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[
"What is the difference between steam, fog and 100% humidity?"
] |
[
false
] | null |
[
"It is all water, water vapor, and air. ",
" \nWater vapor is what the gaseous form of water is called. ",
" \nSteam is created when enough energy (heat) is applied to cause the liquid water to change phases from liquid to gas. Steam is actually clear. The white puffy stuff you see coming off a pot of boiling water is actually steam that has cooled and condensed to form very tiny water droplets that are visible as the puffy stuff rising off the pot. As the tiny droplets rise in the air (because they are hotter than the air around them and less dense) they evaporate due to the air moving past them. ",
" \nFog is water vapor that has condensed into tiny droplets that has approximately the same density as the air around them. So the droplets just kind of float around. If the sun comes out and warms up the fog it will evaporate into the air and the water vapor become clear. ",
" \n100% humidity is rain, or just before rain. There is so much water vapor in the air that given the right temperature water condenses out of the air as raindrops that are heavy enough to fall out of the air. "
] |
[
"This is just my understanding: steam is hot water that has reaches the gas phase. 100% humidity is when the air contains the maximum amount of water that can be dissolved in it. Just like a glass of water can only have so much salt dissolved in it, the same goes for air and water vapors. Fog, is just a fallen cloud maybe? "
] |
[
"Correct on fog. Fog and clouds are both water vapor that has condensed into tiny tiny droplets that are either the same density as the air around them or are light enough to be lifted by wind or updrafts. "
] |
[
"Is nitrogen dioxide a second messenger?"
] |
[
false
] |
I'm pretty sure my biology teacher is mixing up NO2 and NO. NO2 is a toxic brown gas. NO is a common second messenger, noted for its role in the transduction pathway of nitroglycerin. The teacher asserts that NO2 is a second messenger, but I can't find a thing about it on the internet- all of the information is for NO. So, is there something I'm missing? Are both considered second messengers? Thanks!
|
[
"I answered your modmail, but I'll repost the answer here:",
"He might be talking about the nitrite ion, which is NO2-. This is a stable breakdown product of nitric oxide (NO), that can convert into NO in tissue areas that are relatively hypoxic.",
"If he said nitrogen dioxide, he is incorrect and likely just thinking of NO."
] |
[
"Thanks for both replies. You are a minor god of biology."
] |
[
"Nitrate, nitrite, and nitric oxide are biochemical messengers. Nitrogen dioxide I haven't heard of being used by cells. All these molecules are toxic at high concentrations. Even hydrogen sulfide is used as a biochemical messenger. "
] |
[
"Will going for a sunbed give my body vitamin D?"
] |
[
false
] |
And if so, will it give me the same amount as I would from lying in the sun in a warm country for the same period of time?
|
[
"Yes",
"UVB (UV rays between 295 and 297nm) is the radiation needed for your body to synthesize vitamin D in the skin and is also emitted by tanning beds. Whether or not this is equivalent to lying in the sun for the same amount of time is hard to say though if ALL other factors are controlled for e.g. skin exposure, duration, time of day, serum vitamin D levels, inclement weather, etc. then there is no reason to think it wouldn't be the same.",
"From a cost perspective, it would probably be cheaper to buy a bottle of a vitamin D supplement and eat it regularly than shell out for a tanning salon on a regular basis."
] |
[
"Thanks. I'm sure I read something a while ago saying that the amount of vitamin D you can get from consumption is insignificant to how much your body can get from sunlight. I take it that isn't true then?"
] |
[
"Not insignificant but you would have to eat A LOT (more than you would normally eat but less than so much it would make you sick) of the foods that have a dietary level of Vitamin D for it to equal the amount you synthesize just from standing in the sun for a few minutes (again how much sunlight is enough is highly variable)",
"Here",
" is a fairly credible breakdown for both"
] |
[
"Why do wisdom teeth come in so late, and for so many people need to be removed?"
] |
[
false
] |
What biological advantage does it serve that wisdom teeth come in so much later than the rest of the adult teeth? What signals the teeth to be ready to come in? What causes the need for wisdom teeth to be removed? Thanks in advance
|
[
"Teeth come out in an organized fashion with molars coming out one after another as a general rule. Wisdom teeth just so happen to be the last one. Anthropologically, it has been suggested that Wisdom teeth are vestigial, or not really necessary anymore. It was almost certainly an advantage to have many molars when our diet consisted of a lot of course rough food. With cooking, food preparstion, and utensils, that is less of an issue. ",
"There are further evolutionary issues related t\no why we often have difficulties with Wisdom teeth, chief among them that human jaws have generally gotten smaller as we have evolved as a species. "
] |
[
"Wisdom teeth can replace lost teeth. I have two adult teeth that never existed/ didn't come in, and 1 wisdom tooth. Wish braces I closed the gaps and have a normalish mouth.",
"In the wild, someone could loose a few teeth, and then have wisdom come in as replacements. They only overcrowd mouths because modern people take good care of their teeth."
] |
[
"Evolution only operates to make systems work well up and keep you competitive up to the age at which you breed; from then on, you are surplus to requirements, and evolution generally won't fix any problems you have (leaving aside parental/grandparental care etc).",
"So, if - in the ancestral wild - wisdom teeth erupting caused pain and infection in the jaw, even if severe enough to make you starve, as long as it happened after you'd had and raised your kids, it wouldn't matter ",
", and might even be an advantage for your genes, because you'd no longer be around to compete for resources with your kids, who carry your genes.",
"That's why \"ageing\" exists - joints only have to be flexible until breeding age, hair only has to be signal of health and parasite load to breeding age, teeth only have to present to keep you fed until breeding age, your heart only has to be able to sustain prolonged exertion till breeding age... you get the picture. There's generally not a pressure to make you die faster, but there isnt any selection pressure or genetic transmission mechanism to allow individuals who suffer less from the infirmities of age to pass that trait on."
] |
[
"Can you recommend some books on abiogenesis and/or cosmology?"
] |
[
false
] |
Having recently read The Selfish Gene (Dawkins) and The Grand Design (Hawking), I am interested in learning more about cosmology and biology - particularly evolution and abiogenesis. Can recommend some good titles or authors?
|
[
"Origins of Life by Freeman Dyson",
"Life in Space: Astrobiology for Everyone by Lucas John Mix",
"Astrobiology: A Brief Introduction by Kevin Plaxco",
"Life Everywhere by David Darling",
"Rare Earth: Why Complex Life Is Uncommon in the Universe by Peter Ward",
"ALso there are some talks ",
"here",
". Sadly they are RMVB but they are all about active research inAstrobiology"
] |
[
"I didn't read it, but this other book by Simon Singh was pretty good, so I trust that his new book about the Big Bang is similarly good. It's called \"Big Bang\".",
"Then I hear a lot about Bill Brysons \"Short story of almost everything\" or something like that. His other books are extremely funny and he is not a scientist in the slightest, but judging from his other books I believe he is really persistent when it comes to doing his own research. I skimmed it once and it looked pretty good.",
"God my advice sounds terrible. But yeah check those two out."
] |
[
"In particular, I've found two potential buys on Amazon for abiogenesis - has anyone read either of these?",
"Emergence of Life on Earth - Iris Fry",
"Life's Origin - J. William Schopf"
] |
[
"How does the sun revolve around the galactic core?"
] |
[
false
] |
[deleted]
|
[
"The same way Earth orbits the sun without being sucked into it—gravity causes an acceleration toward the center, but tangential velocity keeps it in an elliptical orbit. Black holes aren't magical space vacuums; to outside observers they're basically just massive spheres (modulo some weird effects near the event horizon).",
"Also, the supermassive blackhole at the center is almost negligible compared to the mass of all the ",
" in the core region."
] |
[
"The arms aren't \"real\" structures; they're apparent structures that come from the arrangement of the stars and the way they move. It's not entirely clear what causes them. Until recently it was widely believed that the spirals were sort of \"pressure waves\" rotating around the center. The stars themselves orbit at whatever speed (dependent on their radius), and then these pressure waves travel around at some other speed (which is the same at all radii within the wave), so some stars move along with the waves, some move faster and pass through them in one direction, and others move slower and get passed by them.",
"However, ",
"recent simulations",
" have shown that the spirals may actually be transient features, breaking up and reforming over time spans of millions of years with the \"speed\" of the arm basically matching the speed of the stars at whatever radius, with the note that because the waves are higher density, stars on either side are accelerated (decelerated) in such a way that they move toward the arm."
] |
[
"The arms aren't \"real\" structures; they're apparent structures that come from the arrangement of the stars and the way they move. It's not entirely clear what causes them. Until recently it was widely believed that the spirals were sort of \"pressure waves\" rotating around the center. The stars themselves orbit at whatever speed (dependent on their radius), and then these pressure waves travel around at some other speed (which is the same at all radii within the wave), so some stars move along with the waves, some move faster and pass through them in one direction, and others move slower and get passed by them.",
"However, ",
"recent simulations",
" have shown that the spirals may actually be transient features, breaking up and reforming over time spans of millions of years with the \"speed\" of the arm basically matching the speed of the stars at whatever radius, with the note that because the waves are higher density, stars on either side are accelerated (decelerated) in such a way that they move toward the arm."
] |
[
"How does the vaccine distribution work in the human body. I saw some people say something that it stays at the injection site and others say it doesn’t. Don’t all vaccines spread in the body ?"
] |
[
false
] |
I’d really appreciate some articles/studies showing how distribution works to better understand.
|
[
"The mRNA vaccines do travel away from the injection site, but not via the blood — it's mainly via ",
"lymphatic vessels",
" (Wikipedia link), which takes the mRNA to draining ",
"lymph nodes",
". ",
"With a slightly different and earlier mRNA vaccine -",
"Following longitudinal assessment of the vaccine’s biodistribution after administration to cynomolgus macaques, they found that the vaccine exclusively targeted the injection site and the lymph nodes that drained the tissue of the injection site (Fig. 1a). The vaccine was administered by intramuscular injection in the quadricep muscle of the leg, and consequently ended up in inguinal, iliac and paraaortic lymph nodes",
"--",
"Imaging the early fate of mRNA vaccines",
"Of course, lymph nodes are exactly where you want vaccines to go, since that's where immune activation takes place.",
"Whichever delivery system is used, viral proteins do not initiate immune memory responses in muscles. They must be transported to lymph nodes in order to initiate a response. This transport occurs primarily within antigen-presenting cells (APC), specifically dendritic cells (DC), which are drawn from blood into the vaccination site by local inflammation....The critical next step is entry into tissue-draining afferent lymphatics... Only once delivered to local lymph nodes can the antigen trigger a specific adaptive memory response from naïve B- and T-cells located there.",
"--",
"COVID-19 vaccination – Don’t forget the lymphatics!",
"This is basically the same as any intramuscular vaccine -- muscle cells are not at all good at driving primary immune responses, but lymphatic drainage is very efficient and rapidly moves injected substances to regional lymph nodes; that's how the immune system is \"designed\" to work as it surveys for pathogens."
] |
[
"It was my understanding that the vaccine stimulates your muscles to produce proteins that are in the virus, leading your body to make antibodies for the virus. The antibodies give you the protection and they travel in your bloodstream. ",
"It is certain that the protection does not just stay in the injection site. That doesn't make any sense."
] |
[
"A lot of it drains away into the Lymphatic system.\nAnd the mRNA can also be taken in by muscle cells which begin producing the spike protein for a while until the mRNA is degraded by natural cell processes.\nCells constantly break down and build up their components.\nWhichever cell take in the mRNA will produce the spike proteins.\nThe spike proteins end up in the lymphatic nodes where they are detected by the immune system."
] |
[
"What would theoretically happen to a solid object if it were rotated at relativistic speeds?"
] |
[
false
] |
I was just wondering about what would happen if some solid body, like a sphere, were rotated at speeds comparable to the speed of light. I know about special relativity's implications for an object moving on a straight path at relativistic speeds, but what would this imply for a rotating body? It gets weird when you consider the fact that the outermost parts of a rotating sphere rotate at a faster velocity than the innermost parts.
|
[
"Probably tears itself apart from centrifugal force way before reaching anywhere close to "
] |
[
"tear itself apart/shatter because, well, ratio of circumference to diameter wouldn't, from its own perspective, be equal to Pi anymore. If you want something rigid spinning relativistically, you have to create it already in motion.",
"Some ",
"info on wiki",
" about this."
] |
[
"You would have to have something strong enough to even withstand the force of not tearing itself apart.",
"For example, CDs ",
"http://www.youtube.com/watch?v=JOb6Z5Tja68"
] |
[
"Teaching your child science. Where to start?"
] |
[
false
] |
We are organizing a homeschool group and the oldest three kids are 6 years old. I'm going to be teaching them history and a science. I have no idea where to start with science. Should we study nature? Leaves, trees, anything in the backyard? The Animal Kingdom, classifications and species? Space, planets, and stars? Then you have to explain the laws of gravity and others. There are great science projects we can do involving chemistry, but that seems a little advanced. I could teach anatomy, the human body and it's functions. Where should I start, what do you think is the most important thing kids need to grasp? Help me please!
|
[
"I remember learning science when I was that age, and I've also taught classes at a zoo to kids of all ages. I think when they are younger, kids can have a harder time grasping concepts that they don't see/experiences themselves. Basically, I would probably stick to macroscopic sciences until they are a little older. Things like nature and animals and plants are great because you can go very hand-on with that. The same with the human body, especially things like senses and how we process the world. I think anatomy might be a bit much some of the concepts of how the stuff inside us works could be a little too advanced.",
"I think you also could definitely do space stuff, too. You might want to stick to the solar system and more basic concepts like galaxies and stars, but space is always really cool and there are always great museums/planetariums/science centers you can go to and supplement what you are teaching.",
"I think that chemistry and physics might be a little advanced because kids might have a harder time visualizing the scientific lessons in those subjects because they don't get to interact with them. I hope that makes sense.",
"Also, you can being to teach scientific reasoning skills and experimental skills by having small science labs. These labs don't need to be super advanced but you could help kids go through activities that require thinking of a hypothesis (e.g. Birds chirp more in the morning than at night) planning an experiment (sit outside for an hour in the morning and an hour at night counting bird chirps), taking some data, and then understanding the result. Teaching them how science works is just as important as teaching specific scientific concepts.",
"And a disclaimer, even though I have education experience, I'm not primarily an educator. My ideas are based on my experience with teaching kids at a zoo and with my experiences growing up."
] |
[
"Keep in mind that young children are natural scientist, they are curious about the world around them and want to know how it works. Find out what the kids are interested and engage them, please don't teach at them. The worst thing that could happen is to crush this curiosity with memorization. If it is nature take them to a park and have them discover what animals and plant live by them. If it is space get them a telescope or do one of the scale models of the solar system. If it is chemistry start off with different physical (melting, freezing, magnets) and chemical (baking soda volcano) reactions. and remember that cooking is just chemistry with a yummy result at the end. Show them the basics of the scientific method (hypothesizing, experimenting, recording, and analyzing the results) and let them discover the hidden beauty of the world. Best of luck.",
"edit: spelling"
] |
[
"Start with things they know. Weather, for example. ",
"The precipitation cycle is a good one.How it changes from a gas to a liquid, and how it can even become a solid (hail, snow). Water is a great stepping-stone.",
"It's the first thing I remember learning. "
] |
[
"The speed of gravity: faster than light by >10 orders of magnitude?"
] |
[
false
] |
I imagine this is probably a reasonably well-known "unorthodox" paper in physics circles: , which proposes that the speed of gravity must be much higher than that of light (if not quite infinite). For me his arguments make a lot of sense, and I can't disprove them. Particularly the one about the instability of orbits when gravitational forces are delayed by speed-of-light limits. I assume that, since it's not commonly accepted theory, it must be considered wrong. What is wrong with it?
|
[
"Why do people need to be warned of a pdf?"
] |
[
"There is no experimental evidence to suggest that gravity travels faster than light. There are several experiments being set up to try to detect gravitational waves, and until they start getting results, its too soon to throw out general relativity."
] |
[
"Adobe Reader is so stunningly bad that it frequently crashes people's web browsers."
] |
[
"If we share 98% of our genetic material with chimpanzees, what is the variance within the human population as a whole?"
] |
[
false
] | null |
[
"Not an answer to your question, but just to give some perspective: Humans also share something like 75% of our genetic code with ",
". Comparing percentages doesn't really say much."
] |
[
"The common answer is that on average the genetic similarity of two people is between 99.5% and 99.9%. The answer partially depends on how we define genetic variation (",
"wikipedia",
"). If we just count the variants that have been observed, current databases have about 54 million short variants (changes to a single base pair, small insertions and deletions, etc) and 9 million structural variants (repeated sequences, etc), compared to the roughly 3.3 billion base pairs in the human genome (",
"source",
"). Most of these variants are rare though, so the 99.5-99.9% estimate is probably still fairly accurate.",
"It should also be noted that the amount of variation heterogeneous between subgroups of the human population. For example, there is more genetic variation within African populations that within European populations. ",
"Also, fun trivia: ",
"by some measures there may be more genetic similarity between a man and a male chimpanzee than between a man and a woman",
"."
] |
[
"I think, from what I remember, we share 25% of our DNA with dandelions.",
"An important factor to remember is that it's not just which genes are present - it's also which are turned on/off, depending on the context of other genes' presence/absence or on/off state. So we can share the same genes, but if mine are on and yours are off, that's a \"genetic difference\" as well."
] |
[
"What would happen to a puff of smoke in a vacuum chamber?"
] |
[
false
] |
[deleted]
|
[
"The gaseous part of the smoke, which is invisible, would expand to fill whatever enclosed space it was released in.",
"The part of the smoke that you can see is particulate matter, it is essentially very high molecular weight agglomerations of the products of incomplete combustion. These particles would simply fall like rocks to the bottom of the container because there would be very little gas for them to interact with and become entrained in. They may be slowed a bit by the aforementioned gases, although this would depend on the size of the vacuum chamber."
] |
[
"That makes sense. Now say gravity was negligible...how would the particulate matter act in the presence of the expanding gas? Would the gravitational pull of the particles themselves act upon each other?"
] |
[
"Now say gravity was negligible...how would the particulate matter act in the presence of the expanding gas?",
"Particles will bounce around until they stick either to each other or the chamber walls due to intermolecular forces. The sparse gas would exert drag and slow them down somewhat; the amount of drag would depend on the density of the gases (which is inversely proportional to the size of the chamber).",
"Would the gravitational pull of the particles themselves act upon each other?",
"Not by any measurable amount."
] |
[
"In an 80-year life span, roughly how many generations of bacteria live and die in one's gut?"
] |
[
false
] | null |
[
"The article I linked to doesn't say that this is an exponential phase measurement; could you please explain why you say that it is? I took it to be an estimate of the normal steady-state generation time. When would there be exponential phase growth in the gut, other than after antibiotic treatment?"
] |
[
"The article I linked to doesn't say that this is an exponential phase measurement; could you please explain why you say that it is? I took it to be an estimate of the normal steady-state generation time. When would there be exponential phase growth in the gut, other than after antibiotic treatment?"
] |
[
"…in the intestinal tract, the coliform's generation time is estimated to be 12-24 hours…",
"So about 50 000, give or take, for ",
"."
] |
[
"Why is the hazard/mortality ratio for HbA1c higher for the lowest levels? Is it explained primarily by a significant fraction of the ill population having high RBC turnover?"
] |
[
false
] |
. Risk of death is higher for 4.3/4.4 relative to 4.8. I mean, Mike Lustgarten reports that mortality ratio is lower for fasting glucose of 84 than for 75 (b/c high RBC turnover is an indication of something bad?) And what IS the percent of the population that has high RBC turnover? Like, if you want to do a full analysis of variance of mortality as a function of HbA1c, you want to form a hierarchical model where you explain how variation of mortality explained by HbA1c is DIFFERENT between both high and low levels of HbA1c AND (through cohort matching) what percent of low HbA1c is due solely to high RBC turnover (high RBC turnover is presumably a bad thing). [are there hierarchical linear models that compartmentalize variance between high levels and low levels of HbA1c?]
|
[
"HbA1c is a quantification of the amount of the \"normal\" variant of haemoglobin [HbA]* which has been glycated at sometime during its working life. Glycation means having a glucose molecule permanently bonded to the HbA molecule - the glucose attaches at a characteristic spot on the HbA molecule at a consistent slow rate but the rate is dependent upon the amount of glucose around about (inside a red blood cell [RBC] though this is strongly correlated with the concentration of glucose in the blood.) ",
"RBCs work hard and wear out very quickly. Their half life (the duration at which half of them will have died, and them and their contents have been broken up and recycled) is about three months. Any particular HbA molecule has a limited time in which it may become glycated. Over the course of three months the chance is about 5% if there is a normal amount of glucose around its cell. If a large selection of cells are sampled - a typical blood test sample contains tens of billions of cells - then the average age of the HbA molecules in the sample from a healthy person is three months and around 5% of it is glycated HbA, a.k.a HbA1c.",
"Glucose concentration in blood is actively controlled by your body, dynamically storing and releasing glucose to maintain the level at 3 to 8 mmol/L so that HbA1c level of 5% is consistently found unless the system of control breaks down - this is what happens to a person with diabetes. It is possible find a healthy person with a glucose well above 8 mmol/L if they have just swallowed a load of sugary food, but it will get stored away rapidly and the blood glucose level should be back to normal in an hour. This short blip of high glucose concentration will barely affect the HbA1c percentage**. However, a diabetic whose body fails to control blood glucose levels automatically will have a highly variable and usually a higher average glucose concentration continuously. Thus Hb gets glycated a little more quickly on average throughout its lifetime and the percentage of HbA1c in any sample goes up. ",
"HbA1c is a one trick pony in diagnostics. Its unique trick is to estimate the average amount of glucose in a persons bloodstream over the past three months (or so.) Its useful because a diabetic can tolerate fairly high quantities of of glucose transiently but maintaining a higher glucose level causes the long-term damage. Thus, the momentary blood glucose concentration is not that useful for managing the disease compared to a measurement of the accumulated average glucose.",
"In practice HbA1c is not the definitive diagnostic criterion for diabetes (though it was recommended for a while by W.H.O. Currently they recommend a most uncomfortable and time-consumng Glucose Tolerance Test to be definitive) but it is of greatest utility in helping a person manage their diabetes over the (life)long term and for predicting whether the nastier side-effects of diabetes are likely to appear. (Most of the diabetic problems - retinopathy, nerve damage, kidney failure etc. are caused by glycation of other proteins around the body some of which, unlike Hb, are damaged or disabled by these stuck-on glucoses.) In addition it overcomes a problem with diabetics visiting a clinic for a regular check-up (usually every three months until the diabetic is 'trained' to monitor and deal with their condition by moderating their glucose/sugar intake.) The patient knows that their appointment is due and that they will have their glucose level checked in clinic and will be scolded by the clinician if they have been eating too much so their glucose level is high. It is common for patients to change their diet for the day of the visit. This means the clinician does not get an accurate picture of their state of health and risk factors, but also meant it was quite common for a patient, knowing they had recently over-indulged, to starve themselves on clinic appointment day and to collapse from hypoglycaemia (too little glucose to power their body) often in the clinic waiting room!",
"In diagnostic practice, low levels of HbA1c are not very useful. Any person with a normal rate of RBC turnover, typical HbA and a livable level of blood glucose should always have at least 3.5% of their Hb glycated in any random sample, so a lower level does indicate a problem with the red blood cells, but there are other, better ways to investigate these various problem. ",
"There are a variety of root causes for high RBC turnover that can be diagnosed directly and they will typically associate with anaemia*** and other clinical symptoms so evidence of low HbA1c is usually redundant. Gross trauma or blood transfusions can also mess up HbA1c interpretation but are clear contra-indications for the test. Atypical variants of haemoglobin can cause the rate of glycation to change and give unrepresentative HbA1c results. HbA1c assays most commonly separate the Hb using chromatography so confounding variants can be detected and either accounted for or invalidate the test - though there are some very rare variants that may be missed (this is more of a concern for incorrectly identifying - or failing to identify - high levels of HbA1c and mis-diagnosing diabetes.) ",
"It is possible that occasionally one of these oddities may be noticed due to an anomalous HbA1c in an apparently asymptomatic person but there is not enough consistency, or enough occasions where this is likely to make for a deliberate diagnostic inquiry. However, if whole population HbA1c screening for diabetes were to be attempted (there is believed to be an epidemic of undiagnosed sub-clinical and pre-diabetic people who may only be discovered when they present with an associated condition or collapse into a coma) then mining this free data for indications that might signal, for example atypical Hb variants or chronic low level exposure to carbon monoxide might become worthwhile.",
"~ ~ ~ ~ ~ ~ ~ ~ ~ ~",
"*There are lots of other variants of haemoglobin - many associated with a pathology; for example sickle cell disease is associated which having the HbS variant of haemoglobin in place of the usual HbA. The different variants have differences in how well they glycate so the HbA1c analysis cannot be reliably done for a person without any HbA type haemoglobin.",
"**HbA1c used to be reported as a straight percentage in several countries but by international agreement the measurement has been standardised as the concentration , in mmol/L of glycated Hb as a ratio of the molar concentration of all Hb [ie. \"mmol/mol Hb\"]. This provides a 'nicer' scaling, apparently (5% roughly equals 40mmol/mol) This is a UK biochemists equivalent of Pluto.",
"***NB HbA1c measurements are not themselves affected by anaemia, so long as there are enough RBCs to get a good sample (you'd be dead before that number got so low) since only the ratio of glycated to total Hb is quantified."
] |
[
"You *only check HbA1c levels on people with diabetes. Very high blood sugars tend to kill diabetics slowly. Very low blood sugars will do it quickly. If someone is on glucose lowering meds and their HbA1c is low, they probably have some dangerous hypoglycemic episodes.",
"Edit: * not “only” but “only do the following frequently enough to give significant weight to any trends such as the one OP was asking about”"
] |
[
"I would like to point out some problems with using A1C as a metric for blood sugar stability.",
"Some people have longer living red blood cells and can measure on an A1C test at over 7.0 but not have any blood sugar issues.",
"We would tell a type 1 diabetic that an A1C of 5.5 is perfect and it correlates to an average blood sugar of 100.",
"However if the person spent 40% of the time with a blood sugar of 50 and 40% of the time with a blood sugar of 160 and 20% of the time at 100, A1C would still be 5.5, but they would have spent 1,700 hours out of a healthy blood sugar range and permanently damaging their organs.",
"A person who is chronically hovering around 120 blood sugar would end up with an A1C of 6.6 but be healthier than the first person because they are maintaining stability in a decent range even if that range is a little higher than optimal.",
"I have personal experience seeing the first one happen on multiple occasions.",
"While A1C can certainly be a tool for trends it's like BMI, and especially for type 1 diabetes not a very useful metric anymore.",
"I find this important as type 1s get the shaft in the world where whenever we use the word diabetes we automatically mean type 2 and they are two completely different things that just end up with the same results if ignored."
] |
[
"Is it possible to accelerate to a set speed instantaniously?"
] |
[
false
] |
Hello science people. I was wondering if it is possible (I know its not with current technology but maybe one day) to accelerate to per say 50 km/h without starting at one, two or thee so on and so forth. I was just kind of curious! :) - Cheers
|
[
"Instantaneous acceleration requires infinite power. So no."
] |
[
"Jumping instantaneously from one speed to another speed would require infinite acceleration, and therefore an infinite force, which does not exist. Also, the object being accelerated would feel an infinite g-force (inertial force) and therefore be crushed to zero width."
] |
[
"Thanks lad have a good one"
] |
[
"Why did animals never evolve the ability to synthesize food from sunlight?"
] |
[
false
] |
Somewhat related: did plants and animals evolve independently, or did one come from the other?
|
[
"Some animals do. Corals contain a ",
"photosynthetic algae",
" that directly provides energy to the coral. There's no particular \"why\" beyond that other than it just didn't happen for other animals. ",
"Both plants and animals evolved from bacteria, branching from bacteria separately. The first photosynthetic bacteria were ",
"cyanobacteria",
" (blue-green algae)."
] |
[
"You've got it exactly backwards; a plant develops a large surface area because it can photosynthesize, not the other way around. Early proto-plants and proto-animals were similarly-sized colonial systems. ",
"Your answer attempts to say \"why\" the complex animals we have now haven't gone back and picked up added photosynthesis. The answer, if there is one beyond \"because they just haven't\", is more developmental than any kind of energy equation. Once you get to being a complex multi-organ organism (differentiated tissue types) it's much more difficult (in evolutionary terms) to muck with the basic machinery of energy production to bring in something new, compared to just deciding to consume what's available in the environment. The corals mentioned in my post above are one of the simplest types of animals which was likely necessary for them to accomplish it."
] |
[
"Not for sloths",
" (both fur and camoflage here, and even the suggestion of extra nutrients). Body shape seems to work out fine for both sloths and algae; as I said, the reason it hasn't gone further is either \"it just hasn't yet\" or \"difficulty further integrating systems\" rather than anything to do with shape. "
] |
[
"How come when I hit my dab pen (THC Oil) my head and ears get an intense, burning-like feeling for like 30 seconds or so?"
] |
[
false
] | null |
[
"We can't comment on personal anecdotes / isolated incidents without resorting to speculation which we try to avoid."
] |
[
"Gotcha, wasn't sure if there was anyone else who experiences this and knows exactly what it is. Is there a sub you suggest I post to? I'm genuinely curious why this happens to me."
] |
[
"You can always try ",
"/r/findareddit",
" for help in finding a sub."
] |
[
"Do tornadoes change the contours of the land?"
] |
[
false
] |
When a significant tornado hits, for example, a hill, will there be visible changes do the shape or height of the hill? I'm not interested in wind erosion that takes place over hundreds of thousands or millions of years. Is there ever a significant impact from a single tornado on the contours of the land?
|
[
"Not that I've ever seen. Maybe if it passed over an area dominated by loose sand but usually earth stays pretty much in place. The wind of a tornado is great at getting underneath things that are above the surface but not great at moving things that are flat. Also, the site that a tornado touches down on doesn't look \"hit.\" There isn't any kind of impact that would move the soil."
] |
[
"In response to the second photo, I actually live in Tuscaloosa! Such an exciting place to observe weather. I have definitely seen a lot of tornado tracks, but what I meant was that the actual touch-down point isn't blasted like a meteor hit it (which would change the topography, like in the OP's question). It just looks like the rest of the track."
] |
[
"Also, the site that a tornado touches down on doesn't look \"hit.\"",
"Depends on what you call \"looks hit\" I guess.",
"https://www.nssl.noaa.gov/about/history/may3rd/images/aerial.jpg",
"https://axiomamuse.files.wordpress.com/2011/04/tuscaloosa-aftermath.jpg",
"http://www.weathercast.co.uk/typo3temp/pics/222fcd012d.jpg"
] |
[
"Do scientists/those in software sciences really believe that one day, we’ll be able to type out text messages/words using our thoughts (via implant maybe)? Is this a realistic vision of the future?"
] |
[
false
] | null |
[
"There are already versions of this. See BrainGate or just google \"typing with thoughts\""
] |
[
"Ah I see. In that case, I actually recommend making a new post in our sister-sub ",
"/r/asksciencediscussion",
" which is more geared to such hypothetical / speculative questions and is more about open-ended discussion. I would recommend the using the clearer version of the question you've got in this most recent comment."
] |
[
"I wish this thread blew up because I’d love to read more replies! Where else could I post this to possibly get more traction? And yes that’s amazing. I have seen stuff like that.. I feel like we all forget that this technology exists, so you think we may have it on a consumer level at some point?"
] |
[
"Do animals dance?"
] |
[
false
] | null |
[
"What about birds that seem to dance to music like Cockatoos? ",
"http://www.youtube.com/watch?v=N7IZmRnAo6s"
] |
[
"Fair point. Seems like some do!\nNot sure why the bird does this, would seem odd that this is innate behaviour seeing as music is not a natural phenomenon.",
"For example cobras ",
"\"dance\"",
" to the music of the pipe player but its not the music that's making them do that*; its the ",
"motion of the pipe",
". ",
"*Snakes are in fact deaf."
] |
[
"Yes but obviously not to music, it's normally to attract mates:",
"Video here"
] |
[
"Does chewing food 50 times increase nutrition availability?"
] |
[
false
] |
Additionally, what are the full benefits of chewing a lot before you swallow?
|
[
"To disagree with the other commenters - chewing does affect nutrition. Not in the way you mean in your question, but in several important ways.",
"To be clear, chewing 10 times vs 50 is not nearly the same difference as blended vs chewed. In regards to 1. & 2. (above) the degree of chewing is unlikely to make any serious difference.",
"I could go on with a bunch of other things of decreasing impact, but will finish up with an anecdote, that in Japan, a standard doctors' new patient questionnaire will include questions about food habits, including how long it takes you to eat, and how many times you chew your food. It's not information that's acted upon in any way in most average healthy patients, but it's useful diagnostic information in treatment of a number of conditions, particularly related to elderly care."
] |
[
"It doesn't, and there are no benefits to it. It's crackpottery."
] |
[
"Salivary glands start to function as soon as you take the first bite of food and conyinue to produce saliva as you chew. The mucus from the salivary glands lubricates and binds food as you chew it. Mucus holds the chewed food together in a slippery mass, coating it so it can pass down the esophagus into the stomach without causing damage. Saliva also contains alpha-amylase, an enzyme that begins breaking down starches into a sugar called maltose while still in your mouth. In addition, saliva coats the lining of your mouth and esophagus to aid passage of food and makes dry food more soluble so its flavor can be detected by your taste buds."
] |
[
"When global mean sea level rises by one inch, how are various local high tide levels affected?"
] |
[
false
] |
Is there a dominant pattern where the change is either greater or less than one inch in most places?
|
[
"Local sea level is changing differently than the global average - depending on where you are. (For example see this map ",
"here",
") This variation is due to local temperature/salinity changes, shifting currents and rising or sinking land (due to subsidence, earthquakes etc.).",
"Tides are essentially shifted up or down with the mean. "
] |
[
"If you have a source I can read that supports local high tides increasing by same amount as local mean level, that would be great."
] |
[
"Hmmm, thinking about this a bit further local high tides could change by a different amount than the rise in mean sea level - they could increase faster or slower if there's a change in tidal range (difference between high tide and low tide) due to sea level rise.",
"Sea level rise may in some locations change the resonance of the basin slightly, which could increase or decrease the tidal range. Indeed this seems to be occurring in the ",
"Bay of Fundy",
" where there's evidence of an increasing tidal range - but it's possible that tidal range could decrease in other locations"
] |
[
"If the common flu (Influenza) is caused by a virus, why am I told to put a jacket on when its cold?"
] |
[
false
] |
[deleted]
|
[
"Cold temperature doesn't cause viral diseases, obviously. There is a very strong correlation between cold temperatures and several viral diseases -- influenza and respiratory syncytial virus particularly tend to be much more common in the winter (in temperate climates). The reason for this is still not entirely known, but there is an obvious connection between cold temperatures and people getting sick, even if it's not a direct link.",
"There are other reasons that you may be more likely to get sick if you're both exposed to a virus and to cold. Cold temperatures may be directly stressful, and stress reduces your immune system. The dry conditions associated with cold may lead to respiratory system problems that also increase susceptibility. ",
"So there are lots of reasons for the old saying -- increased exposure to viruses, increased susceptibility, reduced immunity. But if there were no viruses, then you could get as cold as you want and you'd never get a viral disease. There are stories (including, apparently, records, but I haven't looked at them myself) showing that for example whaling crew in the 19th century, cruising around Antarctica for years at a time, were remarkably healthy in terms of infectious disease, simply because the acute viruses like influenza would burn themselves out in the small crew and with no more exposure to new people no new viruses entered the system. They might get scurvy and alcohol poisoning and frostbite and so on, but they weren't getting colds and flu."
] |
[
"also to further prove my point I asked a sick relative to drink directly from a bottle and I breathed in his sneezes and cough air (disgusting but drives my point) and drank from that bottle to expose my throat and nose to the virus",
"...what did you expect to happen?",
"and as expected I got sick shortly afterwards ",
"Err, OK, but why?"
] |
[
"To convince people who don't take facts well. I don't live in a first world country where everyone knows about things like these , here people are adamant and have 0 knowledge about the facts, they would rather wear 10 jackets than just covering thier mouth and getting repeatedly sick"
] |
[
"How do we know the distance of celestial bodies from earth?"
] |
[
false
] | null |
[
"For nearby objects like planets within the solar system: radar. They beam out a radar pulse toward, say, Jupiter and measure how long the light takes to reflect back.",
"For somewhat farther objects like nearby stars, ",
"parallax",
". Hold out a finger in front of your face and close one eye and mark where (among things behind the finger) your finger appears to be. Now do the same with the other eye. It now appears to be in a different place among the background. That's parallax. The same thing can be done with nearby stars and Earth's movement around the sun. At t_0, a star appears at position A among the background (much farther) stars. Six months (half an orbit) later, the star is now apparently at position B among the background stars. They then measure the angular difference between these two apparent positions and use trigonometry to solve for the distance to the star.",
"For farther stars that are still within our Galaxy, they do what's called main sequence fitting. They study the star's spectrum and determine what kind of star it is and how bright it should be (independent of distance). Then they compare its apparent brightness (from Earth) to its absolute brightness and solve for distance.",
"For nearby galaxies: cepheid variable stars. Cepheids are weird stars that pulsate in their brightness. The period of this pulsation is dependent on the star's mass, which influences the average brightness. Like with main sequence fitting, the star's brightness is calculated and compared to its apparent brightness, then the distance can be solved for.",
"For galaxies in clusters beyond our own, they use white dwarf supernovae. Also called Type Ia supernovae, these occur when a white dwarf accumulates matter from a binary companion star. When the WD accumulates enough matter to reach 1.4 solar masses, it undergoes a supernova. This limit is called the Chandrasekhar limit and likely applies to all white dwarfs, meaning all white dwarf supernovae have close to the same absolute brightness and can therefore be used with the brightness as measured from Earth to solve for the distance to the galaxy that houses the white dwarf.",
"For much, MUCH farther galaxies, Hubble's law comes in. This has to do with the expansion of the universe, specifically the fact that the farther away a galaxy is, the faster it recedes away from us. This relationship is described with Hubble's law: d = v/H, where H is the Hubble constant and equals ~70 km/s/Mpc (i.e. for every million parsecs farther away the galaxy is, its recession velocity is another 70 km/s faster). They first calculate the galaxy's velocity using its redshift: the faster something is moving away from an observer, the more stretched out (reddened) its light appears to the observer. So they calculate the velocity from how \"displaced\" along the EM spectrum that certain identifiable spectral patterns are in the galaxy's light, then plug that v into Hubble's law to solve for distance."
] |
[
"Using a variety of techniques to build the so-called \"Cosmic Distance Ladder\". Terence Tau has a really nice set of slides explaining it clearly: ",
"https://terrytao.wordpress.com/2010/10/10/the-cosmic-distance-ladder-ver-4-1/"
] |
[
"Do these measurements get affected by things like refraction off of our atmosphere or other gases present in between these distances?"
] |
[
"Are there issues preventing lux operon expression in eukaryotes?"
] |
[
false
] |
What's the major challenges of getting bioluminescent plants / animals? Are the products toxic to the transgenic organisms? Maybe difficult to cause expression, even with the correct promoters or a visible cell choice (ex: in keratinocytes)? I believe something similar in plant chloroplasts has been done, but I haven't seen it attempted in other organisms.
|
[
"There a two aspects of your question that I would like to answer:\n First, I can confirm, that one can have bioluminescence in transgenic eukaryotes. The luciferase gene (a gene from a firefly) for example is used as a reporter gene in many assays. As I only used in single cells I can't say of the substrate oxyluciferin is toxic for an organism. But also fluorescent proteins like GFP or YFP are wildly used as reportes and have no harming effect on the cell behaviour in an living organism. I believe that in the US GFP transgenic fish are sold as pets but here in the EU this is strictly forbidden (so I can't take home my glowing zebrafish",
"\nFor the second part of your question: I don't know if the lux gene has expressed in transgenic cells but the expression of an operon is difficult because eucaryotic cells can't read operons because their trancriptional machinery differs from prokaryotic. So if they did it, I would assume, they expressed all genes under the control of endogenous promoters. ",
"I will definitely read a bit on that topic an I will write again if I found something:) "
] |
[
"Thanks and very cool! I am familiar with GFP and the use of fluorescence, but it's actually those fish (GlowFish?) that sort of led to the question!",
"A kind of \"why don't we see large bioluminescent transgenic organisms, yet biofluorescent ones are common? (i.e. fish, cats, dogs, mice.)\"\nBut instead of a simple economics for feasibility answer, I narrowed the question."
] |
[
"Okay well I think one of the problems really is the reaction - regardless of possible toxicity of some substrates/ products. \nThe facts that bioluminescent cells need to be exposed to the substrate constantly and also that there is only one photon emmited per reaction (thats why it can be used as a reporter for exact quantification assays). So the organism not only would have to express the luciferase at a very high level but needs to be able to store high amounts of substrate in the cells. \nBut still. In melanin deficient zebrafish with an endodermis-specific promoter it seems like an interesting approach:D "
] |
[
"If a comet is traveling through space, a vacuum, then why does it leave a 'trail' at all?"
] |
[
false
] | null |
[
"Comets only have visible tails when they are near the sun. The sun heats up their surface and some gases and dust boil off - that's the tail. It actually points away from the sun. ",
"Like this",
", not out behind like you may expect."
] |
[
"The force of the solar wind by definition applies velocity to an object in space. However, when considering the speeds at which bodies move when approaching their periapsis, as well as the masses of the object, the forces applied by solar winds would have no major significance to the motion of the body. However, rotational forces can be applied to objects in space by heat differential between the two sides."
] |
[
"It isn't leaving a trail in the usual terrestrial sense.",
"As the comet approaches the Sun, it heats up and the various gasses and ions inside it erupt from the surface. These escape the comet and form the coma, the cloud encircling the actual comet nucleus. Some of the ejected debris is lightweight enough to be pushed significantly by solar wind; these get pushed out to form the tail. The tail of a comet always faces away from the Sun, even on the outbound trip. The particulates aren't really \"leaving a trail\" in space, as they continue to approximately follow the comet's orbit long after. ",
"In 1986, one of the probes sent to intercept Halley's Comet got a ",
"great shot",
" of the nucleus. The jets of gas and dust are clearly visible. "
] |
[
"If you put a TV and it's receiver/aerial inside a Faraday cage would it receive any static or would the screen be blank?"
] |
[
false
] | null |
[
"There will still be a level of static but it will not be coming from outer space. It will be thermal noise in the electronics. The received noise will be less but still present. You would have to cool down your electronics to absolute 0K (impossible) in order to completely negate all of the thermal noise and then still the electronics in the receiver will interfer with itself to some extend and produce a little noise. You can make these levels extremely low. "
] |
[
"I remember a professor saying that noise in signals is like friction in mechanics: you can mitigate it but you cannot get rid of the problem."
] |
[
"That would be an accurate statement yes."
] |
[
"What happens to the food/drinks that \"go down the wrong pipe\" and aren't coughed back up?"
] |
[
false
] |
As many of us know, humans are bad at eating and drinking. Our epiglottises (?) occasionally fail at their ONE job and let small bits of food or drinks into our windpipe. Often, when this happens, we cough up whatever "went down the wrong way" and it's fine. If it doesn't happen, there are potentially really serious effects, including pneumonia. I get all of that. What I don't know (and am having surprising trouble Googling) is what happens if something get coughed up and create a significant-enough problem that it requires medical intervention. Lungs (obviously) don't have stomach acid or muscles designed to break down the thing, so does it just stay there, like the thin layer of crumbs under the couch cushions? Does liquid eventually get absorbed into Gatorade-fueled pleural fluid? What actually happens?
|
[
"The upper branches of bronchi to your trachea are lined with ciliated epithelium, little brush-like projections, that beat rhythmically to help get smaller dust and liquid particles mixing with mucous back up to your pharynx, where you hack a bit and swallow them or spit them out. ",
"Anything too big or too far down gets slowly diluted by mucous producing cells and absorbed (liquids), or potentially walled off and slowly degraded by immune cells like macrophages (solids)."
] |
[
"That's really cool! Thanks so much!"
] |
[
"You got it. The acids, the damage they do to the protective lining of the respiratory tract, and the bacteria involved.",
"The type of pneumonia is known as aspiration pneumonia, and is common in people with dementia who lose the ability to properly swallow."
] |
[
"if we ever run out of copper, for ecample for cables, what's our best bet in terms of price and availability?"
] |
[
false
] | null |
[
"Aluminum's always an option; plentiful, lightweight, excellent conductor, easily reused. ",
"That said, there are drawbacks. Being softer than copper, handling aluminum wires means they're susceptible to breakage. Aluminum also expands more when heated than copper does, and over time this can work wires out of connectors, causing arcs that can start fires. Another issue is that while copper and aluminum both oxidize, copper oxide is conductive, whereas aluminum oxide isn't so much. This can change the properties of the transmission line."
] |
[
"Good explanation and I'll add one more issue - cold flow. Aluminum under pressure will slowly thin itself out, until the connection is loose. This appears to happen even without thermal cycling. Al terminations have to be properly designed and torqued to spec. Periodic thermal scanning or inspection and re-tightening is the best prevention for fires.",
"Also I'll mention \"Penetrox\" and similar products that prevent oxidation in the joint, but must be properly and thoroughly applied.",
"Basically, anyone can terminate copper, but aluminum wiring should be left to electricians. And it should always be accessible due to these maintenance issues. This is why it is legal for service wiring and industrial uses, but not residential branch circuits."
] |
[
"Powerlines are usually aluminium now-a-days due to both weight and costs.",
"The fire issues related to aluminium mainly applies to in-house wiring."
] |
[
"In a exothermic reaction how is energy given out to it's surroundings?"
] |
[
false
] | null |
[
"In an exothermic reaction, the released energy is in the form of kinetic energy of particles in the final state. They heat their surroundings via collisions."
] |
[
"Thanks for replying, \ndoes this mean that in order for a exothermic reaction to occur that there must be a adjacent atom or molecule to actually collide and absorb that kinetic energy at the same time the bond is made?",
"Otherwise, if a bond is made and energy is given out, the only place it can give out the energy is to itself which would be paradoxical as it would heat itself and break the bond it just made."
] |
[
"Thanks for replying, does this mean that in order for a exothermic reaction to occur that there must be a adjacent atom or molecule to actually collide and absorb that kinetic energy at the same time the bond is made?",
"No. If you have an exothermic reaction A + B -> C + D, C and D carry away the excess kinetic energy. There don't have to be any other molecules around."
] |
[
"Just Watched Chernobyl Diaries and Was Wondering"
] |
[
false
] |
[deleted]
|
[
"Cancer and Infertility are the two most common reactions from being exposed to radiation in the generation that was exactly exposed. In the subsequent genereations though, mutatuions will most likely occur in the from of birth defects and genetic abnomalities. As for whether or not what occurs in the movie is probable or possible, no, there is no way for that to occur."
] |
[
"How about because of the laws of the universe?"
] |
[
"And at one point people knew the earth was flat. The closer you get to the speed of light, the more energy it takes to get to the speed of light. So if you are at 99.9999999% the speed of light, you will never reach it because you need an infinite amount of energy to reach 100%. And since we dont really have an infinite amount of energy, it is impossible. You can get close to the speed of light theoretically, however reaching it is impossible. "
] |
[
"Why aren't more vaccines oral?"
] |
[
false
] |
It seems a large problem with vaccination efforts is that it requires a trained nurse to deliver the injection. That hiders vaccination efforts in rural underdeveloped areas. So why don't we have more oral vaccines? (If the stomaches acidity is an issue cant we put it in a capsule...or maybe use a hookworm as a vector) Also, would a skin patch be viable? thanks.
|
[
"Keep in mind, Vaccines as they are are very tricky to produce.\nDelicate protein structures or living organism must make it all the way into the bloodstream intact.",
"The human digestive system has a goal of killing or breaking down anything that gets into it.",
"Even in cases where an alternative route makes it all the way to market, there can be problems with efficacy.. Such as there was last year with the nasal flue vacciine.",
"Finally, there is the cost. Adding the complication of the science needed to produce a biological vector, as you suggest, is difficult. Even if possible, it would cost a company many millions of dollars. It is unlikely the any marketing strategy could be recouped.",
"I have only heard of one case - trying to genetically engineer a certain strain of potato to incorporate hepatitus antigens for distribution in certain areas of africa where it is endemic. Not sure if they ever got it to work. Even then, it seem likely need to eat a good number of such potatoes to build up immunity. It wouldnt be like - oh, ate my potato, won't get cancer."
] |
[
"Intranasal vaccination is already being practiced. In 2015 nasal flu vaccine was introduced in UK. And it is getting more and more traction among doctors as a good way of administrating vaccines.\n",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2846493/"
] |
[
"Intranasal vaccines are an exciting area of advancement in preventative medicine. They do allow for mass immunization programs where compliance and administration are obstacles. Interestingly enough, veterinary science is leading the way in innovations, as the intranasal vaccination of cattle is quite popular (given that thousands in the meat industry have to be vaccinated at the same time and putting an IV line in a grown bull is no easy task). ",
"Many of the advantages and disadvantages of the intranasal/mucosal route have already been brought up here… I just wanted to bring up one more. The proximity of olfactory mucosa to the area of brain membrane with the greatest porosity makes meds cross over the blood-brain barrier with greater ease for this route of administration.... both a benefit for neurologic diseases and a potential risk in some cases. ",
"In addition to influenza, intranasal vaccines are being developed for a number of epidemiologically important diseases, including HIV, CMV, salmonella, and cholera.",
"I don't think it would be a good idea to use an internal parasite as a vector for a vaccine – yes, some like hookworms do inject fluids with anticoagulants into their hosts before consuming blood, but these fluids also contain proteases that would alter the vaccines... Not to mention the fact that hookworm infestation can cause quite a bit of morbidity on its own and would have to be then treated and cured. I doubt many people would agree to voluntarily ingest a parasite if they have a problem even with a shot from a needle. The first principle of medicine is Do No Harm, so you wouldn't give someone a parasitic disease as part of a primary prevention program."
] |
[
"Can we just replace our teeth once all of our adult teeth have grown in, like, with real-looking false teeth that never need to be taken care of and won't rot away?"
] |
[
false
] |
Would it be possible, or economical, if we were to replace our old teeth with, for lack of better term, "super teeth"?
|
[
"Are you talking for some futuristic cosmetic thing that we would do? Hypothetically? Or are you looking to yank?"
] |
[
"Hypothetically, of course. It just got me thinking that dental care is pretty expensive, like braces and fillings. ( I am expected to recieve braces before the end of this month.) Maybe someone should look this sort of thing. "
] |
[
"You would still need to floss and brush for at least cosmetic reasons. Food would still get stuck between teeth and at area. Unless of course you completely chanegd the look of the teeth. "
] |
[
"Am I causing myself any harm by heating my food in a plastic container?"
] |
[
false
] | null |
[
"Heat will thermally degrade some polymers into their constituent monomers and many of them are ",
" carcinogens. You are more likely to melt the polymer than break it down to monomers at microwave heat, however, so it isn't likely there is substantial contamination. Some contain plasticizers like BPA which may affect hormone signaling. If you want to know more about your specific polymer ",
"this long PDF",
" will educate you."
] |
[
"What type of plastic container are you using? Some have known negative side effects. You can find out by examining the bottom for a recycling number. ",
"This isn't a very reputable site, but it should help a bit",
". I hope this extricates your situation."
] |
[
"This is true but also I would like to mention this: it is the dose that makes the poison. Carcinogens exist in many daily items (coffee, for example). I think most of the potential to develop cancer comes from the sun, smoking, pollution poor diet, etc. Cancer can be described as a disease of probability; you could eliminate plastics but they are not the absolute major contribution of disease occurrences. My point is: you can claim that it is possible for the carcinogenic chemicals being able to cause cancer but in the end, will you be preventing such a amazingly large contribution to the disease? \nSorry for the long rant and not having sources but I never see anyone mentioning/looking at the dosage and amounts of carcinogens."
] |
[
"How Does Evolution Explain Disguised Insects Like These?"
] |
[
false
] | null |
[
"At a very basic level: if it's hard for predator or prey to spot you, your chance of surviving to pass on your genes is increased (either avoiding being eaten, or being a more effective competitor for resources). I'm sure a much more informative answer will be provided shortly."
] |
[
"Thank you Lucifer_Box."
] |
[
"Well, on a population level, animals are selected by predators and mates through a process know as natural selection. Animals can only pass on their genes if they can find a mate, and avoid predation. An individual cannot accomplish the feat of natural selection (population level phenomenon). With that being said, these animals over time started to blend in with their habitat. Since we're only speaking of camouflage, and not warning coloration, it is safe to say that if the backdrop for an organism was red, over time directional selection, (one of three main types of natural selection ",
"http://en.wikipedia.org/wiki/Directional_selection",
") would cause the red organisms to be favored in passing on genes (as predators would eat the non-red individuals). These pictures portray one of lifes greatest feats, the ability to adapt. "
] |
[
"How does sun exposure cause skin cancer many years later?"
] |
[
false
] |
I would have thought that a skin cell damaged by the sun would either immediately produce negative effects, or just die and be replaced. What causes the delay?
|
[
"For a normal cell to become cancerous, it must develop specific traits through mutation of its DNA - ",
"the hallmarks of cancer",
". One mutation event (such as a sunburn) can cause, for instance, a gene that regulates the cell cycle to stop functioning. This cell then passes this mutation to its offspring as it divides. In later years, another mutation event might occur in one of the progeny cells that carry this mutation, giving that cell two mutations. In this way, DNA damage is cumulative, and it takes many years and many mutation events for cancer to occur.",
"Lots of discussion here",
"edit: mangled a sentence due to lack of coffee"
] |
[
"The specific mutation mechanism for UV photons is the formation of ",
"thymidine dimers"
] |
[
"I've always been told that one sunburn (that blisters) increases your risk of melanoma by some percentage (I believe 10-20%). So I believe that acute exposure carries a higher risk than prolonged exposure. This makes sense if you think about DNA repair mechanisms having some baseline activity - if the repair mechanisms are overloaded, the risk of mutation would increase."
] |
[
"Is there any evidence of anthropogenic climate change prior to the industrial revolution?"
] |
[
false
] |
Big fat disclaimer: I'm not a fossil fuel apologist nor am I looking for arguments to excuse the current rapid climate change for which we humans are almost certainly responsible. Considering the fact that we can look at ice cores, etc., to makes inferences about past climate trends, I'm curious to know whether there is evidence that earlier human developments, such as agriculture and widespread burning of organic matter, had a measurable effect on global climate. (Sorry if I chose the wrong flair. There's definitely some overlap in this question between earth sciences, archeology, and anthropology.)
|
[
"In short, yes, there is discussion and modeling to consider how preindustrial activity, mainly land use changes and/or deforestation, may have started to modify the climate and the extent to which some of those changes are still influencing the industrial era changes more commonly considered (i.e., large scale use of fossil fuels, etc). Some examples of papers exploring this in detail are ",
"Kaplan et al., 2009",
", ",
"Pongratz & Caldiera, 2012",
", and ",
"Kaplan et al., 2011",
". Others may be able to fill in more details, but it is certainly fair to say that preindustrial anthropogenic activity did/has contributed to climate change, though unquestionably to a lesser extent than the industrial era."
] |
[
"Here's a related paper that explores the climate effect of indigenous population collapses following European contact in the Americas.",
"Koch et al. 2019. Earth system impacts of the European arrival and Great Dying in the Americas after 1492."
] |
[
"Did I read that the plague in Europe killed so many people that more forrests grew and filled in previously farmed fields? Partly causing the little ice age? Or has that been disproven?"
] |
[
"How is it possible for the heat death of the universe to occur when things are always continually interacting somehow?"
] |
[
false
] |
When I first found out about entropy, the reason why I found the heat death of the universe inconceivable was because of the example of "A sugar cube always dissolves in the tea". If this was to happen to the entire universe, it would have eternity to spend in this fluctual state - so, after an unimaginable number of years, wouldn't the cube eventually, by pure chance, come together again? One person told me that a theoretical physicist named Sean M. Carroll had a similar idea (a new Big Bang would eventually happen in the heat death state), but that even he dropped this theory. An ELI5 explanation of why he dropped it went something like this: that theory assumes that universe is in a fluctual state even after the heat death, while fluctuations only happen because there are observers (and if I understood well, the "observer" is not necessarily a human, but it has something to do with wave functions). Since heat death of the universe means there are no more "observers", there are no more fluctuations, no way for the universe to reconstruct itself. After that, my new question became, how is heat death of the universe even possible? What could stop these fluctuations, interactions from happening? It just seems impossible to conceive: you imagine planets, creatures and other things which are negentropic, coming and going, doing their thing, and at one point they are supposed just to stop? Although far from being a physics expert, I think French philosopher Gilles Deleuze argued that entropy doesn't mean that the heat death of the universe must happen. If all that is the case and it is possible that the universe will exist for eternity, I find that to be almost equally inconceivable. It seems logical to say that there is a finite number of abstract qualities which can be combined into concrete "stuff". Wouldn't the eternity of the universe mean that, eventually, same planets would form, same humans would be born, same events would happen? It seems necessary for the universe to have an end, yet the end of the universe seems inconceivable.
|
[
"Entropy is always a tricky subject, but I'll do my best. Entropy is a statistical statement about how spread out or \"useful\" energy is.\nFor example, imagine two tanks of water, a hot one and a cold one. You mix them up and come back an hour later. You will find two tanks of medium temperature water. Entropy is measured by the number of ways you can put stuff together to get the same measurement. That's what entropy increase means here, that the water of two temperatures mixes, because it is statistically most likely. There's almost infinitely many ways to mix all molecules evenly than have them separate into hot and cold. It COULD happen you come back and find one tank with cold water and one tank with hot water, but you never will in reality.",
"On the tanks with two separate temperatures, you could drive an engine, due to flows of water. You cannot do that if it's mixed. ",
"Here's the main point.",
"In high entropy systems, no energy is lost, but it cannot be used for anything.",
"As entropy increases, energy gets more spread out and equalized across the universe. New stars cannot form, because you need energy densely packed for fusion. Climates will die. No wind blows if the air pressure is the same everywhere. If everything is the same, nothing changes, nothing interesting happens anymore. \nThese things don't happen all at once, but slowly, over billions of years, useful energy is slowly lost.",
"Because it is a statistical process, for example air pressure might for a moment change and winds could blow. But these will be very small effects for any meaningful length of time. At one point, due to the increase of the size of the universe, all particles might get removed from each other, to the point they are so far apart nothing can ever happen again and your universe is real kaput. You'll have to go cash in your warranty on a spare."
] |
[
"Even if that kind of spontaneous fluctuation happens, the universe will still spend in inconceivable majority of its time in the heat death state, and an insignificant fraction of time in the \"reconstructed\" states."
] |
[
"There is no guarantee of a second Big Bang, even given an infinite amount of time (and we don’t know that time is infinite). For starters, we don’t know that another Big Bang even has a nonzero probability. If the probability is zero, it stays zero forever. ",
"Additionally, even with infinite time not all things that can happen necessarily will. There are irreversible processes such as the receding of galaxies outside of the observable universe. Even in infinite time some Event X that requires interaction between two galaxies at a far enough distance can go from being very, very unlikely to impossible and will never happen. It’s just one example, but it illustrates the point. For anything that can happen, to happen in infinite time, it needs more than a nonzero probability. It needs a non-zero probability that ",
" is always non-zero for an infinite amount of time."
] |
[
"What are the neurobiological effects of clinical, chronic depression on the brain?"
] |
[
false
] |
All mental illness seem to come back to physical abnormalities/deformities in the brain, which explains why people can't just snap out of there various stats. What specific neurological abnormalities/deformities appear to account for chronic depression?
|
[
"The thing to keep in mind is that depression is a remarkably complicated condition. Beyond the mood-related symptoms, depression can also be marked by difficulties with sleep, appetite, information processing, and attention. Making this even more complicated these symptoms can go in both directions. For example, the diagnosis of depression includes weight loss, weight gain, insomnia, and hypersomnia. The severity of symptoms is also quite heterogeneous.",
"Brain imaging studies have detected disruptions in individual brain regions, most notably the ",
"amygdala",
" and ",
"prefrontal cortex",
". But, like the symptoms of depression, these disruptions also go in both directions. For example, compared to controls, depressed subjects have been shown to have both increased and decreased amygdala volume and both increased and decreased levels of activity in the prefrontal cortex. ",
"The brain systems associated with the symptoms of depression are widely distributed and heavily interconnected. So it is likely that the \"cause\" of depression is probably not located in a discrete region such as the amygdala or prefrontal cortex, but rather somewhere in the broad networks containing these regions. It is entirely possibly that, reflecting the heterogeneity of symptoms, there actually be multiple \"causes\" in different parts of the brain- which might even reflect hypotheses that what we consider depression is actually multiple different conditions pooled together.",
"This summary makes it sound like we know practically nothing about depression and the brain, but we actually know quite a lot. We know that the brain is affected down to the cellular level in depression and we know that, while the effect of the disease on the brain is quite complex and variable, most people with depression respond well to anti-depressant treatment.",
"TL;DR: Depression is associated with lots of structural and functional disruptions in the brain, but there does not appear to be one set of \"abnormalities\" that leads to depression."
] |
[
"I've reading a lot on the neurological architecture of various mental illness lately, so this made a bit if sense. If I read this correctly, it's similar to how the brains of those with BiPolar have some 50 regions/circuits that are affected on a spectrum. Maybe regions 3-40 are totally normal on person A but regions 1, 2, and 41-50 are extra abnormal so they have a worse case than person B, who's regions 1-50 are all mildly abnormal. Is there possibly multiple types of depression, physically speaking, which would require different focuses for treatment, and are just at the edge of understanding/collecting the evidence for? "
] |
[
"It is very possible that there are different causes for the symptoms we currently group together as depression. But its also important to note that bipolar and depression are distinct conditions. Grouping together people with depression and people in a \"depressive\" phase of MDD has led to a lot of confusion in the scientific literature."
] |
[
"What is the point of using specific gravity?"
] |
[
false
] |
In my pharmaceutics course/lab I see a lot of density measurements expressed in "specific gravity". I understand that Specific Gravity is the density of a substance in reference to a "benchmark" substance, but that "benchmark" substance is normally water, which is 1 g/mL. So my question is, why bother having a unit of measurement that is, for intents and purposes, equal to density? Are there instances where the reference substance isn't water and specific gravity would be preferable to use? Edit: I'm flairing this as "Medicine" just because I've only encountered Specific Gravity in my pharmaceutics course. If there is a more appropriate flair I'll change it accordingly.
|
[
"Hello,",
"In thinking about it, and racking my brains, and a spot of research :",
"While specific gravity is indeed similar to density, its not quite the same - the concept of specific gravity is that it is ",
", so not dependent on a single unit of mass or volume.",
"However, it is also a ",
" measure :\n",
"\nin SI notation.",
"Water is the obvious standard for measurement within Earth's atmosphere at room temperature of 273 Kelvin.",
"Since density may be in g/dm",
" or perhaps oz/cubic inch - when dividing the units, they cancel out, leaving a dimensionless figure.",
"the SG of water is of course 1, and most biological materials are very close to that. The elements of mercury and bromine are of course higher, and ethanol and methanol are of course lower. Pitch is probably the highest SG, but there may be higher still.",
"SG generally applies to liquids, and not as often to solids (where density makes more sense) or gases (where pressure or density/volume are more often used), though on occasion the SG ",
" been worked out for these forms of matter."
] |
[
"In my courses on soils, I've seen specific gravity used a lot, typically to define the density of a given soil. My understanding is that it's a simple way to compare soil densities, and can be easily understood by those using any units (since it's relative)."
] |
[
"By having the unit dimensionless, we easily can see the relative density of the substance to water.",
"ie SG of 3 is 3x denser than water, which is an easy factor to use",
"Why not density?",
"3g/mL would be the equivalent density, but how many times denser than your medium is this? it's not 3g/mL, it's 3... so to get 3, we need to then take 3g/mL and divide that by the density of water 1g/mL. So basically by making it unitless we have our multiplication factor given, without this other step. Nothing special, just avoiding a conversion, but it sometimes makes conversions necessary! It's kind of a convenience technique for certain situations. "
] |
[
"Is the Raman scattering process more likely for symmetric molecules than asymmetric ones?"
] |
[
false
] |
For example, I am measuring iso-pentane and normal-pentane (at the same concentrations) and I can't figure out why the the raman shift intensity for iso-pentane is lower than that for normal-pentane. Any ideas?
|
[
"This is a deceptively deep question that has to do with spectroscopy selection rules. If you google \"Raman scattering selection rules\" and take a look at some of the results you'll learn a lot.",
"In this case there's a complimentary distinction between IR spectra and Raman. In a very crude sense, because of the selection rules for Raman, it can be that more symmetrical molecules have selection rules more suited to Raman. Its all to do with group theory and character tables.",
"Edit: ",
"http://en.wikipedia.org/wiki/Selection_rules#Vibrational_spectra"
] |
[
"Group theory is actually quite beautiful, because it can lead to very simple explanations for very complex problems in physics."
] |
[
"Peak intensity is proportional to the number of representations that are raman active (populations) as determined by the character tables for a given molecule. Character tables are derived from the possible symmetry elements a given molecule possesses (matrix math and a lot of playing with models) which then reveal the modes that are active. I would suggest chapters 12 and 13 of Physical Chemistry, A Molecular Approach by McQuarrie and Simon. As I recall, Raman spectroscopy ultimately is a measure of electron cloud polarizability whereas IR action is concerned with changes in bond dipole moment."
] |
[
"Why do people tend to get fatter around when they become middle aged?"
] |
[
false
] | null |
[
"It's mostly due to exercising less and eating more. An increase in \"sedentary behavior\" has perhaps the biggest effect.",
"details:",
"Study after study has documented a slow, seemingly relentless increase in body fat as people go from age 20 to age 60. See ",
"here",
" for example - kind of a depressing study showing virtually every participant in the study gaining a pound or two a year over 7 years. ",
"Here",
" is an equally depressing 10-year followup study showing continued weight gain in most of the ~5000 participants in the study (mix of men & women, black & white).",
"This is NOT explainable by changes in resting metabolic rate (RMR). Resting metabolic rate of \"metabolically active\" tissues (muscles & major organs) actually stays pretty much the same through ages 20-50. (it's higher in kids, because they're growing, and lower in the very elderly, but does not change appreciably during adulthood). ",
"Instead many studies have documented consistent behavioral changes instead, in food intake & especially in activity. From the 7-year study cited at top: \"On average, all groups reported significant decreases in physical activity.\" Almost all groups also reported eating more. The researchers also put the subjects on a treadmill to see how far they could go, and found \"each 60-second decline in exercise duration was associated with an average weight gain of 2.1 kg in women and 1.5 kg in men... Change in physical fitness explained the greatest amount of the variance in weight change.\" ",
"Here",
" is an interesting 2011 study titled \"Who does not gain weight?\" The authors followed 8726 young Australian women and tried to identify which ones did NOT gain weight and why. Results: Less than half of the women managed to not gain weight during the study period. As to why: \"Weight maintainers were more likely to be in managerial or professional occupations; to have never married; to be currently studying; and to not be mothers. Controlling for sociodemographic factors, weight maintainers were more likely to be in a healthy weight range at baseline; and to report that they spent less time sitting, and consumed less takeaway food, than women who gained weight.\" (PS, the \"currently studying\" factor is fascinating to me, because I have a theory that taking classes actually forces you to get tiny little daily bits of exercise simply because of running around the campus - since campuses are typically large and do not allow cars. see below).",
"Here",
", another Australian study showing that even if a person gets enough \"official\" exercise (like the classic 30 min of exercise 3x a week), they will still gain weight if they are mostly sedentary throughout the rest of the day. Daily walking time and other miscellaneous moving-about (going up & down stairs, etc.) have a huge effect on daily energy expenditure. There are a ton of other studies now showing very strong correlations with daily sitting time and weight gain. (search Google Scholar for \"sitting time\") ",
"Just as an anecdotal backup of the above, in my human physiology class I have all students fill out semester-long exercise logs, and we measure RMR and VO2max in a number of the students. (Never published it - I originally was thinking of it just as a class exercise and didn't get the appropriate release forms signed to be able to use the data in a formal publication. So this is admittedly somewhat anecdotal). Anyway, my older students often report they are much less active, basically due to full-time jobs and taking care of kids. I notice a big shift in people's energy expenditure when they get their first \"sitting\" office job and stop running around a college campus. We track #flights of stairs climbed & # minutes walked per day and what I really notice is that the college-age students report an enormous amount of walking and stair-climbing, typically because they are criss-crossing the campus all day running between classes in different buildings. That kind of thing really adds up. They're also often involved in sports teams. And to top it off, they'll also report long, multi-hour stretches of \"fun\" physical activity that aren't organized sports, e.g. going out dancing for 5 hrs, going on bike rides. ",
"So for example the typical 20-year-old will turn in an exercise log that looks like \"Number of flights of stairs walked today = 22. Minutes walked = 70. Other exercise: 1 hr soccer practice then went dancing for a couple hours with my friends - fun!\" ",
"But the older students' exercise logs tend to look more like \"Tried to go for a walk today but could not cause had to work all day, then had to take the kids to soccer. Number flights of stairs walked today = 0, minutes walking = 15 min, other exercise = 0. :( \" Note though that I have relatively few older students so my data are skewed toward the college-age kids, but the trends are unmistakable. ",
"The reality is that it's hard to stay active when you're working a full-time job and stuck in an office all day, and extra hard if you have to spend all your evenings & weekends with your kids. What I advise my students is to do whatever they can, as they age, to work physical activity into their daily commute whenever possible (walking or biking, or taking a walk at lunchtime), so it becomes just part of the daily work routine, and to strenuously resist the temptation to just flop on the couch and watch tv after a long day's work. On quite another note, there's some very encouraging evidence that if you manage to ",
", you can almost completely avoid the famous age-related declines in VO2max, heart rate, endurance, etc. till you reach very old age. Even a 60 year old can still be astonishingly fit ",
" Put bluntly, use it or lose it."
] |
[
"i've read that in more than one place that this what is actually happening is due to reduced activity and not reduced capacity. Looking around at my friends as I approach the big four-oh, this seems to be the case for them."
] |
[
"Then the question becomes, why do people lose the ability to balance their energy consumption with their energy expenditure when they get older?",
"The BMI of humans in their natural environment (hunter-gatherer societies) does not usually increase with age. Is there something in the modern environment that progressively disrupts metabolism and appetite control with age?"
] |
[
"Do photons exert gravitational pull on other photons and objects with mass?"
] |
[
false
] |
[deleted]
|
[
" Yes. Photons contribute to the curvature of the universe because they have ",
", and if you have enough of them you can even make a black hole!",
" Photons, while massless, still have energy. That energy contributes to the energy content of the universe (mathematically, by the way of a thing called the Electromagnetic Stress-Energy tensor). That energy tensor is basically the thing that tells you how matter and energy is distributed in the universe, and thus tells spacetime how to curve. And since curved spacetime tells photons and mass how to move, that means that - yes - photons do interact gravitationally with other photons as well as matter. ",
"As an example, if you could get enough photons in one place then you'll have a high enough energy density to curve the local space into a black hole, all without even using a smidgen of matter. It has a great name too: ",
"kugelblitz.",
"Unfortunately, the density of photons in the universe is only about 500 photons per cubic centimeter, and most of them are very low energy microwaves. For comparison, to make the black hole I described above you'd need about ",
"10",
" photons in one cubic centimeter",
" This energy density (required for photons to produce a black hole) is so high that these conditions don't exist in the universe. The temperature of such a compact collection of photons exceeds the Planck temperature, making it kinda useless to practically discuss or expect in nature. It's just a fun idea that exists on paper. ",
"Anyway, the point I'm trying to make is that the contribution of light to the curvature is basically nothing, so as far as I know it has never been measured, because light is so... ",
" "
] |
[
"Photons don't have reference frames, and it is important to know why. In an inertial reference frame, all the laws of physics hold true, including the finite speed of light. If photons did have reference frames, then they should see other photons going at the speed of light relative to them, but the photon is already going at the speed of light, meaning that other photons should be at rest relative to it. So what would a photon see at light speed, photons shooting forwards or photons at rest? Nothing, because photons don't have reference frames."
] |
[
"1) Photons are always moving at the speed c, in all reference frames.",
"2) An object is not moving in its own reference frame.",
"3) If a photon had a reference frame, it would be both standing still and moving at c, in that reference frame. Which would be a paradox."
] |
[
"Is there a syndrome that describes the sensation of hearing people who aren't really there?"
] |
[
false
] |
[deleted]
|
[
"A syndrome actually means multiple symptoms that concur together that suggest a common pathological cause. What you're describing is either an auditory illusion or an auditory hallucination. ",
"An auditory illusion is an audio misperception of reality; for example, a squeaky door that you think is a cat is a hallucination. In contrast, an auditory hallucination is the perception of sound that is not based on reality; the example would be the thought you can hear someone in the other room when in reality there is complete silence.",
"To have a complete syndrome, you need something in addition to the illusion/hallucination. Is there a specific disease you have in mind?",
"edit: accidentally said illusion twice."
] |
[
"Unfortunately the differential diagnosis for auditory illusions/hallucinations is incredibly broad, ranging psychiatric illnesses, to endocrine disorders, to even things like trauma and toxic exposures. This might be something you'll want to bring up with a primary care physician/general practitioner."
] |
[
"If you're really concerned, you can go check it out with a doctor. An imbalance in the functions of your neurotransmitters can be accountable for all kinds of strange experiences, which might seem like hallucinations. If you have any other symptoms, you should definitely go to a doctor, but I've never heard of any 'condition' with just this one symptom. "
] |
[
"Order, disorder and complexity: how do we choose an order parameter?"
] |
[
false
] |
My research involves looking at statistical systems in physics and comparing them to brain functionality. The concept of an order parameter is very essential when one wants to analyze the system and look for phase transitions. I understand that order/disorder are generally defined by low/high entropy limits, but one also has some choice in how they define what kind of entropy they're interested in (right?). For example in the context of the Ising model some people use the magnetization M as the order parameter and other times the absolute magnetization |M|. In percolation models the largest cluster size is used as the order parameter (which I think strongly resembles magnetization in the Ising model but not exactly). The question is, how do I pick an appropriate order parameter?
|
[
"I don't think there exists a formal algorithm for finding order parameters in systems. However, you might want to look into spontaneous symmetry breaking. Generally speaking, the more disordered phase has a larger symmetry group which leaves it intact, while the ordered phase usually has a subgroup of the disordered symmetry group. For example, the unmagnetized phase in the Ising model has a full rotational symmetry, while the magnetized phase has a {+1, -1} symmetry only (namely: +1 refers to not doing anything to the system, and -1 refers to flipping all spins). ",
"The (large) symmetry group may tell you information about in which geometrical space (ie: manifold) lives a useful order parameter. This basically tells you what your order parameter is. Bear in mind also that there is no reason for an order parameter to be unique, there may be various useful choices of order parameter, and other less useful choices."
] |
[
"Unfortunately the order parameters in a system can be very difficult to find in general. Take one of the most famous phase transitions, the liquid-vapor transition in water. The gas and liquid phases have the same symmetry, but it turns out that the critical point is in the same universality class as the Ising model in an external magnetic field (so the symmetry is broken). So ",
"this phase diagram",
" somehow maps to the vicinity of the critical point in water's phase diagram. ",
"The Ising model has a Z2 symmetry for H=0, implying that there is some emergent Z2 symmetry in water in the critical (\"scaling\") limit, but it takes some work and some tricky arguments to start with a realistic model of water which reduces to an Ising model. For what it's worth, I believe people simply ",
" that water has the same critical exponents as the 3D Ising model, and then theoretical explanations followed. ",
"It is more conventional to call the order parameter of water the density, and then define the first-order phase transition as where the density changes discontinuously, and then the critical point is where the derivative of the density is discontinuous. So this is a definition which has nothing to do with symmetry."
] |
[
"but ultimately it has to do with symmetry breaking right?",
"No, it doesn't have to be related to symmetry breaking. The fact that the liquid-vapor critical point has a line which has behaves like the Ising transition is an emergent phenomenon related to how systems simplify close to their critical points, resulting in many systems having the same critical properties. This is a deep consequence of the ",
"renormalization group",
", which basically says that the symmetry breaking terms in the liquid-gas transition happen to be unimportant at low energies. Similarly, percolation theory and self-avoiding random walks don't involve any symmetry breaking, but both can be mapped to certain limits of magnetic models which do.",
"There are also phase transitions which do not have any relation symmetry breaking. In two dimensions, there is a class of phase transitions related to the ",
"Kosterlitz-Thouless transition",
". There is a rigorous theorem saying that these systems cannot have any spontaneous symmetry breaking, yet there is a transition between a high-temperature phase where correlations between spins decay exponentially, and a low-temperature one where spin correlations decay with a power law. You can then consider something like the inverse correlation length to be an order parameter, and it has nothing to do with symmetry breaking. There are classes of exotic quantum phase transitions which also do not involve any symmetry breaking, but one phase has a special property called topological order which can be detected through a suitably-defined order parameter.",
"Also while we're on the subject, is there an intuitive, qualitative explanation of the difference between first/second order phase transitions?",
"I think the more modern terminology is to distinguish between first-order phase transitions and continuous phase transitions. For a first-order phase transition, the order parameter changes discontinuously, and the correlation length remains finite. In contrast, continuous phase transitions are when the order parameter continuously changes, and the correlation length diverges. This results in scale invariance (and usually conformal invariance), allowing the use of the renormalization group and the emergence of universality. Often continuous phase transitions are second order (there is a discontinuity in the second derivative of F w.r.t. the external field), but for example the KT transitions I mentioned above have a discontinuity like ",
"F ~ e",
"so actually none of the derivatives are discontinuous at T_c (some say this is an \"infinite-order transition\"). Since all second- and higher-order transitions can basically be treated on the same footing, you lump them together now.",
"Wikipedia also defines order parameter as \"the first derivative of the free energy with respect to the external field\".",
"This is true but kind of a tautology. You basically define \"the external field\" as something you can couple to your order parameter field, and then all correlation functions of the order parameter can be given by taking derivatives of the free energy with respect to the external field. For many systems the external field can be related to some physical field, but not always."
] |
[
"Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary 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!
|
[
"Remember that atmospheric pressure is not much. You are currently experiencing 1 atm of pressure and you have no problems with it. The ISS has an internal pressure that is equal to 1 atm. Outside the ISS, in the vacuum of space, the pressure is 0. The pressure difference between space and the inside of the ISS is therefore just 1 atmosphere. That is not much pressure that the ISS needs to withstand. For example in bicycle tires you often have a air pressure as high as 8 bar (8 atmospheres). That means the pressure differential between inside the bicycle tire and outside is equal to 7 bar. Meaning the bicycle tire withstands a pressure differential 7 times higher than the pressure differential that the ISS experiences."
] |
[
"Regular atmospheric pressure is quite strong though. It feels weak because you're completely used to it, but it effectively means that you have over a kilogram of force being applied to your eye right now due to atmospheric pressure. Put 5 mbar of pressure difference behind a door, and there's no way you're going to get that door open anymore."
] |
[
"This is something I’ve always wanted to know;",
"Mostly curious due to NASA’s moon base plan, how do we keep a structure pressurized against the vacuum of space for such a long period of time? Is there a deterioration or maintenance process that would need regular up-keeping? Furthermore, In the vacuum of space, how do we maintain pressure within shuttles and spacesuits? Wouldn’t keeping a pressurized area or object within a vacuum cause the object to expand? I’ve always been so baffled."
] |
[
"What would have happened if the “demon core” was left to go Supercritical?"
] |
[
false
] | null |
[
"What I’m curious about is, what would have happened if the Demon Core was left to go supercritical?",
"It was. Human intervention is not what stopped the chain reactions. The system has a negative temperature coefficient of reactivity, meaning that when it became supercritical, it heated up, and the increase in temperature drove the reactivity back down. It was back to critical again due to thermal expansion in a fraction of a second, before anybody could grab or move anything.",
"Unfortunately, it was still enough to release a lethal dose of radiation, but it wouldn't have done anything else like explode."
] |
[
"what I meant was what if it was just left there, with nobody to stop it.",
"Yes, that's the question that I answered. There's no difference between somebody stopping it and it being left alone, because it stopped itself faster than anybody could grab it."
] |
[
"Yeah I know it went supercritical; what I meant was what if it was just left there, with nobody to stop it."
] |
[
"How to identify intron sequences in mRNA?"
] |
[
false
] |
How do I find the exact place where the intron starts and ends in an mRNA sequence? Thanks in advance!
|
[
"Introns are removed by a ribonuclear complex called a splicesome that recognises motifs called a splice donor site (at the 5' end) and a slice acceptor site (at the 3' end). About 50 nucleotides upstream (before) the acceptor site will be a branch site that is important in excising the intron.",
"What you need to look for is a donor site, which will generally have the sequence (A/C)AG/GUAA. Then the acceptor site downstream will generally have N(C/T)AG/G. About 50 nucleotides upstream will be the branch site with consensus sequence of CU(A/G)A(C/U) followed by a pyrimidine-rich sequence. I say generally here because there isn't an invariant sequence that is always used. The most conserved nucleotides are the AG in the donor, the A in the branch, and the AG in the acceptor. The nucleotides surrounding these determine the strength of the site."
] |
[
"If you are interested in predicting splice sites within an RNA, there are a number of computational approaches that try to search for sequences that fit splice criteria (as Hashshashin7 pointed out). These are not always accurate, since the sequence of the acceptor and donor can be pretty degenerate, but the scores can at least give you an idea of where splicing may take place. NetGene2 (",
"http://www.cbs.dtu.dk/services/NetGene2/",
") is an example of this.",
"That said, RNA splicing within a cell can be pretty messy; an obvious splice site may not be used, or what appears to be a poor junction could be readily spliced. On top of this, some splice sites are used differentially. Deep-sequencing of RNAs is revealing that alternative splicing can be common and result in certain RNAs haveing several isoforms. These alternative RNAs are not simply accidents due to the ambiguous nature of splice motifs, but appear functional and regulated by the cell.",
"Reference: ",
"http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1001229"
] |
[
"It would largely depend on the organism that the mRNA was derived from. While RNA splicing is found in most eukaryotic organisms, predicting introns within an ORF can depend on the organism and sometimes the tissue. Prediction software (such as NetGene2, which I linked) can usually identify potential splice sites, and often give you a score showing how likely (based on the sequence information) a splice junction is used. NetGene2 is especially good at human, worm (C. elegans), and plant (A. thaliana) introns. However, these aren't always accurate, and at least in my work in yeast I've gone through some sequences by hand to see if there are missed junctions. But I would start with these computational predictions, unless you want to look for the splice junctions by eye."
] |
[
"What happened to locust swarms in the US? They were once a major issue and then just seemed to stop, what happened in the US that led to this disappearance when they are still problems elsewhere around the world?"
] |
[
false
] |
Reading historical works, locust swarms seemed fairly common in the US and then just stopped. Is there a scientific consensus as to what caused this decline? How is the US different than other areas of the world that still experience locust swarms?
|
[
"This is a neat question! As it happens, North America is currently the only continent (besides Antarctica obviously) without at least occasional major locust swarms. And the reason for this is because we killed them all! The predominant locust species in North America used to be the ",
"Rocky Mountain locust",
" (",
"). One particularly notable swarm in ",
"1875",
" contained multiple trillions of individuals, and covered an area larger than California.",
"However, it turned out that, though the swarms of this species ranged far and wide, their actual native breeding range was much more restricted, and also under active agricultural development at the time. Through concerted efforts by farmers and governments to destroy these breeding grounds and kill adult locusts, they eventually went extinct, with the last living specimen being seen in 1902 (somewhat analogously to the passenger pigeon). Fun bonus fact: there is a ",
"glacier in Montana",
") containing several million frozen Rocky Mountain locusts!"
] |
[
"That's a pretty inaccurate view of the world. Mosquitos and wasps include thousands of species and both are ecologically important groups of organisms as pollinators, predators, and food sources for other species. Meanwhile, honey bees (the only species of bee that is bred by humans on a large scale) are introduced to North America and have negative impacts on many native species through the spread of disease and competition."
] |
[
"Now if only a complete eradication happened to mosquitos and wasps, and hornets. Nature doesn't need that pile of worthless creatures.",
"After that, breed more friendly bees."
] |
[
"What does it mean for a quark to have 'Spin'?"
] |
[
false
] |
I've read up on this before but I've never truly understood elementary particles having spin. What basically is it?
|
[
"I'm not sure I can give you a satisfying answer, but I'll explain it the best way I can. Elementary particles have angular momentum that is completely separate from any motion the particles are undergoing. This angular momentum is in the direction that would come from the particle spinning about some axis, but it is not caused by physical spinning. This is known because of several things. First, it is not believed that quarks actually have a physical structure, thus spinning them doesn't make sense. Secondly, assuming they do have a physical structure- if we know the value of their angular momentum, we know they'd have to be spinning at such a high rate of speed that relativistic effects would contribute (that faster something is spinning, the more energy it has, and thus the more apparent mass that object has). However, by measuring the apparent mass of the object, we can tell that it is not spinning fast enough to be undergoing relativistic effects. ",
"Continuing, some people will say that it is not a true angular momentum, but a property that behaves like angular momentum. I do not believe this to be the case. The reason, electrons also have a more \"traditional\" angular momentum, that comes about by their orbit around the nucleus. However, their spin and orbit can couple, under a condition called ",
"spin-orbit coupling",
" which means the angular momentum of the spin is actually adding to the angular momentum of the orbit, thus spin does appear to be a real angular momentum. ",
"So, finally, what is spin? Our best answer today is that it is a property of the particle. For instance, an electron happens to have spin 1/2. Much in the same way, and electron also has en electric charge of -e. The charge, mass and spin of an electron are properties of that electron, and as of now there isn't a \"reason\" they act this way, but it is a way that they act. "
] |
[
"Ultimately, these are all mathematical constructs and don't really have a neat intuitive analogy with things with which we're familiar. What they really ",
" is what the math says they are."
] |
[
"Colors aren't forces. They're charges.",
"You know electric charge, right? It comes in two flavors which we call positive and negative. Electrons have one unit of negative charge, protons have one unit of positive charge. Some things, like neutrinos, have no electric charge at all, either positive or negative.",
"There's also a ",
" kind of charge, not an electric charge, but another kind of charge entirely. It comes in ",
" flavors, which we call red, green, blue, antired, antigreen and antiblue. (Some people call them red, green, blue, cyan, magenta and yellow, but these people are jerks and will borrow money with no intent to return it, so they should be avoided.) We called that first kind of charge \"electric charge\" because we came to know of it by studying electrons. But we don't have a neato name for this other kind of charge, so we just call it \"color charge.\" No reason why not, since all these words we're using for these things are purely arbitrary.",
"There is certainly nothing having to do with \"force\" here. But the color charge does give rise, indirectly, to an interaction between color-charged particles called the strong interaction. As photons are to the electric interaction, gluons are to the strong interaction. So I guess if you wanted to, you could call these thing \"strong charge,\" though nobody does, so I wouldn't bother if I were you."
] |
[
"If I'm on the interior surface of a rotating cylinder in space, I'll feel something that I could interpret as \"gravity\". Is it possible to spin a cylinder fast enough to create an \"event horizon\" on the inside?"
] |
[
false
] | null |
[
"Basically, ignoring material constraints, is it theoretically possible to make it so that centrifugal force creates an \"escape velocity\" greater than C?",
"No. The \"gravity\" you are talking about would be caused by the accelerated circular motion of the cylinder walls. The walls would have to move faster than C to prevent light from moving away from them, and that is impossible.",
"Also, would light coming from that surface appear redshifted in some reference frames but not in others?",
"Absolutely. Why not? Any motion, even without acceleration, would produce red shifts and blue shifts."
] |
[
"Are you assuming that your acceleration is equal to C? I don't understand the logic behind that. The units don't match.",
"But think of it this way. The light always moves at C. Therefore, to prevent the light from moving from the periphery towards the center, the wall needs to \"carry\" the photon tangentially with it at C - which is an unachievable velocity for the cylinder wall."
] |
[
"I don't understand why the cylinder walls would have to have a velocity greater than c. Centripetal acceleration is a=v",
" /r so with a r of 1 v would be the square root of c."
] |
[
"does wearing darker coloured NFL jerseys actually have an impact in the heat?"
] |
[
false
] |
I learnt a long time ago that some NFL teams often opt to wear lighter coloured jerseys in warmer situations (i.e. Carolina, Jacksonville & San Diego will wear light colours to make their opponents wear dark colours). I understand the theory behind this, but does it actually make a significant difference? i've also seen teams that chose to wear a light uniform still wear dark helmets and pants, which would (in theory) have the opposite effect. plus, shoulder pads are usually dark coloured (although i'm not sure if been under the jersey prevents this or not).
|
[
"Yes -- assuming the visually dark colors are dark in the infrared (usually true). And the effect is that dark colors absorb more direct sunlight, but they also radiate more body heat into shadows or any environment with a temperature lower than body temperature.",
"In other words, dark colors are a two-way street -- absorbing more heat when the environmental temperature is higher than body temperature, but radiating more heat when the environment is colder."
] |
[
"If you would care to do an experiment. On a hot day wear all white if possible but at minimum a white shirt. Stand outside for an hour just doing stuff, not anything too physical.",
"Then go outside and wear all black if possible, but again a black shirt will do. Then do stuff at equal intensity and make sure they are the same types of fabric.",
"I am sure you will feel a difference. In a weldimg course I was taught to try and wear dark colours because it will absorb light whereas lighter colours would reflect it."
] |
[
"I dunno how you define \"significant effect\", but darker clothing DOES absorb more light, which makes them get hotter. You can test this yourself by putting a white shirt and black shirt outside and feeling the difference in their temperature after half an hour.",
"I wish I could do an energy calculation for you, but this seems to complex and has too many factors to be easy to do : ("
] |
[
"Why is Force equal to the differentiation of Kinetic Energy with respect to displacement?"
] |
[
false
] |
[deleted]
|
[
"*Potential energy"
] |
[
"http://hyperphysics.phy-astr.gsu.edu/hbase/pegrav.html"
] |
[
"http://hyperphysics.phy-astr.gsu.edu/hbase/pegrav.html"
] |
[
"Why does the atomic mass of nuclei change during fusion and fission?"
] |
[
false
] |
I know that the combined mass of nuclei change when fused or fissured. This releases energy according to E=mc But why does the mass change when the number of protons and neutrons stay the same?
|
[
"Atomic nuclei are held together by an amount of nuclear binding energy. In order to form a nucleus from scratch, you not only have to put all of the protons and neutrons together but also insert an extra amount of energy to bind it together. This energy creates a difference between the sum of the constituent masses and the total atomic mass. This difference is (delta)M = (binding energy)/c",
" .",
"Different nuclei require different amounts of binding energy to stick together. When fusion or fission occurs, the amount of energy released is equal to the difference in the total binding energy of the initial atoms and the final product. For example, let's say you fuse two hydrogen atoms into a helium atom. The total binding energy of the two hydrogen atoms is greater than that of the helium atom, so the excess energy is released as radiation.",
"If you are able to measure the energy released in a reaction, you should find that it is equivalent to the mass difference between the initial and final products."
] |
[
"Fission: ",
"1: Potential energy inside the nucleus is converted to kinetic energy of nucleus parts. Mass of potential energy is converted to mass of kinetic energy.",
"2: Kinetic energy of aforementioned parts is converted to kinetic energy of some other particles in collisions. Mass of kinetic energy is converted to mass of kinetic energy. (in other words kinetic energy is distributed or shared) (in other words in a nuclear plant part of mass of nucleus becomes mass of cooling water)"
] |
[
"This difference is (delta)M = (binding energy)/c2 .",
"The watchful eye will probably spot that this is Einstein's famous E=mc² equation right there. That's where the notion of energy and mass being equivalent can be directly seen."
] |
[
"Are there any significant (or minor I suppose) issues with the theory of evolution?"
] |
[
false
] |
I know that this film was basically made out to be bullshit. But in Expelled: No Intelligence Allowed they made claims that there are key problems with evolution, however they never cited any problems. So I thought I would it.
|
[
"At the very heart of it, the answer is no. The theory of evolution is one of the most tested and best supported ideas we have in biology. One famous quote is given as, \"Nothing in biology makes sense, except in the light of evolution.\" -Dobzhansky.",
"Now, within the evolutionary field, there are many issues. For instance, how speciation takes place both within and between niches is still a matter of contention. How we chose to classify animals phylogenetically is an ongoing debate. Any active field will have many such areas.",
"The problem comes with confusing the latter \"issues\" as rejections of the theory of evolution itself."
] |
[
"straight from wikipedia",
"The formal scientific definition of theory is quite different from the everyday meaning of the word. It refers to a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence. Many scientific theories are so well established that no new evidence is likely to alter them substantially. For example, no new evidence will demonstrate that the Earth does not orbit around the sun (heliocentric theory), or that living things are not made of cells (cell theory), that matter is not composed of atoms, or that the surface of the Earth is not divided into solid plates that have moved over geological timescales (the theory of plate tectonics). One of the most useful properties of scientific theories is that they can be used to make predictions about natural events or phenomena that have not yet been observed."
] |
[
"These claims generally arise from lack of knowledge about Evolutionary Theory. The first claim is that we can't fully explain the origin of life yet. This is irrelevant, since evolution does not deal with the origin of life, only how it changes once already established. The only other claim I've heard off the top of my head is that it can't account for complex features like the human eye or an immune system. This is also not true, as these subjects have already been investigated by scientists and explained or are in the process of being explained. One of the main scientists behind the anti-evolution movement is Michael Behe; when he presented his ideas in a court of law, other scientists completely schooled him. Watch the Nova special Evolution on Trial about the Dover case."
] |
[
"Scrubbing off rust with Aluminium"
] |
[
false
] |
I was told by a friend today that you can clean rust of metal by scrubbing it with household aluminium foil. Skeptical but willing to give it a go, i scrunched up some foil and started rubbing the rusted areas, and sure enough, off came the rust. While scrubbing i wondered: What's the chemistry behind this?
|
[
"I would suspect that the layer of aluminum oxide, also known as corundum, on the surface of the aluminum metal provided the necessary Mohs scratch hardness to remove the iron oxide."
] |
[
"Err... Doesn't iron + aluminum essentially give you thermite? "
] |
[
"I'll set alight the foil I used and let you know"
] |
[
"Why does covid hit overweight people harder ?"
] |
[
false
] |
Title basicly. Is it related to the lipids making it easier for it to reproduce ? Or is it their immune system as fast foods are both related to lower immune responses and well, gaining weight as well ? If y'all have videos I love to watch that too :) Edit : no clue why I keep getting downvoted, perhaps its my bad english and I thank you for your patience with my learning of this language xoxox all the best to y'all Edit 2 : thank you so very much for all the answers ! i feel like i learned much today and I'm extra motivated to keep my lifestyle active and healthy !!
|
[
"Obesity causes immunosuppression, through chronic low-grade inflammation, and makes people more susceptible to infections:",
"recent findings have highlighted the substantial impact that obesity and MetS parameters have on immunity and pathogen defense, including the disruption of lymphoid tissue integrity; alterations in leukocyte development, phenotypes, and activity; and the coordination of innate and adaptive immune responses. These changes are associated with an overall negative impact on chronic disease progression, immunity from infection, and vaccine efficacy. ",
"--",
"Impact of Obesity and Metabolic Syndrome on Immunity",
"There is strong evidence indicating that excess adiposity negatively impacts immune function and host defence in obese individuals. ... Obesity is characterised by a state of low-grade, chronic inflammation in addition to disturbed levels of circulating nutrients and metabolic hormones.",
"--",
"The impact of obesity on the immune response to infection",
"While there are probably multiple causes for the link between obesity and worse COVID disease, the immunosuppression and chronic inflammation caused by obesity are probably major factors (",
"The Impact of Obesity and Lifestyle on the Immune System and Susceptibility to Infections Such as COVID-19",
")."
] |
[
"There aren't this many. There are way more than that. If you're overweight, getting into shape is the best thing you could possibly do for your health, especially in the typical case where its also combined with a lack of exercise."
] |
[
"Thank you for taking the time to source so much stuff and to answer so very well ! I didn't know there were this many downsides to being overweight."
] |
[
"If out of the total population on earth, 10% of the people are left handed, why are athletes who are left-handed so disproportionate than the general population?"
] |
[
false
] |
In most sports team I've observed there are approximately 20% of athletes who are left handed. Why is this proportion larger and what chances are there of the total 10 % interested in sports?
|
[
"Because right handed people are less practiced at dealing with their left handedness than left handed people are with dealing with most every one else's right handedness. It gives them a competitive advantage."
] |
[
"Especially in boxing, where your southpaw opponents movements are a complete reversal of what they've spent their whole lives getting used to."
] |
[
"20% of athletes are left handed. ",
"Citation needed."
] |
[
"Why do Airborne Nuclear Detonations Cause EMPs and are the effects to electronic devices permanent?"
] |
[
false
] |
would electronic infrastructure need to be replaced or would the effects "wear off"?
|
[
"Radio and microwaves create currents in conductive objects. This is how radio antennas pick up signals and why forks tend to melt in the microwave.",
"The bright flash of x-rays from the bomb will send a very large number of electrons in the upper atmosphere recoiling at once, producing a very sudden and sharp burst of microwaves (correction: most of the energy is in radio). This induces way too much current in anything resembling a wire or an antenna, and the pulse arrives too suddenly for most circuit breakers to trip in time. The Earth's magnetic field will also recoil and shift back and forth for a few minutes, inducing currents in power lines.",
"Sometimes a power surge just makes software crash and sometimes a part melts and has to be replaced. Many things in Hawaii had to be replaced after the ",
"Starfish Prime",
" incident and that was a while ago with fairly primitive, robust equipment. "
] |
[
"Airbursts emit more EMP because the heat capacity of air is quite low. All of that energy can ionize the air into plasma, but because there's so little density to absorb energy, much of the energy will dissapate in the form of electromagnetic radiation.",
"Underwater or under ground, there's quite a lot of dense matter to absorb energy through phase change, temperature changes, and chemical changes. Much of that energy is \"echoed\" as heat (infra red) and other emissions like visible light because so much of that energy can be spread out over so much dense matter.",
"Even dynamite emits a little bit of RF when it detonates. The electromagnetic spectrum is a continuum. ",
"As to temporary vs permanent effects, there are a few things that can happen. In terms of permanent effects, currents can be induced that are high enough to damage circuit paths in integrated circuits and other transistor devices. Tiny circuit paths can't handle high currents. Even if they are short, they can be exposed to inductive loads via the copper paths that lead to a chip. Big kludgey components like discrete capacitors and resistors outside of a chip are generally more tolerant to induction abuse.",
"A weaker induction field can cause more pernicious wierdness like flipping a bit though. An input pin that is read as a \"1\" instead of \"0\" can cause a program malfunction because the input termporarily went bonkers. In some systems that run short program loops, this might not be a big deal. A servo motion control system might count an extra encoder step which means you may have an accumulated position error, but if the encoder wheel has a \"home\" flag, that error could be cancelled fairly quickly. Data effects could be temporary if some correcting measure is available, but an accidentally exercised a stock trade at a mistaken price would lead to a permanent effect even if no physical damage is done. Financial trade systems probably have significant validation measures in effect though."
] |
[
"Need to be replaced... Components get fried by the pulse. They can be shielded, but that adds weight and expense.",
"We had lightening strike a tree across the road a few years ago. Even though our TV was unplugged because we saw the storm coming, it still died."
] |
[
"Does dissolving one thing in water make dissolving another thing in water more difficult?"
] |
[
false
] |
Like, if I add a bunch of salt to water, then try to dissolve a certain amount of flour, will the amount of flour that I am able to dissolve decrease compared to 'clean' water? A 'yes' or 'no' would be appreciated, but if you can get into the chemistry a bit , that would also be interesting. :D
|
[
"For ideal (dilute) solutions the answer is a qualified ",
". ",
"How much of a salt will dissolve in water at a given temperature only depends on the concentrations of the constituent ions and the disassociation constant of that salt (often called the K_{a} of that substance). The chemical equation for the dissolution of a typical salt like NaCl can be written as ",
"NaCl (s) <-> Na",
" (aq) + Cl",
" (aq)",
"where (s) means solid - not dissolved - and (aq) is aqueous, or dissolved. When you write out the expression for K_{a} you can ignore all solids and liquids that are in great excess, so what you get for that expression is:",
"K_a = [ Na",
" ] [ Cl",
" ]",
"K_a equals some constant value. If the concentrations that you have in your solvent are, when entered into the K_a expression, less than that constant, then more of your salt can dissolve. Notice how the concentration of ",
" ions or things doesn't enter into this. That means that if I have, say, NaCl in my water I can dissolve another different substance like glucose in there as if the NaCl wasn't even there. ",
"This is assuming a couple of things. First, the dissolved things can't interact. Sometimes the combination of ions can make something that is less soluble than the parent substances (which can turn out to be useful if you want to, say, get all of the sulfate out of your water and add barium to turn it into a solid). The other thing is that the second substance can't have any ions in common with the first. If it does, the equilibria overlap and the second salt will dissolve less thanks to what is called the ",
". ",
"As for salt and flour, I would imagine that the salt may cause the big, polar flour molecules to aggregate and become less soluble than if dissolved in pure water. That is my hypothesis but it is easy to test yourself. Dissolve some flour in water, add salt, and see if the flour crashes out as a solid. "
] |
[
"This answer has the perfect level of detail! Thanks a bunch!"
] |
[
"Yes. When you dissolve salt, the sodium and chlorine ions disperse throughout the liquid, between water molecules, and take up space. If you put too much salt, the solution becomes saturated as there is no more space between water molecules so it doesn't dissolve any more. In a salt water solution, there is already less space between water molecules so you wouldn't be able to dissolve as much flour as in pure water before the solution becomes saturated."
] |
[
"are there any mushrooms/fungi that live underwater?"
] |
[
false
] | null |
[
"There’s more than 400 species of fungus that live underwater in various marine habitats but underwater ‘mushrooms’ are rare. Psathyrella aquatica is the only mushroom that I know of that thrives and will fruit underwater. ",
"https://www.researchgate.net/publication/269552443_Psathyrella_aquatica_Fruiting_in_vitro"
] |
[
"According to Penn State, “Mushrooms respire: they take up oxygen and produce carbon dioxide.” Hard to do underwater without gills. ",
"https://news.psu.edu/story/140841/1997/09/01/research/no-more-mush-mushrooms",
"ETA More info here about how hyphae (the little filaments in the soil that terrestrial fungi use for respiration) perform gas exchange: ",
"https://sciencing.com/mycelia-microbiology-16448.html"
] |
[
"i wonder why so few fruiting bodies!"
] |
[
"How common is incest in mammal populations? What impact does it have on their evolution?"
] |
[
false
] |
I've learned that humans are "programmed" to seek mates that look similar to us, but not similar. Is this the case with other mammals? Does inbreeding provide for more genetic oddities that could produce beneficial mutations, or is it generally a path to failed populations?
|
[
"You're right in saying that humans look for similar mates. This is because mates that are too foreign bring with them traits that are less well adapted to your environment which can result in an increased likelihood of death ( A process called ",
"). We don't want mates that are too similar though and humans do this by smell. We can sense things called MHCs in the scent of a potential mate and are more likely to be attracted to them if their MHC is different to ours. Many mammals have similar systems and some like mice won't come into sexual maturity if males that are related to them are around.",
"Inbreeding generally results in population decline and extinction if it lasts too long. The first reason for this is that it results in a reduction in \"",
"\" - an animals capacity to survive to adulthood and produce offspring. It does this by reducing levels of ",
" in the population which is when organisms have different versions of a gene on each chromosome resulting in them producing more varied offspring and (potentially) being better adapted to survive. As ",
" decreases population becomes more uniform and shows less variation meaning the population is less likely to be able to cope with changes in the environment - if something can kill one of them it can kill all of them.",
"As a result of the decrease in ",
" bad \"",
"\" mutations begin to be shown. These are mutations that normally wouldn't be expressed as they are masked by other versions of their gene, but when both copies of a gene are identical and they're bad then the bad trait will be expressed. Examples of recessive diseases include cystic fibrosis and sickle cell anaemia and in inbred populations these conditions a re far more frequent.",
"Inbreeding can remove these deleterious mutations from the population through a process called ",
" by causing individuals with these disorders to die before they mate but in practice this doesn't usually work.",
"",
"n.b. Some plants and animals will purposefully inbreed or breed with themselves to make sure their genes get into the next generation but they try to limit how much they do this."
] |
[
"Devils are not, for the most part, inbred, despite what that headline says. People seem to constantly confuse lack of genetic diversity with inbreeding but they are two different things. Inbreeding means that the individuals have higher homozygosity than would be expected by chance in the given population, due to relatives breeding with one another. Tasmanian devils have low genetic diversity due probably to a series of historical population collapses, but are not inbred."
] |
[
"An interesting case study for this would be Tasmanian Devils- inbreeding is generally a pretty big issue for them, and as a result, a specific kind of cancer was able to rapidly spread between them because of the lack of genetic diversity. At one point they were considered to be near extinction, because the diseases they caught from other Tasmanian Devils was so similar to their own immune system that it fails to fight back to diseases properly.",
"https://www.theregister.co.uk/2007/10/07/tasmanian_devil_cancer_inbreeding/",
"The Tasmanian Devil's future as a species is still uncertain, as far as I know. "
] |
[
"Necessity of a Mars suit?"
] |
[
false
] |
As temperatures on Mars seem to be not too different from what you'd find on Earth's polar regions, wouldn't extreme cold weather gear and a pressurized breathing helmet be sufficient? My guesses why not: - Atmosphere insufficient to achieve the same insulation effect terrestrial cold weather clothing relies on - Low atmospheric pressure would require either pressurization or compression - Other environmental concerns such as radiation, fine dust, etc.
|
[
"The atmospheric pressure of Mars isn't just low- it's REALLY REALLY low (0.087 psi average). It's basically a vacuum. Water above 80F will boil spontaneously. Your body is above 80F. Gas bubbles will form in all exposed liquids, causing death in a matter of minutes. ",
"On Earth, pressures below 10psi are very dangerous. ",
"Pressures below 5psi are deadly via hypoxia",
" - supplemental oxygen is required for life. Pressures ",
"below 1psi are deadly regardless of supplemental oxygen",
" - a positive pressure suit is required. "
] |
[
"The dust found on Mars' surface contains carcinogens and razor sharp particles, meaning protective gear has to be worn as well."
] |
[
"Also no global magnetic field or ozone layer will require protection from solar radiation."
] |
[
"How does this product work?"
] |
[
false
] |
[deleted]
|
[
"As long as it was not conductive once dried there would be no problem applying a liquid to a circuit board that is not plugged in.",
"The only problem I could see would be changing the thermal characteristics of the board."
] |
[
"An extreme example of this is submerged, oil-cooled computers; like KaneHau says, as long as the substance is non-conductive it doesn't pose a risk to the electronics."
] |
[
"And by their nature, hydrophobic materials tend to be non-conductive. The oil used to cool the computers you speak of is in fact hydrophobic.",
"To be hydrophobic, the material has to resist polarizing, and therefore resists forming polar bonds with water (ie wetting). Not polarizing also means it won't carry and electric charge."
] |
[
"After death how long do processes like digestion or cell regeneration continue to go on and what ultimately stops them?"
] |
[
false
] |
I would imagine that the processes don't stop immediately.
|
[
"In short, what ultimately stops cell processes after death is lack of oxygen. Without oxygen ions to fix electrons on the cellular level, cells are unable to function or reproduce, and they begin to decay. ",
"For some cells that require constant oxygen (such as neurons) this can happen almost immediately (within minutes) after death. For other cells that are not quite as oxygen thirsty (such as in the transplant organs) this can take between 30 or 60 minutes. Structural cells which require even less oxygen, such as in bone and connective tissue, can survive for around 24 hours after death before cell death occurs. "
] |
[
"A drop in body temperature from submersion slows the body's metabolic processes, thereby prolonging cell and tissue preservation. ",
"Therapeutic cooling is used in hospitals on witnessed cardiac arrests as soon as they enter the ER, for just this reason. ",
"Edited to add: four hours is a stretch, though, in my experience. "
] |
[
"What happens when you hear about people who have fallen into a lake and are dead for 4 hours then revived? How do the cells survive without oxygen?",
"Edit: As others have noted it's not 4 hours. The longest incident I could find was 80 minutes. Still interesting.",
"Edit 2: Doctors induced hypothermia in this patient for 48 hours while she awaited a liver donor. It was done to preserve her brain. 33 degrees!",
"http://yalemedicalgroup.org/news/article.aspx?id=6556"
] |
[
"Why is The Seven Bridges of Königsberg such a famous question?"
] |
[
false
] |
I'm not a mathematician, but to me the solution is fairly obvious and uniteresting, compared to other famous mathematical riddles.
|
[
"Solution is faulty obvious, the proof of said solution isn't trivial. It's still fairly straightforward but some of the steps of Euler's proof lead to the development of graph theory and topology, and that's why it's viewed as an important problem.",
"Here's some reading if you're interested: ",
"http://www.maa.org/press/periodicals/convergence/leonard-eulers-solution-to-the-konigsberg-bridge-problem"
] |
[
"Would you mind sharing your obvious solution? Seriously!"
] |
[
"The answer is obvious today because we have the techniques of modern mathematics, but in Euler's time, there was no graph theory, and the solution was not obvious at the time. It's famous because it led to the development of a new field of mathematics"
] |
[
"Is there a relation between color blindness and reaction time?"
] |
[
false
] | null |
[
"We are actually very bad at detecting movement of objects that are the same brightness as their background (i.e. defined by color differences alone). ",
"I'm not quite sure what you are trying to ask here -- colorblind individuals will be worse at tasks that require them to use color information that they can't discriminate..."
] |
[
"Essentially:",
"What is the reaction time of a color blind individual to a sudden change that is easily visible due to difference in brightness?",
"How quickly does a color blind individual notice subtle movement in the background compared to someone with average sight. (Both with high difference in brightness and a scenario where objects in the background are hard to distinguish due to similar brightness)",
"I'm pretty sure these questions can't be really answered, though..."
] |
[
"If by sudden change in brightness you just mean that a white light goes on, then there is no difference -- that is detected by the rod system and not by cones."
] |
[
"[Biology] DNA in the Mitochondrion makes little sense to me"
] |
[
false
] |
It is said that Bacteria DNA is in the Mitochondrion but I dont understand how that DNA is able to be in every new Human. When a cell does mitosis or a germ zell meioses what happens that the bacteria DNA in the mitochondrion is in the next cell.
|
[
"Mitochondria divide in a manner similar to bacteria (fission) (from the wikipedia article that you linked). You can read more about it here: ",
"http://www.nature.com/scitable/topicpage/mitochondrial-fusion-and-division-14264007",
". So, you can almost think of the mitochondria as being similar to smaller cells inside your cells that divide on their own, preserving their own DNA. ",
"Since cells have multiple mitochondria, when the cell divides some go to each daughter cell and the fission and fusion process of the mitochondria continue in those cells. You can also read more ",
"here",
"."
] |
[
"laflavor has it correct above. to try to put it in simple terms...",
"Mitochondria have their own dna.",
"The current hypothesis is that mitochondria are essentially \"little bacteria\" that have symbiotically adapted to living inside eukaryontic cells.",
"They recreate and divide on their own to some degree (and here is where I am not totally sure). I believe they do rely on and are regulated by some degree of genetic material from the nucleus.",
"Nonetheless, mitochondria are essentially little symbiotic bacteria living within your own cells, that learned to do a wonderful thing called aerobic metabolism, chemically known as the krebs cycle.",
"There happens to be enough of them in any individual cell, that when it divides, they get spread equally between the 2 daughter cells."
] |
[
"Adding on a bit more here.",
"Each child gets his mitochondria only from their mother. Since sperm carries no organelles, all the mitochondrial DNA you have all came from the few mitochondria that were in the egg from your mother. ",
"EDIT: silly me, sperm do have mitochondria but they are not passed on to the child."
] |
[
"Where does energy come from in an explosion?"
] |
[
false
] |
For example, I was watching Nova's Doc. Hunting the Elements and they were explaining how combustion works with nitrates (loosely): when heat is introduced to nitrates, bonds are broken, and the atoms split up and bond with other 'preferred' atoms creating compounds like H2O, CO2, and O2. But where does the energy that is released (the explosion) come from? Is it a transformation of the initial heat that is introduced? And on a lesser scale. Where does the energy released when two singular atoms bond? Or am I missing something completely..... elementary?
|
[
"The energy that is released comes from energy that was spent to form the explosive, combustable compound in the first place."
] |
[
"The chemical reaction in question is exothermic. So, indeed, the gas are hot (which increases the pressure), and may ignite."
] |
[
"Typically, lots of gas (N2, H2 and CO in the case of TNT) is created in a very small amount of time. That gas then proceeds to expand very rapidly."
] |
[
"What will dehydrate you faster; A wet heat or a dry heat?"
] |
[
false
] |
Assume same everything (sunlight, temperature (let's say 105F), body condition, personal stamina, etc.), except one location is dry and the other humid. Would there be a difference in the rate of dehydration?
|
[
"In a situation where rigorous physical activity is involved, evaporation of sweat from the skin serves as the primary method of heat loss from the body.",
"In high-humidity [wet heat] situations, evaporation of sweat is limited, reducing the body's ability to lose heat. The body will continue to attempt to regulate its temperature via sweating, which takes longer than in a low-humidity environment. As such, a wet-heat can dehydrate you more. But do you sweat and dehydrate ",
"? This is a more complicated question. ",
"However, there are various aspects of human thermoregulation that may limit the validity of this seemingly simple concept.",
"\nFor example some trained athletes begin to sweat copiously at the beginning of physical exertion, well before their body requires such a high level of heat loss via evaporation of sweat. ",
"If such an athlete were thrust into both environments, the body may already be producing as much sweat in a dry-heat situation as it would in a wet-heat situation. The question then becomes: is there a theoretical limit to the rate at which one can sweat? ",
"[side note: During the 2008 Summer Olympics in Beijing, marathon runners found the very high ambient temperature and high humidity effectively nullified any skin heat transfer through sweat. To lose heat, they splashed cool water from the water tables on their bodies. But again, this does not necessarily suggest that the runners were sweating more than they would in a dry heat.]",
"Another possible bias may be the fatiguing of sweat glands-- over extended periods of high exertion, sweat glands begin to decrease average amount secreted. If humidity also affects the efficiency of sweat glands, there may be omitted bias here as well. ",
"Direct sun exposure (or any direct heat applied to the body) may also change how the body regulates its temperature. I hope someone with more knowledge is able to provide a less murky answer. "
] |
[
"I think you also need to take into consideration that in a wet heat, you will regain/not lose water while breathing. So while you may be sweating more to attempt to regulate body temp, you are not losing water via exhalation. While in a dry heat, every breath you exhale also takes with it moisture from your lungs."
] |
[
"Interesting. I wonder if there is a Bear Grylls solution to that if caught in a desert?"
] |
[
"Why do we genetically engineer E. Coli instead of other bacteria?"
] |
[
false
] |
Is it just easier to grow and modify compared to other bacterium?
|
[
"E.coli is widely used because it is well known and easy to grow, as others already pointed out. But it is not alone. There are A LOT of other bacteria equally easy to work with and both Bacillus subtilis and Lactococcus lactis are fairly common model systems.",
"Now, one reason why people tend to stick to E.coli is partly out of tradition and the knowledge that has brought us about it. There is a sequenced genome of more than one strain available which makes working with it much easier. A huge number of established protocols exist so you don't have to put time and effort into figuring out every step of your experiments. As jhawk1729 pointed out there are several modified strains suited for different purposes (assays, protein production...) as well. Yet another point is that results done in the same model system can more easily be compared with each other, basically, the less varying features the better."
] |
[
"The tools don't always transfer to other organisms. For example, if you want high/medium/low expression, you might make a plasmid and choose different 'origins of replication' on that plasmid, which only work in ",
". Then, if you want inducible expression, you'd use the Lac operon, which is recognized by the ",
" Lac repressor. Or they use T7 promoters to transcribe the gene, which you can only get in ",
" T7/DE3 lysogens. Or the use of selectable antibiotic resistance markers that are specific for gram-negative bacteria (like AmpR). You couldn't just put these things in Gram-positive mycobacteria.",
"If you wanted to work in other bacteria, you could certainly do that, but you'd have to develop all the tools from scratch. ",
" is used mostly because all these tools have been developed through the years."
] |
[
"I don't have too much experience with biochemical techniques, but E. coli is pretty easy to grow (the protocol I learned required about 10 hrs of growth), and therefore a good host to do your protein expression. However, I do know other labs who used insect cells, which are even more hardy, but they take longer (multiple days)."
] |
[
"If I pushed a rod that was one light year long, would a person at the other end of the rod see it move at the same time I pushed the rod?"
] |
[
false
] | null |
[
"The push will propogate at the speed of sound in the rod, which is (for a real rod) less than the speed of light. "
] |
[
"The sound propogates through the rod itself."
] |
[
"Edit: Never mind, I know how it works. The material that the rod is made out of determines the speed of sound. Thanks for the answer."
] |
[
"What would happen to a floating helium balloon if it did not burst in the atmosphere?"
] |
[
false
] |
In lieu of this picture from the front page:
|
[
"The buoyancy of the air around the balloon decreases as the air thins out at high altitude. Eventually the balloon will settle at an altitude where this exactly balances out gravity, but no more."
] |
[
"There is a lot of scientific research done in the upper atmosphere with the neutral buoyancy principal. NASA, for example, has balloons that will stay at approximately their target altitude for 100 days with payloads as big as 3600 pounds!",
"Sometimes the balloon doesn't even pop from wear but instead is popped by some mechanism when the payload needs to be returned to ground.",
"source: ",
"http://www.csbf.nasa.gov/balloons.html"
] |
[
"Just for scale, escape velocity 50 km up is still 99.6% of escape velocity at ground level. "
] |
[
"If the earths inner cores are made up of magma, does this magma slowly erode at the earths crust from underneath?"
] |
[
false
] |
I know magma rises through a volcano vent and such, does the magma erode at our from beneath? If so is it substantial? Also does the ratio of crust and other cores change much?
|
[
"No significant part of the Earth is 'made up' of magma. ",
"The inner core is solid. The outer core of the planet (located between roughly 2900 km to 5100 km beneath the Earth's surface) is the only significant layer which is liquid (primarily iron/nickle), but this is molten metal and not technically magma. It is also relatively dense and the only major exchange between the outer core and the mantle (which overlies the outer core) is of heat. This heat does serve to produce magma at this boundary, but not as much as you might think, and that doesn't affect the crust unless that magma rises through the mantle (which, granted, it does do in places).",
"The mantle (about 2850 km thick), which separates the crust from the core of the Earth, is not liquid. It is solid rock (it would shatter if you hit it hard with a hammer), but it has a small fraction of liquid magma between/within rocks/minerals which allow the rock to behave plastically (flow) on long (geologic) time-scales. IIRC mantle rocks are expected to be something close to 2% magma, on average. Isolated parts of the mantle can have much higher magma fractions, such as what you find near mantle plumes, mid-ocean ridges, or around where oceanic crust subducts (sinks) into the mantle.",
"There is still a lot of heat in the mantle, and it can have some complicated impacts on the underside of the crust. When material heats, it is almost universally less dense than it used to be, so heat directly does not \"erode\" away crust. That is, if part of the crust does melt after being heated up, it has a very hard time \"sinking\" away into the mantle. Instead, the resulting magma would either remain in place or rise and either solidify higher up in the crust, or erupt from a volcano and deposit on top of the crust. In all these cases, crustal material isn't really lost to the mantle. If anything, on average, the crust accumulates material this way over time.",
"Crustal material is lost through subduction, both (and primarily) from oceanic plate subduction, and also from continental subduction. But the crust (especially continental crust) is characteristically less dense than mantle rocks, so it is relatively hard for the crust to be lost into the mantle in significant volumes. Being lighter, it tends to remain near the surface unless major forces are in play.",
"So combining the fact that the crustal rocks are naturally less dense than mantle rocks, with the fact that when the crust melts the resulting crustal magma is even less dense, mean that the crust is very resistant to being lost into the mantle.",
"One way in which crust IS \"eroded\" from below is through delamination (i.e. eclogite delamination). The heat from the mantle can change the mineral composition of deep crustal rocks and separate heavy minerals from lighter minerals. The heavier rocks that form from this process can then peel off in large chunks and sink into the mantle, which can have a significant impact on the long-term mass of the crust in certain places (typically below large mountain ranges). But this process also serves to decrease the average density of the remaining crust (since the heavy minerals are more easily lost), so it does have its limits. "
] |
[
"Core and mantle have different compositions so make different solids having different melting points; one is liquid while the other solid at the very same conditions. This is not at all the same as when a hot silicate magma rises upward into crust of similar composition (but colder in temperature), which does tend to produce some \"erosion\" (melting) of the wall rock, and some metamorphism (solid state changes in the wall rock). Down at the mantle-core boundary, there are two distinct materials, and one is solid while the other is liquid, even though they are at the same temperature and pressure. there is no \"erosion\" because the liquid isn't hot enough to melt the solid stuff nearby. "
] |
[
"also relatively dense and the only major exchange between the outer core and the mantle (which overlies the outer core) is of heat. This heat does serve to produce magma at this boundary, but not as much as you might think",
"It’s still up for debate whether there is any partial melt generated at all at the core-mantle-boundary though, right?"
] |
[
"How does fluid loss affect cognitive ability?"
] |
[
false
] |
Earlier, I saw this TIL in : Sports studies have underlined the importance of fluid level in the body. A person who has lost 4% of body weight can lose up to 40% of their psycho-physical ability. However I can't find a source that shows this 40% figure, and I only found that talks about cognitive ability loss after dehydration. Anyone here knows more?
|
[
"In simple terms, your brain needs two things for survival: glucose and oxygen. This is carried and transported by the circulatory system. When the human body experiences an event such as a high concentration of g forces, it cause blood to leave the brain. Also the reason why fighter pilots wear a g suit when doing intense maneuvers. ",
"Due to the fact that the brain is low on these two vital necessities, it deteriorates in thought processes, motor functions, and unconscious \"commands\" to vital organs."
] |
[
"Alright. But how do they quantify the loss in cognitive functions? Glucose levels?"
] |
[
"Alright. But how do they quantify the loss in cognitive functions? Glucose levels?"
] |
[
"What prevents prions from being used as a biological weapon?"
] |
[
false
] |
After reading a bit about prions (i.e., the cause of afflictions like Mad Cow Disease), I am really disturbed. There is no cure for them, and they are seemingly resilient. What prevents their mass transmission, and are they susceptible to being used as a biological weapon?
|
[
"Most of those who do eventually develop spongiform encephalopathies do so after several decades post-exposure. It is not certain how likely you are to develop the disease if exposed, and it is not transmitted between people (who aren't brain eating zombies). In short, it would make a terrible biological weapon. Difficult to deliver, not transmissible, and effective only after decades.",
"There isn't much to be afraid of if proper agricultural practices and regulations are in place (which they are). ",
"Note that these diseases do develop spontaneously on very rare occasions."
] |
[
"Prions are not transmitted by any method we know short of consuming the infected material. This makes them a very poor choice, as you'd need to consume them to get ill.",
"They're also latent, they do not provide reliable disease progression, it can take many years for an infected individual to show symptoms and die."
] |
[
"Prions are not living entities, they're proteins. They also only exist in very specific areas of the host they infect. This means that if you have these proteins and cough, you're not spewing infected proteins on people as they aren't present in your lungs. This makes airborne transmission from person to person impossible, and it also makes contact transmission impossible.",
"I'm not certain if it would be possible to use a waterborne vector to transmit them, but I suspect it wouldn't be effective at getting through a modern water treatment plant."
] |
[
"Can the human acceleration limit be worked around?"
] |
[
false
] |
[deleted]
|
[
"Magnets won't work for this, however the idea of accelerating the whole body evenly is the right solution, though there is no practical way to do that yet.",
"\nRight now what can be done is immersing a person in body-density liquid, this will increase the G-tolerance to an estimated 15~20G; if the person's lungs and other body cavities can be filled with liquid, then the G-tolerance can be even higher -- but perfluorocarbon breathing is still at a very experimental stage. "
] |
[
"Here is perhaps the only research on humans in controlled, very high g situations:\n",
"http://en.wikipedia.org/wiki/John_Stapp#Works_on_effects_of_deceleration",
"\"Stapp demonstrated that a human can withstand at least 45 g (440 m/s²) in the forward position, with adequate harness\"",
"That is for a brief deceleration, though. I'm sure that the survivability of a g-load is dependent on the exposure time. ",
"I think that you're right about this issue being potentially relevant for manned space flight such as during aerobraking. Within our solar system, the velocities are low enough that objects can be aerobraked quite gradually:\n",
"http://en.wikipedia.org/wiki/Aerobraking",
"\nBut if you're on a generation ship going to another star system, you'd rather not have to expend a huge amount of fuel decelerating. "
] |
[
"If the whole body were evenly accelerated, is it true that we would not have the sensation of acceleration (we would feel the same as being in free-fall)?"
] |
[
"Is there any physical way to stop cosmic rays?"
] |
[
false
] | null |
[
"You can put it very deep underground to lower the cosmic ray background."
] |
[
"But is that because of height or because of the rocks/dirt surrounding the place acting as an \"armor\"?"
] |
[
"because of the rocks/dirt surrounding the place acting as an \"armor\"?",
"Yes, it's just the huge amount of material to shield them."
] |
[
"Do we currently have the tech available to give someone a one-way ticket to mars?"
] |
[
false
] |
I understand that new stuff would have to be invented, so by "having the tech" I mean that we aren't inventing a way freezing and then reviving the person when they get to mars. Or we aren't relying on unobtainium to create the ion-blaster rockets. In otherwords, is the tech readily available and "easy" to do given enough time, design, and money. Can we get the person there alive? How would would we handle feeding the person/people? Can we handle radiation problems? What about electricity, would we use something like the curiosity power station to keep things running?
|
[
"Are you thinking of something like ",
"Mars to Stay",
" one-way missions?"
] |
[
"Really, I'm only thinking about the getting there and the landing safely part. I'm wondering if we could do even that much right now. I realize that coming back home will just about double the amount of fuel the ship needs to carry."
] |
[
"There is a big difference between \"tech\" and \"ability.\" We have the technology, but we do not have the manufacturing capability (currently). "
] |
[
"How do rocket scientists ensure that a rocket's mass distribution is balanced throughout a launch?"
] |
[
false
] |
I've been playing a lot of Kerbal Space Program (game where you basically run a space program), and I always need to make sure that my launch vehicle (rocket) is either incredibly balanced, has control surfaces to compensate, or the magic reaction wheels. Otherwise my next stop is the ground, not orbit. Considering the constraints that actual rocket scientists face, what options do they have available to make sure that a rocket doesn't spin out of control?
|
[
"One key consideration is in the \"balancing\", as you said, specifically placing the differing parts of the payload, propulsion, control systems, and other components to move the entire vehicle's center of gravity forward of the center of pressure (where the lift forces are resolved). Ideally you want the center of gravity above the center of pressure and the center of thrust, but have all 3 in line with each other down the axis of the cylinder. This creates natural stability in flight, where if there is a disturbance , such as natural wind turbulence, the vehicle will dampen the disturbance out. This is better for smaller rockets, such as hobby rockets or those that are not for reaching LEO (low earth orbit)",
"",
"NASA- Rocket Stability",
"",
"Other considerations include options like thrust vectoring, where the nozzle of the main motor can adjust the direction of the propulsion stream to create some side forces, normally by gimbaling the nozzle.",
"",
"Gimbaled Nozzle of the Space Shuttle",
"",
"For an idea of what is necessary, generally to launch a rocket that goes even ~10,000 ft, many experiments are performed to calculate and actually observe the center of gravity, the material strength of all the components of the vehicle, determining the center of pressure, how much thrust is produced by the motor, multiple sub-scale launches, and if the control system will work fast enough to keep the vehicle steady. And even then, there is still a chance it will just lawn dart itself or blow up due to catastrophic failure of the motor, which is why all commercial rockets have explosive charges in them to destroy them while they are still in the air, rather than see them crash into someone on the ground."
] |
[
"They use hydraulic actuators on the larger engines (like the J2X) and mount them straight to the combustion chamber (where the fuel and air mix and ignite), meaning that most of the \"rocket motor\" is on this gimbaled system, but the force is not just on the actuators, but the entire system exists in a frame that gets mounted to the vehicle",
"https://www.hydraulicspneumatics.com/sites/hydraulicspneumatics.com/files/1963.12%2072-74%20Fig%201.jpg"
] |
[
"In the case of the gimbal system, I've always wondered how the gimbals manage to move something that carries so much force, fast and precise enough to actually counter any disturbances. How does that work?"
] |
[
"All time zones converge at the earth's poles. So for scientists working near either the north or south poles, what time zone do they actually use?"
] |
[
false
] |
Another way to say it: what time/date is it at the location of the north and south poles right now? How did scientists determine this time/date as the official time to go by at the poles?
|
[
"At the Amundsen–Scott South Pole Station, they decided to use New Zealand time (UTC +12), because all official travel to the station comes to Antarctica out of Christchurch. ",
"Since the North Pole is an iceflow in the Arctic Ocean, it does not have a permanent settlement that would require them to figure out a time zone standard to live by."
] |
[
"Interestingly, if you were to travel around Antarctica you would go through quite a few different time zones. Pretty much every country that has some sort of claim down there has their respective territories on a different time. "
] |
[
"Aha! There was actually a really neat BBC story about this a few weeks ago. Here's the link:",
"http://www.bbc.co.uk/news/world-12849630",
"Go to the article called \"What time is it in Antarctica?\" The video is great."
] |
[
"Within a population, can vaccinated members ever be put at health risk from non-vaccinated members?"
] |
[
false
] |
Simple Scenario: 10 organisms of the same species in a confined setting. 7 are vaccinated for virus X, 3 are not. Expose virus X to the entire population. The 3 are positively infected with virus X. Are the 7 vaccinated members at any risk from being around the infected 3? How would this scenario apply to vaccinations which require a schedule for repeated vaccinations (such as boosters), and virus X was introduced in the middle of an incomplete schedule?
|
[
"The three can still infect the seven uninfected individuals as vaccinations are not a 100% effective. Vaccinations increase the likelihood that you will not contract a disease by building up your immune system to fight off any real infection.",
"In regard to your question of interest, if Virus X was introduced in the middle of an vaccination schedule, it would be more likely that the individuals would be infected, because subsequent booster shots have yet to be given."
] |
[
"I think the analogy is apt. Vaccinations allow the body to create a stockpile of memory cells; they build up the immune system, making it more able to quickly respond to future infection. "
] |
[
"if you mean \"herd\" immunity, i don' think it applies to my question. I'm asking how the 3 could affect the 7, not how the 7 could affect the 3."
] |
[
"Can someone explain histamine to me, and why so many people have too much?"
] |
[
false
] |
Okay, I understand a bit about histamine - it triggers allergic responses (H1), stomach acid production (H2), and affects libido and mental processes (possibly even a contributor to schizophrenia). The only positive I've found is that it helps erectile function & libido. Aside from this, what's good about histamine? Why is it that we frequently have problems with keeping histamine in balance? So many people deal with chronic allergies - runny nose, itching, acid reflux and heartburn, and other negative effects caused by overproduction of histamine. Is there a better way to turn down the dial on histamine other than taking all these histamine antagonist (antihistamine) drugs with their negative side effects? Would there be any downside to producing less histamine?
|
[
"Right, well seeing as I am occasionally credited with discovering the histamine H4 receptor in the brain, I suppose I should take this one. HOWEVER, I am not even close to being an expert on the immune system and allergies.",
"So your first mistake is assuming that histamine is to blame for allergies, while it might be in part what you could call the ",
", it is not actually the root cause. ",
"When someone with an allergy is exposed to an allergen, a complex chain reaction involving different types of immune cells begins. Antigen Presenting Cells active T cells, which then active B cells and then B cells release antibodies to the antigen that then stick to mast cells. When these antibodies are then activated by the antibody, the mast cell \"degraulates\" and releases histamine but also many other inflammatory modulators (Interleukins, cytokins, prostaglandins etc). This is why antihistamines aren't perfectly effecting in treating allergies. The reduce the symptomes, but the interleukins and cytokines etc are still floating around. Indeed, when someone has a severe allergic reaction, antihistamines are seen as a secondary treatment (along with anti-inflammatory steroids, to deal with the protaglandins etc), and adrenaline is the primary treatment.",
"So, why do we have histamine? Or more generally, why do we have mast cells? Because they are there to protect you against pathogens. When the recognize a pathogenic organism (via the antibodies on their surface) the release inflammatory modulators. These compounds allow white blood cells to more easily enter the area via increasing blood flood, making cell walls more permeable and probably other things I can't remember right now. The make the area sore, which probably encourages you to stop fucking with it. I ",
" they also stop blood clotting, which might sound bad, but for small wounds, again, it allows white blood cells to get to the site of infection.",
"So yeah, people with allergies don't just have too much histamine just floating about. They have mast cells that are reacting to antigens, which in turn causes histamine to be released."
] |
[
"It starts back before the mast cells.... Exactly why I don't know... I'm not sure anyone does (though as I say, not an expert on these things). But the problem is that your body is making the antibodies against things it \"shouldn't\"... whether that is pollen or whatever. Then the mast cells pick them up, and by then the mast cells are just doing what they're told. Their purpose is go crazy when their surface antibodies get activated (you can very much think of them like those old school ",
"sea mines",
" with the antibodies being those sensors that stick out). It would be a bad mine that didn't explode when its sensors told it to. The problem here is that the immune system has put the wrong sensors on your mast cells.",
"I always think it's amazing we aren't allergic to more things. How does the immune system know what proteins are \"bad\" and which ones aren't? By the time it is a protein floating around in your blood, it seems tricky (i.e. is that protein from a broken down bacteria (bad) or from a broken down cell of yours (good)). I'm sure someone else knows the general answer, but I sure don't."
] |
[
"Thanks for the great response!",
"So then, would it be correct to say that people who have allergy issues have overly sensitive mast cells?",
"\nOr, does it start back with the T cells or B cells or earlier in the chain? Can anything be done to desensitize things, or would that likely create other problems?"
] |
[
"If energy can neither be created nor be destroyed where does all the energy in the universe came from?"
] |
[
false
] |
If energy can neither be created nor be destroyed where does all the energy in the universe came from?
|
[
"1) The energy of the universe could be zero, as already pointed out.\n2) The law of conservation only states that energy is a constant, the actual value of that constant could be anything so even if the energy has a net positive or negative energy, that's not a problem at all.\nEven worse, energy is not a relativistic invariant, so the total amount of energy varies from one reference frame to another.\n3) Conservation of energy may not be very well defined when you put big bang, GR and cosmology into the subject."
] |
[
"In addition to reasons already given by others, I also want to point out that the law of conservation of energy is not as rock solid as you might think. ",
"To understand why this is the case, we need to examine ",
"Noether's Theorem",
".",
"Noether's Theorem tells us that every differentiable symmetry of the action of a physical system has a corresponding conservation law. ",
"This means, that conservation laws are rooted in a mathematical property called differential symmetry of some parameter. The parameter in question for energy is time. Thus, Noether's theorem tells us, that energy is conserved in a system, if the system is time invariant. That means, that all experiments are independent of time. In other words: it doesn't matter at what point in time I conduct an experiment. ",
"Now that we know, what a conservation law is let us approach the second layer: is the premises of your question true. That is, is energy conserved in our universe. ",
"According to Noether's Theorem, energy is not conserved in our universe. Our universe is expanding. Thus our system is not independent of time. As time invarience is the symmetry corresponding to conservation of energy, and since this time invariance is broken by the expansion of the universe, it follows that energy is not conserved in our universe. ",
"This might seem strange and counter intuitive at first. After all, conservation of energy is ",
" corner stone of high-school physics and matches our experiences in everyday life perfectly.",
"\nHowever, this prediction does indeed match our theories. Dark energy, the mysterious quantity driving the expansion of our universe, is distributed throughout our universe. And all our models state, that the density of dark energy is constant, independently of the expansion of space. This would mean, that dark energy is created through the expansion of the universe, thus violating conservation of energy. "
] |
[
"We don't know. Maybe it's always been here. Maybe it can be created via a process we cannot fathom. Maybe the immutability of the amount of mass-energy in the universe only came to be after some initial creation event. Maybe the answer is beyond our intellect's ability to understand."
] |
[
"How often/likely is it estimated that people get cancer of some kind and their body defeats it, without them ever even knowing they had cancer in the first place?"
] |
[
false
] | null |
[
"I don't know a specific number, but based on probability alone I'd say many times a day. The cytotoxic T-cells of the adaptive immune system and the natural killer (that name is ",
") cells of the innate immune system are the body's own defence against cells that are infected, mutated or otherwise impaired or a danger to the organism. Many would-be cancer cells also undergo programmed cell death called ",
" way before they ever make it that far. This is due to the built-in defenses in our DNA; every cell has a number of different checkpoints that each check that it hasn't acquired cancerous mutations lest it kill itself, and for a cell to finally become a cancer cell it has to somehow have damaged each and all of those control mechanisms.",
"The human organism does not need any one cell, but it is maintaining the integrity of the community of cells that is important. If a cell senses that it is about to become a danger to the community, it is supposed to kill itself before it ever reaches that point. If it fails to do so, our immune system will in theory make sure that it is killed. Those cells that do become cancer cells are often walking a fine balance between the two; they are too far gone to realize that they are dangerous and therefore do not kill themselves as they should, but at the same time they are not always so far gone as to be recognized as dangerous by our immune system."
] |
[
"If a mole is itchy, you should probably go see your GP and/or a dermatologist. It's one of the warning signs that it might be turning into something more serious. The others are irregular borders, uneven colour, size of more than 5mm, asymmetry and any recent changes, i.e. if it looks different from last month.",
"The cancer, which arises in moles (and sometimes healthy skin), is called melanoma and is very rare. It's also got a reasonably high curative rate (through surgery), assuming it is caught before it spreads. The problem is, once it spreads, surgery is not enough and you need chemo. Unfortunately melanoma tends to be very adaptable and is notoriously hard to treat with drugs. It can also be very aggressive. This is why it is important to watch out for it.",
"TL;DR: Your mole is more likely than not fine, but it might be turning cancerous (indicated by the itching). Do not dawdle and have it looked at in case it is. Oh, and do not scratch it regardless."
] |
[
"If a mole is itchy, you should probably go see your GP and/or a dermatologist. It's one of the warning signs that it might be turning into something more serious. The others are irregular borders, uneven colour, size of more than 5mm, asymmetry and any recent changes, i.e. if it looks different from last month.",
"The cancer, which arises in moles (and sometimes healthy skin), is called melanoma and is very rare. It's also got a reasonably high curative rate (through surgery), assuming it is caught before it spreads. The problem is, once it spreads, surgery is not enough and you need chemo. Unfortunately melanoma tends to be very adaptable and is notoriously hard to treat with drugs. It can also be very aggressive. This is why it is important to watch out for it.",
"TL;DR: Your mole is more likely than not fine, but it might be turning cancerous (indicated by the itching). Do not dawdle and have it looked at in case it is. Oh, and do not scratch it regardless."
] |
[
"Since oil is causing so much trouble, and the US is a net exporter of natural gas, Why aren't there more vehicles powered by natural gas on the road?"
] |
[
false
] | null |
[
"One gasoline gallon equivalent (GGE) of compressed natural gas will occupy ",
"0.77 cubic feet of space at 2400 PSI",
".",
"One cubic foot of gasoline = ",
"7.5 gallons",
".",
"So, gasoline is a more compact means of storing energy making it a preferred fuel in cars. "
] |
[
"Not to mention safer. Gasoline is surprisingly safe in a liquid form, at least compared to natural gas under pressure. ",
"And that's without considering the weight and danger of having to compress your natural gas for on-car storage. "
] |
[
"All of the above is absolutely 100% true. It is also not the reason why we use gasoline instead of natural gas. If energy density were the sole concern then Diesel fuel or liquefied natural gas (both of which have a higher energy density than gasoline) would be our primary fuel source. However, as is the case with all technology and systems, politics, existing infrastructure and technological momentum are far more important.",
"The main reason why we use gasoline today is because we used gasoline yesterday. We used it yesterday because we used it the day before and so on. Along the way we have designed and built huge amounts of infrastructure to support this particular piece of technology. As a result, new technology is designed with that infrastructure in mind. This existing infrastructure, as well as the societal constraints (politics and perceptions) surrounding preferred technologies governs what technology develops tomorrow. If we want to discuss why gasoline was used from the beginning that would be an interesting discussion, but I suspect isn't what the OP is interested in. For now, we use it today because we used it yesterday. It isn't fascinating, it isn't really science, but it is definitely true.",
"I should note, this particular explanation follows the model of ",
"technological momentum",
" one of many different theories prevalent in studies of the history of technology. You can read more about them using that wiki page as a starter. Technological development is rarely due to a single factor, and the study of technology can provide some fascinating insight into why things are the way they are today."
] |
[
"Speed Wobble, what is it?"
] |
[
false
] |
Could someone break down what is actually occurring when the phenomenon mentioned above begins? What causes it? Is it different for skateboards (2 wheels) vs a motorcycle? I've been a victim of this dastardly thing when I was younger and received quite a few scrapes, but I don't really understand it. Thanks in advance AskScience!
|
[
"Speed wobble is a resonant condition that can't be easily predicted. This sort of resonant interaction can be either self damping, or divergent depending on the system involved. ",
"The trouble is, it's different for EVERY system. ",
"As for \"what's really happening\" I think I can describe it. We're going to use the cycle explanation, because that's the one I'm most familiar with. ",
"Cycles keep themselves up by constantly correcting towards vertical. If you have ever ridden your bicycle across sand, and gone back to check the tracks, you'll find that the front wheel is weaving back and forth even though you \"feel\" you're riding straight. This is the bike correcting for vertical. ",
"The rate at which the bike makes corrections is depending on many factors, how much trail the bike has, the stiffness of the suspension, the stiffness of the frame, the stiffness of the tires, how high the center of gravity is, how heavy the steering assembly is, and what sort of damping comes from the disconnected load (that is you..) ",
"Sadly, doing the math involved is a bit over my head, but each one of those factors is an input to your vehicle stability. If any two of them start to resonante with each other, the corrections can start to stack on top of each other. That leads to headshake. (or speed wobble) The way that headshake is usually dealt with is by doing something to change the frequency of the system. You can put more weight on the front end, move weight off the front end. Accelerate, or slow down, take a hand off the handlebars, etc... Anything to change the relationship of the masses in question. "
] |
[
"As a skateboarder, this is my response:\nOn your skateboard you have two trucks. Each truck has a base, which is screwed into the board, and the hanger, which the wheels go on. The soft rubbery bits on either side of the hanger are called bushings. What bushings do is enable the truck to return to a neutral position after pressure has been applied to one side. When you turn on your board, you're compressing one side of the bushings. When you're skating in a straight line, the bushings are not compressed. Different durometers (hardness of the bushing) affect how much the bushing will compress when you turn. Harder bushing = harder to compress = less turning ability. This is also affected by how tightly you have your trucks set. Simply tightening or loosening the nut on the kingpin can dramatically change how your board turns.",
"When you get speed wobbles, your board is turning from left to right and back in a very sharp S shape until finally the force and speed of the turns throws you off. The bushings are being compressed, then decompressed, then compressed on the opposite side over and over very quickly; and when your weight is being thrown into it, the force keeps building up and up, so the bushings have to bounce back faster and harder to not break. It also doesn't help that your body is constantly trying to counteract the movement of the board, further adding to the chaos. To counteract speed wobbles all you have to do is turn. If you are making a turn with your body weight, there is no way the bushing can decompress and send you in to a wobble. \"Carving\" is the term used when you make your own nice big S shape down a hill. Most important thing in my experience is confidence. If you know what speed wobbles are, and how to avoid them, you will never get them. ",
"Also take into account your board, flexy boards will translate more of the bounce of the board into your trucks, while stiff boards will not. Tightness of trucks is incredibly important when you're starting out. Tighten your trucks enough, and you won't be able to turn much, but you won't be wobbling at all either.",
"In short: Don't go straight down a hill unless you know what you're doing. Tighten your trucks. Take control of your board, if it starts to wobble, start to carve. Be confident. Wear safety gear for when you do eat it."
] |
[
"That makes sense, I was like 7 and was sitting on my board (a really crappy one) and went straight down a pretty big hill. Your point also brings to light a long-boarder video I just saw, he had the beginnings of a wobble until he hit curves, thank you for clearing that up. "
] |
[
"If I took an air horn into a vacuum, and depressed the button would there be a sound?"
] |
[
false
] | null |
[
"Would something happen? Definitely. Air horns function by releasing a pressurized air though a relatively narrow space. However, as there is no atmosphere for this outgoing air to go into, I expect that two things would happen.",
"Gas molecules in a vacuum won't diffuse, but rather fly ballistically. (Though with an intense pressure wave, there would be some diffusion from particles within the wave bouncing off of each other.) The result of this would be that the air coming out of the horn (and carrying the sound) will really only travel \"forward\" out of the horn. If you stood to the side, you wouldn't \"hear\" anything.",
"You'll notice that I put \"hear\" in quotations. With a horn in an atmosphere, a pressure wave is carrying sound, rather than actual molecules (which are bouncing off of each other, and not really traveling \"forward\" any significant distance.) That's evidently not the case here. It's unclear to me if the pressure waves of sound would just result in molecules diffusing away from each other faster. In any case, the transmission of the sound is based upon the motion of the molecules through space, rather than of the pressure wave. Though a reasonable mass spectrometer could detect the molecules (and their arrival times) to get an idea of what sound was made, I don't know that a person would perceive anything like a regular noise."
] |
[
"will really only travel \"forward\" out of the horn",
"Well there would be a pretty big spread of gas molecules. It's not a laser. Just clarifying."
] |
[
"Thanks dude, but can you explain it like I'm five."
] |
[
"Why is the Earths mantle divided in two? And what is inside the mantle?"
] |
[
false
] |
I’ve read that the mantle inside earth is divided in two and I’ve also not really been able to find out if it’s liquid or something more hard.
|
[
"Are you referring to the upper and lower mantle? The difference is mineralogical. The upper mantle contains olivine, pyroxene, and +/- garnet, spinel. The lower mantle contains denser phases- bridgemanite, ferropericlase, Ca-perovskite. The lower and upper mantle are roughly the same composition, but the tremendous pressure at lower mantle depths forms different minerals."
] |
[
"The Earth's mantle is complex in structure. Very little is liquid, most of it is solid rock (though under significant pressure and heat, so it flows like hot plastic or gum). Melting requires specific conditions (typically decompression near mid-ocean ridge spreading or hydration melting near subduction zones... plus abnormally hot areas that we can't fully explain but may be plumes of hot mantle rock from the core boundary like Hawaii). Even when it does melt, it's usually only like 1-30% of the rock melting, because some mineral phases are less stable than others.",
"Here's a brief overview of the mantle structure (from second year Igneous Petrology; source is JD Winter (2010) Principles of Igneous Petrology)",
"Evidence for this comes from a few key places. Direct evidence of the composition comes from xenoliths, which are chunks of the mantle that are ripped up during certain types of volcanic events (one common one forms kimberlite pipes, which are a major source of diamonds) and included in eruptions. Variations in the geochemistry of different types of oceanic igneous rocks (which are melts of the mantle) tell us that mantle sources can widely vary in isotopic and trace element compositions, leading to the conclusions about heterogeneity.",
"However, some of the best evidence is the coolest: seismic profiles of the Earth. By setting off explosions and monitoring earthquakes, geophysicists can look at how seismic waves are refracted through the crust. This gives us some excellent evidence for things like the Moho (which has a dip in seismic velocity that is typically associated with higher liquid content), the change in mineralogy (which comes with an increase in seismic velocity associated with an increase in density due to tighter packing of the mineral structures), and that it is solid (because s-waves don't propagate in liquids, and we see direct s-wave paths throughout the mantle). This also tells us that the outer core is liquid and the inner core exists and is solid (because of the s-wave patterns). ",
"In short, the mantle is complex and heterogenous because of chemical differentiation during melting to form the crust, the inclusion of subducted surface material, and pressure/temperature differences within the mantle. It is, essentially, a solid except in some localized places where it may be 1-30% liquid."
] |
[
"Well I’ve just been informed that it’s different minerals contained in the upper and lower mantle. So that would mean that it’s mostly solid with some areas being more liquidity like gum right?"
] |
[
"Why is fiberglass safe vs asbestos?"
] |
[
false
] |
They're both made of tiny fibers. What is the difference between them?
|
[
"First of all, the premise of the question is wrong: fiberglass is not safe, especially if it is made out of exceedingly thin fibers. Inhalation of fine fiberglass dust will probably lead to silicosis and other unpleasant health effects.",
"The difference in harmfulness between fiberglass and asbestos is due to the different chemical composition and the ease of forming ultrathin, fine airborn dust. Asbestos is a mineral that naturally separates into fine, fragile fibers. Fiberglass is produced by drawing glass fibers out of a melt. They are much thicker and much less fragile than asbestos."
] |
[
"Fiber glass is not safe. A mask and gloves are recommended when handling, and cutting materials with fiberglass in it produces lots of dangerous particles. ",
"Asbestos is most dangerous when it is ",
"friable",
", or easily crumbled by hand, releasing lots of particles. It also causes cancer somehow. Fiberglass probably ",
"causes cancer",
" too.",
"Fiberglass fibers are typically ",
"5-25 micrometers ",
", while asbestos fibers can be ",
"180A to 300A",
". A angstrom (A) is 1/10,000 th of a micrometer. Therefore an asbestos fiber is 166 to 1,390 times smaller than a glass fiber. I think this is why asbestos is so much worse. I am way out of my depth here, but I think the smaller fibers do way more damage per fiber than the larger ones. ",
"This is with the numbers I managed to find, but there are many different types of fiberglass and asbestos. Also, if anyone finds any mistakes, let me know. "
] |
[
"The jury is still out but the idea is that fiberglass particles are small enough to get in your lungs and cause lacerations but asbestos particles may be small enough to lacerate individual cells and lead to cancer. "
] |
[
"Do prescription pills/medications really expire on the date said on the bottle?"
] |
[
false
] |
Or is it just a scam to keep pharmaceutical companies turning more profits from people throwing medicines away on the expiration date?
|
[
"Also: toxic metabolites may form in certain medications that can/will be toxic."
] |
[
"It is definitely not a scam, over time the chemicals that make up the pill/medicine will degrade. How long it takes the medication to degrade will entirely depend on what medication it is, as some compounds will be more stable than others. ",
"Of course this isn't a black and white issue, it's not as if the day the expiration date rolls around the entire bottle of medication instantly degrades and becomes unusable. That being said, if you medication has expired its probably always best to dispose of it properly and then replace it. "
] |
[
"This depends heavily on the drug. The expiration period is determined by measuring various attributes of the drug over time. Once they are outside of certain limits, the drug is deemed unsafe or ineffective and it thus \"expires\". ",
"Keep in mind that the medication you are taking is chemical that is interacting with it's environment all the time. Light, temperature, moisture, and vibrations can all cause degradation in the product. ",
"For more information, here is the ICH guideline for stability testing: \n",
"http://www.fda.gov/downloads/regulatoryinformation/guidances/ucm128204.pdf"
] |
[
"Is there a geometric shape whose circumference grows as fast as its volume?"
] |
[
false
] | null |
[
"I don't understand what you mean. Grows with respect to what? Also, since circumference and volume have different units, their rates of change also have different units. So those rates are not directly comparable."
] |
[
"I know that the circumference of a circle grows slower than the volume, when the radius is increasing.\nSo I asked myself, how the geometric shape would look like, where the circumference grows as fast as the volume."
] |
[
"See my response below."
] |
[
"Is it possible to remember being born?"
] |
[
false
] |
[deleted]
|
[
"No. \nEpisodic memory starts around 2 years after your birth. Mostly due to the fact that you brain undergoes lots of change that, basically continously reformating, before settling.\nPoor wording, feel free to correct me."
] |
[
"This question is currently impossible to answer, as we do not have any way of directly analyzing the mental experiences of animals. There has been a lot of interesting research in the last 15 years or so on whether animals have episodic memory, largely focused on whether animals can recall what, where, and when an episode took place (referred to as \"WWW\" memory or \"episodic-like\"). However, this cannot answer whether animals have autonoetic awareness (the ability to place themselves mentally in the past, present, or future). ",
"In short, we cannot actually answer whether animals consciously recollect any episode, let alone something as specific as their birth."
] |
[
"If it starts \"around\" two years, is it possible that some people have anomalous development, that are outliers in the dataset if you will, that do retain even small amounts of memory from before that time, just as I imagine there are those that develop significantly later because of some condition or another?"
] |
[
"Did Felix Baumgartner break the sound barrier and experience a sonic boom?"
] |
[
false
] |
The press conference said preliminary results indicate he was travelling at Mach 1.24. Obviously, this is faster than the speed of sound, but was there a noticeable sonic boom? Would he know he was travelling faster than sound? I understand that at such high altitudes the pressure it much less, but what effect would this have had on him exceeding Mach 1?
|
[
"The Mach number is almost always reported relative to ambient conditions (I say ",
" always because sometimes you hear about the Shuttle orbiting at about Mach 25, and there isn't a defined speed of sound up there). This means that Baumgartner was travelling above the local speed of sound. This is really the only relevant one. All the aerodynamic effects that happen around Mach 1 are a result of the local speed of sound, rather than some defined speed.",
"As for how he reached Mach 1.24... well, he must have gone faster than their speedometer showed on the live feed. If 740 MPH is Mach 1.24, that corresponds to an air temperature of 176 K or 100 degrees below 0 Celsius. That said, at 40,000 m, the speed of sound should be (per Standard Atmosphere) about 710 MPH.",
"(And I apologize to everyone for mixing SI and English units... I'm betting there'll be some conversion errors in there.)"
] |
[
"The speed of sound is actually slower at higher altitudes than it is at sea level. Wikipedia shows it doesn't decrease monotonically as you go up, though. ",
"http://en.wikipedia.org/wiki/Speed_of_sound#Altitude_variation_and_implications_for_atmospheric_acoustics",
"At higher altitudes the density of air is less, which drastically reduces the drag as he falls to earth. This is why he was able to reach a terminal velocity over 700 mph, while normal sky divers reach a terminal velocity around 150."
] |
[
"To piggy back on this, Mach 1 is ~761 at sea level and 59 degrees F. Are they calculating Mach 1 for his specific position and wouldn't that require a higher velocity due to to much thinner air? I don't recall the live readout getting over ~740 MPH during the free fall."
] |
[
"What is the medical consensus of vaccinating while presenting COVID-19 or similar viral symptoms?"
] |
[
false
] |
I couldn't find any factual information about that specific instance. Is that being contraindicated in some way? Is it relevant at all? Are there any potential hazards in doing so?
|
[
"Also, you would put others at the vaccine clinic—both staff and other patients—at risk by coming in while symptomatic."
] |
[
"You should not get the vaccine if you are currently infected with Covid-19 or any other current infection. ",
"Depending on the country your in, it's at least ",
"strongly advised",
" to wait until you are fully recovered or you won't even be able to get the vaccination. In Germany for instance, you have to wait 6 weeks after you have recovered from Covid.",
"It's not necessarily dangerous to get the vaccine while being sick with Covid or another viral disease, but it would be a waste of vaccine. Your immune system is already busy with fighting your current infection and you won't be able to build a proper immunisation from the vaccine."
] |
[
"Thanks a lot to you and the community for this vital information. Very much appreciated."
] |
[
"How do your eyes prevent shaking while you're walking?"
] |
[
false
] |
I've paid close attention to how some camera's now use OIS, or optical image stabilization, and EIS, or Electronic image stabilization and I was wondering why my vision isn't shaking while I'm walking. Is it some physical thing near my eyes stabilizing what I see or is that handled by the brain?
|
[
"It is a little of both. ",
"The eyes are able to keep focused on a single point in space despite movement of the head thanks to something called the ",
"vestibular-ocular reflex",
" (VOR). Basically the movement-sensitive parts of the inner ear connect to the eye muscles through a rapid pathway that rotates and translates the eye to compensate for these movements.",
"There is also a ",
"neural component",
". By comparing the retinal position of objects across time (called \"optic flow\") the brain is able to correct for head movements larger than what the VOR can handle. "
] |
[
"I've always been fascinated by this. I've read that it is the fastest reflex in the human body. ",
"To get an idea of just how impressive it can be, stand in front of a mirror and look yourself in the eyes. Now move your body, rotate your head, move in any way you can think of but keep looking into your own eyes. It is really impressive that no matter how your body and head move, your eyes stay locked on!"
] |
[
"There are animals that cannot move their eyes, so of course they lack the reflex, and some vertebrates have vestigial eyes and so may lack the reflex. However, it seems to be shared by even the most ",
"primitive vertebrates",
". If any vertebrates lack it, that is because they lost if later on for whatever reason. ",
"I can't find any vertebrate species with functional eyes that normally lacks a VOR (some humans lose it due to disease but I don't think that is what you mean). Some animals can compensate for movement even ",
"without a VOR",
", but that is under conditions where the vestibular system is not available."
] |
[
"Is there a particular reason why there are few islands in the Arctic Ocean?"
] |
[
false
] |
I was surprised that the most northerly island was just off the coast of Greenland. This seems quite a large area to have no islands at all, especially given that the Arctic Ocean is the shallowest ocean. Is it related to plate tectonics?
|
[
"The short answer is that it has to do with the way plate tectonics force continental basalt, which is the stuff that forms terrestrial topography like islands and continents, away from divergent boundaries in the ocean floor. Look at ",
"this diagram of global continental geology",
", and imagine a soup slowly broiling in a wide pan, with a foamy skin forming on the top. The skin is the earth's crust, and the foam is continental basalt. The hot soup rising underneath, the magma, pushes the skin away from the areas where it is rising to the surface, forming new skin. This process pushes the foam into concentrated areas, while the new areas of skin have no foam at all.",
"Of course, this is overly simplistic, but I hope it was a helpful analogy.",
"Edit: There are also anomalies in the magma system, called \"hot spots,\" which punch though the skin to form island volcanoes, like Hawaii and many of the Pacific island chains. As the crust slowly moves, these hot spots remain stationary, so over millions of years they punch new holes and create new island volcanoes which stretch out like a line in the opposite direction to the movement of the crust. That's why Hawaii's islands seem to be ",
"arranged in a row",
", with the older ones made smaller by erosion over time.",
"This happens more in the pacific because that area of the crust has very wide areas with no divergent boundaries, which would normally release the pressure of rising magma. Instead it tends to burst through as volcanoes in these areas, forming islands."
] |
[
"Well yes, the reasons are unknown. Pressure differential is one theory."
] |
[
"100% with you until that last paragraph. It’s perhaps influenced slightly by the much shorter length of spreading ridges overall in the Pacific, but at the heart of it is the upwelling of various mantle plumes underneath the Pacific basin. For reasons unknown, the Pacific basin has seen more of this kind of action than the Atlantic, the Cretaceous was a particularly active geological period for it."
] |
[
"What would happen to Jupiter if it moved gradually closer to the sun? Could it survive at a distance as close as Mercury?"
] |
[
false
] | null |
[
"Hi Urisk, ",
"What would happen to Jupiter if it moved gradually closer to the sun? ",
"It would completely disrupt the inner solar system. The planets Mercury to Mars and the objects of the asteroid belt would be ejected from the solar system, shot into the sun or flung into highly eccentrical orbits at a minimum. ",
"Could it survive at a distance as close as Mercury? ",
"Sure. There is a whole bunch of massive (exo)planets, orbiting their host stars very closely. They are called ",
"hot Jupiters",
" and their orbits range roughly from 0.015 to 0.5 AU. As a comparison, Mercury has a semi-major axis (average distance to the sun) of 0.387 AU. "
] |
[
"Would certain gases burn off changing the actual planet?",
"No, not really. Jupiter atmosphere is almost completely made of hydrogen and helium, with trace amounts of other gases and elements. Due to the lack of strong oxidizers nothing will actually burn as it comes closer to the sun, but of vourse will heat up. ",
"This may cause the appearance of the upper atmosphere to change, but the overall composition isn't strongly influenced. The heat will also cause the planet to expand slightly if it is at the distance of Mercury. To be significantly bigger than it is now, it would have to be even closer to the sun. ",
"A great comparison is the largest known exoplanet ",
"TrES-4b",
", which is less massive than Jupiter, but gets its huge size from the heat of the nearby star. "
] |
[
"there is a theory known as \"grand tack\" which holds that in the first 10-15 million years of the solar system, jupiter roamed around the inner orbits and gobbled a previous generation of planets. hope it stays where it is, at least for the rest of my life. "
] |
[
"Car engines: Why aren't there 2.0L V4 or 6.0L straight-12?"
] |
[
false
] | null |
[
"Because a 6.0L straight-12 would be gigantic, and there are some V4 motorcycles, but they are not 2.0L.",
"There are not 2.0L V4 car engines because, in general, 2.0L in line-4 engines get more power. V4s are more compact, but a car has to be so big in order to even work; you don't need that compactness. This is why there are motorcycles with V4s to make them skinnier and center the mass better."
] |
[
"I'm batgirl!"
] |
[
"Stem cell research by day, muscle car mechanic by night! (I couldn't resist)"
] |
[
"Does it matter which side of aluminium(aluminum) foil is facing food while cooking for better heating?"
] |
[
false
] |
I remember a science teacher once telling me that the dull side out will help keep more heat directed towards the food. But then I was looking at wikipedia and it states that it doesn't make enough of a difference with reflectivity being 88% for shiny side and 80% for dull side. It sited the Reynold's website for this, but 8% seems like a lot to me, especially if I was cooking something like a roast that takes hours to cook. Would it make much of a difference?
|
[
"A lot of heat gets to your food via conduction and convection, rather than radiant transfer. So, some amount of radiant heat is reflected by the foil, but the air inside the oven and the pan the roast is sitting in will both transfer heat to the inside of the foil regardless."
] |
[
"8% seems like a lot, but I suspect that figure is the difference in reflectivity of visible light.. if the material was isoreflective across the whole spectrum and radiative heat transfer was the only mechanism for heating then yes this might be a problem. However, tinfoil probably absorbs and reflects different wavelengths variously, and radiant heat transfer is not the only method of heating, as 'i_invinted_the_ipod' has said."
] |
[
"That's a good point. I didn't think it might mean only for visible light. I suppose by going with what you and i_invented_the_ipod say that because of the other types of heating going on it would only make a difference in the beginning until the temps had a chance to normalize throughout. I wish I had two roasting pans and meat thermometers. Maybe I could make some sort of delicious experiment out of this."
] |
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