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[
"Why is it so hard to come up with a cure for a Virus, why can we only find ways to prevent them via Vaccines?"
] |
[
false
] | null |
[
"Here's one way to think about it: Because viruses use most of the normal cell machinery to replicate, most of the ways to attack a virus would also attack the normal cell.",
"It's actually really easy to kill viruses, just like bacteria. Heat them to boiling. Radiate them. Soak them in bleach. The problem isn't in killing the pathogen, it's in not killing the host at the same time. You need to target ways in which the pathogen is different from the host.",
"Bacteria have their own complete replication cycle from beginning to end, their own metabolic cycles, and so on. They do everything on their own, with all the various parts being bacteria-specific, and so each of the parts is (at least in theory) a potential target for an antibacterial drug. ",
"Viruses rely on the host machinery for most of their replication. They may only bring in four or five of their own components into a cell, so instead of having hundreds of potential targets they only have a couple. ",
"That's super simplified, but it's the general answer: Bacteria have more targets that are different from the host than viruses do."
] |
[
"We do have antiviral treatments; it's just that the way a virus attacks the body means that preventative treatment (vaccination) is often much more effective. The body is exceptionally good at responding to and eliminating known threats (often eliminating an infection long before symptoms are noticeable), but takes time to learn how to defend itself against a newly encountered strain of virus. During this time before the body is able to mobilize against the unknown threat, the virus can spread and multiply to the point that the immune system is overwhelmed. Our medical technology can only do so much at this point, and it may not be enough if the virus has spread too much, so it's much better to use vaccines to prevent the virus from ever getting a foothold in the first place. A vaccine's whole purpose is to expose the immune system to the virus in a manner that can't harm you, allowing it to learn exactly what that pathogen looks like, and exactly what to do the next time it encounters the enemy. "
] |
[
"Viruses attack our bodies by getting in our cells taking over the machinery, spewing out thousands if not millions of viruses per cell, then killing the cell spewing out those viruses. Anti viral treatments would have to kill all of the invading viruses all throughout the infected area, including getting inside our cells. That's really difficult to get enough anti viral drugs coursing through our bodies to make that happen. Instead it's much easier for our immune system to handle the defense. It's already there and knows what to do.",
"Antibacterials aren't that amazing either. Think of how long it takes for them to actually work. At least a few days to make a real difference and then you still have to take it for around 10 days to make sure you kill almost all of them. Anti virals would be really similar to that. A cold usually doesn't last much more than a week, so it's kinda ridiculous to try to find the right anti viral for each individual virus.",
"Vaccines are so much better because they train our bodies to fight off the viral invaders so they never get a foot in the door in the first place. Why wouldn't you want to take a few shots as a child so you don't get some of the worst diseases known to man? ",
"Certain viruses evolve too quickly for vaccines to work. For example the flu virus switches between a few different invading proteins on top of their proteins changing over time. It makes it really difficult for our bodies to fight them off."
] |
[
"How fast would someone have to move to not be seen moving?"
] |
[
false
] |
Would you have to be moving faster the speed of light to be able to not be seen by anyone? If that makes no sense (and I'm sure it doesn't..) Here's a clip of beating the camera that his teacher had in the class room. the part starts at roughly 28 seconds.
|
[
"Digital video recorders usually have higher frame rates now, but traditionally 24 fps is the standard. So it looks like the kid would have to travel about 10 meters in less than 1/24 = 0.04 seconds, or about 240 m/s (540 mph). Although in that case he may show up for a fraction of a single frame. In order to not show up in a single frame at all, he would have to complete his task between frames, which can be very small. From pictures online, it looks like the gaps between frames are usually less than 5% of the width of a single frame, in which case he would have to travel 20 times faster to not partially show up on a frame."
] |
[
"I should point out that going 540 mph is probably enough to be so blurry and faint that he couldn't be easily identified. ",
"For human eyes, that's more a question for biology than physics, but according to ",
"wikipedia",
" humans can recognize a specific image flashed for as low as 13 ms, so I think this would mean that you couldn't recognize anything that moved past your visual field in less than 13 ms, and wikipedia also seems to imply that you probably wouldn't see ",
" if it was less than 1 ms. So in the case of a visual field covering 10 meters round trip distance, this would mean he would have to travel faster than 770 m/s (1700 mph) in order not to be recognized, and faster than 10000 m/s (22000 mph) in order to not be seen at all. "
] |
[
"Holy shit that's fast. Would there be a speed where you wouldn't be able to see someone with your own eyes? BTW, thanks for the quick response! :D"
] |
[
"Would our sun (Sol) be visible from Alpha Centauri?"
] |
[
false
] |
Imagine an Earth like planet with an Earth like atmosphere in orbit around one of the stars in the Alpha Centauri system. Correct me if I'm wrong but on a cosmic scale it wouldn't make a huge amount of difference which star this planet is in orbit around. Would our star be visible to the unaided eye from this planet?
|
[
"Yes. The two Alpha stars together are about twice as bright as the sun, and the sun would have a magnitude of about 0.5, comparable to Vega as seen from Earth, from Alpha Centauri."
] |
[
"And if anyone wants a picture to show that, ",
"clicky",
". I'm not sure why the Alpha Centauri system is called Rigel Kentaurus in Celestia, but still."
] |
[
"And if anyone wants a picture to show that, ",
"clicky",
". I'm not sure why the Alpha Centauri system is called Rigel Kentaurus in Celestia, but still."
] |
[
"Is the human body affected by the changing seasons?"
] |
[
false
] |
If we don’t grow a winter coat like dogs, we don’t have a set mating season, we don’t migrate, etc, are we affected in any other way? If not, at what point did we lose those traits?
|
[
"Yes, assuming you actually go outside.",
"Your temperature preference should move with temperatures outside as your body's homeostasis primes itself for certain conditions. A good example is if you take someone from Michigan in the dead of winter and drop them in SC, their body is already primed to generate more heat than is necessary for SC weather.",
"The other big noted effect is the rise in depression and poor mood due to lack of Vitamin D production which is driven by sunlight exposure."
] |
[
"A biochemical aspect of this acclimatization process is that cell membranes need to adjust their lipid and cholesterol profiles to allow greater/lesser membrane flexibility with ambient temperatures."
] |
[
"Up until very recently, our bodies were very affected seasonally due to food availability. This affected every aspect of our ancestors' lives, including a sort of mating season (or a higher likelihood of copulation/shagging) when food was more available in the Spring. It's not just a factor of food there or not for energy reasons but also which food types. Science today is finding increasing amounts of research on how different food types affect our behaviour through different bacteria entering and interacting within our gut microbiome. Potentially this could mean that our behaviours may be influenced by the seasons from which foods were available to eat."
] |
[
"Does UV light/radiation pass through clear plastic?"
] |
[
false
] |
Does UV light pass through phone screen clear protectors? The transparent/clear protectors are made of PET and TPU.
|
[
"Depends mostly on the wavelength. UV of ~350-400nm Will pass through most plastics. But less than ~300nm would be absorbed.",
"Here's some graphs of the transmission.",
"http://usa.dupontteijinfilms.com/wp-content/uploads/2017/01/Mylar_Optical_Properties.pdf",
"http://www.hitachi-hightech.com/products/images/10960/uh4150_data1_e.pdf",
"Virtually all plastics cut off hard below 300nm."
] |
[
"PET",
" block UV light under 300nm, similar to glass.",
"TPU",
" starts significant absorption at around 350nm."
] |
[
"There are links in my posts to absorption\\transmission graphs... the TPU's graph is of absorption (normalized extinction, which is proportional to absorption for fixed width of material) - according to the graph, from around 350nm and under, you get a high absorption rate."
] |
[
"Why are ionization energies so much larger than electron affinities?"
] |
[
false
] |
As I understand it, the ionization energy is the energy required to take an electron away, off of an atom. Electron affinity, on the other hand is kind of the opposite, as it's the amount of energy given off when an electron is given to an atom. As such, I thought they'd be similar in terms of value. I've been looking at charts of electron affinity and first ionization energies, and it seems that that's not the case, however. For example, hydrogen has an ionization energy of 1312 kJ/mol... but an electron affinity of only 73 kJ/mol. What's up with that? The electron affinity is less than a tenth of the ionization energy. Both values deal in putting/removing an electron around the hydrogen atom... why does the change in energy vary so much? This doesn't seem to just be hydrogen, either, as even the lowest first ionization energy (Fr, ~380 kJ/mol) is larger than the largest electron affinity (Cl ~349 kJ/mol). I've been trying to understand this and in looking further I've only gotten more confused by looking at standard enthalpy of formation too... If I want to make a mole of NaCl, I'd have to take a mole of Na, and a mole of Cl, and move the electron from every Na atom to a Cl one, right? So that's 496 kJ/mol to take the electrons off of Na, and 349 kJ/mol back when I give them to Cl, so I guessed that this whole process should take 147 kJ. But the standard enthalpy of formation of NaCl is about -411 kJ/mol, which means its an exothermic reaction. Where is this additional ~558 kJ/mol coming from? Apologies if my understanding of these concepts is wrong... but could someone possibly explain why it is this way?
|
[
"These processes are not opposites. This is easier to see if you play one of them in reverse.",
"Let's reverse the ionization. When you look at it in reverse, you have a positive ion and a negative electron coming together to form a neutral atom. A lot of energy is released in this process because the opposite charges attract. So to reverse of this process, a lot of energy must be consumed.",
"Now compare the electron affinity process. You have a neutral atom and a negative electron coming together to form a negative ion. There is no attraction of net opposite charges, so the total energy released is a lot lower.",
"In the formation of NaCl, it is true that it takes more energy to remove the electrons from sodium than you get back by attaching them to chlorine. The rest of the energy comes from the sticking together of the resulting ions; that is, from the formation of the ionic bonds in sodium chloride."
] |
[
"I do not know If I am right (its not my subject) but ionizing means removing an electron so that, in the end, an atom is no longer neutral.",
"Afiliation means adding a electron to a yet neutral atom.",
"So the difference may be due to the shielding of the additional electron from the core. \nThe electrons are bound to the core by Columb forces. In the Hydrogen ionization case, the first electron ist attracted to a full positive charge of the proton. In the Affiliation case, the one electron existing, counteracts some of the charge such that q < 1e"
] |
[
"While it sounds like ionization energy and electron affinity are (equal) opposites, they are not. Ionization energy describes the energy required to remove an electron from a neutral atom (A -> A",
" + e",
" Electron affinity describes the energy released from adding an electron to a neutral atom (A + e",
" -> A",
" Both of these are defined in the gaseous state.",
"In ionization energy, energy is always required to remove an electron - simplest explanation is that that process is separating charge; positive and negative charges attract each other and so it takes energy to pull them apart. Electron affinity is always positive because an electron is being bound into an atom - the electron will 'feel' the positive charge of the nucleus. There will be greater electron-electroj repulsion so that decreases this energy release, but it's doesn't completely cancel out that release because the electrons are each 'in their own lane' so to speak by being in different orbitals and having different quantum numbers. The energy released when adding electrons will go down as the negative charge increases because of electron repulsion and insufficient positive charge to balance that out. Second electron affinities and beyond may be zero or positive, making them unfavorable.",
"In your NaCl example, you're forgetting intermolecular (in this case interatomic or interionic) interactions. Energy is released when you have positive and negative charges coming together. What you have so far with just ionization energy and electron affinity is a sodium atom ejecting an electron to infinity (which takes a lot of energy), an electron coming from infinity to a chlorine atom (which releases some energy) and that leaves you with a sodium cation and chloride anion that are separated at infinity. If you want to calculate the enthalpy of formation, you need to include the lattice energy of putting those ions together in a crystal OR (if this is all in the gas state) the energy released by those ions coming together."
] |
[
"If Earth were to reach its human carrying capacity, would just enough humans die to return to normal levels, or would we die off entirely as a species?"
] |
[
false
] |
the former makes sense to me in an non-human ecosystem, where minimal death occurs until enough resources are left for those that survived. However, I would presume that in the case of humans, we are so dependent on each other in a global sense, that surpassing our carrying capacity would cause a chain reaction of deaths and shortages that would wipe out most, if not all, of our species.
|
[
"We won't hit capacity all of a sudden. ",
"Logistic growth models do well on smaller scales (cities) where resources/space is limited. See: Dallas v. San Jose",
"Population growth will slow, but will population will still increase under this model. This could take the form of higher death rates due to famine or disease. But it is important to realize that it will not be an ",
". It will be gradual, but billions of people will still live. ",
"In the case that we over exert our resources, we may turn towards predator/prey models. The death rate may surpass the birth rate until the population size becomes sustainable. ",
"I'm on my phone right now but there are a lot of good studies about small case predator/prey models. I'm not sure about the extrapolation to humans and the planet wide ecosystem. "
] |
[
"Extrapolation to humans is less of a ecological question and more of an economical question.",
"Ever since Malthus, people have been predicting the point at which given societies (or the planet) would hit carrying capacity. Time and time again, their predictions have been wrong. Why?",
"Because we're able to look at production capacity at any given moment and extrapolate how many lives a system could support - but since we're constantly getting better at using available resources and discovering new resources to replace old ones, carrying capacity becomes a moving target, one that we can never quite pin down.",
"Similarly, when regions do hit \"carrying capacity,\" it's typically because of infrastructural inadequacies, e.g., East Africa, the fall of the Western Roman Empire. Reaching carrying capacity would not only not happen all at once, it would also not happen everywhere simultaneously. The resulting geopolitical instability would be what we'd notice, rather than any sort of \"species die-off\" event."
] |
[
"Yes good point about the differences in sub-regions. ",
"Can physics offer us an upper bound on max capacity?",
"Or can we do a meta study on the upper bounds predicted as a function of time. Is their growth logistic as well? (capping at a proportion of Earthmass*c",
" ?)"
] |
[
"How is it possible that I'm able to see an infinite number in a finite space?"
] |
[
false
] |
Specifically, w/ fractions - Take the fractional number 2/3 for example. When written in decimal form it is: 0.66666666 to infinity, right? OK, then look at any gauge (a weight scale) - and then go ahead and weigh that you know is 1 and 2/3 pds - (1.666666 pds) you can obviously see the item in a finite space, yet it's weight is an infinitely long number? I'm clearly no math-buff, and the answer may be in your face obvious, but seriously - this is bugging me. Thanks in advance! edit: ok, I understand the difference b/w a numeral and number now. But, as I mentioned, isn't there a contradiction occurring when I show one third of 1 on paper in decimal form 0.3333 infinity, but if I take a physical piece of anything and cut it up into how do I represent/see the .3's to infinity? I thought math was "perfect" where everything can convert into anything else, but this seems to be "non-convertible"... edit 2: Folks, thank you for taking the time to explain this to me. I appreciate the effort and patience. Unfortunately, I'm going to have to pack it in, as it's 2 am now, and I can tell my brain is shutting down; so whatever little amount of cognitive function I have is quickly diminishing. I'm also on vacation so I may not get to this first thing tomorrow, but I will sooner than later.
|
[
"You're confusing the difference between a numeral and a number. The number 1/3 is a finite number. It's simply one third of 1. The way we represent 1/3 in our base 10 numbering system is necessarily infinitely long, since 10 does not divide evenly into 3.",
"So, having the decimal representation being infinitely long doesn't mean that the number is infinite. The number is still finite."
] |
[
"Best. Panel Tag. EVER."
] |
[
"I am terrified of the juxtaposition of shady dentists and lasers."
] |
[
"What happens to meat when it cooks?"
] |
[
false
] |
On a molecular level, what happens?
|
[
"Thank you, that was enlightening! What about the color? Beef goes brown and chicken white-ish.. does that have anything to do with the kind or protein/amino acid contained in each variety of meat?"
] |
[
"Thank you, that was enlightening! What about the color? Beef goes brown and chicken white-ish.. does that have anything to do with the kind or protein/amino acid contained in each variety of meat?"
] |
[
"There's an exceptionally complex series of reactions that take place, but one such is the ",
"Maillard reaction",
"."
] |
[
"Do roads lead to allopatric speciation?"
] |
[
false
] |
I know that roads isolate populations in a lot of species. If that's true, will genetic drift eventually cause these separated populations to diverge into new species (assuming the separation is total)?
|
[
"While it is almost certainly true that roads will act as isolating barriers and eventually drive the formation of new species, I know of no study that has actually shown that yet. There are certainly studies that show how animals interact with roads in interesting ways and road-avoidance is common (see the work of ",
"Dr. Jesse Barbar",
"). But actually showing that a road is the primary cause of speciation is a very difficult task especially since the large, heavily-traveled roads that would effectively isolate things are actually a relatively recent development. It takes a long time for species to form, normally on the order of millions of years and major roads have only been around for a couple hundred years if that. Furthermore, it doesn't actually take a lot of migration to keep populations genetically connected (and thwart speciation), in fact a single migrant per generation who successfully breeds will often be enough. As such, the small, rarely-traveled dirt roads in the backcountry are unlikely to have a large effect, while 12-lane superhighways are likely more important. So, while theoretically it's ",
", and I would argue that given enough time it may even be ",
", we don't have any convincing examples of road-driven speciation at present."
] |
[
"If we take your parenthetical assumption, then yes. But there's no reason to make that assumption.",
"For speciation to occur, there needs to be extremely little intermixing after the separation. But roads are poor barriers. First, only large roads present a significant barrier, and those roads don't make a continuous 'fence', so animals can always go around and connect two populations. Second, roads are permeable --animals can walk across them or go under at bridges (streams make good corridors). For plants, wind and insects can carry pollen across. That's certainly enough to prevent speciation. ",
"Like ",
"/u/phodopus",
" I've not seen anything saying that it's happened.",
"Also, just as an aside, the amount of movement is much lower to prevent speciation than is necessarily healthy or desirable for a population. So making roadways more permeable with animal crossings, etc, is still useful."
] |
[
"Yes! Roads are basically imparting a large divide in an ecosystem to create two separate ecosystems for land animals especially. If the road is particularly busy animals will generally stay away resulting in a once uninterrupted ecosystem to be two, practically-isolated ecosystems. If this is the case natural selection can occur very easily through ideas of genetic drift and the founder effect.",
"This is similar to the finches that Darwin observed on the Galapagos Islands. They flew from the continent to the island and adapted to the different environment. They stayed on the island because they could thrive there. Imagine the same situation but instead of an ocean its a road, and instead of thriving in that environment animals are stuck there due to the road."
] |
[
"How would the wolves that dogs evolved from compare to the wolves of today?"
] |
[
false
] |
And, is there any way to know? I'm familiar with the genetics and theories about wolves gradually developing a symbiotic relationship with humans, but I've been around tame wolves before, and it just seems like a stretch to me that they were the precursor to man's best friend. Is it possible that ancient wolves were more docile and gregarious towards humans than the wolves of today?
|
[
"I tried to tease out a good answer for you but I'm not satisfied with it and have to move on. Figured I'd at least contribute what I have though in case someone else wants to continue or you find this stuff interesting.",
"Physical Stuff:",
"Last common ancestor has been dated everywhere from 10-35,000 years before present (ybp) and probably originated somewhere around Europe ",
"ref",
"A 2015 study puts divergance at-least at 27,000 years and sequences the genome of a 35,000 ybp wolf. Found it to be most closely related to ",
"modern arctic breeds.",
" ",
"ref",
"A good candidate for a visual would be the ",
"Beringian wolf",
" who was running around the arctic about 11,000ybp",
"Domestication: ",
"ref",
"Talking off the cuff here now because I feel like domestication is a little bit harder to pin down with hard numbers. Somebody mentioned cats, but mice are also beginning to be thought of as rivaling dogs for first domestication event ",
"Nat. Geo ref",
" and I wouldn't compare our relationship with mice to that with dogs. I'd say it probably really took off after the agricultural revolution, conveniently around the time that some canides adapted ",
"better starch digestion capabilities",
". I won't insult you with the whole 'domestication was gradual and humans applied selective pressure' stuff because I think that is intuitive, but I do think the power of that pressure might not be as intuitive. In the ",
"Russian silver-fox experiment",
" selective pressure was put on wild foxes and they had something resembling a domestic dog within 6-10 generations.",
"The take away that I got from trying to fine-tune something I thought I already knew is that 'evidence is disputed' is a pretty common theme in papers for both domestication and last common ancestor date. I'm thinking that the final book compiling all the evidence still needs to be written and that it will consist of a bunch of different events all inter-mingled over evolutionary time"
] |
[
"Every member of a species is different. Some wolves were just less wary towards humans than others, and they ended up following them and being tamed. And then, by reproduction and generation after generation, they evolved into dogs. "
] |
[
"In the case of cats, we know that they domesticated themselves. They stuck around to eat mice, and were increasingly loving to people as generations went on. ",
"Similarly, wolves were tamed and impressed upon as pups due to close proximity to humans, most likely the omegas of the packs wandered into villages. Willing to be ordered, they were selectively evolved by human beings. Similar to domesticating the dangerous hog into a passive farm pig. "
] |
[
"Does photography really damage artworks?"
] |
[
false
] |
I have been to countless art exhibitions that have an explicit zero-tolerance policy regarding photography. I've always thought it's mostly about copyright, but many places explicitly say that they have such rules in order to "protect fragile artworks". The question is simple: what does photography actually do to artworks? Is there any scientific evidence that it might cause any damage?
|
[
"Light can cause damage to paintings",
" but the significance of damage that may be caused by flash photography is debatable."
] |
[
"If your main concern is to keep people focused on the art and not to have distracting and annoying camera flashes and shutters going off all the time, ruining things for other patrons, I suspect it's far more effective and easier to tell people there's no photography allowed because they might cause damage than to appeal to their concern for the experience of others."
] |
[
"damage that may be caused by flash photography is debatable.",
"Not all that \"debatable\", according to ",
" I would suspect the primary concern is one of copyright. (If you want a photo of a displayed artwork, they'd prefer you buy one at the gift shop.)",
"https://www.arthistorynews.com/articles/2936_Does_flash_photography_really_damage_paintings"
] |
[
"Why does smoke gather in line, as oppose to gathering in a mist as water vapour does?"
] |
[
false
] |
I'm guessing it has to do with the intemollecular forces at work. More particularly the geometry and polarity of the molecules or particles.
|
[
"Smoke is comprised of very fine particulate (as in solid) matter, while water vapor is gaseous and subject to diffusion due to the differences in partial pressures between the source and the surrounding environment. "
] |
[
"But what forces are at work? Why doesn't smoke gather in clumps? What gets me is how the particles disperse, but have some sort of linear cohesion."
] |
[
"This is the topic of ",
"turbulence",
", and is one of the last fundamentally unsolved problems in classical physics. So, good question! No one knows. If you can solve it you'll make a lot of money, because understanding turbulence is incredibly important to a lot of engineering applications. "
] |
[
"Why are magnetic fields a series of lines, instead of one constant field?"
] |
[
false
] |
The title pretty much says it all. In early Physics we learn that magnetic fields are a series of field lines, which go from the north pole of the magnet to the south pole of the magnet. These field lines can be seen experimentally with iron filings around a magnet. My question is why these field lines are present, and why are there gaps between these field lines. Why is there not just one constant field? This leads on to a follow up question: If magnetic fields are a series of field lines, with gaps between the field lines, why does a compass still function in one of these gaps? Do all of the fundamental forces act in this way?
|
[
"Unfortunately your question is based on a misunderstanding. Magnetic fields are continuous vector fields. Field lines are just a visual representation that serves two purposes.",
"One is to show the direction of the field (with arrow heads). The other is to show the strength and gradient, like contour lines on a topographical map. A field line traces some path of constant magnetic field strength. The spacing of the lines shows you how \"steep\" the gradient of the field is."
] |
[
"I think his confusion stems from the observation that iron filings tend to form ",
"bands",
". It seems reasonable to look at a picture like that and assume that the magnetic field only acts along lines (and not in the white spaces between them). The filings weren't placed in bands and then allowed to rotate/orient themselves properly. They were just dropped randomly, and yet still formed into bands. ",
"So why do they form into bands? My guess would be that the filings themselves become magnetized and so they lump together?"
] |
[
"No, the field is continuous in its whole volume."
] |
[
"Two questions regarding radiation"
] |
[
false
] |
Can there be a positron collider? What would be the problems of this? What uses could it have? What would happen if I collided an alpha particle with a beta negative particle? Would I have lithium?
|
[
"There have indeed been colliders that had beams of positrons. For example, the tunnel that now houses the LHC used to house LEP, the Large Electron-Positron collider. At the SLAC National Lab, the SLC (Standford Linear Collider) also collided beams of positrons with beams of electrons.",
"In general, the benefit of electron-positron colliders over colliders that collider hadrons (protons, antiprotons, nuclei) is that the electron-positron collisions are much simpler to analyze. Electrons and positrons are fundamental particles with no apparent substructure, and they do not directly feel the strong force. Thus you get a much cleaner signal in an electron/positron collision than with protons/antiprotons/nuclei."
] |
[
"First you'll have to work on getting an alpha particulate to travel since practically anything it comes in contact with stops it.",
"Particle accelerators are giant vacuum systems; the beams are traveling through vacuum."
] |
[
"Oh wow, I didn't know that! Any idea what would happen if you bombarded alpha particles with beta? would they become lithium?"
] |
[
"If you could measure the distance from a singularity to the inner edge of a black holes horizon would it be infinite because of space stretching or would it have a set distance?"
] |
[
false
] |
Basically I was thinking if the singularity of a black hole hit some unknown degeneracy limit and started pushing back outwards how much space could the singularity expand into? I know for all intents and purposes the inner workings of a black hole are basically separate from our universe, but I was wondering if anyone knew anything about this.
|
[
"The distance you mention cannot be defined; to do so you 'd have to find a set of coordinates (t,x) and a chain of rulers such that",
"It's impossible to do so. This is mostly because the singularity has a structure of an instant in time, not a point in space - it's a spacelike surface. Interestingly you can satisfy 1 and 2 but not 3, in that case the distance measured at time t is arbitrary and decreases faster than light as t passes signaling you'll soon die in the singularity.",
"Anyways if you want to visualize why it's impossible, google the Penrose diagram for a Schwarzschild black hole. This is a representation of the spacetime; only the radial and time dimensions are included and it doesn't represent the geometry completely but it does encode the conformal/causal structure which is all we need. Ok, in English: in the diagram light moves at 45°. Try to draw the chain of rulers satisfying the above and you'll clearly see you can't. Note that at any given time t, the chain must be a spacelike (i.e. more horizontal than 45°) curve."
] |
[
"Yes but the value depends on the clock's worldline. There is a ",
" value though, which iirc is πM in natural units. It has to be attained by a geodesic (since geodesics maximize proper time) and then one must find the optimal geodesics between those going from r=2M to r=0; it turns out it's the one of vanishing ang momentum and effective energy, and has proper time πM."
] |
[
"Do I understand it correctly that we can at least partially address the OP's question by sort of measuring distance with clocks, not rulers? I mean, if we drop a clock in a black hole, then it reaches the singularity in a finite time (by its own measure). So there's no \"infinitely stretched space\" there (I blame the rubber sheet metaphor!)."
] |
[
"What if the size of the matter that is about to enter the black hole alot bigger than the hole of the black hole itself, would the matter entering the black hole be broken down or would the black hole expand in some sort of way or what?"
] |
[
false
] | null |
[
"The way a solid object stays together as one solid object is because of the forces between the atoms and molecules inside the object. If you push or pull one end of it, that pushes or pulls the bit next to it, which pushes or pulls the bit next to that, and so on and so on until the whole object appears to move together.",
"However, it actually takes some time for a push or pull on one side of an object to reach the other side. This is actually much slower than the speed of light - it's the speed of sound. This means there's no need for the entire object to get pulled in at once - one part could cross the event horizon before the other end even knows what's happening.",
"Also, this strength is of course not infinite - if the strength of the bonds in the solid object are weaker than the tidal forces of the black hole, the object will get ripped apart.",
"So the short answer is that it would break down whatever is falling into it.",
"The black hole would also expand a bit, just because it's gaining extra mass. But it's not like it's opening its mouth to suck in something bigger than its diameter."
] |
[
"Its nothing super mind-blowing. By definition, pressure waves travel at the sound speed through a medium, and any disruption to an object creates a pressure wave."
] |
[
"According to ",
"these calculations",
", it varies depending on what part of the star you measure, but it does approach the speed of light."
] |
[
"Is it possible to have a liquid that is less dense than a gas?"
] |
[
false
] | null |
[
"It is not explicitly stated in the question, but I assume the gas and liquid are supposed to be at the same temperature and pressure. This makes it kinda impossible to use liquid hydrogen, since at those temperatures everything else is solid.",
"Because the density of gases strongly depends on the pressure and those of liquids is almost constant, your best bet is at the critical point of a low density liquid. ",
"I can't calculate it as I don't know which equation of state would apply (or to be more precise, I am to lazy to look it up), but tungsten hexafluoride (heaviest gas known at STP, 13 kg/m",
" at the critical point (187.8 deg Celcius, 32.9 bar) of isopentane (very light liquid at STP, 620 kg/m",
" is a good candidate.",
"Edit: Realised 32.9 bar is gonna be too low, gonna need something with a higher critical pressure. Water has a critical pressure of 217 bar, which should work."
] |
[
"It actually has to do with how many atoms are crammed into an amount of space. If you had one atom of hydrogen or helium, you couldn't apply the concept of density, nor the concept of liquid, gas, etc. for that matter."
] |
[
"I don't know of any liquids less dense than a gas, but yes, the liquid would float on the gas in a closed system."
] |
[
"Do blind people dream? If so, are they seeing anything?"
] |
[
false
] | null |
[
"Found this quote to help, \" Yes, blind people do dream. What they see in their dreams depends on how much they could ever see. If someone has been totally blind since birth, they only have auditory dreams. If someone such as I, has had a measure of sight, then that person dreams with that measure of sight. I still dream as though I can see, colors included. For people I've met since, their faces are just blurs or how I imagine they look. To me, someone like my mother looks forever 30. \" \n Cite: ",
"http://van.physics.illinois.edu/qa/listing.php?id=19761"
] |
[
"But say if the person is born blind studies show that most of them dont know how to describe there dream, not ever having seeing things before. ",
"Cite? Blind people don't just dream sounds, smells, touches or experiences? Why couldn't they just describe them that way? "
] |
[
"It depends, If they are born with sight, then lose there vision to day, injury or sickness, But say if the person is born blind studies show that most of them dont know how to describe there dream, not ever having seeing things before. "
] |
[
"For the moon laser bounce experiment, how is the laser aimed?"
] |
[
false
] |
Mechanical Engineering student here, I recently saw the episode of the big bang theory which showed them doing the lunar range experiment, where a laser is fired at the moon, bounces off the reflector and back to the sensor. The time is measured and then the distance can be computed through the D=R*T formula, where R is the speed of light in a vacum. I was wondering, how is the laser aimed so it hits the reflector on the moon? Is it a relatively simple mechanism, or is anyone doing this experiment in need of computer control that will factor time of day and do very precise aiming of the laser?
|
[
"I believe ",
"this",
" video explains it well.. "
] |
[
"Laser or a mirror the laser bounces off of is on an adjustable mount. Point it generally at the moon and let it fly. You can set the laser to a high rep rate or CW and optimize the signal at your detector to see when you are aligned. In the end there is lots of room for error as the laser spot on the moon is rather huge thanks to beam divergence."
] |
[
"Video didn't get into how they aiming process works too much, other than it's very difficult to aim it well enough, and it's a hard experiment because of it."
] |
[
"AskScience AMA Series: I'm Dr. Laurie Santos, Professor of Psychology and Cognitive Science at Yale University. My lab studies what makes the human mind special by examining how monkeys, dogs, and other animals think about the world. AMA!"
] |
[
false
] |
Hi reddit! I'm Dr. Laurie Santos, the Director of the and the . My research explores the evolutionary origins of the human mind by comparing the cognitive abilities of human and non-human animals, in particular primates and dogs. I focus on whether non-human animals share some of the cognitive biases that plague humans. My and has been viewed over 1.3 million times. I was voted one of , and was named in . My new course, , teaches students how the science of psychology can provide important hints about how to make wiser choices and live a life that's happier and more fulfilling. The course recently became Yale's most popular course in over 300 years, with almost one of our four students at Yale enrolled. The course has been featured in numerous news outlets including the , , , , and . I've also developed a shorter version of this course which is . I'm psyched to talk about animal minds, cognitive biases or how you can use psychological sciences to live better. I'll be on around 4 or 5pm EST (16/17 UT), AMA!
|
[
"Give it to me straight, doc! Does my dog really love me, or does she just see me as the benevolent controller of resources?"
] |
[
"The fact that this question was one of the most upvoted is so cool, because it shows just how much of a connection we have with dogs, and how much we want our dogs to care about us. ",
"Sadly the tough thing for scientists is that we don’t yet have great ways to measure dogs' emotions. As scientists, we have great ways to measure how dogs think— what decisions they make and how they think through problems— but testing dogs' emotions— what they feel— has been harder for scientists (despite the obvious anecdotal evidence that dogs obviously feel and experience emotions). The good news is that even though we can’t yet empirically test dogs’ emotions directly, there’s lots of circumstantial evidence that dogs do in fact feel something for us and think of us as more than a food dispenser. My favorite example comes from some work by Nagasawa and colleagues showing that dogs have hacked into the neuroendocrine responses we humans use to bond with our children. When human parents look at their beloved children, we release a hormone called oxytocin that helps with social bonding (at least in this situation.. oxytocin isn't always about being nice). It turns out the same things happens when we look at dogs and when dogs look at us— we both show increased oxytocin levels. Again, this effect isn’t a direct measure of what dogs feel (sadly we don’t have such a measure yet), but it suggests they’re experiencing and looking at us in at least some of the same ways we look at and experience them. They’ve become part of the very same care-taking circuit we use to bond with our own kids. So I take heart in that. These date make me think that dogs think of us as lovingly as we think of them. "
] |
[
"Do animals perceive beauty? Bright orange sunsets, companions of the opposite sex, a lush forest... Can they appreciate these things similar to us, or are we 'special' in this way? Love and appreciate your work!"
] |
[
"Why is anger a symptom of hyperglycemia?"
] |
[
false
] |
What is special about high blood sugar that causes an emotional response like anger?
|
[
"When you are insulin deficient your body is basically hungry and thirsty, so it's similar to the grumpy mood you'd get from being \"hangry\".",
"Your brain cells are low on nourishment because they're unable to utilize the blood sugar, and they're low on fluid because high blood sugar is strongly dehydrating. So your cells are upset and by extension you are upset."
] |
[
"As a type 1 diabetic it can go the other way. I’m angry because of high glucose.",
"Sure, sometime my blood sugar is high because of anger, but that’s obvious. Just feeling pissed off for no reason, then checking my blood sugar to find out why: that’s different, IMO.",
"I was wondering if there is a chemical reaction happening in the brain because of elevated glucose levels; or something like that."
] |
[
"Hmm, confused me there. From high blood sugar? Low definitely does it."
] |
[
"Do bugs take fall damage?"
] |
[
false
] |
I’m genuinely curious lol
|
[
"Tarantulas can't take impact very well. I've had many as pets, lost one to a drop that ruptured her abdomen. Bear in mind that these are fairly massive compared to most terrestrial arthropods, and the species that died was from a desert biome where there probably wasn't a huge \"falling off stuff\" threat."
] |
[
"So this is why most crickets can jump extremely far?"
] |
[
"So this is why most crickets can jump extremely far?"
] |
[
"Would the amount of weight on this planet affect its trajectory?"
] |
[
false
] |
Would either a lesser amount or higher amount of weight affect the overall direction the planet's headed in?
|
[
"If you are asking about adding or removing mass from the Earth, then the effect on the Earth's orbit would depend on how this mass is added or removed.",
"The general answer is yes, there would be a change - adding or removing mass would generally happen by something colliding with the Earth or leaving the Earth, and in either case it would add its momentum to or subtract its momentum from that of the Earth. Most things that collide with the Earth or leave the Earth have such a tiny mass (comparatively) that the effect is negligible, but if the Earth was struck by a sufficiently large object, it would result in a noticeable difference in the Earth's orbit.",
"Consider the extreme example, where Earth is struck by an object of exactly the same mass traveling at exactly the same speed in the opposite direction - the momentum would exactly cancel, and the combined mass would begin falling straight into the Sun."
] |
[
"Objects actually obit around their systems center of mass. So our earth actually orbits a “balancing point” between the sun and the earth. If mass were added to the earth, this balancing point would move toward the earth, therefore affecting its trajectory."
] |
[
"The actual adding and removing of mass will usually exhibit a force, but if I could, somehow, double the earth's mass by magically teleporting extra matter on, the answer would be no. Or, at the very least, \"almost no\".",
"The thing about gravity is that it produces a force that is proportional to mass, meaning the acceleration is the same if you're light or heavy. This is where the famous example of a hammer and feather dropping at the same speed in a vacuum comes from. ",
"Speaking generally, two objects in space will orbit eachother about their combined center of mass. Making the earth heavier would very slightly shift this center of mass a bit further from the sun, and the extra overall mass would make it orbit a tiny bit faster. In practical terms though, you'd need to make the earth a few orders of magnitude heavier to get an actual noticeable effect, because the sun is just so heavy that it basically acts as a fixed point."
] |
[
"How come photons have no mass?"
] |
[
false
] |
[deleted]
|
[
"Not only are photons affected by gravity, they can even create their own gravity. This is because photons have energy, and energy curves spacetime just like mass does. In fact, for the first 80,000 years after the Big Bang, the photons in the Universe had a stronger gravitational pull than all the matter put together!"
] |
[
"Photons take a straight path through space, but near a large object, space is curved by the object's gravity. So, what looks like a straight path to the photon actually looks curved to a distant observer.",
"Not sure what you mean by superheated space - temperature is a property of particles, not spacetime. Photons always move at the speed of light."
] |
[
"Refraction through a medium does not necessarily involve absorbtion and re-transmission. Many of the photons that travel through a sheet of clear glass, for example, are not absorbed and re-emitted - this would ",
" the light since the re-emission is in a random direction, and the glass would look cloudy and not clear. The speed through the medium actually IS slower because of the electric and magnetic properties of the material. The speed of the electro-magnetic wave propogation (light) is 1/sqrt(dielectric permittivity * magnetic permittivity). "
] |
[
"Has there ever been a species whose downfall was a side effect of its evolution?"
] |
[
false
] |
Considering that evolution is when an organism adapts to changes in its environment through mutations in its genes, has there ever been record of a species, or the possibility of one (either in the past or the future), that, while it has adapted to changes and mutated, those mutations allowed other negative mutations to become a part of the species and become its downfall?
|
[
"Any taxa which evolved to adapt to a narrow specialised niche, and then saw that niche go away. Specialised parasites of now extinct species would be a great example."
] |
[
"probably exactly every extinct species"
] |
[
"I think you are misunderstanding what evolution actually means.",
"Considering that evolution is when an organism adapts to changes in its environment through mutations in its genes,",
"Mutations don't \"adapt to their environment, they are spontaneous and completely independent of the need for adaptation. Mutations can be both beneficial and harmful to the species in question, the ones which are harmful are naturally selected against and therefore have a slightly lower chance of surviving to the next generation.",
"If you are talking about cases where species evolved to fill specific ecological niches and then went extinct as those niches ceases to exist, then yes, this has happened an immeasurable amount of time in natural history. "
] |
[
"Why doesn't light diffract through the 'mostly empty space' of an atom?"
] |
[
false
] |
In this case, the 'the slit' is small enough for significant diffraction, right?
|
[
"The fact that an atom is mostly \"empty space\" is one of those facts that you would probably be better off just forgetting. What people generally mean when they say an atom is mostly empty space is that the nucleus takes up a tiny fraction of the volume defined by the electron orbitals. The electrons somehow don't count as filling up any space because they are \"point particles\". But all fundamental particles are point particles, so in that sense all atoms are made of 100% empty space. Even the nucleus is just a bunch of point-like quarks and gluons floating in empty space. But just because fundamental particles are point-like doesn't mean they can't interact with each other. Atoms still repel each other when brought close enough, despite all that empty space.",
"From a visible photon's perspective, the atom has a few charged particles that it can potentially scatter off of. If the photon can excite one of these charged particles it can interact with it, otherwise it just passes through. The quarks in the nucleus are bound so tightly that a visible photon has no chance of being absorbed. The electrons might have a transition that matches the photon energy level, so they can scatter off of those. This is why a gas has atomic absorption lines.",
"So what happens when a photon scatters off a single atom? ",
"This paper",
" shows the result. They trapped a single atom in a vacuum and imaged it. Even when they tuned the illumination to match the atomic transition and focused the illumination down to a diffraction limited spot, you still only get about a 3% change in signal. But the atom does produce a measurable shadow. So light certainly does diffract around an atom, although I wouldn't say it is diffracting \"though\" it exactly."
] |
[
"Yeah, the electron in an atom isn't really a single point taking up 0 volume, it's a wavefunction spread across space. The size of this wavefunction squared tells you the probability of finding the electron at that point*. If you graph this probability as a function of the distance from the nucleus, it looks like this: ",
"http://hyperphysics.phy-astr.gsu.edu/hbase/imgmod2/hy1s.gif",
"As you can see, the probability is spread out over the interior of the the atom. It goes to 0 at the centre, or as you go out to infinity, and for the outer electrons there are a few points inside the atom where it goes to 0, but aside from those points, the electron exists everywhere inside the atom. It's not reasonable to say that an atom is mostly empty space. What an atom is mostly electron wavefunction (at least in terms of volume. In terms of mass, it's mostly the nucleus)."
] |
[
"Semi unrelated question:",
"I heard about all fundamental particles being point particles, but i also seen \"size comparisons\" of quarks etc where up and down quarks are the biggest, and also how high energy neutrinos are bigger than low energy neutrinos. Whats up?"
] |
[
"Regarding the effects of gravity on a black hole as mass is added?"
] |
[
false
] |
[deleted]
|
[
"1.) The only person who could give you an answer would be the first astronaut, or the second astronaut, and that answer could never reach you. ",
"2.) On the way to the event horizon? If you waited long enough, yes. ",
"3.) No one really knows if they do evaporate, and if they do, what exactly that would entail. It's incredibly hypothetical all around."
] |
[
"i don't understand 1. light like is not a word for a particle. ",
"2 yes all the time. it wouldn't suddenly be added but the mass would be there to begin with and it would already have a gravitational effect outside of the black hole. it's not like you teleport in additional mass and it only starts gravitating when it reaches \"the singularity\". "
] |
[
"1) If it has mass it cannot reach the speed of light",
"2) Inside the black hole? Not a physicist in the world could tell you what happens inside a black hole. ",
"3) They in fact wouldn't be, this is the whole quantum information loss paradox of black holes. Hawking radiation comes from particles that pop into existence randomly, NOT from the particles inside the black hole. The particles inside the black hole never leave said black hole, even when the black hole is entirely evaporated. Thus a paradox."
] |
[
"Could we equate the Universe's growth and the accelerated expansion of galaxies to a riding the slope of a \"bubble?\""
] |
[
false
] |
[deleted]
|
[
"Well...every point is the center of the universe. There is no privileged special \"center\" -- this \"things going further away the further they are from you\" thing is actually true for any two points.",
"It's more like the universe is the surface of a balloon. When you are on a balloon being blown up, all of the other parts of the balloon are expanding away from every other part, and the further apart two things are, the faster the relative expansion."
] |
[
"Thank you for this!"
] |
[
"Here is a graph",
" that compares the old and new cosmological expansion models -- the green curve includes the effect of dark energy. See how the dark energy expansion profile begins to increase without bound?",
"Here is an article",
" that explains dark energy."
] |
[
"Is there an equation to figure out the minimal amount of water needed to dissolve something?"
] |
[
false
] |
I'm brewing beer and I need to add priming sugar to the beer to bottle it so it will carbonate. But I don't want to affect the volume of the beer. Is there a way I can find out the minimal amount of water needed to dissolve sugar? I'm sure that different substances will be different, is there a scale for this sort of thing?
|
[
"You can find a simple table ",
"on the right of this page",
" of the solubility of sucrose (normal table sugar) in water.",
"Also, solubility is dependent on temperature of the solute."
] |
[
"/r/Homebrewing",
" "
] |
[
"Just a couple of assumptions needed: the sugar you're using is supposed to be pure dextrose (glucose), correct? That's the most common (only?) sugar for brewing, so I'll use that in my calculations. If it's different, just look up the solubility values and substitute them in. Also, this is for standard temperature (25",
" C).",
"It should be roughly 91 g/100 ml water. Each solid has a different solubility in different solvents, so the best way is to look it up. Google X solubility in Y and you'll have no trouble, especially for common things like sugar and water. ",
"So basically to find out the amount of water needed to dissolve a given amount of sugar, you just have to find out how much sugar you're adding, then multiply by 100 ml and divide by 91 g.",
" mass of glucose x (100 ml H2O/91 g glucose) = volume of H2O needed\n",
"For example, to dissolve 1 g of glucose, you'll need:\n 1 g x (100 ml / 91 g) = 1.0989 ml of H2O",
"So I guess your best bet would be making a large batch of saturated sugar water, then dispense it accordingly. Of course, you'll need something to measure reasonably small volumes like a syringe or pipette. "
] |
[
"Do forces act at the speed of light?"
] |
[
false
] |
Since gravity and electromagnetism propagates at the speed of light, do forces behave in a similar manner? More explicitly, if I had a taut rope that was considerably long connected to an object. When I pull this rope, would the force propagate down the rope at the speed of light? Also, how would this change if the rope were massless?
|
[
"This is the old \"if I had a stick 1 light year long and I pushed it, would it instantly move on the other side\". It wouldn't. Consider sound waves. They are a longitudinal waves of increased and decreased density of air. It propagates at the speed of sound. And in a different medium, like water, it propagates at the speed of sound in that medium. The same goes for your example. When you pull the rope, the rope stretches locally and then this travels down the rope at the speed of sound in the rope material."
] |
[
"That makes complete sense, thank you!"
] |
[
"Another question that came to my mind; what about strong and weak forces? Do we know anything about their acting speed?"
] |
[
"Is it possible for any electric generator to have an efficiency that approaches 100%?"
] |
[
false
] |
I know that different types of generators have a maximum theoretical efficiency (such as wind power) that's determined by the way the energy is physically derived. I also know that it's practically impossible for any generator to have an efficiency of 100% due to energy being given off as heat and whatnot. So, are there any kinds of generators where the efficiency at least approaches 100% rather than a lower value?
|
[
"It depends what you are considering an electric generator. The turbines used in hydroelectric power stations can have efficiencies of up to 95%. The generators they are attached to are typically around 98% efficient. However, overall system efficiency is around 85-90% due to losses in the penstocks, etc."
] |
[
"The only thing I know that approches 100% are trees. Using photosynthesis they >\"transform\" about 90-95% of the sun energy to their cells.",
"The ",
" efficiency of photosynthesis for green plants is ~13%.",
" The number I've seen for trees is about 5% and for crop plants 1-2%. "
] |
[
"The only thing I know that approches 100% are trees. Using photosynthesis they >\"transform\" about 90-95% of the sun energy to their cells.",
"The ",
" efficiency of photosynthesis for green plants is ~13%.",
" The number I've seen for trees is about 5% and for crop plants 1-2%. "
] |
[
"AskScience AMA Series: Been watching \"The Last of Us\" on HBO? We're experts on fungal infections. AUA!"
] |
[
false
] |
Ever since "The Last of Us" premiered on HBO earlier this year, we've been bombarded with questions about Cordyceps fungi from our family members, friends, strangers, and even on job interviews! So we figured it would be helpful to do this AMA, organized by the American Society for Microbiology, to dive into the biology of these microbes and explain how they wreck their special breed of havoc. Each of us studies a different host/parasite system, so we are excited to share our unique (but still overlapping) perspectives. We'll take your questions, provide information on the current state of research in this field, and yes, we'll even discuss how realistic the scenario presented on the show is. We'll be live starting at 2 PM ET (19 UT). Ask us anything! With us today are:
|
[
"Great question. ",
"The answer is Yes! There is something that makes them harder to treat. The main problem is that fungi are much more similar to animals than they are to bacteria (or plants), and consequently there are a lot more \"conserved\" cell structures / genetics (i.e. shared cell machinery and genes from a common ancestor). The practical implication of this is that there are far fewer drug targets in a fungal cell (like enzymes where drugs can interfere) without killing our own cells. As a result, we only have 3 classes of antifungals, and they suck! "
] |
[
"In some of the early episodes, (fictional) experts play up our helplessness against fungal infections, making claims like \"no vaccines, no medicines, no preventatives, no cures, it's not even possible to make them\", but there are a whole bunch of ",
"antifungals",
" in real life.",
"Of course I understand how there might not be a working treatment for a specific novel fungus, but the prologue seems to make a broader claim than that; is there something about fungi ",
" that makes them more resistant or otherwise difficult to treat than bacteria or viruses, or are claims like these just there to make the story more dramatic, but are entirely inaccurate to real life?"
] |
[
"Thanks for the question. Here is an answer to your first question: ",
"The WHO recently published a \"priority fungal pathogen\" list where they rank fungi according to their importance in causing infections in humans. It considers things like the total number of infections globally and also the severity of infections, whether there are treatment options, etc. They rank the highest priority group to include the following:",
"- Candida albicans: a very common yeast that all of us carry in our mouths and in our gut, but which causes a huge number of infections of mucosa (think vaginitis and oral thrush, diaper rash, etc) but also invasive diseases like bloodstream infections in people with compromised immune systems (like receiving chemotherapy) and in hospitals/ICUs with venous catheters. ",
"https://www.cdc.gov/fungal/diseases/candidiasis/invasive/index.html",
" ",
"- Candida auris: the new kid on the block, important for two reasons: 1) it spreads really efficiently between people and can contaminate hospital environments (curtains, bedrails, windowsills, etc) and then infect vulnerable patients, and 2) it can be resistant to one or more classes of antifungals (there are only 3 classes, and sometimes can be resistant to all 3). C auris was only described in 2009 and has spread around the world since. It is the only fungus at the top of the CDC's \"Threat List\" of drug resistant infections. Here is some info from the CDC: ",
"https://www.cdc.gov/fungal/candida-auris/index.html",
"- Aspergillus fumigatus: a ubiquitous mold that all of us inhale spores of every single day (without it causing any problems) but in patients with immune systems that are weakened by diseases like blood cancers or by medicine used to prevent rejection of transplanted organs, it can cause very serious pneumonia ",
"https://www.cdc.gov/fungal/diseases/aspergillosis/index.html",
" ",
"- Cryptococcus neoformans: another yeast, this is found in the environment, and can cause brain infections in people with immune systems weakened by advanced HIV or medications used to prevent organ rejection after transplantation. Cryptococcal meningitis is a leading cause of death related to advanced HIV in many parts of the world. ",
"https://www.cdc.gov/fungal/diseases/cryptococcosis-neoformans/index.html",
" ",
"The full report from WHO can be found here: ",
"https://www.who.int/publications/i/item/9789240060241",
" ",
"With regards to your second question, when people have brain infections caused by fungi they don't turn into zombies, they just get really sick. Fevers, weight loss, seizures or stroke-like symptoms."
] |
[
"In the universe, how do we differentiate antimatter from regular matter?"
] |
[
false
] |
If antimatter can make up regular atoms such as antihydrogen or beyond, how do we distinguish between it and regular matter in the universe? Could there be entire galaxies made out of antimatter? Why is the universe considered asymmetric in regards to antimatter if it behaves similarly except for its interactions with regular matter?
|
[
"If antimatter can make up regular atoms such as antihydrogen or beyond, how do we distinguish between it and regular matter in the universe?",
"Antiprotons have a negative charge and antielectrons (also known as positrons) have a positive charge. Thus the charges are reversed from normal matter. This is very difficult to measure from a distance.",
"Could there be entire galaxies made out of antimatter?",
"Not within the observable universe. If there were, we would see border zones between them and normal matter galaxies where particle-antiparticle annihilation was occurring and giving off characteristic gamma ray signatures. We can't entirely rule out other areas of the universe outside of the observable universe having antimatter dominate, but it's not a particularly elegant solution.",
"Why is the universe considered asymmetric in regards to antimatter if it behaves similarly except for its interactions with regular matter?",
"The universe is considered asymmetric because it ",
" asymmetric: there is more matter than antimatter. In the very early universe, a tiny tiny tiny excess of matter was created. All of the antimatter and almost all of the matter annihilated with each other and produced radiation, but there was that bit of leftover matter, and it went on to create all the stars and planets and galaxies in the observable universe.",
"There is also a key difference in the interactions, known as ",
"Charge-Parity violation",
", which shows that matter and antimatter behave very similarly but are not perfect mirrors of each other. Essentially the universe has a difference between positive and negative charge. Why does this happen? We don't know."
] |
[
"The matter can certainly get away from itself, but not fast enough for the matter and antimatter to segregate into regions larger than the observable universe. That's impossible, because they would have to travel at faster than the speed of light."
] |
[
"I understand that it is asymmetric, I was more wondering how we detect that it is such. Is it only that there aren't any border zones, or is it something more?",
"As far as I'm aware that's the only direct observational method. If there were antimatter within our observable universe we expect that it would have annihilated in the very early universe.",
"As for the border zones, would it have been possible in the extremely early universe (maybe microseconds after the big bang, if such a concept makes sense) for antimatter and normal matter to have combined at one point and then gone their separate ways, leaving one half of the universe antimatter and the other on our side, with little to no interaction afterwards? So you'd have all this baryonic and anti-baryonic matter combining initially, leaving all this gamma radiation around that would eventually become the CMBR, and then you'd have an expanding array of the remaining matter and antimatter in relatively non-interactive swirls throughout the universe due to their lack of proximity. Is that feasible?",
"They can't really go their separate ways, since the universe was expanding faster than they could travel, but if there were primordial differences in the amount of them, then different areas could have different amounts of antimatter. The problem with this is that if the matter excess arises from fundamental physics, as it very well may, then areas of antimatter would implicitly have different laws of physics.",
"Another question: how does the CP violation manifest in the behavior of antimatter? Would it decay faster?",
"Kaons can switch into their antiparticles, and it occurs in one direction with ",
" greater speed than the other. There are a few other examples, it's not so much that a decay happens faster as that a certain type of decay ",
" happen."
] |
[
"How Is Blood Flow Increased to a Particular Area?"
] |
[
false
] |
Let's say I'm at the gym doing biceps curls. How do my biceps signal that they need more blood? And once more blood starts flowing, how exactly does it get directed just to the biceps (as opposed to the heart just pumping more blood to all arteries)?
|
[
"So I'd like to expand this a little bit, but ",
"/u/dblowe",
" has given good information. Exercising muscle sends out locally acting factors that tell the blood vessels to dilate. Prostaglandins are a great example of this. The muscle is using more of the oxygen in the blood, and consequently as blood leaves the exercising muscle, it has less oxygen and more carbon dioxide. Due to the cooperative nature of the hemoglobin molecule, other tissues will have a slightly harder time getting the oxygen they need, but that's basically irrelevant for our purposes. What matters is that carbon dioxide in your blood as a whole is going up, and oxygen is going down. You start to breathe more quickly and more heavily, and your heart starts to pump quicker to match this demand. ",
"Now to ",
", the problem with the the system we have described to this point increases blood flow EVERYWHERE, and especially in tissues with higher metabolic need, like the biceps brachii muscles in your left arm. The right arm is still getting higher blood flow, more than it needs, even though it's not doing anything right? No. There are at least two mechanisms in place to prevent this. One is called metabolic autoregulation and the other is called the myogenic response. Metabolic autoregulation is what caused the arteries in your left bicep to dilate as previously described. Similarly, in your right arm, the perfusion pressure is detected as being greater than it ought to be to meet metabolic need, and the arterial blood vessels constrict to try to maintain blood flow at the proper level (not too much, not too little, juuuuust right)",
"The myogenic response is an intrinsic property of smooth muscle, which is the type of muscle which lines your arteries. It also lines your esophagus, intestines, and many other places. In response to the muscle being stretched (for example, by increased blood pressure in an artery, or a big piece of cake in your esophagus) the muscle will reflexively contract. This does not require input from the brain or higher centers, although it can be modulated by multiple factors. In the case of your esophagus, we can immediately see how this might be helpful -- you bit off more than you could swallow and the muscle contracts to force the bolus of food down your throat. In the blood vessels, the increased blood pressure caused by your heart beating faster/stronger is detected, as the higher pressure causes increased lateral force on the wall of the blood vessel. The artery in your right (unused, not exercising) arm constricts to help maintain blood flow constant to the right arm. Unlike metabolic autoregulation, the myogenic response with respect to the cardiovascular system propagates. Once the downstream vessel constricts, blood builds up further upstream, and then the upstream blood vessel constricts. This helps to \"shunt\" blood away from tissues which do not require that much blood, back to either tissues that do require the increased perfusion, or into the veinous circulation. The veinous circulation is under low pressure and can hold a lot of blood, and this blood is not really doing anything, it is just waiting to be reoxygenated or thrown back into arterial circulation, for example if the veins constrict and your whole body needs more blood flow. ",
"You can see how local mechanisms in the right arm (metabolic autoregulation) might locally prevent the increased flow, and then the myogenic response contributes not only locally, more on a more widespread scale to help maintain adequate flow.",
"You might be wondering how things get back to \"normal\". ",
"At the end of the day, almost all of this can be over-ridden by the brain. For example, a scary movie gets your blood pumping for a moment, but once your brain realizes there is no real danger, everything slows down fairly fast in most cases, there isn't this long lasting uncontrollable response. ",
"here",
" is a source on various types of perfusion regulation. I hope that helped answer your question"
] |
[
"Yep, as mentioned, it's done by controlling the size of the local blood vessels. There are a number of signaling molecules - peptides such as angiotensin, vasopressin, endothelin et al., and other molecules like adenosine, histamine, prostaglandins, and a list as long as most arms. The vascular smooth muscle cells that line the vessels are very senstive to these cues. Exercising skeletal muscles immediately starts sending out such signaling molecules to the local vasculature."
] |
[
"Those are the nuts and bolts, for sure. And this illustrates the sort of multiple, overlapping controls that you find for vital systems like blood flow. You see that for all sorts of essential functions (eating being another notable example) - there are layers and layers of semi-redundant signaling networks, so that all sorts of situations can be responded to and no easy failure can shut things down. A couple of billion years of \"Get this right or die\" will do that for you."
] |
[
"What is scale energy?"
] |
[
false
] | null |
[
"Where did you hear about \"scalar energy\"?"
] |
[
"Video in which a so called healing device was being demonstrated."
] |
[
"Then it's probably nonsense."
] |
[
"Cambrian explosion controversy?"
] |
[
false
] |
Is there a controversy surrounding the cambrian explosion? Ive been told by my brother that this could pose a problem for the theory of evolution, as speciation occurred during that time at too rapid of a rate. after being informed of this, and collecting details relevant to the subject, i decided that he may have been misinformed. what is your standing on this and reasons why, askscience?
|
[
"My understanding is that there is some remaining question about what was actually exploding. This was brought up on the latest SGU podcast... It might not be that organisms and \"life\" had an explosion, but rather there was an explosion of certain characteristics that made the data about creatures from this age more plentiful (ie: Hard parts that fossilize). "
] |
[
"i had similar ideas, thanks for helping out!"
] |
[
"There is really no controversy about this within scientific circles. The issue is that many people hear the term \"explosion\" and mistakenly believe that the sudden appearance of new features happened overnight. Although the term is meant to convey that there was a rapid appearance of those new features, it's a relative term. The Cambrian Explosion lasted approximately ",
"70 to 80 million years",
". Not 8 years or 800 years or 8000 years or 8 million years or 38 million years or 58 million years.... but ",
"!"
] |
[
"What is the physiology behind why hot things, such as wasabi, “clear out your sinuses”?"
] |
[
false
] |
Just had a little too much wasabi with my sushi and it got me thinking...
|
[
"The ears, nose and throat are all connected. That's why ENT doctors are a specialisation, and people can eat a noodle and push it out their nose.",
"When you eat hot/ spicy food, the fumes travel up and irritate the tissue, causing it to react with irritation to \"flush out\" the irritant."
] |
[
"As far as I understand Capsaicin binds to a certain receptor at the end of sensory nerve cells. This receptor (TRPV1) is the same receptor that reacts to burning damage through heat or abundance of protons. The sensory information is transferred to the brain and sensed as heat. Heat of course, like spicy food and acidic substances (those contain many protons). Since these are essentially harmful sensations the receptors, upon activation, also induce the inflammatory response. ",
"This occurs because TRPV1 mediated Ca2+ influx activates Calmodulin and Calcineurin, which both dephosphorylate (activate in this case) inactive NFAT (a transcription factor). Activated NFAT can now move to the nucleus and increase the transcription of inflammation-related genes.",
"I got the latter part from this paper's pathway diagram.",
"https://link.springer.com/article/10.1007/s13238-017-0395-5"
] |
[
"I understand that much. I should’ve been more specific. I’m looking for the physiology behind how capsaicin itself causes increased secretion from your nose leading to the concept of clearing out your sinuses. ",
"I appreciate the input though!"
] |
[
"Best software/program to coordinate use of lab equipment?"
] |
[
false
] |
My group uses sign up sheets and is interested in upgrading to an online based scheduling system. Ideally, you'd select whatever machine you'd want to use and block out a chunk of time. Multiple accounts to access the schedule system preferable. Any recommendations? Thanks in advance!
|
[
"I see a lot of groups use Google Calendar for that kind of stuff"
] |
[
"This is difficult if there are more than three people wanting to use machines. Even the signup sheets are preferable."
] |
[
"This is difficult if there are more than three people wanting to use machines. Even the signup sheets are preferable."
] |
[
"Why does the pitch of a toy with sound effects decrease as the battery expires?"
] |
[
false
] |
Shouldn't only the volume be decreasing? I mean as in Space Odissey with HAL 9000
|
[
"Electronics rely on crystals and oscillators for timing information. Crystals and oscillators are parts which produce a sinusoidal or pulse train pattern of a certain frequency when they are powered on. Many of them vary their output frequency in response to the voltage applied. Here is an example of a VCXO:",
"http://www.abracon.com/Oscillators/ASVV.pdf",
"In the table you can see that at a low control voltage the part puts out 1 MHz and at a high control voltage the part puts out 100 MHz.",
"The timing signal from the crystal is fed into the microcontroller or lower level logic of the circuit which eventually produce the sound effects. Here is an example of an inexpensive microcontroller which nominally has a speed of 20 MHz:",
"http://www.digikey.com/product-detail/en/PIC16F54T-I%2FSO/PIC16F54T-I%2FSOCT-ND/5358244",
"The part expects a 20 MHz timing signal in order to run properly - a lower-frequency pulse train or sinusoid will cause the MCU to run slower, so all of its logic will run slower, so its DACS (digital to analog converters) will produce a lower pitch of sound.",
"Now there are regulators inside of circuits which attempt to compensate for low battery voltage and try to make the electronics behave the same, but at very low battery charge that's not possible. Also, for cheaper electronics they may omit the regulators and run the circuit directly from the battery terminal."
] |
[
"Here is an example of a VCXO:",
"http://www.abracon.com/Oscillators/ASVV.pdf",
"You won't use that in a toy. That's too expensive. ",
"Oscillators in low cost products aren't crystal but RC oscillators or relaxation oscillators which are trimmed to a frequency.",
"In an RC oscillator the frequency is controlled by a resistor and capacitor. In a relaxation oscillator it's a current and a capacitor. The current will be defined by a resistor and a voltage (battery or bandgap reference voltage).",
"As the battery voltage decreases the reference current goes down and so does the frequency. ",
"But it depends on the implementation of the circuit. Other circuits may behave differently."
] |
[
"Not sure if you can, but \"circuit bending\" seems like a relevant keyword here:",
"https://en.wikipedia.org/wiki/Circuit_bending"
] |
[
"How does a commercial jetliner adjust to the uneven thrust distribution when only one of its engines is in use?"
] |
[
false
] |
With the two engines not in the center, but off to the side, and with only one being active, does this cause uneven distribution of thrust and how is it accounted for?
|
[
"The rudder. If I understand your question, commercial jets have a safety test called \"one engine out\" where they have to prove that they can overcome the moment caused by the off center force and land the aircraft. That moment is huge btw "
] |
[
"AMA request because that sounds like a geniunely awesome career."
] |
[
"AMA request because that sounds like a geniunely awesome career."
] |
[
"How do the James Webb Space Telescope cooling systems actually dissipate heat?"
] |
[
false
] |
I've read many articles about the cooling systems aboard the JWST; I understand the engineering of both the passive and active cooling systems, but I don't quite understand how heat is actually lost from the telescope. On Earth, as far as I know, you typically remove heat from something by transferring heat to other matter, but there is not a significant amount of matter in space for the telescope to dispense its heat into.
|
[
"Radiation.",
"There are three modes of heat transfer. Conduction and convection both require contact between substances, but radiation acts across a vacuum and it's pretty simple to figure. You just take the temperature difference between your hot source, and everything it \"sees.\" Electromagnetic radiation does the rest.",
"One interesting time that radiation acts that people don't think much about: a clear cloudless night here on Earth. The ground is looking out at the cold depths of space and radiates heat out into it, which is why clear nights get cold faster than cloudy nights, when the ground is looking at the bottom of the clouds. The clouds might be cold, but space is at nearly absolute zero, and that difference is what drives the amount of heat transferred by radiation.",
"So spacecraft have panels that are pointed at the cold of deep space, and shaded from the sun (because they don't want to gain heat by radiation from the sun) and voilà, heat is radiated from the hot satellite panels to the cold of deep space."
] |
[
"Everything about JWST active and passive cooling"
] |
[
"I struggled a little bit with this part of Transport Phenomena because it never really seemed all that intuitive, so take this with a grain of salt. The ",
"Wikipedia page",
" for black-body radiation has a subsection that covers the temperature relationships between planets and stars that goes into more detail, but the effectiveness of radiative heat transfer is dependent on a lot of different factors. Having larger temperature differences increases the power that's radiated since temperature terms are T",
" and treating space as the ambient temperature is essentially the maximum dT. Cloud cover can add a layer that can reflect that radiation back to earth, along with other atmospheric effects. So to answer your question, I think partially, yes the clouds temperature is a factor"
] |
[
"Why is it so difficult to create an HIV vaccination?"
] |
[
false
] |
It seems that this is one of the few deadly viruses that is mainstream but has no vaccination.
|
[
"HIV is a good virus because it is a shitty virus.",
"To be more specific, HIV has very sloppy replication. HIV has an RNA genome, rather than a DNA genome like we do. When it infects a cell, it transcribes DNA from RNA. This has none of the normal error-checking processes that the opposite process has, so you end up with a lot of errors. Many of the resulting viruses won't work at all. However, some will, and they'll be diverse enough that your immune system can't get a bead on them. Vaccines, much like your immune system, require a steady target or they're useless."
] |
[
"They have one in trial. They do not have a working vaccine. There have been ",
"several HIV vaccines in trial",
" but none have proven suitable for clinical use."
] |
[
"HIV could be considered the \"greatest\" of all human viruses, albeit in a terribly destructive manner. It pretty much has everything in the bag of nasty tricks available to use in replicating itself at your expense.",
"Firstly, HIV is an RNA virus. An RNA virus typically mutates much faster than a DNA virus (Influenza is an RNA virus; Smallpox is a DNA virus). Like the influenza virus, quick mutations can create changes in certain areas which make it difficult to detect. It's also a retrovirus, one that hijacks the human transposon gene system by using our own Reverse Transcriptase (an enzyme which essentially converts RNA into DNA; a reversal of the process of transcription) against us. ",
"To complicate the matter further, it's an enveloped virus. When viruses are done making new copies of themselves within a cell, they burst out, breaking the cell. Enveloped viruses cover their protein capsid (the shell of the virus) with a phospholipid membrane stolen from the cell it reproduced in when it lyses. This confuses the host immune system.",
"Perhaps most unfortunately, the virus directly targets the cells of the human immune system. It targets T-Cells (specific white blood cells which help the body recognize pathogens), recognizing the CD4 antigen receptor and breaking into the cell. It also targets the macrophages which attempt to swallow it, using them as hosts without lysing them to distribute their viral offspring as widely as possible. By targeting these two, HIV essentially shuts down the immune system, making defense nearly impossible. (AIDS is the final stage of the disease \"Acquired Immune Deficiency Syndrome)",
"The only real way to vaccinate for HIV would be to alter the CD4 receptor of the T cells so that they are unable to bind to HIV, without rendering it useless for its actual tasks. Some humans actually have a mutation which accomplishes this, and thus are unable to get HIV. A gene-altering vaccine might be possible, but it would require the location of that trait within the human genome and replacing it without other side effects. Because receptors are protein based, they are coded for by very specific DNA genes, and due to alternative RNA splicing, replacing genes is a dangerous and relatively imprecise art. This is assuming, of course, that the virus did not merely mutate into attacking from a new direction. Viruses are built to steal the mechanisms of their hosts to use in attack.",
"HIV is difficult to treat because of its enveloped nature, and the means by which it attacks the immune defense of the host. An HIV \"cocktail\" is available; however, their side effects are extremely debilitating. They usually consist of a protease inhibitor which attacks both the viral protein replication process and our own, a drug such as acyclovir which prevents the function of reverse transcriptase (also interfering with our own systems), and occasionally other drugs to stop the reproduction of the virus.",
"Stay away from HIV, kids. "
] |
[
"What actually makes new ADP or ATP?"
] |
[
false
] |
Where does ATP or ADP come from originally? I can only find that ATP comes from the phosphorylation of ADP and that ADP comes from hydrolysis of ATP, there must be a starting point where one of the two is produced from its components or something, right? What actually makes ADP before it is used in to make ATP for the first time in ATP synthase? I know that neither can pass across a cell membrane so they must be produced inside, I think? Thanks!
|
[
"ATP/ADP have two major components, the ribose sugar and the adenine nucleobase. The ribose sugar (as ribose-5-phosphate) is made from glucose-6-phosphate via the ",
"pentose phosphate pathway",
", an enzymatic pathway similar to glycolysis that is used to convert glucose into 5-carbon sugars used for other purposes while generating a bit of energy.",
"Ribose-5-phosphate serves as the starting point for ",
"purine biosynthesis",
", in which a series of enzymes assemble the nucleobase portion directly on top of the ribose sugar, with most of the atoms necessary coming from various amino acids or molecules from the Krebs cycle. The pathway shown there only goes up to AMP (adenosine monophosphate), which will be phosphorylated to make ADP, then phosphorylated one more time to make ATP.",
"These pathways are nearly universal, with nearly all known organisms being able to make their own ATP. So while it's a complicated and metabolically expensive process, and organisms prefer to reuse existing ATP/ADP when they can, it's clearly important for them to have the ability to make more when they need to."
] |
[
"As far as I know, all known organisms use ATP, but there are some Archaea that lack the pathway I mentioned to make ATP \"from scratch\" and may be fully reliant on scavenging it from their environment."
] |
[
"To be clear, most Archaea can make their own ATP, it's only a few that can't. Of the ones that can't, some still have a few of the genes needed, but are missing the rest. This is a sign that the group as a whole originally had the pathway, but some individual species have since evolved in a way that they lost it, presumably because they lived in environments where ATP/adenosine was a plentiful resource. ",
"Source article, if you're curious",
"."
] |
[
"Could DNA have a form of primitive \"password protection\"?"
] |
[
false
] |
This question is inspired by a recent post about Covid RNA and why it had a polyA tail (a long sequence of As) at the end. The answers explained that this was a way of tracking the health of the RNA and that it was required for the proteins to be expressed. Could an organism create a unique or semi unique tail (rather than simply a long series of As), a sort of "password", and use that as a form of protection against viruses that would need to know the exact "password" to hijack the specific organism?
|
[
"Bacteria do this! But not exactly in the way you are describing. One protective mechanism that bacteria use to avoid unwanted genetic material (e.g. phages) from hijacking them is to protect their genomes using methylation. The bacteria typically have an enzyme that adds methylation to a certain sequence and a corresponding restriction enzyme that chews up any DNA that isn’t protected by said methylation.",
"As an aside, that discovery was foundational to molecular biology, all from someone looking into how bacteria defend themselves from pathogens."
] |
[
"Somewhat related, bacteria have an antivirus mechanism that is surprisingly similar to computer antivirus mechanisms! They keep a table of \"bad guy\" DNA sequences, and have \"code\" that says \"if you see anything from this table, cut it up\".",
"Scientists discovered they could put their own sequences in the \"table\" and trick the machinery into cutting DNA exactly where they wanted. They could then use this technique to make precise edits to lengths of DNA in living cells. This is the basis of the famous, revolutionary \"CRISPR\" technique that was developed a few years ago."
] |
[
"Humans do have protective mechanism against bacterial DNA. Human DNA sequences of CpG are generally methylated and occurrences of CpG that are un-methylated are very low. Bacteria have numerous CpG sequences, and we have receptors that detect un-methylated CpG and activate an immune response. Bacteria can't methylate those sequences, it would mess up their own gene regulation, and there are too many to mutate them all."
] |
[
"COVID vaccine and effectiveness? Why not only one shot?"
] |
[
false
] | null |
[
"Hi btraber thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Human Body"
] |
[
"'Human Body'"
] |
[
"is it at all statistically possible for a DNA sequence to be coincidentally repeated?"
] |
[
false
] |
i know our sperms each have different dna sequences, however some parts of the sequence can be used to trace one's family lines back thousands of years here is my thought experiment. two people are separated by many generations - enough that neither of them would ever know and it wouldnt be incest or anything (which, is probably very likely with modern couples). is it statistically possible for the offspring to inherit coincidentally the parts from each that essentially recreates a common ancestor? maybe thats a stupid way to design the situation - there could be other factors at play here but the overarching question remains - can it happen?
|
[
"It is possible but highly, highly improbable. ",
"Your entire \"DNA sequences\" as you say (we call it the genome) is about 3 billion letters (\"bases\") long. Each position has four possible values (A, C, G, or T). Among humans it is widely understood that the ",
"nucleotide diversity",
" is about 0.1%, that is, we differ from each other by about 1 in 1,000 bases. So there are about 3 million differences between each human's genome.",
"Let's make a huge simplifying assumptions:",
"each of these differences is a single letter difference at a specific location. (Of course there are in reality all sorts of genomic variants from insertions to deletions to translocations, etc. which would greatly increas But this problem is balanced by the fact that genetic drift within a species is not smoothly distributed.) ",
"Differences between human genomes occur in a even distribution. (Of course genomes are highly sensitive to non-random events like tribes of genetically similar people staying close to each other through generations.)",
"So with these two assumptions, and knowing that there are 3,000,000 differences between each human genome in an evenly distributed way across all human population, then there are 3,000,000 places where we have to choose one of four letters. Using the formula for a ",
"combination",
", we have:",
" 3000000! / (4! * (3000000-4)!)\n= 3000000! / (4! * 2999996!)\n= 3000000 * 2999999 * 2999998 * 2999997 / (4!)\n= 3000000 * 2999999 * 2999998 * 2999997 / (4 * 3 * 2 * 1)\n= 3.37 * 10^24\n",
"So there are 3.37 * 10",
" possible genomes.",
"Let's assume that the total number of humans who have ever lived on earth is about 108 billion, or 1.08 * 10",
" (",
"Source",
".)",
"Almost there. We are now asking for the probability that one of these genomes happened twice. The probability of any of these genomes happening at all is:",
" (1.08 * 10^9) / (3.37 * 10^24)\n",
"which is 3.20 * 10",
"The probability of it happening twice is a Compound Probability. The Compound Probability of A and B is P (A and B) = P(A) * P(B).",
"So, the likelihood of the same genome happening in all of human history is 1.02 * 10",
"*"
] |
[
"other responses suggest yes, with some reasoning, so im curious if you have anything to back this up"
] |
[
"Of course - just like it's possible for two people to have the same lottery number. However, this actually gives DNA testing a bit more mathematical basis - you can present a figure to reflect that the sequence in agreement occurred by chance."
] |
[
"Is there a notable difference of quality of gasoline from one brand to the next?"
] |
[
false
] | null |
[
"My uncle was a chemist for BP and from talking to him I was under the impression that the area you live in and their laws are far more likely to effect your gasoline quality then the brand. Just at their plant they had over 150 variations of gasoline, and they only supplied 3 or 4 states.",
"So really if you want the best gas, look up the regulations in your town and compare them to your other local areas and see which require the least amount of \"environmental additives.\" This is of course, assuming you want to more power/effect from your gas and not \"greener\" gas. You could just as easily do the opposite I suppose."
] |
[
"Most brands have additives. It's what makes Chevron Chevron, and Shell Shell. As for the cleanest/best, that is a highly subjective topic. It can also depend on the type of car you drive, fuel injection, among other things."
] |
[
"This isn't the same question at all. Those are asking about octane ratings. This is asking about differences between gasoline brands."
] |
[
"Could a friction-less string tie a knot that remains tight when no external force is applied?"
] |
[
false
] |
[deleted]
|
[
"When you get into idealized situations like zero friction, it can be important to clarify what else is idealized in this hypothetical world. And it might also be necessary to clarify what \"tight\" means.",
"Some other properties of the string that might matter would be its stiffness or elasticity, both with respect to bending and with respect to compression, and whether these have any hysteresis in them. ",
"To think about the first, you might consider something like piano wire--a very springy wire that likes to spring back to its original straight configuration. If you loosely knot that, it \"wants\" to spring back to straight and is likely to do so, unless the friction is too high. That's an extreme case, but if the friction was truly zero and your string wanted to spring back, it would have nothing stopping it.",
"On the other hand, if you use \"dead soft\" annealed wire, particularly aluminum, you can bend it into any shape and it will stay in that shape, and will be hard to get out of that shape. That's the extreme of hysteresis in its flexibility.",
"But suppose we have a perfectly flexible string--a silk string might approach that. If you knot it, it doesn't want to spring back. Nor does it try to stick in this new shape. However, if it was elastic with regard to compression, if it was knotted tightly, it would be compressed, and would spring out of the tight knot. It would still be knotted but would no longer be tight. On the other hand, if it was compressible with hysteresis--maybe imagine an tube filled with clay--then the compressed part would kind of lock the knot in.",
"Now supposed you have a perfectly flexible but incompressible string. You knot it, pull it tight, and then let go. It won't move when you let go, and will stay in that configuration. Does that count as \"remaining tight\"? I don't know."
] |
[
"It's an interesting example, but it's not one that approximates perfectly flexible. If you bend fishing line in a U shape it will bounce back. It's more like piano wire in that respect."
] |
[
"But suppose we have a perfectly flexible string--a silk string might approach that.",
"A better example might be fishing line. Monofilament fishing line has very low friction, isn't very compressible. The fisherman's knot is designed to deal with this."
] |
[
"Light is created when electrons expel energy and drop to a lower energy level state in an atom... why do they expel energy, tho?"
] |
[
false
] |
What factor causes an electron to decide that it's about time to release another photon and drop to a lower energy orbital?
|
[
"There are two mechanisms:",
"Spontaneous emission",
"Stimulated emission",
"You may have heard of the latter, as it's the ",
" in la",
"r.",
"It should also be noted that there are other ways to create light than electron energy levels."
] |
[
"Excited states are unstable. If the atom is truly isolated from its surroundings, then that emission is a perfectly random event, which occurs with a characteristic rate. The result is that a collection of initially excited atoms will decay to their ground state with a characteristic half-life, just like nuclear decay of radioactive isotopes. ",
"\"Why\" is always a dangerous question in these types of problems; it's hard to give an answer much better than \"because that's just how quantum mechanics rolls\". I'll give a very hand-wavey argument: electrons in atoms are not in a specific location but are sort of \"smeared\" out over a region of space. Those regions of space for different energy levels always overlap a little bit. Here comes the sketchy part: if you imagine the electron as actually being a particle in a specific location that just visits places around the atom proportionally to the density of the wavefunction at each location, once in awhile the electron will end up right smack in the middle of the high-density region of a lower-energy wavefunction, realize that it could release a photon and stay there, and do that. ",
"Mathematically, the probability of a transition is related to the energy difference and what we call the \"matrix element\" for the transition, which is basically the overlap of the two wavefunctions. Interpreting quantum mechanics is something that everyone who studies it struggles with, and I don't think anyone has ever truly understood it. So if this sounds totally preposterous and counterintuitive, don't despair. Everyone agrees with you, it's just the way the world works."
] |
[
"One minor nit to an otherwise excellent answer:",
"If the atom is truly isolated from its surroundings, then that emission is a perfectly random event,",
"If it's ",
" isolated, than that emission ",
" happen, as there's nowhere for it to go. Compare with excited states in cavity QED having much higher lifetimes, because the coupling to the rest of the universe is reduced. It is then effectively more isolated from its surroundings. In many ways spontaneous emissions can be thought of as vacuum-fluctuation stimulated emissions."
] |
[
"Has the Earth's surface been completely resurfaced due to the movement of the tectonic plates?"
] |
[
false
] |
From an article I read on Live Science, it was originally thought that the Earths surface could be completely recycled in roughly 2 billion years with more recent estimates showing as little as 500 million years. If this is correct, how is it that we find fossils older than this such as stromatolites which are about 3.5 billion years old?
|
[
"Ok, so I'm guessing you're talking about this ",
"Live Science",
" write up, which is about ",
"Sobolev et al, 2011",
" (",
")? This is a good example of the importance of actually looking at the original source, not the distilled (and often mangled) write up on the original research. If we look at Sobolev, it's clear from the first line of the abstract that what we're talking about here is the timescale of complete recycling of ",
" (i.e., how long it takes for a piece of oceanic crust/lithosphere to be subducted, reincorporated into the mantle, make it to near the core mantle boundary, and then be brought up to the surface and remelted in a mantle plume) ",
" the recycling of all of Earth's surface as implied by at least the clumsy title of the Live Science write up. ",
"For the concept of whole surface recycling, the fundamental chemical and physical differences between ",
"continental crust",
" and ",
"oceanic crust",
" largely precludes this. Oceanic crust can efficiently subduct because it is denser and thinner meaning that the time scale that any bit of oceanic crust exists at the surface of the Earth is relatively limited. In detail, oceanic crust is almost entirely resurfaced in ~200 million years (here resurfacing implies that the oldest oceanic crust in the ocean basins is ~200 million years old at any given time, distinct from the time scale of recycling as discussed by Sobolev). Continental crust generally does not subduct in the same way or at the same scale os oceanic crust, though it can be removed/recycled through a few processes: (1) erosion (i.e. material is eroded off the continent, deposited in the ocean, and subducted), (2) ",
"subduction erosion",
" (i.e.removal of small parts of continental crust by the subducting plate at a subduction zone) and (3) ",
"delamination",
" (i.e. convective removal of thickened parts of continental crust from below). Estimates of the rate of continental loss vs growth have largely been equivocal (i.e. some have suggested net growth, some have suggested net loss, some have suggested close to a balance, etc), for example, here is a recent discussion by ",
"Hawkesworth et al, 2019",
". But on average, we expect (and observe) portions of continental crust to be very long-lived (e.g. ",
"cratons",
") compared to oceanic crust."
] |
[
"It depends on what is on the overriding plate. If the setup was oceanic crust subducting beneath continental crust and then continental crust on the subducting plate encounters continent, then there would be collision and some amount of deformation. If instead the overriding plate was oceanic, then subduction might just cease or there might be a polarity flip where the oceanic crust that was the overriding plate starts to subduct instead. There are important details with regards to the relative velocities and directions of the plates involved, but that's the general set of outcomes."
] |
[
"Thank you so much for the reply. This is a question that I have been curious about for a long time. You are correct about the article I was referring to. I wasn't sure if links were allowed so I opted to leave it out. I know better for next time. ",
"A follow up question, what happens when continental crust reaches a subduction zone? Does it start to slide over the top of the oceanic crust or do the 2 colliding zones start to lift up and form mountains?"
] |
[
"When working out equilibrium constants, why do we multiply the concentrations of the products as opposed to literally any other mathematical operation?"
] |
[
false
] |
I think my question has more to do with a theory of math than anything else. There's a lot of chemistry that I understand. What I don't always understand is the theory of the math behind the application of chemistry (if that makes any sense). I want to understand the reasons why we carry out certain mathematical operations in certain situations (we can start with the equilibrium constants for now). If a clearer picture can be painted, let me use Boyle's Law as an example of what I mean by "theory of math." P(1)V(1)=P(2)V(2) (I don't know how to do subscripts) (4atm)(5L)=(2atm)(10L) In this example I have a gas that decreased in pressure and increased in volume. I understand that for the two sides to equal, the values must change according to Boyle's Law (increase in pressure equals decrease in volume and vice versa). I can understand why we multiply the numbers to represent Boyle's Law as opposed to adding them or dividing them. I can also directly apply this to examples like taking a ball inflated with air and squeezing it. When I squeeze the ball the volume decreases because I increased the pressure (squeezed it). With equilibrium constants, I can't make sense of why we multiply those numbers as opposed to adding, dividing, or even subtracting them. For what it's worth, I recognize that equilibrium constants are a ratio of product to reactant concentrations for the purpose of analyzing how strong an acid is (or how much any reaction goes to completion). I just don't know why those values are multiplied and not added, which makes more sense to me as it stands.
|
[
"The probability of a molecular collision is proportional to the concentrations of both molecules. If the concentration of one goes to zero, then there is zero probability of reaction. One expression which produces this limit is P = k c_a c_b. The expression P = k (c_a + c_b) implies that there is some probability of reaction even when one reactant is not present. "
] |
[
"Isn't that formula",
"\nG = -RT(ln)Q?",
"\nor is that abother one? "
] |
[
"Isn't that formula",
"\nG = -RT(ln)Q?",
"\nor is that abother one? "
] |
[
"Why do conventional spin echo MRI do not seems to have problem of signal saturation like gradient echo with large flip angle?"
] |
[
false
] |
Hello, I am a radiographer and was taking a course in MRI medical imaging. According to the lecturer, the gradient echo sequence was designed to have a short repetition time (TR) to reduce scan time. However, with short TR, there will be signal saturation for each scan cycle due to the low recovery of longitudinal magnetization after each scan cycle. The solution is to use a small flip angle to compensate for the signal saturation. Then, there is a problem that confused me. If what he said was true, then when we do a conventional spin-echo sequence (use 180 degrees RF pulse for echo). Why the signal saturation is not a problem? I asked this question to my lecturer. He answered that "that's why we should not use too short TR even in conventional spin-echo sequence" I thought of an example. By definition, T1 relaxation time is the time required for the -component of to reach ( ) or about 63% of its maximum value (Mo). Let's say I want to do a T1 weighted scan for a muscle with a typical TR time of 800msec. The T1 relaxation time of a muscle is around 900msec. According to the T1 relaxation equation. after each cycle, the longitudinal magnetization will be recovered to 58.9% of its original value. According to this calculation, then, after 10cycle, there will be only 0.5% of magnetization remains? If using 256 phase encoding level. There should be no signal left at the end of the scan? I know there must be a mistake in my thinking. Because it contradicts the real life situation. What mistake did I make here?
|
[
"I don't completely understand your question either. ",
"You are right, if you repeat a spin-echo experiment with a TR<T1 you will eventually saturate the spin system. Maybe it helps to stress that TR is not the same as TE? By choosing TE<T1 but TR>T1 you would get T1 weighted contrast without saturation. ",
"Graph on top right...",
"Does that help?"
] |
[
"Thank you for your reply.\nDoes it mean that despite of textbook usually said spin echo uses 90 degree RF pulse for each cycle. Actually it is not entirely true?",
"Because the formula that i used to calculate the decay of signal only work if the flip angle is 90 degrees. Do you think it is why my calculation of the decay of signal is appearently faster than real life ?"
] |
[
"Thank you for your reply.\nDoes it mean that despite of textbook usually said spin echo uses 90 degree RF pulse for each cycle. Actually it is not entirely true?",
"Because the formula that i used to calculate the decay of signal only work if the flip angle is 90 degrees. Do you think it is why my calculation of the decay of signal is appearently faster than real life ?"
] |
[
"Are there any biological differences between Male and Female hair?"
] |
[
false
] |
I was curious if mens hair has a different make-up over womens hair? If you were to view the hair at a DNA level, would you be able to identify the sex of the person it came from? The reason I ask is because in general, women have longer hair styles and men usually shorter. Is this 100% cultural? And only happens because we are used to these hair styles as the "norms"? Or is there some deeper biology going on that makes humans lean towards certain hairstyles without their knowledge?
|
[
"Yes, there are (relatively small) differences. For example, ",
"trace metals vary between biological male and female populations",
". This is likely not an intrinsic difference, though, as these same traces also vary by geography and cosmetic treatments (that is to say, environmental factors rather than genetic). Also, they are traces of metals, not the main organic structure of the hair. There are maybe some significant (meaning non-negligible) differences in some biomolecule concentrations, such as a higher level of cysteine in male hair, but the general conclusion is that there ",
"\"are no major gender differences in hair fibre structure or physical properties\"",
". Again this presentation emphasizes environmental factors (mostly hair treatments) as being responsible for most major differences observed. So you'd probably be able to get a pretty good guess, but it would be due to the different treatment tendencies, which are cultural rather than biological. There are also differences in scalp needs (seems to suggest males need more treatment for the scalp) to avoid issues like itchiness and dandruff, which may slightly explain the preference for shorter hair in males, but that would mostly be speculation. A cultural explanation is much, much stronger for the hairstyle differences."
] |
[
"What I love most about this sub is getting answers to questions that I never even knew I had."
] |
[
"Honestly, same here. I guess I'm a materials engineer with a background in physics, working in neuroscience. My experience is only just broad enough that I know what to look for, and I enjoy diving into a random interesting topic and seeing what actual research has to say about it. I can't motivate myself to generate random topics myself, so I get to learn something interesting by checking some of the ones posted here."
] |
[
"How does computer fill the CPU registers with the data fetched from the memory?"
] |
[
false
] |
Hi, I want to understand what happens at the hardware/electric circuitry level. For example, how does computer know that this particular 0 bit goes to the X transistor/gate in the register cell A, and that particular 1 bit goes to Y transistor/gate in the register cell B. How does computer organise massive amount of bit/data allocation? I know that memory and CPU are connected via data bus. Is this data bus actually a collection separate wires or one single lane to different parts of CPU? Thanks for your explanation
|
[
"EDIT-1: My undergraduate is in Computer Engineering. Remember, a single BIT (a 1 or 0) is made up of a single flip-flop. A BYTE (say 32 or 64-bits would be a SERIES of flip-flops. A flip-flop can be derived out of (I believe) 4 transistors - depending on the implementation. A 32-bit BUS (in the physical world) would be 32 copper traces running in parallel.",
"----END EDIT-1",
"",
"The DATA bus is pretty much what you described - a series of wires connecting the CPU and the Memory. For simplicity, lets assume only ONE data bus. It will be n-bits wide (today, DDR memory uses a 64-bit bus width, but dual channel memory can make that effectively 128-bits).",
"",
"BUT,",
"The data bus by itself is useless without an ADDRESS bus. In older CPUs, the ADDRESS bus ran along side the DATA bus, but where the DATA bus terminates at the MEMORY (RAM), the ADDRESS buss terminates at the memory controller. Today, the memory controller is on the CPU die - leaving only the DATA bus connecting RAM & CPU.",
"",
"So,",
"When you want to send a BYTE of data from the CPU <--> Memory, a load/store instruction will provide the ADDRESS of that byte (in memory) to the ADDRESS bus. Once the address bus is electrified with the correct memory address (in the form of 1s & 0s), then and ONLY then will the DATA bus connect that PHYSICAL memory address to the destination register in the CPU (data transfer can work BOTH ways, depending on weather you are LOADING or STORING).",
"",
"In summary, every memory cell in RAM, must have a unique physical ADDRESS in order to be accessed. The width of the address bus, thus, dictates the maximum size of RAM a system may use. In older 32-bit CPUs (Windows XP and earlier) the address bus limited RAM to <4GB.",
"",
"As I'm sure some will point out - there are exceptions to these simplifications and other considerations (Physical vs. Virtual) but I believe this answers the crux of your question - as best as I can see.",
"",
"EDIT2: I chose to explain here the concept of the address bus, as it seemed to be the missing-link in your question. I have also left out discussion of CLOCK signals & CACHE - as I believe they are not entirely relavent to explaining the concept of ADDRESS & DATA busses. But, if you care to explore these topics further, this is an excellent source: ",
"https://www.vitalsource.com/products/the-hcs12-9s12-an-introduction-to-software-and-han-way-huang-v1111806640?term=1111806640"
] |
[
"I feel like understanding old analog computers helps with this, because the basic process hasn’t changed in 60 years. When computer programs were holes punched into sheets of paper (each hole representing a 1, each gap representing a 0, or something like that), the order in which they were fed into the processor (logic gates) told the computer what to do. The speed at which the computer could run through the sheet was the processor speed - operations per second.",
"Extrapolating to today, memory still contains 1s and 0s in a very specific order, which when sent via electrical signals to the processor tells the computer what to do. The only real difference is the data is stored on magnetic disks or solid state memory instead of paper, and the processor can handle billions of 1s and 0s each second.",
"That’s about as far as my understanding goes - hopefully helpful, and hopefully someone else can fill in what I’m missing/wrong about."
] |
[
"If your question is how registers that store data are built out of transistors, then look at a Flip-Flop:\n",
"https://en.m.wikipedia.org/wiki/Flip-flop_(electronics)",
"Short answer: Transistors can be used to build AND and NAND gates which can be built to create latches. A flip-flop is two latches connected serially and clocked at half interval to store the value using the clock edge. \nIt is built such that the output never changes until the input changes which in essence is storing the value. ",
"If your question is how data from memory is stored in cpu, the L2 gets data from L3, which gets its data from external disk. \nThen the L2 data is replicated in L1 and then also stored in register banks inside cpu core for faster operations."
] |
[
"Are carbohydrates and hydrocarbons the same thing?"
] |
[
false
] |
They're both fuel, right? If they are the same, why two different names? If they aren't the same, why such similar names?
|
[
"Sugars are not hydrocarbons. Hydrocarbons contain only carbon and hydrogen. Sugars have oxygen."
] |
[
"Gotcha. Thanks."
] |
[
"Both are very general names. ",
"Hydrocarbons contain only carbon and hydrogen. Carbohydrates contain carbon, hydrogen, and oxygen. Both can be very long or very short, depending on the application. They are NOT the same.",
"Both contribute to different fuels. Hydrocarbons make up a majority of gasoline while carbohydrates make up biomass. Both can be used as fuels or precursors to fuels.",
"The names can be perceived as similar - hydro(H)carbon(C) and carbo(C)hydrate(H) seem to describe the same thing. However, a hydrate contains ",
"water or its elements",
", so it's correct to think carbo(C)hydrate(H2O). According to the wiki article, glucose was initially classified as a carbohydrate before its structure, which does not contain H2O, was well-known, though the name is kept the same for \"historical reasons\" (kept the same since it would take a lot more effort to fix it)."
] |
[
"If I were to measure the mass of a particle while dragging it out of a bound system, would I see its mass gradually increase?"
] |
[
false
] |
I've been trying to wrap my head around where the mass lost to mass defect actually comes from. For example, if I were standing (somehow) on a neutron star and lifted a handful of its matter away from the surface, would the individual particles in that handful grow more massive? I understand that the mass of a bound system is less than the sum of its parts, but is that only when the individual parts are measured when they are very far away from each other?
|
[
"Interesting - thanks for the explanation. As a followup, this seems to imply that if I take any collection of atoms (say, a baseball), partition it in any way I want, and measure the mass of each partition separately, the sum of these masses will always be slightly more than the mass of the baseball measured as a whole. Is this effect due to me ignoring the binding energy holding the partitions together when I measure them separately?"
] |
[
"Interesting - thanks for the explanation. As a followup, this seems to imply that if I take any collection of atoms (say, a baseball), partition it in any way I want, and measure the mass of each partition separately, the sum of these masses will always be slightly more than the mass of the baseball measured as a whole. Is this effect due to me ignoring the binding energy holding the partitions together when I measure them separately?"
] |
[
"Ok great, this is starting to make sense. If you don't mind answering one more, I'm a bit confused by what you said about the second law of thermodynamics. If energy is conserved in the bound system (i.e. mass is reduced to account for binding energy), it seems that any configuration is a lowest energy configuration. Why does the system prefer to reduce its mass, and thus stay bound? "
] |
[
"How fast must a superhero move to be \"invisible\" to an observer?"
] |
[
false
] |
Assuming some superhuman was an averagely sized human being (whatever that may be), and they were to run by a criminal and take their gun, replacing it with a banana or some such thing... how fast would they have to be moving for the criminal not to see them if the criminal was looking directly at the gun in their hand? In other words, how fast would something the size of a person need to be moving in order for me not to see it go by? Or would it always just appear as a blur? I just want to know the minimum speed something as large as a person would have to be moving in order to be undetectable to the human eye. What speed would the superhero need to be moving so that no matter what angle they came at me from, I wouldn't be able to see them move?
|
[
"I bet with proper timing you could move a lot slower and still be unnoticed in the short term. During a saccade, you are basically momentarily blind so if you waited to make your move when somebody was moving their eyes you could do it during the brief period of blindness. "
] |
[
"I think the OP is mostly asking about the limits of human vision IE: some things happen to quickly for us to perceive. I'm willing to bet that you'd need to move more on the order of hundreds of miles per hour vs. any significant fraction of the speed of light. "
] |
[
"I think the OP is mostly asking about the limits of human vision IE: some things happen to quickly for us to perceive. I'm willing to bet that you'd need to move more on the order of hundreds of miles per hour vs. any significant fraction of the speed of light. "
] |
[
"Why does LED glow brighter in Liquid Nitrogen but only for a moment?"
] |
[
false
] |
Seeking input from some LED experts... We were fooling around with some liquid nitrogen at work and noticed when we submerged a red LED, the brightness increased dramatically but only until a certain point. Once the bulb cooled to (seemingly) the same temp as the LN2 (-320F), its brightness dropped off. I'm including a video for your reference. You can see that once the bulb is pulled from the LN2, it's brightness begins to increase once again. There's plenty of experiments detailing how the color changes, but none seem to mention brightness. We know that there is far less resistance when items are cooled so brightness would increase. Can anyone explain why the brightness decreases once the bulb is sufficiently cooled? VIDEO: Thanks!
|
[
"First you made a faulty assumption. That all objects have less resistance as the temperature decreases. Semiconductors don't do this. They have less resistance at higher temperatures. This is because at higher temperatures more charge carriers go from the valence band to the conduction band because they have more energy. It's an exponential relationship. The current is proportional to",
"e",
" - 1",
"http://pveducation.org/pvcdrom/pn-junction/diode-equation",
"http://www.cliftonlaboratories.com/1n400x_diode_family_forward_voltage.htm#Forward_Drop_versus_Temperature_and_Current",
"http://www.isb.ac.th/HS/JoP/vol4iss1/Papers/1LEDTemp.pdf",
"OK, so what are we seeing? Notice the color of the LED changes form red to yellow. As the LED cools, the crystal shrinks and that changes the band gap which changes the color. Human eyes are more sensitive to yellow so this is probably part of the reason it appears brighter even though its intensity might decrease. Eventually it gets so cold that the current drops enough that it appears dimmer.",
"http://www.ecse.rpiscrews.us/~schubert/Reprints/2005%20Chhajed%20et%20al%20%28SPIE%20Photonics%20West%29%20Junction%20temperature%20in%20LEDs.pdf"
] |
[
"My mistake! Thanks for your input and for citing your sources! "
] |
[
"As ",
"/u/FoolishChemist",
" notes, resistance of materials does not always decrease with lower temperatures. ",
"Depending on the material, and the range of temperatures of interest",
", it can increase, decrease, or stay the same. Various thermistors are engineered to have different thermal coefficients for various applications, and high-precision, temperature-stable electronics are often designed to have a very low thermal coefficient.",
"That all aside, in general, most intrinsic semiconductors will have increasing resistance as temperature decreases. Which doesn't matter, nor does it fully answer your question.",
"An LED is a diode (a light-emitting one, as it were). This means it obeys the ",
"diode law",
". The Vth term drops with decreasing temperature, allowing Vd / Vth to get big, and bigger still when you take the exponential e^(Vd / Vth). So, if it follows that equation, why doesn't it just get brighter and brighter the lower the temperature?",
"It's an idealized equation that assumes sufficient charge carriers to move charge across the junction. Implicit in the previous paragraph is the idea that the higher the current, the higher the light output. When electrons go one direction, and (positive) holes travel the opposite direction, they'll annihilate and, in the case of an LED, release some light. ",
"The charge carrier density is ",
" a function of temperature",
"--generally for most semiconductors, the lower the temperature, the lower the number of charge carriers available, and the lower the rate of recombination / annihilation, and the lower the light output.",
"So, for moderately-low temperatures, the first effect dominates for a while and increases the light output. But past a certain point (which you've run into with your red LEDs and liquid nitrogen), the second effect dominates, causing a lowering of light output."
] |
[
"How do anglerfish pass down the bioluminescent bacteria they use to their offspring?"
] |
[
false
] |
I know that most female anglerfish use bioluminescence to attract pray. But how does it get passed down? Is it already present in the sperm/egg?
|
[
"This article here says that the bacteria are leaked from the parents, presumably near the eggs, so it's a form of vertical transmission even if it's not directly through the gametes: ",
"http://bio390parasitology.blogspot.com/2012/03/normal-0-false-false-false.html",
"'",
"There's some good other sources at the bottom, too. edge000 is right in that it's much like ",
" and the Hawaiian bobtail squid. Love that guy :D",
"In plants, there's plenty of cases of microbes being passed on directly through the gametes though. A lot of grasses have fungal endophytes that live inside them, helping to make compounds that herbivores like cattle don't like to eat. They're all passed through the seeds. Most plants have endophytes, but they are usually acquired through the environment once the plants are established. \nMore on grasses and endophytes: ",
"http://microbewiki.kenyon.edu/index.php/Grasses_and_endophytic_fungi"
] |
[
"Ah.. dang, I can't believe I forgot about endophytic fungi. One of my advisors in grad school would be highly disappointed in me right now. I did some work extracting alkaloids from various ergot alkaloid producing fungi.",
"Sometimes people (microbiologists included) fall into the trap of thinking only bacteria in regards to microbes or being animal centric. ",
"A cohort of mine actually worked with a symbiotic relationship between a fungus and a species bacteria that reside in the spores, and were required for the sexual phase. I can't remember the species involved off the top of my head at the moment. "
] |
[
"Check the article I linked, it talks about that, and the comment by ScienceIsMetal below touches on it too. "
] |
[
"Why doesn't a black hole violate the laws of thermodynamics?"
] |
[
false
] |
It seems to me that a black hole decreases the system's and universe's entropy. This is because when matter is confined to one specific region, the total number of microstates decreases dramatically.
|
[
"The entropy of a black hole is proportional to the surface area. In fact, a black hole packs the most entropy that an object can have.",
"One way to think about this is to realize that black holes in general relativity are completely characterized by their mass, spin, and charge. Thus there is a huge collection of initial states that can culminate in equivalent black holes."
] |
[
"gravity beats out the Pauli Exclusion Principle when mass is sufficiently high.",
"I am not sure what you mean by this. The exclusion principle always holds."
] |
[
"I think you have a bit of a misunderstanding.",
"There is a degeneracy pressure associated with the exclusion principle, as you note. As a conventional star collapses, there comes a point at which the exclusion principle for electrons does not allow further collapse, as long as the atoms stay as atoms.",
"If the gravitational effect is strong enough, however, it can become feasible for nuclear reactions (so-called ",
") to occur, in which electrons and protons interact and become neutrons and neutrinos. Thus, it is not that gravity beats the exclusion principle, but that gravity induces nuclear reactions which cause the electrons to disappear, and thus there is no electron degeneracy pressure preventing further collapse at this point.",
"However, the neutrons are also fermions, so they, too, follow the exclusion principle. Thus, after these nuclear reactions produce a neutron star, that neutron star can only collapse so far until the exclusion principle applied to the neutrons prevents further collapse.",
"But I would never call this \"gravity beating the exclusion principle,\" as the exclusion principle always holds. After all, if gravity truly beat the exclusion principle, you wouldn't need to have nuclear reactions to get past the limit imposed by electron degeneracy pressure."
] |
[
"How exactly are enzymes produced?"
] |
[
false
] |
In my bio class, we learned that our bodies produce specific enzymes for different disaccharides. How does this happen? Do we have cells that manufacture them? Also, why exactly do our bodies produce some enzymes always and not others (we usually stop producing lactase by the time we're adults)? You would think that we could use all the energy-rich molecules we can get.
|
[
"Do we have cells that manufacture them?",
"Believe it or not, you are asking about something called ",
"The central Dogma",
" of molecular biology. It is ",
" important.",
"All cell have a \"machine\" (itself an enzyme (well a whole complex factory of enzymes actually)) that is in charge of translating your genetic code into the enzymes you need (because that's what one of the thing your DNA does, code for enzymes that are useful to your body). The machine is called a ",
"ribosome",
". It acts by turning a \"replica\" of sorts of your DNA (the famed mRNA, ",
"messenger RNA",
") into an amino acid chain by using this ",
"code",
"Also, why exactly do our bodies produce some enzymes always and not others",
"Actually, this is related to ",
"gene expression",
". ",
"Another thing our DNA has is sites that either promote or supress expression of some genes. As your body develops, matures, the rates of promotions and expression get tweaked (telomeres, reproduction errors, hormones, all of which affected by environmental factors too). In turns you produce different enzymes, and your metabolism changes accordingly.",
"There are other mechanism of regulation of gene expression besides the (very short) nibblet about translational gene expression I just mentionned. You can start ",
"here",
". ",
"The rabbit hole can get ",
" deep...this is amazing stuff."
] |
[
"Generally speaking, enzymes are coded for the same way other proteins in our body are: DNA is transcribed into mRNA, which is then translated into the enzyme. Each cell produces its own enzymes (in general; this is biology, so someone will probably come along with some exceptions), and different tissues will produce different metabolic enzymes according to their particular functions, needs, and characteristics. At one end, your liver has pretty much every metabolic enzyme, while on the other end, red blood cells can only perform glycolysis. ",
"For lactase in particular, before we started drinking animal milk, the only time we encountered lactose was as an infant or small child drinking breast milk. There was no reason to keep producing an enzyme that we were never using as adults; it was a waste of energy. We're actually unusual because many of us can metabolize lactose as adults; most mammals don't produce much or any lactase after weaning."
] |
[
"Enzymes are proteins, and are manufactured by ribosomes attached to the endoplasmic reticulum (ER.) Many enzymes are holoenzymes, and additionally contain non-protein elements like inorganic ions or specialized catalytic RNA. ",
"I'm sure you know that proteins are composed of amino acids (methionine, serine, tryptophan, et cetera.) Ribosomes assemble the basic polypeptide chain (translation), which is then \"folded\" into a proper shape by chaperone proteins. Depending on the type of protein, additional folding or modification may take place in the ER or Golgi complex. ",
"Mammals in the wild don't consume milk past infancy. From an evolutionary standpoint, it is a huge waste of energy to produce lactase after age 1 or so, since you shouldn't be consuming milk anyways."
] |
[
"We have Einstein's brain preserved in formaldehyde. Are all the synapses still wired up the same as when he was alive? Could some future civilization recreate a form of Einstein from this?"
] |
[
false
] | null |
[
"Recreating a working brain from a preserved specimen would be entirely speculative. We have no idea if something like that is possible.",
"As for Einstein's brain, you may not realize that it was dissected and cut into 240 small cubes of about one cubic centimeter each, then the pieces were distributed to researchers. I seem to recall that some of the pieces went missing also. So the brain isn't intact. Even if it could somehow be made to work again, it would have to be reassembled first, which at this point is unlikely."
] |
[
"There's a 1994 documentary following Kenji Sugimoto as he searches for Einstein's brain. Though it's been disputed how truthful it is, it shows the brain did go missing and was stored in formaldehyde in three jars.",
"It's ",
"available on YouTube",
" and there's more info ",
"on Wikipedia",
" (mild spoilers)."
] |
[
"They recently found pictures and a lot of the missing autopsy data on it"
] |
[
"What would be a commercially viable way of triggering neurons?"
] |
[
false
] | null |
[
"Individual neurons? There is no commercially viable way. You can stimulate a large chunk of the brain with TMS or tDCS or other variants. Those methods are comparatively cheap."
] |
[
"Yes. But zapping an entire lobe does not have a targeted effect. If you stimulate occipital cortex for example, people see phosphenes which are flashes of light. But there is no way to stimulate a particular subset of cells to have someone see a cat, say"
] |
[
"I wasn't quite fair - TMS is a bit more targeted than tDCS, but it's still stimulating tens of thousands of neurons. If applied over motor cortex, you can get specific limbs to twitch. But they will actually move without you feeling like you caused them to move, so sort of the opposite of what you describe. ",
"Also, not that while there is something called repeated TMS (rTMS), generally you do not want to be applying too much stimulation over a prolonged period of time."
] |
[
"Do freely floating objects within the International Space Station gravitate towards the side of the ISS facing the Earth?"
] |
[
false
] |
[deleted]
|
[
"This quesiton is answered by ",
"Wikipedia:International Space Station#Microgravity",
", which is fairly complete and well-referenced. Even if the station were in a perfect, constant orbit, the tennis ball would still move around in the station due to the Earth's gravity. This is the tidal force, and it doesn't necessarily point towards the Earth. Instead, it looks more like ",
"this diagram",
".",
"Any part of the ISS not at the exact center of mass will tend to follow its own orbit. That is, parts on the underside, closer to the Earth are pulled harder, towards the Earth. Conversely, parts on the top of the station, further from Earth, try to fling off into space."
] |
[
"Unless the magic treated the ISS as its default reference frame.",
"Seriously, magic fucks everything up."
] |
[
"I deleted my answer because I forgot to consider tidal forces, so my explanation was sort of inaccurate. ;)",
"Didn't want to mislead anyone. Pretty sure Melchoir upstairs nailed it."
] |
[
"How does the body get Cl to synthesize HCl?"
] |
[
false
] | null |
[
"HCl is produced by the parietal cells of the stomach. To begin with, water (H2O) and carbon dioxide (CO2) combine within the parietal cell cytoplasm to produce carbonic acid (H2CO3). An enzyme called carbonic anhydrase converts carbonic acid into its component ions a hydrogen ion (H+) and a bicarbonate ion (HCO3–).",
"The bicarbonate ion is transported out of the cell into the blood via a transporter protein called anion exchanger which transports the bicarbonate ion out the cell in exchange for a chloride ion (Cl–). This chloride ion is then transported into the stomach lumen via a chloride channel.",
"Prior to this, the hydrogen ion that was formed via the splitting of carbonic acid is transported into the stomach lumen via the H+– K+ ATPase. This channel uses ATP energy to exchange potassium ions in the stomach with hydrogen ions in the parietal cell.",
"This results in both hydrogen and chloride ions being present within the stomach lumen. Their opposing charges leads to them associating with each other to form hydrochloric acid (HCl)."
] |
[
"While this is very in-depth description of how HCl is formed in the body the question may have also been 'how does Cl get into the body' in which case the answer is food! Salt (NaCl) being the obvious one but probably other things as well."
] |
[
"My original answer was legit going to just be “salt” but then I figured someone would have just written what I wrote above.",
"You cannot win.",
"I cannot win*"
] |
[
"If light is shined directly into a mirror, it reflects back. How does it change direction without ever slowing down?"
] |
[
false
] |
The speed of light is constant and never changes, but when an object hits a surface and redirects, its velocity slows to zero and it reverses direction as the surface exerts a force on this. Shouldn't photons behave the same way? Does it have to do with the fact that photons are massless? Or is it something to do with the fact that light have wavelike properties?
|
[
"I'm having difficulty wrapping my head around how the direction can change 180 degrees without slowing too a stop and then speeding up again.",
"It's two separate photons, and it's not instantaneous."
] |
[
"...when an object hits a surface and redirects, its velocity slows to zero and it reverses direction as the surface exerts a force on this.",
"Light cannot accelerate, so this never happens. If you do wish to view light as particles - i.e., photons - then the mirror absorbs the incident photon. The mirror then emits a photon which you see as the \"reflected light\".",
"This is the reason it's helpful to view light as a wave in some context."
] |
[
"It might help to think of reflecting light as a wave and simply to picture a more ordinary wave reflecting:",
"Consider a rope tied to the wall, flick it and a wave travels: the crests will move at a constant speed (depending only on tension and mass of the rope), moving into the wall and away from the wall at the same speed. The leading edge of the crest has already turned around before the trailing edge has hit the wall. ",
"I'm finding this hard to explain without a picture. Try watching this:\n",
"http://phet.colorado.edu/sims/wave-on-a-string/wave-on-a-string_en.html",
"\nFirst, turn off the damping, and slow it down with the tension slider. At the bottom, select and send a pulse and watch it turn around. Set the right end to 'free' and you'll see the pulse comes back in phase, keep it 'fixed' and it changes phase. Both of these circumstances happen in light (depending on the relative index of refraction of the materials involved).",
"Mainly, note how it's different from bouncing!"
] |
[
"How would you refute Bostroms idea of a simulated reality?"
] |
[
false
] | null |
[
"This is more of a philosophy question as the nature of the conjecture: \"what if this were all a simulation?\", is unprovable. ",
"That said there are a couple of rejoinders that may more may not constitue a complete argument against.",
"1) in Bertrand Russell's 'problems of philosophy' he talks about an earlier incarnation of this idea. Namely; \"what if the world isn't real and you are actually a brain in a jar being fed simulated sensory input that is indistinguishable from real sensory input?' Russell's come back is that it could well be true that everything is a simulation but if you have no means of proving it either way then there is really no further discussion you can have about it. Even if it were actually true the nature of the system is such that from where we are with the information we can access we have no choice but to continue on as though everything is real an isn't a simulation. Then there is the whole Russell's teapot thing; many statements about the universe could indeed be true but there's little point in entertaining too many of them until we have some evidence for their truth.",
"2) next there is a generalised computational problem, a simulation of the universe will likely need to be running on a machine more complex than the universe itself. This seems somewhat absurd. A much more parsimonious explanation is that the universe, it's particles and their interactions are real and are actually happening. Then to explain the existance of the universe we only have to call in to existance an object as complex as the universe (i.e. the universe itself). Or to put it more glibly the universe is a device which runs a real time simulation of the universe.",
"3) also a simulated universe utterly begs the question about the nature of the universe. If we are interested in what the universe is and where it came from then stating it is a simulation merely begs the question about what is the nature and origin of this new higher order space that contains the computer running the simulation.",
"For me discussions about 'what if this is all a simulation, dude?' Are among the least useful or interesting stoner/intro philosophy questions."
] |
[
"He does not just say 'what if', but uses some (very wild) guesses for arriving at some probabilities. These guesses are not his own, but instead based on some other papers [1]. His original paper with all the sources can be found ",
"here",
". I think there are a ton of problems with his argument, but for most of them I don't actually know whether they weaken or reinforce his argument.",
"[1] These guesses are really wild, because they are about wild things. How much computation can matter perform in general? How much computational power do you need to simulate earth to a \"good enough\" degree if your simulation-program is very sophisticated? Man, these are really tough questions and accordingly their answers are to be taken with a grain of salt."
] |
[
"He essentially deeply underestimates the amount of computing power you would need to simulate an environment such that simulated human minds won't 'notice any irregularities'"
] |
[
"Why would an un-vaccinated kid be a threat to a vaccinated kid?"
] |
[
false
] |
[deleted]
|
[
"It doesn't (ideally). It is a threat to other unvaccinated kids (especially those who can't be vaccinated for medical reasons) as well as - more importantly - those where the vaccination doesn't provide immunity (vaccines are known to be imperfect).",
"edit: unclosed braces"
] |
[
"See ",
"herd immunity",
" for more about population-level protection from immunity (and why having too many un-vaccinated kids is bad)."
] |
[
"Plus exposing the vaccinated population to many of the live virus allows a greater opportunity for the viral population to take advantage of selection pressure to overcome the body's defenses. Every time you explosive a population to a new potential resource you open the possibility of it developing a way to utilize it, and when that population is billions in number with generation times on the order if minutes, and high genetic variability it won't take long before people who are immune to the old strain aren't immune to the new one. "
] |
[
"If mosquitoes were to go extinct, what would be the negative repercussions (if any)?"
] |
[
false
] |
This question might be better phrased as: what benefit do mosquitoes bring to their eco-systems, other species and the planet as a whole? Assuming some kind of destructive ecological genie were to appear and grant me a wish of one species to wipe off the planet, what reasons should I take into account for choosing mosquitoes? How severely would such an extinction negatively impact eco-systems? Would there be any other repercussions? And (I hope this isn't getting too speculative) might they potentially outweigh the benefits of removing the single vector for Malaria?
|
[
"Assuming some kind of destructive ecological genie were to appear and grant me a wish of one species to wipe off the planet, what reasons should I take into account for not choosing mosquitoes? How severely would such an extinction negatively impact eco-systems? Would there be any other repercussions?",
"Mosquitos are a vital species in the ecosystems they inhabit, at least from a biocentric perspective. The malaria parasite has a number of dead end hosts. If an ecosystem has enough non-human vertebrates, malaria can not become endemic in a region, because the malaria parasite is too likely to end up in a species in which it can not replicate itself. ",
"If an ecosystem has a human population density below 5 people per km and enough non-human vertebrates, the malaria parasite can not establish itself there.",
" This may not be particularly great news for any humans who wish for the human population to grow at the cost of their local ecosystem, but for the non-human species who inhabit these regions where malaria is endemic, it is great news.",
"Now, more importantly, if we know that human population density is restrained by the malaria parasite, we could expect a similar phenomenon to occur in other species. There are four different Plasmodium species that are known to infect rodents. One of these is Plasmodium Berghei. The mosquito ",
"Anopheles Dureni",
" feeds exclusively on rodents, especially Thamnomys surdaster. It transmits Plasmodium Berghei between these rodents. ",
"It's also known that strong interspecific competition occurs between different species of mosquito in the Aedes genus.",
" Thus, if we were to get rid of the species of mosquito that pose a nuisance to humans, we could expect their place to be filled by species that pose a nuisance to non-human vertebrates, affecting their population number.",
"Indirectly this would end up affecting humans, because rodent species diversity through the dillution effect prevents diseases from gaining a foothold in these animals. ",
"When humans disturb a habitat, rodents that harbor hemorrhagic viruses tend to spread rapidly.",
"In conclusion, the mosquito has the effect of controling the population numbers of a variety of vertebrate species, increasing vertebrate biodiversity as a result. Because mosquitos, especially their larvae, are in competition with one another, other species may end up filling the niche currently occupied by species that prey on humans. This could affect the biodiversity of the species preyed on by these other mosquitos, which would end up affecting humans too."
] |
[
"Great answer, thank you! I will take all of this information under consideration in my negotiations with the ecological genie."
] |
[
"You also haven't mentioned a number of organisms that regularly feed on mosquitoes and mosquito larvae, such as frogs and dragon flies. "
] |
[
"If I stick two identical magnets together, do their powers combine into a single magnet that's twice as strong?"
] |
[
false
] |
I was just playing with some magnets this afternoon and I wondered... EDIT: Thanks to everyone for your interesting and detailed answers!
|
[
"In the ideal situation, the resulting magnet is just as strong as the ones you began with, not twice as strong.\nThe way a magnet works is with dipoles. Every atom has a cloud of electrons that is normally centered around the nucleus. Try to think of it as a group of people, where everyone is holding a balloon. What happens in a magnet is that everyone holds their balloon to the left of them. If you look somewhere in the middle, there still is one balloon per person, and there is no actual effect. However, if you look at the right side, you'll see a lot of balloons, in front of the people. At the left side you'll see only people, standing in front of their balloon. Now the side of the balloons is North, and the side of the people is South.",
"If you take two groups of these people and put them together, north to south, you'll see that the groups merge. Where there used to be a north and south pole, they have \"clicked\" together to form more of the neutral middle part. You just end up with a magnet as strong as the first one, but twice as long.",
"If you want a stronger magnet, you can try to stack the two magnets on top of each other, so you get the two fronts of \"balloons\" next to each other. However, this will cost you a lot of effort, as one north pole will push away the other.\nThis kinda makes sense: To create a stronger magnet, we need to put some effort into it. It doesn't just get stronger by itself."
] |
[
"I'm just trying to fill in some cracks. Calculating the actual magnetic field of a magnet is complicated, though from far away a bar or disk magnet is always going to approximate a dipole, because it has a North and a South pole. A simplifying fact that you can use is that an observable magnetic field is only generated by the parts of the magnet where the magnetic moments point out of the surface, i.e. at the poles. Everywhere else in the magnet, the tiny spins that make up the magnetization are canceled out, the North end of one spin is right next to the South end of the adjacent spin.",
"if you have a bar magnet, you really only have to think about the two poles. Now it isn't hard to see how to make the largest possible field. The closer the South end is to the North end, the weaker the field will be, so an semi-infinite magnet, or maybe just really long magnet, will give you just the North or the South field with very small cancellation fields from the South end. It is also easy to see that if you want to double up the North and South end to make them work WITH each other, you can make a new geometry, and have the magnet wrap around into a doughnut with a small gap in the middle.",
"So back to the magnets that you're playing around with, if you simply stick two together the field is not twice as strong immediately next to the magnet, but you've made the magnet longer, so the poles are farther apart and the field near each pole is stronger.",
"An important point though is that if you look from far away (probably several times farther away from the magnet than the size of the magnet), both the single magnet and the two magnets look like a magnetic dipole. And when you stick the two magnets together you double the dipole moment, and thus exactly double the field."
] |
[
"If you have a gram scale (like one of those digital ones that people use to weigh small amounts of food) and those neodymium magnets you can directly measure the force by taping a magnet down to the scale and then holding the magnets you want to test a known distance away."
] |
[
"Why does the metal from meteorites have such a distinctive zig-zag pattern?"
] |
[
false
] |
Like this: or this:
|
[
"That pattern, called a ",
"Widmanstatten pattern",
" is due to the crystallization of iron and nickel minerals in the meteorite cooling very slowly. Here, 'very slowly' means a few hundred or thousand degrees C every ",
". This slow cooling allows for large crystals of these minerals to form. They are actually interlaced crystals of two different alloys of iron and nickel. One type basically grows within the other type. ",
"Here's an excellent review that explains the formation",
".",
"The patterns are visible when meteorites are cut, polished, and etched using nitric acid or ferric chloride. These chemicals dissolve different minerals at different rates so you can eat away at one of the alloys more than the other, giving contrast to the two regions. "
] |
[
"Why do they cool down so slowly?",
"Things in space cool down slowly because there isn't any air or water to transport away their heat. They lose all of their heat through thermal radiation, which is a very slow process. That's how Thermos vacuum insulation works too."
] |
[
"So a meteorite stays hot for hundreds of thausand of years after being expelled from its source planet? Why do they cool down so slowly? "
] |
[
"How much bacteria can you kill by simply washing your hands with hot water...and not seriously burn yourself?"
] |
[
false
] |
No soap is allowed. Just really hot water. Some pain is okay, but no actual burns can result from the process. Also, a side question: would it be better to wash your hands for a short time under extremely hot water, or a longer period of time under slightly cooler water?
|
[
"Hand washing doesn't kill bacteria, it removes bacteria.",
"I did a study in a college biology class, and hand washing without soap was as effective at bacteria removal as washing with soap.",
"Temperature of water made no difference either. Cold was as effective as hot water.",
"The key is the mechanical action of rubbing hands together under running water.",
"There are factors that could change the results. For example, if your hands are covered in grease, or oil, then using soaps, and hot water definitely improves results.",
"As to your specific question, there are established \"kill curves\" for temperature vs time to kill bacteria. The hotter the temperature, the less time it takes to kill the bacteria. These curves are used for determining autoclave cycle times etc.",
"Anyway, wash your hands under running water, and rub vigorously. That's the key."
] |
[
"You can't kill any bacteria. You would need to use water hot enough to burn your hands. Some might be mechanicaly removed into the sink but many would be stuck in fats, oils, and proteins.",
"would it be better to wash your hands for a short time under extremely hot water, or a longer period of time under slightly cooler water?",
"With soap a longer period of time under cold water would be prefered. In fact water temperature while washing with soap has no notable effect on bacterial content.\n",
"source",
"Without soap I'm not sure. A much longer time under cold water will allow more friction at rubbing away the pathogens, but the slightly warmer water for only a slightly shorter time might help dissolve a few lipids which would otherwise remain."
] |
[
"Soap kills some viruses. So it's not completely useless, even if what you said is true."
] |
[
"Can diploid cells discriminate between which gene copy they will transcript?"
] |
[
false
] |
So, diploid organisms have two copies of each chromosome, and thus two copies of every gene (save for allosomes). Can a cell selectively express just one of those copies, or is it always indiscriminate? EDIT: Instead of express, I just mean transcript.
|
[
"In the case of ",
"genomic imprinting",
" they sure can, but otherwise I think its more depenedent on the strength of the promoter in each allele and stuff.."
] |
[
"Yes, but the title and your question are slightly different. Expression refers to the entire process from transcription to the end protein product. Various mechanisms exist to control expression at different levels, one of which is ",
"transcriptional control",
".",
"If, for example, one chromosome has a promoter sequence in front of the gene, and the other doesn't, then only the first chromosome will be transcribed. "
] |
[
"In most cases, both copies will be transcribed (unless there are mutations in the promoters or transcription factors, as already mentioned). This is why people who carry traits (such as sickle cell) will have a population of normal protein and a population of abnormal protein."
] |
[
"If you take the total amount of land mass above sea-level, is it equal to the total amount of sea water?"
] |
[
false
] |
If you remove all water from Earth, can you fill in all of the oceans up to sea-level with the earth above sea-level?
|
[
"Nope! Take a looks at wikipedia's article on ",
"elevation",
", which describes how the average elevation of all of the land is around 0.8km, whereas the average depth of the oceans is 3.7km. Since the oceans comprise about 71% of the Earth's surface, (approximate 2.4:1 ratio of ocean to land), we can estimate that if all the land above sea level were put move to the bottom of the ocean, the average ocean depth would decrease by only 0.33km (to ~3.4km). ",
"I am now really interested in what the average elevation of the entire planet is... "
] |
[
"Supplementary question- if you flattened all the land so there were no continents, just a flat planet with shallow ocean everywhere on top of a single continuous continental plate, would plate tectonics be halted or would the continents be re-establish themselves after a few hundred thousand years?"
] |
[
"Even if we could move all the land to fill in the oceans, the earth would simply be covered by water of the same depth, unless we also moved all the water elsewhere, in which case let's skip flattening the land...",
"edit: just caught first part of OP's post. If we were going to remove the water anyway, we could still flatten the land..."
] |
[
"Why does our voice sound different immediately after waking up and what makes it return to normal?"
] |
[
false
] | null |
[
"You can find the basic answer with a simple Google search / on wiki. Please start there and come back with a more specific question."
] |
[
"I can re-ask/re-submit my question reworded without being banned?"
] |
[
"For sure! We just encourage everyone to check the FAQ, search past posts, or do a quick search online before making a post. We've got some instructions in the sidebar."
] |
[
"Owls have asymmetrically placed ears so that they can judge vertical as well as horizontal displacement. My eyes are on the horizontal but I seem to be able judge height reasonably well. In what ways does my brain compensate for my visual deficiency?"
] |
[
false
] | null |
[
"Edit: Misinterpreted OP's question. ",
"Real answer here",
".",
"The outer part of your ear (the pinna) has a contorted surface that reflects sound in different ways depending on which direction it's coming from. Your brain is able to use this information to help localize sound sources. ",
"There was an experiment done recently in which the subjects put on artificial pinnas (think Spock ears) and they lost their ability to localize sounds in the vertical dimension for a few days, but eventually they adapted to the new pinnas and regained that ability. "
] |
[
"Wow, that was my poor reading comprehension at fault, then. Sorry about that.",
"Your eyes can distinguish height well because the lens of your eye projects the light coming into it right onto your retina, in a layout that's the reverse of what's happening in the world. So what the retina (the field of light-sensitive nerve cells on the back wall of your eyeball) transmits to the early visual processors in your brain is a point-for-point reflection (with some distortion) of the picture coming in through your eye lens. ",
"In short, your eyes represent the vertical dimension well because light from the world falls onto a 2-dimensional surface on the back of your eyeball. That allows it to transmit the vertical as well as the horizontal layout of what you're seeing down the optic nerve to your brain."
] |
[
"I often think I'm getting more stupid and this just proves it. How did I forget how eyes work?",
"Thanks for explaining."
] |
[
"[Physics] Is our perception of elapsed time, since the Big Bang, different than that of another planet traveling at a lesser velocity?"
] |
[
false
] |
Since your perception of time changes with velocity, would our figure of 13.5 billion years since the Big Bang be invalid on another planet traveling half the velocity than our own Earth?
|
[
"One of the postulates of special relativity and thus general relativity is that light has constant velocity in all reference frames (in a vacuum)."
] |
[
"Remember that it is relative. To the other planet and ourselves, time is \"normal\", you both count time \"correctly\". They can't be travelling half our speed because we are stationary. If you said they are travelling half our speed ",
" to the galactic centre for example, then it makes sense. You could also say they are moving past us with a relative velocity of x, this allows you to make the calculation for how you both account for time. ",
"In reference to the big bang, it is a truly simultaneous event. Their accounting of the age of the universe since that time might be 12 billion years compared to our 13.5 BUT another random planet might say it's only been 7 billion. It depends on who you ask AND who you compare them to. Our accounting of 13 billion is just as correct as their 7(compared to us), neither is invalid. "
] |
[
"The universe isn't expanding away from any particular point in space. Space itself is expanding, meaning that everywhere appears to be \"expanding away from\" everywhere else (on a greater than inter-galactic scale)."
] |
[
"Are stars in different locations than we perceive?"
] |
[
false
] |
I was listening to a podcast and it got me thinking, how much does gravity effect starlight? Is our perception of a stars location altered by gravity?
|
[
"Usually, gravitational lensing is pretty weak. If two stars happen to line up, then the background star will be magnified, but only for the short period while the star passes in front.",
"Galaxies have stronger lensing, but this is usually still considered \"weak lensing\". They slightly twist the shape of background galaxies around them, but we can only detect this using statistical methods over a large sample.",
"However, some galaxy ",
" or extremely massive galaxies are massive enough to cause \"strong lensing\". Here we can see background stars and galaxies getting hugely stretched around by the mass of the foreground cluster. You can see a great example ",
"here",
", where a background galaxy has been stretched into a ring shape by gravitational lensing from a foreground galaxy.",
"Of course, the other thing is that light takes time to reach us, so we're seeing stars as they were some time in the past, which also means they're currently in a different location than we perceive them to be."
] |
[
"thousands of miles per second",
"21.6 km/s, and it's travelling roughly towards us, so it's not at a massively different position in the sky than it appears to be."
] |
[
"Wow thanks for your reply! That picture is cool, it always blows my mind how the galaxies look like stars sometimes."
] |
[
"How does the immune system \"remember\" pathogens it has previously encountered?"
] |
[
false
] |
From my understanding of vaccines, the body is exposed to weak versions of a virus or the like and then the immune system after being exposed to it and successfully dealing with the infection will then "remember" this particular strain. How does the immune system remember? Is there a finite amount of memory space? Like can the body only deal with X amount of illness at a time?
|
[
"So you basically have two parts to your immune system. When you first encounter a pathogen your innate immune system is the first to respond. The innate response is non-specific but fast acting, more importantly it is involved with activating the adaptive immune response. The adaptive response is basically the opposite of the innate, it is very specific to the invading pathogen but it takes awhile to initiate.",
"Dendritic cells are the bridge between the two systems. They basically engulf the pathogen, chew it up, then present parts of it to cells in the adaptive system like your T and B cells. The reason the adaptive cells are so specific is pretty complicated but it involves creating thousands of B and T cells all with different receptors and testing whether those receptors are specific for the pathogen that the dendritic cell is presenting. If they are not specific they die which is most of them. If they are specific then they proliferate into either memory cells or effector cells.",
"The effector cells are the ones that combat your illness. The memory cells purpose is to just exist with those specific receptors. They receive survival signals to stay alive and circulate throughout you bloodstream and lymphnodes. If you encounter that pathogen again you might not even realize you are sick because those memory cells with the specific pathogen receptors activate much more quickly than the first time and defeat the infection.",
"There certainly would be a finite amount of memory space but it would be so large you wouldn't reach it in your lifetime. The body can deal with multiple infections at the same time but how many is completely dependent on the types of infections and whether they can overwhelm your bodies immune system."
] |
[
"This is a great answer, however, I am interested in why you think there is finite memory space in the adaptive immune system? I certainly agree that if there was, we would never be able to reach the limit (and thus we cant really test this fact) and our bodies ability to defend itself has much more to do with how many pathogens we are dealing with a one time and how virulent they are.",
"I am simply curious, do you think there is a finite amount of B and T cells we can make? and that the lymphocyte progenitor pool would become exhausted over many exposures?"
] |
[
"The research into antibody diversification is still a very new field but current estimates place the immunoglobulin repertoire (total number of antibody specificities available) at around 10",
" and most people think it is even higher. That is an insanely high number generated from somatic recombination of the genes, but largely from random mutation like somatic hypermutation. There are other diversification methods of course though. ",
"When I claimed a memory limit I did not mean it in the sense that the body can only produce so many cells. The lymphocyte progenitor pool arises from multipotent progenitors that is not exhaustive. I meant in the very scientifically lazy sense that antigen memory is stored as cells and so there would have to be some physical limit. You can't have an infinite number of memory cells at one time so some upper limit exists. Since I have never heard of this discussed once in my immunology education or read about it since, I assume that it is simply high enough that it isn't relevant. "
] |
[
"Why do strings and headphone cables spontaneously wrap around each other when placed in proximity?"
] |
[
false
] |
It seem as if some invisible force pulls them together but I know that gravity is too weak to be the answer. I've always wondered this but today when my ear bud cables twisted around each other it annoyed me enough to finally ask. Of course I've asked the search engines, phrasing the query in many different ways, but can't seem to find the answer to this exact phenomenon. It's like some malicious magical force that exists solely to bedevil us (no, I don't believe in magic, but I like the song).
|
[
"As others have said, yes it's due to entropy. But I want to get to the \"why\" a little more.",
"It's probability. There are thousands, millions, maybe infinite different tangled states a cord can be in, and exactly one non tangled state. Being tangled is the \"natural state\" simply because it's by far the most likely state.",
"\nEvery time you put the cord in your pocket and scrunch it around, you're picking another random configuration. Since \"untangled\" is vanishingly unlikely when picking randomly from all possible configurations, it \"spontaneously\" comes out tangled ~every time.",
"The exact phenomenon you're looking for is Spontaneous Knotting of an Agitated String by the way. Here's the landmark paper on it:",
"Spontaneous knotting of an agitated string",
" - Raymer and Smith 2007",
"Math blog explaining the above paper.",
"Video of Raymer doing a talk",
" on the topic."
] |
[
"What others are talking about is more tendency for strings to tangle, but I think you're talking about something different.",
"I think what happens is that wire is already twisted internally so it wants to untwist, but since there's another wire next to it that's also untwisting they twist around each other instead.",
"It might help if you make a photos of what you're describing."
] |
[
"Ah!! Quick! He's getting to close to the secret rules that run the universe, like where the second sock in the dryer goes! He's on to us!",
"Joking aside, I both love that you asked this, and the responses that are posted. So much of the world we take at face value, \"Because that's just how it is.\" I love the moment when a person decides to stop accepting it as a given and asks why a thing is. At worst the world becomes a little weirder, as the limits of human understanding become a little clearer, but often I've found you get a fun little bit of knowledge that hardly anyone bothers to go for.",
"Kudos!"
] |
[
"Are there any non-poisonous fish other than sharks that can kill a human?"
] |
[
false
] |
I know that sharks are the archetypal aquatic threat to humans and there are numerous other poisonous fish that prove fatal, but I was curious if there are any other predatory/aggressive aquatic animals that can threaten humans without the use of poison?
|
[
"anything in the whale and porpoise family can kill us. some of them can kill is by calling out too close to us. ",
"octopi can kill us by drowning us by removing our mask or breathing apparatus or biting us with their parrot beak.",
"barracuda can kill us with their teeth.",
"swordfish can impale us with their nose spike thing"
] |
[
"Piranhas are like tiny sharks, they won't just attack you like a wasp but may bite if there is blood."
] |
[
"Barracuda if it got you in the right place. Marlin, swordfish, sailfish - obviously. Grouper if you were diving & a big one latched onto your arm, I guess (drowning). Electric eel. I wouldn't be surprised if someone has been killed by a tarpon (or for that matter a carp) jumping out of the water & hitting them in the head.",
"If you take it to \"aquatic animals\" & not just fish....yeah, any whale, dolphin, or pinniped that wanted to ",
" kill you easily if it chose to do so. Also, crocodiles are a thing.....(meets my definition of aquatic)"
] |
[
"Could an astronaut, without a ship, jump from Phobos to Mars?"
] |
[
false
] |
Phobos orbits only 6000 km from the surface of Mars, which is the closest of any moon in the solar system. It has very low gravity. With negligible friction in space, velocity is easier to achieve. How big of a propulsion setup would be required to achieve this travel? More spaceship sized or could it appear as just a dude flying through space? Or would it be more a matter of how long it would take?
|
[
"No.",
"Phobos' escape velocity is like 11 m/s. That's comparable to car speed. I don't think a human can achieve it by just jumping.",
"But even if you managed to jump out of Phobos, it's still orbiting Mars at high speed. The astronaut will keep orbiting Mars the same way because inertia. In order to get down to Mars the astronaut will have to ",
" of all that sideways speed e.g. with retrorockets. And a lot of fuel will be needed for that, so most likely a small spacecraft (comparable to a Soyuz) will be needed. 6000 km isn't a very high orbit but also not a low one, so the spacecraft will need a significantly larger fuel tank than a Soyuz. Even the Space Shuttles would not be able to perform this deorbiting manoeuvre, they had been designed to return only from Low Earth Orbit at an altitude of few hundred km.",
"Then you have all the difficulties of atmospheric entry (heat shield required), parachuting, and slowing down using retrorockets for touchdown. Feasible, sure, but a spacecraft designed specifically for this purpose and for this environment would be required."
] |
[
"Odd thing about escape velocity is that it doesn't matter which direction you're going in, so long as you don't crash into the surface; You can forget the ramp and just get up to that speed, you'll lift off and leave the moon. Might have an issue getting traction with barely any gravity, though."
] |
[
"An astronaut who managed to break the feeble gravitational bonds of Phobos would still find him or herself ~6000 km above the surface of Mars travelling over 2100 m/s parallel to it.",
"Reaching the surface will require lowering the considerable specific energy of this orbit such that its periapsis at least dips into the upper atmosphere where aerobraking and parachutes might be used to lower it sufficiently to reach the surface.",
"This will require a spacecraft of some sort."
] |
[
"Where do I start if I want to become an amateur astronomer?"
] |
[
false
] |
I'm fascinated with astronomy and the cosmos. I would probably hump Carl Sagan's dead, rotting corpse if I could. But for the time being I need a little guidance. I want to study the sky and all of it's celestial bodies. Would I be successful if I just went out and bought a telescope and started pointing it at the sky or would it be a fruitless endeavor? Do I need to join a club or can I just be a solo amatuer? What should I know about amateur astronomy? : Thanks everyone for the awesome replies. I'm gonna contact some of the local university astronomy clubs and make some astro buddies and start off with a pair of binoculars for.
|
[
"/r/astronomy"
] |
[
"First get a know of thy sky. Buy a star atlas and go do some naked eye observing. When you feel comfortable outside then you can look at getting a telescope. Of course depending on where you live there could be an active club I say you get in to."
] |
[
"Lie on your back in a dark field and look.",
"Learn the sky, know the major constellations and how to find the planets. With even a small telescope you can see the moons of Jupiter and the rings of Saturn, which are always neat. Check out local astronomy clubs. If you live near a university, often the physics department has astronomical outreach sessions."
] |
[
"How do ISPs connect to the internet themselves?"
] |
[
false
] |
When I pay my ISP, am I basically just paying for access to their cables?
|
[
"They ",
" the Internet. ISPs connect to other ISPs. "
] |
[
"In return, if you had valuable customers on your ISP network (website hosting servers, email servers, etc), they would pay to have access to YOUR network, and often a deal is worked out for mutual benefit of both parties. ",
"Source: I am a network admin at an ISP."
] |
[
"A better response is that Autonomous Systems (which can include ISPs) connect to each other and peer with each other. ",
"http://en.wikipedia.org/wiki/Autonomous_System_(Internet)"
] |
[
"Why is three of chromosome 21 (Down's Syndrome) more common that three of any of the other chromosomes?"
] |
[
false
] |
Just by searching for "trisomy n" (n in [1..20]) it seems that duplicates of other chromosomes are either extremely rare, or some have never even been documented.
|
[
"The most common are Patau, Edwards, and Down syndrome which are caused by trisomy 13, 18, and 21 respectively. But when I say \"most common\" that may not actually be true. It is entirely possible that the most common trisomy is a random chromosome (let's use the example of trisomy 8) but that is incompatible with life, so any time it happens the fetus dies long before birth. If that's the case then they are more common, but we don't know that because we don't always check why a fetus was aborted, or sometimes a woman may not even know she had a miscarriage. There is one other possible reason why Down syndrome is more common, I can't remember the exact details but sometimes chromosome 21 can fuse with another chromosome (part of it does at least) and this doesn't actually cause any problems but when that person (with the fusion chromosome) has a child they can pass down a full chromosome 21 as well as their chromosome 21 fusion chromosome, so when the child gets one copy of 21 from the mother, and a fusion chromosome, and one copy of 21 from the father they end up with trisomy 21 without actually having three full copies of 21. I don't know that this happens with either of the other common trisomy syndromes."
] |
[
"What seanpbnj is talking about is called a Robertsonian translocation, which can happen between any two chromosomes out of 13, 14, 15, 21, and 22 (the five that look more upside-down-U-shaped than X-shaped.) A normal adult with a balanced translocation has no apparent problems, because the genetic material's all there. When their sperm or eggs try to split those chromosomes evenly, however, you can run into problems. Robertsonian translocations can be involved in Down or Patau syndrome, but not Edwards.",
"And yes, Down is the most common trisomy we see because most trisomies result in miscarriage. Trisomy X in females is actually pretty common, but while Down syndrome is easily diagnosed at birth, most XXX women are never diagnosed at all."
] |
[
"Most trisomies are incompatible with life. This is why we talk about the prevalence of birth defects; you can only look at what proportion of live births have the trisomy, not what proportion of all conceptions had a trisomy. It isn't necessarily more common among all conceptions, but it is the one that is most likely to result in a live birth. So the simple answer is that Down's syndrome is the most likely to result in a live birth."
] |
[
"Given what we know about the human genome, how many genetically unique offspring is one pair of parents capable of producing?"
] |
[
false
] |
I always find it incredible to think about the odds of my existence as a result of my ancestors reproducing with the right people at the right time. I was thinking about the odds of my parents producing a child with my genetic code as opposed to any other genetic combination. How many different potential offspring could a single pair of parents produce? Does genetic mutation allow for practically infinite number of possibilities? What if we ignored mutations for simplicity's sake?
|
[
"First, each parent has two copies of each chromosome they can give you. So already we are at ",
"2^46, or 7 x 10^13\n",
"Now let's add in crossing-over: ",
"This paper",
" states that oocytes have, on average, 70 crossovers, and spermatocytes have, on average, 50 crossovers",
"So let's simplify and say all humans have 120 crossovers in the gametes that go on to form them.",
"How many unique combinations can 120 crossovers produce?",
"We have to make another simplification here. Let's say that crossovers can occur at any place on the genome. That means there are 3 billion potential places for crossover to occur. The number of unique crossovers is therefore the ways you can pick 3 billion things, choosing 120 at a time, or:",
"3,000,000,000 C 120\n",
"Which is 2.6 x 10",
"Adding in our 23 chromosomes from earlier, we get *",
" . Which is a really big number.",
"NOTE: Many of these unique genotypes will be phenotypically identical. Much of the genome is for non-coding regions, etc."
] |
[
"It is an oversimplification in that crossovers don't technically happen at all parts of the genome (centromeres, for instance, don't get many), but in all reality, no two offspring from the same parents will be identical, unless they are twins, even ignoring mutation accumulation. So, yes, in practical terms, there are infinite genetic possibilities. It is true, though, that different parents would create much more genetic diversity than the same parents; even though the progeny are not identical, they more similar than progeny from other parents."
] |
[
"WILD CARD, BITCHES!! I think I'd like to partially hijack this post to ask a similar question.",
"What are the odds of two individuals producing identical twins born from two different pregnancies? I can recall my biology teacher in high school figuring it out on the board, but I can't remember to save my life."
] |
[
"Would gyroscopic precession work in space?"
] |
[
false
] |
claims that a gyroscope functions the same way in space, as it does on earth. Does this mean that the phenomenon occurs in space as well? Does this have any use in rocket science and/or space travel? I get that the spinning object would have to do a lot of RPM to make up for its weight (since gravitational force is determent by weight (Ft=m*g, please correct me if I'm wrong)). But it could lead to some rockets shaped differently, and in turn make space transport cheaper, since a rocket could have room for more stuff? Just a random thought.
|
[
"This effect is actually phenomenally useful for satellites and larger space vehicles, including the ISS. Prior to the invention of ",
"control moment gyroscopes",
" and ",
"reaction wheels",
", satellites had to use thrusters for attitude control. Once the propellant was used up the satellite would drift out of control and become useless. CMG's can do the same job using only a tiny amount of electricity, which solar panels or RTG's can easily provide. "
] |
[
"Yes the gyroscope functions the same way in space. I dont see how this would help in space travel though apart from knowing the orientation of the spaceship. I would like to see your idea. Do you mean an object floating over earth without moving around it? That would not work since the whole system would be affected by gravity and there was no change in torque."
] |
[
"Yes, gyroscopic precession works in space. It requires an external source of torque though - planets, for example, under go perihelion precession which causes their orbits to slowly rotate.\nGyroscopes work the same way in space, since they use the conservation of angular momentum to maintain the orientation of their axis. For example, the Hubble telescopes uses gyroscopes to measure its orientation."
] |
[
"Could you use jet engine with, ramjet and than sramjet in series?"
] |
[
false
] |
Consider that jet engine would be at the front and would have turbine cappable of reducing speed bellow mach 1 and keeping temperature in save level.
|
[
"Short answer is no. The SR-71 used a combined cycle turbine ramjet. However, you couldn't put a scramjet inline without some serious flow conditioning to get it cool enough to use. ",
"Also, it's not really practical to slow down air from hypersonic to subsonic speeds, except until recently where there's been some work (I think in the UK) in magnetohydrodynamics that rapidly extracts energy at an intake to slow and cool the air even up to Mach 7 or so, then reinjects the energy at the outlet. ",
"The ramjet/turbine idea is, for most intents and purposes, the same as an afterburning jet engine. However, putting a scramjet inline doesn't work, as you can't get the air fast enough. The current SR-72 approach, as far as I can tell, uses a parallel system where the scramjet ignites at hypersonic speeds. The big problem before was how to get a jet going fast enough to ",
" a scramjet. SR-71 maxed out around Mach 3.8 due to the inlet cone geometry ingesting the Mach cone at full extension, and at that point less than 10% of the thrust was coming from the turbine (vast majority of air was diverted around the engine to the ramjet/afterburner). ",
"Finally, nothing can do this at sea level because the air is too dense and maybe too hot. You'd probably melt the aircraft and definitely require a lot more power. "
] |
[
"It think even theoretically it is impossible because most of the oxygen would be already consumed after the first part of the engine, so you wouldn't be able to generate energy with another combustion after the first one."
] |
[
"SABRE has been \"just around the corner\" since the 1980s. It's part of the ",
"HOTOL pipe dream",
"."
] |
[
"Is it possible to form an electrolyte in an organic solution without using water or a surfactant?"
] |
[
false
] |
That's it, I just want to know if it's possible and in case it is, how and with what? Thanks
|
[
"Yes, it's very common in electrochemistry experiments to use organic solutions (acetonitrile, ethylene or propylene carbonate, etc.) with salts like tetrabutylammonium hexafluorophosphate (Bu4NPF6) or similar tetrafluoroborate (BF4) salts added for conductivity."
] |
[
"Yes, there are salts that dissolve in organic solvents. One example are Lithium ion batteries. Here, a lithium salt (LiOF6) is dissolved in an organic solvent (methyl or ethyl carbonate afaik) and transport the Li ions from anode to cathode."
] |
[
"Are they easily separatable? And thanks for your response"
] |
[
"If the sum of energy in the universe = zero, then how is the universe expanding?"
] |
[
false
] | null |
[
"You're thinking of the ",
"Zero-energy universe hypothesis.",
" The conservation of energy applies to isolated systems, which are idealizations. Special relativity says that if an observers reference frame is not changing, then energy, as measured, will be conserved(though not all observers can agree upon the measured value) So the conservation laws appear to hold locally. It's not certain whether energy is conserved globally within the context of general relativity, where the effects of an evolving space-time background become significant. "
] |
[
"Keep in mind that expansion is independent of the sum of energy in the universe, whether or not the ",
"zero-energy universe ",
" is true.",
"The expansion is ",
"metric",
", not inertial -- meaning, things are not moving outward into pre-existing or newly-created space. Instead, the expansion is based on the ",
" (called the \"metric\") which is increasing over time. If you have two points, ",
" and ",
", which are at rest with respect to eachother, and separated by some distance ",
", then after some time interval ",
", these two points will be separated by some distance ",
" where ",
" is the increase in the distance between ",
" and ",
". This would be true ",
". Points ",
" and ",
" are still at the same coordinates -- but the distance between those coordinates has increased.",
"This is similar to drawing a coordinate grid on the surface of a balloon, and blowing it up. As you blow it up, any two points on the grid will have the distance increased between them, regardless of whether there is anything ",
" the surface at those points (such as matter, or anything with energy)."
] |
[
"According to einstein's relativity theory, all mass + energy in the universe = zero, right? ",
"No, relativity doesn't say that (as far as I know). As xnihil0zer0 said, it's a hypothesis."
] |
[
"How different are different cancers?"
] |
[
false
] |
As I understand it most treatments are almost the same across the board for different types of cancer, so how much would research into say lung cancer affect research and treatment in say brain cancer? or bladder cancer? Or into other types of lung cancer? What makes these cancers different from each other? Is general cancer research more valuable to the field than research into a specific cancer?
|
[
"Cancer arises when the biochemical mechanisms designed to prevent cells from dividing out of control fail. These are collectively called ",
"the hallmarks of cancer",
", and they form a list of common behaviors that most cancers share.",
"Early treatments for cancer attacked these broad behavior traits. For instance, drugs called \"antifolates\" blocked the activity of folic acid, which is necessary for DNA synthesis. Since cancer cells are dividing very rapidly, they need to synthesize DNA often, and so this drug preferentially kills cancer cells. However, normal cells also need to synthesize DNA, and so there are serious side effects.",
"The thing about the hallmarks of cancer is that there isn't just one mutation that can confer oncogenic behavior. For instance, lets say there is a growth factor that can stimulate cells to divide. A cancer cell may acquire a mutation that lets it produce this growth factor itself. Or it may wildly over-express the receptor for that growth factor, making it hypersensitive to normal amounts of it. Or the receptor could mutate in a way that makes the cell think it is constantly being exposed to the growth factor. All of these mutations have the same effect (up-regulating cell division), but they arise from different mechanisms.",
"Newer treatments for cancer are \"targeted\" - they attack the specific biochemical mechanisms that give rise to the hallmarks of cancer. Many lung cancers overexpress a receptor called ",
", and the drugs cetuximab and erlotnib target this receptor directly. Some breast cancers over-express the receptor for estrogen, and the drug tamoxifen targets this. ",
"In general, these targeted drugs work better than their non-targeted counterparts. But they only work on the specific cancers that possess the vulnerable mutations."
] |
[
"Layman here, but this post is not speculation. I have done a lot of research. Still, I'm noting that I'm a layman so that you know this may contain inaccuracies.",
"I think it's easier to say what cancers have in ",
" with each other. There are certain widely-recognized characteristics of cancer cells called the \"Hallmarks of Cancer\", here:",
"http://en.wikipedia.org/wiki/The_Hallmarks_of_Cancer",
"These are:",
"Self-sufficiency in growth signals: they don't need to be told \"it's time to multiply,\" they always multiply.",
"Insensitivity to anti-growth signals: they disregard the chemicals that tell them to stop growing.",
"Evading apoptosis: when a normal cell detects that it is damaged, it commits suicide. Cancer cells don't.",
"Limitless reproductive potential: normal cells can only reproduce a fixed number of times before a built-in limit kicks in. Cancer cells have short-circuited this limit.",
"Sustained angiogenesis: (for solid tumors) tumors have means to encourage the body to send blood vessels into the tumor. Without this, they would die from lack of blood supply.",
"Tissue invasion and metastasis: tumors spread to other parts of the body.",
"As I see it, the \"hallmarks\" are basically definitional - without these characteristics, we wouldn't call it a cancer. For example, if it didn't grow, that's not much of a cancer.",
"In addition to these hallmarks, there are many characteristics that are shared by many cancers. Here are several that I can think of:",
"Solid tumors tend to have insufficient blood supply in the core. Tumors can be recognized as such by these necrotic regions.",
"Cancer cells tend to consume more glucose than normal tissues. Tumors can be recognized as tumors by their high glucose consumption.",
"There are certain proteins like EpCAM, MUC1, CEA, and others that ",
" occasionally appear in small quantities in normal cells, but they tend to appear in large quantities in cancer cells. Most cancers will express some of these proteins. ",
"Cancers are generally very mutated. They will have \"wholly original\" abnormal proteins in their cell membranes. By wholly original, I mean proteins that don't appear anywhere else in the body or in any other tumor.",
"Because they have wholly original proteins in their cell membranes, there is a risk (from the cancer cell's perspective) that the immune system will see the cancer cell as foreign. The immune system needs to be suppressed to keep the immune system from attacking the cancer cells. Solid tumors emit immunosuppressive chemicals.",
"The built-in limit on the number of times a cell can reproduce, which is present in all normal cells, can be easily suppressed in just a few ways. Almost all cancer cells use one of this small list of tricks.",
"Many tumors exhibit \"aerobic glycolysis.\" Glycolysis is a process that cells can use to produce energy without oxygen. But in general, the body avoids using glycolysis when plenty of oxygen is available. Cancer cells often use glycolysis constantly.",
"That's not meant in any way to be a complete list. It's just what I was able to think of off the top of my head.",
"So to finally answer your question: many experimental cancer therapies attack cells that have these \"cancery\" characteristics. For example, there are therapies that attack cells that express EpCAM. There are therapies that target cells that use telomerase to avoid the division limit. There are therapies that target cells that use glycolysis. There are therapies that target the areas inside of tumors that don't have enough blood supply.",
"These therapies will naturally work on ",
" cancer that has the target characteristic. That, in general, means that the therapy will work on some cancers other than the one they originally were experimenting on, but not all cancers.",
"For example, let's say a therapy is designed to work on cancer cells that have the EpCAM protein on their surface. Many colon cancers have EpCAM, but so do some breast cancers and probably others I'm unaware of.",
"Then, there are some experimental therapies that are called \"targeted therapies.\" That means that these therapies ",
" aimed at some common characteristic of cancer cells - they're aimed at some very specific characteristic of just one particular kind of cancer. Even these therapies can work on more than one cancer - for example, gleevec was targeted at a very specific characteristic of chronic myeloid leukemia. But it turned out to be effective for some gastrointestinal stromal tumors as well. But let's just say the targeted therapies are, well, mostly targeted. ",
"Now, I have a followup question that can probably be answered best by a real doctor.",
"Many \"old\" therapies are DNA damaging agents - for example, fluorouracil. There seem to be a hundred of these, and they use different ones on different cancers. Why is it, for example, that fluorouracil is preferred for colon cancers, but some other DNA damaging agent is preferred for (say) breast cancers?"
] |
[
"Normally you test for genetic factors when a biopsy of the tumor is done. You can't efficiently test every tumor for every mutation, so normally you just test for mutations that are known to play a large role in that specific cancer site. For instance, lung cancers can be tested for EGFR, and breast cancers can be tested for ER/PR and HER2."
] |
[
"If an object leaves the surface of the earth traveling at escape velocity, how far will it travel before its speed approaches zero?"
] |
[
false
] | null |
[
"Hello,",
"We don't offer homework help here."
] |
[
"I'm 35 and graduated. I was looking at this for fun."
] |
[
"Its speed will approach zero asymptotically as the distance goes to infinity."
] |
[
"Why does only the nasal portion of the optic nerve decussate at the optic chiasm? Or is this not the case in all animals?"
] |
[
false
] | null |
[
"Why is the nasal portion split? Well the text book answer is to make sure that the right half of visual space is processed in the left hemisphere. This makes sense as the left hemisphere processes information from the right side of the body.",
"Another answer, which is probably better, has been aluded to before. Depth perception relies on many visual processes, but an important one is that each eye sees slightly different things because of being offset horizontally from each other. To do this comparison, it makes sense that the bits of the retina that see the same part of visual space are processed in the same bit of the brain. Temporal retina of the left eye, and the nasal retina of the right eye both see the right half of visual space, and both of those areas send signals to the left hemisphere, where the can be processed together.",
"This is actually in a relatively small number of mammals, carnivores and primates. Rodents have only a very weak amount of crossing (~10%). Perhaps this makes sense as rodents eyes are generally on the side of their heads, which means only a small portion of their visual fields overlap, and hence there isn't much visual input that needs to be compared between the eyes. On the other hand, there is quite a bit of evidence that rodents might perform depth perception via a different way: where the binocular information is passed between the hemispheres, rather than directly sent there from the eye."
] |
[
"Rodents have only a very weak amount of crossing (~10%). ",
"you have this backwards; almost the entire rodent optic nerve crosses over (",
"ref",
"). the optic chiasm is an almost universal feature of mammal brains (there are cases of achiasmatic animals and humans, in which case weird weird things happen). i think that in this question, the textbook answer is the fundamental one - the optic nerves cross because all the other nerves do too and you need all ipsilateral body-stuff to be in the same side of the brain. the fact that some fibers ",
" cross is where binocular fusion comes into the picture."
] |
[
"here is a great example:\n",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3427398/",
"In this achiasmatic patient, each eye sends its entire output to the ipsilateral hemisphere, and each hemisphere does actually receive that output (you might suppose that the 'not belonging here' output would be ignored and atrophy or something).",
"Long story short (I can give more detail if you like), in this patient the ",
"ocular dominance columns in V1",
" have been adapted into \"contralateral field columns\". In 99.999% of human brains, V1 is organized so that matching inputs from both eyes arrives in immediately neighboring locations, called ocular dominance columns. These inputs as a whole form a \"retinotopic map\" of the two eyes' fields of view, such that if something moves gradually across your visual field (like from your central focus out into the far periphery), you will see a knot of neural activity gradually moving across the cortical surface. You have to look very closely to see that they aren't exactly merged, just sorted into alternating strips of the cortical surface - the OD columns. Each V1, one in each hemisphere, has a map of exactly one half of the visual field, left field in the right hemisphere and vice versa.",
"In this achiasmatic patient, as you move across V1, instead of gradually moving across the visual field and rapidly alternating between the two eyes' inputs, you are rapidly alternating between ",
" of the visual field! The left field and the right field are laid on top of each other, like a butterfly's folded wings, so as you go further into the calcarine, to larger and larger eccentricities, the visual field representation is getting more and more separated. It is insane, I don't know how the visual system deals with this, but it's proof that the cortex can deal with just about any situation. And this isn't the only known case - other patients have been observed who have similar adaptations."
] |
[
"On the American east coast, humidity is lowest during the winter. In the American southwest, humidity is lowest during the summer. Why the difference?"
] |
[
false
] |
Just moved from Washington DC to New Mexico, and noticed that humidity is super low during the summer but higher during the winter, totally opposite to how the east coast is in my experience. Anyone know why this is?
|
[
"It's because you're in a different climate. New Mexico, like Texas and other areas, are subjected to monsoonal variation (wind pattern changes). In the winter, more storm systems are able to affect those areas, dousing them in precipitation. These areas experience higher relative humidity values in the winter months because of this and also the fact that you can have a comparable moisture content in the atmosphere, but be closer to saturation in cooler temperatures."
] |
[
"AZ resident here-",
"There are monsoonal wind patterns that effect precipitation patterns in the desert and high plains in the southwest. ",
"Summer monsoons are frequently very humid with little measurable rainfall. (This year's flash floods here in the Sonoran desert were a bit of an exception to that). Winter months tend to have more precipitation because it's cooler (so it's not evaporating before it hits the ground) and wind patterns change to flow from west to east, bringing in moisture from the Pacific Coast rather than the gulf of Mexico. "
] |
[
"This is correct, and to add since i live in las cruces... NM tends to get a lot of rain in the winter, even though it's not the rainy season per se..."
] |
[
"Why do you represent a plane in 3-D space with the symbol for pi?"
] |
[
false
] |
For example pi1:1x+2y+3z+4=0. pi2:4x-3y-2z-1=0
|
[
"I don't think I've ever seen this done, but why not? Any symbol works as long as it's clear what it means."
] |
[
"There's certainly no convention along the lines of 'if it's a plane in space, represent it with pi'. Where have you seen this?",
"What seems more plausible is that it's just a choice by the authors of whatever you were reading. If pi has no other particular meaning in context, it's just another letter to assign to things."
] |
[
"Ivenever seen this notation, but maybe it's basically short for plane (plane -> p -> pi)?"
] |
[
"How do we know what’s inside our solar systems outer planets?"
] |
[
false
] |
[deleted]
|
[
"First of all, only Jupiter and Saturn are classified as gas giants nowadays. Uranus and Neptun are now classified as ice giants.",
"\nThen even though they are called gas giants they do not only consist of gas. Especially with Jupiter it is so heavy that the pressure inside the planet is so high that we strongly assume that large parts of the interior consist of metallic hydrogen. Furthermore we do assume that the core consists of rocky material. But rocky core most likely comes from the formation of the planets. Moons are too low mass to contribute significantly to the core. \nHow do we probe the planetary interiors? Well mostly gravity measurements. By mapping the different components of the gravity field we can estimate the mass distribution of the interior. Furthermore measurements of the magnetic field place further constraints on the interior. "
] |
[
"For Jupiter and Saturn (at least), we can also probe their sismology : the oscillations of the gas at their surface grives information about their internal structure. One way is trying to reproduce the oscillations frequencies and patterns with numerical simulations using various structure profiles.",
"This is very similar to ",
"Heliosismology",
". "
] |
[
"Short answer: we don't exactly. However, we can infer it by calculating the planet's density (which can imply what kind of materials are there) and combining that with our understanding of physics, chemistry and terrestrial geology we can reasonably speculate what kinds of conditions might be inside the planet, and how that might affect the materials the planet is likely composed of.",
"There are other posts here which can explain this in better detail."
] |
[
"What would actually happen if I stop wearing my retainers?"
] |
[
false
] |
I am talking about how you must wear retainers after you have braces. I am particularly interested since I have been wearing retainers for roughly 8 years now. So far, nobody has been able to give me a straight scientific answer of what would happen. I just get lots of anecdotal evidence of nightmare scenarios ("your teeth will curl into each other causing great unimaginable pain") or completely benign scenarios ("Nothing will happen, it's all a scam"). But nobody has pointed me to any scientific studies or analysis of the long term effects on not wearing retainers and why they occur. My own searches for it were proven worthless as I found only more anecdotal evidence along with the medical advice "Just do what your densit/orthodontist says". I was hoping askscience here might have a better answer for me.
|
[
"I never wore my retainer. It interfered with my singing and gave me a slight lisp. My teeth have moved back (over five years) to basically where they started, however additionally they are all extremely loose. Healthy, but very loose. ",
"So wear your retainer!"
] |
[
"When you stop wearing your retainer your teeth will start to go shift back to the way they were before you had braces. Nothing too bad happens and it is not painful, it is simply a waste of having braces."
] |
[
"basically this. i had one of those perma-retainers that lasted for years but eventually broke out and i never cared to replace it. before braces my teeth were mega-fucked. now i've got one tooth that is drifting into a spin out of orientation with time. it's shit but i count it as a minor casualty in the war against wearing any headgear anymore."
] |
[
"If a single transistor on a modern cpu stopped working, would we notice?"
] |
[
false
] | null |
[
"Yes, that circuit would be inoperable.",
"To answer the inevitable follow-on question: how in the world do chipmakers get away with having to have a perfect record for chip production?",
"The answer: they don't. When they create, say, a 6-core CPU, they test every chip extensively. If they find a fault, they shut down that core - they have engineered it to be able to deactivate parts of the chip selectively (like cores, or cache memory) wherever there is redundancy within the chip. They then sell this chip as a 4-core chip.",
"Yes, it's often true: nearly identical CPUs of a lower grade are ",
" often irregulars of the higher grade chip."
] |
[
"Yup, it's also the reason why CPUs usually have some many configurations despite being almost the same, they bin them, that is after production they are tested, failing components are marked, and then disabled and sold to the fastest model they have (so they might have an 8-core, 6-core, and 4-core version, each with a consumer version and server version (without or with ECC/multisocket support), with 12, 8, or 6MB of cache and each at 5 different clock rates. They only build 8-core server CPUs at 4GHz with 12MB of cache, then they test them. That 6-core 3.5GHz consumer with 8MB of cache is the CPU that only passed those tests (and they loaded it with firmware or something to disable all the bad bits)."
] |
[
"It can depend on ",
" in the circuit the failed transistor lies. Some designs have spare cells that can be used to replace failed cells under specific circumstances. I think this is primarily done for SRAMs, because it's pretty easy to figure out which entry has failed, and then to divert accesses to that entry to some register that has been placed nearby. SRAMs occupy a big chunk of chip space nowadays so this sort of thing can be pretty useful."
] |
[
"Is there are word for when the inhabitants of the environment resemble the environment?"
] |
[
false
] |
I was recently in a park full of Dear’s and Stags and I noticed that the environment was full of old trees that really resembled the antlers.
|
[
"I think the word here is 'coincidence'. The last stag I saw was on heather moorland.",
"There's a confluence here of the brain's exceptional capability to seek out and match patterns (even where none exist, like faces in clouds, or - perhaps - tree branches looking like antlers and vice-versa) and a smidgeon of 'correlation does not imply causation'."
] |
[
"I hear that, I still feel like a word to describe that phenomenon would make a lot of sense.\nI thought of it in the park and also at a later date watching ‘Jurassic Park’ in the Diplodocus scene when they are sitting on the Diplodocus like tree and I found myself reaching for a word that doesn’t seem to exist. "
] |
[
"There's the concept of \"nominative determinism\" where (due to again selection effects in our brain) we perceive a tendency for people to follow professions that their names are suitable for, like 'Bobby Copper the policeman' or 'Daisy Blossom the florist'. Maybe you've just invented 'structural determinism'? ;)",
"But it isn't objectively real, its just a resonance in your mind."
] |
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