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[
"Muscle Hypertrophy, how slow is this process?"
] |
[
false
] |
After asking a bunch of different body builders, I've started to notice that people who are in their 20s with great muscle mass that is clearly very visible even when unflexed, either have been training for nearly a 5-10 years already or use steroids. I've been strength training for 1.5 years, but it is unlikely that an average person would comment that I am extremely muscular unless I flex. It seems as though muscle hypertrophy is a very slow and gradual process. Is there a consensus on the rate at which people can gain muscle?
|
[
"The rate of muscle gain will be down to the exercise you do, your own genetics, and the nutrients available for muscle gain. ",
"Please also note that muscle hypertrophy is not actually an increase in muscle cells, but an increase in the constituents of the muscle cell. Commonly seen as an increase in sarcoplasmic volume (in essence the liquid inside the cell) or an increase of the contractile proteins (the bits that \"pull\" and give force).",
"Muscle Hyperplagia is an increase in the number of muscle cells as a whole, and not the growth of their constituent parts. Perhaps you may wish to investigate this also if you want to generate new muscle tissue as well make the muscle bigger.",
"I'm assuming having the large muscle/ripped look is what stimulated your inquiry.",
"The actual method by which the hypertrophy occurs is largely dependant on your training method. Not being a sports scientist I am unaware of the actual data on which is best. It is worth highlighting; however that your diet and genetics play a part on the gain, not just the exercise.",
"Perhaps also try x-posting this to ",
"r/fitness",
". I am sure there will be a wealth of people to offer up information or opinions on this. Personally I engage in light sports and lots of lifting of textbooks so I lack personal experience of large muscle gain!",
"Hopefully a sports scientist or the chaps at ",
"r/fitness",
" can help with the remainder."
] |
[
"That's the thing, everyone has their own opinions on it. ",
"I'm looking for studies.",
"Of course diet, genetics, and training play a big factor. But generally most people who've worked out for many years achieve a very good muscular physique.",
"I'm not looking to see what way is quickest, I'm just trying to find out how slow or fast this process is. ",
"Those differences in genetics, diet, training, should be minor, maybe if my methods are ineffective, it might take me a year or two longer, I just don't want to be stuck doing something for 4-5 years only to realize, it was all for nothing due to X limitation or Y mistake.",
"My interest was piqued, when I heard of that study about highest metabolism vs lowest metabolism, and how it's only a 760 calorie difference. I mean I don't think genetics and training method should matter as much as consistently eating enough and working out a lot."
] |
[
"Perhaps this may be of interest. ",
"http://www.sci-news.com/medicine/article00560.html"
] |
[
"Does your body still \"recharge\" at all if you are just lying there, eyes closed, not moving, but not sleeping?"
] |
[
false
] |
Wondering because I've heard that if you are trying to nap, but can't really fall asleep, you're still benefitting. Would love to know the actual science behind this, if it exists.
|
[
"Yes, to a certain extent.",
"The body's systems are not usually just \"on\" or \"off\". There are gradients and different levels of activation of each system in the body. Even within the context of sleep, there are different kinds of sleep, with some biological processes occurring at different rates.",
"Several of your body's recovery mechanisms are always active. They are constantly fighting against the damage inflicted on your body over time. Resting just reduces the damage being inflicted, causing the effect of the recovery mechanism to be more pronounced. Other mechanisms will increase or decrease based on your activity level.",
"There are some mechanisms that kick in only when you're actually asleep, so resting is never going to be \"enough\", but you definitely get some benefit."
] |
[
"Many of your body's recovery mechanisms are activated by signals from the brain. Under most circumstances, the brain will continue to operate those mechanisms regardless of how you much attention you're paying to other things. Consider the fact that, no matter how much you're thinking about, your heart will still continue working - that's a system that's controlled by the brain.",
"However, some kinds of input will trigger responses. Particularly relevant are stress responses; the brain's reaction to stress triggers a whole lot of physiological changes, including slowed recovery times.",
"Generally, if the external events aren't stressing you, it probably won't have a noticeable effect. If they do create stress reactions, it can noticeably slow your recovery process."
] |
[
"Recent research indicates that the mechanism that clears toxins from the brain is more active when asleep. ",
"Link",
"Presumably you can't \"fool\" your body into activating this mechanism by resting - you actually have to be asleep."
] |
[
"Why does the order of fusion of elements in a star core go H=>He=>C=>O=>Ne=Si=>Fe? Why does it skip steps?"
] |
[
false
] |
Why does Fusion in a star not follow the order of elements from Lightest to Heaviest in order?
|
[
"Theoretical science = educated guesses? What?"
] |
[
"Each combination has its ",
"own set of reasons for why it happens",
"."
] |
[
"See the ",
"Proton-Proton Chain Reaction",
", OR the ",
"CNO cycle",
". This is then followed by the ",
"Triple Alpha Process",
" ",
"I feel retarded because I just took a stellar physics course 2 semesters ago and can't remember a darn thing. But essentially elements will fuse into isotopes, decay, and fuse again into more stable elements (I think). For the Proton-Proton reaction: we start with Hydrogen (1 proton), two Hydrogens gives us Deuterium (with a plus two charge). The resulting positron and any free electron will annhiliate each other to create a gamma ray. Now we have Deuterium fusing with another free Hydrogen, giving us a Helium isotope (3 protons). From here, depending on the star, there are a few paths to take to get to Helium. To make things easy we'll just go with the \"first\" path, i.e., two of our Helium isotopes fusing to create one Helium (+4) and two Hydrogens. ",
"I skipped the CNO cycle because I'm lazy, sorry :( but the CNO cycle is just another way to create Helium. Which cycle the star uses depends on the temperature of the star.",
"Next is the Triple Alpha Process. This process doesn't happen until the star is running out of Hydrogen to fuse. Two of our formed Heliums fuse to create Berillium (+8) which is quickly hit by another Helium (+4) to create our Carbon (+12). Some Carbon can also fuse with Helium to create Oxygen.",
"the basic ideas here repeat themselves until Iron begins to form. after that, energy input is required to fuse Iron, so there is where things start to go downhill for the star",
"A physicist may want to double check me, I'm just a dumb mechanical engineer >.>"
] |
[
"Do extended regular expressions still denote the same language class?"
] |
[
false
] |
I remember from college this theorem showing that for every regex, you can construct a NDFA that accepts the same language; for evert NDFA, you can construct a DFA accepting the same language; for every DFA, you can define a regular grammar generatig the same language; and for every regular grammar you can build the equivalent regex. Thus those 4 mathematical concepts are bound to the same class of regular languages. But several programming languages have extensions to make regular expressions easier. Do any of those extensions denote any set of strings that cannot be part of a regular language?
|
[
"PCREs can match context-free languages. Here's a proof by construction:",
"Any context-free grammar can be rewritten in Greibach normal form, removing left recursion. That means all productions will be of the form:",
"where ",
"a",
" is a terminal, ",
"A",
" is a (possibly empty) sequence of nonterminal symbols not including the start symbol, ",
"S",
" is the start symbol, and ε is the empty word.",
"We disallow the use of blocks executing arbitrary code (",
"??{}",
"). We use the ",
"(?(DEFINE)...)",
" PCRE groups to rewrite the grammar by translation of:",
"(?<HEAD>...)",
"(?&A)",
"|",
"(?:...)",
"^(?(DEFINE)...)(?&START)$",
"^",
"$",
"By noting that the last non-terminal (edit: in the set ",
"A",
") can only have a production of the form ",
"An -> a",
", it is already in GNF. Therefore we can transform all the non-terminals moving \"backwards\" from the last. This is the method used by Albert, Giammarresi, Wood, \"Normal Form Algorithms for Extended Context-Free Grammars\", 2000 (",
"link",
").",
"You can also note that simple (to write) PCRE expressions can match context-sensitive languages:",
"# {a^n b^n c^n, n>0} (context-sensitive)\n/^ (?: a (?= a* (\\1?+ b) b* (\\2?+ c) ) )+ \\1 \\2 $/x\n",
"As an added bonus, here's ",
"some proofs",
" that matching PCREs with backreferences is NP-hard.",
"To address your question more directly:",
"Regular grammars can be parsed by DFAs. A DFA matches a regular language by keeping in memory exactly one state, and that state's transitions. Alternatively, one non-terminal and its productions.",
"Context-free grammars are matched by ",
"recursive descent (aka top-down) parsers",
". Top-down parsers match a CFL by keeping ",
", and multiple productions for each non-terminal. This can be more easily illustrated by the algorithm for table-driven parsers:",
"procedure Parser:\n /* Push the start symbol S onto the stack */\n stack.push(S)\n /* Initialize lookahead symbol */\n scanner(NextInputSymbol)\n while not Empty(stack) do\n top = stack.peek()\n if top is a nonterminal :\n action = ParseTable[top,NextInputSymbol]\n if action > 0 :\n stack.pop()\n /* Push RHS of production */\n for each symbol on RHS #action do\n stack.push(symbol)\n else print(\"syntax error\")\n else if NextInputSymbol == top :\n /* Match terminal symbol in input */\n stack.pop()\n /* Get next terminal symbol in input */\n scanner(NextInputSymbol)\n else print(\"syntax error\")\n",
"Now as for extensions, there are too many to consider here. Hopefully, it will be enough to temporarily satisfy your curiosity by considering ",
". Most extended regular expressions support the ability to match on an ",
" part of the string - so it can match repeating strings like \"wikiwiki\" or \"papa\". We can prove the language of those strings is not regular nor context-free via the ",
"pumping lemma",
". Since that language is not regular, it cannot be matched by a DFA.",
"This proof should take you only a few hours if you're unfamiliar with the terms, about 20 minutes if you're already familiar with the lemma. I encourage you to try it out."
] |
[
"You can match balanced constructs with PCRE like so:",
"(a(?1)?b)\n",
"and thus your CFG can be matched with ",
"PCRE",
"."
] |
[
"First of all, \"extended regular expressions\" mean something specific (POSIX extended regular expressions), which are equivalent to (N)DFAs. But those are a trivial extension to POSIX standard REs.",
"There are other RE variants, of which the most notable is Perl-compatible REs (aka PCREs), which are built into some languages (Perl, PHP, …), but not into others (Python) — although obviously in the latter you can usually find a 3rd party library that implements them.",
"PCREs are not DFA-equivalent because they include recursion (via the ?R) modifier. Recursion requires unbounded memory, so it takes you out of DFA realm. "
] |
[
"Is the way protons and neutrons are \"packed\" inside the nucleus constant between all nucli with the same number of protons and neutrons?"
] |
[
false
] | null |
[
"I'm talking about the energy levels of the nucleus. If you have two identical nuclei in the ground state, or in the same excited state, their internal structures are completely identical."
] |
[
"Thank you for your reply! i have never considerd that the nucleus has energy levels too!"
] |
[
"Yes, assuming they're in the same state."
] |
[
"Are gravity waves induced at the LHC by speeding gold ions to near lightspeed?"
] |
[
false
] |
If one of the problems of high speed travel (ie approaching lightspeed) is that mass starts swinging towards the infinite. Do particles in accelerators gain mass and has anyone deployed gravity wave detectors to measure this?
|
[
"You're presumably referring to how going fast makes things heavier. This effect doesn't actually exist, its an outdated way of explaining a phenomenon that looks ",
" to a mass increase. Things need more energy to accelerate, which looks like a mass increase in some sense, but they don't have an increased mass in other senses."
] |
[
"Gravitational waves have yet to be directly observed.",
"http://en.wikipedia.org/wiki/Gravitational_waves",
"I assume whoever is the first to detect them will be given a plane-ticket to Stockholm."
] |
[
"You can treat the beam as a ring moving around really fast in a circle. This, however, does not produce gravitational radiation. For graviational radiation, you need the moment of inertia of the system to be changing at a nonconstant rate. For a rapidly rotating ring (or system of rotating point particles), the moment of inertia is constant."
] |
[
"Do modern AI (Artificial Intelligence) programs know how to program themselves?"
] |
[
false
] |
I am wondering if those who are working in the frontier of AI have made one that knows how to change its own program. For example, simple learning is just incorporating knowledge and context; however, if an AI can rewrite its own program or add subroutines, then it seems like that AI would truly be able to learn and expand itself. Have we achieved such a level yet? If not, what would be some difficulties in doing so?
|
[
"Computer scientist here.",
"Many researchers have experimented with ",
"self-modifying AI",
", allowing varying degrees of self-modification up to and including total code revision--the equivalent of writing your kid's entire gene sequence.",
"The best outcomes of which I'm aware have involved the programs with the least amount of freedom to self-modify, though some promising research in neural network design may make that situation short-lived.",
"The primary difficulty is the same as with the gene-sequence analogy. How do you ensure that the result is viable, much less performs the task for which it is intended? It's very difficult to do so without placing significant constraints on the AI, and those constraints must necessarily be placed outside the code which the AI could rewrite.",
"An alternative would be the paradigm used in ",
"genetic algorithms",
", where the code supporting reproduction and fitness testing is maintained outside the program's code. This approach requires significant computing horsepower though, and that requirement increases exponentially with the complexity of the candidate GA. The type of computing power required to develop large-scale AI this way is not likely to be available for some time, if ever."
] |
[
"Your use of the word \"merely\" is amusing."
] |
[
"As a nitpick, the three laws were never intended to actually be used. I, Robot is all about how those three laws can go wrong."
] |
[
"What happens to electricity when it's grounded?"
] |
[
false
] |
Where does the electricity go and what happens to it? I faintly recall something about the changing of the Earth's magnetic poles being related to this.
|
[
"It disperses. I like to compare (for simplicity) electric effects to water and rivers and lakes. Picture grounding electricity as rain landing in the ocean. It found an area of lower potential and now it is at a universal potential distribution where it doesn't have anywhere to go or any reason to go there. Electricity is just moving electrons. Once they get to the earth, the reason that the electrons moved in the first place has a negligible effect on the earth as a whole, so it reaches equilibrium.",
"The reasons for the magnetic poles is drastically more complicated. "
] |
[
"Not in high science, but somewhat educated electrician.",
"Generally, \"grounded\" means going into the earth itself. It's generally considered an object sizable enough to contain lots of electrons to the point where pushing more in or pulling more out will make no difference. This isn't entirely true of course but a close enough estimate. In terms of effects on the earth itself, magnetic phenomena like storms would probably weigh much heavier. This is even considering things like HVDC (essentially shipping electrons from one place to another, using GND as \"common\"). I can't imagine it would have an impact on something so hugely more massive as the internal forces creating the magnetic field unless you're considering chaotic scales similar to Lorenz butterfly type impact (which could just as well and moreso be caused by the odd shift in the plates, a volcano or any other phenomena causing shifts in the earth).",
"What would generally happen at the site should (I think) be that that area now contains more electrons at the moment. Since they repel each other, they won't stay there but rather move apart until they are further away. This would eventually return to stability. By \"eventually\" I mean \"nearly instantly\" - the ground is so massive that a few extra or a few fewer electrons matters very little. Kind of like if a small spec of dust landed on you, you wouldn't feel the immediate \"OMG I'm so much heavier now\" (nor feel the reduced mass if it flew off again)."
] |
[
"I suppose, in a sense. We can generate electricity by burning coal and natural gas. The number of electrons that go into the ground is nothing compared to the number of electrons that are already there. ",
"I'm not sure what you mean by ",
". The planet Earth is electrically neutral. It's has no overall charge. The we can move these charges around to power our homes and whatnot, but there are never any extra. "
] |
[
"When splitting water molecules by electrolysis, how would sperate the hydrogen and oxygen?"
] |
[
false
] | null |
[
"What?",
"If I’m interpreting your question right, the two gasses will collect at the positive and negative poles in the circuit. Putting a test tube or some other container in the water over each pole will collect the gases as they bubble up. "
] |
[
"Each gas will start to bubble up. The water, H2O, separates into hydrogen and oxygen. I can’t remember which, but one of them will collect around the positive pole, and the other at the negative. As they bubble, they rise up through the water, similar to champagne bubbles. Placing the test tubes over each pole allows for the gasses to collect rather than float off into the atmosphere. If I wasn’t on mobile (and a swaying train) I’d get you a link and pictures. "
] |
[
"so how do they collect over the poles? "
] |
[
"Is water on the ocean floor more dense than water on the surface?"
] |
[
false
] |
I know that water is generally considered incompressible, but I read somewhere that it does compress ever so slightly. Is the water pressure at the bottom of the ocean enough to actually compress the water?
|
[
"Nubtom's anwer is true for \"normal seawater\" - but there are also local brine pools next to thermal seeps and hydrothermal fields with salinities about 3 times that of normal seawater which are even denser than that. These ",
"brines pools",
" do not mix with the water column and stagnate at the bottom in third order basins. They even have a surface, and can be described as \"lakes at the bottom of the ocean\". They are one of the weirdest things you can ever see..."
] |
[
"Yes. In fact, at the bottom of the Mariana Trench (11.03 kilometres/6.85 miles below sea level), water is compressed to about 95% of its normal volume, meaning 95 litres down there would weight the same as 100 litres on the surface. The pressure is 1,086 bars/15,750 psi, and the temperature is 1-4 degrees celsius. At the other parts of the ocean floor, the water is probably compressed to 97%-99% of its normal volume."
] |
[
"Really? Cool. I thought the only changes in density were the result of salinity or temperature. "
] |
[
"Probably a stupid question: Why does Ice expand? Don't molecules get closer together as they become solid?"
] |
[
false
] |
My confusion on this is based on one simple premise that I was taught in school. That an elements molecules get further apart when they pass from liquid to gas, and vice versa get closer together and more tightly bonded when passing from liquid to solid. If that is the case (which it may not be) why does water expand when turning to Ice? eg. in an ice-cube tray
|
[
"Your confusion is natural. What you learned is a general rule, but there are exceptions. ",
"Ice lower density is another example of the weirdness of water",
":",
"An unusual property of ice frozen at atmospheric pressure is that the solid is approximately 9% less dense than liquid water. The density of ice is 0.9167 g/cm³ at 0°C, whereas water has a density of 0.9998 g/cm³ at the same temperature. Liquid water is densest, essentially 1.00 g/cm³, at 4°C and becomes less dense as the water molecules begin to form the hexagonal crystals[2] of ice as the freezing point is reached. This is due to hydrogen bonding dominating the intermolecular forces, which results in a packing of molecules less compact in the solid.",
"Basically the point is that the dominating force (hydrogen bonding) favoures a type of structure which then happens to be less closely packed than the average packing of molecules liquid one.",
"Interestingly, once it's solid, it then behaves properly with cold, shrinking slightly when further cooled:",
"Density of ice increases slightly with decreasing temperature and has a value of 0.9340 g/cm³ at −180 °C (93 K).[3]"
] |
[
"Chemically speaking, water is one of the weirdest."
] |
[
"Great answer, thanks! Didn't realise water could be so weird!"
] |
[
"In healthcare, is there any known effect of \"willpower\" on patient outcomes?"
] |
[
false
] |
Past situations like staying awake after a concussion, does a fighting mindset or maintaining positivity/passion about your treatment play a clinically significant role in patient outcomes?
|
[
"Here's a thought from Mayo Clinic (",
"https://www.mayoclinic.org/healthy-lifestyle/stress-management/in-depth/positive-thinking/art-20043950",
").",
"Researchers continue to explore the effects of positive thinking and optimism on health. Health benefits that positive thinking may provide include:",
"It's unclear why people who engage in positive thinking experience these health benefits. One theory is that having a positive outlook enables you to cope better with stressful situations, which reduces the harmful health effects of stress on your body.",
"It's also thought that positive and optimistic people tend to live healthier lifestyles — they get more physical activity, follow a healthier diet, and don't smoke or drink alcohol in excess."
] |
[
"Not my area of expertise but isn't the placebo effect a version of mind over matter? I imagine that same effect can manifest in other ways too.",
"And there's something to be said about how a positive attitude changes how you approach rehabilitation and medication as well"
] |
[
"One of the most interesting theories is ",
"terminally ill patients may be using willpower to spend the holiday with their loved ones",
" and then feel ready to let go and say goodbye.",
"Christmas and New Years are the two of the deadliest days of the year for both cardiac and palliative care deaths. ",
"We know that holidays and celebrations are an important risk factor. There is always a spike of deaths after major holidays, even birthdays. Scientists can eliminate weather, lack of care, delaying-care, etc. You can take an aged care or palliative care facility where resources, food, etc are the same every day, but there is also a spike in deaths ",
" or ",
" a holiday."
] |
[
"How do researchers tell the difference between a placebo effect and a medicine that has a relatively low (but real) success rate?"
] |
[
false
] |
I guess what I'm asking is: what if a medicine works extremely well for a relatively small group of people? Wouldn't that possibly look as if it's just a placebo effect? Further, if it is possible to tell the difference, do you think there's treatments that have been tested and, after getting preliminary results that seemed no better than placebo, were abandoned despite the fact that they may very well work very well for a small group of people? Wow that was a run-on sentence.
|
[
"In most clinical trials the patient do not know if they are getting drug or placebo. Thus the placebo effect will be the same for patients getting the drug and for patients getting the placebo. The clinical studies look for differences between the two groups. In other words: Is placebo + drug better than placebo alone?."
] |
[
"The biggest determinant of \"works\" versus \"does not work\" boils down to two words: statistical significance.",
"If the effectiveness of the treatment is not ",
" different than that of placebo, it does not go further. If it works in a particular population which is a subset of the sample, perhaps it will be researched for that application. If it doesn't show statistically significant effects, it isn't effective. Measurement has to be objective."
] |
[
"Well, studies can be controlled for different population types. But if a medicine isn't any more effective than a placebo, why not just give the placebo? "
] |
[
"Scientifically explain why a table with 4 legs can wobble but one with 3 legs cannot."
] |
[
false
] |
[deleted]
|
[
"It's not really science - more like logic. A two legged (say A-B) structure is obviously unstable, it could fall one way or another. You can stabilize it by putting a third leg (C) in the direction it's going to fall. Now you have a tripod. ",
"Now let's say you put another leg (D) on the side opposite of (C). It has to be the perfect length in order to not wobble. If it's too short, it'll be like making two tripods (A-B-D and A-B-C), separated by the line A-B. ",
"If it's too long, you'll make (D) the new two-legged unstable structure, with A-B as supporting pivots. So your two new tripods are C-D-A and C-D-B. ",
"The existence of two 'tripods' is what accounts for wobbliness. ",
"Note that I never commented on the geometry of the table, it should be general - can be circular, rectangular, or random. Doesn't matter, as long as none of the legs lie on a line connecting two other legs. "
] |
[
"IHTFPhD has the right explanation, but I will give a math spin to it. Any 3 points defines a single plane. In a tripod, it's only natural for that plane to be the floor. But if you have 4 legs, what does that 4th leg do? If it's placed perfectly, it will be part of that plane. But if it's not, it forms a second plane. Then the question is, which plane lines up with the floor? Well, either one will work. A \"wobble\" is the table switching between the two."
] |
[
"Basic geometry.",
"3 points define a plane. That means if you take any 3 points, you can find a plane that passes through them ",
".",
"This is what is happening with a 3 legged table. The top might not be level, but there will always be a configuration where the tips of the 3 table legs (points) will be in contact with the floor (plane), no matter how uneven the legs.",
"Now add a fourth leg. Unlike the previous 3, it has to be ",
" even with the floor. If it isn't exact (or within a tight tolerance due to the table's elasticity), you will get wobble."
] |
[
"Outside of Fecal Transplants, Is There Any Recorded Evidence of Permanent Recolonization of The Gut With So-Called 'Good Bacteria'?"
] |
[
false
] |
I became curious after reading about how a single course of antibiotics may alter bacterial balance for a lifetime, but when I searched for evidence of probiotics permanently 'repopulating gut flora' I couldn't find any.
|
[
"The opinion article from the journal ",
" that the OP's article cites is speaking specifically about the consequences of antibiotic treatment in children. Interestingly, work published in ",
" in December 2011 (",
"Pubmed link",
") found that infants that are formula fed have a more diverse gut microbiota, with breast fed infants had a higher concentration of ",
" bacteria. In adults, the microbiota appears to be pretty stable, according to a paper published in ",
" in 2008",
". They found that 4 weeks after antibiotic treatment the microbiota of 3 adults remained pretty much unchanged. The majority of the microbes that had been lost returned, with a few exceptions.",
"As for probiotics, I found a review in ",
" June 2011",
" that indicates relatively few studies have been done with probiotics in humans. Part of the problem in testing probiotics clinically is in determining what to use as a measure of improvement. With so many different possible gastrointestinal symptoms, what can we use as a standard? Additionally, each individual has an individualized microbiota. This is likely due to differences in the genome of each person. Therefore, every person might respond to the same probiotic treatment differently, making generalizations difficult.",
"For more on this topic you might check out work by Dr. Ruth Ley (",
"Pubmed search",
". Her lab works with mice, looking at the interaction between genotype, microbiota and disease."
] |
[
"Do you have any citations for this?"
] |
[
"Do you have any citations for this?"
] |
[
"What happens on a neurological level when you're mentally drained or burned out?"
] |
[
false
] | null |
[
"Shame that top voted post in that thread is mostly wrong.",
"Glycogen reserves in muscles are depleted by anaerobic exercise not by being awake for a long time. Typically your body goes to reasonable homeostatic lengths to maintain glycogen stores in muscle. What they would have to do with mental tiredness is anyone's guess.",
"The neurotransmitter explanation is also wrong. Neurotranmitters are continually produced and destroyed by the brain in a semi-steady state cycle in the brain, there isn't some store that you're using up as the day goes on. The rate of production and hence the relative concentration of neurotransmitters during the day is indeed principally influenced by a circadian daylight-night cycle. But most neurotransmitters show complex daily patterns of brain concentration with few following a model when they are at their peak in the morning and \"get used up\" as the day goes on.",
"Figure 2 in the following paper measures the levels of 8 neurotransmitters in rat brains over a day-night cycle. For Arginine, Glutamine and 5-HIAA and dopamine there is no significant difference between night and day. DOPAC and HVA show a pattern where the are at their peak level at the start of the night and then fall steadily through the night and into the next day until the middle of the day where they begin climbing back to their highest point at the start of the following night. Glutamata and GABA are perhaps the only 2 that show a pattern where they recover during the night before being depleted throughout the day.",
"http://www.utoledo.edu/med/depts/physpharm/ceder/pdfs/Tamara_-_Circadian_rhythms_of_.pdf",
" I found these 2 articles on the role of glycogen in neural activity.",
"a) neurons do not store glycogen and it's accumulation in neurons can initiate apoptosis (programmed cell death) \n",
"http://www.nature.com/neuro/journal/v10/n11/full/nn1107-1341.html",
"b) Glycogen is instead held in nearby astrocytes where is can be mobilised as a nerual energy store in periods of \nlocal neural hypoglycemia ",
"https://www.ncbi.nlm.nih.gov/pubmed/17659525"
] |
[
"Shame that top voted post in that thread is mostly wrong.",
"Glycogen reserves in muscles are depleted by anaerobic exercise not by being awake for a long time. Typically your body goes to reasonable homeostatic lengths to maintain glycogen stores in muscle. What they would have to do with mental tiredness is anyone's guess.",
"The neurotransmitter explanation is also wrong. Neurotranmitters are continually produced and destroyed by the brain in a semi-steady state cycle in the brain, there isn't some store that you're using up as the day goes on. The rate of production and hence the relative concentration of neurotransmitters during the day is indeed principally influenced by a circadian daylight-night cycle. But most neurotransmitters show complex daily patterns of brain concentration with few following a model when they are at their peak in the morning and \"get used up\" as the day goes on.",
"Figure 2 in the following paper measures the levels of 8 neurotransmitters in rat brains over a day-night cycle. For Arginine, Glutamine and 5-HIAA and dopamine there is no significant difference between night and day. DOPAC and HVA show a pattern where the are at their peak level at the start of the night and then fall steadily through the night and into the next day until the middle of the day where they begin climbing back to their highest point at the start of the following night. Glutamata and GABA are perhaps the only 2 that show a pattern where they recover during the night before being depleted throughout the day.",
"http://www.utoledo.edu/med/depts/physpharm/ceder/pdfs/Tamara_-_Circadian_rhythms_of_.pdf",
" I found these 2 articles on the role of glycogen in neural activity.",
"a) neurons do not store glycogen and it's accumulation in neurons can initiate apoptosis (programmed cell death) \n",
"http://www.nature.com/neuro/journal/v10/n11/full/nn1107-1341.html",
"b) Glycogen is instead held in nearby astrocytes where is can be mobilised as a nerual energy store in periods of \nlocal neural hypoglycemia ",
"https://www.ncbi.nlm.nih.gov/pubmed/17659525"
] |
[
"Ah, sorry, didn't realise. Thanks for the link!"
] |
[
"Have ancient civilizations ever left any 'Easter eggs' for us to find?"
] |
[
false
] | null |
[
"I'm not sure what you mean exactly by 'prank', but if you mean 'left something around just to screw with some future archaeologist' I can tell you from my experience in the field, we often use this as an explanation for stuff we can't understand.... though it's really just a joke.",
"There are plenty of things kicking around that we can't explain fully. The most common ones you hear about are big stuff like Stonehenge, or the Easter Island Heads, but I've used it to explain why there is a biface under a rock that's been flipped on it's side and buried in 2 meters of shell. \nIt's not that we can't explain these existence of these things, it's just that we have competing hypothesis for them. The Easter Island Heads are a popular example in ",
"the media now",
". But that's not ",
", it's just that one competing theory has more support now.",
"The problem is that in the list of competing hypothesis, 'prank' ranks very low down the list. It's really hard to gather any supporting evidence for it. Trust me--I have tried. Seriously. It would make my field reports so much easier to write. But no data means no conclusions. ",
"So, if they have, it would be really, really hard for us to tell.",
"arguments from authority"
] |
[
"Thanks for the vote of confidence-- though I admit it isn't quite the true fallacy, I think people who claim expertise in any area become a little lazy when it comes to providing evidence-- the old\"trust me, I'm a doctor\" bit, though in my lab it's \"Trust me, I'm a scientist\".",
"I wouldn't trust a doctor who didn't offer up evidence when asked for it, and I'd trust them a lot more if they offered it up right away... but again, I was being lazy.. so I wanted to apologize for not meeting my own standards. "
] |
[
"Good response, but I have to say that what you're talking about is not argument from authority. You are a professional archaeologist, trusting an archaeologist about archaeology is as much of a fallacy as trusting a doctor with diagnosing you."
] |
[
"Would the output of a random event/function change every time if we could time travel back in time to witness it again and again?"
] |
[
false
] | null |
[
"Hi goatchild thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Physics\nPhysics"
] |
[
"Physics"
] |
[
"Does the earth's orbit match up the sun's equator? Or is the sun's rotation skewed relative to the orbital plane like the earth's?"
] |
[
false
] |
[deleted]
|
[
"The Sun is tilted by about 7 degrees compared to the orbital plane of the Earth, and by about 6 degrees to the average orbital plane of all the planets (invariable plane). It's not clear why this is the case, but there must have been some large asymmetry in the formation of the Solar System. One possibility is that ",
"Planet 9 is responsible",
"."
] |
[
"It is far more likely due to the angular momentum in the cloud and star rather than invoking planet 9.",
"The stellar spin axis is determined by the net angular momentum in the matter that acrected to make the star. However, this is not necessarily the same as the net angular momentum in all the mater in the cloud (that will in part be the protoplanetary disc). Thus the final protoplanetary disc axis is determined by the angular momentum of this matter too. ",
"In general one would expect these to be reasonably close but encounters between the disc (or forming disc) and a nearby star (which is likely since stellar nurseries are typically tightly packed) can further complicate this."
] |
[
"Sun spots and their groups are long lived enough to observe a rotation. \nInteresting point to note the rotation rate is faster on the equator slowing down towards the poles."
] |
[
"Is there any REAL science behind all the protests against genetically modified seeds or is it just how all these people FEEL about genetically modified anything?"
] |
[
false
] | null |
[
"Everyone please remember this is about the science of GMO's, not a public forum for the airing of grievances or for unsupported studies by biased groups. Please refrain from posting such comments as they will be deleted. ",
" This is also not a place for political arguing and bickering. If you want to discuss the politics of it, please go to ",
"/r/politics",
". "
] |
[
"This topic was has some a few amazing top comments on the subject.",
"\nI also think ",
"/u/spinebag",
" worded ",
"an important aspect better then I can.",
" People are venting about a social issue (how agriculture should take place) which is masked as a scientific debate. I feel this is an important oversight in the current debate and motivations of people.",
"There are alternatives to GMO's, namely the stuff we are using now, nobody is forcing anybody to use GMO's, it's that easy. It's like arguing you should ban trains because you prefer to use the segway."
] |
[
"This gets asked fairly often, you might want to do a search."
] |
[
"can you simplify a²+b²?"
] |
[
false
] |
I know that you can use the binomial formula to simplify a²-b² to (a-b)(a+b), but is there a formula to simplify a²+b²? edit: thanks for all the responses
|
[
"(a + ib)(a-ib) where i",
" = -1."
] |
[
"Consequently, if you can write a prime number as p=a",
"+b",
", and you choose to include i=sqrt(-1) into your number system, then this prime loses it's primeness.",
"For instance, 13=2",
"+3",
", but if I include i=sqrt(-1) I can actually factor it as 13=(2+i3)(2-i3). It is no longer prime!",
"A ",
"Famous Theorem due to Fermat",
" says that this can happen to a prime if and only if after dividing by 4, we get remainder 1. So 5, 13, 17, 29... can all be factored if we add sqrt(-1), but 3, ,7, 11, 19, 23... won't. (2 becomes a square!). This is amazing! The factorization of a number in a complicated number system is governed only by what happens when you divide by 4. (It is actually the first case of ",
"Quadratic Reciprocity",
".) Another ",
"Theorem due to Dirichlet",
" says that half the primes will factor, and half won't. Though there is a mysterious phenomena known as the ",
"Prime Race",
" that says that it will more often then not look like there are more primes that ",
" factor, we need to take into account all primes if Dirichlet's Theorem is to hold. "
] |
[
"\"Simplify\" may not be the best word here; \"factorise\" is probably better."
] |
[
"Do properly doped insulators behave like doped semiconductors?"
] |
[
false
] |
So from what I understand, the main difference between semiconductor and insulator materials is the size of the energy band gap between the valence and conduction bands, and by extension the number of thermal-generated charge carriers in each band. However, in doped semiconductors, the vast majority of the charge carriers are due to electron migration to/from the dopant states that are very close to their respective band energies. So my question is, if you doped an insulative material (band gap >9ev)with elements that had electron states close to the conduction or valance bands, could those produce free charge carriers as effectively as, say, boron or phosphorus in silicon? I tried looking this up on google, but 'doped insulator' just returned a bunch of papers about their possible use as high temperature superconductors, which just confused me further. I should also mention, this is assuming a similarly uniform crystal structure. I know that grain boundaries and other defects increase resistivity in pretty much every material.
|
[
"Of course. Properly doped insulator behaves just like doped semiconductor, because, as you mentioned, the only difference between insulator and semiconductor is the size of their bandgap.",
"The \"doped insulator\" you referred to has many different names in scientific community. For example, TCO (Transparent conductive oxides), wide-bandgap semiconductors, etc. They are studied and used, but just not as often as \"regular\" semiconductors like Silicon. ",
"The reason you see them appear often in applications involving high temperature is because Silicon and others become \"intrinsic\" under high temperature. If bandgap is not high enough, high temperature will cause the population of thermally excited electrons and holes that are intrinsic to the semiconductor material to be much higher than that of the intentionally introduced dopants, thus the semiconductor becomes \"intrinsic\". If bandgap is high, this will not happen."
] |
[
"The volume of the Fermi surface is equal to the number of free charge carriers. If a number of charges are donated to an insulator, the Fermi energy will shift to guarantee that condition.",
"This is easy to see in two-dimensional materials where dopants can be added and the bandstructure measured in real time. Some examples: ",
"http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/Articleimage/2011/JM/c0jm02922j/c0jm02922j-f10.gif",
"https://journals.aps.org/prl/article/10.1103/PhysRevLett.101.086402/figures/3/medium"
] |
[
"To give a quite common example: diamond is considered a good insulator (band gap ~5.5 eV), but can be doped with Boron, which (apart from making the diamond appear blue) makes it conducting."
] |
[
"How is the placebo effect mitigated in experiments studying effect of meditation?"
] |
[
false
] |
For the studies on effect of drugs, I can easily imagine it being done by some fake pills and stuff. But how are the control groups designed for studying effect of meditation?
|
[
"Meditation is not consistent. You don't go through the same mental stages each time. It is more of a cumulative effect over a longer time. What happens in the mind also is highly individual. You can not say that if you tell people to do 'this' then 'that' will be the outcome each time. Any study that claims otherwise is highly wonky. ",
"As such, you can not set up a meaningful trial to start with, leave alone a placebo controlled trial. It would be a bit like trying to determine the effect of watching a real sunset compared to a fake sunset: The setup is meaningless. ",
"The whole question has only arisen due to the vastly overhyped 'mindfulness' money making machine. Take it all with a big load of salt. Most of the claimed effect of these workshops indeed is placebo, imagination, suggestion, wishful thinking. Don't listen to anyone who has not done it for at least ten years. Any initial effect tends to peter out quite rapidly.",
"\nWhile it is true that you can take EEGs of experienced meditators and see different brainwave patterns, this does not mean that the whole, mostly lifelong process is readily accessible to scientific enquiry. ",
"Source: been doing Zazen for more than 40 years........... I know a bit about it."
] |
[
"Meh, if you read the thing, \"real\" meditation gives a pain rating of 3.5(4) and \"sham\" meditation gives 3.7(4). There's no difference.",
"http://www.jneurosci.org/content/jneuro/35/46/15307/F3.large.jpg?width=800&height=600&carousel=1",
"The main \"ingredient\" in the placebo effect is desire to please the researcher, so perhaps the most effective \"sham\" meditation would be to have them do the same thing as the \"real\" meditation group but have the researcher blather on about how stupid meditation is and how it's obviously not going to work. Or maybe have them do \"real\" meditation but then let slip that \"oh, that was totally fake, haha\" just before the test."
] |
[
"Meh, if you read the thing, \"real\" meditation gives a pain rating of 3.5(4) and \"sham\" meditation gives 3.7(4). There's no difference.",
"http://www.jneurosci.org/content/jneuro/35/46/15307/F3.large.jpg?width=800&height=600&carousel=1",
"The main \"ingredient\" in the placebo effect is desire to please the researcher, so perhaps the most effective \"sham\" meditation would be to have them do the same thing as the \"real\" meditation group but have the researcher blather on about how stupid meditation is and how it's obviously not going to work. Or maybe have them do \"real\" meditation but then let slip that \"oh, that was totally fake, haha\" just before the test."
] |
[
"What is more successful in evolutionary terms: fight or flight?"
] |
[
false
] | null |
[
"No. That is, all success is contextual. There is no such general rule. Given predator A the best strategy would be X. But with predatory B the best strategy would be Y. And if you have both A and B then maybe a mix or maybe strategy Z."
] |
[
"Are we all hard-wired to be either flight or fight though? Or does it depend on the situation we find ourselves in?"
] |
[
"Are you talking about people in particular, what is the best for H. sapiens? Even so, as you said it is \"fight or flight\", both options are there. "
] |
[
"How are quantum mechanics and general relativity incompatible?"
] |
[
false
] |
or another way of asking the same thing, why is the 'grand unification' physicists talk about so difficult to achieve?
|
[
"If you try to express the equation for general relativity (the Einstein-Hilbert action) in terms of quantum field theory, you'll can answer containing several infinite terms that don't cancel. Normally this isn't a problem because GR describes really big things and quantum field theory describes really small things."
] |
[
"I've heard that answer often but never specifics. How is the Einstein–Hilbert action changed when expressed in terms of QFT? What terms go to infinity? The way you phrased \"containing several infinite terms that don't cancel\" seems to imply that other quantum theories have infinite terms that do cancel. Can you elaborate on that?"
] |
[
"http://arxiv.org/pdf/0709.3555.pdf"
] |
[
"Would it be possible for scientists to synthesize pure serotonin to be taken as some kind of supplement and effectively cut out SSRI's?"
] |
[
false
] | null |
[
"Serotonin itself can't cross the blood brain barrier, so taking serotonin supplements wouldn't have the effect you're after. You would have to take tryptophan or 5-HTP, which can cross the BBB and can then be metabolized into serotonin. "
] |
[
"The ",
"BBB",
" protects the brain from all kinds of things in our blood normally, and a number of drugs cannot cross it as a result.",
"Even if we delivered tryptophan to the body, we still have biological processes that control our seritonin levels, which would need to be overcome."
] |
[
"But even if that works, there's no particular reason to think it would be better than SSRIs. Doing that would blanket the entire brain in Seratonin, SSRIs only have an effect at synapses where there's Seratonin already."
] |
[
"What reactions happen in the brain when someone experiences in 'epiphany'?"
] |
[
false
] | null |
[
"So, can everyone experience that ahha moment equally or are there some brain more likely than others. "
] |
[
"I don't know of any brain structure / DTI studies of insight. There are individual differences in frequency of insight behaviorally, though. Insight is thought to be correlated with analogical reasoning ability for example (",
"Ansburg 2000",
")."
] |
[
"When researchers study this, they typically call it \"insight\" and is often used in the context of problem solving. There are some interesting behavioral aspects of insight: the longer you are working on a problem, the closer you feel you are to a solution, but if you ask people what they think the answer is, they aren't any closer. That is, people have a sense of \"I'm about to get this\" -- that they are about to have an insight -- but actually we cannot predict when an insight will happen (",
"Metcalfe and Wiebe 1987",
"). To clarify, something special is meant by an insight problem -- it is different from, say, a math problem -- there is no proscribed series of steps to take to reach a solution, you just have an epiphany. For example, problems like rearranging matchsticks that form some Roman numeral equation to form a different equation is an example of an insight problem. Like ",
"these",
". ",
"As for what is happening in the brain, there are a number of studies. It seems like activity prior to getting the problem affects ability to solve it (",
"Kounios, Frymiare, and Bowden 2006",
"). This also occurs for lots of other non-problem-solving behavioral tasks in which neural oscillations prior to doing a trial predict performance on that trial (e.g. ",
"Linkenkaer-Hansen et al. 2004",
"). It is suggested that prestimulus oscillatory activity may somehow enhance processing once the stimulus appears (perhaps in a resonance sort of way). The exact mechanisms are unclear.",
"More generally, we can say there is increased activity in certain parts of the brain when you are having an \"aha\" moment (Qiu et al. ",
"2008",
", ",
"2010",
"), but that's not really informative for ",
" is happening. This activity is different from that observed during non-insight problem solving and it begins a few fractions of a second before the insight strikes (",
"Jung-Beeman et al. 2004",
"), but beyond that we don't really know what is going on. For a review see ",
"here",
"."
] |
[
"What is the actual theoretical energy output of the ITER?"
] |
[
false
] |
In their website they have mentioned the experimental reactor will produce 10 times the energy it is given. Now the energy given i assume is the energy for heating the plasma. Then what about the whole reactor energy consumption. Considering that, what will be actual output power with respect to the power consumed by the whole reactor.
|
[
"ITER won't produce electricity, so you could say it has zero power output.",
"The total power consumption of ITER will vary a lot. Heating is planned to be 50 MW, fusion power is planned to be 500 MW - both only while the reactor is running. Cooling the coils and running all the infrastructure will need some power as well.",
"A commercial power plant would need something of the order of 3000 MW fusion power, converted to 1500 MW of electricity, with a heating power much lower than that."
] |
[
"You could argue that ITER is analogous to CP1 in some ways."
] |
[
"Yea I know that. I also know there were a lot of research reactors in the early days and some were closer to a working commercial reactor than others. I'm just looking for a ballpark-ish analogy in terms of technology readiness level."
] |
[
"There was this male bug I read about once that died within the second it was born. It's sole purpose was to ejaculate and die. Does anyone know the name of this lucky guy?"
] |
[
false
] |
[deleted]
|
[
"Fish and bugs are practically the same thing after all. "
] |
[
"Do you mean the ",
"thrips egg mite",
"? The males have sex with the females while developing inside the mother, and when fully developed they burst their way out of the mother. Males die shortly after, but not in the span of seconds."
] |
[
"hey, fycj tiu, ih"
] |
[
"When people say the universe is expanding do they mean empty space is being created or the actual \"fabric of space time\" is expanding?"
] |
[
false
] |
I mean like is everything becoming larger?
|
[
"If everything was getting bigger, we wouldn't be able to tell that anything was happening!",
"Space is stretching but objects are not.",
"Objects are pulled along by the stretch, but they are only pulled ",
" if they are not stuck together by sticky forces such as gravity or electromagnetism."
] |
[
"No, we're definitely in it - best not to take the analogy too literally :) I was thinking of 1D ants on a 1D piece of elastic.",
"A more faithful analogy would be seeds (=galaxies) in an unbaked seedbread. Put the bread in the oven, the dough (=space) gently expands over time, and the seeds get further apart from each other.",
"If you live inside a seed, nothing is expanding for you. Not unless you start looking out beyond your seed and notice there are other seeds, all drifting away from you.",
"(NB. Unlike an oven, when space expands it gets colder.)"
] |
[
"Imagine a row of ants (=galaxies) standing on a piece of elastic (=space). Now gently stretch the elastic. Do the ants get further apart? Yes. Does an individual ant expand? No, the forces holding ants together are too strong. Do the tiny bugs that live inside the ants expand? No, they don't feel a thing.",
"(NB. Unlike elastic, when space expands it doesn't somehow get 'thinner'. There's just more space.)"
] |
[
"Does the infrared output of the sun fluctuate in such a way that it affects temperatures on earth; or is the change in temperatures on different parts of the earth purely due to fluid dynamics in the atmosphere and the tilt of the earth on its axis?"
] |
[
false
] |
I had read somewhere, some time ago that the intensity of the heat in summer periods on earth could be tied to sunspot activity. I am uncertain if this is true. I am also curious why is it that temperatures on earth are inconsistent. If the infrared output of the sun is constant and the rotation of the earth is constant, why does the eath not stay at an even temperature like rotisserie chicken (for example)?
|
[
"The majority of temperature differences come from the tilt of earth's axis, which causes the sun to be lower in the sky and thus weaker. Differences on a smaller timescale come from the night and day cycle obviously, but also from water releasing heat during nighttime, ice reflecting more sunlight and wind."
] |
[
"Sunspots occur on a cycle that has an 11 year period. For proof of this yourself, you can set up a solar observatory using a cheap telescope to project the image of the sun into a dark box. (Never look directly at the sun, especially through a telescope!)",
"You can also see sunspots if your eyesight is good enough using glasses designed for observing eclipses. I've picked up my glasses from Astronomers Without Borders in the past, but they don't seem to be selling them right now... A list of reputable sellers is available at ",
"https://eclipse.aas.org/resources/solar-filters",
" ",
"There is currently one sunspot visible today, though it will be rotating out of view in a day. We're getting close to solar maximum over the next 3 years, where the number of sunspots will increase, up to a dozen sunspots visible a day, though predictions are showing that this solar minimum will be less impressive than the last 3 were.",
"The highest resolution, nearest-to-real-time images of the sun that you can get 24/7/365 is through the Solar Dynamics Observatory, which publishes images in several wavelengths every 15 minutes, taken by the SDO satellite. ",
"https://sdo.gsfc.nasa.gov/",
" Some members of the SDO team also maintain a page that keeps track of solar flares over the past 3 days, and tries to predict possible flares coming up: ",
"http://lasp.colorado.edu/eve/data_access/flare_watch.html",
" (though this page is definitely more for the nerdier science fan than people who are looking for pretty images).",
"This means that, with an 11 year solar cycle, we can't explain summer's heat or winter's cooling through sunspots or solar flares.",
"Besides that, the solar cycle also wouldn't explain why seasons are opposite in the northern and summer hemispheres. It's currently fall in South America, much of Africa, and Australia, and it's going on to winter in those places.",
"The tilt of our planet does explain the seasons, though.",
"The Earth spins around the axis -- a line between the North and South Poles -- like a top... but compared to our orbit around the sun, the earth is more like a wobbling top (though the \"wobble\" is a bit too slow for people to notice in our lifetimes... one full wobble takes 25,772 years). In summer in the Northern hemisphere, the north pole is more towards the sun... which leads to more daylight the further north you are and also leads to the sun's rays going through less air. In the middle of summer, areas north of the arctic circle experience days where the sun never sets... it just circles around close to the horizon. At the same time, the Southern hemisphere is pointed away from the sun, so it gets less lights and, south of the antarctic circle, has nights that never end.",
"When the Earth orbits to the other side of the sun, it's pointing the other way, and the Northern hemisphere experiences winter while the Southern hemisphere enjoys summer."
] |
[
"The summer-winter difference is caused by the ",
"axial tilt of the earth",
", so that you get more sunlight in the northern hemisphere when it is summer there, and less in the southern hemisphere when it is summer in the north. As the earth goes around the sun each year, it switches from getting more sun in the north to getting more sun in the south, causing it to become winter in the north, and summer in the southern hemisphere.",
"Sunspots follow an 11-year cycle, which does cause some very slight temperature differences.",
"The day-to-day weather variation is because we've got fairly complex system where atmospheric currents interact with land and ocean, which has currents of its own. ",
"Since the Industrial Revolution, humans have also been adding greenhouse gasses to the atmosphere, which has ",
"already caused more than 1°C of warming",
".",
"Over the course of 24 hours, things don't stay at an even temperature like a rotisserie chicken because the earth rotates only once per day, giving lots of time for things to cool off at night."
] |
[
"How do we know how ancient languages sound?"
] |
[
false
] |
Like the title suggests, how do people who study ancient languages like Latin or Ancient Greek know how the letters are pronounced? Do they just compare it to modern languages, or is there another way?
|
[
"in part, they look at the offspring languages and study how they sound. they also look into the morphology of pronunciation and see how people change speech over time in general.",
"that being said, we don't actually know much, we have made a lot of educated guesses where each separately have have a medium-high degree of accuracy.",
"if you learned one of these languages and went back in time to one of these ancient cultures you'd probably sound something like a chinese student attempting to speak english after two months of study. that is to say you'd be nearly understandable and you'd not understand much of what is being spoken.",
"the exception is latin. if you study latin today with good instruction you'd do very well. we have too much information on how latin was pronounced excepting about 4 sounds (w vs v is one of the hotly contended pronunciations). similarly with greek though not as good.",
"the most interesting case is proto indo-european."
] |
[
"considering the linguistic changes over the past 300 years means those guesses are not very scientifically sound.",
"This is outright false, and an insult to the whole field of historical linguistics! Sure, ultimately they're reconstructions and not guaranteed to be accurate, but there's a ",
" of careful science that goes into those reconstructions. You could say the same thing about basically all of prehistory! Just because it's not ",
" doesn't mean it's scientifically unsound!"
] |
[
"considering the linguistic changes over the past 300 years means those guesses are not very scientifically sound.",
"This is outright false, and an insult to the whole field of historical linguistics! Sure, ultimately they're reconstructions and not guaranteed to be accurate, but there's a ",
" of careful science that goes into those reconstructions. You could say the same thing about basically all of prehistory! Just because it's not ",
" doesn't mean it's scientifically unsound!"
] |
[
"Theoretical uses for antimatter?"
] |
[
false
] |
Now assuming that we do find a way to efficiently produce or gather antimatter in large quantaties, what would be some potential uses for it? I know at our current state it is terribly inefficient with very little uses, but at a later state in the understanding of it what are some planned uses or rather theoretically possible uses for it?
|
[
"If you consider positrons to be antimatter, we already have an actual use for them: positron emission tomography (PET) can be used to detect tumours and image brain function."
] |
[
"If you consider positrons to be antimatter",
"There's room for debate?"
] |
[
"Well, the only real uses I know of would be:",
"positron emission tomography (we already use that)",
"Storing massive amounts of energy very compact",
"Fuel for interstellar travel, for example for a Anti-Matter rocket. It is of course way better than a chemical driven rocket, because of the much higher energy density."
] |
[
"How did the systems work on the first NASA spaceships without computers?"
] |
[
false
] |
Google tells me the first space launch was in 1961. However, back then, computers were around the size of a fridge or bigger. How did the life-support, and other systems function on rockets back before modern computers. Was it mostly mechanical? Or was there a mainframe type thing somewhere in the spaceship that could perform necessary tasks?
|
[
"At risk of sounding flippant, the computer on board was called \"The Crew\" with support from additional processing called \"Ground Control\". ",
"The basic critical functions of a NASA mission consisted of basically moving fluids from one tank to another, which can be measured and regulated mechanically. For example, Life support is a calculation of consumption vs supply rate. ",
"One of the best resources I can think of which covers this handily is the story of Apollo 13, including slide rules, mental arithmetic and log tables. Whilst the Film with Tom Hanks in is very good, there are a number of accounts about the mission, but here is what NASA themselves record about the mission: ",
"https://history.nasa.gov/SP-4029/Apollo_13a_Summary.htm",
" "
] |
[
"Funny that you mention Apollo 13. I have it on VHS and I watched a bunch when I was a kid. I'll have to whip out the old vcr and watch it again."
] |
[
"Even in 1944, the V2 rocket used an ",
"analog computer",
" for the auto pilot. I have an original German collectable book from that time on the V2 rocket, and can tell you they had to do some high level math in real time, to stabilize and guide the rocket in flight. There was even discussion of the math involved. No large rocket can really fly without some real time computation to actually fly it. Humans are just not fast enough. Even the so called manual control Armstrong did on the moon landing, was not really \"manual\". His ",
"joy stick control",
" was the input to a flight computer that was actively controlling attitude and thrust levels. He was just telling the computer to \"go there\".",
"Edit: added link to the joy stick control of the LM. ",
"http://www.cdvandt.org/v2__computer.htm",
"A fully electronic general-purpose analog computer was designed by Helmut Hoelzer, a German electrical engineer and remote-controlled guidance specialist. He and an assistant built the device in 1941 in Peenemunde, Germany, where they were working as part of Werner von Braun’s long-range rocket development team. The computer was based on an electronic integrator and differentiator conceived by Hoelzer in 1935 and first applied to the guidance system of the A-4 rocket (Goebbels, the Nazi propaganda minister dubbed, V 2, AOB). This computer is significant in the history not only of analog computation but also of the formulation of simulation techniques. It contributed to a system for rocket development that resulted in vehicles capable of reaching the moon. ",
"Edit: ",
"http://www.cdvandt.org/Hoelzer%20V4.pdf",
"I added links for analog computer. Note this in German, but has some English comments and schematic diagrams."
] |
[
"Everyone gets excited about Moore's Law but why can't we just make CPUs physically bigger?"
] |
[
false
] |
"Moore's Law" states that transistor density on a CPU will double every two years, but instead of continuously pushing to make sure that's true, why don't CPU manufacturers keep the same transistor density but just build a physically bigger CPU? Or I guess what I am asking is: is the current CPU dimensions the most efficient?
|
[
"There are three main reasons:",
"The first and most prosaic is that simply nobody wants large electronic components. We want smartphones that fit in our pockets and laptops that fit in our backpacks, and that's not possible if we keep increasing the physical dimensions of the components.",
"Broadly speaking, the smaller the silicon die (the actual piece of semiconductors and other materials doing the computation) the smaller the power consumption. Not only is this important as a matter of environmental responsibility, but also to increase the duration of the batteries in our portable devices.",
"Thirdly, at the frequencies modern processors run, the transmission delays of signals between processing elements becomes noticeable and important - or, as we like to say, the speed of light is too slow. If you kept increasing the size of the processor it would be hard to have processing speed gains.",
"Nonetheless, CPUs sometimes do increase in size, but each individual transistor's size (roughly, the current ",
"technology node",
") always follows a decreasing trend for the reasons above."
] |
[
"Not only is it possible, but it's what is currently done in most end-consumer microprocessors (like the Intel Core series). This is because it's becoming very hard and costly to increase the clock frequency on the processors, and designers turned to parallelism to improve performance."
] |
[
"I have a stupid question.",
"Wouldn't it be possible to build a bigger CPU chip which is composed of multiple \"cores\" that are somewhat each small within the subset ?",
"It would be similar in a way to plugin multiple CPUs in the same motherboard, but all in one chip so that you can reuse a 1 cpu motherboard with it?"
] |
[
"How much mercury would you need (and in what size container) for a 160lb person to be able to walk across it without sinking?"
] |
[
false
] |
was a question a friend's dad asked a professor and never got a answer, so I was just curious if this could happen, obviously an individuals balance is a key factor here but let's pretend it isn't.
|
[
"The balance is really, really a factor here! But let's ignore that.",
"Let's assume you're standing in mercury. By equating buoyancy and weight we get:",
"Weight of displaced mercury = your weight",
"And so",
"Penetration depth * sole area * mercury density = your mass",
"Using mass = 70 kg, area = 300 cm",
", density = 13.56 g/cm",
" I get that your feet sink by around 20 cm.",
"So I guess that your pool would at least need to be that deep for the concept of floating to make sense, or you'd just be standing on the floor.",
"However, it's really hard to stand like this; it's immensely slippery. You can however just lie down in a pool of mercury and sink I think no more than a couple of cm. There are multiple picture of people doing just that before the devastating effects of mercury poisoning were fully understood, ",
"example",
"."
] |
[
"Elemental mercury really isn't so toxic that the guy sitting on that pool is likely to have any ill effects."
] |
[
"Sitting in a pool, you're bound to have breathed some vapour. There's a risk with any amount, though little. For this particular guy, since he was a mercury worker, the risk wasn't that small.",
"Also if you have any open wound exposed to the metal it gets much worse."
] |
[
"Does a light wave lose energy as it travels farther and farther?"
] |
[
false
] |
I understand a light wave will travel continuously until it strikes a molecule, but does it ever lose some of its energy while traveling without striking a molecule?
|
[
"In a vacuum, electromagnetic radiation nominally travels without losing energy. I say \"nominally\", because if you set that radiation loose in outer space, the waves (or photons) stretch as the universe expands, and therefore lose energy. This is the source of the \"redshift\" of light from distant galaxies, for example.",
"So on Earth... no. In the empty reaches of space... yes, but very slowly."
] |
[
"No, for a photon (which has no mass), E = h*nu, so as the frequency decreases the energy also decreases."
] |
[
"No, for a photon (which has no mass), E = h*nu, so as the frequency decreases the energy also decreases."
] |
[
"Double-Slit-Experiment and Light as waves and particles"
] |
[
false
] |
So my question: When you have your double-slit setup and send through individual phtons you get that string -pattern which essentially means light is particles and waves at the same time. Just to sum it up real short. But when you just think of light as individual photons and send them through the slits individually couldn´t it be that this wave pattern emerges because of the phtons beeing diverted by the material which surrounds those slits? You know because the gravitational force of the material around it (much denser then the air those phtonos traveled through earlier), diverts it, because it has a much bigger mass than those photons? And that this gravitation as slight as it might be, cause this pattern by diverting the photons on their way trough the slits? I hope I didn´t disgrace this subreddit by my question formed by watching BBC Horizon and alcohol. Thank you.
|
[
"also photons dont have a mass soooo gravity doesnt effect them",
"Gravitational Lensing",
" ",
"A loose explanation (I am a physicist, but it's a long time since I've thought about any GR) would be to say that massive objects curve spacetime, as well as sort of 'rolling' along the curves, which is what we see as the gravitational attraction between two massive objects. A photon doesn't have mass, so doesn't itself curve spacetime, but is affected by spacetime curvature, and spacetime curvature is a consequence of mass. So, in this way, the path of a photon is affected by a nearby mass. "
] |
[
"The energy of a relativistic particle is related to its mass m and momentum p through",
"E",
" = p",
" c",
" + m",
" c",
"where c is the speed of light. The photon mass is zero, so we have, for a photon:",
"E",
" = p",
" c",
" --> E=pc",
"So the energy of a photon dependent on its momentum only. Saying a photon is 'just energy' is meaningless. What would be correct would be saying \"a photon's energy is made up only of energy stemming from its momentum\".",
": I'd like to show you all how the energy formula came out before I removed some spaces: E"
] |
[
"Ah yes, the rare and dangerous quadratic-quadratic-quadratic-quartic term. Many good men have been lost to that timorous beastie."
] |
[
"Do irregular sleeping habits irreparably damage our brains?"
] |
[
false
] |
[deleted]
|
[
"I strongly suggest that you see a doctor that specialises in sleep. I'm not saying this because I think you're in grave danger but this is a medical issue and you may get incorrect advice here. "
] |
[
"What was wrong?"
] |
[
"In that case I will add some conjecture as long as you don't take it as medical advice. I would wonder if the twitches are actually caused by stress rather than a reaction to a lack of sleep. You mentioned that you've had issues with your father and perhaps it's taking an emotional toll? Again, this is pure conjecture based on what you told me, I'm not a professional, just a psych student."
] |
[
"Why didn't Eratosthenes assume the Sun's rays were parallel for his experiment?"
] |
[
false
] |
When Eratosthenes famously estimated the size of the Earth by measuring the maximum height of the Sun, why did he assume that the Sun's rays are parallel? That assumption let him conclude the Earth was round. If he'd assumed the rays were not parallel because they were coming from a point source, he could have instead concluded that the Earth was flat and that the Sun was about 600 mi * tan(83°) ≈ 2,300 mi. Why didn't he?
|
[
"If the Earth was a flat disc, then unless the Moon was directly overhead, the Earth would be inclined relative to it, so its shadow would be elliptical instead of circular."
] |
[
"I think (I may have the historical order backwards) that he already knew the Earth is round by observing its circular shadow on the Moon during an eclipse. In fact (I think) that this is how they knew that the Moon is about 1/4 the size of the Earth."
] |
[
"Here's the logic:",
"E knew that the Earth is at least 1000 miles across. People traveled that far.",
"The angular size of the Moon is about 0.5°. Knowing that the Moon is 1/4 the size of the Earth (ie, at least 250 miles across), it must be quite far away, at least 30 thousand miles. ",
"Solar eclipses ton't occur unless the Sun is farther from the Earth than the Moon is. The Sun can't be only 2,300 miles away.",
"Therefore, for practical purposes, the Sun's rays arriving at Alexandria and Syene (500 miles apart) are parallel."
] |
[
"How did the placenta evolve?"
] |
[
false
] |
I recently read & listened to a book by Steve Brusatte about the evolution and rise of mammals. Sadly he fails to get into one of the most fascinating aspects: not laying eggs anymore but giving live birth or putting fetuses in a pouch, in the case of marsupials. Can someone explain, what led to this evolution, where it came from and how it worked?
|
[
"So, the evolution of the placenta is actually a really fascinating topic. Basically, the placenta is an organ that develops in female mammals during pregnancy and allows for the exchange of nutrients, gases, and waste between the mother and the developing fetus.",
"The thing is, not all mammals have placentas. In fact, the evolution of the placenta is thought to be one of the key factors that allowed mammals to become as diverse and successful as they are today.",
"So how did it happen? Well, scientists believe that the earliest mammals were probably small, shrew-like creatures that laid eggs. Over time, some of these mammals evolved to give birth to live young, which provided certain advantages in terms of protecting the developing fetus and increasing its chances of survival.",
"Eventually, these live-birthing mammals began to develop specialized tissues and organs that allowed for more efficient exchange of nutrients and waste between the mother and fetus. These tissues eventually evolved into the placenta we see in modern-day mammals.",
"It's a really cool example of how evolution can lead to some pretty complex and amazing adaptations."
] |
[
"There's evidence that a gene responsible for placental development in humans came from an ancient virus!",
"Syncytin-1",
", a protein coded by the ERV1 gene which is crucial for placental development. Syncytin-1 is a human endogenous retroviral element, viral genetic material that has incorportated into our genome. It is conserved among apes and old-world monkeys.",
"Syncytin-2, another placental development gene, is derived from a different retrovirus."
] |
[
"It's worth noting, in addition to ",
"u/Jason-_B",
"'s excellent comment, that the placenta is not unique to mammals - it's seen in fish, lizards, and snakes as well. More importantly, unlike mammals, the intermediate states are still around, and plentifully represented.",
"In species with internal fertilization, the egg has to spend at least some time in the female regardless, just to add yolk and a shell. But more time in the female also lets her more precisely control the egg's environment, especially temperature, so keeping them interally has advantages (as well as the disadvantage of not being able to ditch them to escape a predator, and being \"weighed down\"). So a lot of species have variable time before laying, all the way up to laying right before hatching. Oxygen, CO2 and water can transfer, but it helps to ditch the shell in that case. However, no nutrient transfer occurs. At the very highest extreme, this is ovoviviparity - where the eggs entirely lack calcified shells, and the mom \"lays\" them immediately before or as the offspring are \"hatching\". From an outside perspective, this looks just like viviparity, but the key is the lack of nutrients - they need a yolk.",
"But if you've got eggs interally for a while, why not transfer some nutreints? There are lots of ways to do this, with the most bizarre probably being some species of caecilians (long, worm-like, burrowing amphibians) in which the mother grows nutritive lining in her uterus, which the young scrape from the walls and eat. However, a common way is to vascularize the yolk sac, squish it up against the uterus, let them fuse, and transfer nutrients across - bingo, you've got a placenta. Some of these are every bit as complex and specialized as mammal placentas.",
"The most useful thing is we have numerous independent evolutions of the placenta outside of mammals (who only evolved it once, as far as we know), as well as living examples of every intermediate you could ask for. There are even species (three-toed skinks) where some populations give live birth and others lay eggs.",
"Even crazier is the exception - Archosaurs (crocodiles, birds, dinosaurs, and their relatives) cannot ever evolve live birth. Unlike other species, the Archosaur embryo uses the calcium in the eggshell for bone calcification and, if the shell is removed, the hatchling is basically a gummy-bird or gummy-gator (obviously non-viable). This means they can never ditch the shell, and never take those first steps. And not a single Archosaur has ever evolved live birth, despite hundreds of millions of years of opportunities, and literally ruling the planet for most of that time."
] |
[
"How does soap remove germs, odors and bacteria from our bodies and hands?"
] |
[
false
] |
[deleted]
|
[
"Soap molecules are hydrophobic on one end, meaning they repel water and stick to things that don't dissolve in water, and on the other end they are hydrophilic meaning they stick to water. So soap can stick to things that don't normally dissolve in water and allow those things to be carried away by the water."
] |
[
"The bacteria and presumably odorants mainly attach to the oils secreted by your skin rather than your skin, for the most part. Soaps have a long tail that prefers to absorb into oily things, and a head that likes to interact with water. So when you soap up your hands, the chemical chain breaks up the oily layer by this effect, and is helped by the friction of your hands that also breaks up the layer mechanically. Then when you add water, the head of the soap attaches to that, and is pulled along with the water. The long chemical chain, oil, bacteria and odorants get pulled along with the head.",
"Also, soap may kill bacteria. The outer layer of bacteria is made of similar material to the long chemical chain of soap molecules, so the long chains insert pretty easily into this outside layer. That causes it to expand, which may interfere with processes in the cell, or cause the bacteria to burst, similar to a water balloon stretched too far. ",
"Some soaps contain other ingredients, specifically for killing microbes. It's not clear that they actually work better than traditional soaps.",
"The hand sanitisers that evaporate without washing, e.g. the sanitiser you use when entering a hospital, work slightly differently. They contain mostly alcohol, which again may insert into the bacteria and break up the oily layer, along with the rubbing. I'm not sure of their exact ingredients, but I would guess that the alcohol helps to trick the bacteria into opening pores in their surface, allowing toxic chemicals to rush in, killing a large amount of the bacteria present on your hands.",
"We use soap because it kills, removes and minimises the bacteria on our body fairly efficiently. I assume your curiosity is just academic, but if you're not convinced that it's important you should google germ theory."
] |
[
"Your body is covered with and contains about 2 pounds of bacteria. Soap breaks up the slime like layer of bacteria on your skin and lowers their numbers. Soap also rids the body of the odor bacteria causes. Essentially you are keeping smelly bacteria numbers down. "
] |
[
"What is the experimental evidence for quantum superposition?"
] |
[
false
] |
I'm told that "a quantum superposition is such that something exists as an infinite number of probabilities until we observe it, at which point the quantum wavefunction collapses and it exists as one thing." This tells me that observation inevitably shows these things as having a position. This tells me that experimental evidence shows these things as having a position. What experimental evidence is there for the whole quantum superposition idea? It seems non-parsimonious, and non-falsifiable. I assume that quantum physicists aren't a bunch of idiots who made it up for no reason, so: what is the experimental evidence for quantum superposition? What are the competing explanations for this evidence, and what causes us to reject those competing explanations?
|
[
"It usually isn't an \"infinite\" number of probabilities. Many superpositions you're familiar with (spin of an electron, eg) are between a small number of states (2 in the case of electron spin, or photon polarization).",
"Anyway, more to your point, there are two philosophical camps divided by ",
"Bell's Theorem",
". Bell's theorem (and the associated experimental evidence from entanglement) tells us that we can either have a local quantum mechanics (nothing happens faster than the speed of light), or a \"realist\" quantum mechanics (that there is some underlying \"true\" state of the particle that surfaces during the measurement, even if that \"truth\" information is hidden somehow). ",
"Now most of the physics people I know keep with the local interpretation without hidden variables. But there are plenty of others who think that particles have real states, but that they can communicate the information about these states faster than light. "
] |
[
"The experimental evidence for superposition is really quite strong. Bjos has already mentioned the double-sit experiment in support. I think the most striking examples of that are the demonstrated single-particle interference of ",
"large biomolecules",
", where large biomolecules are shown to actually be in two places at once."
] |
[
"Bell's theorem (and the associated experimental evidence from entanglement) tells us that we can either have a local quantum mechanics (nothing happens faster than the speed of light), or a \"realist\" quantum mechanics",
"It doesn't tell us that at all. It could also be that QM is ",
" of those things, and that interpretation is the one that's favored by people working most closely on this."
] |
[
"How are gas giants spheres? Wouldn’t the gas just go everywhere in space?"
] |
[
false
] |
Especially Saturn, not only is it gas but it has a ring around it too. How is it not just a bunch of hot gas going in every direction?
|
[
"A small scale model of a gas giant made of the same materials would fly apart in all directions.",
"Jupiter does not explode because of gravity. Gravity pulls all matter towards all other matter (proportional to mass times inverse square of distance, you get the idea), and this tends to squash matter together until it is a sphere or near enough. ",
"Hydrogen molecules are still moving around randomly (with an average speed governed by temperature and gas laws) trying to escape but they don't get very far, gravity brings them back. Jupiter has the mass of 300 Earths, and has a firm gravitational grip on itself. A ball thrown away from Jupiter should return unless it is traveling at a critical speed called escape velocity which is >60 km/s for Jupiter, 134,000 mph."
] |
[
"I'm pretty sure it's because of gravity. ",
"Fun fact: some small percentage of the gases do escape and are lost to the void. The same is true for rocky planets like Earth. Here's an interesting article on the topic. ",
"https://sciencenorway.no/space-space-research/why-doesnt-all-our-air-disappear-into-space/1870565"
] |
[
"Some gas giants (none in our solar system, but maybe around a tenth of exoplanet gas giants) may actually form mostly from gas without any initial core through a mechanism called \"gravitational instability\": essentially just clumps forming in the outer regions of the protoplanetary disk of gas that gradually become denser until they collapse into a planet."
] |
[
"Why does autism seem to affect a lot more males than females?"
] |
[
false
] |
[deleted]
|
[
"Autism gender bias clue found",
"2012",
"\"I think the key to actually developing a treatment for autism is to understand the difference between males and females, why female prevalence is much lower,\" Scherer said in an interview. \"They must have some protective factors in their biology. So we think that this finding may lead us to discovering what those protective factors are.\""
] |
[
"The most common inherited autism-spectrum disorder is ",
"Fragile-X Syndrome",
". Because it is X-chromosome linked, females with the damaged chromosome have another which can synthesize the relevant effected protein, whereas males do not have that fall-back. It is not quite 2:1, and females have a wider spectrum of affectation, but far more males suffer Fragile-X than females."
] |
[
"If you look at women who have Turner's syndrome - one X chromosome - they have a similar incidence of autism to men.",
"There are genes that are not inactivated on the second X chromosome in women."
] |
[
"Quick Question: What is RMSE, and how can I use it to determine how well a model fits a set of data?"
] |
[
false
] |
I'd appreciate it if you wouldn't give me any Google-Yourself responses please. I briefly understand what RMSE is, but I want to know how to explain it. For instance, I made a model for a set of data with a RMSE value of 5.00, is that considered high or low? At what values of RMSE would it be considered a bad fit (above 10, for instance), a moderate fit (5 perhaps) and a very good fit (0.000 for instance)? Also, I'm assuming RMSE must be positive. Mind confirming? Thanks. I really appreciate it!
|
[
"For instance, I made a model for a set of data with a RMSE value of 5.00, is that considered high or low? At what values of RMSE would it be considered a bad fit (above 10, for instance), a moderate fit (5 perhaps) and a very good fit (0.000 for instance)?",
"The premise of your question is flawed. The root mean square error is a scale-dependent measure of error (as you'd know if you understood it as you claimed) so you can't say things like \"5 is moderate, 10 is bad\" (since an RMSE of 5 on one data set could be an excellent fit while an RMSE of 10 on another data set is atrocious). If you're looking for scale-independent ways of evaluating goodness of fit you should start with the ",
"correlation coefficient",
", which is really only appropriate for linear models but should give you some idea of what you're looking for. In short, comparing RMSE for different fits of the same data set is reasonable but comparing RMSE of fits of different data sets is not.",
"Also, I'm assuming RMSE must be positive. Mind confirming?",
"Yes, it must be positive."
] |
[
"Thanks for your response. I did not mean to confuse you, but I'll add that both my models are for the same data set, hence it is valid to compare the two. Correct?"
] |
[
"Yes, it's valid to compare the two, and doing so is straightforward- the one with the lower RMSE is the better fit. For fitting, there are typically two components you want to compare: model complexity and goodness of fit. Goodness of fit can be quantified easily with the RMSE (i.e., whatever fit you use with the lowest RMSE is the best fit), but you also need to look at the model complexity to make sure you avoid overfitting. A typical way to quantify model complexity is to look at how many free parameters (i.e., variables that can change depending on the details of the data set being fit) each model has. If adding a lot of free parameters only gets you a small decrease in RMSE, then you're probably overfitting, and should use the simpler model even though it's RMSE is higher. If, however, your RMSE is dramatically lower for a model with just 1-2 additional free parameters, then the model with extra parameters is probably more representative of the real-world situation.",
"In short, comparing RMSE for two models of the same data set is perfectly valid, and lower is better (unsurprisingly). However, you also need to compare the model complexity in order to avoid choosing a model which overfits yours data."
] |
[
"Could Canine transmissible venereal tumour be considered as an obligate parasite and subsequently a new species in it's own right?"
] |
[
false
] |
Given that the tumour cell line is genetically distinct from the host organism's, for example having less chromosomes and a different chromosomal structure.
|
[
"I'm not very well versed in this particular disease, but it brought to mind human HeLa cells. These cervical cancer cells were extracted from Henrietta Lacks back in 1951, and they are now the oldest and most widely used lineage. Van Valen proposed it should be a new species, but other evolutionary biologists and such said no because its karyotype is too unstable (since it's cancerous) and because there is no direct evolutionary ancestral-descendent lineage. "
] |
[
"Interesting proposition, my first contention with it is that it's unlikely to be an obligate parasite, it can probably be cultured without normal canine cells. As to the genome, that could then be argued for many cancers once they have mutated enough."
] |
[
"Although it's tempting, we probably shouldn't consider it a new species even though it's tough to argue that single-celled parasitic cancers with unstable chromosomes are still \"canines\".",
"However, let me provide a (somewhat weak) counter example. Since in this scenario, the genetic distinction is what we are defining as a \"different species\", then we must also consider eggs and sperm separate species.",
"This is more philosophy than science, because they are clearly different yet the tumor clearly came from a canine originally."
] |
[
"Can objects too small to be visible to the naked eye be made to cast visible shadows?"
] |
[
false
] |
[deleted]
|
[
"I believe that the lightsource would have to be smaller than the object in order to create a shadow larger than the object itself. The object needs to be able to block the light from passing it, if the lightsource is larger than the object, light would be able to pass by all sides of it and wipe out its shadow.",
"If you could create a lightsource even smaller than the object, as you get it closer, the shadow should become larger since more of the light is blocked. I am not sure if there is a lightsource that is small enough to get close enough to be able to cast a naked eye visible shadow though."
] |
[
"Somewhat relevant to your question is a trick often used in electronics. Many fuses have filaments which ",
"are difficult to see",
" by the naked eye. If you want to quickly tell whether or not a fuse is intact (without pulling out your multimeter), a common trick is to set the fuse on a white sheet of paper and look to see if the filament's shadow is broken.",
"Although this is not necessarily a magnification, it is a practical application where a shadow is more easily resolved by the naked eye than a direct image."
] |
[
"Can you explain why the sun creates a shadow of humans and other objects?"
] |
[
"Would an upside down spinning top precess?"
] |
[
false
] |
If you hung a top by the tip and starting spinning it would it wobble and precess like it would if it was on a table? If not, why not?
|
[
"Precession arises from both having an object's angular momentum not aligned perfectly with the stable axis, and from torques exerted on the rotating top. Perfect alignment is incredibly unlikely, and gravity will be applying a torque. In greater detail, vibrations and perturbations in the string will also apply various torques to the top, shifting the stable axis about while the top spins, all the while gravity is acting on it as well.",
"I guess, in a perfectly ideal scenario, there would be no precession, but that scenario is contrived to ignore gravity and the string. If you only have one stable axis, there's no way to perfectly align a real object with it. It's never really in a stable configuration, only somewhat close to it at all times.",
"Whether or not it precesses is a matter of how accurate you want the answer to be. The most accurate answer is 'yes.' The introductory textbook answer might be 'no.'"
] |
[
"Yes, all rotating objects can precess. You won't notice as much on an upside down top because it's no longer spinning in an unstable configuration. Instead of gravity working to knock it over, it will work to hold it straight, minimizing the effects of precession over time, rather than exaggerating them, as normal."
] |
[
"why would something precess if it's in a stable configuration? Sorry, I'm pretty good with newtonian physics I've just never delved into angular momentum and spinning objects very much."
] |
[
"Can a mass spectrometer wipe a credit card or computer hard drive?"
] |
[
false
] |
Our organic chemistry teacher just gave a lecture strongly discouraging us from bringing even cell phones or watches into the lab when we're using a mass spectrometer. Is she as crazy and paranoid as I've always assumed, or is there a real risk of the magnetic field the machine generates causing problems?
|
[
"Mass specs rely on a powerful magnetic field. Depending on the type of mass spec this could be up around the 12 Tesla level (definitely enough to wipe hard drives). It should be shielded, but better safe than sorry. So no, don't take sensitive stuff in there."
] |
[
"A mass spec requires a small, intense magnetic field to operate.",
"But, the machines are required to be constructed so that no significant EM field is produced outside of the machine in operation, and similarly so that the machine is not disrupted by outside EM fields. If you observe your watch being disrupted by the machine you need to turn it off and have it repaired immediately..."
] |
[
"Is that strong enough to cause digital devices to malfunction due to induced currents? Since cell phones don't have any magnetic storage, that's about the only way I can see that a mass spectrometer could cause cell phone malfunctions..."
] |
[
"What effect, if any, would the creation of a gigantic (~60000 ft. high) mountain range have on the spin of the Earth?"
] |
[
false
] |
Was talking with a customer today and while waiting for software updates to download, we somehow got to discussing geology, and he was mentioning that eventually the Rockies would continue growing towards 60,000 feet, and he had made a comment about it throwing the spin of the Earth off if that were to happen. I argued it shouldn't make a huge difference, at least not notably so, as really, 60,000 feet is really not all that huge when compared to the diameter of the Earth, so it would still be basically as flat as it is now, relatively speaking. Can the creation of mountain ranges through any geological processes that exist becomes massive enough to really have an impact, astronomically?
|
[
"I'm going to side-step answering this question directly because there is no physical way to produce a mountain range that high. There are a couple of reasons why. ",
" The crust of the earth is in isostatic equilibrium with the mantle. Imagine a given area of the crust as a block floating in a tub of water and that building a mountain range is like piling material on top of that block. As you add more stuff to your pile, the top of your pile does get higher, but it is not a 1-to-1 increase in elevation because as you pile more stuff, the base begins to sink. In a way, the same thing happens as you build a mountain range. As you thicken the crust, the isostatic response will modulate the elevation (you are building more of a mountain in the mantle than you are on the surface of the earth).",
" As you grow your mountain range and thicken the crust, portions of the crust will sink progressively deeper into the mantle. Eventually, the combination of pressure and temperature will cause various minerals within this portion of the crust to change to different, more dense varieties, forming a rock called eclogite. Rather suddenly (on geologic timescales at least) you now have a piece of crust that is much more dense than what is attached to (the crust above it), but also, more importantly, is more dense than the mantle material adjacent to it. This is inherently unstable and will lead to a process we call \"delamination\" or the formation of a\"drip\", where this eclogitic root of the mountain range drips or peels off the bottom. This will produce an isostatic response that will lead to some increase in elevations, but effectively reduces the crustal thickness as well.",
" As you build a mountain range, you tend to focus precipitation along the flanks and in the higher elevations of the range. Temperature decreases moving up in elevation, so much of this precipitation falls as snow, forming glaciers. Glaciers are extremely efficient erosional agents and thus it has proposed that in most environments, glaciers form a somewhat hard limit on the elevation of a mountain range, with only isolated peaks being able to get much above the elevations at which you form large glaciers. This process is sometimes referred to as the \"glacial buzz-saw\".",
"All together, these various processes put a fundamental limit on the height of mountain ranges. The best we can tell, this limit is likely in the 8-10 km range, basically what we see in the Himalaya today. "
] |
[
"Mt. Everest is at 8.85km while the Rockies are at 4.4km according to Google. 60,000ft in km is 18.3km, so the Rockies would grow to well over twice the altitude of Mt. Everest. That being said, though, the Earth is a very, very smooth sphere. It would serve as an acceptable pool ball if none of its bumps or pits exceeded 28km. So even at 18km, it should have absolutely no effect on the spin or orbit of the Earth. ",
"I have no evidence to back this up, but I don't think it would effect the spin or orbit of the planet even if it exceeded 28km. Mt. Olympus on Mars is actually 22km, and it seems to be doing just fine."
] |
[
" As you build a mountain range, you tend to focus precipitation along the flanks and in the higher elevations of the range. Temperature decreases moving up in elevation, so much of this precipitation falls as snow, forming glaciers. Glaciers are extremely efficient erosional agents and thus it has proposed that in most environments, glaciers form a somewhat hard limit on the elevation of a mountain range, with only isolated peaks being able to get much above the elevations at which you form large glaciers. This process is sometimes referred to as the \"glacial buzz-saw\".",
"Interestingly, though, the \"temperature decreases moving up in elevation\" notion only holds true up to the tropopause at ~10 km (33,000 ft). Above this height, you're in the stratosphere, where temperature actually increases with height.",
"This essentially means that if you did have a 60,000 ft mountain, there would be a cold trap half way up. As air is pushed from sea level up the mountain slope, it would cool, with moisture condensing out as precipitation up to the half-way point. Above this point, though, temperature would start increasing, raising the saturation point and dropping the relative humidity so that there would be no more precipitation. ",
"In other words, you'd end up with a mountain so tall that snow can only fall on its bottom half - the top half would be ice-free barren rock."
] |
[
"If you placed a compass directly on the earth's north or south magnetic pole, how would the needle react?"
] |
[
false
] |
Would the compass needle spin wildly in any random direction? Or would it point to a more predictable direction?
|
[
"If you have the needle horizontal - that is, perpendicular to the ground - then it will spin freely and not prefer any particular direction. If you tilt it, then it will point at the ground."
] |
[
"Thanks"
] |
[
"How close to the magnetic pole would you need to be for this to work, would it work when 1km away from the pole? "
] |
[
"Is it possible to create a piece of foil thin enough to be translucent?"
] |
[
false
] |
Actually, I am not asking about the possibility of making it. Assuming that metallic foil could be made arbitrarily thin, is there a thickness where it would become translucent? Transparent?
|
[
"Yup. Gold works very well for that. Though everything tends to appear very blue when looking through the foil."
] |
[
"Regular aluminum foil is often semi-transparent to light. Compact discs are too — hold one up to a light and see.",
"Astronauts use gold-plated visors on their helmets as well."
] |
[
"Mylar like in the party balloons.",
"http://en.wikipedia.org/wiki/BoPET"
] |
[
"Just saw a commercial for this cancer fighting procedure. How does this compare to surgical methods?"
] |
[
false
] |
[deleted]
|
[
"It will vary from patient to patient, depending on the type of cancer, where it is, its mutations, etc. Your link is to one company that does ",
"radiosurgery",
", which has been around since the 1960s-ish, and is pretty frequently used. The choice of whether to use surgery, chemo, or radiation will all depend on the cancer. For example, if you have a skin cancer that's well defined and easily accessible, surgery is probably going to be the easiest option, you can just remove it and be done with it. Radiosurgery like your link would be best on a solid, internal tumor that's in a place hard to reach with conventional surgery, such as inside the skull. However, radiosurgery is harder to use for diffuse cancers, since it has to pinpoint a location. For example, you can't target leukemia with it, since that's in the blood and all over the body. For something like that, you'd use chemo, which would target all over. That's kinda a simplistic view, and in reality a combination of methods is used, and that's part of the Art of Medicine... deciding what strategy would be best, and tailoring it to the individual patient. Maybe chemo would reduce a patient's quality of life too much, or maybe other medical problems make the risk of dying during surgery too high... There's a lot of factors to consider. There's no one clear cut \"best\" treatment; each case is different."
] |
[
"There are three classes of treatment for cancers: surgery, radiation, and chemotherapy. Surgery is unquestionably the best, if you can completely remove the tumor. Cyberknife is a type of radiation treatment. You use it when either you can't do surgery or a previous surgery did not completely remove the tumor."
] |
[
"This is an unquestionably wrong answer. There are many tumor types where surgery is either not effective or not appropriate.",
"Radiation and surgery are both techniques to achieve local control of a malignancy. Some malignancies (sarcomas for example) are best treated with resection. Some malignancies (many testicular cancers for example) are best treated with radiation."
] |
[
"When you drink a liquid, how does it get out of your stomach without acid coming out aswell? How are they seperated?"
] |
[
false
] | null |
[
"They are not separated. The food/liquid that you eat acts as a buffer, and the mixture is passed along to the small intestine through the pyloric sphincter. The small intestine has both bile produced by the liver and concentrated/stored in the gallbladder and bicarbonate produced by the pancreas added to the mixture from the stomach. These are both bases, and serve to help neutralize the acid and to provide the proper environment for your intestinal enzymes. The stomach is continuously (unless it is suppressed by a physiological action) making more acid from specialized cells."
] |
[
"You wouldn't really flush it out for a number of reasons. Among other things, your GI tract controls how rapidly things leave your stomach. The best you'd do is dilute it, and your stomach is always producing a basal level of acid, as well as acid in response to food entering the small intestine. Additionally, most of your acid is already produced when you eat food, anyway (in response to the smell/taste and to the presence of food in the stomach). So even if you removed all of that acid, you'd still just make it again right away when you ate food.",
"The closest thing to what your referring to can actually be caused by excessive vomiting. This can cause somebody to lose so much acid from their stomach that it actually causes your blood's pH to rise due to loss of protons as they enter the stomach to form new acid."
] |
[
"Thank you for explaining - if you were to just drink lots and lots of water, is it possible to completely flush all the acid out of your stomach then? And if you subsequently ate some food, would it have to hang around in your stomach long enough for it to produce enough acid to start digesting it?"
] |
[
"Does Mass directly generate Gravity? Or is Gravity simply correlated with mass?"
] |
[
false
] |
I'm working on understanding the concepts of Relativity and how Gravity works. I've googled a little but the results I get are usually above my head. I don't need the math or formula's as much as an understanding of the concepts at this point. So... Do we know that Gravity is created by things with mass or is Gravity an observed correlation of Mass?
|
[
"Einstein's field equations can be explained in a single line: ",
"Where is curvature = Where is massenergy \n",
"On one side, you have curvature, this is what a straight line means in our universe. For example, straight lines on a basketball surface are curves. As an ",
" example, mirages happen because light refracts through different density air, so you see patches of sky just above hot asphalt on the highway, the light has followed a curved path. Now take those ideas and melt them together to be curvature of spacetime. The other side is stuff. It doesn't matter what stuff, it could be mass, heat, light. Just anything with massenergy content.",
"Now where is gravity in this picture? Gravity ",
" the curvature.",
"So... Do we know that Gravity is created by things with mass or is Gravity an observed correlation of Mass?",
"Much like electromagnetism, GR has self propagating vacuum solutions. This is the prediction that gravity waves can travel without any connection to stuff. While technically these waves have energy and therefore ",
", they do not need to be \"attached\" to traditional matter in the universe, much like how once emitted, light has little to do with flashlights anymore."
] |
[
"Does this mean that \"Gravity\" is simply the term we use to describe curved space-time.",
"Yes.",
"It's my very uneducated, and rudimentary understanding that Gravity is a force. If I'm understanding you correctly you are saying that it isn't. It's an effect of a force?",
"It is not a force, or at best it represents a generalized concept of force which is a much deeper notion. It's the idea that our universe's geometry is dynamic, that distances and time are malleable like taffy. Imagine trying to draw a circle on a piece of paper, but at the same time the paper is getting bigger or smaller in different places.",
"In the weak field limit, this curvature reduces mathematically to the idea of a potential. With a potential, much like voltage in electronics, you can define forces, from this you get Newton's gravity with the inverse square law we all know and love. For nearly every situation we face on everyday Earth, gravity being described as a force is perfectly alright. We just have to keep in the back of our minds that this picture breaks down and has to be discarded when we want to use GPS."
] |
[
"I understand most of the concept. The problem I have understanding is ",
"Now where is gravity in this picture? Gravity is the curvature.",
"Does this mean that \"Gravity\" is simply the term we use to describe curved space-time. ",
"It's my very uneducated, and rudimentary understanding that Gravity is a force. If I'm understanding you correctly you are saying that it isn't. It's an effect of a force?"
] |
[
"Can an asthma inhaler benefit someone who doesn't have asthma?"
] |
[
false
] | null |
[
"what drug is it? I know that atrovent (ventolin) opens your air ways significantly and is used by runners and weight lifters. However it's not a corticosteriod; which is what you have from the sounds of it. I used an inhaler to reduce phlem build up from envriomental triggers ( i ran a stone saw here on the canadain sheild for a year before schoolio)",
"http://www.webmd.com/asthma/inhaled-corticosteroids-for-long-term-control-of-asthma"
] |
[
"It actually is Ventolin, I mistakenly assumed that it was a steroid. That was the exact answer I was looking for, thank you!"
] |
[
"I'd also like to add that Ipratropium bromide, which may also be in inhalers, is a parasympatholytic. As such, affects would be limiting the parasympathetic system with similar results as albuterol and other beta 2 agonists. "
] |
[
"Lightning equalizes charge between the ground and air - but how does that charge get to be different?"
] |
[
false
] | null |
[
"Thunderstorms have strong vertical atmospheric flow and turbulence, and this sets up processes that can lead to charge separation. Specifically, water droplets tend to be blown upward while ice and hail tends to fall downward. This process extends up through the lower stratosphere. As these two streams of different forms of water cycle up and down they interact and collide with each other, and change (water tends to cool off and form a soft ice called \"graupel\"). The collisions have a tendency to transfer a small amount of static electric charge (similar to rubbing materials together) resulting in negative charges being concentrated near the bottom of the storm and positive charges at higher elevation.",
"These charges will discharge regularly, which is where cloud to cloud and cloud to ground lightning comes from."
] |
[
"Also, the negative charge at the bottom of the storm induces a positive charge in the ground (the ground is conductive, so charges can flow freely within it). Cloud-ground strikes occur between the negative charge region and the positive ground, and intracloud strikes occur between the positive charge region and negative charge region.",
"Less commonly, lightning can go from the positive charge region around the outside of the cloud to strike the ground."
] |
[
"I assume this 'imbalance' is also how these work?",
"https://www.amazon.com/AcuRite-02020-Portable-Lightning-Detector/dp/B00EO1H3X8"
] |
[
"How does a whale defend itself from sharks?"
] |
[
false
] |
saw this video: ... Wondered how a whale could ever possibly go about defending itself. Or is a whale just doomed when a pack of sharks finds it?
|
[
"Same reason a sumo wrestler isn't a defenseless meal for a carnivorous midget with sharpened false teeth. "
] |
[
"Actually I think shark's jaws open pretty wide. In fact, because they're not attached to a skull, they extend out of the face of the shark so that may be able to give them more space to open farther. Not entirely sure though so no one quote me.",
"Edit: might wanna see this: ",
"http://www.youtube.com/watch?v=YEktS4od-hg"
] |
[
"Well, how would a shark bite a whale, in the first place?",
"Their snout would get in the way of biting the body, and the fins/tail are constantly in motion and have a huge force behind them.",
"Not worth it for the shark, if the shark could even manage to bite any part of the whale.",
"Cookie cutter sharks, however, can bite a whale, and indeed they do. These are mostly parasitic attacks, however, and, AFAIK, a whale wont defend itself from this."
] |
[
"What kind of signal transformation algorithm was used to create this optical illusion?"
] |
[
false
] |
I am especially interested in the turning head effect. I'm trying to work out the neurosciences of it, so having some basic info on the signal would be great!
|
[
"I don't know what you mean by 'signal transformation algorithm'. The effect isn't that hard to explain.",
"It's just four images sliced into strips and then spliced into a single image by alternating strips. At any given point, the mask block slices from all but one image, and the brain interpolates the missing parts of the image. The illusion of motion is just the basic moving image illusion present in all films."
] |
[
"I don't think this is an optical illusion as in your brain is miss-processing something you see. This is just a filter being placed over some lines and you interpolate what the image is. "
] |
[
"It would be a form of aliasing, akin to the same reason that wheels look like they're rolling the wrong direction in video clips. "
] |
[
"If we built a clock with a pendulum that swung at 0.99c and left it outside, would the clock after 5 years be old and rusty while the pendulum stayed new?"
] |
[
false
] | null |
[
"As ",
"/u/iorgfeflkd",
" pointed out, the pendulum wouldn't be able to withstand swinging around at 0.99c. Let's just ignore that issue for the sake of argument, though.",
"-Think about how a pendulum moves as it swings back and forth. It starts out up high on one side, then it swings downward, increasing its speed, then it swings up the other way, slowing down, then it stops for an infinitesimal moment at the top of its trajectory before swinging back down the other way. Its speed isn't constant, it's constantly changing. I'd assume that it would be going 0.99c at the fastest point in its trajectory. Also, you'd need an incomprehensibly enormous pendulum for it to get going that quickly, but we can ignore that issue for now for the sake of discussion.",
"-The top of the pendulum, where it's hinged, is moving much slower than the end of the pendulum. Technically, right at the hinge, it's not moving at all-- just rotating a bit. The midpoint of the pendulum would only be going 0.495c at the fastest point in the trajectory. So really, the top of the pendulum would look normal, the far end would look very old, and there'd be a gradient of aging along its length."
] |
[
"Isn't that opposite? The part that is moving fast should look brand new while the rest is old right?"
] |
[
"wut",
" ",
" "
] |
[
"How can there be volcanoes in the middle of a continental plate, like the one in Hawaii?"
] |
[
false
] |
Looking at a world map of geological activity it struck me that Hawaii is nowhere close to the ring of fire surrounding the Pacific plate. Do we understand what’s happening there?
|
[
"It is a ",
"hotspot",
". Below the crust there is a place that is unusually hot, this melts the crust and leads to a volcano. The crust slowly moves across the hotspot, the mountain corresponding to the volcano moves away from it, and a new volcano forms next to it while the other one slowly erodes. Over time an island chain forms, with the biggest island at the location of the hotspot."
] |
[
"There are two competing hypotheses for how hotspots form, and which one is correct would greatly change the answers to your questions. In fact, both hypotheses could be correct, each accounting for different hotspots.",
"1) It is thought that hot, liquid magma can be trapped at the core-mantle boundary near the center of the Earth, and only released after nucleating to an appropriate size. Basically, the plastic mantle above it does not want to give way, but when the ball of liquid mantle is large enough, it attains sufficient buoyancy to break through and become a mantle plume.",
"If this plume reaches the crust-mantle boundary, it will be both liquid and much hotter than the surrounding mantle, and could break into the crust itself, partially melting a channel through, and then pouring into a magma chamber. If this magma solidifies after reaching the crust it simply becomes subsurface igneous rock, or it might breach all the way to the surface and become a volcano.",
"2) Alternatively, it is proposed that inhomogeneity in the near-crust mantle is caused by the non-uniform structure of the crust itself. That is, the crust does not descend into the mantle to uniform depth. As a tectonic plate moves across the mantle, the irregular extensions of crust into the mantle could sort of \"stir\" it, which occasionally causes pressures and tempreatures beneath a specific area of the crust to reach a point that allows partial melting and flow of magma.",
"You can read more at these Wikipedia pages, and the sources they link to: ",
"https://en.wikipedia.org/wiki/Hotspot_(geology)",
"https://en.wikipedia.org/wiki/Mantle_plume"
] |
[
"Thanks! Is there supporting evidence that the magma is unusually hot there? Do we know how the hot spot formed, and why it has stuck around for a few million years?"
] |
[
"How antimicrobial properties are added to dental bone grafts for periodontitis treatment prepared?"
] |
[
false
] | null |
[
"Bad news, it isn't sterile. Infections happen.",
"Good news, incredibly common procedure that is well studied with lots of additional controls in place.",
"The dental surgeon makes you rinse with antimicrobial mouthwash before they anesthetize you, open up your gum, apply another topical sterilizing chemical into the hole, then installs the bone graft. A fancy way of saying they cut you open and clean you out.",
"The simplest bone graft is using your own bone, but this isn't common. No additional additives are required. It starts out sterile (inside you) and is moved into a sterile place (back inside you, but somewhere else).",
"Next most complicated is donor tissue, usually from a dead person who agreed to donate their organs or taken from someone having a hip replacement (big bone, it's getting taken out anyway...) Someone elses bone. Donated bone tissue is sterilized and living tissue removed with fun names such as demineralized freeze-dried (DFDBA) or mineralized freeze-dried (FDBA). All the microbes and tissue is killed by radiation.",
"Third option is bone tissue from a pig. Sounds scary, making you a hybrid animal-human, but before that happens they kill every single living cell in that bone with radiation. There is no marrow, or microbial contamination, or and cell tissue remaining. The only remaining tissue is dead bone skeleton structure, identical to human bone skeleton.",
"Most times, the bone graft is deliberately dead/sterile on arrival. It exists as a blank scaffold for you own tissue to grow into and build.",
"In almost all of these surgeries some bacteria enter the wound site during the procedure, or they enter later during wound healing. It comes from the air in the room, little bits jumping from clothing or in your hair - it only takes literal single cells to form a colony on the surface of the donor tissue and then be incubated inside the perfect growth medium of your mouth. Quick Google reminds me it's about ~1-15% of dental implant surgeries are affected by microbes, but majority of those won't develop an infection as your body can manage small numbers of mild bacteria just fine. So they make you take oral antibiotics for some time after.",
"For some grafts it is possible to cover it with a membrane that is soaked in regular antimicrobial chemicals. Usually just regular boring tetracycline antibiotics. Analogy: soak a t-shirt in antimicrobials then when you wear it, it stops bacteria growing in your arm pits and you won't have smelly pits.",
"Different membranes exist. You can put the entire bone graft in a bag that dissolves, you can put a metal cage over the outside and then remove it later."
] |
[
"that explains a lot, thank's",
"\nBut I was also wondering, if there are any current methods, to make the bone graft itself, natural or synthetic antibacterial?"
] |
[
"Yes, we do it the same way we make objects such as stents or even prosthetics such as artificial hips.",
"We can \"graft\" or glue on antimicrobial chemicals onto the surface in a monolayer that is measured in nanometers. More advanced than simply soaking. You then have a protective but also sacrificial layer on the surface. ",
"More advanced is do both. Have a protective grafted layer of antimicrobials and also fill the device with fluid antimicrobial chemicals. As the surface layer is used up, it refills from the inner storage.",
"It is possible to change the material from bone to something like a metal which has a naturally antimicrobial surface. This the basis for how you can wire someones jaw or put a permanent pin in a broken bone. May be problematic for dental implants where you do want the body to grow it's own tissue into the scaffold."
] |
[
"What’s the difference between a disease and a disorder?"
] |
[
false
] |
Can someone explain the main difference between disorder and disease? Mainly shedding some light on whether or not addiction or alcoholism are diseases or disorders?
|
[
"To my knowledge, a disease is a bad response to internal or external factors (pathogens). For example, a viral illness like the flu or a bacterial one like tuberculosis.",
"A disorder is some sort of body derangement or disruption where something just doesn't function correctly, whether it's mentally or physically. For example, anorexia or bulimia.",
"I would consider alcoholism to be a mental/psychological disorder since your brain is craving a depressant. However, sicknesses caused by alchohol I would consider a disease."
] |
[
"Well, can't you get PTSD, which is a disorder?"
] |
[
"Those are addictions are they not",
"A disorder is something you usually have, you can’t get a disorder (this is a wild guess)",
"A disease is something you can get or be past on it’s biological and is not a “defect” of development etc. ",
"I’m no science expert so take that with a grain of sodium chloride "
] |
[
"Today we learned in bio that most of you're DNA was junk DNA. What would happen if you cloned someone but removed the junk."
] |
[
false
] |
Say you take a newborn child's DNA and you splice out all of the junk. Since the junk DNA doesn't code for anything would they still live?
|
[
"And to actually answer the question.",
"Such a baby would almost certainly not be viable. "
] |
[
"only non functional adaptions that at some point disadvantaged the species would be selected against. "
] |
[
"\"Junk DNA\" is a misleading term. \"Noncoding DNA\" may be more accurate. This large proportion of the DNA performs functions like regulating the amount of protein expression corresponding to each gene. This differential expression can have incredibly profound consequences. In fact, there are entire fields, such as developmental biology, that concern themselves almost entirely with the role of noncoding DNA in the growth of organisms and differences between species.",
"And to answer your question, an embryo, fetus, or infant without this portion of DNA would not have any chance of surviving. "
] |
[
"Hey Science, what would aliens think?"
] |
[
false
] | null |
[
"According to my astronomy professor (who specialized in searching for extraterrestrial life), one thing we will look for life on other planets is oxygen gas. This is because free oxygen is unstable and combines easily with other atoms/molecules. The only process we know of that produces oxygen in large amounts, and the only reason we have a lot of oxygen in our atmosphere, is plant life. ",
"More info: ",
"http://www.askamathematician.com/2010/01/q-why-does-oxygen-necessarily-indicate-the-presence-of-life/"
] |
[
"Well if their telescopes are anything like ours, they won't even know there's a planet here. Even within 100 light years we can't see planets unless they happen to pass between us and the star they orbit. This question is so highly dependent on the level of technology employed by these aliens you could get essentially any answer."
] |
[
"Refer to ",
"this",
". I asked a similar question a few weeks ago."
] |
[
"Is there an effect that is analogous to mechanical cavitation for electrical waves?"
] |
[
false
] | null |
[
"I would not think so since fluids follow the Navier Stokes equations, and do not have a wave like nature, but do have mass, while EM radiation follows the Maxwell equations, are waves, and have no mass. Simply put, you can't remove the EM field from an area. The only thing that comes to mind might be superconductors which eject an outside magnetic field passing through them, only to let it back 'in' suddenly when it's no longer a superconductor. I have no experience with supercomductors though."
] |
[
"There is no phase change there, so not in that sense.",
"When not in a vacuum, there is ",
"https://en.m.wikipedia.org/wiki/Nonlinear_optics",
" , which is interesting, but still not cavitation."
] |
[
"A definition",
"Cavitation occurs when the hydrodynamic pressure exceeds the vapour pressure of a moving liquid. Gas bubbles form within the liquid, which thus becomes a two-phase system. These bubbles will be crushed against the metal surface at high speed, an attack that leads to cavities with rounded contours.",
"The reason for cavitation is usually because of turbulence. As an object moves through water it causes disturbances; if they are slow enough and viscous enough the local pressure differences are predictable and smooth. Whereas if you have mixing or an open system (ie not bounded by a pipe) with not very viscous liquid or very fast flow, you cause vortices and chaotic patterns, which cause local pressure differences and cavitation. It's sort of the difference between having smooth flow, where on a normal distribution, everything is pretty close to a certain pressure, and having chaotic flow, where the distribution of pressures is wider and some proportion of those pressure differences fall under the vapor pressure of the liquid. ",
"Cavitation is interesting because of the mechanical properties of water which cause damage to systems. For electromagnetism you would need something similar, so ask questions like",
"For 1 and 2, yes, my understanding is that this is one of the major issues with plasma containment in fusion reactors (ie, ITER). In this case it may not be the EM itself that causes the issue, but the loss of beam confinement.",
"Again, the nonlinear equations describing the motion of the plasma particles can exhibit chaotic behavior that allows the particles to escape from the confining fields. For example, electrons circulating along the guiding magnetic field lines in a toroidal confinement device called a TOKAMAK will feel a periodic perturbation because of slight variations in magnetic fields, which can be described by a model similar to the standard map. When this perturbation is sufficiently large, electron orbits can become chaotic, which leads to an anomalous loss of plasma confinement that poses a serious impediment to the successful design of a fusion reactor. ",
"source",
"Which brings me to 3) - it's far more common in electronics design to have to worry about inductive spikes, where semiconductors have to take PARTICULAR care against spikes exceeding a certain value. While this isn't ",
" it is most similar to cavitation because a periodic spike, however rare, if it hits a semiconductor, it can damage the semiconductor over time. This can also cause EM - which is not chaotic, it's predictable, but because it's from so many traces it's likely to cause an exception in testing if you don't do clever things to spread the affected frequencies out. Too many switching supplies at exactly 1MHz for example will probably fail your test - it's a stochastic measure to spread that out over different frequencies and get better EMI results. ",
"Ayway hope that answers some of the question.",
"Edit: citation"
] |
[
"If continental crust is not dense enough to be subducted into the mantle, will the production of continental crust at island arc locations eventually result in the Earth's surface becoming entirely continental?"
] |
[
false
] |
[deleted]
|
[
"A couple of things to consider. First, it is not impossible to subduct continental material, just difficult. Small portions of continental crust can be dragged down in subduction zones (though some portion of them make their way back to the surface in the form of High Pressure (HP) or Ultra High Pressure (UHP) terrains). There has also been the suggestion that a process called \"subduction erosion\" is important. As the name implies, this process is one in which a subduction zone \"erodes\" the overriding plate, basically plucking off small bits and entraining these with the rest of the subducted material. Then there is whole-scale continental subduction, which to a certain extent is still somewhat debated. This mostly is thought to happen in extremely large mountain ranges, for example, it's been suggested that subduction of continental crust may be happening in the Pamir mountains, which are part of the Himalaya-Tibetan mountain system.",
"Another thing to consider is that once you form continental crust, you may significantly thicken this crust (and shorten the surface area it takes up) through mountain building. There is of course a limit to how much you can thicken the crust, but this can account for some of the additional surface area produced. This thickening also accounts for a crustal removal mechanism as over-thickening of crust can cause the lower portion to become gravitationally unstable (denser that it's surroundings), detach and sink into the mantle. ",
"In general, we think that the volume of continental crust has increased with time, but through some of the processes I've outlined above, some have even argued that their may be a ",
"net decrease in the volume of continental crust",
". "
] |
[
"Another thing to consider is that once you form continental crust, you may significantly thicken this crust (and shorten the surface area it takes up) through mountain building. There is of course a limit to how much you can thicken the crust, but this can account for some of the additional surface area produced. This thickening also accounts for a crustal removal mechanism as over-thickening of crust can cause the lower portion to become gravitationally unstable (denser that it's surroundings), detach and sink into the mantle.",
"Eclogite delamination would fall under thus category too, correct? It's been hypothesized to account for a significant loss of continental crust material through time if I'm not mistaken."
] |
[
"Yep, the formation and removal of eclogite is the main cause of the delamination/deblobbing/dripping phenomena. "
] |
[
"Do viruses play an important role in balancing the ecosystem, or would things be better if we could eliminate them entirely?"
] |
[
false
] | null |
[
"Bacteria and viruses are part of the global ecosystem and thus have a role to play in maintaining balance. In addition, not all viruses and bacteria are pathogens, meaning not all of them actually cause illness in other life forms. In fact there is current research on using otherwise harmless viruses genetically modified to target and destroy cancer cells.",
"So no, I wouldn't call eradicating them (or any life forms for that matter) a good idea. Building an immunity to the pathogenetic ones through vaccination is a FAR better and more practical idea."
] |
[
"Most of the work on this has been on marine viruses, which are almost unbelievably abundant:",
"…there are about 10 million-fold more viruses in the ocean than there are stars in the universe. … In fact, all the viruses in the ocean end-to-end would stretch further than the nearest 60 galaxies.",
"—",
"Viruses: unlocking the greatest biodiversity on Earth",
"Marine viruses are very important parts of their ecosystems:",
"The discovery that viruses were the most abundant biological entities in oceanic marine environments [7], reaching up to 10",
" viruses mL−1, further stimulated marine virus research. … Later, the expansion of virus research to coral reefs [9], sediments [10,11], the deep biosphere [12], and freshwater environments [13] emphasized that viruses are integrated inhabitants of all aquatic environments. Consequently, the past decades’ research has revealed viruses as key players in the marine ecosystem, from driving bacterial and algal mortality and evolution at the nanoscale, to influencing global-scale biogeochemical cycles and ocean productivity. The research has fundamentally changed our conceptual understanding of the function and regulation of aquatic ecosystems, and the development of molecular tools and DNA sequencing techniques has opened up for the exploration of viral diversity and the genetic mechanisms of virus-host interactions.",
"—",
"Marine Viruses: Key Players in Marine Ecosystems",
"There’s been less work on terrestrial viruses, but they too are critical parts of many ecosystems."
] |
[
"Suddenly removing viruses now would probably be catastrophic, since it would take a lid off of bacterial populations, but if they never existed in the first place bacteria would still have reached some equilibrium state by this point. The viral role in biogeochemical cycles is basically a secondary byproduct of their effect of moderating bacteria and algae which are the ones actually driving much of that cycle.",
"It's an interesting question."
] |
[
"Why can't light travel through walls but other electromagnetic waves can?"
] |
[
false
] |
I looked around a bit for this answer but haven't found anything basic enough/in detail enough. I can be in my house and listen to the radio waves or sit in my chair and be hit by gamma rays from outside (for whatever reason). Why can't visible light go through walls if these other wavelengths on either side of visible can? Also, at what points on the spectrum does this inability to penetrate walls begin?
|
[
"Imagine you have some copper chloride, a salt. You dissolve this in some water. The copper(II) ions dissociate into the solution, which as a result turns bluish. ",
"The reason the solution turns bluish is this: If you shine white light through the solution, the non-bluish wavelengths of light are absorbed. Why can blue light pass through copper(II) ions, but red light can't?",
"You can speak of a material's \"absorption spectrum\", the degree to which it absorbs photons of a particular wavelength. Copper(II) has an absorption spectrum where it absorbs red hues more than blue. ",
"Walls happen to absorb visible light, as you pointed out yourself. So far I haven't answered your question, which is: Why do walls absorb in this particular range?",
"To answer that, I might as well in a sense answer you why copper(II) ions have the absorption spectrum they do. The answer is quantum mechanical, and you'll have to ",
"read up on that on your own",
"! But in general, any absorption (or emission!) of photons comes back to electrons changing between states of different energy. An electron that absorbs a photon gains a corresponding amount of energy, but it will only do this if there a state available for it at this higher energy.",
"In other words, ",
".",
"So coming back to our copper ion solution, blue light passes through because the electrons on the copper ions don't have a corespondingly higher energy state to jump to, so they just chill and let the blue photons pass unhindered. Maybe there are absorption peaks in the UV or IR regime.",
"Things that are opaque are things which you could call \"electronically messy\". The copper solution is somewhat clean - the electrons on the ions are somewhat similar. But solid materials, such as walls, allow the electrons to be in all kinds of states, therefore they can accept photons of all kinds of energies, only more in the visible spectrum than for higher or lower frequencies.",
"A radiowave or a gamma ray doesn't pass through your house or car completely unimpeded - some of it is absorbed. This is in the same way that if you hold up a sheet of paper between your eyes and the sun, the light will still shine through, just not as much. So it's not like they will just pass by completely unhindered. But the level of absorption is different."
] |
[
"Light can travel through walls! Just not the light you can see. Visible light is a very narrow spectrum of the entire electromagnetic spectrum. This light has very specific frequencies and because of that had a very specific energy. Energy = planks constant x frequency. Now this energy must correspond to the difference in electron energy levels allowing for the photon to be absorbed by the wall and therefore the photon can't pass. Now the other wavelength corresponding to, say, radio waves have energies that don't correspond to the electron energy levels and passes through easily. In the end the electron levels are responsible for light passing through. Each material has different electron energy levels so it really depends on the wall and materials involved that determines what light passes."
] |
[
"If you make your walls out of glass or one of the many other transparent materials available then light ",
" pass through walls. Your house has windows, right?",
"In fact, you can make walls which light will pass through but other waves won't.",
"All the other answers are interesting, but I think the real answer to your question is \"because you're conditioned to think of walls as opaque\". The basis of your question is invalid. ",
"Many materials have one or more passbands. Some of those materials have passbands in the visible spectrum and some don't. Some don't have any passbands. There is nothing magic about light that makes it different from other electromagnetic waves, and your question comes up only because your intuition is skewed by the bias of your human existence.",
"EDIT: If you could \"see\" the entire spectrum just about everything would look like a tinted, translucent material. The tint would be from its absorption bands, and the translucency from its passbands. "
] |
[
"When animals ”smile”, does that mean that they are happy?"
] |
[
false
] | null |
[
"Hi BicepsRhydon thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Biology"
] |
[
"”Biology”"
] |
[
"If our fingers are operated by tendons in our forearms, why is it hard to move your fingers when they get cold?"
] |
[
false
] |
[deleted]
|
[
"The problem arises from the joints of the fingers. Each joint has cartilage and on the surface of that cartilage is a protein called lubricin. This lubricates your joints and allows them to move smoothly. Like most liquids, when the lubricin gets cold the viscosity goes up. This increases the friction within the joint and thus makes it more difficult to move."
] |
[
"This question was posted in this sub 3 days ago (",
"here",
"). Here's the answer I posted then:",
"The stiff-finger-joint phenomenon, where it feels like the fingers won't bend, is due to synovial fluid in the finger joints becoming more viscous in the cold. (Edit: This is pretty well established - there has been a fair amount of research on this due to occupational-health-and-safety workplace issues. See source at bottom for a review)",
"The ",
" though - when it feels like you can't hold anything and you keep dropping your keys - is actually due to the forearm having gotten chilled. ",
"BTW if the core of the arm gets below 10C as high up as the elbow, then the nerves that are controlling the muscles almost completely stop working (nerve conduction speed depends on temperature) and then it can feel as if the hand has become almost paralyzed - commands to your fingers seem to have almost no effect.",
"There are a number of fun experiments you can do on this in physiology labs in winter if you have students who have just arrived from a cross-campus trek through the snow. :)",
"more info ",
"here"
] |
[
"The previous poster is correct, the primary contributor to finger joint stiffness when hands get cold is viscosity of the fluid of the finger joints. The issue is exacerbated by the fact that usually the forearm muscles are also slightly chilled, which noticeably reduces the force they can generate. The result is that the forearm muscles cannot fully compensate for the stiffened joints. ",
"See source I posted further down in this thread. PS, this topic was discussed 3 days ago in AskScience."
] |
[
"Why do some GABAergic substances such as Xanax and Klonopin cause significant withdrawals while things such as tea and Ashwagandha do not?"
] |
[
false
] |
This question has always intrigued me and I’m wondering if there’s someone much smarter than I who can help explain
|
[
"If you look through the literature, you'll at best find some vague references to certain teas or ashwagandha maybe sort of indirectly enhancing GABAergic function. You will also find a large volume of literature establishing that alprazolam and clonazepam potently and directly bind to the GABA-A receptor, enhancing flow of chloride ions. It's the difference between just barely tickling something with a feather vs. smashing it with a hammer.",
"Benzodiazepines have a powerful inhibitory effect on neuronal activity, to the extent of being able to stop seizures and even produce amnesia or unconsciousness. If you want tea with anything like a comparable effect, you'd better order the Long Island iced variety."
] |
[
"On mobile so can't post links. Check out the Wikipedia page for \"benzodiazepine withdrawal syndrome\" subsection \"mechanism\" for an introduction to why benzos cause withdrawal in the first place. Alcohol withdrawal is due to the same mechanism.",
"I can only find one very basic study that links ashwagandha to the GABA receptor (Direct evidence for GABAergic activity of Withania somnifera on mammalian ionotropic GABA-A and GABA-p receptors, Candelario et al, J. Ethnopharmacol. 2013), and none in humans. Have you seen more robust evidence that this is the case?"
] |
[
"It's more about their ability to form an addiction to begin with than their ability to cause withdrawals."
] |
[
"Do dogs comprehend speech, or just tone of speech?"
] |
[
false
] |
Do dogs actually understand vocabulary, or do they just understand the tone that you speak in? How much comprehension does a dog actually have when it comes to speech? I ask because if you say to my dog "want to go for a walk?" she goes absolutely apeshit. But if you say "want to go for a burrito?" using an identical tone, she appears to go just as apeshit, even though the words are different.
|
[
"Dogs have the ",
" to understand vocabulary, as do a few other animals. If you have the time for it, ",
"here",
" is a NOVA documentary on the very subject.",
"This requires special training, however. It is quite likely that your dog is only responding to your tone."
] |
[
"It doesn't matter what tone I use, if I say \"ride\", the little furballs go ballistic."
] |
[
"Have you considered the possibility that your poor dog just ",
" wants a burrito?",
"Kidding aside, your actual question of course is ",
" unanswerable, and possibly even meaningless. What's the difference between having a predictable response to a pattern of sounds and actually ",
" those sounds? If you can figure out how to quantify that, let me know.",
"That said, a former significant-other's dog ",
" had a working vocabulary of perhaps two or three dozen words, in both English and Arabic. All the common normal words, obviously: sit, stay, walkies. But bizarrely, he was also able to distinguish homophones. He could suss out the difference between \"stairs\" and \"stares.\" Whether it was contextual or tonal or what I couldn't say, but we did experiments, and the little wiglet never once got it wrong. Downright peculiar, it was."
] |
[
"What kind of hazard symbols were used in the 1950's?"
] |
[
false
] |
Considering both and were all invented after 1950 (1988 and 1960 respectively) What kind of system or symbols were used to indicate hazardous substances before that time? Need this for a project i'm working on to be historically accurate and I've tried searching everywhere but can't find anything at all, so please if anyone knows any examples I would be in your debt. Thanks for reading.
|
[
"If you don't get an answer here, you can perhaps try ",
"/r/askhistorians"
] |
[
"I did actually try posting this question there like a month ago :P But unfortunately I didn't get an answer there so now i've come here in hopes someone might know. There seems to be very little information about this from the internet, the only thing I have concluded is that there really was no official system back then and everyone just kinda did their own thing, but I cannot find any actual pictures on any example. Thanks for the tip anyway though, it is the thought that counts."
] |
[
"I have seen occupational hazard signs from the 40s, and they were really cool. They were hand-painted cartoon drawings trying to represent the hazard. For example, a guy getting shocked would represent an electrical hazard. A skull and crossbones still would represent poison. There would be a lot more text describing the hazard on the sign as well. The style was like what you see in WWII era propaganda. Sadly, I don't have any pictures and they aren't online because they were for that specific site. ",
"The style was kind of similar to (though obviously a lot less scary than) WWI chemical weapons warnings. Examples ",
"https://www.pinterest.com/pin/37928821834597294/",
"https://i.pinimg.com/originals/c4/fe/25/c4fe25bb8d83471ccc8ddcbf72e8a96b.jpg",
"Note the heavy use of text and the nonstandard symbolism."
] |
[
"Is combustion possible without heat? Also, does temperature required for combustion vary dependent upon the substance being ignited?"
] |
[
false
] |
It would be interesting to know if there is any such thing as "cold" combustion. If there is no such thing that we are aware of, what is it about the chemical process of combustion that requires heat? Also, I read that adiabatic flame temperature differs greatly from substance to substance, but from the materials I read, this appears to be how hot something burns and not what temperature at which the substance can be ignited. Does combustion necessitate an oxygen reaction? If so, why is that the case? Thanks in advance!
|
[
"White phosphorus is a very famous example of combustion at room temperature. All combustion is innately exothermic and will generate heat.",
"Also, I read that adiabatic flame temperature differs greatly from substance to substance, but from the materials I read, this appears to be how hot something burns and not what temperature at which the substance can be ignited.",
"The temperature of ignition without an external ignition source is known as the autoignition point of a compound.",
"Does combustion necessitate an oxygen reaction?",
"Any strong oxidising agent can result in combustion."
] |
[
"Interesting, I'll see if I can find some videos of experiments with white phosphorous. Thanks!"
] |
[
"Typical combustion reactions (e.g. hydrocarbons) actually have fairly high activation barriers, it's why there's a catalytic wire in gas stoves to help with ignition, and why you need a flame or spark to start them. If the reaction wasn't exothermic, it wouldn't generate enough heat to sustain the reaction going over the barrier.",
"The ",
"flash point",
" is the temperature at which something is capable of being ignited, but it's really more a physical property. You can't burn a cup of liquid gasoline because you need oxygen and there isn't much dissolved in the liquid. You're burning the vapor that comes off the liquid and mixes with the oxygen. The flash point is the temperature at which enough of the liquid vaporizes to form a flammable mixture in the air above it.",
"Do you mean does combustion require an oxidizer? Yes, by definition. Combustion takes in a reactant (usually hydrocarbons but there are others) breaks them apart and converts them to oxygenated forms. C3H8 becomes 3(CO2) + 4(H2O). If it isn't forming oxygenated products, it isn't combustion. Other types of decomposition exist and don't require oxygen, but they aren't combustion. "
] |
[
"Can stem cells be used to cure herpes?"
] |
[
false
] | null |
[
"Please, do not ask for medical advice. Thanks."
] |
[
"Stem cells. \nAnd what they can do. "
] |
[
"This is probably too wide a question to be of any use in AskScience. You should try to rephrase your question so that:\na) it does not contain any request for medical advice, nor any reference to medical conditions of any particular person; b) it is phrased in such a way that can be answered by the scientific community. Thanks for understanding."
] |
[
"Is there any way that visible light could be strong enough to shine through an object we perceive as opaque?"
] |
[
false
] |
I assume that radiation getting thru unshielded materials is the equivalent of this for non-visible light. If not, why not?
|
[
"Have you ever shined a flashlight through your hand? Certainly intense enough visible light can penetrate an opaque object, as long as it doesn't have an absorption coefficient of exactly 1.0 (which nothing has). However the problem is that for an opaque enough object the light might have to be so bright that the object heats up and is destroyed. That's because an object being opaque to visible light means that it absorbs visible light, and the energy of that absorbed light has to go somewhere (it goes into heat). So for example if you want to see through an opaque object, you can shoot it with a laser, and for many objects you will be able to see the laser light through the other side. But for more opaque objects (like a lump of coal) you would need a laser so bright that it would just light the coal on fire."
] |
[
"You're right that a black hole would be an exception to my statement that nothing has an absorption coefficient of exactly 1.0. "
] |
[
"I'm way above my pay grade here, but isn't the \"blackness\" (light absorbing ability) of a black hole caused by extreme gravitational pull, not by being a certain light-absorbing color?"
] |
[
"Seawater is not drinkable by humans. Would it have been drinkable at any previous point in the earth's history?"
] |
[
false
] |
I gather than seawater is not drinkable mainly for its concentration of salt as described: Was the salt (or other) composition of the ocean different at any point in the distant past, and if so would it ever have been drinkable by humans in quantity?
|
[
"What about at a stage before multicellular life formed? Assume we can travel back in time to sample the water.",
"Is not enough known?"
] |
[
"The water-from-comets theory is not well settled. E.g., ",
"http://en.wikipedia.org/wiki/Origin_of_water_on_Earth",
" It ",
" one of the candidate theories.",
"Ocean salinity seems to be fairly stable. There is evidence for an increase during ice ages (which are geologically brief periods). See ",
"http://en.wikipedia.org/wiki/Seawater#Origin"
] |
[
"The residence time of salt in the ocean is estimated to be millions of years. (",
"source, table 7.3",
"). I think the general thought is that the current ocean salinity of about 3.5% has been stable for hundreds of millions of years but there is no direct data to verify it - there is no good paleo-salinity proxy measurement. I don't know how low the salinity needs to be for safe drinking but it's doubtful the ocean was ever that fresh during the billion years since multicellular life formed. "
] |
[
"When the Vikings visited mainland North America circa 1000 AD, why didn't they carry over so many deadly diseases to the natives as other Europeans did in the late 1400s and early 1500s?"
] |
[
false
] |
Posted this on , but i realized that its not strictly a history question, is it? It might be better posed to those who are more expert on the nature of diseases. The thread from :
|
[
"Because the Norse themselves were largely lacking in epidemic disease, due to living on the periphery of Europe. Vinland was mostly contacted by people sailing from Greenland, which was itself largely populated from Iceland. Iceland didn't encounter smallpox until ",
"1241",
" and the disease was never endemic there...it swept through periodically and died out. The population in Iceland is just too small to support that kind of disease for long periods. The populations on Greenland were even smaller and less able to support such diseases. There's just no good route for disease transfer from small population to small population via infrequent visits between populations.",
"Contrast this with Spanish who were sailing directly from some of the largest cities in Spain to the new world. That kind of direct trip from major disease centers just wasn't happening with the Norse."
] |
[
"The reason that the Central/Western European colonists had so many diseases to bring with them was because: They lived in large, crowded cities; they lived in very close proximity with animals; and they lived in (generally) warmer climates. These factors, combined with a few hundreds years of brewing, larger population size, and a pinch of bad luck, created a situation with more diseases, and more vectors for spread. "
] |
[
"I ",
" he just means a few hundred years of \"letting all those factors brew together to breed both diseases and disease-resistant people\" rather than the technology involved in making beer."
] |
[
"If you were to finish a masters in biology in 1975 and then were teleported to this date, how relevant would your knowledge be?"
] |
[
false
] | null |
[
"Not very."
] |
[
"Sorry this is not an answerable scientific question. If you need help rephrasing this so it is answerable, then please use modmail."
] |
[
"I don't remember exactly what the self-post text said, but it seemed like an interesting question... basically a bit of a fanciful way of saying, \"What major discoveries/changes in accepted theories have happened in the last 35 years in biology?\" I was curious what people with more expertise than I have would say, and I'm sorry that the discussion didn't happen."
] |
[
"What's the smallest object you could 'stand on' that would have the same gravitational pull as earth, but you wouldn't have to worry about getting sucked/collapsing/spaghetification ?"
] |
[
false
] |
Just something I was thinking about...
|
[
"You have two constraints to deal with:",
"The gravitational field g=GM/r",
" = 9.8 N/kg",
"The tidal field f=2GMh/r",
" where h is your height.",
"You can combine these into a restriction on r, independent of mass: r=2hg/f. If you're 6 feet tall and you want a tidal force less than 0.01 g (let's say), then this gives you a radius of 1200 feet."
] |
[
"What about a tidal force of 1g? That seems roughly equivalent to holding myself from a pull-up bar, which isn't enough to cause injury.",
"That gives... an object 12 feet across with a surface gravity of 1g? Is that right? I think there's some second-order effects I'm missing, if I'm not completely wrong."
] |
[
"That would have a mass of about a trillion kg so its Schwarzschild radius is still microscopic. It's a strange situation. Also I'm only considering the axial force; the forces in the other directions probably shouldn't be neglected at this scale."
] |
[
"Why are aurora/northern lights taking place within rings around the poles rather than a disk centered at the poles?"
] |
[
false
] | null |
[
"As ",
"/u/chrisbaird",
" mentioned, the aurora is a magnetic phenomenon. Early theories of the aurora (which informed Kristian Birkeland's ",
"terrella experiments",
") involved charged particles leaving the Sun, streaming along magnetic field lines, and impacting the Earth's outer atmosphere. That would produce, as you say, a disk-shaped aurora.",
"Nowadays we know that the aurora is produced by ",
"magnetic reconnection",
" in Earth's magnetosphere. Magnetic reconnection involves magnetic field lines changing their topology or connectivity. In a nonconducting medium like air, that's no big deal -- but in an electrically conductive medium the connectivity of magnetic field is a quasi-conserved quantity, so it's hard (for example) to splice \"closed\" field lines that connect between Earth's north and south polar regions, into \"open\" field lines that connect Earth's polar regions to the Sun or the outer solar system. Doing so generally requires driving energy. Applying force to a magnetic domain (like the magnetosphere) induces large electrical currents at the domain boundaries. Dissipation of these currents is what causes the reconnection, and the energy contained in the current gets released in a bunch of ways -- one of which is acceleration of electrons to high speed. Reconnection on the Sun can accelerate particles fast enough to create antimatter. Reconnection near the Earth isn't so energetic, but it can generate energetic electrons that excite spectral lines in the outer atmosphere.",
"In general, field lines near the poles are directly connected to interplanetary space, and field lines near the equator are directly connected to the opposite side of the Earth, and moving the boundary between those two zones requires reconnection. The location of that boundary depends on the interaction between the ",
"solar wind",
" and Earth's magnetosphere, and when the equilibrium changes field lines undergo reconnection and accelerate particles inward. Rapid changes in the solar wind interaction move the boundary rapidly, and induce lots of magnetic reconnection -- this both moves and brightens the aurora. The classic example of this is type of event is the impact against the magnetosphere of a solar ",
"coronal mass ejection",
" that happens to contain a countering magnetic field.",
"Even in a steady solar wind there's ",
" aurora, because (you may have noticed this) the Earth is spinning. The equilibrium magnetic latitude of the open/closed field boundary is different at noon than at midnight",
" , so as each bit of Earth travels from one to the other, the associated field reconnects and accelerates particles down into the outer atmosphere.",
"Anyway, the reconnection happens primarily at the open/closed boundary of the magnetic field, which is a sort of vase-shaped locus. The vase intersects Earth in a ring, which is why we have an auroral oval instead of an auroral disk.",
" (Remember, on a planetary scale \"midnight\" is a place, not a time...)"
] |
[
"Free charged particles that are moving tend to spiral around and along magnetic field lines (",
" this is true is another question that has a long answer involving the ",
"Lorentz force law",
"). Most of Earth's magnetic field lines in each hemisphere do not enter Earth's surface at a single point. Most of the field lines enter Earth's surface in a vast ring region. This is because the effective magnetic North Pole (and equivalently the magnetic South Pole) does not lie at the surface of the earth, but lies far below earth's surface. ",
"This drawing",
" is wrong.",
"This drawing",
" is more correct.*",
"High-energy charged particles in the upper atmosphere spiral along the magnetic field lines until they get close enough to earth's surface to encounter thick air, at which point they collide with the air, thereby energizing it and allowing it to emit light as aurora.",
"*Although in this drawing, the north and south magnetic poles are mislabeled. The South Magnetic Pole is actually the one that is close to the North Geographic Pole."
] |
[
"Thanks.",
"\nThen, what happen inside the ring, why no aurora there? not enough charged particles coming through? "
] |
[
"I find that when I get headaches, if I put my cold hands on my temples it goes away. Any idea why this is?"
] |
[
false
] | null |
[
"They sound like they might be migraines. I find a cool dark room helps with mine. ",
"Migraines can be caused by inflammation of the blood vessels in your head. Cooling them can reduce the swelling making migraine easier to deal with. ",
"http://www.medicalnewstoday.com/articles/148373.php"
] |
[
"Thanks for the info. I find I get these headaches from bright lights at night as well. I'm not sure how severe migraines are supposed to be so I always assumed they are just headaches. "
] |
[
"I started when I was twelve. They dissipated when I got glasses. I know I need to check my prescription when I start to get a bunch of them one after the other.",
"Mine get severe enough to cause grand mal seizures."
] |
[
"DNA research has shown that there are brown bears more related to polar bears than other brown bears. Why are polar and brown bears still considered different species?"
] |
[
false
] | null |
[
"Ah. So in that case, I'm actually going to refer you in part to ",
"this blog post",
" by renowned speciation biologist Jerry Coyne. Essentially, mitochondrial DNA can be quite misleading when trying to reconstruct species relationships, because it actually only represents a very small part of the genome. It can therefore be the case that one subgroup of a particular species can be more similar to a different species than to another group of their own species for the mitochondrial DNA, even if that is not true across the vast majority of the rest of the genome (as is the case for the polar bear-brown bear relationship).",
"Your question, and the answer linked above in Coyne's blog, does cut to a more fundamental question though of how it can be the case that members of different species can hybridize with one another (because doesn't the Biological Species Concept mean that if individuals from two different populations are different species only if they can't form hybrids).",
"The answer is essentially that speciation happens along a continuum, rather than instantaneously. Two separate populations of the same species gradually split into separate species via the accumulation of ",
"reproductive isolation",
" over the course of time. When exactly they become \"separate species\" is not a question that has a definitive answer, but generally at some point we start calling them separate species that occasionally form hybrids rather than members of the same species, even if they wouldn't \"formally\" (whatever exactly that means) be considered separate species under the biological species concept. ",
"It's all quite a messy process really."
] |
[
"Lisette Waits et al (1998) ''Mitochondrial DNA Phylogeography of the North American Brown Bear and Implications for Conservation.'' Conservation Biology, Vol 12(2) pgs. 408-417",
"Results show NA bears divide in 4 lineages that split in Asia before they colonized the.continent already: western Alaska, eastern Alaska+northern Canada, southern Canada+contiguous US, and the ABC (Admiralty, Baranof, Chichagof) islands off Alaska. Bears of the ABC are closer to polar bears. "
] |
[
"Before I release this question, can you point us to the DNA evidence you are referring to? I am not aware of any evidence for that specific claim (although I may be ignorant of it if it exists)."
] |
[
"Do hardcore bodybuilders share similar body image disorders anorexics and bulimics do?"
] |
[
false
] |
they seem very obsessive and are willing to do dangerous things like taking drugs or injuring themselves to achieve their goals.
|
[
"This is not my field, but a quick search seem to suggest that it is indeed an observed phenomenon:",
"Muscle Dysmorphia, a type of Body Dysmophic Disorder, was identified by name in the literature in 2002. ",
"Citation",
"A subsequent study in 2004 found that \"The Dysmorphic group reported a pattern of body image disturbance consistent with MD by displaying a high overall level of body image disturbance, symptoms of associated psychopathology, steroid use, and appearance-controlling behavior. Findings generally supported classifying MD as a subtype of body dysmorphic disorder and an obsessive-compulsive spectrum disorder.\" ",
"Citation",
"There have been recent attepts to develop a better measurement tool for identifying the disorder, so it does not appear that the results are all in regarding its prevalence among the general population, or even among those who self-identify as \"bodybuilders.\" ",
"Citation"
] |
[
"It's usually pretty clear. First of all the diagnosis of ",
" mental disorder under the DSM requires that it have an adverse impact on your life or happiness, so if they are acting rationally it probably wouldn't be hurting them and therefore wouldn't qualify. ",
"Second, dysmorhpic disorders are diagnosed on self-assessments as much as on behaviors. So you take two bodybuilders who are both working out 45 hours a week and look about the same, and ask them about themselves. The first one says he's very happy with himself because he's in excellent shape and looks amazing, and he takes pride on being strong and having the discipline to continue his training, but he wants to keep improving so he can win a local bodybuilding competition. The second guys says he can't stand to look in a mirror because he's so flabby and weak, his body doesn't feel like his own because it doesn't match his self-image, working out and bulking up more and more is the only way he can like himself inside his own skin, any week he doesn't get to work out at least 40 hours he feels disgusted with himself and like he can ",
" his body degenerating and melting away when he tries to go to sleep at night. It's pretty easy to tell which of those guys has a dysmorphic disorder, even though their behaviors are the same."
] |
[
"How does one differentiate between rational behavior -- for career reasons, say -- and a body image disorder?",
"What is the diagnostic criteria that separates a Wall Street trader who works ninety hour weeks, and a bodybuilder who obsesses over diet, training, drugs, and appearance? Or an athlete who trains obsessively?",
"Each are arguably sacrificing their health and happiness for career reasons. Does the Wall Street trader also have a mental disorder?"
] |
[
"Has there ever been a known case about your body's immune system detecting your eyes separate immune system? And how does that whole thing work?"
] |
[
false
] |
I have read something that says your eyes have a different immune system than the rest of your body and if your body's immune system found out, than it will attack and you will go blind.
|
[
"This can rarely happen in patients that have trauma to the eye, which exposes previously unknown eye proteins to the immune system. Immune cells recognize these proteins as foreign, and start to attack both the injured and unaffected eye in an autoimmune process leading to blindness."
] |
[
"Your eyes are, to my knowledge, \"immune privileged\" along with your gonads. Meaning they don't have their own immune system but they're effectively a no-fly zone for the rest of your body's immune system. The collateral damage cost would be too high."
] |
[
"And brain. The blood brain barrier blocks a lot of things from crossing. Immune cells, chemicals, etc.",
"It means for certain brain diseases they're always researching for new chemical truants that cross the blood brain barrier. For example malaria can settle in the brain in rare cases and a lot of the treatments won't work because they don't cross the blood brain barrier."
] |
[
"Strange Object near Sun - 30.12.2012 - Anybody know what it is?"
] |
[
false
] |
A friend just posted this picture on facebook and it looks really weird.. Does anyone know what it could be? mirror:
|
[
"I am suspecting it is a sensor glitch. Looking up data ",
"from their website",
" I can't get these exact images, but I can get the ones 5 minutes later. Neither wavelength shows anything in that area.",
"Speculation: It could be a cosmic ray hit on the CCD. If the ray was moving bottom-left to/from top-right in a grazing hit, it could make the short diagonal mark. If it saturated the hell out of some of the pixels that could screw up the readout and make the vertical stripe.",
"Edit: Astronomer friend of mine (not on SDO) agrees that it is some kind of artifact."
] |
[
"It looks a lot like a ",
"sungrazer comet",
", although I didn't think anything had the dynamic range to image one in the same image as the Sun, so I wonder if the above might be a composite image.",
"The tag AIA in the image means ",
"Atmospheric Imaging Assembly",
", an instrument aboard the Solar Dynamics Observatory.",
"[Edit] further information:",
"AIA 171 and AIA 304, in the image, refer to two wavelength filters used on the AIA, the 171 angstrom and the 304 angstrom, so this image is presumably some sort of composite of two images in the hard ultraviolet. The images tags indicate that the image was very recent (today), but I'm unable to find mention of it on the SDO website.",
"[Edit2]: Because the SDO images from the same time don't show this feature, I'm going to agree with Silpion that it was probably a cosmic ray hitting the detector, which may have been removed later with median combine or crreject or something similar."
] |
[
"I strongly agree that it's a cosmic ray. ",
"The amount of pixel bleed going on here is pretty intense. If this were really an astronomical object and not a sensor defect, the sheer amount of extreme ultraviolet radiation said object would be giving off would be totally unprecedented for anything in our solar system. After all, the Sun (which already gives off lots of EUV) is right next to it, and doesn't appear to be anywhere near the CCD's saturation value."
] |
[
"Prolonged exposure to high pressure"
] |
[
false
] |
[deleted]
|
[
"This BBC documentary",
" follows the lives of saturation divers who spend days/weeks at pressure even higher than you specified. There do not seem to be any acute effects of high pressure except very high voices from the helium required in the breathing gas used at that pressure. I'm not sure about possible chronic effects, although I don't think there are any major long-term health consequences.",
"I believe the reason submarines are not pressurized is because of the need to ascend at short notice. If submarines were kept at ambient pressure instead of maintaining a constant 1 atm internal pressure, rapid ascents (often important in emergencies or combat situations) would be impossible because of the effects of decompression on the crew. Also, mixed breathing gas would have to be used at depth, greatly complicating ventilation systems. The mixed gas requirement would also slow descent because atmospheric air would have to be gradually replaced with mixed gas as depth increased.",
"TL;DR prolonged high pressure has no serious effect, submarines are kept at atmospheric pressure to enable quick and simple diving and ascent"
] |
[
"Great answer.",
"There do seem to be some potential side effects of long term saturation diving (see ",
"http://en.wikipedia.org/wiki/Saturation_diving#Medical_aspects",
") but they're really not very well understood. Presumably there's just not the sample size to do proper studies."
] |
[
"Depends on what you're breathing.",
"At 30m, you aren't going to have any problems from short stays (provided you come up slowly enough). But this changes dramatically when you stay longer.",
"After a couple of hours, oxygen toxicity will kick in on your nervous system. It will kick off with some muscle spasms, but after a few hours it can progress to vertigo, severe vomiting, and even seizures. The timeframe on this is highly variable, depending on the person and a lot of other things known and unknown.",
"Breathing oxygen at those partial pressures can also have severe impact ion the lungs. This is actually an area of active research, as it has implications for intubated patients (people on a respirator). The inflammatory tone of the deep lung will go up pretty much as soon as the partial pressure of oxygen does. This is ",
" thought to simply resolve, but prolonged exposure may cause chronic lung disease. However, this is hard to discern because the people who get put on respirators already have 99 problems, and one more ain't gonna do much. The other problem is that a lot of the research focuses on neonates, because there are severe developmental consequences of hyperoxia. ",
"Oxygen at high concentrations is also bad for the retina, but again, most of that work is in neonates.",
"The gist is that breathing compressed air for extended periods of time at a pressure equivalent to 30m is bad for your health. This is easily fixed for prolonged dives by not breathing compressed air, but specific mixes with lower amounts of oxygen in them."
] |
[
"Do binaural beats work? and if so, how?"
] |
[
false
] | null |
[
"It depends what you mean by \"work\". They produce sound, so in that sense they're working. If the people selling them are making specific claims, you have to address those claims one at a time.",
"There's a discussion ",
"here",
" and the conclusion seems to be that they might help you relax if you enjoy the sound, (similar to say, white noise or sounds of the rainforest or something) but they don't do anything special."
] |
[
"Binaural Beats is different than binaural recording techniques.",
"Binaural beats take two tones that are within the auditory range and separate them by a frequency that is beneath the human auditory limit and the theory is that the brain will subtract the tones and hear the difference. The beat part comes from the fact that the sound is derived from a sine wave of different wavelengths, subtracting these two waves from each other creates a series of constructive and destructive spikes which appear to 'beat' at the frequency of the wavelength's difference.",
"Example: 200 Hz Left side, 210 Hz Right side. When piped directly into the ear, the brain doesn't interpret them as different tones, it cancels / filters them and the result is a 10 Hz tone generated and perceivable within the brain.",
"As to whether these beats create the synchronization of the operating frequencies of the brain across hemispheres is up for debate, and even if there is some level of synchronization, does it actually do anything? "
] |
[
"Binaural headphones is just a marketing term because \"binaural\" sounds better than \"stereo\". Binaural recordings on the other hand is something that has been recorded using two microphones. If you have headphones that support stereo (pretty much every pair of headphones released in the last few decades) then they are technically \"binaural headphones\"",
"You can read more about binaural recordings here ",
"http://en.wikipedia.org/wiki/Binaural_recording",
" "
] |
[
"Do animals know to let their eyes adjust to rapid changes in light levels?"
] |
[
false
] |
In other words, do I blind my cat when I turn on the light when he's been sitting in the dark? Do I leave him in pitch darkness when I then turn it off again? Since cats are known to have very good eyes, it could be a dog, for sake of argument.
|
[
"Or the same way your eyes adjust after a few seconds in darkness, just not as well as a cat's."
] |
[
"Or the same way your eyes adjust after a few seconds in darkness, just not as well as a cat's."
] |
[
"I suppose it's more when going into darkness, do animals walk into or trip over things?"
] |
[
"Can someone explain this in layman's terms? (Inbreeding)"
] |
[
false
] |
I'm speaking on the subject this evening and I understand the gist of what's happening but would have a hard time explaining it to an audience. Specifically: "Incest that results in offspring is a form of close inbreeding (reproduction between two individuals with a common ancestor). Inbreeding leads to a higher probability of congenital birth defects because it increases that proportion of zygotes that are homozygous, in particular for deleterious recessive alleles that produce such disorders[95] (and see Inbreeding depression#Inbreeding depression and natural selection). Because most such alleles are rare in populations, it is unlikely that two unrelated marriage partners will both be heterozygous carriers. However, because close relatives share a large fraction of their alleles, the probability that any such rare deleterious allele present in the common ancestor will be inherited from both related parents is increased dramatically with respect to non-inbred couples. Contrary to common belief, inbreeding does not in itself alter allele frequencies, but rather increases the relative proportion of homozygotes to heterozygotes. However, because the increased proportion of deleterious homozygotes exposes the allele to natural selection, in the long run its frequency decreases more rapidly in inbred population. In the short term, incestuous reproduction is expected to produce increases in spontaneous abortions of zygotes, perinatal deaths, and postnatal offspring with birth defects."
|
[
"From what I've been reading, the congenital defects in inbred babies isn't caused directly by the inbreeding but rather the pairing of recessive genes that cause the defects. Given that the parents are related the chances are greater they will both share those recessive genes."
] |
[
"From what I've been reading, the congenital defects in inbred babies isn't caused directly by the inbreeding but rather the pairing of recessive genes that cause the defects. Given that the parents are related the chances are greater they will both share those recessive genes."
] |
[
"Quite right.",
"Let's say there's a recessive mutation that causes a bad congenital defect. Because people who have two copies of the mutation die out/don't breed, it's quite rare to see people born with the defect. The probability that both the mother and father independently inherited the mutation from their parents is therefore low, so few people are born with the defect.",
"If the mother and father are closely related, it's possible that they both inherited the recessive mutation from a single carrier, a common parent or grandparent. If they're both carriers, the probability that a child is born with the defect is much higher.",
"The frequency of the mutation is not increased, but the frequency of people born with two mutant copies (and thus the phenotype) becomes higher if the parents are related."
] |
[
"Is Chaos Theory more theory or hypothesis?"
] |
[
false
] |
Similarly to a , I was wondering if Chaos Theory falls victim to the same flaw as String Theory? (That it cannot be tested.) Would this flaw deem it unworthy of the "theory" title? Please include sources if available--and/or point me towards a means of acquiring more knowledge about Chaos Theory both on a mathematical and "layman's terms" level.
|
[
"Theory does not exclusively mean scientific theory. Group theory cannot be tested experimentally either, but studying group structures is useful and all the theorems of group theory are certainly true (as true as any other theorem in math anyway). Chaos theory is with regards to certain behaviours exhibited by nonlinear dynamical systems, it suffers from the behaviour being very difficult to classify, define, and there being outstanding conjectures about how many systems should exhibit it. So it a 'theory' in the sense of 'theory of gravity', it's a theory in the sense of 'group theory', that is it is a collection of closely related mathematical ideas."
] |
[
"As ",
"/u/dogdiarrhea",
" notes, though many physical systems can exhibit chaotic behavior, Chaos Theory is a mathematical theory, not a physical one. The mathematics of dynamical systems exhibiting chaos would exist apart from any physical manifestation and therefore don't rely upon measurements or physical validation. In contrast, String Theory purports to be a physical theory, which demands some level of testability of hypotheses if it's going to be cast as science. ",
"As for introductions to the subject, I found Ed Ott's book, ",
" to be accessible when I learned this stuff. "
] |
[
"There are plenty of examples of chaos in action, in the natural world. It is bizarre to claim that it is untestable when chaos is just a word used to describe a certain type of pattern. ",
"Complexity Explained, by (my favorite professor) Peter Erdi, is a good textbook. "
] |
[
"Why does the flu vaccine sometimes offer partial immunity? What is partial immunity? I thought a vaccine either worked or it didn't"
] |
[
false
] | null |
[
"Partial immunity happens when a person's immune response to a pathogen (or vaccine) is enough to prevent severe infection or mortality, but they can still become ill. In the case of partial immunity to influenza, the immunity of the person depends on the antigenic relatedness between two (or more) influenza viruses. There are two types of influenza virus that cause epidemics: A and B. These two types are further broken up into different strains, and they are constantly evolving.",
"The flu vaccine in any given year is tailored to give immunity to only a few strains or variants of the two types (A and B) of flu. To other strains only partial immunity will be conferred, and little or no immunity to others. The thing is is that the dominant strains vary from year to year and the vaccine has to be prepared many months ahead of the flu season so the vaccine is made using a predicted estimate of what is coming. For example trivalent flu vaccines are formulated to protect against three flu viruses, and quadrivalent flu vaccines protect against four flu viruses. You get full immunity for the \"main\" strains that year yet only partial for closely related strains.",
"Source",
"Source for different influenza types\n"
] |
[
"A good example is the BCG vaccine for tuberculosis. It's not very effective at all in preventing TB but if used for infants it stops them from getting the most serious forms of the disease such as meningitis. "
] |
[
"Just to add, this also occurs in populations with endemic malaria. Individuals in such populations tolerate infection much more easily than outsiders. Vaccination occurs through repeated infection at regular intervals. "
] |
[
"What would happen if I fell into a tub of superglue?"
] |
[
false
] | null |
[
"Nothing good. Superglue is generally a form of ",
"cyanoacrylate",
", a liquid that will polymerize when very small amounts of water are present. It can be used safely for many applications on the body such as wound closing in place of stitches, but that doesn't mean I would want to be dunked in it.",
"Firstly, since cyanoacrylate starts to polymerize on contact with water it would be instant catastrophy if any got into your nose, mouth, or eyes. Even the sweat induced by your imminent plunge would prove exceptionally detrimental.",
"Secondly, cyanoacrylate reacts violently with cotton, leather and wool. The exothermic reaction is hot enough to cause third degree burns on people that get super glue on their clothes in normal cases, I'm not sure the extent of the reaction if you jumped into a tub full.",
"If you did manage to get in and get out immediately without major infiltrations into your mouth, nose, and eyes and without starting all of your clothes on fire then you would quickly become encased in a thin polymer shell. An immediate acetone bath could remove the polymer, though it would likely be a sticky mess and there are other problems such as severe skin dehydration that might result.",
"The only good thing here is that super glue is likely never left in open containers, else the whole batch will start to polymerize and you will ruin the product. I would still exercise caution around the stuff though."
] |
[
"Wow, thank you so much for such a detailed answer. I just got some on my hand today and imagined the worst case scenario. "
] |
[
"How has this never been used by a Bond villain?"
] |
[
"We are able to catch the common cold year after year so does that mean that the viruses (rhinovirus and—to a lesser extent—Coronaviruses) mutate fast enough that we don’t ever develop full immunity to them analogous to influenza? If so, why isn’t the common cold much more severe?"
] |
[
false
] | null |
[
"“The common cold” is caused by up to 200 different viruses. Even if you were exposed to two every year and developed lifelong immunity, you could still keep getting colds every year of your life. ",
"A few of those viruses mutate quickly (notably influenza, which can cause cold-like symptoms); many do not. There’s no particular relationship between mutation rates and severity. There’s also much less connection between mutation and the ability to develop a strong immune response than you seem to think, and there’s also little relationship between the severity of the diseases and the potency of the immune response to the pathogen."
] |
[
"Sure, not every cause of the common cold is equally prevalent, but the point is that there are so many of them that it doesn’t matter if you’re immune to the top five, or ten, or twenty, something else can come along to cause another cold next year - it doesn’t have to be a mutation that overcomes immunity. ",
"(In practice, of course, you do develop immunity to the most common causes in your area, which is why children are perpetually snot covered while adults are relatively snot-free. Though once you send your kids to school, they start bringing home new agents from their friends, and it’s common for parents to start coming down with colds more commonly after their kids hit school age for a while.)",
"I don’t understand your question about influenza. I think you are making about five incorrect assumptions, but I don’t know which ones."
] |
[
"But there can’t be an equal probability of exposure to all 200 or so cold-causing viruses.",
"\nAren’t there a handful of them which are much more prevalent? Or does the handful constantly rotate maybe?",
"\nAnd what do you mean by:",
"There’s also much less connection between mutation and the ability to develop a strong immune response than you seem to think. ",
"Are you saying antigens are unique to influenza and don’t apply to the viruses I’m talking about?"
] |
[
"Can Black Holes Evaporate Into Neutron Stars?"
] |
[
false
] |
I'm very much a lay-person in science, so all my attempts to Google this answer have directed me to sources very much beyond my ability. My understanding is that a black hole is a very dense thing, and that a neutron star is a less dense thing both caused by collapsing stars that no longer have enough outward force holding up their massive mass. (Forgive me if I don't use any correct terminology). Well, if a black hole can slow evaporate by losing particles through Hawking Radiation does that mean it can one day lose its denseness and become something like a neutron star. Or once something has collapsed to a density of a black hole is it stuck in that density forever? If I got the smallest possible black hole and using magic split it in half so it contained half the mass, would it continue to be a black hole or would it eventually have enough outward force to "uncollapse" and stop being so dense? Thank you
|
[
"The length of time a [non-rotating, neutral] black hole has between now and when it evaporates is a function of its mass and the rate at which it consumes mass/energy. The lower its mass, the shorter its lifetime as it has less mass to radiate away ",
" it radiates more the lower mass it has!",
"With that in mind, we can also see how a black hole gaining more mass will cause its lifetime to get longer.",
"At a large enough mass, the rate at which a black hole radiates energy is lower than the rate at which it receives it from the ",
"cosmic microwave background",
", so any black hole larger than this mass is not currently evaporating, and will have to wait for the CMB to get colder in the future before it does. Black holes with lower masses than this CMB-imposed limit may also not be evaporating if they're consuming additional mass-energy. Assuming a [non-rotating, neutral] black hole is only getting mass-energy from the CMB, the highest mass black hole that we would expect to be shrinking today is about that of the moon.",
"Quantitatively, we expect the lifetime (t) of a black hole (in the absence of ",
" that increases the mass of the black hole) to be:",
"t = 5120 π G",
" M",
" / ħ c",
" ,",
"where G is the gravitational constant, M is the mass of our black hole, ħ is the reduced Planck's constant, and c is the speed of light. This works out to be approximately:",
"t = 2x10",
" ( M / M_sun )",
" years,",
"where M_sun is the mass of the sun. We can see that the lifetime of a solar-mass black hole is far, far longer than the lifetime of the universe so far, and that's before considering CMB consumption. Setting t to the age of the universe and solving for M yields an upper bound on the minimum primeval black hole mass of:",
"20,000,000,000 tons.",
"Modern calculations that account for CMB consumption, etc. have given a more precise upper bound of around",
":",
"500,000,000 tons.",
"or about 0.00000000000000002 times the mass of the sun, so while \"five hundred million tons\" may sound like a lot, it's positively tiny compared to other astronomical objects!"
] |
[
"Thank you for taking the time for such a great answer and including some links too! The maths were beyond my ability, but I was able to follow along with the plain language explanation of them.\nI hadn't even thought about CMB feeding into black holes, but it very much makes sense when you point it out. The fact that this process is so slow that we have to talk about it in terms of exceeding the lifetime of the universe is incredible to me."
] |
[
"Our current theories predict that a black hole of any mass is stable except for emitting Hawking radiation. For example if a black hole of one Earth mass was created, it would stay a black hole of one Earth mass. The more compressed a mass is the stronger gravity pulls that mass together and once enough matter is compressed into a small enough space to make a black hole then nothing known can oppose gravity."
] |
[
"How far away from a lightning strike do I have to be in the ocean not to be electrocuted?"
] |
[
false
] |
[deleted]
|
[
"From personal experience I've been in the water 15-20m from a lightning strike and i didn't feel a thing... apart from the warm ooze of faeces floating around me as i shat myself."
] |
[
"Different scenario... it's very plausible that a kayaker offers a better route to ground for lightning than the 3-4 feet of air the bolt would have to take otherwise - you offer far less resistance as a bag of saltwater and meat, than the air does.",
"Mesarune's answer only really applies if you're basically submerged."
] |
[
"Since electrocution happens when current travels through your body, as long as you are not in the path to ground the electrical current takes, you won't be hurt. In other words, if lightning strikes in the ocean and doesn't directly hit you, you should be fine.",
"Salt water probably conducts electricity much better than you do, so I'd guess that it's even a relatively rare occurrence to be struck while out at sea, but I could be wrong."
] |
[
"How can the mass of a neutral pion be determined, if its quark content can be either (up + anti-up) or (down + anti-down)?"
] |
[
false
] |
Since u and d have different masses. And if the masses of these two possibilities are not the same, why don't we have two particles?
|
[
"It is not \"either or\". It is both at the same time - as superposition. There is only one light superposition and therefore only one particle with one mass. There are other similar particles with much larger masses - the ",
"eta",
" for example. It is a superposition as well, but with u anti-u, d anti-d and s anti-s contributions."
] |
[
"Hadron masses in general are not the sum of the masses of their valence quarks. The masses of the up an down are a few MeV each, but the pion masses are 135 and 139 MeV, and the proton mass (with three valence quarks) is 940 MeV."
] |
[
"Remember though, most of the mass of hadrons is from the binding energy, not its quarks. ",
"But to further explain, up and down quarks have a property called isospin. It's like spin, hence the name. Up quarks are positive 1/2, down -1/2. Like charge, isospin is flipped in antiparticles. The neutral pion is defined as the pi meson that has a zero isospin, opposed to the charged pions. There are multiple ways to get an isospin of zero from up and down quarks. The masses of the two are relatively small and close together, so they blend as mentioned earlier as the two states are roughly symmetrical."
] |
[
"Are there any known computational systems stronger than a Turing Machine, without the use of oracles (i.e. possible to build in the real world)? If not, do we know definitively whether such a thing is possible or impossible?"
] |
[
false
] |
For example, a machine that can solve NP-hard problems in P time.
|
[
"Usually when we talk about hyper computation we ignore runtime complexity. If we just look at what problems are decidable, we believe that no stronger model exists.",
"But if we look at runtime, quantum computation has (at least) a provable quadratic speedup over classical turing machines (grovers algorithm).",
"In the real world we are also not restricted to serial computation. Pi calculus captures parallel semantics and can also compute some problems faster than serial turing machines."
] |
[
"This is true. For example, you could simulate any quantum algorithm on a powerful enough classical computer (it just might take a long time).",
"People might say a quantum computer can solve a problem that a classical computer “can’t”. What they mean by that is a decent quantum computer* could solve the problem in a reasonable amount of time (less than a day, for example) while the world’s greatest classical supercomputer would take an infeasible amount of time (like millions of years).",
"But this is why the previous commentor mentioned that the quantum Turing machine is only different in terms of runtime. It’s worth noting that a quantum computer can run any classical algorithm in the classical runtime, but not all quantum algorithms can be run on a classical computer in the quantum runtime.",
"* "
] |
[
"I thought quantum algorithms were superior for a subset of problems but that theoretically a TM can do anything a quantum computer could do."
] |
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