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[
"Why are small animals like spiders and scorpions sometimes so incredibly venomous? Given the size of their prey, why would they require such potent venom?"
] |
[
false
] |
It doesn't make sense to me that something smaller than the palm of my hand would need a venom so lethal that it could kill a grown adult, considering the size of their prey (which is pretty close to their own size or smaller usually). Why can't they just use smaller doses or a less potent venom instead? (examples - , . Found one of these in my home earlier too, which prompted my investigation and this question)
|
[
"Most highly venomous and poisonous animals co-evolve with another species that evolves an ever-increasing tolerance to the venom. Think of it as an ever increasing evolutionary arms race, so to speak. ",
"For example, the rough-skinned newt, a highly poisonous newt that lives in North American, has enough poison in it to kill 17 humans, if ingested. However, its common predator, the garter snake, eats it without trouble. As the newt evolved to become poisonous, the garter snake evolved to tolerate the poison. The newt evolved further to become more poisonous to combat the snake's tolerance, thus sparking an evolutionary arms race. ",
"This basically explains why certain animals, especially small ones, can pack such a big punch",
"Edit: yeah, my bad, venomous and poisonous are not synonyms "
] |
[
"I noticed you said \"highly venomous newt\" then \"has enough poison.\" Just to clarify, I thought it was:",
"Venom: Animal bites you",
"\nPoison: You bite animal",
"Does this go hand-in-hand with this case? Ingesting the venom is poisonous to humans?"
] |
[
"I thought venoms were usually proteins, which means you could eat them and your stomach acids would denature them without them hurting you. (Neglecting diffusion through the esophageal tract and such.)"
] |
[
"Can it be Too humid in a house during the winter?"
] |
[
false
] | null |
[
"I didn't think I would get sick from too much moisture in the house, but that report worried me. I like the moisture in the house, no static electricity. Thanks for the feedback."
] |
[
"Humidifier are the way to go. there's ones that let you control the level of humidity to prevent mold. "
] |
[
"I doubt you can make yourself sick with too much moisture, considering during the summer you can get near 100% humidity at these same temperatures ~70-80F. I also don't think you need to look for an alternative, since different ways of getting moisture into the air shouldn't affect the outcome much. The difference between a mist humidifier is that the water droplets pull heat out of the air to supply the energy required to evaporate them, while with the simmering pot the energy is supplied by the flame.",
"You might want to be careful about ventilation though. That flame requires oxygen and ventilation, as do you and your family, and ventilation means more dry air from the outside to humidify."
] |
[
"Does the moon being overhead affect your weight on Earth?"
] |
[
false
] |
If you stand on a shoreline, do you weigh (ie force downwards to Earth) more at low tide than high tide, because the moon is closer at high tide and thus exerting a force on you in an upward direction?
|
[
"Yes, it does, but not by very much. The gravity you feel due to the Moon is approximately 3 * 10",
" m/s",
" , compared to about 9.8 m/s",
" due to the Earth, or about 0.0003% of the strength."
] |
[
"What mass of sofa are you using? Guesstimating a sofa at 50kg, that gives you gravity of 10",
" m/s",
" , a ten thousandth of the force from the Moon."
] |
[
"I mean, obviously a sofa ten-thousand times heavier than the one you used..."
] |
[
"How far would the ocean drop if all the fish etc. suddenly vanished?"
] |
[
false
] |
Not including the single celled organisms and all that but the general human-eyeable things. Essentially, what is the volume of all those swimmy things and how much beach would we inherit if they all disappeared?
|
[
" A few microns. ",
" Let's talk about ",
"biomass.",
"\nDifferent people give different estimates, but we can probably get this to an order of magnitude. ",
"For reference, humans (all seven billion of us) put together have about 100 million tons of dry biomass, which is basically a measure of our weight without water, or approximately our carbon content. ",
"Global estimates say there is about 560 billion tons of dry biomass on earth, but only about 1-2% of that is the oceans. That's crazy considering that oceans occupy twice as much of the earth as land. ",
"The most successful species on earth, in biomass alone, is probably the antarctic krill, pushing 400 million tons of wet biomass. ",
"You ever wondered how the largest whales on earth can survive off eating crustaceans smaller than your finger?",
" It's because there's lots of them. ",
"Anyway, ",
"this paper estimates there is about 1 to 2 billion tons in fish, so let's go with that.",
" Assuming the fish has an average density of 1 ton/m",
" (which is approximately the density of water (1000 kg/m",
" and a good estimate for nearly every biological material), then the total volume of fish is: ",
" V = (1 billion tons)/(1 ton/m^3) = 1 billion m^3 \n",
"If the oceans cover 70% of the earth, then area of the oceans is: ",
" A = 4 pi (earth radius)^2 x (0.70)\n",
"to find 3.5x10",
" m",
" is the surface area of the oceans on earth.",
"Dividing the above volume by this area gives us the change in sea level, and is about ",
"2.8 microns.",
" Helpfully, Wolfram informs us that this is close to the radius of an average bacteria. ",
"So again, the short answer is that fish are few and far between and are tiny compared to the ocean, but Wolfram's tangent makes me wonder: why is this answer so close to the radius of an average microorganism? ",
"What if this number was really telling us something about how biomass is distributed in the pyramid of producers and consumers?",
" In other words- the food chain.",
"I'm speculating here, but for the oceans to support this much animal mass, there must be something providing food to support it. Right, biology panelists? If you consider that 1-2 billion tons of fish, but instead imagine that was the mass of bacteria, then this 'sea level drops by 1 bacteria's length' makes sense, at least ",
"if you're a theoretical physicist who answers questions he knows nothing about.",
" This number would mean that if you drew a straight line down in the ocean, on average you would hit about 1 microorganism (some kind of plankton). Of course, the real number is probably much higher as microorganisms and phytoplankton are certainly going to be more abundant by mass than bigger organisms like fish, but I still think this is an interesting observation. ",
"This makes sense to me because real estate is the most valuable resource to these organisms because it guarantees them ",
". That sunlight is used to photosynthesize, and if there is anything that I know about life, it's that it exploits every fucking niche it can; if the conditions are right for photosynthesis, someone will be there to do it. I'd like a biology panelist to weigh in on this, because I may very well be drawing connections where there are none. But I think the hypothesis is solid: no surface area goes to waste, because life, ",
" finds a way. "
] |
[
"Ho-lee shit, man! That's an incredible amount of detail, thank you so much! We've all had this long week working out in CO, took part in a bit of the local flora and came up with that just now so thank you for being so prompt and thorough! Another reason to love this community (and science)! We were all expecting a much different answer :)",
"EDIT: OH! And thanks for the follow up theory because now we're launching in to that!"
] |
[
"Oceans are weird. See, on land most of the dry biomass is tied up in plants, and specifically in wood and roots. You've got a big pile of plant biomass for every animal in that form.",
"In the oceans, you don't have much in the way of big plants. You've just got planktonic algae. Their total biomass is relatively small (though still pretty large) but the turnover time (reproduction>eating) is extremely fast. ",
"To describe it, think of it like this. On land you've got a huge tree, and every so often a deer or bug comes by and eats off a few leaves...a small percentage of total biomass. In the ocean, you've got single-celled algae floating around, dividing in two every hour, and one of those two gets eaten by a copepod or something. ",
"So there's much less biomass but proportionally a whole lot more of it gets eaten every day."
] |
[
"What would be a viable lubricant to -85F?"
] |
[
false
] |
There is a viral video for a gun lubricant, Liberty Lube, that claims it functions to -85F. The video demonstrates it squeezing from the dispenser after freezing in dry ice, while synthetic motor oils and other lubricants are solid. What could this possibly be made of?
|
[
"Their MSDS page is blank!",
" ",
"MSDSs are extremely useful OSHA-mandated documents describing safe handling, poison control procedures, and what is actually in a product if you are curious.",
"This",
" is the MSDS for a functionally similar competitor, although this brand only advertises itself down to -65 F. The sheet identifies the the main ingredient as polyalphaolefin, a class of synthetic oils with extremely low freezing points. From the ",
"CAS number",
" on the sheet it is poly(1-decene) specifically."
] |
[
"To be specific, poly(1-decene) is a polymer. I'm assuming it's a fairly small molecular weight polymer at that, and it seems to be dissolved in 2-ethylhexylacetate. I wonder if we'd be able to find a molecular weight range for the polymer specifically used in these two examples."
] |
[
"Wicked Smaht. Thanks!"
] |
[
"How do devices tell how much battery is left?"
] |
[
false
] |
How do things like my phone know what percentage of battery life I have remaining?
|
[
"Most people think a battery provides a constant voltage while it discharges. This is not the case. In fact, the voltage decreases as it empties, according to a fairly predictable curve. In general, this curve looks ",
"something like this",
". ",
"From there, it becomes fairly easy for Apple, (or Samsung, or whatever manufacturer) to test the battery, and determine the precise voltage which corresponds to any given charge level."
] |
[
"There are actually a lot of different ways.",
"Voltage is a good indicator of %charge, but not a good indicator of remaining capacity (since remaining capacity will change with time).",
"Most modern electronics with lithium-based batteries actually use a combination of metrics to provide an accurate estimation of capacity remaining. Voltage is one, charge current/time is another. ",
"Lithium batteries have a big advantage compared to others - they are extremely efficient. The amount of energy you put in during charging is almost identical to the amount of energy you can then take out during discharge. By monitoring the current/time during charge, you can calculate the amount of energy you have stored (in amp-hours actually, which isn't really a unit of energy, but I suspect it's actually calculated in watt-hours and converted for consumption), and by monitoring the discharge rate you can subsequently predict time-remaining. ",
"So your laptop, for example, knows how much energy it stored in the battery, and then monitors everything (like how much power your wifi is drawing, your cpu is drawing, your speakers are drawing, etc) and calculates how long you have left. ",
"The device usually will also store a history of the battery's charge and discharge cycles, which gives you a good indication of the battery's health. You can see that voltages drop faster (pointing to increasing internal resistance) and your capacity even under light load is dropping. By monitoring that over time you can predict the number of cycles remaining before the battery is useless.",
"For example, my laptop is currently reporting 4978mAh remaining of 5623mAh capacity. It's discharging at about .605A @ 12.068V, and is calculating about 8h 8m left (88%)."
] |
[
"So do they time it or is there an instrument in the device that measures voltage?"
] |
[
"Is there a limit to earthquake magnitude? How big can an earthquake get?"
] |
[
false
] |
The biggest earthquake recorded was the which was 9.5 on the moment magnitude scale. There have been 4 other earthquakes over 9.0 in the last 60 years or so (Alaska, Indonesia, Russia and Japan). These events seem very common on a geological timescale. How big could a once-in-a-million-years event be? Is there any geological evidence for much larger earthquakes in the past? Is there any theoretical limit to the size of an earthquake? Were tectonic plates moving any faster/slower in the past? Would this have any effect on the size of an earthquake? EDIT: As an afterthought, what might be a more interesting question: Rather than the total energy release, how fast it is released. Just to clarify, I am talking about 'natural' earthquakes, not any sort of asteroid strike.
|
[
"Please don't ",
"plagiarize directly from other sources",
". "
] |
[
"There is no theorical limit to the magnitude of an earthquake per say, but there is a physical limit to it as there is a finite amount of earth crust that can move to produce the quake. As an exemple to the absence of a theorical limit, the estimated magnitude of the starquake on the magnetar SGR 1806-20 was 32.0 on the Richter scale. That is about 10",
" times larger than the Valdivia earthquake.",
"I apologize I do not have the knowledge or the sources for any other of your questions."
] |
[
"If you were trying to prove a point, you didn't make that point very clear. You could have linked to the page you got it from, or stated your objections to the question. Instead you pasted as your own a scientific explanation that you didn't write.",
"Moreover, the point of AskScience isn't to answer questions that no one on the internet has ever answered before. The point is to get answers to scientific questions directly from experts, and to have follow-up discussion. For instance, your quote doesn't explain why scientists agree that magnitude 10+ quakes are implausible. "
] |
[
"Politics aside, is there any scientific evidence behind Todd Akin's claim that the female reproductive system shuts down in cases of rape?"
] |
[
false
] | null |
[
"No. ~5% of rape victims conceive. ",
"source"
] |
[
"Cheers. Makes you wonder who these doctors are that are providing politicians with their scientific knowledge. "
] |
[
"Most likely physicians that are in part-time practices and devote some time to lobbying for reform they want. Most likely older. Most likely not up to date. Most important, they are most likely speaking beyond the realm of their expertise...i.e. whoever said this most likely was not an ob/gyn. They could be fake and everything that he said was a lie."
] |
[
"How did we determine the shape of electron orbitals?"
] |
[
false
] |
[deleted]
|
[
"The \"shapes\" you are referring to are probably the probability densities as a function of spatial coordinates. It's a postulate of quantum mechanics that the state of a particle is represented by a wavefunction, and that the modulus squared of the wavefunction is the probability density.",
"The wavefunctions for electrons in an atom come from solving the time-independent Schrodinger equation. For an electron in a Coulomb potential (the hydrogen atom)."
] |
[
"It comes from the standing wave solutions to the Schroedinger wave equation in 3D with a coulomb potential.",
"If you have a system described by a 1D wave, like a violin string, then the standing waves are ",
"sine functions",
". These solutions have an integer number of nodes where the function is always zero. If you have a 2D wave with rectangular symmetry, the solutions are a simply a product of sine function in x and y, like ",
"this",
". In a 3D rectangular volume, you would get a product of sin functions in x, y, and z. The Schroedinger wave equation has the solutions when you trap a particle in an ideal box, where the potential goes to infinity outside the box. In higher dimensions, the nodes become lines (2D) or planes (3D). ",
"Now, when the box becomes round, the solutions get more complicated to write down than a sine function. For a 2D box that is circular, it makes sense to write the solutions in circular coordinates (i.e. r, theta instead of x,y). The solutions are then Bessel functions of r and sine functions of theta. You can see some examples ",
"here",
". Although the functions are more complex, you still see an integer number of nodes. In r the nodes are ring shaped, while in theta the nodes form a line across the circle.",
"For an atom, the potential isn't a spherical box, but a coulomb potential (i.e. -A/r). So instead of having a well defined edge, the solutions decay to zero at larger distances. The functions are even more complicated now, but the solutions still have an integer number of nodes in them as you can see in ",
"this representation",
"."
] |
[
"I'll let you in on a little secret: we don't know the shape of the electron orbitals beyond hydrogen. Not exactly, anyway.",
"Quantum Mechanics is hard. I don't mean in the sense that it's difficult to understand, which it is, but it's difficult in a mathematical sense, too. The only system for which we can solve the Schrödinger equation (which governs all of QM) exactly is the Hydrogen atom.",
"In the case of H, we can solve for steady-state solutions to the Schrödinger equation, this means we're looking for states in which the atom is static and the orbital doesn't change over time. When we do this, we find ",
"these",
".",
"For a hydrogen atom, these solutions are exact",
" But once we introduce multiple electrons, the orbitals start interacting with one another and our simple model becomes a first order approximation. But it turns out that these orbitals we've found make an excellent basis to describe the behavior of the electrons in other atoms. They just won't be \"pure\" anymore, and all kinds of mixing and distortion happens.",
"Ever hear of hybridization? That's exactly what's happening. Two different orbitals mix, and the electrons end up having some properties of both. Of course, this usually isn't so dramatic for isolated atoms, only once we consider molecules or solids. ",
"But I digress, you asked how we know the shape. Well, there's a whole area of study dedicated to determining the energy levels and orbital shapes of atoms (and molecules and solids) to an ever greater accuracy. We've gotten very good at it, and we can determine them to arbitrary precision, but never 100% exact. But good enough. So I lied a little :p",
"I'll just namedrop a few key words here so you have a starting point to google/wiki if you're interested, but going over each of these could probably make me hit the character limit."
] |
[
"Is there a known reason why there are no multicellular prokaryotes? Could there be?"
] |
[
false
] |
I guess I'm confused about the transition from single-cellular to multi-cellular. Is there any reason that a nucleus is absolutely necessary for that? Thanks in advance.
|
[
"Well, depending on how you define \"multicellular\", there might be some prokaryotes that actually do qualify:",
"http://blogs.scientificamerican.com/lab-rat/bacteria-with-bodies-multicellular-prokaryotes/",
"But we do have far more multicellular eukaryotes. The nucleus allows much higher degree of regulation of gene expression, which allows for greater cellular specialization, a critical feature of multicellularity."
] |
[
"There actually are some \"multi-cellular\" prokaryotes, depending on how you define multi-cellularity. You might want to read up on filamentous prokaryotes. This is essentially when bacteria don't completely separate when they multiply, and thus end up producing long branching strings of bacteria. The structures end up resembling what is commonly seen in fungi, and these bacteria may even share nutrients to some degree.",
"Also, I'm not sure how much you know about biofilm formation? The most common existence for bacteria is not as singular free-floating cells, but rather in big communities tied together by \"slime\". While I wouldn't consider cells in a biofilm to really be a \"multi-cellular organism\", it's certainly a cooperative behavior."
] |
[
"The specialization is partly because there is a nucleus and partly because eukaryotes evolved more mechanisms for epigenetic control of gene expression. If you have a nucleus, you don't start to translate RNA as soon as its made. That allows for splicing, or essentially chopping the RNA into different forms. It also allows for small RNA to be used for genetic regulation. ",
"On top of this, eukaryotes have nucleosomes that pack the DNA up. This means that the cell can organize DNA into accessible and inaccessible regions and allows cells to specialize more effectively."
] |
[
"If a person gets an organ transplant (and assuming their body doesn't reject it) is there a point, after the body's cells have been refreshed with new ones, in which the replacement organ will have no DNA of the person that it originally belonged to?"
] |
[
false
] | null |
[
"No, that's not how organ cell replacement works. ",
"As cells in a transplanted organ die, if they are replaced they're replaced by cell division within the donor organ.",
"Since all of the original cells contain the donor's DNA, so will the replacement cells. The new host's DNA is never incorporated the cells of a transplanted organ."
] |
[
"Nine months is actually nowhere near the limit...",
"https://www.scientificamerican.com/article/fetal-cells-microchimerism/"
] |
[
"Ngl that's pretty damn spooky.",
"For the rest of your life, you have someone else's DNA inside you. As opposed to the previous 9-month limit on having someone's DNA in you."
] |
[
"How do the antibodies in a blood donors blood behave in the blood recipients body?"
] |
[
false
] |
[deleted]
|
[
"They work just fine; this is basis of ",
"immunoglobulin therapy",
". However, they don't work very long; half-life of various immunoglobulins is only a few days.",
"What blocks the significant response from the recipient's immune system is that the recipient has to be immunosuppressed to receive a transplant (in which I include whole-blood transfusion).",
"Also worth noting: most cases in which you receive blood from someone, you don't get whole blood — you get only some parts of it (for example, red blood cells or plasma), and those parts don't include antibodies. It's only when you receive whole blood that you are getting everything, and that works pretty much like any transplant does."
] |
[
"PhD here in a closely related topic. Your intuition is correct: the donor antibodies are simply too low in quantity to cause significant problems. ",
"A question on a more dangerous scenario is whether donated B and T cells specific to the ABO antigens can be encouraged to proliferate ( even hypermutate for B cells), thereby leading to the usual cascade of adaptive immune response. We know it doesn't happen too often because else transfusions won't be safe. As far as I know, literature is largely silent on which part of the chain is broken, or if the recipients' own adaptive immune system can somehow recognize and destroy the donor lymphocytes consistently regardless of genetic similarity between the individuals."
] |
[
"Thanks for the response. I would be curious to know where that cutoff exists, I assume one cannot transplant healthy antibodies between individuals of compatible ABO and see an uptake of the immunity so I'm curious how the foreign bodies are signalled."
] |
[
"What happens if water is not permitted to expand when frozen?"
] |
[
false
] | null |
[
"There are other forms of ice which take up less volume than the ice we're most familiar with. These occur at high pressures. ",
"http://en.wikipedia.org/wiki/Ice#Phases"
] |
[
"This happens:",
"http://www.youtube.com/watch?v=UlBFQCXdLXc&feature=youtube_gdata_player",
"Edit: For those who may doubt its authenticity, I've found a better video:\n",
"http://www.youtube.com/watch?v=erlZb8QiPkg&feature=youtube_gdata_player"
] |
[
"Ice is not the only material to do this. Most solids have more than one phase. Material science delves deeply into control the phases of materials to obtain optimal properties. For exam a steel can have vastly different properties based on solely how it is cooled. ",
"This site",
" explains more about the process of making various types of steel. The idea of something only having a solid, liquid, and gas phase is very simplified. "
] |
[
"If E=mc2 holds true then light has mass and if mass and time become infinite at the speed of light. How is lights mass not infinite?"
] |
[
false
] | null |
[
"E = mc",
" only applies to a particle that isn't moving."
] |
[
"So the energy being measured is any other form of energy other that kenitic?"
] |
[
"The energy that has a mass equivalence is the energy present even in a reference frame where the total momentum is zero. So in other words, it's the energy that is ",
" translational kinetic energy of the particle."
] |
[
"AskScience AMA Series: I'm Chiara Marletto - I'll tell you about a new way of formulating physical laws. I'm a quantum physicist and author of \"The Science of Can and Can't\". After this, you'll know the key to recasting the laws of physics to capture things like information, life and even the mind."
] |
[
false
] |
I'm Chiara Marletto and I am a physicist, with a passion for storytelling. I work on fundamental problems in physics, and I love quantum theory - one of the deepest and most fascinating explanations we have for physical reality. I have written a book to outline a radically different approach to expressing physical laws (on which I am currently working) which emerged from the theory of the quantum computer. It holds promise for solving century-old problems in physics, from how to explain information to formulating universal laws about knowledge-creation. I will be here at 12PM ET/5PM BST (16 UT), AMA! Username:
|
[
"I just liked writing a book on these new ideas - I love writing in general and it was natural to collect in a popular book some of the good informal explanations for this new theory I am exploring with my collaborators. I think the standard format of scientific publication is perfectly fine for communicating with other physicists, but I thought it would be a good thing that these ideas are understood and heard more broadly...and the book was a natural choice for that. I suppose I was also hoping that researchers from other fields than physics could perhaps get inspired by the topics I discuss in the book!"
] |
[
"I just liked writing a book on these new ideas - I love writing in general and it was natural to collect in a popular book some of the good informal explanations for this new theory I am exploring with my collaborators. I think the standard format of scientific publication is perfectly fine for communicating with other physicists, but I thought it would be a good thing that these ideas are understood and heard more broadly...and the book was a natural choice for that. I suppose I was also hoping that researchers from other fields than physics could perhaps get inspired by the topics I discuss in the book!"
] |
[
"The theory I am outlining is using the same well-known scientific method - but it's adopting a novel approach to expressing fundamental laws -- not in terms of trajectories and laws of motion like say Galileo and Newton did, but in terms of explanations about which tasks, or transformations, are possible and which are impossible. The hope is that this new mode of explanation allows you to capture more things in physical reality than just sticking to dynamical laws."
] |
[
"Are there any creatures with a single type of cone in their eye?"
] |
[
false
] |
So we humans have 3 color receptors, a dog had 2, and insects like bees have 4. Is there anything with only 1 color receptor?
|
[
"Whales, dolphins, and sharks only have one type of cone receptor---probably there are not much advantage to color vision under water. Some mammals that are active at night also only have one type of cone, e.g. some kinds of bats, hamsters and monkeys.",
"Humans actually have four types of receptors: rods and three types of cones. The rods are used for night vision. In the above species they typically have one kind of rod and one kind of cone, so it's theoretically possible that they could get a little bit of color vision by exploiting differences in sensitivity between the two, but maybe not.",
"One interesting case is squids: they only have one type of receptor cells, but ",
"it turns out",
" they can see colors anyway, by taking advantage of the fact that different frequencies refract differently in the lens of the eye."
] |
[
"probably there are not much advantage to color vision under water.",
"Depends on where you live. Fish that live in shallow, clear waters often have four cone varieties. But for large predators, especially ones that hunt in deeper water, it's not as useful"
] |
[
"Mantis shrimp?"
] |
[
"How do we know the number of stars in a galaxy?"
] |
[
false
] |
So I came across . It says that there are 800 billion stars in it. How do we know the number with any sort of accuracy when (I assume) the resolution of our telescopes is not good enough to count individual stars?
|
[
"They estimate....",
"Useful information includes:",
"\nTotal luminosity",
"\naverage luminosity per star. (After accounting for dust, and for average age of stars, which can be accounted for by measuring metalicity...) ",
"Size",
"\nShape",
"\nRotational speed profile (galactic mass) ",
"Suffice to say they certainly don't count the stars.",
"[Edit: Formatting]"
] |
[
"This is correct.",
"Counting stars isn't even an option - with the exception of the nearest handful of galaxies, we can't even see individual stars to count them."
] |
[
"I'm not certain, but for example, they could measure the area of the Galaxy with the telescope, and then sample different areas to find an average star density (either from counting individual stars which is unlikely, or applying models of similar galaxies that they have already researched) and then calculating how many stars must be in the whole area"
] |
[
"Computers are almost always performing more than one task at once. How do the computers keep these tasks from getting \"mixed up\" with each other?"
] |
[
false
] | null |
[
"This is one of the roles of the operating system. There are some complicated details, but the most important thing here is the concept of ",
"virtual memory",
". With virtual memory, the operating system can present to each process (program) what seems like a continuous block of memory and guarantees that this memory is private to that process. The OS actually has to perform a non-trivial dance where it keeps swapping parts of each process' memory between memory and disk but the end result is that each process does not have to worry about anybody else stepping on its toes. ",
"Since all of the processes have isolated virtual memory spaces, they cannot interfere with one another (more or less). Now all the OS needs to do is remember what step each process is currently at and swap between them as it sees fit. "
] |
[
"Just to clarify, the OS doesn't tell the task when to switch, it tells the CPU (usually via an IRQ). The CPU responds to the IRQ and the OS returns [task swaps] to a different task to give it CPU time. It's not voluntary on the part of the task.",
"In most cases task swaps also occur on syscalls (asking the OS to do something like read from disk). It's not the program that says \"hey put me to sleep while you read this data\" it's the OS that swaps to any free task.",
"From an applications point of view they are continuously running with their own memory state [virtual memory], etc... There are syscalls you can make to get your process details but if you weren't calling those functions you'd have no clue really that your task even stopped at all."
] |
[
"From a program flow point of view syscalls are instantaneous function calls. You'd have to use other syscalls to realize the the systime is not zero [or that walltime != usertime]."
] |
[
"Can someone's upper body be paralyzed while there lower body is functional?"
] |
[
false
] | null |
[
"Yes, there can be a form of central spinal cord injury that leaves the legs working but arms paralised, most of the time it come with impairment of arms, but yes, someone can have \"reverse paraplegia\"",
"I have a friend who is a t1-t4 paraplegic, and out of curiosity we were looking up other levels of paralysis",
"http://emedicine.medscape.com/article/321907-overview"
] |
[
"Yes. We generally call this central cord syndrome and it is not uncommon particularly in the elderly with spinal stenosis who sustained a hyperextention neck injury. Often it is associated with no actual fractures but instead with ligamentous instability.",
"As usual Wikipedia is your friend here. ",
"http://en.wikipedia.org/wiki/Central_cord_syndrome"
] |
[
"Short answer is yes it is possible, but unlikely.",
"Paralysis is caused in most cases by neurological damage. This can occur in several places, but the stereotypical paralysis patient has had a spinal cord injury. If the spinal cord is completely severed, the result is total loss of feeling and movement below the injury. It is also possible to have an injury or lesion that only affects some of the pathways up and down (efferent and afferent) the spine, resulting in partial loss of function, loss of feeling, even phantom pain. Because of the structure of the spinal cord, it is unlikely (nearly impossible) to injure ",
" the pathways to the upper body while leaving the pathways to the lower body intact. ",
"Outside of the spinal column, it is possible to damage the peripheral nerves that connect parts of your body to the spine. These injuries are common, and often result in a loss of feeling or a loss of function in a local area of the body, typically the extremities. Because the sensory pathways and the motor pathways are separate, it is possible to lose sensation and retain control, or vice versa. However, there is not a single location in the upper body where all of the peripheral nerves can be found, and injured, which means it would require multiple injuries to result in a paralysis of the upper body. ",
"Another possibility is to have an injury or lesion in your brain, causing a loss of feeling and/or control. Again, the sensory and control areas of the brain are in different cortices, so losing both would require multiple sites of damage. Theoretically, it would be possible to surgically excise or destroy specific areas of the brain to create such a condition, but those experimental surgeries are generally discouraged. Also of note, a brain injury would likely leave reflexes intact, at least until the muscles and nerves atrophy from disuse. ",
"Further reading:",
"http://en.wikipedia.org/wiki/Spinal_cord#Structure"
] |
[
"If photons have no mass, why can't they escape the gravity of a black hole?"
] |
[
false
] |
[deleted]
|
[
"This is a misconception about black holes. A better way to thinking about it is that every path you could take from inside the event horizon leads back inside the horizon because space curves in on itself."
] |
[
"Photons have no mass, but they are still affected by gravity. This is one of the core results of general relativity."
] |
[
"Because gravity isn't some force proportional to the masses of two objects, as you may have learned in high school. It's a consequence of spacetime being curved. And anything moving through a curved spacetime will follow curved paths, regardless of whether it's massless or not.",
"But wait, there's more! Not only do photons feel gravity, they ",
" as well! This is because in relativity, energy and mass are on the same footing - think E=mc",
" - so if mass gravitates, so does energy. And photons have energy. In fact, for the first 80,000 years or so after the Big Bang, photons were ",
" dominant gravitational influence in the Universe, and the Universe expanded in a qualitatively different way than it did later on when (dark) matter was the dominant force."
] |
[
"Why is it that when I get sleep deprived I get severely depressed? What evolutionary purpose is there for this?"
] |
[
false
] | null |
[
"Also, why do I often have a hard time falling asleep while sleep deprived?"
] |
[
"Actually, one study showed that sleep deprivation led to decreased depressive symptoms in subjects ",
"(source)",
" ",
"and the wiki for sleep deprivation",
"Your situation may be based on your own personal sleep habits and/or potential sleep disorders, and less to do with any ancestral selective forces. ",
"Friendly advice: If you are having problems with sleep and/or depression, consider seeing your doctor."
] |
[
"It is well established that sleep deprivation can lead to mood disorders and depression: ",
"http://healthysleep.med.harvard.edu/need-sleep/whats-in-it-for-you/mood"
] |
[
"How common is it to replicate research within different scientific fields?"
] |
[
false
] |
I was inspired by this post: I work in psychology and I have never read a published attempt to strait up replicate someone else's research. As far as I know there is very little disincentive to publish research that can't be replicated in psychology (let the ripping on psychology as a science commence!). How common is this within other scientific disciplines?
|
[
"Oh man, the first thing that came to mind was ",
"this article",
". If you can't read it, tell me and I'll host the pdf somewhere for you.",
" Basically what happened is that Homme Hellinga, who was a big shot protein designer with a meteoric rise to fame and huge money flowing into his lab turned out to be basing his success on a huge bag of twisted data and cherry-picked results. Lots of professors, excited by his putative \"success\", wanted to collaborate with him but he conveniently didn't reply to their offers because he knew his results were bullshit and non-reproducible and was trying to cover it up long enough until he had secured enough grant money for life (sadly, this worked).",
"One professor (the one who wrote the article I linked to above), disappointed with the silence, tried to go ahead and reproduce Hellinga's results so he could at least get started on building off of Hellinga's results but when it failed time and time again he thought he was doing something wrong, so he kept trying to get in touch with Hellinga to ask him what he could be doing wrong. Hellinga, of course, would not reply. This is a great example of how scientists, when confronted with data that conflicts with what they believe, can have a hard time accepting it. But it's also a testament to the undeniability of data and how reproducibility can convince even the biggest of skeptics.",
"Eventually it got to the point that he characterized Hellinga's failure so dramatically that it was utterly shameful for Hellinga and it made huge waves in the protein design community because for a while some people thought Hellinga's approach was the wave of the future since the results he was claiming were so remarkable. The professor noted how he basically had to waste a ton of time and money trying to build off dishonest results and that while there are plenty of grants that will go to the sexy but spurious results, there is no money to be found in disproving bullshit or independently verifying the reproducibility of data.",
"So the above paper was basically nothing but a huge disproof of a small part of Hellinga's huge mountain of lies, and around the time it came out, several other lines of evidence suggested that other results of Hellinga's were deliberately dishonest and their lab had to retract several papers. When it happened, my professor basically sat the lab down and talked about how even he fell victim to the illusion that Hellinga had cast. He had, in fact, been a reviewer on one of the papers that had been retracted and while he did note that he had had some suspicions about it, he felt that his objections were minor and that advancing protein design was so important that he was willing to look past them to get Hellinga's ideas out there. Now he realizes in retrospect the mistake he made and he taught us how important it is to believe what the data actually tells us and not what we want to believe."
] |
[
"That gets kinda hairy. People do not directly call each other out in my field via publishing non-replicative studies. I could try to rationalize it, but honestly everyone is afraid of pissing off other people in the field due to the fact that it might come back to bite them in the ass. I've had to bite my tongue and just move on when I discovered this one paper was a load of horse shit. The boss knew the PI really well, so when I told her about it she just shrugged and said, \"I guess that must have slipped by him because he was on sabbatical.\" That was the end of the matter. It really annoyed me, and it really chapped my ass whenever I saw that shitty paper referenced. ",
"Two years ago, though, someone published a very tidy and elegant paper that refuted the shit paper. It has really only been a short while since this study came out, but the shit paper no longer gets referenced and it has all but disappeared. Over time, as the science builds on itself, the crap gets filtered out. "
] |
[
"http://care.diabetesjournals.org/content/17/2/152.abstract",
"They replicated basic calculus. Does this count?"
] |
[
"My hair is brown but my facial hair is red. Why?"
] |
[
false
] | null |
[
"bah, stumbled in here via ",
"r/all",
". my apologies."
] |
[
"Off I go!"
] |
[
"Please keep discussion:",
"Civil",
"On topic"
] |
[
"Why are most pain relievers also fever reducers?"
] |
[
false
] | null |
[
"The pain relievers available over the counter are either NSAIDs (like aspirin, ibuprofen, naproxen) or acetaminophen (aka paracetamol or Tylenol.) Both act in some way to reduce the effect of a group of enzymes called cyclooxygenases (COX) which are important in producing inflammation. NSAIDs inhibit COX all over, while acetaminophen seems to only affect it in the nervous system. Inhibiting COX decreases production of stuff that would make certain neurons more sensitive to pain signals. One of the specific molecules COX helps make is prostaglandin E2 (PGE2), which helps alter the thermoregulatory set point of the hypothalamus in the brain. Stopping PGE2 synthesis reduces the fever response.",
"That said, many drugs effective for pain are not effective for fever.",
"https://xa.yimg.com/kq/groups/17820548/206501/name/Mechanism+of+antipyretics.pdf"
] |
[
"In short it is because fever and pain are caused by the same substances acting in different locations and drugs such as ibuprofen and aspirin inhibit the enzymes that produce these substances. ",
"In slightly more detail, inflammation at the site of injuries is characterised by a complex cascade of events. The COX (cyclooxygenase) enzymes produce the molecular mediators of these events, including prostaglandins and thromboxanes. At the site of injury, these substances cause vasodilation and increased vascular permeability (hence redness, swelling) as well as sensitise pain fibres (pain) but they also travel in the bloodstream to the hypothalamus where they increase the temperature set point (fever). Specifically, PGE2 (prostaglandin E2), PGF2alpha, PGI2 are thought to be implicated in the development of fever. Drugs such as ibuprofen, which inhibits COX-1 and COX-2 enzymes, thus reduce pain, swelling and fever etc.",
"Paracetamol/acetaminophen is different and only mildly inhibits the COX enzymes peripherally and has no substantial anti-inflammatory effect. Although it seems to act centrally (in the brain) exactly how it works is not clear.",
"Robbins Basic Pathology - Chapter 2 p 46\nBasic and Clinical Pharmacology 12th - Katzung, Masters and Trevor p 321, p 650"
] |
[
"Why is that? Isnt the difference just that COX-2 is mainly limited to inflamed tissue? "
] |
[
"What defines sentience? Is there a way to test for it?"
] |
[
false
] |
I've always been curious to find the answer to this question. Is it some level of technology that must be attained? Is it some level of communication? Is it a knowledge of self? Some combination of the above? I suppose I'm just trying to determine where sentience begins and ends for humans, and for other species. Edit: It's been pointed out what I'm probably looking for is consciousness.
|
[
"So... everything that's an animal is sentient? Slugs are sentient? Wouldn't that make just about everything sentient that's alive?"
] |
[
"We should expect sentience of some kind or another among all animals that are capable of modifying their behavior in response to stimuli in the short term, which is pretty much all animals. Because animals are capable of volitional movement, they are adapted to react to stimuli through feelings. The best argument for the thesis that animals feel pain is that they behave the same way we do when subjected to stimuli that cause us pain; our behavior is caused by our pain, and so common descent suggests that theirs is too. I believe that the term \"sentience\" as it is often used is a misnomer; what people are asking about it better termed consciousness. "
] |
[
"Hrm... okay, so is it just the mirror test? or is it a wider spectrum? Does that mean that all of those animals are sentient?"
] |
[
"Why do humans scream when they're scared?"
] |
[
false
] |
Is it a defense mechanism, and if so what is it supposed to accomplish?
|
[
"Humans are an extremely social species, and presumably had a tendency to express emotions very clearly/vocally. Screaming quickly gets the attention of all nearby humans that could help, kind of like crying when in pain, etc."
] |
[
"And many animals are naturally afraid of loud noises, including humans."
] |
[
"GAH, FUCK!"
] |
[
"Can cancer \"evolve\" like bacteria to resist treatments if we use those treatments often enough?"
] |
[
false
] | null |
[
"Cancer can acquire resistance to treatment, such as developing T790M mutations in EGFR mutant lung cancers treated with tyrosine kinase inhibitors. As cancer is not spread between individuals, this acquired resistance occurs within a single patient, not within a population like with micro organisms.",
"Individual cancer cells within a patient will show genetic diversity (the degree of which will depend to some extent on the type of cancer). If there are cells that are better adapted to survive the treatment (for example mutations leading to reduced expression of membrane receptors that are targets for anti cancer treatments), then presumably these cells are more likely to survive, and cell clones that are more resistant to treatment can develop."
] |
[
"This is true and also part of the reason treatments are more effective before they metastasize. If you only have a small bit of tumor, it's possible to eradicate it with chemotherapy relatively quickly, but if it's a large mass that has spread diffusely, it's more likely to have picked up resistant mutations. Then, as you do rounds of chemo, giving yourself time to recover in between, you run into the situation where you are killing sensative tumor cells faster than resistant cancer cells. This is when the response to the chemo agent changes and a 2nd or 3rd line agent is tried. "
] |
[
"Cancer doesn’t work and evolve like a virus would, so I would think not, but as it can work hereditarily, then there is a possibility that a stronger ‘version’ of the cancer will be passed down through the generations "
] |
[
"How is the change in magnetic field due to spatial variation different from from motional emf?"
] |
[
false
] |
Consider the case where a wire is moving in a magnetic field, the source of the magnetic field can either be the loop itself(rail) or an externally applied one (magnet). If the conductor where to move, the induced emf would simply be the change in flux, which simplifies to ε = -vBL for motional emf where the charges experience a magnetic force on them. However, if the loop was stationary. And the magnetic field source were to move causing two effects: Change in magnetic field due to it's strength changing. Change in magnetic field due to . If both effects were occurring can represent it. ?
|
[
"I believe it's not. Fixing the conducting loop and moving the magnet, of fixing the magnet and moving the conducting loop are equivalent descriptions of the problem. This can easily be seen by moving into moving frames of reference either centered at the loop or at the magnet. Not considering any acceleration phases, those two frames of reference are inertial frames of reference, and due to the ",
"Lorentz invariance",
" of electromagnetism, physical quantities should have the same value in both frames of reference. ",
" ",
"",
"Now to the question. Consider the case where you fix the magnet and move the conductor. Then, you potentially also get your two contributions you described in your formula:",
"",
"Thus, in a general case, both of your two cases are described by both terms of your equation. "
] |
[
"This is almost purely mathematical. Magnetic flux is defined as B*S, if B is not a function of space (at least localy where your S is). If you want to get the equation you have provided, you just differentiate the magnetic flux over time according to the product rule.",
"",
"ε = -vBL",
"This isn't a correct equation for emf for any given movment of the wire. For any given movment of the wire you would alo have to consider both terms...",
""
] |
[
"Same direction and magnitude, nothing changes.\nDifferent direction, you have to encode the dynamics of your system in B(r,t) or in S(r,t)"
] |
[
"Why some elements violate the octet rule? (I.e. H and He are stable with 2, Be is stable with 4, B with 6, and rows 3+ can have more than 8)"
] |
[
false
] |
[deleted]
|
[
"The octet rule is just a rule. The underlying reality is based on orbitals. Electrons form a sort of a \"standing wave\". Classically, an analogue is an orbit. The plain \"circular\" (ball) orbit is the ",
" orbital. That gives one quantum number (",
"), so at ",
" = 1, 2, 3 ... the electrons are on progressively higher spherical orbits. If electrons are of opposite spin, at each given ",
" you can fit 2 electrons. At the first shell, there's only a ",
" orbital, where you can fit 2 electrons.",
"But, the \"orbit\" can be a figure of eight as well, so there's a new quantum number (",
") for that, resulting in the ",
" orbital. A figure of eight can be in three different orthogonal orientations (see ",
"this picture",
" to understand why), so for ",
", we have three different states each of which can house two electrons: 2 x 3 = 6 ",
" electrons. At the second shell, there is a ",
" orbital and three ",
" orbitals, which in total can house 8 electrons, giving rise to the \"octet rule\". Lighter elements have only ",
" and ",
" electrons so it's easy to describe their behavior only using them.",
"At higher shells, there are several other possible shapes than the plain figure of eight. For these, we get two new orbitals ",
" and ",
" (we run out of stable elements before higher orbitals appear). ",
"Here",
" is a picture of them.",
"Why is this chemically relevant? For lower orbitals, the energy differences are very large, so the chemistry is very stark and simple. But for higher elements, it becomes \"softer\" because the orbitals are closer and closer together (see ",
"here",
"), up to the point that the shells interweave. The result is that a new ",
" orbital of a shell is in fact ",
" than the ",
" or ",
" orbital in the previous shell. So, new electrons added will disappear into the ",
" or ",
" orbital before the ",
" orbital that we associate with the \"octet rule\"; these elements don't obey the octet rule at all.",
"For rare earth elements, when you go up in atomic number, the extra electrons are put into the ",
" orbital of the lower instead of the ",
" orbital of the lower shell. So, these elements can \"eat\" 14 extra electrons before it shows in any way to the outside. Consequently, the 14 different rare earth elements are chemically extremely similar and are very difficult to separate. They will only lose the 2 electrons from the valence ",
" shell and possibly one from another shell, forming only M",
" , M",
" and M",
" ions. The up to 14 \"extra\" electrons don't show up in the chemistry at all."
] |
[
"So I get H, He, and rows 3+ but still don't get B or Be. If one can eat 14 then don't they get 20 not 6 and 4."
] |
[
"Elements H - He have only one ",
" orbital. Elements Li - Be have two ",
" orbitals. Elements B - Ne have two ",
" orbitals and three ",
" orbitals. ",
" orbitals start appearing from Sc on (transition metals); they fit 10 electrons. The next type, ",
", fits 14 electrons. See ",
"this diagram",
"."
] |
[
"Is it possible to separate alcohol from an alcoholic beverage by freezing the mixture and be left with the unfrozen, nearly pure alcohol."
] |
[
false
] |
Ok, I have this bottle of Admiral Nelson rum that I keep in the freezer and when it freezes, only some of it actually turns solid leaving part of the stuff liquid. I am under the assumption that alcohol cannot freeze but I could be wrong about that. So is the stuff that is unfrozen more pure alcohol or is the alcohol to well bound to whatever it is mixed with to separate?
|
[
"Yes, traditionally some apple brandies were made this way (by letting hard cider freeze overnight in winter and then pouring off the alcohol). However, in America this actually counts as distilling, and is illegal."
] |
[
"This is FUD. The amount of methanol present in undistilled cider is trivial, and freeze distilling only concentrates two- or three-fold. The only reason it's dangerous in regular distilling is that one particular segment of the distillate (the heads) is extremely high in methanol.",
"Besides, all the ethanol you're also consuming really helps to mitigate the methanol toxicity."
] |
[
"Alcohol can freeze, but only at much lower temps than the rest of the stuff in the drink. So you could technically make drinks stronger by freezing them and skimming off the liquid alcohol. And actually I think there's a beer company in Scotland or Ireland or something that makes insanely strong beer using this method. I'll see if i can find a link.",
"Edit: ",
"Found it"
] |
[
"I get why being in body temp water and weather is uncomfortable, but why is drinking water that's 98.6 degrees unpleasant?"
] |
[
false
] | null |
[
"I believe the answer is actually rather surprisingly simple.",
"When we drink a substance normally, there is the tactile sensation of the fluid, possible taste (assuming it isn't tasteless) and a temperaature sensation that we are used to. However, when drinking water that is our exact body temperature, the only sensation we feel is the tactile one of the fluid. No taste and no temperature, hence it feels strange.",
"I recall once at school, at a swimming carnival, me and my friends picked up a water bottle that had been in the sun for a while and decided to pour it down the back of another friend. He jumped up and was very unnerved - not because he was wet, but said that it felt very strange - like having dust that was sticky all over him.",
"The only explanation that I can think of to answer your question is that the lack of a temerature response from our nerves makes it feel an alien sensation to us - therefore making your \"drinking body temperature water\" feel unpleasant."
] |
[
"Of course he means Farenheit... You know that 98.6 F is significant, while 98.6 C is not, so why would you even bring it up?",
"And yeah, drinking warm water is extremely unpleasant, and personally, makes me feel sick if I drink it when I'm dehydrated or overexerted."
] |
[
"The OP uses the phrase 'body temp.' Yes, she should have been specific, but in the context of the question, you're just being pedantic."
] |
[
"Orca Whale color scheme"
] |
[
false
] |
Why is it that orcas all have a very similiar color pattern? Dogs of the same breed may look similiar, but don't have the same spots. Every orca I've ever seen looks the same.
|
[
"Dogs have been selectively bred by humans specifically to look different from each other. People like variety, and exaggerate it in dogs. People haven't been breeding killer whales to all look really different, so they pretty much all look similar (in a broad sense). "
] |
[
"Well...no. There's other things which can cause diversity in coloration within a species, too. But people tend to select for really diverse appearances."
] |
[
"So if left on their own, all animals would like nearly identical?"
] |
[
"Is a medications expiry date related in anyway to its packaging method?"
] |
[
false
] |
I have a bunch of medications in pill and capsule form that come in blister packs. Would putting them in to bottles effect their efficacy in anyway? I'm going traveling and prefer hardier bottles to avoid crushing.
|
[
"It certainly can have an effect. If a medicine contains compounds that are air or water sensitive (i.e., they decompose over time under those conditions), then taking them all out and putting them into a bottle would decrease their effective lifetimes. Only your pharmacist could answer that question for certain."
] |
[
"Blister packs also protect the pill itself from moisture and mechanical damage. Coatings can do a great job protecting the active drug from your body (saliva, stomach acid, etc), while still being relatively fragile. This is particularly true for controlled release doses (rapid OR extended release). Personally I'd leave them well enough alone, they're probably packed like that for a reason. If you're really concerned about packing toss them in something sturdy and flat like a tupperware sandwich box.",
"Source: Use to do analytical support for pharmaceutical formulators and physical testing on tablets."
] |
[
"https://www.reddit.com/r/askscience/wiki/sources"
] |
[
"From what sorts of materials would a rover need to be constructed in order to withstand the extreme pressure, temperature, and acidity found on the surface of Venus?"
] |
[
false
] |
Or whatever other environmental challenges you can think of. For a reasonable mission duration. [edit: let's say 90 days minimum] Assume a beefy budget but not unlimited. The laws of physics still apply so weight and method of deployment will factor in. What do you think? Edit: Some great responses; thanks! But I'm seeing some temperatures being tossed about which I'm not sure are accurate. From NASA's Venus Fact Sheet: Surface pressure: 92 bars Surface density: ~65. kg/m3 Scale height: 15.9 km Total mass of atmosphere: ~4.8 x 1020 kg Average temperature: 737 K (464 C) Diurnal temperature range: ~0 Wind speeds: 0.3 to 1.0 m/s (surface) Mean molecular weight: 43.45 g/mole Atmospheric composition (near surface, by volume): Major: 96.5% Carbon Dioxide (CO2), 3.5% Nitrogen (N2) Minor (ppm): Sulfur Dioxide (SO2) - 150; Argon (Ar) - 70; Water (H2O) - 20; Carbon Monoxide (CO) - 17; Helium (He) - 12; Neon (Ne) - 7
|
[
"The key question is \"for how long?\""
] |
[
"The pressure isn't an issue at all... We frequently deal with 600 atmospheres underwater. The problem is heat. You can't even use a glass camera lens at that temperature."
] |
[
"Sure you can use some strong metal for the structure, but I really doubt our silicon/copper/tin/whatever based electronics could be shielded in such a way to work on a planet with a 740 degree C atmosphere. What cooling apparatus could we ever use? How would we power it even if we could develop one?",
"For reference, aluminum, zinc, and magnesium melt at this temperature. Even if you develop some kind of exotic solid state system that doesn't need any of that, then what battery system do you think you can use? Solar panels won't make it and even plutonium melts at this temp, so not RTGs. I guess you could use uranium if your RTG apparatus could handle the temps, but RTGs work on temp difference and they may not even get hot enough to create any energy in a 750c environment. Even if you solve the energy problem, I doubt we can find a battery that will work in those temps for very long. Electric motors and wiring may be an issue as well. Copper doesn't melt until 1000c but I can't imagine running a copper wound motor or its bearings would work at 750c.",
"On top of it, camera technology isn't tough. What CCD could we make that could run at 750c. There are other practical things to consider like what landing system could you use. A parachute system probably won't work as the materials its made out of might melt. Retrorockets only I guess. Then little stuff like making tires and wheels that'll grip using only materials that won't melt. I'm not sure what processor/board could handle this stuff. Curiosity runs on a PowerPC chip hardened to withstand extreme temps and radiation, but not this extreme. You'd have to invent a whole new kind of CPU!",
"I think this is totally impossible, especially given the size and weight constraints of spaceflight. I would argue launching a satellite into Venus's orbit that could drop a bunch of disposable mini rovers/probes is going to be as close to \"roving\" as possible.",
"tldr; electronics hate heat"
] |
[
"Why doesn't all the Uranium in a sample decay at the same time?"
] |
[
false
] |
On the latest Cosmos episode, Dr. Tyson explained radioactive decay. He said that, in a sample of something that contained Uranium, the Uranium decays and eventually turns into lead. So, if you measure the amount of both, you can figure out how old the sample is. Hopefully, I at least understand that part correctly. My question is: why doesn't all the Uranium in the sample decay together? Why is didn't all of it turn into lead if some of it did? Assuming it all decays at the same rate, one might think it should all decay at the same time and there shouldn't be any Uranium left. I'm having a hard time understanding this and couldn't really find an answer on the internet because I don't really know what I'm looking for. Thanks in advance for helping me to understand this!
|
[
"Radioactive decay like this is something that, at this point, we believe is totally random on a single-atom basis. If we have a single radioactive atom, we have no way of knowing when it will decay. With enough radioactive material, though, the decaying process falls into a pattern, because the ",
" of an atom decaying isn't random. So while there is a probability that all the radioactive atoms in a sample could decay at the same time, this chance is ",
" small."
] |
[
"It's not that there are different \"starting points\" - but rather, the entire process of radioactive decay is probabilistic in nature. You cannot point to any one atom and say \"they will decay in 5 minutes\". There simply ",
" a fixed \"decay time\". All the figures you see - rate of decay, or half-life - are statistical figures. They do not describe the behaviour of any single atom, only collections of them."
] |
[
"Ah, ok. That does make sense. I'm obviously not a chemist, but I just inferred from what I learned that constant rate of decay + same starting point => same decay point. So, just to make sure I understand this correctly, there's different starting points. The atoms don't all begin to decay at the same time, which is why samples are usually a mix of lead and uranium."
] |
[
"Why do large icicles appear ribbed?"
] |
[
false
] |
This doesn't seem to be true of all icicles, especially the smaller onee, but most of the large ones (30cm+) appear to have this ribbed affect. What's causing this?
|
[
"This paper",
" (open access) suggests it's a result of dissolved salt. In laboratory experiments, pure water icicles do not form ripples.",
"We don't understand very well what goes on near the fluid-solid interface in solidifying mixtures, but there are weird partially solid \"mushy layers\" that might have something to do with it.",
"Incidentally, the ripple spacing is apparently a constant."
] |
[
"Pretty well summed up by the last sentence \"this elegant example of natural pattern formation remains theoretically unexplained.\" Interesting that someone has actually worked on this professionally though."
] |
[
"Consider this a common sense explanation - with smaller icicle, a water drop can make it all the way to the bottom of the icicle before freezing, and then freeze there. With larger icicles, the water drop may freeze on the way to the bottom and thus create what you're referring to as a ripple."
] |
[
"Biologically speaking, what happens when you get your \"second wind?\""
] |
[
false
] | null |
[
"No one completely knows, but the leading theories are:"
] |
[
"Interesting. I thought point one was a well accepted and demonstrated fact. Why hasn't anyone been able to prove that the body has switched to burning fats during a second wind?"
] |
[
"If you are referring to the phenomenon experienced during intense exercise... The jury's still out. No one really knows (yet!)"
] |
[
"What exactly is an \"engine\" (software-wise)?"
] |
[
false
] | null |
[
"ITs a frame work. Simply put it handles some expected functions, and returns answers and solutions.",
" speaking it is everything that isn't an interface or decoration.",
"If you were to compare it to car analogy, its the chasis, transmission and engine. Later you add buttons/pedals/wheels/seats/bodywrok to make it look and function like you want.",
"You are currently using a web browser, this is built on an engine... a layout engine. webkit if you are using chrome/safari, gecko for firefox etc.. They all have different abilities, but the functionality to tap into these abilities is dependant on the bells and whistles.",
"Chrome and Safari are very different, but they have the same framework.",
"Most programmers will add a good deal of functionality after the engine, even linking two engines together (source and Havock) with their interface to provide a piece of software."
] |
[
"I'd compare a software engine to the powertrain of a car: motor, transmission, driveshaft, wheels, i.e. everything the car needs to move. Software engines are active components, in the sense that they maintain their own internal state and data structures and perform some kind of complex data processing. This is subtly different from software ",
", which tend to be more passive components like a car radio or power steering unit. The car chasis, which provides a structure to bolt everything else onto, is akin to a software ",
".",
"There's a ton of overlap though, sometimes all three words get used interchangeably."
] |
[
"It's vague definition that uses analogy from real world: ",
"Roughly speaking it's the part of the system that does the main work and is the core of the system. You could as well use terms kernel, core, main- etc. to describe it but there are very vague conventions that dictate what word is used. For example in operating systems the equivalent is called kernel, but in databases it's called database engine. "
] |
[
"Can metals be broken/damaged due to the photoelectric effect?"
] |
[
false
] |
Hello, I was reading about the photoelectric effect. I was wondering if the frequency of the EMR was high enough to surpass the work function energy (the energy needed for the electrons to break free from the positive ion metal attraction). Since the electrons in the metal are able to escape. Is it possible for metal to fall apart? Thanks.
|
[
"/u/spaghettiJesus",
"At energies much much higher than the work function, it is possible to induce structural damage. But around the work function it shouldn't happen. "
] |
[
"I think you're making a slight mistake here. In the photoelectric effect phenomenon only electrons are ejected from the surface and as such matter is not lost from the metal.",
"In photoelectric effect the electrons are liberated from the surface of the metal and the excess energy supplied is converted used up to provide kinetic energy to the electron. It's also noteworthy that an electron only has 1/1800 times the mass of a proton and doesnt really affect the mass of a substance significantly or its structural integrity ",
"EDIT: If anyone is still reading this I highly recommend reading reading all the replies. It seems I have made some mistakes."
] |
[
"The electrons liberated are 'free electrons' which are free to move in the lattice of the material. Their presence or lack of them doesn't change the integrity of the metal. ",
"EDIT: this is wrong. Refer to ",
"this comment"
] |
[
"On a molecular level, what makes something adhesive? E.g. tape, glue."
] |
[
false
] |
Follow-up: Are there any solids that won't be adhered to? Maybe only a theoretical substance? Also, what would be special about that substance's molecular structure?
|
[
"Van der Waals forces. It describes how two molecules when close enough attract to each other outside of ionic and covalency, that is, without a chemical reaction. It explains how gecko or house lizards can climb on almost any surface. ",
"So, theoretically, if there is a compound that is totally van der Waal proof, u could have a perfectly non-sticky material."
] |
[
"Just in case you didn't know, there are two types of stickiness, adhesive and cohesive. You asked about adhesive so I'll address that first.",
"The goal in making something adhesive is to maximize the intermolecular forces between the two substrates. To start off, you want a gigantic molecule, a polymer, which bends and flexes pretty easily (this mostly means it has a low ",
"glass transition temperature",
", Tg). Most typically, this is a hydrocarbon chain (with various substituants bonded to it). The polymer has two great advantages for its adhesive strength, first, it has the opportunity for a huge amount of intermolecular bonding (the_Medic_91 and msief mentioned two types of them), and second, it can bend and fit into those microscopic peaks and valleys which makes friction a thing. All of this adds up to the greatest amount of intermolecular forces adhering the polymer to the substrate (both the backside of the tape and whatever the tape's stuck to).",
"But just one polymer can't really do much, that's why there's millions of them. This is where cohesive strength comes into play. Cohesive lets the polymers hold together which makes the thin film a ",
"network",
", rather than just a bunch of molecules on a piece of plastic. Cohesive strength primarily comes from the tangling of these gigantic polymers, and, to a limited degree, their individual adhesion to each other. This can also be called crosslinking, in which one polymer covalently bonds to another, not end-to-end, but somewhere in the middle of either (or both) molecules.",
"Both these qualities need to be balanced though, because flexible, linear chains don't tangle nearly as much as branched, dendritic polymers. But, dendritic polymers don't adhere nearly as well as linear ones do. So, by varying the \"proportions\" of the molecule, people can change around the properties of the coating, i.e. it can be incredibly strong, leave no residue on release, or hold up against high heat. "
] |
[
"As has been mentioned, it's believed that the adhesive properties of certain materials is due to the inherent van der Waals' forces found between the material and the substrate being adhered to.",
"Stick proof frying pans are a good starting point in finding a perfectly non-stick substance. They are typically made from coatings of polytetrafluoroethylene (PTFE or Teflon). This polymer finds it lack of stickiness from the presence of the fluorine atoms along the polymer chain. The fluorine atoms are very poorly polarised and so induced London van der Waals' forces are significantly removed, in turn reducing any materials stickiness to the frying pan.",
"PTFE, for the same reasons, also has a very low surface free energy (comparable to surface tension for liquids). The surface free energy in that sense is a good measure of the stickiness of a substance. The lower the surface free energy of a solid, less is the tendency to cover it's surface. So I guess a perfectly non-stick surface would have a surface free energy of 0. However, this is not possible as this would lead to the material spontaneously producing surface interface. Essentially it would, impossibly, have no self cohesive forces in it's bulk. Van der Waals' forces will always be present as electrons will always be present and so everything always has a surface energy/ tension. ",
"In the end it is impossible to have a perfectly non-stick substance. The best we can do is to try and reduce the surface energy as much as possible."
] |
[
"A journey to the center of the earth?"
] |
[
false
] | null |
[
"Hi ourpablo 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.",
" ",
" "
] |
[
"Can I ask why so many people are asking this question?"
] |
[
"I really couldn't say why others have asked, perhaps they're curious?",
"I've never seen it posted before, the thought just popped through my head today and I figured I'd ask."
] |
[
"If you had an alloy of every metal, would it have properties from every metal?"
] |
[
false
] |
Maybe an odd question, but I feel like you guys could answer it.
|
[
"Alloys don't really approximate combining the properties of the constituents. For example, many alloys are harder or stronger than all of the component metals."
] |
[
"Likely no. The properties of alloys are often quite different to the properties of the component metals, because those properties often are the result of the substance's crystal structure and introducing some dopant (like carbon in steel, say) can completely change the structure and therefore a property like strength. It's not that carbon is stronger than iron. It's just how the structures interact."
] |
[
"It is most likely impossible to make an alloy out of every metal possible. You could easy embed inclusions of every into an alloy, but you wouldn't be able to get a homogenous mixture on all the metal elements due to their varying properties (notably melting point).",
"Some metals are also incompatible with each other. One such example is galvanic corrosion where two stable metals corrode each other when they come in contact due to different electrode potentials and you get an electrochemical oxidation. In this case you would end up with an oxide instead of a metal alloy that you had hoped for.",
"To answer a similar question - if you were to mix many metals together, yes they would all contribute to the overall properties of the alloy as a whole. This is generally referred to as doping. Many alloys used in cutting edge technology, aviation, superconductors have upwards of ten or more metals in their composition - all of which offer so benefit be it corrosion resistance, creep resistance, lower density, higher strength, better conductivity, etc."
] |
[
"What causes the aftertaste one gets when administered certain anesthetics and illicit IV drugs?"
] |
[
false
] |
I had an EGD last week and remembered a medical taste come into my mouth. Some IV users have reported experienced this "taste". What causes it, and why does it have the flavor it does?
|
[
"This happens frequently with IV medications. It seems to be especially common with prefilled saline syringes. ",
"The mechanism is that when certain volatile compounds enter a vein and get circulated, within a few seconds they pass through the lungs. The compounds evaporate into the lung airspace and are exhaled. The smell or aftertaste occurs as they pass through the nose and mouth on the way out. "
] |
[
"Any source on that? I always figured it was because it got into your blood, and the blood passed through your tongue shortly after and got in that way."
] |
[
"I haven't found the original study where I read this.",
"This article mentions it in passing",
", in the conclusions section.",
"We wouldn't expect blood inside your tongue to affect your sensations, because your taste buds point outward. If we inject dextrose, you don't taste sweetness. If we inject highly concentrated saline, you don't taste salt. If we inject promethazine, you don't smell or taste it (which is good, because that stuff stinks)."
] |
[
"If we were to send a man into space at 99.99% of the speed of light. Would the time dilation allow him to live long enough to reach distant stars?"
] |
[
false
] |
Time slows down the closer we get to the speed of light, so if somebody were to approach c, then wouldn't they in turn age slow enough to last a trip to say, Alpha Centauri? EDIT: Thanks for all the awesome responses you gais. From what I'm understanding from the discussions is that the faster the person on the rocket ship travels, he would experience time normally from his perspective, while observers on Earth would see him slow down. And if one were to actually travel at 1c, then the trip from his perspective would seem instantaneous. Thanks again for your inputs!
|
[
"That is correct. If a person is traveling at 0.9999c toward Alpha Centauri relative to Earth, then length contraction means they see the distance between Earth and Alpha Centauri as being about 0.062 light-years. Then they will experience only about 0.062 years, or around 22.5 days, before Alpha Centauri reaches them."
] |
[
"Absolutely. A person traveling to Alpha Centauri from Earth at 99.99998% the speed of light relative to Earth would have the experience of Alpha Centauri rushing toward them (and Earth rushing away from them) at 99.99998% the speed of light for roughly 1 day before the star shot past them.",
"Of course, this ignores the problem of getting up to that speed and slowing down from that speed. If we want to include that, ",
"this site",
" has a handy calculator that assumes you start at rest, want to stop at your destination, and undergo constant magnitude acceleration all the way. Plugging in test values for the acceleration and using Wikipedia's distance of 4.37 light years for the average distance between the sun and Alpha Centauri, we see that you'd need a constant acceleration of around 7400 g (that's 7400 times the acceleration due to gravity at Earth's surface) in order to have the trip seem like only a day to you."
] |
[
"Well that's not too bad. It's only 7384 g more than a human can survive sustained for one minute."
] |
[
"How does suntan lotion protect someone from UV rays?"
] |
[
false
] |
I've always wondered this. Sunblock is just a cream. So how does it actually stop the rays of the sun?
|
[
"Inorganic ingredients like zinc oxide or titanium oxide reflect or scatter ultraviolet (UV) radiation. Organic ingredients like octyl methoxycinnamate (OMC) or oxybenzone absorb UV radiation, dissipating it as heat.\n",
"Source"
] |
[
"Titanium and zinc oxides are wide bandgap semiconductors. They absorb light over their band gaps. Light smaller than the bandgap is not absorbed. Though scattering and other effects also exist. "
] |
[
"Simply, the particles in the sunblock either absorb the UV radiation and/or reflect it, thus preventing your skin from absorbing the harmful radiation."
] |
[
"what are the large voltages described in particle accelerators measured against?"
] |
[
false
] |
in press releases from the LHC, proof of the higgs was demonstrated by evidence occurring at huge voltages. what potential differences are these particles being measured against? and we read claims of gigantic voltages made in reference to the overall power of particle accelerators. what source are these voltages measured against?
|
[
"If you're referring to measurements in \"electron volts,\" that is a unit of energy equivalent to the energy gained by an electron dropping through a potential difference of one volt. The mass of particles is often described in electron volts per c",
" , but the c",
" is usually ignored and we say that the electron has a mass of 511,000 eV, the proton about a billion. The particles in the colliders have a kinetic energy, also described in eV. When they have the same kinetic energy as rest mass energy, they are travelling at 86% the speed of light, and when the kinetic energy is much greater, they are going very close to light speed. The protons in the LHC have about 7 TeV of kinetic energy (in the rest frame of the collider), about 7000 times their rest mass energy, and in the center-of-mass frame of each collision they have about 13 TeV (I think it's designed to go up to 14 TeV).",
"The protons are accelerated to those speeds using electric fields, and those involve the extreme voltages you're talking about."
] |
[
"In the LHC we have bunches that contain about 10",
" protons.",
"The bunch crossing rate (how often bunches of particles meet in interaction points) for the LHC is 40 MHz. We have 2808 bunches around the machine. ",
"At the interaction points the beams are squeezed to a size of a hair to allow more collisions to happen. The big experiments (ATLAS, CMS) can record several events per bunch crossing. That gives us something in order 100M collisions per second.",
"More calculations here: ",
"http://lhc-machine-outreach.web.cern.ch/lhc-machine-outreach/collisions.htm"
] |
[
"In the LHC we have bunches that contain about 10",
" protons.",
"The bunch crossing rate (how often bunches of particles meet in interaction points) for the LHC is 40 MHz. We have 2808 bunches around the machine. ",
"At the interaction points the beams are squeezed to a size of a hair to allow more collisions to happen. The big experiments (ATLAS, CMS) can record several events per bunch crossing. That gives us something in order 100M collisions per second.",
"More calculations here: ",
"http://lhc-machine-outreach.web.cern.ch/lhc-machine-outreach/collisions.htm"
] |
[
"Why do we all have different voices?"
] |
[
false
] | null |
[
"We all have different bodies and brains. Differences in vocal cords, tongue, teeth, and lungs can affect speech, but the brain is the main part. The brain is why lots of people can do foreign accents or impressions but still have a natural speaking pattern separate from those. We pick up our unique way of speaking as children as we learn to talk. Baby babble mostly sounds the same, but by the time kids speak in full sentences they have a much more individual voice. As they grow, kids pick up expressions, vocabulary, and vocal quirks that further separates each kid from their peers."
] |
[
"That would be a stretch. It's more nature and nurture. Your physical characteristics will impact tonality and what not. You're upbringing will impact cadence, pronouncation, and other influences. Finally, your brain will make its own choices combining all this input into your own voice.",
"You can consciously influence some parts like pronouncation and accent if you work at it."
] |
[
"So, the reason of our voices being different than each other is we actually choose our voices."
] |
[
"Why does rotational motion seem to cause an infinite force that has no origin?"
] |
[
false
] |
I am confused about how rotational motion applies forces to a system. Newton set forth a (non-practical) thought experiment of two globes being connected by a string, and both the globes and the string as a whole rotated in a perfect vacuum of space (to clarify: the globes would in this configuration trace a large circle as the entire device rotates). By rotating the globes connected by a string, a basic understanding of angular velocity would show that the globes would feel a force against each other, so, if you put a force measurement device at the center of the string, it should show a force as the globes try to pull away from another, acting a force upon the string. This makes sense to me, because the globes would need to act a force on each other in order to keep them from flying off into space on straight lines, instead of continuing in a circle. However, I am confused about where this force comes from. For example, let's say 50 newtons of force are acted upon the device to start it spinning, and that no other force is added. The globes experience no friction, no gravity, and no other force to slow them down. In this case, would the globes continue infinitely spinning, always measuring the same force on the string? If this is true, I do not understand where this force comes from...it seems as if an extra force would have to continuously be added in order to continue acting a force on the two globes. As another example, let's say you have a non moving box connected to a string in the same type of perfect vacuum, and someone inside of the box. If you act 50 newtons of force upon the string pulling it in the opposite direction of the box, the person inside the box should feel 50 newtons of force against the side of the box that is opposite the pulling direction of the force. This makes sense as a force is added and thus a force is impressed upon the person. Then, after a while, I assume they would feel no force and the whole box would be moving with the person and the string at the same speed through space in the direction the initial force was pulled. However, if you tie the same string and box mentioned above to another identical box/person and apply 50 Newtons of force spinning the whole device, the same way as the two globes were spun, the people in both of the boxes would at first feel a force against the side. But, would they then both infinitely feel a force against the sides of the boxes? Would this force never die down? If this is true, it seems the force must be coming from somewhere, or that something must continue spinning the boxes in order to create these forces. If there is no force added to the system, over time, would the boxes stop spinning and come completely to rest? I realize the string acts a force upon the boxes by holding tension, keeping them together, but it seems illogical to me that with no force added the people in the boxes would consistently feel a force, it seems like that would mean force and energy is created from nothing. Any help would be appreciated, I might just be misunderstanding something elementary but I can’t seem to figure this out. Thanks!
|
[
"Maybe this will help you get thinking in the right direction:",
"In the example of the spinning balls connected by a string, the force that the balls exert on the string is only a reaction to the force that the string is exerting on the balls. Without the string the balls fly off in uniform motion right? So the string is pulling them inwards with a force - a force that ultimately comes from the bonds holding the rope materials together (we usually just model this as a tension force in the rope and let it go at that)",
"it seems like that would mean force and energy is created from nothing.",
"There doesn't have to be a supply of energy involved for a force to be exerted. No energy is expended in or on the system because everything is in equilibrium - the energy of the system doesn't change while it's spinning. The idea that you have to expend energy to exert a force is a mental bias that comes about because that's your experience; if you push on a wall for a while you will get more and more tired even if you don't cause it to change it's state of motion. But the reason you're expending energy in that situation has to do with the physiology and biochemistry of your muscles, not from the physics of the situation."
] |
[
"You can have an infinitely prolonged force if no energy is used. It takes no inherent energy to maintain a force, energy is only used if the force is acted on over a distance. ",
"For instance, you can make a similar analogy with a weight on the end of a string tied to the ceiling. The string pulls up on the weight with a certain force, stopping it from falling to the ground. The weight can hang there forever, because no energy is exerted by the string, because the weight doesn't go anywhere.",
"This misconception might come about because as humans, it takes a great deal of energy to sustain a force. For instance, if you push on a wall, you use a lot of energy, but the wall doesn't move. But this is due to the mechanism of our muscles, which require energy to stay flexed. But if you think about it, the energy we are exerting isn't going into the wall. The energy is actually just wasted as heat. A string, on the other hand, requires no energy to stay flexed, and so no energy is used, and so can stay flexed forever."
] |
[
"Yes. Energy is force times distance (in direction of the force). If there is no relative motion, there is no energy exerted. Force does not intrinsically require energy."
] |
[
"Why do we need a launch system like the space shuttle to get to space?"
] |
[
false
] |
If a plane can travel hundreds or thousands of miles on it's fuel (depending on the plane), why can we not simply fly the short distance into space? (Yes... I understand the occupants need things like air, etc. I'm just asking why we need 'rockets' to get there). EDIT: Air is the answer, I meant for the people inside the vehicle in my clarification.
|
[
"Vehicles attempting to get into space require thrust to counteract the force of gravity constantly acting on them. Planes can't fly into space as they require the atmosphere to generate lift; there is less air the higher they fly so there would be a point on their ascent where there would not be enough lift to allow them to fly higher."
] |
[
"You've answered it yourself - air. Not only does an aircraft need air to be able to generate lift with its wings, it also needs air to combust its fuel within the engines, and air to generate thrust. Aircraft cannot function in a vacuum.",
"Rockets are used because they contain everything neccessary for combustion, and do not require air. They generate thrust by ejecting mass at a high velocity and conserving momentum. They function in a vacuum. "
] |
[
"I realized that once the other person answered, and I feel pretty stupid.",
"For what it's worth, I meant air for the occupants. But still... I feel dumb."
] |
[
"Are there any good examples of species who hit an evolutionary “fork” and further evolved separately into both predator and prey?"
] |
[
false
] |
That’s about it really. I’m asking if the evolutionary trend towards either predator or prey is set in stone.
|
[
"I’m asking if the evolutionary trend towards either predator or prey is set in stone.",
"No, definitely not.",
"It wouldn't be meaningful to say that. ",
".",
"For example, here's the family tree of the placental mammals.",
"- ",
"https://en.wikipedia.org/wiki/Evolution_of_mammals#Molecular_phylogenetics-based_family_tree_of_placental_mammals",
" ",
"You can see that the order Perissodactyla (horses, rhinos, tapirs) is closely related to the order Carnivora (cats, dogs, bears, seals, etc) - ",
"and those groups are more closely related than other groups - ",
"e.g the Perissodactyls (horses, rhinos, tapirs) (herbivores) are more closely related to wolves and lions (carnivores) than they are to goats or cows or camels or elephants (less-closely-related herbivores).",
".",
"Another example might be theropod dinosaurs.",
"Most of them were carnivorous - everybody knows ",
" and the \"raptor\" dinosaurs, ",
"but their cousins the therizinosaurs are thought to have been herbivorous ( e.g. ",
"https://en.wikipedia.org/wiki/Therizinosaurus",
" ).",
"Family tree - ",
"https://en.wikipedia.org/wiki/Ornithomimosauria#Phylogeny",
"The \"tyrannosaurs\" are 4th from the top, the therizinosaurs are 3rd up from the bottom.",
"."
] |
[
"You can pick any two species and they \"forked\" at some point. So in the technical sense, any predator/prey species you pick is an example. I don't think that's what you mean, I think you mean that the split was somewhat proximate. I have no idea what the most related a predator/prey species is, on the scale of things I'm sure there's some predator and prey animal that split \"recently\", but I'm not sure how close they would have to be for it to count for you.",
"And no, nothing in evolution is \"set in stone\", though of course, some evolutionary paths are going to be much more likely than others."
] |
[
"For a more recent example, the cichlid fish in Lake Tanganyika all evolved from a single ancestor species over the past 10 million years. Herbivores, predators, detrivores, and more. ",
"(Other African lakes have had similar cichlid radiations but this is the most extreme example.) ",
"https://en.m.wikipedia.org/wiki/Lake_Tanganyika"
] |
[
"Type of chemical bond between cooked rice sticking to ladle?"
] |
[
false
] |
i have one stupid question or childish question. i used a ladle to take rice. After taking rice from the vessel and you make it dry (as i feel i will wash the vessel in the morning). The next day if i wash, it is very hard to remove the dried rice from ladle. if i put in hot water for few minutes it is easy to wash it or remove it. I am wondering what kind of bond or adhesion is responsible for this rice sticking to the vessel. cooked rice i.e carbohydrate polymer. if you further that is amylose and amylopectin there must be some bond between the steel ladle and this carbohydrate polymer. do you have any idea about it. when a substance is dissolved in hot water/water. it means it forms hydrogen bonding. i believe that's what dissolves means. when starch is dried, it forms retrogradation (becomes harder), it is sort of rearrangement of bonds between amylose and amylopectin and sort of crystallization. hot water (water molecules constantly forming/losing hydrogen bonding with the available neighboring atoms, as it in high energy state) breaks the inter (steel) and intra hydrogen bonding between amylose and amylopectin and competes for hydrogen bonding and i guess that is the reason starch get broken from the surface of steel or am i wrong?
|
[
"Adhesion can occur in a number of different manners, but in this case, you have what are called \"van der Waals interactions\" - when molecules get very close to each other, they tend to stick. In this case, the soft carbohydrates, etc. are close enough to the metal to stick.",
"When you add water, you are hydrating the carbohydrates. The carbohydrates will swell as they interact with more and more water. This swelling puts enough tension on the adhering portion of the molecules that they pull free from the metal."
] |
[
"A water molecule is small and so it will interact with the glass very little, while a starch molecule is comparatively huge and will interact multiple times. It will also be entangled with other starch molecules which themselves are interacting multiple times..."
] |
[
"Thanks for the answer. Is that van der Waals interactions is that much stronger. I learned for instance a water molecule sticks to the glass is due to the van der waals interaction and it is easy to break."
] |
[
"Why do the sea level records from an island in the baltic sea do not show a rise in the sea level over the last 60 yrs?"
] |
[
false
] |
Serious question, I know climate change and the melting oft the ice caps leads to a general rise of the sea level, please don't put me in a corner with people who doubt that fact. I came across records from the coast of the island Usedom today (was looking into something related for work) and it may be a stupid question, but I thought you could see the sea level rise, but there wasn't much of a trend in the data. Is the time period of 60 years too short? Or are there other reasons for this, like tectonic movements or the fact that the water exchange with the Atlantic Ocean is limited?
|
[
"In short: ",
"post-glacial rebound",
". ",
"Longer: A sea level record in a place is a measure of ",
"relative sea level as opposed to eustatic sea level",
", meaning that the observed change in average level of the ocean relative to a fixed point on land is the product of the rate at which sea level is changing, but also the rate at which land elevation is changing (both with respect to some fixed datum). In the case of many places in the northern parts of Eurasia and North America, due to ",
"isostasy",
" and the removal of mass from the land by melting of the ice sheets that existed during the ",
"last glacial maximum",
", the land surface elevation is going up faster than sea level is rising, so in those locations, you observe a relative sea level fall. In the case of Northern Germany / Poland, the rate of post glacial rebound (refer to the map in the first link) is pretty similar to the rate of eustatic sea level rise, so you would expect to basically see not much of a trend."
] |
[
"Very nice answer. On the east coast of N America, Canada and Maine will have much longer to prepare for sea level rise because of glacial rebound while folks in Florida are dealing with it now."
] |
[
"Florida is TOTALLY isostatically rebounding, just for a different reason from what ",
"/u/theprofessoro",
" described.",
"See ",
"this paper",
" for example. Some of the highest points in central Florida are former coastal dunes, higher than the ocean ever got at the time they were made. How did they get there?",
"Basically, Florida is almost entirely made of limestone. Rainwater erodes limestone into caves and sinkholes, taking that mass out to sea. Without that mass, Florida weighs less on the mantle, and rebounds for the same reason that formerly glaciated states are rebounding.",
"Unfortunately, this rise is slower than glacial rebound, on the order of 0.05 cm/yr. Sea level is rising much faster than that, and lots of Florida is still fucked. (Also I'm not sure if coastal Florida near Miami is rising at all.)"
] |
[
"Is it possible for a propeller-driven plane to exceed the speed of sound?"
] |
[
false
] |
I've seen a few accounts of pilots claiming to have broken the sound barrier during dives in prop planes, but have seen no evidence of a plane designed to get much past mach .85 or so. Is there a reason for this, or is it simply that jet technology came along as we were approaching this milestone?
|
[
"A ",
"similar question",
" was asked a few days ago.",
"NACA research",
" in the 1940s suggested that this was feasible, but as you suggested, it was discarded in favor of jet propulsion, which is a much simpler approach to the problem.",
"The problem is that the profile of the blade required to sucessfully operate above Mach .9 is significantly different from the designs used to operate below that speed. Beyond Mach .9, the propeller blades must become significantly shorter and thinner and the blade angle must be decreased compared to blades used on slower aircraft. "
] |
[
"so what your saying is that by having the plane behind the propeller you place the body of the plane right in the explosion part of the sonic boom, thus ripping it apart. Solvable with placing the propeller on the rear end of the plane. perhaps even two propellers, for stability."
] |
[
"so what your saying is that by having the plane behind the propeller you place the body of the plane right in the explosion part of the sonic boom, thus ripping it apart. Solvable with placing the propeller on the rear end of the plane. perhaps even two propellers, for stability."
] |
[
"This piece of paper compressed in a hydraulic press makes a small explosion and changes form. What exactly is happening here?"
] |
[
false
] | null |
[
"It looks like what is happening there is that trapped air in the pockets of the paper get compressed, heat up, and eventually explode outward. In the process, all of the gases leave the paper, the fibre network collapses, and any water adsorbed onto the surface of the paper also evaporates (paper can hold onto quite a bit of water - think of writing on a humid summer day).",
"This dehydration and de-gassing that comes with the compression of the paper might be enough to explain the changes he shows in that video. It's possible theres's some additional chemical changes, but structural and physical changes explain most of it. "
] |
[
"5 days ago",
"6 days ago"
] |
[
"Oops. Sorry my bad! Just saw the video last night, new to me assumed new to everyone."
] |
[
"Does the mass trade of foods like fruits and vegetables between different areas change their soils and hydrology?"
] |
[
false
] |
So I had this thought while eating an imported cucumber from Spain today. Since it's grown in spanish soil, it absorbs nutrients and water from the local soil. When I consume it in Germany, the remains presumably don't make it back to Spain, but stay in Germany after making their way through the local sewage system and a water treatment plant. So if large numbers of foods are exported from Spain to other places over long periods of time, could that lead to a depletion of soils and water ressources in Spain? And does that increase the amount of water and other things elsewhere? Or is the total amount transported just too small to be significant and measurable?
|
[
"Let's consider a few things.",
"First, many of the nutrients that a plant absorbs change in form. If a plant absorbs nitrates (for example), those are frequently turned into proteins for use by that cell.",
"Next, your body will actually use some of the nutrients that the plant provides when you eat it. You will break down the compounds in that plant, keep some of them, and reuse the components for different bodily functions.",
"When those compounds finally leave your body, they enter the wastewater system. The water and waste are treated at a wastewater treatment plant and the treated water is released once it meets specific thresholds. The solid matter is often incinerated, put in a landfill, or reused for use in fertilizers.",
"These fertilizers will usually end up back on the same fields that those plants came from, because growing many plants depletes the soil.",
"So, yes. Growing plants depletes the soil. But the nutrients will be \"replaced\" by fertilizers. The water won't go back to Spain though. Depending on how the wastewater is handled, it could enter the ocean, become drinking water, become water used for irrigation or enter a freshwater source that ends up being accessed for use as drinking water. It likely won't directly end up in Spain."
] |
[
"I do remember reading somewhere that the export of vegetables dries out certain areas in some countries. So especially the exported water could increase drought problems, if I remember correctly."
] |
[
"Keep in mind though that a lot of the actual biomass of the plant is essentially carbohydrates that are made out of carbon dioxide and water. The carbon dioxide comes from the air which is free to move around the world so that doesn't really factor in but I suppose the water The plant took out of the ground and used to make carbohydrates is being transferred to another country or place. Generally though I would assume that the amount of water being transported in food is smaller than that being transported by the atmosphere. I'm just curious if someone has actually studied how much water is transported in this way versus what comes in in the form of precipitation or water drawn from an aquifer."
] |
[
"How does an Atomic Force Microscope work?"
] |
[
false
] |
And is it the finest resolution we have? Third-year physics student, don't be afraid to whip out the math.
|
[
"Finally, a question I have some authority to answer! First up, I'm a PhD candidate very close to submitting my thesis. I've basically been using the AFM to characterize proteins and diseased tissue.",
"So the most basic principle of an AFM is very simple - it's 'feeling' a surface using a tiny 'finger'. Much like how an old gramophone would convert bumps on a record into music, an AFM converts bumps on a surface into a topographical map. Actually ",
"wikipedia",
" has a fairly good in-depth explanation.",
"You ask about resolution - the thing to remember is, AFM is the only (common) microscopic technique providing 3d information. So in the z-axis (up and down), yes it is the finest resolution. You can routinely scan down to 0.1 nm steps in height with a good setup. ",
"In the x,y scale, however, things get more complicated. With the right sample and probe, you can get ",
"submolecular resolution",
", although that's not an easy thing to achieve. These days there are ",
"electron microscopes",
" that can achieve resolution of up to 50 pN. This is really hard, though, because of the ",
"diffraction limit",
" of an electron.",
"Your typical AFM will provide better resolution than your typical other high-res microscopy techniques. Furthermore, it can be operated in a variety of environments and temperatures, such as in fluid (my focus is biological, so I care about physiological environments). ",
"As for whipping out maths, I wouldn't bother unless you're getting into ",
"force spectroscopy",
" using the AFM. But if you have any more technical questions, feel free to ask - I might be able to clarify anything you don't understand from the links.",
"Hooray for AFMs! I'll leave it at that ;)"
] |
[
"I'm in a similar situation to MrsKytro. I'm a PhD candidate working with AFM. I'd like to add more about the mechanism of sensing, if I may. ",
"I use the gramophone analogy as well. The needle on the record looks like ",
"this",
". This is attached to piezoelectric actuators, which can take a voltage and turn it into a motion. So using the piezos, you can bring this needle (tip) down to the surface and move it over a box on the surface of your sample. I typically use scan areas of 50x50 micron or 5x5 micron. ",
"But once the tip is on the surface, how does it sense the bumps on the surface? With a laser. A laser shines on the tip, and then bounces off onto a photosensitive diode. Actually, a set of four PSDs arranged in quadrants. Right before the tip touches the surface, you align the laser so that the reflection from the tip hits right in the middle of the PSDs. When you're scanning, the tip will find a bump, and this will cause the laser's reflection to move up or down on the PSD. The PSD then sends a signal to the piezo to move the tip up or down to re-center the laser. A computer can translate this signal to the piezo into an image. ",
"So to recap, laser bounces off tip onto PSD. As the tip moves, the laser moves too. The piezo moves up or down to keep the laser centered, and that information makes your image. "
] |
[
"Isn't there a 'tapping' and 'hover' mode?"
] |
[
"Trapped organic matter becomes oil, natural gas, or coal. What decides which path a certain pool of matter takes?"
] |
[
false
] | null |
[
"The main element of control is the length of the carbon chains, and this will in turn be influenced by thermal/pressure history and molecular structure of the starting organic matter.",
"Thus, oceanic planctonic algae has a lot of waxes and relatively short (less than 15C) chains and usually breaks into oil and/or gas. Continental plants contain more lignin and cellulose, and thus have longer chains. The'll normally follow the coal route."
] |
[
"In addition to the source of the hydrocarbons, the conditions under which they are buried are a major factor in determining what they end up as.",
"The best type of coal is anthracite which has lots of carbon and very few volatiles/impurities. It is just like lower-quality coal only it has been subject to low-grade metamorphism. Oil and gas are similar; oil will turn into gas ",
"if it is exposed to high enough heat",
". Depending on the local geothermal gradient (basically the rise in temperature as you get deeper into the Earth) you will see gas below oil, or rather, any oil that gets heated too much will burn off into gas. However, eventually once hydrocarbon traps form ",
"you will see the gas move above the oil."
] |
[
"any good articles on this? I'm looking for a good post for ",
"/r/oil"
] |
[
"Do germs have a circadian rhythm?"
] |
[
false
] |
For example say the cold virus? If you get sick with cold in a timezone 12 hours away, do the cold symptoms follow local time? What happens when you return home?
|
[
"However there is a ton of research on the seasonality of viruses (influenza, varicella). Especially recently when concerning the gut microbiome",
"https://europepmc.org/abstract/med/218446",
"https://scholar.google.com/scholar?hl=en&as_sdt=0%2C33&q=virus+seasonality&btnG=#d=gs_qabs&u=%23p%3D-zybWEnZGAsJ",
"https://journals.lww.com/pidj/Fulltext/2007/11001/Respiratory_Syncytial_Virus_Seasonality_in.7.aspx",
"https://www.sciencedirect.com/science/article/pii/S1473309904011776"
] |
[
"Germs are simple bacteria and viruses which don’t have a nervous system. without a nervous system you can’t have a circadian rhythm. ",
"bacteria and viruses don’t sleep or rest. they just kind of exist and move around taking in nutrients to divide. viruses definitely don’t rest or sleep because they aren’t even alive."
] |
[
"I hadn't realized that. This is amazing, thank you."
] |
[
"A Question about Evolution and living in the modern age."
] |
[
false
] |
I'm not sure this question even makes sense, but I've had this thought on my mind lately and thought this might be a good place to discuss it. Evolution caused humans in different areas of the world to grow in different ways. You can look at most people and generally tell what area of the planet their ancestors come from. This means things like the climate, the environment and genetics have a lot to do with how we look and feel today. Now in the 21st century, we can live anywhere on the planet and thrive, but my question is...should we? Specifically is it healthy for somebody with Irish ancestors to live in Mexico and vice versa? If your genetics has made you pre-disposed to living off certain kinds of foods with a specific climate, is it more likely for you to have long term problems if you try and live in a different climate entirely? I ask this mainly because a lot of the sick people in my family live in a very warm climate near a beach, while the others that seem much healthier live further north. We're of mostly European descent and I left a long time ago to move further north because I just couldn't stand the climate. I'm wondering...is there scientific proof that supports the idea of you living in a climate that you are genetically designed for.
|
[
"There is evidence that populations have genetically adapted to their environments. Tibetans, for example, have lower hemoglobin levels to counteract the high altitude they live in. Natives of Central Africa have a high frequency of the sickle cell allele, which is useful in combating malaria. ",
"It's a difficult question to ask whether we should be living in certain places in the world, because technology has allowed us to overcome a lot of the shortcomings in our genetics. Eyeglasses and contact lenses or in-home climate control are good examples of technologies that allow us to expand our functionality and range of habitable climate. It is possible that not being used to a climate could negatively affect one's quality of life (such as pollen causing allergies), but there's a lot of technology to counteract these things. ",
"Mankind has always adapted to its environments, whether through genetic advantages or advancement through technology. That's one of the beauties of living in our current age. "
] |
[
"Strictly speaking, no we shouldnt live in places where our ancestors did not grow. ",
"Prime example for this is vitamin D.\nVitamin D requires exposure to Sun. White people live in the north = low exposure, therefore, their body has adapted such that they dont need as much sun to produce adaquate vitamin D.",
"Black people get a lot of sun, so their body has adapted such that they need 1 hr+ a day to get their dose of vitamin D.",
"Now in their respective environemtn, the white and the black people are healthy, however, if a black man moves to the North and lives in a place like Canada, THen they will have vitamin D deficiency becuase canada does not get much sun.",
"Another example you might wanna look into is sickle cell anemia. (in some african states, the prevelant is actually high beucase it helps counter malaria, however in other parts its low becuase those other parts dont have malaria.",
"I can think of one primary proof for all this.\nI remember looking at a graph of differnet people in the world. It should that the North (ie. US, Canada, Europe) had a lot of cases of vitamin D deficiency, however the south (ie. Africa and south america) did not have as much cases of vitamin D deficiency.",
"so In the end, yes, we shouldn't be moving around as it is not what our body is meant to live in.\nHowever, I should say that due to modern medicine, these changes dont really matter as much becuase for example, the government in Canada And US will add vitamin D supplement in our milk to counteract the lack of sun exposure."
] |
[
"an awesome free article: ",
"http://www.sciencedirect.com/science/article/pii/S096098220902065X",
"Your question makes sense, and the comment of zfishkiller is great. ",
"Consider the timeline graphic of evolution in the article; we humans began to diverge about 150 thousand years ago. Our species however is maybe five million years old.",
"\nDifferent populations of humans can be said to have been evolving to their region for about 100 thousand years, but this is a short time from an evolutionary standpoint. For millions of years we were a tropical species (Inuit peoples have evolved a circulatory system that seems to protect hands from freezing)",
"What I want to express is that even though we have adaptations to the climate of our ancestors, we also have many more years of adaptation to the ancient african climates. We should not limit ourselves to living only in areas that our genomes have been evolving to for only thousands of years, when for millions of years we were a tropical species. "
] |
[
"Would it be possible to drink a mixture of NaOH and HCl?"
] |
[
false
] |
Say you took 0.01M of each and poured each simultaneously down a funnel. In theory wouldn't you just get salty water? Would the funnel just have to be really long? Obviously I'm not going to be trying this any time soon, but my roommates and I were discussing this and I wanted to see what everyone else thought.
|
[
"Disclaimer: NEVER EVER TRY THIS",
"But yes, you'd just get salty water. There are chemistry teachers who have done this as a demonstration."
] |
[
"Stomach acid is strong, actually, HCl is a strong acid. 0.5% doesn't mean it's weak, that's a pH of ",
" 0.87, assuming (incorrectly) that it is diluted in nothing but water."
] |
[
"Seriously? You know what would happen if the titration was even slightly unquenched?"
] |
[
"What effect does isoelectric point have on protein migration in an SDS-PAGE gel?"
] |
[
false
] |
I have three proteins all of slightly, but distinguishable, different sizes. Two of them have come out as the same size? What can affect the migration through the gel?
|
[
"Postranslational modifications (phosphorylation, ubiquitination, sumolation, cleavage by a protease). Degradation when you heat it in sample buffer. Trying a different % gel or running it longer are probably the easiest things to try."
] |
[
"Generally, the SDS masks any charges (because it confers a lot of negative charge itself), so unless your protein is really positive or negative, the effect should be negligible. Of course, you might just have some quality issues with your gel as well. Try changing the concentration of acrylamide (as resolution is concentration dependent), or perhaps a 2D-PAGE gel?"
] |
[
"Forgot PTMs, good call."
] |
[
"Has anyone gotten their Masters and then gotten a PhD in another field? Could you provide me with some insight, please?"
] |
[
false
] | null |
[
"I think ",
"/r/askacademia",
" will be able to help you best."
] |
[
"Try ",
"/r/AskAcademia",
" for best results. "
] |
[
"Thanks. "
] |
[
"What are some usual methods for proving that a number is transcendental? Why is it so hard to prove that a given number is transcendental?"
] |
[
false
] | null |
[
"The argument still holds, because you do still need a proof for each particular number that it satisfies that property."
] |
[
"The argument still holds, because you do still need a proof for each particular number that it satisfies that property."
] |
[
"Essentially there is only one known method to show that a number is transcendental. Every proof has the following basic idea at its core. ",
"Assume the number is algebraic. Construct in a clever way an auxiliary number related to your original number. Use the algebraic assumption to show the auxiliary number is an integer. Use some analysis to show that the auxiliary number is strictly between 0 and 1. Now we have arrived at a contradiction so the original number must be transcendental. ",
"The really hard part of the above proof is correctly building the auxiliary number. If you look at the proof of say the Lindemann-Weierstrass theorem the construction is very nontrivial and non-obvious. "
] |
[
"At the atomic level, what determines the qualities of different metals?"
] |
[
false
] |
It's clear enough that the ability to form metallic bonds is responsible for the properties of metals vs nonmetals. Further it seems pretty clear that electronegativity/atomic radius determines that ability. But what makes, for instance, iron harder than copper? Why can I bend a lead bar with my bare hands but an iron bar is totally immobile? What, on the atomic level, is going on with these properties? Furthermore, why is gold the most electronegative metal? It's apparent that gold is the most corrosion resistant and electronegative among the metals, but why is it that gold is a metal , actually a smaller nucleus, than many nonmetals (Phosphorus and carbon, for instance)?
|
[
"The property of lead you're describing is due to its ductility and malleability (malleable being somewhat loosely defined). Hardness is also related to these two, per its normal definition as a material's resistance to local deformation. Several differences in materials can give rise to more or less ductility. ",
"Crystal structure",
" is probably the most familiar to people. Face Centered Cubic usually produces the most ductile materials because of the close packing. Body Centered Cubic metals are not close packed and are usually less ductile. ",
"Ductility and malleability are related to the ability of a metal to plastically deform. There's two types of deformation when we're talking about materials: elastic, and inelastic (sometimes called plastic). Elastic deformation is what it sounds like: after you stretch it out, it comes back to its original shape and size. Elastic strength is related to the strength of the bonds in the material. Plastic deformation is permanent deformation, which is what we're interested in. ",
"Plastic deformation is associated with the movement of dislocations in a material. A ",
"Dislocation",
" is an irregularity in the structure of a crystalline material. There are two basic types: edge and screw dislocations. You can see the wiki article for some good pictures. When it comes down to it, they're just atoms bonded in a pattern that stretches the bonds a little instead of being in their lowest energy state, the perfect crystal. ",
"These dislocations create shear stresses in the material. They can also move in the crystal when it is stressed. Plastic deformation can be described as the movement of dislocations - its easier to move the dislocations than to break the material. This movement produces changes in the crystal, which can be seen as the large scale deformation.",
"EDIT: Oh right, I was going to write something about ",
"Grains",
". Metals are not usually one big crystal; they're actually a bunch of little crystals all smashed together. These little crystals are called grains. Their size and shape can greatly affect the properties of a material. Smaller grains can slide past one another much more easily, which can make a material more ductile. Non-isotropic grains, long skinny ones for example, can produce greater ductility in one direction than in another (parallel vs perpendicular stress compared to the grain direction). "
] |
[
"This is all generally correct; I'm just elaborating.",
"Dislocations are the flaws in the crystal that permit deformation. If you base the strength of a metal based on the bonding energy between atoms you'll end up over estimating the strength of the material by about a factor of two. It takes much less energy to break and reform bonds near the flaws than in the ideal crystal. Visually you can imagine this like an inch-worm: its easier to pick up one segment at a time and move it over a notch than it is to shift the whole worm sideways at once (where you're shifting every leg simultaneously). Dislocations can only move in specific directions which depends on the arrangement of atoms (ie crystal structure). Iron, being BCC, has fewer of these directions available which makes it less ductile. The most ductile materials are FCC: aluminum, gold, silver, copper...",
"However, one area where bond energy is related to this is in determining the melting temperature of the metal. Metals are more ductile (softer) the closer they are to their melting temperature. If you plot a lot of properties vs T/Tm (",
"homologous temperature",
") you'll see FCC materials generally behave similarly and are very different from BCC materials. Unfortunately iron is a bad example of this because it changes from BCC to FCC at around 900C.",
"Also, I wanted to add a bit of trivia about the deformation of Tin. Dislocations in Tin move at about the speed of audible sound. If you bend a tin wire you can hear it creak as the dislocations move around."
] |
[
"What you're looking at doesn't address the actual mechanism of deformation. It's related, but not direct. \"Particle packing\" is governed mostly by atomic size and crystal structure. Lead is a larger atom, so it can pack less atoms into a given volume, that's all. ",
"Lead is malleable because it can move dislocations easily, which is due to bond strength and crystal structure, which is ",
" related to atomic size and packing. Packing is only tangentially related.",
"Also, with Iron and Copper: you've got it all wrong. You're assuming that double the particles means double the distance between atoms. That's just ... not even close. The \"interaction distance\" between atoms in Iron is 126 pm. Copper is 128 pm. That's not double. A unit cell is the smallest repeatable unit of a crystal. They're not the same size. FCC has more atoms in it because FCC is a more complex pattern. BCC has less atoms in it because its a simpler pattern. That's it. ",
"By solving for particle density, you've essentially already solved for interaction size. If two things have the same particle density, it means they're particles are, on average, the same distance apart... by definition of the term particle density. I have no idea how you jumped to copper being twice as far apart.",
"The kicker is that BCC has less neighbors for each atom, which means that dislocations have a harder time moving."
] |
[
"Is there a medical condition where mammalian red blood cells retain their nuclei?"
] |
[
false
] |
And does it have any adverse effects? Does the body produce more cells to make up for the loss of effective transport capacity?
|
[
"kinda sorta. young nucleated red blood cells can be released into circulation when there is hemolysis. Production of blood is related to oxygen delivery. But nucleated red blood cells are usually larger so no loss of oxygen carrying capacity."
] |
[
"Yes, many conditions cause this. When there is a greater need for red blood cells than ability to produce them, the bone marrow will eventually \"cut its losses\" and will start kicking out immature red blood cells. An occasional nucleated red blood cell is a normal finding on blood smear but an increased number of them signals a pathogenic condition- usually this a secondary finding to a known anemia due to chronic blood loss or chronic hemolysis. This would be the most common reason you would see more than the normal amount of nucleated red cells on smear.",
"Somewhat less common, but worth mentioning: pernicious anemia is due to deficiency of vitamin B12, which is required for proper DNA synthesis. Pernicious anemia causes anemia (I know, duh) and one of the characteristic findings is bizarre multinucleated red cells- mostly in the bone marrow. ",
"Most rarely, acute erythroid leukemia is a form of acute myeloblastic leukemia (AML) in which the erythrocyte line is affected, causing the massive proliferation of red blood cell precursors. They are technically nucleated red blood cells, but they're so immature that you would not really recognize them as red blood cells under the microscope without special stains. This type of AML is extremely rare but it is interesting.",
"To answer the second part of your question- no, not really. Hemoglobin production begins before the nucleus degrades. In a patient with enough nucleated red cells to signal a pathological condition, that pathological condition is more of a concern in any case."
] |
[
"I don't know if your curiosity is general enough for my answer to interest you, but here goes: Birds have nucleated RBCs.\nHere is a good source: In answering the question about why birds have nucleated RBCs, they answer as to why they think mammals don't. ",
"http://www.madsci.org/posts/archives/2000-04/955119937.Cb.r.html"
] |
[
"Is it possible to control a nuclear explosion?"
] |
[
false
] |
I don't mean in terms of a bomb, but could you create some sort of chamber to control a nuclear explosion and focus all the energy in one direction creating a thrust, if this is possible could we apply it to space shuttle's creating "nitrus" for space shuttle? Control the explosion force all the energy in one direction, presumeably behind the shuttle, surging the shuttle forward for however long the blast lasts, then all of the radiation and smoke would leave through vents that would be opened, and the process repeated, is this possible?
|
[
"I don't mean in terms of a bomb, but could you create some sort of chamber to control a nuclear explosion and focus all the energy in one direction creating a thrust ...",
"Yes, this is possible, in fact there was a program to develop this kind of thruster (",
"Project Orion",
"). The only reason it's not being done is public concern over safety. And, since Fukushima and Chernobyl, that concern seems justified.",
"Nevertheless, in the future, I think this idea will be reconsidered. And I think it ought to be."
] |
[
"Not necessarily. A properly designed booster would produce a long-lasting tolerable acceleration rather than a short, unbearable level of acceleration. If this failed, then the idea would have no merit for human space colonization.",
"Oh -- you meant in the even of an explosion? Well, perhaps, but you know, releasing a lot of nuclear fuel doesn't mean there would be a nuclear explosion. Nukes don't work that way -- they are rather tricky to set off in a nuclear-bomb sense."
] |
[
"what about if it launched off earth using regular fuel then kicked into its nuclear power at a safe distance from earth's atmosphere?"
] |
[
"Help write a sci-fi novel. You get to be Xing Mu Sheng. You play earth like a videogame from space. I'm Bai Bai Rou."
] |
[
false
] | null |
[
"Nice idea, but not in ",
"/r/AskScience",
" please."
] |
[
"I wanted to ask scientists so it wasn't a bunch of laymen. Where do you suggest? I'll happily do it elsewhere."
] |
[
"You'd get better writing from ",
"/r/writing",
", that's a nice place with a fair number of readers. Otherwise, try the space or astronomy reddits, since it's kinda space related. Or else ",
"/r/scifi",
" or ",
"/r/sciencefiction",
". Or just try ",
"/r/science",
", perhaps? I really don't know."
] |
[
"Could there hypothetically be two planets in the same orbit?"
] |
[
false
] |
[deleted]
|
[
"could another earth-sized object fit Into earths orbit and be stable?",
"No, there are no stable configurations where two planets could orbit in the same path. You could put the two planets on opposite sides of the Sun, and assuming they're all point masses and there are no outside forces and there are no perturbations of any kind, they'll remain in orbit, but in reality such a system would destablize."
] |
[
"It is more likely to find smaller bodies 60 degrees ahead or behind a planet in its orbit. This is where the so-called Trojan asteroids of Jupiter are found, and one of Earth's Trojans. The point exactly opposite is possible, but orbits here are unstable compared to the ones at 60 degrees.",
"Look up \"Lagrange points.\""
] |
[
"I've actually heard of those, particularly with some asteroids in about the same orbit as earth. ",
"These asteroids are tiny compared to the earth though, could another earth-sized object fit Into earths orbit and be stable? "
] |
[
"How do they measure atomic radii? Or to be more broad, how do scientists work with super small things like atomic particles and protons and electrons, measure them, weigh them, etc.?"
] |
[
false
] |
I've been reading up on my old chemistry stuff (its the most basic of basic intro to chemistry courses, but I'm just curious). It dawned upon me, while I learned about trends in the periodic table (such as, decreasing from left to right or bottom to top), there is no mention of how the pioneers of chemistry came to find these measurements. Do they have super microscopes with tiny nanometer rulers? I understand its probably a very in-depth and complicated subject and my level of knowledge is extremely basic, so maybe my post would be more suited for ?
|
[
"As for getting mass, that's much easier than you might think. If you have a thing and you push on it, F=ma (or F=dp/dt more specifically) you measure how it accelerates and you can tell what its mass is. Well one of the easiest ways of doing this is with charged particles you accelerate the particle with an electric field and then use a magnetic field to turn it. The heavier mass, the wider circle it turns in the magnetic field. Measure how wide of an arc it passes through, and then you can figure out the mass. ",
"Sometimes though, we work backwards. E",
" = (mc",
" )",
" +(",
"c)",
" So if we know the energy and momentum of a particle, we can solve for its mass. Or sometimes we only find the decay products of a particle and have to sum their energy and momenta and reconstruct the mass of the particle that made them."
] |
[
"At least as my memory serves, the atomic radii are actually derived from the bond lengths observed in various types of solids & molecules (ionic and covalent compounds as well as metals). So, for example, you'd be interested in seeing the bond lengths sodium makes when in pure sodium metal as well as in sodium chloride, and working from there. Most of these bond lengths were determined by diffraction experiments or spectroscopic measurements - basically, you scatter something (particles or quanta) off of them, or expose them to a known source of EM radiation, and record its response. ",
"I don't know how much detail you're after, but this is it in a nutshell at the moment since I need to run."
] |
[
"Thank you. Much appreciated! This satisfies my curiosity. Its just one of those things that bothered me as I was reading since it never explicitly says how these values came about."
] |
[
"How do other great apes deal with finger and toenails?"
] |
[
false
] |
As a modern human, the longer our nails get the more of a nuisance they become. It feels as if longer nails inhibit fine dexterity, increase pain sensitivity of digits, and make digits more susceptible to injury under mechanical stress. This would presumably be true in the wild for ancient humans and modern great apes as well. Since there doesn't appear to be the same benefits of unchecked growth as other mammals with claws, it would seem to be beneficial to keep them near the length they are socially acceptable for us today (discounting non-functional fashion). Every depiction I have seen of a great ape in the wild or in captivity seems to reflect this, and their nails seem to be decently maintained. How do great apes go about doing this? Do they really receive enough wear from manual (pedal?) use to counter growth or are there behaviors which are done specifically to curtail nail growth (e.g. raking trees)? Toenails seem especially troublesome, as the nails do not become worn from walking like in the claws of mammalian quadrupeds. How do other great apes deal with finger and toenails?
|
[
"Great apes treat fingernails in different ways.",
"Some allow them to grow until they break off. Others bite them and some even use rough stones as natural fingernail files. Great apes in captivity often need some form of supplemental nail care.",
"Non-human primates often use their forelimbs for locomotion so they may get more wear than humans or any hominid that walked upright."
] |
[
"I'd expect a captive ape to be able to use a nail clipper after being shown what it does."
] |
[
"They're pretty smart, but they also might hurt themselves or clevery use it as a tool for some unintended purpose. So it's all about safety rather than running the risk of what's possible."
] |
[
"If science says that the higher the gravity in a reference frame, the slower time runs in that frame compared to elsewhere, then can you use another force, like centrifugal force, to simulate gravity in a reference frame to slow down time?"
] |
[
false
] |
My thought is that because the passage of time related to gravity is based on different frames of reference, could you exert a force in this frame of reference that is indistinguishable from gravity, and thus slow down time? A force like centrifugal force could be identical to a human in a certain reference frame, but would spacetime be "fooled" by an imitation of gravity, allowing time to slow down?
|
[
"Yes, this is exactly right! A key insight of general relativity is the so-called ",
"equivalence principle",
", which states that the effect of gravity is equivalent to that of being in an accelerating frame of reference. A uniformly rotating object undergoing centripetal acceleration fits this bill fully! So in answer to your question, yes ",
"gravitational time dilation",
" can be mimicked by acceleration in the same way that rotation can be used to ",
"simulate the effect of gravity",
"."
] |
[
"Yes. Its just the expected time dilation as from special relativity. Time passes slower for objects traveling at high speeds than for objects at lower speeds.",
"However whats more interesting and \"looks like\" gravitational time dilation is when you considers observers along various distances from the center of the wheel but still rotating at the same angular velocity.",
"Each of these observers have no relative velocity between each other. But there is still time dilation between them. In their own frame this time dilation appears to arise due to the varying force on each observer, which is stronger further and points away from the center of the wheel.",
"This dilation takes a similar form to gravitational time dilation and increasing gravitational force away from the center of the wheel."
] |
[
"Wait, so...theoretically, one of ",
"these",
" spinning at an extremely high speed could create a distortion in time?"
] |
[
"Why don't new singularities form in the extreme densities and temperatures within a black hole's event horizon?"
] |
[
false
] | null |
[
"I'm not sure exactly what the question is asking, but the event horizon isn't a physical thing or a thing at all. It's just the boundary region where gravitational forces exceed the speed of light; aka anything that goes through it has all future worldlines going towards the singularity. It has an extraordinarily low temperature also, only fractions of a kelvin above absolute zero. "
] |
[
"If a singularity were to form in there, we wouldn't know. There is kind of an event horizon we can't see past."
] |
[
"I realize the event horizon is only a mathematical boundary. What I'm talking about is how matter from the accretion disk behaves as it falls through the event horizon and towards the central singularity. Based on ",
"this clip",
", any infalling material becomes incredibly energized. I'm asking why this super-dense energy cauldron of infalling material doesn't form its own singularities. "
] |
[
"Near Death Experiences?"
] |
[
false
] |
I've been thinking about near death experiences lately.. my mother is a firm believer and tries to get me to read books by people who have died and come back.. I've heard that there are scientific explanations for the "white light" people see and stuff like that.. anyone able to explain it to me? People come back from the dead and claim to have experienced heaven or hell or some other afterlife.. some people even claim to have out of body experiences and apparently have knowledge they shouldn't have.. So I'm asking you guys.. what does science say?
|
[
"Your brain can start to do some really bizarre things when your homeostasis is disrupted. This includes hallucinations, stereotyped behavior, out of body experiences, etc. ",
"There is a bizarre phenomenon you get when someone gets really bad ",
"hypothermia",
" in which they will start undressing and burrowing. ",
"The most common \"near death experience\" is what is known as the out-of-body experience. It is basically a dissociative state and it is not unique to those close to death; it also occurs in pilots pulling huge amounts of g's in training simulators, and in people taking dissociative drugs such as ketamine and phencyclidine (PCP). ",
"Basically, when you boil it down, all of the near-death experiences are hallucinations and dissociative experiences induced by hypoxia and subsequent brain dysfunction. You are your brain, so when it starts going on the fritz, you are going to see some very strange things. \nIf you are the kind of person who thinks alot about heaven and hell, don't be surprised if you hallucinate demons. ",
"If you want to have a dissociative experience, you could try ",
"Salvia",
", if it is legal where you live and you are old enough. "
] |
[
"Oh completely non-credible. I was meaning to point out Michael Shermer's contribution, as it has a very good explanation of the scientific basis of near death experience. I certainly didn't mean to imply that Deepak Chopra has anything useful to say on the subject."
] |
[
"I've had a 'near-death experience' after I accidentally cut myself quite badly, came back in the house and passed out; from my perspective I suddenly found myself standing in a bright white environment and I was aware of some people talking about me but I couldn't speak and I had no memory of how I got there. I became aware of someone close behind me to the right and I turned to ask them what was going on, but the second I tried to speak I heard some amazingly complicated music (sounded like violins with about 15 lines of counterpoint) which sort of froze me in my tracks, then I had a feeling of sort of being pulled backwards, then everything went dark, then I woke up and became aware I was shaking, having some kind of seizure. As I woke up I was stopping shaking, but I couldn't speak or move properly - it was like my body wouldn't respond properly.",
"What had actually happened was I had collapsed due to a dip in blood pressure, and rather than doing the correct thing which would have been to straighten me out on the floor and elevate my legs, my mother and a friend had picked me up off the floor and sat me in a chair thus exacerbating the issue.",
"Needless to say they took me to the emergency room, but during the journey I recovered and felt fine.",
"I was fascinated by the experience and I started researching 'astral projection' and 'out of body' experiences with an aim to inducing them; cutting a long story short I found they are basically sleep paralysis, and during sleep paralysis you are only paralysed from the neck down (meaning you can open your eyes), you will experience anything you can imagine, overlaid on top of what your eyes see, and the experience can be difficult to distinguish from real life. I personally strongly suspect that sleep paralysis and related experiences are basically responsible for a lot of crazy that happens, including alien abductions and such like.",
"Experiments have been done to test if people actually leave their bodies - this has been done under controlled conditions in hospitals where certain patients would report 'leaving their body' under anaesthesia. Objects would be placed in places the patients could not see (such as on a high shelf in the operating theatre) and the patients would be asked to identify the objects if they 'left their body'. To my knowledge nobody has been able to demonstrate this ability under controlled conditions."
] |
[
"How does pure energy interact to form matter?"
] |
[
false
] | null |
[
"Damn you Mr. Spock! Damn you for introducing the conceptual fallacy of \"pure energy\" into popular culture!",
"The issue here is that energy isn't a \"thing,\" it's a property. Things ",
" energy just like they (may) have mass, length, volume, momentum, etc. Rather than reading E=mc",
" to say that mass can become energy, it's more accurate to read it as saying that mass is a type of energy.",
"What most people usually think of as \"pure energy\" is one of three things: ",
"kinetic energy: the energy associated with a thing's motion.",
"heat energy: This is just the overall kinetic energy of all of a thing's constituent particles.",
"electromagnetic radiation: light, microwaves, x-rays, etc. This radiation has energy proportional to its frequency.",
"Since mass is a type of energy, it can be converted into other types of energy, as IAmMe1 ",
"points out",
"."
] |
[
"then why does mine overheat?"
] |
[
"Well, energy has to take some form, i.e. kinetic, the energy of a photon, etc., so \"pure energy\" isn't really the best-defined concept. It's not like energy (well, apart from the possibly nonzero vacuum energy) just \"floats\" around the universe. That being said, a good example of what I think you're trying to get at is ",
"pair production",
"."
] |
[
"How are Neanderthals a different species from Homosapiens if they could produce viable offspring together?"
] |
[
false
] | null |
[
" some scientists consider both different species, others do not. The biological species concept is a human-made concept and there are a lot of grey areas.",
"\nWhat is a species?\nTaxonomists argue all the time about what exactly a species is.\nThe general idea of a species, as I was taught in high school, is a group of organisms that can produce viable offspring together, hence a poodle and a German shepperd are the same species but a tiger and a lion are not (infertile offspring).",
"Evolution is complicated. If two populations slowly move apart genetically there is no clear point in time in which reproduction between the two populations would at of a sudden be impossible. It's a slow process. Maybe best described with an example:",
"Goose 'species' are usually relatively easy to tell apart. The 'species' therefore are clearly phenotypically different. They also have different calls, different mating rituals, and different migration patterns. There can be several 'species' breeding within a small area but they will hardly ever even try to mate with one another because they are so different from each other. However.. In some rare cases they DO mate and this can actually produce fertile offspring. So are all these 'species' that are easily distinguishable from each other and have totally different ecologies, the same species? I'd argue not. These geese species are far enough apart to be quite different and most of the time they will be reproductively isolated from each other but they are not that far yet that they can never produce fertile offspring. \nThese geese don't think about our neatly defined species construct, they just want sex.",
"And then we also have animals that can produce fertile offspring but the offspring is not as healthy. It's all really, really messy.",
"I think the chapter 24 (in my edition) in Campbell's Biology gives a really great overview of the limitations of the different biological species concepts. I've uploaded one of the more informative figures here:\n",
"https://imgur.com/WPZxbPk",
"\n",
"https://imgur.com/FFryjYF",
"I am no expert in the specific case of Homo sapiens vs Homo neanderthalensis. Some authors consider H. neanderthalensis to be merely a different subspecies to Homo sapiens (Homo sapiens neanderthalensis), not a species in its own right. Most of the literature I have recently read does however use the binominal species name for H. neanderthalensis and thus treat it as a seperate 'species'.",
"The current understanding is the following:\nHomo sapiens and Homo neanderthalensis share a common ancestor that lived >500,000 years ago.\nH. sapiens and H. neanderthalensis lived in different parts of the world. H. neanderthalensis inhabited large parts of Europe and Western Asia whilst H. sapiens was for long confined to Africa. They were repoductively isolated for hundreds of thousands of years and thus evolved in different ways. When humans migrated out of Africa into Eurasia ~70,000 years ago (take that number with a grain of salt) both groups were different but not different enough to make having fertile offspring impossible. All modern humans with Eurasian ancestry (everyone except some African groups because they stayed in Africa and didn't meet Neanderthals) carry some of this Neanderthal heritage with them in their DNA. It is usually not more than a few percent but in total ~20% of the Neanderthal genome can be found as little shredded bits in the DNA of different humans alive today. We do see certain parts of our genome devoid of any Neanderthal genes. This is probably due to the fact that Neanderthal genes in these areas of the genome had negative effect. A 2016 study (10.1038/nature17993) found that the amount of Neanderthal genes in humans has actually decreased over time:",
"\"Modern humans arrived in Europe ∼45,000 years ago, but little is known about their genetic composition before the start of farming ∼8,500 years ago. Here we analyse genome-wide data from 51 Eurasians from ∼45,000–7,000 years ago. Over this time, the proportion of Neanderthal DNA decreased from 3–6% to around 2%, consistent with natural selection against Neanderthal variants in modern humans.\"",
"In some cases Neanderthal genes might have helped humans adapt to the new continent they were exploring by giving the carriers immune systems that could cope with the new pathogens better.",
"I think the best article on the subject is a review article by Nielsen et al. published in Nature earlier this year, doi:10.1038/nature21347. Here a link for the people who cannot access the scientific articles for free: ",
"http://sci-hub.cc/10.1038/nature21347",
" ",
"Also this article I quoted a part from is a good read if you are interested: ",
"http://sci-hub.cc/10.1038/nature17993",
"P.S. I am new to the subreddit so please do bother me if I am doing something wrong. Cheers.",
"Edit: formatting.\nEdit: haha, I see I am late. ;-)"
] |
[
" Different species can certainly produce viable offspring. This is covered in ",
"Why can two different species sometimes hybridize and produce viable offspring? Shouldn't they be the same species?",
". Interbreeding between different species is not unusual; there are many unambiguous examples. Even horses and donkeys, the classic example of sterile hybrids, ",
"occasionally have fertile offspring",
".",
" Successful Neandertal/sapiens hybrids were probably very rare. Neandertal/sapiens hybrids were almost certainly very sub-fertile. Male hybrids were probably sterile altogether. That's what we often see today with interspecies hybrids.",
"We find that observed low levels of Neanderthal ancestry in Eurasians are compatible with a very low rate of interbreeding (<2%), potentially attributable to a very strong avoidance of interspecific matings, a low fitness of hybrids, or both. These results suggesting the presence of very effective barriers to gene flow between the two species are robust to uncertainties about the exact demography of the Paleolithic populations, and they are also found to be compatible with the observed lack of mtDNA introgression.",
"--",
"Strong reproductive isolation between humans and Neanderthals inferred from observed patterns of introgression.",
"Our results indicate that the amount of Neanderthal DNA in living non-Africans can be explained with maximum probability by the exchange of a single pair of individuals between the subpopulations at each 77 generations, but larger exchange frequencies are also allowed with sizeable probability. ",
"--",
"Extremely Rare Interbreeding Events Can Explain Neanderthal DNA in Living Humans. ",
"Our integrated demographic analysis of multiple archaic and present-day human genomes suggests a scenario of long-term decline in the populations of Neanderthals and Denisovans, with the consistently small Altai Neanderthal population perhaps reflecting a long period of isolation in the Altai Mountains. In addition, we provide evidence for modern human introgression into the ancestors of this population of Neanderthals, and no such evidence in the European Neanderthals. ",
"--",
"Ancient gene flow from early modern humans into Eastern Neanderthals",
"Genes that are more highly expressed in testes than in any other tissue are especially reduced in Neanderthal ancestry, and there is an approximately fivefold reduction of Neanderthal ancestry on the X chromosome, which is known from studies of diverse species to be especially dense in male hybrid sterility genes. These results suggest that part of the explanation for genomic regions of reduced Neanderthal ancestry is Neanderthal alleles that caused decreased fertility in males when moved to a modern human genetic background.",
"--",
"The landscape of Neandertal ancestry in present-day humans",
"Finally, the reduction of both archaic ancestries is especially pronounced on chromosome X and near genes more highly expressed in testes than other tissues (p = 1.2 × 10(-7) to 3.2 × 10(-7) for Denisovan and 2.2 × 10(-3) to 2.9 × 10(-3) for Neanderthal ancestry even after controlling for differences in level of selective constraint across gene classes). This suggests that reduced male fertility may be a general feature of mixtures of human populations diverged by >500,000 years.",
"--",
"The Combined Landscape of Denisovan and Neanderthal Ancestry in Present-Day Humans."
] |
[
"Yes, but because the species concept is so well, vague, people like to believe what is more convenient for them and I can't really blame them. One example that comes to mind is the yellow wagtail.. One species with a lot of regional variation or a lot of different species? Some organisations count them as seperate species but based on DNA studies and on the fact that there is constant gene flow, I find that a bit silly. Certain keen birders like having long lists with species and love splitting it all up. Whatever rocks their boat.",
"Dynamics in the evolution of sexual traits: losses and\ngains, radiation and convergence in yellow wagtails\n(Motacilla flava)",
"In conservation and law a species is often valued more than a subspecies. \nSo having one 'species' of giraffe or several 'species' of giraffes does matter. (",
"see short essay",
")",
"I work more with insects where the opposite happens al the time.\n",
" is an easily to identify beetle species?\nOops, someone discovered that it is actually two species (now called ",
" and ",
") that look alike but cannot interbreed (penis is shaped differently). All hail the discovery but it can be a bit frustrating if they find out these things after you have been collecting the insects. >.>"
] |
[
"NASA release of close-up Pluto images livestream at 3pm EST"
] |
[
false
] | null |
[
"\"Charon is [geo] active\" - Alan Stern ",
"Image of Hydra! ",
"http://i.imgur.com/FN4BLu7.png",
" ",
"Methane on Pluto! ",
"http://i.imgur.com/fkQELTJ.png",
" ",
"Charon close up! ",
"http://i.imgur.com/SVhOSjj.png",
" ",
": ",
"http://i.imgur.com/meaqdRP.png",
" (no craters!?)",
"Pluto's surface is less than 100 million years old. Young surface! ",
"Pluto has water ice \"in great abundance\" ",
"Pluto is geologically active to explain surface features. ",
"\"No significant exchange of tidal energy anymore\" between Pluto and Charon. Why Pluto and Charon are geologically active is a mystery.",
" ",
"This post has the official NASA live stream, feel free to post images as they are released by NASA in this thread. It is worth noting that messages from Pluto take four and a half hours to reach us from the space craft so images posted by NASA today will always have some time lag. ",
"This will be updated as NASA releases more images of pluto. Updates will occur throughout the next few days with some special stuff happening on July 15th: ",
"Main website: ",
"https://www.nasa.gov/mission_pages/newhorizons/main/index.html",
" ",
" website: ",
"http://pluto.jhuapl.edu/",
" ",
"Twitter: ",
"https://twitter.com/nasanewhorizons",
" ",
"NASA Instagram: ",
"https://instagram.com/nasa/",
"NASA TV: ",
"https://www.youtube.com/watch?v=OX9I1KyNa8M",
" ",
"Alternate Live Stream link: ",
"http://www.ustream.tv/NASAHDTV",
" ",
"NASA TV Schedule: ",
"https://www.nasa.gov/multimedia/nasatv/schedule.html",
" ",
"Reddit Live Feed: ",
"https://www.reddit.com/live/v8j2tqin01cf/",
"The new images from today!",
" ",
"https://instagram.com/p/5HTXKMoaFL/",
" ",
" ",
"http://pluto.jhuapl.edu/soc/Pluto-Encounter/",
" ",
" ",
"https://www.nasa.gov/newhorizons/lorri-gallery",
"Older images: ",
"https://www.nasa.gov/mission_pages/newhorizons/images/index.html",
" ",
"Some extras:",
" ",
"Megathread Ask Your Pluto Questions here!"
] |
[
"To think... such high resolution photographs of an object 3 billion miles away. These images are stunning."
] |
[
"They were throwing around three possible explanations during the press conference, ",
"Sufficient radioactive material generating heat. ",
"Some sort of internal phase change, like the freezing of an underground ocean. ",
"Some unknown mechanism which allowed Pluto to retain its heat of formation better than expected. ",
"The reason tides are out is because Pluto and Charon are already locked together, all the tidal energy has already been spent long ago."
] |
[
"If the major event that triggered the extinction of the dinosaurs never happened, could they have evolved to our level of intelligence?"
] |
[
false
] | null |
[
"That is in fact one of the biggest puzzles in the speculation about extraterrestial life. For us humans, being intelligent seems to be a pretty neat trick in the survival of the fittest. So why is everything else so dumb? As far as we know, we are the only intelligent civilized species in the history of life on earth. Which is ",
": 3.8 billion years is the best guess now. ",
"There are three possible answers to this:",
"a) We only find intelligence important because ",
" have it. Elephants (if they were intelligent) would probably wondering why there are no other land creatures with trunks, despite trunks obviously being useful and beautiful. ",
"b) It ",
" evolve, but geological time just bulldozered over it. A dinosaur civilization with agriculture, oral traditions and the habit of burying its members with flowers would be pretty darn intelligent by our standards. But our chances of finding those dinos are small, let alone our chances of finding out about their intelligence. ",
"c) This one actually borders on (a): intelligence is not that big a deal. Every other animal on the planet seems to cope just fine without it. Dinos had already existed for millions of years without big brains, why would they suddenly start making them now?"
] |
[
"You seem to be missing something like",
"d) Intelligence is both a particularly useful and difficult to evolve trait, like flight. In the history of life on this planet, flight appears to have evolved independently only 4 times yet those animal groups which evolved flight are mostly extremely successful (except for the pterosaurs who ",
" extremely successful until they were wiped out by a certain impact event)."
] |
[
"<IAMNOTASCIENTIST>",
"Time doesn't necessarily equal intelligence. For instance the alligator has been around for about 200 million years, about the same amount of time as mammals. For a really stark example, jellyfish have been around for about 500 million years.",
"Intelligence seems to be a chance occurrence and not directly related to time. That being said more years does equal more genetic mutations which means more of a chance for intelligence to evolve.",
"</BUTIWISHIWAS>"
] |
[
"How much does at-home recycling actually help the environment? I have heard the actual benefit is pretty much nil, is this true?"
] |
[
false
] | null |
[
"If you did not burn the paper for heat you would have to get the energy some other way. In most jurisdictions that means fossil fuels. Incineration can actually be an incredibly green way to acquire energy from waste, as long as the incinerator is properly constructed and filtered.",
"There are even better things to do with organic waste. You can compost it and collect the methane, or use pyrolysis to turn the waste into a sustainable source for oil and chemical feedstock.",
"The primary reason why this is not done more is the cost. In principle we could drastically reduce the amount of waste ending in landfill, and one of the best way to do it is to use pyrolysis and incineration to recover hydrocarbons and energy. The economics of it is another matter. "
] |
[
"I'm a recycle truck driver for a waste company. We currently single stream our recycle (meaning everything dumped together) using sideloaders.",
"This process is extremely efficient and only exists to get people to recycle more and reduce the cost to the consumers. However the downside is cross contamination. I dump on average 6-8 tons per day. Lets say it is 6 tons for arguments sake. About 1/2 ton-1 ton of that is pure trash. Then you have rainwater, oil, and other nastiness which mixes with the trash and other paper products which renders them unrecyclable due to contamination. In all, that 6 tons I picked up, only about 2-4 tons gets recycled.",
"Now you take that to the facility. It needs to be sorted. Which costs fuel for the vehicles at the facility, and then energy to run the machines that sort the materials. Then this must be shipped to be recycled. Paper itself has a nasty by product that looks like sludge.",
"The only REAL worth for recycling is metal. Especially Copper, brass, and aluminum. The paper/cardboard is sometimes so heavily saturated in the market that some companies must pay to have it recycled, rather than being paid for it. This is bad because it means it's cheaper to throw it away than to recycle it. ",
"As for the environmental effect, it works out to be an almost even trade off most times. However, being able to reuse materials instead of putting them in a landfill does help a great deal. "
] |
[
"To add, if paper is decomposed by fungus (fungus are responsible for most plant matter decay because they're better at breaking apart cellulose) the CO2 is likewise directed into the atmosphere. When the carbon is sequestered with filters, we can prevent this.",
"This is why growing forests isn't a long term solution to CO2 sequestration. The only carbon this draws out of the atmosphere is the amount stored in the wood. Once the trees start dying/replacing themselves the net carbon draw from the atmosphere approaches zero if the dead trees are allowed to rot.",
"In order to meaningfully draw out CO2 longterm, you'd need to bury the trees where they can't rot (incidentally, this is approximately how the coal/oil deposits formed in the first place)."
] |
[
"What is the current scientific opinion on how the internet influences our minds/brains?"
] |
[
false
] |
Colloquially, there is a trend to say that the internet has had a detrimental affect not only on social interaction but also on the way in which people learn and retain information. But with developments like Google the pressure to remember things is no longer there. Would that imply that now our brains are being geared more towards other areas of cognition since Google is our sort of external memory? If any one can link to some articles or scientific journals or even books that would be very much appreciated.
|
[
"You may be thinking of ",
"this Science article",
", which reports:",
"This is preliminary evidence that when people expect information to remain continuously available (such as we expect with Internet access), they are more likely to remember where to find it than to remember the details of the item. One could argue that this is an adaptive use of memory—to include the computer and online search engines as an external memory system that can be accessed at will. "
] |
[
"Like outsourcing memory.",
"Would this free up that part of the brain for other uses?"
] |
[
"I remember reading an article where the author posited that the gigantic wealth of instant-access information is making us shift from long-term, single topic attention to short-term, multi-topic attention. That is, where before information would be absorbed by reading articles and books, now we can obtain information quickly and with little I no effort. I don't remember the article, if someone recognizes this please link. "
] |
[
"How does a stem cell know what body part to become naturally?"
] |
[
false
] |
What type of communication happens inside an embryo? What prevents, lets say, multiple livers from forming? Is there some sort of identification process that happens so a cell knows "okay those guys are becoming the liver, so I'll start forming the lungs" ?
|
[
"The process you're referring to is called \"Differentiation\", which in biology refers to stem cells becoming other cell types.",
"Chemically: The chemical properties of the surrounding the cell and available nutrients play a factor. These are things like pH, oxygen levels, CO2 levels etc.",
"Physically: Certain cell types are receptive to different mechanical stimuli and surface properties. If you're trying to grow stem cells on a certain material you can alter it at the nanoscale to promote differentiation into a certain cell type. Another example is repetitive stretching and compression can promote osteoblast (Bone forming) cell differentiation.",
"Biologically: There are tons of biological signals that can promote differentiation in one form or another. Cytokines, proteins, antibodies, hormones etc. There is a common technique called 'Coculturing' where a scientist will grow stem cells and another cell type in the same media. The proximity to the second cell type can determine what type of cell the stem cells ultimately become.",
"Preexisting factors: Not all 'Stem Cells' are the same! There are several classifcations. \"Totipotent stem cells\" can differentiate to become just about any cell type or expand to make more stem cells. \"Pluripotent stem cells\" can become almost every cell in the body. \"Multipotent stem cells\" can become several different types of cells, but not all and are more limited than Pluripotent.",
"This is still a rapidly growing and changing field, and there are certainly blurred lines between those classifications as we learn more about cellular differentiation."
] |
[
"The chemicals surrounding certain stem cells determine what it develops into. Think of it like parenting: different methods of parenting will raise different children, depending on how the child was raised and what the parents did to it."
] |
[
"In addition to chemical stimuli, it has been revealed that the mechanical stresses and forces also play a role in differentiation. "
] |
[
"Can you laser etch a hollow tube in glass?"
] |
[
false
] |
Is it possible?
|
[
"This is actually done by laser sometime, when something special is needed. But yes, drawing capillaries is way easier. Were you thinkign of something specific. "
] |
[
"Yes, \nI was thinking about making a \"passive solar tracking\" glass.\nFilling the glass infront of a solar cell with a bunch of tubes facing many directions acting like tiny fiber optic cables.",
"Have all the ends come down perpendicularly on the cells, to ensure direct sunlight from any angle, so power production would always be at its maximum."
] |
[
"You could but it is easier to draw a hollow tube down into a capillary. It is just a matter of picking the right laser for the glass system"
] |
[
"On a clear night, why do some stars twinkle more than others that appear to be of similar size?"
] |
[
false
] |
I understand that size is relative to our perception, but still.
|
[
"I don't think the time scales for stellar and interstellar processes are right to explain twinkling."
] |
[
"I assume by size you mean brightness. Bright stars do appear to twinkle more than dim stars.",
"But there are a couple of things that may make one star appear to twinkle more than another of the same brightness. If it's lower in the sky, its light is passing through more atmosphere so it will twinkle more. And if the star is above, say, a warm roof from the point of view of the observer, the warm air rising might cause turbulence that would cause greater twinkling.",
"Also, if one of the stars is not a star at all but a planet, it will twinkle much less than the star would, because the brightness variations get averaged out over the planet's disk."
] |
[
"Twinkling (technically called scintillation) is the apparent change in brightness, colour, or even position of a distant and luminous object as viewed through a medium. In our case we're talking about terrestrial scintillation and the medium is our atmosphere. On the whole terrestrial scintillation effects are caused by differences in air density which are often caused by temperature differences. ",
"Differences in air density between you and various objects will cause them to twinkle at varying rates and the effect is often most pronounced the closer you get to the horizon because there is more atmosphere between you and the objects."
] |
[
"Particle physicists of reddit. How does one detect and characterise the many different types of fundamental particles?"
] |
[
false
] |
I'm a chemistry student, so this baffles me.
|
[
"There's been lots of different methods used over the last century or so. It depends on the lifetime of the particle, its mass and charge, the technology available at the time, etc. Most of them work by either directly detecting either ",
"scintillation",
" or ionization. Basically, as a particle passes through a material, the particle interacts with the material and causes a flash of light (scintillation) or causes some of the material to ionize. In modern detectors, these events cause a current to be induced in some sort of electronic detector, which can be recorded by a computer.",
"However, this process only works for some particles. Only charged particles can cause ionization. Charged particles, neutrons, neutrinos, and possibly neutral mesons (I'm not sure) can induce scintillation in certain materials. And photons can be observed directly. Furthermore, this only works for sufficiently long lived particles. All of those have already been discovered (as far as we know).",
"All of the new particles we're hunting for, like the Higgs boson and superparticles, are too short lived to be observed directly. So instead we do a lot of theory to try to guess how these particles will decay. We then look for a spray of these decay products in a certain pattern, known as a jet, as the signature of the particle.",
"In all modern particle experiments, we can't just see one event in a detector and say, \"Yep, there's the particle I was looking for!\" because it can be hard to tell exactly what particle showed up in the detector, and because there are lots of background sources of particles which will show up in detectors. Thus, we observe lots and lots of events so we can do all sorts of statistical analysis to sort it all out.",
"Edit: There's so much to say about how the various detection methods work that I didn't go into any detail. There's whole textbooks just on detector design. If you have more questions, just ask!"
] |
[
"The fundamental thing that allows us to detect subatomic particles is the process of ionization. When an energetic electron/proton/photon/etc comes into contact with an atom, and interacts, it knocks electrons away from the atom. Based on what we do with those electrons, we can figure out the rest.",
"For instance, a very early way to characterize subatomic particle interactions was the ",
"bubble chamber",
". A liquid is held just under its boiling point, and any ionization events cause a tiny bubble to form. In this way, we can actually visualize the particle moving through the liquid by tracking the bubbles.",
"We can get a lot more information by applying a magnetic field across the bubble chamber. Under this field, charged particles move in a spiral trajectory. Uncharged particles go in a straight line. By looking at the curvature of the spiral, you can figure out how much momentum the particle has, or work out the mass. So this type of analysis allows us to characterize the particles in terms of their fundamental properties.",
"Obviously detection methods are much more sophisticated now. I don't work directly in the fields that characterize the more exotic subatomic particles, so my knowledge of those kinds of methods is limited. But I do know that, if you have the tools to detect photons and electrons, and determine their energy, you can look for decay products of exotic particles and their associated energies to validate your theories."
] |
[
"For reference, see the cross-sectional picture of the atlas experiment (at the LHC) here:\n",
"http://atlas.ch/photos/events-general-detection.html",
"In high energy physics, once particles are produced at the collision, here is what we do to identify particles:",
"We use a \"tracker\" to precisely determine the momentum of charged particles in a magnetic field. Charged particles leave an ionization trail in certain materials (modern detectors use silicon), and curve in a magnetic field. The curvature constrains the sign of the charge and the momentum. Note that this only works for charged particles, and it still doesn't tell us what kind of charged particle we are looking at. That is why we have other parts of the detector:",
"The next part of the detector (moving outwards from the collision point) is typically the \"calorimeter\". The purpose of the calorimeter is to absorb and measure the energy of all the particles except muons and neutrinos (muons are long-lived, heavy, and only electrically charged so it happens that they can make it all the way out without interacting with the calorimeters; neutrinos interact only weakly so they are never detected). There is an electromagnetic calorimeter, that is designed to mostly absorb photons and electrons, and then there is the hadronic calorimeter that is designed to absorb protons and neutrons and other hadrons. If we see a track (a charged particle) that is absorbed by the electromagnetic calorimeter, then we probably have an electron. If we see no track (neutral) or a pair of tracks appearing (photon converting to electron pair) that is absorbed by the electromagnetic calorimeter, then we probably have a photon. Similarly for energy deposits in the hadronic calorimeter, we can know if we saw a charged or neutral hadron (we usually can't do much better than that except through careful statistical analysis of millions of collisions, although there are exceptions). Although immediately after the collision quarks may be produced, we cannot see them directly -- they form a spray of mostly anonymous hadrons called a \"jet\" which is detected by the calorimeters. When we see a \"jet\", we think \"quark\".",
"One of the exceptions is called \"b-tagging\". We can identify hadrons coming from \"bottom quarks\" because they have a long lifetime -- they travel for a centimeter or two before decaying. So you look in the tracker for a few tracks originating from a point a centimeter or two from the main collision.",
"After the calorimeters are the muon detectors. These are just trackers that can get the momentum of the charged particles that make it past the calorimeters, which are assumed to be muons.",
"Finally, when we add up all of the energy in the collision, it should sum to zero. If it doesn't, we can calculate that one or more neutrinos must have been produced."
] |
[
"Will cryogenically frozen people ever wake up?"
] |
[
false
] |
Is the practice of cryonics (freezing a terminally ill patient in hopes that medicine will one day be able to wake them up) in any way legitimate? Has the process of freezing a person irreparably damaged cells?
|
[
"You might look at the ",
"FAQ at Alcor",
", and the ",
"FAQ for scientists",
" at the same source.",
"They don't freeze people these days: the process used is vitrification, which minimizes ice crystal formation when performed under ideal circumstances. Fine structure in the brain is preserved. The same would be expected of some plastination techniques, but for various historical reasons those are not used by the community interested in preserving themselves for future revival.",
"An interesting reference is the ongoing Brain Preservation Foundation technology prize initiative:",
"http://www.fightaging.org/archives/2012/03/an-update-from-competitors-for-the-brain-preservation-foundations-technology-prize.php",
"The two current competitors for the BPF technology prize, cryonics spin-off technology company 21st Century Medicine and collaborating scientists in the Max Planck Institute and other research centers, recently put out updates on their progress. You can see images of preserved brain tissue at the BPF website, created with the quite different technologies used by the two teams:",
"Our first team, led by Shawn Mikula (working in the laboratory of Winfried Denk at the Max Planck Institute in Heidelberg), has developed a whole mouse brain chemical preservation and plastic embedding technique. ... As part of the Brain Preservation Technology Prize competition, Dr. Mikula has agreed to demonstrate the quality of ultrastructure preservation which his protocol can achieve.",
"21st Century Medicine's main research has been focused on the cryopreservation of transplantable organs (kidney, heart) and toward decreasing the toxicity of the process to such organs. However, as part of the Brain Preservation Technology Prize competition, they have agreed to demonstrate the quality of ultrastructure preservation that their low temperature vitrification technique can achieve when applied to whole rabbit brains.",
"http://www.brainpreservation.org/content/competitors"
] |
[
"If something is frozen fast enough, the ice crystals will not have time to grow large enough to pierce cell walls. This is why we are able to \"flash freeze\" foods without them turning into mush."
] |
[
"Source?"
] |
[
"Most AI research seems to look to neurology as the answer. What do Neurologists think of the chance of their field producing methods for making an AI?"
] |
[
false
] | null |
[
"Most AI research seems to look to neurology as the answer. ",
"From the machine learning side of the fence, this is really not true.",
"Some proportion of methods were inspired by biology, but that's about it. Not many people (I can't think of any) are relying on Neurologists to crack AI for them."
] |
[
"Ah right sorry if thats wrong. It was just the impression I got.",
"How do you rate the chances at the moment?"
] |
[
"It's inevitable. Human's are just complicated machines, and if we keep working on it we will get there eventually.",
"I can't say when we will get there, or if human-level AI's will be more useful/cost effective than just relying on humans. I imagine they'll be good for something, but it's still an open question of how much.",
"Simple machine learning based methods are everywhere now. They're in the microsoft kinnect, google search, and insurance companies are using/going to use them to predict how healthy you are."
] |
[
"If you were to put 10 box fans in a straight line all facing the same direction (like dominoes); would the air coming out of the last fan be stronger than a single box fan?"
] |
[
false
] |
I know there are probably a lot of variables to deal with here but I'm not sure what they are.
|
[
"Sure, each box fan causes a pressure drop from one side to the other. The magnitude of this drop is roughly related to how much kinetic energy is imparted on the air (i.e. how fast it ends up going). 10 box fans won't cause 10 times the pressure drop of a single fan but it will certainly be fore than a single fan. "
] |
[
"Each added fan will increase the airflow a little less than the previous one did, until you reach a limit (which depends on fan size, speed, strength, angle, and structure as well as the fluid friction of air, interference from surrounding air etc.)."
] |
[
"Don't forget the fan clocking. How the fans interact with one another can greatly affect the net flowrate. If the fan blades at row N+1 is clocked such that it stagnates the air from blades from row N, you're going to get diminishing returns really, really fast."
] |
[
"Is there any intuitive way to visualize the symmetries of the standard model?"
] |
[
false
] |
U(1), SO(2), SU(3), SO(3,1), i keep seeing these again and again when trying to learn about physics, but I have no idea of how to picture these visually as anything other than a bunch of matricies that I don't understand because I don't have a way to picture them. is there any sort of intuitive way to understand then?
|
[
"Do you want to visualise their action or the manifold of the Lie group?",
"U(1) is the group rotations in the complex plane, its manifold is a circle. SO(2) is the group of rotations in the real plane, so it is isomorphic to U(1).",
"I guess you meant SU(2), not SO(2)? SU(2) is the group relating all physically distinct quantum states of a two-level system. It's manifold is a 3-sphere (i.e. the three-dimensional boundary of a four-dimensional ball).",
"SU(2) contains SO(3), the group of rotations in 3D space, as a quotient. The manifold of SO(3) is the 3-sphere with all opposite points are identified. If SU(2) is the points on a 3-sphere, SO(3) is all possible rods connecting opposite points on the same 3-sphere.",
"SU(3) is more complicated, I think. At least I don't have any intuition for it.",
"SO(3,1) is the Lorentz group, i.e. the symmetries of special relativity with 3+1 spacetime dimensions. It consists of SO(3) (3D rotations), boosts (i.e. transformations to moving coordinate frames), and combinations of the two."
] |
[
"I made a ",
"comment",
" explaining how the U(1) gauge group gives rise to electromagnetic fields and charges a while ago. Basically, each point in spacetime has a copy of the group and they're connected to the groups of the nearby points. All the different ways you can put coordinates on these groups gives you different gauges that describe the same physical situation in different ways, while the connections themselves determine what we measure as the field strength."
] |
[
"how do these shapes and rotations correspend to real-world phenomenon though?"
] |
[
"Why do humans or many animal species get life long relationships?"
] |
[
false
] |
So I assume that if animals could spread their seed more they would have a better chance of having descendants. However with a life long partner you can't really do that. Why do so many creatures do this? What advantages are there aside from being able to raise and care/ensure the lifespan of your offspring.
|
[
"Animals with a long gestation period have much more vested in the survival of one offspring. ",
"It's funny because there are reptiles, mammals, even birds and all sorts of other animals that mate for life. ",
"Any insects? I mean, apart from spiders that eat their partners. "
] |
[
"Thats the crux man, to ensure better survival of your offspring and your family it is better to be a tight unit, thus ensuring the genes get passed on. If you just dump em off and bail then you better have loads, or have super self sufficient offspring right away."
] |
[
"The men or the women?"
] |
[
"Do the brains of those with mental illnesses demonstrate any differences with “normal” brains?"
] |
[
false
] | null |
[
"Yes there are neural correlates and markers of various mental illnesses... Do you have a more specific question? It's hard to answer this question generally. Is there a particular illness you have in mind?"
] |
[
"I️ am interested in depression. "
] |
[
"Then I recommend making a new, more specific post along the lines of \"what are the neural correlates of depression\" or \"are there physical differences in the brain of individuals with depression\". However, first I recommend doing a simple Google search -- there is plenty of information available"
] |
[
"Are Wood Peckers ever subject to brain damage? Do they suffer mini-concussions or have they evolved to withstand constant beating on trees?"
] |
[
false
] |
I was just curious about how wood peckers can constantly go throughout their life pecking at bark and hollowing pieces of trees out. I would imagine that beating my face on hard bark most of the time would cause either extreme headaches or brain damage.
|
[
"First, a woodpecker’s skull is built to absorb shock and minimize damage. The bone that surrounds the brain is thick and spongy, and loaded with trabeculae, microscopic beam-like bits of bone that form a tightly woven “mesh” for support and protection. This spongy bone is unevenly distributed in woodpeckers, and it is concentrated around the forehead and the back of the skull, where it could act as a shock absorber. - See more at: ",
"http://m.mentalfloss.com/article.php?id=30731#sthash.flJfBQmM.dpuf"
] |
[
"is this the same way sports helmets such as football are designed?"
] |
[
"Roughly speaking, yes, but we can't achieve the same level of protection because a helmet protects the ",
" whereas a woodpecker protects its ",
". ",
"Helmets (I'm speaking motorcycle since that's what I know) are made of an outer shell to withstand punctures and abrasion and to spread the impact over a larger area. Inside of that is one or more layers of polystyrene that will crush under impact, reducing the sudden deceleration of your skull. Inside of that is a layer of padding for both comfort and to ensure the helmet fits snugly so your skull can't keep moving as the helmet starts slowing down.",
"The problem is that your brain is not rigidly connected to your skull. There is a layer of fluid between your brain and your skull, meant to cushion the brain, but the deccelerations involved here are much more than that little bit of fluid can protect from.",
"Just like when you are carrying a full bowl of water and you stop suddenly, causing the water to possibly slosh out because it ",
" stop as quickly, when your skull stops quickly, your brain may not stop quickly enough either, causing it to slam into your skull. The helmet ",
" by reducing the sudden deceleration, but it cannot guarantee that it will prevent a brain injury.",
"Injuries from sudden twisting motions are also possible as the skull stops twisting and the brain keeps on twisting at the brain stem. Bell Helmets has (licensed?) a ",
"technology that tries to reduce that",
"."
] |
[
"What would happen and what would I feel, if I was exposed to a temperature near absolute zero?"
] |
[
false
] | null |
[
"then the specific heat capacity and the mass of the object will determine the outcome.",
"Specific heat is part of it, but thermal conductivity (specifically, the contact conductance/resistance of the interface) plays a major role as well. If the conductance is very low then it doesn't matter if the SHC is high. ",
"For example, you are much more likely to be burned when touching aluminum than you are nylon, even though nylon's SHC is nearly double that of aluminum. "
] |
[
"then the specific heat capacity and the mass of the object will determine the outcome.",
"Specific heat is part of it, but thermal conductivity (specifically, the contact conductance/resistance of the interface) plays a major role as well. If the conductance is very low then it doesn't matter if the SHC is high. ",
"For example, you are much more likely to be burned when touching aluminum than you are nylon, even though nylon's SHC is nearly double that of aluminum. "
] |
[
"Just thought I would mention that the emmissivity of human skin does come into play here. While a vacuum would preclude conduction and convection, radiation would still rapidly carry heat away from the body. "
] |
[
"Why do people pause their conversations, when in small groups, when they walk past other people?"
] |
[
false
] | null |
[
"As an act of discretion. Often times you care not to share a private conversation with strangers."
] |
[
"The issue I find with this thought is that they show no concern the second I am removed from their peripheral vision and speak at the same level of volume. I haven't seen the same level of discretion when two people are conversing while walking behind strangers or in front of them, while still speaking at a volume that would be easy for others to hear."
] |
[
"Maybe it's a face to face thing."
] |
[
"If bacteria is everywhere and can seemingly grow on anything, then why aren't more colonies visible?"
] |
[
false
] |
Was just wondering since bacteria are on everything; handles/doorknobs, counter tops, floors, soil, underground, lakes/rivers, etc. I mean, we've all seen colonies in our toilets every so often as gross spots that seemingly double in size after a day or two, but seeing as how there are literally trillions in every room, on you, etc., why aren't there more colonies that are visible (on basically every surface) to the naked eye when they multiply so rapidly? And for that matter, why haven't they basically taken over the Earth? You'd think that with such a rapidly evolving, resistant, and plentiful nature, they surely would've overcome all obstacles in the last 3+ billion years and just entirely covered the Earth. I'm glad they haven't, but what's the deal?
|
[
"You don't see them because there isn't enough nutrient density for them to grow into visible colonies. Take a door handle made of metal. Sure there's bacteria there, but there's just not enough biologically available material present to sustain continual growth/division. Most bacteria are not actively dividing, they're just chilling out. The colonies we see in laboratory settings form because they're grown on extremely rich media."
] |
[
"Worth noting that things made of metal usually have very, very, very minimal number so of batcteria living on them as metals are either actively antiseptic or greatly inhibit cell growth ."
] |
[
"I don't believe so. Ceramics are very inert so aren't in any way toxic to bacteria. Bathrooms are \"cleaner\" than kitchens because people are mostly a little more paranoid about keeping their bathroom clean. Plus there is very little in the way of food in a bathroom. Moulds that damp environments tend to thrive better in bathrooms than bacteria do.",
"Kitchens are typically full of raw food, with are good food sources for bacteria and moulds. Also most people keep some form or damp cloth or sponge for wiping surfaces, which is itself probably not replaced or cleaned often enough. Damp cloths are ideal bacterial breeding grounds, which people then use to wipe down their surfaces. If you do keep a cloth like this you should try let it dry out as often as possible and once a week, while damp, microwave it for a couple of minutes."
] |
[
"Does the energy required to heat water increase as the water temperature increases?"
] |
[
false
] |
First time poster. Sorry if this should have been a physics question. If I had water that was 10 degrees Celsius, and I wanted to raise it to 20 degrees Celsius it would require the same amount of energy in joules to do so every time correct? So if I wanted to take that same water and raise it from 20C to 30C, would it require the same amount of energy in joules as the example above? Practical use: I'm about to build a solar heating setup for my pool. I built a controller for the water pump that will pump pool water through the heating coils on my roof. The controller has a temperature probe that will sit inside the coils. The controller senses the temperature inside the coils. Once the water reaches a 'high' temp set point the pump starts running. Once the water drops below the 'low' set point in the coil the pump turns off and waits for the water in the coils to warm up again. I'm trying to figure out if there's an optimal 'high' temp set point I should be aiming for. I can set it up to 99 Celsius. But perhaps it's more optimal to have it cycle at (for example) 60C if the temperature will climb more slowly after that. The idea being that if that's true, theoretically I'd have better results if the pump cycles more often.
|
[
"Thank you for answering my question in a laymans terms. "
] |
[
"Thank you for answering my question in a laymans terms. "
] |
[
"The amount of energy is constant but the rate of transferring heat energy is based on the temperature difference and the materials, for your design I would recommend an often water cycling and set the heat to a comfortable temperature than cycle a very hot water but with lower frequency. "
] |
[
"Why do so many people find rain relaxing?"
] |
[
false
] |
as title.
|
[
"I'm sure there is more to it, including what has already been posted here, but another consideration is the similarity to white noise. There are technical distinctions between the sound of falling rain and true white noise, but the psychological impact of any consistent and familiar background noise is bound to be relaxing. It spares the mind from all sorts of little nearby sounds as well as distant audibles that would otherwise provoke at least a subconscious reaction. "
] |
[
"All of our terrestrial ancestors, including ourselves and all other terrestrial lifeforms, are utterly dependent on it for our survival. I figure we find it soothing for the same sorts of reasons why sugar is sweet, rotting meat is revolting and light is associated with good. Deep, evolutionary reasons."
] |
[
"Part of it is certainly that sunlight (especially blue light from early morning and most of the day) produces serotonin which makes you more alert and more happy. Whereas darker weather, like during the rain, produces melatonin, which relaxes you and makes you sleepy.",
"There are also studies which support various anecdotal evidence where many folks say that rapid barometric pressure change gives them headaches, but no one has been able to identify why, its still in the correlation not causation level of evidence."
] |
[
"What happens to the human body right after an extreme impact to the head, e.g., hockey and football hits?"
] |
[
false
] |
I was watching the clip of Nathan Horton from the Bruins getting blind sided by another hockey player from last night's hockey game. As soon as he hit, it seemed like he was just blankly staring and panting, but what made me cringe is the way his arm settled. It seemed like his arm just kind of tensed and then slowly relaxed. Is this a typical response to severe head trauma?
|
[
"What you saw was a good example of the fencing response, which is typical in head trauma:",
"http://en.wikipedia.org/wiki/Fencing_response"
] |
[
"Spot on! Thanks!"
] |
[
"Now I really want to find a new born baby to try out the ",
"asymmetric tonic neck reflex",
" and ",
"tonic labyrinthine reflex",
"."
] |
[
"Why are gravitational and inertial mass equivalent?"
] |
[
false
] |
My understanding was based loosely on robotrollcall's explanation: that gravitational mass of an object tells space how to bend, and that bending tells the object how to move - or in the case of inertia, how to resist moving. So, say the object is sitting at rest in its own gravitational well from its own frame of reference - so any force applied would result in it being temporarily lifted slightly out of said gravitational well until the force is removed, right? And the pull towards the bottom of the object's frame-of-reference-gravity-well results in a constant equal-and-opposite force to any force applied. Someone told me it wasn't quite accurate without explaining how. I'd really appreciate someone helping me understand this better - this SEEMS to make the gravitational/inertial mass equivalence elegant and simple.
|
[
"Why then is the graviton posited to exist?"
] |
[
"They're equivalent because gravity is a fictional force. It's like centrifugal force - it ",
" to exist, but it's not really a \"force\" in the normal sense. Inertial mass is the tendency for an object to keep going in one direction. If you tie an object to a rope and swing it in circles, its inertial mass will pull you outwards. The bigger the inertial mass of the object, the bigger the force pulling you outwards. There's no ",
" force pulling you outwards, it's just the object refusing to change direction easily, but it feels like a real force. You could say that \"centrifugal mass equals inertial mass\" in that sense, because the bigger the mass of the object, the greater the force pulling you outwards.",
"Gravity is the same, in that gravity is caused by space-time bending. Objects falling under gravity are, in fact, travelling in straight lines through spacetime - it is spacetime itself that is bending. So when you put an object on a table, the table is trying to counteract the objects attempt to move in a straight line (downwards), and the table is exerting a constant force on the object just to keep it in one place. What the table is really doing is counteracting the inertial mass of the object - much like you holding the string of an object stops it from flying outwards as you spin it around. Gravitational mass = centrifugal mass = inertial mass because they all ultimately come just from the inertial mass of the object.",
"Also about your equal and opposite force explanation, I've never heard that before and I don't think it's right."
] |
[
"That's a property of the universe we live in. There's no really better answer than that to a \"why\" question. If you disagree, give me an example of a fundamental physical phenomenon for which there is a satisfying answer as to \"why.\"",
"However, if you want to search for a more fundamental phenomenon that leads to the equivalence principle, there is some discussion that the existence of spin-2 fields in the universe implies equivalence. Here is the 1959 paper that discusses that: ",
"http://isites.harvard.edu/fs/docs/icb.topic1088750.files/weinberg.pdf"
] |
[
"Why does your body flip out when you dream about falling or slipping on ice?"
] |
[
false
] |
My understanding is that your muscles are supposed to be relaxed during REM sleep to the point where they can't really move, but occasionally I wake myself up when dreaming because my legs randomly flail about after falling or slipping in the dream. How is that possible?
|
[
"The same reasons you awake when you are shaken from the outside: your brain keeps a watch on the external world for protection. If you begin to experience hallucinations (\"dreams\") during hypnagogia, what is left of your conscious self integrates these as possibly real, so you wake up. A similar (but different) phenomenon is the brain's misalignment of physical and mental states during sleep paralysis.",
"The transition between wakefulness and NREM somewhat resembles REM at least in theory (in the sense humans are meant to awake ",
" REM, so hypnopompia is naturally REM-to-wakefulness; and in the sense that hypnogognia resembles the waking mind more than NREM as REM resembles the waking mind more than NREM).",
"Search online for hypnogognia; there has been a lot of research on this state."
] |
[
"Hypnic jerk is the name you are looking for."
] |
[
"Hypnic jerk is the name you are looking for."
] |
[
"What are the advantages and disadvantages of substituting sugar with agave syrup/nectar?"
] |
[
false
] |
There seems to be a lot of controversy, some people saying it is still a good substitute for sugar, others saying it is worse than using sugar.
|
[
"Agave nectar can be almost pure fructose, so substituting it for sugar in large quantities is not a good idea."
] |
[
"Ah, I just posted a comment ",
"in the other subthread",
".",
"About glucose: it can easily be metabolized in vast quantities. When you eat bread, pasta, potatoes, stuff like that where the carbohydrate is present as starches, it's eventually broken down to pure glucose and that's how it's taken up by tissues everywhere in the body. Fructose metabolism is very different and takes place almost exclusively in the liver."
] |
[
"I'm wondering if you could elaborate a little.",
"The part that is unclear to me is how the body is affected by high levels of sucrose vs high levels of fructose. I found the ",
"wikipedia",
" explanation but it's a little vague.",
"On one side, agave nectar can be used in lower amounts (because it is sweeter) but on the other hand fructose metabolism seems to have ",
"negative consequences",
".",
"What I'm wondering is: is glucose metabolism also associated with these effects; are they milder or more severe?"
] |
[
"Why do certain parts of our body reproduce themselves when destroyed (eg skin) and others don't?"
] |
[
false
] |
[deleted]
|
[
"Some parts of our body contain cellular machinery to heal wounds, and some do not.",
"In the skin, if you have a deep cut, the stem cells (basal keratinocytes) in the stratum basale need to divide and reform into a single layer to start regenerating skin cells in the epidermal layer above them. If they are too far separated, this regeneration will be incomplete, which is why stitches are sometimes necessary.",
"If you cut off a finger, there's no basal structures that can regenerate and the architecture is so complex, simple cell growth will not suffice.",
"Other areas in your body - like your GI tract - work in much the same way.",
"Your liver can take quite a bit of damage and still regenerate - from as little as 25% of the original structure - largely because other liver cells will proliferate and fill the space, restoring function if not the original architecture."
] |
[
"Cell signaling, but the entire process isn't completely understood.",
"Essentially hepatocytes are quiescent in G0 growth phase until they get a signal through p75 receptors to start growing again. They'll grow until they receive another signal (or lose the original p75 signal) to once again enter the G0 phase.",
"Sometimes hepatic stellate cells in the liver will overgrow in response to injury, laying down fibrotic scar tissue instead of allowing normal hepatocytes to grow. This can lead to cirrhosis."
] |
[
"How come the liver cells do not over profilerate ?"
] |
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