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[
"Are there any materials that are actually far more fit for a purpose or component that we use frequently, but are either poisonous, hazardous, or detrimental to our health?"
] |
[
false
] | null |
[
"Is there a more classic example than ",
"Asbestos",
"?"
] |
[
"came to say the same thing. suspect OP is trying to get someone to write a homework essay for him"
] |
[
"Lead is great in solder and BeO is great for heat dissipation in electronic circuits but their use is diminishing. "
] |
[
"Would a super chimney be an effective means to reduce global warming and generate huge amounts of electricity?"
] |
[
false
] |
[deleted]
|
[
"These structures are more commonly called solar updraft towers:",
"http://en.wikipedia.org/wiki/Solar_updraft_tower",
"But the website you link is not well grounded in reality. Bluntly: the size of the structures it discusses are beyond current human construction capability; asserting that it would be simple (as the page does) is completely wrong. A 5 kilometre tall structure? The tallest structure on earth is barely 800 metres and they needed to invent their own techniques for pumping concrete that high.",
"http://en.wikipedia.org/wiki/List_of_tallest_buildings_and_structures_in_the_world",
"Frankly, the rest of the claims look equally ludicrous. Every single one of the claims in the summary would appear to be wrong.",
"Easiest to prove wrong is the 330,000 MW power generation for a 1km diameter solar tower. Good solar flux (near the equator, sunny, daytime) at the earth's surface for a 1km diameter capture area is just 0.5km",
" * pi * 1kW m",
" = 785MW. Since updraft towers are normally about 0.5% efficient (see Wikipedia link above) the 330,000MW claim is wrong by about 5 orders of magnitude, making an accurate number closer to 4MW."
] |
[
"From a quick browse through the proposed plans on that website, I can tell you that Mike hasn't thought through the system for feeding in air at the base of the chimney. Using extended ducting to get the required air in is much less efficient than not using ducting at all. There will be many sources of friction which will slow down the air flow and reduce the amount of air actually moving up the chimney. For the 5km x 1km chimney, the best possible intake system would be to simply remove 50% of the walls of the chimney at the base, up to a height of 500m. In practical terms the chimney would start off with a circle of closely spaced pillars 500m tall which would provide the foundation for the rest of the construction.",
"WRT to the power production potential of the design, he seems to have selected 26.6% efficiency for the power extraction coefficient. I've no idea where that figure was pulled from, but I can tell you that it is far higher than any existing turbine.",
"I'm not even going to guess at the possibility of making this structurally sound, or the potential damage that it could cause when it collapses."
] |
[
"330,000 MW is ludicrous, the two fission reactors in a Nimitz class aircraft carrier are able to produce 550MWth which ends up being about 190ish MW at the shafts after being turned into steam. ",
"wiki source",
"A nuclear power plant doesn't make anywhere near that much energy.",
"I think if these towers had that kind of potential, every energy company that could afford it would be investing everything they had in trying to make one of these. They would use helicopters to build these towers if they had to."
] |
[
"Why is habituation and homeostasis an almost universal aspect of biological systems? Is there an overarching physical property that leads to this?"
] |
[
false
] | null |
[
"Every living thing we know of beyond a certain complexity is, at it's core, something that maintains its internal order by using energy. Its a thermodynamic system like all others. If life didn't homeostatically regulate itself then it wouldn't exist. Viruses for the most part do not regulate their environment... But only because they use the environment of it's host, modified a little to it's own liking. ",
"So I guess the answer, in some sense, is survival of the fittest. Only complex life that regulates the internal environment to sustain its own system survives, and only the surviving systems reproduce and thrive. But this implies that you can get life that doesn't self-regulate which... Frankly sounds impossible, to me. I can't think of any that doesn't depend on a homeostatic environment at some point in it's life cycle. "
] |
[
"Homeostasis is one of the defining qualities of what we call \"life.\" If you had something that had all the other qualities of life but did not self-regulate, I don't think we would recognize it as being alive. ",
"Consider fire. In some ways it's kind of like a living thing: it consumes fuel, it outputs waste, it reproduces, etc. But because it does not have any self-regulating or homeostatic mechanism, it's just a chemical reaction and not a form of life. "
] |
[
"There's no physical property that perfectly fits the bill (entropy is the closest match but even then you need to make some stretches). So let's do a logical proof and assume the opposite conclusion. Say instead we have an organism with no mechanism regulating homeostasis. What you end up with is an organism that continues to consume a resource, and doesn't let it out in any form. Even if the organism survives this constant increase of that particular resource, it will be constantly changing. Imbalance of consumption forces an organism to change. Consuming more calories than you release as energy will increase your weight, for example. And an organism that is constantly changing can't guarantee that its form tomorrow will be able to survive the way it did yesterday.",
"So the most concise answer I can give is, homeostasis is a survival trait. It's not natural selection in the way you usually think of it. Instead, it's the ability to ",
" a certain property once it has found the Goldilocks Zone. No matter how much creatures mutate, if they weren't able to maintain and regulate the successful parts of their system, the successes would be meaningless and evolution would fall apart."
] |
[
"[META] A legal response to \"Medical Advice on AskScience: The Guidelines\""
] |
[
false
] | null |
[
"Thanks for the opinion. I'm not an affected party, but I can't let this slip by without comment:",
"Simply saying \"This is not medical advice, but...\" when responding to a medical question IS ABSOLUTELY medical advice",
"That said, I am simply offering an overview of applicable law, and am not suggesting that you rely on the information that I am providing; rather, I am offering it for your own (and the rest of the subreddit's) interest in this legal issue.",
"translated: \"This is not legal advice, but...\". lol? Does the same principle not apply for legal advice? Since we're on the topic, what about accounting advice (CPA's) etc.?"
] |
[
"Legal advice has a slightly different standard - it's a two-way thing where a lawyer has to take on a client. Furthermore, legal advice is easier to qualify as not being legal advice semantically than medical advice is. In this case, someone would have to suffer damages from what I wrote here that would not have been suffered otherwise. Essentially, yes, there's definitely a bit of a risk, but since my post was more of a \"don't do this\" than an \"it's okay to do this thing you weren't doing,\" I'll take that risk in the hopes that it prevents much more likely lawsuits from redditors toward AskScience contributors."
] |
[
"Good post; but one of the rules here is only scientific posts, with only infrequent metas originating from mods. That said this is a good writeup and the mods are trying to think of someway to use this (maybe a future meta post; or include in the wiki FAQ which should be upgraded soon) -- with attribution of course. Also, the mods here are totally in agreement against medical advice and have written similar things."
] |
[
"DNA-analysis says \"twice as many women as men passed their genes to the next generation\". What is the reason for this?"
] |
[
false
] |
First of all, ? Some genetic researchers at the University of Arizona in Tucson studied human DNA and found several things. What is interesting, is this: Men and women differed in their participation in reproduction, the researchers report. More men than women get squeezed out of the mating game. As a result, twice as many women as men passed their genes to the next generation. "It is a pattern that's built up over time. The norm through human evolution is for more women to have children than men," said Jason Wilder, a postdoctoral fellow in UA's Arizona Research Laboratories and lead author on the research articles. "There are men around who aren't able to have children, because they are being outcompeted by more successful males." Is this correct? Humans are kinda monogamous so what is the reason for this?
|
[
"Couple of thoughts:",
"Humans may not be as historically monogamous as they are now. There's an interesting article in the last couple of years, I think in National Geographic, of the hunter-gatherer groups that still exist around the Rift Valley and it mentions that their relationships are pretty open, with partners switching fairly frequently.",
"There are other studies that have shown that women want to be in a monogamous relationship with a low-testosterone male, but, when ovulating, prefer to have sex with high testosterone males, even while in a relationship. If we assume desire leads to action, at least occasionally, you'd likely have a situation where fathers are often from the smaller pool of high testosterone men than from the all-man pool.",
"Studies have also shown that there's a small % of people, both male and female, that have sex with large numbers (>50) of the opposite sex. Since women are effectively \"rate-limited\" in terms of having children, whereas men are not, it would then make sense that a smaller pool of men would be responsible for more births.",
"The study itself seems legit, although admittedly makes some assumptions in order to arrive at the conclusions you quoted. These are reasonable conclusions, but could be incorrect. More studies will surely be forthcoming."
] |
[
"You're just getting downvoted, which isn't very helpful. The article isn't doubting that both men and women pass on genes to the next generation, that's a fact. Rather, it's saying that when it comes to selection of mates for procreation, it looks like that a smaller number of men are represented. Think of it this way: In a society of eight men and eight women, and all of the women have two children each by one man and only \"their\" man, the genetics of the resulting children would be equally diverse in the next generation. However, if only two men were with all the women, and then the genes of the other six men could disappear in the next generation."
] |
[
"Slate, Life's Little Mysteries, CNN, YouTube and Softpedia are not acceptable sources."
] |
[
"If scientists found an undiscovered ancient animal with severe deformities, how would they be able to tell that a feature is a deformity or a naturally occurring attribute?"
] |
[
false
] | null |
[
"I can't tell you for all deformities, but I can tell you about most deformities.",
"Virtually all life is symmetrical in some way. From simple cells, to the wonderful fractal maths of the way plants lay out leaves, petals etc. All chordate animals are bilaterally symmetrical. If you find an animal where one leg is very different than the other 3 for example, that's a big clue that the animal suffered a deformity or injury of some kind. There are exceptions, such as the fiddler crab that has one hypertrophied claw and one normal claw. In those cases, the fact that the two claws are obviously functional would tell us that the difference in claw sizes was a useful, functional trait for that crab",
"In the rare case where a change is symmetrical, such as skull bossing from a birth defect or cancer: This is where comparison to bones from living species is helpful. Cancer, leprosy and syphilis make very distinct marks in bone, so a deformity caused by one of those (or a host of others) would be recognized for what it is. However, if the skull bossing is caused by a genetic mutation AND turns out to be beneficial to the critter (such as during mating season battles) then it's not a deformity, but evolution in action. ",
"Finally; finding fossils of any creature is pretty rare, considering the vast numbers of a given species that must have existed. Deformities are rare. If a given deformity is a 1 in a million and 200 million of that species existed in a narrow window of time, then there would only be 200 possible candidates for fossilization out of the many millions. Out of those many millions, we may find only a bare handful of good examples because most won't be fossilized. Most of the those who DO get fossilized don't get found. (remember that fossil bearing rock is being destroyed by nature all the time)",
"The odds of a critter having a deformity, then living to adulthood so its bones would be good fossilization candidates and then dying in a place where conditions were good for fossilization and then being found by a human are very VERY low."
] |
[
"It's a bizarre question for a very simple reason. If it was previously undiscovered, there would be no baseline or comparison to make. Therefore, judgment of a body feature as being deformed is impossible. How could you know?"
] |
[
"Thank you very much for the response. Very educated"
] |
[
"Since E=mc^2, does a photon create a gravitational field ?"
] |
[
false
] | null |
[
"In theory yes, but it's more complicated than just E=mc",
" .",
"One implication of this that was calculated, is if you have a ring of lasers reflecting off mirrors, with a spherical bead in the middle, the gravitational influence of the lasers will very slowly cause the bead to rotate. ",
"Paper here",
"Strangely enough the guy who wrote that paper is now trying to build a time machine."
] |
[
"Gravity is what happens when spacetime is ",
". Because spacetime is curved, objects travelling through spacetime move on curved paths. These curved spacetime paths look precisely like moving under the influence of gravity.",
"Photons are affected by gravity because they live in spacetime. ",
" lives in spacetime, so if spacetime is curved, everything moves on curved paths. So everything is affected by gravity!"
] |
[
"No, according to special relativity the speed of light is c in any reference frame."
] |
[
"Why is beryllium good at detecting radioactivity?"
] |
[
false
] | null |
[
"Detectors themselves aren't generally made of beryllium, but light elements like beryllium can be used to moderate neutrons. It's not usually a first choice; you can just use liquid water or plastic, and beryllium is a fairly hazardous material to work with.",
"Without additional context, I can't really say why they chose beryllium in the movie. It's possible that there isn't any legitimate scientific reason why they chose it."
] |
[
"In what context? What kind of radiation, and what kind of detector?"
] |
[
"I'm not sure, I was watching the new Mission: Impossible movie and they used a beryllium rod close to the balls of plutonium to detect something. "
] |
[
"How much electricity could I generate with a bicycle?"
] |
[
false
] |
We've all seen stationary bicycles retrofitted to turn a car alternator, but what if a person were to build a purpose built generator bike? I'm thinking something along the lines of this modified to replace the rear "wheel" of a stationary bicycle and then through a rectifier to get DC. Would it really be possible to generate 1000 watts of power on your morning workout?
|
[
"As a cyclist who trains with a power meter, I can answer this question pretty thoroughly...",
"1000 Watts is a sprint effort. Nobody (even pro cyclists) can do that for more than a minute or so. I know a pro cyclist who went several months without ever going above a thousand watts, even for one second (he's a tiny climber), but he felt that was kind of pathetic when he noticed. Most people can hit over a thousand watts in a sprint.",
"Professional cyclists can typically do 400W for an hour (all-out effort), the best cyclists in history could do almost 500 (maybe Cancellara can, Lance was just below 500W and Cancellara is bigger than him).",
"Most people who are pretty fit can do 200W for an hour, I can do about 280W for an hour but I'm also pretty light. 100W is almost painfully easy, barely a workout.",
"Hope this calibrates you. This article might help: ",
"http://www.cyclingtipsblog.com/2009/07/just-how-good-are-these-guys/"
] |
[
"From ",
"wikipedia",
" a bicyclist can reasonably produce about 3-5 Watts/ kg for an hour at a time. Assuming you're about 70 kg, and your equipment was efficient, you might produce 300W*h in a workout- pretty close to what you were looking for. Assuming a price of electricity of 10 cents/kW-hour, you might produce about 3 cents worth of electricity per day."
] |
[
"As a casual gym visitor sustaining 100w for an hour is pretty damn hard work!"
] |
[
"What exactly about antibiotics causes them to interfere with birth control pills?"
] |
[
false
] | null |
[
"The most accepted theory for this unfortunate effect is that broad spectrum antibiotics reduce levels of intestinal bacteria, which metabolize estrogen components of the contraceptive pill to allow the liposoluble part back into circulation in the body. When bacterial levels are reduced, there is a significant increase in estrogen excretion [1]. To put it bluntly, a microbial imbalance leads to a metabolic imbalance, which leads to a hormonal imbalance and babby formed [2].",
"Sources: [1] ",
"http://www.medicinaoral.com/pubmed/medoralv14_i3_p123.pdf",
"\n[2] ",
"http://www.sciencedirect.com/science/article/pii/S0029784401015320"
] |
[
"A quick google turned up ",
"this article",
" which gives a fairly simple description of what's going on. To put it in context, hormonal birth control works by regulating the amount of estrogen and progestogen in the body, or in some cases only progestogen. When there's a lot of estrogen and progestogen around, the brain doesn't secrete the hormones (FSH and LH) that cause ovulation.",
"Some antibiotics (enzyme inducers) increase the rate at which the liver breaks down estrogens and progestogens. This means that the body needs to produce more of these hormones to have the amount it \"wants\", and it also produces FSH and LH at the same time, which in turn make the ovaries more likely to release an egg.",
"The perhaps more obvious reason antibiotics reduce the effectiveness of birth control that includes estrogen is that after the liver breaks down estrogen, bacteria put the pieces back together and it gets reabsorbed back into circulation. If these bacteria are killed with antibiotics, it leads to less circulating estrogen and a lower effective dose. As before, low estrogen leads to FSH/LH production leads to ovulation.",
"Note that progestogen is only affected by enzyme inducers, so for those on progestogen only birth control, most antibiotics are OK.",
"Edit: clarified details regarding progestogen."
] |
[
"The only antibiotic that's ever been shown to have any kind of effect on the birth control pill and other kinds of hormonal based antibiotics - and by that I mean an effect on the action of the compounds responsible for preventing pregnancy - is Rifampin.",
"Other antibiotics can make you feel queasy and cause vomiting, which could disrupt the pill's workings if you vomit it back up, but unless it's Rifampin it's not going to alter the efficacy of the ingredients once in the bloodstream."
] |
[
"AskScience AMA Series: I'm the Director of the Addiction Institute at Mount Sinai who studies the neurobiological effects of cannabis and opioids. AMA!"
] |
[
false
] |
Hi Reddit! I'm Dr. Yasmin Hurd, the Director of the Addiction Institute within the Mount Sinai Behavioral Health System, and the Ward Coleman Chair of Translational Neuroscience and Professor of Psychiatry and Neuroscience at the Icahn School of Medicine at Mount Sinai in New York. I'm an internationally renowned neuroscientist whose translational research examines the neurobiology of drug abuse and related psychiatric disorders. My research exploring the neurobiological effects of cannabis and heroin has significantly shaped the field. Using multidisciplinary research approaches, my research has provided unique insights into the impact of developmental cannabis exposure and epigenetic mechanisms underlying the drug's protracted effects into adulthood and even across generations. My basic science research is complemented by clinical laboratory investigations evaluating the therapeutic potential of novel science-based strategies for the treatment of opioid addiction and related psychiatric disorders. Based on these high-impact accomplishments and my advocacy of drug addiction education and health, I was inducted into the National Academy of Medicine, complementing other honors I have received in the field. Recently, I was featured in the NOVA PBS film " ," which premiered in September and explores the little-known risks and benefits of cannabis use. I'll be on at 3 p.m. (ET, 20 UT), ask me anything!
|
[
"In your study what is considered smoking too much cannabis? And what are the negative effects of a daily smoker"
] |
[
"Hey, 3 in 1:\nWhat can you tell us about the interaction between Marijuana and ",
"A)depression",
"B)anxiety",
"C)attention disorders\n?",
"thanks for playin!"
] |
[
"We don’t really classify cannabis in regard to \"too much\" use. We normally operationalize cannabis use in regard to frequency such as multiple times a day, daily, weekly, monthly or as cannabis use disorder in regard to mild, moderate and severe use depending on the negative symptoms it presents for that person. Daily smokers generally can experience change in mood, short-term memory impairment, altered sense of time, and even hallucination in those using high THC potency"
] |
[
"What prevents fruits from rotting before they ripe?"
] |
[
false
] | null |
[
"First \"ripe\" simply means being ready to eat.",
"\nThis isn't a natural or objective measurement. It's entirely dependent on how humans generally like to eat an object. ",
"If we look at items like berrys, apples, oranges, and other common fruits they are attached to the plant and are \"alive\", being fed by the host plant. They don't rot (absent disease) for the same reason people don't rot while walking around each day. ",
"With that said some items like, bananas \"ripen\" as they die; some like hákarl rot to the point of being offensive to other cultures. So they have to rot to ripen. "
] |
[
"The cells in the fruit can continue to replicate and renew the fruit while new energy is being pumped in. At some point, the host organism stops investing energy in keeping them alive -- causing them to drop and decompose or decompose while still connected.",
"And it's not a bright line difference. An unripe apple can have intact fruit meat in some places and be rotting in others."
] |
[
"Similar to other organisms, plants also have hormones. Completely different structure, even some gases are hormones for them, but comparable functions.",
"External factors and some from the \"mother\" plant and mostly the seed inside the fruit influence the concentration and type of these hormones. The hormones control the stages of development of the fruit, like growth, sugar uptake and storing, phases of inactivity during unsuitable circumstances, and at some point the separation from the \"mother plant\". After leaving the \"mother plant\", there are no nutrients and other agents provided to the fruit to maintain it´s structure. ",
"\"Ripe\" is just the stage of development we like to eat. Doesn´t meant anything to the plant. The intervall between being \"ripe\" and rotting juts depends on the environment. Fruits are mostly intended to be eaten, so the seeds are propagated. The fruit rotting is the fruit being eating on a tiny scale. At some point bacteria and fungi settle in and start to digest the nutrients. These small organisms release byproducts that smell bad and can be toxic to us. The changes in color come from the exposure to air (oxidation) and the organisms breaking down the original structure, drying it out etc.",
"Putting them in a fridge reduces the growth of microorganism. So it slows the rotting down. Rotting is not an \"action\" or \"condition\" induced by the fruit, but by external factors."
] |
[
"What is that \"drop\" you feel in your stomach when you receive bad news?"
] |
[
false
] | null |
[
"Glad to see others have heard of the second brain. If you tie this together with \"Start With Why\" (on mobile, sorry no link) by Simon Sinek (Ted talk available) it can be quite interesting. Essentially, the oldest part of our brain, or animal brain, which is responsible for the majority emotions and decision making doesn't interface well with our frontal cortex, which is why we get \"gut feelings\". Our decision making and emotion has a hard time being articulated by the new brain which contains language."
] |
[
"Glad to see others have heard of the second brain. If you tie this together with \"Start With Why\" (on mobile, sorry no link) by Simon Sinek (Ted talk available) it can be quite interesting. Essentially, the oldest part of our brain, or animal brain, which is responsible for the majority emotions and decision making doesn't interface well with our frontal cortex, which is why we get \"gut feelings\". Our decision making and emotion has a hard time being articulated by the new brain which contains language."
] |
[
"What about the one you feel when you drop on a roller coaster or go down a ramp in a car or on a bike?"
] |
[
"Since there are gaseous planets, can there be gaseous moons?"
] |
[
false
] | null |
[
"The issue is that small bodies don't have the gravity to permanently trap gas around them. Unless the body is at least a certain size, IE very large, you'll get a rocky body instead of a gas giant. At which point is it really a moon or is it a binary planetary system?"
] |
[
"It should be noted that gas giants aren't gas the whole way through, or even most of the way through: the pressure is such that most of the matter is no long gaseous, but liquid or even solid (though at the densities and pressures estimated for the cores of those planets, the common definitions for phases of matter kinda breaks down).",
"If you accept that a \"gaseous moon\" can still have a core, but with a truly massive amount of atmosphere, then I don't see any reason why we couldn't have a ",
"gas dwarf",
" orbiting a larger planet."
] |
[
"What is the distinction between a moon and a binary planet? Do planet-moon systems have barycenters inside the planet?"
] |
[
"Even if it's immeasurable by current technology, does turning on my porch light brighten the entire world by some infinitesimal degree?"
] |
[
false
] | null |
[
"Let's say you turn on a 60 Watt bulb with a 5% conversion to 550 nm (green) photons. This is roughly 8x10",
" photons per second. If we ignore absorption, and distribute them uniformly throughout the atmosphere (within 100 km of the earth's surface), that leaves roughly 1 photon per 10 m",
" of air per second, which is not measurable.",
"Realistically, would your photons ever travel from Kansas to China? No, they would be absorbed long before they ever made it that far."
] |
[
"What does \"brighten the entire world\" mean? Are you asking if you turn on a lamp in Berlin does it brighten a room in Wellington? No."
] |
[
"No, I understand that enclosed spaces are likely to not be illuminated due to their power to impede the passage of photons. Because light emanates in all directions from a fixed point, though, one would presume that any and all light that originates outside would go on to illuminate every other external surface. If this isn't the case, what is it that causes photons to weaken as they travel further from their origin?"
] |
[
"What is stopping us from growing stem cells?"
] |
[
false
] |
In a lab, the same way we grow regular, fully differentiated cells, from practically any other part of the body? Are stem cells like the Pokemon Eve, and can evolve (differentiate) into a set which doesn't contain another stem cell?
|
[
"Stem cells are finicky, for one. Also, there are adult stem cells and embryonic stem cells. Adult stem cells are not as robust as embryonic stem cells. However, embryonic stem cells can only be harvested from human embryos in a process that destroys the embryos so there are major ethical considerations. The U.S. currently prohibits embryonic stem cell research. However, even in nations that allow and actively pursue this research, the progress has been slow because of the aforementioned finicky nature of embryonic stem cells.",
"You may be interested to know that there have been some recent advances in stem cell research. Korean scientists recently created insulin-producing cells from embryonic stem cells created with the nuclei of adult skin cells. I think that putting an adult cell nucleus into an unfertilzed ovum and coaxing it to divide a few generations may change the ethical debate substantially. On the other hand, it opens up the full-on cloning concerns.",
"Here's a news brief about the insulin-producing cells. ",
"http://dailydigestnews.com/2014/04/insulin-producing-cells-created-from-skin-cells-of-32-year-old-woman/",
"It's intricate and nuanced. Anyone that slams their fist down and says either this stuff should proceed without restriction or that it should be sealed in a vault and buried at sea is betraying a severe lack of understanding of the science of stem cell research. The discussion is a very important component of the science."
] |
[
"We don't grow regular, fully differentiated cells in the lab. In the lab, we either grow some sort of cancer cell, some sort of immortalized cell line that was ",
" normal, or some sort of stem cell line.",
"I'm being generous here about the definition of stem cell, so this isn't specific to embryonic or adult stem cells, pluripotent, totipotent, multipotent, etc."
] |
[
"If people are growing skin in lab, it is likely that they are using skin stem cells, which are needed to replenish a cell population with a lot of turnover. ",
"Cells in multicellular organisms have evolved to closely monitor signals from other cells within the body to understand what they should and should not be doing. Stem cells are under a remarkable amount of control because they are allowed, under the right conditions, to proliferate and turn into other cell types.",
"This makes the culturing of cells from multicellular organisms difficult, since we need to provide a similar cocktail of signals that cells might find in the body. In the absence of appropriate signals, most cells die to prevent themselves from doing the wrong thing, like go all cancerous and crazy.",
"Being curious about stuff is always a good thing, keep asking questions. "
] |
[
"Do we know in what direction we'd need to accelerate towards, such that we'd lose all the moment we have gained from the motion of the cosmos?"
] |
[
false
] | null |
[
" Yes. Go 380 km/s towards the constellation Leo.",
" The cosmic microwave dipole has a rest frame. We can tell because we see a ",
"dipole moment in the CMB.",
" This just means that we see the CMB a litter warmer in one direction, and colder in the other. This means we're moving (relative the CMB rest frame) in the warmer direction (which is warmer due to the blueshift of the photons), which is centered near the constellation Leo. The amount of relative blueshift/redshift\ntells us our speed - ",
"about 380 km/s",
". "
] |
[
"We're traveling at whatever speed up to the speed of light that you want. No reference frame is more valid than the next. "
] |
[
"There is a frame of reference that provides us a speed relative to the cosmic background radiation. Some people use this as a \"default\" reference frame and you can cite our speed based on that frame of reference.",
"You're right that it's not particularly more valid than any other, as far as physics equations go, but it's the most stable \"background source\" that we can measure against."
] |
[
"What happens in the brain when a deaf (from birth) person reads?"
] |
[
false
] |
I was thinking about how when I read silently to myself, I "hear" the words I'm reading in my head. When I read the word "window" I "hear" it, know what it is, and continue on. I don't "see" in my mind's eye a picture of a window unless I need to (e.g. to solve a puzzle I might picture various kinds of windows). Then I wondered, for someone who has never heard the the pronunciation of the word or know what it sounds like, what happens when they read the word "window"? Do they picture it in their mind's eye or does something else entirely different take place?
|
[
"I'd like to add a follow up question.",
"I recall hearing that deaf schizophrenics experience sign hallucinations rather than voices in their heads. Would this be in the same relative area as to what would be happening here with deaf people reading?"
] |
[
"I am half deaf, and while it means little in this situation, I have thought this idea for as long as I had hypothesised it myself;\nHumans as a species are drawn to symbols and imagery - rock paintings, car insignia, flag emblems, you name it.\nYou don't need to speak to be able to learn. You need to understand how to read. Deaf people learn sign language and use it to learn English (as an example) literature.\nInstead of teaching kids 'A', 'apple', and the sound of the word, replace vocals with a sign for apple. It's all just learned associations. Deaf people will probably visualise the literature and are able to distinguish by the differences in spelling."
] |
[
"We do it all the time, like when you are out on the street, you don't keep telling to yourself \"car, bus, yellow, dog\", etc, you just look at those things and know what they are, same thing with words, if you see the word \"dog\", you don't have to read it to your brain like it's a 5 year old, once you see the word \"dog\" that's it, the brain knows without having to listen to your inner voice, how to do it? you can start slowly, looking at a word at a time and forcing yourself to read it in \"silence\", and with time and practice you will read complete pages in seconds and getting and understanding all of it, because what is slowing us down is the sound of our voice reading to our brain at the same speed that we talk, which we do at a slow speed"
] |
[
"What happens in our bodies when we die via blood loss?"
] |
[
false
] |
and more specifically, why does losing too much blood cause us to die? do our hearts shut down? do our lungs stop working? it's always confused and perplexed me.
|
[
"Short version: the bottom line is that your blood contains nutrients needed by your organs to keep you alive. Losing blood means you lose nutrients and oxygens necessary for viability.",
"Longer version (at physiological level):\n1) Losing approximately 10% of our blood volume will cause increase of heart rate, constriction of arterioral beds, vein, and venous reservoir in your skin and muscle. Antidiuretic hormone for water retention and reabsorption to compensate for volume loss is also secreted. In addition, renin-angiotensin system, a hormone family that regulates blood pressure and fluid balance is also activated.\n2) With 15-20% hemorrhage, your vessels are further constricted and your heart rate is also increasing (tachycardia). At this time, your body also need to compensate for the lack of oxygen by going to a process called anaerobic glycolysis, which is an alternative pathway in cellular respiration pathway to keep your cells alive. However, the by-product of this alternative pathway is lactate, whose accumulation in the plasma can cause acidosis. Compensatory rapid breathing is also ensued to compensate the lack of oxygen.\n3) Major blood loss will result in irreversible tissue damage due to anoxia (depletion of oxygen), hypercapnia (elevation of carbon dioxide), and acidosis. As a result, cardiac output decreases and therefore causing impaired perfusion in medullary vasomotor center (an area that controls blood pressure and other homeostatic processes) which results in death.",
"Source"
] |
[
"There is a limit to how much blood pressure your heart and blood vessels can generate. If the volume of your blood gets too low, you cannot pump enough blood and therefore oxygen to your brain, so it stops working and you die."
] |
[
"But still valid nonetheless - Some of the methods were as simple as picking up the severed head immediately following and talking to it, to see if they could elicit a response from a still conscious person."
] |
[
"Scientists is this feasible?"
] |
[
false
] | null |
[
"Depending on how you set up your variables and frame of reference, technically speaking the universe could be described that way mathematically.",
"Edit: ",
"The Coriolis Effect"
] |
[
"Going to take a look at this later can't on my phone"
] |
[
"All motion is relative, so I don't think it can be said to be impossible. In fact, it is definitely true if you simply pick the correct frame of reference. So you can ",
" the motion of the universe this way. But it you can't really come up with a way to ",
" the motion of the universe this way. ",
"Choosing such a system means that you have to replace our theories of gravity, at the least, with something else. Perhaps General Relativity, too. And the existing theories have been shown to be quite accurate, so I think you're going to have a bad time. "
] |
[
"Is economics a science ? Is there a simple, systematic way to understand economics ?"
] |
[
false
] |
I've always been skeptical about the fact that economics is a science, mainly because I can't quite grasp it. Please hold on, and change my mind (and probably others' too). One thing that comes to my mind is that there is no Nobel prize in economics (actually there is, but it's not given out by the Nobel academy so it is different from the other nobel prizes indeed). Also,[This link]( ) says that the 2008 crisis is partly due to the fact that the Black-Scholes equation was wrongly used. It therefore makes me believe that economists back then did not really understand their models, at least when the economy itself had substantially changed in a very short period of time. Another interesting point is that economics is hard to grasp, maybe because it relies on a lot of technical stuff implemented in the real world. I used to learn physics through simple models, where you could study the influence of the hypothesis of a model on the outcome of that very model. That is a very efficient way to learn "hard" science and I wondered if it is possible to learn economics that way. In any case, how did you learn it ? I'm deeply worried for the robustness of our understanding of economics, on the one hand from economists themselves (is it a science?) and on the other hand from the major part of a country's population. Especially in these times, keeping key thematics unreachable for the bulk of the population, such as world/country economics, is a threat to doing the right choices as a citizen. That is why I'm asking here and hopefully not insulting anyone with these questions.
|
[
"Science isn't a thing in and of itself. Science measures and describes things. So, sure, every time you push a bowling ball off a table, it will fall. That's physics. However, if you repeatedly push a cat off that same table, what will happen? Will it fall? Jump? Scratch the heck out of you? See, that's biology, which is also a science. And there's a good deal of math mixed into the equation of cats in terms of probability and more.",
"Economics is a science, but as per the above, it's more like biology than physics.",
"Another example: weather forecasting. Weather forecasting is all about math and science. But no matter how much of in expert you are, you can never say anything besides \"I'm pretty sure that...\" (Pretty sure it will rain, or snow, or whatever.)",
"So, yeah, economics. It's as finicky as a cat. It's as unpredictable as the weather. But science it is, it is."
] |
[
"This is an interesting question and for some an offensive one :)",
"There is a quite common agreement in philosophy of science that anything that is a science must either be an empirical science or a formal science.",
"Empirical sciences are descriptions of fact (the universe). physics is the front runner example of empirical science, but also biology, sociology or even psychology. They all describe reality and an important fact is, theoretically they can fail on reality, when reality just suddenly isn't the way it is expected to be.",
"Then there are formal sciences. These are sciences of \"pure logic\". The front runner example here is mathematics. Formal sciences take postulates and then work through what these mean. Philosophy puts (or saves :) itself here as formal science. There aren't many formal sciences. Law in states with a roman law system is also a formal science -- in common law systems it's more empirical based though. Theology could also be put here.",
"So now where do we put economics? This is an interesting question and used to be a matter of great scholarly debate, the \"",
"methodenstreit",
"\" (a German word, because back that day Germany/Austria used to be the worlds scientific center, before they destroyed it all). One group wanted to put economics as formal science, supposing the \"",
"homo oeconomicus",
"\" at it's center, a theoretical abstraction of a human born with a \"",
"utility vector",
"\" and from this derive a huge structure just as mathematics from a few assumptions and thus be infallible as mathematics can't fail on reality. The other wanted to derive knowledge by observing and abstracting reality. Long story short, in most regards, the formalists won.",
"Nowadays when you enroll in economics 101 this is just the way it's taught. Starting with the utility vector of the homo oeconomicus and then deriving all kinds of conclusions from this. However, especially in macro oeconomics they do check real statistical data to test and proof their theories. Also there are moral limits to the \"experiment\" you see in most other empirical science, you just can't deliberately run a state into the ground to test if your theory saying it would in case you do this or that is right. Also before somebody angrily calls me out, economics is a huge field, of course there are also subdivisions",
"So in fact, it is complicated. Economics is in a complicated limbo between being a formal and an empirical science.",
"Also a common accepted consensus in theory of science is, and albeit it's major task is to draw a line between science and non-science. This line is definitely not thin and clear, it's curvy and blurred with many gray areas. So in case of economics, some areas are definitely science some maybe are not -- in a philosophical sense.",
"I remember my philosophy professor. One day she told she just heard an interview on the radio with two leading economists, one claiming in the current situation the key interest rate should definitely be raised and the other claiming with the same confidence it should be lowered -- \"how can this be a science if they disagree on such a basic fact and have no way to proof which one of them is right\". Also this may be oversimplified by a lot, but it's also funny that they indeed model an extremely complicated system, but have only one input variable -- the key interest rate. (Well there is more, but it's the main)",
"I've been mostly talking about political economy, there is also business economics, which is again a very different story. But again it's complicated, suffers in basic similar issues than economics plus another issue. While science by itself can go arbitrarily complicated and thus precise with it's models -- being \"as simple as possible but not simpler\" -- business economics also suffers from the fact of having to stay compatible with the average manager. Their management models are of no use, if no non-scientists can understand them.",
"So no, it's not simple to say if economics is a science or isn't and there is no simple systematic way to understand humanity in all it's complications. Since economy in it's broader sense encompasses everything humans think and do...",
"EDIT: some of the worst grammar errors, I'm too tired for the rest.",
"EDIT2: One thing I'd like to point out, thinking about your question and how my answer might relate or not relate to it, the quality of the state of the art is not actually a factor if something is to be considered a science. A science might still be relatively young and have bad models/theories but still be a science, on the other hand, a craft might be well developed, but not a science. Thus the issue with economics is more it's limbo state between being an empirical science or a formal science, and in being observant or being normative than in how good it actually is or isn't.",
"LAST EDIT: (I swear); This is extremely difficult question to answer in a reddit post. I suppose if I'd go with this as research question for a PhD thesis to a philosophy professor (with specialization on philosophy of science), most would tell me to look for another, more narrow question\""
] |
[
"I wanna point out that the example with the cat above is much better described as ",
"ethology",
", while the word ",
"biology",
" is usually taken to mean the study of e.g. cells, evolution, genetics, and the physiology of organisms. No doubt the two are related, and ethology can easily be considered part of, related to, or an extension of biology, depending on who you ask. Biology is, however, much more of a \"white lab coat and endless measurements\"- kind of science than repeatedly pushing a cat of the table.",
"Also, what did the poor cat do?"
] |
[
"When some species lose a limb, the limb continues to move. When others lose limbs they go limp immediately... what's causing one to move but not the other?"
] |
[
false
] |
This question brought to you by weed and
|
[
"This is a good answer, but the effect can also vary on the way the host organism's nervous system is organised. For example, most limbs of most organisms will twitch in response to salt water due to the ions, but octopus arms actually retain some functionality after having been severed. I remember reading one paper in which the arm was severed and would attempt to feed food placed on it to where the mouth would have been. This was attributed to the fact that an octopus' brain is distributed across its body rather than having a single, centralised location as most higher organisms do. ",
"Related effects have also been observed whereby the octopus appears to literally be in two minds about a situation. When placed in an unfamiliar container with food at one end and a rock to hide under at the other, the octopus can have 4 arms trying to swim in 1 direction and 4 in the other."
] |
[
"This is likely dependent on nerve stimulation. Possibly how the nerves are severed, what nerves in particular exist on the appendage, and how damaged they are.",
"The salt water in the starfish's environment may also play a part in it. Take ",
"this other example",
" of a dead squid moving after soy sauce is poured over it. The electrolytes in the soy sauce are enough to trip the action potentials in the animal's nerves and cause motion. It could be a similar mechanism for the starfish.",
"That's a great video btw. Offers a great explanation."
] |
[
"Cool! Do you have links to vids?"
] |
[
"How much do aerodynamics matter in relation to a vehicle's MPG?"
] |
[
false
] |
A friend of mine used to work at a major car company. He told me that he learned (second-hand) that vehicular aerodynamics don't have much of an effect on modern vehicles at normal (<100mph speeds). So do they actually have a noticeable effect? For example, my truck weighs ~4400lbs and has about 260 bhp with 280 ft-lbs torque. I average about 18mpg. Would I get any noticeable increase if I were in a corvette or ferrari of identical weight, with all other factors being equal? Edit: To be more clear, I think it's obvious to most that a more aerodynamic vehicle will have a positive effect on gas mileage, I'm just unclear as to whether that effect is noticeable in the real world.
|
[
"Although not directly answering your question, Mythbusters did an amusing episode where they covered a ",
"car in clay",
" and put a bunch of dimples in it like a golf ball. They ended up with about a +10% boost in MPG due to less drag going well less than 100MPH.",
"Here's a short video of it",
"."
] |
[
"This should be interesting for you:\n",
"http://gcep.stanford.edu/pdfs/ChEHeXOTnf3dHH5qjYRXMA/10_Browand_10_11_trans.pdf",
"On the side, the equation for drag has (amongst other things) 3 parameters that really matter. There's the speed at which you are traveling through the medium, the drag coefficient of the object (this is based on geometry), and the frontal surface area. For example, if you had two identically shaped cars, but one was a 10% scale up of the other, they would have the same drag coefficient, but one would have a surface area ~20% greater, and so would suffer from ~20% more drag.",
"For your case you should keep in mind that while a corvette or ferrari would likely have a lower drag coefficient than your truck, they also have much lower surface area (maybe even less than half), which would also do quite a lot.",
"Another thing to point out is that the velocity term in the drag force equation is actually a velocity squared, so you can get significantly larger increases in drag as you increase velocity at higher velocities. So yes, in a way your friend is certainly right. Compared to the case of 100mph, the drag component of a car traveling at say... 50mph is much much smaller (1/4 of the force in fact)."
] |
[
"If there were no friction, you would only need to use energy to accelerate up to speed. Just like you were in space-- you'd keep right on going at 55mph if you took your foot off the gas when you reached it.",
"This obviously does not happen-- friction is slowing the car down, and so some power is required to keep it moving. But if you're holding a steady speed on a flat road, ",
" is going to overcoming friction. It's not all air friction-- some is between the tires and road, some is in the car itself in axle bearings and cylinder heads and so forth.",
"It looks like aerodynamic drag accounts for ",
"half of your energy expenditure (pdf link)",
" at highway speeds. Even small reductions in drag should certainly be noticeable in the real world."
] |
[
"What types of evidence go into diagnosing mitochondrial diseases?"
] |
[
false
] |
Given Justina Pelletier's case, I was curious whether mitochondrial diseases are difficult to diagnose. Are muscle biopsy, biochemical tests, and genetic tests a gold standard? What other factors must/might one consider? I am NOT seeking medical advice! Rather, I am curious about what types of evidence might a doctor consider that would lead to a diagnosis of mitochondrial disease.
|
[
"That depends on the disease - I'm not a clinician, but have been working with DNA sequencing for a long time.",
"The genome of the mitochondria is incredibly small compared to the rest of the cell, and there are usually plenty of mitochondria per cell, which makes it easy to harvest a lot of it from a small amount of tissue. I would imagine that the gold standard for most mitochondrial diseases would simply be to collect the DNA and sequence it, looking for deleterious variations. For instance, changes to sequences that truncate proteins - the machinery that makes things happen in the cell and in the mitochondria. Kind of like discovering a missing drill bit in your tool box... or a missing drill.",
"Of course, there are plenty of other things an MD might consider along the way, but in the end, they'll probably go out to do some sequencing to see what happened. ",
"What is more interesting is that we're almost getting to the point where MDs may want to sequence not just the mitochondrial genome, but the whole cell genome to look for disease markers... which IS my field. The whole genome has two copies of 3 billion bases, which makes it a lot larger than the 16,600 bases or so in the mitochondria."
] |
[
"You are probably right. I may have had the same visceral reaction to the parents as the Children's Hospital doc. Dad strikes me a narcissistic Personality and mom as borderline. Even if true, that doesn't mean the child isn't sick. The truth will eventually come out."
] |
[
"Sort of... the problem is that 80% of mitochondrial diseases are mutations in the nuclear genome that encode for mitochondrial proteins. It's a mess-- typically they'll run mtDNA first to rule that out, but then do nuclear sequencing of the 1500 genes that they know affect mitochondrial function (although there are still some that haven't been discovered, so sometimes they'll do outright whole exome sequencing). But then usually it comes back as a varient of unknown significance since they don't yet know what is pathogenic. To make it worse, negative mtDNA sequencing in blood doesn't even rule out an mtDNA mutation... sometimes disease burden in blood is low enough that all they find are healthy mitochondria, even if in organ systems there are a lot of unhealthy ones.",
"To the OP, barring a definitive genetic diagnosis (which only 25% of patients with clinically diagnosed mitochondrial disease are able to get), nothing completely rules in our out mitochondrial disease-- the diagnosis is made on a combination of biopsy results, labs, family history, ect."
] |
[
"What is the \"holy grail\" of your field, what is needed to obtain it, and how will this impact the world?"
] |
[
false
] |
[deleted]
|
[
"An unambiguous and universally-applicable site index for tree quality. In Urban Forestry, the national standard for trees (ANSI) specifically does not ensure quality, and only serves to standardize tree nursery practices. The vast difference between planting sites and tree quality results in huge monetary losses in maintenance, tree death, and growth stunting. Currently, no objective and broad-spectrum criterion exists in order to optimize possible tree growth and obtain the most ecosystem services per tree for the money spent on it. If we do come up with such a site index for trees, we can ensure that urban forests develop as predicted with minimal losses, maintenance, and a more stable ecosystem for a longer time period."
] |
[
"I plan on doing high energy physics so i'll answer for that:",
"The 'holy grail' for high energy physics I think is the Theory of Everything. A unification of the four fundamental interactions - gravity, electromagnetism, the weak force, and the strong force - at extremely high energies (the type of energies that existed at the very beginning of the universe). Right now we have Quantum Chromodynamics: the strong force; and the Electroweak interaction: E&M and the weak force unified. The next step is to fully validate EWK by finding the Higgs. After that, we have to come up with ",
" (GUT) that will unify the electroweak and strong force.* This will have to be experimentally verifyed. Next, some form of workable quantum gravity will have to be devised and verified, and only then will we be able to start on the TOE.",
"Got a lot of work ahead of us."
] |
[
"Computer graphics: The holy grail was used to be creating photorealistic images and videos. Graphics researchers succeeded, but realized that the solution has a significant disadvantage -- the requirement for hundreds of thousands of expert man hours. So the new holy grail is to make the creation and manipulation of visual content easy for all users.",
"Computer vision: The holy grail is human-like understanding of visual stimuli. Once achieved it will be an enormous boon to robotics, automation, and safety. We can do better than humans in some tasks, but I think humans are the obvious benchmark."
] |
[
"Do all steroid hormones increase blood glucose and cause diabetes?"
] |
[
false
] |
We all know that a chronically high cortisol can lead to diabetes due to cortisol increasing glucose levels. Is this also true for adrenal androgen steroids like DHEA(S) and androstenedione?
|
[
"No, androgen receptor activation seems to improve glucose metabolism through a few pathways from what I remember. B-cell activation as well as increased GLUT1 expression and well the increase in the skeletal muscle ability to store glycogen. ",
"There are many negative effects to chronically elevated androgens, however..."
] |
[
"That was essentially the premise behind the development of SARMs (selective androgen receptor modulators) but in trials they never quite panned out, and negative effects were still apparent (dyslipidemia, hypercholesterolemia, elevated liver enzymes, suppression of the hypothalamic-pituitary axis, etc...) So right now it doesn't seem possible in practice with available drugs."
] |
[
"Steroid induced diabetes is ICD10 code E09.9. You treat like you treat type 2 diabetes primarily; they need more prandial insulin than basal so the dosages are a little different. You can get glucoses of 400s on steroids. Diabetes is diagnosed with fasting glucose > 126 x 2."
] |
[
"Is it possible to make a vaccine for any virus?"
] |
[
false
] |
Wouldn't it be possible to encounter a virus for which we can't get the vaccine or it is too complex to be achieved in a reasonable time?
|
[
"Consider that a virus proliferates by integrating its gene in a cell of the host. A necessary step for that is the binding of the virus to an extracellular receptor. In other words, the virus must at some point in its self-replication cycle bind to a native protein.",
"In other words, a virus contains at least one structural unit that must be able to interact with a structural unit of the host. That therefore becomes the possible point of attack for the immune system. Most vaccines work by \"training\" the immune system to recognize that structural unit of the virus that must interact with host for replication.",
"Now this may sound simple, but HIV is very instructive to show that it isn't. The key structural unit for HIV is called ",
"gp120",
". However, this protein unit is structurally rather flexible. It therefore appears that if we just inject people with isolated gp120 (or some variation thereof), the antibodies that are created against isolated gp120 do not work against HIV. Protein structural units can be flexible and only under certain condition, like binding, do they undergo an ",
"induced fit",
". Viruses are known to cover their protein structural units with sugars, so for most of its time in the body, the virus does not expose its structural unit that can bind to the receptor, or conversely, be targeted by antibodies.",
"Bottom-line, no vaccine exists against HIV, despite considerable effort since the 1980s. That does not mean it is impossible. But for the reason above (plus possible additional ones), it has been tough to create a vaccine that can neutralize HIV. But worth noting: there are ",
"HIV infected humans that through their own immune system have developed neutralizing antibodies",
". That is proof that there are antibodies within the human repertoire that can neutralize HIV. The hard part is to induce those specific antibodies to be created with a vaccine.",
"But your question mentions time. That's really the key point. The ability to create a vaccine in a certain amount of time is not guaranteed, as shown by HIV. It is noteworthy that due to natural selection, less deadly variants of a virus typically arises over time, which means that there are natural ways for viruses to become less problematic. Still, that would likely involve mass death, so hardly a good fix.",
"So I think strictly speaking, it should be possible to make a vaccine for any virus because a virus must be able to interact with the human body to proliferate. However, the time it takes to develop that vaccine can be very long with current technology. It is tempting therefore to consider other non-vaccine ways to deal with viral infections, like a short-term therapeutic, which can buy us time. However, now we're talking huge costs per dose, so it's not a scalable solution for pandemics at this point."
] |
[
"A+ reading man :)",
"You touch upon it, and I just wanted to add an underlining, that the time perspective is the important factor as to whether we can make a vaccine. ",
"Medicine is a constant evolving field, and as such what seems insurmountable by today’s technology might be nothing but a common cold a short skip into the future. Pair that with the exponential acceleration we see technology develop in our current civilization and it can be within a matter of years we go from having serious illness becoming mundane."
] |
[
"Yes, it is surely possible but it makes much much time, efforts, hard work, research and money. Humans have been making vaccines for different viruses since 1000 thousands of years. So, in order to make our future generation and the current generation healthy and to make them safe from every virus we need to make vaccines, then only we can make not only our civilization but also other living beings safe and protected from any virus so that we could survive 1000s of years from harmful viruses and disease."
] |
[
"Is there an actual exchange of photon particles (electromagnetic force carriers) between two magnets? And if so, do these photons have a specific wavelength?"
] |
[
false
] |
And in a related question, is there a theoretical mesh size for a Faraday cage where it would stop a compass from pointing to the earth's magnetic pole?
|
[
"No, magnets don't emit photons. Quantum electrodynamics uses an approximation involving 'virtual photons', but this is just an abstraction to help understand the underlying theory. ",
"The equivalent to Faraday cage would be something like a magnetic shield built of some material like ",
"Mu metal",
". The shielding effect has more to do with the magnetic permeability of the material vs. the frequency of the field, rather than mesh size."
] |
[
"Faraday cages are only effective versus time-varying fields. With these, the size of the mesh determines what frequency range the cage is effective at shielding. ",
"As ",
"/u/just_commenting",
" mentioned, there is shielding for magnetic fields with consists of either a high magnetic permeability material or a layer of superconducting material. The first provides a preferred path for the magnetic flux while the second forcefully excludes the fields through the ",
"Meissner Effect",
". ",
"Both magnetic shielding and RF shielding are very sensitive to how the full shield is sealed together. I know someone that worked on professional pager repair, and the work could only be done inside a double-walled Faraday cage with bank vault-like doors. Even with both doors closed, if the sealing bolts weren't closed, the pagers could still get pages. In my work with superconducting resonators (very sensitive to applied magnetic field) I've seen poorly performing tests that were entirely caused by the magnetic shielding not being well connected, making it essentially useless. ",
"Edit: Read twice, submit once."
] |
[
"It's best not to view virtual photons as actual particles at all. Virtual photons are not proper perturbations in the field like normal photons, but are more like incoherent vibrations."
] |
[
"Why are the pores on the face so much larger than anywhere else on the body?"
] |
[
false
] |
Reposted at the request if
|
[
"Age is a factor in the pore size, as when you age the skin on your body starts to lose its elasticity, causing it to stretch and the pores to enlarge. Sun damage can also thicken skin, which can cause larger pores. Prolonged sun exposure over time can also sap collagen, elastin and water from your skin, which causes the tissue beneath your skin to shrink and pull at the edges of your pores, making them sag and look bigger.",
"These are just some reasons that the pores on the face are larger than anywhere else on the body. Hope this helped. :)"
] |
[
"I don't see what age has to do with it since your whole body is the same age. Are you saying that the larger pore size is just because we don't cover up our face as much as the rest of our body?"
] |
[
"There's also an oil production component to it. The more oil that an area of skin produces, the more pools in the pores, stretching them out (hence the difference in pore size between, say, your nose and your arm). As the skin gets older, it doesn't bounce back as easily (lack of elastin) and the pores are permanently larger. That's why babies have barely visible pores.. It all goes downhill when puberty hits. ",
"Skin condition has a huge genetic component as well, so there are always going to be folks who hit the lottery jackpot with smooth, flawless skin and small pores. "
] |
[
"Why is it that digital storage sizes are powers of 8?"
] |
[
false
] |
I was looking through a variety of hard drives and USB memory sticks, I have curiously asked this my self for a while, but if anyone knows, please could you tell me why, is it because the way NTFS and FAT32 work? Or is there a longer story than that? Thank you for looking :-)
|
[
"I don't think NTFS nor FAT32 use that much space, Just let's do the math.",
"What they are selling you is one terabyte. ",
"The term Tera- impies that it's expressed in decimal and not in binary",
" so 1 Terabyte by definition has 1000",
" bytes (NOTE that it's not 1024) so what they are promissing is 1 000 000 000 000 bytes. ",
"Now when your computer reads how much space a drive has it expresses it in binary not in decimal so you have to convert it to ",
"gibibytes",
" wich gives you ",
" 1000000000000 Bytes / 1024 = 976562500 Kibibytes\n 976562500 Kibibytes / 1024 = 953674.31 Mibibytes\n 953674.31 Mibibytes / 1024 = 931.322 Gibibytes\n",
"So thats where windows gets the 931Gb that shows for your new 1Tb drive. ",
"I don't think NTFS ocuppies more than a few megabytes for an empty drive, let alone \"reserve\" 69 Gigabytes for just a table. Any home computer would shit himself if it had to search something in a 69Gb file, And I know it for experience."
] |
[
"Powers of 8? Do you mean powers of 2? It's possible you're thinking of the number 8 in terms of the common acceptance of there being 8 bits in 1 byte, but the sizes of digital information storage tiers are commonly prefixed according to a base 2 definition.",
"(2",
" = 1024 bytes = 1 kilobyte",
"(2",
" = 1 megabyte",
"(2",
" = 1 gigabyte",
"There is also a base 10 definition, which is more rounded and nice to work with for the layman and consumer. It more closely emulates the milli, centi, deci prefixes of the ubiquitous metric system.",
"Because there are 8 bits in 1 byte, and in ASCII, binary slots (0s and 1s) 8 bites wide can represent all 256 possible characters, and since a character can either \"be there\" or \"not be there\", like each of these characters in the sentences you're reading on your screen - it makes sense then that digital data, in general, not just digital storage, is represented in base 2 form.",
"Um, I have to go to lunch soon with my team, and I won't be coming back to my computer afterwards, but I'm sure someone can finish my line of thought, or correct it, if need be."
] |
[
"You lose ",
" space to that, but it's not nearly as significant as the 2",
" vs 10",
" conversion. With all the compounding of that 1000 vs 1024 error on the way up to terabyte scale, you end up with a situation where \"1 TB\" to a hard drive manufacturer is only \"931 GB\" for software."
] |
[
"Where do we draw the line between species?"
] |
[
false
] |
What's the difference between you and me? I know that we are very similar genetically, but at some point there has to be a blurry line, right? At what point do we decide "ok, that's a new species", instead of "that's the same species with the typical genetic differences"? Edit: Cool, thanks for the replies!
|
[
"We live without a strong definition. The definition is SUPPOSED to be that those within the same species can produce fertile offspring (the mating of a male donkey and a female horse (a mule) almost never produces a fertile offspring - there have been fertile females, but no fertile males) ",
"this is generally true and a basically true way to proceed ",
"However - there are a variety of instances in which this just doesn't hold. For regular animals this happens with hybridization and ring species - both of which have to do with adjacent animals sharing genes (look further into those if that is along the lines of what you were asking - it's definitely where the line becomes \"blurry\" as you said)",
"EDIT: forgot to explicitly say that there are other exceptions - generally dealing with things that reproduce asexually - or things that don't exist anymore that can't be tested (extinct creatures)"
] |
[
"overall excellent answer, but I'd dispute that ring species are an issue. You seem to be making the common mistake of thinking of animals in terms of individuals rather than populations. In a ring species, even if certain individuals may not be fertile with other individuals, the population as a whole is still a single breeding population. ",
"You broader point about the line being a bit blurry is still accurate though, as reduced fertility and behavioral differences can make populations functionally reproductively separated even though biologically they could still produce fertile offspring (hybrids). An example would be coyote wolf hybrids."
] |
[
"Afaik it's when two different organisms can no longer procreate. For instance, when one group of a certain species is isolated from the rest, the small group tends to have a faster genetic drift (punctuated equilibrium is the concept that smaller groups change DNA faster).",
"At one point, the DNA becomes different enough that most of each population can't procreate with the old group.",
"There's actually a new species (or almost species) of mosquitos that have evolved in the London Underground. Most of the underground mosquitoes can no longer mate with the original group, but a few of them still have enough of the original genes that they can."
] |
[
"Is it possible to calibrate an optical instrument using the cosmic background radiation as a source?"
] |
[
false
] |
[deleted]
|
[
"The cosmic microwave background is in the microwave range, how would that help for optical instruments?"
] |
[
"A more polite answer would be",
"No. Because the CMBR is in the microwave range and optical instruments mostly work in the visible light range."
] |
[
"I was wondering about that as I wrote My answer. But my point wasn’t to answer the question but to example a better way to phrase the OC’s answer. So I let it go.",
"But thank you for the info! I’ve never really considered microwave focusable through a lens."
] |
[
"Stemming from a TIL post (\"TIL the human womb is the oxygen equivalent of the top of Mt Everest, designed to keep the fetus asleep 95% of the time\"), what is the true oxygenation level in the womb and what percentage of the time are fetuses asleep?"
] |
[
false
] |
was posted on TIL, and basically the comments didn't really provide a clear explanation of their reasoning behind their title. Is the oxygenation of blood from the placenta truly equal to "the top of Mt Everest" and what percentage of the time are fetuses asleep in the womb? Are these directly related or independent of one another?
|
[
"That's actually not a bad comparison, sort of. There is about half as much oxygen at the top of Mount Everest as there is at sea level, in terms of partial pressure. There is about half as much oxygen in fetal blood as there is in adult blood. So on that point, it's about right.",
"Fetal blood is not the same as adult blood though, in that fetuses use fetal haemoglobin rather than the adult variety, and this form is better at functioning in a low-oxygen environment. But overall, yes, fetal blood is very low in oxygen, and the fetus (especially in the first trimester) is essentially developing in a low-oxygen environment: ",
"https://www.sciencedirect.com/science/article/pii/S1297958901001795",
"However, the reason for this is not known, though there are many theories. The most straightforward theory is simply from evolutionary biology - if our ancestors basically didn't have fancy things like umbilical cords, and an egg-bound fetus inevitably had low-oxygen compared to what a breathing adult would experience, then early development necessarily occurred in a low-oxygen environment.",
"If there was either no evolutionary route for changing this, or no advantage to doing so, it should not come as a surprise that the fetus is kept in a state of low-oxygen tension."
] |
[
"Stem cell quiescence and differentiation is greatly altered in conditions of hypoxia. Could be related to that."
] |
[
"They also have adapted erythropoietin secretion and oxygen sensing mechanisms."
] |
[
"Would a helium filled balloon rise faster than a regular air filled balloon when placed under water?"
] |
[
false
] |
[deleted]
|
[
"Yes, but insignificantly so. The difference between the density of helium and that of water is insignificantly larger than the difference between the density of air and that of water."
] |
[
" since I was curious, I calculated the speed at which the drag forces would equal the buoyant forces for both a helium balloon in air and an air balloon in water. At a speed of 5.51m/s, the drag force will equal the buoyant force for the helium balloon in air, and at a speed at 5.87m/s the drag force will equal the buoyant force for an air balloon/helium balloon in water. And now that I reread this comment, I realize I spent a lot of equations and calculations first answering the question wrong and then accounting for drag. I'd say this answer is a bit misleading since drag importantly relies on shape and fluid density, whereas buoyancy is related to the volume and density of the displaced fluid, so if you had odd shaped (torpedo-like) balloons I'm assuming the drags would be much smaller and the differences may be more pronounced.",
"This is correct but I believe the question is asking about a balloon filled with air underwater versus a balloon filled with helium underwater. God, it's been forever since basic physics but essentially the ",
"buoyant forces",
" are the same (Fb = volume displaced fluid * weight of displaced fluid * gravity) as the water displacement is equal (assuming balloons of equal volume). However, the force of gravity on the balloons would be different - according to this ",
"website",
" (too lazy to check up otherwise) helium is about 7 times less dense than air. The mass of the balloons are therefore different (assuming equal volumes) and thus the force of gravity is weaker on the balloon filled with helium. ",
" again, as pointed out below, the drag force will soon equalize the velocities of both balloons, so this overly detailed explanation is only really applicable when t=0 and therefore isn't practical.",
"So the acceleration of the helium balloon is also about 7 times faster than the air balloon under water, even though the buoyant forces are the same. ",
" but as OneShotHelpful pointed out below, the drag forces will equalize the velocities fairly quickly due to the dense nature of water, so actually (see my post further below) both balloons will rise at the same speed."
] |
[
"You need to account for drag, too, which will be the great equalizer here."
] |
[
"number of protons in the universe"
] |
[
false
] |
I've often seen it said on the internet that there are 10 protons in the universe. How was this number derived and is it meaningful ?
|
[
"1) We know how much mass a proton has.",
"2) We know that the sun comprises 99.86% of the mass of our solar system. So we assume that the mass of the universe is overwhelmingly dominated by stellar objects. (We may add a bit of mass to account for nebulas, etc.)",
"3) Based on our observations, we can estimate the mass of the average star.",
"4) Based on our observations, we can estimate the number of stars in the average galaxy.",
"5) Based on our observations, we can estimate the number of galaxies in the observable universe.",
"6) Number of protons in a star * Number of stars in a galaxy * Number of galaxies in the observable universe = Number of protons in the observable universe."
] |
[
"Nice explanation, you might want to stress the \"observable\" part, though."
] |
[
"the observable universe is an unknown fraction of the universe though right ?"
] |
[
"Why do we get headaches when we look at screens too long?"
] |
[
false
] | null |
[
"Not just looking at screens, but any kind of eye strain can lead to tension headaches caused by reduced blood circulation in the muscles around the eyes."
] |
[
"Then I must ask, how does looking at a screen reduce blood circulation in the muscles around the eye?"
] |
[
"Admittedly I'm no expert in anatomy, so maybe someone with a bit more knowledge on the subject could add to this, but essentially when focusing on an object the muscles around the eye tighten and this contraction makes less blood flow through the muscles."
] |
[
"Why have CPUs been limited in frequency to around 3.5Ghz for so many years? What prevents us from increasing the frequency to 10, 100, 1000Ghz?"
] |
[
false
] | null |
[
"(Disclaimer: Possibly a too-dumbed-down version)",
"http://en.wikipedia.org/wiki/Transistor#Transistor_as_a_switch",
"http://en.wikipedia.org/wiki/Leakage_(electronics)",
"The individual bits in your computer aren't so much 1 and 0 as they are High and Low voltage, with 'on' and 'off' being relative. To reach a desired frequency the bits need to be able to increase or decrease their voltage fast enough to reach the high/low voltage threshold before they're accessed during that cycle.",
"To stop your computer from melting due to heat the high voltage used has to be as low as possible. Current hardware uses such a minute amount of voltage that the background ",
"crazy physicsy magic",
" makes a significant difference to the signal where before it wasn't really noticeable. This is also (I believe?), in addition to the time it would take to ",
" drain the transistor, the reason the \"off\" threshold can't simply be zero.",
"Overclockers get higher frequencies by increasing the voltage to allow for stronger(faster) on-off signals, but have to compensate by bolting 1kg of copper (or compressor from an old fridge) on the cpu to keep it from spontaneously combusting ."
] |
[
"(Disclaimer: Possibly a too-dumbed-down version)",
"http://en.wikipedia.org/wiki/Transistor#Transistor_as_a_switch",
"http://en.wikipedia.org/wiki/Leakage_(electronics)",
"The individual bits in your computer aren't so much 1 and 0 as they are High and Low voltage, with 'on' and 'off' being relative. To reach a desired frequency the bits need to be able to increase or decrease their voltage fast enough to reach the high/low voltage threshold before they're accessed during that cycle.",
"To stop your computer from melting due to heat the high voltage used has to be as low as possible. Current hardware uses such a minute amount of voltage that the background ",
"crazy physicsy magic",
" makes a significant difference to the signal where before it wasn't really noticeable. This is also (I believe?), in addition to the time it would take to ",
" drain the transistor, the reason the \"off\" threshold can't simply be zero.",
"Overclockers get higher frequencies by increasing the voltage to allow for stronger(faster) on-off signals, but have to compensate by bolting 1kg of copper (or compressor from an old fridge) on the cpu to keep it from spontaneously combusting ."
] |
[
"(Disclaimer: Possibly a too-dumbed-down version)",
"http://en.wikipedia.org/wiki/Transistor#Transistor_as_a_switch",
"http://en.wikipedia.org/wiki/Leakage_(electronics)",
"The individual bits in your computer aren't so much 1 and 0 as they are High and Low voltage, with 'on' and 'off' being relative. To reach a desired frequency the bits need to be able to increase or decrease their voltage fast enough to reach the high/low voltage threshold before they're accessed during that cycle.",
"To stop your computer from melting due to heat the high voltage used has to be as low as possible. Current hardware uses such a minute amount of voltage that the background ",
"crazy physicsy magic",
" makes a significant difference to the signal where before it wasn't really noticeable. This is also (I believe?), in addition to the time it would take to ",
" drain the transistor, the reason the \"off\" threshold can't simply be zero.",
"Overclockers get higher frequencies by increasing the voltage to allow for stronger(faster) on-off signals, but have to compensate by bolting 1kg of copper (or compressor from an old fridge) on the cpu to keep it from spontaneously combusting ."
] |
[
"Why do some metals glow red hot at their melting point (i.e. Iron, nickel, etc) while others (i.e. Aluminum) are silver when molten?"
] |
[
false
] | null |
[
"Different melting points.",
"\nAt roughly around 700°C (=1292°F) the human eye notices a faint dark red glow.\nAluminum is already molten at this temperature wheras iron needs a lot more heat and is already glowing bright yellow (around 1550°C (=2822°F))"
] |
[
"The colour of glowing metal is dominated by ",
"black-body radiation",
", which depends on temperature rather than chemistry. If you continue heating liquid metals you will see the colour change with increasing temperature."
] |
[
"Things glow \"red hot\" due to black body radiation, which depends only on temperature. Anything hot enough would glow in the viaible range. ",
"The reason iron glows near his melting point and alominium doesn't is that the melting point of iron is much higher, thus by the time it melts it reached a temperature in which things glow in the visible range. Some things glow well before their melting point, like stone and some ceramics. ",
"(it is important to note that everything always glows, just not in light you can see). "
] |
[
"Are there alternative treatments to antibiotic resistant infections?"
] |
[
false
] |
Recently, there have been a slew of articles about bacteria that are now resistant to our antibiotics of last resort. Apparently, will be the first to cross the finish line. Barring the discovery of new more potent antibiotics, what will medicine do to fight these antibiotic resistant infections?
|
[
"Billions are spent annually funding many avenues of research looking for new drugs. The catch is, as soon as a new drug get through trials and FDA or similar for approval, bacteria have already developed resistance to it. ",
"To keep from being a total storm cloud, the hope is that these new drugs can target different points of weakness in an infection, and combinations of drugs can be used in a treatment. "
] |
[
"In eastern Europe bacteriophages have been used for a long time to fight infections. Phages are pretty much everywhere and they selectively infect bacteria. You can take a sample of phages and select the right one for your infection. Of course bacteria evolve and can develop resistances against phages as well, but it could buy us some time.",
"Also I've recently read about chemists using a synthesis method to make new antibiotic-like meds. If I've understood it correctly there is some randomness involved so that they get a variety of new structures which are then being screened."
] |
[
"My understanding was that, as you said, combination therapy is quite important: ",
"https://en.m.wikipedia.org/wiki/Combination_therapy"
] |
[
"I have a question about magnetism and google didnt give me an answer"
] |
[
false
] |
I was just wondering what happens if you bend a magnet (like physically bend the damn thing). Say you have a long thin magnet with the field passing through the width instead of the height. If you bend that magnet so that the ends meet, would you have a circle where the entire outside is a single pole? If so, say you have 2 of these things and put them flat on a table, can they repel each other constantly? (if both their outside poles are the same anyway) What if you take a plate like this instead of a stick and fold it into a sphere? Does it act like a magnet with a single pole, the other pole being the inside? It's been on my mind all day and it would be nice of someone knew the answer. It's probably silly but I would like to know anyway
|
[
"No. Such a thing would be a magnetic monopole, and they don't exist (they might exist in quantum theory, but that is an entirely different thing). As all the field lines have to connect a northpole with a southpole, it is impossible to contain a single magnetic pole inside something.\nIn the case of the ring, the magnetic field lines would just wrap around the ring.\nYour proposed sphere-monopole wouldnt be magnetic at all."
] |
[
"Monopoles don't exist.",
"http://en.wikipedia.org/wiki/Magnetic_monopole#Searches_for_magnetic_monopoles"
] |
[
"When you try to bend a modern, realistic magnet it will snap in half, so this scenario uses an imaginary magnet with perfect properties.",
"If the magnet's electrons were all spinning in the same direction, and it was impossible to reverse any of their spins, you'd end up needing an ",
" force in order to bend that magnet into a complete loop. The ",
"magnetic field lines",
" represent the field. Whenever they're really packed dense, the field is stronger. It's obviously stronger at the poles. With that in mind, imagine ",
"this scenario",
". The poles are now switched 90",
" and are color coded. If you look at the third step, imagine the magnetic field lines getting super compressed between the two faces. Now if one face was completely red, and one was completely blue, that would be no problem. But because each of the like-poles are sitting next to each other, they are repelling with an incredible force.",
"A very similar question was asked in ",
"this thread",
" just yesterday. "
] |
[
"What would you see if a particularly accident prone astronaut shone a flashlight at you while falling into a black hole?"
] |
[
false
] |
Say you're somehow static relative to the singularity. I know light can't escape the event horizon so what would be seen by you from the flashlight in the fractions of a second (from your perspective) before it is crossed?
|
[
"So, you don't actually observe the astronaut crossing the event horizon. What happens, from your frame of reference, is that the astronaut gets more and more time dilated, and moves slower and slower as they approach the event horizon. This means that the light gets dimmer and dimmer, because the time between each photon being emitted gets larger and larger. Also, each photon gets stretched out more and more, so your white light looks redder and redder, until it disappears out of your vision."
] |
[
"Lower power over a longer time interval is what happens.",
"The light doesn't have a hard shut off, but there is a stage where you're getting photons far too slowly and with such low energy that it's considerably less than the background."
] |
[
"The light doesn't have a hard shut off, but there is a stage where you're getting photons far too slowly and with such low energy that it's considerably less than the background.",
"The intensity drops exponentially. You quickly receive the last photon ever. A bit later you can calculate a 10",
" probability to receive another one but that doesn't really matter any more."
] |
[
"If a small object is in orbit of a larger object, will the smaller object crash into the large object eventually?"
] |
[
false
] |
There is no debris of any size in this hypothetical.
|
[
"If the two are in an isolated orbit with no external perturbations, the orbit will still decay over a very long time due to gravitational radiation."
] |
[
"Roche radius",
" all up in here. In the radius- collision. Outside- perfectly fine."
] |
[
"That's a completely different issue: inside the Roche radius (which is different depending on the size and composition of the orbiting object) the orbiting object will ",
", not decay in its orbit. "
] |
[
"How do animals become larger? Or rather, what determines their size?"
] |
[
false
] |
Spurred on by this of a replica whale heart. I don't even know how to word this properly. What determines the equilibrium size of an animal?
|
[
"Well, that whale heart sure is astonishing. The reason that whales can be so big—larger than any terrestrial animal—is they live in water. The limiting factor to land animal size is gravity. As animals grow in size, their mass grows as the cube ( d",
" ) of their dimensions, while the surface area they use for support only grows as the square ( d",
" ). ",
"Cube-square law.",
"Whales are not bound by this restriction, as the water they live in creates a buoyant force around their entire underside. (This is why whales die when they are \"beached\" on land—gravity ",
" crushes their organs.)",
"In a more general case, animals typically stay the same size over short stretches of evolutionary time because getting bigger means you need more nutrients. And getting more nutrients means exposing more surface area to the environment, which is hindered by the cube-square law. There are many evolutionary adaptations which solve this particular problem. One is lungs. Have you ever seen a lung up close? ",
"They are really branched on the inside.",
" If you unfolded all those branches, you would end up with A LOT of surface area, which we use for gas exchange, to get oxygen into our blood. The circulatory system (arteries and veins) is also an adaptation for delivering more nutrients to internal cells. ",
"Capillaries show a similar branching pattern to the lungs.",
"Does that answer your question somewhat?"
] |
[
"Another interesting tidbit.. because of the cube/squared law warm-blooded species have a definite maximal-size advantage over other animals. It is much easier to attain and maintain an optimal body temperature for large mammals as they can metabolize heat which radiates from the inside out. Cold blooded animals are restricted because they have to have heat radiated (or conducted) from the outside in (much more difficult as body volume increases).",
"This is one of the main reasons why people think dinosaurs were probably not (completely) cold-blooded.",
"EDIT: I neglected aquatics again.. added conduction to the body heat statement."
] |
[
"Never turn your back on the aquatic mammals."
] |
[
"What (if any) are the hazards of being exposed to perfluorocarbons?"
] |
[
false
] |
Recently in New York City the MTA is starting an airflow test in the subway. This makes it seem like they are putting millions of people in danger. Is this safe or should I start taking a taxi for the month?
|
[
"That card looks like it was made by someone other than the MTA for no reason other than to scare you. The amounts of these perfluorocarbon gases released are so small that there are probably far greater concentrations of compounds that are legitimate concerns, like hydrogen sulfide and carbon monoxide, and even those shouldn't be a concern. ",
"That said, the card is probably referring to studies where animals were exposed to high levels of one particular (unnamed, which is a red flag) perfluorocarbon that ended up causing problems. There are plenty of perfectly safe materials that will cause problems at high enough concentrations (oxygen, for example). ",
"See this ",
"press release",
" from Brookhaven National Lab for details."
] |
[
"Perfluorocarbon tracers",
" are chemically inert and not dangerous at all to inhale, unless you are inhaling so much that it is reducing your oxygen intake. In other words, don't breathe it ",
".",
"The stress experienced by an uninformed person reading that scare flyer would have a far greater health impact than tracer gases would ever present."
] |
[
"That card looks pretty false. I'd like to think the state wouldn't straight up expose millions of people to a gas paraphrased by the card to not be fully understood with respect to health effects. ",
"I may only have a bachelor's in chemistry, but ignore this, the taxis are too expensive."
] |
[
"Is it possible to see the constellations that we see from Earth from other parts of the milky way?"
] |
[
false
] |
[deleted]
|
[
"Yes, from another nearby solar system (usually), but no, not from the other side of the Milky Way. None of the constellations have stars with similar distances from Earth, so if you start moving around, the apparent alignment of those stars would change slightly from what we see normally. Most of the stars are far enough away that just moving to the next star system over wouldn't change much, but a few nearby stars would significantly change position. For instance, Alpha Centauri, the brightest star in the constellation Centaurus, and the nearest star system to the Sun, would be in a completely different position, as would Sirius (the brightest star in Canis Major), Procyon (the brightest star in Canis Minor), Vega (the brightest star in Lyra), Altair (the brightest star in Aquila), Fomalhaut (the brightest star in Piscis Austrinis) and of course a ton of other somewhat nearby stars. Not to mention that, when you go to another star system, the Sun would become a star in the night sky, possibly belonging to a constellation. For instance, from Alpha Centauri, the Sun would appear to be the brightest star in the constellation Cassiopeia, on the leftmost end (with respect to our northern pole)"
] |
[
"Constellations are man-made assignments to groups of stars that happen to be somewhat close in the sky from our point of view. You get different constellations just from asking different cultures ",
"."
] |
[
"That's interesting, thank you for answering!",
"I wonder what constellations they have on the other side of the galaxy. They as in aliens. We all know we cant be the only ones lol"
] |
[
"What is the Riemann Zeta Function, and what's the point of it?"
] |
[
false
] |
I've read into this thing via wikipedia and wolfram mathematica, and I still have no idea what it's trying to do.
|
[
"Let's first describe something that's NOT the Riemann zeta function.",
"Consider these series:",
"2",
" + 2",
" + 2",
" + 2",
" + 2",
" + ... = 2",
"3",
" + 3",
" + 3",
" + ... = 3/2",
"4",
" + 4",
" + 4",
" + ... = 4/3",
"We know these values because they are geometric series. We can think of these numbers as values of a function f of a variable x, which is",
"x |---> x",
" + x",
" + x",
" + ...",
"In general, not all x will be in the domain of f, because the above series will be meaningless. For instance, the series will diverge if you plug in x between 0 and 1, and be meaningless if x is 0.",
"But on the other hand, we can use the geometric series formula to calculate f(x), and we get f(x) = 1/(1-x). Now, this function on the right hand side has a bigger domain than f(x) -- it makes sense to evaluate it on any x other than 1, and we might call it the \"continuation of f.\" We can even consider it as a function on the complex numbers, again there's no problem in the domain except x= 1.",
"(Note two, if you have more background: you might object -- we took a function defined for x > 1, and then continued it with some formula. But what if we found some different way to \"continue\" it? Who says this formula is the best? We could've chosen any formula we liked for x<1 and said, \"ok,\" this \"continues\" f. There is a precise sense, coming from complex analysis, in which this is the best continuation of f, but if you're willing to believe this, you can understand the rest of the answer without taking anything else on faith.)",
"The Riemann zeta function is what we get when we put the variable in the exponent, rather than the base: so, consider the series",
"2 |----> 1/1",
" + 1/2",
" + 1/3",
" + ... = 1 + 1/4 + 1/9 + ... = ?",
"3 |-----> 1/1",
" + 1/2",
" + 1/3",
" + ...= 1 + 1/8 + 1/27 + ... =?",
"It's not hard to see that if we plug in any real number greater than 1, these series converge. The function that takes x to the value of this series is written x |---> zeta(x) (actually, traditionally the variable is written as s for whatever reason when we talk about the zeta function).",
"So,",
"zeta(s) = 1",
" + 2",
" + 3",
" + ...",
"This series converges for s > 1.\nWhat IS hard to see is what these values converge to. Euler famously proved that",
"zeta(2) = pi",
" / 6",
"and in general one has nice formulas for zeta of even integers in terms of Bernoulli numbers and powers of pi. The values of zeta at odd integers are not known (we can approximate them as well as we like with a computer, and Apéry proved zeta(3) is irrational, and this is more or less all that's known).",
"Now you might ask, does zeta admit a continuation like our function f did? The answer is yes: there's a closed-form formula for zeta, but it's nowhere near as easy to calculate with as 1/(1-x). So in fact, one can \"extend\" zeta to the complex plane (except for s = 1, where it turns out to have a \"pole\" just like 1/(1-x)), and then it makes sense to ask what something like zeta(-1) is. (It's -1/12, and it's been a fad on the internet recently to see people say things like\n1 + 2 + 3 + ... = -1/12\nwithout explaining where this comes from!)",
"So OK, what's the point of it? This is a little more difficult to explain if you have less mathematical background, but recall our function f from above. Then one has the fundamental identity",
"zeta(s) = f(2",
" )*f(3",
" ) * f(5",
" ) * f(7",
" ) *f(11",
" ) * ...",
"where the bases of the exponents showing up on the right hand side are only the prime numbers, and nothing else!",
"This identity actually isn't very hard to prove (at least formally) when the series both converge -- if you are comfortable with infinite products; you might try it as an exercise.",
"What this means is that zeta is a function of a complex variable that \"knows\" something about the primes, and since we know lots about functions of complex variables, and basically nothing about primes, this is a very good thing. For example, Euler used the zeta function to prove that the series",
"1 + 1/2 + 1/3 + 1/5 + 1/7 + ...",
"of the reciprocals of the primes diverges. Riemann used it to prove very tight estimates on the number of primes less than a given n, but he had to assume that zeta(s) is never 0 unless s is a negative odd integer or the real part of s is 1/2, and he was unable to prove this assumption.",
"That assumption is the famous \"Riemann hypothesis\" and is still open over 150 years later. It is perhaps the most famous open problem in number theory, primarily because many good results, like Riemann's original result, are contingent on it being true."
] |
[
"What are you understanding and not understanding about it and what would you like to know? It's tough to answer your question because it is a bit vague. Also what are your expectations for a \"point\" of a function and what it must try to do? Practical applications? Appearance in nature? "
] |
[
"I'm only a physicist and not a mathematician, but wouldn't it be more correct to say that the Riemann hypothesis is actually a problem in complex analysis that happens to have (HUGE) applications to number theory?",
"The zeta function is just some meromorphic function and we want to find its roots.",
"How serious are people about proving the hypothesis? Somebody once told me that probably every mathematician tries to prove the thing one weekend for fun, without success.",
"What kind of techniques do people try to throw at the problem? Is it \"standard\" complex analysis stuff, or do people often bring in techniques from fields that are somehow connected to complex analysis, like Conformal Field Theory?"
] |
[
"What selection pressures caused gender/sex to evolve?"
] |
[
false
] |
Since life came from a single celled organsim, what are the selection pressures that could've caused mutations/genes that resulted in genders? Bonus questions I'd much appreciate if you could answer: What selection pressures along with changes in genes caused different developments of sexual reproduction mechanisms? In essence how is it that some species reproduce in a manner that is completely different from a species whom not long ago came from the same ancestor? Are their species where more than two genders/sexes evolved? Thanks in advance.
|
[
"There's a pop science book that has a good overview of some of the theories related to it called The Red Queen by Matt Ridley.",
"One of the more popular theories is that sex evolved to fight off disease. The longer lived the species, the more likely they are to have sex, because viruses and bacteria have very short lifespans. If we didn't have sex, we would reproduce much faster. We wouldn't have to find a mate, and our genes would almost always be expressed. ",
"However, a virus would be able to figure out vulnerabilities, by mutating over time. Your child would have the very same vulnerability. ",
"It's been suggested that humans can subconsciously tell who has different immunities than themselves through smell and taste. People \"prefer\" smelling the sweat of people more genetically different than themselves. ",
"Basically, over 80 years, a disease catches up to your immune system which is made up of x number of locks. The disease had multiple attempts to your one set and has now found the keys. If your child were born asexually, he would have the same locks. But you had sex with someone with a very different set of locks and you randomly swapped them around. Now that disease is at square one. ",
"Bananas are an example of the issues of asexuality, since they are grown asexually. People used to eat a different banana species, but it was wiped out by Panama disease and we switched to a different type that was thought to be resistant. But there's another strain of that disease originating in Malaysia that kills off bananas even quicker. Scientists are trying to create resistant species before the disease can spread to the western hemisphere.",
"As to whether there are species with more than two sexes, yes. But they tend to be extremophiles. I believe some slime molds do. I remember reading about it in the book I mentioned. He spoke about why it's an exception, and that basically unless there are extenuating reasons to have multiple sexes, the vast majority of species will go to a 2 sex default. I remember this portion the least. "
] |
[
"As to whether there are species with more than two sexes, yes. But they tend to be extremophiles. I believe some slime molds do.",
"Actually many fungi have large numbers of \"mating types\", which are essentially sexes. The number of mating types depends on the species of fungus: some only have two, but some have thousands. To reproduce successfully, the fungus just needs to find someone with a different mating type than itself (which makes sense given the earlier discussion of genetic diversity). ",
"Source"
] |
[
"Your response seems to mostly be about sexual reproduction. It seems to me that it could be possible to have a species with sexual reproduction but only one gender - there would have to be some mechanism to prevent self-impregnation."
] |
[
"Why do you salivate so intensely when you're about to vomit?"
] |
[
false
] | null |
[
"Just to be slightly more specific, from wikipedia:\n\"Increased salivation to protect tooth enamel from stomach acids. (Excessive vomiting leads to dental erosion). This is part of the PNS output.\"",
"http://en.wikipedia.org/wiki/Vomiting#Pathophysiology",
"It's pretty cool to read the ways your body deals with vomiting"
] |
[
"Just to be slightly more specific, from wikipedia:\n\"Increased salivation to protect tooth enamel from stomach acids. (Excessive vomiting leads to dental erosion). This is part of the PNS output.\"",
"http://en.wikipedia.org/wiki/Vomiting#Pathophysiology",
"It's pretty cool to read the ways your body deals with vomiting"
] |
[
"You salivate because emesis (the act of throwing up) is heavily mediated by the parasympathetic nervous system. The PNS serves as your \"rest and digest\" system. Increase in parasympathetic tone will increase gut activity and increase secretions in general.",
"tl;dr Parasympathetic stimulation=increased secretions "
] |
[
"If I'm sitting on the 12th floor of our condo (~120-150 ft), how far out can I see until the ocean disappears over the horizon?"
] |
[
false
] |
Approximately. According to my brother and Life of Pi (which I haven't validated for myself), you can see ~2 miles to the horizon from sea level. Assuming that's close to accurate, I was wondering just how much that distance increases according to height. Or rather, what the relationship is between height relative to ground (sea level in this case) and the distance to the horizon, taking into account the curvature of the Earth. I imagine there's a decently simple way to to it mathematically, but I've yet to really sit down and work it out. Thanks reddit!
|
[
"The maths comes out ",
"quite simple",
", it's sqrt(2*R*h), where R is the radius of the Earth (about 6500 km) and h is your height above the surface.",
"Plugging in 150 feet gives you about 24 kilometres, or 15 miles."
] |
[
"would it be further if you take refraction into account?"
] |
[
"Atmosphere. ",
"seemingly it would be further but over a distance as short as that, probably not by much.\n",
"http://en.wikipedia.org/wiki/Atmospheric_refraction#Terrestrial_refraction"
] |
[
"What would happen if two black holes collided?"
] |
[
false
] |
What I mean is, what would happen if two black holes collided, like two asteroids colliding. would they both merge and make one black hole as massive as the sum of both of their masses? If one was larger, would the larger one absorb the smaller one? What would happen?
|
[
"They would merge to form one large black hole. This process would generate a large gravitational wave signal -- gravitational waves, which are predicted by general relativity, have never been directly observed -- as they spin in towards each other and merge. Groups such as LIGO and VIRGO are designed to look for such signals, and should have sufficient sensitivity by ",
"2017",
".",
"There's a nice description of black hole mergers ",
"here",
"."
] |
[
"This is one of the things projects like LIGO and VIRGO should be able to answer. Gravitational wave detection is very hard, because it requires extremely sensitive measurements. In about 5 years, LIGO, for example, expects to have the sensitivity to address this question meaningfully and to begin doing gravitational wave astronomy in earnest. LIGO has a lot of information for the public about their project and it's scientific goals ",
"here",
"."
] |
[
"How often does this occur?"
] |
[
"What are the obstacles for a mission to Europa ?"
] |
[
false
] |
As far as I know, there is no mission planned to explore Europa and its supposed oceans. Why is that ? Is seems that technologically it's not unfeasible: We know how to send rovers, we have , and while I'm not sure, it doesn't feel super difficult to imagine a robot melting the ice (through radioactivity maybe?) until it reaches the liquid oceans and then send pictures / data of whatever it finds there. But as there is no mission planned or even talked about (not that I've heard of), despite the fact it's regularly quoted as the "most likely place to have life", there must be some severe obstacles.
|
[
"Sure, but we already have procedure for that, right ? I remember the rover we put on mars was carefully decontaminated."
] |
[
"Technologically it's entirely possible to go to Europa. The problem is undoubtedly finding the (political and public) motivation to do so. Cassini and the Huygens probe were launched under a similar premise, explore Saturn and Titan, which was the most likely life supporting planet, with it's thick atmosphere and high concentrations of organic carbon. It cost over $3 billion. I'm sure that we can recycle a large portion of that design work, but it's still not an easy sell, especially when you consider what practical gains come from such a mission."
] |
[
"I might be wrong but I believe there would be practical gain as to know that life can develop in different environments than the terrestrial one.",
"\nAs for the political and public motivation, how is that worse than, say, send a rover to Mars ? (or basically any scientific research that doesn't have any direct benefit) "
] |
[
"How can a constant vary?"
] |
[
false
] |
I've been doing some reading about varying constants and I can't understand it. I just can't get past the name... it is very oxymoronic. I try to read the articles online and understand the concept but I always get hung up on the principle. It is very counter intuitive. Could someone explain how its possible? If the fine-structure constant varies over time wouldn't it not be a constant?
|
[
"Something can be a constant over time, or over space, or both.",
"So in this case, the fine structure constant is constant over space, but not over time."
] |
[
"For example, Hubble's constant is the reciprocal of the age of the universe."
] |
[
"A useful analogy, but let's just for clarification note that Newton's gravitational constant G is a universal constant (6.67E-11 N/(m/kg)"
] |
[
"Can someone explain natural logs to me in a straightforward manner? Maybe using graphs?"
] |
[
false
] |
I use them for work and grad school all the time, but I really don't fully understand what a natural log of a number is (or a log, obviously). I've read a lot of posts here on but still it hasn't sunk in.
|
[
"The whole argument is based on the idea that e",
" is close to 1+",
" for small ",
". This is not true for large ",
". If you like you can draw the graphs and see for yourself."
] |
[
"The natural log of a number ",
" is the power you need to raise Euler's number ",
" to to get the number ",
". ",
"That is, ln(A) = B, e",
" = A. ",
"It's used a lot in systems involving growth as the function e",
" is one where the rate of change of the amount of stuff is proportional to the amount of stuff. This means the slope of a function e",
" is e",
" For example, the rate of reproduction of a group of animals is proportional to the size of the group of animals. ",
"Since y=e",
" is a common general function, then the natural log ln(y) = x is also common. "
] |
[
"For small x, e",
" is very close to 1+x. (since the slope of e",
" is also e",
" the slope at x = 0 is e",
" = 1. So 1+x is the tangent line of e",
" at the point (0,1)) Taking the log of both gives:",
"e",
" ~ 1+x",
"ln(e",
") ~ ln(1+x)",
"x ~ ln(1+x)",
"if x = A/B -1, and A/B ~ 1 means that x ~ 0",
"A/B - 1 ~ ln(A/B)"
] |
[
"Does Einstein's theory of relativity connect electric and magnetic fields?"
] |
[
false
] | null |
[
"Yes; namely under changes of inertial frames in relativity (Lorentz transformations) E and B fields mix into eachother.",
"Super minimal example to show this: static charge, there's only an E field. You change reference frame, it gets moving and therefore part of the E has turned into a B. ",
"Said in modern words, this implies E and B must be part (components) of a larger object that \"transforms well\" under Lorentz transformations, that is to say it doesn't mix into anything else, just into itself. This object is the Maxwell tensor F."
] |
[
"Yes! In fact Einstein's original paper on special relativity is \"On the Electrodynamics of Moving Bodies\" (well it's actually \"Zur Elektrodynamik bewegter Körper,\" but you get the point). A short description is that electrostatics (Gauss's Law) plus special relativity (the Lorentz transformation) give you electrodynamics, that is, electricity and magnetism (ok, you need a few other things like the superposition principle). If you're interested this is the approach, Edward Purcell, who won a Nobel prize for his work on nuclear magnetic resonance which is the technology behind MRI machines, wrote an introductory (at the college level) book on E&M that teaches magnetism as a result of electrostatics and relativity. It's a really beautiful book that enjoys a great reputation among students and physicists.",
"It's worth pointing out that viewing magnetism as emerging from electricity and relativity is of course ahistorical.\nMaxwell's synthesis of the subject was published in 1865, forty years before Einstein's paper, but classical electrodynamics is consistent with special relativity (unlike Newtonian mechanics for example). Indeed, the laws of classical electrodynamics directly led to Einstein's theory of special relativity, hence the name of the paper."
] |
[
"Yes, it's covariant. The potential is not gauge-invariant though, unlike F, and therefore it's not observable. A description of the physics using A is redundant because of the gauge symmetry, while directly using F has no ambiguity. However, the variational formulation cannot be done unless you use A as your fundamental variable.",
"This is not really affected much by relativity, btw."
] |
[
"Dan Freedman claims that newborn infants have distinct cultural differences. How is this possible?"
] |
[
false
] |
He did a study on newborns in the '70s and concluded that their different behaviors were cultural:
|
[
"Newborns though. A day old."
] |
[
"Right, but how would parenting affect newborns?"
] |
[
"Right, but how would parenting affect newborns?"
] |
[
"We all know that hot air rises, but my question is why the energy of the atoms is seemingly directed upward?"
] |
[
false
] | null |
[
"I think you have the reasoning confused here. Hot air rises because it has expanded. Charles law tells us that with pressure being unchanged, an increase in temperature means an increase in volume. The less dense air floats the same way that oil floats on water."
] |
[
"This is not density-driven buoyancy but so-called ",
"granular convection",
". It seems odd to give an example in which the denser object can rise due to size differences when trying to explain hot air rising. The only similarity, it seems, is that something is rising."
] |
[
"This is not density-driven buoyancy but so-called ",
"granular convection",
". It seems odd to give an example in which the denser object can rise due to size differences when trying to explain hot air rising. The only similarity, it seems, is that something is rising."
] |
[
"What are the forces that are causing this? (.gif inside)"
] |
[
false
] |
I saw this is a "WTF" thread, and I was wondering what caused it... it seems like it could be the result of a really intense vacuum?
|
[
"To test the car's resistance to an internal vacuum and to see that if it does implode, it won't throw shrapnel or anything like that I guess."
] |
[
"You pump steam inside the tank car. As the steam condenses, it creates a vacuum. This vacuum destroys the car."
] |
[
"This one was done on purpose as a demonstration to show the effects of pulling a vacuum on it. This can happen when the product is pumped out of the car but the relief valves are left in the closed position."
] |
[
"[Materials Science] If I wanted to leave a message for future denizens of Earth what is the most enduring media/method I could use?"
] |
[
false
] |
Words carved in stone? USB stick embedded in plastic?
|
[
"Here's an article about ",
"using Platinum and Sapphire",
". They hope it will last 1 million years."
] |
[
"granite, possibly, although carving something on the moon is the most enduring thing I can think of."
] |
[
"The oldest samples we have from Earth are zircons so that would be a good suggestion. For protection I would stick that zircon in a granite and then it should live a good long time."
] |
[
"Settle a bet: would lightning do anything to a tank?"
] |
[
false
] |
My friend and I are at an impasse. He claims that a lightning strike on a tank would, at the very least, disable its electronic systems. I, on the other hand, believe that the electricity would take the path of least resistance straight through the hull and into the ground. My contention is that modern battle tanks, developed during the Cold War, were shielded against EMP to make them better survive a nuclear blast, and that the electronic systems should thus be isolated from the hull itself. Assume, for this scenario, that the lightning strikes the hull and not an antenna, which we both agree would have deleterious effects on at least the radio systems.
|
[
"I'm going with \"nothing\"",
" for a regular ol' steel-armor-plated tank. At least, for some value of \"nothing\" -- I assume you don't really care if there's cosmetic damage on the tank.",
"Tanks with active armor are a different story, of course. Also, I don't know the electrical properties of DU armor - could be a different story. But steel? Yah, that'll do ya."
] |
[
"The tank hull would form a Faraday cage to protect the insides of the tank, this also protects any ungrounded circuitry in the tank.",
"As for shielding against an EMP - that is utterly irrelevant, the magnetic shockwave from an EMP is negligible compared to the voltage in a direct lightning blast."
] |
[
"Because the tank has a metal frame, the voltage will go through the frame and since metal has very low resistivity the frame will conduct charge in a uniform way. Anything that is inside the frame is going to be protected as there will be an equal amount of charge on either side, so no current will pass through.",
"Cars that get zapped often have no electrical problems at all for this same reason, even though the electrics in a car is not shielded in any way."
] |
[
"Is eating fruit important, or when people say 'fruit and vegetables', are the vegetables the important part of that?"
] |
[
false
] |
[deleted]
|
[
"Doing surveys to determine the benefits of diet is typically fraught with challenges presented by confounding variables, and the limited accuracy of self-reporting.",
"... What does the evidence suggest?",
"The evidence suggests that in the short term (like a year) humans can do just fine with very little in the way of fruits and vegetables. For celebrated examples you can look at Derek Nance or Vilhjalmur Stefansson. (It's worth pointing out that these 'meat only' eaters did eat things we don't usually eat in the U.S. today like organ meat.)",
"... might well achieve the same result ...",
"A salient question here is \"what are you trying to achieve by eating fruits and vegetables?\" In other words, suppose you switched to 'all vegetables' instead of 'fruit and vegetables,\" and it turned out that it didn't work. How would you notice?"
] |
[
"\"Good amount of sugar\" reads \"lots of calories\" to me, regardless of pancreas impact.",
"I suspect that's what he meant."
] |
[
"The five portions of fruit and veg aren't exact so much as a convenient number of a food group that contains a lot of important micronutrients. Like rufus said, you can get (most of) these micronutrients elsewhere such as by rating the organs of animals, but eating some vegetables can be easier and cheaper than subsisting on organ meat.",
"As far as I can think of there are not really micronutrients we get from fruit that we can't get from elsew here. Scurvy is the classic difeciency example though, due to long periods without vitamin C, and treated by the concumption of citrus which is very rich in vitamin c. You can also get it from many vegetables though.",
"Fruits role in the world is a very energy dense treat to tempt potential seed carrying animals in. It served that pur pose for humans too for a long time, as an energy rich food, and it still does despite our relative plenty now!"
] |
[
"How can you tell the temperature of an atom?"
] |
[
false
] |
I'm reading books on particle physics and I still can't figure out how you would find the temperature of an atom? Lets say a hydrogen atom. Is the electron in a higher orbit?
|
[
"A single atom doesn't have a temperature. By definition, temperature is an ",
" measurement of the vibrational energy of a ",
" of atoms or molecules."
] |
[
"By definition, temperature is an average measurement of the vibrational energy of a group of atoms or molecules.",
"Almost... it's really a convolution of entropy (randomness) and energy (translational, rotational, vibrational, electronic, magnetic...).",
"Specifically:",
"T = dE/dS",
"That is, temperature is the rate of change of Energy (E) with respect to Entropy (S).",
"S = k ln(W)",
"W := number of indistinguishable ways the system can be arranged.",
"I know it's a little abstract, but I thought I'd weigh in with a more precise definition."
] |
[
"We can use the ",
"Kinetic Theory of Gases",
" to approximate it, but like previous commentators have said, temperature is really a macro property and not easily applicable to an individual atom.",
"From the Kinetic Theory of Gases, the temperature is",
"T = mass * average velocity / (3*boltzman's constant)",
"edit: forgot your concluding question. Temperature is frequently associated with the whole atom moving. Your hydrogen atom would just be zipping around faster at higher temperatures. Electrons can contribute to temperature (more specifically the heat capacity) as theorized by the ",
"Drude model",
" where they're treated like an electron gas in metals. I'm not sure how to associate higher orbits with temperature, but I bet there's a relationship in the heat capacity of a plasma."
] |
[
"How far are we from curing cancer?"
] |
[
false
] |
And what are the biggest challenges we're having tackling this problem?
|
[
"Cancer is not a single entity but a category of many diseases with different underlying etiologies, and consequently, different targets for treatment. Even within any one organ system, like \"lung cancer\" there are many kinds of common and rare cancers that have little in common at the cellular and molecular level. Cancer research is mostly not focused on a singular \"cure for cancer,\" but rather on very specific targets focused on specific forms of cancer. Treatments for all cancers with the \"curative\" effectiveness parallelling that of antibiotics for infections are very distant. ",
"Nevertheless, there have been many breakthroughs for some specific cancers, and with emerging technologies like pharmacogenomics, the prognosis associated with a cancer diagnosis should continue to improve in the years ahead.",
"This comic",
" addresses these issues in illustrated form."
] |
[
"There have been tremendous breakthroughs for several types of cancer, including leukemia in kids and also breast cancer (a topic I'm working on) has seen lots of improvements in the last twenty years. ",
"For breast cancer, improvements in (early) diagnosis and improvements in treatment have meant the world of difference for many patients. \nThis has led to 5-year-survival rates going up from 50% to 80% in the last 40 years (see here: ",
"http://info.cancerresearchuk.org/cancerstats/types/breast/survival/",
" ). ",
"Which is quite something. ",
"But we aren't curing every patient yet. And also for cancer of the breast, there are several (sub)types with different prospects for the patients, and also very likely they need different therapies. But we are only starting to understand that now...",
"One of the biggest challenges in cancer is that the cancer cells have a very high DNA mutation rate, which can make the cancer you have resistant to the therapy you receive. When you receive a certain kind of chemo, most cancer cells will die, but there might be cells that have acquired a mutation which allows them to survive this chemo - and these will then keep growing and will not die because of the chemo. \n(It is a bit like with bacteria, who can also mutate to become resistant to a certain type of antibiotics).",
"So for cancer, all kinds of wonderful drugs have recently been developed, drugs that target a certain characteristic or mechanism that the cancer cells depend on. And often you see a good initial response to the treatment, but then later it turns out that some cancer cells had lost this characteristic, or weren't depending on that mechanism anymore; and they survived the drug you gave and keep growing happily. "
] |
[
"As a cancer researcher myself, I can say that while we are still not at a cure for cancer, we are at a turning point. There was a recent article in Cell titled \"The Evolving War on Cancer\" by Daniel Haber that discusses our current position on the war on cancer in detail. Below is a key summary of the article:",
"\"The Next Steps in the War\non Cancer\nThe War on Cancer has not been lost, nor\nis it won. Instead, we are now at a turning\npoint, where fundamental knowledge\ngathered over the past 40 years can, for\nthe first time, be applied directly to the\ncare of patients with cancer. Early results\nin selected types of cancer are exciting in\nthemselves and in what they forecast for\nthe future of cancer treatment. However,\nthe rush for translational applications of\nthese initial breakthroughs should not be\ninterpreted as evidence that we now\nknow all we need to know about the pathogenesis,\nprogression, and vulnerabilities\nof cancer. Far from it, basic research in\ncancer biology is progressing as never\nbefore. New and unpredicted discoveries\ncontinue to shed light on fundamental\nmechanisms, from new insights into\nlong-studied genes like p53, to advances\nthat are transforming the fields of cancer\nmetabolism, chromatin regulation, and\nnoncoding RNA biology. There is still\nmuch to discover, and continued support\nfor basic research is essential to continue\nthe progress in the War on Cancer.\""
] |
[
"Serious question - how can I make my flatulence smell better?"
] |
[
false
] | null |
[
"Not likely. 1-2 liters/day would make him violently ill."
] |
[
"4 eggs in the morning. but then again ive been doing that my whole life without problems."
] |
[
"4 eggs in the morning. but then again ive been doing that my whole life without problems."
] |
[
"An average tennis ball floats in the centre of a hollow sphere made of extremely dense material, floating in space. Is the tennis ball \"squeezed\" by the sphere's \"gravity well\" toward the centre, or pulled outward by the gravity of the walls all around?"
] |
[
false
] |
In other words, if you have a hollow sphere made of, say, neutron star material, does the entire sphere make a impression in spacetime - ie, gravity is highest at the centre of the sphere? Or, does spacetime mirror where the mass is, meaning gravity is highest the closer you are to the walls, and lowest in the middle of the sphere?
|
[
"The tennis ball floats as if it was in space without any other mass around. The gravitational attraction from each side of the shell exactly cancels the attraction from the other side - this is called Newton's shell theorem. "
] |
[
"Also, so long as the shell is a uniform sphere, the tennis ball need not be in the centre of said sphere. The gravitational field would be equal at all points within the sphere!",
"References:\n",
"https://en.wikipedia.org/wiki/Shell_theorem",
"\n",
"http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/sphshell2.html"
] |
[
"Have you heard of ",
"r/writingprompts",
" ?"
] |
[
"If you were stranded in the desert and all you had was a bottle of Tums..."
] |
[
false
] |
I'm learning about acids and bases in Chemistry right now and one of the most common examples of how to tame an acid is taking antacid tablets (such as Tums which is Calcium Carbonate). These tablets will turn the HCl in our stomachs (which causes heartburn) into water (and salt). My question is, if you were stranded in the desert with no water, but happened to have a bottle of tums, would the water produced in the reaction be sufficient enough to keep you from becoming dehydrated too quickly?
|
[
"No. Gastric acid is partly produced from the reaction: CO2 + H2O -> H2CO3 -> H+ + HCO3-. The neutralization of the acidic protons in stomach acid with antacid would produce bicarbonate, which can be converted back into water and carbon dioxide by carbonic anhydrase. In other words, this is the opposite reaction of the above, and the net reaction yields no excess, \"new\" water.",
"edit: also, stomach pH is homeostatically regulated, so the increased gastric pH by antacid consumption will cause the production of more gastic acid, which will probably wipe out any potential gain in net water by the neutralization reaction."
] |
[
"if you balance the equation you'll see that you're missing two H's and an O..."
] |
[
"if you balance the equation you'll see that you're missing two H's and an O..."
] |
[
"Are sonic booms found in solids/liquids?"
] |
[
false
] |
If so, how do they differ in nature from the gaseous phenomenon, and where would they be found in practice.
|
[
"Wouldn't basically any liquid undergo ",
"cavitation",
" and become gas if an object attempted to pass through it at the speed of sound in said liquid? I would imagine you would run into a similar issue smacking two solid objects together at the speed of sound.",
"That said, the sound waves would still become stacked at the front of the object if you did move an object through a solid or liquid at any velocity. Much like how the waves at the front of a ship become stacked in front of the ship. One key difference is that the speed of sound in most liquids and solids is much higher than it is in gas. It's because the atoms in a liquid or gas are much more tightly packed with one another. Basically one atom hits the next which hits the next much sooner, transferring the sound more quickly. "
] |
[
"Cavitation will still happen at some speed, there just won't be any vapor pressure (gas) in the cavities then."
] |
[
"Yes, but as ",
"/u/Dubanx",
" points out, the pressure changes associated with the shock will transform some of the liquid to vapor, so it's inevitably going to be a mixture of solid/liquid and gaseous phenomena.",
"One situation where this occurs in practice is asteroids and comets striking planets. They're typically going faster than the speed of sound in the planet's interior, so they create shock waves in the planet. The physics is basically the same as in gases, it's just that the waves travel faster and the amount of compression is usually less."
] |
[
"How is it possible to identify different bombs by the radiation?"
] |
[
false
] |
I'm watching and in the movie, by analyzing the charred remained of Baltimore, they are able to figure out which EXACT weapon was used. From doing a bit of research, this seems to be an actual thing -- but there isn't a reasonable explanation. Thank you!
|
[
"One thing to be aware of is that only a tiny portion of even the most efficient atomic bomb is actually turned into energy. As shown in a previous thread ",
"here",
" these devices convert at most only about one kilogram (a bit over two pounds) of matter to energy. The rest of the material forming the bomb is blown apart, with some portion transmuted into other elements and isotopes by the radiation from the explosion(s). ",
"Atomic bombs come in a variety of ",
"designs",
" . Each design contains different amounts of different elements in different proportions. Even the two atomic bombs dropped on Japan in WWII were of two different designs: ",
"Fat Man",
" and ",
"Little Boy",
" and used two different elements in their primaries (plutonium vs uranium 235). Later designs added other materials such as tritium, lithium hydride, and uranium 238.",
"So, fallout material from the atomic bomb is detected by its radioactivity. Detailed analysis will reveal both the elements that make up that fallout and what isotopes are present and in what proportions. Using the known and limited nuclear reactions present in the various types of bombs, it is possible to work out what the end products of each would be and compare to what is present in the fallout.",
"As a very simplified example, an atomic bomb is detonated. The fallout includes substantial amounts of plutonium, uranium 238 and lithium. The bomb would then be known to have a plutonium core (vaguely similar to the Fat Man in overall shape), have used lithium hydride for fusion, and uranium 238 for a final fission reaction. Overall, this is a fission-fusion-fission type bomb and far more advanced than the original atomic bombs. ",
"The real experts are able to determine even more details using ratios of various elements and the overall yield of the weapon.",
"To recap, each atomic bomb leaves the huge majority of it's material behind when it explodes. Each design uses different chemical elements in different proportions. Experts are able to use the residue to determine the elements and their proportions used in the bomb, which gives the details of it's design."
] |
[
"It's called nuclear forensics. It's possible to detect if the nuclear device was uranium or plutonium in few hours, but detecting design, age (time elapsed since production or last purification)\n, production process and history may take several weeks or months. ",
"The process of figuring out the details can speed up if they find isotopic match in some database. Databases contain an analysis of the history and composition of the samples from their originating source, indexed records of nuclear material properties, production locations, and use histories. International databases contain records from experimental and commercial nuclear reactors and U.S. of course has good records of it's own military reactors and weapons. If the recovered material is registered in a database, then it can be matched with high confidence.",
"The plot in the movie was plausible, because plutonium for the bomb was manufactured in the U.S. It's not always possible to identify bombs from other countries with the same accuracy because not all countries cooperate or they may have spoofed the databases. "
] |
[
"these devices convert at most only about one kilogram (a bit over two pounds) of matter to energy. The rest of the material forming the bomb is blown apart",
"Just to be clear: yes, that much matter turns into energy, but you have to split a lot more than 1 kg of atoms to get 1 kg of energy, because each fission releases only about 0.1% of the total mass-energy. So for a 1 kg energy release you need to fission 1000 kg of uranium. A substantial fraction does remain unfissioned though, depending on bomb type."
] |
[
"Do athletes like Terrance Knighton, who have a high body fat percentage but great cardiovascular fitness, still run the risks of obesity-linked diseases?"
] |
[
false
] |
According to the CDC: Obesity increases the risk of many health conditions, including the following: Coronary heart disease, stroke, and high blood pressure. Type 2 diabetes. Cancers, such as endometrial, breast, and colon cancer. High total cholesterol or high levels of triglycerides. Liver and gallbladder disease. NFL defensive tackle, , is listed at 6'3" and 335 lbs. Judging by photos, I would think its's safe to assume that he has a high body fact percentage. While he doesn't have cornerback speed, he's still capable of . Keeping in mind that Knighton exerts those kinds of efforts upwards of 40 times per game, I would assume that he has higher than average cardiovascular fitness. There are plenty of players like this in the league ( is another example), so how are these men's health affected by their weight considering their excellent athleticism?
|
[
"http://www.ajconline.org/article/S0002-9149(11)03387-X/fulltext",
"In conclusion, National Football League players from the 1959 through 1988 seasons had decreased overall mortality but those with a playing-time BMI ≥30 kg/m2 had 2 times the risk of CVD mortality compared to other players and African-American players and defensive linemen had higher CVD mortality compared to other players even after adjusting for playing-time BMI.",
"One issue that has been raised is that BMI values have gone through the roof, so there is likely a higher incidence of cardiovascular disease in more recent generations, if the link between BMI and CVD holds. I do not know of a more modern study.",
"As someone that has performed at a very high level in endurance sports, I would challenge your assumption that these players have good cardiovascular fitness. They are unbelievably strong, but the kinds of efforts they perform do not really put much load on the cardiovascular system when compared to sports that are primarily focused on aerobic exertion.",
"My suspicion is that they are cardiovascularly fitter than the average sedentary person, but they are hopelessly short of athletes whose sports are largely cardio driven (running, rowing, cycling, xc skiing, etc). Big reductions in CVD are seen in those populations. I suspect the extra body mass carried by NFL players during their sedentary times is a net negative for long-term health outcomes.",
"That, plus all the injuries."
] |
[
"This may answer your question, but it deals with studies on sumo wrestlers (so its taken to even a farther extreme):",
"http://examine.com/faq/can-you-be-healthy-and-obese.html",
"Essentially, their extreme athleticism is not enough to counteract their risk."
] |
[
"I played football in the SEC. Not pro level, but the next best thing. And yes, I had Olympic and other nationally recognized strength trainers. We burned for long periods of time without rest. It isn't 5-10 seconds on and 30 seconds - minutes off like playing in a game with commercial time.",
"We did drills running through sand for minutes at a time. Does it build leg power? Sure does! It also drains you aerobically extremely quickly.",
"We lifted for power of course, but it was also breakneck pace and cardio was a big part of what we did. This is as an offensive lineman, probably the least \"cardio intensive\" position on the field besides specialty teams.",
"Your line coach doesn't care if you can bench 50 lbs more than the guy across from you. He cares that you are still able to function after a 15 play drive in the fourth quarter. And guess what, judging from your post I'm guessing you never played, but by the end of a long hard drive a lineman's lungs will be on fire. It isn't as light of a pace as you would expect."
] |
[
"Is there a reason to discourage appropriate usage of antibiotics?"
] |
[
false
] |
My six week old daughter was recently hospitalized with a viral infection and was given antibiotics in the course of her treatment. I've had several people comment on how horrible it is for a baby to have antibiotics. The nature of the comments indicated that antibiotics are a bad thing for people to take. I'm aware of the rise of antibiotic-resistant bacteria and understand that we may be entering an age where the efficacy of antibiotics is diminished, but is there a physiological reason why antibiotics should be avoided? Are there serious long or short term side effects?
|
[
"I’m glad you raised this question because it is extremely important to curb inappropriate antibiotic use for many reasons. Of course, inappropriate use of antibiotics leads to resistant bacteria, but like all medications, antibiotics have other side effects.",
"The side effects depend on the antibiotic. Just like there are different classes of blood pressure medications that work in different ways, different antibiotics kill or inhibit the growth of bacteria in different ways, and they all have their own side effects.",
"Among the different side effects include kidney damage, hearing loss, and seizures. Some can even cause discoloration of the teeth. These side effects can be permanent. By killing bacteria, antibiotics can also change the balance of natural bacteria in your intestines, leading to growth of an opportunistic bacterium such as ",
", which causes a very serious infection.",
"Another side effect that is not unusual is the destruction of bacteria that help produce clotting proteins. Believe it or not, bacteria in your intestines help produce Vitamin K, which is essential for blood clotting. This is why newborns are given a Vitamin K shot (having never been exposed to the environment, newborns initially have no bacteria in their gut and therefore cannot synthesize Vitamin K which puts them at risk for bleeding disorders)."
] |
[
"I don't know if the highest proportion of resistant strains are produced from patients in the ICU. As an ICU physician, I do feel confident in saying that antibiotic use is usually justified because it keeps these patients alive, and we make every effort to narrow the specificity of the antibiotic down as soon as possible.",
"What I do know is that even in the community there is a significant development of antibiotic resistance. For example, urinary tract infections that are commonly caused by ",
" were once easily treated with an antibiotic called ciprofloxacin but have been developing significant resistance. Likewise, gonorrhea used to be easily treated with third generation cephalosporins, but also are developing significant resistance. These data are provided by the WHO at ",
"http://www.who.int/drugresistance/documents/surveillancereport/en/",
"And these are community infections--not ones we really see in critical care."
] |
[
"Of course, inappropriate use of antibiotics leads to resistant bacteria",
"Isn't it true that most resistant strains are the product of long term critical care, i.e. NICU,refractory infections, or long term care of immune suppressed patients? "
] |
[
"Why is light attracted to black holes if it has no mass?"
] |
[
false
] |
Does light have mass? Because how can it be pulled by gravity without mass?
|
[
"You're right that there's a contradiction here with ",
" gravity, which is what is taught in intro physics courses in high school and college. In Newton's physics, gravity is a force of attraction between two masses - which means that in Newton's physics, massless light is ",
" by gravity (OK yes it's more complicated than this, see the edit at the end). ",
"Of course, we can see that light ",
" affected by gravity. This was not observed until Einstein came along and revised Newtonian gravity with his theory of ",
", which predicted light being affected by gravity. Einstein explained gravity as an emergent phenomenon, a result of the curvature of space-time around energy densities (which almost always is effectively the same thing as mass). If the space is curved, the mass of the thing traveling through it doesn't really matter (if it's small), the path is determined by the curvature. General Relativity revolutionized the way we think about gravity, and remains the best theory of gravity we have today. It is also one of the most thoroughly tested theories in physics, and has passed every observational test so far with flying colors. ",
"In everyday situations, there is no perceptible difference between General Relativity and Newtonian gravity. You can tell the difference on Earth's surface with ",
" careful measurement, but you really have to work for it. And Newton's gravity is so much simpler, mathematically, than General Relativity, while working very well for situations 99.9% of people will encounter, so it remains what is taught in introductory courses. The further one progresses in physics education, the more one hears something along the lines of \"Remember what we told you last year? That wasn't ",
" right, it really works more like this...\" ",
"It helps to think of these different theories as ",
". Newtonian physics is a model that matches the real world very well in certain circumstances. When you get into ",
" circumstances, though, like light near a black hole, you need a better model. General Relativity is that better model. There may come a point where we need an even more accurate model than GR, but we haven't yet found that limit - especially since any new model would need to replicate everything GR can explain.",
"EDIT: So, yes, the history is more complicated than I made it seem. It's more complicated than taking the limit of particle mass going to zero as well, though, as some below suggest. Though von Soldner calculated the angle of expected deflection of a particle with zero mass in 1804, another assumption goes into that: that light is a particle that interacts with gravity at all. If light is purely a wave, then you ",
" expect the deflection under Newtonian physics, and this wasn't settled at the time. For most of the 19th century, \"wave\" was more popular than \"particle\" for a number of reasons. I'm not a science historian; it's not clear to me whether a typical physicist in, say, the 1850's would expect light to be bent by gravity or not, but I'd put $20 on a majority for \"not\". Of course, today we think of it as ",
" wave and particle, and part of the beauty of GR is that it doesn't actually ",
", the path is affected either way."
] |
[
"Exactly. Even though light is massless, it travels in a straight line. If you curve the space the light is traveling through, it’s straight line will curve along with it even though it has no mass. ",
"A black hole curves the space within its event horizon so much that the straight line bends towards its center (never allowing anything to escape)."
] |
[
"Try thinking of it this way. Objects always travel in a straight line. Gravity can cause the straight line itself to be curved."
] |
[
"Can a star reform into a another star after it dies?"
] |
[
false
] |
My knowledge is that stars form from the compression of nebulae due to gravity untill it becomes super hot and eventually undergoes fusion. Once a star "dies out" and turns into a red giant and eventually another nebula, could this nebula form into another star?
|
[
"Short version: sort of... The elements released from a planetary nebula would diffuse throughout the neighborhood, and enrich existing molecular clouds with heavier elements. But most star formation regions are quite massive (",
"at least a few solar masses, up to a couple thousand",
"--see page 2.) And it's not clear to me what proportion of enrichment comes from PNs as opposed to supernovae.",
"Long version:",
"So stars are complicated--red giants especially. ",
"Red giants are stratified",
", which means they have different layers that are (primarily) made of a single element (heavier stuff near the core, since elements fuse sequentially in shells on the red giant branch--the RGB). Depending on their mass, those layers will be different. For instance, low-mass stars (below ~0.4 solar mass) can't make anything heavier than helium. So when they finally burn out (which takes a LOOOOONG time, since ",
"main-sequence lifetime goes as the negative-three power of mass",
"--see page 9 of that reference), there won't be much of anything in the way of heavier elements, in the first place.",
"However, once you get over ~0.4 solar masses, you can start to fuse helium into carbon (triple-alpha process). And as mass increases, more stuff can get made, up until iron (and if you're making iron, you'll go supernova, not make a planetary nebula).",
"But remember how I said that the stars are stratified with the heavier stuff near the core? If the star just became a planetary nebula at the snap of the fingers, then none of the heavier stuff would ever make it out. Well, there are these things called \"dredge-ups,\" where a convective outer envelope suddenly intrudes into a radiative zone. This is like stirring a flavored lemonade. Everything starts to mix up, so the envelope is enriched with heavier elements and the core is (somewhat) depleted. In heavier stars, this can occur ",
"several times",
" (see page 13).",
"But how much will all this enrich the ISM relative to other sources? Well, it's not really clear to me--perhaps a stellar evolution person could chime in. ",
"This",
" seems to suggest that the PN mass is 0.1-0.2 solar masses (so, between 1% and 25% of the total mass of the star). And ",
"this source",
" states that supernovae (depending on the type) eject between 1 and several solar masses. HOWEVER, supernovae are relatively uncommon, since they (mainly) occur in high mass stars. A quick calculation with the (admittedly shaky) ",
"Salpeter Initial Mass Function",
" suggests that, assuming average supernova ejecta and PNs respectively have about 2 and 0.2 solar masses of heavy elements, planetary nebulae should dominate enrichment by a factor of 4 (or so). But there are other wrinkles, like stars evolving in pairs, which people still tend to ignore.",
"Also, both PNs and SNe are not all heavy elements (except for SNe type Ia, which are literally just a white dwarf core and have no hydrogen at all). I can't find any more specific info quickly, and my stars professor is out of his office right now.",
"EDIT: I tracked down my resident stars expert, and he referred me to BEJ Pagel's text \"Nucleosynthesis and chemical evolution of galaxies\" and various papers by ",
"Matteucci",
" (keywork--nucleosynthesis). If y'all want to hear more, I can do some reading and report back. The gist, though, seems to be that it depends on your models of binary star evolution, and what elements you're concerned with."
] |
[
"If the star went in a nova or supernova, it will rerelease the 'star stuff' which pockets together with other star stuff and eventually reached a mass where the body of mass can undergo fusion, starting a new star"
] |
[
"what is the heaviest element our Sun producing? "
] |
[
"If I tried to run a computer in the vacuum of space, would it overheat or freeze?"
] |
[
false
] |
If I brought my desktop computer to space and managed to get it running (I'd imagine wall outlets aren't common there) would the chips overheat because the fan isn't circulating air through it? Or would they freeze/boil depending on whether or not they were in direct sunlight?
|
[
"Thermal radiation can occur in a vacuum. Its how the sun heats the Earth."
] |
[
"Interesting question. Heat loss in space is often mistaken in popular media. The conduction of heat in space is low as a result of the lower particle density. Primarily objects lose their heat through thermal radiation. I would imagine the computer would overheat as conduction is the primary method of CPU/GPU cooling in computers."
] |
[
"The same way they cooled the lunar rover: with a radiator."
] |
[
"What was the slowest observed wave we know of?"
] |
[
false
] |
I was just looking at some antibacterial gel, and it looked like a standing wave, but it doesn't appear to be moving. What is the slowest wave we've seen. It doesn't have to be an E&M wave, but could be a liquid wave. You don't need to historically know the slowest wave, you could give me a theoretical minimum if you wanted.
|
[
"It cannot be stressed enough: the planck scale has no other significance than being the limit where we expect quantum gravitational effects to be important for what is physically going on. It is NOT the smallest possible lenght."
] |
[
"If you stretch the meaning of 'wave', you can include various long-term periodic processes like\n",
"Predator-prey dynamics",
" which oscillate over years, or the movement of planets (1 year for Earth to loop around the Sun ), or ",
"observe beats between two periodic processes with close frequences",
".",
"Or you can look at ",
"phase velocity",
" which can, in principle, be arbitrarily slow.",
"Edit: formatting."
] |
[
"I don't think there could be a physical limit to how slow waves can travel, nor can there be a maximum wavelength. Vibrations and waves are caused by a beautifully simple principle, and the physical incarnations of that principle have no end to their variety. \nOne interesting example is ",
"this timelapse of Saraha Desert dunes",
", filmed over two years for David Attenborough's Africa series."
] |
[
"Ask Anything Wednesday - Engineering, Mathematics, Computer Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"Highly unlikely. For one, quantum computers need to be cooled a lot, in some to temperatures 0.02 Kelvin (0 Kelvin is -273.15 Celsius). They are very hard to make and operate, thus cost a lot, d-wave is estimated to cost $15 million, although it's just an estimation by BBC. Then there is the problem that they don't bring a whole lot to a home setting, due to how they work. They are great at solving complex and long tasks, like for example code breaking, a quantum computer could relatively quickly break modern code based on multiplying large prime numbers but a \"classical\" computer wouldn't finish for dozens of years if not longer. For quantum computers to excell at something that thing must have repeatable and foreseeable solution and current microprocessors just keep jumping from one thing to another.",
"So the answer is no, at least not in housholds. My guess is that quantum computing will be industrialized fairly quickly, something like by 2030. But household use is a long way from now."
] |
[
"Most streets we build are made of concrete or tarmac, but they wear down rather quickly. Are there more durable materials being developed for better streets in the future?"
] |
[
"I asked before at a bad time I think I got caught in the moderator. I would not blame anyone for putting the work thorium in the spam filter.",
"My cousin has started posting heavily about Thorium reactors recently. I've looked at some of it and the designs look like the old breeder reactor designs that were made back when we thought uranium was scarcer than it is. From what I understand both Thorium and Uranium 238 cannot be used as reactor fuel directly but they can absorb neutrons and become useful fuel.",
"But this is what confuses me: I thought, and my reading confirms that the reason that reactors shut down is because the buildup of waste absorbs too many neutrons and the chain reaction slows or stops. Used fuel rods still have most of the U-235 left in them, and can be reprocessed to remove the fission byproducts.\nIf this is the case I would expect breeder reactors to be much more sensitive to these neutron absorbing elements because they use neutrons to make fuel as well as burn it, forcing more shutdowns and less running time. However, long run times without refueling are often cited by thorium boosters as a major advantage of the design. How does that work?",
"At the same time I'm seeing that the navy is looking to make atomic reactors for submarines with 30 years of fuel built in, how do these designs avoid the fission poisoning problem?"
] |
[
"How did they discover that Europa had liquid oceans underneath its ice?"
] |
[
false
] |
I never understood the concepts
|
[
"From Wiki:",
"The first hints of a subsurface ocean came from theoretical considerations of tidal heating (a consequence of Europa's slightly eccentric orbit and orbital resonance with the other Galilean moons). Galileo imaging team members argue for the existence of a subsurface ocean from analysis of Voyager and Galileo images. The most dramatic example is \"chaos terrain\", a common feature on Europa's surface that some interpret as a region where the subsurface ocean has melted through the icy crust. This interpretation is extremely controversial. Most geologists who have studied Europa favor what is commonly called the \"thick ice\" model, in which the ocean has rarely, if ever, directly interacted with the present surface.",
"The best evidence for the thick-ice model is a study of Europa's large craters. The largest impact structures are surrounded by concentric rings and appear to be filled with relatively flat, fresh ice; based on this and on the calculated amount of heat generated by Europan tides, it is predicted that the outer crust of solid ice is approximately 10–30 km (6–19 mi) thick, including a ductile \"warm ice\" layer, which could mean that the liquid ocean underneath may be about 100 km (60 mi) deep. This leads to a volume of Europa's oceans of 3 × 1018 m3, slightly more than two times the volume of Earth's oceans."
] |
[
"The short answer is that geologists sat down and created models to show how the surface features could be created by tidal movement. ",
"A person I've had the pleasure of working with over the years is, quite literally, the top authority in the world on this specific subject. He was the one who discovered this. I was just chatting with him, and he provided this insight as well: ",
"\"The real smoking gun was that the magnetometer on Galileo measured a dipole during close flybys of Europa. If Europa has an ocean (with salts) then an induced magnetic field should be detectable. And it was\" ",
"I'm trying to see if he can create an account and provide a more detailed answer. "
] |
[
"Here is what I found on NASA's website: ",
"Why do we think that Europa has a subsurface ocean?\nThere are several strong pieces of evidence that suggest an ocean exists on Europa:",
"The magnetometer aboard the Galileo spacecraft detected signs of an induced magnetic field near Europa's surface, clear evidence for a conductive substance less than about 30 kilometers (about 20 miles) or so below. This is strong evidence for some amount of salty liquid below the surface. But the Galileo spacecraft was not designed specifically to test the hypothesis of a subsurface ocean on Europa. To know for sure whether Europa has an ocean, a spacecraft would need to carefully measure the tidal fluctuations of Europa's surface as it orbits Jupiter. This would require a spacecraft to either to go into orbit around the moon or make repeated flybys with the right geometries.",
"Europa's surface features (including bands, ridges, chaos terrain, and multi-ringed impact structures) suggest that there is warm, mobile, glacier-like ice at relatively shallow depths that sometimes has reached the surface. The presence of an ocean would make Europa's frozen surface flex more under its daily tides, cracking and warming the ice, to help explain its strange surface geology. For example, Europa's bizarre curved fractures (called cycloids) probably owe their origin to cracking in response to the flexing of Europa's icy shell on the very rapid time scale of its 3.55-day rotation. Creating large fractures in this way this requires large tides, best facilitated by liquid water. Also, Europa's multi-ringed impact structures suggest that Europa's largest impact scars punched all the way through the ice shell into an ocean.",
"Judging by the pattern of the satellite's large-scale fractures, the surface of Europa may have \"slipped\" relative to its interior (processes called \"nonsynchronous rotation\" and \"polar wander\"). A subsurface ocean would greatly facilitate this slipping, allowing the ice shell to slide over the fluid ocean. Such slipping would be much more difficult if the ice shell was in direct contact with rock.",
"Source"
] |
[
"Why are atoms the way they are?"
] |
[
false
] |
[deleted]
|
[
"The positive/negative charges hold the electrons and protons together, so without these opposite charges, the particles would just zoom past each other and there would be no atom. ",
"So the nucleus of the atom is a whole bunch of protons, but all protons have the same positive charge, and like charges ",
". How do all those protons stay confined to the very small space of the nucleus? It turns out that there is an additional force at work, a force that we can't experience because it only has about the range of a lead nucleus. The Strong Nuclear Force is a force that works on quarks, the things that protons and neutrons are made of, and this force holds protons and neutrons together. But if we had just 12 protons in the nucleus of an atom, then the electric force might still be able to push some protons out, so neutrons are also in there to increase the binding power of the protons to the nucleus. So neutrons are the glue that holds the nucleus together.",
"There's a nice little exposition about it ",
"here",
"."
] |
[
"I would not say that range of a force and strength of it are inversely proportional. The Strong Force behaves very differently to Electromagnetism and Gravity. I would look at ",
"This post here",
" for a good explanation."
] |
[
"Why is the strength of strong force so much stronger than gravity, but gravity seems to have a much larger range? Is gravity's strength more \"spread out\" so to speak, because of its wider range?"
] |
[
"Is there any chance that manmade aid pollution will someday ground our flights in the same way that volcanic ash has this week?"
] |
[
false
] | null |
[
"Any chance? Sure, thermonuclear war with enough bombs could do the trick and be considered man-made pollution.",
"Is it likely from ordinary consumption, burning of fossil fuels? I would bet against it. Mainly as (a) there is a finite amount of fossil fuels that could be burned and currently with catalytic converters and other green technology we produce low levels of smog (and it even the smog produced is harmless to planes, unlike the volcanic ash which is glassy and larger in nature), and (b) if it got close to the levels where it became a constant problem, our planes would likely be designed to withstand it. E.g., we'd develop get engines that can be cleaned, fly through particulate ash, fly below or above the ash level, etc.",
"Caveat: This is outside my areas of expertise as I am a physicist; but the question is highly hypothetical. But interesting to think about."
] |
[
"No.",
"The damage is due to silicate particles melting to glass in the combustion chamber. You need a lot of power to get such particles airborne, and to keep a critical density in the air as they settle out.",
"The atmospheric man-made aerosols do not have the composition nor the density to damage engines."
] |
[
"A relevant quote: \"Thank god men cannot fly and lay waste the sky as well as the earth.\" - Thoreau"
] |
[
"If the Universe is about 13.82 Billion years old and some of the farthest galaxies, such as UDFy-38135539, are around 13 billion light years away how do we know they are not red-shifted because the light was emitted when the universe was still in its early expansion?"
] |
[
false
] |
To expand on this, could they be, in their preset, local time, moving toward us and how would we know?
|
[
"The universe is still expanding; it wasn't something that stopped early on, but something has, in fact, be speeding up as time goes on. ",
"There was a moment of extra-fast expansion, in the first fraction of a second, but there were no galaxies possible then."
] |
[
"here the object was when it left",
"Only in the universal coordinate system at that time. This means if I have a point at x=0 (it) and x=1 (me), maybe when the light reaches me the sending object is at x=-0.5 and I'm at x=2.",
"Expansion of the universe is tricky."
] |
[
"To answer this question we first need to realize that red or blue shift isn't due to the fact that the galaxy is moving toward or away from us; it is due to the fact that space itself is expanding, thereby stretching the light waves traveling through the space and causing them to shift toward the red side of the spectrum. ",
"If, at any time, the universe were to begin contracting, the red-shifted light would begin to shift towards the blue side of the spectrum. We would notice this blue shift and know that the universe is contracting. It would not matter how, or when, the light was red-shifted, it would begin to blue-shift regardless. ",
"Since we don't see a blue-shift, we know the light is still being red-shifted, meaning the universe is still expanding and the galaxy is still moving away from us.",
"However, if we were to see a blue shift, it would not mean the galaxy suddenly switched directions and is now heading in our direction. It just means the universe has \"switched directions.\" The galaxy would still be moving away from us, but the \"surface\" it is moving on would be contracting (like two ants walking away from each other on a deflating balloon; they can still walk in opposite directions as the balloon surface shrinks faster than their pace and brings them closer together).",
"TL;DR: ",
"We know the red-shift isn't solely due to early expansion because the light is still red-shifted. If the universe were contracting, we would see blue-shift (even in \"old\" light), which we don't.",
"To expand: no it is not moving toward us. We know this because there is no blue-shift to indicate this. Even if it were \"moving toward us\" because of contracting space, it would still be moving away from us in terms of the direction of its inertia."
] |
[
"In the event that the earth’s magnetic field were to “flip”; aside from compasses working backwards, what would actually happen that effects humans?"
] |
[
false
] | null |
[
"a lot of electronic would likely get screwed up/destroyed, even if they didnt have magnets in them.",
"When the magnetic field \"flips\", which would take a while, not an instantaneous thing to my understanding, there would be periods where the magnetic field that protects us from solar flares and ion bombardments from the sun suddenly wouldn't do as good a job at protecting us. And a lot of sensitive electrical equipment on the ground could get screwed up.",
"You can google the 1859 solar storm event, in which an intense solar storm hit earth with enough electrical energy that telegraph lines were able to run on just the current generated by the storm, after operators took the batteries out of their machines.",
"That kind of intense storm hitting during a time of weakened magnetic protection could have not so good impacts on our more sensitive modern electronics."
] |
[
"Is there a way we could protect them? Am computater man."
] |
[
"Most things can be protected by switching them off, and ideally disconnecting them from the grid."
] |
[
"What determines the reverse voltages of diodes?"
] |
[
false
] |
Recently been doing some research on early rectifiers and have learned that almost all common metal oxides will work as a diode, but usually at pretty low backward voltages. The most common were cadmium selenide and copper oxide, but improvised homebrew diodes can apparently be made with ferric oxide or zinc oxide. The issue with them always seems to be the high forward and low backward voltages, cadmium selenide (AKA "selenium rectifiers" in old radios and amps) is 1V forward and 25V reverse, while zinc oxide is 3V at best and copper oxide is often as low as 1V in reverse. Why is this? I know it's something to do with band gaps but how do those relate to actual voltages?
|
[
"Basically it's the potential required to start a so-called avalanche breakdown of the insulating layer. When a sufficient potential difference is applied across a diode in the reverse direction, it will cause charge carriers to accelerate. In avalanche breakdown, the charge carriers collide and free more charge carriers from electrons in the insulating layer.",
"I'm not particularly sure about selenium or metal rectifiers, but I imagine that it's a similar phenomenon. I only know for sure that this is what happens with semiconductor diodes"
] |
[
"Doesn't this depends on whether it's avalanche or zener?"
] |
[
"No, because all diodes exhibit both phenomena. Zener breakdown is a quantum mechanical phenomenon, where electron tunneling occurs. This will happen below the avalanche point.",
"When a diode is given a potential difference that exceeds it's peak inverse voltage rating, it will be avalanche breakdown that will be the primary cause of reverse current flow. However, in general avalanche breakdown results in catastrophic failure of the part, or at least irreversible damage.",
"To control these phenomena, semiconductor manufacturers put different concentrations of dopants (i.e. impurities) in the semiconductor material, and zener diodes are so doped that zener breakdown is preferentially selected for and controlled.",
"edit: fixed a typo."
] |
[
"\"uranium is needed to make nuclear energy and nuclear weapons\", is this statement (from Pew poll) true?"
] |
[
false
] | null |
[
"Then yes, the poll is technically wrong."
] |
[
"Fissile material is necessary for a fission reactor/bomb. Only two elements have isotopes that are feasible to use in these situations: uranium and plutonium.",
"A certain isotope of thorium is fertile, so it can be used to breed a fissile isotope of uranium. And as for that example of polonium, that wasn’t used in the assassination due to being fissile (which it isn’t), it was just used because it’s radioactive."
] |
[
"But \"nuclear\" just refers to the use of \"nuclear energy\", doesn't it? That includes radioactive decay energy. Not just fissibility.",
"The wikipedia page for ",
"nuclear powers",
" says \"The term includes nuclear fission, nuclear decay and nuclear fusion.\" So even simple radioactive batteries qualify as \"nuclear power\". At least, that's how I took the question."
] |
[
"Did fungi ever engage in Endosymbiosis?"
] |
[
false
] |
A random question that came to my mind yesterday: As far as I know both plant and animal cells developed due to endosymbiosis, does this also apply to the cells of fungi? If yes than what exactly happened, they can't have chloroplasts inside their cells because they are not engaging in photosynthesis but are there mitochondria inside them or something completely different but similar in function?
|
[
"No fungi have mitochondria like ALL eukaryotes and received them in the same exact endosymbiosis event as ALL eukaryotes. That's not the same as what you stated."
] |
[
"As far as we know, all mitochondria are the result of an endosymbiosis event that only happened once in the entire history of life on Earth. Rather than being acquired separately in animals, plants, and fungi, the origin of mitochondria dates back to some single-celled eukaryote that was an ancestor of all of these groups (and other modern single-celled eukaryotes too); ",
"this study",
" estimates the date of this event at around 1.2 billion years ago. ",
"This website",
" also has a good brief overview of the subject.",
"In contrast to mitochondria, the story of how chloroplasts found their way into various groups of eukaryotes is much more complicated; I actually just wrote a ",
"comment on this",
" a few days ago."
] |
[
"Thanks for the correction"
] |
[
"What occurs in the body to cause instantaneous death?"
] |
[
false
] | null |
[
"\"Instantaneous death\" is not particularly well-defined. Indeed, \"death\" isn't particularly well-defined, and all the tests we do in order to try to figure out whether someone's dead take seconds, at least, to perform. So if someone ",
" die instantaneously then we'd never know whether they had or not."
] |
[
"You're thinking of it like a heart attack, in which you feel chest pain and anxiety before a dysrhythmia, leading to death. Heart stopping (asystole) or any other life threatening dysrythmias will almost immediately cause unconsciousness because the brain isn't receiving enough blood (oxygen/glucose) from inadequate blood pressure. Brain tissue dies 5-7 minutes later due to high oxygen needs.\nI guess it depends how you define death. Is the unconsciousness from asystole death? Or is it the massive brain infarction that results a few minutes later? In my mind it's a spectrum condition."
] |
[
"That seems rather self explanatory, your body would disintegrate and you would no longer perceive reality due to a lack of sensory organs and a brain to interpret their data."
] |
[
"What causes color degradation?"
] |
[
false
] |
I was just wondering exactly how does natural light (sun) degrade (bleaching/white washing) images like posters or paint on a building? Is it the sun reacting to certain things here on the earth? Edit : Fixed spelling error
|
[
"The short answer is that sunlight causes irreversible changes in the compounds and molecules that gave a material its color in the first place. Due to these changes, the material gradually loses the ability to specifically absorb (and reflect) in the visible spectrum. The net result is a the tell-tale faded appearance of objects that have been exposed to sunlight for a long time. ",
"If you want to dig in deeper things become very messy. The reason is that there are a lot of different mechanisms through which sunlight can change materials. We often sweep all these mechanisms in the umbrella term ",
"photodegradation",
". But the actual chemical changes that take place will be specific to the material in question. In fact, in most cases more than one reaction is possible. For example, here ",
"are some of the pathways you might see",
". One common theme to these changes is that very often you break up larger dyes into smaller bits. For organic dyes you generally only get strong absorption in the visible for extended structures. As a result once you start breaking up the dyes, the smaller fragments will stop absorbing visible light. The final mess of byproducts will then often have a typical off-white appearance. ",
"In order to illustrate what I wrote above, let's take a concrete example. One common dye is called Orange II and it has ",
"this chemical structure",
". Notice how there are two rings with alternating double bonds (we call these aromatic rings), linked by a nitrogen-nitrogen double bond. This extended ring structure is what allows this compound to strongly absorb blue and green light and to reflect the yellow-red part of the spectrum. Now as you might expect this compound will initially have a ",
"vivid orange color",
". However, if you expose this dye it to light, over time this color will go away and you will be left with a product that is mostly clear, ",
"as shown here",
"."
] |
[
"Yes, glass can significantly reduce the degradation. The reason is that most kinds of glass are very good at blocking UV rays, which are the biggest culprits in promoting these chemical changes. For example, even a 2mm thick sheet of soda lime glass (the glass in common window panes) can ",
"block off virtually the entire UV component of sunlight."
] |
[
"So then things like glass or plexiglass can block out certain spectrums of light and can either increase or decrease the degradation? "
] |
[
"I have COVID antibodies and have been donating plasma, will my body replace the antibodies that I donated (is there a finite amount)?"
] |
[
false
] |
I’ve gone 3 times, and curious if my body is replacing the antibodies I donate or not.
|
[
"Your body produces, on top of antibodies, memory cells. Thece \"memory\" cells are stored in your body and have the ability to produce the same antobodies when the body is re-infected. Antibodies tend to die overtime anyway and these memory cells tend to stay much longer."
] |
[
"When you are exposed to the virus, your body will make memory B cells which produce antibodies and live inside germinal centers within your lymph nodes and spleen. These cells are always producing low levels of antibodies and will ramp up production when you are re-exposed to help fight the infection. These are long-lived cells and can survive and make antibodies for decades.",
"\nSo to answer your question: your body will replace the antibodies lost when you donate plasma (or blood). ",
"The people receiving your plasma/blood, however, will have a finite number of antibodies (that they receive from the transfusion) which will eventually run out since they do not have the memory B cells."
] |
[
"Thank you for your donations.",
"My mother believes she caught COVID-19 back in March. She got tested for antibodies a month ago and recently donated plasma. They told her she couldn't give it again because the antibodies had fades too much and typically start to fade after 90 days, although some people lose them much quicker. Time will be the cause of you losing them, not the donations."
] |
[
"Why is prediabetes reversible as opposed to type 2 diabetes? At what point does it become irreversible?"
] |
[
false
] |
Are these just labels on a spectrum of intensity?
|
[
"Prediabetes means you are at a stage where you have enough insulin to keep you normal at baseline, and only fails when you eat too much calories, especially sugar. ",
"Type 2 means you don’t have enough insulin that you will have abnormal blood sugar either all the time, or even with regular intake.",
"It is basically labels on a spectrum, weight for example can change your insulin resistance, so if you loose a bunch of weight you can move from type 2 to prediabetes and even to normal, but that is rare",
"However a lot of diabetes damage is irreversible, such as atherosclerosis and neuropathy."
] |
[
"depends on how much insulin your body can still secrete. Once the overloaded beta cells die, they never recover. This is a progressive process. That being said the biological pathways for insulin resistance (the second key part of prediabetes and type 2 diabetes) seem poorly and incompletely understood. At least to me."
] |
[
"Once the overloaded beta cells die, they never recover. ",
"Although there is ",
"islet cell transplantation",
". So technically, even beta cell death is reversible using surgery."
] |
[
"If your body was completely hydrophobic (like in this .gif), would you be able to swim faster in water, or would you be much slower?"
] |
[
false
] |
If your entire body was coated in some hyrdophobic substance, like in for example, would you move quicker or slower in water? Would you be able to generate more or less pull? and would drag forces affect you more or less? Thanks! EDIT: Thanks guys, a lot of great information here!
|
[
"Okay. You would not suffer skin friction drag, but you would still be subject to pressure drag. Which might lead you to think you would be faster. \nBut you because you can't cause any friction on the water you can't propel yourself nearly as well. Most of the force generated when you swim isn't actually from the water you push on directly. It's from the water that it sucks along with it. This is known as the venturi effect. \nIf you cant drag water and cause this vorticity you can't propel yourself. \nIf you had a different source of propulsion like a propeller then yes you would be faster. ",
"As far as buoyancy is concerned. It would be marginally different. The buoyancy force is equal to the weight of the water your body displaces.You are still (almost) the same size so there is no effect on buoyancy. "
] |
[
"There's a lot of attention here, and a lot of wrong answers by people that know some fluid mechanics, but not quite enough to know the full relationship between skin friction and drag.",
" By ",
" I mean a material where there will be zero friction at the interface. This result is known as D'Alembert's paradox, and was an important conundrum in the early development of the mathematics of fluid mechanics. It turns out that a body in an inviscid, incompressible fluid (as water was described at the time) can experience no drag. Clearly these 18th century mathematicians knew that boats experienced forces, hence the \"paradox.\"",
"Those here who have taken some fluid mechanics would say \"but it's not an inviscid fluid, and high Reynolds numbers flows have most drag due to pressure, not skin friction, so in the lack of skin friction you can still have pressure drag.\" Well, it turns out that all of the pressure drag in a high Reynolds number incompressible flow can be traced back to vorticity, and in fact all of the vorticity in the flow can be traced back to a flux of viscous stress at the surface of the body. It turns out that even in an extremely high Reynolds number flow where inertial forces dominate the viscous ones, you still need that small-but-finite viscous effect at a boundary in order to induce any kind of turbulence at all. Without a no-slip or partial-slip boundary condition, there's no mechanism to induce any drag on a body.",
"Mind you, this is based on a \"perfectly hydrophobic\" surface, a theoretical construct that obviously doesn't exist in reality, but is just a model.",
" I ran some simulations and I'm inclined to think I'm incorrect for asymmetric bodies =)"
] |
[
"I don't think I agree with your assessment: ",
"This is known as the venturi effect. If you cant drag water and cause this vorticity you can't propel yourself.",
"This is also a pressure effect, and skin friction shouldn't have much to do with that either. As long as your hands and feet leave a wake in the water, you're ok.",
"If you doubt this, think about Reynolds number -- active swimming is undeniably turbulent, and inertial forces dominate there, skin friction will only account for a smallish percentage of the forces at play. (Edit for clarity: I'm talking about the flow around the hands and feet when I assert that it's \"undeniably turbulent\")",
"I think, overall, being covered in a hydrophobic substance would have little effect on casual, active swimming. You might only start to see differences at the Olympic level."
] |
[
"How far is the focal point for human eyes when resting?"
] |
[
false
] |
[deleted]
|
[
"The focal length going into the eye is 23-24 mm. Coming out it is about 17 mm. The difference is the refraction boundary at the cornea. "
] |
[
"Huh? A focal point is at the focal length, it is the point of convergence for light that enters the lens parallel. "
] |
[
"I believe what your asking about is dark focus. Or rather what would what would our eyes focal point be if there was no stimulus present? If you put someone in a room that has no stimulus for which we can focus, our eyes tend to accommodate about 1-1.5D. For a patient with no refractive error this would put their focal point between 66-100cm. In every day life this phenomenon results in something called 'night myopia'. At night our eyes tend to accommodate about 1D resulting in slightly decreased visual acuity."
] |
[
"Why don't we have plagues of locusts anymore the way we did in the late 1870s?"
] |
[
false
] | null |
[
"Interesting article",
" on the status of ",
" (the Rocky Mountain locust), with the possibility that it still exists, somewhere.",
"Over the past century, this disappearance has baffled entomologists and ecologists. The collapse came, after all, before the advent of synthetic insecticides, such as DDT, or even modern farming techniques. Consequently, the leading theory for the crash seems vaguely unsatisfactory to many in the broader community of insect study. That theory holds the species was wiped out by a series of developments that played out between 1875 and 1900 in the valleys of the upper river basins along the Northern Rockies—the natural home range of the locusts between irruptions out onto the prairies. Loss of beavers caused by the earlier fur trade era increased flooding, for example. The valleys filled with foraging cattle and sheep and irrigated crops such as alfalfa supplanted native grasses in the bottomlands. The gold and silver mining era brought a comparatively large number of people to the valleys and local agriculture burgeoned to support the human populations.",
"According to this theory, the environmental disturbance to the montane valleys arrived as the insects had retrenched into a natural nadir—a population bottleneck—awaiting the next drought and re-emergence as migratory locusts. Grasshopper egg clusters were trampled by domestic ungulates or flooded out by spring torrents or summer irrigation. The already isolated populations of proto-locust grasshoppers, spread out among valleys along the spine of the continent, could not hold out and M. spretus became extinct.",
"Anyway- there's a lot more in the article. Complex subject."
] |
[
"If I remember correctly (this all comes from my memory of some NatGeo special I watched years ago), it takes a specific set of environmental events to trigger grasshoppers to morph into locusts. I think a very wet growing season followed by a long, hot drought is the usual cause. ",
"I think it's been artificially triggered in a lab setting by taking adequately fed grasshoppers and putting them in a too-small enclosure with not enough food."
] |
[
"So this is in the USA, specifically in the Rocky Mountains right? The title and text of the OP should be edited and be more concise..."
] |
[
"Is there any reason as to why many horn-growing animals (moose, deer) shed their antlers once a year?"
] |
[
false
] | null |
[
"They are dead tissue once the velvet comes off, and generally, each year they come back larger, if the animal is in good health, so it is advantageous to show the status of the animal by shedding and regrowing. They also become damaged during the rut, and cannot repair themselves, so if they weren't shed and replaced, they'd be broken down to nothing."
] |
[
"I don't know why, but I do know that horns and antlers are not the same thing. Antlers are shed; horns are permanent."
] |
[
"Antlers are bone whereas horns are keratin (hair)."
] |
[
"500 tons of phosphate leaked into the Nile river. What are the health risks?"
] |
[
false
] |
So 500 tons of phosphate were leaked into the Nile river stream as a cargo ship carrying the amount sank. What health risks are there to people drinking this water and is it possible for drinking water to be safe due to normal filtration problems? The ministry says its safe but they might be just saying that cause of political reasons.
|
[
"Well, there's not tons of information, but I certainly don't trust the ministry as quoted here:",
"The Ministry of Irrigation declared the state of emergency as a precautionary measure as ",
".",
"First, ",
" refers either to an ion (PO4",
" ), or to any of a huge number of compounds containing it. Without knowing the counter ion(s), the phosphate might be soluble, and it might not. It also might be poisonous or it might not. The phosphate ion itself is a critical nutrient that every single organism on Earth, and even viruses, use to join their genetic material together. It's also critical for metabolism, storing energy, and activating proteins, etc.",
"Phosphate is not usually the limiting factor for growth in aquatic environments, but it is provided in many fertilizers, and so the major health risk I'd look towards from a non-toxic phosphate spill is an algal bloom. Algae might grow rapidly, sometimes producing toxins that can affect aquatic life or people consuming the water/food from contaminated sources. Another possibility is depletion of oxygen in the water as the algae respire and bacteria begin to decompose them. However, the classical cases of these dangerous situations occur in lakes and the ocean, and I'm less certain of the effects on a river, where flow is constant and unidirectional.",
"I'd watch for more details, because it's hard to give specifics as of yet."
] |
[
"If they're saying that the phosphate spilled is \"insoluble\", it might be because it's some insoluble heavy metal salt, like lead phosphate, which would definitely be a health risk."
] |
[
"It depends on the type of phosphate that was spilled. If it's phosphoric acid or or some tribasic phosphate salt, that would be more serious in the short term than something like dibasic sodium phosphate.",
"If the government is calling it insoluble as ",
"/u/sagan_drinks_cosmos",
" mentioned, that could be an indication that it is something like lead phosphate, in which case the toxicity would come from low concentrations of lead ions in the water. That would absolutely be a health risk.",
"Also, all of the stuff I talk about below was assuming it's a soluble phosphate salt, and that any health risks would come from the phosphate ion itself, rather than whatever cation it is present with, since the only thing that we \"know\" at this point is that whatever spilled included phosphate ions.",
"Just from some ",
" informal, back-of-the-napkin math, I'd estimate that the concentration of phosphate would be around 2 ppm after 24 hours (500 tons of phosphate ion, average water flow of 2,830,000 L/s ",
" ). That's definitely on the high side of things as far as drinking water contaminants go, but it's consistent with the maximum allowable concentration for other inorganic anions on the US Environmental Protection Agency list of drinking water contaminants ",
" (the phosphate ion doesn't have a specific entry). At that level, the most likely health risk would be mild skin irritation, but I'd be surprised even to see too much of that. ",
"The larger issue with a phosphate spill is ecological, in that it is releasing a large amount of plant nutrients that the local ecosystem might not be able to cope with. It could lead to increased algae growth in the area, which in can \"harm water quality, food resources and habitats, and decrease the oxygen that fish and other aquatic life need to survive.\" ",
"Of course, without more information, it's always better to be cautious, so it would probably be best to avoid drinking/bathing in this until the situation is clearer, if possible.",
" : ",
"http://en.wikipedia.org/wiki/Nile",
" : ",
"http://water.epa.gov/drink/contaminants/",
" : ",
"http://www2.epa.gov/nutrientpollution/problem"
] |
[
"Why are the blades on wind turbines so long?"
] |
[
false
] |
I have a small understanding of how wind turbines work, but if the blades were shorter wouldn’t they spin faster creating more electricity? I know there must be a reason they’re so big I just don’t understand why
|
[
"A wind turbine doesn't really care how fast it is spinning as far as the power output is concerned. For example if you take a small electric motor, it will probably require 1% of a horsepower to spin at several thousand revolutions per minutes (rpm). A container ship engine rotates only at a few hundred rpm but outputs tens of thousands of horsepower. The power output is only proportional to the rotation speed for a given design.",
"A longer blade means that you can harvest more wind energy. The power is basically dependent on the area of the disk covered by the path of the blades. So making a blade twice as long increase the energy output roughly by 4. ",
"Moreover wind turbine blades are essentially wings. And wings are the most efficient (the least drag) when they are as long as possible. At the tip of the blade there are all sorts of turbulences that reduces blade efficiency. "
] |
[
"Other people have covered the idea that the longer the blades, the larger the crosssectional area, the more wind you can capture, but I want to go into some detail on the idea of how fast the blades should spin. ",
"So to understand this, first off it is important to note that there is a maximum possible wind turbine efficiency of 59%. This is called the Betz limit. I can try to summarize the math if people are curious, but the simplest explanation is just to think of an air molecule passing through the turbine, if all the speed was removed from the particle, it would just sit on other side and get in the way of the incoming air. So the air leaving the turbine needs to still have some velocity, the maximum efficiency occurs when the air leaving has 1/3 the velocity of the air entering, which will give an efficiency of 16/27 or ~59%. ",
"Now how close a turbine can get to the Betz limit involves some complicated aerodynamics, but it depends on the turbine design, and the tip speed ratio (how fast the tip spins retaliative to the upwind speed) If you spin too slow, wind slips between the blades unused, but if you spin too fast, the turbulence created reduces your energy. The most efficient turbine design we have found is the three blade turbine, which can reach up to ~80% of the Betz limit at its optimal tip speed ratio of ~ 7x. ",
"Here is a chart of the rotor efficiency of different turbine designs as a function of tip speed ratio",
"I actually teach a course on renewable energy engineering, so I really enjoy these questions. "
] |
[
"It's also worth noting that while a larger rotor has a greater power output, the spacing of the turbines from each other is also proportional to the rotor diameter. In fact both the spacing and power output are proportional to d",
" . So the maximum power output you can achieve per land area (i.e. MW/m",
" ) with a windfarm is actually (mostly) independent of the rotor diameter. The main reason people build big turbines is simply due to the higher windspeeds at higher altitudes, and the economies of scale."
] |
[
"How is radiation transformed into heat?"
] |
[
false
] |
Say we have a cloud of hydrogen gas in space with an average kinetic energy and a nearby star shines light through this gas. The electromagnetic waves with the right frequency will be absorbed by the hydrogen and re-emitted with the exact same frequency while all the other light is transparent to the cloud. If this is the case then how will the gas cloud heat up ( I'm assuming it will)? I'm also confused as to how solid objects become heated. I've read that it's helpful to think of the electrons in the solid as vibrating springs with certain frequencies and if EM waves have the same resonant frequency the springs with absorb that light and the vibrating will increase. Why is this process different from individual atoms absorbing and re-emitting photons (i.e why don't the vibrating strings re-emit the photon leaving the solid with no net energy gain)?
|
[
"I think some things need to be clarified. First, one of your statements is wrong.",
"The electromagnetic waves with the right frequency will be absorbed by the hydrogen and re-emitted with the exact same frequency",
"Each compound has its own ",
", that is which wavelengths it absorbs and how likely it is to absorb them, and an ",
", that is which wavelengths of photons it will emit when excited electrons drop in energy level. ",
"This",
" is a decent surface explanation. The point is that when the light gets absorbed and excites electrons, it does not mean it will be emitted at the same wavelength.",
"A weird thing about photons is that even though they have no mass, they ",
" have momentum. This is trippy, but true. So when they hit something, they can actually impart some velocity to the matter. This is the premise for ",
"solar sails",
". If we look at light going through a big cloud of hydrogen gas, the photons are going to push those atoms, speeding them up, but they all bump into each other and their average kinetic energy goes up, thus raising their temperature. ",
"The difference for solids versus individual atoms is NOT different (unless we are talking about crystal lattices), it is just that solids are so dense that the tightly bunched atoms absorb photons much better, and bump into each other much more, so you see them get hot from light much faster than a gas."
] |
[
"Is it actually momentum or is it the excited state of the atomic nucleus that imparts a small amount of kinetic energy? Is the wavelength has changed that means some of the energy of the photon has been absorbed into the nucleus which excites it, thus allowing it to move (causing heat radiation). Does that really mean the photon has momentum? Sounds to me more like a consequence of the interaction between the photon and the nucleus."
] |
[
"Photons have momentum proportional to their frequency. Look up compton scattering for the experimental proof and a discussion of the implications."
] |
[
"Can the human eye detect a Gamma Ray Burst from a near distance? Or are Gamma Rays frequency too high?"
] |
[
false
] | null |
[
"The human eye can't see gamma rays, although at some point, the gamma rays may damage the eye enough so that you'd be able to know that something is happening.",
"That said, while much of the energy from gamma ray bursts is released as gamma rays, not all of it is. They are usually bright in the visual spectrum as well, so you'd be able to see ",
". "
] |
[
"Human eye can only see things between ultra violet and infra red. That's why they are called such things. The lowest frequency we can see is red, and the highest we can see is violet. Anything beyond those are not in our visible range. Gamma Rays have frequencies much higher than violet visible light. "
] |
[
"Well the very definition of Gamma Ray puts them outside the visible wavelengths. The visible spectrum is (roughly)from 300 to 700 nm (10",
" m). Gamma Ray's are on the order of less than 10 pm (10",
" m). As other posters have stated, events that produce gamma rays also tend to produce light at other wavelengths as well, those of which that fall in the visible range you would see. Which is why when a GRB (gamma ray burst) is detected, telescopes all over the world working in many different wavelength ranges slew to look at the spot it was detected from."
] |
[
"Before we cut our fingernails, what was their purpose and how long would they typically be?"
] |
[
false
] | null |
[
"We won't cease to have nails \"because of evolution\". Things disappear only if there is an evolutionary (i.e. survival) advantage to doing so. That's why we still have nails and male nipples."
] |
[
"Farmers and tradesmen rarely if ever, need to cut their nails. "
] |
[
"The fingernail helps the pad of the finger to maintain grip (it prevents it from rolling) so they still serve a function. They also represent the remnants of claws from our ancestors of course. Typically nails would not have grown terribly long in ancient times due to the large amount of manual labor the typical person would have been doing on a daily basis."
] |
[
"x^2-y^2 = a* sin(x^2), what is special about a?"
] |
[
false
] |
I was just playing around with a graphing calculator and worked out that as a approached 7.789705767492725 from below you get a zero at around 2.77944 for x - y = 7.789705767492725 * sin(x ) or in other words 2.7794338 - (7.789705767492725 * sin(2.7794338 )) gets really close to zero. I figure there must be something special about those numbers in terms of some mathematical constants, but I can't work out what they are.
|
[
"Instead of working with x",
", let's see what happens with z=x",
". If y is zero, then the equation becomes z=a*sin(z). After moving things around a bit to get sin(z)/z=1/a, this happens when f(z)=sin(z)/z intersect the horizontal line at height 1/a. The graph of it looks like ",
"this",
". This means that if you graph the horizontal line y=1/a, and count the intersections of it with the graph of f(z)=sin(z)/z, then for each intersection (with z positive) there will be exactly two zeros of x",
"-y",
"=a*sin(x",
").",
"For example, if a=1, then there is exactly one z with sin(z)/z=1, and that is z=0. So the x that makes this happen is x=0. Plug x=0 into x",
"-y",
"=sin(x",
") and you'll get that we must have y=0. This is the one exception to our counting rule since x=0 is the only solution to x",
"=0. But this is a kinda trivial example.",
"Another example, if a=pi/2*sqrt(2), then sinc(pi/4) = 2*sqrt(2)/pi = 1/a. So if we plug x=+-sqr(pi)/2 into x",
"-y",
"=(pi/2*sqrt(2))sin(x",
"), then we'll find that we need y=0. So x=+-sqr(pi)/2 is a zero.",
"Finally, perhaps an even more interesting example with a=9pi/(2*sqrt(2)). The equation sin(z)/z = 2*sqrt(2)/9pi has ",
" solutions: z=9pi/4,-9pi/4 and approximately z=2.85225,-2.85225,8.42274,-8.42274. If x",
"=(Any of the positive z), then the graph of x",
"-y",
"=9pi/(2*sqrt(2))sin(x",
" will have to have y=0. This means that the graph of this one has six zeros (two for each positive one). ",
"See Here",
"In general, since sin(x)/x bounces up-and-down with smaller and smaller amplitude, it will cross the line 1/a more often with larger a. ",
"What about your numbers? Well, you found that if z=2.77943382, then sin(z)/z is approximately equal to 1/7.789705767492725. It does not appear to be a \"nice\" value that you can plug in to sin(z)/z and get an exact answer via trig. "
] |
[
"Thanks so much for your thoughtful answer. And thank you for introducing me to the function sinc(x).",
"What I do wonder about though is, in the the line of reflection between the greatest two zeroes of x",
" see ",
"here",
"Whatever a is the line seems to be down the line x = 2.77943382, or if there are no zeroes in that area then a local min/max. That is why I think there is some easier way of expressing that number."
] |
[
"i would not advise thinking of the \"greatest two zeroes\" of ",
" as reflections about ",
" for as long as you dont know what exactly is going on there. if you suspect a reflection to exist, examine it further, but dont allow suspicions to muddy the clarity of your process. ",
"i would argue that as ",
", the points of your curve where ",
" become arbitrarily close to ",
" for ",
" \"small\". your reflection line then lies halfway between \"x~sqroot(2 pi)\" and \"x~sqroot(3 pi)\", but ",
" which is close but not equal to your mystical ",
".",
"finally, i would suggest for you to just play around a little more, for example to look at stuff like ",
" where ",
" takes a couple of meaningful values, like ",
" (",
" is your original query, of course). the ",
" function returns the absolute value of the argument, which is probably helpful (you dont seem to be incredibly interested in whatever happens at ",
", which is the sort-of-weak spot of the ",
" function; it is helpful everywhere else, though).",
"as for ",
": you can find closed-form-expressions that solve ",
" in a straightforward fashion. however, the equation ",
", or equivalently, ",
" does not have a neat solution in elementary form other than ",
". your number ",
" is the squareroot of the next-to-smallest positive solution of ",
". this can be easily verified as ",
" needs to suffice both equations, ",
" and ",
". "
] |
[
"If you made a spherical shape of magnets all on the negative side and put a magnetic bearing in the middle would it levitate?"
] |
[
false
] | null |
[
"What do you mean the negative side?",
"Metal is attracted to both the north and the south side of a magnet.",
"A magnetic bearing would have one side which is north and one side which is south. If you put it in a sphere with all the south facing in, one side would repel but hte other would ATTRACT and it would fly quickly to the edge due to the magnetic attraction.",
"It is impossible to make a magnet with only one pole. this is the \"no monopoles\" idea of magnetism and while physicist have spend year and years looking for a magnetic monopole, they do not seem to exist in the universe."
] |
[
"Magnets with one pole do actually exist, physicists can engineer the poles in such a way. Smarter Every Day has a video on this, thought I'm unsure whether the video talks about magnets with one pole."
] |
[
"Magnets with a single pole absolutely do not exist. This would be a Nobel prize to discover one. People have been searching for a very long time due to an argument about charge quantization by Dirac.",
"You can get things that sort of look like a magnetic monopole ",
" a material, a sort of effective monopole. However the type of monopoles in a spin ice are absolutely not actual magnetic monopoles. Certainly not something you could make anywhere and use them to levitate."
] |
[
"How often can a person get dengue fever?"
] |
[
false
] |
[deleted]
|
[
"Not sure, but you certainly can get it more than once. I had always thought that subsequent infections have increased likelihood of haemorrhagic fever, but don't know a ref for that. So best to try not getting it more than once (and once is usually enough incentive to avoid A.Aegypti)"
] |
[
"Infection with dengue provides some resistance to that serotype, but introduces the risk of DHF if infected with a different serotype"
] |
[
"Thanks for the answer. Yeah I've had it officially 3 times and the fourth time is susceptible. ;)"
] |
[
"Our brains store so much information; is there a limit?"
] |
[
false
] |
[deleted]
|
[
"From the way that I understand it, it is definitely finite, but not in the way a hard drive is finite. I remember learning a theory before in which memory is frequently rearranged and patterns are recognized and stored (reminds you of .zip compression, no? :P )",
"Anyways, here's a little excerpt from an ",
"article",
" I was reading about fruit flies:",
"\"Because housing flies in a complex social environment for 5 days increases the number of synaptic terminals in projections from the large ventral lateral neurons (LNVs) (20), we asked whether social enrichment would impair LTM. We used pigment-dispersing factor (pdf)–GAL4 to drive expression of a green fluorescent protein (GFP)–tagged construct of the postsynaptic protein discs-large (UAS-dlgWT-gfp) in flies exposed to increasingly larger social groups. The number of dlg-positive terminals increased with the size of the social group (Fig. 3, A and B). To determine whether the saturation of dlg-positive terminals had functional consequences, male Canton-s (Cs) flies were socially enriched in a group of 90 flies and then exposed to spaced training for courtship conditioning (Fig. 3C). Cs flies that had been maintained in social isolation displayed normal LTM (Fig. 3D). However, enriched flies had no LTM when trained either immediately after enrichment or after 1 day of delay.\"",
"Basically, the flies that were in a highly social environment were basically losing their ability to isolate thoughts into their long-term memory, while the other set of flies maintained this ability."
] |
[
"Yes. Information is a physical property and only so much can be encoded within a limited space or upon a given amount of mass.",
"Of course, our brains aren't ",
"black holes",
", so our limits are a lot less than the absolute ones. Estimating how much information a brain actually could hold isn't straight forward, but I've heard a number in the petabytes ",
"thrown around before",
"."
] |
[
"It depends on what you mean by \"information\". If you just mean the ability to record daily events that we observe/experience then there really doesn't seem to be a limitation for some unique ",
"people",
". These people can recall minutiae of of events every day that is mind-boggling. They literally do not seem to forget anything. The obvious question is - why can't everyone do that? Certainly that could be helpful, right? Well, it turns out that for most of these people, this ability is horribly distracting and makes it difficult to function. Imagine that every simple experience you have reminds you of a similar experience you have had in the past, which reminds you of other and these memories keep happening, all day, every day. Us \"normal\" people who forget experiences over time seem to have a filter that allows the trivial events to fade into the background because they really aren't useful in day-to-day life and it seems that if we hold on to them that it can become much more difficult to function. So the brain has an amazing ability to recall events, but it is lessened for most of us to allow us to cope with living. "
] |
[
"In Earth travel, we use North, South, East, and West, plus altitude for three-dimensional travel. Since those are all relative to the Earth, what do they use for space travel?"
] |
[
false
] | null |
[
"Pretty much on every planet or moon it is possible to define North, South, East and West based on the body's rotation. Alternatively, they can be defined based on the Solar System's North and South (as the IAU did with Uranus, whose extreme axial tilt makes the rotational North opposite to the Solar System's North, but for all the other planets it's the same).",
"However this isn't very precise to plan spacecraft trajectories. There are more precise reference frames based on longitude and latitude, so a prime meridian is defined pretty much arbitrarily as they did on Earth. It's also quite common to use Cartesian reference frames centered on a planet but with the axes based on far away celestial objects because they don't rotate with the planet, so you have an inertial reference frame.",
"In deep space, far away from any planet, we use a reference frame centered on the Sun, with the X axis pointing along the ecliptic plane parallel to the vernal equinox (the intersection between Earth's equatorial plane and the ecliptic plane), the Z axis pointing North from the Sun, and the Y axis pointing 90° ahead of the X axis following the right hand rule.",
"It is possible to define others, it depends on each particular trajectory. Basically you need a center (a planet, the Sun, etc), a fundamental plane (the ecliptic plane, the planet's equatorial plane, etc) and a direction for the X axis."
] |
[
"Im a 6-DOF simulation engineer at NASA, so this is right up my alley. There are tons of different coordinate frames one can use to navigate 3D space, the key is know what kind of rotation matrix/quaternion you need to navigate from frame to frame. To name a few, there's topodetic, topocentric, PCI, PCR, J2K, M50, NED, DSL...the list goes on and on. I can give you more info tomorrow when I'm back at my desk if anyone is interested."
] |
[
"Being things tend to move in elliptical patterns I would have thought something like polar coordinates would be used. Is there a particular reason a Cartesian coordinate system is used? "
] |
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