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[
"If life exists elsewhere in the universe, how similar should we expect its biochemistry to be to our own?"
] |
[
false
] | null |
[
"It's really hard to say, as we only have one data point to work off.",
"I'd wager most astrobiologists agree that the ",
" of life must be similar- that any kind of life must have some sort of genetic inheritance, some sort of metabolism, and some sort of compartmentalisation (to name a few). There are exceptions to this, however; for example adherents of ",
"autopoiesis",
" reckon that the genetic material may be optional.",
"As for the biochemistry: as ",
"/u/Callous1970",
" pointed out, many of the materials that are central to our biochemistry seem to be ubiquitous: amino acids, nucleobases, lipids. That doesn't rule out alternative biochemistries, however. Most immediately, the specific choice of the core amino acids, nucleobases, and lipids isn't obviously optimal or predetermined: many non-biological molecules in these groups are found under prebiotic conditions. On the face of it, there's no reason why other biologies could not have ended up with different sets of amino acids, lipids, and so on. Why not ",
"PNA",
"-based life? And of course, even if life shared our biochemistry, on the face of it there'd seem to be no good reason why it might not be enantiomeric to us (using D-amino acids and L-sugars).",
"This is especially compelling when you consider that at least some core parts of our biochemistry - big chunks of the genetic code, numerous amino acids, phospholipids at least one nucleobase, and probably DNA itself - are likely to be later evolutionary inventions rather than being determined at the origin of life. We know a lot more about the role of contingency in evolution than we do in abiogenesis, so it seems fair to say that if we ran the tape again, a good chunk of our biochemistry would be different.",
"There's a school of thought that some or all of the reactions that led to the selection of our biochemistry are ",
"predisposed",
" - meaning that, owing to the stability of the products or efficiency of the reactions, these products ",
" to form and are disproportionately likely to be used by incipient life forms. One simple but intriguing illustration of this concerns homochirality: on the face of it, there's no reason to believe that L-amino acids would be favoured over D-amino acids (or D over L sugars). And indeed there are several mechanisms (most notably the ",
"Soai reaction",
") which can conceivably get us from a racemic world to a homochiral world. However, owing to ",
"chiral physical forces",
" in the universe, when we look at the chirality of materials on, say, comets, we find a bias towards L-amino acids. Blackmondin particular has done some creative and brilliant work showing how a very small bias towards one enantiomer can give rise to enantiomerically-enriched solutions, and how this chirality can be transferred between amino acids and sugars or ",
"can influence the synthesis of RNA",
". ",
"On this view (which I'm not saying Blackmond endorses), a great deal of our biochemistry is very favourable - the choice of amino acids and nucleotides, the particular enantiomers of those species, and so on - and might well be found elsewhere.",
"My own view, tentatively, is that the choice of amino acids and nucleotides is based on sound reasons, though the particular monomers involved I'd guess is a matter of contingency. There are good reasons for the development of very diverse, phospholipid-based lipid membranes, but the particular compositions will certainly be an evolved feature and hence contingent. And there's no way arsenic is in any polynucleotide backbones."
] |
[
"Answers like these always amaze me. I mean I didn't understand anything when you started to use these technical terms but I still understood more or less what you wanted to say and it amazes me that people know so much about stuff like this that they can write almost 4000 characters about it. ",
"OTOH I really like the thought behind this question. My (layman) view on it is that it is rather unlikely to find life that is similar to Earth life just due to the thousands upon thousands of possibilities and different circumstances under which life could conceivably develop which makes it unlikely that it would be similar ( but then again I know near to nothing advanced about biology or that stuff to argue with you x) )"
] |
[
"There's a lot less life than people imagine. You might think people and zebras are different but you'd be a long way off the mark. ",
"There's only a few types of different of life.",
"Even these all use CHON as their base. Carbon, Hydrogen, Oxygen and Nitrogen are abundant throughout the universe and formed earlier in a stars life. I would bet that it's always the go-to combination for life everywhere."
] |
[
"Deep ocean pressure and shipwrecks"
] |
[
false
] |
got me thinking about this, because it says the pressure at 4-500m would push a champagne cork into the bottle. Usually Randall is spot on with these sort of things, but if it's true how can a press release like , apparently from a reputable company that deals in ultra rare wines, be real?
|
[
"The wine collector is referring to wines of the same ",
" that were on the Titanic, not actual Titanic wine bottles. The xkcd comic is in fact referring to a full champagne bottle."
] |
[
"Hmm...didn't see that caveat in the press release. Do you know of another source?"
] |
[
"FTA: ",
"The wines are considered way past their used by date, however it is not beyond the realms of possibilities that the buyer may sneak an opening of one of the 6 bottles to really see if the wine is beyond drinking."
] |
[
"What is heat, and what is happening during heat transfer?"
] |
[
false
] |
I've read wikipedia and other sources, but I'd like it explained by AskScience, as their explanations seem to be easier to understand and include more current understanding by the science community. My current understanding is that 'heat' is kinetic energy at an atomic level. A way to understand it is to think of an atom as vibrating in place, or in the case of a gas, literally moving through space. The faster it moves/vibrates through space, the 'hotter' it is. When I pour hot coffee into a cold glass of water, what is happening? Is it true that heat cannot be conducted across a vacuum?
|
[
"Conduction occurs in solids and liquids, and theoretically in gases, although the mean free path of gas molecules is so large as to make conduction in gases largely indistinguishable from convection. In conduction, the kinetic energy of molecules in direct contact with one another is transferred through collisions or bonding forces. For example, you heat a block of aluminum, the surface particles start to vibrate, and in doing so, they transfer some of that kinetic energy to their neighbours, making the neighbouring particles vibrate while losing energy themselves. As long as you continue to apply heat to the surface (excite the surface molecules), that transfer will continue and heat will penetrate into the material. Only when there is no differential in kinetic energies (i.e. neighbouring molecules already vibrating at the same speed) does heat flow stop.",
"Convection occurs through the bulk movement of heated fluid, so only in liquids and gases. An example would be the air in immediate contact with the heated aluminum surface. Energy is transferred from the energetic aluminum to the immediately adjacent air molecules by conduction. As a result of the increased kinetic energy, the air in the conduction region at the aluminum surface becomes less dense as collisions force the oxygen and nitrogen molecules further apart, and this heated gas is displaced by denser, cooler air (buoyant force) from the environment. The rising hot air carries with it heat that may be subsequently transferred again. Meanwhile, the new cool air in contact with the aluminum is heated, and the process continues, carrying heat away from the aluminum until there is no differential - i.e. until the aluminum is at the same temperature as the surrounding air. This is referred to as natural convection. You can also have forced convection, where instead of relying on buoyant forces to cause the bulk air movement you move air artificially, using a fan or something. This is a much more efficient way of removing heat than natural convection, and is how the heat sink and fan in a PC removes heat from the CPU.",
"Finally, you have radiation (radiative heat transfer, distinct from particle radiation). In contrast to the first two methods, radiation does not require a medium, as instead of transferring energy through particle collisions, radiation transfers energy directly through space. As long as there is a temperature differential between two objects, energy will be radiated from the hot one to the cool one. An easy way to see this in action is to notice how the air on an evening with significant cloud cover can be significantly warmer than that on a completely clear night - the difference is that the cloud both reflects heat and prevents radiative heat loss to space. On a clear night, the cool blackness of space is an ideal heat sink for radiative heat loss. Similarly, have you ever stood close to a raging campfire and felt the heat coming off it? That heat is not conducting through the air to you, nor convecting (it is convecting, but generally straight up into the atmosphere). What you feel is the radiative heat. This is also why heat rejection from spacecraft is so difficult, because without the ability to conduct or convect heat away, radiation is the only mechanism that can be used for cooling."
] |
[
"although the mean free path of gas molecules is so large as to make conduction in gases largely indistinguishable from convection. ",
"Eh? The mean free path of a gas molecule at STP is minuscule. Did you mean something else?",
"(Otherwise, a very nice explanation of heat transfer mechanisms.)"
] |
[
"Yes, sorry. I meant that convection (bulk fluid movement) in a gas space dominates heat transfer, as compared to pure conduction through a gas, as one might measure in the absence of gravity."
] |
[
"AskScience Cosmos Q&A thread. Episode 11: The Immortals"
] |
[
false
] |
Welcome to AskScience! If you are outside of the US or Canada, you may only now be seeing the tenth episode aired on television. If so, This week is the eleventh episode, "The Immortals". The show is airing in the US and Canada on Fox at Sunday 9pm ET, and Monday at 10pm ET on National Geographic. Anyone can ask a question, but Popular science shows, books, and news articles are a great way to causally learn about your universe, but they often contain a lot of simplifications and approximations, so don't assume that because you've heard an answer before that it is the right one. If you are interested in general discussion please visit one of the threads elsewhere on reddit that are more appropriate for that, such as , in , in , and in . Please and . We'll be removing comments that break our rules and some questions that have been answered elsewhere in the thread so that we can answer as many questions as possible!
|
[
"Okay, so we're messing up the planet. What can the average middle class person really do about it? Seriously, I would like to know. What could we do that would have the biggest impact?"
] |
[
"Tyson is a natural in this episode. Can anybody provide some sources on the \"asteroid ark\" theory? I don't find it hard to believe that it is ",
", I just want some more in-depth science to back this theory."
] |
[
"There are a whole host of ways that humans are impacting the planet, but for the moment let's just focus on carbon footprint and energy usage. ",
"According to the EPA",
", transportation and electricity generation are the two biggest causes of CO2 emissions. One thing you'll find is that there are a whole lot of actions you can take which will both save you money and reduce your greenhouse emissions. ",
"This EPA page has a list of many ways to reduce your energy usage",
".",
"Biking, walking, public transit, and carpooling are all good ways to considerably reduce the amount of CO2 emissions that you are responsible for, and the first two are also good for your health. For quite a lot of people, there are coworkers who live nearby enough that carpooling makes sense as an option (plus, then you don't have to drive as often and can work or nap in the car). Depending on the length and location of your commute, biking/walking/public transit may also be good options. Also note that airplanes emit a considerable amount of greenhouse gases, so long-distance trips are not without cost. Trains are more energy-efficient (and comfortable), although admittedly slower.",
"When you next buy a car, buy one with good fuel efficiency. It doesn't have to be a hybrid or electric or anything, since those tend to be rather expensive, just a car that gets good mileage. This has the personal financial benefit of costing you substantially less in gas money. The ",
"EPA keeps lists of fuel-efficient cars",
".",
"If you move to a different home, consider how it will impact your energy usage. A location near your work will mean shorter commutes, a location near transit routes can mean less driving. A smaller house will typically have lower energy usage, as will a better-insulated house. Apartments and town houses will often have lower energy costs.",
" ",
"Heating and cooling are the biggest domestic energy uses, so take it easy on the heat and AC. If it gets cool enough at night during the summer, you can open up all the windows of your house at night and then close them (and the shades) in the morning and the house will stay cool through much of the day. In the winter, turn the heat down and use it as an excuse to wear pajama pants and slippers all the time. And of course, turn off the lights when you leave the room (and turn on fewer lights when you're in the room), don't leave computers running when you're not using them, and even unplug electronics entirely when they're not being used--they actually still consume power while plugged in and turned off. Take shorter showers-- many places are running into water scarcity issues, and heating the water also costs energy.",
"Just use less stuff. Everything we have and use takes energy to manufacture, and that energy very often comes from burning fossil fuels. Sewing up or patching a piece of clothing rather than buying a new one, reusing your grocery bags, etc., recycle your recyclables (aluminum production is very energy-intensive), these all reduce your carbon footprint. Take your leftovers home from restaurants instead of just throwing out perfectly good food.",
"Eat less meat. Food animals such as cows have a pretty considerable carbon impact. Clearing land for growing animals and crops is also a major source of habitat destruction in the Amazon and elsewhere, which lessens the planet's ability to absorb all the carbon dioxide that we're producing. ",
"Buy food that is grown in your region. It doesn't have to be from the farm three miles away, but something that can be grown in your area in season will have lower energy costs than buying produce out of season. Buying strawberries in November means that they've probably been imported from Chile or elsewhere, and those large container ships burn through an enormous amount of fuel. Farmers markets are becoming quite common and they tend to have quite delicious fresh food.",
"Grow your own food! During WWII, the \"Victory Garden\" initiative resulted in approximately 1/3 of the vegetables grown in the US being grown in peoples' own gardens. If you have any yard space, you can easily grow your own fruits and vegetables. Chicken-keeping is also growing in popularity. Growing your own food is generally cheaper than buying it, and having extremely fresh food is very nice. Even if you don't have a huge yard, you can put in some planters and grow some veggies. Here's a pretty good guide on ",
"starting a home garden",
".",
"Seriously, they actually do take note when a large number of their constituents are bothering them about an issue. They have the ability to institute better fuel efficiency standards and environmental protections, so you should let them know that their voters consider the environment important."
] |
[
"Frost Wedging in the Grand Canyon?"
] |
[
false
] |
I know I saw a couple of documentaries (one was on the BBC, and the other National Geographic) which mentioned that the Grand Canyon got it's shape due to a freeze and thaw form of frost wedging which causes sections of rock to break away. I can't, however, seem to find references online which back that up. Did I imagine it?
|
[
"Perhaps you're thinking of Bryce Canyon? ",
"This link",
" says that it's the most important form of erosion at Bryce: ",
"Snow in the winter melts a little every day and flows into joints. At night it freezes and expands, breaking the rock into smaller pieces. This is called frost wedging. Bryce Canyon experiences over 200 days of freeze/ thaw during the year. The frequency of frost wedging in this region makes it the most important type of weathering at Bryce Canyon. ",
"Generally, the freeze/thaw cycle drives the sculpting of pillar-like formations (called ",
"hoodoos",
"), so it is likely an active process in the Grand Canyon as well."
] |
[
"The Grand Canyon got it shape due to the Colorado River flowing past the ",
"Kaibab Plateau",
" as it lifted up. While the rims of the Grand Canyon have a fairly high elevation (the north rim being a bit higher), overall the Grand Canyon does not experience a ton of freezing weather once you get down into the canyon a bit whereas the amount of rain (particularly during late summer -- monsoon season) can be fairly significant.",
"As mentioned in other posts, some of the canyonland's parks (like Arches, Bryce etc...) where you see natural arches (not bridges -- natural bridges span water, arches do not) the primary cause of erosion is the slow wedging action of water/ice. Much of these areas are also at a higher elevation. 4-5000 ft for ",
"Arches",
", and 8-9000 ft at the rim for ",
"Bryce Canyon",
".",
"While that doesn't prove anything one way or another for the wedging, I'm guessing that maybe the documentary that you saw may have listed freeze/thaw cycle as one of the erosion methods -- much like it is many places in the world.",
"From ",
"National Geographic Education",
"\"Ask students if they can find the Colorado River at the bottom of the canyon in this photograph. Explain that over several million years, this river eroded the rock layers and made it possible for us to see them. The river once flowed at the top layer but now flows where we see it today.\""
] |
[
"overall the Grand Canyon does not experience a ton of freezing weather",
"Freezing weather is ",
"quite common at the rim of the canyon",
" (around 7000 ft, 2200 m elevation); the average low temperature is below freezing six months out of the year! Even assuming that the canyon floor (around 2500 ft, 750 m) is 10 C (18F) warmer (which would be expected given a 1500m elevation change and a lapse rate of 6C/km), the average low temperature December-February would still be near freezing, meaning there are probably dozens of freezing nights per winter even at the canyon floor.",
"I'm not saying you're wrong, the Colorado River is clearly the main formative force, but frost wedging should definitely not be discounted. I wouldn't be surprised if it were a major factor in modern-day erosion in the upper half of the canyon."
] |
[
"Does the speed of light have any special meaning? Why is it the speed that it is? Is the scalar value of the velocity (disregarding units) unique somehow?"
] |
[
false
] |
[deleted]
|
[
"It's the scale at which one unit of distance equals one unit of time. Imagine we measured horizontal distances in leagues and vertical distances in fathoms. We would need a conversion scale to tell us how many fathoms were in a league (~3038 or so). Well c is the scale that tells us how many seconds a meter is and how many meters a second is."
] |
[
"yeah, the units aren't important. It doesn't matter if it's meters and seconds, or furlongs and fortnights. The value, the number itself will change depending on which units you use, but at the end of the day it's always the ratio between equal units of space and time."
] |
[
"yeah, the units aren't important. It doesn't matter if it's meters and seconds, or furlongs and fortnights. The value, the number itself will change depending on which units you use, but at the end of the day it's always the ratio between equal units of space and time."
] |
[
"How much would the average human life expectancy increase if we developed cures for all cancers?"
] |
[
false
] |
Let's suppose that we find something that does for cancer what penicillin and vaccines did for infectious diseases. Edit: It just occured to me that the answer to my question might be the same as the answer to the question "how much higher is the average life expectancy of people who don't die of cancer than the life expectancy of the general population?"
|
[
"It would take pretty intensive statistical work to accurately guess the effect this might have. ",
"Cancers affect different populations of people, curing one cancer might add an average of 70 years to a lifespan, where another type might add at best 1 year (think cancers caused by immunodeficiency like HIV, cure the cancer they still die in year). Figuring out what kills these people now isn't that difficult we can just look at the top killers, but we have to go by age group; how many kids that are cured of childhood cancer would die a few years later for some other cause?",
"you could look at some of the more common cancers, say breast cancer or prostate cancer and these cancers hit people in their late 40s - 60s most commonly; and total cancer incidence peaks at around 75 years of age. ",
"While I don't know for certain I would have to guess that by this age a percentage of mortality is a result of other age related disease processes, and people die of things like COPD and heart disease before cancer gets to them, so after 75 cancer incidence decreases as a result of a declining population. Even without cancer the human body deteriorates with age, heart, lung, kidney, function all decline... your brain decreases in size all this stuff starts to add up, for most people right around the time cancer strikes.",
"If I had to wager I'd say it adds 5-10 years to life expectancy, proabably more in the middle of that.",
"In any event lets just say we cured all that other disease too and peolpe live till their organs can no longer function; from my understanding the lungs run out of gas first and their function deteriorates to the point where it can no longer sustain life at about 150 years ",
"http://ars.els-cdn.com/content/image/1-s2.0-S0165614798012450-gr4.gif",
" this is a graph of basic lung function type test, sadly it isn't extrapolated out all the way but you will see the normal lung is going to cross the death line at about 150years."
] |
[
"Interesting, I didn't know that about the lungs. "
] |
[
"It would increase average lifespan, but probably not ",
" lifespan, which might be more what you're really wanting to know. There is an oddity in the graph of cancer incidence vs. age, where it peaks in the 70s or 80s, but then goes back down again. That suggests that people who live to 100 or whatever have something that's protecting them to some degree against getting cancer as much as you might expect. A lot of the world's longest-lived people didn't die of cancer, but of something else. "
] |
[
"Why do volcanoes keep erupting after the initial 'burst'?"
] |
[
false
] |
I've always thought of them as a pimple on the surface of the earth...once the pressure is released, it just kind of oozes. But watching the video from Kilauea, it seems to still be erupting relatively violently
|
[
"Volcanoes are fed by magma plumbing systems, and there's various ways of forming that magma. HOwever, basically it's about generating melt in the very upper bit of the mantle, that can then pool against the base of the crust and eventually make its way up to the surface. The way it does that is by exerting tensile stresses on the rock above; basically the magma is buoyant, higher volume than its solid equivalent, and therefore pushing up and out. Eventually it will form fractures through which it can travel.",
"As it passes up through the crust it will often end up sat in particular regions for a while before it builds up the stresses necessary to travel up further. AS it sits there it can assimilate crustal rocks around it, and it canstart to cool and crystallise which changes the chemistry of the magma that remains liquid. These processes build up the concentrations of volatile components like carbon dioxide, sulphur oxides, water, etc. These storage areas are known as magma reservoirs, and they can be big - cubic kilometers without much trouble at all. And a volcano may have ",
"several different levels of magma storage on its plumbing system",
"Now, Hawaii is unusual in that it's a hotspot volcano so is sat on relatively thing oceanic crust. That means there's not quite as much opportunity for storage systems to build, but they're still there. ",
".",
"The Hawaii storage system is intersting: \n",
"https://ars.els-cdn.com/content/image/1-s2.0-S0016703713003256-gr9.jpg",
"Basically it's quite shallow, and it's quite broad. That means if you tap it from the side you can drain large volumes out of it. It also has a decent amount of volatiles in it, so once the eruption starts and the pressure in the system drops, these gases start coming out of solution, expanding, maintaining the pressure and driving the eruption further - it's like keeping a constant pressure on a syringe; more magma gets squeezed out. This means it can erupt for long durations",
"You have to also consider the volumes involved. The Hawaii magma reservoir is on the order of cubic kilometers volume. We've seen a few hundred thousand cubic meters of lava erupted."
] |
[
"It's not clear whether you meant that it is water or a mantle plume that exclusively keeps a volcano active long term, but neither is true. ",
"Magma plumes feed some volcanoes yes, though many more are related to seafloor spreading or subduction processes, which can also be active for many millions of years. In fact, seafloor volcanism at ocean ridges not only accounts for the vast majority of volcanism on Earth, but is the most continuous and long lived in terms of eruptions. Typical lifetime of a spreading ridge seems to be around 200-300 million years; the volcanism from the Hawaii hot spot is about 80 million years old. ",
"Also, the water which has caused a few explosive eruptions at Kilauea recently has been regular groundwater rather than anything held in the magma solution due to immense pressure. It has been due to the falling lava lake which descended below the water table, allowing water to run on to the top of the lava column and create steam-driven blasts. You seem to have described the situation more typical of subduction zone volcanism, in which water and other volatiles are a part of the magma when it is first generated in the mantle, which contributes to explosive eruptions upon rising through the crust and decompressing. "
] |
[
"To add a caveat to the thread, Kilauea is a hotspot volcano which behaves differently and has a different structure compared to a classic volcano that form along actual fault lines, like subduction faults for example. "
] |
[
"How does the presence of a cell wall impact endocytic activity in fungi and plant cells?"
] |
[
false
] |
[deleted]
|
[
"No the question is perfectly clear and they meant endocytosis. OP is wondering how a cell can effectively endocytose when there is a physical barrier on the outside of its plasma membrane. This would be in contrast to amoebae or animal cells like macrophages that aren't surrounded by a cell wall."
] |
[
"Ok, plants don't generally endocytose, but you didn't actually explain ",
" pinocytosis works in the presence of a cell wall, you only stated that it ",
" work and ",
" that's important, so OP's question still is unanswered."
] |
[
"Oh, correct... Brain didn't click on the word :(",
"In that case the response would be ",
". It is said to be more difficult, because of the pressure I talked about in the parent comment, but I don't really agree with this interpretation, to be honest. As said before, plasmodesma means that the cells have other ways to communicate and pass big proteins to one another, so endocytosis is just not needed as much.",
"Phagocytosis is typically absent in plants, but smaller examples (pinocytosis) are observed and work just fine in plants. One important role of endocytosis is to regulate the membrane surface by absorbing some of it (exocytosis having the opposite effect, it adds molecules to the membrane). Plants heavily rely on exocytosis to create the cell wall, so they ",
" a the oppsite mechanism to work. The machinery is there and is able to perform with the same reactivity as in an animal. when triggered with the right signaling molecules."
] |
[
"What are the source of electrons when generating energy via turbines (steam, wind, etc.)?"
] |
[
false
] |
I understand the concept of electricity generation by a metallic rotor surrounded by a magnet, but I don't understand how electrons are continuously transmitted because I don't understand where they are transmitted from.
|
[
"I find it's easiest to think of electricity in terms of fluid moving through a pipe. The electrons are \"water drops\" that flow around a circuit. The voltage is the pressure differential - think of it as how tilted the pipe is, or how strong the pump at the source is. Current is the mass flow rate of the electrons/water drops. Resistance is the backpressure caused by the pipe diameter: smaller diameter causes higher resistance. This analogy works really well for analogue circuits: capacitance is the \"holding capacity\", and a capacitor is essentially like a holding tank. Inductors are the momentum of the water flow, they cause the current to continue to want to flow even if the pumps are shut off. If you study the equations, they work out to essentially the same math.",
"There is one more thing in the analogy that is really important to understand: both electrical and pipe flow systems must create a ",
", that is, there must be a source or a sink for the system to sustain flow. For electrical circuits, the ground is the source and sink for the flow, and for fluid circuits, it's some sort of large reservoir - such as the sea or aquifers(e.g. \"flows into the groundwater, pumped from a lake fed from precipitation of said groundwater\"). The fact that we don't often think of water being pumped as a circuit is that the \"back end\" of the loop, from seas to rain to reservoirs, happens passively, but it's still there. The water has to come from somewhere.",
"OK, to finally answer your question: this is essentially the same thing that happens with electricity generation. If you have electricity flow from the plant to your house, and your house is grounded (it should be), and the plant is grounded (most definitely), then the circuit is from the plant, through the wires, to your house, ",
". That answers part of your question: the electrons are \"generated\" (really found) from the ground, the wires, everything in the circuit. They were already there, they're just being pumped now. This is true regardless of generation method: the generator is the ",
", and whether you power it with wind or water or steam, it's still just pumping electrons through this sort of circuit.",
"The other half is in understanding that mains electricity is ",
". If it were direct current, it would require the plant to force the electrons out of the ground and down the wire, then pump them back out of the ground, incurring the cost of resistance in the entire circuit, including the ground (or, equivalently, pumping electrons the other direction through the circuit). This is essentially what we have to do with water, though we can count on plants, sunlight, precipitation, and so on in the water cycle to move the water through the back side of the circuit. With electricity, though, there's a better way: alternating current is like the pump switching back and forth. In this view, while the generator drives the voltage low (negative to ground), it's pushing electrons through the wire toward your house and its grounding (recall that the flow of electrons is from negative to positive poles). When the generator drives the voltage high (positive to ground), it's ",
" electrons out of the ground from your house (and all the others on the circuit) and through the wire towards itself. By doing this, we essentially get more efficiency; the further from the plant in a DC setup, the more resistance you see from the ground; with AC, this is essentially not true and the main limiter is line/equipment losses."
] |
[
"They are not so much transmitted from one place to another, they are rather moved around in a loop. The magnets, if you like, provide the force to move them, and the load, whatever that is, provides the resistance."
] |
[
"They don't actually. They mostly move around their initial position. What goes around is the effect. Potential is what moves fast and what goes around. Current is more of a manifestation of this. Both are extremely esoteric concepts. To be frank, at a basic level, we do not understand what current is. People say that it is the movement of electrons because that explains it to a layman. It is however much more complicated."
] |
[
"Can you see the international space station from earth?"
] |
[
false
] | null |
[
"You don't even need a telescope, it's rather bright (about as bright as Venus last time I saw it). You can use ",
"this applet",
" to find when it will next go across your area. It's usually visible for about 3-4 minutes at a time."
] |
[
"Here",
" is another page you can use to find out when it's the best time for you to observe it."
] |
[
"It can be seen as a point of light with the naked eye and a general shape with binoculars, even. ",
"Here's",
" a website that'll tell you when and where to look."
] |
[
"At what point will we be forced to concede that the Higgs doesn't exist? What direction should we expect future research to take if that ends up being the case?"
] |
[
false
] | null |
[
"Kids today, I swear. So impatient. The Z boson was predicted theoretically in 1967; it was detected unambiguously for the first time in 1983. The top quark was predicted in 1973 and not detected until 1995.",
"We've been looking for the Higgs for about fifteen minutes. You can start talking about being \"forced to concede\" around 2060."
] |
[
"The collider hasn't even powered up yet!"
] |
[
"The W and Z were first detected at the Super Proton Synchrotron. It started in 1976 but the W and Z weren't conclusively observed until 1983. This shit takes time. The LHC has been colliding since 2010, but won't go up to full power until 2014."
] |
[
"If a person has been depressed for a long time, is there some kind of 'damage' to their brain, and can anti-depressants reverse the damage?"
] |
[
false
] | null |
[
"I'm a doctor and have done lots of reading in this area so can shed some light. ",
"",
"There is a neuroplasticity hypothesis of depression whereby as a response to stress our brains change at the cellular level in a dysfunctional way. This has been demonstrated by studies in mice, brain imaging and postmortems of depressed patients. Namely these changes are:",
"",
"In the prefrontal cortex and hippocampus. The prefrontal cortex is the part of the brain responsible for higher brain functions such as decision making, planning, concentration and personality development. The hippocampus is key in learning and memory, and has connections to the ventral tegmental area which is important in motivation and reward processes.",
"In the amygdala, which is responsible for the 'fight or flight' response, research has shown that there is actually an increase in synapse formation between neurons which may explain why anxiety is co-morbid with depression.",
"",
"There has been research to show that anti-depressants can reverse the changes seen in the prefrontal cortex and hippocampus. The time it takes for anti-depressants to work is in parallel to the time course for the maladaptive neuroplastic changes to be reversed.",
"",
"TLDR; Yes there are bad changes associated with a depressed persons brain, yes antidepressants have been linked with a reversal to some of them."
] |
[
"Yes, here's an ",
"article",
" that shows how people that are depressed have increased DNA damage markers, inflammatory markers, and oxidative markers in the brain when compared to healthy individuals. Essentially making people that are depressed age faster than those that typically aren't. The study also shows that anti-depressents do decrease all of those markers which is great news. \nCommenting on what others have already said though, the most helpful thing you can do is find a therapist and/or psychiatrist that you can trust and have them help you decide what the best thing is for you. Also, everyone's different and will react to anti-depressents in different ways, but for a large number of people it does help. It helps balance the chemistry out in your brain. Exercise, healthier diets, a bit of trusted and comfortable social interactions will all help tip the scales towards a healthier brain chemistry as well."
] |
[
"Do you know if natural recovery from depression without the use of medication can cause this process to begin reversing as well? I had severe depression for 4 years, and I definitely have felt these effects. It's been 1 year since I have recovered from said depression. If the process does reverse, it's definitely slow enough that it's hard to notice."
] |
[
"I just bought a re-usable toy hand warmer for my son that works by \"clicking\" a small metal clip inside the sachet of clear liquid. The liquid turns opaque in an instant and the sachet becomes warm. How does it work?"
] |
[
false
] |
.. or to be more precise - the sachet is "recharged" by placing it in hot water. Eventually the white crystals dissolve and the liquid returns to it's clear state so the process can be triggered again (up to around 10 times apparently). Is the energy from the hot water somehow being stored in the liquid and then released when the metal clip activates it? and if so, how is it being released and turned into heat again?
|
[
"The sachet is filled with a supersaturated solution of ",
"sodium acetate",
". By clicking the metal clip, you're providing a nucleation site for crystals to form. Since the crystallization of sodium acetate is quite exothermic, heat is released.",
"When you place the sachet under hot water, you're heating the solution up to redissolve those crystals, turning it into a supersaturated solution again. So the energy provided in the water is stored in the form of the dissolved solute - that is, breaking up the lattice energy of the crystals and driving the sodium acetate into solution. This energy is returned when the solute forms crystals."
] |
[
"Probably not a good idea. In addition to possibly being contaminated by whatever was used to create the hand warmer, a super-saturated solution would probably taste terrible and/or be lethal. For example, compare pouring vinegar on a salad with pouring pure acetic acid on a salad."
] |
[
"A supersaturated solution means you're dissolving as much as the water can dissolve - and then some more. So it is very concentrated."
] |
[
"If I have High cholesterol but very low blood pressure, does that mean I don't really have a cholesterol \"problem?\""
] |
[
false
] | null |
[
"Ok, sorry, it didn't even occur to me that medical questions could be construed as advice in the litigious sense... I get it. I will rephrase it so that it is strictly a scientific question."
] |
[
"This has been removed because seeking for ",
"medical advice",
" on ",
"/r/AskScience",
" is against our guideline.",
"Please see our ",
"FAQ."
] |
[
"If I remove the question about lipitor, can it count as a science question? "
] |
[
"What causes that distinctive smell of a person who comes indoors after being outside in cold weather?"
] |
[
false
] | null |
[
"I really misread that for a second..."
] |
[
"I'd like to know this, too. It's kind of a sharp ozone, but much more satisfying."
] |
[
"your brain tumor?"
] |
[
"Does Oxygen therapy increase the risk for ARDS?"
] |
[
false
] |
I seem to remember someone saying in a thread once that giving hospital patients too much oxygen can increase the risk for ARDS, but I can find anything on it.
|
[
"Respiratory Therapist here! According to Egan's \"Fundamentals of Respiratory Care,\" oxygen toxicity is one of the risk factors for ALI (acute lung injury) and ARDS (acute respiratory distress syndrome). There are certainly many other risk factors, such as direct injury to the lung (pneumonia, aspiration, near drowning, or contusions) or indirect, such as systemic sepsis, burns, pancreatitis, etc. ",
"In order for oxygen toxicity to occur and potentially lead to ARDS, a patient must be exposed to very high concentrations of oxygen for extended periods of time, generally greater than 24 to 48 hours at around 100%. ",
"Of course, there is a balance that has to be kept. While oxygen toxicity can be detrimental, the effects are typically not as bad as an anoxic injury (lack of oxygen). So as an RT one of my jobs is to attempt to decrease the amount of oxygen that any patient is receiving while avoiding causing them harm through a lack of O2.",
"Let me know if you have any other questions regarding this!"
] |
[
"According to Egan's again, in 0-12 hours one might experience tracheobronchitis and substernal chest pain. In 12-24 there may be a decrease in vital capacity (the total amount the lungs can inhale exhale at maximum). At 25-30 hours there can be a decrease in compliance (softness/stretchiness of the lung) and an increase in the gradient between the oxygen concentration in the alveoli vs arterial concentration. At 30-72 hours, there is a definite decrease in the capacity of the alveoli to diffuse O2/CO2.",
"We do attempt to avoid this if possible in a healthcare setting. However, there are times when a patient already has some sort of pulmonary issue and 100% oxygen is required for extended periods of time in order to keep the body supplied with the oxygen it requires for basic functioning. While there are other avenues that we can take to improve the patient's lung function, sometimes long exposure to high concentrations of oxygen is required."
] |
[
"As far as I know, there have not been significant studies regarding long-term high levels of oxygen on people who are not on a ventilator.",
"There are people who are prescribed oxygen therapy at home due to lung disease. These are typically people with diseased like chronic obstructive pulmonary disease from smoking. These people need the extra oxygen to achieve normal levels of oxygen in their body.",
"I'd predict if normal people were exposed to chronically higher levels of oxygen, there wouldn't be much change in their body. We know that people who are exposed to chronically lower levels of oxygen develop higher levels of hemoglobin. This is because hemoglobin is the primary carrier of oxygen in the body. Over 99% of the oxygen in your body is typically bound to hemoglobin, and the remaining amount is dissolved directly into the blood.",
"We also know that at sea level, the amount of oxygen at room air (21%) is already enough to keep at least 99% of hemoglobin filled with oxygen in a normal person, so increasing the amount of oxygen to 50% would not produce any significantly improved function."
] |
[
"If gravity is caused by massive objects warping spacetime, then when I hold my pen above the ground, is the force I'm applying with my hand un-warping the pen's spacetime, and that's why it doesn't move?"
] |
[
false
] |
I understand why a traveling object move through space would get pulled towards a massive object since the mass is warping spacetime and the straight pathway now brings the traveler close to it. But I'm having trouble understanding how this would make an object I'm holding start to accelerate towards the mass when I'm no longer holding it.
|
[
"Ok I think I get what you're saying and I hope you indulge me saying it back in my words as a confirmation.",
"NO.1 So if the pen was far enough out in space such that it wasn't subject to any gravitational influence (and at rest in respect say to the inertial reference frame of us on Earth) you would say it was traveling a ",
" line through ",
" or \"",
"\" spacetime.",
"NO.2 So when the pen is back here on Earth, it is now subject to Earth's gravitational influence which curves spacetime so at the moment I release it from my hand it starts traveling a ",
" path through \"",
"\" spacetime.",
"NO.3 When I hold the pen, I'm applying a force that causes it's pathway in spacetime to ",
" instead of proceeding in a ",
" manner so you would say is it now traveling a ",
" path through ",
" spacetime.",
"Would you say my statements are correct?",
"If so then it stands that the suggestion from the title of my post is false. The force I apply with my hand doesn't warp or curve space time, it just curves the pen's pathway which in effect cancels out the effect of the Earth curving the spacetime to begin with.",
"EDIT: Originally I wrote \"space\" a few times when I meant \"spacetime\"."
] |
[
"An object with no forces on it follows a straight line through spacetime; this is the cause of gravitational attraction, as you point out.",
"But once another, non-gravitational force acts on the object, it follows a ",
" path through curved spacetime (just like in Newtonian mechanics, an external force causes an acceleration); in your example of holding a pen, the force is just enough to curve the pen's trajectory through spacetime so that it stays at rest relative to the Earth.",
"By the way, the curving of space",
" is crucial for understanding gravitational forces; curving space alone doesn't cut it. (It can't explain the attraction of objects at rest, for example.)"
] |
[
"Just to summarize what you are saying and make it more clear: the pen is not motionless with respect to earth because the mass in your hand unbends spacetime by the same amount that earth bends it. Rather, the electromagnetic force exerted by the atoms in your hand on the pen (the electomagnetic force is far stronger than gravity) stop the pen from traveling through a straight line in a warped spacetime (which would be the falling motion) and instead force it to travel a curved path (with looks like no motion to you)."
] |
[
"What causes the 'blue electricity' of lightning and tasers and such?"
] |
[
false
] | null |
[
"To more explicitly state what other answers are hinting at, the taser is pumping a lot energy into the air molecules that are around the terminals. This excites them and moves their electrons into high-energy states, and as they drop back to a low-energy state, they emit photons. While the air is mostly nitrogen and oxygen, oxygen is likely to just form ozone when it's excited like this instead of emitting photons, and thus nitrogen dominates the emission. Most of nitrogen's photons are in the blue/violent end of the spectrum because of the electron configuration in nitrogen atoms."
] |
[
"I went looking on Google. It took roughly 4 seconds to find this answer: The high voltage causes the airs electrons to jump to very high energy levels, some high enough to ionise (and thus conduct). The ones that dont quite ionise fall back to their original level, releasing a high energy photon, generally in the blue to UV area."
] |
[
"A taser is basically an incomplete circuit with a large power source. There's two pins that have a gap between them and breaks the circuit. But there's enough electricity going through the circuit to let the electricity to \"jump\" from one pin to the other, completing the circuit. Anything that comes into contact with the pins completes the circuit and the electricity goes through whatever it is in contact with. "
] |
[
"Why do suspended particles settle out as a heap when their medium is rotating?"
] |
[
false
] |
If I swirl a cup of tea, Alka-seltzer, or other liquid with suspended particles in it, the particles will tend to settle out as a heap in the center of the container. Why does this happen? Is it a result of the differing linear velocities resulting from circular motion, or is there another effect that explains this phenomenon?
|
[
"This is the \"",
"teacup effect",
"\", and, curiously, it was first explained rigorously by Einstein."
] |
[
"Just so I have it straight:",
"http://upload.wikimedia.org/wikipedia/commons/thumb/7/77/Tea_leaf_Paradox_Illustration.svg/213px-Tea_leaf_Paradox_Illustration.svg.png",
"Thanks. I had guessed that the settling pattern was a result of circular motion in that particles tend to settle slower in faster moving liquid, but it seems it wasn't that simple."
] |
[
"Yeah, that's exactly it. The rotation of the liquid forms a toroidal vortex, which moves down the outer walls of the vessel and up the center; however, the particles are too heavy to be carried up by the flow, so they get stuck at the bottom of the center."
] |
[
"How did the solar system take its current form?"
] |
[
false
] |
So, my guess is that for our solar system it all started with a huge cloud of space dust having mainly hydrogen, helium and all other elements in trace amounts... The dust had some initial angular momentum and therefore our solar system is more or less planar, the plane being perpendicular to the original angular momentum vector... But why is that the sun is a huge ball of nuclear gas and then we have solid planets mercury, Venus, earth and mars and then gaseous planets Jupiter and saturn. I can't seem to grasp why this non uniformity and is there any reason that most of the hydrogen went to the centre and the heavier elements for the planets? Is there any computer model where someone has used particle methods to stimulate the formation of a solar system, yeah I know this simulation will bring all comps to their knees...
|
[
"And Space Answers as well!",
"http://www.spaceanswers.com/solar-system/why-are-planets-closer-to-the-sun-more-dense/"
] |
[
"And Space Answers as well!",
"http://www.spaceanswers.com/solar-system/why-are-planets-closer-to-the-sun-more-dense/"
] |
[
"For the lazy, from Space Answers:",
"The planets in our Solar System formed from the solar nebula – the disc of gas left over from the formation of our Sun. Over time, this material began to collide and stick together, forming larger clumps that could collide with other larger clumps and gradually gather more and more matter. All of the planets in our Solar System began to form this way, but close to the Sun the temperature was too high for volatiles (gases like water and methane) to condense, so only the materials with a higher melting point (and higher density) were able to form at this point. The gas giants on the other hand, formed far enough away from the Sun that the temperature was cool enough for these volatile gases to condense, and form these huge, less dense planets."
] |
[
"How is the mortality rate for COVID-19 calculated?"
] |
[
false
] |
I've seen estimates of 1%-5%. Looking at the total deaths vs. total recoveries yields a much higher number. What other factors are considered in the calculation?
|
[
"There are a number of ways of calculating the death rates of a virus.",
"The key number is the Case Fatality Rate, which is simply the number of deaths divided by the number of total cases (currently about 4-5%).",
"But there are estimates of asymptomatic carriers, which increase the number of cases, and drops that number to about 1%.",
"The other two methods are more informational, which is the comparison of dead to recovered (~15%) and the comparison of the dead compared to the population (~40/million population worldwide, ~1417/million in New York)"
] |
[
"Two components: # deaths from COVID and # identified cases. The first number is theoretically easy to measure. Mortality data can be routinely collected from hospitals, death records, etc. The source of error here is in how a \"death from COVID\" is defined. In the US, if a death occurs and the patient is found to have COVID, then it's COVID-related and counted. It doesn't matter what they actually died from because it's very hard to figure out did COVID exacerbate the heart failure and cause death or did they just incidentally have COVID? ",
"The other number is way more dubious. Think about when you identify a case. Case aren't identified unless they're symptomatic enough to seek care. Are you going to go to the doctor if you have some sinus pressure and a few sniffles? Probably not. Are you going to go if you feel like your lungs are filling up and can't breathe? Probably. The first person is not identified whereas the second is. Another effect of this way to counting is that you're only observing the really symptomatic cases so it makes sense that the mortality rate is higher. That's why you have to do seroprevalence studies to see how many people have actually been infected. From the data, there does appear to be a substantial asymptomatic rate."
] |
[
"There are a few reasons, especially in play while an outbreak is ongoing. For one thing, not all recoveries actually get tested and confirmed as recovered, especially when testing is scarce. So the number recovered can be an undercount. For another, since it usually doesn't take the same amount of time for recovery and death to occur, during an outbreak one number may lead or lag the other.",
"In the end it's quite clear the actual mortality rate for coronavirus is definitely closer to deaths/cases than deaths/recovered, and probably quite a bit below deaths/cases because mild cases tend to not be counted."
] |
[
"Do rams have higher rates of brain injuries than other mammals?"
] |
[
false
] |
American football players tend to be more likely to have brain injuries than non-players. Seems to me that rams would suffer from similar issues. If they don't, why?
|
[
"Rams are specifically evolved for ramming into things, hence the name, while humans - professional football players or not - have not evolved for this function. Rams have very thick skulls and additional layers of muscle supporting their necks."
] |
[
"That's precisely why I'm curious if there is a higher rate of brain injuries in rams than in other mammals. Have rams evolved enough to not get brain injuries as a result of ramming?"
] |
[
"They've clearly evolved to reduce brain injuries:",
"“The large horn cores and expansions of the corneal and frontal sinuses of males, together with their internal bony septa, form a system believed to protect the brain by absorbing the impact of clashes during fighting” ",
"(Shackleton 1985)",
".",
"Arguably, woodpeckers have ",
"even more extreme",
" adaptations.",
"That said, I'm not aware of any post mortem studies looking for rates of brain damage in these species."
] |
[
"What determines the amperage limit for a given density or thickness of a material?"
] |
[
false
] |
For example, a 34 gauge wire is going to fail at a lower amperage compared to a 0 gauge wire. How is that determined?
|
[
"I think that the ratings you see in the AWG wire tables are based on a conservative estimate of the allowable temperature rise in the wire under some nominal environmental conditions, which will be different for chassis wiring versus power transmission cable, versus other configurations. Some ",
"engineering notes for copper wire are found here",
". "
] |
[
"But how are the fundamentals of that determined? Does it depend on the crystalline structure of the material involved?"
] |
[
"Yes and no. The no part first:\nIn practice, the most important factors are the geometry and the enviroment near the conductor. For any given material you can determine a conductivity, usually per length. Depening on your geometry you can then calculate the power that needs to be dissipated for a given current and per lenght of conductor, for wires this is straight forward. The main questions now is, can your conductor dissipate all that heat? That is to say, for a stable system (i.e. after you let everything sit for a while) the rate of heat flow from the cable will be exactly the same as your dissipated power, which is determined by the heat difference between conductor and enviroment and a lot of other factors in the enviroment's make up. For example, are we under water/oil, in plain air or stuck in conrete? If in liquid or air, can it flow? If so, how fast? Most of the time you can't change these factors, so you simply assume the worst possible, plausible enviroment. Now your heat dissipation per lenght of conductor is only depending on your diameter. Keep in mind that your electrical conductivity will increase with r",
" while thermal conductivity will increase linearly.\nIn the end, you will end up with a theoretical value for the expected temperature.\nAcceptable temperatures are determined by rule of thumb, i.e. building codes and so on. In most cases it must be low enough so the wire doesn't melt and that nothing can catch fire.",
"The yes part:\nThe microscopic structure of the material \"only\" determines, how good the conductivity for a given lenght will be, so it does depend on it somewhat."
] |
[
"Why does my laser appear to stop at a certain distance?"
] |
[
false
] |
I own several high power personal lasers green and blue (500mw & 1W). When I shine them up at the sky at night they appear very bright (light sabre-like) but seem to stop at a particular altitude... like a mile or two at the most. I would think that it would diffuse?
|
[
"It's likely not your laser dissipating, but the lack of things for the laser to hit at higher altitudes. You can't \"see\" a laser beam, you can only see when it hits something: in your case dust and other aerosols in the atmosphere. Aerosols tend to stick ",
"in the lowest few kilometers of the atmosphere",
", so I would assume you can't see your laser any more because there aren't enough particles up higher to scatter the light."
] |
[
"You should be able to test this easily by firing at different angles; given this hypothesis, it should end at the same ",
" even if the angle is such that it appears several times longer. "
] |
[
"I'm not sure, but doesn't the fact that one is effectively looking along the length of the beam guarantee the appearance of an 'end' to it, regardless of the conditions, just by the geometry of the situation? ",
"Eg. if you had an infinitely long, straight glowing rod in vacuum, and held it out like the beam from a laser, you should still see it \"stop at a point\" where it converges with your line of view."
] |
[
"Why is it that microorganisms can develop resistance to medicines, but I have not heard of any organisms becoming resistant to soap?"
] |
[
false
] | null |
[
"One must also understand that natural selection has requirements in order for it to succeed in altering allele frequency in the subsequent generations. In your example, the assumption is that certain bacteria have variabilities in their resistability to soap, these variabilities in resistability confer a difference in survivability, and this trait can be passed on to future generations. This would lead to natural selection.",
"However, the problem is that these variabilties in resistability do not confer a difference in survivability, because the survivability in response to harsh detergents or bleach is 0. These agents will basically invariably break open the cells and/or cause them to die. This is definitely true of bleach, and definitely true of harsh detergents. No matter what pre-existing genetic variability exists for survivability, exposure to bleach makes the survivability of all genotypes 0. The environmental pressure is too great to overcome. An analogy could be trying to get mice to be able to breathe underwater indefinitely; it would not happen no matter how many mice you surveyed, despite there being variability in the length they could hold their breaths underwater.",
"Note though that your garden variety hand soap does not primarily work to break open the cells, it just washes them away as has been mentioned already. But harsh detergents are used in biology for the very reason of breaking open cells and getting the contents inside of them."
] |
[
"Soap in itself doesn't kill bacteria.",
"Whoa whoa whoa, it sure as shit does. Detergents, like the stuff that makes soap, well, soapy, disrupt and solubilize cell membranes, which does kill bacteria. Pretty well, in fact. ",
"I'm going to ",
"cite",
" the last time this question was asked. ",
"Here's",
" some technical literature that discusses lysing cells using detergents. "
] |
[
"Soap in itself doesn't kill bacteria.",
"Whoa whoa whoa, it sure as shit does. Detergents, like the stuff that makes soap, well, soapy, disrupt and solubilize cell membranes, which does kill bacteria. Pretty well, in fact. ",
"I'm going to ",
"cite",
" the last time this question was asked. ",
"Here's",
" some technical literature that discusses lysing cells using detergents. "
] |
[
"Can two elections touch?"
] |
[
false
] |
I was wondering if it was possible that two elections touch each other, and what would happen if they did. I know Coulombs Law is F=KQq/r so my best guess would be that the force required would just get higher and higher as the distance got smaller until it was infinity, but I'm not sure so I wanted to get your take on it.
|
[
"Coulomb's law ceases to be valid once distance grow sufficiently small (once you start getting in the angstrom range perhaps?). You have to calculate the interaction with QED, which once again, stops being valid after a point where you reach the so-called Landau pole, after which you need to pull out the full standard model. I have no idea what that standard model predicts about the behavior of electrons a very small distance apart, probably nothing too bizarre, they might shoot away from each other. It further behooves us to consider the possibility that the SM is only valid up to certain energies, as yet unreached in experiments, beyond which a different theory would take over.",
"Also, electrons are point particles in QM, so to get them to touch, the distance between them would have to vanish. You have to also keep in mind that once you get to QM ranges, you have to specify the wavefunctions of the electrons, and not just positions."
] |
[
"That's not entirely true. That only applies to fermions. Bosons do not follow the same quantum state rule and can occupy the same space."
] |
[
"I'm assuming the OP was referring to \"touching\" quantum state. Based on that, you asserted \"nothing ever touches\" I'm just clarifying that bosons are contradicting \"nothing\"."
] |
[
"I have 20/20 vision. When I put on glasses, everything is blurry but when I cross my eyes, everything looks clear. Why?"
] |
[
false
] | null |
[
"When you cross your eyes you focus your eyes on 2 different things, but the focus remains the same. Glasses change the focal point which will make things blurry - unless they're ",
" glasses and your built-in focal point is off by the amount the glasses are correcting for."
] |
[
"There are three factors contributing to this:",
"Most glasses have different prescriptions (refraction indices) at the edges than at the centers. ",
"Polarized glasses tend to skew things near the periphery. ",
"Most glasses are thicker toward the edges than in the center.",
"Wearing prescription or reading glasses offsets your vision by design. Normally they would correct the offset of near/farsightedness, but in this case they're actually causing the offset. It's possible that these factors are offsetting that offset, thus resulting in zero."
] |
[
"offset the offset. makes sense. thank you!"
] |
[
"Do identical twins have identical DNA?"
] |
[
false
] | null |
[
"At the very moment that the zygote splits, sure, the DNA will be remarkably similar. However, as the individual embroys grow and the DNA is replicated, mutations accumulate in the individual genomes which ultimately change genetic similarity, even if the changes are super minute."
] |
[
"This is very interesting. Thank you so much. A few more questions then, if I may. Are these epigenetic changes detectable? In a forensic context, would two identical twins be distinguishable by their DNA? What environmental circumstances give rise to most epigenetic modifications? Do unrepaired modifications cause neoplasms?"
] |
[
"This is very interesting. Thank you so much. A few more questions then, if I may. Are these epigenetic changes detectable? In a forensic context, would two identical twins be distinguishable by their DNA? What environmental circumstances give rise to most epigenetic modifications? Do unrepaired modifications cause neoplasms?"
] |
[
"If skin cells are one of the fastest replicating cells, how come moles, and birth marks don’t disappear over time?"
] |
[
false
] |
Same goes for warts and scars.
|
[
"Moles are still skin cells. So imagine you have an area of skin, and some part of it is “mole” cells and some is regular cells. Both parts are sluffing (losing skin cells) at similar rates, and then replacing those cells at similar rates. So the shape and structure of moles might change overtime, but on average they don’t change much because they are “in sync” with the growth/loss of the cells around them."
] |
[
"There's quite a bit of half truths and misinformation in this answer. Scars are extracellular and do not have anything to do with stem cells.",
"Scars are produced from a wound site where the fibroblasts in the dermis are laying down extracellular proteins such as collagen. Normally they do this slowly and very controlled. In a wound situation fibroblasts migrate to the wound site and lay a much of this extracellular matrix down as fast as possible to get the wound closed quickly by creating a structure for the keratinocytes to attach to and migrate over from the surrounding epidermis. This is to prevent infection and other problems associated with loss of skin barrier function. "
] |
[
"There's quite a bit of half truths and misinformation in this answer. Scars are extracellular and do not have anything to do with stem cells.",
"Scars are produced from a wound site where the fibroblasts in the dermis are laying down extracellular proteins such as collagen. Normally they do this slowly and very controlled. In a wound situation fibroblasts migrate to the wound site and lay a much of this extracellular matrix down as fast as possible to get the wound closed quickly by creating a structure for the keratinocytes to attach to and migrate over from the surrounding epidermis. This is to prevent infection and other problems associated with loss of skin barrier function. "
] |
[
"What is it in grass that makes it so itchy?"
] |
[
false
] |
Why does grass itch so much? I would speculate that its perhaps something to do with how sharp it is ... I'm picturing like microscopic little paper cuts being the cause of the itchiness but its just a guess. Is there something else at work here?
|
[
"Wait, really? So this isn't normal? I just assumed everyone got itchy when they rolled in grass without a shirt on (for instance). It never even occurred to me that it might be an allergy."
] |
[
"From my experiences as a child, every single one of my friends who rolled on grass without a shirt on got itchy. Since I find it very unlikely that all of my friends were allergic to grass, there must be some other explanation."
] |
[
"My hypothesis: grass itches because you are allergic to grass."
] |
[
"Is it possible that there are other colors that we humans cant see/have not found yet?"
] |
[
false
] | null |
[
"Colors are a psychological not physical property. "
] |
[
"Other animals may be sensitive to light outside of the typical visible range for humans. For example bees are sensitive to light in the UV range. Human photoreceptors are actually also sensitive to light in that range, but the lens filters it out. In early versions of cataract surgery, lenses were replaced with a material that did not filter out UV. Those people reported seeing more blues and purples in the environment. Whether those are unique color experiences is hard to say.",
"There's also a few people who are tetrachromats and have four cone receptor types. None of them except perhaps for one are able to discriminate hues differently than trichromats. For that one person, they may have some unique color experiences in the sense that two hues that look identical to us appear different to her."
] |
[
"Yeah I understand that, but is it possible that maybe a certain animal can see a color we can't? Or is it all based on the RGB Spectrum we have now?"
] |
[
"Cell Automaton/Computer Science Question"
] |
[
false
] |
I recently read about cell automatons and I find these intriguing. For biochemical/molecular biology purposes, in what instance would someone construct a cell automaton to model something? I am thinking maybe to extrapolate some aspect of cell behavior given certain conditions. Also, what programs do people usually use to code biochemical/molecular biology models? I am not well versed in CS language so excuse me if my question is worded strangely.
|
[
"Not my sub-field, but I'll try.",
"Cellular automaton can be used to model extremely complex systems which have simple interaction rules. Fluid dynamics is one thing that comes to mind. Particles have extremely simple rules for interacting: bounce around. ",
"However, I can't find much post-80s. Probably because methods for numerically solving equations, massive parallelization, and CPU speed in general took off in the 90s.",
"You might have a look at:",
"http://www.amazon.com/Cellular-Automata-Modeling-Collection-Alea-Saclay/dp/0521673453",
"For some ideas. But please, check libraries before you buy a book like this."
] |
[
"Ah well I stand corrected. Biology is not my field."
] |
[
"As far as I know, CA are not used to model anything. They are mostly used to demonstrate and study how seeming chaos arises out of simple rules. They might have some applications in cryptography, but this is basically taking advantage of the \"chaos\" property they exhibit while still having a definite rule to begin with. ",
"Basically, you can seed an algorithm with a key, encrypt it using a CA, and the end result would be something that would resemble random noise (\"chaos\"). But if you knew the rules the CA was using, and you knew the key seed, you could decrypt the message. "
] |
[
"Can an unvaried diet cause the human body to learn to digest a certain (type of) food faster?"
] |
[
false
] |
I know that the ranks carbohydrate-comprised foods according to their effect on glucose levels. But are these rankings always accurate throughout an individual's life? Would, given sufficient repetition, the body adapt to process a certain food (e.g. Pizza) faster?
|
[
"Kind of. I might replace the word ::faster:: for ::more efficient::. The bacteria that thrive in your gut are the ones that eat what you’ve been eating lately.\nThis is why sometimes we get gassy or weird stools when traveling to foreign countries of different cuisine- your microbiome aren’t optimized for that cuisine."
] |
[
"The problem with rabbit starvation isn't because it's just meat. Since the meat is so lean, the caloric intake is only protein which the body can only process a certain amount. This leads you to have a caloric deficit because you can only get a portion of what you eat. If the meat is fat, you will be fine."
] |
[
"There are examples of people living with for very limited, but abundant, nutritional sources, including the native people of Canada in the extreme North surviving off mostly fish and seal, and the Nomadic Bedouin’s living off their camel herds. They did have other plant foods but I believe a majority of their normal daily caloric intake would be similar. These guys aren’t eating pizza though, but natural (not processed) foods so maybe that the s the key?"
] |
[
"How variable is human flexibility?"
] |
[
false
] |
Do we all have a base flexibility, or is it just that "naturally more flexible" people do more workouts and perform more motions that require flexibility? If I gain flexibility, then stop stretching, will I lose it as quickly as I gained it. Is my upper limit drastically different from somebody else's? I can never remember being able to touch my toes, do I ever have a chance of putting my hands flat on the floor with straight knees?
|
[
"Range of motion is partly result of the stretch reflex. When you train flexibility, a lot of it is training your stretch reflex; when people are anesthetized, they have a larger range of motion. But people's skeletal joints vary by a ton anatomically, as do the locations and size of muscles which also impact range of motion. In fact even the ",
"number of muscles",
" varies a lot from person to person, which can also impact range of motion. ",
"Its well known that women are on average more flexible than men, particularly in a few areas, like the hips and lumbar spine, which is probably important for pregnancies. You will not lose flexibility as fast as you gain it, and it will be easier to retrain after you become less flexible. Your upper limit on flexibility can be very different from some people, for instance the femoral head can vary a ton and cause very different ranges of motion. Some people will also be able to stretch their muscles and tendons more too. ",
"I can never remember being able to touch my toes, do I ever have a chance of putting my hands flat on the floor with straight knees?",
"In addition to flexibility this also depends on the relative lengths of your torso, legs and arms. But yeah, probably you'll be able to do that with enough work. When I started working out, I went from never coming closer than an inch to my toes(male) to being able to put my knuckles on the floor without specifically stretching for that. But I have also always been able to put my foot behind my head, so take that with a grain of salt."
] |
[
"Thank you! You're completely right."
] |
[
"There's certainly peer-reviewed literature on this, and IFLScience have done a ",
"great job of summarising",
" whether stretching improves both flexibility, and chance of injury. The main findings (with links to the journal articles):",
"\"",
"Stretching acutely increases flexibility",
"\" (acutely meaning 'over a short period of time', in contrast to chronically)",
"\"",
"The evidence from randomised studies suggests that muscle stretching, whether conducted before, after, or before ",
" after exercise, does not produce clinically important reductions in delayed-onset muscle soreness in healthy adults",
"\" (also available ",
"here",
")- this one's a ",
"Cochrane",
" Systematic Review, so it gets an extra helping of scientific credibility."
] |
[
"With modern technology and measuring devices, how much warning will there be of the next Yellowstone supervolcano eruption?"
] |
[
false
] | null |
[
"WE can't forecast ",
" volcanic system particularly well at the moment. The Yellowstone system is one that has very long repose times (long periods between activity), and a wide range of activities (can throw out thousands of cubic kilometers, or can erupt a few hundred cubic meters). It's not erupted in recorded memory, so we have no previous dataset of deformation / seismic response etc to go on. And there's a huge magma storage system down there, but we have no real idea of how full it is, or how fluid and eruptable that magma is, or how well connected the different pockets of it are.",
"So without knowing exactly what the eruption conditions are likely to be, we can't precisely say how close to them we are. However, best estimates place us at thousands of years away from a super eruption, simply due to the fact that the magma chamber appears to be very far from its previous max capacity. And always remember, the supereruptions are the rarest and least likely activity that Yellowstone produces. By far the bigger risk are hydrothermal explosions or smaller volume eruptions. Supereruptions are so low probability that the risk is not really quantifiable in a meaningful way.",
"I strongly recommend reading this excellent document from the USGS (especially the conclusions):\n",
"http://www.researchgate.net/profile/Robert_Smith55/publication/258032883_Preliminary_assessment_of_volcanic_and_hydrothermal_hazards_in_Yellowstone_National_Park_and_vicinity/links/00b7d5298cd880ca4d000000.pdf",
"And a recent summary paper on imaging the magma chamber here\n",
"http://onlinelibrary.wiley.com/doi/10.1002/2014GL059588/epdf"
] |
[
"We use seismic tomography to try and image the subsurface (a bit like ultrasound), but it has very limited resolution at those depths. Drilling at those depths into hot materials is not really feasible, and the last thing you want to do is drill into a eruptable magma. Even then, a drill core only tells you about the stuff you've drilled into and the Yellowstone system covers thousands of square kilometers, that we need to understand in 3D down to depths of tens of kilometers; so tens or hundreds of thousands of cubic kilometers that we need to develop a high resolution model of. We would ned to know the stress state across that volume, where the old faults and fractures are, how well sealed they are, how rock strength properties vary across that volume, and more importantly we need to know how much magma is coming up, how it mixes with existing magma, and what the precise chemistry of those is so we can understand any mixing reactions (which can trigger eruptions).",
"The analogy I would use is that we are at the equivalent of a Victorian doctor with a stethoscope being asked to diagnose a genetic disorder he has never seen before in a 2 month old foetus, in the womb of an unco-operative mother, while a brass band marches past."
] |
[
"there's a huge magma storage system down there, but we have no real idea of how full it is, or how fluid and eruptable that magma is, or how well connected the different pockets of it are.",
"Im not familiar with Volcanology at all but is there a technical limit as to why we cant find this info? Is there no way to probe the rock and magma beneath? "
] |
[
"How much does glucose consumption vary from brain to brain and how much could it effect overall metabolism?"
] |
[
false
] |
Alternatively: could person A who is mentally 'slow' have a slow metabolism whereas person B that is mentally 'busy' have a fast metabolism?
|
[
"So, ",
"this",
" paper states that the brain uses around 60% of our overall glucose that we contain in our body during a resting state (glucose is the main energy source for the brain, except for periods of starvation where it can utilize other energy sources to maintain itself). The brain relies, obviously, on the body for glucose to use, and areas such as the hypothalamic arcuate nucleus and in the hindbrain can sense, integrate, and regulate energy homeostasis and glucose levels and signal to the rest of the body (peripheral parts) through a dedicated neuronal network. Also, centrally, hormones insulin and glucagon-like peptide-1 can also help monitor peripheral glucose uptake. Glucose insulin receptors and glucose transporters in the brain also play roles in glucose mediation. ",
"In the hypothalamus, hormones such as hypothalamus, pro-opiomelanocortin, MCH, and neuropeptide-Y (NPY) and agouti-related peptide (AgRP) and regulate glucose use in an antagonistic way. ",
"According to this paper",
", \"defective neuronal maintenance in these cells has severe consequences for peripheral metabolism. Defective autophagy in POMC neurons can lead to lifelong metabolic defects such as peripheral glucose intolerance and obesity\". ",
"Now, to answer your main question: glucose consumption varies from brain to brain, but not by a lot - \"normal\" people, with no neurological issues, use around the same. ",
"This paper",
" showed that overall, women have a lower metabolic rate than men, which would lead to an overall lower glucose metabolism ",
" via the brain as well (",
" this does nothing in regards to how efficient women's brains are compared to mens - usually women are smaller and thus do not NEED as much glucose as men anyways, as one example). I could not find a specific paper about brain glucose consumption from person to person, though many have studied glucose consumption during strenuous mental activity, physical activity, and others. But overall, the differences do exist, but are ",
" not significant. However, in people with issues with glucose metabolism, including problems from tumors in the hypothalamus to decreased production of hormones like MCH/NPY via other issues or a genetic component, could definitely effect brain glucose consumption and how efficient it uses the glucose it DOES uptake (as the Mergenthaler et al. study in the previous paragraph stated).",
"Someone could chime in with more info as i'm currently enthralled by the MLB World Series and just wanted a quick comment!"
] |
[
"This may be a silly question but could someone with a disability effecting the brain be treated with high glucose intake, provided they process glucose like you and I?"
] |
[
"Hey, thanks for the reply! Appreciate it"
] |
[
"[Mathematics] What number refers to the number of possible orderings of natural numbers?"
] |
[
false
] |
The number of unique orderings of a set of length n is n! and as such it seems logical to me that the number of unique orderings of the natural numbers is Aleph null factorial, but what does it mean to take the factorial of an infinitely large number as infinity minus one is still infinity(i think). I was also thinking about the Continuum hypothesis which says that the cardinality of the set of real numbers is 2 raised to the Aleph null. x! grows faster than 2 so would that make the number of unique orderings of the natural numbers to be larger than the set of real numbers(assuming that we are able to take the factorial of Aleph null)? Apologies if my question makes assumptions which are incorrect, but thanks for reading!
|
[
"A rather simple way to encode numbers between 0 and 1 to all possible orderings of natural numbers would be to create decimal number between 0 and 1, and type each integer in order, in base-2, then use 5 as separator. So if your ordering starts like 1, 5, 16, 4, 2, ... Then we'd have our encoding of",
"0.1510151000051005105...\n",
"Or to replace 5 with clearer separator",
"0. 1 | 101 | 10000 | 100 | 10 | ...\n",
"It's quite easy to see that if n'th digit of two orderings differs, then the encoding differs, so it's an injection from all orderings to the interval ]0, 1[, and as such, there are at most as many orderings as there are real numbers."
] |
[
"From your response it seems clear to me that the number of unique orderings must be smaller than the set of real numbers, and in fact I am under the impression that it is even smaller than the set of real numbers between zero and one",
"Watch out: It might sound counterintuitive, but the set of all reals and the set of all reals between 0 and 1 have the same cardinality, even though the latter is a proper subset of the first. "
] |
[
"It's pretty easy to show that N! = 2",
" using Cantor's Bijection theorem.",
"Elements of 2",
" are functions f:N -> {0,1}. Elements of N! are bijections g:N->N.",
"To inject 2",
" into N! , you can have g be the bijection that exchanges 2n and 2n-1 iff f(n)=1.",
"To inject N! into 2",
" you can \"write out\" the sequence g(1),g(2),g(3)... and binary encode it (using ASCII or whatever scheme you like), then the corresponding f is 1 iff the the nth binary digit of the encoding is 1."
] |
[
"Do dogs taste spicy foods like humans do?"
] |
[
false
] |
Do they have different taste buds? Less taste buds? More? The spicy food in particular I'm curious about is jalapeños (was going to feed my dog a piece of my slice of pizza with a jalapeño on it, but I thought I'd ask here before I made him sick)
|
[
"You wont make him sick. ",
"In most developing countries, dogs eat what humans eat. I think Americans and the others in developed countries got suckered into feeding dogs dog-food... it is sooooo good for the dogs. In India for example, dogs reared by vegetarian families thrive (not survive - thrive) on veggie food.. including rice, curry etc. ",
"Your dog will be able to decide if he wants the jalapeno or not - and may decide to eat just the rest of the pizza. They have a great sense of smell - and the ability to decipher what is edible and what is not. "
] |
[
"And indians eat like 10 gms of protein.. are healthy.. survive.. have long lives on vegetarian food.",
"Sorry, that's just plain wrong. No healthy adult survives on 10g of protein per day.",
"You need a minimum of 12% of your daily calories from protein. If your daily diet is 2000 calories, you need 240 calories from protein, meaning 60 grams per day.",
"Now if you are small in stature and very thin and don't do manual labor, you may be able to get by with fewer calories. If your daily diet was only 1500 calories per day, then you'd need 180 calories from protein, or about 45 grams per day.",
"If you eat much less protein then that, you will get protein-calorie imbalance diseases such as ",
"kwashiorkor",
", which was quite common in India a few decades ago. Even today, after the Green Revolution in India, the rate of protein-calorie malnutrition is between ",
"pretty high",
". These people are not healthy.",
"That said, the average Indian ",
" get enough calories and enough proteins per day. Contrary to popular belief, vegetarian foods can be great sources of protein, you just have to eat the right ones.",
"Among popular food items in India, which are good protein sources (per 100 grams of dry, raw food):",
"Between these and other sources of protein, most Indians get sufficient proteins to be healthy. Also remember that even vegetarian Hindus are usually lacto-vegetarians, meaning they drink milk and eat cheese/yogurt/etc. These things are good protein sources.",
"Also remember that 15% of India's population is Muslim, another 2-3% is Christian. These people eat meat. And among Hindus, probably somewhere between 20-25% are also meat eaters."
] |
[
"Really? That's cool. I didn't know that.\nI was told because they're carnivores, it's best if they eat mainly meat. I have read that they eat greens in order to control upset stomachs (which explains why we see dogs eating grass from time to time)."
] |
[
"What would a firework look like if it was set off in space?"
] |
[
false
] | null |
[
"Except it wouldn't trail down like the common umbrella shape most long bursts have. It would be more of a spherical pincushion all the way through the burn. "
] |
[
"If its made with substances that can chemically react without the presence of oxygen then it would look the same as it does here. It would be visible at night if it was large and detonated somewhere around low earth orbit (we can clearly see the flash off the space station solar panels)"
] |
[
"If it was fired on orbit then yes its in freefall. If it was launched straight up from the earth in a non orbital trajectory it would still have the umbrella shape. Carful about thinking of space as equal to no gravity. "
] |
[
"What is stopping scientists from adding more and more neutrons to an atom to create an infinite amount of isotopes?"
] |
[
false
] | null |
[
"What you’re talking about is referred to as the neutron drip line, which is the upper bound on the number of neutrons a stable isotope can have before it starts “dripping” particles. ",
"In an atom, there are several forces at play. The balance of these forces on an individual nucleon is the amount of energy that it would take to rip that particle out of the nucleus. It’s called separation energy. ",
"After a certain size, the forces can’t be balanced and the isotope becomes unstable. In other words, the separation energy becomes negative and the particles fall off.",
"Look up the table of nuclides and you can see the specific ratios between neutrons and protons where stable isotopes exist. In elements up to calcium, the ideal ratio is 1:1. The ratio gets larger as the number of protons increase because the forces inside an atom scale differently across distance. For the heaviest stable isotopes, the ratio is about 1.5:1. After this point, neutrons start dripping off and adding protons won’t help to balance because they’ll drip off too.",
"The specific behavior of the forces makes certain combinations more stable than others. Check out the island of stability and magic numbers for more details on that. This is an area of active research and not well understood; we’ve found neutron drip lines for elements only up to neon."
] |
[
"Neutrons and protons are fermions, so every state can only have one of them. Protons and neutrons have different states as they are different particles. A (ground-state) nucleus will have all the lowest energy levels filled up to some point. With a \"good\" proton to neutron ratio the highest filled energy levels for protons and neutrons are similar. If you keep adding neutrons they'll occupy higher and higher energy levels, and beta- decay to convert a neutron to a proton is possible. Try to add even more neutrons and you reach a point where the neutron has so much energy that it can be emitted directly."
] |
[
"I am having trouble understanding how turning a neutron into a proton makes the nucleus more stable. It would seem like the added electromagnetic force would only increase the repulsion, so what is really going on? Why is a Hydrogen atom with just a proton more stable than with added neutrons? What is causing the potential gap that is stronger than the strong nuclear force?"
] |
[
"How does paper get recycled?"
] |
[
false
] |
(Note that this is tagged as biology since I'm not sure what else to tag it as, but biology seemed the closest) I've always seen that paper, glass, plastic, etc., is supposed to be recycled, and I get how most things are: they get melted and reformed into something with a different shape and purpose. but paper? that stuff can't melt. how does it get recycled?
|
[
"I think ",
"this article",
" shows the process reasonably well."
] |
[
"it's weird to think that it becomes almost like a paste, but thanks!"
] |
[
"The same way it’s made in the first place. Paper is wood that has been pulped to smaller fibers and mixed with a binder.",
"The wet pulp is formed, molded and pressed, then dried, which gives you paper.",
"In most cases there are additional steps in the process to align and untangle the fibers, bleach the pulp to make it whiter and even add chemicals to make it more opaque. But that is the basics.",
"To recycle it, you simply have to chop it back up and wet it down back to pulp, then follow the same process.",
"New pulp is often added because each time you recycle, the fibers get smaller and smaller which makes the finished product rougher in texture.",
"It can even be done at home by using shredded paper, mixing it with water and the binder (corn starch works) in a blender, spreading it out on a fine screen and applying pressure.",
"You can’t use coated papers or items that won’t absorb the water properly or prevent the fibers from sticking together."
] |
[
"Why don't teeth heal by themselves?"
] |
[
false
] |
So when we get cavities we have to get a filling because it would grow back naturally, whereas, if I cut a chunk on muscle out it will repair and grow back. Why is this?
|
[
"Teeth form from a multistep extracellular mineralization process. This process begins with a mix of \"soft\" proteins and minerals (mainly calcium) which auto-assemble into a very tough mineral deposit. This mineralization occurs in very thin layers, each taking several weeks to mature. You can think of building a tooth as a project similar to building the Hoover Dam, in which layers of concrete are poured one atop the other. The next layer of concrete cannot be poured until the underlying layer has cured. Likewise, in tooth formation, the next layer of mineral cannot be deposited until the preceding layer has had time to mature (harden). ",
"This initial hardening step, however, is not the end of the story. The fully assembled layers of enamel take years to completely mineralize. It is important that the layers mineralize in concert as this makes our teeth less prone to chipping and wear.",
"As a result of this multistep process, the outer portions of the tooth (the \"crown\") are the areas that were deposited first and are also the toughest. In the instance of a chip, the tooth cannot heal for three important reasons. First, there are no cells near the damage that can produce new enamel. Second, even if there was a new wave of enamel formation, the long timescale required to transition from \"soft,\" immature enamel to \"tough,\" fully mineralized enamel is very long. The soft enamel would quickly wear away from use. Third, the mechanical properties of the tooth require that different layers of enamel mineralize simultaneously. Laying a fresh layer of enamel atop mineral enamel is akin to repairing a pothole with asphalt. The repaired area would be much more prone to mechanical damage at the interface between \"old\" enamel and \"new\" enamel."
] |
[
"There are reports of humans developing multiple sets of deciduous teeth, so we do have the capacity to support multiple rounds of tooth formation. The short answer is that we don't fully understand why we develop our permanent teeth early in life and maintain them throughout adulthood. This is a trait that we share with other primates and most other animals, suggesting that most animals have need of only one set of deciduous teeth and one set of permanent teeth. ",
"Sharks form teeth in a manner very different from other non-fish animals. Their teeth form in a process similar to fish scale formation. As a result, the teeth are easily shed and need to be replaced constantly. Elephants are the only known mammal to continually replace permanent teeth throughout adulthood. Despite this constant replenishment, there are reports of severe tooth wear in elder elephants. This observation suggests that tooth replenishment is only necessary when feeding habits require it.",
"In the case of humans, cavity formation and tooth wear have been observed in fossils of early humans. Indeed, tooth wear is observed in all animal species. The main differences we see among animals with different feeding habits is not in the number of sets of teeth they produce, but in the shape and mechanical properties of the permanent teeth. Animals whose feeding habits rigorously wear teeth develop teeth with thicker crowns and whose shape reduces wear.",
"These findings indicate that the purpose of baby teeth is strictly to function during development, not to replace worn teeth. The adult teeth, in most instances, have mechanical properties to satisfy the needs of typical feeding habits over a typical lifespan. As animals evolve different feeding habits, the mechanical and morphological properties of the adult teeth evolve to match these habits.",
"What we may be observing in the current human population is a sort of evolutionary trap. Our feeding habits have changed rapidly over the last 10,000 years. This change in behavior has most certainly outpaced the rate of change one would expect through evolutionary means. So although our teeth may have the mechanical where-with-all to satisfy the needs of an early human, whose average lifespan is just shy of 30 years and whose diet consists of berries, nuts, and raw meat; our current diets, rich in simple carbohydrates, have imparted a new challenge to these old teeth in the form of cavity formation. A similar phenomenon was observed during the advent of the windmill, when humans ate a diet rich in refined flour. Stones from the milling process caused teeth to prematurely chip and wear. As our ancestors did not habitually feed on stones, our teeth were unable to meet the requirements for such a diet."
] |
[
"The tooth is made of enamel which is not alive and so cannot repair."
] |
[
"When a napkin is dipped in water, where does the energy come from that allows the water to travel up the napkin, against gravity?"
] |
[
false
] | null |
[
"Whoa nelly, there is a lot of crazy semi-science going on here, I'll try to get at the heart of the problem:",
"Capillary action in this case is due to the high porosity of cellulose based materials (like napkins). Water has very favorable interactions with cellulose due to hydrogen bonding and wants to adhere to it. Upon contact, a concentration gradient is established, and water is drawn up into the napkin until it reaches an equilibrium state where the napkin has no more free \"spots\" for water to interact. The reason water goes against gravity is that the favorable interactions between water and cellulose WAY overcome gravity.",
"Now where does the energy for this come from. The answer is (as always) derived from gibbs free energy i.e. entropy and enthalpy. The act of water swelling cellulose is actually ",
"(gives off heat), as are most spontaneous processes, so this system doesn't need heat input to work. So water swelling cellulose is favorable because it gives a negative gibbs free energy value. ",
"Edit: I feel obliged to correct my explanation of the thermodynamics of this system. The energy for the napkin to be wetted is derived from the favorable interaction of cellulose with water, as opposed to less favorable interaction of cellulose with air. This actually ends up increasing the entropy of the system, since the surface of cellulose now has many more states it can sample as water molecules interact with it. Entropy can increase without heat input. The heat emitted is due to to the fact that we are breaking water-water interactions and replacing them with less favorable water-cellulose interactions. The difference in energy between the two interactions is released as heat. This replacement is driven by the fact that increasing entropy is always favorable in a system."
] |
[
"Hmm... that is actually not a trivial question. I think the answer is yes, but the difference would be ",
". Hot water has more energy to propel the water molecules more quickly through the porous substrate."
] |
[
"So boiling water would spread faster than say near freezing water? "
] |
[
"If low testosterone males experience chronic fatigue, why aren't women tired all of the time?"
] |
[
false
] | null |
[
"A woman's ovaries and adrenal glands will produce testosterone but on a much lower level than a man's testes. If a woman's body fails to produce appropriate levels (there's a sweet spot-not too much, not too little) of testosterone for the female body, she will probably exhibit symptoms. She could experience fatigue, hot flashes, mood swings, hair loss, lowered interest in sexual activity, and/or depression (to name only a few symptoms) if she doesn't have enough testosterone, and hair growth/loss, infertility, obesity, and/or menstrual irregularity if she has too much testosterone. There are many synthetic and bioidentical hormone therapy treatment options available to treat low testosterone for both men and women; however, insurance companies usually won't cover treatment for women."
] |
[
"http://www.nejm.org/doi/full/10.1056/NEJMoa0911101#t=articleResults",
"Some men, a small proportion, have fatigue, but it's a relatively rare symptom compared to others. Fatigue is reported in less than 20% of patients even at the lowest testosterone levels.",
"Edit. On women.",
"http://aje.oxfordjournals.org/content/153/3/256.full#T1",
"Physical activity was not associated with testosterone concentrations in any of the 3 years of examination (table 2). Women in the upper tertile of the physical activity distribution had testosterone concentrations similar to those in women in the lowest tertile of physical activity cross-sectionally and across time. The grams of protein, fat, or carbohydrate intake, as well as total energy intake (calories), were not associated with total testosterone concentrations (data not shown). ",
"http://edrv.endojournals.org/cgi/content/meeting_abstract/33/03_MeetingAbstracts/SUN-76",
"These preliminary results suggest that testosterone treatment reduces fatigue, and that short-term responses in fatigue may be dependent on administration mode. Future directions should include longer-term interventions to determine whether testosterone ",
"In older men."
] |
[
"part of it is because we have estrogen. a female steroid hormone which has an extremely similar chemical compound to testosterone. made from the same precursor and can even be made from testosterone. ",
"http://en.wikipedia.org/wiki/File:Steroidogenesis.svg"
] |
[
"How does freezing solutions of ethanol work?"
] |
[
false
] |
I was reading ethanol's on wikipedia, and was a little confused by the freezing temps given for aqueous solutions. For example, it states that a 13.78% by weight solution will freeze at -6.1˚C. Does this mean that no freezing will occur until the solution is lowered to -6.1˚C? Does it also mean that when solids begin to appear they will be 13.78% by weight ethanol?
|
[
"First question: Yes, the freezing point works the same way regardless of whether it's pure or a solution. ",
"Second question: No, much as where distillation results in a vapor with a higher ethanol content (initially), freezing results in ice with a lower alcohol content (initially). You could say this is because ethanol has a different solubility in liquid water compared to ice. Enriching stuff that way is known as ",
"fractional freezing",
", and it's occasionally done with ethanol. But it can't be used to concentrate ethanol to the extent that distillation can.",
"(as the article points out, one shouldn't think of it as the alcohol and water freezing separately; that's not how it happens. Nor does distillation result in that kind of separation)"
] |
[
"Here you go",
".",
"The solid curve is missing because it is in such vast favour of one component or the other that it basically lie on the vertical axis.",
"For understanding solid/liquid phase diagrams, check out ",
"this example",
"."
] |
[
"Thanks.",
"Then is it possible to plot a liquid/solid composition graph similar to the vapor-liquid equilibrium?",
"I saw a post on ",
"/r/mead",
" of someone saying they were going to try freeze distillation, and I was trying to figure out how much alcohol would be lost as solids in the process."
] |
[
"Regarding the transfer of energy"
] |
[
false
] |
I was reading the article about the fan in the room and it got me to thinking... if I had a large sealed room filled with air of different temperatures (hot spots and cold spots) the air would start to circulate of it's own accord until the hot air was at the top and cold at the bottom. But during the process of the air equalizing, it would be creating friction(heat). Increasing the the overall temperature of the air. What would be lost to produce this heat? I get that the motion of the air is reduced to cause friction, but what is lost to create the motion? I'm thinking pressure has something to do with it, But then wouldn't the pressure also be increased with the increase of temperature?
|
[
"Gravitational potential energy associated with the distribution of densities."
] |
[
"Great answer. To elaborate for the OP, the pockets of denser cold air act like any object in a gravity field: if you let them fall to a lower position they will have a little more motion and a little less gravitational potential. This is where the small amount of heat comes from. If it's a rigid container the pressure will increase proportionally with the heat."
] |
[
"thanks for the elab. I had originally ruled out Gravitational potential energy, as I figured that the room as a whole, would still hold the same amount of Gravitational potential energy regardless of what happens inside, but I was wrong."
] |
[
"What is the status of and the general consensus on the Energy Catalyzer?"
] |
[
false
] |
For anyone who doesn't know, is its Wikipedia page. It seems that one scientist has come up with a possible mechanism, that the Nickel could form a Bose-Einstein condensate and this would provide a mechanism for a copper-nickel conversion with low-energy gamma rays, provided the reaction takes place at ~22 bar and above nickel's Curie temperature. All I've been able to find recently outside of the Wiki page is a bunch of blog articles that mostly deal with the apparent conspiracy of the device's suppression. I'm suspicious of the lack of investment, lack of academic frenzy, and general secrecy that this device has.
|
[
"They have neither been able to properly demonstrate their claims, nor provide a physical mechanism for how it happens. Sounds a lot like BS to me. If they won't patent their device and allow people to look inside of it, then it sounds like a scam to rob investors of their money. ",
"Fusion happens when nuclei, which are both positively charged, have sufficient energy to over come their repulsion and bind together. ",
"nuclear fusion just heats the whole mess up so hot that some fraction of the nuclei have sufficient kinetic energy to overcome that barrier. Other types, like inertial confinement, are more controlled and directed motion, but still the same principle. So when they can't propose a mechanism of action to get through this coulomb barrier (one that passes peer-review into a proper journal), then all we can rely on are their experimental setups. And while their experiments make grand claims, they don't open the box and let people confirm those claims. How do we know there isn't just a battery and another container of copper powder they stir into the container of nickel powder? "
] |
[
"Do you know how cold we have to get things to form ",
"condensates",
"? Nano-Kelvin. ",
"And if they're not doing open-box demonstrations, they're not doing demonstrations. They're doing magic shows. Science is about independent reproduction of data. Anyone anywhere should be able to rebuild my experiment, and produce the same data (within error bars) as I got. If they're not willing to let go of their experimental setup, then they don't have an actual scientific experiment."
] |
[
"If it's not open and reproducible it can't be included in our body of knowledge of objective truths. The ",
" of their device boils down to \"this black box, when fed these inputs, will output energy like ",
".\" We should ignore all the claims about nickel turning into copper or whatever unless we can make ",
" tests on those claims. From a business standpoint, if that black box can produce more useful energy than input energy, then horray, they can make money on it. But I disagree that we've advanced scientific knowledge sufficiently.",
"I know that standard electric generation works in the way that they claim because I can rotate a coil of wire near a magnet and measure a current. I can perform other experiments to confirm every aspect of Electromagnetism and I have a scientific body of knowledge about how it works.",
"Had I instead invented a black box wherein we shoot steam in one end and out the other, and have two wire leads coming out across which is an alternating voltage difference, I may have an invention worth selling, but I haven't advanced ",
" understanding."
] |
[
"To what extent can parents' DNA be reverse-engineered from their child's DNA?"
] |
[
false
] |
A child obtains 50% of their genetic material from their mother and 50% from their father. If a child's genome is mapped, how much of their parents' genomes could be reliably inferred from this? Can we determine more about their mother's genome than their father's? I'm guessing that in terms of genes, we will know what the parents contributed together, but not which parent contributed which allele? What effect will recombination have?
|
[
"research engineer here:",
"A haplotype (haploid genotype) is a group of genes in an organism that are inherited together from a single parent.",
"As the human genome consists of two homologous sets of chromosomes, understanding the true genetic makeup of an individual requires delineation of the maternal and paternal copies or haplotypes of the genetic material.",
"Recognizing the importance of haplotypes, several groups have sought to expand our understanding of haplotype structures at the level of both populations and individuals. Initiatives such as the International Hapmap Project and the 1000 Genomes Project have attempted to systematically reconstruct haplotypes through linkage disequilibrium measures based on populations of unrelated individuals. However, the average length of accurately phased haplotypes generated using this approach is limited to ~300 kb. Alternatively, genotyping parent-child trios can determine whole-genome haplotypes in the child, but such methods are constrained by their higher cost and the sample availability of the two biological parents.",
"Numerous experimental methods have also been developed to facilitate direct haplotype phasing of an individual, including long-fragment-read sequencing, mate-pair sequencing, fosmid sequencing, and dilution-based sequencing. At best, these methods can reconstruct haplotypes ranging from several kilobases to about a megabase, but none can achieve chromosome-spanning haplotypes. Whole-chromosome haplotype phasing has been achieved by sequencing based on fluorescence-activated cell sorting, chromosome-segregation followed by sequencing and chromosome microdissection–based sequencing. However, these methods only phase a fraction of the heterozygous variants in an individual, and more importantly, they are technically challenging to perform or require specialized instruments. Recently, whole-genome haplotyping has been performed using genotyping from sperm cells; however, this approach is not applicable to the general population and requires the deconvolution of complex meiotic recombination patterns.",
"Computational analysis has shown that an important factor in haplotype reconstruction from DNA shotgun sequencing methods is the length of the sequenced genomic fragment. For example, longer haplotypes can be obtained using mate-pair sequencing (fragment or insert size, ~5 kb) compared with conventional genome sequencing (fragment or insert size ~500 bp) (Supplementary Fig. 1a). However, it is technically difficult to isolate and sequence DNA fragments that are longer than what is already obtained using fosmid clones. Hence, using existing shotgun sequencing approaches, it is difficult to generate haplotype blocks longer than 1 million bases, even at ultra-deep sequencing coverage.",
"In the human cell line, ...they obtained chromosome-spanning haplotypes at ~81% resolution with an accuracy of ~98% using just 17× coverage of genome sequencing. These results establish the utility of proximity ligation and sequencing for haplotyping in human populations.",
"source 1",
"source 2: I've modeled genetics and complex protein interactions for my job"
] |
[
"There is no known way to determine this. Most of the previous post was about creating phased haplotype maps, which are reconstructed sequences we believe come from a single haplotype. These can at theoretical best only cover one whole chromosome (and even that's a longshot with the current technology), there's no way we know of to phase across chromosomes to determine which ones came from the same parent.",
"It may be possible in the future that we'll find something like maybe certain epigenetic tags that are only inherited from the mother or the father and these might be usable to attribute a phased haplotype to one parent, but for now we have nothing like that that I'm aware of.",
"Alternately, if some way could be developed to phase the haplotype across chromosomes, we would be able to identify which haplotype came from the father, at least for males, since only the father can contribute the Y chromosome. I can't even think of a way that might be possible.",
"tl;dr: There's no way now, but there's some far out possibilities that might make it possible in the future, who knows?"
] |
[
"Thanks for your detailed answer. I'm not sure what it's telling me in terms of what we can deduce about paternal and maternal genomes solely from a child (i.e. if we don't have access to the parents). ",
"How do we determine where a particular haplotype comes from - the father or the mother? "
] |
[
"It's impossible to determine a particle's position and momentum at the same time. Do atoms exhibit the same behavior? What about mollecules?"
] |
[
false
] |
Asked in a more plain way, how big must a particle or group of particles be to "dodge" Heisenberg's uncertainty principle? Is there a limit, actually? EDIT: Thanks for reaching the frontpage guys!
|
[
"The larger the particle the less consistently the interference is displayed. Buckyballs still show nice wavelike behaviour though."
] |
[
"If you could make a slit small enough, yes it would. But nobody can make a slit small enough.",
"Edit: the slit has to be comparable in size to the de broglie wavelength of the object of interest, which is teeny tiny itsy bitsy (technical term) for a tennis ball."
] |
[
"A small expansion of your statement: it's not just that a particle's position and momentum can't be determined at the same time. A particle can not simultaneously have a precisely defined position and momentum."
] |
[
"What can color change tell you about the qualitative study of an equilibrium reaction?"
] |
[
false
] |
So we're doing a lab tomorrow and I just want to get a head start on understanding some of the questions. This is what we're doing. First off, here's the equilibrium reaction for the lab. Fe (aq) + SCN (aq) <-> FeSCN (aq) We're mixing 5.0 mL of 0.0020 mol/L KSCN solution with 5.0 mL of distilled water in a test tube. Then we obtain a 0.20 mol/L sample of Fe(NO3)3 solution in a dropper bottle. Each of these are colorless. When 1-2 drops of Fe(NO3)3 are added to the test tube containing the KSCN solution, FeSCN is formed. This turns dark orange red (read this off the Internet). One of the questions asks what possible combinations of ions could account for this result. I don't get how combinations of the Fe and SCN could account for this red color change. I get that they're spectator ions, but... not sure what about the combinations. I read something about how the color intensity can tell you about the concentrations, but I'm not sure if turning red means anything. I mean obviously the concentrations of Fe and SCN are decreased because they're being used up to form the product. I'm a little confused, can anyone help?
|
[
"I have a question.",
"How come it goes to FeSCN",
" and not Fe(SCN)3 ?"
] |
[
"Because it is an ion in solution. Same reason why the chlorine in salt becomes Cl",
" and not Cl2 when it is dissolved in water."
] |
[
"Hmm, that's a good question. Probably has something to do with it being ionized I suppose.",
"Any idea on my question though?"
] |
[
"What is dandruff and how does it form?"
] |
[
false
] | null |
[
"Sebum is the oily stuff your skin releases, and more of it is released on your scalp than most other places on the body.",
"There is a fungus that every human has that feeds on sebum.",
"The dandruff comes from your body having an inflammation response to the fungus, which leads to a faster pace in skin cells being grown.",
"Thus with more skin growing than usual more of it flakes off, which is the dandruff.",
"Some people have a greater inflammation response to the fungus than others do, thus why some people have lots of dandruff, and others seemingly have none."
] |
[
"And the solution?"
] |
[
"So be bald?"
] |
[
"Why the hype about the gut microbiome?"
] |
[
false
] |
From what I've gathered, which is very little, there does not appear to be any intriguing findings coming out of the research. The research basically confirms what everyone already thought (which is important at some level), that being what a person eats changes the microbe population in the gut. What am I missing? Also, if you have a good review on this subject handy I'd like to read it. Thanks.
|
[
"It has important implications for treatment. We were generally aware that the microbe population can change, but once we have a better understanding of those changes, we can start developing therapeutic recommendations to improve the microbiome. Stool transplants are one example of a therapy being developed as a result of studying changes in the gut microbiome, and when the dietary implications are better understood, we can start making recommendations in that area as well. But we've got to get a better handle on the basic science first."
] |
[
"More on treatment: C. diff is a common hospital infection that occurs after taking antibiotics. Antibiotics can wipe out some of your normal gut flora = C. diff takes over because nothing is there to compete. By understanding the gut micro biome, we can predict who is more at risk for C. diff (besides past C. diff infections). A new treatment, fecal/stool transplant or 'repoopulation,' as Jetamors stated, will help prevent these infections. Fecal transplants is putting healthy 'poop' through someone's GI tract to re-establish the flora. This prevents C. diff from ever forming."
] |
[
"Key points: good digestion is key to good metabolism and technology is getting affordable."
] |
[
"How does an RNA 'know' which DNA strand to copy during transcription?"
] |
[
false
] |
Since RNA is single stranded, and each base codon codes for an amino acid, what DNA strand is copied greatly influences the protein being formed. If both strands had the chance of being copied then you could have two proteins being coded by one gene. Proteins which could have vastly different functions. Is my understanding correct? Bonus question: Also, since you have two copies of each gene along each chromosome? what determines which chromosome is copied?
|
[
"Just as an intro, DNA is made up of nucleotides, which in turn are made up of the nucleobases that you probably know about (A, T, G, and C in DNA). Each of these nucleosides contains a five-carbon sugar (deoxyribose, in DNA). All the sugars in DNA are put together in the same direction, so that the 5th carbon of one sugar bonds with the 3rd carbon of the next sugar; its 5th carbon bonds to the 3rd carbon of the next sugar; and so on.",
"This means that each strand has two ends; one ends in the fifth carbon (the 5' (5 prime) end), while the other end is the 3rd carbon (the 3'-end). The other strand is reversed; so where one strand has the 5' end, the other has the 3' end.",
"Now transcription in eukaryotes only occurs in one direction: 3' to 5'. That is, the RNA polymerase moves down one strand from the 3'-end towards the 5' end. The strand it reads is called the antisense strand, because the RNA that comes out will LOOK like the other strand - the sense strand (due to the complimentary pairing of the nucleotides, except for U replacing T).",
"Now, each strand has a direction in 3' to 5', so both can be read by RNA, as long as there is a start sequence that says \"Here's a gene to read!\". Interestingly this means that genes can overlap, and the antisense strand for one gene might be the sense strand of a different gene that reads that strand from the other direction for a different gene!",
"EDIT: Just realised I forgot to answer your original question. RNA knows ",
" strand to copy because it finds the sequence of code that says \"Here's a gene to read\", termed a promoter, which causes an RNA polymerase to bind to the strand and transcribe the code in the 3' to 5' direction, creating mRNA, until it reaches a sequence that tells the polymerase to stop."
] |
[
"Yup, it's the promotors and whatnot that trigger expression of a gene, without those (or with just the mirror image of them) the gene won't be expressed. Also remember that there are start/stop codons, and those aren't matched on the mirror image strand.",
"Interestingly, some retroviruses, like HIV, have overlapping genes, where different proteins are coded by the same section but offset by one or two nucleotides. This has the advantage of greater efficiency, shrinking the RNA package that needs to be delivered by the virus, and also increasing mutation rate (since a single nucleotide flip will have more change than with traditionally encoded genes). Of course it has disadvantages as well, though with the typical strategy of replicating the virus a hojillion times any less healthy offspring just die while the healthy ones live on."
] |
[
"RNA doesn't know anything. ",
" ",
"RNA doesn't know anything. Genes occur on both strands of DNA in a chromosome. Transcription of DNA into RNA occurs when RNA polymerase, the enzyme that makes RNA, is recruited to the region just upstream of the beginning of a gene. Depending on the type of gene we're talking about and what organism this is occurring in, how RNA polymerase and the proteins that recruit determine where a gene starts can vary. The general idea is that proteins called \"transcription factors\" recognize specific sequences of DNA in the upstream region of a gene. Different genes will have different sequences of DNA, and so different transcription factors will bind there. These transcription factors interact with RNA polymerase and other transcriptional machinery, which go on to actually transcribe the gene. ",
"Bottom line: genes occur on both strands of DNA, and proteins figure out where to transcribe. ",
"So far as I know transcription occurs at equal rates at each copy of a gene on homologous chromosomes. "
] |
[
"Is there a terminal velocity to 'natural' objects in space?"
] |
[
false
] |
Following the on regarding the impact on Jupiter, I was wondering if there is a top speed that comets and other elements can achieve (and if there is any registered) or if there is just limited by the gravitational pull of the planets 'that goes by'. Sorry for the layman terms...
|
[
"Sort of, but only in the sense that nothing can go faster than the speed of light. This isn't really \"terminal velocity\" with the real definition given by the other posters."
] |
[
"Just as an aside, this is known as the ",
"GZK limit",
" for single particles. Bulk matter has a considerably lower limit as you mentioned."
] |
[
"There is a sort of analogue to terminal velocity here, which is that aside from the speed of light itself, which is an absolute theoretical limit, as an object gets closer to the speed of light it would start being bombarded by highly energetic blue-shifted cosmic background radiation, not to mention high-speed collisions with any stray matter (atoms, dust, cosmic rays) in the space it's traveling through. So the actual \"speed limit\" for a material object is somewhere below the speed of light - it's the speed at which it would be destroyed. Someone else will have to figure out what that number might be.",
"\"As you approach the speed of light you will be heading into an increasingly energetic and intense bombardment of cosmic rays and other particles. After only a few years of 1g acceleration even the cosmic background radiation is Doppler shifted into a lethal heat bath hot enough to melt all known materials.\" -- ",
"The Relativistic Rocket"
] |
[
"Are there any GMOs that out compete their wild-type counterparts?"
] |
[
false
] |
[deleted]
|
[
"Mosquitos",
", which they are already talking about using in ",
"Florida",
" ",
"There are in fact tons of GMO animals, ",
"glowing fish",
", cows that produce human ",
"antibodies",
" or ",
"breast milk",
" in their milk, ",
"goats",
" that have silk in there milk. ",
"Here is a new species of ",
"lizard",
" created in a lab. "
] |
[
"Basically: have we been able to one-up evolution?",
"I know what you are asking but make no mistake, when you express the algorithms which govern natural selection, it is a law, as immutable as the laws of thermodynamics (and really just a complicated extention of those latter laws).",
"So even in the case of something like Papayas, we aren't one-upping evolution. GM tech is wholly dependent on evolution and the laws of natural selection. The technology works because of evolution, not despite it.",
"But back to your question, you might take a more broad appraoch and ask which monocultured crops can grow in the wild (GM or not)? All GM and classical tech changes are made with the selective environment of the farm in mind, not the wild. The papaya is the best example where a wild survival advantage was conferred, but even then, ringspot virus does not exist everywhere, and non-GM papaya will grow just fine either in the wild or on farms in places like Australia and South America."
] |
[
"The GM mosquitoes have been release in several countries. These buggers were designed to have non-viable offspring. Not exactly what you are asking, but it's reported that these mosquitoes were able to ",
"reduce the population of mosquitoes in the Caymans by 80%",
" so in my opinion they out performed their natural counterparts and successfully prevented reproduction. "
] |
[
"How do the bacteria that work for human food digestion get in?"
] |
[
false
] |
As far as I know, its impossible for one species to spawn another, so humans, or any other animal that needs them, cant create the vital bacteria themselves. So are the bacteria injected by the mother to the fetus already pre birth? Or do the bacteria get in post birth? If so do they get in with the food we eat or crawl their way in? Tagged as biology instead human body because reasons.
|
[
"The bacteria are initially acquired from passage through the birth canal. After a few years, the initial microflora are replaced by microbes the child acquires from its environment through ingestion (food, dirt, contact with other humans, etc.)."
] |
[
"What about children born via caesarean section? "
] |
[
"There's an excellent, albeit slightly old, review here: ",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3110651/",
"In short, there are differences, and those may be associated with the increase of some kinds of diseases seen in non-vaginal births. (Or they may not be; it's early days yet for this research.) "
] |
[
"How can a black hole be so much smaller than a neutron star? Aren't neutron stars already super dense and without orbitting electrons, so without any void between nucleons?"
] |
[
false
] | null |
[
"That's not... known for an astrophysical black hole. All we know is that the radius of the mass is less than the Schwarzschild radius.",
"You're assuming that there's a physical singularity at the centre of the black hole. But I think it's much more likely that GR simply breaks down and we need quantum gravity... like, say, string theory. ;)"
] |
[
"Neutron stars form when the energy available from gravitational collapse is greater than the energy needed to overcome electron degeneracy pressure by forming neutrons from protons and electrons.\nTheoretically a higher available gravitational energy would overcome the neutron degeneracy pressure and form an even denser form, possible quark based at some point. But as ",
"/u/rantonels",
" says, we cannot know because we cannot observe inside a black hole, therefore unless we are lucky enough to witness a black hole forming and have a chance to take some measurements during the process ",
" understand what we see we can't know."
] |
[
"From the outside, it doesn't really matter what's inside a black hole, it's cut off from the rest of the universe.",
"Note that even a neutron star is dense enough to be a black hole if it's large enough. A neutron star larger than 14 solar masses would become a black hole because it would have an event horizon larger than itself. In actuality, neutron stars can't get that large, they collapse into more compact objects. From the perspective of our Universe, what's inside a black hole is academic, since there's no way for structure inside a black hole to interact with the Universe outside.",
"Edit: one additional comment. There is a common misconception of black holes in a sort of quasi-Newtonian sense, as objects which have such strong gravity that the escape velocity is higher than the speed of light. This is very much the wrong view of black holes, they are entirely creatures of relativity. The event horizon of a black hole is a one way door. Around the black hole space-time is bent by gravity so much that within the event horizon the only paths in space-time that go forward into the future also go toward the singularity, there are no routes out of the black hole once inside."
] |
[
"What natural evidence proves that living organisms can evolve from non-living matter?"
] |
[
false
] |
What natural evidence/occurrences proves that living organisms can evolve from non-living matter? Moreover, just because an act can be completed in a lab under perfect conditions doesn't constitute an act to be naturally able to occur. Is the latter statement also a fair argument?
|
[
"Not really.",
"We know that amino acids can ",
"form during electrical discharges",
". We know that amino acids can ",
"spontaneously form chains",
" - thus, we get basic proteins, no life necessary. We know that some kinds of protein encourage similar proteins to form. Thus, you get competing species of protein, and natural selection.",
"Saying, 'oh, you only did that in a lab' isn't a good argument, since the lab is set up to replicate the conditions of the time in question. In fact, you can't do this 'out' of the lab, because any setup to let you observe it ",
" a lab! We've proven that these things ",
" happen. We've got good evidence that conditions were pretty good for these processes on the early earth. Since it is possible, all we can talk about is how probable it is. "
] |
[
"This question has nothing to do with evolution. The transition between non-living matter and living-matter that you're referencing is abiogenesis."
] |
[
"I know of a couple other papers that are worth mentioning.",
"This one",
" showed that specific RNA sequences were able to indefinitely catalyze the replication of their own sequences.",
"This one",
" (lay ",
"summary",
") showed that the replication of lipid vesicles (which spontaneously occur when detergents are dissolved in water) was enhanced from hours to minutes by the replication of contained nucleic acid sequences."
] |
[
"Why is it hard to create a cream that can change skin color?"
] |
[
false
] |
Between tanning and skin lightening/whitening, it's pretty obvious that a lot of people want to modify their natural skin color. Yet, despite the billions in potential revenue from the creation of a successful product, spray on tans make you look like an oompa-loompa, and skin whiteners simply don't do anything. I can only assume that altering skin color is really difficult if no one has figured it out yet. But why? Any biologists/chemists want to fill me in on the complexities of altering the skin's melanin content?
|
[
"Had vitiligo."
] |
[
"Had vitiligo."
] |
[
"There is some research being done in this area. I know someone who did a bit of work for a large cosmetics company, looking at tyrosinase inhibitors for use in skin whiteners. Tyrosinase is part of the pathway that produces melanin, so inhibiting it reduces melanin production, resulting in paler skin.",
"From what I recall of the presentation I saw, it proved to be a fairly challenging target. It has a large, open binding site with two copper ions - it is hard to design a small molecule that will bind in such a site. In addition to that, a compound for cosmetic use has to be stable enough to sit in a pot of cream for a couple of years without breaking down or otherwise reacting with the other components of the product.",
"If memory serves, there are some tyrosinase inhibitor products on the market for cosmetic use, but the active ingredient isn't that potent. They are mostly designed for use on a localised area where there is an over-production of melanin rather than the whole face/body."
] |
[
"How do dogs recognize other dogs?"
] |
[
false
] |
It baffles me that dogs can recognize dogs they have never met before, often from a great distance (suggesting smell is not a factor), and when different dog breeds look so different from one another. I have found scientific evidence suggesting that there is some level of recognition, or at least differential interest, between dogs, but no explanation as to HOW it happens.
|
[
"This can't be right for all cases. I know dogs that look out the window and will react to every passing other dog. No way when someone opens a car and a dog gets out, that the dog locked inside the house will smell the other dog so fast. "
] |
[
"I agree, and this article agrees with you: ",
"https://blogs.scientificamerican.com/dog-spies/do-dogs-know-other-dogs-are-dogs/"
] |
[
"Thanks. Now as you say it. I've shown printed dog pictures to dogs and they looked more interested at it than just a random picture of a landscape. "
] |
[
"Why do our thumbs have 1 joint less than our finghers?"
] |
[
false
] | null |
[
"And why is it gone?"
] |
[
"I'm not sure why exactly the intermediate phalanx is missing in the thumb, but I would bet it has a lot to do with the evolution of thumb opposition (the \"opposable thumb\"). There is a rare malformation called a Triphalangeal thumb where the thumb has all three phalanges, just like the other fingers, and the thumb is no longer opposable. In fact, it looks just any other old finger. There's a great photograph of one on the ",
"wikipedia page for Triphalangeal thumb."
] |
[
"The difference between your fingers and thumb is the lack of a fifth metacarpal bone in your thumb"
] |
[
"[Computer Science] Why does solid state memory (SSDs, Ram) come in intervals of 2^x?"
] |
[
false
] |
[deleted]
|
[
"As you probably know, modern digital computers mostly use binary. Processor instructions are provided in binary form, and numbers are represented in binary formats. And sending an address to a storage device is also done in binary. ",
"When you are going to store something in memory, you need to tell the storage device what memory location to put it in. That is done by providing a memory address (or a set of addresses). Since addresses are also provided in binary, every time you increase the number of address bits, you double the number of possible storage locations. So generally, new storage devices must be at least 2x as large as the previous largest one. And if it isn't, there will be potential memory locations which are not actually addressable. ",
"For example, let's say your old storage device had 4 address lines. This means that it can store data in 16 different locations (24 = 16). If you add one address line, it can now store data in 32 different locations. Making a storage device that could only hold 25 different pieces of data would mean that there were 7 addresses that were not usable with a 5-bit address scheme, and 4 bit addressing would be insufficient to access them all. ",
"If nothing else, that means some complexity must be added to the controller so that if you try to store something in one of those 7 locations an error gets sent back. Otherwise, one of the other locations will be incorrectly overwritten and/or data will be lost. ",
"Since this is the natural progression of things in binary addressing, people rarely have made storage devices that didn't work on powers of 2. It's just asking for trouble, and it has become a de-facto standard now. And from an engineering point of view, it just makes sense. ",
"Of course, there are exceptions. If you look at a DVD and see how many bits/bytes are actually written on one, you will find it is not a power of 2. But those controllers are fairly sophisticated, and there's no reason to mandate that every DVD be the same length. (If every sector is completely used, it will have a power of 2 of \"user data\". But not actual data.) "
] |
[
"In solid state memory, there absolutely ",
" 16 storage locations which are addressed. They are physical, permanent places on the die that you can point to. If you have a very small finger and exceptionally good eyesight. It is different for disc memory, and since SSDs mimic disc to some extent, you can say that it is an inference on SSDs. But not on DRAM or SRAM. ",
"But it's an unimportant distinction anyway; the point is that the number of address lines sets the maximum number of addresses, and that's a power of 2. "
] |
[
"SSDs currently use 8 GB ",
"NAND",
" dies so their storage is limited to multiples of 8 GB. They're usually following the powers of 2 because they just double the dies per package to increase the size. Keep in mind this is arbitrary and there's a lot of drives that don't double their sizes. Using some Corsair drives as an example, they have 8 packages, so 1 die is 64 GB, 2 dies is 128 GB, 3 is 192 GB, 4 is 256, etc. Any SSD that isn't in a multiple of 8 is most likely just being more honest about the usable space.",
"RAM is in powers of 2 because the computer works in base 2. It would be possible to make RAM with a size not in base 2, but it would add needless complexity and make calculations harder."
] |
[
"Can a single atom be magnetic?"
] |
[
false
] | null |
[
"Yes. A single atom can have a magnetic dipole moment."
] |
[
"As long as the electron spins are aligned? "
] |
[
"The magnetic moment of the entire atom is determined by the sum of the magnetic moments of the nucleus and the electron cloud."
] |
[
"is time dilation theoretically possible? if so, how? anddoes it occur anywhere we know of?"
] |
[
false
] | null |
[
"Time dilation is not only possible, it definitely happens.",
"https://en.wikipedia.org/wiki/Tests_of_special_relativity",
"https://en.wikipedia.org/wiki/Tests_of_general_relativity"
] |
[
"could theoretically one child be 10 years old and another child be 50 years old?",
"Yes.",
"so not only are \"clocks\" moving slower, but actual physiological effects happen slower as well?",
"Yes."
] |
[
"what an incredible concept"
] |
[
"Why is the HPV vaccine not recommended for people over 26 years of age?"
] |
[
false
] |
Also, how likely is it to be beneficial for someone who's already sexually active? I mean, how likely is it that a person who has had several partners has already come into contact with every strain that's present in the vaccine?
|
[
"Because you have to get the vaccine prior to exposure. Otherwise it doesn't work.",
"The hight rates of prevalence (up to 80%) means that, statically, by the time you're 26 or older it's pointless to get it. There's no actual health risk and if you've not had sex before than, yes, go out and get it.(1)",
"Source: I work in vaccine development. Have spoken to the co-inventor of the HPV vaccine, and sat through hundreds of hours of lectures/presentations/Grand Rounds/Clinical Case Rounds/etc. on this subject.",
"Footnote: (1) NOT to be taken as medical advice. Talk to your doctor. "
] |
[
"A lot of health policy is based on the allocation of limited health resources. ",
"Not true. Health policy is based on the allocation of limited resources, ",
"How are these different exactly?"
] |
[
"Full disclosure: I am an immunologist, I work on vaccines and immunotherapies, including those for HPV.",
"The reason it is not recommended for people over 26 years of age is due to the fact that the pharma companies who make the vaccine - Merck and GSK - have not done a study that provides data to suggest efficacy in this age group. More to the point - they don't know if/how well it would work in an older agegroup. Since no study has been done in an older population, the FDA can not/will not recommend it in an older population.",
"I_am_a_BalbC was on the right track as to why they haven't done this type of study in an older agegroup. By your mid-20s most Americans have been exposed to hundreds of HPV serotypes. However, this fact in and of itself is not enough to prevent an HPV vaccine from having efficacy in an older agegroup. In fact, infection with the low-risk serotypes included in the Merck vaccine can self-resolve, with no protective immunity induced. This means that people could get infect with HPV serotype 11 (as an example), the infection could clear, and that same person can get infected again because they don't have an immune response that prevents infection. The vaccines DO drive an immune response that prevents infection, and thus in these types of patients, it MIGHT be efficacious. Thus, I_am_a_BalbC's response was close, but not correct in this regard. There are groups of patients that can get infected, clear, and get infected again. The vaccine could theoretically work in these cases.",
"Truly, the reason that this type of study WON'T be done is twofold -\n1. From a business standpoint it doesn't make sense for Merck or GSK. They are already hitting the targets that they want, spending money on a bigger study that may or may not allow them to recommend the vaccine to a wider target base just isn't fiscally worth it to them.\n2. From an epidemiology standpoint - vaccinating children prior to exposure will help stem/stop the spread of the variants that cause overt HPV disease in the younger generations. For those of us who are older and may already be infected, the current vaccines that are being marketed wouldn't help clear the virus after infection. New immunotherapies are in the works by a number of companies to address that need."
] |
[
"How does being blind at birth affect someone's sexuality/sexual development?"
] |
[
false
] | null |
[
"This is a really hard question because I do not think we have adequately answered from a research perspective if sexuality is something that is coded at birth or something learned.",
"New studies show that gender forms in the mind which helps define the roles we will play in sexual relationships. However most of this research is being used to prove gender is a mental construct while avoiding the behaviors that lead to that construct.",
"It's clear that culturally, once we know we are having a boy or a girl we start to paint the room certain colors and decorate it with certain objects (that is our parents raise us to have a gender). A great majority of this would be lost to a blind child as they would not know there room is painted blue (a \"boy color\") nor be able to see the objects. I still think there will be plenty of room for parents to program gender though.",
"From this, I think it's clear to conclude that if the baby was not intersexed (thus having more sexual complexity) that they would be more gender-neutral (sometimes refered to as gender blind) than a counterpart that can see because they would miss out on some (not all) the gender programming. ",
"Nonetheless, I think we could say by mean average of American parenting that the blind kid would still be encoded with a gender."
] |
[
"I could be mistaken but a post is being \"shuffled\" around based on a few levels of activity. One of which is commenting. If a commentor adds somewhat anecdotal comments atleast that's action for the thread which gets it attention.",
"I have had a number of posts where I have done this, I have gotten negative karma yet its clear that my post got some of the commentors involved int he thread (they replied to me and then opened a new comment).",
"More to the point why should such a person care about their karma? This is askscience so I would say most of us a bit more thoughtful and well... fuck if I care about internet points."
] |
[
"I could be mistaken but a post is being \"shuffled\" around based on a few levels of activity. One of which is commenting. If a commentor adds somewhat anecdotal comments atleast that's action for the thread which gets it attention.",
"I have had a number of posts where I have done this, I have gotten negative karma yet its clear that my post got some of the commentors involved int he thread (they replied to me and then opened a new comment).",
"More to the point why should such a person care about their karma? This is askscience so I would say most of us a bit more thoughtful and well... fuck if I care about internet points."
] |
[
"What food contains gold in it?"
] |
[
false
] |
[deleted]
|
[
"Pure gold is nonreactive and nontoxic, but has no nutritional value and is not used biologically by any known organism. It does not appear naturally in any food.",
"It is approved has a food additive, because it is decorative, and because people like to say, \"hey, I just ate some gold\"."
] |
[
"anything decorated with gold leaf I guess.\nAlso not so much a food, but Schnapps Cinnamon contain Gold flakes"
] |
[
"Are you asking having discovered ",
"E175",
"? I'm sure there are traces of it in many things but as an additive ",
" it's used mainly as decoration eg. in Goldschlager."
] |
[
"What is the body's physiological response to getting kicked really hard in the balls and why is it so different from being kicked anywhere else?"
] |
[
false
] |
[deleted]
|
[
"Testicles are internal visceral organs that have migrated out of the body cavity - as such, they have visceral innervation rather than somatic. Visceral innervation is known for producing intense pain when the capsules surrounding organs are stretched. Classically, issues like bowel obstructions or stones (gall- or kidney-) produce similar feelings of pain. Testicles hurt when hit because any other visceral organ would hurt when compressed - this is why punches to the back overlying the kidneys are so painful. ",
"The fact that you feel it in your abdomen is likely simply due to the way nerve tracts run (again, visceral sensation), and is known as ",
"referred pain",
".",
"Before anyone starts on 'why did we evolve this weakness' type questions (they invariably pop up on this question), look over ",
"this page",
" first."
] |
[
"Visceral pain is commonly associated with nausea",
", and thought to be related to autonomic activity."
] |
[
"Why do I feel incredibly sick when it happens?"
] |
[
"What is the fastest moving celestial object we have found?"
] |
[
false
] | null |
[
"This is an extremely vague question. However, if you want to know what star in the Milky Way has the highest velocity relative to the Sun, it appears to be a star known as ",
"SDSS J090745.0+024507",
" moving away from us with a velocity of about 850 kilometers per second. Such hypervelocity stars are likely ejected from the nucleus of the Galaxy in 3-body interactions with the central supermassive black hole and another star.",
": see Silpion's comment below. Neutron stars have been found at even higher velocity."
] |
[
"Faster neutron stars have been seen",
", at up to 1500 km/s. These are probably the result of asymmetric core-collapse supernovae."
] |
[
"Nice, I forgot about those."
] |
[
"How come it seems that the majority of dna mutations result in cancer of some type?"
] |
[
false
] |
If I understand it correctly, cancer is the result of losing growth or meiosis inhibitors. This seems like a decently specific change. When you have a dna mutation, what gets messed up should be random. How come out of the trillions of potential changes that the mutation could have made, destruction of cell growth inhibitors is by far the most common?
|
[
"Mutations happen all the time, but they mostly will harm the cell enough for it to just die off (and you never see it). Mutations that predispose to cancer can be of various kinds. Some of them are: Mutations in genes that keep cells alive (so the cells are kept alive even if they should die), mutations in genes that kill cells (so the cells aren't killed even if they should be), mutations in error-correction genes (so the random errors that happen in DNA replication don't get fixed and tend to add up), mutations that make the chromosomes unstable, and so on. Even mutations in genes that control how easily (or not) a cancerous cell can move around the body (=metastasis) could affect your risk of getting a (metastatic) cancer. ",
"So cancer is really what happens when a cell does not get signals (or ignores them) to stop growing/to die when it is supposed to, or gets too many \"stay alive\" signals. The actual mutation can be in a lot of different parts of those pathways."
] |
[
"It's a kind of confirmation bias. Why are all toupees terrible? Because we only notice the terrible ones. The rest hide in plain sight.",
"We see mutations that cause cancer because the other mutations have no effect (which we don't see) or cause cell death (which we don't see, or we don't recognise as a mutation) . We mainly see the ones that cause run-away growth, aka cancer."
] |
[
"Only a tiny fraction of mutations lead to cancer. "
] |
[
"So how old is the water I'm drinking?"
] |
[
false
] |
[deleted]
|
[
"It really depends on your definition of old. ",
"If you take a sample of water as a sort of bulk material object, it has a history and special properties, such as dissolved minerals and pH. Those bulk properties will change a lot any time the sample environment changes, for example moving from the pipes in the ground into your digestive system. From that perspective the water gets new life in each different use as it moves through the water cycle.",
"If you look at a water sample as a collection of H2O molecules that happen to be connected to other stuff, then the state of the H2O is the focus. From that perspective, state changes from gas to water to ice could be considered a type of rebirth, or it could be considered the continued life of the specific H2O molecules.",
"If you consider the trajectory of the specific H2O molecules in question, then your water is as old as the last time the H2O emerged from some other chemical process. From that perspective, new water is being \"born\" in the tailpipe of a car, as complex hydrocarbons and oxygen are burned to produce H2O and CO2. In that case much water would be extremely ancient, moving between different thermal states but having the H2O molecules remain whole."
] |
[
"Mods forgive me, but ",
"The Oatmeal",
" seemed extremely relevant."
] |
[
"Water is a byproduct of metabolism, and hydrogen is often stripped from the oxygen to produce alcohol groups, acids, ketones, or even just adding a hydrogen to carbon and water is produced again in breaking down those molecules. I would really love if someone could calculate the turnover rate of water molecules in all biomass into different molecules and the rate they are converted back. Then we could see how long it would take to turnover the total volume of water on earth from biological sources. Of course, we would also have to have some way of approximating the water turnover rate from nonbiological sources, but I have no idea where to even start on that. ",
"Edit: also acid and base solutions have OH- and H30+ groups which would mean these water molecules most likely won't get back the exact same hydrogen they lost, changing which specific atoms are in each specific molecule. "
] |
[
"What is the temperature of a black hole and why?"
] |
[
false
] |
[deleted]
|
[
"The temperature of a black hole is inversely proportional to its mass. The numerical value for the temperature in Kelvin works out to be [(1.23 x 10",
" kg)/M] K, where M is the mass of the black hole.",
"In classical general relativity with a quantum mechanical description of other particles, black holes radiate a thermal spectrum of particles, corresponding to this temperature."
] |
[
"Mini black holes have never been observed, in a particle accelerator or elsewhere.",
"But you are correct that the smaller a black hole, the higher its temperature. When a black hole reaches its final stages of evaporation, its temperature is very high and it is expected to release high energy gamma rays."
] |
[
"Does this value also apply to the mini black holes created in particle accelerators? If so due to the small mass wouldn't this be an incredibly high temperature?"
] |
[
"What prevents a normal, healthy heart from going into cardiac arrest during very, very intense exercise?"
] |
[
false
] |
[deleted]
|
[
"The heart adapts to higher rates. For instance heart rate is normally controlled by the sino-atrial node by a balance of sympathetic (+) and vagal (-) inputs. But the heart also gets sympathetic inputs to other parts of the muscle which alter the action potentials and conduction (e.g. shortening it), so that the fast rate doesn't cause problems. The atrio-ventricular node in a healthy heart won't conduct rates higher than 150-200. Arrest rhythms can be 300 beats per minute because they are generated in the ventricle itself or down an abnormal pathway. ",
"There is also probably regulation upstream of this, i.e. in the hormones and nerves. Some states and drugs can cause arrhythmias through abnormal stimulation so intense exercise must not cause as much. "
] |
[
"I'm going off of memory here, but you have to consider the fact that the heart does need time between contractions of atria and ventricles for the vessels to fill with blood. If the heart is contracting ",
" fast, there is insufficient filling time. Further, during exercise, the heart has the benefit of regular muscle contraction to aid in bringing blood back to the heart. The 'muscle pump' helps to more quickly fill the right atria. In clinically significant tachycardia, the extra help in bringing blood back to the heart is not there."
] |
[
"Thanks for this. Interestingly, when I had AVNRT the doctor mentioned to me that the rates that I had were some of the fastest he had seen. 290 bpm. I can tell you, it was not fun at all."
] |
[
"A few questions about the Human Heart"
] |
[
false
] | null |
[
"These are fairly easy figures to research, and the project seems to be very entry level. Instead of spoon feeding some answers here are some ways to expand your search:",
"1) search for cardiac pressure-volume loop making sure to understand end diastolic and end systolic volumes for both atria and both ventricles to determine \"empty space\" and how much blood is in the heart before it beats.",
"2) search for cardiac output and how it is determined to determine how much blood is pumped per minute and to calculate how much blood flows per beat.",
"3) Search for ejection fraction to lead you in the right direction for how forceful the heart beats. Also look into cardiac contractility."
] |
[
"It seems entry level because I'm a high school student, and I didn't think to look for those kinds of things, thanks, that should help a lot."
] |
[
"Of course, one of the hardest parts of any research is figuring out where to start.",
"Good luck and if anything is still confusing feel free to PM me and I will help out to the best of my capacity."
] |
[
"Are there any molecular similarities between something being 'freezer burnt' Vs. being burnt by a flame?"
] |
[
false
] | null |
[
"Not really.",
"\"Freezer burn\" comes about when the water in a substance freezes, but is allowed to migrate to the surface and sublimate away. It's essentially slow-motion freeze drying, and in the process wreaks a lot of physical havoc on cellular tissue. Molecularly, there's not much change - proteins remain proteins, carbohydrates stay in their original forms - but the physical structure of an object can be damaged.",
"Burning with heat is a massive chemical change. Nearly every molecule will be broken down by high heat, and organic molecules are particularly vulnerable. Proteins will first denature (like cooking an egg white) and then start breaking down into other molecules. Carbohydrates will caramelize, and then start breaking down until only carbon remains."
] |
[
"As someone in the industry, is there anything you do to consider the action of freezing? For example, what is done for food that is intended to be frozen?"
] |
[
"depends what you mean by molecular? On a physiological level they both cause damage by transfer of energy to/from the affected tissue. The resulting damage is due to cell and protein destruction and local/systemic inflammation. A hell of a lot of other specific stuff goes on but they're effectively two paths that converge on the same point."
] |
[
"If you were on a train travelling at 50m/s, standing at the back, and fired a bullet travelling at 100m/s in the opposite direction, hiw fast would the bullet be travelling relative to an observer on the platform?"
] |
[
false
] | null |
[
"Approximately 50 m/s."
] |
[
"But why? There is no force on the ball by the train..."
] |
[
"Why would that matter?"
] |
[
"If I wire a capacitor in series with a battery powered motor, will the motor have a greater power output?"
] |
[
false
] |
I know capacitance is amount of charge per volt, and motors depend on charge. Will the force that drives the motor increase with higher capacitance?
|
[
"That last bit is important: batteries are DC (zero frequency) so a capacitor in series breaks the circuit: the motor would be turned off, so zero power out."
] |
[
"A capacitor wired in parallel with the battery will act in the same manner as the battery, storing charge. The difference is that the energy density is lower, but the current capacity higher, so the capacitor can help to \"stiffen\" the supply voltage against transient current demands.",
"A capacitor wired in parallel with the motor will act as a crude high-pass filter, providing a current bypass when the voltage frequency exceeds the corner frequency of the first-order filter, but in a battery driven system, frequency is zero, so the capacitor will do nothing except store charge.",
"A capacitor in series anywhere in your circuit will interrupt the circuit except at high frequencies (again, only applicable to AC)."
] |
[
"it helps to understand that a capacitor is simply 2 metal plates that are not touching each other. cutting a wire in half is making a capacitor. again this is for DC only, way different when were talking about AC or RF"
] |
[
"Salt vs. Health . Is there evidence or not?"
] |
[
false
] |
Last weeks I've been seen submissions that bash the common belief that salt consumption in excess is bad for your health. Is this true or not?
|
[
"Is this true or not?",
"It is complete baloney.",
"The link between salt, hypertension, and stroke is almost universally accepted in the medical community. The evidence is very strong and there is almost no controversy among experts. Note that this is on a community level; some individuals may not be sensitive to salt.",
"The studies I am most familiar with were performed in Japan. Here's a description of the study and a reference. I think the original is in Japanese, unfortunately.",
"From ",
"http://www.worldactiononsalt.com/evidence/population_studies.htm",
"Japan : In the late 1950s the Japanese became aware that certain parts of Japan , particularly the north, had a high salt consumption and deaths from stroke were amongst the highest in the world. It was then found that the numbers of strokes in different parts of Japan were directly related to the salt intake. In view of these findings, there was a Government campaign to reduce salt intake, which was successful in reducing salt intake over the following decade from an average of 13.5 grams per day to 12.1 grams per day. However, in the north of Japan the salt intake fell from 18 grams per day to 14 grams per day. At the same time, there was a fall in blood pressure both in adults and children, and an 80% reduction in stroke mortality (1). At the time of this fall and the reduction in stroke mortality, there were large population increases in fat intake, cigarette smoking, alcohol consumption and an increase in weight. It would appear that the Western influence which was rapidly overtaking Japan seemed to have little effect on blood pressure, provided salt intake was reduced, and overall the reduction in salt intake appeared to be associated with large falls in deaths from stroke.",
"Iso H, Shimamoto T, Yokota K, et al. [Changes in 24-hour urinary excretion of sodium and potassium in a community-based heath education program on salt reduction]. Nippon Koshu Eisei Zasshi. 1999;46:894-903.",
"Here's",
" a meta-review looking at the available data. It found significant impact of salt on blood pressure.",
"Believe it or not, there is a pro-salt lobbying group called the ",
"Salt Institute",
". Their website reads like tobacco company propaganda."
] |
[
"Not an expert, but I read up on this study a bit: it is controversial and contradicted by other studies. I think currently there is no good consensus, partially because these kinds of epidemiological studies are really hard to control, and no one has the ability to run a truly controlled experiment. ",
"From ",
"here",
":",
"Perhaps the study did not have look at enough patients to uncover a statistically significant effect. This possibility is raised by Francesco Cappuccio, who heads the World Health Organization Collaborating Centre for Nutrition at the University of Warwick, UK. \"The only problem here is that they're not statistically significant and the reason for that is the meta-analysis is too small,\" Cappuccio says. He notes that low-salt diets did show a trend towards protecting against cardiovascular disease. ",
"Taylor thinks the best explanation is that patients cut their salt intake early on in the studies but eventually allowed their intake to creep up, masking any benefit. \"They're intensively followed up for a couple years, and 8 or 10 years later these people's behaviour has probably reverted to what it was,\" he says."
] |
[
"I had read somewhere that these studies suggested that, among the people who do not suffer from hypertension and stroke, those who consumed more salt lived longer. ",
"I'm by no means an expert, so please consider this a question and not a challenge to your response."
] |
[
"Does the human body lose more fat/calories shivering from coldness or sweating from hotness?"
] |
[
false
] | null |
[
"It's being studied",
"http://onlinelibrary.wiley.com/doi/10.1111/j.1467-789X.2010.00851.x/abstract",
"Meanwhile, recent studies of the role of brown adipose tissue (BAT) in human thermogenesis suggest that increased time spent in conditions of thermal comfort can lead to a loss of BAT and reduced thermogenic capacity. Pathways linking cold exposure and adiposity have not been directly tested in humans. Research in naturalistic and experimental settings is needed to establish effects of changes in thermal exposures on weight, which may raise possibilities for novel public health strategies to address obesity.",
"BTW, be careful with detailed disclosure of development of novel machines on an internet forum. Maybe your friend and MIT wants to acquire IP"
] |
[
"Yes. Shivering is the body activating the skeletal muscles to generate heat from their inefficiencies. Sweating is the release of moisture from the pores, and while this is not a zero energy action, it would be much less than shivering."
] |
[
"Yes. Shivering is the body activating the skeletal muscles to generate heat from their inefficiencies. Sweating is the release of moisture from the pores, and while this is not a zero energy action, it would be much less than shivering."
] |
[
"What if the Golbach conjecture get verified ?"
] |
[
false
] |
Any odd number superior than three can be written as a sum of two prime numbers What would be its implications -in mathematics ? EDIT attempt : I am in the app, it's Goldbach.
|
[
"Not really too many direct consequences, it's not like the Riemann Hypothesis or anything. However, the methods to prove it are likely to be novel and interesting and can perhaps provide us with a new way to look at other problems."
] |
[
"OP stated it wrong, it's \"every even integer number greater than 2 is expressible as the sum of 2 primes\". The odd version states \"every odd integer greater than 3 is expressible as the sum of (at most) 3 primes\" which in the case of 23 has a few solutions ",
"(I forgot to say that the Odd Goldbach Conjecture was resolved in 2013!)"
] |
[
"It should be every ",
" number larger than 2 can be written as a sum of two primes."
] |
[
"When sp hybridization what benefits does Raman spectroscopy provide over IR spec? (grad student in chem)"
] |
[
false
] | null |
[
"A good home for this question is ",
"/r/AskScienceDiscussion",
".",
"Please see our ",
"FAQ."
] |
[
"I read the FAQ why is this question a bad fit for askscience?"
] |
[
"The question is mostly an open discussion on research techniques/technologies. It is also bordering on homework help. If you can be a bit more specific in explaining your question, focusing on the theory and specific details of the techniques so others can benefit from this discussion, then I will let it through."
] |
[
"What would it take to put a country like USA or Canada in as severe an economic collapse as Zimbabwe around 2008?"
] |
[
false
] | null |
[
"It happened to Rome in a pretty big way when they were still the top dog of the world. Of course this was like 1700 years ago and the idea of inflation hadn't really occurred to anyone yet. It got bad enough that the armies wouldn't accept the worthless currency and the empire started paying them with the goods that they would have bought with their pay. This led to an entirely new tax scheme that involved everybody basically being locked into their current profession and the value of land being assessed and assigned a specific value, which was used to determine how much of the military each province was to feed and outfit. This is widely regarded as the transition into manorialism, which in turn led to the feudalism that was present throughout Europe in the medieval preiod.",
"What were we talking about again?"
] |
[
"So in other words, what you would need to turn the US into an African country is a total erosion of our existing laws, business morays, and sensibilities.",
"Just for future reference, morays are eels - mores are customs.",
"I very much like the idea of a business moray, but I'm not sure if they make suits to fit. Perhaps they could get away with a pinstripe sock."
] |
[
"So in other words, what you would need to turn the US into an African country is a total erosion of our existing laws, business morays, and sensibilities.",
"Just for future reference, morays are eels - mores are customs.",
"I very much like the idea of a business moray, but I'm not sure if they make suits to fit. Perhaps they could get away with a pinstripe sock."
] |
[
"If space based telescopes cant see planets how will the earth based European Extremely Large Telescope do it?"
] |
[
false
] |
I thought hubble was orders of magnitude better because our atmosphere gets in the way when looking at those kinds of resolutions. Would the same technology work much better in space?
|
[
"By being much much bigger. The big advantage of space telescopes is no atmosphere, meaning no seeing (the twinkling of stars) and no atmospheric absorption of light. The big disadvantage is price and size - it is extremely expensive to launch a space telescope, they can only be a few meters across.",
"Land based telescopes on the other hand can easily be made enormous. We have adaptive optics and other systems nowadays to compensate for seeing. This allows us to negate many of the problems of the atmosphere and use enormous land telescopes."
] |
[
"Normally the sharpness of a picture is limited by the diameter of the mirror. Get a bigger mirror and you can make sharper images. The 8.2 meter mirrors in the VLT are about the biggest we can make with current materials.",
"Another way to increase sharpness is to compensate for deformation of the mirrors. These are so big that they bend under their own weight, and the frame contains hydraulics to compensate for that. After moving a mirror the parabolic shape distorts through the weight of the system, and hydraulic rams bends the mirror bed to restore a perfect parabola.",
"The third trick is adaptive optics. The air between the telescope and the object you are looking at moves and deforms. The VLT has hundreds of small motors under each mirror and a laser-system that takes snapshots of the atmospheric distortion. The motors deform the mirror in the opposite way from the atmospheric distortion, and the result should be undeformed images.",
"And the fourth and final trick is to couple all four telescopes and make them operate as one. There is a network of tunnels and mirrors below the four VLT telescopes to allow this. By very precisely aligning the mirrors you can have those four 8.2 meter mirrors operate as one 130 meter mirror, with regards to sharpness. ",
"(source: former coworker went on to design part of the mirror system under the VLT)"
] |
[
"There are some wavelengths of light that our atmosphere completely blocks.",
" To see light in these regions of the spectrum, our only option is to go to space."
] |
[
"Why can't we make an influenza vaccine that covers all possibilities?"
] |
[
false
] |
So in a class I am currently taking, my group members and I are researching the influenza virus. I learned about how hemagglutanin and neurominadase have 16 and 9 subtypes, respectively. With this we can name strains such as H1N1 (hemagglutanin subtype 1 & neurominadase subtype 1). I also learned how two different strains attack the same cell and reassortment occurs leading to a new "mixed" strain. Theoretically 256 different strains could be produced. Now to my question. Why can't we make a vaccine that covers all the possible outcomes? And how can old strains (like H1N1) come back and infect us again?
|
[
"You answered your first question with your second. The problem with flu vaccines isn't the multiple strain possibilities, it's the fact that individual strains aren't even covered by the same vaccine.",
"(By the way, your strain count is outdated. There are now 18 HA and 11 NA subtypes, counting the new bat strains. Also, 16 x 9 = 144, not 256.)",
"The problem with flu is that the HA, which is where most of the immunity is targeted, can mutate the places where antibodies bind without losing its function. Many other viruses have similar or higher raw mutation rates to influenza; the difference is that when they mutate, they lose fitness dramatically. For whatever reason, influenza HA can tolerate a huge number of mutations without losing its biological function. ",
"That means that even the same strain of influenza can mutate and evade the population immunity, fairly quickly. The flu vaccine needs to be modified every few years to accommodate this. The vaccine against the H3N2 influenza strain from ten years ago is not effective against the strain today, and today's vaccine probably won't be effective against whatever H3N2 viruses circulate in 2020. ",
"So it's not \"merely\" a question of developing 144 or 198 vaccines, because even if those all worked today, in a few years they'd be outdated.",
"Research today is focused on identifying vaccines that aren't as easily evaded by mutation. There may be regions on HA that can't tolerate mutation, for example, and maybe targeting those regions will make a broadly function influenza vaccine. Or perhaps it's possible to force the body to make a wider range of antibodies, or to make antibodies that are more forgiving of changes; or perhaps it's possible to harness other branches of immunity that are more cross-reactive among strains. But influenza is an incredibly successful virus, and it's been very successful for a long time. It's not an easy target."
] |
[
"Wow thank you so much for the detailed response! And thanks for the update/correction. So basically HA and NA subtypes don't mean that they are the same. So a subtype has similar structure but it can also have variation. Before I was under the impression that a subtype was the smallest unit to be mutated."
] |
[
"Yeah, the small point mutations in HA (and to some extent NA) are the most important for ongoing changes in the vaccine. Occasionally new subtypes can enter the human population (such as in 1968, when an avian H3 strain recombined with the human H2N2 to make H3N2) and that can sweep the population as a pandemic and cause larger mortality, since there isn't even any weak immunity to it. But in general, a half-dozen small changes in HA are enough to make it resistant to previous vaccines.",
"That's why the 2009 H1N1 pandemic could occur in spite of the presence of human H1N1 strain already. The 2009 H1N1 had circulated in pigs for many decades, undergoing slow changes in its HA that were unrelated to the faster changes going on in the human H1N1 strains. Accordingly, humans born after the 1960s or so were not resistant to the swine version, and it was able to circulate unaffected by the population immunity. "
] |
[
"What happens to a body builder's muscles if he suddenly stops exercising?"
] |
[
false
] | null |
[
"As others have said, the muscles will atrophy. The SAID principle states that your body will adapt to the demands placed on it. For a body builder, that is the heavy weight lifting. If the person stops this, then the body will also adapt the other way, recycling the muscles so to speak for other things the body feels it should use the proteins for. This process can actually be measured 48 hours after a sharp drop in activity for a muscle, such as a casted limb. The process is gradual, but with the exception of losing innervation (sch as with paralysis) the lost muscle can be regained with work. ",
"If the diet was maintained, the body builder would also have a large caloric excess, resulting in adipose tissue(fat) being deposited on their body. "
] |
[
"They would stop gaining muscle. If the imbalance were bad enough, then the body could, in theory, use protein from elsewhere. For example, Bro only lifts upper body, but tries to avoid eating protein. If this imbalance got bad enough, Bro would begin losing muscle mass in their legs to compensate. ",
"Side note: Unless I am mistaken, the bodys maximal intake per day for protein is 1.5g per kg of body weight. Anything beyond that will be filtered out or just stored directly into fat/burned for energy.",
"Source: text books from grad school, will look for the articles they cited when I get home tonight. Also others have linked a few below.",
"Edit: added burned for energy, and source addendum."
] |
[
"What about the opposite: if they stopped eating as much but continued trying to gain muscle, would their muscles still atrophy to be used for energy?"
] |
[
"What kind of MPG would a human get?"
] |
[
false
] | null |
[
"A lot.",
"One gallon of gasoline has 114,000 BTUs of energy, or 29,000 kcalories. So 1/10th of a gallon of gasoline would provide 2900 kcals, which is about the daily needs of a young reasonably-active male.",
"Now, drinking gasoline for your caloric needs will probably kill you ",
" ",
" But as many graduate students know, it is possible for ethanol to be used as a primary source of nutritional energy (in conjunction with caffeinated beverages.) There are 5736 calories/liter in 100% ethanol. In that case, the FDA standard daily needs of 2500 calories/day would be provided by 0.44 liters of 100% ethanol, or 0.968 liters of 45% ABV liquor. I suggest bourbon."
] |
[
"I jumped the gun and drank quite a bit of ethanol before I read your last reccomendation. What do I do now?"
] |
[
"Quick! Drink a bit more so you have more energy and then run a marathon. That will use up all the ethanol energy so it won't kill you, also if you don't have enough energy the marathon will kill you.",
"Good luck!"
] |
[
"When a neuron dies, do its neighbors form new connections?"
] |
[
false
] |
I apologize if my understanding of neurons is wrong and makes this question moot. What happens to the neurons that receive information from the now dead neuron - do they realize it's dead or do they just process the signal from the dead neuron as a 0, off, no, etc.?
|
[
"It depends on how the neuron died.",
"Neurons can die naturally in a process called apoptosis, critical in child brain development. In apoptosis a neuron will shrivel up, die, and glial cells will discard it. The neighboring neuron that it was connected too will simply no longer receive a (typically inhibitory or excitatory) signal from the dead neuron. Most neurons receive multiple inputs signal so the loss usually won't be significant. Glial cells can also release growth factors causing other neurons to fill in the space and form new connections, which your brain does constantly anyways.",
"OTOH, if the neuron dies by necrosis due to toxicity or physical damage then there's often long term negative effects on the neighboring neuron. For instance, a necrosed neuron may burst all of its excitatory neurotransmitters into extracellular fluid. This causes extreme excitatory events in the neighbors that can affects firing patterns. Necrosis can also change the neighboring cells genetically or cause new connections that are ultimately detrimental (for instance autonomic dysreflexia in people with spinal cord injury)."
] |
[
"I don't know if there is anything like spreading necrosis? Death from necrosis often causes neighboring neurons to go through apoptosis which is typically harmless to surrounding neurons.",
"Toxins and viruses can spread down a chain of connected neurons causing death in each one. Seizures can also spread very far and if are bad enough will lesion large chunks of brain tissue."
] |
[
"Could toxic necrosis almost start a chain effect of the death of neurons? The death of one impacts another severely and in doing so that one effects another, etc? I realize the number of neurons in the brain, but how would something like this be stopped or eradicated?"
] |
[
"TIL there were 30,000 eletric cars running in the beginning of the 20th century. How were their lead-acid batteries charged?"
] |
[
false
] | null |
[
"Before widespread electrical grids, generators were used. Once available, they were charged from the grid, just like today.",
"Not all were powered with lead acid. Some of them were using nickle iron batteries. Our local electric vehicle association has a ",
"Detroit Electric",
"\"The front and rear compartments were filled with the optional Nickel-Iron batteries which gave it a range of close to 100 miles. The still fully-operational batteries finally had to be replaced in the late 1980s due to the Bakelite cases starting to leak. \"",
"\"A 1936 letter from the Edison company to Dr. ffrench acknowledges the longevity of the car's nickel-iron based Edison cells. Indeed, these cells performed well in the car for 75 years. \""
] |
[
"It wasn't all that expensive as compared to the car. In the early 1900s, electricity was ~20 cents per kilowatt-hour - somewhat pricey by today's standards, especially adjusted for inflation - but nowhere near the ~$2,000 that purchasing an average electric car seems to have cost, based on what numbers I can find.",
"The cars didn't go very fast, though. With a top speed of ~20 mph and an average range of 50-60 miles, the expense of topping off the battery was not the limiting factor - rather, it was the fact that the car was not as useful outside of cities as its steam- or gasoline-based contemporaries. Electrics were often used as a 'city car' by the relatively wealthy.",
"As for the availability of charging stations, by the 1910s electricity was common enough that the vehicles could be charged at home or in town, and the low power requirements of the cars put no significant burden on even basic electric systems. Remember, this was still thought of as a 'horseless carriage' of sorts, so it only needed to put out around 1 horsepower (0.75 kW).",
"However, in the 1890s there was a short-lived service that would simply swap a new, fully charged battery for your car's old one - the success of this service implies that charging took a while around that time."
] |
[
"While electricity in one's own home was a bit of a luxury circa 1900, individuals wealthy enough to purchase an electric car either had home power or were within driving distance of a place where the cars could be charged."
] |
[
"If the human body relies on electricity in order to function, is there a possiblity of there ever being a short circuit?"
] |
[
false
] |
Where is the power source for the electricity? Is is the brain? Is it the cells themselves, do they act like countless little batteries connected in parallel?
|
[
"Per Wikipedia: ",
"A short circuit...is an electrical circuit that allows a current to travel along an unintended path, often where essentially no (or a very low) electrical impedance is encountered.",
"As other users have pointed out, the body does not use the same mechanisms to create a current that electronics use. While it is true that current comes about from the movement of charges particles (classically, the movement of electrons; though, the reality is the opposite case), neurons, neuron fibers, and muscle fibers do not \"push\" these charged particles from one end to the another. The charged particles accomplishing this task in the body are, of course, ions; mainly Potassium, Sodium, Chloride, and Calcium ions. ",
"The mechanism of current production can get a bit messy in neurons and cells, but the TL;DR of the process is that a current is generated in these cells when there is a net movement of ions ",
" that pushes the cell to a certain threshold voltage (either towards the positive or the negative...if you want more detail on this, please ask). This change in what is termed \"membrane potential\" happens locally in a single given spot and, if strong enough, can induce a change in membrane potential in a consecutive spot. The change in potential propagates down the cell (an event that is termed as the propagation of the Action Potential) and eventually reaches the end of it (in the case of the neuron, the change in potential propagates down the axon, and reaches the synapse, where a signal is sent to another neuron/muscle). Herein lies the difference between the \"electric\" cells of the body and the electronic components of a computer. In the body, current flow is generated by moving ions ",
" across cell membranes; whereas in wires, current is generated by pushing electrons in a ",
" fashion from one end to the other.",
"With that in mind, to answer your question: can we ever \"short circuit\" an \"electrical\" body circuit? No, you can't; at least not using the classical definition of a short circuit. There are many things that can go wrong with the electrical processes in the body, but they aren't like short circuits in which a path of no resistance blows the circuit. The processes that govern neuron and muscle action are very intriguing, I suggest you look into them and find a good diagram like ",
"this",
".",
"If you want more information, please ask. I find this all very fascinating. There are also a few cases where there is current flow directly from one cell to another; in such cases, one could say the cells' electrical properties are similar to that of a wire, but only for a very, very short distance and time.",
"Edit: I completely forgot your other question! I apologize.",
"Where is the power source? Simplified answer: everywhere. The energy the cells use to create these action potentials is generally stored in the change in voltage that occurs across the cell membrane. The voltage change induces a shape change in membrane proteins that open or close to let the ions in or out of the cell. When they open or close, this further changes the voltage which can open even more channels to let even more ions in/out. It's a wicked cool positive feedback loop."
] |
[
"Lovely answer. I'll add two more things: The power source, specifically, is the sodium-potassium pumps that are responsible for generating the resting (default) membrane potential. And the pumps are powered by ATP molecules, which are produced by the mitochondria via cellular respiration, which is essentially a controlled burning of glucose. So ultimately the energy comes from the potential energy stored in the chemical bonds of glucose.",
"The second thing is I have a proposal for a \"short circuit\", which is what happens when you give someone a big injection of potassium. This immediately negates the separation of ions that produces the resting potential. And that's why potassium chloride is a euthanasia drug. A large dose stops the heart (and skeletal muscles, and neurons) because cells can no longer maintain a normal resting potential."
] |
[
"Actually, there is at least one medical condition that does meet the definition of a short circuit: Wolf-Parkinson-White. It's the result of the derangement of the normal electrophysiology of the heart.",
"Normally in the electrical depolarization of the heart, an electrical impulse is generated in the sinoatrial node, travels across the atria, and pauses for a brief time (usually less than 0.12 seconds) at the atrioventricular (AV) node before reaching the ventricles (the big muscles at the bottom of the heart that do most of the pumping). The AV node acts as a gateway for electrical impulses coming from above, limiting the number of electrical depolarizations reaching the ventricles, preserving cardiac output. ",
"In Wolf-Parkinson-White, an accessory pathway exists (the bundle of Kent) that allows impulses to bypass the AV node and conduct directly to the ventricles. If these individuals experience an atrial tachycardia like SVT or atrial fibrillation, it can be life threatening as the ventricles begin beating so fast that they no longer pump an adequate amount of blood to supply the body's need."
] |
[
"What are the string-like structures on the iris?"
] |
[
false
] |
Seen here is an eye with a blue iris, but what are those string-like structures in the iris, that surround the pupil?
|
[
"They are the parts (named below) within the Iris Dilator Muscle which are what physically contract to change the size of the pupil. ",
"\"The pupillary dilator consists of a spokelike arrangement of modified contractile cells called myoepithelial cells.\"",
"FROM: ",
"http://en.wikipedia.org/wiki/Dilator_pupillae"
] |
[
"This is known as the ciliary body. It is a ring-shaped structure with ridges called ciliary processes that surround the lens. The lens is suspended from the ciliary processes by zonular fibers that extend between these structures. The ciliary body is associated with the ciliary muscle. The ciliary muscle's function is in accommodation - the changing of the shape of the lens to focus on near or distant objects. When this muscle is in a relaxed state, the zonular fibers that are extending from the ciliary processes are pulling the lens so that it lays in a flat shape. This is best for focusing on objects that are far away. When you want to focus on a nearby object instead, the ciliary muscle will contract. This will move the ciliary body and processes close towards the lens, relaxing the zonular fibers. Without this tension, the lens becomes rounder, accommodating for near vision."
] |
[
"Though you are correct about function of the ciliary body, it is not visible from the front of the eye - it is positioned behind the iris, as is the lens. OP is asking about the fibers visible as a part of the iris itself, which I would agree are the fibers of the dilator pupillae muscle, which are arranged in a radial fashion."
] |
[
"Would car brakes work on a frictionless road?"
] |
[
false
] | null |
[
"Car tires would not work on a frictionless road."
] |
[
"but you could still get a car moving with other means, could you not?"
] |
[
"It would be more like a sled than a car, I think, and you would have to introduce friction to slow or stop it. "
] |
[
"Are the laws of the universe assumed to be constant? If so how, why?"
] |
[
false
] |
The question is posed at 7:00 in the following video: Would someone care to elaborate on this? I'd be interested to hear a rebuttal of the entire thing, but I'm primarily curious about this specific question. EDIT: I'd like to thank everyone for contributing to this discussion.
|
[
"Not ",
", no. All scientific theories are based on empirical observations. The basic function of science is to propose and test hypotheses that help us to understand and predict the behavior of the world around us. More parsimonious hypotheses are favored -- if you can explain something simply, then there is no utility provided by including redundant complexity. This is essentially Occam's razor.",
"In developing a model of any system, it is natural to begin with as simple a model as possible and to see how much it is capable of explaining. Where it fails is in indication of where the assumptions of the model do not hold. This is precisely how Einstein's relativity grew from Newton's classical physics, and similarly quantum theory from classical physics.",
"In building physical theories of the universe, the premise that laws are unchanging is a natural starting point. It just happens that models based on this premise have excellent explanatory power.",
"As a philosophical point, science (and life itself) could not achieve any success if there were no consistent physical laws, as it would be impossible to make any future predictions. The fact that science is so successful in making predictions and explaining empirical observations indicates that laws are either constant or very nearly constant on the timescales on which we use them.",
"Of course, there may well be secular changes in the laws of physics. Indeed, many scientists have in fact explored theories in which the laws of the universe are changing in time."
] |
[
"I can't address the questions about physical constants, but I can address a few of the many unfounded claims made by Mr. Sheldrake. In particular, he makes a great argument to ignorance about developmental biology, saying that we simply don't understand how it functions, and therefore his idea notion of morphic resonance is supported. This is simply not the case. We know a rather great deal about development, and the factors that determine morphology. We can go through and ",
"Stain embryos to see which genes are being regulated in areas",
", and thereby which ones influence the development of structures. Our knowledge isn't complete, and there's many things things we'd like to know, but to say we're stumbling in the dark without any information is absurd.",
"And the claim that all DNA does is code protein is almost silly. And as a supposed biochemist, Mr. Sheldrake should know better. It codes for RNA which produces protein, sure, but it also codes for the RNA sometimes for the RNA's sake, with RNA sometimes forming important structural elements for some processes. And the DNA also says when to turn protein production on and off, how much to make through interference, promotion, inhibition, etc. Those proteins interact through ",
" laws, not through some half-baked idea of 'morphic resonance'. Those interactions are complicated, and we don't know everything about them, but his argument seems to be similar to saying \"All you can do is change your car's wheel direction and speed. I don't see how you can drive to downtown Seattle in it. Therefore, magic.\"",
"When Mr. Sheldrake began talking about people 'feeling eyes on the back of their heads,' I almost threw my laptop in disgust. He knows this issue has been examined, and there's no evidence for it whatsoever. People like Sean Carol have ",
" him, in public, such things don't exist to the best of our very well established knowledge. His public insistence for his pseudomystical 'physics' malarkey shows he's either wilfully ignorant, seriously deluded, or possibly just cynically lying to sell some books.",
"I can't believe I've wasted 30 minutes on this."
] |
[
"\"In an evolutionary universe, why shouldn't the laws themselves evolve?\"",
"Wow, face-palmed on the first sentence. The laws of nature are what allow evolution to occur in physical structures. The idea that this somehow entails that the laws themselves are variable, let alone subject to a form of evolution, is an unfounded non sequitor.",
"Are the laws of the universe assumed to be constant? If so how, why?",
"Well, what would the universe look like of the laws ",
" constant? You would still need some lower level set of laws governing the variation in the higher level laws. If you are trying to create a model of the universe, which is the goal of science, you need to have constant laws at the lowest level, else you cannot make predictions.",
"Now the other side of things. There are cases where science seems to assume that certain things are constant. These aren't really assumptions. Rather, they are the result of a a lack of evidence of variation combined with the parsimoneousness of the theories in which they are constant. If they are observed to vary, or if a theory with better predictive power claims that they vary (but not in a way inconsistent with prior observations), then science will immediately discard the belief that they are constant."
] |
[
"Quantum Physics, Mechanics, Etc. Any Books?"
] |
[
false
] | null |
[
"We have a book list in the sidebar."
] |
[
"I will start on the basics of the quantum physics so thank you for that but could you also direct me to something that specifically goes over virtual particles?"
] |
[
"This sub doesn't do book suggestion posts. Maybe try ",
"/r/askphysics",
", ",
"/r/physicshelp",
", ",
"/r/physics",
", or ",
"/r/suggestmeabook"
] |
[
"How exactly are quantum tunneling and nuclear fusion related?"
] |
[
false
] |
I was taught that quantum tunneling is necessary for nuclear fusion to happen but I am unsure how that exactly happens.
|
[
"Tunneling is essential to fusion in the sun. If you were to ignore quantum effects and just consider the amount of energy it would take to bring two protons together against their electrostatic repulsion, you'd find that this energy (called the \"Coulomb barrier\") is ",
" than the average kinetic energy of protons in a gas with the temperature of the sun.",
"In other words, protons in the sun vey rarely have enough energy to overcome each others' mutual Coulomb barriers.",
"Luckily when you \"turn on\" quantum mechanics, you allow for tunneling to occur. Since protons are not just particles but also waves, they don't have definite positions in space. They have wavefunctions, which can overlap in space. A proton can tunnel through the barrier of another proton even if their relative energy is less than the Coulomb barrier.",
"George Gamow was the first to do a calculation combining classical kinetics and quantum tunneling. He discovered the ",
"Gamow window",
", which is a range of energies where fusion in the sun primarily happens."
] |
[
"I found a good answer to that: ",
"http://astronomy.stackexchange.com/questions/14018/what-would-the-sun-be-like-if-nuclear-reactions-could-not-proceed-via-quantum-tu",
"...and the explanation continues from there. It's very interesting, and includes some good discussion as well. "
] |
[
"If we \"turn off\" quantum tunneling again, wouldnt a star like our sun just compress itself further untill the coulomb barrier gets reached with the increasing temperature?",
"Or would it become a neutron star or something before that?"
] |
[
"Does a strong immune system lower one’s risk of cancer?"
] |
[
false
] |
Trust me I am aware that cancer comes from our cells and is not some infection, but the immune system is made up of cells as well.
|
[
"Our immune system does prevent cancer all the time. As cells become cancerous, they express certain molecules that are not normally present in healthy cells. Immune cells recognize that and get rid of those problematic cells before they grow into a tumor. Well, most of the time anyway. ",
"I've not encountered any evidence for \"strong\" immune system lowering cancer risk, but we do know suppressed immune system does increase the risk. AIDS is a prime example. Before the advent of HAART medications thanks to which people with HIV can live relatively healthy lives without progressing to full-blown AIDS, one of the first noticeable sign was Kaposi's sarcoma, which we now rarely see. AIDS patients are also at increased risk of lymphoma, cervical, and anal cancers (",
"https://www.cancer.org/cancer/cancer-causes/infectious-agents/hiv-infection-aids/hiv-aids-and-cancer.html",
")",
"We also now have a new type of therapy that uses our immune cells to fight cancer: ",
"https://www.cancer.gov/about-cancer/treatment/research/car-t-cells",
"",
"Bottom line: weakened immune system does increase risk of cancer. If you have healthy, intact immune system, our immune cells are already detecting and killing cancerous cells (we call that \"immune surveillance\"), up to a point."
] |
[
"There are loads of cancer immunotherapies other than CAR T cells that utilize the immune system to fight cancer."
] |
[
"Yes you're right. I thought of CAR-T cell therapy as a good example because that is the first time that we engineered T cells to directly recognize cancer cells. Other immunotherapies up to that point have been by way of preventing the inactivation of T cells (i.e. inhibiting CTLA4, PD-1, or PD-L1)."
] |
[
"If I'm alone in a remote battlefield (or whatever) with an open wound, do I stand a better chance at avoiding infection by introducing maggots?"
] |
[
false
] |
Here's what I'm talking about: . I mean, I understand that disinfection is an intelligent precaution in a medical environment, but the breakthrough came from WW2 battlefields. Those soldiers got the all-natural cure, and turned out pretty well.
|
[
"non-expert here.",
"For the effort you would need to keep maggots that are not contaminated, you could instead keep rubbing alcohol.",
"Maggots are typically used to clean off dead tissue, not disinfect open wounds."
] |
[
"Maggots are typically used to clean off dead tissue, not disinfect open wounds.",
"Good clarification."
] |
[
"Yes, as put before. Maggots only eat dead tissue, and are good for removing it from a wound, but shouldn't have an effect on the infection, and if anything, could make it worse, if they wern't sterile before entering the wound."
] |
[
"If one cat sees and hears another cat purring, does it understand or interpret the purring cat as being happy?"
] |
[
false
] | null |
[
"They also purr under heavy stress (such as severe pain), but it's a different, coarser kind of purr. Some theories say this is intended to be a self-calming mechanism."
] |
[
"We're not sure why cats purr, but one of the theories is that it's used as a way for nursing females to communicate with their kittens - this could also be interpreted as a cat saying the he or she is not a threat to other cats. "
] |
[
"Cats also purr when they are engaging in a fight with another cat. This may be relevant. I don't have any answers, though."
] |
[
"How does an equalizer work?"
] |
[
false
] |
Specifically, how does it affect the volume of only specific frequency range(s) and is this mechanism significantly different for the different types of EQ? Assume a fairly basic understanding of sound and electronics.
|
[
"An equalizer can be implemented in digital or in analog circuitry, but the basic concepts are similar. Divide the spectrum into different bands, and for each band have a band-pass filter. Send the sound through all of the filters in parallel, and each band-pass filter will output only the sound within its band, cutting off all of the others (mostly). Then mix the outputs of all of the band-pass filters together again, but put in a circuit with the ability to adjust the amplitude of each first. ",
"So now some bands can be mixed down with respect to the others. (Alternatively, you can adjust the amplitude of the whole signal going into each band-pass filter.) When the bands are re-mixed together (and amplified, if required) the sounds in some are reduced in amplitude. "
] |
[
"In an analog filter, you use different values for the inductors and capacitors (and resistors). Inductors and capacitors respond differently to changes in current/voltage, and that allows you to make circuits that will resonate only at certain frequencies. You can arrange things to either pass those frequencies through the circuit and block others, or to pass those frequencies to ground (thus \"dumping\" them) and not do so for other frequencies. This allows for various ways to filter according to frequency. ",
"Using those tricks, you can make low-pass filters, high pass filters, band-pass filters, or notch filters (the opposite of band-pass). There are multiple ways to skin each of those cats (Butterworth, Chebyshev, etc.), with various trade-offs. Analog filters are always imperfect, and to achieve very rapid roll-off at some frequency(s), you'll get some unwanted side-effects. If you want a really good analog filter, you generally have to add a lot of stages (more components). But if you want a cheap, pretty good filter, analog is usually the way to go. ",
"Digital filters work quite differently. The sound is first digitized (turned into a string of numbers) and mathematical tricks are used to essentially change from the time domain to the frequency domain, and then the unwanted frequencies can in effect be stripped away and the process reversed, going back from frequency to time domain and from digital back to analog. Digital filters are generally more expensive to implement, but they have various advantages too. They can be made much less sensitive to temperature fluctuations and can be much more flexible in the choices of frequencies for pass/block. And they can almost perfectly roll off at the desired frequency(s) without as many unwanted side-effects. "
] |
[
"OK that makes sense, but how are the frequency ranges isolated? What is the mechanism that achieves this?"
] |
[
"Could Earth capture new asteroids into its orbit? If so what would happen?"
] |
[
false
] |
The moon currently orbits the Earth and Mars is surrounded by Deimos and Phobos. Is it possible for any near flying asteroid to be captured as well? Is the earths gravitational pull strong enough to hold them? I know size plays a role as smaller asteroids would be pulled through the atmosphere and destroyed, larger simply bypassing and shooting off into space. Is there a magical mass/size that would be just far away to survive and enter orbit? What would happen if there was another satellite in orbit around earth? If it collided with the moon? Thanks in advance!
|
[
"I highly recommend playing with ",
"this gravity simulator",
".",
"If you assume just two bodies (the earth and the incoming asteroid), then capturing is not possible. The incoming body may come close to earth, but it will be moving too fast to be captured. It may just sail by with a slight bend, or it may slingshot around.",
"The only way captures happen is when you add a third body. That could be another asteroid that is also making a close approach to earth at the same time, but in most likelihood, it would be our moon. As the asteroid approaches, the moon would absorb most of its kinetic energy, slowing it dramatically. If it happens just right, it may end the encounter with the moon with just the right trajectory and speed to enter a new tight elliptical orbit around the earth.",
"Of course, with the moon being so much larger, and obviously intersecting our new asteroid-moon's orbit, the new orbit would only be stable for a short time (possible a few thousand years). Eventually it would either crash into the moon, be disrupted by the moon enough to crash into earth, or be flung far away again.",
"Of course, if the third body was another asteroid, then a stable orbit could be made. Basically, two asteroids would interact far away from the earth-moon system, and one of the asteroids would be left with a trajectory that is almost motionless to earth. It would be just enough to keep it from falling back to earth, and the new asteroid-moon would orbit the gravitational center of the earth and the other moon. Of course, if the apogee was ever close enough to the first moon, then things would eventually be disrupted, so the entire orbit would need to be much further out than the first moon's orbit.",
"tl;dr: It's nearly impossible, especially in a mature star system as our own."
] |
[
"It's just the way that things happened. For a planet our size, existing in a mature star system such as ours, ending up with 0, 1, or 2 moons is the most likely outcome. Venus, for example, has 0.",
"Since our first moon is so large, the chance of having another decently sized moon (even 1/1000th the size of the first) is extremely unlikely (nearly zero chance). Finding a stable orbit around two bodies as big as the earth and moon is very difficult. Play with that simulator, and try to make one, if you don't believe me."
] |
[
"If you have RES, you should be able to ",
"save comments for later",
". ",
"Even without RES, you should be able to save the whole article, and then find the comment later."
] |
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