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[
"What happens between the time a zit \"isn't ready\" and the time it is?"
] |
[
false
] |
[deleted]
|
[
"Increased levels of DHT causes an increased production of sebum, which in turn increases the activity of keratinocytes (a type of skin cells). Increased cell to cell adhesion due to keratinization interferes with normal desquamation (shedding) of the skin. Cellular debris and sebum produced by the skin starts accumulating, forming a comedo, a \"not ready\" zit.",
"If the comedo opens up, it forms a black head, and are rarely further inflamed.",
"However, if the comedo stays narrow and intact, increased pressure from the accumulation of debris and sebum may cause the follicle to rupture, allowing bacteria (",
") to go in. When these bacteria do infiltrate the area, there is an immune response, causing inflammation. The macrophages (part of the immune system) are attracted to this site to kill the bacteria. Some enzymes secreted by these macrophages weaken the follicular wall, making it \"ready\"."
] |
[
"It's a \"side effect\" of the hydrolytic enzymes secreted by macrophages originally intended to be used against the bacteria."
] |
[
"So popping is the \"desired\" result that the immune system is looking for? Or is there another reason to weaken the follicular wall?"
] |
[
"Why do exercises such as running that increase your heart rate make your heart stronger, but heart rate increase from stimulants such as Adderall, or excitement from video games, not make your heart stronger?"
] |
[
false
] | null |
[
"The same question was asked a few months ago, here is the answer:",
"\"Because when you exercise, you release a lot of catecholamines and other stress hormones. They are good in short bursts and they actually desensitise your body (in this case the receptors in the heart are lowered) to them over time; so that when you're not exercising, you're actually at a lower \"stimulation level\" than those who don't exercise.",
"By this same desensitising mechanism blood vessels (mainly arterioles) are actually way more relaxed and your BP is as such lower than people who don't exercise. There are other muscular and citokine-related mechanisms by which this happens as well.",
"But catecholamines are actually bad in the long run. They promote a general inflammatory state (that's good for short bursts; it helps repair the muscles afterwards) that when maintained constantly, such as when you take stimulants (and to a lesser degree if you get used to live under unmanaged stress) helps the deterioration processes of blood vessels and the formation of atherosclerosis. Constant higher blood pressure (which also happens when taking stimulants), does this too as a completely independent, but related, mechanism; it \"hardens\" the arteries, because they are elastic tubes that need to do this to adapt to constant higher BP's. Again, citokines play into this as well.",
"Also exercise makes muscles more permeable to glucose independent of insulin (via raising the number of some kind of transporter over another), so it helps lower and maintain a more stable glucose levels throughout the day, while stimulants raise blood glucose levels. This also plays tremendously into the atherosclerogenesis.",
"There are plenty of other mechanisms, many of which I don't remember too well to explain here, and others that haven't been discovered yet.\""
] |
[
"Please cite your ",
"source",
" whenever you directly quote anyone. Thanks!"
] |
[
"I'm not sure I accept this. Professional athletes train for much longer daily than, say, amphetamine's half life.",
"I believe the vasoconstrictive properties of stimulants are to blame here, for raising blood pressure much higher than a person exercising at the same heart rate, simply putting too much stress on the heart. To top that off, plenty of stimulants are cardiotoxic, like cocaine."
] |
[
"Is there any example of electromagnetic force affecting gravitational force?"
] |
[
false
] |
[deleted]
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[
"There are things that could happen, but that we haven't detected. Examples are the gravitational field from electromagnetic radiation or fields. The magnetic fields of neutron stars might contribute non-negligibly to their gravity. There have been searches on Earth for violations of the equivalence principle, where different atomic compositions might cause objects to fall differently, but these have all come up negative."
] |
[
"It doesn't really make sense to say that a force has gravity. You could say system bound by the electromagnetic force has a gravitational field."
] |
[
"My Newtonian worldview says that if gravity bends light, then the source of the gravity has to be affected as well because of conservation of momentum. Is this incorrect in GR?"
] |
[
"Is it strictly the force of Gravity which causes fast spinning object to \"fly apart\"?"
] |
[
false
] |
A sample video: This video is on a macro scale. Does it work the same on a micro scale? Is this experiment with magnets dealing with centripetal or centrifugal force? What's the difference? It seems counter-intuitive that the same force that "crushes" sub-atomic particles to over come the strong nuclear force can also do the opposite in some cases. Is that what fission is? Gravity and the nuclear forces acting together? Can elements or molecules fly apart into separate particles simply by spinning really fast? Has this ever happened and does it ever happen in nature? These may seem like stupid questions but it's late and I honestly can't get my head around it.
|
[
"Gravity doesn't really have anything to do with the tops flying apart. Let's consider one ball in the top. It's going in a circular motion around the axis of the top. For it to do that, there needs to be a force constantly pointing in the middle. If there was no force, then the ball would move in a straight line, not in a circle. In this case all the balls are magnetic so that force is the magnetic force. This is the centripetal force, centripetal meaning centre seeking. The force makes the ball turn towards the centre.",
"The centripetal force needs to be bigger for a faster spinning top. As the rotational velocity increases, at some point the force needs to be bigger than the magnetic force between the magnet balls is. At that point the magnetic force is no longer able to keep the balls in circular motion. Thus they're going to fly in the direction they were moving, that is tangentially away, and the top breaks apart.",
"Centrifugal force is something a bit more complicated. It arises only when we choose to look at the situation from a different perspective. Instead of a top, consider being in some spinning amusement park ride or something similar. It is natural for us to think that if we're sitting or standing still, then we're stationary. But we might be sitting inside a car of an amusement park ride and the car itself is spinning. So we're sort of pretending that we're not spinning even though we really are. That's a rotating reference frame we're using then. And in this situation we get some extra forces that seem to be there because we're pretending to be in a different situation than it really is. We can mathematically say what these extra forces are and then they perfectly compensate for our less than accurate choice of reference frame and so our math will describe what will actually happen.",
"The two forces that arise in this situation are the centrifugal force and the Coriolis force. Centrifugal force is sort of the opposite of centripetal force. Remember that the centripetal force keeps you in circular motion. But in our rotating reference frame we are stationary, we're not moving at all. If we're not moving at all then we can't be accelerating in any direction and so the sum of all forces on us needs to be zero. The centrifugal force balances the centripetal force. It is exactly as strong but in the opposite direction. You yourself feel it as if something was pushing away from the axis of rotation. Coriolis force is a bit more complicated but similarly only arises when you're looking at things in a rotating reference frame.",
"Someone looking at the ride from outside would feel no need to think of it as a rotating reference frame (unless they specifically wanted to do so) and they probably wouldn't think about the centrifugal force at all. To them it just seems like you're in a circular motion and the centripetal force is what keeps you in the circular motion."
] |
[
"Centripetal force is the real force, and it's the force that pulls an object inward (centripetal means center seeking) to prevent it from flying away as it moves in a circle.",
"You FEEL centrifugal force when you spin an object, say a ball on a string, because the ball pulls outward trying to travel in a straight line. The string applies the centripetal force to keep the ball spinning in a circle on that string. ",
"The magnetic force here is applying the centripetal force, keeping the magnets together. When it hits the side/wall, that force is strong enough to push the magnetic balls out of their hexagonal shape and into a new configuration. ",
"What do you mean by \"work the same on a microscale\"? ",
"Nuclear fission involves shooting high energy particles into stationary target atoms. The collision rips apart the target atom(s). ",
"When dealing with subatomic particles, the interparticle forces become REALLY strong at close distances, so you'd need to spin them way too fast to get something similar like this to happen. I don't know how fast you'd have to get the electron spinning around a hydrogen atom before it just released because of a lack of centripetal force from the EM interaction between the proton and electron, but I bet it's faster than the speed of light, as the electron is already moving at something like 0.001 the speed of light. ",
"Fusion, what happens in the Sun and other stars, IS a combination of Gravity, EM, and Strong Nuclear force working together to create a stable ball of Hydrogen fusion. "
] |
[
"Centripetal and centrifugal forces are closely related concepts, but viewed from different frames of reference. When something rotates or turns, the velocity changes direction. This is an acceleration, even if the object doesn't speed up or slow down. From Newton's laws, that means there must be a net force. ",
"If you are in an \"inertial\" frame, meaning non-accelerating and not rotating, you see a net force pointing towards the center of the rotation. In ths example, the net force fom the magnets provides the force that prevents the bals from moving in a straight line. the is centripetal force. ",
"If however you are on the rotating object, when you rewrite the equations for the rotating observer, a new term pops out that corresponds to the observer feeling a force to the outside of the rotation. This is why you get thrown to the outside of a turning car. Note that the force isn't \"real\". It only exists because you're describing things in terms of a non-inertial (accelerating) frame. This is called centrifugal force.",
"In the case of these tops, magnets are providing the centripetal force. Gravity isn't really critical to the demonstration at all. ",
"Edit: Gravity is much weaker than the other force in nature. The only reason that it is so important on astronomical scales is that matter tends to be neutrally charged. It really doesn't have anything to do with most microscopic processes except on the most extreme scales (very near a black hole for example), and we don't have an understanding of how gravity works on the microscopic level in those cases."
] |
[
"Do seeds carry more nutritional value than their flesh/meat?"
] |
[
false
] |
Let me clarify that I have no idea what to call the edible parts of a fruit like orange or watermelon therefore I’m referring to it as flesh/meat. As for the question. I am wondering if seeds in fruits carry more nutritional value than their flesh. Someone I know told me that grape seeds carry more vitamins and phytonutrients, therefore it was better to get grapes with seeds and eat the whole thing rather than get seedless grapes. So is this true. And if it is, does this also happens in others fruits/berries ?
|
[
"I mean seeds do have some good nutrients. The endosperm of seeds are basically stored nutrients for the actual \"baby\" plant inside.",
"Sometimes theyre too densely packed to actually have us utilize tho. That or they are toxic to people and arent worth the time.",
"All grains are the endosperm of plants and we just extract eat rhem when their carbs are available"
] |
[
"I think the key thing you need to understand is that fruits are not all the same. This is true for grapes but not always for others, so please don’t start eating cherry pits. ",
"You have to look into each one individually to see whether the “I heard from someone” statements you’ll hear throughout your life are correct. This is true for anything in biology and usually life in general."
] |
[
"I am not debating whether the seed of one fruit or another is edible, but if the seed itself has generally speaking more nutritional value than the fruit itself."
] |
[
"Why can't we know the velocity and the position of subatomic particles at the same time?"
] |
[
false
] | null |
[
"I wasn't comfortable with this concept until I saw it demonstrated like ",
"this",
"Once you start thinking of particles as summations of waves, uncertainty follows quite naturally."
] |
[
"It's not that we can't know them at the same time, it's that we can't know them to ",
" at the same time. This is the uncertainty principle, which comes about because position and momentum (related to velocity) are non-commuting operators. One very loose way of thinking about this is to use the fact that particles can be described in terms of waves. A particle that passes through a narrow gap (small uncertainty in position) will diffract out widely, meaning that there is a large uncertainty in its momentum. "
] |
[
"This is a property of all waves. A real wave is this thing that has wiggles of length W and the wave extends over some distance L. The velocity is related to the length of wiggles W and the spread in position is just the distance L.",
"If you wanted to know the position of a wave accurately, then you want L to be as small as possible If you wanted to know the velocity of a wave, then you need to measure at least one wiggle, W, which is the wavelength. Hence it's impossible to measure both L and W to arbitrary precision."
] |
[
"Are there any animals that display a sense of humor?"
] |
[
false
] |
I know animals like to play and sometimes do things because of the conditioned response they get out of us. But I was thinking there's got to be some animals that do things just for shits and giggles... for instance, slapping another animal in the face repeatedly and enjoying the easy game... or "laughing" at another making a fool of themselves. Maybe that's also a projected definition of humor on my part. EDIT: I was thinking silly acts that serve no purpose in establishing hierarchy or training for adulthood, only personal amusement. Stupid music, but I rest my case with video.
|
[
"Definitely. just take a look at this and tell me the monkey has no humour",
"http://www.youtube.com/watch?v=MdA-y6J-KnY"
] |
[
"I don't have a link to the journal article on-hand, but I am aware of at least one documented case of this.",
"In order to keep the bonobos of the Iowa Great Ape Trust in line, every now and again, caretakers dress up in a gorilla suit and make some random appearances around the borders of the faclity. Basically, just a way to let the others know that it's not safe out there. One of the bonobos became aware that the gorilla was a human in a suit with a mask, and, being one of the more social of the group, asked a caretaker to wear the mask and go into the room of another bonobo. When the victim showed signs of distress, the first bonobo showed pleasure. ",
"The finer details of the story are escaping me right now, as I read the article some years ago, but the overall point is there: an ape played a trick on another ape that served no purpose other than one purely social.",
"Check out some of the scientific publications to come from that great ape trust, there's some gems."
] |
[
"Not humour but definitely playing:",
"http://www.youtube.com/watch?v=TMCf7SNUb-Q"
] |
[
"I'm a global warming skeptic, here are some of my points. Where am I wrong?"
] |
[
false
] |
[deleted]
|
[
"Look at the temperature fluctuations in the last 5000 years. You'll realize the mercury bouncing up a few degrees isn't uncommon, at all.",
"Response",
".",
"If you glance at any graph, you'll realize that the temperatures rose 800 years before the CO2 levels started rising",
"Response",
".",
"Other greenhouse gases, predominantly water vapor make up about 4% of the atmosphere.",
"Response 1",
". ",
"Response 2",
".",
"Volcanoes alone exceed that number.",
"Response",
".",
"All human activity combined produces 6.5Gt of CO2 per year. [...] All animals combined (meaning respiration, decomposition, etc) produce 150Gt of CO2.",
"Response",
".",
"Honestly, you can find the rest for yourself. ",
"They're all on this page."
] |
[
"First off, please use the search function, all of these points have already been addressed, multiple times in fact. We've had many long discussions on this topic. I'm not going to rehash all of the calculations here, sorry.",
"I will say this, please don't take this as an insult it's not meant to be, but you're not qualified to be making these conclusions, and you would be best to trust the expertise of those who are qualified. Do you go in to your doctor's office and second guess their diagnosis? What about your auto mechanic? You probably know significantly more about both of those subjects than you do about climatology or atmospheric chemistry. ",
"Unless you're prepared to justify why your thinking some how trumps the National Academy of Science, which is arguably the most prestigious scientific body in history, then you should consider reading conclusions of experts rather than making them on your own.",
"Here's what the National Academy of Sciences has to say about ",
"global climate change",
".",
"Edit: All of questions are literally addressed in this pdf entitled ",
"Understanding and Responding to Climate Change",
"Sorry for coming across as grumpy on this issue, but it's on par with people arguing against evolution, and I've been talking to the Health and Safety people all day..."
] |
[
"First off, he has to be reading a certain brand of sources if he's going to state that \"Volcanoes alone exceed that number [6.5 Gt]\". The real figure are more something like 26.4 Gt (human, per year, including land use) compared to 0.3 Gt from volcanoes. ",
"What the OP claims as evidence, isn't evidence according to any expert in the field. You can't say very much about figures taken out of thin air."
] |
[
"What makes cats go crazy over catnip?"
] |
[
false
] |
Do other animals have similar effects to it? Are there any other known things that cause a similar effect in different animals?
|
[
"What is catnip, anyway?\nCatnip is a member of the mint family, which has about 250 species. The essential oil in catnip, nepetalactone, has a powerful effect on cats who are sensitive to it, turning even the most sedentary couch potato into a flipped-out ball of ecstasy.",
"Smelling vs. eating\nThe most intense catnip experience is an olfactory one—your cat smells the herb and promptly goes nuts. Researchers aren't sure what the neurological explanation is, but it's thought that catnip mimics feline \"happy\" pheromones and stimulates the receptors in the brain that respond to those pheromones. When eaten, however, catnip seems to have the opposite effect: the cat may become very mellow.",
"http://www.humanesociety.org/animals/cats/tips/catnip.html"
] |
[
"For more clarification, it actually mimics feline sex pheromones, and that's why cats are are so into it. I'm not aware of any other animals that like it, but it would interesting to test it out on various types of wild cat as well as animals that are very closely related to cats...",
"For more info:\n",
"http://www.scientificamerican.com/article/experts-how-does-catnip-work-on-cats/",
"http://www.compoundchem.com/2014/06/08/catnip/"
] |
[
"Valeriana officinalis is also used as catnip the valerian acts as a a GABA-analog and binds with GABA therefore reducing GABA activity. This results in a hypnotic or sedative state. There is not an extensive amount of research on this though. "
] |
[
"Using a telescope, how likely is it that we could someday be able to see an event that took place, say, 50 years ago?"
] |
[
false
] | null |
[
"Like in space ? You can do that by simply looking at a distance of 50 light years away and you will see what was happening 50 years ago.",
"What we see of the sun is 8 minutes old. When we look at proxima centuri we see what was happening 4 years ago. ",
"If you are referring to what was happening on earth. Then we have to invent faster than light space travel. Travel really fast and then look back. All I can tell you there is that we are not likely to figure that out anytime soon"
] |
[
"It is technically true that, if there happened to be an enormous mirror 25 light-years away, any light from earth that reflected off of it and came back to the Earth to be observed by telescopes would be from 50 years ago, and would depict events that happened at that time.",
"In practice, that's totally impossible to actually do. Even if there happened to be a planet-sized perfect quality mirror 25 light-years away oriented perfectly right, it's practically impossible to build a telescope on Earth that can see everyday objects as close as the Moon. The idea of a telescope that could focus on a 25-ly away item closely enough to see meter-sized details not just on itself, but in a reflection of something 25-ly away, is basically absurd. I don't feel like trying to calculate it right now, but there probably wouldn't be enough light making the round trip to make it possible to see anything more than that there was probably a planet there."
] |
[
"Most of the stars you can see with the naked eye are over 50 light years away. You see the light they emitted over 50 years ago. Once in a while a supernova is visible to the naked eye, in that case you can see \"live\" an event that happened thousands, maybe even hundreds of thousands of years ago.",
"An event on Earth? You can't. There is no suitable giant mirror in space that would reflect Earth's light back."
] |
[
"What are the ingredients to create human stomach acid(s) and why do we always have enough of it?"
] |
[
false
] |
I eat quite a lot but almost never drink anything other than water. So I don't take any liquid acids. What are nutrients/sources for the body to generate stomach acids? I can imagine that some fruits and vegetables, being very high in water content and often acidic, could be a source. What else is there? What about meat? Maybe I'm ill-informed, but I don't think I've ever heard of a case where someone's diet is so bad that they couldn't generate the required pH levels required for proper digestion. So I guess the building stones for stomach acid are very abundant?
|
[
"There are cells in the stomach lining called gastric chief cells which secrete acid using a system of ",
"ionic pumps",
". This results in the net transfer of hydrogen and chloride ions being transferred across the stomach lining. These together are known as hydrochloric acid, a fairly strong acid (HCl). Chloride ions can be provided by dietary salt (sodium chloride) and it is not just essential for acid secretion but also a wide range of other mechanisms, notably muscle contraction."
] |
[
"Salt is sodium chloride (NaCl). When they break apart, the chloride is used to make hydrochloric acid. Yes a lot of water comes from your food: vegetables and fruit having lots of water. Meat, not so much, as you could tell. Now please go drink some water."
] |
[
"You can form an acid and a base from a salt. It's the reverse of a neutralization reaction. Acids and bases aren't conserved - they can be neutralized, created and destroyed in multiple ways.",
"Separately, it doesn't make sense to separate your consumption of solids and liquids, since so many foods are mixtures or emulsions. Someone could argue that you had orange juice and orange pulp instead of saying you just had an orange. You get plenty of minerals from orange juice and pulp too. So imagine everything you consume (solids and liquids) going through a a blender (your mouth + stomach) as the basis of your consumption."
] |
[
"Can some shoot some numbers and maths at me regarding how big a melting glacier has to be to raise sea levels?"
] |
[
false
] |
I am finding it very hard to see how one ice shelf or glacier melting could raise the sea levels by a measurable amount... Or any number of glaciers really. I just feel like the oceans are too big for the levels to be raised several ft. It doesn't seem like we have enough ice on the planet to do that compared to the size of the oceans. Genuinely curious as this boggles my mind. Thanks in advance!
|
[
"OK, so area of the oceans is 361 million square kilometers.",
"We'll ignore sea ice (e.g. north pole ice cap) as that is buoyantly floating. However, we do need to consider ice which is sat on top of land. That is primarily Greenland (2,166,086 km²) and Antarctica (14,000,000 km²).",
"So, we've got about 16 million square kilometers of ice, versus about 360 million square kilometers of ocean. That means that for every 1 m of ice melted, we raise sea level by 1/(360*16) m, which is 0.0444 m. So, that's only 4cm. Doesn't seem too bad. Until you realise that the average icecap thickness on both Greenland and Antarctica is in the region of about 2 km. Suddenly melting is able to produce well over 60 m of sea level rise globally, even with a generous wiggle room for the volume reduction between ice and water, and the fact rising sea levels will lead to a slightly increased ocean surface area.",
"It also ignores the fact that warming oceans will expand too, contributing an extra bonus bit of sea level rise.",
"If you do the maths a lot more precisely and carefully, the number you reach is about 70 m potential rise."
] |
[
"No worries. People tend to vastly underestimate how thick ice can be in these places, and how big Greenland and Antarctica really are."
] |
[
"Thank you, I hadn't considered some of those factors. It just seemed as though something was missing. "
] |
[
"How can adrenaline slow your bleeding?"
] |
[
false
] |
So I recently just found out that adrenaline can actually be injected into you. I thought it was just something your body produced, and apparently it can be used to slow your bleeding. So with that knowledge here is my question. If adrenaline makes your heart pump faster then why or how does it slow down bleeding if your heart is pumping more blood?
|
[
"ER tech here. Adrenaline, or epinephrine as we call it in medicine, is responsible for the fight or flight response. In addition to raising the heart rate, it is a vasoconstrictor, ie, it causes your peripheral blood vessels (as well as those in your digestive organs) to constrict, slowing down the blood flow to those parts of the body that are not necessary for fight or flight (which is why people get a hollow feeling and become pale when adrenaline is released in their system, because there is less blood flow to the skin and digestive organs). This, in combination with increased heart rate, raises the blood pressure and increases blood flow to the skeletal muscles, ensuring they have the flow they need to sustain higher output than normal. It is because epinephrine/adrenaline acts as a vasoconstrictor, that frequently a small amount of it is mixed in with lidocaine (a numbing agent) for injection into wounds that need to be sutured, as it reduces the bleeding in the wound allowing for better visibility while suturing. It will reduce or stop bleeding from veins, especially smaller ones, but will do absolutely nothing to stop arterial blood flow. ",
"Tl, dr: It causes your veins to narrow thereby reducing the blood flow through them.",
"Edit: I have been corrected, my last statement above is incorrect. Adrenaline does also act to constrict arteries, and there are cases where a severed artery in a limb has squeezed off to the point that blood has been able to clot and stem the bleeding. However, the pressure in the main arteries is high enough to sustain blood flow to the necessary regions."
] |
[
"Vascular surgeon here. I’m sorry, but the latter half of your statement is just not true. Vasospasm and vasoconstriction is far more pronounced in the arteries. In some cases, it is the only thing that slows bleeding enough to allow for hemostasis and can give us time to find a more permanent treatment.",
"Now direct pressure is a good way to control any surface bleeding. In veins this can often allow for enough time for hemostasis to be obtained from local coagulation. For smaller arteries like radial, ulnar, and tibial arteries it can also allow time for enough vasoconstriction and coagulation to obtain hemostasis. Sometimes the plug gets ejected and bleeding will resume if the vasoconstrictor effect wears off.",
"For the record, veins are proof that god hates vascular surgeons."
] |
[
"Surgeon here. Everyone’s saying no, and the correct answer is probably no, but honestly if you are in the hospital and your blood pressure is low because you are hemorrhaging, and we can’t catch up quickly enough with blood transfusions to get your blood pressure up, we’re going to give you a medication very similar to epinephrine (probably norepinephrine aka levophed) with a very similar mechanism of action in order to keep your blood pressure up while we try to get control of the bleeding and transfuse new blood into you. ",
"So honestly it’s not the worst idea I’ve ever heard. I can’t recommend it but if you’re about to pass out from hypotension due to blood loss and have an epipen on hand?"
] |
[
"If two fermions with the same spin can't occupy the same position, how 'close' can they be?"
] |
[
false
] |
I'm almost certain I'm not grasping even the basics here, but does 'position' in this sense mean the same spot in space, or space-time? Or is this some other meaning of position that isn't quite like the colloquial use?
|
[
"Two identical fermions can have the exact same spatial wavefunction, as long as they have different spin projections (or some other quantum number different).",
"If they have all other quantum numbers the same, in principle their spatial wavefunctions can be arbitrary unless they're exactly the same. So they can be as \"close\" together as you want, they just can't be in the exact same quantum state."
] |
[
"It’s because of the way fermions are defined. Identical particles must either have totally symmetric or totally antisymmetric state vectors under particle exchange in order for the system to have the right permutation symmetry. Fermions are defined to be the ones that are antisymmetric. The Pauli exclusion principle follows directly from this."
] |
[
"Why is that? "
] |
[
"Would it be possible for a human being to actually walk on water? [Please, bear with me]"
] |
[
false
] |
During a discussion about magicians last night, someone made the argument that they feel that if a human being can float on water whilst on their back without any aides, it might be possible for a human being to train themselves to 'float walk' on water. Instinctively, I said this wasn't possible but the idea behind it has got me wondering about the science. Any thoughts brave knights of knowledge?
|
[
"Only if it's frozen. Otherwise, you'd have to displace your own weight in water before you started to float. You'd but in up to over your neck in fresh water. A bit less in very salty water, which has a greater density."
] |
[
"You could walk on liquid water if: you were not on earth...",
"If you were on a planetary body with a minute fraction of earth's gravity, and enough pressure for liquid water to exist, I could see it happening. Of course the 'splashing' from your steps would basically turn the room into a giant mixture of churning air and water taking quite a while to settle down so you could do it again."
] |
[
"In that video, the illusionist is clearly standing on a platform about 5-10 cm below the surface of the water. You can't see the platform due to the reflection of the sky and other incident light.",
"They rarely show a close up of is lower legs but when they do, you can see that his feet are totally submerged. He is not standing on the water at all."
] |
[
"How is it that we can we control some of our body's 'automatic' functions (blinking, breathing) but not others (heartbeat, sweating, digestion, hair growth)?"
] |
[
false
] |
What's going on in the brain that stops us controlling the others/everything?
|
[
"Simply put, we're not wired that way. Grandiose oversimplification incoming...",
"There are two descending (that is, information and instruction that starts in the brain and descends to the organ in question) forms of motor control (that is, contracting muscles to effect a physical change) in the body. There is the somatic system, which we can control, and the autonomic system, which ticks away quite happily without our input.",
"A note on Somatic control: The cortex is, schematically, the highest seat of consciousness we know of, and it enjoys its position at the head of a strict and complicated pecking order. The cortex can send descending information (i.e: I want to pick up this specific pen or blink my eyes) by relaying the command down this pecking order (edited very slightly along the way), before synapsing on the muscle/s you want contracted. At the same time, reflexive proprioceptive input reinforces and edits the instructions when they achieve the result you want (i.e.: pressure pads on your fingers let you know the pen is in your grasp). The key to this tract is the multitude of links between the cortex and the muscle; muscles used in conscious control are significantly linked to your seat of consciousness.",
"A note on 'automatic' control: A great deal of ascending and descending information in the brain will never make it to the cortex. This is chiefly to save 'processing power' for the more important tasks (imagine being inundated by reports about the growth of each individual pubic hair...!), or because the response would be more efficient if it never had to make it that high up. For example, if I am violently shoved from behind, the ascending information from my skin and inner ears will synapse at a level below the cortex to co-ordinate a compensatory response in my legs. I am not conscious of the specifics of what my legs are doing to keep me upright, and if it made it as far as my cortex it would have taken to long to effect a response and I'd have a shiny bruise on my face (note: this is strictly speaking a somatic response, but I'll highlight it because it illustrates that a lack on conscious control over our bodies is not always a bad thing, survivally speaking).",
"At a more microcosmic level, the heart can respond to a higher volume of blood to eject from its ventricles by ballooning its walls out to eject more blood in the next beat, making sure the muscles involved aren't stressed unduly. You will likely never be aware of this.",
"Your confusion comes from the fact the muscles used for blinking and breathing enjoy input from both somatic and autonomic nervous systems: I can exert control on my muscles of breathing consciously (like you are now, suck it), or unconsciously (if someone shouts \"boo\" behind you, expect to hyperventilate). Some nerves in the body have no such conscious connection, and thus however much we may be able to conceptualise vasodilation, we can't drop our blood pressure as easily as we relax the muscles of the eye.",
"This was surprisingly hard to pare apart and I'm sure I've missed something. If anything is unclear then it's my fault and please let me know."
] |
[
"That all makes perfect sense, thanks! :)",
"So in a nut-shell: Autonomic systems run themselves, but some varying degrees of Somatic 'override'. Right?",
"So really a more interesting question might be; what happens when those 'overlaps' aren't normally developed? If mix-ups can happen with something like synesthesia, can mix-ups happen with these systems?"
] |
[
"Your nut-shell description is more or less correct, though I think I've committed a few cardinal sins of neurology in general by using the broad terms.",
"The question you've provided is is poetically possible (though in the below example not due to developmental pathology) and fascinating to see; one case comes to mind is that of the facial muscles.",
"There was a patient we saw a while back who had Bell's Palsy, which is a disease that harms the cranial nerve involved in the muscles of facial expression. When directed to consciously smile, only one side of her mouth upturned, rather like a sneer. However when she was told a joke or saw a loved one, there was a much more pronounced raising of the mouth on both sides! It was a fascinating demonstration of the way that though conscious control was impaired (thanks to the Bell's Palsy), other mechanisms of muscle contraction can still be intact, though slightly further out of our control (likely an intact transmission between emotional centres of the brain and the facial nerve).",
"Side note: This does not imply that different nerves innervated the same muscle (because in this case they don't), rather that the facial nerve wasn't completely lesioned and that fibres from emotional centres seemed more intact.",
"Generally speaking the somatic (voluntary) and autonomic (automatic) nerves, though they start in the same place, take up very different courses and never the twain shall meet. Though in some cases they end up in the same place, they'll be triggered for very different reasons and it's hard to imagine examples where one nerve's function would be 'mistaken' for another. Thus, it's impossible to ever be consciously aware of many autonomic responses, and try as you might you can never control hair growth with the POWER OF THE MIND, whatever the hair-treatment clinics may tell you. :)"
] |
[
"When you fold a piece of paper, are you actually putting stress on any chemical bonds?"
] |
[
false
] | null |
[
"I can't imagine any significant protein content making it through a pulp and paper mill... paper is made primarily of cellulose, a polysaccharide. "
] |
[
"I can't imagine any significant protein content making it through a pulp and paper mill... paper is made primarily of cellulose, a polysaccharide. "
] |
[
"Yes. However a polymeric material like paper will first try to relieve stress by changing the organization of the polymer chains in the material. You can think of it like pulling on a pile of spaghetti. You are untangling things, but eventually you reach a point where you are breaking spaghetti. This would be bond scission."
] |
[
"What gives rise to the phenomenon of friction?"
] |
[
false
] |
[deleted]
|
[
"At the atomic scale, even the smoothest surfaces will be very rough and jagged. Also, two surfaces will never touch, they always have some gap between them. So say we have two surfaces with atomic \"spikes\". Due to the electrons in the atoms, the edges of these spike will carry a slightly negative charge. So, moving the top surface means moving some spikes (top surface) closer to other spikes (bottom surface). The negative charges repel eachother, so you will notice some resistance, which is what we call the force of friction. "
] |
[
"As a physicist, I'm not completely happy with that explanation, since friction costs energy. If you have on stationary charge and you push another one (with the same sign) along it, at first, when you're approaching, you need to do work upon it, but you get the same energy back when you're past the stationary charge - the net work is zero.",
"P.S. I wouldn't have a simple, better answer at this time."
] |
[
"The loss of energy comes from the deformation of the two solids as they slide across each other, and from the heat and (sometimes) light created as well."
] |
[
"How different is our vision from the other apes?"
] |
[
false
] | null |
[
"Depends on the ape. Overall, humans and other apes have comparable visual acuity, color sensitivity, and capacity for object recognition, but ",
"here are a few differences",
":",
"Humans possess slightly different ratios of cones (cells that respond to different wavelengths of light and allow us to see color) and are \"red-shifted\" compared to other apes.",
"Humans possess a higher rod:cone ratio, meaning they can perceive differences in a wider range of light/dark environments.",
"Compared to other apes, human visual perception of local visual stimuli is more influenced by global factors. That is, the contexts in which local visual stimuli are seen have greater impact in humans on how those stimuli are perceived. This may be because humans operate in relatively varied contexts and have to make complex decisions based on the global information found in those contexts."
] |
[
"Yeeaaah that occurred to me as I was writing it but ball is life man and I got committed to the characters"
] |
[
"At least to me, that example doesn't really seem to emphasize a difference in vision or understanding of context, but in experience. ",
"The human only knows it's a fake rubber nose because he has seen a fake rubber nose before, the orangutan only thinks it's fruit because he has seen fruit before. Had the human never seen a clown nor plastic red balls but only fruit, while the orangutan had seen red plastic balls and clown before, I would image you could just as easily flip the roles. "
] |
[
"Why are there things i can only remember when i'm doing it?"
] |
[
false
] |
For example, game mechanics.
|
[
"Humans have several different \"kinds\" of memory. ",
"Autobiographical:",
" Your memories of events that have happened to you personally. ",
"Semantic:",
" Your knowledge of facts. ",
"Procedural:",
" Your knowledge of how to perform certain tasks. ",
"Procedural memory is very interesting, and can persist even when other parts of human memory have given out completely. For example, patients who've sustained damage to their hippocampus often have trouble forming new autobiographical memories, but they can still make new procedural memories. ",
"Procedural memory is often ",
"context dependent",
", meaning it's easier to remember the procedure when you're actually doing it. To use your example, if you're trying to explicitly remember a particular game mechanic, you might be trying to tap into your autobiographical or semantic memory, which may not be the best way to remember something so procedural. But when you sit down in front of the game, you're back in the context in which you originally learned it, which is important for memory in general and procedural memory in particular. "
] |
[
"Great answer. But isn't it also ",
"priming",
"?"
] |
[
"Quite possibly. Most of my priming research involves semantic priming, but there could well be some response priming in OP's scenario. "
] |
[
"(Geology) The \"polar wander hypothesis\" was debunked, but isn't the phenomenon of a wandering pole an actual thing since we've observed that magnetic North moves?"
] |
[
false
] |
My textbook says As paleomagnetists sampled and measured older and older rocks, . This was called the “polar wander hypothesis” at first. But then they ran into a problem. Each continent had a completely different polar wander curve, which only converged on a common magnetic pole today. These data seemed to suggest that the magnetic field had behaved very strangely in the past, with multiple directions of magnetic north that no longer exist. As outrageous as that idea seemed, the only alternative was just as radical: . But when you lined up the polar wander curves for two different continents, like Europe and North America, you found that they matched once you moved the continents back together as Wegener had suggested. What I'm confused about is my book saying, "the continents had moved through time, so it was " because isn't that not completely true since magnetic North DOES move? We've observed this movement, so isn't my book completely dismissing the idea of a "wandering pole" incorrect? Everything I've watched and read online only talks about the effect of continental drift on the apparent wander curves, but they haven't talked about how the magnetic North pole does, in fact, move. Can't the movement of the magnetic North pole have had at least a influence on the polar wandering curves?
|
[
"Your book is correct that the idea of a wandering magnetic pole as the primary reason for variations in the orientation of remnant magnetic field that differ from today's orientation has been rejected. Within this, there is some nuance that is not reflected in the passages you highlighted, and generally are things that would be covered in courses which cover paleomagnetic data in more detail (i.e., mostly graduate level courses in plate tectonics, geodynamics, or geomagnetism, etc). To break this down, we can consider three broad types of \"movement\" of the geomagnetic pole or movement relevant for considering preserved geomagnetic pole positions and the detail form of apparent polar wander paths.",
"The first is ",
"geomagnetic secular variation",
", which is maybe the type of movement you're thinking of. This describes the relatively fast, e.g., on the order of ~1 degree/year, ",
"\"wandering\" of the geomagnetic pole",
" and why if you need to use a compass for precision navigation (e.g., in an airplane) you need to occasionally update the declination of your compass (which in this case describes the angular correction necessary to account for the difference between the current position of the geomagnetic pole with respect to the rotational axis of the Earth). However, the critical bit here is that on long-time scales, what we refer to as the \"geocentric axial dipole\" or GAD hypothesis holds. GAD suggests that from a time-averaged perspective, that secular variation \"averages out\" and that the time-averaged position of the geomagnetic pole is coincident with the rotational axis. One colorful way I've seen this described in geomagnetic texts is \"a drunk (the instantaneous position of the geomagnetic pole) staggering around a light pole (the rotational axis)\". If you were to track the drunks staggering and find the average position, it would be approximately that of the light pole. This means that when we estimate the implied position of the geomagnetic pole as measured from preserved remnant magnetism in old rocks (i.e., the position of the virtual geomagnetic pole, or VGP), we need to average over sufficient time, usually a few tens to hundreds of thousand years, to ensure that our VGP is not biased by secular variation. An abundance of evidence suggests that GAD holds for the majority of Earth's history (e.g., ",
"Tanaka et al., 1995",
", ",
"Swanson-Hysell et al., 2009",
", ",
"Veikkolainen et al., 2014",
", ",
"Panzik & Evans, 2014",
"). ",
"The second form of movement we can consider is the \"flipping\" of the poles, i.e., the reversal of the polarity of the magnetic field or ",
"geomagnetic reversals",
". In terms of geomagnetic reversals, these are not really \"flips\" in a simple sense, but more like a somewhat chaotic drift of the geomagnetic poles from being near one rotational axis to the other (e.g., ",
"Channel & Lehman, 1997",
"). In detail though, while we can still approximate the positions of the two magnetic poles (i.e., approximate the field as a ",
"dipole",
") during a reversal, in reality what seems to happen during reversals is that (1) the overall field intensity is significantly diminished and (2) the non-dipole components (i.e., multi-pole components of the field) become more dominant during the reversal (e.g., ",
"Valet et al., 2005",
", ",
"Valet & Fournier, 2016",
"). So while we can think about the two poles drifting significantly during these reversals, reality is a bit more complicated. The timescale of the portion of the reversal characterized by rapid motion of the dipole portion of the field is relatively quick (geologically speaking), with some perhaps occurring within a century (e.g., ",
"Sagnotti et al., 2014",
", ",
"Sagnotti et al., 2015",
"). In terms of most geologic records, the polarity flips are instantaneous and it actually requires pretty specific environments (with high deposition rates and good preservation, etc) for us to \"see\" any detail within the reversal in terms of changes in VGP position besides the \"flip\". ",
"Finally, while large-scale and persistent polar wander is demonstrably false, there is ",
"true polar wander (TPW)",
", i.e., the shift of the solid Earth with respect to the rotation axis. TPW is not really meaningfully related to either secular variation or geomagnetic reversals. TPW occurs as a slow drift, with estimates of a upper limit of shift of ~1-2 degrees per million years (e.g., ",
"Tsai & Stevenson, 2007",
"). This means that it's slow enough that it can largely be ignored on human timescales (and it's not important for considering secular variation, etc), but can be important for accurate considerations of past motion of plates on geologic timescales (e.g., ",
"Steinberger & Torsvik, 2008",
"). I.e., for extremely accurate plate reconstructions, we do need to account for TPW when considering VGPs, but in terms of the difference between a given VGP and the rotational axis of the Earth, the overwhelming majority of that difference is a result of past plate motion, not TPW.",
"If you want to take a real deep dive into all of this, there is an excellent freely available text on ",
"paleomagnetism by Rob Butler",
". It's a little out of date in some sense, but it does a really good job of covering many of the basics."
] |
[
"Thank you so much for such a great reply! I'll definitely be checking out that paleomagnetism text you mentioned."
] |
[
"Awesome reply. I didn't even know I was interested in this, but I'll be damned if I didn't find that an interesting read!"
] |
[
"Does 'bracing for impact' actually help during minor impacts?"
] |
[
false
] |
Even mentally?
|
[
"Many people here talk about grabbing onto stuff etc. but there's a much simpler view.",
"Bracing for impact does help. You basically do this by contracting mucles and breathing out, anything else is optional or rather situational. \ncontracting muscles prevents impact from deforming your organs and helps muscles absorb the shock. breathing out prevents compression of your diaphragm/lungs during impact, thereby prevents getting the \"wind knocked out of you\" and more serious lung damage.",
"while you probably refer to accidents and such, this can also be observed in martial arts, where an impact is absorbed with less damage by contracting mucles and exhaling."
] |
[
"Bracing may help reduce traumatic brain injury by increasing the blood in the veins surrounding the brain. The Valsalva maneuver is increasing the pressure in your lungs (i.e. \"bearing down\") which causes some blood to back up into the venous system. There's a collar is development for contact sports which recapitulates this.",
"http://bjsm.bmj.com/content/early/2016/06/15/bjsports-2016-096134.full"
] |
[
"I did a summary of the studies they ran about it on my blog, haven't done much recently though, I'm on a little hiatus due to being balls deep in board exams\n",
"https://thedrugdebrief.wordpress.com/2016/06/19/the-q-collar-protecting-your-brain-from-your-skull/"
] |
[
"What exactly would the landscape of the British Isles have looked like prior to human cultivation?"
] |
[
false
] |
When you look at the landscape of the United Kingdom today, the vast majority of it consists of either towns or farmland. The human race has left an enormous impression on what Britain looks like, perhaps more so than most other nations on Earth. What would Britain have looked like during, say, the middle Paleolithic? Or at least before the development of agriculture. I've always imagined it to be heavily forested, perhaps resembling rural Canada or Scandinavia today. But I have no real knowledge on this subject - is my view in any way accurate? Or is there even any way of knowing for sure?
|
[
"This is actually an area of ongoing debate. In the past, it has generally been assumed that Britain was largely covered by forest - primarily because forest is seen as the inevitable result of succession given the ecological conditions in Britain. Note that in most of Britain this climax community is temperate broadleaf or mixed woodland, where as your vision of Canada and Scandanvia might well be of boreal coniferous forest.",
"However, in 2000 Frans Vera published a book called \"Grazing ecology and forest history\" which suggested that prior to human arrival and dominance, large grazing herbivores (e.g. aurochs, the extinct ancestors of domestic cattle) would have had a strong effect on the landscape by browsing on trees and shrubs and hence preventing succession from occuring. This, coupled with other disturbance forces such as wildfires, storms, diseases and pests, and floods, with have lead to a relatively open park-like mosaic of wood and grassland. One question that this hypothesis answers is: where did all the open-country species live? Many species in Britain (noteable many butterflies and wildflowers) are strongly associated with open landscapes and direct sunlight, and would not be found in continuous woodland.",
"So, how can we find out? One of the most common techniques is to analyse long term sediment cores from lakes. Pollen is trapped in the sediment, and changes in the presence and relative abundance of different species' pollen can indicate changing plant communities. Furthermore, sediment also contain fungal spores; certain spores are associated with herbivore dung, and therefore the abundance of these spores can be used as an indicator of the abundance of herbivores and hence infer the grazing pressure. Another technique is to use ecological inferrence - we can use exclosure or introduction experiments to try and understand the impact that the presence or abscence of large mammals would have had on the vegetation, and then try and estimate which situation is most applicable to Britain.",
"However, part of the reason that this debate is still ongoing is that the arrival of humans into Northern Europe coincided with the end of most recent glacial period; as such the impact of human arrival is confounded with changing climatic conditions and natural recolonisation of species into previously ice-covered areas.",
"Further reading: ",
"https://www.britishwildlife.com/site/issue/211117/volume-20-number-5-up-june-2009",
" (not sure if the pdf is online anymore - pm me if you want a copy)\n",
"http://www.pnas.org/content/113/4/847.abstract",
" \n",
"http://www.sciencedirect.com/science/article/pii/S0006320701001628",
"Hope this helps (and sorry for the essay) - happy to answer any questions!"
] |
[
"(and sorry for the essay)",
"I come here for the essays! Nothing more frustrating than an answer that has a couple of sentences for an answer and barely hints at the reasons behind it. This was very interesting."
] |
[
"Scotland is still mostly preserved.",
"Just to jump in here, this is very much largely not the case. Whilst of course there are fragments of native woodland in Scotland, the landscape of the highlands is largely artificial/human-derived. Much of the heath and moorland is a result of human factors that result in the maintenance of dwarf-shrub dominated vegetation. Heath and moorland are maintained by a combination of deer overpopulation (kept at artificially high numbers for shooting), which hampers natural regeneration of forests and keeps heathland vegetation shorter, as well as the burning of heather in grouse shooting moors, which keeps the heather short and young, as well as increases the amount of territorial patches available for grouse. There is also a huge amount of grazing by sheep and cattle in these areas, in both heath and grassland. In addition, a lack of natural predators such as wolves and lynx also allow an overabundance of herbivores, further exacerbating these problems. Whilst obviously almost all landscapes in the world are affected by human action in some way, I think it's very important to consider the extent to which human intervention affects the shape of these environments, especially when what can look like a very stark and wild environment is actually highly artificial. ",
"There are of course many areas of semi-natural or human-mediated environments such as meadows, grassland, the machair vegetation on the west coast, as well as wetland areas and bogs, but again these environments in many cases exist simply due to a lack of utility, or are sometimes even actively defined as requiring human intervention (e.g. cutting or grazing meadows). ",
"All this said, there's a lot we don't know about the vegetation history of the highlands - for example, as far as I know, we have no records of the height of the tree line (the altitude at which trees are unable to grow) at the tops of mountains, so it is hard know, were one to want to restore more of the native pine forest, where to restore it or how high to expect it to grow. As ",
"/u/must-be-thursday",
" also noted, it has been suggested that much of the UK was a mixture of grassland/pasture and forest, though this idea is not universally accepted. Certainly, the extent to which this would have existed in Scotland is likely different to its extent in England due to its rugged and mountainous terrain, which leaves more forest relatively inaccessible to grazing animals and restricts the movement of herbivores. "
] |
[
"How come some moon phases can be seen during the daylight and some can only be seen at darkness?"
] |
[
false
] |
[deleted]
|
[
"The Moon is always half lit and half in darkness - the lit half is the half that faces the Sun. We see different phases because we are seeing the Moon from different angles, so sometimes we see more of the lit half, and sometimes we see more of the dark half. As the Sun is much further away than the Moon is, the Sun is almost exactly in the same direction from the Moon as it is from the Earth.",
"Basically, this means that the angle between the Moon and the Sun in the sky is connected to the phase of the Moon. If the Sun is close to the Moon in the sky, that means the Sun is close to directly behind the Moon, and we're seeing almost entirely the shadow side - maybe a little bit of a bright crescent at the end. If the Moon is opposite the Sun in the sky, then we're seeing the Full Moon completely lit by the Sun. If the Moon is 90° across the sky from the Sun, then we're seeing the lit and shadow sides edge-on, and we see a half Moon.",
"If the Moon is opposite the Sun - as it is during a Full Moon - then the Sun rises as the Moon sets, and vice versa. So in that case, you don't see really them at the same time - i.e. you don't really have a Full Moon during the \"day\". But the closer the Moon is to the Sun (i.e. the smaller the lit crescent of the Moon appears), the more the Moon and Sun are up at the same time, and the more the Moon is up during the day."
] |
[
"This is basically a geometry problem",
"The Moon is always half lit and half unlit. The half that's lit will always be facing the Sun. So basically, when you look at the moon, remember that the lit side is pointing at the sun.",
"So, if you can see a full Moon, or something close to a full Moon, the Sun must be behind you. This can only make sense if the Earth is between the Sun and the Moon. So, the Moon must be on the night side of Earth. ",
"If you have a new Moon, or something close to it, then the lit side must be pointing away from the Earth, towards the Sun. So the Moon has to be between the Earth and the Sun, so it must be on the day side."
] |
[
"When the moon is full, it's on the opposite side of the Earth from the Sun; when the moon is new, it's on the same side. As the moon waxes from new towards full, it will rise and set later and later after the sun. So a waxing crescent moon would be seen in the western sky shortly after sunset. As it grows more towards waxing gibbous it will set later and later after the sunset, to the point where when the moon is full, it will rise as the sun sets. Then as the moon wanes it continues to rise and set later, to the point where a waning crescent moon would be seen in the eastern sky just before sunrise. Finally when the moon is new again, it rises and sets with the sun and you don't see it at all (unless they happen to line up perfectly with the Earth, as happens once in a while, and you get a solar eclipse).",
"Here's a good resource that might help you"
] |
[
"Is it possible to change a specific base for another specific base, at a specific location within the genome? What is the most common method to achieve this?"
] |
[
false
] |
I've read a bit about site directed mutagenesis but just wondered if we can mutate a specific base for another. Thanks in advance.
|
[
"Hmm, are you talking about humans or just in general? I'm not sure of a technique that would allow you to change one specific base for another precisely, but this is possible with common techniques. For instance, you could use a CRISPR-Cas9 type system to target a specific region in the genome and then use a PCR product that you've manipulated to have the one specific base substitution. Now, that would in itself be sort of difficult because you'd need to change your targeted sequence at one location, but you could do it by designing primers with your substitution and working backwards.",
"I hope that made sense. You're basically just swapping out a targeted region of the genome with a modified one nucleotide substitution that you've made by PCR."
] |
[
"I assumed the process could be applied to a variety of species. It did make sense, thanks. Is site directed mutagenesis most commonly carried out by PCR based method? "
] |
[
"Well I work with drosophila (fruit fly) and we use a similar method so I suppose you could apply it to most species in vivo. But yes, most site directed mutagenesis is going to be based around PCRs because that's one of the easiest ways (that I know of, anyways) to cause a mutation in a gene and introduce it to an organism."
] |
[
"How can Mars ever be colonized without a protective ozone layer, thick atmosphere, and a strong magnetic field?"
] |
[
false
] | null |
[
"Hi plokijuhytrew thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Planetary Sci"
] |
[
"I am on mobile using Redditisfun. I have no idea how to flair, or if I did, flair what.",
"Is this some sort of cult?"
] |
[
"Why are sunburns, chemical burns, and burns from high heat all burns?"
] |
[
false
] |
Sunburns, chemical burns, and burns from high heat all look and feel similar, but their causes are very different. What do they all have in common, and more broadly what makes an injury a burn rather than something else?
|
[
"Medical terms (both casual and formal) are based on symptoms, not cause. All those mentioned result in pain, inflammation, and possibly scarring in the skin."
] |
[
"UV radiation, caustic chemicals, and flames all cause tissue damage that leads to inflammation. Free radicals are produced, white blood cells invade, and dendritic cells become active. The pain is often due to spillage of inflammatory mediators that trigger nociception in the local area. This can be done through things like substance P. Heat can also directly trigger nociception in pain nerves by activating heat sensitive ion channels like TRPCs. Because it’s essentially all nerve activation, third degree burns often lose feeling because there is no route for nociception when the nerves die."
] |
[
"They are all related by the type of pain felt. Burns have a burning sensation as opposed to stabbing, itching, or other sort of pain. It is really more a quirk of the English language than anything. There are probably languages that are more specific words for different the types of pain and related injuries which use different words for these different injuries."
] |
[
"Is the digestive process always first-in, first-out, or can quickly digestible meals \"pass\" slower digesting meals in the intestines?"
] |
[
false
] |
Google searches only seem to bring up information on constipation.
|
[
"Yes, the muscle ring between stomach and small intestine is coordinating some interesting stuff, like a bouncer in a club.\nLiquids in general go through the stomach faster, because they can flow through the muscular fissures of the stomach lining (like a motorcycle ignoring the traffic jam by driving around the cars). However, fat is kept longer inside the stomach, because the small intestine needs time to prepare for fat digestion (bile acids, enzymes from pancreas, bile acids need to be recycled if the fat content was too large). \nThe muscle ring also checks for acidity (not acidic enough? no entry! Can feel like heartburn if muscle reacts too strong), as well as particle size (not small enough? No entry! Come back once the stomach muscle has ground you to powder!)",
"Simple sugars and starch are already digested inside the mouth, and some can be absorbed/taken up in the stomach, same with alcohol. Rest makes it into the small intestine. Most of the stuff we can get energy out is digested and taken up here. The rest (water, bile, and undigested material, like fiber (or milk sugar if you are intolerant) moves to the colon: bacteria will digest what they can. If high energy stuff made it to the colon, the bacteria will throw a wild party, and you end up passing wind. The colon is where the water is absorbed, and if that does not happen, you end up with diarrhea (sugars bind water, so if you are lactose intolerant...). But many bacteria die daily as well, and they end up in the poop, too. Most of poop is dead bacteria, some leftover coloring from dead red blood cells (the brown in poop), and the occasional undigested sweet corn kernel and fiber not even the bacteria could handle. ",
"Additionally, the body also a priority list of what to use first: Alcohol is always first, then fructose (because it needs to be turned into glucose first, so glucose will be turned into fat for storage during that time, because the body cannot have glucose floating around, aka diabetus), then glucose, and then fat. Protein is preferred to be used as building material, not energy. Unless you are sick as hell or on a diet, then the protein will be taken out of your muscles for energy production. "
] |
[
"Basically yes. Slower digesting foods, complex carbohydrates such as sweet potatoes and grains, will stay in your system breaking down longer than quicker digesting carbohydrates (sugars). The foods all break down as soon as they're in your stomach and interact with enzymes so it's not based on first in first out exactly"
] |
[
"To add to what ",
"u/easyson",
" said, it's important to realize that a \"meal\" or even \"food\" really ceases to exist shortly after exiting the stomach. At that point you just have chyme, which is food + bile salts + water, and your small intestine starts the major nutrient absorptive process. So slower-digesting \"food\" wouldn't get passed over by quicker-digesting food, because theres no distinction left."
] |
[
"Why is it that the days I don't go to the gym I get extremely depressed?"
] |
[
false
] | null |
[
"First, please talk to a doctor. You seem to be treating your depression with exercise. While this may work in the short-term, it is obvious that you haven't completely controlled the problem. This is serious, and you require the opinion of a trained professional.",
"In terms of why exercise might help your depression, exercise induces the release of several neurotransmitters that are implicated in depression. While the precise mechanisms that cause depression are complicated, most doctor first prescribe medications that act on serotonin receptors or transport molecules, and this is thought to correct an existing imbalance in serotonin transmission. Exercise, especially exhaustive exercise, induces the release of serotonin. This may help balance the system temporarily.",
"Exercise also increases the transmission of dopamine and endocannabinoids in the brain, which produce the rewarding feeling and the \"runner's high\"."
] |
[
"Well, the post was removed, but here's a ",
"relevant scene from ",
"."
] |
[
"thank you for the response"
] |
[
"Why do we always try to stop the swelling that occurs upon spraining or breaking a bone?"
] |
[
false
] |
[deleted]
|
[
"Just a nurse here, but unmitigated swelling can lead to vascular compromise i.e. compartment syndrome. This can lead to ischaemia and tissue loss. The body uses inflammation as a blanket response to injury until a more appropriate response can be delivered. I'm at work and unable to really delve into it deeper, so hopefully someone else can pick up my slack :)"
] |
[
"Not only that but depending on the injury, the swelling could \"fix\" (as in, immobilise) the area in an awkward fashion, making addressing the injury harder. Take a joint dislocation - it's often said that it needs to be addressed before joint swelling kicks in otherwise manipulating the limb/extremity back to where it belongs gets progressively harder and thus more painful and likely to cause secondary damage."
] |
[
"The swelling might cut blood supply to the area due to pressing blood vessels, which then leads to that area start dying off due to lack of oxygen. ",
"In another case the swelling can crush organs and essentially damage/kill them, or prevent their proper function (imagine having swelling in your lungs, which would prevent you to breath). That is the medical reason to counter-act swelling.",
"The other reason, and most common really as people dont think of swelling in those terms, is that it limits movement and is annoying as hell, not to mention it \"looks\" bad, in peoples minds if the swelling is gone, the affected area must then, be better."
] |
[
"why does the LHC have to be so big?"
] |
[
false
] |
cant you aquire the same data on a more efficient and less costly scale?
|
[
"The goal of the LHC is to collide particles at very high speed. So you need to make the particles travel a long distance in order to have enough time to accelerate them before the collision. That's why the LHC is circular: the particles travel several laps and are accelerated frequently.",
"But a particle moving in a curved line will emit some radiation and lose some energy. The more curved the trajectory, the more energy the particle loses. If you want the particles to have very high energies, you need to make them run in circles but with the less curved trajectory as possible: you need a very big circle."
] |
[
"For the LHC, it's simple: they took the tunnel used by the previous collider (the LEP). Cheap and fast.",
"For the LEP, it was a compromise between \"how big do we want our collider to be?\" and \"how many billions euros can we get?\"."
] |
[
"Sadly, scientists must sometimes deal with the fact that money is not infinite. By using the old LEP tunnel and not digging a new one, CERN managed to save tons of money that could then be spent on other areas of the LHC budget."
] |
[
"Can a deaf-blind person learn how to speak? If so, how?"
] |
[
false
] |
Assuming full deafness and full blindness from birth, can someone be taught to speak? Assuming speaking involves some acceptable measure of pronunciation, grammar, etc. If this is possible, how? Primary evidence would be highly appreciated.
|
[
"Yes. I have a friend who was born deafblind and he speaks, albeit not well. ",
"Teaching people with this condition to use their voice is an extremely difficult task. They feel the larynx and the breath coming.out of the nose on closed-mouthed consonants like M and N....",
"I have immense respect for the deafblind who can speak. "
] |
[
"Thank you for the first-person response. Learning language with only one sense sounds like an incredibly arduous task.",
"I theorized that if a blind person can turn braille (touch) into language, and a deaf person can turn sign language (sight) into language, then it seems possible that a blind-deaf person could turn vibrations into language (though at greater difficulty)."
] |
[
"Helen Keller was not born blind and deaf; it was not until she was 19 months old that she contracted an illness described by doctors...",
"I'm aware of Helen Keller, but she wasn't born blind and deaf. She had 19 months worth of exposure to language and seeing the world before she lost her hearing and sight."
] |
[
"With growing water shortages, will we ever see water tankers crossing the globe like we see oil tankers today?"
] |
[
false
] | null |
[
"There is plenty of fresh water, and it is pretty easy to make it from sea water...the issue is one of transport, not supply.",
"The current water delivery infrastructure is based mostly on gravity...divert water from uphill to where you want it to be downhill. The problem is the ocean is as downhill as you can get. So whether you use desalination or cargo ship, having a whole bunch of water at sea level doesn't do you much good."
] |
[
"The technology for desalination isn't the limiting factor, it is an abundant source of cheap energy. No matter which desalination technology you choose, either some form of vacuum-distillation (probably ",
"multi-stage flash distillation",
") or a membrane based technology like ",
"RO",
" they all take quite a bit of power to produce water on a large scale. So it will all come down to an economic cost analysis of whether it is cheaper to ship the water or build the desalination plant + power source (if not available). ",
"There are some interesting solutions to the power problem on the not-to-distant horizon that ",
" help swing it in favor of desalination plants if they pan out, such as ",
"LFTR",
"Edit: my guess is that shipping fresh water would only really be viable for short-term emergency situations. Anything medium to long term would require a desalination plant of some sort."
] |
[
"The cost of energy to desalinate will be superseded by the cost of fresh water and/or transport fresh water from one place to another "
] |
[
"How much would life on Earth change if the Earth's axis was tilted at 24 degrees?"
] |
[
false
] |
[deleted]
|
[
"A tilt of 24",
" is ",
"within the normal range of axial tilts",
" the Earth experiences. Over 41,000 years, our tilt varies from 22.1",
" to 24.5",
" and back again. This axial tilt range is quite a bit smaller than that experienced by some other planets - for instance, Mars' axial tilt has ranged anywhere from 0",
" to 60",
" over the past tens of millions of years. \nSome analyses hypothesize that our relatively small range of axial tilts is owed in large part to the tidal forces of our relatively large Moon.",
"When our planet experiences slightly larger axial tilts near 24.5",
" we tend to get slightly stronger seasons; similarly the slightly smaller axial tilt of 22.1",
" favors slightly weaker seasons. However, since small axial tilts mean weaker summers particularly in polar regions, it's theorized that when the phase of small axial tilt also lines up with the 26,000 axial precession cycle and the 112,000 precession of our orbit's perihelion, it produces an especially weak summer near the poles, triggering the glacial period of an ice age. This is the basis for ",
"Milankovitch cycles",
".",
"I've read articles and watched documentaries about how drastic of a change Earth would experience if it was x feet closer/farther away from the sun",
"This is generally not true - or at least the references I've seen to this have usually come out of a desire to prove that our planet was intelligently designed by a divine creator. These claims don't stand up to scientific scrutiny until you start getting to really large astronomical distances, not generally measured in feet."
] |
[
"We're currently at 23.5",
" and headed for smaller tilts. ",
"The cycles don't line up to set the stage for another glacial period for ",
"another 50,000 years",
", but there's also good evidence that we've pumped enough CO2 into the atmosphere that ",
"we'll be skipping glacial periods for at least 500,000 years."
] |
[
"Where are we at right now as far as tilt?"
] |
[
"Why do jet streams only occur at high altitudes?"
] |
[
false
] |
Additionally, do jet streams remain constant or do they 'die out' like gusts of wind?
|
[
"Jet streams are driven by differential heating between the equator and mid-latitudes that is then modified by the earth's rotation via the Coriolis force. The flow is at all levels of the atmosphere but there less friction at high altitudes so the flow is stronger there. Friction at the ground reduces the flow close to the ground. Jet streams can be highly variable due to instability processes but they do not die out like gusts of wind."
] |
[
"Would the friction at ground level be due to physical objects such as trees and buildings?"
] |
[
"Yes, but also the ground itself and topography. The variability of the Jet Stream is amplified by flow over mountains."
] |
[
"As an example, if Penicillin gets inhibited by penicillinase, why don't we take another drug beforehand that would inhibit penicillinase so that Penicillin would be an effective antibiotic again?"
] |
[
false
] |
College Bio student and I just thought of this, of course someone else probably already though of it but I just want to know the reason why it doesn't work
|
[
"It does work. This is a common strategy for improving the effectiveness of certain antibiotics. Augmentin is an example of an antibiotic that uses this strategy. It's a combination of a pencillin derivative antibiotic (ampicillin) and a compound (clavulanic acid) designed to inhibit the enzyme that some bacteria use to resist ampicillin (beta lactamase)"
] |
[
"It definately isn't as easy as you make it sound out to be. Developing a drug against an enzyme usually involves years of research by medicinal chemists. And even if a suitable compound has been identified it can be impossible to make it properly bioavailabe. ",
"The compound might even have severe side effects on your own body."
] |
[
"There are many different ways that bacteria biochemically resist antibiotics. They can break down the antibiotic, they can change how they express certain proteins that the antibiotic targets, they can produce more pumps to remove the antibiotic from their cells, etc. ",
"In some cases we understand how the method works, but don't have any chemicals that fight it. In other cases, we have chemicals but they cause more harm to the patient than good. Some mechanisms of resistance are either so effective that the idea of making a chemical counter attack is nonsensical or not understood well enough to be at the point where we can try to develop drugs to block them. ",
"Even if we could treat all of these mechanisms effectively with other drugs, this wouldn't solve the problem, it would only buy us time. Bacteria are always evolving. Spending time and money investigating chemical defenses against resistance mechanisms is the same kind of drug development as designing new antibiotics. In most cases, you get more effective medications from developing new antibiotics rather than new adjuvants. "
] |
[
"Why do eggs become hard when boiled while potatoes become soft?"
] |
[
false
] |
[deleted]
|
[
"Regarding the eggs, Harold McGee explains it well in ",
" ",
"Page 1",
", ",
"Page 2",
"I'm not sure about the potatoes.",
"FYI though, cooking at or bellow 100°C mostly changes hydrogen bonds, very few covalent bonds are effected. Most of cooking therefore comes from protein denaturation, which is what I suspect is occurring when potatoes, or any other vegetable, softens. "
] |
[
"Proteins have hydrophobic (water insoluble) and hydrophillic (water soluble) regions on the strand of amino acids. A protein is folded in such a way that the insoluble regions associate and interact with other hydrophobic regions while the hydrophillic regions are capable of solubilizing the protein in an aqueous environment. Denaturing by heat ruins these folds and the protein, with exposed hydrophobic regions, are no longer soluble. Hence the hard egg.",
"I am not so sure about the potato. It's mostly starch which is insoluble. I want to say the hot water breaks the glycosidic bonds between the sugar monomers in the long starch chains. Imagine you vacuum seal a rock and then hit the bag with a jackhammer, the bag may retain volume and shape but is now full of a fractured, soft substance"
] |
[
"Potatoes are composed primarily of starch(carbohydrates, combination of amylose and amylopectin) while egg, both white and yolk, are protiens in a native form. ",
"The native form of the starch is a hard, crystalline granule. When heated in the presence of moisture, the granule first swells, then 'gelatinizes'. This new form is much softer and has more moisture.",
"When eggs are heated, the energy imparted on the proteins causes them to change their confirmation and form an irreversible(I say irreversible because in theory if you found the right combination of activation energies and pathways, you could uncook an egg. It's ust never been done and probably never will) gel. The new gelled egg protein is very thermodynamically stable.",
"TL:DR Potatoes are carbohydrates, eggs are proteins. BIG difference."
] |
[
"Why did evolution through natural selection favour putting testicles in a scrotum rather developing more heat resistant sperm."
] |
[
false
] |
[deleted]
|
[
"Probably just the testes were slightly external by some mutation, and this gave slightly higher sperm survival rates and it snowballed from there. However your phrasing of the question suggests that you are thinking of evolution as making concious choices. The only real reason that evolution 'picks' one solution over another is if it happened first, by chance. It is pretty much impossible for it then to go back and pick a better solution, since going back would be less favourable (or the change would never have happened in the first place)."
] |
[
"Evolution pushes towards local peaks rather than global maximums. "
] |
[
"Evolution pushes towards local peaks rather than global maximums. "
] |
[
"If a woman's eggs are fully formed at birth, why does having children later in life increase the risk of developmental disabilities?"
] |
[
false
] | null |
[
"source: biomedical sciences major with a few courses in genetics.",
"the simple answer is, eggs aren't fully formed at birth. i believe they become arrested at... metaphase I? then after menstruation, eggs continue to go through the first phase of meiosis and stop again into meiosis II until fertilization does (or doesn't) happen. therefore, eggs still have a lot of work to do, and damage early on (the normal course of a woman's life) can affect them quite a bit later on down the road. the ova that a woman has at 35 have been exposed to a lot more chemicals and what-have-you han a man's sperm when he's 35, because he will constantly produce new sperm while her eggs have been beaten up by life for 35 years.",
"hope that makes sense."
] |
[
"you're right, but i wouldn't say that ",
"paternal age",
" holds much of a candle compared to ",
"maternal age",
". at age 40, there's a 1 in 100 chance a woman's child will have down syndrome.",
"why down syndrome in particular? that one's pretty cool, actually. down syndrome is one of the few chromosomal defects (i mean like a trisomy/monomy kind of thing) a fetus can have without the body spontaneously aborting it. most other chromosomal defects will not ever come close to term."
] |
[
"Men's children are at greater risk later in life as well. I'd assume this is mostly due to replication errors in the germ cells that produce sperm. "
] |
[
"How does restricting Internet work?"
] |
[
false
] |
Now when Net Neutrality is in the news all the time, I'm wondering how restricting the content works? Can it be avoided with a VPN?
|
[
"There are plenty of ways to deny service, particularly so if it is done by the operator providing the service.",
"Connectivity. You may be connecting to some sort of access point, like a WiFi AP, which does not provide service unless you follow specific procedures. This is usually some trivial registration or authentication step, but it could involve more intrusive steps (downloading some 3rd party monitoring software, providing your location, identifying with some 3rd party - like commonly posting on Facebook - etc). This may appear benign, but it is the combination of this practice with network analytics that makes it valuable for an ISP.",
"Point-to-point control. Your ISP provides you with an IP route to the rest of the world, and thus controls almost anything on it. It is able to restrict you to using their own DNS servers, thereby redirecting your connection attempts to servers under its control. ",
"Name lookups",
" are not only used to access the web, so effectively other services, like your email connections, or your unencrypted connections to a file service, may be completely ",
"hijacked",
". It may disallow connections to any IP, unless some desirable property is reflected in your subscription (e.g. you've paid a premium to use, say, ",
"www.bing.com",
"). It may decide to temporarily redirect all your requests to a server of its choice, making you watch advertisements every hour on the hour, until you can visit YouTube again.",
"Traffic shaping / differentiated services. Your operator is able to ",
"prioritise",
" your use of its resources at will. It may decide to limit certain kinds of traffic in the morning & late evening, to avoid diurnal peaks in traffic and influence its capacity planning (to their benefit, of course). It may decide to prioritise certain kinds of traffic for subscribers which pay extra. It may prioritise certain kinds of traffic for ",
" that pay extra - for instance, it may prioritise downstream traffic from an ad agency which has paid to...",
"Content rewriting. There have been disturbing instances where operators have been injecting (ad) content inside web pages. An operator may decide to promote use of unencrypted web traffic, in which they can promote advertising, over encrypted. An operator may rewrite or exclude content; sometimes it is the case that some service operators do this for legal reasons (e.g. Google removes neonazi listings in compliance with German law). Your service provider may do the same, not only for services that it provides directly (which makes the implementation trivial), but also for traffic that it routes.",
"Monitoring and inspection. Since your operator controls your traffic, it can do whatever they want with it. Your packets are inspected, classified, accepted, rejected, or modified accordingly, and only then forwarded, and forwarded to whichever network service provider makes sense (just to clarify, that last part is already the case; it's primarily business interest decides internet interconnection). It is possible to accurately identify any type of traffic you generate and any publicly available protocol in use. Your operator can charge you differently based on the services you use at any level (e.g. TCP vs UDP, HTTP vs BitTorrent, VPNs vs telnet) at will, penalise you for harming its infrastructure (e.g. by - arbitrarily or not - deciding that VPNs hurt their profit margins), prevent you from harming its profit model (e.g. by using service provider A for your video streaming rather than provider B), report you to the authorities for conducting suspicious activities (e.g. attempting to encrypt all your traffic), and so forth. Firewalls and DPI systems, centralised or distributed, which can handle any amount of traffic are cheap to acquire and, quite frankly, relatively easy to build. Your operator is capable of analysing your internet behaviour, intercept your private data, and derive your habits, putting it in a position of ownership of a vastly underestimated treasure trove of information. Knowledge over ",
" subscribers do provides the insight into ",
" to better monetise it by introducing restrictions.",
"Compromise. As your ",
", your operator may posit you need to make certain security and privacy compromises; use their proxies, compromise your end-to-end security by using their gateway(s) for access, accept viewing content from ",
" content distribution network, accepting their certificate authorities with no outside validation of this ",
"trust",
", give up the right to use certain services like VPNs, etc. Compromising your privacy means handing over valuable information, and allowing your operator to exert more control over your internet use: whereas an operator may not have been able to inspect the content of an encrypted end-to-end connection, by allowing it to do so it is enabled to restrict your traffic based on that content.",
"Denial of service. As technically crude and blunt as it is effective, it is not unprecedented to simply ",
"reject service",
" when it is allowed. This can be done in a granularity of a single connection (e.g. as with firewalls resetting TCP connections to a - possibly malicious - host), or at a level of as much as an autonomous system, by cutting off its ",
"BGP",
" routes towards others.",
"Some of the above can be avoided with a VPN, and some not. A VPN for instance will not help if your ISP performs content inspection and wants to disallow all VPN connections. It might help if it performs content rewriting, and you route your web traffic through the VPN, assuming you're allowed to and it's not compromised via some other means.",
"This is really a very wide topic to post technical info on all of the above. If you wants specifics on something, ask away!"
] |
[
"Wow, wouldn't have thought I'd get that detailed answer, thank you very much! Very interesting topic indeed, and (if possible) now I'm even more concerned about net neutrality..."
] |
[
"It's worth noting that your ISP probably knows you're using a VPN and could just as easily throttle your internet for that reason."
] |
[
"Where do dead bacteria go?"
] |
[
false
] |
For example, when you cook meat to kill all of the bacteria, aren't you technically eating dead microorganisms? This could be a really stupid question, but I was always curious about it. Does your body use the dead bacteria it eats for any purpose or does it just flush it out during excretion?
|
[
"Sort answer : yes you eat the dead microorganisms. They are digested and passed just as other organic matter. ",
"Longer answer : furthermore, you actually eat live microorganisms all the time. Bacteria are everywhere! Additionally Your gut is actually full of a microbiome containing one of the densest concentrations of bacteria in the planet. In your colon. Most of your poop is live bacteria by mass. There are also many viruses and fungi. There are even virises that only infect the bacteria. (bacteriophages). This microbiome helps you digest things and even provides you with specific vitamins. These microorganisms are replicating and dying inside you at every moment. It is estimated that there are over ten times the amount of bacterial cells inside and on your body than human cells in your body. That's right, you're more bacteria than human by an order of magnitude! This is possible because bacterial cells are considerably smaller than human cells. ",
"Feel free to ask any more questions",
"PhD in pathobiology "
] |
[
"In some cases, antibiotics can knock out most, but not all of the bacteria in our gut. That leaves the few bacteria remaining to thrive because there is no competition. This is the case with Clostridium dificile infections. They usually only happen after taking antibiotics. "
] |
[
"Great questions! Clostridium is a great example. Most of our bacteria are good and outcompete the bad bacteria for resources. If too many of the bad bacteria outcompete the good, you will get sick. This also happens in food poisoning. \n Yes we have a wonderful immune system constantly monitoring our gut bacteria. Some of our immune system cells undergo complicated and special development in our intestines. There they get trained from early on not to attack the normal bacteria in our gut. If this complicated process goes wrong you get autoimmune disease where your immune system rejects certain foods (Chrone's disease). \n This is also why you may get diarrhea when traveling. When traveling, especially outside the country, your body is exposed to and ingesting new bacteria it is not trained to recognize. You're immune system rejects the new bacteria even if it's not bad for you and you can get diarrhea. Sometimes these new bacteria outcompete your normal good ones and they will stay with you for a while. "
] |
[
"If dark matter (the non-baryonic kind) is real, does the theory predict that dark anti-matter should also exist?"
] |
[
false
] | null |
[
"There are people who believe that dark matter is baryonic anti-matter. The idea is strange antimatter formed into stable quark nuggets when the universe formed. Because they're so dense they can account for the dark matter, but still be rare enough to be \"dark\" to us. This model solves two problems, the matter/anti-matter asymmetry and the the dark matter problem. ",
"Another model is that the dark universe is as complicated as the one we see and that the dark matter is a whole SU(3)xSU(2)XU(1) field theory similar to the standard model, complete with dark antimatter. This other side is \"dark\" because it interacts with Standard Model through a single vector boson interaction. "
] |
[
"There are some people who think that dark matter is actually positrons and are looking for evidence of its annihilations.",
"There are a lot of theories for what dark matter is; some may have antiparticles and some may not. The general term for a particle that's its own anti-particle is Majorana, and there is research into whether Majorana dark matter can exist: ",
"http://arxiv.org/abs/1005.1286",
"If anyone figures out what the stuff actually is, I'll give you a more complete answer."
] |
[
"There are many theories of what dark-matter is. None are completely accepted. The easiest explanation is that right now our models of galactic motion that are based on the physics we currently know fail in a consistent way. In trying to explain this discrepancy, we need a label to talk about it. \"Dark matter\" is what we call the error in the model."
] |
[
"Could a purely analog video signal hold enough data to transmit a 1080 high res video?"
] |
[
false
] |
I've been watching a bunch of videos on how old tv works and it got me wondering. If we hadn't developed digital signals, could analog signals be pushed to HD levels or is there a physical limit? Also, wasn't sure if this fit the physics flair, sorry ahead of time.
|
[
"HD video ",
" transmitted as analog signal - e.g. the Japanese HDTV standards that started in 1960s (that's not a typo). E.g. the system introduced in 1972 had 1125 lines. E.g. the MUSE/HiVision standard from the 1980s was like this too, fully analog, delivering 1125 lines (1920x1035 resolution) interlaced at 60Hz.",
"There is nothing intrinsic in this that would prevent it from being done. In fact, the common digital standards today like HDMI (not DisplayPort) are still mimicking the frame organization of the old analog TV, including lines, VSYNC, HSYNC, etc.",
"Also, there have been plenty of video and computer monitors that were running 1920x1200 or higher resolutions at 60-75Hz over the good old VGA interface (which is a purely analog signal, unlike DVI or HDMI) or component one (5 BNC cables, one per color + VSYNC + HSYNC).",
"The reason why this is being done digitally today is mainly the complexity and bandwidth requirements of the analog transmissions schemes. And when talking about cable transmission (e.g. to a monitor), analog connections are very sensitive to noise and distortions caused by the cabling (e.g. ghosting due to reflections in a poorly terminated cable). So such cables have to be thick and unwieldy due to the necessary shielding."
] |
[
"Yes, it would be possible to transmit a high-resolution analog signal, it would just require an absurd amount of power. Both analog and digital are transmitted via ",
"electromagnetic radiation",
", the major difference between the form in which they are encoded. \nIn specific, digital signals can use ",
"error correction codes",
" to eliminate errors that may occur in transmission, while analog signals can not. Thus, in practice, the power level would need to be amplified to the point of 0 error to account for the loss of coding. At the same time, the optimal encoding strategy for the analog signal (given that it will be distorted by noise) is to encode as a digital signal, see ",
"rate distortion theory",
".",
"Furthermore, yes there is a physical limit to the amount of information you can send over a channel. It is called the ",
"channel capacity",
", and is one of the fundamental areas of study in information theory. One well-known capacity result is that of an AWGN bandlimited channel, named the ",
"Shannon Hartley theorem (PDF)",
", having a maximum of ",
" bits/second, where ",
" is the bandwidth of the channel and ",
" is the signal to noise ratio. This also holds true for continuous signals as well."
] |
[
"As a ballpark, the uncompressed bandwidth of a 1080p 60hz video is roughly 30 times greater than a standard-definition video signal (480i 30hz or thereabouts).",
"So yes, you could broadcast high-def TV using the old analog system, but there would only be enough bandwidth in the VHF and low UHF radio spectrum for ",
"."
] |
[
"If Cavendish bananas were targeted by a disease not unlike the Gros Michel bananas, what would be the next species in line to replace the Cavendish?"
] |
[
false
] |
[deleted]
|
[
"Heeyyyyy I just spent two months in Central America researching this exact question and consulting with the experts of banana pathology and the top figures of the banana industry. First, I must say that your hypothetical scenario is already happening. Panama disease (Fusarium oxysporum cubense) is what wiped out the Gros Michel. Since new strains of Panama disease have popped up, that first one was named \"Race 1.\" Race 4 is now spreading around Asia. As soon as it gets to the Americas, it's basically game over for Cavendish exportation.",
"So which will be the replacement? What I found was that the top dogs of industry basically refuse to think about this possibility. First, they say that Race 4 has been contained in Asia long enough that it looks like it won't reach the Americas. While I was there, it was officially confirmed in Jordan. There are even whisperings in Brazil and Bolivia. It's going to happen. The pathologists all know it. The most reasonable industry execs and the pathologists have been concerned with making contingency plans for containing Panama disease once it appears - quarantines, burning plantations, etc. But that will only slow the spread.",
"The truth is that none of the top figures in the banana world are really planning to replace Cavendish. They don't want to. But they're dreaming. There are breeding facilities around the world, but the best one - the most prominent, oldest, and that which has produced the most results - is FHIA (Fundación Hondureña de Investigación Agricola, or the Honduran Foundation of Agricultural Research). FHIA has bred a number of bananas that are resistant or tolerant to Panama disease race 4, as well as other banana maladies like black sigatoka. Some of the other breeding institutions have made some resistant bananas, but nothing like FHIA quality. There is also some GMO banana research, particularly in Belgium, but again, nothing resultant quite like the FHIA hybrids.",
"So I do honestly believe that when the crisis hits, perhaps with the urging of some of the pathologists/breeders, worried exporters will start to incorporate FHIA hybrids and those will eventually take over.",
"So which are the top contenders? Basically, as of now, I see four FHIA hybrid bananas that could potentially become the staple of banana exportation.",
"FHIA-01 (AKA Goldfinger). FHIA's first success. A very strong banana, but its flavor is probably not what the American and European market would want. It was bred from a Brazilian prata (apple-flavored banana). People in Brazil like apple-flavored bananas, which are tart more than sweet. But Americans who have tried them don't like them. Honestly, neither do I. I don't think this one is it.",
"FHIA-02 (AKA Mona Lisa). It's a little sweeter than Goldfinger, but still more tart, and it has lots of post-harvest problems. For example, the fingers (individual fruits) tend to fall off the bunches, and they ripen somewhat inconsistently.",
"FHIA-17. This was bred from Gros Michel, so it tastes more like Gros Michel. It's sweet and strong. However, people in industry don't really think of it as a viable contender for the export market because it isn't like a Cavendish, since it was bred from Gros Michel.. True, but Gros Michel is better than a Cavendish! They're worried about familiarity, but when Gros Michel disappeared, Americans caught on to Cavendish (which was inferior). So why wouldn't we eventually catch on to a banana that's somewhat unfamiliar but better? This would be a great replacement, in my opinion.",
"FHIA-23. Another Gros Michel hybrid. Same deal as FHIA-17. ",
"The FHIA hybrids are not perfect. They don't have as good yield as Cavendish, and they take a long time to harvest and ripen. The big companies like Chiquita and Dole are pretty secretive about their research, but I believe that they are working, either with FHIA or on their own, to breed a resistant Cavendish cultivar. This is a very difficult task. Cavendish is nearly impossible to breed - it basically never gets seeds, which are needed for breeding, whereas Gros Michel gets them once in a while. The top banana pathologist in Central America (who used to work at FHIA, a huge figure in the banana world) basically told me it wasn't going to happen.",
"But it might be some time before Panama disease Race 4 forces substitution. Maybe the GMO people will make some progress, but that would require not only success on their part, but also changes in public perception and laws against GMOs (come on people!). But I'd say that if this happened tomorrow, it would be FHIA-17 or FHIA-23.",
"I know a LOT about bananas and would be happy to answer other questions."
] |
[
"so the bananas that we buy at the market are genetics clones of each other. there's a fungal plant pathogen called ",
" that causes banana wilt, and since the bananas are all clones of each other (ie no genetic diversity) a strain of ",
" could potentially wipe out all the bananas.",
"I should say that Cavendish is a cultivar (short for cultivated variety) so they aren't a separate species. They belong in a subgroup of the banana species.",
"There is a strain of Fusarium oxysporum cubense, called Race 4, that is highly virulent and can resist the plant immune system. Yes plants have their own immune system. The way that the fungus affects plants is that it releases effector proteins called Avrs to suppress the innate immune response. Plants affected by this co-evolved and express Immunity genes (I) to block the Avrs, but the fungus evolved in response to evade the I genes, and so on. ",
"see figure 4",
". note: this is concerning tomato plants but I imagine a similar mechanism is at play in the ",
":banana relationship",
"So we will have to genetically engineer and breed a durable cultivar of banana that can resist fungal effector proteins. ",
"another source"
] |
[
"There is really VERY little export of Gros Michel. The chances are tiny that if you're strolling through a market, you'll encounter one. I can't find them in the US. When I was in Central America, I worked with one organic farmer who sold some to a company that made baby food with them in Germany. I don't know the brand. I did hear about one other guy exporting them to Germany, but I don't know if it was for baby food or whole fruit, and I don't know if it was for expensive specialty stores either. Do a Google Image search - the easiest way to tell is the shape of the bunch. Cavendish bananas have long, pointy, vertical stems that meet way above the fingers, whereas Gros Michel bunches are joined closer to the fruits themselves, almost like a section of a circle."
] |
[
"How can the diameter of the Universe exceed its age?"
] |
[
false
] |
The Universe is 13.8 billion years old and the observable Universe is about 93 billion light years across. How is this possible? If I had to guess, I'd wager that the Universe must have expanded faster than the speed of light at some point in its evolution. I'm not sure if that makes sense though, and details would be lovely.
|
[
"I think the most concise answer is \"expanding faster than light\" means nothing since the amount of expansion does not have units of velocity.",
"The amount of expansion from time t to today (t_0) is given by the ratio between the size today and the size at time t. This is a dimensionless ratio and cannot really be compared with c.",
"Now, you can take two specific points (for example, here and a galaxy currently at the edge of the observable Universe) and you'll find that their distance increases, indeed \"faster than light\". But this is not an actual speed you can measure, it's just a coordinate speed in some coordinate, it is not physically meaningful. It's just that space inbetween them is getting bigger. ",
"If you were to perform a measurement of the galaxy's velocity, you would actually need to be close to it (you can only perform local measurements). You will always measure a speed less than c.",
"At any given time, in any possible expanding Universe, there are galaxies far away enough that the distance between them increases faster than light."
] |
[
"The diameter of the ",
" universe might be infinitely large. Because of that, for any finite rate of expansion there are always parts of the universe that ",
" to be moving away from us faster than the speed of light. However, the diameter of the ",
" universe is set not by the expansion alone but by the farthest points that have been able to send a photon to us since the universe became transparent. So it might help to think about the journey of a photon coming from the edge of the (currently) observable universe to you. ",
"That photon started off as a bit of near-IR radiation when the universe was 300,000 years old and became transparent. At that time the universe had a temperature of around 3000 K (see ",
"this chart",
"). The current observable universe was only about 0.1% as big then, so it was only about 0.1 billion light years away from the point where the earth would eventually exist. It seems like that photon should have gotten here a long time ago.",
"But the space between us kept increasing. In an infinitely big universe, no matter what the rate of expansion is there will be things that seem to be moving away from you at speeds faster than the speed of light. If you double the size of the universe every year, then anything more than one light year away seems to be moving more than a lightyear away from you in a year. If you only expand by only 0.1% in a year, then anything more than 1000 light years away away from you seems to be moving more than a light year away in that year. Early on, the place where the earth was seemed to be moving faster than the speed of light away from our photon. So after traveling for a billion years, the point where the earth would eventually form was now billions of light years away from the photon instead of 0.1 billion light years. The universe expanded by a factor of around 200 over that timeframe.",
"But the rate of expansion was slowing. The photon was turning the tide in its journey. Over the next 13 billion years, the universe only expanded by a factor of 5-6. The distance between the photon and the earth began to decrease, in spite of the expansion. It finally makes it to earth and gets detected as part of the cosmic microwave background. Even though it started out as an IR photon, it has been redshifted down to a microwave. It's wavelength actually maintains the same ratio to the size of the observable universe throughout the trip.",
"So that is what determines where the \"edge\" of the observable universe lies. It is a complex function of the rate of expansion of the universe over the last ~14 billion years. It has to be larger than 14 billion years because while the photon really did travel 14 billion light years to get to us, the space it crossed on that journey has been expanding over that time too."
] |
[
"If that photon had started out as red light, it would have shifted to a different frequency of microwave background as photons that started out as blue light, correct? ",
"Correct. The redshift defines the ratio of the wavelength now to what it was then, so it is a scaling factor.",
"Can we learn anything from observing the background microwave light at close but slightly different frequencies (like independent slices), or are things too jumbled up to glean much information from doing that at this stage?",
"Yes we can! The wavelengths follow a blackbody spectrum, and if the ratio between different wavelengths changes that means one part of the universe was a bit hotter than another. These temperature fluctuations in the cosmic microwave background are very small but have taught us important things about the universe. One is that we are moving a bit compared to the \"average\" speed of the universe. This shows up as a small Doppler red shift on top of the data. The second is that the temperature fluctuations that remain after that show how homogeneous the early universe was. It turns out it was very homogeneous, more than we could explain at first. That is a big reason why we think cosmic inflation occurred.",
"Read more here",
"."
] |
[
"How common are gaseous planets?"
] |
[
false
] |
Is there any way to know how often gaseous planets are formed rather than rocky planets? What are the reasons?
|
[
"Based on observations by the Kepler Space Telescope, smaller radius (rocky) planets are more common than large radius planets. See Figure 2 in Borucki et al. 2011 (",
"ApJ ADS link",
", ",
"arXiv PDF",
")."
] |
[
"Kepler candidates are possible planets (not only those that we think might be habitable) detected using the transit method. After accounting for observational biases (for example, how smaller planets are harder to observe (which is why the number drops off at small radius) and orbital geometry (the planet has to pass between the star and us to be observed)), Kepler candidates should be representative of all planets.",
"It might also be worth noting that this data is only from the first few months of Kepler's operation, so it is limited to relatively short period orbits (because they want to have at least two transit events)."
] |
[
"The paper ",
"The Snow Line and the Frequency of Giant Planets",
" might well answer your question. (Continue to read until \"[...] shows the likelihood of a star harboring at least one gas giant planet as a function of stellar mass for our baseline model.\")"
] |
[
"Does sugar-free gum (with sugar alcohols) produce an insulin response?"
] |
[
false
] |
I have a pack in front of me right now. It contains Maltitol, Sorbitol, Mannitol, Aspartame, Acesulfame-Potassium, and Sucralose. Would this be diabetic-friendly, in that it would not cause a blood sugar spike that would in turn cause/require an insulin response?
|
[
"The sugar alcohols you listed (maltitol, sorbitol, mannitol) all can potentially cause a change in blood sugar and affect insulin response, although usually to a much less degree than \"normal\" sugar. They can also give you diarrhea (a common question that diabetics get asked if they present with diarrhea is if they use a lot of those substances in their diet). The artificial sweeteners, the rest on your list, generally are considered insulin neutral although you'll see some debate."
] |
[
"It's same with xylitol. It does not absorb as fast as sugar, so it does not increase blood sugar levels or hyperglycemia in humans. ",
"For dogs it's different thing. Hypoglycemia that can kill from 100 mg/kg and if it goes over 500 mg/kg it can cause liver failure. "
] |
[
"In some cases, the body is conditioned to release insulin upon receiving a sweet tasting stimulus (think Pavlov's Dogs), meaning your body will prepare to process incoming sugar."
] |
[
"There's been a lot of speculation about whether people who have received the Covid-19 vaccine may still spread the virus to others. Is this common for other vaccines?"
] |
[
false
] |
I understand that everyone wants to be careful about over promising what the vaccines may do for us until the data is in, but I was wondering whether this is just erring on the side of caution of if there's a history of vaccines for other diseases protecting the recipient from getting sick but not preventing them from spreading it to others. Edit: since the question may not be crystal clear:
|
[
" viral vaccines ",
" block transmission, or greatly reduce it - smallpox, measles, mumps, rubella, polio, etc etc. ",
"Influenza vaccine is not sterilizing, and does allow some transmission even in vaccinated people. (Influenza is always an exception to other viruses. Because it’s an exception, it’s exceptionally important, so people think about flu before they think about measles, mumps, etc.) Even for influenza, though, vaccination greatly reduces shedding and transmission of the virus.",
"The odds are pretty good that any effective COVID vaccines will be sterilizing, or close to sterilizing, but we won’t know until the tests are done. Preliminary data from the AstraZeneca vaccine trials strongly suggests that the vaccine either eliminates, or greatly reduces, transmission; so did the Moderna trial. ",
"This is one of those things where the media have done a terrible job conveying information accurately. We have been through this already several times during this pandemic. Scientists said early on, “We don’t know if the virus induces antibodies,” and there were a million hysterical posts saying “the virus doesn’t induce antibodies!” Then scientists said “we don’t know if the antibodies are protective”, and there were a million people saying “the antibodies aren’t protective!” Then they said “we don’t know if vaccines will work”, and the response was “vaccines won’t work!” Now we're at the point where scientists say, \"We don't know if the vaccines block transmission,\" and there's this rock-solid certainty that the vaccines won't block transmission. I know this is a stressful time, but the fifth or sixth time around this rollercoaster people should start recognizing the pattern.",
"Also see these ",
"r/askscience",
" threads:",
"Why can you still infect others with covid-19 after vaccination?",
"Why - despite having millions of people which have already been vaccinated - we don't really know if vaccinated people do transmit covid or not?",
"How to test transmission of COVID-19 after vaccination?",
"How common is covid-19 reinfection? Are there any published statistics?"
] |
[
"Thanks for the in-depth response.",
"Regarding your last paragraph, I agree 100% and I certainly wasn't trying to infer any sort of \"the sky is falling\" feeling on my part. I was genuinely wondering if this is a common precaution to take because we've been burned by vaccines in the past, if it's just erring on the side of caution because it would be bad science to make statements about something that's so-far unknown or if there was something else going on."
] |
[
"A lot of it is also the question of \"how do we stop a pandemic\" rather than \"well, what's safe enough for something fairly rare?\"",
"For something like measles, most people are vaccinated, and it's pretty rare that you'd encounter someone who has recently been exposed to the measles virus anyway. So a vaccinated person is unlikely to be exposed, and even if they're shedding viruses for a little while, unlikely to then expose anyone else who may be vulnerable. Not impossible, just unlikely.",
"But now, where we're in a stage where most people are not vaccinated, and vaccinated people are much more likely to be exposed, even a small risk has an impact."
] |
[
"Questions about Origin of Life/Evolution"
] |
[
false
] |
As far as I know, it is thought that all living creatures on Earth descended from one organism. Essentially, when life began, it happened only that one time and all other life afterwards has evolved from it, right? Why, in the more than 3 billion years since life began on Earth, has it not begun again (and again and again millions of times over) creating completely independent lines of evolution? If the origin of life is so rare on Earth (occurring only one time in billions of years) why do so many people on Reddit seem to hope/believe that we will find life on exoplanets, or even Mars for that matter? Why do so many people support funding for SETI? I apologize if I am completely misunderstanding the math or science behind this and I don't mean to offend anyone who is a suporter of SETI. I fully support SETI if there is reason to believe it could be used to find extraterrestrial life, but it just seems to me that we would be naive to assume there is life out there (within any type of reach) when we can't even fully understand the origins of life on Earth, which occurred only once in more than 3 billion years.
|
[
"Great questions and without answering it directly, I'd like to point out viruses which are very much 'life-like' with an independent origin. Perhaps if we found viruses on another world we would then consider them true life. ",
"I think a lot of it has to do with the statistics of the situation. Life has originated here at least once in our 4.1 billion years. Given that the universe is ~14 billion years old and we are but one sample out of potentially millions of planets like ours, the statistics would strongly support the coincidence of life occurring independently elsewhere too.",
"As to why life hasn't re-originated several times on earth. I think a lot of it has to do with competition. It's difficult to create self-replicating entities when all the stuff required for self-replication and organization has been \"dibs'ed\" by the present fauna. ",
"-Just my speculations. "
] |
[
"I guess I never though of it that way. Once life began, anything coming after it has almost no chance of surviving due to competition from what already exists. Thanks!"
] |
[
"Well, you pose an interesting question. Let's start with life. Most of the scientific establishment agrees that life started out in what was called an \"",
"RNA world.",
"\" RNA (a similar molecule to DNA) is capable of acting like an enzyme (like proteins). This activity is referred to as ribozyme activity. The Ribozyme activity allowed the RNA to self replicate themselves. At this point in the earth's history discrete cell structure were not present. Essentially all the genetic information was contained within the ancient oceans. At some point, some genetic material eventually ended enveloped and protected within a membrane. This protection would have conveyed an advantage to this one RNA/DNA strand and allowed it to become dominant. Eventually there would have been differentiation and over the next 3 billion years (a staggering amount of time) this cell would have evolved into all the species in existence. The problem is we don't know how many times this enveloping event occurred. There very well could have separate lineages of enveloped DNA/RNA that died out. Or their could have been a vast amount of enveloped genetic information, but a bottle neck occurred favouring only one of these primitive cells. Under certain conditions biological molecules are readily produced abiogenically (not from a living source). These conditions are widespread in our universe and our universe is vast, so there is a high probability of life somewhere outside earth. There is something called the ",
"Drake equation",
" which calculates how likely there is to be life on another planet with the technology to detect communications from SETI. Even the most liberal values input into the Drake Equation tell us that there is probably life outside of earth with the technological capacity to receive messages from earth. Sorry if that's a bit long winded. Let me know if you need any points of clarification."
] |
[
"What is your brain doing when you're trying to remember something?"
] |
[
false
] |
Specifically if you know you know something and are trying to search through your thoughts for the answer?
|
[
"The short answer is that a precise answer is waiting further research. The most compelling answer today is that declarative memories are enduring patterns of changes in connectivity between neurons in association neocortices. These areas are indexed by the hippocampus (if they are fairly recent) or by the prefrontal cortex (if they are older). You are trying to remember something, so you start with a clue that you think is involved in that memory. The clue goes the association neocortices, and activation from the association cortices activates the indexing unit (let's call it the hippocampus for now), and it then activates all the association neocortexes that are part of the indexes related to the clue. So a recurrent wave of excitation goes back to the association neocortices and becomes part of consciousness. Your consciousness is bombarded by things associated with the clue. You may recollect something else about that memory based on this process, and then an activation triggered by the original clue PLUS the new information goes to association cortices -> hippocampus -> back to association cortices resulting in a second bombardment. You repeat this process until one memory beats the others down and is satisfactorily correct enough that consciousness will accept it. ",
"Also, Ray Kurzweil doesn't understand jack about the brain. "
] |
[
"The top post, which was removed because it was both speculative and inaccurate, cited Kurzweil."
] |
[
"Folks, this is ",
"/r/askscience",
". If you don't have some level of expertise in the subject, or don't have a scientific source to back up your ideas, then don't comment. ",
"As always, please refrain from anecdotes, speculation, jokes, and off-topic discussion.",
"Thanks."
] |
[
"Is there any evidence that prehistoric man suffered from acne?"
] |
[
false
] |
Fighting with my teenage daughter to wash her face. Her defense included her reasoning that prehistoric man didn’t have face wash, since no cave drawings depict acne, so she doesn’t need to wash her face. I know, I know. Ridiculous. I’ve already countered with the fact that they didn’t have pollution in the air, their food didn’t have chemical additives, etc. But was hoping that this community could back me up on the caveman acne front. Edit: thanks guys for all the wonderful input! I really appreciate the responses from so many different perspectives. Just wanted to clarify that she doesn’t currently have acne, other than the occasional pimple or zit; and she does have good body hygiene. Her argument is that she doesn’t want to remove all of her natural oils with any harsh (or even gentle) cleansers; she’s very much into natural products. Since she is now a little wearing makeup, I think it’s important that her face be cleaned every day.
|
[
"Acne prevalence is correlated with westernization of societies. Here they found no prevalence of comedones in Kitavan islanders in Papua New Guinea and Aché hunter gatherers in Paraguay.",
"https://jamanetwork.com/journals/jamadermatology/fullarticle/479093",
"Moving from a rural lifestyle to an urban lifestyle also is correlated with an increase in acne prevalence. Here they follow a cohort which moved from rural communities to urban communities in Mali.",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5046992/",
"I think it’s safe to assume that some of the communities with low acne prevalence do not have face wash. That isn’t to say that is the causative factor however."
] |
[
"We published a little paper a few years ago about the human Acne bacterium P.acnes being found as a endophytic inhabitant of the domestic grapevine",
"There are a few interesting calculations there on the time when symbiosis began between humans and grapevines.... And P. acnes",
"If you have trouble finding it let me know, it's from Campisano et al",
"Edit: thank you for silver!!"
] |
[
"Acne isn't really caused by improper facial hygiene. It's caused by hormonal imbalances that cause over secretion of sebum from the sebaceous gland in your hair follicles which clog them and provide a good microbiome for P.acnes bacteria to proliferate. The best treatment for that is topical or systemic antibiotics to kill the bacteria although it will cause resistance over time. You can also use steroids to reduce inflammation but that also comes with problems. Some treatments remove oil and the secretion from the skin which helps open pores and reduce acne. But for your daughter, it's not really to do with poor hygiene so be easy on her. It's already hard enough having acne I'm sure. Go to a GP to get medication."
] |
[
"If protons sometimes include the heavy charm quark, does it mean proton mass fluctuates?"
] |
[
false
] |
I read from this how it was discovered that protons sometimes contain the charm quark and antiquark which themselves are "heavier than the proton itself". I don't know what to make of this. Doesn't it mean that proton mass changes?
|
[
"These quarks are heavily \"off-shell\" -- they don't always have the same values of certain parameters (like mass) that regular (\"on-shell\") quarks have. They can exist in this way because they are \"internal\" to a reaction; they are created and then absorbed again on very short timescales, rather than propagating outwards toward a detector.",
"In general, though, every unstable particle has some uncertainty in its mass (we call this the \"decay width\", as it can be measured from the width of the corresponding peak in a mass histogram). The proton, however, is stable (as far as we can tell, anyway), so this doesn't apply."
] |
[
"These are \"virtual\" charm quarks. Quantum mechanics permits quantities like energy and mass to be violated for very short intervals. Given that the proton lives for a very long time, its mass must be stable. The charm quarks it contains, however, can only appear and disappear basically instantaneously. This happens often enough, though, that there is actually a finite probability that you can find a charm quark in a proton at any time."
] |
[
"There is no \"sometimes\" involved here. The proton mass is constant and doesn't change because energy is conserved.",
"The situation is similar to e.g. an electron in an atom. It has a wavefunction, which can be interpreted as probability density to find the electron at a given spot ",
" you measure its position, but it cannot be interpreted as \"sometimes it's here\" otherwise. The electron energy doesn't change before the interaction either, even though different places have a different electrostatic potential.",
"If you collide something with a proton then the collision process will involve charm quarks with some probability, but this doesn't mean anything changes in the proton before the collision."
] |
[
"How does the body deal with artificial sweeteners such as aspartame, acesulfame and etc? In the end is it more healthy or less than real sugar?"
] |
[
false
] |
Different sweeteners carry different properties and health issues. But in general will you be better of just having regular sugar or using artificial sweeteners? A lot of people claim you will get more fat from drinking diet coke, some say you won't get fat at all. Whats the truth here? And how does it work? I know too much sugar will cause you're insulin to shoot up, and with no way to spend all those calories, they end up in the fat depots. So there's no doubt you will get fat if you over consume. The focus here is on the artificial sweeteners and how they compare to sugar.
|
[
"It depends on which artificial sweetener you're talking about. Aspartame is broken down normally and has caloric content, there's just so little (compared to an equivalent sweetness of sugar) that you get a small fraction of the calories in a traditionally-sweetened beverage.",
"There's no evidence that artificial sweeteners contribute to weight gain or inhibit weight loss. ",
"Here",
" is a page with some info on aspartame and insulin. ",
"Here",
" is another page on fat loss. Both are sourced."
] |
[
"All I can tell you is that there's really no evidence that diet coke is bad for you, or that any of the ingredients are bad (unless allergies or something uncommon). Nor diet drinks in general. Even caffeine has pretty good evidence of being generally good for you. As long as you're getting plenty of water and not getting so much caffeine that it's affecting your sleep.",
"Occasionally you'll see someone post a link to someone saying aspartame causes this or that, or phosphoric acid, but these arguments are routinely shot down on this sub and on ",
"r/skeptic",
"."
] |
[
"I think the discussion was more based on the effects they have in terms of nutrition and digestion, but it's important to consider dental health, too."
] |
[
"Is it possible to have a region of a gravitational field with non zero curl?"
] |
[
false
] |
Yes curl as in mathematical curl in the vector field. In what situation(s) would this happen, if it is possible?
|
[
"Gravity is a conservative force (hence path independent) so it has no curl. If it had curl, you could have an infinite power generator in that region, where you climbed up a gravity well in one direction, moved around, then fall back down the gravity well in another direction, and could extract energy along the way. A slope could be steeper uphill than downhill, or vice versa."
] |
[
"So, gravity is a ",
"conservative force, so it's curl will always be zero",
". But I'm curious, what sparks such a question, because the answer might be boring, but the reason to ask might lead to something much more interesting."
] |
[
"I was just curious, I am studying mathematics at university but due to the coronavirus I am not having any classes (not even online), but I always have enjoyed studying maths, I am currently studying calculus III and differential equations, amongst some other things"
] |
[
"Why is space in the Cassini \"Pale Blue Dot\" picture bluish instead of black?"
] |
[
false
] |
is a marvel, but it does leave me with the question: why is the empty space there bluish instead of pitch black? and while we are at it, why is the outermost ring a very bright purple while the rest are varying shades of brown?
|
[
"Just to avoid confusion: that is not the \"Pale Blue Dot\" picture. ",
"This",
" is. Your image is called \"The Day the Earth Smiled\"."
] |
[
"Have a look here: ",
"http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA17171",
"Things to note: ",
"While ",
"/u/localhorst",
" is right that many space picture have altered colours, this one here is a natural-color image, according to the image description.",
"The blue glow emanates from the bright band at the bottom of the picture, which has been cropped off the image posted on reddit earlier. Outside the glare from this band (e.g., at the very bottom), the sky is indeed black.",
"My guess would be that the glow is due to debris or ice crystals that scatter sun light towards the camera (remember that the sun is roughly straight ahead, but occluded by Saturn), similar to a ",
"halo",
"."
] |
[
"NASA explains how it's done with the Hubble pictures:",
"http://hubblesite.org/gallery/behind_the_pictures/meaning_of_color/"
] |
[
"Question about Inflation (in cosmology) and the Big Bang"
] |
[
false
] |
[deleted]
|
[
"So very early in the universe there was a very brief period of very rapid accelerated expansion. This is called inflation. Then after inflation there was a period of radiation domination, then after the universe cooled some more there was a period of dark matter domination. During both of these periods the expansion of the universe was decelerating. However, recently we have come into a period of dark energy domination where the expansion of the universe is accelerating again."
] |
[
"It's fair to say there are phases, but it's not fair to say they correspond to different forces. It's all gravity, it just depends on what type of energy is the most dominant in the universe at that time.",
"And yes I did mean to say dark matter. The phases go",
"Inflation (Cause = unknown, effect = rapid accelerated expansion)",
"Radiation Domination (Cause = gravity of photons and neutrinos, effect = decelerated expansion)",
"Matter Domination (Cause = gravity of dark matter and regular matter, effect = decelerated expansion)",
"Dark energy domination (Cause = gravity of dark energy, whatever that is, effect = accelerated expansion)"
] |
[
"It's fair to say there are phases, but it's not fair to say they correspond to different forces. It's all gravity, it just depends on what type of energy is the most dominant in the universe at that time.",
"And yes I did mean to say dark matter. The phases go",
"Inflation (Cause = unknown, effect = rapid accelerated expansion)",
"Radiation Domination (Cause = gravity of photons and neutrinos, effect = decelerated expansion)",
"Matter Domination (Cause = gravity of dark matter and regular matter, effect = decelerated expansion)",
"Dark energy domination (Cause = gravity of dark energy, whatever that is, effect = accelerated expansion)"
] |
[
"Why does a neutrophil have a lobed nucleus?"
] |
[
false
] |
None of the biology teachers at my college could answer this question, and now I really want to know. So, why does a neutrophil have a lobed nucleus?
|
[
"The multi-lobed nucleus of the neutrophil arises during its formation, and is an artifact of the genetic events which occur during cell differentiation. During the differentiation of eukaryotic cells, the genetic activity of many regions of the genome is down regulated (transcriptional silencing) through a wide variety of mechanisms. During neutrophil differentiation, most ",
"chromatin",
" condenses into ",
"heterochromatin",
"; some of these heterochromatic regions associate with the nuclear envelope and form filament-like structures. As a result, the mature neutrophil nucleus typically consists of a linear array of three or four lobes joined by thin chromatin filaments. Analysis of live neutrophils reveals that nuclear shape can vary considerably in terms of the shape of lobes and the length of filaments. It has been hypothesised that this may increase the fluidity of the cell, enhancing the ability of the neutrophil to squeeze through small gaps during diapedesis and chemotaxis, though the function of the nuclear filaments remains uncertain.",
"A handy reference"
] |
[
"Side question...",
"Are some, all, or any of those regions still known to be present & identifiable after NET formation? Or do all the histones come off? Or is that even known?",
"That is, say you have an inflamed area in which NET formation is likely, and you have DNA free in the area. ",
"Is it possible to identify some of that DNA as \"Yes, that was from a neutrophil and therefore possibly from NET formation\" or (more importantly) \"No, that is not from a neutrophil and therefore definitely not due to NET formation.\" ",
"I was thinking through FISH or in situ PCR or something like that; you could use some of the different chemically protective effects of chromatin/heterochromatin to differentiate."
] |
[
"Ah, that would be a problem. Well unfortunately now we’re getting to an area where your guess would be as good as mine. I can tell you that the dense chromatin packing unfolds to produce a chain of nucleosomes in NETs, so you wouldn’t be able to compare it to live cell DNA. I have seen papers where they identified NETs in the sputum of cystic fibrosis patients using confocal microscopy by double staining for DNA, histones, elastase, and myeloperoxidase, then looking for overlap. Scanning electron microscopy and atomic force microscopy were also used. ",
"Here’s a good paper"
] |
[
"What is the purpose of eye color?"
] |
[
false
] |
Overall, what does eye color do and what was its purpose in evolution, many species of animals don't even have eye color.
|
[
"well brown is one of the darkest colours and therefore provides the largest amount of protection (people from areas of high sun intensity tend to have brown eyes). The brown colours comes from Melanin. So far so good.",
"Blue and green though come from ",
"Reyleigh scattering",
" on the iris. Essentially the wavelengths of light scatter on the stroma of the eye. Shorter wavelengths scatter most (hence blue and green). This is also the same reason why the sky is blue! So the eye doesn't have any green or blue pigments, the colouration occurs due to the structure of the iris. In different conditions the eye colour can change.",
"If you want to read more about other colours (I have no idea about Amber and such :( ) check out ",
"good old wikipedia",
"EDIT: also, you're welcome!"
] |
[
"UV Protection",
" two evolutionary means of protecting your cells that are absorbing light. Either replace them or protect them. Melanin or other pigments absorbs the UV light providing protection for the interior receptors. ",
"Pretty much the same reason for skin colour! (question below: yes melanin is responsible for hair, skin and eye colour of humans)."
] |
[
"Huh, that's pretty cool to know! Thanks for the answer! But do you have any idea why specifically brown or blue or green etc.? Maybe brown I could understand because Melanin is brown in many other cases, but blue or green seems kind of out there, as Melanin is brown in ",
" cases, could you shed any light on that subject? :)"
] |
[
"How is energy conserved for a redshifted/blushifted photon?"
] |
[
false
] |
When a photon is emitted from a moving source it's frequency (and hence energy from the Planck relation E=hf) changes depending on whether or not the light source is moving towards or away relative to the observer. (Ignoring gravitational redshift to make it simpler) For a blue-shifted photon, eg the frequency is doubled, where does the extra energy come from? Conversely, if the frequency is halved for a red-shifted photon, where did the energy of the "original" photon go? Many thanks in advance :)
|
[
"There is no extra energy. You are confusing measurements made by different observers. Suppose I emit a photon of some freuency f, corresponding to some energy E. You are moving at some speed away or towards me, and so you see a different frequency, and hence different energy. ",
"Conservation of energy does not mean the energy is invariant, i.e., measured to be the same by all observers. Even in classical physics, we make this distinction. I am at rest in my own frame, and so I have zero kinetic energy, which is conserved. Suppose you are in some other frame moving at speed v with respect to me, and there are no forces on me. Then you measure my kinetic energy to be some positive number, which is also conserved. ",
"Energy is conserved in each frame, but it is not invariant across frames. "
] |
[
"How is energy conserved for a redshifted/blushifted photon?",
"It depends on the mechanism underlying the redshift/blueshift -- there are three different ones, and whether/how energy is conserved is different for each.",
"In your question, you seem to be asking about ",
", which is one of the three types. ",
"/u/Midtek",
" already covered this for you so I'll just restate his answer first briefly, and then I'll mention the other two for comparison.",
": This is caused by relative motion between a source and a receiver. The source emits a photon with a certain energy, while the receiver absorbs the photon with a different amount of energy. Why the difference and where did the extra energy go? In relativity, energy is only conserved within a single reference frame: the total energy for a system may be different in other reference frames. In this case, both the source and the receiver see the energy as being conserved -- the source emits with a certain energy and also sees the receiver absorb that ",
" amount of energy; meanwhile, the receiver sees the source emit a ",
" amount of energy, and it also absorbs that same amount. Neither observer agrees on the total amount of energy, but both observers agree that however much energy it is, that amount is both emitted and absorbed in full. So energy is still conserved in every situation it is expected to be -- and unsurprisingly, it is not conserved in situations that it is not expected to be.",
": This is caused by the source and receiver being in two different gravitational potentials. Both observers see the kinetic energy of the photon changing between emission and absorption, unlike in Doppler shift where both observers see the energy staying the same. In this case, the missing or added energy comes from or goes to the potential energy of the photon. A redshift decreases the kinetic energy but increases the potential energy, while blueshift does the opposite. Note however that this is a simplification (arguably an oversimplification). In truth, general relativity is needed to describe gravity and in general relativity there are some technicalities that make it difficult to construct a meaningful definition of energy that can be compared between arbitrary reference frames. So the description involving gravitational potential energy is a simplification that borrows from the Newtonian limits of GR.",
": This kind of shift is redshift-only (in nature), and is related to the metric expansion of space. As you may know, space is expanding with the passing of time, and the type of expansion is metric expansion, which has significant differences compared to ordinary inertial expansion. In metric expansion, ",
" distances increase in size -- including the wavelengths of photons. Since the wavelengths are getting longer, the frequency is getting lower, and the energy is also getting lower. Like with gravitational shift, all observers see the decrease in energy. However, ",
" with the simplified gravitational redshift presented above, there is no potential energy associated with the decrease of energy: a photon in an expanding space does not gain potential energy to balance out a decrease in kinetic energy. Rather, space that is expanding metrically happens to ",
" violate conservation of energy. The technical reason for this is because such a system no longer possesses time-translation symmetry (due to the metric expansion), and that symmetry is a requirement for the law of energy conservation to hold. Consequently, photons are ",
" losing energy over time due to the expansion of space, and that energy is ",
" gone completely -- it doesn't \"go anywhere,\" it simply no longer exists anymore. Very much like how velocity is not conserved (even though momentum is): if a slow, heavy object collides with a stationary light object, the light object will gain much more velocity than the heavy object had (new velocity is \"created\" so-to-speak).",
"Hope that helps!"
] |
[
"Will a sufficiently rapidly rotating disk hanging on the ceiling illuminate a room?",
"Does a fast moving solar panel generate electricity at night?"
] |
[
"Why don't any states use carbon monoxide smothering as an execution method?"
] |
[
false
] |
I know this is morbid as all hell, but my mind goes into dark places when I'm severely bored. I am aware of the irony involved: trying to kill a person as painlessly as possible seems to be a contradiction, but once again, I'm not here to discuss morality other than minimization of suffering in the condemned. Ignoring all morality about whether or not executions should be performed, the current methods (Lethal injection, electric chair, hanging, firing squad and gas chamber) seem to be painful to the condemned or not really effective. Why not put the prisoner in a chamber, do all the ceremony, then have the switch fill the chamber with a high concentration of CO? Wikipedia says that concentrations of about 1.28% render you unconscious in 2-3 breaths and dead in under 3 minutes. The prisoner isn't subjected to any pain and simply dies in their sleep.
|
[
"There's no need to flood a chamber with CO, that's a little silly. There's no reason we can't sedate someone and give them a breathing mask that delivers CO or N2. That would definitely be more effective and less painful than our current methods."
] |
[
"True, but the OP was asking about monoxide, which should work. Nitrogen would at least be less dangerous when venting the chamber after use."
] |
[
"Oops. Yes - misread."
] |
[
"Does sunlight lose energy as it travels?"
] |
[
false
] |
Why does the sun heat heat a planet like mercury more than a planet like Neptune? If space is a vacuum, where does the energy go that is lost between the sun and a planet?
|
[
"The flux from the sun, the amount of energy landing on a given area, is inversely proportional to the square of the distance. ",
"If a certain amount of energy per square meter is received at some distance, say 1 million kilometers, then at 2 million only ¼ the energy per square meter would be realized. 10 million is 1/100, 100 million 1/10000, etc. ",
"The reduction is due to the sun is essentially a point source when at a decent distance, and the radiation photons become further apart from each other over distance because they are diverging. So at great distances there are fewer photons arriving in the square meter than at a closer distance. "
] |
[
"The flux from the sun, the amount of energy landing on a given area, is inversely proportional to the square of the distance. ",
"If a certain amount of energy per square meter is received at some distance, say 1 million kilometers, then at 2 million only ¼ the energy per square meter would be realized. 10 million is 1/100, 100 million 1/10000, etc. ",
"The reduction is due to the sun is essentially a point source when at a decent distance, and the radiation photons become further apart from each other over distance because they are diverging. So at great distances there are fewer photons arriving in the square meter than at a closer distance. "
] |
[
"Likely not on the scale of the solar system, but it's still good to point it out to avoid misconceptions like space = vacuum everywhere."
] |
[
"What if there was an infinite slope of snow, and a snowball started rolling down it, picking up snow as it went at the rate of S. As it is constantly increasing mass, would it ever reach terminal velocity?"
] |
[
false
] |
[deleted]
|
[
"What about the increasing diameter of the snowball? I guess we could throw \"infinitely sticky snow\" onto the list of assumptions, but if we didn't, wouldn't the snow on the outside of the snowball eventually be moving so fast that it would fling itself off at a rate equal to the rate the snowball was picking up snow? If that were true, the mass and drag force would eventually be constant ..."
] |
[
"No.",
"Terminal Velocity occurs when an object falls through a fluid at such a velocity that the Force due to Gravity is equal to the upward Force of Drag.",
"Force of Drag increases with velocity until you reach a velocity at which the forces acting on the object are in balance causing a constant velocity (no acceleration).",
"The problem with your question comes from the snowball picking up snow as it went. An infinite slope would mean it would constantly pick up more and more snow, thereby increasing its mass. Since the Force due to Gravity is directly proportional to mass (F = m g), as mass increases, so too will the Force of Gravity acting upon it.",
"Since Force due to Gravity will constantly increase, it will never reach terminal velocity."
] |
[
"Good job, but you're forgetting that drag force also increases with cross sectional area, which should go like mass",
" (assuming the snow doesn't compress significantly), so both forces have direct mass dependence. However, since the exponent is larger for gravity (1>2/3) your conclusion stands."
] |
[
"What causes adhesion between ultra-smooth surfaces?"
] |
[
false
] |
I recently re-glued a rear-view mirror to a windscreen. A small bit of solvent completely removed all the residue of the old bond and the surfaces seemed completely flat and clean. The new bond is completely solid. this made me wonder about how the adhesive worked and led me to do some reading. It wouldn't seem to be chemical or diffusive adhesion, because the surfaces were unaffected and restorable. And it wouldn't seem to be dispersive or electrostatic adhesion due to the strength of the bond. That leaves mechanical adhesion. However, the surfaces are quite smooth and wouldn't seem to offer the roughness and pores generally cited as necessary for mechanical adhesion. Would the explanation just be that even ultra-smooth surfaces are still rough at the sub-microscopic level? That would seem a bit wishful.
|
[
"Structural adhesives form covalent bonds along many branched chain polymers. If the surface can be chemically bonded too, it doesn't matter how smooth it is to a certain extent. Surely, a rougher surface has much more surface available for the adhesive to form a better bond, but the strength of the bond for a rear-view mirror doesn't need to be very strong (100 psi) compared to strong adhesives that can bond to smooth surfaces in aerospace (5000 psi), so you may have a weak bond and just not be aware of it."
] |
[
"So, if I understand, you're saying that structural adhesives rely on chemical bonds rather than mechanical adhesion? "
] |
[
"Most adhesives that people deal with (Elmer's/wood/super/etc) are mechanical adhesives. They work by filling small voids in the surface before hardening and mechanically locking the adherands together. Stronger (i.e. structural) adhesives work generally by forming a network of covalent, polar or hydrogen bonds with the surface, depending on the adhesive and what it is meant for. High shear strengths and moisture resistance are generally achieved with chemically bonded adhesives."
] |
[
"If a parent's DNA is damaged after birth, will the DNA passed onto offspring contain similar damage?"
] |
[
false
] |
[deleted]
|
[
"Depends where the damage occurs. Even before birth only DNA damage that occurs in your parents gametes (reproductive cells) may be passed down to offspring. Any other DNA damage to all other cells do not affect the offspring (not counting for any epigenetic effects of course [which is a newer area of genetics not too well studied {due to it being young idea} that may change the behaviour of genes even in offspring])"
] |
[
"Just to add to this, we use the terms somatic cells and germ line cells. Somatic cells are simply everything that isn't part of the germ line. The germ line are those cells that eventually undergo meiosis and divide into sperm (for example).",
"If germ line cells are damaged, then yes, it will be passed on.",
"There are, however, other changes that can be made to your DNA. Firstly, some bases of DNA can be modified (methylated) and DNA is also wrapped around a complex scaffold of proteins, and depending on the status of the scaffold, genes can be switched on or off, or the volume changed, if you will forgive the terrible analogy. ",
"These epigenetic changes are only recently now known to be hereditary. Examples of passing on these changes are mothers who become obese during pregnancy are more likely to have children who later in life become obese, and depressed or anxious mothers are more likely to have children who suffer from these problems too.",
"If you're wondering how these are ethically tested, we (roughly) feed mice high fat diets. They're essentially all siblings, so that takes other background genetic factors out of it."
] |
[
"Just a stab in the dark... you don't happen to program in lisp, do you? ;)"
] |
[
"In light of water shortages around the world, could we simply dehumidify and purify water to make it drinkable? Or gather water droplets from heat and desert areas?"
] |
[
false
] |
The core of my question being "what is the easiest way of producing water depending on where you live?" Obviously this heavily varies around the world but in areas where heat gathers could we simply not 'harvest' the water? Secondly, what could be the effect worldwide if we began to dehumidify large areas like forests or deserts?
|
[
"Yes, but it requires a lot of energy to cool to below the dewpoint, and the environment you’re in is going to need to have a fair amount of humidity. There just isn’t any humidity in the desert. ",
"places that have humidity, and the temperature is fairly close to the dewpoint so that you don’t need to use a lot of energy, also experience rain… It’s easier just to collect rain.",
"EEVblog and Thunderf00t have covered this in detail ",
"https://www.eevblog.com/2017/02/22/eevblab-30-popular-science-fail-waterseer-debunk/",
"https://youtu.be/LVsqIjAeeXw"
] |
[
"Good sources you beat me to it "
] |
[
"IF the temperature of the moist air drops below the dewpoint at night you can use ",
"fog nets",
", else, if you ",
" have humidity in the air, you can use a dehumidifier, but that is energy intensive (5 litre/kWh?). "
] |
[
"Why does Thermus thermophilus have reverse transcriptase capability?"
] |
[
false
] |
I realize the title is oversimplified, and also that asking why a particular organism evolved in a certain way is sort of missing the point but I had to shorten it for the title. I'm taking a molecular diagnostics class and we are discussing the use of the Tth polymerase enzyme isolated from for reverse transcriptase PCR procedures. It seems odd that a bacteria would have a reverse transcriptase enzyme and some brief research has uncovered a lot of the industrial and scientific applications, but no real discussion of what purpose RT activity could possibly serve for the organism. I'm curious if anyone has any insight on this, or whether it is just accepted as 'how it is' because evolution isn't a precise or intelligent process. My professor does not know either.
|
[
"Interesting question, and unfortunately my answer won't be conclusive, just intuitive. It seems from what ",
"wikipedia",
" and a ",
"vendor",
" say on their websites, the polymerase is a normal DNA polymerase that has RT activity. But, it only has that activity in the presence of manganese. Manganese isn't really present in biological environments, but can sub in for magnesium in the lab. It behaves similarly to magnesium in enzymes, but not exactly. ",
"My interpretation of this is that the RT activity of the enzyme is an off-target activity of the enzyme. Remember, the difference between DNA polymerase and reverse transcriptase is whether or not it cares that it's using RNA as the template. This can happen when there's no need for the enzyme to counter-select, which you seem to be getting at. There's not much reason to have a dedicated RT; there's also no reason to select against an RT activity with manganese, which Tth won't see in it's natural environment. ",
"So to me, at least, it looks like an off-target, but surprisingly robust activity of the enzyme. Which we can exploit in the lab."
] |
[
"I was sort of wondering if the gene to make Tth polymerase might be viral in origin from early in the evolution of ",
"- obviously viruses have the ability to implant their own genetic material within other organisms and of course it would make sense for an RNA virus to have a reverse transcriptase enzyme and conceivable that it could have transferred that to a host. However that doesn't explain the need for manganese as a cofactor if manganese isn't common in biological environments."
] |
[
"Well I should add the caveat that I don't know a lot about the T. thermophilus natural habitat. Maybe it's full of manganese. ",
"But anyway, for enzymes that turn over substrate, the assumption is usually that magnesium is the physiological cofactor. I know Mn is in some enzymes as part of a permanent prosthetic group, like within a porphyrin. ",
"Please take all of this with a grain of salt. My expertise is kinases - a polymerase expert might have different views. "
] |
[
"Why does the Higgs mechanism give the same mass everywhere?"
] |
[
false
] |
So symmetry breaking via the Higgs mechanism gives certain particles mass, right? But the symmetry breaking can happen in more than one way. I mean, that's what it essentially means, right? An arbitrary quantity becomes 'special', which breaks the symmetry, and the arbitrary quantity is part of a family of equally valid arbitrary quantities. If the symmetry can be broken in more than one way, wouldn't it essentially have to have occurred that way, because the Universe cooled extremely rapidly after the Big Bang, meaning that the symmetry would be broken fast enough at multiple points in space that they could not smooth out to the same value, because the break propagates at at most the speed of light. So shouldn't that mean different pockets of the universe measure different masses of the various particles given mass via symmetry breaking?
|
[
"Ok. Thanks for entertaining this string of questions."
] |
[
"Ok. Thanks for entertaining this string of questions."
] |
[
"Ah ok, so then in the case of the Higgs mechanism, you get the same vacuum expectation value of the higgs field regardless of the way the symmetry breaks, right?",
"Is there a form of symmetry breaking in the Standard Model that gives you different results depending on how exactly it happens?"
] |
[
"If gut bacteria in mice can effect obesity, presumably some similar effect can be manufactured in humans."
] |
[
false
] |
I read this article about gut bacteria transplants from obese mice, resulting in increased obesity in the recipient mouse; There are also some interesting articles about fecal transplants which are readily findable on google. This makes me think that someone should get right on a human analog straight away. Find some healthy human skinnies and sample their gut flora, and record frequencies of the observed strains, and then feed the results to some fatties. With a whole bunch of skinnies, and a whole bunch of fatties, and tables of the various frequencies of bacteria how hard would it be to come up with some strains that are associated with reduced appetite? (I spent a month or so in India, and I can confirm that some gut bacteria are associated with rapid weight loss... and violent brown rain... however I didn't put all the weight back on for a year or so after) so its not just a short term effect. I am happy to volunteer for the experiment, if someone can put it together.
|
[
"In regards to the paper you reference, they don't quite show what you are proposing. They show that microbiota from obese mice to normal mice promotes obesity, but they don't show the reverse; that microbiota from normal mice can revert obesity in obese mice. Since that is a simple experiment and it's not included in the paper, that likely means they tried it and it doesn't work. ",
"Plus, the \"obese\" mice they used were TLR5 knockouts which prevents them from recognizing certain pathogenic bacterial components. Thus the microbiota of these mice ought to be enriched for pathogenic bacteria which, when transferred to normal mice should mess up a number of things. It's not surprising that weight control could be one of them. But since a TLR5 defect is probably not the main issue in human obesity, this system probably isn't the most relevant. ",
"There seems to be some potential in the idea, but the main problem I see now is that we don't understand the microbiota well enough to start manipulating it at that kind of level. Researches have shown all sorts off effects in mice when you skew the colonic flora from the nutritional effects you mention here to the development or inhibition of colitis. Furthermore, most of the species of bacteria in the microbiota are not cultureable, making studying them and creating unique microbiota \"cocktails\" difficult. Anyway, I think it's going to be a little while before we start swapping poop with each other to cure obesity. "
] |
[
"well at the very least, I would be interested in the mechanism by which the bacteria were causing the host to act in ways that resulted in obesity.",
"I guess the simplest mechanism would be for the gut bacteria to directly inhibit the vagus nerve, basically the opposite of this;\n",
"http://www.popsci.com/science/article/2011-03/pacemaker-your-gut-feigns-fullness-tricking-you-eating-less",
"They could operate on the cannabinoid receptors in the brain, but that seems far fetched considering their location.",
"So the idea would be to either block their anti-satiety mechanism, or to work out some way to kill or inhibit the activity of those bacteria that have similar properties to the obesity ones."
] |
[
"I would be surprised if bacteria were causing their effects directly through the nervous system, particularly because obesity is much more than just impaired satiety and overeating. Additionally, you have to have dysregulated and skewed metabolism that promotes the accumulation of fats which is typically the result of endocrine dysfunction more than nervous. If anything I would guess interference with leptin, ghrelin, etc. "
] |
[
"How does a flamethrower prevent the back flow of combustion as it shoots a stream of ignited fuel?"
] |
[
false
] |
In a flamethrower like as the fuel gets shot out of the barrel, it gets ignited creating stream of fire. I'm assuming the fuel gets ignited after it exits the barrel, cause in the gif, theres no visible flame at the tip of the barrel. But how does the flamethrower prevent the flame from spreading into the barrel and ignite the fuel that's being constantly spewed out? Or if not that, how is combustion of the fumes prevented?
|
[
"This device has no barrel - it's a torch with a two handed grip, plain and simple. Fuel and air mix outside of the fuel hose, which allows combustion. Inside the fuel hose, there is nothing but fuel, so combustion cannot occur."
] |
[
"Things need the fire triangle to burn. These are heat, fuel, and an oxidizing agent (for simplicity oxygen - O2). These 3 items all have minimum values they need to support their function. Example a little heat might not cause combustion but add a little more to the fuel/O2 and you get fire. The liquid fuel in the pipe is missing both the heat and the Oxygen. \nIn addition when you dig a little deeper you will find that almost all fuels must convert to vapor to burn so seeing as the fuel in the pipe is still liquid this also reduces the possibility of combustion. If you look closely you can see that the flames don't actually appear until the liquid fuel is a few inches from the tip at the point where enough of the fuel has vaporized to support the combustion."
] |
[
"Trying to think of a fuel that burns in the liquid state, but having trouble thinking of one, maybe you can help out? Gasoline, diesel, and kerosene does not burn in the liquid state. I don't even know if there is a liquid state of carbon, or if it would burn in that state. Paraffins doesn't burn in the liquid state. So what fuels should I be thinking of?"
] |
[
"Can vaccines be made for any pathogen?"
] |
[
false
] | null |
[
"Cancer is not a pathogen. Pathogen is an infectious agent. ",
"https://en.wikipedia.org/wiki/Pathogen",
" ",
"Although some cancers are proved to be caused by viruses we can't do vaccine against cancer per se. We only can make vaccines against microorganism that cause cancers as we did against human papillomavirus. But it's only some cancers like cervical cancer or hepatocellular carcinoma(hepatitis b or c- we only have hep b vaccine).",
"To simplify cancer is an uncontrollable сell division. Something causes mutation in genes. For example radiation, chemicals or infection. To reduce the risk we need to stop exposure to these things. Bad thing we didn't discover these things for all types of cancer.",
"Unfortunately cancer mechanisms are too complicated and cancers are too different to make one magic shot to prevent it."
] |
[
"We can make vaccines for every pathogen available. But it's not the fast process. Sometimes it's really hard to isolate the antigens.\nBacteries and viruses mutate therefore making of vaccines is very time and money consuming process. So scientists concentrated of making them for most dangerous pathogens which kill and disable people(for example diphteria, tetanus, hepatitis B, poliomyleitis, smallpox in the past etc)."
] |
[
"Viruses (like HPV) tend to cause cancer because they have the ability to insert their DNA into the human genome. This can interrupt otherwise normal gene and cause misformed proteins to be made. Most vaccines are made by pinpointing a viral/bacterial “antigen” or protein expressed by the virus that immune cells can recognize as “bad.” Vaccines help the immune system recognize this faster and ultimately have a faster response. However, this is almost impossible with cancer because even if it can be caused by a virus, cancer is your own human cell. We can’t easily make a vaccine to a cancer cell that wouldn’t ultimately get your immune system to kill all of your cells. It’s very hard for the immune system to recognize a cancer cell from a normal cell."
] |
[
"Why does the earths core generate a magnetic field? "
] |
[
false
] | null |
[
"The rotation of liquid metals in the earths core is thought to create the magnetic field. This is known as the ",
"Dynamo theory"
] |
[
"Probably an old e&m book?",
"The Earth-core Dynamo is much better understood today than back before the 1970s. Modern modeling even produces the chaotic pole-flipping. A few different teams are even building physical models (",
"sphere full of liquid metal",
", sodium pumped through tubes, etc.)"
] |
[
"Just wanted to thank you for that interesting word."
] |
[
"Does soapy water flow through pipes more quickly than plain water?"
] |
[
false
] | null |
[
"Observations. It's not always true (for example, in low-pressure or low-density situations). But you can put tracer particles in a flow and watch how they move."
] |
[
"Fluids obey the so-called ",
" condition, meaning that the fluid's velocity at surface of the pipe is exactly zero.",
"I've never studied fluid dynamics before but how do we know that fluids have a no slip at the boundary condition?"
] |
[
"Fluids obey the so-called ",
" condition, meaning that the fluid's velocity at surface of the pipe is exactly zero.",
"I've never studied fluid dynamics before but how do we know that fluids have a no slip at the boundary condition?"
] |
[
"When were dates invented? And if it was a long time ago, how did they calculate 365 days for the earth to rotate around the sun?"
] |
[
false
] | null |
[
"It is quite easy to note the day of the year with the longest or shortest hours of daylight. All one needs do is count between two successive midsummer days and you'll get the number of days in a year.",
"We use the ",
"Gregorian calendar",
" adopted on 24 February 1582, itself a variation on the precursor Julian calendar which had existed since Roman times. There ",
"isn't a specific date known for the invention of the calendar",
" although humans have been noting the passage of time for centuries."
] |
[
"As for your second question, ",
"Hipparchus",
" calculated the year to be 365 days by counting the days between two equinoxes using a ",
"armillary sphere",
"."
] |
[
"Try ",
"/r/AskHistorians"
] |
[
"How fast would a spaceship need to go to reach Alpha Centauri in 1-2 months, and is that speed physically possible?"
] |
[
false
] | null |
[
"You would have to go 24-48 times the speed of light and that is not physically possible."
] |
[
"I see. What about at 50% the speed of light with 8 years or 25% at 16 years?"
] |
[
"It's four light years away."
] |
[
"If I stick my head out of a car window at 65 mph and try to look directly ahead I’m effectively blinded by the air rushing passed my eyes. How does a cheetah see and track prey when running at top speed?"
] |
[
false
] | null |
[
"Full disclosure, I'm an optometrist for humans, not for cheetahs.",
"It's because they (and many birds and reptiles) have a ",
"Nictitating Membrane",
".",
"It is a transparent ‘third eyelid’ that covers the eye and allows them to see while also maintaining protection over their cornea. From SeaWorld's website: \"",
"A nictitating membrane further shields and protects the eyes during fast sprints",
".\"",
"Humans (and many other mammals) have a vestigial remnant of this membrane called the ",
"Plica Semilunaris",
". It’s that half moon sliver of tissue next to the ",
"Caruncle",
" (which is the little yellowish/reddish blob in the very inferior/nasal corner of your eye).",
"Edits. \n1. I'm embarrassed I forgot the vestigial remnant is the Plica Semilunaris (now linked above), not the Caruncle.\n2. Shoutout to ",
"/u/OmegaGreed",
" and others for encouraging me to research this a little further, I'm learning so much! There are clearly (and not surprisingly) a wide variety of Nictitating Membranes across animal species, even among cats. While some (most?) are definitely not transparent enough to be useful during hunting, the Cheetah's must be.",
"\nThis makes sense to me because on the one hand, I definitely agree that a cheetah running at 65 mph will not experience the same shearing force due to air across their cornea as someone sticking their head out of the window of a car, due to the aerodynamics of car vs. cheetah head. Despite this, when you are traveling at speeds anywhere near 65 mph, that shearing force would definitely be strong enough to strip away your tear film. This is problematic because even if their cornea had a different type of innervation, such that this didn't cause them ",
" per se, your tear film plays a ",
" role in your visual acuity. In fact, ",
"the air/tear-film interface [is] the most significant component of the total refractive power of the eye",
"."
] |
[
"Bunnies have a nictitating membrane as well. They use it to protect their eyes in a fight.",
"This can be problematic if you're trying to bond bunnies and they start going at it with each other which means you need to get in there and separate them. If they put down their membranes it messes up their already bad eyesight and means they can do stuff like try to ravage your shoe because they think it's the other bunny.",
"Good times."
] |
[
"I think, in addition to the nictitating membrane that ",
"/u/slevayyoung",
" mentioned, (Edit: actually, having thought about it, I'm not sure the nictitating membrane is involved at all) it also has to do with the amount of air being displaced by a car. A car is obviously much larger than a cheetah, so a larger volume of air is being turbulently displaced as the car is moving forward. A lot of this turbulent air rushing past the car is actually moving faster than 65mph (from the perspective of a passenger in the car) as it gets pushed around the car. ",
"Additionally, cars are streamlined, so when you open the window and stick your head out, you are pushing your head directly into this turbulent stream moving around your car. It's a bit like sticking your head into the wake of a motorboat. ",
"Cheetahs displace much less air than a car, and their eyes are also directly at the front of their body as it's moving, so they don't have to deal with any of the wake of the air they are displacing.",
"Edit: Actually, after thinking about it some more, I'm not convinced the nictitating membrane is involved. Certainly it would be pretty helpful to be able to use it like a pair of goggles, but, ",
"at least in housecats",
", the nictitating membrane is not transparent enough to see through like glass. Good eyesight is pretty important when you're chasing extremely fast prey over uneven ground. Cheetahs have long eyelashes and hooded eyes to help keep debris out, and given that they only reach their top speeds for a few seconds at a time, I don't think the wind would be that much of a factor."
] |
[
"Why don't solid things react?"
] |
[
false
] |
[deleted]
|
[
"No, its not true. ",
"There is an entire field of people",
" dedicating to studying the chemistry of the solid state. "
] |
[
"Solids can react with liquids. ",
"Sodium reacts violently with water",
", for example."
] |
[
"Cesium ",
"fucking explodes",
" when exposed to water. Does that count?"
] |
[
"Could Dark Matter explain Neutrinos traveling Faster Than Light?"
] |
[
false
] |
I was just musing to myself and thought of this...is it possible that Neutrinos have been observed by the OPERA experiment traveling faster than light because the emitted photons have been caught up and re-emitted by Dark Matter? The neutrinos, being highly non-interactive, would then arrive at the detector more quickly than the photons. Any physics people able to answer?
|
[
"If photons interacted with dark matter, it wouldn't be dark."
] |
[
"Dark matter is characterized by the fact that it doesn't interact with electromagnetism AT ALL, including the absorption and re-emission of photons. Light passes right through it unaffected."
] |
[
"A little clarification on what seems to be your thoughts: c, the speed of light, is the speed that massless particles are thought to move at in our universe. When you hear talk of 'the speed of light in a vacuum' being different than the speed of light in a substance, that is a macro level observation of the average speed of photons being lowered. This means that c is(with our knowledge of physics) the universal speed limit. So even if photons WERE absorbed and re-emitted by dark matter(which has been pointed out that a definition of dark matter is that it only interactions gravitionaly, not electromagnetically(which is light)), it still wouldn't have an effect on c, the speed of light.",
"tl;dr(which I don't like, if you ask a question read a response), the idea of something with mass(neutrinos) traveling faster than something without mass while IN BETWEEN interactions(photons) does not fit with or understanding of physics."
] |
[
"Why is Planck temperature the hottest that something can get and what is happing to the atoms at that point?"
] |
[
false
] | null |
[
"The Planck temperature T_P is the scale of temperature at which quantum-gravitational effects are dominant. Quantum gravity prevents you from overcoming T_P (within an order of magnitude), making it a type of \"absolute hot\".",
"A way to heuristically understand that temperatures T quite larger than the Planck temperature are impossible is to remember that a system in thermal equilibrium at temperature T has energy fluctuations of typical size ΔE ~ k_B T. For T >> T_P, ΔE >> E_P (Planck energy) = M_P/c",
" (Planck mass). Since black holes have masses always larger than the Planck mass, this means black holes are produced by thermal fluctuations. However, black holes are states at thermal equilibrium, at a temperature T_BH << T_P, which means we are simultaneously much hotter and much colder than T_P, a contradiction. In fact, the larger T, the bigger the black holes, the colder the black holes, the more serious the paradox.",
"This is nothing else than yet another example of the UV <-> IR correspondence that exists in quantum gravity, which means trying to probe beyond the Planck scale always seems to map you back to ",
" the Planck scale, making it a sort of absolute limit.",
"At the Planck temperature, everything is destroyed. You ask about atoms, but those decompose at an immensely lower temperature when k_B T ~ binding energy of atoms, which is very roughly about 10000K, after which you have a plasma. At temperature which I guess are around the 10",
" K mark even nuclei are unstable. When k_B T ~ 140 MeV hadrons themselves come apart and dissolve in a soup of quarks and gluons (quark-gluon plasma). And so on and so on. (I hope I didn't get any of these wrong).",
"We don't know what kind of structures can exist between this and the (presumably) much much higher Planck temperature or what phase transitions separate them. However we know nothing, even in principle, can survive this temperature. What happens at the Planck temperature is literally absolute chaos: all information is irreparably scrambled in the most efficient way possible. If you lower any kind of information-storing structure of any kind in a Planck-temperature bath, the information will become comppetely unrecoverable to you in the shortest time possible. ",
"This insight comes again from black holes, which are perfect scramblers of information, and nothing can scramble information faster. It is easy to show that throwing something into a black hole and waiting to receive the resulting Hawking radiation is the same as throwing it into a Planck-temperature bath. The thing can also be reformulated in terms of chaos theory, and the insight is that quantum-gravitational systems have in a sense the maximum possible amount of chaos, where chaos is quantified by the ",
"Lyapunov exponent",
".",
"So, what does space look like at the Planck temperature? Hard to tell without choosing a specific theory of quantum gravity, but we know spacetime itself should be boiling and bubbling in some way, since thermal fluctuations involve also large deformations in the geometry of spacetime."
] |
[
"At temperature which I guess are around the 10",
" K mark even nuclei are unstable.",
"I don't think this is even close, to have K_b T equal to the binding energy of a nucleus you would need temperatures of the order of 10",
" K, 4 orders of magnitude higher. I suppose the real calculations would need to consider entropy, but I still think you are out by orders of magnitude, the binding energy per nucleon in He is about 7 MeV."
] |
[
"you're right, I knew I'd get that wrong. I moved it up to 10",
"K, I guess it's a more reasonable ballpark."
] |
[
"]The moon rotates the earth slow enough that it doesn't seem to move in realtime. Are there, or is it likely that there are planets in the universe where an observer like us would see an orbiting object move in realtime? Basically a faster moving moon or sun that I'd visibly moving to the naked eye."
] |
[
false
] |
The moon rotates the earth slow enough that it doesn't seem to move in realtime. Are there, or is it likely that there are planets in the universe where an observer like us would see an orbiting object move in realtime? Basically a faster moving moon or sun that is visibly moving to the naked eye.
|
[
"Here",
" is a real-time video of Mars' moon phobos transiting in front of the sun."
] |
[
"The moon is visibly moving, you just aren't patient enough, or zoomed in enough, or watching for events that make it noticeable. Astronomers regularly watch ",
"Lunar Occulations",
" where the moon passes in front of a star. Many are ",
"naked eye events",
" since the star is quite bright. Like the upcoming July 16 occulation of Aldeberan which will be easily visible if you are in the right area."
] |
[
"That's neat, thanks. So if I was on Mars I could see phobos moving like that?"
] |
[
"Why is it that if you run your hands under warm water after they have been outside in the cold, they get itchy?"
] |
[
false
] |
Im talkin like if you had a snowball fight, with bare hands. Then went inside and warmed them with hot tap water.
|
[
"Check out articles on \"urticaria.\" Your body could be releasing histamines in response to the sudden rise in body temperature. The kind of urticaria this falls under would be cholinergic urticaria. ",
"Edited to include a good link on how this works"
] |
[
"The mostly likely explanation is that the rapid change in temperature either directly depolarizes the nerve cells responsible for sensing itch, or the change in temperature causes a nearby cell type to release itch mediators such as histamine, which would then go activate the aforementioned nerve cells. given the fact that this activity often is reported to cause pain, i would put my money on the former explanation."
] |
[
"Yes this. This just a personal anecdote, but I live in a colder climate and whenever I go to run, for the first five minutes my legs get brutally itchy. Apparently it's somewhat common among runners."
] |
[
"Is it incorrect to say that something is from a 'different dimension' or 'parallel dimension'? Wouldn't it be from a different point on a dimension that everything is in?"
] |
[
false
] |
I think of a dimension as being like an axis on a graph. You're located , rather than , per se. So there could be a universe parallel to our own, meaning that it's located at a different point on some dimension, but to speak of a 'different dimension' or 'parallel dimension' is incorrect, right? This has always botherd me in sci-fi. Am I right, or am I missing something?
|
[
"yeah the sci-fi meaning of dimension is very different than our scientific one. ",
"this is what we usually mean"
] |
[
"Part of your problem is that 'parallel dimension' is not a scientific term, did you mean parallel universe? So it appears you are making an argument about a term that a scientist wouldn't use.",
"A scientist would definitely be interested in finding additional spacial dimensions or parallel universes. But those both have very specific meanings that are not equivalent.",
"So you can't really make an argument based on how Sci-fi uses those terms because they are not how a scientist would use them.",
"I hope that makes sense, I'll define extra dimensions and parallel universes better if you are interested."
] |
[
"Yeah, that was actually my point, that they say 'parallel dimension' when such a term is meaningless. They really mean a parallel universe, meaning that it's a universe located at a different point on some dimension beyond the first 4 (including time), to our own.",
"That's what I thought anyway, I was just seeing if my understanding of the scientific meaning of dimension and universe were accurate."
] |
[
"Why aren't there an excessive amount of fossils right at the KT Boundary?"
] |
[
false
] |
I would assume (based on the fact that the layer represents the environmental devastation) that a large number of animals died right at that point but fossils seem to appear much earlier, why?
|
[
"If a mass extinction occurs over, say, 100 years, there are probably actually fewer deaths during that century than in the previous century. Over the course of any given century, pretty well every animal living at the start will have died. In a stable population, these will be replaced by new births and there will be many generations of roughly consistent deaths and births. But if species are dying out, then halfway through the century, there will have been fewer births to contribute to additional deaths later in the century so by the end of the century there will have been fewer deaths than average, despite every member of the species dying."
] |
[
"To put it a different way, the number of animals alive at any one time is relatively small compared to the amount that die within a geologically identifiable period of time."
] |
[
"The premise is false: ",
"66-million-year-old deathbed linked to dinosaur-killing meteor: Fossil site preserves animals killed within minutes of meteor impact -- ScienceDaily",
" ",
"Consider that fossilization is rare, so such finds will be rare, but it only takes one to comprise \"an excessive amount of fossils\"."
] |
[
"Do we have a wider field of view when our pupils dilate in the dark?"
] |
[
false
] |
In the dark our pupils get wider, which I would imagine means there is a larger angle of light that we can see, and the opposite for our pupils shrinking in brightness. Is this actually how it works?
|
[
"Your field of view is determined by a patch of light-sensitive receptors that activate neurons on the back of your eye. Additionally, the stereo image collection of two eyes. ",
"While more light is collected, the opening of your pupil does not significantly affect your maximum field of view. ",
"Think about it like this, if you if you take the glare guard off a camera lens, more light comes in, but It doesn’t change field of view because it is already collecting the maximum possible angle. ",
"Only a very tiny pinhole is required to obtain a very wide angle at distance.",
"A larger field of view would come from, say, placing our eyes further apart (fish)."
] |
[
"The fact that lots of most commenters miss is that, unlike a camera which has a fixed sensor that is more than covered in a field of light going through the lens, the eye has a retina (\"film\") that covers the entire inside of the eyeball forward to roughly the midline. This is why ophthalmologists dilate your eyes when looking for damage because they can more easily see all of the \"film\" when they position themselves to look into the eyeball at oblique angles through a dilated pupil.",
"That said, most of what we interpret as vision is really the macula, a central high-density patch of cells called cones where the lens focuses the light. The remainder of the retina/film (made of rod cells) does receive some light coming in from outside the central portion of your vision, but rod cells are poor at distinguishing features and colors (though work better in low light) so your peripheral vision is not crisp in the same way the edges of a photograph are about the same quality as the center.",
"Dilating your eyes probably does expose more of the peripheral retina to incoming light from incident angles and marginally increase field of view theoretically, but since you don't really use anything but the central vision for picking out details, I don't think you would really notice this in a meaningful way. Also in reality, your brain is very good at \"stapling\" multiple \"photos\" together in a seamless way as a lot of our apparent field of vision is really your brain trying to create a cohesive interpretation of our environment as our vision constantly scans back and forth."
] |
[
"Fish don’t have larger field of view because of eyes further apart - it’s because their eyes point different directions. Our eyes pointing the same direction trades the larger field of view for better depth perception in our limited field of view"
] |
[
"Why does defogging windshields require outside air?"
] |
[
false
] |
If I use the recirculate option with the air pointed at the windshield, it seems like the glass gets foggier, but if I use air from the outside, the fog goes away very fast. Why is this?
|
[
"The air inside has higher humidity, due to your presence.",
"When you run the defogger, it automatically uses the air conditioner, which removes humidity. If you turn it to the hot position the heat added from the engine cooling system overwhelms the cooling effect of the AC, but the moisture has been removed already.",
"It is more important to blow dry air on the inner surface of the window than warm air, although heat certainly helps."
] |
[
"It is more important to blow dry air on the inner surface of the window than warm air",
"What about your rear defroster? (as we call them in the US) In many cars, mine included, this works purely on the principle of heating the window such that the temperature of the window is above that of the dew point of air around it."
] |
[
"Indeed, but this is designed for the external frost. It also repels the internal fog, but is pure inductive heating by electric elements, not something you would ever get in a front windshield."
] |
[
"How to properly cite someone's work in a blog?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"This is not a science-based question.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"I am having hard time finding suitable subreddits. Cna you recommend? Thanks.,"
] |
[
"Not really sure. Maybe ",
"/r/askacademia",
"."
] |
[
"Why are some substances easily absorbed by the skin while other substances are not?"
] |
[
false
] | null |
[
"It all about fat solubility and to a lesser extent molecular size. The more fat soluble a substance is the easier it is absorbed through the skin. That's why you can have fentanyl and GTN patches and steroid creams. A paracetamol or aspirin patch wouldn't get through the skin very easily. "
] |
[
"And to supplement this correct answer, some papers:",
"Frasch, H. F. (2002) ",
"A random walk model of skin permeation",
". Risk Anal. 22, 265-276 (Obligatory immature comment: what a journal name!)",
"Potts, R. O., and Guy, R. H. (1992) ",
"Predicting skin permeability.",
" Pharm. Res. 9, 663-669",
"I think both of these models specifically relate to an aqueous (water-based) delivery. Using different solvents greatly affect a molecule's skin permeability. For example, KCN (potassium cyanide) in water isn't ",
" bad on your skin, but KCN in DMSO is quickly lethal due to the combination of enhanced cation solubility and enhanced skin permeability. Or so I was told; no one in the lab tried it out."
] |
[
"So is it because steroid creams are considered cholesterols that they are able to be absorbed through the skin more readily as compared to an aspirin patch?"
] |
[
"Is there a point where walking becomes more efficient that cycling when going up a steep hill?"
] |
[
false
] | null |
[
"This is an interesting question from a high school physics perspective. I'm not sure it is entirely answerable, because a lot would depend on how efficient the two machines are, how heavy the bike is, how heavy the runner is, coefficient of friction of tires, shoes, etc, which would require a few assumptions.",
"I am an avid trail runner and mountain biker, and I can tell you that empirically yes, there is a point where a reasonably fit runner can propel themselves up a hill faster than a reasonably fit biker on a fairly typical bike and typical trail. It is about the point that it gets not so fun to ride a mountain bike up a hill for a sustained period of time."
] |
[
"You also have to consider the bike wanting to roll back downhill. Friction holds you in place on foot, on a bike you are constantly fighting gravity pulling you back. It's the difference between picking something up and putting it on a shelf vs. holding it."
] |
[
"That exact question is addressed in David Wilson's \"",
"Bicycle Science",
"\" book. Don't have the reference handy, but it is an interesting read."
] |
[
"Why don't we experience G forces from relative motion?"
] |
[
false
] |
I know that we are travelling an indeterminate speed through space due to Earth's rotation, it's orbit, the sun's galactic orbit, ect. My question is, since that motion constantly changes in direction due to it's circular nature, and acceleration is what causes us to feel G forces, why does changing velocity relative to our relativity cause G forces? How come changing direction in a plane causes G forces, yet while hurtling at thousands of kilometers per hour through relative space in a constantly changing direction doesn't seem to cause any G forces at all?
|
[
"You've just discovered the equivalence principle.",
"The bottom line is that a change of direction or relative velocity is ",
" an acceleration … and being relatively stationary is not necessarily the absence of acceleration."
] |
[
"Think of it this way: how do you feel a G-force when in a car taking a hard turn? You feel it in several ways, such as a pressure on your internal organs, the fluid in your inner ear rushing to one side, etc. You can feel these things because the car is only pushing on you from the outside, which changes the pressure distributions throughout your body.",
"Now suppose that every part of you were pulled in one direction at the same time: all of your organs, all the fluid in your inner ear, everything pulled in a certain direction with the same acceleration. You would have absolutely no way of knowing (without looking at some other reference point) that you were accelerating. This is the case for astronomical forces; we are so far away from the sources that they pull on everything around us uniformly, and so we can't detect them."
] |
[
"The equation is a=(2 pi/T)",
" r, where T is the time of the orbit and r is the radius.",
"Earth: T=24 hours, r=6380 km, a=0.003 g.",
"Sun: T=1 year, r=150 million km, a=0.0006 g",
"Galaxy: T=200 million years, r=30000 lightyears, a=0.00000000003 g"
] |
[
"Half life period of radioactive substance?"
] |
[
false
] |
I know that half life period is the the time required for a substance to decay half of it's initial amount.My question is that many radioactive element have a huge life time in order of billion years.so how some atoms of the radioactive substance stays without decaying for such a long time. radioactive elements are unstable and and gain stability by decay process so why not every atom decay as fast as possible. I also don't understand concept of probability in radioactive decay.
|
[
"...radioactive elements are unstable and and gain stability by decay process so why not every atom decay as fast as possible.",
"For the same reason any other kinetic process has varying lifetimes. Imagine a ball on a hill. It could be a very, very steep slope, so the ball rolls down quickly. It could be such a gentle slope that it rolls down very slowly. It could be right on the tip of a hill and will not roll down unless perturbed by wind. In all these cases, the ball is unstable, and can get to a lower energy state (downhill), but just because that is true doesn't mean it must reach that state as fast as possible.",
"Add the fact that there is also another case - a ball being in a small depression beside a cliff - meaning it is actually ",
" at a local minimum, and needs to overcome a higher energy state before it can reach some lower energy state.",
"I also don't understand concept of probability in radioactive decay.",
"It means that all the parameters of radioactive decay - such as half-life - are statistical measures that apply to a population of atoms. Given a single atom you cannot predict when it will decay. Like if you flip a whole box of coins, you can fairly confidently say that half the coins will be heads. But if you're flipping a single coin, you cannot confidently say \"this one will be heads\", only that there is 50% chance it will be."
] |
[
"All atoms of a single element, yes. Atoms of different elements no. "
] |
[
"I was under the impression OP was asking specifically about atoms of the same long half-life element.",
"So, the downhill ball example is not appropriate to explain why some atoms of the same element decay early and others not. ",
"The ball example is a classical view and the classical example does not provide a high enough (for me) fidelity as an explanation.",
"Tunneling through a potential barrier is fundamentally different from classical barrier interactions like a ball and a hill."
] |
[
"Why does fire behave differently in zero gravity?"
] |
[
false
] |
I came across from another post and was wondering why gravity has any affect at all on fire.
|
[
"Ever blown on a lit candle? Notice how, by moving the air around the candle, you can get it to point different directions? That's because the shape of a flame is due to ",
" - hot air is less dense than cold air, thus will rise to the top, while cold air from the surrounding is drawn to the base of the flame.",
"In microgravity conditions, there is very little convection. That is to say that things with different density will not sort themselves out like they do on Earth. The result is a reaction front that starts from the center and expands outwards in a sphere. The flame then dies out quickly since the reaction cannot continue without a fresh source of oxygen, which is normally supplied via convection. ",
"This video",
" shows the fire in action."
] |
[
"Follow up question, would I be able to smoke a cigarette in space ?"
] |
[
"Clarify; are you asking about in a vacuum, or in a space ship/station?"
] |
[
"When measuring length contraction/time dilation of an object in a medium other than a vacuum; do you account for the reduced speed of light?"
] |
[
false
] | null |
[
"No! The fact that it's light that travels at ~300,000km/s is irrelevant to special relativity; it was only the motivation behind it. What matters is that ",
" can travel ",
" than that speed. In fact, it's possible that light itself doesn't even travel that fast: There are experiments trying to determine (indirectly) the photon mass, though so far they have all only produced upper limits, so the photon might well be massless. If it's not, it would mean that light actually travels slower than the (so-called) speed of light!",
"But what really matters is that there is ",
" cosmic speed limit that holds for every inertial reference frame, and when you make things go really really fast so their kinetic energy is much larger than their rest energy (their mass times that speed squared), they approach that speed. Which is what we observe in the universe.",
"By the way, in a medium with an index of refraction greater than one, you can have particles that travel faster than the speed of light in that medium. These particles, if they are electrically charged, leave behind an electromagetic shock wave somewhat analogous to the sonic boom a supersonic jet produces. This is called Cherenkov radiation. It is used in some particle detectors (including many neutrino observatories and the ATLAS experiment at the Large Hadron Collider), and it's the reason why people think of radioactive material as producing a blue glow."
] |
[
"How do they travel faster than light?"
] |
[
"So say they are electrons and they have a couple MeV of energy, and their rest mass is only 1/2 MeV. That means they must be traveling at some 0.97c, where c is the cosmic speed limit ... regardless of how fast photons or light waves or anything else travels. If you're in a medium where light waves propagate at 0.75 c (like, say, water), then the electron is humming along much faster than light.",
"Just because it enters the water, that doesn't mean it will slow down until it has an interaction strong enough to ",
" it slow down (or more likely create a big splat). The same would be true for a high energy photon: a 2MeV gamma ray would not simply slow down, but would sail straight through and then interact with an electron, slam it out, scatter off in a different direction, maybe convert into an electron/positron pair, and then you also have a big splat.",
"So it's only that they travel faster than the speed of ",
" light waves in that medium."
] |
[
"If light can be interpreted as a stream of photon particles, then these particles' momentum must be subjected to the uncertainity principle. Does this mean the speed of light varies a little bit, or do these particles form an exception?"
] |
[
false
] | null |
[
"The momentum of a photon isn't based on its speed, it's based on its frequency or energy. The relationship is basically p=E/c=hf/c where p is momentum, E is energy, c is the speed of light, h is Planck's constant, and f is frequency.",
"As to whether the wavelength of light jiggles due to uncertainty; I don't actually know.",
"edit: I'm going to quote Wikipedia on this one:",
"More generally, the normal concept of a Schrödinger probability wave function cannot be applied to photons. Being massless, they cannot be localized without being destroyed; technically, photons cannot have a position eigenstate |R>, and, thus, the normal Heisenberg uncertainty principle ΔxΔp > h / 2 does not pertain to photons."
] |
[
"When you you introduce relativity then it becomes related to energy in the expression I just posted, instead of just p=mv. If m=0 then the relationship is just E=pc. If p=0 then the relationship is the familiar E=mc",
" ."
] |
[
"E",
" =p",
" c",
" + m",
" c"
] |
[
"How can light put force on objects?"
] |
[
false
] |
So in my physics class our teacher mentined that up until Albert Einstein, Light were considered an electromagnetic wave-form (Translation may be incorrect, im swedish) but he found out that light can also be considered a particle (the photon). He showed this by taking a cameraflash or something, which light up very strong for a very brief moment. He held it very close to a cymbal, and when it flashed sounded kind of faintly as if it would have been hit gently. This confuses me a lot because we had just gone through what happens when 2 objects collide, which leads me to think that the photons would have had to slow down when transferring some of its momentum in order to give the cymbal speed for it to sound. At the same time I know that the speed of light is "static" and that photons are massless (right?). Wouldnt the photons just bounce off then in order to keep their momentum/speed? What am I missing?
|
[
"Could you elaborate on the sound a bit more? I find it very hard to believe that a flash or light could transfer enough momentum to a cymbal to make it sound. It could be more of a thermal effect, but even then that is unlikely.",
"The sound could have been the capacitor in the flash mechanism recharging. ",
"Lets assume light with a wavelenth of 575 nm, yellowish light.\nE=hv=hc/lamba so the energy of one photon here is ~3.5E-19 J\nWell now we have to figure out how many photons we have from the flash. \nWell lets think of the sun. Sun light provides about 1500W/m",
" 1 watt is 1J/s so using our yellow light 1500w/m",
" =1500J/s*m",
" *(1photon/3.5E-19J)=4.3E20 photons/sm",
"Lets assume he was using a fairly standard \"crash\" cymbal with a diameter of 0.5m (area~0.20 m",
"Normal sunlight would impart 0.20m",
" *4.3E20photons/sm",
" *3.5E-19J/photon=30J/s into the cymbal. ",
"Even assuming a flash that is 1000x the intensity of sunlight, the duration of the flash is on the order of milliseconds so the energy transfer would be on the order or one order above that which is transfer from sunlight over one second. Now what effect this will have on the cymbal? that gets more complicated.",
"one to bring up is the crookes radiometer ",
"http://en.wikipedia.org/wiki/Crookes_radiometer",
"Light energy from photons cant even move these little foil blades in a mostly evacuated bulb (it is actually a thermal effect, it does not function in a more evacuated bulb). This leads me to conclude that a camera flash could not induce audible vibration in a much more massive cymbal under ordinary atmospheric conditions.",
"Notes: I rounded a lot to keep things simple. My train of thought may be a bit scattered as I am battling a cold right now. "
] |
[
"which leads me to think that the photons would have had to slow down when transferring some of its momentum",
"This is where the problem comes from: momentum is only velocity dependent for massive objects. For light, the momentum is ",
" dependent. When light strikes an object and transfers some momentum to that object, the frequency of the light goes down."
] |
[
"Does that also mean that higher frequency gives higher energy?"
] |
[
"How would different musical instruments react to being played in a zero gravity environment?"
] |
[
false
] |
For example, a piano, a guitar, a trumpet.
|
[
"Looking at a piano and how the keys work, it seem like the hammer striking the wire might be affected by gravity. Specifically, after it strikes the wire, it appears to fall back to its initial position due to gravity. (I know nothing about the internals of a piano except what the ",
"picture on wikipedia",
" suggests.) Without gravity, I'd imagine the hammer might bounce around a bit and may not come to rest in the proper position."
] |
[
"This ",
" column",
" may answer your question."
] |
[
"An issue may be one of stance. For instance a trumpeter may be able to propel themselves backwards."
] |
[
"Why do certain vaccines require a booster?"
] |
[
false
] |
Prevnar requires a booster called Pneumovax. From my understanding, the reason it requires a booster is that Prevnar and Pneumovax target different agents and, therefore, it creates different antibodies. In the case of shingrix and its booster, I don't think that the shingrix booster targets different variants of the disease like Prevnar and Pneumovax. So, if the body creates immunological memory after the initial shingrix vaccination why does it require a booster? From my understanding, immunological memory lasts for most of an individual's lifetime, so what makes Shigrix unique? Is it due to the fact that it is a herpes related virus?
|
[
"It's to boost your titer high enough. After initial exposure to a challenge, you'll have a high response then scale back. Look at it like the US before we decided to keep a standing army. You build up your forces and after you win you don't want to be spending a bunch of money on an army for an enemy that is gone, but you won't go to no army. The enemy comes back and you're more ready than the first time, but not what you could have been. After that, you scale back your army, but you keep more around after that time because they came back once they could do it again. Take a look at the chart here ",
"https://www.quora.com/What-is-the-time-frame-for-an-antibody-to-form-after-an-MMR-vaccine",
" . Your immune system is doing a great job at resource management. If something keeps coming back though, you'll have a standing army ready to fight. Shingles would be like the Confederates coming back (hanging out in your nerves waiting for the right time). Your body's armed forces need to be reminded to keep up defenses against it."
] |
[
"Certain vaccines such as the diphtheria vaccine do not produce absolute immunity. Instead it is a protective antitoxin vaccine (it contains the diphtheria toxoid) that lasts about 10 yrs, hence why a booster is needed once a decade. Tetanus vaccine as well delivers the tetanus toxoid and must be “boosted” to continue providing passive immunity."
] |
[
"Different pathogens and toxins have varying degrees of antigenicity, which is the ability\nto stimulate an immune response. \nIt might be about size or about glycoproteins on the coat.\nIf an organism has a very high degree of antigenicity, a booster vaccine may not be necessary.\nMost often it is best to challenge our immune system a second time, however, so\nthe memory of the pathogen invading is well scripted.\nOccasionally a third challenge is in order."
] |
[
"What is the minimum molecular density required to conduct sound?"
] |
[
false
] |
Everyone (I should think) knows that there is a relationship between molecular density and the potential for acoustic conductivity (I'm not a scientist, so forgive me for using the best descriptive terms I can muster.) For example: As I understand it, we hear sound "better" under water because water has a higher density than air and therefore has a greater ability to conduct sound with less volume and signal degradation over xyz distances. This explains how whales and other creatures communicate over long distances. I could be wrong about the exact details, but I think you follow me. So what is the minimum density required for an acoustic medium to conduct sound? How far apart can molecules get before the sound waves don't cause them to bump together and get that wonderful music to your ears? I'm asking because I am picturing galaxies and planets and the like forming from dust and gas etc, and I'd love to imagine how that would sound. At some point I'd imagine they gather enough density for you to hear something. Anyone have any insight into these issues?
|
[
"Great question, and there's a surprisingly simple answer.",
"Basically, if you want sound to be supported, you want the medium to look \"continuous\" to the wave. Otherwise, too much of the energy gets scattered and turned into heat. The more continuous, the better the wave will conduct.",
"Of course, \"continuous\" will vary from wave to wave, because the fundamental measure of distance for a wave is the wavelength. Since the wavelength depends on the frequency and the soundspeed of the medium, so too will the minimum number of particles required for the medium to support sound. As a rule of thumb, let's just say that a cube measuring one wavelength on each side should contain at least 1 billion particles. Using the soundspeed, that gives us a maximum frequency for waves in a medium. For air at STP, that gives us a value in the tens of MegaHertz, which is right around the point where the absorption of sound by the air really starts to pick up."
] |
[
"As far as I know, there is no minimum, at least for sound in the purest sense (there is undoubtedly a minimum density required for your ear drums to register sound waves, but that doesn't seem like the question you're asking). \"Sound waves\", or acoustic oscillations as they're generally called outside the realm of everyday experience, can propagate through nearly any medium. They are routinely measured by radio astronomers in gas clouds with densities as low as ~1 atom/cm",
" , while cosmologists measure the so-called \"baryon acoustic oscillations\", or BAOs, in the material of the universe when it was only ~500,000 years old."
] |
[
"So cool. Appreciated!"
] |
[
"What is the lowest radio frequency?"
] |
[
false
] |
Is there a minimum frequency for electromagnetic radiation? Below a certain frequency, would the energy of each photon be below some quantum limit? Do AC power lines emit photons of 60Hz (50Hz) radiation? Would there be any effects one could test for to exhibit the particle nature of such low frequency radiation?
|
[
"There is no lower limit to radio frequency. All radiation has a quanta of hv, where v is the frequency and h is planck's constant.",
"Below a certain energy, it gets hard to detect individual photons, so then radiation is detected with antennas. Antennas need to be a good fraction of the wavelength of radiation. Thus the size of the antenna places technological limits on the lowest practical radio frequency.",
"Very low frequency radiation (<100 Hz) has some applications. The US Navy used to maintain a facility to transmit signals on 76 Hz to submarines. These signals were the only one capable of penetrating seawater to submarine depth. The bandwidth on these signals was very small. They could only send a few characters per minute and the antennas were 30 miles long but hugely inefficient."
] |
[
"I can think of one minimum, but it's not very helpful: 2 attohertz = 2x10",
" Hz. Any oscillatory process that radiates photons with a frequency smaller than that would take longer than the age of the universe to complete.",
"In principle, there's no lowest frequency, but very low frequency photons are very hard to detect because they carry so little energy."
] |
[
"Wikipedia: Communication with submarines",
" (with pic)"
] |
[
"Does fat spoil in the body? Does the body keep track of what fat is newer, and \"rotate stock\", so to speak?"
] |
[
false
] | null |
[
"Fats are also called lipids (I will use this term later). When fat spoils, it is called ",
"rancidification",
". Fat in our bodies is stored in special types of cells called ",
"adipocytes",
". ",
"When our bodies store energy, these adipocytes take up more fat, and they can proliferate, too. When our bodies need energy, the adipocytes can mobilize their fat stores for the rest of the body to use. ",
"About ten percent of our fat cells are renewed annually",
".",
"There are three mechanisms which lead to rancidification: spontaneous ester hydrolysis, reaction with oxygen free radicals, and breakdown by microbes. In a healthy human, there generally should not be any microbes in the connective tissue layers, so the third option shouldn't happen. The second option does occur, and it is called lipid peroxidation; however, this typically happens to the lipids that make up the membranes of our cells and not to the lipids that are stored within the vacuoles of our adipocytes. Furthermore, the damaged cell membrane lipids often cause the cell to die via apoptosis or necrosis and everything gets recycled. Again, you are not going to wake up one day and find that the fat in your butt has gone rancid because you didn't ingest enough antioxidants. Finally, PubMed searches for rancid, ester hydrolysis AND rancid, adipos AND rancid, and lipid hydrolysis AND rancid all turned up zero pertinent results (i.e. all of them referred to fat rotting in dead organisms, not live mammals). So I wouldn't worry about it."
] |
[
"This is a wonderfully understandable reply. I especially loved \"Again, you are not going to wake up one day and find that the fat in your butt has gone rancid because you didn't ingest enough antioxidants.\""
] |
[
"Brave, but stupid."
] |
[
"If everything in the Universe is constantly expanding, can/do we measure changes in size/space on an atomic level?"
] |
[
false
] | null |
[
"No. The expansion only applies on the largest scales. On smaller scales where you have things like galaxies and planets, there is no real expansion.",
"But be careful, because this is the sort of question that often gets people saying things which are completely incorrect. As a rule of thumb, if someone says that things on Earth (say) don't expand because intermolecular bonds or gravity or whatever \"overcome\" the expansion, don't listen to them. With one notable exception (which I'll mention soon), the expansion is ",
" some universal force which fills everywhere and everything. It's an effect which occurs on the largest scales, where the Universe appears to be uniform, and is more like the upward motion of a ball thrown into the air than the upward motion of a propelled rocket. Once the ball turns around and starts to fall, there's no more \"upward force\" trying to bring it up, and similarly when a part of the Universe starts to collapse and form galaxies, there's no residual \"expansion force\" doing things on smaller scales.",
"There is one exception to this, which is the cosmological constant that may be causing the expansion of the Universe to accelerate. If the acceleration is due to a cosmological constant, that actually modifies Newton's gravitational force so that there is indeed some effect felt on small scales. In some more exotic cases, the cosmological \"constant\" can grow stronger with time, resulting in a \"big rip\" that eventually tears apart objects on the smallest scales. There are also models in which the accelerated is caused by something which wouldn't affect anything here on Earth, though, so we await more data to know for sure!"
] |
[
"No, the expansion of the universe only effects objects that are not bound by other forces. In this sense everything in our own galaxy and the galaxies around ours are not effected by expansion. Only galaxies and clusters not gravitationally bound to one another are effected by the universes expansion."
] |
[
"At what scale does expansion stop (assuming no cosmological constant)? To me, it doesn't seem right that there is a sudden discontinuity between expansion and non-expansion. Shouldn't there be galaxies in between, that are weakly expanding?"
] |
[
"Is there a way to describe the growpattern of a tree mathematically?"
] |
[
false
] |
Im interested in the texture cuts have for cg reasons. The wood texture generator is really bad though since there are no rings for branches in vertical cuts and so on... If someone has already done it, where can I find it? If not, why is it so hard to do?
|
[
"i did a research project in college that studied the reiterative nature of tree branches and showed that stresses on a tree branch (both from environmental factors and the weight of previously grown offshoots) affected the future growth patterns of the branch"
] |
[
"Not completely accurately but there a few different ways. I think the best way to generate something that looks like a plant or tree is an L-system.",
"http://en.wikipedia.org/wiki/L-system",
"I'll just mention this because I can't remember how it works but power series have some deep relation to botany. I believe, less so, the Fibonacci sequence also does, but this has mostly been debunked as a coincidence and moreover that the model doesn't fit perfectly. Sorry but I can't find that reference at the moment."
] |
[
"Yes, this. You don't want fractals or L-systems, those are hacks that react to some of the observed shapes of trees. Instead, to make accurate CG trees, you need to \"grow\" them, as their shapes are very strongly influenced by their lifetime history of light, nutrients, water, and (most appropriate to your question) stress. Look for ",
"books by Claus Mattheck",
", he lays it out.",
"Summary: trees grow by increasing the radius of their structures---adding new material to both sides of the vascular cambium. More material is added where and when the cambium is under compressive stress. Now, computing stress in growing trees isn't as simple as just assuming a uniform, isotropic material, but that'll get you better trees than anyone else in CG has done before (AFAIK), and it'll get youfar more realistic cross-section detail."
] |
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