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[
"I bought salsa the other day and it just exploded in my face when I took it out of the fridge... why...?"
] |
[
false
] |
So I bought a combo of salsa and bean-dip at costco the other day. The bean-dip container was stacked on top of the salsa contained and the two were wrapped together with plastic wrap. Anyways, when I took the salsa and bean dip out of my fridge, two weeks after buying them, I noticed that the salsa was bulging from its top and bottom. I take the wrapping off and my roommate comes in and gawks at the mutated salsa container. Then it just explodes. The cap flies off (found it behind my fridge), salsa splatters the entire kitchen, and I have a loud ringing in my ears for about 5 minutes... I don't understand how this happened, all I wanted were some chips and salsa...
|
[
"When something starts to decompose, it releases gasses. So in the closed jar of salsa built up pressure. So when you released it all of the pressure released, Salsa was pulled along with the escaping gasses."
] |
[
"If your salsa was contaminated, bacteria could produce gasses which would build up in the container. "
] |
[
"Thank you!"
] |
[
"Are the Hubble \"deep field\" photos in true color or false color?"
] |
[
false
] |
I can't find any information online but I would really like to know the answer. I would assume it is a false color photo but I want to be positive. If they are in "false color", what would I really see if I hypothetically had superhuman vision which granted me the ability to see what Hubble captured for myself?
|
[
"Nothing except your eyeballs are in true color. \"Color\" is purely a human perception."
] |
[
"The Hubble deep fields have been released many times in slightly different variations and depending on the one you're referring to, the wavelengths used vary -- but for all deep fields the images are false color.",
"In ",
"this version",
", as referenced on ",
"the HubbleSite page here",
", all of the light came from the near infrared."
] |
[
"The ones I saw were corrected for red shift. So it wasn't a \"straight out of camera\" image but each galaxy was supposed to have been corrected (within the limits of the amount of red-shifting) so it looked like what it would look like in an inertial reference frame."
] |
[
"Aside from the light from the sun, does the moon emit light?"
] |
[
false
] |
[deleted]
|
[
"Yes, but it's much less radiation than that emitted by most objects on Earth.",
"It's also immensely dimmer compared to Earthshine, light reflected from Earth to the Moon and back, that occasionally makes the silhouette of the night side of the Moon visible in front of a dark sky."
] |
[
"But it ",
" produce light, correct? It's not visible, but it does shoot off light, right?"
] |
[
"No. The surface of the night side of the moon is pretty cold, too cold to emit in visible light by blackbody radiation. Consider that the night Earth is much warmer and still it's completely dark.",
"You need to be at least several hundred degrees before you start glowing in visible.",
"Anything with a positive temperature emits blackbody radiation, but the total intensity goes like T",
" and the spectrum is peaked at a wavelength that goes like T ^ -1. So the blackbody radiation of something as cold as the nightside moon is very faint, and peaked at long wavelengths."
] |
[
"Why do stars seem to \"twinkle\" at night, even on a really clear night?"
] |
[
false
] | null |
[
"Planets do not twinkle the way stars do. In fact, this is a good way of figuring out if a particular object you see in the sky is a planet or a star. The reason is that stars are so far away that they are essentially points of light on the sky, while planets actually have finite size. The size of a planet on the sky in a sense \"averages out\" the turbulent effects of the atmosphere, presenting a relatively stable image to the eye.",
"Same source."
] |
[
"Stars twinkle because of turbulence in the atmosphere of the Earth. As the atmosphere churns, the light from the star is refracted in different directions. This causes the star's image to change slightly in brightness and position, hence \"twinkle.\" ",
"Source"
] |
[
"As others have mentioned, it is atmospheric distortions.",
"If you are interested, we actually have a method to ",
" stars called Adaptive Optics. Basically we use a small scope to view stars near the target object of our main telescope. A computer observes the twinkle and deforms a small mirror in realtime to remove the twinkle.",
"In situations where we can't find an adequate star, we project a laser into the upper atmosphere to make an artificial star and study the twinkle of the laser.",
"Here you can see our laser creating an artificial star to observe the twinkle"
] |
[
"Why are electrons attracted to protons and through what medium do forces of attraction propagate?"
] |
[
false
] |
Why are electrons attracted to protons? What forces drive that interaction? I've always been told in science classes that positives are attracted to negatives, but why?
|
[
"Okay, not \"why\" in that sense of the word. Maybe ",
" is a better question to ask. ",
"If I asked you why gas pressure increased when (all other things being equal) temperature increased, you'd be able to give me an answer to that question.",
"Now, I'm not trying to conflate quantum physics and the gas laws, I just wanted to know what forces of attraction are."
] |
[
"Okay, not \"why\" in that sense of the word. Maybe ",
" is a better question to ask. ",
"If I asked you why gas pressure increased when (all other things being equal) temperature increased, you'd be able to give me an answer to that question.",
"Now, I'm not trying to conflate quantum physics and the gas laws, I just wanted to know what forces of attraction are."
] |
[
"Here's Feynman's response to more-or-less your question",
"."
] |
[
"Do humans heal at different rates?"
] |
[
false
] |
If yes, what is the range of difference?
|
[
"Yes, of course. You need only look at an older person and a younger person to see the difference in rates of healing. There's no real 'range' as it depends on a myriad of factors, such as nutrient availability, collagen deposition, clotting, immune response, chronic disease states, and so forth, all of which will be superior (though you can find exceptions) in a younger body (say, 24) vs an older (64). "
] |
[
"I would think it has a lot to do with nourishment. If your body has all the tools it needs to rebuild and repair it will do so quicker than if it doesn't. If you're asking \"all nutritional factors being equal\" then I have no idea."
] |
[
": Yes. Wounds in the mouth heal faster than skin cuts."
] |
[
"If we can not travel faster than light, how can we image the early universe?"
] |
[
false
] |
I am always amazed by the early universe images and by the cosmic microwave background radiation images. However, I don't understand how can we detect now those radiation? so at t(0) (i.e. Big Bang) we have a rapid expansion. Radiation emitted from this event should be traveling at the speed of light. 13.7 billion years later (now), We are acquiring images of this early event. Did we travel faster than light at one point? EDIT: I tried to explain my question with a small illustration ( ).
|
[
"This is an analogy one of my astronomy professors used, and I think it works pretty well:",
"Imagine you are in the stands of a soccer stadium. Now imagine everyone in the stadium cheers once, all at the same time. What do you hear?",
"You would first hear the people closest to you, they are loud, and then the people a few rows away, etc. It would be a long cheer that slowly gets quieter.",
"Now imagine the stadium is infinitely large. The same cheer happens. What do you hear?",
"You would hear a cheer forever. It would continually get quieter. The sounds you hear at a later point in time come from those that were initially sitting further away.",
"For a final analogy, you could make the stadium expanding at all times. Now, you hear a doppler effect as well. The cheers get quieter and lower pitch over time."
] |
[
"This is an analogy one of my astronomy professors used, and I think it works pretty well:",
"Imagine you are in the stands of a soccer stadium. Now imagine everyone in the stadium cheers once, all at the same time. What do you hear?",
"You would first hear the people closest to you, they are loud, and then the people a few rows away, etc. It would be a long cheer that slowly gets quieter.",
"Now imagine the stadium is infinitely large. The same cheer happens. What do you hear?",
"You would hear a cheer forever. It would continually get quieter. The sounds you hear at a later point in time come from those that were initially sitting further away.",
"For a final analogy, you could make the stadium expanding at all times. Now, you hear a doppler effect as well. The cheers get quieter and lower pitch over time."
] |
[
"The photons we see from the Cosmic Microwave Background comes from when the universe was about 400,000 years old, this was after inflation. Before an age of 400,000 years the entire universe was opaque and photons couldn't travel very far without being absorbed. The only way to understand the universe before it became transparent is to look at non-photon sources like the Hydrogen to Helium ratios or to try to reconstruct what the universe did to come into thermal equilibrium. Inflationary theory is the best attempt to under stand how the universe got into equilibrium and was able to create the Cosmic Microwave Background."
] |
[
"What percentage of Earth's diameter is solid?"
] |
[
false
] | null |
[
"Not sure what you mean by this, but an interesting note on earth's diameter. The highest mountain on earth is 8km, the lowest crevice about 15km that's 23km of up and down. the diameter of earth is around 6000km...",
"If earth was shrunk down to the size of a bowling or pool ball it would be the smoothest one in existence"
] |
[
"haha wouldn't know, you try measure :P"
] |
[
"Everything is more-or-less solid except the ",
"outer core",
". Calculating the solid percentage is left as an exercise to the student. Edit: To be fair, you need to know the total radius (not on the figure) or 6371 km."
] |
[
"Is there an organism that could go extinct and have no repercussions on the ecosystem?"
] |
[
false
] | null |
[
"This was the answer I came looking for. Mosquitoes seem like one of the few species on the planet whose detrimentality exceed their benefits. Aren't there actual efforts to try and bring them to extinction? ",
"Edit: Out of the dozens of replies I've received commenting on the potential environmental impact of the loss of the mosquito, only one has bothered to correct themselves, noting the fact that my comment is in direct reply to an article detailing the insignificance of the mosquito's impact on its environment. Not complaining nor anything else of that nature, just find it fascinating. "
] |
[
"This was the answer I came looking for. Mosquitoes seem like one of the few species on the planet whose detrimentality exceed their benefits. Aren't there actual efforts to try and bring them to extinction? ",
"Edit: Out of the dozens of replies I've received commenting on the potential environmental impact of the loss of the mosquito, only one has bothered to correct themselves, noting the fact that my comment is in direct reply to an article detailing the insignificance of the mosquito's impact on its environment. Not complaining nor anything else of that nature, just find it fascinating. "
] |
[
"a lot of flagship species, that is species that organisations and charities can rally behind as a symbol and to gain support (like pandas for the WWF), are often not very important when compared to other endangered organisms. Also the spotted owl is a good example of a threatened animal that really wouldn't have an effect especially since the reason it is in the decline is the growth of barred owl which fills a similar role. "
] |
[
"If we were able to stand next to the Curiosity rover on Mars while it sang happy birthday to itself, would it sound different than it would sound on Earth?"
] |
[
false
] | null |
[
"The main change would be the fact that the sound wouldn't travel nearly as far, due to the lower atmospheric pressure. I've heard conflicting things about the pitch change, but according to ",
"this",
" article, you'd just sound larger, with a slight high-frequency accentuation due to the reduced air density. For comparison, that article mentions that Venus (with ~92 Earth atmospheres' pressure at mean surface level) would make us sound like bass Smurfs."
] |
[
"Assuming you mean an alien with human-like speech, or a human that can somehow survive lead-melting temperatures and crushing pressures... then I'm not sure about the specifics of the vocal cord structure, but they would definitely sound much higher-pitched here than there. Assuming their voice sounded like ours while on Venus, they'd probably get a serious case of chipmunk voice on Earth, and would have much less vocal projection.",
"Also, they'd die more-or-less instantly from severe decompression, like bringing a deep-sea fish up to the surface - but that's beside the point."
] |
[
"Very, very interesting. Question: what would 'someone' from Venus sound like on Earth? Would their vocal chords be substantially different from ours? How would they react to our atmosphere?"
] |
[
"What's the difference between using a 12V car battery and a 12V duracell battery when powering electronics?"
] |
[
false
] |
[deleted]
|
[
"If you put the two batteries in ",
"series",
" and there is no or minimal resistance between them, then you will get 12V. However, the amps from the duracell batteries will be reduced. Power is Voltage*amps, so depending on the cell size then you can figure out how long you can run the monition (if at all). Car batteries have around 500-800 cold cranking amps (amps at 0C temperature). Lamp batteries have around 26 amp hours. So assuming the car battery has 500 amp hours, it has about 20 times more power than the dual lamp battery configuration."
] |
[
"When you say that a car battery has 500 amp hours, that means that even though the potential of the car battery is at 12V, it has enough material inside it to support 500 hours of supplying 1 amp to a 12V load? So that would be the main difference between a lamp battery and a car battery (both at 12V)? That is, the lamp battery does not have as much material making it up (cells, electrolyte, etc.) so the lamp battery can't supply power for as long?"
] |
[
"Thévenin's theorem doesn't say anything about how actual batteries perform in the real world, it's a way to abstract out some complexity in circuit calculations.",
"If you try to draw 2 amps from a 12v deep cycle battery (pulling that out of thin air), you'll get a sustained 24W-ish output for days (depending on the battery capacity). If you try to draw 2 amps from two lantern batteries in series you'll get a rapidly decreasing amount of power because the cells in those batteries can't handle that current load.",
"For an example, check out the \"constant current performance\" graph of this 6v lantern battery: ",
"http://data.energizer.com/PDFs/529-4D.PDF",
" If you try to get 2A from those batteries (1A each in series) you'd get maybe an hour before you're below 4.8v per battery."
] |
[
"Do post-lead elements retain their unstable-ness even after forming compounds? If so, why?"
] |
[
false
] |
Hi, title really says it all. I tried searching online for an answer but I'm taking my GCSEs next year, and so far my teacher hasn't gone through anything about it as far as I could recall. Could I request that the answer and reasoning be simplified for me to understand? Thanks!
|
[
"Are you referring to stability in terms of radioactive decay? If so, then there is almost no effect on radioactivity whether the atoms are bonded to other atoms.",
"The energy associated with nuclear activity is much higher than that associated with chemical bonding, so the effect of bonding activity is minimal on the radioactivity of the nucleus."
] |
[
"A quick chemistry-based way of explaining it is that radioactivity is almost exclusively a \"nucleus thing\" while chemical bonding is almost exclusively an \"electron cloud thing\". ",
"The stability or instability of a nucleus is a property of the nucleus itself and doesn't depend on other nuclei that may be \"connected\" to it through chemical bonding."
] |
[
"It is likely that the molecule breaks apart due to the decay or does some other chemical reaction afterwards."
] |
[
"Why does hair stop growing?"
] |
[
false
] |
Like why does our arm hair stop at a certain length, same with any kind of bodily hair, even the hair on our head stops eventually
|
[
"Our hair follicles go through growth and dormancy cycles. Basically an anagen phase for growth, a catagen phase to stop growth, a telogen phase for resting (where the hair generally remains intact until growth starts again).",
"All of the hair on our bodies basically grows at the same rate (0.5 inches per month), but the length of the anagen phase for follicles differs depending on where on the body they are. Head hair follicles tend to have a growth phase lasting something like 6 to 8 years (with staggered transitions between the catagen and telogen phases so all your head hair isn't shed at once). The anagen phase for arm and leg hair is quite a bit shorter at a few weeks.",
"Since the growth phase is so much shorter, the hairs are usually very short and get cycled through more often. This means the hair will grow, then the follicle will sit there at rest, then the hair will be shed and it'll start another growth phase. There's usually a bunch of follicles with staggered growth phases so you're basically always growing some hair and always have some resting at full length on much of your body.",
"So arm hair 'stops' at that length because the follicles on our arms and legs have an anagen phase that only allows for about half an inch of growth. Since your head hair can have 8+ years between growth cycles, it can reach lengths of over 4 feet before the follicle sheds the hair and a new growth phase starts.",
"As a random aside: These phases are also why you need to have repeated laser hair removal treatments to truly stop hair growth, since most systems can only get the hair in one phase. You need to keep coming back so you can get follicles that weren't in the right phase before."
] |
[
"Why do arm hairs or embarrassing lip hairs grow and stay blond at the base, but turn dark at the ends, making them more visible."
] |
[
"How does it know when to stop growing? Like if you trim your beard it will grow back to the length it was. Not that I have one worth trimming."
] |
[
"What gives lightning its color?"
] |
[
false
] |
What gives lightning its color? I know that lightning bolts are essentially plasma. So does it have to do with the argon concentration in the atmosphere? Thanks :)
|
[
"Hey that's a good question. I don't know much about lightning, but argon effects will not be enormous because argon is only about 1% of the gas in the atmosphere. Most of the gas is nitrogen, so you would expect nitrogen effects to dominate. ",
"All colors, infrared, x-rays, red, blue, are photons with a specific energy. Green is about 2.5 electronvolts. Red is like twoish. X-rays can have like 100,000. It's a continuous spectrum all the way up to I think where the photons can have so much energy that they create a black hole or something, or nearly 0, where you basically can't detect them. ",
"Those photons are often created by electrons transitioning between energy states. An electron moving from a high-energy state into a lower energy state will release one or more photons, usually just 1 photon that has the energy that the electron lost. If one of your nitrogen atoms loses a weakly bound (i.e. valence) electron, and another electron falls into that hole, a photon is released, maybe with a color that you can see. If a core electron is lost and then filled, then the electron falling into that hole releases a high-energy photon with a color that you cannot see. In equilibrium, the probability of an electron being missing from an energy level depends on the temperature of the gas, you'd have to look into the thermodynamics of gases to understand the likelihood of an energy state being unoccupied for a given temperature. ",
"But, there's your answer. Lightening is bluish-white because it is a very high temperature gas, and electrons are not just transitioning between specific states with fixed energies (like in a laser or light emitting diode) but rather between many states with a broad range of energies. So you get a lot of colors out at once and it looks white. If there are lots of one type of gas and the lightening bolt is very much like a plasma in one gas species, then the lightening bolt can be one color instead of white, e.g. red, because one or a few electron transitions can dominate, like what happens in a neon plasma. ",
"That, along with the emission spectrum from a black body for a given temperature, should be enough to get you started. Have fun!"
] |
[
"Not Argon, but the more common gasses that make up our atmosphere, primarily Nitrogen.",
"I answered this with more depth in this thread a while back so I will cite it instead of pasting the response here: ",
"https://old.reddit.com/r/askscience/comments/c6dgoi/what_gives_the_purple_tint_to_lightning_bolts/"
] |
[
"Color is actually determined by wavelength. Brightness is determined by the amount of radiation"
] |
[
"What varieties of memory are there and how do they work?"
] |
[
false
] |
FormerlyKnwnAsPrince informs me that "There are MANY types of memory, and this skill learning is a specific type of memory called implicit or procedural memory. Long term memory generally refers to declarative memories" This leads me to believe there are several types of memory and not just STM and LTM. In fact I know there isn't, there's another kind of memory before short term that pretty much lasts for a second, the "current" memory, or something. Anyway, what are the main types of memory and how they work? How do they relate to each other?
|
[
"Very detailed question, but i'll take a stab at it. I majored in Neuroscience and am now a first year medical student so I know a fair bit about this but I'm no expert.",
"The cerebellum helps to coordinate movement and accounts for one type of memory. This structure has an extraordinarily repetitive/simple neuronal structure and almost everything that makes your cerebellum different from mine is learned. This type of memory would be active if, for instance, you're a baseball catcher and someone hits a foul ball. You would see the ball coming down and ",
" where to move your glove to get in front of it. This type of memory is going to be important in actions such as throwing a football or texting without looking.",
"The hippocampus is the site of additional memory functions. There are cells in your hippocampus that form a grid, and fire whenever you are in one area of the grid. The hippocampal grid cells are always helping you to localize yourself in 3D. Other hippocampal cells deal with other aspects of spacial mapping. This type memory is very important in knowing where your favorite restaurant is and enables you to walk around your house in the dark without bumping into things.",
"Everything else:\nHere is where it gets complicated. Almost everything else you ",
" is encoded as a representation of the internal state it evokes and in relationship to other things you know. This type of memory is diffusely located throughout the temporal cortex and is processed in the oribitofrontal prefrontal cortex.",
"To illustrate, imagine someone says to me, \"Kim Jong Il.\" Here's what happens in my brain:",
"The words Kim Jong Il are processed by my auditory cortex and converted into meaning. Now this is a ",
" and not a string of words. This gets loaded into my working memory (localized in dorsolateral prefrontal cortex.) It calls up everything I know about Kim Jong Il. I think to myself, \"he is a bad man.\" This is because my ventromedial prefrontal cortex has already associated KJI with negative affect and this visceral emotion (processed in my amygdala) is bound to the ",
" in working memory. Things like North Korea, famine, Kim Il Sung, all get called up secondarily, not directly from my working memory but almost bittorent-like, from the cells that were already activated.",
"This doesn't cover all types of memory, but is as good of a introduction as I can muster. This is as accurate as I can be, but there are still no absolutes in neuroscience. Every day we learn more about the brain!"
] |
[
"Yeah awesome example of how memories are processed differently. This question starts getting at the various ways we recall previously stored info. I remember in one class we watched a documentary video about people who can recall everything they did, every day, prompted just by the date. There's actually a fair number of these people, and in the vid they put them in a fMRI and after the video the professor led our class in discussing what could be happening.",
"So these people with superior autobiographical memory seemed to almost have OCD, but the thing they obsessed about was themselves. It was calming, soothing, relaxing for them to remember bits of their lives. Like, today is Feb 11. One woman in the video would have went through every other Feb 11 she experienced and rated them in order of which year was best.",
"The reason I'm talking about these people is because I feel it's the best way to address your question.",
"When they were put under fMRI, two things were immediately apparent. They had bilaterally enlarged caudate nuclei as well as enlarged medial temporal areas. Two things:",
"Basically, they had an enhanced ability to ",
" the broad, generalized knowledge in their temporal lobes as fitting to the category ",
". When it came time to pull up everything they did on X day, they didn't have to wait for what I called the bittorrent-style secondary activations. Their hippocampi were able to directly activate relevant circuits.",
"IMO, when someone loses autobiographical knowledge only, I would immediately assume there was a problem with classification/retrieval, and all their autobiographical memories are lying dormant throughout the temporal cortex.",
"EDIT: See ",
"here",
" to learn more."
] |
[
"How does autobiographical memory remain distinct from factual memory e.g. how can an amnesiac forget his life but not what a car is?"
] |
[
"Do you know any fun, hands-on, science activities (in any science discipline) that uses commonly found or inexpensive materials?"
] |
[
false
] | null |
[
"See this recent reddit post on askreddit: ",
"http://redd.it/q5jfa",
" -- lots of ideas here."
] |
[
"I do a DNA extraction with school groups that uses household things. It is normally done with strawberries, but I'm sure that any fleshy fruit could be used. Here's how it works:",
"Materials:\n* Lysis buffer (900 mL water, 100 mL shampoo, 2 tsp salt)\n* Ice cold ethanol (we use everclear and it must be ice cold)\n* Ziploc bags\n* Coffee filters\n* Plastic cups\n* Fruit of choice",
"Procedure:\n1. Mash fruit in ziploc bag. The more it is mashed the more DNA you get. Talk to students about mechanically destroying tissues and cells.\n2. Add 10 mL lysis buffer and mash this in the bag. Talk about chemical lysing of cell membranes.\n3. Filter liquid from solids using coffee filter and suitable vessel. We use plastic cups to collect the liquid (this usually takes about 20-30 minutes). Discard solids.\n4. Slowly pour liquid from step 3 into ice cold ethanol.\n5. Watch as a \"snotty\" layer seperates into the ethanol. This is the DNA.",
"After writing that I realized that I have no idea what materials we have in the States that are taken for granted, but hopefully you can get your hands on some suitable replacements."
] |
[
"I worked in a lab on a university campus taking ",
" down to just DNA, and these are pretty much the important steps."
] |
[
"Are you able to target a specific element in a compound using EM waves at a resonate frequency of that atom?"
] |
[
false
] |
If so, how would if effect the atom? I have a hunch that it'd either heat up or release an electron. Just thought there would be many interesting applications for such technology.
|
[
"An electron in an atom resides in an atomic orbital. However, if the atom is part of a compound, the electron will reside in a ",
" orbital - meaning that being in a compound changes the energy landscape of that atom.",
"What this means is that you're now looking at the ",
" to absorb a photon, as opposed to any particular atom. While it is true that you ",
" use photons that happen to match energy level transitions of a specific bond in the molecule, you are no longer exciting or ionizing an ",
".",
"In terms of using particular wavelengths of light to excite a molecule, that's the entire basis of spectroscopy, be it UV-vis, IR, microwave, NMR, etc. So in a way, you are probing for the type of atoms that exist in the compound."
] |
[
"Microwaves work via dielectric heating, not any resonance coupling with water. Water just happens to be both ubiquitous, quite polar, and mobile as to respond strongly to the changing electric field."
] |
[
"I'm pretty sure that that's how microwave ovens work. The wavelength of the microwaves has been selected to excite the water molecules in food."
] |
[
"Tissue rejection in the case of limb/organ transplants. Can someone explain to me how tissue rejection is overcome, ultimately, in the case of transplants? Do they take anti-rejection drugs forever? Does the transplanted limb or organ ever become genetically identical to the recipient's?"
] |
[
false
] |
Excerpt from article: Marrocco is taking anti-rejection medication, which can lead to side effects like infection and organ damage. But he's received an infusion of the donor's bone marrow cells to further prevent rejection of his new arms. That infusion allows him to take only one anti-rejection drug instead of the usual three-drug cocktail. So, what's the ultimate result? Does the body eventually accept the foreign tissue on its own and the need for meds ends? Or does the tissue eventually become part of his own? When the cells die and are replaced, do they have the donor's DNA or the recipient's DNA? Will the arm ever become genetically identical to the recipient's?
|
[
"There are several types of transplant rejection. Let's review them!",
": This occurs immediately after the transplant. It's a type of hypersensitivity reaction (type II, or antibody-mediated, to be specific), which occurs because the recipient already has antibodies against the donor tissue. This occurs, for example, against improper ABO blood transfusions. The result is that the grafted vessels become blocked, which leads to the death of the graft. The graft itself will become cyanotic or mottled.",
": This happens 1-4 weeks after the transplant. This is a cell-mediated response that happens because cytotoxic T cells are reacting to foreign MHC complexes. This can be reversed with immunosuppressants, such as cyclosporine or muromonab-CD3. If it isn't reversed, it results in a vasculitis (vascular inflammation) of the graft vessels with dense interstitial lymphocytic infiltrate, i.e., lots of white blood cells in the tissue.",
": This occurs months to years after the transplant and is caused by self cytotoxic T lymphocytes thinking that Class I MHC-nonself is actually Class I MHC-self presenting a foreign antigen. This miscommunication is irreversible and results in T-cell and antibody-mediated damage to the vessels called obliterative vascular fibrosis. In essence, the graft tissue and its vessels become scar tissue.",
": Graft-vs.-host disease is when the transplant is rejecting the host, not vice versa as in the previous examples. The onset of this condition is variable, but it happens when CD4+ and CD8+ T cells from the donor tissue attack the immunocompromised recipient. This causes rash, jaundice, hepatosplenomegaly, and diarrhea. It's most common after bone marrow or liver transplants because these tissues normally contain numerous lymphocytes."
] |
[
"Best response IIT. I would like to add to answer the OP's questions:",
"tissue rejection is overcome with immunosuppressive drugs. These drugs act mainly on T-cells and NK cells that recognize host from foreign.",
"Yes, transplant recipients are an these drugs indefinitely. ",
"No, the transplanted organ only receives nutrition from the host, it replicates its cells using its own DNA and will do so for the life of the transplant."
] |
[
"i'd like to point out that the body may initially accept a transplant, but it may reject it sometime in the future (months to years) via the indirect pathway of chronic rejection. Foreign dendritic cells will travel to secondary lymphoid tissues (lymph nodes), where they will eventually undergo apoptosis. cellular fragments from the foreign DCs are taken up by self DCs, where they are expressed to appropriate T cells for immune activation and antibody production, leading to rejection of the graft. preventing chronic rejection of the graft is very difficult; the drugs used for acute and hyperacute rejection don't work in this case. this is why HLA matching is so important for some transplants.",
"but for your question, hyperacute rejection occurs via humoral immunity, or the antibodies already present in the blood. these antibodies normally bind the foreign antigens and initiate inflammation and rejection. acute rejection occurs via T cells activated by foreign DCs expressing different HLA allotypes. anti-rejection drugs taken for some time after the rejection will prevent inflammation (steroids inhibit NFkB and various pro-inflammatory cytokines), inhibit leukocyte proliferation (azathioprine inhibits DNA replication), and block T cell signal transduction (cyclosporin A blocks production of IL2). there are also other drugs being used. ",
"after a short amount of time, acute rejection decreases as foreign DCs from the graft are re-populated by self immature DCs. initially, these foreign DCs would activate T cells and create a strong inflammatory response (acute rejection), but the drugs prevent this. With time, these foreign DCs die, inflammation of the organ drops, and antibody levels in the blood decrease. this will take many days, depending on the person. Immature DCs lack the proper co-stimulatory complexes necessary to activate T cells; they must express an HLA:antigen complex and travel to secondary lymphoid tissues before becoming mature DCs able to activate T cells. ",
". But the decline in the direct pathway usually yields to a rise in the indirect pathway of rejection",
"sources: ",
"http://www.ncbi.nlm.nih.gov/pubmed/12216939",
", my textbook"
] |
[
"I am a traditional photographer and have a solution of Ferrous Sulfate for development. If I dilute it, will its shelf-life be reduced?"
] |
[
false
] |
For full disclosure, I know next to nothing about chemistry. I'm in a remedial course this semester, but most of it is going over my head. HOWEVER, I'm using the Wet-Plate Collodion process to make photographs, and a lot of the chemicals used in the process are strange and bizarre to me. I've looked over my notes, googled endlessly, and I'm still unsure of an answer to this question. What I'm concerned about is if I dilute my Ferrous Sulfate solution, which is a developer, will it still be reliable over a good amount of time (i.e., months) to do all that chemical reaction hoo-hah so that it can give me a developed photograph? It might be worth noting that for processing, I already dilute the solution 1:3 with tap-water, but I throw it out at the end of every session. Most other developers, whose chemistry I am ignorant of, exhaust when left out in the air within a few hours. I've heard that oxidation is the primary culprit; if I store the diluted solution in an airtight container, will it be alright? Terribly sorry if this isn't the right place, but it's an awfully obscure question to ask . I figure since I'm working with chemicals, chemists might be able to answer my question! Apologies if this is worded weirdly or confusing.
|
[
"Also try cross posting to ",
"/r/photography",
". It can't hurt. "
] |
[
"Any exposure to oxygen will hurt you here. Obviously an airtight container is a must, but water itself has a substantial amount of dissolved oxygen (this is how fish breathe under water) so you are certainly going to reduce the shelf life by diluting it. Perhaps not by much, the easiest way to determine this would be to test it. ",
"Why do you want to dilute it in advance?"
] |
[
"If you put it in an airtight container, it will oxidize very slightly from the oxygen trapped between the bottom of the lid and the surface of the solution, but once that oxygen is exhausted it will be stable."
] |
[
"Do scientists have the capability to integrate \"upgrade\" capabilities into spacecraft years after they launch?"
] |
[
false
] |
Since missions for spacecraft take years to begin collecting data from launch to target, the technology aboard the craft is only as up-to-date as it was prior to launch. In the years following launch, there could be so many advances and breakthroughs which could have been a better option for the mission. Do scientists have the ability to program upgrades, either through sending information to reconfigure systems, or is it stuck with what it was originally built with?
|
[
"Although that would be cool to be able to send updates and patches to spacecraft, unfortunately it cannot happen. Much of the way data is collected depends on the physical instruments. Luckily, our analysis and collection tools on Earth can easily be upgraded. For example, to boost the signal from Voyager, the satellite dishes that collected the downlink signal were made larger on Earth. However, the data actually collected cannot be improved because an instrument such as a spectrometer cannot be improved upon in a non-physical way. There isn't really a way to send a piece and install it onto a spacecraft traveling away from Earth, because our propulsion systems haven't advanced much, with most the spacecraft's speeds coming from gravity assists, so a second spacecraft would take a LONG time to catch up, and thus it would just be easier to send an upgraded spacecraft.",
"Interestingly, there have been instances of physical upgrades to spacecraft. Besides the ISS being put together, the most famous is probably the Hubble telescope. Back when it was first launched, the mirror wasn't the correct shape, resulting in bad pictures. There were a series of missions where astronauts physically put in extra parts to fix it, which had to be super meticulous, but it was successful. Hope that helps!"
] |
[
"Although that would be cool to be able to send updates and patches to spacecraft, unfortunately it cannot happen. ",
"Wasn't there a craft that had an issue with its transmitter after launch which meant sending back full resolution pictures would take way too long, so they upgraded/changed the software to use some sort of gif type compression, which wasn't originally written into the crafts software?"
] |
[
"Thanks so much for taking the time to explain. I see it I terms of how I work in graphic design. If the client doesn't provide images that are high enough resolution, there isn't much I can do to sharpen them, even with the latest editing software. "
] |
[
"Combining Light for a specific wavelength?"
] |
[
false
] |
Greetings AskScience, I was wondering if you could explain what happens when you take 2 coloured light sources, and combine them for a different perceived colour. Take using a Red and a Blue LED and ending up with a Purple/Violet colour, or using an RGB LED with a Red and Blue die. What I guess I am getting at, is this. Is it possible to use something like an RGB LED to output at any single wavelength I want, and would something like a Plant be able to differentiate each wavelength that makes up the "resultant", or would it see 2 separate wavelengths and I would need an emitter that outputs at the specific wavelength I need? They don't make LEDs in every wavelength, and I want to do some botany/electrical/lighting experiments on Arabidopsis Thaliana.
|
[
"Thanks for the info. I will have to figure out a way to generate a variable frequency. I am wondering if maybe using a white light source, most likely something like a Halogen, and then using something like a colour filter wheel would work.",
"As for the nonlinear thing, is that an example of say firing a red laser beam into a specific element crystal rod and getting a green beam out or something like that?"
] |
[
"Long story short, you need the exact emitter.",
"Pretty much every optical system you're likely to encounter in day-to-day life is linear. Linear systems preserve frequency: if you put in a 500 THz sine wave, you get out a sine wave at 500 THz and only at 500 THz. Send in both 600 nm and 520 nm light, and out will come both 600 nm and 520 nm, dimmed or brightened in different amounts depending on wavelength (frequency). So 'combining' light, even when passing it through glass or some other material while you're doing so, isn't going to make new wavelengths, different from those you put in. (There are exceptions to this; they involve 'nonlinear optics' and afaik don't see much use outside of labs at the present time.)",
"So why do you see different colors when you look at a combined red+blue beam? It's because your eyes are shitty detectors when it comes to frequency. They have lots of cells essentially 'aimed' in various directions, so you can tell pretty well where a photon came from based on which cell it hit. But you really have no good way for determining the energy (frequency) of that photon. What ends up happening is there are three types of cells and each type will only respond to a ",
"particular range of wavelengths",
" -- without actually keeping any more data than \"",
"\". Your brain then takes a bunch of data from these cells, says \"*oh hey, we're getting a lot of reports from cells that detect between 500 and 650, barely anything from the cells from the cells that detect 500-600, and tons from 425-475. Color that purple!\".",
"This",
" is a rough chart that shows what colors you perceive based on what's coming in. If it's on the 'horseshoe' that makes up the outside border, it's a single wavelength hitting your eyes. If it's in the middle area, it's some collection of wavelengths, which isn't uniquely identifiable -- a mix of equal parts 490 and 560 hitting your eyes will look the same as 3 parts 500nm to 1 part 700nm."
] |
[
"Yeah, a white-light source and some sort of filter is the easiest and most versatile way to generate a good variable-wavelength source. A ",
"diffraction grating",
" working as part of a monochromator gives you the most control. If you can get a nice large grating, then the rest of the monochromator basically consists of two slits, one to limit what angle the incoming light hits at, and another to limit what section of the resulting 'rainbow' comes out. I don't think it should be too terribly difficult to get a decent grating, but absorbing filters (essentially colored glass) are certainly also an option, though it's harder to know what exactly is getting through with those. I guess if you're really on a budget you could even rig up a CD or two as a poor man's grating. In any case, remember to measure the amount of light coming out the plant-facing end of your lightsource, since your white-light likely isn't going to be uniformly bright across all wavelengths.",
"And yeah, I actually completely forgot about green laser pointers! There the nonlinear effect creates harmonics at integer multiples of the driving frequency (1064 nm -> 532 nm in this case), and the remainder of the original frequency (in the IR actually) is filtered out."
] |
[
"Why does someone get more drunk if they don't eat beforehand? Even if the food \"soaks up the alcohol\", assuming the same amount, wouldn't all the alcohol still get absorbed by the body?"
] |
[
false
] |
Of course, I would love to see studies and maths and other such explanations behind this. Also anything about eating after drinking alcohol is also helpful to answering the question.
|
[
"Peak concentration is not solely related to bioavailability but also to rate of absorption."
] |
[
"Alcohol is also eliminated from the bloodstream more quickly when food is eaten.",
"Source"
] |
[
"That kinda makes sense. So it's not the total amount over x period of time, but amount over x time divided by absorbtion rate?"
] |
[
"How can Einstein's theories be used to predict the orbit of Mercury?"
] |
[
false
] |
[deleted]
|
[
"I think what you're getting at is that Newtonian gravity didn't correctly predict the ",
"precession of the perihelion of mercury",
"'s orbit. And General Relativity did correctly retrodict the measured value."
] |
[
"Yes. A lovely word. Particularly as we do invent theories that ",
" make predictions of measurements had those measurements not already been made. "
] |
[
"retrodict? ",
"Is that word in common usage in physics? I've never seen it before. Quite a useful word though."
] |
[
"How many different antibiotics are there?"
] |
[
false
] |
I have wondered this for quite some time: How many different antibiotics are there that I can theoretically "switch between" if I develop a resistance to one of them. I know there is a on Wikipedia. Can I count every single one on there as an alternative? Is the resistance dependent on how they are grouped ? Also, is there a limit as to how many antibiotics can be developed? Or is it just a matter of effort being put into research?
|
[
"How many different antibiotics are there that I can theoretically \"switch between\" if I develop a resistance to one of them.",
" resistance is not what you need to be concerned about, it's the bugs'. You can pretty much look at each of the classes there and say that a bug that's resistant to one of those drugs is resistant to the rest of the class. Generally.",
"But not all antibiotics affect all bugs the same way or even at all. There is more genetic similarity between you and a a fruit fly than there is between some pathogenic bacteria. Remember we are talking about a hugely diverse group of organisms here.",
"As for a limit....I wouldn't rule out the possibility of there being a limit, but whatever it is we are nowhere near it. All we need is a required mechanism that is different enough from anything we have. And there are a lot of those.",
"New antibiotics generally aren't researched because there's no money in them. The research is done at the academic level, but the drug companies just can't make much money off of them, and they are the ones that have to put out the major cash to get by phase trials for FDA approval."
] |
[
"Some are, some aren't. I'm working with a startup to develop an antibiotic right now, but it's not for phase trials. Even if we get the next round of the grant, which is roughly 8 times what we got for the first round, it's nowhere near enough to run phase trials. They are expensive, time consuming, and risky. And the profit margin just isn't there; no incentive."
] |
[
"Do the drug companies not get given grants by the government if they're in low demand, a la if they were developing an orphan drug?"
] |
[
"How much can DNA tell about a persons ancestry?"
] |
[
false
] | null |
[
"Mitochondrial DNA is often used as an ancestral lineage tracer in that is is inherited solely down the maternal line. Upon formation of the zygote, male mtDNA is ubiquitin tagged and subsequently degraded within the cell. This means that, bar random mutation, your mitochondrial DNA should be a perfect replica of your mother's. ",
"As such, tracing a maternal line is relatively simple due to the fact that it is not \"clouded\" by meiotic recombination. "
] |
[
"This means that, bar random mutation, your mitochondrial DNA should be a perfect replica of your mother's. ",
"This is actually a pretty huge assumption, too. mtDNA lacks typical repair mechanisms and is, therefore, more prone to mutation than nuclear DNA. The reason mtDNA is so great for tracing lineage is because there is no recombination between the mtDNA of different individuals - it all comes from one individual."
] |
[
"Which grandmother of two, great-grandmother of four, etc.? Oh, never mind, I see what you're saying. It's always from mother to mother, so all of the mtDNA of the mothers who produced the boys in all of the past matings was lost in your matrilineal line. It's only conserved if they produced girls, and only if those girls produced girls, and so on."
] |
[
"Was the salinity level of the ocean the same during the eras of the dinosaurs?"
] |
[
false
] |
I found an article claiming it was twice as salty but it was from the daily mail so I'm not taking that on faith. Do we know how the salinity level of the ocean has changed over the last 200 million years? Has it remained relatively constant, has it slowly increased or decreased? Do we know if major specific (relatively) rapid changes ever happened?
|
[
"Do we know, yes, and with some accuracy. Evaporites (does what it says) provide a snapshot of salinity. The percentage salinity varies from a maximum of about 5% 300mya to around 3.5% today. It has both increased and decreased during that period, the main driver being glaciation effectively removing water from the oceans.",
"The key driver in oceanic salinity is glaciation"
] |
[
"Fascinating, thank you"
] |
[
"It’s an interesting thought isn’t it? The Earth is over 4 billion years old, so why aren’t the oceans completely saturated with salt? ",
"There are two main sources of oceanic salinity, erosion and tectonic. The latter consisting mostly of deep sea vents out gassing chlorine and sodium. However, the rate of addition is balanced by a number of processes. The following subtract salt from the oceans: the creation of evaporites, reaction with deep sea basalts, and burying by tectonic activity. The rate of addition and subtraction are in balance. Sometimes one will be favoured, sometimes the other, but always in approximate balance. Such a system is known properly as a ‘dynamic equilibrium’, and perturbation of natural dynamic equilibria is generally thought to be a fundamentally bad idea."
] |
[
"How are genes for disease resistance in plants identified and extracted for use in crop plants?"
] |
[
false
] | null |
[
"While I cannot speak for disease resistance in particular I can speculate that it follows a model, much as has been done in the search for genes that can make crops drought resistant. In which he model species Arabidopsis thaliana is used, picked because it is itself drought resistant. The plants genome has been sequenced, and much work done in investigating it's response to physiological stressors. Genes were compared to those found in non-drought resistant species, as well as looking for genes that were up-regulated in water poor situations, these genes were then isolated, tested in various manners.",
"I believe if I remember correctly many of the pest resistant crops were made by genetically engineering a BT toxin system into the plant so that pests were killed, or by altering the BT toxin system so that previously impervious pests became susceptible.. it has been a long time since i read papers on this specific subject, but this should give a simple idea into how candidate genes are identified. For more on specifics i would suggest using google scholar and looking ino both arabidopsis and BT toxins."
] |
[
"Well you don't at first, this is where testing is done. ",
"The gene is isolated, using PCR and specific primers, and then transferred into a plasmid (a piece of non-genomic DNA used by bacteria) which is then put into a specific bacterial species called agrobacterium which then transfects the DNA into a plant. a specific portion of the plasmid is inserted at random into the plant, usually one thing included is a resistance cassette, we can then put a chemical in the growth media that will kill all cells without the specific resistance we choose. And a specific expression promoter is chosen as well so that the gene will be expressed in our new plant or expressed at a specific time. We then grow against controls and see if the plant is more or less resistant.",
"We can also do tests in the original plant where we knock out specific genes and see if the particular resistance we are looking at is lost."
] |
[
"Genes for disease resistance can be roughly split up into three classes based on the proteins that they encode: Pattern recognition receptors (PRRs), Signalling Components (SCs), and Transcription Factors (TFs). PRR genes (also called R-genes, for Resistance-genes) encode receptors that are localized at the cell-surface as well as within the cell, which recognize pathogen compounds such as bacterial flagellin (flg22). The protein becomes activated, and interacts with SCs, which act on TFs, initiating all sorts of defence responses such as the production of reactive oxygen, thickening of cell walls, and deliberate cell death at the site of infection. This is the result of TFs binding to DNA and influencing the expression of other, defence related genes.",
"Identification:\nDefence related genes of either class can be identified by creating a large amount of plants in which randomly genes have been switched off, then infecting them with a pathogen. The plant variants that show most symptoms of disease are taken to the lab, where their genome is analysed and the gene which was switched off is identified. Alternatively, by accessing the entire sequence of a plant's genome, one could look for genes which have a high similarity to genes of which you already know they encode defence-related proteins, switch them off, and see what happens if you then infect those plants.",
"Extraction and use in crop plants:\nExtraction of a gene is usually done by PCR. This method needs a vial of water which contains the DNA that we want to extract. We can make this by grinding a piece of plant that is known to contain the gene. PCR is then performed, which is a chemical reaction that copies a specific stretch of DNA millions of times. The components (primers) used in the PCR reaction can be selected so that only the target gene is amplified. The DNA containing our gene is present in high concentration, now, which enables purifying it, sticking it into a circular DNA backbone (vector) for storage, and keeping it in the fridge for whatever you want to do with it.",
"Currently, most plant pathology research that aims to create transgenic plants which are resistant to a specific class of pathogens do so by inserting one or more known PRR genes. These genes encode the PRRs which are responsible for initial detection, whereupon signalling and defence responses can take place. Inserting a signalling component or transcription factor has little use when detection fails in the first place. With any luck, the newly inserted PRR is able to latch onto the existing signalling components in the crop, which adds resistance. If not, some other required genes may have to be added, as well. But the necessary components are not always known; hence plant pathology research is investigating this for loads of PRRs as we speak.",
"Source: graduate student in molecular plant pathology"
] |
[
"How NASA chooses where to point Hubble?"
] |
[
false
] | null |
[
"For Hubble (and just about any other telescope), time allocation - and hence the targets observed - is based on proposals by the astronomical community. These are submitted in response to a \"Call for Proposals\".",
"Each proposal must justify why the requested observations are worth doing, and also that the expected result can be achieved using the proposed technique/instrument/observing time. A telescope allocation committee (TAC), made up of a selection of scientists from working in astronomy, review the proposals and allocate time to those which are judged the best. This process usually happens twice a year, although it can vary between telescopes/observatories (Hubble time allocation occurs on an annual basis).",
"In most cases, it is also possible to request a small amount of observing time at short notice, either to follow up especially interesting recent discoveries (perhaps the discovery of a very interesting planetary system), or to observe an unusual event that is occurring somewhere in the universe (e.g. an exceptionally close or unusual supernova).",
"There are also further complications to time allocation due to long-term projects, or with time allocation being divided between countries/institutes who contribute to funding.",
"This news announcement",
" (simply the first result on Google) gives some details of the Hubble time allocation for Cycle 21 (October 1 2013-September 30 2014). In total, 1094 proposals were submitted, requesting 6 years of observing time for a period only lasting a year! Oversubscription factors of several hours requested per available hour are normal for most large facilities. The TAC consisted of 137 astronomers, with the requirement that 15% of time was allocated to the European Space Agency in return for their contributions.",
"The results of time allocation are generally public, even if the exact details of the observations are kept confidential for some time. The allocations for Hubble in Cycle 24 can be found ",
"here",
", with previous cycles listed ",
"here",
".",
"If you want more details, there's plenty of results on Google if you use terms such as \"Hubble Time Allocation\" or \"Hubble Call for Proposals\"."
] |
[
"NASA delegates the job to the ",
"Space Telescope Science Institute",
" (or STScI). It's an organization formed from various Universities. They have a governing structure and whatnot. Anyway, astronomers make various proposals on research to be done with Hubble and then those are reviewed, judged, and prioritized. Then all of that is used to create an actual observing schedule for the telescope. It's very similar to the way observing time on any major observatory works. As you might imagine there is a ",
" of complexity underneath everything and striking a balance on what to observe is always a challenge because there's much more demand for Hubble time than there is actual available observing time. They plan a year's worth of observations at a time, so that they can be reactive to changing astronomical needs year over year. One of the big things they're looking at in the near term is the JWST (which the STScI will also control) and trying to coordinate cooperative observations between both telescopes for improving science return as well as helping to calibrate JWST."
] |
[
"Thank you so much for your answer, this was really clarifying. :D"
] |
[
"Is it possible to make metallic hydrogen on earth?"
] |
[
false
] |
I am just wondering if it would be possible to make metallic hydrogen on earth, or is this beyond our capabilities right now? If so are we close? I read that metallic hydrogen would be a good alternative fuel, as the only by product would be water.
|
[
"Hydrogen is the simplest element, consisting of one proton and one electron. In atomic form, the electron is in the simplest atomic orbital, the spherically symmetric 1s orbital, the only orbital in which the wave function can be calculated exactly analytically. Hydrogen is the most abundant element, accounting for approx. 75% of the universe’s mass. At terrestrial temperatures and pressures, hydrogen tends to exist as a stable, colourless, diatomic gas. ",
"At more exotic temperatures and pressures, hydrogen can exist in other phases, as shown by James Dewar in 1899 when he first isolated solid hydrogen [1] by decreasing the temperature of molecular hydrogen below it’s melting point (14.01 K). The phase diagram for hydrogen is very complicated and there are several different phases within the solid phase, which are hard to discern as solid molecular hydrogen does not respond well to x-ray crystallography [2], however, using reflection electron diffraction, it has been shown that hydrogen in this form exists in a crystal lattice structure [3]. ",
"It was theorised in 1935 that although solid hydrogen has a large band gap and as such is an insulator, that given high enough pressure the conduction and valence bands could be ‘pushed’ closer together. The intramolecular distance between hydrogen atoms in this phase is 0.75 Å and the intermolecular distance between hydrogen atoms is 3.3 Å. If the lattice is compressed (i.e. placed under extreme pressure) then the intermolecular distance is reduced until the lattice resembles a simple lattice and it was theorised that at this point, the material would exhibit metallic properties [4]. This transition would come about with several measureable physical changes, the hydrogen would now be able to conduct electricity and would have a higher density. Moreover, it has been predicted that not only would metallic hydrogen be conductive, it would be a super conductor [5]. ",
"It is thought that metallic hydrogen may be like diamond in that although it requires a high energy environment to be formed it may be metastable at a range of temperatures and pressures, meaning it could be used in applications as a high temperature superconductor [6]. Metastable metallic hydrogen has also been suggested as an efficient rocket fuel due to its high density of hydrogen and the amount of energy stored in the crystal lattice [7]. The phase of metallic hydrogen has been heavily debated and interestingly, theoretical studies have suggested that metallic hydrogen will be a quantum fluid, because of atomic zero-point vibrations [8]. This is also where the superconducting properties of metallic hydrogen come from, as a quantum fluid has superconducting properties [9].",
"For many years studies of metallic hydrogen were confined to theory as it was calculated that metallisation of hydrogen would require pressure in the order of megabars, much higher than the current technology could manage. The first metallised occured in 1995 by shocking liquid hydrogen with a gas gun originally designed to test ballistic missiles [10]. This gas gun can create pressure in the order of mega bars, sufficient to metallise hydrogen. Whilst the hydrogen was subjected to these high pressures, the resistivity was measured and at approx. 1.4 megabars the resistivity dropped significantly, to a value typical of liquid metal. Up to the point of metalisation the resitivity drops exponentially, showing that the hydrogen passes through a semiconducting supercritical fluid phase. As a result of using a gas gun to ‘shock’ the hydrogen to create a high pressure environment, the experiment was carried out at approx. 3000 K, far too high to be of practical use. ",
"Another method of applying pressure to hydrogen is using diamond anvil cells, which use flawless diamonds as anvils that are pressed together to create extreme pressures. Diamond is used for its hardness and also for its optical accuracy allowing experimenters to view the opaqueness of the sample and take a Raman spectrum in addition to measuring the resistivity of the sample. This method has some issues however, when super pressured hydrogen comes into contact with diamond, it infiltrates it and the diamond becomes cloudy and brittle, breaking very easily [11]. This problem was addressed by Eremets and Troyan in 2011 by coating the diamond in a thin layer of sputtered copper or gold, such that the diamond is still optically accurate and has no Raman activity, but the hydrogen and diamond never come into contact [12]. This method has another advantage in that it can be carried out at any temperature. The experiment appeared to be successful as their results showed a drop in electrical resistance as pressure increased, as well as photoelectric activity characteristic of metal. At this point, the sample also became opaque and the shift in the Raman spectrum was characteristic of a metal, rather than hydrogen. This result was surprising, as the metallisation appeared to occur at pressures much lower than previously expected. Subsequent studies of first-principles metadynamics simulations have provided support for these claims, showing that metallisation can occur at pressures much lower than was originally thought [13]. ",
"Although this experiment gave very promising results, it was not without its criticisms. For each result reported by Eremets and Troyan, there is at least one rebuttal, claiming that their results can be explained by phenomena other than metallic hydrogen. The sample becoming opaque can be explained by hydrogen reacting with the metal coating on the diamonds; the reduction in resistivity can be explained by deformation of the anvils and the electrodes shorting out; the change in the Raman spectrum can be explained by increased background [14-16]. In addition, Eremets and Troyan reported that electrical resistance increases as the temperature drops, a result contrary to the regular behaviour of metals [14]. Strong arguments can be made for both sides and as the research is still very new, not much can be said conclusively. That said, this experiment may have created metallic hydrogen and at the very least has opened up a new avenue for future research to use in the quest of understanding the different phases of hydrogen.",
"The pressures involved with metallising pure hydrogen are impractically high, current methods of creating high pressure environments are confined to the realm of research. For more practical methods of creating metallic hydrogen, research is being undertaken to find ways lowering the pressures required for metallisation. One method is to dope the hydrogen with an electropositive element, such as lithium. LiHn materials are predicted to become stable and metallic at approximately one quarter of the pressure required for pure hydrogen, with the most stable of these, LiH6, being predicted to be super conducting [17]. Another avenue of doping being explored is using silane, SiH4, in conjunction with molecular hydrogen to also lower the pressures required to form metallic hydrogen by forming a lattice in sheets, similar to graphite [18]. In addition to doping, there is promising research that shows that application of an electric field to aid nucleation could also reduce the pressures required [19]. This research also suggests that this method may create metastable metallic hydrogen once removed from the external field and the high pressure environment. These methods show promise of being viable methods of economically creating metallic hydrogen. However, this research is very topical and currently none of these have been tested experimentally. ",
"Much of the research into metallic hydrogen has been motivated by a want to explain what is happening in the interior of the Jovian planets. The make up of these planets is largely hydrogen and because of their size the pressures in the interior of these planets is very large, this naturally suggests that their interiors are made up largely of metallic hydrogen. Research into this has given evidence that water/hydrogen interface is not favourable, giving evidence that there is no distinct boundary between the mantle and the core of Jupiter [20] and provides an explanation for the origin Jupiter’s large magnetic field [21]. As hydrogen is also a major component of stars, the study of metallic hydrogen can give an insight into stellar building blocks. An understanding of the properties of metallic hydrogen and the structure of its phases gives implications to a wide array of stellar physics. The compressibility of metallic hydrogen is dependent on whether the structure is body centre cubic or layered packing and depending on this, our understanding of the physics of the photosphere could drastically change [22]. "
] |
[
"References: "
] |
[
"I did a project on this and there has been a few claims of creating metallic hydrogen over the years. These use methods which should produce the pressures required for metallic hydrogen. The problem is when you are dealing with such high pressures, there are lots of things that can go wrong to give false positives. ",
"You are right in thinking that metallic hydrogen would be a brilliant fuel source, but manufacturing it seems to be too energy intensive at the moment."
] |
[
"Why are humans the only creatures (to my knowledge) that care about covering up with clothing?"
] |
[
false
] |
From some light research it's easy to tell that humans are the only creatures that wear clothing to cover their bodies up almost completely. Why is this? There are times when it can be cold, and wearing something warm is better, but a time ago, I'd imagine people simply didn't care. What changed, and why did we change? Thanks.
|
[
"Yeah, pretty much.",
"Clothing was originally just for warmth but eventually we got the idea in our heads that covering up was appropriate. Its not a natural feeling though. If you took a child and raised it in a naked environment (like parents raising a child nudist) they would have no bashful feelings about nudity.",
"Ite entirely based on society. We have created this social law that clothing is needed and if we break that rule (outside of sex or bathing or etc) then we should feel bad."
] |
[
"No other vertebrates habitually wear clothes, as far as I know. ",
"But there are examples of invertebrates creating or using things in the environment for shelter and cover. Whether they 'care' about it or not is another question.",
"The best known is probably the caddis-fly larva, or the hermit-crab; but arguably the silk cocoons made by spiders and other arthropods for moulting or egg protection could be seen as a form of clothing, as could even the shell of a mollusc."
] |
[
"I read somewhere that even the children of nudists go through a phase where they want to cover up their bodies, related to puberty. The shame they feel seemed to be coming from the children, not society. Can you expand on this?"
] |
[
"When a geological event is \"overdue,\" does it actually have a higher chance of happening soon, or does that conclusion come from a misunderstanding of statistics?"
] |
[
false
] |
People will say things like "that volcano is overdue for an eruption" or "California is overdue for an earthquake." what exactly does that mean? Does the probability of an event continue to increase over time, or is it a gambler's fallacy--they assume that because it hasn't happened for X years, and it on average happens every X-1 years, that it must happen soon, whereas in reality it's independent of previous eruptions? Thanks for your answers! TL;DR for most events (earthquakes, volcanoes), there seems to be a consensus that the event becomes more and more likely as stress/pressure builds up; the system is dependent on time elapsed. A couple questions have asked about the case of magnetic pole shifts. I've always thought this was a cyclical event, but could we get an expert opinion on the idea of being "overdue" for a pole shift?
|
[
"Yes ",
" no. You're quite right that, when scientists talk about something happening \"on average every <foo> years\", they are implying a model of uniform, time independent probability - so \"overdue\" just means that it's been longer than the average since the last one. ",
"But some geological events (like earthquakes) do ",
" have time-independent probablities. California's earthquakes are releases of built-up strain (and stress) as the crustal plates slide over each other (and catch at corners and such), so \"overdue\" implies that there's more strain (and stress) than usual in the fault. Hence an overdue earthquake is more likely on a day to day basis than is a not-yet-due one.",
"Edit: stress/strain. Thanks, syds, pokeyhokie, and venividivixi."
] |
[
"As a general trend, yes. But specific earthquakes are all over the board, of course. It depends on exactly what moves against what, releasing strain where.",
"These types of prediction are very complicated. For example, Hollister, CA (east of Monterey Bay, about 100 miles south of San Francisco) hasn't had a large earthquake in a very long time, which is surprising considering that it contains the fastest moving slip fault in the world (it's worth driving through town to see it, by the way -- it is continually ripping peoples' houses apart). Since the fault slips all the time, in a gazillion very tiny earthquakes more like a constant \"grind\" than a large \"pop\", there isn't much strain to release. But places like Hayward (east SF bay), that have an obvious fault and not much slippage, are more likely in trouble."
] |
[
"Follow up question. ",
"Will 'overdue' quakes be of higher intensity due to more potential being stored?"
] |
[
"How would life look like if Earth was 10% bigger"
] |
[
false
] | null |
[
"10% higher gravity",
"This is not necessarily true, and depends heavily on how the mass is distributed, how the increase in mass compares to the increase in diameter, and so forth. A bigger planet could theoretically have equal or even less gravity at its surface, as we are further away from the core/bulk of the mass."
] |
[
"Yes, but the answer is wrong. Surface gravity with respect to earth is expressed as g = m/r",
"A planet 5 times the mass of earth, with a radius 150% of earth's, would have a surface gravity of 2.2 times as strong as Earth's, not 5 times. ",
"g = 5/(1.5",
" = 2.22",
"There are more variables at work than simply \"+1% mass = +1% gravity\""
] |
[
"Suggesting the rise of intelligent life as a product of the time/rate of evolution implies a direction or motivation to evolution that doesn't exist. It does not move 'towards intelligence.' "
] |
[
"Why don't trains have better stopping systems?"
] |
[
false
] |
This thought was promoted watching a video of an emergency stop on a freight train from over in ( ) It takes a scarily long time for a loaded fright train at speed to stop. We've had major improvements in braking in cars (abs, ebd, etc.) Why haven't we seen similar improvements in train braking? Obviously there is much more energy involved in stopping a train at a given speed than a car, but surely some of the ideas would apply a.
|
[
"I think this is the most important point. But I think you maybe didn't go far enough. If a freight train is going at speed and suddenly grabs the tracks, what good will it do? With that amount of weight, I suspect that the tracks would bend like spaghetti noodles and you'd get a train derailment."
] |
[
"It seems like there would be an issue with whatever the train is transporting. If there are 300 people in the train, stopping a fast-moving train within a 50-foot span might be the ",
" thing the conductor could do."
] |
[
"Do you have any conception about how much a fully loaded train weighs? An average freight train can weigh up to 10,000 tons. It takes a lot of energy to stop that much weight traveling at high speeds. Indeed, at about 60 mph (around 100 kph) a 10,000 ton freight train's kinetic energy is comparable to the energy of a one ton bomb! Slowing down a train too quickly could release that energy into too small an area, with disastrous results, such as melting the track or the wheels. Also, slowing down the train too quickly runs the risk of causing the train to derail."
] |
[
"Why would Rüppell's Vulture ever need to fly at the extreme height it has been known to reach?"
] |
[
false
] | null |
[
"To beat the other vultures.",
"\"Bet you five pieces of carrion I can fly 11,000 meters high!\"",
"\"No way, bro. You're on!\"",
"But seriously, I think this gives us a big clue: ",
"...using their exceptionally keen eyesight to find large animal carcasses, or carnivores which have made a kill. ",
"This suggests that they can easily survey a huge amount of land that way."
] |
[
"It might be able to spot things that would indicate a carcass, other circling vultures, groups of animals, etc. Also, if you are above another bird, then that bird can't see you, but you can see it. The higher you fly, the safer you are from being attacked by other birds."
] |
[
"It might be able to spot things that would indicate a carcass, other circling vultures, groups of animals, etc. Also, if you are above another bird, then that bird can't see you, but you can see it. The higher you fly, the safer you are from being attacked by other birds."
] |
[
"How does studying other scientific fields unrelated to your specialty help you become a better scientist?"
] |
[
false
] |
Backstory: I go to the University of Buenos Aires, where before starting your undergrad education you must spend a year studying some "general" subjects somehow related with what you want to study (that means that, for example, since I'm pursuing a Computer Science degree I will study the same than all exact sciences. This is intended more as an entrance test than as another year of studies, and while I didn't learn very much on fields I am good at (such as most Mathematics and Psychics), I know a lot about (and almost failed due to) Chemistry. How will knowing a little Chemistry help me on becoming a better scientist, even if I will probably never get a chance to use this knowledge?
|
[
"If you are going to be an actual scientist, I would hope you would at least know the basics/intro of every major field, because it lets you understand how different aspects of the world works, gives you a basic introduction in case you ever do need to rely on it, or an appreciation of the history and path science has taken.",
"Scientific disciplines are now becoming much more disciplinary. I don't know about computer science, but neurobiologists have to know something from a huge range of fields- a lot of physics, some chemistry when you are dealing with drugs and solutions and such, and a lot from other fields of biology like genetics and molecular biology that doesn't immediately relate to everything in neurobiology.",
"And honestly, you computer scientists and engineers have nothing complain about when taking unrelated classes. A lot of general chemistry is applicable to a lot of things in everyday life; a year of organic chemistry and memorizing/learning how to synthesize organic compounds is hardly applicable to either lab work or everyday life. I've also had to take multiple literature classes, history classes, philosophy, public health, etc. They do it because they want you to be well educated, and not a one-trick pony.",
"Also, a lot of college is really learning how to learn, and gaining those work skills that you can use in the future. You'll going to have to be constantly learning new things in science anyway, and lots of what you learn now in computer science may become obsolete or outdated, and you'll have to learn new things in the future."
] |
[
"I wish I'd had more of an interdisciplinary science education. I'm from the UK, and the qualifications en route to a degree are:",
"I really wish I had more biology in particular, since a large part of applied physics is actually medical physics and who knows, I might have gone into this with a little more knowledge of it. So, in short, keeping your education as broad as possible for as long as possible is probably a good idea. "
] |
[
"Bottom line, it's quite common and (IMO) exciting to work with other fields. Being able to converse across disciplines is useful if you ever find yourself needing to work together in some fashion. In my field, scientific computing, this is absolutely essential. Partly because I participate in a \"mathematical and computational consulting\" service at my university, and partly because I think it's fun, I've become reasonably informed about diverse topics like animal behavior, bioinformatics, a lot of physics and physical chemistry, economics, and sociology. You find dynamical systems and interesting computational problems everywhere, ",
". ",
"Computer science is great and all, but I think a lot of the fun comes in making it useful to non-computer scientists. ",
"Lastly, it's not a bad idea to expose yourself to new experiences and other ways of learning, teaching, and researching. What's there to lose?"
] |
[
"Why do I sometimes shudder, violently and involuntarily when tasting something very bitter?"
] |
[
false
] | null |
[
"People have an innate aversion to bitter tastes (which can even be seen in babies). It's thought that the reason behind this is so we can avoid ingesting anything that might be toxic to us. Experiments involving primates and humans found that typical reactions to bitter tastes include gaping and head shaking. It's thought that this happens because that would help get the bitter (and possibly toxic) food/liquid out of the mouth to avoid it being ingested."
] |
[
"Secondary reflex to the sympathetic nervous system."
] |
[
"I realize this is unnecessarily pedantic, but the lack of a comma after \"involuntarily\" really bugs me. And I can't edit. Oh well."
] |
[
"Is the universe flat? What does this mean?"
] |
[
false
] |
I hear some physicists say " the universe is flat." I am trying to wrap my head around this idea. It is obviously 3 dimensional. We see stars in all directions of the night sky. We exist in 3 dimensional space. What does this mean? Not flat like a sheet of a paper.
|
[
"In this setting, what \"flat\" describes isn't so much the difference between a piece of paper and a piece of cake so much as it is the difference between a piece of paper and the surface of a basketball. It's about a property known mathematically as \"intrinsic curvature\", which measures how parallel lines behave in space: if space is flat, parallel lines stay the same distance apart forever, but if space is curved, they may either come together or drift apart (depending on the type of curvature)."
] |
[
"https://www.khanacademy.org/science/cosmology-and-astronomy/universe-scale-topic/big-bang-expansion-topic/v/big-bang-introduction"
] |
[
"Since the question about what it means for the universe to be flat was already answered, I'll answer your other question:",
"The universe is locally curved, but entirely flat overall. The reason the universe can be locally curved, yet flat overall is because some parts of the universe have positive curvature (like the surface of a sphere), and some have negative curvature (like the surface of a saddle). The positive curvature and the negative curvature pretty much exactly cancel each other out on the whole of the universe."
] |
[
"Could you theoretically \"push\" a singularity?"
] |
[
false
] |
Would it be possible to exact a force on a black hole to move it in another direction? Or is the gravity too strong
|
[
"Two masses will feel each other's gravitational field and respond to them regardless if they are singularities or not. A black hole singularity will still feel other objects' gravitational fields and orbit them like any other celestial bodies."
] |
[
"The blackhole would gain an electric charge. You could then use a ridiculously strong electric field to move the blackhole."
] |
[
"Static electric fields don't contain electromagnetic waves/photons, so there's no problem. It's not that the electromagnetic force or field can't escape, it's only particles which cannot.",
"The reason why you can still detect gravity and electric fields can be seen because both forces satisfy a form of ",
"Gauss' law",
" which lets you effectively measure mass/charge from a distance. Just measure the flux of the gravitational or electric field through a sphere containing (but outside of) the black hole. All other forces are short-ranged so you can't measure things like color charge or baryon number. (This is vaguely the intuition behind the no-hair theorem)."
] |
[
"Gauge spinors?"
] |
[
false
] |
Has anybody looked at the possibility of fields which transform as spinors under some gauge group? If they have (a link to an arxiv paper or two would be nice), what kind of compensating fields can be introduced? What do the interaction terms looks like? etc.
|
[
"What do you mean by \"spinor\" exactly? I think of projective representations, but the action must be invariant under gauge transformations, so if you had projective reps which are invariant then the gauge symmetry will just be the universal cover anyways (this distinction will not affect the gauge field/connection, which transforms in the adjoint which is the same for the universal cover). This is why you usually see gauge theories in terms of SU(N) (which are all simply connected = have no projective reps)."
] |
[
"Thanks, I hadn't really thought about it very hard. I just had the simple line of thought: there are gauge scalars (don't transform), gauge vectors (the fermions) and gauge connections (the gauge bosons), why no spinors."
] |
[
"Well this depends on what you mean by \"spinor\" and \"vector.\" Ordinarily I think of having an SO(3) group (more generally SO(p,q)), and defining spinors to be the projective representations. But in the Standard Model, we have SU(3)xSU(2)xU(1), which doesn't have any projective representations. So I would say that there cannot be spinor reps for SU(N) YM (unless the definition of spinor is different from what I'm saying).",
"As an example, all of the left-handed fermions are in the fundamental rep of the SU(2) gauge group, which is simply the standard spin-1/2 representation which I think you're calling a \"vector.\" I suppose you could think of the gauge group as SO(3) instead and then say that the fermions are in projective spinor reps, and either way the gauge fields are identically in the dim-3 rep (the \"SO(3) vector\"). In other words, having an SO(N) gauge theory with spinor reps doesn't seem any different than simply defining a ",
"spin(N)",
" gauge theory.",
"Here's a stack exchange post",
" about SU(N) vs. SO(N) which might be worth reading; I think the second highest post is basically saying what I am."
] |
[
"What Causes The Stimulation That Opens Na+ Channels?"
] |
[
false
] |
In my physiology books, it states, "When a cell is stimulated, depolarisation starts to occure due to some of its voltage-gated Na+ channels being open." I think I understand that the channels are opened because an electrical impulse reaches a certain voltage to open the gate (though, wouldn't this change the electrical gradient?). But also, where does that stimulus come from? Where does it originate? And, again, wouldn't this change the very electrical gradient that would cause the Na to move into the cells in the first place? Or does it merely decrease the gradient, but not enough to stop rapid flow?
|
[
"That's not a great sentence.",
"",
"So voltage gated Na+ channels are gated by ",
". So what starts them opening is depolarization. If that initial depolarization is strong enough, then positive feedback happens, as the sodium channels open, which causes Na+ to move into the cell, which depolarizes the cell more, which opens more sodium channels, which depolarizes the cell more etc etc etc...",
"",
"So what causes the initial depolarization? Well that depends, some cells have ion channels that are always leaking in positive charge, which means the neuron fires spontaneously. However, most neurons aren't like that. So what drives them to fire action potentials are \"excitatory post-synaptic potentials\" (EPSPs). So another neuron will release the neurotransmitter glutamate, which will bind to glutamate receptors like the AMPA receptor. These allow Na+ to move into the cell, depolarizing the cell. Each synapse might only cause an EPSP that is 0.1 mV in size (though some cells have massive EPSPs) and so many synapses are required to become active at once to produce the required ~20/30 mV or so of depolarization needed to cause the positive feedback loop that is the upswing of the action potential."
] |
[
"A) Ignore the Na-K ATPase. As far as you could be concerned, it is only there to establish [K+]i >> [K+]o. ",
"B) So we have lots of K+ inside the cell, and lots of Na+ outside the cell, and lots of open K+ channels. So K+ leaves the cell and it makes the cell sit at about -70 mV. The equilibrium potential of K+ is about -90 mV [i.e. at -90 mV, the electrical force on a K+ ion is equal and opposite to the \"force\" on the ion due to the chemical gradient]. So why doesn't the cell sit at -90 mV? Because there are some open Na+ channels. In fact, we can figure out the membrane potential with the goldman equations which goes like:",
"membrane potential = RT/F * ln[ (GNa*[Na+]o + GK*[K+]o)/(GNa*[Na+]i + GK*[K+]i) ]\n",
"Where GNa is the conductance of the membrane to Na, and GK is the conductance of the membrane to potassium. What we see is that the membrane potential is an average of the equilibrium potential for all the ions, but weighted by how conductive the membrane is to those ions. i.e. if the membrane is more conductive to K+ than Na+ then the membrane sits near the equilibrium potential for K+ (-90mV). If the membrane potential is more conductive to Na+ than K+, then the membrane potential will will sit nearer to the equilibrium potential for Na+ (+40 mV). So the ratio of the conductivity of those two ions (give or take) decide the membrane potential.",
"SO, when a EPSP happens, the membrane transiently becomes more conductive to Na+, which makes the membrane potential move slightly towards +40 mV.",
"OR, you could just say: when AMPA channels open, Na+ goes into cell, this makes the cell more positive."
] |
[
"I guess I'm wondering how those initial leaks lead to depolarization. More positive charge is leaving the cell than entering it, mostly through the Na-K ATPase and the K leak channel. I guess I'm not sure what would suddenly change this and start the chain reaction (I'm familiar with the steps once this chain reaction begins).",
"I mean, with the previously mentioned pump and leak channel, how is it that depolarization begins, and what is the voltage threshold for the initial Na gates to open? I know it's like -50mV for all to open, and - 70mV for them to deactivate."
] |
[
"How de we prove/know what the Sun is made out of?"
] |
[
false
] | null |
[
"By optical spectrometry.",
"Simplifying a bit:",
"If you look closely enough at the spectrum of light you get from the sun (by passing daylight through a prism), you'll see that there are gaps (or lines) in it. These gaps are caused by gases in the sun absorbing light of those missing frequencies, meaning that it never reaches us.",
"Every element when heated gives off a spectrum of light with its own distinct pattern of lines, and it just so happens that the lines for the sun correspond to the elements hydrogen and helium. Hence we know that the sun is composed of hydrogen and helium."
] |
[
"In fact, helium was observed in the sun’s spectral lines before it was observed on Earth—that’s how it got its name."
] |
[
"The only thing I see as wrong (as a spectroscopist) is that it's not so much that there are \"missing\" frequencies, more so that when you heat/burn hydrogen it'll give off a VERY specific frequency of light. ",
"The sun itself is a blackbody, giving off ALL frequencies of light. (As anything would do at that temp.) However, we can still see the hydrogen/helium \"lines\" within that full spectrum of light.",
"What you described are \"",
"Fraunhofer lines",
"\"",
"What hydrogen gives off is the \"",
"spectral lines",
"\" or \"",
"atomic spectra",
"\" of that particular element. "
] |
[
"How do we know that a black dwarf star exists if it's never been seen before?"
] |
[
false
] |
[deleted]
|
[
"It's thought that they don't exist yet, because there hasn't been enough time for white dwarves to cool. Because white dwarves are radiating away all this energy, it is thought that eventually it will cool through this process. If that is wrong, astronomers in a trillion years can find out."
] |
[
"I'm referring to proton decay and very long term quantum tunneling effects as matter seeks ever higher levels of entropy."
] |
[
"I'm pretty sure it would do neither of those things. White dwarves do not undergo fusion, they're kept alight by heat left over from their past life, and typically consist mostly of Carbon. By the time it's a black dwarf, all that heat energy is gone, and there's even less ability to fuse anything, so it'll still be mostly carbon. "
] |
[
"Why does bread becoming soggy when heated in a microwave and crispy when toasted in an oven?"
] |
[
false
] | null |
[
"I would think its because bread is relatively moist, and microwaves are particularly efficient at heating water. Toasting it heats the water out of it, microwaving heats the water in it."
] |
[
"As said the microwave heats by exciting the water molecules in the item being heated. In bread this destroys the structure of the bread, and instead of it being delicious and fluffy, it is dense and goopy. The structure in the bread that had many many air pockets, which makes it seem soft, are ruptured and collapse, leaving just the dough in a dense structure.",
"The oven heats from the outside with heat instead of radiation, the structures stay intact, but become brittle as the water is driven out, simulating \"crisp.\""
] |
[
"Precisely. In a toaster, it's a dry heating element. You're basically dehumidifying the toast as well as heating the outer layer of it. In a microwave, you're heating the water inside the toast, causing steam, which has no where to escape and while it does heat your bread, it doesn't dry the moisture."
] |
[
"Is it possible to insert an entire bacterial genome INTO a yeast genome and have the yeast GROW the bacteria within itself?"
] |
[
false
] |
So I was just wondering if there was any way to insert the entire coding genome of a bacteria into the genome of a yeast in order to grow both yeast and bacteria. Would there be any way to maintain the growth of a yeast cell while it also produces and grows bacteria from within the cell? Sorry if my question is confusing, I'm not really sure how to ask it.
|
[
"No, at least not the way that you word it. If you were to just have a machine, plop one genome into another organism, then tell it to go, you wouldn't get very far. The reason is that the \"shell\" of the yeast would not know what to do with the genome. All of the transcription factors and polymerases (the machinery for reading DNA) would not be nearly close enough for anything to happen. ",
" you were to somehow be able to get over the hurdles of initiating transcription, transcribing DNA to RNA, then translating the protein product, the cell would still not know what to do with it. Especially in the case of prokaryotes vs. eukaryotes, the trafficking machinery is wildly different, the proteins - though similar in many cases - would be way too different to work, and many metabolic pathways in the yeast would effectively die. ",
"A better way would be to put yeast into yeast or bacteria into bacteria. Some tantalizing hints that this is possible have come from the literature.",
"Synthetic chromosome arms function in yeast and generate phenotypic diversity by design\n",
"http://www.nature.com/nature/journal/v477/n7365/full/nature10403.html",
"Complete Chemical Synthesis, Assembly, and Cloning of a Mycoplasma genitalium Genome\n",
"http://www.sciencemag.org/content/319/5867/1215.abstract",
"(sorry about the paywalls if you can't read these, you might find them on google by searching the title. I'll try to get some actual articles if anyone requests. A good popular press account - ",
"http://www.economist.com/node/9333408?story_id=9333408",
" )",
"These are examples of synthesizing the host genome and reinserting an artificial genome back into the ",
" organism, which is extremely difficult. DNA doesn't tell the story of the organism, even in zygotes, where a host of egg proteins and mRNAs are present in the cell, even in gradients (in metazoans at least) to induce front-back or top-bottom polarity. Its wildly complicated. The goal is to get a minimal cell, finding the smallest compliment of DNA and the proteins (RNA's too) that would be necessary for life. Craig Venter as well as others are pursuing this goal to eventually get synthetic cells that produce a wild array of things, here's one paper on the topic from a personal friend of mine.",
"Towards synthesis of a minimal cell\n",
"http://www.nature.com/msb/journal/v2/n1/full/msb4100090.html",
"EDIT: A lot of the above is paywalled. Wikipedia actually has a really nice account of some of Venters work.",
"http://en.wikipedia.org/wiki/Mycoplasma_laboratorium"
] |
[
"Into the yeast genome and grow a bacreria? Nah, that's be impossible. ",
"But you could probably, through thousands of generations force endosymbiosis of a bacteria into the yeast. Preferably, you could start with a bacteria that is pathogenic with yeast. Each generation you kill all the bacteria except those that kill the yeast the slowest, or something. Eventually you might end up with commensalism. ",
"Then you'd have to force vertical transmission. I haven't got a clue where you'd start with trying to force a vertical transmission relationship.",
"I think I've seen a paper where they forced vertical transmission relationships between anemones and Zooxanthellae, but if it does exist, not sure whether it could be applied to our attempt to create endosymbionts in yeast."
] |
[
"There are a number of reasons. The largest point against your scenario, in my opinion, is the compartmentalization of eukaryotic cells (like yeast). In order for the bacterial genome to be transcribed and replicated, it must be localized in the nucleus of the yeast. This means that it would be physically separated from the proteins it encodes. Assuming that a pseudo-cell started to form within the yeast's cytoplasm (and wasn't degraded by the yeast), how would the bacterial genome move into the pseudo-cell?",
"Additionally, different membranes are composed of different types of lipids. Changing part of the yeast's membranes to match the bacterial membrane could cause all sorts of metabolic problems for the yeast cell as its organelles have reduced function. And how would the bacterium or pseudo-cell generate energy? It would be competing with the yeast's mitochondria for electron donors and protons."
] |
[
"Is there a maximum sound? A loudness at which the medium itself begins to rip apart or react or something?"
] |
[
false
] |
How many decibels at stp for the local average surroundings would that be? Would it just correspond to whatever pressure the nitrogen/oxygen mix condenses at? How would a system with sound of this intensity traveling through it behave? And related, but can compressional waves still travel through neutron stars and/or black holes?
|
[
"The process by which water rips apart under strong enough sound is called cavitation."
] |
[
"Aye, but loudness corresponds to the amplitude/energy of the sound wave, which is in turn related to the change in pressures. I guess I should have specified that, rather than the human perception of loudness.",
"Though it seems in ",
"wiki'ing",
" this just now I've found the answer to my first question ",
"Though it's unsourced, and I'm still not too clear as to what sort of distortion would occur. It makes some intuitive sense that that's what would be the case, though..."
] |
[
"There is a difference between loudness and pressure waves. Consider the following points and evaluate whether your personal definition of \"loudness\" works for what you wanted to find out:",
"Every man-made sound-producing medium has different durability.",
"Every stable system that happens to produce sound has a different durability, of which its instability is not necessarily reflected by how much sound it produces. A house made of symbals and hi-hats produces a lot more sound when you shake it up to the point of instability than a house made of bricks.",
"Loudness is merely the human neurological interpretation of pressure waves, usually air.",
"Your ears have a specific range of sensitivities to these pressure waves, so more energy at a different frequency is not necessarily loud to you. For example, dog whistles.",
"Damage to your hearing apparatus, specifically your middle and inner ear, begins at ~90 dB.",
"The maximum \"loudness\" that you can hear before your ears sustain crippling damage is about 190 dB.",
"If you question is only about pressure and not ",
", you'll have to ask physicists."
] |
[
"How did Gödel, in his incompleteness theorems, prove a statement that applied to all formal systems, using a formal system?"
] |
[
false
] | null |
[
"I'm going to assume you mean formal systems that attempt to describe the natural numbers (i.e. can perform arithmetic) here. While the proofs of Godel's actual theorems are incredibly complex and incomprehensible, how he proved that the theorems applied to all formal systems was actually quite simple. Godel's theorems apply to all formal systems of axioms that express elementary arithmetic and are consistent, and of which theorems may be listed in an effective procedure, i.e. a method for creating and testing statements about the system in a finite number of steps and could theoretically be done by a human. Godel's proofs relied ",
" on these assumptions and therefore apply to all of the formal systems that fit his criteria (which, incidentally, any formal system that attempts to characterize the natural numbers must) because his proofs were completed without loss of generality."
] |
[
"Great explanation! So essentially, Gödel proved the incompleteness theorems for \"a non specific formal system that can describe the natural numbers\" (my phrasing). In doing so, he proved the theorem for as general a case as possible, thereby applying to all formal systems that describe natural numbers? "
] |
[
"Exactly. It's interesting to note that mathematicians in general rarely solve the general case right off the bat; a common technique is to solve special cases and identify common properties or methods used to solve them that could be implemented into a general solution."
] |
[
"Why do hurricanes only hit eastern North America?"
] |
[
false
] | null |
[
"They are called cyclones and typhoons in other parts of the world. The storms require the warm water and weather conditions of the tropics to form, and generally travel in a western direction until the begin to degenerate and then fall into an easterly flow."
] |
[
"Technically they are tropical cyclones, and they are called hurricanes, cyclones or typhoons depending where they occur in the world. This ",
"map",
" explains the names well.",
"Hurricanes",
" happen on both sides of the American continent, but those happening on the West occur south of the US, hitting Mexico and very few parts of Central America."
] |
[
"The currents run in opposite directions. ",
"North > South on the Pacific coast and South > North on the Atlantic so the water on the pacific coast is much cooler as its coming from Arctic regions instead of equatorial. "
] |
[
"Does water immediately start freeze after reaching 0 degrees?"
] |
[
false
] |
Also: can water still be liquid below 0 degrees and freeze over 0 degrees?
|
[
"In general, the answer to all of these is yes, but it depends. Water generally needs a nucleation point to freeze ... a particle of dust, an irregularity in the container, or another crystal of ice. You can supercool water with high purity, where you get the water well below freezing, and it remains a liquid. If you add something, some dust, or perturb it (common demonstration is chilling higher purity bottled water like Fiji Water, then rapping the bottle on a table), and it will rapidly freeze through, though the results tend to be quite slushy. ",
"Adding an impurity like salt will also lower the freezing point.",
"Take a look at a phase diagram for water. It actually gets quite complex at very high and very low pressures and temperatures, and you can get some very weird phases of ice, even at high temperatures."
] |
[
"Titan, one of the moons of Saturn, is believed to have ice VI as one of its layers, I believe."
] |
[
"Sort of, but think of temperature as an average energy in a given medium. You may have some spots that are colder than others, so while the average or a given spot may read 1C you may start to freeze in another spot. Pressure is also a factor here as well. With water, increased pressure will lower the freezing point. Additionally, there is the mineral content of the water that can also lower freezing point. Assuming standard pressure and temperature and distilled water, and provided that there is a nucleation point, yes, it will start to freeze at 0 degrees.",
"See ",
"Phase Diagram"
] |
[
"What is the \"best\" design for a fan?"
] |
[
false
] |
How and why are all of these different (beyond just aesthetics)? Would someone like to give a basic explanation of the aerodynamics of fan blades, and electric motor efficiency? I'd like to understand why some applications use few blades, and others use many. How does blade width, length, shape, and pitch affect its ability to move air? How does fan housing/shrouding contribute to the issue? And how much does an optimal blade design contribute to airflow when compared to motor efficiency improvements? I expect that there are some efficiency envelopes that would need to be calculated. Has anyone already done the math? If so where can I find it? I expect that these are complicated issues I'm asking about, so I'd appreciate some general knowledge and explanation, and then if you could, point me to further reading. Thanks!
|
[
"You're asking for someone to explain 4 years worth of university fluid dynamics to you in a few paragraphs.",
"When I build up the courage I'll give it a shot!",
"For now you should know though that there is no \"best design\". Fans are different shapes because they are serving different purposes, and have different design considerations."
] |
[
"killing power"
] |
[
"killing power"
] |
[
"What is physiologically happening when our \"stomach drops\"? ie upon hearing bad news, looking down from a great height, etc"
] |
[
false
] | null |
[
"Physiology and Anatomy Major (for the time being) here. ",
"So its important to note that there are two sub systems in the nervous system. The first is the sympathetic and second is the parasympathetic nervous system. The sympathetic nervous system innervates most of your skeletal muscles (the ones used for movement), your eyes, heart and adrenal glands (I'm probably forgetting a few). The parasympathetic innervate your internal organs mainly the digestive and excretory systems. ",
"Through certain stimuli one of these two sub systems are activated. In moments of great danger or stress your sympathetic nervous system is highly active while your parasympathetic system decreases activity. This rapid change in the state of consciousness results in the loss of sensation in the stomach and intestines. This is also why your body is pumping blood a lot faster and your eye movements increase. The activation of the sympathetic nervous system is often associated with the \"fight or flight\" response."
] |
[
"While tesnaku is correct in asserting that the sympathetic system is probably activated, he/she's confusing a few critical points that I want to clear up. I would wager that the reason why you experience this physical sensation of a drop/butterflies is most likely due to ",
"splanchnic vasoconstriction",
" leading to shunting of blood from the viscera. This is mediated by the release of ",
"NE",
" and ",
"Epi",
" as part of the stress response. You can think of it as a system your body activates to get you ready in the event that you have to move quickly by shunting blood away from your gut and to the muscles.",
"The churning/\"dropping\" aspect is a little less simple to explain but it may be due to the release of serotonin from ",
"enteroendocrine",
" cells that line the gut. This increases rhythmic ",
"smooth muscle contraction",
" which normally serves to move food along, and increases secretion from many of the glands that line the gut which serves to lubricate food as it moves along. This is a little counter-intuitive as one of the major aspects of the sympathetic response is to decrease gastrointestinal smooth muscle activity, so the uncomfortable churning may be due to dys-synergy between these two mechanisms. ",
"Some points of contention with regards to your post:\nThe sympathetic nervous system is a component of the ",
" nervous system, which means that it interacts with smooth muscle and glands, and that it does not not interact with skeletal muscle. There are entirely separate systems that coordinate skeletal muscle contractions/relaxation to facilitate movement.",
"Also, for the most part all the internal organs receive innervation from ",
" the sympathetic and parasympathetic systems--which is why your heart rate can rise (sympathetic) when you're about to go for a run, and then fall (parasympathetic) back to the resting rate when you're all finished. You can think of it as being something akin to a room with both an air-conditioner and a heating system that are both active and linked to a thermostat. You set it to 75o (or 75 heart beats per minute) and the two systems work antagonistically to keep the room within a few degrees of your set point. Which of the two systems dominates during different states of activity is organ-dependent. Your heart, for instance, normally beats between 60-100 times per minute, but would, if given the option, like to beat faster but is being slowed down by the parasympathetic system--it is said to have primary parasympathetic tone. ",
"This is a good overview: ",
"http://www.neurophysiology.ws/autonomicns.htm"
] |
[
"That question is asking about the feels on the stomach driven by physical effects like going over a hill quickly in a car. This post is asking about psychological effects like realizing you've made a terrible mistake."
] |
[
"Nothing can travel faster than light, but relative to what? Any other object?"
] |
[
false
] |
[deleted]
|
[
"There are no frames of reference in which something appears to be going faster than the speed of light."
] |
[
"No matter what speed you are travelling at, or if you are accelerating or not, ",
" nothing will appear to be moving faster than light. Not just to you, but to ",
". Nobody will agree on how fast anyone is moving, or how fast time passes, or the lengths of objects. But ",
" will agree what the speed of light is. To ",
", no matter where they are or how fast they are moving, light will appear to move at the same speed."
] |
[
"No matter what speed you are travelling at, or if you are accelerating or not, ",
" nothing will appear to be moving faster than light. Not just to you, but to ",
". Nobody will agree on how fast anyone is moving, or how fast time passes, or the lengths of objects. But ",
" will agree what the speed of light is. To ",
", no matter where they are or how fast they are moving, light will appear to move at the same speed."
] |
[
"Statistically, when can we expect another active igneous province on earth?"
] |
[
false
] |
Also, for what percentage of time, over the course of earth's history, have there been active igneous provinces?
|
[
"I'm going to assume you're asking about \"Large Igneous Provinces\" or LIPs (e.g., ",
"Bryan & Ernst, 2008",
")? While there have been a lot of suggestions that there may be some periodicity to LIP eruptions, it remains an open question. ",
"Ernst et al, 2005",
" provides a summary (and I couldn't find much in the way of more recent work on periodicity in LIPs, but I don't work on them so there may be more recent work that I'm not aware of). In detail, the rate is a bit tricky to figure out (assuming there is a periodic rate to extract) because we have an incomplete record of oceanic LIPs (lost to subduction) and generally an incomplete record of LIPs prior to the Phanerozoic. Those caveats aside, various estimates have suggested an average rate of 1 continental LIP ever 20 million years (average rate maybe faster, closer to 1 LIP ever 10 million years if you include oceanic LIPs). Times series analyses of LIPs suggested a hierarchy of cycles (e.g., ",
"Prokoph et al, 2004",
"), so a simple, average recurrence interval is unlikely to be very useful in prediction (and again, there is a lot of uncertainty in the underlying assumption that there is any periodicity in LIP eruption and that they're not all stochastic). But the start of the last LIP (the Columbia River Basalt) happened ~17 million years ago, so if we applied that average 20 Ma recurrence interval, we could expect one ~3 million years in the future.",
"In terms of the proportion of the geologic record these represent, it's important to remember that LIPs, by definition, are discrete (on the scale of geologic time) events. Also, even though they tend to last 10s of millions of years, as emphasized in Bryan & Ernst, they are usually characterized by >75% of their volume being emplaced in short (few million years) periods within the broader eruptive sequence. I'm not aware of a formal calculation of percentage of geologic time (and again, you'd be running up against the incompleteness of the record of LIPs), but it would depend on whether you're thinking about that full duration or the individual productive pulses. We can do some super simple approximations and take the record assembled by Prokoph et al (154 LIPs over 3500 million years of time) and estimate percentages of time. We can do this by considering the full duration of LIPs and use a pretty long length (e.g., 10 million years) as the full duration or the time spanned by productive periods of LIP eruptions (we'll assume 1 million year length for these). Respectively, this would suggest around ~44% of the last 3500 million years would have some LIP technically erupting, but only ~4% of that time would be characterized by really productive eruptive periods. This is super back of the envelope (and the 10 million year length is probably too long for many LIPs), but is probably sort of in the right order of magnitude."
] |
[
"<different Redditor> ",
"I don't know anything about \"active igneous provinces\".",
"If the question was",
"\"",
" could we reasonably expect to see the next active Large Igneous Province on Earth? ",
"would a likely answer be ",
"\"The East African Rift System / Rift Valley in Africa\" ?"
] |
[
"No, as there is already a LIP there (e.g., ",
"Ayalew & Gibson, 2009",
") associated with the Afar plume (e.g., ",
"Chang et al, 2020",
"). The conventional model is that LIPs often reflect the initial eruption of a plume head, so the next LIP would likely form where the next plume forms."
] |
[
"Can bleach expire/'go bad'?"
] |
[
false
] |
If bleach has an expiration date, what would happen to it if it went past the date?
|
[
"Bleach is usually NaOCl, which is a relatively stable compound, but it does interact with air a bit, and this volatility is what gives it its strong smell of chlorine. If the lid is kept on and is hermetically sealed, the bleach inside will stay at a steady state indefinitely. The only way it can \"expire\" is through not putting the cap on and it all airs out. "
] |
[
"The active ingredient in regular bleach is NaClO - sodium hypochlorite. It really shouldn't lose potency with time in a sealed container.",
"Non-chlorine bleach is usually H2O2 - hydrogen peroxide. It does decompose with time, especially in the presence of sunlight or tiny amounts of a catalyst. This is why it often comes in thick or dark-colored bottles; if the bottle were clear then light would destroy it rapidly. The decomposition products are oxygen and water. Your clothes won't get as clean.",
"Sometimes the container will fail eventually. Some general caution is advised whenever picking up really old bottles of whatever. "
] |
[
"Over time, sodium hypochlorite will degrade to form sodium chlorate and sodium chloride. This degradation is temperature dependent and can be slowed by the addition of sodium hydroxide (lye), which most manufacturers do add. Room temperature storage can usually yield a 2 year expiration (based on concentration of hypochlorite ion). The most common possible adverse effect would be a build up of pressure due to oxygen formation. ",
"As available hypochlorite concentration decreases, bleaching power and disinfection power is reduced. "
] |
[
"How long do you need to stay under the sun to absorb the same amount of radiation as one xray scan?"
] |
[
false
] |
I've just recieved an xray for my foot and wondered, the sun also emits radioactive rays, and of course, chance of cancer increases? But is the amount near a days worth of staying in the sun (negligible) or something that takes you months?
|
[
"When we talk about “radiation absorbed” we mean “ionizing radiation”, which can take many forms (gamma rays, x-rays, UV) - the point is that ionizing radiation has the ability to degrade molecules in your body. An ionizing radiation dose is measured in a unit called Sieverts (Sv). Most doctors would say that a single chest X-ray you’d get at a hospital would deliver about twenty-millionths of a Sievert (20 microsieverts). ",
"As a human just living on earth, you probably receive about 10 microsieverts a day from background sources, including the sun. So a chest x-ray is like receiving two days worth of normal background radiation all at once. ",
"You need to receive up into the hundreds of millisieverts or 10s of sieverts in a short period (like getting, say, 50,000 chest x-rays SIMULTANEOUSLY) to get acute radiation poisoning."
] |
[
"It really depends on where you are. The more atmosphere between you and the sun, the more harmful radiation gets deflected or absorbed/transformed before it gets to your skin.",
"Also, the more ozone between you and the sun, the more protected you are.",
"So people at the South Pole and airline pilots are exposed to much more ionizing radiation than someone who sits all day on a beach in Florida."
] |
[
"Two of the biggest factors are probably increased life expectancy plus medical diagnostic ability. Humans over the past 200 years have nearly doubled their life expectancy. Cancer is a disease caused by genetic mutations, which increase in frequency and accumulation as we age. Plus, medical knowledge has vastly increased and we can better positively identify and report cancers now."
] |
[
"How does zero point energy not correlate with a temperature at absolute zero?"
] |
[
false
] |
As above, how can kinetic energy exist (in the form of ZPE) at absolute zero without being related to a net positive temperature? Isn't temperature a measurement of the kinetic energy present in a system?
|
[
"Isn't temperature a measurement of the kinetic energy present in a system?",
"No. The formula <KE> = (3/2)kNT only applies in classical non-relativistic non-magnetic systems. (Here <KE> is average total kinetic energy, k is Boltzmann's constant, and N is the number of particles). The more general definition of temperature is defined so that a system should be in its quantum mechanical ground state at absolute zero. The zero-point motion of the system does not contribute to the entropy or the temperature."
] |
[
"The 1.5RT formula is the result of statistical mechanics of a monoatomic ideal gas, using classical physics, as mentioned.",
"Relativity and QM are not included, as the two fields only started to emerge around the same time as Gibbs published the defining work of SM 1902. I wouldn't know if we have a SR and/or QM complaint version of SM, but I would bet it would exist though."
] |
[
"The 1.5RT formula is the result of statistical mechanics of a monoatomic ideal gas, using classical physics, as mentioned.",
"If <KE> is defined as the average total kinetic energy (energy due to translational momentum rather than rotational/vibrational energy or interactions), then the formula holds for ",
" classical non-relativistic non-magnetic system with translational degrees of freedom, not just the ideal gas.",
"I wouldn't know if we have a SR and/or QM complaint version of SM",
"We do. It turns out that Gibbs' original work was general enough that incorporating SR and QM is not even that difficult (though there was some novel work to be done in the early days QM)."
] |
[
"What are some fun, easy science experiments for elementary-aged kids?"
] |
[
false
] |
I'm starting a new science outreach program and am looking for some interesting, but relatively simple experiments to do for elementary school kids. Any ideas?
|
[
"Electricity that works with 3-5 graders. If you have the funds, purchase small light bulbs, c batteries, and wire. You can get a bulb holder too that has clips for the wires, but thats not necessary. Cut and strip wires so that each kid (or small group) has 3 wires. Start off by giving the kids one wire, one bulb, and one battery. Without directions, tell them to get the light to light up. I usually give 7-10 min. Once a group gets it and there is extra time, you can give them an extra wire and make them do it with another wire. ",
"If you want to make this a module, you can get them to bring in a small box or shoe box and have them make a room with a light switch (brass paper braids). ",
"If you want to just do it for a day, after they get the light bulb to light, get everyone together with their batteries. Take two yard sticks and place them so that they will hold batteries in a straight line between them. Get two pieces of wire 3-5 ft long. Get a regular light bulb (60W) and you hold the wires to the light bulb contacts. Ask the kids to guess how many batteries it will take to light up the big bulb. Whoever says one, get them to put the first battery down and hold the wires to the sides of it. Keep it going until it lights up pretty bright.",
"This lesson gives you an opportunity to teach the basics of electricity and warn about the dangers of down powerlines and home electrical outlets.",
"Balloon rockets. This works with younger elementary school kids better but is real cheap. Buy string, cylindrical balloons (like balloon animal balloons but wider and shorter). Take a piece of string and tie it to the top corner of the tile ceiling in the room. Have the kids tape a balloon to a straw and then when it's their turn have them blow it up and pinch it. Help them feed the free end of the string thru the straw. Have them let go and watch it hit the ceiling. ",
"I know this sounds lame but the 1st graders I've done it with enjoyed it. It gives you an opportunity to talk about the relationship between volume and pressure in easy and very rudimentary terms."
] |
[
"Try headrush\n",
"http://headrush.discovery.com/"
] |
[
"Try Headrush\n",
"http://headrush.discovery.com/"
] |
[
"Relativistic position uncertainty..."
] |
[
false
] |
So I was thinking about how length contracts at relativistic speeds and how a particles loose their position information when they have really well defined momentum. Are these two related somehow? Am I making any sense? I'll try with an example: Let me say that I fired an electron in front of me (1 km away) to a really really high speed of 0.99c such that it's length contracts to just . Now what's 1 kilometer to me is just 141 meters for that electron (that wat relativity says right! if no please correct me). If I assume that I know it's speed very accurately (measured in particle accelerator or w/e) I cannot know where it exactly is in that 1 kilometer - it could be anywhere in 141 meter chunks of space inside that 1 kilometer (like in the middle, or in the beginning or w/e) So there's sort of like an error in measurement between me and the electron that I cannot know it's true speed and it cannot know it's tru distance (1 km versus the 141 meter) - is this what gives rise to uncertainty principle? (if not gives rise to, is it atleast related to it somehow?)
|
[
"No, I'm sorry, they are completely unrelated. Length contraction arises from special relativity, and the Heisenberg uncertainty principle arises from non-relativistic quantum mechanics.",
"The mathematical formulation of each phenomenon makes it apparent that neither requires the other:",
"http://en.wikipedia.org/wiki/Length_contraction#Derivation",
"http://en.wikipedia.org/wiki/Heisenberg_uncertainty_principle#Mathematical_derivations",
"Also, this is not true:",
"it could be anywhere in 141 meter chunks of space inside that 1 kilometer"
] |
[
"It's not related at all, and it only seems like it could be because your understanding of relativity is flawed.",
"You're correct that relativity says 1000 m is 141 m for an electron moving at .99c. But there's no correspondence between the intervals like you're imagining, where the 141 meters the electron sees corresponds to some particular 141 meters you see. The 141 meters is the ",
" which you see as being a thousand long, just viewed from a different frame of reference. You can't worry about how long the interval \"really\" is, because the entire point of relativity is that lengths are only defined given some arbitrary frame of reference.",
"The uncertainty principle is an entirely different thing. At very small scales, it turns out that position and momentum aren't really things, in that there's no single number which you can meaningfully say is \"the position\" or \"the momentum\". You have probability distributions of both, and it turns out (for reasons I can get into if you want) that narrowing the distribution of one widens the distribution of the other."
] |
[
"oh, ok. I just saw a wild co-relation then I guess. additional ques if you could answer it as well oh kind physicist: where am I exactly going wrong in my thought process? (i can take a guess but better have someone knowledgeable point it flat out than getting lost in thoughts again, right?)",
"edit: didn't catch your edit there, reading now...",
"edit: ",
"Also, this is not true:",
"it could be anywhere in 141 meter chunks of space inside that 1 kilometer",
"I guess this is where my understanding of relativity was breaking. Thanks again."
] |
[
"Best place to launch a space shuttle?"
] |
[
false
] |
If you had the resources to launch a space shuttle from any point on earth, which point and why? For example if you could launch one from the summit of Mount Chimborazo or the equator which would be better?
|
[
"The best place to launch something into orbit is typically on the equator.",
"If you're above the equator, you can't launch anything into an orbit with a lower inclination. As an extreme example, if you were on the north pole, you could only launch satellites into a polar orbit. However, on the equator, you can choose what inclination to launch a satellite, whether into an equatorial orbit or a polar orbit or anywhere in between."
] |
[
"What matters the most is usually the highest velocity, if the pad is moving faster then it's a lower delta-v to orbit (so usually the equator). With that said, depending on your ship, the mountain may very well be better because of the lower air pressure, it would significantly reduce the drag experienced during the first stage of flight, I can't find what is the velocity of that mountain is, so I can't compare the velocity of the ground, but I know there is a ",
"ship that does launches from the equator",
" and I don't know the math and numbers to actually calculate what is better for common launch vehicles."
] |
[
"Launching from the Equator offers the highest initial velocity because the Earth's angular momentum is greatest at it's widest point perpendicular to the direction of rotation. It also offers the best options for orbit trajectory."
] |
[
"Will a photon traveling perfectly away from the center of a black hole, but inside the event horizon, fall back on itself or be able to escape?"
] |
[
false
] |
I pictured something like this: A follow-up question: Will the photon come to a literal stop for a brief moment while it decelerates and then begins accelerating at the center?
|
[
"There is no direction \"perfectly away\" from the singularity in a black hole. Every path starting from inside the event horizon leads towards the singularity due to the curvature of space-time.",
"Will the photon come to a literal stop for a brief moment while it decelerates and then begins accelerating at the center?",
"Photons can neither accelerate nor decelerate, they always move at the speed of light."
] |
[
"Once you're inside the black hole, the only way ",
" can ever, possibly go is towards the center. This is because inside the black hole, the radial direction flips roles with the ",
" direction. Outside the horizon, everything has to move forward in time - inside, everything has to move inward in radius!"
] |
[
"Based on this line of reasoning, what (if anything) can be implied about a masses movement through time inside the event horizon?"
] |
[
"My boyfriend has these weird marks on his bicep, that he says are from injections where the needle was heated until it was red-hot..."
] |
[
false
] | null |
[
"I am from russia and while i dont have those marks (i am 23), my mother does, as well as many other people around that age from eastern countries. I assume you mean the marks that look something like this:",
"http://www.ediblegeography.com/wp-content/uploads/2009/10/smallpox-vaccination-scar.jpg",
"\nEdit: Reading the sources more carefully, i am not sure if the needle is the culprit, or the vaccine itself. At least it's a starting point for your research ;)",
"http://library.cqpress.com/cqresearcher/file.php?path=/images/CQ_Researcher/r20030207-needle.jpg",
"Here's a bit info on that:",
"http://www.bt.cdc.gov/agent/smallpox/vaccination/facts.asp#",
"http://www.straightdope.com/columns/read/2324/how-long-does-a-smallpox-vaccination-protect-you"
] |
[
"This is unscientific without photo/s. ",
"Very true. I will hazard a guess anyway ;)",
"The BCG vaccine (to prevent complications from tuberculosis) is usually injected subcutaneously (under the skin, but not in the muscle) on the side of the left shoulder. The vaccine contains cow protein therefore causes the injection mark to fester. This leaves a distinctive scar. Knowing the place and look og the typical scar health care professionals can fairly securely deduce whether or not someone was inocculated against TB. ",
"The BCG vaccines are part of immunization schemes in most developing countries."
] |
[
"amazing! thank you SO much this is exactly it! He's 18, but he's from the middle east, so it makes sense according to a couple other sources i found! he was pretty young when they did it, so maybe he's not remembering the hot part correctly, but it definitely looks like the same as the mark you showed.",
"thanks again so much!!!!"
] |
[
"How did HIV cure cancer in the 7-year old girl?"
] |
[
false
] |
Here's a link to an article: My question specifically is how did they "alter" the HIV virus strand to target cancer cells? What process method was used? (A link to a scholarly article would be nice) What possible risk are their by using this form of treatment? And finally do you think this can be used for all or many types of cancer?
|
[
"They used a disabled form of HIV (one that cannot give you the AIDS, I'm assuming they removed the viral genes), and modified it by adding a specific gene that produces the \"chimeric antigen receptor\". This receptor gets expressed in the cells infected with the modified HIV, and is displayed on the surface of those T cells. With this receptor, the T cells are able to attach to the cancerous B cells (which have a protein that is recognized by the chimeric antigen receptor) and then they can destroy them.",
"Edit: I should add that the T cells become altered, because genes carried by HIV can be integrated in the host cell (via a viral enzyme known as Integrase). So once infected by the modified HIV, the T cells will now have the chimeric antigen receptor gene integrated in the chromosome of those infected T cells."
] |
[
"Legend_Floyd has it right. In a little more detail, the virus is split into 3 separate chunks, so that no single one alone is infectious (and recombination between 3 is unlikely). Also many of the viral proteins are truncated and self inactivating elements are added. The important thing is that the virus functions as a gene delivery system - i.e. it gets the genes that you want (in this case the receptors and associated genes that allow the T-cells to recognize the cancerous cells) into the T-cells. There is nothing special about it being HIV - similar systems are derived from other lentiviruses. In fact I would not really call this virus HIV (more correctly a \"HIV-derived lentivirus system\"), but more people are likely to understand \"HIV\" then \"lentvirus\" and it makes for a better headline."
] |
[
"It's an interesting question, but a little outside the bounds of this particular application. The only point of \"HIV\" here is as a delivery system. The \"payload\" is the genes that encode the proteins that reprogram the T-cells to kill all B-cells. If you could come up with a payload that would kill HIV, then yes, you could use a lentivirus to get it into cells. There are certainly a lot of good candidate genes for this kind of payload, but I don't know that they would really be more effective and safe then current therapy.",
"However, I can think of several more exotic methods that qualify as \"using HIV to kill itself\", but they aren't quite this, require a lot different background info and context, and aren't really ready for prime time in patients. So I'll pass on going into any depth on them - just know that your question is not a stupid one."
] |
[
"Which cognitive functions are affected by depression, and how?"
] |
[
false
] |
I've learned that depression affects short term memory. What other cognitive functions are affected by depression, and what do we know about the underlying mechanisms?
|
[
"This ",
"blog post",
" does a good job of answering your question and citing relevant sources. ",
"Here is a list of several impairments in cognitive function that have found to be associated with depression:",
"Patients with depression compared to non-depressed individuals possess several notable differences in brain structure",
". Specifically, a depressed person is more likely to have a larger volume of cerebrospinal fluid and bigger lateral ventricles, but a smaller basal ganglia, frontal lobe, gyrus rectus, hippocampus, orbitofrontal cortex, and thalamus. It has been proposed that the many memory deficits observed in depressed patients are due in part to smaller hippocampal volume. "
] |
[
"The hippocampus and frontal cortex impairments are what contribute to memory dysfunction, feelings of worthlessness, and suicidal thoughts. Functional imaging studies have shown hippocampal atrophy in depression and reduction of neuronal density and size of populations of neurons in the cerebral cortex as well. There's also evidence that the nucleus accumbens and amygdala are affected resulting in anhedonia, anxiety and reduced motivation. The hypothalamus involvement is suggested by the neurovegetative symptoms that accompany depression such as too much/little sleep, loss of appetite/energy. The main connection between all the above structures is that they are components of the limbic system. ",
"In terms of mechanisms: depression shows clear derangement of the biogenic amines (serotonin, NE, dopamine). Decreased serotonergic transmission in depression allows the pharmacological intervention of TCA's and SSRIs (these antidepressants override the recycling of serotonin). TCA's also block the reuptake of NE, which is deranged in depression as well. The prefrontal cortex is densely innervated by both NE and dopamine and thus derangement in these amines manifests as decreased processing speed, working memory, and attention.",
"I'll also add that there's a serotonin transporter gene (SERT) located on chromosome 17 that has been linked to depression. A functional polymorphism is found in the promoter region of the gene consisting of either a 44 base pair insertion or deletion; depending on whether an individual is homozygous for the absence of the insertion they could have an increased risk for developing depression."
] |
[
"Enlarged CSF and ventricles coupled with smaller brain structures can indicate a few things. The first being a neurodegenerative process where cells are dying (this is seen in Alzheimer's and Parkinson's). Also, it could indicate a developmental problem where there is a lack of neurotrophic factors to insure cell survival, or some mechanism where there is to much \"pruning\" during development. Either way, not good and hard to fix. Although, some psychoactive drugs have been shown to increase spine density, and increase volume of certain brain areas."
] |
[
"Does the volume of water on earth fluctuate from day to day?"
] |
[
false
] |
[deleted]
|
[
"Technically yes, since water vapor has more volume than water. But the vast majority of the mass of H2O on the planet at any given time is water, and for every bit evaporated in one part of the world, a similar amount condenses somewhere else, so any difference would be insignificant."
] |
[
"Less technically, there is also a fluctuation because free water is sequestered into the mantle via subduction and released from there via volcanic activity. Also, sequestration into and release from aquifers is not necessarily equal."
] |
[
"A bit. Some water is split into oxygen and hydrogen in the atmosphere (hydrogen escapes over time). We get a little bit of new water from ice from asteroids hitting Earth. Living objects convert water to other things, and other things to water. Burning biological material typically releases water (vapor). Some water is created or destroyed in other chemical processes independent of life.",
"If you count ice and water vapor separately then you also have the conversion between liquid water and these two other phases of water."
] |
[
"How hard is it to see myelin formation on an MRI?"
] |
[
false
] | null |
[
"That depends a little on what you mean exactly. You can see highly myelinated regions easily on an MRI. You can even figure out which way the axons (on average) must be travelling. So see myelin is easy.",
"But if you wanted to watch myelination and demyelination, that would be very difficult, unless you were talking about some theoretical disease that cause huge amounts of (de)myelination to occur. This is simply because of the poor spatial resolution of MRIs. You would need many cubic millimeters of myelin to appear or dissapear/or even larger regions consistantly loosing significant fractions of myelin, before you could see it on an MRI."
] |
[
"Diffusion tensor imaging is an MRI technique that is often used to measure white matter integrity. One DTI measure is fractional anisotropy, which can range from 0-1 based on the movement of water molecules. If the myelin is intact, then water molecules should only be moving (diffusing) along one line, resulting in an FA value closer to 1 but if the myelin is damaged, water may be diffusing in multiple directions, resulting in a lower FA value, closer to 0.",
"Another MRI imaging technique is white matter tractography. I'm not particularly knowledgeable about this, other than to tell you that it's a way to trace the paths of white matter through the brain. The scans are very time-intensive, and so sensitive to movement, but it's amzing to be able to measure this, and the images are both technically amazing and beautiful."
] |
[
"Thank you very much for this."
] |
[
"What kind of experiments are the astronauts doing on the ISS?"
] |
[
false
] |
Are they doing astronomy, weather science, or just seeing how things act without gravity?
|
[
"The short answer is that they do all of those things. With every supply load going up to the ISS they get lots of stuff that people back on earth wants them to do experiments with.",
"A lot of them has to do with how we as a humans will handle living in space for longer periods, which will happen if we are to colonize Mars for example. And that is why they do such experiments as testing the grip strength of mice to study how your muscles atrophy.",
"But as you said it's a lot of studies on how physics behave in a micogravity environment to be able to see if there are things that can be done in space that can't be done on earth."
] |
[
"To add to this: when I was doing undergrad research on magnetic coupling, we wanted to study them in space. So we applied to have our experiment taken to the ISS but were ultimately denied. I imagine nearly every university on Earth has experiments they submit to be taken to the ISS"
] |
[
"During his speech in my hometown, Hadfield answered that he convinced his commanders to ",
" to discover the acoustics of an instrument in space, playing his guitar both for pleasure and for work.",
"Then he was given a cease and desist for having played ",
" and posting it on YouTube.",
"That didn't stop him from playing for it for us on stage.",
"Wonderful speaker. ",
"Edit: corrected guitar reference that wasn't completely accurate"
] |
[
"What does \"popping\" joints in your fingers/toes/knees/etc. actually do?"
] |
[
false
] | null |
[
"No. ",
"Donald Unger",
" won the Ig Nobel Prize for cracking the fingers on his left hand but not his right every day for 60 years, in order to show that there was any connection to arthritis. There was no difference after 60 years."
] |
[
"I answered this a year ago. ",
"Read there",
" or reprinted here because electrons are cheap.",
"Physician here, with an undergrad in physics, I have also taken classes in Naval Architecture, where cavitation is a pretty big deal. In preparing this answer, I also discussed it with one of my partners, an osteopath, and checked pubmed. I am not a spine surgeon, though I have worked with a few in the OR.",
"The leading hypothesis is that that the popping sound is due to cavitation of synovial fluid in the facet joints. This has not been proven experimentally, but other mechanisms seem less plausible. Cavitation, the rapid phase change of a fluid in a region of negative pressure (and usually a fair amount of shear) occurs on a microsecond timescale, and to visualize it, you'd have to peer through the spinal muscles while they're moving (imagine trying to look sideways through a stack of pork chops). I'm not aware of any safe-for-humans radiographic techniques that could by employed. Ultrasound would have the best bet, but it's \"shutter speed\" is too slow, refraction through the layers of strap muscles would introduce a lot of refraction planes, etc, etc. If there's an echocardiographic technician who reads this, they might be able to demonstrate a jet artifact, but the bubbles are extremely short-lived.",
"The bubbles are, with a great deal of certainty, water in the gas phase. It is almost certainly not \"dissolved gases\" that come out of solution. Simply because of their low concentrations (millimoles vs the solvent, water, being 55 moles) and the short time scale, the odds of migrating sufficient mass of any dissolved product to the boundary of an expanding bubble is extremely unlikely, never mind the fact that the forces as soon as a bubble forms are actively moving everything else out of the way. You could test this. Collect enough synovial fluid, put it in a cavitation chamber (an optically clear chamber capped by speakers), and you can generate cavitation by setting up a standing wave. A stroboscopic spectrometer could then be used to evaluate the absorption spectra of the bubbles.",
"Alternative hypotheses generally involve ligaments or tendons slipping over each other or bones: This might seem possible in the hand, except the tendons are midline, and retinacular ligaments form tunnels through which the tendons pass, prohibiting much side-to-side movement. In the back this is essentially impossible as the ligaments are mostly little more than microfibers attaching the bones to the muscles. Again, the pork chop illustration is relevant.",
"My DO colleague says that many spinal manipulation techniques may cause cavitation, but mainly it's the stretching on ligaments that feels good.",
"Edit: I got my back cracked several times during research for this answer. I do it for you reddit.",
"Edit: Cavitation it is! In fact, it appears to be bubble formation, not collapse that initiates the sound wave we hear. ",
"Article",
" with ",
"video",
"!"
] |
[
"that's why he got the ",
" Nobel prize (it's a parody prize for silly/stupid science)"
] |
[
"Are more turns and smaller wire diameter better than less turns and larger diameter in an electromagnet?"
] |
[
false
] |
[deleted]
|
[
"The magnetic field strength of a solenoid (cylindrical coil of wire) is B = μIN/L. ",
"μ is just a constant depending on the magnetic properties of what's inside the coil. Something magnetic like iron would make it higher than air. L is the length, let's say we keep that constant. ",
"So that leaves N, the number of turns, and I, the current, as both being proportional. ",
"With N, doubling the number of turns would double the length of wire, which would double the amount of copper. So a proportional relation, twice as much copper, twice as much field strength. ",
"With I, it is a little more complicated. Doubling the amount of copper would double the cross sectional area. Doubling this would halve the resistance. The power, which let's say needs to stay constant to avoid overheating, is P = I",
" R. So if we halve R with twice the size of wire, that means I",
" can be twice as large. Which means I is only sqrt(2) times larger. So twice as much copper, only means a sqrt(2) increase in current and therefore only a sqrt(2) increase in field strength. This isn't quite the same overheating temperature limit though, as even with the same heat generation, we now have more mass to spread the heat over as well as more surface area to dissipate heat. In addition, the wire overheating is a little more complicated as they are all wrapped up together. But simplistically, more coils would be better. ",
"But there's yet more issues that may come into play:",
"I've assumed you can simply supply whatever current you need to reach the ampacity of the solenoid wires. Really, if you have a voltage source the resistance will determine your current. Too much lenth of a high gauge wire and you will get almost no current, few turns of a low gauge and you'll get a lot of current, but you'll be back to worrying about overheating or exceeding the capacity of your power supply. ",
"Higher guage wire or mutiple layers of wires stacked will and at what factor you stack then push the current further out radially. While ideally the radius doesn't matter, realistically it does unless your solenoid is infinitely long. ",
"The length also needs to come into play. It effects the total heating and beat dissipation, which is no simple matter. As well, a very short length with a very large amount of stacked turns would seem like the way to maximize the strength, but again that pushes more out radially and shortens the length making the formula less ideal and more dependent on radius. ",
"Your limit for overheating is going to be very dependent on what your installation is. ",
"If you stick a iron core inside, there is things to consider with regards to strength. ",
"If you care about response time, there's even more considerations. ",
"All in all, it's no simple one eqaution engineering task to globally say how to maximize a electromagnet. "
] |
[
"With N, doubling the number of turns would double the length of wire, which would double the amount of copper. So a proportional relation, twice as much copper, twice as much field strength. ",
"And twice as much heating.",
"If you want to keep things consistent, consider it for both scenarios, not just for one. Or better, consider a fixed amount of copper: If you replace one strand by two strands of half the cross section, you can reduce the current by a factor 2 and get the same magnetic field as the number of turns doubles. The resistance goes up by a factor 4, but the power P = I",
" R stays the same.",
"For the same amount of copper and the same magnetic field strength the heating power is the same no matter which cross section you use."
] |
[
"doubling wire diameter doubles the strength of the electromagnetic field",
"Nope. The thicker wire just allows more current before overheating. That is because it has a lower resistance. ",
"Which is better? It all depends on your goal. If you just want a stronger magnet, then more current and more turns are needed. The actual design will take things like power consumption, voltage, weight, size, duty cycle, temperature rise, etc into consideration. Ten turns at a one amp is as strong as a hundred turns at 0.1 amp, or one turn at 10 amps. The SI unit, ampere-turn is the product of the two factors. "
] |
[
"Does the decay energy affect the power output in a betavoltaeic battery?"
] |
[
false
] |
I mean does a low energy beta emitter produce as much power as a higher power emitter? (in a power cell) (if so - why? why can't we use the higher energy electrons better?) As far as I understood it it isn't the extra electron produced that "becomes" the power but it has something to do with a technology like solar cells? (could we use other materials to capture for instance gamma rays to produce power?) What happends to the electron later - Does it add to the power output by itself so to speak? (if we just packed a beta emitter inside a metal casing, would the casing get a higher voltage potential from capturing the electrons?) Are there even vast differences between beta decay energies of different isotopes to begin with? (I'm having some problems finding tables of beta decay energies and are finding weird (what seems like probability) graphs of energies. Cobalt-60 beta decay energy seems to be comparable(-ish) (in orders of magnitude) to carbon-14 decay energies if I understand things right). I know this is a lot of jumbled together questions, but I guess my main curiosity is the title one. Thank you
|
[
"A higher decay energy will produce more electron/hole pairs per decay. Measured relative to decay power (decay energy * decay rate), there is no large difference.",
"(if we just packed a beta emitter inside a metal casing, would the casing get a higher voltage potential from capturing the electrons?)",
"Yes, but that would be horribly inefficient.",
"Are there even vast differences between beta decay energies of different isotopes to begin with?",
"~20 keV (tritium as notable example) to the low MeV range. Yes."
] |
[
"Are there even vast differences between beta decay energies of different isotopes to begin with? (I'm having some problems finding tables of beta decay energies and are finding weird (what seems like probability) graphs of energies. Cobalt-60 beta decay energy seems to be comparable(-ish) (in orders of magnitude) to carbon-14 decay energies if I understand things right).",
"Beta decay energies tend to be around 1 MeV, but there is some variance spanning between a few keV to a few MeV. There's also the fact that beta particles are not monoenergetic, since the final state in a beta decay has three particles. All three share the decay energy, and how much each one gets is not uniquely determined, as it would be for a two body final state."
] |
[
"The beta particle, neutrino, and daughter nucleus all split the energy given off by the decay. Total energy and momentum are conserved."
] |
[
"Why will your eyes hurt looking at the sun, but not at a lightning strike?"
] |
[
false
] | null |
[
"Sun damage to the eyes (called solar retinopathy) damages the retina with bright lights. While the sun can cause that, so can other bright lights, such as arc welders or lasers. The more powerful the source, the less time it takes to cause damage. I would guess that the flash of a lightening strike, while fairly bright, is usually too distant and too fast to cause much serious damage. If you were much closer to a lightening strike, I would guess the flash may be enough to cause some damage. ",
"Additionally, sunlight puts out a lot of UV radation, which is significantly more damaging to the eyes. "
] |
[
"Damage from hazards tend to result from the severity of the hazard and the time of exposure. Consider a lighting strike takes 200 milliseconds consisting of 30 millisecond strokes (Wikipedia), whereas your exposure to the sun depends on how long you look. Consider also that much of photo retinopathy is due to photochemistry resulting in oxidation, buffering effects would be expected due to antioxidants present in the cells."
] |
[
"Additionally, sunlight puts out a lot of UV radation, which is significantly more damaging to the eyes. ",
"So does a lightning strike. They are hotter than the surface of the Sun, they emit a larger fraction of the energy as UV. In addition, if you are close you have less protection from the atmosphere.",
"But lightning bolts are very brief, so damage from their light is unlikely."
] |
[
"Geologists - Can you explain the plate boundary between Europe and Africa and the location of the Alps to me? (See details)"
] |
[
false
] |
So I am reading a bit about the alps after a vague mention of plate boundaries in a documentary. The thing that doesn't make sense to me is this: Some maps of the plate boundaries show the boundary basically as a line that goes from the Straight of Gibraltar under the boot of Italy and onward to the east. Another maps show a fault like a thumbs up going up basically where Italy is, but otherwise follow the same border. Question one - Is there a difference I am missing between plate boundaries and fault lines that would explain the different maps I've seen. Question two - Based on that - are the Alps right at the border of two plates meeting or not? The maps that show the plate boundary to the south of Italy make it look like there's approximately 1000km from the boundary to the alps. Maybe this is insignificant, but I don't understand why crumpling and uplifting is happening there and at the principle boundary. TLDR: Where is the actually boundary between the European and African continental plates? Is there a different between plate boundary and fault lines? Where are Alps relative to the plate boundary boundary/local fault lines? Why are Alps where they are relative to said boundary/lines?
|
[
"The key here is mostly the distinction between major, minor, and micro plates. When most non-geologists (or even non-tectonic geologists) think of 'tectonic plates', they usually think of some set of pretty large plates ",
"like this",
". In reality, we often further subdivide portions of ",
"those plates into smaller bits",
", either minor (smaller than major plates, but still pretty big and may make it onto 'major plate' maps depending on the size and purpose of the map, e.g. the ",
"Nazca plate",
" is technically a minor plate but is usually on major plate maps whereas the ",
"Somali plate",
" is often not distinguished from the African Plate) or micro (usually pretty small and within or near a plate boundary zone). So, the formal division between the major African and Eurasian plates basically runs down the center of the Mediterranean, but the Alps are mostly demarcated by the boundary between the Eurasian and the ",
"Adriatic plate",
" a micro-plate representing portions of former African plate continental material that rifted off of Africa and then collided with Eurasia. The Adriatic plate still moves somewhat independently from the Eurasian plate, so it is recognizable as an active and independent microplate, but it shares a more recent geologic history with the Eurasian plate (as opposed to the African plate) so in large scale maps, it gets lumped in with Eurasia. We also sometimes distinguish microplates which were formally independent, but now, through the process of ",
"suturing",
" are basically part of another plate, e.g. the ",
"Iberian plate",
" which is part of the Eurasian plate now. The geology and geologic history of the Alpine region is ridiculously complicated, so I'll stop there for this part of the question.",
"A fault, at the most general, is a discontinuity between rock masses that has accumulated displacement (as opposed to just a fracture, which is a discontinuity, but besides a small amount of separation, will not have any displacement across it). All plate boundaries are made up of faults, but not all faults are plate boundaries, i.e. you can have a fault within a plate, but if it is not a plate boundary, the fault will not completely divide a plate (it will not reach the edges) and will also not tend to fully separate the lithosphere on either side of it (an independent plate is a separate chunk of lithosphere, so to be a plate boundary fault, said fault needs to cut the entire lithosphere). ",
"Now, plate boundaries are rarely a single fault, they are usually fault systems. For example, the Pacific-North American plate boundary is often described as the ",
"San Andreas fault",
", but in reality, in most sections of the plate boundary, the boundary is a set of faults, e.g. in the northern zone near San Francisco, the ",
"San Andreas, San Gregorio, Hayward, Rodgers Creek, and Calaveras faults",
" all make up portions of the boundary (with some extra minor faults as well). The San Andreas fault (in the northern zone at least) tends to mark the actually plate boundary (i.e. where you cross from material with a different geologic history) but all of these faults are considered part of the plate boundary zone because they all partially accommodate the differential motion between the Pacific and North American plate.",
"This is also where the concept of microplates come in handy, especially in continent-continent collisions. The collision between two large continental plates can get pretty messy, so there are often regions between what we can clearly define as major plate 1 and major plate 2 that are behaving semi-independently and/or have distinct geologic histories. If they are moving independently from either major plate, we might classify them as a microplate. If they have distinct geology, are bounded by sutures, and are not moving independently of at least one of the plates, they would be better classified as a ",
"terrane",
" where they might have been a true microplate in the past, before suturing was complete on at least one side. Within a microplate and/or terrane, there will also likely be lots of faults which we would generally consider part of the plate boundary zone between the major plates."
] |
[
"Thank you so much for the explanation! If you happen to have a bit more time - could you give more information on the history of the Alpine region or link a good explanation on it?"
] |
[
"This is a pretty thorough pair of reviews from ",
"Schmid et al, 2004",
" and ",
"Handy et al, 2010",
". The latter has a good series of paleogeographic maps and cross sections tracking the evolution of the Alpine system through time."
] |
[
"Why didn't the universe collapse into a black hole at the Big Bang (when all matter was at the same point in space)?"
] |
[
false
] |
I don't know if I'm misreading what the Big Bang is, but it seems that all energy in space was located at one point at the start of the universe, and with post, it seems that it would definitely be enough to turn the universe "into" a black hole. edit: I meant in the title, not matter.
|
[
"Don't think of the Big Bang as an event that's associated with a single point somewhere in space. Think of it as an event that's associated with ",
" points in space."
] |
[
"It doesn't make any sense, no. The concept of size is not applicable to space.",
"English is not the language of physics. Maths is the language of physics. So there's only so far we can go with words. The metric equation that describes the large-scale geometry of the universe includes a numerical coefficient called the scale factor, and the scale factor is a function of time. That means the distance between any two fixed coordinate points depends on the age of the universe.",
"It's a bit pointless to try to turn that into some kind of simplistic metaphor. It is what it is; the universe does what it does. It isn't like anything."
] |
[
"Imagine you have an aquarium completely full with water in space. Let's ignore *how water would behave in the vacuum of space, this is about the absence of gravity. The water fills the aquarium completely, so it's a solid block.",
"That's the very first moment of the universe-reality. The water depicts energy.",
"What has happened since then at varying speed (fast in the beginning during the phase we call \"Big Bang\", later at a slower rate) is that the walls of the aquarium are pulled outside: The glass room is getting bigger. The water is drifting along aimlessly, forming little gaps in some places, and later the gaps are so big that it's instead just single drops drifting around and a few larger blobs.",
"That's the ",
"Metric Expansion",
". And this is how the universe began and has developed since. The big difference to reality is that space was an aquarium of ",
" size right from the start, so there are no outer walls that are pulled away, instead the space between space is growing (as if it were made of pixels, and new pixels are interjected between those all the time). Also, energy behaves \"a little\" different than water."
] |
[
"Unlike the rest of reddit, /r/AskScience is not about discussion or speculation: it is about authoritative answers from genuine experts."
] |
[
false
] |
[deleted]
|
[
"Couldn't disagree more. This subreddit isn't only about being \"correct\". And even if it was, I have seen multiple times where the panelists have been wrong, even about things in their own area of expertise (myself included).",
"What we don't want, is people taking everything somebody says as gospel just because they have a coloured tag. Additionally, I have seen it where panelists reply with very brusque answers without explaining themselves, or the reason/principle behind their answer. I think that is much worse for this reddit than \"non-specialists\" answering things to the best of their knowledge.",
"What we ",
" in this subreddit is intelligent, detailed answers. If you don't have a Master's or a PhD, I don't care. Provide references for any crazy things you bring out of thin air, and explain yourself clearly. That should be enough."
] |
[
"I disagree. Many of the answers I've given in the past were ones I could have given by the time I was in the second year of my bachelor's degree."
] |
[
"I have to admit that I have a very different conception of this subreddit and what it should be. And I’ll also admit that I do feel invested: this is the only subreddit that I routinely check and read all the posts. I have learned so much, and it genuinely warms my heart to listen to people who are passionate about what they do and sharing it with others. For this reason I must vehemently degree with your conception of what this subreddit is supposed to be. You seem to want to turn this subreddit into an archive or encyclopedia where each thread has one and only one answer, and once the question is answered it is sequestered away, maybe to be read by a person or so every year brave enough to use reddit’s search function. What a squandering of vast potential. No discussion you say? Then why even call ourselves a community? I can get more interaction from an ATM. This place should be a golden tree of discussion. No speculation you say? How else can new ideas be forwarded and tested? All my favorite moments in graduate school were when people unabashedly threw out an idea just to see if it would stick. I have seen these ideas turn into grant proposals, articles and dissertations. No, I don’t like your vision at all.",
"Your vision captures everything I feel is wrong with academia. Here I work to produce knowledge to be consumed by an extremely small handful of people, locked away atop an ivory tower. But I have seen knowledge flourish when placed into the hand of interested students, I know that reward of being an educator. I can understand your worry of the spread of misinformation. If a person is wrong, correct them. Take some passion in what you do and be an educator. It seems everyone is so afraid of being wrong, and that everyone can only see corrections as a personal attack. But we’re all wrong. Hell I just wrote a chapter of my dissertation that I am sure someone will rip apart for being wrong wrong wrong, but nothing ever changes unless someone puts themselves out there.",
"I want this subreddit to most certainly be about discussion and about speculation. I want it to be about experts who are passionate about their field talking with people who are passionate to learn it (Whoever came up with the AskScience AMA series is brilliant). If someone takes the time to write a comment, even if it isn’t factual, it deserves to be responded to, not just down voted. I want every dumb question asked. I want every wild and crazy idea thrown out there. I find it inspiring and a true pleasure. ",
"I don't know if I can muster a TL:DR, but I will say that sometimes the answers are really not as important as the questions.",
"/ rant"
] |
[
"How much power do I have over myself?"
] |
[
false
] |
[deleted]
|
[
"Since things like psychotherapy and mindfulness meditation are scientifically proven to improve the lives of depressives, even without medication, I'd say quite a bit.",
"This is a moral and philosophical beehive, however. How about those who are never able to get out of depression -- are they more sick, or simply too useless or unskilled to get their thoughts back on track? Is it ",
" (whatever that means), or just a defense mechanism reacting when you try to turn those negative spirals?",
"But the short answer to your question is yes, kind of. You can change the release of neurotransmitters through thoughts (think happy thoughts: ",
"1",
", ",
"2",
", sorry for lack of full text) or actions (sex, workout). Then again, one of the documents linked discuss how personality and motivation is influenced by for instance genetic sensitivity to dopamine in the brain. And there are many more neurotransmitters than the famous few (serotonin, dopamine, epinephrine) that we haven't even studied much. So it's not that simple. ",
"But if you meditate, focus on thinking about the good things in life and possibly talk to a therapist about it, and do actions that stimulate the right moods, chances are you'll be a happier person. Even if you're unhappy to begin with."
] |
[
"I'd like to add: How much power do we have over ",
" our conditions? When one becomes overly cynical and pessimistic over years or decades, how can one break free?"
] |
[
"This is more complex than neurochemistry, which mediates the strength of connections, but also has a lot to do with structure i.e. which neurons connect to which neurons.",
"Both the strength and structure of neural connections is incredibly changeable (plastic) so, by repetitively stimulating desirable populations of neurons, new \"thought processes\" can be learned and may eventually become habitual.",
"The key is: practice, practice, practice.......and also exercise."
] |
[
"When the space shuttle piggy backs the 747 like we saw in so many photos recently, does it provide extra lift or just dead weight?"
] |
[
false
] |
I'm talking about in this scenario: So, extra lift? dead weight? What kind of adjustments must the pilots make to fly around like that?
|
[
"Yes, but you need to change it's angle of attack continuously ( i.e spin it). This is why a footballer can make a curved kick to bend the trajectory of a spherical football. "
] |
[
"I am pretty sure the shuttle is positioned to provide near neutral lift or it would make it very difficult to to fly. The shuttles body itself provides some of the lift. it appears that it is positioned at a slightly positive angle of attack. The result is that the lift from the shuttle is nearly equal to the weight of the shuttle"
] |
[
"From my best understanding of what my Aero Professor said in lecture the other day:",
"The wings on space shuttle arent really designed to provide lift. The shuttle is a Delta Wing design, but the body of the craft is technically a lifting body, meaning the fuselage itself provides some lift. ",
"Also, when mounted on the 747 the Shuttle is inclined slightly giving it a greater angle of attack on the free stream velocity than if it were mounted flat, increasing lift. ",
"So yes, it does provide some lift but not much. Overall it is mostly dead weight.",
"Source: Aerospace Engineering Major"
] |
[
"How do black holes absorb light if they rely on based gravity, which is based on mass, to draw things in?"
] |
[
false
] | null |
[
"Mass ",
" gravity. Something doesn't need to have a mass to ",
" to gravity. One way of seeing this is the equivalence principle: the motion of an object in a gravitational field is totally independent of its mass. A larger mass doesn't fall faster than a smaller mass. Similarly, something will still fall if its mass is so small it is zero."
] |
[
"Indeed, but the missing piece is Newton's second law tells us how a force affects the motion of an object. So if we are talking about the motion of mass m1, then you need:",
"Gm1m2/r",
" = m1 a",
"and lo! m1 cancels out from both sides, leaving a description of the motion of the object that is independent of m1",
"(i.e. as the force goes to zero, the effect of the force via Newton's second law goes to infinity, and when you consider both effects in tandem, they both cancel out)"
] |
[
"Correct me if I’m wrong, but if the equation for the force between two objects Gm1m2/r",
" and since the mass of one of the objects is zero, wouldn’t the force be zero?"
] |
[
"Why are oil stained napkins transparent?"
] |
[
false
] |
If you've ever held an oil stained napkin to a light, you can see through it! This isn't the case with wet, water logged napkins. What causes oil stained napkins to be transparent? Is this property exclusive to lipids?
|
[
"The short answer is that oil acts as an ",
"index-matching medium",
" for the paper. What that means is that oil has a refractive index similar to that of paper, or at least more similar than the refractive index of air. As a result, the napkin scatters much less light, which in turn allows more light to simply be transmitted through the paper. The end result is that the paper looks more translucent.",
"The more detailed explanation for this effect is that, the way light \"distinguishes\" what medium it travels through is (to a good approximation) simply determined by the ",
"complex refractive index",
" of the material in question. In the case of paper, the refractive index is usually about 1.5. What is also important here is the fact that paper is made out of a bunch of irregular cellulose fibers, which is why it looks very rough ",
"under high magnification",
". Normally air fills these pores and its refractive index is very close to 1. As a result of this index mismatch and its rough structure, the paper scatters incoming like crazy through a process called ",
"Mie scattering",
". This diffuse reflection makes the paper look white, for the same reason that clouds or milk look white. But when you fill the pores with water or oil, which have a refractive index that is close to that of cellulose, then you effectively get a much more homogeneous medium, which scatters light far less, which in turn allows more of the original beam of light to pass through. Water with a refractive index of 1.3 does a decent job of bridging the gap, but oil with a refractive index of 1.5 works ",
" well.",
"A related effect is how you can create polymer balls that look invisible in an index matched solvent, ",
"as shown here",
". Again, the idea is that because the refractive index of the balls and the liquid is the same, the light effectively just encounters one continuous medium. As a result there is little reflection/scattering at the ball/liquid interface so you can't even tell the balls are there."
] |
[
"Very well put!",
"I want to add that the phenomenon of impedance matching isn't limited to visible: it is important for sound waves (a megaphone bridges the gap between the acoustic impedance of your respiratory system & that of the open air), lower-energy electromagnetic waves in electronics, and presumably other fields also."
] |
[
"For anyone who is interested, here is a great video visually showing the phenomenon. You can see how exactly the wave behaves when it encounters a medium change.",
"https://youtu.be/DovunOxlY1k",
"Go to 20:00 (20 minutes). At this moment, the man visually shows how waves get reflected due to impedance mismatchs between the two medium.",
"The entire video is great by the way too. Amazing explainations and visualizations on wave behaviour and some basic calculations regarding them. "
] |
[
"What could have caused a violent reaction between 2 store-bought pool chlorine brands?"
] |
[
false
] |
A Tale of Two Chlorines Can someone please explain why I had a sturdy plastic bucket literally explode into fragments when I mixed 2 different brands of pool chlorine together? I've never seen something explode like that when exposed to open air. So what I would normally do is mix the chlorine with pool water and then pour everything into the pool, no problem. One day we switched chlorine brands, so I poured the last little bit of the original chlorine into the bucket (there might have been a little water in the bucket to begin with) and topped up with the new chlorine. I noticed vapor coming off the mixture almost immediately as I started mixing. The reaction started bubbling and boiling and within about 10 seconds, the mixture started putting out a thick yellow cloud. This was when I knew I had to GTFO, mainly to avoid breathing in any of the noxious fumes. I can't quite remember if I was going to call someone or to get water to dilute the mixture. I turned around and started walking and as I turned a corner about 5 meters away from where the bucket was left standing, I heard an incredibly loud bang and saw pieces of the red bucket fly past me and land in the pool and on the lawn over 10 meters away. There was literally nothing left at ground zero other than a few white stains from the powder. It was a really powerful explosion. This happened quite some years ago when I used to look after the pool at home, so the details may be a bit sketchy. I've always thought about that incident, what if I hadn't moved away? I could have been permanently blinded, or developed some kind of respiratory issue, possibly even hearing damage? P.S. the brands were HTH and Clarity in that order (i think) There was no outside contamination that I know of. Edit: Thanks for the replies and explanations so far. I'm glad I'm not the only one surprised/confused by this. Just a couple things, This a long time ago like I said, so it might not have bubbled for 10 seconds, the gas might have been green instead of yellow, etc. All I know for sure is that it was loud, it started raining red plastic bits, there was definitely no lid on the bucket and that there were 2 brands of chlorine in a bucket.
|
[
"According to the MSDS of ",
"HTH",
", the source of chlorine for the disinfectant is calcium hypochlorite. It also contains some calcium hydroxide and calcium carbonate to keep the pH above 7 which prevents the creation and release of poisonous chlorine gas. I couldn't find any information on Clarity as a pool disinfectant. However, it is likely that the Clarity brand contained ",
"Dichlor",
" which is an acid based pool disinfectant (pKa = ~6 for the non-chlorinated isocyanuric acid - dicloroisocyanuric acid will definitely be much more acidic). Mixing the acid pool disinfectant with the calcium hypochlorite produced green chlorine gas, which you observed, and a lot of heat.",
"",
"EDIT 1: Are you sure Clarity is specifically a pool disinfectant? I did some more digging and found a general peroxide disinfectant called ",
"Clarity",
". Peroxides also react with hypochlorites to generate heat but oxygen gas instead. This also removes the chlorine source giving dissolved chloride. I'm now unsure how the chlorine gas (which it what you seem to describe) is produced.",
"",
"EDIT 2: Clarity is most likely trichlor or dichlor which produces chlorine gas and a lot of heat when mixed with hypochlorites. This seems to be a very explosive reaction. see this ",
"video",
" posted by ",
"u/Vew",
" below."
] |
[
"It is also possible that the Cal hypo product added with the small amount of water added a lot of the heat too. I worked for a pool company and the first thing they explained was how if you add small amounts of water to Cal hypo products they have a nasty tendency of catching on fire or exploding. Since I'm not the smartest of people a couple of the other employees and me tested this and it quite violently set on fire I'm sure with the other product it just made it more violent."
] |
[
"Yes, this is what I originally thought was the case for the OP. It sounds like the OP added a whole load of undissolved hypochlorite which while dissolving will produce loads of heat. It's the first error made in any chem lab. People forget - dissolving substances (edit) can be very exothermic."
] |
[
"Does the space shuttle generate lift when riding piggyback on a 747?"
] |
[
false
] |
Basically how does having the space shuttle riding piggyback affect the dynamics of flight? does the shuttle help create lift or is the drag negate all of that?
|
[
"Without digging way into the physics, I'd say more drag than lift. Particularly with the aparatus that holds it to the seven four installed.",
"Maybe some lift at higher airspeeds, but the airframe combo is probably speed limited while being hauled.",
"The shuttle is designed to produce lift at high speeds and high angles of attack."
] |
[
"I'm pretty sure they are there for enhanced stability- I'd guess that orbiter does quite the number on airflow around the empenage when it's attached. Probably partially blanks the vertical stab of the 747, necessitating extra vertical stab help. Raises the question of rudder effectiveness while the orbiter is mounted. Hmmmm.",
"Now that I think about it, the initial glide tests on the orbiter were done by separating it from the 747 in flight, ",
"video here",
", so at least under some speeds and conditions, the vehicle does produce some lift- or at least enough directional stability to not fall out of the sky while it noses over to an effective speed."
] |
[
"What is the purpose of the unusual horizontal fins on the back of the lifter?"
] |
[
"To what extent is determinism true?"
] |
[
false
] |
I was having a discussion about free will and determinism and there are a couple of points that I need clarification on. Basically, if we knew all of the laws of physics and all of the properties of every particle in the universe could we predict the future? If there is an element of indeterminism is it evident at all scales or, for example, are things less predictable on a small scale and more predictable on a large scale? (I suppose I mean that even if everything is probabilities on the quantum scale does it follow that everything is still probabilities on a large scale, whether the probabilities are the same or not)?
|
[
"The answer is yes and no. There are many tricky issues regarding predictability, some are just a matter of complexity and others are really inherent to physics.",
"First, at small scales, it seems like quantum mechanics only allows us to answer certain questions probabilistically. So, if your question is: \"Where is the electron located now?\" then you can never have a fully deterministic answer to this question. If you're smarter and ask: \"what is the probability distribution of the position of the electron?\" then you have full determinism again, since the evolution laws of quantum mechanics are unitary.",
"Secondly, effects of small scales decouple from large scales, which means that if you want to predict the future, you are better off not caring about all of the laws of physics, you just need to know the laws of physics that operate on the length scales that you are interested in. In other words, you can predict with arbitrarily good precision the movements of the planets around the sun without ever considering that the sun is made out of quarks.",
"So, suppose that you have a bunch of particles and you want to compute the time-evolution of this system, with the best precision you can have given your current knowledge of the laws of physics. For a few hundred particles, it already becomes impossible to write a computer code that will be able to exactly simulate the evolution of this system in a reasonable time-scale, simply because the complexity of the problem scales exponentially with the number of degrees of freedom you have. ",
" While this is true and you might buy yourself some time, all it takes is for me to slightly increase the amount of complexity, and you're again waiting the age of the universe for the end of your calculations. ",
"And even if by magic you came up with an exponentially faster computer, you still have to take into account the fact that you have chaotic behavior in your systems, meaning that slightly changing initial conditions will give you completely different time evolutions, so before you come up with problems because of your incomplete knowledge of the laws of physics, chaos will kill your ability to predict the future, unless you know the initial conditions with an arbitrarily good precision."
] |
[
"I feel like you haven't made strong statements differentiating between predictability and determinism, which is something that I haven't fully understood about quantum mechanics (and related).",
"I realise that it's impossible for us to know know the states of any particular system enough to predict it accurately (Heisenberg), and I understand that even small imperfections in our measurements predictions can propagate up to mean that we can't predict things accurately at all at even the macroscopic level - i.e. we can't predict the worlds weather because we can't account for every butterfly.",
"But whether we can accurately predict something is a separate question to whether it's deterministic. For example, if I roll a dice under a box, you might not have enough information to predict the dices outcome, but that does not mean that the dice exists, as a probability cloud of all the states at the same time, even if that is a convenient way for you to think about when considering dice outcomes.",
"My question is, when we talk about probability distributions of electrons, is that actually a description of how the electron exists, or is it just a useful way of thinking about it since the electron will always be 'under the box'? Of course it could be that there isn't a meaningful distinction between these two things, since we can never 'see' an electron, and the idea of it 'being' in one particular place may not be meaningful.",
"And this gets back to the determinism question. Even if we take it as a given that the universe is not ",
", is it such that there are infinite outcomes, or is there only one outcome, even if it's actually impossible for us to predict it?"
] |
[
"Basically, if we knew all of the laws of physics and all of the properties of every particle in the universe could we predict the future?",
"Unfortunately, this question is not yet resolved -- it is an outstanding question. Different interpretations of quantum mechanics either preserve or violate determinism. What we ",
" know is that ",
" the universe is deterministic, then the missing variables that we don't know must be global variables rather than local -- ",
"Bell's theorem",
" rules out local variable theories from ever being able to reproduce all of the predictions of quantum mechanics, and experimental tests so far indicate that nature favors QM over a completely local theory.",
"If there is an element of indeterminism is it evident at all scales or, for example, are things less predictable on a small scale and more predictable on a large scale?",
"It could in principle become evident at any scale, but for the most part it involves only very small scales. Until quantum mechanics came about, classical mechanics seemed to have no problems describing how macroscopic objects move, while being completely deterministic. So only when quantum effects become amplified to macroscopic scales, is it possible for nondeterministic effects to become evident on those scales.",
"(I suppose I mean that even if everything is probabilities on the quantum scale does it follow that everything is still probabilities on a large scale, whether the probabilities are the same or not)?",
"It follows that everything is still probabilities, but the probabilities are not the same. This is very closely related to the concept of ",
", which has a simple analogy in terms of ",
" and ",
".",
"When you look at a macroscopic system, there are generally a certain number of degrees of freedom. For example, an ideal gas in a box, has degrees of freedom including temperature, pressure, volume, density ... and with just a handful of these quantities, you can more or less completely characterize the macroscopic behaviour of the system. However, on the microscopic scale, there is a much greater number of degrees of freedom -- including the positions/momenta of each particle, for example. \"Zooming out\" to a larger scale seems to result in less information being needed to describe the system (at least approximately, at that scale). Most of the microstates end up becoming trivial, and the macrostates that they are mapped to approach a singular value (for example, temperature is a statistical effect, the thermal energy of each individual particle doesn't really matter as much as the average value).",
"It's a little bit like dice. If you roll a single 6-sided die, you get a number from 1-6. If you roll a second die yielding another number 1-6, you have 36 total \"microstates,\" corresponding to the number pairs ",
". However, if you define a macrostate to be the addition of the two microstates, then you end up with only ten possible macrostates: 2-12. Then each of the microstates maps to one of the macrostates -- some macrostates have more microstates mapped to them than other macrostates do.",
"Notice how for the ",
", every result has an equal probability: you are just as likely to roll (1, 2) as you are to roll (4, 4). However, for the ",
", certain states are more probable: You are more likely to roll a 7 than a 12. That is because there are more microstates corresponding to the macrostate of 7 (a whole six microstates: {(1, 6), (2, 5) ... (6, 1)}), than there are corresponding to the macrostate of 12 (only one microstate: {(6, 6)}).",
"So we say that certain macrostates are \"",
"\". Even though the microstates may be individually indeterminate, the macrostate might be very precisely determined, due to a high number of microstates corresponding to it and a low variance. This is just like the above gas example -- even though the thermal energy of any individual molecule of gas might have a big variance and might be indeterminate, the collective thermal energy tends toward an average value -- and the average value (the macroscopic temperature) may be known and easily determined, while the individual values may be unknown and difficult to determine.",
"Does that help?"
] |
[
"Why did this water filter turn black?"
] |
[
false
] |
[deleted]
|
[
"The filter contains carbon black as one of the filtering elements.",
"Some of the smaller carbon black particles escaped the inner filter and have become impregnated in the outer filter, turning it black."
] |
[
"I may be really wrong here but carbon black would not be used as a filter material... it is a nasty material, maybe \"black colored activated carbon\" is what you meant to say?"
] |
[
"That's what the manufacturer calls it. You're right, it's probably activated carbon, though."
] |
[
"Do nervous systems themselves produce heat?"
] |
[
false
] |
Since the nervous system is carrying electricity for signals (even if it is a minute amount in terms of amperage or voltage), it has to produce some kind of heat unless the tissue that makes up the nervous system conducts without resistance, right? If so then, if we could somehow "overclock" our brains, we could potentially cause them to overheat and fry them just like circuits in a computer or a copper wire with too much resistance.
|
[
"The brain isn't governed by a clocking type system. Parts all work independantly and dependantly depending on what they're doing and trying to do. Everything in the body has an electrical resistance, including our neurons and synapses, therefore heat has to be given off. There are many ways to overheat the brain, but \"overclocking\" the brain wouldn't give off enough heat in order to raise the body's temperature to a point where you would get heat stroke, you'd more likely end up having a stroke or becoming catatonic if you suddenly had all your neurons firing."
] |
[
"Many neurotoxins cause nerves to fire uncontrollably, or interfere with their ability to stop firing.",
"Nerve action potentials are electrochemical, not strictly electrical. While preparing to fire, sodium ions are pumped out and potassium ions are pumped in, while these gated channels in the cell membrane won't let them return to equilibrium while the nerve is still charged. Neurotransmitters received at one end start this wave of depolarization; letting the ions out at one end causes nearby gated channels to open, which neutralizes more of the neuron, which allows nearby gated channels to open and neutralizes more of the neuron until we get to the next synapse which releases neurotransmitters in response to depolarization.",
"It takes energy to re-establish the ion gradient, and firing constantly tires the cell and causes oxidative stress. Heat production is not usually an issue although the energy used for normal brain activity does make a significant amount of heat."
] |
[
"Interesting question. The idea of currents in neurons bothered me a lot when I was taking electrophysiology, so I will do my best from what I have been taught by my professors.",
"It isnt the current that carries a signal in a neuron, the neuron couldnt give two hoots about the current, the neuron cares about the depolarization caused by a current. When an action potential aka signal comes rolling by the neuron (lets think of it like a wire, long conducting tube) it opens some channels in the membrane that let ions flow in/out aka current. But this is different from the current we think of in circuits because the flow of current is in a direction perpendicular to the direction of information flow. ",
"So the current isnt important, it does not carry information. But when a current is allowed to flow it changes the cells potential in THAT region which in turn makes subsequent section conduct current which changes the potential in THAT region and so on and so on. This depolarization is what carries information.",
"These currents or ion flow occurs through channels. These channels conduct currents in the pico amp range, really really tiny and really really really transient. So because of this and the because our cytosol is fairly good conductor the heat generated is negligible compared to the heat generated by normal metabolic activity.",
"In light of all this you could potentially ask, what if we opened all the channels, adding up all the currents and then let it run for a really long time, what about the heat generated then? ",
"First, these channels have a refractory period. They close after a set time, something on the micro-milli second range, and they cant be opened again for something on the order of a hundred milli seconds.",
"Lets assume you got around that problem, for there to be a Na+ current you need a Na+ gradient and a open channel to conduct it. But the cell can only develop a limited gradient, the gradient gets dissapated something on the order of a few thousand action potentials if you dont give it enough time to recover.",
"So in conclusion to fry a brain by 'overclocking' it seems a REMOTE possibility at best."
] |
[
"Are Black Hole forming Supernovae less energetic than Neutron Star forming Supernovae?"
] |
[
false
] |
I've been wondering about this for a while but haven't really had anyone to ask. Nothing suggests this is true, but knowing some basics about how supernovae occur, I can't figure out why it wouldn't be. From what I understand, Supernovae occur when Fusion sharply cuts off due to the forming of Iron-56 which can't fuse and release energy, therefore the radiation pressure cuts off so the star's own gravity can finally cause the star to collapse. The actual supernova itself is a combination of two factors. Firstly, when the electrons are forced into the protons, a vast number of high energy neutrinos are produced. These are absorbed by the incoming matter due to the sheer number of them, and this forces the collapsing star back on itself. That was just a precursor to see if my current knowledge is correct. This point is what leads to my question. The second factor that causes a star to get blown outwards is the contact of the incoming shockwave with the incompressable core, so the shockwave has no choice but to rebound outwards. In the case of a neutron star forming, this is true so it seems to stand true. when a black hole forms the force is such that even the core is incompressable and can in fact be compressed infinitely to a singularity as not even neutron degeneracy pressure can withstand it. As such, the shockwave will simply be absorbed into the singularity as the black hole forms rather than rebound, therefore less energy is reflected back onto the collapsing mass so the supernova is less energetic. Why is this not the case? Also, as an aside, is Neutron Degeneracy pressure which prevents every supernova-undergoing star from collapsing into a full black hole rather than a neutron star the same as the strong force?
|
[
"A large star collapsing to a black hole would not produce a supernova.",
"Well now I'm very confused because I always heard that black holes were ",
" by supernovae. Maybe I or my sources conflated the phrase \"collapse of a star\" with \"supernova\" and that caused the confusion?"
] |
[
"A large star collapsing to a black hole would not produce a supernova.",
"Well now I'm very confused because I always heard that black holes were ",
" by supernovae. Maybe I or my sources conflated the phrase \"collapse of a star\" with \"supernova\" and that caused the confusion?"
] |
[
"Supernovae that form black holes can actually be more powerful than neutron-star supernovae. Neutrinos and other normal drivers of supernovae indeed tend to drop in energy as the core mass increases, not because the central object is a black hole, but because the central mass is larger and it's harder to escape. ",
"Because of the energy of the shockwave you mention and conservation of angular momentum, the black hole can't form immediately except for the heaviest progenitors (and the heaviest progenitors nowadays often blow away their outer envelopes and aren't so heavy when they go supernova). Instead, a rapidly rotating neutron star that would collapse to a black hole if not for the rotation is produced first. This neutron star can produce as many neutrinos as an ordinary neutron star - so as I stated before, the fact that a black hole is eventually produced is not very important. Meanwhile, some material from the stellar envelope falls back towards the central object, producing an accretion disk. ",
"If the rotation is weak and the disk is low in mass, the supernova can be significantly weaker than an ordinary one, as you stated. But if the rotation of the neutron star and the resulting black hole is rapid enough, and the disk is massive enough, it can produce powerful magnetic jets that create a \"hypernova\", an abnormally powerful supernova, and possibly a gamma-ray burst. So everything depends on rotation and magnetic fields -which is an old joke in the astrophysical community.",
"P.S. The neutron degeneracy pressure has nothing to do with the strong force - in fact, it isn't related to any force at all. It actually is just a result of the fact that fermions (such as neutrons) take up space (or in quantum terms, take up states) and you can't crush them too far without them resisting it. Contrast that with light, which is happy to pile everything into one state in lasers."
] |
[
"Help finding the IR Identification Chart from a few weeks ago..."
] |
[
false
] |
Can't...find it using both reddit's search and google. Not remembering the key phrases used in the post either though... help plz!
|
[
"http://www.reddit.com/r/chemistry/comments/il2ya/ir_an_illustrated_guide/"
] |
[
"http://toeholds.files.wordpress.com/2010/09/ir-illustrated.png",
" Is this what you're talking about?"
] |
[
":)",
"Sweet. Someone's actually ",
" for it. FWIW, I've finally put pen to tablet for ",
", and when it's done and checked for factual accuracy by NMR-theory folks (that's Rupert here) I'll post it up to ",
"r/chem",
"!"
] |
[
"How do societies/cultures 'lose knowledge'?"
] |
[
false
] |
The Greek and the Romans (and I'm sure other cultures too) seem to have had an amazing level of knowledge and wisdom in a wide variety of fields. They created things like the Baghdad Battery, the Antikythera Mechanism, special cements which helped create Aquaeducts that are still around millenia later. Also knowledge about astronomy, the human body and many other things I forgot about (pun bad, but intended). Many things took centuries to be re-discovered. How does this happen and what else might we have collectively forgotten over time?
|
[
"Usually it’s simply because the average person doesn’t know the exact ins and outs of the most advanced technology of the time. If many people die at one time due to disease or conquest, most of the information about a society dies with them. Think about it, if civilization fell chances are most people wouldn’t be able to build an iphone or a computer or a tank from pieces they had lying around. Even then, it probably would be shoddy and entirely from memory. Today, we do have better access to information storage with things like computers and the internet, but with an EMP of some kind it would wipe all of that out. All of the internet and our digital stores: gone. The only things surviving would be physical documents and memory, both of which naturally degrade over time. ",
"Sometimes, though, it’s a deliberate sabotage. The Library of Alexandria was burned as an attack, and that’s the biggest thing I think of when I hear “lost knowledge”. ",
"Other times, it’s because certain information is considered sacred and only specific people are allowed to have access to it. It’s one of the reasons almost nothing is known about Native American culture, they are very secretive about their practices.",
"In general, there are many reasons information can be completely lost from memory. "
] |
[
"Sorry to be a pedant here, but it’s a common misconception that the Great Library of Alexandria was burned intentionally by Caesar. To quote from the wiki ",
"“[Julius Caesar’s] soldiers set fire to his own ships while trying to clear the wharves to block the fleet belonging to Cleopatra's brother Ptolemy XIV. This fire spread to the parts of the city nearest to the docks, causing considerable devastation.” This included the library and approximately 40,000 of the scrolls within sadly",
"Sorry for no link, on mobile",
"Edit: I found a better quote",
"The Greek Middle Platonist Plutarch (c. 46–120 AD) writes in his Life of Caesar that, \"[W]hen the enemy endeavored to cut off his communication by sea, he was forced to divert that danger by setting fire to his own ships, which, after burning the docks, thence spread on and destroyed the great library.\""
] |
[
"To add to that, even with YouTube, much of how to do things is a practiced skill. Each person who does it has to learn crucial details by doing and personal observation. It’s getting better with CNC and 3d printing but even that has a lot of undocumented and poorly documented knowledge involved. "
] |
[
"Does how hydrated you are effect how strong caffeine effects you?"
] |
[
false
] |
This is a question that came out of a conversation about how transgender hormone replacement therapy for MtF people can decrease alcohol tolerance because you have less water in your body. This lead to the question of whether or not the amount of water in your system can effect how much caffeine you absorb from coffee. I looked it up and besides the mass of articles saying coffee dehydrated you, I only found one source that was kinda close which said that if you're more hydrated when you drink coffee you'll get better effects from the caffeine, and another article saying that drinking a lot of water will help flush your system of caffeine. The only remotely close article was written 6 years ago and lacks any medical sources. I'm just a barista with a very basic understanding of how caffeine effects the body, mostly through my own experience. The somewhat contradictory information isn't very helpful and I was wondering if there was anyone who knows this stuff who could help me out.
|
[
"Caffeine is absorbed by the gut and dissolves in both the body's water and fat molecules. The \"strong effect\" of caffeine is dependent on your body's tolerance and how quickly it takes for the caffeine to peak in your blood. As far as how long it takes for caffeine to peak in your blood, the biggest factor will be whether or not you have food in your stomach. Drinking coffee on an empty stomach will have a more dramatic caffeine effect. As far as your question on hydration, the caffeine will dissolve and travel through your blood stream more quickly if your body is hydrated."
] |
[
"You should be wary of the places you came across saying \"coffee dehydrated you\". ",
"Though certain beverages will hydrate you more than others, coffee is still a net-hydrator.",
" What's more, ",
"studies of habitual coffee drinkers find no evidence of dehydration with even 3-6 cups a day",
". The Mayo clinic ",
"lays this myth to rest simply with",
": ",
"Drinking caffeine-containing beverages as part of a normal lifestyle doesn't cause fluid loss in excess of the volume ingested."
] |
[
"Not your primary question, but the issue with MTF transitions isn’t hormone replacement, it’s the drug Spironolactone, which blocks testosterone (I’ve been on it for the treatment of PCOS) but it’s primary use is as a potassium-sparing diuretic. And it does such a good job at that that I had to keep soy sauce packets with me to maintain my electrolyte balance. Someone actually in the field might correct me but I believe taking estrogen actually makes you retain more water."
] |
[
"How does heat get lost in space?"
] |
[
false
] | null |
[
"radiative cooling via ",
"thermal radiation"
] |
[
"Heat is the result of excited, highly energetic atoms. When heat is given off, these atoms are going from a higher energy state to a lower energy state. So a coal would extinguish in space if it was burning, but that energy would hypothetically be in the carbon atoms of the coal still. Since \"space\" lacks a medium that can capture heat's convection and conduction, the energy in the atoms of carbon would dissipate only through electromagnetic radiation, and quickly at that. So the heat energy dissipates throughout space as electromagnetic radiation, if I understand it correctly."
] |
[
"Heh. Well at least I understood what you were saying. I checked out that thermal radiation wiki and thought I was going to have to do an askscience \"What the hell is thermal radiation?\" But then I read the wiki again and noticed \"Thermal radiation is electromagnetic radiation...\" so I'm going to assume that heat loss is due to light, which requires no medium to pass through, works in a vacuum, and answers my question. Thanks guys. :D"
] |
[
"How would random fluctuations in the level of entropy come about? (obvious Layman)"
] |
[
false
] |
I just don't get how a constantly rising level of entropy would ever fluctuate let alone fluctuate into an extremely low entropic state. All help is appreciated.
|
[
"So to answer this question, we need to look at what entropy is. It's often described as the amount of disorder in a system, but I don't really like this. Disorder isn't really a well defined physical quantity. What ",
" a well defined physical quantity (and directly related to entropy) is something called multiplicity.",
"To get a picture of multiplicity, consider flipping 100 coins. There's 100 possible outcomes (all heads, one tail, two tails,...). However, these are not equally likely. The chances of getting all heads is 1/(2",
" ) = 7.89x10",
" % since there is only one way to do it. Whereas the chances of getting 50 heads is (100C50)/(2",
" ) = 7.96%. This outcome has the highest multiplicity and thus the highest entropy.",
"Now imagine you have 100 coins all heads up and you change it randomly a little bit at a time. Let's do this by randomly picking a coin and flipping it. After a while you would end up very close to having half heads and half tails. Even if you kept flipping coins after reaching equilibrium, the number of heads would deviate from 50 by only a little bit (over 95% chance to stay between 40 and 60).",
"In real life situations, instead of having 2",
" possible configurations, there are more like 10",
" most of which are effectively identical. Thus the system will quickly tend toward the state of highest entropy and tend to stay there, even though there is nothing making it do so besides simple probability."
] |
[
"I just don't get how a constantly rising level of entropy would ever fluctuate let alone fluctuate into an extremely low entropic state. All help is appreciated.",
"It is important to emphasize the role of chance in earthly processes. Entropy must increase overall in a closed system, but this doesn't mean there are no local apparent violations.",
"Let's say there is a closed system, one in which overall entropy increases (as it must). But let's make a model we can easily understand -- the flipping of a coin. A coin would normally be perfectly fair, but it' s an entropy-coin, so it always favors the \"house\" (i.e. nature) by producing 55 heads outcomes on average for 100 flips.",
"That's a good example of a natural system -- the sun rises and sets, various thermodynamic processes take place, but it's like a perpetually flipping coin that has a built-in bias in favor of increasing entropy. Very easy to understand.",
"But in such a model, does the coin always produce exactly 55 heads outcomes for every 100 flips? No, of course not. Sometimes it produces 45 heads, sometimes 65. And very rarely, it produces no heads outcomes at all (with a probability of about 2",
" ).",
"My point is that a random process only needs to honor entropy on average, not in every instance. The overall outcome must increase entropy, but anything might happen on a given day.",
"A more concrete example is the classic experiment of opening a bottle of perfume. It is very likely that the perfume will escape and fill the room, and that is the expected outcome that agrees with entropy.",
"What is the probability that the perfume will spontaneously reassemble in the bottle again? Very, very unlikely, ",
". And if it did happen, it would not violate entropy, because the overall entropy would continue to increase.",
"The perfume is just like the flipped coin that could produce a long string of tails with a very low probability."
] |
[
"Thank you. I feel I have a much better understanding now."
] |
[
"Using the DNA is a code? or like a code analogy, how does that translate into attributes we can identify with?"
] |
[
false
] |
For example, if human DNA is like a code. How does a cell translate that code into attributes like blue eye color. Is DNA similar to a "programming code/instruction" or does DNA contain sequences that are associated with attributes that are used during protein synthesis. ...ignore what I said above, basically how would you describe DNA to a lay person from the DNA gene sequences...to human attributes we can identify with.
|
[
"The double-strandedness of DNA is the secret to its replication; you might say the very secret of life:",
"T always pairs with A",
"C always pairs with G",
"So they are two complementary strands.",
"When the two strands separate to replicate, each becomes a template.",
"A new complementary strand forms by the pairing of bases with the template strand, and voila...",
"You now have two double-stranded DNA molecules identical to the one you started with."
] |
[
"Your first sentence is a bit misleading, since it implies that all genes are encoded on one strand only. Both strands code, but each individual gene is located either on one strand or the other."
] |
[
"DNA sequence is DIRECTLY related to protein sequence. DNA is transcribed into RNA and RNA is coded in clumps of 3 called 'codons' and each codon codes for an amino acid. Many amino acids in a chain make a protein. ",
"So let's take the DNA sequence:",
"TACAGTCTGACGGATCGG",
"The RNA is the complementary sequence to that where G and C are paired and A and T are paired, but RNA incorporates U instead of T. ",
"So the RNA is:",
"AUGUCAGACUGCCUAGCC",
"Now separate that into chunks of 3",
"AUG UCA GAC UGC CUA GCC",
"This corresponds to a protein of sequence:",
"Met-Ser-Asp-Cys-Leu-Ala",
"You can see the classical chart for what codons code for which amino acids ",
"here",
".",
"If that protein is a protein for the iris of the eye that has a blue pigment... bam. Blue eyes."
] |
[
"According to the tests, I'm colorblind, but I've never noticed problems with color vision. Is this normal?"
] |
[
false
] |
I fail every part of the Ishihara test except for plate #1 - the 'cyan and orange' one. However, when doing the Farnsworth Munsell 100 test online, on a calibrated monitor, I test in the midrange of male color vision capabilities. I have never had a problem with my color vision, do color correction on photos and video with no problem, but these simple dot tests stump me every time. Failing the Ishihara tests in high school kept me from joining the military in any technical field, but it has not stopped me from doing a great amount of work with color in my professional career - from wiring, to paint matching, to graphics and photography. Am I atypical, or do the standard screening tests determine "deficiencies" that make no real difference?
|
[
"Just FYI - did the FM100 test again, and got a 36. Not perfect, but according to the summary after doing the test at ",
"http://www.xrite.com/custom_page.aspx?pageid=77&lang=en",
" it said my color vision was somewhere around the 40th percentile."
] |
[
"just to chime in: I just took that test and scored a 12. I also work a lot with color (although I was doing it on an uncalibrated monitor, which is what I blame on getting a 12)."
] |
[
"I scored a 7 and I'm pretty happy with that."
] |
[
"Are there any downsides to Fusion energy research? If not with the reactors themselves, then weapons they would enable?"
] |
[
false
] |
Fusion energy is the holy grail of energy sources and I know it avoids all the nasty byproducts of fission - such as meltdowns, radioactive waste, rare source of fuels. However, fusion as a weapons technology is also much more preferable to fission - in terms of potential yield, commonly occurring fuel with no radioactive signature, and lack of long term fallout. I was wondering if there are any downsides to fusion research - specifically, are there certain pathways for fusion which are dual use? Right now, even fusion bombs are very hard to create. You basically need a fission reaction to boostrap the fusion (which often then goes on to just bootstrap a third fission reaction). However, would fusion energy success allow for the creation of a ? From what I have read, creating fusion bombs and energy require quite different triggering processes, but there are many pathways to fusion, ranging from plausible hot ignition to pretty unlikely cold fusion. Could any of these make Fusion Bombs easier and more accessible to create?
|
[
"The biggest issue is, that we simply don't know (yet). But I wouldn't be that quick in glorifying fission, at least in the way you do. ",
"Uncontrolled meltdowns are improbable (as it requires power input to output any energy), fuels (typically deuterium and tritium) aren't ",
" more prolific than uranium and there are radioactive byproducts. Tritium itself is radioactive and ",
" to be kept away from environment and high-energy neutrons from the reaction are absorbed, creating unstable isotopes from surrounding material. The whole reactor is (to a certain extent) a radioactive waste product, once decommissioned.",
"But the interesting question is: Why do you consider military technologies a downside to doing research?"
] |
[
"But the interesting question is: Why do you consider military technologies a downside to doing research?",
"I think the point about this is that military power isn't the goal that he wants to have achieved by making fusion a viable energy source. In so far it is a downside because it would eventually lead to war or could at least instead of providing a basis to create basically free energy which would be a first step towards solving poverty.",
"Also having components that can't really be traced due to no radioactive signature would make weapons using fusion way more dangerous tools for terrorists.",
"At least this is how I interpret OP's question."
] |
[
"This is correct. Right now Nuclear proliferation is strictly controlled and easy to monitor. I was wondering if fusion research could make that a futile endeavor."
] |
[
"why is it an artichoke oxidizes very quickly when cut, but cucumbers oxidize very slowly?"
] |
[
false
] | null |
[
"Cut fruits and vegetables turn brown due to the oxidation of polyphenols by an enzyme polyphenol oxidase, which is released when cells are cut. The rate of browning depends on various factors, such as the phenolic content of the food, the polyphenol oxidase content of the food, the oxygen content of the air, the temperature, the pH of the food, and the presence of antioxidants such as vitamin C. I would hypothesize that these factors are at play, hopefully someone can find data to support which factor is dominant in this case. ",
"Source: MS in food science. "
] |
[
"What's the purpose of polyphenol oxidase? Does an oxidized fruit/vegetable provide less antioxidants for our bodies when we eat them?"
] |
[
"Polyphenol oxidase is usually part of a defense mechanism which protects damaged parts of the plant from infection. The compounds it produces can kill bacteria and fungi"
] |
[
"What is the melting point of roads?"
] |
[
false
] | null |
[
"http://en.wikipedia.org/wiki/Asphalt_concrete",
"Mixing is generally performed with the aggregate at about 300 °F (roughly 150 °C) for virgin asphalt "
] |
[
"Thanks"
] |
[
"It should be noted that asphalt doesn't have a defined \"melting\" point like e.g. ice. As you increase the temperature, it gradually behaves more and more like a liquid. Over a pretty large temperature range, asphalt is basically a ",
"viscoelastic",
" material. This means that it doesn't flow instantaneously, but if you put a force on it for a long time it will behave like a really viscous liquid."
] |
[
"OHow does our large intestine not suffer from the output of stomach acid?"
] |
[
false
] | null |
[
"As food progress through the intestines, the pH increases because of the chemical released has a tremendously higher pH then the stomach acid."
] |
[
"So there is not some hunk of muscle that acts as a doorway from the stomach itself...its just a gradual ph progression that breaks it down?"
] |
[
"not much muscle, because the intestines are LONG and they have their pH increased until it reaches near biologically acceptable pH."
] |
[
"Why do rough surfaces encourage nucleation of CO2 in fizzy drinks?"
] |
[
false
] |
Just went to a cafe, got a bottle of Coke, put a paper straw in it, and it started bubbling up, out of the bottle and straight onto the table and onto me. I know that rough surfaces, such as a paper straw, or mentos do encourage nucleation of CO2, but could somebody explain why this happens to me? Thanks, Noah
|
[
"The amount of gas that'll dissolve into a liquid depends on the pressure. During packaging, lots of gas is dissolved into the soda using high pressure. When you open the soda, the system isn't at equilibrium anymore, and all of the gas inside the soda ",
" to come out of solution and gasify.",
"The problem is inside the homogeneous body of the soda, it's actually very hard to build a bubble of gas. If some gas particles start to coalesce out of solution into a bubble, the cohesion of the surrounding liquid tends to collapse the bubble. This is just surface tension. A big enough bubble will be able to hold itself together against the liquid, because it has a smaller surface-to-volume ratio, but a small bubble is going to collapse very quickly.",
"If you know some thermodynamics, the issue is that the free energy is stuck at a metastable equilibrium. The amount of gas coming out of solution to form a bubble, and thus the amount of free energy liberated, is proportional to r",
", whereas the surface area of the bubble, and thus the amount of energy required to form the liquid-gas interface, goes like r",
". No matter how you pick the coefficients, Ar",
" - Br",
" will always be positive close to 0. So small bubbles will always be energetically unfavoured.",
"Rough surfaces provide what are called \"nucleation sites\". Cracks and valleys on the surface mean you don't need to produce the whole spherical surface to start accumulating some gas. The edges of the scratch in the glass or fibres of the straw or whatever effectively give you some \"free\" surface area that you don't need to pay any thermodynamic free energy to maintain against surface tension."
] |
[
"I will consider water as the solvent, as is the case for Coke, and I will consider the surface to be chemically inert, which is mostly true for a paper straw or sand dust, but not sugar.",
"The first point to establish is that the Coke, fresh out of the can or bottle, is ",
" in equilibrium. Carbon dioxide has been dissolved in the water and in the can or bottle is in equilibrium (more or less) with a pressurized atmosphere within the can or bottle. Once you remove the pressure and pour the Coke liquid into a glass, the equilibrium is for some amount of the carbon dioxide to become gas an escape into the surroundings. As you are aware of, if Coke is left in a glass for long, the fizz is lost.",
"But this re-equilibration is not instant, there is some hurdle to the process. For water that process will almost always be surface tension. Water molecules really \"like\" other water molecules. That's a way to say that the interaction energy (or free energy) of water with water is in relative terms very favourable compared to most other interactions between water and some other molecule. That is especially true if the other molecule is non-polar or only weakly polar, which is the case for most gases. ",
"Carbon dioxide can dissolve in water thanks to some polarity and interactions that are possible with the oxygen atoms of carbon dioxide. A gas like helium would not dissolve in water in any meaningful quantity. But as stated above, once fresh out of the can, there is more carbon dioxide in the water.",
"So it forms bubbles, the fizz. However, forming bubbles forces water molecules to have an interface with gaseous carbon dioxide. That is something the water \"does not like\". This manifest itself as surface tension, in macroscopic terms, work must be done in order to create the interface between bubble and water. That work becomes the free energy barrier to instant re-equilibration.",
"Now enters the inert rough surface. What it does is that it provides a means to create bubbles with less work. A first rough approximation is that a bubble can form with half the work because only half the surface area between gas in the bubble and water has to be created in order to make the bubble come about. But if the surface is very rough with lots of small crevices, that reduction is even greater because now the surface that has to form with water is even less. At a sufficient size of the bubble, gravity becomes a stronger force and buoyancy kicks in and the bubble drifts to the top and into the surrounding.",
"I can imagine experiments where surfaces with different coatings are used to see how much they promote bubble formation, perhaps even inhibit it, though given the polarity of water that should be a lot less likely. If you ever study capillary forces, wetting and the Young equation you are more or less doing that but under more controlled conditions.",
"This is basically the same process why throwing some salt into boiling water alters the character of the boiling, before the salt has dissolved. It is also related to the crystallization of super saturated solutions, but then it is a solid that forms in a solvent rather than gas escaping.",
"Finally, I have summarized all this assuming no chemical reaction are involved. If such are part of the process, then it is possible those are rate-limiting instead and therefore addition of inert surfaces may not make a difference. But that's a different story and should not matter to the specific example you've given."
] |
[
"What you're referring to is called a \"nucleation site\". For a proper bubble to form enough CO2 has to gather. But not enough CO2 can gather on smooth surfaces or in the liquid before it will just dissolve away again. A nucleation site can act as a \"save place\" for the CO2 to gather and form bubbles, without dissolving again. ",
"In chemistry, often a stone-like object with loads of nucleation sites is added to a mixture before boiling, because otherwise bubbles might not form. You can superheat a liquid if no bubbles form, which could be extremely dangerous."
] |
[
"How do they make the first down line on the TV?"
] |
[
false
] |
If it were just superimposed on top of the TV feed, surely the line would be at the "front" of the image and the players would appear "behind" it?
|
[
"A simple Google search answers this",
". It's actually very complex."
] |
[
"The easiest way to do this would be to have a mounted camera that feeds information about which direction it is pointing and the level of zoom into a computer. From there a projection matrix could be calculated to map the 3d view onto a 2d plane. Each individual pixel color could then be matched to a pre-photographed image that has the same projection. If the colors reasonably match, the line can be drawn on that pixel. Then apply the inverse matrix and draw the line on top."
] |
[
"This is what he is talking about",
". Players pass over it so it looks as if it is painted on the field. I am interested as well."
] |
[
"If I were on a space station 2 light years away?"
] |
[
false
] |
Ok, so basically say I, right now, was instantaneously teleported via some kind of magic to a space station 2 light years away. I have a telescope on this space station that is so powerful I can see people walking around on city streets in minute detail, would the planet I see be Earth in the year 2017? And if so could I theoretically see myself walking around on the surface of planet back in 2017?
|
[
"Yes, because the light takes two years to reach you, so you're seeing a two year old image.",
"You would of course need an enormous telescope to see that level of resolution - ",
" bigger than a planet. You also can't actually use this to see into your own past, because you can't travel faster than light - this only works in a hypothetical thought experiment where you can magically teleport, or at least travel faster than light. So even though an alien civilization in the Virgo Cluster might see the Milky Way as it was when dinosaurs were (just) still on Earth, you can't fly to the Virgo Cluster and build a giant telescope and use it to directly observe dinosaurs."
] |
[
"In principle yes, in practice the amount of light you get back is negligible. You can't even hand-wave that away with a larger telescope as the black hole will set a hard limit.",
"A simple mirror works better.",
"/u/Calricium",
": You'll never see yourself at a time before you set up some elaborate scheme, but after you started you can see yourself in the past. If it doesn't have to be two years you can simply look into a mirror, you see yourself from a few nanoseconds ago."
] |
[
"Actually, everything you see is about 13-100 milliseconds in the past. That's the amount of time it takes for the signal to travel from your eye, down your optic nerve, to the visual processing center of your brain and form the image. Everything you see, everything, happened in the past.",
"There's all kinds of tricks that your brain uses to try and make this gap smaller. For example, if you're swinging a bat at a ball, it will do you no good to swing at where the ball was 13 milliseconds ago. Your brain will process the image, predict where the ball will be in 13 milliseconds, and form that image in your brain. This is partially the reason why so many optical illusions work, your brain isn't processing the image it sees, it's processing the image it EXPECTS to see a handful of milliseconds later."
] |
[
"If we are 99.9% empty space, along with everything else - Why can't we see through each other and see through walls?"
] |
[
false
] | null |
[
"The oft quoted \"empty space\" idea is describing the space in between the electron shells and the nucleus, which is inside the atom.",
"However, if you get light with a short enough wave length then we can see through things. That's how x-rays work!"
] |
[
"Electron shells are not discrete orbits around the nucleus like a planetary system. The electron cloud occupies all the space around the nucleus. This \"empty space\" idea mainly comes from the distribution of mass in an atom and a general confusion about what size means on the quantum scale."
] |
[
"Because the signal we perceive (visible light) is dominated by the signal which 'bounced' back at us than the signal which 'passed through' the object.",
"The wavelength of visible light is large enough that it doesn't fit through the 'holes' you described.",
"When light is travelling through a substance and 'impacts' another substance a number of interactions occur. These interactions can include reflection, refraction, and scattering. The details of what happens is governed by the wavelength and properties of the two substances.",
"For light continuing to travel through the second substance, we look at refraction. Simply put, some substances are easy to travel through (air) while others are more difficult. We call this the metric the Refractive Index. What matters is how the two substances compare to each other. When there is a large difference (speaking of the 'easy' moving into 'difficult'), it is more likely the light will be reflected back into the first substance and none of it will enter the second substance. ",
"For a light behind a wall: light travels through the air, impacts the wall, where it is reflected by the wall, and then returns backwards into the air.\nFor a light behind a glass of water: light travels through the air, impacts the water, is refracted by the water, travels through the water, impacts the air on the other side, is refracted, and finally continues forward into the air.",
"When you look at a wall, you are seeing light that has bounced all over the place. After all the interactions are complete, the reflected or scattered light is going to be MUCH stronger than any tiny amount which successfully passed through the wall. Therefore we cannot 'see' through walls."
] |
[
"If travelling really fast slows down time, does travelling really slow, speed up time?"
] |
[
false
] | null |
[
"No. In special relativity, it's never possible to ",
" time, only slow it down."
] |
[
"Faster things than Earth experience time more slowly.\nSlower things than Earth must experience time more quickly no? ",
"If you can’t speed up time how can you travel near the speed of light, experience time going so slow your grandchild out ages you but then be able to return to Earth and experience time as normal. Returning to Earth would make time speed up for you no? Or at least appear to.",
"Forgive me if my logic is off this is confusing."
] |
[
"Slower things than Earth must experience time more quickly no?",
"What do you mean by \"slower than Earth\"? There is no such thing as an absolute speed, if that's what you're getting at. The speed of any object is relative, and the minimum speed that anything can have is zero. If an object is moving at zero speed relative to you in flat spacetime, the derivative of the coordinate time with respect to the proper time of the object is exactly 1. If the object is moving with nonzero speed, then dt/dT is strictly greater than. There is no way, in special relativity, to make dt/dT < 1. In other words, there is nothing you can do to this object to make its coordinate time tick ",
" than its proper time."
] |
[
"On the design of spacecrafts: Why is it better to have a vertical launch rather than a take off like an airplane and a gradual ascent out of the atmosphere?"
] |
[
false
] |
There are undoubtedly many things that I do not know about aeronautics and flight, but it just intuitively seems to me like it would be easier to launch our spacecrafts like planes and then gradually gain altitude until they are in orbit. Can someone explain why we don't do this, and instead launch straight up with rockets?
|
[
"Long story short, rockets provide enough thrust to make it worthwhile to get some altitude first so you can do your lateral thrust with less air drag.",
"As we develop better technologies it may become more efficient to use horizontal launches with air-breathing engines.",
"http://en.wikipedia.org/wiki/SSTO",
"Some proposed variable-geometry engine designs could transition between rocket and scramjet operation modes."
] |
[
"I think a lot of the reason that we build large rockets is that we'd need an unrealistically-large lift-producing aircraft to launch the substantial payloads that are frequently required.That, and we spent a ton of money in the 20th century learning about vertical launch rockets, so now they're less expensive than a new, horizontal-launch system."
] |
[
"I just want to emphasize that the (prospective) advantage of horizontal launch is the use of air-breathing engines for part of the ascent. ",
"Use of air-breathing engines in launch is almost an end unto itself; it reduces propellant requirements dramatically because you don't need to bring your own oxidizer for that leg of the flight. "
] |
[
"At what stage do people typically \"feel\" cancer? How is it possible for someone to just get diagnosed at stage 4, at that point of metastasization shouldn't the person be in massive pain at stage 3 already?"
] |
[
false
] |
Just heard at Alex Trebek (Jeopardy! Host) was diagnosed with stage 4 pancreatic cancer. From what I know pancreatic cancer takes a long time ( ) and doesn't present a lot of symptoms at first. I understand normal people not having the time or money or even access to get checkups so they ignore that pain in their side that comes and goes until its too late, but again, Alex doesn't have any of those problems. Hes also 78, and shouldn't men be getting colonoscopies like every 10 years after 50? How does something like this slip through the medical health cracks for someone like Alex.
|
[
"There's no answer to this as it is vastly vastly different between any of the 200+ types of cancer, and even within a type it can depend on where exactly the tumor is.",
"For example, the most common subtype of Non-Hodgkin Lymphoma shows up as a very rapidly growing lymph node in the neck or chest (over a few weeks). It can grow so quickly that you end up with serious problems from the size of the tumor, and if you're not treated you die in less than a year. The second most-common subtype of Non-Hodgkin lymphoma grows so slowly you might not experience any symptoms for years, and it's only noticed when a doctor feels that you have a small lump somewhere. People can survive for 10+ years. That's two subtypes of the \"same\" cancer!",
"Pancreatic cancer is a really nasty one because there are usually no symptoms--or very nonspecific ones--until it's grown large enough that treatment has become just about impossible. A colonoscopy does ",
" detect pancreatic cancer. In order to \"see\" the tumor, you have to get an ultrasound, abdominal CT scan, or MRI--none of which are recommended to get routinely."
] |
[
"There are a ton of reasons why you might do abdominal scans--if you had severe pain or gastrointestinal issues they might do one to check what's going on. Scans aren't given out super easily, though--for one, CT scans to the abdomen actually expose you to a decent amount of radiation, which isn't something you want to do very often. MRIs are very expensive, and there are lots of different types you can do that are good (and not good) for different things. Endoscopic ultrasounds (where they stick a tube down your throat to do it) are fairly safe, but they do have some risks. You also would have to be looking right at the pancreas to find a tumor there.",
"Pancreatic cancer is going to most likely cause just weight loss and maybe nausea/diarrhea, which the doctors probably won't do a scan for right away. By the time you get even ",
" symptoms, though, it's often too late for the disease to be curable. Also, the vast majority of people with these symptoms ",
" have pancreatic cancer, so it's not really useful to send everybody who starts losing weight in to check their pancreas."
] |
[
"Cancer cells don't have a nerve supply, so they can't feel pain directly. You only feel pain when the cancer cells injure the normal tissue around them.",
"Different body parts feel pain through different mechanisms, and many parts of the body do not have pain receptors at all. Most of your gastrointestinal tract does not have pain receptors - the lining of your stomach and intestines can feel pain, but the gut tissue itself cannot. For this reason things like pancreatic cancer and colon cancer do not cause pain until they are very advanced."
] |
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