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[
"How would one calculate the partitioning of water between two hygroscopic materials in a sealed chamber with a known volume of water vapor?"
] |
[
false
] | null |
[
"place both the materials on a balance, record. then put them in the sealed chamber for a very long time to reach equilibrium. record the difference. that is the amount of water that went into each."
] |
[
"Good idea. I imagine it would work assuming both materials were approaching 100% water-less beforehand. ",
"But there must be equations governing the system in question. And surely there'd be some amount of water vapor left in the gas within the hermetic chamber. I'm wondering if anybody can point me towards such equations."
] |
[
"while it might be hard to get to 100% free of water if you put the material in a dessicator, or a vacuum oven if it is thermally stable at elevated temperatures, you could get it quite dry. The reason why you want to leave the system undisturbed for a long time is that the system will tend to equilibrium (It would be good to thermally insulate the chamber) and the ratio of the mass of water absorbed by equal moles of each material would be the partition constant. ",
"Perhaps i am misunderstanding you. are you asking about the relative amounts in each one of the materials and then the amount left as vapor?"
] |
[
"How are proteins in their tertiary structure stabilised by the \"hydrophobic effect\"?"
] |
[
false
] |
The lecturers at my uni aren't too great at explaining this
|
[
"Proteins exist in an aqueous environment, and water itself is a polar molecule, that is, there is a separation of charge on a water molecule. The oxygen is negatively charge, while the hydrogens are positively charged. ",
"Now you through a protein into the mix, which consists of a long chain of different amino acids with differing \"side chains\" that are chemically quite different. Some are polar: arginine, lysine, histidine (positively charged); glutamic acid, aspartic acid (negatively charged); serine, threonine, asparagine, gluatamine (no charge). The rest are nonpolar or hydrophobic. ",
"The polar residues, whether charged or uncharged, form hydrogen bonds with water through various means, releasing energy. A release of energy is indicative of a favorable interaction when it comes to enthalpy (heat released due to the formation of hydrogen bonds between polar amino acid side chains and the environmental water molecules). Since nonpolar residues lack this ability to form hydrogen bonds with the environmental water, it is natural to find the lowest energy conformation of the polypeptide chain, where the nonpolar residues are said to be \"excluded\" from the aqueous environment.",
"This favorable conformation for the nonpolar side chains is difficult to achieve with simple primary or secondary structure. In the three-dimensional structure of a protein, this is possible. In essence, what is known as a hydrophobic cage is formed, with water being excluded from the inside crevices and creases of the three-dimensional structure of the protein. This frees up more water molecules that then escape from the interior of the folding protein and then form favorable hydrogen bonding interactions with the exposed polar residues. The \"freeing up\" of the water molecules is another way of expressing the increase of entropy of the system. An increase in entropy, combined with the favorable interactions of the newly excluded water with the exposed polar side chains giving off heat (a decrease in enthalpy of the system) leads to a more stable overall protein. ",
"Typically, protein stability refers to the amount of heat one must add to the system in order to unfold the protein (begin breaking hydrogen bonds, among other bonds). Thus, the more heat we release via the hydrophobic effect, the more stable the protein will become.",
"I should also note that the hydrophobic effect is far from the only contributing factor when it comes to protein stability, but it is a very important one."
] |
[
"Tertiary structures are really stabilized by the hydrophobic effect by the removal of nonpolar groups from the aqueous environment, and are a consequence of the polarity. The polarity of the functional groups are what contribute to the structure of the protein, and are what provide the shape and, consequentially, utility. "
] |
[
"This is an excellent answer.",
"It's also worth noting that the laws of entropy still apply in protein folding and stability - that systems moving towards a disordered state are inherently favourable.",
"Although it might seem counter-intuitive for a tightly folded protein to add to the disorder of a system, it comes down to the amount of water molecules in solution which are able to order themselves against the outside of the protein. A folded protein with a lower surface area/volume ration presents as little of itself as possible to the surrounding water, meaning only the smallest amount of H2Os are capable of aligning with the hydrophobic outside of it in an ordered fashion. An unfolded protein has a much higher SA/vol ratio and can order many more waters. ",
"As ",
"/u/Stanage",
" said there are many factors in protein folding and stability but it's one of those annoying topics where you really have to consider them all to have any confidence in your answer."
] |
[
"Why don't dogs live as long as humans? Are we increasing their life expectancy as we increase ours?"
] |
[
false
] | null |
[
"The answer is yes; but mostly no.",
"Let me explain; in the future our medical knowledge will increase; including that for animals and we will be able to tailor diets, medical knowledge, and medicine to enlongate life for dogs, cats and humans.",
"However life expectancy is not due to medical knowledge; well to a certain extent it is; but how fast we age and our maximum age are not.",
"There are a few reasons that determine how long an organism can live; a big one is telomeres. Telomeres are DNA at the end of the strands which are mostly \"junk\" DNA. As our cells replicate DNA will not replicate; well no organism will replicate 100% correctly; and damage is done to the DNA as this happens. The damage is done to the ends of your DNA moreso then the middle for an example; so the telomeres are long strands of \"junk\" DNA which take the brunt of the damage caused; think of them as the caps on the end of your shoe laces; when they are gone your shoe laces fray and fall apart. Simliarly telomeres will shorten and break over time; when it reaches your main sequence DNA it causes major damage and the organism will die very soon.",
"http://en.wikipedia.org/wiki/Telomere",
"So all animals have differening lengths of telomeres, dogs much shorter than humans.",
"However that is only one reason; our cells actually have repair mechanisms to help these last longer; and repair certain parts of our system; but again over time these repair mechanisms \"gum\" up and start to be less effective.",
"If medical technology advances to the point we can lengthen Telomeres; repair the repair mechanisms; and cure things like cancer and other diseases we would be truly biologically immortal. We'd have to do the same to dogs as well.",
"Some animals are actually biologically immortal; there is a jellyfish which when it grows to an adult \"forces\" itself to go into it's puberty stage over and over; repairing damage and essentially living forever.",
"http://en.wikipedia.org/wiki/Turritopsis_nutricula",
"So to repeat; dogs, and cats have shorter telomeres and age and die quicker; we have longer telomeres and can live longer; other organisms have longer telomeres than us; some trees live for thousands of years, some animals for hundreds; some are biologically immortal.",
"Now you may ask why are all organisms not biologically immortal? Why would evolution not select for that? Well evolution doesn't select for anything specific; just what works at the time; in that place; under that enviroment to prolong and pass on beneficial genes.",
"So yes; dogs and cats and humans will live longer in the future; but unless we can overcome the limitations of telomeres and repair mechanisms we will still always be restricted to a maximum age; just as dogs and cats will; and will still age. The maximum for a human is roughly 140 years."
] |
[
"Less resources available to your family, and to a greater extent, your immediate community/tribe if you're still around consuming them. "
] |
[
"Less resources available to your family, and to a greater extent, your immediate community/tribe if you're still around consuming them. "
] |
[
"why do the low notes on a piano carry for much much longer than the high notes?"
] |
[
false
] |
if you slam an A in the first octave and an A in the last octave, the former will continue to output sound for much longer than the latter. why is that?
|
[
"Because the energy in the vibrating piano wires dissipates a small percentage each vibration. So the note 'lasts' not a period of time, but a number of vibrations. Lower notes period of vibration is longer. So they last longer too."
] |
[
"And the lower note strings have the highest mass/unit length so they store much more energy than the much thinner high note strings."
] |
[
"It's likely more due to internal friction than aerodynamic drag. The vibration of a string in vacuum would still attenuate in the same way."
] |
[
"Do deaf schizophrenics hear voices?"
] |
[
false
] |
I was reading a cyanide and happiness comic that jokes about this and raised the question, what happens with a deaf schizophrenic?
|
[
"According to my Abnormal Psychology Textbook, \"using SPECT (Single photon emission computed tomography) to study cerebral blood flow of men with Schizophrenia, researchers in London made a surprising discovery. They found that the part of the brain most active during hallucinations was Broca's area. This is surprising because Broca's area is known to be involved in ",
", rather than ",
". Because auditory hallucinations usually involve understanding the \"speech\" of others, you might expect more activity in Wernicke's area, which involves language comprehension. These observations support the metacognition theory that people that are experiencing hallucinations are not hearing the voices of others but are listening to their own thoughts or their own voices and cannot recognize the difference.\"",
"As far as I know, deaf people can talk to themselves in their own mind in some sort of way, so I would expect that deaf schizophrenics hear auditory hallucinations."
] |
[
"Please keep discussion:",
"Civil",
"On topic",
"Free of anecdotes"
] |
[
"Wow - that's incredible and I didn't know that. Years ago I read ",
"The Origin of Consciousness in the Breakdown of the Bicameral Mind",
" and found the theory to be fascinating even though it technically would be non-testable.",
"What you're saying supports the idea that conscious thought evolved post-speech development.",
"For those unfamiliar with ",
"Bicameralism",
" the idea is basically this: Humans evolved as social creatures, interacting and evolving the ability to help each other. Passing knowledge on to each other and subsequent generations was key. So imagine this scenario - you're teaching your child how to make a fire and you're talking through the steps to him. Next time when you're alone you find yourself talking through the steps to yourself because it's easier to remember.",
"In fact, back then maybe it was the only way to remember? Talking difficult problems out loud to ourselves is still something many people do today to help figure through the issue. Almost as if wiring internally in the brain didn't exist and so words have to go out your mouth and into your ears - the \"long way around\" so to speak.",
"Anyway, some day, you just don't speak the words out loud, but you hear them in your head instead. Whoa! What was that? Must be the gods talking to me directly.",
"In any event, the theory doesn't have a lot of supporting evidence beyond the writing styles of the earliest human writings. Julian Jaynes uses epics like the Illiad and Odyssey to show that initially all the characters had gods talking directly to them for specific direction, which eventually gave way to people having their own will irrespective of gods.",
"It's a fascinating theory that's totally unprovable, but in my heart it just seems to explain so much about the origin of religions, how gods spoke to people directly, why talking to yourself helps you work through a particularly thorny problem, how schizophrenics hear voices today - and now you bringing up how those hallucinations happen in the speech production centers instead of language comprehension."
] |
[
"May be a dumb question, but do stars of the same mass also have the same volume?"
] |
[
false
] |
Given that stars are mostly made of the same stuff (hydrogen and helium) and gravity is only dependent on mass, I figured equal stellar masses would have similar densities.
|
[
"Depending on the point in their lifecycle they have different ratios of hydrogen/helium/other elements. Stars of the same mass and the same composition are very similar."
] |
[
"This answer is good.",
"For ops benefit I'll add that temperature is variable that affects density as well. A star that's burning hot has great outward pressure against gravity and so a larger volume. ",
"Vzq's lifecycle/composition comes into play here: As a star gets old it runs out of all that good H/He fuel to burn and so cools down. As a result it settles down to a more dense, lower volume state."
] |
[
"The answer is, as all good answers in science are, it depends. ",
"Stars on the main sequence (the predominant life stage of stars) generally follow something called the ",
"mass-radius relation",
". This means, for a given mass, all stars will have approximately the same radius, within error of course. So in general, barring other factors, yes two stars of the same mass and life stage will have the same volume.",
"But things like stellar rotation rate can actually change the shape of a star, going from sphere to oblate sphereoid (think squished sphere) if it is spinning fast enough. So if you have two stars of the same mass, but one is spinning very quickly and the other slowly, they will have different volumes because the quickly spinning one will be deformed. ",
"Likewise, as a star enters the end of its life cycle, it will enter what is called the red giant phase. This occurs when a star has fused hydrogen in its core to the point that there isn't enough left to maintain hydrogen fusion and it instead starts fusing helium. At this point there is significantly greater outward radiation pressure from the core, and the star inflates to a huge degree, but doesn't change its mass. So two stars of the same mass, but different life stages will again be different volumes. ",
"Some of the things that others have mentioned like temperature and composition don't actually impact the volume, at least not in the way they are thinking. Generally, all of the other elements beyond hydrogen and helium make up about ~1.5% (for solar compositions, less for older stars). So, while yes composition may have an effect, it will be very small and likely unmeasurable. ",
"Temperature on the other hand is more of a consequence of mass and life stage. Similar to the above, main sequence stars also follow something called the mass-luminosity relation. This means for a given mass, all main sequence stars will be radiating the same total energy outward, again within error. The effective temperature of a star is proportional to the luminosity divided by the surface area, which for a sphere is 4 * pi * r",
" But since all stars of the same mass have the same luminosity as well as the same radius, they also have the same temperature. This of course is a simplification, as stars don't have just one temperature, but have many different ones for the different parts of the star, like the core, atmosphere, or corona. But these will also be equivalent between stars of the same mass. Later on in life, as a star enters the red giant stage and burns helium in its core, the core temperature rises drastically to create the additional radiation pressure, but because the outer layers inflate so much, the start actually has a cooler effective temperature because the luminosity is radiated over a much larger surface area."
] |
[
"How is it possible for scientists to study and discover about things millions or billions kms away from us when we haven’t even discovered everything that is in our planet?"
] |
[
false
] | null |
[
"Why are those things mutually exclusive?"
] |
[
"I don't really know what kind of answer you are looking for... we have telescopes?"
] |
[
"We do send underwater vehicles to explore the deep ocean and we have detailed atlases of the ocean floor... Again, I'm not really sure what you are trying to ask."
] |
[
"If starlight is extremely old, if someone were to get into a spaceship and fly towards a very distant star, would that star seem to age very rapidly as the ship approached?"
] |
[
false
] |
I know that many stars are many lightyears away from the Earth, meaning that the light that reaches us from them is old, often very old. If we were to fly towards one, would that star seem to age at an accelerated rate of viewed from the ship?
|
[
"All stars except our sun are very many light years from earth. The closest star (other than Sol) is Proxima Centauri at 4.2 light years. The farthest object we've seen is about 13.2 (updated from my mistaken 13.7) billion light years away.",
"So the answer is yes to your question. If we look at Proxima Centauri we are seeing it as it looked 4.2 years ago. If we were to instantaneously travel half way to it, it would look as it did 2.1 years ago, etc. ",
"However, we have no ships that can get anywhere near the speed necessary to observe it aging (e.g., at top speed, you are still a small small fraction of the speed of light - so the effect of aging you witness would be too small to be noticed based on the lifetime of the observer)."
] |
[
"You can not travel faster than the speed of light. In fact, as a physical object (with mass) you can't attain the speed of light at all."
] |
[
"Light always travels towards you at c. But when you fly towards the star at high speed, space seems to contract, so the light is covering less distance to get to you.",
"So the answer must be yes, flying towards a star will make it seem to age very rapidly."
] |
[
"Would it be possible to have a Jupiter sized Earth-like planet?"
] |
[
false
] |
in science, started me wondering about planetary scale. Is it possible for solar systems to scale in such a way that an Earth-like planet could be the size of a gas giant in our solar system? *Could there be a habitable planet the size of Jupiter somewhere floating among the cosmos?
|
[
"~1000 Earth Masses of metals is about the most you can hope to find around a solar type star for planet formation. ",
"COROT-20 b",
" may be such a planet, although it also has ~3 Jupiter masses of gas on top of the hundreds of Earth masses of rock and ice, so you'd probably call it a Jupiter type planet.",
"And therein lies the rub. Making a thousand Earth mass rocky planet isn't totally out of the question. How to keep it from ending up with a thick hydrogen atmosphere might be."
] |
[
"Exactly. Even Venus has a surface pressure equivalent to being under 1km of Earth's oceans because of it's thicker atmosphere. But even if we assume that the atmosphere on a hypothetical Jupiter sized terrestrial planet is proportional in thickness to Earth's atmosphere (or even the same thickness as Earth's), the gravity of the planet would still be cause for extreme surface pressure. "
] |
[
"It's not within our abilities today to start a terraforming project. In the longer term, her comparable surface gravity makes Venus an ideal target for terraforming, yes. When? I wouldn't know how to speculate. More than ten years, less than a thousand?",
"Maybe I shouldn't be negative, but if the Earth has a runaway greenhouse, we're probably toast. Fixing the Earth's greenhouse problem is more plausible than adapting to Venusian conditions, I think."
] |
[
"Are there colors that do not present themselves in animals and plants? Or is there a least common color in the wild?"
] |
[
false
] | null |
[
"There's not a great numberl of blue animals in nature and human eyes respond least well to blue frequencies."
] |
[
"If you look on the electromagnetic spectrum, \"visible\" light is a tiny portion, bordered by the UV/Gamma and Infrared/Microwaves. Obviously, all of these frequencies are of light, it just happens that that tiny portion is what our eyes can pick up. So if our eyes were capable, theoretically we would be able to see colors of frequencies other than we currently know and perceive. "
] |
[
"Not sure if this is what you are getting at but as far as I know there is only one species of mammal, a mole, that has iridescent fur."
] |
[
"Why do lower frequencies penetrate materials better than higher frequencies?"
] |
[
false
] |
For example, sound and radio waves (WiFi)
|
[
"Other people gave answers for light, but the answer for sound is slightly different.",
"Ultimately it comes down to wavelength. For sound passing through a wall, if the wavelength of the sound is much larger than the thickness of the wall, then the wall will appear to be like a thin membrane and will move in its entirety with the sound, causing it to transmit almost all of the acoustic energy to the other side. The mass of the wall also figures into this, as a thin piece of drywall will stop a lot less sound than an equal thickness steel or concrete wall.",
"Bulk absorption in a material is also lower for low frequency sounds. IE, even without walls and such, low frequency sounds will carry further than high frequency ones. This is a bit harder to explain, but there are a few reasons. The first has to do with heat transfer and viscosity of materials. Basically, a sound wave creates a spatial and time varying change in pressure, which results in a local change in temperature. High pressure zones have higher temperatures than low pressure zones. Heat will transfer between these two zones, causing the air to heat up (very slightly) and robbing the sound of some energy. To put it simply, the spatial variation in temperature is more dramatic for short wavelengths, so they lose energy at a relatively higher rate. Likewise with viscosity, where high wavelengths have more dramatic shifts in particle velocity, causing energy to be lost to friction.",
"The second mechanism has to do with random variation. Small eddy currents in the air, tiny particles that reflect sound, etc, can cause sound to scatter and form less coherent wavefronts. The relative size of the variation is what matters, and long wavelengths essentially see a medium that looks more homogenous than a short wavelength would. Think of it kind of like pointillism, there are tiny spots of color, but if you back out far enough you stop seeing the specks.",
"The third mechanism is very similar to the electron relaxation that others mentioned for optics. Different molecules have frequencies that they oscillate at, and when you have sound above those frequencies they will excite the molecules, causing energy to be absorbed. Lower frequencies excite fewer of these molecules and get absorbed less.",
"The fourth mechanism has to do with the continuous nature of the acoustic medium. Sound travels through a material by having molecules smack into each other in sequence, causing the wave to propagate. This works really well if there are a lot of collisions in a wavelength, but if there aren't enough collisions then a considerable amount of the coherent energy in the wave converts to random molecular motion (heat). Basically, when the wavelength of the sound is on the order of the mean free-path (the average distance a molecule travels between interactions) a lot of energy gets lost.",
"Hope that answers your question!"
] |
[
"If a photon doesn't have enough energy to raise a particle of the matter its \"penetrating\" to a higher energy level, then the photon just passes through.",
"Which means that higher energy photons interact with more particles.",
"Higher energy means higher frequency.",
"So lower frequency waves \"penetrate\" materials better, because photons with lower frequencies don't have enough energy and simply \"pass through\" without interacting with the matter.",
"(P.S. Drunk. Didn't proofread. Not even sure I'm making any sense.)"
] |
[
"Wow. Thank you."
] |
[
"AskScience AMA Series: IAmA PhD student who manipulates microscopic particles using light"
] |
[
false
] |
I am a third year PhD student (in the UK) who works daily with optical tweezers. My research interests lie in soft matter and specifically colloid physics. The bigger picture in my work is understanding of the glass transition. Optical tweezers is a technique developed in the 1980s whereby the forces due to a single, tightly focused laser beam are used to manipulate objects with dimensions in the nanometre to micron range. This is often done inside a microscope such that the effects of the laser light on the sample can be observed and recorded. The very first optical tweezers were capable of trapping only a small number of particles simultaneously, typically just 1 or 2. Since then a number of modifications and refinements have been made to the apparatus allowing the simultaneous and independent manipulation of many objects. The apparatus I designed and built in the first year and a half of my PhD and currently work with is what is known as holographic optical tweezers (HOT), although it may perhaps be more accurate to call it diffractive optical tweezers. My setup allows me to simultaneously and independently manipulate up to approximately 50 particles (at least that's the most I've tried to date). I feel that I should highlight the fact that I am not one of the many people pushing the limits of what optical tweezers can do. I'm not developing fancy new algorithms or refining the technique, I'm simply employing it is a tool to do the science I am interested in, namely: soft matter. The equipment I designed and built is by no means the state of the art (10 years ago it may have been, but today it is becoming fairly commonplace). I look forward to answering any questions you may have about any aspect of my field, although I don't intend to go into specifics about my experiments. Questions specifically on glasses and the glass transition may be answered by EagleFalconn, who works in a similar area and has previously provided excellent descriptions of glasses elsewhere on this subreddit. Furthermore, any questions about studying physics in the UK are welcome.
|
[
"Can you describe your research a bit more? What size/type of colloidal particles do you use? Do you move them closer to each other until they look glassy?",
"Do you deal with/care about colloidal crystals that are held together with DNA?",
"Were you at the ACS Colloids conference in Montreal last summer?"
] |
[
"My research: I've described a little in my first answer, at least regarding my use of optical tweezers. Colloid-wise I use commercial polystyrene microspheres in the 2 to 5 micron range as well as smaller poly-methylmethacrylate particles synthesized in our lab. My experimental procedure is to use optical tweezers to hold a subset of the particles in a sample stationary and observe the effect of the obstacles, walls or confining environments on the rest of the sample. Structural and dynamic properties of materials are greatly modified compared to their bulk behaviour when near a wall and since many industrial, chemical and natural processes occur in porous media then understanding exactlyhow the structure and dynamics change in these situations is critical. ",
"Also, I have recently (last two weeks) branched out into trying to build some microscopic colloidal machines powered using optical tweezers. This work is, however, in its infancy.",
"I have nothing to do with DNA mediated interactions with colloids and I largely try to suppress crystallisation by using polydisperse samples that do not readily crystallise.",
"I was not at the ACS meeting, no, although I think my supervisor was."
] |
[
"Firstly: the glass transition. I don't know about the rest of the world, but I certainly remember being taught about the differences between solids, liquids and gases in secondary school. Microscopically, we were taught, the particles of a liquid are randomly arranged while the particles of a solid form a regular pattern or lattice. Of course, what we were being taught about were crystalline solids. Everyday experience with glass (window glass being the obvious example, although many materials can form glasses) tells us that glasses behave in a solid-like manner - that is that they do not flow like a liquid. However, microscopically, the particles of a glass have no long-range positional order - essentially a snapshot of a glass looks very much like a snapshot of a liquid. Glasses are amorphous solids as opposed to crystalline solids.",
"If, on cooling a fluid, one can somehow inhibit crystallisation, one can cool the fluid below its normal freezing temperature and create a supercooled fluid. At some temperature, this supercooled fluid may 'fall out' of equilibrium - this non-equilibrium state is what we call a glass and the temperature at which it occurs is called the glass transition temperature.",
"How do optical tweezers aid the investigation of the glass transition? Well, in a supercooled fluid we observe what is known as dynamic heterogeneity, which essentially means that you will have some regions of the fluid that move much mroe quickly than other regions - the dynamics are hetergeneous. These dynamic regions often have a characteristic size. Using optical tweezers I can take a supercooled fluid of colloidal particles and hold a subset of them stationary such that they can no longer rearrange with respect to their neighbours. By holding particles separated by a certain distance still I can probe this dynamic lengthscale. For instance, if the dynamic lengthscale is, say 4 particle diameter, then if I hold a few particles separated by this distance still, the whole sample in that region should stop moving, or at least no show any rearrangements. Secondly, I can build an artificial 'wall' of particles held in optical tweezers and observe the effect of this wall on the mobility of particles nearby in the vicinity of the glass transition. Properties of materials near walls and under confinement differ vastly from their bulk properties, and since I can build 'walls' with controlled properties I can investigate the intricacies of the behaviour of glassy materials near walls.",
"As I have mentioned above, much of my work is using optical tweezers to define environments with obstacles, walls or confinement and to observe the effect of these features on bulk behaviour, and it is in this manner that optical tweezers can help probe the properties of matter.",
"Thanks for your questions."
] |
[
"What is the use of the laser in laboratories?"
] |
[
false
] |
I've seen them in movies and shows and many real life experiments but I never got what they were, can someone explain?
|
[
"Light (or more generally radiation) from a laser has several properties which can make it very useful for laboratory research. The light is ",
"coherent",
" which means (among other things) that interference can be observed. It can also be (almost) completely monochromatic so the light source contains waves of only one frequency, or equivalently that the photons all have the same energy, and it is possible to generate either continuous wave (cw) or pulsed laser light. This means that it is possible to achieve extremely high intensities, and very short pulses. This is useful for exploring effects due to strong electric fields, or time dynamics on an extremely short time scale (ns, ps, fs, or even atto-seconds).",
"The invention of the laser opened up entirely new areas of research in light and matter interaction, non-linear optics, for example. ",
"Asking what lasers are, or what they are used for, are different questions. They are useful for research in imaging, 2d & 3d-scanning, microscopy, optical tweezers, optical parametric amplifiers (non-linear wavelength converters), raman spectroscopy, molecular dynamics, excited state lifetimes, telecommunications, and the list goes on, and on...."
] |
[
"An example I can think of off the top of my head is ",
"Laser Spectroscopy",
".",
"Transient absorption is probably the easiest to explain of this type. Basically you hit your sample with a fast, high intensity pulse of laser light. You then monitor the absorbance spectra of the sample. This allows us to investigate very fast processes like confromational changes of retinal in the eye (This is on the ~100 femtosecond time scale I believe.)"
] |
[
"It's what my wife does. I call her an electron photographer. She calculates \"the migratory pattern of the elusive silicon conduction electron\" (to be said in a NatGeo presenter voice)."
] |
[
"Why does a capacitor eventually have the voltage of the connected battery?"
] |
[
false
] |
When a capacitor collects negative charge on one plate, it repels further incoming current, and also repels the negative charges on the other side of the plate so that the second plate is positively charged. So additional electrons will be repeled by the negative plate but shouldn't they also be attracted to the positive plate? How do we know current stops when the capacitor voltage is equal to the battery voltage?
|
[
"So additional electrons will be repeled by the negative plate but shouldn't they also be attracted to the positive plate?",
"Yep, until the attraction and repulsion are balanced out by the voltage. (The battery also applies a force on the electrons, in addition to the electrostatic forces between the plates and electrons.)",
"How do we know current stops when the capacitor voltage is equal to the battery voltage?",
"The current stops when the capacitor voltage equals the battery because at that point the capacitor forces balance out the battery forces.",
"If there is too little charge on the capacitor plates, the voltage across the capacitor is smaller than the driving voltage of the battery, so electrons experience a net force and keep getting pushed so as to increase the plate charge.",
"If the electrons were to \"overshoot\" and build up more charge on the capacitor than expected, the voltage across the capacitor would be larger than that across the battery and so the electrostatic forces will push the electrons back to their default (zero applied voltage) configuration.",
"This is a specific example the very general idea in physics of a stable equilibrium: you have a variable/a degree of freedom (here the charge on the capacitor) that is subject to forces that tend to restore it towards an equilibrium value."
] |
[
"As long as it ",
" have the voltage of the cell or battery of cells to which it's connected, there's a conductor (ie whatever is connecting the capacitor to the cell or battery) with a potential difference across it ... so current flows through it in such a way as to increase the charge of the capacitor."
] |
[
"Awesome, everything makes sense now. Thanks all!"
] |
[
"Do sleeping pills decrease the quality of sleep?"
] |
[
false
] |
I know that we don't really know a whole lot about what goes on during sleep, so I'm curious if there's any way to quantify a change in quality of sleep when it is (at least partially) artificially-induced. I'm thinking of mainly OTC sleep aids (diphenhydramine) but I'm also curious about stronger prescription drugs.
|
[
"There's are a number of ",
"different sleep aids",
" that influence sleep architecture quite differently. Acute insomnia can sometimes be remedied by various benzodiazapines or Z-drugs - Z-drugs are similar to Benzos but have reportedly lower dependency rates- like Zoplicone. These drugs tend to influence delta waves (0-4Hz) and represent Stage 4 of sleep. Here we get deep sleep (",
"cite",
"). Zoplicone also tends to reduce REM duration (",
"Cite",
"). Benzo's and Z-drugs achieve sedation by influencing the inhibitory system of the brain (GABA) and thus can cause excess daytime sleepiness. Also, addiction. ",
"Antipsychotics are also used in extremely small concentration (e.g. ",
"Quetiapine",
"). These drugs can have extremely long sedative periods, and reduce total sleep latency. Antipsychotic drugs are not given because chronic insomnia is noted as a psychotic symptom, but because these drugs have general sedative qualities. As a result, they are normally given to people who have chronic insomnia which cannot be resolved with therapy, or have exceed the recommend usage time of Benzos. Like the benzos mentioned above, antipsychotics have a history of reducing REM and elicit a general feeling of restlessness after sleep. ",
"The one everyone knows, diphenhydramine, is in fact very interesting. Drugs that induce sedation/anesthesia are normally exclusively GABA agonists/NDMA antagonist - main targets. However this compound is influences histamine, particularly the H1 receptor type. These drugs tend to increase recorded delta activity, thus leading the individual in a longer state of deep sleep (",
"cite",
") - as recorded on EEG power spectra. Further, REM has been shown to be notably disrupted - as with most other sleep aids. ",
"What is important to remember as to why sleep architecture gets disturbed is because sleep is not a static phenomenon. What I mean is that there are many different ",
"sleep stages",
" that are tightly regulated. As someone who has devoted their career to electrophysiology, it is a very beautiful orchestra of changes. We see hyperactive EEG contrasted with very slow brain patterns. Sleep medications force the brain into a state of sedation and somnolence by potentiating inhibitory activity onto the brain. If you increase inhibition, you slow brain activity, and if you slow brain activity you achieve sleepiness. Now once you fall asleep, these medications are still exerting their effects, so your brain cannot go through the natural rhythms of sleep with this heavy hand of inhibition these drugs are having. "
] |
[
"First off, awesome summary. I'd like to summarize and add a few things though.",
"Let's talk about levels of sleep (from awake to REM)-\nWe have N1, N2, N3/N4, and then REM. Generally, N3 sleep (or deep sleep) and REM are considered the most beneficial. N3 sleep is thought to be restorative to energy, and REM is thought to be important in memory.",
"As far as drugs (I'd like to hit all of them) go, the two major headings of drugs that are used for sleep are either central nervous system drugs or cardio/lung drugs.",
"\nBenzodiazepine type (Z-drugs, and benzos) - Increase GABA activity leading to decreased wakefulness. These drugs generally reduce amount of N1 sleep. Drugs with benzo structure decrease N3/N4 sleep, and those without it don't affect this stage. None of these really affect REM. So, while they reduce some stages, it's not really known what effect this has.",
"Melatonin type (Ramelteon, melatonin) - Bind to melatonin receptors and inhibit wakefulness. These have no effect on the phases of sleep, and moreso just help the onset of sleep along.",
"Antiepileptics (Phenobarbital, gapapentin, pregabalin) - Older drugs like phenobarbital initially increase total sleep and N3/N4 time, and inhibit REM. The new drugs, like gabapentin and pregabalin, enhance GABA activity and cause some sedation effects, reducing time to sleep and increasing N3/N4 time.",
"Antidepressants- This is sort of up in the air. Some make you sleepy, some wind you up. Most lengthen time it takes to get to REM, and reduce amount of time there. However, SARIs may enhance slow wave sleep.",
"Analgesics- NSAIDs might hurt sleep by blocking prostaglandins (which might make you sleepy), but if you're in pain that might keep you awake anyway. Opiates in the short-term keep you up, but long-term use shows decreased N3/N4 time and increased N2 time.",
"CNS stimulants (Ritalin, Sudafed, caffeine)- Likely increase N1, decrease N3/N4, and suppress REM. Tolerance is rapid, and rebound sleepiness happens when you stop taking them.",
"\nBeta adrenergic blockers (metoprolol, anything -lol except sotalol and atenolol)- Most generally increase wakefulness at night, inhibit REM, and also increase daytime sleepiness. These are due to competing effects.",
"Alpha adrenergic agonists (clonidine)- Suppresses REM and causes shifts to N1/awake, but also can cause daytime sleepiness.",
"Theophylline- Increases stage 1 sleep",
"References upon request, but all of these are generally from UpToDate, and cited from \"The effect of drugs on sleep quality and architecture\". If you have access, there is more info. If you have more questions, I'm happy to hunt down individual sources for you. Sorry for the lack of major citations otherwise.",
"Edit: Ninja edit for clarity from the post below. Thanks Neuraxis!"
] |
[
"Well melatonin can be used as a alternative way to help correct sleep rhythms. For example, one study found that the circadian shift elicited by weekend sleep patterns can indeed be corrected with the use of melatonin (",
"cite",
"). However its corrective properties are heavily dependent on when the compound is actually taken (",
"cite",
"). In terms of treatment with insomnia, as far I as understand, there have been no conclusive evidence suggesting it works on anyone other than the eldery (",
"citation 1",
", ",
"citation 2",
"). Thus the potential for insomnia-treatment is more for age-related insomnia than general. ",
"In sum, it definitely does influence the brain much more differently than these drugs cited. For one thing, melatonin is not an exogenous compound, and influences the circadian nuclei of the brain establishing proper sleep cycles. These other drugs elicit sedation through heavy handed inhibition."
] |
[
"Why do cats love to sit in boxes? No, seriously. Why?"
] |
[
false
] |
We're all aware of the phenomenon. Place an open box in the middle of the room. Or even something flat like a newspaper. And sooner or later your cat will sit on it like a watchtower. So why is this? It's not particularly warm, soft, or high up. Is there some natural behavior that domesticated cats are mimicking when they do this? (I know this isn't as intellectual as the usual questions on this sub, but I am genuinely curious about it. And I could use a break from mind-bending quantum physics) While I appreciate all the responses, the general consensus seems to be "nobody really knows for sure". So until proven wrong, I state that they use the boxes as transmogrifiers when we're not looking. This explains why they stare at us while sitting in them.
|
[
"Boxes allow at least partial concealment. Cats may enjoy that because they're both ambush predators and small animals that need to watch out for predators. ",
"I don't think cats have such a strong preference for flat objects like newspapers. Maybe it is just memorable when a cat sits on an object but not memorable when a cat sits on the normal floor. It could also be that the flat objects your cat sits on smell like you from you handling them and the cat likes that. Finally, if cats do indeed prefer to sit on flat objects instead of the floor, it may stem from their desire to be clean. Cats are ambush predators and smell could give away their position to prey. Maybe cats hope to keep themselves clean by sitting on a clean object rather than the \"ground.\" "
] |
[
"I don't exactly know how to respond to this thread. I think we can learn a valuable lesson here about how anecdote can contribute to on-topic discussion on this forum. ",
"First, as to the question, I too have cats and anecdotal evidence from that experience. We can combine our several experiences to comprise a larger data set. Cats appear to generally like boxes, cardboard, little flat areas that are kind of defined to be apart from the surrounding area, etc. That's all useful addition to the discussion at hand. And we can notice some trends in the data. They seem to like confined-ish spaces or defined areas. ",
"But let's try to keep the speculation to a minimum beyond that. We do try to take the goal of scientific answers seriously around here. "
] |
[
"my cats will also jump at the opportunity to sit on a newspaper or plastic bag in the middle of the room, but I think more than anything, it's just that it's new. They walk by and say, \"Hmm. That wasn't there before. Better investigate,\" and apparently cat investigation mostly involves sitting on things. "
] |
[
"Should I speed up or slow down to decrease the chance of my car being blown off the road?"
] |
[
false
] |
My sister is in northern Ontario, where I hear it is a fairly blustery day today. My assumption would be that speeding up would provide more kinetic energy while decreasing the available traction. Would the decrease in traction be worse than the increase in momentum?
|
[
"This may not be scientific information but it well tested empirical data. Slow down! Here is why. If the wind takes you for a bit of a ride you may be able to find an escape route before you have a real problem. In general if the situation is unsafe or even in question, slow down. Now, on with the science. This is ",
"r/askscience",
" not ",
"r/commonsense",
".",
"EDIT: Actually I think that my 20 years of empirical driving in high winds with multiple types of vehicles and multiple wind conditions could be considered science. "
] |
[
"How your momentum affected the wind would depend on in which direction the wind was blowing and the direction in which the car is moving. Momentum is a vector quantity. Assuming that the wind was directly perpendicular to your car, the momentum of your car due to its moving forward would have no effect on the wind. There would have to be some component vector of the car that cancelled out some component of the wind in order for your momentum to counteract the wind.",
"Basically you would have to drive at some angle that was toward the wind in order for the car's momentum to have any effect, and unless you were driving directly into the wind the effect would only be partial, based on the angle. "
] |
[
"This is what I was suggesting also. I am actually not sure why I was down-voted, as I used actual physics to back it up, and you were upvoted for anecdotal evidence. Speeding up does almost nothing except make it more dangerous if you get blown off the road."
] |
[
"Left a container of white rice in the fridge too long. It turned green/blue moldy. Where does the pigment come from?"
] |
[
false
] |
Can pigment be formed from two substances that doesn't contain the color?
|
[
"... you know, for a friend."
] |
[
"How much moldy rice would someone need to eat in order to cure a case of syphilis?"
] |
[
"I could be wrong, but this seems like a variation on the question \"when I drink purple grape juice and pee yellow, where does the purple go?\"",
"When molecules of any colour are metabolised, they are broken down into simpler bits and reassembled to form new molecules with new properties that could include a different colour. The \"colour\" of a molecule is determined in the following way: ",
"Photons/light hits the molecule, transferring energy to it. This energy excites some electrons into occupying a higher energy level. These electrons are unstable and soon return to their normal energy level, losing the potential energy in the form of a photon. Because electrons can only occupy very specific energy levels, they only emit a specific wavelength of photon when they fall from one level to another.",
"The molecules composing the white rice emit photons at nearly all the wavelengths/ energy levels of visible light and so they look white. These molecules are broken down by the mould and reassembled into new ones that apparently only emit photons in the green/blue range (about 450-550 nm wavelength)",
"If I misunderstood the question, I apologize."
] |
[
"What is the evolutionary point of photosynthesising vitamin d?"
] |
[
false
] | null |
[
"Human body"
] |
[
"Human body"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Genetic mutations and errors in DNA replication?"
] |
[
false
] |
1.) I understand that a silent mutation always affects the genotype and not the phenotype, but considering an alternate base pair is replacing an existing one (but still not changing the amino acid), isn't it fair to say that silent mutations do produce a change in the primary sequence of the encoded protein? (Example: the mRNA sequence UAC codes for Tyrosine, but if the sequence is subject to mutation, UAU also encodes for Tyrosine, avoiding the Wobble effect for further complication) 2.) Understood: mutations are completely random, and can be advantageous or disadvantageous. But, according to my professor, "the ability of a community of organisms to adapt to the environment," can make mutations only advantageous. How can this be? 3.) If DNA gyrase is inhibited, wouldn't it be fair to say that since DNA replication is being affected, the cell would not be able to synthesize peptidoglycan or begin transcription and translation? Thank you for your help
|
[
"A is the correct answer because it is referring to a ",
" of organisms, not a single organism. On the whole, the ability to mutate is advantageous because it allows, every once in a while, for an organisms in a population to acquire a positive trait.",
"Also, to clarify on the last point. Transcription and translation would be fine because gyrase (topoisomerase) is involved in replication, not protein synthesis."
] |
[
"1) The base pairs tell specific RNAs what amino acids to recruit, ",
" which one to produce. Since silent mutations result in the same amino acid being recruited, the protein does not change.",
"2) I think you are misquoting your professor, especially since you only put part of what he said in quotes. I don't know why he would say that.",
"3) Yes, which is why many antibiotics are inhibitors of gyrase "
] |
[
"Thank you so much for your clarifying that for me. I appreciate your help. ",
"For number two though, the question actually read \"Considering the ability of a community of organisms to adapt to the environment: A.)mutations are advantageous B.) mutations are disadvantageous C.) Both are correct\"\n*According to him, A is the correct answer :/",
"In regard to number three my professor only considered that DNA replication would be affected, but he listed the three other biological processes I mentioned as not being affected. ",
"I actually tried talking to another professor today about it, but he wasn't much help. I think he was just being loyal to his colleague. "
] |
[
"Could you make some sort of 'boat' to float in the atmosphere?"
] |
[
false
] |
[deleted]
|
[
"Boats on water float because they are buoyant. Buoyancy occurs when the object weighs less than the stuff it's displacing. To create something that's buoyant in air it necessarily has to be lighter than the air. The easiest way to do this is with a gas. To contain a gas in your craft it would have to be sealed. ",
"Sound familiar? What you're describing as a \"boat to float in the atmosphere\" is essentially - an enclosed space filled with a gas that's lighter than air. A balloon, zeppelin, dirigible. "
] |
[
"No, but ",
"this",
" is a pretty cool video of an aluminum foil boat floating on sulfur hexafluoride. "
] |
[
"No solid or liquid is lighter than air. ",
"Good response, but this one part isn't entirely true. There are effective solids that are lighter than air, and I suppose they could be fashionable into a boat. That's being a bit nit-picky of me though.",
"Another thing to note is that buoyancy on water is easy because of the large difference in weight between air and water (about 1000 fold at sea level). Since the difference in air weight varies very slowly (and pretty smoothly) up into the atmosphere, it's much, much harder to get any sort of boat effect. Unless, of course, you create a balloon/zeppelin as you mentioned."
] |
[
"Probably a very basic question about evolution..."
] |
[
false
] |
Probably just exhibiting my ignorance here, but natural selection via mutation would surely produce a lot of "failed" mutations right? In fact it must logically be something like 99% of mutations. Surely there should be many more "defected" organisms showing up in the fossil record?
|
[
"Most deleterious mutations wouldn't survive the egg or the womb. Most of the rest wouldn't survive infanthood, and so on. There not being many mutations to start with, the number of deleterious mutations surviving long enough to be trapped as fossils would be very small.",
"These two penguins are slightly different in appearance",
", but it would be a daunting challenge to count ",
"how many deformed penguins there are in this photo",
"."
] |
[
"Fossilization is a rare event. The odds of any individual of a species becoming a fossil are low, and there were undoubtedly species that never left a single fossil (or that we haven't found yet). In general, the more common a species is, the more likely one of its individuals will leave a fossil.",
"Think of natural selection acting as filters on different life stages. Many genetic mutations are lethal, such that the embryo dies during development. Other mutations may cause the offspring to die young, before it can reproduce and pass on the mutation. The mutations that have the greatest likelihood of showing up as fossils are ones that have become relatively common in a species and so are ",
" defects, because if they were, natural selection would not have favored them. These 2 points (strong selection against deformities, rarity of fossilization) contribute to the likelihood that a single deformed individual (assuming the defect is due to genetic mutations and not injury or disease) becomes fossilized is very low. "
] |
[
"Most mutants (with harmful mutations) can be expected to be less physically fit than a healthy dinosaur. A less fit dinosaur is even more likely to be eaten, and its body destroyed. ",
"Edited to clarify that a mutant would need a harmful mutation to be less healthy"
] |
[
"In a vacuum, will an electron cloud expand to fill a volume like a gas?"
] |
[
false
] | null |
[
"In a sense, yes. If you have a particle in a box and you expand the size of the box, the wavefunction of the particle will evolve with time such that it \"occupies\" the entire available volume.",
"There are two limits to consider: the limit where the box is expanded rapidly (the sudden limit), and the limit where the box is expanded slowly (the adiabatic limit).",
"In the adiabatic limit, the box size is varied slowly, so if the particle starts in the ground state of the well at t = 0, it will remain in the ground state as the well expands, even though the actual ground state wavefunction and energy are changing with the size of the well. So the wavefunction will expand with the box as you slowly make it bigger.",
"In the sudden limit, the box is rapidly jerked to a larger size, so the wavefunction of the particle doesn't have time to change. So immediately after the box size is increased, the wavefunction will still be localized in the region of space that was originally available. As time goes on though, the wavefunction will evolve such that it occupies the entire volume of the box.",
"So either way, you end up with a wavefunction which extends throughout your larger box."
] |
[
"There is no hard cutoff, these are just limits where the time-scale for the perturbation go to zero (sudden) or infinity (adiabatic) respectively."
] |
[
"The probability density will not be uniform. The energy eigenstates for a particle in a box are sinusoidal. So there will be nodes and maxima in the probability density, but the wavefunction will still \"occupy\" the whole box."
] |
[
"Is there anything in what this guy says? (Some probably insane youtube video about the magnetosphere)"
] |
[
false
] |
TL;DW - This guy is saying data is missing from the magnetosphere data on the NASA website for March 12th 2012 and that it may be a magnetosphere reversal? (Which, in my laymen head, doesn't make sense since I thought the magnetosphere didn't really have poles). Just curious whether this is crazy or could make sense?
|
[
"The guy doesn't seem to postulate what the cause is of the event, just that there appears to be a reversal that occurred and that the data for this time frame has now been removed.",
"I am not an expert on this field, but I will say that it is not uncommon for experimentalists to hide data of interesting events until they have analyzed it. This has two reasons - 1. so that the data can be analyzed properly by experts, 2. so that people don't jump to conclusions and start spreading hard-to-destroy rumours about the results."
] |
[
"Due to the solar wind, the magnetic field lines are distorted from what would be approximately symmetrical shape, into one that is 'drawn out' into a tail facing away from the sun. It seems that by reversal he means that he believes something on the dark side of Earth distorted the field to face in the opposite direction, something stronger than the solar wind. ",
"However, as ignatiusloyola mentioned it is not common for scientific results to be hidden from the public (unless the research itself is confidential, such as private company R&D, classified military projects etc) but this does not apply to this kind of research. There are countless unaffiliated bodies monitoring the magnetosphere, and even the big NASA ones will have lots of involvement from external institutions such as universities from all around the world. Basically, although it is not likely for data to be hidden from the public to hide some disastrous event like he claims, I also doubt it could be done even if they wanted to. "
] |
[
"Perfect answer, I didn't know they do that. Thanks!\nKinda backfired though if they did it for the second reason lol There's quite a few sites/videos about it.",
"Oh and also what I meant for the reason was, is there any reason it would reverse or could?"
] |
[
"How do astronomers know how far a star or galaxy is from us?"
] |
[
false
] |
[deleted]
|
[
"A few different ways;",
"Lasers",
"Parallax",
"Standard candles",
"Red Shift",
"For more detail on how astronomers measure distance this Wiki page has a good list of techniques;",
"https://en.wikipedia.org/wiki/Cosmic_distance_ladder"
] |
[
"Good list. I would add that Cepheids/variable stars are also used as standard candles (it says so at the link, but might be worthwhile to mention explicitly, since this method (discovered in 1912) was the first standard candle)."
] |
[
"And there's also two main types of Cepheids, which need to be differentiated in order to accurately determine their distances. The reason why they work so well as distance indicators is because their brightness is directly proportional to the length of their pulsation period (the time it takes for the star to return to maximum brightness). However, it took a while for astronomers to realise that there is second class, the Type II Cepheids, which are approximately 1.6 ",
"magnitudes",
" dimmer than a Type I of equal period.",
"There are also some related classes of stars, like the Delta Scuti, RV Tauri (sometimes considered a high-luminosity extension of Type II Cepheid class), and RR Lyrae variables, which have similar period-luminosity relationships, so those are important as well."
] |
[
"Why do all the planets roughly orbit the sun on the same equitorial plane and also the same direction?"
] |
[
false
] |
This bugged me for years and I still can't find a satisfactory answer.
|
[
"They all formed from the same accretion disk so they rotate on the same plane and in the same direction that the original disk rotated in. "
] |
[
"The search bar is your friend. This question gets asked almost on a weekly basis ",
"http://www.reddit.com/r/AskReddit/comments/ijote/what_causes_the_planets_to_orbit_the_sun_on/"
] |
[
"It is thought (and now substantially confirmed by observing such phenomena from afar) that forming solar systems go through a period in which the young star is surrounded by an \"accretion disk.\" Enormous amounts of dust and gas avoid either being pulled into the star or drifting off into interstellar space by maintaining an orbit that balances gravity's inward tug with the outbound component of that matter's velocity.",
"Because other matter will fall into the star or drift away from the young solar system, this accretion disk provides nearly all the material to shape new planets. Over time, larger rocks are drawn to one another. As great masses cohere, they pull dust and gasses toward themselves. Over enormous spans of time, this disk of material is transformed into planets, planetoids, and clearly defined belts of debris. Because these objects emerged out of a single disk rotating in a specific direction, planets inherit this momentum and it is reflected in the paths of their orbits.",
"A proper astrophysicist may be able to offer more clarity here, but my understanding of \"why is it always a disk?\" is simply that other configurations lack sufficient stability. If a spherical cloud of dust and gas were to form, orbital momentum that would be just right for sustainability along an equatorial plane would be inadequate at other latitudes on the sphere. Some of that matter might be pulled into merger with the disk, but most would fall into the star itself. Likewise multiple overlapping disks would tend to pull together in a single disk (for cases of similar rotation) or rob one another of momentum (causing material to spiral inward until the most massive of the original disks was reduced to a remnant of its original form.) ",
"To put it simply, the accretion disk is the only shape that permits dust and gas to remain in orbit long enough for that material to form new planets. Other shapes may form in the cosmos, but they will fail to endure long enough to act as planetary nurseries. "
] |
[
"The World's Population is circa 50% male, 50% female. What, if any, biological mechanism ensures such a ratio between the genders?"
] |
[
false
] |
[deleted]
|
[
"I cannot give you an expert answer, but while you wait for one you might like to read this wikipedia article.",
"http://en.wikipedia.org/wiki/Fisher's_principle"
] |
[
"Related question",
".",
"Do some men have a higher count of sperm carrying a Y Chromosome than they do carrying a X chromosome?"
] |
[
"circa is latin for \"around.\" I've seen circa used for other things than time."
] |
[
"Ignoring computer power, is there a maximum limit of the speed of the internet?"
] |
[
false
] |
Like with the fastest computer/router would we have theoretically infinite speeds?
|
[
"One person answered in terms of speed and the other person answered in terms of bandwidth.",
"Bandwidth (really ",
"symbols per second",
" is limited by how quickly you can meaningfully vary your signal. This is capped by the frequency of the light you are using to send the signal and how much noise there is in the line. The light in a standard near-infrared fiber optic cable is oscillating 230 trillion times per second, and your hard drive and your routers cannot even come close to handling what the cable is technically capable of sending.",
"If terabits per second isn't enough for you then you might try just bumping up the frequency. There is no hard upper limit to the frequency of light, although you might not want x-ray internet. You can also have multiple lines and various encoding schemes, or fill a station wagon full of SD cards...",
"Ping is completely separate. It's a round-trip response time usually measured in ms, and there is an unbreakable hard cap because of the speed of light. A straight glass cable over the surface of the Earth between New York and Sydney would have a ping of about 160 ms. Real-world internet is anywhere near this because routing and repeating infrastructure is already pretty awesome.",
"Internet optimized solely for ping would use a vacuum tube instead of a cable and cut that time down to about 106 ms (( distance / c) *2). Light's progress is effectively about 1/3 slower in glass than in vacuum. Any scheme to speed up a signal beyond that will fail, and if there's anything you think would allow you to then you should probably go back and be sure you understand it.",
"So the ultimate sci-fi internet would be x-rays flying through vacuum, and would download movies much faster than current internet but only give you a very slight improvement in ping-heavy applications like Counterstrike."
] |
[
"High-speed trading is interested in every millisecond reduction in ping. There are microwave transmitters set up because microwaves in air travel faster that infrared in fibers. And if it would be feasible today they would send neutrino beams directly through the Earth to avoid delays from the curvature."
] |
[
"Any scheme to speed up a signal beyond that will fail, and if there's anything you think would allow you to then you should probably go back and be sure you understand it.",
"There is one other theoretical way, though it would likely induce high latencies in signal generation and detection. If we could figure out a way to easily generate, direct and detect neutrinos, it would be possible to send a near-lightspeed neutrino beam through the Earth - giving a round-trip ping for two antipodal points of 85 ms, as opposed to ~133 ms for a lightspeed signal going along the Earth's surface."
] |
[
"How many calories are burned by donating blood?"
] |
[
false
] |
If course most is burned in replacing the blood cells, but how many calories are involved?
|
[
"Edit...I may have ",
" misunderstood OP's question. My answer below stays. ",
"According to the University of California, San Diego, your body does burn roughly 650 calories during the replenishment process after donating blood, as it must first increase your blood volume again, which takes less than two days, and then replenish all of your missing red blood cells, which can take a while longer. ",
"However, as you've already stated, that doesn't account for the actual donation process. ",
"The average donation takes roughly 30 to 45 minutes, where 15-30 of those minutes is spent squeezing a ball. Aside from chatting and basic bodily functions, this ball is the only physical activity you are participating in. You are in a reclined seat, relaxed, with your feet, up, etc. Unless donating really makes you nervous, thus spiking your heart rate while you donate, then your body is only spending energy on basic functions and that soft squeezable ball. So how many calories do you burn just squeezing that thing? Although it isn't exactly scientific, the website \"ChaCha\" states that you would burn roughly 5 calories while squeezing a stress ball for 20 minutes. In fact, you will burn more calories through simply existing during the donation than you would squeezing the ball. Using a Basal Metobolic Rate calculator (what you burn by existing), a man who is 6' tall, 180 pounds, and 30 years old burns just over 1,800 calories per day for basic bodily functions. 30 minutes of that is still almost 40 calories. A female who is 5'6\", 120 pounds, and 30 years old still has a BMR of roughly 25 calories burned in 30 minutes. However, as you've seen, BMR's can vary wildly from person to person. Male? Female? Tall? Short? Skinny? Large? All of those factors impact your BMR. Then there's a difference in what you burn while sleeping vs awake, walking vs sitting, etc. Those who maybe talk more during the donation may burn a minuscule amount of calories more, you could burn a few more if you're pulse was maybe higher than what it normally is at rest, and any other myriad of factors and circumstances can contribute to this.",
" Not enough to matter, you'll burn more by simply existing during the donation. You burn a metric shit tonne of calories replenishing your lost blood, though. Roughly 650 calories. "
] |
[
"In my state, you can only donate whole blood every 8 weeks, because that is the conservative estimate for how long it will take until all of your red blood cells are replaced after donating. This puts you at 650 calories extra that are burned during 8 weeks (in theory), which technically averages out to only about 11 or 12 extra calories burned per day for 56 days. Obviously the burn isn't consistently spread over that time period, as most of the calories burned will occur in the immediate weeks after donating, to replace the water, plasma, and a good chunk of the red blood cells. ",
"However, due to how few calories you burn over time, donating blood can not be viewed as a practical weight loss option. You'd run out of blood and die, if you tried to donate quickly enough to lose weight. Regular donating does have its health benefits, though, even if weight loss isn't an immediate side effect to it. "
] |
[
"Is there a frequency and volume at which you could donate blood such that it is safe yet contributes to weight loss? Not that I'd advocate it instead of healthy diet/exercise, but I'm curious. I'm referring specifically to the calories burned through replenishing the blood/cells rather than the actual act of giving."
] |
[
"Can someone explain FTL in general relativity?"
] |
[
false
] |
Lawrence Krauss says at 51:10 minutes in his "A Universe from Nothing" lecture that eventually galaxies will move away from us faster than the speed of light and disappear. I've been doing a bit of reading and am beginning to understand this concept, but can someone explain it to me in more simple terms so that a non-science college student can understand it? Thanks guys
|
[
"Lawrence Krauss is actually wrong on this one. At any point in time, sufficiently far galaxies will recede with speeds greater than the speed of light. The threshold distance for this is the Hubble distance, d = c/H. If you plug this in to the Hubble law, v= d*H, it's easy to see that v>c for these galaxies.",
"Contrary to common belief, even among experts like Krauss, these distant galaxies do not become invisible. In fact, the Hubble distance right now is at something like redshift 1.6. We routinely observe galaxies with a higher redshift than that, the record being at something like 7 or 8. The CMB is observable and at redshift 1100. Why light from these galaxies can reach us has to do with the expansion of the Universe. ",
"Honestly, it's a bit technical and really hard to explain. The reason why this is not a problem for relativity is that it only states that superluminal speeds are impossible in ",
". In curved spacetime, inertial frames can only be defined locally. Someone living in such a distant galaxies would not be able to pass a lightray. ",
"Source",
" (Note that Krauss' misconception is mentioned in paragraph 13 of appendix B.)"
] |
[
"If the acceleration continues, in the future the galaxies will seem to recede faster than the speed of light, even though they are not actually moving FTL. It's just that the light emitted from those galaxies will never be able to reach us given the speed of the expansion. ",
"Galaxies beyond the Hubble sphere do not become invisible to us.",
"Also, even without dark energy the Hubble distance is always finite, which means there are always galaxies that recede FTL.",
"Edit: for what it's worth, Feynman, Weinberg, Peebles, Peacock and Hubble didn't get it completely right either. Of course, neither did I. I was blown away when I first read this paper."
] |
[
"Try this Khan Academy video:",
"http://www.khanacademy.org/video/radius-of-observable-universe?playlist=Cosmology%20and%20Astronomy"
] |
[
"Is it possible to store analog information on a microchip?"
] |
[
false
] |
I’m curious about modern analog information storage, which aren’t magnetic tape, optical, etc Could anyone point me to more information on this technology if it exists? I have read some about memristors and phase change storage, but that uses a special type of glass.
|
[
"Yes, by converting to digital and storing that. Sorry if that sounds cheeky (or even assholey), but it is actually the best answer to your question since the digital signal will result in the most accurate reproduction of the signal; this is what I will justify here.",
"The main reason that digital will outperform analog is ",
"noise",
". Noise is ever-present in all signals (even in microprocessors) and is actually the reason why digital will outperform analog. Indeed, without noise, clearly analog would be superior since all data sequences could be considered as a single analog value. For example, 01001..., could be encoded as the analog value 0{2",
"} +1{2",
"}+0{2",
"}+0{2",
"}+1{2",
"}....",
"Anyway, the noise present when reading the analog signal limits the amount of information that can be observed per unit time. The exact amount of information (measured in bits) that can be transmitted per unit time subject to a given noise is called the ",
"channel capacity",
", where the term \"channel\" is used to describe the stochastic relationship between signal and observation. The most famous channel capacity is that of the iid additive white gaussian noise channel, specifically ",
", described by the ",
"Shannon-Hartley theorem",
".\nThus noise restricts the analog source to only being able to convey a finite (or digital) amount of information at any given time. Obviously, longer times may given more data, but that data is still finite.",
"Furthermore, storing data digitally will always be easier to maintain. Digitally storing data allows for things like ",
"error correction codes",
" that prevent errors in future replications of the data. If the data was stored in a more analog form, then every time that data had to be transferred (say from μprocessor to μprocessor) more noise would be added to the signal, degrading the copy. Digital prevents this.",
"So, in the end, a digital representation is the best way to store information about an analog source."
] |
[
"You can buy specialized ",
"sample-and-hold components",
" that store an analog voltage. ",
"Similar circuits",
" can also be built from individual components. ",
"Before microprocessors became fast enough to handle sound, audio delays were made using ",
"bucket-brigade devices",
". They worked by transferring analog voltages through a series of analog circuits with a small delay between each. ",
"I'm sure they could be put on a microchip (the BBDs were already integrated circuits), but I don't think there is a strong business case for using it for storage. As ",
"u/ericGraves",
" says, your best bet is to convert to digital and store that instead."
] |
[
"Yes. Some researchers have developed a chip for neural nets, where each cell / transistor can be set to a continuous (= analog) resistance. In practice, the values of resistance will exist as digital information before being programmed as analog information on the chip, but the storage really is analog.",
"Source: ",
"https://youtu.be/GVsUOuSjvcg"
] |
[
"How does a drug ever completely leave your system if it just keeps decreasing by half?"
] |
[
false
] |
If a drug has a half-life of 1 day, then after a day, its amount has decreased by half. After another day, you’re at 25% and so on. But if it just keeps reducing by half, how do you ever reach zero? You don’t. It would be a tiny tiny minuscule amount but never zero, so I’m very confused.
|
[
"Molecules of drugs are discrete units. Each unit has a certain chance over time to be eliminated from the body through whatever mechanism it’s metabolized. Half-life is simply a description of the rate of that process. Ultimately, you end up with some small amount of drug (theoretically, one molecule) that is eliminated and the drug is gone."
] |
[
"Thank you, this helps a lot!! You can’t have half of a molecule"
] |
[
"See also ",
"Achilles and the tortoise."
] |
[
"Has Io ever been seriously considered a possible site for extraterrestrial life?"
] |
[
false
] |
In Arthur C. Clarke's "2010", humanity finds extraterrestrial life for the first time on Jupiter's moon Io. In the years since, I can't recall any "real" cases for Io being a likely spot to find life in our solar system other than Earth. Has Io ever been a serious candidate for finding life? If not, why did Clarke choose it for his novel?
|
[
"Interactions with Jupiter’s magnetosphere expose Io to some very intense radiation, and gravitational interactions with Jupiter tidally heat it’s core to the point where it’s highly volcanically active. Through a combination of the radiation and the heat any water that was once on Io is long gone, and it’s generally a very hellish place. There is no real chance of subterranean oceans and everything about that moon is very hellish.",
"Granted, there are bacteria on Earth that thrive next to volcanoes and that don’t need much water but that is only after billions of years of evolution and even then it would be a stretch for even the most extreme Earth bacteria to survive there.",
"One possible reason Io was considered a place to find life is that volcanic activity is believed to be an important in the development of life, and Io certainly has no shortage of volcanoes."
] |
[
"\"Io is generally considered a poor candidate for life because of all the radiation Jupiter blasts it with. In addition, no organic molecules have been detected on its surface, and it has only an extremely thin atmosphere devoid of detectable water vapor.\"",
"https://www.space.com/8564-jupiter-volcanic-moon-io-target-life.html"
] |
[
"He wrote that in 1982. A few years after Voyager revealed that it was geologically active. ",
"But this was before a lot of science from the likes of The Galileo and Cassini-Huygens and New Horizons missions. It’s important to put his fiction in context with the knowledge that was available to him at that time, not what we currently know. ",
"I don’t have information specifically to this point, but it’s very possible that we didn’t know just how devoid of water Io was at he time. Or maybe it was just a detail he missed. "
] |
[
"Why are all adults prescribed the same dosage antibiotic regardless of weight?"
] |
[
false
] |
I recently ran a course of cefdinir, which was the first time I had taken this particular antibiotic. As I was poking around online reading about it I noticed that dosages for children under 12 are based on weight. So many mg per Kg. That leads me to my question as to why adults aren't also dosed like this. It seems a 150lb man would be prescribed an identical dose as a 500lb man. So why aren't dosages based on weight, and are equal dosages equally impacting across a wide spectrum of adult body types?
|
[
"Children have immature organ systems and have to be dosed accordingly. In theory a child's body weight should be fairly proportional to their actual growth development. Adults regardless of size should have a fairly standard efficiency in regards to organs such as liver and kidney clearances. A 500 lb man is going to mostly be that heavy based on adipose (fat) tissue which doesn't contribute to clearance or tolerance levels to medications. So in theory that 500 lb and 150 lb adult should be able to tolerate the same amount of medicine up to a maximum safe and effective amount. Now on the flip side we do see adjustments in certain medications based on age and previous medical conditions that might compromise these same organ systems in an otherwise healthy adult. Geriatric dosing is normally less due to decreased rate of clearance.",
"TLDR : Children have immature organ systems whereas all healthy adults should have close to the same clearance rates despite weight as their organs are fully developed."
] |
[
"Depends on the drug. Every drug has two doses - the dose where it starts having the desired effect (killing bugs, in this case) and a dose where it starts causing problems (mostly tummy upset for cephalosporins). These doses are found out by trial and error and can later be calculated from body weight, lean body weight (if the drug doesn't get into fat), skin surface area (yes really) or other values based on how the drug interacts with the body.",
"Where these doses are only slightly different then we do calculate dosing individually (heparin injections, for example). Where they're far apart it simply isn't needed-the same dose in a wide variety of people will be both safe and effective.",
"The variation in children's sizes means we usually have to work it out individually (a 16 year old would just laugh at the safe dose for a newborn). Even then, you'd probably be surprised at how relaxed some of the doses are - compare paracetamol/acetaminophen with ibuprofen (do Americans call it that? It's our widely available NSAID)."
] |
[
"Doc here. Adult human easily range in weight from 90 or so pounds to 500+. There's actually not a lot of evidence-based guidelines out there for weight-dosing antibiotics and it's really difficult in the clinical setting to get a blood level on most antibiotics you're prescribing. So much of what we end up doing is based on clinical experience rather than science. My suspicion is that physicians regularly under medicate obese patients, who often appear to fail antibiotic treatment when prescribed at dose for \"normal\" weight individuals. "
] |
[
"Should mathematical models make qualitative or physical sense?"
] |
[
false
] |
[deleted]
|
[
"Paul Dirac ",
"wrote",
": \"it is more important to have beauty in one’s equations than to have them fit experiment\". I'm not sure everyone would agree with that, though :)",
"I'd say it depends on what you mean. If you're talking about finding an empirical relationship, just some equation that reproduces observation without any actual physical model behind it, that is, just curve-fitting, then it doesn't have to make physical sense. But ",
" it doesn't have a physical model behind it, it doesn't give you any insight into how or why it works, and it has no real predictive power outside of the data you used to create the model. In short: it doesn't actually tell you something you don't already know.",
"A theoretical physical model has to 'make sense', in the sense that you can't make completely ad-hoc assumptions, or ones at odds with known physics. But you can still make assumptions known to be unrealistic. For instance, you might assume that gas molecules have no volume and don't interact with each other, which is the starting point for the Ideal Gas Law. Obviously this will never be exactly true, but it turns out to still be a useful relation. Given this approximation, you can also predict that this model must - at the very least - be asymptotically exact as the pressure goes to zero. This kind of thing - approximations that lead to an exact result at some limit - is extremely common in physics.",
"There are often cases where the two are combined as well - taking the exact results at the limit x->infinity and x->zero and mixing them in some empirical fashion to get a model that works for finite x. Which is one example of a 'semi-empirical' model. ",
"Purely-empirical models can be useful for engineers, but don't teach us anything, so it's not really science. While a theoretical approximate model that doesn't even qualitatively describe something is completely useless (except insofar it informs you that the things you've neglected are of critical importance to what you want to describe). So anything truly useful has to be somewhere in-between those extremes."
] |
[
"Paul Dirac is a good one to quote for this question, but not in the way you quoted him. Isn't he a bit notorious for his Large Numbers Hypothesis, where he basically is just playing with numbers to see the answers he wants?"
] |
[
"Not exactly, if I understand what data mining is. Dirac found relationships between physical constants of the universe, which are assumed just to be numbers, not patterns in collected data. Maybe the same ideas apply though? Not sure, I'm definitely not an expert on either of those things."
] |
[
"Questions about perpetual motion."
] |
[
false
] |
[deleted]
|
[
"What exactly is perpetual motion?",
"Motion with no energy input.",
"Why is it impossible?",
"In practical terms, friction. In general terms, no process can convert/transfer energy with 100% efficiency, so some is always lost, meaning any system eventually loses usable energy over time without an input from an external source.",
"Is a completely self-power machine an example of perpetual motion?",
"It depends on what you mean by \"completely\" and \"self-powered\". If you mean both words literally and as strictly as possible, then yes."
] |
[
"Ok so what about a machine that is powered once via electricity and then uses that to power it self forever?",
"It's okay to have some initial energy input, the important thing is that you can disconnect your machine from anything external and have it run indefinitely.",
"EDIT: sorry I'm not giving more information. I just think I may have something amazing here",
"That's okay, but please be aware that lots of people have thought they've invented perpetual motion machines without ever being correct. The laws of physics actively forbid it, especially in the case of a machine that you can extract energy from without affecting the machine's running.",
"In general for real machines, the limiting factor is that you're always losing energy somewhere. It might not be obvious where, but friction is unavoidable - whether the mechanical kind or a more subtle equivalent electrically or whatever."
] |
[
"Unfortunately no, it wouldn't. The generator will not be 100% efficient, so it can't collect all the energy from the wheels and so can't feed it back to them without them losing energy and slowing down.",
"In addition, the wheels will themselves not be 100% efficient, with energy at all mechanical stages being lost to friction as heat and sound. That means the generator can't possibly collect enough energy to keep the wheels turning in the first place, they can only lose energy.",
"So, the wheels lose energy to friction and drag ",
" to the generator itself, and get less energy than this returned to them via the generator, so the vehicle can only slow down."
] |
[
"Is there a temperature at which water will ignite?"
] |
[
false
] | null |
[
"No. Water won't ignite because it already is a product of combustion. You get water by burning hydrogen."
] |
[
"Yes, like anything else. But first, the hydrogen and the oxigen in the water (H₂O) will separate forming O₂ and H₂. ",
"Take a look here:",
"https://en.wikipedia.org/wiki/Water_splitting#Thermal_decomposition_of_water"
] |
[
"Everything that you interact with is defined as a chemical formula. (Think of making a cake, and the chemicals are the raw ingredients).",
"A water molecule is H2O (2 atoms of Hydrogen for every atom of Oxygen).",
"The \"recipe\" for water is:",
"2 * H2 + O2 -> 2 H2O",
"The Hydrogen is still there, but not in the recognizable form. Think of eggs in cake."
] |
[
"Geostationary orbit vs tall tower."
] |
[
false
] |
Ok, I'm generally scientifically literate, but I've never quite wrapped my head around this: I'll describe the picture, can someone explain it to me in sensible physics terms. A geostationary sattelite is 35,786 km above kenya, on the equator, with my twin sat in it. He steps out of the satellite and orbits the earth. I build a 100m high tower directly below the satellites stationary point, climb it and step off. Splat. I build a 100km high tower as before, climb it and step off. Splat (though somewhat later after stepping off). If I build a 35,786km high tower, and climb it, will I be orbit ? Why ? Is it because my potential energy climbing all those stairs is enough to achieve orbit ? Many thanks everyone, some very lucid descriptions. Of course, its clear now that whirling around on a 35000km long tether made of tower, I'd be whipping along at quite a clip. Thus orbit. Thank you, .
|
[
"OK - first take a look at this: ",
"https://docs.google.com/drawings/d/1zp_HHPnwQIk0iopDHy5OBzCutwJI9tA7FJLuuFhVPfU/edit?hl=en_US",
"Anything at altitude is subject to gravity, which will draw it back towards the planet's centre of mass. First, let's look at object A. The green arrows indicate the gravitational vector. The only way to keep this satellite in a stable orbit, is for it to be moving sideways fast enough that the 'fall' due to gravity maintains it at the orbit altitude.",
"Object B is in a higher orbit, and you'll see that it has a smaller gravity vector. Similarly, to maintain its orbit it needs less orbital velocity.",
"Hence, low earth orbit objects need a high orbital velocity (the ISS orbits about 16 times a day, at 27,700 km/h), while high orbits have a lower orbital velocity (geostationary satellites travel only one orbit a day, at about 11,000 km/h).",
"Back to the original question - while you would be stepping off your building and dropping, you would be imparted with enough velocity to maintain a geostationary orbit. Bare in mind - this only works at geostationary altitude. If you stepped off higher up you would be placed in an orbit for which you were travelling too fast, and hence you would prograde away, while if you stepped off at lower altitude you would be travelling to slowly and would follow a retrograde orbit to eventually burn up in the atmosphere."
] |
[
"While you're correct, I think this is a complicated way of looking at this topic.",
"The entire tower is stationary compared to the ground, meaning that the entire tower has the same angular velocity. As you climb you maintain this angular velocity along with the tower. But to maintain a particular angular velocity while gaining altitude your tangential speed must increase along with the tower's. ",
"So while you are propelling yourself ",
" the tower is accelerating you ",
" with every step because each step is moving faster than the previous one."
] |
[
"And you did an excellent job explaining that. Part of the OP's question though, was where he would get the energy to put him into that orbit. ",
"I wanted to clarify this by saying that it's the tower itself that provides this, with a frictional force on the climber.",
"Edit: This means that when you climb the tower you steal enough of the tower's kinetic energy through friction to put you in orbit."
] |
[
"With such a high r0, why didn't measles just burn itself out?"
] |
[
false
] |
I've seen speculation floating around the internet that we will get to herd immunity faster with the delta variant because it spreads so quickly, but I wonder even if that is the case, why didn't we develop enough herd immunity naturally for measles to simply burn itself out (for reference, measles has an r0 of 12-18 compared to the delta variant's 5-9.5). I guess I'm generally curious as to why some viruses burn themselves out (or mutate to become far less deadly, like Spanish flu) but others do not. Thanks !
|
[
"It's because of cities.",
"If a population is large enough, the influx of new susceptible individuals can keep up with the epidemic loss of susceptible to immunity and death. (In the case of measles, it's mainly immunity, which is close to life-long following infection. However, in the first half of the 20th century and earlier measles mortality was far higher than it is today, for reasons not well understood, so death contributed as well.)",
"Give the rate of transmission of a disease, you can calculate the size of a connected population needed to sustain the disease. In the case of measles, it works out to around 250,000 to 500,000 people in contact with each other (",
"Measles Periodicity and Community Size",
"). ",
"Communities of that size are only a few thousand years old, but then measles is probably not much more than a thousand or so years old -- it jumped into humans, probably from cattle, somewhere around 1000-2000 years ago (",
"Origin of measles virus: divergence from rinderpest virus between the 11th and 12th centuries",
"). ",
"Obviously, the \"connected\" part of the equation is important, and when measles was prevalent (pre-vaccination) what happened was intermittent enormous very fast epidemics, every few years, with intervals in between of very low infection. During those periods the virus shouldered in cities (",
"Periodicity, synchronization and persistence in pre-vaccination measles",
"), and then once the number of susceptible victims built up enough, the disease spread out like waves from the cities (",
"Travelling waves and spatial hierarchies in measles epidemics",
")."
] |
[
"If (1-immunity rate) * r0 < 1, a disease will die out. So if r0 = 5, a greater than 80% immunity rate is required; r0 = 10, 90%. ",
"But r0 is not some fixed constant of nature; it's an average that can vary according to behaviors, like hygiene and mask-wearing, and conditions, like outdoors in the sun vs indoors in a hospital or a crowd. ",
"If a virus is more deadly, it tends to isolate those affected, thereby reducing its r0; hence there is selection pressure to decrease the severity of symptoms. That can be negated if there's social pressure to crowd or discard PPE despite symptoms."
] |
[
"This is a fantastic answer, backed up by extensive references. This kind of answer is why I keep clicking on reddit threads."
] |
[
"Why do baked goods kept in air tight containers remain fresher when they are still exposed to air inside vs being a vacuum or alternate gas?"
] |
[
false
] |
Another instance may be a plastic bag which still contains a volume of air inside. Also this is not limited to baked goods but they were the best example of a food product highly impacted.
|
[
"A lot of times the \"freshness\" of a food depends on water. A cracker left out on a humid day will absorb a good deal of water from the air, which will leave it \"soggy\" and it'll lose its crisp texture.",
"By the same token, a lot of baked goods will actually lose water to the air. By keeping them in a baggy, they can only lose so much water to the atmosphere before the air inside the bag becomes fully saturated with water, and the baked good can't lose any more. With the cracker example, the cracker will only absorb as much water as is in the air in the bag.",
"Something to notice - when you put a warm piece of cake or bread or muffin in a bag, you'll see condensation almost immediately on the inside of the bag. That's good evidence that the food is rapidly losing moisture. It's also why you should wait for the food to cool before you bag it. If you don't all the water that leaves while it's hot will sit in the bag and then reabsorb into the food, giving it a spongey soggy texture."
] |
[
"interesting points, so within that container would likely then be a localized higher or lower relative humidity respectively, not necessarily a chemical reaction or gas change..."
] |
[
"On the other hand, it is good to put hot, moist breads in a bag if you intend to microwave them later."
] |
[
"What is the difference between a proton pump and a proton shuttle?"
] |
[
false
] |
My biochemistry textbook seems to differentiate between pumps and shuttles. However, it never really defines "shuttle" outside of "shuttles allow movement across mitochondial membranes." However, I'm fairly sure that is the definition of a proton pump. What am I missing here?
|
[
"I haven't heard the term shuttle used much, if at all. Perhaps you could provide some more context? Using you example, it says, \"allow movement...\" which implies to me that they are either talking about proton channels, i.e. facilitated diffusion, or antiporters, which exchange one molecule for another. Proton pumps, however, most definitely require ATP to function.",
"The only time I have seen the term proton-shuttle used was to describe the action of histidine within the carbonic anhydrase reaction, but that has nothing to do with mitochondrial membranes."
] |
[
"Oh, haha, it's a verb. In this case it means: to move molecules across a membrane."
] |
[
"Perhaps \"shuttle\" refers to moving protons from one location in the cell to another, versus pump refers to movement across the membrane"
] |
[
"How could someone escape from a black hole? Is it even possible?"
] |
[
false
] | null |
[
"By definition it is impossible.",
"If light cannot escape nothing else can (since nothing can go faster than light...essentially the escape velocity for the black hole is faster than light speed). The event horizon defines the boundary where you are far enough from the singularity that at least light can escape...any closer and that's it...stuck in the black hole forever."
] |
[
"well, eventually the equivalent of your mass would be released into the universe through hawking radiation. so you wouldn't really be \"stuck in the black hole forever\". "
] |
[
"One could not."
] |
[
"How is it possible that viruses lead to the origin of life if viruses need a living host to survive?"
] |
[
false
] |
According to the virus-first hypothesis, DNA-based viruses predate cellular life and contributed to its formation. There's evidence supporting this, namely that virus genomes do not contain cellular homologs. How is this possible if viruses need life to survive and replicate? I must be missing something here. Thanks!
|
[
"DNA does fold and do this and that, but generally tends to be more boring than RNA. RNA is really neat because it can encode genetic data AND serve as an enzyme. Ribosomes? Those have RNA. Transfer RNAs, those perform a function like a protein. ",
"Why am I saying this? A relevant hypothesis is the \"RNA world\" hypothesis. This hypothesis posits that before cells, there were just self replicating nucleic acids (i.e. RNA) that gradually became more sophisticated. ",
"Presumably RNA World became more sophisticated and became virus world which lead to the cell world we live in. ",
"The theory was posited by Eugene Koonin who is a computationalist I've met IRL.. he probably argued based on the sequences being different in viruses and let the biologists sort out the rest."
] |
[
"I am a senior biology major in college, I'm pretty familiar with the RNA world hypothesis. I'm more interested in the virus-first hypothesis, hence the specificity of the question. I do tend to think the RNA world hypothesis makes a bit more practical sense, but the virus-first idea is still a relevant idea that I'd like to unpack a bit more!",
"I just can't seem to understand, despite the evidence for this virus-first hypothesis, how this would be possible if it contradicts the notion of what a virus is. Viruses before cells would mean that the viruses had no hosts to actually replicate! How do the scientists that posit the virus-first hypothesis is sound while reconciling the fact that viruses need cells to survive and reproduce?"
] |
[
"My understanding is that this theory was bolstered by giant viruses that have larger genomes and suggests that cellular life and modern viruses are descendants of a virus-like organism that could replicate itself without a host but lacked cellular features like a cell membrane (possibly a protein structure like a capsid instead).",
"There's also viral eukaryogenesis, which was also bolstered by giant viruses and suggests that the eukaryotic nuclear genome is a result of endocytosis of a virus, possibly a giant virus. In theory, evidence of this includes the double-walled nuclear membrane reminiscent of the mitochondria. These theories aren't mutually exclusive though.",
"I think one key point to remember through all this though is that the definition of a virus is a concept humans created as a convenience. In general this is true for most of biology, as we attempt to explain observations of veeery complex systems which we definitely did not understand when most of the basic terminology was created and we still barely understand today. Obviously there were no hosts before there were hosts, so it wasn't a \"virus\" in that sense, but modern viruses may be closer to the most primitive ancestors of modern life than modern cells."
] |
[
"AskScience AMA Series: We are experts here to answer your questions on shortages of laboratory testing supplies for COVID-19 and other infectious diseases. AUA!"
] |
[
false
] |
Since March, clinical microbiology laboratories have faced shortages of testing supplies, including SARS-CoV-2 molecular test reagents. Due to the growing demand and need for COVID-19 testing, production of supplies required to test for other infectious diseases has dwindled. This has led to a ripple effect of shortages and is causing a major delay in testing for common infections, such as urinary tract infections, sexually-transmitted infections including chlamydia and gonorrhea, gastroenteritis and cystic fibrosis. Join us today at 2 PM ET for a discussion organized by the American Society for Microbiology (ASM) on approaches being taken to catalogue, track and address these supply shortages. In particular, we'll discuss a new platform developed by the Association for Supply Chain Management and the ASM to monitor real-time levels of, and demand for, COVID-19 testing supplies down to the level of individual laboratories. We'll also answer your questions about future decisions about supply chain management of laboratory reagents and testing protocols. Ask us anything! With us today are: Links:
|
[
"It takes time to develop a test for a novel agent. Although there have been rapid antigen tests for influenza and RSV for decades, we have never had one for a coronavirus, so development takes time. It also takes time to ensure the accuracy of these tests prior to them becoming widely available. Rapid molecular tests came along relatively quickly in the pandemic."
] |
[
"Why haven’t rapid tests become more available? Does money have something to do with it?"
] |
[
"The numbers on your site showing the lack of testing equipment is stunning- 70% don't have the reagents and materials they need to test for sexually transmitted diseases? Is this COVID related or are US clinics always running this much of a material deficit? What effects does this have on getting efficient and accurate diagnostics to patients?"
] |
[
"Can a tidally locked planet still rotate on an axis if its pole is pointed at its star?"
] |
[
false
] | null |
[
"So if dramatically tilted planet like Uranus, was within tidally locking range of its star would it be immune to tidally locking or would its tilt be corrected so that it can be tidally locked?"
] |
[
"Hm, the poles of astronomical bodies are where the axis of rotation meets their surface. For an object to be tidally locked to another, its axis of rotation must be perpendicular to its orbital plane... so the pole of a planet tidally locked to a star cannot be pointed at the star. ",
"In other words, if you draw the orbit on a piece of paper as a circle, the axis of rotation of the planet must be pointing out of the paper, otherwise the planet won't be able to rotate so that the same face always faces the star."
] |
[
"Part of the process of tidal locking would be rotation of the pole to a perpendicular axis."
] |
[
"Adderall works by increasing the dopamine and norepinephrine available in between synapses. Is there a way to do this naturally?"
] |
[
false
] |
[deleted]
|
[
"Simply making more won't release more. You need something to release that Dopamine or Norepinephrine (I.E. Adderall, Cocaine) I'm not sure if there is a way to release more naturally other than doing more of what normally releases it.\n Dopamine is that rewarding feeling you get after completing something you worked really hard on or something really good overall. It helped us because without dopamine it would be harder for us to tell if we were doing something good or not. An example is if you are out and starving, and you eat your brain releases Dopamine to let you know you did a good thing, this in turn will keep you coming back because you associate it as good. Therefore we know to eat. "
] |
[
"Simply making more won't release more. You need something to release that Dopamine or Norepinephrine (I.E. Adderall, Cocaine) I'm not sure if there is a way to release more naturally other than doing more of what normally releases it.\n Dopamine is that rewarding feeling you get after completing something you worked really hard on or something really good overall. It helped us because without dopamine it would be harder for us to tell if we were doing something good or not. An example is if you are out and starving, and you eat your brain releases Dopamine to let you know you did a good thing, this in turn will keep you coming back because you associate it as good. Therefore we know to eat. "
] |
[
"I would really like an answer to this as well."
] |
[
"Electron, Muon, Tau, why are there only 3 orders?"
] |
[
false
] |
There are 3 orders of electrons, 3 orders of neutrinos and 3 orders of quarks. Is this correct? Does the standard model predict 3 orders? If so why? If not, then are there any predictions regarding a 4th (or 5th etc.) Are there any theoretical constraints on further orders of particles?
|
[
"I'm going to give an answer from a mostly experimental point of view. Just to clear up the nomenclature, these \"orders\" are usually called \"",
"generations",
"\". Electrons, muons and taus are collectively called charged leptons. Neutrinos are the neutral leptons. They form a set of 6 particles, similar to the quark flavours.",
"In-line links are mostly Wikipedia articles, numbers in square brackets are journal papers.",
"Murray Gell-Mann",
"'s original 1964 ",
"quark model",
" ",
"[1]",
" contained only three quarks: up, down and strange. This came about as a way to explain the quantum numbers ",
"isospin",
", ",
"3",
", and ",
"strangeness",
", ",
". This superceded ",
"the eightfold way",
".",
"Six years later, ",
"Glashow",
", ",
"Iliopoulos",
", and ",
"Maiani",
" came up with the ",
"GIM mechanism",
" ",
"[2]",
" to explain flavour-changing weak currents, specifically why charged currents require Δ",
"=1 and neutral currents heavily favoured Δ",
"=0. An important result was that it demanded there be a fourth quark: the charm quark. This was confirmed with the discover of the ",
"J/ψ",
" in 1974 ",
"[3]",
"[4]",
".",
"Meanwhile, starting in 1963, ",
"Nicola Cabbibo",
" introduced the idea of weak universality and what would later become quark mixing ",
"[5]",
". With the discovery of the charm quark, mixing was described by a 2×2 rotation matrix (Cabbibo matrix) with a single common angle (Cabbibo angle).",
"Also in 1964 came the discovery by ",
"Cronin",
" and ",
"Fitch",
" of ",
"CP violation",
" in neutral kaon decays ",
"[6]",
". In 1973, ",
"Kobayashi",
" and ",
"Maskawa",
" realised that CP violation could be explained by introducing complex phases to the quark mixing matrix ",
"[7]",
". This requires that the mixing matrix be at least 3×3, so the Cabbibo matrix was extended to become the ",
"CKM matrix",
" and thus another 2 quarks were predicted: the top and the bottom. The bottom was confirmed quite quickly in 1977 with the discovery of the ",
"ϒ",
"[8]",
". The top quark came much later, in 1995 ",
"[9]",
".",
"The CKM matrix can be parametrised by 3 mixing angles and a CP-violating complex phase. Much of the field flavour physics is dedicated to measuring these parameters. These measurements can be used to test its unitarity: each row and each column should sum in quadrature to 1. If they do not, that suggests the existence of a fourth generation of quarks.",
"The CKM fitter group keep track of the measurements of CKM parameters.",
"http://ckmfitter.in2p3.fr/www/results/plots_moriond14/ckm_res_moriond14.html",
"To summarise, the first row sums in quadriture to 0.9999±0.0006, the second row to 1.024±0.032, the first column to 1.000±0.004 and the second column to 1.025±0.032.",
"The history of the second and third generations of lepton is rather more empirical discovery rather than theoretical prediction.",
"The idea of electrons predates ",
"JJ Thomson",
"'s discovery in 1897 ",
"[10]",
". The positron was predicted by ",
"Dirac",
" in 1928 ",
"[11]",
" and discovered by ",
"Carl Anderson",
" in 1932 ",
"[12]",
". Anderson also discovered the muon in 1937 ",
"[13]",
". The tau was discovered by ",
"Martin Perl",
" in 1975 ",
"[14]",
".",
"Pauli",
" predicted the existence of the electron neutrino in 1930 in order to explain the kinematics of ",
"beta decay",
". Neutrinos were first detected by ",
"Cowan and Reines",
" in 1956 ",
"[15]",
". In 1957, ",
"Bruno Pontecorvo",
" predicted both that there might be more than one generation of neutrino, and the phenomenon of neutrino oscillation ",
"[16]",
". In 1962, ",
"Lederman",
", ",
"Schwarz",
" and ",
"Steinberger",
" discovered the muon-neutrino ",
"[17]",
". Direct detection of the tau neutrino came much later in 2000 at the ",
"DONUT",
" detector ",
"[18]",
".",
"Between the discovery of the tau and direct detection of the tau neutrino, a very important result came out of ",
"LEP",
": precision measurement of the width of the ",
" resonance ",
"[19]",
" ",
"[20]",
" ",
"[21]",
" ",
"[22]",
". The width of a resonance is partly a function of how many final states the particle can decay into, and the ",
" can decay to neutrino-antineutrino pairs. The measured width constrains the number of light neutrinos to 3, which means that if there are 4th generation neutrinos, they'll either be very heavy or 'sterile'. In the Standard Model, the number of charged leptons is necessarily the same as the number of neutrinos.",
"In addition, there is also a mixing matrix for neutrinos: the ",
"PMNS matrix",
", which parameterises the mixing between mass and flavour eigenstates. This was introduced by Maki, Nakagawa and ",
"Sakata",
" in 1962 ",
"[23]",
" in direct response to Pontecorvo's predictions. Neutrinos are really hard to detect ",
"[citation needed]",
", so the measured angles and of the PMNS matrix have large errors, and the CP-violating phase hasn't even been measured yet ",
"[24]",
"! The unitarity of this matrix also puts a constraint on the existence of a fourth generation of neutrino ",
"[25]",
".",
"The status of PMNS parameters is tracked by the Nu-Fit group:",
"http://www.nu-fit.org/?q=node/75"
] |
[
"Could you clarify your question? Is it more along the lines of what evidence is there that there are 3 generations of quarks and leptons, or are you asking why universe is how it is?",
"Unfortunately, the latter isn't really answerable."
] |
[
"This is ridiculously in depth. Thank you for the effort."
] |
[
"Why does time seem to pass so quickly when significant events are happening or you're having fun, but time passes so slow when nothing of interest is happening?"
] |
[
false
] | null |
[
"I think in order to understand this we would need to know more about the biological basis of both the perception of time and of concentration. Intense concentration seems anecdotally (uh-oh) to force awareness in ways that are actually MORE evolutionarily useful. If while running away from a panther or searching for your lost children or making love or working intently on building a shelter you were acutely aware of the passage of time it could decrease your ability to perform. ",
"While it's behind a paywall, here's a quickly scrounged up paper about a potential relationship between neurogenesis and time in memory\n",
"http://www.nature.com/neuro/journal/v9/n6/full/nn1707.html"
] |
[
"And in retrospective it often flips. ",
"(\n which makes perfect sense: nothing happens - nothing to remember. \n (\n all as long you don't remember the feeling of \"it felt like it took forever\" \n which is sort of a flashback, making it happening again(in your head)\n )\n)\n"
] |
[
"when you are so bored and nothing is happening you will start to be conscious of the time passing. kinda like (when will this end!). but when your having fun you're not thinking about time at all and so it fly's by!"
] |
[
"Do polymers made of oxygen exist?"
] |
[
false
] |
Do polymers exist made up of oxygen only? As in [-o-o-]n sort of thing.
|
[
"Not to my understanding. Based on the instability of ozone (O3), I'd venture a guess that the bonds in an 'oxygen polymer' would break really easily. ",
"While there are larger ",
"allotropes of oxygen",
", they mostly exist in pretty specific situations, and they aren't polymers in sense you're talking about."
] |
[
"No, the oxygen-oxygen bond is to fragile to exist as a repeat unit in a polymer structure. ",
"Organic peroxides",
" are generally not very stable. In fact ",
"benzoyl peroxide",
" is many times used as an initiator in polymerizations due the fact the O-O bond easily forms radicals. ",
"One theorized polymer but never truly produced in practice you may be interested in is ",
"linear acetylenic carbon",
". It consists of alternating single and triple carbon bonds. The difficulty of making this polymer in real life highlights how difficult making a polymer with -(O-O)- bonds would be. "
] |
[
"You can make ",
"oxygen crystals",
" at low temperature. That is \"sort of like\" a polymer.",
"As the pressure of oxygen at room temperature is increased through 10 GPa (1,450,377 psi), it undergoes a dramatic phase transition to a different allotrope. Its volume decreases significantly,[6] and it changes color from blue to deep red.[7] This ε-phase was discovered in 1979, but the structure has been unclear. Based on its infrared absorption spectrum, researchers assumed in 1999 that this phase consists of O\n4 molecules in a crystal lattice.[8] However, in 2006, it was shown by X-ray crystallography that this stable phase known as ε oxygen or ",
"[9][10] No one predicted the structure theoretically:[5] a rhomboid O8 cluster[11] consisting of four O2 molecules."
] |
[
"Would anti-matter react with virtual particles?"
] |
[
false
] |
Would anti-matter react with the virtual particles that pop in and out of existence. That would make a anti-matter storage device hard to construct right?
|
[
"Would anti-matter react with the virtual particles that pop in and out of existence. ",
"Probably not in the way you are thinking...",
"I think what you mean is that if I have a positron (an anti-electron) stored properly, could an electron (created from a vacuum produced e+/e- pair) then annihilate with my stored (real) positron.",
"If that is what you mean, then the answer is definitely no. For a virtual particle e+/e- pair to be produced, it also means they ",
" to annihilate each other, and they can't go off and annihilate with some other real particle. If this was possible, we could count this as a measurement, and virtual particles are unmeasurable because of the Heisenberg uncertainty principle.",
"It's also lucky this doesn't work, because otherwise people studying antimatter would have their hands full..."
] |
[
"No. A virtual particle is just a way of interpreting an annoying term inside an integral."
] |
[
"Yes you understood what I ment. Thanks for the explanation. You comment that the virtual pair of particles must annihilate each other to be produced in the first place is interesting. Will read up on why that is. "
] |
[
"People cannot live in Pripyat, but they live in Hiroshima and Nagasaki. What is the difference in atomic after-affects (radiation) in a bomb context versus that of a reactor meltdown context?"
] |
[
false
] |
[deleted]
|
[
"Think of the contamination like this: there is a question of ",
" contaminating material there is total, and ",
" it is on any given piece of the ground.",
"The contaminating material is primarily fission products, the left-over \"half-split\" nuclei from nuclear fission. In the case of Hiroshima and Nagasaki, about 1 kg of fission products were created. (1 kg of material fissioning completely releases about 17 kilotons of energy.) ",
"For Chernobyl, about 200 kg of fission products were released. So already, you are going to have a 200-fold difference to account for.",
"At Hiroshima and Nagasaki, the bombs were detonated high in the air. Their fireballs never touched the ground. As a result, their fuel was vaporized as a light, hot gas. The cloud was moved by the wind, and the fission products were able to stay aloft for a long time. They eventually did fall back down to earth (as \"fallout\"), but by that time they had dispersed enough so that no individual part of the ground received very much exposure. (It is the difference between, say, having 1 kg of caffeine all at once — which would kill you immediately — or dispersing 1 kg of caffeine across the entire country — which would have no effect.)",
"At Chernobyl, the fuel was not nearly as hot as Hiroshima, and was much lower to begin with. It was mixed with burning graphite and other elements. This meant that much of it came back down relatively quickly, meaning very high concentrations of material in areas of Ukraine and Belarus. ",
"You can have nuclear weapons that are just as contaminating — there are weapons with multi-megaton yields (and thus have as many fission products as a reactor), and if you detonate a weapon on the ground, you mix the fission products with heavier particles and so they fall out sooner, contaminating quicker and more densely. Castle Bravo is a famous example of a weapon contamination of this sort, rendering some areas not safely inhabitable for long periods, because it was a 15 Mt (68% from fission = 600 kg of fission products!) weapon that was detonated on a coral atoll, creating ",
"a huge radioactive plume as the radioactive byproducts fell down to Earth",
"."
] |
[
"People cannot live (safely, long term) in the ",
"Bikini Atoll",
" either, despite that being bombed and not a reactor. Nor the neighboring ",
"Rongelap",
".",
"Reactors have a lot more fissile material in them than bombs, additionally, the massive explosion of bombs spreads the material out. So with Chernobyl you had tons of material that was ejected from the reactor core (in a steam explosion, not nuclear), from large chunks of fuel and graphite, to smaller particles, to molecules, and the distance they traveled matched that. The smallest spread ",
"in a plume over large parts of Europe",
" - the areas of highest fallout (Austria, Finland, Sweden) are ones that got snow/rain in the following days, which carried the radioisotopes down into the ground where they remain.",
"With a bomb, all the material is completely vaporized. With Hiroshima and Nagasaki, the bombs exploded about 500 meters up in the air, which helped the fallout disperse a lot. (However, that wasn't why the bombs were detonated at altitude; rather the height was chosen to maximize damage) The ",
"Castle Bravo",
" test at Bikini caused a great deal more fallout than expected, and (as other Bikini tests) was detonated more or less on the ground. Bravo also had a particularly 'dirty' uranium tamper.",
"So in short, bombs also have enough radioactivity to make areas uninhabitable for a long time, and it's more a matter of whether the conditions of the bomb and its detonation are such that you'll end up with that level of radioisotopes in the ground."
] |
[
"In addition to what the other people have mentioned, the timing of the radioactivity is also different. For atomic bombs, the entire bomb is vaporized and then mixed into the fallout material, so all of the different isotopes produced in the reaction end up contaminating things. Most of these elements have a half-life of just a few days or weeks (see ",
"table III here",
"), so much of the radioactivity decays quickly (large areas are initially deadly, but you can go out of your fallout shelter after a month, and they will be long-term inhabitable again after a few years). Then there are a few long-lived products, mainly Cs-137 and Sr-90, which stay around for centuries.",
"In a reactor meltdown, the temperatures never get high enough to vaporize most of the elements in the reactor fuel, so most of the fuel stays in the reactor. Most of the emissions are from fission noble gases (which immediately escape into the atmosphere)... and Cs-137! (See ",
"table 4.1-2 here",
".) In one way this is better than an atom bomb, because a smaller fraction of the reactor fuel leaks out, but the element that ",
" leak out has a half-life of 30 years. So if an area was contaminated it will not get better any time soon."
] |
[
"Breaking down water."
] |
[
false
] |
My question is if we start to break down water into oxygen and hydrogen on a large scale would that ultimately lead to water disappearing altogether? I've studied the water cycle but I'm not sure how to include those gases into the cycle.
|
[
"If you broke down all the water into hydrogen and oxygen, then there wouldn't be any water left.",
"However, any time you burn something with hydrogen in it (or just burn hydrogen), one of the products of the reaction is water. If you put the hydrogen through a fuel cell, then you make water as well.",
"Try it out sometime--Light a match and hold it close to a cold window, or hold a piece of cold glass about a foot over your kitchen range. You'll see water condense from the flame.",
"Basically, if we're going to break water down on a large scale, we're going to do it for a reason. That reason is probably going to be to use the hydrogen as a fuel. And whenever we use the fuel, we get all of the water back."
] |
[
"I wrote about this a few weeks ago! Check it out: ",
"http://electroncafe.wordpress.com/2011/04/11/split-that-water-part-i/"
] |
[
"You're missing the point: we split H2O to O2 and H2 ",
" combine them back together and produce energy (a.k.a. burning). The byproduct of burning H2 is steam, so the water will go back to the water cycle. If we somehow store all the produced H2 and O2 and never use it, we'll effectively remove some water from the water cycle. The actual effect will be negligible though, there's a lot of water out there ;)"
] |
[
"It seems that infectious diseases that kill too quickly never have a chance to spread. How often are people the first and only (or among very few) to die of a novel but short lived infectious disease?"
] |
[
false
] | null |
[
"There are several avian influenza viruses that have a high mortality rate in humans, but that transmit very poorly between humans. Viruses like H5N1, H5N6, H7N9 have killed thousands of people worldwide, each time because of a direct contact with an infected bird. ",
"However, the lack of transmission is probably not because the virus kills too quickly, but more because of the way it infects. It’s believed that these viruses are much better at infecting deep in the lungs than in the nose and throat, so on the one hand they cause severe pneumonia and lung damage, but on the other they don’t shed large amounts of virus in outgoing breaths."
] |
[
"To name a few from recent memory, SARS, MERS, Ebola.",
"Ebola is a special case though. First discovered in 1976, it has a natural reservoir. It can exist in bats and apes and re-infect humans from that source. But once it does it rarely travels from human to human, as you need direct contact with bodily fluids. Which is why with a death rate of over 80%, it causes the death of a few thousand and no more.",
"Without that natural reservoir, Ebola would quickly die out."
] |
[
"Add rabies to the list too. 100% mortality rate once symptoms appear, but difficult to get infected by. ",
"Plus lots of natural reservoirs (bats, raccoons, etc)."
] |
[
"Do black holes really vary in size or does the collapsed point in space just vary in intensity?"
] |
[
false
] | null |
[
"Every amount of mass has some radius that, were it all to be compressed within the radius, it would form a black hole. This is called the Schwartzchild radius, and it's calculated by the formula r=2GM/c",
" . G is the gravitational constant, and c is the speed of light. These are both constant, so the math works out the same for them every time and the quantity of mass is the only variable that can alter the radius.",
"Interestingly, smaller black holes will spaghettify you much faster than larger black holes will. This is because of the tidal force. Anything that enters a black hole is stretched apart by its gravity. The gravitational force weakens with distance; the parts of you closer to the black hole (say, your feet, if you're falling straight in) end up attracted by its gravity more forcefully than the parts away from you (like your head, in this analogy). This effect magnifies as you are stretched more and more until... well, spaghettification is the scientific term for this for a reason.",
"With larger black holes, the difference in position of your head and your feet, relative to the size of the black hole, is smaller than it is with smaller black holes. Your feet will still be pulled more forcefully than your head, but the difference won't be as drastic. With a large enough black hole, you might be able to survive a decent part of your trip to the singularity.",
"So, the size of a black hole is dependent solely on its mass, but a more massive black hole will take longer to destroy you. Either way, you aren't getting out."
] |
[
"I think he was referring to the singularity itself with his question and wet her or not it can have different sizes or if it is only the event horizon being 'blown up' in different sizes (as in: the 'visible' part of a black hole).",
"\nAnd, if I am informed correctly, the singularity is basically the same every time when it comes to 'size ' (even though I wouldn't call it this way, because it is infinitely pulled together by gravity). ",
"Again: only referring to the singularity itself, not anything around it."
] |
[
"It's also important to point out that black holes technically don't have any size, they are infinitely dense with a finite mass. The \"black hole\" part of the black hole is just the region where nothing can escape, thus appearing black. This radius will vary based on the mass of the black hole and it's angular momentum."
] |
[
"how do airplanes deal with fuel ullage? Would the engines flame out if an airliner tried to fly upside down?"
] |
[
false
] |
The direction of gravity will change as the plane banks and pitches up or down. So how do they make sure the fuel doesnt accumulate in a corner away from the pipes? What about those planes used to simulate 0G? Also how do they deal with the shifting center of gravity during banks as fuel sloshes outwards in one wing and inward in another?
|
[
"Yes it's possible. A lot of planes cannot fly upside down, including modern jet trainers, and many modern airliners. Here's an article on the famous Spitfire fighter and how its engine would die when inverted: ",
"https://www.popularmechanics.com/flight/a22201/brass-ring-spitfire-engineering-wwii/",
"Similar issue with race cars and oil/fuel. Pulling too many gs around a corner can cause non-race engines to become fuel or oil starved as the liquids flow away from the collection point.",
"In race cars they use vaccuum systems and sprayers to keep oil moving rather than having a sump full of oil to pull from.",
"In rocket engines, fuel tanks are often pressurized with an inert gas that expands as the tank empties to keep the fuel pushed against an inlet. You can prevent sloshing in this design by having a movable seal (like a piston head) between the expanding inert gas and the fuel."
] |
[
"Most passenger jet aircraft have multiple tanks in the wings so fuel won't travel very far during turns as the wings point up or down. Also, before the fuel goes into the engine pylon, it will flow into a special smaller tank where fuel pumps are located which will be submerged even during prolonged turns so that the engine won't be starved of fuel.\nThe fuel systems are different for every aircraft type but what I described is generally true for most jet aircraft.\nAs a bonus I want to mention that large aircraft have a very large tank in between the wings, in the fuselage below the passengers. This fuel is used up first, whereas fuel in the outer wing tanks is used up last. This is to reduce wing bending moments."
] |
[
"The direction of gravity will change as the plane banks and pitches up or down.",
"The perceived gravity vector in a plane won't change as much as you might think. In a bank, the wings will still generate lift in the \"airplane-relative-up\" direction, and the occupants (and fuel) won't feel any sideways acceleration. Sideways acceleration only happens in a slipping/skidding turn (nose not aligned with the direction of flight), which pilots generally try to avoid.",
"Acceleration and deceleration (or pitch at constant speed) does influence the perceived gravity vector, and the ullage of the fuel. Many aircraft have fore and aft outlets in the fuel tanks to make sure that fuel will flow through at least one of them.",
"Sloshing is dampened by baffles in the tanks, and isn't too noticeable. In many GA aircraft it is common to draw fuel only from one tank at a time, and even with several gallons of imbalance the CoG of the aircraft doesn't shift by any appreciable amount. In larger airliners, fuel tanks have to be balanced actively to a certain degree, but they can still tolerate substantial left/right shifts of the CoG."
] |
[
"How does sunscreen work?"
] |
[
false
] |
Is it as simple as physically absorbing / reflecting the sunlight? If so, how does it remain effective after being rubbed into the skin to the point that it isn't readily visible to the naked eye?
|
[
"Both. There are two classes of sunscreens, chemical and physical:",
"Organic sunscreen molecules, chemical sunscreen, absorb UV radiation and release it as heat or visible light. UV light excites electrons in the sunscreen which reach an excited state. As the electrons drop back to their ground state, they release heat or visible light. ",
"Inorganic sunscreens, physical blockers, can both reflect and scatter UV radiation. ",
"This PDF is a bit old but most of the sunscreens mentioned in it are still in use today:",
"http://www.fda.gov/ohrms/dockets/dailys/00/Sep00/090600/c000573_10_attachment_F.pdf",
"Bit easier to read:",
"http://www.smartskincare.com/skinprotection/sunscreen_fundamentals.html",
"Probably more than you want to know:",
"http://www.eadv.org/fileadmin/cme/Sunscreens_-_what_s_important_to_know.Revised.pdf",
"Also be aware that the SPF rating system in the US only applies to UVB radiation. We don't currently have a UVA rating system. The FDA has updated the labeling laws on sunscreens and they go into effect this year. You won't see anymore 100+ SPF sunscreens being sold. Also banned are the terms \"sunblock\" and \"waterproof\". ",
"http://www.fda.gov/forconsumers/consumerupdates/ucm258416.htm"
] |
[
"Thanks!"
] |
[
"http://en.wikipedia.org/wiki/Sunscreen",
" scrolldown, see illustrative pic"
] |
[
"Does quantum theory depend on the uniformity of nature?"
] |
[
false
] |
'Uniformity of nature' as in the principle that the future will resemble the past, in that when sufficiently similar situations recur, similar effects follow. So "induction" I guess.
|
[
"in that when sufficiently similar situations recur",
"Determinism? Most models of quantum mechanics rule out determinism and replace it with stochasticism (ie: \"true randomness\" exists in some sense)"
] |
[
"So uniformity of nature doesn't deal with quantum mechanics? Are they on some other level? "
] |
[
"All of science depends, more or less, on the principle of uniformity."
] |
[
"If I built a lightning rod high in the air with a giant coil between the rod and the ground, would lightning pass through it and therefore create a giant fluctuating magnetic field for a few seconds?"
] |
[
false
] |
Assuming that the material can withstand the current involved, of course. In theory, if there is no electricity flowing through the coil before the strike, then the top of the lightning rod should be at ground voltage, right? So, being in close proximity to the sky, and if lightning takes the path of least resistance, shouldn't it strike the rod?
|
[
"If you get a lightning strike, you will get a big magnetic pulse from the coil. It would have a fairly interesting (and varied) fluctuation. The main discharge of lightning typically has multiple \"strokes\" separated by 10s of milliseconds. So you wouldn't get one big magnetic pulse, you'd get several smaller ones. ",
"Whether or not the lightning actually strikes your lightning rod has nothing much to do with the coil. The tip of the rod will be at Earth ground IFF you connect the far side of the coil to the Earth. If not, the entire floating assembly is going to be at the potential that the nearby air is. And that may not be Earth ground. ",
"Don't confuse \"circuit ground\" with \"Earth ground\". They aren't necessarily the same. The former is simply a reference potential in a circuit....it can be any potential. Earth ground is the potential of our planet. They are only the same thing for sure if the circuit ground is electrically connected to Earth ground. ",
"Lightning is a complex, multi-step process, and it could hit something else nearby rather than your rod even if the far side of the coil is at Earth ground. The maximum E-field gradient is a major contributor to determining where lightning will go, but it isn't the only one. If lightning always took \"the path of least resistance\" then it wouldn't branch, and it would never hit the ground near trees or buildings. Also, your coil is going to change things for the strokes after the first one. I cannot predict whether or not they would hit the rod, since you will have changed its potential, but the ionization path would still exist. ",
"(Like all electricity, lightning follows ",
" available paths, with the ones with the least resistance getting more current. If you poke a bunch of holes in the bottom of a bucket, the water doesn't flow out just through the biggest hole.) "
] |
[
"If we were talking about a heavy duty coil, how the impedance of the coil effect this. With a nearly instantaneous (or several nearly instantaneous) discharge, wouldn't we get a pretty sizable back EMF? "
] |
[
"I assume so, yes. You'd get a big dI/dt which would drive a big dH/dt which would in turn create a significant dE/dt & resulting dI/dt in the opposing direction. So you'd probably need a good simulation to figure out what the potential at the tip would be after the first stroke. It might be raised significantly and affect the probability that the next stroke would even hit there, even though the ionization path from the cloud would still be in place. Or it might just reduce the amount of current flow on the next strike. "
] |
[
"If the planet Mercury's day is twice the length of its year, what path does the sun take through the Mercurian sky?"
] |
[
false
] |
Does the high eccentricity of its orbit matter at all?
|
[
"I wouldn't say that it's same as Earth, just longer. There would be all kinds of interesting effects.",
"First it's good to know about the different kinds of days there are. On Earth the different types of day are almost the same length, varying only by some minutes. But on Mercury they are vastly different. First, the sidereal day. That is the day measured from distant stars. Pick some star (other than the Sun) and wait for it to do 360 degrees around the planet and return to its original position. Or you can also visualise this so that you're looking at the solar system from above and are stationary and not rotating yourself. Sidereal day is the time it takes for one point on the planet to do a full 360 degrees around the planet. Sidereal day on Earth is 23 hours, 56 minutes and 4 seconds. And on Mercury it's 58.6 Earth days (solar days to be specific, see next paragraph) or 2/3 of a Mercury year.",
"Then there is the solar day, which is what people usually think (without knowing it) when they refer to a day in everyday situations. That is the time it takes the Sun to return to the same point in the sky again. For example, the time from sunrise to the next sunrise. On Earth this is 24 hours. On Mercury it is 176 Earth solar days.",
"Here",
"'s a good picture to explain where the difference between sidereal and solar days comes from. The picture is from the perspective of Earth. During one day, Earth moves a little bit so the location of the Sun changes in relation to distant stars. So the Earth needs to rotate a bit more than one full rotation with respect to stars for the Sun to return to its original location.",
"On mercury one orbital period is 88 Earth solar days. So Mercury does 2/3 of a full orbit when it rotates around itself once (relative to other stars) so the location of the Sun changes dramatically in this time. So the difference between a solar and sidereal day on Mercury is much greater.",
"But here's where it gets really interesting. Mercury's orbit is very eccentric. The orbital speed of a planet depends on the distance to the Sun. When Mercury is closest to the Sun, it's orbital speed is much greater than at the furthest point. At the closest point its orbital speed is 58 km/s. At the furthest it's 38 km/s. This is quite a big change and does affect how the Sun appears to move in the sky. Look at ",
"this",
" diagram. The small red line marks a specific location on the surface and how it rotates while Mercury orbits the Sun, going from location 1 to location 2 and 3 and so on, location 7 would be at 1 again. So the whole diagram (if you include location 7=1) is two Mercury years, one Mercury solar day.",
"Now then Look at positions 2 and 3. They're 1/3 Mercury year apart. At location 2, the Sun is about to rise as seen from the red line. At 3 it's still rising. This is because near the Sun, Mercury moves much faster. So the apparent motion of the Sun, as seen from the surface slows down. And then while Mercury gets further from the Sun again, the apparent motion speeds up. So the Sun seems to take fast bursts across the sky when Mercury is furthest from the Sun and then stand still when it's closest to the Sun.",
"And it gets even more interesting. At its closest to the Sun, Mercury actually orbits so fast that the apparent motion of Sun not only stops completely but starts to go backwards. This means that if you're at the spot on Mercury where you can see a sunset when Mercury is closest to the Sun, you'll see the Sun set first (very slowly), then it starts to move backwards and rises at the same horizon where it just set, and then sets again."
] |
[
"This will probably help",
". It simulates what the sun would look like from Mercury's surface."
] |
[
"That is freakin' AWESOME!"
] |
[
"How do we tell apart matter and antimatter?"
] |
[
false
] |
They both have mass, reflect light, have charges, etc. right? So, while electrons and positrons have opposite charges, complete anti-atoms would have 0 charge just like normal matter. Since they have identical charge, probably reflect light the same way, etc. how do we tell them apart? Perhaps there isn't really any less antimatter than matter, but we just can't tell it's something else? Also, what formations of antimatter are there in the universe? Does it form anti-systems with anti-planets and anti-moons?
|
[
"Taste it. If it tastes like a burst of gamma-rays, it's antimatter.",
"Seriously though, if there were entire planet's, solar systems, galaxies, or gas clouds made of antimatter then they would interact with the interstellar or intergalactic medium. These annihilations would produce gamma rays we could detect. Wherever ther was an antimatter something, we would see a gamma-ray hotspot."
] |
[
"Anti-matter annihilates when it comes into contact with matter.",
"Essentially if your anti water touched some water you'd end up with gamma rays and no water. This would be the end-all test which would identify the two apart. Also when you measure objects in the sky you never really see widespread high energy explosions like you'd see with a universe comprised of roughly 1:1 ratios (or really any ratio which includes a substantial amount of anti-matter) Even if the mixture was heterogeneous where entire anti-planets and stars formed, space isn't nearly as empty as sometimes portrayed and those would light up like Christmas trees (a very distinct Christmas tree) or much more likely, the interstellar gas clouds would.",
"There is also evidence that anti-matter acts differently then matter does in some ways which may or may not make it less stable than normal matter. I do not feel confident on commenting on that however.",
"Edits: Now anti-matter isn't all that uncommon however, at least in particle forms. Many nuclear reactions produce anti-particles, in fact there is some anti-particles bombarding Earth right now in the form of cosmic rays of which some contain trace positrons and anti-protons."
] |
[
"So we're basically assuming that there is little antimatter basing on the fact that there are too few effects of matter-antimatter collisions present?"
] |
[
"Chemists: How long does cologne keep before changing scent? Are there any fragrances that spoil faster/slower than others?"
] |
[
false
] |
[deleted]
|
[
"More curious than concerned. I took a bunch of organic chemistry, so was looking for a slightly more detailed answer..."
] |
[
"More curious than concerned. I took a bunch of organic chemistry, so was looking for a slightly more detailed answer..."
] |
[
"Why the hell would you even think he'd be concerned. And what kind of shitty answer is that?"
] |
[
"Can someone decode this paper for me? How can an occupation of being a mathematician correlate to higher birth defects in the baby?"
] |
[
false
] |
Is it just one of those correlation != causation things?
|
[
"The study seems pretty underpowered. For mathematicians, in 3 out of the 5 defect categories listed, they observed no significant association between the defect and paternal occupation of mathematician. For the other 2 defects, Anorectal atresia/stenosis and Coarctation of the aorta, the association is barely significant and the numbers of observations (3 and 7 respectively) are very small. In short those observed associations are likely not to be real. It would not surprise me at all if those results did not replicate in another study.",
"If we assume they ARE real then the association is likely caused by a confounding variable. It seems that they corrected for maternal age and lifestyle variables, but not for paternal age and lifestyle. It is possible that the age of the father or whether he drinks and/or smokes has a small affect on the chances of fathering a child with certain birth defects. Maybe mathematicians tend to be older when they have children or drink more than the average male in the study population.",
" Actually in the case of mathematicians the two \"significant\" associations have Odds Ratios (ORs) of less than 1 meaning that mathematicians are ",
" likely to father children with those birth defects than the average man. I still think those observations are probably not real."
] |
[
"SPECULATION: paternal age is a known correlational factor for higher birth defects (older is worse). Perhaps some of those occupations relate to people becoming parents at older ages?"
] |
[
"Many of these jobs that are here are those that are exposed to some form of chemical. Various solvents used in industries can cause ",
"birth defects",
".",
"I will say that many of those jobs seem very far removed from such chemicals...mathematicians included. However, the paper does not really attempt to explain the ",
" of the issue. They simply want to bring to light that some professions may have hidden factors that would cause birth defects in children.",
"On a more speculative note, many of these jobs that don't involve chemicals involve a lot of inactivity and sitting."
] |
[
"If I microwave two pieces of food, should I double the cooking time? What's the relationship?"
] |
[
false
] |
Also, how does density, surface area, and mass affect the relationship with total microwave time? I've always been curious about this. Thanks in advance. edit: sorry, I mean "two identical pieces of food"
|
[
"Microwaves are tuned to the ",
"quantized rotational absorbance",
" of water, so the amount of energy absorbed is related to the amount of water. The microwave wil put out a specific wattage and this is the maximum amount of energy it can output, if the max is being absorbed, then you would need 2X the time to add 2X the energy. However, if the limiting factor is the amount of water in the food item, or the positioning in the microwave (microwaves have \"hot spots\") then you can get 2X energy absorbed in less than 2X time. ",
"Since all of this is hard to measure and predict, it's generally much easier to just put it in for a little longer, and if you need more time just add it. "
] |
[
"I was bored and worried what if you wanted to make 13 rolls? Or PI/2 rolls? So I curve fit it fit it for you just in case you ever run into the situation and need to figure it out quickly.",
"PreFlipTime=5+((10/3)Rolls)\nPostFlipTime=(3*Rolls)-6",
"Or",
"PostFlipTime=(0.9*PreFlipTime)-10.5"
] |
[
"No, the formulas are consistent with you :)"
] |
[
"How much do tidal forces affect volcanic and magmatic activity?"
] |
[
false
] |
For anything from Hawaii to Yellowstone, or even for similar things like oil deposits, how much does the tidal force from the moon affect them?
|
[
"As ",
"/u/Ocean-Chemist",
" stated, there is no consensus as to whether tidal forces are relevant with respect to volcanic eruptions on Earth. Personally I suspect in my professionnal opinion that if they are relevant at all, they aren't relevant very much.",
"HOWEVER, there is no controversy whatsoever about tidally-driven volcanism beeing a thing elsewhere in the solar system, where the tidal forces involved are much greater than those in the Earth-Moon system. For instance, Tidal forces are believed to be the driver of volcanic activity on the jovian moon Io (",
"reference 1",
", ",
"reference 2",
", ",
"reference 3",
") as well as for the hydrothermal activity underlying Enceladus (",
"reference 1",
", ",
"reference 2",
", ",
"reference 3",
"). You will note however that in those cases the mass responsible for the tides is disproportionately greater than that of our Moon."
] |
[
"Does the Moon help mix the mantel? "
] |
[
"My understanding is that tidal triggering of earthquakes and eruptive activity is a somewhat of a controversial topic. ",
"Tolstoy (2015)",
" found a relationship between seafloor eruptions at mid-ocean ridges and neap tides (among other findings!) - and cites a bunch of other research on tidal triggering of volcanism and seismicity that you might find interesting. "
] |
[
"Physics is the same no matter what time direction you are going in, is there an exception?"
] |
[
false
] |
here is the article I read. ( )
|
[
"T-symmetry",
" is when physics is unaffected by the direction of time. T-violation is when it's different. ",
"The most familiar, everyday example of T-violation is ",
"entropy",
" (a measure of the 'disorder' of a thermodynamic system), which must always increase as per ",
"the 2nd law of thermodynamics",
". ",
"On a quantum level, it's only in the last few years that ",
"T-violation has been directly observed",
" in the ",
"weak interaction",
". ",
"However, T-violation has been indirectly inferred for over 50 years with the observation of CP-violation, which is when physics (in this case just the weak interaction) disobeys the combination of ",
"charge",
" (C, replacing particle with antiparticle) and ",
"parity",
" (P, reversing space) symmetries. Note that the weak interaction also violates C and P individually. Under the hypothesis that the combined symmetry of ",
"CPT",
" is always conserved, ",
"CP-violation",
" implies T-violation.",
"Further reading:",
"Wikipedia articles:",
"\n",
"http://en.wikipedia.org/wiki/Arrow_of_time",
"\n",
"http://en.wikipedia.org/wiki/Entropy_%28arrow_of_time%29",
"\nA thing I wrote:",
"\n",
"https://drive.google.com/file/d/0B_C8NJNxwF5ybGdfTlUwQmRSckk/view"
] |
[
"It's a mistake to connect increase in entropy to CPT. If you set up a random system with low entropy, it will increase in both directions of time. I don't think any physicists would seriously suggest entropy would magically decrease in one direction because of CP asymmetry. "
] |
[
"Is the second law of thermodynamics invariant under CPT symmetry?"
] |
[
"Do multidimensional (more than 3D) mathematics and physics have practical use that we can face in everyday life?"
] |
[
false
] | null |
[
"Yes yes and more yes!",
"The mathematics used in multidimensions is really the same thing as saying that the problem is multivariable. In fact almost any real world problem you solve will be more than 3 variables (dimensions). In fact describing one of the the simplest possible situtations, a single point particle moving in a potential is a 6 dimensional problem! (3 variables for momentum and 3 for position)",
"Imagine the engineering that had to go into cars and planes... the types of models engineers work with to understand dynamics are incredibly complex and certainly more than 3 dimensions. ",
"Nearly every single robot that works in a factory is programmed with models that use more than 3 variables (think of a robotic arm with several joints and all the degrees of freedom it has!). ",
"Models that companies use to look at the stock market are built on hundreds (thousands?) of variables.",
"Signal processing (internet, phone, television) is necessarily a multidimensional problem. ",
"Bottom line, any time you hear 'multi-dimensional' think 'multi-variable'... and our civilization, with all of its technical knowledge, certainly depends on solving these types of problems. "
] |
[
"It's curious how we imagine multidimensional problems as complex graphs (like 3d projection of tessaract), trying to \"break\" our standard 3d perception.\nBut you are completely right - math is all about multivariable problems and often there is no need to imagine it in graphical way.\nNow I understand naivety of my question."
] |
[
"One of the most fascinating aspects of mathematics I've encountered in my engineering studies is non-dimensionalization of partial differential equations. A complex relationship of six or more variables in a brutal PDE, with some clever manipulation of dimensioned quantities can become a simple ordinary differential equation. ",
"I'm looking at you Reynolds, Prandtl, et. al. "
] |
[
"Do the Alpha Centauri stars and the Sun originate from the same supernova?"
] |
[
false
] |
So I was thinking of how new stars are born from the remains of dead stars, or nebula, that form accretion disks thanks to gravity. Since nebulas are pretty big and can stretch for lightyears, is it plausible that the matter found in the accretion disks that formed our Sun and the stars of Alpha Centauri, comes from the same dead star?
|
[
"No, stars can't form from supernova remnants and planetary nebulae themselves, but from gas clouds (cold molecular clouds in particular) that got enriched by material from those stellar remnants. ",
"The sun is an intermediate population I star, which means, the gas cloud it had formed from was enriched with metals of countless progenitor stars, not just a single one. The sun is a metal rich star, and particularly rich for its age of 4,6 billion years. ",
"is it plausible that the matter found in the accretion disks that formed our Sun and the stars of Alpha Centauri, comes from the same dead star? ",
"We can't exclude the possibility, that one or more progenitors enriched the the cold molecular clouds that the sun and Alpha Centauri have formed from (its really unlikely that it was the same one), but after such a long time we can't proof that either. Essentially, it wouldn't make any difference. ",
"Furthermore, its not useful to think that Alpha Centauri and the Sun share a common origin, just because we are close. It just happens to be near us at this point in time. Alpha Centauri is roughly 2 billion years older than the solar system, so it's unlikely it has formed from the same gas clouds as the sun."
] |
[
"Supernova explosions can trigger a star formation event in a molecular cloud close to the shockwave, but supernovae themselves contribute very little to the mass of a newly formed star. They do contribute the bulk of the \"metals\" that form the solar system that results from the collapse of the cloud, metals meaning any element that's heavier than Hydrogen and Helium, and that will determine the metallicity of the resulting star. Supernovae seed newly formed systems of the Iron, Silicon, Copper, Gold, Platinum, etc. that will form interplanetary dust and the planets themselves, but the total mass is still very small compared to the mass of the star (the Sun accounts for 99% of the mass of the Solar System, and of the remaining 1%, 90% is hydrogen and helium from the gas giants. Terrestrial planets like ours are simply too small to be more than a blip in the chart)",
"Metallicity is one of the main methods of detemining the age of a group of stars, and individual elemental concentration help tell if a star formed alonside another. In this case Alpha Centauri is older and has different composition to our Sun, so they didn't form together. The Solar System formed more than 4.5 billion years ago, and the entire Milky Way rotates on its axis once every 250 million years, with every individual star having its own different orbit. So the Sun and its sisters have had billions of years to drift apart and mix with other stars."
] |
[
"https://en.wikipedia.org/wiki/HD_162826",
"It's quite difficult to discover stellar \"siblings.\" This Wikipage explains why."
] |
[
"Does Reading Prevent Cognitive Decline?"
] |
[
false
] |
Hello, if you are a regular reader, is there a chance that you can prevent developing Alzheimer's or dementia? I just want to know if reading a book can help your brain become sharper when remembering things as you grow old. I've researched that reading is like exercising for your body. For people who are doctors or neurologists , are there any scientific explanation behind this? thank you for those who will answer!
|
[
"it definitely does",
". I'm not sure how much causality has been established though, it could very well be that people less likely to experience cognitive decline are also people who read books.",
"That said, there's also the fact that people who lose their hearing often rapidly decline in cognitive ability. Continued mental stimulus seems to be required for the brain to stay healthy."
] |
[
"Also, cognitive decline may result in a reduced preference for and enjoyment of reading."
] |
[
"This study suggests",
" reading is protective of cognitive function in later life. Frequent reading activities were associated with a reduced risk of cognitive decline for older adults at all levels of education in the long term.",
"From the article:",
"Participants:",
"A representative sample of 1,962 Taiwanese community-dwelling older persons aged 64 and above, followed up in four waves of surveys over 14 years.",
"Measurements:",
"Baseline reading frequencies were measured based on a scale of leisure activity. The Short Portable Mental Status Questionnaire was used to measure cognitive performance. We performed logistic regression to assess associations between baseline reading and later cognitive decline. Interaction terms between reading and education were to compare the reading effects on cognitive decline at different education levels.",
"Results:",
"After adjusting for covariates, those with higher reading frequencies (≥1 time a week) were less likely to have cognitive decline at 6-year (adjusted odds ratio [AOR]: 0.54; 95% confidence interval [CI]: 0.34–0.86), 10-year (AOR: 0.58, 95% CI: 0.37–0.92), and 14-year (AOR: 0.54, 95% CI: 0.34–0.86); in a 14-year follow-up, a reduced risk of cognitive decline was observed among older people with higher reading frequencies versus lower ones at all educational levels."
] |
[
"How do pets view TV?"
] |
[
false
] |
I have always wondered if they don't understand the moving image on the screen or if they know there are humans projected on a screen. Do they think we are crazy for staring at it for hours?
|
[
"We talked about this in one of my neuroscience classes. They see things at different frame rates than people do, so it looks like a series of odd pictures. They probably think we see the same thing. But some dogs like those pictures (e.g., my sister's dog barks at any horses/dogs on tv)",
"EDIT: Add on: There are cognitive processing experiments that are actually very sensitive and impressive on detecting how things are processed between different humans and different species. Dogs still react to conditioning and stimuli (e.g., for basics, Pavlov's dog). Using a variety of simple tasks and different intensities/durations/alternations of stimuli, it is actually relatively easy to assess basic stimuli response. It gets tricky when you move into subjective areas (e.g., emotions), but simple things such as visual processing are actually rather easy to detect, interpret, and label. Even things as intense as mapping out different neural cell responses along the visual processing pathways have been done."
] |
[
"iirc, the flicker fusion threshold of dogs (and likely cats) is significantly higher than humans (by an order of magnitude). i think that, however, modern hdtvs at 120hz and 240hz exceed even this",
"however, even though they can see fluid motion on tvs, the question remains whether their perception of what's occurring is in any way really comparable. vision may not be the keystone sense for pets that it is for humans. sounds or scents may be more enthralling to them. further, their field of vision, depth perception, and available color spectrum will not be the same as ours. ",
"http://www.vmcli.com/veterinary-articles-can-my-dog-watch-tv.html",
"http://onpoint.wbur.org/2009/09/22/a-dogs-eye-view"
] |
[
"Apparently octopuses can only see HD"
] |
[
"If the COVID vaccine teaches our immune system to attack COVID’s spike protein that binds to ACE2, won’t the immune system also attack angiotensin II which was originally meant to bind to ACE2?"
] |
[
false
] | null |
[
"Antibodies aren’t mirror images of the things they target, so even antibodies that target the RBS won’t target angiotensin. ",
"Many if not all viral vaccines target the receptor binding region of the virus, and overlapping immunity to the receptor is simply not a problem."
] |
[
"Antibodies are very specific to their antigen: just because angiotensin binds there does not mean the vaccine will elicit a response against it. Antigens are determined by amino acid sequence AND 3d structure of the protein. There would need to be a very high similarity in sequence between two proteins to be targeted by the same antibody."
] |
[
"I already answered this question a few days ago in this ",
"/r/askscience",
" post: ",
"https://old.reddit.com/r/askscience/comments/k4ndl7/how_do_we_know_that_covid19_vaccines_wont_teach/"
] |
[
"How is the immune system involved with acne?"
] |
[
false
] |
So everyone I get sick, my acne goes away. Is this because my immune system is focused on better things? I’m confused how this works…
|
[
"I don't think that's entirely correct. Yes, your immune system directs the inflammatory response. However, acne itself would not occur in the absence of bacterial overgrowth. ",
"As you know, a whitehead is a clogged pore, and doesnt always have painful inflammation. A blackhead has the clog so superficial that there isn't much deep bacterial colonization. Acne was originally believed to be caused by bacterial overgrowth of a whitehead. ",
" is ",
"an aerotolerant anaerobe",
" which means that it grows best in the sealed, airless environment of a deep clogged pore [1] but is able to maintain some presence on your skin outside of a clogged pore, which is responsible for its ability to survive on your skin in between acne breakouts. ",
"Once the pore is clogged, it provides the perfect growth environment. The bacteria concentrate in significant amounts, enough that the digestive enzymes (lipases) they produce to break down your skin oils (lipids) are enough to compromise the lining of the hair follicle. That causes them to invade the skin from within, which naturally triggers an immune response that they wouldn't when they're barely colonizing your skin. ",
"The article linked above showed that the two common strains of Cutibacterium acnes strongly degrade the bond between skin cells after 48 hours of colonization [1], which is a major factor in their invasion and subsequent immune reaction. ",
"Additionally; the compromised barrier in the follicle has been linked to staphylococcus infection ",
"[2]",
" which further increases the immune response. ",
"From here on, I would only be able to hazard a guess as to why specifically you experience a clearing of your acne during an illness. I don't think that's universal - for example, anecdotally ",
"some people report worsening acne during illness",
". The response to acne depends on the production of TNF-a, IL-1, IL-8 and IL-12 and subsequent recruitment of neutrophils. Neutrophils are responsible for the most extreme symptoms of local inflammation as they release oxidants. For some people, I would assume that increased neutrophil recruitment and production during illness causes an improvement in the body's elimination of the acne causing bacteria. For others, the increased immune response may tip the balance from whitehead to full blown pustules breakout."
] |
[
"Again, there hardly seems to be a consistent outcome. Some people seem to go into overdrive and \"beat\" the acne while others seem to trigger the inflammatory response that turns whiteheads into pustules."
] |
[
"Thanks for the response! \nI thought your immune system is what caused acne in the end. Because your immune systems response to a clogged pore is to make it red and inflamed in hopes of clearing it out?"
] |
[
"Can we (humans or animals in general) obtain hydration from the water vapor in the air? Do I need to drink less on humid days than I do on dry ones?"
] |
[
false
] |
Follow-up: Assuming same volume of input liquid water and work performed under lab conditions, etc. "All things being equal" will a man working in arid conditions be more dehydrated than a man working in humid conditions? What's happening either way? Does the water vapor condense in our systems back into a liquid? I presume this doesn't happen in the lungs, I see that having ill effects. Maybe in the mouth/throat where it can condense on the walls and trickle to the stomach? Is it absorbed in vapor form by alveoli?
|
[
"Air within the lungs that participates in gas exchange is 100% humidity and body temperature. This means that since the air you're breathing actually has more water content than outside air unless that air is 37C and 100% humidity. Because of this we cannot obtain water from the air.",
"I think it's fair to say a person in arid conditions will become more dehydrated than one working in humid conditions, but there is a net loss of water through breathing either way, not a gain."
] |
[
"It's not typically taught in a biology class.",
"A lot of anatomy courses leave it out too."
] |
[
"Fascinating! Thank you for that. I can't remember if I may have once known this from Bio classes or not. "
] |
[
"Ask Anything Wednesday - Economics, Political Science, Linguistics, Anthropology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"I recall reading somewhere that the language you speak alters your perception. Have there been studies to find out to what degree it might do this?",
"i.e. We have a lot of sentences that start with \"I\". Does that effect how we think towards being more interested in our selves? "
] |
[
"Are there any organizations actively working towards artificial general intelligence?"
] |
[
"Yes indeed! ",
"A lot of corporations, organizations, and universities have been seriously working to achieve General AI since the late 1950's. ",
"This ranges from tech companies like IBM (evolving Watson to do more and more, as well as even inventing special circuits and processors to do specific AI and general AI work), as well as Google (who a few years ago hired Ray Kurzweil to work on more General AI related projects)...",
"to tons of Microsoft projects in this area...",
"to many Chinese companies... ",
"to financial-trading companies, several universities, AI Foundations, and even actual governments...",
"NOTE: ",
"a lot of the general AI projects are kept relatively \"secret\" by many corporations/organizations, and especially by governments. ",
"So... who really knows what kind of progress governments have been making in this field!? ",
"So yes... most organizations don't really reveal much about the projects and/or the media doesn't pay too much attention to the projects... ",
"For now... ",
"In the end: ",
"No one is going to go too crazy about reporting on a non-successful or partially-limited-successful General AI test. ",
"But once general AI is achieved... then you'll certainly hear about it! ",
"In fact... if the AI evolves rapidly at that point... ",
"then the AI itself might contact you directly to let you know about its existence... talking with you directly through your email, social media, and devices! ",
"So... you'll know it when it happens! "
] |
[
"Can sound travel faster than light in a dense enough medium ?"
] |
[
false
] |
Considering that sound travels faster in denser mediums, can sound go faster than light if it travels in a dense enough medium ? How dense would it have to be ? Does anything that dense exist ?
|
[
"The sound speed in a very dense medium, like the core of a neutron star, could in theory be almost as large as the speed of light in vacuum. Sound waves cannot be faster than the speed of light in vacuum, according to relativity, otherwise they would violate causality. Physically that would mean that you would be able to conceive situations where you could \"hear\" yourself before talking (chronal acausality). Mathematically, what happens is that the equations of relativistic fluid dynamics become ill posed if the sound speed exceeds the speed of light in vacuum."
] |
[
"Sound is just a wave of moving particles. You can think of it almost like a chain of dominoes. It propagates when one particle shifts into another and transfers momentum. ",
"The speed of sound is limited by how fast those particles can move, and that is limited by the speed of light."
] |
[
"The speed of sound cannot exceed the speed of light. In fact, it may be the case that the speed of sound ",
"cannot exceed 57% the speed of light",
", which is the speed that sound propagates through a hyper-relativistic gas. However, inside neutron stars there may be sound waves faster than this."
] |
[
"Why does Mars have a slightly larger axial tilt than Earth without similar evidence of a proto-planet impact?"
] |
[
false
] |
I learnt that Earth has its axial tilt because of an impact with a proto-planet that also created the moon. While Mars also has two moons, they are 10 and 10 times smaller than our own moon. Why doesn't Mars posses a similarly proportional sized moon?
|
[
"It does have an enormous basin possibly the remnant of a large impact. It is thought that several moons were formed, but the largest ones eventually recollided with the planet. Follow this link for one theory",
"https://www.space.com/33335-huge-moons-may-have-hit-mars.html"
] |
[
"While its true that most observations about axial tilt in our solar system are the product of planetary collisions, there are some that can't be adequately explained that way (Uranus). People have come up with other mechanisms that have been shown in simulations to cause axial miss-alignment over longer periods of time. Its been shown that the axial tilt of mars has changed dramatically in \"cosmically recent\" timescales. Its possible that mars's tilt is a product of gravitational influence rather than collision. This could also explain why mars has such an elliptical orbit."
] |
[
"Yup, it would be one of the many challenges of colonising Mars - protecting from solar radiation. "
] |
[
"Is the human race showing any signs of natural selection and evolution?"
] |
[
false
] |
I was reading this news: and it says that Asian Elephants are being born tusk-less as a result of severe poaching. this occurred in the short time-span of 100years or so. So, is there anything that we have observed? are we smarter than our ancestors? are we physically weaker too?
|
[
"This is an example my Physical Anthropology 101 professor used: the existence of Tay-Sachs Disease in the Ashkenazim Jewish community. Of course, Tuberculosis was a problem in larger cities throughout the medieval period. At the same time, Jews were generally segregated into their own quarter of the city and due to the \"chosen people\" idea and other factors, largely produced children with fellow Jews. The Tay-Sachs gene, when present passed from both parents, will kill the child before they can produce their own children, but when only one copy is present, the child will be highly resistant to Tuberculosis. If the gene was strictly harmful, I would expect the mutation to die out after a few generations, but because it produced such a benefit to the survival of those who had only one copy of the gene, it proliferated in that limited community. This mutation occurred and was beneficial, so in the limited Jewish community, it spread. "
] |
[
"That would be an example of heterozygote advantage. Malaria resistance from a single copy of the sickle cell gene is another example; if you're homozygous (two copies of the allele) for sickle cell, you get sickle cell disease. If you're homozygous for normal blood cells, you're vulnerable to malaria. But, if you're a heterozygote, with one copy of each allele, you're malaria-resistant without getting full-blown sickle cell disease.",
"This becomes relevant to human evolution because sickle cell anemia is a problem for people who live in, or had ancestors from, regions where malaria is endemic (principally Africa). In the US, where malaria has been eradicated since the early 1950s, there has been a decline in the incidence of sickle cell anemia, as it no longer confers any kind of survival advantage but can be deleterious in homozygotes. One very basic definition of evolution is a change in the proportion of alleles in populations, which is clearly observed by the decline in sickle cell disease in populations of African Americans.",
"Sickle Cell Anemia / Balancing Selection"
] |
[
"Sickel-cell anemia",
" is ",
" the same: Homozygous is deadly, heterozygous reduces the severity of malaria. Their ",
"source",
" seems to have disappeared, but that Wikipedia page claims that in some areas, as many as 45% of people are heterozygous for it.",
"Edit: And ep0k beat me to it by 5 hours, I probably shouldn't post before I'm awake enough to read."
] |
[
"Do dogs of one breed prefer to be with their own breed over others or are they all just dogs to them?"
] |
[
false
] |
Also other animals that have breeds, like cats, sheep, cattle etc.
|
[
"Please no more anecdotes about your dogs. Please stick to scientific information gleaned from studies. ",
"Thanks."
] |
[
"I don't know what they ",
", but I've seen research that indicates that different breeds communicate using different signals. ",
"For example, from \"Paedomorphosis affects agonistic visual signals of domestic dogs\" by Goodwin, Bradshaw, and Wickens, ",
"Visual communication between domestic dogs (reviewed by Bradshaw & Nott 1995) is conventionally described in terms of the signals per-formed by the wolf during dominance/submission interactions within the pack (Scott & Fuller 1965; Abrantes 1987). Inherent in this convention is the assumption that, during the 12 000 years since the dog began to be domesticated, the behavioural repertoires of the two species have not diverged. Whilst such an assumption may be valid for breeds of dogs that have retained a wolf-like appearance, in many modern breeds most or all of the ancestral structures used for signalling (e.g. the muzzle, the area around the eyes, the ears, the tail) have been substantially modified by selective breeding. ",
"... ",
"The videotaped observations showed that each breed performed a different range of ancestral dominant and submissive behaviour patterns during intra-group signalling (Table III), ranging from two (Cavalier King Charles spaniel) to 15 (Siberian husky). ",
"- ",
"http://www.sciencedirect.com/science/article/pii/S000334729690370X",
" (full text is readily available if you practice google-fu). "
] |
[
"breeds of dogs that have retained a wolf-like appearance, in many modern breeds most or all of the ancestral structures used for signalling (e.g. the muzzle, the area around the eyes, the ears, the tail) have been substantially modified by selective breeding.",
"Sounds like it has more to do with the morphology of different breeds than with individual breeds. From what I understand, a German shepherd and a Labrador would probably still be able to communicate these signals to one another, while a pug would not."
] |
[
"Why can't we supress sound by sending opposite waves? (or can we)"
] |
[
false
] |
This is something I've been having around my mind since i was a kid. When I learned that sound was just momentary compressions of air, I thought if I could capture somehow what the exact sound waves coming to me were like, and , pressure of air (waves) would neutralize each other, thus killing that sound. Is that possible? If not, why not?
|
[
"Yes, we can!",
"Although it's not perfect, because the shape of sound waves is complex and becomes distorted by differences in air density, reflects off surfaces, etc... so the hard part is making the opposite waveform exactly opposite.",
"If you have a stereo system with separate speakers that use plain old jackless speaker wire, play a mono sine wave through the speakers. Then hook one speaker up with the wires in the opposite orientation as the other. This makes the speakers \"out of phase\". Now point them at each other and then move the speakers together/apart until you find the point at which the sound is most quiet. This distance is a multiple of the sound's wavelength and should confirm for you that you can in fact cancel sound out with the opposite. It won't necessarily be very effective, though. You might have to listen carefully. I imagine it would work best in a fairly empty room with sound dampening foam/tiles on the walls so that sounds don't reflect around.",
"More info is here",
". As it turns out, this is how noise cancelling headphones work."
] |
[
"Is that possible? If not, why not?",
"Yes and no.",
"What you are describing is called ",
"active noise cancellation",
" and is the way devices like noise canceling headphones work. Set up a microphone in one location, use the sound at that location to predict the sound at another location an instant later, and send a sound with the same amplitude but opposite phase to that location to cancel it out. It works pretty well.",
"Of course, this method has some limitations. The biggest one is that you can't cancel out the sound everywhere. The phase at a receiver is a function of the distance to the source. Since the sources of your \"sound\" and \"anti-sound\" are not located at the same spot, that means that receivers at different locations will receive different phases. Thus, the wave won't cancel out as well at some locations, and will even have some points where the noise is amplified by the \"anti-sound\" source.",
"Luckily, noise canceling headphones only really need to cancel the noise out at the listener's ear, and any additional noise can be largely contained in the earpiece. But there are definitely limits on how and when active canceling can be effective."
] |
[
"I'm a DJ, and when in setting up my speakers in a room, depending on the room arrangement, my two subwoofers have 'hot spots' within the room where they are louder, and others where it's not so loud. It's the same idea, due to the sound waves bouncing differently off the walls, and at different angles causing the phasing to be opposite.\nFor this reason, many subwoofers have a 'phase switch' to swap the phase by 180 degrees in order to make up for the lost volume."
] |
[
"According to Special Relativity the mass of an object increases as its speed increases, does this mean that if I brought a highly accurate weighing scale on a aircraft I would appear heavier than on ground?"
] |
[
false
] |
Disregarding factors that would probably disturb the experiment (I am no scientist by a long shot but): Centrifugal force, reduced gravitational force due to height, "shaking", and probably some other things I have never even heard of.
|
[
"Not exactly. \"Mass\" itself doesn't increase once you increase velocity. The faster an object moves, the harder it is to accelerate it, though. This is only due to the properties of special relativity, an in order to interpret that in a classical context, objects are often said to have a \"relativistic mass\", which increases with velocity. ",
"Nevertheless, if you are inside an object moving fast with respect to another observer, this is your reference frame and from your point of view, your velocity is 0. Think about this: you are moving very fast with respect to the same, and the sun is moving very fast with respect to the center of the galaxy and so on..."
] |
[
"Could you elaborate on the difference between \"harder to accelerate\" and \"mass increase\".",
"So if mass remains unchanged, does f=ma no longer apply?"
] |
[
"I'm kind of surprised that none of the answers so far have pointed out that your question is ill-posed. Special relativity concerns itself only with inertial frames of reference, which means that you cannot have acceleration or gravity (though these are actually the same thing under Einstein's principle of equivalence)",
"Simply not true. Special relativity can handle accelerating frames just fine.",
"http://math.ucr.edu/home/baez/physics/Relativity/SR/acceleration.html"
] |
[
"If people had a speech disorder growing up can they retain that learning disability when they learn a new language?"
] |
[
false
] |
I was wondering if this is common because I find myself suffering from a speech disorder I had when I was younger and resolved it, as I now try to learn French.
|
[
"It depends on the disorder. Aphasia is pretty much something you're stuck with regardless of language as it results from damage to the parts of your brain that contribute to language production (Broca's and Wernicke's areas, for example). Stuttering is more behavioral and can be untrained but might need to be re-untrained with acquisition of a new language, or it may not. "
] |
[
"Speaking totally anecdotally, yes. I have a minor impediment (I hope this is what you mean) where I don't fully pronounce R's. Spanish's rolling R's are all but impossible, even though my English R's are nearly normal. "
] |
[
"You can correct that fairly simply. A speech therapist can show how to articulate the R's. The fact that your English R's are normal is precisely because they're articulated in a different way than our Latino R's. 4 op: I can also confirm that you can have a minor speech disorder using one language, and speak normally in other."
] |
[
"I read that elephants are now being born without tusks because of poaching, is this how you can control evolution? If human beings had their pinkies chopped off, would that result in humans eventually being born without a pinky finger?"
] |
[
false
] | null |
[
"It's not that elephants who have tusks removed give birth to elephants with no tusks. Rather elephants with smaller tusks are less likely to be poached. So they breed. Their children with large tusks get poached. Their children with even smaller tusks are more likely to survive. And on and on. It's the same with how we selectively breed cattle or horses or anything to get the traits we want."
] |
[
"But elephants are now being born without tusks completely."
] |
[
"Indeed. Eventually, tusks become smaller through selection until they are not noticeable. Some elephants will still be born with smallish tusks, others with no visible tusks. If poaching stops, perhaps large tusks will again become signifiers of health or strength and larger tusks will be selected for and tusk length will increase."
] |
[
"What is going on in the human brain when someone has multiple personalities?"
] |
[
false
] |
When the person switches to a different personality why does the person not remember anything the other personality is doing?
|
[
"First of all, ",
" is really, ",
" poorly studied. Knowledge about it is based largely on case studies, and there's a relative paucity of neuroimaging studies in the area.",
"The notion that DID is even a distinct personality disorder is heavily contested, as people diagnosed with it tend to have extremely high rates of comorbidity with additional psychiatric diagnoses. As such, it very well may be that DID isn't really a \"thing\" in and of itself so much as a summation of borderline personality, post-traumatic personality, and other mood and dissociation disorders. Often the argument is between three camps:",
"That said, some research in the neurology of DID has been done. The results of ",
"this study",
" suggest that hippocampal and amygalar volume is reduced in DID patients. These findings correspond to impairments in memory as well as (depending on which part of the amygdala is most reduced in volume) fear processing. However, ",
"these findings are also true of people with post-traumatic stress disorder (PTSD)",
", which hearkens back to the fact that DID may be less a distinct disorder so much as a combination of PTSD and other issues.",
"I'll note also that both PTSD and DID cases tend to be what is called ",
", meaning they are more inclined to hypnotism. However, this idea, like everything else to do with DID, has been contested."
] |
[
"Many strange phenomena have been both reported and studied in DID. Sometimes one personality will be left handed, even though the primary/original/whatever personality is right handed. When studied, that personality will indeed show a preference for using the left hand and perform better with the left hand than the right. However, this difference appears to be due to decrease in right-handed performance rather than increase in left handed performance. So personalities can show different patterns of abilities, but this is due to deficits, rather than enhancements. The same seems to be the case with memory: a personality can fail to recall memories, but this is more likely a problem with retrieval of the memory than encoding of the memory. In other words, the memory is there, but not all of the personalities can retrieve it."
] |
[
"In clinical settings, \"multiple personalities\" is called Dissociative Identity Disorder. As mentioned in other comments, DID is quite controversial and poorly studied. The few brain imaging studies on DID have pointed to ",
"decreased volume",
" in brain regions such as the amygdala and hippocampus, but the sample sizes on these studies are quite small and the diagnosis of DID is quite difficult. All of which is a long way of stating that, if DID is a real diagnosis, we really don't have good data about what is happening in the brain. "
] |
[
"When light beams create destructive interference, where do the photons go?"
] |
[
false
] |
Prompted by (where I kept hoping someone with a background with optics would show up to help) asking about the possibility of "light cancelling filters" - I know how sound can have destructive interference, since "sound" is actually the effect of compression and rarification of a medium. When "sound" waves are subject to destructive interference, the compression and rarification waves cancel out, leaving the medium at neutral state. However, light is composed of photons. So what happens when two light beams of the same frequency but 180 degrees out of phase are combined? I've done some research, and found a lot of articles stating that destructive interference happens, but nothing goes into detail about "how"
|
[
"when two beams of light destructively interfere, they only do so in ",
" location. There will always be other locations in the optical system where there is constructive interference which contain the seemingly missing energy. The entire system still contains the same amount of energy when you take all interferometer outputs into account.",
"Source: My MS thesis research was all interferometry (i did research related to LIGO)"
] |
[
"So you're saying you can't have an \"active light canceller\" in the same way you can have active noise cancellation? ",
"Active noise cancellation works with destructive interference which has the effect of nullifying the compression and rarification waves in the medium. ",
"With two beams of light in a vacuum, you can't end up with \"nothing\" - so what happens? Is it that you can ",
" have diffraction ",
" and not full cancellation?"
] |
[
"So you're saying you can't have an \"active light canceller\" in the same way you can have active noise cancellation? ",
"interference is a behavior of waves, regardless of the ",
" of wave, so what I said above is true of sound waves as well. Noise cancelling headphones are designed to be noise cancelling where your ear is. "
] |
[
"Is the earth getting lighter or heavier?"
] |
[
false
] |
I'm very interested to know whether the earth is getting heavier or lighter every year. I would assume that such things as cosmic dust, meteors, etc. make it heavier. and things like space probes / mars rovers, evaporation of gasses in the atmosphere, etc. would make the earth lighter. And is the earth getting heavier or lighter affecting the rotational speed of the earth?
|
[
"Yes, ",
"Estimates for the mass of material that falls on Earth each year range from 37,000-78,000 tons. Most of this mass would come from dust-sized particles."
] |
[
"well Earth is Slowing its rotation as a result of the tidal drag from the moon. This is the Primary method of slowing our rotation. ",
"the rate we are increasing our diameter is so very very very slow that I doubt the acquisition of a few tens of thousands of tons of material a year is measurable on the rate of rotation. "
] |
[
"does it absorb at a larger rate than the rate we send items into outer space? "
] |
[
"Question about muscle fatigue."
] |
[
false
] |
Hi, and sorry for my english. So, my question is this: does 'isolated' muscle fatigue affecting other muscle performance? Let me expand on this. Imagine that i can do 15 bicep curls before i can't do them anymore in one set. Now, let's say i will do something completely isolated from biceps, like a calf raise in an exersice machine for a 1/3/6/9/12 hours straight (or many multiple isolated excersices) Will it affect my ability to perform a bicep curl? Obviously with some resting time to regain your breath. If yes than why? What mechanism will cause my performance to drop?
|
[
"The first main source of energy comes from muscle glycogen stores. Thsee depleted very rapidly, prompting a switch to oxidation pathways. When your muscle fatigues (using your rep range of.15) it is because the glycogen stores within the muscle.have been depleted. At this stage there should be no detriment to performance in other groups. However, when you depleted those stores you must rely now on glucose uptake.from the blood.and oxidation of fatty acids. Usingmultiple groups or large muscles will use.this.at a higher rate, meaning a detriment to performance as the fuel supply dwindles.",
"Sorry for random periods...big thumbs on a small screen"
] |
[
"That wasn't really helpful, sorry. I got into the argument about it, my argumentation was that if you ran a marathon you obviosly will not be able to do same amout of reps because you will feel exausted(and he agreed to it), but his responce to that was that running is a exercies that uses all of your muscles (even if it's swinging your arms, for 2 hours straight it's no joke), I couldn't find any information on that myself, so i came here for help."
] |
[
"Those are two different energy systems. Resistance training uses primarily carbohydrates for energy, whereas a marathon uses primarily fat. I'm going to try to simplify the physiology aspect by summarizing to the point that the body tries to conserve glucose, and that glucose is the limiting factor to an endurance event. When glucose stores run low, the Krebs cycle begins to work slower, eventually leading to not enough available fuel to continue. If one were to attempt resistance training after depleting their carbohydrate stores, they would only be able to complete a few reps (using the creatine phosphate system) and would then require time to replenish the stores."
] |
[
"How do photons carry \"information\" from a point in the universe to our brains that becomes an image?"
] |
[
false
] |
If everything we see in the world, and more specifically, the photons travelling from distant planets/stars is how we perceive it after the time it's taken the photons to travel to our eyes, does that mean the photons carry "information" of the image that our brain interprets? The way I'm thinking about it is, if there was nothing to obstruct our view of a planet, our brains are processing the information, from the past, of that planet. Could you theoretically instantly travel another 100 light years away in the opposite direction of where those photons originally would have hit the receptors in your eye, and see 100 light years + your original position, years into the past? Follow-up: If i'm asking the right question, then is it possible that we can build a machine that can collect that information from photons at an arbitrary point in the universe and and form a discernible image from the information in the photon at a specific time?
|
[
"A photon carries information by its direction relative to your eye by where it hits your retina and color by the wave length of the light. And of course also intensity, but that's an accumulative effect by the number of photons.",
"You're always seeing the past. The further away the source is the further into the past you're seeing. The human eye has no where the resolution to see our planet from 100 light years away, but the information would still be there in the abstract sense.",
"You can't extract all the information from a photon. Because of quantum effects, any measurement of an unknown photon will necessarily disturb it causing you to lose information. This is closely related to (but not exactly the same) as the uncertainty principle. This idea is used in quantum cryptography and generally called entropic uncertainty."
] |
[
"I'm having a hard to time trying to formally express what the way I'm thinking about this. ",
"So let's say the particles that make up the moon; It's not the actual particles that make up the moon that are travelling to my eye, generating my visualization of the moon. It's the photons that are traveling back from the moon are essentially generating that image after the brain computes the data. Correct? ",
"I suppose a second analogy is something like a projector. \nA projector produces an image in the projection machine itself. It is later projected by light to the wall. Is it because the light is carrying a \"copy\" of the data, of the original image to the wall?"
] |
[
"you're mixing levels of information here.",
"an image is formed on the retina - it is made up of photons. this image carries ",
" information, but less than you think. it is highly ambiguous about its source, if you want to think about visual information in terms of the image being \"about something\". in this case, for any given image, there are ",
" possible sources! so an image made up of photons isn't that informative about its source.",
"the image is absorbed by the nervous system, and, in essence, compared with other images that have been absorbed during the nervous system's lifetime. the information in the past experiences are combined with the information in the image, resulting in ",
" and new things are learned.",
"so, what kind of information do you mean? visual information carried by photons is very sparse (except in a sense that is uninteresting to us), and very ambiguous. it could in principle be coming from ",
". on the other hand, visual information generated by the nervous system is extremely dense and precise - you ",
" what you're seeing - but it isn't made out of photons."
] |
[
"Where did energy originate from?"
] |
[
false
] |
[deleted]
|
[
"This video is about pretty much exactly what you are asking for, watch it!",
" "
] |
[
"Thank you kind sir/lady of science!"
] |
[
"Excellent question, great answer. "
] |
[
"Question about drug half life."
] |
[
false
] |
If a drug is stated as having a half life of 35 hours is there a degree of error that you can assume? i.e different people metabolising at different rates and other factors. Is there a formula for working out amounts of the drug in the body after a given time?
|
[
"Good question. The distribution and metabolism of drugs is called \"pharmacokinetics.\" It's very important (in terms of safety and efficacy) to know how long the drug persists in the body and how it is metabolized, so research into this is part of the reason why pharmaceuticals are expensive to develop!",
"Human beings vary in their ability to metabolize different drugs. This results from several factors, including gender, activity, weight, diet, and so on. Also important are genetic differences: people of an Egyptian background often are called \"slow acetylators\"-- a consumed drug is modified by the body as part of a mechanism which promotes detoxification and clearance of the drug (or its metabolites) from the body. So certain drugs whose excretion processes rely on acetylation do not last as long inside some Egyptians! As for formulas, half-life is defined as the amount of time it takes for half of the drug to be rendered inactive (through clearance or metabolism), and it will generally follow an exponential decay curve. ",
"TL;DR: There will always be a degree of error; the metabolism of drugs can be modeled using a formula (typically an exponential decay formula).",
"Source: I took a high-level class with the inventor of one of the top 10 most profitable drugs in the US."
] |
[
"There are all sorts of models for drug levels in the body, depending on all sorts of factors--how it is metabolized, if it passes through the kidneys, etc. In many cases, the models for calculating drug levels in the blood will involve using a system of differential equations, where each organ involved in the drug processing is represented separately. When it comes down to it, however, these are all just models that need to be fit with real blood-level data to be useful, so there's no way of fully knowing how a drug will act in the body a priori without actually giving the drug to test subjects.",
"The ",
"wikipedia article on pharmacokinetics",
" makes for an interesting read, and it looks like they link to a bunch of freeware which can be used for calculations like this. "
] |
[
"Depends on the drug, what you mean by continuous usage, and so on. If you let me know the drug, I can do a literature search, but a pharmacologist or a doctor would know best--pharmacokinetics is extremely complicated (not even the best drug chemist in the world could answer this question just by knowing the chemical structure of the drug), and a good chunk of the billion or so dollars that it takes to bring a drug to the market goes into determining the appropriate dose.",
"As an aside, a friend of mine accidentally swallowed some sort of pain medication when he was little--he said he still tested positive several years later. Just an anecdote though, not sure about the story's accuracy."
] |
[
"Are +∞ and -∞ the same point on the number line?"
] |
[
false
] |
[deleted]
|
[
"You are correct, this is the ",
"Projectively Extended Real Line",
" and it looks like a circle. But there are other ways to do it, like the ",
"Extended Real Line",
", which just caps both ends of the real line with two points that we call -∞ and +∞. You can get the projective real line from the extended real line by wrapping the extended real line into a circle.",
"Both of these have their different uses for different situations.",
"The Extended Real Line is good for analysis and a lot of applications. Here it is important to distinguish between going to -∞ and +∞. This will help you find out if things diverge because they grow too much or grow too negative. In this case, since both infinities are at the end, we only have to check their limits as we approach from ",
" side. This means that the limit of f(x) at x=∞ only cares about what f(x) does for large and positive x, it doesn't matter what f(x) does for negative x. For example, the limit of e",
" at x=∞ is ∞ , whereas the limit of e",
" at x=-∞ is zero. If -∞ and +∞ were the same point, we would have to say that e",
" does not have a limit at infinity, but if we separate the points, then we can talk about them.",
"The Projective Real Line is more significant arithmetically. If we have 1/0=∞, then we can ",
"define arithmetic using this new point",
" (though, there are a lot of special cases and undefined expressions). In particular, ",
"So we can't distinguish between -∞ and +∞ in the Projective Real Line because we want to be able to do arithmetic like above. Distinguishing between -∞ and +∞ is then like trying to distinguish between -0 and +0. On the Projective Real Line, 0 and ∞ are kinda like partners or bizarro copies of each other. A lot of the special things that 0 does have a corresponding special thing that ∞ does and vice versa. For instance we have",
"0*x = 0, whenever x is ",
" ∞",
"0+x = x, for any x",
"x/0 = ∞, whenever x is ",
" 0",
"Correspondingly, we have",
"∞*x = ∞, whenever x is ",
" 0",
"x+∞ = ∞, for any x",
"x/∞ = 0, whenever x is ",
" ∞",
"Now, if we have f(x) and we want to find the limit of f(x) at ∞, then it will only exist if we get the same value by approaching from both the left and the right of infinity. In common terms, we need the limits of f(x) at x=-∞ and x=∞ to be equal. So e",
" has no limit at x=∞ on the projective real line. However, limits with infinite value are nicer, because if you get ∞ on one side and -∞ on one side, since -∞=∞, we get that the limit is ∞. For instance, on the projective real line, the limit of 1/x at x=0 is ∞. ",
"Some functions behave extremely well on the Projective Real Line. In particular, ",
"Rational Functions",
" are really great. As you suggested, they become continuous everywhere on the Projective Real Line. The limits at -∞ and ∞ are always equal for a rational function. Asymptotes play the bizarro role of zeros. For a rational function f(x), every asymptote is just a point where f(x)=∞. In fact, if the asymptote is positive on one side and negative on the other, then this just means that f(x) passes through infinity and winds around the circle (which is what the projective real line is) once. If f(x) does not change signs on either side of an asymptote, then the function hit infinity and bounced back. Compare this to a zero, f(x)=0. If you are positive on one side of the zero and negative on the other, the the function f(x) just passes through the x-axis at that point, but if it is the same sign on both sides, then it bounces off the x-axis. ",
"Here is a function where it's zeros and asymptote just passes through the x-axis and infinity respectively.",
"Here is a function where it's zeros and asymptote both bounce off the x-axis and infinity respectively.",
".",
"It's unfortunate that we can never explicitly graph what is going on at infinity. Or is it? If f(x) is a rational function, you can switch the classical graphical view to look at the lines at infinity by just graphing 1/f(x).",
"This is how infinity sees the first function above",
"This is how infinity sees the second function above",
".",
"Note that the zero here is what the asymptote was before, and in the first it just passes through and in the second it bounces off. Just as polynomials are completely determined by their zeros, rational functions are completely determined by their zeros ",
" infinities.",
"As you said, if we look at a coordinate graph made on the projective real line, then you will get a torus. In this way, rational functions are just really nice ways to wrap the circle around the torus. For instance, f(x)=1/x wraps the circle around the torus once while looping it through the middle once. But f(x)=1/x",
" will wrap it around once, but when it tries to loop around the middle, instead of passing through, it will bounce off so 1/x",
" does not loop through the middle.",
"It may be apparent that I'm biased towards the Projective Real Line rather than the Extended Real Line. But in the field of ",
"Algebraic Geometry",
" (a very powerful field of math), it becomes natural to \"complete\" things like the real line by projectively extending them and in this context, the rational functions on the corresponding objects can teach us a lot about what we're trying to understand. In this way, projectively extending things has very deep arithmetic significance. There is a corresponding significance in ",
"Complex Analysis",
" when we extend the complex plane into the ",
"Riemann Sphere",
", and on the Riemann Sphere a lot of analysis things become more complete. In fact, the it is really only with the real line that you see the different infinities, distinguished by how you can approach them. Typically, projectively extending things is more natural to work with."
] |
[
"I think an worthy clarification here is that there exist multiple number lines. The answer to OPs question is Yes on the Projectively Extended Number Line, No on the Extended Number Line, and isn't well posed on the Real Number Line because ∞ is not on that number line."
] |
[
"Wow, a great read! Thank you."
] |
[
"Is it possible to travel AT the speed of light?"
] |
[
false
] |
From what I know, it is not possible to travel FTL but I am having trouble finding anything that says that we can/can't travel at the speed of light. Is it possible to do so? If not than are speeds near LS possible? Such as 99.99% the speed of light.
|
[
"It is not possible for anything with mass to travel at exactly the speed of light. Speeds very close to the speed of light are entirely possible, however, and massive particles reach speeds greater than 99.99% of the speed of light (typically written .9999c) in particle accelerators every day."
] |
[
"You do not view the speed limit ",
" in the correct way. ",
" is, with respect to (for example) force required to accelerate to it, an asymptote. The limit of this force is infinite as you approach ",
"!",
"You will be able to keep accelerating just as nornal, but your deltaV will get smaller and smaller and trend asymptotically towards 0. That is, for the same speed increase (i.e. acceleration) more and more energy will be required.",
"It might help to view ",
" as an infinity even though the actual speed is finite. As something with mass increases in speed towards ",
", its energy will increase towards infinity."
] |
[
"You do not view the speed limit ",
" in the correct way. ",
" is, with respect to (for example) force required to accelerate to it, an asymptote. The limit of this force is infinite as you approach ",
"!",
"You will be able to keep accelerating just as nornal, but your deltaV will get smaller and smaller and trend asymptotically towards 0. That is, for the same speed increase (i.e. acceleration) more and more energy will be required.",
"It might help to view ",
" as an infinity even though the actual speed is finite. As something with mass increases in speed towards ",
", its energy will increase towards infinity."
] |
[
"Conservation of Information in Quantum Mechanics"
] |
[
false
] |
Now, I know that I don't have a great understanding of Quantum Mechanics, but I've had a few Physics courses in college going through introductory Modern Physics, but something that's always puzzled me is the idea tossed around that Quantum Mechanics implies a random universe. Now, my understanding is that even in Quantum Mechanics, Information is preserved. (For simplicity, I'm less interested here in the Black hole information paradox) If Information is preserved, doesn't that mean that given complete knowledge of the state of the world at any given time we can predict what the state of the world at any given time in the past or future will be? If this is true, and Quantum Mechanics conserves Information, then I don't understand how it is random. It seems that future states of the universe are defined deterministically by previous ones.
|
[
"We currently don't know how quantum mechanics really works. As far as we can tell, it's truly random, but it's possible that there are hidden variables which would tell us what will happen if we could see them. Until we are able to learn more either way, we simply don't know whether the universe is deterministic or not.",
"What I mean by randomness is (in the form of an example), a particle may be in the spin state 1/sqrt(2) * ((up state) + (down state)). This means that when we measure its spin, there's a 50% chance of it being in either state (it has to choose one when we do the measurement). So far as we can tell, there is no way to predict which one it will choose.",
"I don't know much about information as it is mathematically described, but I'm fairly sure that either there is no law of conservation of information (as you understand it, anyway), or such a law does not imply determinism, otherwise I think it would be a more important topic - we certainly haven't proven determinism, either way."
] |
[
"if I'm not mistaken, when we talk about conservation of information, we talk about the conservation of the ",
" of information. To use a completely ",
" analogy, it's like a hard drive filled with different kinds of files. It doesn't matter what the data on the drive say, it just matters that you can't put more than 1 TB on it. Ultimately information means something to us in the context of thermodynamics and entropy, it doesn't mean that it's a record of the history of the particle."
] |
[
"doesn't that mean that given complete knowledge of the state of the world at any given time we can predict what the state of the world at any given time in the past or future will be",
"To add onto what shavera said, what you're talking about here is determinism, not conservation of information, and these are two mostly unrelated concepts. As shavera rightly points out, conservation of information is about the information carrying capacity of systems.",
"The fact that measurement outcomes are apparently random in QM does not mean information is not conserved, since it's not the outcome that matters, it's the ability to communicate a message with that outcome."
] |
[
"Why and how did the Earth form so that only the huge land mass of Pangaea protruded from the ocean?"
] |
[
false
] |
[deleted]
|
[
"Earth's tectonic plates float and move around on the mantle. The last time the continental plates happenned to to drift together to form a super-continent is called Pangaea. However, Pangaea was not the first (or for that matter it won't be the last) time that all the Earth's continents were together. The continents are constantly moving, the Earth did not ",
" with Pangaea.",
"Here's the wikipedia article on supercontinents that has a list of ",
"major supercontinents",
" form Earth's history."
] |
[
"How did scientists look at the earth we have today and manage to deduce so many previous supercontinents with enough accuracy to name them? What evidence do they look for?"
] |
[
"Naming them doesn't require accuracy, just imagination. To answer your question properly though, the main source of information for reconstructing positions of past landmasses is palaeomagnetism. This is the same sort of geophysics which was used to prove sea-floor spreading and energise the whole plate tectonic revolution in the 60s, and yet some of the techniques remain sufficiently niche such that it is often referred to as 'palaeomagic' by many geologists. ",
"Put simply, palaeomag techniques make use of the fact that certain minerals will retain a record of the past direction of Earth's magnetic field. A preferred direction of growth for these certain minerals whilst in a weak magnetic field like the Earth's dictates the natural remanent magnetisation (NRM) for the rock area, which can be measured. ",
"The actual palaeomag techniques for determining all that are a bit beyond my explaining, but measurements can provide the three dimensional geometry (azimuth and inclination) as well as the intensity of magnetisation. Simple trigonometry applied to the inclination can determine the ",
" that the host rock formed in, though never the ",
". ",
"For reconstructing supercontinents older than Pangea, p-mag data must also be combined with field evidence and high-precision geochronology. Field evidence includes describing and mapping ancient sutures between continents welded together and previously separate terranes. Distributions of flora and fauna are also used to aid reconstructions.",
"Unsurprisingly, the further you go back in time, the ropier the reconstructions get, but this is mainly in terms of where exactly in the globe a supercontinent might have been, and the shape of the continental edges. The notion that they were all joined together at various times is (slightly) easier to prove with all of the above. "
] |
[
"Is it possible to create an \"icethrower\"? (Like a flamethrower but cold) Or are powers like that of Iceman impossible?"
] |
[
false
] | null |
[
"As opposed to heating radiation (infrared, for example) you cannot emit cooling radiation, which means that the only way to cool something is to throw a cold substance at it -- preferably one that goes through a phase change like liquid nitrogen or \"dry ice\" (frozen carbon dioxide) -- or to encase it in/surround it with an environment of low temperature (like a freezer).",
"The biggest problem is to keep whatever cooling substance you throw from absorbing too much heat before reaching its target. And the amount of cooling substance would be considerable too for anything bar the smallest objects.",
"So, no Iceman I'm afraid."
] |
[
"Well, sure. I mean, the basic principles of a flamethrower isn't that you're shooting 'heat', it's that you're firing flammable fluid that's ignited as it exits the weapon. Similarly, you could construct a weapon that fires a particulated cold substance, like liquid nitrogen or what have you. The problem, of course, being that most substances of that sort are going to rapidly vaporize or sublimate upon hitting air, particularly when rendered into a form that has a lot of surface area.",
"I don't know enough about cold substances to suggest something that would work better, though."
] |
[
"without the aid of a freezing chemical like liquid nitrogen.",
"Well, since you're comparing the concept to a flamethrower, remember that flamethrowers ",
" work by shooting a burning fluid (usually a liquid fuel in military flamethrowers, though civilian versions for de-icing and such commonly use propane)."
] |
[
"Is raw cookie dough actually dangerous?"
] |
[
false
] |
Ok, I understand the raw ingredients being unsafe to eat, but c'mon, who doesn't love buying tubes of cookie dough and going to town? Is it actually really harmful? Or is it just a kind of disclaimer incase the slim chance of getting harmed from it happens?
|
[
"it's a disclaimer of sorts. One of the ingredients of cookie dough as you undoubtedly know is eggs. eggs are a known carrier of salmonella bacteria and you could contract a salmonella infection from a raw egg. cooking eggs kills the bacteria and so cooking the cookie dough effectively eliminates the chances of you picking up the infection"
] |
[
"Wow. That means if I eat a raw egg every day of my life, and I'm lucky enough to live 80 years, I will eat one contaminated egg in my lifetime.",
"I'll play those odds. Pass the cookie dough.",
"maths:\n2.3 million contaminated eggs in 69 billion total eggs = 1 in 30,000 eggs is contaminated. There are almost 30,000 days over 80 years."
] |
[
"From Wikipedia:",
"A study by the U.S. Department of Agriculture in 2002 (Risk Analysis April 2002 22(2):203-18) suggests the problem is not as prevalent as once thought. It showed that of the 69 billion eggs produced annually, only 2.3 million are contaminated with Salmonella—equivalent to just one in every 30,000 eggs—thus showing Salmonella infection is quite rarely induced by eggs. ",
"So you will probably be fine, but it's an unnecessary gamble."
] |
[
"How does a spinning object “know” it’s spinning?"
] |
[
false
] |
I’m confused about rotating frames of reference. I get that there is no universal frame of reference and thus no universal definition of what is moving and what is not. However, acceleration is universal but requires energy. So I’m confused about a rotating frame of reference. If you have a wheel spinning in space how does it “know” it is spinning and not that the space around it is spinning instead and the wheel is still? It seems to work like acceleration but with no energy input, how does that work? This might be very complicated but I’ve been wondering about it. Thanks!
|
[
"The laws of physics have to be modified in non-inertial frames, and that leads to experimentally observable differences between inertial and non-inertial frames.",
"An inertial frame is one in which Newton's first law holds (an object at rest with remain at rest, and an object in motion will remain in motion with constant velocity). If you run an experiment and find that Newton's first law is violated, then you've shown that your lab frame is non-inertial.",
"Specifically, to test whether your frame is rotating, you could try to observe the effects of centrifugal or Coriolis forces.",
"An example of this would be the Earth itself, which rotates about its own axis once per day. So a frame of reference fixed with respect to the surface of the Earth is not inertial. And one way to experimentally prove that is with a ",
"Foucault pendulum",
". The pendulum precesses due to the Coriolis force."
] |
[
"It depends on how precisely you're able to measure things. When you get up and walk around, you don't feel a Coriolis force acting on you. And if you were to stand at the equator and at one of the poles, you wouldn't be able to sense the tiny difference in your effective weight due to the centrifugal force. But with a very precise scale, you could measure the difference.",
"If you had extremely precise instruments, you could in principle detect the corrections due to the revolution of the Earth around the sun, and the revolution of our solar system around the center of the galaxy, etc.",
"Those effects are extremely small. So the fact that they're very hard to measure also means that they're not significant for most intents and purposes."
] |
[
"but how would you attempt to find the most \"stationary\" object in the Universe.",
"Relativity says that that doesn't exist."
] |
[
"Is the total number of possible Calabi Yau space's expected to be finite?"
] |
[
false
] |
In my (armchair physicist style) education about string theory, I've heard that the number of possible Calabi Yau manifolds quickly grew to an unmanageable quantity. Mathematically speaking is it possible that there is an infinite amount of them? Or do we have reason to believe that there is a limited set of possible shapes these curled up dimensions can take? Thanks!
|
[
"All tori are one (complex) dimensional Calabi-Yau manifolds, and there are infinitely many tori, so there are infinitely many Calabi-Yau manifolds. This is from ",
"wiki",
". ",
"I think the frear is over the number of ",
" or ",
" of Calabi-Yau manifolds, and I don't know the answer to that question."
] |
[
"To my understanding, they are the curled up shapes that the dimensions themselves take. The dimensions being the degrees of freedom in which the strings vibrate. ",
"It gets very hard to describe what a dimension IS exactly, as it's not like little blobs of something. The extra dimensions aren't placed IN our universe, they are PART of the universe in the same way our large scale 3 dimensions are (theoretically)"
] |
[
"To expand your answer. These extra dimensions are presumabley no different then x, y, or z, or, left or right. There are just additional ones. We experience them somewhat like ants do in a 2-dimensional ant farm, except the glass panes are only separated by the planck length, they do not crush us, and there may be 5-12 of them. A lot of damage has been done to this concept by sci-fi \"alternate dimensions\". ",
"http://www.protozoic.com/content/images/0905/ants1full.jpg"
] |
[
"Why does a pressure decrease in a liquid phase (propellor in water) cause vapour to form, while a pressure decrease in a gaseous phase (propellor in air) sometimes cause water droplets/ice to form?"
] |
[
false
] |
In an attempt to answer 's question in post, I ran into what seems to be a contradiction. I can explain why a decrease in pressure under water causes cavitation, and (with some help from google, my thermodynamics has apparently become a bit rusty) I can explain why a decrease in pressure in air causes a temperature drop, and therefore causes water droplets/ice particles to form. However, when I ask myself what the most important difference is between these two situations, why a drop in pressure has opposite consequences in these systems, I can't really come up with something reasonable. Below is my original response to , which I've removed because my grasp of the matter isn't all that great, and that really doesn't put me in a position to explain it to others. well, cavitation is specific for liquids, the pressure difference causes "cavities" in the liquid phase. (pressure is very low. So low in fact, that the water there would rather be a gas. ). The condensation is similar to cavitation in that it is caused by a low pressure area (caused by the propellor). The time that it takes to form these low pressure regions is very short. Because of this, the low pressure air doesn't have time to attract heat from it's surroundings, meaning that it also cools down very quickly (which is called an adiabatic process). When we look at the phase diagram again, we can see that a drop in temperature will cause the water vapour in the air to want to be either a liquid or a solid, which is what you see.
|
[
"This is a great question.",
"I think part of the cause of your confusion is that in the case of the water cavitation problem, you're talking about basically pure water, so the phase diagram of water tells you what you need to know - at constant temperature, a pressure drop gets you water vapor.",
"When a fluid accelerates, it lowers the temperature of the flow. The first law of thermodynamics (conservation of energy) in 1D along a streamline without heat addition tells you",
"h_1 + 1/2 u_1^2 = h_2 + 1/2 u_2^2\n",
"where 1 and 2 are two points in the flow, h is enthalpy, and u is velocity. h=CpT, where Cp is the specific heat of the fluid in question and T is the temperature. Water has a 4 times higher heat capacity than air, so this means that increasing the speed of an air flow will result in 4x larger temperature change than the same speed change in water. When this temperature drops past the dew point, you get condensation."
] |
[
"I think it can be thought of this way: a pressure decrease in a liquid allows the liquid to boil/vaporize. The part you're having trouble with seems to be water/ice precipitating from depressurized air. The water vapor condenses when it gets below the \"triple point,\" right? So as the air pressure drops, I'd imagine the ",
" humidity goes to 100%, and precipitation would occur. The air itself is still gaseous though. ",
"Does that make sense? "
] |
[
"The air expands and therefore cools as a result of the lower pressure. Liquid water doesn't. That's what the difference is. So the expansion of the air follows a line on that phase diagram that goes down and to the left (but nearly horizontally - look at the scale of the y-axis), but the expansion of the water follows a line on that phase diagram that goes essentially vertically. That's why expansion of the air moves from a vapor region into a liquid region, but expansion of the water moves from a liquid region into a vapor region.",
"e: Actually, the water in the air isn't even in a vapor region to begin with - those phase diagrams don't show the effect of/allow for relative humidity or anything, they're for bulk samples of water, and water alone. You can still think of it that way if it helps you understand the principle though."
] |
[
"How can matter enter a black hole?"
] |
[
false
] |
[deleted]
|
[
"If we drop a clock in a black hole and observe it from distance, the time shown on the clock would slow down until it reaches the horizon, where it would freeze. ",
"This part is correct. The object would then gradually get redshifted until it's no longer visible and eventually detectable. ",
"So from the clock's perspective, the whole time of the external universe(?) would pass before it enters that black hole. ",
"That part isn't true. For an observer falling into a black hole, nothing spectacular would happen when crossing the horizon. Time would pass at the normal rate (as it always does in your own frame of reference) and the universe would look much the way it did before you crossed the horizon. "
] |
[
"Also, the infalling observer sees only a finite history of the universe, contrary to the very incorrect but popular \"they see the entire history of the universe sped up in an instant\"."
] |
[
"Time is relative, every observer experience time to be flowing at a normal rate for themselves, but will see other objects as going faster or slower through time depending on their velocity (special relativity) or acceleration (general relativity) "
] |
[
"If the earth travels at roughly 30 K/ph, or just above mach 88, why doesn’t it seem to make a sound?"
] |
[
false
] |
Exactly as the title implies, if the earth is traveling at mach 88, why isn’t everything blown out of the atmosphere by a massive sonic boom? Why are we able to accurately launch objects into and out of orbit? I get that sound doesn’t travel in a vacuum, but why isn’t sound generated in atmosphere by this movement? As an extension, why isn’t our atmosphere shaped more like the tail of a comet than a sphere? EDIT: I messed up the title, it’s KPS not KPH.
|
[
"It's not technically correct to say that the earth travels \"at 30 km/s\" because speed isn't an absolute quantity. Speed is always relative to something else. When you say a car drives at 100km/h, really we mean that the car moves at 100km/h compared to the ground. If you're driving in your car on the motorway going at 100km/h (compared to the ground) and another car overtakes you at 105km/h (compared to the ground) it's exactly as valid to say that other car is moving 5km/h (compared to you). And from your perspective, that's exactly what it looks like, the car slowly comes up to you from behind and then slowly moves away again in front.",
"This is a very important part of physics: In the universe there is no perspective that is more fundamental than any other. It's all relative to something else. (and this is what the Theory of Relativity is named for!) ",
"And that's great, because, as you've said, the earth is moving very quickly (compared to the sun), and it's moving even more quickly (compared to the centre of the galaxy) but since it's practically not moving at all (compared to us) we don't fall off. Another way of looking at that is that both us and the earth are moving at the same speed.",
"Of course the reason the earth isn't really moving (compared to us) is that we're gravitationally stuck to it. The atmosphere isn't moving much (compared to the earth) for the exact same reason that we're not moving much (compared to the earth): we're gravitationally stuck to it. In other words, the atmosphere is travelling with us. It's the same reason you don't feel wind in a car when the windows are shut, the air is travelling with you.",
"And that's also the reason we're not getting a sonic boom: The earth may be moving quickly (compared to the sun), but the earth is not moving quickly at all (compared to the atmosphere). A sonic boom happens when an object moves through a gas faster than the speed of sound in the gas. But the earth isn't really moving through the atmosphere at all! The earth is stationary (compared to the atmosphere).",
"If instead the atmosphere was stationary compared to the sun, then the earth would be moving very fast indeed through the atmosphere, and there would be a collossal sonic boom shockwave, as well at colossal frction heat, mach 88 winds, and general apocalypse."
] |
[
"Nebulae are still incredibly low density structures - they will contain fewer atoms per unit volume than the best vacuums attainable by human technology. So it doesn't really make sense to talk about them having sonic booms.",
"There are structures that look a bit like the ",
"shockwaves that form behind a supersonic object",
", but these are formed by electromagnetic interactions between ionised material in the gas and magnetic fields "
] |
[
"They are much denser than the volume around them, but that is still an extremely good vacuum."
] |
[
"With increasing medical treatments for birth defects and genetic illnesses, are we effectively nullifying Darwin's 'survival of the fittest'?"
] |
[
false
] | null |
[
"\"Survival of the fittest\" is a bit of a mis-characterization of natural selection. It's those who are best able to adapt and therefor reproduce who influence the direction of the species. ",
"That said, not it will not. We're continuing to evolve as humans. We may be evolving differently than we would without modern medicine and the like, but we'll still evolve as each generation selects for different traits. "
] |
[
"So what you're saying is, because we have the ability to fix any undesirable traits, we're effectively driving our own evolution?"
] |
[
"To some extent, perhaps, though I don't think we have a deep enough knowledge to figure out how we'll evolve in response to our actions in each generation."
] |
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