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[
"AskScience FAQ Friday!"
] |
[
false
] |
Welcome to , our new weekly feature highlighting some of the most frequently asked questions on ! We'll be posting a different FAQ each week and opening up the thread for follow-up questions and discussion. We're starting things off with an astronomy question: One of the most common misconceptions about the expanding Universe is that the expansion is an effect that fills up all of space, and the only reason the Moon isn't expanding away from the Earth is because gravity "overcomes" the expansion force. This isn't right. For the most part, the expansion is effectively due to inertia. The Universe somehow got a "kick" around the time of the Big Bang - we don't understand how yet because we don't understand physics at those times, but it must have happened - and the Universe was left expanding ever since, simply because there was nothing to stop it from doing so. As Newton taught us, an object in motion will stay in motion unless acted upon by an external force. Just the same, an expanding Universe will keep expanding unless a force acts on it. The only relevant force in this picture is gravity - or, at very small scales, the other fundamental forces - so for most of our Universe's history, it expanded at a decreasing rate. In less prosaic terms, the galaxies in the Universe flew away from each other, but they slowed down over time because of their mutual gravitational attraction. All this is to say that if a part of the Universe is a bit denser than the rest, it will expand more slowly, until its gravity forces the expansion to reverse and collapse. This is how the structure in our Universe - galaxies and clusters of galaxies - formed. Of course, once they've collapsed, they're no longer expanding. There is no residual expansion force inside them, trying to pull things apart. One of my favorite analogies is to imagine throwing a bunch of balls up in the air, at slightly varying speeds. The ones thrown up at the slowest speeds will fall down while the other balls are still climbing in the air. Are those falling balls still affected by some "upward force," even once they've crashed back to the ground? Of course not! Just so, there's no (or negligible) expansion left over in parts of the Universe which have collapsed to form structures. There is one important exception to this. The expansion of the Universe is currently accelerating, rather than slowing down. This is likely due to a "dark energy," or even a modification of gravity itself, which leads to repulsive gravity at extremely large distances. Whatever this is, whether modified gravity or dark energy, it is present on small scales as well, because it permeates space evenly. However, it is only noticeable at the very largest distances in the observable Universe: within our own cluster of galaxies, it has essentially no effect. Thanks to for this answer. Some similar questions and food for thought: What have been wondering about the expansion of the universe? We will be here to discuss any follow-up questions below! As always, the apply. Thank you for being part of the AskScience community!
|
[
"How does accelerating expansion fit into this? That would seem to imply that there is actually some \"upward force\" pushing things apart?"
] |
[
"Not really. The main thing I wanted to get across with this answer was that space isn't expanding everywhere, only \"overcome\" by other forces. If you're in a region where the Universe isn't expanding, there's no expansion, period, just like a ball that was thrown in the air and fell back to the ground isn't trying to go back up.",
"Put another way, the expansion of the Universe makes sense on the largest distance scales, where we can talk about different collapsed (non-expanding) regions moving away from each other. On smaller scales, it applies less and less."
] |
[
"Are the fundamental forces what keeps matter from expanding along with space?"
] |
[
"Why is hot water \"cloudy\" in the glass but becomes clearer as it cools down?"
] |
[
false
] | null |
[
"It has to do with the solubility of gases in the water. Hot water has a lower gas solubility than cold water, so when you take cold water that is saturated with gas, then heat it up, the gas will come out of the solution, making a cloudy appearance to the water.",
"As the temperature drops, the solubility increases, and the gasses can reabsorb in the water (or some of them have simply diffused out of the water and into the atmosphere.",
"Here is a graph that shows the relationship between the solubility of Nitrogen in water as a function of temperature",
"Conversely, if you wanted to make some very pretty and clear ice that an ice sculpter could use, you would boil the water and then freeze it. Almost all of the gas will leave the water due to the low solubility of gas in water, and when you freeze it, there will be no entrapped gasses and the ice will become clear and beautiful. It will also not \"crack\" when you put it into a glass of room temperature water/soda/whatever, as the \"cracking\" of ice is the entrapped gas bubbles (which is why ice you make usually is cloudy in appearance) expanding due to higher temperatures and cracking the ice."
] |
[
"Thanks!"
] |
[
"I suppose that is at one atmosphere, at 78% composition. If I interpret that correctly, a liter of water at 4°C is about a one molar solution of N",
". That's interesting considering that in its gaseous form, it would occupy a space about 23 times greater."
] |
[
"Specific minimum distance for a 1s electron?"
] |
[
false
] |
I know, I know; this is a shameful gap in my knowledge as an upper division science student, but I couldn't immediately come up with the answer, and my notes from gen chem contained little that I didn't think would be tested (a pox on younger me). I realize the mean radius of a 1s orbital will be stupidly small, but is there some hard measurement in angstroms for say, a hydrogen's electron lower bound?
|
[
"If I'm getting what you're saying correctly, the electrons (s orbital ones) can exist anywhere that isn't entirely occupied by the mass of protons and neutrons, with no repulsion from spaces close to it otherwise?",
"Well, technically the S, P, D and so on orbitals are only approximations that we get by ignoring the existence of the nucleus, replacing it with a static Coulombic potential centered at the origin.",
"Are you using neighborhood in the topological sense?",
"Yes. For any such orbital, the probability density is non-negative and not identically zero in any (topological) neighborhood of the origin. Thus, when you integrate over such a neighborhood to determine the probability of locating the electron there, the result will be nonzero."
] |
[
"There is no lower bound.",
"In any orbital, the probability of finding the electron in any neighborhood of the origin is nonzero. In the non-S orbitals the probability density ",
" the origin is zero, but for the S orbitals even that is positive."
] |
[
"Electrons and protons can actually occupy the same space, because they're different particles. Kind of counterintuitive.",
"It's actually possible for the electron to get \"captured\" by the proton and produce a neutron and a neutrino, but I'm unaware if this has been observed in plain hydrogen."
] |
[
"Is there any way to measure the intensity of an emotional experience?"
] |
[
false
] |
I can compare two experiences, say looking at a painting and eating a meal, and say that I enjoyed both but preferred one over the other. Is there a way to measure this enjoyment? Furthermore, are there some emotions that we are able to better measure than others?
|
[
"It's a difficult question. Emotional intensity depends on many factors. If you're lost in the woods, a kind stranger with a map and a GPS can elicit very intense emotions in one. The same stranger passing you on the street probably wouldn't even be noticed by you at all. So we could say that desperation or need is sort of like an emotional spring. Which means that in order to measure emotional intensity, we would have to find a way to measure the extent to which this \"emotional spring\" is loaded.",
" could potentially act as a neural correlate of this, given its properties. According to the reward-prediction error (RPE) model of dopamine, dopamine signals the discrepancy between expected and actual reward. \"Reward\" is a pretty loosely defined term in this tradition, however. $10 is a good reward for a homeless man, but not worth even the effort of reaching out your hands for someone like Bill Gates. So it's obvious that \"reward\" must be a subjective thing, and that it must depend on your needs and wants. Which means that it works out to be a pretty good proxy for the \"loadedness\" of your \"emotional spring\".",
"But we shouldn't neglect other neuromodulators, such as ",
" (norepinephrine for you pesky Americans). Noradrenaline signals surprise/novelty in terms of your sensory stream as compared with your prior beliefs. The locus coeruleus-noradrenaline system is, essentially, an adaptive gain system that tells you whether what's happening right now is strange enough to warrant your full attention. Very high levels of noradrenaline corresponds to intense focus and attention, which can serve to boost emotional intensity.",
"Noradrenaline levels can be measured by pupillometry, given that levels of noradrenaline correspond to pupil dilation when illumination levels have been controlled for. Measuring dopamine levels would be a bit more difficult, I assume. However, I've heard that dopamine levels can be measured via spontaneous eyeblink rates, so perhaps you could measure both just by measuring the eyes.",
"According to folk psychology, we can read people's emotions by looking into their eyes--the windows of our souls. And neurobiological research seems to back up this intuitive idea. Which is a bit surprising.",
"Of course, there are other substrates that should be mentioned (like serotonin, for instance), but I think I'll stick with these two.",
"Aston-Jones, G., & Cohen, J. D. (2005). AN INTEGRATIVE THEORY OF LOCUS COERULEUS-NOREPINEPHRINE FUNCTION: Adaptive Gain and Optimal Performance. ",
", ",
"(1), 403–450. ",
"https://doi.org/10.1146/annurev.neuro.28.061604.135709",
"Bouret, S., & Sara, S. J. (2005). Network reset: a simplified overarching theory of locus coeruleus noradrenaline function. ",
", ",
"(11), 574–582. ",
"https://doi.org/10.1016/j.tins.2005.09.002",
" ",
"Predictive Reward Signal of Dopamine Neurons | Journal of Neurophysiology. (2010). Retrieved July 30, 2020, from Journal of Neurophysiology website: ",
"https://journals.physiology.org/doi/full/10.1152/jn.1998.80.1.1",
" ",
"Taylor, J. R., Elsworth, J. D., Lawrence, M. S., Sladek, J. R., Roth, R. H., & Redmond, D. E. (1999). Spontaneous Blink Rates Correlate with Dopamine Levels in the Caudate Nucleus of MPTP-Treated Monkeys. ",
", ",
"(1), 214–220. ",
"https://doi.org/10.1006/exnr.1999.7093",
" ",
"Preuschoff, K. (2011). Pupil dilation signals surprise: evidence for noradrenaline’s role in decision making. ",
", ",
". ",
"https://doi.org/10.3389/fnins.2011.00115",
" "
] |
[
"Well, with science we can measure dopamine and oxytocin. ",
"Non verbal cues- flushing, widened pupils, faster breathing. Would Indicate excitement/arousal. \nMeanwhile- fear and sadness have subtle facial movements and eye reactions/eye movement. ",
"Check out body language. Most of human communication is non verbal and we are emotional creatures. Or ,watch YouTube reaction videos without the sound on. It provides lots of insight."
] |
[
"It's a huge area of debate, and it will depend heavily on the emotion you're discussing. For example: ",
"Some people argue that discrete emotions (e.g. happy, sad, angry, afraid) don't even really exist. Other people argue pretty much all emotions are discrete and definable. Some people are in between, and think some of the more \"basic\" emotions like fear definitely exist, because of their very clear expression on virtually every measure, but are more skeptical of ones like happiness that seem more subjective."
] |
[
"When did \"sleeping\" evolve? What are the most primitive organisms that we know of that sleep?"
] |
[
false
] |
Was reading an askreddit thread about "weird and common things" and sleeping is brought up. It still seems so strange to me that organisms evolved the need for sleep. For one thing it makes us completely vulnerable to predators. Do we have any idea when this habit first appeared in the evolutionary timeline?
|
[
"Tangent question, is sleep what evolved or the state of being awake? As in, did multicellular organisms first evolve to walk around, eat, reproduce, then sleep and recover.. or did they evolve to stay in a neutral state then get up, eat, and reproduce? "
] |
[
"Sure! Most organisms contain circadian clocks. This allows them to keep approximately 24-hour time even in the absence of any environmental time cues. Ordinarily circadian clocks are synchronized to environmental time cues, such as light/dark or temperature cycles.",
"Circadian clocks time everything from gene expression to hormone release to when to feel tired and go to sleep. They are also why it takes several days to transition to a new time zone (jet-lag) or to a new schedule.",
"Generally it is advantageous for an organism to have a circadian clock that can be synchronized to the day length because it allows the organism to anticipate changes in the environment (e.g., it can predict when energy will be available). This advantage in terms of evolutionary fitness has been demonstrated in both ",
"cyanobacteria",
" and ",
"mice",
".",
"The mechanism that generates the clock differs between species. In mammals the clock involves complex feedback loops between genes and their translated proteins. In cyanobacteria, it's a simple chemical feedback loop between three proteins and ATP that can be generated in a test tube with no cells."
] |
[
"Probably neither. Organisms evolved circadian (and possibly other) rhythms first, so there was never a uniform pattern of cellular activity across the day in multicellular organisms."
] |
[
"Are the \"Three Laws of Robotics\" something that will actually be applied to AI in the future?"
] |
[
false
] |
If so, what are the chances that it will work forever?
|
[
"Those laws are very flawed, and don't answer how to deal with moral conflicts.",
"Which, I believe, was the whole point of the series."
] |
[
"This question is essentially unanswerable, because we don't know enough about what true AI would be like, if we were able to create it.",
"Nevertheless, I think the answer you're looking for is 'maybe, but only incidentally'. There's nothing particularly special about the laws as a way of protecting humans - wikipedia even has a handy section on the available ambiguities and loopholes. If we wanted to create an AI with limitations embodying the spirit of the three laws, it's hard to imagine a situation where we wouldn't have to be much more elaborate and precise about what we needed. Again, of course, this runs into the problem of understanding exactly what an AI would be."
] |
[
"Those laws are very flawed, and don't answer how to deal with moral conflicts.",
"They would not be used by any practical AI designer."
] |
[
"Would the Moon be a good location for a telescope?"
] |
[
false
] |
Would there be any benefit to building a telescope on solid ground versus floating through space? Would the Moon's atmosphere be enough to have any effect?
|
[
"Not only possible but has been ",
"suggested",
" that robotic landers deploy such a thing. It is likely that it will not only be desirable to have radio telescopes on the Moon at some point but it may actually become necessary. The far side of the Moon is likely to soon become the only place we can be free of radio frequency interference that already prevents us from observing a great number of galaxies and other sources. This is likely to get far worse as we become more and more a wireless society."
] |
[
"I can think of several disadvantages of a lunar scope vs a space-based telescope:",
"A lunar scope has to land and deploy on the moon, adding significant cost and risk.",
"The moon blocks half of the sky. This is also a problem for LEO telescopes and the Earth (Hubble) and is one of the reasons why The Webb telescope is at a Lagrange point far from earth.",
"It's daytime for something like 14 days at a time on the moon, except for weird places like at the poles. Conversley, it's also nighttime for a long time when you most need power for your scope operations. I'm guessing this would require large batteries or the use of a nuclear battery, adding complexity."
] |
[
"Wouldn't dust be a problem?"
] |
[
"Does the weight of food have any bearing on its caloric density?"
] |
[
false
] |
Like the title says, obviously there isn't necessarily a clear '1 kg of food = X calories', as it's easy to come up with a counter example. However, is there relationship there? I have a hard time imagining a 1000 calorie bit of semi-dense foam (think like a 100 cm3 cube of foam?), but I can imagine eating a (comparatively) heavy 100 cm3 cube of butter or something similar that might contain 1000 calories. UPDATE: In light of the answers to the original question (thanks everyone, good insights all around!) a quick follow up, is there a maximum amount of calories that a piece of food can contain for a particular density? Is it strictly limited by the size of a molecule of fat/etc. ?
|
[
"Not entirely but it does happen often that heavy, dense foods tend to have more calories than light foods mainly because most light foods have water in them. For instance 5oz of chicken breast is about 230 calories. 5oz of broccoli is around 50 calories. Same weight, big calorie difference. "
] |
[
"I think you mean cubic centimeters (cm3). Trying to visualize the question. In some ways weight can correlate with calories just by suggesting a higher density. A lot of the highest calorie foods will be dense with sugars or fats like your butter example. However foods can also be dense with water and plant fiber and be relatively low in calories (celery, lean meats, grapes).",
"",
"Edit: the lean meats probably isn't the best example. But it is still less calorie dense than butter and foods high in oils or sugar."
] |
[
"It depends on the compositions and how much of it is digest able. Some foods are full of water like cucumbers, and they don’t have much calories. A price of bacon is almost all fat with little water, which makes it more energy dense "
] |
[
"Can our brain know what time it is while we're asleep?"
] |
[
false
] |
Is our biological clock aware of the solar clock?
|
[
"Yes! Each cell has a set of specific genes which are transcribed and/or translated rhythmically. For most people, each cycle takes about ~24.3 hours. This coincides with day length and is known as your body's circadian period. As it's slightly longer than 24 hours your body needs to keep re-adjusting to changing day length (if you kept cycling at 24.3 hours you would eventually be waking up naturally later and later until you are out of sync with everything around you).",
"To keep in sync with the external environment your body clocks entrain to the solar clock as you said. To prevent too much information, you have a master circadian clock in the suprachiasmatic nucleus (the SCN) which is a structure in your hypothalamus coordinating all of your peripheral body clocks in each cell. The action of the SCN is directly controlled by light. ",
"Thus, for a quick answer, your body cells are an orchestra and the SCN is a conductor keeping them in check. Each cell knows what time they think it is and runs accordingly, but the solar clock is used to keep re-adjusting the actions of each cell to match the changing external environment."
] |
[
"Right, so that's actually a very difficult question. In essence, the main control genes which are activated by light actually promote lots of downstream effects in different cells and tissues. The SCN is a collection of cells and so it communicates as other nerve cells do (i.e. deplolarisation or neuronal firing). The SCN neurons project to many regions of the brain, and the effects could range from inducing gene expression to promoting release of signalling molecules to promote the production and release of hormones. So the SCN communicates primarily 'electrically' but the output of that electrical impulse can affect the target cells in many different ways"
] |
[
"Also the stream of information isn't 'constant' in that sense. Seeing light in the morning will entrain you to your external environment, but it only takes that one instance of light (assuming it is of moderate intensity and duration) to let your body know it is awake at the correct time. The SCN is actually very interesting because the whole process of circadian gene DNA transcription, translation and then protein degradation takes ~24h. But for circadian hormones (such as melatonin, the hormone of darkness produced by the pine gland) to peak at the correct time (2 am) the pineal needs to be running 12 hours behind the SCN. So really, there isn't a constant stream of information from the outside, but your individual cells may see it as a constant stream as the signal from the SCN may take a very long time to reach its target. ",
"Edit: pineal gland"
] |
[
"Why does the combusting side of a log segment into squares? Also, elementally speaking, what is the white ash that remains?"
] |
[
false
] | null |
[
"It doesn't segment into squares. It segments into rectangles. This seems like a bit of a nit-pick, but it's important. The reason is the grain of the wood. The longitudinal (along the length of the log) splits are due to the grain breaking open.",
"After this has occurred, and as the structural integrity of the wood starts to break down, existing stresses in the wood cause segments to start contracting. Once the contraction exceeds the strain allowed in the lateral direction, the wood will snap. This will generate the lateral segmentations.",
"TL;DR - Longitudinal splits are from the grain of the wood, lateral splits are from the longitudinal columns breaking."
] |
[
"The chemical composition of ash varies depending on what was in the wood, as you might expect. ",
"This article",
" shows that the elemental content of the ash of several types of wood or bark is primarily calcium, potassium, and magnesium, plus lower amounts of other elements (document page number 111). The actual compounds formed varied, but calcium carbonate was the primary compound detected using x-ray diffraction in the ash from lower temperature combustion. ",
"I don't have a good answer to your first question. Anyone else? "
] |
[
"In fact, potassium was first isolated (and then named) from potash- the ashes of plant matter.",
"As ",
"/u/ArcFurnace",
" mentioned, carbonates are formed during low temperature combustion... CaCO3 being the primary component. But at higher temperatures, you will drive off carbon dioxide and be left with CaO. "
] |
[
"Why does hematite exist in gray and red varieties?"
] |
[
false
] |
I'd assume that the red variety is oxidized/rusting (ie, Fe2+), but wikipedia lists hematite as being Fe(III)2O3, ie, not oxidized/rusting and therefore gray. Does the red variety only exist when the hematite crystal comes into contact with oxygen to make it rust? Or am I completely off track on this?
|
[
"First off, you have it backwards: ferric iron (Fe3+) is ",
" oxidized than ferrous iron (Fe2+). Oxidation is the ",
" of electrons, so when ferrous iron is oxidized to ferric, its oxidation state goes from +2 to +3: ",
"+2 - (-1) = +3 ",
"Likewise, when ferric iron is ",
" (gains electrons), it forms ferrous iron:",
"+3 + (-1) = +2",
"As for color, hematite looks the reddest in rocks when present in small quantities. Large chunks of hematite tend to resemble pewter. Consider the dark coloration of ",
"Meridiani Planum",
", a hematite-rich plain on Mars, in contrast with the more common, relatively hematite-poor (and therefore reddish) Martian soil. "
] |
[
"Thanks for the answer and the clarification of oxidation/reduction."
] |
[
"While I'm not entirely sure of the exact reason for haemetite (I'm guessing it's different crystal structure), many materials have two or more structures that are stable under normal conditions. The first examples I can think of are carbon, phosphorus and sulphur. Carbon has graphite and diamond (and others), phosphorus has white and red (and others) and sulphur has many allotropes too.."
] |
[
"If the gravitational attraction between the sun and the moon is greater than between the earth and the moon, why isn't the moon in independent orbit around the sun?"
] |
[
false
] |
The Sun's gravitational pull on the Moon is over twice as great as the Earth's pull on the Moon I think the answer has something to do with , but my physics intuition on centripetal acceleration isn't working for me right now..
|
[
"The moon ",
" orbiting the sun, with the Earth, which is experiencing the ",
" acceleration (more or less) as the moon, so they move together.",
"If the Earth weren't here, the moon would look like it was orbiting the sun, just wobbling a lot.",
"EDIT: Remember, ",
" the Earth and the moon are falling towards the sun ",
" Relative to each other, they're not moving much from this."
] |
[
"You should be looking at the acceleration, not the force.",
"The force is less on the moon, but the moon also has less inertia. These two factors neatly balance out to give the same acceleration. This is for the exact same reason that two objects of different weights fall to earth at the same rate.",
"As Kepler discovered the orbital distance only depends on how fast you are going - your orbital velocity. Mass doesn't factor into the equation."
] |
[
"The moon's orbit around the sun is everywhere-convex, so you could argue that the moon is orbiting independently around the sun. The slightly lesser pull between the earth and the moon keep the two together."
] |
[
"I know our cells use ATP and GTP for hydrolysis and other energy needs. Why don't cells use cytidine triphosphate or thiamine triphosphate as much as the other two classic triphosphate nucleotides?"
] |
[
false
] | null |
[
"Mainly because there was never any selecting pressure to do so. Evoluton of bioenergetic sustems is a very complex process; ATP:ADP concentration have to be kept far far far far away from chemicsl equilibrium otherwise delta G would be 0 and you could not extract energy."
] |
[
"Thank you for your answer! If you don't mind me asking a follow up question; do our cells maintain ATP concentrations beyond random diffusion? Do our cells have a gradient in certain regions of the cell? If so how do they accomplish this?"
] |
[
"Yes they do; they can change the local concentrations of ATP when it is required. For instance, in filopodia or during developmental growth cones, ATP is required at these edges of the cell for cytoskeletal dynamics that are occurring. That's just one example, but even in an apparently \"non-active\" cell there is not just a uniform level of ATP everywhere. This paper found a depletion of ATP in the mitochondrial matrix relative to cytoplasm.",
"http://www.pnas.org/content/106/37/15651.full",
"A few other papers have looked at similar concepts using imaging and show that, in response to some stimulation, subcellular ATP patterns change.",
"http://www.nature.com/srep/2014/141006/srep06522/full/srep06522.html",
"\n",
"http://www.sciencedirect.com/science/article/pii/0014482787902370"
] |
[
"How do we know the interaction rate of neutrinos? (Light-year of lead, etc)"
] |
[
false
] |
An oft-cited scientific fact is that a solid block of lead one light-year in length would only stop half the neutrinos that are to pass through it. How do we know this? We can only detect particles by interacting with them, right? So how do we know if the particles are there or not if only 50% of them interact? How do we know that it isn't just 5% that interact and 95% pass through? Given that we can't make a block of lead that large, how can we make meaningful measurements on a laboratory scale? How did CERN make a neutrino detector? How do they know that the neutrinos they detected came from their experiment (as opposed to random neutrinos flying by from elsewhere in the universe)? I'm an engineer and I've taken graduate level quantum mechanics and solid state physics, so feel free to use (a little) jargon while explaining.
|
[
"How do we know this? We can only detect particles by interacting with them, right? ",
"Sort of; you can also detect missing particles from missing energy/momentum using known conservation laws. You know beta decay (neutron decays to proton and electron and a neutrino) right? If you try to exclude the neutrino, you can't get experiment to jive with conservation of energy/momentum. Basically, if you had n -> p + e; you have that the momentum of the proton and electron are equal and opposite; and the energy of the electron and proton solely arises from the mass difference (M_n - (M_e + M_p))c",
" ~ 782 keV. Thus two independent equations and two unknowns (magnitude of the velocity of each particle), so you would predict that beta decay must occur at the same velocities (unless there's a third particle), but that's not what experiments showed. You can also analyze by looking at how there's missing angular momentum. So Pauli in the 1930s first came up with neutrinos to carry off the necessary angular momentum; it wasn't until nuclear reactors came about that we could create intense enough beams of neutrinos to detect them. ",
"So how do we know if the particles are there or not if only 50% of them interact? How do we know that it isn't just 5% that interact and 95% pass through? Given that we can't make a block of lead that large, how can we make meaningful measurements on a laboratory scale?",
"Rather than measuring the attenuation coefficient directly; you count the number of interactions from a very intense beam. Neutrinos interacting with individual nucleons (particles in the nucleus). If alpha (the attenuation coefficient is about 10",
" then if you shoot through a beam with say 10",
" neutrinos into a deep 10m water pool (with detectors that can detect the specific reactions expected), you should be able to detect roughly ~100000 distinct events. ",
"How do they know that the neutrinos they detected came from their experiment (as opposed to random neutrinos flying by from elsewhere in the universe)?",
"Statistics. You measure the background rate when the neutrino beam is off; you subtract this averaged rate from your expected signal. You do simulations and complicated analyses so while any particular event may be noise from some other source, you can say with strong statistical confidence that your result is true.",
"It should be noted that electroweak theory (and the measurements of the W and Z bosons) allows you to predict these interaction rates."
] |
[
"So how is this rectified with the recent OPERA experiment showing that neutrinos move faster than the speed of light?",
"By saying the OPERA result is probably wrong. "
] |
[
"You can calculate the probability amplitude of a neutrino interacting with another particle or material (based on its density) via the weak force (since neutrinos have no charge and don't interact with the strong force). That is all. It's a probability, with a degree of certainty one can say that there will be 50% on the other end of block of lead but yes, there very well can be 70% or 90% but in the large scale test it will tend towards 50% or whatever the probability is.",
"EDIT: grammar"
] |
[
"Why does ethyl alcohol evaporate out of your beer/wine/booze so slowly?"
] |
[
false
] |
[deleted]
|
[
"Alcohol and water aren't an ideal solution, but the general principle of ",
"Raoult's Law",
" applies to your question. Here's a two-part explanation. Skip the first part if you already understand vapor pressure.",
"A liquid will evaporate until enough of it is in the vapor that the vapor and liquid are in equilibrium. The relationship is given by the vapor pressure of the liquid (varies with temperature). For example, for water at 25 C (room temp) has a vapor pressure of ",
"3.2 kPa",
". Atmospheric pressure is about 101 kPa, so at equilibrium, the air above at container of water will have about (3.2/101) 3% water by mole fraction.",
"If you mix two liquids, then the each contributes to the vapor pressure in proportion to how much (mole fraction) of each liquid there is. That's Raoult's Law. So if you have 25% (mole fraction) alcohol and 75% water, then you get only 25% of the alcohol's vapor pressure. Pure ethanol at 25 C is about 8 kPa. A 25% mixture would only have a partial vapor pressure of ethanol around 2 kPa and would evaporate 4 times slower than pure alcohol. So yes, beer will lose its ethanol slower than liquor.",
"A couple things to remember, alcohol and water don't actually form an ideal mixture and the vapor pressures don't combine proportionally, but it's close enough to answer your question. Also, alcohol is listed as %alcohol by volume, which is different than mole fraction. You have to convert in a calculation similar to ",
"this one",
".",
" Ethanol will evaporate more slowly from beer (lower alcohol%) than liquor because the vapor pressure of ethanol is lower above the beer. "
] |
[
"Ethanol will evaporate more quickly than water, but in an ethanol-water solution, the ethanol and water will interact and this will slow it's evaporation compared to pure ethanol."
] |
[
"Yes. Below answer is related to why.",
"Edit: This is why 160 proof liquor smells like liquor. What is happening is that the azeotrope discussed below can be broken down thermally(randomly), and the ethanol molecule can go into the gas phase if it has enough energy. The more ethanol molecules you have relative to water molecules, the higher your partial pressure of ethanol above the drink will be.",
"Double edit: This is also why vodka is often served ice cold. It lowers the partial pressure of the ethanol, which will evaporate from solution and find its way to your olfactory nerves, making for a less pleasant drink. (Also, impurities in the alcohol are much more damaging (or beneficial, depending) to the flavor than the ethanol itself, and follow the same behavior)."
] |
[
"Is Sugar in the Raw really healthier than normal sugar?"
] |
[
false
] |
I never understood the difference between the two. I know sugar in the raw "contains more natural minerals" that are removed when it is refined to white sugar.
|
[
"\"contains more natural minerals\"",
"The term \"natural\" is a bit loaded. The connotation implies that it's more wholesome or good for you (because nature is always good right?), but the truth is most minerals are naturally occurring and that has no bearing on whether they're good for you or not.",
"From what I can find raw sugar is virtually the same as regular sugar just with some molasses.",
"Raw sugar is regular sugar which is less processed, which means ",
" There are some nutritional benefits to molasses: it's got some minerals and a bit of vitamin B6. Eat a tablespoon of molasses, and you'll get 20% of your iron.",
" There's so little of anything else in it that the packets declare it \"Not a significant source of calories from fat, saturated fat, cholesterol, dietary fiber, vitamin A, vitamin C, calcium and iron.\" That's why it tastes like sugar, with a slight molasses-y tang, rather than like molasses.",
"Found that here : ",
"http://askville.amazon.com/RAW-SUGAR-health-benefits-raw-sugar/AnswerViewer.do?requestId=7528359"
] |
[
"\"natural\" is beyond loaded, it's a false distinction."
] |
[
"To speak to that fact:",
"Mercury is mostly inert (unless refined) but still all natural.",
"Lava is all natural.",
"Horse hair is all natural.",
"Oleander is all natural.",
"None of these are good for you and are at best, unpalatable.",
"EDIT: Snake venom is all natural."
] |
[
"What would the perception of time be like to a person who could live forever?"
] |
[
false
] | null |
[
"This is a hypothetical that, I feel, reaches beyond the scope of ",
"r/askscience",
". Too much speculation is needed. ",
"/r/transhuman",
" might be a better place to ask."
] |
[
"I don't feel it's too hypothetical. I'm sure at some point in the future, thanks to medical breakthroughs, certain people will be able to live to be 150 if not 200 years old. "
] |
[
"I agree that average life expectancy is tending to increase and that long life times are quite likely in the near-ish future. However, the issue of how those lives will be experienced is another matter.",
"However, I had taken on the idea of 'immortal' lives and used that as the basis for suggesting it was speculative. A mere couple of hundred years is much more amenable to extrapolation from current experience.",
"I agree that time tends to telescope as you have more past to compare things to (and habits form such that there is a relative decrease in variation of experience). However, in the moment, time is still experienced much the same irrespective of age. As such, I would place a distinction between perception of grand flow of time (years) and the perception of immediate time (seconds, minutes and hours)."
] |
[
"Why are bubbles always spherical when blown?"
] |
[
false
] |
Whenever bubbles are blown, they appear to always be in a spherical shape of different sizes. Why not cubes or other shapes?
|
[
"There are primarily two forces to consider: pressure and surface tension. There is an outward force due to the difference in pressure between the inside and outside of the bubble, and there is an inward force due to surface tension.",
"The force due to the pressure gradient is trying to increase the volume but the force of surface tension is trying to decrease the surface area. These forces reach equilibrium at the shape which minimizes the surface area for a given volume: the sphere."
] |
[
"Similar processes are why planets are spherical, free floating cells are spherical, and why oil in water is spherical!"
] |
[
"You can see the push and pull of this if you blow a really big bubble. The film of soap and water doesn't start out perfectly even in thickness and so it doesn't e wet a perfectly even force against the air pressure. This makes the bubble oddly shaped and it will become more and more spherical until it gets there, pops, or wind acts to deform the shape in a different way."
] |
[
"Can we, given today's technological llmitations, passively refridgerate/cool something indefinitely? If not, how long can we make it last?"
] |
[
false
] |
I think I'm phrasing it correctly, but if not, what I mean is: Could we currently create a powerless cooler or thermos that would keep something cold indefinitely?
|
[
"Cold is a relative term. For instance, we can passively cool buildings. Westinghouse claims their new AP1000 nuclear reactor can passively cool the core for 72 hours; after which is just need a top up. ",
"If you can put something in a sufficient cold environment, this would help (maybe space?).",
"All-in-all, the Second Law of Thermodynamics is going to answer your question with a no. Due to Thermalization, it is impossible to keep something indefinitely \"cooler\" than it's environment. ",
"Edit: In regards to your second question, you want to look into ",
"R-Values",
". R-50 seems to be the highest value I could find. You can find commercially available stuff in the 40s. "
] |
[
"This was a much more informative answer than I expected, thank you!"
] |
[
"From your description, you seem to be asking if we can create a perfect insulator, a material that will not transfer heat between an object and its surroundings.",
"The answer to that is no. There will always be some heat transfer."
] |
[
"Are humans the only species with (nearly/seemingly) unrestricted hair growth, in terms of length?"
] |
[
false
] |
It seems like most animals either have fur or short hair. Hair seems pretty uncommon as it is, much less the ability to grow super long hair. Since other animals don't seem to have the ability to cut their hair, I would assume it would be a noticeable trait. Maybe not?
|
[
"All hairs grow in cycles typically described in 3 stages; Anagen, Catagen and Telogen.",
"The Anagen phase is the growth phase, the length a hair grows to is determined by the length of the anagen phase for that particular type of hair follicle. ",
"In the Catagen phase the follicle detaches from the hair root and the hair stops growing. ",
"After Catagen the follicle enters the telogen or resting phase where no new hair is produced. If the hair falls out (which it will) the follicle remains \"empty\" until the new anagen phase begins. This phases usually last about 2 or 3 months in humans.",
"This continuous cycle gives the impression that the hair in most places is somewhat static but in fact it is continually cycling but never getting longer than it's anagen phase will allow.",
"The anagen phase is different for different follicles on different parts of your body. Hair grows at about an eight of an inch a week so you can roughly estimate the anagen phase for most types of hair that isn't being shaved or cut. My arms hairs are all roughly about 3/4 of an inch so they likely grow for about 7 weeks. Cat hairs are about 1 to 2 inches longs, so likely somewhere near 2 months of growth. Human head hair on the other hand has a very, very long anagen phase, and has an anagen phase of up to about 6 years.",
"It's really not clear why human head hair grows for so long. The usual evolutionary reason is that any physical trait that appears to offer no immediate selection advantage AND is costly to maintain (requires an amount of food/resources) probably has some sexual selection reason for existing. The peacock's tail is one classic example and perhaps human head hair has a similar purpose."
] |
[
"Horses can have pretty impressive manes and tails. ",
"http://arabianhorselovers.webs.com/andalucion.jpg",
" ",
"http://www.horsenation.com/wp-content/uploads/2013/04/guiness-record-longest-horse-tail.jpg",
" ",
"http://www.horsenation.com/wp-content/uploads/2013/04/longest-horse-mane-tail.jpg",
" ",
"http://www.horsenation.com/2013/04/15/12-freakingly-long-manes-andor-tails/",
"There are also some other animals with long hair - I'm not sure whether their hair stops growing or just breaks off or gets worn off when it gets too long. ",
"http://3.bp.blogspot.com/-Ezb6J0AUOdo/Tf5kJD5C9vI/AAAAAAAAAkQ/w0eQIx0yRF8/s1600/bovine%2B01%2B-%2Byak%2B05.jpg",
" ",
"http://nursemyra.files.wordpress.com/2011/10/gradient-goat.jpg",
"Also, in the case of \"woolly\" animals like sheep or alpacas, the hairs might be as long, but because they're curly you can't normally see that. ",
"http://static-l3.blogcritics.org/10/11/01/147597/sheep.jpg",
" ",
"http://bioweb.uwlax.edu/bio203/s2012/sanderfo_ange/Unshorn_alpaca_grazing.jpg",
" ",
"Or I guess sometimes you can - ",
"http://roughfellsheep.co.uk/images/rough_fell_sheep~AP-YKI1DD-TH.jpg",
" "
] |
[
"Interesting that all of the examples of animals with extremely long hair have been subject to artificial selection. Horses are a really cool example because ",
"wild horses",
" have short manes whereas ",
"feral horses",
" grow these crazy dreadlocks that usually end up getting ripped out after a year or so."
] |
[
"[ASTRONOMY] Did galaxies form at roughly the same time throughout the observable universe?"
] |
[
false
] |
The farthest observed galaxy is 13.2 billion light years away. This puts it's formation at around 480 million years after the big bang. The Milky Way (to my understanding) is estimated to be 13.2 - 13.4 billion years old. Does this mean that the energy that coelesced into the matter that formed the galaxies was spread throughout the universe in a relative instant? Was this due to expansion of space itself (faster than the speed of light?) How can galaxies be around the same age, yet be 13.2 billion light years away from eachother? Sorry for so many questions, this has been on my mind for a while.
|
[
"Great question! The universe is isotropic, meaning that it looks relatively the same no matter where you look in the sky. This means that on large scales, there will not be a particular area of space that has older galaxies than another area of space. So, many of the oldest galaxies are spread out.",
"The Big Bang did not start at a set point in space nor time. Space is expanding in all directions. The ",
"Hubble Constant",
" shows that space appears to expand faster the farther away an object is. Galaxies that are 13.2 billion light years away from us now were not always so far. The primordial matter from the Big Bang spread out with the expansion of space, as is still happening, so yes it was due to the expansion of space. Galaxies themselves however, coalesced because of gravity. Simulations show that ",
"dark matter",
" forms a large web-like structure, and where the large nodes of the web are, galaxies will form. This happened all over the universe over a period of a few billion years, so not all galaxies are the same age. In fact, galaxies are still forming, especially from ",
"galactic mergers",
". Hope that helps!"
] |
[
"galaxies are where they are because of dark matter. dark matter is the primary source of gravity, so any normal matter clumps according to the dark matter distribution."
] |
[
"Wow thanks for the great answer. It finally \"clicked!\""
] |
[
"If a made-up food had the texture, smell and look of a normal strawberry, but had the taste of a banana, would my mind blend the flavors together to make it seem like strawberry-banana?"
] |
[
false
] | null |
[
"Yes, but only because of the smell. You can only taste a few basic tastes (sweet, sour, bitter, salty and that mythical umami) with your tongue, the complexities of food come from smell. Classic example? Food tastes all kinds of dull when you're stuffed up.",
"Try this: take a bite of strawberry and hold a stick of chocolate under your nose. You end up with something that vaguely tastes like chocolate covered strawberries."
] |
[
"There's noting mythical about umami"
] |
[
"A \"savoury\" flavour. (soy sauce as an example.)\nIt is the flavour of MSG."
] |
[
"What was the first commercial device to use strong encryption?"
] |
[
false
] |
Was it the AT&T TSD 3600? And is that why the NSA was so panicky in implementing the clipper chip into this device? Before this device were all commercial telecommunications open to being wire tapped by law enforcement agencies? Sorry for all the questions, just trying to understand. Thanks in advance.
|
[
"How do you define strong encryption?",
"The enigma machine used pretty damn strong encryption in the 1940's - although it was probably not what you would consider a \"commercial\" machine - even though 40000 were made."
] |
[
"IIRC early basic versions of the enigma were sold commercially. I’m on mobile but I’ll try and find a link."
] |
[
"There were other products for secure telephone before, but the TSD 3600 was the first widely available one. There were other commercial encryption products before, particularly the Enigma, which was originally designed for the commercial market to secure telegrams. ",
"Describing the NSA as \"panicky\" is overstating it a bit. During the development process, AT&T approached the US government about it, who raised concerns that it would interfere with the ability to wiretap telephone calls subject to a subpoena (this concern was the beginning of what we're still seeing today with regards to government concerns with end-to-end encryption).",
"AT&T cooperated with the government in developing the Clipper chip, but AT&T really misjudged the market. The TSD 3600 was $1000 in 1982, which is the equivalent of $2600 today. While law enforcement could wiretap telephone calls, the process was relatively cumbersome at the time, and the mass intercept of data wasn't even remotely feasible. Telegrams in the early 20th Century presented some unique security challenges, but in the 1990s, unencrypted telephone and fax communication was \"secure enough\" for commercial purposes."
] |
[
"If a drug or vaccine fails an animal trial, how can scientists be certain that it will similarly fail a human trial, given the different physiologies between species?"
] |
[
false
] |
Scientists often use mice to test for drugs and vaccines, but we know that not all successes in rodent trials translate to successes in human trials due to the different physiology between species. But what about the reverse? Could there be drugs that might have worked in humans but weren’t successful in rodent trials and were therefore never pursued further?
|
[
"This is a great question. The answer is not trivial, but essentially researchers typically know how conserved a drug target is among different species and use this information to predict whether the same outcomes would be likely to be observed in rodents, and primates/ humans. ",
"The use of computational biology to predict differences among species has been a game changer in this regard. Because of the cost and effort involved in the drug discovery process, most projects run through many possible scenarios virtually before they even start to order materials. Things like divergence in the target among species would be flagged from the beginning and would be addressed in the planning documents. ",
"Another way to address this potential issue is to use human or humanized tissue in the mouse. For example, human cancer tumors can be transplanted into mice and then the anti cancer drug is given to see if the tumor shrinks. ",
"Source: work in the drug discovery field"
] |
[
"Could there be drugs that might have worked in humans but weren’t successful in rodent trials and were therefore never pursued further?",
"Yes, but the research path is also usually not totally linear. To get to a drug which can be used in a human there is frequently a lot of optimization, or would otherwise be a rare find in nature, and would probably be tested in a number of animal models. In different diseases, our animal models vary substantially in how well they replicate the disease and model drug response. There will also be differences between animal models depending on what aspects of the disease they model and/or how disease is induced (e.g. we don't know what causes Alzheimer's so the models are both poorly predictive and very diverse in nature). The upshot is that animal models are ",
" either very well validated and predictive of human outcomes, or very contrived and sensitive to treatment."
] |
[
"... Also, often when a drug gets all the way to animal trials and then fails, it will be because the animals die from the drug, get really sick, develop cancer etc. Surely, there could be species specific differences so that this wouldn't be the case in humans - but, ethically, you can't really move on to human trials with a drug that is deamed dangerous in smaller animals. And I don't think anyone would sign up for such a drug trial either."
] |
[
"Can we find complementary colors for non-visible wavelengths of light?"
] |
[
false
] | null |
[
"I love your question. The answer is probably the one cited by the Wikipedia quote on \"Primary colors\":",
"Primary colors are not a fundamental property of light but are often related to the physiological response of the eye to light. Fundamentally, light is a continuous spectrum of the wavelengths that can be detected by the human eye, an infinite-dimensional stimulus space.",
"Citation",
"The interpretation to make is that primary colors and complementary colors do not exist on their own -- instead they are a trick of the way our eyes see color. Since they don't come out of some mathematical or physical construct, such concepts will only work for light that humans can see.",
"TL;DR: No, complementary colors only exist for visible light."
] |
[
"This is only peripherally related, but there is a great ",
"podcast episode",
" of NPR's Radiolab that explores what it would be like to actually see a much broader spectrum of colors than humans are capable of seeing (being able to see what is currently outside the visible spectrum). Some animals see a much wider spectrum of light, and they use music to help visualize what it would be like to see as other animals do. "
] |
[
"Thanks! I thought that this might be true. If there ",
" primary colors for non-visible wavelengths of light, I assumed it would be because of a relation between complementary colors and their respective wavelengths. In the absence of said relationship, your response answer my question nicely. Again, thanks!"
] |
[
"A serious poop question."
] |
[
false
] | null |
[
"Your intestines will continue to absorb water from the fecal matter, making it denser and harder to pass. If you hold it long enough you may get ",
"impacted",
", and require medical help.",
"Unless you suffer from chronic constipation, or you've ingested a lot of something likely to ",
" constipation, I wouldn't worry too much about holding it for a reasonable time."
] |
[
"Eh. Unless you've got diarrhea, the water content of your poop isn't really significant. Better to get rid of it while you can, rather than add severe constipation on to the rest of your survival woes."
] |
[
"Eh. Unless you've got diarrhea, the water content of your poop isn't really significant. Better to get rid of it while you can, rather than add severe constipation on to the rest of your survival woes."
] |
[
"Is each neutron star a new \"element\" composed of a huge number of protons/neutrons?"
] |
[
false
] |
I am familiar with the element on the periodic table, and they go up to a certain atomic weight and then they are too big and fall apart (sorry for not knowing the right terminology for that). But I picture that black holes must have enough force to collapse the nuclei of neighboring molecules together to form new elements -- elements that are stunningly dense. Is this true or am I missing some huge piece of the picture?
|
[
"http://en.wikipedia.org/wiki/Neutronium"
] |
[
"False, neutron stars do have protons, but it's certainly not an even number, there are very few protons and a high number of neutrons, which most models predict.",
"Though we don't know for certain, we don't know much about neutron stars to begin with, other then what models suggest. Remember, we call them neutron stars because at those pressures models suggested they should be composed of neutrons, further models give a difference in layers and refine what most likely is the make-up of said star.",
"In the core, most likely neutrons don't exist, but a quark-gluon plasma.",
"http://en.wikipedia.org/wiki/File:Neutron_star_cross_section.svg"
] |
[
"Things become black holes when the Schwartzschild radius is bigger than the radius of the object."
] |
[
"Does temperature have any effect on Kinetic or potential energy?"
] |
[
false
] |
[deleted]
|
[
"Thermal energy is a different category from kinetic or potential energy. It is possible to trade one for the other (for instance, when you stop a ball, some of the kinetic energy becomes thermal energy due to friction).",
"Generally though, thermal is more distinct from kinetic + potential energy for reasons of scale. In the above example, the kinetic energy of a rolling ball gets converted to thermal energy as it slows down due to friction, but for all practical purposes the change of the ball's thermal energy virtually insignificant, it would take a really accurate thermometer to detect the change.",
"On the other hand it is very difficult to convert thermal energy into kinetic or potential energy, because of what's called entropy (things tend to move toward disorder, and thermal energy is more disorganized than kinetic energy).",
"So for most practical purposes when we talk about kinetic + potential energy we ignore thermal energy and vice versa."
] |
[
"If the ball exchanges heat with other objects (e.g. your 'templates'), then the ",
"internal energy",
" of the ball will change in proportion to the increase or decrease in its own temperature. The change in the ball's internal energy from the heat exchange with those hot or cold objects will not affect its mechanical potential energy or kinetic energy to a first approximation. Some mechanical perturbations on its trajectory might accompany the heat exchange, depending on the exact mechanism, but these would normally be small effects."
] |
[
"To a first approximation and for most temperatures, the temperature will make no effect. However, generally when gas is heated or cooled it expands/contracts, which makes it less/more dense (pV ~ NkT for medium-high gas temperatures), and therefore there is less/more resistance to an object traveling through it. It does not ",
" to change density, as you can add gas or change its pressure to compensate, but usually that is the effect of changing the temperature. ",
"A similar effect will happen to the ball, to a smaller degree, as cooling or heating the ball will cause it to contract/expand, increasing its profile and therefore its drag coefficient. ",
"A ",
" smaller effect is that when you heat the ball, you will increase its mass ever so slightly by E = mc",
" , which means that it will be ever so slightly more resistant to aerodynamic drag than it would be classically, ",
" it were not for the fact that heating the ball causes it to expand and increase its drag coefficient.",
"For most temperatures, however, these effects are minor. If you could keep the surrounding gas density constant, then you would not notice any significant effect on the trajectory of the ball, as the magnitude of the typical velocities of the gas particles are much higher than the velocity of the ball, and so temperature plays a negligible effect on drag.",
"The exception to this is if the surrounding gas is ",
" cold, as then the velocity of the ball becomes comparable to that of the surrounding gas, and the equations governing the drag on the ball will not be the same. "
] |
[
"If every pore in your skin was completely cleaned out would your skin have any noticeable change? How much stuff would be taken out?"
] |
[
false
] | null |
[
"Your pores routinely produce protective oils and secretions which protect your skin and allow helpful microbes to live on your skin surface which reduce the chances of harmful micro organisms from taking residence. The result of the cleaning would only be very temporary as your body is always producing secretions. I'm sure the visual appearence would be no different than any dry skin you've observed on yourself before. You may be at some minor increased risk of infections if your entire body surface was stipped of this. Applying a moisturizer to combat your now dry skin without your body oils only traps water from contacting your dry skin instead of retaining it like they work. Visually though, I don't see what benefit you may be looking for besides better defined pores? Removing all the sloughed skin cells only reveals them more. It's only a visual distraction in my opinion when they are blocked or heavily soiled with dirt or makeup."
] |
[
"It's not up to the mods to discredit bad science; that's your job if you know it. Simply calling someone out without offering a counter view is quite useless."
] |
[
"It's not up to the mods to discredit bad science; that's your job if you know it. Simply calling someone out without offering a counter view is quite useless."
] |
[
"If you fill a perfectly sealed diamond box with water and froze it would it break?"
] |
[
false
] |
If you fully filled a diamond box with water, then froze it what would happen? Would the water not turn to ice? Would the box break? EDIT: Im saying as if hypothetically the water just appeared inside of a hollow diamond.
|
[
"You're constraining the volume of the system. If the diamond box (note - diamond is actually pretty brittle) didn't break, then you'd be balancing the temperature of the water against the increasing pressure due to the water/ice phase change. As the water starts to freeze, then the pressure increases, making it more difficult for the rest of the water to freeze.",
"Whether or not the diamond would break would depend on a lot of other factors; the thickness of the diamond, the internal volume of water, the degree of supercooling...."
] |
[
"Depends on the rate of cooling because ice has several different crystalline structures and can become amorphous. Also how many atmospheres of pressure could build inside the diamond before it breaks as some types of crystalline structures have a higher density than normal ice."
] |
[
"Interesting answer about the pressure exerted by expanding ice ",
"here",
":",
"If you completely freeze the ice it expands 9%. If you try to SQUEEZE the ice back down to the original size, you would need to push with a pressure of about 790 megapascals of force. (8,800,000,000*0.09) That is about 114,000 pounds per square inch, and is a simple estimate of the pressure that ice could exert when it freezes, under ideal conditions. ",
"Now, this estimate is not actually correct because in the process of freezing under pressure, these high pressures can transform the ice into type 3 or 5, and it is difficult to know what will exactly happen."
] |
[
"If there were no day/night and only the same light level outside, how long would humans be awake for and sleep?"
] |
[
false
] |
I remember something like this was asked before, but could't find the post.
|
[
"/u/whatthefat",
" gave a lot of good answers to sleep related questions in the past",
"see, for example:",
"http://www.reddit.com/r/askscience/comments/1amf7t/is_sleep_only_an_evolutionary_byproduct_of_the/c8z7phx",
"http://www.reddit.com/r/askscience/comments/1day1r/is_our_circadian_rythm_fixed_is_it_possible_to/",
"http://www.reddit.com/r/askscience/comments/1ooufd/do_astronauts_aboard_the_iss_still_have_an/"
] |
[
"Doesn't blue-ish light inhibit melatonin production? (ie. Don't you need light to stop making melatonin during the day?) I'd assume that if you only ever had blue light you'd have sleep issues..."
] |
[
"Doesn't blue-ish light inhibit melatonin production? (ie. Don't you need light to stop making melatonin during the day?) I'd assume that if you only ever had blue light you'd have sleep issues..."
] |
[
"How can pain relievers like ibuprofen sometimes eliminate pain when all they really address is the sensitivity of nociceptors after tissue damage, not the nociceptive response to noxious stimuli in the first place?"
] |
[
false
] |
It seems like this would just keep the pain from getting worse by inhibiting the production of prostaglandins and keeping the nociceptive threshold normal, not relieve the pain present at the normal threshold being caused by the underlying stimulus. Is it because ibuprofen also inhibits the production of prostaglandins that result in inflammation, and inflammation is the underlying pain stimulus that's being eliminated? If that's the case, is ibuprofen unable to relieve pain that isn't caused by inflammation?
|
[
"One of the prostaglandins produced by COX is PGE2. This prostaglandin doesn’t just cause pain, it ",
" the skin to pain. By blocking the production of this prostaglandin, NSAIDs raise the threshold for pain, effectively removing it. "
] |
[
"It doesn't raise the threshold ",
" much. Better off just taking some opioids and numbing yourself up entirely"
] |
[
"It doesn't raise the threshold ",
" much. Better off just taking some opioids and numbing yourself up entirely"
] |
[
"Why are some viruses more difficult to make vaccines for?"
] |
[
false
] |
[deleted]
|
[
"It doesn't work for all viruses because all viruses are unique. ",
"HIV for example undergoes very rapid mutations and also infects CD4+ cells. This means for HIV you could have a vaccine that eliminates one subset of HIV particles but allows the thousands of other subsets to preset. Additionally because it infects CD4+ cells (these cells are what stimulate B-cells to produce antibodies) the amount of antibodies produced is drastically reduced eventually causing AIDS.",
"Comparing HSV and Varicella zoster (the causative agent of chickenpox) is much better. This is because both of these viruses are part of the herpesviridae family. So why do we have a vaccine for Varicella but not HSV? Well, this is what is still trying to be answered and we are getting closer. I recommend you read this ",
"paper.",
" Essentially they differ slightly in genes they have at their disposal, differ slightly in outer surface proteins and also differ in the infection course that they follow. Just those few differences are enough to cause a problem for vaccine development. Also of note, an HSV vaccine has just passed safety trails in humans meaning in 5-10 years there possible could be a successful HSV vaccine on the market.",
"As for your next question vaccines are not cures. In medicine there are 3 types of care. Prophylactic (pre-treatment) which is vaccines. Curative, which is actually curing the problem, for example penicillin is a cure for syphilis. And lastly Palliative which is essentially reducing pain and disease symptoms without actually getting rid of the cause.",
"Hope that helps somewhat. ",
"Edit: I should mention there are another subset of vaccines termed 'therapeutic vaccines.' These vaccines are made and intended to be 'cures' but to my knowledge there hasn't been a bonified therapeutic vaccine demonstrated only some that have been demonstrated to prolong life slightly putting them more in the palliative care designation. "
] |
[
"A very simple way of conceptualizing what the heck a vaccine is is in this way:",
"Picture a car. On its surface it has different contours (windshield wiper, bumper, etc.). Now, imagine a big human cell that sort of attaches itself to, say, the bumper. It's really good at recognizing the bumper, and so it goes around attaching to bumpers.",
"That's essentially what happens in the immune system. A virus, with a given shape, floats around and one of our immune cells attaches itself to that virus. It recognizes a given pattern, called an ",
".",
"Some viruses are so sneaky that they're able to change their epitopes all the time. Or, there are SO MANY different types of that kind of virus (how many different Ford cars are there?) that even if you're really good at detecting one of them, you might not be so good at detecting that slightly different one.",
"That's why you get the common cold so often, by the way."
] |
[
"I like the other answer provided, but I do want to add on that you (OP) have a bit of a misconception about how vaccines work.",
"Vaccines do not technically introduce antibodies to your system. Vaccines contain one of three things: attenuated (weakened) live pathogens, dead pathogens, or pieces of pathogens. In all cases, the point is to introduce ",
" (immune stimulating \"things\"- can be carbohydrates, proteins, whatever- usually on the surface of the virus or bacteria) into the body. From there, the immune system can recognize the antigen as foreign and mount a response by producing antibodies and memory cells which persist for a long time afterwards. This is called ",
", and after sensitization subsequent encounters with the same antigen will result in a much stronger and more rapid immune response, hopefully killing the pathogen before it is able to establish an actual infection. The same thing happens naturally- once you have chicken pox you don't usually get it again (shingles notwithstanding), for example. Immunization just \"skips\" the first infection and takes you right to sensitization and protective immunity without the danger of actually having the illness.",
"Oh, and since you may ask- yes, viruses are not traditionally considered to be alive. For the purpose of vaccines, you may prefer the term \"non-infectious\" to describe dead viruses."
] |
[
"Is the erectile tissue in a penis found anywhere else (bodywise) in anything biological?"
] |
[
false
] |
Basically, is there a species out there that has erectile tissue somewhere in/on their body other than their penis? Or is it unique to the penis?
|
[
"Nasal turbinates. The maze of your sinuses is regulated by erectile structures that can block your nasal passages. They are responsible for a 'stuffy nose.'",
"Precisely how related the structures are is up for discussion. Nosebleeds and 'honeymoon rhinitis' are an uncommon effect of Viagra, which suggests some similarity.",
"Erectile penises are also present outside mammals, such as turtles. Turtle penises are remarkably similar despite apparently evolving independently. Perhaps the building blocks for erectile tissue can be found hidden in our amniote ancestors.",
"http://www.bioone.org/doi/abs/10.1093/icb/42.2.216?journalCode=icbi",
"\n",
"https://ir.library.oregonstate.edu/xmlui/handle/1957/35986",
"http://www.rsm.ac.uk/media/pr111.php"
] |
[
"The most notable example is the female clitoris which both contains erectile tissue and displays tumescence (erection) with arousal. This is understandable when your remember that the ",
"clitoris and the penis are homologous",
" and have a common embryologic origin.",
"Side note: The clitoris can even experience priapism (painful prolonged erection) similar to what you may have heard about in men during Viagra commercials."
] |
[
"does that mean that some decongestants could cause temporary impotence."
] |
[
"Can we replicate the process of making fossil fuels?"
] |
[
false
] |
Had a question asked by a fourth grader that got me thinking. I’m not concerned if it’s viable, economical, or practical. But theoretically could we replicate conditions over a period of time to create crude oil? What would be the rough requirements and timeframe to make this happen?
|
[
"Yes, and it's been done for quite a while, usually in the context of trying to understand the details of and controls on natural petroleum formation. There are hundreds of papers published on these types of experiments looking at different aspects of the system, for example here is one by ",
"Epistalie & Tissot, 1980",
", where they use ",
"pyrolysis",
" (i.e., heating organic material in an oxygen free environment, which is also a key part of natural petroleum production) experiments to test the role of the presence of different minerals on the formation of petroleum. Another interesting example is ",
"Saxby & Riley, 1984",
", where they point out that most of these types of experiments heat the organic materials up very quickly compared to what would happen in nature, so they ran experiments where they heated their samples up slowly over several years and were able to produce something very similar to certain types of natural petroleum. These examples are not meant to be exhaustive, but just to demonstrate that yes, we can experimentally produce petroleum by starting with similar materials and simulating similar conditions as would happen in natural petroleum forming systems.",
"As for the ingredients and conditions, you need (1) the right starting materials, i.e., certain types of organic matter will breakdown to produce ",
"kerogen",
" which in turn will break down to produce petroleum (e.g., ",
"Pepper & Corvi, 1995",
"), (2) the right chemical environment, i.e., presence or absence of certain elements and compounds seem to be important in petroleum formation (e.g., ",
"Lewan, 1998",
") and critical here is a lack of oxygen, and (3) the right temperature conditions as the thermal breakdown of original organic material to kerogen and its breakdown to petroleum all occur at specific temperatures and these temperatures depend on all of the above along with the rate of heating (e.g., ",
"di Primio et al., 2000",
", ",
"Schenk & Diekmann, 2004",
", and the Saxby & Riley paper from above, among many others). For the first, most of these experiments start with natural \"source rocks\", i.e., the types of rocks from which petroleum is formed in nature, and the most of the other conditions are relatively easy to achieve in a lab. As for the timeframe, this was already covered a bit above, but you can produce something like petroleum with much more rapid heating than what you'd see in nature (i.e., these experiments may take a few hours to a few weeks to run, generally), but as hinted at in several references, the details change as the heating rate changes.",
"Finally, as you suspect, these types of processes are not efficient or useful in a producing fuel sense (i.e., most of these experiments are probably putting more energy in than they would get out if they used this petroleum for fuel and are operating on very small quantities), but have been incredibly important for our understanding of petroleum forming environments."
] |
[
"Finally, as you suspect, these types of processes are not efficient or useful in a producing fuel sense (i.e., most of these experiments are probably putting more energy in than they would get out if they used this petroleum for fuel and are operating on very small quantities), but have been incredibly important for our understanding of petroleum forming environments.",
"These processes are being looked into for military purposes. Naval fleets use enormous amounts of diesel fuel and in the case of aircraft carriers also kerosene. Nuclear power plants that convert atmospheric CO2 or algae and other stuff floating in the ocean and seawater into hydrocarbon fuel would make carrier groups to be independent of supply lines to keep the support ships of the aircraft carrier redundant because enormous amounts of energy can be stored in a ship in the form of reactor grade uranium. Allowing decades worth of fuel to be transported with the ship or a jetfighter doing a supplyline with nuclear fuel sufficient to supply a carrier group of fuel.",
"We also have a fleet of vehicles like tractors, mining trucks, large planes and rockets that are very hard to electrify because of the energy they need to move and do useful work. Batteries can't replace a 1m3 diesel tank and carbon capture + synthetic fuel production is likely going to be the way how we power those vehicles in the future."
] |
[
"Do you know what the actual efficiency of those processes is in theory or practice though? Seems like you'd still run into the issue the previous poster mentioned.",
"Uranium has a energy density 1 000 000 times that of fossil fuels. Even if the process was 0.1% efficient you would be able to carry at least a 100 time more fuel with you. The military is will to pay the money for a technology like this because of strategic independence. Running out of fuel is a very bad thing when fighting a war.",
"We know how energy dense we can technically make batteries. The ideal situation would be a lithium air cell (40 MJ/Kg) and those reach the energy density of diesel(44 MJ/Kg). However that is far of future tech and technically burning lithium via a slow chemical reaction. We can't make those yet with current technology. We are going to be building skyscrapers with graphene before batteries like these are figured out and rechargeable. The best batteries we can currently make in a lab are around 2.5MJ/kg. Diesel with a 34% efficient gets us 15 MJ/Kg of useful energy. Lithium ion batteries get us 2MJ. That is a 7.5 times difference.",
"A large combine can use 70+ L of diesel fuel per hour. When harvesting they can be working 24 hours a day with a rotating crew and a fuel truck in the harvesting fleet.",
"70 L of diesel fuel with 15 MJ/L of usefull energy is around 1 GJ/hour. If we were working with battery packs of lithium ion batteries that we could plug in and out of the combine we would be changing a 5 ton battery every hour.",
"A tractor with a 1M3 fuel tank carries 1 metric ton of fuel with it. Plus 2 tons for engine + drivetrain. So 3 tons for the power infrastructure on a tractor. This is a 7-10 ton tractor in reality.",
"That tractor with a battery would carry 7.5 ton with 500 kg for engines, wires and everything else to drive the tractor would carry 8 tons of weight. This tractor would be 12-15 tons in reality. it would also need somewhere to put 6 m3 of battery.",
"When batteries hit 10 MJ/kg it might start to make sense to start using them to drive light tractors. Weight more however is a bad thing for a tractor as soil compacting lowers crop yields and farmers don't want that.",
"I am thus far skeptical that batteries are going to be used in heavy vehicles in the next 20 years. People really underestimate how much of a mobile powerplant a medium or large size tractor is."
] |
[
"Why does facial hair grow at different rates based where it is on the face?"
] |
[
false
] | null |
[
"Facial hair growth is dependent on androgen receptors specifically for dihydrotestosterone.",
"http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2265.1993.tb02420.x/abstract",
"This study shows beard hair follicles are largely comprised of dihydrotestosterone being that it is necessary for said growth. ",
"http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2265.1994.tb02483.x/pdf",
"This one shows different hair follicles having varying sensitivities to androgen is attributed to differential growth rates.",
"Hair growth treatments like minoxidil stimulate hair growth by increasing blood flow to targeted areas, and therefor increasing the amount of nutrients received at those points. There haven't been any clinical studies showing the effects on facial hair, but that is also an option to seek out to at least try to get \"mature\" hair follicle growth in targeted areas.",
"Blame it on the ge-ge-ge-ge-ge genetics, baby.",
"Edit: Corrected a speculation. Added citation for correction."
] |
[
"So this would explain why I've heard that people taking anabolics, even women have increased facial hair. Now is this caused only by increased dihydrotestosterone levels in the blood, or do some of the supplements increase the androgen receptor activity? "
] |
[
"I think the real question here is why does hair grow at uneven rates on any part of your body? I'm sure that Facial hair, body hair, and head hair are all plagued by this."
] |
[
"Members of the cat, dog, bear genus are common apex predators. What can you predict about a given environment by knowing the apex predator?"
] |
[
false
] | null |
[
"I'm still a student, but let me give some small insight on this. ",
"Apex predators can be keystone predators - meaning they exert an unequal influence on the trophic system. If they disappear, the whole system is severely damaged. But that's a different matter (but I recommend a ",
"book!",
")",
"Let's compare two keystone predators - bears and wolves - and the interactions they might have on deer populations. ",
"Wolves are pack hunters. They directly chase and take down their prey. Because of this, wolves choose some prey over others. A wolf pack might kill a straggler - a weak, older deer, or one with injuries. They might also go for a large prize, maybe a massive buck with a large rack that slows it down (damn you sexual selection!). ",
"The main takeaway is that ",
". Wolves aren't likely to select young over full adults - a major advantage of pack hunting is to take down large and difficult-to-catch prey, so they would be squandering that if they targeted the little ones. ",
"Bears, on the other hand, are ambush predators. They sit and they wait for something to encounter it (then they might stalk it). I think most big felids are this way too. Because of this, bears have a lower amount of choice in prey selection. You don't see bears chasing herds of elk across mountain valleys, or working in packs to cut off their unwary prey. They sit, and they wait, and then they maul. ",
"The impact of this is that less experienced prey ends up making the fatal mistake of walking into a grisly (grizzly? har har) death. It's usually young deer that wander a bit too far away from their mothers, or the starving young adult who is going into new territory to find food. ",
".",
"Think about the ecological impacts on a species from these two predation pressures. The death of an old/sick/injured deer is likely to not cause a lot of harm (note that it won't cause a lot of ",
" - not that it won't influence) to the population. That old deer isn't likely to produce any more children, and the sick or injured one is likely to die soon anyway, and probably wouldn't be selected to mate with. A large buck might be quickly replaced by other rivals following his death, and his children (his ",
") are still alive. ",
"The loss of children, on the other hand, has profound effects on population dynamics. A baby deer killed represents a complete loss in investment of the parents, and any possible chance of those genes being spread by that child. Not only has all the work you've put into raising your child go to waste, but all the missed opportunity costs (energy, time, more breeding). No genes will be passed on from all that work. A child will not increase a population via his offspring or his offsprings offspring. A dead elder killed by wolves might not produce any more children - but a dead child will result in the loss of potential offspring that compounds across generations. ",
"."
] |
[
"By knowing just the species of apex predator involved? Not too much by itself. Many ecosystems have historically had (for example) all three types in your example, and as whole clades these are very wide ranging groups over broad habitat and prey types. Maybe you'd learn something obvious if you knew them to species (\"hmm, random ecosystem X has 3 Arctic predators, we must be in the Arctic.\")",
"Now, if you know the ",
" of each relative type, you might start to learn something. The overall productivity of the ecosystem, or perhaps the type of dominant terrain for hunting over."
] |
[
"Truth is not much. You must first consider historical ranges and extinct species, because if you just looked at where apex predators are now the only thing it would likely correlate to is low human population density. Looking at this you would find large cats, pack-hunting canids, and largely omnivorous bears on every continent with the exception of Antarctica and Australia. Antarctica for obvious reasons and Australia for some less obvious reasons than you would think.",
"Within these groups it is possible to distinguish some environmental conditions, looking at things reversely rather than which species best occupy a niche in that environment. For instance lions, leopards, and cheetahs have historic ranges covering the majority of the African continent, with some obvious geological/biome barriers such as the Sahara and the dense rain forests in the middle of the continent that the three species are not as likely found. However within these species you have populations that have adapted to certain vegetation types, biomes, and terrains for instance most lions prefer savanna biomes, but there are those that inhabit and are adapted to desert, thicket, grassland and almost every biome in Africa because of there ability to hunt in prides. Cheetahs because of their cursorial hunting strategy only inhabit open vegetation types such as grassland, savanna, karoo. ",
"However mountain lions/cougar/panthers (whatever you choose to call them) in North America and the Puma in South America all all ambush predators that again are largely one species but are adapted hunters for all biome types with some exceptions (deserts largely due to lack of prey). Same is true for snow leopards, tigers, and other large cats that inhabit Asia. However again you have to look at historic ranges and extinct species. So North Africa and the middle east once largely contained lions, leopard, cheetah.",
"Grizzlies once ranged to the Mississippi and black bears almost all of north america both being largely herbivorous they are not restricted to prey densities. Brown bears once had ranges covering most of europe and asia. The atlas bear once inhabited parts of northern Africa and the middle east(not so much). The spectacled bear in SA, and the two pandas in parts of Asia that evolved in the herbivore direction. Wolves in once covered NA & parts of CA, Europe, Asia and hyenedaie were once prevalent world wide as well. Wild dogs once ranged throughout all of sub-sahara Africa. ",
"So no, I really don't think you can predict the environment which a certain apex predator inhabits, because even for individual species their ranges are massive and usually cover multiple vegetation types and biomes. This is because they are forms that are adaptable, few apex predators have narrow diets, they are able to move to new locations and find different prey. A prime example of this is that grizzly bears, which we think to be northern mountain bears that kill elk. But actually a large portion of their range was in the great plains and many were actually more adapted for open plains because of their large claws, which they used for digging up roots to eat (among other things). But with the expansion of human across the American great plains their range retreated to just the mountainous areas of North America and everyone thinks they are \"mountain bears\". But truly they aren't and if given the opportunity they will expand their range back into the plains (which we've seen and I've done work on). And there's really no bigger difference in environment than boreal and open grassland. "
] |
[
"What is it about grapefruit that interacts with some medications?"
] |
[
false
] | null |
[
"Grapefruits contain organic chemical compounds called furanocoumarins. these compounds affect the enzymes used by the body to metabolise many drugs in the body. Cytochrome p450 is a common enzyme used by the body to 'break-down' drugs and when preoccupied by the chemicals in grapefruit juice allow for drugs ingested to linger longer in the body, having possible undesirable effects, or unpredictable effects."
] |
[
"Seldane, a formerly popular allergy drug, would in extreme cases produce a toxic compound that killed a few people "
] |
[
"Yes, really. ",
"Ritonavir",
" is an HIV protease inhibitor that can be used to treat HIV on its own, but has severe side effects in therapeutic doses. However, it is an inhibitor of CYP450, just like grapefruit juice. It is now given in lower amounts along with other HIV drugs to boost their effects by blocking the CYP450 system that would normally break them down.",
"So in theory, but less practically, grapefruit juice could be used to the same effect."
] |
[
"Have there ever been any cryptozoological creatures that were later found to be real in the past couple centuries? Would the Panda count?"
] |
[
false
] |
As I understand it, Western civilization had never seen or come in contact with pandas until the early 20th century. There were cases of merchants selling panda fur in the 19th century, but I can't seem to find any information as to whether or not westerners usually assumed the animal to be real. Was the existence of pandas a subject of debate or skepticism in scientific circles shortly before they were confirmed? If so, I was also wondering if there were any other animals that might have been considered speculations or cryptozoological since the renaissance. I'm aware that there's pretty much no chance of bigfoot or Nessie being real, but are there any animals out there, that haven't been confirmed to exist, but are still plausible or probable? Sure, there may be tons of insects and fish, but anything larger? The only other creature that immediately comes to mind is the giant squid.
|
[
"The answer is a big \"it depends\".",
"On the one hand, you have tales of sea monsters, hairy wild men, and dragons from many cultures. Does the discovery of giant squid and whales, great apes, and dinosaur bone validate these tales, or is it mere coincidence.",
"On the other hand, you have things like the King Cheetah, first sited in the 1920's, but whose existence was subject to debate until photographed in the 1970's. So you have a creature that was doubted but later proven, but it hardly reaches legendary status.",
"Part of the problem is the cryptozoology isn't really a science, so there are no standards to go by. You have legendary creatures who vaguely resembles later discoveries (kraken -> giant squid), and you have exotic creatures the western world was skeptical about for a while, but turned out to be real (pandas, gorillas).",
"What you don't have is a well described legendary creature who very specifically matches a later discover. Or at least I am not aware of any. "
] |
[
"The platypus was for a couple years considered to be a hoax when the first pelts were sent back in 1798. They actually cut open the bill to make sure there were no stitches holding the insane looking animal together"
] |
[
"The Mountain Gorilla and ",
"Okapi",
" are both considered to be former cryptozoological creatures as I understand it"
] |
[
"What became of the star that supernova'd prior to the formation of Sol - is there any way we could locate its remnant?"
] |
[
false
] | null |
[
"Supernova remnants expand quickly - at thousands of km/s - and start to dissolve into the galactic background of gas after tens of thousands of years. This is quite quick, and much much younger than the age of the Sun, which is 5 billion years old. The supernova remnant is long gone, and we've orbited the Milky Way so many times since then that it wouldn't be anywhere near us anyway.",
"As a side note for clarification: you're correct that there was probably a supernova ",
" the formation of the Sun, which enriched the gas that the Sun formed from, and possibly triggered the collapse of the Sun's molecular cloud. However, there's sometimes a misconception that the Sun ",
" a supernova remnant, which is incorrect - the Sun formed from a molecular cloud, which is a massive (like a million times the mass of our Sun), dense, turbulent cloud, and a very different kind of object to a rapidly expanding (and low mass) supernova remnant."
] |
[
"Lots of supernovae, but the heavy elements get mixed into the galaxy's \"interstellar medium\" as a whole, and a molecular cloud condenses from that medium. It comes out the same as \"what tree produced the oxygen I'm breathing?\""
] |
[
"Wow, thanks for answer, but follow up question:",
"So I'm envisioning a molecular cloud somewhat akin to eagle nebula - dense, and high metallicity - where did all that metallicity come from, if not ",
", or perhaps several or many, prior supernovas?"
] |
[
"How does combustion power a rocket?"
] |
[
false
] | null |
[
"For the type of rocket that uses combustion at all, the combustion is what ",
" the exhaust gas that is being pushed out the back to make the thrust. There ",
" gas to be \"lit on fire\" until you ",
" that exhaust gas by burning the rocket's fuel.",
"The rocket has some burnable fuel which will be a solid or liquid(s). Burning the fuel turns it into a much larger volume of products, for 2 reasons:",
"So now you're generating huge volumes of hot gas ",
" from small volumes of solid or liquid fuel. The rocket is built strong so all that gas can't just explode in all directions - the only path available is out the nozzle at the back of the combustion chamber. ",
"Then, because of equal-and-opposite reactions, all the hot exhaust flying out the nozzle in one direction pushes the rocket in the opposite direction.",
"You absolutely can have a rocket with no combustion, think of the hobby rockets where you pump a bottle up with air pressure then release it. The air shoots out the nozzle and the bottle flies away. Rockets using combustion are doing the same thing, just using combustion to generate the compressed gas inside of them rather than a bike pump."
] |
[
"What is a propellor doing on the front of a plane if not acting like a compressor, pushing air backwards? Don't even need a nozzle or tank, that just adds complexity and extra steps (though, that's kinda what a jet engine is, I suppose...)"
] |
[
"No, the temperature itself helps as well. If a gas is hotter, the gas molecules themselves will be moving faster, which means that after expanding through the same pressure ratio, you get a faster-moving exhaust flow which gives a higher thrust.",
"For example, if you have nitrogen gas at 20 atm of pressure and room temperature, and expand that through an ideal nozzle to 1 atm of pressure, the exhaust jet will move at about 780 m/s. If the nitrogen gas is instead at 2000 K, with the same pressure ratio, the exhaust velocity will be about 2020 m/s."
] |
[
"Current vaccines are essentially a weakened virus/microbe. Is it possible to contaminate an other person with this weakened vaccine?"
] |
[
false
] | null |
[
"Yes, it is, but it depends both on the nature of vaccine and the immune system status of the person who is infected. Some vaccines are completely dead and are incapable of infecting anyone (there are exceptions to this but it would be an incredibly small possibility) and then there are live attenuated vaccines which are still living. These vaccines are no problem for a competent immune system to handle, however, if the person is immunocompromised, it is possible they could not mount a proper immune response to the vaccine and would become infected."
] |
[
"Not all current vaccines are weakened pathogens, although some are. The FluMist, oral rotavirus, and MMR vaccines are all what are called \"attenuated\" vaccines, which replicate in the host and induce strong immunity. In contrast, the flu shot, DTaP, pneumococcus are examples of \"inactivated\" vaccines, where the pathogen is treated to prevent replication.",
"Attenuated vaccines can and do spread between people, although it varies by vaccine. That is why you should not get the FluMist if you are around people on chemotherapy, since their immune system may be too weak to effectively prevent the weak virus from causing issues (potentially). In almost all cases, spread of attenuated vaccines causes no harm, and can actually help keep immunity levels high in a population. The risks of any complications are associated with other problems, typically a severely weakened immune system. In that situation, most people would still be better off with exposure to an attenuated form, rather than the truly dangerous pathogens that circulate in nature."
] |
[
"In the case of the live attenuated virus, they are infected with the same pathogen as was in the vaccine, it's weaker, but if the immune system isn't strong enough to eliminate the virus, it really is a moot point it was weakened in the first place.",
"As a side note, all vaccines could be said to \"weaken\" the immune system since while it's busy mounting an immune response to the vaccine it is more susceptible to other invading organisms. This is why people think they get the flu from the vaccine but instead they were just infected by some other bug."
] |
[
"When does one use \"data\" as singular or plural?"
] |
[
false
] | null |
[
"Singular in this case. ",
"More reading"
] |
[
"Data is in fact plural. The singular of data is datum. However, you almost never concern yourself with an individual datum, so data tends to be used as both the singular and plural. In your example, the strictly correct sentence would be",
"\"The data in this study were ....\"",
"but no one is going to care either way."
] |
[
"In that case it would be singular. You are defining the data as a single set belonging to the study. You should use \"was.\"",
"If you were referencing multiple sets of data which you were making a distinction between you would use were. Ex. \"The data from trials 1 and 2 were...\""
] |
[
"Does your brain absorb information while asleep?"
] |
[
false
] |
Does your brain absorb information while asleep Through listening does your brain feed that information into the subconscious? Has anyone tried this? Playing a lecture or a podcast but you fall asleep
|
[
"There are studies that have shown that reinforcing previously learned information is probably a real thing, but TMK actual sleep-",
", as in \"acquiring new information,\" is still much in doubt.",
"Your brain for sure processes information while you sleep, though, and many people (including me) find it helps with problem-solving and creativity."
] |
[
"www.livescience.com/amp/64920-how-learn-during-sleep.html",
"Not the paper in question that I read. But I dunno, take it for what it is."
] |
[
"www.livescience.com/amp/64920-how-learn-during-sleep.html",
"Not the paper in question that I read. But I dunno, take it for what it is."
] |
[
"Are the blackholes in center of galaxies formed by super gigantic stars?"
] |
[
false
] |
I understand that if a star is huge in mass it can form a blackhole and that at the center of the galaxy there is a blackhole. Does that mean that, for example at the center of the Milky Way, there was once a gigantic star that has collapsed? Or is it more likely that it was a blackhole that has simply gotten bigger over time. Wouldn't there be a threshold as well to as of how big a star can be before it becomes a black hole or is it simply just how much fuel it has?
|
[
"The black hole in the galactic centre (Sg A*) is far too massive to have formed from a single star (it is of the order of a few million solar masses, stars are rarely found above a hundred solar masses due to stability). Thus, it must have grown over time from coalescing black holes plus accreted matter.",
"This is actually a major area of research, because there is a 'missing link' stage in black hole growth between stellar mass black holes and supermassive black holes, which to date nobody has been able to find evidence for."
] |
[
"That is actually the astronomers' version of the chicken or the egg. Did the galaxy form first and the mass in the center collapsed to form a black hole, or did the black hole form first and the matter organized around it to form the galaxy. It is possible in the first moments after the big bang, there were some areas that were dense enough to form primordial black holes and these could have been the seeds for the galactic supermassive black holes.",
"http://en.wikipedia.org/wiki/Supermassive_black_hole"
] |
[
"Yeah, that was my own thought. I was thinking about how a nucleas becomes unstable once too big and wonder whether or not that'd apply to a star to some extent(i.e too big for it's own good). Let me to wonder whether or not the black hole in center of galaxy was formed from a huge star or just a normal sized one that gathered a lot of mass.",
"In terms of the missing link, why can't they just presume that it's been there for a long time and therefore taken in a lot of mass making it supermassive or is there something else to it?"
] |
[
"When we talk to ourselves or read inside our heads, how is it possible that we can 'hear' what we are saying/reading?"
] |
[
false
] |
[deleted]
|
[
"During internal monologues the parts of your brain associated with speech is actually active and sending information to the areas associated with the understanding and reception of sounds. It is theorised that there is a corollary discharge of neurons during this process that tells the brain this is internally generated speech and not external. It is thought disruption of this labelling may cause auditory hallucinations in some mental illnesses such as schizophrenia. ",
"Everything that we perceive (sounds, vision, touch) is the processing of external information by the brain. Therefore these perceptions that we assume are so concrete and real can easily be fabricated by the brain. I suppose internal monologues are sort of an example of voluntarilly brain generated perceptions with hallucinations being an involuntary example. "
] |
[
"That is a thing? What is it called? I'm having a hard time comprehending how you retain what you read, or how think about what you are going to write/say."
] |
[
"No because the communication is from the area that creates speech to the area that receives and understands speech. When actually talking there will be signalling to the primary motor cortex to make the movements to produce speech as well. Therefore the lack of internal labelling (corollary discharge) causes the internally generated information to be processed by the region that understands speech as external stimulation. ",
"Edit: grammar "
] |
[
"What would the practical applications be if superconductors were to be discovered?"
] |
[
false
] | null |
[
"Superconductors have been discovered, do you mean ",
" superconductors?"
] |
[
"There is nothing in the question which implies it. But anyway, they could have practical applications like lossless power transmission, strong magnetic fields without the need for expensive cooling, and very good magnetic shielding."
] |
[
"Yes, that's kinda implied. "
] |
[
"If a pregnant woman gets sick with a cold or an immunization like a flu shot does the fetus develop antibodies/immunity?"
] |
[
false
] | null |
[
"No.The mother will produce antibodies and pass them on to the fetus."
] |
[
"It is passed on through the placenta.\nAll of the mothers immunity is passed on during the last three months of pregnancy and when the baby is born immunity starts to decrease after the first few weeks.Breast milk also contains antibodies so the baby is protected for as long as the mother breast feeds.After that immunization is required."
] |
[
"Thank you, do you know how it is passed on? Like is all the mothers immunity passed or just immunity that is currently being used. Like if the mother is fighting an active infection is only that immunity passed or does all immunity pass?",
"I guess I am curious in general about how immunity passes from one entity to another. I know one of the big benefits of nursing is passing on immunity but I don't have a very firm understanding on the how. "
] |
[
"Carbon Fiber vs. Carbon Nano-tubes"
] |
[
false
] |
I was wondering about the difference between carbon fibers and carbon nano-tubes, both in structure and utility. Sadly Google didn't provide any help and the Wikipedia article was to dense for me to understand. Hopefully you guys can help.
|
[
"What is commonly referred to as \"carbon fiber\" is usually in reality a ",
"carbon-fiber-reinforced polymer",
", which is basically a composite material consisting of sheets of ",
"carbon fibers",
" and some sort of epoxy bonding them together.",
"Actual carbon fiber sheets are essentially \"blankets\" of mostly carbon atoms in a hexagonal matrix.",
"Carbon nanotubes, on the other hand, are a ",
"fullerene",
" which means they are composted purely of carbon atoms. In the case of nanotubes, they're analogous to a carbon fiber sheet being rolled up into a miniscule tube (only a handful of atoms in circumference), giving them incredibly high tensile strength.",
"A \"sheet\" of carbon nanotubes would actually consist of many tubes woven together, but not chemically bonded as in a sheet of carbon fibers."
] |
[
"To expand on this, the most common use of nanotubes today is the reinforcement of the tensile strength of polymers, not as a pure construction material themselves. The nanotubes function similarly to iron rebar in concrete."
] |
[
"Just to try and highlight the differences in structure: ",
"The main differences in structure can be boiled down to order vs. disorder.\nCarbon nano-tubes have a very defined/ordered structure-its a rolled up sheet of carbon (in a hexagonal pattern with sp2 bonding) forming a closed tube- closed along its axis, not necessarily at its ends. ",
"Carbon fibers on the other hand have a much less well defined/ordered structure. The fiber itself is also orders and orders of magnitude larger than the size of a single carbon nanotube. The carbon fiber can contain regions graphite-where the carbon is very ordered into sheets of hexagonal carbon stacked on top of one another, and regions of completely amorphous carbon-meaning there is no crystal structure (specific ordering or shape) what so ever. There can also be regions in the fiber which are in between (in terms of order/disorder) the well ordered crystalline graphite and completely disordered/random amorphous carbon-- these regions would probably look something like the molecules the fiber originated as. For example, carbon fibers can be made from ",
"PAN",
", so parts of the carbon fiber can look like these long chains, just without all the nitrogen on the chain. On the topic of nitrogen, most carbon fibers are also not 100% pure carbon, they can contain small amounts of oxygen and nitrogen and any other atoms that were present in the original polymer/material used to make the carbon fiber. Carbon nano-tubes on the other hand are an allotrope of carbon- and are defined as containing only carbon. (Though of course when actually synthesizing carbon nano-tubes, there are some impurities or some atoms/molecules are specifically/purposefully doped into/onto the nano-tube.)",
"tl;dr: ",
" well-defined well-ordered allotrope of carbon. ",
" Orders of magnitude larger (in diameter and length) than nano-tubes, consist of many different regions of crystalline (ordered) and amorphous (not-ordered/disordered) carbon. ",
"Edit: Apparently \"good\" carbon fiber is mostly graphitic- but can very in how those graphite sheets are bonded/interact with one another. ",
"http://en.wikipedia.org/wiki/Carbon_(fiber)"
] |
[
"What are career prospects for an Environmental Science major like?"
] |
[
false
] |
I've started studying environmental science at a large university. I haven't decided on any specialization. What are career prospects like for someone with a BS in Environmental Science? I'd rather do work for business than in academia. I've heard a lot about so-called "green jobs" but is it just a hype bubble ready to burst?
|
[
"I've two friends who focused on Geographic Information Systems within their Environmental Science degrees. One is now starting a part time gig with a radio station and the other is currently unemployed. I think this might, perhaps, speak more about the prospects within GIS than Environmental Science."
] |
[
"Many of my friends that graduated with a B.S. in Environmental Science are working at some capacity in the government, either on a local, state or national level. There are surely private sector jobs, but I am unfamiliar with their prevalence."
] |
[
"I was told by a professor in my college that the head of our biosystems engineering department was contacted by a group from Australia and they are looking for 5,000 recruits to be put on a starting wage of 60,000 (I'm assuming Euro) for ",
"Master graduates in my field",
". "
] |
[
"When is an approaching object's pitch highest?(Doppler effect)"
] |
[
false
] |
[deleted]
|
[
"As others have said, the apparent pitch is only affected by the relative velocity between the object and observer. The faster the object moves with respect to the medium (air), the more compressed the sound waves in front of it and the more spread out behind it. If the observer lies stationary directly on the object's path, it witnesses the same compression and spreading the entire duration of the object's approach and departure, respectively. If the observer is off to the side of the path, the compression would be closest to how it would be in the first scenario when the object is farthest (the first waves from the object to hit the observer). The effect of the compression seems to diminish as the object gets closer(an effect of trigonometry), reducing to 0 just as the object passes by the point where it is closest to the observer (the direction of the compression is perpendicular to the observer at this point). all of this then happens in reverse as the object gets farther away from the observer."
] |
[
"Doppler effect is from two objects' relative velocity and doesn't have anything to do with distance if the two objects are moving directly toward or away from each other. Assuming there isn't acceleration involved, the pitch would be the same (frequency + relative velocity) during the entire approach, would be the actual frequency during the moment when the two objects meet, and would be the same (frequency - relative velocity) during their departure. If they aren't heading directly toward each other then there will be a change in relative velocity that will be greater if the distace of the closest point is greater. Think of it like a circle drawn around one object and the other moving tangent to that circle to better imagine this scenario."
] |
[
"Yes. Without velocity, there would be no apparent shift in the frequency. If you have a device that can measure the frequency as it runs along its path from approach to CPA and past, you can use those frequency shits to determine the velocity of the object. "
] |
[
"\"Hot topic\" diseases get a lot of research attention (and money). But what about cosmetic diseases like seborrheic dermatitis? Have there been any recent revelations in determining its cause, or innovations in treating this annoying and unsightly (but harmless) disease?"
] |
[
false
] | null |
[
"The thing with medicine is studying one thing usually has far reaching results for many diseases (even the non threatening but annoying ones)",
"Chronic conditions like that tend to be rooted in Immune system disorders where the body attacks itself or is over sensitive. Now it may not be the center of attention in regards to medical research but studies into treatments in auto-immune disease would also lead to treatments in skin disorders.",
"Perfect example is Viagra. There was no research group looking for a cure for erectile dysfunction. They were actually studying heart medication and found it had the side effect of causing erections.",
"So basically what i'm saying is don't get frustrated because medicine tends to touch upon all areas."
] |
[
"Here",
" is a review article from 2009 going over the latest research in that area."
] |
[
"latest research... 3 years ago :("
] |
[
"Do we know why the speed of light is what it is, or just that it must be what it is?"
] |
[
false
] |
I spent the day trying to find a nice answer to the why, which lead me on a nice journey into zero-point energy and the possibility that quantum vacuum might be the origin of the speed of light, but didn't really get a nice answer.
|
[
"The only meaningful question is \"why is the speed of light finite?\" Well, it just is. ",
"Obviously, there are two possibilities: particles can have arbitrarily large speeds or they can't. If you insist that physical laws cannot violate causality and physical laws take the same form in all inertial frames, then each of these possibilities leads inexorably to either the Galilean transformations (for arbitrarily large allowable speeds) or the Lorentz transformations (for bounded allowable speeds). The parameter ",
" in the Lorentz transformations can be shown to be the least upper bound of allowable speeds, and the Galilean transformations are formally identical to the Lorentz transformations with ",
" --> infinity.",
"So where does light fit into this? It really doesn't. However, you can show that if there exists an object or signal or whatever whose speed is precisely equal to ",
" (whether ",
" is finite or infinite), then that object or signal must have speed ",
" in ",
" reference frames. Similarly, if there is some object or signal which has a frame-invariant speed, that speed must be ",
". This is a consequence of the transformations. Again, I emphasize that this has absolutely nothing to do with the speed of light.",
"It is then an experimental fact that the speed of light in vacuum is frame-invariant. Thus the speed of light in vacuum must be the value of the parameter ",
".",
"There is no fundamental reason why ",
" has to be finite as far as we know. It just is."
] |
[
"It just is.",
"That's the unsatisfying answer I was finding."
] |
[
"This question doesn't really make sense. What could you possibly mean by everything happening at once?",
"Also asking what would happen if the speed of light were infinite is much too speculative a question to offer much of a meaningful answer. "
] |
[
"How do painkillers work?"
] |
[
false
] | null |
[
"It depends what kind of painkiller you mean.",
"NSAIDs are the mild analgesics that you'd take for minor-to moderate pain (like aspirin or ibuprofen). These drugs work by inhibiting COX-2 enzymes, which convert arachidonic acid to small molecules called prostaglandins. When we feel pain, it can be an acute-reflexive burst designed to move your finger away from the stove, or a more chronic-dull ache over time from lingering damage and stimulation. For the chronic dull ache, prostaglandins and other neuropeptides like substance P, bradykinin, or histamine will sensitize the nociceptor (the fancy name for a pain transfering neuron) causing it to more easily fire off excitatory action potentials to the brain which cause the sensation of pain (it usually fires from mechanical stimulation). With an NSAID, you remove some of those factors that sensitize the nociceptor so you get less pain signal going up (and less inflammation as well, because prostaglandins are inflammatory mediators).",
"Opioids are stronger because they work both on inhibiting the pain signal from going up, and on inhibiting the brain's signal going down to continue release of the sensitizing neuropeptides, though this depends on which neurons are inhibited by opioid binding. Opoids also cause a ton of dopamine to be released, which is why they feel so good to use, so even if you still have some pain, you won't care. ",
"Sedatives (like barbiturates) can also have an anti-pain effect, but this is more so due to release of endogenous opiates like beta-endorphin or enkephalin as well as extra GABAergic stimulation against excitatory pain neurons. ",
"Finally, there's also acetaminophen (tylenol) which has an unknown mechanism of action. We don't know how it works, be we know that it isn't inflammatory like an NSAID, even if they're about as potent as an NSAID."
] |
[
"Oh i get it now, thank you."
] |
[
"Oh i get it now, thank you."
] |
[
"Last summer, there was big news about a robot set to explore some tunnels of the Great Pyramid. Googling gives me nothing but articles about the exploration, not the results. Anyone in the know?"
] |
[
false
] | null |
[
"The event you speak of might be the one that took place in 2002 and was a tremendous publicy-stunt by ",
"Zafi Hawass",
", the egyptian minister for antiquities. Kind of a narcissist. Video was transmitted world-wide, allegedly live.",
"See also ",
"Upuaut-project",
" ... this engineer did initially develop the robots used in the Cheops pyramid."
] |
[
"This is the closest my googling can bring me - \n",
"http://www.drhawass.com/blog/djedi-team-robot",
"This is the official page of the team that did it.",
"Edit - ",
"http://www.drhawass.com/events/mystery-hidden-doors-inside-great-pyramid-0",
"There is a National Geographic video of this."
] |
[
"Related - ",
"http://www.youtube.com/watch?v=PnNO9S_W1V8",
"After they drilled through the second door they found...",
"another door"
] |
[
"How can pure substances have multiple triple points?"
] |
[
false
] |
So a triple point is defined as "the temperature and pressure at which three phases (gas, liquid, and solid) of that substance may coexist in thermodynamic equilibrium" but my textbook also says "a pure substance can have a number of triple point, but only one triple point has a solid, liquid and vapor equilibrium. If it's defined as the point where gas, liquid and solids meet... and there's only one such point... how are there multiple? My best guess is the "(gas, liquid, and solid)" bit doesn't account for allotropic transformations while my textbook does. Stuff like Ice IV and ice V count as different states so if 3 of those states (where 2 or more could be solid, just different types) converge thats a triple point. Also apparently there's 19 types of water ice so thats just wild. Anyway, is my assumption correct?
|
[
"Your assumption is correct, there are multiple solid phases. So the solid-liquid-gas triple point is the unique point where the gas and liquid phases are at equilibrium with ",
" solid phase out of the multiple. The other triple points involve multiple solid phases."
] |
[
"Multiple solid phases are obviously the most common, but multiple liquid phases is possible as well, e.g. in helium."
] |
[
"Regular liquid and superfluid."
] |
[
"Can music affect an animal's mood and/or behavior?"
] |
[
false
] | null |
[
"This is true. I think the question would be better asked as \"Does ",
" music affect another species mood/behaviour?\""
] |
[
"Parrots would give that question a yes.",
"http://news.nationalgeographic.com/news/2009/04/090430-birds-dance-rhythm.html",
"http://www.youtube.com/results?search_query=parrots+dancing+to+music&oq=parrots+dancing+to+music&gs_l=youtube.1.0.0.4317.10613.0.13437.24.19.0.5.5.0.222.2875.1j16j2.19.0...0.0...1ac.1.SyS95JRqh2M"
] |
[
"Does it affect your mood and/or behavior? It sure does mine and I'm pretty confident that I am an animal. Unless you are a robot I'm pretty sure you are too. So yes, music clearly affects animal behavior and mood."
] |
[
"Antineutrinos or neutrinos?"
] |
[
false
] |
Are there more neutrinos or antineutrinos in the universe, as far as we know?
|
[
"On average throughout the universe the neutrino density is dominated by the cosmic neutrino background. I think this should have equal numbers of neutrinos/antineutrinos.",
"Here on Earth however the neutrino density is dominated by solar neutrinos, which are almost entirely matter neutrinos."
] |
[
"I think this should have equal numbers of neutrinos/antineutrinos.",
"I would be very careful with this statement. There are bounds on the chemical potential of the cosmic neutrino background, but they are pretty weak. The strongest bound comes from BBN and states neutrino asymmetry can be as big as eta_nu ~0.01 (the baryon asymmetry eta_B is 10",
" for comparison).",
"I think as there ight have been non-thermal productions of neutrinos in the early universe it is not rally surprising that an asymmetry could have been generated (especially considering leptogenesis scenarios)"
] |
[
"So if there are more neutrinos than antineutrinos in the universe, is that due to \"nonthermal production\" of neutrinos in the early universe? What does that mean, and might there be other causes of the possible asymmetry? ",
"Also, are only neutrinos produced in core collapse supernovae, or antineutrinos too?",
"Thanks!"
] |
[
"Is alchemy theoretically possible, with science not with magic?"
] |
[
false
] |
If we had the technology to manipulate atoms, could gold be created from something else like Mercury? I was thinking about alchemy and was curious as to whether or not a Mercury atom would be turned into a gold and a hydrogen atom if we could remove a proton. Additionally, is there any discussion on whether or not this will ever be possible on a small or large scale?
|
[
"This is possible and actually how we are discovering new atoms. This process basically involves intense heat and pressure that creates extremely unstable atoms that are not found anywhere but the laboratory. That is how many of the unnamed elements (Uu_) were discovered, although they are to stable to isolate and maintain. ",
"The real possibility of alchemy is happening every day, and is a process known as alpha decay. This is when a large atom decays and emits an alpha particle, which in reality is the nucleus of a helium atom (2 protons and 2 neutrons). For example when uranium decays (atomic number, 92) it releases an alpha particle and becomes thorium (atomic number 90). "
] |
[
"It is possible to change the number of Protons in a nucleus so one element converts into another. If I remember correctly, the name of the process is transmutation. It works by smashing smaller nuclei to larger nuclei to make a new elements.",
"Still, the process is very expensive, and it requires massive amounts of energy. Another drawback is that the amount of matter that comes out is very small. Not enough to pay for the process."
] |
[
"Yes and no... By radiating one nuclide with something like neutrons, you can cause absorptions and transmute them into other nuclides. So yes you can and we do transmute nuclides all the time in reactors. For example oxygen absorbs a neutron and through some nuclear processes becomes a nitrogen atom. However, The vast majority of the time, if you change element with an absorption reaction, the result is almost always radioactive and will eventually decay. In theory, yes you can create gold from other elements. However, the starting elements would be more expensive than the gold you are creating and the gold would be radioactive.",
"However, sometimes you want radioactive isotopes, for example in medicine or plutonium production. In these cases you literally are doing exactly what alchemy tried to accomplish (other than the obtaining gold part)."
] |
[
"Can organic matter be magnetic?"
] |
[
false
] |
I was bored so I decided to rip open a cigarette and run a magnet through the tobacco to see what would happen. Shockingly a few things were stuck to the magnet. I check to see if they were just getting stuck to the magnet but there was attraction as it would pull the bits. So are cigarette companies putting metal in cigarettes or can an organic object be magnetic? I can make a video if anyone is interested.
|
[
"Organic ferromagnets do exist, but they're a bit of a curiosity (they don't even have their own page on Wikipedia). If you have access to Materials Science and Engineering (Elsevier), you can have a look at ",
"this",
" review. Basically, materials that have high-spin polyradicals can form ferromagnets (and ferrimagnets and antiferromagnets) in the solid state. Some conjugated pi-systems involving heteroatoms display this property. Alternatively, metal-organic compounds like some metallocenes can be ferromagnetic as well.",
"However, a different question is if biological ferromagnets exist. The trick with molecular magnetic materials is that they require pretty specific engineering. With the exception of metal-organic compounds (rare in biological systems, as they're typically only found in the active site of enzymes), it's statistically impossible that a molecule that's not designed to be ferromagnetic still is a ferromagnet. On top of that, the polyradical structure of these compounds probably makes them unstable in a watery environment such as a biological body. This means that biological ferromagnets would only exist if there would be a very big reproductive advantage associated with them, which is unlikely for a tobacco plant."
] |
[
"There's all sorts of crap in cigarettes, I'm now curious what could be magnetic. Make a video- and do a comparison of a magnet and not a magnet, as well as cigarette and, say, dried tea, to show that A: we're really seeing magnetic attraction. and B: It's something specifically in a cigarette that's magnetic."
] |
[
"I would say no. First, I believe your question is if organic matter can be attracted by magnets (to BE a magnet, that is to become a permanent magnet, is a whole other story), and the property of attraction by magnets is called ",
". Wikipedia has an ",
"excellent list",
" of ferromagnetic materials, and none of them is anywhere near organic.",
"Ferromagnetism depends only on the atomic or molecular structure of the material, not of its shape, size or array, and that it pretty interesting. This property, in the quantum world, means that the spins of the atoms tend to align themselves and create a surplus of spins pointed to one side (like some sort of \"magnetic charge\", but you can never tell anyone I used that expression, I get my licence revoked). If you get a material with a full electronic shell (all orbitals are filled), each orbital will host two electrons with opposite spins and this will not allow the material to have more spins to one side than to the other, hence, no such material can be attracted by a magnet. As all organic matter is based on carbon covalent bonds, it will not be possible.",
"So the final answer would be no, all you got was weird ferromagnetic compounds used by the tobacco industry to spice a little bit your cigarette."
] |
[
"Why is GPS more accurate at getting my cellphone location than cell tower triangulation?"
] |
[
false
] |
Is it just the accuracy of the times involved or is there something else?
|
[
" Individual cell towers can't pinpoint your location as effectively as GPS because they can't measure distance directly, whereas GPS receivers can. That inaccuracy means that GPS will almost always win over tower triangulation. GPS also uses something more sophisticated than triangulation to determine your distance.",
"The mechanisms that they use to determine your position are completely different, and this accounts for the discrepancy in the accuracy. Cell towers use ",
", where ",
" are measured. GPS uses ",
", where ",
" are measured.",
"Let's talk about each one.",
"First, let's take a look at a typical cell phone tower. Here's ",
"an illustrative picture",
". You can see that the tower consists of sets of triangular arrays. Typically, each set of arrays belongs to a different provider (or it might be the same provider adding more bandwidth or upgrading service).",
"Most of the time towers will look like the one in the picture, with three arrays per set. But sometimes you'll only see one or two arrays, especially in rural areas, where there's no need to service one or more directions. Otherwise, in denser service areas, the \"cells\" of a cell tower grid wind up forming ",
"roughly hexagonal shapes",
".",
"Each of the three arrays in a set covers one-third of the service area of the tower -- you can see this in the grid shown above, where ",
". That mean each array covers a wedge approximately 120 degrees wide.",
"By convention, we call the antennas that service each wedge α, β, and γ -- the lowercase Greek letters ",
", ",
", and ",
". We call the wedges \"sectors\".",
"Cell phone tower triangulation works by measuring the \"distance\" to a phone the tower for each sector that can see it. The distance is not an actual physical distance, but rather is estimated based on signal strength and the round-trip time of the signal. This is not a very accurate measurement, especially in urban environments where there can be lots of reflections and interference.",
"That means that the antenna can't precisely determine its distance to the phone. Instead, the phone can only be located within a distance band -- a portion of the sector that's a particular distance away from the tower.",
"In this example, one of the sector antennas of our tower has located a phone in between signal levels L2 and L3.",
" * )) )) ))///////)) )) ))\n /_\\\n / \\\n Tower L0 L1 L2 ★ L3 L4 L5\n phone\n",
"The tower doesn't know anything more than that the phone is somewhere between signal strength L2 and signal strength L3, but this is an area 120 degrees wide from the sector antenna relative to the tower, and several miles thick. So it's not very accurate.",
"This information from a single tower is combined with information from other towers. \nWhen two sector antennas detect a phone, we know that the phone must be in the area that their sectors overlap. Likewise, when three antennas come into play, we know that the phone must be in mutually overlapping area.",
"But the area covered by a tower is frequently large, and they aren't always laid out in a way that's suitable for triangulation. Even in an urban environment with lots of towers, often the best you can do is a fraction of a square kilometer. ",
"In this diagram",
", for example, even with cell towers that cover a rather small radius, the best we can do is about 600' accuracy, the largest circle that will cover the red shaded area.",
"GPS is a constellation of satellites that orbit the Earth, combined with an algorithm for decoding the transmissions from those satellites, with the goal of having at least six satellites be visible in the line-of-sight for an unobstructed observer. Since GPS satellites are specifically designed for positioning, unlike cell towers, the satellite configuration is set up so as to try to maximize the number of satellites visible in the sky at a given moment.",
"The satellites each have an expensive atomic clock that is very precise and synchronized to all the others. Each satellite transmits a repeating string of information over and over, starting from a particular time (e.g. \"today at midnight\").",
"GPS receivers have cheap quartz clocks. They also play the same repeating string of information, starting at the same time. Since the satellite's broadcast travels at the speed of light and not instantaneously, it will slightly lag behind the receiver's playback. A receiver can determine how far away it must be from a satellite by measuring the lag between its own playback and the received signal.",
"By listening to the satellites, the GPS receiver can also work out how far off it must be from the expensive atomic clocks. There will only be one time that minimizes the error from all the satellites, which determines your position very accurately.",
"Practically speaking, this means that you can get GPS resolution of a few square meters as opposed to fractions of a square kilometer. Overall, GPS is significantly more accurate."
] |
[
"relativity actually causes some 'substantial' drift for them. It is a REALLY tiny amount, but it is enough that after a few days without being updated from the ground, your GPS would start reporting you several meters away from your position, this error growing constantly.",
"Actually the amount is not tiny at all: IIRC the numbers correctly, their clocks are 7 microseconds/day slower due to their relative velocity, while our clocks are 56 microseconds/day due to us being in a stronger gravitational field (i.e. higher acceleration), so if the clocks weren't corrected for the resulting 49us/day drift that would result in 0.3 * 1000 * 49 = 14 km drift per day (1 light nanosecond (10",
" s) is 0.3 m).",
"However it's pretty much irrelevant, because this drift can be accounted for systematically, and any small changes in the satellite's orbit (that could change the drift rate) introduce an incomparably bigger error directly.",
"Edit: what really is a problem that needs constant correction appears to be the the precision of the atomic clock onboard, ",
"here",
" it says that it's one part in 10",
", which means that they can drift off by up to 80 ns per day."
] |
[
"There are two substations (probably more that are kept secret as a backup) and every time a GPS satellite passes within range, the substation updates the satellite so it is correctly set. This is very important because at the speeds the satellites are moving, and at the precision the atomic clocks are operating at, relativity actually causes some 'substantial' drift for them. It is a REALLY tiny amount, but it is enough that after a few days without being updated from the ground, your GPS would start reporting you several meters away from your position, this error growing constantly."
] |
[
"By what mechanism do you become more flexible when you stretch daily?"
] |
[
false
] |
I started working out this year, and on top of the muscle, I've noticed that I'm massively more flexible, which I assume is due to my long stretching routine before working out. I know that muscle builds with use because it is damaged, then repairs itself to be even stronger. Do you become more flexible in the same way
|
[
"Tendons get damaged and repair the same way. Flexibility, anatomically speaking, isn't just about muscles. It is also about tendons. As extreme example, people who become demented or paralyzed develop contractures, where muscles and tendons become rigid over time (as in, they can no longer be stretched even by another person).",
"If you use steroids as means to build muscle mass, your tendons may not develop fast enough. This may lead to muscles becoming too strong for tendons and cause ruptures."
] |
[
"So just bending down and touching my toes is doing some small amount of damage to my tendons, which they will heal and come back with a wider range of motion?"
] |
[
"Little bit of elasticity can be added easily. Achieving olympics-level gymnastics flexibility would take quite a bit of training. It is same as with muscles in that sense. Also note that many usual muscle training exercises also have an effect on tendons."
] |
[
"How accurate is philosopher Slavoj Zizek's claim that in quantum physics, \"the idea is that the universe is a void, but a kind of positively-charged void. Particular things appear when the balance of the void is disturbed\"?"
] |
[
false
] |
[deleted]
|
[
"It's much too vague a statement to say anything meaningful about it. Also the universe appears to be charge neutral, why this is the case is not well understood, but ultimately must be related to charge conservation and whatever physics caused the early universe matter/antimatter asymmetry, the ladder still being an unsolved problem. So I don't see what he means by \"positively charged void.\"",
"As far as quantum physics allowing things to appear out of nowhere, it has to do with the fact that nature doesn't seem to like to play favorites. An electron may be spin up, or spin down, or both at the same time as long as all three situations equally satisfy the physical laws. Now extend this idea to not just say an electron's spin, but how many particles the state has. If we have three states which equally satisfy the mathematics each with a different number of particles, then all three solutions can be expressed. ",
"More mathematically, what this means is that the Hamiltonian of a system doesn't necessarily have to commute with the number of particles, N. Let's say we have a state |E> which is a perfectly well defined energy state, it might be expressed as a combination of \"particle number states.\" It might look like this, ",
"|E> = a|N,1> + b|N,2> + c|N,42>"
] |
[
"Zizek's description sounds reminiscent of the Dirac sea - the positively-charged universe with just enough electrons to balance the charge. \"[T]hings appear when the balance of the void is disturbed\" could mean departures from this ground state to create observable electrons and holes.",
"I'm not sure Zizek has much of a point beyond trying to sound erudite when referencing quantum physics, especially if he is indeed appealing to models that have been out of fashion for nearly 90 years."
] |
[
"As a general rule of thumb, whenever a philosopher talks about physics or quantum mechanics roll your eyes, extend your index fingers, angle your arms towards your ears and push inwards, creating a firm air-tight seal preventing the entrance of sound into the aural canal. This will help mitigate the headache resulting from the intellectual equivalent of nails on a chalk board that is guaranteed to follow. That video is just total gibberish."
] |
[
"Does the Earth/Moon system weigh less than the Earth and the Moon would on their own?"
] |
[
false
] |
I'm reading about particle physics here so I'm likely to have made mistakes on both the small and large scales, but here goes: The energy in a system is distributed between movement energy and interaction energy. The negative interaction energy between a proton and an electron in a hydrogen atom is what keeps the whole thing stable. It would need energy to eject the electron. That negative interaction energy also means that the hydrogen atom has less mass than the sum of a lone proton and a lone electron. By analogy, the moon is in our obit thanks to gravity and it would take loads of energy to eject it. Does that analogy stretch as far as negative interaction energy and the Moon/Earth system having less mass than they would by themselves? What's the difference?
|
[
"Yes, and the difference is about ",
"800 million tonnes",
". Sounds like a lot, but if you compare it to the mass of Earth or the Moon it's a very small difference."
] |
[
"Is this assuming that 800 million tons of mass (converted to energy) originating from the Earth and the Moon would be used to move the Moon out of orbit?",
"It could.",
"It would make Earth and/or the Moon lighter depending on where you take it from, yes. The combined mass of the system would stay the same.",
"If you take the energy from Mars then you increase the total energy in the Earth/Moon system and therefore increase its mass."
] |
[
"So a really hot object is more massive than that object near absolute zero?",
"Yes.",
"Energy in the center of mass frame matters."
] |
[
"On stomach bacteria"
] |
[
false
] |
The symbiotic relationship between us and the bacteria in our stomachs has always fascinated me. I know that, at a certain stage in utero, some bacteria flows from the mother to the offspring, but I had a few questions regarding that process and the process by which this relationship developed. What is the current state of scientific understanding of the evolution of this process? What chemical signals, if any, prompt the aforementioned flow from mother to child? How can these bacteria not pose some threat in a new child? How did our stomachs come to provide such a beneficial environment for bacteria? How are these bacteria specifically evolved to live within humans where other bacteria wouldn't be? How do we regulate the amount of bacteria-what keeps in from growing ad infinitum, so to speak? Specifically what role does it play? I just feel like it's a subject that could explain a lot about human evolution.
|
[
"Swabbing the birth canal and inoculating like that is genius honestly. I have never heard of that. There are numerous studies about C-section babies having impaired microflora-",
"http://jn.nutrition.org/content/138/9/1796S.long"
] |
[
"Swabbing the birth canal and inoculating like that is genius honestly. I have never heard of that. There are numerous studies about C-section babies having impaired microflora-",
"http://jn.nutrition.org/content/138/9/1796S.long"
] |
[
"We are finding that some microorganisms actually utilize our signaling molecules such as norepinephrine and insulin",
"Can you explain more about this? I find this stuff fascinating.",
"It's my understanding that research is suggesting that to some extent our guts \"think\" for themselves. I'm sure this is a gross over-simplification, but is this what they mean?"
] |
[
"When the universe enters heat death, what will the average temperature of the universe be? Will it be absolute zero?"
] |
[
false
] |
Heat death as in all protons have decayed and all black holes have evaporated. (I realize proton decay and heat death are unproven theories, but I'm curious about what would happen in these scenarios). In heat death, there will be no more interaction between particles and no more baryonic matter, right? Does this mean entropy has gone as far as it can? Does "temperature" even have a meaning at this point?
|
[
"The name \"heat death\" is a little misleading. It's often taken to imply that the Universe will be very hot in this end state. Rather, it's a condition where all the Universe's useful energy has been converted into waste heat. The eventual temperature could be 5K or 5000K - if everything is the same temperature, no useful work can be done. Realistically, the heat death of our universe will likely be extremely cold, but the point is that it'll be the same temperature everywhere.",
"Absolute zero is a state of minimum entropy because as you cool something, you shrink the range of energy states available to it - a decrease in entropy. When you've cooled something as far as it will go (i.e. absolute zero) then you have also shrunk its range of energy states as far as it will go: a state of minimum entropy."
] |
[
"It'll be the opposite of absolute zero, in a sense. Absolute zero is defined as the temperature at which entropy is at a minimum, but the heat death of the universe occurs when the universe reaches maximum entropy (no further work can be done).",
"Temperature would still have a meaning - if some heat were mysteriously introduced to a heat death universe, the entropy of the universe would change by a certain amount and from that you could derive a temperature."
] |
[
"I'm confused about it being the opposite of absolute zero. That is correct, as absolute zero is indeed defined as minimum possible entropy, but does that mean the universe will be ",
" during heat death? How can that be? Also, why is absolute zero defined as minimum entropy instead of maximum entropy?"
] |
[
"Why is it that batteries cannot be charged quickly?"
] |
[
false
] |
It seems it takes no time at all to drain a battery but to charge it is just the opposite. What gives?
|
[
"chem eng here. well recharging a battery is reversing a chemical reaction and the rate at which you can do this is limited by the rate of ion transport to the electrodes. if you go pumping high voltage and current into a system which cannot react fast enough, you will risk decomposing your reagents and damaging the battery. there are different media such as solutions, gels and pastes, each with different properties. a paste may be slow or impossible to recharge but offers the advantage of no spills."
] |
[
"Physicist here.",
"Can I assume that the battery is uniform and spherical?"
] |
[
"It also exists in a frictionless vacuum."
] |
[
"Are speedreading school legit or a hoax, howmany words per second can the brain actually read retaining all the information?"
] |
[
false
] |
[deleted]
|
[
"I don't have any numbers on this but speedreading is legit. It's achieved by reading in chunks instead of word-by-word, and minimizing or even eliminating silent speech (don't think about the sound of the words while reading). However, while it's faster to get a general understanding of the text than traditional reading, it's impossible to retain all the information through speedreading alone, because you'll mostly be skimming and looking for key words. So it's useful for magazines and newspaper, not at all for academic articles."
] |
[
"it is legit, but as you said it has pros and cons. pro: you can quickly get an idea about the general information of the text, con: it is not in-depth at all and you might skip some vital information which can obscure the main point"
] |
[
"Every reading teacher knows that frequency can and should be increased in order to comprehend material. A rate of 90 WPM is necessary for the brain to maintain information while reading. By doing eye tracking exercises, the rate can increase to higher levels. Achieving a rate of 250 WPM is about 12th grade level. By the time you have reached that rate, the mere familiarity of words and understanding of vocabulary, enable one to increase the rate while comprehending quicker. This is a brief rundown but speed reading is not only possible but, is very helpful for getting through new information quickly while allowing you to recognize information needing more scrutiny at the same time. "
] |
[
"Has the placebo effect been adequately studied?"
] |
[
false
] | null |
[
"What would that mean? Giving people sugar pills and telling them that they are actually medicine? That's not ethical... The goal is to develop a pill that does something over and above the benefit conferred by the placebo effect, and, if there is an effect, then that's good too (assuming the pill is effective -- otherwise, why pay for it?)"
] |
[
"There's a long discussion of both positive and negative placebo effects on the wiki for placebo... Research is ongoing to uncover mechanisms, although it seems like there may be many different kinds of effects..."
] |
[
"I'm not really sure what you're asking / what kind of answer you are looking for. Yes, there is lots of research on the placebo effect..."
] |
[
"Does polarization take vector components of the electric field component of light?"
] |
[
false
] |
I'm trying to understand linear (I think?) polarization of light. The only way i can have it make sense in my brain is if the polarizing filter "selects" the vector component of the electric field parallel to the direction of polarization. For instance, take the typical exam question of 3 polarizing filters. 2 filters placed one after each other with a 3rd filter in between, and the 2 outer filters are placed so that their directions of polarization are perpendicular from each other. Without the third filter between them, no light would get through, but place the filter in the middle at a 45 degree angle, and all of a sudden some amount albeit, a small amount, manages to get through. The only way I can picture this happening is if the the first filter takes only vertical components of incident light, and the second takes the the vector component of the light parallel to its direction of polarization, and then the same thing happens with the last one. Sorry if that was long winded or unclear!
|
[
"I'm not completely sure I understand your question, but a polarizer basically projects the vector onto the polarization direction. I think that's what you're saying. "
] |
[
"You are correct. In the case that you described, about (100/sqrt(2))% of the light incident on the second and third filter should make it through, which is exactly what you would expect if the electric field vectors can be expressed as a pair of vectors on an arbitrary set of perpendicular axis."
] |
[
"Exactly. Some polarizing filters are literally grates of fine wire, so that only electric fields perpendicular to the wire can get through. ",
"The fun part is that it happens even with only one photon, so it's not possible for this explanation to work at that small of a scale. This is an example of how Maxwell's equations for electromagnetism have to be modified to work with quantum mechanics. In that case it's an example of linearity of a 1 qubit quantum state."
] |
[
"If I attempted to hang myself from the ceiling of an elevator using a belt and it began to free-fall ... would there be slack in the belt?"
] |
[
false
] | null |
[
"Yes, always a little. The belt before the free fall would stretch a little resulting in an upward force that keeps you into place. As soon as the elevator starts its free fall, the tension would pull you towards the ceiling a little resulting in a slack. If the belt would be infinitely stiff, there would be the stretching of the body that would cause a little relative upward acceleration with respect to the elevator that would cause the slack. "
] |
[
"When the elevator stops will his head get ripped off?"
] |
[
"Depends on the amount of time the elevator was free falling before it stopped instanteniously. When they are in free fall, the belt does not exert force around op's neck. when it stops suddenly the force around op's neck is dp/dt. dp is the transfer of momenta and dt is the time over which the acceleration changes which is very small. If the elevator travels for more time or more distance under free fall, the momentum transfer, dp, would be more and hence the force exerted would be more. This is also the reason why jumping off tall buildings kills people. ",
"If the force and pressure around op's neck is above the threshold level of force required to rip off the head, then yes."
] |
[
"Is there a principle that governs the distribution of the elements?"
] |
[
false
] |
Tried Googling the answer, couldn't figure out how to phrase it better, but I'm curious about the principles governing the distribution of elements - do the heavier ones occur with a linear or logarithmic amount less than the lighter ones? Is the distribution between elements 'smooth' or clumpy around certain elements that were favored in solar and supernova processes, leading to abundance of say, Silicon or Carbon?
|
[
"Try looking up ",
"atomic abundance",
". In short, most of the matter of the universe was formed in the big bang. After that, elements are formed by a variety of processes, through nuclear fusion (light elements, primarily), nuclear fission (heavy elements), radioactive decay (nuclei that are unstable), and other means."
] |
[
"The relative abundance of the elements in the universe is governed by the previous frequency of the nuclear reactions that form isotopes of elements, the stability of those isotopes, and the previous frequency of processes that transmute each nuclide. There are clusters of more abundant elements such as iron, but a detailed knowledge of nuclear chemistry and astrophysics is required to understand why a given element/cluster of elements is favored. "
] |
[
"There's no set trend at work here. Of course the most abundant element is Hydrogen and Helium comes a close second. Then, in your star cores you get what's called \"Helium Burning\" so you get elements like Beryllium, Boron and Carbon. That's what happens in majority of stars. The heavier elements will have to be made in larger, hotter stars so they're less common... usually at around 6E8 K you get Carbon Nitrogen cycles that get you as heavy as Sulfur. Then you need to go even hotter to get elements like Argon and Iron. At this point, you hit a dead end because Iron is the most stable heavy nucleus. To make elements that are heavier, stars will have to go supernova.",
"You'd therefore expect that abundances be \"clumped\" around Hydrogen and Helium, Carbon, and then Iron. It's more to do with nuclear stability and how abundant the parent stars are..."
] |
[
"Does your finger print change as you grow? I.e. could you store the finger prints of babies in a database and they'd still be the same when the people were adults?"
] |
[
false
] | null |
[
"Finger prints have two characteristics: permanence and uniqueness. This means that every person has a unique set of fingerprints which only grows in size as a baby comes out of the womb and becomes an adult over time. Basic pattern remains the same. Age and the abrasive nature of some professions can just alter the clarity of finger prints. "
] |
[
"The skin may be wrinkled, but the pattern ingrained is the same. If you were to unwrinkle the skin (ie stretch it out) it would remain the same"
] |
[
"Going off of this, what if one were to consider an elderly person? Would sagging/wrinkling of the skin have any affect on the similarity of the prints?"
] |
[
"What effects would I notice if I could adjust the circumference of my car wheels whilst driving?"
] |
[
false
] |
If I could somehow quickly and significantly change the diameter of the wheels on my car while travelling at a certain speed... would I slow down, speed up or maintain speed? Let's say 'significant' is adding a few inches to the front and back wheel diameter, and I'm driving at 100kmh. Apologies in advance for my inane question, it's something I used to imagine as a kid would allow cars to get an INSTANT TURBO but somehow I doubt science would have backed me up :)
|
[
"Essentially the same thing that happens when you shift gears. Making the wheel larger would be like upshifting; making it smaller, downshifting.",
"In fact that's exactly what's happening inside the transmission. When you shift up a gear, you're just moving to a set of gears where the drive gear (analogous to the wheel) is relatively larger."
] |
[
"Perhaps, though in a typical passenger car, the wheels are only about 5% of the total mass of the car. The angular momentum of the wheels has only a small effect on acceleration.",
"A car enthusiast/racing magazine (Grassroots Motorsports) recently tested the effects of wheels with increasing angular momentum on performance (increasing the total wheel mass, and moving the mass closer to the outside, by using a larger rim) and the effect was measurable, but small."
] |
[
"But if you think that the drive wheel is your pedals, the drive wheel is getting relatively bigger (to your gears)."
] |
[
"Why is americium used in smoke detectors rather than any of the other various radioactive elements?"
] |
[
false
] |
It seems to me like it would be easier to acquire something like uranium or thorium, since they have longer half lives. Does it have to do with the quantity of alpha particles they emit?
|
[
"Alpha radiation is needed because of it's relatively short mean free path. The idea behind smoke detectors is that there is a little detector close(ish) to the americium source. If there is not fire, the alpha particles can travel more or less freely to the detector which registers a current (alpha particles are charged).",
"If we have a fire, we have very dense smoke that will fill the area in between the source and the detector. Since alpha particles are stopped relatively easily, the smoke will not allow the alpha particles to reach the detector, we will see a drop in current/voltage and the fire alarm is triggered.",
"For things like beta/gamma rays, they interact weakly enough with the smoke, and so they will hit the detector regardless. The whole point of using an alpha source is because they will not make it through smoke, while other sources of radiation will."
] |
[
"Americium has a half life of ~250 years, so practically it's going to last longer than fire codes would let you use it."
] |
[
"It does. You want a lot of alpha particles (because they're how the device works) and as little beta or gamma radiation as you can get."
] |
[
"Why do creatures eat?"
] |
[
false
] |
Seems like a stupid question, but it occurred to me- Plants seem to me like a perfect lifeform to have dominated the earth. They had free and available energy and practically unlimited space to spread out and reproduce. Limited competition was necessary as the resources they needed were easy to get and came to them. It seems like that's a recipe for practically unlimited growth and evolution. But at some point some creature somehow learned to consume another one, and the whole stretch of predation of other living things began. It's inefficient, requires additional metabolic processes to get at the energy inside the victim, and limits a species' growth to the number of other creatures it can catch and eat. That's not so much of an issue if your victim is a plant, as they're plentiful all over the planet and don't run much. But then comes non-plant eaters, and things really get weird, as they eat mobile living creatures, which they have to chase and kill to get at their energy. That's more than inefficient, it's dangerous- the victim could fight back and injure or kill them first, or the predator could fail to kill it, thus leaving them short the energy they spent and still without sustenance. The point is, it seems that life evolved towards the best most efficient forms to allow survival, at what point does eating other creatures ever follow that logic? Why not just stick with plantlike creatures? Why did eating evolve at all?
|
[
"This movement, and higher brain function, requires more energy than can be gathered from the sun.",
".....directly.",
"Animals have a really great strategy. They let the plants do all the work of concentrating the energy for them."
] |
[
"Eating gathers energy more efficiently than photosynthesis, relative to weight of the energy gathering organs. If you look at plants, they typically do not have enough energy to move, whereas animals (which eat) can move very far/fast. This movement, and higher brain function, requires more energy than can be gathered from the sun. "
] |
[
"You seem to be under the impression that photosynthetic plants are entirely self-sufficient. This is completely false. Photosynthetic plants have no way of fixing nitrogen, which is essential to survival. \"Fixed\" nitrogen is non-elemental nitrogen, in the form of nitrates, etc. Atmospheric N2 is unusable by most living things. Bacteria in the soil typically are the nitrogen fixers of the world, and they get their energy by feeding on plants (you can see these: certain legumes like soy beans have little nodes on their roots which are nitrogen-fixing bacteria). The other rich source of fixed nitrogen is decaying organic matter, such as dead animals.",
"Also, wherever there is a niche in the environment, that niche will be filled by a new species. Immobile photosynthetic plants fill a certain niche with a particular demand for nutrients and a particular role in the ecosystem. Animals fill a completely different niche. It would be far more shocking if animals hadn't evolved at all."
] |
[
"Why do antibodies for diseases like chickenpox stay in your body for years, while they only last a few months for other diseases?"
] |
[
false
] | null |
[
"There are white blood cells in your body that have memory, like a seasoned vet from a war. Some are hyper alert for signs of infection. Others pump out antibodies instead. Over time these seasoned vets die and their memory fades. This happens with the tetanus vaccine, and is why you need boosters.",
"Chicken pox is a tricksy one because the virus (Varicella Zoster) hides in your nerves after the first infection. Because it never really goes, the body's immune memory never fades. If healthy, those seasoned vets keep the chicken pox virus suppressed. This is also why you sometimes get shingles when you're tired or sick because the infection comes back out of the nerves.",
"Some viruses like measels wipe out your seasoned vets early making you vulnerable to previously encountered illnesses. This is one of the reasons it can be so deadly and vaccination against it is absolutely essential."
] |
[
"It gets a bit more complicated! Some extra factors are if the organism mutates frequently like the flu, which needs a new vaccine every year. This is like the virus strapping on a fake nose and glasses and walking past the guards.",
"Another factor is also how strong a reaction to your body the infection causes. Chicken pox, for whatever reason, produces a really strong response. Studies estimate we lose about half out memory after vaccine exposure after about four or five decades. There is also the possibility we encounter those types of infection really often, rebooting memory, but don't notice because our bodies stop it before it becomes clinically noticable.",
"As a modern reference, the concept of causing a poor immune response for memory is one of the reasons making a good coronavirus vaccine (not just for covid) is hard. This reason, alongside huge variability of organisms and frequent genetic change, is why we also won't really see a vaccine for the \"common cold\", for example"
] |
[
"Thanks! I’m wondering about the evolutionary advantage of chicken pox hiding in neurons indefinitely. One might think that’s a clever strategy to stay alive, but as you said, it also keeps the immune system primed for future infections, which is ultimately to the detriment of the virus.",
"For these reasons, I might also guess that a chickenpox infection would provide longer lasting immunity than a vaccine. Is that correct or no?"
] |
[
"In layman’s terms, what are the differences between various units of “brightness”?"
] |
[
false
] |
I’m a fanatic of flashlights. I have a few powerful flashlights that are often described as being “brighter than the sun” by my friends when I show them off. What measurement could I utilize to compare the “brightness” of my flashlights to that of the “brightness” of the sun? I’m still a noob to the flashlight subreddit, though I have heard of various units such as lumens, lux, and candela; I have also heard of , regarding the local differences of “brightness” between stars in the sky.
|
[
"This is actually an optics question (or radiometry, more precisely), not an astronomy one, although astronomy does have its own measure of brightness (or magnitude). The term \"brightness\" is measured by the photometric quantity \"luminance.\" Fundamentally, there are two types of units for measuring how things emit or absorb photons: radiometric, and photometric. Radiometric units are simply power related, like watts, watts/m",
" etc. Photometric units are basically these units scaled by how humans perceive light, so they weight photons in the green higher than other wavelengths, and don't take into account infrared or UV at all because we can't see them. ",
"The unit of \"brightness\" is luminance, which is the photometric equivalent of radiance. This is kind of a complex unit to understand conceptually, since it takes into account both the size of the thing emitting the light, how much light it is emitting, and what angle it is emitting it into. From wikipedia, radiance is defined as:\n\"radiance is the radiant flux emitted, reflected, transmitted or received by a given surface, per unit solid angle per unit projected area.\" Basically, a source will have higher radiance if it has a smaller area, a higher power output, or is emitting radiation into a narrower angle (like a spotlight). Luminance is the same, but with Lumens instead of Watts for the unit of \"power\". If you take the power emitted in lumens and divide it by the angle over which it is emitted, you get intensity, which is lumens/steradian or more commonly \"candela.\" Luminance is then candela per square meter, taking into account the area of the source. This is cd/m",
" which is also called \"nits\" and is what brightness of displays/monitors is measured in. Radiance/luminance are kind of conceptually complex quantities, and can be confusing. Radiance is also conserved through a system, so being farther away from something doesn't lower its radiance, at least as long as you can resolve the object. If you have a source of a given size and move it farther away from your eye, your eye will get less light from it because it is capturing a smaller solid angle of the radiation. However, the object will also appear smaller, which would raise the radiance. These effects cancel out as long as you can resolve the source with your eye. If you can't, you will just have a diffraction limited spot if the source is very small (like a star) so when it gets farther away it won't be appearing any smaller.",
"In astronomy there are more confusing units like \"absolute magnitude,\" but I don't know as much about those so I will let someone else handle that."
] |
[
"In astronomy there are more confusing units like \"absolute magnitude,\" but I don't know as much about those so I will let someone else handle that.",
"Magnitude is a type of unitless scale, and there are two types: absolute and apparent.",
"Absolute magnitude is a measure of how much light something emits, while apparent magnitude is how bright it is from a given distance. They are a logarithmic scale with a base of the fifth root of 100, this means that for each 5 steps in magnitude, the brightness multiplies by 100 (i.e about 2.512 for each step). Because astronomers like to be confusing, the lower the magnitude, the brighter the object.",
"Historically, the star Vega has been used as the \"zero point\" of the scale (further back in history it was Polaris). So Vega has an apparent magnitude of 0 and an absolute magnitude of 0, a star with an apparent magnitude of -1 would appear to be around 2.5 times brighter in the sky.",
"Absolute magnitude is defined by what the apparent magnitude would be at a specific distance, 1 parsec (about 3 light years)."
] |
[
"As I said, astronomers like to be confusing, so the lower the number the brighter the object.",
"Venus has an apparent magnitude of around -2 to -5, Sirius A the brightest star is around -1.46, Uranus is around 6.",
"6 is roughly the limiting magnitude for naked eye observations, with anything higher being too dim to see. This dates back all the way to Ptolemy, who attempted to classify stars into 6 groups, where group 1 was the brightest."
] |
[
"Shouldn't we be able to make a fairly accurate map of the visible (and not visible) universe, based on the galaxies we can see, their distances, speeds, accelerations, etc?"
] |
[
false
] |
[deleted]
|
[
"My very rough attempt at visualizing what a map of the universe might look like.",
"There is no \"centre\" of the universe, \"where the big bang happened\". Rather, as we look at distant galaxies, we observe that every single one is moving away from us (on your map, some are moving towards us). The observation that every single galaxy is moving away from us does not mean that the Milky Way happens to be \"at the place where the big bang occurred\", but rather it ",
"means that the universe as a whole is expanding",
". (Read the section entitled: ",
".)",
"When the whole universe is expanding, it doesn't matter which galaxy you happen to be in, when you look at the rest of the galaxies they will all seem to be moving away from you.",
"Another way of thinking about this is to picture that spacetime itself is expanding, not just the distance between the galaxies is increasing."
] |
[
"no lots of people have noticed that, I wouldn't think too much into it though. humans are really good at finding patterns, even when they aren't there, and if there is some connection it is more likely something statistical than meaningful."
] |
[
"no lots of people have noticed that, I wouldn't think too much into it though. humans are really good at finding patterns, even when they aren't there, and if there is some connection it is more likely something statistical than meaningful."
] |
[
"How do concentrated salt solutions kill bacteria?"
] |
[
false
] | null |
[
"By sucking them dry through osmosis. Bacterial cell walls are permeable to water, so when placed in an aqueous solution with more junk than is inside the cytoplasm of the bacterium, the water inside wants to get out and dilute the solution.",
"Some bacteria like saltwater, but you can always dissolve more salt in the water until it's hypertonic relative to the cytoplasm. "
] |
[
"Just to define osmosis:",
"Everything will naturally move from a high concentration area to a low concentration area - think of a drop of dye being dropped into a bowl of liquid. The dye naturally spreads through the liquid until its spread out (low concentration) instead of staying in one drop (high concentration). This is called diffusion.",
"Osmosis is specifically when water does this across a membrane."
] |
[
"Because proteins require water molecules to fold properly and to be dissolved in the first place. Removing all the water will cause the proteins (and all other biomolecules, like DNA) to form crystals. Upon rehydration those might dissolve again, but most likely they won't do so in the correct conformation (and some won't redissolve at all)."
] |
[
"Do protons and neutrons touch each other within the nucleus an atom?"
] |
[
false
] |
We’ve all seen the models of atoms which show a pile of protons and neutrons, making of the nucleus. Is this model accurate? More specifically, is there a measurable distance between the individual protons and neutrons, or are they “touching” in the way people normally use the word?
|
[
"They don't have well-defined positions in space, but we can talk about the spatial extent of their wavefunctions.",
"Heavy nuclei (A ~ 100) have radii on the order of ~ 10 femtometers, while a bare nucleon has a radius of around ~ 1 femtometer. So in heavy nuclei, protons and neutrons are packed very tightly together. The density of nuclear matter is enormous, about 10",
" times the density of water."
] |
[
"Quarks are identical particles just like electrons. So if you want to describe the quantum state of a nucleus in terms of quarks, it still has to be antisymmetrized with respect to exchange of ",
" two identical particles.",
"But most nuclear structure models (the exception being lattice QCD) ignore quarks and treat nucleons like the fundamental units that the nucleus is made of."
] |
[
"At that scale are quirks still clearly associated with individual baryons, or is it like valence electrons in (some) molecules where they can move between atoms, or are not clearly associated with any single atom?"
] |
[
"Are flies and other bugs aware that we are trying to kill them when we swat at them?"
] |
[
false
] | null |
[
"AFAIK, the brains of creatures like flies (and pretty much all bugs) give the creature drives (find food, mate, etc) and instinctual responses (avoid dying), while equipping them with the software to process external stimuli to such an extent that it allows the creature to respond to the environment in useful ways. What qualifies as \"useful\" is different from species to species. That's why flies are drawn to foods that we wouldn't think of eating - because the fly can eat them so it has a drive to. ",
"When it sees a swatting hand coming, the response from it's instinct to not die makes it avoid getting smashed as best it can. I don't know whether or not a fly forgets the hand as a threat or if it just immediately reverts to whatever it was doing before it dodged. I suspect the latter, since I also suspect that the fly doesn't have the cognitive software required to make pattern matching associations since flies don't really live long enough for that to be useful. ",
"TLDR: Probably not, probably yes, and probably yes. "
] |
[
"Do they forget as soon as they dodge our hands what just happened?",
"Insects can be conditioned to avoid something that they find attractive. ",
"http://www.jneurosci.org/content/31/20/7240.full",
"\nBut conditioning takes more than one instance of danger in a location where there is something attractive (such as food). So the insect will try again until it either gets the message, or is killed."
] |
[
"This really can be reduced to the question \"Are flies and other bugs aware?\" ",
"The answer to that depends very much on what you think 'aware' means - but in a simple sensory way, yes, of course they are aware of the stimulus of a fast-moving thing near to them, that's how they are able to move away from it. Whether that means that they have any higher 'awareness' of what might happen if they didn't dodge, is a question that it's pretty hard to answer in any unambiguous way. ",
"Look at it this way - are you 'aware' that it's necessary to breathe to stop yourself from dying of oxygen starvation? Well, actually you probably are as most of us are taught to understand that these days, but imagine nobody had ever told you that. You'd be very unlikely to be 'aware' of that fact at all, and yet it wouldn't have any impact on your ability to breathe. "
] |
[
"In large desert plains around the world, is there less oxygen in the air?"
] |
[
false
] |
Given that flora whilst in photosynthesises creates oxygen, and a desert generally lacks flora and in most cases fauna as well. Would this result in less oxygen than average? as I've learnt to be approximately 19-21%
|
[
"There might be some small variations in oxygen content, but the amount is going to be very small. Here is my reasoning. Plants make O2 from the CO2 in the air. CO2 has a current concentration of 400 ppm. Even if the plants could take all the CO2 and make it into oxygen (they can't, but as a best case scenario) the oxygen content would increase by 400 ppm or 0.04%. In reality I would expect this to be less than 0.001%.",
"Also at night plants breath oxygen and produce CO2, so the daily increase in O2 is muted."
] |
[
"I doubt there would be any noticeable difference to a human. Currently, Earth's atmosphere is composed of approximately 200,000 ppmv oxygen or about 20% of the total gases in the atmosphere. If you believe there would be less oxygen then it has to be replaced by something else which you imply would be CO2 due to lack of plants. The atmosphere is currently composed of approximately 400 ppmv of CO2 or about .04% of the total gases in the atmosphere.\nWithout even going into how well mixed the surface of the Earth is or getting into atmospheric constituent changes due to elevation since we are discussing the desert which I'm assuming to be at sea level, I think you should see that 200,000 is a much bigger number, 3 orders of magnitude larger, than 400. So any increases in CO2 due to lack of uptake by plants is not going to be noticeable to a human.",
"Beyond this simple thought experiment, keep in mind that the majority of source of oxygen is phytoplankton which resides primarily in the oceans.",
"Further, and to maybe go a bit deeper in understanding, parts per million is just a ratio so you can in theory increase any constituent of the atmosphere without another decreasing. For example CFC's were injected into the atmosphere leading the depletion of the ozone layer. This didn't mean we reduced any of the other constituents, we just added more of another or in this case, added a brand new one.",
"That being said, you will notice the air is much drier since there is usually close to no water vapor in the air near the surface in a desert. Water vapor is dependent on geographic location across an isobaric region."
] |
[
"wow, didn't realise plant breathed oxygen at night, learn something new everyday"
] |
[
"Is cannabis a vasodilator, or vasoconstrictor?"
] |
[
false
] |
I've seen many conflicting arguments online. Forums say it's a dilator while some websites say it is a constrictor.
|
[
"The active ingredients in cannabis activate receptors of the endocannabinoid system, which is widespread throughout the entire body and brain. These receptors come in a variety of forms (the three most popularly studied of which are called CB1, CB2, and GPR55/CB3, although there are others besides these), and the molecules that activate these receptors come in an even larger variety of forms. Keep in mind that we've only known about this system since about 1992, and it is so complex and involved in so many different body processes that we're only starting to get a glimpse of how powerful it is. It has an influence on the skeletal system, urinary system, circulatory system, respiratory system, and actually I could just name every other system in the body because the endocannabinoid system is ubiquitous. ",
"The endocannabinoid system appears to act as a modulator of body functions, like a dimmer switch. So for example, it doesn't just strictly \"turn on\" bone formation, but it up-regulates or down-regulates bone formation according to the body's needs. The same seems to be true for all of its functions. ",
"We humans have been domesticating cannabis for thousands of years, and have produced hundreds of strains containing all sorts of molecules that activate the endocannabinoid system in different ways. It is entirely plausible, perhaps even inevitable, that some strains of cannabis act as vasodilators, while other strains act as vasoconstrictors. That being said, it is also plausible that cannabis might tend to change this modulation consistently in one direction (e.g. it usually stimulates appetite rather than suppressing it; or as the other commenters have said, it appears to usually trigger vasodilation rather than vasoconstriction).",
"The fact that you can get medicinal marijuana from a dispensary, and look over dozens of strains which describe themselves simply as \"Clear, Alert, Sociable\" while giving a raw percentage of THC, without telling you any of the dozens of cannabinoid molecules that they contain nor their specific effects, indicates that a ton of research is needed to elucidate just how we can tailor this plant to do exactly what we need it to do for each person (e.g. stop seizures, mitigate bipolar mood swings, control cancer growth, etc.). Cannabis is probably the single most promising source of new pharmaceuticals in the entire world, yet the state of the science for medicinal marijuana is absolutely abysmal. But it's a start."
] |
[
"It's reasonably ubiquitous to assume the different ",
"terpenes",
" in the pollen produce different effects other than just aromatic diversity."
] |
[
"It's reasonably ubiquitous to assume the different ",
"terpenes",
" in the pollen produce different effects other than just aromatic diversity."
] |
[
"While in High School, my science teacher explained evaporative cooling as \"the warm molecules evaporate, leaving only the colder molecules behind\". This didn't sound completely right then, and still doesn't now, is it?"
] |
[
false
] |
[deleted]
|
[
"Check out the ",
"Maxwell-Boltzmann distribution",
" for the speeds of gas molecules at a given temperature. You will find that there exists molecules with a wide range of kinetic energy."
] |
[
"The language is a bit wooden, the way you quote it, but you could say that is indeed the case. Not all molecules have the same speed, and of course the fastest ones are more likely to escape."
] |
[
"Temperature is a statistical value. It doesn't make much sense to speak of the temperature of one molecule. But if by \"warm\" you mean \"which has an energy higher than the average for a distribution of molecules at this temperature\" then it's absolutely correct."
] |
[
"Why must steam from a turbine be sent through a cooling tower?"
] |
[
false
] |
It seems like a pointless waste. Why isn't the steam, for example, sent through pipes and used to preheat the feed water? I do understand that water must be cold before it can be used to drive a turbine. But why can't you cool it off by transferring heat to the water that has already entered the heating phase? Apologies for inventing terminology...
|
[
"Thermodynamically speaking to get energy from the steam you have to have a flow of heat. so with out a cold spot to dump that heat you have no way to power the turbine.",
"secondly a bunch of power plants never use evaporation cooling, They just use a single pass water source such as a river. The places that do use cooling towers do it because of either regulations controlling how much heat they dump back into rivers or a lack of other good ways to cool the plant.",
"Also in the inner loop of the plant the steam has to be re-condensed into water so that the steam can be pumped back into the boiler to be turned into steam again to power the turbine.",
"hopefully I've answered your question somewhere along the way....",
"here's a picture showing how all the cooling loops interact.",
" Note that tertiary loop can either be cooling towers or a stream/lake/river/ocean"
] |
[
"Actually, Water must be hot (its usually superheated steam) to run a turbine. Turbines work by lowering the enthalpy of the fluid driving them, and to have high enthalpy a fluid must be hot. What you don't want is the steam condensing inside the turbine as that will damage the turbine.",
"Outlet steam often is used to preheat other fluids. This is called regeneration (I'd provide a link, but I can't find one; A thermodynamics textbook should have the appropriate info). However, it doesn't work on every design as the steam may not be hot enough to provide any useful preheating, so they just condense it before releasing it to the environment."
] |
[
"Your third sentence is correct. The vapor leaving the cooling tower is only used to absorb heat from the condensing of the steam loop and is evaporated off.",
"Depending on the cooling tower and design of the plant, that visible vapor is usually not \"steam\" as in superheated vapor. The actual temperature of the water vapor could be anywhere from 50 deg F to 200 deg F, and if it happens to be above the current dew point of the air around it, it will condense into visible vapor. It's a similar phenomenon to fog or when you see your breath when it's cold."
] |
[
"Why are ppm and mg/kg used interchangeably in some fields?"
] |
[
false
] |
I'm a physician looking through some environmental science literature. I've noticed that ppm and mg/kg are being used as synonyms. However, remembering my chemistry, it seems that you'd need to account for the molar masses of your compounds to convert from one measure to the other. So do these terms represent a mass fraction or a molar fraction?
|
[
"You are right; ppm are count ratios aka molar ratios, whereas mg/kg are weight ratios. They are only interchangeable if weight-to-count ratios, aka molar masses, are the same for the numerator and the denominator. ",
"Without knowing which fields you are talking about, it's hard to say how they justify the assumption of ~equal molar masses."
] |
[
"ppm is an ambiguous term, just like how percent solution can refer to %v/v, %v/w and %w/w. ppm doesn't specify what a \"part\" actually is. It can be a part by moles, a part by volume or a part by weight. If we use use weight/weight, 1ppm= 1/1000000=1mg/1000000mg."
] |
[
"I've actually been working with mycotoxins for the past year and we use ppm and mg/kg interchangeably because we are assuming a weight ratio. For example, in a sample of corn you might find 20 ppb of aflatoxin. In plant pathology that would equal 20 nanograms per gram. When we use the parts per notation we are using a ratio of weight not a stoichionetric ratio like what you might come across in general chemistry."
] |
[
"Can I have an \"electricity leak\" similar to how I can have a water leak in my house that will drive up my electric bill?"
] |
[
false
] | null |
[
"Exceptions to this are if you have wiring that is creating a short somewhere or allowing power to flow to ground",
"so the answer is, yes you can. I mean, how hard is it to find a ground?"
] |
[
"The answer given by ",
"u/brandonsmash",
" is completely wrong. You absolutely can leak electrical current from your house to ground, and it would increase your electric bill. It is usually difficult to do, but happens quite often due to poor wiring, or workmanship. \nSource: am an electrician and have observed and fixed current \"leaks\" on numerous occasions. "
] |
[
"In short, you can't have an \"electricity leak\" but it is possible to have a circuit that uses current despite being nominally off.",
"That sounds exactly like an \"electricity leak\"."
] |
[
"Why haven't plants evolved the ability to fix nitrogen from the air to use for growing?"
] |
[
false
] |
Why are only things like bacteria capable of performing this reaction? The amount of free nitrogen in the air is enormous, if a plant could use this for growth and reproduction, the evolutionary advantage would be huge compared to normal plants, since nitrogen is often the major limiting nutrient in soils. What is it about bacteria that makes this N2 to NH3 (ammonia) reaction only possible in them?
|
[
"While I don't know the exact underlying genetics (see edit), but I think I can partially answer the question from an ecological perspective. The reason is likely to be that it would be less competitive for the organism to do the process itself than having another organism (bacteria) to accomplish the task. That's why we have different organisms filling out various ecological niches instead of one that can do ",
".",
"There are limitations to these tricky reactions. In this case:",
"Enzymes responsible for nitrogenase action are very susceptible to destruction by oxygen. Many bacteria cease production of the enzyme in the presence of oxygen.",
"You essentially have two mutually incompatible environmental requirements (plant cells like to be aerobic because aerobic respiration is much more efficient and anaerobic environment makes nitrogen fixation possible). Therefore, the better arrangement would be a symbiotic relationship between a plant (such as those in the legume family) and the nitrogen fixing bacteria.",
"EDIT: Here's a short ",
"relevant article",
" on nitrogenase and bacteria-plant interaction.",
"EDIT2: Proofreading..."
] |
[
"Just wanted to add to the above response - ",
"cyanobacteria",
" are capable of both photosynthesis and nitrogen fixation. To circumvent the incompatible environmental requirements, one will observe differentiation in cyanobacteria, culminating in the formation of ",
"heterocysts",
". "
] |
[
"Just wanted to clarify that not all cyanos can fix N, it's mainly organisms in the nostoc and oscilllatoriales that can do it. Also i'll mention that the oscilllatoriales are paraphyletic, and many of the genus names (leotolyngbya, anabaena, ",
") are paraphyletic as well. You can blame the water quality people for this, who named a lot of these critters before the advent of molecular taxonomy (see Malcolm Potts' Ecology of Cyanobacteria for a thorough review. That might not be the actual name, it's sitting in my desk right now). ",
"This is also a niche thing - heterocystic N fixation takes a TON of energy, since the heterocysts have to be anoxic inside. So when there is labile N available, heterocystic N fixers may get outcompeted by cyanos that don't bother making expensive heterocysts.",
"EDIT: the rabbit hole of cyano competition and N goes a lot deeper, with uptake affinity variability, which is related to the oligotrophy/copiotrophy continuum. Think about which side of that continuum heterocystic cyanos (or N fixers in general) are more likely to occupy. "
] |
[
"Is there an equal amount of matter as there is anti-matter in the universe?"
] |
[
false
] | null |
[
"No; there's more matter than antimatter, to the point that almost all of the stuff floating around in the Universe is what we'd call matter. This is one of the bigger mysteries in physics, since generally you'd expect the two to have been created in equal amounts in the early Universe. There are speculative theories which try to ",
"explain this asymmetry",
", and it's hoped that the Large Hadron Collider will ",
"be able to rule out or confirm",
" many of those."
] |
[
"Antimatter stars or galaxies would produce and emit antimatter particles that would, when coming into contact with the normal interstellar or intergalactic medium, produce energy from annihilation. We haven't observed any such energy, so we're fairly sure we haven't seen any structures like this."
] |
[
"Given enough antimatter ingredients, yes, they'd behave just like matter and form atoms, molecules, planets, proteins, and overpriced sushi restuarants. Chances are, however, that there isn't much antimatter out there."
] |
[
"What is the practical reason diplomatic immunity exists?"
] |
[
false
] |
[deleted]
|
[
"Consider that, in even the most Freedom loving countries, finding a reason to arrest and incarcerate someone is a trivial matter. Meaning a government so inclined to lock someone up can find the pretext to do so.",
"However, there is the knowledge that, what we can do to theirs, so they can do to ours, so it is, essentially, a gentlemen's agreement not to dick around with each others' diplomats."
] |
[
"It's to prevent an ambassador from being persecuted, framed, prosecuted, etc. in performing their duties -- Especially during chaotic times such as wartime. ",
"In the case of a crime being committed that is not related to their duties on the job the host country would generally waive the diplomats immunity and allow them to be prosecuted.",
"Take an example. The ambassador is accused of spying. Whether or not it's true is irrelevant. Local laws may call for his arrest, jailing, or execution. In this case the host country wouldn't want their diplomat protected."
] |
[
"Everyone has been mentioning extreme examples of the government purposely trying to get the diplomat. There are other reasons, like not arresting the diplomat for something they didn't know they couldn't do here but could in their country, turning right on a red light, or smoking weed. "
] |
[
"Why do we square then square root in standard deviation, as opposed to simply taking the modulus of all values? Surely the way we do it puts additional weighting on data points further from the mean?"
] |
[
false
] | null |
[
"You are absolutely correct. The choice of variance/standard deviation as a go-to metric for population variability has been contested, for exactly this reason. A more direct & sensible metric would be the ",
"absolute mean deviation",
", i.e. f(x) = | x - µx | for a random variable x. However absolute values make the mathematics very cumbersome. For one, functions containing absolute values must usually be treated piecewise, with different definitions for when the argument is positive vs negative; and two, such a function is not continuously differentiable in calculus.",
"Polynomials (e.g. squares & square roots) on the other hand, are much easier to work with, in part because they are continuously-differentiable. Note that many statistical proofs depend on the mathematics of calculus.",
"In general, the algebraic properties of variances are very nice. To some, the fact that observations far from the mean receive higher weight is actually considered an advantage. I myself tend to agree that this is a flawed standard & it is certainly NOT true what you commonly hear from stats professors, \"the standard deviation is how far, on average, a randomly-sampled observation will lie from the mean\" (of course, that would be the absolute mean deviation)."
] |
[
"More generally, there's the concept of the p-norm, which is defined by ",
"||x||",
" = (|x",
"|",
" + ... + |x",
"|",
")",
".",
"So the cases you're talking about in the title are p = 1 and p = 2.",
"You can see visually what surfaces of constant p-norm look like in two dimensions ",
"here",
".",
"Different p-norms may be useful in different circumstances. For example, both p = 1 and p = 2 are used for regularizing regression problems, called LASSO regression and Ridge regression, respectively.",
"In practice, Ridge regression is good at making the values of all of the parameters generally small, whereas LASSO is good at making individual parameters zero (sometimes called ",
").",
"So in practice, you'd choose whichever is better for your specific application, or simply try both and see which performs better."
] |
[
"In addition to the absolutely correct things that have been said by others, I'd add the fact that the standard deviation is related naturally to the normal distribution, and the normal distribution arises naturally through the central limit theorem. So if you accept that calculating averages is a \"natural\" thing to do then you are a couple steps away from using something that naturally gives variance (and standard deviation) as a parameter of interest."
] |
[
"What are some of the most controversial science/tech issues today?"
] |
[
false
] | null |
[
"You'll have a hard time finding something which is \"socially/politically relevant\" AND the subject of actual scientific debate. Most political issues involving science have a fairly clear scientific consensus. ",
"Though \"debate\" is perhaps the wrong word, the effects of nano-materials on health is an up and coming issue with lots of needed pending research. It's too early for anyone to say whether or not there is a potential problem, but such materials are soon going to become commonplace and may have risks."
] |
[
"Haha, that's nice of you.",
"I won't be done for a few months. But perhaps I'll keep you posted."
] |
[
"Haha, that's nice of you.",
"I won't be done for a few months. But perhaps I'll keep you posted."
] |
[
"If mRNA vaccines remain proven safe, is it actually necessary to go through new trials each time when vaccinating for a new strain or another disease?"
] |
[
false
] |
Obviously it's best to be careful about these things. That said, with this new form of vaccination, a lot of the uncertainty of 'old school' vaccines is out of the picture, right? Supposing the method of getting mRNA into the body remains the same, and the proteins produced are innocuous – is there still reason to think that there could be unforeseen side effects?
|
[
"For a completely new virus, sure - you'd definitely need new trials.",
"For a modified vaccine targeting a new strain, probably not in the long term (maybe the first few times it's done for a given vaccine). Or greatly reduced compared to the original trials. ",
"Inactivated virus and protein based COVID vaccines needed full trials despite using well understood production methods and adjuvants, but an updated inactivated or protein based seasonal flu vaccine doesn't need a new clinical trial."
] |
[
"In addition to human safety, vaccines are generally only approved it they are effective.",
"So even if you're 100% sure of the safety of an mRNA delivery system, you still have to perform trials to see if it actually works."
] |
[
"Phase III trials indeed can take a long time and a large number of people. But you have to do it the hard way, waiting for people to naturally get infected and seeing if the vaccinated group had less infections than the placebo group.",
"The Phase II trials are the ones that primarily look at antibodies. The presence of antibodies doesn't guarantee that the antibodies are protective, but it's a good sign that the study should proceed to phase III trials. Conversely, if the antibodies are not there it can be a sign that the tests should be abandoned.",
"To summarize:"
] |
[
"Do theoretical physicists represent observation abstractly in mathematics? If so, how?"
] |
[
false
] |
I have the vague understanding that all possible values of a quantum measurement get modeled mathematically as a probability wave that collapses on observation. For example, I recall Richard Feynman explaining the uncertainty principle. He said no matter what you do, you can't know the heading and position of a certain particle. Then he listed a bunch of ways you could try and observe both, and showed how each observation introduced uncertainty somewhere else. I get that you can model the specific particle interactions in each case (and I think that's what Feynman diagrams are actually for, right?). But my question is... Do physicists model the abstract concepts of "observation" and the state of what information (or how much information) is "known" and "not known" to the observer over time? In other words, is there a mathematical representation of epistemology that physicists use when they think about observation? And if so, what does it look like?
|
[
"Yes, the mathematical operation indicating observation of a quantity is given by the corresponding Hermitian operator. For example, with appropriate assignment of axes and such, the (one dimensional) position operator is just x, the momentum operator is -i * hbar * d/dx, and you can directly show that momentum and position do not commute by just taking the commutator of momentum and position [x,p]=xp-px= (x)(-i * hbar * d/dx) -(-i * hbar * d/dx)(x)= -i * hbar * (-1)=i * hbar. So you know immediately there must be some uncertainty principle for position and momentum, and the value of uncertainty should be in the neighborhood of hbar (hbar/2 to be exact)"
] |
[
"You're answer was fine, but I felt compelled to point out that your derivation of the commutator of x and p is not formally correct. The answer is correct, but to be rigorous you should act the commutator on a state, i.e. [x,p]|psi>= ...",
"I just didn't want anyone to put that on an exam or anything."
] |
[
"Thanks! I'm not sure I understand the math. but I think I get the gist. You're saying that position * momentum != momentum * position and so whichever observation you do first changes the value you get for the other.",
"I guess what I was really asking was whether the observer was actually represented in the equations as a symbol, the way agents are in ",
"epistemic modal logic",
".",
"But... Having read up on the terms in your response, I see now that the observer's knowledge isn't really relevant to physics: only the actual observation event matters. ",
"Fair enough. :)"
] |
[
"Do photovoltaics or fossil fuels generate more pollution per kilowatt of power?"
] |
[
false
] |
Specifically, is the pollution created during the manufacture of photovoltaic material greater or lesser, per kilowatt of power, than the pollution created by the conversion of fossil fuels to power?
|
[
"The nice thing about solar cells is that they generate no pollution or CO2 emissions when they produce electricity, however, you are right that they require an input of energy for their manufacture with all the associated generation of pollution and CO2. To gauge whether solar cells still provide a net plus from an environmental standpoint, you can consider something called their \"energy payback time,\" which is defined as the amount of time they they need to operate before they will generate enough total energy to offset the energy required for their manufacture. This ",
"chart from NREL",
" summarizes the energy payback times of currently used photovoltaic cells. ",
"As you can see, the payback times are generally under 3 years and are projected to be even lower in the future. When you consider that the lifetime of the cells is about 30 years, this means that over 90% of the energy they produce can be considered to be \"clean energy,\" devoid of the negative externalities of pollution and CO2 emission. In other words, even when you account for the initial energy you have to invest in the manufacture of solar cells, the technology still represents a very viable route towards producing energy in a way that minimizes carbon emissions and other forms of pollution."
] |
[
"That chart is almost certainly the result of a cradle-to-grave ",
"Life Cycle Assessment",
". In wiki's own summary:",
"Cradle-to-grave is the full Life Cycle Assessment from resource extraction ('cradle') to use phase and disposal phase ('grave'). For example, trees produce paper, which can be recycled into low-energy production cellulose (fiberised paper) insulation, then used as an energy-saving device in the ceiling of a home for 40 years, saving 2,000 times the fossil-fuel energy used in its production. After 40 years the cellulose fibers are replaced and the old fibers are disposed of, possibly incinerated. All inputs and outputs are considered for all the phases of the life cycle.",
"It's a tedious process to identify and characterize all stages of the product's life cycle (i.e. a panel needs ",
" many kg of silicon and the mine uses ",
" much fuel which generates ",
" much greenhouse emissions), but it's not conceptually all that difficult."
] |
[
"Silicon is not mined like iron or coal. It is reduced from silicon dioxide- sand mines, or quartz rocks. You drive out to a desert, shovel a bunch of sand, and drive back. No fuss, no mining. Its a billion dollar industry in the US and most of it is done in Texas. Silicon makes up 28% of the crust and silica is insanely common.",
"It is refined in arc furnaces by heating it up with carbon, which turns into CO2. For each pound of silicon, the initial purification besides electricity for heat creates 1.5lbs of CO2, which is very little compared to how much you can do with a pound of silicon (a pound of coal, for instance, creates 3.6 pounds of CO2). ",
"Silicon takes more energy to melt than steel, but this is also small compared to how much energy it will go on to make. The purification process is much more involved than other metals, but again... doesn't compare to how much power a solar cell will create. "
] |
[
"How come old people have a circle on their upper arm?"
] |
[
false
] |
It looks like a weird circle shaped imprint and I'm not sure how to describe it but its usually like the top of their arm on the side facing out. Not all people have it but it seems mostly really old ones have one. I don't know a single person my age with one, does it just grow later on?
|
[
"It's a smallpox vaccination scar. Pretty much all kids in developed nations used to be vaccinated for smallpox, and just about every kid in the world was vaccinated from the late 60s to early 70s, till the disease finally died out, due to a massive coordinated worldwide vaccination effort organized by the World Health Organization. So the scars you're seeing are basically battle scars from the biggest vaccination war ever, and it's the only time (so far) that we actually succeeded in driving a disease to extinction.",
"(edit: I meant, only time we've driven a ",
" disease to extinction. We've also knocked out 1 animal disease.)"
] |
[
"The round mark on the upper arm that the OP is describing is classic for the smallpox vaccination. It was typically on the left upper arm and is about the size of a dime. ",
"Here's",
" a popular press article and ",
"here's",
" a picture of a typical smallpox vaccination scar.",
"There was also an ongoing campaign to vaccinate against polio, and many people got confused about which vaccination left the scar (especially if the kids got the vaccines near the same time). Many people assume that the smallpox scar is the polio scar, especially since smallpox has now dropped out of public consciousness; but if it's on the left arm, is slightly depressed and is about the size of a half-a-dime to a dime, it's almost definitely from the smallpox vaccination. (edit: there's a form of tuberculosis vaccine that can leave similar scars. But it less consistently leaves a scar, the scar usually doesn't look quite the same, and in the USA there's never been a mass vaccination with that vaccine anyway, so those scars are less common. It's common in certain other countries though)",
"BTW the reason smallpox vaccination left such a distinctive scar is that the hallmark of this disease is that it forms really horrible skin pustules that leave some ",
"pretty hideous scarring",
". (This was an incredibly important disease in human history. It used to sweep through human populations periodically and kill about 1/3 of children, and a large % of survivors were left terribly scarred. It devastated the Americas and is one of the reasons that the Aztecs and Incas were conquered.\n) Anyway - the vaccine typically made just 1 small pustule, at the site of injection, which left that distinctive round scar. ",
"Fun fact, it's thought that the reason \"milkmaids\" turn up in so many stories and nursery rhymes as the prototypical \"pretty\" country lass is that milkmaids often were immune to smallpox and were less likely to have smallpox scarring on their faces. This is because they'd often been exposed to cowpox, a related virus, which made them immune to smallpox - basically they'd vaccinated themselves accidentally. This in fact is what led to the development of vaccinations; smallpox was the first disease ever vaccinated against - in a very famous series of experiments by Edward Jenner proving that exposure to cowpox could make people immune to smallpox. And, that gave us the words \"vaccination\" and \"vaccine\", which are derived from Latin \"vacca\", \"cow\" - because \"vaccination\" originally meant \"to inoculate with material from a cow\" - pus from a cowpox blister!",
"edit: for more info see the book \"Angel of Death\" by Gareth Williams for a general history of smallpox; ",
"this WHO page",
" for a short history and big gallery of photos about the smallpox eradication effort; and ",
"here",
" for a nice (and peer-reviewed!) history of Jenner and vaccination."
] |
[
"This is a good answer. ",
"I'll add that sometimes you'll see ",
"similar scars",
" on younger people from other countries. These are likely BCG vaccination scars. The BCG vaccine is an anti-TB vaccine used in some parts of the world, although it isn't used in America due to variation in and controversy over its effectiveness."
] |
[
"Is there evidence for long-term variation or change in our physical constants?"
] |
[
false
] |
I work in an EMC test house and often have to consider the accuracy of my measurements and the instruments used in those measurements. To ensure that our equipment is giving us good data, we have to periodically send the equipment to calibration labs, where they go through a battery of tests. I'm not an expert on the process, but I'm assuming that, among other things, the person in charge of calibration uses signal sources with known output to make sure the instrument's measurement accuracy is within certain tolerances. The signal source's output in this case is measured often to make sure that it is within the range of what is appropriate for the battery of tests. The instruments that perform these measurements are themselves calibrated from time to time in much the same way as our device. The point of all this is to account for electrical components which have been worn out, and to discover anomalies generated by the design and configuration of those instruments. My question comes because I don't really understand the process by which these components wear out, but I'd like to present a few more examples of processes with similar consequences but different causes. First, I want to bring up the example of volcanic activity. Besides the ash and lava ejected from underground chambers, which return to the surface, there's a release of gasses which remain in the atmosphere indefinitely. These gasses, which I assume contributed to the mass of the earth beneath our feet before eruption, would have to contribute to the weight of the atmosphere after eruption. I realize that the magnitude of the change in masses of earth and atmosphere is insignificant next to their total masses, but on a long time frame (say millions of years) where volcanic output is constant on average, wouldn't the absolute value of atmospheric pressure change, as well as the gravitational constant? Since we assume that the value of pressure is constant, whenever we see barometers giving a reading outside the expected value and alter its calibration, aren't we making those barometers more and more inaccurate? Second, the kilogram. The magnitude of the kilogram is expected to be exactly the same everywhere because it is based on the International Prototype Kilogram (IPK) which is kept in France. Excuse the skip in logic here, but my mind goes back to the example of the unopened six-pack of cola which, after years of sitting on a shelf, is opened to reveal that they are half-empty. How do the standards institutes verify that the IPK of today has the same mass as the IPK of 1980 or 1939? Can we be absolutely positive that our measurements are ever accurate? Can anyone shed some light on how smarter men and women have solved these problems, or if they have?
|
[
"Can you clarify your question, please? Are you asking about physical constants, or are you asking about experimental precision? If it's the first, the answer's no, and if it's the second, that's just engineering and repetition."
] |
[
"What I'm trying to posit is that the change in accuracy of a single measurement device or groups of the same device over time would imply, with several degrees of separation, that there is change in the constants. I realize now that the kilogram was a poor example to use since mass is directly tied to the amount of matter that an object consists of, but I'm curious as to how a physicist would begin to explore the hypothesis. If you begin with the assumption that the constants are not constant with respect to time, how do you begin to prove or disprove it?"
] |
[
"Except not really. The Webb paper that first suggested that turned out to have a catastrophic methodological error that invalidated the results."
] |
[
"If you are living in a cold country, is it still necessary to buy efficient light bulbs?"
] |
[
false
] |
[deleted]
|
[
"You have a good point. Such a good point in fact, that when the EU banned incandescent bulbs a German businessman started importing them as \"heat balls\".",
"The funny thing about this is that incandescent bulbs are fairly efficient when they are used as heaters, throwing off around 95 percent of the energy they draw as heat. In colder climates, using the bulbs for lighting isn't always an inefficient choice as the bulbs add to the warmth of the home.",
"Source"
] |
[
"They certainly generate heat, but there are better ways of heating. ",
"Heat pumps",
" are much more efficient, as they move heat around rather than just generate it.",
"If the temperature difference between outside and inside is not too great, they can warm the room by 3 to 4 times more than a resistive heater would, for the same energy cost. In very cold climates you can use ",
"Geothermal heat pumps",
", where the source of heat is the ground rather than the air.",
" typos."
] |
[
"Ha, I like that!",
"Do you think that there are figures to back this claim up?",
"Edit: just noticed the relevant username!"
] |
[
"The 'book detector' when I walk in/out of my university's library causes a high pitched sibilance in my earphones. Why?"
] |
[
false
] |
On entry or exit at my university's library, stock standard iphone 5 earphones let out a high pitch noise while listening to music. Why?
|
[
"The book detector is emitting a radio signal which would energize and RFID chips in the book detector tags. Your earphones are acting as antennas and picking up the signal. You can sometimes get the same effect if your phone is sending/receiving a lot of data near some speakers."
] |
[
"Kind of like how many MP3 players wouldn't play FM radio without anything plugged into the headphone jack (to act as an antenna). Even my bathroom alarm clock/radio uses its power cord as a receiver for FM."
] |
[
"Kind of like how many MP3 players wouldn't play FM radio without anything plugged into the headphone jack (to act as an antenna). Even my bathroom alarm clock/radio uses its power cord as a receiver for FM."
] |
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