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[
"Are mental health issues a human problem?"
] |
[
false
] |
[deleted]
|
[
"Animals (at least dogs/cats) definitely have behavioral problems that if similar behaviors were occurring in humans would be categorized as a mental neurosis. Its surprisingly common to prescribe drugs to \"neurotic\" pets to deal with behavioral problems (e.g., composure (mostly L-theanine) for OCD dogs as a preventative that makes dogs/cats calmer in certain situations where they otherwise freak out without having other obvious sedative effects ",
"[composure company fact-sheet]",
" and a ",
"[L-theanine has been shown to reduce certain anxiety in dogs compared to placebos]",
" from quick google scholar search). Also, stories like the guy who was always well behaved and then freaks out one day, happens with pets as well (though usually there are plenty of early warning signs). E.g., brain tumors/hyperthyroidism/dementia often result in behavioral changes including aggression as well.",
"(Not my particular expertise; though my fiancee is a veterinarian who just opened a practice so I hang out at a vet office/veterinarians on a daily basis.)"
] |
[
"While my expertise doesn't cover animals, ",
"this thread",
" appears to have some helpful information in answering your question."
] |
[
"There are many cases of animals in bad conditions in zoos exhibiting behavior such as pacing, obsessive grooming and self harm, which, if they were present in a human would certainly signify mental illness. ",
"http://www.usask.ca/wcvm/herdmed/applied-ethology/behaviourproblems/zooanim.html",
"These are attributed to lack of stimuli, boredom drives them mad or what we can understand as madness. ",
"Edit - these sterotypic movements also occur with autism in humans, I wonder if there could be connexion there? "
] |
[
"How do researchers check for West Nile Virus in mosquitoes, and how does that procedure work?"
] |
[
false
] | null |
[
"You test for the virus RNA by PCR. Grind up flies, extract all RNA, reverse transcribe to get DNA, & use primers specific for a conserved region of the viral genome to amplify that region (if its there). You can then run a gel of each sample to see if the region has been amplified."
] |
[
"RT-PCR means reverse transcriptase not real time. Real time PCR is sometimes referred to as qPCR or quantitative PCR. Same basic principles, different techniques."
] |
[
"Typically you use a light trap baited with CO2 (a small chunk of dry ice) to collect them. There is a fan that sucks them into the trap so they can't get out. The traps are collected and the mosquitoes are sorted by species (by trained entomologists or vector specialists). The mosquitoes of the correct species from one trap are then pooled (typically at most 50 mosquitoes). You can do this to save cost and time, as knowing the result for an individual mosquito isn't important. The pool is then ground up and the testing is performed by real time PCR (RT-PCR). "
] |
[
"What is happening when I feel like I can hear something that looks loud but is actually silent?"
] |
[
false
] |
is an example. Simply looking at it induces almost a shadow of a sound (I don't know how else to explain it) in my mind. What is going on when this happens to me?
|
[
"What we see can affect what we hear (and vice versa!) as in the ",
"McGurk effect",
". Not only are there direct connections between primary auditory (A1) and primary visual (V1) areas, but there is plenty of feedback from higher cortical areas to earlier ones. I'm unaware of studies on implied sounds, but it has been found that showing static images that contain implied motion (e.g. a plane flying to the right) activate motion sensitive cortical areas (",
"Kourtzi and Kanwisher, 2000",
")."
] |
[
"A Bayesian view of cognition might argue that what you are describing is the general case for all of perception -- the output of perceptual processes is the combination of past experience and most likely expectations. There are several such probabilistic models of cue integration. "
] |
[
"Very cool! Thank you for answering!"
] |
[
"Are birds beaks attached to their skull? If so, How are they pigmented so much?"
] |
[
false
] | null |
[
"Yes, their beaks are \"attached\" to the skull, but they are not bone in the standard sense. They are made from keratin, which is a fibrous protein, instead of the collagen and calcium phosphate matrix that their bones are made from. ",
"Keratin is more common to be colored than bone. I don't have the specifics for how, but keep in mind that other brightly colored animal parts like feathers and hair are also made from Keratin."
] |
[
"Typically bird beaks have a bone core, which is covered with a keratin sheath. It's the keratin part that has color, while the bone inside provides structural support. In the top photo on this page you can see how that yellow keratin layer sits on top of the bone: ",
"http://drvector.blogspot.com/2006/04/bird-parts_24.html",
" ",
"Keratin is also the main ingredient in feathers, mammal hair, fingernails and claws, pangolin scales, the outer layer of turtle shells, etc."
] |
[
"The structural part of the feathers is keratin, yeah. Bird beaks are kinda the same as rhino horns in setup."
] |
[
"This is a sample question from the Praxis Middle school Science Test. I am not pleased with the \"correct\" answer. Am I being ridiculous?"
] |
[
false
] | null |
[
"So, we don't do schoolwork questions... But the answer isn't D ",
" you only have ten days of data. You can't say there's no effect after ten days, which is what D is saying. Based on the data, yes, there is some effect. You can't conclude anything more specific than that. That's why A is the right answer."
] |
[
"It's not really school work it's for the teacher certification test, and I'm not looking for an answer, I'm looking for a debate on the validity of the question and answers.",
"My argument is that you can only draw conclusions about the first ten days. There is no additional data other than that, so wouldn't statement D be more accurate. The data shows an effect, but only in the first ten days."
] |
[
"You can submit to ",
"/r/AskScienceDiscussion",
" if you want, but D is saying there is no effect after 10 days, and that is not a conclusion you can draw from those graphs."
] |
[
"How efficiently do humans breath?"
] |
[
false
] |
[deleted]
|
[
"Human (and most mammalian) lungs are pretty crap at breathing. ",
"On average, humans use and absorb around 4 percent of the oxygen they take in from air ... (21 percent in, 16 percent out) ",
"--",
"The Chemical Composition of Exhaled Air From Human Lungs",
"That's why you can resuscitate people by blowing into their mouths (CPR) - even when you breathe out, there's plenty of oxygen left in your breath. ",
"By comparison, birds have a much more efficient respiratory system,especially in conditions where there's low oxygen -- like, for example, at altitude; humans wearing oxygen tanks on top of Mount Everest can look up at bar-headed geese flying well above them. ",
"The reciprocating pattern of ventilation in the mammalian lung results in three shortcomings compared with the bird lung. ... some birds are superior to any mammals in their maximal oxygen consumption in relation to body weight ... But for those who work on the mammalian lung, it is fascinating that evolution found a better solution for the structure–function relationships of the lung in birds than in mammals.",
"--",
"The human lung: did evolution get it wrong?",
"Early work on rates of extraction seemed to confirm the predicted benefits of unidirectional flow. For example, Bernstein and Schmidt-Nielson mea- sured extraction of oxygen in the fish crow (Corvis ossifragus) of 31%, concluded this value was twice as high as what would be expected for a mammal of the same size ... data from a range of birds and mammals indicate that there is a surprisingly wide range of extractions measured in both lineages, perhaps obscuring the functional underpinning of these differences in lung design. However, this may not be true when PIO2 is reduced (e.g., at high altitude)",
"--",
"The Evolution of Unidirectional Pulmonary Airflow",
"The ability of birds to survive, let alone to exercise, under the extreme conditions of high altitude is well beyond the reach of the non-flying mammals. ... Extrapolating measurements made on human beings at the altitude of Mount Everest, Dejours (1982), West (1983) and Scheid (1985) estimated that, if the human alveolar lung was replaced with the avian parabronchial lung, for the same arterial blood gas levels, a human would be able to ascend 780 m higher.",
"--",
"WHAT IT TAKES TO FLY: THE STRUCTURAL AND FUNCTIONAL RESPIRATORY REFINEMENTS IN BIRDS AND BATS",
"Although the structure of the human lung appears to be well suited to its primary function of gas exchange, the lung is very vulnerable to minor insults, such as retained secretions. This vulnerability stems from the fact that the delicate alveolar tissue is responsible for both ventilation and gas exchange. Evolution found a better arrangement in the bird where the ventilation and gas exchange functions are separate.",
"--",
"How Well Designed Is the Human Lung?"
] |
[
"Good stuff but your first statement is very miss-worded. 16 is 24% of 21. E.g",
". Yes that's 4% of the total air, but we'd use more & less of the available O2 if there was a higher & lower proportionon respectively."
] |
[
"It depends. Your tissues can extract more or less oxygen from the blood depending on their oxygen requirements.",
"We measure the amount of oxygen bound to hemoglobin with SaO2 (oxygen saturation of hemoglobin in capillary blood). We can also measure the amount of oxygen bound to hemoglobin in venous blood as SvO2 (when it’s done delivering to tissues). A normal SaO2 is typically over 90% (can change based on elevation/ disease) and a normal SvO2 is typically around 70%.",
"The short answer: roughly 20-25% of the oxygen that connects to hemoglobin will be utilized during normal activity in a healthy person at sea level.\n—\nThe longer answer.",
"Once inhaled, oxygen moves down a concentration gradient to your bloodstream via the alveolar-capillary membrane, this efficiency honestly depends on a plethora of factors and I’m not sure it is routinely measured. Once oxygen dissolves into the bloodstream (measured as PaO2), a group of factors (pH, Temperature, 2-3-DPG) determine how well it binds to hemoglobin (termed the hemoglobin dissociation curve). The oxygen is delivered to tissues (DO2). The tissues use it (VO2), and the circulation returns to the lungs to load on more oxygen. As your body’s oxygen requirements increase, you can calculate the oxygen extraction ratio (how much we extract from blood for tissue energy production) by taking VO2/ DO2, which is (SaO2-SvO2)/(SaO2).",
"Edit: I forgot, we do measure the amount of oxygen that is transferred across the alveolar membrane. It’s called the Aa gradient (alveolar-arterial gradient) and it can help determine the integrity of the membrane itself. The calculation is [(FiO2/100)*(Patm-47)-(PaCO2/0.8)-PaO2]\nWhere FiO2 is the % of oxygen in the air you breathe, Patm is atmospheric pressure, 47 is the water vapor pressure, and 0.8 is the respiratory quotient (VCO2/VO2)."
] |
[
"Why nothing can go faster than the speed of light?"
] |
[
false
] | null |
[
"Physics"
] |
[
"Physics"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
" ",
"Also consider looking at ",
"our FAQ",
".",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"What things will we simply never know?"
] |
[
false
] |
Obviously it is difficult to predict, but are there some things which we will never be able to uncover? In writing this question I am mainly thinking about space, and how certain restraints may prevent us from knowing certain things.
|
[
"For starters: The answer to your question."
] |
[
"That's because it doesn't even make sense to think of irrational numbers as having a representation which can be expressed with decimals. That's like saying \"we'll never know the prime factorization of pi\"..."
] |
[
"But you just answered his question with, \"The answer to your question.\"",
"Oh shi-"
] |
[
"Why are there many more species and higher density of Megafauna in Africa versus North America?"
] |
[
false
] |
[deleted]
|
[
"There are several working hypotheses that explain the disappearance of megafauna all over the world around the time of the ",
"Pleistocene",
". These are not mutually exclusive, but could have acted in conjunction with one another. The pleistocene lasted from about 2.5 mya to 11,000 years ago. Humans speciated some 250,000 years ago. The extinction event period that we are interested occurred over many thousands of years, from about the time of our arrival the turn of the pleistocene into holocene.",
"See this article for more details: ",
"Quaternary Extinction Event",
"Climate change: \"At the end of the 19th and beginning of the 20th centuries, when scientists first realized that there had been glacial and interglacial ages, and that they were somehow associated with the prevalence or disappearance of certain animals, they surmised that the termination of the Pleistocene ice age might be an explanation for the extinction\"...\"Some evidence weighs against climate change as a valid hypothesis as applied to Australia. It has been shown that the prevailing climate at the time of extinction (40,000–50,000 BP) was similar to that of today, and that the extinct animals were strongly adapted to an arid climate. The evidence indicates that all of the extinctions took place in the same short time period, which was the time when humans entered the landscape.\"",
"The arrival of humans coincided with increased hunting and sophisticated hunting that prey and predators alike could not cope with. Populations were decimated, and the whole food web collapsed resulting in a disappearance of the megafauna. ",
"see this photo",
". Why this hypothesis works: we see this especially true on islands (e.g New Zealand and moas), where once humans arrive, populations of lucrative animals are hunted to extinction. Moreover, we see more recent examples - like the dodo, or passenger pigeon - so it is entirely possible for us to hunt a species to extinction. Problems, many species did end up surviving - like the bison in north america, and some species extinction events preceded human arrival. Also this: \"Eugene S. Hunn, President of the Society of Ethnobiology, offers a dissenting view. He points out that the birthrate in hunter-gatherer societies is generally too low, that too much effort is involved in the bringing down of a large animal by a hunting party, and that in order for hunter-gatherers to have brought about the extinction of megafauna simply by hunting them to death, an extraordinary amount of meat would have had to have been wasted\". However does not mean hunting did not contribute to the problem, but perhaps another factor - like climate change - was the primary instigator. ",
"Another hypothesis which fits in with overhunting is the second-order predator hypothesis",
"More on africa: Africa and Asia are the only regions that have megamammals weighing over 1000 kg today. However, during the early, middle and late Pleistocene some large animal forms disappeared from these regions without being replaced by comparable successor species. Climate change has been cited as most likely causing the extinctions in Southeast Asia. ",
"Here you can see that Africa and Asia were not spared",
" And it is worth noting that many animals that we think of as 'African' actually migrated from Asia.",
"Disease: humans and our livestock/domesticated animals spread diseases to wild populations as we spread around the world.",
"Asteroid or comet: This may not be enough explain how this extinction event or events has been and continues to occur over the past 200,000 years or so. Additionally, no \"smoking gun\" has been found - e.g. there is little evidence of a comet smashing into earth that would create the damage necessary to have an extinction event that we are seeing today. Moreover, the extinction events were not uniform in time, but occurred at different times on different continents and different animals were targeted.",
"Technically, the quaternary extinction event is ",
"ongoing",
", and we have probably entered the ",
"6th major extinction event on this planet",
". The five that preceded us were caused by a combination of volcanic and asteroid related events. The difference with our current 6th mass extinction is that we are the cause. ",
" - stable climate in Africa combined with species that were used to predation levels by humans (not naive) probably contributed to their survival. In North America and elsewhere - but not Australia, unstable climate contributed to megafaunal upheaval which was not helped by the arrival of humans who hunted the naive animals."
] |
[
"And it is worth noting that many animals that we think of as 'African' actually migrated from Asia.",
"TIL. Examples?"
] |
[
"This is me making an educated speculation, but from what I've heard and read, the climate of Africa was much different, and much more habitable, in the prehistoric past. ",
"Imagine that the jet stream that circulates air across the Atlantic, making Florida hot and Britain rainy, was not there (per se). Imagine that this jet stream actually made the whole Sahara a livable climate, instead of an unusable sand pit. So the Sahara was pretty open to life, until the climate shifted, leaving the Nile as the only true oasis left, (and I believe that's why history saw such a vibrant civilization form there, because people had no choice but to flock.)",
"But back to the amount of species, it probably has to do with this as well. If Asia and North America were covered in ice (as I believe they were), Africa would be the place that most species were able to gain a foothold and adapt. This gave them a great advantage because they have likely been able to live uninterrupted in Africa since they came about, albeit they may have had to flee the Sahara. Also, being megafauna (lions, elephants), they were likely the top predators if anyone did come to disturb them. ",
"Also, interesting point, there is also more genetic variation in humans across Africa than compared to Africans vs non-Africans. This may have to do with a bottleneck in human history, where only 3000 or so humans still survived. This is why we all can trace our mitochondrial DNA back to a single woman in Africa (Eve). After the bottleneck, people either travelled out of Africa, keeping their DNA somewhat stagnant compared to the larger pool in Africa, where with more people ",
", the chance for random changes in DNA was higher."
] |
[
"Bayes Theorem in your field."
] |
[
false
] |
I've noticed a significant trend in psychological science to adopt Baysian approach to test hypothesis. For example, , , have all made compelling arguments to adopting this approach over typical analysis of variance tests. So I'm curious which disciplines use this approach in addition to standard regression or analysis of variance techniques. *EDIT-- This subreddit isn't my own way to demonstrate I know a couple things about Bayesian cognition. I'm much more interested in how other disciplines use this method. Also Bayes theorem is: P(A|B) = (P(B|A)*P(A))/P(B)
|
[
"phylogenetic systematists (the people who make evolutionary trees) are using Bayesian methods more and more. As far as I can tell its because the previous approaches used parsimony primarily. And we know a lot more about how evolution works than to assume nothing. For example they partition genes and functional units and take into account some transitions between bases are more likely than others. My understanding is that bayesian approaches allows you to specify these priors (information we already have) and thats what makes them more realistic and adaptable than previous methods."
] |
[
"no, not quite, i dont think (but I am a bit unsure what you mean, so let me know if this doesnt help). Previously, we would take every base pair change and put it in the pot and say, we will use parsimony and treat every base pair (or even morphological trait) as an independent character that may inform our hypothesis of relationships. But now we can say, using bayesian methods, these base pairs are more likely to change together with these other ones because they are part of the same gene. Or maybe mitochondrial as opposed to nuclear. So partitioning the data uses prior information in a way we couldnt be just throwing them all into a giant parsimony pot where they were all considered independent. "
] |
[
"Bayesian stats are used all the time in bioinformatics. Caught me a bit by surprise coming from a frequentist ecology background but I've been told it's even working it's way in there as well."
] |
[
"Do audiovisual illusions like McGurk Effect only apply to speech?"
] |
[
false
] |
For example, if say someone pretended to hit their head, but in reality I just subtlety made a bumping noise, would people percieve it as if the noise came from the person who 'hit their head'? this is a dumb example, but im basically wondering is the audio illusion from overall associations of sounds with the things that make the sounds, or is it with only speech recognition?
|
[
"It does not. The McGurk effect is a cross modal illusion, which happens when one of your senses “hack” another. Speech is cross modal, hence the illusion, it works very well with anything visual/auditory and in theory it should with other senses (less obvious though). ",
"Here is a famous non speech example",
". In the case of the McGurk, visual information is processed more rapidly, which triggers an oscillatory response from the visual area. The auditory information does the same in auditory cortex. At some point, both are supposed to be integrated into one big coherent audiovisual perception, which is speech. But since the auditory information is lagging, if the visual information is slightly different, it will shift the oscillatory response toward the perception matching the visual information. ",
"Source: I’m a neuroscientist and I worked on the McGurk effect."
] |
[
"It seems like a fascinating illusion; kind of wish that I were capable of experiencing it. I have autism spectrum disorder and have wondered why it's common for people with ASD to be immune to the McGurk effect, and if it has been possible to explore the reasons for this.",
"I have wondered if our tendency to be hyposensitive and/or hypersensitive to different kinds of sensory stimuli (not to mention difficulty parsing sensory information) might prevent certain forms of perceptual phenomena from occuring, or if a deficit or difference in some other area is a more salient factor."
] |
[
"No, for example -people often hear a thudding type noise when they see something that looks like it is landing hard and causing vibration but not actually making noise",
"If you know about the concept of neuroplasticity -it has an effect on what noises we hear and causes what are kind of illusions. Native Hindi speakers can discern two different 'd' noises that sound the same to people who did not grow up hearing Hindi. English speakers can very easily discern the words \"pen\" and \"pin\" but many language speakers dissimilar to English cannot. German people who did not grow up hearing English (which today is essentially none of them) often could not perceive \"th\" sounds -if you've heard stereotypical German accents where \"the\" is pronounced like \"ze\", it is based on this -back in the day German people usually couldn't hear th sounds",
"If you've ever heard someone trying to learn a language or tried to learn a language yourself and just not been able to get certain sounds right -this is often why. When the brain did not grow connections to be able to perceive certain sounds, you cannot hear them and your brain creates an illusion of a sound you do know.",
"There are also tons of visual illusions that we perceive 24/7 the time but do not notice"
] |
[
"How did ancient humans get sodium?"
] |
[
false
] |
Humans need ~2000mg of sodium each day. These days that's easy to get because of table salt and because salt is added to most foods but how did ancient humans who ate plants and meat found In nature got any sodium?
|
[
"2000mg is only 2g, which is a really tiny amount of salt. I would assume that ancient humans got it from the meat they ate, since animal meat, blood and whatnot also have sodium in it. ",
"Sodium is such a common mineral in nature, you’d be hard pressed to find a food that is totally devoid of it. In fact, us modern humans don’t actually need to add any salt to our cooking. As long as we eat a balanced meal every day, we’ll get all the sodium we need. Adding salt to food is pretty much just to make the food taste better."
] |
[
"Sodium is everywhere including in plants. Take a look at this shot of a burning log/camp fire from my spectrometer. That big spike that you see at 589 nm is atomized sodium. That other spike at 766 nm is potassium.",
"https://imgur.com/a/bzDYc3q"
] |
[
"You also don't need 2g per day, that's a guideline, and has also been interpreted to mean you shouldn't have more than 2g per day which is also wrong."
] |
[
"Use lower pressure to assist in generating electricity, possible?"
] |
[
false
] |
This thought popped in my head the other day but I'm absolutely certain I'm missing a crucial point. To generate electricity we very often use some method of converting water to steam which then drives a turbine, correct? Well, I was thinking, when you lower the pressure water will boil at a much lower temperature and therefore need less energy to turn into steam, right? Would it be possible to create a pressure vessel with "permanent" lower pressure and get much more steam for less energy? I apologize if this is hard to understand, English is my second language.
|
[
"Well I kinda see where op is going with this. In a closed system where the water is under less pressure and a turbine is also within said system and it is engineered so the water can condensate and come back to the starting point, then couldn't you just set the contraption in a slightly warm place and it will produce electricity? \"Warm\" relative to the bp of the water ",
"Boiling Point Vs. Pressure Chart"
] |
[
"Water boils faster in lower atmospheric pressure in an open system because the pressure created by expanding water vapour has some place to go. If you make some sort of closed system, the expansion of steam would increase the pressure inside your system. I don't think it's possible to make a \"permanent\" low pressure system if steam is involved, since if you lower the pressure then less work is generated."
] |
[
"Wat? How do you propose a turbine in a dam works?",
"No. The energy required to create and maintain the pressure gradient would wash out the savings achieved by creating a larger pressure differential.",
"As a side note, the principle you envision is used for ",
"refrigeration",
"."
] |
[
"Is there always a test that can be done to check if a number is divisible by a given prime?"
] |
[
false
] |
For example, if a number ends in 0, 2, 4, 6, or 8, it's divisible by 2. If its digits add up to a number that's divisible by 3, it's divisible by 3. If it ends in 0 or 5, it's divisible by 5. If you keep chopping off the last digit, doubling it, and subtracting that from the remaining number, and you finally get an answer divisible by 7, the number's divisible by 7. Is there (or is there believed to be) a test like this for every prime number?
|
[
"Step 1: find n such that 10",
" - 1 is exactly divisible by p. For p = 7759, n = 3879.",
"Step 2: for i ranging from 0 to n - 1, calculate 10",
" mod p. For p = 7759 and n = 3879, the list begins like this 1, 10, 100, 1000, 2241, 6892, 6848, 6408, 2008, 4562…, but I won't write the whole thing out.",
"Now the rule is:",
"Starting at the end of your number, pair off each digit with the corresponding number from the list in step 2. When you run out of numbers in the list, start over. For example, to test whether 74307943 is divisible by 7759, that would look like this:",
"and then add up all of those results:",
"3 * 1 + 4 * 10 + 9 * 100 + 7 * 1000 + 0 * 2241 + 3 * 6892 + 4 * 6848 + 7 * 6408 = 100867",
"and repeat:",
"7 * 1 + 6 * 10 + 8 * 100 + 0 * 1000 + 0 * 2241 + 1 * 6892 = 7759",
"Since 7759 is divisible by 7759, 74307943 is also divisible by 7759."
] |
[
"Yes. For example, the rule for 11 is \"alternately add and subtract digits\": 1234 → 4 - 3 + 2 - 1 = 2 → not divisible by 11.",
"Note that 1/11 = 0.090909…",
"Both the rule (which can be written as [1, -1]) and the fraction (which can be written as [0, 9]) repeat after two numbers. This is not a coincidence; it's relatively simple to prove that if 10",
" - 1 is divisible by p, then both the rule and the fraction will have an n-number repeat.",
"For example, 1/7 = 0.142857, and the rule for divisibility by 7, if I recall correctly, is [1, 3, 2, -1, -3, -2]. 864192 → 2 + 3 * 9 + 2 * 1 - 4 - 3 * 6 - 2 * 8 = -7 → divisible by 7.",
"Edit: apply rule starting with least significant digit."
] |
[
"I agree with your example, but the question is:",
"Is there (or is there believed to be) a test like this for every prime number?",
"And I think the answer is no. Although some of the smaller numbers have easy tricks to remember, I don't think one could say that a test exists for every prime. Besides, of course, just dividing by the prime.",
"I would say that:"
] |
[
"How heavy is fire? If something catches on fire is it heavier or lighter?"
] |
[
false
] | null |
[
"Fire essentially consists of gases heated to high temperatures. If the mass of the flames is included with the mass of whatever is burning, then it makes the substance heavier, as the oxygen from the air has combined with the fuel, adding mass. However, since the hot products of the reaction are carried upwards by the rising, hot air, the mass of the fuel goes down as the products are carried away. If the total mass of the air and fuel are considered, the products are an incredibly tiny amount lighter than the reactants, as a small fraction of the mass of the fuel is stored in the molecular bonds as energy, which is liberated as heat during the reaction."
] |
[
"Fire isn't a substance or some kind of matter, it's a reaction. (technically the exothermic chemical process of combustion), It has no weight or mass of it's own. Whatever is on fire has it's own weight, but fire, flames, combustion of any kind, does not."
] |
[
"Because the stuff that's burning has weight and mass, and fire can not exist without something to burn. The fire is not being directly affected by gravity, but by how gravity is affecting everything fueling the fire."
] |
[
"What makes diamonds so strong? Would it be possible for us to synthesize a material stronger than it, or have we proved that the structure of diamond is the strongest possible?"
] |
[
false
] | null |
[
"...very tightly bonded to another ",
" in a rigid crystal...",
"3 = graphene, fullerenes, nanotubes, (graphite),..."
] |
[
"...very tightly bonded to another ",
" in a rigid crystal...",
"3 = graphene, fullerenes, nanotubes, (graphite),..."
] |
[
"You've got it mostly right, except your definition of hardness. The original empirical hardness scale developed by Moh was a good start, illustrating that a harder material would scratch a softer one. It's still relatively useful when you just want a rough estimate (\"what abrasive should I polish this tooth with?\").",
"The problem is that scratching is a very complicated problem. The propensity of a material to be scratched depends on the stress state at the point of the scratch. This stress state is a function of many things, including the shape of the tip at the scratch point. It's at this point when scratching becomes a very poorly designed test method. ",
"While standard scratch tests do exist, hardness is now usually measured by indentation with a well defined loading condition. These tests generally probe the resistance of a material to non-fractural plastic deformation. The field of fracture mechanics is also interested in how fracture mechanisms change hardness.",
"So, just remember that hardness is a complex beast. "
] |
[
"Have there been any conclusive studies about sleep-learning?"
] |
[
false
] |
[deleted]
|
[
"Short : ",
" (the mental process) to be able to write something in your long term memory.\nexp : Simon and Emmons 1956.\nStudent in psychology here"
] |
[
"Not sure about learning by playing tapes in one's sleep, but stimulating the scalp with relatively low currents at rhythms similar to natural non-REM sleep rhythms has been shown to enhance learning of tasks learned earlier that day. ",
"citation"
] |
[
"Simply put : ",
"More precisely : it gives no great effect, even no effect at all."
] |
[
"How high can a helicopter fly before the air is too thin for its rotors to keep it in the air?"
] |
[
false
] | null |
[
"The CH-47 Chinook twin rotor helicopter is used by the USAF to rescue climbers on Mount Denali (McKinley) in AK. It can reach an altitude in excess of 19000 to land at an elevation of around 18000. The biggest problem at that point is restarting the engines, so a special storage device directs pure oxygen into the engine inlet to restart."
] |
[
"This helicopter landed at 8805 metres",
"This page says the record is 12442 metres"
] |
[
"19000 what? Feet? Metres?"
] |
[
"Does this study imply that people will live longer if they worked out *without* taking (much) protein?"
] |
[
false
] |
Long-term low-protein, low-calorie diet and endurance exercise modulate metabolic factors associated with cancer risk1,2,3
|
[
"I think the answers you are looking for are at the end of the paper. The authors say:",
"In conclusion, our data show that the consumption of a low-protein, low-calorie diet; exercise training; and decreased adiposity are associated with low plasma insulin, C-peptide, FAI, leptin, and C-reactive protein and high SHBG concentrations, which are circulating factors linked with some types of cancer.",
"High concentrations of those factors (except lower for SBGH) are associated with different types of cancers. This doesn't necessarily mean that high concentrations of these factors cause cancer. It means when you find certain types of cancer, you are likely to find high concentrations of some of these factors too.",
"Their experiments showed that 3 things: exercise, a low protein/calorie diet, and low adiposity, are all associated with lower concentrations of these factors (and higher SBGH). This, again, doesn't necessarily mean that lower levels of these factors (and higher SBGH) will lead to a reduced cancer risk. But, as the authors say:",
"These results help to identify potential mechanisms by which long-term lifestyle modifications in diet or physical activity can selectively reduce circulating factors that are associated with increased cancer risk.",
"This idea has yet to be proven and the association observed in this study is only shown with 21 people. And unfortunately, it would be difficult to try to provide proof for this idea:",
"A long-term randomized controlled trial would be needed to determine cause-and-effect relations.",
"It seems that this was a relatively small but practical study that looked at the associations between several cancer-related factors and diet/exercise that may prepare the way for more investigation into this potential relationship."
] |
[
"It should also be noted that:",
"Subjects consuming a low-protein, low-calorie diet... strictly avoided processed and refined foods (eg, partially hydrogenated oils, refined flours, sweets, free sugars, and soft-drinks)",
"So, low-protein/low-calorie + restriction of foods generally associated with weight gain / metabolic syndrome makes finding a cause-and-effect even more difficult."
] |
[
"I'd be interested as well, although to clarify they didn't participate in weight training, only endurance/running exercises. ",
"I bring up weight training because every study I've come across advises to consume more protein that the RDA. ",
"http://www.jissn.com/content/9/1/54",
"For maximal muscle hypertrophy to occur, weightlifters need to consume 1.2-2.0 grams (g). protein kilogram. (kg)-1 and > 44–50 kilocalories (kcal).kg-1 body weight daily [1-9]. ",
" (RDA) for protein (currently 0.8 g.kg-1) which meets the needs of 97.5% of all healthy adult Americans not engaged in weightlifting with the intent of gaining muscle mass [8].",
"Bolding is mine.",
"It appears the ",
"low-protein diet",
" from the study constituted a ~.73g.kg ratio, which to me doesn't seem that much lower than the .8g.kg RDA.",
"I couldn't find any studies on the effect of weight training and cancer risk/prevention. "
] |
[
"If the moon-phase is dependand on the core shadow of the earth, why is the light sometimes circular?"
] |
[
false
] |
What I mean is basically this: If you think about shadow of the earth, its a big cone thingy, which puts a shadow on the moon, which would explain , but why is there also phenomenon? I always wondered this.
|
[
"The shadows you see there aren't the shadow of the earth being projected on the moon, they are the sides of the moon which are facing away from the sun. In a full moon, the earth is \"directly\" between the sun and the moon, so the entire half of the moon that faces the earth reflects sunlight. In a new moon, the moon is between the earth and the sun, so no light is reflected at all (also, in a new moon the moon is only visible during the daytime, as you face away from the moon at night). At partial phases as in your picture, the moon is at some angle between new and full, so a portion of the moon reflects towards earth and the rest reflects away from earth. At all times* half of the moon is lit up, it's just a matter of how much reflects towards earth.",
"There are special cases, eclipses, where shadows are actually being cast. Lunar eclipses are when the Earth casts a shadow on the moon, and solar eclipses occur when the moon casts a shadow on the earth. These are relatively uncommon however.",
"relevant picture"
] |
[
"http://i.imgur.com/zwfWZ.png",
" \nThis will help maybe, i made it in paint :D"
] |
[
"Thanks a lot! :)"
] |
[
"Why is fire hot?"
] |
[
false
] |
Is it the stored energy between the bonds and the “fire” is ripping the bonds apart? So then how does that work for gas. If you were burning O2 would the fire break it down to 2 Os? And if that’s the case would fire be able to burn just O. I was wondering this because I was cooking and I was wondering where all that gas went. And what it became after it was burnt. Or does it straight up become energy (the heat that you feel)
|
[
"Lets say a simple fuel: Hydrogen",
"If you burn that you get Dihydrogenmonoxide or simply Water",
"Another simple and more common fuel: Carbon\n(coal, wood, paper) \n Carbondioxide CO2",
"your gas stove is a little bit more complicated:",
"Propane C3H8 + 5 O2 = 3 CO2 + 4 H2O",
"it always depends on what you are burning for what you get and how much of it",
"Edit:\n\"Just burn Oxygen\" doesn't work because \"burn\" means reaction with Oxygen",
"Where does the gas go? \nIn the smoke and steam that your flame gives off (you cant see it on a gas stove)"
] |
[
"Usually, breaking bonds ",
" energy, and doesn't generate any. What happens when stuff burns is that its constituent atoms combine with oxygen. This ",
" a bond, which releases energy. You can imagine this process like two magnets snapping together - it releases a lot of energy and knocks small nearby objects flying. This makes nearby atoms/molecules vibrate, which is heat. Side note: You mentioned that oxygen burns. It doesn't. Oxygen causes other things to burn, but you can't set oxygen on fire."
] |
[
"Oh that’s right, combustion reactions. Totally forgot!"
] |
[
"Why do some things burn and some things melt?"
] |
[
false
] | null |
[
"Burning and melting are two different reactions chemically.",
"Burning happens when the substance reacts with a gas in the air, rapidly oxidizing (oxidation is where a substance loses electrons). Usually, it is being oxidized by oxygen (hence the name). The oxidation reaction produces a lot of light, which is what you see as fire, along with heated soot from the substance flying up into the air.",
"Melting on the other hand is where the molecules in a substance start shaking so violently that they lose structure, like a building collapsing due to a hurricane.",
"We can predict whether a substance will burn or melt at a high temperature based on whether it has a low electronegativity/ionization energy, and loses electrons to oxygen under heat. Without oxygen/some other oxidizing agent, the substance would continue to heat until it melts."
] |
[
"Wood pyrolyses in an environment absent of oxygen - it decomposes into simpler molecules which are given off leaving behind a carbon rich material.",
"Some of the individual components of wood, cellulose, have been shown to melt however. This is given to that fact that cellulose has much less chain cross linking. This further leads to a distinction between two types of polymer: thermosetting and thermoplastic polymers.",
"Thermosetting polymers are tougher due to chain cross linking and as such char/ decompose before melting. On the other hand, thermoplastics deform and can melt at increased temperatures due to a lack of chain cross linking."
] |
[
"So, without oxygen, an object that would usually burn, such as wood, would melt at a high enough temperature?"
] |
[
"I'm trying to wrap my head around the concept of dark matter"
] |
[
false
] | null |
[
"It's matter which is literally dark. Because most of our techniques for analyzing things in space boil down to \"let's look at the light coming from them\", it's difficult to determine what it is. It's ",
" difficult to observe; its gravitational effects are fairly noticeable."
] |
[
"We know dark matter doesn't emit/adsorb elecromagnetic radiation (EMR) because we can't see it, only its effects on other matter through gravity.",
"What dark matter is and why it doesn't emit/adsorb anything we simply don't know. The current best theory is that dark matter consists of ",
"WIMPs",
", Weakly Interacting Massive Particles. You should think of this as a cloud of particles which pass through everything, much like neutrinos. "
] |
[
"Albeit while usually not in the visible spectrum, regular baryonic matter (with a temperature greater than absolutely zero) does emit EMR via blackbody radiation."
] |
[
"Why is glass not crystalline?"
] |
[
false
] |
My understanding of glass was that it was that its a noncrystaline solid. Which right off the bat is confusing because theres something called "crystal glass". But in addition, I was looking at [wikipedia](&) about glass ceramics, which have both crystal and crystal aspects. In particular: Glass-ceramics are mostly produced in two steps: First, a glass is formed by a glass-manufacturing process. The glass is cooled down and is then reheated in a second step. In this heat treatment the glass partly crystallizes. In most cases nucleation agents are added to the base composition of the glass-ceramic. These nucleation agents aid and control the crystallization process. Because there is usually no pressing and sintering, glass-ceramics have, unlike sintered ceramics, no pores. So it sounds like if you melt down a bunch of stuff and mix it together, it will cool down and become glass. But then they heat it up again and cool it down again, and it becomes crystal. I dont get how that works. They mention "nucleation agents", but also say "in most cases", implying its not always required. What exactly is a glass and what causes it to be that way?
|
[
"Glass is by definition a non-crystalline solid, meaning it is made up of molecules that have no long range order.",
"Glass can be made up of lots of different materials, silicon oxides are really common example. SiO2 can be crystalline (mineral quartz) or amorphous (fused quartz). The same is true for lots of materials we use in different glasses, they can have both crystalline and amorphous structures depending how we construct them.",
"For example, if you melt down silica into a molten state, and cool it down very quickly, the molecules will be frozen in place in an amorphous state. If you cool it down very very slowly, with the introduction of a seed crystal or a nucleation site, the molecules will move into an ordered crystalline state before they solidify.",
"In the text you quote they are producing a semicrystalline state, that consists of small ordered regions surrounded by amorphous glass, as a means to get rid of the pores that are often present in some crystals.",
"Finally, you mentioned crystal glass. That's actually a misnomer, it's just a common name for a certain type of lead based glass."
] |
[
"When you cool down a substance, under certain circumstances, the molecules in the liquid and unable to rearrange into a nice repeatable lattice (crystal) in time. ",
"This has to do with the diffusivity of the diffusive mode associated with the relaxation of concentration gradients (or rather, the switching of two atoms/molecules on some appropriately defined grid) tending towards zero. Low diffusivity here means that that mode of transport happens slowly.",
"When it becomes hard for atom A to switch with atom B, then the substance freezes in, for example, an ",
"B",
"BBB",
"BB shape (with random letters outside what I've listed); amorphous, random structure. If it is easy for the atom A to switch with atom B, then you get a pattern like ",
"B",
"B",
"B",
"B",
"B",
"B (letters repeat); a crystalline, repeated pattern. The reason why you get this pattern when it is easy for them to exchange with each other is that this pattern is usually has the lowest energy, and systems like to be in the lowest energy state they can occupy.",
"Once the substance is in a glass form (",
"B",
"BBB",
"BB) it can be reheated to increase the diffusivity of that mode and allow some swapping of A and B components to happen (so you might something like ",
"B",
"B",
"BB",
"BB). Basically the pattern of the atoms or molecules is no longer completely (or mostly) random, but has some structure in it, just not a very high (or perfect) amount of crystallinity.",
"Adding nucleation agents helps increase the ",
" ability of the atoms/molecules to rearrange correctly to form a crystal.",
"The exact definition of a glass is actually very contentious, because glasses are what is called 'meta-stable'. This means that that the atoms/molecules are in a very stable arrangement, that will last for a very very long time (in what the average person calls glass's case, usually longer than you'll live), but due to the laws of thermodynamics, there is nothing stopping rearrangement from happening (just happening slowly) . . . and in fact the glass wants to rearrange (because the crystal form is lower energy). Basically meta-stable means it is not truly stable for very long times (where 'very long times' is a relative term).",
"So after many years, for example, perhaps all the atoms in the sample will jiggle in such a way that the fourth A in ",
"B",
"BBB",
"BB will shift to the right and become ",
"B",
"B",
"BB",
"BB, leading to a lower energy ",
"B",
"B",
"B pattern in the middle there, which is even less likely to be destroyed by a swap of atoms than the previous pattern due to its lower energy. Far in the future, the substance may eventually relax back into what we would call a crystal. ",
"So when is a substance a glass (i.e. a solid material with amorphous structure), and when it is just an transient snapshot of the atoms arranged in an unstable way? If we were to look at a fluid in super slow motion (or just a snapshot of the particle positions) it would look exactly like a glass (amorphous everywhere), but we don't call fluids glasses because the particles very quickly rearrange themselves. But 'very quickly' is relative, hopefully you can see the problem here.",
"When we study the dynamics of glasses, we can see that as they form everything slows down . . . but they only slow down, never stop . . . and there is nothing saying we couldn't watch for a longer period of time and eventually see a crystal form. This makes it really hard to draw a line and say 'this is a glass' and 'this isn't a glass' because it depends on your observation time.",
"This is a super interesting and active area of research."
] |
[
"I believe crystal glass is actually the lead free alternative to crystal."
] |
[
"How do scientists know if an animal is for sure extinct? or is it just a hypothesis"
] |
[
false
] |
I've kinda wondered this for years, do scientists actually know if an animal is extinct or is it more or less of a guess? I know ive read that they classify an animal is extinct when it is beyond a reasonable doubt that the last of its kind has died, but what about deep sea creatures? I can see us being able to pretty much know for sure when it comes to land dwelling animals, but the ocean is a different story altogether is it not? Thanks! And sorry if this is a silly question
|
[
"Interesting question!",
"There is indeed no way to know for certain. However, often heavily endangered species are conserved by human efforts. When we stop observing a species in the wild, and a last known member of that species dies, that may be the time at which we deem a species extinct. But if a new member of that species is discovered later, the date could be revised.",
"A case in point is the Galapagos turtle, which Radiolab produced a phenomenal episode on: ",
"http://www.radiolab.org/story/resurrections/",
".",
"--- SPOILER ALERT ---",
"The creature was thought to be extinct, but then a last male turtle was discovered. When it failed to reproduce, scientists discussed how they might go about producing genetically similar offspring from closely related species."
] |
[
"There's also the case of the ",
"stick insects of Ball's Pyramid"
] |
[
"It is more or less a calculated guess. It can be pretty hard to keep track of the number of animals of a certain species. However, there is also a thing called 'functional extinction'. If a species doesn't have enough members males and females can have a hard time finding eachother and reproducing (the Allee effect) and even if they reproduce, offspring will be very closely related to one another and incest gives a lot of problems for a population. It's not like you can start a population with just one male and one female, the genetic diversity would be way too low. We've seen examples of this with plants, bananas are all clones with the same genetic code and it's not uncommon for a disease to wipe out entire plantations, and keep in mind that we take drastic measures to protect these plants. In any case, you can determine a critical size beyond which it's very unlikely for the population to recover. In this case, a rough estimate of the number of animals can suffice to see if a population has any chance of survival. So sometimes 'extinct' mean they will die out eventually but it might take some time. Especially for a species like turtles who can live hundreds of years, it's entirely possible a few are hiding out there, but it's not very likely a healthy group of new turtles will emerge in the future."
] |
[
"Would playing a piano in zero G cause rotation? (See assumptions)"
] |
[
false
] |
My five year old asked me this, I was unable to answer. We were looking at pics of astronauts in ISS on Christmas. He asked if you could play a piano in space. I said yes, but if you just tried to play the keys you'd just push off the piano and float away from it. (Assuming, if I'm correct, a floating piano, which has more mass than the player.) Anyhow, we came up with a scenario where you could strap an astronaut to a floating piano like you could strap an astronaut to a bed or an exercise machine so that playing wouldn't just make you drift away. Then he wanted to know if playing the piano would make you spin around because 1) the force on the keys and 2) the teeny little hammers. No...clue..at...all...
|
[
"If the astronaut were strapped to the piano, then no. Angular momentum can only be changed by an ",
" torque. The only way you could get spinning in such a scenario is if the astronaut pushed off of the piano and floated away. If the direction of the push was misaligned to his or center of mass, the astronaut would start spinning while floating away from the piano.",
"Also that's an excellent question for an adult to ask, let alone a five year old! Keep up the good work, both of you :)"
] |
[
"Thanks, my son has a lot of great questions. And I'm lucky to have a five year old that watches Big Bigger Biggest instead of Barney. ",
"I totally get what you're saying. If he pushed off, say, cross handed so he rotated his torso while pushing off, that would change his center of mass, spinning him. ",
"I think the follow up question then is what would the effect be of the hammers hitting the strings on an upright piano floating in space, to its position in space. Assuming that a piano is floating in space and some force is applied downward on the keys (by a strapped in astronaut) but the result is that hammers in the upper cabinet of the piano strike strings. Does the hammer hitting the string and converting the energy to sound work efficiently enough to cancel out any motion that might impart to the piano? What about a grand piano where the hammers strike (I think) top down?",
"....because I know he'll ask. "
] |
[
"The striking of the hammers against the strings would again qualify as an internal force, and therefore cause no bulk motion of the piano.",
"Everything inside the piano is attached to the piano in some way. The keys are attached to little hinges that let them move. The hammers are similarly attached, and are linked to the keys. The ends of the strings are tied off inside the piano. The hammers may impart a force on the strings, and this force may transfer to the body of the piano, but this force will be exactly cancelled out by the force the strings exerted on the hammers.",
"I said bulk motion up there because all of these parts of the piano will of course be vibrating. On earth, when a piano key is struck, the hammer hits a string and causes it to vibrate. This string then vibrates the air around it, which travels to your ears and produces music. Here, the string stops vibrating relatively quickly as it loses energy to the air. This of course can't happen in space, since there's no air to lose energy to. Instead, the string would likely vibrate for a fairly long time. It might lose a bit of energy at its ends where it's connected to the piano, causing the piano to slightly vibrate as well. Eventually, all of this vibrational energy would be dissipated as heat and you'd have an ever-so-slightly warmer piano than when you started. I'm not sure how long this process would take, though my guess would be that it depends very strongly on the properties of the strings. It would certainly last much longer than would ever be possible on earth."
] |
[
"Are there equations that describe the effects that a magnetic field has on a plasma?"
] |
[
false
] |
Preferably simple ones... I'm really bad at math.
|
[
"A plasma is effectively a collection of pseudo-free electric charges. A magnetic field ",
" exerts a force ",
" on an electric charge ",
" traveling at velocity ",
" according to:",
" = ",
" ",
" x ",
"If you analyze this equation, you find that free electric charges with an initial velocity tend to spiral around magnetic field lines. Once an electric charge starts traveling in a circle, it acts like a little magnetic dipole (a little permanent magnet). Using the above equation and doing some fancy math (doing a multipole expansion) and making an approximation, you can derive the equation:",
" = ",
" grad ",
"where ",
" is the effective dipole moment of the spiraling electric charge. The gradient operator simply measures how fast the magnetic field is changing from one point in space to the next. The gradient of B points away from regions where the magnetic field lines are pinched together. Therefore, the electric charges in a plasma spiral around the magnetic field lines and are repelled from regions where the magnetic field lines converge. These effects can be used to trap a plasma in a magnetic field."
] |
[
"Yes, to an approximation. (I don't know if \"orbit\" is the best word in this context as the trajectories are much more complicated than planetary orbits). For instance, the Van Allen belts are plasmas that are shaped by earth's natural magnetic field. The shape of the belt's effectively show the shape of the magnetic field."
] |
[
"Yes, to an approximation. (I don't know if \"orbit\" is the best word in this context as the trajectories are much more complicated than planetary orbits). For instance, the Van Allen belts are plasmas that are shaped by earth's natural magnetic field. The shape of the belt's effectively show the shape of the magnetic field."
] |
[
"If the universe was formed in a single event, why isn't it homogeneous? As in, why do stars and planets have vastly different compositions if they originated from the same point?"
] |
[
false
] | null |
[
"The leading theory is that during the period of cosmic inflation, in which the universe expanded much faster than the speed of light, quantum mechanical fluctuations were collapsed and then magnified as they expanded, which lead to the fluctuations that caused galaxies and the like.",
"Planets and stars have different compositions because they did not originate from the same point. The first generation of stars would have all had the same composition, but once they fused heavier elements (up to iron and heavier in big star collapses) and then supernova'd them into the universe, new stars formed from their remains and so have different compositions."
] |
[
"Yes we are, via spectroscopy. Different elements emit and absorb light at very specific yet unique wavelengths, and so by observing which wavelengths of light come to us from distant stars, we can tell what elements compose the star.",
"And as far as old, distant stars being relatively homogenous, I can't say for certain or cite any articles but there should be a very clear pattern of older stars containing fewer metals (anything heavier than Helium, to an astronomer)"
] |
[
"Are we able to determine the basic composition of very distant stars, say 10+ billion light years distant? If so, do they indeed show a much simpler and homogeneous composition?"
] |
[
"If someone tried to raise an ape as their child, in what areas, if any, would it be able to function as a normal human?"
] |
[
false
] | null |
[
"There is no chance of chimps speaking as they don't posses the correct vocal chords, jaw or sinus anatomy.",
"They can (disputably) be taught sign language and plenty of chimps and other higher primates have been taught to sign",
"https://en.wikipedia.org/wiki/Great_ape_language",
"https://en.wikipedia.org/wiki/Washoe_%28chimpanzee%29",
"With regards, raising chimps as children, this has been attempted at least once (maybe twice) most famously in Herb Terrace's experiment with Nim Chimpsky",
"https://en.wikipedia.org/wiki/Nim_Chimpsky",
"Roughly chimp development races ahead of human infants for the very earliest initial phase around acquiring coordinated movement but fairly quickly they are overtaken by human infants across the board in all cognitive and language abilities.",
"The full story of Nim's life is kind of sad and related in the Documentary Project Nim.",
"http://www.npr.org/2011/07/20/138467156/project-nim-a-chimps-very-human-very-sad-life",
"tl;dr: No monkey butlers any time soon.",
"edit: \nadding the Lucy story that slazar4 linked. The radiolab documentary is really, really sad.\n",
"https://en.wikipedia.org/wiki/Lucy_Temerlin"
] |
[
"Susan Savage Rumbaugh, the researcher who taught Kanzi (a bonobo) to communicate via lexigram, is currently raising Kanzi's son as a human child at the Great Ape Trust. His name is Teco, and you can see some of the videos of him ",
"here",
". ",
"The science behind ",
"Kanz",
"i's speech is a little fuzzy, but he apparently began spontaneously learning lexigrams while watching his mother get taught. He is now extremely proficient with them, and can respond to an extremely wide variety of English commands, such as \"put the pine needles in the bowl\" and \"Bring the ball that is outside back in here\", etc etc (this involves fairly complex prepositional phrases, making it pretty impressive). ",
"\"Paul Raffaele, at Savage-Rumbaugh's request, performed a Haka for the Bonobos. This Maori war dance includes thigh-slapping, chest-thumping, and hollering. Almost all the bonobos present interpreted this as an aggressive display, and reacted with loud screams, tooth-baring, and pounding the walls and floor. All but Kanzi, who remained perfectly calm; he then communicated with Savage-Rumbaugh using bonobo vocalizations; Savage-Rumbaugh understood these vocalizations, and said to Raffaele, \"he'd like you to do it again just for him, in a room out back, so the others won't get upset.\" Later, a private performance in another room was successfully, peacefully, and happily carried out.\""
] |
[
"I'd suggest you read this article on Lucy the chimp, who was raised by two biologists from infancy. ",
"Some of the highlights of the experiment include Lucy being only attracted to human males and pleasuring herself using a vacuum cleaner and a playgirl magazine. Also, she reportedly acquired a taste for gin and learned to prepare tea for her \"father\". ",
"Fascinating read. ",
"http://en.m.wikipedia.org/wiki/Lucy_Temerlin#section_1"
] |
[
"Do lungs fill top to bottom or bottom to top or all at once?"
] |
[
false
] |
Hi ,when we inhale, does the air fills up the bottom of the lung first, or top of the lung first, or all at once first? Similarly , when we inhale, does our chest rises first, or stomach expands first, or stomach and chest expand at the same time? What about exhale?
|
[
"Generally speaking, lungs fill bottom to top. This is due to most thoracic expansion being caused by the diaphragm. Your diaphragm is kind of an upside-down \"U\" shaped muscle, that when it contracts, turns into a shorter upside-down \"u\", basically flattening out. That gives the lower third of your lungs, also called the \"dependent zone\", some room to expand so it does. ",
"You also have a variety of accessory respiratory muscles around the thorax that expand the rib cage, allowing expansion of other proteins of the lung. These muscles aren't usually used for \"quiet inspiration\", but when someone is exercising or has COPD, they begin to be a lot more involved. In those cases, the whole lung expands at the same time.",
"During exhale, you will have contraction of abdominal muscles to help generate pressure to expel air, along with relying on elastic recoil of the parenchyma the lung as well as elastic recoil of the chest wall. As a side note, the contraction of abdominal muscles during expiration creates what is called the \"respiratory pump\" which aids in returning blood to the heartz so that's neat."
] |
[
"It really depends on posture and position and whether you (can) use your diaphragm or thorax muscles more. There are reflexes and breathing exercises that optimise air and blood flow into more segments. Normal breathing is usually a mix of the chest and the stomach expanding.",
"Normal, unforced exhalation is passive, the muscles used to inhale relax again and elastic fibers in the lung tissue retract and push the air out again. Only in forced exhalation like e.g. coughing, sneezing or blowing you use muscles to compress either the stomach or the chest or both - depending on which area was expanded in the inhalation before, and which ones can contract.",
"Sorry, there's no easy answer, breathing is quite complex and can change drastically between two breaths. It's hard to study, too - conscious breathing patterns are very different to regular reflexive patterns."
] |
[
"Are you familiar with paradoxical breathing? ",
"If lungs fill bottom to top, stomach should expand first, followed by chest.",
"",
"I do not understand that when I am in my maximal inhalation, my stomach contracts but not expands. However my chest expands"
] |
[
"Why does wind feel cold, even though the air it is comprised of may be at a comfortable temperature?"
] |
[
false
] | null |
[
"It's basically to do with thermodynamics and the time your body is in contact with the surrounding air. Humans cool down by dilating blood vessels and effectively making their skin as hot as possible. When two materials with different temperatures come into contact, the hotter one transfers heat onto the colder one.",
"In still air, the air around your body will be hotter than the air everywhere else. This air will have to be replaced by cooler air through movement or convection.",
"By adding wind to the equation, we drastically increase the movement of air over the hot skin. This allows the cooler air to quickly replace the air warmed by your skin, thus making you lose heat quicker and making you feel as if the air is colder."
] |
[
"Same answer as the previous times it was asked. The rate of thermal heat transfer by conduction increases with the temperature difference. Bigger temperature gradient, faster heat loss. That means the temperature of an object, initially at 30 degrees above than room temperature, will drop by 10 degrees more quickly than an object 10 degrees higher than room temperature will drop by the same amount. Even though the amount of heat given off is the same (normally it would be roughly equal), it's transferred faster when the difference is bigger.",
"So you have 'wind chill', or in technical terms 'forced convection'. Your body will lose heat more rapidly to the surrounding air if it's moving more, because the heated up air closest to your body is moved away more rapidly, meaning the average temperature of the air next to your skin is lower - (while your body is at a constant temperature), hence a higher rate of heat transfer. ",
"If you are standing still and the air around you is as well, the only thing transporting warm air away from you is 'natural convection', the rising of warm air (or sinking of cold air) due to its lower (higher) density. ",
"The thermal energy of air is very large compared to the kinetic energy of your typical wind, so you don't feel warmed by a wind either, even if it's at the same temperature (within its own frame of motion). Unless it's a very powerful jet of air."
] |
[
"Heat transfer will occur if there is a gradient. So generally hot->cold or cold->hot. If you continually pass air over your skin, the air won't reach equilibrium with your temperature, so it will feel much colder. "
] |
[
"Do we know enough to figure out where viruses came from and what micro-organisms might be their closest relatives?"
] |
[
false
] |
[deleted]
|
[
"Viruses aren't really related to microorganisms because they aren't really organisms. A virus and a bacteria are fundamentally different enough that it isn't likely that they share a history anytime in the last billion years."
] |
[
"agreeing the connections are still very obscure it is important to remember that viruses are not composed of living cells. The only means of viral replication is by way of host cells utilizing the lysogenic and lytic cycles. "
] |
[
"no, the connections are still obscure. all micro-organisms use DNA, while viruses use RNA-based genomes. the two might have evolved separately, or one might have come from the other. but the common ancestors (those that depended even more on RNA for catalysis and information storage than modern cells) are either extinct or so rare that no one has found one yet. "
] |
[
"What have we learned or plan to learn from Ingenuity (the helicopter on Mars)?"
] |
[
false
] |
Pretty simple question. I'm all for remotely flying a helicopter on another planet , but I got curious what we could learn from it. Geology, thin atmosphere flight, etc. I'm a layperson and I'm curious what the plan is/was.
|
[
"What they intend to learn from Ingenuity is how to build and operate a helicopter that can fly autonomously on Mars, and what problems they will encounter from doing so. The idea is to use this knowledge to build more aircraft that can be used for gathering data and scouting the best paths for rovers.",
"You have to crawl before you can walk, or in this case you have to fly before you can fly and do science."
] |
[
"Wikipedia has an overview",
"."
] |
[
"Could be used to safely land rovers in the future? Or would it need to be too big?"
] |
[
"What are capacitors used for and how do they work?"
] |
[
false
] |
I know that capacitiors are found in most electronic circuit boards and I understand that they store electricity. But how do they store electricity, and why would you want to store it when you can use batteries? What else do they do with it? So many questions. EDIT: Spelling. EDIT 2: Thanks for all the answers! :)
|
[
"In modern terminology, the phrase \"storing electricity\" is essentially meaningless. The term \"electricity\" is ambiguous and might refer to current, or voltage (potential), or energy, or power, or charge. Capacitors store energy in an electric field.",
"As a shorthand, we often say that capacitors \"store charge\", although this is not really correct. The overall charge on the capacitor is always neutral. But the positive charge may be more on one plate and the negative charge may be more on the other plate. When we say the capacitor \"stores charge\" we are thinking about cases where one terminal of the capacitor is tied to ground (or another large charge reservoir) so that we don't worry about the charge on that plate, and we are only thinking about the ungrounded plate.",
"More accurately, a capacitor stores energy in the electric field between the two plates. This field is caused by the separation of charges between the plates.",
"What are they used for?",
"One main use is to store energy near a point of load, so that it can be supplied quickly to a device (an amplifier or logic chip, for example) that needs it. A capacitor used this way is often called a \"power supply bypass capacitor\".",
"Another main use is in a filter to control what frequencies of signal may pass from one part of a circuit to another. ",
"Why not use batteries instead? ",
"Batteries would respond more slowly and have higher equivalent series resistance (which causes energy losses). Also no battery chemistry I know of is well suited to being repetitively charged and discharged as much as is required for many capacitor applications. A capacitor in an RF filter might be charged and discharged hundreds of millions of times per second."
] |
[
"Just to clarify, in a more general sense, a capacitor is defined as an object that stores charge. Colloquially, people refer to capacitors as the circuit elements that have a net neutral charge, with oppositely charged elements; this is delineated as 'mutual capacitance' when context doesn't make it obvious ( ",
"http://en.wikipedia.org/wiki/Mutual_capacitance",
" ).",
"Another important use of capacitors is in the generating of oscillating voltage (very useful!).",
"http://en.wikipedia.org/wiki/LC_circuit"
] |
[
"A capacitor works the same way a mass does in a mass-spring-damper. In dynamics, it sources a current to resist changes in voltage, and can source more current if it has more capacitance. This is the same as a mass generating a force to resist a change in velocity in a 1D system."
] |
[
"If water is clear and water vapor is white, why are storm clouds grey?"
] |
[
false
] |
Is it from the condensation of the water drops in the clouds blocking out light from the sun? Or is it possible to create a grey/black form of water vapor?
|
[
"Water vapor is not white. Water vapor is clear. Clouds are made of small droplets of liquid water or solid ice; those small particles are what appear white.",
"Clouds are white due to ",
"Mie scattering",
". Tiny particles in the air tend to make light \"scatter\", since there are so many small individual surfaces for light to reflect or refract off. And since Mie scattering works roughly the same on all wavelengths, the scattered light is white.",
"Storm clouds are dark because you are underneath a very deep cloud. A lot of light has already been scattered away, so a lot less of the original sunlight is getting through, making the cloud appear grey. "
] |
[
"Mostly. Due to the fact that liquid water has a slightly blue color, there is some absorption of long wavelengths that give clouds a blue and ",
"sometimes greenish tint",
". But the main reason dark clouds appear \"dark\" is because a lot of light has been scattered away."
] |
[
"Nope, that's a very common misconception! ",
"Water is indeed blue on its own",
", due to the fact that it mildly absorbs red light."
] |
[
"Did the speed of the JWST decrease between yesterday and now? Why? How?"
] |
[
false
] |
Look how the speed decreased from launch. It reached 9km/s at launch. But now it's at 1.8km/s. How does it work?
|
[
"Earth's gravity is doing the trick. If it moves faster than the speed of a circular orbit, then orbital dynamics mandate it will gain altitude. At this point the force of gravity will not be perpendicular to the velocity, so it will pull backwards from the telescope, causing it to slow down. Another way to reason about it is that it's gaining potential energy from ascent, so it must lose kinetic energy to compensate. This is intended as it's meant to reach L2 point, it was launched fast enough to ascend to the point's altitude of 1.5 million km, but not faster so it doesn't escape.",
"Most of the speed loss occurs in the lowest altitudes, where Earth's gravity is still strong. After a while the speed will asymptotically approach its hyperbolic excess speed. That's most likely near-zero, as they must have calculated it to come to an almost complete stop when it reaches L2, so it can perform the orbit insertion manoeuvre with as little propellant as possible. (As launch costs are so high, trajectories are always calculated to perform manoeuvering with the smallest possible velocity change)."
] |
[
"It's what you can remember from physics classes at school - kinetic energy gets exchanged for potential energy when you're moving further away from gravity source. If you throw something up then it will slow down up until it stops entirely when reaching the highest point (and then starts moving faster and faster again when heading back closer to the source of gravity). In this particular case JWST will fire engines to fix it's orbit once it reaches the highest point, so it's not going to \"fall back\" closer to Earth any more."
] |
[
"I was confused because I thought that the telescope will continue to accelerate until it reaches the midpoint of the journey",
"What would cause that? :) To accelerate you need either to be dropping down into gravity well (aka: falling) or use propulsion (aka: fire engines).",
"Will it start to accelerate when it gets to the moon?",
"What? It's not heading to the Moon. It's heading towards L2 point, and once it reaches it, it will fire the engines to \"circularize\" the orbit, so it doesn't fall back towards Earth (it would not hit Earth though, it would pass maybe 200 km above the surface at the closest)."
] |
[
"Is one side or spot of the Sun known to be hotter than the rest?"
] |
[
false
] | null |
[
"The Sun varies massively in temperature across the whole disk but not really in the systematic way you are implying (cooler on one side). Instead it has a fairly complex pattern at all scales, from both very small fine scale variations to very large changes in temperature that span across huge fractions of the Sun's surface.",
"This is an image of the solar granulation taken by DKIST earlier this year",
". What you are seeing is convection, the centre of each of those granules is hotter, rising material and the dark inter-granular lanes are cooler, sinking material. For reference: each granule is about 1000km wide. The average temperature of the photosphere is about 6000 K the variation you see here is a few hundred K (perhaps as much as 700-1000).",
"You can get more extreme and larger sized variations ",
"with sunspots",
", these are regions where the magnetic field is larger and so the increase in pressure leads to expansion and thus cooling of the material. Sunpsots can be <4000K which is a big difference. However, an interesting thing about this kind of image is that the gas that is in the sunspot is still EXTREMELY bright, it is just far far less bright than the surrounding photosphere so looks much darker by contrast. You can see from the surrounding granules how much larger sunspots are.",
"There are funnily enough much bigger temperature variations in the Sun when you get to the higher levels of atmosphere, the corona and chromosphere.",
"It can be dangerous to talk of \"temperature\" when you are not talking about a black body and while the photosphere is very nearly a black body, the corona and chromosphere are very decidely not. You might already know that the corona has a temperature of millions of kelvin, so many many times hotter than the photosphere, but you might not know that the variations (both spatially and in time) across it are also much larger.",
"Something I do is generate maps of temperature via something called an inversion, this is where I take a bunch of information from ",
"maps of intensity of light at specific wavelengths",
" and turn it into a map of material at specific temperatures.",
"I very quickly ran this type of calculation on some observations of the Sun from 2014 ",
"and plotted some specific temperatures here",
" while it is very rough as it was done in a hurry it does illustrate the idea. The colour map is a measure of \"how much material\" not directly temperature so bright areas are where there is a lot of stuff at that temperature and each figure is a different temperature band. The labels above each plot are the log of the temperature that plot is showing so 6.0 is 1 million K and 7.0 is 10 million K. EDIT: reran my program and fixed the labels.",
"What you should see is complex structures and shape, generally the bright parts in these images (where there is lots of hot material) correspond to the parts of the photosphere where there are sunspots and other magnetic activity. So while the photosphere is cooled by the magnetic field the magnetic field heats up the outer layers of the atmosphere."
] |
[
"Looking from a long distance away, the Sun has the same effective temperature from all different directions, since it is close to being an ideal sphere in shape.",
"However, there are some stars which spin much faster than the Sun, and they bulge out around their equator (looking like an M&M or a Smartie), so that the distance from the centre of the star to the poles can be up to 30% smaller than the distance from the centre to the equator. This difference in height of the star means that the poles of these stars can be much hotter than their equators!",
"For example, the star Vega is 25% wider across the equator compared to the pole to pole distance, and the poles are at 10,000 K but the equator is only 7500 K.",
"The Sun rotates slowly, so this effect is tiny. But for faster spinning stars, we can measure it.",
"You can see Vega with your eyes, it's one of the brightest stars in the Northern hemisphere Summer skies."
] |
[
"How would our solar system be changed if our sun acted like the mentioned star Vega?"
] |
[
"I need to come up with a 5th grade science lesson plan. What are some topics that are important for a kid that age to be exposed to?"
] |
[
false
] |
My task to is to design a science lesson plan that I will present to two classes of 5th graders. The lesson plan must include an experiment that the kids will perform themselves (in groups of 7). I would prefer to design an experiment beyond what is shown in every classroom. So what are some topics in science that you feel like more young people should have a better understanding of? My safety considerations include no chemicals beyond what can be purchased at a grocery store and no current in excess of normal wall current.
|
[
"Mix yeast with varying amounts of sugar and put it in an upside down test tube, then measure the size of the bubble as a function of time and sugar concentration."
] |
[
"Your best bet is to ask a 5th grader what is interesting to them.",
"Science (the scientific method, more specifically) is about asking questions and logically approaching the answer. You need to get kids away from thinking that \"science\" is only happening when there are colored tests tubes and barometers around. ",
"Most of the time the only exposure kids have to science isn't actually science, it's demonstrations of interesting physical phenomena (e.g. vinegar and baking soda mixing). These types of demonstrations are usually followed by a brief explanation of the fundamental physics or chemistry involved (e.g. acid base reactions). However, the kids usually aren't interested in the level of detail around the explanations of the phenomena (e.g. they only want to see the foam).",
"Find some 5th graders and ask them questions that ",
" would like to know the answer to. Then ask them to think about that they may guess an answer to be. Then you help them propose a test of their answer. Then you just naturally proceed with the scientific method.",
"With kids (and non-scientists in general) the biggest hurdle in teaching science is that it doesn't have to be about complicated math or expensive instruments. It is about asking questions."
] |
[
"evolution"
] |
[
"Is the current lethal injection the most humane way to kill someone?"
] |
[
false
] | null |
[
"The answer to this question depends on knowing what is the least painful or frightening to kill a person. Science can answer those questions."
] |
[
"There's an interesting documentary ",
"How to Kill a Human Being",
", where a British journalist investigates the science and ethics behind state execution. He pushes himself to the brink of death several times to determine the most humane way to perform an execution. "
] |
[
"If you want most painless method, high caliber bullet to the head would be it. Anything that blows your brains out faster than neurons can signal is painless. Of course, giving free opiates and/or other medication before the execution to take out the anxiety would be even more humane. ",
"even more humane option"
] |
[
"Why is the allergic response different than the immune response?"
] |
[
false
] |
In my physiology class, like most classes, we're learning that the allergic response is a hypersensitive response to nonpathogenic antigens. We learn about it as a facet of the immune system. But if it's the immune system? Why isn't it a normal immune response? If it's only for nonpathogens, why is there a response at all? The symptoms are so different, I can't tell why the allergic response exists at all--it doesn't actually seem to do anything to support the goals of the immune system.
|
[
"I learned in my EMT class that an allergic reaction is just an extreme reaction to something, it's because your body sees the allergen as a foreign body that doesn't belong and it tries to fight it despite it not being harmful. So basically from my limited understanding it's kind of an error that the human body is born with or develops over time."
] |
[
"There are children born and breastfed who develop allergies. So I doubt it's about eating the wrong food. There's a chance it's related to gut flora."
] |
[
"Very generally the processes in a normal immune response and an allergic response are the same, the problem is that in an allergic reaction the body is targeting a non-dangerous molecule (e.g peanuts). In the case of autoimmune diseases (e.g diabetes or rheumatoid arthritis), the immune system targets its own cells.",
"In the case of anaphylaxis this immune response to the allergen is so extreme it can kill a person because immune molecules cause their airway to swell up and their blood pressure to drop massively"
] |
[
"Is there an stoping point for radioactive half life decay?"
] |
[
false
] |
Learning about the decay of isotopes in high school, wondering if there was a point where the process stops? Maybe when there's only one atom left? Please enlighten me.
|
[
"Take one atom. What does a half-life mean for that one atom? Well it means that in one half-life there's 50% chance of decaying over that stretch of time. So when you have a ",
" of atoms, statistically half of them decay within each half-life. But when you get to that last atom, you keep proceeding through time with 50% 50% 50%... until eventually it decays.",
"Suppose you had 1000 coins, and you flip them, remove all the heads, then keep repeating. Once you get to 1 coin, you keep flipping it til it turns up heads. "
] |
[
"There's a series of fun science activity to demonstrate this with ",
"candy",
" although I modify it to graph each type of candy's half life as to simulate and discuss that different elements/isotopes have different half-lives (peanut M&Ms, plain M&Ms, skittles, etc.)"
] |
[
"Technically, it will stop when that last atom decays. However, we are dealing with such huge numbers of atoms (remember a mole of a element has 6.0221415 × 10",
" atoms) that, effectively, this point is never reached. The real limit on radiometric dating is our ability to measure small amounts of material."
] |
[
"What gives an object its colour? What exactly is happening at the molecular/atomic level?"
] |
[
false
] | null |
[
"Photons are either absorbed or reflected by the material. Our eyes detect these photons and register them as different colours. Longer wavelengths are “warmer” colours, shorter wavelengths are “colder” colours, from red through violet. White is when every photon is reflected (though a pure white is pretty impossible, most whites reflect most light but not all) and black is when everything is absorbed (though most blacks still reflect a bit)."
] |
[
"It’s about the energy and corresponding wavelength an object has. For example carrots contain β-carotene. β-carotene has a linear conjugated π electron system (a kind of chemical structure in which you have a single and double bond x times). The electrons along the system moves similar to a 1D infinitely deep potential well. So when when you calculate the energies of the energy levels in β-carotene you can calcultate the relating wavelength. This shows that it absorbs blue-green and violet and so it reflects orange and thus carrot is for example orange. I learned this with molecular physics so I was quit suprised when heard of this."
] |
[
"Could you please elaborate a bit more?"
] |
[
"When studying the brain, implanted electrodes are used to measure/model activity but wouldn't we need to know which neurotransmitters are being used in that activity?"
] |
[
false
] | null |
[
"Right, they do not measure neurotransmitters directly. Understanding what is going on with neurotransmitters would be a different level of explanation (a different question with a different answer). ",
"Think of it like asking \"how does texting on your phone work?\" You can answer that in lots of different ways: by describing how the software that your phone runs works, by describing the sensors that detect your fingerpresses, by describing the hardware that runs the software, by describing the transistors and chips that make up the hardware, by describing the electrical signals being sent between different parts of the phone, etc. Depending on what kind of mechanism/process you are interested in studying, you would use a different approach and different tools. ",
"In the same way, we can answer some specific questions about how the brain works by using electrodes and studying patterns of neural firing. We can answer different questions by looking at neurotransmitters."
] |
[
"Using your texting analogy, would it be fair to say electrodes let us know who is texting who and when, but we don't know the message that's being sent?"
] |
[
"No. Neurotransmitters aren't the message themselves. Information is carried in the patterns of neural firing and connections between neurons. There's nothing special about the neurotransmitters."
] |
[
"Will the whole universe eventually become one big black hole?"
] |
[
false
] | null |
[
"No - the Universe could, in principle, end up in a \"big crunch,\" collapsing back down to nothing, but the expansion is presently accelerating, and unless that somehow stops, there's no recollapsing."
] |
[
"The universe has no center. Even an object with the mass of the observable universe wouldn't be enough to stop objects at the edge of the observable universe from receding."
] |
[
"There are different theories. One of them does speculate that eventually gravity will overcome whatever force has expanded our galaxy and eventually (a very long time even cosmologically speaking) will contract back in again.",
"Right now the most accepted theory seems to be that the universe will die a \"heat death\" by expanding forever. Objects will continue to give off heat while the increasing distance between objects mean more and more of this heat (in the form of radiation or escaped energetic particles) won't be recovered by other objects."
] |
[
"Why is there no perception of depth while we look up at the sky?"
] |
[
false
] |
[deleted]
|
[
"One of the ways that depth is perceived by the difference in convergence of your eyes when looking at different objects.",
"Right now, I'm going to guess, and presume for the purposes of this example, that you have a screen 1m away from you, and a wall 2m away from you. I'm also going to assume that your eyes are 60mm apart (I'll be calling this the 'inter-ocular distance')",
"Using trigonometry, we know that the angle that each eye is converging at (the angle in from each eye looking perfectly straight ahead) can be calculated with:",
"tan(angle) = (inter-ocular / 2) / distance\n",
"or",
"angle = atan((inter-ocular / 2) / distance))\n",
"So, to calculate the convergence angle for the screen and the wall:",
"screen angle = atan(30 / 1000) = 1.7 degrees\nwall angle = atan(30 / 2000) = 0.86 degrees\n",
"So it's about a degree difference - this is a very obvious difference, and you can easily tell that they are at different distances while keeping your head still (more on that later)",
"Now, let's use buildings as our second example. One at 100m away, and the second at 200m.",
"near angle = atan(30 / 100000) = 0.017 degrees\nfar angle = atan(30 / 200000) = 0.0086 degrees\n",
"So now we're only taking a difference of 0.01 degrees. This is a relatively imperceptible depth difference. However, your brain can still perceive depth between objects at that distance. This is because moving your head from side to side gives your brain images from more widely differing viewpoints than your two eyes on their own. Let's say you lean one way and then the other, moving your head about 50cm in each direction. This gives you an effective inter-ocular of 1m.",
"So now we're getting",
"near angle = atan(500 / 100000) = 0.286 degrees\nfar angle = atan(500 / 200000) = 0.143 degrees\n",
"Much more of a difference between the angles, and you can now perceive the depth.",
"You can see where this is going, I'm sure...",
"Let's stop the head movement, and go back to just our eyes, and look at the two closest stars to us. We're going to need those distances in mm",
"The Sun - 1AU, or 1.5 x 10",
" mm",
"Alpha Centauri - 4.366 Light Years, or 4.1 x 10",
" mm",
"So, rather than objects where one is twice as far as the other, in this case, one is approximately 300,000 times further than the other.",
"So, let's figure out those angles again:",
"sun angle = atan(30 / 1.5 x 10^14) = 1.1 x 10^-11 degrees\nalpha centauri angle = atan(30 / 4.1 x 10^19) = 4.2 x 10^-17 degrees\n",
"The difference between these two numbers is absolutely minuscule.",
"So where is this limit? At what distance do we lose depth perception and things could just be on a sphere? We need to know ay what point the changing angle of an eye actually makes a difference.",
"This page",
" says that the spacing of resolvable objects to a human eye is 0.3 arc-minutes. (There are 60 arc-minutes in a degree, and 60 arc-seconds in an arc-minute). So let's assume that any angle difference less than 0.3 arc-seconds is imperceptible. This is 0.005 degrees.",
"So it seems that in my earlier example with the buildings, your eyes can see a very slight difference - the equivalent of 2 pixels. I'm going to say that this depends on your eyesight, though.",
"So, at what distance does it make no difference?",
"distance = 30 / tan(0.005) = 343775 mm ~= 344m\n",
"So anything further away than 344m, if you're keeping your head perfectly still, cannot be differentiated in depth.",
"If you are allowed to move your head by 1m, then this becomes",
"distance = 500 / tan(0.005) = 5729577 mm ~= 5.73km\n",
"I hope this has been of some help to you - for further reading, look up the definition of a parsec - this is how we tell the distances to some stars - we use the earth going round the sun as our two 'eyes', so our inter-ocular distance becomes 2AU, or approximately 3 million km."
] |
[
"Most of our methods of ",
"depth perception",
" are minimized at large distances, the sky being an extreme case of this. Others just aren't relevant for the night sky.",
"One special case is the ",
"moon",
" on the horizon (even if various explanation are debated...)."
] |
[
"I'm not sure I agree with you about the thing with the moon at the horizon - this isn't depth perception - this is size perception."
] |
[
"What would it feel like if a human were in a superposition?"
] |
[
false
] |
[deleted]
|
[
"What..what are you even asking?"
] |
[
"Yes, but I'm not quite sure you understand what it is, based on your question. Things are only in quantum superposition until they are measured, but when you are referring to stuff outside of the quantum level, superposition doesn't actually apply. In fact, Schrodinger's Cat was originally posited as a thought experiment demonstrating the ridiculousness of quantum superposition. Now, that doesn't mean quantum superposition is useless, but it definitely has no meaning when you're talking about a cat or a human. The cat isn't ",
" in a superposition of both states, it's definitely one or the other. Quantum superposition posits otherwise, however, and that's why Schrodinger's Cat was an argument via RAA against quantum mechanics."
] |
[
"Do you know what a quantum superposition is?"
] |
[
"Why are the solar panels on ISS different from the ones usually seen here on earth?"
] |
[
false
] | null |
[
"Space is a very harsh environment. Anything sent into space will likely need to be highly customized in order to function for any length of time.",
"\nFirst is weight. Sending mass into space is expensive, so lowering weight is a high priority. The solar arrays for space missions are made much thinner than cheap-o solar cells you buy at ‘Solar Cells R Us’ and thus save on expensive fuel.",
"\nSecond is volume. Solar arrays need large surface areas in order to collect maximum sunlight. Large areas are incompatible with rockets moving at Mach 5+. So the solar arrays must fold into tiny packages to fit into cramped rockets.",
"\nThird is radiation. Space, even within the Van Allen Belts, has lots of high-energy particles whizzing around that like to wreak havoc on materials, especially solid-state electronics such as solar cells. Special cell materials are used, along with redundancy, to give the cells longer life in such a brutal environment.",
"\nFourth is physics. The solar arrays must deploy remotely, since there is rarely someone present to do it manually. Deployment is usually a one-time action, so many cell arrays are basically designed using springs. Think of your umbrella that opens at the push of a button. Getting them going is fairly straight-forward, but the lack of air in space means there is little damping like we get here on Earth. The cell array springs out, hit the end and much of that deployment energy bounces back from the end. It keeps bouncing back and forth until is dissipate as (mostly) heat. That means that the array support mechanism must be strong enough to handle that shock without transmitting the shock back into the satellite, space station, etc. it is connected to. Transmitting that shock can rattle other things loose and cause other problems.",
"\nFifth, more physics. As the ISS transitions from full sun (in front, on sides of Earth) to darkness (in Earth’s shadow), the drastic heats differences cause the solar array materials to expand and cools. All the components, including the cells themselves as well as the support structure, must be able to tolerate the expansion and contraction caused by the heating and cooling. This motion is usually exhibited as vibration. You’re no doubt familiar with this as the creaking sounds old houses make in the middle of the night as they cool. These pops send shock waves down long panels, another factor the matrials and design must handle.",
"\nThese requirements, plus many more, require lots of custom design and test to make sure they don’t fail or worse, cause problems for other parts of the space station. "
] |
[
"From the wiki: ",
"",
"\" ",
"Gallium arsenide",
"-based solar cells are typically favored over ",
"crystalline silicon",
" (residential) because they have higher efficiency and degrade more slowly than silicon in the radiation present in space.\"",
"",
"Also the ISS array wouldn't have a protective glass as residential panels do."
] |
[
"I don’t know, but I’ll be sure to ask the next time I talk with some of the solar array folks I know.",
"\nThere’s a good chance the answer is ‘no’. The more efficient, modern semiconductor materials tend to be less reliable in high radiation environments. That may not apply to solar cells though. "
] |
[
"Isnt it strange that both Neptune and Jupiter have a single great storm on their surface?"
] |
[
false
] |
Is there some phenomenon or set of processes at work in a gas giant that would favour a single, long lived, localised storm rather than a series of smaller randomised ones (like our hurricanes)? Neptunes Great Dark Spot:
|
[
"mo' money mo' problems (solved)"
] |
[
"Some research was done about twenty years ago where some team actually spun a disk of fluid, maybe while also inducing a temperature gradient across it. I'm fairly sure I read about it in Scientific American, but I can't find it now.",
"At a significant range of speeds and temperature gradients, they observed a \"great red spot\" phenomenon where a single stable \"storm\" would consistently form about 50-60% on the way toward the edge of the disk from the center with a similar shape and behavior to the \"great spots\" seen on all the gas giants.",
"They couldn't really use it to confirm \"great spots\" would inevitably occur on gas giants, since they didn't have a way at the time to do the experiment using a sphere, but it was a very interesting result and the pictures were cool."
] |
[
"It's interesting. We don't yet know if it's strange. The difference being that they are (to the best of my knowledge) active areas of research. But we could find that the dynamics of gas giants somehow favors long-lived storm (so they wouldn't be strange)"
] |
[
"Are there any studies that have analyzed risk adverseness varying by location in the United States?"
] |
[
false
] |
[deleted]
|
[
"People in certain parts of the country are more accepting of certain risks, but it is difficult to compare these risks. ",
"For example people in hurricane prone regions are more accepting of hurricane risks while people in earthquake prone regions are more accepting of the earthquake risks. Similarly people in tornado prone regions are more accepting of tornado risks and people in crime ridden cities are more accepting of crime risk. ",
"These risks all have different probabilities and severity of impact, and it is difficult to quantify exactly. If are born into that region you may accept the risk so seem to have a higher risk tolerance that would not be acceptable for someone else from another part of the country, so they won't live there.",
"California and Florida have earthquakes and hurricanes, but they also have nice climates, so people still want to live there."
] |
[
"On mobile so I can't do a thorough search for a link, but I have heard references to a study that linked risk aversion to political identity and that varies with location so I wouldn't be surprised if they mention it deep in the paper. ",
"So if you're looking and not having any luck, try search terms about political views."
] |
[
"That's definitely a good idea but I do think you might run into issues trying to tease out who doesn't have insurance by choice vs. those who don't have it because no insurance company will offer it to them at an affordable price (if at all).",
"There are certain places, particularly flood areas, where insurance companies just won't write business for those homes. ",
"However, I think your idea would be very good for determining how risk adverse people are for something like car insurance."
] |
[
"Is there a relationship between being gay and being transsexual?"
] |
[
false
] |
According to this report the incidence of lesbian, gay and bisexual identity among transsexuals is higher than that of the cisgendered. Is there a similar pattern in regard to gender expression? Meaning that there is a statistical higher incidence of gender play among transsexuals? Would this not mean there is a biological relationship between these characteristics? What would we mean by a biological source for gender expression?
|
[
"As far as is well-established we know these important things on the subject (not all-inclusive, just data I am familiar with, obviously):",
"1) Gender identity is significantly programmed into a human being since before demonstrable conscious thought can take over. Baby boys have habits baby girls don't and vice versa. They have experimentally allowed boys and girls to choose preferences for colors and objects, without prior bias (no prior exposure or social-gender pressure), and yet differences emerge even before words do.",
"2) Homosexual tendencies are separate and distinct from transsexual tendencies. Homosexuals identify themselves with their actual gender overwhelmingly. Gay men do not want to be women (in large). They identify as men attracted to other men. Transsexual phenomena seem to occur as the result of a person being born a gender but feeling incorrectly assigned. They are men who feel like they should be women, for example. In most studies I've seen, this is obvious from a young age that their behavior is consistent with this \"incorrect\" gender assignment.",
"3) It seems to be largely a result of biological programming. If gender identity were not programmed, why do we find these wonderful patterns of gene expression, hormone levels, neuronal patterning distinct not only to hetersexual males and females, but in homosexual males as well? Why is it that the sexually dimorphic region of the brain in the hypothalamus is similarly sized in many gay men and women, but as many as three times larger in heteronormative males? Why do homosexual men have higher hormone levels than males or females? It seems that there is biological ramifications of gender and sexual identity. We still have plenty to find, but yet, we have good evidence there is plenty to find.",
"Where to look? The genetic code of course! If it expresses, it must be there, at least in part."
] |
[
"2) Homosexual tendencies are separate and distinct from transsexual tendencies. ",
"But the report I cited says otherwise. What is the gay or bi identity rate among transsexuals? Note I'm not saying it is a direct correlation. I'm saying there is a relationship. The two rates would need to be more similar. Although perhaps a trans person might be more likely to express gay orientation having broken one social barrier already. Though this would rely on a serious level of denial in the wider population."
] |
[
"The report you found suggests what exactly? I am saying homosexuality is independent of transexuality. That your gender identity is not dependent on who you find attractive, that the two are universally distinct. This is supported by the overwhelming numbers of homosexual individuals who feel correctly gender assigned, and the transexual individuals who may be heteronormative for their own gender identity or not. There is no evidence I have ever read or come across that suggests the rate of gender misassigned individuals have a statistically increased or decreased attraction to their original gender relative to other individuals of the gender with which they identify."
] |
[
"Why is it dysfunction and not disfunction?"
] |
[
false
] |
[deleted]
|
[
"It says this post has already received two comments but I don't see them, so I will add mine.",
"The difference between the dis- prefix and the dys- prefix is minute but significant nonetheless. ",
"\"Dis\" is Latin and means \"apart\" or \"opposite of\"; so working with your examples you have:",
"approve and disapprove - disapprove being the complete opposite of approve, so you could also say \"not approve\".",
"\"Dys\" on the other hand is Greek and means \"bad\", \"ill\" or \"abnormal\": again with your example you have:",
"function and dysfunction - the main difference here, however, is that dysfunction does not mean \"not function\", but more along the lines of \"not funtion properly\" or \"function abnormaly\".",
"Other examples are dyslexia and dyspnea. Dyslexia does not mean that you have an inability to read, just that there are difficulties processing and you have trouble reading. Similarly dyspnea isn't the absence of breathing but difficulty breathing/shortness of breath.",
"So in short: ",
"dis = separate/opposite",
"dys = abnormal/bad"
] |
[
"That is an interesting observation; from a strictly etymological viewpoint you would think it would have to be dysability seeing as disability implies a complete lack of ability as opposed to an impairment or limitations.",
"Here is what I found in the medical dictionary of the Free Dictionary",
":",
"\"dis- (dis), This Latin prefix denotes separation (disjunction), opposition (discord), or negation (disability). There is currently a tendency to extend its range of meanings to include those of Greek dys- (or to respell the Greek prefix dys- as dis-).",
"In two, apart; un-, not; very.\""
] |
[
"This all makes perfect sense, until you think about the word \"disability\"."
] |
[
"How are a non-planetary nebulas created?"
] |
[
false
] | null |
[
"In short, gas in galaxies cools until it is able to ",
"collapse",
" under it's own self-gravity. The reason it needs to cool is because thermal pressure support prevents counters the gravitational force. As the cloud starts to collapse under gravity, it heats up, so it actually needs to keep cooling.",
"Cooling mainly happens by basically happens by: atoms collide, converting some of their kinetic energy (i.e., heat) to internal energy by promoting electrons to higher energy states. These electrons will then emit light and go back to their original, lower energy level states, and the emitted light carries heat away from the system.",
"There are actually ",
"multiple cooling mechanisms",
"...the one that is dominant depends on the properties of the gas (mostly temperature). What I described above is \"collisional excitation\", which is generally the last stage of cooling before stars start forming."
] |
[
"Gravitational collapse. You’ll have to specify what you’re asking about in particular though.",
"‘Planetary nebula’ is a notoriously bad name, coined before we knew what they were and for some reason not ditched. They are actually ionized gas expelled highly evolved (meaning nearing the end of their lifecycles) stars."
] |
[
"Additionally, nebulae are shaped by the stars they produce. Once denser knots of dust and gas start to light up as stars, these stars produce radiation which ionizes and exerts pressure on the surrounding nebular material, carving out huge bubbles and voids. One of the best examples of this can be seen in the so-called \"",
"Pillars of Creation",
"\", part of the Eagle Nebula."
] |
[
"Evidence for Existence of Planet \"Vulcan\""
] |
[
false
] |
Since the newly discovered planet around Alpha Centauri B is probably far inside the goldilocks zone, this question occurred to me. Is the fact that many of the planets we find have very short orbital periods, is this circumstantial evidence of a planet "Vulcan" that was once inside the orbit of Mercury? UPDATE: I'm not saying that there is currently such a planet. I'm asking is this circumstantial evidence that such a planet once existed before spiralling into the sun.
|
[
"The reason we tend to find planets with short orbital periods is that our detection methods are biased towards them. Planets closer to the star exert a stronger gravitational pull, making it easier to detect the change in the star's velocity."
] |
[
"This bias is also present in the transit method of detecting planets, since you need multiple observations of transits to confirm detection, and a shorter orbital period means it will take less time to get those multiple observations."
] |
[
"No, it's not circumstantial evidence for this. First, why would it have spiraled in if it had existed? In fact, we have every reason to think, based on the laws of physics, that such a planet would not have spiraled in. Secondly, there are the points elsewhere in this thread about planetary detections being biased towards planets with small orbits, so we do not know what the actual relative likelihood of small orbit planets is. Third, the logic isn't sound. After all, is the fact that most planets in our Solar System have moons circumstantial evidence that Venus once had a moon? "
] |
[
"Is ATP transported between cells, or by the bloodstream? or at all?"
] |
[
false
] |
[deleted]
|
[
"A review from 1982 that looked at different studies on ATP said data suggests that ATP can cross the cell membrane.",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2595991/pdf/yjbm00108-0006.pdf",
"More recently there was a review of ATP release in blood vessels. ",
"https://academic.oup.com/cardiovascres/article/95/3/269/376915",
"\nLong story short, it appears ATP can be released/transported from different cell types. ",
"The specific mechanisms of how ATP is transported between cells seems to vary depending on cell-types but can include exocytosis, hemi-channels, ABC transporters, etc."
] |
[
"Additionally, ATP can be loaded and released in a vesicular mechanism from neurons.",
"\nSawada, K., Echigo, N., Juge, N., Miyaji, T., Otsuka, M., Omote, H., et al. (2008). Identification of a vesicular nucleotide transporter. Proc. Natl. Acad. Sci. U.S.A. 105, 5683–5686. "
] |
[
"ATP has a variety of roles as a signaling molecule that communicates the health of nearby cells among other things, which is most of what ",
"/u/Aelintari",
" 's second link is about. In this role the concentrations are tiny.",
"Large amounts of extracelluar ATP are both a cause and a result of inflammation, and are a harbinger of programmed cell death.",
"The extracellular release of ATP can be triggered by a wide range of stimuli such as mechanical stress, cell membrane damage, inflammation, hypoxia, and excitation of neural tissue, and by cell growth and death. Although the concentration of ATP extracellularly is 1000-fold lower compared with the intracellular space, it can still exert precise, albeit partially unknown, signaling function on the cell membrane",
"http://jasn.asnjournals.org/content/26/5/1007.full",
"Removing extracellular ATP with systemic apyrase treatment not only prevented IL-1β accumulation but also the production of inflammasome-independent cytokines such as TNF and IL-10. In addition, ATP removal also prevented systemic evidence of cellular disintegration, mitochondrial damage, apoptosis, intestinal barrier disruption and even mortality. ",
"https://www.nature.com/articles/cddis201470",
"As I learned it a long time ago, ATP belongs inside cells. If it is outside of cells in significant amounts that's one way of saying trouble.",
"If you just inject a lot of it directly into a human heart to see what happens,",
"Continuous ATP injection induced chest symptoms in 13 of the patients and second-degree atrioventricular block in one, but these complications disappeared immediately after the end of ATP infusion.",
"https://www.ncbi.nlm.nih.gov/pubmed/12381087",
"Every once in a while you find a study that makes you wonder. "
] |
[
"What is the minimium number of base pairs need to act as a \"primer\" for PCR?"
] |
[
false
] |
I'm having trouble with RT-PCR and can't seem to find my problem. I have to redesign primers because the previous Grad student used Taqman and I am using Sybr green. any tips for primer design would also help. Yes I googled this, yes I asked every professor, yes I looked in the text book.
|
[
"The minimum depends on a bunch of things. The smaller the primer, the lower annealing temperature (melting temp = Tm) you use. The lower temperature and the smaller the primer, the higher the probability for nonspecific binding and mis-priming. Usual primers are >18 bp to give a gap between annealing and extension temperature and to ensure specificity but for some applications they can be much shorter. For instance, random hexamer priming uses, well, 6 bp primers. ",
"For predesigned qPCR primers the ",
"Harvard Primerbank",
" website has always worked for me. Many companies offer predesigned qPCR primers (likely the same ones as the Harvard bank) with guarantees that they will work. ",
"IDT",
" would be one that we have used with success.",
"If you are free-form designing primers, I have had good luck using the ",
"MIT Primer3",
" web-app. \nThere are a number of general rules for primer design -- no inverted repeats within a primer >4 bp and between primer sets, GC content to target Tm, etc. Primer3 takes these into account (and gives you the option of straying from default settings). The ",
"source code",
" is freely available if you want to take things apart. ",
"For SyBr qPCR, I like to add a few rules: first, I like my Tm to be as close to 60C because most of the SyBr master mixes work with a combined annealing/extension step at 60C. You should check out your master mix specifically to be sure, though. I got some from an off brand manufacturer and it was using an old formulation with a separate extension at 72C -- correcting this fixed my low C[t]s. ",
"Additionally, if at all possible, if you can design a primer to span an exon/exon junction in the cDNA, this greatly increases your specificity by reducing priming from genomic contamination. Lastly, you may wish to BLAST your results against the cDNAs of the organism you are looking for to make sure there is no cross-homology on the 3' end of the primer that may lead to mispriming. For custom designed oligos, it may also be worthwhile to do a dissociation step in the qPCR to generate a melting curve. Analysis of this, coupled with running the product on an agarose gel, can reassure you that you are specifically priming the target of interest. A brief background can be found numerous places on the web, but check out ",
"page 21 here",
"."
] |
[
"This.",
"You may also find it helpful in switching from TaqMan to SyBr to change the positioning of the primers so that one of them crosses an exon-exon boundary in the mRNA/cDNA you are targeting. A lot of TaqMan users do this with the probe instead, so it's possible that you are amplifying genomic DNA in your sample using their primer design rules."
] |
[
"I'm not sure - maybe in human/mouse. I've always worked in non-model organisms, so I align genomic and cDNA and target primer design to the boundary region in ",
"primer3",
"."
] |
[
"I'm curious, how do we know about the position of a celestial object millions or billions of light years away ?"
] |
[
false
] | null |
[
"All of our distance measures start and are calibrated by parallax. The greatest parallax we can observe is when the Earth is at opposite ends of its orbit (observe a star’s position once, then again half a year later). The most accurate parallax measurements have been done by the Hipparcos mission and its follow-up, Gaia.",
"Most astronomical objects are too far to discern their distance from parallax, so astronomers use other distance measures as “standard candles” (an old term from astronomers trying to measure the brightness of a star/planet using an actual candle of known brightness). Examples of this are Cepheid variables and Type Ia supernova (“type one-A”). Like the old-fashioned candles these have a known true brightness (their “luminosity”) so we can compare that with their apparent brightness to get their distance.",
"But for distant galaxies the expansion of the universe itself is used to determine their distance. The further away the galaxy, the greater it is receding away from us (on average), and thus the greater its redshift."
] |
[
"Parallax is only useful for objects very very close to us within our own galaxy."
] |
[
"Parallax is only useful for objects very very close to us within our own galaxy."
] |
[
"How does an entire power grid fail, as in India right now or in the US and Canada in 2003?"
] |
[
false
] |
I was wondering what exactly causes the failure of an entire power grid, and why fixing it is not as simple as selectively switching off parts of the grid and hooking them up again iteratively. Are there pieces of equipment that are destroyed in the process?
|
[
"Nuclear engineer here (I work in a power plant).",
"There is a lot of talk about cascading failures. To understand why they are such an issue, you need to remember two things. First, heat generated in lines, transformers, breakers, is proportional to current drawn, and second, there is a very strict balance between how much \"Load\" is on the grid (how much power draw there is) and how much power is being generated on the grid. This balance is both in terms of VARs (imaginary power units) as well as VA (Volt-Amp, Apparent Power). ",
"So to better understand this, imagine the following situation. You have very little available electrical margin on your grid. Something happens (say a tree hits a line) and causes a fault on a cross connect between two regional areas. This line disconnects the two regions. One region had more power available than load, and the other region had more load than available generation. On region 1, the power stations will runback due to the load reject. If the load reject is severe enough, the power transient will cause the generator to go into a load reject trip to protect itself from the power transients on the grid. This would cause power stations on grid 1 to fail. These stations going down will cause the loads on grid 1 to pull in power from anywhere they can. Say they pull power in from another regional line, but that line now becomes overloaded. Overloading the line causes increased temperatures and leads to failures. These failures can cause other parts of the grid to become unbalanced, and so-on and so-forth. A well designed grid protection system will be able to detect this and stop it from crossing from major regions, but that's not always the case.",
"The real simple answer is you throw that load balance off, and when power margins are tight to begin with, the grid cannot handle that very well. ",
"As for why you can't \"just fix it\". Firstly, big power plants will need to go through their cooldown/heatup cycles. There may be damage caused as a result of the sudden load reject. In the case of nuclear power plants, there are very few plants that can handle a full load reject without a reactor scram, and recovering from a scram usually takes a few days to do equipment inspections and the like. Field equipment like lines, transformers, and switchgear, all need to be inspected and repaired. Finally, when the grid is brought back online, you ALWAYS have to maintain a balance between power and load, and as a result, depending on how bad the outage is, you need to bring it up very slowly and in a very controlled fashion to prevent sudden load transients from putting you back into a total blackout condition."
] |
[
"This is why I come to AskScience. An informative, full, yet ",
" answer. I knew that it was about load vs generation, but not the specifics, and this answer made perfect sense and gave me a sense of how it actually goes down. Upvotes for you!"
] |
[
"Generally when a failure of that magnitude happens it's several bad things happening all at once. Any large process or system, especially one THAT large, has \"catches\" in place so that if something causes failure in one part of the system, that failure won't happen in other parts of the system. However, if that system isn't properly maintained or the people working with it don't handle things the way they're supposed to, the whole system can go down. The Northeast power failure in 2003 happened the way it happened (according to official findings) due to a combination of cascading bad luck, bad maintenance practices, errors on the part of operators, and subsequent equipment failure because of all of the above."
] |
[
"When does Hooke's law break down?"
] |
[
false
] |
Hooke's law is the approximation that the spring force is linear with respect to displacement. However, that's just a first order approximation, and obviously, springs can become deformed (just ask all the clicky pens I've disassembled.) I was wondering, how true is this approximation for most springs.
|
[
"Good question!",
"Hooke's Law is simply a linear (1st order) approximation of the actual behavior of springs, and for most common conditions it holds true. That's what makes it useful. You could imagine that as we push any conditions to extreme, then the linear approximation will no longer hold. The most obvious example is if the displacement is too large, then the spring will permanently deform or break. And you can only compress the spring so much due to physical limits.",
"Source",
" - upper limits are called the limit of proportionality, and then the elastic limit.",
"We assume in Hooke's law that it does not have a dependence on other factors, but this is again an approximation. If temperature is too high then the spring material would soften or start melting, and if the temperature is too low then the material will become too brittle and will break. If the surrounding fluid is viscous, then there will be a significant damping term. "
] |
[
"Every spring (or other elastic material) has some maximum force after which it will break or become deformed. This force is given by:",
"F",
" = (Ed",
" (L-nd))/(16(1+ν)(D-d)",
" n)",
"where:",
"E is Young's modulus",
"d is the spring's wire's diameter",
"L is the spring's free length",
"n is the number of windings",
"ν is the Poisson ratio",
"D is the spring's outer diameter",
"Young's Modulus",
" is the proportion between stress and strain and is a modernized version of the k in Hooke's law.\n",
"The Poisson ratio",
" is, roughly, the ratio of the fraction of transverse expansion to the fraction of compression when an elastic material is compressed in one direction.",
"See ",
"http://www.pss-corp.com/pdf/coiling_01.pdf",
" for more.",
"Edit: formatting"
] |
[
"You can type all Greek letters by doing the html entity for them: &<letter>;. Like π is π. To capitalize just use the uppercase -- δ is δ but Δ is Δ."
] |
[
"Random vs. systematic error"
] |
[
false
] |
I understand the basic concepts of the two different types via wiki and other sources but I'm really struggling with some examples. like if you only take one measurement would it be considered random even though if you took multiple measurements it would be systematic? what kind of error would it be to make multiple dilutions using volumetric flasks instead of just one? really any help would be appreciated, I can give specific examples if that would help you help me. THANKS!
|
[
"For systematic error visualise a ruler that has somehow been miscalibrated so it starts on 0.1 instead of 0 or a set of scales that has been miscalibrated so it says -0.1 kg when nothing is on it.",
"For random error think of background noise that would make a microphone produce slightly higher or lower sounds than expected, or background radiation that varies."
] |
[
"Systematic errors are due to errors in measurement. They can be reduced by techniques such as ",
" equipment calibration, etc. ",
"Random errors are due to the random nature of the thing being measured. They can sometimes be reduced by techniques such as taking multiple measurements. ",
": Corrected statement about reduction to fix obvious fallacy."
] |
[
"Are you sure of what you're saying? Systematic errors, by definition, cannot be reduced by taking multiple measurements. "
] |
[
"What's the biggest change in a single species caused by evolution in recorded history?"
] |
[
false
] | null |
[
"Evolution generally requires tens of thousands of years to make noticeable progress; despite shaping all life on our planet, in broad strokes it is a fairly weak force. Thus, it takes far longer to see big change in populations than the length of time we've been writing things down. Not to mention, most ancient texts are just information about how much grain some random guy bought from some other random guy. Very little writing described the natural world in vivid detail until ",
" more recently in human history. ",
"Small changes are happening all the time, but they're generally so small as to be undetectable. That being said, we have seen some ",
"noticeable changes in species",
" over the last few hundred years, but these changes are almost always the result of human manipulation. Green anole lizards have adapted to be better climbers as a result of an invasive species entering their habitat (READ: human caused). Chinook salmon have also gotten smaller to avoid pressures from human fishers. Another example: we can take Trinidadian guppies from areas where one colour pattern is favourable and move them to an area where a different colour pattern is favourable. In a few generations, their offspring will have the second colour pattern even ",
" crossbreeding with the locally coloured fish. None of this is ",
" natural selection though, since none of these scenarios would occur were it not for human activity.",
"We can also see evolutionary changes on a jacked up time scale by looking at artificially bred species of plants and animals that humans have manipulated. Basically we make \"evolution\" happen faster by putting much more intense selection on certain traits than any trait would normally have in nature. This makes the shift in the species towards that trait occur faster. For example, this ",
"painting",
" shows how much we've changed watermelons since the renaissance. We can also see this kind of rapid change in the difference between, say, chihuahuas and wolves. Again, none of this is truly \"evolution\" since it only happens because of human interference."
] |
[
"None of this is really natural selection though, since none of these scenarios would occur were it not for human activity.",
"Ehh, I disagree. It's still natural selection if the selection is happening stochastically, as opposed to a person actively choosing what individuals get to contribute to the gene pool. The mechanisms involved are indistinguishable from those that would operate under any other change in the environment. Humans just happen to be the dominant reason why natural environments are changing at the moment, so such cases are especially easy to find and study.",
"Nowhere in the definition of the word \"evolution\" does it say that it can't be cause by human activity, either."
] |
[
"So a lot depends on how you define evolution here. Are you talking purely natural processes or do we include ourselves as an agent of evolution with our selective breeding and even mutation breeding in plants. ",
"All of our agricultural plants and animals have had many, many generations of Selective Breeding applied to them by us. But evolution is a 2nd stage process. 1st stage is Mutation. 2nd stage is successful propagation.",
"Now we run into two problems with mutations and animals. Firstly we can almost never be certain how long a particular mutation has existed. Secondly it's unethical to create new ones i.e. artificially induce mutations in animals through radiation or other means.",
"However looking at the plant kingdom there's been a number of Mutation breeding successes: ",
"https://en.wikipedia.org/wiki/Mutation_breeding#Notable_mutagen_varieties"
] |
[
"How is Titan able to retain an atmosphere?"
] |
[
false
] |
From what I’ve heard, Titan has a nitrogen atmosphere much taller than our own due to its lower gravity. It sounds like it has a pretty tenuous hold. Is this a permanent feature? How is it not stripped away by solar winds?
|
[
"It is far away from the Sun, not much solar wind, in addition it is protected by Saturn's magnetic field.",
"It is cold, the molecules have a low average velocity, they are unlikely to escape even with the lower escape velocity."
] |
[
"Plus something is replenishing it, in particular the methane. It's probably reasonable to assume some kind of cryovolcanic activity."
] |
[
"Why can't the same be said for Triton or Io then? Are they just too small?"
] |
[
"What exactly do muscle building steroids do and why are they bad for you?"
] |
[
false
] | null |
[
"Not true. at. all.",
"Anabolic steroids, as MaxSoftcore mentioned promote the synthesis of muscle tissue. They do not give you more energy, nor do they make you produce more testosterone. Anabolic steroids will artificially offset the bodies' natural homeostasis which results in a DOWN regulation of testosterone. Your body uses feedback loops to maintain normalized functionality of all bodily processes; steroid (anabolic in the O.P.'s case) balance is controlled by the hypothalamic-pituitary-testicular axis. Each of these glands produce hormones that interact with a gland downstream or upstream to up or down regulate production of the gland specific hormone. Too much of one hormone will result in the body attempting to shut down production by increasing or decreasing another hormone (in Testosterone's case GnRH, FSH and LH are down regulated when there is too much testosterone, and upregulated when there is too little). ",
"Introducing exogenous testosterone into the system will throw this system out of balance, GnRH, FSH and LH will drop to near zero, the testes will not receive any chemical message to produce testosterone and will cease to produce any at all. Testosterone is then broken down into other hormones, one of which is estradiol which is feminizing.",
"So, taking extra testosterone or other anabolic that mimics testosterone's effects causes an imbalance in the body's ability to maintain consistent positive and negative feedback loops; it can't shut off the influx of anabolic despite shutting down all natural production.",
"MaxSoftcore also made a point about the nature of delivery. IV hormones will avoid the liver on the first pass through the body, orally injested hormones will first pass through the liver and then into the body. The amount of enzyme within the liver capable of processing the oral steroids is limited and will be overwhelmed, resulting in toxic buildup of the first-pass steroid and shunting processing to other pathways that often result in toxic byproducts."
] |
[
"Not true. at. all.",
"Anabolic steroids, as MaxSoftcore mentioned promote the synthesis of muscle tissue. They do not give you more energy, nor do they make you produce more testosterone. Anabolic steroids will artificially offset the bodies' natural homeostasis which results in a DOWN regulation of testosterone. Your body uses feedback loops to maintain normalized functionality of all bodily processes; steroid (anabolic in the O.P.'s case) balance is controlled by the hypothalamic-pituitary-testicular axis. Each of these glands produce hormones that interact with a gland downstream or upstream to up or down regulate production of the gland specific hormone. Too much of one hormone will result in the body attempting to shut down production by increasing or decreasing another hormone (in Testosterone's case GnRH, FSH and LH are down regulated when there is too much testosterone, and upregulated when there is too little). ",
"Introducing exogenous testosterone into the system will throw this system out of balance, GnRH, FSH and LH will drop to near zero, the testes will not receive any chemical message to produce testosterone and will cease to produce any at all. Testosterone is then broken down into other hormones, one of which is estradiol which is feminizing.",
"So, taking extra testosterone or other anabolic that mimics testosterone's effects causes an imbalance in the body's ability to maintain consistent positive and negative feedback loops; it can't shut off the influx of anabolic despite shutting down all natural production.",
"MaxSoftcore also made a point about the nature of delivery. IV hormones will avoid the liver on the first pass through the body, orally injested hormones will first pass through the liver and then into the body. The amount of enzyme within the liver capable of processing the oral steroids is limited and will be overwhelmed, resulting in toxic buildup of the first-pass steroid and shunting processing to other pathways that often result in toxic byproducts."
] |
[
"So why is that bad for you. I mean I personally don't want to shrink my testicle but if someone else doesn't mind whats to stop them?"
] |
[
"Planets can have rings. Can stars have the same sort of rings?"
] |
[
false
] |
I don't think Sol's asteroid belt would count as a ring because, I assume, it's not nearly as dense as the rings around Saturn. Can a star even have a ring so dense as to be very visible? Thanks in advance!
|
[
"It is definitely possible. ",
"First, a solid celestial body would have to enter the star's sphere of gravitational influence. Then, it would have to pass through the Roche limit. That's the distance where the tidal forces will rip the object apart. ",
"If the object wasn't on a collision trajectory with the star before disentegration, then it will form a ring around the star."
] |
[
"Depends on the mass of the star. The Roche Limit is directly proportional to the mass of the star. ",
"But, if there are planets in the star system as well, I doubt the ring would last long."
] |
[
"If you don't think the asteroid belt counts as a ring (it ",
" the actual solar equivalent of having a ring), then not really. The reason it can't have a dense ring of small particles in very close proximity like Saturn is because of how stars are born. Once the accretion disc has built a body large enough to begin fusion, the star \"lights up\" and blows away the rest of the disc, except for things that are a combination of too far and too massive. This would be the planets and the asteroid belt."
] |
[
"Are the numbers of nucleotide pairs between healthy humans of the same gender the same?"
] |
[
false
] |
I read that the number of nucleotide pairs in each set of our chromosomes is around 3 billion. Each person has 2 sets (in most cells), each from one parent, so the total would be 6 billion nucleotide pairs. I think this number assumes that the chromosomes are unduplicated, otherwise the number would be double, but I'm not sure. Please correct any points above if I'm wrong. Assuming the above is correct, then I would have 6 billion something nucleotide pairs in all cells except germ cells. Does everyone else of my gender (M) who is healthy have the exact same number of nucleotide pairs as mine? My guess is it should also be 6 billion something, but I wonder if every healthy individual of my gender shares the exact same number. Please add extra useful information if possible. I'm not a trained biologist. I just get overly interested in the subject as I plan to get my genome sequenced. Thanks!
|
[
"The number would be close but not identical, it actually isn’t going to be identical between all of your cells either. You have telomeres at the ends of your chromosomes which are basically just extra DNA to make sure u don’t lose anything important. These can vary in length due to a number of reasons (and can actually be an indirect indicator of genome health).",
"As for other people they will also have different copies of genes which may not be the same length as yours, but they’ll be close. ",
"Then there are things like transposons (selfish genes) which replicate themselves within your genome (kinda like very privative viruses). Non-coding DNA will differ somewhat as well. ",
"So theres a bit of variation but overall yes, every “healthy” males has around the same amount of DNA, but not exactly the same."
] |
[
"No, the number of base pairs won't be exactly the same. Even in healthy individuals there are different numbers of what we call \"tandem repeats\" - these are small sequences of DNA that can be repeated varying numbers of times.",
"To illustrate, ",
"Fondon and Garner (2004)",
" found that varying numbers of tandem repeats were associated with different morphological features in 92 dog breeds. That is to say, the number of repeats in the genes they looked at correlated with the dogs' physical features. For example, the gene runx-2 has two repeating regions, and it was found that the longer the gene was (due to having more repeats in both regions) the more bent the dogs' faces looked."
] |
[
"yes, close but not the same number. The differing numbers of nucleotide pairs and the way their organized is what causes genetic diversity in humans and all other animal species."
] |
[
"The heatwave in India has killed over 2,000 people with temperatures between 40 & 48 C. Few years back a lethal london heatwave was ~32 C. I live in a country where it's not unusual to get to 52 degrees Celsius. Usually it's between 45 and it's a mild inconvenience. What's happening?"
] |
[
false
] | null |
[
"I bet you don't have to work outside for 10 or 12 hours in that heat though? And I bet you've got a top of the range air conditioning system? ",
"I doubt a lot of the poor in India can afford to just stay indoors under expensive air conditioning.",
"And in London - not many people have air conditioning. Not only that but they aren't used to the heat so they don't treat it with the respect that it deserves. And it doesn't take that much to kill old people..."
] |
[
"Humidity can be a huge factor as well.",
"If the air outside has low humidity your body can easily cool off."
] |
[
"Fair point. Just to be clear and as a response to your answer, I wasn't trying to belittle the issue or any of the deaths. Just curious as we play football in that heat sometimes and at the end we're thirsty and sweaty. But yes I do spend more time indoors than outdoors, but there are days when I'm exposed to the heat for a significant part of the day and at the end I'm uncomfortable and sticky and cranky a bit, but nowhere near death."
] |
[
"What is actually happening while I sleep? And why do I need it?"
] |
[
false
] |
I keep hearing about how the brain "repairs" itself or it "cleans itself up" and all sorts of stuff that sounds like mumbo-jumbo to me. I get that it probably is doing something like that but when someone says "repairs itself" I like to picture my brain physically healing and that just sounds silly. And when I hear cleaning itself up I picture fans blowing the dust out. What is going out, without getting too technical? I am not biology student but I'm no idea either. I love reading about things like physics around here because I can understand them without getting into the technical aspects as a non-science student. What happens during sleep, and why does my brain require me to sleep?
|
[
"I can only speak about certain specifics regarding the neuroscience of sleep:",
"You regenerate ATP during slow-wave sleep. Vital for neural functioning",
"You consolidate memories, probably! It's not entirely clear, but is very, very likely.",
"Without sleep (and because of ATP and a few other things), you'd literally go insane and then die."
] |
[
"But what about things like that sort of crazy sleeping pattern people can learn to have? The one where they break up their sleeps across the day and get much less sleep yet insist they are healthy while doing it? Something about maximizing the amount of REM sleep?",
"It can be nonsense.",
"Both REM and SWS sleep are critical. Without a good enough amount of both, you will suffer from some cognitive decline (nothing permanent, just less concentration, less focus, etc...).",
"People who do the 20 minute bursts are insane. It's not good. Polyphasics with 1-2 hours are, too. The reason they say they are \"fine\" is because it's easiest to wake up during REM and get back to whatever you do, cognitively speaking.",
"If someone insists they be awake for more than 16 hours a day (especially us graduate students!), that's fine. But try to get sleep in one shot. If you're in a crunch, it's OK to get a nap. But stick to what the body wants during normal lighting conditions (about 5-8 hours, varying with age, gender and individual differences).",
"Some neat studies have been to take away lighting (i.e., lighting cycles; constant levels of lighting) and see what kind of schedule people fall into. Curiously, it's about a 26 hour schedule. I think sleep stays around the 7-8 hour mark, though. I'll have to find the study.",
"Intro neuroscience text books do a good job at explaining it. I recommend Purves (though it's a graduate level book, I believe)."
] |
[
"I will see if I can find the book in a store and flip through it on a lunch break or something, though it's not really a subject that deeply interests me. It's just a question I can't get out of my head lately. "
] |
[
"Is the plane of Earth's rotation around the Sun parallel to the plane of the Sun's rotation around the center of the Milky Way?"
] |
[
false
] |
If not, what is the angle between them? If so, is it just a coincidence?
|
[
"In this ",
"image",
" the red line repesents the plane the planets orbit in, and the yellow line the milkyway, was made using ",
"stellarium",
"."
] |
[
"For the lazy, ",
"the ecliptic plane is off by about 60",
" to the galactic plane",
" (another way to phrase the OP's question)."
] |
[
"Is it strange that this is the case, ie, are most planetary systems' ecliptic planes not-so-close to the galactic plane? Also, does the sun rotate on an axis nearly perpendicular to the the solar system's ecliptic plane?"
] |
[
"Are extra spatial dimensions something we can accurately perceive with a trained mind?"
] |
[
false
] |
On that note, it seems the only way to begin to perceive these dimensions is by seeing wireframe shapes in constant rotation. I feel that there is a way to perceive these in our mind with extra mental senses, maybe artificial senses of time/space and seemingly impossibly connected points in space (like how worm holes are theorized in sci Fi movies) that we could conjure in our imaginations with enough focus and mental exercises. Is that how you high level physicists are trained to understand quantum physics and string theory?
|
[
"Yes, a trained mind can perceive spatial dimensions of any dimension! You just have to train yourself to look at these spaces through the lens of equations, rather than trying to perceive it with the mind's eye. ",
"The mind's eye is not good enough to really understand 3 dimensions, so adding more will just increase the inaccuracy. But we can look at them using equations and functions, and this lens is powerful enough to even understand infinite dimensional spaces and highly contorted, very noneuclidean spaces that couldn't even exist in our universe.",
"Linear Algebra",
" is the mathematical field where you learn to abandon the crutch of visualization and gain the ability to use the seemingly unlimited power of equations to understand very large spaces. But this only works with flat spaces. Once you no longer are burdened by the restrictions of visualization, you're free to use equation and functions to explore spaces impossible to visualize using ",
"Differential Geometry",
". It is with Differential Geometry, far removed from primitive visualizations, that people study and think about String Theory etc.",
"Learning to intuitively understand geometric objects using only equations is like going Super Sayan. It unlocks so much more mathematical power and flexibility than anyone who is trying to picture things."
] |
[
"I entirely agree with ",
"/u/functor7",
" that the best option is to turn to equations and other more abstract representations that scale better with increasing dimension. However...",
"There are other visualizations of higher-dimensional objects than just wireframes that are good to know, but most stop being good after 4-5D or so. For example, surfaces and curves in 4D can be more easily visualized when the fourth dimension is represented as ",
" or shading. An \"intersection\" where the points are different colors isn't really a 4D intersection at all, so it becomes easier to see how an extra dimension lets you move parts around each other. For example, you can undo any knot in 4D. There are also various forms of simplified diagrams that can tell you qualitative information about how a higher-dimensional object is glued together out of simpler pieces.",
"We can also \"suppress\" some dimensions if they're unimportant. The basic logic of a wormhole can be treated with 2D surfaces: if it's spherically symmetric then we can just make one dimension radial, another dimension time, and suppress the angular directions because they don't change anything. Then we get a 2D visual of most of the important features of a 4D object. In a similar vein we can try to represent the extension of concepts from 2D to 3D and then repeat it from 3D to 4D. This is good for analyzing higher dimensional analogues: how to build up hypercubes, hyperspheres, simplices, n-tori, etc.",
"You can also imagine high-dimensional spaces as ",
" of some physical system. A double pendulum traces has a torus as its state space, since it's parametrized by two independent angles. More complicated robotic arms, particle configurations, probabilistic setups, etc. can be equivalently phrased as some form of motion in a complicated high-dimensional geometry. We can work that analogy the other way to understand the geometry in terms of the familiar systems.",
"While equations are really the meat of our descriptions, and often necessary to even figure out visualization methods in the first place, it's still helpful to have various \"coping mechanisms\" like these that you can switch between as desired, to get intuition for different parts of the setup even if you can't visualize the coherent whole.",
"For resources on this stuff there's",
"G. Francis' ",
"pretty much any of J. Scott Carter's and Masahico Sato's books and papers (mostly on 4D surface knots, the papers are obviously technical but often have good visuals). I really recommend ",
" and ",
".",
"the beautiful 4D puzzle game ",
".",
"the ",
"dimensions",
" youtube series (",
" the \"imagining the 10th dimension\" video you'll probably stumble across, it's entirely nonsense)",
"The comic ",
"Here's Looking at Euclid",
". Very light walk through curved geometry. Not directly about higher dimensions, but goes into the differences between the interior and exterior views of a shape, which is important.",
"The contents of this ",
"MathOverflow thread",
"."
] |
[
"We define ordinary 3-and-lower-dimensional spaces using mathematics too, so one should not be so surprised that the same approach works for higher dimensions as well. :)"
] |
[
"Is it possible to know what sound is recorded by only looking at data graphs?"
] |
[
false
] |
[deleted]
|
[
"There's actually a word for what differentiates the sound of a piano from the sound of a bell (assuming they're the same note). It's called ",
". (pronounced TAM-BER)",
"http://en.wikipedia.org/wiki/Timbre"
] |
[
"It's pretty easy to tell a bell and a piano apart by visual examination. Bells are quite simple - basically a sine wave at a particular frequency, which decreases in intensity exponentially over time. A piano has a much more complicated waveform, due to additional resonances in the body of the instrument, the other strings, etc."
] |
[
"As a recording engineer, I can tell you that after looking at waveforms for hours, it becomes easy to see which instruments are which by the waveforms, even discerning which kick drums are which, etc. ",
"As for seeing a waveform without first hearing the sound to associate it, I suppose it could be done. Each instrument has a unique ",
"ASDR envelope",
" that would be even more useful than seeing the frequency of the wave. ",
"Voices have very dynamic envelopes, but always have a sloped attack and release. Something like a harpsichord (which has plucked and damped strings) has a very sudden attack and release. Distorted electric guitars have messy, complex waveforms, but if allowed to ring out past the decay of the attack, can result in simpler frequencies. ",
"Here's",
" a primer on harmonics and distortion."
] |
[
"I have learned that schizophrenia onset occurs very suddenly in approximately a person's twenties. Has there ever been a reported case of someone emerging from their condition just as rapidly, to go on and lead a completely normal life?"
] |
[
false
] |
[deleted]
|
[
"When interviewed carefully, families of schizophrenic patients are often able to describe vague and subtle changes that preceded the frank onset of psychosis by months or even years.",
"There are people who respond well to medication and can live fairly normal lives. Brief psychotic spells that do not recur might very well be diagnosed as ",
" rather than schizophrenia, though. If you're into papers ",
"here",
" is one that looks at long-term outcomes in patients with their first episode of psychosis. They found 42% had \"good outcomes.\""
] |
[
"Yes. To mention some other things, schizophrenia is a pretty hefty diagnosis, so I imagine there's quite a bit of caution whenever it's diagnosed. If brief psychotic disorder is too short, then you may want to consider looking into schizophreniform disorder--that requires symptoms of more than one month, but less than 6 (based on the DSM-IV)."
] |
[
"Fascinating. Thank you."
] |
[
"Why is Mitochondrial Eve dated to 150-170,000 years go?"
] |
[
false
] | null |
[
"We know how fast genetic changes occur. If we look at all mitochondrial dna and count the number of genetic differences between all we have cataloged, we can follow backwards to they would all effectively be the same. Depending on fastest estimates and slowest estimates of genetic drift, it's roughly 150k-170k years ago.",
"And basically this means that we only know of one female at that point. We can see nobody else beyond her because we have no mitochondria that show genetic differences that come out older than that. Either they all died out, or they were bred out of the population."
] |
[
"Because you are missing part of the definition. Mitochondrial Eve is defined as the most recent maternal common ancestor."
] |
[
"The title of \"Mitochondrial Eve\" is defined as the ",
" matrilineal common ancestor of all living humans. If we trace the ancestry of all living humans through their mother's side, all lineages pass through M.E. before they get to any generations further back, and once you're past M.E. all the lineages look identical."
] |
[
"Imagine a large air filled balloon tethered to the bottom of a body of water. It is completely submerged. There will be a tension on the tether. What mechanism could be used to turn this into useful energy and can you estimate how much energy per volume of air it might yield?"
] |
[
false
] |
Curious.
|
[
"The mere presence of tension cannot yield energy. No net work is being done on the water or the balloon or the tether. If you release the balloon so it rises to the surface, then you could use the movement of the tether to do work (have it turn a crank, say)."
] |
[
"I see. Thank you."
] |
[
"This is essentially one of the ways you can harness tidal energy, but it would require a changing tension caused by the tide. "
] |
[
"Electron Spin Question"
] |
[
false
] |
When the spin of an electron is mentioned, does that mean that the electron is actually spinning or is it a mathematical property?
|
[
"So what is spin? It's a quantized intrinsic internal angular momentum. Let's go word by word from last to first. ",
"Momentum is a measure of motion, the tendency for an object to maintain said motion. ",
"Angular momentum is a measure of motion around some axis. ",
"Internal angular momentum is like the distinction between the earth rotating on its own axis and orbiting the sun. In the rotational case, the axis passes through the object, and in the orbit case the axis of rotation is outside of the object.",
"Intrinsic Internal Angular Momentum means that it's a momentum that ",
" come about from the particle ",
" spinning. These are point particles, they can't really spin in any meaningful sense. This is why I went into the detail of the rotations of Lagrangians. Even though these are point particles and can't spin, when we rotate around them, there's a conserved quantity.",
"Quantized Intrinsic Internal Angular Momentum. Instead of taking on just ",
" value, there are only certain allowed ",
" of angular momentum. But what's a little different is that some particles can have half the \"basic\" unit of angular momentum. The physics of these half-spin particles is much different than those who have the whole unit, so it's ",
" the same as just saying that the basic unit should just be defined as half its value. In particular, the angular momenta can ",
" increase/decrease in whole units, not in half-steps. (ie -3/2, -1/2, 1/2, 3/2)."
] |
[
"It's not spinning in the classical way, like a top or a sphere or something. But you can measure a intrinsic spin angular momentum.",
"So, I wouldn't say that it's a mathematical property... more of a physical property that doesn't really have a good classical, everyday-experience analog."
] |
[
"The idea of of a spinning electron comes from the idea that if you have a loop of wire carrying a current, the charges carrying the current are spinning around the loop. When carrying a current, a loop generates a magnetic field.",
"Similarly an electron generates its own magnetic field and thus in the early days of quantum mechanics, it was intuitive to think of the electron as a spinning charge... much like a current loop. In reality, an electron does not actually spin but the name \"spin\" stuck."
] |
[
"Why do spinning hub caps appear to spin in the opposite direction?"
] |
[
false
] | null |
[
"This is called the ",
"wagon wheel illusion",
" and the wiki page is pretty good.",
"Edit: I should add that I am happy to answer additional or clarifying questions, but I would start on the wiki page."
] |
[
"The rolling shutter effect is an effect of the camera, not an illusion (i.e. percieved effect). The rolling shutter effect happens because the shutter closes in finite time and in that time the subject may have had time to move."
] |
[
"That's because it's not quite the whole story. See the ",
"top comment about the wagon-wheel effect",
", which is a perceptual phenomenon that is observed in real-life (i.e., not caused by the delivery medium, as this comment suggests) under continuous lighting conditions (i.e., not because of strobing). Therefore a correct and complete answer should address how the body receives and processes visual information - i.e., it's a lot more complicated, with various hypotheses, than the answer above makes it."
] |
[
"Is there a distance at which the interaction between the gravity fields of two black holes would cause one another to effectively 'break open' and allow matter and energy stored within them to escape the system?"
] |
[
false
] | null |
[
"All space within the event horizon points towards the center (or is a closed loop back towards it)",
"There is no such thing as out. If two particles could talk to each other inside a black hole it would go like this: ",
"1: which way is out?",
"2: what is out?",
"1: Where am I going if I go this way?",
"2: Towards the center...",
"1: (turns around) ok what about this way?",
"2: towards the center...",
"If you move, you are going towards the center... Move faster? OK go towards the center faster...",
"The problem isn't a lack of energy to escape, it is a lack of path. ",
"The mass of the back hole doesn't attract particles such that they cant overcome it (which is why there is a misconception that maybe a big explosion or something could overcome it etc...), it warps space so they have no choice..."
] |
[
"The real reason why nothing could escape from a black hole, ever, is that space-time around a black hole is knotted into itself. If you start from inside a black hole, and plot all trajectories around you, all of them end up in the center of the hole. ALL OF THEM. Even if you move in a \"straight line\". There is no trajectory that you could possibly draw that leads outside.",
"You're like an ant walking on the inside of a balloon - no matter how far you go, you're still inside. Only the black hole is even worse - no matter what you do, ",
". This is true even if you ignore the gravity pull - it remains true ",
". Just draw all trajectories with pen and paper (where the \"paper\" is space/time inside a BH), and you'll find that any trajectory, no matter what direction it starts, is only moving towards the center.",
"Don't even try to visualize it, it's impossible. Space/time inside a black hole is basically a broken mess.",
"I'm asking about a seriously high-velocity impact.",
"Velocity makes no difference. They just merge. They are not regular bodies anymore, but rather space/time knots with bizarre properties."
] |
[
"No. If two black holes approach closely enough they'll simply merge. A singularity can't be broken apart by any level of gravitational attraction, because the gravity at the singularity is effectively infinite."
] |
[
"Why can't we create underwater breathing technology"
] |
[
false
] |
by mimicking what happens in fish' gills? Edit: I mean by "extracting dissolved oxygen from water to stay submersed indefinitely." (thanks ragnarokrudolph)
|
[
"We are endothermic and have a high metabolic requirement--one that is further stressed when we are submerged. Animals with gills, on the other hand, are almost exclusively poikilothermic and require much less oxygen. For us, the challenge is getting enough oxygen from the water to sustain our metabolism."
] |
[
"Or really really large gills."
] |
[
"Or really really large gills."
] |
[
"Do the centers of galaxies revolve around anything?"
] |
[
false
] |
[deleted]
|
[
"Galaxies don't really revolve around black holes in their center, because they have comparatively small masses. Instead, if you take spiral galaxies as example, the disk revolves around the galactic nucleus, while the stars of the disk influence each other gravitationally. You don't really have Keplerian orbits in a spiral galaxy, except for objects within a particular stellar system. ",
". Does this go higher? ",
"We know that there are dwarf galaxies that orbit bigger galaxies, such as the Andromeda satellites or our magellanic clouds, but that seems uncummon for bigger galaxies. It isn't completely outruled, but the universe is still to young for non dwarf galaxies to have stable orbits around other galaxies, except for a few exceptions. "
] |
[
"It's true that the accretion disks of heavy active black holes can emit so much light that it significantly slow down further infalling, but that happens much earlier before the black hole has half the mass of the disk and has not directly to do with the orbits of the disk matter. ",
"Whether a black hole is active or inactive depends on of there is enough material in its vicinity, which is often (but not necessarily) the case after galaxy mergers. In that cas, you have many unstable orbits which can spiral down to the center and are consumed by the black hole."
] |
[
"It's true that the accretion disks of heavy active black holes can emit so much light that it significantly slow down further infalling, but that happens much earlier before the black hole has half the mass of the disk and has not directly to do with the orbits of the disk matter. ",
"Whether a black hole is active or inactive depends on of there is enough material in its vicinity, which is often (but not necessarily) the case after galaxy mergers. In that cas, you have many unstable orbits which can spiral down to the center and are consumed by the black hole."
] |
[
"Is all cell growth asexual reproduction?"
] |
[
false
] |
I know single-celled organisms can reproduce asexually, but when a cell in a multicellular organism divides is that considered asexual reproduction too? Bonus points for sources.
|
[
"Well, no.",
"\nAsexual reproduction refers to reproduction of an ",
" that involves no gametes.",
"\nReproducing a cell by mitosis within a multi-cellular organism isn't biological reproduction. ",
"I'm not sure which sort of sources you would want before you award the bonus points.",
"\n",
"But here are more sources than anyone would ever want to see.",
" ",
"And ",
"here",
" is ",
" Source. "
] |
[
"Asexual reproduction refers to reproduction of an organism that involves no gametes.",
"Isn't it more appropriate to state sexual reproduction requires exchange of genetic material? I've read somewhere that bacterial conjugation falls under the category of sexual reproduction while it doesn't deal with gametes."
] |
[
"Well, you're not ",
".",
"\nBut the bacterial conjugation is more like ",
" sexual reproduction.",
"\nIt's the exchange of genetic material, but there isn't a zygote produced from there. So it's not ",
" sexual reproduction; it's just kind of a grey area. ",
"(Edit: I think the bacterial conjugation would be far more accurately described as 'asexual mixis'; but I've never heard anyone call it that before.)"
] |
[
"Do different isotopes of elements have different proportions of allotropes?"
] |
[
false
] |
For example Sulfur 32 will have a majority of S8 allotropes because that's the most stable one. If neutron number changes the stability of the atom, will it also change the stability of the allotrope? (Say if I had a pure sample of Sulfur 34)
|
[
"There's three examples I know of. Naturally, these effects are pronounced for light elements where the additional neutrons are more proportionally significant. ",
"here",
"-Semiconductor guys studied isotope induced strain in single crystal silicon growth for wafers. Less strain equals fewer defects."
] |
[
"Different allotropes are more of an expression of temperature, pressure and chemical environment and express chemical (think of it as inter atomic) stability rather than a result of nuclear stability."
] |
[
"Indeed, allotropes are linked to the number of electrons in the atom, not the neutron number in the nucleus. \nOne example yet : a crystal of pure 241 Pu will be different from a crystal of 239Pu, because the latter decays via alpha emission with breaks apart the lattice structure, where as the 241Pu decays via beta emission, which more or less does nothing to the crystal structure.",
"This sould be the only way in which the isotopes number can influence on the cristalline structure of an element, as far as I can say. "
] |
[
"Are there any theories about, or is it likely that humans will eventually evolve into separate species?"
] |
[
false
] | null |
[
"So, the thing is that \"species\" are not really what you probably think they are. Most people have this concept of these neatly divided categories that things fall into because they have some intrinsic property. I.e. humans are humans because they have a certain quality of human-ness, chimpanzees all have some sort of chimpanzee-ness quality, and banana slugs all have some sort of....banana slug-ness.....quality, or something like that.",
"This obviously is an extreme example, and you may not actually hold such a belief (or maybe you do, I don't know), but before we start to talk about \"whether humans will eventually evolve into a separate species\", we need to be sure we understand what a species ",
".",
"A \"species\" is really just an artificial category we create to bin together organisms that all have a certain degree of genetic similarity to one another. We biologists have come up with all kinds of different ways to do this consistently (and you can read about them ",
"here",
", if interested), but we have yet to develop a single species concept that applies uniformly across all life forms (",
"). ",
"That's a bit of an academic digression, however, as you're only concerned with the species concept as it applies to humans, and by far the most widely applied species concept for large animals is the biological species concept, which states that two individuals who are able to mate and produce fertile offspring are members of the same species, while those who cannot (i.e. those who are reproductively isolated) are members of different species.",
"By this metric, all humans currently alive are undoubtedly of the same species. So I might reword your question to:",
"And the answer to this is probably yes (so long as our lineage doesn't go extinct first). Evolution at the genetic level never stops, and if you let it go long enough you will eventually accumulate enough differences such that reproduction would not be possible, at which point we would consider it a \"different species\". How long might it take? Well that's something we really have no way of knowing. A global catastrophe that wiped out the majority of the human population and exerted extremely strong selection pressures on those that remained could certainly make it happen pretty quickly, whereas if the human population remains the size it is, and as interconnected as it is, then it could take a really really really long time.",
"It's occurred to me that you might be interested not so much in this sort of technical, genetics stuff, but rather in whether humans might one day evolve to grow wings, or be 8 feet tall, or have pig-like snouts......or something. And the answer to this is that we really don't know, and can't predict (well, the example I gave are all extremely unlikely, I think, but the point is that we really can't predict what morphological changes there might be in the future, because we don't know what sort of selection pressures there might be).",
"I also noticed 0xDEAD ",
"addressing the issue of diverging into two separate species",
". I believe he is assuming that your question is about whether humans could split into two separate, coexisting species. And I completely agree with him that this seems incredibly unlikely. As long as we are able to travel freely around the globe, and people from geographically separated populations are thus able to mate with one another and ensure that the human population remains a single, if slightly subdivided, gene pool, then there is little to no chance that the species could split into two separate ones."
] |
[
"Until we develop space travel and colonize other planets/moons."
] |
[
"Agreed entirely. Never say never, but probably not terribly likely.",
"A population being physically isolated on an extraterrestrial body, that's probably the most likely way we get a new species."
] |
[
"How can a guitar amplifier pick up radio waves and play them?"
] |
[
false
] |
[deleted]
|
[
"Radio signals are at a much higher frequency than humans can hear, so an essential aspect of this is that the amplifier also forms a ",
"diode detector",
" that happens to be tuned close by a radio station and therefore is capable of demodulating it.",
"My explanation of this would be that the transistors inside the device act as diodes under certain circumstances, and then the characteristics of the circuit and ambient conditions combine to create an appropriate filter to allow the transistor to demodulate a particular range of AM radio stations, which then passes through the rest of the amplifier as described by Bucky. There aren't many AM stations left, so even with a relatively wideband filter you can pick up just one station clearly."
] |
[
"This isn't all that uncommon. It used to happen to me quite a lot when I had my old Marshall JMP out on tour. It has something to do with the broadcast being picked up in the internal wiring of the amplifier. Think of the wires inside as an antenna. After the antenna picks up the signal, the amp simply does it's job. It makes the signal more powerful and sends it to the speaker. "
] |
[
"To reduce this phenomena add tin foil to the back side of the amp. When I'm on tour and have some sort of RF interference this is what we do to cut down on it "
] |
[
"At what point will the our eyes stop recognizing higher definition videos?"
] |
[
false
] |
For the sake of clarity, lets say the video is on a 50 inch monitor. We are currently at 1080p right now and I truly dont know what anything higher would look like.
|
[
"It's a function of screen size and distance from the screen."
] |
[
"Not exactly on the last statement.",
"24\" - mostly 1920x1080 and 1920x1200 ",
"30\" - 2560x1440 and 2560x1600",
"27\" - any of above, not sure which one is the most widespread for this size",
"As to OP's question - doubling the pixel density on monitor, f.e. having 3840x2400 24\" monitor would do wonders to the clarity of the text you read on it. Just compare text on the monitor and in the book or magazine."
] |
[
"this video",
" is in 4k resolution, which is 4096 x 3072. ",
"this wiki page",
" touches on some potential applications for much higher resolutoins. Remember, both the screens and the source material would go up in resolution, and would blend in to our \"real life\" environment more and more as they did so.",
"1080p is really quite a low resolution, 24\", 27\", and 30\" monitors all use higher resolutions."
] |
[
"How do fiber optic cables work?"
] |
[
false
] |
So I was wondering how internet connections work and send information? So basically the coax cable (copper) used to be the main broadband medium, but companies like AT&T and Verizon have upgraded to fiber optics. How does light transfer information through a fiber optic cable? Does Comcast also have fiber optics?
|
[
"The data is usually encoded using intensity modulation...making the light brighter/dimmer, very rapidly. A light source, such as an LED, is rapidly modulated between bright and dim; the light travels down the fiber until it reaches its destination (or a repeater); a detector turns the light back into an electrical signal. ",
"It isn't quite as simple as \"low\"=0/\"bright\"=1; a more complex encoding is used to help reduce the chance of receive errors and maintain synchronization between sender and receiver. A single fiber can also carry multiple wavelengths (colors) simultaneously to increase bandwidth. ",
"As internet traffic from various low-bandwidth channels comes together, it is aggregated and sent along higher-bandwidth channels, using different protocols. This typically happens multiple times before it makes it to the internet backbone. Of course, multiple points the reverse then must also happen...the frames must be dismantled and re-assembled to send the packets to the right locations. ",
"Comcast surely has fiber optics in its internal network and connection to the internet, and in routing of traffic to/from neighborhoods. Whether or not they have it available to the customers' residences is going to vary by location; you should contact them if you want to know for your area. "
] |
[
"You forget to mention the most important part. An optical fiber guides light down its axis by continually reflecting the light off the inside of the walls of its core via total internal reflection. Basically, by having a core with a higher index of refraction than that of the surrounding cladding layer, the light is internally reflected and guided near losslessly. There is some loss though, so that signal weakens after traveling a large distance and must be amplified every so often to send it very long distances. There is also the problem of dispersion, where the index of refraction of the fiber is slightly different for different wavelengths of light traveling through. This causes the different wavelength components of the waveform to travel at different speeds, causing the waveform to spread out and deform as it travels. If the waveform deforms too much, the information coded in the waveform is lost. Clever design must be used to minimize and deal with dispersion."
] |
[
"Yes, it is not only theoretically possible, it is a fundamental building block of almost every network in existence."
] |
[
"About the origin and nature of STDs"
] |
[
false
] |
I can't really narrow this question down to specific diseases, so please bear with me... If everyone on the planet currently infected with an STD be at viral or bacterial vanished, would the threat of gonorrhea, syph, hiv, etc. be gone as well? If not, how would one go about getting infected with them if there are no more infected partners to have sex with? I realize there is probably a big difference in regards to viruses and bacteria, so if anybody has an answer, please distinguish between the answers for the two.
|
[
"If everyone on the planet currently infected with an STD be at viral or bacterial vanished, would the threat of gonorrhea, syph, hiv, etc. be gone as well?",
"It's not an easy question to answer, and it depends on the nature of each individual STD, the mechanism of transfer, and where they originated. The one I know the most about is HIV, so I will discuss the prospect regarding it specifically.",
"So, what do we know about HIV? It's a virus (obviously - it's in the name), and it's of relatively recent origin (estimated somewhere in the last century). We have managed to trace its evolution and it turns out that it most likely was transferred to humans via apes. Interestingly, this has happened no less than 5 times with different types and subtypes of the virus. The 2 major types are HIV-1 and HIV-2. Within HIV-1 there's at least 4 subtypes designated M (Main), O (Other), N (Not M or O) and P. The origin of HIV-2 is most likely transfers from sooty mangabey monkeys, while HIV-1 M and N are most likely from independent transfers from chimpanzees, O and P independent transfer from gorillas. The likely locations of all of these are in west Africa where humans and apes come into close contact (probably in the form of eating bushmeat, but there's room to hypothesise for those with a dirty mind!). ",
"So, if everyone with HIV disappeared, would it re-emerge? That depends on the practices that led to it arriving in the first place. If people stopped eating bushmeat or any other contact with apes that carry the simian form of the virus (SIV), then probably. It was probably the close genetic relationship between apes and humans that allowed the transfer, but it's always possible (though less likely) that we could get it or something similar again from another source (e.g. feline immunodeficiency virus from cats) ",
"As for other STDs, it depends on each individual story of how and why it is in humans. Humans haven't been around forever, and things like viruses or bacteria don't just magically appear out of nowhere. They either developed with us, or developed in another organism and then jumped to humans. In a case of everyone disappearing who had an STD that developed over millennia in humans, it would be unlikely to arise again. If it's a more recent animal transfer, then it would be much more likely to reappear, like how HIV has several independent transmissions. ",
"New STDs will undoubtedly arise in the future, just as HIV did last century. It could be a case of a human disease evolving a new transmission pathway through sexual contact or a new transmission of an animal infection to humans that exploits sexual contact. There are many, many possibilities, so all we can really do is hypothesise and study the diseases around today."
] |
[
"Evolution by natural selection. Viruses can evolve faster than almost any other life(?) form, due to their rapid reproduction/multiplication and error-prone DNA-related proteins that are responsible for copying the viruses genetic code."
] |
[
"Ah, I see. By niche you mean the behavioural patterns in humans caused by there being no viruses. I thought you were suggesting that viruses would change their strategy because there's less \"competition\" in the STI world or something, which wouldn't make sense."
] |
[
"Why did the inner solar system's material accrete in to larger bodies rather than grind itself down to dust?"
] |
[
false
] |
Is this material still warm and 'tacky' enough to stick together? Or is there enough heat from impact that rocky material sticks together more than it breaks apart? Or do I have a total misconception about this process?
|
[
"There is, in fact, a wide gap in our understanding of how accretion works. It's very easy to stick molecule sized particles together, as they tend to stick electrostatically. It's also easy to get big particles to stick together due to gravity.",
"But when you get centimetre sized particles, they find it very hard to stick together, and they tend to either bounce off or break each other apart. There's a lot of research into ways that they could stick together, but it has to be done in zero-g (drop towers or parabolic flights (or possibly eventually the ISS)) as even very weak gravity is enough to make shooting particles together very very difficult (they just miss)."
] |
[
"Water sticks together due its surface tension (electrostatics), not gravity.",
"At small scales the kinetic energy of particles is enough to make them not stick together by gravity. You only get gravity starting to make stuff 'clump' together when its large enough."
] |
[
"Water sticks together due its surface tension (electrostatics), not gravity.",
"At small scales the kinetic energy of particles is enough to make them not stick together by gravity. You only get gravity starting to make stuff 'clump' together when its large enough."
] |
[
"Will there be an eventual limit to physical/athletic world records? It seems every year we run/pitch/jump/swim a mph/second faster/ foot higher. Will humans continue to become bigger stronger faster or will the body hit a point where it becomes physiologically impossible?"
] |
[
false
] | null |
[
"Please everyone this is not the place for speculation or answers that start with \"I'm not a scientist but. .. \" or \" I heard somewhere that. . . \". This is asking for certain biological and biomechanical factors that may limit mobility. All answers should be sourced and scientific. "
] |
[
"It seems that we're within reach of a 2-hour marathon but won't be able to push much beyond that. ",
"http://news.discovery.com/adventure/extreme-sports/two-hour-marathon-111017.htm"
] |
[
"Worth noting that the improvements have been getting smaller and smaller over time. There was almost as much improvement in marathon times in the fifteen years 1905-1920 as there has been 1920-present. ",
"Speeds in cycling have actually dropped in recent years, likely due to more effective anti-doping controls. Some of these 'records' remain as records however as drug use was never proven at the time. ",
"It's very possible that the likes of Marco Pantani's 1997 record 37m35s for climbing Alpe D'Huez will never be beaten for this very reason (most sub-40m times and even a good few over were probably pharmaceutically assisted, who knows what the drug-free record actually is.)"
] |
[
"If we can calculate/know the speed and direction of particles in the universe, couldn't we theoretically know the future? What is the counter argument for a deterministic view of the universe?"
] |
[
false
] |
This plays into whether we actually have any willpower (i.e. can actually make choices). I know one theory is that quantum events in our brains could be the source of our (potentially perceived) willpower, but to me it still seems possible for choice to remain just an illusion. I know this may count as a philosophy question as well, but I'd love to hear the science side first.
|
[
"We can't know both the speed and position of a particle with arbitrary accuracy. Heisenbergs uncertainty principle, which is one of the cornerstones of quantum mechanics, states that the more accurate our measurement of the position of a particle, the less accurate its speed measurement will be and vice versa.",
"Ultimately, that's a fairly hard restriction in simulating our universe.",
"Furthermore, there's a more philosophical aspect to it. Suppose we could simulate our universe on some large computer. We can then see the results and potentially take actions based on what we learn. However, the simulation has to take into account this as well, in order for it to be accurate. The computer that runs the simulation has to include itself running the simulation in its simulation."
] |
[
"Quantum mechanics makes it impossible to predict some outcomes. Depending on your how you interpret quantum mechanics, this could either be because (a) the universe is fundamentally non-deterministic, (b) it is deterministic but some \"hidden variables\" can't be measured, so we can't predict the outcomes, or (c) the multiverse is deterministic but we are only get to experience one branch of the multiverse at a time in our minds. These different interpretations carry lots of interesting philosophical implications but all of them are equally good at matching any empirical observation we make about the world.",
"As far as free will goes, I would emphasize that removing determinism doesn't really solve anything. When you make one choice instead of the other, it is either because of (1) your internal state evolving in a deterministic way to some inputs or (2) your internal state plus a few random quantum mechanical coin flips produced the outcome. Being dependent on the coin flips might make you less predictable, but it isn't giving you any real freedom that wasn't there before.",
"My feeling on the free will side of things is that there is no problem with saying that someone made a hard choice because they had more willpower or moral character than someone else. These are just shorthand ways of trying to sum up the very complex internal states of a human brain. But getting to the point where you have a brain that we would characterize as having lots of willpower or whatever had to be the result of events in the past, like the genetics you inherited, or your upbringing, or maybe even a few random fluctuations due to quantum mechanics. If you feel the fact that you weren't ultimately in control of your history means you don't have free will now, then you don't. But if you define free will in terms of whether your current internal states can influence the world around you, then that is compatible with physics as we know it."
] |
[
"I think, even more important than Rannasha's point, is that the Heisenberg uncertainty principle doesn't just rely on ",
" of particles. It (at face value) is inherent to particles themselves; if a particle has a well-defined position, ",
", it cannot have a well-defined momentum. Among other paired particle characteristics.",
"Secondly, there are some things in the universe that at least appear to be entirely random. For example, when a radioactive particle will decay. It doesn't matter if you model that particle perfectly in every respect; you won't be able to determine when decay will occur, only the chance of decay at any given moment.",
"There are some models of physics that attempt to pull in determinism for things like radioactive decay, but generally they have been wrought with issues (which one may or may not consider a strike against them) and are limited by Bell's Theorem so that aside from exceptions like Many Worlds, you have to accept non-local hidden variables, which many people consider philosophically difficult. Bohm's model is one of these deterministic approaches. In the classical model of quantum mechanics, events are truly random and you can't perfectly calculate the future even with perfect knowledge of the present.",
"To the philosophical point of your question about free will from the perspective of science, it might be worth reading ",
"this paper, The Ghost in the Quantum Turing Machine",
", which does the best job I've come across of addressing free will from a hard-physics angle. It won't answer your question; it only tackles one aspect of it, but it does attempt to constrain the sort of approach to free will that is compatible with physics as we understand it."
] |
[
"Why do things like glue, sticky notes and other adhesives like that become \"unsticky\" when it's cold?"
] |
[
false
] |
[deleted]
|
[
"Most glues conform to the shape of whatever they are bonding to. If there are microscopic ridges on a surface the glue would fill them This increases surface area for chemical bonding and attraction which is the primary way the glue sticks.",
"When its cold the glue can contract and it may not conform to the surface anymore if it contracts at a different rate than the material its bonded to. Also the glue will harden and may not be able yield when the material its bonded to puts a stress on it or vice versa. "
] |
[
"Exactly what I was looking for, the chemistry of it. Thanks! "
] |
[
"The glue gets harder, therefore less sticky. Similar to hardened glue"
] |
[
"My 3 yr old wants to know why the center of strawberries (the pith?) sometimes have empty space inside"
] |
[
false
] | null |
[
"The hollow centers are caused by the strawberries growing too fast from either too much water or too much fertilizer. AKA it's like a gap between your teeth that happens when they spread too fast, wild strawberries don't get gaps as much but farm grown ones that are given growth boosters tend to get a gap."
] |
[
"It is caused by fast growth rate, hence why smaller ones don’t always have that hollow. Technically, all strawberries have it, because the strawberry fruit is actually a modified stem/flower, which is hollow. However, on smaller strawberries the hollow is too small to see because the more natural smaller strawberries are given the time to fully mature and fill in the hollow as they grow"
] |
[
"Ok. Let's be clear here. This makes it sound like slightly less fruity. What we are talking about is, properly ripened strawberries are a ruby, borderline translucent color throughout. Like a gem. Their flavor tastes like you extracted the strawberry essence from an entire box of grocery store strawberries and compressed it into one strawberry. It's actually ludicrous how different these two are. It is an entirely different fruit. ",
"Proper strawberries are to early picked strawberries as apples are to apple jacks, if the apple jacks actually did taste like apple. They don't but you get the idea.",
"Jam made from these strawberries because let's be honest if you go to a u-pick and get some. You aren't coming home with a pint. Anyway if you make jam with them it makes regular strawberry jam taste like a sugary confection.",
"Look up in your state where they have strawberry fields and go to them. I am in Michigan and they are open in the spring."
] |
[
"Eridanus Supervoid, how is it that something that large can be completely empty?"
] |
[
false
] |
Also, is it possible for galaxies to move inside the supervoid and fill it out?
|
[
"It's not completely empty. There's still stuff there, just a lot less than the average of the universe. One principle of cosmology is the idea that at very large distances, the universe \"looks the same\" in any direction. Imagine you have a jar. You carefully lay a layer of blue marbles on the bottom, then a layer of yellow on the blue, and white on the yellow. Now you shake the jar up. Things should get pretty mixed up. It's still ",
" to find areas in the jar where you have a bunch of blue marbles and nothing else, but it's just not very likely. This is something similar. It's odd to have a void that big, but not ",
" based on our current models of how the universe came about.",
"Yes, there is nothing technically preventing anything from filling that void, but since matter has gravity associated with it, it means things that are clumped together exert more gravity towards each other and that makes them clump even more. It's basically not likely that anything will ever fill that void."
] |
[
"a lot less being about ~20% less in this case, so there is still quite a lot of 'stuff' there"
] |
[
"Thank you very much! That actually clears up a few questions I had :)"
] |
[
"Why is it so hard to remember our dreams but not our memories?"
] |
[
false
] | null |
[
"The basic idea is based on the number of neurological pathways that are activated. This can be observed in a few different ways.",
"\nFirst and foremost, most memories that we do tend to remember are associated with strong stimuli, whether that be a smell, taste, pleasure, pain, etc. This also explains why we have an easier time remembering vivid dreams and nightmares.",
"\nA second way to explain differences in neurological connections has to do with your state when you are thinking of these things. Often times you wake up and move on with your day before really thinking much about your dream. This is contrasted by memories in the sense that you most likely would be wide awake when the memorable instance occurred.",
"\nTo expand on the basic principle, it helps me to put in in terms of the way we learn/memorize things. The first time you do something, you're just creating certain neurological pathways. Through repetition, previous pathways are solidified and additional pathways are created, leaded to enhanced ability to recall the information. You are essentially moving items in \"short-term\" memory to \"long-term\" memory. ",
" Greater activation of neurological pathways with strong stimuli, we don't (usually) take time to think about our dreams. This is similar to how we learn/memorize new information."
] |
[
"Sure, let me try to find one. This post was based on knowledge as a biology major currently pursuing a master's degree in exercise physiology."
] |
[
"Sure, let me try to find one. This post was based on knowledge as a biology major currently pursuing a master's degree in exercise physiology."
] |
[
"Is the amount of virus material you recieve important in the course and severity of the disease?"
] |
[
false
] |
I can image with 1 virus particles you only infect one cell and it takes a while yo infect and thus kill other cells. in that tima the body can start working on an immune response. With recieving millions of virus particles those infect millions of cells that will die from reproducing the virus and also will be ahead of any immune response. Could this be explaining some of the health care and often younger cases dying?
|
[
"Yes. Like anything exponential, the initial amount and the rate of growth matter. So a small amount is better than a large amount. ",
"For a small amount of virus, the immune system also has more time to develop antibodies."
] |
[
"Yeah using the word Chinese flu isn't really convincing me being knowledgeable. First of all it has nothing to do with influenza viruses. Second it did originate from China but the tragic epidemic unfolding in the US has shown China did eventually find a good policy in fighting the epidemic and much of the US government has shown little of being a developed country at all."
] |
[
"It's apparent that you are pushing the name for political reasons as no one in the scientific/health community names viruses after places. ",
"It's also apparent that you don't have any background in this topic and are here to push your narrative or stir the pot. This sub is for science not your ideology."
] |
[
"If sound travels best through solids, why is it harder to hear things when there is a wall between?"
] |
[
false
] |
[deleted]
|
[
"Sound travels nicely through the wall. It doesn't like the barrier between the wall and the air. It doesn't like to change from wall to air. Some is lost to reflection, etc.",
"Put your ear up to the wall, pressed against, and knock on the wall."
] |
[
"To elaborate, you get reflections whenever there is a change in the stiffness (a.k.a. impedance). Some of the energy continues on, a small amount is lost to heat, and some is reflected back.",
"Similar effects happen if you are underwater. It is easy to hear sounds that came from underwater. You can hear the buzz of a motorboat for quite a distance. Scuba diver buddies can get the other's attention by clinking two metal object together, or pounding fist to palm; the sound is very clear. But if someone above water tries to call, you're probably not going to hear them.",
"For residential walls it is complicated by the structure. They are mostly air inside so the most effective transmission happens through the wall stud. When building a duplex they build it with double studs so that one set is coupled to each interior wall."
] |
[
"Sound travels best through homogeneous solids. Most walls, at least \"normal\" residential walls in the US (i.e. the only kind I know much about) are a mixture of wood studs, gypsum sheetrock, and possibly some additional form of insulation. The variation in consistency tends to cause lots of deflection in all directions as well as absorb the pressure waves with the air pockets between the bits of solid. ",
"The Acoustical Society of America has done a fair amount of research on this topic, e.g. ",
"http://scitation.aip.org/content/asa/journal/jasa/92/4/10.1121/1.404482"
] |
[
"Are viruses alive?"
] |
[
false
] | null |
[
"Viruses basically mark the border between what is clearly alive and clearly isn't. ",
"You will not be able to get a clear yes or no answer on this as arguments against viruses being alive are undermined by the accepted aliveness of symbiotic animals. ",
"Ex. A virus does not really independently have there own metabolism, cannot survive independently, and do not respond to changes in the environment... except for while in a host cell.",
"TL;DR - Viruses are classic example of yes/no scientific discussions and the limit of the consensus on life/notlife "
] |
[
"This issue is debated, and you won't find a single answer everyone agrees on. This is because the rules for what characteristics define life aren't agreed upon.",
"The more traditionally minded people (for lack of a better label) define life by meeting requirements like cellular structure, growth, metabolism, adaptation, response to stimuli, and reproduction. While viruses reproduce, respond to stimuli (docking to a cell), they aren't made of cells, don't really grow (unless their initial construction counts as growth), don't metabolize (arguably), etc. ",
"So they fail traditional criteria… but are the criteria justified to begin with? That's where the real debate is.",
"A person opposed to the aforementioned rules would argue something like “",
"”. Should life require cells? That may be a really arbitrary rule. Consider this thought experiment:",
"Optimus Prime and the transformers arrive on Earth. A small pink critter yells to them “",
"”. Grimlock says “",
"”, but then Optimus stops him and says “",
"”. Ironhide then argues “",
"”. Optimus is forced to concede to Ironhides unassailable logic. And then Grimlock steps on Spike.",
"To me, it seems pretty darn arbitrary to say life must be made of a particular structure just because we're familiar or comfortable with it, right? Why would cells, or nano-machines, or any other building block be particularly important? If a robot is able to eat material, and make more of themselves, why can't we say that's alive?",
"And then there's the whole must-reproduce-on-its-own requirement. Viruses can't make more viruses without hijacking something like a cell to manufacture them. Arguably such a requirement would mean things like ",
"this",
" aren't alive. Yet intuitively I think most people would expect such a thing to be considered alive.",
"The lesson to take away from this is that the traditional rules for defining what is or isn't alive are in fact not rules, but rather heuristics. And like any heuristic, it may work sufficiently well for 99% of the things you analyze, but will yield poor or debatable results on edge-cases. And this heuristic was designed based on commonly observed things here on Earth, not because of any particularly natural or fundamental rules.",
"In attempting to do away with arbitrary criteria, some people have other alternate definitions for life, ",
"based on Entropy",
", which tends to be virus-inclusive."
] |
[
"Humans can't survive without consuming other living things, so why should viruses be defined based on what they eat?"
] |
[
"Why do wounds inside the mouth heal more quickly than on other parts of the body? Does this mean spitting on a wound will quicken the healing process?"
] |
[
false
] | null |
[
"A few things factor into it:",
"The epithelium (outer layer of cells) inside the mouth has a much higher rate of turnover than the skin covering your body. That is, the cells at the surface die and slough off much quicker, and are replaced more rapidly by the dividing cells underneath. ",
"The epithelium inside the mouth is mostly known as \"non-keratinized,\" compared to the epithelium of your skin, which is \"keratinized.\" The difference can be seen in this picture ( ",
"http://www.anatomyatlases.org/MicroscopicAnatomy/Images/Plate22.jpg",
" ), although bear in mind the image on the left side is from the esophagus, which, while similar, is not entirely the same in structure as the mouth. You can see at the surface of the skin on the right, there is a thick layer of acellular material - this is keratin (the same material that makes up your fingernails), and its the remnants of dead epithelial cells, which solidified to form that layer upon their death rather than immediately sloughing off. Because keratin is acellular (i.e., dead), it can only be replaced by cells from immediately underneath it, while in the event of an injury deep into the cellular layer of the mucosal epithelium, cells are able to migrate laterally to help \"fill the hole,\" so to speak. This phenomenon is depicted in this picture ( ",
"http://www.burnsurgery.org/Modules/BurnWound/rationale/images/fig8.gif",
" ), where live epithelial cells from hair follicles migrate laterally to \"fill in the hole\" left by a severe burn. ",
"The deeper layers of the oral mucosa have a much richer blood supply than the skin, which means that the inflammatory mileau and repair elements are much more readily accessible to an injury in the mouth compared to the skin.",
"Spitting on a cut will not help quicken the healing process - your mouth is colonized with a broad host of aerobic and anaerobic bacteria, and spitting on a wound will increase the chance that it becomes infected."
] |
[
"Last line:",
"Therefore, licking would be a way of wiping off pathogens, useful if clean water is not available to the animal or person."
] |
[
"Although spitting may provide more bacteria, ",
" may actually help to remove other larger infective bodies.",
"From the Wikipedia:",
"A common belief is that saliva contained in the mouth has natural disinfectants, which leads people to believe it is beneficial to \"lick their wounds\". Researchers at the University of Florida at Gainesville have discovered a protein called nerve growth factor (NGF) in the saliva of mice. Wounds doused with NGF healed twice as fast as untreated and unlicked wounds; therefore, saliva can help to heal wounds in some species. NGF has not been found in human saliva; however, researchers find human saliva contains such antibacterial agents as secretory IgA, lactoferrin, lysozyme and peroxidase.[6] It has not been shown that human licking of wounds disinfects them, but licking is likely to help clean the wound by removing larger contaminants such as dirt and may help to directly remove infective bodies by brushing them away. Therefore, licking would be a way of wiping off pathogens, useful if clean water is not available to the animal or person.",
"http://en.wikipedia.org/wiki/Saliva",
"\n",
"http://en.wikipedia.org/wiki/Wound_licking"
] |
[
"How many arteries are there at the base of each finger?"
] |
[
false
] | null |
[
"Where exactly? The digital arteries coming from the palmar arch split up in that region."
] |
[
"That should be roughly where they split up into two branches per finger."
] |
[
"Let's say at the MCP joint, next to the long finger"
] |
[
"What is the benefit of breathing into a bag during hyperventilation?"
] |
[
false
] |
As I understand it (I'm an undergraduate bio major), hyperventilation occurs due to increased plasma CO2. Increasing your breathing rate causes more CO2 to be expelled. By breathing into a bag, you increase the amount of CO2 that you are breathing in, so your plasma CO2 increases. But isn't this exactly why you are hyperventilating in the first place?
|
[
"Increased plasma CO2 isn't the only cause for hyperventilation (anxiety induced being one other), in those cases the CO2 levels are normal and blowing it off causes an increase in blood pH. Recycling the air will get you to hold on to the CO2 and prevent the alkalosis.",
"Alkalotic pH can cause dizziness, visual impairment, syncope, and seizure activity (secondary to cerebral vasoconstriction); paresthesia, carpopedal spasm, and tetany (secondary to decreased free serum calcium); and muscle weakness (secondary to hypophosphatemia).",
"Source: Harrison's Guide to Internal Medicine"
] |
[
"As a respiratory therapist, I support this comment."
] |
[
"hyperventilation occurs due to increased plasma CO2",
"...and panic. Then the symtoms of respiratory alkalosis cause more panic and the whole thing spirals out of control. That's where the paper bag thing comes from."
] |
[
"What is different neurologically between sleep and a coma?"
] |
[
false
] |
I was taught that damage to the RAS causes comas. Is this the only cause? Do coma patients dream? Do they go through brain wave cycles similar to a sleeping human?
|
[
"They do not go through brainwave cycles anything like sleep. The EEG of patients who are comatose are varied but generally involve a high degree of non-reactive or only partially-reactive generalized arrhythmic slow activity. In some cases, they can show frontally-predominant monomorphic alpha or theta frequencies; but mostly it's pretty disorganized.",
"Non-REM sleep, on the other hand, has much more synchrony, observable in widespread symmetric patterns such as spindles, slow waves of sleep, and vertex sharp waves.",
"Coma results either from lesions of the brainstem (ie, components of the RAS), or ",
" widespread lesioning of the cerebrum."
] |
[
"What about medically induced coma? I've heard that when people are in a medically induced coma they were dreaming about stuff."
] |
[
"I have personally supervised putting patients into medically-induced comas. Their EEG shows diffuse slowing or even suppression dependin on the depth. Patients with really bad traumatic brain injury are often put into a barbiturate coma to limit intracranial pressure. They push pentobarbital until the EEG shows a suppression-burst pattern, with alternating short periods of flat lines and bursts of fast activity.",
"These EEGs show significant derangements of normal cortical function.",
"It's ",
", in the lightest stages before waking when being brought out of an induced coma, that the patient may have dream-like experiences. I can't say for sure. I have heard reports of people saying they dreamed.",
"During the deep and sustained parts of a medically-induced coma, there is no EEG evidence of dreaming.",
"It's worth saying that patients who are put into a medically-induced coma (MIC) are already usually pretty bad off from the brain's perspective. Otherwise, there would be no reason for the MIC. So these are not typically people who are awake and oriented and able to do arithmetic before or even after the MIC."
] |
[
"We've been hearing about the soon-to-come male contraceptive pill for years and years now, why is it not on the market yet?"
] |
[
false
] | null |
[
"This is doubly true for anything that affects reproduction. That male contraceptive might be 99.9% effective, but what happens in that 0.1% where it fails? Does it have a teratogenic (ie, mutation causing) effect on the offspring? For that matter, does it have an effect (on users or potential offspring) when it stops being taken? These questions have to be answered fairly definitively before a new drug will be approved. Otherwise we could end up with another ",
"thalidomide",
" incident."
] |
[
"This is doubly true for anything that affects reproduction. That male contraceptive might be 99.9% effective, but what happens in that 0.1% where it fails? Does it have a teratogenic (ie, mutation causing) effect on the offspring? For that matter, does it have an effect (on users or potential offspring) when it stops being taken? These questions have to be answered fairly definitively before a new drug will be approved. Otherwise we could end up with another ",
"thalidomide",
" incident."
] |
[
"While this is certainly true, I'm pretty sure that there have in fact been specific announcements about upcoming male contraceptive pills."
] |
[
"Is there an upper limit to how fast a fluid can saturate paper through capillary action?"
] |
[
false
] |
I dropped a thin sheet of paper into water and noticed it was almost immediately saturated. Has anyone studied different fluids in different types of paper to see how quickly capillary action operates?
|
[
"Can't give you a number, the problem's too complicated. A Google Scholar search turned up a couple of review articles on the subject:",
"https://aip.scitation.org/doi/abs/10.1063/1.1722370",
"\n",
"https://journals.aps.org/pr/abstract/10.1103/PhysRev.17.273",
"but the overall physics is pretty straightforward. Surface tension creates a driving force pulling the fluid farther into the paper, but the fluid's viscosity (thickness) creates a drag force slowing it down. The flow speed will depend in a fairly complicated way on how porous the paper is, the surface tension of the liquid, and its viscosity.",
"Another important point is that the capillary force is only \"pulling\" at the front of the wet region, but the drag force from viscosity is felt throughout, so as the wet region grows you'd expect its growth rate to slow down over time."
] |
[
"The washburn mothod, as outlined ",
"here",
", is widely used to measure surface energies of powdered materials.",
"As can be seen by the given definition in the link, the time taken for a given mass of liquid to uptake into a porous column of material is dependent on many properties of the system under study namely the surface energy of the solid (or liquid, as expressed by simga*contact angle), the capillary constant which takes into account the (average) pore size of the material, the viscosity of the liquid and finally the liquid's density. The amount of liquid taken up by the column of powder does reach a limit in a given amount of time.",
"This gives good approximations and ",
"can be used to work out the surface energies of different porous papers",
".",
"Edit: I wasn't happy with giving company white papers so ",
"here's",
" the original paper."
] |
[
"Who thought watching liquids absorb into powders could be so interesting."
] |
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