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[
"If you look at an object thats orange, it reflects orange, so is the object really orange?"
] |
[
false
] | null |
[
"No, the color of an object is the color of the light it emits. Every other definition is non-sensical."
] |
[
"That's semantics, not physics."
] |
[
"Techinically your not wrong..im just looking for a more definitive definition for \"color\""
] |
[
"If you could make a race car's tires, and the road it drives on, out of any materials know to man, what combo would perform the best?"
] |
[
false
] |
Cost and resources do not apply. Is asphalt and rubber the best? Or can we do better?
|
[
"Well it depends what you mean by \"perform the best\".",
"Let's start off at the most basic level. Wheels work because of friction. An ideal wheel is one that does not slip at the point of contact. Imagine a car on ice - it wouldn't be going anywhere. The higher the ",
"coefficient of friction",
" the better. This allows the wheel to convert as much energy as possible to forward motion.",
"Another big factor is ",
"rolling resistance",
". A common misconception is that this resistance is due to friction; really, it is due to the deformation of the tire. Because of this factor, you would want a wheel that is as perfectly rigid as possible. The less the wheel deforms, the less energy is lost due to rolling resistance.",
"Well, these two factors alone would mean you want a really hard material for your tire in contact with another material that provides as much friction as possible. ",
"Metal on metal does that job well.",
" This is one of the reasons why trains are so efficient at transporting cargo - they are \"the best\" at efficiently converting energy into forward motion and then maintaining that forward motion.",
"The way you put it, a race car with train-like wheels on a train track would be the best race car you could get based on the mechanics of wheels only. Unfortunately, cost and resources do apply to the real world. We couldn't just turn all the roads into rails - that would introduce a mind boggling number of engineering challenges. Not only that, but you loose out a number of other benefits to traditional rubber tire trucks/cars such as maneuverability and not necessarily needing a paved road to travel on. As far as the real world is concerned, asphalt and rubber is incredibly efficient and economical for the purposes it is used for."
] |
[
"One thing to add, rolling resistance isn't strictly related to the tire deforming, it's caused by the tire absorbing energy when it's depressed but not pushing back with the same force when it lifts off (so it absorbs a portion of the energy). If the tire is very very hard and very \"springy\" then you can have the best of both worlds. An example would be copper on cast iron (wiki says that's better than rubber on concrete and steel on steel). And then the wheel would be tiny strips of metal mounted on perfect springs. The tire will deform significantly and have a large contact area but not absorb the energy and thus have very little rolling resistance.",
"As for how I would do it, if it has to be \"wheels\" and drive like a car I'd say some hole and peg system (such that the tire interlocks with the road), and then the force is on the side of the tread and not bound by the coefficient of friction. If money was really no option I'd just make the entire road of superconducting metal and then levitate my car with a superconducting electromagnet, and just use electro-magnetic propulsion...but really that's the future of maglevs."
] |
[
"Engineering Toolbox tells me that aluminum on aluminum has a very high coefficient of friction (1.05), about twice that of steel on steel (0.5) and actually a little bit higher than rubber on asphalt (0.9). Aluminum would also have a low rolling resistance (not as low as steel, but lower than rubber). Additionally, aluminum is stronger than rubber so you could modify the wheel/tire and make it narrower and lighter than a normal tire, improving your braking and acceleration times.",
"However, you also have to consider that though a stiffer tire will reduce rolling resistance, it will also have other effects on traction, even with a high friction coefficient. When you go around a turn, the body of the car will lean to the outside of the turn and lift your inside tires off the ground and try to roll your outside tires on to their edge. Your suspension will push them back down, but it's not able to keep them perfectly oriented. Normally, rubber tires are able to deform and keep the contact patch against the ground up to a certain extent, but that margin would be much lower with a stiffer material like aluminum.",
"You wouldn't want any kind of adhesive because then you're wasting energy breaking the bonds to move forward. You wouldn't want any kind of interference like a peg board because then you'd be losing energy to friction between the peg and the inside surface of the hole (on top of having to dissipate a ton of heat)."
] |
[
"How does our lack of secondary Olfactory organs alter our perception compared to animals with them?"
] |
[
false
] |
From what I've read, we're the odd ones out for our lack of a secondary olfactory sense organ. I never thought that whiskers and antennae were akin to smell, but it must give another level of depth to the animals world. What does science say?
|
[
"Its near impossible to accurately compare our perception with that of another species. Its hard enough to compare my perception with yours: ",
"https://www.youtube.com/watch?v=evQsOFQju08&list=TLCi3WNoJP4r2N-FhFE_QV-FOZqgFBLhCC",
"But suffice it to say, while we are lacking in the smell department, we have advanced in the sight department which helps compensate."
] |
[
"True, I guess we only know our own perception. It just seems that there's an entire other complexity to things that were missing out on, such as how ants can follow pheromone trails so perfectly. I think we could probably put that sense to use better than other species. Especially considering that most animals do have these systems, why would our evolutionary line have dropped them? "
] |
[
"Its tricky to answer questions which begin \"why would evolution\"",
"The best answer is probably going to be a little vague: At some point the benefit of perceiving the world as we do, was greater than retaining a reliance on pheromones or secondary olfactory organs. As that happened there was no pressure to maintain those organs, and they gradually were lost."
] |
[
"If I bombarded a covalently bonded molecule with beta radiation, would the constituent atoms separate from each other?"
] |
[
false
] |
[deleted]
|
[
"Yes, and you actually don't even need beta particles to do it. Beta rays are just electrons with a lot of kinetic energy. I don't know if you have heard of mass spectrometry, but it is an analytical technique to quantify and detect compounds. We can tell what the compounds present are by looking at their fragmentation pattern. A very common form of ionization and fragmentation is to use thermal electrons. Basically you use a filament like in a light bulb to produce electrons with heat energy. It is very common to use around 70 electron volt (eV) electrons which are far less energetic than beta particles which have energies in the 1000s or millions of eV. So yes you can fragment covalent molecules with high energy electrons. Great question."
] |
[
"Thank you for the great answer and taking the time to reply. I had not heard of mass spectrometry before this."
] |
[
"The answer above was perfect, I just thought I would add a little something to help picture it a little better.",
"This may seem a little counter intuitive, but the beta radiation in fact knocks electrons from the bonds, forming a cation and a radical, instead of adding electrons to the bonds to form two anions. (I don't know if you already knew that, it's just a common misconception)"
] |
[
"Could a bird fly in a large rotating wheel space station with artificial gravity?"
] |
[
false
] |
If you have a rotating wheel space station, large enough and filled with air, could a bird of some sort, fly in it? Or what would happen as the bird took flight from the ground?
|
[
"The air inside the space station is moving with the wheel as one body so the bird is not detached from the system when it is in flight, so it would be able to fly like it would on Earth and wouldn't be weightless.\nImagine a humming bird hovering beside a flower on this space station. To the observers on the station it is hovering in mid air, 'detached' from the floor and walls etc of the spinning station, however from an observer outside of the station it is rotating around in a circle with the rest of the station in order to stay above the flower and therefore experiences the same artificial gravity effects the rest of the stuff on the station experiences.",
"\nHowever, you do get pseudo-forces such as centrifugal and coriolis effects. Depending which way the bird flew round the station would increase or decrease it's apparent weight, and by flying 'up' or 'down' it would experience a force that would appear to push it to the side, perpendicular to the way it's flying, which is the coriolis force. "
] |
[
"No, because the air is moving with the rotation of the space station."
] |
[
"The only experiments I know of looking at anything like this involve ",
"pigeons going for a ride",
" (video) in the \"",
"Vomit Comet",
"\". While these parabolic dives are done to generate a weightless environment, they also subject the plane's contents (passengers and pigeons included) to positive and negative g-forces. The period in which the pigeons are exposed to a negative g-force is a decent proxy for simulated artificial gravity like you'd find in a rotating wheel space station: it's an inertial force giving the feeling of weight, and it's oriented away from the earth.",
"The pigeons in the video are disoriented as all heck but they can fly. So the actual mechanics of flight aren't really an issue here. The bigger problem revealed in that video is their ability to spatially orient themselves. Bird brains (or ",
"dinosaur brains",
", actually - shameless paleo plug) are highly adapted to flight. Rapid changes in direction are something that they need to be able to process if they want to fly successfully; spatial disorientation that results in falling out of the sky is quite a bit more catastrophic than tripping. ",
"Based on what we know, which is very little, the ",
"pigeons in that video",
" (PDF) consistently did a few things at various points in the ",
"flight trajectory",
": ",
"So these changes in g-force trigger responses in them. The do seem to use that to orient themselves to a perceived \"down\" and \"up\". If the space station's artificial gravity is similar to the g-forces generated by the parabolic flight of the Vomit Comet, the pigeons' reaction to negative g-forces indicates that they would be able to fly using the centrifugal force for spatial orientation.",
"The only problem I could see is that the Coriolis effect at that scale might impact their equilibrium. Humans run into this as well, and have shown ",
"they can adapt",
" (PDF) to some extent. Flight makes that more complicated, as other commenters have mentioned. Every time the bird would fly up or down in its frame of reference, which is towards and away from the axis of rotation, it would appear to be deflected from its course as in ",
"this animation",
". It would have to correct for that, and I'm not sure it it could."
] |
[
"Quantum dynamics and stationary states"
] |
[
false
] |
I'm reading the book "Introduction to Quantum Mechanics" by Griffiths. In chapter 2, he shows how to use separation of variables to separate the Schrodinger equation into time-dependant and time-independant parts. He says that this method can always be applied when the forces involved are conservative. He also shows how the probability density derived from the solutions do not depend on the time-dependant part, which means (I think) that even though the wavefunction evolves in time, the actual probability associated with a measurement remains constant. My question is, if this is true, then how does anything ever change in the universe? If all the probabilities of everything are stationary, then why do things move? I'm sure I'm missing something mathematical here, as math is not my strong suit. Sorry for the stupid question.
|
[
"The probability for energy does not change on time because the forces are conservative. However, generally speaking the probability of other observables does evolve in time because the phase factors for each stationary state oscillate with different frequencies; Hence the time-evolution of the spatial wavefunction results from the interference of the energy states."
] |
[
"The motion in this picture comes from the the interference between the various stationary states, which is time dependent because the phase of each energy eigenstate evolves at a different frequency.",
"To get a good feel for it, spend some time playing around with ",
"http://www.falstad.com/qm1d/",
" (",
")\n It allows you to set up initial states with gaussians in position and momentum space, or even by setting the relative amplitudes and phases of the energy eigenstates by playing with the phasors at the bottom.",
"It actually time-evolves initial states by the technique of separating them into stationary states and then rephasing the stationary states."
] |
[
"I see now, thanks."
] |
[
"How is a pulsar made to rotate 700 times a second? What happens that gives it this rotational speed?"
] |
[
false
] |
[deleted]
|
[
"Observe closely what happens when the skater pulls in her arms. Now transpose to a collapsing star."
] |
[
"Conservation of angular momentum. If you spin in an office chair with your arms out, and then pull your arms in, you'll notice that you start spinning faster. The same thing has happened with pulsars, except they've gone from tens of millions of km across to merely tens of km across. That necessitates a colossal increase in angular velocity.",
"Pulsars are neutron stars, so they're held together against the rotation by their immense gravity arising from their density."
] |
[
"To further illustrate this point: A star's core prior to going supernova could be something like a few times 100,000 km in radius. A neutron star is about 10 km in radius. So it's like if a skater with arms that reach 1 meter from the center of their body were to contract so that their entire body was less than ",
"."
] |
[
"What is that smell of rain exactly?"
] |
[
false
] |
Can't exactly describe it, but you know what I mean.. There is a distinct smell in the air just before rain or during rain..
|
[
"When it is about to rain, the barometric pressure drops. ",
"If the pressure drop is rapid, a low pressure system is approaching, and there is a greater chance of rain . ",
"Wikipedia",
"Consequently, more VOCs (volatile organic compounds) evaporate. This is a consequence of ",
"Le Chatelier's principle",
": in addition to shifting ratios of gas phase reactants, changing the pressure will change the composition of phases in the system. If the pressure drops, the shift will be from a liquid or an absorbed state to a gaseous state.",
"Organic (adsorbed) ⇌ Organic (gas)",
"or",
"Organic (liquid) ⇌ Organic (gas)",
"The ",
"VOC",
"s that we smell can come from a variety of sources: manufactured products (typically indoors), decaying organic matter in the soil, or ",
"organic compounds produced by plants",
" (e.g. the scents of flowers, pine needles, cut grass, fruit, etc...). ",
"Additionally, it should be noted that humans continually filter out a lot of information (particularly when things are constant... such as background noise), but are more likely to notice changes (e.g. movement). Hence we rarely notice the array of smells normally present in the air. For instance, having just arrived at a smoker's home, I will immediately notice the smell of the chemical constituents of smoke adsorbed to the couch and the carpet. But, after a few days or even hours, I might stop noticing the smell. The organic compounds in the air have not disappeared: it is only that I have stopped perceiving them. Thus we might notice a sudden increase in some smell, even though it is around us all of the time."
] |
[
"No, that is the smell of rain. What you describe, ",
"geosmin",
" is one ",
" of rain, in the same way that ",
"vanillin",
" is one component of the taste and aroma of ",
"vanilla",
". It contributes to the smell; it is incorrect to say that it ",
" the smell. ",
"Quoth Wikipedia",
":",
"Geosmin, which literally translates to \"earth smell\", is an organic compound with a distinct earthy flavour and aroma, and is responsible for the earthy taste of beets and ",
" (petrichor) or when soil is disturbed.",
"(emphasis mine)"
] |
[
"That is correct, but that's not the smell of rain.",
"Rain smells different in cities with no parks, to being out in a forest/grassland, all because of acintobacteria producing geosmin."
] |
[
"If you traveled 66 million light years from Earth (instantly) and could look back on Earth's surface, would you be able to see what Earth looked like 66 million years ago?"
] |
[
false
] | null |
[
"I'm not going to check the actual age, I'm going to focus on the photon density you could see at that distance. ",
"In a shell around the earth at any given time, the photon density is roughly 10",
" photons per cubic metre. This is a very rough approximation, but it should be sufficient. If someone has a better figure, let me know.",
"The volume of a 1 km shell would be roughly 501000000 km",
" and would have about 5,010,000,000,000,000,000,000,000,000,000 photons. The earth reflects about 25% of that, leaving 1,252,500,000,000,000,000,000,000,000,000 photons to work with.",
"The volume of the shell, expanded out to 66 million light years, would be about 4.9 * 10",
" km",
" With the same number of photons (we'll assume even dispersion) that would mean that a telescope with a 6 m aperture (a fair bit larger than the Hubble) would capture 7.23 * 10",
" photons for every 1 km shell that passed by. Roughly 18 million would pass by per minute, meaning that you would see a photon that reflected off the Earth roughly once every 350,000 years. ",
"No, you couldn't see the Earth, let alone the dinosaurs. There simply aren't enough photons to really see anything there. "
] |
[
"Yes, the light you see from a star millions of light years away shows the star's position and activity from millions of years ago. With a powerful enough telescope you would see 'history' on another planet. "
] |
[
"Yes!"
] |
[
"Is it bad to not fully charge a rechargeable battery?"
] |
[
false
] |
I am being told that if I plug in my phone before it is low on energy it is bad for the battery, and if I take it off the charger before the battery is fully charged it is also bad for my battery. Is this true? If so what is the reason? Thanks
|
[
"This is completely wrong with lithium batteries. Lithium cells generally like being stored cool and at about 40% charge. To prolong life, you should neither fully discharge them nor fully charge them; they like being in the middle of their charge region. (Source: I have built an electric car doing quite a bit of studies about my LiFePO4 batteries). ",
"Other chemistries, such as NiMH, NiCd or Pb will work differently. NiCd, which are now uncommon, will need to be fully discharged once in a while. "
] |
[
"Is there anything wrong with letting my electronics charge up all night long? I've heard conflicting information about proper charging methods and it sounds like you're the guy to ask. "
] |
[
"Android phones charge to an optimum level for Li-Ion, I believe around 90-95% and then bounce around in that range, but the OS will report 100% regardless of the current actual charge. A lot of people experience a severe drop in the displayed battery charge early after pulling the phone of the charger for this reason.",
"SBC kernels charge to a true 100% and then trickle charge as necessary to alleviate this \"issue\", and a lot of people have reported a noticeable increase in battery charge over the day due to it. I suspect a large portion of that is placebo, but there is no question that there is more charge from the start of the day.",
"SBC kernels, as I understand it, will not overcharge the battery but trickle charge as necessary to keep it at 100% while it's on the charger.",
"In the interest of information, there have been reports of possible severe battery/phone damage due to SBC kernels, but the reports of such are easily dismissed as ",
" logic fallacies. There hasn't been any concrete evidence linking the two and widespread use of SBC kernels with no such issues suggests the occurrences were more than likely coincidence."
] |
[
"Just how out dated are our space probes?"
] |
[
false
] |
If we could pull some Star Trek shit (just as an example) and replace Voyager I with a state of the art probe, how much more in depth would the results be? Same thing goes with all probes we've sent out. With the rate our computer processing speed is increasing, data storage increases and overall technology evolution, how much more information would we gain if we could magically replace all current probes with state of the art ones? I'm aware it's not possible but I don't know how else to illustrate the question
|
[
"The voyager probes are over 30 years old, and they took a few years to spec and build, meaning the tech is 35 years from the bleeding edge of science. As an example of this - data storage on the Voyager probes is done on an 8 track tape recorder.",
"'how much more in depth' the information you gather would depend on whether you're doing a straight replacement, or putting together a new ideal probe for what Voyager is about to go and do. You also have to consider whether this magical upgrade is going to worry about keeping the probe small and lightweight enough to keep within its original mission parameters. And, of course, budget. ",
"Finally, there is also the question of whether we are upgrading to deal with the science questions of 30 years ago, or if we are allowed to upgrade to answer new questions which have arisen since?"
] |
[
"I'm saying, replace Voyager with ST: Voyager (oh god, I went there)\nLets give it all the best equipment we currently have and it gets to replace the original. For simplicity lets say it's replacing for the same mission. Basically how much information are we losing by the technology being so old?"
] |
[
"How are you measuring the information lost?",
"Modern storage holds millions of times more information in the same space compared to mid-70s technology. The utility of that information probably does not scale well. How many more questions could we answer? A hundred? A thousand?",
"In addition, the methods of analyzing data have improved since the Voyager launched. Without knowing the details, I can still be fairly confident we've used its data to draw conclusions about the universe that its creators never anticipated. How could we account for this consideration?",
"A probe tuned for the goals of the 1970s will neglect some capabilities that we now know are desirable and probably include some capabilities that are not particularly worthwhile. What is lost or gained by this constraint?",
"There is fundamentally no way to provide a solid and meaningful answer to your question. An astrophysicist may be able to provide some insight, but there is only speculation until we have the data you're asking about."
] |
[
"What's the absolute worst result of a geomagnetic storm? Also, what are the durations of these events?"
] |
[
false
] |
I've heard that solar flares can royally screw with communications equipment and long-distance power lines. In the insurance industry there's the term 100-year flood, against which people prepare for making safety standards. The solar cycle is 11 years but it experiences upticks and downswings - what would a 1000-year geomagnetic storm do?
|
[
"Well, a 500-year geomagnetic storm ",
"hit in 1859",
". Telegraph systems failed, aurorae turned night into day. Problem is, nowadays we have satellites, lots of sensitive electronics, power grids etc. Think how reliant we are on electricity... a 1000 year storm poses a very serious threat to transport, clean water, refrigeration - you name it. We're also heavily reliant on satellites for GPS technologies, satellite TV, satellite internet etc. ",
"Even 11-year storms",
" pose some threat to power grids, space craft and radio communication.",
"The economic impact from ",
" (ie. damage to power grids) produced by an event of the magnitude of that in 1859 today would be $1-2 trillion dollars just in the US. Something 3 times the strength of such an event could cause an economic impact of around $44 billion dollars globally from loss of service income from spacecraft, $24 billion in terms of spacecraft losses - not to mention from everything non-spacecraft related.",
"Source of most of that information is ",
"this excellent lecture",
"."
] |
[
"No. Be afraid."
] |
[
"do you mean $1-2 ",
"?"
] |
[
"What is gravity? What are the 4 forces in general?"
] |
[
false
] | null |
[
"Every analogy breaks down if you take it far enough. The only thing that's exactly like something is the thing itself. So you'll just have to take it in broad strokes.",
"http://xkcd.com/895/"
] |
[
"Answering the first part of your question:",
"http://www.reddit.com/r/askscience/comments/18yug5/whats_our_best_theories_on_what_causes_gravity/",
"http://www.reddit.com/r/askscience/comments/nlwsl/so_we_know_what_gravity_does_but_are_there_any/",
"http://www.reddit.com/r/askscience/comments/ee63i/what_gets_turned_into_gravity/",
"http://www.reddit.com/r/askscience/comments/ncn4x/does_every_object_have_its_own_gravity_and_what/",
"http://www.reddit.com/r/askscience/comments/1ej3tq/we_feel_gravity_and_know_its_rules_but_what_is/",
"http://www.reddit.com/r/askscience/comments/gjb0h/what_causes_gravity/",
"http://www.reddit.com/r/askscience/comments/rizh8/how_does_the_gravity_work_on_earth/",
"http://www.reddit.com/r/askscience/comments/fkqkz/question_on_gravity/"
] |
[
"Thanks for the xkcd! This scenario pops up a lot."
] |
[
"What is the consistency of outer space? Does it always feel empty? What about the plasma and heliosheath and interstellar space? Does it all feel the same emptiness or do they have different thickness?"
] |
[
false
] | null |
[
"Space is not empty at all! We have entire branches of astronomy dedicated to studying the stuff between stars and galaxies (the so-called interstellar medium and intergalactic medium). The density of the interstellar medium is about one atom per cubic centimeter, and the density of the inter-galactic medium is much lower."
] |
[
"1 atom per cubic centimeter. It won't feel any different from the interplanetary space in the solar system. It's just a big nothing. It is not technically empty but for human scales it is very much empty. There is nothing there to touch, so you won't \"feel\" anything.",
"\nBut scientifically it is very interesting and not empty, like tvw said. Since Voyager 1 has \"left\" the solar system now it is in the interstellar medium and hopefully it can give us some in-situ data about it. "
] |
[
"So if I stuck my hand out of a spaceship window, and disregarding everything else that might happen, would it have a texture? Like if I wave my hand in front of me, there's a little bit of drag on it and I feel wind. \nDoes the interstellar medium feel different?"
] |
[
"Are internal combustion engines the most efficient way to burn gasoline?"
] |
[
false
] |
Noob here, if gasoline had to be used to say, make electricity, what would be the most effective method? ICE? Turbine?
|
[
"The most efficient combustion engines currently are \"combined cycle\" turbines. Typically a gas turbine, similar to a jet engine but designed to produce power to a driveshaft rather than thrust, produces some power and the hot exhaust is then used to power a steam turbine for more power. The efficiency can be around 60%. The two-stage approach is what enables it to be more efficient than any single stage engine.",
"In power stations these normally run on natural gas, but it shouldn't be too hard to make a turbine run on petrol."
] |
[
"No. A gas turbine engine would be the most efficient way to burn gasoline. And this goes for most hydrocarbon fuels. ICEs typically don't exceed 25% efficiency, whereas turbines approach 99% in jet engines. ",
"So why do cars still use ICEs? Because turbine engines can't idle and they're only good at very high RPMs."
] |
[
"And a turbine isn't as responsive (throttle) and they are large and unpractical for a car or truck"
] |
[
"Do animals sleep-walk?"
] |
[
false
] | null |
[
"Yes.",
"Edit: ",
"This one",
" might be a better example of sleepwalking. The dog is actually upright and walking yet completely asleep."
] |
[
"SO CLOSE!. I was thinking the same thing."
] |
[
"yes, they even have what would be considered the opposite of sleep-walking, sleep paralysis "
] |
[
"What marks where one gene ends and another begins in a DNA thread?"
] |
[
false
] | null |
[
"Genes typically have a sequence up stream from the gene which is called the promoter and signals to the polymerase where to start copying from: ",
"http://en.wikipedia.org/wiki/Promoter_(genetics)",
"All genes end with a \"stop\" codon which tells the polymerase to stop copying, ATT, ACT, ATC are the DNA sequences for these codons: ",
"http://en.wikipedia.org/wiki/Stop_codon"
] |
[
"Just as a side note genes usually posses more than one stop codon when they end. It's more of a stop stop stop stop message, as a single stop codon can frequently passed over due to ",
"nonsense suppressor",
" tRNA. "
] |
[
"I'd like to clarify something here.",
"A gene is not analogous to the coding sequence. Not all genes code for proteins.",
"Arguably, a gene starts at the transcription start site (TSS) and ends at the transcriptional end site (TES). This comprises untranslated regions at both ends of the resulting piece of RNA. They rarely contribute to the end product, but are critical for the regulation of gene expression (stability, export to other cellular compartments...)."
] |
[
"Do magnets work at absolute zero?"
] |
[
false
] |
Do magnets work at absolute zero? I know that atoms will no longer move at absolute zero so I was wondering if that means they will not attract towards one another either. And if that is true, does mean the temperature of a magnet will affect how strong it is?
|
[
"Yes, many materials are magnetic at zero temperature. Your misunderstanding is here:",
"I know that atoms will no longer move at absolute zero so I was wondering if that means they will not attract towards one another either.",
"First of all, it isn't quite true that all motion stops at absolute zero - in quantum physics your minimum energy state has ",
"zero-point motion",
". Also, even if they are not moving, this doesn't mean that they stop interacting with each other. Magnetic properties often depend on the interplay between the magnetic moments of electron spins, the Coulomb repulsion due to their charge, and exactly how the electrons are arranged in the material."
] |
[
"It's really not possible to \"stop\" an electron - this would violate the Heisenberg uncertainty principle. There's always some spread in either the position or momentum of a particle. You can have electrons \"localized\" around a certain position with a fairly narrow width (insulating materials are well-described by the electrons being localized and unable to easily move around). "
] |
[
"exactly, it's the energy resulting from Heisenbergs uncertainty principle applied to a bound state."
] |
[
"Are there black holes that feed on galaxies?"
] |
[
false
] |
We know theres a black hole at the center of every(?) galaxy but is it possible for a black hole to exist that feeds on entire galaxies? Probably a stupid question, sorry.
|
[
"Not really. It's actually quite hard to get something into a black hole. Their gravity is strong, but they're very small in radius for how massive they are. Stuff will generally just swing by a black hole, unless it's really really close. Even then, it'll get torn apart into a disc of matter around the black hole - an accretion disc - that will only slowly drip onto the black hole. The problem is that you need to get rid of the angular momentum (i.e. the spin of the gas), otherwise the gas just stays in orbit the whole time. So in the end, supermassive black holes end up taking up just a tiny fraction of the mass of a galaxy.",
"For the Milky Way, our supermassive black hole (known as Sag A*) is about a million times the mass of the Sun. But the Milky Way is a ",
" times the mass of the Sun. So our supermassive black hole is only one millionth of the mass of our galaxy.",
"The biggest black holes we've seen are about 10,000 to 50,000 times more massive than Sag A*. They are in more massive galaxies than our Milky Way, but they're still only a few percent of the Milky Way's mass. And their sizes are still much less than a light year - i.e. the typical distance between two adjacent stars is much bigger than the diameter of the most massive supermassive black holes."
] |
[
"A light year isn't related to the actual time that light takes to go somewhere - it uses the speed of light in a vacuum in flat space.",
"Honestly, in astronomy we typically use parsecs instead, where a parsec is a bit over three light years. But the general public is more used to light years for some reason."
] |
[
"To add to that, there's the Eddington limit, which puts a quite hard limit on how much matter a black hole can eat."
] |
[
"Why do our bodies decompose when we die but not when we’re alive?"
] |
[
false
] | null |
[
"We actually do, we normally would only see it as an infection. ",
"We are constantly under attack by plenty of microorganisms but we most oftenly than not, manage to keep them at Bay with white blood cells or other defenses.",
"What happens when we die is living cells are no longer fighting the invading microorganisms for which they manage to get a foothold of our bodies without resistance."
] |
[
"So really our immune system is the main defense that we have. Sounds like a lot of work for this system. How does it manage to fights all these microorganisms at once especially when we get sick (flu, cold, etc..)"
] |
[
"It's a lot easier to keep things at the door when we are taking showers, washing our hands, and other hygiene. Our white blood cells are always throughout the body and when something is wrong they know to converge and overwhelm the new foreign cell(s) before they can get a foothold."
] |
[
"What happens to the matter in our bodies when we lose weight? Do we pee/poop/sweat it out?"
] |
[
false
] |
The matter doesn't just vanish. For example if someone loses 20 pounds, where does the 20 pounds go?
|
[
"You breath it out as carbon dioxide and water."
] |
[
"You know how we breathe in oxygen and breathe out carbon dioxide? That carbon comes from fats and sugars in our body."
] |
[
"The reverse happens with plants. Most people think the mass of trees (mostly carbon, hydrogen and oxygen) come from the soil, but if that were the case, there would be a hole in the ground around trees. In fact, it's mostly from the air.",
"It goes to show how we tend to ignore the mass of gases, but it's all very significant."
] |
[
"Why do I sink faster in water than others?"
] |
[
false
] | null |
[
"To rephrase what Zerowantuthri said. Fat is a lot less dense than water, so pure fat actually will float. Muscle is much more dense than water, so pure muscle will sink readily. Its the mix of fat and muscle in people which makes it easier or harder to float. More fat = easier to float, more muscle = harder to float"
] |
[
"Buoyancy in water is all about water displacement.",
"Generally the fatter you are the easier it is to float. If you are more muscular with very little fat then you will sink. This is why it takes a toll on you. You have to work to stay afloat where others can do little to no work for the same effect."
] |
[
"My first question was going to be whether you've ever broken a bone. I saw an article posted here on reddit about a guy with the same issue and it turned out he had a condition that gave him very dense, strong, heavy bones. Look it up. I can't remember what it's called."
] |
[
"Why don't we simulate neural activity on a small scale with computers?"
] |
[
false
] |
For instance: A neuron is a biological I/O system, whereby neurotransmitters are used create a flow of information in a synapse, and more importantly the entire brain. Couldn't we just do this? Even on a small scale, such as making a digital signal get transmitted among a network of virtual "cells".
|
[
"We do, such as the Blue Brain project. The best way to examine this is via numbers. There are ~100 billion neurons in the brain each with thousands of connections. A typical brain by most estimates has ~100+ trillion synapses. To be clear: ~100,000,000,000,000. ",
"Now imagine if every synapse you where simulating only could be in just 2 states. For every cycle it would be like asking the entire planet, 10 times, a yes or no question. The typical brain can fire a synapse up to 50 times per minute. For simplicity sake will say 60.",
"So, to simulate just 1 minute of human brain time we are talking ~6,000,000,000,000,000 synapse calculations, ~100,000,000,000,000 synapse objects, ~100,000,000,000 neuron objects, all the inputs (eyes, nose, etc,) a bunch of stuff going on I'm leaving out, and, to top that all off, none of those is as simple as a transistor. A basic has multiple chemicals that can travel the cleft, different amounts of said chemicals, chemicals in the cleft, and on, and on. ",
"In short, each human brain is really quite remarkable in it's organic computing power. And while we can meet and even exceed it with computer technology in some area's, duplicating it as a whole is still fairly far outside our reach. ",
"Edit: readability",
"\nEdit2: Numbers"
] |
[
"IBM claimed a cat brain but as many have pointed out, it in no way was even near the power of a real cat brain.",
"http://news.discovery.com/tech/cat-brain-computer-hype.htm"
] |
[
"Definitely! At a theoretical level we should be able to refine our models of neural networks so that they more closely mimic actual neurons.",
"Once you get into the details though... It's non-trivial to identify which aspects of a cell are relevant. Does the location of specific receptors have an influence in firing or is firing just the simple summation of input weights? That's a really important question, and it may be the case that location of receptors does matter. In that case, this greatly complicates the modeling of a single neuron. Unfortunately, modeling in general is often a trade-off between computational efficiency (the ability to actually make the model run) versus realism (the ability to model things as they actually are)."
] |
[
"What is the equation that governs the speed at which a smell propagates through air?"
] |
[
false
] |
Suppose I fart. What is the time it takes for my fart to reach the noise of someone 3.14159 meters away?
|
[
"Fokker-Planck equation",
"https://en.wikipedia.org/wiki/Fokker-Planck_equation"
] |
[
"o.o How do I use this?"
] |
[
"You need to know the initial distribution of the smell after you fart. You can consider it to be a gaussian with a very small width. If there is no wind, then it means that the drift term is negligible. So now you know f(x,0), using the second equation in \"One dimension section\", you can solve for f(x,t). Since it is a differential equation that discribes a boundary value problem. Once you know f(x,t) you know how much is the intensity of smell at a given distance. This however assumes that the response of our nose to the smell is linear. ",
"Also, we have ignored the drift term. If you want to be thorough then you have to consider the wind and the fact that your fart has directionality. So close to the source it will smell more in a certain direction for a small period of time. "
] |
[
"My supermarket now only sells flouride free tooth paste. Are there any legitimate reasons to do this, or is it just mass paranoia?"
] |
[
false
] | null |
[
"A study that was in Nature found that fluoride in toothpaste was beneficial.",
"The results showed that less wear was produced in the presence of the fluoride toothpaste than in the presence of the non-fluoride toothpaste with an otherwise identical formulation (P < 0.001), and that the amount of tooth wear in vitro was not significantly affected by differences in fluoride concentration and hardness of enamel.",
"http://www.nature.com/bdj/journal/v176/n9/abs/4808450a.html"
] |
[
"I skimmed over your large post and it seems to be centered around ",
" fluoride in drinking water. If you're ingesting toothpaste, you're doing it wrong (i.e. fluoride in toothpaste is relatively topical in application by comparison)"
] |
[
"This was my response to someone else who wanted to know about fluoride concerns, so it may not make 100% sense here but I think it should do the job:",
"So far, and this is nothing new, the only positively attributed source of concern regarding fluoridated water involves fluorosis in developing children. In most industrial countries this is easily accounted for, and not much of a problem. Some communities naturally have more than that in their water. In a systematic review encompassing 214 studies there was no evidence of other detrimental outcomes from fluoridation (",
"http://www.ncbi.nlm.nih.gov/pubmed/11021861",
"). Another one, from Europe, found the same thing \n(",
"http://www.ncbi.nlm.nih.gov/pubmed/19772843",
"). ",
"Singapore, Israel, Australia and South Africa all began fluoridation to positive success in their communities (Israel’s: ",
"http://www.ncbi.nlm.nih.gov/pubmed/8897750",
" ; if you want the others just look they should be in the related citations section). As far as the assertion that areas without fluoridation may experience a decline in the overall caries experience, this is likely due to the increasing prevalence of fluoride-containing toothpastes and treatments, which can be controlled for if that is an issue. For the majority of the underserved population, however, this is not an issue. ",
"The increase in general worldwide understanding of dental health is also a likely contributor.\nThe Indian Journal of Dental Research performed an extensive review of the overall safety of fluoride and found it very safe (",
"http://www.ijdr.in/article.asp?issn=0970-9290;year=2009;volume=20;issue=3;spage=350;epage=355;aulast=Dhar",
"). Unless people ingest 8g of fluoride at a single time, or at concentrations of 8ppm over a LONG time, there are no reported issues with it. Their research found that even at concentrations of fluoride at 100x normal drinking water levels there were no genotypical effects in mice.",
"The Journal of Molecular, Cellular, and Biological toxicity had a 2010 article (",
"http://biblioteca.cinvestav.mx/indicadores/texto_completo/academica/SET/s.1.2.1.pdf",
") which examined all of the different ways that fluoride could affect people beyond teeth/bone mechanisms. They found both positive and negative effects in different systems, but the majority of the studies were using fluoride levels at 20-150x the amount put into water. None of the human studies they found (2) involved optimally fluoridated samples. The most they came up with is that more research was needed.",
"Even going so far as to look up the research heavily quoted by your source, there isn’t much there. The work of Dr. Luke was on 11 cadavers from the same region; median age of 82. Even then she found that although there was an increase in Fluoride concentration around the pineal gland, and that varied between individuals and was similar to calcium concentrations in that region. She never made any connections to an effect this could have on children. Not exactly damning evidence overall. Her work in gerbils found some negatives, but even she says she doesn’t go as far as to say that work could be extrapolated to humans. She even asserts that dentists give children and infants fluoride earlier than normal, but dentists today are advised against any supplemental fluoride as it is unnecessary. ",
"Frankly, nobody is going to argue we shouldn’t investigate the safety of these items. Fluoride has been accused of everything from being the work of the devil to a communist plot. But there is little evidence whatsoever to show that in the amounts recommended, it is dangerous. "
] |
[
"How does our body's immune system distinguish between pathogenic microorganisms and commensal?"
] |
[
false
] |
Microorganisms are an essential part of our body and even some of the pathogenic (potentially) microbes are also present on our body, classic example being Candida albicans. So how does our body allow such microbes to sustain in/on our body? And what makes our body to show an immunological response if such microbes are introduced externally? Do these have some different kind of proteins on their surface? How exactly is the distinction made?
|
[
"Yes and no, separation is an important part of keeping microbes out of areas where they can cause damage however the immune system regulates all microbes to some extent and recognizes them based on a variety of factors but some have a privileged status. This isn't really my area but commensal microbes engage in crosstalk with the immune system which is necessary for long term colonization. ",
"Here's an article with more information: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4109969/"
] |
[
"Your body doesn't. It's more microaganisms stay in their place, and don't travel to areas that can harm you. Bacteria on your skin is natural but is opportunistic ,if it enters a cut for example, it can cause infection. Even healthy gut bacteria are separated from your tissue via mucus layers."
] |
[
"Microorganisms actually within your body itself (not the GIT, lungs, skin etc) are always eliminated (well at least attempted to). On the other hand the immune system on the skin and mucous membranes are far more tolerant of microbes, a full immune response will not be triggered by the presence of microbes. Exactly how the immune system moderates the microbes at these sites is a pretty big topic."
] |
[
"What happens if you do not complete a course of antibiotics?"
] |
[
false
] | null |
[
"There is a small but significant chance that your body hasn't cleared the targeted bacteria. You then run the risk of a recurrent infection with the same organism. Additionally, you contribute to antibiotic resistance as the surviving bacteria have a higher chance of advantageous mutations."
] |
[
"Not completely finishing a course of antibiotics may lead to a resurgence of the bacteria that survived the incomplete course. It can also lead to the emergence of drug resistance."
] |
[
"Bacterial resurgence. The bacteria could become resistant to the antibiotics that you were given. You could then spread that resistant bacteria around so that others could have issues getting rid of the bacteria with prescribed antibiotics. ",
"Do us all a favor. Finish do what your doctor tells you. This helps reduce the possibility of drug resistant bacteria. "
] |
[
"What caused the Cambrian Explosion?"
] |
[
false
] |
The Cambrian explosion was a period in geological history starting from 542 million years ago in which most classifications of life appeared. Is there any consensus in the scientific community as to what caused it?
|
[
"It's what's called an adaptive radiation. These can be caused by mass extinctions that leave many niches vacant, or by drastic environmental changes that cause new niches to form. It can also happen, as in the case of the first land-dwelling creatures, when species themselves discover a new environment full of previously unclaimed niches. We mostly agree that it was caused by the latter, but we cannot be certain what specific factor caused it. Many speculate that it was caused by changes in oxygen levels that supported previously impossible levels of respiration or the formation of the ozone layer that provided protection from previously destructive levels of solar radiation.",
"It is important to note that at the time it happened, the 'most classifications of life' that you speak of were still very closely related. These classifications (domain, kingdom, phylum, class, order, family, genus, species - which are being done away with for exactly this reason) only represent a useful way for organizing species. They do not reflect the true divergences between species. When the radiation first started, the species would be separated by no more than one 'level' or classification - species. They have only become phyla over the many years since they first diverged."
] |
[
"Along with being an adaptive radiation, the cambrian explosion is also due to the origin of hard body parts which fossilize well. Beforehand most everything had a soft body which decomposes too quickly for a proper fossil to be formed. So part of the huge \"explosion\" is the fact that suddenly (as in \"over the course of 10-20 million years\") there were a ton of things that easily leave fossils.",
"It is likely that the advent of hard body parts initiated the adaptive radiation resulting in many more animals than previously, but the \"explosion\" at the end of the precambrian is certainly due to a bias in the ability of organisms to form fossils as well."
] |
[
"Exactly. It's really more of an explosion of fossils, rather than an explosion of life."
] |
[
"What exactly is the difference between nuclear fuel used for power generation vs bombs and why does fission cause only heat generation in one but an explosion in the other?"
] |
[
false
] | null |
[
"The differences are in the way they are designed, and the enrichment of the fuel.",
"Lets talk about bombs first. Nuclear bombs utilize very high enrichment fuel (>90%). Nuclear bombs are designed such that when they are assembled into a critical mass, the goal is for them to go prompt critical, then release as much energy as possible before the bomb blows itself apart. Nuclear bombs have no control systems, and all feedback mechanisms are designed to try and make the bomb as effective/efficient at releasing energy as possible.",
"Nuclear reactors are very different. They generally utilize low enerichment fuel (<5%), (exception: naval reactors). Nuclear power plants are designed and operated such that they cannot maintain full core criticality on prompt neutrons alone, they rely on delayed neutrons. Prompt neutrons are generated in about 10",
" to 10",
" seconds, while delayed neutrons take several seconds to be generated. Because power reactors rely on delayed neutrons, their power changes take several seconds to occur, and this allows time for active control systems or passive feedback mechanisms to control reactor power. (Passive feedback mechanisms include the Doppler effect, voids/boiling, temperature effects, liquid density effects, etc) In a worst case scenario, it buys enough time for reactor protection system to automatically scram the reactor on high flux signals. Nuclear reactors utilize sufficient negative reactivity coefficients that they cannot undergo rapid out of control power loops (some exceptions, like when Chernoby's RBMK reactor was operated inappropriately. Part of this was the particular design of this plant, part of it was the way it was inappropriately operated). ",
"Both \"reactors\" (bomb and power) generate heat. The difference is how fast you get to that peak power output. Bombs get there in moments, while nuclear reactors take quite a while. A nuclear bomb will go from completely subcritical to an explosion (several orders of magnitude) in moments. The worst a nuclear power reactor can do, is about a 2-3 times power increase, before negative reactivity coefficients pull this down, and/or a reactor scram terminates the power increase.",
"Just an interesting anecdotal data point, the worst case reactivity increase that I've seen in a commercial BWR happened when a reactor cooling valve opened at the maximum possible rate due to a control system error during plant startup testing, which caused the valve open signal to bypass the valve motion limiter. The sudden increase in cooling reduced the steam voids in the reactor, which led to a prompt neutron reactivity spike of just over 300% neutron flux, which was terminated by a reactor scram in about 1.1 seconds. No fuel damage occurred because 2 seconds of a flux spike does not allow enough time for heat to transfer to the fuel cladding and cause damage. The plant was a ~3000 MWth BWR."
] |
[
"Uranium is usually used for power generation, and is mined from Uranium ore, which is mostly U-238 with a small amount of U-235. The latter is the fissionable component (i.e., the radioactive part).",
"In low concentrations, U-235 will decay in a fission reaction (it breaks apart), with heat as the by-product. Power plants use Uranium that has been enriched to about 5% U-235, which produces a lot of heat, but not quickly enough to cause an explosion.",
"Weapons-grade Uranium is enriched to about 90+% U-235. It also produces heat, but in this case, the heat is produced so quickly that an explosion occurs."
] |
[
"I want to correct a lot here. Both U-238 and U-235 are fissionable, U-235 however is also fissile. That means it can fission by any energy neutron. ",
"U-235 decays by alpha decay, not fission. I don't even think it spontaneously fissions as a decay, if it does it is extremely unlikely. ",
"Reactors use anywhere from natural uranium up to 95% enriched uranium. Most reactors use between 3-5% enrichment. Research and medical reactors use 20% and sometimes 90%, although that is changing due to proliferation concerns. ",
"The difference between a bomb and reactor, besides all the obvious ones is how quickly one causes fission. In a bomb, you cause a lot of fission in around 1 microsecond. In a reactor, you cause roughly the same amount of fission, but over the course of 24 hours. So it is all about the reaction rate, if it is fast you have a bomb. If you control it and release the energy slowly, you have a reactor."
] |
[
"How do snakes right themselves underwater?"
] |
[
false
] |
Do snakes have the ability to change their orientation underwater? If their top is facing down can they 'roll over'?
|
[
"Yes, in the same manner cats use to self right in mid air. If you bend your body into a 'u' shape and roll your body along your spine, you play the rotational inertia of your body along its curved spinal axis against the (much larger) rotational inertia of your u-shaped body pivoting on a straight axis through your center of mass. Requisite video showing cats falling here: ",
"https://youtu.be/RtWbpyjJqrU"
] |
[
"Snakes are excellent swimmers and mostly use lateral undulation to move under water - basically by conforming their body they can push against the water, the same way you would push with your limbs to turn yourself over."
] |
[
"Haha, I love smarter everyday, I was hoping for the cat video and you delivered!",
"Cheers"
] |
[
"Are there any specific geological features on Earth that contribute to the abundance of life?"
] |
[
false
] |
Things such as placement of continents/continental plates, ocean currents. Could the presence of those features on other planets be an indication of habitability?
|
[
"There are a bunch. Off the top of my head (others are welcome to complete the list):",
"A strong magnetic field, which acts as a radiation shield.",
"Large liquid water oceans, whether ice-covered or not.",
"active geothermal systems - From the observation of LAWKI, chemautotrophy is one of the 2 pathways we can verifiable affirm to be able to support complex ecosystems. In our case this is a corollary of active plate tectonics, but the jovian moons show that tidal forces can also be an effective driver for such.",
"Mostly transparent atmosphere (for photosynthesis sake - not necessary for life ",
", but it ",
" open up options).",
"Broad continental shelves. Continental shelves are the tropical rainforests of the ocean. Throughout history, when the number and size of the shelves was reduced, so was overall biodiversity. Pangea? Oceanic extinction event.",
"Dynamic geological processes. In our case plate tectonics, although I suppose we might discover other types through studying exoplanets and our own solar system. Without such dynamics, key limiting elements get locked away and the biological system collapses."
] |
[
"I don't think you're looking for the biggest answer: The existence of fluids. The very presence of water and air - and their stability over long timespans - is the biggest thing that has brought the Earth to the point it's at today. But I'm guessing you aren't looking for this kind of broad geochemical answer.",
"More specifically? A high degree of ocean mixing certainly has helped. It's both kept temps relatively bounded at some kind of \"middle\" temperatures, and also helped various chemical and living components run into each other. In order to get that movement it helps to have a World Ocean like we have.",
"A relatively heterogeneous continental layout helps to increase the number of niches available and to provide redundancy. Some kind of continental layouts would be better and worse for oceanic conditions but I don't know what that would be exactly.",
"Could the presence of those features on other planets be an indication of habitability?",
"Yes, but hold on. Even less suitable places could be habitable for us. What you're asking about is suitability to ",
" all that life, which is a much higher standard.",
"By this point we could live on the Moon or Mars because we've figured out how glass and metal and ceramics work."
] |
[
"The moon is big factor for life getting out of the ocean and onto land. \nThe moon cuasese tidal exchange. This ring and falling of the sea creates places where plants and animals get stranded and must adapt to air or die. (Tide pools) \nThis is a leading theory on how and why life left the ocean and populated land. "
] |
[
"How is measles back?"
] |
[
false
] |
If the disease was none existent in many countries, how can new kids without vaccines get them? Is it possible for diseases to be completely wiped if everyone gets vaccinated for generations?
|
[
"Because people move around and if it's not wiped out everywhere, it can be carried to places with insufficient vaccine coverage and start to spread again.",
"Yes, it is possible to wipe out a disease with good vaccine coverage. We did it with smallpox. We're close to doing it with polio. These are strictly human diseases. Now, we can't do that with a disease that is carried by animals and gets re-introduced to humans periodically, like Zika or Dengue or Ebola."
] |
[
"Now, we can't do that with a disease that is carried by animals and gets re-introduced to humans periodically, like Zika or Dengue or Ebola.",
"It is more difficult but not necessarily impossible. A lot of countries got rid of rabies, for example, several other countries brought down the rate a lot. ",
"Here is a map",
"."
] |
[
"Yes but that is because of a concerted effort to vaccinate domestic animals, which are the main intermediaries between wild animal reservoirs and humans. And some places also make an effort to vaccinate wild animals. Nevertheless, this can decrease but typically not eliminate a disease because coverage in wild animals is far lower than in humans or domestic animals. "
] |
[
"How are we now getting warm colors in CFBs?"
] |
[
false
] |
For as long as I can remember, fluorescent lights were always blue, or a cool red. How are we now developing CFBs that have the warm white light? One of the sites I looked for them said 'use where color enhancement is not an issue'. What's different about the materials used in them?
|
[
"So the reason they're called ",
"\"flourescent\" lamps",
" is because the light that's actually produced inside the tube is UV light. The glass is coated with a material that absorbs the UV and re-emits it in lower frequency visible light. Previous coatings preferentially emitted towards the bluer end of the visible spectrum, but newer coatings are somewhere in the \"warm color\" region. "
] |
[
"Because it can be lost as heat in certain instances. Essentially, the UV light pumps up the electron to an excited state, but when the electron decays back down to its relaxed state, it can give off some lower frequency light ",
" heat up its surroundings (the glass, etc.). And since heat is entropically favorable, if that process can happen, it does."
] |
[
"Why exactly is the energy lost?"
] |
[
"If a 50 year old person receives a 20 year old heart in a transplant does the heart \"remain\" younger than the rest of the patient's own cells?"
] |
[
false
] |
If so is it theoretically possibly to live longer by simply replacing your organs as they get "worn" out?
|
[
"Not really a meaningful question considering most foreign organs get rejected after about 10-15 years because despite our best efforts of immunosuppression the human immune system really does not like having non-self tissue around. The cell material is in theory more fresh and could survive longer in situ, but practically that's not a thing that will happen. In a nonexisting hypothetical world where complications in surgeries of people in old age don't exist you could maybe replace all organs every 10 years, but the limiting factor in this equation is the age of your brain, the quality of your cardiovascular system and the quality of your immune system over a lifetime."
] |
[
"Well, foreign is pretty much anything that a) doesn't share the very specific subtype of MHC class I (the protein that carries and represents the antigens of a cell - imagine it's some kind of grail like protein that in itself can vary greatly within different people because of the large amount of allels in the gene pool coding for it), b) doesn't share the assortment of proteins represented as antigens on MHC I that the immune cells are not used to, c) doesn't exprime MHC-I in the first place (for example tumor cells or virus infected cells), d) does not fit into the specific innate OR adapted patterns of the immune cells already available in the body (won't go into detail on that one since there are quite a few mechanisms at work here and I'm on phone right now) and e) that has immune cells that are not used to the host's patterns (similar to the previous one, but also has different ramifications like graft versus host disease).",
"These factors are majorly predetermined by genetics, and because of the intricate nature of the process one has to be very very genetically close or identical to not get rejected in the long run. It is true though that identical twins who share their exact genetic material fare a way, way lower risk of rejection, and in fact don't have to take immunosuppression at all. I hadn't considered the possibility of lab grown organs yet and don't know if there would be other complications at play other than the fact that some organs are just a nightmare to surgically take out and completely replace, and as said the only thing we can't or shouldn't really replace is the brain (although maybe it could be possible to selectively replace specific damaged areas? I don't know) and I'd consider it technically... very difficult to replace the vascular system or the (adaptive) immune system. But still in theory a possibility."
] |
[
"Thanks! I hadn't considered the immune response. I find it interesting that the immunosuppresive sirolimus has extended lifespan in mice and wonder if there's a connection between the activity of the immune system and lifespan in general."
] |
[
"How can some black holes be bigger than others?"
] |
[
false
] |
[deleted]
|
[
"There are 2 comments I cant see, maybe they have already explained...",
"A black hole can be considered to have no spatial dimensions - a singularity. (this may actually be because the laws of physics start doing strange things in a black hole)",
"A black hole however, has other properties such as mass, charge, and angular momentum.",
"Not all black holes have the same mass (or charge and angular momentum).",
"The mass of a black hole (really of any body) determines its gravitational field. The heavier an object the more it pulls you.",
"The event horizon of black holes is not really a physical surface. It is the boundary of a region where the pull of gravity is so strong that light and matter cannot escape and eventually end up in the singularity.",
"And since the gravitational field is determined by the mass of the black hole so is the size of the region where even light cannot escape.",
"Hope this helps."
] |
[
"Thanks, it does!"
] |
[
"The ",
" \"black hole\" doesn't just refer to just the singularity inside. It refers to the whole region of space inside the event horizon. Just like if you dig a hole in the ground the term \"hole\" doesn't just refer to the bottom, it refers to all the empty space you created. "
] |
[
"More efficient to discharge/recharge a laptop or leave it plugged in?"
] |
[
false
] |
What's the most cost-effective/energy efficient way to run a laptop? Is it to use it unplugged until the battery is dead (or nearly dead) then plug it in and continue to use as it recharges, before repeating, or to keep it always plugged in? Or to use until the battery dies, then let it recharge before turning it back on again? Obviously recharging without using means you can't get as much work out of it, I'm just wondering about energy usage and cost (including "green" cost). There would be, of course, battery life-cycle issues to think about too... what would these be? edit: just found this related thread which might help answer some of this:
|
[
"Adding to this -",
"While your laptop may automatically conserve power while running on battery, you still have to charge the battery between cycles.",
"Some management software may do this on its own when the machine is plugged in anyway (think Lenovo) - the battery contains some power management circuitry that will halt the charging process, and allow the laptop to use the battery. Typically, there are charge and discharge thresholds: the laptop will use the battery when the charge level is above 85%, and charge the battery to 95% when it drops below that threshold.",
"Finally, we can't assume that charging the battery works at 100% efficiency. Some of that energy is lost as heat during the charging process - both in the battery, as well as in the AC adapter and the conductors between.",
"Most efficient? Running the laptop without the battery inserted and with the adapter connected, with the energy-saving profile selected.",
"Of course, then you'd have yourself a desktop :)"
] |
[
"No, but it lets the battery live longer."
] |
[
"Most Laptops switch to a powersave mode when unplugged, meaning you will use less energy if you only use the laptop while it is unplugged and charge it while it is turned off. On the other hand, most of the powersave-functions are actually implemented in software, so switching to 'powersave-profile' (or however it is called in your case) will lead to almost the same energy-saving.",
"That said: a Li-Ion batterys lifetime depends on a) temperature and b) number of charge-cycles. Furthermore I imagine that the manufacturing and shipping for the battery is non-negligible, at least when compared to the quite modest power your average laptop uses. This means that the 'greenest' option might be (no expert on the env. impact of a battery replacement) to run your laptop plugged in (with a 'powersave-profile') and remove your battery from the laptop as soon as it is charged because otherwise the heat produced by your laptop will shorten its lifetime."
] |
[
"What do the \"morning after pill\" actualy do?"
] |
[
false
] | null |
[
"The \"morning after pill\" contains levonorgestrel, which is a hormone. This hormone can prevent ovulation. Sperm can survive in the uterus for a few days, but if you prevent the female from releasing an egg, they will have nothing to fertilize and pregnancy can be averted."
] |
[
"You're on the right track. Levonogestrel is the hormone in the \"morning after pill\". It falls under a class of hormones called progestins. The primary function of a progestin used for birth control depends on the kind, dose, and the route of administration.",
"Just to be clear, the typical oral contraceptive pill that someone takes daily has both estrogen and a progestin.",
"Injection: a whopping dose of provera will shut down ovulation for months (sometimes even year even though it's only good for 3 months reliably).",
"IUD: actually also contains levonogestrel - it works primarily but increasing cervical mucous so that sperm can't get in the uterus",
"Implant - etonogestrel, inhibits ovulation and thickens cervical mucous",
"progestin only pills - typically just thicken cervical mucous, 50% of the time inhibits ovulation. May also slow the movement of sperm through the Fallopian tubes and thin the lining. Other progestins probably do these latter things too but their other impacts are more prominent. ",
"Morning after pill - a one time big dose of progestin that ideally inhibits ovulation for a brief period of time. Does not have a sustained contraceptive impact.",
"Estrogen and progestin pills - thicken cervical mucous and inhibit ovulation and the other stuff above."
] |
[
"Many thanks."
] |
[
"Can we estimate where the barycenter of the universe is?"
] |
[
false
] | null |
[
"The barycenter of the universe is not a well-defined concept. Whether the universe is unbounded (e.g., flat Euclidean 3-space) or bounded (e.g., a 3-sphere), there is simply no such thing as the barycenter.",
"Precisely, to be able to talk about the center of mass of some collection of particles, you need to be able to talk about their positions and then be able to ",
" those positions as vectors in some weighted sum. In other words, the concept of center-of-mass exists properly only in a vector space. The universe is generally described as what is called a manifold, which does not have any vector space structure to it. (There are some manifolds that can be given a vector space structure, like flat ",
", but in that case, there would still be no center-of-mass since the mass is more or less distributed evenly in all directions.)",
"If the mathematical language is too complex, consider two simple examples:",
"The universe is flat ",
", so just normal 3-dimensional space that most people are used to thinking about. The mass is evenly distributed throughout all of space. So if you wanted to compute the center-of-mass via the usual formulas, you get divergent integrals. The center-of-mass simply does not exist.",
"The universe is S",
", the 3-sphere. For simplicity, you can instead imagine that space were two-dimensional, and so the universe would be S",
", the 2-sphere (i.e., the surface of a baseball). If this sphere were considered as embedded in 3-dimensional space and the mass were distributed evenly, you would want to somehow say that the center-of-mass is the center of the sphere. But the center of the sphere is not on the sphere. So as far as a hypothetical being living on the surface is concerned, the center-of-mass does not exist."
] |
[
"Strictly speaking, there is generally no center-of-mass on a manifold. Even in a region of spacetime where there is exactly one black hole has no center-of-mass. Again the issue is that there is no vector space structure, so it's not possible to define center-of-mass. (There's also the issue that although a spacetime with a single, non-rotating black hole is spherically symmetric, there is no concept of \"center\" at all. The region that corresponds to \"r = 0\" isn't actually part of the spacetime.)",
"Of course, you ",
" approximate the region of space containing our galaxy as flat and all planets, stars, black holes, etc. as point particles. So you can come up with a center-of-mass in this approximate model. I don't know the precise calculation, but I would guess it would be somewhere near the geometric center of the galaxy since the mass distribution is more or less axially symmetric.",
": Someone asked a good question but then deleted the comment while I was writing a response. :( The question was something along the lines of \"is there any strict sense in which we ",
" make sense of center-of-mass? Answer:",
"A vector space structure is a minimum (since you need to sum position vectors of particles), and manifolds do not have to have a vector space structure even it's possible to give them one.",
"Regardless, the only real manifolds that can be given a vector space structure to begin with are the Euclidean spaces ",
" (this is ",
" with zero curvature). So the absolute best-case scenario you can come up with in general relativity where the concept of center-of-mass even makes sense if you can choose your time coordinate so that time slices (essentially all of space at each instant in time) is the Euclidean space ",
". Then it might make sense to talk about a center-of-mass of some mass distribution in space, but only at that instant in time.",
"The only spacetime for which this is possible is, unsurprisingly, an FLRW spacetime in which the spatial curvature is zero. That is, the center-of-mass of a mass distribution can make sense ",
" at a given instant in time in an expanding universe in which space is the usual (flat) ",
". But for such spacetimes, the mass-energy is uniformly distributed, and so the center-of-mass does not exist.",
"The moral of this story: center-of-mass is never a meaningful concept in general relativity. To make any sense of the concept you ",
" to make some Newtonian approximations."
] |
[
"Thank you for the answer! I wish there was an answer to the question as I had imagined it. I appreciate you helping me grasp the concept of a barycenter and its inability to be applied to the universe as a whole. ",
"As a follow up, could you calculate the barycenter of something like our galaxy? If you include the supermassive black hole at the center of our galaxy, is it possible for a barycenter to be outside the event horizon of said black hole? "
] |
[
"How does the groundwater filtration system at Fukushima work?"
] |
[
false
] |
I was reading about the plan for Fukushima and became curious about for Cesium removal. How does it work? Bonus points - why aren't they worried about other radioactive particles?
|
[
"This system uses the principle of ",
"ion exchange",
" to strip cesium from water. The contaminated water is passed through beds of ",
"ion exchange resin",
" beads (called ion exchange columns). ",
"The canisters in the green room image are the ion exchange columns. The resin's chemical properties have it initially bonded to one type of cation via a weak ionic bound (positively charged cation attached to a negatively charged site on the resin molecule). When in contact with a different type of cation, which would form a more suitable bond with the resin, the first cation is rejected in favor of second cation. In this case, the resin favors cesium and will bond with it if given the opportunity. I don't know off-hand what the initial cation is, but I would guess potassium. ",
"Thus contaminated water can be stripped of its cesium. The resin is then stored for waste processing/disposal and the clean water is returned to the ground. In the green room picture, you see the canisters have crane hook-ups. When the canister is fully loaded with cesium, the tubing is removed and the canister is replaced with a fresh one. The loaded resin can then be vitrified (turned to glass) for long-term stability. This glass waste can then be buried.",
"Source: I worked on the conceptual ",
"design",
" of a skid-mounted water filtration system for Fukushima remediation.",
"Edit: Expanded a bit."
] |
[
"Perhaps you can clear up another related question.\nHow does freezing the ground not expand the water when it freezes, pushing up on the surface?"
] |
[
"The purpose of the freezing is to create a containment wall of ice around the contaminated area. Liquid water can't pass through a wall of ice. This containment prevents contaminated water from escaping the area, allowing them to pump up only the contaminated ground water for processing within."
] |
[
"Why haven't non-functioning, vestigial genes mutated into gibberish by now?"
] |
[
false
] |
Humans and apes have defunct genes for tails and vitamin-C. Birds have defunct genes for teeth. Since there is no selective pressure to keep them from accumulating mutations over time, and since they are millions of years old, why haven't they become gibberish whose original function is unintelligible?
|
[
"Genes that have lost their functions but resemble their \"original\" gene enough to be identified are called ",
"pseudogenes",
". If a gene has mutated completely to gibberish ie. lost all gene-like features it would be indistinguishable from background DNA sequences. So possibly some (or maybe lots) of genes have mutated as you described, but we'll never be able to find them."
] |
[
"For starters, genes aren't a clear cut as \"Gene X does Y.\" There's a very complex interplay between various parts of the genetic structure of an organism. A change in a single gene can have effects all throughout an organism. For example, the genes that used to create teeth in birds would have played roles in how their skull and mouth were structured and disrupting that would render their beak useless. ",
"Also, evolution isn't about removing useless genes. There's no \"cleanup\" process. Traits only disappear from a species if those traits are selected against (i.e. they create a survival or reproductive disadvantage). Even then, it takes time. For organisms as complex as apes or birds, a million years is pretty trivial.",
"Finally, what's commonly perceived as \"useless\" or negative traits can actually have an advantage (which ties back in to the interplay of genes). Sickle-cell anemia is the classic example. Actually having sickle-cell is a bad thing and, until recently, was mostly fatal. But being a ",
" of sickle-cell anemia provides a resistance to malaria. "
] |
[
"The vestigial genes the OP asks about don't code for protein and therefore can tolerate mutations better that protein coding regions.",
"Mutations like you describe in bone are inconsequential to evolution as they aren't passed down to offspring."
] |
[
"What happens to light when it enters a black hole?"
] |
[
false
] |
If I were to bombard a black hole with a huge number of photons, would the black hole behave any differently afterwards? Would I be able to measure any differences in terms of mass/event horizon?
|
[
"Technically it will become more massive, not \"heavier\". \"Heavier\" would imply an increase in weight which is relative to gravitational effects of other bodies, the black hole would have more apparent weight from the Sun's gravitational pull than from the Earth, for instance, while mass would be constant."
] |
[
"When a crazy hobo shows up on your doorstep in 4 years asking if the photons stretch as they near the singularity, you better remember you said that."
] |
[
"Depending on how you shoot them in you could alter the spin of the black hole as well. Increase the angular momentum enough and you could alter the accretion disk and relativistic jets, yes?"
] |
[
"Why do radio waves get blocked by chain link fences?"
] |
[
false
] |
I was once in my physics lecture, and the professor was talking about how different materials attenuated different frequencies of electromagnetic waves differently, and mentioned how everyday chain link fences could block long wavelength radio waves. This never made intuitive sense to me. Why does wavelength matter? Wouldn't amplitude actually make the difference for what does and does not "hit" the gratings of a chain link fence? Couldn't a long wavelength wave fit through a small space just as well as a short wavelength?
|
[
"and mentioned how everyday chain link fences could block long wavelength radio waves. ",
"It's because the wavefront diffracts (bends around) the wire in the fence making circular wave fronts, which will interfere and cancel themselves out. This only happens when the spacing between the diffraction grating is less than the wavelength of the EM waves. It'll look like the ",
"top picture on this page.",
"Couldn't a long wavelength wave fit through a small space just as well as a short wavelength?",
"So short wavelengths can all fit through the holes in the fence, while the big stuff has to pass through by diffraction. "
] |
[
"Also",
"Wouldn't amplitude actually make the difference for what does and does not \"hit\" the gratings of a chain link fence? ",
"The amplitude of an electromagnetic wave doesn't really refer to the physical \"size\" of the wave, but rather to the magnitude of the electromagnetic field",
"Edit: spelling"
] |
[
"What? You know radio waves are several meters peak-to-peak, right?"
] |
[
"Chemical Equation in Glow Sticks?"
] |
[
false
] |
[deleted]
|
[
"Commercially available glow sticks contain three primary ingredients. 1) a peroxide such as hydrogen peroxide or sodium peroxide, 2) diphenyl oxalate, 2) and various fluorescent dyes or (fluorophores). The type of dye or dyes used depends on the desired color of the glow stick.",
"Additional secondary ingredients may be added, first to stabilize the peroxide during storage. Second, to modify the rate of reaction depending on the brightness, time of use, and operating temperature desired.",
"The reaction is as follows: The peroxide reacts with the diphenyl oxalate to produce an unstable high-energy intermediary called 1,2-Dioxetane Dione (simplified linear formula: HO-CO=CO-OH)",
"(Phenyl)-O-CO-CO-O-(phenyl) + H2O2 -----> 2 Phenol + OH-CO=CO-OH.",
"1,2-Dioxetane Dione is capable of transferring it's chemical energy to a variety of compounds. In the glowstick, the 1,2-Dioxetane Dione decomposes into 2 molecules of CO2 and H2O. In the process, transferring chemical energy (usually) to the fluorescent dye, which cause the dye to enter a \"photochemically excited state.\" ",
"The dye then rids itself of this excitement energy by emitting a photon of light in a specific frequency and returning to it's normal ground state. ",
"OH-CO=CO-OH* + Dye -----> 2CO2 + H2O + Dye* ------> 2CO2 + H2O + Dye + Light.",
"Hope this explains it."
] |
[
"My understanding is that the reaction is generally basically",
"Luminol + O2 -> Excited Luminol -> Ground State Luminol + Light",
"You get the O2 by reacting H2O2 with Sodium Hydroxide.",
"I believe there are variations on this theme (e.g. catalysts) but this is the basics."
] |
[
"My understanding (which is far from expert) is that Luminol (or other fluorescent compound), Sodium Hydroxide and H2O2 are the compounds that are present, before things begin. The point is that the H2O2 is in the glass vial inside the glowstick, and the dye (be that Luminol or something else) is in the outside, with the NaOH.",
"This",
" article largely agrees with me, but it neglects the NaOH. I am relatively confident however that NaOH is in your average glowstick, because I've opened several up and seen how basic they are first hand."
] |
[
"If we see through a \"pinhole\" formed by closing the index finger and thumb, why don't we see an inverted image?"
] |
[
false
] | null |
[
"Consider a ray of light that comes from above. As it enters your eye it will hit the bottom part of your retina. So the image is inverted on your retina already. If you add another aperture (without a lens) in front of your eye, it does not change the path of the ray, it will continue in a straight path as normal."
] |
[
"Won't a ray of light coming from above be focused by the lens to hit the upper part of the retina?"
] |
[
"No. See ",
"here"
] |
[
"What are the ecologically equivalent large terrestrial scavengers that T-rex is compared to?"
] |
[
false
] |
I know there is some debate about whether the T-Rex was able to kill its prey, and I have seen they say it was a huge scavenger, but unlike many other dinosaurs, I don't realize exactly which animal can they compare it to, since I do not know of any huge modern terrestrial scavengers, can someone please fill me in?
|
[
"is there such a thing as a huge terrestrial scavenger?",
"Not currently, and there's a theory that a large non-flying terrestrial obligate scavenger is impossible, because they couldn't be energy-efficient enough to find enough carrion to survive. (Vultures manage by being very energy efficient.) ",
"(I think that this might be mentioned in Bakker's ",
") ",
"(And theory not proven one way or the other, as far as I know.) ",
"Possible extinct examples of huge terrestrial scavengers: ",
"Andrewsarchus",
" (Though really we know almost nothing about it, so your guess is as good as anybody's.) ",
"The ",
"entelodonts",
" or ox-sized \"giant pigs\" (They were pig-like but not true pigs.) Again, we're not really sure what they were eating - the best guess seems to be that they did a little of everything - herbivory, scavenging, and at least some of them were apparently fast enough to do some active predation. ",
"Fun, huh",
"?"
] |
[
"Actually they just found a T-rex tooth fused to a prey dinosaur's spine which allowed them to infer that if the T-rex was a scavenger, it was probably facultatively so. BUT...answering your question, most canines would be a good example of a predator who acts as a facultative scavenger."
] |
[
"I know plenty of those! I mean lions and bears are also facultative (thank you for the term) scavengers, but I was wondering if T-rex is to be compared, it should occupy a well established niche, right? So is there such a thing as a huge terrestrial scavenger? Our the fact that all big carnivores are predators supports that T-rex was a predator? Thank you for replying, anyway!"
] |
[
"Magnetic acceleration based weapons?"
] |
[
false
] |
[deleted]
|
[
"The US navy, along with BAE systems, a British engineering firm, have already made and test fired a magnetic railgun with some success.",
"Yes the weapon does exist, but, only as a test weapon. The benefits of this weapon are its incredible accuracy and power. The slug can be fired at speeds up to mach 7. The flames you see behind it is the air being vaporised.",
"The effect on something taking that hit would be unimaginable. It would obliterate almost anything. The problem would be stopping the round after it had impacted its target. Say you were hitting a building with a slug travelling at mach 4, it would strike the building, completely destroy it and then carry on like nothing has happened, thats the problem they're facing.",
"Another benefit is that the ammunition is non-volatile and completely safe to transport. "
] |
[
"It doesn't make sense to use a lightweight material as the projectile, not enough mass and therefore kinetic energy. I believe they use tungsten projectiles."
] |
[
"In a railgun it doesn't matter if it's magnetic, the induced current due to (I believe) Lorrentz law. There are prototype railguns that use a small aluminum armature that vaporizes and creates a plasma armature that propels a plastic slug.",
"However, with a Coil gun does require a strong ferromagnetic projectile as it creates a magnetic field then propels the projectile. I have a working 1KJ coil gun used for experimentation and theory."
] |
[
"When talking about the age of the universe, which reference frame are scientists using?"
] |
[
false
] |
I understand that, the stronger the gravitational field the slower time would pass - wouldn't it mean that the early (more dense)universe had a slower clock overall? When the number 13.8 Billion years is mentioned, which reference frame has experienced all this time?
|
[
"Astronomers are generally using the cosmic microwave background frame (the frame in which the CMB is isotropic), but it actually doesn't matter that much. The percentage of matter that experiences strong gravitational fields or moves at relativistic speeds relative to the CMB frame is negligible. Any observer who is not deliberately spending time in a relativistic spaceship or orbiting a black hole will measure almost the same age for the universe."
] |
[
"This is correct - we are moving at about 0.1% of the speed of light relative to the CMB. Typical orbits speeds for stars and galaxies are ~0.01-1% of the speed of light (~30-3000 km/s). So the relativistic effects are only a small correction."
] |
[
"Sounds more like a venture opportunity than a restriction!"
] |
[
"Is it physically possible to evolve a wheel?"
] |
[
false
] |
Title pretty much sums up the question. Is it at all possible for an animal to evolve a rotating wheel, or wheel-like apparatus, as a means of transportation?
|
[
"Yes! To escape predation, the ",
"golden wheel spider",
" forms a wheel-like shape by folding its legs around its body. This shape allows the spider to quickly \"cartwheel\" down the sand dunes of its native habitat.",
"Video of the golden wheel spider in action",
"Ridin' dirty version - this spider rollin', they hatin'",
"That said, I am unaware of any animal that has evolved a wheel-like apparatus in place of a limb. I suppose the evolution of a biological wheel is possible, but it is difficult to imagine a natural environment in which this would be useful. Wheels are really only useful on hard, flat surfaces like roads which generally don't occur in natural environments. "
] |
[
"Some bacteria do, actually. ",
"http://cronodon.com/BioTech/Bacteria_motility.html"
] |
[
"I suppose it comes down to how you define a wheel. While the spider obviously doesn't use an axle, its body does ",
"rotate around a specific axis",
"."
] |
[
"How are electrical signals traveling on neurons directed to its target?"
] |
[
false
] |
How do cells differentiate between an electrical signal traveling down an axon that is destined for different areas, for example the right great toe versus the left gastrocnemius? Cell biology textbooks does a great job at explaining the process by which the signal is passed between cells but how it reaches it's target is a mystery to me.
|
[
"What ",
"/u/unia_7",
" said. Each nerve carries a large number of individual axons. Each axon either goes to one group of muscle fibers, or from one sensory receptor. ",
"That said, an axon CAN split in two and make synapses onto multiple separate target neurons. But it can't 'route' electrical signals down one branch vs. another. A branched axon duplicates the information it transmits; it can't selectively route information."
] |
[
"I appreciate your username in the context of your area of expertise. Love it.",
"Feel free to delete this when you read it as it obviously violates sub rules."
] |
[
"The textbooks don't explain it because there is nothing to explain. The cells don't differentiate anything, it's a one origin to one destination signal conduction.",
"A single axon runs to one single area (say, a receptor on your toe) and nowhere else. It never splits into two and never merges with another axon."
] |
[
"Did some dinosaurs have hair instead of feathers?"
] |
[
false
] |
Scientists love the idea that dinosaurs had feathers that relate them to modern birds. But I read this article which talks about a dinosaur fossil that had "little 'fuzzy' feathers, almost like hairs." To me, a lot of fossils of larger carnivorous dinosaurs look like they had fur around them instead of feathers. is also a close up picture of sinosauropteryx (a small bipedal theropod, largest specimen measuring 3.5ft) feathers, which to me look more like hair. Now, ignoring the theory that dinosaurs most likely had feathers and correlations that got with that theory, and focusing on fossils, could dinosaurs have had hair? Is there fossil evidence that shows dinosaurs (the ones that seem to have hair) in fact did not have hair, and what seems like hair is in fact feathers? It's hard to tell just by looking at pictures if it's feathers or hair, and I want to know if paleontologists know for certain that it's feathers and not hair. edit: is a picture of the whole sinosauropteryx fossil
|
[
"They wouldn't have hair in the strictest sense because mammals are quite distantly related to birds, and their common ancestor did not have hair. It would have evolved independently. Hair, feathers, and scales are all ",
"integumentary structures",
", though they're all formed in different ways. ",
"Feathers",
" really take the cake in terms of complexity (",
"full source",
" and ",
"gratuitous photo of structural color in a feather",
"). We can't ignore the idea that dinosaurs had feathers, because birds are theropod dinosaurs. There's really no question there, and it's kind of a big deal. The interesting thing is how decoupled feather evolution has become from bird evolution. It used to be one of the things we thought made birds so special! ",
"As you might expect from such a complicated structure, feather evolution is equally complicated and something we're still trying to work out. What does something that's sort-of a feather look like? Which structures that we find in the fossil record represent the early stages of feather evolution? About 15 years ago some ",
"hypothetical intermediate stages of feather evolution were proposed",
" based heavily on feather development, and they looked ",
"like this",
". ",
"We know we have feathers for sure starting at ",
"Coelurosauria",
", and we have structures that may or may not be homologous moving farther down towards the group Dinosauria as a whole (note that in the tree I linked to, birds fall within Maniraptoriformes). These structures are affectionately referred to as \"dinofuzz\". \n We also have feathers preserved in amber that ",
"look just like the intermediate steps proposed earlier",
" for feather evolution (check out figures 1 and 2). There are several instances of this, in fact, including ",
"this megalosaur",
" and ",
"these fibers in Canadian amber",
". ",
"We also have very distantly-related dinosaurs that have some sort of integumentary structure, like ",
" and ",
" (",
"full source",
" for ",
"). They also had some scales, and we have skin impressions of dinosaurs without anything like these structures, including several ",
"mummified hadrosaurs",
". Did they evolve independently of feathers, or did they share a common structure and diversified from that? At what point is a feather a feather?",
"We even have some pterosaurs with fuzz, referred to as \"",
"pycnofibers",
"\". Their structure is different than dinofuzz, so it's been assumed that these fibers evolved independently. The thing that complicates this is the fact that a type of keratin thought to be unique to feathers ",
"also exists in embryonic alligator scales",
". Alligators and their relatives are the closest living relatives to birds (and other dinosaurs), and pterosaurs are more closely related to dinosaurs than alligators. ",
"This means there could be a common component to all of these structures, and the evolution of pycnofibers isn't entirely independent of feathers. It could be that there were animals that had scales and these different structures arose independently using a common developmental basis. That could mean that the precursor of feather were found within a much smaller group of dinosaurs (like theropods or saurschians) rather than all dinosaurs or all archosaurs, and what we see in pterosaurs, ornithischians like ",
", and theropods are separate structures.",
"This is a longer response than I was going for on the subject, but it is interesting. Let me know if I missed anything you were wondering about.",
"This",
" is a great paper on feathered dinosaurs, although it's from 2003 and a lot of discoveries have been made in the last 10 years. Unfortunately it's behind a paywall."
] |
[
"This was interesting to read and is exactly what I was looking for. I wish I could give more upvotes. Thanks for putting time into writing it. "
] |
[
"Cool, glad I could help!"
] |
[
"Are tractor beams scientifically possible?"
] |
[
false
] |
Watching Star Wars right now and I was curious if tractor beams could actually work/exist.
|
[
"Very small things can be manipulated using a focused laser. It's called optical trapping or optical tweezers. There is a similar effect that can be done with sound waves called acoustic levitation.",
"Optical tweezers",
"Acoustic levitation"
] |
[
"/u/iorgfeflkd",
" gave a good answer, but optical tweezers do not scale well.",
"You could give the opposing ship an enormous electrical charge (say, with a particle beam) and give yourself an opposing charge. This is one ",
"proposed way to steer an asteroid",
". You don't really want a giant spark as soon as the Millennium Falcon lands though, but at the engineering level required for the rest of Star Wars I'm sure they'd find a solution."
] |
[
"You missed his point about the spark, when the opposing charges come close they will discharge with a lightning bolt. That might cause damage so before they come too close you need to ground at least one end but that is not an easy task in space."
] |
[
"If you compress a gas or liquid enough, would it eventually become a solid because it’s molecules are so tightly packed?"
] |
[
false
] | null |
[
"Eventually, yes."
] |
[
"Like how much pressure would there need to be. Would it turn into a black hole possibly at that point since it’s so dense?"
] |
[
"Take water, for example. ",
"Here",
" is the phase diagram. At 200 degrees Celsius, you have to compress it to at least 3 GPa, and it will become solid."
] |
[
"How does the depo-provera birth control shot fail?"
] |
[
false
] |
From what I understand, the depo shot works by keeping you from ovulating and thickening the mucus in your cervix to make it more difficult for sperm to reach the egg. If this is true, how could it fail? Does the body "accidentally" release an egg during one of your cycles? Or is the shot 100% effective (with perfect use) for some women and not for others?
|
[
"The \"depo-shot\" is Medroxyprogesterone, a form of progestrin. As you stated this hormone causes ovulation to fail and the mucus of the cervix to thin. Your explanations are also correct. Hormones do not work perfectly on every person all of the time. There are a large amount of environmental and genetics factors controlling your hormone levels. The body may, under certain specific conditions, fail to react to the shot do to increased levels of other hormones that cause ovulation to occur anyway."
] |
[
"Thank you for your explanation! If I may I'd like to ask a few follow-up questions. ",
"So, the way you stated it led me to believe that, if a woman reacts as she is supposed to, the depo shot would be 100% effective for her unless she changed some aspect of her diet/environment in a way that effects the hormones that dictate her cycle. Is that accurate? Do we know what changes may affect these hormones?"
] |
[
"I'm sure that information is available, but I'm afraid I don't know enough to say what they are. As far as I know the depo shot is considered pretty close to 100% accurate, but it does fluctuate slightly on a person to person basis. Not sure I can give you all the answers you want though."
] |
[
"How can I test the double slit experiment at home?"
] |
[
false
] |
I failed miserably on my first attempt. Slits cut into a beer box and flashlight. The folks at said I need a laser and that the slits I made where probably too big. My question is this. Is there a way to conduct this experiment at home? I have a laser pointer. How should I construct the slits? what measurements have to be exact, i.e. distance of the slits to the wall or laser, slit size etc? Thank you.
|
[
"I did this by taking a piece of glass and holding it over a candle to get a nice thick layer of black soot on it, then holding two x-acto knife blades parallel to each other and scraping two nice thin lines right next to each other in the soot."
] |
[
"On a similar note, you could do a ",
" \"slit\" interference patter, by just shining a laser past a hair. Just hold one across the top of a laser pointer.",
"For extra credit, use the interference pattern to measure the width of the hair.",
"Edit: I always manage to have at least ",
" typo in any of my posts that gain attention. Fixed."
] |
[
"Not quite the same, but ",
" Will produce a nice interference pattern. See ",
"for example here",
"."
] |
[
"My Brain is odd, anyone know what it is?"
] |
[
false
] | null |
[
"Hello,",
"We can’t advise you about this here."
] |
[
"Whoops, my apologies, what would be a good place to post this?"
] |
[
"You should discuss it with your medical professional."
] |
[
"Transporting P. Chrysogenum samples?"
] |
[
false
] | null |
[
"It would be easier to simply FedEx them than trying to bring them with."
] |
[
"But then I will have to fill out similar paperwork for FedEx, no?"
] |
[
"PPQ 526 permit.",
"And here's where it starts.",
" Unfortunately, you need a Level 2 account, whatever the heck that it. Might be free.",
"Probably best to contact the USDA directly (APHIS PPQ), and see if you need one for fixed samples."
] |
[
"Why do so many archaegenetics and population genetics studies only seem to use mtDNA and yDNA, and not autosomal DNA?"
] |
[
false
] |
*archaeogenetics
|
[
"mtDNA and Y chromosome DNA are the two pieces of the human genome that do not undergo recombination every generation. Essentially, they don't get reshuffled like everything else does. So, the mtDNA you get from your mom is exactly the same as your mom got from her mom....plus any mutations that have occurred. So, literally, the mtDNA you carry is a direct descendant of mtDNA that some woman had a million years ago carried down mother to daughter for all those years. The same goes for Y chromosome in men. This simplifies things a lot.",
"But, it does lose a lot of ancestry based just on chance. So, it is important to not forget the other chromosomes in descent. Good ancestry analysis looks at all chromosomes for small parts that come from specific regions of the world. Just looking at mtDNA and Y chromosome can easily hide your true ancestry if used as the only source of information.",
"Example...If your mother's maternal grandmother was Irish and your dad's paternal grandfather was Irish but every other ancestor you have was Chinese, your mtDNA and Y chromosome would agree you are Irish. But 14 of 16 ancestors in your great-grandparent would actually be Chinese."
] |
[
"To be brief, it's because they are thought to be relatively easy to understand as they represent a single uniparental lineage that doesn't recombine. Further, especially for mtDNA, it is much cheaper to genotype or sequence than whole genomes.",
"Uniparental lineages, in particular mtDNA, have problems though that are seldom addressed in the literature. They can come under selection, and their history is not necessarily neutral, nor is it necessarily representative of the rest of the genome with regard to demographic history for this reason. A good overview of this was given by Balloux in: ",
"http://www.nature.com/hdy/journal/v104/n5/full/hdy2009122a.html",
"To give a more anecdotal example of the issues of uniparental markers, I can actually use my own genome. With regard to my autosomes, most of my ancestry is from England or Ireland and this shows when you analyse them. However, my direct paternal ancestor was a Jewish migrant from Europe, and my direct maternal ancestor was Aboriginal Australian. As such, my Y lineage is one that is seen most often in the Near East, and my mtDNA lineage is specific to Aboriginal Australians. The fact that this can happen is often underappreciated in the literature."
] |
[
"In addition to the other answers you got here, for ancient genetics the main reason mtDNA is most common is because its much easier to recover from historical or ancient samples. There are thousands of copies of each mt chromosome per cell compared to only 2 copies of each autosomal chromosome, so each mtDNA gene will be present thousands of times more in a given sample."
] |
[
"How do some fabrics \"keep you cool in the summer and warm in the winter?\" Or, is this just an advertising gimmick?"
] |
[
false
] | null |
[
"As this is a very specific question, and relies largely on which product you are talking about, could you provide a link to a specific product you are wondering about?"
] |
[
"Just googling \"Warm in the winter, cool in the summer\" gives lots of products saying this. One of the more interesting I found was a kilt company saying wool did this, since it was a natural material. Of course, the reasoning is a common fallacy, but is there anything to such a claim? How hard is it to make something that actually is cool in the summer and hot in the winter? "
] |
[
"Thermal energy storage in general, and phasechangematerials (PCMs) in particular, have been a main topic in research for the last 20 years, but although the information is quantitatively enormous, it is also spread widely in the literature, and difficult to find. In this work, a review has been carried out of the history of thermal energy storage with solid–liquid phasechange. Three aspects have been the focus of this review: materials, heat transfer and applications. The paper contains listed over 150 materials used in research as PCMs, and about 45 commercially available PCMs. The paper lists over 230 references.",
"\"Review on thermal energy storage with phasechange: materials, heat transfer analysis and applications\" Applied Thermal Imaging Volume 23, Issue 3, February 2003, Pages 251–283",
".",
"NASA's Innovative Partnership Program has a page on \"Phase Change Fabrics Control Temperature\"",
". ",
"Out of ",
"649 for the year so far",
", Google Scholar tracks at least 40 articles on Phase Change Materials published ",
". "
] |
[
"When some animals become an Alpha or leader of the pack they undergo physical changes (silverback, baboon) how does the animals body know it's the leader?"
] |
[
false
] |
ok so I've always wondered how exactly the animals body knows it's the leader of the pack, head honcho, alpha etc. what causes the changes (hormones?) but more importantly how does the animals body know this is the case? edit: Seems I was incorrect about silverbacks, but I'm sure I've seen animals where the alpha looks very different from the rest (not just bigger etc, but different colourings) edit2: Thanks for all the replies guys, there have been a lot of interesting comments and a good few citations that I'm going to read up on.
|
[
"They don't undergo physical changes; I'm not sure where you're getting that from. ",
"All adult male (over 11 years old) gorillas are silverbacks",
". "
] |
[
"Queen Naked Mole Rats secrete a hormone that represses the metamorphosis of other females into queens. When the queen dies, many females begin to change into queens, the first one to fully change begins to secrete the repressor hormone, causing the other females to revert to their original state."
] |
[
"To add some details: Gorillas acquire silver coloration at age 12-15 yrs (depending on subspecies) regardless of their social status. The chart in ",
"this paper",
" lays out the age range of silver coloration in the different subspecies.",
"However, in other species there can be socially driven effects. Baboons and mandrills only have high testosterone levels if they are dominant breeding males, and the high testosterone drives development of the secondary sexual traits. So in those species, males of the same age can look very different depending on their social status and T level. ",
"See here for an example from mandrills",
"."
] |
[
"What causes diarrhea? Specifically why and how is a virus causing the body to expel massive amounts of water?"
] |
[
false
] |
Im in pain, distract me with science
|
[
"There are 4 mechanisms of diarrhea. Osmotic, permeability increased, secreting and abnormal motility (peristaltic)",
"All of them can coexist, and in an inflammation, they usually do, but those are the mechanisms of diarrhea.",
"TLDR:",
"Specifically in regards to the virus, it probably will replicate in enterocytes (or some other intestinal cell depending on the virus). It will cause damage there, (decreasing the amount absorbed increasing osmotic pressure if it is in enterocytes [point 1]) and inflamation, increasing blood flow. This will increase the peristaltism [point 4]. In response to the infection, the immune system will respond secreting immunoglobulines and some other things point 3] and it will probably have some damage in the cells that will cause a \"leakage\" [point 2]. As there is more stuff in the lumen, that won't be absorbed (virus, inmunoglobulines...) there will be an increased osmotic pressure [point 1].",
"Edits:"
] |
[
"Certain viruses and bacteria have the ability to activate ion channels that are part of the normal mucosa in the gut. When these are constitutively activated you lose lots of electrolytes and with that, water osmotically follows causing the diarrhea and dehydration."
] |
[
"Consitutively is a new word for me.",
"\nFilters. (biochemistry, of a metabolic process) At a constant rate regardless of physiological demand. adverb."
] |
[
"I was just wondering what forces are at play in a bicycle..."
] |
[
false
] |
So I just finished my last year of High School (holy crap) and I have this burning question which has bothered me since I was about four: how does a bicycle stay up? Now, through two years of physics study, I have learned that the bicycle is in a state of equilibrium. I know that the body balances the torque in the left-right direction, but the bicycle is always easier to ride when it is in motion (but moving faster =/= more balance). The wikipedia article "Bicycle and motorcycle dynamics" does not help because I don't understand calculus. Layman answer please!
|
[
"A bike is upright if the ground reaction force balances all the other forces the bike experiences: gravitational, aerodynamic, gyroscopic, intertial/centrifugal. There's no simple answer other than understanding balance of a device on a surface under gravitational pull traveling through air.",
"Center of mass is the easiest concept I can think of that would explain it."
] |
[
"The gyroscopic action of the wheels is almost unimportant. Hardly the \"main force.\""
] |
[
"The main force that keeps a bicycle balanced is the turning of the wheels which act as a gyroscope; the faster they spin the easier it is to balance since the wheels want to stay in there current orientation (vertical) and they will stay vertical as long as the forces that tilt the wheel (gravity/center of balance ) are less weak then the gyroscopic force of the wheels.",
"here is a demonstration if you want to see what i am talking about\n",
"http://www.youtube.com/watch?v=8H98BgRzpOM",
"Edit: this is not the only reason but one of the main contribution to the stability of a bicycle while it is moving."
] |
[
"If I increase my vocabulary will I increase my IQ?"
] |
[
false
] | null |
[
"IQ is essentially just a standardized test score, and just like any test you'll get better results by studying for it. Most IQ-tests are composed of analytical and visual-spacial problems, and I don't think memorizing vocabulary will help you with those.",
"Whether IQ tests correspond to intelligence is another matter entirely."
] |
[
"This response is mostly true. If the \"IQ\" you are talking about is the overall score from a psychological assessment measure such as the Weschler Intelligence Scale for Children--4th Edition or Weschler Adult Intelligence Scale (These are commonly used measures by psychologists for assessing cognitive ability), then you are on the right track. Spoiler alert: a part of the Verbal Comprehension section of these tests looks directly at one's ability to explain word meanings. So yes, if you improve your vocabulary, and your ability to orally explain word meanings accurately, then your IQ will improve.",
"Your secondary question is interesting. There is no direct way to measure intelligence. Psychologists can't just open up your brain and pull out a pure number. \"IQ\" tests are our best estimate of cognitive, or intellectual functioning. This is all based on skills deemed valuable by society, such as ability to explain abstract relationships, recognize patterns, demonstrate flexible and efficient memory skills, and on and on. ",
"Hope that was helpful, I'm currently finishing up a School Psychology MA/Ed.S. program. "
] |
[
"Well, do they?"
] |
[
"Philosophers, what is your opinion on Christopher Langan's Cognitive Theoretical Model of the Universe? (link)"
] |
[
false
] | null |
[
"We don't take philosophy questions in ",
"/r/askscience",
". I suggest you submit to ",
"/r/askphilosophy"
] |
[
"that explains why there was not a philosophy tag, i apologize!"
] |
[
"no worries."
] |
[
"Can you build muscle mass on your face with the right exercises just like you could with your biceps and thighs etc.?"
] |
[
false
] | null |
[
"Yes, absolutely. ",
"However, the chances of you actually causing a visible change are pretty small. One of the few exceptions to this are dedicated boxers/fighters. Mike Tyson, for example, use to chew entire packs of gum at once to strengthen his jaw muscles, and if you look at pictures of him at his prime compared to now, you'll see that he has much more pronounced masseters (if you clench your jaw and feel your face around where your molars are, you can feel that muscle kind of ball up). ",
"However, most muscles in your face have a much smaller cross-sectional area than the masseter. Most muscles in your face are very thin. For example, you have your buccinator muscles that are your cheek muscles. Most face muscles are similarly thin, so even when you work them out, a large relative change in CSA is actually a very small absolute change. That is, I can increase the CSA of my buccinator 30%, and it might have gotten a millimeter thicker (just pulling numbers out of my ass here, but you get the idea).",
"So yes, you can make them bigger, but since they're such small muscles anyway, you will barely perceivable increases in size."
] |
[
"you can definitely build your jaw muscles by chewing on tough things or springs. You can get better control of your facial muscles by practicing expressions, although I don't know if they get more massive or not."
] |
[
"Interesting. Would that be better or worse for wrinkles?"
] |
[
"Does blocking our eye vision for long periods of time stops melanin production?"
] |
[
false
] |
Can melanin production be stopped if something like a eyepatch blocks the eye vision for several weeks? People who doesn't take sunlight for some time have whiter skin than before. Can this apply to the eye color as well?
|
[
"No, because melanin is a skin pigment produced in response to sunlight (specifically UV light) striking the skin. One cannot get tanned from simply looking at the Sun, so wearing an eyepatch will not affect melanin production. Melanin production is based on genetics and exposure to sunlight."
] |
[
"I know it was a little difficult to understand, but OP was talking specifically about the melanin in the iris of the eye.",
"\nBasically he is asking if everyone would have blue eyes if they were locked in a basement for a long time...."
] |
[
"Eye color is determined by a variety of ",
" as well as structural aspects of the iris. ",
"Isn't melanin the primary pigment you are describing here?",
"melanin production in the eye and in the skin occur by two different mechanisms and have two different purposes. Thus, wearing an eye patch for an extended period of time would not change the color of your eye.",
"You basically said \"skin and eye melanin are different, thus the answer is no.\" I like the use of the \"thus\", but unfortunately this doesn't actually tell us anything specific about why wearing an eye patch wouldn't change the color."
] |
[
"If spinal damage can cause paralysis, how can quadriplegics have functional organs?"
] |
[
false
] |
[deleted]
|
[
"Organ function is not necessarily dependent on central nervous system stimulation. Many organs are controlled through complex feedback loops that depend on various factors in the bloodstream, for example. Other organs such as the GI tract have a 'separate' ",
"nervous system",
" that partially regulates its activity. ",
"With that said, damage to the nerve tracts in the spinal cord can result in impairments beyond simple voluntary muscle paralysis. For example, damage to the autonomic nerves (above the level of T6) that innervate the cardiovascular system can lead to autonomic dysreflexia, in which the heart and vasculature lose their coordinated response to stimuli. Similarly, temperature control can also be affected. Damage to the phrenic nerve (arising at the level of C3,4,5) can result in diaphragmatic paralysis, which can range from total inability to breathe to greater risks for pneumonia/atelectasis. The bowel can either exhibit an upper motor neuron pattern of injury (hyperreflexive) or a lower motor neuron (hypotonic), depending on the location of the lesion. ",
"To your specific point, the vagus nerve is not 'safe', but due to its origin and course it is not contained within the spinal cord itself. It can still be injured, of course - a common example is with patients who are post-cardiac transplant. Their heart lacks the vagal 'brake', and tends to beat faster than a normal heart. ",
"Lastly, I'll just say a general note that in neurologic disorders location is key. Depending on where the lesion is, it is possible to have very specific, focal deficits. It is also possible to have global impairments across a wide range of functions. So it really depends a lot on the specific injury in each case."
] |
[
"The vagus nerve is not safe from damage it just does not course with the spinal cord. An injury to the neck can transect the spinal cord without any damage to the vagus. Thus, parasympathetic innervation to the heart, lungs, gut, etc. is intact. Until you get to the distal large intestine where parasympathetic innervation comes from the sacral splanchnics. Also, remember that the gut tube has the enteric nervous system that is also independent of the spinal cord."
] |
[
"You are assuming that someone with a spinal injury has a total transection of the spine. This is not usually that case. Usually the spinal injury is partial. The spinal cord has several pathways (\"tracts\") with different functions, such as motor, sensory (touch), position sense, vibration, temperature. ",
"So a spinal cord injury has to be defined by both the level and the motor and sensory impairment. For example, this person broke his neck and he has a motor injury to the level of X on one side or both sides, and a sensory level to Y on one or both sides.",
"Then there is the autonomic nervous system which is important for many things including the control of organs. The parasympathetic nerves (eg. vagus) arise from the brain and brainstem and do not pass down the spinal cord. The sympathetic nerves do travel in the spinal cord and may be injured. ",
"The visceral organs also have their own local nervous system (the enteric nervous system) that controls their normal functions. These neurons are located within the organ itself for the most part."
] |
[
"How does the Axiom of Regularity prevent a set from containing itself?"
] |
[
false
] |
[deleted]
|
[
"First, let's answer your title question. Let ",
" be a set. Then {A} is a set by axiom of pairing, and the axiom of regularity says that there must be some element of {A} that is disjoint from {A}. But the only element of {A} is A. So regularity says that A is disjoint from {A}, which implies A is not an element of A. (Otherwise, A would be an element of both A and {A}, and so A and {A} would not be disjoint.)",
"Now let's see why your example is not a counterexample. For one, how do you even construct the set A = {A, {1}}? What axioms do you use to construct it? The axioms only let you build sets from essentially the empty set and the various axioms like pairing, union, etc. You should find that it's not possible to construct a set A such that A = {A, {1}}.",
"More precisely, suppose there ",
" a set A such that A = {A, {1}}. Now consider the set B = {A}. By regularity, there must be some element of B that is disjoint from B. Since A is the only element of B, regularity says that A and B must be disjoint, but this is nonsense since A is an element of A ∩ B. (By construction A is an element of B, and by assumption A is an element of A.) This contradiction of regularity means that A was not a set to begin with."
] |
[
"Re-read it yourself. Is A assumed finite, perhaps implicitly? "
] |
[
"A is an arbitrary set."
] |
[
"Does antimatter have an equal form of electricity, or would it operate differently?"
] |
[
false
] | null |
[
"The antimatter versions of ordinary matter particles have the opposite charge, for example electrons are negative but positrons (the antimatter equivalent) are positive. The charges still obey the same electrical laws as the charges of ordinary matter, and an electric circuit made from antimatter would behave the same as the same circuit made of ordinary matter, since opposites still attract and likes repel. "
] |
[
"Weak interaction is not invariant under charge conjugation. It couples only to left-handed fermions and right-handed anti-fermions."
] |
[
"Weak interaction is not invariant under charge conjugation. It couples only to left-handed fermions and right-handed anti-fermions."
] |
[
"Why are certain chemical substances addictive and some are not, some are highly addictive and some are mildly addictive?"
] |
[
false
] |
I was reading an article about how Marijuana was so much better than alcohol and one of the arguments the article made was that Alcohol is an addictive substance whereas Marijuana isn't. I also know that when it comes to Psychoactive substances there is a spectrum of addiction, MDMA isn't addictive while Cocaine is highly addictive, whereas Opiades are severely addictive. What causes such drastic differences in the way we "crave" certain substances?
|
[
"Fascinating question! First, let's avoid the pitfall of failing to define our terms. People use \"addiction\" to mean a lot of stuff, and even standard definitions don't line up perfectly. What it means to me is compulsive, chronic use of a craved substance despite harmful, where tolerance develops with repeated use and withdrawal occurs if it is stopped; the substance takes over one's life. This is more than mere dependence, and more than mere abuse. It's a big deal.",
"The curious thing is that some substances undergo prolonged debate over whether they're truly \"addictive\" or \"substances of abuse.\" Heroin, now the very model of an addictive drug, was once marketed as a more potent version of morphine without the addiction. (Both \"aspirin\" and \"heroin\" are Bayer trade names.) Currently, pregabalin is a controlled substance while gabapentin isn't, though they're in the same class of drugs. Marijuana is still controversial, as it doesn't promote the same compulsive use in animal models as cocaine and heroin, but then we're not rats. When arguing whether a substance is addictive, I'm reminded of the quote from ",
": \"We would have injected vitamin C if only they'd made it illegal.\"",
"So, what makes a drug addictive? You're likely to get some pat answers about dopamine levels, probably about dopamine being the \"happy juice\" that drives addiction. While this isn't wholly wrong, it's neither adequate nor entirely right. Some addictive drugs, particularly the amphetamines and cocaine, directly promote dopamine release or prevent its recycling. Others, however, hit entirely different targets. Alcohol, benzodiazepines, and barbiturates all work on GABA, broadly decreasing brain function. Our receptors for \"endogenous morphines\" (\"endorphins\" for short, because we discovered them in the wrong order) are targeted by opioids; likewise, we were smoking cannabis long before we named the endocannabinoid system. Then there's the nicotinic acetylcholine receptor, without which tobacco would just be another plant. On the other hand, we use L-DOPA to treat Parkinson's; it directly increases dopamine production, yet isn't a drug of abuse. (The trouble with neurotransmitters is when they all interact and screw up our tidy diagrams.)",
"One of the foremost theories involves various drugs converging on the mesolimbic dopamine pathway and the nucleus accumbens, a pathway and region strongly implicated in motivation/learning/reward/pleasure. Chronic use appears to induce changes on the cellular level, including protein synthesis and which genes get used. It makes a lot of sense that different drugs should have the same effect, as addicts frequently abuse multiple substances, and substituting one for another doesn't solve the problem. At the same time, some have argued that different drugs are simply different, that opioids and stimulants really aren't causing the same problem. Moreover, there's strong evidence for changes to the frontal cortex, more associated with decision-making and complex thought.",
"Then again, all of this is still dependent on the user. Familial patterns and genetic studies support a strong role for heredity, while environmental factors (notably sexual abuse) can't be overlooked. Prescription opioid abuse is an epidemic problem, yet lots of people hate taking them even for serious pain. Two people might take the same drug daily for a year, with one becoming addicted and one dropping it without too much trouble.",
"This get to a common problem in psychiatry/psychology/neurology/neuroscience. You can model the same thing at different levels and using very different concepts. Addiction involves changes at the level of the cell, tissue, organ, human, and group of humans. If it were easy, we'd have it figured out. ",
"Sources: Drew heavily on the articles in this Nature Neuroscience review\n",
"http://www.nature.com/nrn/focus/addiction/index.html"
] |
[
"I have some major issues with this answer.",
"First off, the evidence very strongly does NOT suggest that dopamine release is pleasurable or rewarding. The current evidence appears to indicate that the firing rates of VTA dopaminergic neurons convey information about reward expectancy and/or changes in reward expectancy (known as \"reward prediction errors\"). This is NOT the same thing as being pleasurable, and in fact both unexpected pleasurable AND unpleasurable events can produce dopamine release in the mesolimbic circuit.",
"This answer also wholly neglects the distinction between dopamine release in the mesolimbic pathway and dopamine release as some kind of general brain phenomenon, perpetuating the pervasiv ebut extremely wrong notion that neurotransmitters have some kind of global brain \"level\", when in actuality there are always many separate populations of neurons that release a given neurotransmitter, and their activity is independent of each other.",
"Furthermore, the notion that \"THC doesn't cause any long-term changes in the function of your neurons\" is completely untrue. The brain absolutely exhibits homeostatic changes in receptor expression etc. in response to chronic administration of cannabinoid agonists or antagonists.",
"This answer goes beyond presenting a \"simplified\" account of the neurophysiolgoy of addiction, to the point of being essentially pop-pseudoscience, and in my opinion should simply be retracted in its entirety.",
"Source 1: Role of dopamine release in mesolimbic circuit",
"Source 2 ,same topic",
"Source 3, same topic",
"Source 4, discussing the circuitry of the nucleus accumbens and reviewing evidence that dopamine is not linked to pleasure, but rather to learning about reward-associated cues without being rewarding itself",
"Source 5, showing that chronic usage of marijuana DOES produce long-lasting downregulation of CB-1 receptors"
] |
[
"I have some major issues with this answer.",
"First off, the evidence very strongly does NOT suggest that dopamine release is pleasurable or rewarding. The current evidence appears to indicate that the firing rates of VTA dopaminergic neurons convey information about reward expectancy and/or changes in reward expectancy (known as \"reward prediction errors\"). This is NOT the same thing as being pleasurable, and in fact both unexpected pleasurable AND unpleasurable events can produce dopamine release in the mesolimbic circuit.",
"This answer also wholly neglects the distinction between dopamine release in the mesolimbic pathway and dopamine release as some kind of general brain phenomenon, perpetuating the pervasiv ebut extremely wrong notion that neurotransmitters have some kind of global brain \"level\", when in actuality there are always many separate populations of neurons that release a given neurotransmitter, and their activity is independent of each other.",
"Furthermore, the notion that \"THC doesn't cause any long-term changes in the function of your neurons\" is completely untrue. The brain absolutely exhibits homeostatic changes in receptor expression etc. in response to chronic administration of cannabinoid agonists or antagonists.",
"This answer goes beyond presenting a \"simplified\" account of the neurophysiolgoy of addiction, to the point of being essentially pop-pseudoscience, and in my opinion should simply be retracted in its entirety.",
"Source 1: Role of dopamine release in mesolimbic circuit",
"Source 2 ,same topic",
"Source 3, same topic",
"Source 4, discussing the circuitry of the nucleus accumbens and reviewing evidence that dopamine is not linked to pleasure, but rather to learning about reward-associated cues without being rewarding itself",
"Source 5, showing that chronic usage of marijuana DOES produce long-lasting downregulation of CB-1 receptors"
] |
[
"Is there any empty space in the circulatory system?"
] |
[
false
] |
So is every blood vessel in a closed circulatory system completely filled with blood at all times - or are there times where there are empty spaces where no blood resides at all? Is the heart constantly full of blood - or does it have some empty space? When thinking about the circulatory system, I always imagined blood being pumped into empty space from the heart into the arteries and then into subsequent blood vessels - but I am not sure this is the correct model.
|
[
"The heart, unless contracting, is full of blood as well as the circulatory system. If by \"empty space\" you mean that there would be a void where the circulatory system component had literally nothing, that would be a collapsed vessel, which is a problem. This is why when you are injured, you bleed from any injury site, irrespective of your heart beating. While you will bleed more when it does beat, the system is full of blood/lymph/fluid.",
"Blood (components) prevent your cells (most of them) from freaking out that they are starving or running out of oxygen. These cellular/chemical triggers cause a big problem and thus, you would want your cells to be bathed in blood (components) as much as possible."
] |
[
"If by \"empty space\" you mean that there would be a void where the circulatory system component had literally nothing, that would be a collapsed vessel, which is a problem.",
"Maybe a bit nitpicky, but that's not necessarily the case! Body veins can have variable amounts of blood volume inside them depending on the fluid volume status of your body, thanks to their material properties (high compliance, low elastic retraction). This is why the veins are also called the capacitative system. When fluid volume is especially low, veins can appear collapsed in an 8 figure kind of way. They will still conduct blood because the 2 pores of the 8 are still permeable."
] |
[
"The heart is never depleted of blood even after contraction, there will always be residue in the shape of endsystolic volume after ejection. The above post is not entirely correct, I'll write a reply shortly."
] |
[
"If you place a tree that normally experiences seasons in an artificial environment without seasonal temperature changes, will it keep its leave year round? Will this be detrimental to it?"
] |
[
false
] | null |
[
"When I lived in the tropics I noted that deciduous trees would still shed but would grow back their leaves pretty well immediately. Thar said, I am sure a botanist would be able to give you a better answer. Plants have been grown in glass houses for centuries."
] |
[
"Is that a dedicated shedding phase or single leaves that fall off here and there pretty much continuously? What determines the lifespan of a leaf?"
] |
[
"My original reply was about deciduous trees, So yes it is a one off event annually, the big difference with what happens in cold climates is that the deciduous tree grows its leaves back pretty well immediately. You might say a nap rather than dormancy."
] |
[
"What is the critical mass of gas required for it to stick together in deep space due to gravity and not disperse due to diffusion?"
] |
[
false
] | null |
[
"So, while FuzzyDarkMatter does have a pretty strong answer to this as is, I think I want to add that this is a well-studied problem in physics. In fact, like most things, we have a name for it: the ",
"Jeans instability",
"! This is a simple equation which tells you what the balance is between hydrostatic pressure of the gas pushing outward (due to temperature and the like) and gravitational forces attracting everything toward the center of mass. This allows us to determine at what size gas clouds will be able to form stars."
] |
[
"There is no single answer to your question. The atoms in the gas has a certain average kinetic energy determined by the temperature. If the temperature is too high, the kinetic energy per atom is so large that the gas will not be gravitationally bound. Roughly this is what happens when supernovae go off in a a galaxy. They heat the gas in a galaxy to the point where the gas can escape the deep gravitational well of the galaxy + dark matter halo.",
"If the temperature is too low on the other hand, the gas cloud will collapse under its own weight because the pressure can't balance the cloud's gravitational pull. The mass (for a given temperature) above which a gas cloud would collapse under its own weight is known as the Jeans mass or the Bonnor-Ebert mass (these concepts are very similar, so is often used interchangeably). This is important for understanding star formation and determining the characteristic masses of stars that form in molecular clouds. ",
"There is a middle-ground between the two extremes above where the gas pressure (due to the kinetic energy of the atoms) neatly balance the gravitational force. This is known as hydrostatic equilibrium and is important in understanding the structure of stars (why they don't collapse under their own weight), and the gas in galaxy disks, which are not flat like pancakes precisely due to the pressure of the gas."
] |
[
"I have written a post a few months ago in ",
"r/Physics",
" about just this, where I derived the size of a Jupiter-like planet in terms of fundamental constants (link: ",
"https://www.reddit.com/r/Physics/comments/8zagwp/the_size_and_mass_of_jupiter_in_terms_of/",
").",
"In a nutshell, dense low temperature spheres of atoms, like planets, can still be stable against gravitational collapse even without thermal gas pressure. In this case, pressure is due to something called electron degeneracy pressure. Basically it arises because electrons are fermions, and fermions can't share the same quantum state and so resist confinement (thus generating a kind of pressure). This leads to an upper size limit on low-temperature spheres that is comparable to that of Jupiter."
] |
[
"Can your circulatory system become dependent on compression garments?"
] |
[
false
] |
[deleted]
|
[
"I guess another way of putting my question would be \"Does long-term use of compression (like compression socks all day every day) cause your system to establish homeostasis that would then be thrown off if you stopped using compression?\" It's my understanding that, even though the treatments are used differently, they still have a bearing on overall circulation. I've heard things like corsets can cause leg swelling, so I figured that toothpaste tube effect could work in the other direction as well."
] |
[
"I'd say in the long term, probably yes. \nJust like wearing a bra tells your breast supporting tissue it doesn't need to work to its full potential and becomes weaker, same thing happens with those tissues in your leg. But it may not be enough to have an impact on overall circulation, and may not be irreversible.\nNow lets say if you are a healthy person who has to stand still for many hours a day, its less damaging (and even recomended) to wear compression socks for hours than to let your blood stagnate and slowly damage your veinous system anyway.\nHowever if you need compression socks because the veins in your legs are damaged and standing causes you to drop your blood pressure, your homeostasis is already off balance and the socks only helps you enough to solve this problem. \nI dont have a very long medical experience, but I have never seen a patient who needed to change their socks for stronger ones after a while (provided they wear it correctly) because their veins grew even weaker, if that is your concern.\nI hope my answer helps. (And sorry about any bad english)"
] |
[
"That does clarify things. Thank you! (And as an ESL teacher, I hereby give you an A on this writing exercise. ⭐💯)"
] |
[
"[Biology] Does irreducible complexity have any merits at all?"
] |
[
false
] |
Of course this pertains to evolution. Are there any examples of a "new" complex feature evolving from random mutations and/or natural selection since our study of evolution? Or does our knowledge of DNA make this a worthless argument plagued by over simplifications.
|
[
"So far, no. No one has found an irreducibly complex system.",
"Using irreducible complexity is an argument from ignorance. You are basically saying, \"I can't think of a way this complex system could have evolved, therefore it could not have evolved.\" It's about as arrogant as you can get."
] |
[
"No because all life is a product of evolution. Whether we know the exact steps of a certain path of evolution is irrelevant."
] |
[
"Well, if that's your reasoning, sure. But that's a bit of a red herring. The argument I quoted above is what the IC community says (and yes, I have known several of them. I was in their camp for a period of time).",
"But the reasoning you quoted is not the reasoning anyone I know uses in regard to evolution; typically it's \"The only mechanism by which any diversification of life has ever been known to arise is by evolution. Therefore, this feature is likely to be the result of evolution.\""
] |
[
"Did birds and animals like squid or octopus develop beaks seperately, or do they share a common ancestor?"
] |
[
false
] | null |
[
"They developed them separately. Current knowledge is that birds evolved from small dinosaurs, who had normal toothed jaws. This theoretically happened around the ",
"mesozoic era",
", which started around 250 million years ago.",
"Squids and octopi, on the other hand, are evolved from earlier forms of mollusks, which separated themselves out from other life forms in the some time during the ",
"cambrian era",
", which ended about 450 million years ago."
] |
[
"I can't get too in-depth about structure.",
"A bird's beak is made of keratin, which is a protein, whereas a mollusk beak is made from a mix of calcium carbonate and protein (the same substance as the shells of their mollusc relatives like clams, snails, and oysters."
] |
[
"Convergent Evolution at it's finest! Beaks are super useful for many different situations like obtaining food or burrowing into something"
] |
[
"Is there a theory for or a way classifying errors that occur only sometimes?"
] |
[
false
] |
Within the little programming experience I've had it generally seems that either theres an error in my code and it will compile or it wont. I know that then there are run time errors or exceptions that can occur when a possibility isn't accounted for. Furthermore I know that in C you have to free up memory after its use otherwise a perfectly functional program can take up more and more space over time and eventually just crash every time it opens. The point is that these all seem to me like examples of a pathological problems that will at one point or another render the program unuseable. However, while browsing the internet or on my smart phone I often encounter errors that can easily be solved by resarting the app or refreshing the page. Sometimes they happen rarely, other ones happen half the time you try the action, but the other half the time it works. Are these really just a coffeed out programers who put a > instead of a >= hidden somewhere in 1000 lines of code or is there something about complex, multi layered programs that generates this kind of behavior that you wouldn't see in a simple one?
|
[
"Aside from amoralnihilist's answer, which was mostly adequate, there is something else to consider:",
"Are these really just a coffeed out programers who put a > instead of a >= hidden somewhere in 1000 lines of code ",
"Maybe, but that wouldn't be the whole story...",
"or is there something about complex, multi layered programs that generates this kind of behavior that you wouldn't see in a simple one?",
"Think about the examples you gave: the internet and a smart phone (the internet, or some kind of network, again). Any number of things could cause an error and they might not be local to your phone.",
"If some system between you and the server you are communicating with drops some packets or something somewhere takes too long to respond then you might get an error that you wouldn't get when everything works as planned. These errors might put your application in an unstable state and restarting might solve that.",
"amoralnihilist makes a good point, but I don't think he is necessarily touching on your exact question. You seem to be asking about a program being deterministic, and it should be. With the exact same input (including random number seeds/random numbers, etc.) it should behave exactly the same every time. But with the level of complexity of today's programs, that input is rarely actually exactly the same. For example, any program that has the current time as an input will essentially never have the same input and therefore will not necessarily behave the same way every time it is run. Whether it runs correctly according to that input brings us into amoralnihilist's point.",
"But what you are observing has more to do with a program's input changing and therefore its behavior changing. Occasionally that change in behavior manifests as an error that didn't normally happen given some other different input."
] |
[
"Senior developer here.",
"I have seen problems that appear infrequently (observed/reported in less than 1:100.000 cases) or that are extremely hard (or impossible) to reproduce in a controlled environment; they're extremely hard to fix because of the lack of information about the conditions under which a problem occurred. There is, indeed, a huge problem whenever there seems to be an issue that does not have 100% reproduction rate, with clearly defined steps.",
"A few examples of underlying causes of the tricky problmes include:",
"uninitialized variables - might have a default, predictable behaviour in controlled environments but will produce random results in the field",
"lack of error checking - parameter validation, handling failures (e.g. temporary loss of Internet connectivity)",
"sequencing problems - thread synchronization, access to shared resources, deadlocks",
"subtle problems residing at very low levels - drivers, API calls (operating systems and frameworks aren't perfect)",
"system configuration - other software or mods interfering with the normal, expected behaviour of your own software",
"These usually reflect some kind of bad practice, either at the programming level (e.g. based on assumptions, without proper handling of unexpected scenarios) or at the product management level (e.g. \"if it works don't mess with it\", \"it's ready for the market\", etc.)",
"The proper way to beef up your existing code is to use tests:",
"unit tests",
" - whenever you write/change a portion of code (e.g. a function) you should write associated tests that check if it (still) behaves in the intended way",
"integration tests",
" - usually applied for larger modules / groups of modules, taken as black boxes (i.e. \"I don't know how it works but I know what it should do\") and checking for proper functionality",
"code coverage - using tools that determine what logical branches of your code have been used in the previous cases; lack of coverage means that there are pieces of code that haven't been used, and implicitly tested properly, which means you need to write even more tests",
"beta testing - preferably using an enhanced product to save information about usage habits and detailed information about problems that appear",
"It is important to test both against \"acceptable\", expected use and also erroneous use (e.g. passing invalid arguments, having exceptions thrown or or errors returned by dependencies).",
"From the management point of view, problems can be avoided by:",
"establishing a good set of specifications for the product(s) and checking against them regularly",
"setting workable deadlines (there's a whole theory on risk management here - the bottom line is that you can lose more money by releasing a faulty product than postponing its release)",
"planning for refactoring & maintenance - managers will usually shy away from these things because it involves time spent with no immediate benefit (e.g. no new features)",
"Of course, there are a lot more bullets for each list and lots to talk about each one; this should give you a brief overview of the process and some of its points of potential failure."
] |
[
"TL;DR you can never guarantee your program is correct",
"It's not as simple as that, though (I realize that is your TL;DR). It's not that it is always correct, I think he is asking about it being deterministic, behaving the same way every time with the exact same input. He isn't realizing that what constitutes input in a program is more complicated than he likely realizes."
] |
[
"Is there an actual label to the \"shower principle\"? Is this phenomenon explained/researched at all?"
] |
[
false
] |
I heard the term "shower principle" on a TV shower recently and have been curious to learn more about the actual phenomenon. It's basically when in you've been stuck on a problem and the solution presents itself to you in the most benign of settings (like while taking a shower). What is the basis of this? Has any research been done surrounding how "turning your brain off" can lead to increased creativity?
|
[
"My only guess would be that a lot of people tend to shower first thing in the morning. That would make it the first time they revisit the problem that day. There is some evidence that our unconscious works on problems without our active involvement and sleep/dreaming could help with that.",
"There have been some recent threads in this subreddit on sleep with good citations but here's the wiki on unconscious problem solving.",
"http://en.wikipedia.org/wiki/Unconscious_cognition"
] |
[
"Also anecdotal, but I've also experienced that many times with various instruments, songs, etc. I've even found that to be the case with rhythm games like Rock Band."
] |
[
"The only explanation that even approaches a scientific one that I have heard has to do with the link between the relative prevalence of different frequencies of brain waves and certain mental states. Alpha waves seem to be possibly related to a state of relaxation or reflection. If certain activities lead to the promotion of certain brain waves being more prevalent, then this might be an explanation. Of course this could also be the tail wagging the dog. I would love to see some serious research on this, most of the EEG / biofeedback info pertaining to this that I can find is suspect to say the least. "
] |
[
"Will any primate preferentially choose bananas when presented with a choice of fruits?"
] |
[
false
] |
I'm just wondering about the whole 'monkeys love bananas' stereotype.
|
[
"I worked in a monkey research lab at one point and have also worked with great apes. Contrary to the stereotype, bananas aren't always the most-preferred treat. I used to bring in a variety of different fruits to the Rhesus and pig-tailed macaques to see what they liked best, and they all had different favorites. We would try to feed them each their favorite fruit on days when they got \"chaired\" (horrid thing, that's a whole nother story, but basically the monkey would be tied to a chair for about 8 hrs while it had various experiments done. Us animal care workers kind of decided that any monkey that was chaired would get all its favorite treats all day. Some of the monkeys seemed to regard this as a fair deal, others were not impressed) Anyway seedless grapes were always a winner. (btw a lot of research labs use grapes as rewards, but that's also because the grapes are easy to handle and are small) I had several monkeys that really preferred Honey Nut Cheerios to anything else, and one who adored kiwifruit. Bananas were generally appreciated but didn't seem to be more or less favored than any other fruit.",
"Then the gorillas I worked with loved to eat paper towels - go figure - that was actually their favorite treat, and you could even get them to trade you things for a brown paper towel. Occasionally a zoo visitor drops something into the gorilla enclosure, or a keeper forgets a broom or something in the enclosure. The keepers had worked a deal with the gorillas about it, such that the gorilla would go get the whatever-it-was, and bring it to the keeper, in exchange for a brown paper towel. Which the gorilla would then eat like it was the most delicious leaf ever. ",
"At the time I was with the gorillas, I was working with a zoo nutritionist who was doing a lot of experiments on adding \"treats\" and other enrichment to the animals' diets. She would rotate various items in and out of their diets. They get bored of a lot of things over time and sometimes prefer something novel. I remember her adding popcorn to the gorillas' diet at one point. ",
"Rabbits, however, will always sell their soul to the devil for a piece of banana. In my experience anyway. (I also worked in a rabbit/ferret vet clinic)"
] |
[
"I think monkeys are stereotypically paired with bananas because both bananas and (many) monkeys happen to live in tropical climates. ",
"I have it personally from Mike Tomasello (a famous cognitive scientist and primatologist) that \"There is nothing so horrible that a chimp would not do it for a grape.\""
] |
[
"It is true, I work with chimps and after they taste a grape for the first time they become obsessed. Cooked white rice is also a wonderful treat. "
] |
[
"How to compressed files (.rar, .zip) work?"
] |
[
false
] |
I just don't understand them. I download 1MB of files, unpack it using a program like WinRar, and suddenly I have 2MB of files. How can a program like WinRar use 1MB of input to find the correct 2MB of output? Try to keep it at least a bit simple, I don't know a terribly large amount about computers. Thanks!
|
[
"The file is scanned for patterns, and then a substitution system kicks in. ",
"Lets say that 1010101010101010 is found 100 times in the code of the file.",
"\nThen all we do is say A = 1010101010101010, so I store A and its value in a database; and now I've reduced the size of that information from 16 digits to 1. ",
"Then I look far more repeat sections of code and continue.",
"\nThat's why some file formats compress better than others. ",
"How stuff Works",
" "
] |
[
"It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity, it was the season of Light, it was the season of Darkness, it was the spring of hope, it was the winter of despair, we had everything before us, we had nothing before us, we were all going direct to Heaven, we were all going direct the other way",
"\nA best of times, A worst of times, A age of wisdom, A age of foolishness, A epoch of belief, A epoch of incredulity, A season of Light, A season of Darkness, A spring of hope, A winter of despair, we had everything B, we had nothing B, C to Heaven, C the other way"
] |
[
"417 bytes -> 267 bytes",
"$ echo \"It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity, it was the season of Light, it was the season of Darkness, it was the spring of hope, it was the winter of despair, we had everything before us, we had nothing before us, we were all going direct to Heaven, we were all going direct the other way\" | compress | hexdump -C",
"00000000 1f 9d 90 49 e8 80 b8 13 66 0e 08 3a 68 ca 80 10 |...I....f..:h...|\n00000010 53 66 8e c0 37 66 0e a6 69 d3 90 05 88 34 02 09 |Sf..7f..i....4..|\n00000020 1a 44 a8 f0 ce 1b 39 0e 41 40 94 48 71 8e 45 8c |.D....9.A@.Hq.E.|\n00000030 03 0b 1e 4c 08 22 cc 19 85 23 ef a4 99 43 e6 4d |...L.\"...#...C.M|\n00000040 9b 93 19 55 72 6c f9 52 64 44 33 6f de b0 99 89 |...Url.RdD3o....|\n00000050 c6 4d 43 93 17 73 6e 64 59 06 ce 9b 31 68 7c 2e |.MC..sndY...1h|.|\n00000060 2c 33 b4 8c 19 9c 29 97 2a 6c fa 34 ea c8 34 6e |,3....).*l.4..4n|\n00000070 c6 c8 29 43 a6 ce 50 3a 79 b0 6a 5c a9 70 4e 99 |..)C..P:y.j\\.pN.|\n00000080 82 6f dc 48 65 92 e6 0c 1a 3a 6a 75 b2 74 0b 57 |.o.He....:ju.t.W|\n00000090 ee 48 22 61 e4 ac 31 3a 07 29 ca b5 3b e7 c0 91 |.H\"a..1:.)..;...|\n000000a0 03 f6 8c 54 34 6f e0 94 c9 ab 75 20 58 3a 65 e4 |...T4o....u X:e.|\n000000b0 48 25 d3 10 4e 98 34 72 2c de 51 88 26 0c 19 10 |H%..N.4r,.Q.&...|\n000000c0 65 ec 64 ce 83 b0 f1 54 a0 63 41 d4 41 3a 1a 44 |e.d....T.cA.A:.D|\n000000d0 e9 d3 6e de b4 76 e3 98 21 6c 85 b3 45 77 cc ac |..n..v..!l..Ew..|\n000000e0 30 0c 1b 36 20 ce bc 71 4d 06 74 99 31 02 e9 bc |0..6 ..qM.t.1...|\n000000f0 01 81 e4 ad 6a 37 c2 07 12 6f 79 3c f9 72 de 20 |....j7...oy<.r. |\n00000100 9a 8f 85 ce 56 24 47 cd 04 f3 28 00 |....V$G...(.|\n"
] |
[
"My physics teacher told us today that photons and light have mass. Everything I have read so far has said photons are massless? Can anyone clear this up?"
] |
[
false
] | null |
[
"Photons indeed do not have rest mass. I think your teacher meant to say momentum rather than mass. Light has momentum but not rest mass.",
"Explanation link: ",
"https://secure.wikimedia.org/wikipedia/en/wiki/Mass%E2%80%93energy_equivalence#Massless_particles"
] |
[
"You can calculate a relativistic mass: ",
"http://www.weburbia.com/physics/photon_mass.html",
"This is however an out of date way of defining mass. Relativistic mass is really the same as energy so you are calling the same thing by two different names."
] |
[
"Ask him to show you a photon that's not in motion. Light always moves at ",
" relative to any observer. The idea of a \"motionless\" photon is meaningless. It really does sound like your teacher is confused about how photons can have momentum but not mass. In which case you should refer him to AskScience's favourite equation:",
"where E is energy, m is mass, p is momentum and c is the speed of light. A photon has m=0, so E=pc. So if you take the energy of a photon and divide by the speed of light, you get its momentum. "
] |
[
"Why is carbon dioxide the gas we use to make drinks fizzy?"
] |
[
false
] |
[deleted]
|
[
"It dissolves very easily, and is ridiculously easy to obtain. Carbon dioxide is produced as a side effect in many processes, one of them being the brewing of alcohol, so you don't need any real effort to obtain it."
] |
[
"CO2 is a byproduct of fermentation(yeast eat sugar and produce CO2 and ethanol), so beer, champagne, and other alcoholic carbonated drinks get their carbonation as a matter of course, so long as the last stages of fermentation occur in a sealed vessel. ",
"There are some natural springs that produce carbonated water and there was a belief that it held natural healing powers. In the late 18th century, people began devising ways of carbonating water to mimic this natural \"fizzy\" water.",
"One can also Nitrogenate liquids, but it's much more difficult to keep in solution. That's why stouts like Guiness need those widgets in their bottles and cans to keep releasing nitrogen while they're being drunk. Without them, the nitrogen comes out of solution very quickly. The bubbles that are produced are also much smaller than CO2 bubbles, which gives beer on nitro a smoother, creamy head.",
"Water can also be oxygenated (think fish tanks), but it doesn't produce the pleasant bubbly feeling that carbonated water provides.",
"So, CO2 is used because it's the easiest to produce while still giving the drinker that pleasant bubbly sensation."
] |
[
"Ever tasted a really stale carbonated drink? That's what you would get if you used, say, nitrogen. Aside from the fact that nitrogen wouldn't dissolve that well, it would taste bland because it would lack that slighty stingy taste you get in a carbonated drink. These drinks, whether it's just sparkly water or a coke, usually \"bite\" a bit. That effect in the taste comes from acid, which happens to be produced when you throw CO2 into water - the reaction, in addition to hydrogen ions, gives some H2CO3.",
"Force nitrogen into the water and it will sparkle similarly, with bubbles. There may even be some drinks that use nitrogen for that, it's possible since it's also not particularly hard to do."
] |
[
"Is there some biological reason that rabbits and other small animals wait to cross the street until i'm 3 feet from them in my car?"
] |
[
false
] | null |
[
"For anyone that hasn't heard of the term \"tharn\", it's a word from the ",
"Lapine language",
" used in Richard Adams' book ",
"Watership Down",
". I also wanted to post the links because it's a story about a group of rabbits, which is very fitting for the original question. Nice reference."
] |
[
"For anyone that hasn't heard of the term \"tharn\", it's a word from the ",
"Lapine language",
" used in Richard Adams' book ",
"Watership Down",
". I also wanted to post the links because it's a story about a group of rabbits, which is very fitting for the original question. Nice reference."
] |
[
"I don't know about the darting out, but I can speak a little to the freezing. First, it is interesting to think about the results of a conditioned fear task. Take a rat in a ",
"skinner box",
", and turn a light on. The rat will not do anything. Briefly electrify the floor, and the rat will jump. Now, turn the light on and then electrify the floor. Fairly quickly, the rat will learn that the light signals shock. This is classical conditioning. Remember Pavlov's dogs that (hypothetically) learn to salivate to the ringing of a bell. So we have the unconditioned stimulus (US, does not need to be learned) of food that causes a dog to salivate (unconditioned response, UR) that is paired together with a conditioned stimulus (CS, does need to be learned) of a bell, so that the bell will eventually produce the conditioned response (CR) of salivating when it hears the bell.",
"Now in conditioned fear, you have the shock (US) elicits jumping (UR) (you do not have to teach the rat to do this). The light (CS) is paired with the shock (US) so that eventually the light will produce a CR. What is the CR? Most people that have taken PSY 101 will say the rat will jump when he sees the light, but in fact, the CR will be freezing (the UR and CR do not have to be same behavior, even though almost all intro examples have them as the same). Why is this? Think about what the experiment is modeling. The skinner box is (for example) a snake. The shock is a nip on the foot of the rat. If a snake nips his foot, he will jump. The light is the visual of the snake. If a rat sees a snake, his best move is to be very still so the snake will not notice him.",
"Biologically, what is going on? Sensory information is sent to the lateral nucleus of the amygdala. So both the sensory information from the somatosensation of getting shocked and the visual information of the light. Synaptic connections are strengthened in the lateral nucleus so that the light input is enough to then send a signal to the central nucleus (obviously the shock does not need any strengthening, it would already send the information on). From the central nucleus, I believe, the freezing behavior is mediated be pariaqueductal gray area. The central nucleus has many outputs that cause a variety of behavioral and biological responses to fear. Included in this is the dorsal motor nucleus of vagus nerve that can cause urination and defecation, so there is a biological mechanism where fear can cause you to crap your pants.",
"Disclaimer: fear repose is not my area of research. I may have over simplified parts of this.",
" Freezing is an adaptive response to fear mediated by the amygdala and periaqueductal gray in the brain."
] |
[
"Can we vaccinate against things like snake venoms?"
] |
[
false
] |
I'm mid microbiology class and we're on immunity. Obviously we talk about vaccines and it's nice and straight forward. Dump dead viral bits into the body and memory cells and antibodies get made, done, easy. But snake venom is just an enzyme, which is just proteins, so is it possible to make a preventative vaccine for similar things?
|
[
"In principle, yes. Anti-venoms are just purified antibodies for a particular venom. The problem with doing this practically is the response time. A Mamba will kill you in about 20 minutes, that means irreparable damage in much, much less time. Your immune system doesn't stand a chance."
] |
[
"Pretty much. It's worth noting that all venoms have lethal doses meaning that there is some small quantity of any venom that your immune system can handle, it's pretty much just a question of whether it can deal with the amount delivered before you die. ",
"I'm not sure, but I'd also expect that simply covering the venom in antibodies would slow down/prevent their effects prior to their degradation so instantly hitting you with a massive antibody dose would be far more effective than having the lymphocytes recognize the venom, proliferate, and produce the antibodies on their own which can take days to get up to full effect."
] |
[
"The snake venoms are not ‘just enzymes’. Basically, they are in major mass not enzymes. In many cases they contains three-finger neurotoxins (inhibitors of various neuroreceptors, acting much quicker than any immune system response - just see Naja neurotoxin II or bungarotoxin or mentionned mamba’s toxins). Or various lipid bilayer destroyers like cardiotoxins/cytotoxins. Or thrombin-like pro-coagulant, failing your coagulation system. Or hemorragins (these are enzymes), quickly damaging endothelium.",
"The main word here is ‘quickly’. Your own immune system has no time to engage the response before snake toxin will kill you.",
"But you can (and recommended) inject ready polyclonal antibodies (say, goat or rabbit) to diminish the fatal effects. However, in case of mambas, see snakes, some bungarus and other - you have too little time tho to do this.",
"Hello from snake/mollusk toxinologist"
] |
[
"How many of the 118 elements on the periodic table are located on our planet and how many do we suspect exist outside of our world?"
] |
[
false
] |
I'm just curious, do we suspect there could be thousands/millions of unidentified elements within our universe or are we confident that we've identified most of them? Also, we are constantly searching the universe for potentially inhabitable planets (i.e., oxygen, h2o rich). Do we know if there are elements similar to these which could allow for human consumption? In other words, what are the odds of an unidentified element that humans could breath that is different than oxygen or drink other than water? Edit: words and rephrasing
|
[
"We've discovered all the naturally occurring elements. New elements being discovered are highly unstable, artificial elements that are made in particle accelerators. There are almost certainly no more stable elements to be found. Unless there's another intelligent race playing with particle accelerators somewhere, it's possible that super-heavy elements like those in the Z > 110 range have only ever existed on Earth. "
] |
[
"We've discovered all the naturally occurring elements.",
"To add a bit, what made the Periodic Table such a valuable tool back in the day was its ability to ",
" what properties undiscovered elements would have. Made it easier for scientists to find those elements, since they could ignore energy levels, atomic weights, etc., that were far outside of the predicted values."
] |
[
"Thank you for taking the time to respond. ",
"I'm curious to know, of all elements essential to Human life, and those that we currently use in technology (you've mentioned lithium, so my mind immediately thinks lithium-ion batteries), have we reached a ceiling with regard to our advancements using elemental properties, or are there currently studies to utilize additional elements in ways we know of but cannot yet create? Further, are there active studies to find ways to utilize elements in unique ways we have not used before?"
] |
[
"How difficult would it be to genetically engineer poison resistant plants, such as monsanto and others have, but license the genes as open source?"
] |
[
false
] |
Instead of trying to fight big money through legislation, the idea is to remove the need to sign contracts. I personally would rather see poisons removed from agriculture, but if we are going to use them anyway... And while we are on the topic, what about engineering crops for traits that are actually useful, such as root nodules on non-fabacae plants, higher production, etc. The inspiration stems from the article about people doing biotech in their mom's basement. I know it would be a lot of work, but would it be possible?
|
[
"Developing the strains would of course take a lot of time, money, and luck.",
"However the bigger hurdles probably involve ",
"IP law",
", dealing with regulatory agencies, and marketing/distribution.",
"Determining whether something infringes a patent requires a lot of lawyers, as there are a lot of patents written to be maximally nonspecific.",
"In the current political climate, this kind of product can't really make it into the general public food supply without being demonstrated 'safe' and approved by regulatory agencies, which is very time-consuming and expensive. It's difficult to convince people to invest in this sort of thing when they are not guaranteed a return.",
"It's more feasible if it's the kind of thing that individuals would grow for themselves and not distribute, but developing and using it would make one a target for monsanto+friends' accusations of infringement, e.g. 'we patented anything that improves plant growth and involves nitrogen-fixing metabolic pathways and you'd better hire a bunch of lawyers for several years if you want to argue.'",
"So the bigger problem is socioeconomic, not scientific."
] |
[
"There is a growing DIY-Bio scene.",
"If you're interested in that kind of thing you might like subscribing to the DIY-bio google group.",
"http://groups.google.com/group/diybio?pli=1",
"there's lots of discussion about these issues. "
] |
[
"Engineering plants with resistance to pesticides requires that you have a gene that confers resistance to said pesticide. If you have that then it is pretty easy to get the gene into the plants. After you PCR the F1 generation and find some homozygous/heterozygous plants you can simply keep mating until you have a stable population. ",
"So it's not that hard, however how are you going to find the necessary resistance genes? "
] |
[
"Is molten glass also molten sand?"
] |
[
false
] |
A has made me aware of a planet where 2,000 Fahrenheit glass rains sideways or something similar. My thought process then shifted to realizing this glass would likely be in a liquid state much of the time it flies around in the winds. This mental image then made me ask myself "Why didn't they call it molten sand?" So in any event; Is there any actual scientific distinction between liquid sand and glass? When you melt glass are you not returning it to the same form it had after sand was melted?
|
[
"Sand is a grain size definition, not a material definition- specifically a grain of material between 0.064mm and 2mm in diameter. It can be made of all sorts of things, but usually primarily it consists of Silica,( i.e Quartz ,from which glass is made) feldspar and small rock fragments. In tropical places there is generally a lot of calcite too from coral. Sand varies in composition and can consist of all sorts of different combinations of the above.",
"So to answer your question, if you melt sand you don't necessarily get glass. While the silica that goes into glass typically comes from sand, only specific types of sand do and to say 'molten sand' could mean molten pretty much anything. ",
"When you melt a pane of glass you don't return it to 'sand' because sand refers to the grains. Think of it like taking chocolate chips, melting them in a pot, cooling, then melting again. While the material is still the same, quartz in the case of glass, melting a pot of solid chocolate doesn't really make 'molten chocolate chips' again, just molten chocolate indistinguishable from melting say a block of chocolate."
] |
[
"In a geological sense, yes, pellets of rubber 1mm in diameter would be considered sand when observed in a geological setting. I doubt if you made a pile of 1mm diameter rubber pellets people would call it sand (no idea what they'd call it tbh) but geologically, yes it'd be sand.",
"And yes, saying molten glass probably wasn't entirely accurate as most glass contains other materials like sodium oxide and calcium oxide which I doubt was in the rain. That said, it is possible to make pure ",
"SiO2 glass",
", though strictly speaking it's not really 'glass' if its molten. "
] |
[
"Exactly the explanation I was looking for.",
"So basically the key is the Silica/Quartz? Glass is reformed Silica (and I assume other material varying with the glass being formed). Thus it would be more accurate to say that the planet that prompted this question has high concentration of molten Silica on it's surface.",
"Thank you very much. As an additional question: If Sand is a grain size definition does that mean that sand can be any natural material? Assuming that material can hold a grain size between 0.064mm and 2mm diameter. Could I make rubber sand if I was able to break it into appropriate size pieces?"
] |
[
"Why does viewing infrared light through a CMOS camera allow it to be seen?"
] |
[
false
] |
A CMOS camera is sensitive to lower frequency infrared light, but what is elevating the frequency of the light into the visible spectrum so it can be seen on a screen? I would expect either the display to not be capable of displaying this light or the viewer to not be able to see it. My question is directed primarily to the EEs that may be able to explain at what point in the image processing the conversion happens. Edit: Read wiki incorrectly related to frequency. by CMOS pixels (and CCD pixels) are sensitive to a whole range of EM frequencies, infrared included. They cannot distinguish colors themselves, rather they rely on filters (like a bayer filter) to only allow a certain color to be recorded by a certain pixels. If the infrared light is bright enough to get past these filters, it will be recorded as if it were visible light. When the sensor is read, and the image reproduced the leaked infrared will be interpreted as Red, Green, or Blue (depending on which filters it got past) and show up on your screen. At no point is the camera know it's processing infrared light and converting it, it's just confuses IR for visible because it doesn't know better.
|
[
"CMOS pixels (and CCD pixels) are sensitive to a whole range of EM frequencies, infrared included. They cannot distinguish colors themselves, rather they rely on filters (like a ",
"bayer filter",
") to only allow a certain color to be recorded by a certain pixels. If the infrared light is bright enough to get past these filters, it will be recorded as if it were visible light. ",
"When the sensor is read, and the image reproduced the leaked infrared will be interpreted as Red, Green, or Blue (depending on which filters it got past) and show up on your screen.",
"At no point is the camera know it's processing infrared light and converting it, it's just confuses IR for visible because it doesn't know better."
] |
[
"I understand we aren't truly seeing infrared, my question is more to the EEs that may be able to explain at what point in the image processing the conversion happens."
] |
[
"This likely explains why the color shows up whitish, because the IF light is leaking past multiple (all) filters.",
"Exactly what I was looking for. Thank you!"
] |
[
"Fragile telescope mirrors and launching them into space?"
] |
[
false
] |
We all know that during launch there's immense vibrations and pressures on human occupants, but when launching something like Hubble, or James Webb, or we could even go with Curiosity, how is it these vibrations aren't just destroying these mirrors that presumably are extremely fine-tuned and fragile? In my immature mind, I picture NASA wrapping it in thousands of layers of bubble wrap, but then without a human counterpart there to unwrap it in space, and no robotic machinery able to do such work, how is it these things are safely launched up?
|
[
"Telescope mirrors aren't as fragile as you might think. There's a 2.7 m telescope in Texas that was shot (yes, shot with a handgun) several times. The operators of the telescope just covered up the holes and kept on going. Telescope mirrors are much thicker than you'd expect and have support systems that ensure the mirror doesn't sag or bend."
] |
[
"i would also assume that the one in texas doesn't have a weight budget though, so i think that the frame and support system for a space telescope will face many more technical challenges than a ground based one. Also, while a hole in the mirror (as long as it didn't shatter) doesn't matter much much to a telescope, a miniscule bend or distortion over a larger area has a huge deleterious effect on the image quality. "
] |
[
"The Harlan J. Smith Telescope",
"\"The telescope was the victim of an act of vandalism in February 1970. A newly-hired worker suffered a mental breakdown and brought a handgun into the observatory. After firing one shot at his supervisor, the worker then fired the remaining rounds into the Primary Mirror. The holes effectively reduced the 107-inch (2.7 m) telescope to the equivalent of a 106-inch (2.7 m) telescope, but did not affect the quality of the telescope's images, only the amount of light it can collect\""
] |
[
"Can someone clarify the relationship between relativity and electron orbitals?"
] |
[
false
] |
video (from a YouTube channel I frequently enjoy watching) seems to use the idea that electrons orbit a nucleus in a fashion as an explanation for how relativistic effects cause a lower than expected melting point for mercury. I'm no chemist or physicist, but I remember being taught, and the wikipedia article seems to agree, that the Bohr model was a poor approximation of what's actually going on. Because of the wave-particle duality of the electron, it is more accurately represented as a probability function s.t. the electron is most likely to be in a certain "cloud" zone defined by the probability wave function. This always seemed to me to say it is unequivocally false that an electron "orbits" the nucleus as a planet orbits a star (and I believe I've had professors tell me that outright). What, then, does the paper referenced in the video actually mean when it says that electrons gain energy as a result of traveling relativistic speeds. Doesn't this require an interpretation that the electron is actually a particle traveling some trajectory? Is this a case of "we use the model which is convenient," is it a poor analogy, or am I completely missing some important concepts (or, of course, some combination of those)? I can't seem to find a free link to the paper, but 's a paid version. I'm not a complete layman, but I only took basic college engineer level Chemistry and Physics so any attempt to target the explanation to that knowledge level would be much appreciated.
|
[
"The Bohr model is indeed false, and electrons don't 'orbit' the nucleus in any way. An orbit is a trajectory, and the classical notion of objects following precise trajectories is just fundamentally invalid in quantum mechanics, because the uncertainty principle dictates that position and momentum can't simultaneously be well defined. ",
"However, quantum mechanics does ",
" change the fact that electrons and other particles still have momentum (even if it's not an exact value), and that this momentum is affected by Special Relativity. ",
"We don't switch to the Bohr model (although as a parenthesis, Bohr and Sommerfeld created a more elaborate Bohr model that included relativistic effects, a few years before modern quantum mechanics). You use a relativistic quantum-mechanical treatment, which in this case means using the ",
"Dirac equation",
" rather than the non-relativistic ",
"Schrödinger equation",
" to describe the electrons. ",
"In simplified terms you could say you 'just' swap the classical expression for kinetic energy E = p",
"/2m to ",
"Einstein's relation",
" E",
" = p",
"c",
" + (mc",
")",
" (which becomes the more famous E = mc",
" when p=0)."
] |
[
"Well, depends on what you mean by 'computational perspective'. Most quantum chemistry books are about solving these equations, but they don't usually include any code or algorithms, and very little (if anything) about the numerical methods at all. The bulk of the work and approximations are physics and pure math, just getting them into a form where they ",
" be solved numerically. But if I were to name one, ",
"Helgaker and Olsen's book",
" is very comrpehensive, has a bit more about the methodology (such as the various integration methods) than most."
] |
[
"It's the nuclear stability that causes heavy elements to decay, but it's true that relativistic effects are more significant as elements get heavier. Below the fourth row or so, calculations without any relativistic corrections are largely useless, and you need increasingly accurate ones as you go farther down. ",
"You can sort of simulate the effects by modifying the Schrödinger equation with what's called an 'effective core potential', but when it comes to lanthanides and actinides and above, you really need to work with the Dirac equation. (Which is avoided if you can, since it's much more computationally expensive)"
] |
[
"Is the global rise in cancer cases due to better detection techniques of the modern sciences or due to anthropogenic reasons?"
] |
[
false
] | null |
[
"We can't answer this authoritatively, precisely because there was no comprehensive screening and detection in the past. Direct historical evidence is scant, as most cancers are soft-tissue cancers where the evidence rots and disappears relatively quickly. A few pieces of historical evidence show us that cancers did exist in antiquity: ",
"evidence of bone cancers has survived",
", the bones themselves being much more durable than soft flesh, and ",
"Egyptian mummies have provided evidence of soft-tissue cancers",
" such as breast cancer. ",
"But, these are just a few data points out of a long span of history. The fact that they exist and we can find them does suggest that cancer was not extraordinarily rare in the past. It does not establish anything stronger, such as allowing us to estimate the historic rate of cancer in the population.",
"Since direct physical evidence really isn't available, we can ask whether the medical profession kept adequate records. Unfortunately, the reality is that doctors in the past did not have anything like our modern diagnostic criteria. They certainly didn't have our modern diagnostic equipment. These two factors together meant that diagnoses were only general at best, and it is highly likely that many supposed cancers were other diseases, and many cancers were missed. Modern scientific oncology and pathology didn't really begin to develop until the mid to late 1800's, well after industrialization had taken hold in many places. ",
""
] |
[
"Increases in cancer are a sign of a healthy society.",
"Cancer is almost entirely a disease of the elderly. People who get cancer have survived to become elderly. If you want to nearly eliminate cancer from your society, bring back smallpox and yellow fever, let tuberculosis and HIV spread unchecked and untreated, stop vaccinated for measles and mumps, return to Victorian childbirth practices. Encourage heart attacks and traffic accidents. Cancer rates will drop precipitously! ",
"If you want to ask real questions about cancer rates, ask about ",
" cancer rates - are people getting more or less cancers at the same age? ",
"Turns out that, at least in the US, age-matched cancer mortality are dropping, and have been for decades. A major contributor to this is the drop in smoking rates, but there are other factors as well. ",
", beginning with children and young adults and now including all age groups. During the second half of the 20th century, each successive decade of births from 1925 to 1995 experienced a lower risk of cancer death than its predecessor at virtually every age for which such a comparison can be made. A major decline in cancer mortality has been occurring in the United States for the past 50 years, affecting birth cohorts born as long as 80 years ago. ",
"--",
"The Decline in U.S. Cancer Mortality in People Born since 1925",
"(Obviously there are scenarios in which increasing cancer rates are ",
" the sign of a healthy society, no need to well-actually me.)"
] |
[
"What do you think about the studies showing that the consumption of animal products also affects the cancer rates in industrialised countries?",
"My English is not that good. Please overlook that."
] |
[
"Why are some of the earliest cave paintings therianthropes (animals turning into humans)?"
] |
[
false
] |
Some of earliest human art (32,000 BC) are depictions of therianthropes, and I was wondering what the reason could be.
|
[
"Anthropologist here: we just don't bloody know. All we know about the people who painting those images is that, well...they painted those images. The incomplete record of the past is what makes archaeology so fascinating and frustrating at the same time. Most of the big questions are unanswerable. All we can really do is poke at the edges with pointy sticks.",
"Many different anthropologists will tell you many different things. People will drone on about spirituality, totemism, shamanism, sympathetic hunting magic, etc.",
"While all of those are certainly possibilities, I firmly believe that an imaginative and creative mind has been a defining characteristic of the human race since the \"Great Leap Forward\" of approximately 50,000 years ago when we start seeing art in the archaeological record. I try not to read too much into the art left by ancient people, and simply choose to appreciate it for a beautiful and mysterious glimpse into the mind of another human being an almost inconceivable number of generations ago.",
"By the way, I find some of the more famous therianthrope paintings you're referencing incredibly haunting, and they have been the inspiration for an RPG session (Hunter: The Reckoning, if you're curious) that my friends and I still talk about sometimes. [/stereotype]",
" Shout-out to user ItsMrBrown: he is absolutely correct in pointing out the \"human turning into animals\" theme in cave art is absurdly rare, and that even normal human images are extremely rare. It's just that the examples that do exist are quite dramatic."
] |
[
"Worth adding that, if we're talking about paleolithic art in Europe at least, therianthropes are really really rare - most of the time it's just plain animals that are drawn. And surprisingly few humans, too! (although I don't know if that's the case around the world - just Europe.) You definitely get the feel of a more animal-centric world."
] |
[
"By the way, I find some of the more famous therianthrope paintings you're referencing incredibly haunting",
"Could you please give examples?"
] |
[
"Why are testicles considered a gland and ovaries are organs? Or what is the difference between a gland and an organ?"
] |
[
false
] | null |
[
"An organ is a bunch of tissue that's generally connected, and works together to serve a function. Doesn't all have to be the same type of tissue: eg, the heart is an organ, but there's muscle, fat, nerve, connective tissue, etc etc.",
"A gland is a type of organ that makes stuff (generally fluids, often hormones). Ovaries and testes both act as glands, since they make and release the 'sex hormones' (oestrogen, testosterone, and all the other related ones). "
] |
[
"they are both glands and organs. ",
"An organ is just a body structure that serves a function",
"A gland is an organ that serves its function by excreting a substance that have effects else where outside the organ. ",
"If the substance is directly secreted via a collecting system it is an exocrine gland like the salivary gland which secretes saliva that works in your mouth. ",
"If the substance is something that goes straight to blood stream, usually a hormone, it is an endocrine gland like your thyroid. "
] |
[
"A gland is defined as a body tissue that releases a hormone. A hormone is defined as a molecule that is released by one tissue, travels through the blood or other medium, and acts on some other tissue.",
"The testis release testosterone, a hormone, that causes multiple effects on many distant tissues (secondary sex characteristics including hair growth on the face and underarms, for instance) Thus, they are considered a gland. By this definition ovaries are also a gland, as they release hormones including estrogen, progesterone, etc, "
] |
[
"If space is a vacuum, why do astronauts need insulated suits?"
] |
[
false
] |
I was just reading a recent AskSci and this intrigued me. Also if you were to float without a suit, what would be the detrimental effects, and how fast would you get radiation poisoning?
|
[
"Radiant heat transfer doesn't require a propagation medium. At body temperature, you are giving off infrared photons."
] |
[
"I may be wrong, but I doubt it's an effective mechanism. Generally when we make a laser, the laser mechanism produces heat and needs to be cooled itself. Heat isn't ",
" energy, it's also about entropy, and my instinct is that a laser is too \"organized\" to be an effective heat emitter. I mean think about how hard it is to get heat to do any kind of work. "
] |
[
"According to ",
"this estimate of the radiation dose rate",
" in interplanetary space, you would never get acute radiation poisoning. Radiation poisoning starts around 5 Sv over a very short time period, and the unshielded dose estimate in space is less than 1 Sv per year."
] |
[
"Recently there's new milk being marketed here as A2 casein milk. They claim normal (A1 casein) milk is dangerous and can trigger diabetes, heart disease and even autism. Is there any real evidence to support their claims?"
] |
[
false
] | null |
[
"According to ",
"this",
" EFSA study....",
"EFSA has carried out a detailed review of the available scientific literature that addresses possible health effects of β-casomorphins and related peptides, and in particular β-casomorphin-7 (BCM7), a peptide sequence present in the milk protein β-casein. A few studies have suggested that BCM7 may contribute to increased risk of certain non-communicable diseases, such as autism, cardiovascular diseases and type I diabetes. EFSA undertook this work as part of its regular monitoring and assessment of possible emerging risks associated with the food chain. ",
"Peptides are fragments of proteins that can be released during digestion of food or in some cases also during food processing. There have been claims of both health benefits and risks in relation to peptides. ",
"EFSA decided to establish a Working Group in order to review the scientific literature on this subject and assess the need for EFSA to carry out a formal risk assessment. ",
"Based on this review, EFSA concluded that a cause and effect relationship is not established between the dietary intake of BCM7, related peptides or their possible protein precursors and non-communicable diseases. Consequently, a formal EFSA risk assessment is not recommended.",
"EFSA didn't think that, in a preliminary investigation, the claims warranted a full investigation. "
] |
[
"Thanks muchly for the link. I found a transcript from a news report on the issue in which the vast majority of professionals interviewed voice agreement with the EFSA findings. ",
"http://www.abc.net.au/7.30/content/2010/s2866747.htm",
"*edited: clarity"
] |
[
"Are they making more money from the \"New Milk\"?",
"Yes? Then of course it's all about money."
] |
[
"Will eating too few calories really prevent or hinder weight loss? If so, what's occurring biologically that makes this happen?"
] |
[
false
] |
During my research on fitness, I've found a lot of information about "starvation mode," or some other state that your body enters when you're not eating a sustainable amount of calories, which prevents you from losing weight efficiently. On most fitness subreddits, it seems like people think this doesn't actually happen, but I keep finding a LOT of other forums that swear it's true and warn against it during diet planning. Even on MyFitnessPal (popular food tracking app that I use frequently), if I track a certain amount of calories for a day (1200, which I feel is a pretty arbitrary number, especially if they give the same advice to every user despite their body composition), a warning comes up telling me that I'm eating too few calories and that I won't be able to lose weight that way. Is this true? What's going on biologically that prevents you from losing weight if you eat too little? It just seems counterintuitive to me, so I'm really confused. Also, how can you accurately determine a sustainable amount of calories for your own body?
|
[
"Starvation mode happens when you're actually starving, as in, haven't had enough to eat for a long time. Even then it's barely significant:",
"http://en.wikipedia.org/wiki/Starvation_response",
"On average, the starvation response of the individuals after isolation was a 180 kcal reduction in daily total energy expenditure. 60 kcal of the starvation response was explained by a reduction in fat-free mass and fat mass. An additional 65 kcal was explained by a reduction in fidgeting, and the remaining 55 kcal was statistically insignificant."
] |
[
"I think too much emphasis is put on this. Most dieting for weight loss is mild dieting with only a relatively small reduction in caloric intake. I'm skeptical that this has any major effect upon metabolism (except for mild weight loss).",
"The physiological changes associated with starvation occur, not surprisingly during periods of starvation. A typical weight loss diet isn't the same as starvation. I think it is incorrect to draw a conclusion about dieting from our knowledge of prolonged fasting and starvation.",
"I can guarantee that if you do starve yourself you will lose weight. However, you shouldn't do this because your body will break down your muscles to use as an energy source and you will weaken. ",
"It is true that severe diets are associated with weight gain, but when you have a closer look it appears that the mechanism for weight gain with severe dieting is almost certainly a rebound weight gain on cessation of the diet. Almost all people who do severe diets do them only for a relatively short time and then resume their previous eating habits, and then diet again and again. Long term this pattern of on-off dieting causes weight gain, but it isn't because their body is in a \"starvation mode\".",
"Addit: the 1200cal/day is arbitrary. It isn't simple to work out your caloric requirements accurately as it would depend upon your age, gender, build, basal metabolic rate, and amount of activity, and so on. At a minimum you need to adjust it for body weight."
] |
[
"Ah, now ",
" makes sense, thank you! I always thought it seemed a little dramatic to call it \"starvation mode\" when I've just eaten a couple hundred calories less than normal o.o but it's petty logical that weight loss would subside under those conditions"
] |
[
"Can an object ever reach actual terminal velocity?"
] |
[
false
] |
My understanding is that terminal velocity is the point where an object's kinetic force is equal to the resistance it faces. As it reaches terminal velocity, it is accelerating slower and slower until... See there's the thing. If it's accelerating exponentially slower, does that mean it never actually stops accelerating? I guess this could be likened to a black hole, where time "slows down" exponentially as an object reaches the event horizon. Can an object reach true terminal velocity?
|
[
"The object asymptotically approaches the terminal velocity, as you guessed. However, this is only in spherical-cow theory. In reality, aerodynamics are very complex and involve a lot of random elements and an object will jitter about the terminal velocity, so for all intents it has been reached.",
"Also note that as an object falls, it enters thicker atmosphere with lower terminal velocity. So it's quite reasonable for an object to be faster than the terminal velocity and asymptotically slow down as the value keeps dropping."
] |
[
"So in theory, in a completely controlled environment where there was only one axis of motion and there were no other factors to consider, it would never reach true terminal velocity?",
"That's pretty fucking crazy."
] |
[
"This is the difference between talking to a mathmatician and an engineer. The math says it will never reach it, but the engineer will point out it actually does in reality. If you were to model every atmospheric particle's motion, you'd see the velocity reach the terminal velocity. But the math you're looking at is a model with simplifications and assumptions that make it inaccurate.",
"This is like hearing physics \"breaks down\" at the Plank length or temperature. Nothing in real life \"breaks\", but rather the accuracy of the mathmatical models of physics and their errors from reality become significant."
] |
[
"Does time occur from the perspective of a light beam?"
] |
[
false
] | null |
[
"So lightspeed from the perspective of a beam of light is infinite? I thought that c was a constant."
] |
[
"For the beam, no time passes, but for an outside observer in another inertial system it takes time for the beam to get somewhere. Its relative to the system you are observing from. That is why the theory is called the theory of relativity.",
"A light clock gives a nice picture of these things:\n",
"This is a nice one."
] |
[
"No! Sorry. I realize i was not very clear. For the outside observer, time seems to have stopped in the reference frame of the light beam. This is nicely illustrated by the time clock which is moving at the speed of light itself, so it will never \"tick\". For the photon itself, time passes completely normal in its own system and the observer is frozen."
] |
[
"If the frequency of a cat's purr is shown to accelerate healing of bone, muscle, tendon and ligament tissue, and increase bone density; and if a cat's purr is at or about the same frequency as a diesel engine; how come long-distance truckers don't have awesome bones?"
] |
[
false
] |
[deleted]
|
[
"List real sources.",
"As someone that knows a little about bone physiology, this sounds like complete bullshit."
] |
[
"A cat's purr is comprised of more than just a single frequency, as is a diesel engine, as are most other sounds. A cat's purr doesn't sound much like a diesel motor now, does it?"
] |
[
"A diesel engine produces far more than a single frequency."
] |
[
"When I'm boiling a pot of water, the steam is not terribly visible, but when I turn the heat off, steam BILLOWS out of the pan. My question: if there is suddenly less heat, why is there suddenly MORE steam?? Why isn't it the other way around?"
] |
[
false
] | null |
[
"The steam was there all along, but you couldn't see it. When you see the \"steam\", you actually see the water vapor condensing back into water. When the heat is on, the steam had more energy and doesn't condense as much, so you see less."
] |
[
"maybe he should boil a less energetic water ... like VitaminWater?"
] |
[
"I'd have said 'had a higher temperature', it's more specific. And less association with people talking about energy when smoking pot, really energy an often hijacked term.."
] |
[
"In Lorentz transformations, why is gamma defined the way it is?"
] |
[
false
] |
Where γ = 1/sqrt(1-v²/c²). Why isn't it defined as just sqrt(1-v²/c²)?
|
[
"Well, gamma itself isn't anything physical. It's just a dimensionless quantity defined for mathematical convenience. So you can define it any way you find convenient. You can define it that way (adjusting the transforms accordingly) if you like. ",
"But since the term tends to always occur in the denominator, it's considered more convenient to use the inverse of that. Multiplication is just viewed as a bit more \"simplified\" than division. Perhaps because when you see a denominator, you should instinctively worry about what happens when it becomes zero. (That doesn't happen here - but that's all the more reason to 'hide' it away)."
] |
[
"Yeah, that's what I would say too. Plus perhaps there is some motivation to have gamma increase as speed increases."
] |
[
"Your first equation should be given with a triple equal sign. It is a definition, not an equality."
] |
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