriend's in medical school, so she frequently smells like the anatomy lab--sometimes even after a shower. I want to get her a custom fragrance for her birthday, and was wondering if there are particular scents I could layer into the brew to counter this specific challenge of her day-to-day. She normally likes floral scents, though if something spicy or citrus works better, I'd want to include it, no?
|
[
"Are you trying to counter the smell of the decaying corpse itself, or perhaps the compounds used to preserve it? After being around corpses for a few years, I got disgusted with the smell of formalin.",
"If you can find a place to get a sample, I would offer Boucheron for women: (\"Launched by the design house of Boucheron in 1988, BOUCHERON is a Women's fragrance that possesses a blend of citrusy tangerine and bitter orange, florals jasmine and orange flower, sandalwood, amber and vanilla. It is recommended for evening wear.\").",
"I found I was less objectionable after a stint moving corpses with Boucheron for men, and I recall the scent for women being quite nice.",
"I hope you find what you need, in any regard. You might try a different soap and a gentle scrub to be helpful as well. I swear that stuff gets into the pores or binds with the skin."
] |
[
"Here's what I found on a med student's forum (",
"http://forums.studentdoctor.net/showthread.php?t=727250):",
"\"General tips (from the forums and elsewhere):",
"* buy extra, and change out of, your scrubs!\n* For the hands, I recommend double gloving. Some people put soap on in between the gloves, but that's just too much effort. Then, run home as fast as you can to shower.\n* Get scrubs solely for anatomy. Wash them in bleach/detergent every couple of days. Keep then at school if possible when you are not taking them home to wash.\n* Put your hair in a bun WET and go to lab. Some how this helps keep your hair from smelling.\n* Swimmer's shampoo- use it as both bodywash and shampoo. Works much better than regular soap or shampoo.\n* Nitrile gloves as first layer (next to skin) and over top latex. The latex is cheap an can be replaced a few times during lab.\"\n",
"Hope this helps!"
] |
[
"She says that the cadavers last pretty much all term, so I guess that means preserving agents, yes. Which is mainly...formalin, you said?"
] |
[
"Seriously, do I have ADD/ADHD?"
] |
[
false
] | null |
[
"Medicine"
] |
[
"Medicine"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"medical or safety advice",
"/r/AskScience",
"guidelines",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"In this day and age, with all this negative criticism, why aren't we seeing more operating systems created from the core/kernel instead of just alternative distributions? Is it really so hard that we're still relying on 20+ year old core-coding?"
] |
[
false
] | null |
[
"This is an answer targeted at a layman, so I've simplified a number of complex topics substantially.",
"I'm going to assume that you are talking about 'personal computers' - Desktops, Laptops and the like. Portable computers and embedded computers are another interesting topic, as are very large computers but I'm not really going to talk about those. I'll call these mid-size everday computers PCs.",
"The three dominant operating systems for PCs today - Windows, Mac OSX and Linux - are all fairly new implementations. The mean age of a line of code in the kernel of these operating systems is much less than twenty years. However, they trace their design and implementation heritage back a long way. The current Windows line goes back to the early 90s, to the start of Windows NT. Linux and MacOS (and many of the ideas in Windows) have a much longer heritage. They are both based on a set of ideas which have come to be called Unix, and which date back in a fairly similar form to the late 1960s. Neither of these operating systems share a considerable amount of code with the original Unix, but do share a lot of the core ideas. Many of the core ideas in them are even older.",
"Even iOS (on your iPhone) and Android (on your android phone) trace their lineage back to Unix and share core components with OSX and Linux, respectively.",
"So why are we happy with two forty-year-old operating systems and one twenty-year-old operating system? Mostly because they have changed massively over the intervening period (here's a ",
"graph of the growth of Linux",
" so you can see how much). To explain how, I'm going to break the software typically called an operating system kernel into 3 pieces: the interface, the device drivers and the core kernel.",
"The interface is what programs use to talk to the kernel. They interact with the kernel to do anything they need to do to interact with the world - graphics, sound, networking, getting user input, etc. These interfaces change slowly, mostly because of the requirement for compatibility. You don't want every kernel update breaking all your programs. An operating system writer also wants an interface similar to what other operating systems have, to make it easy for people to move their existing programs to the operating system ('porting'). So one of our three pieces changes very slowly. Introducing large changes here is very expensive, because it requires changes to all the programs that run on that operating system.",
"The drivers change fastest. These are the pieces that interact with hardware, and new hardware comes out all the time. The operating system needs to support it, and grows drivers. Operating systems typically employ a technique called 'hardware abstraction', where the drivers expose a common set of behavior for a given set of devices (sound playing devices, for example) to the layers above. This means support for new hardware can be added without changing all parts of the kernel.",
"Finally, the core kernel. In my (very simplistic) breakdown of the kernel, this is what's left. It includes the software that sits between the interface and the hardware, and provides services to programs. It provides fair access to memory, processing and input/output capabilities. It stops one program from stepping on another's toes. It It stops one user from reading another user's files. These capabilities do change, but they seldom change in a revolutionary way. The basic functions of a computer have changed little over forty years. Computers are massively more capable now, but are not too fundamentally different. The lack of fundamental changes has meant that many of the ideas from the 60s and 70s are still relevant.",
"This isn't to say that operating systems aren't still an active area of research - they are. There are new ideas all the time - but the ones that get adopted are the small improvements rather than revolutionary changes.",
"If somebody started over, could they build an operating system that addressed all the negative criticism about the state of computing today?",
"That depends on what problems you are concerned about. Your question isn't clear on what those are."
] |
[
"reinventing a new kernel from scratch would be a waste of time.",
"Reinventing a new kernel from scratch for commercial reasons is very likely to prove a waste of time (or at least very expensive and risky). On the other hand, implementing a new kernel (or a new operating system paradigm) for academic reasons can be very fruitful.",
"Consider ",
"Plan 9",
". In any real commercial sense, Plan 9 was a failure. However, the ideas developed, tested and tried in Plan 9 didn't die with the project. Many of those ideas live on in the systems we use every day. It's end-to-end multi-alphabet support is ground breaking. The dominant way to express Unicode online (UTF-8) grew out of Plan-9. Many of it's distributed systems ideas are in wide use. The pure 'everything is a file' paradigm has informed many recent design decisions in the Linux kernel.",
"So no, reinventing is not a waste of time. Maybe a waste of money, but only as much a waste of money as any research is."
] |
[
"because the kernels we have now are not actually all that old. the linux kernel is in constant development and is very good. reinventing a new kernel from scratch would be a waste of time."
] |
[
"Historian with a couple questions on disease evolution in the 1400s."
] |
[
false
] |
I have some questions on the state of disease at the time or European encounter of the Americas. Smallpox and several other European diseases as I understand it evolved in part due to the proximity of Europeans to domestic livestock. I'm guessing this has to do with animals like pigs that root in their own wastes. Is this pretty much correct? Native Americans had dogs mainly and they are more or less clean animals (plus since they aren't packed together, raised as food). Some might argue the concentrated numbers of Europeans in cities, but there were several cities in what will be Latin America that had similar populations as those in European cities.
|
[
"For the case of smallpox, it's actually thought to have come from a rodent virus between ",
"16,000 and 68,000 years ago",
" in Africa. Since it's very unlikely that the same virus would evolve twice, the isolation of America meant this virus would not reach it until transmitted by humans (much much later on). The reasons for its spread in Europe probably are as you postulate, close proximity to animals and each other.",
"Many other diseases did occur through zoonosis (transmission from animals and then adaptation to humans) so being in close proximity to animals will have helped this. As with smallpox it comes down to the fact that there will only be one foci for the emergence of a virus, due to odds (basically), which then goes on to infect substantial numbers of people and then become historically recognised. In order to achieve this sustained infection there needs to be high density of people and people to record it. Chances are that there were many zoonosis infections in native America, but maybe the populations weren't dense enough to sustain it or they simply weren't recorded.",
"An yes, certainly animals like pigs that are in their own waste will be prime candidates for the emergences of disease simply through likelihood of exposure which then allows evolution to take place. ",
"I hope I haven't missed the point of what you were getting at with your original ideas, let me know if I have and I'll try and re-phrase"
] |
[
"Thanks, that makes sense on the smallpox idea. If we peg that somewhere around the 16,000 years ago date, the initial groups crossing the Bering Land Bridge would have been crossing into the Americas at the same time smallpox was making its debut. ",
"It also makes sense on the Native American front. There was a degree of contact between various groups of Natives, but it was very irregular and the groups were isolated from each other for fairly long periods of time (in terms of disease transmission and time for a disease to run through the entire group). Furthermore, when they did trade or come into contact with other groups, it was mainly the immediate neighbors. I'm not aware of any trips by Canadian Natives to trade with Natives in South America (which would have spread any local diseases across the continents). "
] |
[
"I'll have to take your word for all that, but it seems I've helped :). Also pretty interesting, even though I'm a scientist now, I've always enjoyed history, so nice to combine the two"
] |
[
"A few years ago it seemed that Ebola was apocalyptic, yet we stopped it. How were we successful is stopping it from becoming a global pandemic?"
] |
[
false
] |
in*
|
[
"No one expected it to be a global pandemic, except for the people who profit from panic (i.e. the news media).",
"And we didn't stop it. Another Ebola epidemic is going on right now, with no signs of being controlled, and the news media have decided that they don't care, so you don't know about it.",
"WHO Statement, Apr 12 2019",
"Ebola Epidemic in Congo Could Last Another Year, C.D.C. Director Warns (Mar 16, 2019)",
"The world’s second-worst outbreak of Ebola is underway in Congo. Where is the concern? (Mar 15, 2019)"
] |
[
"The only piece of good news on this Ebola outbreak is that the vaccine seems to work really well. ",
"The data are clear: Ebola vaccine shows ‘very impressive’ performance in outbreak (Apr 12, 2019)",
"The vaccine became available very late during the last big outbreak, and since the cases were already fading away it was hard to be sure how effective it was - though the preliminary data were very encouraging. Now, in the face of a severe ongoing epidemic, it seems clear that the vaccine is really good. That's fantastic, and raises the ",
" possibility of stopping future outbreaks before they start.",
"The problems are social (people don't trust the vaccinators and health care workers -- understandable, since these people have been lied to, assaulted, and stolen from by everyone they've dealt with all their lives) and economic (the vaccine is expensive and hard to deliver)."
] |
[
"With pandemics, a key thing is isolating those who’ve been exposed into a closed area, and treating them there as possible. The idea is similar to a forest fire; let the problem burn itself out. ",
"If the contaminated population is allowed to spread and infect new populations, it will keep spreading. Quarantining the infected limits that spread."
] |
[
"How accurate is \"Breaking Bad\"?"
] |
[
false
] |
EDIT: To clarify, I mean the "chemistry" that is discussed/portrayed
|
[
"As a chemist there have been a couple of other occasions when I've noticed things that aren't quite right, but I forget them now. The last one I remember is how their final product appears - a giant single crystal 'glass' slab in what appears to be a baking tray. Anyone who has ever tried to grow crystals will tell you that making a single crystal that big is mind-blowingly difficult, and takes incredibly amounts of time and very very precise control of the environment in which the crystallisation is occuring. I imagine their crystallisation is a solubility-based one, resulting from solvent evaporation (they appear to be using ether all the time), however the amount of meth they crystallise in a single tray is far far too high for the amount of solvent the tray could fit."
] |
[
"Maybe some specifics would help (OP and others, feel free to add/edit):",
"Can you dissolve a body with HF?",
"Would the \"Heisenberg method\" of producing Methamphetamine, really be superior to other methods ie. using Sudafed?",
"Is it that easy to make ricin?",
"Etc.."
] |
[
"If you just write down the recipe and follow instructions you're most of the way there, but there are of course some subtleties that come with practice and experience.. hence Heisenberg is the man, but hence mexicans can still cook meth in their kitchen at home. I guess it would be like asking a random person off the street to perform 'Twinkle Twinkle Little Star' after watching a maestro play it a few times on the Piano- if they wrote down what keys to push in what order they could probably get most of the way there, but it wouldn't be quite as good."
] |
[
"Why is evolutionary psychology frowned upon?"
] |
[
false
] |
[deleted]
|
[
"You nailed it when you described how untestable yet plausible these ideas are. Popular notions can take hold very quickly because they make sense to people. This doesnt make them right or even science though. ",
"Evolutionary psychology can test some of their claims and assumptions, but there are quite a few folks out there who play fast and loose- which gives the field as a whole a bad name. My prediction is that these are growing pains that are prevalent in lots of young fields. They will learn how to mature from speculation to a predictive science. ",
"But just beware- with this as with every science- dont trust a newsreporter to do the job for you. If you really care about the answer, read the original research and make up your own mind. And if you need help... AskScience!"
] |
[
"I've heard that many psychologists are dismissive of evolutionary psychology. ",
"Actually, it's many scientists in general. Some EP researchers are fine. However, a lot (I'm not saying the majority) are not. Why?",
"They retrofit ideas and concepts now to something that cannot be studied and usually do not have testable hypotheses. Effectively making stuff up at times. ",
"Opinion: Honestly, there is little purpose to fitting psychological mechanisms so far back into human development. It tells us nothing about now. Studying things now tells about now. Keeping good records of studies and publishing results will be good for future generations to understand how we \"evolved\" psychologically speaking. "
] |
[
"I think evolutionary psychology's best purpose is in giving lay persons a framework around which to understand medical and psychological phenomenon and scientific research. For a scientist, having an evolutionary psychology perspective doesn't really help much. Before becoming an AskScience panelist I never thought about things from an evolutionary psychology perspective. I never thought that way as a physician, and I never thought that way in doing my research. It just wasn't relevant. However, since joining AskScience, I've found that lay persons LOVE it when medical phenomenon are put into that perspective. I'm not exactly sure why, but it seems that for some people having a \"why\" helps them sleep at night. The problem is that even when backed by \"evolutionary psychological science\" that \"why\" explanation is usually just a guess. Sometimes it's a peer reviewed guess, but a guess nonetheless. "
] |
[
"how do even-dimensional waves behave?"
] |
[
false
] |
I recently read about a theoretical space with more than 3 spatial dimensions. I'm interested in the sound waves propagation part, it's basically saying that in a space with an odd number of dimensions (like ours) sound would behave as it usually does, BUT with a space with an even number of dimensions things would be different. It's giving an example with waves propagating on a 2D surface (the classic pebble in the water), saying waves “double back” on themselves. can anyone explain why does this happen? why in 2D, and how would it be in 4D? How would a 4D wave propagation pattern look like crushed down in a 3D tesseract?
|
[
"WARNING: I reached the character limit for my original explanation, so I am splitting into two posts. The second is found as a reply to this one. The explanation is long, but your question is not exactly simple to answer. This first post contains the maths and the second post answers your questions and comments using the results described in this first post.",
"You are referring to what is called \"Huygens's Principle\". The exact statement of this principle and the maths needed to answer your question in full detail are a bit complicated (what you would see in an intro graduate course in partial differential equations). So I will try my best to explain it.",
"First of all, the wave equation is the following partial differential equation:",
"u_tt-u_xx-u_yy-u_zz = 0",
"(The subscripts are meant to stand for partial derivatives. So \"u_tt\" means we have taken the partial derivative of u, with respect to time, twice.)",
"The solution we seek is u, and it is a function of three spatial variables (x,y,z) and one temporal variable t. The solution u might be temperature or energy. In two dimensions, u might be the height of some water wave. The point is that you should think of u as the \"wave\", which depends on (x,y,z,t). Also keep in mind that I have only written the wave equation in 3 spatial dimensions, but we can have any number of spatial dimensions. For instance, in two dimensions, the equation is",
"u_tt - u_xx - u_yy = 0",
"Okay, so how do you solve such an equation? Suppose we were seeking a solution u(x,y,z,t) on all of R",
" so for all (x,y,z). (We usually assume the domain of t is just [0, Inf).) It turns out that to get a solution, we need to provide two pieces of initial data:",
"g(x,y,z)\nh(x,y,z)",
"The function g is meant to be the value of u at time t=0. So g(x,y,z) = u(x,y,z,0). The function h is meant to be the value of u_t at time t=0. So h(x,y,z) = u_t(x,y,z,0). If this were a two-dimensional problem, you could think of g as the initial height of the wave and h as the initial velocity. Once you are given g and h, you can construct the solution to the problem for all times t.",
"Now this is where the part about even and odd dimensions comes into play. If we are working in an odd number of dimensions, it turns out that we can make what's called a \"change of variable\" to reduce the equation to one that is easily solved. (This is where some of the more complicated math starts to appear.) The change is done in steps. Most of the details in these steps are not necessary to understand the final result, but if you have taken at least some Calculus 3, it might interest you to pursue this further.",
"(1) STEP 1:\nInstead of considering u, g, and h, we consider their so-called \"spherical means\". We define some other function U(x,y,z,r,t), which is the average of u on the sphere of radius r, with center (x,y,z). We do the same for G and H. Then we fix (x,y,z) and consider U, G, and H as functions of (r,t). Note that is for any number of dimensions. We reduce the problem to finding the solution for a function that depends on only two variables, instead of any number of variables.",
"(2) STEP 2:\nWe find the partial differential equation that U(r,t) must satisfy. The equation it satisfies is the \"Euler-Poisson-Darboux\" equation. The equation in N spatial dimensions is",
"U_tt - U_rr - (N-1)/r * U_r = 0",
"We supplement this equation with the initial data G and H. So U(r,0) = G(r) and U_t(r,0) = H(r).",
"(3) STEP 3:\nThe Euler-Poisson-Darboux equation can be solved very easily if N is odd. We make one more change of variables and consider the function V = rU. Then V satisfies the equation",
"V_tt - V_rr = 0",
"which is the one-dimensional wave equation. This is really easy to solve, although I will omit the details. Suffice it to say there is an easy formula for the solution.",
"So the moral so far is that if we make some clever changes of variables, then wave equation in an odd number of dimensions can eventually be reduced to solving the one-dimensional wave equation. So what happens with an even number of dimensions? ",
"Well... the substitution V = rU doesn't actually work. In fact, if N is even there is no simple linear transformation that will transform the Euler-Poisson-Darboux equation into the one-dimensional equation. So the idea is to use the so-called \"method of descent\". If N = 2, then we regard it as a solution in three-dimensions, but in which the third variables just does not appear. The math gets a little complicated to get a bona fide solution in two dimensions only, but it works. For other even dimensions, we proceed similarly. For N = 4, we consider it as a problem in 5 dimensions in which the last variable doesn't appear. For N = 6, w consider a 7-dimensional problem first, and so on.",
"Okay, so what happens after all this math is done?",
"The formulas for the solutions in any number of dimensions are known, and can be looked up. There is one crucial difference between the formulas for odd dimensions and the formulas for even dimensions.",
"Both sets of formulas express u as the time derivative of a sum of some integral of g and some integral of h. In all dimensions, the integrals are related to the so-called \"region of influence\" at a point X.",
"C(X,t) = {Y in R",
" such that ||X-Y|| <= t}",
"(Note that X is a N-dimensional vector.) This region is also sometimes called the \"light cone\" for the point X. Quite simply, given the point X, the region C(X,t) is all those points where the solution u is possibly affected by the initial data given at X. That's why C(X,t) is called the \"region of influence\" for X.",
"If N is odd, then those integrals I mentioned above are calculated only on the ",
" of this region, also sometimes called the \"light-like\" events. If N is even, then those integrals are calculated over the ",
" region. This is what is referred to as Huygens's Principle. In other words, a \"disturbance\" originating at X propagates along a sharp wavefront (the boundary of C) in odd dimensions, but in even dimensions it continues to have effects even after the leading edge of the wavefront passes."
] |
[
"So now let's answer your questions and comments. (I reached the character limit for the original post.)",
"I'm interested in the sound waves propagation part",
"The discussion here holds for all waves. In the math above, the speed of the wave is just 1. But we can add a multiplicative constant to the equation to get a different speed. It does not change the formulas for the solution in any meaningful way. So the discussion above holds for sound waves, water waves, light waves, etc.",
"it's basically saying that in a space with an odd number of dimensions (like ours) sound would behave as it usually does",
"So let's be precise about what we mean by \"as it usually does\" and put it in the context of Huygens's Principle. Suppose I am 100 meters away from you and I active a blowhorn (one pulse for 1 second, say). The sound wave travels from me in all directions. Think of a dot on me that, when I activate the blowhorn, begins to expand as one sphere in all directions, centered on me. Technically speaking, this sphere has a very small thickness, corresponding to the 1 second that I let the blowhorn activate for. The spherical sound wave expands from me. Once it reaches a radius of 100 meters, you begin to hear the sound. For the next 1 second, you hear the blowhorn. Then the spherical wave has gone past you, never to return. So you no longer hear the sound wave. (Fun question, if you were traveling at the speed of sound and riding the spherical wave, do you think you would just continually hear the blowhorn?)",
"This is how sound, or any wave really, works in 3 dimensions. The waves arrives at our location, we detect it, the waves passes, and we never detect it again. Let's put it context of Huygens's Principle. My location is X and I am going to cause a disturbance (the sound wave). According to Huygens, that disturbance will propagate along a sharp wavefront and affect points only on the boundary of my region of influence. That is, my initial disturbance can influence only the expanding sphere and nothing inside of it.",
"BUT with a space with an even number of dimensions things would be different. It's giving an example with waves propagating on a 2D surface (the classic pebble in the water)",
"Yes, things are different. If my location is X and our world is only two dimensions, then Huygens says that my disturbance will not only influence everything on the expanding sphere, but continue to influence everything inside it. So you would hear nothing until the spherical wave reached you. Then you would begin to hear what you would normally. But after the 1 second has passed and the spherical wave has passed you, you will continue to hear the blowhorn. Now, this doesn't mean you would continue to hear the same blare for all eternity. The energy of the wave is highest on the boundary of the sphere and lower inside it. So your perception would likely be the following. You would hear the blowhorn as you would normally in 3 dimensions, then once the initial 1 second blare is over, you would hear the same sound continually fade until the energy (amplitude) is so low that it it is imperceptible to you. The frequency shouldn't change, so you will hear the same ",
". It's just as if someone is dialing back the volume gradually until you can no longer hear it.",
"You can see this effect in surface waves on water, like when you drop a pebble into a still pond. When you drop the pebble, what do you see? You see circular waves emanate from the source (drop point). If these waves acted like three-dimensional waves, you would see ",
" circular disturbance emanate from the source and then expand forever. (Not quite forever, as the energy does get dissipated, and if the source is close to the edge of the pond, you will see reflection. But we can ignore those effects.) But that's not what you see in the real world since the surface of the water is two-dimensional. You see something that looks as if circular waves ",
" to emanate from the source, well after you have dropped the pebble. (In reality, new source waves are not being created, as if you were dropping a pebble at regular intervals. What you perceive to be new source waves are really just the effects of the original wave in its entire region of influence.) The original circular wave, according to Huygens does not affect only the water on the edge of the disc (the circle), but ",
" water within the disc.",
"can anyone explain why does this happen? why in 2D, and how would it be in 4D? How would a 4D wave propagation pattern look like crushed down in a 3D tesseract?",
"So first of all, I can't tell you how you would perceive a 4D wave, because we just don't live in a 4D world, at least not in world in which we can perceive 4 spatial dimensions. Also, a \"tesseract\", by definition, is just a 4D cube. So it makes no sense to talk about a \"3D tesseract\". I am also not sure what you mean by \"a 4D wave crushed down in a 3D tesseract\". A 4D waves lives in 4D-space, not 3D space.",
"The mathematical explanation given above is why waves are different in even and odd dimensions. The exact step where the difference matters is when we solve the Euler-Poisson-Darboux equation by a simple linear change of variables. It turns out it's just not possible in even dimensions. That explains the math behind it, but not much of why it should happen physically. I'm not really sure there is much physical intuition. (It's not required all the time to have some intuitive explanation of why things occur, sometimes the math is all you have.)",
"All I can say is that the method to obtain solutions in even dimensions uses the solution in odd dimensions. So, for instance, in 3D, the solution influences only the surface of a sphere, and not the inside of it. Since the 2D solution is built from the 3D solution, you can imagine that the 2D solution uses all of the information on the boundary of the sphere. But since the boundary of the sphere itself is two-dimensional, we find that 2D waves influence 2D regions. That is, 2D waves do not influence just the 1D circle, but the entire 2D disc. That's the best I can really say. But again, that's an intuition we get from the maths and not from anything physical. I also find this result to be very surprising and interesting and have never found an adequate explanation from physical principles only. ",
"If you are interested in this subject, you can look into a first course in partial differential equations."
] |
[
"First of all, a huge THANKS for your time and for your awesome reply!\nLet's get cracking!",
"I can't tell you how you would perceive a 4D wave, because we just don't live in a 4D world, at least not in world in which we can perceive 4 spatial dimensions. Also, a \"tesseract\", by definition, is just a 4D cube. So it makes no sense to talk about a \"3D tesseract\". I am also not sure what you mean by \"a 4D wave crushed down in a 3D tesseract\". A 4D waves lives in 4D-space, not 3D space.",
"When I said \"tesseract\" I was meaning \"section\", I think. It should be possible to have 3D sections of the 4D wave, does it make sense? Like putting a 2D surface near the source of a spherical wave and looking at the wave passing through that surface. Given a 4D wave equation this should give you the possibility to set a \"viewpoint\" relative to the source, i.e. putting a 3D space somewhere near the source point of the 4D wave, and thus seeing this 3D section of the wave varying over time. Is it possible? What would be the equation that does this?",
"That explains the math behind it, but not much of why it should happen physically. I'm not really sure there is much physical intuition. (It's not required all the time to have some intuitive explanation of why things occur, sometimes the math is all you have.)",
"Disappointing and fascinating at the same time.",
"But again, that's an intuition we get from the maths and not from anything physical. I also find this result to be very surprising and interesting and have never found an adequate explanation from physical principles only.",
"Very interesting indeed! But maybe, and I'm saying MAYBE, it can be seen as; one dimensional waves are just one dimensional, they can't influence anything else, when it's a 2D wave it starts to interfere with itself, in 3D it has one further dimension to \"let out\", so interference in the first two doesn't happen, and so on. I don't know if this actually makes sense...",
"and finally",
"(Fun question, if you were traveling at the speed of sound and riding the spherical wave, do you think you would just continually hear the blowhorn?)",
"from what I know, if you were traveling exactly at the speed of sound you shouldn't hear anything, because the air pressure is not varying for you as you are tailing the wave, thus remaining constantly in a point where the wave is still. Actually, you are standing in a point where there is a bias, that would likely decay with time, as the wave dissipates."
] |
[
"If i stare at a specific point in a pattern, why do the surrounding points disappear?"
] |
[
false
] |
I was staring at a line in my tile floor, and the lines around it disappeared as i kept my focus.
|
[
"I think this would be better placed in neuroscience, because it has to do with how your brain processes information. ",
"It is due to something called ",
"Troxler's Effect",
". you can read about this on the wiki page, but basically the sensory neurons get \"used\" to the unchanging stimulus and so begin to ignore it. Same thing happens when you sit perfectly still, you can't feel your shirt!"
] |
[
"To add onto this: The peripheral vision which encompasses the surrounding disappearing lines uses rods to process the visual information. Many rods can be tethered to one ganglion cell leading to the optic nerve. The convergence of many rods onto one cell helps you see your surrounding a little better when your brain isn't focusing on it. Rods are phasic receptors. Phasic receptors start out by sending quick action potentials but soon stop the action-potential process so the brain can focus on other things than on processing unimportant information (like if your arms are touching the desk when you type, you don't even notice it or feel it until you think about it). ",
"Cones however are used for the item your eye is focusing on. There is one cone per ganglion cell so their visual information is more direct and therefore more accurate in the information it sends to the brain. Cones are tonic receptors which is the opposite of phasic receptors. Your brain continues to process and focus on information that tonic receptors share."
] |
[
"Neuroscience and cognitive science will provide explanations at different levels of representation here, which are certainly equally \"valid\" or explanatory.\nFrom a cognitive or perceptual point of view, I would point out visual attention that is known to modulate even early-stage visual processing, and that is sensitive to change. (See also \"Change blindness\", etc.) An expert in visual perception and processing may be able to say more."
] |
[
"Is there an advantage, from an engineering point of view, in having two separate \"on\" and \"off\" switches in a circuit (or a device) rather than a dual-function switch?"
] |
[
false
] | null |
[
"Separate on and off switches is the same as two switches IMO. ",
"In memory operations (and many other cpu pipeline operations, or in general Boolean logic) you can have a third state: ",
"don’t care",
". ",
"This is used to speed up addressing or make it more general, ",
"for example",
". "
] |
[
"Thanks - your example reminds me of how we would approach this problem in software development. Having separate \"off\" switches gives you the ability to give controls to the end-users."
] |
[
"I can see the application of a second switch in a logic gate. I was more curious about the electrical/electronic machines world. "
] |
[
"Is anything really possible? Such as anything I can imagine scientifically be created?"
] |
[
false
] | null |
[
"Examples- superman \nPokémon \nTeleportation\n6 foot walking taco that shits ice cream. "
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Well how do I go about posting this question?"
] |
[
"Can anyone explain the weak nuclear force to me?"
] |
[
false
] |
I've read around a bit online, and have a understanding of the weak nuclear force, but a few points are kind of baffling me. For instance, where do the W and Z bosons "come from", and what precisely is happening when a quark's flavour changes? Furthermore, the W and Z bosons are said to be elementary particles, yet in beta decay (for example), the W boson decays into an electron and antineutrino. What's going on here?
|
[
"Basically, it's like a tennis ball that when it hits something, the thing it hits transforms.",
"That's my understanding, anyway.",
"What's going on here?",
"Basically what's happening is conservation of energy. The energy from the boson is converted into an electron and an antineutrino. Quantum numbers are preserved as well because electron+anti(electron or neutrino)=0. "
] |
[
"W and Z bosons comes from particles that have weak charge. This is like asking \"where does light (photons) come from?\" Photons come from particles that have electromagnetic charge. And yeah, as far as we know W and Z bosons are elementary, but just because they can decay into two different particles doesn't mean they weren't originally elementary. An electron and positron can anhihilate to form 2 photons, but that doesn't mean that electrons and positrons are really photons. "
] |
[
"This won't answer your question but I did ask about the W and Z bosons last week. ",
"This may be fun reading",
" until one of our resident particle scientists show up.",
"You also may want to sort this subreddit by new and dig around the posts from the last two weeks (there aren't many). There's tons of really awesome information on particle theory."
] |
[
"Why do most depression medication give side effects that include suicidal thoughts?"
] |
[
false
] |
[deleted]
|
[
"That is a really, really good question and the short answer is that we just don't know yet. It seems to be due to two different, but related effects: anti-depressants have a \"lag-phase\" of a 3-4 weeks before they really become effective and they can lead to wild mood swings in patients with underlying bipolar disorder, which is why they aren't recommended as a single medication for those diseases.",
"First of all, to be clear, ",
"there isn't yet a rigorous cause-effect relationship between suicide rates and anti-depressives",
", but strong evidence that there may be one in certain groups. One reason that makes it so hard is that clinical guidelines do not allow suicidal patients to be involved in studies for marketing a new drug for safety reasons. They look at instead \"suicidality\", which is a tendency to think about suicide. Plus, there is a lot of evidence that suicide rates have actually ",
" since the widespread use of newer anti-depressants. But it is incredibly difficult to get any statistically significant relationship from such a complex problem.",
"As to your questions about possible processes, we don't know that either, but its important to know what these drugs do first. Whether its an MAOI or SSRI like prozac, the primary mechanism is to increase the levels of serotonin or norepinephrine in the CNS by either blocking their reuptake or blocking their degradation. Serotonin is particularly important, since it regulates \"",
"sleep, cognition, sensory perception, motor activity, temperature regulation, nociception, mood, appetite, sexual behavior, and hormone secretion",
".\" Elsewhere on this thread, people have mentioned other changes occurring along with the primary mechanism of anti-depressants that basically leads to higher levels of the neurotransmitters seretonin and norepinephrine. These other changes are adaptive changes that occur with all of this extra neurotransmitter and may lead to an overall increase in ",
"seretonin receptor numbers or sensitivity",
", neurogenesis in the hippocampus, and/or changes in downstream products like Brain derived neurotropic factor. There is a lot of very interesting research still waiting to be done in this area and my anticipation that better therapeutics will come as a result with more efficacy and fewer side effects.",
"The other effect, a switch to a manic like episode, is even less well understood and I'm a bit less qualified to talk about it since I'm a biochemist and not a psychiatrist, so maybe one can chime in. It seems that the abrupt mood improvement that anti-depressants cause can lead to a ",
"an overall mood destabilization",
", exasperating the cyclical nature of these diseases in patients with underlying bipolar, a bit like alcohol does. Its easy to see how this could be problematic before the actual therapeutic benefit of antidepressants is realized."
] |
[
"The really important thing to remember here is that if even teeny tiny percent of the clinical trial reports suicidal thoughts during the course of the trial for the drug, then the drug company has to report it in their advertising. These suicidal thoughts may or may not have been related to the effects of the drug."
] |
[
"Unfortunately I can't offer your guys proof that what I am saying is true, but my father, who is a psychiatrist, has confirmed this. The medications don't \"cause\" suicidal thoughts, so much as coming out of the depression but still having it a bit is a critical period for this."
] |
[
"How much water is in a cloud?"
] |
[
false
] |
Since clouds are dense enough that we can see them and dense enough to block sunlight, how much water would I have if I condensed the vapor from a cloud that's, let's say, 3,000 cubic meters into liquid? (Not sure if that's a reasonable cloud size.)
|
[
"You can see clouds not because they are \"dense\" enough, but because they have tiny particles (dust, ice, water droplets) that scatter light. A sheet of glass is much denser than a cloud, but clear glass is also more transparent.",
"This is a pretty complex subject, but a couple easy things to remember are:",
"moist air is lighter than dry air, all else (temperature, pressure) being equal. This means that moist air will rise in a column of air, if it's free to move.",
"clouds aren't actually just moist air, they do have moist air but they also have tiny water droplets, ice particles, and dust particles. It's water in different phases, gaseous, liquid and solid. In comparison to moist air (where all the water is in a gaseous state), a cloud is somewhat denser, again all else being the same.",
"So what happens is that moist air rises (because it's less dense than dry air). As it rises, it cools down and starts to condense. This produces tiny water droplets (like 1/1000 the size of a raindrop), and if it's high enough, ice particles as well. A cloud generally stabilizes at a height where its density is about the same as the air around it. However, individual droplets of water or ice are still heavier than the rest of the cloud, and would fall. They are held up by updrafts, or upward movements of air. It takes a very small updraft to hold up clouds, since the droplets are so small.",
"Of course, when the droplets get larger then the updraft is no longer able to keep them aloft, and we have rain.",
"If you want to see the math regarding all this, ",
"this paper shows the calculations",
". It's pretty math-heavy, so be warned.",
"As for your other question, a 3000 cubic meter cloud would be tiny. Most clouds are much larger. A typical cumulus cloud ",
"is about a cubic kilometer in volume, and has about 500 tons of water",
". Larger clouds can be much, much heavier. A big stormcloud could have over a million tons of water."
] |
[
"You heard wrong: the orders of magnitude aren't even close. ",
"Only 0.001% of the Earth's total water is in the atmosphere",
", and only some of that is in clouds (the rest is water vapor)."
] |
[
"You heard wrong: the orders of magnitude aren't even close. ",
"Only 0.001% of the Earth's total water is in the atmosphere",
", and only some of that is in clouds (the rest is water vapor)."
] |
[
"Why do we observe constellations from Earth?"
] |
[
false
] |
Astronomers of antiquity observed more or less the same constellations as we do today. How is this so, given Earth orbits the sun, which in turn orbits the galactic centre (and the galaxies move further away from each other!)? Are the stars in the major constellations in our 'arm' of the Milky Way, or at least a neighbouring arm, and so move with us around the galactic centre? I am in London and see a limited amount of stars given smog etc, but lately I noticed Orion, viewed two nights in a row and directly to the South can appear differently e.g. Narrower or taller which suggests the configuration of Earth and the stars does slightly morph. Is it fair to say that we only see a glimpse of the stars' configuration, given our ~70-80 year lifespan as compared with that of stars and the cosmos (hence it appears as a 'snapshot' to us mere humans)? Thanks in advance to my favourite reddit in the cosmos! EDIT: more detail about observing Orion
|
[
"Astronomers of antiquity observed more or less the same constellations as we do today.",
"Actually, we can see from star charts made by the ancient Greeks that the constellations have changed shape slightly since then. Edmund Halley was the first to notice it. Here's a nice little explanation of constellations: ",
"http://spaceplace.nasa.gov/review/dr-marc-space/constellations.html",
".",
"Are the stars in the major constellations in our 'arm' of the Milky Way, or at least a neighbouring arm, and so move with us around the galactic centre?",
"The brighter an object is, the farther away we can see it. So Mars and Jupiter look pretty bright in the night sky, but they're very close. You can also see other galaxies, which are much farther away but much bigger. Between these two extremes, most of the stars in the major constellations are in our stellar neighborhood. But the brightest-looking stars are not necessarily the closest.",
"I noticed Orion can appear differently e.g. Narrower or taller ",
"Are you looking at Orion at different times of the night (when Orion is closer or farther away from the horizon)? I think what you're experiencing is an optical illusion, the same one that makes the Moon look bigger when it's near the horizon. The Bad Astronomy blog has ",
"a nice explanation",
" of this. The constellations don't change from night to night enough for us to see. It takes thousands of year for a perceptible change (see that first link)."
] |
[
"Yeah, and to give a scale, the stars with the ",
"highest \"proper motion\"",
" are moving at a few arcseconds per year. 1 arcsecond per year for 2000 years is only about 0.5 degrees of change.",
"Most stars move much more slowly than that. ",
"Here is an animation of the fastest star over 20 years of observation",
". See that most of the other stars don't move significantly during that time."
] |
[
"they are moving, and they do change shape . . .over time . . . a LOOOOOONNNNNNNGGGGGGG time. Even with everything moving around as fast as it does, it still takes hundreds of years for us to notice a change. Go to starryNight or any other star software, set the time flow as fast as you can and you will see the small changes taking place."
] |
[
"A two part question on lighting dimmer switches..."
] |
[
false
] |
When you have a light on a dimmer switch that is turned almost all the way down, is it using less electricity or is some of the energy "wasted" by the dimmer? The dimmers in my house give off some form of EM interference which is picked up by audio recording equipment so presumably some of the energy is "wasted" in this manner. When my lights are dimmed, they give off a very high pitched (Some people can't really hear it so it's well above 10kHz) buzzing noise. What causes this?
|
[
"http://home.howstuffworks.com/dimmer-switch.htm",
"I'm not an engineer, but the 'old way' appears to simply be increasing the resistance (which would produce more heat). The new method takes advantage of alternating current to switch on the circuit for a fraction of the phase. Maybe this switching is causing the high frequency noise (probably around 16-18kHz) .",
"EDIT: From the link:",
"If you hook up a really cheap dimmer switch, you may notice a strange buzzing noise. This comes from vibrations in the bulb filament caused by the chopped-up current coming from the triac."
] |
[
"So the buzz is caused by the filament being ",
" moved? By what mechanism is the filament moved? Some kinda induced magnetism? 16-18kHz sounds about right. Good to know that I can still hear up that high but bad to know I've got ",
" cheap dimmer switches..."
] |
[
"This sudden shift in voltage changes the magnetic field abruptly, which can cause the filament to vibrate -- it's rapidly drawn to and repelled by the metal arms holding it in place. In addition to producing a soft buzzing sound, the abruptly shifting magnetic field will generate weak radio signals that can cause interference on nearby TVs or radios!",
"Go buy a new switch!"
] |
[
"Is there a material with an electrical resistivity of 10^7 to 10^8 Ohm-m?"
] |
[
false
] | null |
[
"The closest thing I can think of is PVC which has a resistivity of about 10",
" You could maybe coat a sheet of aluminium foil with pvc, which could give you both the right thickness and resistance."
] |
[
"Some type of doped glass might work. Glass itself has around 10",
" doping could bring that down a bit. \nAlso consider what temperature you want to run it at. According to this, the resistivity can change dramatically: ",
"http://www.memsnet.org/material/glasssio2bulk/"
] |
[
"Thanks, I'll look into it! Where did you get that info on PVC's resistivity?"
] |
[
"Is a coma \"restful\"? If I were hit in the head and knocked out for eight hours, would I wake up feeling like I had slept for eight hours?"
] |
[
false
] |
[deleted]
|
[
"No, comas are not restful.",
"Sleep has an actual structure to it. One cycles through non-REM stages I, II, III, IV, and back down, then through REM and the same thing all over again. Whatever the brain is actually doing during this time, it's replenishing you.",
"A coma is an abnormal state of unconsciousness and profound lack of responsiveness to outside stimuli. Comas are much more serious than they are typically seen. A coma means your brain is pretty severely out of whack, in ways that don't always get 100% back to normal.",
"Compare an electroencephalogram (brain wave study) during coma and during sleep. Sleep has an orderly structure: vertex sharp waves, K complexes, spindles; slow waves of sleep; rapid eye movements, sawtooth waves; and so on, depending on the sleep stage. A coma will show disorderly, arrhythmic slow waves generalized over the entire brain that aren't reactive to outside stimuli.",
"If anything, people coming out of comas are typically still very groggy and lethargic. It's not like any sort of orderly awakening. It will to a large degree depend on what caused the coma.",
"Most concussions result in very short-lived, if any, periods of unconsciousness. If one were hit on the head and remained unconscious for many hours, a more severe injury might be implicated. Things like contusion or diffuse axonal injury, even traumatic hemorrhage. One is unlikely to feel rested waking from one of those injuries."
] |
[
"Well I'll be honest, it's a science question that wouldn't be hard to hit up google with."
] |
[
"Well I'll be honest, it's a science question that wouldn't be hard to hit up google with."
] |
[
"Why can't some build immunity against allergies?"
] |
[
false
] |
I have basic immune system knowledge but not enough to answer this question. I'm pretty sure that the only thing that should make an allergy different from other antigen responses is that it's physical, but why don't memory cells help during the second response, building eventual immunity?
|
[
"It's a good question. My answer is hazy, because to be honest, the knowledge is a bit hazy. ",
"B cells are not a homogenous population. There exist three main types of B cells: B1, B2 and marginal zone B cells. B2 are what we think of as \"classical B cells\". All three types can form plasma cells and produce antibodies, but only B2 can form memory cells (although there seems to be a decent amount of evidence that B1 and MZ cells form long-lived plasma cells. ",
"B1 and MZ have a polyclonal set of BCRs, whereas B2 B cells tend to be more monoclonal. B1 and MZ cells are also more capable of T cell independent activated by stimulation either through polyclonal activation of their BCRs (normally through repeating motifs in bacterial polysaccharides) or through stimulation of the BCR in tandem with stimulation of Toll-like receptors. ",
"This causes activation, differentiation, antibody class-switch recombination to IgE. IgE is the allergen associated antibody when it binds, say, pollen then binds to Fc(epsilon)I on mast cells. These mast cells are then activated and degranulate, dumping histamine into the surroundings. That's your allergic response.",
"But - and here's my best shot at your answer - the original stimulus came from T-cell independent B cell activation of B1 or MZ which cannot then go onto form a memory response.",
"Addition: Also you have to bear in mind that an allergic response is a response to a totally harmless antigen. It's almost an auto-immune reaction against a foreign antigen - it shouldn't happen and doesn't serve any benefit. By forming a memory response, all you would do is increase the potency of response, which wouldn't help anything.",
"To further the auto-immune analogy - we do actually see that removal of Breg cells (analogous to Treg cells, which we know are vital in auto-immune condition suppression) leads to increased allergic response.",
"B cells are classified into classical CD5- conventional B cells and CD5+ B1 cells. The latter produce multi-specific autoantibodies and are thought to be involved in autoimmune diseases. However, evidence supporting a B cell negative regulatory function has accumulated over the past 30 years. Multiple reports have suggested that absence, or loss, of regulatory B cells exacerbates symptoms of both allergic (including contact hypersensitivity and anaphylaxis) and autoimmune (such as experimental autoimmune encephalomyelitis, chronic colitis, and collagen-induced arthritis) diseases, and in lupus-like models of autoimmunity. Regulatory B cells are characterized by production of the negative regulatory cytokines, IL-10 and TGF-β. ",
"Allergy Asthma Immunol Res. Jul 2011; 3(3): 168–177."
] |
[
"Thank you! "
] |
[
"It's not my area of expertise - I had a quick search as I hadn't heard it before and:",
"Compared with participants who regained their allergies, the individuals capable of eating the food without a problem had roughly twice as many peanut-specific regulatory T cells, a type of immune cell that helps to dampen allergic responses.",
"I assume that Bregs secreting TGFb direct Th0 cells to become iTregs in the periphery?"
] |
[
"What, if anything, limits electromagnetic radiation to gamma rays on the high end and radio waves on the low end?"
] |
[
false
] |
Are there waves that are just so big that nobody has experience them fully in the human experience? I mean long, long waves that haven't passed through entirely Earth yet with one frequency over millions of years? I'd bet there's some fundamental constant that bounds them with an upper and/or lower limit, but like I said I'm just guessing here. I suppose the fact that at some point you're not gonna be able to get any less distance between the waves due to planck lengths and whatnot which will keep them from going higher energy than gamma.
|
[
"There is no physical constraint on the longest possible radio wave, but we use the same term (ELF, or extremely low frequency) for all radio waves 3hz or below. Gamma rays have an extreme upper bound in frequency where their wavelength is the same as the planck length, and at 1.022 MeV, photons interact with matter to for electron-positron pairs.However, \"gamma rays\" includes all particles with freuencies greater than 10",
" hz."
] |
[
"I thought planck's length would be a limit?"
] |
[
"Plank units are too often cited as some kind of limitation. Really they are just a possible point where our current understanding of physics ends, not some place where nothing is allowed."
] |
[
"How efficient are antennas in comparison to florescent or LED light sources?"
] |
[
false
] |
RF and visible light are different colors of the same phenomena. So how different are antennas to LEDs? If I was able to see visible light as well as 100MHz light, would a 60W radio amplifier connected to a good antenna shine as bright as a 60W LED light bulb? Bonus question: Parabolic metal antennas work as curved mirrors. Do we know of a material that works with RF the same way as glass does with visible light? Can we make RF lenses (see-through rather than reflective)?
|
[
"Interesting question.",
"So, antennas are very efficient in certain configurations. Again, using your example, a single-bay FM radio antenna rated for up to 1kW would be about 45% efficient. That's really bad, as far as antennas go ... more in a bit.",
"But the circuits that drive the antenna are less efficient. To use your 100 MHz example, if you pick up a PTEK LPFM transmitter capable of 330 Watts Total power output, would be approximately 67% efficient at maximum power. At a lower power, it would be somewhat more efficient, but the specification doesn't say. I'll use the 67% figure.",
"And you have some signal loss in the cabling to go from your transmitter, at ground level, to the antenna up on the tower. We'll take a guess at this and call the coax 95% efficient, but this can be a major loss if you have a very tall tower.",
"All in all, this system would be about 29% efficient at producing RF output at 100 MHz.",
"Now, back to the antenna. In the VHF, it is easy to create more efficient antennas by simply stacking elements, which effectively makes the antenna flatter - sending less signal into space and more towards the ground. The cheap antenna with poor efficiency I cited above has a stacked cousin which has a rated gain of 2.05, or 205%. If you redo the math with this antenna, you're suddenly 130% efficient! No laws of physics being violated, its just a quirk of how the regulations for Radio Frequency works.",
"Also: We can make RF lenses. You know them as satellite dishes :)"
] |
[
"Well satellite dishes reflect the RF into the receiver. I was thinking of something that refracts the RF akin glasses. "
] |
[
"In theory, yes. but I haven't been able to identify any materials that have Fresnel indexes cataloged at VHF frequencies. ",
"This could be because the \"slit experiment\" is more difficult to run outside the visible spectrum, because you can't use a piece of paper, a prism and a protractor to figure out the refraction. Instead you need a transmitter that can emit a wave very directionally and a detector that can find a wave at a specific angle. And the setup would be fairly large - since the wavelength at VHF is in the single-digit meters compared to the hundreds of nanometers at visible light."
] |
[
"What causes head-rush when we stand up too fast? What do we \"see\" when this occurs?"
] |
[
false
] |
As the title asks. When you stand up too fast from a sitting/laying down position and your vision goes dark and you start to see "images". What causes this?
|
[
"When you are sitting down you are a bit compressed and when you stand up quickly, your blood suddenly has to fill the parts that didn't have so much blood due to the compression. This causes a drop in blood pressure resulting in the brain not getting enough blood, so it starts shutting down, which you feel as a head rush."
] |
[
"Orthostatic Hypotension",
" is the technical term. "
] |
[
"Yup, orthostatic hypotension. ",
"The lower blood pressure and blood flow in your head causes the visual problems as well, there's temporarily not enough oxygen to process the signals that come from the eyes correctly."
] |
[
"Where is the Andromeda galaxy visible with the naked eye--anywhere on Earth, from the ISS, from the Moon, from the dark side of the Moon, etc?"
] |
[
false
] |
I know that it it's nigh on impossible to see it--despite it's size. But can the astronauts on the ISS see it, where the Apollo astronauts able to see it, could it be seen on the dark side of the Moon, would you have to get further from the Sun, what would it take?
|
[
"It is visible from pretty much anywhere in the northern hemisphere that's reasonably dark. It won't be the brightest thing out there, but it'll be a reasonably bright and noticeable fuzzy patch in Andromeda, near Cassiopeia. Because it appears fairly near the north celestial pole, it's not visible from far southern latitudes. ",
"could it be seen on the dark side of the Moon",
"There is no such thing as the dark side of the Moon; there's the ",
" side, but it's not always dark."
] |
[
"From ",
"the Wikipedia page",
":",
"At an apparent magnitude of 3.4, the Andromeda Galaxy is one of the brightest Messier objects,[15] making it visible to the naked eye on moonless nights even when viewed from areas with moderate light pollution. "
] |
[
"I'm not sure what you're asking. For it to be as bright as the Milky Way is to us, you'd need to be in the spiral of Andromeda."
] |
[
"Are there any attempts to explain the cause/source of the existence of newton's laws, if so then how successful are they?"
] |
[
false
] | null |
[
"Yes, Lagrangian and Hamiltonian mechanics explain Newton's laws as arising from optimizing a quantity known as the \"action\" (which in many common systems would the be the difference between the kinetic and potential energies). These theories have been ",
" successful, to begin with they are much more easily generalized to modern topics like general relativity and quantum mechanics, where Newton's laws fail to hold. In addition they have inspired many topics in other fields, including optimization, geometry, and partial differential equations (you'll note my flair bears the name of Hamilton). At the end of the day these topics basically build on top of calculus, but I think that the unique points of view offered by Lagrangian and Hamiltonian mechanics have been important in many of the discoveries. ",
"Sorry, this comment may not make much sense, I'm running on no sleep unfortunately."
] |
[
"...energy and momentum, which are always conserved.",
" always."
] |
[
"Calling it the \"principle of extreme action\" is misleading though since the solutions to the Euler-Lagrange equations do not necessarily give an extreme value of the associated functional. (This is also why \"principle of least action\" is misleading.) Solutions of the EL equations are guaranteed only to give stationary values of their associated functionals (under some mild conditions like convexity and the like). The most accurate term should be \"principle of stationary action\"."
] |
[
"Growing Hopper Crystals?"
] |
[
false
] |
I got a batch of pure (99.9% grade, i believe) bismuth, and I want to melt it down to make some . I've read some on how to grow them, but nothing with a scientific explanation how to make them the best. Any help would be appreciated.
|
[
"I'm not sure you can do much better than listen to the people who've already done it. Even research papers might not amount to much more than \"this is how we did it\". ",
"See, growing crystals is a pretty difficult topic. A whole field in itself (there's even a \"journal of crystal growth\"), because there are just so many variables involved. I can't say I know much myself. I don't even think crystallographers always know; I suspect they often just try stuff on the basis of random hunches. Sometimes even without hunches. It's a bit of a black art.",
"So there's not much advice I can give other than to follow those who've succeeded in making nice crystals. (There's certainly no straightforward scientific theory of crystallization on the lines of 'If you do ",
" your crystals will look like ",
"'.) I don't even know much about it myself.",
"Apart from what they said there, since Bi is easily oxidized, I'd suggest doing it under an inert gas (argon or nitrogen) if you have any, to avoid loosing all your bismuth to oxidation if you do repeated melting. And/or get some flux to put into the melt. That may affect the crystals. But it might not too. Hard to say."
] |
[
"I attended a lecture called \"none of your bismuth\" at burning man... it was burning man, so I don't remember every detail, but I can say for certain that it was done in the middle of a dust storm, with a camp stove. You shouldn't have any problem pulling it off at home."
] |
[
"Thanks for the response. From what I've read, the oxidation creates that shiny outer coating, so when would I expose it to oxygen if I melt it down in a surrounding with inert gas?"
] |
[
"Why are particle accelerators like the Large Hadron Collider in Europe built underground?"
] |
[
false
] |
I imagine that particle accelerators would be a lot cheaper and easier to build if they were above ground.
|
[
"There are a few reasons that particle accelerators are generally built underground. The main reason of course being ",
"Synchrotron radiation",
". In addition, building underground makes it easier to achieve stable thermal conditions which matters more than you might expect.",
"You could build an above ground accelerator, but the amount of radiation shielding needed would likely make it more expensive than simply drilling a tunnel. In a tunnel you can simply use plaster and/or concrete for the walls, no other radiation shielding needed."
] |
[
"Also: cosmic rays, and in the case of the LHC, above-ground would have to contend with major roads and villages. ",
"It's also worth noting that synchrotron radiation isn't a very big deal in proton accelerators (as opposed to electron), though radiation is still a significant issue in the case of a beam stability problem, beam halo, etc, so it's a good idea to build underground. "
] |
[
"17 miles in circumference, under the french/swiss countryside, under villages and major roads, etc. "
] |
[
"Some years ago I watched a video showing the effects of the earth slowing its rotation and eventually stopping. (Basically chaos) My question: Would there be similar effects if the sun slowed down or stopped its rotation?"
] |
[
false
] | null |
[
"If the sun were to suddenly stop spinning there would be no change in the orbit of the planets at all. It wouldn't even largely decrease radiation emotions, although it may decrease light by a negligible amount due to the loss of efficiency for convection within the sun. But as ",
"u/SAR-Paradox",
" pointed out, the sun rotate because of the conservation of rotational energy in the original disk of primordial dust that formed our solar system. But that energy were suddenly lost in the sun only, there would be no real change. "
] |
[
"Presumably there would be an increase in rate of fusion as gravity would no longer have to provide a centripetal force to keep the sun bound, so radiation pressure would need to up its game to match this, but I have no idea whether this effect would be significant."
] |
[
"What would this \"chaos\" be?"
] |
[
"Do the atoms and/or electrons in a wall *feel* anything when a radio wave passes through them? i.e. do they move at all?"
] |
[
false
] | null |
[
"Yes. If you drive a piece of material with a sinusoidally-varying electromagnetic wave, the medium will respond with a time-dependent polarization and magnetization. This corresponds to the charged particles inside the material oscillating back and forth, producing tiny instantaneous electric currents and dipole moments."
] |
[
"But the loose interaction as a photon passes by is what leads to an index of refraction.",
"http://laser.physics.sunysb.edu/~jennifer/reference/index/indexrefraction.html",
"Waves that are encountered by any kind of matter will have a transmission of energy. This will cause the electrons into a vibrational motion. When the electrons move they generate a field causing a change in the transmitted wave. The electrons will move at a resonant frequency to the vibration of the electrons. If the frequency of the incident ray of light's electromagnetic wave does not have a frequency matching this then the energy produced from this will create a new electromagnetic wave. This wave will have a phase change from the origninal wave. This change is a phase shift that slows down the propagated wave. The photons that travel through the material still travel at the speed of c. It has already been determined that photons never travel at a speed other than that of c. They travel through the empty space inbetween the atoms. They continue to travel until they encounter another partice within the material. The whole process is repeated and another new wave is produced. This cycle repeats as the wave travels through the media encountering particle after particle. The time delay that it takes for all the photons to travel between the interatomic void is what causes the net speed of transfer to be slower than the speed of c. The amount of time delay usually depends on the optical density of the material. This describes how an electromagnetic wave can move through a material. "
] |
[
"But the loose interaction as a photon passes by is what leads to an index of refraction.",
"http://laser.physics.sunysb.edu/~jennifer/reference/index/indexrefraction.html",
"Waves that are encountered by any kind of matter will have a transmission of energy. This will cause the electrons into a vibrational motion. When the electrons move they generate a field causing a change in the transmitted wave. The electrons will move at a resonant frequency to the vibration of the electrons. If the frequency of the incident ray of light's electromagnetic wave does not have a frequency matching this then the energy produced from this will create a new electromagnetic wave. This wave will have a phase change from the origninal wave. This change is a phase shift that slows down the propagated wave. The photons that travel through the material still travel at the speed of c. It has already been determined that photons never travel at a speed other than that of c. They travel through the empty space inbetween the atoms. They continue to travel until they encounter another partice within the material. The whole process is repeated and another new wave is produced. This cycle repeats as the wave travels through the media encountering particle after particle. The time delay that it takes for all the photons to travel between the interatomic void is what causes the net speed of transfer to be slower than the speed of c. The amount of time delay usually depends on the optical density of the material. This describes how an electromagnetic wave can move through a material. "
] |
[
"How can I access scholarly articles?"
] |
[
false
] |
[deleted]
|
[
"You could try asking on ",
"http://www.reddit.com/r/scholar",
" , it's a whole sub-reddit for requesting articles"
] |
[
"Case closed!"
] |
[
"You might want to try the local community college. You would have to go to their library, but you can email yourself the PDFs."
] |
[
"Do, or rather, can animals choose whether or not they want offspring?"
] |
[
false
] |
Do some animals reject mates for life and remain celibate out of choice?
|
[
"I'm not aware of \"celibate,\" but zoopharmacologists (people who study animal use of medicines) have found that elephants will eat the bark of a certain tree to induce labor and/or early-terminate a pregnancy, and I've heard of other species re-absorbing their young when the local dominant male gets supplanted so that they don't have to go through the process of labor just so the new male can kill their offspring. ",
"This all comes from behavioral ecology literature but I think a quick Google search will bear those out. "
] |
[
"I dn't know about animals in the wild, but when kept as pets, many birds will not reproduce unless provided with an appropriate place for a nest. Not sure if you can really consider it their choice, but at least this shows that they know they should only lay eggs when they find the right conditions."
] |
[
"In general, this would be ",
" (especially given that out-crossing is demonstrably more favorable than inbreeding). However, a genetic mutation or injury could potentially inhibit those standard behaviors.",
"As noted in some of the other comments, there are certainly cases where animals receive environmental cues that cause them to temporarily avoid reproducing (not enough resources for offspring, wrong season, illness, hostile surroundings, etc...) Pregnancy for many animals (especially mammals) is an extremely costly endeavor and selective pressure would again maximize efficient use of resources. ",
"Humans are animals and clearly there are some who make this choice:\n",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2868060/",
" - So in the case of mankind - ",
"But is that a choice driven biology or merely the sapience that comes with being human.",
"Copulation during pregnancy and during non-fertile periods has been observed in apes and other mammals. Taken alone this suggests a strong behavioral inclination towards mating regardless of offspring production.",
"I think a big barrier to overcome in answering this question is ",
". This probably enters into a psychological/philosophical realm that current science is ill-equipped to investigate. "
] |
[
"Why does the density of the universe have anything to do with its shape?"
] |
[
false
] |
According to this posted on TIL, the geometry of the universe is decided by its density and that because matter is not dense enough to cause a big crunch (or at least it does not appear to) we are therefore led to conclude that the universe is most likely flat and infinite. Why is that conclusion valid? Why can't the universe just be large enough (but finite) that the density of matter is equivalent to or less than what would be required for it to be infinite and flat? I don't see what does density have to do with the geometry of the universe at all?
|
[
"In general relativity, geometry and energy-momentum are inextricability linked. The fundamental equation of GR, G",
" = 8pi T",
", expresses this connection. Consequently, a dense, homogeneous, expanding universe must be closed, and a thin one must be open.",
"Note: I'm ignoring the cosmological constant (dark energy)."
] |
[
"The mechanism for gravity is actually the curvature of spacetime. The more dense a spot is, the more the space there gets depressed, and the more \"attraction\" you get.",
"We realized that there is a number, represented by Omega, that determines if our universe is heavy enough for a big crunch or not. If omega were greater than 1, our universe would be saddle shaped, having negative curvature, and eventually collapse on itself. Right at 1, and our universe is flat. Below 1, and our universe is bulbous, has a positive curvature, and would rapidly push itself apart.",
"We have empirical evidence that our universe is flat. A simple way of putting it is that light, when not affected by gravity, moves straight. Two beams moving parallel will remain the same distance apart. This is not the case for, say, Earth, which has a positive curvature. If you are in NY and I'm in LA and we both travel straight north, we will actually be getting closer and closer to each other even though we were moving parallel to each other.",
"We know that Omega has to be just about 1, and that is also how we know how much dark energy there has to be in the universe. The matter that is accounted for only makes up about .35 Omega. So the rest has to be dark energy keeping our universe flat",
"So because of this, we know our universe is not heavy enough to collapse back in on itself, so it will continue to expand forever.",
"Hope this helps. Anyone feel free to correct me or ask me to elaborate on anything."
] |
[
"I don't think it could ever be infinite. It just means that the universe will expand and expand and entropy will increase and increase."
] |
[
"If a point is translated a unit either up, down, left, or right, determined randomly, in a two dimensional cartesian plane every second for an infinite amount of seconds, what position would it approach as the amount of seconds approaches infinity?"
] |
[
false
] |
I envision the origin (assuming it starts at the origin) to be the most likely destination for the point after n iterations. However, I doubt that if I carried out this experiment 1000, 10,000, or 1,000,000 times that the point would fall anywhere close to the origin. Is there even an answer to this question?
|
[
"The average displacement of a 2D random walk is zero, but the root-mean-square displacement is proportional to the square root of the number of steps. This lets you define a \"radius of gyration\" which tells you the average size of a random walk."
] |
[
"It's a question of combinatorics. ",
"Handwavingly, you'd count the number of possible paths of a certain length that will let you return to 0 and contrast that with the total number of paths of that length. As it turns out, in 1d and 2d the asymptotic behaviour of these quantities leads to a probability of 1 that you will return to the origin after a finite number of steps, but for 3d and higher the total number of paths grows too fast compared to the number of paths that'll let you return to 0. ",
"A nice proof is given here: ",
"https://www.math.ksu.edu/~cnmoore/randomwalk.pdf"
] |
[
"Also, for a 2 dimensional random walk, with an increasing number of steps the probability of returning to the origin approaches 1 (despite the RMS distance from origin increasing).",
"However, this isn't true for 3 or more dimensions."
] |
[
"If the chemical trypotran(can be found in milk, and banana's) has an effect on the production of dopamine in the brain, wouldn't that actually have the reverse effect on the body by not producing it's own natural level?"
] |
[
false
] |
[deleted]
|
[
"First off, you are talking about tryptophan, the amino acid? What is the exact question you are asking?"
] |
[
"I suspect Thrownaway200 is talking about this:",
"http://en.wikipedia.org/wiki/Tryptophan#Use_as_a_dietary_supplement_and_drug",
"Specifically:\n\"... Tryptophan has shown some effectiveness for treatment of a variety of other conditions typically associated with low serotonin levels in the brain.[27] ...\"",
"Guessing on a translation of Thrownaway200's question:\n\"Does Tryptophan's effect on serotonin levels cause the brain to compensate, thus eliminating the effect?\""
] |
[
"Tryptophan (not ",
") is a chemical precursor to 5-HTP, which is a chemical precursor to 5-HT, aka serotonin (not ",
"). Here's a ",
"fancy pic",
" from wikipedia.",
"Ingesting foods that contain tryptophan can increase the available serotonin in you brain, but it will not adversely impact your body's ability to produce it's \"own natural level\". Serotonin is naturally synthesized from chemical precursors (tryptophans) that come from food, so eating foods that contain tryptophan is how your body gets its \"own natural level\". "
] |
[
"Is it possible for a tornado to destroy a skyscraper?"
] |
[
false
] |
Reading a story related to the EF5 tornado that hit Moore, OK. on Monday, someone in comments said that these types of tornadoes could destroy skyscrapers in midtown Manhattan. Could an EF4 or EF5 actually destroy the structure, or would it just cause all windows to be blown out? Thanks.
|
[
"Depend's on your definition of \"destroy\", it could surely do significant damage but I do no know of any collapses due to tornado. The damage will be greatly dependent on the building geometry, lateral force resisting system, surrounding buildings and terrain and can be difficult to predict. ",
"Let's first take the example of residential home. The roof system of the house will act as the diaphragm holding the walls of the house together. Any wind force will create uplift (upward pressure / suction) on the flat or angled faces away from the wind. The large winds in a tornado will lift off the roof of the house, thus comprising the diaphragm and the houses's ability to resist any lateral load.",
"The same phenomenon will happen on tall buildings, but the consequences will be greatly dependent upon the lateral force resisting system of the building and its geometry, that said, commercial buildings are not designed to withstand 200mph winds as consistent with EF4/5 tornadoes. The exterior cladding, particularly glass as you have indicated, will be broken and is the typical observed damage of a tall building in a tornado. In theory, after the glass is broken the winds will be flowing through the building and not only around it; however, even if this does reduce the lateral force on the building (due to the reduced area of wind being resisted) the uplift issue as described for the residence will remain. The combined action of a substantial lateral force and uplift force could definitely damage the substructure if significant enough.",
"A modern tall building in a seismic region would fare much better as it is designed and detailed to under go large plastic deformations and absorb significant amounts of energy. ",
"Another issue is the effect of the surrounding tall buildings (as is the case in Manhattan) will effect the wind profile and speed the buildings are being subjected to. However, I would only be speculating on what that effect would be.",
"Source: PhD student in structural engineering and grew up in Oklahoma City"
] |
[
"I know this is probably a stupid question, but could you give me a little more insight? I'm not an engineering minded guy.",
"On 9/11, hijackers flew jumbo jets into the world trade centers. These were metal objects, filled with jet fuel, and they collided with the buildings at 400+ mph from what I understand. Even then, the buildings didn't immediately fail. The burning of the jet fuel eventually weakened the structures to the point of failure. ",
"The tornado in Oklahoma had wind speeds of 300 mph; I'm sure that tall buildings are built to withstand certain expected environmental forces, like earthquakes to a certain magnitude, hurricane force winds (cat. 5 being 155 mph+)",
"I guess I just wondered if the tornado would actually cause the building pillars to snap and fail. There are tornadoes that occur in places like Houston and Dallas, and these are major cities with tall buildings (taller than 40 floors)."
] |
[
"The frame of the Metro Tower in Lubbock was ",
"severely damaged",
" in a 1970 tornado."
] |
[
"Are the relativistic time differences between clocks on the Earth and the clocks in GPS satellites, due to the reduced gravity 12,500 miles up or the speed at which the satellites travel or both?"
] |
[
false
] |
An object that travels faster relative to another has an internal clock that 'runs' slower, while an object closer to a gravitational source does the same thing, so which of these (the distance from the gravitational center of the Earth or the orbital speed) has the greater effect on the clocks in the GPS satellites?
|
[
"The velocity causes the clocks to fall behind by 7 microseconds per day. The lower gravity causes them to go faster by 45 microseconds per day. Net result is that they go about 38 microseconds per day faster than clocks on the surface. So the gravity has a bigger effect and also the two effects are in opposite directions. ",
"Source"
] |
[
"The clocks on the satellites run slower than those on the ground by about 7 microseconds per day due to the (special) relativistic effect of their high speed. They run ",
" by about 45 microseconds per day due to the (general) relativistic effect of the \"reduced\" gravity."
] |
[
"Both, but the gravitational effect is stronger."
] |
[
"Can metallic objects passed through and electromagnetic field cause a measurable differance?"
] |
[
false
] |
[deleted]
|
[
"If I'm not mistaken this is how guitar pickups work."
] |
[
"Not really sure what you're talking about here. What is the setup you're envisioning here? What is the battery hooked up to? In general, yes, metallic objects brought through/into an electromagnetic field will be detectable - assuming relative motion between the object and the field - due to the induction of current in the object and a resulting generation of an opposing field (Lenz's Law) that ultimately appears as a change in the impedance seen by the source."
] |
[
"I don't know enough about the properties of batters as far as their behaviour as a voltage source goes, but monitoring the voltage is probably not the best way to do it; you'd be better off measuring the current. You should indeed see a drop in the current when you sweep the electromagnet past a metallic object."
] |
[
"With the knowledge we have at hand, what will the earth be like in 100 years?"
] |
[
false
] |
I'm thinking along the lines of developments in technology, including nano-tech and the development in neuroscience in conjunction with replacing limbs and some senses, e.g. sight, or even enhancing the human body as it is, and how our push forward will affect us socially, as well as affecting military protocols and acts of war. Will war, for richer nations, be solely based on robotics, drones, and biological agents, instead of the use of ground troops? And what about environmentally? What would happen if one summer, the ice caps DID melt, and year upon year, ice continued to disappear around the spring/summer seasons? How would that affect our coastal regions and what action would it spurn?
|
[
"And to make up from my earlier snarky comment:",
"What was life like 100 years ago?",
"Locomotives and coal fired ships were the best transportation you could get. Automobiles, electricity, and radio were in their infancy. Television wouldnt be invented for another 2 decades. The Internet as we know it would take 8 decades. ",
"Imagine a world where you ride a horse and people die from things like an infected cut. Where paper mail and news take weeks to cross the country. A world where you spend a month traveling from America to Europe. ",
"Now project 100 years ahead.",
"Today, Space travel, nanotechnology, fusion, quantum computers and solar power are in their infancy. "
] |
[
"I do think that we will plateau relatively soon, every great leap ends with a long period of same old same old until the next great innovation.",
"Who knows what that will be."
] |
[
"I can't account for all the changes that we will see in 100years, but on the basis on the environmental changes I can come with some theories.",
"first: I'm at the moment doing a Master in Environmental and landscape geography at the University of Bergen under professor Anders Lundberg (the master thesis is about environmental changes on beaches in southern Norway). I got a bachelor in Environmental and resource studies.",
"The thing with melting ice caps you need to remember is that the more heat you get in any region of the world, lets say around Greenland, would meen more water vapor in the air. This would mean more presipitation in the form of snow in the higher regions. That is why we today see a decline in the ice cover in Greenland along the coast, but a increase in the higher regions. So in short, its not going to melt all at once like some films make you belive. ",
"When/if this happen you would of cource get a higher water level, causing some cities to be in danger of flooding if something isn't done. The time frame we are talking about here is something like atleast 10-20years if I'm to be kind with the numbers. Within that time most cities would have made some sort of flood controll or other modifications to hinder any seriouse damage.",
"If we look at the environmental impact of melting ice caps we have several stands to take.",
"First we could see that some of the glacier dams of water could give a catastrophic water release resaulting in a total hault of the gulf stream that carries warm water from the gulf and up north to england, norway, iceland and so on. (this would also affect many animals that relly on this stream, like the freshwater eel). This stream is in some part responsible for the heating of the nothern regions and could if we are looking at the worst possible senario cause a minor iceage for the northern parts. More likely is longer winters and colder summers. ",
"The melting ice caps would also reduce the amount of sunlight that is reflected back into the atmosphere, causing even more of our water to evaporate. Seeing as water vapor is one of the biggest greenhouse gasses this would speed up the heating of earth, melting more ice and you get the picture. This would then again cause areas like africa and middle america to become more like dessert (in the sense that you can't really grow anything there), but again make the northern areas more prosperous giving a higher yield of wheat etc.\nYou could say that it makes everthing that is extreme more extreme. Places where it is hot gets hotter, and cold places gets even colder, atleast in the start.",
"If we take this a step further the new found temprature boost over the whole world could melt the perma frost in the siberian marshes which contains high amounts of methane gas, wich also is a huge greenhouse gas, much more damaging then CO2, this would again speed up the globalwarming, and you get a snowballing effect.",
"What sosial implications this can have I leave to other people, and I left much I wanted to say out because this became a wall of text. But I guess people will fill in the blanks."
] |
[
"Do we see any stars from out of the milky way, or maybe whole galaxies, with the bare eye?"
] |
[
false
] | null |
[
"You can just about make out the ",
"Andromeda galaxy",
" with your naked eye (if you live in the northern hemisphere). You will probably need to travel to a very dark area to do so but it is relatively easy to find, have a google for a guide if you are interested, it is near the constellation Cassiopeia (the big W on the opposite side of the north star from the plough). It will sadly only look like a very faint, grey, fuzzy blob.",
"The Andromeda galaxy is about 2 million lightyears away which compares to about 10,000 lightyears for the most distant visible stars in our galaxy. This makes it by far the most distant object observable with the naked eye.",
"If you live in the south, you can see the large Magellanic cloud. This is also extragalactic and it (along with it's small friend) is known as a satellite galaxy. Satellite galaxies are basically small clusters of stars which orbit their host galaxy (the milky way in the case of the LMG and SMG)."
] |
[
"And to complete the answer - no individual stars are visible with the naked eye which are not part of our galaxy."
] |
[
"also, even the stars we do see are only from a very small fraction of our galaxy."
] |
[
"We hear a lot about new ways to generate electricity, such as fusion. But are there any new developments in the way we harness heat and transform it into electricity?"
] |
[
false
] |
I hear a lot about fusion and "new-generation" fission reactors being potentially revolutionary in the way we generate electricity. However, it is my understanding that it will be a new way to generate heat, while we will still use old-school steam turbines to convert heat into electricity. My question is, are there any theoretical or "moonshot" ideas of a more efficient way to electricity
|
[
"It’s a really good question that basically comes down to thermodynamics, how to use energy in the form of heat to do work. There are very few losses in the actual generator, and likewise you simply combust natural gas, that can be done quite efficiently (nat gas furnaces are efficient into the upper 90s of percentages). So the issue is in changing heat to work. You do this with some kind of thermodynamic process, called a cycle. ",
"The two most common are the Brayton Cycle and the Rankine Cycle. The Brayton is what’s happening in a jet engine - it’s a combustion turbine that compressed a working fluid, combusts it, and then expands it (work is extracted during expansion). The Rankine is a steam turbine and it’s the classic power plant picture - heat a fluid to steam, expand it through a turbine to extract work, condense it, re-heat to steam and repeat. Both of these are fundamentally limited by the Carnot efficiency, which is the theoretical maximum efficiency of the thermodynamic cycle. ",
"A modern thermal power plant maximizes efficiency but combining both. A Combined Cycle Gas Turbine plant will basically have a jet engine at that front, take the hot exhaust (sometimes heat it further) and use that to make steam, which powers another turbine. Assuming no extra heating of the exhaust, the efficiencies add because it’s the same energy source (burning natural gas), which powers two cycles, a Brayton and a Rankine cycle. This makes for a pretty efficient system. Ultimately, Carnot efficiency relates maximum efficiency to differences between temperatures, that’s why you burn something, it makes a temperature difference when one area is now hotter than the ambient. This means your efficiency can only go up if the combustion is hotter and the cooling is cooler. The truth is there isn’t all that much further that this can be pushed. It’ll get better over your time, but it’s hard to imagine a “moonshot” as you say, because you can’t really disrupt thermodynamic limits. ",
"That’s just the thermodynamics of thermal systems though, in answer to your question. Fuel cells, solar cells, etc, have a lot more runway to get vastly more efficient. That’ll be pretty cool."
] |
[
"Very nearly all forms of electrical generation come from a heat transfer. This includes fossil fuels, fission, fusion, many types of solar (but not all), geothermal, and I'm sure I'm missing others. Exceptions:",
"-Windmills: kinetic energy in the air to electricity",
"-Hydroelectric: varies, but in dams it's gravitational potential energy into kinetic water into electricity, and in wave/paddlewheel it's kinetic water to electrical",
"-Chemical: Strictly speaking, batteries generate heat, but it's as a strictly waste product. The electricity comes from the energy difference between compounds.",
"There's not much to be done in terms of more efficient heat conversion: IIRC, the solar farms that use molten salt for heat gathering retain more than 90% of the heat before being used for generating power, and there are hard limits to how efficient that heat transfer can be.",
"It's been a LONG time, but I think a non-mixing water to water heat transfer peaks somewhere around 70% efficiency, for example."
] |
[
"Fuel cells basically do direct chemical energy to electrical energy conversion, and therefore should theoretically be more efficient than extracting that energy with a combustion step. ",
"I believe that modern hydrogen fuel cells, which are approaching 60% efficiency, capture a greater percentage of the chemical energy in H2 than you could realistically obtain by burning it. Or, at the very least allow you to attain those high efficiencies without high temperatures in a small form factor, and that getting the same efficiencies via combustion would require large combined cycle type turbine with very high temperatures and attendant costs and complexity."
] |
[
"How fast would a metal object have to move through Earth's magnetic field to generate significant electrical current?"
] |
[
false
] |
Say you have a 10 meter long conductor. How fast would it need to move to generate a few milliamps? Enough to light a low power LED?
|
[
"Nope, but I just went searching for it. Turns out there's a wikipedia page about them: ",
"Magnetorquer",
"A magnetorquer or magnetic torquer (also known as torque rod) is a satellite system for attitude control, detumbling, and stabilization built from electromagnetic coils. The magnetorquer creates a magnetic field that interfaces with an ambient magnetic field, usually Earth's, so that the counter-forces produced provide useful torque.",
"Enjoy."
] |
[
"I'm pretty sure some satellites (or at least designs for satellites) actively interact with the Earth's magnetic field (by inducing currents) to torque themselves, in order to save, or even slowly reset their gyros."
] |
[
"I'm pretty sure some satellites (or at least designs for satellites) actively interact with the Earth's magnetic field (by inducing currents) to torque themselves, in order to save, or even slowly reset their gyros."
] |
[
"How can dark matter be huge a substantial part of our universe but we can't see or detect it?"
] |
[
false
] | null |
[
"In much the same way as how bacteria and atoms were a huge, substantial part of our day-to-day lives but we couldn't see or detect them either.",
"We don't currently have the means to meaningfully observe and explore dark matter. That doesn't mean it can't possibly exist. It just means our understanding is limited by our technological capacity and the length of time we've had to look for it (based on when we discovered evidence suggesting the existence of it)."
] |
[
"Thanks, helps me understand it a lot better. "
] |
[
"We can detect it by its influence on other things as ",
"/u/astri-oh",
" pointed out. We can't see it because it's thought not to interact with light, therefore it does not absorb or emit."
] |
[
"Do imaginary numbers have any practical applications?"
] |
[
false
] | null |
[
"Of course, why wouldn't they? They're just as real as normal numbers, which is to say not at all. Complex numbers are a nifty way to encode 2D translations, 2D rotations and scaling compactly as addition and multiplication. Very convenient. ",
"Electrical engineering, fluid dynamics, quantum mechanics and much more all explicitly use them. ",
"At the core, though, Complex Numbers are just the part of the basic vocabulary needed to speak \"math\". This is true of everything in math. All the math that you learn in high school and college is just the basic vocabulary of math. And ",
" is the real application: To make you fluent in a complicated and precise communication scheme."
] |
[
"Electrical engineers for its rotational properties to study the periodic behavior of circuits. (See ",
"this",
").",
"Fluid dynamics uses it because you can encode fluid motion as a differentiable function on the complex plane. (See ",
"this",
")",
"Quantum Mechanics uses it because quantum states can look the same, but have different \"phases\", which is a rotation in complex space that doesn't manifest directly but can change how states interact. (See ",
"here",
")",
"Fourier Transforms are used to understand functions by breaking them up into oscillatory components, using complex numbers. These are used literally everywhere, from Number Theory to computer vision and everywhere in between. (See ",
"here",
")",
"Control Systems use complex numbers to encode complicated systems into the complex plane. How this encoding works determines what will happen to the system. (See ",
"here",
")",
"They pop up all over the place."
] |
[
"If you have an alternating current, and a circuit with such interesting components as capacitors and inductors as well as resistors, then you can model the voltage as V0 e",
" instead of V0 cos(wt). The real voltage is the real part of the complex voltage, of course. But why do this? Because then, inductors and capacitors become components with imaginary resistances, and you can just use Ohm's law (with complex numbers) to obtain the (complex) current from the (complex) voltage. It's by far the easiest way to analyse LCR circuits. ",
"In quantum mechanics, particles aren't little point-sized objects, they literally are a complex-valued wave that satisfies a simple differential equation. The physical universe is literally made of complex numbers."
] |
[
"So we know how dominance and recessiveness work for Mendelian traits because we were taught about Punnett Squares in school. But how do dominance and recessiveness work for more complex/polygenic traits?"
] |
[
false
] | null |
[
"For any given gene we don't really know how dominant or recessive various alleles will be, as for most genes we don't even know what they do yet, or only have a very rudimentary understanding of what they may be involved in. In general, the extreme dominant/recessive traits we study in school are rare and most functional alleles will be exist somewhere in the middle of dominance/recessiveness. Most cases of complete dominance is where the 'recessive' alleles in simple not functional in some way. Also the traits we study in school generally have two alleles, black/white or there/not for example, but (again with the exception of non-functional genes/proteins), genes may have many different alleles and some may be very similar to another, while others are very different. For complex traits therefore the question gets even more messy, because each trait is determined by multiple genes which each have their own complex situation of dominant/recessive alleles. TBH, as a research geneticist, I don't really hear the terms dominant/recessive used much at all, its not really a useful way of looking at most traits or genes as they are more complicated than that, but it may just be the field I'm in. ",
"I think its worth pointing out that most of the Mendelian traits we were taught at school are not simple Mendelian traits at all, ie eye colour, hair-colour, tongue rolling, hairline, ear-lobedness. Certain coat colours in animals and flower colours in plants are though. Like I said, simple Mendelian traits are quite rare. The utility in doing punnent squares is really to understand inheritance rather than figure out phenotypes accurately IMO. "
] |
[
"The same way they work for everything else, except that you also include epistasis and other interactions. So let's take height, for instance. Let's say there are 200 genes that dictate it. In a simple model, just imagine that each gene contributes some number of inches or fraction thereof to your total height, and there are many alleles of each.",
"So for this polygenic ",
" trait, what it would mean for allele A of gene 135 to be dominant over allele 'a', is that the height contributed by genotypes AA and Aa are the same, while genotype aa makes a different contribution.",
"You can get all the normal varieties here. In incomplete dominance, AA and aa make different contributions, but Aa is somewhere in between. The only difference between this and simple mendelian traits is that you can't even narrow down the genotype of an organism by its phenotype, since the phenotype is arrived at by taking the combined contributions of all 200 loci.",
"In the case of a polygenic ",
" trait, we can still have dominance and repressiveness, but we must consider epistasis (this also matters for quantitative traits, but it's far more obvious for qualitative ones). Imagine you are studying the genes that control a cat's coat color. You know of a mutation that causes the cat to become black, and you know that the black allele is recessive and simple mendelian. You also know of a mutation that causes the cat to become white, and this mutation is ",
" recessive and simple mendelian.",
"But these phenotypes are incompatible, so what happens if you are mutated for both? Well, it turns out you get a white cat. The white gene is considered to be \"epistatic\" to the black gene. This word means that a mutation in the white gene overrides the phenotype that would be expected from the genotype at the black locus.",
"So as you can see, even in the case of complex traits, recessiveness and dominance are still defined the same way that they are for simple Mendelian traits, but while imagining the rest of the genome constant. Once you start considering complex combinations of genotype, there is a whole added layer of complexity, but all of those interactions get different definitions."
] |
[
"Before I start forgive me for any inaccuracies and feel free to add elaborate or correct me if you see anything wrong.\nThis is a very complicated topic we still don't understand fully in humans but we do understand that for at least some characteristics it has to do with Barr bodies and epigenetic inheritance, now that in English really means that for each cell one chromosome is \"turned off\" and the Gene's on the other are expressed. A common example of this is tortise shell colored cats, they get their different fur colors because one color is expressed on one chromosome and one is on the other, and as they are selected randomly throughout the cats skin it forms a mosaic of color.",
"Another way this is explained specifically through non humans but in some fish and other species is operon activation, which is when a large string of genes that control something are switched on or off by an activating gene before them. An example of this would be in the stickle back fish it has an operon that triggers whether or not it grows a pelvic fin at all.",
"Additionally we have incomplete dominance or codominance which are usually explained in school with punnet squares so I won't go into them now.",
"If you have any questions or corrects please comment, I'm always trying to learn and understand I know this is not a comprehensive list of the ways just some common ones (I'm only a freshman bio major in college I know there's lots to come)"
] |
[
"What's the deal with Bell's Paulsy - how does it occur and what's actually happening? Why would it happen to a 10 year old?"
] |
[
false
] | null |
[
"You can find basic info with a simple Google search which will lead you to the NINDS website... Do you have a more specific question? "
] |
[
"I mean sure... How does it occur ",
"? All I can find is \"damage or trauma to the facial nerves,\" but where would that damage or trauma come from? And again, why would it occur with a child? I had it when I was 10 and was told it's extremely rare in kids.",
"I might just be dumb, but ELI5 don't allow these sort of questions :P"
] |
[
"There are sections on this on the wiki for Bell's Palsy. Causes unknown. Could be inflammation of a facial nerve caused initially by a viral infection although there are lots of other possible causes and risk factors. As to why you in particular had it as a kid isn't something that can be answered."
] |
[
"How are eggs shaped so perfectly?"
] |
[
false
] |
If what I have read is correct, forming the egg shell is the last step. How is the shell formed around a soft egg without various deformations, and with nearly perfectly circular cross sections?
|
[
"I actually have chickens, their eggs are all shapes and sizes.\n",
"Example",
"\nThe ones you see in the store have been picked from all the colorful ones and all the \"misshapen\" ones so that they all look the same color, size, and shape."
] |
[
"Exactly, the reason they're all the same shape is they only sell you the ones that are the \"right\" shape."
] |
[
"The eggs you will buy in a store will all roughly be same shape, like w3rthlessspe0n said. But if you ever get the chance to raise chickens (or buy farm fresh eggs) you will see more interesting shapes. They range in both shape and size, and once my father found an egg no bigger than a gumball and perfectly round in shape. "
] |
[
"If salmon return to the same river every year, why are there salmon in more than one river?"
] |
[
false
] |
Did they just get lost? Did humans move salmon eggs around? Did separate river ecosystems all evolve to have the same species?
|
[
"I think it would be similar to how insects and birds that are on the mainland can also be found on islands - a small number of fish get lost and manage to find another river to breed in. If separate rivers evolved separately, they would be different species (though they may still be able to interbreed). "
] |
[
"I don't know the answer to this. I live and work on the east coast (no salmon) but as a fish ecologist, I have a few good ideas.",
"The most reasonable to me is that not ",
" salmon return to the same river. In any population, there are going to be some strange individuals who are not exactly like their parents. This coupled with natural selection is the driving force behind evolution. So for whatever reason, one or a handful of salmon began using a different river, and found it to be beneficial. That salmon's offspring became a different population in a different river. This seems most likely to me because as you probably know there is a metric shit ton of salmon that try to move up river seach year (although there are less each year recently). So a salmon that happened to find itself in a suitable river with no competition or predators would probably have a huge ecological advantage.",
"Another reason is that rivers change over time. They wander, they capture each other, they might not flow as strongly some years, etc. Especially at the end of the last ice age when there was a ",
" of fresh water flowing from places it hadn't flown before, rivers in northern areas have change a lot.",
"As far as separate river ecosystems evolving to have the same species, that is unlikely. Salmon spawn in rivers, but they spend most of their lives in the ocean. Also, from what I understand, there are several species of salmon that inhabit different river systems on the Northern Pacific coast."
] |
[
"just looked it up, someone said they could do DNA testing insted of physical tagging, i couldnt find any evidence of someone doing it though"
] |
[
"What kind of success did alchemy have?"
] |
[
false
] |
You always hear about the outlandish failures of alchemy: it failed to turn lead into gold, failed to make people immortal, failed to create the fabled fifth element (æther). But what success did alchemy have? Since so may people believed and practiced it for so many hundred years I'd assume it made some progress or had some experimental successes it could show off. Am I right? If so, what kind of successes did they have? [Added a "chemistry"-flare since it forced me to add one, when this question is more for the historians of science.]
|
[
"One of the kings of the German kingdom of Saxony, Augustus the Strong, hired an (al)chemist call Böttger to invent a method of making gold - he failed entirely, but in the process came up with a technique of making high quality porcelain, which started large scale production in Meissen in 1710. Until then, porcelain manufacture had been a well-kept Chinese secret, so being the first to be able to produce comparable porcelain in Europe made the Saxony a lot of money."
] |
[
"The chemistry flair works quite well, actually, since \"alchemy\" and \"chemistry\" are basically the same word. The \"al\" of \"alchemy\" is just the Arabic word for \"the\". I forget offhand what the original Arabic origin of \"chemy\" meant, but you can see the relation to \"chemistry\".",
"From a 21st century perspective, we do have a clear distinction between the two, but that's something that developed over time. Alchemy morphed into chemistry as we figured out and formalized the scientific method, and started to abandon the old \"four elements\" model of matter.",
"Now that's not to say that alchemists didn't try to change lead into gold, or figure out how to make humans immortal, but that isn't all there was too it. There were tons of quacks going around selling elixirs, but there were also people genuinely trying to figure out how the world worked, and the very best would employ techniques not totally different from the scientific method. Maybe they couldn't turn lead into gold, but they might discover some new alloys along the way. Likewise, they never found that elixir of life, but they were still developing new ways of working with and analysing chemicals. As an example, phosphorus was discovered by someone trying to make a philosophers stone: \"Hennig Brand - Wikipedia\" ",
"https://en.m.wikipedia.org/wiki/Hennig_Brand",
"Tldr: while their major aims were to modern eyes silly, alchemists were still often very intelligent people who needed to think up new tools and techniques to advance their work. Alchemy wasn't a science, but it was a precursor to science, and modern chemistry grew from it."
] |
[
"This is exactly the kind of thing I was looking for. Thank you very much! If you have more examples please share!"
] |
[
"What's the difference between carbonite and carbon dioxide? They both have the same formula . . ."
] |
[
false
] |
[deleted]
|
[
"Carbon dioxide is a neutral species. On the other hand, carbonite is a double charged ion, which can be written as [CO2]",
". In other words, if you find a way to remove the two excess electrons from carbonite you can get carbon dioxide. "
] |
[
"That's the carbonate anion. The -ite and -ate denote different chemical formulas."
] |
[
"Lithium is able to form a carbonite, but only under extreme cold (15 Kelvin). (wikipedia)"
] |
[
"How nutritious are animal organs (besides skeletal muscle)? Should we be eating some of them?"
] |
[
false
] |
I understand not eating brains (mad cow disease) and intestines (poop). But what about things like livers, kidneys, bone marrow?
|
[
"People eat a lot of offal meat. Prior to supermarkets and pre-packaged meat, it was very common to eat pretty much every part of an animal.",
"Liver",
" is not only tasty, but incredibly high in iron and a bunch of other vitamins/minerals. Have you ever heard the expression, \"what am I? Chopped liver?\"? This refers to ",
"food",
".",
"Heart",
", being basically all muscle, is very high in protein.",
"Intestines are very commonly eaten as well, most commonly as ",
"casings",
" for things such as sausages.",
"Have a look through the Wikipedia article on ",
"offal",
" for a lot more of the \"other\" parts of an animal that are readily consumed and highly nutritious."
] |
[
"Years ago, PBS aired an installment of the NOVA series called ",
"Becoming Human",
" where the opinion of anthropologists studying human origins was put forth that our early ancestor's ability to use tools allowed us to scavenge the carcasses of animals killed by other top predators and extract bone marrow that would otherwise have not been accessible. This extra source of fat and protein nourished, among other things, the development of a larger brain with the potential for higher intelligence."
] |
[
"I know in some cultures the gallbladder and other organs of certain snakes are eaten or used as medicine. Is there any scientific backing to this? My gut tells me no, and a google search turns up a myriad of results."
] |
[
"Since we now have superconductors that exist well over the boiling point of liquid nitrogen, why haven't we built super excellent power storage facilities with them?"
] |
[
false
] | null |
[
"Because a superconductor will wind up storing any power that you put into it in the form of a magnetic field. One of the fundamental properties that separates a superconductor from a \"perfect\" classical conductor (just a metal with infinite conductivity) is that a superconductor will expel magnetic field lines from its interior except for a very small skin depth near the boundary of the superconductor, known as the ",
"Meissner effect",
". This is the reason why magnets can \"float\" above a superconducting plane. ",
"However, a big enough magnetic field on the superconductor surface will wind up driving the superconductor through a phase transition back to its ordinary conducting state. That means if you want to use a superconductor to store energy in the form of a magnetic field outside of it, you are fundamentally limited in the amount of energy you can store by how strong that field can be. ",
"Also, near this point, any fluctuation in temperature that goes unnoticed and uncorrected can break the superconductivity. If enough current is going around in the superconductor, this section of broken superconductivity will spread fast (by joule heating in the normally conducting sections) can do nasty things like ",
"melt your superconducting magnets",
". "
] |
[
"Thanks for the informative reply. I found more info about a couple of SMES installations. It sounds like these are used more as backup power during large transients. "
] |
[
"Doesn't the Meissner effect only apply for a certain superconducters? There's a distinction between type 1 and type 2 which relates to their expulsion of magnetic fields."
] |
[
"Is it possible for a large celestial body to collide with another at low speed?"
] |
[
false
] |
For example if something the size of the moon were trailing the earth but at a only slightly faster speed. I'm going to assume the earths gravity would increase the velocity of the object, but I'm wondering if it would need to be a planet obliterating event without the high relative speeds?
|
[
"If the bodies collide, or even just come close, at slow relative speed, then their gravity certainly cause them to properly collide and the effects will be devastating for both. Even if you magically place the two so that their surfaces just touch at zero relative speed, they will very quickly merge and become a single blob of something once you remove your magic from the picture.",
"So then you could maybe think of something where the two planets orbit each other at an extremely close range. This still won't work. Just the tidal forces alone are enough to rip the planets apart even without them ever touching each other.",
"In fact this is thought to be one way a planetary ring can form. A moon for some reason gets so close to the primary planet that the tidal forces break the moon apart. See ",
"Roche limit",
"."
] |
[
"Hmmm that makes a lot of sense. ",
"There goes my science fiction vision of a double planet. "
] |
[
"Hmmm that makes a lot of sense. ",
"There goes my science fiction vision of a double planet. "
] |
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